SYNTHESIS, CHARACTERIZATION, AND PARAMETERIZATION OF
ANIONIC AND NEUTRAL MONODENTATE LIGANDS
AND THE ADDITION OF A PYRROLE LIGAND TO A SURFACE

By
Nicholas Alexander Maciulis

A THESIS
Submitted to
Michigan State University
in partial fulfillment of the requirements
for the degree
MASTERS OF SCIENCE
Chemistry
2012

ABSTRACT

SYNTHESIS, CHARACTERIZATION, AND PARAMETERIZATION OF
ANIONIC AND NEUTRAL MONODENTATE LIGANDS
AND THE ADDITION OF A PYRROLE LIGAND TO A SURFACE

By

Nicholas Alexander Maciulis

The main body of this thesis concerns determining the donor ability of ligands
0

bound to a d chromium center. Synthetic protocols and characterization data for a
i

variety of chromium(VI) nitrido compounds of the general formula NCr(NPr 2)2X are
reported, where X is a variety of mono-anionic ligands. Using spin saturation transfer or
line shape analysis, the free energy barriers for diisopropylamido rotation were studied. It
is proposed that the estimated enthalpic barriers, Ligand Donor Parameters (LDPs), for
amido rotation can be used to parameterize the donor abilities of this diverse set of
anionic ligands toward transition metal centers in low d-electron counts.

The

last

chapter

of

the

thesis

is

devoted

to

placing

the

5,5-

dimethyldipyrrolylmethane (dmpm) ligand on a surface. The dmpm ligand was protected
and coupled to a borylated polystyrene resin. The straight-forward route to placing a
ligand on a surface has been developed. A detail on the synthesis and characterization is
also discussed.

ACKNOWLEDGEMENTS

I first would like to thank my parents Algimantas and Margarethe Maciulis for supporting
my interests and encouraging me to pursue my dreams.
I also want to thank the Chemistry Faculty at Alma College, especially Dr. Nancy Dopke
for giving me the chance to work in her lab and Dr. Sean Mo for nurturing my curiosities in
chemistry. My experience with them was wonderful and I will never forget them.
Aaron, thank you for giving me a chance to work in your lab and learn about synthetic
inorganic chemistry. The lessons and techniques I learned will always be with me for the rest of
my life.
I would also like to thank my committee members for being patient, understanding and
for providing insight and guidance in my research.
To Dan Holmes and Kermit Johnson: I would not have been as successful with my
research if it wasn’t for you. You were always helpful, whether it was fixing problems with the
NMR instrument or interpretation of data or teaching me kinetic experiments I will always be
thankful.
To my lab mates: Steve DiFranco, may you find peace and happiness when you get your
PhD. Without your synthetic skills, this chromium project would not be as complete as it is.
Amila, may you find a job that pays you lots and lots of money.
To Sebastian Jesberg for being a true friend and who was always ready to talk about life’s
problems and support my decisions.
To Allison Brown for keeping me sane during my time at graduate school.

iii

To everyone else that I have associated with I thank all of you for support and moral. In
these last few months I have gotten to know many of you and I am sad that I am leaving because
I am saying goodbye to some very amazing people. I hope you all are successful and happy with
your lives.

iv

TABLE OF CONTENTS

LIST OF TABLES……………………………………………………………………………...viii
LIST OF FIGURES………………………………...………………………………………….....ix
LIST OF SCHEMES…………………………………………………...………………………..xii
LIST OF ABBREVIATIONS……………………………………..…………………………....xiii

Chapter 1: Metal Centers and their Ligands
1.1: Introduction…………………………………………………………………………...1
0
1.2: Investigation of the Probe for Donors Bound to a d Chromium Center………...…..6
REFERENCES…………………………………………………………………………..10

Chapter 2: Synthesis of Chromium Compounds
i
2.1: Synthesis of NCr(N Pr2)3…………………………………………………...……....14
2.2: Synthesis using Protonolysis
2.2.1: Protonolysis using Lutidinium Salts………………………………………16
2.2.2: Protonolysis using HX…………………………………………………….16
2.3: Synthesis using Salt Metathesis
2.3.1: Salt Metathesis using Thallium Salts………………………..…………….18
2.3.2: Salt Metathesis using Sodium Salts……………………………………….19
2.4: Synthesis using Ligand Exchange with Lithium Salts………………………………20
2.5: Synthesis using Ligand Exchange with Lithium to Zinc Transmetalation………….21
2.6: Synthesis using Ligand Exchange with Mg(R)2…………………………………….21
i

+

-

i

+

-

2.7: Synthesis of [NCr(N Pr2)2DMAP ][BF4 ] and [NCr(N Pr2)2HMPA ][PF6 ]...........22
2.8: Synthesis using Tin(IV)-Catalyzed Decomposition of Cationic BF4 Salt………….23
2.9: Experimental Section
2.9.1 General Procedure………………………………………………………….24
i
2.9.2 NCr(N Pr2)3 (1)……………………………………………………………26
i

2.9.3 NCr(N Pr2)2(Cl) (3)………………………………………………………..26
i

2.9.4 NCr(N Pr2)2(Br) (4)………………………………………………………..27
i

2.9.5 NCr(N Pr2)2(OTf) (5)……………………………………………...............28
i

2.9.6 NCr(N Pr2)2(OAd) (6)……………………………………………………..28
i

2.9.7 NCr(N Pr2)2(OSiPh3) (7)………………………………………………….29
i

2.9.8 NCr(N Pr2)2(O2CPh) (8)…………………………………………..............29
i

2.9.9 NCr(N Pr2)2(O-p-(OMe)C6H4) (11)………………………………………30
i

2.9.10 NCr(N Pr2)2(O-p-(SMe)C6H4) (12)……………………………………..31
v

i

t

2.9.11 NCr(N Pr2)2(O-p-( Bu)C6H4) (13)……………………………………….31
i

2.9.12 NCr(N Pr2)2(O-p-(F)C6H4) (14)…………………………………………32
i

2.9.13 NCr(N Pr2)2(O-p-(Cl)C6H4) (15)………………………………...............33
i

2.9.14 NCr(N Pr2)2(O-p-(CF3)C6H4) (16)………………………………………33
i

2.9.15 NCr(N Pr2)2(OC6F5) (17)………………………………………..............34
i

2.9.16 NCr(N Pr2)2(SPh) (18)…………………………………………...............35
i

2.9.17 NCr(N Pr2)2(OPth) (19)………………………………………………….36
i

2.9.18 NCr(N Pr2)2(OBn) (20)…………………………………………………..36
i

2.9.19 NCr(N Pr2)2(NO3) (21)…………………………………………………..37
i

2.9.20 NCr(N Pr2)2(Pyrrolyl) (22)……………………………………………….38
i

C6F5

i

C6H3(CF3)2

2.9.21 NCr(N Pr2)2(Pyr

) (23)………………………………………………38

2.9.22 NCr(N Pr2)2(Pyr

) (24)………………………………………..39

i

2.9.23 NCr(N Pr2)2(Indolyl) (25)………………………………………………..40
i

2.9.24 NCr(N Pr2)2(Carbazolyl) (26)……………………………………………41
i

2.9.25 NCr(N Pr2)2(N(Me)Ph) (27)……………………………………………...41
i

2.9.26 NCr(N Pr2)2(NCO) (28)………………………………………………….42
i

2.9.27 NCr(N Pr2)2(NCS) (29)…………………………………………………..43
i

2.9.28 NCr(N Pr2)2(CN) (30)……………………………………………………43
i

2.9.29 NCr(N Pr2)2(NMe2) (31)…………………………………………………44
i

2.9.30 [NCr(N Pr2)2(DMAP][BF4]) (32)………………………………..............45
i

2.9.31 NCr(N Pr2)2(F) (33)……………………………………………………...45
i

2.9.32 [NCr(N Pr2)2(HMPA][PF6]) (34)………………………………..............46
i

2.9.33 NCr(N Pr2)2(CH2Si(Me)3) (35)………………………………………….47
i

2.9.34 NCr(N Pr2)2(CH2C(Me)2Ph) (36)……………………………….............47
i

2.9.35 NCr(N Pr2)2(CH2C(Me)3) (38)…………………………………..............48
i

i

2.9.36 NCr(N Pr2)2(CCSi( Pr)3) (39)……………………………………………49
i

t

2.9.37 NCr(N Pr2)2(CC Bu) (40)………………………………………...............50
REFERENCES…………………………………………………………………..53

Chapter 3: Kinetic Experiments and Discussion of the Results
3.1: Overview of Kinetic Experiments…………………………………………………..56
3.2: Measuring T1s and Apparent T1s of Exchanging Resonances……………...............58
3.3: Spin Saturation Magnetization Transfer and the Eyring Equation………………….64
3.4: Control Experiments
‡
3.4.1 Investigation of Solvent Effects on T1s and ΔG ………………………….68

vi

‡

3.4.2 Investigation of Magnetic Field on T1s and ΔG ………………………….68
‡

3.4.3 Investigation of Paramagnetic Materials on T1s and ΔG …………………69
i

i

3.5: CLSA and Eyring Plots of NCr(N Pr2)2NMe2 and NCr(N Pr2)2OAd……………..69
‡

‡

‡

3.6: Discussion of ΔG , ΔH , and ΔS and Ligand Donating Parameter………..............71
3.7: Sterics Investigation using Percent Buried Volume and Solid G…………...............78
3.8: Comparison with Literature
3.8.1: LDP vs. pKa Values of HX Compounds………..………………...............83
3.8.2: LDP of Phenoxides vs. Hammett Parameters……………………………..84
13
3.8.3: LDP vs. C NMR Chemical Shifts in Tungsten Metallacycles………….85
3.8.4: LDP vs. AOM of Cr(III) Complexes……………………………...............86
3.8.5: LDP vs. Values from Electronic Spectra of Cp*2TiX Complexes……….87
3.9: Conclusion…………………………………………………………………………..91
REFERENCES…………………………………………………………………………..94

Chapter 4: Hydroamination on a Solid Support
4.1: Hydroamination and Rational for Surface Chemistry………………………………98
4.2: Synthesis of dmpm Ligand and Attachment to Polystyrene Beads...……………...100
4.3: Experimental Section
4.3.1: General Procedure……………………………………………….............103
4.3.2: Synthesis of H2dmpmPhBr………………………………………………104
4.3.3: Synthesis of OCSidmpmPhBr…………………………………………...104
4.3.4: Synthesis of Me2SidmpmPhBr…………………………………………..105
4.3.5: Borylation of Polystyrene Beads………………………………………...105
4.3.6: Coupling of dmpm derivative to polystyrene beads……………………..106
4.4: Conclusion and Future Work………………………………………………………107
REFERENCES…………………………………………………………………………109

APPENDICIES
A1: Instructions for pw90 using Varian………………………………………………………...113
A2: Instructions for T1 Determination using Varian…………………………………………...116
A3: Instructions for Spin Saturation Magnetization Transfer Experiment using Varian………119
B1: Selected Eyring Plots for Chromium Nitrido Complexes………………………………….122
C1: Error Equations for SSMT…………………………………………………………………126
D1: Eyring Plots for CLSA Experiments……………………………………………………….128

vii

LIST OF TABLES

Table 1: Data from paramagnetic doped experiment…………………………………………….69
Table 2: Data from Eyring plots for selected chromium complexes in CDCl3………………….71
Table 3: Values for LDP (kcal/mol) for 1-41……………………………………………………74

viii

LIST OF FIGURES

Figure 1.1: CO stretch and back-bonding effects on measurements….…………………………..3
Figure 1.2: Tolman Map…….…………………………………………………………………….4
Figure 1.3: Amides with different R and X substituents ……….………………………...............6
Figure 1.4: Amido resonance forms……………………………………………………………….7
Figure 1.5: Bonding and antibonding orbitals available for chromium and ligands.……………..8
Figure 1.6: Three types of donors bound to chromium……………….…………………………..9

Figure 3.1: Simulated NMR spectra of two site exchange at different rates….…………………56
Figure 3.2: Kinetic Scheme for two site exchange…….………………………………...............58
1

i

Figure 3.3: H NMR spectrum of NCr(N Pr2)2 I at 25 ºC….…………………………………....59
Figure 3.4: T1 and apparent T1 of 2 at different temperatures…….………………….................60
Figure 3.5: Amido rotation and exchange of equivalent methyne peaks………………………...61
Figure 3.6: 2D NOESY spectrum of 2 at –60 ºC……………...………………………...............62
Figure 3.7: Homo-decoupling experiment of 2 at 25 ºC……………...…………………...……63
1

1

Figure 3.8: The top H spectrum is of 2 before irradiation and the bottom H spectrum is after
irradiation………………………………………………………………………………64
Figure 3.9: Presat pulse sequence……………………………………………………………….65
Figure 3.10: Simulated and experimental spectrum of 31 (top) and 6(bottom)…...…………….70
i

Figure 3.11: LDP (kcal/mol) values of NCr(N Pr2)2 X and the associated error……….............73
Figure 3.12: Space filling model of Chloro 3 (left) and Indolyl 25 (right) inscribed in a sphere
that shows a radius of 3.5 Ǻ.…………………………………………………………...78

ix

Figure 3.13: The %Vbur for the ligands in this study. Values are for the percentage volume
occupied by the ligand in the sphere of radius 3.5 Ǻ from the chromium center……...79
Figure 3.14: The solid angle model from the Solid G program for 25 with Indolyl (green),
diisopropylamido (yellow and blue), and nitrido (red)………………………...............80
Figure 3.15: The percentage of the chromium coordination sphere shielded, Gm(L), from the
Solid G program for the ligands used in this study……..…………..............................81

Figure 3.16: Plot of pKa in water versus LDP…………………………………………………..83
Figure 3.17: LDP versus Hammet parameters of the para-substituted phenoxides…………….84
Figure 3.18: Alkylidene-imine (left) and alkyl-amido (right) resonance forms………...............85
Figure 3.19: Alkylidene shifts of C1 carbon versus LDP……………………………………….86
Figure 3.20: Plot of experimentally determined eσ and eπ values for Cr(III) complexes versus
LDP……………………………………………………………………………………87
Figure 3.21: Plot of ΔExz in wavenumbers……………………………………………...............89

Figure A1.1: pw90 of 2 at 25 °C………..……………………………………………………...115
1

Figure A1.2: Bad pw90 due to poorly tuned H channel…...………………………………….115
Figure A2.1: Spectra of T1 experiment of 2………………………..……………………..……116
Figure A2.2: T1 determination from magnetization versus time plot of 2…..…….…………...118
Figure A3.1: Placing right and left cursors on septets belonging to 2……………………….....120
Figure A3.2: Setting offsite point equidistant from the septet for saturation…………………..121

Figure B1.1: Eyring plot of 2…………………………………………………………………...122

x

Figure B1.2: Eyring plot of 30………………………………………………………………….122
Figure B1.3: Eyring plot of 12………………………………………………………………….123
Figure B1.4: Eyring plot of 6…………………………………………………………………...123
Figure B1.5: Eyring plot of 20………………………………………………………………….124
Figure B1.6: Eyring plot of 1…………………………………………………………………...124
Figure B1.7: Eyring plot of 1 in d-toluene……………………………………………………...125

Figure D1.1: Eyring plot of 31………………………………………………………………….128
Figure D1.2: Eyring plot of 6…………………………………………………………………...128

xi

LIST OF SCHEMES
i

Scheme 2.1: Synthesis of NCr(N Pr2)3 (1)…….……………………………………………...…15
Scheme 2.2: Intermetal atom transfer reaction…………….………………………….................15
Scheme 2.3: Protonolysis using lutidinium salts……….………………………………………..16
Scheme 2.4: Protonolysis using HX compounds……………….……………………………….17
Scheme 2.5: Salt metathesis using thallium salts….…………………………………………….18
Scheme 2.6: Synthesis using sodium salts……………….………………………………………19
Scheme 2.7: Synthesis using ligand exchange with lithium salts….……………………………20
Scheme 2.8: Synthesis using ligand exchange with lithium to zinc transmetalation……………21
Scheme 2.9: Synthesis using ligand exchange with MgR2 compounds…………………………21
Scheme 2.10: Synthesis of neutral donors..……………………………………………………...23
i

Scheme 2.11: Synthesis of NCr(N Pr2)2F (33)………………………………………………….23

Scheme 4.1: Proposed mechanistic pathway for hydroamination and iminoamination................98
Scheme 4.2: Synthesis and protection of H2dmpmPhBr……….………………………………101
Scheme 4.3: Borylation of polystyrene resin…………………………………………………...102

xii

LIST OF ABBREVIATIONS

LDP = Ligand Donating Parameter
SSMT = Spin Saturation Magnetization Transfer
CLSA = Complete Line Shape Analysis
NMR = Nuclear Magnetic Resonance
NOE = Nuclear Overhauser Effect
AOM = Angular Overlap Model
EPR = Electronic Paramagnetic Resonance
%Vbur = Percent Buried Volume
DMAP = 4-Dimethylaminopyridine
HMPA = Hexamethylphosphoramide
OBn = Benzyloxy
OPth = κ(O)-N-oxy-phthalimide
OAd = Admantoxide
t

O BuF6 = Hexafluoroterbutoxide
OTf = Trifluoromethanesulfonoxide
THF = Tetrahydrofuran
BOC = N-tert-butoxycarbonyl
HBPin = Pinacoleborane
TBAF = Tetrabutyl Ammonium Fluoride
TPP = Tetraphenylporhinato Dianion
OEP = Octaethylporphinato Dianion

xiii

DMA = N,N-dimethylacetamide
DME = 1,2-Dimethoxyethane (glyme)
NHC = N-heterocyclic Carbene
dmpm = 5,5-dimethyldipyrrolylmethane
t

Bu = tert-Butyl

Me = Methyl
Ph = Phenyl
i

Pr = Isopropyl

xiv

Chapter 1: Metal Centers and their Ligands
1.1 Introduction
Many everyday products that we depend on, such as plastics and fuels, were created or
modified using a catalyst. Humanity truly benefits from these products without realizing how
much effort was put into researching them. From plastic bags to Tupperware to “O”-rings used in
space shuttles, the physical properties of polymers are dependent on the molecular weight and
tacticity. This, in some respects, is determined by the catalyst. It is the ligands bound to the metal
that affect the reactivity of the catalyst that ultimately determines the tacticity and molecular
1

weight, which determines the physical properties of the polymer.

Another area of interest that is dependent on the activity of a catalyst is generating fuels
2,3

for future use. Currently, oil refinement and “cracking” use catalysts

to improve the gas

performance and reduce pollution. But there is a push for moving towards a hydrogen economy.

4

5

Nocera published papers discussing a new cobalt complex that splits water into H2 gas and O2
gas. This gives a promising outlook for a cleaner future because the conditions for H2 generation
using the reported methods are at ambient conditions, while previous routes used the water-gas
shift reaction to generate H2 that was energy intensive and produced CO2 as an unwanted by6

product.

In regards to sustainability, another area of immense importance is nitrogen fixation. Fritz
Haber discovered a route to generate ammonia by mixing N2 and H2 but it is energy intensive
7

8

and requires harsh conditions. Studies of enzymes that naturally reduce N2 to NH3 have led to

1

break-through designs in transition metal complexes that coordinate N2 and hydrogenate the
9

unsaturated dinitrogen molecule. Only once the most promising catalytic system is found and
the correct ligand set is identified will the issues of sustaining a growing society be met.
A long time goal in the world of academics and industry has been controlling the
0

reactivity of a catalyst. There is no doubt whether a transition metal center is d , such as
10

Schrock’s Catalyst,

8

11

or d as in Wilkinson’s catalyst,

that the activity of both systems rely

heavily on the ancillary ligands. It is the electronic and steric effects of the ligand that play a role
in determining the activity and selectivity of the metal center.
Part of the difficulty in designing a catalyst is deciding on which ligands to choose for a
system and how their donor ability affects reactivity. Typically, the choice of ligand is dependent
on 1) analogy to a similar reaction in the literature, 2) picking ancillary ligands already available
in the lab, and 3) an educated guess based on experience in the field. If there was a way to know
the donor ability of a ligand, one could tune the catalytic system to meet the needs of the catalyst
without as much trial and error. This would speed up progress in science to meet the needs of a
st

society in the 21 century.
A famous study in gauging donor properties of ligands is the study of phosphine ligands
by Tolman.

12

He looked at the how the electronic and steric factors of the R groups on phospine

ligands affected the donor ability of the phosphorous atom bound to Nickel by observing the CO
12,13

stretches in the IR.

Figure 1.1 shows some different resonance forms of CO bound to an

electron rich metal center.

2

M

C O

M C O

M C O

Figure 1.1: CO stretch and back-bonding effects on measurements
In the case of Tolman’s system, a strong phophine donor will push more electron density
on the metal favoring the resonance form on the left and result in a high stretching frequency that
is similar to the normal range of free CO stretching frequencies. While a poor donor or electronwithdrawing ligand will favor the form on the right and cause a lower CO stretching frequency.
This effect is seen throughout the different Ni(CO)3PR3 complexes.
Another key factor that affects the reactivity of many ligand complexes is the sterics. In
Tolman’s original study, he looked at homo-leptic phosphines that formed a cone shape. By
treating the metal center as the apex of the cone, the sides of the cone were determined by the
van der Waals radii of the outermost atoms. Combining the steric and electronic parameters
produces the graph in Figure 1.2.

3

ELECTRON
WITHDRAWING
PF3

2110

PCl3

2100

PO
2090

νco(A1)

2080

2070

2060

CN

P(OCH2CH2Cl)3 P(OPh)3

3
PO

PO

3

3

PO

PO

PO

P(C6F5)3
3

3
3
iPr
P(O )3
PPh2C6F5
P(OEt)3
P(OEt)2Ph
P(OMe)Ph2
PMePh2
PMe2Ph
PPh3
P(CH2Ph)3
PEt2Ph
PMe3
P(NMe2)3
PEt3 P
PBu3
3
P(iPr)3
PCy3

2050
100
ELECTRON
DONATING

P(OMe)3

110

120

130

140

150

160

170

180

PO

P

3

3

P(tBu)3
190

Θ
LARGE

SMALL
13

Figure 1.2: Tolman Map

4

This study gave insight into choosing ligands with specific properties that dictate the
reactivity of a catalytic system and has contributed to the development of chemistry for late
transition metal systems. One can even see these steric and electronic effects explaining reactions
and mechanisms found in the literature. No where in the literature has these parameters been
more important than in homogeneous catalysis. For example, hydrogenation reactions involving
the RhClL3 catalyst increases in the following order where L = P(p-C6H4F)3 < PPh3 < P(p14

C6H4OCH3)3.

This can be explained by the fact that increasing the donor ability of the group

in the para-position increases the reactivity of the catalyst.
Even the sterics of the phosphines has a huge influence on the reaction. As an example,
product distribution of propylene dimerization in a Ni(C3H5)L·AlCl3 system changes with
i

15

increasing size of L ligand for the order of PMe3, PEt3, and P( Pr)3.

These are only a few

examples, but the point is that Tolman’s study of the electronic and steric components of
phosphines ligands has made an important impact on how chemists approach the design of their
catalysts.
Although, this has been immensely useful for later transition metals, early transition
metal catalysts in higher oxidation states prefer anionic ligands over ligands with dative
16

interactions to stabilize the high positive charge.

A common method has been to base donor

strength of a ligand on its pKa. One can rationalize that the resonance forms and
electronegativity of the substituents bound to the ligand will either increase or decrease the donor
ability but to what extent is unknown. To this date there has not been a study in determining
donor ability of anionic ligands for early transition metal centers.

5

0

1.2: Investigation of the Probe for Donors Bound to a d Chromium Center
As in Tolman’s system, the donor ability of one ligand had an effect on the other ligands
bound to it. So adding a ligand that has a feature that would be easy to measure would allow us
to put a number to it and compare donor ability of different ligands. Searching through the
17

literature one finds that amides have been exhaustively studied using NMR.
study

17f,g

An interesting

looked at the effects of electronegativity of the R substituents bound to the carbonyl

carbon on the barrier of rotation of the amide (see Figure 1.3).

X
R

N

X = O, S
R = CH3O, CH3S, CN, EtCO,
CH3C C
Figure 1.3: Amides with different R and X substituents
As the R substituents increase in electron donation from CN to CH3O, the barrier of rotation of
the amide lowers. This study showed that the barrier of rotation of an amide can be used as a way
to rate the donor ability of the R substituents. We could adopt this concept and apply it to a metal
system to determine the donor ability of ligands bound to a metal center. Amido ligands show
some of the interesting features when bound to transition metals in higher oxidation states. They
can form both σ- and π- bonds that have different contributing resonance forms based on the
18

Lewis acidity of the metal center.

The left form in Figure 1.4 is an amido but if there is an

6

open orbital with the correct symmetry then the lone pair can donate forming a pseudo-imido
shown on the right.

M NR2

M NR2

Figure 1.4: Amido resonance forms
The imido resonance structure contributes to bonding in nitrodo complexes of the
i

formula NCr(N Pr2)2X. Thus, a series of compounds were synthesized in which the X ligand was
varied with different anionic ligands. All of the orbitals on chromium and the ligands involved in
bonding are shown in Figure 1.5. The lone pairs on the three ligands will compete for the two
empty p-orbitals on chromium, although there will be some mixing with the dx2-y2 and dxy
orbitals due to symmetry. As shown in Figure 1.5, there is competition for the empty orbitals on
chromium. A strong X donor will compete stronger with the lone pairs on the amido ligand
resulting in a lower barrier of rotation about the chromium nitrogen bond, whereas a poor X
donor will compete poorly with the amido, giving a higher barrier of rotation.

