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dissertation entitled

sanwst'é, SWMCW‘Q, Md R24 eta/3%,
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presented by
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To AVOID FINES return on or before date due.
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1/93 chIRC/Duouepes-pja

Synthesis, Structure, and Reactivity of Group 13 Diketiminate Complexes

By

Baixin Qian

A DISSERTATION

Submitted to
Michigan State University
in partial fulfillment of the requirements
for the degree of

DOCTOR OF PHILOSOPHY

Department of Chemistry

1 999

SW37;

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ABSTRACT
Synthesis, Structure, and Reactivity of Group 13 Diketiminate Complexes
By

Baixin Qian

Compared to transition metal imido (M=NR) and oxo (M=O) coordination
complexes, the examples of main-group metal analogues are limited. Metal-ligand
interactions in main group analogous complexes are intrinsically different from those of
transition metal, and main group complexes may exhibit different reactivity. Thus we
have targeted the synthesis and characterization of main group imido and oxo complexes.

Chapter 1 describes our attempts to synthesize imido and oxo indium complexes
supported by a hydrotris(3-tert-butylpyrazolyl)borate ligand, Tp3'tB". The synthetic
approach involved oxidation of a mono-valent indium complex with organic azides and
N20, respectively. The reaction between [Tp3'tB"]In (l) and ArN3 yielded a tetraaza-Z—
butene-l ,4-diyl indium(III) complex, [Tp3"B"]InN4Ar2, (4 Ar = Ph, 5 Ar = p-Tol) which
presumably forms through a 2 + 3 cycloaddition between In=NAr and ArN3 {[Tp3’tBu] =
hydrotris(3-tert-butylpyrazolyl)borate}. Efforts to trap the proposed terminal imido
3-’Bu

intermediate, [Tp ]In=N Ar, were not successful. When compound 1 was treated with

excess N20, B-H bond cleavage led to degradation of the ligand and tetrakis(3-tert-
butylpyrazolyl)borate (6) was isolated and structurally characterized. This result
suggested that the 8—H functionality should be protected or ligands devoid of B—H bonds
should be used for preparing LIn=O (L = uninegative ligand). We choose the latter

strategy, eliminating the issue of B-H incompatibility with certain oxidants.

fiDikcim‘.
xj'ztsdzone (in.
311: metal cc
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isn'ipnsniomiin
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1...}; L‘\ludi.ii

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"‘4 l' ’; >3
' {1:3ch

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will C,
.'r~.,‘ "
- “Vt.
:3“

B—Diketiminate ligands satisfy this criterion and the synthesis from 2,4-
pentanedione and amines allows for the tuning of steric and electronic properties to
stabilize metal centers in novel geometries and oxidation states. However, initial efforts
were not successful. Treatment of InCl with Li(Tol2nacnac) (16) generated a
disproportionation product, In(Tolgnacnac)3 (27) (TolznacnacH = 2-(p-tolylamino)-4-(p-
tolylimino)-2-pentene), albeit in low yields, and the desired In(I) complex was not
observed.

To develop synthetic protocols for introducing fldiketiminate ligands to group 13
elements, we have investigated the chemistry of tri-valent group 13 compounds in their
highest oxidation state where disproportionation cannot happen. Thus, complexes with
the general formula, M(Tolznacnac)X2, (M = B, A], Ga, In; X = F, C1) were synthesized
and fully characterized. Because boron behaves differently from the rest of group 13
elements, the coordination chemistry of boron is described in Chapter 2. The outcome of
the methylation of B(Tolznacnac)F2 (28) depended on the nature of the nucleophile. The
reaction between compound 28 and two molar equivalents of MeLi gives a three-
coordinate boron complex (29) which is complicated by ligand methylation. However,
freshly prepared MgMeI selectively delivers two methyl groups to the boron center,
generating the four-coordinate boron complex B(Tolznacnac)Me2 (31). A methyl
abstraction reaction between compound 31 and B(C6F5)3 cleanly generates a cationic
boron complex, [B(Tolznacnac)Me]+[BMe(C6F5)3]’ (35) which is characterized by
solution NMR spectroscopy, elemental analysis, and molar conductivity measurements.

Chapter 3 concentrates on the synthesis and characterization of aluminum(III) and
gallium(III) coordination complexes supported by diketiminate ligands, especially
Tolznacnac. Salt elimination reactions between MC13 and one molar equivalent of
Li(Tolznacnac) (16) afford four-coordinate M(Tolp_nacnac)Cl2 (37 M = Al, 38 M = Ga).
Attempts to introduce two or three Tolznacnac ligands to a single metal center were not

successful. Since cationic amidinate aluminum alkyl complexes can polymerize ethylene

22. rill conduit
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under mild conditions the alkylation chemistry of 37 and 38 was investigated. In contrast
to boron chemistry, M(Tolgnacnac)Me2 (39 M = Al, 40 M = Ga) can be prepared by
treatment of M(Tolgnacnac)C12 with two molar equivalents of MeLi. We also attempted
to prepare cationic aluminum alkyl complexes by methyl group abstractions. With the
appropriate match of diketiminate ligand and weakly coordinating anion, an aluminum
cationic complex (64) has been characterized by solution NMR.

For aluminum(III) and gallium(HI) diketiminate complexes the maximum
coordination number is four. However, indium(III) can be supported with one, two, or
three Tolznacnac ligands. Chapter 4 describes the synthesis and characterization of four-,
five—, six-coordinate indium complexes. A trigonal pyramidal geometry is observed for
the indium center in five-coordinate In(Tolznacnac)2Cl (67) with C1 in the equatorial
plane. In(Tolznacnac)3 (27) adopts a pseudo-octahedral geometry for the indium center.
The 1H NMR spectrum of compound 27 contains several unusual high field chemical
shifts and those unusual high field shifts can be explained by the ring current shielding
effects using a model derived from the X-ray data.

Recent efforts to stabilize In(I) compounds through use of bulky B—diketiminate
ligands have been successful (Chapter 5). In contrast to the disproportionation observed
in Tolgnacnac system, mono-valent In(Dipznacnac) (72) can be prepared in 56% yield
(DipznacnacH = 2-(2,6-di-isopropyl)phenylamino-4-(2,6—di-isopropyl)—phenylimino-2-
pentene). Single crystal X-ray diffraction analysis establishes that 72 is monomeric in the
solid state and that In(I) is two-coordinate. Using the driving force of oxidization from
In(I) to In(III), several novel complexes have been prepared. In contrast to the
decomposition of Tp'uB" described in Chapter 1, 72 reacts with N20 generating an oxo-

bridged dimer (75).

To my family and friends

 

 

 

When 1 mm
exgcnencc Ill IL‘\Cdi
agnomchllic the
members. Especial}
its: a co-wlcr.
my to .1 Mon t
lam grateful for .1
grams. Ling in. ;

Man) of I
ngle crisul X-r;
timed bx the
to PYOVIClCd h}

1:521:23 of Hell

ACKNOWLEDGMENTS

When I came to Michigan State University from China in 1993 , I had little
experience in research. I would like to thank Professor Mitch Smith for his guidance in
organometallic chemistry. I am happy to work with the former and current group
members. Especially, I collaborated with Sung W. Baek who initially was a REU student,
later a co-worker. It was Sung who found that MeMgI selectively delivers two methyl
groups to a boron center. I appreciate the helps from Drs. Huang, Johnson, Le, Ward and
I am grateful for a Carl H. Brubaker Endowed Fellowship in 1998. Finally, I thank my
parents, Lingyan, and other friends.

Many of the compounds reported here have been characterized by NMR and
single crystal X-ray diffraction methods. The single crystal X-ray equipment at MSU was
supported by the National Science Foundation (CHE-9634638), and the NMR equipment
was provided by the National Science Foundation (CHE-8800770) and the National

Institutes of Health (l-S l O-RR04750-Ol ).

vi

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(:1ka 1

TABLE OF CONTENTS

LIST OF TABLES ............................................................................................................. X
LIST OF FIGURES .......................................................................................................... XII
LIST OF ABBREVIATIONS ........................................................................................ XVI
INTRODUCTION ............................................................................................................... 1
SYNTHETIC CONSIDERATIONS .......................................................................................... 2
MAIN-GROUP IMIDO AND Oxo COORDINATION COMPLEXES ........................................... 3
SUB-VALENT GROUP 13 ELEMENT CHEMISTRY ............................................................... 4
Mono-valent Group 13 Complexes ............................................................................. 5
Mono-valent Group 13 Element Cyclopentadienyl Complexes ................................. 6
Reactivities of Mono-valent Group l3 Complexes ..................................................... 9
Mono-valent Group 13 Element hydrotris(pyrazolyl)Borate Complexes ................. 10
Mono-valent Group 13 Element Alkyl And Aryl Complexes .................................. 10
Mono-valent Group 13 Element Arene Complexes .................................................. l 1
Formal Di-valent Group 13 Element Chemistry with M-M Bond ........................... 11
Group 13 Element Chemistry with M—M Bonds ...................................................... ll
MOLECULAR ORBITAL CONSIDERATIONS ....................................................................... 13
LIGAND CONSIDERATIONS FOR KINETIC STABILIZATION ............................................... 14
CHAPTER 1 ...................................................................................................................... 17
INTRODUCTION ............................................................................................................... 17
RESULTS AND DISCUSSION ............................................................................................. 18
Reactivity of In(Tp3“B") ................................................... . .......................................... 18
Synthesis and Structure of nZ-Tetraaza-2-butene—1,4-diyl Indium(III) ..................... 19
Reaction of In(Tp3'tB") With N20 .............................................................................. 22
Synthesis of Diketiminate Ligands ........................................................................... 27

vii

Structure at C
Attempted 51
CHAPTER: .........
lViRCtDl‘C’ilON .
"HIS AND D
S)Tlil’lt‘\li\ In.
Alltlttton C
)lttlttl Absti
CHAPTER? .......
inittnt‘mt A
items on I
Stnthexix at:
Stnthcus .tn
Complms.
S}lliil€\1\ of
Synthesis 0t
Reactitnt c
Cl-iPTERt .....
[\TRDDI'CHQ
RES—ITS AND
Tohndtnag
“fit-1 lat

it“!

.....

Structure of Diketiminate Ligands ............................................................................ 29

Attempted Synthesis of In(Tolznacnac) .................................................................... 35
CHAPTER 2 ...................................................................................................................... 36
INTRODUCTION ............................................................................................................... 36
RESULTS AND DISCUSSION ............................................................................................. 36
Synthesis and Structure of B(Tol2nacnac)F3 ............................................................. 36
Alkylation Chemistry ................................................................................................ 38
Methyl Abstraction Reactions ................................................................................... 44
CHART ER 3 ...................................................................................................................... 48
INTRODUCTION ............................................................................................................... 48
RESULTS AND DISCUSSION ............................................................................................. 48
Synthesis and Structure of M(Tolznacnac)Clz (M = A1, Ga) .................................... 48

Synthesis and Structure of Aluminum and Gallium Dimethyl Diketiminate

Complexes ................................................................................................................. 51
Synthesis of Bis-organoaluminum Complexes ......................................................... 58
Synthesis of Mixed Organoaluminum Complexes ................................................... 61
Reactivity of Al(Tolgnacnac)Me2 .............................................................................. 75
CHAPTER 4 ...................................................................................................................... 80
INTRODUCTION ............................................................................................................... 80
RESULTS AND DISCUSSION ............................................................................................. 80
Tolznacnac Ligation .................................................................................................. 80
Methylation of Tolgnacnac Indium Complexes ........................................................ 90
CHAPTER 5 ...................................................................................................................... 94
INTRODUCTION ............................................................................................................... 94
RESULTS AND DISCUSSION ............................................................................................. 95
Synthesis and Structure of In(Dipznacnac)Cl2 .......................................................... 95
Reactivity of In(Dipgnacnac)Clz ................................................................................ 97

viii

Stutht’six an
Rctctitu} ul
CHIPIER 6 .......
General C or
Equilibrium
S)’Ilillt‘\l.\....
X-rar Strut
ENTER 7 .....
APPEXDlX .-‘
APPENDIX I
APPENDIX (
BBLIOGRAPI

Synthesis and Structure of In(Dipgnacnac) ............................................................... 98

Reactivity of In(Dipgnacnac) ................................................................................... 100
CHAPTER 6 .................................................................................................................... 106
General Considerations ........................................................................................... 106
Equilibrium Constant Determination ...................................................................... 106
Synthesis .................................................................................................................. 107
X-ray Structure Determination ................................................................................ 137
CHAPTER 7 .................................................................................................................... 143
APPENDD( A ............................................................................................................. 147
APPENDIX B ............................................................................................................. 148
APPENDIX C ............................................................................................................. 149
BIBLIOGRAPHY ........................................................................................................... 15 l

Table 1.0123:
Table 1. Selet‘tel
Table 3. Summurj
Table 4. Selected
Table 5. Silllliflur:

TabTe 6. COTT‘IPJH

Table 8. Select“

Table 9. NMR el.

35. m 36. ..
Table 10. Summ.
Table 11. Selecte
Table 12. Summ.
Table 13. Seleete
Table 14. Select:
T1blelS.Sun:m.
Table 16. Summ.
T1blel7.SeIette

TIME 18. SUP)":

IIII

LIST OF TABLES

Table 1. Comparison Of Tp, Cp, and diketiminate ligands. .............................................. 15
Table 2. Selected bond distances (A) and angles (deg) for compound 4. ....................... 20
Table 3. Summary of crystal and refinement data for compounds 4 and 6. ..................... 25
Table 4. Selected bond distances (A) and angles (deg) for compound 6. ....................... 25
Table 5. Summary of crystal and refinement data for compounds 11, 14, and 21. .......... 32

Table 6. Comparison of selected bond distances and angles of compounds ll, 14, and 21.
................................................................................................................................... 33
Table 7. Summary of crystal and refinement data for compounds 28, 29, 30, and 31. 44
Table 8. Selected bond distances (A) and angles (deg) for compounds 28, 29, 30, and 31.
................................................................................................................................... 44
Table 9. NMR chemical shifts for backbone CH and BMe resonances in compounds 31,
35, and 36. ................................................................................................................. 46
Table 10. Summary of crystal and refinement data for compounds 37 and 38 ................ 50
Table 11. Selected bond distances (A) and angles (deg) for compounds 37 and 38. ...... 51
Table 12. Summary of crystal and refinement data for compounds 39 and 40. ............... 53
Table 13. Selected bond distances (A) and angles (deg) for compounds 39 and 40. ...... 53
Table 14. Selected bond distances (A) and angles (deg) for compounds 44 and 46. ...... 55
Table 15. Summary of crystal and refinement data for compounds 44 and 46. ............... 57
Table 16. Summary of crystal and refinement data for compounds 41 and 42. ............... 61
Table 17. Selected bond distances (A) and angles (deg) for compounds 41 and 42. ...... 61
Table 18. Summary of crystal and refinement data for compounds 50 and 51. ............... 65
Table 19. Selected bond distances (A) and angles (deg) for compounds 50 and 51. ...... 66
Table 20. Summary of crystal and refinement data for compounds 53, 54, and 55. ........ 70
Table 21. Selected bond distances (A) and angles (deg) for compounds 53, 54, and 55.71

Table 22. Summu
Table 13. St‘lt’t‘lt‘u
Table 24. S 111111.11
Table 25. Seiette.
Table 16. Selecte.
Table 27. Selectet
Table 28. Samara
Table 29. Selecte.
Table 30. Seieete
Table 31. Saturn.
Table 32. Seleere

Table 33. Seiet‘te

Table 22.
Table 23.
Table 24.

Table 25.
Table 26.
Table 27.
Table 28.
Table 29.
Table 30.
Table 31.
Table 32.
Table 33.

Summary of crystal and refinement data for compounds 58 and 60. ............... 75

Selected bond distances (A) and angles (deg) for compounds 58 and 60. ...... 75
Summary of crystal and refinement data for compounds 66, 67, 27, 68, and 69.
........................................................................................................................... 82
Selected bond distances (A) and angles (deg) for compounds 66 and 68. ...... 83
Selected bond distances (A) and angles (deg) for compounds 67 and 69. ...... 86
Selected bond distances (A) and angles (deg) for compound 27. ................... 88
Summary of crystal and refinement data for compounds 70 and 72. ............... 97
Selected bond distances (A) and angles (deg) for compound 70. ................... 97
Selected bond distances (A) and angles (deg) for compound 72. ................. 100
Summary of crystal and refinement data for compounds 74 and 75. ............. 103
Selected bond distances (A) and angles (deg) for compound 74. ................. 103
Selected bond distances (A) and angles (deg) for compound 75. ................. 105

xi

figure 1. Anant-
amrner ..........

, ) ‘ ‘ I]
Figure .. RUt n 1
figure 3. Resonar

figure 1. I-tl-I-p
element.

figure 5. Fermatt
figure 6. Structur

figure 7. Three x.
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figure 8. Equzlrb'
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figure 9. Stbertta
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figure 10. REAL“
ITEMS ...........

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LIST OF FIGURES

Figure 1. Amine-accelerated OsO4 catalyzed dihydroxylation of alkenes (L = tertiary

amine). ......................................................................................................................... 1
Figure 2. Resonance structures A, B, and C of an oxo complex. ...................................... 1
Figure 3. Resonance structures D and E of an imido complex. ......................................... 2

Figure 4. n—d-Jt-p interaction between d orbitals of a metal and p orbitals of a main-group

element. ....................................................................................................................... 2
Figure 5. Formation of Al—N clusters from different aryl amines. .................................... 4
Figure 6. Structure of M(CO)2 (M = A1, Ga, In). ............................................................... 5

Figure 7. Three schematic structural representations of (ML),, (monomer, H; tetramer, I;
hexamer J). .................................................................................................................. 7

Figure 8. Equilibrium between monomeric tetrameric (Ale*)4 and Ale* in a benzene
solution. ....................................................................................................................... 8

Figure 9. Schematic representation of hydrotris(pyrazolyl)borate ligands, [TpRR 2] where
R and R2 are the substituents at 3, 5- -position in the pyrazolyl ring, respectively... .10

Figure 10. Reaction pathways for M2X4 (M = Ga, In) in aromatic solvents and in Lewis
bases. ......................................................................................................................... 1 1

Figure 11. Synthesis of dipotassium tris[(2,6-dimesitylphenyl)cyclogallene]
K2[(MCSQC6H3)G3]3 (MCS = C6H2-2,4,6—Me3). ......................................................... 12

Figure 12. Synthesis of a gallyne Na2[(2,4,6-Mes*3C6H2)Ga2] (Mes* = C6H2-2,4,6-'Pr3)
containing the shortest Ga-Ga bond. ........................................................................ 13

Figure 13. Pictorial representations of metal-based orbitals in three- (L), two- (M), and
one-coordinate (N) mono-valent group 13 complexes .............................................. 13

Figure 14. Different nitrogen containing ligand sets (salen O; diimine P; amidinate Q;
troponiminate R; diketiminate S). ............................................................................. 14

Figure 15. Schematic illustration of cone angles and wedge angles of MCp*2 systems. 15

Figure 16. X—ray crystal structure of In(Tp3'IB")(N(Ph)—N=N—NPh) (4) with thermal
ellipsoids drawn at the 50% probability level. .......................................................... 20

Figure 17.3 + 2 Cycl3o;Bu -addition between AIM and the proposed indium imido
intermediate (Tp “)In=NAr. ................................................................................... 22

Figure 18. X-ray crystal structure Of H[B(C3H2N2-3-’Bu)4] (6) with thermal ellipsoids
drawn at the 50% probability level. .......................................................................... 24

xii

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Figure 19. Resonance structures T and U of I-I[B(C3HN2-3,5-Me2)4] (6) ........................ 26

Figure 20. Synthesis of diketimine R'RznacnacH. ........................................................... 29
Figure 21. X-ray crystal structure of TolgnacnacH (11) with thermal ellipsoids drawn at
the 50% probability level. ......................................................................................... 32
Figure 22. X-ray crystal structure of DipznacnacH (14) with thermal ellipsoids drawn at
the 50% probability level. ......................................................................................... 33
Figure 23. X-ray crystal structure of 21 with thermal ellipsoids drawn at the 50%
probability level ......................................................................................................... 34
Figure 24. X-ray crystal structure of B(Tolgnacnac)F2 (28) with thermal ellipsoids drawn
at the 50% probability level. ..................................................................................... 37
Figure 25. Alkylation reactions of B(Tolgnacnac)F2 (28). ............................................... 38
Figure 26. X-ray crystal structure of 29 with thermal ellipsoids drawn at the 50%
probability level ......................................................................................................... 40
Figure 27. Three potential reaction pathways for converting 28 to 29. ........................... 41
Figure 28. X—ray crystal structure of 30 with thermal ellipsoids drawn at the 50%
probability level ......................................................................................................... 42
Figure 29. X—ray crystal structure of 31 with thermal ellipsoids drawn at the 50%
probability level ......................................................................................................... 43
Figure 30. Methyl abstraction reaction of compound 31. ................................................ 45

Figure 3]. X-ray crystal structure of 37 M = A], 38 M = Ga with thermal ellipsoids
drawn at the 50% probability level. .......................................................................... 50

Figure 32. X-ray crystal structure of 39 with thermal ellipsoids drawn at the 50%
probability level ......................................................................................................... 52

Figure 33. X-ray crystal structure of 40 with thermal ellipsoids drawn at the 50%
probability level ......................................................................................................... 52

Figure 34. X-ray crystal structure of 44 with thermal ellipsoids drawn at the 50%
probability level ......................................................................................................... 55

Figure 35. X-ray crystal structure of 46 with thermal ellipsoids drawn at the 50%
probability level ......................................................................................................... 56

Figure 36. X-ray crystal structure of 41 with thermal ellipsoids drawn at the 50%
probability level ......................................................................................................... 59

Figure 37. X-ray crystal structure of 42 with thermal ellipsoids drawn at the 50%
probability level ......................................................................................................... 60

Figure 38. X-ray crystal structure of 50 with thermal ellipsoids drawn at the 50%
probability level ......................................................................................................... 63

xiii

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Figure 39. X-ray crystal structure of 51 with thermal ellipsoids drawn at the 50%

probability level ......................................................................................................... 64
Figure 40. X-ray crystal structure of 53 with thermal ellipsoids drawn at the 50%
probability level ......................................................................................................... 67
Figure 41. X-ray crystal structure of 54 with thermal ellipsoids drawn at the 50%
probability level ......................................................................................................... 68
Figure 42. X-ray crystal structure of 55 with thermal ellipsoids drawn at the 50%
probability level ......................................................................................................... 69
Figure 43. Deprotonation of a diketiminate methyl group involving a bulky anion. ....... 72
Figure 44. Sequential deprotonation and alkylation of 39. .............................................. 73
Figure 45. X-ray crystal structure of 58 with thermal ellipsoids drawn at the 50%
probability level ......................................................................................................... 74
Figure 46. X-ray crystal structure of 60 with thermal ellipsoids drawn at the 50%
probability level ......................................................................................................... 74
Figure 47. Synthesis of MeAl('Bu2nacnac)(,u2-Me)B(C6F5)3Me (63). ............................. 77
Figure 48. Methyl abstraction reaction of 44. .................................................................. 78
Figure 49. Ligation indium(HI) with Tolznacnac. ............................................................ 81
Figure 50. X—ray crystal structure of 66 with thermal ellipsoids drawn at the 50%
probability level ......................................................................................................... 82
Figure 51. Schematic representation of an aminotroponiminate ligand ........................... 84

Figure 52. X-ray crystal structure of 67 with thermal ellipsoids drawn at the 50%

probability level ......................................................................................................... 85
Figure 53. Aromatic region of ‘H NMR (300 MHz, CDCI3) spectrum of 27. ................. 87
Figure 54. X-ray crystal structure of 27 with thermal ellipsoids drawn at the 50%

probability level ......................................................................................................... 88
Figure 55. Simplified representation of interactions between hydrogen atoms and aryl

rings. .......................................................................................................................... 90
Figure 56. Schematic representation of a diphenyltriazenide (dpt) ligand ....................... 91

Figure 57. X—ray crystal structure of 68 with thermal ellipsoids drawn at the 50%
probability level ......................................................................................................... 92

Figure 58. X-ray crystal structure of 69 with thermal ellipsoids drawn at the 50%
probability level ......................................................................................................... 93

Figure 59. X-ray crystal structure of 70 with thermal ellipsoids drawn at the 50%
probability level ......................................................................................................... 96

xiv

figure 60. X-rat e
prttbabrltt} let

figure 61. Another
figurebl. H .\'.\11

figure 63. X-rh e
prebahrlu) let

figure 64. Synthc.

figure 65. Tran e

probabiliti lei

figure 66. DCilfilll

Figure 60. X-ray crystal structure of 72 with thermal ellipsoids drawn at the 50%

probability level ......................................................................................................... 99
Figure 61. Another view of the molecular structure of 72. ............................................ 100
Figure 62. 1H NMR spectra of 72 (A) and 74 (B) in ’Pr regions. ................................... 101
Figure 63. X-ray crystal structure of 74 with thermal ellipsoids drawn at the 50%

probability level ....................................................................................................... 102
Figure 64. Synthesis of the oxo-bridged dimer 75. ........................................................ 104
Figure 65. X-ray crystal structure of 75 with thermal ellipsoids drawn at the 50%

probability level ....................................................................................................... 104
Figure 66. Definition of the cone angle for Dipgnacnac in compound 72 ...................... 151

XV

Tlm
’ v. .. ..
..{_..tltli.ltH ..... .

A‘IiR

LIST OF ABBREVIATIONS

acac ................................................................................................................ acetylacetonate
CCD ................................................................................................. Charge Coupled Devise
CN ...................................................................................................... Coordination Number
Cp .............................................................................................................................. (C5H5)'
Cp* ......................................................................................................................... (C5M65)_
d ................................................................................................................................. doublet
Dep ................................................................................................................... C6H3-2,6-"Et2
Dip .................................................................................................................... C6H3-2,6-'Pr2
DipznacnacH ........................ 2-(2,6-iPr2-phenylamino)-4-(2,6-iPr2-phenylimino)-2-pentene
eq ............................................................................................................................. equation
ESR ............................................................................................... Electron Spin Resonance
i .......................................................................................................................................... iso
IR .............................................................................................................................. Infrared
m .................................................................................................................................... meta
m .............................................................................................................................. multiplet
mp ..................................................................................................................... melting point
It .................................................................................................................................. normal
NMR ....................................................................................... Nuclear Magnetic Resonance
o ..................................................................................................................................... ortho
p ...................................................................................................................................... para
Ph ................................................................................................................................ Phenyl
Py .............................................................................................................................. pyridine
q .................................................................................................................................. quartet
sept .............................................................................................................................. septet

xvi

Trinaenat‘ll .........

I

t ..................................................................................................................................... triplet

terr .............................................................................................................................. tertiary
Tol .................................................................................................................................. tolyl
TolgnacnacH ................................................... 2-(p-tolylamino)—4-(p-tolyliminO)-2-pentene
Tp ................................................................................................ hydrotris(pyrazol y1)borate

xvii

 

The then‘nx'.
rel". extablixhedl T
regent \tnrhexis.
-111.}1I0\}lailttns o'

Hill 030; di-i‘llld‘

:ataijnt upon tut-cl.

ll

figure 1. Amine

Elli 1.

in tree I:

.‘tfitTTOTilC t1“:

...eeetinn 1616.1.

:t-"n‘. ' '
......ett‘s. Sit?

1..
f'TT‘FF-‘l '\
-:'n.‘\ -

STI‘LlL‘TL

INTRODUCTION

The chemistry of transition metal imido (M=NR) and oxo (M=O) complexes is
well established.1 Transition metal imido and oxo complexes find wide applications in
organic synthesis. For example, osmium tetraoxide (OsOa) catalyzes the asymmetric
dihydroxylations of alkenes in the presence of chiral amines. The treatment of alkenes
with 0504 affords osmium(VI) glycolates, which give 1,2-diols and regenerate the

catalyst upon oxidative workups (Figure l)?-3

O
_ 0804 O\\ 1 fl H202 m
L O//CI)S O - 0304 HO OH

L -L

Figure 1. Amine-accelerated 0804 catalyzed dihydroxylation of alkenes (L = tertiary
amine).

In view of simple valence bond theory, oxo (02‘) and imido (NR2“) ligands are
iso-electronic and both form double bonds with the metal centers. However, a closer
inspection reveals that both of them may form triple bonds with metals. For terminal oxo
complexes, single, double, and triple bonding between the metal oxygen are possible
(Figure 2 structures A, B, and C, respectively).

M-O' :

 

 

M=§ M o:

A B C

Figure 2. Resonance structures A, B, and C of an oxo complex.
For terminal imido counterparts, both bent and linear geometries are possible
(Figure 3). This makes the determination of the bonding mode Simpler for imido

complexes than the oxo cases, since it is easier to locate an R group than an oxo lone pair.

Figure 3. Remitar‘.

 

Because the
0' and NR". .1 h:
tetueen a transitit't

higher bond orders

Figure 4. r—d-x-p n

element.

Synthetic C ()nSldt‘l
The stnthe~

natal centers and ll
1. Elirninati

raiser can )‘telc‘

eifntnates tine equr

This. type of r

Wits.

CD'Tat'NHr

Figure 3. Resonance structures D and E of an imido complex.

Because the d orbitals of the transition metal effectively interact with p orbitals on
02' and NRZ’, a higher order bonding ensues. Figure 4 shows the n-d-nr-p interaction
between a transition metal and a main-group element. These interactions may lead to

higher bond orders between the metal and the ligand.

39 P as a”
M L M L
Figure 4. 7r-d-7r—p interaction between d orbitals of a metal and p orbitals of a main-group
element.
Synthetic Considerations
The synthesis of complexes containing multiple bonds between the transition
metal centers and ligands can be delineated into 4 parts.
1. Elimination of an a—group, especially a—H as shown in eq 1, from a suitable
precursor can yield imido complexes. For example, Cp*Ta(NHR)Me3 (Cp* = C5Me5)
eliminates one equivalent of methane to generate a terminal tantalum imido complex (eq

l).4 This type of reaction is especially relevant for high valent early transition metal

 

centers.

T

. - CH4 H

Cp Ta(NHR)Me3 > T

Me’g- a\C *
Me‘ 9
R = CM93
= CH20M€3

= Me (1)

2. Atltllllt‘
nut also generate

OethHfiibltn.

3. Elt‘t‘llttt‘

2. Addition of an electrophile (Y) on the nitrogen in a nitrido complex (MEN)
may also generate an imido complex (M=NY).5 For example, a methyl group adds to a

OSEN(CHgSiM3)4, forming Os=NMe(CH2SiM3)4 (eq 2).6

 

- Me
1TH [MeaoiIBFu' N
2‘“ 05 ‘FW' R = CHZSiMe; Ru. «(1%
R (2)

3. Electrophic attack of a group (Y) on the B—nitrogen of a diazenido ligand as

shown in eq 3 can generate a special class on nitrogen-substituted imido compounds.7

 

 

 

’Pr
/ . _
Ni V /’Pr +
th N Ph2 ”5“
[PM WMP HBr_. th N th Br'
Plin. II .\\\P—'
th ll' th P/VIV\P4
/N _ th Br Ph2_
[Pr (3)

4. Oxidative addition of organic azides or oxygen to low-valent metal complexes
may also be used for preparing imido or oxo complexes. Organic azides RN3 are used as
sources of nitrenes (NRZ’).8a9 Oxygen or N20 can be used sources of 0210,11

Compared to the transition metals, the examples of main group imido and oxo
complexes are limited. Because the main-group metal’s d orbitals are less available, the
bonding pictures for main group imido and oxo complexes may be different from their
transition metal homologues.

Main-group lmido and 0x0 Coordination Complexes

Aluminum imido complexes form clusters and aluminum organo oxo complexes

are ill defined as typified by the complex nature of methylaluminoxane (MAO), the

activator common used for olefin polymerization.12 Trimethylaluminum reacts with

primary ahl an
Tlliru]. tthit‘h .

lloaeter. the ties:

 

 

 

the ball of the Ar ;.

figure 5. FOITTT‘JTTUT
\l'e aunt in
hidannn states hi i

.l
“5".“
“kalfillb

Q. .' w
.th talent (Irou [I
Group 14 ,
Pets. ‘1;
mutpw
1
if HV‘WCTCY

HT ‘-\‘
RNITPalETTT o

Tttt

primary aryl amines, losing one equivalent of methane and yielding [(Me2A1)2(,u-
NHAr)2], which eliminates another equivalent of methane to afford imido complexes.
However, the desired imido intermediates oligomerize to different degrees, depending on

the bulk of the Ar group (Figure 5)_I3,i4

 

I ,Ar Ar \ /
—‘,' |—:N_)\|/ Ar=Ph 1... 'Al/ \Al_.,,..t Ar_Mes AI—AARITAN-Ar
AL'Il’ r’l lbl 'CH4 " \ / \ -CH4 / \l \1
‘N—Al/ \Ar NI"! [ti—Al
Ar, \ ’Ar Ar

Mes = C6H2-2,4,6-M93
Figure 5. Formation of Al-N clusters from different aryl amines.

We want to prepare low coordination number group 13 element complexes in low
oxidation states by employing bulky ligands. Ultimately, we want to find a catalytic cycle
that may be useful in atom-transfer reactions or other small molecule activation
processes. Our synthetic approach centers on a two-electron oxidation of low valent
main-group metal coordination complexes with simple substrates such as organic azides
and nitrous oxide. The next section discusses the chemistry of low-valent group 13
elements.

Sub-valent Group 13 Element Chemistry

Group 14 and 15 elements complexes of the general formula of RE=ER with
stable-multiple-bonding characteristics are well developed (E = Si, Ge, P, As, Bi, and
Sb). 15.16 However, the number of analogous group 13 complexes are limited. The study
of low-valent group 13 element chemistry may lead to new bonding structures with
higher-bonding-character (> 1) metal—metal bonding. The interaction between mono-
valent group 13 metals has been the subject of theoretical calculations and it depends on

the nature of the ligand and the geometry of the metal complexes.” In a molecular dimer,

L—M—M—L, a bent geometry with a L—M—M angle close to 120° results in an Optimum

 

oterlap populatit‘
inter tron.”

Although '.

   
  

alert 10, +1 and -
complexes are etc.
In contrast i

gulp 13 complete

 

canletes hat e be

nonttarhnntl coir:

tangle

.1165 15 slit)“ 1‘

:rpaued electron in

figure 6. Structure
Ah initto C;
fig} bet“ een CLI

TP‘PCCITICIV)‘I3 A

centres hate nt

1

“TI.
wart.
11 ll haliJC‘

,_r.
«.15.,

"i ‘1‘! 100m TCT“
. ll

overlap population. For 3-D solids, a ligand-metal—metal angle of 90° gives the best
interaction. 1 8

Although the most common oxidation state for group 13 elements is +III,19 sub-
valent (0, +1 and +H) group 13 element complexes are known. Some low-valent group 13
complexes are excellent reducing agents except for thallium complexes.

In contrast to the vast amount of transition metal carbonyl complexes, zero-valent
group 13 complexes are extremely rare. Dicarbonyl aluminum, gallium, and indium
complexes have been established by matrix isolation ESR and IR study, whereas
monocarbonyl complexes are not observed.20‘22 The structure of the dicarbonyl
complexes is shown in Figure 6 (structure F). The metal center is sp2 hybridized with an

unpaired electron in a p, orbital perpendicular to C—M—C plane.22

//0 y
:L—M/C
0/ \ X
\\\0 Z
G

Figure 6. Structure of M(CO)2 (M = A1, Ga, In).

Ab initio calculations performed on Al(CO)2 and A1(CO) suggest that the binding
energy between carbonyl and aluminum center is weak (17.4 kcal/mol and 2.6 kcal/mol,
respectively).23 At present, synthetic applications of these zero-valent carbonyl
complexes have not been found.

Mono-valent Group 13 Complexes

Mono-valent group 13 halide complexes are known. Both indium(I) and
thallium(I) halides are thermodynamically stable against disproportionation in the solid
state, and both are commercially available. Aluminum and gallium mono-hadides are not

stable at room temperaturez‘it25

\luntr-t at

C131 are onl) stab

 

metal with H.\ A
ea it. The gaxet

1w
btdrneen htprut...

M=AI.G

lluno-taleni G ['1

The uhrqu
czirtt-‘ttetex,3j Etc
biotin. 3“” The
aides and Cp~ t
'ecl on the nut
11672-11 instulttll’t

C15 3.

l“"“§taph\ l‘

tincture [l is

reenance caleul

L11

Mono—valent halide complexes of lighter group13 elements such as MCl (M = A1,
Ga) are only stable at high temperatures. Their synthesis involves the heating of liquid
metal with HX (X = Cl, Br, 1) gas at high temperatures (800—1000 0C) in high vacuum.
(eq 4). The gaseous MX is trapped in a toluene/diethyl ether matrix at 77 K and the

hydrogen byproduct is removed by a pump.26

800 - 1000 °C
4 ><10'5 mmHg
M = A1, Ga
X = Cl, Br, I (4)

 

M =Al, Ga; X=CI, Br, I

Mono-valent Group 13 Element Cyclopentadienyl Complexes

The ubiquitous cyclopentadienyl (Cp = C5H5) ligand stabilizes a variety of metal
complexes.27 Except for boron, mono-valent group 13 cyclopentadienyl complexes are
known. 283‘ They have been prepared by metathesis reactions between mono-valent
halides and Cp‘ (Cp = C5H5) delivering reagents. The stability and structure of MCp
depend on the nature of metal. Ale is only stable at temperatures below —60 °C and its
thermal instability thwarts efforts to obtain the solid state structure by X-ray
crystallography. However at low temperatures in solution, a tetrameric (Ale)4, (Figure
7, structure I) is proposed based on 27Al NMR data (5 —l l l) and quantum chemical

resonance calculations (5 —105).28

Morton

finmllhme
Rumali
Gan h
’fikmédlnllst
it lili-sill‘ttl“ 1C
’6. NMR of (
incahuhuedt
Aseafl;
b1 Fischer an
imtdenu of

3-"“-’lr.'Cpc;‘tn

lnCt3 .

Sohd s
T.

one

Chill“.
,ezchons K

M

i
L t L,M\ M r
.Méét e W7

M /M
L '1"
L
Monomer Tetramer Hexamer
H I J

Figure 7. Three schematic structural representations of (ML). (monomer, H; tetramer, l:
hexamer J).

