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dissertation entitled
INVESTIGATION OF STOICHIOMETRIC AND CATALYTIC
B-C BOND FORMATION BY GROUP 9 TRANSITION
METAL BORYL COMPLEXES
presented by

Jian-Yang Cho

has been accepted towards fulfillment
of the requirements for

Ph . DL degree in Chemi stry

- Maegan

j"

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Date 1 (L’q .. 02-

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__...____ , - w

INVESTIGATION OF STOICHIOMETRIC AND CATALYTIC B—C BOND
FORMATION BY GROUP 9 TRANSITION METAL BORYL COMPLEXES

By

Jian-Yang Cho

A DISSERTATION
Submitted to
Michigan State University
in partial fulfillment of the requirement
for the degree of

DOCTOR OF PHILOSOPHY
Department of Chemistry

2002

ABSTRACT

INVESTIGATION OF STOICHIOMETRIC AND CATALYTIC B-C BOND
FORMATION BY GROUP 9 TRANSITION METAL BORYL COMPLEXES

By

J ian-Yang Cho

C-H bond activation has attracted considerable attention since hydrocarbon
feedstocks are ubiquitous. However, the catalytic functionalization of hydrocarbons still
represents a long-standing challenge in homogeneous and heterogeneous catalysis. Since
applications of arylboronate esters in cross-coupling chemistry are expansive, the
transformation depicted below would have broad appeal.

Ar-H + H-BXZ ——> Ar-BXZ + H-H

In 1999, our group demonstrated the first thermal, catalytic aromatic borylation
reaction catalyzed by Cp*Ir(PMe3)(H)(BPin). In order to understand this important
transformation, detailed mechanistic studies were carried out. Through detailed
investigations, a remarkably selective iridium catalyst system was discovered for
aromatic borylation reactions.

Borylations of various mono-substituted arenes provide essentially a statistical
distribution of m- and p-C6H4(X)(BPin). This unique steric directing effect in aromatic
borylation provides a complementary means for regioselective functionalization of
aromatic compounds. For example, 1,3-disubstituted benzene rings are selectively
borylated at the 5-position. With the exception of electron-deficient arenes, this is
typically the least activated site towards aromatic substitution. Using this new

methodology, a variety of arylboronic esters can be synthesized in a relatively simple and

efficient way directly from corresponding arenes and pinacolborane or pinacol diboron
catalyzed by the new iridium catalyst system.

The new iridium catalysts tolerate the entire range of aryl halides, ether, and ester
functionalities and selectively functionalize aromatic C-H bonds. This remarkable
selectivity broadens the potential applications for aromatic borylation.

Stoichiometric reactions of (PMe3)4Ir(BPin) and fac-(PMe3)3Ir(BPin)3 with arenes
were examined. Both Irl and Ir"I boryl complexes can effect benzene borylation.
However, their reactions with iodobenzene differ substantially under both stoichiometric
and catalytic conditions.

In order to further investigate the possibility that metal boryl complexes are
intermediates in borylation reactions, several derivatives containing alkyl, aryl, or silyl
ligands were synthesized and fully characterized.

Preliminary mechanistic studies on the new iridium catalyst system were carried

”W catalytic

out and presently a mechanism involving Ir!" and Irv intermediates in an Ir
cycle is suggested. Correlations between the stoichiometric and catalytic reactions

provided a deeper insight into the mechanism of aromatic borylation.

T 0 my family and wife for their support and love

iv

ACKNOWLEDGMENTS

First, I would like to thank my research advisor, Mitch Smith, for his guidance
and assistance throughout my graduate career at Michigan State University. He taught me
the qualities for pursuing the truth in science and gave me the opportunity to work on
some exciting chemistry. Although the life for being a graduate student is tough, it
equipped me with essential tools and knowledge to face future challenge. I will always
appreciate that.

I am thankful to Dr. Odom and Dr. Maleczka for their stimulating discussions
during our joint group meetings and Dr. Jackson and Dr. Pinnavaia for serving on my
guidance committee.

My thanks also go out to Dr. Carl Iverson for his patient teaching and sharing of
experiences during my first year here. I was very lucky to work with some talented
postdoctoral associates, Dr. Man Kin Tse and Dr. Daniel Holmes. I learned a great deal
from them. I will value the friendships I gained in my time at MSU. They are Chris
Radano, Jim Ciszewski, Chen-Yu Yeh, Baixin Qian, J ie Fang, and Kuei-Fang Hsu. Their
encouragement makes my graduate life more passable. Special thanks go to Jim and
Kuei-Fang for their help in obtaining X-ray crystal structure. I also appreciate my best
partners in Taiwan, Dr. Yih-Hsing Lo and Yi-Wei Chao, for their long-distance
friendships.

Finally, I would like to thank my best friend, my soulmate, and my wonderful

wife, Mi-J in Chae, for her love, support, and sacrifice. Thank you for everything. I also

would like to express my appreciation and love to my family in Taiwan: Dad, Mom, my
elder brother, and my younger sister for their love, encouragement, and emotional
support. I could not have gotten through this without them. My appreciation also goes out
to my father and mother in-law in South Korea for their caring and support. Thank you so

much.

vi

TABLE OF CONTENTS

LIST OF TABLES .................................................................................... x
LIST OF FIGURES ................................................................................. xii
LIST OF SYMBOLS AND ABBREVIATIONS ............................................. xvii
CHAPTER 1
INTRODUCTION
C-H Bond Activation and F unctionalization of Hydrocarbons ........................ 1
Thermodynamics of Borane F unctionalization of OH Bonds ........................ 4
Stoichiometric and Catalytic Borylation Reactions ..................................... 5
Synthetic Routes to Arylboronic Esters ................................................... 9
CHAPTER 2

MECHANISTIC INVESTIGATION OF Cp*Ir(PMe3)(H)(BPin) CATALYZED
BORYLATION REACTIONS

Comparison between Cp*Ir(PMe3)(H)(BPin) and Cp*Rh(n4-C6Me6) Pre-catalyst
Systems in Borylation of Various Substituted Arenes ................................. 12

Metathesis Reactions between Cp*M(PMe3)(Ph)(H) (M = Ir, Rh) and

Pinacolborane in C6D6 ..................................................................... 18
Mechanistic Studies of The Original Iridium System ................................. 26
CHAPTER 3

CATALYTIC BORYLATION REACTIONS OF AROMATIC COMPOUNDS

Screenings of Phosphine Ligands, Other Donor Ligands, and Metal Complexes
for Catalytic Benzene Borylation ......................................................... 36

Borylation of Substituted Benzenes ...................................................... 42

vii

Steric, Electronic, and Directing Effects in Aromatic Borylation ................... 48
Competition Reactions ..................................................................... 56
CHAPTER 4

SYNTHESIS, CHARACTERIZATION, AND REACTIVITY OF IRIDIUM BORYL
COMPLEXES

Synthesis and Characterization of an Irl Boryl Complex .............................. 58

Substitution and Oxidative Addition Reactions of IrI Boryl Complexes ............ 68

Synthesis and Characterization of an Ir"I Boryl Complex ............................ 74

Synthesis and Characterization of Novel Metal Boryl Complexes Containing

Alkyl, Aryl, or Silyl Ligands ............................................................. 76

Oxidation Chemistry of IrI Complex with Boranes .................................... 93
CHAPTER 5

PRELIMINARY MECHANISTIC STUDIES OF THE IRIDIUM/PHOSPHINE
CATALYST SYSTEM FOR AROMATIC BORYLATION

Stoichiometric Reactions of Ir1 and Ir!" Boryl Complexes with Arenes ............ 96
Correlation between Phosphine Ligands and Catalytic Activity ................... 108
Stoichiometric and Catalytic Borylations of Iodobenzene .......................... l 10
Kinetic Isotope Effects in Aromatic Borylation ...................................... l 12
Mechanistic Discussions ................................................................. l 18
CHAPTER 6
EXPERIMENTAL
General Considerations .................................................................. 126
Syntheses ................................................................................... 128
Screening Experiments .................................................................. 135
NMR Tube Reactions .................................................................... 137

viii

Kinetic Isotope Effect Experiments .................................................... 143

Arylboronate Ester Syntheses ........................................................... 146
Competitive Borylation Experiments .................................................. 160
Kinetics Experiments ..................................................................... 162
Crystal Structure Determinations and Refinement ................................... 164
APPENDIX A
Summary of Crystal Data and Structure Refinement ......................................... 167
APPENDIX B
Derivation of Rate Expressions for Chapter 4 ................................................. 173
APPENDIX C
Kinetic Details ..................................................................................... 176
BIBLIOGRAPHY ................................................................................. 1 79

ix

LIST OF TABLES

Table 1. Isolated yields (based on HBPin) and isomer distributions for catalytic
borylation of aromatic hydrocarbons catalyzed by solutions of compounds 1 and 3 ...... 13

Table 2. Relative ratios of arylboronic esters for borylations of equimolar mixtures of
substituted arenes catalyzed by compounds 2 and 3 ............................................ 17

Table 3. Selected bond lengths [A] and angles [°] for 14 ...................................... 34

Table 4. Summary of borylation of benzene with HBPin in the presence of 2 mol% pre-
catalyst at 150 °C .................................................................................... 37

Table 5. Borylation reaction of benzene with HBPin in the presence of 2 mol% 13 and 2
mol% chelating phosphine ligand ................................................................. 38

Table 6. Borylation reaction of benzene with HBPin in the presence of 2 mol% 13 and
nitrogen, oxygen, or sulfur containing ligands .................................................. 39

Table 7. Borylation of benzene with HBPin in the presence of various metal precursors
(M) and ligands ...................................................................................... 41

Table 8. Ir-catalyzed aromatic borylations. Reactions are run in neat arene, [Ir] = 2 mol%,
[P]:[Ir] = 2:1, and yields are reported for isolated materials ................................... 42

Table 9. Borylations of unsymmetrical 1,2- and 1,4-disubstituted arenes with HBPin in
the presence of 2 mol% l3 and 2 mol% dmpe. Reactions run in neat arene, and yields are
reported for isolated materials ..................................................................... 48

Table 10. Ligand repulsive energies (in kcal/mol) computed using the universal force
field and A-values (in kcal/mol) for a variety of organic substituents ....................... 50

Table 11. Comparison of isomer distribution between the experimental values and the
calculated values derived from pure steric effect (ER) .......................................... 52

Table 12. Borylations of mono-substituted arenes with HBPin in the presence of 2 mol%
13 and 2 mol% dmpe. Reactions run in neat arene. Isomer distribution is obtained from
area ratios in GC-FID chromatograms ............................................................ 53

Table 13. Comparison of isomer distribution between the experimental values and the
estimated values derived from selectivity in borylation of mono-substituted arenes ...... 55

Table 14. Relative ratios of arylboronic esters for borylations of equimolar mixtures of

substituted arenes catalyzed by 2 mol% 13 and 2 mol% dmpe ................................ 56
Table 15. Selected bond lengths [A] and angles [°] for 17 .................................... 65
Table 16. Selected bond lengths [A] and angles [°] for 18 ..................................... 67
Table 17. Comparison of boryl resonances of complexes 15, 17, 22, 23 and 24 in 11B
NMR spectra ......................................................................................... 73
Table 18. Selected bond lengths [A] and angles [°] for 25 ..................................... 76
Table 19. Selected bond lengths [A] and angles [°] for 28 ..................................... 88
Table 20. Selected bond lengths [A] and angles [°] for 29 .................................... 91

Table 21. Comparisons of XzB-Ir-PMe3mm, to Bpm bond distances of iridium boryl
complexes ............................................................................................ 92

Table 22. Borylation reactions with HBPin in a molar ratio 1:1 mixture of C6H6/C6D6 or
1,3,5-C6D3H3 catalyzed by Ir' and Ir‘" sources at 150 °c, [Ir] = 2 mol%, [PMe3]:[Ir] 2
2:1 ................................................................................................... 116

Table 23. Stoichiometric borylation reactions of 18 and 25 with a molar ratio 1:1 mixture
Of C6H6/C6D6 OI' 1,3,5-C6D3H3 at 150 0C ....................................................... 1 18

xi

LIST OF FIGURES

Figure 1. Various pathways discovered for the activation of OH bonds ..................... 4

Figure 2. Functionalization of hydrocarbons by transition metal boryl complexes under
photochemical conditions ........................................................................... 6

Figure 3. Selective functionalization of alkanes by transition metal boryl complexes. . ....7

Figure 4. The first thermal, catalytic example of aromatic borylation reaction .............. 8
Figure 5. Reaction of BzPinz in pentane catalyzed by Cp*Re(CO)3 ........................... 9
Figure 6. Traditional and direct routes to arylboronic esters from aromatic
hydrocarbons ......................................................................................... l 0
Figure 7. Resonance structures of ethyl benzoate and N,N-diethyl benzamide. . . . . . . . 1 6

Figure 8. Initial proposed catalytic cycle for catalytic functionalization of hydrocarbon
C-H bonds ............................................................................................ 19

Figure 9. The reaction between Cp*Ir(PMe3)(Ph)(H) (5) and HBPin in C6D6 at 150 °C
after around 37% conversion from Cp*Ir(PMe3)(Ph)(H) to Cp*Ir(PMe3)(H)(BPin): (a) 1H
NMR spectrum of Cp* region; (b) lH NMR spectrum of aromatic
region ................................................................................................. 20

Figure 10. The metathesis reaction between compound 5 and HBPin in CbDb at 150
°C ...................................................................................................... 21

Figure 11. Thermolysis of Cp*Ir(PMe3)(H)(BPin) (1) in C6D6 ............................... 22

Figure 12. 1H NIVIR and 3|P{1H} NMR spectra of the thermolysis of compound 1 in
C6D6 ................................................................................................... 22

Figure 13. The reaction of compound 4 with HBPin in C6D6 at elevated temperature. . ..23

Figure 14. Plot of ln([4]t/[4]o) vs. time (s) for the reaction of compound 4 with [HBPin] =
0.551 M and [HBPin] = 1.103 M in C6D6 at 95 °C, respectively ............................. 25

Figure 15. Eyring plot for the reaction of compound 4 with HBPin in C6D6. ([4]o = 0.046

M; [HBPin]o = 0.551 M; T = 338.15 to 388.15 K, AH1= 25.6 kcal/mol and AS‘ = -53
en.) .................................................................................................... 26

xii

Figure 16. Potential crossover products from pseudo double-labeling crossover

experiment ............................................................................................ 27
Figure 17. Separation of compounds 2, 8, and 9 in a GC-MS chromatogram ............... 28
Figure 18. Pseudo double-labeling crossover experiment ..................................... 29

Figure 19-1. The chromatogram of the crude mixture from benzene borylation with
pinacolborane in the presence of 10 mol% of compound 8 and 10 mol% of compound
9 ....................................................................................................... 30

Figure 19-2. The chromatogram of the crude mixture from benzene borylation with
pinacolborane in the presence of 10 mol% of compound 8 and 10 mol% of compound
9 ....................................................................................................... 31

Figure 20. Borylation reactions of anisole with 20 mol% loading of compound 1 and
compound 11, respectively ......................................................................... 32

Figure 21. ORTEP diagram of (MesH)Ir(BPin)3 (14). Thermal ellipsoids are shown at
25% probability ...................................................................................... 33

Figure 22. Benzene borylation with HBPin catalyzed by 2 mol% 14 and 4 mol%
PMe; ................................................................................................... 34

Figure 23-1. GC chromatogram of borylation of 1,3—dichlorobenzene catalyzed by the Rh
pre-catalyst 3 .......................................................................................... 46

Figure 23-2. GC chromatogram of borylation of 1,3-dichlorobenzene catalyzed by the Ir
pre-catalyst 13 and dppe ............................................................................ 47

Figure 24. The calculated value of isomer distribution of the borylation of 1,4-
C6H4(CI)(CF3) ....................................................................................... 51

Figure 25. The estimated value of isomer distribution of the borylation of 2-
chloroanisole ......................................................................................... 54

Figure 26. Two potential catalytic cycles for aromatic borylation: (Left) involving Irv”I

intermediates; (right) involving Ir"W intermediates ............................................ 59
Figure 27. Cyclometallation of tris(trimethylphosphine)neopentyliridium(I) complex. . .60
Figure 28. The reaction between mer-(PMe3)3Ir(BPin)(H)(Cl) (15) and KO’Bu .......... 60

Figure 29. Deborylhalogenation reaction between complex 16 and KO’Bu ................ 62

xiii

Figure 30. ORTEP diagram of mer,cis-(PMe3)3Ir(BPin)2Cl (17). Thermal ellipsoids are
shown at 25% probability .......................................................................... 64

Figure 31. Syntheses of mer,cis-(PMe3)3Ir(BPin)2Cl (17) and (PMe3)4Ir(BPin) (18). . ....66

Figure 32. ORTEP diagram of (PMe3)4Ir(BPin) (18). Thermal ellipsoids are shown at

25% probability ...................................................................................... 67
Figure 33. The reaction between compound 18 and dppe ...................................... 68
Figure 34. H2, R3SiH, and HX' oxidative additions to IrX(CO)(dppe) complexes. . . . . ....71

Figure 35. Catecholborane (HBCat) oxidative additions to IrX(CO)(dppe) complexes...7l

Figure 36. Pinacolborane (HBPin) oxidative addition to compound 18 ...................... 72
Figure 37. Chlorocatecholborane (ClBCat) oxidative addition to compound 18 ........... 73
Figure 38. Synthesis of fac-(PMe3)3Ir(BPin)3 (25) ............................................. 74

Figure 39. ORTEP diagram of fac—(PMe3)3Ir(BPin)3 (25). Thermal ellipsoids are shown at
25% probability. All oxygen and carbon labels are omitted for clarity. Hydrogen atoms
are also omitted for clarity ......................................................................... 75

Figure 40. Reported complexes containing a boryl ligand and a o-bound carbon

ligand .................................................................................................. 77
Figure 41. The reaction between (PMe3)4Rh(Me) and BzCatz ................................ 78
Figure 42. The reaction between (PMe3)4Ir(Me) and HBPin in pentane ..................... 79

Figure 43. The resonance of the methyl group of fac-(PMe3)31r(Me)(H)(BPin) (26) in the
1H NMR spectrum ................................................................................... 81

Figure 44. The resonances of PMe3 groups of fac-(PMe3)3Ir(Me)(H)(BPin) (26) in the 1H
NMR spectrum. The peaks denoted with an asterisk (*) are due to PMe3 and BPin

resonances of compound 27 ........................................................................ 81

Figure 45. NOE experiments of compound 26 (Irradiation of the hydride resonance at
-11.30 ppm) ........................................................................................... 82

Figure 46. NOE experiments of compound 26 (Irradiation of the Me resonance at 0.40
ppm) ................................................................................................... 83

xiv

Figure 47. The resonances of PMe3 groups of fac—(PMe3)3Ir(Me)(H)(BPin) (26) in the
3|P{1H} NMR spectrum. The peaks denoted with an asterisk (*) are due to PMe3
resonances of compound 27 ........................................................................ 84

Figure 48. HETCOR experiment (1H, 31P) to correlate the resonances of PMe3 groups in
the lH NMR spectra to those in the 3 lP{1H} NMR spectra .................................... 84

Figure 49. The reaction between (PMe3)4Ir(Me) with 9-BBN ................................ 85

Figure 50. The NMR reaction of (PMe3)3Ir(Ph) with HBPin in toluene-d3 at room
temperature .......................................................................................... 87

Figure 51. ORTEP of mer—(PMe3)3Ir(BPin)(H)(Ph) (28). Thermal ellipsoids are shown at

25% probability ...................................................................................... 87
Figure 52. The reaction between (PMe3)4Ir(BPin) (l8) and HSiEt; .......................... 89
Figure 53. ORTEP of fac-(PMe3)3Ir(H)(BPin)(SiEt3) (29). Thermal ellipsoids are shown
at 25% probability ................................................................................... 91
Figure 54. The reactions of Ir(PMe3)3(COE)(Cl) (30) with nitrogen-containing boranes
including H[B(NH)2C6H4], H[B(NH)2C10H6] (HBDAN), and H[B(NMe)2C6H4] ......... 95
Figure 55. Thermolysis of 18 in C6136 at 150 °C ................................................ 97
Figure 56. Thermolysis of 18 in C6D6 at 150 °C: 1H NMR spectrum before
thermolysis ........................................................................................... 98
Figure 57. Thermolysis of 18 in C6D6 at 150 °C: 1H NMR spectrum after thermolysis.
Small peaks around 1.28-1.42 ppm and 1.57-1.60 ppm were not identified ................ 99
Figure 58. Plot of ln([18]t/[18]0) vs. time (min) for the thermolysis of 18 in C6D6 at 130
°C .................................................................................................... 100
Figure 59. Two potential pathways to account for the stoichiometric reaction between 18
and C6D6 ............................................................................................. 101
Figure 60. Plot of 1/k0bs vs. [PMe3] of the thermolysis of 18 in C6D6 in the presence of
various concentrations of PMe3 .................................................................. 102
Figure 61. Our proposed mechanism for the thermolysis of 18 in C6D6. . . . . . . . ............103
Figure 62. The process of thermolysis of 25 in C6D6 at 150 °C ............................. 103

Figure 63. Concentration of each species relative to internal standard (CbMeo) vs. time
(min) for the thermolysis of 25 in C6D6 at 150 °C measured by 1H NMR ................. 105

XV

Figure 64. Plot of ln([25]t/[25]o) vs. time (min) for the thermolysis of 25 in CbDb at 150

°C ..................................................................................................... 107
Figure 65. The reaction of (PMe3)4Ir(H) (37) with HBPin and BzPinz ..................... 108
Figure 66. 1H, 11B, and 31P{1H} NMR spectra of the off-white precipitate from the
reaction between 18 and C6H51 ................................................................... l l 1
Figure 67. Thermolysis of 25 in iodobenzene .................................................. l 12
Figure 68. The process of reversible formation of nz—arene complexes .................... l 13

Figure 69. Observed kH/kD in the activation of a 1:1 mixture of CbHo/CODO by the

intermediate [Cp*Rh(PMe3)] ..................................................................... 1 14
Figure 70. A trisboryl complex [Ir((dtbpy)(COE)(BPin)3] isolated by Miyaura and co-
workers .............................................................................................. 119
Figure 71. Possible mechanisms for Ir"I borylation reaction ................................ 120
Figure 72. Thermolysis of compound 28 in C6D6 at 50 °C ................................... 121
Figure 73. A putative mechanism for aromatic borylations catalyzed by iridium boryl
complexes .......................................................................................... 123
Figure 74. Iridium tris(boryl) intermediate in borylation reactions ......................... 124

xvi

BDAN
BzPinz
ClBCat
COD

COE

dddd

6.11.
E120

equiv.

HBPin

Hz

LIST OF SYMBOLS AND ABBREVIATIONS

Angstrom

B(NH)2C10H6

bis(pinacolato)diboron, Me4C202B—B02C2Me4
chloro-catecholborane

1,5-cyclooctadiene

cyclooctene

pentamethylcyclopentadienyl, nS-C5(CH3)5
degrees Celcius

doublet

doublet of doublet of doublet of doublet
deuterium

entropy units

diethyl ether

equivalent

facial

gas chromatography

hour

pinacolborane, HBOZCZMe4

hertz

infrared

coupling constant

xvii

kcal
kH/kD

kobs

mer
min
mL
mmol
mM
mol
MS
NMR
Ph
PMe;
PPh3

Pin

rate constant
temperature in Kelvin
kilocalorie

ratio of isotope effect on observed rate constant
observed rate constant
liter, generic ligand
multiplet

methyl, -CH3
meridional

minutes

milliliters

millimole

millimolar

mole

mass spectrometry
nuclear magnetic resonance
phenyl, -C6H5
trimethylphosphine
triphenylphosphine
pinacol, 1,2-02C2Me42'
quartet

singlet, seconds

triplet

xviii

tetrahydrofuran

delta, ppm for NMR spectroscopy
change in enthalpy

change in entropy

ligand hapticity of number “n”

microliters

xix

CHAPTER 1

INTRODUCTION

C-H Bond Activation and Functionalization of Hydrocarbons

The selective transformation of carbon—hydrogen bonds to other functional groups
represents a long-standing challenge in homogeneous and heterogeneous catalysis,
because C-H bonds are the most ubiquitous chemical linkages in Nature. Elucidating the
requirements necessary to effect their cleavage or their transformation into other bonds is
based on our fundamental understanding of their chemical reactivity. Over the past two
decades, many examples of OH activation at transition metal centers were reported.1 It
has been a topic of great interest to the organometallic chemists. Saturated hydrocarbons
are major constituents of natural gas and petroleum, but there are very few practical
processes for converting them directly to more valuable chemicals. The lack of reactivity
of alkane C-H bonds can be attributed to their high bond energies (typically 90-104
kcal/mol) and very low acidity or basicity. Despite the fact that C-H bonds are more
difficult than other types of linkages to cleave, such as CC] and C-Br, they are not
completely inert. Alkanes have been known to undergo a number of solution and gas-
phase reactions that involve free radicals as intermediates. They exhibit some preference
for reaction of tertiary C-H bonds over primary or secondary. There are also some
examples of alkane reactions with superacids2 or ozone3; however, they are usually very
unselective. In recent years, considerable work with stoichiometric activation of C-H

bonds suggests that homogeneous organometallic systems can overcome some of these

selectivity problems.4 Many examples suggest that a regioselectivity pattern with (Le, 1°
> 2° > 3°) can be obtained. Despite the success in this area, few systems are capable of
subsequent substrate functionalization and regeneration of the metal species as required
for catalytic turnover. Thus, developing a method not only to selectively activate but also
functionalize C-H bonds of hydrocarbons has been a “Holy Grail” in synthetic
chemistry.1C

Selective catalytic hydrocarbon functionalization is not unknown. In fact, Nature
performs ambient temperature alkane functionalization constantly, and sometimes with
excellent selectivity, through the use of oxygenase enzymes. Those, which belong to the
monooxygenase cytochrome P-4505 and methane monooxygenase6 (MMO) families,
have received a considerable amount of attention. These enzymes catalyze the
incorporation of molecular oxygen into alkane C-H bonds with the simultaneous loss of
water and oxidation of NADPH or NADH. In the case of cytochrome P-450, the enzyme
active site has been found to contain an iron porphyrin complex with a sulfur-bound
cysteine, which mediates the cleavage of 02 to generate an iron-oxo complex. This oxo
complex is considered to be the active oxidant of alkane C-H bonds. The efficiency of
biological oxygenase systems has stimulated a significant body of research devoted to
developing both structural and functional mimics designed to oxidize alkane.7

Pathways discovered for activation of C-H bonds include (i) oxidative addition of
R—H to transition metal, (ii) 0 bond metathesis between M-R’ and R-H, 1,2-addition of R-
H to M=X (X=O, NR, CR2), (iii) electrophilic activation in the reaction of M-X (X=
halide, hydroxide, trifiate, etc.) and R-H to generate M-R and HX, and (iv) metalloradical

activation. Oxidative addition reactions are typical pathways for late transition metal

complexes. For example, Cp*Ir(PMe3)(H)2 (2, Cp* = nS-C5Mes) loses H2 under photo-
irradiation to generate the reactive species “Cp*Ir(PMe3)”, which subsequently activate
the OH bonds of hydrocarbon substrates to form a metal alkyl hydride complex.8 o-Bond
metathesis occurs mostly in early transition metal complexes. These reactions usually
result in the interchange of metal and hydrocarbon alkyl fragments.9 1,2-addition
reactions involve the addition of an alkane to metal-nonmetal multiple bond.10 However,
the scope of this type reaction and its potential for alkane functionalization remains
unclear. Electrophilie activation reactions involve an electrophilic metal center, which
attacks C-H bonds of alkanes to form functionalized alkanes directly. This type of
reaction is usually carried out in a strongly polar medium such as water or anhydrous
strong acid. One example in which the reaction between the Rh (II) porphyrin complexes
and alkane C-H bonds with the involvement of free alkyl radical, generated through
abstraction of a hydrogen atom from alkane by the Rh center is classified as
metalloradical activation (Figure 1).H

Systems that can selectively and catalytically functionalize the OH bonds of
hydrocarbons are extremely rare. There are some examples of functionalization processes
mediated by homogeneous transition metal complexes, including dehydrogenation of
alkanes,l2 carbonylation of benzene,13 carbonylation of pentane,l4 and acceptorless
dehydrogenation of cyclic alkanes by iridium complex with PCP type ligand.IS

Mechanistic insight into the fundamental processes and solutions of potential
problems towards to the functionalization of hydrocarbons have been studied extensively

and well developed in many stoichiometric reactions. Currently the biggest challenge in

this field is to develop better catalysts system to activate and functionalize the C -H bonds

of hydrocarbons for practical applications.

Oxidative addition

LnM" + R-H ——> LnMX+2(R)(H)
Sigma-bond metathesis

LnMx-R + R'-H———> LnMLRH R-H
1,2-addition

LnMX=Y + R-H —-» LnIyIX-T (Y = 0, NR, CR2)
R H

Electrophilie activation

 

LnMx-Y + R-H LnMx-R + H-Y (Y=halide, hydroxide, triflate, etc.)

Metalloradieal activation . ”I
R-H (porphyrInIRh (R)
{(porphyrinIRh"}2 -— 2 (porphyrin)Rh".—' .

(porphyrin)Rh"'(H)

Figure 1. Various pathways discovered for the activation of OH bonds.

Thermodynamics of Borane Functionalization of C-H Bonds

Since the importance of boryl complexes as proposed intermediates in the

transition metal catalyzed functionalization of organic compounds, studies concerning the

fundamental properties and reaction chemistry of transition metal boryl complexes have
been initiated since early 19905. Transition metal-ligand covalent bond energies are
important in understanding catalysis. However, there has been few data available for
boranes and no thermochemical data for transition metal boryl complexes until 1994. In
that year, Rablen and Hartwigl6 reported calculation of B-H and B-C bond dissociation
energies (BDEs) for a series of boranes. From the established thermochemical and
computational data of borane reagents, the reaction in equation 1 is essentially
therrnoneutral. Moreover, from calculated BDE’s for B-H, C-H, and BC bonds,
synthesis of aryl boronic esters directly from boranes and arenes should be

thermodynamically feasible.

CH4 + HBCat =————————- CHaBCat + H2 AH° =-2.1kcal/mol (1)

Stoichiometric and Catalytic Borylation Reactions

In 1995, Hartwig et al.17 reported the functionalization of hydrocarbons by the
reaction of arenes and alkenes with (CO)5Mn(BCat), (CO)5Re(BCat), and
CpFe(CO)2(BCat) under photochemical conditions (Figure 2). Although dehydrogenative
borylation of benzene has not been observed previously before this report,

dehydrogenative borylation of alkenes has been observed in catalytic chemistry. 1 8

(CO)5M—BCat T Q—BCat + HBCat + M2(CO)10 + H2 + Re3(CO)12H3

M = Mn 45% 10-20%
M = Re 55%

a Q
,.Fe-—-BCat ————> BC t + F +H
0C / hv, 1 h Q 3 DZ 2

87%

Figure 2. F unctionalization of hydrocarbons by transition metal boryl complexes under

photochemical conditions.

Waltz and Hartwig” in 1997 reported selective functionalization of alkane at
terminal position to produce alkylboronate esters, which are common reagents in organic
synthesis. They found that photochemical reaction of Cp*Fe(CO)2(BCat’) (Cp* = C5Me5,
Cat’ = 1,2,-O2C6H2-3,5-(CH3)2), Cp*Ru(CO)2(BCat’), and Cp*W(CO)3(BCat’) with a
series of alkanes gives alkylboronate esters with functionalization of alkane exclusively
at the terminal position (Figure 3). The boryl complexes are rare chemical reagents that
react selectively at the terminal position of alkane to provide simple functionalized
products. From their mechanistic analysis, they believe ligand dissociation is induced
photochemically and that thermal reaction of the resulting intermediate occurs with
alkanes. They pointed out that CpFe(CO)2(BCat) can functionalize arenes but not
alkanes, presumably because of the presence of spz—hybridized C-H bond in the Cp ring,
which is preferred to be fiinctionalized than alkanes. Therefore, they prepared a

derivative of this complex with the spz-hybridized position blocked to solve the problem.

Indeed, the elimination of all accessible sp2 positions on the metal boryl complex does
account for the unusual reactivity observed. Reaction with pentane gave l-pentylboronate
ester as the only functionalization product in 85% yield. Reaction with ethylcyclohexane
gave (2-cyclohexyl)-1-ethylboronate ester as the only functionalization product in 74%
yield. Interestingly, selectivity for the two terminal position of isopentane was good.
Functionalization at the less hindered position occurred in 55% yield, whereas

functionalization at the more hindered terminal position occurred in only 2% yield.

 

 

 

0C :4— /\/\ > MBCat' + HBCat'
M= Fe 28% ~ 10%
M = Ru 40% trace
hv M: /\/\/BCat'
85%
M OT O‘L
Q9 Me BCat'
och. MB, —— 74%
W 0

Me >

55% 2%
by O
t O-BCat'

22%

 

I \
BCat' +

 

 

Figure 3. Selective functionalization of alkanes by transition metal boryl complexes.

Hartwig et al.20 also examined the photochemical reaction of CpFe(CO)2(BCat) in
a variety of mono-substituted arene solvents including C6H5(Me), C6H5(OMe), C6H5(Cl),
C6H5(CF3), and C6H5(NMe2). They found the reaction of CpFe(CO)2(BCat) with
substituted arenes resulted in formation of only meta- and para—substituted arylboronate
esters for all substituted except anisole, which showed substantial amounts of ortho-
substituted product. For N,N-dimethylaniline, it showed a preference for reaction at the
para position.

In 1999, Iverson and Smith21 reported the first thermal, catalytic aromatic
borylation reaction to synthesize aryl boronic esters directly from arenes and
pinacolborane by pre-catalyst Cp*Ir(PMe3)(H)(BPin) (Figure 4). They demonstrated the

catalytic viability of equation 2 for the first time.

:fi‘

Ir ''''' I o
O I
17 mol/o Me3P/ \ BPin

 

CsHe+H' >CHBPin+ H
BP'” 150 °C,120h 6 5 2

53%

Figure 4. The first thermal, catalytic example of aromatic borylation reaction.

Ar-H * HBX2 --———- Ar-BX2 + H2 AH° ~- 3.1 kcal/mol (2)

The findings was discovered in investigating stoichiometric B-C bond formation
in reactions between Cp*Ir(PMe3)(Ph)(H) and HBPin in C6D6. They noticed the
substantial quantities of arylboron products were produced from catalytic solvent

activation.

Aside from methane-to-methanol conversion,22 catalytic C-H functionalizations
for unactivated hydrocarbons are extremely rare. Since applications of boronate esters in
Miyaura-Suzuki cross-coupling chemistry are expansive,23 the demonstration of catalytic
viability of equation 2 is significant.

Later in the same year, Chen and Hartwig24 reported catalytic, regiospecific end-
functionalization of alkanes by the rhenium complex, Cp*Re(CO)3, under photochemical
conditions. They suggested that the terminal boronate esters are kinetic products, and the
selective firnctionalization most likely results from a regiospecific reaction of the

rhenium bis-boryl complex with the alkane primary C-H bond (Figure 5).