7

dz2, pz

dxz, px

dyz, py

dxy

dx2-y2,

N

N

X
a2

2e

N

a1

1e

Figure 1.5: Bonding and antibonding orbitals available on chromium and ligands. The isopropyl
groups on the amido ligands have been replaced by methyl groups for clarity. For interpretation
of the references to color in this and all other figures, the reader is referred to the electronic
version of this dissertation.
Since the dx2-y2, dxy, px, and py orbitals on chromium have similar symmetry, there will
be mixing. Therefore, barrier of rotation of the amido ligands will also be influenced by donors
3

without lone pairs such as a sp carbon with α-hydrogens (X type) or neutral donors (L type) that
only bind to the metal center through dative interactions. The latter requires the formation of a
cationic chromium complex. Figure 1.6 shows the X, LX, and L type ligands
chromium system.

8

19

studied on the

N

N

N

r
N C X
N

M

r
N C
N

r
N C
N

Y
L

Figure 1.6: Three types of donors bound to chromium
X = I, Br, Cl, F, NCS, NCO, O2CPh, CN, OC6F5, SPh, NO3, PyrC6H3(CF3)2, PyrC6F5,
t

t

i

Pyrrolyl, O BuF6, Indolyl, F, Ph, OPth, OSiPh3, CC Bu, CCSi Pr3, O-p-(CF3)C6H4, O-pt

(Cl)C6H4, O-p-(F)C6H4, O-p-(SMe)C6H4, OPh, O-p-(OMe)C6H4, O-p-( Bu)C6H4, Carbazolyl,
i

OBn, N Pr2, OAd, N(Me)Ph, NMe2
M = C, Si; L= HMPA, DMAP; Y= BF4, PF6
The beauty of our system is that we can investigate anionic and neutral donor ligands.
This will allow us to determine the overlap between some other famous studies such as the
Tolman map. The barrier is then measured using Spin Saturation Magnetization Transfer
(SSMT)

20

or Complete Line Shape Analysis (CLSA)

21

techniques.

It has been shown that knowing the donor ability of phosphines through Tolman’s
electronic parameter improves the selectivity and reactivity of the catalyst. Knowing the donor
ability of anionic ligands will help our understanding of reactivity in earlier high-valent
transition metals. Knowing the donor abilities for both neutral and anionic ligands will allow for
a faster development of catalysts and improvement of designs that will speed up the process for
discovery eventually benefiting the standard of life for humanity.

9

REFERENCES

10

REFERENCES

1) (a) Flook, M. M.; Ng, V. W. L.; Schrock, R. R. J. Am. Chem. Soc. 2011, 133, 1784-1786 (b)
Shaver, M. P.; Cameron, D. J. A. Biomacromolecules 2010, 11, 3673-3679 (c) Takeuchi, D.;
Matsuura, R.; Park, S. Osakada, K. J. Am. Chem. Soc. 2007, 129, 7002-7003 (d) Bierwagen,
E. P.; Bercaw, J. E.; Goddard III, W. A. J. Am. Chem. Soc. 1994, 116, 1481-1489

2) Schwarzenbeck, E. F. Origin and Refining of Petroleum, Chapter 5, 1971, 94-112, Advances
in Chemistry Vol. 113

3) (a) Zaera, F. J. Phys. Chem. Lett. 2010, 1, 621-627 (b) Zaera, F. J. Phys. Chem. B 2002, 106,
4043-4052 (c) Martens, J. A.; Tielen, M.; Jacobs, P. A. Catal. Today 1987, 1, 435 (d)
Martens, J. A. Jacobs, P. A.; Weithkamp, J. J. Appl. Catal. 1986, 20, 239-281 (e) Weitkamp,
J. Ind. Eng. Prod. Res. Dev. 1982, 21, 550-558

4) Gregoire-Padró, G. E. Energy Fuels 1998, 12, 1-2
5) (a) Surendranath, Y.; Dincǎ, M.; Nocera, D. G. J. Am. Chem. Soc. 2009, 131, 2615-2620 (b)
Kanan, M. W.; Nocera, D. G. Science 2008, 321, 1072-1075

6) (a) Dufour, J.; Serrano, D. P.; Galvez, J. L.; Moreno, J., Gonzalez, A. Energy Fuels 2011, 25,
2194-2202 (b) Wang, L.; Murata, K.; Inaba, M. Ind. Eng. Chem. Res. 2004, 43, 3228-3232
(c) Wang, D.; Czernik, S.; Chornet, E. Energy Fuels 1998, 12, 19-24

7) Haber, F.; van Oordt, G. Z. Anorg. Chem. 1905, 47, 42-44

8) (a) Barney, B. M.; McClead, J.; Lukoyanov, D.; Laryukhin, M.; Yang, T.-C.; Dean, D. R.;
Hoffman, B. M.; Seefeldt, L. C. Biochemistry 2007, 46, 6784-6794 (b) Dos Santos, P. C.;
Igarashi, R. Y.; Lee, H. I.; Hoffman, B. M.; Seefeldt, L. C.; Dean, D. R. Acc. Chem. Res.
2005, 38, 208-214 (c) Igarashi, R. Y.; Laryukhin, M.; Dos Santos, P. C.; Lee, H. I.; Dean, D.
R.; Seefeldt, L. C.; Hoffman, B. M. J. Am. Chem. Soc. 2005, 127, 6231-6241 (d) Duyvis, M.
G.; Wassink, H.; Haaker, H. Biochemistry 1998, 37, 17345-17354 (e) Burgess, B. K.; Lowe,
D. J. Chem. Rev. 1996, 96, 2983-3012

9) (a) Kimura, T.; Koiso, N.; Ishiwata, K.; Kuwata, S.; Ikariya, T. J. Am. Chem. Soc. 2011, 133,
8880-8883 (b) Reithofer, M. R.; Schrock, R. R.; Müller, P. J. Am. Chem. Soc. 2010, 132,
8349-8358 (c) McNaughton, R. L.; Roemelt, M.; Chin, J. M.; Schrock, R. R.; Neese, F.;

11

Hoffman, B. M. J. Am. Chem. Soc. 2010, 1321, 8645-8656 (d) Schrock, R. R. Chem.
Commun. 2003, 19, 23899-2391 (e) Shaver, M. P.; Fyzuk, M. D. Adv. Synth. Catal. 2003,
345, 1061-1076 (f) Yandulov, D. V.; Schrock, R. R. Science 2003, 301, 76-78 (g) Birk, T.;
Bendix, J. Inorg. Chem. 2003, 42, 7608-7615 (h) Leung, S. K. Y.; Haung, J. S.; Liang, J. L.;
Che, C. M.; Zhou, Z. Y. Angew. Chem., Int. Ed. 2003, 42, 340-343 (i) O’Donoghue, M. B.;
Zanetti, N. C.; Davis, W. M.; Schrock, R. R. J. Am. Chem. Soc. 1997, 119, 2753-2754

10) (a) Schrock, R. R.; Murdzek, J. S.; Bazan, G. C.; Robbins, J.; DiMare, M.; O’Regan, M. J.
Am. Chem. Soc. 1990, 112, 3875-3886 (b) Thorn-Csányi, E.; Zilles, J. U. J. Molec. Catal. A
2002, 190, 85-100 (c) Schrock, R. R.; DePue, R. T.; Feldman, J.; Yap, K. B.; Yang, D. C.;
Davis, W. M.; Park, A. DiMare, M.; Schofield, M. Organometallics 1990, 9, 2262-2275

11) Osborn, J. A.; Jardine, F. H.; Young, J. F.; Wilkinson, G. J. Chem. Soc. A 1966, 1711-1732

12) Tolman, C. A. J. Am. Chem. Soc. 1970, 92, 2953-2956

13) Tolman, C. A. Chem. Rev. 1977, 77, 313-347

14) (a) Montelactici, S.; van der Ent, A.; Osborn, J. A.; Wilkinson, G. J. Chem. Soc. A. 1968,
1054-1058 (b) Tolman, C. A.; Meakin, P. Z.; Lindner, D. L.; Jesson, J. P. J. Am. Chem. Soc.
1974, 96, 2762-2774

15) Bogdanovic, B.; Henc, B.; Karmann, H.-G.; Nüssel, H.-G.; Walter, D.; Wilke, G. Ind. Eng.
Chem. 1970, 62, 34-44

16) Sanderson, R. T. Inorg. Chem. 1986, 25, 3518-3522

17) (a) Kemnitz, C. R.; Loewen, M. J. J. Am. Chem. Soc. 2007, 129, 2521-2528 (b) Rablen, P.
R.; Miller, D. A.; Bullock, V. R.; Hutchinson, P. H.; Gorman, J. A. J. Am. Chem. Soc. 1999,
121, 218-226 (c) Perrin, C. L.; Thoburn, J. D.; Kresge, J. A. J. Am. Chem. Soc. 1992, 114,
8800-8807 (d) Mann, B. E. J. Magn. Reson. 1977, 25, 91-94 (e) Drakenberg, T.; Dahlqvist,
K.-I.; Forsén, S. J. Phys. Chem. 1972, 76, 2178-2183 (f) Sandström, J. J. Phys. Chem. 1967,
71, 2318-2325 (g) Fryer, C. W.; Conti, F.; Franconi, C. Ric. Sci., Parte 2, Sez. A. 1965, 35,
788-793
18) Crabtree, R. H. The Organometallic Chemistry of the Transition Metals 5th Ed. New Jersey:
John Wiley and Sons, Inc. 2009

12

19) Green, M. L. H. J. Organomet. Chem. 1995, 500, 127-148

20) (a) Dahlquist, F. W.; Longmuir, K. J.; Du Vernet, R. B. J. Magn. Reson. 1975, 17, 406-410
(b) Jarek, R. L.; Flesher, R. J.; Shin, S. K. J. Chem. Edu. 1997, 74, 978-982

21) (a) Binsch, G. J. Am. Chem. Soc. 1969, 96, 1304-1309 (b) Allerhand, A.; Gutowsky, H. S.;
Meinzer, R. A. J. Am. Chem. Soc. 1966, 88, 3185-3194 (c) McConnell, H. M. J. Chem. Phys.
1958, 28, 430-431

13

Chapter 2: Synthesis of the Chromium Nitrido Complexes
i

2.1: Synthesis of NCr(N Pr2)3 (1)
Development of nitrido transition metal complexes has been growing due to interest in
1

2

3

NACM catalysis, nitrogen fixation, and atom transfer reactions. Compared to other transition
metal nitrido moieties, few examples of chromium nitrido complexes exist. Previous synthetic
4

routes included oxidation of chromium in the presence of ammonia, decomposition of sodium
3c

azide,

5

and photolysis of chromium azido complexes. An interesting approach developed in

the Cummins’ lab, involved oxidative cleavage of nitric oxide on chromium(II) nitrosyl
compounds by V(THF)(Mes)3, yielding chromium(VI) nitrido complexes.

6

In the beginning of this chapter, I present a convenient and efficient synthesis of our
i

3

chromium(VI) nitrido starting material, NCr(N Pr2)3 (1), through atom transfer. The red-brown
i

i

Cr(N Pr2)3 complex with D3 symmetry was synthesized by mixing 3 equivalents of LiN Pr2 to a
7

t

heterogeneous solution of CrCl3 in ether. NCr(O Bu)3 was synthesized using common starting
8

materials. To (NH4)2Cr2O7 in 1,2-dimethoxyethane was added Me3SiCl, HN(SiMe3)2, and
t

NEt3. The reaction then stirred for one day with an excess of BuOH. After twelve hours of
t

stirring, BuOH was removed in vacuo, and the canary yellow product was sublimed at 40 ºC
t

under vacuum. NCr(O Bu)3 is light sensitive and should be stored in a dark container and in the
freezer.

14

i

Scheme 2.1: Synthesis of NCr(N Pr2)3 (1)
t

i

Addition of solid NCr(O Bu)3 to Cr(N Pr2)3 in pentane with stirring for two hours induced a
i

three-electron, atom-transfer reaction affording NCr(N Pr2)3 (1) in high yield.
Atom transfer reactions resulting in chromium nitrido complexes were first reported in
9

V

II

V

1985, reaction of NMn (TTP) with Cr (TTP) in THF cleanly generated NCr (TTP). An
10,11

investigation by Bottomley and Neely

on substituent effects on porphyrins in intermetal

transfer reactions provided an explanation for the driving force.

Scheme 2.2: Intermetal atom transfer reaction
In the reversible reaction shown in Scheme 2.2, exchange between the chloro and nitrido
axial ligands resulted in a net two electron, atom transfer. Their rate data suggest that the
12,13

addition of electron donor groups to the porphyrin

on the chromium(III) acceptor shifted the

reaction towards the right. Stronger donating ligands are required to stabilize the higher positive
charge on chromium. This is seen in our atom transfer reaction, shown in Scheme 2.1, that
i

produces the robust compound, NCr(N Pr2)3.

15

2.2: Synthesis using Protonolysis
2.2.1: Protonolysis using Lutidinium Salts
Protonolysis of 1 with the appropriate 2,6-lutidinium halide ([HLut][X]), where X is Br
or Cl in CHCl3 at mild temperatures affords complexes 3 and 4. This method is similar to the
published procedure

15,16

i

for making NCr(N Pr2)2I (2). [HLut][Cl] and [HLut][Br] can be

conveniently prepared by addition of HCl or HBr to 2,6-lutidine in THF under a nitrogen
atmosphere.

Scheme 2.3: Protonolysis using lutidinium salts

2.2.2: Protonolysis using HX
Alkoxides are common ligands found in the literature for high-valent metals. Changes in
the electronics of the group bound to the oxygen in an alkoxide can have a significant impact on
t

its donor properties. For example, by replacing a methyl group in O Bu with a CF3 group,
1a

molybdenum and tungsten nitrido complexes increased reactivity in NACM reactions.

Knowing the donor ability of different alkoxides may explain the reactivity of catalytic systems
that rely on alkoxides, and discover an overlooked ligand.
16

Following a similar procedure

to make 9 and 10, addition of one equivalent of the

corresponding alcohol, silanol, carboxylate, and thiolate to 1 generated fifteen complexes cleanly

16

with relatively high yields. In most cases, HX compounds were added to a near frozen solution
of 1 in toluene and allowed to warm to room temperature and stir for 1.5 hours. In the case of
triflic acid, a near frozen solution of DME/pentane was required to generate 5 cleanly. In other
cases, longer reaction times and higher temperatures were required; for example reaction of 1adamantanol with 1 required heating at 90

ºC

for three days. Removal of solvent and

diisopropylamine in vacuo and crystallization from pentane gave compounds 5, 6, 7, 8, 11, 12,
13, 14, 15, 16, 17, 18 and 19 in 52-94% yields.

NCr(NiPr2)3
1

HX

NCr(NiPr2)2(X)

-HNiPr2

O
X = OTf (5), 70%
OAd (6), 70%
O N
OSiPh3 (7), 72%
O2CPh (8), 88%
O
OtBuF6 (9)
OPh (10)
O-p-(OMe)C6H4 (11), 87%
O-p-(SMe)C6H4 (12), 92%
O-p-(tBu)C6H4 (13), 94%
O-p-(F)C6H4 (14), 88%
O-p-(Cl)C6H4 (15), 85%
O-p-(CF3)C6H4 (16), 82%
OC6F5 (17), 76%
SPh (18), 75%

(OPth, 19), 52%

Scheme 2.4: Protonolysis using HX compounds

17

2.3: Synthesis using Salt Metathesis
2.3.1: Salt Metathesis using Thallium Salts
Although thallium is toxic and has a lack of stability with some X substituents, it avoided
unwanted reduction seen with other reagents (vide infra), and the thallium reagents are easy to
18

prepare. Following literature procedures,
HX substituents generated TlX

addition of thallium ethoxide to the corresponding

and ethanol that were easily removed by filtration and
1

distillation. Unfortunately, obtaining H and

13

C NMR data on the thallium pyrroles was not

possible due to insolubility.
Substituted pyrroles HPyr

C6F5

and HPyr

C6H3(CF3)2

19

effects on pyrrole-based ligands on hydroamination rates.

were prepared to study substitution
Their results indicated that electron

withdrawing groups present on the pyrrole made the nitrogen a worse donor to titanium. With
our system we can determine the donor abilities of pyrrole and substituted pyrroles and show that
electron-withdrawing groups do in fact make pyrrole a worse donor.

NCr(NiPr2)2I +
2

TlX

F3C
F5

X = OBn (20), 90%
NO3 (21), 75%
Pyr (22), 80%

NCr(NiPr2)2(X)

-TlI

CF3

N

N

C6F5, 23 , 63%
(Pyr
)

C6H3(CF3)2, 24 , 71%
(Pyr
)

Scheme 2.5: Salt metathesis using thallium salts

18

Reaction of TlX with 2 led to precipitation of yellow TlI in hexanes or toluene, which
i

was easily removed by filtration. The reaction cleanly gave new NCr(N Pr2)2(X) complexes 20i

24. In the production of NCr(N Pr2)2(NO3) (21), tetrahydrofuran (THF) was used as the solvent
due to low solubility of thallium nitrate in other organic solvents.

2.3.2: Salt Metathesis using Sodium Salts
i

The three complexes NCr(N Pr2)2(X), where X = NCO (28), NCS (29), and CN (30)
i

were prepared using commercially available sodium salts and NCr(N Pr2)2I (Scheme 2.6). Long
reaction times and mild heating were required due to low solubility of the sodium salts in organic
solvents, even in acetonitrile. The use of 1,4-dioxane in the preparation of 28 and 29 helped the
reaction to proceed. The use of cyclic ethers has been known to help sodium salts dissociate and
17

increase solubility of the complex in solution.

In the case of using NaCN, reaction only

occurred within the presence of one equivalent of 15-crown-5 ether.

NCr(NiPr2)2I + NaX
2

-NaI
CH3CN

NCr(NiPr2)2(X)
X = NCO (29), 60%
NCS (30), 52%
CN (31), 43%

Scheme 2.6: Synthesis using sodium salts

19

2.4: Synthesis using Ligand Exchange with Lithium Salts
Reaction of lithium reagents with 2 has been shown to result in reduction to the known
15,16

nitrido chromium(V) dimer.

Transmetalation using phenoxide 10 proved to be a viable route
i

in preparing indolyl (25), carbazolyl (26), N-methylanilide (27), CH2Si(Me)3 (35) CCSi Pr3
t

(39), and CC Bu (40).
The syntheses of 25 and 26 compares their donor abilities with pyrrole, as the lone pair
on the nitrogen is known to be less involved in the conjugation of the ring.

21,22

Preparation of

carbon bound donors was of keen interest because the absence of lone pairs on the α-carbon
might allow us to distinguish between σ- and π-effects. As shown in Scheme 2.7, the lithium
salts were added to a cold stirring solution of 10 in hexanes with short reaction times.

NCr(NiPr2)2OPh + LiX
10

-LiOPh

NCr(NiPr2)2(X)

X = indolyl (26), 42%
carbazolyl (27), 35%
N(Me)Ph (28), 44%
CH2Si(Me)3 (38), 73%
CCSi(iPr)3 (41), 83%
CCtBu (42), 98%
Scheme 2.7: Synthesis using ligand exchange with lithium salts
In the case of neopentyl (38), adamantoxide (6) was used as the transmetalation partner, because
the reaction with 10 only resulted in reduction. The alkynyls 39 and 40 are stable at room
temperature, while the alkyl complexes 35 and 38 need to be covered and stored in the fridge.

20

2.5: Synthesis using Ligand Exchange with Lithium to Zinc Transmetalation
To study the effect of sterics in the barrier of rotation in amides, dimethylamido (31) was
synthesized. Shown in Scheme 2.8, treating ZnCl2 with an excess amount of LiNMe2 in
DME/THF mixture presumably generates an amido zincate complex.

23

Addition of this mixture

i

to 10 cleanly produces NCr(N Pr2)2NMe2 31, while addition of the LiNMe2 direct to 2 only
resulted in reduction.

NCr(NiPr2)2(NMe2)
NCr(NiPr2)2OPh + 8.5 LiNMe2/4.25 ZnCl2
DME/THF
31
10
Scheme 2.8: Synthesis using ligand exchange with lithium to zinc transmetalation

2.6: Synthesis using Ligand Exchange with MgR2
One of the earliest chromium(VI) alkyl complexes reported in the literature was
i

NCr(N Pr2)2CH2SiMe2Ph (36). We wondered if neophyl analogue would have different donor
15

properties than 36. Using conditions
Mg(CH2C(Me)2Ph)2

24

similar to those used to prepare 36, 0.7 equivalents of the

was added to 1 equivalent of 2 in ether, affording the σ–complex,

i

NCr(N Pr2)2CH2C(Me)2Ph (37).
i
i
NCr(N Pr2)2(CH2C(Me)2Ph)
NCr(N Pr2)2I + 0.7 Mg(CH2C(Me)2Ph)2
ether
2
37
°
°
-78 C to 25 C
1 hr
-MgI2

Scheme 2.9: Synthesis using ligand exchange with MgR2 compounds
21

Reaction of the Grignard reagent, BrMgCH2C(Me)2Ph instead of the dialkyl magnesium
compound only resulted in halide exchange between I and Br. It was observed that the addition
of MgBr2 or MgCl2 to 2 also resulted in halide exchange. As with all σ-complexes, they are
stable at room temperature for short periods of time and slowly decompose in the presence of
i

light forming a black solid, free amine, and the imine Me2C=N Pr (vida infra). It is likely this
15, 25

occurs as a β–H abstraction by the leaving alky group.
i

In an attempt to synthesize NCr(N Pr2)2CH2SnMe3 (42), 0.5 equivalents of
Mg(CH2SnMe3)2, prepared from two equivalents of ClMg(CH2SnMe3)

26

and dioxane, was

added to a cold, stirring solution of 10 in cold ether. To our surprise, the product was
i

1

16

NCr(N Pr2)(OPh)2 (41), which matched the H NMR spectrum reported in the literature.

Browsing through the literature provides some clues as to what may have happened. Tin(IV)
alkyl complexes display a varied reactivity ranging from being a coupling partner in Stille
27

Coupling,

28

29

a catalyst,

and stabilization of cationic radicals on the carbons bound to tin.

Further investigation is warranted to understand this phenomenon and determine by what
mechanism the bisphenoxide was generated.

i

i

2.7: Synthesis of [NCr(N Pr2)2DMAP][BF4] and [NCr(N Pr2)2HMPA][PF6]
The desire to see how neutral donors compare to anionic donors fueled the route for
cationic complexes. This result might overlap with the neutral members commonly found in the
Tolman map.

30

Addition of a mixture of AgBF4 and DMAP or AgPF6 and HMPA in acetonitrile

22

to a stirring solution of 2 in chloroform yielded the corresponding cationic complexes.
Unfortunately, the cationic complexes are only stable at room temperature for short periods of
time (< 4 hours) and must be stored in the refrigerator.

NCr(NiPr2)2I + AgY + X
2

i
[NCr(N Pr2)2(X)]Y

CH3CN/CHCl3
2 h, RT
X = DMAP (32), HMPA (34)
Y = BF4, PF6

Scheme 2.10: Synthesis of neutral donors

2.8: Synthesis using Tin(IV)-Catalyzed Decomposition of Cationic BF4 Salt
10 mol %
i
[NCr(N Pr2)2(DMAP)]BF4
32

FSnBu3

i
NCr(N Pr2)2(F)

4 h, RT

33

-DMAP⋅BF3
i

Scheme 2.11: Synthesis of NCr(N Pr2)2F (33)
Many attempts to synthesis the fluoride (33) were made. The only successful route was
i

catalytic decomposition of the cationic complex [NCr(N Pr2)2(DMAP)]BF4 (33) using FSnBu3
at room temperature. The expected byproduct, DMAP·BF3, was detected in the

19

F NMR

spectrum of a reaction to form 33.
i

The uniqueness of our system is that a diversity of NCr(N Pr2)2X compounds can be
synthesized. If anyone who would want to place their ligands on our system they can use any of
the selected synthetic routes to do so. Also, we have found conditions to put difficult ligands,
such as alkyls that are known to be prone to reduction, onto the chromium or for other high
23

oxidation state metals. Also, we have discovered that for our system Sn(IV) complexes are
catalytically active by doing ligand swap with free compounds in solution or with ligands on
chromium.

2.9: Experimental Section
2.9.1 General Procedure:
All reactions and manipulations were carried out in a MBraun glovebox under nitrogen
atmosphere and/or using standard Schlenk techniques. Ethereal solvents, pentane, hexanes,
toluene, and benzene were purchased from Aldrich Chemical Co. and purified through alumina
columns to remove water after sparging with dinitrogen to remove oxygen. HCl in diethyl ether
was purchased from Aldrich Chemical Co. and used as received. All NMR solvents were
purchased from Cambridge Isotopes Laboratories, Inc. Deuterated toluene and benzene was
distilled from sodium benzophenone ketyl. Deuterated chloroform was distilled from calcium
hydride under dry dinitrogen atmosphere. The NMR solvents were stored in the glovebox in
glass containers with a stopcock. The reagent 15-crown-5 was dried by making a toluene
solution and refluxing with a Dean-Stark trap overnight. ClMgCH2C(Me)2Ph and
trimethylsilylmethyl lithium were purchased from Sigma Aldrich and were used as received.
(Triisopropylsilyl) acetylene and tert-butyl acetylene were purchased from Sigma Aldrich and
were distilled under nitrogen and freeze-pump-thawed before being brought into the dry box.
Lutidinium iodide was prepared using the literature procedures.
i

i

t

16

i

Compounds NCr(N Pr2)2I 2,

i

NCr(N Pr2)2OPh 9, NCr(N Pr2)2O BuF6 10, and NCr(N Pr2)2CH2Si(Me)2Ph 36 were made
15,16

following literature procedure.