Gan is stable at room temperature, but it is highly volatile and can not be
Obtained in a solvent-free state. Mass spectrometric and NMR data suggest Gan exists
as half-sandwich complex (Figure 7, Structure H) in the gas phase and in solution. The
7|Ga NMR of Gan contains a high field resonance (5 —714), which compares well with
the calculated value (5 —696).32

As early as 1957, the first organometallic indium(I) complex, InCp, was reported
by Fischer and Hofmann. The synthesis involves the treatment of InCl3 with four
equivalents of LiCp. InCp; is then reduced by the last equivalent of Cp‘, giving InCp (eq

5 ).30 InCp can also be prepared by metathesis reactions starting from InCl.33

- 3 NaCl

lnCl3 +3 Nan InCp3 Cp InCp + 3/2 sz

 

 

(5)

Solid state structures of InCp and Tle contain zigzag chains of [M(n5-C5H5)]...
In one chain, indium/thallium and C5115 rings alternate.34‘36 There are weak In—In
interactions (3.986(1) A) between inter-chains. However, in the gas phase, an Open

sandwich structure is determined with a much shorter In—centroid distance (1.59 A).37

Suhttitunt
cont-pines. The 1
reaction betu eer'

.thp‘ l\
decomposition at
at Iii-honled to
care tetrahedron
iata tugged an .
(tilt the tetrartier
nanomer L1? “.1.“

energy is calcula

Substitution of Cp by Cp* (Cp* = C5Me5) leads to stabilization of mono-valent
complexes. The original synthesis of MCp* (M = A1, Ga, In, Tl) involved metathesis
reactions between M(I) halides and Cp*Li or Cp*zMg.

Ale* is stable at room temperature and can be sublimed with very little
decomposition at 140 °C.38 X—ray analysis reveals an A14 tetrahedron and the Cp* ligands
are nS—bonded to the aluminum centers (Figure 7 I). The Al—Al distance (2.769 A) in the
core tetrahedron is shorter by 0.09 A than that in aluminum metal. Solution 27Al NMR
data suggest an equilibrium between a tetramer and a monomer. At room temperature
only the tetramer is detected by 27Al NMR. On raising the temperature above 60 °C, the
monomer appears and its concentration increases with temperature.28 The tetramerization

energy is calculated as —36(5) kcal/mol.7-5t38

PP'
Al
/1. ——~—— 4 ©
* /Al’—‘>AL * 1
Op Cp* Cp Al
Tetramer Monomer

Figure 8. Equilibrium between monomeric tetrameric (Ale*)4 and Ale* in a benzene
solution.

Gas phase electron diffraction determines the structure of Ale* to be monomeric
and least-squares refinements yield a C5,. symmetry with Al—C distance of 2.388(7) A and
perpendicular Al—ring distance of 2.063(9) A39

The structures of Gan* and InCp* are similar. Both are hexameric in solid state
with weak metal-metal interactions. The metal-metal distances are in the range of
3.943(l)—4.l733(3) A405“ Both of them are monomeric in gas phase and in solution,
and the gas phase metrical data are close to that of the solid state structure“,43 The

structure of Gan* is significant because shorter Ga—Ga contacts might be expected from

the smaller ionic

 

inathallium.“ 1'

[King tlu
been prepared at
long and identica

Alternattt
nub p011\_\ltlm It
for synthesis of .-‘
Reactiiities of .\

blontHci
nenbonding eiec
transition metal t

Thelone
ll 1111 complete
min intermedi;
the nature of [‘1
:‘t'nenzatton.SS t

cements. affordi

2 MCp'

the smaller ionic radius of Ga. Tle* is polymeric with a zigzag chain of alternating Cp*
and thallium.44 It also is monomeric in the gas phase.45

Using the even bulkier C5(CH3Ph)5. In[C5(CH2Ph)5] and Tl[C5(CH3Ph)5] have
been prepared and their structures have been determined. Both solid Structures contain
long and identical M---M interactions (3.63 A, M = In, Tl).46'48

Alternatively, Ale* and Gan* can be prepared by reductive dehalogenation
with potassium metal in hydrocarbon solvents, eliminating the need for special equipment
for synthesis of AlCl and GaCl.49'51
Reactivities of Mono-valent Group 13 Complexes

Mono-valent group 13 complexes can act as O—donor ligands because of
nonbonding electron pair (lone pair). In this context, they can act as a ligand in stabilizing
transition metal complexes exemplified by Cr(CO)5(Gan*).5lt52

The lone pair of electrons can be oxidatively removed, resulting in more stable
M(III) complexes. For example, (Ale*)4 and Gan* react with organic azides yielding
imido intermediates which dimerize to afford [Cp*Mmg-NRHZ (eq 6).53~54 Depending on
the nature of the organic group in azides, C-H activation may compete with the
dimerization.55 (Ale*)4 reacts with a variety of oxidants such as tellurium and selenium

elements affording heterocubanes of (AlTeCp*)4 (AlSeCp*)4.50

 

 

‘i
2 RN /N\
2 MCp* 3 2 c *—M=N—R C *-M M—C *
_2 N2 9 p \N/ p
I
R (6)

 

llonntalenl G“

The hid“

1
meta} completes :

. en cemnrehenxit

figure 9. Schemattt

R and R: are the SU

in“'B“TG
been Wilmi-
{eta indicated bf
llono-taleni CWT

Bulky talk.)
airpteres. The 1‘}
If" C1166 1n.m

llebl

distances clt:

More recer

...”.rperes suppt’1

emtnattons I€\

Mono-valent Group 13 Element hydrotris(pyrazolyl)Borate Complexes

The hydrotris(pyrazolyl)borate ligand (structure K) is able to Stabilize various
metal complexes including gallium(l), indium(I). and thallium(I), and its chemistry has

been comprehensively reviewed.56'58

 

 

Figure 9. Schematic representation of hydrotris(pyrazolyl)borate ligands, [TpRle] where
RI and R2 are the substituents at 3,5-position in the pyrazolyl ring, respectively.

[Tp3.5-'Bu2]Ga’59 [Tp3-Phlln,60 [Tp3'tB“]In,61v62 [Tp3.5-’Bu2]1n,62 and [Tp3.S-(CF3)3]In63
have been prepared by metathesis reactions. All structures are monomeric in the solid
state as indicated by single crystal X-ray analyses.
Mono-valent Group 13 Element Alkyl And Aryl Complexes

Bulky alkyl and silyl ligands are also able to stabilize mono-valent group 13
complexes. The syntheses and structures of [B(CMe3)3]4,64 and [MC(SiMe3)3]4 (M =
A1,65 Ga,66 In,67~68 and T169) were reported. All structures contain M4 tetrahedra with
M—M distances close to those of the native metals.

More recently, Power and co-workers reported the synthesis of In(I) and Tl(I)
complexes supported by C6H3-2,6-Trip2 (Trip = C6H2-2,4,6—'Pr3). X-ray structure

determinations revealed one-coordinate metal centers.70~7'

10

Mono-talent (ir

 

Mono-t .r“
comprehensirel}
in the solubilrt}

insoluble in arena.

   

E‘IOVCT} different i

The arene—
teahlnhed by sin
cmrdinaretl to 1110
formal Di-Ialent I

T'nlike AlX
certigr'etes or 1', If -
bell-bl bond for
.llBr; Can he prep.

Lacroentit} of Al.\

. e ,
1"” '(CSHell;

Mono-valent Group 13 Element Arene Complexes

Mono~valent gallium, indium, and thallium arene complexes have been
comprehensively reviewed.72 The interaction between arene and Ga(l) is used to account
for the solubility of Ga+[GaCl4]' or GaClz in aromatic solvents. Though K+[GaCl4]' is
insoluble in aromatic solvents, Ga+[GaC14]’ forms a 7% (w/w) solution in benzene and
two very different resonances (5 —650 and 247) are observed by solution 71Ga NMR.72

The arene—M(I) complexes (M = Ga,73'7S In,76’77 and T178) were rigorously
established by single crystal structural analyses. The results indicate that M(I) is
coordinated to two nb-benzene rings.
Formal Di-valent Group 13 Element Chemistry with M—M Bond

Unlike Ale, GaXz and Ian are diamagnetic.79‘83 In contrast to the mixed-valent
complexes of [{ no-(C6H6)}3M]+[MX4]' formed in aromatic solvents, Lewis bases induce
the M-M bond formation for GaXz and Ian (Figure 10).84’85 Also anisole adducts of

AlBr; can be prepared from AlBr and thermodynamic consideration casts doubt on the

o O

.. 2E) t
O O X
M2X4 X‘/“'A_§A:
" ”O

0

true identity of A1X2.82t86»87

 

 

tine-(CsHenaMrthn'

Figure 10. Reaction pathways for M2X4 (M = Ga, In) in aromatic solvents and in Lewis
bases.
Group 13 Element Chemistry with M-M Bonds

LiCH(SiMe3)2 reacts with (donor)X2M—MX2(donor) (M 2 Ga, In) affording
[CH(SiMe3)3]2M-—M[CH(SiMe3)3]3.88389 Because (donor)X2Al—AIX2(donor) is not

readily available, the dialane complex of [CH(SiMe3)2]2Al—Al[CH(SiMe3)3]2 has been
prepared by the reduction of [CH(SiMe3)2]2A1C1 with potassium metal.90

Small molecules can insert into M—M bonds,91'93 and one-electron reductions of
organometallic complexes containing Al—Al and Ga—Ga have been reported where EPR
data support a one-electron M—M 7r-bond.94'96 Employing suitable ligands, Robinson and
co-workers have reported the synthesis of cyclogallanes that exhibit aromatic character

(Figure ll).97»98 Theoretical calculations performed on model complexes of M2(GaH)3

(M = Li, Na, K) support this notion.99

Mes K [Ar
0 4“ er
a —’ ——Ga
2 "' 2 KCl Ar \|Ga
Mes K ‘Ar

Figure 11. Synthesis of dipotassium tris[(2,6-dimesitylphenyl)cyclogallene]
K2[(Mes2C6H3)Ga]3 (Mes = C6H2-2,4,6-Me3).

Using bulky aryl ligands, the coordination number of Ga can be lowered and the
number of bonding electrons in the Ga—Ga framework can be increased. Thus a complex
with the shortest Ga—Ga bond has been reported with a Ga—Ga distance of 2.319(3) A at
21 °C, and the product is proposed as a gallyne with a triple bond.100 However, there is a
debate about the nature of Ga—Ga bond. Cotton and co-workers have proposed a structure
containing a double bond, i.e. Na2[R—Ga=Ga—R] based on a density functional theory
calculationlm Schaefer and co-workers, using high level ab initio and density functional
quantum mechanical methods, suggest Ga—Ga triple bonds, composed of two dative and

one iztbond.102

it)?

bin

“'11
‘ '

1
II H

‘I..r.
r

if,

7..

.r-V‘u‘b
o =.

FPure

Mes* Mes* ,Nfal Mes*

6 Na ,' \
Mes* GaC|2 Mes* O GaEGa O Mes*
' 4 NaCl \\ I,

\ I
Mes* Mes* Na Mes*

 

Figure 12. Synthesis of a gallyne Na3[(2,4,6—Mes*3C6H3)Ga2] (Mes* = C6H2-2,4,6-‘Pr3)
containing the Shortest Ga—Ga bond.
Molecular Orbital Considerations

Assuming only the s and p orbitals make major contributions in bonding
interactions, pictorial representations of metal-based orbitals in three-, two-, and one-
coordinate mono-valent group [3 complexes are shown in Figure 13. In the three-
coordinate geometry, the metal is sp3 hybridized with a lone pair of electrons at the metal.
In this sense, the metal’s frontier orbital in structure L is isolobal with a methyl ligand.

In structure M, the empty pz orbital is perpendicular to the base plane and the
frontier orbitals are similar to a boryl fragment (R'RZB’) or a carbene. With a matching
co-ligand, it is possible to construct monomeric complexes with double bond characters
between a metal and the co-ligand. In structure N, the metal is sp hybridized, leaving two

empty p orbitals. Thus the frontier orbitals in are Similar to carbonyl groups (CO).103

I
’I I,”

o 7. 2. —°. 2
. 8 8" x y

sp3 sp2 sp
L M N

Figure 13. Pictorial representations of metal—based orbitals in three- (L), two- (M), and

one-coordinate (N) mono-valent group 13 complexes.

Ligand Considerations for Kinetic Stabilization

Suitable ligand sets can stabilize metal complexes in which the metal centers are
in novel oxidation states, have low coordination numbers, and alter the course of catalytic
reactions. Figure 14 shows several examples (far from being exhaustive) of non-
cyclopentadienyl ligands. Jacobsen and co-workers developed a salen-Mn(III) system,
(Figure 14 O) which catalyzes asymmetric epoxidations of alkenes.104 Diimine (P) late
transition metal complexes polymerize ethylene and (Jr-olefins.105»106 Since late transition
metals are less oxophilic than early transition metal and more functional group tolerant,
functionalized olefins can be polymerized.107 Amidinate (Q) and troponiminate (R) also
have been used in stabilizing transition metal and main-group complexesmib109
McConville and co-workers found that chelating diamide titanium complexes gave the

first living Ziegler-Natta catalysts for a—olefin polymerizations.1 10,1 1'

R/H R —|2‘
R2 R>‘_< R‘ R2
Q? ,3 QR?“ ,9
N O
‘i - “r - “I -
e . .
2
R -N\\l; N--R‘2 R\NK)N’R
R1 II“ R2 R2
R
P Q R

Figure 14. Different nitrogen containing ligand sets (salen O; diimine P; amidinate Q;

troponiminate R; diketiminate S).

14

Table 1 lists similarities and differences between hyrdotris(pyrazolyl)borate,
cyclopentadienyl, and diketiminate ligands. The charge of the three ligands is —1 and the
most common coordination number is 2 for diketiminate.

Table 1. Comparison of Tp, Cp, and diketiminate ligands.

 

Tp Cp Diketiminate
Charge —1 —1 --1
Number of electron donated 6 6 4
Coordination number 3 3 2
Cone angle (°) 2653 r71b 239. 9C
Wedge angle (°) 35a 55" 37C

 

aValue based on [Tp‘ Btr]Co(NCS) Rheingold, A. L.; Ostrander, R. L.; Haggerty, B. S.;
Trofimenko, S. Inorg. Chem. 1994, 33, 3666-3676.b Value based on ZGC* 2C1; system
with d(Zr—C5 ring centroid): 2.22 A, Janiak, C.; Lange, K. C. H.; Versteeg, U.; Lentz,
D.; Budzelaar, P. H. M. Chem. Ber. 1996, 129, 1517—1529. c Value based on X-ray
structure of In(Dipznacnac) (72), Qian, B, Smith, M. R, 111, unpublished results.

Table 1 also lists two specific examples ([Tp3't8“]Co(NCS) and ZGC*) of cone
angles for Tp and Cp, respectively. The values of cone angles and wedge angles can be
changed by varying substituents on the ligands. An illustration of cone angles and wedge
angles for MCp*2 is shown in Figure 15. For the diketiminate ligand, a wedge angle Of
37° is estimated from the positions obtained from the Single crystal X-ray analysis. See

Appendix C for details of the calculation.

 

. M wedge angle

    

Figure 15. Schematic illustration of cone angles and wedge angles Of MCp*2 systems.

There are several reasons to employ the diketiminate ligand (S) to support group
13 elements. First, its electronic and steric properties can be easily tuned to match the
metal’s requirements. Second, of structures Q, R, and S the diketiminate ligand is the

most steric demanding. Thus it may be possible for diketiminate ligand (S) to stabilize a

15

low coordination sphere by filling the space around the metal center. Third, its has
received less attention than tetraazamacrocylic derivatives which were reviewed.1 12“ 13
Fourth, its facile synthesis makes systematic explorations possible. We were able to
prepare the free ligand on a 50-gram scale in less than one week from inexpensive
starting materials.

Although diketiminate ligands (S) have been known for a long time, the chemistry
is limited when compared to known Cp ligands. Early investigations involved
spectroscopy studies of transition metal complexes supported by diketiminate ligands.1 14'
“6 In addition to our investigations,‘ '7'123 other groups have used diketiminate ligands
to carry out stoichiometric and catalytic reactions.124‘132 We use Theopold’s
abbreviation of R'Rznacnac for ,B-diketiminate, highlighting its similarity to

acetylacetonate (acac).126

Chapter 1

REACTIVITY OF INDIUM(I) HYDROTRIS(3-TERT-
BUTYLPYRAZOLYL)BORATE AND SYNTHESIS OF DIKETIMINATE
LIGANDS

Introduction

Bulky tris(pyrazolyl)borate ligands are able to stabilize a variety of metal
complexes,5657 and the coordination chemistry of indium(HI) supported by
pol y(pyrazolyl)borate ligands is well developed.133

To stabilize indium(I), it is essential to use a bulky protecting group at the 3-

3-Me

position of the pyrazolyl ring. For example, when K(Tp‘ ) is reacted with InI, the

disproportionation indium(HI) product of [In(Tp3'Mc)2]I is isolated instead of the desired
mono-valent complex, In(Tp'TMe).134 Bulkier hydrotris(pyrazolyl)borate derivatives
stabilize indium(I) centers and the syntheses and structures of In(Tp‘i‘ph),6O In(Tp3'tB")
(1),61 In(Tp3'5'tBuz),62 and In(Tp3'CF3)63 have been reported. In contrast to the
Oligomerization observed in the indium(I)-cyclopentadienyl system, all of the indium(I)
hydrotris(pyrazolyl)borate complexes are monomeric in the solid state.

The chemistry of indium(I) supported by hydrotris(pyrazolyl)borate is limited.
Dias and co-workers reported a transmetallation reaction between In(Tp3'IB") (1) and
ZnEt2, affording Zn(Tp3‘IB”)Et.61 Oxidative addition of 12 and Sg to In(Tp3'5'tBuz)

3

generated In(Tp"5’tB"3)I2 and In(Tp3'5'lB“2)(n2-S4), respectively.135 Similarly a terminal

3.5-’Bu2

selenido indium complex of (Tp )In=Se was reported.136 Because indium imido and

U

I
oxo complexes supported by TpH3 are not known, we attempted to prepare them

through oxidative group transfer reactions.

Results and Discussion
Reactivity of In(Tp3"B“)

The mono-valent indium complex of In(Tp'i'tB") (1) was prepared by a metathesis
reaction between InCl and T1(Tp3 '18“), where Tp3 '13” is viewed as a trident analogue of the
Ir-bonding Cp’. However, that reaction is heterogeneous in nature as both InCl and TlCl
are virtually insoluble in the organic solvent.6"62 We decided to investigate a
homogeneous transmetallation reaction using InCp* as the indium(I) starting material.
When InCp* and T1(Tp3"B") were mixed in a 1:1 ratio in a benzene-d6 solution, two new
products of 1 and Tle* were observed in a small quantity and an equilibrium was
reached in 3 days at room temperature (eq 7). The equilibrium constant was determined
to be 3.5 i 0.7 at room temperature (eq 8). Therefore 1 and Tle* are favored only to a

small extent over InCp* and T1(Tp3 18"). It appears that the success Of the synthesis of 1

starting from InCl and Tl(Tp3'!B”) is due to the heterogeneous nature of TlCl and InCl.

InCp" + Tr(Tp3"B”) In(Tpa’tB”) + Tle* (7)
1
K..., = [1][T|Cp*]/[lnCp*][Tl(Tp3’tB”)] = 3.5 i 0.7 (8)

Another transmetallation reaction occurred, instead of the formation of an adduct
[(Tp3‘lB")In—>A1Me3], when 1 was mixed with one molar equivalent of AlMe3 (eq 9). The
thermo-instability of InMe was indicated by a black precipitate (presumably indium
metal) in that reaction. This reaction indicates that the ligation in 1 between indium and

T1918“ is fairly weak, though detailed thermodynamic data are not available.

In(Tpa‘IB”) + ArMe3 —> Ar(Tp‘3"B")Me2 + “InMe” (9)
1 2

18

Similar to a report by Parkin and co-workers,‘35 treatment of an ethereal solution
of l with one equivalent of I2 yielded a two-electron oxidation product of In(Tp3’tB")I2 (3,
eq 10). The 1H NMR spectrum of 3 shows a 2:1 pattern for the three 3-tert-butylpyrazolyl

resonances, indicating a static structure for compound 3.137

In(Tps'tB”) + 12 —> tn(Tp3"B“)r2 (10)
1 3

Synthesis and Structure of nz-Tetraaza-Z-butene-l,4-diyl Indium(III)

When a solution of l in pentane was treated with an excess of MN; (4
equivalents), a yellow solid immediately precipitated in moderate yields, and N2 gas was
evolved (eq 11). The yellow solid was formulated as nz-tetraaza-Z-butene-1,4-diyl
indium(HI), In(Tp3'IB“)[N(Ar)—N=N—N(Ar)] (4 Ar = Ph, 5 Ar = p-Tol) based on the
results of lH, l3C{'H} NMR, IR, elemental analysis (C, H, N), and X-ray structural

determination.

 

/
H-B—N—N In - N2 H-B N\ ‘ /|n\
\N—N’ tBu N\ N’t'Bu T
VTBU Bu Ar (1 1)
1 4 Ar = Ph
5 Ar = p-Tol

The X-ray structure of 4 was solved and its simplified molecular structure is
Shown in Figure 16. Disordered tert-butyl group C(6) and a toluene molecule at half
Occupancy are omitted for clarity. Table 3 summarizes the crystal data and refinement

parameters. The selected bond distances and angles for compound 4 are listed in Table 2.

l9

     

M

1150133)
13%“
{a
7
C(29) {a
g,
C(27)

Figure 16. X-ray crystal structure of In(Tp3JB")(N(Ph)—N=N—NPh) (4) with thermal
ellipsoids drawn at the 50% probability level.
Table 2. Selected bond distances (A) and angles (deg) for compound 4.

 

In-N(2) 2.225(11) N(4)—N(5) l.26(2)
In—N(l2) 2.282(9) N(5)—N(6) 1.38(2)
In—N(22) 2.276(9) N(6)—C(36) 1.41(2)
In—N(3) 2.110(9) B—N(21) 152(2)
In—N(6) 2.104(9) B—N(1) 154(2)
N(3)—N(4) 1.388(14) B—N(l 1) 157(2)
N(6)—In—N(3) 73.8(4) N(2 r )—B—N( 1) 1 12.9(1 1)
N(6)—In—N(2) 106.6(4) N(21)—B—N(l 1) 108.2(1 1)
N(3)—In—N(2) 105.9(4) N(1)—B—N(ll) 109.7(12)
N(6)—In—N(22) 157.8(4) N(5)—N(6)—In 1 15.7(7)
N(3)—In—N(22) 100.2(3) N(4)—N(3)—In 1 13.6(7)
N(2)—In—N(22) 95.5(4) N(5)—N(4)—N(3) 1 18.5( 10)
N(6)—In—N( 12) 100.8(4) N(4)—N(5)—N(6) r 16. 1(9)
N(3)-In—N(12) 159.5(4) N(2)-In—N(l2) 94.6(4)

 

20

3-’B . . .
u). and a dramonrc nz-tetraaza-2-

Indium(III) in 4 is supported by one n3-(Tp
butene-1,4—diyl ligand and the geometry for five-coordinate indium(HI) is square
pyramidal with N (2) at an apical position. Indium is displaced 0.404(5) A above the plane
defined by N(3), N(6), N(12), and N(22). As expected, the In—N(2) (2.225(11) A) is the
shortest in the three In—Tp‘i"Bu bonds. The average distance of (2.261 A) of In—Tp3’tB"
bonds is significantly longer than that (2.107 A) of In—N(3) and In-N(6), indicating a
higher bonding order between indium and N4Ph2 than that between indium and Tp3't3".
The average distance of (2.261 A) of In—Tp‘uB" bonds in 4 is shorter than that in 1
(2.488(6) A)62 and is comparable with other indium(HI)-Tp complexes (2.168(14)—
2.230(l3) A).138 The disparate bonding distance between N(4)—N(5) (126(2) A) and the
pair N(3)—N(4) (1.388(14) A) and N(5)—N(6) (138(2) A) supports the formulation as an
nz-tetraaza-2-butene-l,4-diyl. Such ligands are common for transition metals, but not for
main-group elements. 139

The solution data for compounds 4 and 5 reflect dynamic exchanges at all
temperatures, in contrast to a static structure for compound 3. The lH NMR spectra of 4
and 5 contain one set of resonances for three pyrazolyl groups and one set of Ar
resonances, and the integration shows that there are two Ar groups per Tp3'tBu ligand.

We propose that compounds 4 and 5 form through a 3 + 2 cyclo-addition reaction
between ArN3 and an indium imido intermediate, (Tp3"B“)In=NAr (Figure 17). Though
organo-azides are well known for 1,3-dipolar cycloaddition reactions,”0 the proposed 3

+ 2 cyclo-addition reaction is unprecedented in an indium system. However, there were

several such examples in low-valent transition metal systems.1412142

21

 

:—\| ArNS N\| — /Ar
6 - —N
/" -N N ”

 

1 Ar
InZN/
J r‘
NthN
/ v
v Ar
/ ’Bu Ar
/ N 1,
N = _ 41:“ N N—\-In/ \IT
N N—N Bu |
V’Bu Ar
4Ar=Ph
5Ar=p-Tol

Figure 17. 3 + 2 Cyclo-addition between ArN3 and the proposed indium imido
intermediate (Tp3'!B“)In=NAr.
The 3 + 2 cyclo-addition reaction is fast and irreversible. Attempts to trap or

o u -t
observe the imido Intermediate (Tp3 B"

)In=NAr at low temperatures were not successful.
When a solution of 4 in toluene was treated with p-TOIN3, the indium-containing product
was recovered by addition of pentane. Its 1H NMR spectrum indicated no incorporation
of p-Tol into the precipitate. Compounds 4 and 5 are stable when in solid forms under an
inert atmosphere, but solutions Of 4 and 5 decompose to intractable materials in a few
hours at room temperature.
Reaction of In(Tp‘uB“) With N20

We also attempted to prepare a terminal indium oxo complex by oxidation with

N20. Exposing a solution of compound 1 to an excess of N20 yielded H[B(C3H2N2-3—
'Bu)4] (6) as the only identified product in low, but reproducible yields (eq 12). The Tp

22

containing product for the N20 and 02 reactions appears to be identical. Although
compound 1 is stable towards dry oxygen in the solid state, a rapid decomposition of the

ligand is observed in a benzene solution.

In(Tpa'tB“) + N20 —> an H[B(C3H2N2-3-’Bu)4] + unknowns (12)
1 6

The identification of compound 6 was supported by 1H, HB, and '3 C { IH} NMR,
IR, and single crystal analysis, but elemental analysis values (C, H, N) were consistently
lower than that calculated for 6. The solution 1H and '3 C{ l H} NMR spectra of 6 indicated
one set resonance for the 3-tert-butylpyrazolyl groups. The IR spectrum lacked B—H
stretches which typically show in the region of 2400—2600 cm", and the B—H coupling
was not detected in the single sharp resonance in the H B NMR Of 6. We were not able to
observe H[B(C3H2N2-3-'Bu)4] by 1H NMR between 5 20 and 5 —10. However, we solved
the crystal structure of 6 (Figure 18), and its X-ray data summary is listed in table 3 and

selected bond distances and angles are listed in table 4.

23

 

 

 

C(9)
C(4) 15
12,091 :-=
(9‘2 ,g.
I. _—/
N(2) 0(6)
\v
5‘"
C(3)

Figure 18. X-ray crystal structure of H[B(C3H2N2-3-’Bu)4] (6) with thermal ellipsoids

drawn at the 50% probability level.

24

Table 3. Summary of crystal and refinement data for compounds 4 and 6.

 

4°0.5(C7H3) 6

Formula C3650H4831nN 10 C28H45BN8
Formula weight 752.48 504.53
Temperature / K 173(2) 173(2)
Wavelength / A 0.70926 0.71073
Crystal system Monoclinic Monoclinic
Space group P21/n P21/c
Unit cell a / A 1627(2) 10.229(2)
b / A 9.880(7) 13.842(3)
c / A 2434(2) 21.650(4)
[3/ ° 108.77(7) 9698(3)
V/ A3 3705(5) 3042.7(10)
Z 4 4
atcar./gcm‘3 1.349 1.101
F (000) 1564 1096
Crystal size 0.30 x 0.25 x 0.20 0.25 x 0.20 x 0.20
9 range / ° 2.24 to 22.47 2.01 to 25.02
Indexranges OShS15,0SkS10,—26 0ShS12,0SkSl6,—25

S l S 24 S l S 25
Ref. collected 4228 5672

Independent reflections 4158 (R(int) = 0.0893) 5350 (R(int) = 0.0962)
Data / res. / parameters 4109 / 0 / 420 5340 / 0 / 334

GOF on F2 0.864 1.395

Final R (1 >2 0(1)) R1 = 0.0542, wR2 = 0.1607 R1 = 0.0530, wR2 = 0.1432
R (all data) . R1 = 0.0808, wR2 = 0.2008 R1 = 0.1520, wR2 = 0.1734
Lgst diff. pk and hole/eA”3 0.860 and —1.272 0.232 and —0.246

Table 4. Selected bond distances (A) and angles (deg) for compound 6.

 

1.525(4) N(1)—N(2) 1.365(3)
B—N(l 1) 1.520(4) N(l 1)—N(12) 1.375(3)
B—N(21) 1.576(4) N(21)—N(22) 1.357(3)
B—N(31) 1.527(4) N(31)—N(32) 1.387(3)
N(l 1)—B—N( 1) 109.7(2) N(l l)-B—N(21) 108.5(2)
N(11)—B—N(31) 109.9(3) N(1)—B—N(21) 108.6(2)
N(l)—B—N(3 1) 110.7(3) N(31)—B-N(21) 109.4(2)

 

The X-ray structure analysis unequivocally established the atom-connectivity for
compound 6. The results Show that a pseudo-tetrahedral boron is coordinated by four 3-
tert-butylpyrazolyl groups and all four tert-butyl groups are at the 3-position of pyrazolyl
group. Compound 6 could be formulated as tetrakis(3-tert-butylpyrazolyl)borate
(structure T Figure 19). Our result agrees well with a 3,5-dimethyl pyrazolyl analogue,
H[B(C3HN2-3,S—Me2)4] documented in literature.143 It is generally difficult to directly

locate a hydrogen atom by X-ray diffraction methods, but there is circumstantial evidence

25

for the location of H[B(C;H31\';-3-'Bu).;] as H122) labeled in Figure 18 by inspecting the
juxtaposition of the four pyrazolyl groups. cenain bond distances and angles. H(22) was
put at a calculated position and refined as a riding model. The spatial proximity between
N(22) and N(32) (2.673(4) A) implies an intramolecular hydrogen-bonding interaction
N(22)—H---N(32) (N(22)—H 0.86 A; H---N(32) 2.061(4) A). Alternatively. compound 6
might be seen as Lewis acid-base adduct between tris(3-ter1-butylpyrazol_vl)borane'4'1
and neutral 3-tert-buty1pyrazole or its tautomer (structure U Figure 19). That contribution
leads to an elongation of the B—N and a shortening of the N-N distances for the
protonated pyrazolyl group (21), relatively to others. Indeed. the expected trend was
observed in the X-ray crystallographic study. B-N(21) (1.576(4) A) is the longest of the
four B—N bonds and the distance of N(21)-N(22) is the shortest (1.357(3) A) in four

pyrazolyl rings (Table 4).

Figure 19. Resonance structures T and U of H[B(C3HN2-3.5-Me2)4] (6).

Although several tetrakis(substituted-pyrazolyl)borate complexes including
potassium tetrakis(3-tert-buty1pyrazolyl)borate are known. the decomposition of a B-H
bond in the Tp ligand under such mild conditions is unusual.""5~146 The B—H bonds are
very robust as K(Tp3"B") and '1"1(Tp3 J8“) are air-stable. Moreover, B—H bonds in Tl(Tp3'

I 1 u .l o a o o
Bu) rema1n intact even when '1‘1(Tp3 8“) IS treated w1th aqueous hydrochlonc and.”7 It

26

appears that the indium metal plays a role in the cleavage of B—H bonds in Tp3"Bu

3-‘Bu

because T1(Tp‘ ) does not react with N20 under similar reaction conditions. The fate of
the indium metal and the source of NH proton in compound 6 are not known.

Similar B—H cleavage in hydrotris(pyrazolyl)borate ligands was also observed.
When TiCnglz was treated with two molar equivalents of K(Tp3'5'Mez), tetrakis(3,5-
dimethylpyrazolyl)borate was isolated in low yields along with a titanium(III) complex
(eq 13).”3 In addition to the B-H cleavage, there are other decomposition pathways for
hydrotris(pyrazolyl)borate ligands that have been documented in literature. Reger and
Coan reported hydrotris(pyrazolyl)borate partially decomposes to give neutral 3,5-
dimethylpyrazole in the reaction between Ian and 1((Tp3 ‘5'M°2).148 Metal-coordinated

Tp3'5'Mcz is also susceptible to halogen substitution at the 4-position in the 3,5-

dimethylpyrazolyl ring in the presence of excess halogen.149
TiszClg + K(Tp3'5’M92) —> H[B(C3HN2-3,5-Meg)4] + TiCp2(Tp3'5'M92) (13)

The degradation of the ligand suggests that the B—H functionality needs to be
protected or removed to prevent ligand degradations. Kitajima and co-workers used an iPr
protecting group at the 5-position of pyrazolyl Tp3 ‘51?” to stabilize copper oxo
complexes,150 but we chose the latter strategy, eliminating the issue of B—H
incompatibility.

Synthesis of Diketiminate Ligands

There are two general methods for preparing diketiminate ligands. One,
developed by Lappert and co-workers, involves coupling of alkali metal
bis(trimethylsilyl)methyl with two equivalents of PhCN as shown in eq 141251151”2 The
need for a bis(trimethylsilyl)methyl precursor limits its synthetic application. Moreover,

only symmetrical ligands can be prepared by this route.'27~153

27

'\|| Meask /'-‘\ ,SiMe3
2| + Li[CH(SiMe3)2] _.

Ph 1311J\/k Ph

The ligands we have used are diketiminates which can be prepared from

(14)

condensation reactions between 2,4-pentanedione and primary amines (Figure 20).1 15,1 16
The advantage of this straightforward method is that various amines can be used to tune
the steric and electronic properties of the diketiminate ligands. The first condensation
reaction yields B—ketoamines 7, 8, 9, and 10 in 83-94% yields after azeotropically
removing water. Complex 7 can be condensed with another equivalent of p-TolNHz-HCI,
giving TolgnacnacH-HCl (19) in 55% yield. Compound 19 was deprotonated with KOH
to give TolznacnacH (11) in almost quantitative yields. When bulkier ArNHz (Ar = C6H2-
2,4,6-Me3, C6H3-2,6-Et2, C6H3-2,6-iPr2) was used, the yields of the second condensation
reaction plummeted (< 5%), and we were not able reproduce the results of a literature
report.128 After several failures, we found that addition of one equivalent of TsOH-HzO
in the second condensation reaction dramatically increased the yields (12 Ar = C6H2-

2,4,6-Me3 88%. 13 Ar = C6H3-2,6-Et2 76%, 14 Ar = C6H3-2,6-iPr2 80%).

28

Flgun: 2|

1
o o ArNH2 o my A’

- H20 /

 

7 Ar‘ = C6H4-4-Me 83%
8 Ar1 = C6H2-2,4,6-M93 91%

9 Ar1 = C5H3-2,6-Et2 94%
10 Ar1 = 05H3-2,6-’Pr2 93%

”X - H20
N112Ar2

1 + X
A12\N HN,Ar KOH 2

M N’N

 

11 Ar1 = Ar2 = C5H4-4-Me 95% X = Cl. 0T8
12 Ar1 = Ar2 = C5H2-2,4,6-Me3 88%

13 Ar1 = A? = C5H3-2.6-Et2 76%

14 Ar1 = A12 = CGH3-2,6-’Pr2 80%

Figure 20. Synthesis of diketimine R'RznacnacH.

Asymmetric diketiminate R'RznacnacH (Rl ¢ R2) can also be prepared as
DipiPmacnac (15) indicates. When a low boiling alkyl amine is used in the condensation,
activation of the ketoamines is needed. Activation of compound 10 with [OEt3]+[BF4]’
and subsequent treatment with iPrNHz generated 15 in moderate yields. The advantage of
this reaction is the mild reaction conditions.

Structure of Diketiminate Ligands

Solution NMR spectra for symmetric diketimines of 11, 12, 13, and 14 are

consistent with C2,, symmetry which can be explained by a fast proton transfer between

two nitrogen and fast rotations around N—Ar bonds eq 15.

Ar\N HN,Ar Ar\NH N,Ar

M M (15)

29

I)

Thcucidic
Metiminute in g
in pentane so 1h.
lithium dilctimm.
radii} dissulxc 11
appropriate metal

slim’nution of sul 1.

Ar
\N Hl

)V

The neutral
tzietimines teq 17
5.1..." ' ‘
MKL‘ImmeS lll lll

rjxtineticall} useful

AR
NH 1

A)

ll,

14‘.

The chlondL

The acidic NH in fi-diketimines can be deprotonated with "BuLi, yielding lithium
fi-diketiminate in good to excellent yields (eq 16). And such reactions can be carried out
in pentane so that coordinating-solvent-free lithium diketiminate can be prepared.
Lithium diketiminate complexes 16, 17, and 18 are yellow to pale yellow solids and
readily dissolve in toluene. Reactions between lithium diketiminate complexes and
appropriate metal halides introduce the B—diketiminate ligand to the metals with the

elimination of salt.

AKIN HN' Ar ”BuLi Ar\ N/LI\N,Ar
—_'n
M -BuH M (1.)
11 Ar = p-Tol 16 88%
13 Ar = can-26.1312 17 84%
14 Ar = C(,11_.-2,6-"r>r2 18 93%

The neutral [i—diketimines also react with strong acids to give protonated [3-
diketimines (eq 17). The protonated products are much less than soluble than the free [3-
diketimines in non-polar organic solvents. The protonated diketimines are also

synthetically useful in introducing the ligand to metal centers.

Ar\NH N, Ar HX + X
I Al’\ ’Pl‘\/L«’\ , Al'
M N N

 

\ H H (17)
11 Ar = p-Tol 20 X = Br 69%
11 Ar = p—Tol 21 X = I 72%
11 Ar = p-Tol 22 x = OTf 98%
14 Ar = C6H3-2,6-’Pr3 24 x = on 92%

The chloride anion can be substituted with a bulky tetraaryl borate (eq 18).