0. ,0 2.4-5? 0 *Re co
:1: .343. + R-H ° p ( )3 : R-BPin + HBPin
Q Q hv, CO, 25°C

R = n-C5H11

 

Figure 5. Reaction of B2Pin2 in pentane catalyzed by Cp*Re(CO)3.

Synthetic Routes to Arylboronic Esters

The palladium-catalyzed cross-coupling reaction between organoboron
compounds and organic halides or tn'flates provides a powerful and general methodology
for the formation of C-C bonds. Arylboron reagents are typically synthesized in a
multistep process: (1) halogenations of arenes to form aryl halides, (2) treatment of aryl
halides with magnesium to generate their Grignard reagents, (3) reactions of Grignard

reagents with trialkyl borate to give final corresponding arylboronate esters. Miyaura et

al.25 have described a clever arylboronate ester synthesis where the generation of
Grignard and lithium reagents is avoided by using palladium catalysts to effect the
desired transformation from borane reagents and halogenated arenes. Since halogenated
arenes required for these approaches must be synthesized from hydrocarbon feedstock,

direct routes to the arylboron reagents from hydrocarbons are attractive (Figure 6).

 

[Traditional Method]
l X] M9 E“01:03
QH—{w wow»
Ether - MgX(OR)
[Miyaura et al.]
Q 1 X1 "Pd", BzPinz or HBPin, Base Q
H .___p X 1‘ BPin
DMSO

[ Direct Method I

catalyst
H + H-B(OR)2 H s B(OR)2
’ 2

Figure 6. Traditional and direct routes to arylboronic esters from aromatic hydrocarbons.

 

 

 

 

 

 

 

 

 

Several research groups26 including our group have achieved functionalization of
hydrocarbons using a borane as an approach in stoichiometric and catalytic reactions
under photochemical or thermal conditions. A milder reaction condition, higher turnover
number, more efficient system is desirable. Furthermore, Knochel27 and co-workers

recently reported the kinetic and thermodynamic aspects in OH bond activation by direct

10

borane-hydrocarbon dehydrogenation. On the basis of a better understanding of the role
of transition metal boryl complexes in the organic transformation reactions, our ultimate
goal is to develop a better catalytic system not only to activate but also functionalize

hydrocarbon C-H bonds to well utilize ubiquitous hydrocarbon feedstock.

11

CHAPTER 2
MECHANISTIC INVESTIGATION OF Cp*Ir(PMe3)(H)(BPin) CATALYZED

BORYLATION REACTIONS

Comparison between Cp*lr(PMe3)(H)(BPin) and Cp*Rh(n4-C6Me6) Pre—catalyst

Systems in Borylation of Various Substituted Arenes

In 1999, our group reported the first thermal, catalytic example of aromatic
borylation reactions to generate arylboronic esters directly from unactivated arenes and
boranes by pre-catalyst Cp*Ir(PMe3)(H)(BPin) (1, Cp* = nS-CsMes).2' Subsequently,
Hartwi g and co-workers reported alkane and arene borylations with the use of much more
reactive Rh pre-catalyst, such as Cp*Rh(n4-C6Me6) (3).26a Given the broad utility of
arylboronic esters in Pd-catalyzed cross-couplings with aryl and alkyl halides,23 we were
curious as to the extent of regioselectivity and functional group compatibility for
analogous transformations of substituted arenes.26b In an initial borylations of substituted
arenes, 20 mol% solutions of 1 or Cp*Ir(PMe3)(H)2 (2) were dissolved with HBPin in
neat arene solvents, and the reactions were run at 150 °C. Once borylation has
commenced, 31P NMR spectroscopy indicated that compound 1 is the predominant Ir
species in solution with small quantities of compound 2 present in each case. Analogous
borylations were also performed using the more active pre-catalyst 3. After the borane
was consumed, product ratios were determined by GC analysis of crude reaction
mixtures. Isolated yields of isomer mixtures are reported in Table 1, and the product

assignments were corroborated by comparisons to authentic samples.

12

Table 1. Isolated yields (based on HBPin) and isomer distributions for catalytic
borylation of aromatic hydrocarbons catalyzed by solutions of compounds 1 and 3.

 

Arene

Product(s)

% yield (parazmetawrtho),
time'I

% yield (parametazonho),
timeb

 

13.
:3

53, 120 he

92, 2.5 h“

 

:0
3
Q
Q

91 (33.9:62.0:4.1),e 51 h

72 (32.5:62.7:4.9),/ 3.5 h

 

I!
3
CD
I‘/‘
/
0
<31

99 (33.3:66.7:0.0), 17 h

84 (33.3:66.7:0.0), 1.5 h

 

PinB

I“
/
0
Z
0

55 (19.5:79.0:1.6), 65 h

65 (25.4:66.9:7.6), l h

 

PinB

I“
/
Z
Z
:3”

65 (42.9:54.9:2.1), 3.5 h

 

E
3
W
I“
/
0
I
3
Q
N

52 (31.1:68.0:0.9), 142 h

67 (33.2:66.l:0.7), 2 h

 

 

 

 

 

Pin

«A?

F3C F3 81,610h 86,3h
Q BPin
F3C F3
60,g 151 h 73,”4h
Pin
-- 41, 6 h
N/_\ N/ BPin
F F F F 81,’18h 41,/0.511
FQ~H FQBPM
F F F F
F -- 46,“ 0.5 h

 

 

NEt2
: 1O

 

 

| /
/
O

 

 

C :DEI Pine}, \ OEt -— --(33.0:57.4:9.6),’"1h
O _ O
PinB/x NEtz -- 50(14.0:27.7:58.3), 0.511

 

 

" 20 mol% 1, generated in situ from compound 2 and HBPin at 150 °C. b 2 mol% 3 at 150 °C. ‘ 20 mol% l
at 150 °C. d GC yield reported in reference 18c. ‘ < 1% of the isomer mixture is C6115CH2BPin. / 3% of the
isomer mixture is C6H5CH2BPin. 8 3% of the isolated product is m-C6H4(Me)(CH2BPin). hp 12% of the
product is m-C5H4(Me)(CH2BPin). ' 4% of the isolated product is isomers of C6F4H(BPin). ’ 16% of the
isolated product is isomers of C6F4H(BPin). " Reaction was run in a 2:1 mixture of 1,3,5-C6H3F3zp-xylene-
dlo. ’ C6HF3(BPin)2 (7%) and an isomer of C5H3F2(BPin) (6%). "' Products were not isolated.

13

In a simple assay of regioselectivity, toluene borylation primarily gave a statistical
distribution of m- and p-C6H4Me(BPin). In order to address the reversibility of the
borylation reactions, the catalytic borylation of C6D6 by HBPin in the presence of m-
C6H4Me(BPin) was examined. Isomerization of m-C6H4Me(BPin) to p-C6H4Me(BPin) or
generation of toluene would indicate that borylation is reversible. Under typical reaction
conditions where C6D6 is converted to C6D5BPin, m-C6H4Me(BPin) does not isomerize
and toluene is not eliminated. Thus, the borylation products are kinetically determined. It
is noteworthy that arene C-H bonds are functionalized in the presence of weaker benzylic
C-H bonds. A range of monosubstituted arenes was examined to determine whether
reaction conditions would tolerate heteroatom substituents and to assess the generality for
statistical meta/para substitution. The results in Table 1 indicate that meta/para ratios are
predominantly statistical with the largest deviations occurring for N,N-dimethylaniline,
which favors para substitution, and anisole, which favors meta substitution. For Rh-
catalyzed reactions, the deviations were relatively small, but meta borylation of anisole is
pronounced for Ir system. Since cumene gave a statistical distribution of meta and para
borylation products, electronic effects are responsible for enhanced para selectivity for
N,N—dimethylaniline. Benzylic activation of toluene increased for Rh (~3 % PhCH2BPin)
versus Ir (~1 % PhCH2BPin).

The aversion from borylation ortho to aromatic substituents suggested that
selective borylation should be possible for 1,3-disubstituted arenes. We initially
examined this possibility for 1,3-C6H4(CF3)2 and found exclusive borylation at the 5-
position in reactions catalyzed by solutions of 1 or 3. For the borylation of m-xylene

mediated by compound 3, benzylic activation increases significantly relative to that for

14

toluene. It appears that steric directing effects will extend to heterocycles as aromatic
borylation of 2,6-lutidine occurs exclusively at the 4-position. Directing effects based on
steric effects in aromatic substitution are uncommon, and electronic effects generally
dictate the substitution pattern. For example, in the Friedel-Crafis alkylation of 3-
chlorotoluene, no meta-substitution products are observed since Me group is an ortho-
and para-directing activator and Cl is an ortho- and para-directing deactivator.
Generally, selective meta functionalization is difficult and requires strong electron-
withdrawing groups for electrophilic or —donating groups for nucleophilic aromatic
substitution, respectively. The unique steric directing effect in aromatic borylation
provides a complementary mean for regioselective functionalization of aromatic
compounds.

Fluorinated arenes were also tested for compatibility. II- or Rh-catalyzed
borylation of C6HF5 gave C6F5BPin as the primary product. Similarly, compound 3
catalyzes borylation in a 2:1 mixture of 1,3,5-C6H3F3 and p-xylene-dlo to yield
C6H2F3BPin as the major product. Attempts to prepare the di- and triborated compounds,
CbHF3(BPin)2 and C6F3(BPin)3, from stoichiometric amounts of 1,3,5—C6H3F3 in p-
xylene-dm yielded significant quantities of C6H3F2(BPin) (~60% of the borylated
products). The selectivity for C-H activation is significant considering that Rh-catalyzed
reactions of silane with CoHFs give C-F activation products exclusively.28

For arenes bearing ester and amide functionality, reduction of the carbonyl groups
could potentially compete with aromatic borylation. Since HBPin reacts sluggishly in
uncatalyzed hydroborations, selective aromatic borylations of aryl esters and amides

seemed possible. Hence, catalytic borylations of ethyl benzoate and diethyl benzamide by

15

compound 3 were examined. In both instances, the reactions gave primarily aromatic
borylation. For ethyl benzoate, meta/para borylation dominates with a modest increase in
ortho borylation (p:m:o = 1.00:1.74:0.29), whereas diethyl benzamide gave 0-
C6H4(C(O)NEt2)(BPin) as the major isomer (p:m:o = 1.00:1.98:4.17). The shift in
substitution pattern is consistent with chelate-directed borylation at the ortho position.
Since resonance structure B has a larger contribution for an amide relative to an ester
(Figure 7), chelation of the amide oxygen to Rh or B in the catalytically active species is
more favorable for the amide. The statistical metazpara ratio for the minor isomers

suggests that chelate and sterically directed pathways compete.

ph E ‘——> Ph/NE a E = NEt2, OEt
A B

Figure 7. Resonance structures of ethyl benzoate and N,N-diethyl benzamide.

To probe the role of electronic effects, relative product ratios from catalytic
borylations in equimolar mixtures of substituted arenes were determined (Table 2).
Electron-deficient arenes are generally more reactive in both systems, and relative rate
differences for Ir are slightly more pronounced than those for Rh. Ir-catalyzed borylation
in neat N,N-dimethylaniline was extremely slow. Factors besides deactivation of the
arene ring may be responsible for the reduced reaction rate; such as, possible

coordination of the nitrogen lone-pair electrons of aniline to the Ir metal center, which

16

would block the active site around Ir. This may explain why cumene borylation in N,N—

dimethylaniline/cumene mixtures was suppressed relative to borylation in neat cumene.

Table 2. Relative ratios of arylboronic esters for borylations of equimolar mixtures of
substituted arenes catalyzed by compounds 2 and 3.

X—Q/YO XOBPin: Y_</'————\\/>8Pin

(Catalyzed by solutions of (Catalyzed by solutions of

 

 

 

 

 

 

 

2) 3)
x = C133, Y = CH3 89.0:11.0 73.0:270
x = OCH3, Y = CH3 62.0:38.0 51049.0
x = N(CH3)2, Y = CH3 -- 40.8:592
x = N(CH3)2, Y = CH(CH3)2 310690 40.1 :59.9

 

 

A comparison of pre-catalysts l and 3 in borylations of various substituted arenes
revealed that the Ir system was more selective toward arene C-H activation. Given the
importance of selectivity in chemical synthesis, these findings spurred a detailed

investigation of the original Ir system.

17

 

Metathesis Reactions between Cp*M(PMe3)(Ph)(H) (M = Ir, Rh) and Pinacolborane

in C6D6

Fundamental understanding of hydrocarbon activation by “Cp*M(PMe3)” (C p* =
C5Me5, M = Ir, Rh) has been studied extensively by Jones’ and Bergman’s research
groups. In the iridium system, Bergmanla and co-workers showed that, upon irradiation,
an excited state of Cp*Ir(PMeg)H2 is formed. This rapidly extrudes H2, and leaves behind
the reactive, coordinately unsaturated intermediate “Cp*Ir(PMe3)”. The intermediate
inserts into a C-H bond of R-H via a three-center transition state, and leads to the
formation of Cp*Ir(PMe3)(R)(H) complexes. At the same period of time, Jones and co-
workers studied the related rhodium complexeslb to determine the relative stabilities of
the Cp*Rh(PMe3)(Alkyl)(H) and Cp*Rh(PMe3)(Aryl)(H). They found a slight kinetic
preference for benzene over propane and overwhelming thermodynamic preference for
benzene oxidative addition. For the Cp*Rh(PMe3)(Ph)(H) (4) complex, a reversible
reductive elimination of benzene was found to occur at convenient rate upon heating to
~ 60 °C in C6D6 solvent, producing Cp*Rh(PMe3)(C6D5)(D). With a detailed picture of
transition metal mediated C-H activation established by several research groups, we
chose a Lewis acidic reagent, boranes, as an approach to convert activated alkyl and aryl
groups to functionalized organic products. Our initial proposed catalytic cycle is shown

below (Figure 8).

18

R—H + H—BXZ = R—BX2 + H2 AH°~-3.1kca|/mo|

 

R—H
HX, gar
M
/
M= Ir, Rh
M--.. M ......
/ '1”sz Me P/ IR
M°3P (III)\H 3 (|||)\H
H—ex2
H2 _ ¢ ,
M .....
/ "'H
M
93': (|'|)\H
H_BX2 R—BX2

Figure 8. Initial proposed catalytic cycle for catalytic functionalization of hydrocarbon

C-H bonds.

In the proposed catalytic cycle, the reactive unsaturated intermediate

“Cp*M(PMe3)” can activate the C-H bond of hydrocarbons to form Cp*Ir(PMe3)(R)(H).

Hopefully the metathesis reaction between HBX2 and Cp*Ir(PMe3)(R)(H) can release R-

BX2 and generate Cp*Ir(PMe3)H2. Then the dihydride complex can react further with

HBX2 to generate Cp*Ir(PMe3)(H)(BX2), followed by reductive elimination of HBX2 to

19

regenerate the reactive 16 electron intermediate “Cp*M(PMe3)” to complete the catalytic
cycle. In order to test the viability of this proposed catalytic cycle, the metathesis reaction
between Cp*M(PMe3)(Ph)(H) (M = Ir, Rh) and HBPin in C6D6 were examined. For the
reaction between Cp*Ir(PMe3)(Ph)(H) (5) and HBPin in C6D6 at 150 °C, after around
37% conversion (based on 1H NMR Spectra) from Cp*Ir(PMe3)(Ph)(H) to
Cp*lr(PMe3)(H)(BPin), the ratio between C6HsBPin and C6DsBPin was found to be

around 1:23 (Figure 9).

(a) .‘j Cp*Ir(PMe3)(Ph)(H) (5)
Cp*Ir(PMe3)(H)(BPin) (1) I

2.20 " ' 2.10" ' “2.00“ "1.90” 1.80" A 1.70

(b) ‘
.I
PthPin 5 PhBPin 5
'8.007 ”17.80 ' V 97.60 ' ' V7.40 ' '720 A A 7.00

Figure 9. The reaction between Cp*Ir(PMe3)(Ph)(H) (5) and HBPin in C6D6 at 150 °C
after around 37% conversion from Cp*Ir(PMe3)(Ph)(H) to Cp*lr(PMe3)(H)(BPin): (a) 1H

NMR spectrum of Cp* region; (b) 1H NMR spectrum of aromatic region.

20

Substantial quantities of arylboron products were produced from catalytic solvent
activation. Hence, we conclude that catalytic borylation is much faster than metathesis
reaction between compound 5 and HBPin in C6D6, even though the metathesis process is

viable (Figure 10).

¥ CsHsBPln ! HBPin H2 g
I
Ira. - Ir ''''' 3.4 1. ll' """ I '
1., + __Z__. "H / BPIn
Me3P/ \HcfiHS HBP'” Me3P/ \ Meal” \H
H

(5) (1)
Figure 10. The metathesis reaction between compound 5 and HBPin in C6D6 at 150 °C.

Thermal borane elimination from Cp*Ir(PMe3)(H)(BPin) (1) was assessed by
heating C6D6 solution of the pure compounds. After two weeks at 200 °C and one day at
280 °C, the formation of C6D5BPin was not detected (Figure 11). If HBPin is reductively
eliminated from compound 1, the reactive intermediate “Cp*Ir(PMe3)” can activate C-D
bond of C6D6 to form Cp*Ir(PMe3)(C6D5)(D), which can react further with HBPin
through metathesis process to generate C6D5BPin. Since only small quantities of
Cp*Ir(PMe3)(C6D5)(D) (6) were generated in the reaction afier prolonged thermolysis,
the HBPin reductive elimination pathway is not kinetically competent to account for
catalysis. Therefore, a pathway involving HBPin reductive elimination to generate an
active catalyst can be eliminated. The final 1H NMR and 3 1P NMR spectra of the reaction
are shown in Figure 12. The moderate quantities of BPin-O-BPin observed may result

from the reaction between trace moisture and HBPin.

21

 

g12 2 weeks 1 day
+ excess CSDB > 280 °C A’ XCstBPIn

lr"'u, '
/ BP'" 200 °c

 

M83P
(1) H
2 /|r""IIBPin + "H20" 7‘ 2 /|r""uH + PinB—O—Bpln
Me3P \ M63P \
H H
(1) (2)

Figure 11. Thermolysis of Cp*Ir(PMe3)(H)(BPin) (l) in C6D6.

BPin-(l) BPin-O-BPin

Cp*-(1) and Cp*-(2)
PMe3-(1) \
lHNMR
.' PMe3-(2) '
‘ Cp*-(6) ~ I
» 1 II
9: K2 A U. ‘1 ’L ‘1 22 . -
2.40 I I 2.20 T "2.00“ ‘ 1.80 ”001.6? "TKO ' “1.20 ‘ 1.00
I
3'P NMR f (1)
I,
l *1 (2)

<6) :
I '-
WW‘WWWWWUWLLENVIW‘MWW: . , ; ,WWWWWWW
-38 -39 -40 -41 -42 ~43 -44 -45 -46 -47 -48 -49
Figure 12. 1H NMR and 3|P{'H} NMR spectra of the thermolysis of compound 1 in

C6D6.

22

The analogous reaction in the Rh system was also examined. Benzene reductive
elimination from Cp*Rh(PMe3)(Ph)(H) (4) occurred before metathesis reaction took
place. In the reaction of compound 4 with HBPin in C6D6 at elevated temperature,
compound 4 reductively eliminated C6H6, followed by oxidative addition of HBPin to
form Cp*Rh(PMe3)(H)(BPin) (7) (Figure 13).

Simplified rate expressions can be derived by applying the steady-state
approximation. Application of the steady-state approximation to Figure 13 gives the rate

law and kobs expression shown in Equations 3 and 4.

h'n,” = Rh ———-> Rh-u,” .
Me3P/ \ CGH5 k4 Me3P/ HBPin MegP/ \ BP'“
H H
+
4 [7]
l l CeHs

Figure 13. The reaction of compound 4 with HBPin in C6D6 at elevated temperature.

- dl4]
dt

 

= k... [4] <3)

MkflHBPM]
k_1[CSH6] ""' k2[HBPIn] (4)

 

kobs

hkflHBPm]

1f k-1[CeH6] >> K2[HBPIn] kObS = k_1[CGH6] (5)

 

23

If k-1[C6H6] >> k2[H;BPin], kob, is expected to exhibit a first order dependence on
[HBPin] as shown in equation 5. This is indeed the case as shown in Figure 14. The
kinetic data are consistent with this proposed rate law. The kobs was measured from 65 to
115 °C, and activation parameters were determined from the temperature dependence of
kobs. From the Eyring plot (Figure 15) over this temperature range, activation parameters
were obtained: AH“t = 25.6 kcal/mol and AS: = -5.3 e.u. For a comparison, Jones and co-
workers found that a reversible reductive elimination of benzene from compound 4 in
C6D6 solvent at ~60 °C to form Cp*Rh(PMe3)(C6D5)(D) followed first-order kinetics
over a 46-degree temperature range. From the Eyring plot of the first—order rate
constants, they obtained the activation parameters for arene loss: AHI = 30.5 (8) kcal/mol
and AS: = 14.9 (2.5) e.u. They stated that the positive value for the entropy of activation
is consistent with the formation of an intact, dissociating benzene molecule in the
transition state.29 In the reaction of compound 4 with HBPin in C6D6, the small negative
value for the entropy of activation suggests that the transition state of the reaction is more
ordered than the ground state. From the activation parameters established by Jones and
co-workers, the kobs for benzene elimination at 75 °C is calculated to be 6.98 x 104 s'1 and
the kobs for the reaction of compound 4 with IIBPin in C6D6 at 75 °C is 5 x 10'5 5“. Since
the overall rate kobs for the reaction of compound 4 with HBPin at 75 °C (5 x 10'5 s") is
smaller than kobs for benzene elimination at 75 °C (6.98 x 10“1 s"), the rate determining
step must involve a process other than benzene elimination. This piece of evidence

suggests that H-B activation is the rate-determining step in this reaction.

24

 

 
    
    
 

y = -0.0003X + 0.0015

R2 = 0.9994
-15 _ 1.103 M

|n(l4]1/l4]o)

y = —0.0006x - 0.0276
R2 = 0.9942

 

 

 

'5 T I I I I I I

0 1000 2000 3000 4000 5000 6000 7000 8000

time (s)

Figure 14. Plot of ln([4]t/[4]o) vs. time (s) for the reaction of compound 4 with [HBPin] =

0.551 M and [HBPin] = 1.103 M in C6D6 at 95 °C, respectively.

25

 

L.
o

L.
N

 

ln(kobs/T)
i;

y = -12881x+ 21.102

 

 

-16
R2=0.9963
-18
0.0025 0.0026 0.0027 0.0028 0.0029
1rr

Figure 15. Eyring plot for the reaction of compound 4 with HBPin in C6D6. ([4]o = 0.046
M; [HBPin]O = 0.551 M; T = 338.15 to 388.15 K, AH: = 25.6 kcal/mol and A81: -5.3

e.u.).

Mechanistic Studies of The Original Iridium System

Compound 1 was stable in benzene solution after prolonged thermolysis, which
excludes the pathway involving the elimination of HBPin from Cp*Ir(PMe3)(H)(BPin)
(1). Regarding the possibility of PMe3 dissociation pathway to generate Cp*Ir(H)(BPin),
an analog of Hartwig’s proposed intermediate in the Rh system,268 we designed a pseudo
double—labeling crossover experiment to probe the PMe3 dissociation pathway. Two
labeled complexes Cp*Ir(P(CD3)3)(H)2 (8) and (C5Me4Et)Ir(PMe3)(H)2 (9) were

prepared. If phosphine does dissociate from Cp*Ir(PMe3)(H)(BPin), we expect to see the

26

two crossover products, Cp*Ir(PMe3)(H)2 (2) and (C5Me4Et)Ir(P(CD3)3)(H)2 (10) (Figure

16). Surprisingly, those iridium complexes can be easily quantified by GC-MS (Figure

17).
;CH3 gCH3
: Il : lI ' lI : ll
r ””””” + r"-a = I"... + r"-.,
/ ”H / "'H / "’H / "H
(0301313 \H MeaP \H (0301313 H MeaP \
H

(8) (9) (8) (9)

crossover products >_:<CH3
: l t I

Ir ----- + Ir .....
/ "H "H

Me3P (DaC)3P/
(2) H (10) H

 

 

 

 

Figure 16. Potential crossover products from pseudo double-labeling crossover

experiment.

27

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28

Benzene borylation with pinacolborane in the presence of 10 mol% of compound
8 and 10 mol% of compound 9 was carried out (Figure 18). The reaction proceeded
smoothly to generate C6H5BPin and H2 as products. From the chromatogram of the crude
mixture (Figure 19) there was no crossover products observed. Crossover during catalytic

borylation was minimal. Therefore, phosphine dissociation pathway is unlikely.

10 mol% 8 and 10 mol% 9 .
HBPin + CBHB 150 °C ~* CeHsBPm + H2

 

Figure 18. Pseudo double-labeling crossover experiment.

29

 

 

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31

However, added PMe3 strongly inhibited catalysis where HBPin was present. The
finding raised possibility that small quantities of phosphine free Irv species could be
active. Cp*IrH4-x(BPin)x species30 (where x = 1, 2) formed in the thermolysis of Cp*IrH4
(11) and HBPin and Cp*Ir(H)2(BPin)2 (12) are Ir analogs of other intermediates proposed
by Hartwi g in the Rh system. Anisole borylation with 20 mol% loadings of compound 11
and 1 were compared (Figure 20). The isomer ratios for 11, o:m:p = 3:49:48; for 1, 03171:}?
= 2:79:19. From this experiment, Cp*IrH4-x(BPin)x intermediates could be eliminated

because the borylation regioselectivities for 11 and 1 differed substantially.

 

OMe + HBP' = 2
'" 150°C

o:m:p=2:79:19

 

20 mol% 11 PinB®OM H
+ ' 3 e *
Q—OMe HBPII‘I 150 °C 2

o:m:p=3z49248

Figure 20. Borylation reactions of anisole with 20 mol% loading of compound 1 and

compound 11, respectively.

Exclusion of a simple phosphine dissociative pathway narrows the plausible
catalysts to two choices: (1) Ir phosphine species arising from Cp* loss or (2) species
where both Cp* and PMe3 have been lost. The latter possibility is intriguing in light of

Marder’s synthesis of (116-arene)1r(BCat)3 complexes (where Cat = ortho-catecholate)

from (Ind)Ir(COD) (13, where Ind = nS-C9H7, COD = 1,5-cyclooctadiene) and HBC at in

32

arene solvents.31 Using an analogous route, we prepared (MesH)Ir(BPin)3 (14, where
MesH = 116-mesitylene) in 19% yield from compound 13 and HBPin in mesitylene
solvent?“ Single crystals of 14 were grown from pentane at —30 °C and the structure was
further confirmed by single—crystal X-ray crystallographic analysis. The molecular
structure of 14 is shown in Figure 21 and the distance from Ir(1) to the center of the

mesitylene ring is 1.880 A.

 

Figure 21. ORTEP diagram of (MesH)Ir(BPin)3 (14). Thermal ellipsoids are shown at

25% probability.

33

Table 3. Selected bond lengths [Al and angles [°] for 14.

 

Bond Distance [A] Bonds Angle [°]
Ir(1)—B(1) 2.051(1) B(1)-Ir(1)-B(2) 80.6(4)
Ir(1)-B(2) 2.021(1) B(1)-Ir(1)—B(3) 81.7(4)
Ir(1)—B(3) 2.039(1) B(2)-Ir(1)-B(3) 83.8(4)

 

Compound 14 reacts with benzene at 150 °C to produce Ir metal and three
equivalents of C6H5BPin, but it does not catalyze C6H5BPin formation from benzene and
HBPin. Thus, it appears that phosphines or related donor ligands are required for
catalysis. Using the lability of the mesitylene ligand in 14, Ir phosphine species can be
generated in situ from 14 and appropriate phosphines. Borylation of benzene with the use
of 2 mol% 14 and 4 mol% PMe3 was found to be a viable pre-catalyst for aromatic

borylation reactions (Figure 22).

2 mol% 14, 4 mol% PMe3
CeHe + HBPin = C5H5BPin + H2

150 ° , 15 h
C 98% 60 yield

 

Figure 22. Benzene borylation with HBPin catalyzed by 2 mol% l4 and 4 mol% PMe3.

From the experiments discussed previously, we ruled out a H-B elimination
pathway, PM63 dissociation pathway, and a pathway where the active species is
generated from both Cp* and PMe3 loss. The remaining candidates for active species are
iridium phosphine boryl complexes. Syntheses of some model complexes to examine

their stoichiometric reactions with arenes and screening for different metal complexes

34

and ligands combination for catalysis would hopefully help to determine the identity of
the active species and understand the mechanism of the aromatic borylation in this
system.

In this chapter, through detailed mechanistic studies of the original Ir pre-catalyst

system, we suggest that active species are iridium phosphine boryl complexes.

35

CHAPTER 3

CATALYTIC BORYLATION REACTIONS OF AROMATIC COMPOUNDS

Screenings of Phosphine Ligands, Other Donor Ligands, and Metal Complexes for
Catalytic Benzene Borylation

From mechanistic investigation of the initial Cp*Ir(PMe3)(H)(BPin) (1) pre—
catalyst system, it was found that the use of 2 mol% (MesH)Ir(BPin)3 (14) and 4 mol%
PMe3 was a viable pre-catalyst for aromatic borylation reactions. The low isolated yield
of 14 hampered screening efforts and precluded practical applications despite dramatic
improvement in catalytic activity. Hence, we sought alternative means for generating
active catalysts. Because NMR indicated virtually quantitative generation of 14 from
(Ind)Ir(COD) (13), in situ generation of active catalysts by phosphine addition to 13 was
examined.32 This approach was successful and we were able to conduct systematic
studies of the effects of different phosphine ligands, various donor ligands, and metal
complexes on catalytic activity.

First, as shown in Table 4 different ratios between PMe3 and “Ir” were examined
for catalytic activity. The results showed that borylation rates were appreciable when
[P]:[Ir] < 3:1 but decreased dramatically when [P]:[Ir] ratio equaled or exceeded 3:1
(Entries 2-5). Several other mono-dentate phosphine ligands including PEt3, P’Pr3, P'Bu3,
PCy3, and PPh3 were also tested as ligands for the catalytic borylation of benzene giving

moderate GC yields (Entries 6-10).

36

 

2 mol% 13 or 14, x mol% PR3
+ HBPin > Qapm + H2
150 °C

Table 4. Summary of borylation of benzene with HBPin in the presence of 2 mol% pre-
catalyst at 150 °C.33

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Entry Pre-catalyst [P]:[Ir] Ratio Reaction Time (h) Y(‘l’./eol)d
1 P112; 21 15 98
2 P152; 1 :1 5 87
3 Flt/1:3 2:1 18 87
4 Flt/1:3 3:1 57 0.4
5 Flt/1:3 4:1 20 O
6 1311;} 2: l 13 79
7 P3113 2:1 93 80
8 P’IBA‘U3 2:1 21 71
9 PC; 21 46 79

10 Pi>i13 2:1 58 69

 

 

 

Reactions run in neat benzene. GC yields based on HBPin.

In addition to mono—dentate phosphine ligands, chelating bidentate phosphine

ligands were examined (Table 5). A dramatic increase in catalytic activity and turnover

numbers were observed for the bidentate phosphines.

37

n

2 mol% 13, 2 mol% RZP

 

PR2
9: <::>8-BP01 + H2
A

Table 5. Borylation reaction of benzene with HBPin in the presence of 2 mol% 13 and 2
mol% chelating phosphine ligand.33

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

. Pre-catalyst Temperature Reaction Time Yield
Entry L'gand Loading (°C) (h) (%)
1 thP PPh2 2 mol% 150 2 95
//\
2 thp PPh2 2 mol% 150 16 87
/\
3 "I192P PMez 2 mol% 150 3 79
4 MezP PMe2 2 mol% 150 2 84*
5 CY2P PCY2 2 mol% 150 3 86
6 Q 2 mol% 150 0.8 78
PhZP PPh2
7 Ph2P Pth 2 mol% 100 7 88
/\
8 MezF’ PMez 2 mol% 100 77 18
9 M6213 PMez 2 m0]% 100 31 96
10 Csz PCy2 2 mol% 100 96 86
/_\
11 MezP PMez 0.2 mol% 150 9 85*
12 MezP PMe2 0.02 mol% 150 61 9O

 

Reactions run in neat benzene. GC yields based on HBPin.*Isolated yield.

Chelating phosphines as ligands substantially increased catalytic activity and

TONS as highlighted for 1,2-bis(dimethylphosphino)ethane (dmpe) (Entry 12), where the

effective TON of 4500 represents an improvement of more than 1000-fold over pre-

catalyst Cp*Ir(PMeg)(H)(BPin) (1). Furthermore, the borylation reactions can be run at

38

 

100 °C with a reasonable rate by using 1,2-bis(diphenylphosphino)ethane (dppe) as the
ligand (Entry 7).
Besides phosphorous containing ligands, nitrogen, oxygen, and sulfur containing

ligands were also screened for catalytic activity as shown in Table 6.

2 mol% 13, 2 mol%X

x
Q + HBPin A = Q—BPin + H2

Table 6. Borylation reaction of benzene with HBPin (0.7 M) in the presence of 2 mol%

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

13 and nitrogen, oxygen, or sulfur containing 1i ands.
. Ligand Temperature Reaction Yield
Entry L'gand Loading (°C) Time (h) (%)
N
1 l \ 4 mol% 100 31 69
/
S
2 (\ /7 4 mol% 150 15 8
IT N
3 M 2 mol% 150 0.2 85
—N N—
4 /_‘ ’_\ 2mol% 150 <1 85
5 MezNUNMez 2 mol% 150 6 52
(We
6 2 mol% 150 14 1 1
0M9
7 /0\/\O/ 2 mol% 150 14 7
8 2 mol% 150 1 6
9 2 mol% 150 2.7 73
10 2 mol% 150 16.3 66
11 2 mol% 100 1.5 86

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Pre-catalyst Temperature Reaction Yield
Entry Pre'cata'y“ Loadigg (°C) Time (b) (0/0)
12 2 mol% 100 1 82
13 _ _ 2 mol% 100 1 84
N N
14 / \ / \ 2 mol% 50 16 85

 

 

 

 

 

 

 

 

Reactions run in neat benzene. GC yields based on HBPin.