The 3-substituted pyrroles, Hpyr

24

C6F5

C6H3(CF3)2

and Hpyr

,

19

where prepared as previously reported.
18

literature procedure

(Pyrrolyl)thallium(I) was prepared similar to the

using 1.1 equivalents of freshly filtered TlOEt in ether, which was added

to cold pyrrole in ether. The product precipitates as a colorless solid with low solubility in
common organic solvents. This same procedure was used to generate TlPyr
TlPyr

C6F5

24

. Mg(CH2C(Me)2Ph)2,

31

Mg(CH2Si(Me)2Ph)2,

C6H3(CF3)2

32

and neopentyl lithium

and

were made

following literature procedures. Spectra were taken on Varian instruments located in the Max T.
Rogers Instrumentation Facility at Michigan State University. These include a UNITYplus 500
spectrometer equipped with a 5 mm Pulsed-Field-Gradient (PFG) switchable broadband probe
1

13

and operating at 499.955 MHz ( H) and 125.77 ( C), and a UNITYplus 300 spectrometer
1

operating at 299.976 MHz ( H). Complete Line Shape Analysis (CLSA) was performed on
35 1

gNMR, available as a free download.
CHCl3 in CDCl3 as 7.24 ppm.
77.0 ppm.

19

13

H NMR chemical shifts are reported relative to residual

C NMR chemical shifts are reported relative to

13

CDCl3 as

F NMR chemical shifts are relative to external, neat FC6H5 as –113.15 ppm. Silicon
29

NMR was taken on a 600 MHz instrument operating at 119.16 MHz ( Si) and referenced with
SiMe4 at 0.00 ppm. The quaternary carbons in the CN, NCS and NCO compounds in

13

C NMR

have very long relaxation times, requiring the delay time to be set to 15 seconds for the
acquisition. Melting points are uncorrected.

25

i

2.9.2 Synthesis of NCr(N Pr2)3 (1): Under an inert N2 atmosphere, a 250 mL Erlenmeyer flask
i

was loaded with Cr(N Pr2)3 (1.15 g, 3.26 mmol, 1 equiv.) and pentane (~25 mL). In a separate
t

flask, a pentane solution (50 mL) of freshly sublimed NCr(O Bu)3 (0.931 g, 3.26 mmol, 1 equiv.)
t

was prepared. The yellow solution of NCr(O Bu)3 was added slowly in portions over ~10 min to
i

the rapidly stirring Cr(N Pr2)3 solution. The solution rapidly turned beet red, and stirring was
continued for 1.5 h after addition was complete. The volatiles were removed in vacuo, and
acetonitrile (100 mL) was added. After stirring for 5 min, the mixture was filtered through a
fritted glass funnel, and the solids were washed with acetonitrile (2 × 10 mL). The solids were
transferred to a vial and dried in vacuo yielding the title compound as dark red microcrystals
(1.06 g, 2.90 mmol, 89% yield). If necessary, 1 can be further purified by recrystallization from
1

concentrated pentane solution at −35 °C. H NMR (500 MHz, CDCl3, −30 °C): 4.33 (br sept,
3H, CH(CH3)2), 3.42 (br sept, 3H, CH(CH3)2), 1.43 (br d, 14H, CH(CH3)2), 1.05 (br d, 14H,
CH(CH3)2). Melting point and room temperature NMR spectroscopy were in agreement with
16

literature values.

i

2.9.3 Synthesis of NCr(N Pr2)2(Cl) (3): Under an inert atmosphere a pressure tube was loaded
with 1 (0.400 g, 1.09 mmol, 1 equiv.), 2,6-lutidinium chloride (0.392 g, 2.73 mmol, 2.5 equiv.),
and a stirbar. CHCl3 (~35 mL) was added. The tube was sealed and removed from the drybox.
The tube was set in a 60 °C oil bath, and the reaction was stirred for 12 h. The tube was taken
back into the drybox, and the volatiles were removed in vacuo. The residue was extracted with

26

pentane and filtered. The solvent was removed yielding 3 as an orange powder (0.270 g, 0.895
mmol, 82% yield). Diffraction quality crystals were obtained from a concentrated pentane
solution at −35

°C.

1

H NMR (500 MHz, CDCl3, 25

°C):

5.24 (sept, JHH = 6.61, 2H,

CH(CH3)2), 3.82 (sept, JHH = 6.21, 2H, CH(CH3)2), 1.91 (d, JHH = 6.42, 6H, CH(CH3)2), 1.49
(d, JHH = 6.28, 6H, CH(CH3)2), 1.25 (d, JHH = 6.33, 6H, CH(CH3)2), 1.13 (d, JHH = 6.57, 6H,
CH(CH3)2).

13

1

C{ H} NMR (125 MHz, CDCl3, 0 °C): 59.20, 57.10, 30.36, 29.92, 21.45, 19.90.

Mp: 157-158 °C.
i

2.9.4 Synthesis of NCr(N Pr2)2(Br) (4): Under an inert atmosphere, a pressure tube was loaded
with 1 (0.120 g, 0.328 mmol, 1 equiv.), 2,6-lutidinium bromide (0.092 g, 0.49 mmol, 1.5 equiv.),
and a stirbar. CHCl3 (~25 mL) was added. The tube was sealed and removed from the drybox.
The tube was set in a 60 °C oil bath and stirred for 12 h. The tube was moved back into the
drybox, and the volatiles were removed in vacuo. The residue was extracted with pentane and
filtered through Celite. The solvent was removed in vacuo yielding 4 as an orange powder (0.060
g, 0.17 mmol, 52% yield). Diffraction quality crystals were obtained from a concentrated
1

pentane solution at −35 °C. H NMR (500 MHz, CDCl3, 25 °C): 5.28 (sept, JHH = 6.51, 2H,
CH(CH3)2), 3.81 (sept, JHH = 6.31, 2H, CH(CH3)2), 1.89 (d, JHH = 6.31, 6H, CH(CH3)2), 1.50
(d, JHH = 6.26, 6H, CH(CH3)2), 1.28 (d, JHH = 6.40, 6H, CH(CH3)2), 1.14 (d, JHH = 6.64, 6H,
CH(CH3)2).

13

1

C{ H} NMR (125 MHz, CDCl3, −5

19.78. Mp: 160-164 ºC.

27

°C):

59.34, 57.40, 30.20, 29.54, 21.29,

i

2.9.5 Synthesis of NCr(N Pr2)2(OTf) (5): Under an inert atmosphere, a scintillation vial was
loaded with 1 (0.30 g, 0.82 mmol, 1 equiv.), pentane (10 mL), and a stir bar. The solution was
cooled to near frozen in a liquid nitrogen cooled cold well. To the rapidly stirring solution, 1.55
M triflic acid in a DME (533 μL, 0.826 mmol, 1.01 equiv.) was added dropwise. The reaction
was allowed to come to room temperature and stirred for 4 h. The volatiles were removed in
vacuo, and the residue was taken up in a minimal amount of pentane (2 × 10 mL) and filtered
through Celite. The filtrate was concentrated in vacuo. Cooling the pentane solution to −35 °C
1

yielded 5 as red-orange crystals (0.238 g, 0.573 mmol, 70% yield). H NMR (300 MHz, CDCl3,
25 °C): 5.31 (sept, JHH = 6.66, 2H, CH(CH3)2), 3.94 (sept, JHH = 6.35, 2H, CH(CH3)2), 2.02
(d, JHH = 6.35, 6H, CH(CH3)2), 1.48 (d, JHH = 6.35, 6H, CH(CH3)2), 1.31 (d, JHH = 6.35, 6H,
CH(CH3)2), 1.16 (d, JHH = 6.35, 6H, CH(CH3)2).

19

F NMR (564 MHz, CDCl3, 25 °C): −76.65.

Mp: 198 °C (sub).
i

2.9.6 Synthesis of NCr(N Pr2)2(OAd) (6): Under an inert atmosphere, a pressure tube was
loaded with 1-adamantanol (0.042 g, 0.27 mmol, 1 equiv.), toluene (10 mL), and a stirbar. To
this solution, 1 (0.10 g, 0.27 mmol, 1 equiv.) in toluene (8 mL) was added. The pressure tube
was sealed and placed in a 90 °C oil bath. The reaction stirred at this temperature for 3 d. The
tube was taken back into the glove box, and the volatiles were removed in vacuo. The residue
was extracted with pentane and filtered through Celite. The solution was concentrated to ~5 mL
and placed in a −35 °C freezer yielding red-orange crystals of 6 (0.080 g, 0.191 mmol, 70%
1

yield). H NMR (500 MHz, CDCl3, −40 °C): 4.75 (br sept, 2H, CH(CH3)2), 3.54 (br sept, 2H,

28

CH(CH3)2), 2.08 (app s, 3H, Ad CH), 1.71 (d, JHH = 2.5 Hz, 6H, Ad CH2), 1.63 (d, JHH = 5.5
Hz, 6H, CH(CH3)2), 1.54 (app s, 6H, Ad CH2), 1.40 (d, JHH = 5.5 Hz, 6H, CH(CH3)2), 1.0713

1.02 (m, 12H, CH(CH3)2).

1

C{ H} NMR (125 MHz, CDCl3, −35 °C): 74.0, 57.4, 53.4, 47.0,

36.2, 31.0, 30.0, 29.3, 21.0, 19.5. Mp: 120-125 °C.
i

2.9.7 Synthesis of NCr(N Pr2)2(OSiPh3) (7): Under an inert atmosphere, a scintillation vial
was loaded with 1 (0.70 g, 0.19 mmol, 1 equiv.), toluene (~5 mL), and a stirbar. A solution of
HOSiPh3 (0.053 g, 0.19 mmol, 1 equiv.) in toluene (5 mL) was added slowly. As the reaction
stirred it gradually turned from the beet color of the starting material to orange. After 16 h, the
solution was dried in vacuo. The residue was extracted with pentane and filtered through Celite.
The filtrate was concentrated (~5 mL) in vacuo. The pentane solution yielded orange crystals of
1

7 (0.075 g, 0.14 mmol, 72% yield) at −35 °C. H NMR (500 MHz, CDCl3, 0 °C): 7.64 (d, JHH =
6.34, 6H Ar-C-H), 7.49-7.26 (m, 9H Ar-C-H), 5.01 (sept, JHH = 6.61, 2H, CH(CH3)2), 3.63
(sept, JHH = 6.20, 2H, CH(CH3)2), 1.60 (d, JHH = 6.39, 6H, CH(CH3)2), 1.39 (d, JHH = 6.29,
6H, CH(CH3)2), 1.09 (d, JHH = 6.53, 6H, CH(CH3)2), 1.00 (d, JHH = 6.29, 6H, CH(CH3)2).
13

1

C{ H} NMR (125 MHz, CDCl3, 25 °C): 138.7, 135.3, 128.9, 127.2, 58.4, 55.4, 30.2, 29.5,

21.4, 20.6. Mp: 115-120 ºC.
i

2.9.8 Synthesis of NCr(N Pr2)2(O2CPh) (8): Under an inert atmosphere a scintillation vial was
loaded with 1 (0.150 g, 0.409 mmol, 1 equiv.), a stir bar, and toluene (8 mL), and placed in a
liquid nitrogen cooled cold well until nearly frozen. Benzoic acid (0.050 g, 0.41 mmol, 1 equiv.)

29

in toluene (1 mL) was added. The reaction was allowed to warm to room temperature and was
stirred for 6 h. Over that time the solution changed from the beet color of the starting material to
dark orange. The volatiles were removed in vacuo, and the residue was extracted with pentane (2
× 5 mL) and filtered through Celite. Concentrated solutions cooled to −35 °C yielded 8 as red1

orange crystals (0.140 g, 0.360 mmol, 88% yield). H NMR (500 MHz, CDCl3, 0 °C): 8.02-8.00
(m, 2H Ar-o-C-H), 7.45-7.41 (m, 1H Ar-p-C-H), 7.37-7.34 (m, 2H Ar-m-C-H), 5.60 (sept, JHH =
6.29, 2H, CH(CH3)2), 3.86 (sept, JHH = 6.47, 2H, CH(CH3)2), 1.94 (d, JHH = 6.31, 6H,
CH(CH3)2), 1.53 (d, JHH = 6.37, 6H, CH(CH3)2), 1.18 (d, JHH = 6.40, 6H, CH(CH3)2), 1.13 (d,
JHH = 6.46, 6H, CH(CH3)2).

13

1

C{ H} NMR (125 MHz, CDCl3, 0 °C): 171.5, 133.5, 131.4,

129.9, 127.9, 58.2, 57.0, 30.7, 30.1, 22.2, 21.7. Mp: 121 °C (dec).
i

2.9.9 Synthesis of NCr(N Pr2)2(O-p-(OMe)C6H4) (11): Under an inert atmosphere, a
scintillation vial was loaded with 1 (0.15 g, 0.41 mmol, 1 equiv.), toluene (5 mL), and a stirbar.
The solution was frozen in a liquid nitrogen cooled cold well, then removed to a stir plate. To the
thawing solution of 1 was added a solution of HO-p-(OMe)C6H4 (0.051 g, 0.41 mmol, 1 equiv.)
in toluene (5 mL) over 5 min. The reaction was stirred and was allowed come to room
temperature. After 1.5 h, the orange solution was dried in vacuo. The residue was extracted with
pentane and filtered through Celite. The filtrate was concentrated (~5 mL) in vacuo. Cooling
concentrated pentane solutions to −35 °C yielded dark orange crystals of 11 (0.139 g, 0.356
1

mmol, 87% yield). H NMR (500 MHz, CDCl3, −38 °C): 6.89 (d, JHH = 8.50, 2H, Ar-m-C-H),
6.71 (d, JHH = 9.00, 2H, Ar-o-C-H), 4.99 (sept, JHH = 6.50, 2H, CH(CH3)2), 3.72 (s, 3H, Ar-p30

OCH3), 3.71 (sept, JHH = 6.50, 2H, CH(CH3)2), 1.82 (d, JHH = 6.00, 6H, CH(CH3)2), 1.43 (d,
JHH = 6.00, 6H, CH(CH3)2), 1.15-1.13 (m, 12H, CH(CH3)2).

13

1

C{ H} NMR (125 MHz,

CDCl3, −35 °C): 161.3, 152.3, 117.6, 113.5, 58.0, 55.5, 54.9, 30.3, 29.9, 21.3, 21.0. Mp: 102104 °C.
i

2.9.10 Synthesis of NCr(N Pr2)2(O-p-(SMe)C6H4) (12): Under an inert atmosphere, a
scintillation vial was loaded with 1 (0.15 g, 0.41 mmol, 1 equiv.), toluene (5 mL), and a stirbar.
The solution was frozen in a liquid nitrogen cooled cold well, then removed to a stir plate. To the
thawing solution was added HO-p-(SMe)C6H4 (0.057 g, 0.41 mmol, 1 equiv.) in toluene (5 mL)
over 5 minutes. The reaction was stirred and allowed to come to room temperature. After 1.5 h
the orange solution was dried in vacuo. The residue was extracted with pentane and filtered
through Celite. The filtrate was concentrated (~5 mL) in vacuo. Cooling concentrated pentane
1

solutions to −35 °C yielded dark orange crystals of 12 (0.153 g, 0.376 mmol, 92% yield). H
NMR (500 MHz, CDCl3, −10 °C): 7.14 (d, JHH = 8.64, 2H, Ar-m-C-H), 6.88 (d, JHH = 8.64,
2H, Ar-o-C-H), 5.02 (sept, JHH = 6.21, 2H, CH(CH3)2), 3.73 (sept, JHH = 6.09, 2H, CH(CH3)2),
2.40 (s, 3H SCH3), 1.83 (d, JHH = 6.08, 6H, CH(CH3)2), 1.44 (d, JHH = 6.18, 6H, CH(CH3)2),
1.14 (d, JHH = 6.00, 12H, CH(CH3)2).

13

1

C{ H} NMR (125 MHz, CDCl3, −10 °C): 165.7,

130.2, 125.7, 118.2, 58.2, 55.3, 30.3, 30.0, 23.3, 21.3, 21.0, 18.6. Mp: 112-115 °C.
i

t

2.9.11 Synthesis of NCr(N Pr2)2(O-p-( Bu)C6H4) (13): Under an inert atmosphere, a
scintillation vial was loaded with 1 (0.15 g, 0.41 mmol, 1 equiv.), toluene (5 mL), and a stirbar.

31

The solution was frozen in a liquid nitrogen cooled cold well, then removed to a stir plate. To the
t

thawing solution was added HO-p-( Bu)C6H4 (0.061 g, 0.41 mmol, 1 equiv.) in toluene (5 mL)
over 5 min. The reaction was stirred and allowed to come to room temperature. After 1.5 h, the
orange solution was dried in vacuo. The residue was extracted with pentane and filtered through
Celite. The filtrate was concentrated (~5 mL) in vacuo. Cooling concentrated pentane solutions
1

to −35 °C yielded dark orange crystals of 13 (0.16 g, 0.385 mmol, 94% yield). H NMR (500
MHz, CDCl3, −25 °C): 7.16 (d, JHH = 8.62, 2H, Ar-m-C-H), 6.88 (d, JHH = 8.62, 2H, Ar-o-CH), 5.00 (sept, JHH = 6.35, 2H, CH(CH3)2), 3.71 (sept, JHH = 6.23, 2H, CH(CH3)2), 1.82 (d,
JHH = 6.18, 6H, CH(CH3)2), 1.44 (d, JHH = 6.35, 6H, CH(CH3)2), 1.24 (s, 9H C(CH3)3), 1.13
(d, JHH = 6.35, 12H, CH(CH3)2).

13

1

C{ H} NMR (125 MHz, CDCl3, −35 °C): 164.4, 141.3,

125.5, 116.5, 58.1, 58.0, 55.0, 33.9, 31.5, 30.3, 30.0, 21.2, 20.9. Mp: 188-190 °C.
i

2.9.12 Synthesis of NCr(N Pr2)2(O-p-(F)C6H4) (14): Under an inert atmosphere, a scintillation
vial was loaded with 1 (0.15 g, 0.41 mmol, 1 equiv.), toluene (5 mL), and a stirbar. The solution
was frozen in a liquid nitrogen cooled cold well, then removed to a stir plate. To the thawing
solution was added HO-p-(F)C6H4 (0.046 g, 0.41 mmol, 1 equiv.) in toluene (5 mL) over 5 min.
The reaction was stirred and was allowed to come to room temperature. After 1.5 h, the orange
solution was dried in vacuo. The residue was extracted with pentane and filtered through Celite.
The filtrate was concentrated (~5 mL) in vacuo. Cooling concentrated pentane solutions to −35

°C yielded dark orange crystals of 14 (0.136 g, 0.360 mmol, 88% yield). 1H NMR (500 MHz,
CDCl3, −30 °C): 7.38 (d, JHH = 8.63, 2H, Ar-m-C-H), 6.95 (d, JHH = 8.63, 2H, Ar-o-C-H), 5.06

32

(sept, JHH = 6.48, 2H, CH(CH3)2), 3.75 (sept, JHH = 6.42, 2H, CH(CH3)2), 1.84 (d, JHH = 6.35,
6H, CH(CH3)2), 1.45 (d, JHH = 6.43, 6H, CH(CH3)2), 1.16-1.11 (m, 12H, CH(CH3)2).

13

1

C{ H}

NMR (125 MHz, CDCl3, 0 °C): 163.2, 157.3, 117.9 (d, JCF = 7.8), 114.9 (d, JCF = 22.4), 58.3,
55.3, 30.3, 30.0, 21.3, 21.1.

19

F NMR (564 MHz, CDCl3, 25 °C): –126.8. Mp: 81 °C (dec).
i

2.9.13 Synthesis of NCr(N Pr2)2(O-p-(Cl)C6H4) (15): Under an inert atmosphere, a
scintillation vial was loaded with 1 (0.15 g, 0.41 mmol, 1 equiv.), toluene (5 mL), and a stirbar.
The solution was frozen in a liquid nitrogen cooled cold well, then removed to a stir plate. To the
thawing solution was added HO-p-(Cl)C6H4 (0.053 g, 0.41 mmol, 1 equiv.) in toluene (5 mL)
over 5 min. The reaction was stirred and was allowed to come to room temperature. After 1.5 h,
the orange solution was dried in vacuo. The residue was extracted with pentane and filtered
through Celite. The filtrate was concentrated (~5 mL) in vacuo. Cooling concentrated pentane
1

solutions to −35 °C yielded dark orange crystals of 15 (0.137 g, 0.348 mmol, 85% yield). H
NMR (500 MHz, CDCl3, −40 °C): 7.06 (d, JHH = 8.99, 2H, Ar-m-C-H), 6.84 (d, JHH = 8.76,
2H, Ar-o-C-H), 5.01 (sept, JHH = 6.26, 2H, CH(CH3)2), 3.73 (sept, JHH = 6.26, 2H, CH(CH3)2),
1.82 (d, JHH = 6.29, 6H, CH(CH3)2), 1.42 (d, JHH = 6.04, 6H, CH(CH3)2), 1.12 (d, JHH = 6.57,
6H, CH(CH3)2), 0.996 (d, JHH = 6.18, 6H, CH(CH3)2).

13

1

C{ H} NMR (125 MHz, CDCl3, −20

°C): 165.3, 128.5, 123.1, 118.7, 58.3, 55.4, 44.8, 30.3, 30.1, 23.2, 21.3, 21.0. Mp: 124-125 ºC.
i

2.9.14 Synthesis of NCr(N Pr2)2(O-p-(CF3)C6H4) (16): Under an inert atmosphere, a
scintillation vial was loaded with 1 (0.15 g, 0.41 mmol, 1 equiv.), toluene (5 mL), and a stirbar.

33

The solution was frozen in a liquid nitrogen cooled cold well, then removed to a stir plate. To the
thawing solution was added HO-p-(CF3)C6H4 (0.066 g, 0.41 mmol, 1 equiv.) in toluene (5 mL)
over 5 min. The reaction was stirred and was allowed to come to room temperature. After 1.5 h,
the orange solution was dried in vacuo. The residue was extracted with pentane and filtered
through Celite. The filtrate was concentrated (~5 mL) in vacuo. Cooling concentrated pentane
1

solutions to −35 °C yielded dark orange crystals of 16 (0.143 g, 0.336 mmol, 82% yield). H
NMR (500 MHz, CDCl3, 3 °C): 7.37 (d, JHH = 8.58, 2H, Ar-m-C-H), 6.95 (d, JHH = 8.58, 2H,
Ar-o-C-H), 5.07 (sept, JHH = 6.29, 2H, CH(CH3)2), 3.76 (sept, JHH = 6.22, 2H, CH(CH3)2),
1.85 (d, JHH = 6.04, 6H, CH(CH3)2), 1.46 (d, JHH = 6.03, 6H, CH(CH3)2), 1.15 (d, JHH = 3.72,
6H, CH(CH3)2), 1.02 (d, JHH = 6.34, 6H, CH(CH3)2).

13

1

C{ H} NMR (125 MHz, CDCl3, 3

°C): 169.1, 126.3 (quar, JCF = 3.79), 117.7, 117.6, 58.5, 55.7, 30.4, 30.2, 23.3, 21.3, 21.1. 19F
NMR (564 MHz, CDCl3, 25 °C): −64.24. Mp: 131-132 ºC. Anal. Calcd: C, 53.38; H, 7.56; N,
9.82. Found: C, 53.40; H, 7.77; N, 9.80.
i

2.9.15 Synthesis of NCr(N Pr2)2(OC6F5) (17): Under an inert atmosphere, a scintillation vial
was loaded with 1 (0.15 g, 0.41 mmol, 1 equiv.), toluene (5 mL), and a stirbar. The solution was
frozen in a liquid nitrogen cooled cold well, then removed to a stir plate. To the thawing solution
was added HOC6F5 (0.075 g, 0.41 mmol, 1 equiv.) in toluene (5 mL) over 5 minutes. The
reaction was stirred and was allowed to come to room temperature. After 1.5 h, the orange
solution was dried in vacuo. The residue was extracted with pentane and filtered through Celite.
The filtrate was concentrated (~5 mL) in vacuo. Cooling concentrated pentane solutions to −35

34

°C yielded dark orange crystals of 17 (0.16 g, 0.385 mmol, 76% yield). 1H NMR (500 MHz,
CDCl3, −20

°C):

5.12 (sept, JHH = 6.50, 2H, CH(CH3)2), 3.81 (sept, JHH = 6.50, 2H,

CH(CH3)2), 1.87 (d, JHH = 6.50, 6H, CH(CH3)2), 1.41 (d, JHH = 6.00, 6H, CH(CH3)2), 1.26 (d,
JHH = 6.50, 6H, CH(CH3)2), 1.16 (d, JHH = 6.00, 6H, CH(CH3)2).
CDCl3, —20 ºC): 143-137, 58.7, 56.4, 30.4, 29.8, 21.6, 20.6.

