carbenes in ruthenium based olefin metathesis catalysts and … · ii carbenes in ruthenium based...

Carbenes in Ruthenium Based Olefin Metathesis Catalysts and Stabilization of Low Coordinate Boron Species

by

Fatme Dahcheh

A thesis submitted in conformity with the requirements for the degree of Doctor of Philosophy

Department of Chemistry University of Toronto

© Copyright by Fatme Dahcheh 2014

ii

Carbenes in Ruthenium Based Olefin Metathesis Catalysts and Stabilization of Low Coordinate Boron Species

Fatme Dahcheh

Doctor of Philosophy

Department of Chemistry

University of Toronto

2014

Abstract

Since their discovery, carbenes have been widely used as organocatalysts and as superb ligands

for transition metal-based catalysts. They have also, more recently, been shown to stabilize

reactive and low-valent main group systems.

Catalytic olefin metathesis has proven to be a powerful tool in various chemical fields. Research

in this area has received considerable attention specifically with the development of new

catalysts. The vast majority of catalysts developed, thus far, have been modifications to the

Grubbs catalyst architecture. The research presented herein focuses on the development of a new

route for the synthesis of new olefin metathesis catalysts and testing their activity.

A new method of preparing ruthenium alkylidene complexes starting with bis-carbene RuHCl

species and alkenyl sulfides is developed. This provides a route to bis-mixed carbene ruthenium

alkylidene complexes with a hemilabile tridentate carbene and conveniently installs both an

iii

alkylidene fragment and a thiolate in one step. The resulting Ru-alkylidene species are either

inactive or minimally active for the standard metathesis tests. The species generated by the

addition of one equivalent of BCl3, however, show improved activity for ROMP, RCM and CM

either at room temperature or at slightly elevated temperatures. Halide exchange for these

systems results in enhanced metathesis activity for the standard tests where catalytic olefin

metathesis was observed at room temperature.

Cyclic (alkylamino)carbenes are utilized to stabilize iminoboryl moieties which have only been

previously stabilized in the coordination sphere of transition metals. Some of the species are also

shown to undergo [2+2] cycloaddition with CO2. CAACs are also used for the synthesis of a

boron derivative, which is isoelectronic with singlet carbenes, namely a borylene. This species is

shown to react with CO and H2, but in contrast with carbenes, it acts as an electrophile and

therefore mimics the behavior of metals.

iv

Acknowledgments

I would like to take the opportunity to recognize the many people who have assisted and

supported me during my studies. First and foremost, I would like to thank Professor Doug

Stephan for his continued support, guidance and encouragement throughout this degree. I would

also like to thank him for the support which allowed me to travel to many conferences to present

my work as well as setting up an exchange at UCSD with Professor Guy Bertrand which has

proven fruitful.

I would also like to thank all Stephan group members, both past and present, for helpful

chemistry (and general) discussions and for making the lab a very enjoyable place to work.

Particularly, I would like to thank the individuals who took the time to review and edit this

thesis, specifically Dr. Roman Dobrovetsky, Dr. Adam McKinty, Dr. Michael Boone,

Dr. Michael Sgro, Conor Pranckevicius and Lauren Longobardi. I would also like to thank

Dr. Datong Song and Dr. Robert Morris for serving on my committee for the past four years and

offering helpful advice throughout.

I would also like to thank all of the support staff in the Department of Chemistry at the

University of Toronto, specifically Rose Balazs and Giordana Riccitelli and the staff at

ANALEST for their help in obtaining quality elemental analysis results. I must also thank the

staff in the NMR facility for their assistance in the set up of experiments and general help with

NMR related inquiries. Specifically, I would like to thank Dr. Darcy Burns and Dmitry Pichugin

for helping me run specialized NMR experiments and set up Variable Temperature NMR

experiments. I would like to thank Dr. Alan Lough for his assistance with X-ray crystallography

and Dr. David Martin at UCSD for DFT calculations.

Finally, I would like to thank my family and friends who have supported me for the last four

years.

v

Table of Contents

Acknowledgments .......................................................................................................................... iv

Table of Contents ............................................................................................................................ v

List of Schemes .............................................................................................................................. ix

List of Figures .............................................................................................................................. xiii

List of Abbreviations .................................................................................................................. xxii

Chapter 1 Introduction .................................................................................................................... 1

1.1 Carbenes .............................................................................................................................. 1

1.1.1 Synthesis and Isolation of Stable Free Carbenes .................................................... 2

1.1.2 Carbenes as Ligands for Transition Metal-Based Catalysts ................................... 5

1.1.3 Carbenes in Stabilizing Low-Valent and Reactive Species .................................... 6

1.2 Catalytic Olefin Metathesis ................................................................................................. 9

1.2.1 Well-Defined, Homogenous Catalysts .................................................................... 9

1.2.2 Mechanism of Catalytic Olefin Metathesis ........................................................... 10

1.3 Nitrile Butadiene Rubber .................................................................................................. 12

1.4 Lanxess Project ................................................................................................................. 13

1.5 Scope of Thesis ................................................................................................................. 14

References ..................................................................................................................................... 17

Chapter 2 Synthesis and Characterization of Bis-Mixed-Carbene Ruthenium-Alkylidene-

Thiolate Complexes ................................................................................................................. 22

2.1 Introduction ....................................................................................................................... 22

2.1.1 First Isolated Transition Metal Based Alkylidene Complex ................................. 22

2.1.2 Modifications to Grubbs’ Catalyst ........................................................................ 22

2.1.3 Bis-Carbene Olefin Metathesis Catalysts .............................................................. 24

2.1.4 Routes to Ru-Alkylidene Complexes .................................................................... 25

2.2 Results and Discussion ..................................................................................................... 30

vi

2.2.1 Synthesis of Ru-Hydride Complexes .................................................................... 30

2.2.2 Synthesis of Ru-Alkylidene Complexes Using Aryl-Alkenyl Sulfides ................ 33

2.3 Reactions of Ru-Hydride Species with Ethyl Vinyl Sulfide ............................................. 41

2.4 Conclusion ........................................................................................................................ 48

2.5 Experimental Section ........................................................................................................ 48

2.5.1 General Considerations ......................................................................................... 48

2.5.2 Synthetic Procedures ............................................................................................. 48

2.5.3 X-ray Data Collection and Reduction ................................................................... 61

2.5.4 X-ray Data Solution and Refinement .................................................................... 61

References ..................................................................................................................................... 65

Chapter 3 Catalytic Olefin Metathesis .......................................................................................... 68

3.1 Introduction ....................................................................................................................... 68

3.1.1 Types of Olefin Metathesis Reactions .................................................................. 68

3.1.2 Catalyst Screening ................................................................................................ 69

3.1.3 Acid Assisted Olefin Metathesis ........................................................................... 71

3.1.4 Halide Abstraction for Activation of Metathesis Catalysts .................................. 73

3.1.5 Cross Metathesis of NBR and 1-Hexene .............................................................. 74

3.2 Results and Discussion ..................................................................................................... 74

3.2.1 ROMP of 1,5-Cyclooctadiene ............................................................................... 75

3.2.2 RCM of Diethyl Diallylmalonate .......................................................................... 78

3.2.3 CM of 5-Hexenyl Acetate and Methyl Acrylate ................................................... 80

3.2.4 Trends in Catalytic Olefin Metathesis .................................................................. 83

3.2.5 Cross Metathesis of NBR and 1-Hexene .............................................................. 83

3.3 Conclusion ........................................................................................................................ 86

3.4 Experimental Section ........................................................................................................ 87