2,2’-bipyridine (bpy), 1,10-phenanthroline, 4,4’-di-tert-butyl-2,2’-bipyn'dine
(dtbpy)26f were found to be good ligands for borylation (Entries 3, 4, 11, 12, and 13). For
bpy, the borylation occurred at relatively low temperature (50 °C) at an appreciable rate,
and good yield (Entry 14, 85% yield). Attempts to reduce pre-catalyst loading to 0.02
mol% yielded significant quantities of decomposition and PinB-O-BPin. The use of
thiophene, veratrole, DME, and 2,2’-bithiophene were inefficient as ligands for
borylation of benzene (Entries 2, 6, 7, and 8). Ligands containing both ”hard” N and
“soft” P were also examined (Entries 9 and 10). Catalysts containing 2—
(diphenylphosphino)-2’-(N,N-dimethylamino)biphenyl and 2-(dicyclohexylphosphino)-
2’—(N,N-dimethylamino)biphenyl did not exhibit any advantages in catalysis over
chelating phosphine ligands, dppe and dmpe, or chelating nitrogen ligands, bpy, 1,10-
phenanthroline, and dtbpy. N,N,N,N-tetramethylethylenediamine (TMEDA) performed
marginally as a ligand (Entry 5, 52% yield).

Besides 13, different metal complex precursors were investigated. Since the
approach where we generated active catalysts in situ from (Ind)Ir(COD) (13) and

phosphine ligands was successful, we were interested if the active catalysts can be

40

generated in situ from the precursor [Ir(COD)Cl]2, which is the starting material for the
preparation of 13, or even IrC13-xH20. In addition, some of the related Rh complexes

were also screened for catalysis. The results are summarized in Table 7.

 

1 or 2 mol% "M", 2 mol% fl .
+ HBPin 4' BP'” " “2
A

Table 7. Borylation of benzene with HBPin in the presence of various metal precursors
(M) and ligands.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Entry Pre-catalyst Pizzjtflgfi Tempeglture Reactig; Time Yzzlp
o

1 “32.22% 3 3
o

2 33 33
o
. o

4 ”€33.33” 33 3
o

s ”magpie: 33 -—
o

6 (“33.2% 33 3
o

v “(2.33% 33 33

 

 

Reactions run in neat benzene. GC yields based on HBPin.

[Ir(COD)C1]z is an air-stable, commercially available iridium(I) compound and
has been demonstrated to be a good catalyst system in conjunction with dmpe,33 bpy or
dtbpy (Entries 1, 2, and 3).34 In contrast, IrCl3°xH20 and [Rh(COD)Cl]2 were poor metal
precursors for catalytic borylation (Entries 4, 5, 6 and 7), and no borylation occurred for

the [Rh(COD)Cl]2/dppe pre-catalyst system after 15 hours at 100 °C (Entry 5).

41

Borylation of Substituted Benzenes

. . . . . . . 23
S1nce applications of boronate esters 1n cross-couplmg chem1stry are extenswe,

a convenient way to expand the library of boronate esters is desired. With this goal in

mind, borylations of a variety of arenes were carried out. The results are summarized in

Table 8.

Table 8. Ir-catalyzed aromatic borylations. Reactions are run in neat arene, [1r] = 2

 

 

 

 

 

 

 

 

 

 

 

 

mol%, [P]:[Ir] = 2: 1, and yields are reported for isolated materials.33
. . Temp Time Yield
Entry Substrate Product Arene.HBP1n Catalyst QCL (h) (°/o)
1 O‘F /_E F 10:1 13/dppe 100 17 84
BPin
2 00' /__§ Cl 10:1 13/dppe 100 17 83
BPin
3 Oar /_\\ Br 10:1 13/dppe 100 17 90
BPin
4 O, -- 10:1 l3/dppe 100 60 --
5 O" Q‘l 10:1 l4/dppe 100 57 77
BPin
B F B F
6 r O ' Q 4:1 l3/dppe 100 14 81
BPin
F F
7 OF FQBPin 4:1 13/dmpe 150 1 63
F F
F PinB F
8 CF F—QBPin 1:5 13/dmpe 150 62 76
F PinB F

 

 

 

 

 

 

42

 

 

Temp Time Yield

Entry Substrate Product ArenezllBPm Catalyst (°C) (h) (o/o)

 

cu
BPin 1:1.5 l3/dppe 100 14 89
c

 

 

11

c:
CIE
Br Br

10 Q DBPM 1:1.5 l3/dppe 100 17 92
Br Br

BPin

 

Me Mei—QM? 12:1 l3/dmpe 150 112 68
Cl

12 Q CI~Q~CI 4:1 l3/dmpe 150 39 76

 

CD

Me
CI
BPin
33 QM

pmaQMe 12:1 13/dmpe 150 10 85
Me Me

 

14 Q0 PinB‘QCI 9:1 l3/dmpe 150 12 98
Cl

 

Cl
15* Q0149 PinBQOMe 1:3 13/dmpe 150 95 62
OMe OMe

 

 

 

 

 

 

 

 

 

 

Isolated yields based on HBPin. *Reaction run in cyclohexane.
13: (Ind)Ir(COD); 14: (MesH)Ir(BPin)3; dppe: 1,2-bis(diphenylphosphino)ethane; dmpe:
1 ,2-bis(dimethylphosphino)ethane.

Dramatic differences in chemoselectivities between Ir and Rh catalysts were
found for halogenated substrates, where the Ir catalysts preferentially activate C-H bonds.
Thus, good yields of mono- or triborated products of 1,3,5-trifluorobenzene were
obtained by adjusting the arenezHBPin ratio (Entries 7 and 8). In contrast, previous

attempts to effect multiple borylations of 1,3,5-trifluorobenzene with the use of Rh

catalysts 3 led to increased defluorination.26b Ir-catalyzed borylations of 1,3-

43

 

dichlorobenzene and 1,3-dibromobenzene generate meta-functionalized products in high
yields (Entries 9 and 10), whereas dehalogenation is the dominant pathway in Rh-
catalyzed reactions.35 A dramatic example of the difference between Rh- and Ir-catalyzed
borylation is shown in Figure 23 where the GC chromatograms of 1,3-dichlorobenzene
borylations catalyzed by a Rh pre-catalyst and catalyzed by a Ir pre-catalyst are
compared. In the Rh-catalyzed borylation, dechloronation is a competitive side reaction
pathway; on the contrary, in the Ir-catalyzed borylation a clean single product was
obtained. The finding that aromatic C-Br bonds survive in the Ir-catalyzed reactions
contrasts Pd-catalyzed reactions of boranes and aryl bromides, where the C-Br bonds are
converted to C-B or C-H bonds.36 Because aryl iodides have the weakest carbon-halogen
bonds, they are susceptible to reductive cleavage by transition metals. Hence it is not
surprising that the Ir catalysts generated from 13 are ineffective for the aromatic
borylation of iodobenzene (Entry 4). However, iodobenzene and HBPin reacted smoothly
to yield a mixture of C6H4(I)(BPin) isomers when active catalysts are generated from the
Ir"I source, (MesH)Ir(BPin)3 (14), and dppe (Entry 5). With the success in borylating
iodobenzene, Ir catalysts have been shown to be compatible with the entire range of aryl
halides.33 We also demonstrated that cyclohexane can function as an inert solvent (Entry
15), which is useful in borylations of more valuable substrates.

Ir catalysts selectively borylate symmetrical 1,2-disubstituted arenes including 0-
xylene, 1,2-dichlorobenzene, and veratrole at the 4-position to give a single borylation
product (Entries 13, 14, and 15). Symmetrical 1,4-disubstituted arenes can also be
selectively borylated at the 2-position (Entries 11 and 12). Borylations of 1,4-

disubstituted arenes proceed slower than the corresponding 1,2- and 1,3-disubstituted

arenes presumably due to steric bulkiness of the two substituents in 1,4-disubstituted
arenes. Attempts to borylate 1,3,5-trichlorobenzene led to unidentified decomposition
species and PinB-O-BPin. Borylation of 1,4-C6H4(Br)(F) occurred selectively at the
postion ortho to F most likely due to the different steric bulkiness between Br and F

(Entry 6).

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Steric, Electronic, and Directing Effects in Aromatic Borylation

From previous studies as shown in Table 8, borylations of symmetrical 1,2- and
1,4-disubstituted arenes give a single borylation product. In order to study the roles of
steric and electronic effects on the selectivity for the borylation reactions, borylations of
unsymmetrical 1,2- and 1,4-disubstituted arenes were compared. The results are

summarized in Table 9.

Table 9. Borylations of unsymmetrical 1,2- and 1,4-disubstituted arenes with HBPin in
the presence of 2 mol% l3 and 2 mol% dmpe. Reactions run in neat arene, and yields are
reported for isolated materials.

 

 

 

 

 

 

 

 

 

 

Entry Substrate Product Distribution (°/o)* T839 22;!
F I F |
l F3C‘O—Cl 3C C 30 C 5 78
PinB BPin
11.82882
2 MeOOF MeO F MeO F 23 62
PinB BPin
66:93.4
3 MeOOCI MeO CI MeO Cl 23 62
PinB BPin
68.0:32.0
4 00m Cl Me Cl Me 44 88
PinB BPin
43.5:56.5

 

48

 

 

 

 

 

Entry Substrate Product Distribution (°/o)* Time “em
(11) (%)
5 QCI PinBQ—OMe PinB—Q01 12 73
OMe 9' OMe
48.52515
6 GM PinBQ—OMe PinBQMe 12 77
OMe Me 0M8
36.3:63.7
7 QM PinBQMe PinBQCI 16 89
Cl 0' Me
62.2:37.8

 

 

 

 

 

 

 

* The product distribution was determined from the area ratio of each isomer in the GC chromatogram of
the crude reaction mixture. One of the products from borylation of an unsymmetrical 1,2- or 1.4-
disubstituted arene was independently synthesized according to the literature.25

Calculated ligand repulsive energies, ER, have been demonstrated in White and
co-workers report37 to provide reliable steric parameters for ligands in organometallic
systems. ER is defined as the amount of pure steric repulsion between a ligand and the
prototypical molecular fragment to which it is bonded [Cr(CO)5] or [CpRh(CO)]. Other
parameters such as Taft-Dubois steric parameter, B’s, and A-values38 are used as standard
measures of steric effects in organic chemistry. However, the experimentally based
measures, B’s and A-values, are a product of both steric and electronic effects. Therefore,
ER values are applied here in order to assess the pure steric effect on borylation reactions.

Selected ER values and A-values are listed in Table 10.

49

Table 10. Ligand repulsive energies (in kcal/mol) computed using the universal force
field and A-values (in kcal/mol) for a variety of organic substituents.

 

 

 

 

 

 

Substituent ER (kcal/mol) A-value (kcal/mol)
F 0.28 0.25
Cl 1 0.53
Me 18 1 .74
OMe 37 0.75
CF3 44 2.5

 

 

 

 

 

If only steric effects are considered, we can calculate and predict the isomer
distribution for borylation of unsymmetrical 1,4-disubstituted arenes and compare that to
experimental data. Since, for a 1,4-disubstituted arene, both substituents have two ortho
sites, the calculated isomer distribution ratio can be determined by using the relative ER
values of the two different substituents. For present purposes, it was assumed that ortho
substitution would preferably occur adjacent to the substituent with the smaller steric
factor (ER). For example, the ER value for CF3 group is 44 and the ER value for C1 is 1;
therefore, the isomer distribution for 1,4-C6H4(Cl)(CF3) borylation is expected to be 1:44
(22:97.8) for 1,3,4-C6H3(Cl)(BPin)(CF3) to 1,2,4-C6H3(Cl)(BPin)(CF3) on the basis of
ER values as illustrated in Figure 24. The result differs from the experimental value of
11.82882 (Entry 1). Apparently, other factors are also involved in determining the isomer
distribution. In order to determine if a trend exists for various unsymmetrically 1,4-
disubstituted arenes, their borylation chemistry was investigated. The comparison of

isomer distribution between the experimental values and the calculated values derived

50

from ER values for other unsymmetrical 1,4-disubstituted arenes are summarized in Table

11.

F3C-Q'Cl

ER value: 44 (CF3) 1 (Cl)

substitution ortho to CF3 substitution ortho to Cl

F3C Cl F3C CI
PinB BPin
Expected ratio: 1 : 44
= 2.2% : 97.8%

Figure 24. The calculated value of isomer distribution of the borylation of 1,4-

C6H4(C1)(CF3)-

51

Table 11. Comparison of isomer distribution between the experimental values and the
calculated values derived from pure steric effect (ER).

 

 

 

 

 

. 0 Calculated
Entry Substrate Isomer erture(Ai) (from ER) (0/0)
I .
1 F3C2©LC PinB BPin 2.2.97.8
11.8:882
MeO F MeO F
M o F ’
2 e «0 PM BPin 0.8.99.2
66:93.4
MeO CI MeO Cl
M 0 Cl '
3 e O. PinB BPin 2.6.97.4
68.01320
(:1 Me CI Me
Cl M '
4 ® 8 PinB BPin 94'7'5'3
43.5:56.5

 

 

 

 

 

 

The data summarized above suggest that the electronic effects and other effects
such as chelate—directed effects of substituents also contribute to the resulting isomer
distributions. It was therefore seemed of interest to evaluate borylations of unsymmetrical
1,2-disubstituted arenes to assess the electronic effects of substituents for these aromatic
borylation reactions. In order to obtain a qualitative understanding of electronic effects,
the experimental data are compared to the calculated isomer distribution data, which are

derived from the selectivities observed in borylation of mono-substituted arenes (Table

12).

52

Table 12. Borylations of mono-substituted arenes with HBPin in the presence of 2 mol%
13 and 2 mol% dmpe. Reactions run in neat arene. Isomer distribution is obtained from
area ratios in GC-FID chromatograms.

 

Isomer Distribution Selectivity
(garazmetamrtho) (°/o) (parametazortho) (“/o)

P' B
QOMe m GOMe 19.1:76.0:5.0 3211638242

P. B /

O—Me m ><:\>_Me 31.6:67.1:1.3 48.1:51.0:1.0
P'nB ,

Om ' QC. 23.1:76.9:0.0 37.5:62.5:0.0

Arene Products

 

 

 

 

 

 

 

 

 

The isomer distribution of borylation of each substrate including anisole, toluene,
and chlorobenzene is determined from the area ratio of each isomer in the GC
chromatogram. For present purposes, it was assumed that the response factors were
similar because the molecules are isomers. Therefore, we deemed it unnecessary to make
calibration curves for these screening experiments. In each mono-substituted arene,
borylation can occur at either of two meta positions, two ortho positions, and one para
position. The reported selectivities are obtained by dividing the GC isomer distribution
for each isomer by the potential number of sites of borylation (e.g. for meta position
divide by 2). Then the selectivity of para substitution is normalized to 1.00, and meta and
ortho selectivities are based on the normalized value. For example, for anisole borylation
the selectivity for parazmetazortho is 1.00:1.99:O.13 (= 32.1:63.8:42) and for
chlorobenzene borylation the selectivity for para:meta:ortho is 1.00:1.67:0.00 (=
37.5:62.5:0.0). The method for calculating the estimated value of isomer distribution for
unsymmetrical 1,2-disubstituted arenes is illustrated for the borylation of 2-chloroanisole

(Figure 25). For isomer (A), the borylation occurs at the position meta to Cl and para to

53

OMe group, the estimated selectivity for isomer (A) is the sum of the two normalized
selectivities of the mono-substituted arenes (1.67 and 1.00). For isomer (B), the
borylation occurs at the position meta to OMe group and para to C1, the estimated
selectivity for isomer (B) is the sum of the two normalized selectivities of the mono-
substituted arenes (1.99 and 1.00). The estimated selectivity for borylation of 2-

chloroanisole is obtained as 2.67:2.99, which is equal to 47.2:52.8.

PinB. : :Cl 3:0
OMe PinB OMe

(A) (B)

 

 

1,67 (meta to Cl) 1.99 (meta to OMe)
+ 1.00 (para to OMe) + 1.00 (para to Cl)
2.67 2.99

(A):(B) = 2.67:2.99 = 47.2%:52.8%.

Figure 25. The estimated value of isomer distribution of the borylation of 2-

chloroanisole.

54

Table 13. Comparison of isomer distribution between the experimental values and the
estimated values derived from selectivity in borylation of mono-substituted arenes.

 

 

 

 

 

 

 

 

 

. Observed Estimated
Entry Substrate Isomer Mixture (%) (°/o)
1 Q0 PinB OMe PinB CI 48.5:51.5 47.2:528
OMe Cl OMe
2 QMe PinBQOMe PinBQMe 36.3:63.7 40.8:592
OMe Me OMe
3 QMG PinB Me PinB‘Q'C' 622:37.8 56.4:436
CI Cl Me

 

 

From the comparison in Table 13, the experimental isomer distribution data
observed for those three 1,2-disubstituted arenes are similar to the estimated ones. The
small deviations between the observed values and estimated values might result from the
different dielectric constants of these substrates since the borylation reactions were
carried out in neat arenes solvents (8 (chlorobenzene): 5.69; 8 (anisole): 4.30; 8 (toluene):

2.38; 8 (2-chlorotoluene): 4.72; 8 (Z-methylanisole): 3.50; 8 (2-chloroanisole): N/A).39

The results for borylations of 1,2-disubstituted arenes give some indication of the
electronic effects of various substituents. It is clear from assessing and comparing the
electronic effects for borylation of 1,2-disubstituted arenes and the steric effects from the
ligand repulsive energies, ER, that the methoxy group has a meta directing effect
contributing to the isomer distribution in borylation of Z-methylanisole and 2-

chloroanisole.

55

Competition Reactions

To probe the role of electronic effects in the new Ir catalyst system (2 mol% 13

and 2 mol% of dmpe), relative product ratios from catalytic borylations in equimolar

mixtures of substituted arenes were determined (Table 14).

Table 14. Relative ratios of arylboronic esters for borylations of equimolar mixtures of
substituted arenes catalyzed by 2 mol% 13 and 2 mol% dmpe.

 

Equimolar Mixtures of

Borylation Product Distribution

 

 

 

 

 

 

 

 

Entry Substituted Arenes
F3C F3C
1 b / Q QBPM/ Dem
F3C F30
35:96.5
cu F3C c1 F3C
3 Q/ Q 9333/ CW
CI F3C Cl F3C
48.52515
3 @_ flow} 4;)» /3.c—§}e.
PinB Pin
51.92481
4 cn—Q—cu/F3C—QCF3 CI‘QCI /=ac~§—>~CF3
Pin Pin
993207
5 3—<}3/ 4} egg. / Q.
PinB PinB
98.7:1.3

 

56

 

For borylation of 1,3-disubstituted arenes, steric effect directs borylation in the
meta position. Therefore, in the competition reaction between m-xylene and 1,3-
C6H4(CF3)2, the arene selectivity, 3.5:96.5 (Entry 1), is solely governed by the relative
electronic nature of the two arenes. As mentioned previously, it was found that electron-
deficient arenes borylate faster than electron-rich arenes. In the competition reaction
between 1,3-C6H4(C1)2 and 1,3-C6H4(CF3)2, the arene selectivity was found to be
48.5:51.5 (Entry 2). Switching substrates from 1,3-disubstituted arenes to 1,4-
disubstituted arenes, dramatically different arene selectivities were observed. In the
competition reaction between p-xylene and 1,4-C6H4(CF3)2, the selectivity changed from
35:96.5 for the 1,3-disubstituted variants to 519248.] (Entry 3). Similarly, in the
competition reaction between 1,4-C6H4(C1)2 and 1,4-C6H4(CF3)2, the selectivity is
changed from 48.5:51.5 for 1,3-disubstituted variants to 99.3:0.7 (Entry 4). These results
undoubtedly demonstrate that steric effects play a crucial role in the borylation of 1,4-
disubstituted arenes.

The results from screening experiments show that any changes in phosphine
ligands, other donor ligands, or metal complexes have dramatic effect on the catalytic
activity. Steric effect governs the regioselectivity of aromatic borylation. For borylation
of symmetric 1,2-, 1,4- and symmetric or unsymmetric 1,3-disubstituted arenes, a single
borylation product is obtained. In addition, for borylation of unsymmetric 1,2- or 1,4-
disubstituted arenes, product distribution is the result of steric, electronic, and some type

of chelate-directed effect depending on the substituents such as a OMe group.

57

CHAPTER 4
SYNTHESIS, CHARACTERIZATION, AND REACTIVITY OF IRIDIUM BORYL

COMPLEXES

Synthesis and Characterization of an IrI Boryl Complex

In order to gain mechanistic insight into the Ir—catalyzed borylation reaction and
establish the most likely overall mechanistic pathway, it is important to examine the
viability and determine the rates of each individual stage. Halpem’s4O stepwise analysis
of the mechanism by which Wilkinson’s catalyst catalyzes olefin hydrogenation provides
a significant “take home lesson”; namely, that the identification of a dominant or
detectable species in a catalytic system may lead to incorrect interpretations of the
reaction mechanism. Only when kinetic and thermodynamic measurements define the
role of the complexes along the actual reaction path can the mechanism be defined. A
multi-step reaction is very complicated, and the dominant mechanism changes when the
nature of the pre—catalyst, the ligand, and/or the substrate is altered.

From a mechanistic standpoint, there are two potential catalytic cycles involving

oxidative addition and reductive elimination from Irv"I and/or Irm/v intermediates with Irl

and Ir'" boryl intermediates being the most likely C-H activating species in the Irw”

llIN
Ir

and/or cycles, respectively as shown in Figure 26.

58

lllll IIIN

LI Ph -H L HBPin
H2 [LAT—BPin] H2 ;|r_BPin Ph‘H
lr' L I .
BPin
lrlll
H H - BPin
L,.| m m L,_| _Ph Lli'ggm L, IIBPin
L/:'_H '7 Ir L’lr L—;lr'—BPin er er Lillr-Ph
BPin BPin H #1 3pm
lrlll
”I \\ BPin 4
L, ' .
L,, I H HBP' L ( llr-BPin
.r_ _ .
HBPin L’ Ph-BPin '” H Ph BPIn

 

Figure 26. Two potential catalytic cycles for aromatic borylation: (Left) involving Ir'i'”

[v . .
Ir"I intermediates.

intermediates; (right) involving

From competition reactions of mono-substituted arenes, it was found that
electron-deficient arenes borylate faster than electron-rich arenes. The general observed
trend suggests that the iridium metal center is electron rich, which implies that Irl
intermediates may be the active species in the catalytic borylation reactions. In order to
examine that possibility, the Ir1 boryl complex, (PMe3)4Ir(BPin), was first synthesized to
evaluate its stoichiometric reaction with arenes.

Flood41 and co-workers’ studies on the mechanism of cyclometallation, i.e.
oxidative addition of a C-H bond of a ligand to form a chelate complex, of
tris(trimethylphosphine)neopentyliridium(I) compound showed that the mechanism

involves direct, concerted oxidative addition and reductive elimination of the C-H bond

59

interconverting the square-planar Irl and octahedral Ir'” centers without PMe; dissociation

 

 

(Figure 27).
pit/19371 of + Me3CCH2Li ‘PMeg figé
Me3P7lr‘-PMeg o = Me3P;-lr Me3P;!r
Me3P 93111309340 C Me3P -—>V 0 °C Me3P pMe3

Figure 27. Cyclometallation of tris(trimethylphosphine)neopentyliridium(I) complex.

At first, the 16-electron square planar complex, [(PMe3)3Ir(BPin)], the proposed
key intermediate in the borylation reactions, was the target complex to be synthesized.
Initially, we attempted to use a dehydrohalogenation route to synthesize
[(PMe3)3Ir(BPin)] from the reaction between mer-(PMe3)3Ir(BPin)(H)(Cl) (15)42 and
KO’Bu (Figure 28). However, there was no reaction at room temperature, and at elevated
temperature the reaction proceeded slowly to generate a complex mixture of Ir products.
Several other reagents including NaN(SiMe3)2 and 'BuLi were also used and these
attempts were unsuccessful. Presumably, [(PMe3)3Ir(BPin)], a coordinatively unsaturated
16-electron square planar complex, is unstable, thus rendering its isolation and

characterization difficult.

BPin PM

|,PMe3 f 83
Me3P;Ir—H + KO‘Bu Me3P7lr-BPin + ’BuOH 3» KCI
Me3P ('31 Me3P

(15)

 

Figure 28. The reaction between mer-(PMe;)3Ir(BPin)(H)(Cl) (15) and KO’Bu.

6O

In 1997, Marder, Norman, and co-workers reported the synthesis of a low valent,
electron-rich, late transition metal boryl complex, (PMe3).4Rh(BCat),43 from the reaction
between (PMe3)4Rh(Me) and BzCatz with MeBCat as byproduct. With this information in
hand, we targeted (PMe3)4Ir(BPin), which is a coordinatively saturated l8-electron
complex and is presumably more stable than the original 16-electron target. In 1982,
Thorn and Tulip44 reported the preparation of (PMe3)4Ir(H) from the reaction of
[(PMe3)4IrH2]Cl, which can be prepared at ambient temperature by purging dihydrogen
gas into a THF solution of (PMe3)4Ir(Cl), and KO’Bu through a dehydrohalogenation
route. A similar reaction was carried out to first synthesize [(PMe3)4Ir(H)(BPin)]Cl (16)
by addition of HBPin instead of H2 to the THF solution of (PMe3)4Ir(Cl). This attempt
was successful and compound 16 was prepared in 71% yield. The structure of 16 was
assigned according to 1H, 1'B, and 31P{1H} NMR spectroscopy. In the 1H NMR
spectrum, a doublet of quartet is observed in the hydride region at —13.16 ppm (ZJHP =
119.0 Hz, 18.7 Hz), indicating a trans relationship to a PMe3 group and a cis to three
PMe3 groups. A singlet at 1.22 ppm integrating to 12 protons is assigned as the resonance
of BPin group. There are two sets of doublets and one triplet corresponding to three
different PMe3 groups at 1.61 ppm ((1, 2Jim = 8.2 Hz, 9H), 1.63 ppm ((1, 2JHp = 7.3 Hz,
9H), and 1.74 ppm (t, 2JHP = 3.4 Hz, 18H, two mutually trans PMe3). In the 3'P{‘H}
NMR spectrum, there are three different phosphorous resonances. A broad peak is
observed at -67.2 ppm (the PMe3 trans to BPin group), a quartet is observed at —60.1 ppm
(ZJpp = 20.8 Hz, the PMe3 trans to hydride), and a triplet is observed at -55.2 ppm (ZJpp =
22.9 Hz, two mutually trans PMe3 groups). In the 11B NMR, a broad peak is observed at

32.8 ppm. Unfortunately, its reaction with KO’Bu proceeded through an undesired

61

deborylhalogenation pathway instead of dehydrohalogenation pathway to give
(PMe3)4Ir(H) and 'BuOBPin as products (Figure 29). Presumably the formation of
’BuOBPin is thermodynamically favored. Since deborylhalogenation is a dominant
reaction pathway, a process involving the synthesis of a diboryl complex in the first step,
and the reaction with KO’Bu through the deborylhalogenation pathway to give a IrI boryl

complex would be a possible synthetic route.

 

Dehydrohalogenation
KOtBU X Phgemggj 18 OH
op * U
_ KCI M6313" Ir
BPine
— PMe CI
PMQ Cl HBPin,THF Hallie—3]
Me3P- lr- PMe3 25 °C 2d = P-lr-
, a s
Me3P' y MeegPl BPin (16)
PM83
‘50—‘31 Me P-li‘PMe3 + 'BuOBPin
'KCl 3 .‘JPMea’
Deborylhalogenation

Figure 29. Deborylhalogenation reaction between complex 16 and KO’Bu.

mer,cis-(PMe3)3Ir(BPin)2Cl (17) was prepared from the reaction between B2Pin2
and (PMe3)4Ir(Cl) in a THF solution at 70 °C for one day. The complex was purified by
recrystallization from a pentane solution at -30 °C to give spectroscopically pure
compound 17 in 74% yield (Figure 31). The 1'B NMR spectrum shows two boryl
resonances at 28.0 and 36.5 ppm and the 31P{'H} NMR spectrum exhibits a broad singlet

at —51.4 ppm due to trans coupling to a boron nucleus (”B, spin 3/2, 80.4% natural

62

abundance, 10B, spin 3, 19.6% natural abundance)45 and a doublet at —41.1 ppm (ZJpp =
26.9 Hz). The catecholate analogue, mer,cis-(PMe3)3Ir(BCat)2Cl, was previously
prepared via a different route by Dai and co-workers.46

Single crystals of 17 and B2Pin2 co—crystallized from pentane at —30 °C and the
structures were established by X-ray crystallographic analysis. The molecular structure of
17 is shown in Figure 30. Selected bond distances and bond angles are given in Table 15.
The molecular structure of 17 consists of an octahedral geometry with phosphines ligands
in a meridional arrangement. The two BPin groups are cis to each other with the B(1)—
Ir(1)—B(2) angle of 77.97(19). The boron trans to chloride has an Ir-B bond distance of
2.057(5) A, which is the same (within statistical error) as that in the compound mer-
(PMe3)3Ir(BPin)(H)(Cl) (15) (2.054(3) A). The other Ir-B bond distance is 2.114(5) A.
Among those Ir-P bond distances in complex 17, the two trans phosphine ligands have Ir-
P distances of 2.328(1) and 2.320(1) A, respectively, which are very similar to the two
trans Ir-P distances in compound 15 (2.3277(8) and 2.3147(8) A). Furthermore, the PMe3
ligand trans to BPin in compound 17 has a substantially longer Ir-P distance of
2.3921(13) A. This suggests that the BPin group has a larger trans influence than a PMe3

ligand.

63

 

Figure 30. ORTEP diagram of mer,cis-(PMe3)3Ir(BPin)2Cl (17). Thermal ellipsoids are

shown at 25% probability.

64

Table 15. Selected bond lengths [A] and angles [°] for 17.

 

Bond Distance [A] Bonds Angle [°]
Ir(1)-B(1) 2.114(5) B(1)-Ir(1)-B(2) 78.0(2)
Ir( 1 )-B(2) 2.057(5) B(l )-Ir(1)-P(3) 87.9(1)
Ir(1)-P(3) 2.328(1) B(1)-Ir(1)-P(4) 164.3(1)
Ir(1)-P(4) 2.392(1) B(1)-Ir(1)-P(5) 86.3(1)
Ir(1)-P(5) 2.320(1) B(1)-Ir(1)-C1 102.7(1)
Ir(1)-Cl 2.560(1) B(2)-Ir(1)-P(3) 96.8(1)
B(2)-Ir(1)-P(4) 86.5(2)
B(2)-Ir(1)-P(5) 97.2(1)
B(2)-Ir(1)-Cl 179.3(2)
P(3)-Ir(1)-P(4) 96.0(4)
P(3)-Ir(1)-P(5) 163.33(4)
P(3)-Ir(1)-Cl 8305(4)
P(4)-Ir(1)-P(5) 9384(5)
P(4)-Ir(1)-Cl 9288(4)
P(5)-Ir(1)-Cl 8303(4)

 

The reaction between compound 17 and KO’Bu in the presence of 2 equivalent
PMe3 was carried out at ambient temperature to give (PMe3)4Ir(BPin) (18) in good yield
(The product always contained a small amount of (PMe3)4Ir(H) (ca. 3% by 1H NMR) due
to its considerable moisture sensitivity) (Figure 31). Complex 18 is fluxional in solution
as evidenced by the appearance of a singlet at —57.5 ppm at 298.15 K (25 °C) in the
3 lP{‘H} NMR spectrum where it displays a doublet (-562 ppm, 2Jpp = 32.8 Hz, 3P) and
a broad quartets (-57.7 ppm, 1P) at 213 K (-60 °C). The low temperature-limiting
spectrum indicates a trigonal bipyramidal geometry with the BPin group occupying an

axial site.

65

BPin

 

. THF 1 p e
(PMe ) Ir(Cl) : B Pin e .. ‘_ -
34 2 2 70°C,12h nggAr M913
CI
(17)
74% yield

KO’Bu,PMe3,THF 53"”. ea t
> Me P-lr. + B OBP'n
17 25 °C, 90 min,- KCI 3 I Was U '
PM83

(18)
92% yield

 

Figure 31. Syntheses of mer,cis-(PMe3)3Ir(BPin)2Cl (17) and (PMe3)41r(BPin) (18).

Single crystals of 18 were grown from pentane at —30 °C and the structure was
further confirmed by single—crystal X-ray crystallographic analysis. The molecular
structure of 18 is shown in Figure 32. Selected bond distances and bond angles are given
in Table 16. From the X-ray structure, the Ir(1)-P(1) distance of 2.334(2) A, is
significantly longer than Ir(1)-P bonds of the other equatorial PMe3 ligands (Ir(1)-P(2),
2.287(2) A, Ir(1)-P(3), 2.282(2) A, and Ir(1)-P(4), 2.270(2) A). The result can be

rationalized by assuming a large trans influence of BPin group.

66

 

Figure 32. ORTEP diagram of (PMe3)4Ir(BPin) (18). Thermal ellipsoids are shown at

25% probability.

Table 16. Selected bond lengths [A] and angles [°] for 18.

 

Bond Distance [A] Bonds Angle [°]
Ir(1)-B(1) 2.147(9) B(1)-Ir(1)-P(1) 178.0(2)
Ir(1)-P(1) 2.334(2) B(1)-Ir(1)-P(2) 85.1(2)
Ir(1)-P(2) 2.287(2) B(1)-Ir(1)-P(3) 85.0(2)
Ir(1)-P(3) 2.282(2) B(1)-Ir(1)-P(4) 82.2(2)
Ir(1)-P(4) 2.270(2) P(2)-Ir(1)-P(3) 119.8(1)
P(2)-Ir(1)-P(4) 119.1(1)
P(3)-Ir(1)-P(4) 1 18.0(1)
P(1)-Ir(1)-P(2) 95.8(7)
P(1)-Ir(1)—P(3) 96.1(7)
P(l)-Ir(1)-P(4) 95.8(8)

 

67

Substitution and Oxidative Addition Reactions of Ir1 Boryl Complexes

(PMe3)4Ir(BPin) (18) underwent a variety of substitution and oxidative addition
reactions. It reacted with dppe in C6D6 at room temperature for 3 days to give
Ir(PMe3)2(dppe)(BPin) (19) as the major iridium containing complex as shown in Figure
33. The reaction resulted in the replacement of 2 PMe3 ligands with the chelating
phosphine ligand, 1,2-bis(diphenylphosphino)ethane (dppe). The structure of 19 was
assigned according to 1H, 11B, and 3 1P{1H} NMR spectroscopy. In the 1H NMR
spectrum, a singlet at 1.10 ppm is assigned as the resonance of the BPin group. There is a
triplet corresponding to two PMe3 groups at 1.33 ppm (ZJHP = 3.3 Hz, 18H) and a
multiplet in the region of 1.92-2.18 ppm corresponding to four protons of the two CH2
groups on the backbone of dppe ligand. In the aromatic region (6.98-7.12, 7.16-7.28,
7.72-7.89, and 7.91-7.98 ppm) there are 20 protons corresponding to the protons for the
four phenyl groups of the dppe ligand. In the HB NMR, a broad peak is observed at 38.8
ppm. In the 31P{1H} NMR spectrum, there are three different phosphorous resonances. A
broad peak is observed at 46.1 ppm for the Pth trans to BPin, a doublet of triplet is
observed at 39.1 ppm (J = 141.6 Hz, 13.4 Hz) for the Pth cis to BPin, and a doublet of

doublet is observed at —58.9 ppm (J = 141.6 Hz, 26.8 Hz) corresponding to two PMe;

groups.