19

13

1

C{ H} NMR (125 MHz,

F NMR (564 MHz, CDCl3, 25

°C): −161.70 (dd, JFF = 37.22 Hz, 13.54 Hz, 2F), −167.25 to −167.46 (m, 2F), −173.58 (tt, JFF =
44.56 Hz, 13.54 Hz, 1F). Mp: 129-132 ºC.
i

2.9.16 Synthesis of NCr(N Pr2)2(SPh) (18): Under an inert atmosphere, a pressure tube was
loaded with 1 (0.10 g, 0.27 mmol, 1 equiv.), toluene (5 mL), and a stirbar. To the stirring
solution of 1 was added thiophenol (0.030 g, 0.27 mmol, 1 equiv.) in toluene (5 mL). The
pressure tube was sealed, placed in a 65 °C oil bath, and stirred for 20 h. The reaction was taken
back under an inert atmosphere, and the volatiles were removed in vacuo. The residue was
extracted with pentane and filtered through Celite. The solution was concentrated to ~5 mL and
placed in a −35 °C freezer yielding red-purple crystals of 19 (0.077 g, 0.21 mmol, 75% yield).
1

H NMR (500 MHz, CDCl3, −4 °C): 7.62-7-60 (d, 2H, Ar-o-C-H), 7.12-7.09 (t, 2H, Ar-m-C-H),

6.99-6.96 (t,1H Ar-p-C-H), 5.23-5.18 (sept, 2H, CH(CH3)2), 3.72-3.67 (sept, 2H, CH(CH3)2),
1.75-1.731 (d, 6H, CH(CH3)2), 1.49-1.47 (d, 6H, CH(CH3)2), 1.13-1.11 (d, 12H, CH(CH3)2).
13

1

C{ H} NMR (125 MHz, CDCl3, −4 °C): 141.95, 132.58, 127.87, 123.94, 59.00, 55.95, 30.34,

29.91, 21.96, 20.38. Mp: 118-120 ºC.
35

i

2.9.17 Synthesis of NCr(N Pr2)2(OPth) (19): Under an N2 atmosphere a scintillation vial was
loaded with N-(hydroxy)phthalimide (HOPth, 0.081 g, 0.494 mmol, 1 equiv), CHCl3 (5 mL), and
a stir bar. To this slurry was added 1 (0.181 g, 0.494 mmol, 1 equiv) in CHCl3 (5 mL). The
solution turned orange and stirred for 16 h at room temperature. The volatiles were removed in
vacuo, and the residue was extracted with toluene (3 × 5 mL). This solution was filtered through
Celite, and the filtrate was concentrated to 8 mL. Diffraction quality crystals of 18 were grown
1

from toluene solution at −35 °C (0.110 g, 0.257 mmol, 52%). H NMR (500 MHz, CDCl3, −2

°C):

7.68-7.67 (m, 2H, Phth), 7.59-7.57 (m, 2H, Phth), 5.13 (sept, JHH = 6.5 Hz, 2H,

CH(CH3)2), 3.82 (sept, JHH = 6.5 Hz, 2H, CH(CH3)2), 1.93 (d, JHH = 6.5 Hz, 6H, CH(CH3)2),
1.41-1.38 (m, 12H, CH(CH3)2), 1.16 (d, JHH = 6.5 Hz, 6H, CH(CH3)2).

13

1

C{ H} NMR (125

MHz, CDCl3, −2 °C): 20.38, 21.66, 56.10, 58.52, 122.32, 129.72, 133.30, 163.75. M.p. 179 °C
(dec).
i

2.9.18 Synthesis of NCr(N Pr2)2(OBn) (20): Under an inert atmosphere, a scintillation vial was
loaded with 2 (0.075 g, 0.19 mmol, 1 equiv.) and hexane (10 mL). This was cooled to near
frozen in a liquid nitrogen cooled cold well. In a separate vial, TlOBn (0.065 g, 0.21 mmol, 1.1
equiv.) was slurried in THF (2 mL), and a stir bar was added. The solution of 2 was then added
dropwise over 5 min to the rapidly stirring slurry. The reaction was allowed to come to room
temperature and stir for 16 h, during which yellow TlI precipitated. The volatiles were removed
in vacuo. The residue was extracted with pentane and filtered through Celite. The filtrate was
concentrated in vacuo. Cooling a concentrated pentane solution to −35 °C yielded 20 as orange

36

1

crystals (0.641 g, 0.172 mmol, 90% yield). H NMR (500 MHz, CDCl3, −45 °C): 7.55 (d, JHH =
7.0, 2H, Ar-o-CH), 7.30 (app t, JHH = 7.5, 2H, Ar-m-CH), 7.20 (t, JHH = 7.5, 1H, Ar-p-CH),
5.47 (s, 2H, CH2), 4.75 (sept, JHH = 6.0, 2H, CH(CH3)2), 3.59 (sept, JHH = 6.0, 2H,
CH(CH3)2), 1.61 (d, JHH = 6.0, 6H, CH(CH3)2), 1.35 (d, JHH = 6.0, 6H, CH(CH3)2), 1.04 (br s,
12H, CH(CH3)2).

13

1

C{ H} NMR (125 MHz, CDCl3, –40 ºC): 143.9, 127.8, 127.3, 126.6, 80.3,

57.5, 54.1, 30.1, 29.4, 21.3, 20.7. Mp: 139-140 ºC. Anal. Calcd: C, 61.09; H, 9.46; N, 11.24.
Found: C, 60.87; H, 9.16; N, 11.22.
i

2.9.19 Synthesis of NCr(N Pr2)2(NO3) (21): Under an inert atmosphere, a scintillation vial was
loaded with TlNO3 (0.203 g, 0.763 mmol, 3 equiv.), a stir bar, and THF (8 mL). To the slurry of
TlNO3 was added 2 (0.10 g, 0.25 mmol, 1 equiv.) in THF (5 mL). The reaction was stirred for 16
h at room temperature, after which time the volatiles were removed in vacuo. The residue was
extracted with pentane (3 × 10 mL) and filtered through Celite. Removal of volatiles in vacuo
yielded the title compound as a red-orange powder (0.063 g, 0.19 mmol, 75% yield). Diffraction
1

quality crystals were obtained from a pentane at −35 °C. H NMR (600 MHz, CDCl3, 25 °C):
5.54 (sept, JHH = 5.35, 2H, CH(CH3)2), 3.92 (sept, JHH = 6.41, 2H, CH(CH3)2), 1.95 (d, JHH =
6.21, 6H, CH(CH3)2), 1.55 (d, JHH = 6.23, 6H, CH(CH3)2), 1.22 (d, JHH = 6.35, 6H,
CH(CH3)2), 1.13 (d, JHH = 6.32, 6H, CH(CH3)2).

13

1

C{ H} NMR (125 MHz, CDCl3, 25 °C):

59.80, 58.12, 31.06, 30.00, 22.41, 22.03. Mp: 77 ºC (dec).

37

i

2.9.20 Synthesis of NCr(N Pr2)2(Pyrrolyl) (22): Under an inert atmosphere, a scintillation vial
was loaded with 2 (0.100 g, 0.254 mmol 1 equiv.), a stir bar, and toluene (8 mL). A slurry of
freshly made thallium pyrrole (0.695 g, 0.257 mmol, 1.01 equiv.) in Et2O (5 mL) was added to
the stirring solution. The reaction was allowed to stir for 20 h at room temperature, during which
yellow TlI precipitated. The precipitate was removed by filatration, and the volatiles were
removed in vacuo. The residue was extracted with pentane (3 × 10 mL) and concentrated in
vacuo to ~5 mL. Cooling the concentrated solution to −35 °C yielded red-orange crystals of 22
1

(0.068 g, 0.20 mmol, 80% yield). H NMR (500 MHz, CDCl3, −10 °C): 6.94-6.81 (m, 2H, pyrCH), 6.26-6.17 (m, 2H, pyr-C-H), 5.10 (sept, JHH = 6.09, 2H, CH(CH3)2), 3.77 (sept, JHH =
5.52, 2H, CH(CH3)2), 1.83 (d, JHH = 4.64, 6H, CH(CH3)2), 1.55 (d, JHH = 5.03, 6H,
CH(CH3)2), 1.16 (d, JHH = 5.16, 6H, CH(CH3)2), 1.05 (d, JHH = 4.30, 6H, CH(CH3)2).
13

1

C{ H} NMR (125 MHz, CDCl3, −10 °C): 129.2, 107.3, 58.0, 56.0, 30.3, 30.1, 22.0, 21.3. Mp:

125-6 ºC.
i

2.9.21 Synthesis of NCr(N Pr2)2(Pyr

C6F5

) (23): Under an inert atmosphere a scintillation vial

was loaded with 2 (0.100 g, 0. 254 mmol 1 equiv.), a stir bar, and toluene (8 mL). A slurry of
freshly made Tl(Pyr

C6F5

) (0.112 g, 0.257 mmol, 1.01 equiv.) in Et2O (5 mL) was added to the

stirring solution. The reaction was allowed to stir for 20 h at room temperature, during which
yellow TlI precipitated. The precipitate was removed by filtration, and the volatiles were
removed in vacuo. The residue was extracted with pentane (3 × 10 mL) and concentrated in
vacuo to ~5 mL. Cooling the concentrated solution to −35 °C yielded red-orange crystals of 23
38

1

(0.080 g, 0.16 mmol, 63% yield). H NMR (500 MHz, CDCl3, 0 °C): 7.35-7.32 (m, 2H, pyr-CH), 6.91-6.88 (m, 2H, pyr-C-H), 5.15 (sept, JHH = 6.28, 2H, CH(CH3)2), 3.82 (sept, JHH = 6.37,
2H, CH(CH3)2), 1.87 (d, JHH = 6.07, 6H, CH(CH3)2), 1.57 (d, JHH = 6.07, 6H, CH(CH3)2),
1.18 (d, JHH = 6.29, 6H, CH(CH3)2), 1.11 (d, JHH = 6.33, 6H, CH(CH3)2).

13

1

C{ H} NMR (125

MHz, CDCl3, 25 °C): 143.76 (dm, JCF = 255.75 Hz), 137.90 (dm, JCF = 248.5 Hz), 137.33 (dm,
JCF = 243.13 Hz), 130.98, 130.63, 112.47, 108.97, 58.46, 56.59, 30.37, 30.24, 22.10, 21.29.

19

F

NMR (564 MHz, CDCl3, 25 °C): −142.47 to −142.57 (m, 2F), −163.35 (t, JFF = 42.86 Hz, 1F),
−164.77 to −164.95 (m, 2F). Mp: 169-171 °C.
i

2.9.22 Synthesis of NCr(N Pr2)2(Pyr

C6H3(CF3)2

) (24): Under an inert atmosphere, a

scintillation vial was loaded with 2 (0.100 g, 0. 254 mmol 1 equiv.), a stir bar, and toluene (8
mL). A slurry of freshly made Tl(Pyr

C6H3(CF3)2

) (0.124 g, 0.257 mmol, 1.01 equiv.) in Et2O (5

mL) was added. The reaction was allowed to stir for 20 h at room temperature, during which
yellow TlI precipitated. The precipitate was removed by filtration, and the volatiles were
removed in vacuo. The residue was extracted with pentane (3 × 10 mL) and concentrated in
vacuo to ~5 mL. Cooling the concentrated solution to −35 °C yielded red-orange crystals of 24
1

(0.098 g, 0.18 mmol, 71% yield). H NMR (500 MHz, CDCl3, 0 °C): 7.85 (s, 2H, Ar-o-CH),
7.49 (s, 1H, Ar-p-CH), 7.29-7.28 (m, 1H, pyr-CH), 6.88-6.87 (m, 1H, pyr-CH), 6.52-6.52 (m,
1H, pyr-CH), 5.15 (sept, JHH = 6.0, 2H, CH(CH3)2), 3.81 (sept, JHH =6.0, 2H, CH(CH3)2), 1.86
(d, JHH = 6.0, 6H, CH(CH3)2), 1.57 (d, JHH = 6.0, 6H, CH(CH3)2), 1.20 (d, JHH = 6.0, 6H,

39

CH(CH3)2), 1.11 (d, JHH = 6.0, 6H, CH(CH3)2).

13

1

C{ H} NMR (125 MHz, CDCl3, 25 °C):

138.84, 131.27 (q, JCF = 32.5 Hz), 130.63, 128.45, 124.26, 123.72 (q, JCF = 270.9 Hz), 121.84,
117.30 (s, br) 106.02, 58.28, 56.43, 30.37, 30.22, 21.99, 21.35.

19

F NMR (564 MHz, CDCl3, 25

°C): −62.85 (s). Mp: 116-122 °C.
i

2.9.23 Synthesis of NCr(N Pr2)2(Indolyl) (25): Under an inert atmosphere, a scintillation vial
was loaded with 10 (0.100 g, 0.278 mmol, 1 equiv.), a stir bar, and hexanes (8 mL). This was
cooled to near frozen in a liquid cooled nitrogen cold well. Freshly prepared lithium indolide
(0.034 g, 0.28 mmol, 1.00 equiv.), in toluene (5 mL) was added dropwise over 5 min to the
thawing solution of 10. The reaction was allowed to stir for 20 h while warming to room
temperature. The volatiles were removed in vacuo. The residue was extracted with pentane (3 ×
10 mL) and filtered through Celite. The filtrate was concentrated to ~5 mL and cooled to −35

°C, which provided crystals of 25. The crystals were redissolved in cold pentane and filtered to
remove remaining lithium salts. Recrystalization at –35 °C from pentane yielded pure 25 as
1

purple crystals (0.045 g, 0.12 mmol, 42% yield). H NMR (500 MHz, CDCl3, –21 ºC): 8.06 (d,
JHH = 8.5, 1H, H-7 ind), 7.55 (d, JHH = 8, 1H, H-4 ind), 7.37 (d, JHH = 3, 1H, H-2 ind), 7.15 (t,
JHH = 6.8, 1H, H-5 ind), 7.03 (t, JHH = 6.8, 1H, H-6 ind), 6.54 (d, JHH = 3, 1H, H-3 ind), 5.18
(sept, JHH = 6.50, 2H, CH(CH3)2), 3.74 (sept, JHH = 6.50, 2H, CH(CH3)2), 1.73 (d, JHH = 6.50,
6H, CH(CH3)2), 1.59 (d, JHH = 6.50, 6H, CH(CH3)2), 1.19 (d, JHH = 6.50, 6H, CH(CH3)2),

40

0.97 (d, JHH = 6.50, 6H, CH(CH3)2).

13

1

C{ H} NMR (125 MHz, CDCl3, –21 ºC): 144.5, 133.4,

128.8, 120.6, 119.1, 118.7, 115.9, 102.3, 58.1, 55.8, 30.6. Mp: 194-196 °C.
i

2.9.24 Synthesis of NCr(N Pr2)2(Carbazolyl) (26): Under an inert atmosphere a pressure tube
wasloaded with 10 (0.150 g, 0.417 mmol 1 equiv.), a stir bar, and hexanes (8 mL). Freshly
prepared lithium carbazolide (0.072 g, 0.42 mmol, 1.00 equiv.) in toluene (5 mL) was added to
the solution of 10. The vessel was sealed, removed from the box, and stirred in a 45 °C oil bath
for 16 h. The pressure tube was taken back into the dry box, and the volatiles were removed
under reduced pressure. The residue was extracted with pentane, and filtered through Celite. The
filtrate was concentrated to ~5 mL and cooled to −35 °C, which provided crystals of 26. The
crystals were redissolved in cold pentane and filtered to remove remaining lithium salts.
1

Recrystalization at –35 °C from pentane yielded pure 26 (0.063 g, 0.146 mmol, 35% yield). H
NMR (500 MHz, CDCl3, −20 °C): 8.02 (d, JHH = 7.58, 2H), 7.97 (d, JHH = 8.33, 2H), 7.40 (d,
JHH = 7.71, 2H), 7.17 (d, JHH = 7.28, 2H), 5.30 (sept, JHH = 6.18, 2H, CH(CH3)2), 3.79 (sept,
JHH = 6.21, 2H, CH(CH3)2), 1.69 (d, JHH = 6.07, 6H, CH(CH3)2), 1.62 (d, JHH = 6.21, 6H,
CH(CH3)2), 1.21 (d, JHH = 6.08, 6H, CH(CH3)2), 0.96 (d, JHH = 6.29, 6H, CH(CH3)2).
13

1

C{ H} NMR (125 MHz, CDCl3, −20 °C): 149.28, 125.02, 124.78, 119.15, 118.76, 114.96,

58.09, 55.81, 31.00, 29.47, 22.69, 22.26. Mp: 158-160 ºC.
i

2.9.25 Synthesis of NCr(N Pr2)2[N(Ph)Me] (27): Under an inert atmosphere, a scintillation vial
was loaded with 10 (0.150 g, 0.417 mmol 1 equiv.), a stir bar, and hexanes (8 mL). This was

41

cooled to near frozen in a liquid nitrogen cooled cold well. Freshly prepared lithium N-methyl
anilide (0.047 g, 0.42 mmol, 1.0 equiv.) in toluene (5 mL) was added dropwise over 5 min. The
reaction was allowed to stir for 20 h with warming to room temperature. The volatiles were
removed in vacuo. The residue was extracted with pentane and filtered through Celite. The
filtrate was concentrated to ~5 mL and cooled to −35 °C, which provided crystals of 27. The
crystals were recrystallized from cold pentane to obtain dark purple crystals of pure 27 (0.068 g,
1

0.184 mmol, 44% yield). H NMR (500 MHz, CDCl3, –10 °C): 7.45-7.33 (m, 2H, Ar-C-H),
7.32-7.24 (m, 3H, Ar-C-H), 5.10 (sept, JHH = 6.09, 2H, CH(CH3)2), 3.77 (sept, JHH = 5.52, 2H,
CH(CH3)2), 1.83 (d, JHH = 4.64, 6H, CH(CH3)2), 1.55 (d, JHH = 5.03, 6H, CH(CH3)2), 1.16 (d,
JHH =5.16, 6H, CH(CH3)2), 1.05 (d, JHH = 4.30, 6H, CH(CH3)2).

13

1

C{ H} NMR (125 MHz,

CDCl3, −55 °C): 158.6, 127.9, 118.8, 115.5, 57.5, 53.2, 41.7, 29.9, 29.3, 22.0, 21.3. Mp: 194-6

°C.
i

2.9.26 Synthesis of NCr(N Pr2)2(NCO) (28): Under an inert atmosphere a pressure tube was
loaded with sodium cyanate (0.083 g, 1.271 mmol, 5 equiv), 1,4-dioxane (8 mL), and a stir bar.
To the stirring cyanate solution was added 2 (0.100 g, 0.254 mmol, 1 equiv), in acetonitrile (~8
mL). The pressure tube was sealed and placed in a 45 °C oil bath and stirred for 20 h. The tube
was returned to the dry box, and the volatiles were removed in vacuo. The residue was extracted
with pentane and filtered through Celite. The solution was concentrated to ~5 mL and placed in a
1

−35 °C freezer, which yielded light orange needles of 28 (0.047 g, 0.153 mmol, 60% yield). H
NMR (500 MHz, CDCl3, 25 °C): 5.04 (sept, JHH = 6.34, 2H, CH(CH3)2), 3.81 (sept, JHH =

42

6.28, 2H, CH(CH3)2), 1.90 (d, JHH = 6.36, 6H, CH(CH3)2), 1.47 (d, JHH = 6.29, 6H,
CH(CH3)2), 1.23 (d, JHH = 6.34, 6H, CH(CH3)2), 1.10 (d, JHH = 6.50, 6H, CH(CH3)2).
13

1

C{ H} NMR (125 MHz, CDCl3, 25 °C): 149.7, 58.8, 57.1, 30.549, 30.2, 21.5, 21.3. Mp: 115

°C (dec).
i

2.9.27 Synthesis of NCr(N Pr2)2(NCS) (29): Under an inert atmosphere, a scintillation vial was
loaded with 2 (0.100 g, 0.254 mmol, 1 equiv.), toluene (5 mL), and a stirbar. To this solution,
sodium thiocyanate (0.062 g, 0.763 mmol, 3 equiv.) in acetonitrile (10 mL) was added. The
reaction stirred at room temperature for 3 d. The volatiles were removed in vacuo. The residue
was extracted with pentane, and filtered through Celite. Cooling concentrated pentane solutions
of the crude product to −35 °C yielded yellow-orange needles of 29 (0.043 g, 0.132 mmol, 52%
1

yield). H NMR (500 MHz, CDCl3, −13 °C): 5.10 (sept, JHH = 6.31, 2H, CH(CH3)2), 3.86
(sept, JHH = 6.40, 2H, CH(CH3)2), 1.92 (d, JHH = 6.23, 6H, CH(CH3)2), 1.45 (d, JHH = 6.23,
6H, CH(CH3)2), 1.28 (d, JHH = 6.23, 6H, CH(CH3)2), 1.11 (d, JHH = 6.29, 6H, CH(CH3)2).
13

1

C{ H} NMR (125 MHz, CDCl3, −13 °C): 189.8, 59.3, 57.9, 30.7, 30.4, 22.0, 21.6. Mp: 138-

142 °C.
i

2.9.28 Synthesis of NCr(N Pr2)2(CN) (30): Under an inert atmosphere, a scintillation vial was
loaded with sodium cyanide (10.6 mg, 0.216 mmol, 1 equiv.) in acetonitrile (~10 mL), freshly
dried 15-crown-5 (47.6 mg, 0.216 mmol, 1 equiv.), and a stir bar. After stirring for 5 min, 2
(0.085 g, 0.216 mmol, 1 equiv.) in acetonitrile (5 mL) was added. The reaction stirred at room

43

temperature for 6 h. The volatiles were removed in vacuo, and the residue was extracted with
pentane and filtered through Celite. Cooling concentrated pentane solutions of the crude product
1

to −35 °C yielded orange crystals of 30 (28.7 mg, 0.093 mmol, 43% yield). H NMR (500 MHz,
CDCl3, −6

°C):

5.13 (sept, JHH = 6.29, 2H, CH(CH3)2), 3.88 (sept, JHH = 6.04, 2H,

CH(CH3)2), 1.89 (d, JHH = 5.63, 6H, CH(CH3)2), 1.54 (d, JHH = 5.63, 6H, CH(CH3)2), 1.36 (d,
JHH = 5.84, 6H, CH(CH3)2), 1.13 (d, JHH = 5.84, 6H, CH(CH3)2).

13

1

C{ H} NMR (125 MHz,

CDCl3, −6 °C): 143.9, 58.5, 57.9, 57.7, 31.1, 31.0, 30.7, 30.5, 23.1, 22.6, 22.4, 21.9. IR: C–N
–1

stretch appears at 2172 cm . M.p.: 180 °C (dec).
i

2.9.29 Synthesis of NCr(N Pr2)2(NMe2) (31): Under an inert atmosphere, a vial was loaded
with ZnCl2 (0.293 g, 2.15 mmol, 4.23 equiv), a stirbar, and THF (15 mL). This was cooled in a
liquid cooled nitrogen cold well for 10 min. The vial was moved to a stir plate, and a chilled
solution of LiNMe2 (0.220 g, 4.31 mmol, 8.47 equiv) in THF (4 mL) and DME (4 mL) was
added dropwise. The reaction stirred for 1 h and was allowed to come to room temperature,
during which the mixture turned cloudy white. To this suspension was added a solution of 2
(0.200 g, 0.509 mmol, 1 equiv) in THF (2 mL) dropwise. The reaction stirred at room
temperature for 4 h and turned bright red. The volatiles were removed in vacuo. The residue was
extracted with pentane and filtered through Celite. The pentane was removed in vacuo. The
complex was recrystallized from a minimum of acetonitrile (~4 mL) and red crystals of 31 were
1

isolated (0.110 g, 0.354 mmol, 70%). H NMR (500 MHz, CDCl3, 25 °C): 3.89 (sept, JHH =
6.43, 4H, CH(CH3)2), 3.55 (s, 6H, N(CH3)2), 1.31 (d, JHH = 6.27, 12H, CH(CH3)2), 1.23 (d,

44

JHH = 6.34, 12H, CH(CH3)2).

13

1

C{ H} NMR (125 MHz, CDCl3, 25 °C): 54.5, 53.7, 26.4, 25.1.

Mp: 52-57 °C.
i

2.9.30 Synthesis of [NCr(N Pr2)2(DMAP)]BF4 (32): Under an N2 atmosphere, a scintillation
vial was loaded with 2 (0.177 g, 0.450 mmol, 1 equiv), 4-dimethylaminopyridine (0.055 g, 0.450
mmol, 1 equiv), and a stir bar. To this vial, CHCl3 (8 mL) was added, and the solution was
stirred for 10 min. A solution of AgBF4 (0.096 g, 0.495 mmol, 1.1 equiv) in acetonitrile (4 mL)
was added over 5 min. The reaction stirred at room temperature for 1 h. The brown suspension
was filtered through a glass frit with Celite as a filtering agent. The filtrate was dried in vacuo
and washed with pentane (2 mL). The residue was extracted with CHCl3 (2 × 5 mL). These
extracts

were

filtered

through

Celite

and

dried

under

vacuum

yielding

i

[NCr(N Pr2)2(DMAP)]BF4 (32) (0.124 g, 0.261 mmol, 58%). This was used without further
1

purification in the synthesis of 33. H NMR (500 MHz, CDCl3, 0 °C): 8.21 (d, JHH = 7.0 Hz,
2H, Ar-H), 6.68 (d, JHH = 6.5 Hz, 2H, Ar-H), 5.50 (sept, JHH = 6.0 Hz, 2H, CH(CH3)2), 3.93
(sept, JHH = 6.0 Hz, 2H, CH(CH3)2), 3.12 (s, 6H, N(CH3)2) 1.86 (d, JHH = 6.5 Hz, 6H,
CH(CH3)2), 1.55 (d, JHH = 6.5 Hz, 6H, CH(CH3)2), 1.23 (d, JHH = 6.5 Hz, 6H, CH(CH3)2),
1.15 (d, JHH = 6.5 Hz, 6H, CH(CH3)2).

19

F NMR (564 MHz, CDCl3, 25 °C): –151.9 ppm.

i

2.9.31 Synthesis of NCr(N Pr2)2(F) (33): Under an N2 atmosphere, a scintillation vial was
n

loaded with FSn Bu3 (3.38 mg, 0.011 mmol, 10 mol%), THF (1 mL), and a stir bar. A solution
i

of [NCr(N Pr2)2(DMAP)]BF4 32 (0.052 g, 0.109 mmol, 1 equiv.) from the previous step in THF
45

(8 mL) was added. The reaction stirred for 4 h at room temperature. The volatiles were removed
in vacuo, and the residue was extracted with pentane (2 × 5 mL) and filtered through Celite. The
pentane solution was concentrated to ~5 mL under vacuum, and held at −35 °C yielding 33 as
1

red-orange crystals (0.015 g, 0.054 mmol, 49%). H NMR (500 MHz, CDCl3, 25 °C): 5.08
(sept, JHH = 6.5 Hz, 2H, CH(CH3)2), 3.81 (sept, JHH = 6.0 Hz, 2H, CH(CH3)2), 1.94 (d, JHH =
6.5 Hz, 6H, CH(CH3)2), 1.44 (d, JHH = 6.5 Hz, 6H, CH(CH3)2), 1.23 (d, JHH = 6.0 Hz, 6H,
CH(CH3)2), 1.12 (d, JHH = 6.5 Hz, 6H, CH(CH3)2).
21.21, 21.45, 30.15, 30.22, 56.63, 58.65.