3.4.1 General Considerations ......................................................................................... 87

vii

3.4.2 Synthetic Procedures ............................................................................................. 87

References ................................................................................................................................... 106

Chapter 4 Synthesis of Bis-Mixed-Carbene Ruthenium-Alkylidene Complexes Through

Anion Exchange ..................................................................................................................... 108

4.1 Introduction ..................................................................................................................... 108

4.1.1 Halide Variation in Grubbs Catalyst ................................................................... 108

4.1.2 Pseudo-halides as Ligands in Ruthenium Metathesis Catalysts ......................... 108

4.2 Results and Discussion ................................................................................................... 109

4.2.1 Synthesis of Ru Complexes ................................................................................ 109

4.2.2 Standard Olefin Metathesis Tests ....................................................................... 116

4.2.3 Cross Metathesis of NBR with 1-Hexene ........................................................... 120

4.3 Conclusion ...................................................................................................................... 121

4.4 Experimental Section ...................................................................................................... 122

4.4.1 General Considerations ....................................................................................... 122

4.4.2 Synthetic Procedures ........................................................................................... 122

4.4.3 Standard Metathesis Reaction Tests ................................................................... 128

4.4.4 Cross Metathesis of NBR and 1-hexene ............................................................. 133

4.4.5 X-ray Crystallography ........................................................................................ 135

References ................................................................................................................................... 138

Chapter 5 Carbene Stabilized Iminoboranes ............................................................................... 140

5.1 Introduction ..................................................................................................................... 140

5.1.1 Iminoboranes and Iminoboryl Transition Metal Complexes .............................. 140

5.1.2 Carbenes in Stabilizing Low Valent Boron Species and Boron Centered

Radicals ............................................................................................................... 142


5.2.1 Synthesis of Iminoborane species ....................................................................... 145

5.2.2 Reactivity of Iminoboranes with CO2 ................................................................. 158

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5.3 Conclusion ...................................................................................................................... 162





References ................................................................................................................................... 179

Chapter 6 A Room Temperature Stable Organoboron Isoelectronic with Singlet Carbenes ..... 182

6.1 Introduction ..................................................................................................................... 182

6.1.1 Borylenes: Group 13 Carbene Analogues ........................................................... 182

6.1.2 Transition Metal Borylene Complexes ............................................................... 184

6.1.3 CO Adducts of Carbenes and of Boranes ........................................................... 185


6.2.1 Reduction Route to Borylene Synthesis ............................................................. 187

6.2.2 Reactivity of Borylenes ....................................................................................... 194

6.3 Conclusion ...................................................................................................................... 198





References ................................................................................................................................... 205

Chapter 7 Summary .................................................................................................................... 208

7.1 Summary ......................................................................................................................... 208

ix

List of Schemes

Scheme 1.1.1 The Wanzlick equilibrium. ...................................................................................... 2

Scheme 1.1.2 In situ preparation of imidazol-2-ylidenes. .............................................................. 2

Scheme 1.1.3 Nitrogen atom transfer using a carbene stabilized phosphinonitrene. ..................... 8

Scheme 1.2.1 Depiction of olefin metathesis. ................................................................................ 9

Scheme 1.2.2 Synthesis of the first well-defined Ru olefin metathesis catalyst. ......................... 10

Scheme 1.2.3 Chauvin’s mechanism of olefin metathesis. .......................................................... 11

Scheme 1.2.4 Olefin metathesis mechanism with Grubbs I. ........................................................ 12

Scheme 2.1.1 Synthesis of the first isolated transition metal alkylidene. .................................... 22

Scheme 2.1.2 Synthesis of the first ruthenium alkylidene. .......................................................... 26

Scheme 2.1.3 Synthesis of Grubbs I catalyst using phenyl diazomethane. .................................. 26

Scheme 2.1.4 Synthesis of Grubbs I catalyst using a sulfur ylide. ............................................... 27

Scheme 2.1.5 Synthesis of Grubbs I catalyst via an indenylidene intermediate. ......................... 27

Scheme 2.1.6 Synthesis of Grubbs I catalyst from Ru(0) species. ............................................... 28

Scheme 2.1.7 Synthesis Ru-alkylidenes from dithioacetals and Ru(PPh3)3(H)2. ......................... 28

Scheme 2.1.8 Synthesis of a ruthenium phosphonium alkylidene complex. ............................... 28

Scheme 2.1.9 Synthesis of a vinylalkylidene using propargyl chloride. ...................................... 29

Scheme 2.1.10 Synthesis of a Ru-alkylidene using vinyl chloride. ............................................. 29

Scheme 2.1.11 Synthesis of a Ru-ethylidene using vinyl chloroformate. .................................... 29

Scheme 2.2.1 Synthesis of 2-1 to 2-3. .......................................................................................... 30

x

Scheme 2.2.2 Synthesis of 2-4 to 2-8. .......................................................................................... 33

Scheme 2.2.3 Synthesis of 2-10 and 2-11. ................................................................................... 37

Scheme 2.2.4 Synthesis of 2-12 to 2-14. ...................................................................................... 38


Scheme 2.3.2 Synthesis of 2-21. .................................................................................................. 44

Scheme 2.3.3 Synthesis of 2-22 and 2-23. ................................................................................... 46

Scheme 3.1.1 Common olefin metathesis reactions. .................................................................... 69

Scheme 3.1.2 Standard test reaction for ROMP. .......................................................................... 70

Scheme 3.1.3 Standard test reaction for RCM. ............................................................................ 70

Scheme 3.1.4 Standard test reaction for CM. ............................................................................... 70

Scheme 3.1.5 Lewis acid assisted RCM. ...................................................................................... 71

Scheme 3.1.6 Use of acid as a phosphine scavenger. ................................................................... 72

Scheme 3.1.7 Activation of metathesis catalysts with BCl3. ........................................................ 72

Scheme 3.1.8 Activation of metathesis catalyst through halide abstraction. ............................... 73

Scheme 3.1.9 Synthesis of a 4-coordinate olefin metathesis catalyst by halide abstraction. ....... 73

Scheme 3.2.1 List of catalysts used for catalytic olefin metathesis. ............................................ 75

Scheme 4.2.1 Synthesis of 4-1 and 4-2. ..................................................................................... 110




xi

Scheme 5.1.1 Synthesis of iminoboranes via thermally induced elimination of Me3SiX. ......... 140

Scheme 5.1.2 [2+2] Cycloaddition reactions of amino iminoboranes. ...................................... 141

Scheme 5.1.3 Reaction of an amino iminoborane with CX2. ..................................................... 141

Scheme 5.1.4 Synthesis of iminoboryl transition metal complexes. .......................................... 142

Scheme 5.1.5 Reactions of an iminoboryl complex with various substrates. ............................ 142

Scheme 5.1.6 Synthesis of a neutral borolyl radical. ................................................................. 144


Scheme 5.2.2 Synthesis of 5-2 to 5-4. ........................................................................................ 147

Scheme 5.2.3 Synthesis of 5-5 to 5-7. ........................................................................................ 151


Scheme 5.2.5 Reaction of 5-11 with NaBPh4. ............................................................................ 157

Scheme 5.2.6 Synthesis of 5-12 to 5-14. .................................................................................... 158

Scheme 5.2.7 Reaction of a π-conjugated iminoborane with CO2. ............................................ 161

Scheme 6.1.1 Schematic representation of singlet carbenes A, nitrenes B, borylenes C, and

Lewis base-borylene adducts D. ................................................................................................. 182

Scheme 6.1.2 Synthesis of a stable diborene stabilized by NHCs. ............................................ 183