 

BPin BPin
M P i ‘PMe3 * dppe Ph P i ‘PMea 2 PM
33 — “PM > 2 — r' + e3
1 ea 25 °C,3da s I Was
PMe3 y PPh2
(1s) (19)

Figure 33. The reaction between compound 18 and dppe.

68

Compound 18 reacted with HBPin in C6D6 to give mer,trans-(PMe3)3Ir(BPin)2(H)
(20) as the initial predominant species, and this kinetic product gradually isomerized to
fac-(PMe3)3Ir(BPin)2(H) (21) afier heating at 70 °C for 11 hours. The structure of 20 was
assigned according to 1H, HB, and 3'P{1H} NMR spectroscopy. In the 1H NMR
spectrum, a doublet of triplet is observed in the hydride region at —12.36 ppm (ZJHP =
117.0 Hz, 21.7 Hz), indicating a trans relationship to a PMe3 group and a cis orientation
to two PMe3 groups. A singlet at 1.22 ppm is assigned as the resonance of the two
mutually trans BPin groups. A doublet is observed at 1.49 ppm (J = 8.0 Hz, 9H)
corresponding to the PMe3 trans to hydride and a triplet is observed at 1.74 (J = 3.4 Hz,
18H) corresponding to the two PMe3 groups, which are trans to each other. In the HB
NMR, a broad peak is observed at 38.9 ppm. In the 31P{'H} NMR spectrum, there are two
different phosphorous resonances. A triplet is observed at —59.6 ppm (J = 22.0 Hz) for
the PMe3 trans to H and a doublet is observed at —50.8 ppm (J = 22.0 Hz) for the two
mutually trans PMe3 groups. The structure of 21 was also assigned according to 1H, ‘1B,
and 3'P{'H} NMR spectroscopy. In the 1H NMR spectrrun, a doublet of triplet is
observed in the hydride region at —11.66 ppm (ZJHp = 118.1 Hz, 18.1 Hz), indicating a
trans relationship to a PM63 group and a cis to two PMe3 groups. A singlet at 1.29 ppm is
assigned as the resonance of the two chemically equivalent BPin groups. A virtual triplet
is observed at 1.41 ppm corresponding to the two PMe3 groups trans to BPin and a
doublet is observed at 1.58 ppm (J = 8.0 Hz) assigned as the PMe3 trans to hydride. In
the 1]B NMR, a broad peak is observed at 38.6 ppm. The 31P{'H} NMR spectrum of 21
displays a triplet at —56.6 ppm (J = 22.0 Hz) for the PMe3 trans to H and a broad

resonance at —61.8 ppm for the two PMe3 groups trans to BPin.

69

Eisenberg and co-workers47 reported that the oxidative addition of catecholborane
(HBCat) to the Ir(I) cis-phosphine complexes IrX(CO)(dppe) (X = Br, I; dppe = 1,2-
bis(diphenylphosphino)ethane) proceeds stereoselectively under kinetic control. In their
original studies on H2, R3SiH, and HX' oxidative additions to IrX(CO)(dppe)
complexes,48 they reasoned that both H2 and R3SiH add to the IrX(CO)(dppe) complexes
as nucleophiles. The addition occurs over the OC-Ir-P axis because the 7r* orbital of CO
is able to stabilize the developing transition state by reduction of electron density of the Ir
dz2 orbital, thus minimizing the repulsive 4e' interaction between the filled dz2 and ob
orbitals of H2 and R3SiH. On the contrary, hydrogen halides (HX') approach
IrX(CO)(dppe) in aprotic media as electrophiles. Therefore, interactions that retain or
enhance electron density at the metal center will favor addition along that pathway. Thus,
HX' addition is preferred by bending the X-Ir-P axis because this pathway leads to an
antibonding interaction between an occupied pz orbital of X and the dz2 orbital of Ir, thus
enhancing the ability of Ir to donate electrons to the incoming electrophile (Figure 34).49
Since oxidative addition of catecholborane to IrX(CO)(dppe) complexes (X = Br, I)
resembles HX' additions, the result implies that catecholborane approaches the metal
center as an electrophile in accord with the view that the vacant B pz orbital can overlap

with the filled dz2 of Ir (Figure 35).

7O

(nucleophile) H-Y

H Q Q . .
Oé_'r—PPg—* + HY X—lripPfl 12* ”antibonding
Y - H, R381 CO d22\v dzz p2
Ir-CO Ir-X

(stabilized) (destabilized)

8‘ 8+
(electrophile) X'-H

+ HX'
H32 ——-> .371. P3 F3:
00’ oc )'(

2
X' = Br, | dz [’2

Figure 34. H2, R3SiH, and HX' oxidative additions to IrX(CO)(dppe) complexes.

(electrophile) (E E)
6+
8‘ 5kg); 0 B, ,o
.P H P
33:»? .3231: _. _. .,1_.2
oc :31”? oc ,2
x, P
00

Figure 35. Catecholborane (HBCat) oxidative addition to IrX(CO)(dppe) complexes.

Pinacolborane (HBPin) oxidative addition to compound 18 gives complex 20 as
the kinetic product with the two BPin groups trans to each other. The result can be
rationalized by assuming that pinacolborane (HBPin) approaches the Ir metal center as an
electrophile in accord with the results for HBCat. Furthermore, the backbonding

interaction between the filled Ir metal dz2 orbital and the empty B pz orbital, as HBPin

71

adds in the P-Ir-B plane, provides additional stabilization to the five-coordinate species,

as shown in Figure 36.

 

(kinetic product) (thermodynamic product)
BPin . Bp PMe3
1 PMe3 3 HBPm _]_{]e e3 11312.11
Me3P- 'r'PMe3 W Me;1,P-;lr-70 °C MegP: lr- BPin
(18) (20)n (21)
- PMR . HBP/
Me3P- lr- PBPein
M6313!

 

 

d22 . M93 dzz op 33
Me3P’ 3. empty 9: Me3P empty Pz
M93P( M83P; 08% g
958 8%H antibondin

empty Pz g/I C5)

(electrophile)
Figure 36. Pinacolborane (HBPin) oxidative addition to compound 18.

The reaction of 18 with Chlorocatecholborane (ClBCat) proceeded at room
temperature to give mer-(PMe3)3Ir(BPin)(BCat)(Cl) (22) as the major product with the
BPin group trans to the chloride ligand as shown in Figure 37. The geometry of 22 was
assigned according to 1H, HB, and 31NH} NMR spectroscopy. In the 1H NMR
spectrum, a singlet at 1.18 ppm is assigned as the resonance of the BPin group. There is a

doublet at 1.29 ppm (J = 7.3 Hz) corresponding to the PMe3 trans to BCat and a triplet at

72

1.47 ppm corresponding to two mutually trans PMe3 groups. An AA'BB' pattern is
observed at 6.84 and 7.19 ppm in the aromatic region, which corresponds to the four
protons of the catecholate. The HB NMR spectrum displays two well-separated
resonances at 28.1 and 41.6 ppm, respectively. By comparing the resonances of boryl
groups in compound 15, 17, mer—(PMe3)3Ir(BCat)(H)Cl (23),42 and mer,cis-
(PMe3)3Ir(BCat)2Cl (24)46 as summarized in Table 17, we assigned the resonance at 28.1
ppm as the BPin group and the resonance at 41.6 ppm as the BCat group. The 3'P{IH}
NMR spectrum of 22 displays a broad peak at -56.2 ppm assigned as the PMe3 trans to
BCat and a doublet at —39.3 ppm (J = 29.3 Hz) corresponding to two mutually trans

PMe3 groups.

BPin BPin

 

| .PMe3 * ClBCat, - PMe3 |‘PMe3
Me3P—jr'PMe3 25 °C 3 d > Me3P;lr-BCat
, a s
PMe3 y Me3p Cl
(18) (22)

Figure 37. Chlorocatecholborane (ClBCat) oxidative addition to compound 18.

Table 17. Comparison of boryl resonances of complexes 15, 17, 22, 23, and 24 in 1]B
NMR spectra.

 

 

 

 

 

 

 

 

 

 

 

Complex 15 17 22 23 24

BPin trans to Cl (ppm) 28.5 28.0 28.1 -- --
BCat trans to Cl (ppm) -- -- 32.8 32.6

BPin trans to PMe3 (ppm) -- 36.5 -- -- --
BCat trans to PMe3 (ppm) -- -- 41.6 -- 41.7

 

73

 

Ill

Synthesis and Characterization of an Ir Boryl Complex

The Ir'” boryl complex, fac-(PMe3)3Ir(BPin)3 (25) can be easily prepared in

essentially quantitative yield by addition of a slight excess of PMe3 to (MesH)Ir(BPin)3

(14) in benzene solution at ambient temperature (Figure 38).

Q . BPin
| PMea (5 equw.). CoHe l BPin

 

...,,,, . = Me P-lr'-BPin
Ir BP'” 25 °C, 30 min Mea3p' I
PinB BF," PMea
1
(14) (25)

99% isolated yield

Figure 38. Synthesis of fac-(PMe3)3Ir(BPin)3 (25).

Crystals suitable for X-ray analysis of 25 were grown from pentane at —30 °C.
The molecular structure of 25 is shown in Figure 39. Selected bond distances and bond
angles are given in Table 18. The complex adopts a facial geometry with all three PMe3
ligands trans to the BPin groups. The 11B NMR spectrum shows only one boryl
resonance at 36 ppm and the 31P {'H} NMR spectrum shows one broad singlet at -64 ppm
due to a trans coupling to the boron nucleus. A similar compound, fac-(PEt3)3Ir(BCat)3,
was previously prepared by Marder and co-workers via the displacement of the
mesitylene ligand of (MesH)Ir(BCat)3 with 3 equivalent of PEt3.31 fac-(PEt3)3Ir(BCat)3
has similar spectroscopic properties as compound 25. In the HB NMR spectrum, a broad

peak was observed at 44.7 ppm corresponding to the three BCat groups and in 31P{'H}

74

NMR spectrum, a broad peak was observed at —32.1 ppm corresponding to the three

PMe3 groups.

 

Figure 39. ORTEP diagram of fac—(PMe3)3Ir(BPin)3 (25). Thermal ellipsoids are shown
at 25% probability. All oxygen and carbon labels are omitted for clarity. Hydrogen atoms

are also omitted for clarity.

75

Table 18. Selected bond lengths [A] and agles [°] for 25.

 

Bond Distance [A] Bonds Angle [°]
Ir(1)-B(1) 2.106(2) B(1)-Ir(1)-B(2) 82.3(7)
Ir(1)-B(2) 2.148(2) B(1)-Ir(1)-B(3) 79.4(6)
Ir(1)-B(3) 2.082(2) B(2)-Ir(l )-B(3) 81 .9(7)
Ir(1)-P(1) 2.352(4) B(1)-Ir(1)-P(1) 169.2(5)
Ir(1)-P(2) 2.353(4) B(1)-Ir(1)-P(2) 91 .5(5)
Ir(1)-P(3) 2.347(4) B(1)-Ir(1)-P(3) 89.6(5)
B(2)-Ir(1 )-P(1 ) 90.8(5)
B(2)-Ir( l )-P(2) 90.9(5)
B(2)—Ir(1)—P(3) 169.6(5)
B(3)-Ir(l)-P( 1) 91 .4(5)
B(3)-Ir(l)-P(2) 169.0(5)
B(3)-Ir( l )-P(3) 90.1(5)
P(1)-Ir(1)-P(2) 97.1(2)
P(1)-Ir(1)-P(3) 962(2)
P(2)-Ir(1)-P(3) 95 .9(2)

 

Synthesis and Characterization of Novel Metal Boryl Complexes Containing Alkyl,

Aryl, or Silyl Ligands

In transition metal catalyzed hydroboration of unsaturated hydrocarbons and
borylation reactions of alkanes and arenes, an intermediate containing a boryl ligand and
a o-bound carbon ligand has been proposed. Several theoretical studies also support the
interrnediacy of such metal complex. However, only a few of this type of metal
complexes have appeared in literature (Figure 40). One of them, reported by Crabtree50
and co-workers in 1993, was an unprecedented IrIV boryl complex,
[Ir(PMe3)3(biphBF)Cl]+I'. Knorr and Merola42 reported the preparation and
characterization of mer-(PMe3)3Ir(BCat)(trans-{CO2CH3}=CH {CO2CH3})(C1) in which

the vinyl group arises from insertion of dimethyl acetylenedicarboxylate into the Ir-H

76

bond of mer-(PMe3)3Ir(BCat)(H)(Cl). Another case is the report by Roper, Wright, and

co-workers of the synthesis of cis- and trans-[Os(BCat)(o-tolyl)(CO)2(PPh;1)2].5’I The

complex with o-tolyl and BCat groups cis to each other was unstable at room

temperature. o-tolleCat was slowly eliminated from the complex at room temperature in

i benzene solution to give the orthometallation product, [Os(C6H4PPh2)(H)(CO)2(PPh3)].

On the other hand, the complex with o-tolyl and BCat groups trans to each other was

stable under reflux in benzene for 2 hours. Their observations indicate that the

requirement for facile reductive elimination is that the aryl and BCat ligands be adjacent

to one another.

0 PMe3
II ,PMe3

|r\\ PMe3
CI

 

 

-03” l

PPh3
oc,, ,,,,, I ..... .R

o
00/ l S\B\’O

PPh3 0D

R = o-tolyl

o, o
T 0PMe3
H
M63P7llr'ޢ<R
R
Me3P Cl
R=C(O)OCH3
PPh3
Rh,“ | (.00
"08
00/ | \Bjo
PPh3 0
R=o—to|yl

Figure 40. Reported complexes containing a boryl ligand and a o-bound carbon ligand.

77

There are several cases where the authors imply the intermediacy of such a
complex. For example, the reaction of (PMe3)4Rh(Me) with B2Cat2 resulted in the
formation of MeBCat and (PMe3)4Rh(BCat).43 The authors reasoned that the reaction
proceeded via oxidative addition of the B-B bond followed by rapid reductive elimination

of MeBCat (Figure 43).

 

-PMe3 TM‘P
(PMe3)4Rh(Me) 3 13202112 —» 08th “Pl/lea
CatB 1 PMe3
Me
i\ MeBCat
+ PMe3
(PM83)4Rh(BCat) l (PM93)3Rh(BC81) I

 

Figure 41. The reaction between (PMe3)4Rh(Me) and B2Cat2.

Although transition metal alkyl boryl complexes have been proposed as
intermediates in stoichiometric and catalytic alkane borylation reactions, no such species
have ever been isolated. In an attempt to synthesize this type of species in the “Ir(PMe3)n”
system, we examined the reaction between (PMe3)4Ir(Me)52 and HBPin in pentane
solution. The reaction occurred immediately at ambient temperature to generate an
isomer mixture of fac-(PMe3)3Ir(H)(Me)(BPin) (26) (83%) and mer-

(PMe3)3Ir(Me)(H)(BPin) (27) (17%) in 75% yield (Figure 42).53

78

Me PMea BPin

 

Me3p;ir-PM83 HBPT, penténet Me3P;lr‘lePin * Me3P;ir‘5Me3
Me3P PMe3 25 C. 5 mm MeaP [1‘6 Me3P “he
fee-(26) mar-(27)
830/0 I 170/0

Figure 42. The reaction between (PMe3)4Ir(Me) and HBPin in pentane.

Complex 26 adopts a facial geometry with BPin, H, and Me groups all trans to a
PMe3 group. The geometry of 26 was assigned according to 1H, 1'B, and 31P{'H} NMR
spectroscopy. In the 1H NMR spectrum, a doublet of triplet is observed in the hydride
region at —11.30 ppm (ZJHp = 140.4 Hz, 18.9 Hz), indicating a trans relationship to a
PMe3 group and a cis to two PMe3 groups. From 0.37 to 0.42 ppm, there is a peak with a
dddd pattern corresponding to a methyl group which is cis to three different PMe3 groups
and a hydride ligand as shown in Figure 43. A singlet at 1.25 ppm is assigned as the
resonance of BPin group, and there are three sets of doublets corresponding to three
different PM63 groups at 1.17 ppm (2J11p = 6.4 Hz, PMe3 trans to BPin), 1.35 ppm (2J11p =
7.3 Hz, PMe3 trans to hydride), and 1.47 ppm (ZJHp = 7.9 Hz, PMe3 trans to Me) as
shown in Figure 44. In the 31P{'H} NMR spectrum, there are three different phosphorous
resonances for complex 26 as shown in Figure 47. A broad peak is observed at -63.3 ppm
(the PMe3 trans to BPin group), a doublet of doublet is observed at ~56.83 ppm (ZJpp =
13.4 Hz, 23.2 Hz, PMe; trans to hydride), and a doublet of doublet is observed at -55.16
ppm (ZJpp = 13.4 Hz, 18.3 Hz, PMe3 trans to Me). The assignment of different PMe3
groups in 1H NMR spectra was established by one-dimensional Nuclear Overhauser

Effect (NOE) experiments (Figures 45 and 46). In the NOE experiment, the hydride and

79

the methyl resonances of compound 26 were irradiated in order to establish the through
space relationships to identify their trans PMe3 groups. Irradiation of the hydride
resonance at 8 -1 1.30 resulted in enhancement of the peaks at 0.40, 1.17, 1.25, and 1.47
ppm. Therefore, the peak at 5 1.35 is the PMe3 trans to hydride. Irradiation of the methyl
resonance at 6 0.40 resulted in enhancement of the peaks at 6 -11.30, 1.17, 1.25, and
1.35. Therefore, the peak at 8 1.47 is the PMe3 trans to the methyl group. The assignment
of the different PMe3 groups in 3|P{'H} NMR spectra is based on two—dimensional
Heteronuclear Chemical Shift Correlation (HETCOR) experiment ('H, 31P) to correlate
the resonances of PMe3 groups in the 1H NMR spectra to those in the 31NH} NMR
spectra (Figure 48). The cross peak (a) presumably comes from a 3J coupling. In two-
dimensional heteronuclear NMR, couplings through two or more bonds are very much
smaller than directly bonded couplings but do not necessarily fall off regularly with the
number of bonds, 3J being sometimes larger than 2.1. To our knowledge, this is the first

structural characterization of a transition metal alkyl boryl complex.

80

iris
Me3P;—Ir‘—BP1n
M P 1
e3 Me

fee-(26)

0.50 0.48 0.46 0.44 0.42 0.40 0.38' 0.36 0.34 0.32

Figure 43. The resonance of the methyl group of fac-(PMe3)3Ir(Me)(H)(BPin) (26) in the

lH NMR spectrum.
PMe3
M P ir‘HBP‘n
e - - I
. MegP’l
BPrn of 26
I fee-(26)
PMe3 0f 26 PMe3 of 26
PMe3 of 26
I1!
* '1‘
1.60" ' 1.50. ' ’ '1710 1.317 ’ ' "1.207

Figure 44. The resonances of PMe3 groups of fac-(PMe3)31r(Me)(H)(BPin) (26) in the 1H

NMR spectrum. The peaks denoted with an asterisk (*) are due to PMe3 and BPin

resonances of compound 27 .

81

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83

PMe3 of 26 PMe; of 26

\l‘iii iii PMe3 trans to BPin

-5 -56 -5 -6 6O -62 -64 ~66

Figure 47. The resonances of PMe3 groups of fac-(PMe3)3Ir(Me)(H)(BPin) (26) in the

3'P{1H} NMR spectrum. The peaks denoted with an asterisk (*) are due to PMe3

resonances of compound 27.

1 g; 'H NMR spectrum

ill

Vi} iii 1,
' lV

 

3'P{'H} NMR spectrum ___,.,

 

 

1

-59 —1 a)
'1 .
-58-l
“:31, 4 I <7€~J‘l~\
- 5’ .. 1 1 ' \' . 22.-:2.
————r . “Q /'

11;“) -55 1

:41 '“i\ \PMe3 trans to H
i
Z

 

 

 

 

"5311 PMC3 trans to Me
-52

- 51 i
'Y 1‘11 VT ‘6 "Y'V‘TT‘I‘T'W’TT'TT‘I‘Y'TT'r'TYT ‘ Y " T r VTTfi’T'TT—YTT'W'TTTTYT'TT‘VT’X'T ' V'TI 1'7""! TY'TT—TT‘Y T'T'T YWW'T‘WW ' 7" 1 1- "Y—YV "1““

1.. 1.6 10‘ 1.2 1.0 00. 00‘ 00‘ 0.2 0.0 '002

’1 (9”)

Figure 48. HETCOR experiment ('11, 3 IP) to correlate the resonances of PMe3 groups in

the 1H NMR spectra to those in the 3 lP{'ILI} NMR spectra.

84

In the reaction of (PMe3)4Ir(Me) with 9-BBN reported by Baker and co-workers,
the reaction led to the isolation of a boroethyl-metal compound, which most likely results
from OH activation of transient MCBC3H14, formed by borane oxidative addition and
alkylborane reductive elimination or via a direct o-bond metathesis pathway (Figure

49).54

-PMea H, 1Mpuine3

 

 

 

(PMe3)4lr(Me) + HBR2 Rze’lr‘PMe3
Me
HTMSfi (PMe3)3|r(H)
”slap 93 +
R22 PMea MeBR2

Figure 49. The reaction between (PMe3)4Ir(Me) with 9-BBN.

A complex with the formula fac-(PMe3)3Ir(BPin)(D)(C6D5) was proposed as an
intermediate in the stoichiometric reaction between (PMe3)4Ir(BPin) (18) and C6D6.
Attempts to synthesize this target compound were undertaken. Therefore, a NMR
reaction between (PMe3)3Ir(Ph)55 and HBPin in toluene-d3 was carried out. The reaction
occurred immediately at room temperature to yield mer-(PMe3)3Ir(BPin)(H)(Ph) (28)
(~95%), fac-(PMe3)3Ir(D)(H)(tolyl-d7) (~5%), and less than 5% of PhBPin as byproduct.
The trace amount of PhBPin was presumably formed by reductive elimination from the
isomers with the BPin and Ph groups cis to each other (Figure 50). In a larger scale
reaction in pentane, the product was isolated in 95% yield. The crude product can be

further purified by recrystallization from pentane at —30 °C to give colorless crystals

85

suitable for X-ray analysis. From the ORTEP plot of complex 28 (Figure 51), the
structure consists of an octahedral arrangement of ligands with the three PMe3 groups in a
meridional arrangement, the hydride trans to one of the PMe3 groups, and the phenyl
group trans to the BPin group. Examination of the 1H NMR spectrum of the complex is
consistent with the X-ray data. Thus, the hydride resonance shows as a doublet of triplet
at —11.32 ppm (ZJHp = 131 Hz, 20 Hz), indicating it is trans to a PMe3 group and cis to
two mutually trans PMe3 groups. A singlet corresponding to the resonance of the BPin
group is observed at 1.16 ppm, and an overlapped doublet and triplet is observed at 1.41
ppm, which corresponds to the resonance of the three PMe3 groups. For the phenyl group
protons, a multiplet from 7.17 to 7.20 ppm and a broad peak at 7.98 ppm integrate in a 3
to 2 ratio. Surprisingly, a broad peak at 7.98 ppm is observed, which may result from the
hindered rotation about the iridium phenyl bond. The single crystal of 28 shows that the
iridium atom is at the center of a distorted octahedral geometry with a P(2)-Ir(1)-P(3)
angle of 166.29 (8) and C(41)-Ir(1)-B(5) angle of 167.7 (3). Selected bond distances and
bond angles are given in Table 19. From the space-filling model of 28, it is clear that
there is steric interactions between the protons of the phenyl group and the protons of the
PMe3 groups (P(2) and P(3)), which may impede rotation. The 3‘P{]H} NMR spectrum
shows a triplet at —57.8 ppm (2Jpp = 22.9 Hz), which is the resonance of the PMe3 trans to
hydride and a doublet at -45.6 ppm (2Jpp=22.0 Hz), which is the resonance of two
mutually trans PMe3 groups. This is a rare example of a stable transition metal complex

containing boryl and o-bound phenyl ligands.

86

 

 

 

 

 

\PMea HBPin, toluene-d3 Fiat? H (PM83
MeaPylr-Ph . = Me3P—1r‘-BP1n or Me3P—1r'—BPin . 28
25 °C, 1 mm ’1 ’ 1
Me3P Me3P Ph Me3P Ph ~ 95%
$707 0708 M P I .Wea
Me P—Ir‘— <——— 63 7 r‘
Me33P’I MeaP
PM83
~ 5%
PhBPin
< 5%

Figure 50. The NMR reaction of (PMe3)3Ir(Ph) with HBPin in toluene-d3 at room

temperature.

 

Figure 51. ORTEP of mer-(PMe3)3Ir(BPin)(H)(Ph) (28). Thermal ellipsoids are shown at

25% probability.

87

Table 19. Selected Bond lengths [A] and angles [°] for 28.

 

Bond Distance [A] Bonds Angle [°]
Ir(1)-B(5) 2.097(6) B(5)-Ir(1)-P(1) 94.6(2)
Ir(l)-P(1) 2.328(2) B(5)-Ir(1)-P(2) 90.0(2)
Ir(1)-P(2) 2.288(2) B(5)—Ir(1)-P(3) 90.5(2)
Ir(1)-P(3) 2.288(2) B(5)-Ir(l)-C(41) 167.7(3)
Ir(1)-C(41) 2.194(5) P(2)-Ir(1)-P(1) 96.8(7)

P(2)-Ir(1)-P(3) 166.4(6)
P(3)-Ir(1)-P(1) 96.75(6)
C(41)-Ir(1)-P(1) 97.7(2)
C(41)-Ir(1)-P(2) 88.2(2)
C(41)-Ir(1)-P(3) 88.4(2)

In their synthetic study of fac-(PMe3)3Ir(Me)(H)(SiR3)55 by Aizenberg and
Milstein, they established the order of trans influence: SiEt3 > SiPh3 > H > CH3 based on
X-ray structural data. A good trans-influence ligand could weaken the bond between the
metal and the trans ligand. This is a thermodynamic effect. The study shows that silyl
group has stronger trans influence than hydride. Moreover, in the computational study by
Sakaki and co-workers,56 they noted that the trans influence of the boryl group is stronger
than the very strong trans influence of silyl group. We deemed it of interest to establish
experimentally the stronger trans influence of a boryl group than that of a silyl group.
Thus, we decided to explore the reaction between (PMe3)4Ir(BPin) (18) and HSiEt3. The
reaction proceeded slowly at room temperature over 2.5 days to give fac-

(PMe3)3Ir(H)(BPin)(SiEt3) (29) as the only observed product (Figure 52).

88

BPin [I’Mea

 

, 1 25 °C. 2.5 days .H
Me3pl'1r-PMe3 + 14311513 0 H > Me3ls;1r-BPin + PMe3
M P e .

(18) fee-(29)

86% yield

Figure 52. The reaction between (PMe3)4Ir(BPin) (18) and HSiEt3.

The product was then recrystallized from a concentrated pentane solution at —30
°C to give 83 mg of colorless crystals in 86% yield. The structure of 29 was established
by 1H, llB, 3'P{1H} NMR spectroscopy. In the 1H NMR spectrum, a doublet of triplet is
observed in the hydride region at ~12.30 ppm (hydride, 1H, 2JHp = 117.0 Hz, 17.0 Hz),
indicating that it is trans to a PMe3 group and cis to two PMe; groups. A singlet at 1.29
ppm is assigned as the resonance of the BPin group. There are three sets of doublets
corresponding to three different PMe3 groups at 1.25 ppm (2.11“) = 6.7 Hz, PMe3 trans to
BPin), 1.37 ppm (ZJHp = 7.3 Hz, PMe; trans to SiEt3), and 1.46 ppm (ZJHp = 7.6 Hz, PMe;
trans to Me). There is no symmetry about the Ir metal center, which renders the molecule
chiral. Thus, the CH2 groups of SiEt3 are diastereotopic and should exhibit complex
coupling patterns. Indeed, three diastereotopic protons of the CH2 groups of SiEt3 are
observed from 0.84 to 0.95 ppm and there are twelve protons in the region of 1.35-1.45
ppm which include the other three diastereotopic protons of the CH2 groups of SiEt; and
nine protons from the CH3 groups of SiEt3. In the 3]NH} NMR spectrum, there are three
different phosphorous resonances. A broad peak is observed at -66.4 ppm corresponding
to the PMe3 trans to BPin group, a doublet of doublet is observed at —64.2 ppm (2Jpp =

31.3 Hz, 19.8 Hz, PMe3 trans to SiEt3), and another doublet of doublet is observed at

89

—58.1 ppm (ZJpp = 19.8 Hz, 19.8 Hz, PMe3 trans to H). The assignment of the PMe3
groups in the 1H NMR spectrum is established by one-dimensional Nuclear Overhauser
Effect (NOE) experiments and the assignment of the PMe3 groups in the 3‘P{'H} NMR
spectrum is based on two-dimensional selective decoupling experiments ('H, 31P) to
correlate the resonances of PMe3 groups in the 1H NMR spectrum to those in the 3 lP{1H}
NMR spectrum. Complex 29 adopts a facial geometry with BPin, SiEt3, and H groups all
trans to different PMe3 groups. Single crystals of 29 were grown from pentane at —30 °C
and the structure was further confirmed by single—crystal X-ray crystallographic analysis.
The molecular structure of 29 is shown in Figure 53. Selected bond distances and bond
angles are given in Table 20. From the single X-ray structure of 29, Ir(l)-P(3),m,,, 10 3pm
bond length is 2.359(2) A, Ir(1)-P(4),,,,., ,, 31w bond length is 2.334(2) A, and Ir(1)-
13(2),","510 H bond length is 2.319(2) A. The Ir-P bond length is directly proportional to the
magnitude of the trans influence of the trans ligand; namely, the longer the Ir-P bond, the
stronger the trans influence. It obviously shows that the order of trans influence is BPin>
SiEt3 > H. To our knowledge, this is the first structural characterization of a transition

metal boryl complex containing a silyl group.

90

 

Figure 53. ORTEP of fac-(PMe3)3Ir(H)(BPin)(SiEt3) (29). Thermal ellipsoids are shown

at 25% probability.

Table 20. Selected Bond lengths [A] and angles [°] for 29.

 

Bond Distance [A] Bonds Angle [°]
Ir(1)-B(1) 2.077(8) B(1)-Ir(1)-P(2) 92.5(2)
Ir(1)-P(2) 2.319(2) B(1)-Ir(1)-P(3) 166.5(2)
Ir(1)-P(3) 2.359(2) B(1)-Ir(1)-P(4) 82.9(2)
Ir(l)-P(4) 2.334(2) B(1)-Ir(1)-Si(5) 85.1(2)
Ir(1)-Si(5) 2.422(2) P(2)-Ir(1)-P(3) 100.9(7)
P(2)-Ir(1)-P(4) 102.6(8)
P(2)-Ir(1)-Si(5) 94.5(7)
P(3)-Ir(1)-Si(5) 91.9(7)
P(4)-Ir(1)-P(3) 95.9(7)
P(4)—Ii(1)-Si(51 159.4(7)

 

91

Several novel iridium boryl complexes have been synthesized, and a strong trans
influence of the boryl ligand has been observed in those complexes by comparing lr-P
bond distances to the Ir-Pmm, to 3pm bond distance. In those complexes, significantly
longer Ir-Pmm, 10 3pm bonds were observed compared to other Ir-P bonds in the complex.
Ir-Pmm, to 3pm bond distances in those complexes are compared and summarized in Table

21 with the angles of PinB-Ir-PMe3(trans).

Table 21. Comparisons of X2B-Ir-PMe3,,a,., to 3pm bond distances of iridium boryl

 

 

 

 

 

 

 

 

complexes.

Complex Bond Bond Length (A) Trans Ligands Angle (°)
17 PinB-Ir-PMe3 2.392( 1) PinB-Ir-PMe3 164.3(1)

18 PinB-Ir-PMe3 2.334(2) PinB-Ir-PMe; 178.0(2)

24 CatB-Ir-PMe; 2.399(1) CatB-Ir-PMe3 172.2(2)
PinB—Ir-PMe3 2.35 2(4) PinB-Ir-PMe; 169.2(5)

25 PinB-Ir-PMe; 2.353(4) PinB-Ir-PMe3 169.0(5)
PinB-Ir-PMe3 2.347(4) PinB-Ir-PMe3 169.6(5)

29 PinB-Ir-PMe3 2.359(2) PinB-Ir—PMe3 166.5(2)

 

 

 

 

 

 

92

 

Oxidation Chemistry of Ir1 complex with Boranes

In contrast to the catecholboryl complexes, the corresponding compounds with
other substituents (e. g. N, S) on boron are rather rare. In the past, B-H oxidative addition
was exploited as a general synthetic method for preparing boryl compounds. A common
theme in these reactions is the use of low-valent metal precursors containing readily
dissociable ligands. This creates vacant sites in the metal coordination sphere, which
allows for the oxidative addition of the boron reagents to the electron-rich metal center.
This method was exploited to examine the reaction of several nitrogen-containing
boranes including H[B(NH)2C(,H4], H[B(NH)2C10H6] (HBDAN), and H[B(NMe)2C6H4]
with (PMe3)3Ir(COE)(Cl) (30). The results are summarized in Figure 54. Similar to the
reactions of compound 30 with HBPin and HBCat, H[B(NH)2C6H4] reacts with
compound 30 to give mer-(PMe3)3Ir[B(NH)2C61-I4](H)(Cl) (31) with the boryl group trans
to Cl and H trans to PMe3 as the only observed product. Since, as discussed earlier, the
borane approaches the metal center as an electrophile, H-B addition is preferred by
bending Cl-Ir-P axis to form compound 31. Therefore, compound 31 is the kinetic
product of the reaction. Consideration of the trans influence for the various ligands in
compound 31 suggests that it is also the thermodynamic product. Changing the borane
source to HBDAN gives two isomers mer-(PMe3)3Ir(BDAN)(H)(Cl) (32) and mer-
(PMe3)3Ir(H)(BDAN)(Cl) (33) in a 90.4296 ratio. The geometries of these two complexes
were determined by 1H, 1‘B, and 31P{‘H} NMR spectroscopy. The formation of the other
isomer is presumably due to the bulkiness of the BDAN group, which might have

interactions with methyl groups of a PMe3 ligand. It is expected that replacing the H

93

atoms on the N atoms of -[B(NH)2C6H4] with methyl groups would increase the steric
bulkiness of the boryl group. We, therefore, examined the reaction of
(PMe3)3Ir(COE)(Cl) (30) with H[B(NMe)2C6H4]. This reaction produced an isomer
mixture of mer—(PMe3)3Ir[B(NMe)2C6H4](H)(Cl) (34) and mer-
(PMe3)3Ir(H)[B(NMe)2C6H4](Cl) (35) in a ratio of l4.4:85.6. The geometries of these two
complexes were determined by ]H, 1‘B, and 31P{'H} NMR spectroscopy.
Characterization details of compounds 31, 32, 33, 34, and 35 are included in the
experimental section. The reaction between compound 30 and H[B(NMe)2C6H4] suggests
that steric factors can influence the outcome of boryl complex formation.