19

13

1

C{ H} NMR (125 MHz, CDCl3, 25 °C):

F NMR (564 MHz, CDCl3, 25 °C): −145.24. M.p.

100-102 °C.
i

2.9.32 Synthesis of [NCr(N Pr2)2(HMPA)]PF6 (34): In a 20 mL scintillation vial equipped
with a stir bar was loaded with 2 (0.050 g, 0.14 mmol, 1 equiv.), HMPA (0.025 g, 0.14 mmol, 1
equiv.) and 3.0 mL of CHCl3. This was allowed to stir for ten minutes. A solution of AgPF6 (XX
g, XX mmol, 1 equiv.) in 3.0 mL of acetonitrile was added over five minutes. The reaction
stirred for one hour at room temperature. The solution was filtered through a glass frit with
Celite as a filtering agent. The filtrate was dried in vacuo and washed with pentane (2 mL). The
residue was extracted with CHCl3 (2 × 5 mL). These extracts were filtered through Celite and
i

1

dried under vacuum yielding [NCr(N Pr2)2(HMPA)]PF6 (34). H NMR (500 MHz, CDCl3, 25

ºC): 5.24 (sept, JHH = 6.5 Hz, 2H, CH(CH3)2), 3.93 (sept, JHH = 6.5 Hz, 2H, CH(CH3)2), 2.68
(d, JHH = 10 Hz, 18H, N(CH3)2), 1.94 (d, JHH = 6.0 Hz, 6H, CH(CH3)2), 1.43 (d, JHH = 6.5 Hz,

46

6H, CH(CH3)2), 1.25 (d, JHH = 6.5 Hz, 6H, CH(CH3)2), 1.20 (d, JHH = 6.5 Hz, 6 H,
CH(CH3)2).
i

2.9.33 Synthesis of NCr(N Pr2)2(CH2SiMe3) (35): In a 20 mL scintillation vial equipped with
a stir bar was loaded with 10 (0.050 g, 0.140 mmol, 1.0 equiv.) and 8 mL of pentane. This
solution was placed into a liquid nitrogen cooled cold well to cool for 5 min. To this cold,
stirring solution was added 0.139 mL of 1.0 M LiCH2SiMe3 dropwise. The solution was allowed
to warm up to room temperature and stir for 1 h. The solution turned from orange-red to a
yellow-brown color. The pentane solution was cooled and then filtered through Celite to remove
LiOPh. The solution was concentrated in vacuo and placed in a freezer yielding yellow-orange
1

crystals (0.036 g, 0.10 mmol, 73%). H NMR (500 MHz, CDCl3, 1.67 ºC): 4.93 (sept, JHH = 6.0
Hz, 2H, CH(CH3)2), 3.52 (sept, JHH = 6.0 Hz, 2H, CH(CH3)2), 1.60 (d, JHH = 6.5 Hz, 6H,
CH(CH3)2), 1.41 (d, JHH = 6.0 Hz, 6H, CH(CH3)2), 1.14 (d, JHH = 6.5 Hz, 6H, CH(CH3)2),
1.12 (d, JHH = 6.5 Hz, 6H, CH(CH3)2), 0.056 (s, 9H, Si(CH3)3), -0.033 (s, 2H, CH2Si(CH3)3).
13

1

C{ H}NMR (125 MHz, CDCl3, 10 ºC): 56.1, 53.5, 30.8, 29.4, 29.0, 22.4, 20.1, 1.6.

29

Si

NMR (119.16 MHz, CDCl3, 25 ºC): 2.078 (s, CH2Si(CH3)3). Mp: 90-92 ºC.
i

2.9.34 Synthesis of NCr(N Pr2)2(CH2C(Me)2Ph) (37): A 20 mL scintillation vial equipped
with a stir bar was loaded with 2 (0.020 g, 0.10 mmol, 1 equiv.) and 2 mL of ether. This solution
was placed into a liquid nitrogen cooled cold well to cool for 5 min. To this cold stirring solution
was added a cold solution of Mg(CH2C(Me)2Ph)2 (0.011 g, 0.04 mmol, 0.7 equiv.) in 2 mL of

47

ether dropwise. This was allowed to warm to room temperature and stir for 1.5 h. A white solid
precipitated, and the solution turned yellow-brown. The solvent was removed in vacuo and the
brown solid dissolved in hexane. The solution was cooled to –35 ºC and filtered through Celite
to remove MgI2. The solution was concentrated in vacuo and placed in a freezer yielding yellow1

orange crystals (0.019 g, 0.048 mmol, 95% yield). H NMR (500 MHz, CDCl3, 25 ºC): 7.33 (d,
JHH = 7.5 Hz, 2H, ortho), 7.13 (app t, JHH = 8.0 Hz, 2H, meta), 6.98 (app t, JHH = 7.0 Hz, 1H,
para), 4.74 (sept, JHH = 6.5, 2H, CH(CH3)2), 3.40 (sept, JHH = 6.5 Hz, 2H, CH(CH3)2), 1.49 (s,
6H, C(CH3)2Ph), 1.47 (s, 2H, CH2C(CH3)2Ph), 1.45 (d, JHH = 6.0 Hz, 6H, CH(CH3)2), 1.32 (d,
JHH = 6.0 Hz, 6H, CH(CH3)2), 1.05 (d, JHH = 6.0 Hz, 6H, CH(CH3)2), 1.01 (d, JHH = 6.0 Hz,
6H, CH(CH3)2).

13

1

C{ H} NMR (125 MHz, CDCl3, 25 ºC): 154.7, 127.7, 125.5, 124.5, 64.7,

55.8, 53.3, 39.6, 32.0, 31.0, 28.9, 22.7, 19.7. Mp: 71-73 ºC.
i

2.9.35 Synthesis of NCr(N Pr2)2(CH2CMe3) (38): A 20 mL scintillation vial equipped with a
stir bar was loaded with 6 (0.027g, 0.065 mmol, 1.0 equiv.) and 4 mL of pentane. This was
placed into a liquid nitrogen cold well to cool for five min. To this cold stirring solution was
added LiCH2CMe3 (0.005 g, 0.065 mmol, 1.0 equiv.) in 3 mL of cold ether dropwise. Over a
period of one h a white solid precipitated. The solution was pumped dry, and the product was
dissolved in pentane. The pentane solution was cooled to –35 ºC and filtered through Celite to
remove LiOAd. The solution was concentrated in vacuo and stored in the freezer yielding
1

crystals ( % yield). H NMR (500 MHz, CDCl3, 2 ºC): 4.85 (sept, JHH = 6.5 Hz, 2H,

48

CH(CH3)2), 3.49 (sept, JHH = 6.5 Hz, 2H, CH(CH3)2), 1.58 (d, JHH = 6.0 Hz, 6H, CH(CH3)2),
1.41 (d, JHH = 6.0 Hz, 6H, CH(CH3)2), 1.26 (s, 2H, CH2C(CH3)3), 1.14 (d, JHH = 6.5 Hz, 6H,
CH(CH3)2), 1.11 (d, JHH = 6.0 Hz, 6H, CH(CH3)2), 1.09 (s, 9H, CH2C(CH3)3).

13

1

C{ H} NMR

(125 MHz, CDCl3, ºC): Mp:
i

i

2.9.36 Synthesis of NCr(N Pr2)2(CCSi Pr3) (39): A 20 mL scintillation vial equipped with a
stir bar was loaded with 10 (0.050 g, 0.140 mmol, 1.0 equiv.) and 5 mL of hexane. This was
placed in a liquid nitrogen cooled cold well to cool for 5 min. To this cold stirring solution was
i

added a cold solution of LiCCSi Pr3 (0.026 g, 0.140 mmol, 1.0 equiv.) in 5 mL of hexane. The
reaction was allowed to warm up to room temperature and stir for 1.5 h. The solution was cooled
to –35 ºC and filtered through Celite to remove LiOPh. This solution was concentrated in vacuo
1

and then placed in the freezer yielding orange crystals (0.052, 0.115 mmol, 83% yield). H NMR
(500 MHz, CDCl3, –18 ºC): 5.05 (sept, JHH = 6.0 Hz, 2H, CH(CH3)2), 3.72 (sept, JHH = 6.5 Hz,
2H, CH(CH3)2), 1.80 (d, JHH = 6.0 Hz, 6H, CH(CH3)2), 1.48 (d, JHH = 6.5 Hz, 6H, CH(CH3)2),
1.25 (d, JHH = 6.5 Hz, 6H, CH(CH3)2), 1.10 (d, JHH = 6.5 Hz, 6H, CH(CH3)2), 1.00 (br s, 21H,
Si(CH(CH3)2)3.

13

1

C{ H} NMR (125 MHz, CDCl3, –20 ºC): 150.4, 119.0, 57.5, 55.8, 30.6,

30.4, 21.9, 21.4, 18.8, 11.4.

29

i

Si NMR (119.16 MHz, CDCl3, 25 ºC): –6.108 (s, CCSi Pr3). Mp:

109-110 ºC.

49

i

t

2.9.37 Synthesis of NCr(N Pr2)2(CC Bu) (40): In a 20 mL scintillation vial equipped with a stir
bar was loaded 10 (0.037 g, 0.102 mmol, 1.0 equiv.) and 7 mL of hexanes. This was placed in a
liquid nitrogen filled cold well to cool for five min. To this cold stirring solution was added a
t

cold solution of LiCC Bu (0.009 g, 0.1 mmol, 1.0 equiv.) in 2 mL of ether. The reaction was
allowed to warm to room temperature and stir for 1 h. Over this period, the solution turned from
dark-red to light orange-red. Then the solvent was removed in vacuo. The product was dissolved
in pentane, chilled, and filtered through Celite to remove LiOPh. The cold solution was
concentrated and placed in a freezer at –35 ºC yielding bright red-orange crystals (0.035 g, 0.101
1

mmol, 98% yield). H NMR (500 MHz, CDCl3, 1 ºC): 5.07 (sept, JHH = 6.5 Hz, 2H,
CH(CH3)2), 3.69 (sept, JHH = 6.0 Hz, 2H, CH(CH3)2), 1.80 (d, JHH = 6.5 Hz, 6H, CH(CH3)2),
1.46 (d, JHH = 6.5 Hz, 6H, CH(CH3)2), 1.25 (d, JHH = 6.5 Hz, 6H, CH(CH3)2), 1.17 (s, 9H,
C(CH3)3), 1.10 (d, JHH = 6.0 Hz, 6H, CH(CH3)2).

13

1

C{ H} NMR (125 MHz, CDCl3, 25 ºC):

127.0, 114.7, 57.4, 55.6, 31.7, 30.6, 30.3, 28.9, 21.7, 21.1. Mp: 110-112 ºC.
Synthesis of Reagents:
TlOBn: In the dry box, a scintillation vial was loaded with benzyl alcohol (0.150 g, 1.39 mmol,
1 equiv), pentane (3 mL), and a stirbar. The solution was cooled to near frozen in a liquid
nitrogen cooled cold well. The vial was moved to a stir plate, and freshly filtered TlOEt (0.349 g,
1.40 mmol, 1.01 equiv) in pentane (3 mL) was added dropwise. The reaction was allowed to
come to room temperature with stirring. After 2 h, the volatiles were removed in vacuo yielding
TlOBn as a white powder (0.415 g, 1.33 mmol, 96%).

50

1

H NMR (500 MHz, C6D6, 25 °C): 4.92 (s, 2H, PhCH2O), 7.06-7.09 (m, 1H, p-Ar-H), 7.19-

7.21(m, 2H, m-Ar-H), 7.23-7.25 (m, 2H, o-Ar-H).

13

1

C{ H} NMR (125 MHz, C6D6, 25 °C):
18e

66.58, 127.07, 127.81, 128.86, 146.53. M.p. 74-76 °C (Lit.

74-78 °C).

i

LiCCSi( Pr)3: In a 20 mL scintillation vial equipped with a stir bar was loaded
tri(isopropyl)silylacetylene (0.20 g, 1.1 mmol, 1 equiv.) and 8 mL of hexane. The solution was
placed in a liquid nitrogen cooled cold well. To this cold stirring solution was added 1.6 M nbutyl lithium in hexanes (0.625 mL, 1.10 mmol, 1.0 equiv.) by syringe. The solution was allowed
to warm to room temperature and stir for 1 h. The solvent was removed in vacuo leaving a sticky
oil. This was used directly in the next reaction. (0.181 g, 0.9 mmol, 87.4% yield). This is a slight
33

modification of the literature procedure.
t

LiCC Bu: In a 20 mL scintillation vial equipped with a stir bar was loaded 3,3-dimethyl-1butyne (0.100 g, 1.21 mmol, 1 equiv.) and 5 mL of hexane. This solution was cooled for 5 min in
a liquid nitrogen cooled cold well. To this cold stirring solution was added 1.6 M n-butyl lithium
in hexanes (0.760 mL, 1.21 mmol, 1.0 equiv.) and was allowed to warm to room temperature and
stir for 1 h. Over this period the solution turned cloudy and a white precipitate formed. The
solvent was removed in vacuo leaving a white solid. (0.101 g, 1.1 mmol, 96% yield). The
melting point matched the reported literature value.

51

34

REFERENCES

52

REFERENCES

1) For a few prominent examples: (a) Wiedner, E. S.; Gallagher, K. J.; Johnson, M. J. A.; Kampf,
J. W. Inorg. Chem. 2011, 50, 5936-5945 (b) Heppekausen, J.; Stade R.; Goddard, R.;
Fürstner, A. J. Am. Chem. Soc. 2010, 132, 11045-11057 (c) Geyer, A. M.; Wiedner, E. S.;
Gary, J. B.; Gdula, R. L.; Kuhlmann, N. C.; Johnson, M. J. A.; Dunietz, B. D.; Kampf, J. W.
J. Am. Chem. Soc. 2008, 130, 8984-8999 (d) Gdula, R. L.; Johnson, M. J. A. J. Am. Chem.
Soc. 2006, 128, 9614-9615 (e) Chisholm, M. H.; Delbridge, E. E.; Kidwell, A. R.; Quinlan,
K. B. Chem. Commun. 2003, 126-127

2) (a) Schrock, R. R. Chem. Commun. 2003, 19, 2389-2391 (b) Shaver, M. P.; Fyzuk, M. D. Adv.
Synth. Catal. 2003, 345, 1061-1076 (c) Yandulov, D. V.; Schrock, R. R. Science 2003, 301,
76-78 (d) Birk, T.; Bendix, J. Inorg. Chem. 2003, 42, 7608-7615 (e) Leung, S. K. Y.; Haung,
J. S.; Liang, J. L.; Che, C. M. Zhou, Z. Y. Angew. Chem., Int. Ed. 2003, 42, 340-343

3) (a) Chang, C. J.; Low, D. W.; Gray, H. B. Inorg. Chem. 1997, 36, 270-270 (b) Laplaza, C. E.;
Johnson, A. R.; Cummins, C. C. J. Am. Chem. Soc. 1996, 118, 709 (c) Kol, M.; Schrock, R.
R.; Kempe, R.; Davis, W. M. J. Am. Chem. Soc. 1994, 116, 4382-4390 (d) Woo, L. K. Chem.
Rev. 1993, 93, 1125-1136 (e) Woo, L. K.; Goll, J. G.; Czapla, D. J.; Hays, J. A. J. Am. Chem.
Soc. 1991, 113, 8478-8484 (f) Woo, L. K.; Goll, J. G. J. Am. Chem. Soc. 1989, 111, 37553757

4) Ozawa, H. T.; Yoshida, H.; Imori, Y.; Kuribayashi, Y.; Nankano, E.; Azuma, N. Inorg. Chim.
Acta 1998, 281, 207-212

5) (a) Meyer, K; Bendix, J.; Bill, E.; Weyhermuller, K.; Wieghardt, K.; Nuber, B. Inorg. Chem.
1998, 37, 5180-5188 (b) Niemann, A.; Bossek, U.; Haselhorst, G.; Wieghardt, K.; Nuber, B.
Inorg. Chem. 1996, 35, 906-915

6) Odom, A. L.; Cummins, C. C.; Protasiewicz, J. D. J. Am. Chem. Soc. 1995, 117, 6613-6614

7) Alyea, E. C.; Basi, J. S.; Bradley, D. C.; Chisholm, M. H.; Chem. Commun. 1968, 495

8) Chiu, H. T.; Chen, Y. P.; Chuang, S. H.; Jen, J. S.; Lee, G. H.; Peng, S. M.; Chem. Commun.
1996, 139-140

9) Takahashi, T. PhD Dissertation, University of Michigan 1985

53

10) Neely, F. L.; Bottomley, L. A. Inorg. Chem. 1997, 36, 5432-5434

11) Bottomley, L. A.; Neely, F. L. Inorg. Chem. 1997, 36, 5435-5439

12) Dorough, G. D.; Miller, J. R.; Huennekens, F. M. J. Org. Chem. 1951, 73, 4315-4320

13) Buchler, J. W.; Dreher, C.; Lay, K. L.; Raap, A.; Gersonde, K. Inorg. Chem. 1983, 22, 879884

14) Chen, S.; Chisholm, M. H.; Davidson, E. R.; English, J. B.; Lichtenberger, D. L. Inorg.
Chem. 2009, 48, 828-837

15) Odom, A. L.; Cummins, C. C. Organometallics 1996, 16, 898-900

16) Odom, A. L.; Cummins, C. C. Polyhedron 1998, 17,675-688

17) (a) Stuhl, L. S.; Carter, S. J. Organometallics 1988, 7, 1909-1918 (b) Liesegang, G. W.;
Farrow, M. M; Vazquez, F. A.; Purdie, N.; Eyring, E. M. J. Am. Chem. Soc. 1977, 99, 32403243 (c) Izatt, R. M.; Terry, R. E.; Haymore, B. L.; Hansen, L. D.; Dalley, N. K.; Ayondett,
A. G.; Christensen, J. J. J. Am. Chem. Soc. 1976, 98, 762-767 (d) Frensdorf, H. K. J. Am.
Chem. Soc. 1971, 93, 600-606

18) (a) Buzzeo, M. C.; Iqbal, A. H.; Long, C. M.; Millar, D.; Patel, S.; Pellow, M. A.;
Saddoughi, S. A.; Smenton, A. L.; Turner, J. F. C.; Wadhawan, J. D.; Compton, R. G.;
Golen, J. A.; Rheingold, A. L.; Doerrer, L. H. Inorg. Chem. 2004, 43, 7709-7725 (b) Burke,
P. J.; Matthews, R. W.; Gillies, D. G. Dalton Trans. 1980, 1439-1442 (c) Candy, C. F.;
Jones, R. A.; Wright, P. H. J. Chem. Soc. C 1970, 2563-2567. (d) Candy, C. F.; Jones, R. A.
J. Org. Chem. 1971, 36, 3993-3994 (e) Sidgwick, N. V.; Sutton, L. E. J. Chem. Soc. 1930,
1461-1473

19) Swartz, D. S. II; Staples, R. J.; Odom, A. L. Dalton Trans. 2011, 40, 7762-7768

20) Rose, T. L.; Kon, A. B. Inorg. Chem. 1993, 32, 781-782
21) Krygowski, T. M.; Cyrański, M. K. Chem. Rev. 2001, 101, 1385-1419

54

22) (a) Anderson, H. J.; Bauer, L. J. Chem. Educ. 1999, 76, 1151 (b) Katrizky, A. R.; Karelson,
M.; Sild, S.; Krygowski, T. M.; Jug, K. J. Org. Chem. 1998, 63, 5228-5231

23) Fleckenstein, J. E.; Koszinowski, K. Organometallics 2011, 30, 5018-5026

24) Anderson, R. A.; Wilkinson, G. J. Chem. Soc. Dalton 1977, 809-811

25) Song, J. I.; Berno, P.; Gambarotta, S. J. Am. Chem. Soc. 1994, 116, 6927-6928

26) Seyferth, D.; Rochow, E. G. J. Org. Chem. 1955, 20, 250-256

27) Hollingworth, G. J.; Perkins, G.; Sweeney, J. J. Chem. Soc., Perkin Trans. 1996, 1, 19131919

28) (a) Rasmussen, K. G.; Juhl, K.; Hazell, R. G.; Jorgensen, K. A. J. Chem. Soc. Perkin Trans.
II 1998, 1347-1350 (b) Doolan, P. C.; Gore, P. H.; Hollingsworth, R.; Waters, D. N.; AlKa’bi, J.; Farooqi, J. A. J. Chem. Soc. Perkin Trans II 1986, 501-506

29) Butcher, E.; Rhodes, C. J.; Standing, M.; Davidson, R. S.; Browser, R. J. Chem. Soc. Perkin
Trans. II 1992, 1469-1474

30) Tolman, C. A. Chem. Rev. 1977, 77, 313-348

31) Collier, M. R., Lappert, M. F.; Pearce, R. J. Chem. Soc. Dalton Trans. 1973, 445

32) Schrock, R. R.; Fellmann, J. D. J. Am. Chem. Soc. 1978, 100, 3359-3370

33) Li, J.; Zhang, K.; Zhang, X.; Chi, C.; Wu, J.; Huang, K. W. J. Org. Chem. 2010, 75, 856-863

34) Miller, M. J.; Lyttle, M. H.; Streitwieser, A. J. Org. Chem. 1981, 46, 1977-1984

35) http://home.cc.umanitoba.ca/~budzelaa/gNMR/gNMR.html, 8/23/2010

55

Chapter 3: Kinetic Experiments and Discussion of the Results
3.1: Overview of Kinetics Experiments
The kinetics for this project concern the dynamic rotation of the amido ligands on the
chromium nitrido complexes. Measuring the barrier of amido rotation using NMR is a developed
science. For example, the measured barrier of rotation of N,N-dimethylacetamide (DMA) by
1

2

3

4,5

various NMR techniques, such as SSMT, CLSA, and EXSY is 73 ± 5 kcal/mol.

The use of

these techniques is dependent on the rate of exchange. Shown in Figure 3.1, slow exchange on
6

5

the NMR timescale for two site exchange in a simulated spectrum appears as two separate
peaks. Fast exchange causes the two peaks to coalesce into one peak.

5

Figure 3.1: Simulated NMR spectra of two sites exchanging at different rates
56

The majority of our chromium nitrido complexes fall in the slow exchange regime at
room temperature. Due to this phenomenon, the technique most suited for our compounds to
measure the exchange on the amido ligands is SSMT, with one expection. CLSA was used on
i

NCr(N Pr2)2NMe2 (31) because the exchange limit was too fast to measure using SSMT on our
current instrumentation.
But before the experiment can be performed a few parameters for the experiment must be
7

determined to allow for reliable data collection. An accurate 90° pulse width of the exchanging
peaks is needed because this will give better signal for our peaks, which results in a more reliable
T1. Using the 90° degree pulse width, T1 is then determined by the inversion-recovery
8

experiment. Once these have been determined, the spin saturation experiment can begin. Below
is a description on preparation of the sample, a detailed discussion on T1, and a description of the
SSMT experiment.

3.1.1 Preparation of the Sample
The sample was weighed out so the concentration is between 0.0222 M and 0.0333 M.
Then 0.075 mL of CDCl3, d-toluene or d-benzene was added to the weighed sample and loaded
into a JY tube. The sample was taken out of the glovebox and freeze-pump-thawed to remove
any dissolved oxygen or gases. This is important because the presence of dissolved gases such as
oxygen can shorten T1s, which may affect our measurements.

57

9

3.2 Measuring T1s and apparent T1s of exchanging resonances.
In spin saturation magnetization experiments involving exchange between two sites, the
rate is determined by the ratio of the fractional decrease in integration of one site in the presence
of saturation of the other to its T1. In a system experiencing two site exchange (Figure 3.2), the
relaxation of spins for peak A is dependent on the rate of decay from the excited state A* to the
ground state A; the same is true for peak B. When T1A = T1B, the source of relaxation is the
1a,c

same. In this case, the T1 of the peak experiencing exchange is measured without saturation.

But if T1A and T1B differ by more than 30% or if more than two peaks are experiencing
exchange, the T1 of the peak experiencing exchange in the presence of saturation is measured
10

and is known as the apparent T1.

k
A*

B*
k

1

1

T1A

T1B
k
A

B
k

Figure 3.2: Kinetic scheme for two site exchange
In our chromium nitrido system, both T1 and apparent T1 of the septet corresponding to the
i

isopropyl methyne hydrogens were measured. For example, in NCr(N Pr2)2I (2) these septets
appear at 5.32 and 3.78 ppm (Figure 3.3). The deshielded peak was chosen for saturation.

58

1

i

Figure 3.3: H NMR spectrum of NCr(N Pr2)2I (2) at 25 °C
This peak was chosen because the control experiment that compensates for decoupling sidebands
would not saturate other peaks that could affect exchange. Data for both the T1 and apparent T1
of the peak at 5.32 ppm are shown below for 2. The relationship between T1 and apparent T1
(T1app) is:

T1app

M zA (∞)
= A
T1 Eqn. 1
M z (0)

where Mz(∞) is the intensity (or integrated area) of the resonance upon saturation (applied for, at
least, 5 × T1) of the exchanging site and Mz(0) is the intensity of the resonance with no
saturation.

59

Figure 3.4: T1 and apparent T1 of 2 at different temperatures
At 285 K and below, 2 does not experience exchange of the isopropyl groups on the
NMR timescale as seen by the lack of change in chemical shifts and linewidths of the
exchanging sites. At this extreme, Equation 1 simplifies to T1app = T1. This was observed in
our experiments. Above 335 K, exchange is fast on the NMR timescale (k >> δa – δb) and
individual peaks are not observable. In the temperature regime where the exchange can be
measured, T1 increases with temperature. The opposite is observed for T1app, as expected from
Equation 1. This data tells us that only the measurement of the T1 and not T1app is required for
the kinetic study. T1app is only measured when the two exchanging peaks have T1s that differ by
more than 30%.