30

  
   

X11} (1.01.11
respecthely). A \llli,

11glc>lorthcdilc1ury

 

”'01 Li+[BArf4]' + [BArml'
Ar\ N/kV/LN Ar Ar\ ’ ‘ ’ ‘

-LiC| N’ ‘V' ‘ ’A'
H H H

(l8)
19 Ar = p-TOl 25 Al‘f = C6H3-3,5-(CF3)2 62%
l4-HC1 Ar = C6H3-2,6-’-Pr3 26 Arr = C6F4-4-Si'BuMe2 73%

X—ray crystal structures for compounds 11 and 14 were solved (Figures 21 and 22,

respectively). A summary of the data is listed in Table 5 and the bond distances and

angles for the diketimine ring are shown in Table 6.

31

Table 5. Sum mart

_____________———-—

__________——————

luuuulu
Formula weight
lenperature l K
Cnstul system
Space group
[tit tell at A

11/31

(' /J A

0. _
fl/

I” C

l'fA"
Z
deal. l .\\g l m.
Cu s61 size
Inlet range.

All ref. 11nd. r
D113; {'55. / p!
CUP 0“ F:

M “W3 11/ >
till data)

1;: diff— PC:
Cale ’/ C. A -f.

Hg““e '3 «

(1‘
1 [1
t...

V l

H-d

Table 5. Summary of crystal and refinement data for compounds 11, 14, and 21.

 

 

 

    

 

11 14 21
Formula C19H22N2 C58H84N4 C19H231Nz
Formula weight 278.39 837.29 405.29
Temperature / K 173(2) 173(2) 173(2)
Crystal system Monoclinic Monoclinic Triclinic
Space group P2)/c P2 )/n P T
Unit cell a / A 15.066(3) 15. 1039(3) 7.9306(2)
b / A 6.0674(12) 18. 15770( 10) 11.1063(3)
c / A 18. 184(4) 20.1169(4) 11.1107(3)
a/ ° 86.53
fi/ 0 9937(3) 97.647000) 70.7800(10)
y/ 0 86.7410( 10)
V/ A3 1640.0(6) 5468.0(2) 921.68(4)
Z 4 4 2
dca1./Mg/m3 1.127 1.017 1.460
Crystal size 0.25 x 0.20 x 0.20 0.22 x 0.18 X 0.15 0.28 x 0.25 X 0.25
Index ranges —19ShS 19, —8Sk —20ShS l9,—24S —10ShS 10,—14S
S6,—24SlS22 kS24,—26SlS23 kS12,-14SlS14
All ref. (Ind. ref) 9664 (3830) 49137 (12970) 9412 (4247)
Data/res./par. 3829/0/ 199 12970/0/564 4247/0/ 199
GOF on F2 0.972 1.044 0.589
R1 (wR2)[l >2 0(1)] 0.0507 (0.1410) 0.0985 (0.1939) 0.0219 (0.0682)
(all data) 0.0874 (0.1621) 0.2465 (0.2482) 0.0259 (0.0713)
Lgst diff. peak and 0.246 and —0.226 0.390 and —0.251 0.464 and —O.481
hole / e. A ‘3
C(12) C(10)
“ \\\~ C(9)
1mg, C(9) \A {\\\
l.) ‘\ C(11) ‘ {$4
\'-\\ \\\‘ 1
C(16)
'l” (1% N(1) H(l) N(2 7,“ A“
C(8) V '5‘ 0(5) (7157 y”: er C(17)
‘9” J . C(18)
t
CH) ("5) f‘ "\\‘ Ins.
@3 0(2) ['24, C(4) VA?
‘ 0(3) 0(5)
C(1)

Figure 21. X-ray crystal structure of TolznacnacH (11) with thermal ellipsoids drawn at

the 50% probability level.

32

C(13)

 

figure 22- X-r.

the 50

CC pfObdf
Table 6. Com .
\p

C1341(3)

 

<\
0(4) VIM/49 C(27)

A)

C(28)

2}
C(29)

 

Figure 22. X-ray crystal structure of DipgnacnacH (14) with thermal ellipsoids drawn at
the 50% probability level.

Table 6. Comparison of selected bond distances and angles of compounds ll, 14, and 21.

 

 

11 14 21
N(1)-C(2) 1.355(2) 1.328(3) 1.348(3)
C(2)—C(3) 1.373(2) 1.403(4) 1.389(3)
C(3)—C(4) 1.434(2) 1.399(4) 1.400(3)
N(2)-C(4) 1.305(2) 1.315(3) 1.333(3)
N(l)—C(2)—C(3) 120.9(2) 120.9(3) 121.6(2)
C(2)—C(3)—C(4) 126.4(2) 125.9(3) 126.9(2)
N(2)—C(4)-C(3) 120.5(2) 120.8(3) 121.9(2)

 

The intra-molecular hydrogen bond in diketimines is broken upon treatment of
strong acids. To minimize repulsion between two nitrogen atoms, the U-shaped
diketimines change to W-shaped conformation. The change has been confirmed by a

structural analysis of 21. Its structure contains the ligand as F as an ionic pair, as shown

33

infigue33.Se
structural 211131))

phetttl.”4

figure 23 X
. ~r;

:r‘b '-
db1}1[.\"l€\'el

C
Ompiiri)
11') 3‘16

in Figure 23. Selected bond distances and angles are listed in Table 6. The result of the
structural analysis compares well with a similar structure where the aryl groups are

phenyl.154

C(1) 0(5)
(”I '2,

   

"
‘8' C(16)

45.117
C(19)
Figure 23. X-ray crystal structure of 21 with thermal ellipsoids drawn at the 50%
probability level.
Comparing to 11, the bond distances in 21 suggest greater electron delocalization

in the pentene backbone. In 21, the C(2)—C(3) distance (1.389(3) A) is comparable with

34

031-04) one
than C13 l-Cl-i
Attempted S}
We attt
treated with or
uelds. The the
ungle crystal

shown in C ha;

C(3)—C(4) one (1.400(3) A) while in 11 C(2)-—C(3) distance (1.373(2) A) is much smaller
than C(3)—C(4) one (1.434(2) A, Table 6)
Attempted Synthesis of In(Tolznacnac)

We attempted to use Tolznacnac to support indium(I) complexes. When InCl was
treated with one equivalent of Li(T012nacnac) (l6), In(Tolznacnac)3 (27) is isolated in low
yields. The indium(III) product 27 has been identified by solution spectroscopy methods,
single crystal X-ray diffraction, and an independent synthesis from InC13. Details are

shown in Chapter 4.

35

lntroduction
Beeuu
to use diketirr
to stabilize in.
complexes to ‘.
'eehemistrt'
The ste-
Changing the
Wallfldione'l
570L113 l3 COmF
Remus and D
511111195), and

When

Chapter 2

SYNTHESIS, STRUCTURE, AND REACTIVITY OF fi-DIKETIMINATE
BORON(III) COMPLEXES

Introduction

Because Tp ligands are not able to support indium oxo complexes, we attempted
to use diketiminate ligands to support indium(I) centers. However, Tolgnacnac is unable
to stabilize indium(I) centers because of the disproportionation of indium(I) diketiminate
complexes to indium(III) and indium metal. That disproportionation prompted us to study
the chemistry of hi gh-valent species.

The steric and electronic properties of diketiminate ligands can be easily tuned by
changing the amine starting materials in the condensation reaction with 2,4-
pentanedione.114'116 We wished to use B—diketiminate ligands to prepare monomeric
group 13 complexes in novel geometries and to investigate their reactivities.

Results and Discussion
Synthesis and Structure of B(Tolznacnac)F2

When BF3'OE12 was treated with one equivalent of Li(T012nacnac) (16) in
toluene, the B—diketiminate boron(III) difluoride complex, B(Tolznacnac)F2 (28) was
isolated in 46% yield (eq 19). Compound 28 was characterized by conventional
spectroscopic methods. Variable temperature (VT) IH NMR data (toluene-d3, -50 to 50
0C) were consistent with the presence of a C2 axis containing boron and the methine
carbon of the diketiminate ligand in compound 28. The llB NMR spectrum of compound
28 exhibited a 1:221 triplet ('JB_F = 29.1 Hz) at 5 2.0, and the l9F NMR spectrum revealed

36

alzlzlzl qua

consistent s11)

BFg-C

The s
refinement dc
boron center '
The atoms in
essentially c0
1.384(3) .51. C
suggest that
delocalization
5131116611 ~50
and distance
those of 2.2-d
141.1312) All

C(12)

figure 24. x

:1 the 300
r PR

a l:l:l:1 quartet at 6 —128.9 with a similar value of 'JB_F. The solution NMR data are

consistent with a monomeric boron species. 155

BFa-OEIQ + Li(To|2nacnaC) —> B(To|2nacnac)F2 + UP (19)
16 28

The solid state structure of 28 was solved (Figure 24). Cell parameters and
refinement details for 28 are listed in Table 7. The structure contains a pseudo-tetrahedral
boron center with the diketiminate ligand nz-bound to boron through the nitrogen atoms.
The atoms in the diketiminate backbone (C(2), C(3), C(4), N(l) and N(2)) and B are
essentially coplanar. The similar bond distances for the C—C and N—C pairs (C(2)—C(3) =
1.384(3) A, C(3)—C(4) =1.401(3) A; N(1)—C(2) = 1.339(3) A, N(2)—C(4) = 1.347(3) A)
suggest that the It electrons of N(l)—C(2)—C(3)—C(4)—N(2) are delocalized. The
delocalization is also confirmed by the chemical equivalence of symmetry related protons
between —50 °c and +50 °C in its ‘H NMR spectrum. The average (1.404(4) A) of B—F
bond distances in structure 28 (B-F( 1), 1.411(3) A; B—F(2), 1.396(3) A) are very close to
those of 2,2-difluoro-l,3,4,6-tetramethyl-3-aza—1-azonia-2-bora-4,6-cyclohexadiene (B—F
1.403(2) A)”6 and 4,4-difluoro-1,3,5,7,8-pentamethyl-3a,4a-diaza-4-bora-s-indacene
(B—F 1.394(3) A).157~158

 

Figure 24. X-ray crystal structure of B(Tolgnacnac)F2 (28) with thermal ellipsoids drawn

at the 50% probability level.

37

Alkylation C he

Ditluorir
literature. Vinar
to stabilize the
reactivity at his

reagents u as ex;

2 LiM

Figure 25. All“

Tret‘ttmc
Mi‘C .
- ATOI’CF

Cs‘lp‘
TE’ -
)Elr’ldl’lCEg fllf ‘

“(ed a 5m;

(’1;
’I

Alkylation Chemistry

Difluoride compounds related to compound 28 have been described in the
literature. Vinamidine boron difluoride was used as a ligand, binding in and ns-fashion,
to stabilize the tricarbonylchromium fragment.159 Since our interests centered on the
reactivity at boron, alkylation of compound 28 with various lithium and magnesium

reagents was examined (Figure 25).

urn

F
J

p—To|\ /B\N,p-To|

M

 

28
2 LiMe 2 LiCHZSiMea 2 Flng
rt
M3381 Fifi
p-Tol\ ,B. ,p-Tol P'T0'\ ,3\ ,pm p-Tol\ /B\ ,p-Tol
N N N N N
29 550/0 30 470/0 31 R: M6 660/0

32 F1: "Pr 56%
33 R: CzH3 500A)
34 F1: C3H5 69%
Figure 25. Alkylation reactions of B(Tolznacnac)F2 (28).
Treatment of compound 28 with two equivalents of MeLi generated B[T]2-
Me2C(NTol)CH=C(NTol)Me]Me (29) in 61% yield. The desired dimethyl boron
compound 31 was not detected in the crude reaction mixture. The nonequivalent methyl

resonances for the ligand backbone in the 1H NMR spectrum for compound 29 initially

suggested a structure of (nl-Tolgnacnac)BMe2 where the Tolgnacnac ligand was n1-bound

38

to. the Blle; ntrtiets

 

structure since the 1
Three h)drrtgen atru
suggested it) a qua
because compound
tetueen 585 and
electrophilic than 1
mine-based ligunr.
rteihjilatiun 0n the

The struetr
iittracrion anal) s1
listed in Table 8.1
iuruni360017t: l.
and B—C (B~Cr
iazahurulidine.H
itstcinces in the C

.1) are no lOHEen

to the BM62 moiety. However, the integration of resonances did not support the "arm-off"
structure since the highest field peak (5 —0.009, C6D6) assigned to B(CH3)2 integrated as
three hydrogen atoms instead of the expected six. Methylation at the imine-carbon was
suggested by a quaternary carbon resonance in its l3C NMR spectrum (6 54.94, C6D6)
because compounds 28 and the related aluminum alkyl complexes lack resonances
between 6 85 and 5 30 in their 13C NMR spectra. Although imines generally are less
electrophilic than corresponding aldehydes or ketones, the nucleophilic addition in an
imine-based ligand has literature precedent. Jordan and co-workers reported a similar
methylation on the dibenzotetraazaannulene ligand of a zirconium complex.160

The structure for compound 29 has been confirmed by single crystal X-ray
diffraction analysis (Figure 26, Table 7), and selected bond lengths and bond angles are
listed in Table 8. The boron center in 29 is planar, as indicated by the sum of angles about
boron (360.0(7)°). The bond distances of B—N (B—N(1), 1.431(6) A; B-N(2), 1.425(6) A)
and B—C (B—C(21), 1.563(7) A) in 29 resemble those in 1,2,3-trimethyl-1,3,2-
diazaborolidine.161 In contrast to the delocalization observed in compound 28, the C—C
distances in the C3N2B ring in compound 29 (C(2)—C(3), 1.305(6) A; C(3)—C(4), 1.488(6)

A) are no longer equivalent because of quaternary carbon C(4).

39

C(13)

Figure 26. X-
prohabilit} lesc'

Three r
391Figure 27)
addition to the
could precede
from a methyl
be excluded b
Conditions (tit
'sere mixed it
unreaeted 28

methylation 0

3
C(10) ls.)

(‘3 C(11)
C(13)

 

Figure 26. X-ray crystal structure of 29 with thermal ellipsoids drawn at the 50%
probability level.

Three potential reaction pathways could account for the formation of compound
29 (Figure 27). The first one involves an alkylation at boron followed by a nucleophilic
addition to the imine-carbon (pathway i). Conversely, the nucleophilic addition to carbon
could precede the alkylation at boron (pathway ii). Lastly, compound 29 could also result
from a methyl migration in B(T012nacnac)Me2 (31) (pathway iii). The last possibility can
be excluded because independently prepared compound 31 is stable under the reaction
conditions (vide infra). To distinguish between pathways i and ii, compound 28 and MeLi
were mixed in a 1:1 molar ratio at —78 °C. Under these conditions, a mixture of 29 and
unreacted 28 is observed by 1H NMR. Thus, we cannot determine whether the initial

methylation occurs at the boron or at the ligand backbone.

40

\f
MeLi AKN ,B\ N’ Ar MeLi

 

 

 

- UF M - LiF

i
E: IF F T
Ar\ NI B\ N, Ar _—__-> ii MeLi Ar\ N, B\N MeLi Ar\ N’ B\ N, Ar
M -|-1F 701 -11.: M
28 29

111

Megs/1e Me

Ar = PM 2 MeLi Ar\ , 8. Ar migration

 

 

 

—2LiF M

Figure 27. Three potential reaction pathways for converting 28 to 29.

When a more hindered alkyl lithium reagent, LiCHgSiMeg, is used, alkylation at
boron and deprotonation of the Tolznacnac ligand occur, yielding B[n2-
CH2=C(NTol)CH=C(NTol)Me]CH2SiMe3 (30) in 47% yield (Figure 25). Presumably
since CstiMe3 is more sterically demanding than Me, the deprotonation of a methyl
group is favored over a nucleophilic attack at an imine-carbon. Compound 30 has been
characterized by spectroscopic methods and single crystal X-ray diffraction. The
molecular structure for compound 30 is shown in Figure 28. Like compound 29, boron is
three-coordinate in 30, and B—C and B—N distances in the structures for compounds 29
and 30 are similar. The biggest structural difference between 29 and 30 is an apparent
delocalization along the diene backbone of the chelating dianionic ligand in 30 as
indicated by similar C—C distances for carbons from C(1) through C(5): C(l)—C(2) =
1.413(3), C(2)—C(3) =1.395(3), C(3)—C(4) = 1.389(3), and C(4)—C(5) =1.427(3) A. The
l'B NMR chemical shifts are diagnostic for the coordination number for boron center and

compounds 29 (5 31) and 30 (5 33) are similar to that for (BMeNMe)3 (5 35.9). ‘62

41

Fig)

@101

 

C(15) C(1)

 

'1'.
. 414 )3

A
III,

3., 21
C(22) ( ) C(23)

Figure 28. X-ray crystal structure of 30 with thermal ellipsoids drawn at the 50%
probability level.

When compound 28 is treated with two equivalents of freshly prepared MeMgI in
Et20, the desired dimethyl product B(Tolznacnac)Me2 (31), forms (Figure 25). In this
case, the methylation exclusively occurs at boron, and compound 29 cannot be observed
in the reaction mixture. In addition to symmetric peaks for the ligand, the lH NMR
spectrum for compound 31 contains a high field singlet (5 —0.44, 6H) which is assigned
to BMez. The 1'B NMR chemical shift of 31 (5 1.07, Dy, = 259 Hz) is consistent with
tetrahedral boron. Inter-conversion between compounds 29 and 31 does not occur after
prolonged heating solutions of 29 or 31 in toluene at 70 °C. Attempts to make
B(T012nacnac)FMe by mixing 28 with one equivalent of MeMgI at different temperatures
invariably lead to 31 and unreacted 28.163 Other di-organo complexes, (Tolznacnac)BR2
(R = "Pr (32); R = C2H3 (33); R = C3H5 (34)), can also be synthesized from compound 28
and the corresponding Grignard reagents (Figure 25).

The solid state structure of compound 31 was determined and its X-ray structure

is shown in Figure 29. Its structure contains a pseudo-tetrahedral boron center (Table 8).

42

Despite (1
ll. compo;
10130 ‘
1 Tfi-hthf
distance.

1 "1‘ “
“N-W

111311116 .

Fl.gllre

1:111:81)

Despite the higher coordination number for 31 than for 29 and 30, the B—C bond lengths
in compound 31 (average = 1.623(4) A) are longer than those in compounds 29 (1.563(7)
A) or 30 (1.567(3) A) (Table 8). The elongation of the B—C bonds in 31 is consistent with
a re-hybridization for boron from sp2 in 29 or 30 to sp3 in 31. The longer B-N bond
distances in compound 31 (average = 1.615(3) A) relative to compound 28 (average =

1.552(3) A) can be explained by a weaker inductive effect of a methyl group relative to a .

        

fluorine.
C(1)
c.
\ C(11)
C(15 "\Q C(10)
(hr.
"’,’\ ‘.
C 16 ‘*

l \ C(6) A019)
7“ \‘ ’ S =-. A
III _ . “E ~ ‘3'"
C(19) IIII‘ "C1 (S ‘ \‘z§ '

\.. ( 8) U C7) * C(12)

C(17)

Figure 29. X-ray crystal structure of 31 with thermal ellipsoids drawn at the 50%

probability level.

43

Table 7. Sum...
/

 

Formula
Til.
Temperature .1 .5
Crsstal s)stert~ 1
Space group .
Tmt tell u l A
b/ .1
cl A

 

x.

11.1/.119/m‘
Size mm

C}

mange l 3

Rel. Collected
D3121} reggpar'
00F ( F-
R1311 (131:1)

11951 (111.1. pk ‘
I . 1.3, ~ s

Table 8. Selects

Table 7. Summary of crystal and refinement data for compounds 28, 29, 30, and 31.

 

 

28 29 30 31

Formula C|9H2]BF2N2 C21H37BN3 C23H31BN351 C31H27BN3
F.W. 326.19 318.26 374.40 318.26
Temperature / K 173(2) 173(2) 173(2) 173(2)
Crystal system Monoclinic Monoclinic Monoclinic Tri_c_linic
Space group . P2./n C2/c P2t/c P 1
Unit celloa / A 13. 133(3) 40.617(8) 6.2891(13) 7.679(2)

b / A 7.312(2) 6.1689( 12) 25.017(5) 7.899(2)

c / A 18.537(4) 15.096(3) 14.543(3) 17.726(4)

05/ ° 9983(3)

[3/ ° 103.14(3) 97.77(3) 9573(3) 9259(3)

O y/ ° 115.42(3)
V/ A‘ 1733.4(6) 3747.7(13) 2276.7(8) 948.3(3)
Z 4 8 4 2
d,,../Mg/m-‘ 1.250 1.128 1.092 1.115
Size mm 0.20 x 0.18 x 0.30 x 0.22 x 0.28 x 0.26 x 030 x 0.25 x
0. 18 0.20 0.26 0.25
6 range / ° 1.73 to 28.20 2.02 to 28.31 1.63 to 28.23 2.35 to 28.21
Ref. Collected 10162 (3993) 6635 (3797) 26000 (5489) 10662 (4366)
Data/res.{par. 3993 / 0 / 217 3797 / 0 / 217 5489 / 0 / 244 4366 / 0 / 217
GOF / F ' 1.444 1.022 1.437 1.420
R (all data) R1 = 0.0959, R1 = 0.2401, R1 = 0.0873, R1 = 0.1108,
wR2 = 0.2215 wR2 = 0.2595 wR2 = 0.2082 wR2 = 0.2349

Lgst diff. pok 0.440 and - 0.288 and — 0.468 and - 0.443 and —
and hete/eA‘3 0.400 0.327 0.473 0.432

 

Table 8. Selected bond distances (A) and angles (deg.) for compounds 28, 29, 30, and 31.

 

 

28 29 30 31
B-Ca 1.563(7) 1.567(3) 1.619(4)
B—Ca 1.626(3)
N(l)—B 1.550(3) 1.431(6) 1.438(3) 1.610(3)
N(2)—B 1.553(3) 1.425(6) 1.445(3) 1.615(3)
N(1)—B-N(2) 108.6(2) l 18.5(4) l 16.9(2) 105.0(2)
N( l )—B-Ca l 19.6(4) 121 .9(2) 109.9(2)
N(2)—B—Cf’ 121.9(4) 121.1(2) 110.2(2)
N( l )-B—C" 109.6(2)
N(2)—B—Ca 109.6(2)

 

” C“ is carbon directly bonded to boron, specifically, 29 C(21); 30 C(20); 31 C(20) and

C(21).

Methyl Abstraction Reactions

Methyl abstraction from compound 31 to generate a cationic boron center was
examined. Unlike its aluminum analogue, A1(Tolznacnac)Me2, which undergoes an aryl-
Me exchange with B(C6F5)3,”7 compound 31 reacted with B(C6F5)3, giving
[B(Tolgnacnac)Me]+[BMe(C6F5)3]' (35) in 70% yield (Figure 30). Compound 35 can be

anMahuan

zwflmnon.

Py

ngure 30. Metl
The ”[3
comPOUnd 35, 1

-148 (U: : 3O

formulated as an ionic compound with discrete cation and anion, or as a methyl-bridged

 

 

 

zwitterion.
Mg Pile B(C F ) r l\|/|e 1 +[BMe(Cst)3l-
" 6 5 3
P'Tol\ /B\ ,p-Tol P‘T°'\N/B\N/P‘T0|
70% M
31 35
FY 760/0

' Py‘ ye ‘ +[BMe(CGF5)3]’

/
py= N: \> p-Tol\NéN,p-Tol

)VK

 

 

36

Figure 30. Methyl abstraction reaction of compound 31.

The 11B NMR spectroscopy provides strong evidence for the ionic formulation for
compound 35. Its 11B NMR spectrum contains two peaks at 5 37.1 (Dy, = 1200 Hz) and 5
-l4.8 (1202 = 30 Hz). The broad resonance (6 37. 1) for [B(Tolgnacnac)Me]+ is in the region
of three-coordinate boron, and it appears in a slightly lower field relative to compounds
29 (5 30.7) and 30 (6 33). The sharp resonance at 5 -14.8 is assigned to [BMe(C6F5)3]‘
because its chemical shift and narrow line-width are consistent with a tetrahedral boron.
Therefore, the HB data support three- and four-coordinate boron centers expected for the
discrete pair, [B(Tolznacnac)Me]+[BMe(C6F5)3]".164

A molar conductivity experiment also supports the ionic formulation for
compound 35. The molar conductivity for a methylene chloride solution of 35 (AM = 1.6
x 10‘2 szmol") is similar to that for [”Bu4N]+Br‘ (AM = 1.2 x 10'2 szmol'l). Thus,

compound 35 is largely dissociated in methylene chloride solution.

45

A comparison of lH and ‘3 C { 1H} NMR data for 31 with those for 35 provides
further evidence supporting the ionic structure. A change in boron hybridization from sp3
in 31 to sp2 in 35 enhances delocalization in the C3N2B ring in 35. A stronger ring current
effect should make methine in the diketiminate backbone and BMe less shielded in 35
than those in 31. The expected deshielding of the NMR resonances for CH and BMe in
35 is experimentally observed (Table 9). Upon delocalization, the resonance for CH in 35
moves downfield by 1.91 ppm relative to that in 31 (64.82).

Table 9. NMR chemical shifts for backbone CH and BMe resonances in compounds 31,

 

 

35, and 36.
31 35 36
CH 4.82 6.73 5.76
CH 95.18 111.62 101.81
B(CH3) —0.44 0.27 0.073
B(CHg) 8.22 10.7 10.2

 

We surveyed the reactivity of compound 35 towards olefins and Lewis bases. In
contrast to cationic amidinate aluminum alkyl compounds, compound 35 did not
polymerize olefins under similar conditions.'65 A possible explanation for the difference
in reactivity between B—diketiminate and amidinate group 13 compounds is that C3N2M
(M = B or Al) heterocycle is a six-electron n—system, while the CNzM counterpart is a
four-electron 7r-system. Thus, the diketiminate system may be sufficiently stabilized that
olefin coordination is unfavorable.

We also attempted to abstract a methyl group from the three-coordinate boron in
29, but this reaction was complicated. We propose that the stability of a boron cation
depends on the ligand, the geometry of the boron, and the counteranion.

More surprisingly, compound 35 did not bind diethyl ether or propylene oxide.
Nonetheless, compound 35 reacted with pyridine, forming the adduct,
[B(Tolznacnac)(Py)Me]+[BMe(C6F5)3]‘ (36) (Figure 30). The IH NMR spectrum of

compound 36 contained a resonance at 6 0.48 that is assigned to [BMe(C6F5)3]_. The

46

slight change from 6 0.41 in 35 implies that an interaction between [B(Tolznacnac)Me]+
and [BMe(C(,F5)3]’, are present in 35, albeit weak. '66

The ”P NMR data for compound 36 (6—167.2, —l64.6, —132.7) are virtually
identical to those for compound 35 (6—167.2, —164.5, -132.9), and the HB NMR
spectrum of compound 36 contains two peaks at 6—15.23 (s, vy, = 65 Hz) and 6 —4.19
(s, Dy, = 80 Hz). Both resonances have narrow line widths, indicating pseudotetrahedral
boron centers, and the diketiminate boron resonance at 6 —4.19 is shifted to higher field
relative to compound 35. This is consistent with the reduced aromaticity when the boron
center rehybridizes to Sp}. The lH NMR spectrum for a mixture of 36 and pyridine
contains one set of pyridine resonances that differ from those of pure 36 or pyridine.
Thus, the exchange between the bound pyridine in 36 and free pyridine is rapid on the

NMR time scale.

47

Chapter 3

SYNTHESIS, STRUCTURE, AND REACTIVITY OF B-DIKETIMINATE
ALUMINUMGII) AND GALLIUM(III) COMPLEXES: ROUTES TO CATIONIC
ALUMINUM COMPLEXES

Introduction

Aluminum alkyl complexes can oligomerize ethylene at high temperature and
high pressure, but B—Hydride elimination limits the chain growth.167 Recently, Jordan
and a co-worker reported cationic aluminum alkyl complexes supported by amidinate
ligands are able to polymerize ethylene to high molecular weight polymer.165 In the
preceding chapter, we described the synthesis of a cationic boron complex, however, it
does not interact with ethylene. We intended to expand similar chemistry to aluminum
and gallium, targeting the synthesis of cationic aluminum complexes as potential catalyst
for ethylene polymerization. Herein, we wish to present the results on the coordination
chemistry of Al(III) and Ga(III) supported by a fi-diketiminate ligand.
Results and Discussion
Synthesis and Structure of M(Tolznacnac)Clz (M = A1, Ga)

The reaction of Li(Tolznacnac) (16) with one equivalent MC13 affords the

dichloride M(Tolgnacnac)C12 (37 M = A1, 38 M = Ga) in good yield (71%) (eq 20).

48

C CI
1

Li
p-Tol / \ ,p-Tol - - M
MC|3 + \N -—-L—'9|—> p-To|\ / \ ,p-Tol

M M (20)

16 37M=Al7l%

H‘—

38M = Ga 89%

Compounds 37and 38 have similar solubility. Both of them are sparingly soluble
in aliphatic hydrocarbon solvents and can be crystallized as pale yellow crystals from
aromatic solvents. Compound 37 and 38 are moisture-sensitive and gave TolznacnacH
(11) as the primary organic hydrolysis product. Attempts to introduce two or three
Tolznacnac to aluminum or gallium failed. Neither halide metathesis reaction of
compound 37 and 38 with Li(Tolgnacnac) (16), nor treatment of MC13 with two or three
equivalents of 16 afforded compounds that could be isolated.

Solid state structures of 37 and 38 were solved (Figure 31) and are iso-structural.
A crystallographic two-fold rotational axis passes through M (M = A1, Ga) and C(3). One
half of one molecule defines in the asymmetric unit. Table 10 summarizes the crystal data
and refinement parameters and Table 11 lists the selected bond distances and angles for

compounds 37 and 38.

49

 

Figure 31. X-ray crystal structure of 37 M = A1, 38 M = Ga with thermal ellipsoids

drawn at the 50% probability level.

Table 10. Summary of crystal and refinement data for compounds 37 and 38

 

 

37 38
Formula CquzlAlClzNz C19H21C12GaN2
Formula weight 375.26 418.00
Temperature / K 142(2) 173(2)
Crystal system Monoclinic Monoclinic
Space group C2/c C2/c
Unit cell a / A0 15.014(3) 15.161(3)
b / A 7.782(2) 7.795(2)
c / A 17.037(3) 17.038(3)
. ° 102.97(3) 103.22(3)
V/ A3 1940.0(7) 1960.2(7)
Z 4 4
dcal./Mg/m3 1.285 1.416
Abs. coe. / mm"' 0.383 1.679
F (000) 784 856

Crystal size
Index ranges

Ref. collected
Independent reflections
Data / res. / parameters
GOF on F2

Final R [I >2 0(1)]

R (all data) .
Lgst diff. pk and hole/eA‘3

0.15 x 0.12 x 0.12
—15$hS20,—9Sks 10,
—21 s l S 22

5875

2291 [R(int) = 0.0354]
2291 /0/ 110

1.248

R1 = 0.0493, wR2 = 0.1488
R1 = 0.0660, wR2 = 0.1558
0.492 and —0.51 1

0.20 x 0.15 x 0.15
—15$h$14,—10$ks7,
4451321

2721

1768 [R(int) = 0.0147]
1768/0/ 110

0.928

R] = 0.0329, wR2 = 0.1052
R1 = 0.0385, wR2 = 0.1121
0.518 and —0.526

 

50

Table 11. Selected bond distances (A) and angles (deg.) for compounds 37 and 38.

 

 

37 38

Al—N 1.850(2) Ga—N 1.896(2)
Al—N(A) 1.850(2) Ga—N(A) 1.896(2)
Al—Cl 2.1238(9) Ga—Cl 2.1664(9)
Al—C1(A) 2.1239(9) Ga—C1(A) 2.1664(9)
N—C(2) 1.345(3) N—C(2) 1.336(3)
N-C(6) 1.442(3) N—C(6) 1.452(3)
N-Al—N(A) 9940(12) N-Ga—N(A) 100.16(13)
N—Al-C1(A) 1 1356(6) N—Ga—C1(A) 113.48(7)
N(A)—Al-C1(A) 1 1004(6) N(A)—Ga—C1(A) 109.90(8)
N—Al—Cl 1 1004(6) N—Ga-Cl 109.90(8)
N(A)—Al—C1 1 1356(6) N(A)—Ga—Cl 1 1348(7)
C1(A)—A1—C1 109.95(6) Cl(A)—Ga—Cl 109.72(5)

 

Single crystal analysis of structures 37 and 38 indicate that both of them are

monomeric and the metal center is pseudo-tetrahedral. Delocalization in the diketiminate
ring is observed.
Synthesis and Structure of Aluminum and Gallium Dimethyl Diketiminate
Complexes

We tested dimethylation of compounds 37 and 38. When ethereal suspensions of
37 and 38 were treated with two equivalents of MeLi, the dimethyl complexes of 39 and

40 were isolated in moderate to good yields, respectively (eq 21).

M(Tolznacnac)C|2 + 2 MeLi -—> M(Tolgnacnac)Mez + 2 LiCl (21)
37 M = A1 39 64%
38 M = Ga 40 74%

The solution NMR data indicate a C2,, symmetry for compounds 39 and 40. The
1H NMR resonances for the We in 39 and 40 appear at typically high-field (39 6 —1.05,
40 —0.63). Despite the highly polar metal—carbon bonds, compounds 39 and 40 are stable
even in wet organic solvents. Only at elevated temperatures (refluxing wet THF) do

compounds 39 and 40 hydrolyze.

51

The solid structures of 39 and 40 were solved (Figures 32 and 33). Only one of
two crystallographically independent molecules is shown in Figure 33. Similar to the
dichloride analogues, both dimethyl aluminum and gallium complexes are pseudo-

tetrahedral.

 

Figure 32. X-ray crystal structure of 39 with thermal ellipsoids drawn at the 50%
probability level.

 

Figure 33. X-ray crystal structure of 40 with thermal ellipsoids drawn at the 50%

probability level.

52

Table 12. Summary of crystal and refinement data for compounds 39 and 40.

 

 

39 40

Formula C21H27A1N2 C42H54Ga2N4
Formula weight 334.43 754.34
Temperature / K 142(2) 173.1(1)
Wavelength / A 0.71073 0.71073
Crystal system Monoclinic Monoclinic
Space group P2./c P2./c
Unit cell a / A 8.737(2) 18.291(4)

b / A 14.114(3) 13.089(3)

c / A 17.021(3) 16.883(3)

. [3/ ° 9382(3) 9056(3)

V/ A3 2094.4(7) 4041 .9(14)
2 4 4
d cal. / Mg / m3 1.061 1.240
F(000) 720 1584
Crystal size 0.18 x 0.16 x 0.15 0.25 x 0.25 x 0.25

Index ranges

Ref. Collected
Independent reflections
Data / res. / parameters
GOF on F 2

Final R [1 >2 0(1)]

R (all data) -
Lgst diff. Pk and hole/eA‘J

—9ShS9,—10.<.k$15,—
1831317

—24ShSS,—14Sks 15,
—22Sl$21

8078 19766

2965 [R(int) = 0.0995] 8939 [R(int) = 0.0277]
2965/0/218 8939/0/433

0.960 0.939

R] = 0.0543, wR2 = 0.1142
R1: 0.1260, wR2 = 0.1276

0.217 and —0.165

R1 = 0.0424, wR2 = 0.1274
R1 = 0.0697, wR2 = 0.1438
0.515 and —0.411

Table 13. Selected bond distances (A) and angles (deg) for compounds 39 and 40.

 

 

39 40

Al—N(l) 1.905(3) Ga—N(1) 1.981(2)
Al—N(2) 1.906(3) Ga—N(2) 1.981(3)
A1-C(21) 1.952(4) Ga—C(21) 1.961(3)
Al—C(20) 1.962(4) Ga—C(20) 1.972(3)
N(1)—C(2) 1.335(4) N(1)-C(2) 1.331(4)
N(1)—C(6) 1.436(4) N(1)—C(6) 1.435(4)
N(2)—C(4) 1.333(4) N(2)—C(4) 1.332(4)
N(2)—C(13) 1.443(4) N(2)—C(13) 1.437(4)
N(1)—Al—N(2) 9470(14) N(1)-Ga—N(2) 93.38(10)
N( 1 )—A1-—C(2 1) 109.6(2) N( 1 )—Ga—C(2 1) 112.82(13)
N(2)—Al-C(21) 1 1 1.2(2) N(2)—Ga—C(21) 1 10.79(13)
N(1)—Al—C(20) 112.6(2) N(1)—Ga—C(20) 107.13(13)
N(2)—Al—C(20) 1 1 1.4(2) N(2)—Ga-C(20) 110.91(14)
C(21)—A1—C(20) 1 15.5(2) C(21)—Ga—C(20) 118.9(2)

 

The best way to prepare 39 is to treat TolznacnacH with one equivalent of AlMe3,

losing CH4 and generating 39 in a quantitative yield. This methane elimination reaction is

quite general as other diketimines work well (eq 22).

53

 

M M (22)

'BuznacnacH R = 'Bu 44 72%
12 R = C6H2-2,4,6-MC3 45 93%
14 R = C6H3-2,6-‘Pr2 46 75%

Except for compound 44, compounds 45 and 46 are air-stable, implying the aryl
substituents on two nitrogen atoms stabilize the metal—alkyl bonds. Their NMR data are
similar to those of compound 39 and indicate a C2,. point symmetry for compounds 44,
45, and 46.

To further probe the ligand’s effect on aluminum’s environment, crystal structures
for compounds 44 and 46 were solved (Figures 34 and 35). Table 15 summarizes the
crystal data and refinement parameters and Table 14 lists the selected bond distances and

angles for compounds 44 and 46.

54

 

Figure 34. X-ray crystal structure of 44 with thermal ellipsoids drawn at the 50%

probability level.

‘
~

0

~

\V’

01
V

Table 14. Selected bond distances (A) and angles (deg.) for compounds 44 and 46.