Scheme 6.1.3 Formation of a borane through C-H activation of a transient borylene. .............. 183

Scheme 6.1.4 Formation of a borirane by trapping of a transient borylene. .............................. 183

Scheme 6.1.5 Synthesis of a bis-CAAC-borylene. ..................................................................... 184

Scheme 6.1.6 Synthesis of the first terminal borylene complexes. ............................................ 185

Scheme 6.1.7 CO fixation to a CAAC and a DAC. ................................................................... 186

xii

Scheme 6.1.8 Synthesis of tris(trifluoromethyl)borane carbonyl adduct. .................................. 186

Scheme 6.1.9 Synthesis of pentaarylborole-CO adduct. ............................................................ 186

Scheme 6.1.10 Synthesis of Piers borane-CO adduct. ............................................................... 187


Scheme 6.2.2 Synthesis of a neutral boron-containing radical stabilized by a CAAC. ............. 191



xiii

List of Figures

Figure 1.1.1 Singlet and triplet forms of a carbene. ....................................................................... 1

Figure 1.1.2 First isolable and crystalline carbenes. ...................................................................... 3

Figure 1.1.3 Select examples of carbenes. ..................................................................................... 3

Figure 1.1.4 Steric environment differences between phosphines and carbenes. .......................... 4

Figure 1.1.5 Carbene coordination to metals and p-block elements. ............................................. 4

Figure 1.1.6 Fischer and Schrock carbene complexes. .................................................................. 5

Figure 1.1.7 Carbene-stabilized main group species in the (0) oxidation state. ............................ 7

Figure 1.1.8 Carbene stabilized paramagnetic main group species. .............................................. 7

Figure 1.1.9 Stable oxyallyl radical cation. ................................................................................... 8

Figure 1.2.1 Generalized structure of a Mo-based Schrock-type catalyst. .................................... 9

Figure 1.2.2 First and second generation Grubbs catalysts. ......................................................... 10

Figure 1.3.1 Depiction of functional groups found in Nitrile Butadiene Rubber. ....................... 12

Figure 1.3.2 Depiction of hydrogenated Nitrile Butadiene Rubber. ............................................ 13

Figure 2.1.1 Grubbs’ catalysts and a generalized structure of a Ru olefin metathesis catalysts. . 22

Figure 2.1.2 Examples of 4- and 6-coordinate Ru-alkylidene olefin metathesis catalysts. ......... 23

Figure 2.1.3 Generalized structures of NHCs used as ligands for Ru olefin metathesis catalysts.

....................................................................................................................................................... 24

Figure 2.1.4 Examples of bis-carbene Ru-alkylidene complexes. ............................................... 25

Figure 2.2.1 POV-ray depiction of the molecular structure of 2-1. ............................................. 31


xiv





Figure 2.2.7 POV-ray depiction of the molecular structure of 2-8.. ............................................ 37

Figure 2.2.8 POV-ray depiction of the molecular structure of 2-12. ........................................... 39


Figure 2.2.10 POV-ray depiction of the molecular structure of 2-14. ......................................... 40





Figure 3.2.1 ROMP of 1,5-cyclooctadiene using 2-4. ................................................................. 76

Figure 3.2.2 ROMP of 1,5-cyclooctadiene using 2-8. ................................................................. 77

Figure 3.2.3 ROMP of 1,5-cyclooctadiene using 2-12. ............................................................... 77

Figure 3.2.4 RCM of diethyl diallylmalonate using 2-4.. ............................................................ 78

Figure 3.2.5 RCM of diethyl diallylmalonate using 2-8. ............................................................. 79

Figure 3.2.6 RCM of diethyl diallylmalonate using 2-12. ........................................................... 80

Figure 3.2.7 CM of methyl acrylate and 5-hexenyl acetate using 2-4. ........................................ 81

Figure 3.2.8 CM of methyl acrylate and 5-hexenyl acetate using 2-8. ........................................ 82

xv

Figure 3.2.9 CM of methyl acrylate and 5-hexenyl acetate using 2-12. ...................................... 82

Figure 3.2.10 CM of NBR and 1-hexene using 2-4 and Grubbs II at 45 °C. ............................... 85

Figure 3.2.11 CM of NBR and 1-hexene using 2-4 at 60 °C. ...................................................... 86

Figure 4.1.1 Alkoxide and electron deficient aryloxides as ligands on olefin metathesis catalysts.

..................................................................................................................................................... 109

Figure 4.1.2 Z-selective olefin metathesis catalyst with a thiolate ligand. ................................ 109






Figure 4.2.6 ROMP of 1,5-cyclooctadiene with 4-1. ................................................................. 117

Figure 4.2.7 RCM of diethyl diallylmalonate with 4-1. ............................................................. 118

Figure 4.2.8 RCM of diethyl diallylmalonate with 4-3, 4-4 and 4-6. ........................................ 118

Figure 4.2.9 CM of 5-hexenyl acetate and methyl acrylate with 4-1. ........................................ 119

Figure 4.2.10 CM of 5- hexenyl acetate and methyl acrylate with 4-3, 4-4 and 4-6. ................ 120

Figure 4.2.11 CM of NBR and 1-hexene with 4-1 at 25 °C. ..................................................... 121

Figure 4.4.1 1H NMR spectrum of 4-3 in C6D6. ........................................................................ 126

Figure 4.4.2 13

C{1H} NMR spectrum of 4-3 in C6D6. ............................................................... 127


Figure 4.4.4 13


xvi

Figure 5.1.1 Carbene stabilized neutral diborene. ..................................................................... 143

Figure 5.1.2 Carbene stabilized diboryne and diborabutatriene. ............................................... 144

Figure 5.1.3 Examples of carbene stabilized boron centered radicals. ...................................... 144


Figure 5.2.2 POV-ray depiction of the molecular structure of the cation of 5-2. ...................... 148







Figure 5.2.9 POV-ray depiction of the molecular structure of 5-10. ......................................... 156

Figure 5.2.10 POV-ray depiction of the molecular structure of the cation of 5-11a. ................ 157

Figure 5.2.11 POV-ray depiction of the molecular structure of 5-12. ....................................... 159

Figure 5.2.12 POV-ray depiction of the molecular structure of 5-13.. ...................................... 160

Figure 5.2.13 POV-ray depiction of the molecular structure of 5-14. ....................................... 161


Figure 5.4.2 11

B{1H} NMR spectrum of 5-1 in C6D6. ............................................................... 171

Figure 5.4.3 13


Figure 5.4.4 29

Si{1H} NMR spectrum of 5-1 in C6D6. .............................................................. 172

xvii

Figure 5.4.5 11



Figure 5.4.7 13


Figure 5.4.8 29


Figure 6.1.1 Orbital interaction between borylenes and metal fragments. ................................ 185

Figure 6.2.1 POV-Ray depiction of the molecular structure of 6-1. .......................................... 189

Figure 6.2.2 Representation of the SOMO of 6-1 with isovalue at 0.06 a.u. ............................. 190

Figure 6.2.3 Experimental X-band EPR spectrum of 6-1 in toluene at 280 K (green) and

simulated EPR spectrum (blue) with the following set of hyperfine coupling constants: a(B) =

4.7, a(N) = 18.4 and a(Cl) = 2.5 MHz......................................................................................... 190


Figure 6.2.5 a) and a’): highest occupied molecular orbital (HOMO) of 6-2, and of 6-2* with a

frozen C-B-N angle at 155°, respectively. b-d) and b’-d’) lowest unoccupied molecular orbitals

(LUMO) of 6-2 and 6-2*, respectively. ...................................................................................... 193