10

60

For all of the chromium nitrido compounds, their NMR spectra show two septets that
represent

the

methyne

protons

on

the

N

HA

HB

groups.

N

HB

Cr
N

isopropyl

Cr

X

HA

N

N

HB

X
N

HA

HB
HA

Figure 3.5: Amido rotation and exchange of equivalent methyne peaks
Protons HA and HB shown in Figure 3.5, are in two different chemical environments. For
the chromium complex on the left, HA is syn to the nitrido and HB is anti to the nitrido. As the
diisopropyl amido ligands rotate about the chromium-nitrogen bond, protons HA and HB
1

i

12

exchange positions. The H NMR spectrum of NCr(N Pr2)2I

in Figure 3.3 has two septets and

four doublets. Since these peaks are inherent in all of our series, understanding the orientation of
the diisopropyl amido peaks will help us make sure we are doing the correct measurements and
know what we are doing in our kinetics experiments.

61

Figure 3.6: 2D NOESY spectrum of 2 at –60 ºC
62

Assignment of the chemical shifts for HA and HB of 2 are based upon the 2D NOESY
spectrum (Figure 3.6). In the spectrum, positive resonances are in red, while negative are in
blue. Thus, for this small molecule, red cross peaks represent exchange and blue cross peaks
represent NOE’s.

11

The blue arrows on the structure show observed NOE interactions between

the methyne and methyl protons. The resonance at 3.83 ppm is assigned to HA since it shows
NOE interactions with all four methyl resonances. HB is assigned to 5.35 ppm and has two NOE
interations. The spectrum in Figure 3.6 is of 2 at –60 ºC, where no exchange between the
methyne peaks occurs. There is free rotatation about the N—C bond bearing HA allowing
interaction with all methyl groups. HB cannot rotate as freely and does not come within the NOE
limit of 5 Å. Furthermore, it is plausible that since HB spends more time closer to the metal
center, it experiences a greater downfield shift due to the deshielding zone of the metal center. A
homo decoupling experiment also confirms assignment as shown in Figure 3.7.

Figure 3.7: Homo-decoupling experiment of 2 at 25 ºC

63

3.3 Spin Saturation Magnetization Experiment
In the spin saturation magnetization transfer experiment, the more shielded methyne is
saturated with a radio frequency pulse, while the change in the integration in the more deshielded
peak is observed. To account for spill over, an offsite point equidistant from the exchanging peak
is saturated. The reason for choosing the right peak for irradiation is because the offsite point
cannot be on or near a peak that is experiencing exchange with the observed peak. As shown in
Figure 3.7, the septet at 3.53 ppm and the doublet at 1.85 ppm are coupled, and if the doublet
was irradiated it could transfer some of its magnetization over to the septet giving erroneous
results. In Figure 3.8, the spectrum on the bottom is the end result of saturation; the height and
area of the observed peak experiencing exchange will depend on how much exchange is
occurring.

1

1

Figure 3.8: The top H spectrum is of 2 before irradiation and the bottom H spectrum is after
irradiation.

64

The saturation pulse sequence shown in Figure 3.9 illustrates why an accurate T1 is
required for the experiment. The saturation delay (satdly) is set to 5 × T1. If satdly is too short,
T1 will have time to relax, resulting in a larger peak, and give unreliable data.

Figure 3.9: Presat pulse sequence
In Figure 3.2, [A] and [A*] are the ground and excited spin-state populations for site A
(or peak), and [B] and [B*] are the ground and excited spin-state populations for site B (or peak)
13

for a site experiencing two site exchange.

T1A and T1B are the spin lattice relaxation times and

k is the rate constant for exchange between site A and B.
d[A] = -k [A] + k [B] = -d[B]
dt
dt

Eqn. 2

d[A*] = -k [A*] + k [B*] = -d[B*]
dt
dt

Eqn. 3

Equations 2 and 3 are the rate equations for ground and excited spin states without spin-lattice
relaxations.
M - MA
dMA
= OA
T1A
t
d

M - MA
dMB
= OA
T1B
t
d

Eqn. 4 and 5

In Equations 4 and 5, MA = [A] – [A*] and MB = [B] – [B*] are the net-magnetizations between
exchanging sites A and B. And MOA and MOB are net magnetization at equilibrium.

65

dMA -k M - M + MOA - MA
= ( A
B)
T1A
dt

Eqn. 6

MOB - MB
dMB
= k (MA - MB) +
T1B
dt

Eqn. 7

Combining Equations 2, 3, 4, and 5 gives Equations 6 and 7, which are the rate equations for net
magnetization in the presence of chemical exchange and with spin lattice relaxation processes.
When T1A and T1B are close in value, then T1A = T1B = T1. The rate of exchange is the same
for both exchanging sites.
If site B is selectively irradiated without affecting the nearby exchanging peak, the
population difference between the ground and excited spin states will be equal to 0. MB = [B] –
[B*] = 0 and the signal will be absent from the NMR spectrum (see Figure 3.8) giving Equation
8.

MOA - MA
dMA
= -k (MA - 0) +
T1A
dt

Eqn. 8

The saturated spin-state in site B will transfer to site A through internal rotation or
exchange and result in a reduced signal of site A, or peak in our experiment. The intensity of
signal will vary depending on rate of exchange. The faster the exchange the smaller the peak and
the slower it rotates, the larger the peak. If the sample is cooled to the point where the rotation is
frozen out, an NOE will occur instead of exchange.

14

If saturation is long enough to reach steady

state, then dMA/dt = 0 giving Equation 9.
‡

Once all of the data has been collected the ΔG barrier of rotation can be calculated using
15

the Eyring Equation.

Integration of the observed peak with (MA) and without (MOA)

66

saturation was performed and used to determine the rate of exchange between the methynes
using Equation 9.

k=

1 MOA
-1
T1A MA

Eqn. 9

Where MOA is integration before spin saturation magnetization transfer and MA is after
integration after exchange. Then the T1 of the exchanging peak was determined using the
inversion recovery method. By knowing the temperature of the experiment, the barrier of
rotation of the amido can be determined using the Eyring Equation shown in Equation 10.

-∆G/RT
k = κ k bT exp
h

Eqn. 10

Where kb is the Bolztmann constant, T is temperature (K), h is Planck’s constant, κ is the
transmission coefficient and in this case it equals 1, k is the rate of exchange determined using
-3

-1

-1

Equation 9 and R is the gas constant (1.987×10 kcal·mol ·K ).
In the SSMT experiment, 3 runs were collected at one temperature, or as close as possible
to one temperature allowed by the instrumentation. Unfortunately, the temperature deviated ±1

ºC,

while in a few cases by as a much as 5 ºC. Temperature was measured by a methanol
16

standard.

67

3.4 CONTROL EXPERIMENTS:
‡

3.4.1 Investigation of Solvent Effects on T1 and ΔG

A series of control experiments were performed to investigate the techniques for sources
of error. To see if the solvent had an effect on the T1 values, four different SSMT experiments
were run using d-toluene, d-benzene, and CDCl3 solvents and gave similar energy barrier
numbers that fell within the error bars. Comparison of our SSMT value of 16.1 kcal/mol for 9
with literature is in good agreement, 16.0 kcal/mol.

18

Our value was determined in CDCl3, while

the one in the literature was determined in d-benzene. Compound 1 was studied in CDCl3 and dtoluene, because the compound, 31, had to be cooled to –80 ºC where CDCl3 would freeze. For
‡

31, the solvent chosen was d-toluene. The ΔG values 13.1 and 12.8 kcal/mol in CDCl3 and dtoluene, respectively, were determined for 1. Although, these results suggest that solvent
interactions play little to no role in the experiment; a more polar deuterated solvent was not
tested, which may coordinate to the chromium center and affect the barrirer of rotation or affect
the transition state of rotation of the amido ligands.

17

‡

3.4.2 Investigation of Magnetic Field on T1 and ΔG

To see if the field had an effect on the barrier of rotation, SSMT on 2 was performed on
both a 500 MHz and a 300 MHz Varian NMR instrument. The results showed similar values:
18.2 and 18.3 kcal/mol, respectively.

68

‡

3.4.3 Investigation of Paramagnetic Materials on T1 and ΔG

18

Paramagnetic materials in solution are known to hasten the spin lattice relaxation T1.

Since the rate is very sensitive to the T1 value, the barrier of rotation calculated could give
misleading results. In one experiment, we ran SSMT on 2, and in another experiment doped the
sample with Cr(acac)3, a paramagnetic compound often used to speed up relaxation times.

19

Table 1: Data from paramagnetic doped experiment of 2
‡

MOA

MA

T1

ΔG (kcal/mol)

Temperature

Pure Sample

100

76.1

1.082

18.3

27.5 ºC

Doped Sample

100

89.8

0.4393

18.5

28.4 ºC

Run

‡

As indicated in Table 1, the T1 for the pure sample is 1.082 and ΔG is 18.3 kcal/mol.
‡

The T1 for the doped sample was about twice as fast, 0.4393, but ΔG was 18.5 kcal/mol.
Essentially, the paramagnetic dopant affected the T1 and exchange relaxation equally. So, if
‡

there were samples that contained even a small percentage of paramagnetic materials the ΔG
values obtained are well within the error of the experiment.
i

i

3.5: CLSA and Eyring Plots of NCr(N Pr2)2NMe2 (31) and NCr(N Pr2)2OAd (6)
Due to the temperature limit of –80 ºC on current NMR instrumentation, we could not
obtain the two well resolved septets required for the SSMT experiment for 31. In this case

69

2

CLSA was used, and a barrier of 9 kcal/mol was obtained. A sample of spectra from the CLSA
experiment is shown in Figure 3.10 for compounds 31 and 6.

Figure 3.10: Simulated and experimental spectrum of 31 (top) and 6 (bottom)
To determine if numbers from complete line shape analysis agree with spin saturation
transfer experiments, complete line shape was performed on 6. The barrier to rotation determined
by CLSA was 12.7 kcal/mol, and the value found using SSMT was 12.8 kcal/mol.

70

‡

‡

‡

3.6 Discussion of ΔG , ΔH , and ΔS and Ligand Donating Parameter
‡

The ΔG barrier to rotation is the amount of energy in the system that has to be overcome
for the diisopropylamido ligand to rotate. Rotation about the diisopropylamido ligands is
dependent on temperature due to the entropy factor.Thus, six different compounds spread over
‡

i

the series were investigated to extract ΔS from Eyring plots. Chosen were NCr(N Pr2)2I 2,
i

NCr(N Pr2)2CN

i

(30),

NCr(N Pr2)2O-p-(SMe)C6H4

i

(12),

i

NCr(N Pr2)2OBn

i

(20),
‡

NCr(N Pr2)2OAd (6), and NCr(N Pr2)3 (1) to see the effect of sterics and temperature on ΔS .
Table 2: Data from Eyring plots for selected chromium compounds in CDCl3
‡

‡

‡

ΔG
ΔH
ΔS
Compound (kcal/mol) (kcal/mol) (cal/mol·K)
18.6 ± 0.3
15.8 ± 0.3
-9.4
2
16.9 ± 0.6
12.4 ± 0.4
-16.4
30
14.5 ± 0.6
13.6 ± 0.3
-3.3
12
13.2 ± 0.8
11.9 ± 0.3
-6
20
12.8 ± 0.4
10.5 ± 0.3
-10
6
13.1 ± 0.8
11.6 ± 0.3
-5.1
1
b
1
12.8 ± 0.6
12.4 ± 0.3
-1.6
a
The temperature range of the data points for the Eyring plots
b

Temp.
(K)
302
274
245
217
233
226

Temp
a
Range
47
37
43
36
30
27

229

30

Thermodynamic data extracted from experiment performed in d-toluene
Table 2 shows thermodynamic terms for each compound in CDCl3. Caution must be
‡

taken as the temperature ranges are quite narrow for both runs and since ΔS is extrapolated from
21

the fit the errors are quite large.

Eyring plots for the selected compounds are in the selected
‡

text and figures section B1. The value -9.0 cal/mol·K was chosen for ΔS for all of the
compounds because that number from Iodide is the largest temperature range and had the least

71

‡

amount of error. The only exception was 31, where the ΔS = –4.1 cal/ mol·K came from the
LSA data.

72

i

Figure 3.11: LDP (kcal/mol) values of NCr(N Pr2)2X and the associated error

73

Table 3: Values for LDP (kcal/mol) for 1-41
X=

LDP

NMe2 (31)
OAd (6)
N(Me)Ph (27)
i
NPr 2 (1)
OBn (20)
Carbazolyl (26)
O-p-(OMe)C6H4 (11)

9.34 ± 0.32
10.83 ± 0.24
10.86 ± 0.23
11.12 ± 0.23

a

11.15 ± 0.23
12.04 ± 0.25
12.14 ± 0.24

t
O-p-( Bu)C6H4 (13) 12.18 ± 0.25
OPh (10)
12.38 ± 0.25
O-p-(SMe)C6H4 (12) 12.51 ± 0.26
12.64 ± 0.23
O-p-(F)C H (14)
6 4

O-p-(Cl)C6H4 (15)

12.81 ± 0.23

O-p-(CF3)C6H4 (16)

13.00 ± 0.28

CCSi Pr3 (39)

13.19 ± 0.25

OSiPh3 (7)
OPht (18)
F (33)
Indolyl (25)
t
CC Bu (40)

13.28 ± 0.27

CH2SiMe3 (35)

13.71 ± 0.27

CH2CMe3 (38)

13.78 ± 0.27

CH2Si(Me)2Ph (37)

13.79 ± 0.28

O BuF6 (9)

13.89 ± 0.26

CH2C(Me)2Ph (36)

13.96 ± 0.26

NO3 (21)
Pyr (22)
SPh (19)
OC6F5 (17)

14.15 ± 0.29

Pyr

14.33 ± 0.28

i

13.35 ± 0.23
13.39 ± 0.27
13.40 ± 0.25
13.62 ± 0.27

t

Pyr

C6F5

14.16 ± 0.28
14.22 ± 0.27
14.32 ± 0.28

(23)

C6H3(CF3)2

(24)

CN (30)
O2CPh (8)
NCO (28)
NCS (29)
Cl (3)
Br (4)

14.36 ± 0.28
14.40 ± 0.27
14.45 ± 0.28
14.51 ± 0.29
14.86 ± 0.30
15.05 ± 0.29
15.45 ± 0.30

74

Table 3 (cont’d)
OTf (5)
I (2)
b
HMPA (34)

15.75 ± 0.29
15.80 ± 0.30
16.76 ± 0.30

(OPh)2 (41)

16.86 ± 0.32

DMAP (32)

16.94 ± 0.27

b

a

value determined in d-toluene
b

counter ions

Foremost, compounds 2, 3, 4, 21, 28, 29, 30, and 33 descend in order of donating ability,
which follows the same trend seen in the spectrochemical series

22

of the same compounds.

Unfortunately, it is not known whether σ or π donations dominate in bonding.
Looking at the carbon bound donors, the LDPs are within error of each other, have a
3

narrow range, and follows the general trend of going from sp to sp agrees with stronger M—C
bonds with increasing s-orbital participation. The bond distance between carbon and chromium
3

for the alkynyls 39 and 40 is 1.996 and 1.978 Ǻ respectively, much shorter than the sp -bound
i

i

carbons which range from 2.041 to 2.085 Ǻ. It is not known why NCr(N Pr2)2CCSi Pr3 (39) is
i

t

2

significantly different from the alkyls but not NCr(N Pr2)2CC Bu (40). Unfortunately, no sp bound carbon donors could be synthesized at this point in time. All routes led to decomposition,
1

12

and H NMR showed products of β-hydride elimination.

The pyrrolyl complex (22) and its derivatives show interesting and broader range of
1

donor properties. For all cases, both H NMR and x-ray diffraction confirm that pyrrole is bound
75

1

η through the nitrogen. Pyrrolyl was a far poorer donor than indolyl, which was a poorer donor
than carbazolyl. This is consistent with the expected availability of the nitrogen lone pair for
donation in these particular heterocycles. The pyrrolyl ring’s aromaticity depends upon the
nitrogen lone pair to reach the 6 π-electrons required by the Hückel rule for aromaticity. As a
consequence, the aromatic stabilization energy of pyrrole directly competes with π-donation,
23

which leads to pyrrole being a poorer π-donor.

For indolyl and even more so for carbazolyl,

the aromaticity of the 5-membered heterocycles must compete with the 6-membered
24

carbocycle(s) in resonance form contributions to the aromaticity.

As a result, the nitrogens in

indolyl and carbazolyl seem to donate more strongly to the metal center than pyrrolyl because of
the greater availability of their nitrogen-based lone pairs.
As for the substituted pyrrolyl ligands 23 and 24, the LDP numbers are within error of
pyrrolyl 22. A recent study demonstrated that electron withdrawing groups on pyrrole ligands
25

bound to a titanium center had faster rates of hydroamination that were significantly different.

This suggests that our system isn’t sensitive enough to small differences of LDP between very
similar ligands.
Small differences in donor ability can also be seen with the para-substituted phenoxide
series. Only two phenoxides have LDPs significantly different, O-p-(CF3)C6H4 (16) and O-p(OMe)C6H4 (11), whereas the rest overlap in between. Looking at the series, the trend indicates
that more electron-withdrawing groups in the para position the worse of a donor the phenoxide
becomes. The effect of having more electron-withdrawing groups on the phenyl ring is more
pronounced in the pentafluorophenoxide ligand (17), where the LDP is 14.32 kcal/mol.

76

The strongest donors appear to be the alkoxides and amides. Changes in the electronwithdrawing groups bound to the β-carbon can cause the oxygen of alkoxides to become a very
t

poor donor as in the case of O BuF6 (9). Change in the β-element from carbon to silicon, as in
going from adamantoxide (6) to triphenylsiloxide (7), also results in a higher LDP. Silicon is
26

known to be Lewis acidic and could be π accepting from the oxygen lone pairs.

In the case of

the amides, differences in the LDP may be more likely due to steric interactions. This difference
will be discussed in more detail in Section 3.7.
Of interest to our group is how our system compares anionic to neutral donors. Neutral
donors especially DMAP and HMPA have higher LPDs than most of ligands, although it is not
yet known what affect the presence of a counter ion has on our measurements. More studies are
on their way to follow up these questions.
In an attempt to place a tin alkyl onto the phenoxide, a ligand swap occurred and formed
a bis(phenoxide) chromium nitrido complex 41. Although, this complex has been synthesized
and structurally characterized,

18

it was of interest to compare it with the rest of the series. With

an LDP of 16.86 kcal/mol, it appears to be a worse donor. Replacing the second
diisopropylamido ligand with a worse donor should cause the remaining diisoproplyamido to
donate more strongly, hence a higher barrier of rotation.
As an interesting note, the T1 values for the two peaks corresponding to the methynes
differed by 36% requiring the use of the apparent T1. Caution must be taken for this number
because only one run was performed and the entropy for this compound may differ from the

77

current system with two amido ligands. Further study is needed, but this demonstrates that monodiisopropylamido complexes can be studied with our system.

3.7 Sterics Investigation using Percent Buried Volume and Solid G
As one can imagine, the donor ability of a ligand can be affected by its size and shape.
Investigation of sterics by Tolman’s cone angle

27

provided researchers with valuable

information for optimization of catalysts. Although the cone angle is useful for comparing steric
interactions for phosphines, it fails when applied to more encompassing ligands such as NHCs
29

or pincer ligands.

28

In our study, sterics was investigated using two different parameters: Percent

Buried Volume (%Vbur)

30

31

and Solid G.

Figure 3.12: Space filling model of chloro 3 (left) and indolyl 25 (right) inscribed in a sphere
that shows a radius of 3.5 Ǻ
To determine %Vbur of the ligands, crystallographic bond distances and angles were
30

entered into SamVca, a web-based utility developed by Cavallo and co-workers.

A sphere

encompasses the molecule starting from the metal center with a radius of 3.5 Ǻ, which is the
default radius set by the program, shown in Figure3.1.

78

Figure 3.13: The %Vbur for the ligands in this study. Values are for the percentage volume
occupied by the ligand in a sphere of radius 3.5 Ǻ from the chromium center.

79

Solid G treats the metal center as a point source of light and projects the shadows of the
31

ligands onto a sphere larger than the molecule.

An example of the Solid Angle Model is shown

in Figure 3.14 for indolyl 25, where the molecule is in a similar orientation as in the right of
Figure 3.12. The Solid Angle Parameters for the series of X ligands are shown in Figure 3.15.
The x-axis values are in percentage of the sphere occupied by the X ligand.

Figure 3.14: The Solid Angle Model from the Solid G program for 25 with indolyl (green),
diisopropylamido (yellow and blue), and nitrido (red)

80

Figure 3.15: The percentage of the chromium coordination sphere shielded, GM(L), from the
Solid G program for the ligands used in this study.

81

There are obvious differences in how the two methods, %Vbur and Solid Angle, describe
the sterics in the chromium system. For example, the phenoxides and halides change order
within the series between the two methods. The pyrrolyl ligands go from being very large in
%Vbur to less sterically encumbering in Solid Angle. The perspective changes depending on the
method used, but the amido ligands show the same trend in both methods. Smaller sterics may
explain why the dimethyl amido is a much better donor than the bulkier diisopropylamido
ligands.
Likewise, there is no obvious correlation between the donor abilities of the donor ligands
with bond distances. For the chromium nitrido distance, the distance is similar for all of the
complexes measured so far. For example, the nitrido distances in the poorly donating triflate 5,
strongly donating and relatively small benzyloxy 20, and the large diisoproplyamido 1 were
found to be 1.543(3), 1.543(2), and 1.544(3) Ǻ, respectively. The Cr—N (nitrido) values range
from 1.524(3) in nitrate (21) to 1.553(4) in O-p-(CF3)C6H4 16 for the whole series.
Steric factors seem evident in the tris(diisopropylamido) complex 1 according to other
data (vide infra), but it is difficult to discern this from the X-ray diffraction studies alone. The
average Cr—N (amido) distance in the published structure for 1 is 1.842(3) Å. This distance in 1
is somewhat larger than many of the derivatives prepared. For example, the average Cr–
N(diisopropylamido) distances for a few derivatives are: Cl 3 1.813(2), OBn 20 1.823(1), OAd 6
1.822(7), N(Me)Ph 27 1.830(2), and OTf 5 1.805(3) Å. However, the average diisopropylamido
distance in 1 is very much in line with the sterically less encumbered NMe2 31 with average Cr–
N distances of 1.842(4) Å; incidentally, 31 was one of the compounds examined that displayed
full molecule disorder in the X-ray diffraction experiments. The disorder was fully modeled.

82

3.8 Comparison with the Literature
3.8.1: LDP versus pKa Values of HX Compounds
How does our LDP compare with the literature? Many organometallic chemists gauge
donor ability by checking the pKa of the free ligand. This quick check is reasonable in that a
stronger acid, lower pKa, will lose a proton better because the electrons in the conjugate base are
more stable and donate less electron density. Whereas, a weaker acid, higher pKa, has a stronger
conjugate base that is less stable, therefore, has more electron density to donate.
33

of pKa in water

with LDP of the ligands is shown in Figure 3.16.

Figure 3.16: Plot of pKa in water versus LDP

83

32

Comparison

As seen in Figure 16, pKa is at best a rough estimate for donor ability. Contributing
resonance forms of a ligand that affect the pKa also affect donor ability. An explanation for why
pKa does not correlate very well with LDP is that a proton bound to the ligand doesn’t have πorbitals to accept electron density from the lone pairs on the ligand, while chromium does.

3.8.2: LDP of Phenoxides versus Hammett Parameters
Hammett parameters are a proven method for evaluating electronic effects in aromatic
systems. By studying the reaction rates and equilibrium constants of para and meta-substituted
benzoic acid derivatives, the donating effect of the group in the para and meta position can be
determined.

34

We were interested in seeing how the σp of para-substitution would correlate with

the substituted phenoxides.

Figure 3.17: LDP versus Hammet parameters of the para-substituted phenoxides

84

In Figure 3.17, LDP is compared to the Hammett σ parameter for para-substituted
phenoxides. With the exception of 11 and 16, phenoxides have LDP parameters that are within
error of each other. The series of LDP versus the Hammett Parameters (σp) for the substituents
reveals a linear correlation. This suggests our system has the ability to determine electronic
effects on ligands.

3.8.3: LDP versus

13

C NMR Chemical Shifts in Tungsten Metallacycles

In the past our group published a paper where a tungsten metallacycle was prepared to
35

investigate carbonyl olefination.

It was observed that the W—C bond would range between

double bond and single bond depending on the X ligand bound to tungsten. Changes in the X
ligand directly affected the

13

C NMR chemical shift of C1, suggesting two contributing

resonance forms occurring in the metallacycle (see Figure 3.18).

Ar

Ar
N
X

N

C1

X

W

X
Ar

X

N

Ar

C1

W
N

Ar = 2,6-di(i so-propyl)phenyl
X = OEt, O-p-(OMe)C6H4, OC6F5, Cl, OTf/Cl
Figure 3.18: Alkylidene-imine (left) and alkyl-amido (right) resonance forms

85

Figure 3.19: Alkylidene shifts of C1 carbon versus LDP
Unfortunately, the paper only covered the synthesis and investigation of five compounds.
But, there is good correlation between the X ligands studied using the

13

C NMR chemical shifts

in the tungsten system and the LDP values of our chromium system. Although, we did not study
a ligand containing an ethoxy group, we substituted the LDP value from OBn (20). Also, one
tungsten metallacycle contained a mixture of Cl and OTf as ligands. In this case, we averaged the
LDP values for Cl (3) and OTf (5).