(PMe3)4Ir(BPin) and fac-(PMe3)3Ir(BPin)3 have been prepared in order to
examine their viability to be the OH activating species in the catalytic borylation
reactions. Furthermore, Several novel Ir boryl complexes containing alkyl, aryl, or silyl

ligands were synthesized and fully characterized.

94

H

N f:

H-B, D HN. ,NH
N B

 

 

 

H M P |I‘J134M93
PMe Ir COE Cl > e —r'-
( 3)3 ( X ) 25 °C, overnight M3 p"
93 CI
(30)
(31)
’1 CO
1. O
H—B‘ H N N H H
til 0 ‘3’ H PM K:
H I ‘\PM63 I .‘ e3,
(PM63)3IF(COE)(CI) o . = M63P71r.‘H + Me3P71r—B\
(30) 25 C, ovemrght Me3P Cl Me3P Cl '1 O
(32) (33)
90429.6
Me
”I; § 1
”'5‘ MeN NMe
‘ ’ H Me
iie '13 ,PMea .PMealN
(PMe3)3lr(COE)(CI) 25°C _ht = Me3P71r'——H + Me3P71r—B\
(30) '°"e""9 Me3P cr Me3P or Me
(34) (35)
14.4:856

Figure 54. The reactions of (PMe3)3Ir(COE)(Cl) (30) with nitrogen-containing boranes

including H[B(NH)2C6H4], H[B(NH)2C10H6] (HBDAN), and H[B(NMe)2C6H4].

95

CHAPTER 5

PRELIMINARY MECHANISTIC STUDIES OF THE IRIDIUM/PHOSPHINE

CATALYST SYSTEM FOR AROMATIC BORYLATION

For many systems, catalysis by organometallic compounds is known to go
through several of the following reactions: coordination of ligands to metals, oxidative
addition, insertion and reductive elimination. In order to elucidate the mechanism of a
homogeneously catalyzed reaction, it is a good idea to study the mechanism of each
individual step in a series of relatively elementary chemical reactions by using tools such
as kinetics, stereochemical studies, and spectroscopy. Irnportantly, each step must be
shown to be kinetically and thermodynamically reasonable. Preliminary mechanistic
studies of the Ir-catalyzed aromatic borylation were carried out and discussed in the
previous chapter. Initially, it was deemed of importance to determine the viability of Ir1
and Ir'" boryl intermediates as the CH activating species in the Irm" and/or Ir"W cycles,
respectively. Thus, the stoichiometric reactions of compounds 18nd 25 with benzene
were examined.

Stoichiometric Reactions of Ir1 and Ir Boryl Complexes with Arenes

Thermolysis of (PMe3)4Ir(BPin) (18) was carried out in C6D6 at 150 0C, the
reaction proceeded smoothly to give the corresponding iridium deuteride complex,

(PMe3)4Ir(D), and C6D5BPin (Figure 55).

96

BFHn

I \PMe3 _l ‘PMea '
M83P_!r'PMe3 C606 150°C M93P ir'PMezg * C5058P|n

PMe3 PMe3

(13)

Figure 55. Thermolysis of 18 in C6D6 at 150 °C.

From 1H NMR spectra, more than 95% (PMe3)4Ir(D) was generated from

stoichiometric reaction between 18 and C6D6 as shown in Figures 56 and 57.

97

 

 

 

 

 

 

 

 

b.o 0.0 m.o 0.." H!" «In m..." win min win h.d min
Pb .lH—rr_- _—» _—_»___P__~Frbbh_hbebhphL_» P—pppr»_h_~_
325.32%
Eangezev

 

.m_mbo§ofi 20.39 82.58% m2 Z I. ”Do of S eDeU E a“ mo max—9522. 6m gnaw:—

 

 

98

5.55 5532.:

 

 

flour—BE 8: 803 Ema co;

Hm.“ can Ema Nv._-mm._ 9:58 3on £26 .mmmboctofi Baa 83.50on MEZ I. ”Up of E eQeU E w— mo max—05.83% Km 2:”?—

99

Kinetic studies of the thermolysis of 18 in C6D6 were carried out and the reaction

rate of the thermolysis was found to follow first-order kinetics as shown in Figure 58.

 

  
     

 

 

 

0
-0.5 l
5'0
1:: -1
§
E" -1.5
y = -0.0416x - 0.0978
-2 R2 = 0.9962
-2.5
0 10 20 30 40 50 60
time (min)

Figure 58. Plot of ln([18]t/[18]o) vs. time (min) for the thermolysis of 18 in C6D6 at 130

°C.

There are two potential pathways to account for the stoichiometric transformation
between 18 and C6D6 (Figure 59). One of them involves dissociation of PMe3 to generate
a 16-electron intermediate, [(PMe3)3Ir(BPin)], followed by reaction with C6D6 to give
products. The other potential pathway involves dissociation of two PMe3 ligands and
generation of a 14-electron intermediate, [(PMe3)2Ir(BPin)], which subsequently reacts

with C6D6 to give the final products.

100

k1

 

 

 

 

 

13 [(PMe3)3lr(BPin) + PMe3] (PMe3)2lr(BPin) + PMe3
1 16 e‘ K2 14 e‘
[(3 0606 k4 C606
(PMe3)4|r(D) + CngBPin (PMe3)4lr(D) + CngBPin

Figure 59. Two potential pathways to account for the stoichiometric reaction between 18

and C6D6-

From the steady-state approximation, the rate law of the reaction is derived as

below.

d[18]

"T = Km [18] (6)

k0 k1k-2kalceDellpMeal + k1k4[(313'-'313](k2 + kalceDeD (7)
05 =
k-1k-2IPM9312 + (k-1k4 + szsllceoellpMeal + k41C606](k2 + kslceoel)

 

Phosphine inhibition experiments were carried out to determine whether the
reaction goes through a 16-electron intermediate or a 14-electron intermediate.
Experiments of thermolysis of 18 in C6D6 in the presence of various concentrations of
[PMe3] were examined. From 1/k0bs vs. [PMe3] plot (Figure 60), l/kobs obviously shows
first order dependence on [PMe3]; therefore, the experimental data are consistent with the

mechanism involving a 16-electron intermediate.

101

 

500
450
400 -
350 -
300

250

200 ,-

1 /kobs

 

y = 3275.2x + 32.689
R2 = 0.9956

   

150
100
50

 

 

 

0 0.02 0.04 0.06 0.08 0.1 0.12 0.14
[PMes] (M)

Figure 60. Plot of 1/k01,S vs. [PMe3] of the thermolysis of 18 in C6D6 in the presence of

various concentrations of PMe3.

From the results of phosphine inhibition experiments, a mechanism of the
stoichiometric transformation is proposed in Figure 61. In the proposed mechanism, the
reaction goes through phosphine dissociation to generate a l6-electron intermediate,
[(PMe3)3Ir(BPin)], which can activate the CD bond of C6D6 to form
[(PMe3)3Ir(BPin)(C6D5)(D)]. This intermediate reductively eliminate C6DsBPin to
generate [(PMe3)3Ir(D)], which is followed by re-coordination of PMe3 to form the

observed product, (PMe3)4Ir(D).

102

PMe3 - PMea

 

 

 

 

 

BPin C D
MesP Irvaes Me3P- 1r‘-PMe3 6 6
°PMe M p
PMe3 3 e3
(13)
M p ”1’88
6 r-
M33P7' 6 5
M83
PMe -PMe3 D
Me3P— ir.PMe3 —- Me3P- Ir- PMe3
PMe3 3 ’PM93 MeaP CeD5BPin

 

 

Figure 61. Our proposed mechanism for the thermolysis of 18 in C6D6

Storchiometric reaction of 25 with arenes was investigated by the thermolysis of
25 in C6D6 at 150 °C. The thermolysis of 25 gave fac—(PMe3)3Ir(D)3 as the final iridium

containing product and generated 3 equivalents of C6D5BPin. The thermolysis of 25

proceeded in a stepwise procedure as shown in Figure 62.

BPin BP'

I BPin * C6'36 l D.n
Me3P;Ir- BPin —'__.’ Me3P- lr-BPin
M93P PlMe3 - C6058P'n Me3P' PM63

1251 mm
+ CSDS ' CngBPin
D BPin
ID + C606 D
“£1932; Ir D W Me3P; -|:r--D
' In
83 PMe3 6 5 MegPI PMe3
(36i-d23

Figure 62. The process of thermolysis of 25 in C6D6 at 150 °C.

103

The process of thermolysis of 25 was monitored by 1H, HB, and 3'P{]H} NMR
spectra. Figure 63 displays the course of the reaction (the relative concentration of each
species to C6Me6 (as an internal standard) versus time (in minutes)) as monitored by 1H

NMR.

104

 

 

 

 

3
. faC-P3II‘B3 X
. faC-P3II'B2D X
A fac-P3IrBD2 x
2 5 ° fac-P3IrD3
. X C6D5BPin
x
o e; 2
*" <1)
<3 2..
E e
g '2
<6
8 “g 1.5 4 x
8 .9
m m
a 9
8 9
a: .E 1 0 . x
o - . o
x
0.5 ° A A ’
x I -
. A
. A
i A A ’
0 I e e c k 3 + f a a
0 1500 3000 4500 6000 7500
Time (min)

Figure 63. Concentration of each species relative to internal standard (C6Me6) vs. time

(min) for the thermolysis of 25 in C6D6 at 150 °C measured by lH NMR.

105

The results showed that there was an induction period in the beginning of the
thermolysis. Complex 25 was gradually converted to fac-(PMe3)3Ir(BPin)2(D) (21-d1) and
generated 1 equiv. of C6D5BPin in the first step. Then fac-(PMe3)3Ir(BPin)2(D) (21-(11)
was converted to fac-(PMe3)3Ir(BPin)(D)2 (36—d2) and the reaction generated a second
equiv. of C6D5BPin. Finally, fac—(PMe3)3Ir(BPin)(D)2 (36-d2) was transformed to fac-
(PMe3)3Ir(D)3 as the final iridium containing product and the reaction generated the third
equiv. of C6D5BPin.

The kinetic data for the thermolysis of 25 in C6D6 showed that the reaction did not
follow first order kinetics (Figure 64). Furthermore, the thermolysis was strongly
inhibited by external phosphine ligands. The inhibition phenomena are consistent with
the observations in catalytic reactions where the reaction rate decreases dramatically
when [P]:[Ir] ratio equals or exceeds 3:1. Detailed discussions will be included in the

section followed by next paragraph.

106

 

 

 

 

I

-O.5 —

I
In"
9'.
:c: -1.5 e
-2 _
I
'2.5 I I F I I
O 500 1000 1500 2000 2500 3000
Time (min)

Figure 64. Plot of ln([25]1/[25]0) vs. time (min) for the thermolysis of 25 in C6D6 at 150

°C.

107

fac-(PMe3)3Ir(BPin)(H)2 (36) and fac-(PMeg)3Ir(BPin)2(H) (21) were prepared
independently from the reaction of (PMe3)4Ir(H) (37) with HBPin and B2Pin2,
respectively (Figure 65). Compound 37 reacted with HBPin at room temperature and
generated a mixture of mer,cis-(PMeg)3lr(BPin)(H)2 (38) and fac-(PMe3)3Ir(BPin)(H)2
(36). After 6 days at room temperature, compound 36 was the predominant species in the
reaction mixture. Similarly, compound 37 reacted with B2Pin2 at 60 °C and yielded a
mixture of mer,trans-(PMe3)3Ir(BPin)2(H) (20) and fac—(PMe3)31r(BPin)2(H) (21).
Compound 21 was the predominant species after the temperature was increased to 100 0C
for 7 hours. The geometries of 20, 21, 36, and 38 were determined by 1H, HB, and

3 IP {'H} NMR spectroscopy and summarized in the experimental section.

 

 

 

-PMe3 '1' PMe3 F.) M33
(PMe3)4lr(H)+ HBPin 25°C MeaP;111-1 .— Me3P;Ir‘-H
(37) M8313 BPin 25 C M6313 éPin
(33) (36)
BPin
. 'PMea l.PMes 7533111
(PM93)1|r(H)+ B2P|nz W Me3P;llr’-H 100°C 711 Me3P-(—1’r‘—BPin
(37) MesP BPin ' Me3P H
(20) (21)

Figure 65. The reaction of (PMe3)4Ir(H) (37) with HBPin and B2Pin2.

Correlation between Phosphine Ligands and Catalytic Activity

Since both IrI and Ir"1 boryl complexes can effect stoichiometric borylation of

benzene, they are potentially viable candidates to be the C-H activating species for

108

catalytic borylation reactions. However, the stoichiometric reactions of (PMe3)4Ir(BPin)
(18) and fac-(PMe3)3Ir(BPin)3 (25) with benzene exhibit dramatically different
reactivities in terms of phosphine dependence. The thermolysis of Ir!" complex 25 in
C6D6 is strongly inhibited by external phosphine ligands, whereas the thermolysis of Ir1
complex 25 shows inverse first-order dependence on [PMe3]. For catalysis to occur it is
usually required to produce vacant coordination sites in organometallic complexes. Since
both compounds are coordinatively saturated 18-electron complexes, it is not surprising
that the stoichiometric reaction of 18 or 25 with benzene proceeds slowly at elevated
temperature. As previously mentioned it was shown that a phosphine dissociation
pathway is responsible for generating active species to activate C-H bonds of benzene in
the stoichiometric reaction of 18 with benzene. Furthermore, in the catalytic borylation
reactions, the reaction rate was shown to be dependent on the nature of phosphine ligands
and the relative concentration between phosphine ligands and iridium metal complex.57 In
particular, borylation rates were appreciable when [P]:[Ir] < 3:1 but decreased
dramatically when [P]:[Ir] ratio equaled or exceeded 3:1. The fact that phosphine
inhibition is observed in the thermolysis of complex 25, which contains three PMe;
ligands, in the presence of external phosphine ligands is consistent with the inhibition
phenomena seen in catalytic reactions when [P]:[Ir] ratio equals or exceeds 3:1. The
thermolysis of IrI complex 18, however, shows inverse first order dependence on [PMe3].
The reaction rate decreases when the concentration of PMe3 increases. Since the
thermolysis of 18 is not completely shut down when [P]:[Ir] >> 3, the observation is not

not consistent with that in catalytic reactions. These experimental observations support a

109

mechanism involving an Ir!“ boryl intermediate being the C-H activating species in these
catalytic borylation reactions.

Substantially improved catalytic activity was observed with the use of bidentate
chelating phosphine ligands including 1,2-bis(diphenylphosphino)ethane (dppe) and 1,2-
bis(dimethylphosphino)ethane (dmpe). This observation strongly supports the viability of
bisphosphine intermediates. A further piece of evidence is that the 18-electron
bisphosphine compound, (PMe3)2Ir(H)5, is an effective pre-catalyst for aromatic

lll

borylation. Those data imply a mechanism involving Ir and Irv intermediates in a Ir"W

catalytic cycle.

Stoichiometric and Catalytic Borylations of Iodobenzene

Previously it was found that iridium catalysts generated from an Irl source,
(Ind)Ir(COD) (13) and dppe, were ineffective for the aromatic borylation of iodobenzene.
However, iodobenzene and HBPin reacted smoothly to yield an isomer mixture of
C6H4(I)(BPin) when active catalysts were generated from an Irm source, (MesH)Ir(BPin)3
(14) and dppe. Both the 11’ boryl complex, (PMe3)4Ir(BPin) (18), and the 11‘" boryl
complex, fac-(PMe3)3Ir(BPin)3 (25) can effect stoichiometric reactions with benzene to
produce PhBPin and the corresponding hydride complexes. However, the arene products
from stoichiometric reactions of 18 and 25 with iodobenzene differ substantially.
Specifically, compound 18 reacted rapidly with iodobenzene at room temperature to form
an off-white precipitate, but isomers of C6H4(I)(BPin) were not detected, even after

prolonged thermolysis. Analysis of the 1H and 31P{1H} NMR spectra of the off-white

110

precipitate from the reaction indicated that the material contained a number of species,
which could not be identified (Figure 66). Presumably, the reaction proceeded via
oxidative addition of iodobenzene to complex 18 to form [(PMe3)3Ir(I)(C6H5)(BPin)]
followed by several potential reaction pathways to generate a variety of products. For

example, [(PMe3)3Ir(I)(C6H5)(BPin)] could eliminate C-B or I-B bonds.

1H NMR spectrum ':

'.
,/i “
/ _. l ' .
r‘ \ ‘5 ”A- __ _ «‘._~ ‘ _, 14‘1"} L]. Jr»): ‘_A 1K, J‘\_ 1.. .44 ‘~ . . '_,/ ‘v‘ i r ‘

\1 ‘ l

2.60 2.40 2.20" “”2100“ '1."80'T‘1.60 ' 1.40” ”1.20 ‘

1'B NMR spectrum
1 1
"78"”63“ 5040 "30 2‘0 10’ '0 8 11’0" 1208180140 £63160" 470

31P{1H} NMR spectrum

  
  

 

 

 

 

 

 

 

Figure 66. 'H, “B, and 3‘P{‘H} NMR spectra of the off-white precipitate from the

reaction between 18 and C6H5I.

lll

Conversely, thermolysis of 25 in iodobenzene at 150 oC produced, in addition to a
45% yield of PhBPin, m- and p-C6Ha(I)(BPin) in 54% yield (Figure 67). The significant
quantities of PhBPin formed were presumably generated from a competitive C-I

activation pathway followed by PhBPin reductive elimination.

 

fac-(PMe3)3Ir(BPin)3 150°C 4* \—\/ I + Q—BPin

(25) BPin
(54% 60 yield) (45% 60 yield)

Figure 67. Thermolysis of 25 in iodobenzene.

The previous paragraph demonstrates that borylation products of iodobenzene are
not obtained when IrI sources are used under stoichiometric and catalytic conditions,
whereas, Ir"l complexes effect both stoichiometric and catalytic borylations. Furthermore,
in situ generation of “Ir”I species” from an IrI source, compound 13, and dppe has been
demonstrated to be a viable way to generate effective catalysts for borylation of
iodobenzene. These experimental observations are consistent with a mechanism

111

involving Ir and IrV intermediates.

Kinetic Isotope Effects in Aromatic Borylation

112

The isotope effects involved in the activation of arene C-H bonds by the
intermediate [Cp*Rh(PMe3)] have been investigated by Jones and F eher.5 8 In their study
of reductive elimination of arenes from aryl hydride complexes Cp*Rh(PMe3)(Aryl)(H),
they discovered that a low—energy pathway existed for the interconversion of the carbon
attached to the metal. The isomerization was found to occur in a sequential [1,2] fashion,
and it can be accommodated by the reversible formation of an nz-arene complex as

shown in Figure 68.

i9: ‘59:: 592:

I
/Rh"'PMe3 —— Rh _. H,Rh-"PMe3

H I "'PMea
{ > 1)

Figure 68. The process of reversible formation of nz-arene complexes proposed by Jones

 

 

and Feher.

The photolysis of Cp*Rh(PMe3)(H)2 offers a convenient method for the
photoinduced generation of the coordinatively unsaturated intermediate [Cp*Rh(PMe3)]
by elimination of dihydrogen. The active species is able to activate OH or CD bonds
under conditions of kinetic control. Jones et al. conducted a kinetic isotope experiment by
irradiating Cp*Rh(PMe3)(H)2 in a 1:1 (vzv) mixture of CsHs/C6D6 at 10 0C, which
resulted in the evolution of H2 and the formation of the benzene C-H/C-D activation
products Cp*Rh(PMe3)(C6H5)(H) (4) and Cp*Rh(PMe3)(C6D5)(D). Quenching of the

reaction with CCla forms the corresponding chloro derivatives Cp*Rh(PMe3)(C6H5)(Cl)

113

and Cp*Rh(PMe3)(C6D5)(Cl). Mass spectral analysis of this mixture revealed a 1.05:1
ratio of the products in which C6H6 versus C6D6 has been activated (Figure 69). Since
benzene is not labile in the products Cp*Rh(PMe3)(C6Hs)(H) and
Cp*Rh(PMe3)(C6D5)(D) under the condition of the experiment (10 °C), this ratio reflects
the kinetic isotope effect for arene complexation and/or C-H bond activation. This small
value of kszD was consistent with there being little or no C-H bond breaking in the rate-

determining step.

 

kHIkD = 1.05 Z 1.00

Figure 69. Observed kH/kD in the activation of a 1:1 mixture of Cng/CbDb by the

intermediate [Cp*Rh(PMe3)].

In order to access the C-H bond-breaking step, Jones et a1. carried out a similar
kinetic isotope effect experiment with 1,3,5-C6D3H3 and kH/kD was determined to be 1.4.
Because complexation of [Cp*Rh(PMe3)] to 1,3,5-C6D3H3 can produce one possible 112-
arene complex, the ratio kH/kD for this reaction reflects only the isotope effect involved in
the cleavage of the C-H. Since both experiments involve bimolecular activation of the
benzene C-H/C-D bond ([Cp*Rh(PMe3)] + benzene), their observation of different
kinetic isotope effects for these two experiments prove that a direct insertion of

[Cp*Rh(PMe3)] into the OH bond of benzene is not occurring. In other words, they have

114

determined that the activation of arene C-H bonds by [Cp*Rh(PMe3)] proceeds through
an intermediate complex, [Cp*Rh(PMe3)(n2-C(,I{6)].

In order to have a deeper understanding of the mechanism of borylation by
(Ind)Ir(COD) (13)/2 PMe3 or (MesH)Ir(BPin)3 (14)/2 PMe3 pre-catalyst system and
hopefully identify the rate-determining step in the catalytic borylation reactions,
borylation reactions in a molar ratio 1:1 mixture of C6H6/C6D6 and separately in 1,3,5-
C6D3H3 were carried out. If a kinetic isotope effect is observed for the borylation reaction
in a molar ratio 1:1 mixture of C6H6/C6D6, it may result from coordination of C6H6 vs.
C6D6 or from the C-H/C-D bond breaking step. On the other hand, the kinetic isotope
effect for the borylation reaction of 1,3,5-C6D3H3 can only result from the C-H bond
activation step since there is only one arene for coordination. The results from

experiments of catalytic reactions are summarized in Table 22.

115

Table 22. Borylation reactions with HBPin in a molar ratio 1:1 mixture of C6H6/C6D6 or
1,3,5-C6D3H3 catalyzed by Irl and IrIll sources at 150 °C, [Ir] = 2 mol%, [PMeflzLIr] = 2: 1.

 

 

 

 

 

Entry Pre—catalysts Substrate Product Distribution”
(MesH)Ir(BPin)3 (14) Molar ratio 1:1 CstBPinszHsBPin
1
rr'" (gm/C11)6 1.00:2.28 (100% conversion)
14 C6D2H3(BPin):C6D3H2(BPin)
2 193,59'C6D3H3
Ir'" 1001.94 (100% conversion)
(Ind)Ir(COD) (13) Molar ratio 1:1 CgDsBPinzCoHsBPin
3
Ir' c.5H1,/(:6D6 1002.29 (100% conversion)
13 C6D2H3(BPin):C6D3H2(BPin)
4 1,3,5,-C6D3H3
rr' 1.00:2.06 (100% conversion)

 

 

 

 

 

 

Comparison of the results in Table 22 shows similar kH/kD values for the
borylations of C6H6/C6D6 (1:1) and of 1,3,5-C6D3H3 by Irl or Irm. Furthermore, it appears
that the kinetic isotope effect is essentially identical from the IrI and Ir"1 pre-catalyst
sources, which suggests a similar or same active species. The large observed kinetic
isotope effect in borylations of CeHe/CeDs (1:1), which is different from Jones’ case,
suggests that arene coordination cannot be the rate-determining step. If the arene
coordination is the rate—determing step, we expect to see no or, at most, a very small
kinetic isotope effect since it does not involve the OH bond breaking event. However,
current data cannot distinguish whether C-H bond breaking or reductive elimination of

the arylboronic ester is the rate-determining step (see Figure 73). If reductive elimination

116

of the arylboronic ester were the rate-determining step, we would expect to see a small
secondary isotope effect because the reaction does not involve cleavage of C-H/C-D
bonds. The expected small isotope effect differs from relatively large observed kH/kD
(2.06 and 1.94) for the borylations in 1,3,5-C6D3H3 fi'om Irl and Irl" sources, respectively.
However, it is important to remember that any step prior to the rate-determining step can
contribute to the observed kinetic isotope effect. Therefore, the current data cannot
definitely determine the actual rate-determining step in the borylation reactions.
Stoichiometric borylations of (PMe3)4Ir(BPin) (18) and fac—(PMe3)3Ir(BPin)3 (25)
in a 1:1 mixture of CfiHb/CfiDfi and separately in 1,3,5-C6D3H3 were also examined.
Thermolysis of 25 in a 1:1 mixture of C6H6/C6D6 and separately in 1,3,5-C6D3H3 at 150
oC gave similar kinetic isotopes effect kH/kD as compared to the catalytic borylation
reactions, whereas thermolysis of 18 in a 1:1 mixture of CgHg/C6D6 and separately in
1,3,5-C6D3H3 at 150 °C gave relatively larger kinetic isotope effect kH/kD than those

observed in catalysis as shown in Table 23.

117

Table 23. Stoichiometric borylation reactions of 18 and 25 with a molar ratio 1:1 mixture
Ofchb/C6D6 OI‘ 1,3,5-C6D3H3 at 150 °C.

 

 

 

 

 

 

 

 

 

Entry Iridium Complex Substrate Product Distribution59
fac-(PMe3)3Ir(BPin)3 Molar ratio 1:1 C6DsBPin:C6H5BPin
l
(25)
C6H6/C6D6 1.00:2.53 (100% conversion)
11,111
25 C6D2H3(BPin) : C6D3H2(BPin)
2 193959-C6D3H3
Ir'” 1001.93 (100% conversion)
(PMe3)4Ir(BPin) (18) Molar ratio 1:1 C6D5BPin:C6H5BPin
3
Ir] CdidC6D6 1.00:2.67 (100% conversion)
18 C6D2H3(BP11’1)2C6D3H2(BP111)
4 1,3,5,-C6D3H3
Ir' 1002.37 (100% conversion)

 

Mechanistic Discussions

The existence of an arene coordination step in the catalytic cycle of aromatic

borylation by 13/2 PMe3 or 14/2 PMe3 pre-catalyst systems cannot be completely ruled

out based on the present data. However, Miyaura26f and co-workers reported the isolation

of a trisboryl complex [Ir((dtbpy)(COE)(BPin)3] as shown in Figure 70, which is

chemically and kinetically competent to be an intermediate in the catalytic process in

their pre-catalyst system (3 mol% 1/2[IrCl(COE)2]2/dtbpy). Based on a lesson from

118

 

Halpem’s work in elucidating the mechanism of the hydrogenation reaction catalyzed by
Wilkinson’s catalyst, (PPh3)3Rh(Cl), isolation of a stable olefin complex is inconsistent
with an 112—arene complex pathway. Therefore, the arene coordination step prior to C-H

bond activation seems unlikely.

 

[ll’(COE)2Cl]2 * + szlnz

mesitylene

   

Figure 70. A trisboryl complex [Ir((dtbpy)(COE)(BPin)3] isolated by Miyaura and co-

workers.

There are two potential pathways for the active species to react with an arene.
One possibility is that it proceeds through oxidative addition of a C-H bond of an arene to
give an Irv intermediate followed by reductive elimination of an arylboronate ester to
give the corresponding hydride complex. Another option is that the corresponding
hydride complex is formed in a one-step “o-bond metathesis” reaction as shown in
Figure 71. o-bond metathesis has been confirmed only for (10 complexes of the early

transition metal and lanthanides, where oxidative addition is precluded.

119

PinB \BPin

(PR312‘-‘-
+ Ph- 4"\ Ph - Ph-BPin
PinB H

111 . IrV intermediate
[(PR3)2lr (BPIn)3l
C-H activating species

+m 1 ,BPin‘ 1/Ph-:3Pin

[(PRsizlr“'(BPin>21Hil

(PR3)2(BPin)2'r~/.‘ ’:Ph
\H’

o-bond metathesis
transition state

Figure 71. Possible mechanisms for Ir"I borylation reaction.

Although we have not yet investigated the mechanism of the borylation
extensively, we have obtained qualitative information regarding this question. From the
kinetic studies of the stoichiometric reaction of (PMe3)4Ir(BPin) (18) with benzene, we
established that the intermediate [(PMe3)3Ir(BPin)] activates the C—H bond of benzene.
Furthermore, in the stoichiometric reaction of fac-(PMe3)3Ir(BPin)3 (25) with benzene, a
transient species similar to [(PMe3)2Ir(BPin)3], presumably generated in the reaction
mixture, activates the C-H bond of benzene. Therefore, oxidative addition of a C-H bond
of an arene to an iridium boryl complex is a viable reaction pathway. In order to evaluate
PhBPin reductive elimination, we examined the thermolysis of compound 28 in C6D6.
Compound 28 has the BPin group trans to the phenyl group and it is stable at room
temperature. Before reductive elimination of PhBPin occurs, compound 28 is expected to
isomerize to another isomer with the BPin group and the phenyl group in a cis geometry.

Thermolysis of compound 28 in C6D6 at 50 °C was carried out and the reaction was

120

monitored by 1H, 11B, and 31P{1H} NMR spectroscopy. At 50 OC, compound 28 was
converted to a mixture of fac-(PMe3)3Ir(C6D5)(D)(H) (39), fac-(PMe3)3Ir(BPin)(H)2 (36),
and (PMe3)4Ir(H) (37), and PhBPin was produced. After 55 hours, compound 28, 39, 36,

and 37 were in the ratio of 16:73:11:<1 (Figure 72).

BPin

I APM83 C6061 " PhBPin
Me3P711—H o =
M6313 FLh 50 C, 55 h

,PMe3
Me3P;|r -H
Me3P

(28) 1 0506

 

 

 

(28)3(39)=(36)I(37) = 16:73:11:<1

Figure 72. Thermolysis of compound 28 in C6D6 at 50 °C.

Presumably reductive elimination of PhBPin from compound 28 generates an
intermediate, [(PMe3)3Ir(H)], which can subsequently activate a C-D bond of CbDr, to
form compound 39. Compound 36 most likely comes from the oxidative addition of
HBPin to the intermediate [(PMe3)3Ir(H)]. HBPin could come from a minor pathway

involving H-B reductive elimination from compound 28. The generation of PhBPin from

121

the thermolysis of compound 28 in C6D6 shows that PhBPin reductive elimination is a
viable pathway as well. In addition to some other observations discussed previously: (1)
Borylation products of iodobenzene are not obtained when IrI sources are used under
stoichiometric and catalytic conditions, whereas Ir"I complexes effect both stoichiometirc
and catalytic borylations. (2) Improved catalytic activity is observed with chelating
phosphines and inhibition is observed when [P]:[Ir] ratios equal or exceed 3:1, strongly
supporting the viability of bisphosphine intermediates. (3) The l8-electron bisphosphine
compound, (PMe3)2Ir(H)5, is an effective pre-catalyst for borylation. Therefore, we
presently favor the simple scheme which involves a direct oxidative addition of a CH
bond of an arene to the proposed active species, [(PR3)2Irm(BPin)3] to form an lrV
intermediate, [(PR3)2Ir"'(BPin)3(H)(Ph)]. Reductive elimination of PhBPin from the Irv
intermediate, [(PR3)2Ir"‘(BPin)3(H)(Ph)], gives [(PR3)2Irm(BPin)2(H)], which converts to
[(PR3)2IrV(BPin)3(H)2] in the presence of HBPin. After releasing H2, the reaction
regenerates [(PR3)2Irm(BPin)3], the proposed C-H activating species, to complete the

catalytic cycle as shown in Figure 73.

122

H2 [(PR3)2|r"'(BPin)3] ch6
C-H activating species
HBPin
PinB OBPin
(PR31211"'(H)18P1n>2 (P8312 11‘“
. /1
PinB H

QBPin

Figure 73. A putative mechanism for aromatic borylations catalyzed by iridium boryl

complexes.

An interesting reactivity was observed in the thermolysis of fac-(PMe3)3lr(BPin) 3
(25) in C6D6 in the presence of 10% of (MesH)Ir(BPin)3 (14). The reaction proceeded at
100 °C instead of occurring at 150 °C to generate a mixture of fac-(PMe3)3Ir(BPin)2(H/D)
and fac-(PMe3)3Ir(BPin)(H)(D) in approximately 62:38 ratio and C6D5BPin after 33.5
hours. The hydride presumably comes from a PMe3 ligand. As has been discussed earlier,
the mesitylene ligand of compound 14 is very labile presumably due to the very strong
trans influence of the BPin group, therefore, it is most likely that 14 acts as a phosphine

trap, which facilitates the PMe3 dissociation from compound 25 in the thermolysis

123

reaction of 25 in C6D6. The actual role of complex 14 in the reaction and the difference in
terms of reactivity require further elucidation.

Miyaura, Ishiyama, and co-workers60 recently developed a new catalyst system
(1.5 mol% [Ir(OMe)(COD)]2/ 3 mol% dtbpy) for borylation of arenes at room
temperature with a stoichiometric amount of boron reagent (B2Pin2) and arene to
produce the corresponding arylboronates in high yield. This new system has extended the
functional group tolerance to a CN group. The high catalyst efficiency of
[Ir(OMe)(COD)]z can be attributed to the more facile formation of iridium boryl
complexes. Iridium triboryl complexes have been implied as possible intermediates in the
borylation of arenes. Presumably, the transmetallation reaction between B2Pin2 and
[Ir(OMe)(COD)]z results in the formation of an Irl boryl complex after releasing
MeOBPin. The Irl boryl complex then undergoes oxidative addition of B2Pin2 to yield an

Ir'" triboryl complex as shown in Figure 74.

 

+ szlnz + szinz gpin
I -OR + B P' | -BP' ——> — '
[r] 2 1n2 _ MeOBPin [r] In [éréinBPln

[Ir] = [lr(bpy)(COD or COE)]

Figure 74. Iridium tris(boryl) intermediate in borylation reactions.

The results from preliminary mechanistic studies on the new iridium catalyst

[V .
I“ catalytic

system indicate that a mechanism involving Ir!" and Irv intermediates in an Ir
cycle is most likely. Correlations between the stoichiometric and catalytic reactions

provided a deeper insight into the mechanism of aromatic borylation.

124

Our studies allow arylboron species to be prepared in an economical fashion and
also demonstrate that C-H bond activation and functionalization can be developed into a
practical synthetic tool. Future work is needed to further elucidate the mechanism for
aromatic borylations catalyzed by iridium boryl complexes in order to have a deeper
understanding for this important transformation. With the rapid advances in this area, we
expect that Ir-catalyzed borylations of aromatics will certainly find acceptance in the

synthetic arsenal of organic chemists.