 

 

46
Al—N(A) 1.945(2) Al—N(1) 1.922(2)
Al-N 1.945(2) A1—N(2) 1.935(2)
Al—C(8) 1.997(2) Al—C(30) 1.958(3)
Al—C(8A) 1.997(2) Al—C(31) 1.970(3)
N—C(2) 1.342(2) C(10)—C(9) 1.381(4)
N—C(4) 1.521(2) C(10)-C(11) 1.396(4)
C(l)-C(2) 1.525(3) N(1)—C(2) 1.350(3)
C(2)—C(3) 1.409(2) N(1)—C(6) 1.456(3)
N(A)—Al-N 101.97(9) N(l)—Al—N(2) 9618(9)
N(A)—A1-C(8) 107.76(8) N(1)—Al—C(30) 1 10.79(1 1)
N—Al—C(8) 109.83(7) N(2)—Al—C(30) 1 14.49(11)
N(A)—Al-C(8A) 109.83(7) N(1)—Al—C(31) 108.67(11)
N—Al-C(8A) 107.76(8) N(2)—Al—C(31) 107.15(11)
C(8)—A1-C(8A) 118.46(12) C(30)—A1—C(3 3 117.4003)

 

55

 

Figure 35. X-ray crystal structure of 46 with thermal ellipsoids drawn at the 50%

probability level.

56

Table 15. Surm

/

10111111111
Formula weigh
lempettiture 1 ‘
\1'111e1ength / .»'
(mm 85 xte 11‘
Space group ‘
11111ce11 111 A
I) /
r 1
5
1,131
Z
deal. /.\1g ,/
F1000)
Crystal size
Mex ranges
Ref. e011eete
Independent
1311.11 roes‘ 1’
00F on F‘
111131 R 11 >
111.111 data)
Abs. strum

A111
“1331:1110
9116 11.111 of
1S a1111031 1
C0‘T‘P‘OUnd
(115131an 3
iminutes 11
m‘ini'lmize c

nfigs.

Table 15. Summary of crystal and refinement data for compounds 44 and 46.

 

 

44 46

Formula C|5H31A1N2 C3|H47A1N2
Formula weight 266.40 474.69
Temperature / K 173(2) 142(2)
Wavelength / A 0.71073 0.71073
Crystal system Orthorhombic Monoclinic
Space group o Fdd2 P21/n
Unit cell a / A . 17.7984(2) 12.6955(7)

b / A 23.8428(1) 19.4992(11)

c / A 8.1599(1) 13.4623(8)

. B/ ° 116.8980(10)
V/ A3 3462.77(6) 2972.1(3)
Z 8 4
dcal./Mg/m3 1.022 1.061
F (000) 1184 1040
Crystal size 0.30 x 0.25 x 0.25 0.18 x 0.15 x 0.14
Index ranges -23Sh$23,—31$k£ —16Sh$ 14, —25$k$25,
30,—1051510 —17SlSl6

Ref. collected 9873 17525
Independent reflections 2063 [R(int) = 0.0238] 6926 [R(int) = 0.0703]
Data / roes / parameters 2063 / 1 / 83 6926 / 0 / 307
GOFonFZ 1.185 1.017

Final R [1 >2 0(1)]

R (all data)

Abs. structure par. .
Lgst diff. pk and hole/eA"3

R1: 0.0411, wR2 = 0.1335
R1 = 0.0439, wR2 = 0.1360
0.0(2)

0.258 and —0.262

R1 = 0.0723, wR2 = 0.1670
R1: 0.1432, wR2 = 0.1950

0.410 and —0.385

 

Aluminum centers in structures 44 and 46 adopt pseudo-tetrahedral environments.
A crystallographic two-fold rotational axis passes through A1 and C(3) in structure 44 and

one half of one molecule of 44 is independent. The six-membered chelate ring of AlC3N2

is almost planar in 39 and 44. When the N substituent is changed to C6H3-2,6-'Pr2 in

compound 46, the six-membered A1C3N2 ring is no longer planar. Both A1 and C(3) are
displaced at the same side from the plane of N(l), N(2), C(2), and C(4). A model
indicates that the deviation from planarity in 39 and 44 to a boat geometry in 46 may

minimize contacts between aluminum methyl groups and isopropyl groups on the phenyl

fings

57

 

Synthesis of Bi
Treatme

generates bis-01‘

131.

 

Autotgn.i

 

C0mp0u1
cnstals. Due 10
81111 011 and it 11

Solid st.
summarizes the

Synthesis of Bis-organoaluminum Complexes
Treatment of 37 with two molar equivalents of lithium or Grignard reagents

generates bis—organoaluminum complexes in moderate to good yields (M = Li, MgBr, eq

23).
A|(To|2nacnac)C|2 + 2 MR —9 Al(To|2nacnac)R2 + 2 MCI (23)
37 41 R = C3H5 77%
42 Ph 64%

43 CHzSiMeg 53%

Compounds 41 and 42 were isolated as analytically pure crystalline yellow
crystals. Due to the high solubility of 43 in all common organic solvents, 43 was obtained
as an oil and it was characterized by IH NMR.

Solid state structures of 41 and 42 were solved (Figures 36 and 37). Table 16
summarizes the crystal data and refinement parameters and Table 17 lists the selected

bond distances and angles for compounds 41 and 42.

58

Figure 36.

probabiht} 1

C(25)
‘8)
1};— 4
0”" 01201“‘C(2)
1" C 9 :\\x .
r ) 0181012‘219121) c123)

   

C(15) C119)

0 ‘4')
(T: $.. \\\"- a
" ‘ ‘C’ ‘4 C(14) A 1‘,

0110) g; $2

,5 A 911.?)55' ‘
i C 13 § 1 2:7"
C(11) C(5 - ( (.614 \L’ C(15)
N(1)' ' ‘ “7 C(17)
N(2) C(18)
{e
C(1) 1:
C(5)

Figure 36. X-ray crystal structure of 41 with thermal ellipsoids drawn at the 50%

probability level.

59

g

Figure 37.
probability

 

 

 

Figure 37. X-ray crystal structure of 42 with thermal ellipsoids drawn at the 50%

probability level.

60

Table 1

_________

11m
Fomtul;
Temper
C {15131
Space
l'nit eel

1’1A‘

Z
dcfl./h
Crystal 5
Grunge 1
Index ral

Ref. coll.
Indepenc
DMa/re~
COFon

Final R [,
R1311 dat

Table 17
\

Table 16. Summary of crystal and refinement data for compounds 41 and 42.

 

 

41 42

13011111113 C25H31A1N2 C31H31A1N2
Formula weight 386.50 458.56
Temperature / K 173(2) 123(2)
Crystal system Triclinic Monoclinic
Space group P 1 mm:
Unit cell a / A . 8.6951(3) 13. 1422(2)

12 / A 9.1990(2) 13.8421(1)

c / A 15.2885(6) 14.0460(2)

(1/ ° 82.9550(10)

B / ° 75.4950(10) 99.7350(10)

o y/ ° 77.964(2)
V/ A3 1 154.66(7) 2518.30(5)
Z 2 4
dcal./Mg/m3 1.112 1.209
Crystal size 0.22 x 0.20 X 0.20 0.22 x 0.20 X 0.20
6 range / ° 1.38 to 28.24 1.96 to 28.33
Indexranges —11$h$11,-12$k$ —l7ShSl6,—18$ks
12,—1951520 18,—1831318

Ref. collected 1 2069 1 8487
Independent reflections 5325 [R(int) = 0.0554] 5943 [R(int) = 0.0497]
Data / res. / parameters 5325 / 0 / 253 5943/ 15 / 294
GOF on F2 1.044 1.578

Final R [1 >2 0(1)]
R (all data) .
Lgst diff. pk and hole/eA'3

R1: 0.0701, wR2 = 0.1729
R1 = 0.1486, wR2 = 0.2051
0.464 and —0.408

R1 = 0.0939, wR2 = 0.2539
R1 = 0.1348, wR2 = 0.2729
1.717 and —0.849

 

Table 17. Selected bond distances (A) and angles (dog) for compounds 41 and 42.

 

 

 

41 42

Al-N( 1) 1.902(2) Al—N( 1) 1 .918(12)
Al—N(2) 1.903(2) Al—N (2) 1.917(12)
Al—C(20) 1.965(3) Al—C(20) 2.077(12)
Al—C(23) 1.985(3) Al-C(26) 1 .99(2)
N(1)—C(2) 1.344(4) N(1)—C(2) 1.33(2)
N(1)—C(6) 1.443(3) N(1)—C(6) 1.39(2)
N(2)—C(4) 1.343(4) N(2)—-C(4) 133(2)
N (2)—C( 1 3) 1.441(4) N (2)—C( 1 3) 1.45(2)
N(1)—Al—N(2) 96.03(1 1) N(2)—Al—N( 1) 96.3(5)
N ( 1 )—A1—C(20) 1 l 1.12(12) N(2)—Al—C(26) 109.6(6)
N (2)-A1—C(20) 1 10.94(13) N(1)—A1-C(26) 108.9(6)
N(1)—Al—C(23) 1 13.58(12) N (2)—Al—C(20) l 12.8(5)
N(2)—Al—C(23) 1 1 1.03(13) N(1)—Al—C(20) 1 12.9(5)
C(20)—Al-C(23) 1 12.98(14) C(26)—Al—C(20) 1 14.8(6)
Synthesis of Mixed Organoaluminum Complexes

We attempted to prepare compounds with the general

A1(Tolznacnac)R'R2 (R1 at R2). We envisioned a sequential alkylation of 37 with

61

approprldle

ii-
41

O

A111

\l'he
methyl eom
Though PU“
from a com

Alter
also too 10\
detised to
Tol;nacnaeH
'11s obtaine
rele110ns. us
"aluminum cc

\Ve c
alblanon l't
generated A]

through seqt

appropriate Grignard or lithium reagents. Thus. we tested the mono-methylation of 37 (eq

24)

A1(To|2nacnac)Clz + MeLi —> A|(Tolznacnac)ClMe + Al(To|2nacnac)C|2
37 48 37
+ A|(To|2nacnac)M92 (24)
39

When 37 was treated with one equivalent of MeLi in ether, the desired mono-
methyl complex 48 was observed, along with 39 and unreacted 37 in a 6:1:1 ratio.
Though pure 48 could be isolated after repeated recrystallizations, its low yield stemming
from a competition between 37 and 48 for MeLi made eq 24 synthetically unfeasible.

Alternatively, protonation of 39 with HCl also generated 48, but the yield was
also too low to be synthetically useful (eq 27). A double-methane elimination was
devised to circumvent these problems. After stirring AlMe3 with slurries of
TolgnacnacH-HCI (19) for several hours, a homogeneous solution formed. Compound 48
was obtained in high yield (eq 25). Though compound 48 undergoes substitution
reactions, using various lithium or Grignard reagents, yields for the desired mixed organo
aluminum complexes A1(Tolgnacnac)R'Me (R1 at Me) are low.

We decided to prepare derivatives of complex 48 to increase the yields in the
alkylation reactions. The reaction between AlMe3 and TolznacnacH-HX smoothly
generated Al(Tolznacnac)MeX (X = Cl, Br, I, OSOgCFg; eq 25). This reaction proceeds
through sequential deprontonation of TolgnacnacH-HX with A1MC3, followed by the

chelation of the B—diketiminate ligand.

62

All

To
compound
data and r:

for compo

Ct

Figure 33
”Obi-1131111)

AlMe3+ TolznacnacH-HX —-> Al(To|2nacnac)MeX + 2 CH4 (25)

19 X = Cl 48 84%
20 X = Br 49 75%
21 X = I 50 81%
22 X: 0302CF3 51 86%

To further probe their solid state structures, X-ray crystal structures for
compounds 50 and 51 were solved (Figures 38 and 39). Table 18 summarizes the crystal
data and refinement parameters and Table 19 lists the selected bond distances and angles

for compounds 50 and 51.

 

Figure 38. X-ray crystal structure of 50 with thermal ellipsoids drawn at the 50%

probability level.

63

 

O
__"
K)

Figure 39.

probability

F13)

‘-F11)
54;)“01211 ‘9131
F12) \‘V s (“2‘
0(1) 7’7" fl C(15)
93v
“4‘ C(14) [[1,0(19)

:\ ‘\‘
'

 

Figure 39. X-ray crystal structure of 51 with thermal ellipsoids drawn at the 50%

probability level.

Table 18. E

_____.————-"

_________
Formula
Formula 1.11
Temperatui
0151111 515‘
Space grou
[7011 cell 11.

171A

Z

11 cal. / .\l_
Abscoe. / 1
F1000)
Cnstal size
(flange / 3
Index rangt‘

Ref. collect
Independer
Data / res. 1
GOF on F”
Final R 1 I >
1111111 data)
.10301U16 3t

Table 18. Summary of crystal and refinement data for compounds 50 and 51.

 

 

50 51
FOI'ITIU13 C20H24A11N2 C21H24A1F3N203S
Formula weight 446.29 468.46
Temperature / K 173(2) 173(2)
Crystal system Orthorhombic Orthorhombic
Space group Pbcn P212l21
Unit cell a / A . 9.01 160(10) 7.562(2)
b / A 14.16670( 10) 12.049(2)

o c / A 33.55810(10) 25.411(5)
V/ A3 4284.18(6) 2315.4(8)
Z 8 4
d cal. / Mg / m3 1.384 1.344
Abs.coe. / mm" 1.539 0.226
F (000) 1792 976
Crystal size 0.22 x 0.22 x 0.20 0.25 x 0.12 x 0.05
9 range / ° 2.43 to 28.28 1.60 to 28.18

Index ranges

Ref. collected
Independent reflections
Data/ res. / parameters
GOF on F2

Final R [1 >2 0(1)]

R (all data)

Absolute structure par
Lgst diff. pk and hole/eA‘3

—11$hS11,—18Sk$ 18,
—43 $1344

36172

5207 [R(int) =0.0296]
5207/0/217

1.383

R] =0.0504, wR2 = 0.1779
R1=0.0619,wR2=0.1846

0.445 and —1.386

65

—10£h$ 10,—15Sk$ 15,
—33 S l S 32

25453

5471 [R(int) = 0.1255]
5471 /0/280

1.102

R1 = 0.1022, wR2 = 0.1868
R1: 0.1770, wR2 = 0.2183
0.6(2)

0.301 and —0.307

Table 19. S

_________._——

1211’”
Al-Nt 11
Al—Nl 31
AM 161

.\'1 l t—Al-Nt
N1 1 1—Al—Cl
Kilt—A141

Al-0111
Al—Ntl)
Al—Nt 1)
Al-Ct’ 1'1
F11 1—C1231
17131—022 1
F131—C132 1

01 1 1—A1—.\'
01 1 ‘1—A1—.\'
Nlll—Al—N
011 1—Al—C
Ntlt—Al—C
.\'111-.~\LC
w
In t
tetrahedral.
110m 0'.
C01111101111115
found that
1“ Cl- Br. I.
The

the EXPt‘rir

Table 19. Selected bond distances (A) and angles (deg.) for compounds 50 and 51.

 

 

 

 

50

I—Al 2.5966(11) N(1)—C(2) 1.348(5)
Al—N(1) 1.881(3) N(1)—C(7) 1.450(4)
Al—N(2) 1.880(3) N(2)—C(4) 1.350(5)
Al—C(6) 1.947(4) N(2)—C(14) 1.452(4)
N(1)—Al-N(2) 97.25(13) N(1)—Al—I 106.01(10)
N(1)—Al—C(6) 116.8(2) N(2)—Al—I 108.50(10)
N(2)—A1—C(6) 1 15.5(2) C(6)—Al—I 1 1 1.5(2)
Al—O(1) 1.841(4) N(l)—C(4) 1.344(7)
Al—N(2) 1.873(4) N(l)—C(8) 1.437(6)
Al—N(l) 1.875(4) N(2)—C(15) 1.435(7)
A1—C(1) 1.928(6) O(1)—S(1) 1.504(4)
F(1)—C(22) 1.323(7) O(2)—S( 1) 1.416(5)
F(2)—C(22) 1.324(8) O(3)—S( 1) 1.410(5)
F(3)—C(22) 1.314(8) S(1)—C(22) 1.814(7)
O(1)—Al—N(2) 106.1(2) O(3)—S(1)—O(2) 119.7(4)
0( 1 )-Al—N( 1) 107.8(2) O(3)—S(1)—O( 1) 112.4(3)
N(2)—Al-—N(l) 99.1(2) O(2)—S(1)—O(l) 111.6(3)
O(])—Al—C(1) 107.6(2) O(3)—S(1)—C(22) 105.2(4)
N(2)—Al—C(1) 117.9(2) O(2)-S(1)-C(22) 105.8(4)
N(l )—A1-C(1) 1 17.5(2) O(1)—S(1)—C(22) 99.6(3)
S(l )—O(1)—Al 133.7(2) N(1)-C(4)-C(5) 123.3(5)

 

In the solid state structures of 50 and 51, the aluminum centers are pseudo-
tetrahedral. The triflate ligand is nl-bonded to aluminum and pyridine is not able to
displace OTf to generate a cationic aluminum triflate complex. We tested the reactivity of
compounds 48, 49, 50, and 51 towards various lithium or Grignard reagents, and we
found that compound 51 gave the best yields. We note that OTf is the best leaving group
in Cl, Br, I, OTf.

The results of substitution reaction of 51 are listed in eq 26 (M = Li, or MgX, see

the Experimental Section for details).

66

Alfie

 

 

X-ra1 1‘
Table 20 sumr

selected bond

C110)

0:11

inbabilin 11-

Al(To|2nacnac)MeOTf + RM -> Al(To|2nacnac)MeR + MOTf (26)
51 52 R = C3H5 53%
53 CH281MC3 66%
54 CH(SiMe3)2 4.8%
55 Ph 74%
56 O'Bu 52%

X-ray crystal structures for 53, 54, and 55 were solved (Figures 40, 41, and 42).
Table 20 summarizes the crystal data and refinement parameters and Table 21 lists the

selected bond distances and angles for compounds 50 and 51.

 

 

C(14)
C(13) § v \
C(10) St
’9
(i/ (1\‘§.‘)=0(5)( (g (slum ‘fi;
I'll/‘vr “m“ ‘3; {vi/5E ' \1?)
C(8) ’ (111'; 150141 “11‘s“ ..
. ¢ 1
C(9) 10:61. [5111. 1‘1“; \‘
vN(A)

  

" z
\\A\ -
\‘W 0(2) IF C(2A) _,
C(1) C(3) \‘l

C(1A)

Figure 40. X-ray crystal structure of 53 with thermal ellipsoids drawn at the 50%

probability level.

67

 

 

 

Figure 41. X

PTObabllll) le\

   

C-I C(4) C(3) C(2) "'4
— ‘lh. s‘
C(18) 6f) " C(6) '3” C(10)

C( 1 7) ('lv'iiE\ ‘
"I! V C(12)

C(16) {1" fi‘ ' N(1) “' '\

'~;¥‘ N 2 , ’ 12 __
C(19) (;_\ C(13) ( ) AIV (’4 .042. " 7.!
E 1.), C 7 5 C(9)
’ ’ C(27)_ ( ) 0(8)

“‘1 ‘7') C(14) 5

C(15) 222/ C(21)
C(24) Sim!"
" C(22)
(Ill, 'mt‘dfl.
' \r ‘5/
C(26) 3'“) C(25)
C22)
C(23)

Figure 41. X-ray crystal structure of 54 with thermal ellipsoids drawn at the 50%

probability level.

68

 

O
_J
. ‘ I?

Figure 42. :

PTObabllit}' 1e

C(20)(
C(10) C(11) N 1
C(12) (3% Q‘ S (l
’22). “2443‘th ‘
‘ C(9) Q, " C(6)
C(8) C(7)

 

Figure 42. X-ray crystal structure of 55 with thermal ellipsoids drawn at the 50%

probability level.

69

Table 20. Su

f

 

_'_._—————'

Formula
lorruuluoer;
Temperature
Corral outer:
Space group
l'rru cell (2 l A
bl A
t/ A

(I
ll
., Y
l’lA
Z
deal. /.\lg / m

Crustal sue
lntler ranges

A
'1.

/v
r:
I

Ref. Collected
Dulu l res. ] p;
GOFon F‘

final R [1 >2 ,

ll ’3” data)

Lgst diff; pk .
uol j -.~
{\QK\

Table 20. Summary of crystal and refinement data for compounds 53, 54. and 55.

 

 

53 54 55

Formula C24H35A1N281 C27H43A1N2512 C52H53A12N4
Formula weight 406.6] 478.79 792.98
Temperature / K 173(2) 173(2) 173(2)
Crystal system Orthorhombic Triclinic Triclinic
Space group o ana P 1 P 1
Unit cell a 4 A 13.067(3) 8.792(2) 12.055(2)

b / if. l6.859(3) 9.803(2) 12.558(3)

c / A 1 1.592(2) 17.1 19(3) 16.255(3)

01/ ° 9907(3) 7152(3)

[3/ ° 9566(3) 8625(3)

0 )I/O 9525(3) 8297(3)

V/ A3 2553.8(9) 1441.1(5) 2315.6(8)
Z 4 2 2
dear/Mg/m‘ 1.322 1.103 1.137
Crystal size 0.24X0.22x0.20 0.18x0.15x0.10 0.15 x0.15x0.10
Index ranges -12Sh.<.7,—21$ —11.<.hSll,—13S -lShSlS,—16S

Ref. Collected
Data / res. 1 par
GOF on F“

Final R [1 >2 0(1)]

R (all data)

Lgst dioff. pk and
hole/eA’3

k S 21, —6 S I S 15
6481

2544/0/ 136
1.198

R1 = 0.0834, wR2 =
0.2080

R1 = 0.1658, wR2 =
0.2386

0.487 and —0.309

“13,-2231322
16284

6690 / 0 / 289

1.061

R] = 0.0844, wR2 =
0.1795

R]: 0.1624, wR2 =
0.2140

0.409 and —0.407

ks 16,-21 $132]
25604

10589 / 0 / 523
0.977

R1: 0.1195, wR2 =
0.1976

R1 = 0.3398, wR2 =
0.2812

0.439 and -0.370

 

70

   
    

Table 21. S

/

Al-XrA)
ALN

Al-C 1 1 l)
ALOID

 

MAkALN
.\3 A 1—Al—Cl ,
N-Al—C 1 l l 1

Al-Xr 31
Al—Xr l l
.’\1‘C1:Ol
Al—C 12 l 1

N'rll-Al-Xl 1
err—Al—C 12
Al-Nll)
Al—CQO)
Al—Cr‘ll)
erl—Al—Nll
Nlll—Al—C 12
.\'r 1
They
We sensitl‘
nucleophiles
fielded 53 i,

W 33 low a

Table 21. Selected bond distances (A) and angles (deg.) for compounds 53, 54, and 55.

 

 

 

 

 

 

53
Al—N(A) 1.908(3) Si—C(l3) 1.885(9)
Al—N 1.908(3) Si—C(13A) 1.885(9)
Al—C(1 1) 1.960(6) Si-C(l4) 1.901(7)
Al—C(12) 1.974(6) N—C(2) 1.335(5)
N(A)—Al—N 95.4(2) N(A)—Al—C(12) 109.8(2)
N(A)-Al—C(l 1) 109.5(2) N—Al—C(12) 109.8(2)
N—Al—C(l 1) 109.5(2) LC(1 1)—Al—C(12) 120.2(3)

54
Al—N(2) 1.914(3) Si(2)—C(27) 1.871(4)
Al—N( 1) 1.928(3) Si(2)—C(26) 1.874(4)
Al-C(20) 1.964(4) Si(2)—C(21) 1.878(4)
Al—C(21) 1.982(4) Si(1)«C(21) 1.860(4)
N(2)—Al—N(l) 95.18(14) N(2)—Al—C(21) 118.6(2)
N(2)—Al—C(20) 107.5(2) N(1)-Al—C(21) 108.7(2)
N(1)—Al—C(20) 109.9(2) _ C(20)—Al—C(21) 115.1(2)

55
Al—N(2) 1.894(5) N(2)—C(4) 1.344(7)
Al—N(l) 1.902(5) N(2)—C(13) 1.443(7)
Al—C(20) 1 959(6) N( 1 )—C(2) 1.337(7)
Al—C(21) 1.978(6) N(l)—C(6) 1.441(7)
N(2)—Al—N(1) 95.8(2) N(2)—Al—C(21) 107.8(2)
N(2)—Al—C(20) 112.1(3) N(1)—Al—C(21) 110.2(2)
N(1)—Al—C(20) 1 12.7(2) C(20)—Al—C(21) 1 16.3(3)

 

The yields of mixed organo aluminum complex Al(Tolznacnac)MeRl (R1 at Me)
were sensitive to the steric bulk of the incoming of a nucleophile. The bulkier
nucleophiles gave lower yields. Treatment of 51 with one equivalent of LiCstiMeg
yielded 53 in 66% yield, while the yield of a similar reaction involving LiCH(SiMe3)2
was as low as 5%. We propose that bulky nucleophiles do not fit well into ligand pocket
and tend to have side reactions.

We also tested a reaction between 51 and one equivalent of 'BuLi, and no
alkylation product of A1(Tolznacnac)Me’Bu was observed. Instead a complicated mixture
of products formed based on 1H NMR measurements. We were not able to identify any of
product, however, when the product was quenched with D20, a deuterium incorporation

into the ligand backbone’s methyl group was observed. A control experiment with H20

71

yielded (ml)

the ligand 1).

 

p-Tol

Ol

“gm-e 4,
B
“as Ire-.11
“’18 add
Com“?
“1 hith
1?“qu

9‘ CW3 CI

yielded only TolznacnacI-I. It appears that a bulky base deprotonates the methyl group in

the ligand backbone rather than attacking aluminum (Figure 43).

t

 

 

 

 

Mg Bu
2!
M
_. P-To|\ / \N,p-Tol
X
Me on Mg OTf
E] 2!
M M
p-ToI\N/ \N,p.Tor _, p-Tol\ / \N,p-Tol
51
_ DZO H20
1 .
OTf = OSOZCF3 ‘
P‘To|\ ,p-Tol F’T°'\NH NIPTO'
NH N M
/|\/“\/D \
11-d 11

Figure 43. Deprotonation of a diketiminate methyl group involving a bulky anion.

Based on these results, we modified the ligand backbone. A THF solution of 39
was treated with one equivalent of KN(SiMe3)2 for one hour, and then an excess of Mel
was added. Subsequent workup afforded a methyl substituted diketiminate aluminum
complex 57. This reaction could be carried out three more times, eventually yielding 60
which is stable towards KN(SiMe3)2 (Figure 44). We note that analogous reaction
involving TolgnacnacH and KN(SiMe3)2 is messy. It appears that AlMez serves a

protecting group during deprotonation and alkylation.

72

 

 

Condition :1: l .

“111844381,
X-ra) (-

46"- Tuble 23 ,

1116 selected b0
80111 st

p333 [hrOU :11)

Me? ’Me Me,’ 'Me

p'T0|\ /A|\ /p'T0| a p-TOI\ /A|\N/p'T0|

N N ___ N
Me”. 'Me a/( M/ M
p-Tol\ IAlxN,p-Tol 57 51:

39 M%A{Me MgN’Me
p-TokN/ \N,p-Tol a p—Tol\ / \ ,p-Tol

9941—299

59 60

Condition a: 1 eq. KN(SiMe3)3, THF, 5 eq. Mel

Figure 44. Sequential deprotonation and alkylation of 39.

X-ray crystal structures for compounds 58 and 60 were solved (Figures 45 and
46). Table 22 summarizes the crystal data and refinement parameters and Table 23 lists
the selected bond distances and angles for compounds 58 and 60.

Both structures of 58 and 60 have a crystallographic two-fold rotational axis

passes through Al and the backbone middle carbon (58 C(4), 60(7), respectively).

73

Figure 15

11111011111111)

0‘)

(1‘1“)

   
    
 

C(11) C(1)
1'” C(9) (a;
- \ /,
C313)“. C(10) C(1A)
1“ U '17-; A' 1.2.831 7
.‘V - s) N N A g////".
Cm '9 0(5) so .— ) 1‘"
C(6) C(12)
g‘, 9.. (9,
(2‘ C(3) (2; 0““
C(2) 0(4) -1
'3'
Figure 45. X-ray crystal structure of 58 with thermal ellipsoids drawn at the 50%
probability level,
C(14)
C(1) \\\\
13‘ C(10) ‘
(31?;
M CM) 0(9) v V.
V, ,

 

Figure 46. X-ray crystal structure of 60 with thermal ellipsoids drawn at the 50%

probability level,

74

Table 22. Summary of crystal and refinement data for compounds 58 and 60.

 

 

58 60
Formula C23H31A1N2 C25H35A1N2
Formula weight 362.48 390.53
Temperature / K 173(2) 173(2)
Crystal system Monoclinic Monoclinic
Space group C2/c C2/c
Unit cell a / A 15.4503(3) 22.502(5)
12 / A 7.8396(2) 8.510(2)
c / A 18. 1260(5) 14.119(3)

o [3 / ° 99.2040(10) 120.49(3)
V/ A3 2167.23(9) 2329.7(8)
Z 4 4
dcal./Mg/m3 1.111 1.113
Abs.coe. / mm’l 0.102 0.099
F (000) 784 848
Crystal size 0.20 x 0.20 X 0.20 0.15 X 0.12 x 0.10
9 range / ° 2.28 to 28.30 2.10 to 28.45 deg.
Index ranges —20$hs20,—105ks —30$h$29,—ll Sks

10,—24SIS23 11,-1831518

Ref. collected 12073 10936

Independent reflections
Data/ res. / parameters

GOF on F2

Final R [1 >2 0(1)]

R (all data)

Lgst diff. pk and hole/eA'3

2622 [R(int) = 0.0345]
2622/ 0/ 119
1.217

R1 = 0.0496, wR2 = 0.1558
R1 = 0.0674, wR2 = 0.1679

0.279 and —0.253

2833 [R(int) = 0.1062]
2833/ 0/ 128

1.242

R] = 0.1063, wR2 = 0.2201
R1 = 0.1835, wR2 = 0.2475
0.453 and —0.435

Table 23. Selected bond distances (A) and angles (deg) for compounds 58 and 60.

 

 

60

Al—N 1.9110(14) Al—N 1.896(3)
Al-N(A) 1 .9109( 14) Al—N(A) 1.896(3)
Al-C(l) 1.966(2) Al—C(1) 1.952(4)
Al—C(1A) 1.966(2) Al—C(1A) 1.951(4)
N-C(3) 1.336(2) N-C(6) 1.339(4)
N—C(5) 1.442(2) N—C(8) 1.436(4)
N(A)-Al—N 9539(8) N—Al—N(A) 95.6(2)

N(A)-Al-C(1) 108.80(7) N—Al—C( 1A) 1 12.3(2)
N—Al—C( 1) 1 1 163(6) N(A)—Al—C( 1 A) 107.3(2)
N(A)—Al—C( 1A) 1 1 163(6) N—Al—C(1) 107.3(2)
N—Al—C( 1 A) 108.80(7) N(A)—Al-C( 1) 1 12.3(2)
CQ)—Al—C(1A) 1 18.24(12) C(LA)-Al-C(1 ) 119.5(3)

 

Reactivity of A1(Tolznacnac)Me2

Since the methyl groups in 39 have anion characteristics, 39 reacts with Br¢nsted

acid or Lewis acids. Treatment of 39 with one equivalent of dry HCl in ether gave 48 in

~5% yield, and the major product was the protonated TolgnacnacH l9 (eq 27).

75

Al('

Tre
color than

"ASMC" 11

All

To
lllEIi‘l}’1 gr.
and the 111
obtain 61
unsuccess
1h? produ
Ali/TOIInu
Starting fr
111311 gener

Fc
‘FJH4F1 :
fOUI' chen

that 13 11111

Al(‘|

T17

tempera“

A|(Tolgnacnac)Me2 + HCI —> Al(To|2nacnaC)MeCl + TolgnacnaCHoHCl (27)
39 48 19

Treatment a mixture of 39 and silver triflate with toluene resulted in an instant
color change. Triflate methyl complex 51 was isolated in 32% yield, and the presence of

“AgMe” was marked by its degradation to silver metal(eq 28).

A|(To|2nacnac)Me2 + AgOTf —9 A|(To|2nacnaC)Me(OTf) + “AgMe” (28)
39 51

To generate a cationic aluminum complex, we also tried to abstract one of the
methyl groups from 39 using B(C6F5)3. Instead, an Ar-Me exchange reaction dominated
and the desired cationic complex was not isolated (eq 29).117 We have not been able to
obtain 61 in its analytically pure form because all attempts to crystallize 61 were
unsuccessful. However, we have the following data to support the formulation of one of
the products as 61: (i) a high-field triplet (5 —0.18, 15111421 = 1.6 Hz) that is assigned to
Al(Tolgnacnac)Me(C6F5) in the lH NMR spectrum and (ii) an independent synthesis
starting from 51 and LiC6F5 afforded a yellow oil that is spectroscopically identical to
that generated in eq 29.

For B(C6F5)2Me (62) the following evidence is offered: (i) a quintet at 5 1.33
(l5 JH-F1 = 1.8 Hz) that was assigned to CH3B(C6F5)2 where the H—F coupling arose from
four chemically equivalent ortho fluorines and (ii) a resonance in the HB spectrum (5 72)

that is intermediate between BMe3 (5 86.0) and BPh3 (5 60.0).

A|(To|2nacnac)Meg + B(C5F5)3 -> AI(To|2nacnac)Me(C6F5) + B(CsF5)2Me (29)
39 61 62

To gain more insight, the reaction (eq 29) was monitored by NMR at low

temperature in CDgClg. The complex lH NMR spectrum that resulted when 39 and

76

B(C-11:51.1 were 1
cationic specir
However. a 51
[BtCth1ghle]'.

Sttitt‘hir
bridged ulumin
equivalent of B
be )leAlt’Bugn
the stoichiomet
consistent 11111
cquiralent of .
aluminum com
pTOdUCI (Flgtm

hours. We We“

1

Figure 47. Syn

Tamar}
etamined [he re
are used b91111,
b01116 amOnS. 1
between [Pb-C)

1,.
1droearb0ng an
i l

B(C6F5)3 were mixed at —50 °C could not readily be interpreted in terms of a simple
cationic species or rotamers of [{(Tolznacnac)AlMe}2(p2—Me)]+[B(C6F5)3Me]'.
However, a single resonance in llB NMR (5 —l4) indicated the formation of
[B(C6F5)3M€1_-

Switching from p-Tol of 39 to tert—butyl of 44 made observance of a methyl-
bridged aluminum complex possible. Treatment of a pentane solution of 44 with one
equivalent of B(C6F5)3 led to formation of an immediate precipitate, which we propose to
be MeAl('Bu2nacnac)(uz-Me)B(C6F5)3Me (63). When the reaction was carried in C6D6,
the stoichiometric ratio between 44 and B(C6F5)3 was found to be 1:1. This finding is not
consistent with a three-coordinate aluminum cation which might react with another
equivalent of 44, to form a bimetallic cationic complex. Moreover, three-coordinate
aluminum complexes are extremely rare. We propose the methyl-bridged structure for the
product (Figure 47). Compound 63 was unstable and it decomposed in solution in a few
hours. We were not able to determine its solid state structure.

B(CsF513

Me,1 'Me
44 63
Figure 47. Synthesis of MeAl(’Buznacnac)([12-Me)B(C6F5)3Me (63).

Tetraaryl borate anions are less prone to aryl group transfer. For this reason we
examined the reaction between 44 and [Ph3C]+[B(C6F5)4]'. The fluorinated phenyl groups
are used because the electron-withdrawing abilities of fluorine might stabilize the bulky
borate anions. However, the identification of the products of the reaction between 44
between [Ph3C]+[B(C6F5)4]' were hampered by their poor solubility in aromatic

hydrocarbons and their instability in halo-hydrocarbons. Marks and co—workers recently

77

reported the 5121
substituted with
[thCl’lBtCth

is insoluble. 1 9“

 

B((3131:.

Figure 48 MCI
Combm

b1‘pr0duC[ and
1

ts NMR data 11'

reported the synthesis of an aryl borate with the 4-position of the aryl group was
substituted with a lipophilic tert-butyldimethylsilyl (TBS) group. This substitution makes
[Pth]+[B(C6F4-4—Si’BuMe2)4]’ slightly soluble in benzene, whereas [Ph3C]+[B(C6F5)4]'
is insoluble.168

F_ p 1;

Meg [CPha]+ ’8 Al ’3
'Bu\N/ \N,’Bu B(C6F4-4-Si’BuMe2)4]‘ u\N/ \N2 u

M -CPh3Me i M i

44 B(C5F4-4-Si'BuMez)4]'
K J

6

_,§

 

 

 

 

 

I + 'Bu’ \Al’ 'Bu
'Bu\ / \ ,tBu _Py Mel [MG Me

 

 

 

 

B(CSF4-4-Si‘BuMe2)4]' - B(C 1= 4 Si’BuMe )1
6 4' ' 24

65 64

Figure 48. Methyl abstraction reaction of 44.

Combination of the Marks’ anion and 44 in 1:2 molar ratio gave cationic di-
aluminum complex 64 (Figure 48). The identification of 64 is based on analyses of the
byproduct and the NMR data. The CPh3Me byproduct was authenticated by comparing

its NMR data with literature values and an independent synthesis from CPthl and MeLi.

78

The NMR 01
resonance (5
indicated the
expected. Tl
formation. 1
supporting 11
with 111) pgr
We were 111)!
workers rep.
Preli
conditions 1
co-trorkers
11111611011113“

complexes

The NMR of 64 is consistent with the methyl bridged structure. Only one high-field
resonance (5 —0.l9) that integrated as 9H was observed in 1H NMR spectrum. VT NMR
indicated the resonance started to separate at about —30 °C into three peaks, not two as
expected. The low temperature NMR data might be complicated by some rotamer
formation. Jordan and co-workers observed such a phenomenon.165 Other evidence
supporting the dimer structure came from reactions with Lewis bases. Treatment of 64
with dry pyridine led to 65 and 44. The generation of ‘44 implied an adduct nature for 64.
We were not able to get X—ray quality crystals of 64 and 65. We note that Lappert and co-
workers reported the synthesis of cationic aluminum diketiminate complexes. ‘69
Preliminary result indicats that 64 does not polymerize ethylene under the
conditions that were reported for aluminum amidinate systems.165 Recently, Jordan and
co-workers reported reversible ethylene cycloaddition reactions of cationic aluminum 5-
diketiminate complexes.”O Therefore, unlike amidinate, B—diketiminate aluminum

complexes are not ethylene polymerization catalysts.