86

3.8.4: LDP versus AOM Parameters of Cr(III) Complexes

Figure 3.20: Plot of experimentally determined eσ + eπ values for Cr(III) complexes versus LDP
Donor properties of ligands can be determined using visible absorption spectroscopy to
assign energy transitions. These values can be parameterized as σ and π donor energies, eσ and eπ
36

respectively, using the Angular Overlap Model (AOM).

There is a strong correlation shown in

Figure 3.20 of AOM parameters versus LDP, but only when combining both σ- and π- effects.

3.8.5: LDP versus Values from Electronic Spectra of Cp*2TiX Complexes
In 1996, Lukens, Smith, and Andersen

37

reported a “π-donor spectrochemical series for

X” in Cp*2TiX titanium-(III) compounds with a large number of X ligands. The study employed
1

EPR and absorption spectroscopy to elucidate the electronic structure of d titanium complexes.
Of specific interest in the context of this paper, Andersen and coworkers reported a singly

87

occupied a1 to b2 energy gap, which “depends directly upon the π-donor ability of X”. Mach and
38

coworkers have since extended the system to include additional alkoxide ligands.
A plot of the energy gap, a1 (approximately nonbonding)

38

and the b2 π-antibonding

orbital (∆Exz) in Cp*2TiX Andersen complexes versus LDP for all X in common between the
two studies is shown in Figure 3.21 (blue and red circles). In the case of X = OMe, the value for
∆Exz was correlated with the LDP value for 20 in the plot (blue line). The obvious outlier is X =
N(Me)Ph (red circle), which is well away from what seems to be a linear correlation between the
Cp*2TiX spectroscopic data and LDP. Andersen and coworkers centered much of their
discussion on the differences between X = N(Me)Ph and the other compounds, and this is quite
obvious in Figure 3.21 as well. Also plotted in Figure 3.21 are Mach’s data (green squares) on
t

Cp*2TiX, where we used our X = OAd data for their X = O Bu example.

88

–1

Figure 3.21. Plot of ∆Exz in wavenumbers (cm ) [Andersen data
38

Mach’s data

37

(red and blue squares),

(green squares)] versus LDP (kcal/mol) for X. For the data represented by circles,

methylcyclohexane was the solvent. The data represented by green squares were taken in either
hexane or toluene. The data for X = NPh(Me) was not used in determining the linear fit to the
Andersen data (blue line)
There are indications that the X = N(Me)Ph in Cp*2TiX has little or no π-effects to the
nitrogen; although there are indications of agostic effects to the methyl.

41

In the structure from

X-ray diffraction, the Cp*(centroid)–Ti–N–Me average dihedral in the X = N(Me)Ph complex is
86.9°. In other words, the large N(Me)Ph ligand rests in the plane bisecting the Cp*-Ti-Cp*
unit, and the nitrogen lone pair is orthogonal to the empty orbital of appropriate symmetry to act

89

as an acceptor. Consequently, the experimental Ti–N bond distance is quite long at 2.054(2) Å.
30

This is similar to Ti–N(pyrrolyl) distances,

usually a much weaker donor than N(Me)Ph (vide

supra). This distance is also much closer to the Ti–N single bond distance of 2.07 Å than the
39

Ti=N distance of 1.77 Å using Pyykkö’s radii.

In contrast, Ti–NMe2 distances, where there is

40

a strong dative π-bond, are typically ~1.90 Å.

It can be concluded that the lack of correlation for X = N(Me)Ph is due to a deficiency of

π-bonding in the Cp*2TiX system due to steric effects that do not allow the amido to reach the
electronically preferred geometry, as readily seen in both the X-ray diffraction study and in
correlations with LDP.
The exact cause for the two different slopes of the Andersen and Mach data is unknown;
however, there are several small differences in the data sets, solvents, slightly different
instrumentation, and possible differences in concentration. In addition, the Andersen data are
relative to Cp*2TiH as ∆Exz = 0, and we did not adjust the baseline in the Mach data similarly.
If the data from the two groups are taken all together and linearly fit, the line obtained is y =
2

2

20761 – 1205x with a much worse R of 0.93 versus the R = ~0.99 obtained fitting the data
from the two groups independently. This fit for Mach’s data is for only four points from the four
new alkoxides in common between our study and Mach’s reports. In addition, one of the four
points was done with a substitution in the LDP value, tert-butoxide for 1-adamantoxide.
Overall, the LDP correlate fairly well with the Cp*2TiX spectroscopic data in cases
where steric effects are not apparent, i.e., all X ligands in common between the two studies
except for where the X ligand is an amido derivative.

90

3.9 Conclusion
We have shown the versatility of our system. We can look at the donor properties of
ligands that are anionic donors with and without lone pairs and neutral donors. Such a broad
scope allowed us to compare ligands within a series, such as amides or phenoxides, and different
ligands, such as halides versus alkoxides. These types of single parameter studies should not
replace full mechanistic and computational studies for systems; instead this is a quick technique
that will hopefully be useful for the discussion of properties and mechanisms for metal
complexes in low d-electron counts.
We have demonstrated that there is good correlation with AOM, Anderson’s data, and
Hammett parameters. Although, there was poor overlap with pKa, our series appears to give
insight into the donor properties of ligands and perhaps will be useful to research groups
interested in catalyst design. Using steric parameterization, such as %Vbur and Solid G, may be
required to gain a good understanding of the sterics in a system and they may impact donor
ability. If another system under study does not correlate at all with LDP, there is any number of
possible explanations ranging from differences in ligand donor properties, differences in metal
acceptor properties, steric interactions, or simply a lack of correlation of the property being
measured with ligand donor ability.
There are many avenues to explore with this system. The synthetic method used to
synthesize the two neutral donors, DMAP and HMPA, should also work for placing phosphines
and NHCs onto the chromium center. If that is possible, then we could see how the LDP of our
27

ligands compare with the Tolman Electron Donating parameter.

But understanding the effect

of the counter ion in the SSMT experiment is still under investigation. It would also be of interest

91

to see how the change in the metal affects the LDP of the ligands. Changes in orbital overlap
may have a pronounced effect on the donor properties of the ligands.
The synthesis and study of 41 demonstrates the potential for studying the donor
properties of bidentate or two different mono-anionic ligands with our chromium system. It
would be of interest to see how sterics, ring strain, and conjugation on the metallacycle formed
by the bidentate ligand affect LDP. Of special interest would be investigation of bidentate
ligands that have a neutral and anionic donor component.
Parameterizations similar to ours have been successful in explaining reaction mechanisms
and trends in activity. For example, Basolo, Pearson, Burdett, and many others used AOM to
explain reactivity of later transition metal systems. Hopefully, LDP will be useful in ongoing
catalytic studies in our group and on high valent metal complexes.

92

REFERENCES

93

REFERENCES

1) (a) Jarek, R. L.; Flesher, R. J.; Shin, S. K. J. Chem. Educ. 1997, 74, 976-982 (b) Mann, B. E.
J. Magn. Reson. 1977, 25, 91-94 (c) Dahlquist, F. W.; Longmuir, K. J.; Du Vernet, R. B. J.
Magn. Reson. 1975, 17, 406-410 (d) Forsén, S. J. Chem. Phys. 1963, 31, 2892-2901

2) (a) Binsch, G. J. Am. Chem. Soc. 1969, 96, 1304-1309 (b) Allerhand, A.; Gutowsky, S. H.;
Jonas, J.; Meinzer, R. A. J. Am. Chem. Soc. 1966, 88, 3185-3194 (c) McConnell, H. M. J.
Chem. Phys. 1958, 28, 430-431

3) Vassilev, N. G.; Dimitrov, V. S. Magn. Reson. Chem. 2001, 39, 607-614 (b) Kessler, H.;
Oschkinat, H. Griesinger, C. Bermel, W. J. Magn. Reson. 1986, 70, 106-133 (c) Bauer, C. J.;
Freeman, R.; Frenkiel, T.; Keeler, J. Shaka, A. J. J. Magn. Reson. 1984, 58, 442-457

4) Drakenberg, T.; Dahlqvist, K.-I.; Forsén, S. J. Phys. Chem. 1972, 72, 2178-2183

5) Gaede, H. C. NMR Exchange Spectroscopy Modern NMR Spectroscopy in Education,
Chapter 13, 2007, 176-189

6) Bryant, R. G. J. Chem. Educ. 1983, 60, 933-935

7) (a) Hull, L. A. J. Chem. Educ. 1990, 67, 782-783 (b) Harris, Robin. Nuclear Magnetic
Resonance Spectroscopy. London: Pitman Books Limited, 1983.

8) (a ) Lorigan, G. A.; Minto, R. E.; Zhang, W. J. Chem. Educ. 2001, 78, 956 (b) Jackman, L.
M.; Cotton, F. A. Dynamic Nuclear Magnetic Resonance Spectroscopy; Academic Press:
New York, 1975

9) Although, our samples were prepared in a dry box under N2 atmosphere we took extreme
precaution to obtain accurate data that had a limited number of reasons for introducing error
into our experiment.

10) (a) Perrin, C. L., Johnston, E. R. J. Magn. Reson. 1979, 33, 619-626 (b) Mann, B. E. J.
Magn. Reson. 1977, 25, 91-94

94

11) Yan, J.-L.; Mao, X.-A.; Shen, L.-F. Chem. Phys. Lett. 1997, 272, 278-283

12) Odom, A. L.; Cummins, C. C. Organometallics 1996, 15, 898-900

13) Forsén, S.; Hoffman, R. A. J. Chem. Phys. 1963, 39, 2892-2901

14) Klochkov, V. V.; Shaikhutdinov, R. A.; Khairutdinov, B. I.; Klimovitskii, E. N.; Findeisen,
M.; Berger, S. Appl. Magn. Reson. 2003, 24, 97-103

15) (a) Laidler, K. J. J. Chem. Educ. 1984, 61, 494-498 (b) Laidler, K. J.; King, M. C. J. Phys.
Chem. 1983, 87, 2657-2664 (c) Eyring, H. J. Chem. Phys. 1935, 3, 107-115

16) (a) Drakensberg, T.; Dahlqvist, K.-I.; Forsén, S. Acta Chem. Scand. 1970, 24, 694 (b) Van
Geet, A. L. Anal. Chem. 1968, 40, 2227-2229

17) (a) Rablen, P. R.; Miller, D. A.; Bullock, V. R.; Hutchinson, P. H.; Gorman, J. A. J. Am.
Chem. Soc. 1999, 121, 218-226 (b) Drakensburg, T.; Dahlqvist, K.-I.; Forsén, S. J. Phys.
Chem. 1972, 76, 2178-2183

18) Odom, A. L.; Cummins, C. C. Polyhedron 1998, 17, 675-688

19) Drago, R. S.; Zink, J. I.; Richman, R. M.; Perry, W. D. J. Chem. Educ. 1974, 51, 371-376
(b) Drago, R. S.; Zink, J. I.; Richman, R. M.; Perry, W. D J. Chem. Educ. 1974, 51, 464-467

20) Harris, Robin. Nuclear Magnetic Resonance Spectroscopy. London: Pitman Books Limited,
1983

21) Isbrandt, L.; Tung, W. C.-T.; Rogers, M. T. J. Magn. Reson. 1973, 9, 461-466

22) Atkins, P.; Overton, T.; Rourke, J.; Welle, M.; Armstrong, F. Shriver and Atkins Inorganic
Chemistry 4th Ed. New York: Freeman and Company, 2006

23) Harris, S. A.; Ciszewski, J. T.; Odom, A. L. Inorg. Chem. 2001, 40, 1987-1988

95

24) (a) Hou, D.-R.; Wang, M.-S.; Chung, M.-W.; Hsieh, Y.-D.; Tsai, H.-H. G. J. Org. Chem.
2007, 72, 9231-9239 (b) Balaban, A. T.; Oniciu, D. C.; Katritzky, A. R. Chem. Rev. 2004,
104, 2777-2812

25) Swartz II, D. L.; Odom, A. L. Organometallics 2006, 25, 6125-6133
26) (a) Varga, V.; Císaŕová, I.; Gyepes, R.; Horáček, M.; Kubišta, J.; Mach, K. Organometallics
2009, 28, 1748-1757 (b) Damoun, S.; Langenaeker, W.; Van de Woude, G.; Geerlings, P. J.
Phys. Chem. 1995, 99, 12151-12157

27) Tolman, C. A. Chem. Rev. 1977, 77, 313-348

28) Arduengo III, A. J.; Krafczyk, R.; Schmutzler, R. Tetrahedron 1999, 55, 14523-14534

29) (a) Azerraf, C.; Gelman, D. Organometallics 2009, 28, 6578- 6584 (b) Benito-Garagorii, D.;
Kirchner, K. Acc. Chem. Res. 2008, 41, 201-213 (c) Yoon, M. S.; Ryu, D.; Kim, J.; Ahn, K.
H. Organometallics 2006, 25, 2409-2411 (d) van der Boom, M. E.; Milstein, D. Chem. Rev.
2003, 103, 1757-1792 (e) Moulton, C. J.; Shaw, B. L. J. Chem. Soc., Dalton Trans. 1976,
1020-1024

30) Clavier, H.; Nolan, S. P. Chem. Commun. 2010, 46, 841-861

31) Guzei, I. A.; Wendt, M. Dalton Trans. 2006, 3991-3999

32) (a) Rahman, M. M.; Liu, H.-Y.; Prock, A.; Giering, W. P. Organometallics 1989, 8, 1-7 (b)
Canty, A. J.; Lee, C. V. Organometallics 1982, 1, 1063-1066

33) (a) Fickling, M.M; Fischer, A.; Mann, B.R.; Packer, J.; Vaughan, J. J. Am. Chem. Soc. 1959,
81, 4226-4230 (b) R. D. Howells, J. D. Mc Cown Chem. Rev., 1977, 77, 69–92 (c) Hall,
H.K., Jr. J. A.m. Chem. Soc. 1957, 79, 5441 (d) Brownstein, S.; Stillman, A.E. J. Phy. Chem.
1959, 63, 2061-2062

34) Hansch, C.; Leo, A; Taft, R. W. Chem. Rev. 1991, 91, 165-195

96

35) Lokare, K. S.; Odom, A. L. Inorg. Chem. 2008, 47, 11191-11196

36) Hoggard, P. E. Structure and Bonding 2004, 106, 37-57

37) Lukens, W. W. Jr.; Smith III, M. R.; Andersen, R. A. J. Am. Chem. Soc. 1996, 118, 17191728

38) (a) Gyepes, R.; Varga, V.; Horacek, M.; Kubista, J.; Pinkas, J.; Mach, K. Organometallics
2010, 29, 3780-3789 (b) Varga, V.; Cisarova, I.; Gyepes, R.; Horacek, M.; Kubista, J.; Mach,
K. Organometallics 2009, 28, 1748-1757

39) (a) http://www.chem.helsinki.fi/~pyykko/, 5/23/2011 (b) Pyykkö, P.; Atsumi, M. Chem. Eur.
J. 2009, 15, 12770-12779

40) For example, amidobis[1,3-bis(trimethylsilyl)cyclopentadienyl]titanium(III) has a Ti–NH2
distance of 1.933(3) Å. (a) Sofield, C. D.; Walter, M. D.; Andersen, R. A. Acta Cryst. C
2004, 60, 465-466. The compound H2NTiCp*2 has a Ti–N distance of 1.944(2) Å. (b)
Brady, E.; Telford, J. R.; Mitchell, G.; Lukens, W. Acta Cryst C 1995, 51, 558-591. Neither
of these NH2 complexes has a statistically significant difference in the Ti–N distance from
the value in Me(H)NTiCp*2, however.

97

Chapter 4: Hydroamination on a Solid Support
4.1: Hydroamination and Rationale for Surface Chemistry
Traditionally, imines are synthesized by condensation of an aldehyde or ketone with a
1

primary amine. Even in the presence of an acid or heat the scope of the reaction is limited.
Generation of imines can be accomplished in an atom-efficient way through hydroamination of
2

alkynes and primary amines using transition metal catalysts. With this new methodology, we
gain access to a variety of imines with specific frameworks and functional groups not accessible
3

using traditional methods. Many imines produced using transition metals can be used to
generate new heterocycles found in pharmaceuticals and natural product synthesis.
R4N

N(H)R4

2
R
3
R

4

2
R

N 1
R

3
R

H
N 1
R

1
H2NR

1
R
H
1 N
R

1
R
N

2
R
3
R

3
R
2
R

1
H2NR

Ti
NR4

N
3
R

Ti
Hydroamination
1
R
N

3
R

Ti

2
R

2
R

Iminoamination
4
C N R

Scheme 4.1: Proposed mechanistic pathway for hydroamination and iminoamination

98

We believe that our catalytic cycle follows a similar mechanistic cycle as elucidated by
5

Bergman. Shown in Scheme 4.1, one equivalent of a primary amine will deprotonate 2
dimethylamido ligands and generate the imido titanium complex, the active catalyst. In the
presence of an alkyne, [2 + 2]-cycloaddition occurs forming a 4-membered metallacycle that can
be protolytically cleaved by another primary amine to generate an enamine with catalyst
reformation.
Depending on other compounds present in solution the catalytic cycle may take a
different route, and Iminoamination

2b

will occur with the addition of isonitrile. This 1,1-

insertion of the isonitrile into the titanium-carbon bond forming a 5-membered metallacycle. In
the presence of excess primary amine, the metallacycle is protolytically cleaved, regenerating the
imido titanium catalyst and a tautormer of a 1,3-diimine. In some cases,

2b

excess isonitrile will

result in 4-component coupling (4CC) products that can cyclize to form 2,3-diaminopyrroles.
A more recent study investigated the activity of a titanium hydroamination catalyst with
6

ligand modification. Evaluation of the 2-aryl substituted dmpm ligand was based on the rates of
hydroamination. The results suggest that adding electron withdrawing substituents to the pyrroles
made the titanium catalyst more active. Unfortunately, these active ligands are expensive to
make, and it would be advantageous to make them reusable. This is one of the main driving
forces for placing our catalyst on a surface.
Our approach to binding the titanium catalyst to the surface is to attach the selected
ancillary ligand to a surface that will hold onto titanium. This method is commonly found in the
7

literature. The surface of choice for our titanium catalyst is polystyrene beads because of their

99

ease of use and the absence of functional groups, such as carbonyls, that could interfere with the
activity of our catalyst.
This approach has many potential benefits; the current workup for hydroamination
reactions involve removal of solvent through vacuum, distillation of product or column
chromatography, and discarding of the catalyst. The last step is problematic, especially since the
synthesis of the ligand was time intensive and expensive. By binding the elaborate ligand to a
surface, it will be easily recovered and simplify the workup to removal of the catalyst by
filtration and removal of solvent in vacuo to isolate the product. Not only is recovering the
catalyst more efficient, but reduces the amount of waste produced.
Another issue with our catalyst is the lack of reactivity after cooling incomplete reactions.
When the temperature of a reaction is cooled down to room temperature to check the progress of
a reaction, the catalyst can not be reactivated by heating the reaction mixture. One explanation is
that the titanium imido catalyst cannot re-enter the catalytic cycle when its cooled, because it
forms stable dimers. These dimers are known to form throughout group 4 transition metals and
8

could be very stable. By binding the catalyst to a surface, the titanium will avoid dimerization,
as in solution, and, hopefully, remain active after being cooled to room temperature.

4.2: Synthesis of dmpm Ligand and Attachment to Polystyrene Beads
We chose the dmpm ligand because it demonstrates some of the highest activity for
6

hydroamination with titanium, and the synthesis and workup is straightforward. The dmpm
9

ligand is synthesized by reaction of pyrrole and acetone with 10 mol% TFA. The condensation
reaction needs to be covered if the experimental conditions require long reaction times because

100

pyrrole is known to polymerize and form mixtures of porphyrins in the presence of light and
10

oxygen.

After many attempts to place the dmpm ligand onto the surface, the most successful route
11

was using Suzuki-Miyaura conditions to couple the dmpm ligand to polystyrene.

To

accomplish this, the dmpm fragment needed to contain a halide. Therefore, we selected 4bromoacetophenone as a ketone in our synthesis of H2dmpmPhBr because Suzuki-Miaurya
Coupling works better if the coupling partner is iodide or iromide and on an aromatic ring.

40

H
N

10 mol % TFA
12 h

Br

25 °C

Br

Br
1) 2 KH
2) Me2SiCl2

O
N
H
HN

12

DMF
1) 2 h
2) 12 h

N
Si N

Scheme 4.2: Synthesis and protection of H2dmpmPhBr
In control experiments it was found that the nitrogens on the dmpm ligand needed to be protected
or else it will react with the palladium catalyst during the coupling reaction. Using a BOC group
resulted in the formation of a very stable bridging carbonyl that could not be deprotected, even
using TBAF at higher temperatures. Instead, pyrroles were protected with a bridging dimethyl
silane using conditions found in the literature.

13

THF was investigated as a solvent for placing

the Me2Si group on dmpm because it is more volatile and makes the workup easier than using
DMF as the solvent. Unfortunately, this resulted in low yields, even when heated.

101

HBPin
1.5 mol % [Ir(COD)Cl]2
3 mol % dtbpy
PS

Cyclooctane

BPin
PS

150 °C
12 h

Scheme 4.3: Borylation of polystyrene resin
The coupling partner is the borylated polystyrene

14

beads made by adding iridium catalyst and

HBPin at 150 ºC in cyclooctane. To get good borylation, the PS beads had to swell in
cyclooctane for 12 hours.

15

Collection of the beads on a frit yielded grey beads that showed

characteristic B—C and B—O stretches in the IR. To certify that the BPin group was bound to
styrene and not free HBPin physisorbed in the polystyrene resin, the borylated beads were placed
in a Soxhlet extractor and washed with dichloromethane overnight. No change in weight or in IR
spectrum was observed after drying, indicating that the BPin was on the surface.
The optimum coupling conditions were determined to be refluxing the borylated beads
16

with catalyst and OCdmpmPhBr under N2 atmosphere in acetonitrile.

Again, better yields are

obtained when the beads swell in the solvent for long periods of time, such as 6 h. As with the
workup for the borylation, the beads were placed in a Soxhlet extractor and washed with
dichloromethane to remove any starting materials. After drying under vacuum, the light-brown
beads changed in weight. The absence of B—C and B—O stretches and the presence of N—C
and C—O stretches in the IR suggests that the OCdmpmPh fragment was bound to the surface.

102

4.3: Experimental
4.3.1 General Procedure:
All reactions and manipulations were carried out in an MBraun glovebox under nitrogen
atmosphere and/or using standard Schlenk techniques. Ethereal solvents, pentane, hexanes,
toluene, acetonitrile, and benzene were purchased from Aldrich Chemical Co. and purified using
alumina columns to remove water after sparging with dinitrogen to remove oxygen. 4bromoacetophenone and dicyclobiphenylphophine were purchased from Sigma Aldrich and
stored under N2. N,N-dimethylformamide (DMF), dimethyldichlorosilane, and cyclooctane were
purchased from Sigma Aldrich and distilled from MgSO4 under N2 atmosphere and stored under
N2. [Ir(COD)Cl]2 and Pd(OAc)2 were purchased from Strem Chemicals and stored under N2
atmosphere before use. K2CO3, was purchased from Jade Scientific and used as received.
HBPin was purchased from BASF and stored under N2 atmosphere before use. The polystyrene
resin was purchased from ChemPep, dried under vacuum, and stored under N2 atmosphere
before use. Trifluoroacetic acid (TFA) was purchased from EMD Chemicals and used as
received. Spectra were taken on Varian instruments located in the Max T. Rogers
Instrumentation Facility at Michigan State University. These include a UNITYplus 500
spectrometer equipped with a 5 mm Pulsed-Field-Gradient (PFG) switchable broadband probe
1

13

and operating at 499.955 MHz ( H) and 125.77 MHz ( C), and a UNITYplus 300 spectrometer
1

operating at 299.976 MHz ( H). Samples for IR were prepared in Nujol form and collected on a
Nicolet IR-42 Mid-IR spectrometer.

103

4.3.2 Synthesis of H2dmpmPhBr
To a 250 mL Schlenk flask equipped with a stir bar was loaded with 4-bromo-acetophenone (3.0
g, 15 mmol, 1 equiv) and pyrrole (42 mL, 603 mmol, 40 equiv). The flask was covered and
trifluoroacetic acid (0.12 mL, 1.5 mmol, 0.1 equiv) was added by syringe. After stirring for 12 h
at room temperature, Na2CO3 (1.6 g, 15 mmol, 1 equiv) was added in 10 mL of water and stirred
for 10 min until bubbling stopped. Both water and pyrrole were distilled off under vacuum
leaving an oily brown solid. This oily solid was titrated with toluene and placed under vacuum 5
times to give an off-white solid. The product further purified by column chromatography
1

[Alumina: CH2Cl2]. H NMR (500 MHz, CDCl3, 25 ºC): 7.76 (br s, 2H), 7.37 (d, JHH = 9.0
Hz, 2H), 6.97 (d, JHH = 9.0 Hz, 2H), 6.67-6.65 (m, 2H), 6.17-6.15 (m, 2H), 5.94-5.92 (m, 2H),
2.01 (s, 3H).