125

CHAPTER 6

EXPERIMENTAL

General Considerations

All manipulations were performed using glove box, Schlenk, or vacuum-line
techniques. Pentane, diethyl ether, and tetrahydrofirran were pre-dried over CaCl2 and
distilled from Sodium/benzophenone ketyl. Toluene and benzene were pre-dried over
CaCl2 and distilled from Sodium metal. Methylene chloride was pre—dried over C aC l 2 and
distilled from CaH2. Cyclohexane was purified and dried according to the method
reported by Perrin and Armarego.6| Hexamethyldisiloxane, decane, and dodecane were
distilled from sodium metal.

CDCl3, tetrahydrofuran-d3, p-xylene-dm, cyclohexane-d12, and 1,3,5-C6D3H3 were
dried with and vacuum transferred from 3A sieves. Benzene-d6 and toluene-d3 were dried
with, vacuum transferred from 3A sieves, and stored over a sodium mirror. CD2C12 was
dried with 4A sieves.

HBPin was purchased from Aldrich, further purified by stin'ing with PPh; to
remove BH3, and then vacuum distilled to give the borane as a clear viscous liquid.
B2Pin2 was purchased from Frontier Scientific and used as received. PMe3 and PMe3-d9
were purchased fi'om Aldrich and vacuum transferred to an air—free flask respectively
before use. PEt3, P'Pr3, P’Bug, PCy3, PPh3, 1,2-Bis(diphenylphosphino)ethane (dppe), 1,2-
Bis(diphenylphosphino)propane (dppp), Bis(dimethylphosphino)methane (dmpm), 1,2-
Bis(dimethylphosphino)ethane (dmpe), 1,2-Bis(dicyclohexylphosphino)ethane (dCype),

1,2-Bis(diphenylphosphino)benzene (dppb), 2,2’-dipyridyl (bpy), 4,4’-di-tert-butyl-2,2’-

126

dipyridyl (dtbpy), 2-(diphenylphosphino)-2’-(N,N-dimethylamino)biphenyl, 2-
(dicyclohexylphosphino)-2’-(N,N-dimethylamino)biphenyl, 1,10-phenanthroline, and
2,2’-bithiophene were used as received from commercial sources. 1,2-dimethoxyethane,
N,N,N,N-tetramethylethylenediamine (TMEDA), thiophene and triethylsilane were
distilled prior to use.

Substrate: anisole, N,N-dimethylaniline, 2,6-lutidine, benzotrifluoride, N,N-
diethylbenzamide, ethylbenzoate, 1,3,5-C6H3F3, and 4-fluorobromobenzene were distilled
and further dried by passing through a column of activated alumina prior to use. C6HF5
and l,3-bis(trifluoromethyl)benzene were distilled and then dried over 4A sieves,
followed by vacuum transfer to an air-free flask. m-xylene, p-xylene, o-xylene,
fluorobenzene, chlorobenzene, bromobenzene, 1,2-dichlorobenzene, 1 ,3-
dichlorobenzene, 1,3-dibromobenzene, 4-chlorobenzotrifluoride, 4-fluoroanisole, 4-
chloroanisole, 4-chlorotoluene, 2-chloroanisole, 2-chlorotoluene, and 2-methylanisole
were distilled from Sodium metal. Veratrole and l,4-bistrifluoromethylbenzene were
distilled from CaH2. 1,4—dichlorobenzene was sublimed prior to use.

Starting materials: [Ir(COD)Cl]2,62 [Ir(COE)2Cl]2,62 (Ind)Ir(COD),“
(PMe3)41r(Cl),64 (PMe3)4Ir(H),44 (PMe3)4Ir(Me),52 (PMe3)3Ir(Ph),55 Cp*Rh(n4-C6Me6),65
Cp*Irtn4-C6Me61,“ Cp*1r(PMes)(H)2,67 Cp*IrtPtCDihxrlh,“ (CsMe4Et)Ir(PMes)(H)2,"7
(PMe3)2Ir(H)5,68 Cp"‘IrH4,69 and Cp"‘Ir(PMe3)(H)(BPin)21 were prepared according to
literature methods.

1H and 13C{'H} NMR spectra were recorded on Varian Inova—300, VXR-SOO, or
Inova—600 spectrometers and referenced to residual proton solvent signals. llB, 19F, and

31P{lH} spectra were recorded on Varian VXR—300 or Varian [nova—300 spectrometers,

127

operating at 96.29, 282.35, and 121.49 MHz respectively and referenced to external

standards. Boron chemical shifts were referenced to a neat BF 3-Et2O external standard.
Fluorine chemical shifts were referenced to a neat CFC13 external standard. Phosphorous
chemical shifts were referenced to an 85% phosphoric acid external standard. Elemental
analyses were performed at Michigan State University using a Perkin Elmer Series II

CHNS/O Analyzer 2400. GC-MS data were obtained using a HP 61 800A GCD system.

Syntheses

(MesH)Ir(BPin)3 (l4). Complex 13 (2.54 g, 6.11 mmol) and HBPin (3.91 g,
30.55 mmol) were dissolved in 32 mL mesitylene. The light brown solution was then
heated at 75 °C for 48 h. The reaction mixture turned to dark brown after 24 h at 75 °C.
Mesitylene was removed under high vacuum to give viscous dark brown oil. The crude
mixture was then triturated with hexamethyldisiloxane (3 x 2 mL). A white solid (797
mg, 19%) was obtained after filtration and washed with cold hexamethyldisiloxane. mp
140 °C (dec). IH NMR (600 MHz, Cst) 8 1.33 (s, 36H, 3 BO2C6H12), 2.24 (s, 9H, 3
CH3), 5.62 (s, 3H, 3 CH). ”B NMR (Cst) 6 32.5. '3C{‘H} NMR (300 MHz, C6D6) 6
19.7 (s), 25.7 (s), 81.0 (s), 97.0 (s), 118.05 (8). Anal. Calcd for C27H43kB206: C, 46.77;
H, 6.98. Found: C, 47.13; H, 7.18.

mer-(PMe3)3Ir(BPin)(H)(CI) (15). A solution of PMe3 (102 mg, 1.34 mmol) in 2
mL THF was added dropwise to a solution of [Ir(COE)2Cl]2 (200 mg, 0.22 mmol) in 4
mL THF solution. The reaction mixture was stirred at room temperature for 2 h. The

solvent was then removed under reduced pressure. The residue was redissolved in 6mL

128

THF and a solution of HBPin (65 11L, 0.45 mmol) in 2 mL THF was added dropwise. The
reaction mixture was stirred at room temperature overnight. Next day, the solution was
filtered through celite to remove trace suspension. The filtrate was pumped down to give
a spectroscopically pure white solid (243.0 mg, 93%). The product can be recrystallized
from concentrated THF solution at —30 °C to give colorless crystals. mp 170-172 0C
(dec). 1H NMR (C6D6) 5 -9.66 (dt, J= 136.4 Hz, 21.8 Hz, 1H, hydride), 8 1.04 (s, 12H,
BO2C6H12), 1.37 (d, J = 7.9 Hz, 9H, PMe; trans to hydride), 1.62 (t, J = 3.7 Hz, 18H, 2
PMe3 trans to each other). l3C(‘H1 NMR (C6D6) 6 18.4 (d, J: 26.7 Hz), 20.7 (dt, J: 3.5
Hz, 19.1 Hz), 25.8 (s), 80.8 (s). ”B NMR (C6D6) 6 28.5. 3‘P1‘H} NMR (C613,) 6 —46.1
(t, J = 20.6 Hz, 1P, PMe3 trans to hydride), —40.4 (d, J = 21.4 Hz, 2P, 2 PMe3 trans to
each other). Anal. Calcd for C15H4oIrBClO2P3: C, 30.86; H, 6.91. Found: C, 30.91; H,
7.06.

mer,cis-(PMe3)3Ir(BPin)2(Cl) (17). A solution of B2Pin2 (191 mg, 0.75 mmol) in
5 mL THF was added to a suspension of (PMe3)4Ir(Cl) (400 mg, 0.75 mmol) in 30 mL
THF in a schlenk tube. The reaction mixture was heated at 70 °C for 1 day. The orange
suspension gradually changed to a gray color suspension. The reaction mixture was
cooled down and filtered through celite to remove gray precipitates. The filtrate was then
pumped down to give a colorless crystalline solid. The crude product was recrystallized
from pentane at —30 °C. The product was collected as colorless crystals (390 mg, 73%).
mp 156-158 °C (dec). 1H NMR (C6136) 6 1.10 (s, 12H, 302C6H12), 1.22 (s, 12H,
BO2C6H12), 1.31 (d, J = 6.9 Hz, 9H, PMe-5 trans to BPin), 1.72 (t, J = 3.6 Hz, 18H, 2
PMe3 trans to each other). 13C(‘H} NMR (Cst) 6 15.9 (t, J: 19.1 Hz), 19.4 (d, J: 41.3

Hz), 25.4 (s), 81.9 (s). ”B NMR (C6D6) 6 28.0, 36.5. 3‘P1‘H} NMR (C6D6) 6 -514 (br,

129

1P, PMe3 trans to BPin), -41.1 (d, J = 26.9 Hz, 2P, 2 PMe3 trans to each other). Anal.
Calcd for C21H51IrB2C104P3: C, 35.53; H, 7.24. Found: C, 35.48; H, 7.60.

(PMe3)4lr(BPin) (18). A solution of PMe; (161 mg, 2.12 mmol) in 4 mL THF
was added to a solution of 17 (500 mg, 0.7 mmol) in 5 mL THF in a schlenk tube. A
solution of KO’Bu (158 mg, 1.4 mmol) in 5 mL THF was then added to the reaction
mixture. The reaction mixture was stirred at room temperature for 90 min. The solvent
was removed under reduced pressure. The product was extracted with 8 mL pentane. The
pentane filtrate was then pumped down to give a white solid (402 mg, 92%). The material
always contained a small amount of (PMe3)4Ir(H) (37) (ca. 3% by 1H NMR) due to its
considerable moisture sensitivity). The product was recrystallized from a concentrated
pentane solution at -30 0C to give colorless crystals. mp 130-137 °C (dec). 1H NMR
(Cng, 25 °C) 6 1.24 (s, 12H, 302C6H12), 1.58 (br s, 36H, PMe3). ‘3C1'H1 NMR (C601,,
25 °C) 6 26.8 (s), 28.9 (m), 81.0 (s). ”B NMR (C6D6) 6 38. 3'P{'H} NMR (C6D6, 25 °C)
5 —57.5 (br s, 4P). Anal. Calcd for C13H431IBOZP4Z C, 34.67; H, 7.76. Found: C, 34.76; H,
7.89.

fac—(PMe3)3Ir(BPin)3 (25). A solution of PMe3 (220 mg, 2.9 mmol) in 2 mL CgHr,
was added a solution of 14 (400 mg, 0.58 mmol) in 4 mL C6116 in a vial. The reaction
mixture was stirred at ambient temperature for 30 min and the solvent was removed
under reduced pressure to give a white solid (461 mg, 99%). The product was
recrystallized from a concentrated pentane solution at —30 °C to give colorless crystals.
mp 184 °C (dec). 1H NMR (CeDe) 5 1.34 (s, 36H, BOzCoHiz), 1.52 (m, 27H, PMe3).

l3C(‘H} NMR (C6D6) 23.7 (m), 26.5 (s), 80.4 (s). “B NMR (C6D6) 6 36.0. 3"1>{‘H} NMR

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(C6D6) 8 —64 (br, 3P). Anal. Calcd for C27H63Ir8306P3: C, 40.47; H, 7.92. Found: C,
40.72; H, 8.01.

fac-(PMe3)3Ir(BPin)(H)(Me) (26). A solution of HBPin (27 mg, 0.21 mmol) in 2
mL pentane was added to a solution of (PMe3)4Ir(Me) (100 mg, 0.21 mmol) in 4 mL
pentane. The reaction mixture was stirred at ambient temperature for 5 min and the
solvent was then removed under reduced pressure to give an isomer mixture of fac-
(PMe3)3Ir(BPin)(H)(Me) (26) and mer-(PMe3)3Ir(Me)(H)(BPin) (27) in a ratio of 83:17
(94 mg, 75%). fac—(PMe3)3Ir(BPin)(H)(Me) (26). 1H NMR (CsDe) 8 -11.30 (dt, J = 140.4
Hz, 18.9 Hz, 1H, hydride), 0.40 (m, 3H, Me), 1.17 (d, J = 6.4 Hz, 9H, PMe3 trans to
BPin), 1.25 (s, 12H, BOzCsHiz), 1.35 (d, J = 7.3 Hz, 9H, PMe3 trans to hydride), 1.47 (d,
J = 7.9 Hz, 9H, PMe3 trans to Me). ‘3C{‘H} NMR (CgDo) 6 -36.3 (dt, J = 62.5 Hz, 7.6
Hz, Me), 19.9 (ddd, J= 24.7 Hz, 5.5 Hz, 2.7 Hz), 20.9 (dt, J= 21.3 Hz, 2.7 Hz), 22.0 (td,
J = 18.5 Hz, 4.1 Hz), 25.8 (s), 25.9 (s), 80.1 (s), 80.2 (s). 1]B NMR (C6D6) 8 38.6.
3'P{'H} NMR (C6D6) 6 -63.3 (br, 1P, PMe3 trans to BPin), -56.83 (dd, J = 13.4 Hz, 23.2
Hz, 1P, PMe3 trans to hydride), -55.16 (dd, J = 13.4 Hz, 18.3 Hz, 1P, PMe3 trans to Me).
mer-(PMe3)3Ir(Me)(H)(BPin) (27). 1H NMR (CeDe) 5 -11.98 (dt, J = 131.9 Hz, 23.0 Hz,
1H, hydride), -0.06 (m, 3H, Me), 1.19 (s, 12H, 302C6H12), 1.14 (d, J = 29.9 Hz, 9H,
PMe3 trans to hydride), 1.54 (t, J = 3.4 Hz, 18H, 2 PMe3 trans to each other). ”B NMR
(C6D6) 6 38.6. 3"1>{‘H} NMR (C6D6) 6 - 57.8 (t, J= 22.9 Hz, 1P, PMe3 trans to hydride),
-48.2 (d, J = 22.9 Hz, 2P, 2 PMe3 trans to each other). Anal. Calcd for C1611431rBO2P3: C,
34.11; H, 7.69. Found: C, 33.64; H, 7.70.

mer-(PMe3)3Ir(BPin)(H)(Ph) (28). A solution of HBPin (55 mg, 0.43 mmol) in 2

mL pentane was added to a solution of (PMe3)3Ir(Ph) (194 mg, 0.39 mmol) in 5 mL

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pentane. The reaction mixture was stirred at ambient temperature for 30 min and the
solvent was removed under reduced pressure to give mer-(PMe3)31r(BPin)(H)(Ph) (241
mg, 95%). The product was recrystallized from a concentrated pentane solution at —30 °C
to give colorless crystals. mp 118 °C (dec). IH NMR (C6D6, 25 °C) 8 -11.32 (dt, J = 131
Hz, 20 Hz, 1H, hydride), 1.16 (s, 12H, BO2C6H12), 1.41 (m, 27H, PMe3), 7.17-7.20 (m,
3H), 7.98 (br, 2H). 13C{1H} NMR (C6D6, 25 °C) 5 21.5 (d, J= 24.7 Hz), 22.2 (dt, J= 4.5
Hz, 19.1 Hz), 26.0 (s), 80.0 (s), 120.7 (s), 126.9 (s), 148.2 (br), 150.6 (br). 11B NMR
(C613,) 6 35.8. 3‘P{'H} NMR (c6136) 6 —57.8 (t, J= 22.9 Hz, 1P), -45.6 (d, J: 22.0 Hz,
2P). Anal. Calcd for C21H45IrBO2P3: C, 40.32; H, 7.25. Found: C, 39.95; H, 7.38.
fac—(PMe3)3Ir(BPin)(H)(SiEt3) (29). A solution of HSiEt3 (17 mg, 0.15 mmol) in
2 mL C6H6 was added to a solution of 18 (92 mg, 0.15 mmol) in 3 mL C6H6. The reaction
mixture was stirred at ambient temperature for 2.5 days and the solvent was removed
under reduced pressure to give colorless solid. The product was recrystallized from a
concentrated pentane solution at —30 °C to give colorless crystals (83 mg, 86%). mp 134-
136 °C. ‘H NMR (C6D6) 6 -12.30 (dt, J: 117.0 Hz, 17.0 Hz, 1H, hydride), 0.84—0.95 (m,
3H, diastereotopic CH of CH2 groups of SiEt3), 1.25 (d, J = 6.7 Hz, 9H, PMe3 trans to
BPin), 1.29 (s, 12H, BO2C6H12), 1.37 (d, J = 7.3 Hz, 9H, PMe3 trans to SiEt3), 1.46 (d, J
= 7.6 Hz, 9H, PMe3 trans to hydride), 1.35-1.45 (m, 12H, diastereotopic CH of CH2
groups and CH3 groups of SiEt3). ”B NMR NMR (C613,) 6 36.3. ”C(‘m NMR (C60,)
5 10.7 (d, J= 1.9 Hz), 13.1 (dd, J= 5.8 Hz, 7.7 Hz), 24.6 (dt, J= 25.9 Hz, 4.8 Hz), 25.3
(dt, J = 22.1 Hz, 3.8 Hz), 25.4 (dt, J = 24.0 Hz, 3.8 Hz), 27.2 (s), 27.4 (5), 81.32 (s), 81.34

(s). 3'P{‘H} NMR (C6D6) 6 -66.4 (br, 1P, PMe3 trans to BPin), -64.2 (dd, J = 31.3 Hz,

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19.8 Hz, 1P, PMe3 trans to SiEt3), -58.1 (dd, J = 19.8 Hz, 19.8 Hz, 1P, PMe; trans to
hydride). Anal. Calcd for C21H551rBozP3Si: C, 38.00; H, 8.35. Found: C, 38.38; H, 8.52.

mer-(PMe3)3Ir[B(NH)2C6H4](H)(Cl) (31). A solution of PMe; (102 mg, 1.34
mmol) in 2 mL THF was added dropwise to a solution of [Ir(COE)2Cl]2 (200 mg, 0.22
mmol) in 4 mL THF. The reaction mixture was stirred at room temperature for 2 h. The
solvent was then removed under reduced pressure. The residue was redissolved in 6mL
THF and H[B(NH)2C6H4] (51.7 mg, 0.44 mmol) was added to the mixture. The reaction
mixture was stirred at ambient temperature for 12 h and then filtered through celite to
remove trace suspension The filtrate was pumped down to give a white solid (226 mg,
88%). mp 170 °C (dec). ‘H NMR (CD202) 6 9.90 (dt, J = 138.2 Hz, 20.9 Hz, 1H,
hydride), 1.53 (t, J = 3.6 Hz, 18H, 2 PMe3 trans to each other), 1.63 (dd, J = 7.5 Hz, 0.9
Hz, 9H, PMe3 trans to hydride), 5.83 (br, 2H, 2 NH), 6.64-6.66, 6.81-6.83 (m, 4H, C6H4).
‘3C{‘H} NMR(CD2C12) 6 19.3 (d, J= 26.9 Hz), 20.4 (dt, J: 4.3 Hz, 18.9 Hz), 108.7 (s),
117.5 (s), 139.0 (s). ”B NMR (CD202) 6 24.9. 3'P{‘H} NMR (CD202) 6 —48.2 (t, J =
20.8 Hz, 1P, PMe3 trans to hydride), —39.7 (d, J = 20.8 Hz, 2P, 2 PMe3 trans to each
other). Anal. Calcd for C1 5H34IrBClN2P3: C, 31.40; H, 5.97; N, 4.88. Found: C, 31.34; H,
5.79; N, 4.89.

mer-(PMe3)3Ir(BDAN)(H)(Cl) (32) and mer-(PMe3)3Ir(H)(BDAN)(Cl) (33). A
solution of PMe3 (102 mg, 1.3 mmol) in 2 mL THF was added dropwise to a solution of
[Ir(COE)2Cl]2 (200 mg, 0.22 mmol) in 4 mL THF. The reaction mixture was stirred at
room temperature for 2 h. The solvent was then removed under reduced pressure. The
residue was redissolved in 6 mL THF and HBDAN (74.5 mg, 0.44 mmol) was added to

the mixture. The reaction mixture was stirred at ambient temperature for 12 h and was

133

then filtered through celite to remove trace suspension. The filtrate was pumped down to
give an isomer mixture of 32 and 33 in a ratio of 90.4:9.6 (200 mg, 72%). mer-
(PMe3)3Ir(BDAN)(H)(Cl) (32). 1H NMR (CDzClz) 8 -10.60 (dt, J = 137.5 Hz, 20.8 Hz,
1H, hydride), 1.63 (d, J = 6.4 Hz, 9H, PMe3 trans to hydride), 1.65 (t, J = 3.5 Hz, 18H, 2
PMC3 trans to each other), 5.49 (br, 2H, 2 NH), 6.19 (d, J = 7.5 Hz, 2H, BDAN), 6.86 (d,
J: 8.5 Hz, 2H, BDAN), 7.03 (dd, J: 7.6 Hz, 8.0 Hz, 2H, BDAN). “B NMR(CD2C12) 6
28.0. ‘3C{‘H} NMR(CD2C12) 619.0 (d, J = 26.8 Hz), 20.3 (dt, J = 3.4 Hz, 18.9 Hz),
104.0 (s), 115.8 (s), 118.4 (s), 128.0 (s), 136.8 (s), 142.7 (d, J= 1.4 Hz). 3‘1){‘H} NMR
(CDzClz) 5 —49.2 (t, J = 20.8 Hz, 1P, PMe3 trans to hydride), —39.7 (d, J = 20.8 Hz, 2P, 2
PMe3 trans to each other). mer-(PMe3)3Ir(H)(BDAN)(Cl) (33). 1H NMR (CDzClz) 8 -
23.97 (td, J = 16.0 Hz, 10.1 Hz, 1H, hydride), 1.50 (d, J = 6.6 Hz, 9H, PMe3 trans to
BDAN), 1.56 (t, J = 3.3 Hz, 18H, 2 PMe3 trans to each other), 5.74 (br, 2H, 2 NH), 6.18
(d, J= 7.3 Hz, 2H, BDAN), 6.82 (dd, J= 8.7 Hz, 12.4 Hz, 2H, BDAN), 6.99 (d, J= 8.0
Hz, 2H, BDAN). “B NMR (CD2C12) 6 38.6. 3‘P{1H} NMR(CD2C12) 6 —52.4 (br, 1P,
PMe3 trans to BDAN), —43.1 (d, J = 26.9 Hz, 2P, 2 PMe3 trans to each other). Anal.
Calcd for C19H361rBC1N2P3: C, 36.58; H, 5.82; N, 4.49. Found: C, 36.62; H, 5.87; N,
4.43.

mer-(PMe3)3Ir[B(NMe)2C6H4](H)(Cl) (34) and mer-(PMe3)3Ir(H)[BG‘JMe)2C6
H4](Cl) (35). A solution of PMe3 (102 mg, 1.3 mmol) in 2 mL THF was added dropwise
to a solution of [Ir(COE)2Cl]2 (200 mg, 0.22 mmol) in 4 mL THF. The reaction mixture
was stirred at room temperature for 2 h. The solvent was then removed under reduced
pressure. The residue was redissolved in 6 mL THF and H[B(NMe)2C6H4] (53.7 mg, 0.37

mmol) was added to the mixture. The reaction mixture was stirred at ambient temperature

134

for 12 h and then filtered through celite to remove trace suspension. The filtrate was
pumped down to give an isomer mixture of 34 and 35 in a ratio of 14.42856 (220 mg,
82%). mer-(PMe3)3Ir[B(NMe)2C6H4](H)(Cl) (34). ‘H NMR(CD2C12) 6 -1075 (dt, J =
139.0 Hz, 19.6 Hz, 1H, hydride), 1.47 (t, J = 3.5 Hz, 18H, 2 PMe3 trans to each other),
1.68 (dd, J = 6.9 Hz, 0.8 Hz, 9H, PMe3 trans to hydride), 3.28 (s, 3H, Me), 3.55 (s, 3H,
Me), 6.77-6.85 (m, 4H, C6114). “B NMR (CD2C12) 6 28.6. 3‘P{‘H} NMR (CDZClz)
5 —54.9 (t, J = 22.0 Hz, 1P, PMe3 trans to hydride), —39.4 (d, J = 22.0 Hz, 2P, 2 PMe3
trans to each other). mer-(PMe3)3Ir(H)[B(1\lMe)2C6H4](Cl) (35). 1H NMR (CDzClz) 8 -
23.97 (td, J = 14.3 Hz, 12.2 Hz, 1H, hydride), 1.38 (t, J= 3.3 Hz, 18H, 2 PMe3 trans to
each other), 1.54 (d, J = 6.7 Hz, 9H, PMe3 trans to [B(NMe)2C6H4], 3.35 (s, 3H, Me),
3.68 (s, 3H, Me), 6.77-6.85 (m, 4H, C6H4). ”B NMR(CD2C12) 6 38.3. '3C(‘H} NMR
(CDzClz) 5 20.0 (dt, J = 5.5 Hz, 18.9 Hz), 20.3 (d, J = 22.0 Hz), 32.1 (s), 32.8 (s), 106.2
(s), 106.6 (s), 117.0 (s), 117.2 (s), 140.6 (d, J = 3.4 Hz), 141.8 (d, J = 4.8 Hz). 3‘P(‘H}
NMR(CD2C12) 5 —50.6 (br, 1P, PMe; trans to [B(NMe)2C6H4], -40.6 (d, J = 26.9 Hz, 2P,
2 PMe3 trans to each other). Anal. Calcd for C17H33IrBClN2P3: C, 33.92; H, 6.36; N,

4.66. Found: C, 34.10; H, 6.35; N, 4.57.

Screening Experiments

The general procedure for the synthesis of phenylboronate esters, catalyzed by 13
or 14/a monodentate phosphine ligand, is illustrated by the following example. Decane
(0.626 M in benzene, 50 11L, 0.031 mmol), HBPin (51 11L, 0.351 mmol) were charged

into a J. Young NMR tube. 13 (3 mg, 7.3 x 10'3 mmol) was charged into a GC-vial and

135

dissolved in C6H6 (150 uL). PMe3 (1.5 uL, 0.015 mmol) was added into the solution of
13 via a microsyringe. The mixture was then transferred into the J. Young NMR tube.
Benzene (150 uL x 2) was used to wash the residue to the J. Young NMR tube. The
reaction mixture was heated at 150 °C and monitored by HB NMR spectra. After HBPin
was consumed, an aliquot of the reaction mixture was diluted with CHzClz and a GC-FID
chromatogram was obtained. From the calibration curve of PhBPin vs. decane, GC yield
of PhBPin formation was obtained. The results of borylation of benzene catalyzed by 13
or 14/a monodentate phosphine ligand are summarized in Table 3.

The general procedure for the synthesis of phenylboronate esters, catalyzed by
13/a chelating phosphine ligand, is illustrated by the following example. Decane (0.626
M in benzene, 50 111., 0.031 mmol), HBPin (51 11L, 0.351 mmol) were charged into a J.
Young NMR tube. 13 (2.9 mg, 7.0 x 10‘3 mmol) and dppe (2.8 mg, 7.0 x 10'3 mmol) were
charged into two separate GC-vials and dissolved in C6H6 (150 uL x 2). The mixture was
then transferred into the J. Young NMR tube. Benzene (150 11L) was used to wash the
residue to the J. Young NMR tube. The reaction mixture was heated at 100 0C or 150 °C
and monitored by 11B NMR spectra. Afier HBPin was consumed, an aliquot of the
reaction mixture was diluted with CHzClz and a GC-FID chromatogram was obtained.
From the calibration curve of PhBPin vs. decane, GC yield of PhBPin formation was
obtained. The results of borylation of benzene catalyzed by l3/a chelating phosphine
ligand are summarized in Table 4.

The general procedure for the synthesis of phenylboronate esters, catalyzed by
13/a nitrogen or oxygen or sulfur containing ligand, is illustrated by the following

example. Dodecane (0.471 M in benzene, 50 1.1L, 0.024 mmol), HBPin (51 uL, 0.351

136

mmol) were charged into a J. Young NMR tube. 13 (2.9 mg, 7.0 x 10'3 mmol) and bpy
(1.1 mg, 7.0 x 10’3 mmol) were charged into two separate GC-vials and dissolved in C6H6

(150 uL x 2). The mixture was then transferred into the J. Young NMR tube. Benzene

(150 uL) was used to wash the residue to the J. Young NMR tube. The reaction mixture
was heated at 100 °C or 150 0C and monitored by HB NMR spectra. After HBPin was
consumed, an aliquot of the reaction mixture was diluted with CH2C12 and a GC-FID
chromatogram was obtained. From the calibration curve of PhBPin vs. dodecane, GC
yield of PhBPin formation was obtained. The results of borylation of benzene catalyzed

by 13/a nitrogen or oxygen or sulfur containing ligand are summarized in Table 5.

NMR Tube Reactions

Metathesis reaction between Cp*Ir(PMe3)(Ph)(H) (5) and HBPin in Cans.
Cp*Ir(PMe3)(Ph)(H) (9 mg, 0.019 mmol) and HBPin (28.7 mg, 0.224 mmol) were
dissolved in C6D6 (540 uL) and the mixture was transferred to a J. Young NMR tube.
The reaction mixture was heated at 150 °C in an oil bath and monitored by 1H, HB, and
3'P{‘H} NMR.

Thermolysis of Cp*Ir(PMe3)(I-I)(BPin) (l) in C6D6. Compound 1 (10 mg, 0.019
mmol) dissolved in C6D6 (550 11L) was transferred to a J. Young NMR tube. The solution
was heated at 200 °C in an oil bath for 2 weeks and 280 °C for 1 day. The reaction was
monitored by 1H, llB, and 3|P{1H} NMR.

Metathesis reaction between Cp*Rh(PMe3)(Ph)(H) (4) and HBPin in C6D6.

Cp*Rh(PMe3)(Ph)(H) (10 mg, 0.026 mmol) and HBPin (39 mg, 0.305 mmol) were

137

dissolved in C6D6 (550 11L) and the mixture was transferred to a J. Young NMR tube.
The reaction mixture was heated at 95 °C in an oil bath and monitored by IH, HB, and
3'P('H} NMR.

Crossover experiment. Cp*Ir(P(CD3)3)(H)2 (8) (10 mg, 0.024 mmol),
(C5Me4Et)Ir(PMe3)(H)2 (9) (10.1 mg, 0.024 mmol), and HBPin (15.5 mg, 0.121 mmol)
were dissolved in C6H6 (550 11L) and the reaction mixture was transferred to a J. Young
NMR tube. The reaction mixture was heated at 150 °C in an oil bath and monitored by
HB NMR. Afier HBPin was consumed, an aliquot of the reaction mixture was diluted
with CHzClz and a GC-MS chromatogram was obtained. From the chromatogram of the
crude mixture there was no crossover products observed. Therefore, crossover during
catalytic borylation was minimal.

Anisole borylation catalyzed by Cp*IrH4 (11). Cp*IrH4 (11) (10 mg, 0.030
mmol) and HBPin (23 mg, 0.180 mmol) were dissolved in a 1:2 (V/V)
anisole/cyclohexane solution (500 uL). The reaction mixture was transferred to a J.
Young NMR tube, heated at 150 °C in an oil bath, and monitored by I'B NMR. After
HBPin was consumed, an aliquot of the reaction mixture was diluted with CHzClz and a
GOP ID chromatogram was obtained. The isomer ratio of C6H4(0Me)(BPin) (o:m:p) was
determined to be 3:49:48.

Thermolysis of (MesH)lr(BPin)3 (14) in C6116. (MesH)Ir(BPin)3 (14) (15.2 mg,
0.022 mmol) dissolved in C6H6 (550 11L) was transferred to a J. Young NMR tube. The
solution was heated at 150 °C in an oil bath and monitored by HB NMR. After complex
14 was consumed, an internal standard solution (decane/CoHo) was added to the reaction

mixture. An aliquot of the mixture was diluted with CHzClz and a GC-F ID chromatogram

138

was obtained. Thermolysis of 14 in C6H6 produced 3 equivalents of PhBPin and black
iridium metal.

14 + excess HBPin in Cng. Compound 14 (10 mg, 0.014 mmol) and HBPin (11
mg, 0.086 mmol) dissolved in C6D6 (550 11L) was transferred to a J. Young NMR tube.
The reaction mixture was heated at 150 °C in an oil bath and monitored by HB NMR.
After 5 h at 150 °C, the reaction led to decomposition and PinB-O-BPin. No C6D5BP1n
was observed.

14 + excess HBPin in C5D; in the presence of 2 equiv. of PMe3. Compound 14
(10 mg, 0.014 mmol) and HBPin (11 mg, 0.086 mmol) dissolved in C6D6 (550 11L) was
transferred to a J. Young NMR tube. PMe; (3 11L, 0.029 mmol) was added to the NMR
tube via a microsyringe. The reaction mixture was heated at 150 °C in an oil bath and
monitored by 1'B NMR. After 5 h at 150 °C, HBPin was completely converted to
PhBPin.

14 + 2 equiv. PMe; in toluene-d3. Compound 14 (10 mg, 0.014 mmol) dissolved
in toluene-d3 (500 1.1L) was transferred to a J. Young NMR tube. PMe3 (3 11L, 0.029
mmol) was added to the NMR tube via a microsyringe. The reaction was monitored by
1H, HB, and 31P{1H} NMR at room temperature. The reaction generated a mixture of
compound 25 and (n6-C7Dg)1r(BPin)3 in a 2:1 ratio.

37 + HBPin in C6D5. (PMe3)4Ir(H) (37) (15 mg, 0.030 mmol) dissolved in C6D6
(332 11L) in a GC vial was transferred to a J. Young NMR tube. Additional C6D6 (166
11L) was used to wash the residue into the NMR tube. HBPin (4.4 11L, 0.030 mmol) was
added into the NMR tube via a microsyringe. At room temperature, the starting material

was gradually converted into a mixture of mer,cis-(PMe3)3Ir(H)2(BPin) (38) and fac-

139

(PMe3)3Ir(H)2(BPin) (36). The sample was allowed to stand at room temperature for 6
days to give compound 36 as the predominant species. mer,cis-(PMe3)3Ir(H)2(BPin) (38).
lH NMR (CsDo) 6 -12.18 (dt, J: 114.7 Hz, 23.2 Hz, 1H, hydride trans to PMeg), -10.46
(q, 1H, hydride trans to BPin), 1.21 (s, 12H, B02C6H12), 1.49 (d, 9H, PMe; trans to
hydride), 1.69 (t, J = 3.5 Hz, 18H, 2 PMe; trans to each other). 1‘B NMR (Cng) 5 38.6.
3‘1>{‘H} NMR (Cng) 6 -58.1 (t, J = 22.6 Hz, 1?, PMe3 trans to hydride), -48.1 (d, J =
22.6 Hz, 2P, 2 PMe3 trans to each other). fac-(PMe3)3Ir(H)2(BPin) (36). 1H NMR (Cng)
5 -11.83 (symmetrical second order m, 2H, hydride), 1.25 (s, 12H, BOngHrz), 1.32 (d, J
= 7.0 Hz, 9H, PMC3 trans to BPin), 1.69 (d, J = 7.6 Hz, 18H, 2 PMe3 trans to hydride).
”B NMR (C6D6) 6 38.6. 3‘1>(‘H} NMR (C6D6) 6 -62.0 (br, 1P, PMe3 trans to BPin), -
54.59 (d, J = 23.2 Hz, 2P, 2 PMe3 trans to hydride).