79

SYNTH‘

 

lntroduCtion

Tile mOSI
tire and 51""
chmucterizedm’
chelating 11911“)
colignnds.“7 51”
116111062 .1
achieve higher 0
ligand to . Indec
resulting four-. 1
and reactis'ity 01‘
Results and Dis
lolgnacnac Lig:

LilTOifllt
rFigure 49). Int
indiumtlll) ch10
66 is sparingly
recrystallized fr

vecrr .,. -
f DROP}. e

Chapter 4

SYNTHESIS, STRUCTURE, AND REACTIVITY OF fi-DIKETIMINATE
INDIUM(III) COMPLEXES

Introduction

The most common coordination number for group 13 metals is four. However,
five- and six-coordinate organometallic group 13 compounds have been
characterized.170'172 For aluminum and gallium, we were only able to introduce one
chelating fi-diketiminate ligand to the metal centers along with two other 77'-
coligands.l ‘7 Since the calculated radius of In3+ is the greatest in the series of Al3+ (0.51
A), Ga3+ (0.62 A), and In“ (0.81 A),'73 we reasoned that the indium might be able to
achieve higher coordination number (> 4) by accommodating more than one Tolznacnac
ligand to . Indeed, indium could be supported with one, two or three Tolznacnac ligands
resulting four-, five- or six-coordinate indium. Herein we report the synthesis, structure,
and reactivity of indium(III) complexes supported by fi-diketiminate ligands.122
Results and Discussion
Tolznacnac Ligation

Li(Tolgnacnac) (16) is an excellent Tolznacnac ligand transfer reagent for indium
(Figure 49). In(Tolznacnac)C12 (66) was prepared in 81% yield by treating a slurry of
indium(HI) chloride with one equivalent of 16 in ether at room temperature. Compound
66 is sparingly soluble in saturated hydrocarbon solvents and could be conveniently
recrystallized from toluene. Compound 66 was characterized by lH, l3C{1H} NMR

spectroscopy, elemental analysis and X—ray crystallography. The NMR spectra of

80

 

compound 66 at

equivalent and
l

teruperature H

to 25 °C in tolue

Figure 49. L1;

The so
was consisten
selected bond
features a pse
an essentially
of indium‘s l
acute than 111.
ligand symme
The average 1
found in othe

3“‘1‘4’96246

compound 66 at room temperature indicated C2,. symmetry as the two p-tolyl groups were
equivalent and only two aromatic proton resonances were observed. A variable
temperature 1H NMR study showed that the C2,. symmetry was maintained from —70 °C

to 25 °C in toluene-d3.

 

    
 

 

16
InCI ; In Tol nacnac Cl
3 81% ( 2 ) 2
66
3 Li(Tol2nacnac) 2 Li(To|2nacnaC) 15
54% 64% 62%
In(TolznacnaC)3 1 16 In(Tolznacnac)2Cl
56 °/o
27 67

Figure 49. Ligation indium(HI) with Tolznacnac.

The solid state structure of 66 determined by X-ray diffraction method (Figure 50)
was consistent with the solution data. The X-ray data are summarized in Table 24 and
selected bond distances and angles for 66 are listed in Table 25. The monomeric structure
features a pseudo-tetrahedral indium center with a chelating Tolznacnac ligand that forms
an essentially planar six-membered ring (In, N(1), N(2), C(2), C(3), and C(4)). Because
of indium’s larger size relative to Al and Ga, the N-In—N angle (94.41(10)°) is more
acute than that of Al (99.40(12)°) and Ga (100.16(13)°) analogues.117 The Tolznacnac
ligand symmetrically binds to indium with an average In—N bond distance of 2.106(5) A.
The average value of In-Cl bond distances (2.341(2) A) in 66 is comparable with those
found in other four-coordinate indium compounds: (InMeC12)2, 2.384(1) A; InMeCl3‘,
2.341(2)—-2.409(2)13.).174175

81

 

 

 

figure 50. Xraj
probability level.

Table 24. Surnm

06:“
Formula C“;
F.W. 972.
Temp/K 173
System
Space grOUp
alA

C(3)
723‘

   

  

Figure 50. X-ray crystal structure of 66 with thermal ellipsoids drawn at the 50%

 

 

probability level.
Table 24. Summary of crystal and refinement data for compounds 66, 67, 27, 68, and 69.
662(C7H3)o.5 67 27 68 69

120111111121 C415H46C14IN4 C38H42CIIDN4 C57H631nN6 C21H27IIIN2 C39H451nN4

F.W. 972.2 705.03 946.95 422.27 684.61

Temp. lK 173(2) 173(2) 173(2) 173(2) 173(2)

System Monoclinic Triclinic Monoclinic Monoclinic Monoclinic

Space group P21/c P l P21/c P21/c P21/n

a / A l7.421(4) 1 1.189(2) 13.863(3) 8.827(2) 12.5168(1)

b / A l6.084(3) 12.842(3) 13.815(3) 27.572(6) l3.4196(1)

c / A 15.976(3) l3.500(3) 25.847(5) 8.642(2) 21.3735(3)

a / ° 105. 16(3)

[3/ ° 9269(3) l 1052(3) 97.17(3) 9314(3) 102.979(1)

y/ °° 91 . 15(3)

V / A3 4472(2) 1740.0(6) 491 1 (2) 2100.3(7) 3498.40(6)

Z 4 2 4 4 4

Crystal size 0.30 X 0.25 0.15 X 0.12 0.17 X 0.15 X 0.28 X 0.26 0.20 X 0.15
x0.20 X0.12 0.13 X022 X015

Index —23Sh_<_23 —14ShSl4 —l8ShSl8 -10$h$11 —l6$h$15

ranges —20$ks21 —17Sk$17 —185k38 —36Sks33 —l7SkSl7
—20_<_1520 —l7SlSl7 —34SIS33 —6Sl$11 -28SI<S8

Ref. collect 46394 20288 29251 12975 34514

Data/res/par 10657/0/469 8 1 30/0/397 l 1 506/0/577 4977/0/217 8281/0/397

GOF on F2 0.863 0.924 0.919 1.081 1.051

R1 (all data) 0.0534 0.2142 0.1615 0.0658, 0.1797

wR2 0.1204 0.2176 0.1951 0.0923 0.2163

Lgst pk. and 0.593 and — 1.242 and — 1.861 and — 0.454 and 2.391 and —

hole/eA'3 0.564 1.208 1.479 —0.S47 1.631

 

82

181119 25. St’it‘t

’_______..———

 

lnlll—b’tll
lntll—Clt 11
In 1 l—C 1131
Nth-C121
hill-C161
11111—041
bill—C1131
011-021
C12eC13t
031—041
Cut—C151

 

N1 1 Hut 1 1—.\'1 21
.\'tl1—lntl)—Clrl
N121—lntl‘1—Cltl
Ntll—lnll l—Cltl
Ntll—lntll—C 11:
Cl111-ln111—Cl1
Cll)—.\'ll)—Ct()
C(3)-N1 1 1-1111 1
Clot—Ni l 1—ln1 1
When 61
Was isolated
C0Impound 67
chloride with 1
67 were as sin
.\'.\1R 5 2.27.
backbOne. The
Square Pyrami.
HOWCVCT. \!T I

are presenr be 1,

Table 25. Selected bond distances (A) and angles (deg.) for compounds 66 and 68.

 

 

66 68

In( 1 )-N( 1) 2.107(2) In—-N( 1) 2.206(2)
In( 1 )-N(2) 2.104(3) In-N(2) 2.198(3)
In( t )—Cl(1) 2.3348(11) In-C(20) 2.165(4)
In( 1 )—cr(2) 2.3466(11) In-C(21 ) 2.138(4)
N(1)—C(2) 1.339(4) N(l)—C(2) 1.326(4)
N( l)—C(6) 1.450(4) N(l)—C(6) 1.435(4)
N(2)—C(4) 1.343(4) N(2)-C(4) 1.331(4)
N(2)—C(l3) 1.440(4) N(2)—C(13) 1.438(4)
C(1)—C(2) 1.512(4) C(1)—C(2) 1.523(4)
C(2)-C(3) 1.410(5) C(2)—C(3) 1.405(5)
C(3)—C(4) 1.396(4) C(3)—C(4) 1.411(4)
C(4)—C(5) 1.515(4) C(4)—C(5) 1.512(5)
N(l)—In( 1 )—N(2) 94.41110) N(l)—In—N(2) 86.52(10)
N(1)—In(l)—Cl(l) 1 17.4718) N(1)—In—C(20) 106.44(t3)
N(2)—In(l)—Cl(l) 110.87(8) N(2)—In—C(20) 105.88(14)
N( 1 )—In( 1 )—C1(2) 108.24(8) N( 1 )—-In—C(2 1) 108.39(12)
N(2)—In( 1 )—Cl(2) 1 1790(8) N(2)—In-C(2 1) 107.05( 14)
Cl(l)—In(l)—Cl(2) 107.90(5) C(20)-In—C(21) 132.8(2)
C(2)-N(l)—C(6) 120.4(3) C(2)—-N(l)—C(6) 120.6(3)
C(2)—N(l)—In(1) 121.7(2) C(2)—N(l)—In 125.0(2)
C(6)-N(1)—In(l) 117.8(2) C(6)—N(l)-In 113.9(2)
C(4)—N(2)—C(13) 120.4(3) C(4)—N(2)—C(13) 120.3(3)

 

When 66 was treated with one equivalent of 16 in toluene, In(Tolznacnac)2Cl (67)
was isolated in 62% yield after recrystallization from toluene/pentane mixture.
Compound 67 could also be prepared in comparable yields by mixing indium(Ifl)
chloride with two equivalents of 16 (Figure 49). At room temperature, NMR spectra of
67 were as simple as those of 66, with single resonances for p-Tol groups (Ar-Me 1H
NMR 5 2.27, '3 C NMR 5 24.74) and the four methyl groups on the ligand pentene-
backbone. The NMR spectra of 67 at room temperature were consistent with either a
square pyramidal indium center with Cl at the axial position or a fluxional process.
However, VT 1H NMR showed that two different N—Tol groups in one Tolznacnac ligand
are present below —70 °C. Thus compound 67 is fluxional at room temperature.

Consistent with the low temperature NMR data, X-ray diffraction analysis
revealed a trigonal pyramidal indium with the chloride at the equatorial position (Figure

52). The C1, N(2), N(3), and In are essentially planar as the sum of appropriate angles

83

moundindiu
ln—N(3L 8‘
MSMr0p0nin1
meanalpos
M—Nwzuecl
MNgshs
nwmnri
1C).\’C("Buj1.‘

teUaphenylpl

mesrst

around indium is 360.0(4)° (Table 26). The chelating angles in the structure of 67 (N(1)—
In—N(2), 86.9(2)°; N(3)-In-N(4), 86.7(3)°) are much greater than those of
bis(troponiminate) indium chloride (74.58(10)°, 74.6l(10)°).176 N(l) and N(4) occupy
the axial positions with an angle of N(l)—In—N(4) 176.3(2)°. Other angles between N”—
In—Ncq are close to 90 ° (86.7(3)—lOl.5(3)°). The average bond distance (2.189(9) A) of
In-Neq’s is slightly shorter than that of In—Nax’s (2.212(1) A). The In—Cl bond distance
(2.396(2) A) in 67 is close to those in other five-coordinate indium complexes
(CyNC('Bu)NCy)2InCl (2.405(1) A),177 (CyNCHNCy)21nCl (2.383(9) A),178 and
tetraphenylphorphinato)indium(III) chloride (2.369(2) A).179

R1_|'
I

Figure 51. Schematic representation of an aminotroponiminate ligand.

84

 

Figure 52. X-ray crystal structure of 67 with thermal ellipsoids drawn at the 50%

probability level.

85

Table 26. Selected bond distances (A) and angles (deg) for compounds 67 and 69.

 

 

67 69

In—Cl 2.396(2) In—C(20) 2.152(8)
In—N(l) 2.214(7) In—N(l) 2.264(6)
III—N(2) 2.183(6) Iii—N(2) 2.208(6)
In—N(3) 2.195(7) In-N(3) 2.191(6)
Iii—N(4) 2.209(7) In—N(4) 2.282(6)
N(1)—C(2) 1.336(10) N(1)—C(2) 1.312(9)
N( 1 )—C(6) 1.463(10) N(1)—C(6) 1.431(9)
N(2)—C(4) 1.344( 10) N(2)—C(4) 1.310(9)
N(2)—C( 13) 1 .441 (10) N(2)—C( 13) 1.458(8)
N(3)—C(22) 1.332(1 1) N(3)—C(22) 1.333(9)
N(3)—C(26) 1.435(11) N(3)—C(26) 1.442(8)
N(4)—C(24) 1.327(1 1) N(4)-C(24) 1.314(9)
N(4)-C(33) 1.436(11) N(4)-C(33) 1.433(9)
Cl—In—N(l) 88.1(2) C(20)—In—N(l) 96.7(3)
Cl—In—N(2) 124.8(2) C(20)—In—N(2) 124.2(3)
Cl—In—N(3) 133.7(2) C(20)-In—N(3) 132.1(3)
Cl—In-N(4) 88.7(2) C(20)—In—N(4) 99.6(3)
N(l)—In—N(2) 86.9(2) N(1)—In—N(2) 81.6(2)
N( 1 )—In—N(3) 94.3(3) N( 1 )—In—N(3) 88.9(2)
N(1)—-In—N(4) 176.3(2) N(1)—In—N(4) 163.7(2)
N(2)—In—N(3) 101.5(3) N(2)—In——N(3) 103.7(2)
N(2)—In—N(4) 96.3(3) N(2)—In—N(4) 89.5(2)
N(3)—In-N(4) 86.7(3) N(3)—In—N(4) 79.9(2)
C(2)—N( 1 )—C(6) 1 18.7(7) C(2)—N( 1 )—-C(6) 1 17. 1(6)
C(2)—N(1)—In 121.6(5) C(2)—N(l)—In 120.3(5)
C(6)—N(l)—In 119.6(5) C(6)—N(1)—In 12mg

 

Three Tolznacnac ligands were introduced to indium to give In(Tolznacnac)3 (27,

Figure 49). Synthetically, 27 could be prepared in sequential or one-pot reactions. The

NMR spectra of 27 indicated a D3 point symmetry with hindered rotations around N—Ar

bonds. A single set of Tolgnacnac ligand and four p-phenylene proton resonances were

observed, as each resonance appeared as a doublet of doublets (dd) in the lH NMR

spectrum of 27 (Figure 53). One aromatic tolyl resonance showed an unusual chemical

shift (vide infra). Consistent with 'H NMR data, the '3C{‘H} NMR spectrum of 27

showed two diastereotopic aromatic carbon pairs with equal intensity at 6 126.66, 126.74;

l27.44, 127.56 for the four phenylene carbons.

86

 

 

 

 

 

 

 

 

 

 

 

 

 

 

(JUN... J L

I T I I I I 1 I I I I I I I I I I T l T T I
7.0 5.9 6.0 5.7 ppm

 

Figure 53. Aromatic region of lH NMR (300 MHz, CDC13) spectrum of 27.

Based on the reaction conditions, only the racemate of 27 was obtained. VT 1H
NMR experiments indicated that the interchange rate between two enantiomers were
slow between 25 °C and 95 °C in toluene-d3. The solid state structure of 27 was
successfully solved and refined in a centro-symmetric P21/c space group (Table 24). The
geometry of indium is pseudo-octahedral (N(1)—In-N(6), 177.8(2)°; N(2)—In—N(3),
177.6(2)°; N(4)—In—N(5), l78.l(2)°, Table 27). Other N-In—N angles are between
83.0(2)° and 96.2(2)° (Figure 54). The average In—N bond distance (2.260(11) A) is close

to those reported for six-coordinate indium complexes (2.216(3)—2.283 A)_138,180-185

87

    

(a) 01151

‘ K ’ 3." i A," t. I/
C(34) ‘1“ ‘(W 2"} ‘ /;‘

Figure 54. X-ray crystal structure of 27 with thermal ellipsoids drawn at the 50%

 

probability level.

Table 27. Selected bond distances (A) and angles (deg.) for compound 27.
In—N( 1) 2.255(5) N(2)—C(13) 1.420(7)
In—N(2) 2.266(5) N(3)—C(21) 1.330(7)
In—N(3) 2.262(5) N(3)—C(25) 1.451(7)
In—N(4) 2.259(5) N (4)-C(23) 1.335(7)
In—N(5) 2.272(5) N(4)—C(32) 1.419(8)
In—N(6) 2.248(5) N(5)—C(40) 1.313(7)
N(1)-C(2) 1.333(8) N(5)—C(44) 1.442(7)
N( 1 )—C(6) 1.432(8) N(6)—C(42) 1.347(7)
N(2)-C(4) 1.342(7) N(6)—C(5 1) 1.428(7)
N( l)—In—N(2) 86.7(2) N(2)—In—N(6) 95.4(2)
N(1)—In-N(3) 93. l (2) N(3)—In—N(4) 86.2(2)
N(1)—In—N(4) 83.7(2) N(3)—In—N(5) 94.7(2)
N ( l)—In—N(5) 94.6(2) N(3)—In—N(6) 84.8(2)

88

N( l )—In—N(6) 177.8(2) N(4)—In—N(5) 178.1(2)

N(2)—In—N(3) 177.6(2) N(4)—In—N(6) 95.5(2)
N(2)—In—N(4) 96.2(2) N(5)—In—N(6) 86.2(2)
N(2)—In-N(5) 83.0(2) C(2)—N(D—C(6) 1 166(5)

 

While both 66 and 67 spontaneously decomposed to the free ligand, TolznacnacH,
as the sole soluble organic product upon being exposed to the moisture in the air, 27 was
stable for a few hours under similar conditions. The introduction of three Tolznacnac
ligands to the indium center not only protects the polar In—N bonds, it brings the ligands
close to each other as well. Unusual chemical shifts for certain protons in 27 were
observed. One of two ortho-hydrogen atoms (relative to N) in the p-phenylene was not
only the most shielded (5 5.64) of the four p-phenylene protons (5 5.64, 6.78, 6.87, 6.95)
in 27 (Figure 53), but also it was the most shielded compared to those in related indium
complexes 66 (5 7.01), 67 (5 6.57), and free ligand TolznacnacH (5 6.84). Due to the
spatial proximity of the ligands in 27, only one ortho-hydrogen projects into the
diamagnetic anisotropic part of an aryl ring of adjacent Tolznacnac ligand (Figure 55).
We noted that the alkene proton (5 3.86) on the ligand backbone in 27 was more shielded
than those in 66 (54.93), 67 (54.61) and TolznacnacH (54.82). As shown in Figure 55,
H(26) is above aryl ring C(6) by 2.461 A and H(41) is above aryl ring C(13) by 3.549 A.
The solution NMR data are consistent with the solid state structure obtained from single
crystal analysis. Based on the X-ray data, Figure 55 highlights the interactions between
phenylene proton H(26) and a relevant aryl ring with only one shown for clarity. A
similar H(41)-ring interaction is also depicted. Similar high-field 1H NMR chemical

shifts are observed in bis-diketiminate zirconium complexesm

89

  

    

 

1] / {5.
/ C 11

\1’9/ ( )

85.54 H(26)

H(29) 056.87

Figure 55. Simplified representation of interactions between hydrogen atoms and aryl
rings.
Methylation of Tolznacnac Indium Complexes

The alkylation of compounds 66 and 67 using appropriate amounts of methyl
lithium were attempted. When 66 was treated with two equivalents of methyl lithium in
ether, In(Tolznacnac)Me2 (68) was isolated as a yellow crystalline solid in moderate yield
(eq 30). Similarly, In(Tolznacnac)Me2 (69) could be prepared from 67 and one equivalent

of methyl lithium (eq 31).

In(Tolgnacnac)C|2 + 2 MeLi —> In(Tolgnacnac)Mez (30)
66 68 45%

In(Tolgnacnac)ZC| + MeLi -> In(Tolznacnac)2Me (31)
67 69 56%

90

The 1H and l3C{1H} NMR spectra for 68 and 69 were straightforward with
symmetrical ligand environment as all the tolyl and pentenyl backbone methyl groups are
identical. The highfield resonances corresponding to In-CH3 (68, 5 0.018; 69, 5 —0.48)
were observed both as a sharp singlet in their 1H NMR spectra. Also In—CH3 (68, 5—8.15,
CN = 4; 69, 5 -10.98, CN = 5) were observed in their 13C NMR spectra (CN is the
coordination number for indium). Barron et al. reported a linear relationship between the
carbon chemical shift for methyl indium complexes and indium’s coordination number.
For example, InMe3(3,5-Me2Py), CN = 4, 5 -7.1; InMe2(dpt)(3,5-MezPy), CN = 5, 5 —
5.6; InMe(dpt)2(3,5-Me2Py), CN = 6, 5 -3.2 were reported (Py = pyridine, Hdpt = 1,3-

diphenyltriazene). Our findings contrast with the trend for the dpt system.182

.~ ,. ‘1-
Ph’N\N’N‘Ph

Figure 56. Schematic representation of a diphenyltriazenide (dpt) ligand.

X-ray crystal structures for both 68 and 69 were determined and the summary of
crystal and refinement data is listed in Table 24. Like 66, the solid state structure of 68
contains a pseudo-tetrahedral indium center (Figure 57). Presumably due to the methyl
inductive effects in 68, the average In—N length (2.202(4) A) of 68 is significantly longer
than that in 66 (2.1055(4) A) (Table 25). Also, the chelate angle of N—In—N in 68
86.52(10)° is smaller than that of 66 (94.41(10)°). The average In-C bond distance (2.152

(6) A) in 68 is close to those of other tetrahedral indium complexes (2161—2183

A). 175,186

91

 

Figure 57. X-ray crystal structure of 68 with thermal ellipsoids drawn at the 50%
probability level.

The solid state structure of 69 is shown in Figure 58. That it contains a more
distorted trigonal bipyramidal indium center than that in 67 is reflected by a smaller angle
of N(1)—In—N(4) in 69 (163.7(2)°) than that in 67 (176.3(2)°) (Table 26). The methyl
group is on the base plane as the sum of the appropriate angles around indium is 360(4)°.
The In—Nax bonds (2.264(6) A, 2.282(6) A) are a little longer than those of In—Nsq
(2.208(6) A, 2.191(6) A). As expected, the average In—N bond distances in 69 (2.236(14)
A) are longer than those of 67 (average = 2.200(14) A). The In—C bond distance
(2.152(8) A) in 69 is close to those in other reported five-coordinate indium alkyl

complexes. 2132—2158 A.I82.186-188

92

C(32)

 

fl!
C(12)
'92
"h
‘\ '1' C(9)
0(1) 1

1

c 3 7
C(21), ( {/fl
.1 (‘
C(23)»~

Figure 58. X-ray crystal structure of 69 with thermal ellipsoids drawn at the 50%

probability level.

93

Chapter 5

SYNTHESIS, STRUCTURE, AND SMALL MOLECUE ACTIVATION
CHEMISTRY OF AN INDIUM(I) COMPLEX SUPPORTED BY A BULKY [3-
DIKETIMINATE LIGAN D

Introduction

Chapter 4 describes the synthesis and structural characterization of indium(HI)
complexes supported by one, two, or three Tolznacnac ligands. Though indium(HI) is the
predominant oxidation state, indium(I) complexes are also known. Preliminary results
described in Chapter 1 indicate that the Tolgnacnac ligand is not suitable for indium(I)
stabilization.

Because one advantage of fi-diketiminate ligands is that they can be easily tuned
electronically and sterically to stabilize metal centers in novel geometry and oxidation
state, we decided to use a bulkier B—diketiminate ligand, specifically, Dipznacnac
[DipgnacnacH = 2-(2,6-di-iso-propylphenylamino)-4-(2,6-di-iso-propylphenylimino)-2-
pentene]. We hoped that the bulky ligand would stabilize indium(I) by making one of
disproportionation products unfavorable since indium(HI) in 27 is already crowded with
one of ortho-protons poking into an aryl ring (eq 32, L = uninegative ligand). This
chapter describes the synthesis, structural characterization, and reactivity of an indium(I)

complex supported by Dipgnacnac.

lnL —> 1/3 lnL3 + 2/3 In (32)

94

Results and Discussion

Synthesis and Structure of In(Dipznacnac)Clz

A simple metathesis reaction between InC13 and one equivalent of Li(Dip2nacnac)
(18) afforded In(Dipgnacnac)C12 (70) in 72% yield. The solution NMR data are consistent
with a C2,. point group symmetry, like In(Tolgnacnac)C12. The two methyl groups on an
isopropyl group are diastereotopic and all isopropyl groups are equivalent.

The solid state structure of 70 was determined by X-ray diffraction (Figure 59)
and was consistent with solution NMR data. A summary of X-ray data is listed in Table
28 and selected bond distances and angles for 70 are listed in Table 29. The metric data
for indium in 70 is very close to In(Tolznacnac)C12 (66) with only a slight increase in In—
N distance (2.129(2) A) in 70 versus (2.106(4) A) in 66, Consistent with elongated In—N
distances, the chelating angle of N(1)—In—N(2) (93.96(5)°) in 70 is slightly less acute than
that in 66 (94.41(10)°). However, in contrast to the planar six-membered ring made from
C(2), C(3), C(4), N(l), N(2), and In observed in 66, the ring is folded in 70 with In and
C(3) displaced at the same side from the plane defined by C(2), C(4), N( 1), and N(2).

95

      

C(29) ,-.,=—:
.~/// ‘1
C(13) 22:1!
'1‘?) 0(8)
[30(27) C(12) 0(7) %
Cl 2 (A
A) 0,: C(9)
1111' '
“<21 N" . 1‘ n
':\n¢§/‘}l ”(g 1 -._. " C(10)
” 7 ' \v
C(4) ”‘ 0(2) C(1) C(11)
C(15)"
. 25 ‘ h ’
{’9 ( ) Gr C(17)1C(16)
C(26) C|(1)

Figure 59. X-ray crystal structure of 70 with thermal ellipsoids drawn at the 50%

probability level.

96

Table 28. Summary of crystal and refinement data for compounds 70 and 72.

 

 

70 72
Formula C29H4|CIzlnN2 C29H4|IIIN2
Formula weight 603.36 532.46
Temperature / K 173(2) 173(2)
Crystal system Monoclinic Monoclinic
Space group o P21/n P21/n
Unit cell a / A 0 12.929 (1) 12.6312(1)
b / A 20.0253(1) 16. 1932(2)
c / A 13.4433(1) l4.2100(2)
o [3/ ° 1 18.053(1) 105.430(l)
V/ A3 3071 .67(3) 2801 .73(5)
Z 4 4
d cal. / Mg / m3 1.305 1.262
Abs.coe. / mm“1 0.962 0.861
F (000) 1248 1 112
Crystal size mm 0.28 x 0.26 X 0.25 0.30 x 0.21 x 0.20
6 range / ° 1.80 to 28.05 1.92 to 28.16
Index ranges -16Sh$ 16;—26Sk326; -16Shs l6;—2OSkS 16;
—16Sl$l7 —l8SlSl8
Ref. collected 30284 24850
Independent reflections 7181 [R(int) = 0.0179] 6604 [R(int) = 0.0265]
Data/restraints/parameters 7181 / 0 / 307 6604 / 0 / 289
GOF on F2 1.324 1.473

Final R [1 >2 0(1)]
R (all data)
Lgst diff. pk and hole/cA‘3

R1 = 0.021 1, wR2 = 0.0605
R1 = 0.0247, wR2 = 0.0616
0.520 and —0.640

R1 = 0.0345, wR2 = 0.1001
R1 = 0.0462, wR2 = 0.1038
0.631 and —0.686

Table 29. Selected bond distances (A) and angles (deg.) for compound 70.

 

In—N(2) 2.1212(12) C(1)—C(2) 1.527(2)
In—N(1) 2.1372(11) C(2)—C(3) 1.423(2)
In—C1(2) 2.3456(4) C(3)—C(4) 1.418(2)
In—C1(l) 2.3767(4) C(4)—C(5) 1.523(2)
N(2)—In—N(1) 93.9615) N(2)—In—Cl(1) 107.58(3)
N(2)—In—Cl(2) 1 1509(3) N( 1 )-In—Cl( 1) 106.83(3)
N(1)—1n—C1(2) 1 16.63Q) Cl(2)—In—Cl(1 ) 114.57(2)

 

Reactivity of In(Dipznacnac)Clz

Preliminary results show that one of chlorides can be substituted with an alkoxyl

group. Treatment of 70 with one molar equivalent of KO’Bu in toluene afforded 71 in

low yields (eq 33).

In(Dipgnacnac)Clg + K(O’Bu) —> In(Dipznacnac)(O’Bu)Cl + KCI

70

71

97

(33)

In contrast to the chemistry of Tolznacnac, attempts to introduce two or three
Dipznacnac to indium(III) failed. When compound 70 was treated with one molar
equivalent of 18 in toluene, a complex mixture resulted. A mixture of InCl3 and two
molar equivalents of 18 also led to a mixture. In both cases, we were not able to isolate
pure compounds from the mixtures. Thus it appears that bis- and tris-Dipznacnac

indium(III) complexes are not favored.

Synthesis and Structure of In(Dipznacnac)
Dipgnacnac increases the kinetic stability the indium(I) diketiminate complexes.
After stirring a mixture of 18 and one molar equivalent of InCl in toluene for 5 days, a

mono-valent indium complex 72 was isolated as pale yellow crystals in 56% yield.

Li(Dip2nacnac) + lnCl —> In(Dipznacnac) + LiCI (34)
18 72 56%

The identity of 72 is established by NMR, elemental analysis, and single crystal
diffraction methods. Solution NMR data indicated a C2,, point group symmetry for 72. VT
NMR spectra showed that the symmetry is maintained between —70 oC and 30 °C.
Furthermore, the X-ray structure of 72 was solved (Figure 60). Crystal and refinement
data for 72 are summarized in Table 28 and selected bond distances and angles are listed
in Table 30. In the solid state 72 is monomeric and the shortest intermolecular In---In
distance is 8.491(2) A. In this sense, the indium(I) center is two-coordinate and In, N(l),
N(2), C(2), C(3), and C(4) are virtually coplanar. Consistent with the lower oxidation
state for indium in 72, the average (2.288(3) A) of In—N distances in 72 is greater than
that in In(III) diketiminate (2.104(3)—2.272(5) A) complexes, despite of the lower
coordination number for indium(I) in 72. The chelating angle N(1)—In—N(2) in 72
(81.28(7)°) is more acute than that in 70 (93.96(5)°). The elongation of In—N bond and

98

the shrinkage of chelating angle in 72 are consistent with the trends observed in low-

valent indium hydrotris(pyrazolyl)borate complexesfizt133

C
.6) C128)
11117 ‘43
A’C(13)“/II'
C(12) C(29)y'
(1) 0 5842))0127
C1 CU 5' (s)
.7», \\ U‘
u C(6) "
0(9) '3 Cm
'2) N(2)

    

: 0111)

   

0 10 0C(15)
‘ ’ is at C(24)
C(16)
.th §‘
C(17) “
C(26)

Figure 60. X-ray crystal structure of 72 with thermal ellipsoids drawn at the 50%
probability level.

Figure 61 offers another view of the molecular structure of 72 and highlights
possible intramolecular indium(I)—carbon contacts in the molecular structure of 72.
Indium lies only 0.026(2) A above the least squares plane defined by C(13), C(17), C(26)
and C(29). The distances between indium and C(13), C(17), C(26), C(29) are in the range
of 3.950(3)—4.064(3) A and the In-C values approach the sum of van der Waals radii of
indium and methyl 11.90 + 2.00 = 3.90 A).

99

 

Figure 61. Another view of the molecular structure of 72.

Mono-valent indium complexes with low coordination number (CN) are rare. In
1998, Power and co-workers reported the synthesis and structural characterization of
In(C6H3-2,6-Trip2) (Trip = C6H2-2,4,6-iPr3) with the CN of indium being one.70 To our
knowledge, there is only one two-coordinate indium(I) complex documented in the
literature the dimer {In[pg-OC6H2-2,4,6-(CF3)3]}2.139 Several three-coordinate indium

tris(pyrazolyl)borate complexes are known.61'63 Hence compound 72 represents the only

example of a monomeric two-coordinate In(I) complex.

Table 30. Selected bond distances (A) and angles (dog) for compound 72.

 

In—N( 1) 2.285(2) N(2)—C( l 8) 1.440(3)
In—N(2) 2.290(2) C( 1 )—C(2) 1.519(3)
N ( 1 )-C(2) 1.328(3) C(2)—C(3) 1.407(3)
N(1)—C(6) 1.445(3) C(3)—C(4) 1.415(3)
N(2)—C(4) 1.335(3) C(4)—C(5) 1.521(3)
N(1)—In-N(2) 81 .28(7) C(4)—N(2)—C( 1 8) 1 19.4(2)
C(2)—N( 1 )—In 130.1(2) C(4)—N(2)—In 130.29(14)
C(6)—N(1)—-In 108.44(14) C(18)—N(2)—In 1 10.28(14)

 

Reactivity of In(Dipznacnac)

Compound 72 reacts with a variety of mild oxidants, affording oxidative addition

products. Treatment of an ethereal solution of 72 with one molar equivalent of 12 yielded

100

In(Dipznacnac)Iz (73) in excellent yield (eq 35). The solution NMR of 73 indicates C2,,

symmetry.

In(Dipznacnac) + 12 —> In(Dipgnacnac)12 (35)

72 73 93%

Similarly, treatment of a pentane solution of 72 with excess Mel afforded 74 in
85% yield after recrystallization (eq 36). The structure of 74 was established by NMR

and an X-ray structure analysis.

In(Dipgnacnac) + Mel —> In(Dipgnacnac)Me| (36)

72 74 85%

The NMR data of 74 indicates a C, symmetry and hindered N—Ar rotations. In
contrast to a C2,, symmetry in 73, the degeneracy of methine resonances is broken in 74.
Two 'Pr groups on the same phenyl ring are diastereotopic and two sets of resonance are

observed for the two 'Pr groups in NMR spectra of 74.

 

 

 

 

 

 

 

 

 

A A
1 1‘ I
. 'f 1.1“
”310’!“ EL 11 a DVD.) L.
1 ,‘(WUA U.
____~1J.LL 11.1-...... J k A J U
"TV—“If“fl * "1 TWW ""*”I'T"""I"T‘ "Ifi" ”Ti-firms 1'1”???"mfi7h‘77‘I—rT'TTT'm' ' aw r . . r_T*11 1 1 v1.11 (11.1.1 11111”?
3.6 3.4 3.2 3.0 2.8 2.5 2.4 2.2 2.0 1.8 1.6 1.4 1.2 PPM

Figure 62. IH NMR spectra of 72 (A) and 74 (B) in 'Pr regions.

101

Consistent with the solution NMR data, a pseudo-tetrahedral indium was revealed
(deg) are listed in Table 32.

in an X-ray structure analysis of 74 (Figure 63). Crystal and refinement data for

compound 74 are summarized in Table 31 and selected bond distances (A) and angles

Similar to that of 70, the chelating ring of C3N21n in 74 is puckered with In and
C(3) displaced at the same side from the plane of N( 1 ), N(2), C(2), and C(4).
Kw \

   

   
 

1' C(28)
=‘ . 1'” 029
'C(12) C(27) x1 ( )
0(7) 011)
C18) ,1; .11. C1) 12. C(1 5) C123)
1111‘ " (7.";\\ :1 ‘v
v “‘3' N11) '" N(2) 1’:
A“ .1
" 114011
C(9) (’4. 5,11) C(30)
.14
«C(15)
0110) :54;

C(22)
\

2.1
C(19) 5

C(24

I],

V

I
\O

C (21 )
0.1
probability level.

Figure 63. X-ray crystal structure of 74 with thermal ellipsoids drawn at the 50%

102

Table 31. Summary of crystal and refinement data for compounds 74 and 75.

 

 

74 75
Formula C 30H44 HDN 2 C70H94ID2N402
Formula weight 674.39 1253.13
Temperature / K 173(2) 173(2)
Crystal system Monoclinic Monoclinic
Space group o P21/n C2/m
Unit cell a / A 19. 1074(3) 17.5488(2)
b / A 8.65710(10) 20.574613)
c / A 20.17330(10) 1 1.5066(2)
6/ °C, 112.9050(10) 127.506(1)
V/ A3 3073.84(6) 3295.7718)
Z 4 2
d ca1. / Mg / m3 1.457 1.263
Abs.coe. / mm“ 1.792 0.744
F (000) 1360 1312
Crystal size mm 0.21 x 0.12 x 0.12 0.22 x 0.20 x 0.20
6 range / ° 1.88 to 28.18 1.77 to 28.32
Index ranges -24 S h S 24, —11 S k S 11, —22 S h S 22,—20 S k S
—26SlS26 27,—14S1S 14
Ref. collected 29455 13945
Independent reflections 7215[R(int) = 0.0370] 4039[R(int)=0.0200]
Datalrestraints/parameters 7215 / 0 / 307 4039/0/169
GOF on F3 1.108 1.249
Final R [1 >2 0(1)] R1 = 0.0425, wR2 = 0.1440 R1 = 0.0319, wR2 = 0.1108
R (all data) R1 = 0.0610, wR2 = 0.1537 R1 = 0.0340, wR2 = 0.1125

Lgst diff. pk and hole/eA”3 1.554 and —1.869

1.168 and —0.917

Table 32. Selected bond distances (A) and angles (deg) for compound 74.

 

In—N(1) 2.158(4) N(2)—C(18) 1.458(5)
In—N(2) 2.17214) C11)—C12) 1.53316)
Iii—C(30) 2.31314) C(2)—C(3) 1.420(6)
In—I 2.738315) C(3)-C(4) 1.407(6)
N(l)—In—N(2) 90.54114) N(l)—In—I 109.16(10)
N(1)—In—C(30) 113.76114) N(2)—In—I 104.1319)
N(2)—In—C(30) 12020113) C130)—1n—1 115.92110)

 

In contrast to the B—H cleavage in Tp3°tBu when In(Tp3'tB") was treated with N20,

compound 72 reacted with N20 to give the oxo-bridged dimer 75. Its NMR data are

simple, with only one new set of resonances for Dipznacnac. Since NMR data could not

distinguish between an indium oxo complex and an oxo-bridged indium(HI) dimer

(Figure 64), we attempted to solve the crystal structure of 75. X-ray diffraction analysis

indicated an oxo-bridged dimer. The molecular structure of 75 is shown in Figure 65.

103

 

 

' lo ' Dip’ \In/N‘oip
In 5
Dip\ / \ ,Dip N20 . In . :\
——_> D \ / \ ID __> Q 0
Nd 'NZ Ip Nd Ip a!
/|\/K In
_ 1 Dip\ / \ ,Dip

Dip = 2,6-iPr2-CgH3
72 75

Figure 64. Synthesis of the oxo-bridged dimer 75.