13

C NMR (127 MHz, CDCl3, 25 ºC): 146.5, 136.8, 131.2, 129.3, 120.7, 117.2,

108.4, 106.5, 44.5, 28.7. MS m/z 316.
4.3.3: Synthesis of OCdmpmPhBr
Under a nitrogen atmosphere, a 250 mL Schlenk flask equipped with a stir bar was loaded with
H2dmpmPhBr (6.20 g, 19.7 mmol, 1.0 equiv.) and 50 mL of CH2Cl2. To this stirring solution
was added BOC2O (10.7 g, 49.2 mmol, 2.5 equiv.) and DMAP (0.361 g, 2.96 mmol, 0.15 equiv.)
as solids. Then triethylamine (2.75 mL, 18.7 mmol, 1.0 equiv.) was added and the flask was
sealed and stirred for 16 h. The reaction was stopped and the solvent was removed in vacuo
leaving behind an off-white solid. The solid product was dissolved in a minimum amount of
ether (~7 mL) and was layered with pentane (~20 mL). This was placed in the fridge at –10 °C
1

to crystallize out over night resulting in a white solid. H NMR (300 MHz, CDCl3, 25 ºC): 7.47
104

(m, 2H), 7.33 (d, JHH = 8.40 Hz, 2H), 6.98 (d, JHH = 8.7 Hz, 2H), 6.33-6.31 (m, 2H), 6.15-6.13
(m, 2H), 1.98 (s, 3H). MS m/z: 340.
4.3.4 Synthesis of (Me2Si)dmpmPhBr
In a glove box, a 25 mL scintillation vial equipped with a stir bar was loaded with H2dmpmPhBr
(0.5 g, 1.6 mmol, 1 equiv) and DMF. The solution was chilled in a liquid nitrogen filled cold
well. To this cold stirring solution was added KH (0.13 g, 3.2 mmol, 2 equiv). The mixture was
allowed to warm to room temperature and stir for 2 h. This solution was cooled in a cold well,
and to this cold stirring solution was added Me2SiCl2 (0.20 mL, 1.6 mmol, 1 equiv) in 2 mL of
cold ether. The solution was allowed to warm to room temperature and stir for 12 h. The solution
1

was pumped down, leaving a yellowish oil. H NMR (500 MHz, CDCl3, 25 ºC): 7.25 (d, JHH =
14 Hz, 2H), 6.80-6.78 (m, 2H), 6.70 (d, JHH = 14 Hz, 2H), 6.44-6.42 (m, 2H), 6.35-6.32 (m,
2H), 1.95 (s, 3H), 0.082 (s, 6H). MS m/z 372.
4.3.5 Borylation of Polystyrene
In a dry box, a 500 mL 3-neck flask equipped with a stir bar was loaded polystyrene resin (3.00
g, 3.4 mmol, 1 equiv.) and 60 mL of cyclooctane. This was allowed to stir over night. To this
stirring solution was added [Ir(COD)Cl]2 (0.030 g, 0.45 mmol, 1.5 mol %) and di-tertbutylbipyridine (0.24 g 0.89 mmol, 3 mol %). The mixture stirred for 5 min. Then a solution of
HBPin (3.12 g, 29.8 mmol, 1.0 equiv.) in 10 mL of cyclooctane was added. This was sealed,
taken out of the dry box, and placed under a nitrogen atmosphere on the Schlenk line. A reflux
condenser was attached to flask, and the solution was refluxed for 12 h at 150 ºC. The reaction
mixture was cooled to room temperature and the beads were collected by filtration on a fritted

105

funnel. 10 mL aliquots of dichloromethane were added to the 3-neck flask and poured into the
frit to remove any residual catalyst. The beige-colored resin was washed with 10 mL of
deionized water followed by 20 mL of dichloromethane. The resin was then moved to a Soxhlet
thimble and continuously rinsed with dichloromethane for 16 h to remove any traces of the
iridium catalyst. The resin was carefully moved to a 10 mL round bottom flask and placed under
a vacuum over night to remove any traces of solvent. (4.21 g, 9.52 mmol, 39% yield). IR: (Nujol,
-1

cm ) 1361.4 (B—O), 1140.9 (B—C).
4.3.6 Coupling of OCdmpmPhBr to BPin Resin
In a dry box, a 150 mL Schlenk flask equipped with a stir bar was loaded with BPin Resin (0.100
g, 0.787 mmol, 1.0 equiv.) and 20 mL of acetonitrile. The solution was allowed to stir for 4 h. To
the stirring suspension was added Pd(OAc)2 (0.009 g, 0.0394 mmol, 5 mol%), PCy2Biphenyl
(0.028 g, 0.0787 mmol, 10 mol%), OCdmpmPhBr (0.230 g, 0.787 mmol, 1.0 equiv.) and K2CO3
(0.115 g, 0.787 mmol, 1.0 equiv.). The flask was covered with a septum, taken out of the dry
box, and placed under an N2 atmosphere. A reflux condenser was attached that was connected to
the Schlenk line. The suspension refluxed at 100 ºC for 16 h. The reaction was cooled to room
temperature. To the reaction was added water (~10 mL), and it was stirred for 10 min. The
heterogeneous mixture was poured into a frit to collect the grayish-brown beads, which were
washed with water (3 × 10 mL) and dichloromethane (3 × 10 mL). The beads were collected into
-1

a vial and dried under vacuum overnight. (0.1139 g, 0.340 mmol, 47% yield) IR: (Nujol, cm )
1743 (C—O).

106

4.4: Conclusion and Future Work
Modifying the beads to couple a dmpm derivative to the surface has been shown to work.
The groundwork has been laid for attaching a dmpm ligand to a surface. All that remains to be
tested is adding the titanium catalyst and studying the catalyst under hydroamination reactions.
These experiments are sure to reveal interesting aspects of hydroamination and answer some of
the questions put forth in Section 4.1.

107

REFERENCES

108

REFERENCES
th

1) (a) McMurry, J. Organic Chemistry 6 Ed. Brooks Cole, 2003 (b) Panunzio, M.;
Zarantonello, P. Org. Proc. Res. Dev. 1998, 2, 49-59 (c) McNaught, A. D.; Wilkinson, A.
nd
IUPAC Compendium of Chemical Terminology, 2 Ed. Oxford: Blackwell Scientific
Publications, 1997

2) (a) Reyes-Sánchez, A.; Cañavera-Buelvas, F.; Barrios-Francisco, R.; Vifeuentes-Vaca, O. L.;
Flores-Alamo, M.; García, J. J. Organometallics 2011, 30, 3340-3345 (b) Barnea, E.;
Majumder, S.; Staples, R. J.; Odom, A. L. Organometallics 2009, 28, 3876-3881 (c) Swartz,
D. L.; Odom, A. L. Organometallics 2006, 25, 6125-6133 (d) Odom, A. L. Dalton Trans.
2005, 225-233 (e) Cao, C.; Ciszewski, J. T.; Odom, A. L. Organometallics, 2001, 20, 50115013 (f) Johnson, J. S.; Bergman, R. G. J. Am. Chem. Soc. 2001, 123, 2923-2924 (g) Kim, Y.
K.; Livinghouse, T.; Bercaw, J. E. Tetrahedron Lett. 2001, 42, 2933-2935 (h) Beller, M.;
Thiel, O. R.; Trauthwein, H.; Hartung, C. G. Chem. Eur. J. 2000, 6, 2513-2522 (i)
Kawatsura, M.; Hartwig, J. F. J. Am. Chem. Soc. 2000, 122, 9546-9547 (j) Weber, L.;
Barlmeyer, M.; Quasdorff, J. M.; Sievers, H. L.; Stammier, H. G.; Neumann, B.
Organometallics 1999, 18, 2497-2504 (k) Walsh, P. J.; Baranger, A. M.; Bergman, R. G. J.
Am. Chem. Soc. 1992, 114, 1708-1719

3) (a) Nugent, T. C.; El-Shazly, M. Adv. Synth. Catal. 2010, 352, 753-819 (b) Ngai, M.-Y.;
Barchuk, A.; Krische, M. J. J. Am. Chem. Soc. 2007, 129, 12644-12645 (c) Krska, S. W.;
Zuckerman, R. L.; Bergman, R. G. J. Am. Chem. Soc. 1998, 120, 11828-11829 (d) Cantrell,
G. K.; Meyer, T. Y. J. Am. Chem. Soc. 1998, 120, 8035-8042 (e) Cantrell, G. K.; Meyer, T.
Y. Organometallics 1997, 16, 5381-5383

4) (a) Fustero, S.; Sánchez-Roselló, M.; Barrio, P.; Simón-Fuentes, A. Chem. Rev. 2011, 111,
6984-7034 (b) Chen, F-E.; Huang, J. Chem. Rev. 2005, 105, 4671-4706 (c) Kitajima, M.;
Misawa, K.; Said, N. K. I. M.; Horie, S.; Hatori, Y.; Murayama, T.; Takayama, H. J. Nat.
Med. 2006, 60, 28-35 (d) Sáéndez, C.; Salas, J. A. Nat. Prod. Rep. 2006, 23, 1007-1045 (e)
Kitajima, M. J. Nat. Med. 2007, 61, 14-23

5) (a) Baranger, A. M.; Walsh, P. J.; Bergman, R. G. J. Am. Chem. Soc. 1993, 115, 2753-2763
(b) Walsh, P. J.; Baranger, A. M.; Bergman, R. G. J. Am. Chem. Soc. 1992, 114, 1708-1719

6) Swartz II, D. L.; Odom, A. L. Organometallics, 2006, 25, 6125-6133

7) (a) Guinó, M.; Hii, K. K. Chem. Soc. Rev. 2007, 36, 608-617 (b) Shin, J.; Jensen, S. M.; Ju, J.;
Lee, S.; Xue, Z.; Noh, S. K.; Bae, C. Macromolecules 2007, 40, 8600-8608 (c) Lenaerts, P.;
109

Driesen, K.; Deun, R. V.; Binnemaus, K. Chem. Mater. 2005, 17, 2148-2154 (d) Benaglia,
M.; Puglisi, A.; Cozzi, F. Chem. Rev. 2003, 103, 3401-3429 (e) Leadbeater, N. E.; Marco, M.
Chem. Rev. 2002, 102, 3217-3274 (f) McNamara, C. A.; Dixon, M. J.; Bradley, M. Chem.
Rev. 2002, 102, 3275-3300 (g) Iiskola, E. I.; Timonen, S.; Pakkanen, T. T.; Härkki, O.;
Lehmus, P.; Seppälä, J. V. Macromolecules 1997, 30, 2853-2859 (h) Bonds Jr., W. D.;
Brubaker Jr., C. H.; Chandrasekaran, E. S.; Gibbons, C.; Grubbs, R. H.; Kroll, L. C. J. Am.
Chem. Soc. 1975, 97, 2128-2137 (i) Collman, J. P.; Hegedus, L. S.; Cooke, M. P.; Norton, J.
R.; Dolcetti, G.; Marquardt, D. N. J. Am. Chem. Soc. 1972, 94, 1789-1790

8) (a) Lober, C.; Vendier, L.; Inorg. Chem. 2011, 50, 9927-9929 (b) DeKock, R. L.; Peterson, M.
A.; Reynolds, L. E. L.; Chen, L-H.; Baerends, E. J.; Vernooijs, P. Organometallics 1993, 12,
2794-2805 (c) Walsh, P. J.; Hollander, F. J.; Bergman, R. G. Organometallics 1993, 12,
3705-3723 (d) Arney, D. J.; Bruck, M. A.; Huber, S. R.; Wigley, D. E. Inorg. Chem. 1992,
31, 3749-3755 (e) Thorn, D. L.; Nugent, W. A.; Harlow, R. L. J. Am. Chem. Soc. 1981, 103,
357-363

9) Lindsey, J. S.; Boyle, P. D.; O’Shea, D. R.; Wagner, R. W.; Hung, C. H.; Miller, M. A.;
Littler, B. J. J. Org. Chem. 1999, 64, 1391-1396

10) (a) Zhang, X.; Zhang, J.; Song, W.; Liu, Z. J. Phys. Chem. B 2006, 110, 1158-1165 (b) Zhou,
M.; Heinze, J. J. Phys. Chem. B 1999, 103, 8451-8457 (c) Baltazzi, E.; Krimen, L. I. Chem.
Rev. 1963, 63, 511-556

11) Miyaura, N.; Suzuki, A. Chem. Rev. 1995, 95, 2457-2483

12) (a) LeBlond, C. R.; Andrews, A. T.; Sun, Y.; Sowa Jr., J. R. Org. Lett. 2001, 3, 1555-1557
(b) Suzuki, A. J. Organomet. Chem. 1999, 576, 147-168

13) Jolicoeur, B.; Chapman, E. E.; Thompson, A.; Lubell, W. D. Tetrahedron 2006, 62, 1153111563

14) Shin, J.; Jensen, S. M.; Ju, J.; Lee, S.; Xue, Z.; Noh, S. K.; Bae, C. Macromolecules 2007,
40, 8600-8608

15) (a) Walsh, D. P.; Pang, C.; Parikh, P. B.; Kim, Y. S.; Chang, Y. T. J. Comb. Chem. 2002, 4,
204 (b) Sarin, V. K.; Kent, S. B. H.; Merrifield, R. B. J. Am. Chem. Soc. 1980, 102, 54635470

110

16) Billingsley, K. L.; Anderson, K. W.; Buchwald, S. L. Angew. Chem. Int. Ed. 2006, 45, 34843488

111

APPENDICIES

112

APPENDICIES

A1: Instructions for pw90 using Varian
The maximum signal produced from a length of a pulse described in microseconds is
called the 90° pulse-width (pw90). The pw90 value is dependent on many factors including the
type of nucleus, pulse power, preparation of research sample, NMR tube, and probe tuning. In
most cases the default pw90 is sufficient to obtain data, but in the case of more advance
experiments such as kinetics, it is crucial to get accurate data. The maximum signal where the
signal to noise ratio is favorable is at the 90° pulse. Finding the 90° pulse is time consuming but
a much easier method is finding a null point (360° pulse) in the spectrum of the peak of interest.
Dividing this pulse number by 4 will give the desired 90° pulse.
1) Acquire a clean and well shimmed spectrum of your compound. If shimming is an issue,
1

then tuning of the H channel may be required.
2) Type pw90? (This reports the 90° pulse-width currently used as default. Remember this
number.)
3) Type array (Allows you to set up an arrayed experiment.)
Then you will need to answer the following questions (highlighted in blue).
Parameter to be arrayed: pw (pw = pulse width)
Enter number of steps in array: 10 (this is the number of points to check for 360° pulse)

113

Enter starting value = (4*pw90) – 1 (The pw90 is the number from step 2. In this case if
your pw90 was 11, then the starting value you would be entering is 43. If you don’t see a null
point, pick a number smaller than the pw90 reported in step 2 and start over.)
Enter array increment: 0.5 (This is the point that a spectrum is taken of the sample.
Although, larger increments can ballpark where the pw90 is located, smaller increments are
required for obtaining accurate pw90.)
4) Type pw[1]=1 (This will replace the first array with 1 μs pulse. This way the phasing will
start off positive and the rest of the spectra should be inverted and slowly becoming positive
with time.)
5) Type da (displays the array)
6) Type ds (display spectrum. Expand around the peak or peaks of interest.)
7) Type gain=’y’ (Turns automatic gain off which is not allowed in arrayed experiments.)
8) Type d1=3 (Sets d1 to 3 seconds. This is the recycle delay that is seen in a pulse. See
figure below. It is the time before the sample is pulsed. The d1 should be set to at least 1.5
times your T1. If you don’t have a feel for what the T1 might be for your peak of interest you
may have to play around with the T1 determination to get an idea.)
9) Type nt=2 time (nt is the number of scans, which for most cases 2 or 4 scans should be
fine. Typing time will tell you how long the run will take.)
10) Type go
Once the experiment is finished….
11) Type ai

(absolute intensity, meaning is scales the peaks correctly)

12) Type wft

(weighted Fourier transform)

114

13) Type dssh (display stacked plots horizontally You should get something that looks like
what is shown in Figure A1.1.)

Figure A1.1: pw90 of 2 at 25 °C
14) Type dssl (Look for the spectrum with the lowest peak intensities that is close to a null
where the peaks are going from negative to positive. This is your determined value.)
15) Type pw90=your determined value/4

(for example, if the null point in the arrayed

was associated with 44 then pw90=44/4.)
16) Type pw=pw90 (resets the pw to the new pw90)
17) Type pw?

(Checks to see what the current pw90 is set to)

18) Type gain=’n’ (Turns autogain on.)
19) Type ga (Obtain a new spectrum with the best signal to noise ration using the new
pw90.)
Trouble Shooting:
Sometimes, when you search for a pw90 doing the arrayed experiment the peaks appear to relax
back but then get inverted as shown in Figure 2.

1

Figure A1.2: Bad pw90 due to poorly tuned H channel

115

1

If this happens, it means that the H channel was not properly tuned. Tuning the probe should
fix this problem. Even when this doesn’t happen it might be a good idea to check the instrument
before doing the experiment.)

A2: Instructions for T1 Determination using Varian
The Longitudinal or Spin Lattice Relaxation Time (T1) is a time constant for the return of
excited spins back to equilibrium. Knowledge of the T1 of a signal of interest is important for the
setup of some 1D and 2D NMR experiments. Determination of the T1 will be done by the
inversion recovery method. A 180° pulse will be applied to the sample and time between the
180° pulse and the 90° pulse (read pulse) will be incremented. The signals will be inverted and
will begin to recover as the time between the 180° and 90° pulses are increased. Once signals are
positive and the spins have reached their equilibrium magnetization then you can determine the
T1 value of the peak(s) of interest.
1) Obtain a clean and well shimmed spectrum of your sample using your pw90.
2) Type gain=’y’

(Turns off autogain for arrayed experiment.)

3) Type fn=2*np (Includes zero-filling to improve the spectrum.)
4) Type ga
5) Type dot1

(Command to set up a T1 experiment. You will be prompted to answer

the questions highlighted in blue.)
Enter the minimum T1 expected (sec): 0.5 (0.1 to 1 sec would be an okay starting point.)

116

Enter the maximum T1 expected (sec): 3 (It might be a good idea to choose as large a range
as possible the first time you do the experiment. Setting the minimum to 0.1 and maximum to
10 will give you an idea but the experiment might take a while.)
Enter the number of transients: 0.15 (The time the experiment will take. You can also set the
time by typing nt=the number of scans you want and typing go.)
6) Type dg

(Display parameters)

7) Type ga
8) After the experiment finishes, type wft dssh. (This Fourier Transforms your spectra and
displays them horizontally. Your screen should look like what is shown in Figure A2.1. What
you are seeing is the spins relaxing back to equilibrium as the increment of time (d2) between
180° pulse and the 90° pulse increases.)

i

Figure A2.1: Spectra from T1 experiment of NCr(N Pr2)2I (2)

117

9) Type dssl (This displays the numbered experiments. Look for the very last spectrum. In
this spectrum the spins will have relaxed back to equilibrium.)
10) Type ds(# of last spectrum)

(Displays the last spectrum in the arrayed experiment.)

11) Expand in on the peak(s) of interest and chose the threshold of the most middle of the
peak. Therefore, if you have a septet, then set the threshold to include the middle and highest
peak.)
12) Type dll (Displays the listed line frequencies and intensities.)
13) Type fp (Measure the intensity of each line in dll listing in arrayed spectra.)
14) Type t1

(Performs a T1 determination using exponential curve fitting. If you type

expl(# of selected line), you will see a graph similar to the one shown in Figure A2.2. The
T1 is determined from the equation of the line from plotting the intensity of the peaks
(magnetization/intensity) versus time.

Figure A2.2: T1 determination from magnetization versus time plot of 2
118

15) Type printon t1 printoff (This will print the T1 values of the peaks selected along with
the error in the T1 values based on the fit of the curve.)

A3: Instructions for SSMT Experiment using Varian
Spin saturation magnetization transfer is an NMR technique used to determine the
exchange rate between nuclei that have two distinct chemical shifts that still experience
exchange in the slow regime on the NMR timescale. Two experiments will be performed: first,
one of the exchanging peaks will be irradiated and second, it will not be irradiated. The
difference in height of the observed peak experiencing exchange will be recorded. Combining
the T1 and the change in magnetization (peak integration) rate for the exchange can be
determined. Since the rate of exchange is very dependent on temperature it is required that the
sample equilibrates to the desired temperature for at least ten minutes before beginning the
experiment.
1

First, turn the spinning off and acquire a quality H spectrum of the sample. It is important to
turn the spinning off because NOE can contribute to the transfer of magnetization.
1) Choose the option Presat from the menu.
2) Type satdly= #

(set satdly equal to at least 5 × T1)

3) Type satpwr=-4

(satpwr is the amount of energy going into the sample to irradiate

the peak; if satpwr is too high it will saturate the other peak)
4) Type pw90= #
5) Type dps

(set pw90 to the value determined in the first experiment)
(dps is display pulse sequence to make sure everything is set up

correctly for experiment)

119

6) Type ds

(ds is display spectrum)

7) Type aph vsadj

(to see the whole spectrum and expand upon the region of

exchange)
*A special note: When expanding around two peaks experiencing exchange, it is important
to give enough room on both sides of the peaks that is greater than the distance between the
two peaks experiencing exchange. The reason for this is that if the window is too small and
the offsite peak is set by the computer it will choose the left most position the cursor sees on
the screen, which is the end of the screen. If the offsite point is not equally distant from the
peak experiencing exchange then the irradiation will be offset and contribute to error in the
peak integration.
8) Place the cursor on the right peak. Type sd (sd = set decoupler frequency)
9) Place the left cursor on the left peak and the right cursor on the right peak that are
experiencing exchange. See Figure A3.1.

Figure A3.1: Placing right and left cursors on septets belonging to 2
10) Type cr=cr+delta

(This moves the cursors to the left of the left most peak that is

equal to the distance between the two exchanging peaks. This is done to account for
decoupler spillover. See Figure A3.2.)

120

Figure A3.2: Setting offsite point equidistant from the septet for saturation
11) Type sda

(Sets the decoupler to the new offsite saturation
frequency.)

12) Type gain=’y’
13) Type da

(Displays saturation frequencies set for the peaks.)

14) Type satfrq=value,value

(Enter the two saturation frequencies listed from typing da.)

15) Type dof=0

(Sets decoupler to a single frequency, but not be used during

experiment.)
16) Type ss=-2

(ss=steadystate, allows for relaxation back to equilibrium before

making scans.)
17) Type nt= #
18) Type go or ga

121

B1: Eyring Plots for Selected Chromium Nitrido Complexes
i

Eyring Plot for NCr(N Pr2)2I (CDCl3)

-3
-4

y = -7939.5x + 19.079

-5

2

ln(k/T)

R = 0.9694
-6
-7
-8
-9
-10
0.00295

0.00305

0.00315

0.00325
1/T

0.00335

0.00345

0.00355

Figure B1.1: Eyring Plot of 2
i

Eyring Plot for NCr(N Pr2)2CN (CDCl3)
-4
y = -6246.7x + 15.51

-5

2

ln(k/T)

R = 0.9614
-6
-7
-8
-9
0.0033

0.0034

0.0035

0.0036
1/T

Figure B1.2: Eyring Plot of 30

122

0.0037

0.0038

Eyring Plot for OPhSMe (CDCl3)

-2

y = -6862.4x + 22.097

-4

ln(k/T)

-3

R = 0.9825

2

-5
-6
-7
-8
-9
0.0036

0.0037

0.0038

0.0039

0.004
1/T

0.0041

0.0042

0.0043

0.0044

0.0044 0.00445

0.0045

Figure B1.3: Eyring Plot of 12
i

0

Eyring Plot of NCr(N Pr2)2OAd (CDCl3)

-1
y = -5286.9x + 18.747

ln(k/T)

-2

2

R = 0.9994
-3
-4
-5
-6
0.0041 0.00415 0.0042 0.00425 0.0043 0.00435
1/T

Figure B1.4: Eyring Plot of 6

123

i

Eyring Plot of NCr(N Pr2)2OBn (CDCl3)
-2

y = -5982x + 20.787
2

R = 0.9948

ln(k/T)

-4
-6
-8
-10
0.004

0.0042

0.0044
1/T

0.0046

0.0048

Figure B1.5: Eyring Plot of 20
i

Eyring Plot of NCr(N Pr2)3 (CDCl3)
-3.5
y = -5852.8x + 21.191
2

ln(k/T)

R = 0.9961
-4.5

-5.5

-6.5
0.0041

0.0042

0.0043

0.0044

1/T

0.0045

Figure B1.6: Eyring Plot of 1

124

0.0046

0.0047

0.0048

i

Eyring Plot of NCr(N Pr2)3 (d -toluene)

-2
-3

y = -6240.9x + 22.955

ln(k/T)

-4

2

R = 0.9871

-5
-6
-7
-8
0.0041

0.0042

0.0043

0.0044

0.0045

0.0046

1/T

Figure B1.7: Erying Plot of 1 in d-toluene

125

0.0047

0.0048

C1: Error Equations for SSMT
The equation for relating the experimental observables to the rate constant, k, is Eqn 1
below. In Eqn 1, MOA is the integral before irradiation, which is set to 100, and MA is the
observed integral after irradiation. The T1 is found using the inversion recovery method, and the
error in T1 is calculated by Varian software VNMR 61c or VNMR J22d, both software gave
similar results. The error in integration was set to 0.1 with the integration of the peak before
irradiation set to 100. The error in temperature, εT, was ±1 ºC. The propagation of error in the
system, error in k (εk), is found using Eqn 2.

Where, ε1/T1 and εMOA/MA are found using Eqns 3 and 4, respectively.

126

The free energy of amido rotation was found using Eyring equation in the form shown in Eqn 5.
The error in ΔG was calculated as shown in Eqn 6.

127

D1: Eyring Plots for CLSA Experiments
i

2.5

LSA Eyring Plot of NCr(NPr 2)2NMe2 (d- toluene)
y = -4701.3x + 21.614
2
R = 0.9976

2

ln(k/T)

1.5
1

0.5
0
-0.5
0.0041

0.0042

0.0043

0.0044
1/T

0.0045

0.0046

0.0047

Figure D1.1: Eyring plot of 31

ln(k/T)

i

2
1.8
1.6
1.4
1.2
1
0.8
0.6
0.4
0.2
0
-0.2
0.0033

LSA Eyring Plot of NCr(N Pr2)2OAd (CDCl3)

y = -6433.4x + 23.21
2

R = 0.9811

0.00335

0.0034

0.00345 0.0035
1/T

0.00355

Figure D1.2: Eyring plot of 6

128

0.0036

0.00365