37 + BzPinz in C6D6. B2Pin2 (7.9 mg, 0.031 mmol) dissolved in C6D6 (166 11L)
was transferred to a J. Young NMR tube which was charged with (PMe3)4Ir(H) (37) (15.4
mg, 0.031 mmol) in C6D6 (166 11L). Additional CoDo (166 1.1L x 2) was used to wash the
residue into the NMR tube. The reaction mixture was heated at 60 °C and monitored by
lH, HB, and 3'P{1H} NMR spectra. The starting material was gradually converted into a
mixture of mer,trans-(PMe3)3Ir(BPin)2(H) (20) and fac-(PMe3)3Ir(BPin)2(H) (21). fac-
(PMe3)3Ir(BPin)2(H) (21) was the major species after the temperature was increased to
100 °C for 7 h. mer,trans-(PMe3)3Ir(BPin)2(H) (20). 1H NMR (C6D6) 5 -12.36 (dt, J =
117.0 Hz, 21.7 Hz, 1H, hydride trans to PMe3), 1.22 (s, 12H, B02C6H12), 1.49 (d, J = 8.0
Hz, 9H, PMe3 trans to hydride), 1.74 (t, J = 3.4 Hz, 18H, 2 PMe3 trans to each other). “B
NMR (e.u.) 6 38.9. 3'P{‘H} NMR (Cst) 6 -59.6 (t, J = 22.0 Hz, 1P, PMe3 trans to

hydride), -50.8 (d, J = 22.0 Hz, 2P, 2 PMe3 trans to each other). fac-(PMe3)3Ir(BPin)2(H)

140

(21). mp 120-122 °C. 1H NMR (CoDo) 5 -11.66 (dt, J= 118.1 Hz, 18.1 Hz, 1H, hydride
trans to PMe3), 1.29 (s, 24H, B02C6H12), 1.41 (W, 18H, 2 PMe3 trans to BPin), 1.58 (d, J
= 8.0 Hz, 9H, PMe3 trans to hydride). '3C{‘H} NMR (C6D6) 6 23.7 (dt, J: 26.9 Hz, 5.3
Hz), 25.1 (br), 25.8 (s), 26.3 (s), 80.3 (s). “B NMR (C6D6) 6 38.6. 3‘1>{‘H} NMR
(C6D6) 5 -61.8 (br, 2P, 2 PMe3 trans to BPin), -56.6 (t, J = 22.0 Hz, 1P, PMe3 trans to
hydride). fac-(PMe3)3Ir(BPin)2(H) (21) was independently synthesized and isolated in 80
% yield. Anal. Calcd for C21H521rB204P3: C, 37.34; H, 7.76. Found: C, 37.35; H, 7.72.

18 + dppe in C6D6. Dppe (8 mg, 0.020 mmol) dissolved in C6D6 (166 uL) was
transferred to a J. Young NMR tube, which was charged with 18 (12.5 mg, 0.020 mmol)
in C6D6 ( 166 11L). Additional CoDo (166 11L) was used to wash the residue into the NMR
tube. The reaction mixture was allowed to stand at room temperature for 3 days to give
Ir(PMe3)2(dppe)(BPin) (19) as the predominant species. 1H NMR (C6D6) 6 1.10 (s, 12H,
BOzCsHiz), 1.33 (t, J= 3.3 Hz, 18H, 2 PMe3), 1.92-2.18 (m, 4H, CH2), 6.98-7.12, 7.16-
7.28, 7.72-7.89, 7.91-7.98 (m, 20H, phenyl groups of dppe). “B NMR (C,D,) 6 38.8.
3‘1>(‘H} NMR (Cst) 6 —58.9 (dd, J = 141.6 Hz, 26.8 Hz, 2P, 2 PMe3), 39.1 (dt, J =
141.6 Hz, 13.4 Hz, 1P, PPh2 cis to BPin), 46.1 (br, 1P, Pth trans to BPin).

18 + HBPin in C6D6. Compound 18 (12.8 mg, 0.021 mmol) dissolved in C6D6
(500 pL) was transferred to a J. Young NMR tube. HBPin (3 uL, 0.021 mmol) was added
to the NMR tube via a microsyringe. The reaction was monitored by 1H, 1'B, and 31P{1H}
NMR at room temperature. mer,trans-(PMe3)3Ir(BPin)2(H) (20) was the initial
predominant species, and it gradually isomerized to fac-(PMe3)3Ir(BPin)2(H) (21) after

heating at 70 °C for 11h.

141

18 + ClBCat in C6D6. Compound 18 (12.1 mg, 0.019 mmol) and ClBCat (3 mg,
0.019 mmol) dissolved in C6D6 (500 uL) were transferred to a J. Young NMR tube. The
reaction was monitored by 1H, 11B, and 31P{1H} NMR at room temperature. After 3 days
at room temperature, the predominant species in the reaction mixture was mer-
(PMe3)3Ir(BPin)(BCat)(Cl) (22) with BPin group trans to Cl. 1H NMR (c613,) 6 1.18 (s,
12H, BOZCOH12). 1.29 (d, J = 7.3 Hz, 9H, PMC3 trans to BCat group), 1.47 (t, J = 3.7 Hz,
18H, 2 PMe3 trans to each other), 6.84, 7.19 (AA'BB', 4H, BCat). "B NMR (C613,) 6
28.1, 41.6. 3‘1>{'H} NMR (C613,) 6 —56.2 (br, PMe3 trans to BCat), —39.3 (d, J: 29.3 Hz,
2 PMe3 trans to each other).

Thermolysis of 18 in C6D6. Compound 18 (10.2 mg, 0.016 mmol) dissolved in
C6D6 (500 11L) was transferred to a J. Young NMR tube. The reaction mixture was heated
at 100 °c in an oil bath and monitored by 1H, ”B, and 3‘1>{‘H} NMR. After 38 h at 100
°C, complex 18 was converted to (PMe3)4Ir(D) and C6D5BPin.

Thermolysis of 25 in C6D6. Compound 25 (15 mg, 0.019 mmol) dissolved in
C6D6 (500 11L) was transferred to a J. Young NMR tube. The reaction mixture was heated
at 150 °C in an oil bath and monitored by 1H, 1'3, and 3'P{1H} NMR. The reaction gave
fac-(PMe3)3Ir(D)3 as the final iridium containing product and generated 3 equiv. of
CgDsBPin.

Thermolysis of 18 in C5H51. Complex 18 (12 mg, 0.019 mmol) dissolved in
C6H51 (500 uL) was transferred to a J. Young NMR tube. The reaction resulted in
immediate white precipitation. The reaction mixture was heated at 100 °C for 1 h in an

oil bath. No isomer mixture of C6H4(I)(BPin) was detected by GC-FID.

142

Thermolysis of 25 in C6H51. Compound 25 (11.6 mg, 0.014 mmol) dissolved in
C6H51 (500 uL) was transferred to a J. Young NMR tube. The reaction mixture was
heated at 150 °C for 29 h in an oil bath. The reaction produced m- and p-C6P14(I)(BPin) in

54% GC yield, in addition to a 45% yield of PhBPin.

Kinetic Isotope Effect Experiments
Catalytic borylation in a molar ratio 1:1 mixture of C6H6/C5D6 with the Irl

pro-catalyst (2 mol% 13 and 4 mol% PMe3). A solution of (Ind)Ir(COD) (13) (6 mg,
0.014 mmol) in C6H6/C6D6 (1:1) (175 uL x 2) was mixed with a solution of PMe3 (3 11L)
in Cng/Cng (1 :1) (175 uL x 2). The solution mixture was then transferred to a J. Young
NMR tube. Additional CgHb/Cng (1:1) (175 11L x 4) was used to wash the residue into
the NMR tube. HBPin (104 11L, 0.717 mmol) was added to the NMR tube via an auto-
pipette. The reaction mixture was heated at 150 °C in a constant temperature oil bath
(Cole-Parmer Polystat Constant Temperature Circulator). The reaction was monitored by
HB NMR. The ratio of C6D5BPin : C6H5BPin determined from GC-FID after calibration
was 1.00:2.29.

Catalytic borylation in a molar ratio 1:1 mixture of C6H6/C5D6 with the Ir"l
pre—catalyst (2 mol% 14 and 4 mol% PMe3). A solution of (MesH)Ir(BPin)3 (14) (10
mg, 0.014 mmol) in C6H6/C6D6 (1:1) (175 11L x 2) was mixed with a solution of PMe3 (3
uL) in CgHg/Cng (1:1) (175 11L x 2). The solution mixture was then transferred to a J.
Young NMR tube. Additional CgHg/Cng (1:1) (175 uL x 4) was used to wash the

residue into the NMR tube. HBPin (104 1.1L, 0.717 mmol) was added to the NMR tube via

143

an auto-pipette. The reaction mixture was heated at 150 °C in a constant temperature oil
bath (Cole-Farmer Polystat Constant Temperature Circulator). The reaction was
monitored by 11B NMR. The ratio of C6D5BPin : C6H5BPin determined from GC-F ID
after calibration was 1.00:2.28.

Catalytic borylation in 1,3,5-C6D3H3 with the Irl pre-catalyst (2 mol% l3 and
4 mol% PMe3). A solution of 13 (3 mg, 0.007 mmol) in 1,3,5-C6D3H3 (166 11L) was
mixed with a solution of PMe3 (1.5 uL) in 1,3,5-C6D3H3 (166 11L). The solution mixture
was then transferred to a J. Young NMR tube. Additional 1,3,5-C6D3H3 (166 uL) was
used to wash the residue into the NMR tube. HBPin (52 11L, 0.358 mmol) was added to
the NMR tube via an auto-pipette. The reaction mixture was heated at 150 0C in a
constant temperature oil bath. The reaction was monitored by HB NMR. The ratio of
1,3,5-C6D2H3(BPin) : 1,3,5-C6D3H2(BPin) determined by the ‘H NMR of the crude
mixture was 1.00:2.06.

Catalytic borylation in 1,3,5-C6D3H3 with the Ir"1 pre-catalyst (2 mol% 14
and 4 mol% PMC3). A solution of 14 (5 mg, 0.007 mmol) in 1,3,5-C6D3H3 (166 11L) was
mixed with a solution of PMe3 (1.5 11L) in 1,3,5-C6D3H3 (166 11L). The solution mixture
was then transferred to a J. Young NMR tube. Additional 1,3,5-C6D3H3 (166 uL) was
used to wash the residue into the NMR tube. HBPin (52 uL, 0.358 mmol) was added to
the NMR tube via an auto-pipette. The reaction mixture was heated at 150 °C in a
constant temperature oil bath. The reaction was monitored by 1'B NMR. The ratio of
1,3,5-C6D2H3(BPin) : 1,3,5-C6D3H2(BPin) determined from the 1H NMR of the crude

mixture was 1.00:1.94.

144

Thermolysis of 18 in a molar ratio 1:1 mixture of C6H6/C6D6. Compound 18
(25 mg, 0.060 mmol) dissolved in CgHg/CoDo (1:1) (166 11L x 2) was transferred to a J.
Young NMR tube. Additional CgHg/CgDr, (1:1) (166 11L) was used to wash the residue
into the NMR tube. The reaction mixture was heated at 150 °C in an oil bath and
monitored by 11B and 3 IP{'H} NMR. The ratio of C6D5BPin : C6H5BPin determined from

GC-F ID after calibration was 1.00:2.67.

Thermolysis of 25 in a molar ratio 1:1 mixture of C6H6/C6D6. Compound 25
(32 mg, 0.040 mmol) dissolved in C6H6/C6D6 (1:1) (166 11L x 2) was transferred to a J.
Young NMR tube. Additional C6H6/C6D6 (1:1) (166 11L) was used to wash the residue
into the NMR tube. The reaction mixture was heated at 150 °C in an oil bath and
monitored by 11B and 3 lP{1H} NMR. The ratio of C6D5BPin : C6H5BPin determined from
GC-FID after calibration was 1.00:2.53.

Thermolysis of 18 in 1,3,5-C6D3H3. Compound 18 (25 mg, 0.060 mmol)
dissolved in 1,3,5-C6D3H3 (166 11L x 2) was transferred to a J. Young NMR tube.
Additional 1,3,5-C6D3H3 (166 uL) was used to wash the residue into the NMR tube. The
reaction mixture was heated at 150 °C in an oil bath and monitored by 11B and 3 1P{‘H}
NMR. The ratio of 1,3,5-C6D2H3(BPin) : 1,3,5-C6D3H2(BPin) determined from the lH
NMR of the crude mixture was 1.00:2.37.

Thermolysis of 25 in 1,3,5-C6D3H3. Compound 25 (32 mg, 0.040 mmol)
dissolved in 1,3,5-C6D3H3 (166 uL x 2) and transferred to a J. Young NMR tube.
Additional 1,3,5-C6D3H3 (166 11L) was used to wash the residue into the NMR tube. The

reaction mixture was heated at 150 °C in an oil bath and monitored by 1'B and 31P{'H}

145

NMR. The ratio of 1,3,5-C6D2H3(BPin) : 1,3,5-C6D3H2(BPin) determined from the 1H

NMR of the crude mixture was 1.00:1.93.

Arylboronate Ester Syntheses

The general procedure for the synthesis of arylboronate esters, catalyzed by
solutions of compound 1, is illustrated for the synthesis of 1,3,5-C6H3(CF3)2(BPin).
Compound 1, (80 mg, 0.15 mmol) and HBPin (96 mg, 0.75 mmol) were dissolved in 4
mL 1,3-bis(trifluoromethyl)benzene and heated at 150 °C in a constant temperature
circulator for 10 hours in a thick—walled, air—free flask. The solution was then transferred
to a vial and the solvent was removed under vacuum at room temperature. The residue
was chromatographed on a silica gel column, eluting with CHzClz, to yield 1,3,5-
C6H3(CF3)2(BPin) as a colorless solid (182 mg, 81% based on HBPin). mp (65-66 °C). ‘H
NMR (CDC13) 6 1.35 (s, 12H, 302C6H12), 7.92 (s, 1H), 8.22 (s, 2H). ‘3C{‘H} NMR
(CDC13) 5 24.8, 84.9, 123.5 (J = 272.4 Hz, 2C), 124.7, 130.9 (J = 32.7 Hz, 2C), 134.7
(2C). ”3 NMR(CDC13) 6 30. ‘91: NMR(CDC13)5 —63. Anal. Calcd for C14H15BF602: C,
49.44; H, 4.45. Found: C, 49.55; H, 4.53. GC-MS (m/z) 340.

The general procedure for the synthesis of arylboronate esters, catalyzed by
solutions of compound 1, generated in situ from compound 2, is illustrated for the
synthesis of CgHaMe(BPin). Compound 2, (70 mg, 0.17 mmol) and HBPin (133 mg, 1.04
mmol) were dissolved in 4 mL toluene and heated at 150 °C in a constant temperature
circulator for 10 hours in a thick—walled, air—free flask. The solution was then transferred

to a vial and the solvent was removed under vacuum at room temperature. The residue

146

was chromatographed on a silica gel column, eluting with CHzClz, to yield
C6HaMe(BPin). The reaction gave 3 isomers, m-CgHaMe(BPin) : p-CgHaMe(BPin) : 0-
C6H4Me(BPin) in the ratio of 62:34:4 (173 mg, 91% based on HBPin). The identity of o-
C6HaMe(BPin) and p-C6H4Me(BPin) were established by comparing spectroscopic data
to those in the literature,25 and by comparing GC-MS data for the mixture to data for the
independently prepared pure isomers. The identity of m-C6H4Me(BPin) was confirmed
by independent synthesis of an authentic sample using the literature method.2 m-
CgHaMe(BPin) was isolated as a colorless solid. mp 34-35 °C. 1H NMR (CDC13) 5 1.33
(s, 12H, BOzC6H12), 2.34 (s, 3H, Me), 7.25 (m, 2H), 7.59 (m, 1H), 7.62 (s, 1H). ”B NMR
(CDCl3) 5 30.7. Anal. Calcd for C13H19B02: C, 71.59; H, 8.78. Found: C, 71.36; H, 9.33.
GC-MS (m/z) 218.

The general procedure for the synthesis of arylboronate esters, catalyzed by
solutions of compound 3, is illustrated for the synthesis of 1,3,5-C6H3(CF3)2(BPin).
Compound 3, (5 mg, 0.013 mmol) and HBPin (90 mg, 0.70 mmol) were dissolved in 550
11L 1,3-bis(trifluoromethyl)benzene and heated at 150 °C in a constant temperature
circulator for 3 hours in a J. Young NMR tube. The solution was transferred to a vial and
the solvent removed under vacuum at room temperature. The residue was
chromatographed on a silica gel column, eluting with CHzClz, to yield 1,3,5—

C6H3(CF3)2(BPin) as a colorless solid (203 mg, 86% based on HBPin).
F F
F BPin
F F

C6F5(BPin). Catalytic addition of HBPin to C6HF 5 using solutions of compounds

1 (generated in situ from compound 2) and 3 gave C6F5(BPin) as a colorless solid (205

147

mg, 81% based on HBPin, and 85 mg, 41% based on HBPin, for 1 and 3, respectively).
mp 35-36 °C. 1H NMR(CDC13) 6 1.36 (s, 12H, BOngHrz). ”B NMR (CDC13) 6 29. "’1:
NMR (CDCl,) 6 -129.5 (m, 2F), —149.7 (m, 1F),—161.9(m, 2F). Anal. Calcd for

CtzleBFstz C, 49.02; H, 4.11. Found: C, 48.33; H, 4.59. GC-MS (m/z) 294.

C6H4(CF3)(BPin) (isomer mixture). Catalytic addition of HBPin to
benzotrifluoride using solutions of 1 gave 2 isomers, m-C6Ha(CF3)(BPin) : p-
C6H4(CF3)(BPin) in a 2:1 ratio (202 mg, 99% based on HBPin). HBPin addition
catalyzed by solutions of 3 gave m-C6Ha(CF3)(BPin) : p-C6Ha(CF3)(BPin) in a 2:1 ratio
(161 mg, 84% based on HBPin). The proton chemical shifts of the two isomers were
determined by selective decoupling of peaks in the aromatic region. m-C6H4(CF3)(BPin).
lH NMR (CDCl3) 5 1.34 (s, 12H, BOzCoth), 7.47 (t, 1H), 7.68 (d, 1H), 7.96 (d, 1H),
8.05 (s, 1H). “B NMR (CDC13) 6 30.2. ”F NMR(CDC13) 6 —62.9. p-C6Ha(CF3)(BPin).
lH NMR (CDCl;) 6 1.34 (s, 12H, 302C6H12), 7.59 (d, 2H), 7.89 (d, 2H). “B NMR
(CDCl3) 5 30.2. 19F NMR (CDC13) 5 -63.3. Anal. Calcd for C13H16BF302: C, 57.39; H,

5.93. Found: C, 57.48; H, 6.40. GC-MS (m/z) 272.

C6H4Me(BPin) (isomer mixture). Catalytic addition of HBPin to toluene using
solutions of 3 gave 3 isomers, m-C6HMe(BPin) : p-C6H4Me(BPin) : 0-C6H4Me(BPin) in

a 63:32:5 ratio (110 mg, 72% based on HBPin).

148

Me

C6H4(0Me)(BPin) (isomer mixture). Catalytic addition of HBPin to anisole
using solutions of 3 gave 3 isomers, m-C6H4(0Me)(BPin) : p-C6H4(0Me)(BPin) : 0-
C6Ha(OMe)(BPin) in a 67:25:8 ratio (106 mg, 65% based on HBPin). The proton
chemical shifts of the 2 major isomers were determined by selective decoupling
experiments and by comparison to spectra of independently prepared authentic samples.
m-C6H4(0Me)(BPin). 'H NMR (CDC13) 6 1.33 (s, 12H, BOszth), 3.82 (s, 3H,
OMe), 7.25-7.44 (m, 3H), 7.00 (m, 1H). ”B NMR(CDC13) 6 30.8. p-CoHrt(0Me)(BPin).
1H NMR (CDC13) 5 1.31 (s, 12H, BOzCéle), 3.81 (s, 3H, OMe), 6.88 (d, 2H), 7.74 (d,

2H). “B NMR (CDC13) 6 30.8. Anal. Calcd for c,,H,9Bo3: C, 66.70; H, 8.18. Found: C,

66.69; H, 8.50. GC-MS (m/z) 234.

QNMez
BPin

C6H4(NMe2)(BPin) (isomer mixture). Catalytic addition of HBPin to N,N-
dimethylaniline using solutions of 3 gave m-C6Ha(NMe2)(BPin) : p-C6Ha(NMe2)(BPin) :
0-C6H4(NMe2)(BPin) in the ratio 55:43:2 (113 mg, 65% based on HBPin). The proton
chemical shifts of p-C6Ha(NMe2)(BPin) and m—C6Ha(NMe2)(BPin) isomers were
determined by selective decoupling and NOE experiments. Resonances in the aromatic
region were assigned to m- and p-CgHa(NMe2)(BPin) isomers by selective decoupling
experiments. Resonances for the methyl groups of We; in m- and p—C6Ha(NMe2)(BPin)
were assigned to each isomer based on one-dimensional NOE experiments. In the NOE

experiment, the methyl resonances of the NMez groups were irradiated in order to

establish through space relationships with their respective aromatic protons. Irradiation of

149

the methyl resonance at 5 2.97 resulted in an enhancement of the peak at 56.68,
corresponding to the aromatic protons assigned to p-C6Ha(NMe2)(BPin). Irradiation of
the second methyl resonance at 5 2.95 resulted in enhancement of the peaks at 5 6.85 and
5 7.21, corresponding to aromatic protons assigned to m-C6H4(NMe2)(BPin). The
integration of the methyl resonances of We; by deconvolution of the peaks, indicates a
higher percentage of the meta isomer with respect to the para isomer. From the
integration of the 1H NMR spectrum, the peaks in the GC-MS were assigned accordingly
to each isomer. m-C6H4(NMe2)(BPin). 1H NMR (CDC13) 5 1.33 (s, 12H,
B02C6H12), 2.95 (s, 6H, N (CH3)2), 6.85 (m, 1H), 7.17-7.28 (m, 3H). “13 NMR(CDC13)
5 31.1. p-C6H4(NM62)(BPin). 1H NMR(CDC13) 5 1.32 (s, 12H, BOzCole), 2.97 (s, 6H,
NMez), 6.68 (d, 2H), 7.69 (d, 2H). ”3 NMR (CDCl;,) 6 31.1. Anal. Calcd for

C14H22BN02: C, 68.04; H, 8.97. Found: C, 67.84; H, 9.11. GC-MS (m/z) 247.

BPin

C6H4(CHMe2)(BPin) (isomer mixture). Catalytic addition of HBPin to cumene
using solutions of 3 gave 3 isomers, m-C6H4(CHMez)(BPin) : p-C6H4(CHMe2)(BPin) : o-
C6H4(CHMez)(BPin) in a 66:33:] ratio (115 mg, 67% based on HBPin). The proton

chemical shifts of the 2 major isomers were determined by selective decoupling
experiments. m-C6H4(CHMe2)(BPin). lH NMR (CDC13) 5 1.24 (d, 6H, 2Me), 1.33 (s,
12H, BOzCsle). 2.91 (m, 1H, CH), 7.27-7.33 (m, 2H), 7.62 (d, 1H), 7.65 (s, 1H). HB
NMR (CDC13) 6 31.1. p-CsHa(CHMe2)(BPin). 1H NMR (CDClg) 61.23 ((1, 6H, 2Me),
1.32 (s, 12H, BOzCole), 2.91 (m, 1H, CH), 7.22 (d, 2H), 7.73 (d, 2H). “B NMR

(CDC13) 6 31.1. GC-MS (m/z) 246.

150

Me Me

BPin
1,3,5-C6H3Me2(BPin) Catalytic addition of HBPin to m-xylene using solutions of
3 gave 1 major product. 1,3,5-C6H3Me2(BPin) was isolated as a white solid (119 mg,
73% based on HBPin). mp 90-91 0C. lH NMR (CDC13) 6 1.33 (s, 12H, BozC,H.2),
2.30 (s, 6H, 2Me), 7.09 (s, 1H), 7.42 (s, 2H). l3C(‘H} NMR (CDC13) 6 21.1, 24.8, 83.6,
132.4, 132.9, 137.1. ”B NMR (CDC13) 6 30.9. Anal. Calcd for CraHerOZ: C, 72.44; H,

9.12. Found: C, 72.38; H, 9.44. GC-MS (m/z) 232.

Me N Me
\

I /
BPin
2,4,6-C5NH2Mez(BPin) Catalytic addition of HBPin to 2,6-lutidine using
solutions of 3 gave 2,4,6-C5NH2Me2(BPin), isolated as colorless crystals after
sublimation of the crude product under high vacuum at 70 °C (67 mg, 41% based on
HBPin). mp 82-83°C. 1H NMR (CDC13) 5 1.32 (s, 12H, BOszle). 2.49 (s, 6H, 2Me),
7.28 (s, 2H). “B NMR (CDC13) 6 30.8. Anal. Calcd for C13H20BN02: C, 66.98; H, 8.65;

N, 6.01. Found: C, 66.79; H, 9.09; N, 6.40. GC-MS (m/z) 233.

quwaz
BPin
C6H4(C(O)NEtz)(BPin) (isomer mixture). Catalytic addition of HBPin to
C6H5(C(O)NEt2) using solutions of 3 gave m-C6Ha(C(O)NEt2)(BPin) : p-
C6H4(C(O)NEt2)(BPin) : 0-C6Ha(C(O)NEt2)(BPin) in the ratio 28: 14:58. The product was

distilled from the reaction mixture using a Kugelrohr distillation apparatus and collected

151

as a colorless viscous liquid (106 mg, 50% based on HBPin). For isomer mixture: 1H
NMR (CDCl3) 51.04 (m, 3H, CH3), 1.23 (m, 3H, CH3), 1.28, 1.33, 1.34 (s, 12H,
B02C6H12), 3.20 (m, 2H, CH2), 3.55 (m, 2H, CH2), 7.23-7.26, 7.30-7.74, 7.75-7.81 (m,
4H). l3C(‘H} NMR (CDC13) 612.36, 12.78 (br), 13.56, 14.05 (br)(NCH2_(;H3), 24.76
(B02C2(QH3)4), 39.04 (br), 39.64, 42.87, 43.16 (br) (NQHZCH3), 83.23, 83.52, 83.82
(B02§_2(CH3)4), 125.27, 127.58, 128.08, 128.71, 130.34, 132.34, 134.64, 134.88, 135.16,
136.60, 139.74, 142.20 (aromatic resonances), 171.02, 171.17, 171.50 (carbonyl
resonances). ”B NMR (CDC13) 6 28.7. IR (neat, cm") 660 (m), 783 (w), 858 (m), 965
(m), 1103 (m), 1146 (s), 1223 (w), 1287 (m), 1321 (m), 1356 (s), 1428 (m), 1634 (s).
Satisfactory combustion analysis has not been obtained. GC-MS (m/z) 303. The identity
of isomer products was established by comparing spectroscopic data to the independent
synthesis of authentic samples using the literature method,25 and by comparing GC-MS
data for the mixture to data for the independently prepared pure isomers. m-
C6H4(C(O)NEt2)(BPin). 1H NMR (CDC13) 5 1.07 (t, 3H, CH3), 1.21 (t, 3H, CH3), 1.32 (s,
12H, BOzCsle), 3.22 (br, 2H, CH2), 3.52 (m, 2H, CH2), 7.30-7.47 (m, 3H), 7.79 (s, 1H).
o-C6H4(C(O)NEt2)(BPin). 1H NMR (CDCl,) 61.04 (br, 3H, CH3), 1.28 (br, 3H, CH3),
1.28 (s, 12H, BOzCsle). 3.20 (q, 2H, CH2), 3.56 (q, 2H, CH2), 7.27 (d, 1H), 7.30-7.40
(m, 2H), 7.79 (d, 1H). p-C6H4(C(O)NEt2)(BPin). lH NMR (CDC13) 5 1.06 (br, 3H, CH3),
1.23 (br, 3H, CH3), 1.34 (s, 12H, BOngle), 3.19 (br, 2H, CH2), 3.53 (br, 2H, CH2), 7.34

(d, 2H), 7.81 (d, 2H).

<\:\>-C(O)0Et
BPin

152

C6H4(C(0)0Et)(BPin) (isomer mixture). Catalytic addition of HBPin to
C6H5(C(O)0Et) using solutions of 3 gave m-C6H.t(C(O)OEt)(BPin) : p-
CbHa(C(O)OEt)(BPin) : o-C6114(C(O)0Et)(BPin) in the ratio 57:33:10. The identity of
isomer products were established by comparing GC-MS data for the mixture to data for
the independently prepared pure isomers using the literature method.25 m-
C6H4(C(O)0Et)(BPin). 1H NMR (CDCl3) 51.34 (s, 12H, BOzCsle), 1.38 (t, 3H,
CH3), 4.36 (q, 2H, CH2), 7.42 (t, 1H), 7.96 (d, 1H), 8.11 (d, 1H), 8.44 (s, 1H). 11B NMR
(CDC13) 6 30.8. p-C6H.t(C(O)OEt)(BPin). ‘H NMR (CDC13) 6 1.34 (s, 12H,B02C6H12),
1.38 (t, 3H, CH3), 4.36 (q, 2H, CH2), 7.84 (d, 2H), 8.00 (d, 2H). “B NMR (CDC13) 6

30.9. GC-MS (m/z) 276.

F

F‘QBPin

F

2,4,6-C6H2F3(BPin). 3 (5 mg, 0.013 mmol) and HBPin (90 mg, 0.70 mmol) were
dissolved in 550 11L of a 1:2 ratio of xylene-(110 and 1,3,5-C6H3F3, and heated at 150 °C
for 30 min in a J. Young tube. The solution was then transferred to a vial and the solvent
removed under vacuum at room temperature. The residue was chromatographed on a
silica gel column, eluting with CHzClz, to yield 2,4,6-C6H2F3(BPin) (83 mg, 46% based
on HBPin). 1H NMR (CDCl3) 6 1.34 (s, 12H, Bozcan), 6.58 (m, 2H). ”B NMR
(CDC13) 6 29.4. ”17 NMR (CDCl3) 6—103.8(m, 21:), —97.1 (m, 1F). Anal. Calcd for
C12H14BF302: C, 55.85; H, 5.47. Found: C, 56.08; H, 5.59. GC-MS (m/z) 258.

The general procedure for the syntheses of the following arylboronate esters: 13

(2.9 mg, 0.007 mmol) and dmpe (1 mg, 0.007 mmol) dissolved in an arene (166 11L x 2)

153

were transferred to a J -Young NMR tube, which was charged with HBPin (51 11L, 0.351
mmol). Additional arene (166 11L) was used to wash the residue to the NMR tube. The
reaction mixture was then heated at 150 °C for xx h. The reaction was monitored by the
disappearance of the resonance of pinacolborane in the 11B NMR spectra. After the
reaction was done, an aliquot was taken for GC—FID and GC-MS analyses. The reaction
mixture was then transferred to a vial and the substrate was removed under vacuum (in
some cases with gentle heating). The residue was dissolved in CHzClz and passed through
a silica gel column using CHzClz as eluting solvent. The filtrate was then pumped down
to give the corresponding spectroscopically pure arylboronate esters.

PinBQ-Cl

Cl

1,2,4-C6H3(Cl)2(BPin). The borylation product was isolated as colorless oil (93.9
mg, 98%). 1H NMR (CDC13) 6 1.32 (s, 12 H, Bozcan), 7.41 (d, J = 8.0 Hz, 1H), 7.57
(dd, J = 8.0 Hz, 1.5 Hz, 1H), 7.84 (d, J: 1.5 Hz, 1H). 13C NMR (125 MHz, CDC13) 6
24.8, 84.3, 130.0, 132.3, 133.8, 135.5, 136.6. “B NMR (CDCl,) 6 30.0. Anal. Calcd for

CizHlsBClez: C, 52.80; H, 5.54. Found: C, 53.09; H, 5.77. GC-MS (m/z) 273.

CI c1
BPin

1,4,5-C6H3(Cl)2(BPin). The borylation product was isolated as a colorless solid

(72.6 mg, 76%). mp 46-48 °C. 1H NMR (CD2C12) 6 1.35 (s, 12H, BOzCole), 7.29 (d, J =

8.3 Hz, 1H), 7.33 (dd, J= 2.4 Hz, 8.8 Hz, 1H), 7.67 (d, J= 2.4 Hz, 1H). l3C(‘H} NMR

(CDC13) 6 24.8, 84.5, 130.7, 131.7, 132.1, 136.0, 137.7. “B NMR (CDC13) 6 29.9. Anal.

Calcd for CrzHrsBCIZOZ: C, 52.80; H, 5.54. Found: C, 53.19; H, 5.71. GC-MS (m/z) 273.

154

PinB—Q—Me

Me

1,2,4-C6H3(Me)z(BPin). The borylation product was isolated as colorless oil
(69.2 mg, 85%). 1H NMR (CDC13) 6 1.32 (s, 12H, 302C6H12), 2.25 (s, 3H, Me), 2.26 (s,
3H, Me), 7.12 (d, J: 7.3 Hz, 1H), 7.53 (d, J: 7.3 Hz, 1H), 7.57 (s, 1H). '3C{‘H} NMR
(CDC13) 6 19.4, 20.0, 24.8, 83.5, 129.1, 132.4, 135.8, 135.9, 140.1. “B NMR (CDC13) 6
30.6. Anal. Calcd for C14H21B02: C, 72.44; H, 9.12. Found: C, 72.26; H, 8.98. GC-MS

(m/z) 232.

Me Me
BPin
1,2,4-C6H3(BPin)(Me)2. The borylation product was isolated as colorless oil
(55.4 mg, 68%). 1H NMR (CDC13) 6 1.33 (s, 12H, B02C6H12), 2.29 (s, 3H, Me), 2.48 (s,
3H, Me), 7.04 (d, J: 7.7 Hz, 1H), 7.11 (dd, J= 2.2 Hz, 7.7 Hz, 1H), 7.56 (d, J: 2.2 Hz,
1H). 13C(‘H} NMR (CDC13) 6 20.7, 21.7, 24.8, 83.3, 129.7, 131.5, 133.8, 136.3, 141.7.

“B NMR (CDC13) 6 30.9. Anal. Calcd for CnHeroz: C, 72.44; H, 9.12. Found: C,

F3C‘QCI
A

BPin

72.00; H, 8.59. GC-MS (m/z) 232.