Figure 6.2.8 Calculated transition state for the activation of H2 by 6-2. ................................... 197

Figure 6.2.9 a) Primary interaction between the LUMO of 6-2* and theorbital of H2. b)

Secondary interaction between the HOMO of 6-2* and the * orbital of H2. ........................... 197


Figure 6.4.2 11


Figure 6.4.3 13


xviii

Figure 6.4.4 29


xix

List of Tables

Table 2.5.1 Select crystallographic parameters for 2-1 to 2-4. .................................................... 62

Table 2.5.2 Select crystallographic parameters for 2-5, 2-6, 2-8 and 2-12. ................................. 63

Table 2.5.3 Select crystallographic parameters for 2-17, 2-18, 2-21 and 2-22. ........................... 64

Table 3.1.1 Standard olefin metathesis reactions using common catalysts. ................................ 71

Table 3.4.1 ROMP of 1,5-cyclooctadiene with 2-4. .................................................................... 88





Table 3.4.6 ROMP of 1,5-cyclooctadiene with 2-12. .................................................................. 90



Table 3.4.9 RCM of diethyl diallylmalonate with 2-4. ................................................................ 92

Table 3.4.10 RCM of diethyl diallylmalonate with 2-5. .............................................................. 93




Table 3.4.14 RCM of diethyl diallylmalonate with 2-12. ............................................................ 95


xx


Table 3.4.17 CM of 5-hexenyl acetate and methyl acrylate with 2-4. ......................................... 98





Table 3.4.22 CM of 5-hexenyl acetate and methyl acrylate with 2-12. ..................................... 100



Table 3.4.25 GPC data for CM of NBR and 1-hexene using 2-4 and Grubbs II at 25 °C. ........ 102

Table 3.4.26 GPC data for CM of NBR and 1-hexene using 2-4 and Grubbs II at 45 °C. ........ 103

Table 3.4.27 GPC data for CM of NBR and 1-hexene using 0.14 phr of 2-4 at 45 °C. ............. 104

Table 3.4.28 GPC data for CM of NBR and 1-hexene using 2-4 at 60 °C. ............................... 105



Table 4.4.3 ROMP of 1,5-cyclooctadiene with 4-3, 4-4, and 4-6. ............................................. 129





xxi


Table 4.4.9 CM of 5- hexenyl acetate and methyl acrylate with 4-1. ........................................ 131

Table 4.4.10 CM of 5- hexenyl acetate and methyl acrylate with 4-2. ...................................... 132




Table 4.4.14 GPC data for CM of NBR and 1-hexene using 4-1 at 25 °C. ............................... 134

Table 4.4.15 Select crystallographic parameters for 4-1 to 4-3. ................................................ 136

Table 4.4.16 Select crystallographic parameters for 4-5 and 4-6. .............................................. 137

Table 5.4.1 Select crystallographic parameters for 5-1 to 5-4. .................................................. 176


Table 5.4.3 Select crystallographic parameters for 5-10, 5-12 to 5-14. ..................................... 178


xxii

List of Abbreviations

° degree

°C degrees Celsius

Å angstrom, 10-10

m

atm atmosphere

Ar Aryl

CAAC Cyclic (alkyl)(amino)carbene

Cy-CAAC 1-(2,6-diisopropylphenyl)-3-cyclohexyl-5,5-dimethylpyrrolidin-2-ylidene

CD2Cl2 deuterated dichloromethane

calc calculated

cat. catalyst

CCD charge coupled device

CM cross metathesis

cm centimeter

cod cyclooctadiene

cot cyclooctatriene

Cp cyclopentadienyl

Cp* pentamethylcyclopentadienyl

Cy cyclohexyl

d doublet

xxiii

DAC diamidocarbene

dd doublet of doublet

DCM dichloromethane

Dipp 2,6-diisopropylphenyl

equiv. equivalent

Et ethyl

Et2O diethyl ether

FTIR Fourier transform infrared

g gram

GC-MS gas chromatography-mass spectrometry

GOF goodness of fit

h hour

Hz Hertz

I nuclear spin

IDipp 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene

IMe 1,3-bis(methyl)imidazol-2-ylidene

IMes 1,3-bis(2,4,6-trimethylphenyl)imidazol-2-ylidene

IMes-Cl2 1,3-bis(2,4,6-trimethylphenyl)-4,5-dichloroimidazol-2-ylidene

Im(OMe)2 C3H2(NCH2CH2OMe)2

Ind indenyl

xxiv

iPr iso-propyl

m meta

m multiplet

Me methyl

Me2Im(OMe)2 C5H6(NCH2CH2OMe)2

Mes mesityl, 2,4,6-trimethylphenyl

min minute

mL milliliter

mm millimeter

mmol millimole

NHC N-Heterocyclic carbene

1Jxy n-bond scalar coupling constant between X and Y atoms

NMR nuclear magnetic resonance

o ortho

OTf triflate, trifluoromethanesulfonate

p para

PDI polydispersity index (Ð)

Ph phenyl

phr parts per hundred rubber

POV-Ray Persistence of Vision Raytracer

xxv

ppm parts per million, 10-6

q quartet

RCM ring closing metathesis

ROMP ring opening metathesis polymerization

RT room temperature

SIMes 1,3-bis(2,4,6-trimethylphenyl)-4,5-dihydroimidazol-2-ylidene

SIDipp 1,3-bis(2,6-diisopropylphenyl)-4,5-dihydroimidazol-2-ylidene

t triplet

tBu tert-butyl

Tol toluene

THF tetrahydrofuran

TMS trimethylsilyl

1

Chapter 1 Introduction

1.1 Carbenes

A carbene is defined as a divalent carbon atom with only six valence electrons and attempts to

prepare the parent carbene, CH2, by dehydration of methanol were reported as early as 1835 by

Dumas.1 The prospect of a stable, isolable carbene was, at that time, quite reasonable since the

tetravalency of carbon had not yet been established. It was not until the early 1900s that

Staudinger and Kupfer demonstrated that carbenes, generated in situ from diazo compounds or

ketenes, were highly reactive species.2

Free carbenes can exist in two spin states: singlet or triplet (Figure 1.1.1) with the substituents on

the carbon atom dictating which spin state will be more preferred.3 Bulkier substituents force the

carbene to adopt a less bent geometry, which results in a smaller σ-pπ separation and thus

favoring a triplet state. Steric effects determine the ground-state spin multiplicity only as far as

the electronic effects are negligible, which is rarely the case.4,5

Therefore, careful consideration

of the substituents can favor the formation of either a singlet or a triplet carbene.

Figure 1.1.1 Singlet and triplet forms of a carbene.

A significant discovery for carbene chemistry occurred during the 1950s when Breslow6 and

Wanzlick7 realized that the stability of a carbene could be dramatically enhanced by the presence

of amino substituents (Scheme 1.1.1). They were, however, unable to isolate monomeric

carbenes.

2

Scheme 1.1.1 The Wanzlick equilibrium.

Twenty years later, Wanzlick and co-workers showed that imidazolium salts could be

deprotonated to generate the corresponding imidazol-2-ylidenes, but these could only be isolated

when trapped using phenylisothiocyanate or mercury acetate (Scheme 1.1.2).8,9

Scheme 1.1.2 In situ preparation of imidazol-2-ylidenes.

1.1.1 Synthesis and Isolation of Stable Free Carbenes

The first stable and isolable carbene, a phosphino(silyl)carbene, was reported by Bertrand and

co-workers in 1988 but it was not until 2000 that a crystalline analogue was synthesized and

crystallographically characterized (A and B in Figure 1.1.2).10,11

3

Figure 1.1.2 First isolable and crystalline carbenes.