   
     
  

a-
\1")
Q!) -'

I. \\1
677/, C 1 (277/05 ‘4

A, ‘9’”) 1‘ ‘
$1 1 ,.; ‘__.
.419
. 0(3)
610(2)

   
  
 

N 5
. C(11) 1.; C(1)
/, ‘ ‘. A /
[A "“ (lllfit‘cuol
’ O I.
C C(12)
C(6)

017)

Figure 65. X-ray crystal structure of 75 with thermal ellipsoids drawn at the 50%

probability level.

104

Table 33. Selected bond distances (A) and angles (deg) for compound 75.

 

In—O 2.04112) In—O(A) 2.05812)
O-In(A) 2.05812) In—N(C) 2.16712)
In—N 2.16712) Inn-In(A) 2.9630(3)
N—C(2) 1.33813) o--.0#1 2.83112)
O—In—O(A) 87.4218) N(C)—In—N 88.69110)
O—In—N(C) 120.74(6) O—In—In(A) 43.9316)
O(A)—In—N(C) 121.5116) O(A)-In—In(A) 43.4816)
O-In—N 120.7416) N(C)—In—In(A) 135.6515)
O(A)—In—N 121.5116) N—In—In(A) 135.6515)
In—O—In(A) 92.5818) C(2)—N—C(4) 1 17.312)

 

Symmetry transformations used to generate equivalent atoms: (A) —x + l, —y + 1, —z + 1;
(C) x, —.v+ Lz.

Compound 75 sits on a crystallographic center of inversion and has a
crystallographically imposed mirror plane that passes through In, 0 and C(3), such that
only a quarter of one molecule defines the asymmetric unit. The center of inversion is at
the midpoint between In and In(A). Though oxo-bridged indium complexes are less
common compared to alkoxyl-bridged indium complexes, 113,-, 1121-, fly, and pg-oxo
indium complexes are known.190‘194 The structure of compound 75 can be compared
with an In404 heterocubane and a more square-shaped InzOz is observed in 75 (O—In—
O(A) 87.42(8)°, In—O—In(A) 92.58(8)°) than in the In404 heterocubane (O—In—O 844(2)—
84.8(2)°, In—O—In 95.0(3)—95.3(2)°).195 Since oxygen in 75 is two-coordinate, the In-O
distance (2.050(3) A) in 75 is shorter than that in the In404 heterocubane (average

2. 138110) A).

105

Chapter 6

EXPERIMENTAL SECTION

General Considerations
General procedures are listed in Appendix A. In(Tp3 'tB "),61,62 Tle*,44 InCp"‘,43
T1(Tp3"B"),I96 A11Tp3"B“)Me2,I97 Ary1azides,l98 [OEt3]+[BF4]’,199 [H(OEt2)2]+[B{C6H3-
3,5 -(CF3)2 }4]',200 [Li(OEt2)3]+[B(C15F4-4-Si'BuMe2)4]‘,168 LiCHZSiMe3,201
'Buznacnac,202 B(C6F5)3,203 LiCH(SiMe3)2,204 [CPh3]+[B(C6F5)4]",205 [CPh3]+[B(C6F4-4-
Si’BuMe2)4]‘,168 KN(SiMe3)2,206 Ph3CMe,207 and KO’Bu208 were prepared according to
the literature procedures.
2,4-pentanedione, 2,4,6-trimethylani1ine, and 2,6-diisopropyl aniline were
distilled prior to use; p-toluidine was sublimed before use. MeMgI, "PngBr, and
(C3H5)MgBr ether solutions were freshly prepared from corresponding halides and
magnesium tumings. (C2H3)MgBr and MeLi ether solutions were purchased from
Aldrich and their concentrations were determined by titration. AlC13 and GaCl3 were
sublimed before use. Ian and InCl were purchased from Strem and used as received.
Equilibrium Constant Determination
An equilibrium (eq 7) between InCp*, T1(Tp3"B“) and In(Tp3'tB") (1), Tle* was
explored in both directions. InCp* (5.9 mg, 0.024 mmol) and T11Tp3"3“) 113.8 mg, 0.024
mmol) were dissolved in C6D; (0.5 mL) and the solution was transferred to a scalable
NMR tube. The NMR tube was flame-sealed. The NMR tube was kept in the dark
because significant decomposition was observed on exposure to light. The reaction was
monitored by 1H NMR and an equilibrium was reached within three days at room

temperature. The equilibrium constant {Keq = [l][Tle*]/[InCp*][T1(Tp3'tB")], eq 8} was

106

calculated by careful integration of the appropriate peaks in 1H NMR spectra. The
equilibrium constant (eq 8) calculated from the reaction of l (12 mg, 0.024 mmol) with
Tle* (8.2 mg, 0.024 mmol) was identical within experimental error. The error in
determining Kgq was estimated by assuming an error of 5% in each integration. The value
of K1,q was determined to be 3.5 i 0.7 at 298 K.
Synthesis

Al(Tp3'tB")Me2 (2). A solution of AlMe3 (2.0 M, 0.1 mL, 0.2 mmol) in hexanes
was added to a solution of l (0.10 g, 0.21 mmol) in hexanes (5 mL) at —78 °C. After the
mixture was stirred at room temperature for 12 h, it was filtered. Compound 2 was
collected after removal of hexanes (70 mg, 76%). The identity of Compound 2 was
established by an independent synthesis. '97

In(Tp3’tB“)Iz (3). A solution of 12 (43.2 mg, 0.17 mmol) in ether (5 mL) was
added to a solution of 1 (84.2 mg, 0.17 mmol) in ether (5 mL) at —78 °C. The mixture
was stirred overnight at room temperature, during which time the brown color lightened
to pale amber. The mixture was filtered and ether was removed under reduced pressure.
The resulting off-white residue was washed with cold pentane to give colorless 3 (42 mg,
34%). Compound 3 can be recrystallized from ether. mp 165 °C (dec). 1H NMR (C6D6,
300 MHz) 5 8.34 (d, J = 2.2 Hz, 1H), 7.29 (d, J = 2.4 Hz, 2 H), 5.85 (d, J = 2.4 Hz, 2H),
5.56 (d, J = 2.2 Hz, 1H), 1.50 (s, 18H), 1.04 (s, 9H). MS (EI, 70 ev) 623 (19%, M“ — I),
496 (3.23%, M+ — 2I). Anal. Calcd for C21H34B121nN6: C, 33.63; H, 4.53; N, 11.20.
Found: C, 33.25; H, 4.60; N, 10.85.

In(Tp3'tB")[N(Ph)—N=N-NPh] (4). A solution of PhN3 (0.13 mL, 0.14 g, 1.18
mmol) in pentane (5 mL) was added to a solution of 1 (0.17 g, 0.34 mmol) in pentane (10
mL) at room temperature. The colorless solution immediately turned yellow. Gas
evolution was observed, and a yellow precipitate deposited. The yellow precipitate was
collected by filtration and washed with pentane (0.15 g, 61%). Compound 4 can be
recrystallized from toluene at —30 °C. mp 135—136 °C (dec). 1H NMR (C6D6, 300 MHz)

107

57.27 (d, J = 2.5 Hz, 3H), 7.25 (m, 4H), 7.05 (m, 4H), 6.71 (m, 2H), 5.79 (d, J = 2.5 Hz,
3H), 1.06 (s, 27H). l3C1 1H} NMR (061)..) 5 167.86, 150.54, 139.07, 129.23, 119.68,
118.59, 105.02, 33.10, 30.52. ”B{ 'H) (C6D6, 96 MHz) —3.2 121,, = 98 Hz. IR (nujol mull,
KBr plate) 2511 (w, vB_H). Anal. Calcd for C33H44BInNm: C, 56.11; H, 6.27; N, 19.82.
Found: C, 56.14; H, 6.20; N, 19.75.

In(Tp3'tB“)[N(p-Tol)—N=N—N(p-Tol)] (5). Compound 5 was prepared in a fashion
similar to that of 4 starting from 1 and p-tolylazide (yellow solid, 65%). mp 151—153 °C
(dec). 'H NMR (Cst. 500 MHz) 6 7.30 (d. J = 2.5 Hz, 3H), 7.171d, J = 8.5 Hz, 4H),
6.87(d, J = 8.5 Hz, 4H), 5.81 (d, J = 2.5 Hz, 3H), 2.09 (s, 6H), 1.09 (s, 27H). l3c1‘H}
NMR (C6D6, 125 MHz) 5 167.76, 148.45, 138.96, 129.75, 128.29, 118.72, 104.95, 33.07,
30.57, 20.69. IR (nujol mull, KBr plate) 2498 (m, 113-"). Anal. Calcd for C35H43BInN10:
C, 57.24; H, 6.54; N, 19.06. Found: C, 57.21; H, 6.58; N, 18.81.

H[B(C3H2N2-3-'Bu)4] (6). An excess of N20 (4.1 mmol, 7 equivalents) was
vacuum transferred into a frozen solution of compound 1 (0.29 g, 0.58 mmol) in benzene
(15 mL) using liquid nitrogen. The mixture was allowed to warm to room temperature
and was stirred for 24 h. No precipitation was observed. The lH NMR spectrum of the
crude product contained the resonances for 6 and an unknown complex with a broad peak
(5 1.30, v», z 150 Hz.). Colorless 6 crystallized from a concentrated pentane extract at —
78 °C in a low but reproducible yield (38 mg, 17% based on pyrazolyl group). mp 122—
l 25 °C (dec). 1H NMR (300 MHz, C6D6) 5 7.28 (d, J = 1.5 Hz, 4H), 5.99 (d, J = 1.5 Hz,

4H), 1.24 (s, 36H). The resonance for NH could not be located between 5 20 ppm and 5 —
10 ppm. '3c1‘H} NMR 175 MHz, C6D6) 5162.2, 136.2, 102.13, 32.10, 30.62. “B NMR
(96 MHz, C6D6) 0.56 (s, 120,: 43 Hz). 1R (Nujol mull, KBr plate) 3183, 3133, 1514, 1460,
1365, 1250, 1209, 1151, 1103, 1051. Satisfactory elemental analysis (C, H, N) was not
obtained for this compound. Anal. Calcd for C28H45BNg: C, 66.66; H, 8.99; N, 22.20.
Found: C, 49.62; H, 7.04; N, 14.93. When the reaction was performed at —50 °C (toluene-

(18) and monitored by NMR, reaction intermediates were not observed.

108

4-(p-tolylamino)-3-pentene-2-one (7).209 A one-liter round bottom flask was
charged with 2,4—pentanedione (100 g, 1.0 mol) and freshly sublimed p-toluidine (107 g,
1.0 mol). Dry toluene (500 mL) was added to the flask and a Dean-Stark apparatus was
used to azetropically remove water. The mixture was heated at 130 °C for 8 h to give a
brown solution. All toluene was removed by a rotary evaporator and the resulting brown
oil was diluted with hexane (100 mL). The solution was kept at —30 °C overnight. Yellow
7 crystallized and was collected by suction filtration (156 g, 83%). mp 66—69 °C.
Literature 67—68 °C.209 lH NMR (CDC13, 300 MHz) 5 12.38 (br, s, 1H), 7.12 (d, J = 7.5
Hz, 2H), 6.97 (d, J = 7.5 Hz, 2H), 5.18 (s, 1H), 2.32 (s, 3H), 2.07 (s, 3H), 1.94 (s, 3H).
l3C1‘H} NMR (C130,, 75 MHz) 5 195.8. 160.6, 135.9, 135.4, 129.5, 124.7, 97.10,
29.03, 20.81, 19.68.

4-(2,4,6-trimethylphenylamino)-3-pentene-2-one (8). A procedure similar to
that of 10 was used to prepare 8 as a pale yellow solid (91%). mp 66—68 °C. 1H NMR
(CDC13, 300 MHz) 5 11.80 (8, br, 1H), 6.88 (s, 2H), 5.17(s, 1H), 2.26(s, 3H), 2.13 (s,
6H), 2.08 (s, 3H), l.60(s, 3H). l3C{'H} NMR (CDC13, 75 MHz) 5 195.84, 163.08,
136.99, 135.68, 133.83, 128.84, 95.60, 29.03, 20.90, 18.85, 18.12.

4-(2,6-di-ethylphenyIamino)-3-pentene-2-one (9). A procedure similar to that of
10 was used to prepare 9 as a colorless oil (1 15-1 17 oC/0.15 mm Hg) in 94% yield. 1H
NMR (CDCI3‘ 300 MHz) 5 12.01 (s, 1H), 7.22—7.10 (m, 3H), 5.18 (s, 1H), 2.62—2.40 (m,
4H), 2.09 (s, 3H), 1.60 (s, 3H), 1.15 (t, J = 7.5 Hz, 6H). ‘3C1‘H1 NMR 1CDC13. 75 MHz)
5 195.92, 162.98, 141.82, 135.14, 127.84, 126.40, 120.36, 95.64, 29.02, 24.72, 18.95,
14.54.

4-(2,6-di-iso-propylphenylamino)-3-pentene-2-one (10). A 250-mL round
bottom flask was charged with 2,4-pentanedione (40 g, 0.40 mol), TsOH-HZO (0.46 g, 2.5
mmol), and 2,6-diisopropyl aniline (47 g, 0.27 mol). The mixture was heated to reflux
with a minimum amount of toluene in a Dean-Stark apparatus for 8 h. After removing the

solvents, the mixture was vacuum distilled (105 °C/0.01 mm Hg) to give pale yellow 10

109

which solidified upon standing overnight (65 g, 93%). mp 49—51 °C. 1H NMR (CDC13,
300 MHz) 512.06(s,br, 1H), 1.18 (d, J = 6.9 Hz, 6H), 7.26 (m, 1H), 7.15 (d, J = 7.1 Hz,
2H), 5.18 (s, 1H), 3.00 (sept, J = 6.8 Hz, 1H), 2.09 (s, 3H), 1.60 (s, 3H), 1.12 (d, J = 6.9
Hz, 6H). l3C{‘H} NMR (CDC13, 75 MHz) 5 195.9, 163.2, 146.2, 133.4, 128.2, 123.5,
95.53, 29.03, 28.41, 24.54, 22.61, 19.10.

2-(p-toly|amino)-4-(p-tolylimino)-2-pentene (Tolznacnac) (11). To a suspension
of 19 (82 g, 0.26 mol) in water (500 mL) was added a solution of potassium hydroxide
(29 g, 0.52 mol) in water (150 mL). The mixture was stirred for 30 min during that time a
yellow oil separated. The mixture was extracted with diethyl ether (3 X 150 mL). After
the ether extracts were dried over magnesium sulfate, ether was removed by a rotavapor.
The resultant oily liquid was diluted with hexanes (30 mL), and was cooled to —30 °C
overnight to start crystallization. Pale yellow diketimine was collected by suction
filtration, and washed with small amount of cold hexanes (69 g, 95%). mp 67—70 °C. lH
NMR (CDC13, 300 MHz) 12.62 (br s, 1H), 7.07 (d, J = 8.1 Hz, 4H),. 6.84 (d, J = 8.1 Hz,
4H), 4.83 (s, 1H), 2.31 (s, 6H), 1.98 (s, 6H). l3C1‘H) NMR (CDC13, 75 MHz) 159.5,
143.1, 132.6, 129.2, 122.6, 96.80, 20.76, 20.60.

2-(2,4,6-tri-methylphenylamino)-4-(2,4,6-tri-methylphenylimino)-2-pentene
(Mesznacnac) (12). Compound 12 was prepared in a procedure similar to that of 14 as
colorless solids in 88% yield. mp 79—81 °C. 1H NMR (CDCl3, 300 MHz) 5 12.2 (s, br,
1H), 6.86 (s, 4H), 4.85 (s, 1H), 2.26 (s, 6H), 2.12 (s, 12H), 1.69 (s, 6H). l3C1'H} NMR
(CDC13. 75 MHz) 5160.91, 141.09, 133.45, 131.75, 128.37, 93.21, 20.80, 20.26, 18.26.

2-(2,6-di-ethylphenylamino)-4-(2,6-di-ethylphenylimino)-2-pentene
(DepznacnacH) (13). Compound 13 was prepared in a procedure similar to that of 14 as
colorless solids in 76% yield. mp 84—86 °C. 1H NMR (CDC13. 300 MHz) 5 12.18 (8, br,
1H), 7.18-7.05 (m, 6H), 4.88 (s, 1H), 2.70—2.40 (m, 8H), 1.71 (s, 6H), 1.18 (t, J: 7.5 Hz,
12H). '3C1'H} NMR (C130,, 75 MHz) 5160.92, 142.32, 137.84, 125.84, 124.65, 93.34,
24.61, 20.55, 14.40.

110

2-(2,6-di-iso-propylphenylamino)-4-(2,6-di-iso-propylphenylimino)-2-pentene
(DipznacnacH) (14),127,128 A 250-mL round bottom flask was charged with 4-(2,6-di-
iso-propylphenylamino)-3-pentene-2-one (34 g, 0.13 mol), TsOH (22.6 g, 0.13 mol), 2,6-
diisopropyl aniline (23 g, 0.13 mol). The mixture was stirred with a minimal amount of
toluene in Dean-Stark apparatus in an oil bath heated at 170 °C for 24 h. After the
mixture was cooled to room temperature, it was diluted with ether (100 mL) and washed
with an aqueous solution (100 mL) of KOH (14.6 g, 0.26 mol). The water layer was
separated from the organic layer, and the water phase was back extracted with ether (20
mL). The combined organic phase was dried over MgSOa. Colorless analytically pure
DipgnacnacH was obtained by recrystallization from hexane/MeOH (43.4 g, 80%). mp
138—140 0C. (Lit. 140—141 °C.123) 1H NMR (CDC13, 300 MHz) 512.12 (8, br, 1H), 7.12
(m, 6H), 4.86 (s, 1H), 3.1 l (sept, J = 6.9 Hz, 4H), 1.71 (s, 6H), 1.20 (d, J = 6.9 Hz, 12H),
1.11 (d, J = 6.9 Hz, 12H). '3C1'H} NMR 1CDC13, 75 MHz) 5161.18, 142.44, 140.69,
125.06, 123.00, 93.18, 28.17, 24.20, 23.22, 20.74.

2-(2,6-di-iso-propylphenylamino)-4-iso-propylimino-2-pentene (15). A
methylene chloride 15 mL) solution of [OEt3]+[BF4]'199 (1.6 g, 8.4 mmol) was added to a
methylene chloride (5 mL) solution of compound 10 (1.98 g, 7.7 mmol) at room
temperature with stirring. After the mixture was stirred at that temperature for 30 min, a
methylene chloride (10 mL) solution of freshly distilled ‘PrNHz (2.2 g, 38 mmol) was
added. After the mixture was stirred at room temperature for 5 h, all volatile materials
were removed under vacuum. The yellow tar was treated with KOH (0.43 g, 7.7 mmol)
water solution. The organic layer was dried over MgSO4. The resulting oil was subject to
fractional distillation affording pure product as yellow oil (105—1 10 °C/0.1 mm Hg, 1.49
g, 65%). 1H NMR (CDCI3, 300 MHz) 5 10.84 (s, br, 1H), 7.1—6.8 (m, 3H), 4.56 (s, 1H),
3.66 (sept, J = 6.3 Hz, 1H), 2.85 (sept, J = 6.9 Hz, 2H), 2.01 (s, 3H), 1.58 (s, 3H), 1.16 (d,
J = 6.9 Hz, 6H), 1.12 (d, J = 6.3 Hz, 6H), 1.09 (d, J = 6.9 Hz, 6H). l3C{'H} NMR

111

(CDC13, 75 MHz) 5 165.82, 154.47,]3794, 123.20, 122.54, 122.22, 92.48, 44.13, 28.03,
24.31, 23.88, 22.41, 21.50, 19.17.
Li(Tolznacnac) (16).117 A solution of 11 (20 g, 72 mmol) in pentane (350 mL)
was treated with a hexane solution of "BuLi (45 mL, 1.6 M, 72 mmol) with stirring at 0
°C. After the addition, a yellow precipitate formed and the stirring was maintained for
another 10 min at that temperature. The mixture was let to warm to room temperature and
was stirred for another 2 h. The yellow mixture was reduced in volume to about 250 mL.
Yellow 16 was collected by filtration under nitrogen (18 g, 88%). mp 185—187 °C (dec).
lH NMR (C6D6, 300 MHz) 5 6.91 (d, J = 8.1 Hz, 4H), 6.61 (d, J = 8.1 Hz, 4H), 4.67 (s,
1H), 2.15 (s, 6H), 1.79 (s, 6H). ‘3C{'H} NMR (Cst, 75 MHz) 5 165.6, 151.4, 131.2,
129.6, 124.3, 95.49, 23.08, 20.87. Anal. Calcd for ClontLisz C, 80.26; H, 7.44; N,
9.85. Found: C, 80.18; H, 7.15; N, 9.50.
Li(Dep2nacnac) (17). Compound 17 was prepared in a fashion similar to that of
18 starting from 13 and one equivalent of "BuLi in pentane as colorless solids with 84%
yield. mp 208—210 °C (dec). 1H NMR (C6D6, 300 MHz) 5 7.20—7.09 (m, 6H), 4.79 (s,
1H), 2.42 (q, J = 7.5 Hz, 8H), 1.70 (s, 6H), 1.19 (t, J = 7.5 Hz, 12H). '3C{‘H} NMR
(C6D6, 75 MHz) 5 163.36, 151.14, 136.10, 125.68, 122.69, 92.82, 24.92, 23.04, 14.26.
Li(Dip2nacnac) (18). A solution of freshly recrystallized 14 (21.1 g, 50 mmol) in
pentane (200 mL) was treated with a solution of "BuLi (2.5 M, 20 mL, 50 mmol) in
hexane at 0 °C with stirring in 30 min. The mixture was heated to reflux for 1 h, giving a
homogeneous pale yellow solution. The solution was concentrated to about 20 mL during
which time colorless 18 crystallized out. After the mixture was cooled at -30 °C for 2 h,
1 8 was collected by filtration (19.9 g, 93%). mp 158—160 °C (dec). lH NMR (C6D6, 300
MHz) 57.18 (m, 6H), 4.86 (s, 1H), 3.09 (sept, J = 6.9 Hz, 4H), 1.80 (s, 6H), 1.17 (d, J =
6.9 Hz, 12H), 1.15 (d, J = 6.9 Hz, 12H). l3C{ lH} NMR (C6D6, 75 MHz) 5 164.0, 149.2,
140.7, 123.4, 123.3, 93.01, 28.21, 24.08, 24.02, 23.35. Anal. Calcd for ConaiLisz C,
82-04; H, 9.73; N, 6.60. Found: C, 82.63; H, 9.64; N, 6.65.

112

 

2-(p-tolylamino)-4-(p-tolylimino)-2-pentene hydrochloride (19). Yellow 7 (112
g. 0.59 mol) and TolNHg-HCl (84.7 g, 0.59 mol) were suspended in anhydrous ethyl
alcohol (600 mL) in a one-liter flask at room temperature The mixture was heated to boil
until the volume of brown solution was reduced to about 250 mL. After the solution was
cooled to room temperature it was further cooled to -30 °C overnight. Yellow compound
19 was collected by filtration, washed with copious amount of hexanes and diethyl ether,
dried thoroughly under vacuum (103 g, 55%). mp 193—195 °C (dec). 1H NMR (CD3OD,
300 MHz) 7.15 (br, s, 4H), 6.98 (br, s, 4H), 5.50 (br s, 1H), 2.60 (s, 6H), 2.31 (s, 6H).
l3C{ lH} NMR (CD301), 75 MHz) 170.7, 139.2, 135.5, 131.1, 126.4, 93.14, 22.46, 21.05.
2-(p-tolyIamino)-4-(p-tolylimino)-2-pentene hydrobromide (20). A solution of
freshly recrystallized 11 (7.7 g, 28 mmol) in ether (50 mL) was treated with HBr water
solution (48% by weight, 4.0 mL, 35 mmol) at 0 °C. A pale yellow precipitate formed
immediately. The yellow precipitate 20 was collected by suction filtration, washed with
hexanes and dried under vacuum (6.9 g, 69%). mp > 220 °C. 1H NMR (CD3OD, 300
MHz) 5 7.15 (m, 4H), 7.00 (m, 4H), 5.49 (s, 1H), 2.61 (8, br, 6H), 2.31 (8, br, 6H).
”C{ 'H} NMR (cogoo, 75 MHz) 5 170.7, 139.2, 135.5, 131.1, 126.4, 93.09, 22.56,
21.06. Anal. Calcd for C longBl‘NzI C, 63.51; H, 6.45; N, 7.79. Found C, 63.48; H, 6.49;
N, 7.81.
2-(p-tolylamino)-4-(p-tolylimino)-2-pentene hydroiodide (21). Compound 21
was prepared in a procedure similar to that of 20 from 11 and hydroiodic acid (47% by
weight) in a yield of 72% as a pale yellow solid. mp 214—215 °C. 1H NMR (CD3OD, 300
MHz) 5 7.18 (m, 4H), 6.98 (m, 4H), 5.48 (s, 1H), 2.60 (8, br, 6H), 2.31 (8, br, 6H).
l3C{'H} NMR (CD3OD, 75 MHz) 5 170.6, 139.1, 135.4, 131.1, 126.4, 93.21, 22.72,
2 l -08. Anal. Calcd for ClgHngNgi C, 56.16; H, 5.71; N, 6.89. Found C, 55.45; H, 5.68; N,
6.84.
2-(p-tolylamino)-4-(p-tolylimino)-2-pentene trifluromethanesulfonic acid (22).

Compound 22 was prepared in a procedure similar to that of 24 from 11 and neat triflic

113

acid in 98% yield as a pale yellow solid. mp 173-175 °C (dec). 1H NMR (CD3OD, 300
MHz) 5 7.14 (m, 4H), 6.98 (m, 4H), 5.45 (s, 1H), 2.59 (5, br, 6H), 2.31 (8, br, 6H).
l3C{'H} NMR (CD301), 75 MHz) 5170.7, 139.2, 135.5, 131.1, 126.4, 121.8 (q, 1.10,: =
317 Hz), 93.10 (br), 22.44, 21.04. ”F NMR (CDgOD, 282 MHz) 5—79.5 I)», = 3.6 Hz.
Anal. Calcd for C30H23F3N203S: C, 56.06; H, 5.41; N, 6.53. Found C, 56.00; H, 5.47; N,
6.49.

2-(2,4,6-tri-methylphenylamino)-4-(2,4,6-tri-methylphenylimino)-2-pentene
hydrochloride (23). IH NMR (CD3OD, 300 MHz) 5 6.73 (s, 4H), 4.29 (s, 1H), 2.64 (s,
6H), 2.22 (s, 6H), 1.93 (s, 12H). ‘3C{'H} NMR (C0301), 75 MHz) 6 171.53, 139.75,
135.47, 132.74, 130.02, 90.49, 21.21, 21.12, 17.46.

2-(2,6-di-iso-propylphenylamino)-4-(2,6-di-iso-propylphenylimino)-2-pentene
trifluromethanesulfonic acid (24). A solution of triflic acid (1.85 g, 12.2 mmol) in
diethyl ether (15 mL) was added to a solution of 14 (5.1 g, 12.2 mmol) in ether (60 mL)
at room temperature. The mixture was stirred for 5 min at that temperature and a
colorless precipitate formed. The precipitate was collected by filtration, washed with
ether (2 x 20 mL) and pentane (2 X 10 mL), and dried in vacuum overnight (6.4 g, 92%).
mp 225—228 0C. lH NMR (CDC13, 300 MHz) 5 9.30 (s, 2H), 7.14 (t, J = 7.8 Hz, 2H),
6.90 (d, J = 7.8 Hz, 4H), 4.26 (s, 1H), 2.49 (sept, J = 6.9 Hz, 4H), 2.44 (s, 6H), 0.94 (d, J
= 6.9 Hz, 12H), 0.74 (d, J = 6.9 Hz, 12H). '3C{'H} NMR (CDC13, 75 MHz) 6171.41,
144.85, 131.34, 129.20, 123.73, 120.18 (q, Jc_p = 318 Hz), 91.55, 28.22, 24.13, 22.41,
21.81. ”P NMR (CDC13,282 MHz) 5-78.80 (s, Dy, = 8.2 Hz).

[TolznacnacH2]+[B{(C6H3-3,5-(CF3)2}4]' (25). A suspension of
[H(OEt2)2]+[B{C6H3-3,5-(CF3)2}4]’200 (1.3 g, 1.3 mmol) in toluene (10 mL) was treated
with a solution of compound 11 (0.36 g, 1.3 mmol) in toluene (10 mL) at room
temperature. After the mixture was stirred at that temperature for 1 h, a two-layer system
developed. The top layer was decanted and the bottom layer was put under vacuum. The

resulting yellow oil was triturated with pentane to give 25 as pale yellow solid (0.71 g,

114

62%). mp 107—109 °C. 1H NMR (CD2C12, 300 MHz) 57.71 (m, 8H), 7.51 (m, 4H), 7.02
(m, 4H), 6.73 (m, 4H), 5.38(s, 1H), 2.34 (s, 12H), 2.28(s, 2H). ”m 'H} NMR (CD202, 75
MHz) 5 170.5, 162.9 (q, lJ3.c = 49 Hz), 139.3, 135.8, 135.5, 131.1, 130.5 (q, 210.}: = 30
Hz), 126.3, 125.8 (q, '10,: = 270 Hz), 118.5(br), 93.03, 22.36, 21.00. “B NMR (CD2C12,
96 MHz) 5—6.32 (u), = 3.0 Hz). ‘91: NMR (CD2C12, 282 MHz) 5—62.6. Anal. Calcd for
C51H35BF24N2: C, 53.61; H, 3.09; N, 2.45. Found: C, 53.70; H, 3.03; N, 2.40.

[DipznacnacHzflB(C6F4Si'BuMe2)4]' (26). A solution of compound 14 (0.24g,
0.57 mmol) in ether (10 mL) was treated with 1 M HCl ether solution (0.60 mL, 0.60
mmol) at 0 °C. A white precipitate formed immediately and the mixture was further
stirred at that temperature for 5 min. An ether solution (10 mL) of [Li(OEt2)3]+[B(C6F4-4-
Si’BuMe2)4]"68 (0.70 g, 0.60 mmol) was added to the white suspension. After the mixture
was stirred at room temperature for 12 h, all volatile materials were removed under
vacuum. The white solid was extracted with methylene chloride (2 x 15 mL). The
methylene chloride filtrate was reduced in volume to about 2 mL and cooled to -30 °C
overnight. Colorless compound 26 was collected by filtration, washed with pentane (2 x 5
mL), and dried under vacuum (0.62 g, 73%). mp 169-172 °C (dec). 1H NMR (CDC13, 300
MHz) 57.34 (s, 2H), 7.23 (t, J = 7.8 Hz, 2H), 6.98 (d, J = 7.8 Hz, 4H), 4.50 (s, 1H), 2.49
(sept, J = 6.6 Hz, 4H), 2.42 (s, 6H), 0.88 (d, J = 6.6 Hz, 12H), 0.83 (s, 36H), 0.78 (d, J =
6.6 Hz, 12H), 0.23 (s, 24H). ”m ‘H) NMR (CDC13, 75 MHz) 6172.1, 148.7 (d, '10.: =
240 Hz), 148.2 (d, lJ(;_F= 240 Hz), 144.8, 133.4 (br B—C), 130.2, 124.8, 124.3, 108.0 (t,
21C-.. = 32.6 Hz), 92.36, 28.40, 26.32, 23.85, 22.64, 22.57, 17.54, —3.88 (t, 410.: = 4.0
Hz). “B NMR (CDC13, 96 MHz) 5—16.4 (6,, = 27 Hz). ”P NMR (CDC13, 282 MHz) 6—
130.79(m), —132.50(m). Anal. Calcd for C77H103BF16NZSi4: C, 62.32; H, 7.00; N, 1.89.
Found: C, 62.42; H, 7.25; N, 1.87.

In(Tolznacnac)3 (27). A Schlenk tube was charged with InCl (1.17 g, 7.78 mmol)
and 16 (2.21 g, 7.78 mmol) in a glovebox. The mixture was stirred with ether (50 mL) at

room temperature for 50 h. The mixture was filtered and 27 was purified by repeated

115

 

recrystallization out of toluene/pentane (0.85 g, 34% based on ligand). See Chapter 5 for
alternative preparations and characterizations.

B(Tolznacnac)F2 (28). A solution of 16 (7.0 g, 25 mmol) in toluene (10 mL) was
added to a solution of freshly distilled BF3-0E12 (3.5 g, 25 mmol) in toluene (20 mL) at 0
°C. Upon warming to room temperature, a precipitate formed. After 12 h, the mixture
was filtered and the filtrate was concentrated to afford compound 28 as yellow crystals
(3.7 g, 46%). mp 189—190 °c (dec). lH NMR (300 MHz, CDC13) 6 7.08—7.17 (m, 8H),
5.16 (s, 1H), 2.33 (s, 6H), 1.87 (s, 6H). l3C{'H} NMR (75 MHz, CDC13) 5 163.51,
138.52, 136.79, 129.43, 127.24, 95.15, 21.31, 21.03. HB (96 MHz, CDC13) 52.0 (t, 1:2:1
J = 29.1 Hz). 19F NMR (282 MHz, CDC13) 5—128.9 (q, 1:1:1:1, J = 29.8 Hz). LRMS
326.2 (M+, 45). Anal. Calcd for ClgHngFzNzi C, 69.96; H, 6.49; N, 8.58. Found C,
69.74; H, 6.45; N, 8.44.

B[Tf—Me2C(NTol)CH=C(NTol)Me]Me (29). A stirred suspension of 28 (0.88 g,
2.7 mmol) in diethyl ether (20 mL) was treated with MeLi (1.4 M, 3.8 mL, 5.4 mmol)
ether solution at 0 oC and the reaction mixture was warmed to room temperature. After
being stirred for 12 h, the mixture was filtered and the solvent was removed from the
filtrate to give a yellow oil. The oil was extracted with pentane and the solvent volume
was reduced to ~2 mL. Compound 29 crystallized upon standing overnight at -78 °C as
pale yellow crystals (0.52 g, 61%). mp 87—90 °C (dec). 1H NMR (500 MHz, C6D6) 57.05
(d, J = 8.3 Hz, 2H), 6.90 (m, 4H), 6.82 (d, J = 8.3 Hz, 2H), 4.45 (q, J = 1.0 Hz, 1H), 2.12
(s, 3H), 2.07 (s, 3H), 1.58 (d, J = 1.0 Hz, 3H), 1.33 (s, 6H), -0.0090 (s, 3H). l3C{‘H}
NMR (75 MHz, C6D6) 5143.21, 143.02, 135.24, 135.12, 132.05, 130.09, 129.41, 129.11,
109.04, 54.94, 31.87, 21.23, 20.91, 20.87, 1.7 (viz: 50 Hz). HB (96 MHz, CDC13) 530.7
(Dy, = 283 Hz). Anal. Calcd for C21H37BN2: C, 79.25; H, 8.55; N, 8.80. Found C, 79.03;
H, 8.52; N, 8.78.

B[nZ-CH2=C(NTol)CH=C(NTol)Me]CH2SiMe3 (30). A 100-mL Schlenk tube
was charged with 28 (0.46 g, 1.4 mmol) and LiCHZSiMe320' (0.26 g, 2.8 mmol) in a

116

glovebox. Diethyl ether (20 mL) was added to the mixture at 0 °C with stirring. After 30
min, the mixture was filtered and the solvent was removed under vacuum. The resultant
orange oil was taken into pentane, and compound 30 crystallized as a pale yellow solid
(0.25 g, 47%) upon standing at —80 °C overnight. mp 78-80 °C (dec). 1H NMR (300
MHz, CDC13) 5 7.20 (d, J = 8.1 Hz, 2H), 7.16 (d, J = 8.1 Hz, 2H), 7.05 (d, J = 8.1 Hz,
2H), 6.98 (d, J = 8.1 Hz, 2H), 5.40 (s, 1H), 3.51 (s, 1H), 2.83 (s, 1H), 2.34 (m, 6H), 1.57
(s, 3H), —0.13 (s, 2H), —0.44 (s, 9H). '3C{ ‘H} NMR (75 MHz, CDC13) 6149.44, 142.09.
141.41, 140.43, 136.02, 135.84, 130.01, 129.62, 129.35, 104.68, 79.34, 21.10, 20.97,
20.90, 5.06 (Dy, = 43 Hz), 1.07. “B NMR (96 MHz, CDC13) 6 33 (0,, = 475 Hz). LRMS
373 (M+ - H, 55). Anal. Calcd for C23H31BN2Si: C, 73.78; H, 8.55; N, 7.48. Found C,
73.52; H, 8.29; N, 7.45.

B(Tolznacnac)Me2 (31). A stirred suspension of 28 (0.48 g, 1.5 mmol) in diethyl
ether (15 mL) was treated with an ethereal solution of MeMgI (1.2 M, 2.4 mL, 2.9 mmol)
at 0 0C. After 5 min, the mixture was filtered and the solvent was removed under
vacuum. The crude product was extracted with pentane, and compound 31 crystallized
and was isolated as yellow crystals (0.31 g, 66%) upon standing at —80 °C overnight. mp
115—1 18 °C. 1H NMR (300 MHz, CDC13) 57.09 ((1, J = 8.1 Hz, 4H), 6.90 (d, J = 8.1 Hz,
4H), 4.82 (s, 1H), 2.31 (s, 6H), 1.66 (s, 6H), —0.44 (s, 6H). '3C{‘H} NMR (75 MHz,
C6D6) 5 162.23, 143.36, 135.50, 129.46, 127.54, 95.18, 21.77, 20.92, 8.22 (br, s, v), = 64
Hz). ”B NMR (96 MHz, C6D6) 6 1.07 (s, 6,: 259 Hz). LRMS 318 (W 1), 303 (M+ —
Me, 100). Anal. Calcd. for C21H27BN2: C, 79.25; H, 8.55; N, 8.80. Found C, 79.32; H,
8.61; N, 8.76.