C6H3(Cl)(BPin)(CF3) (isomer mixture). The borylation product was isolated as
colorless oil (375 mg, 78%). The ratio of 1,2,4-C6H3(Cl)(BPin)(CF3) to 1,3,4-
C6H3(Cl)(BPin)(CF3), determined by GC-FID of the crude reaction mixture, was 88:12.
1,2,4-C6H3(Cl)(BPin)(CF3). lH NMR (CDC13) 5 1.36 (s, 12H, BOzCsH12)s 7.44 (d, J =

8.5 Hz, 1H), 7.56 (ddd, J: 8.3 Hz, 2.4 Hz, 0.7 Hz, 1H), 7.92 (d, 2.2 Hz, 1H). 13C(‘H}

155

ma (CDC13) 6 24.8, 84.7, 124.0 (q, J: 272.0 Hz, 1C), 128.4 (q, J: 3.5 Hz, 1C), 128.5
(q, J: 32.9 Hz, 1C), 129.9, 133.3 (q, J: 3.5 Hz, 1C), 143.5. ”B NMR (CDC13) 6 30.0.

“’1: NMR (CDC13) 6 —62.8. Anal. Calcd for C13H15BC1F302: C, 50.94; H, 4.93. Found: C,

MeO—C\>—F
—\

BPin

51.27; H, 5.05. GC-MS (m/z) 306.

C6H3(F)(0Me)(BPin) (isomer mixture). The borylation product (55 mg, 62%)
was isolated as colorless oil. The ratio of 1,4,6-C6H3(F)(0Me)(BPin) to 1,4,5-
C6H3(F)(0Me)(BPin), determined by GC-FID of the crude reaction mixture, was 93:7.
1,4,6-C6H3(F)(0Me)(BPin). 1H NMR (CDC13) 6 1.34 (s, 12H, 802C6H12), 3.78 (s, 3H,
OMe), 6.92 (m, 2H), 7.18 (m, 1H). '3C{‘H} NMR (CDC13) 6 24.8, 55.8, 83.9, 116.0 (d,
2JCF = 25.9 Hz) 119.2 (d, 3Jcp = 8.6 Hz), 120.1 (d, 3Jcp = 8.6 Hz), 155.3 (d, 4JCF = 1.9
Hz), 161.7 (d, lJCF = 243.6 Hz). “B NMR (CDC13) 6 29.8. ”’1: NMR (CDC13) 6 —114.3.
1,4,5-C6H3(F)(0Me)(BPin). 1H NMR (CDC13) 6 1.30 (s, 12H,BOzC6H12), 3.88 (s, 3H,
OMe), 6.88 (d, J = 8.2 Hz, 1H), 7.64 (dd, J= 8.2 Hz, 1.5 Hz, 1H), 7.77 (d, J: 1.5 Hz,
1H). l3C(‘H} NMR (CDC13) 6 24.8, 56.7, 83.7, 112.2 (d, 3JCF = 6.7 Hz) 118.3 (d, 2JCF =
23.0 Hz), 122.4 (d, 2JCF = 21.1 Hz), 157.0 (d, lJCF = 238.8 Hz), 160.4 (d, 4JCF = 1.9 Hz).
“B NMR (CDC13) 6 29.8. "’17 NMR (CDC13) 6 —125.6. Anal. Calcd for C13HrgBFO3: C,

61.94; H, 7.20. Found: C, 61.83; H, 7.45. GC-MS (m/z) 252.

MeO—C\>‘Cl

BPin
C6H3(Cl)(OMe)(BPin) (isomer mixture). The borylation product was isolated as

colorless oil (58 mg, 62%). The ratio of 1,4,6-C6H3(Cl)(OMe)(BPin) to 1,4,5-

156

C6H3(Cl)(OMe)(BPin), determined by GC-F ID of the crude reaction mixture, was 32:68.
1,4,6-C6H3(Cl)(OMe)(BPin). ‘H NMR (CDC13) 6 1.35 (s, 12H,BOzC6H12). 3.77 (s, 3H,
OMe), 6.85 (dd, J: 8.6 Hz, 3.1 Hz, 1H), 7.17 (d, J: 3.3 Hz, 1H), 7.22 (d, J = 8.6 Hz,
1H). ‘3C(‘H} NMR (CDC13) 6 24.7, 55.5, 84.1, 117.9, 120.9, 130.2, 130.9, 157.6. “B
NMR (CDC13) 6 30.2. 1,4,5-C6H3(Cl)(OMe)(BPin). 1H NMR (CDC13) 6 1.33 (s, 12H,
BOzCole), 3.78 (s, 3H, OMe), 6.76 (d, J = 8.8 Hz, 1H), 7.30 (dd, J = 8.8 Hz, 2.9 Hz,
1H), 7.59 (d, J = 2.7 Hz, 1H). l3C(‘H} NMR (CDC13) 6 24.7, 56.1, 83.7, 112.1, 125.4,
131.9, 136.0, 162.7. “B NMR (CDC13) 6 30.2. Anal. Calcd for C13H18BC103: C, 58.14;

H, 6.76. Found: C, 58.20; H, 6.97. GC-MS (m/z) 268.

CI
PinBQOMe

C6H3(Cl)(OMe)(BPin) (isomer mixture). The borylation product was isolated as
colorless oil (69 mg, 73%). The ratio of 1,2,4-C6H3(Cl)(OMe)(BPin) to 1,2,5-
C6H3(Cl)(OMe)(BPin), determined by GC-FID of the crude reaction mixture, was 51:49.
1,2,5-C,H,(Cl)(0Me)(BPin). 'H NMR (CDC13) 6 1.31 (s, 12H, BOzC6H12), 3.88 (s, 3H,
OMe), 6.88 (d, J: 8.3 Hz, 1H), 7.65 (dd, J: 8.1 Hz, 1.5 Hz, 1H), 7.78 (d, J: 1.5 Hz,
1H). I3C{'H} NMR (CDC13) 6 24.8, 56.0, 83.8, 111.4, 122.3, 134.7, 136.5, 157.4. ”B
NMR (CDC13) 6 30.2. 1,2,4-C6Hs(Cl)(OMe)(BPin). ‘H NMR (CDC13) 6 1.32 (s, 12H,
BOszle), 3.91 (s, 3H, OMe), 7.31-7.35 (m, 3H). 13C(‘H} NMR (CDC13) 6 24.8, 56.1,
84.0, 117.7, 126.0, 127.9, 129.7, 154.6. “B NMR (CDC13) 6 30.2. Anal. Calcd for

C13H18BCIO3: C, 58.14; H, 6.76. Found: C, 58.12; H, 6.84. GC-MS (m/z) 268.
Me

/ \
PinB/_ OMe

157

C6H3(0Me)(Me)(BPin) (isomer mixture). The borylation product was isolated
as colorless oil (67 mg, 77%). The ratio of 1,2,5-C6H3(0Me)(Me)(BPin) to 1,2,4-
C6H3(0Me)(Me)(BPin), determined by GC-FID of the crude reaction mixture, was 64:36.
1,2,5-C,H3(0Me)(Me)(BPin). lH NMR (CDC13) 6 1.34 (s, 12H, BOszle), 2.24 (s, 3H,
Me), 3.87 (s, 3H, OMe), 7.15 (d, J: 7.3 Hz, 1H), 7.23 (s, 1H), 7.33 (d, J= 7.1 Hz, 1H).
13C(‘H} NMR (CDC13) 6 16.4, 24.8, 55.4, 83.6, 115.5, 127.3, 130.2, 130.3, 157.4. ”B
NMR (CDC13) 6 30.6. 1,2,4—C6H3(0Me)(Me)(BPin). 1H NMR (CDC13) 6 1.33 (s, 12H,
B02C6H12), 2.22 (s, 3H, Me), 3.84 (s, 3H, OMe), 6.82 (d, J: 8.2 Hz, 1H), 7.59 (s, 1H),
7.65(d, J: 8.2 Hz, 1H). ‘3C{'H} NMR (CDC13) 6 15.9, 24.8, 55.2, 83.5, 109.3, 125.9,
134.3, 137.2, 160.5. ”B NMR (CDC13) 6 30.6. Anal. Calcd for C14H21B03: C, 67.77; H,

8.53. Found: C, 67.76; H, 8.39. GC-MS (m/z) 248.

MeO / \ Me

BPin

C6H3(0Me)(Me)(BPin) (isomer mixture). The borylation product was isolated
as colorless oil (67 mg, 77%). The ratio of 1,4,6-C6H3(0Me)(Me)(BPin) to 1,4,5-
C6H3(0Me)(Me)(BPin), determined by GC-FID of the crude reaction mixture, was 70:30.
l,4,6-C6H3(0Me)(Me)(BPin). 1H NMR (CDC13) 5 1.34 (s, 12H, BOzCole). 2.26 (s, 3H,
Me), 3.78 (s, 3H, OMe), 6.74 (d, J = 8.4 Hz, 1H), 7.16 (ddd, J = 8.4 Hz, 2.4 Hz, 0.7 Hz,
1H), 7.45 (d, J = 2.4 Hz, 1H). 13C{'H} NMR (CDC13) 5 20.2, 24.8, 56.1, 83.3, 110.8,
129.2, 132.8, 137.0, 162.4. ”B NMR (CDC13) 6 30.7. 1,4,5-C6H3(0Me)(Me)(BPin). 1H
NMR (CDC13) 5 1.32 (s, 12H, BOzCoth), 2.45 (s, 3H, Me), 3.78 (s, 3H, OMe), 6.85 (dd,
J= 8.4 Hz, 3.1Hz, 1H), 7.05 (d, J= 8.2 Hz,1H), 7.28 (d, J= 2.9 Hz, 1H). 13C{1H} NMR

(CDC13) 5 21.1, 24.8, 55.3 (d, J= 2.0 Hz), 83.4, 117.0, 120.3, 130.8, 136.8, 156.9. HB

158

NMR (CDC13) 5 30.7. Anal. Calcd for C14H21BO3: C, 67.77; H, 8.53. Found: C, 67.50; H,

8.61. GC-MS (m/z) 248.

C6H3(Cl)(Me)(BPin) (isomer mixture). The borylation product was isolated as
colorless oil (74 mg, 84%). The ratio of 1,4,5-C6H3(CI)(Me)(BPin) to 1,4,6—
C6H3(Cl)(Me)(BPin), determined by GC-FID of the crude reaction mixture, was 57:43.
1,4,5-C6H3(Cl)(Me)(BPin). ‘H NMR (CDC13) 6 1.32 (s, 12H, BozczHrz), 2.47 (s, 3H,
Me), 7.06 (d, J: 8.3 Hz, 1H), 7.24 (dd, J: 8.3 Hz, 2.4 Hz, 1H), 7.69 (d, J: 2.4 Hz, 1H).
l3C(‘H} NMR (CDC13) 6 21.5, 24.9, 83.8, 130.5, 130.8, 131.2, 135.4, 143.1. ”B NMR
(CDC13) 6 30.9. 1,4,6—C,H3(Cl)(Me)(BPin). ‘H NMR (CDC13) 6 1.35 (s, 12H,
BOszle). 2.28 (s, 3H, Me), 7.11 (ddd, J: 8.3 Hz, 2.0 Hz, 0.7 Hz, 1H), 7.21 (d, J= 8.3
Hz, 1H), 7.46 (d, J = 2.0 Hz, 1H). '3C{'H} NMR (CDC13) 6 20.6, 24.8, 84.1, 129.2,
132.5, 135.4, 136.6, 136.9. “B NMR (CDC13) 6 30.9. Anal. Calcd for C13H13BC102: C,

61.83; H, 7.18. Found: C, 62.15; H, 7.22. GC-MS (m/z) 252.
CI
PinBL_\ Me

C6H4(Cl)(Me)(BPin) (isomer mixture). The borylation products (79 mg, 89%)
were isolated as colorless oil. The ratio of 1,2,5-C6H3(Cl)(Me)(BPin) to 1,2,4-
C6H3(Cl)(Me)(BPin), determined by GC-FID of the crude reaction mixture, was 62:38.
1,2,5-C6H3(Cl)(Me)(BPin). 1H NMR (CDC13) 5 1.32 (s, 12H, B02C6H12). 2.38 (s, 3H,
Me), 7.20 (d, J = 7.5 Hz, 1H), 7.52 (dd, J: 8.8 Hz, 0.9 Hz, 1H), 7.76 (s, 1H). 13C{"H}

NMR (125 MHz, CDC13) 6 20.2, 24.9, 84.0, 130.5, 132.8, 134.3, 135.2, 139.2. ”B NMR

159

(CDC13) 6 30.9. 1,2,4-C6H3(Cl)(Me)(BPin). 1H NMR (CDC13) 6 1.33 (s, 12H,
BOzCsle), 2.37 (s, 3H, Me), 7.32 (d, J: 8.0 Hz, 1H), 7.55 (dd, J: 7.5 Hz, 0.9 Hz, 1H),
7.65 (s, 1H). l3C(‘H} NMR (125 MHz, CDC13) 6 19.7, 24.9, 83.9, 128.6, 133.5, 135.3,
137.3, 137.8. ”B NMR (CDC13) 6 30.9. Anal. Calcd for C13H13BC102: C, 61.83; H, 7.18.

Found: C, 61.94; H, 7.42. GC-MS (m/z) 252.

Competitive Borylation Experiments

Competition between Toluene and Anisole Using Solutions of 2

Cp*Ir(PMe3)H2 (2) (15 mg, 0.037 mmol) was weighed in a test tube, and a pre—mixed 1:1
mole ratio of toluene (256 mg) and anisole (300 mg) was added to dissolve the catalyst.
Then HBPin (27 11L, 0.185 mmol) was added to the test tube via syringe. The solution
was transferred to a J. Young NMR tube, and the reaction was heated at 150 °C in a
constant temperature circulator. The conversion of the reaction was monitored by the
disappearance of the resonance for pinacolborane in the 11B NMR spectrum. The isomer
ratios were determined by integrating the peaks in the GC-MS spectra, after correcting
for the response factors determined from equimolar mixtures of independently
synthesized arylboronate esters. The ratio of 0-, m-, p-C6H4Me(BPin) : -, m-, p-
C6H4(0Me)(BPin) is 38:62.

Competition between Toluene and Benzotrifluoride Using Solutions of 2

The procedure is the same as that in the competition between toluene and anisole using
solutions of 2. Toluene (242 mg) and benzotrifluoride (383 mg) were used. The ratio of

0-, m-, p-C6H4Me(BPin) : m-, p-C,H4(CF3)(BPin) is 11:89.

160

Competition between Cumene and N,N-Dimethylaniline Using Solutions of 2

The procedure is the same as that in the competition between toluene and anisole using
solutions of 2. Cumene (280 mg) and N,N-dimethylaniline (282 mg) were used. The ratio
of C6114CH(CH3)2(BPin) : o-, m-, p-C6Ha(NMe2)(BPin) is 69:31.

Competition between Toluene and Anisole Using Solutions of 3

Cp*Rh(n4-C6Me6) (3) (5 mg, 0.013 mmol) was weighed in a test tube, and a pre-mixed 1:
1 mole ratio of toluene (256 mg) and anisole (300 mg) was added to dissolve the catalyst.
Then HBPin (90 mg, 0.70 mmol) was added to the test tube via syringe. The solution was
transferred to a J. Young NMR tube. The reaction was heated at 150 °C in a constant
temperature circulator, and the reaction was judged to be complete by monitoring the
disappearance of the resonance for pinacolborane in the 11B NMR spectrum. The isomer
ratios were determined by integrating the peaks in the GC-MS spectra, after correcting
for the response factors determined from equimolar mixtures of independently
synthesized arylboronate esters. The ratio of o-, m-, p-C6H4Me(BPin) : -, m-, p-
C6H4(0Me)(BPin) is 46:54.

Competition between Toluene and Benzotrifluoride Using Solutions of 3

The procedure is the same as that in the competition between toluene and anisole using
solutions of 3. Toluene (242 mg) and benzotrifluoride (383 mg) were used. The ratio of
o-, m-, p-C6H4Me(BPin) : m-, p-C6H4(CF3)(BPin) is 27:73.

Competition between Cumene and N,N-Dimethylaniline Using Solutions of 3

The procedure is the same as that in the competition between toluene and anisole using

solutions of 3. Cumene (280 mg) and N,N-dimethylaniline (282 mg) were used. The ratio

of C,H,CH(CH,)2(BPin) : 0-, m-, p-C,H.,(NMe2)(BPin) is 60:40.

161

Competition between Toluene and N,N-Dimethylaniline Using Solutions of 3

The procedure is the same as that in the competition between toluene and anisole using
solutions of 3. Toluene (250 mg) and N,N-dimethylaniline (329 mg) were used. The ratio
of o-, m-, p-CgHaMe(BPin): o-, m-, p-C6H4(NMe2)(BPin) is 59:41.

Competition Experiments Using Solutions of 13 and dmpe

The general procedure is illustrated by the competition reaction between m-xylene and
1,3-bis(trifluoromethyl)benzene using solutions of 13 and dmpe. (Ind)Ir(COD) (13) (2.9
mg, 0.007 mmol) and dmpe (1 mg, 0.007 mmol) were weighed into two separate GC
vials, and a pre-mixed 1:1 molar ratio of m-xylene and 1,3-bis(trifluoromethyl)benzene
solution (166 11L x 3) was added to dissolve the catalyst. The solution was transferred to a
J. Young NMR tube, which was charged with HBPin (51 11L, 0.351 mmol) and the
reaction mixture was heated at 150 °C in a constant temperature circulator. The
conversion of the reaction was monitored by the disappearance of the resonance for
pinacolborane in the HB NMR spectrum. The product ratios were determined by
integrating the peaks in the GC-FID spectra. The ratio of 1,3,5-C6H3Me2(BPin) : 1,3,5-
C6H3(CF3)2(BPin) is 35:96.5. The results of borylation of equimolar mixtures of two
different substituted arenes catalyzed by 13 (2 mol%)/dmpe (2 mol%) are summarized in

Table 13.

Kinetics Experiments
A typical experimental run for the reaction of Cp*Rh(PMeg)(Ph)(H) (4) with 12

equiv. of HBPin in C6D6 is described as follows: Two samples were prepared at the same

162

I?!“ Inumflw

time. In a drybox, compound 4 (18 mg, 0.046 mmol) and HBPin (80 11L, 0.55 mmol)
were placed in a 1 mL volumetric flask and the flask was filled with C6D6 to the mark.
The solution in the volumetric flask was mixed well and distributed equally to two J.
Young NMR tubes. The kinetic experiments were run twice at different temperatures to
ensure the reproducibility. The temperature range is from 65 °C to 115 °C. The kinetics
was carried out at 65, 75, 85, 95, 105, and 115 °C. The reactions were heated in a
constant temperature oil bath (Cole-Palmer Polystat Constant Temperature Circulator).
At specific intervals the NMR tubes were removed from the oil bath and quenched by
rapid cooling in an ice bath. The 1H N1V£R spectra were then recorded at 25 i 0.5 °C on a
VXR-SOO spectrometer. The progress of the reaction was monitored to 3 half-lives by
measuring the ratio of the intensity of the Cp* of 4 versus the total “intensity” of the Cp*
resonances of 4 and Cp*Rh(PMe3)(H)(BPin) (7).

A typical experimental run for the phosphine dependence on the thermolysis of 18
in Cng is described as follows: Four samples were prepared at the same time. In a
drybox, compound 18 (60 mg, 0.096 mmol) was placed in a 1 mL volumetric flask and
the flask was filled with C6D6 to the mark. The solution in the volumetric flask was
mixed well and a 200 uL portion of the solution was added to four J. Young NMR tubes
respectively via an auto-pipette (100 11L x 2). C6Me6 (15.6 mg, 0.096 mmol) was placed
in a 1 m1 volumetric flask and the flask was filled with C6D6 to the mark. The solution in

the volumetric flask was mixed well and a 200 uL portion of the solution was added to

the four J. Young NMR tubes respectively via an auto-pipette (100 11L x 2) as an internal
standard. Pre-calculated amount of Cng, was added into each of the four NMR tubes to

make the total volume of the solution to 700 1.1L. In the end, different quantities of PMe3

163

were added to the four NMR tubes respectively via a microsyringe. The experiments
were carried out at 130 °C in a constant temperature oil bath (Cole-Palmer Polystat
Constant Temperature Circulator). At specific intervals the NMR tubes were removed
from the oil bath and quenched by rapid cooling in an ice bath. The 1H NMR spectra
were then recorded at 25 :1: 0.5 °C on a Inova-600 spectrometer. The concentration range
of PMe3 is from 0.00828 M to 0.828 M. The progress of the reaction was monitored to 3
half-lives by measuring the ratio of the intensity of the PMe3 of 18 versus the total

“intensity” of the PMe3 resonances of 18 and 37-d1.

Crystal Structure Determinations and Refinement

Crystals grown at —30 °C were covered in Paratone N and moved quickly from a
scintillation vial to a microscope side. A suitable crystal was chosen and mounted on a
glass fiber. The data collection were carried out at a sample temperature of 173(2) K on a
Bruker AXS three-circle goniometer with a CCD detector. The data were processed and
reduced utilizing the program SAINT PLUS supplied by Bruker AXS. The structure were
solved by direct methods (SHELXTL v5.1, Bruker AXS) in conjunction with standard
difference Fourier techniques. The figures shown were produced using ORTEP and
ellipsoids are at the 25% probability level. Tables of pertinent data collection parameters
for all compounds crystallographically characterized are given in appendix A.

Single crystals of 14 were grown from a pentane solution at —30 oC and the
structure was further confirmed by single—crystal X-ray crystallographic analysis.

Single crystals of 17 and B2Pin2 co-crystallized from a pentane solution at —30 °C

and the structures were established by X-ray crystallographic analysis.

164

Single crystals of 18 were grown from a pentane solution at —30 °C and the
structure was further confirmed by single—crystal X-ray crystallographic analysis.

Crystals suitable for X-ray analysis of 25 were grown from a pentane solution at
—30 °C.

Single crystals of 28 were grown fiom a pentane solution at —30 0C to give
colorless crystals suitable for X-ray analysis.

Single crystals of 29 were grown from a concentrated pentane solution and the

structure was further confirmed by single—crystal X-ray crystallographic analysis.

165

APPENDICES

166

Appendix A. Surmnary of crystal data and structure refinement for compound 14.

Empirical formula
Formula weight
Temperature (K)
Wavelength (A)
Crystal system
Space group

a (A)

b (A)

C (A)

01, deg

13. deg

16 deg

Volume (A3)

Z

Density (calculated) (Mg/m3)
Absorption coefficient (mm'l)

F (000)

Crystal size (mm3)

Theta range for data collection, deg
Index ranges

Reflections collected

Independent reflections
Refinement method

Data / restraints / parameters
Goodness-of-fit on F2

Final R indices [I>2sigma(I)]

R indices (all data)

Largest diff. peak and hole (en/3(3)

(32711451331106

690.26

173(2)

0.71073

Monoclinic

P2(1)/n

10.211(3)

16.822(4)

18.362(5)

90

92.907(5)

90

3150.2(14)

4

1.455

4.273

1388

0.32 x 0.30 x 0.28

1.64 to 23.28

-1 1<=h<=10, -18<=k<=18, -20<=l<=14
14167

4535 [R(int) = 0.1070]
Full-matrix least-squares on F 2
4535 / 0 / 349

0.944

R1 = 0.0453, wR2 = 0.1056
R1= 0.0715, wR2 = 0.1146
1.604 and -1.635

167

Appendix A (cont). Summary of crystal data and structure refinement for compound 17.

Empirical formula
Formula weight
Temperature (K)
Wavelength (A)
Crystal system
Space group

a (A)

b (A)

c (A)

01, deg

B. deg

7, deg

Volume (A3)

Z

Density (calculated) (Mg/m3)
Absorption coefficient (mm'l)
F(000)

Crystal size (mm3)

Theta range for data collection, deg
Index ranges

Reflections collected

Independent reflections
Refinement method

Data / restraints / parameters
Goodness-of-fit on F2

Final R indices [I>2sigma(I)]

R indices (all data)

Largest diff. peak and hole (e.A'3)

C21H5132CIIIO4P3

557.84

173(2)

0.71073

Monoclinic

P2(1)/c

11.4474(13)

l7.2608(19)

19.579(2)

90

92.162(2)

90

3865.9(8)

6

1.438

3.681

1708

0.42 x 0.40 x 0.38

1.57 to 23.28

-12<=h<=12, -19<=k<=19, -21<=1<=21
31832

5555 [R(int) = 0.1432]
Full-matrix least-squares on F 2
5555 / 0 / 391

1.052

R1 = 0.0320, wR2 = 0.0874
R1 = 0.0363, wR2 = 0.090
1.786 and -1.656

168

Appendix (cont). Summary of crystal data and structure refinement for compound 18.

Empirical formula
Formula weight
Temperature (K)
Wavelength (A)
Crystal system
Space group

a (A)

b (A)

c (A)

0t, deg

13, deg

16 deg

Volume (A3)

Z

Density (calculated) (Mg/m3)
Absorption coefficient (mm'l)
F(000)

Crystal size (mm3)

Theta range for data collection, deg
Index ranges

Reflections collected

Independent reflections
Refinement method

Data / restraints / parameters
Goodness-of-fit on F2

Final R indices [I>2$igma(I)]

R indices (all data)

Largest diff. peak and hole (e.A'3)

C18H481311’02P4

31 1.73

173(2)

0.71073

Triclinic

P-l

9.290(3)

12.408(5)

12.458(5)

90.107(5)
99.436(6)

90.221(6)

1416.4(9)

4

1.462

4.949

628

0.43 x 0.31 x 0.28

1.64 to 23.31

-10<=h<=7, -13<=k<=13, -12<=1<=13
6368

4039 [R(int) = 0.0226]
Full-matrix least-squares on F 2
4039 / 0 / 252

1.103

R1 = 0.0380, wR2 = 0.1022
R1 = 0.0394, wR2 = 0.1035
2.484 and -1.546

169

Appendix (cont). Summary of crystal data and structure refinement for compound 25.

Empirical formula
Formula weight
Temperature (K)
Wavelength (A)
Crystal system
Space group

a (A)

b (A)

c (A)

0t, deg

B. deg

16 deg

Volume (A3)

Z

Density (calculated) (Mg/m3)
Absorption coefficient (mm'l)
F(000)

Crystal size (mm3)

Theta range for data collection, deg
Index ranges

Reflections collected

Independent reflections
Refinement method

Data / restraints / parameters
Goodness-of-fit on F2

Final R indices [I>2sigma(I)]

R indices (all data)

Largest diff. peak and hole (e.A'3)

C27H63B3II‘06P3

801.31

173(2)

0.71073

Monoclinic

P2(l)/c

17.808(4)

11.073(3)

19.023(5)

90

90.106(4)

90

3751.0(15)

5

1.774

4.651

2050

0.44 x 0.28 x 0.26

2.13 to 23.28

-19<=h<=18, -12<=k<=12, -12<=1<=21
16587

5396 [R(int) = 0.0595]
Full-matrix least-squares on F2
5396 / 0 / 362

1.037

R1 = 0.0743, wR2 = 0.1796
R1 = 0.1012, wR2 = 0.1971
3.058 and -1.864

170

Appendix (cont). Summary of crystal data and structure refinement for compound 28.

Empirical formula
Formula weight
Temperature (K)
Wavelength (A)
Crystal system
Space group

a (A)

b (A)

c (A)

0t, deg

13. deg

Y: deg

Volume (A3)

Z

Density (calculated) (Mg/m3)
Absorption coefficient (mm'l)
F(000)

Crystal size (mm3)

Theta range for data collection, deg
Index ranges

Reflections collected

Independent reflections
Refinement method

Data / restraints / parameters
Goodness-of-fit on F2

Final R indices [I>23igma(I)]

R indices (all data)

Largest diff. peak and hole (e.A'3)

C21H44BII'02P3

499.59

173(2)

0.71073

Monoclinic

P2(1)/n

10.740(2)

16.687(3)

15.145(3)

90

90.069(4)

90

2714.3(10)

5

1.528

5.109

1252

0.42 x 0.35 x 0.24

1.82 to 23.28

-11<=h<=11, -17<=k<=18, -16<=1<=16
12074

3908 [R(int) = 0.0288]
Full-matrix least-squares on F2
3908 / 0 / 266

1.119

R1 = 0.0282, wR2 = 0.0647
R1 = 0.0346, wR2 = 0.0669
1.110 and -0.912

171

Appendix A (cont). Summary of crystal data and structure refinement for compound 29.

Empirical formula
Formula weight
Temperature (K)
Wavelength (A)
Crystal system
Space group

a (A)

b (A)

c (A)

0t, deg

15. deg

16 deg
Volume (A3)
2

Density (calculated) (Mg/m3)

Absorption coefficient (mm'l)
F(000)

Crystal size (mm3)

Theta range for data collection, deg
Index ranges

Reflections collected

Independent reflections
Refinement method

Data / restraints / parameters
Goodness-of-fit on F2

Final R indices [I>2$igrna(I)]

R indices (all data)

Largest diff. peak and hole (e. A'3)

C21H54B1r02P3Si
530.12
173(2)
0.71073
Monoclinic
P2(l)/c
l9.733(8)
10.280(4)
16.1 19(7)
90

1 10.168(7)
90

3069(2)

5

1.434

4.559

1348

0.36 x 0.34 x 0.26

2.20 to 23.28

-21<=h<=21, -7<=k<=l 1, —16<=l<=1 7
9405

4175 [R(int) = 0.1122]
Full-matrix least-squares on F2
4175 / 0 / 278

1.056

R1 = 0.0472, wR2 = 0.1208
R1 = 0.0506, wR2 = 0.1238
3.122 and -2.075

172

’31
1
g
a. 1

ti

 

APPENDIX B. Derivation of Rate Expressions for Chapter 5

 

 

k1 k
[18]-————= (PMe3)3|r(BPin) + PMe3] 2 [(PMe3)2|r(BPin)+ PMe3]
1 [3] K2 191
R3 CSDS k4 C606
(PMe3)4lr(D) + ceogepin (PMe3)4|r(D) + CngBPin

From the Figure above, the time dependent concentrations for 18, B, and C are

governed by the Equations B1, B2, and B-3:

d[18]
_—dt_ = k1[18] ' k.1[B][PMe3]
(Bl)
d[B
dt = k11131- KtlBlIPMea] - k213] + K2[C][L] - kBIBHCoDol
(32)
d C]
—d, = kzlal - KzlcllLl - memos]
(33)

Application of the steady state approximation to [C] yields Equation B4, and

combination of the steady state expression for [B] and Equation B4 gives B5.

d[C] _ k213]
dt ' 0 :3 [°] K2[PM931+ moons]

 

173

{
it
~ -—

 

 

(B4)

——d[B] k [18] ’ k [B][PMe ] + k [B] + k [B][C D ] k-ZKZIBHL]
dt = 0 Z) 1 " " 3 2 3 6 6 K21PM631+ 1619st

 

(BS)
Rearrangement of Equation B5 gives Equation B6. The first order rate law in
Equation B7 follows fi'om substitution of the expression for [B] (Equation B6) in

Equation B1:

 

B _ < k1ik-21PM33] + k4ICGDGD > [18]
k—tk-le’lV'ea]2 + (k-1K4ICSDB] "’ szalcesDemPMeal + k4IC606Kk2 "‘ k3ICSDGD

(B6)

 

_ d[18] _ < k1K2k3IC606HPMeal + ktk4[0606](k2 + kalCeDc—sl) > 18]
dt K1K21PM9312 + (K1k4106061 + K2k310606])[PMeal + k4lCeDol(k2 + k3[Cng])

(B7)
From Equation B7, kobs (Equation B8) and l/kob, (Equation B9) can be extracted:

k1K2k3[Cng][PM63] + k1k4[CGDB](k2 1’ k3lCBDGD

 

kobs =
k,1k-2[PMe3]2 + (K1k4 + k-2k3)[CSD6][PMe3] + MCGDGK'Q + k3lceDel)

(BS)

174

1 1 k-lk-21PM9312 + k_1k4[Cng][PMe3]

 

 

kobs k1 k-110606KK-2k31PMes] + k4k2 + k4kalceDsl)

(39)

If the reaction only goes through intermediate B to yield products (k4 = 0), l/kobS

can be derived in Equation B10. If the reaction only passes through intermediate C to

yield products (k3 = 0), l/kobs can be derived in Equation B11.

1 1 K1

— +

k... ' k. ktkalCoDol

 

 

 

[PMe3]

1 1 + K1K21PM9312+K1k41C606HPM33]

 

 

kobs k1 k1k2k41C606]

175

(1310)

(1311)

 

 

 

APPENDIX C. Kinetic Details

Data for the reaction of Cp*Rh(PMe3)(Ph)(H) (4) with 12 equiv. HBPin in C6D6.

The progress of the reaction was monitored to 3 half-lives by measuring the ratio
of the intensity of the Cp* of 4 versus the total “intensity” of the Cp* resonances of 4 and
7. The experiments were performed at various temperatures in a constant temperature oil
bath.

[4] = 0.046 M; [HBPin] = 0.551 M

 

Temperature (°C) kobs (599.1)
65 1.27 x 10'5
75 4.0 x 10‘5
85 1.38 x 10'4
95 3.37 x 10‘4
105 9.8 x 10'4
115 2.0 x 10'3

 

Data for the reaction of Cp*Rh(PMe3)(Ph)(H) (4) with 24 equiv. HBPin in C6D6.
The progress of the reaction was monitored to 3 half-lives by measuring the ratio
of the intensity of the Cp* of 4 versus the total “intensity” of the Cp* resonances of 4 and

7. The experiments were performed at 95 i 0.5 °C in a constant temperature oil bath.

176

[HBPin] k,,,, (scc")

 

0.551 M 3.37 x 10“

1.103 M 6.80x10“1

 

Data for the phosphine dependence on the thermolysis of (PMe3)4Ir(BPin) (18) in
C6D6 at 130 °C.

The progress of the reaction was monitored to 3 half-lives by measuring the ratio
of the intensity of the PMe3 of 18 versus the total “intensity” of the PMe3 resonances of
18 and 37-d]. The experiments were performed at 130 :t 0.5 °C in a constant temperature
oil bath.

[18] = 0.0275 M; [C6Me6] = 0.0275 M

 

 

[PMesl (M) k... (sec")

0 0.0417
0.0083 0.0170
0.0138 0.0138
0.0207 0.0097
0.0276 0.0072
0.0552 0.0044
0.1380 0.0021

177

BIBLIOGRAPHY

178

 

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(52) Thorn, D. L. Organometallics 1982, 1, 197-204.

(53) The ratio was determined from the integrations of pinacol resonance in the 1H NMR
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(54) Baker, R. T.; Ovenall, D. W.; Calabrese, J. C.; Westcott, S. A.; Taylor, N. J.;
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182

(57) See Table 4 in the Chapter 3.

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(59) The product distribution between C6D5BPin and C6H5BPin was determined by
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The product distribution between C6D2H3(BPin) and C6D3H2(BPin) was extracted from
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before acquiring 1H NMR spectra.

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(67) Janowicz, A. H.; Bergman, R. G. J. Am. Chem. Soc. 1983, 105, 3929-3939.

(68) Barefield, E. K. Inorg. Synth. 1974, 15, 34-38.

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