Following the seminal work of Bertrand, in 1991 Arduengo and co-workers reported the

isolation of the first crystalline N-heterocyclic carbene12

(NHC) (C in Figure 1.1.2). Since their

discovery, NHCs have found broad applications as organocatalysts as well as ligands for

transition metal-based catalysis. Over the last 25 years there have been numerous reports

detailing the syntheses of variations on NHCs as well as new classes of carbenes. Shown in

Figure 1.1.3 are select examples of carbenes reported in recent literature.13-27

Figure 1.1.3 Select examples of carbenes.

4

Several variations, including acyclic and cyclic carbenes, variable ring sizes, heteroatoms within

the heterocycle, and an all-carbon cycle, have been reported. In recent years anionic, dianionic,

and mesoionic NHCs have also been reported (Figure 1.1.3). Of particular relevance to this

thesis, however, are cyclic (alkyl)(amino)carbenes (CAAC).28

First reported in 2005 by Bertrand and co-workers, replacing a σ-withdrawing and π-donating

nitrogen center in an NHC by a σ-donating, but not π-donating, carbon center leads to the

formation of stable and isolable cyclic (alkyl)(amino)carbenes. This substitution makes CAACs

more nucleophilic but also more electrophilic than NHCs which is evidenced by the smaller

HOMO-LUMO gap for CAACs compared to NHCs.27

Figure 1.1.4 Steric environment differences between phosphines and carbenes.

In addition, the presence of a quaternary carbon center α to the carbene center results in a steric

environment that is markedly different than those of phosphines and NHCs (Figure 1.1.4). The

quaternary carbon center is also well situated for implementing stereochemical induction.

There are a number of ways to denote carbenes bound to transition metal centers and main group

elements (Figure 1.1.5).29

As such, the following formalism will be used throughout this thesis.

Figure 1.1.5 Carbene coordination to metals and p-block elements.

5

1.1.2 Carbenes as Ligands for Transition Metal-Based Catalysts

While carbenes (especially NHCs) have been widely used as organocatalysts,30-35

their success as

ligands will be further discussed as it is more pertinent to this thesis. It is worth mentioning that,

although the isolation of a free carbene was a synthetic challenge, the first transition

metal-carbene complexes were reported by Chugaev36

as early as 1925. In the 1960s, there was

also the pioneering work by Fischer and Maasböl37

as well as the work by Öfele38

. NHC

transition metal complexes have been known and their organometallic chemistry was also

investigated by Lappert39

.

One can distinguish coordinated carbenes as two extreme types: a Fischer and a Schrock type.3

For a Fischer type carbene, direct donation from the carbene to the metal center predominates

and the carbon tends to have a partial positive charge (electrophilic). Such carbenes typically

have π-donor substituents (R = OMe or NMe2). In contrast, a Schrock type carbene involves

covalent bonding between the carbon and the metal center. Each of these bonds is polarized

toward the carbon making it have a partial negative charge (nucleophilic). These carbenes

typically have non-π-donating R groups (Figure 1.1.6).

Figure 1.1.6 Fischer and Schrock carbene complexes.

Fischer-carbene complexes are usually formed with low oxidation state, late transition metals

that have π-acceptor ligands, whereas Schrock-carbene complexes are formed with higher

oxidation state, early transition metals that have non-π-acceptor ligands. Since NHCs have two

π-donor substituents at the carbene center, NHC complexes may be classified, at a first glance, as

Fischer-type compounds. However, NHCs bind to transition metals only through σ donation,

with negligible π-back-bonding, and are therefore not Fischer-type carbenes.

It has also been shown experimentally that NHCs are not phosphine mimics, as catalysts

employing NHCs rather than phosphines show enhanced activities.40

In general, NHC-ligated

6

transition metal complexes are less air and moisture sensitive than their phosphine analogues,

explained by the fact that NHCs are more strongly bound to the metal center.41,42

Employing NHC ligands in transition metal catalysis has led to several breakthroughs in

enhancing the catalytic activity for a number of valuable organic transformations. These include,

but are not limited to, Heck,43-45

Suzuki,46,47

Sonogashira48,49

, Kumada50,51

and Stille52

couplings,

aryl amination42,53

and amide α-arylation54

, as well as hydrosilylation.55

More recently, through

the synthesis of chiral NHCs, a number of transformations with high levels of enantioinduction

have been reported. A famous example of the impact NHCs have had on catalysis is olefin

metathesis56

where replacing a phosphine with an NHC highly improves the stability and activity

of the catalyst (discussed in detail in Section 1.2).

Over the past few years, CAACs have also garnered attention as viable ligands for transition

metal-based catalysts as they were shown to stabilize low coordinate metal centers.57,58

The first

example of α-arylation of ketones and aldehydes with aryl chlorides under ambient conditions

was demonstrated using a Pd-based catalyst utilizing a CAAC ligand.57

Cyclic

(alkyl)(amino)carbenes were also shown to stabilize a cationic gold complex which catalyzes the

coupling of enamines and terminal alkynes to generate allenes with subsequent loss of imines.58

Treating the same gold complex with NH3 or hydrazine results in the formation of very efficient

catalysts for the hydroamination of a variety of non-activated alkynes and allenes with ammonia

or hydrazine.59,60

CAACs were also shown to be effective ligands for Ru-based catalysts for olefin metathesis61

especially for the ethenolysis of methyl oleate,62

a process that transforms internal olefins

derived from seed oils to terminal olefin feed stocks.

1.1.3 Carbenes in Stabilizing Low-Valent and Reactive Species

Over the past decade, there have been significant advances in the isolation of stable, low

oxidation state main group compounds which has been largely enabled through the use of neutral

donors to stabilize such species. For example, singlet carbenes such as NHCs and CAACs have

been used as ligands to stabilize main group molecules in their zero oxidation state.26,63,64

Select

examples will be discussed here and boron-based systems will be discussed in Chapters 5 and 6.

7

Robinson and co-workers have reported the isolation of diatomic main group molecules in low

oxidation states which are stabilized by two carbenes. The phosphorous,65

arsenic,66

and silicon67

analogues have been stabilized by two NHCs (A and B in Figure 1.1.7). Bertrand and co-workers

have also shown that larger polyatomic molecules with main group elements in the zero

oxidation state can be isolated when capped by carbenes (C in Figure 1.1.7).68

Figure 1.1.7 Carbene-stabilized main group species in the (0) oxidation state.

Carbenes were also shown to stabilize phosphorus radicals where phosphinyl radicals,69

a

phosphinyl radical cation,70

and a phosphonitride radical cation71

were isolated and fully

characterized (Figure 1.1.8).

Figure 1.1.8 Carbene stabilized paramagnetic main group species.

Bertrand and co-workers demonstrated that carbenes could also be used to stabilize and isolate

organic radical cations (Figure 1.1.9).72

Treating a less bulky carbene such as the anti-Bredt

NHC27

with CO results in the attack of two carbene molecules at the carbon center forming an

oxyallyl species, which can be protonated and then oxidized to form an oxyallyl radical cation.

8

Figure 1.1.9 Stable oxyallyl radical cation.

More recently, carbenes have been utilized to stabilize phosphinonitrenes which were then used

as nitrogen atom transfer agents (Scheme 1.1.3).73

This report by Bertrand and co-workers

demonstrated how main group compounds can mimic the chemical behavior of transition metals,

an observation that has been utilized in recent years to use main group systems to effect

transformations that were otherwise limited to transition metals.