B(Tolznacnac)"Pr2 (32). Compound 32 was prepared in a fashion similar to
compound 31 starting from 28 and two molar equivalents of "PngBr in 56% yield as
bright yellow crystals. mp 98—102 °C (dec). 1H NMR (300 MHz, CDCI3) 5 7.10 (d, J =
8.1 Hz, 4H), 6.97 (d, J = 8.1 Hz, 4H), 4.59 (s, 1H), 2.34 (s, 6H), 1.63 (s, 6H), 1.20 (m,
4H), 0.73 (t, J = 6.9 Hz, 6H), 0.11 (m, 4H). l3C{ 1H} NMR (75 MHz, CDC13) 5 163.81,

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142.49, 135.41, 128.82, 127.47, 93.56, 27.81 (1)172 = 34 Hz), 22.03, 20.98, 19.35, 18.52.
HB NMR (96 MHz, CDC13) 54.3 (uh: 377 Hz). Anal. Calcd. for C25H35BN2: C, 80.21;
H, 9.42; N, 7.48. Found C, 80.44; H, 9.54; N, 7.34.

B(Tolznacnac)(C2H3)2 (33). Compound 33 was prepared in a fashion similar to
compound 31 starting from 28 and two molar equivalents of (C2H3)MgBr in 50% yield as
yellow solid. mp 85-88 °C (dec). lH NMR (300 MHz, CDC13) 57.04 ((1, J = 8.1 Hz, 4H),
6.93 (d, J = 8.1 Hz, 4H), 5.87 (dd, J = 4.5, 13.2 Hz, 2H), 5.28 (dd, J = 4.5, 13.2 Hz, 2H),
5.03 (s, 1H), 5.02 (dd, J = 4.5, 13.2 Hz, 2H), 2.29 (s, 6H), 1.79 (s, 6H). '3C{'H} NMR
(75 MHz, CDC13) 5 162.06, 148.12 (v12, = 30 Hz), 142.37, 135.41, 128.83, 127.43,
121.45, 96.70, 21.88, 21.04. HB NMR (96 MHz, CDC13) 5—1.2 (v9, = 240 Hz). Anal.
Calcd. for C23H27BN2: C, 80.52; H, 8.16; N, 8.17. Found C, 80.44; H, 8.04; N, 8.07.

B(Tolznacnac)(C3H5)2 (34). Compound 34 was prepared in a fashion similar to
compound 31 starting from compound 28 and two molar equivalents of (C3H5)MgBr in
69% yield as a pale yellow solid. mp 53—58 °C. 1H NMR (300 MHz, CDC13) 5 7.09 (d, J
= 8.1 Hz, 4H), 7.02 (d, J = 8.1 Hz, 4H), 5.78 (m, 2H), 4.73 (s, 1H), 4.59 (m, 4H), 2.32 (s,
6H), 1.64 (s, 6H), 1.12 (d, J = 7.5 Hz, 4H). '3C{'H} NMR (75 MHz, CDC13) 6163.92,
142.41, 142.04, 135.76, 129.01, 127.92, 110.63, 95.27, 30.98 (1)-,5: 32 Hz), 21.99, 20.80.
11B NMR (96 MHz, CDC13) 50 (1)), = 31 Hz). Anal. Calcd. for C25H31BN2: C, 81.08; H,
8.44; N, 7.56. Found C, 80.77; H, 8.40; N, 7.50.

[B(Tolznacnac)Me]+[BMe(C6F5)3]‘ (35). A 100-mL Schlenk flask was charged
with B(C6F5)3 (0.54 g, 1.0 mmol) and 31 (0.34 g, 1.0 mmol). Toluene (15 mL) was added
at 0 °C with stirring. After 10 min, the reaction mixture was concentrated to ~2 mL and
layered with pentane. After cooling to —30 °C overnight, an oily solid deposited at the
bottom of the Schlenk flask. The mother liquor was decanted and the solid was washed
with pentane. After drying under high vacuum, compound 35 was collected as colorless
solid (0.61 g, 70%). mp 83—87 °C (dec). 1H NMR (300 MHz, CDC13) 57.34 (d, J = 8.1
Hz, 4H), 6.94 (d, J = 8.1 Hz, 4H), 6.73 (s, 1H), 2.42 (s, 6H), 2.25 (s, 6H), 0.41 (s, br, 3H),

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0.27 (s, 3H). ‘3C{‘H} NMR (75 MHz, CDC13) 6 170.58, 148.23 (d, 'Jc_p = 236 Hz),
140.53, 137.42 (d, '10.: = 242 Hz), 137.34, 136.48, (d, '10.: = 246 Hz), 131.43, 128.01
(B—C, br, W, = 120 Hz), 124.95, 111.62, 22.67, 21.03, 10.7 (br, 1)), = 113 Hz), 1.43 (br,
6,, = 30 Hz). “B NMR (96 MHz, CDC13) 637.1 (0.), = 1200 Hz), —l4.8 (61,: 30 Hz). 19F
NMR (282 MHz, CDC13) 5 —132.9 (m), —164.5 (m), —167.2 (m). Anal. Calcd. for
C39H27B2F15N2: C, 56.42; H, 3.28; N, 3.37. Found C, 56.10; H, 3.24; N, 3.33. For
conductivity measurements, solutions were prepared in a glovebox. The molar
conductivity of a solution of 35 (4.7 x 10’3 M) in methylene chloride was 1.6 x 10’2
szmol"'. The molar conductivity of ["BuaN]+Br' solution at the same concentration was
AM = 1.2 x 10‘2 Sm2m01"'.

[B(Tolznacnac)(Py)Me]+[BMe(C6F5)3]’ (36). A stirred suspension of compound
35 (0.30 g, 0.36 mmol) in toluene (5 mL) was treated with an excess of pyridine (0.5 mL,
6.2 mmol) at 0 °C. Upon addition, the color of mixture turned yellow. A11 volatile
materials were removed under vacuum, and the resulting yellow oil was triturated with
pentane to give compound 36 as yellow solid (0.25 g, 76%). mp 107—109 °C(dec). 1H
NMR (300 MHz, CDC13) 58.49 ((1, J = 5.1 Hz, 2H), 8.11 (t, J = 7.5 Hz, 1H), 7.63 (dd, J
= 5.1, 7.5 Hz, 2H), 7.13 (d, J = 8.1 Hz, 4H), 6.53 (d, J = 8.1 Hz, 4H), 5.76 (s, 1H), 2.32
(s, 6H), 1.97 (s, 6H), 0.48 (8, br, 61,: 10 Hz, 3H), 0.073 (s, 3H). ”q 'H} NMR (75 MHz,
CDC13) 5 168.4, 148.2 (d, 'Jc_p = 227 Hz), 145.69, 141.78, 139.03, 138.54, 137.37 (d,
'10,: = 240 Hz), 136.12 (d, ‘ch = 247 Hz), 130.63, 129.09 (0., = 150 Hz), 126.11,
125.79, 101.81, 22.30, 20.88, 10.2 (6),: 141 Hz), 5.26 (01,: 47 Hz). "B NMR (96 MHz,
CDC13) 5—4.19 (s, viz: 80 Hz), —15.23 (s, viz: 65 Hz). ”P NMR (282 MHz, CDC13) 5 —
132.7 (m), —164.6 (m), -167.2 (m). Anal. Calcd. for C44H32B2F15N3: C, 58.11; H, 3.55; N,
4.62. Found C, 58.22; H, 3.63; N, 4.54.

A1(Tolznacnac)C12 (37). A solution of freshly sublimed A1C13 (1.07 g, 8.0 mmol)
in ether (10 mL) was added to an orange solution of 16 (2.3 g, 8.0 mmol) in toluene (20

mL) at 0 °C. The cloudy mixture was allowed to warm to room temperature and stirred

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for 12 h. The mixture was filtered and the filtrate was reduced in volume to ~5 mL.
Yellow 37 deposited overnight at —78 °C. The solid was isolated by filtration, washed
with copious amounts of pentane and dried in vacuo (2.1 g, 71%). mp 199—201 °C (dec).
lH NMR (CDC13, 300 MHz) 57.18 ((1, J = 8.4 Hz, 4H), 7.05 (d, J = 8.4 Hz, 4H), 5.16 (s,
1H), 2.33 (s, 6H), 1.88 (s, 6H). l3C{'H} NMR (CDC13, 75 MHz) 5 171.0, 139.7, 136.8,
130.0, 126.5, 98.29, 23.26, 21.02. 27A] NMR (CDC13, 78 MHz) 6 98.6 (v), = 189 Hz).
LRMS 374 (M+, 1). HRMS Calcd for C19H21A1C12N2: 376.0868. Found: 376.0862. Anal.
Calcd for CI9H21A1C12N2: C, 60.81; H, 5.64; N, 7.46. Found: C, 60.87; H, 5.47; N, 7.35.
Ga(Tolznacnac)C12 (38). An orange solution of 16 (1.52 g, 5.4 mmol) in ether
(20 mL) was added to a solution of freshly sublimed GaC13 (0.94 g, 5.4 mmol) in ether
(10 mL) at —78 °C with stirring. The mixture turned cloudy upon being warmed to room
temperature, and was further stirred at that temperature for 12 h. The mixture was filtered
and filtrate was reduced in volume to about 5 mL. Compound 38 crystallized at —78 °C
overnight and was collected by filtration as yellow crystalline solid, washed with pentane
(2 x 5 mL), thoroughly dried under vacuum (2.0 g, 89%). mp 195—197 °C (dec). 1H NMR
(CDC13, 300 MHz) 57.18 ((1, J = 8.1 Hz, 4H), 7.06 (d. J = 8.1 Hz, 4H), 5.06 (s, 1H), 2.33
(s, 6H), 1.91 (s, 6H). '3C{ 'H) NMR (CDC13, 75 MHz) 6 170.0, 140.3, 136.8, 130.0,
125.9, 96.94, 23.52, 21.03. LRMS 418 (M+, 17), 381 (M+ — Cl, 9). Anal. Calcd for
C19H2IC12GaN2: C, 54.59; H, 5.06; N, 6.70. Found: C, 54.53; H, 5.18; N, 6.61.
Al(Tolznacnac)Mez (39). Method 3: A solution of A1M63 (2.0 M, 7.2 mmol) in
hexane (3.6 mL) was added to a solution of 11 (2.0 g, 7.2 mmol) in pentane (20 mL) at 0
°C with stirring. The mixture was stirred at 0 °C for 5 min and then allowed to warm to
room temperature and stirred for an additional hour. The mixture was filtered and the
filtrate reduced in volume to 3 mL. Pale yellow 39 deposited overnight at —78 °C. The
solid was collected by filtration, washed with cold pentane, and dried in vacuo (2.2 g,
90%). Method b: An ethereal solution (2.0 mL) of MeLi (1.4 M, 2.8 mmol) was added to

a stirred ether suspension (15 mL) of 37 (0.50 g, 1.3 mmol) at 0 °C. The mixture was

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allowed to warm to room temperature and stirred for 14 h. The solvent was removed in
vacuo and the residue extracted with pentane. The pentane extracts were reduced in
volume and 39 deposited at —78 °C (0.28 g, 64%). Method c: An ethereal solution (1.0
mL) of MeLi (1.4 M, 1.4 mmol) was added to an ethereal suspension (20 mL) of 48 (0.38
g, 1.1 mmol) at 0 °C. The mixture was allowed to warm to room temperature and stirred
for 5 h. The solvent was removed in vacuo and the residue was extracted with pentane.
The pentane extracts were reduced in volume and 39 deposited at —78 °C (0.30 g, 84%).
mp 110—1 13 OC (dec). 1H NMR (CDC13, 300 MHz) 57.12 ((1, J = 8.1 Hz, 4H), 6.88 (d, J
= 8.1 Hz, 4H), 4.83 (s, 1H), 2.32 (s, 6H), 1.78 (s, 5H), —1.05 (s, 6H). '3C{'H} NMR
(CDC13, 65 MHz) 5 167.9, 142.8, 135.1, 129.6, 126.0, 96.02, 22.90, 20.96, -9.67 (br, v0,
= 16 Hz). 27A1 NMR (CDC13, 78 MHz) 5 143 (via, = 3900 Hz). LRMS 319 (M+ — ME,
100). Anal. Calcd for C21H27A1N2: C, 75.42; H, 8.14; N, 8.37. Found: C, 75.07; H, 7.97;
N, 8.18.

Ga(Tolznacnac)Me2 (40). An ethereal solution (2.5 mL) of MeLi (1.6 M, 4.0
mmol) was added to an ether suspension (20 mL) of 38 (0.83 g, 2.0 mmol) at 0 °C. After
the mixture was stirred at room temperature for 12 h, the mixture was filtered. Compound
40 crystallized out of pentane at —78 °C as pale yellow crystals (0.52 g, 70%). mp 89—91
°C (dec). lH NMR (CDC13, 300 MHz) 5 7.10 (d, J = 8.1 Hz, 4H), 6.84 (d, J = 8.1 Hz,
4H), 4.65 (s, 6H), 2.31 (s, 6H), 1.77 (s, 6H), —0.63 (s, 6H). ”q 'H} NMR 6165.9, 144.2,
134.5, 129.5, 125.4, 94.52, 22.96, 20.93, —7.77. LRMS 361 (M+ — Me, 100). Anal. Calcd
for C21H27GaN2: C, 66.87; H, 7.22; N, 7.42. Found: C, 66.88; H, 7.19; N, 7.39.

Al(Tolznacnac)(C3H5)2 (41). An ethereal suspension (10 mL) of 37 (0.33 g, 0.88
mmol) was treated with an ether solution (3.5 mL) of Mg(C3H5)Br (0.50 M, 1.8 mmol) at
0 °C. After the mixture was stirred at room temperature for 24 h, all volatile materials
were removed. The oily residue was extracted with pentane. Pure 41 was obtained by
recrystallization out of pentane at -80 °C overnight as yellow crystalline solids (0.26 g,

77%). mp 57—59 °C. IH NMR (CDC13, 300 MHz) 57.13 ((1, J = 8.4 Hz, 4H), 6.95 (d, J =

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8.4 Hz, 4H), 5.72 (m, 2H), 4.86 (s, 1H), 4.39 (m, 2H), 4.32 (m, 2H), 2.33 (s, 6H), 1.80 (s,
6H), 0.89 (d, J = 8.4 Hz, 4H). '3C{ ‘H) NMR (CDC13, 75 MHz) 6169.08, 142.28, 141.15,
135.55, 129.71, 125.97, 105.54, 97.26, 23.00, 20.97, 19.46 (01,, = 25 Hz). Anal. Calcd for
C35H31A1N2: C, 77.69; H, 8.08; N, 7.24. Found C, 77.92; H, 8.01; N, 7.27.

A1(Tolznacnac)(C6H5)2 (42). Compound 42 was prepared following a procedure
similar to that of 41 starting from 37 and two equivalents of PhMgBr as crystalline
yellow solids in a yield of 64%. mp 102-104 °C (dec). 1H NMR (CDC13, 300 MHz) 5
7.44-7.38 (m, 4H), 7.20—7. 10 (m, 6H), 6.90 (d, J = 8.1 Hz, 4H), 6.70 (d, J = 8.1 Hz, 4H),
5.05 (s, 1H), 2.20 (s, 6H), 1.89 (s, 6H). '3C{'H} NMR (CDC13, 75 MHz) 6 169.33,
147.70 (w, = 25 Hz), 142.31, 138.02, 135.22, 129.42, 127.00, 126.56, 126.20, 97.36,
23.26, 20.87. Anal. Calcd for C31H31A1N2: C, 81.20; H, 6.81; N, 6.11. Found C, 81.08; H,
6.89; N, 6.20.

Al(Tolznacnac)(CH28iMe3)2 (43). Compound 43 was prepared as a pale yellow
oil following a procedure similar to that of 41 starting from 37 and two equivalents of
LlCHleMC3 in a crude yield of 53%. Due to its high solubility in pentane, analytically
pure material was not obtained. lH NMR (CDC13, 300 MHz) 5 7.16 (d, J = 8.1 Hz, 4H),
6.88 (d, J: 8.1 Hz, 4H), 4.90 (s, 1H), 2.32 (s, 6H), 1.80 (s, 6H), —0.29 (s, 18H), -1.27 (s,
4H).

Al(‘Bu2nacnac)Me2 (44). Compound 44 may be prepared as crystalline yellow
solids by the same procedure described for 39 (Method a) starting from AlMe3 and one
equivalent of lBuznacnacH202 in 72% yield. mp 118—121 °C (dec). 1H NMR (C6D6, 300
MHz) 64.34 (s, 1H), 1.81 (s, 6H), 1.36 (s, 18H), —0.115 (s, 6H). '3C{'H} (C6D6, 75
MHz) 5 166.9, 100.7, 56.29, 32.31, 25.99, 1.54 (1)62 = 77 Hz). LRMS 251 (M+ — Me,
100). Anal. Calcd for ClnglAlsz C, 67.62; H, 11.73; N, 10.51. Found: C, 67.54; H,
11.73; N, 10.30.

Al(Me82nacnac)Me2 (45). Compound 45 may be prepared as crystalline yellow

solids by the same procedure described for 39 (Method a) starting from A1Me3 and one

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equivalent of 12 in 93% yield. mp 125—127 °C (dec). IH NMR (CDC13, 300 MHz) 56.87
(s, 4H), 4.99 (s, 1H), 2.25 (s, 6H), 2.15 (s, 12H), 1.67 (s, 6H), —1.09 (s, 6H). '3C{'H}
NMR (CDC13, 75 MHz) 5 168.92, 140.37, 134.92, 133.30, 129.16, 95.76, 22.67, 20.82,
18.48, —8.68 (br, 1),, = 21 Hz). Anal. Calcd for C25H35A1N2: C, 76.89; H, 9.03; N, 7.17.
Found: C, 76.78; H, 9.08; N, 7.08.

Al(Dip2nacnac)Me2 (46). Compound 46 may be prepared as crystalline yellow
solids by the same procedure described for 39 (Method a) starting from AlMe3 and one
equivalent of 14 in 75% yield. mp 163—164 °C (dec). lH NMR (CDC13, 300 MHz) 6
7.14—7.25 (m, 6H), 5.12 (s, 1H), 3.22 (sept, J = 6.9 Hz, 4H), 1.23 (d, J = 6.9 Hz, 12H),
1.14 (d, J = 6.9 Hz, 12H), —1.00 (s, 6H). '3C{‘H} NMR (CDC13, 75 MHz) 6 169.56,
144.22, 140.7, 126.5, 124.0, 97.02, 28.02, 25.15, 24.61, 23.58, —10.78 (br, Dy, = 17 Hz).
27Al NMR (cock, 78 MHz) 6160 (v... = 4056 Hz). LRMS 459 (M+ — ME, 100). Anal.
Calcd for C3)Ha7A1N2: C, 78.44; H, 9.98; N, 5.90. Found: C, 77.73; H, 10.00; N, 5.79.

Al(Tolznacnac)[CH(SiMe3)2]Cl (47). An ethereal solution (10 mL) of
LiCH(SiMe3)2204 (0.42 g, 2.5 mmol) was added to a toluene solution (15 mL) of 37 (0.94
g. 2.5 mmol) at 0 °C. The mixture was allowed to warm to room temperature, stirred for
10 min, and then filtered. The ether was removed in vacuo and the residue was extracted
with pentane (3 x 10 mL). The combined pentane extracts were reduced in volume to ~5
mL. Pale yellow 47 deposited overnight at —78 °C and was collected by filtration (0.54 g,
43%). mp 159—162 °C (dec). IH NMR (CDC13, 300 MHz) 57.06—7.18 (m, 8H), 5.08 (s,
1H), 2.34 (s, 6H), 1.84 (s, 6H), —0.23 (s, 18H), —1.65 (s, 1H). '3C{ 'H} NMR (CDC13, 75
MHz) 5 169.3, 141.5, 136.2, 129.7, 126.7, 98.05, 23.69, 21.00, 3.26, -1.88 (br). LRMS
483 (M+ — Me, 6). HRMS Calcd for C26H40A1C1N2Si2; 498.2234, Found; 498.2241. Anal.
Calcd for C26H40A1C1N28i2: C, 62.55; H, 8.08; N, 5.36. Found: C, 61.90; H, 7.81; N,
5.67.

Al(Tolznacnac)MeCl (48). Method a: A ether solution (2.0 mL) of MeLi (1.4 M,

2.8 mmol) was added to a stirred suspension of 37 (1.07 g, 2.8 mmol) in ether (15 mL) at

123

0 oC. The mixture was allowed to warm to room temperature and stirred for 14 h. The
mixture was filtered and the filtrate reduced in volume to ~3 mL. Pure compound 48 can
be obtained by repeated crystallization from toluene at —78 °C (0. 15 g, 15%). Method b: A
hexane solution (7.2 mL) of AlMe3 (2.0 M, 14.4 mmol) was added over a five-minute
period to a stirred toluene suspension (100 mL) of dry 19 (4.55 g, 14.5 mmol) at 0 °C.
The mixture was stirred at room temperature for 4 h, during which time, a clear yellow
solution formed. The solution was reduced in volume to ~20 mL and layered with
pentane (30 mL). Cooling at -78 °C overnight deposited 48 as a pale yellow solid which
was isolated by filtration, washed with pentane and dried in vacuo (4.3 g, 84%). mp 129—
133 °C (dec). 1H NMR (CDC13, 300 MHz) 57.15 ((1, J = 8.4 Hz, 4H), 7.01 (d, J = 8.4 Hz,
4H), 5.07 (s, 1H), 2.33 (s, 6H), 1.86 (s, 5H), —0.98 (s, 3H). l3C{'H} NMR (CDC13, 75
MHz) 5 169.1, 141.3, 136.0, 129.8, 126.2, 97.81, 23.13, 20.98, —10.9 (br, v6, = 30 Hz).
27A1 NMR (CDCl3) 5 126 (viz, = 3920 Hz). LRMS 354 (M+, 5), 339 (M+ — ME, 100).
Anal. Calcd for C30H24A1C1N2: C, 67.70; H, 6.82; N, 7.89. Found: C, 67.82; H, 6.84; N,
7.91.

Al(Tolznacnac)MeBr (49). A toluene suspension (50 mL) of 20 (3.71 g, 10.3
mmol) was treated with 2.0 M AlMe3 hexane solution (5.2 mL, 10.4 mmol) at 0 °C. A
gas formed at this stage. The mixture was stirred at room temperature for 6 h, during
which time, a clear yellow solution developed. The solution was reduced in volume to 10
mL, layered with pentane and cooled to —80 °C overnight. Pale yellow crystalline solid
was collected by filtration, washed with pentane and dried under vacuum (3.1 g, 75%).
mp 135—138 °C (dec). lH NMR (CDC13, 300 MHz) 57.15 (m, 4H), 7.04 (m, 4H), 5.10 (s,
1H), 2.33 (s, 6H), 1.85 (s, 6H), —O.89 (s, 3H). ”m 'H} NMR (CDC13, 75 MHz) 6169.4,
141.1, 136.1, 129.8, 126.2, 93.16, 23.17, 20.98, —9.80 (br, by, = 21 Hz). Anal. Calcd for
C20H24A1BrN2: C, 60.15; H, 6.06; N, 7.01. Found C, 59.62; H, 6.09; N, 6.96.

Al(Tolznacnac)MeI (50). Compound 50 was prepared in a procedure similar to

that of 49 from AlMe; and one equivalent 21 in a yield of 81% as a yellow solid. mp

124

164—165 °C (dec). lH NMR (CDC13, 300 MHz) 57.15 ((1, J = 8.1 Hz, 4H), 7.09 (m, 4H),
5.15 (s, 1H), 2.33 (s, 6H), 1.84 (s, 6H), -O.86 (s, 3H). ”q 'H} NMR (CDC13, 75 MHz) 6
169.6, 140.9, 136.2, 129.8, 126.3, 98.67, 23.23, 21.00, —6.59 (br, 1);, = 30 Hz). Anal.
Calcd for C20H24A11Nz: C, 52.82; H, 5.42; N, 6.27. Found C, 53.18; H, 5.59; N, 6.09.

Al(Tolznacnac)Me(OTf) (51). Method a: Compound 51 was prepared in a
procedure similar to that of 49 starting from AlMe3 and one equivalent 22 in a yield of
86% as a yellow solid. Method b: A Schlenk flask was charged with 39 (0.75 g, 2.24
mmol) and AgOTf (1.15 g, 4.47 mmol) and toluene (20 mL) was added at -78 °C. The
mixture immediately turned black. The reaction was slowly warmed to room temperature.
After 12 h, during which time a silver mirror developed inside the Schlenk flask, the
mixture was filtered. The filtrate was concentrated, layered with pentane, and cooled to —
78 °C. Yellow 51 deposited overnight, was collected by filtration, washed with pentane,
and dried in vacuo (0.34 g, 32%). Using of one equivalent AgOTf led to the same
compound 51, but in lower yield. We were not able to observe 27Al NMR signals for 51.
mp 140 oC (dec). IR (nujol mull, KBr plate) 1537, 1383, 1302, 1244, 1203, 1109, 1031,
1020, 943. 1H NMR (C6D6, 300 MHz) 5 7.00 (m, 4H), 6.87 (d, J = 8.1 Hz, 4H), 4.85 (s,
1H), 1.99 (s, 6H), 1.54 (s, 6H), —0.62 (s, 3H). l3C(‘H} NMR (C6D6, 300 MHz) 6171.0,
141.0, 136.8, 130.46, 126.1, 120.0 (q, 'Jc_p = 316 Hz), 99.28, 22.88, 20.78, —14.1 (br, 0%
= 75 Hz). ‘91: NMR (C6D6, 282 MHz) 6—77.9 (s, u), = 8.9 Hz). LRMS 453 (M+ - ME, 5).
Anal. Calcd for C21H24A1F3N203S: C, 53.84; H, 5.16; N, 5.98. Found: C, 53.44; H, 4.98;
N. 5.92.

Al(Tolznacnac)Me(C3H5) (52). Compound 52 was synthesized from 51 and one
equivalent freshly prepared Mg(C3H5)Br in a fashion similar to that of 53 in 53% yield as
pale yellow crystalline solids. mp 75—78 °C (dec). 1H NMR (CDC13, 300 MHz) 5 7.12 (d,
J = 8.1 Hz, 4H), 6.91 (d, J = 8.1 Hz, 4H), 5.78 (m, 1H), 4.84 (s, 1H), 4.39 (m, 1H), 4.31
(m, 1H), 2.32 (s, 6H), 1.79 (s, 6H), 0.87 (d J = 8.4 Hz, 2H), —1.05 (s, 3H). '3C{‘H}
(CDC13, 75 MHz) 5 168.5, 142.5, 141.8, 135.3, 129.7, 126.0, 104.9, 96.68, 22.94, 20.96,

125

20.82 (br, Dy, = 32 Hz), -10.91 (br, Dy, = 27 Hz). Anal. Calcd for C23H29A1N2: C, 76.64;
H, 8.04; N, 7.77. Found: C, 76.64; H, 8.16; N, 7.73.

A1(Tolznacnac)Me(CHZSiMe3) (53). An ether solution (10 mL) of Li(CH28iMe3)
(0.15 g, 1.6 mmol) was added slowly to a suspension of 51 (0.73 g, 1.6 mmol) in ether
(15 mL) at —78 °C with stirring. The mixture was allowed to warm to room temperature
and stirred at that temperature for 5 min. After the mixture was pumped down, the
residue was extracted with pentane and colorless crystals of 53 were collected by
filtration (0.42 g, 66%). mp 91—93 °C. lH NMR (CDCl3, 300 MHz) 57.11 (s, J = 8.4 Hz,
4H), 6.87 (8, J = 8.4 Hz, 4H), 4.85 (s, 1H), 2.32 (s, 6H), 1.78 (s, 6H), 1.21 (s, 2H), -1.04
(s, 3H), —0.35 (s, 9H). '3C{‘H} (CDC13, 75 MHz) 6, 167.8, 142.9, 135.1, 129.8, 126.0,
96.56, 23.04, 20.95, 2.01, —3.09 (Dy, = 21 Hz), -8.37 (Dy, = 23 Hz). Anal. Calcd for
C24H35A1N2Si: C, 70.89; H, 8.68; N, 6.89. Found: C, 70.89; H, 8.70; N, 6.92.

Al(Tolznacnac)Me[CH(SiMe3)2] (54). Compound 54 was synthesized from 51
and one equivalent LiCH(SiMe3)2 in a fashion similar to that of 53 in 4.8% yield as pale
yellow crystalline solids after repeated recrystallization out of pentane. mp 87-89 °C. 1H
NMR (CDC13, 300 MHz) 5 7.12 (d, J = 8.1 Hz, 4H), 6.90 (d, J = 8.1 Hz, 4H), 4.86 (s,
1H), 2.32 (s, 6H), 1.75 (s, 6H), —0.23 (s, 18H), —0.76 (s, 3H), -1.80 (s, 1H). '3C{'H}
(CDC13, 75 MHz) 5 168.2, 142.8, 135.4, 129.5, 126.5, 96.69, 23.41, 20.96, 3.63, —0.16
(Dy, = 17 Hz), -3.99 (Dy, = 26 Hz). Anal. Calcd for C27HagAlNZSi2: C, 67.73; H, 9.05; N,
5.85. Found: C, 68.01; H, 9.09; N, 5.86.

Al(Tolznacnac)MePh (55). Compound 55 was synthesized from 51 and one
equivalent freshly prepared PhMgBr in a fashion similar to 53 in 74% yield as pale
yellow crystalline solids. mp 98—100 °C. 1H NMR (CDC13, 300 MHz) 5 7.50 (m 2H),
7.22 (m, 3H), 7.02 (d, J = 8.1 Hz, 4H), 6.76 (d, J = 8.1 Hz, 4H), 4.97 (s, 1H), 2.27 (s,
6H), 1.86 (s, 6H), —0.96 (s, 3H). '3C{‘H} (CDC13, 75 MHz) 5168.6, 151.4 (br, 6,, = 30
Hz), 142.6, 137.2, 135.1, 129.5, 127.0, 126.6, 126.0, 96.92, 23.04, 20.92, —13.08 (Dy, = 31

126

Hz). ). Anal. Calcd for C26H29A1N2: C, 78.75; H, 7.37; N, 7.06. Found: C, 78.47; H, 7.42;
N, 7.04.

A1(Tolznacnac)Me(O‘Bu) (56). A Schlenk tube was charged with 51 (0.25 g,
0.54 mmol) and KO’Bu (60 mg, 0.54 mmol). Toluene (10 mL) was added and the mixture
was stirred at room temperature for 12 h. After filtration, the solvents were removed
under vacuum. The pure product 56 was obtained by a recrystallization out of pentane at
—30 °c as a yellow solid (0.11 g, 52%). mp 128-130 °C. 1H NMR (CD2C12, 300 MHz) 6
7.22-7.18 (m, 4H), 7.10—7.01 (m, 4H), 5.01 (s, 1H), 2.35 (s, 6H), 1.84 (s, 6H), 0.94 (s,
9H), —1.14 (s, 3H). ”Cl 'H} NMR (CD2C12, 75 MHz) 5168.35, 143.00, 135.72, 129.63,
126.77, 96.94, 67.91, 33.56, 23.18, 21.05, —9.99 (br, Dy, = 50 Hz).

Al(TolznacnacMe)Me2 (57). A THF solution (10 mL) of 39 (0.38 g, 1.1 mmol)
was treated with a THF solution (10 mL) of KN(SiMeg)2 (0.22 g, 1.1 mmol) at 0 °C. The
resultant mixture was stirred at room temperature for 30 min during which time a bright
yellow color developed. The solution was cooled back to 0 °C, and was treated with
freshly distilled Mel (0.3 mL, 5 mmol) through a syringe. A white precipitate formed
immediately. The mixture was filtered after 30 min at room temperature. After
recrystallization out of pentane at —78 °C, a pale yellow crystalline solid was collected
(0.28 g, 72%). mp 127—131 °C. 1H NMR (CDC13, 300 MHz) 57.15 ((1, J = 8.4 Hz, 4H),
6.90 (d, J = 8.4 Hz, 4H), 4.85 (s, 1H), 2.33 (s, 6H), 2.11 (q, J = 7.5 Hz, 2H), 1.81 (s, 3H),
1.03 (t, J = 7.5 Hz, 3H), —1.40 (s, 6H). ”q ‘H} (CDC13, 75 MHz) 6173.0, 168.1, 153.1,
142.9, 142.2, 129.6, 126.3, 126.0, 94.24, 28.19, 23.05, 20.96, 13.52, -9.70. LRMS 347
(M+ — H, 2), 333 (100. M’r — Me). Anal. Calcd for ngHnglNz: C, 75.83; H, 8.38; N,
8.03. Found: C, 75.70; H, 8.48; N, 8.09.

Al(Tol;nacnacMe2)Me2 (58). Compound 58 was prepared starting from 57 in a
fashion similar to that of 57 in 63% yield as a colorless solid. mp 148—159 °C (dec). 1H
NMR (C6D6, 300 MHz) 57.00 ((1, J = 7.8 Hz, 4H), 6.89 (d, J = 7.8 Hz, 4H), 4.86 (s, 1H),
2.05 (q, J :75 Hz, 4H), 2.03 (s, 6H), 0.92 (t, J = 7.5 Hz, 6H), —0.37 (s, 6H). 13C{'H}

127

(C6D6, 75 MHz) 5 173.7, 142.91, 135.2, 130.0, 126.7, 93.41, 28.66, 20.83, 13.87, —8.76
(br, Dy, = 50 Hz). LRMS 458 (M+, 4), 361 ( M+- H, 9), 347 (M+ — Me, 17). C23H31A1N2
Calcd C 76.21, H 8.62, N 7.72

Al(TolznacnacMe3)Me2 (59). Compound 59 was prepared starting from 58 in a
fashion similar to that of 57 in 65% yield as a pale yellow solid. mp 164—168 °C (dec).
lH NMR (CDC13, 300 MHz) 57.17 (d, J = 8.1 Hz, 4H), 6.91 (d, J = 8.1 Hz, 4H), 4.82 (s,
1H), 2.64 (sept, J = 6.9 Hz, 1H), 2.33 (s, 6H), 2.18 (q, J = 6.9 Hz, 2H), 1.06 (m, 9H), -—
1.07 (s, 6H). ”a 'H} NMR (CDC13, 75 MHz) 6173.3, 134.9, 142.2, 129.6, 126.4, 89.34,
31.26, 28.33, 20.97, 13.72, —9.76 (br, D1,, = 29 Hz). LRMS 458 (M+, 4), 376 (M+, 9), 361
(M+ — Me, 100). C24H33A1N2 Calcd C 76.56, H 8.83, N 7.44

A1(TolznacnacMe4)Me2 (60). Compound 60 was prepared starting from 59 in a
fashion similar to that of 57 in 71% yield as a pale yellow solid. mp 200—202 °C (dec).
lH NMR (CDCl3, 300 MHz) 57.1 1 (d, J = 8.1 Hz, 4H), 6.86 (d, J = 8.1 Hz, 4H), 4.87 (s,
1H), 2.63 (sept, J = 6.9 Hz, 2H), 2.32 (s, 6 H), 1.06 (d, J = 6.9 Hz, 12H), —1.09 (d, 6H).
l3Cl'H} (CDC13, 75 MHz) 6 177.4, 142.4, 134.8, 129.6, 126.3, 86.36, 31.41, 22.41,
20.96, —9.84 (br, Dy, = 20 Hz). LRMS 458 (M+, 4), 375 (M+ — Me, 45). C25H35A1N2 Calcd
C 76.88, H 9.03, N 7.17.

Al(Tolznacnac)Me(C6F5) (61) A pentane solution (20 mL) of B(C6Fs)3 (0.60 g,
1.2 mmol) was added to a stirred pentane suspension (5 mL) of 39 (0.39 g, 1.2 mmol) at —
78 °C. The mixture was allowed to warm to room temperature and was stirred for 24 h.
The mixture was filtered and the filtrate placed under vacuum. The resulting yellow oil
(0.90 g) contained both 61 and B(C6F5)2Me (62) in a 1:1 mole ratio. The oil was put
under high vacuum at 45 °C overnight to remove the relatively volatile 62. The gel
residue was taken into pentane and the solution was concentrated, and cooled to —78 °C.
A colorless oil 61 deposited overnight, was isolated by decanting, and dried in vacuo
(0.37 g, 65%). Attempts to crystallize this oil have been unsuccessful. The identity of 61

was confirmed by an independent synthesis. An ethereal suspension (20 mL) of

128

compound 51 (1.31 g, 2.8 mmol) was treated with an ether solution of C6F5Li which was
generated by treating freshly distilled C6F5Br (0.69 g, 2.8 mmol) with "BuLi (2.5 M, 1.1
mL, 2.8 mmol) at -78 °C. The mixture was warmed to room temperature and was stirred
at room temperature for 2 h. After filtration and solvent removal, an oil remained. All
attempts to crystallize the product were unsuccessful and chromatography on silica gel
gave decomposition. Nonetheless, the chemical shifts of the major component in 1H
NMR spectra of the crude reaction mixture corresponded to those assigned to 61
generated in the reaction between 39 and B(C6F5)3. In 61, the two carbon atoms directly
attached to aluminum were not observed in '3 C NMR spectra. Spectroscopic data for 61:
‘H NMR ((26136, 300 MHz) 6 6.80 (m, 8H), 4.88 (s, 1H), 1.93 (s, 6H), 1.60 (s, 6H), —0.18
(t, 51114: = 1.6 Hz, 3H). '3C{ 'H} NMR (C6D6, 75 MHz) 6 169.6, 151.1 (d, 'Jc_p = 238 Hz),
147.5 (d, 'Jc_p = 240 Hz), 142.1, 137.4 ((1, 1Jo): = 260 Hz), 136.1, 130.3, 125.9, 98.25,
22.86, 20.74. ”P NMR (C6D6, 282 MHz) 6—121.7 (m), —154.9 (m), —162.4 (m). LRMS
486 (M+, 1), 471 (M+ - ME, 12). HRMS: Calcd for C26H24A1F5N2; 486.1675, Found:
486.1701. Compound 62 was spectroscopically identified in the mixture of product. Since
its pure material was not obtained 13C data were not possible for 62, but we were able to
assign its 1H and l9F NMR data by comparing the spectrum of the reaction mixture with
61. Spectroscopic data for 62: 1H NMR ((361),, 300 MHz) 61.33 (quintet, SJ,HF = 2.0 Hz).
"B NMR (C6D6, 96 MHz) 6 72 (br, 6,, ~252 Hz). ”P NMR (c6136, 282 MHz) 6—1300
(m), -147.0 (m), —l61.3 (m). LRMS 360 (M+, 15).

MeAl(‘Buznacnac)(,uz-Me)B(C6F5)3 (63). A pentane solution (5 mL) of 44 (0.17
g, 0.64 mmol) was added to a pentane/toluene (1:1, 10 mL) solution of B(C6F§)3 (0.33 g,
0.64 mmol) at 0 °C. A white precipitate formed immediately. The precipitate was
collected by filtration washed with pentane (3 x 10 mL) (0.31 g, crude yield 62%).
Further purification was hampered by its instability. 1H NMR (CDC13, 300 MHz) 5 5.06
(s, 1H), 2.20 (s, 6H), 1.48 (s, 18H), 0.79 (8, br, 3H), —0.094 (s, 3H). “B NMR (CDC13, 96

129

MHz) 6 —15.4 (Dy, = 38 Hz). ”P NMR (CDC13, 282 MHz) 643.5 (m), —162.2 (m), —
166.1 (m).

[Alz(‘Buznacnac)2Me3]+[B(C6F4-4-Si'BuMe2)4]‘ (64). A Schlenk tube was
charged with 44 (0.23 g, 0.88 mmol) and [Ph3C]+[B(C6F4-4-Si'BuMe2)4]’ (0.57 g, 0.44
mmol) in a glovebox. Toluene (30 mL) was added to the Schlenk tube at 0 °C with
stirring. In minutes, a yellow homogeneous solution was obtained. The mixture was
stirred at room temperature for 2 h to give a colorless solution. All volatile materials were
removed under high vacuum, giving a pale yellow oil. And it was washed with pentane to
give a white solid. The pentane filtrate contained predominantly Ph3CMe, whose identity
was confirmed by comparing 1H and 13C NMR spectra with those of an authentic sample.
The white residue was taken into toluene, and resultant filtrate was concentrated to about
2 mL, layered with pentane cooled to —80 °C overnight. A pale yellow oil deposited
during that time and was collected by decanting, washed with copious amount of pentane.
The yellow oily material turned to free flowing powder upon being pumped under high
vacuum. It is not very stable at room temperature and a solid sample was stored in —80 °C
freezer. mp 109—1 11 °C (dec). ' H NMR (C6D6, 300 MHz) 5 4.87 (br, Dy, = 22 Hz, 2H),
2.01 (s, 12H), 1.26 (s, 36H), 0.93 (s, 36H), 0.30 (s, 24H), —0.19 (s, 9H). '3C{‘H} NMR
(C6D6, 75 MHz) 5 171.1 (Dy, = 100 Hz), 149.4 (d, J = 242 Hz), 149.2 (d, J = 234 Hz),
135.2 (Dy, = 120 Hz, B—Ar), 108.4 (t, J = 32.4 Hz, Si—Ar), 105.2 (Dy, = 200 Hz), 57.91,
32.32. 26.60, 25.85, 17.79, —O.68 (s, 6., = 20 Hz, A1—C),—3.59 (t, J = 4.2 Hz). “B NMR
(C60,, 96 MHz) 6—16.3 (n, = 28 Hz). ”P NMR (C,D,, 282 MHz) 6—130.1 (m), —130.9
(m). Anal. Calcd for C77H119A12BF|6Si4Naz C, 58.46; H, 7.58; N, 3.54. Found: C, 56.27;
H, 7.30; N, 3.11.

[Al('Buznacnac)(C5H5N)Me]+[B(C6F4-4-Si'BuMe2)4]' (65). A toluene solution
(10 mL) of compound 64 (0.31 g, 0.20 mmol) was treated with dry pyridine (0.3 mL, 4
mmol) at —78 °C. The colorless mixture was stirred at room temperature for 1 h. All

volatile materials were removed under vacuum and the residue was washed with pentane

130

(3 x 10 mL). The pentane filtrate contained only Ph3CMe and 44. The pentane insoluble
material was re-dissolved in toluene. The toluene filtrate was reduced in volume and
layered with pentane, cooled to —80 °C overnight. A colorless solid deposited and was
collected by filtration (0.18 g, 64%). Compound 65 decomposed in solution in 12 h at
room temperature. Its '3 C data were incomplete. 1H NMR (C6D6, 300 MHz) 5 8.01 (m,
2H), 7.39 (m, 1H), 7.04 (m, 2H), 4.66 (s, 1H), 1.91 (s, 6H), 1.17 (s, 18H), 0.88 (s, 36H),
0.26 (s, 24H), —0.24 (s, 3H). 19F NMR (C6D6, 282 MHz) 5—129.8 (m), —131.3 (m).
In(Tolznacnac)Clz (66). An ethereal solution (20 mL) of 16 (0.99 g, 3.5 mmol)
was added to a suspension of indium(III) chloride (0.77 g, 3.5 mmol) in ether (30 mL) at
0 °C. After the resultant mixture was stirred at room temperature for 24 h, it was filtered.
The filtrate was reduced in volume to about 10 mL and was cooled to —80 °C overnight.
Yellow crystalline 66 was collected by filtration, washed with a copious amount of
pentane and dried under vacuum (1.3 g, 81%). mp 177—180 °C (dec). 1H NMR (CDC13,
300 MHz) 67.16 (m, 4H), 7.01 (m, 4H), 4.93 (s, 1H), 2.32 (s, 6H), 1.92 (s, 6H). ”q 'H}
(CDC13, 75 MHz) 5 171.1, 142.8, 136.4, 130.3, 124.6, 96.51, 24.28, 20.97. Anal. Calcd
for C19H31C121I1N23 C, 49.28; H, 4.57; N, 6.05. Found C, 49.04; H, 4.52; N 6.06.
In(Tolznacnac)2Cl (67). Method a: A Schlenk tube was charged with 66 (0.71 g,
1.5 mmol) and 16 (0.44 g, 1.5 mmol) in a glovebox. Toluene (20 mL) was added to the
Schlenk tube that was immersed in an ice-water bath. After the mixture was stirred at
room temperature for 24 h, it was filtered. The filtrate was reduced in volume to about 3
mL, and was layered with pentane (10 mL) to initialize crystallization. The mixture was
kept at —80 °C overnight and a yellow solid of 67 was collected by filtration, washed with
pentane and dried under vacuum (0.67 g, 62%). Method b: An ethereal solution (10 mL)
of 16 (1.13 g, 4.0 mmol) was added to a suspension of InC13 (0.44 g, 2.0 mmol) in ether
(25 mL) at 0 °C. After the resultant mixture was stirred at room temperature for 24 h, it
was filtered. The solid residue was further extracted with fresh ether (2 x 10 mL). The

combined filtrate was reduced in volume to about 3 mL. After the mixture was cooled to

131

—80 CC overnight, yellow 67 was collected by filtration. washed with pentane and dried
under vacuum (0.90 g. 64%). mp 160—163 °C. 1H NMR (CDC13, 300 MHz) 56.92 ((1, J =
8.4 Hz. 4H), 6.57 (d. J = 8.4 Hz. 4H), 4.61 (s, 1H), 2.27 (s, 6H), 1.67 (s, 6H). l3Cl‘H}
(CDC13. 75 MHz) 5 168.8. 145.7, 133.9, 128.8, 125.7, 96.26, 24.74. 20.94. Anal. Calcd
for ngHngllnNa: C, 64.74; H, 5.96: N, 7.94. Found C, 64.00; H, 5.99; N, 7.89.

In(Tolznacnac)3 (27). See Chapter 1 for an alternative synthesis. Method a. A
Schlenk tube was charged with 67 (0.55 g, 0.78 mmol) and 16 (0.22 g, 0.78 mmol). After
the mixture was stirred with toluene (30 mL) at room temperature for 24 h, it was filtered.
The filtrate was concentrated and layered with pentane. The pale yellow solid of 27 was
collected by filtration, washed with pentane and dried under vacuum (0.41 g, 56%).
Method b. A mixture of InCl; (0.26 g, 1.2 mmol) and 16 (1.0 g, 3.5 mmol) in toluene (35
mL) was stirred at 80 °C for 48 h. After the mixture was let to cool to room temperature,
pure 27 was obtained by crystallization out of toluene/pentane (0.60 g, 54%). mp > 245
°C. IH NMR (CDC13. 300 MHz) 5 6.95 (dd, J = 2.1, 7.8 Hz, 2H), 6.87 (dd, J = 2.1, 7.8
Hz, 2H), 6.78 (dd, J = 2.1, 8.1 Hz, 2H), 5.64 (dd, J = 2.1, 8.1 Hz, 2H), 3.86 (s, 1H), 2.27
(s. 6H), 1.21 (s, 6H). l3C{'H} (CDC13, 75 MHz) 5166.5, 148.8, 132.6, 127.56, 127.44,
126.74, 126.66. 96.03. 25.84, 20.87. Anal. Calcd for C57H631nN6: C, 72.29; H, 6.71; N,
8.88. Found C, 72.43; H, 6.72; N, 8.77. LRMS 669 (M+ - Tolznacnac, 87)

In(Tolznacnac)Me2 (68). An ethereal solution (15 mL) of In(Tolznacnac)C12
(0.44 g, 0.95 mmol) was treated with an ethereal solution of MeLi (1.6 M, 1.2 mL, 1.9
mmol) at 0 0C. After the mixture was stirred at room temperature for 12 h, it was filtered.
The crude product was taken into pentane and pure 68 crystallized out of pentane at -30
°C overnight as shiny bright yellow crystals (0.18 g, 45%). mp 115—1 17 °C (dec). 'H
NMR (C6D6, 300 MHz) 5 6.87 (d, J = 8.4 Hz, 4H), 6.83 (d, J = 8.4 Hz, 4H), 4.66 (s, 1H),
2.04 (s, 6H), 1.75 (s, 6H), 0.018 (s, 6H). l3C{ IH} (GD, 75 MHz) 5 166.5, 147.1, 133.9,
130.2, 124.6, 95.88, 23.44, 20.79, -8.15. Anal. Calcd for C21H27InN2: C, 59.73; H, 6.44;
N, 6.63. Found C, 59.67; H, 6.35; N, 6.67. LRMS 422 (M+, 5), 407 (M+ — Me, 100).

132

 

In(Tolznacnac)2Me (69). An ethereal solution (0.75 mL) of MeLi (1.4 M, 1.1
mmol) was added to a suspension of 67 (0.74 g, 1.1 mmol) in ether ( 15 mL) at 0 °C
through a syringe. After the mixture was stirred at room temperature for 12 h, it was
filtered and the residue was extracted with fresh ether (2 x 10 mL). The volume of the
combined filtrate was reduced to about 2 mL when crystallization started to occur.
Colorless crystals of 69 were collected by filtration, washed with cold pentane and dried
under vacuum (0.43 g, 56%). mp 220—221 °C (dec). IH NMR (C6D6, 300 MHz) 5 6.89
(d, J = 8.1 Hz, 4H), 6.51 (d, J = 8.1 Hz, 4H), 4.95 (s, 1H), 2.08 (s, 6H), 1.87 (s, 6H), —
0.48 (s, 3H). ”Cl 'H} (C61)... 75 MHz) 6166.4, 148.3, 133.2, 129.1, 126.4, 97.05, 24.51,
20.81, -10.98 (Dy, = 33 Hz). Anal. Calcd for C39HaslnN4: C, 68.42; H, 6.62; N, 8.18.
Found C, 68.15; H, 6.71; N, 8.02. LRMS 669 (M+ — Me, 0.33), 407 (M+ — Tolgnacnac,
14).

In(Dipznacnac)Clz (70). A 100-mL Schlenk tube was charged with InC13 (0.84 g,
3.8 mmol) and 18 (1.61 g, 3.8 mmol) in a glovebox. After the mixture was stirred with
diethyl ether (40 mL) at room temperature for 48 h, the mixture was filtered. The
concentrated filtrate was cooled to —80 °C overnight to yield pure colorless product (1.66
g, 72%). mp 115-1 18 °C (dec). 1H NMR (C6D6, 300 MHz) 5 7.08 (m, 6H), 4.63 (s, 1H),
3.38 (sept, J = 6.9 Hz, 4H), 1.49 (s, 6H), 1.40 (d, J = 6.9 Hz, 12H), 1.11 (d, J = 6.9 Hz,
12H). ”cl ‘H} (C613,, 75 MHz) 6172.7, 143.6, 140.3, 128.0, 124.8, 96.37, 28.66, 25.28,
24.60, 24.34. Anal. Calcd for C39H41C121nN2: C, 57.73; H, 6.85; N, 4.64. Found: C,
57.99; H, 7.04; N, 4.69.

In(Dipznacnac)(O’Bu)Cl (71). A Schlenk tube was charged with 70 (0.16 g, 0.26
mmol) and freshly sublimed KO'Bu208 (30 mg, 0.26 mmol). Toluene (15mL) was added
at room temperature and the resultant mixture was stirred at that temperature for 3 h. The
mixture was filtered and the crude product was recrystallized out of pentane at -30 °C as
colorless crystals (61 mg, 35%). One alkyl carbon resonance was missing in its 13C

NMR. lH NMR (C6D6, 300 MHz) 5 7.10 (m, 6H), 4.64 (s, 1H), 3.64 (sept, J = 6.9 Hz,

133

2H), 3.27 (sept, J = 6.9 Hz, 2H), 1.54 (s, 6H), 1.52 (d, J = 6.9 Hz, 6H), 1.49 (d, J = 6.9
Hz, 6H), 1.18 (d, J = 6.9 Hz, 6H), 1.12 (d, J = 6.9 Hz, 6H), 0.99 (s, 9H). ”q 'H} (c613,,
75 MHz) 5171.57, 144.10, 143.30, 141.34, 127.44, 124.75, 124.16, 95.63, 70.81, 34.02,
28.91, 27.97, 26.22, 24.72, 24.66, 24.32.

In(Dipznacnac) (72). A 100-mL Schlenk tube was charged with InCl (0.11 g,
0.73 mmol) and 18 (0.31 g, 0.73 mmol) in a glovebox. The Schlenk tube was taken out of
the glovebox and submerged in a dry—ice cold bath. Toluene (15 mL) was added and the
resultant mixture was further stirred at room temperature for 120 h. The mixture was
filtered. All volatile materials in the filtrate were removed under vacuum. The solid
residue was taken into pentane (40 mL) and resultant filtrate was concentrated and cooled
to —30 °C overnight yielding pale yellow 72 (0.22 g, 56%). mp 98—101 °C (dec). 1H
NMR (C6D6, 300 MHz) 5 7.10 (m, 6H), 5.05 (s, 1H), 3.23 (sept, J = 7.2 Hz, 4H), 1.74 (s,
6H), 1.25 (d, J = 7.2 Hz, 12H), 1.15 (d, J = 7.2 Hz, 12H). l3C{‘H} (C6D6, 75 MHz) 6
164.0, 145.0, 142.2, 125.7, 124.0, 98.08, 28.32, 25.77, 24.40, 23.81. Anal. Calcd for
ngHaiInsz C, 65.41; H, 7.76; N, 5.26. Found: C, 65.19; H, 8.10; N, 5.58.

In(DipznacnacH; (73). A brown solution of 12 (38 mg, 0.15 mmol) in ether (4
mL) was added to a solution of 72 (80 mg, 0.15 mmol) in ether (2 mL) at 0 °C. Upon the
addition, the brown color of I; quickly disappeared and a pale yellow solution was
obtained. After being stirred for 5 min, the solution was concentrated (1 mL) until
crystallization happened. The mixture was layered with pentane and colorless product
was collected by filtration (0.1 1 g, 93%). mp > 230 °C. 1H NMR (C6D6, 300 MHz) 57.08
(m, 6H), 4.73 (s, 1H), 3.49 (sept, J = 6.9 Hz, 4H), 1.51 (s, 6H), 1.40 (d, J = 6.9 Hz, 12H),
1.13 (d, J = 6.9 Hz, 12H). '3C{‘H} (C6D6, 75 MHz) 6171.86, 143.80, 140.90, 128.10,
124.77, 97.06, 28.82, 26.77, 24.69, 24.42. Anal. Calcd for C29H41121nN2: C, 44.30; H,
5.26; N, 3.56. Found: C, 43.76; H, 5.11; N, 3.71.

In(Dipznacnac)MeI (74). A yellow solution of 72 (0.1 1 g, 0.21 mmol) in pentane
(5 mL) was treated with freshly distilled Mel (64 11L, 1.0 mmol) at 0 °C with stirring. The

134

 

mixture turned colorless upon addition and was further stirred at room temperature for 5
min. All volatile materials were removed under vacuum to give a colorless solid which
was recrystallized out of pentane (0.12 g, 85%). mp 208—211 °C (dec). 'H NMR (C,D,,
300 MHz) 5 7.10 (m, 6H), 4.83 (s, 1H), 3.83 (sept, J = 6.9 Hz, 2H), 3.20 (sept, J = 6.9
Hz, 2H), 1.55 (s, 6H), 1.44 (d, J = 6.9 Hz, 6H), 1.22 (d, J = 6.9 Hz, 6H), 1.21 (d, J = 6.9
Hz, 6H), 1.07 (d, J = 6.9 Hz, 6H), —0.042 (s, 3H). l3C(‘Hl (C6D6, 75 MHz) 6172.20,
144.83, 142.57, 142.33, 127.12, 125.30, 123.88, 97.12, 28.88, 28.56, 28.16, 24.73, 24.41,
24.26, 24.15, —6.69. Anal. Calcd for C30H44HnN2: C, 53.43; H, 6.58; N, 4.15. Found: C,
53.35; H, 6.21; N, 3.97.

[In(Dipznacnachz-OHZ (75). A solution of 72 (0.090 g, 0.17 mmol) in toluene
(5 mL) was exposed to an atmosphere of N20 (about 20 molar equivalent) at room
temperature. After the mixture was stirred at that temperature for 2 h, the volume of the
mixture was reduced to about 1 mL. A colorless solid that fell out was collected by
filtration and was washed with pentane (2 X 5 mL), and dried under vacuum (71 mg,
76%). mp 198—200 °C (dee).'H NMR (C61), 300 MHz) 6 7.14—7.09 (m, 2H), 6.99—6.97
(m, 4H), 4.75 (s, 1H), 3.16 (sept, J = 6.9 Hz, 4H), 1.40 (s, 6H), 1.15 (d, J = 6.9 Hz, 12H),
1.08 (d, J = 6.9 Hz, 12H). l3C(‘Hl (C6D6, 75 MHz) 6171.30, 144.17, 142.91, 126.64,
124.44, 95.39, 28.50, 25.17, 24.89, 24.13. Anal. Calcd for [CqualInNZO]2: C, 63.50; H,
7.48; N, 5.11. Found: C, 63.31; H, 7.40; N, 5.13.
X-ray Structure Determination

The details of the procedures in X-ray structure determination and refinement are
listed in Appendix B. X-ray quality crystals of 40.5(C7H3) were grown from a
concentrated solution of 4 in toluene at —30 °C. Data sets were collected at -100 °C on a
Rigaku MSC/AFC6S X-ray diffractometer. Compound 4 crystallized in a monoclinic
crystal system. Cell parameters and refinement parameters are listed in Table 3. The
choice of space group P2l/n was based on intensity statistics and successful refinement of

the structure in P21/n space group. The positions for indium atoms were obtained from a

135

 

Patterson map. Starting with the indium, all non-H atoms were located by two cycles of
structure factor calculations followed by a difference map. One of the ’Bu groups
displayed rotational disorder and was subsequently refined with split occupancies for
C(7)—C(9) and C(7a)—C(9a) of 63% and 37%, respectively. Close inspection of the
difference map revealed the presence of a disordered toluene molecule at the inversion
center. The selected bond distances and angles are listed in Table 2. The molecular
structure is shown in Figure 16 and the toluene salvation molecule is not shown for
clarity.

X—ray quality crystals of compound 6 were grown from a concentrated solution of
6 in hexane at -30 °C in a glovebox. Data sets were collected at —100 °C on a Rigaku
MSC/AFC6S X-ray diffractometer. Compound 6 crystallized in a monoclinic crystal
system. Cell parameters and refinement parameters are listed in Table 3. The choice of
space group P21/c was based on intensity statistics and successful refinement of the
structure in P2./c space group. This structure was solved by the direct methods. The
selected bond distances and angles are listed in Table 4. The molecular structure is shown
in Figure 18.

X-ray quality crystals of compounds 11 and 14 were grown from concentrated
solutions of 11 and 14, respectively, in hexane at —30 °C. The data were collected on a
CCD machine and details are listed in Appendix B. Compounds 11 and 14 crystallized in
monoclinic crystal systems. Cell parameters and refinement parameters are listed in Table
5. The choices of space groups P2./c for 11 and P21/n for 14 were based on intensity
statistics and successful refinement of the structure. These structures were solved by the
direct methods. The selected bond distances and angles are listed in Table 6. The
molecular structures of 11 and 14 are shown in Figures 21 and 22, respectively.

X-ray quality crystals of compound 21 were grown from a concentrated solution
of 21 in methyl alcohol at —30 °C. Compound 21 crystallized in a triclinic crystal system.

Cell parameters and refinement parameters are listed in Table 5. The choice of space

136

 

groups P 1— for 21 was based on successful refinement of the structure. The structure was
solved by the direct methods. The selected bond distances and angles are listed in Table
6. The molecular structures of 21 are shown in Figure 23.

X-ray quality crystals of 28 were grown from a concentrated solution in toluene at
—30 °C. The data were collected on a CCD machine and details are listed in Appendix B.
Compound 28 crystallized in monoclinic crystal systems. Cell parameters and refinement
parameters are listed in Table 7. The choice of space group P21/n for 28 was based on
intensity statistics and successful refinement of the structure. The structure was solved by
the direct methods. The selected bond distances and angles are listed in Table 8. The
molecular structure of 28 is shown in Figure 24.

X-ray quality crystals of 29 were grown from a concentrated solution in pentane
at —30 °C. The data were collected on a CCD machine and details are listed in Appendix
B. Compound 29 crystallized in monoclinic crystal systems. Cell parameters and
refinement parameters are listed in Table 7. The choice of space group C2/c for 29 was
based on intensity statistics and successful refinement of the structure. The structure was
solved by the direct methods. The selected bond distances and angles are listed in Table
8. The molecular structure of 29 is shown in Figure 26.

X-ray quality crystals of 30 were grown from a concentrated solution in pentane
at —30 °C. The data were collected on a CCD machine and details are listed in Appendix
B. Compound 30 crystallized in monoclinic crystal systems. Cell parameters and
refinement parameters are listed in Table 7. The choice of space group P21/c for 30 was
based on intensity statistics and successful refinement of the structure. The structure was
solved by the direct methods. The selected bond distances and angles are listed in Table
8. The molecular structure of 30 is shown in Figure 28.

X-ray quality crystals of 31 were grown from a concentrated solution in pentane
at -30 °C. The data were collected on a CCD machine and details are listed in Appendix

B. Compound 31 crystallized in triclinic crystal systems. Cell parameters and refinement

137

parameters are listed in Table 7. The choice of space group P I for 31 was based on the
successful refinement of the structure. The structure was solved by the direct methods.
The selected bond distances and angles are listed in Table 8. The molecular structure of
31 is shown in Figure 29.

X-ray quality crystals of 37 were grown via pentane diffusion into a concentrated
toluene solution at room temperature. Compound 37 crystallized in a monoclinic crystal
system. The space group C2/c was chosen over Cc based on intensity statistics and the
successful refinement of the structure. The structure for 37 was solved by the direct
methods. Al and C(3) were located on a two-fold rotation axis, therefore Z = 4. Its
relevant details and data statistics were summarized in Table 10. And the selected bond
distances and angles are listed in Table 11. The molecular structure of 37 is shown in
Figure 3].

X-ray quality crystals of 38 were grown from a concentrated solution in toluene at
—30 °C. Compound 38 crystallized in a monoclinic crystal system. The choice of space
group C2/c was based on the successful refinement of the structure. Its relevant details
and data statistics are summarized in Table 10. And the selected bond distances and
angles are listed in Table 1 1. The molecular structure of 38 is shown in Figure 31.

X-ray quality crystals of 39 were grown from a concentrated pentane solution
cooled to -78 °C. Compound 39 crystallized in a monoclinic crystal system with
systematic absences indicating the space group P2./c. Its relevant details and data
statistics are summarized in Table 12. And the selected bond distances and angles are
listed in Table 13. The molecular structure of 39 is shown in Figure 32.

X-ray quality crystals of were grown from a concentrated solution in pentane
cooled to —30 °C. Compound 40 crystallized in a monoclinic crystal system with
systematic absences indicating the space group P21/c. Its relevant details and data
statistics are summarized in Table 12. And the selected bond distances and angles are

listed in Table 13. The molecular structure of 40 is shown in Figure 33.

138

X-ray quality crystals of 44 were grown from a concentrated solution in pentane
cooled to —78 °C. Compound 44 crystallized in an orthorhombic crystal system with
systematic absences indicating the space group Fdd2. The absolute structure parameter
was refined to 0.0(2). Its relevant details and data statistics are summarized in Table 15.
And the selected bond distances and angles are listed in Table 14. The molecular
structure of 44 is shown in Figure 34.

X-ray quality crystals of 46 were grown from a concentrated solution in pentane
cooled to —78 °C. Compound 46 crystallized in a monoclinic crystal system with
systematic absences indicating the space group P21/n. Its relevant details and data
statistics are summarized in Table 15. And the selected bond distances and angles are
listed in Table 14. The molecular structure of 46 is shown in Figure 35.

X-ray quality crystals of 41 were grown from a concentrated solution in pentane
cooled to —30 oC. Compound 41 crystallized in a triclinic crystal system. The structure
was solved by the direct methods. Its relevant details and data statistics are summarized
in Table 16. And the selected bond distances and angles are listed in Table 17. The
molecular structure of 41 is shown in Figure 36.

X-ray quality crystals of 42 were grown from a concentrated solution in
toluene/pentane cooled to --30 °C. Compound 42 crystallized in a monoclinic crystal
system with systematic absences indicating the space group P21/n. The structure was
solved by the direct methods. Its relevant details and data statistics are summarized in
Table 16. And the selected bond distances and angles are listed in Table 17. The
molecular structure of 42 is shown in Figure 37.

X-ray quality crystals of 50 were grown from a solution in toluene of 50 at -30
CC. Compound 50 crystallized in an orthorhombic crystal system with systematic
absences indicating the space group Pbcn. The structure was solved by the direct

methods. Its relevant details and data statistics are summarized in Table 18. And the

139

selected bond distances and angles are listed in Table 19. The molecular structure of 50 is
shown in Figure 38.

X-ray quality crystals of 51 were grown by diffusing pentane into a solution of 51
at in toluene —30 OC. Compound 51 crystallized in an orthorhombic crystal system with
systematic absences indicating the space group P212121. The structure was solved by the
direct methods. The absolute structure parameter was refined to 0.6(2). Its relevant details
and data statistics are summarized in Table 18. And the selected bond distances and
angles are listed in Table 19. The molecular structure of 51 is shown in Figure 39.

X-ray quality crystals of 53, 54, and 55 were grown from concentrated solutions
of compounds 53, 54, and 55 in pentane at —30 °C, respectively. Compound 53
crystallized in an orthorhombic crystal system with systematic absences indicating the
space group ana, and compounds 54 and 55 were triclinic. Their relevant details and
data statistics are summarized in Table 20. And the selected bond distances and angles
are listed in Table 21. The molecular structures of 53, 54, and 55 are shown in Figures
40, 41 , and 42, respectively.

X-ray quality crystals of 58 and 60 were grown from concentrated solutions of
compounds 58 and 60 in pentane at —30 °C, respectively. Both compounds 58 and 60
crystallized in a monoclinic crystal system with systematic absences indicating the space
group C2/c. Their relevant details and data statistics are summarized in Table 22. And the
selected bond distances and angles are listed in Table 23. The molecular structures of 58
and 60 are shown in Figures 45 and 46, respectively.

X-ray quality crystals of 66 were grown from toluene solutions at —30 °C.
Compound 66 crystallized in a monoclinic crystal system. The choice of space group
P2./c was based on the systematic distinction and the successful refinement of the
structure. Its relevant details and data statistics are summarized in Table 24. And the
selected bond distances and angles are listed in Table 25. The structure contains two

chemically equivalent, but crystallographically different molecules of In(Tolznacnac)C12

140

and half a toluene in the asymmetric unit cell. Thus the toluene methyl carbon C(42) was
refined with half occupancy. For clarity, only one of two molecules are shown and the
toluene solvate is omitted in Figure 50.

X—ray quality crystals of 67 were grown from toluene solutions at —30 °C.
Compound 67 crystallized in a triclinic crystal system. The choice of space group P 1—
was based on the successful refinement of the structure. Its relevant details and data
statistics are summarized in Table 24. And the selected bond distances and angles are
listed in Table 26. The molecular structure of 67 is shown in Figure 52.

X-ray quality crystals of 27 were grown from toluene solutions at —30 °C.
Compound 27 crystallized in a monoclinic crystal system. The choice of space group
P2i/c was based on the systematic distinction and the successful refinement of the
structure. Its relevant details and data statistics are summarized in Table 24. And the
selected bond distances and angles are listed in Table 27. The molecular structure of 27 is
shown in Figure 54.

X-ray quality crystals of 68 were grown from pentane solutions at —30 °C.
Compound 68 crystallized in a monoclinic crystal system. The choice of space group
P2./c was based on the systematic distinction and the successful refinement of the
structure. Its relevant details and data statistics are summarized in Table 24. And the
selected bond distances and angles are listed in Table 25. The molecular structure of 68 is
shown in Figure 57.

X-ray quality crystals of 69 were grown from toluene solutions at -30 °C.
Compound 69 crystallized in a monoclinic crystal system. The choice of space group
P2./n was based on the systematic distinction and the successful refinement of the
structure. Its relevant details and data statistics are summarized in Table 24. And the
selected bond distances and angles are listed in Table 26. The molecular structure of 69 is

shown in Figure 58.

141

X-ray quality crystals of 70 were grown from a concentrated toluene solution at —
30 OC. Compound 70 crystallized in a monoclinic crystal system. The choice of space
group P2l/n was based on the systematic distinction and the successful refinement of the
structure. Its relevant details and data statistics are summarized in Table 28. And the
selected bond distances and angles are listed in Table 29. The molecular structure of 70 is
shown in Figure 59.

X-ray quality crystals of 72 were grown from a pentane solution at —30 °C.
Compound 72 crystallized in a monoclinic crystal system. The choice of space group
P21/n was based on the systematic distinction and the successful refinement of the
structure. Its relevant details and data statistics are summarized in Table 28. And the
selected bond distances and angles are listed in Table 30. The molecular structure of 72 is
shown in Figure 60.

X-ray quality crystals of 74 were grown from toluene solutions at —30 °C,
respectively. Compound 74 crystallized in a monoclinic crystal system. The choice of
space group P21/n was based on the systematic distinction and the successful refinement
of the structure. Its relevant details and data statistics are summarized in Table 31. And
the selected bond distances and angles are listed in Table 32. The molecular structure of
74 is shown in Figure 63.

X-ray quality crystals of 75 were grown by slowly evaporating a benzene solution
of 75 at room temperature. Compound 75 crystallized in a monoclinic crystal system. The
choice of space group C2/m was based on the systematic distinction and the successful
refinement of the structure. The center of compound 75 is also the inversion center in the
unit cell. A crystallographic plane passes through In, 0, and C(3). Its relevant details and
data statistics are summarized in Table 31. And the selected bond distances and angles
are listed in Table 33. For clarity the two solvating benzene molecules are not shown in

Figure 65.

142

Chapter 7

SUMMARY

Mono-valent indium(I) compound 1 readily undergoes two-electron oxidation
reactions with mild oxidant 12 and ArN3 (Ar = Ph, p-Tol), generating indium(IH) products
In(Tp3"B“)l2 (3), In(Tp3'tBu)[N(Ar)—N=N—N(Ar)] (4 Ar = Ph, 5 Ar = p-Tol) respectively.
We pr0pose that compounds 4 and 5 form through a 3 + 2 cyclo-addition reaction
between ArN3 and an indium imido intermediate, (Tp3"B“)1n=NAr. The ligand degrades
to tetrakis(3-tert-butylpyrazolyl)borate (6) with B—H bond cleavage when a benzene
solution of 1 is treated with an excess of N20. Though the details of ligand
decomposition are unknown, it appears that indium plays a role. That decomposition
leads us to use alternative ligands and we have chosen fi-diketiminate ligands. The
synthesis of B—diketimines 11—14 has been optimized and it can be carried out on a 50-
gram scale. The free B—diketimines can be protonated with strong acids or deprotonated
with "BuLi. Lithium diketiminate complexes are used as ligand transferring reagents.
Tolznacnac is not able to support indium(I) because treatment of InCl with
Li(Tolznacnac) (16) generates only a disproportionation product In(Tolznacnac)3 (27).

The B-diketiminate boron(III) difluoride complex, 28, provides synthetic entry to
various boron alkyl complexes. While alkyllithium reagents give products that arise from
ligand deprotonation or nucleophilic attack at the ligand imine carbons, alkyl magnesium
halides cleanly afford the dialkyl products, (Tolznacnac)BR2, (R = Me (31); R = "Pr (32);
R = C2H3 (33); R = C3H5 (34)). Methyl abstraction from compound 31 by B(C6F5)3 gives

a cationic boron diketiminate compound, 35. Compound 35 is less Lewis acidic than

143

 

B(C6F5)3; however, a stable adduct, [B(Tolznacnac)(Py)Me]+[BMe(C6F5)3]‘ (36), forms
upon addition of pyridine to compound 35 in toluene.

Our initial results suggest that B—diketiminate ligands are well-suited for
stabilizing various alkyl aluminum and gallium complexes. A single-methane elimination
reaction between B—diketimines and AlMe3 afforded dimethyl B—diketiminate aluminum
complexes (39, 45, and 46) in excellent yields, and a double-methane elimination
reaction between protonated B—diketimines and AlMe3 yielded methyl aluminum
complexes (48, 49, 50, and 51). The triflate complex (51) reacted with various lithium or
Grignard reagents affording mixed alkyl complexes Al(Tolp_nacnac)MeR (52 R = C3H5
53%; 53 CHZSiMeg 66%; 54 CH(SiMe3)2 4.8%; 55 Ph 74%). The yields of the
substitution reactions depends on the bulk of incoming nucleophiles. The bulkier the
nucleophiles, the lower the yields. Using a tert-butyl anion, a deprotonation reaction was
observed. We confirmed this side reaction by methylation of that deprotonated site.
Under the conditions we explored, up to four methyl groups could be introduced to the
ligand backbone as indicated by compound 60. With the match of B—diketiminate ligand
and counter anion, a cationic aluminum complex is prepared. However, it did not interact
with ethylene.

Indium(HI) can be ligated with one, two, or three Tolznacnac ligands using salt
elimination reactions to form four-, five-, and six-coordinate indium complexes,
respectively. Introducing more Tolznacnac ligands to the indium center, not only leads to
lengthening of In—N bonds, it brings the ligands into proximity as well. Thus certain
protons in the most crowded indium complex 27 were strongly shielded by the benzene
ring currents. The chloro- and dichloro-indium complexes 66, 67 reacted with appropriate
amounts of methyl lithium yielding the corresponding methyl analogs 68, 69 in moderate

yields.

144

 

The bulky Dipznacnac ligand is able to stabilize In(I) centers and the first
monomeric two—coordinate indium(I) 72 was obtained. The reactivity of compound 72 is

dominated by the oxidation of In(I) to the more common In(III).

145

 

APPENDICES

146

APPENDIX A

GENERAL EXPERIMENTAL PROCEDURES

All manipulations were carried out under an inert atmosphere (N2 or Ar) using
standard Schlenk techniques unless noted otherwise. Toluene, THF, ether, and pentane
were freshly distilled over sodium/benzophenone ketyl and were saturated with N2 or Ar
before use. Methylene chloride was freshly distilled over calcium hydride. NMR solvents
were dried over activated 4-A sieves, and vacuum transferred to air-free flasks. Common
chemicals were purified by established procedures.210 NMR spectra were obtained on
Varian Gemini—300, VXR-300, [nova-300, or VXR-500, at room temperature (25 °C)
unless noted otherwise. The lH and '3C{ 1H} NMR chemical shifts were referenced to the
deuterated solvents. The IIB NMR chemical shifts were referenced to a neat BF3-(OEt2)
(5 0) as an external standard. The 19F NMR chemical shifts were referenced to a neat
CFC]; (50) as an external standard. IR spectra were obtained on a Nicolet IR/42 between
nujol KBr plates. Uncorrected melting points of crystalline samples in sealed capillaries
(under an argon atmosphere) were reported as ranges. Elemental analyses (C, H, N) were
performed by Desert Analytics, Tucson, Arizona or Dr. Huang of MSU on a Perkin

Elmer CHN 2400 Series II CHNS/O Analyser.

147

 

APPENDIX B

DETAILED PROCEDURE FOR X-RAY STRUCTURE DETERMINATION

Except for those of In(Tp3'tB“)[N(Ph)—N=N—NPh] (4) and H[B(C3H2N2-3—’Bu)4]
(6) all X-ray diffraction data were collected on a Siemens SMART CCD diffractometer
using Mo-Ka radiation (11 = 0.71073 A). The data were collected at 30 seconds per frame.
Initial cell parameters were calculated from three sets of fifteen frames. All data sets were
collected over a hemisphere of reciprocal space. Following integration using the SAINT
program, final unit cell parameters were obtained by least—squares refinement of strong
reflections. Absorption and decay corrections were applied to the data by SADABS. The
structures were solved by direct methods and refined using the SHELXTL programs.
Calculations were based on F2 data. Unless noted otherwise, all non-hydrogen atoms
were refined using anisotropic displacement parameters and all hydrogen atoms were
placed in calculated positions and refined as riding models. Three of the parameters are
defined below.

GOF = 121w<F.-°- — Fc2)2]/(n — p11” (37)

where n is the number of reflections and p the total number of parameters refined.

R1 = ZIIFOI — IFCIIIZIFOI (38)

wR2 = [£[w(Fo‘°'—Fc2)21/Z[W(Foz)zll'/’ (39)

148

 

APPENDIX C

CONE ANGLE CALCULATION FOR 72

The cone angle a for 72 is shown in Figure 66 and is expressed in eq 40.
a = 360° — 2 cos'l(r1/r2) (40)
where r] is the van der Waals radii (2.0 A) of methyl groups, and r2 is the average

(4.005 A) of In---C distances.

Thus,
a = 239.9° (41)
wa = 90° — 2 tan—'(rilr2) (42)

where r. is the van der Waals radii (2.0 A) of methyl groups, and r2 is the average
(4.005 A) of InmC distances.

Thus,

wa = 37° (43)

(1* CD ..

Figure 66. Definition of the cone angle for Dip2nacnac in compound 72.

 

149

 

 

APPENDICES

150

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