Scheme 1.1.3 Nitrogen atom transfer using a carbene stabilized phosphinonitrene.

9

1.2 Catalytic Olefin Metathesis

Olefin metathesis is a C−C bond forming reaction that proceeds through scission, redistribution,

and bond formation of two molecules containing an alkene functionality.74,75

A generic reaction

depicting catalytic olefin metathesis can be seen in Scheme 1.2.1.76

Scheme 1.2.1 Depiction of olefin metathesis.

1.2.1 Well-Defined, Homogenous Catalysts

1.2.1.1 Schrock's Catalyst

With the isolation of the first transition metal alkylidene complex in 1974, which was shown to

effect olefin metathesis,77

Schrock and others reported the synthesis of several other early

transition metal alkylidene complexes.78,79

Most notably are the W and Mo imido, alkylidene

complexes depicted in Figure 1.2.1, with the Mo species being commercially available as

"Schrock's Catalyst".80

While these early transition metal alkylidene species are extremely active

for olefin metathesis, their extreme reactivity renders them quite functional group intolerant.

Figure 1.2.1 Generalized structure of a Mo-based Schrock-type catalyst.

1.2.1.2 Grubbs Catalyst

Due to the laborious preparation and extreme sensitivity and functional group intolerance of

Schrock's W and Mo metathesis catalysts, new catalysts with better functional group

compatibility were sought out. Based on earlier reports that ill-defined Ru species were effective

10

in ring opening metathesis polymerization (ROMP), the synthesis of well-defined Ru catalysts

was investigated by Grubbs and co-workers. The first well-defined Ru-based catalyst was the

alkylidene species A which is formed through the ring opening of diphenylcyclopropene by

Ru(PPh3)3Cl2 (Scheme 1.2.2).81

This complex was found to be active for ROMP, and exchanging

PPh3 ligands for PCy3 results in a complex that is active for cross metathesis.82

Scheme 1.2.2 Synthesis of the first well-defined Ru olefin metathesis catalyst.

This discovery prompted further research in catalytic olefin metathesis chemistry and, while the

new Ru based systems are less active than Schrock’s systems, they are significantly more stable

and functional group tolerant. A large library of Ru-based olefin metathesis catalysts became

available as new methods for the preparation of Ru-alkylidene complexes (discussed in

Section 2.1.4) were developed.83

Of major significance to this field was the report of

(PCy3)2Ru(CHPh)Cl2 and (SIMes)(PCy3)Ru(CHPh)Cl2 known as Grubbs I and Grubbs II,

respectively (Figure 1.2.2),82,84

where the substitution of PCy3 for SIMes in the second

generation system increased the activity of the catalyst dramatically. These catalysts are

currently used for a variety of commercial applications.85,86

Figure 1.2.2 First and second generation Grubbs catalysts.

1.2.2 Mechanism of Catalytic Olefin Metathesis

A number of possible mechanisms for catalytic olefin metathesis were initially reported,75

with

Calderon proposing the formation of a cyclobutane in the coordination sphere of the metal

11

center87

and Grubbs proposing a metallacyclopentane intermediate.88

Around the same time,

Pettit proposed an intermediate in which four carbon atoms form sigma bonds with the metal

center,89

and Chauvin proposed a mechanism involving a metal alkylidene species undergoing a

[2+2] cycloaddition with an olefin to afford a metallacyclobutane which can undergo either

constructive or non-constructive olefin and alkylidene formation (Scheme 1.2.3).90

Through

labeling experiments and analysis of the distribution of metathesis products Chauvin’s

mechanism gained support and is now the accepted mechanism for catalytic olefin

metathesis.91,92

Scheme 1.2.3 Chauvin’s mechanism of olefin metathesis.

With Grubbs-type systems, there are additional considerations when discussing the catalytic

cycle. Based on kinetic data, it was determined that phosphine dissociation is necessary to

generate the 4-coordinate active species (Scheme 1.2.4).93-95

This was considered for the rational

design of the second generation system, as well as a number of other derivatives, where a

stronger donor is introduced trans to the PCy3 to facilitate phosphine dissociation and thus

enhance rate of catalysis and activity. The incoming olefin could then bind to the active

4-coordinate species, either trans or cis to the neutral ligand. This coordination mode influences

how the metallacyclobutane forms with the metal and in the case of the first and second

generation Grubbs catalyst, as well as derivatives, it has been determined that coordination trans

to the neutral ligand (phosphine or NHC) is the favored pathway.96

An example of cis

coordination will be discussed in Section 2.1.2.

12

Scheme 1.2.4 Olefin metathesis mechanism with Grubbs I.

1.3 Nitrile Butadiene Rubber

Modification of Nitrile Butadiene Rubber (NBR) through olefin metathesis is a specific

industrial application of catalytic olefin metathesis. NBR is a co-polymer of butadiene and

acrylonitrile which is formed on an industrial scale by anionic, emulsion polymerization.97

The

resulting polymer contains cis- and trans-alkene functionalities, vinyl groups, and nitrile groups

(Figure 1.3.1). The nitrile groups give NBR useful properties such as stability in oils, fats and

fuels, low permeability, and high temperature resistance.98

NBR is used in a number of machine

parts and belts, for automotive tubing, and even in the soles of running shoes.

Figure 1.3.1 Depiction of functional groups found in Nitrile Butadiene Rubber.

13

Modifications to crude NBR results in the formation of polymers with tailored properties for

specific applications. For example, cross metathesis of NBR with 1-hexene99,100

lowers the

molecular weight and narrows the polydispersity of the resulting polymer. The residual double

bonds of the resulting polymer can then be hydrogenated to form HNBR (Figure 1.3.2).98,101

HNBR is still extremely resistant to oils and fuels, has better thermal stability than NBR, and is

resistant to ozone and oxidative aging. This high strength polymer has numerous oilfield and

automotive applications.

Figure 1.3.2 Depiction of hydrogenated Nitrile Butadiene Rubber.

1.4 Lanxess Project

Laxness is a multinational specialty chemicals and polymers company and is the world's largest

manufacturer of NBR and HNBR. To accomplish the modifications to NBR described in

Section 1.3, the ruthenium based Grubbs II catalyst is used for the cross metathesis with

1-hexene and Wilkinson's Catalyst is used for the hydrogenation to HNBR. The hydrogenation

process is costly as the catalyst is based on the precious metal Rh. A system using a cheaper

technology would be advantageous and economically beneficial to Lanxess. The use of Grubbs II

requires licensing of the technology which adds considerable cost to the process.

The work presented in Chapters 2 through 4 was sponsored by Lanxess. In general, the goals of

the collaboration are twofold; the development of new catalysts based on less expensive metals

that effect the hydrogenation of NBR, and the development of new proprietary olefin metathesis

14

catalysts that effect the cross metathesis of 1-hexene and NBR. The focus of the majority of this

thesis will be on the development of novel olefin metathesis catalysts. While the current patent

literature is extensive and covers a broad range of catalysts, systems involving tridentate and

hemilabile tridentate ligands are absent.

1.5 Scope of Thesis

The goal of this thesis is to use carbenes for two main purposes. The first was developing

proprietary olefin metathesis catalysts for the cross metathesis of NBR and 1-hexene using a

hemilabile tridentate NHC as one of the neutral donors on a Ru-based system. In Chapter 2, the

synthesis and characterization of bis-mixed-carbene ruthenium-alkylidene-thiolate complexes is

explored. These systems are synthesized by a new route to form Ru-alkylidenes from bis-carbene

RuHCl starting materials and alkenyl sulfides. This new method is safe, high yielding, and uses

inexpensive starting materials. It also conveniently installs the alkylidene fragment as well as

transfers a thiolate in one step. Chapter 2 also discusses how the use of ethyl vinyl sulfide results

in the formation of Ru-alkyl and Ru-vinyl species rather than the expected Ru-alkylidene

compounds.

In Chapter 3, the complexes synthesized in Chapter 2 are tested for catalytic olefin metathesis.

They are used in a variety of reactions including ring opening metathesis polymerization, ring

closing metathesis, cross metathesis and the metathesis of NBR and 1-hexene. The use of BCl3

as an additive was proven necessary to activate the previous complexes, where it is believed to

act as a halide-abstracting agent to form a cationic Ru-center, which then effects metathesis.

Chapter 4 describes the synthesis of bis-mixed-carbene ruthenium-alkylidene complexes, which

are obtained from compounds synthesized in Chapter 2 through anion exchange. The complexes

are tested for a variety of metathesis reactions including, ROMP, RCM, CM and cross metathesis

of NBR with 1-hexene. These systems are shown to be more active, and in the bis-halide systems

BCl3 is no longer a necessary additive.

The second goal of this thesis is to employ carbenes as stabilizing ligands for the isolation of

reactive boron species. As such, Chapter 5 describes the use of cyclic (alkyl)(amino)carbenes for

the stabilization and isolation of iminoboranes. These systems are generated under ambient

conditions, in contrast to previously-reported iminoboranes syntheses. CAACs are shown to

15

replace transition metals that have been used for the synthesis and stabilization of iminoboryl

moieties. The intermediates to these iminoboranes are also isolated and are shown to undergo

[2+2] cycloaddition reactions with CO2.

Finally, in Chapter 6, CAACs are used to stabilize a boron (+2) and a boron (+1) system. This is

the first example of a mono-carbene stabilized borylene. This boron (+1) species is shown to be

very electrophilic and is able to activate H2 and strongly bind CO, two reactions that have not

been previously demonstrated with boron Lewis acids.

The entirety of the synthetic work and characterizations described in this thesis were performed

by the author with the exception of elemental analysis and EPR measurements, which were

completed in house by departmental staff. DFT calculations were performed by Dr. David

Martin in Professor Guy Bertrand’s lab at UCSD.

Portions of the work presented herein have been discussed in the following publications:

Chapter 2:

1. Dahcheh, F.; Lund, C.L.; Sgro, M.J. and Stephan, D.W. Multidentate Carbene-Ru-Based

Metathesis Catalysts. US Patent Application 61827152, filed May 24, 2013. Patent

Pending.

2. Reprinted with permission from: “Dahcheh, F. and Stephan, D.W. A New Route to

Ruthenium Thiolate Alkylidene Complexes. Organometallics 2013, 32, 5253-5255”.

Copyright (2013) American Chemical Society.

3. Reproduced from: “Dahcheh, F. and Stephan, D.W. Reactions of Ruthenium Hydrides

with Ethyl Vinyl Sulfides. Dalton Transactions 2014, 43, 3501-3507” with permission

from The Royal Society of Chemistry.

Chapter 3:



Pending.

16

Chapter 4:



Pending.

Chapter 6:

1. Dahcheh, F.; Martin, D.; Stephan, D.W. and Bertrand, G. Synthesis and Reactivity of a

CAAC-Aminoborylene Adduct: A Hetero-Allene or an Organoboron Isoelectronic with

Singlet Carbenes? Angew. Chem. Int. Ed. 2014, Accepted, DOI:10.1002/anie.201408371.

The following work was also completed during the completion of this degree, but has not been

included in the thesis:

1. Sgro, M.J.; Dahcheh, F. and Stephan, D.W. Synthesis and Reactivity of Ruthenium-

Hydride Complexes Containing a Tripodal Aminophosphine Ligand. Organometallics

2014, 33, 578-586.

2. Dahcheh, F. and Stephan, D.W. Ruthenium and Rhodium Complexes of Thioether-

Alkynylborates. Organometallics 2012, 31, 3222-3227.

17

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(62) Anderson, D. R.; Ung, T.; Mkrtumyan, G.; Bertrand, G.; Grubbs, R. H.; Schrodi, Y.


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(64) Wang, Y. Z.; Robinson, G. H. Inorg. Chem. 2011, 50, 12326.

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Robinson, G. H. J. Am. Chem. Soc. 2008, 130, 14970.

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Robinson, G. H. Chem. Eur. J. 2010, 16, 432.

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Robinson, G. H. Science 2008, 321, 1069.

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129, 14180.

(69) Back, O.; Donnadieu, B.; von Hopffgarten, M.; Klein, S.; Tonner, R.; Frenking, G.;

Bertrand, G. Chem. Sci. 2011, 2, 858.

(70) Back, O.; Celik, M. A.; Frenking, G.; Melaimi, M.; Donnadieu, B.; Bertrand, G. J. Am.

Chem. Soc. 2010, 132, 10262.

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(74) Grubbs, R. H. Handbook of Metathesis; WILEY-VCH Verlag GmbH and Co.: Germany,

2003; Vol. 1.

(75) Astruc, D. New J. Chem. 2005, 29, 42.

(76) Grubbs, R. H.; Chang, S. Tetrahedron 1998, 54, 4413.

(77) Schrock, R. R. J. Organomet. Chem. 1976, 122, 209.

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Schrock, R. R. J. Organomet. Chem. 1993, 459, 185.

(79) Schrock, R. R.; Murdzek, J. S.; Bazan, G. C.; Robbins, J.; DiMare, M.; O'Regan, M. J.

Am. Chem. Soc. 1990, 112, 3875.

21

(80) Schrock, R. R. Acc. Chem. Res. 1986, 19, 342.

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3974.

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2039.

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2010, 31, 1616.

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22

Chapter 2 Synthesis and Characterization of Bis-Mixed-Carbene

Ruthenium-Alkylidene-Thiolate Complexes

2.1 Introduction

2.1.1 First Isolated Transition Metal Based Alkylidene Complex

In seeking avenues to new metathesis catalysts, a key facet involves strategies to install

Ru-alkylidene moieties. The first isolated transition metal alkylidene complex was based on Ta

and reported by Schrock and co-workers in 1974 (Scheme 2.1.1).1-3

This synthetic route opened

up the field of well defined olefin metathesis catalysts.

Scheme 2.1.1 Synthesis of the first isolated transition metal alkylidene.

2.1.2 Modifications to Grubbs’ Catalyst

Since the discovery of Grubbs catalysts (A, B, and C in Figure 2.1.1), numerous modifications

have been undertaken to improve activity and stability,4 and numerous systems capable of olefin

metathesis have been developed with a generalized structure (D in Figure 2.1.1) shown below.

Based on the accepted mechanism of Ru catalyzed olefin metathesis, the only essential ligand on

the metal center is the alkylidene.5-7

This indicates that the other ligands are open for

modification to alter steric and electronic properties which affects catalyst activity, selectivity,

and stability.

Figure 2.1.1 Grubbs’ catalysts and a generalized structure of a Ru olefin metathesis catalysts.

23

Whereas the majority of systems reported thus far are 5-coordinate species, there are examples of

both 4-coordinate and 6-coordinate systems capable of olefin metathesis. In 2004, Piers and

co-workers reported the synthesis of a 4-coordinate Ru-phosphonium alkylidene species (A in

Figure 2.1.2).8 These 14e

- phosphonium alkylidene complexes were found to be rapidly initiating

olefin metathesis catalysts.9 There is also the possibility of introducing a 6th ligand to the

coordination sphere through chelation as was demonstrated by Grubbs and co-workers in

2011.10-12

. Such systems (B in Figure 2.1.2) were shown to be effective Z-selective olefin

metathesis catalysts.

Figure 2.1.2 Examples of 4- and 6-coordinate Ru-alkylidene olefin metathesis catalysts.

The Z-selectivity is due to the chelating anion occupying the coordination site trans to the NHC

during the catalytic cycle. This geometry forces the incoming olefin to bind cis to the NHC

which is also locked in place by the cyclometallated NHC ligand. The resulting

metallacyclobutane intermediate is formed in a side-on fashion and as such the substituents on

the metallacyclobutane are forced to point away from the Mes group and the resulting olefin that

is produced adopts a Z-conformation.13

In further attempts to increase catalytic activity and catalyst stability, over 400 complexes

containing different NHC ligands have been prepared.14

A summary of generalized structures is

depicted in Figure 2.1.3.

24

Figure 2.1.3 Generalized structures of NHCs used as ligands for Ru olefin metathesis catalysts.

Through modifications to the NHC ligand, catalysts with increased activity for specific

applications and catalyst properties, such as aqueous15,16

and asymmetric17-19

catalysis, were

accessible. Nonetheless, the Grubbs II catalyst or Hoveyda-Grubbs catalyst provide reasonable

activity and stability for most olefin metathesis applications and therefore remain the most

widely applied catalysts in the ruthenium based family.14,20,21

2.1.3 Bis-Carbene Olefin Metathesis Catalysts

One of the modifications applied to Grubbs’s catalysts include replacement of both phosphines

with NHCs. Herrmann22

and co-workers, in 1998, and Grubbs23

and co-workers, in 2003,

prepared bis-NHC ruthenium alkylidene complexes (A and B in Figure 2.1.4). While these

species displayed enhanced stability, the activity was modest compared to the second generation

Grubbs catalyst. This is presumably a result of the strong binding of the carbene to the metal

center which disfavors dissociation.

25

Figure 2.1.4 Examples of bis-carbene Ru-alkylidene complexes.

Several other reports have examined the impact of varying the electronic and steric nature of the

carbenes on the catalytic activity. Plenio and co-workers24,25

introduced electron-poor NHCs in

the bis-NHC ruthenium systems which improved the activity in RCM and ROMP reactions (C

and D in Figure 2.1.4). It was shown in these reports that the electron-poor carbene dissociates

while SIMes stays ligated providing access to the active, 4-coordinate species. Nolan and

co-workers26

studied the impact of introducing one smaller NHC, (E in Figure 2.1.4), in mixed

carbene Ru-indenylidene complexes. Compounds with a smaller carbene showed improved

activity in RCM at very low catalyst loading. In all cases, bis-carbene Ru-alkylidenes metathesis

catalysts are active at elevated temperatures (80 - 120 °C) and are thought to proceed via carbene

dissociation.

2.1.4 Routes to Ru-Alkylidene Complexes

The different known methods for synthesis of Ru-alkylidene complexes have been

comprehensively reviewed by Fogg and Foucault.27

The following are select examples of the

most common routes.

26

The first well-defined Ru-based olefin metathesis catalyst was reported by Grubbs and

co-workers4,28

and was synthesized by the ring opening of 2,2-diphenylcyclopropene with

Ru(PPh3)3Cl2 to give the corresponding vinylalkylidene (Scheme 2.1.2). This method requires

the difficult synthesis of the cyclopropene and the corresponding vinylalkylidene initiates more

slowly than the typical benzylidene.20,29

Scheme 2.1.2 Synthesis of the first ruthenium alkylidene.

Following this discovery, a method to generate an alkylidene through the use of diazomethanes

as transfer reagents was reported by Grubbs and co-workers (Scheme 2.1.3).4 This route is high

yielding and provides a direct pathway to the ruthenium benzylidene and consequently first

generation Grubbs’ catalyst (Grubbs I). Diazomethanes are, however, shock sensitive and

explosive and therefore must be handled with extreme caution.

Scheme 2.1.3 Synthesis of Grubbs I catalyst using phenyl diazomethane.

In 2001, Milstein and co-workers developed a method using a sulfur ylide as an alkylidene

transfer reagent.30

This method provides a safer synthetic route over the use of diazomethanes

and offers a direct route to the ruthenium benzylidene. A stoichiometric amount of thioether

waste is, however, generated (Scheme 2.1.4). This method is also not general and low-yielding if

the phenyl group is changed to other alkyl substituents such as methyl.

27

Scheme 2.1.4 Synthesis of Grubbs I catalyst using a sulfur ylide.

The reaction of Ru(PPh3)3Cl2 with 1,1-diphenyl-2-propyn-1-ol occurs with the loss of H2O to

produce a Ru indenylidene species, which undergoes an exchange reaction by subsequent

addition of PCy3 (Scheme 2.1.5).31

This complex is active for olefin metathesis but is slower

initiating than Grubbs I catalyst. This Ru-indenylidene complex, however, can be used to

synthesize Grubbs Catalyst by the addition of an excess of styrene.

Scheme 2.1.5 Synthesis of Grubbs I catalyst via an indenylidene intermediate.

While the previous routes utilized Ru dichloride species, Grubbs and co-workers also developed

a method for preparing Ru-alkylidene complexes by reacting Ru(0) species and

dichloroalkanes.32

For example, heating Ru(cod)(cot) in the presence of PCy3 and Cl2CHPh

results in the formation of Grubbs I catalyst (Scheme 2.1.6). In an analogous route, mixing

RuH2(H2)2(PCy3)2 with cyclohexene results in the in situ formation of a Ru(0) species which

subsequently reacts with Cl2CHPh to also give Grubbs I catalyst.

28

Scheme 2.1.6 Synthesis of Grubbs I catalyst from Ru(0) species.

Recently a new method of preparing ruthenium alkylidenes from Ru(0) starting materials and

dithioacetals has been developed (Scheme 2.1.7). This method conveniently installs the

alkylidene fragment as well as a tridentate dithiolate ligand in one simple step.33

Scheme 2.1.7 Synthesis Ru-alkylidenes from dithioacetals and Ru(PPh3)3(H)2.

A unique example of modification to the Grubbs framework came from the Piers' group where

they found that protonation of a Ru carbide species with Jutzi's acid leads to the formation of the

Ru-phosphonium alkylidene (Scheme 2.1.8).8

Scheme 2.1.8 Synthesis of a ruthenium phosphonium alkylidene complex.

29

In addition to the previous routes, several methods for generating Ru-alkylidene using Ru

hydrides have been reported. Reacting Ru(PPh3)3HCl with 3-chloro-3-methyl-1-butyne followed

by phosphine exchange affords the Ru vinylalkylidene (Scheme 2.1.9).34

Scheme 2.1.9 Synthesis of a vinylalkylidene using propargyl chloride.

Grubbs and co-workers have used vinyl chlorides in combination with RuHCl(PCy3)2(H2) to

yield Ru-alkylidene complexes (Scheme 2.1.10). This route, however, is not synthetically viable

as isolation of the complexes is problematic and is low yielding.35

Scheme 2.1.10 Synthesis of a Ru-alkylidene using vinyl chloride.

Alternatively, starting from [Ru(PiPr3)2HCl]2, this synthon can be converted to an alkylidene

(Scheme 2.1.11) via the addition of vinyl chloroformate.36

Scheme 2.1.11 Synthesis of a Ru-ethylidene using vinyl chloroformate.

This reaction proceeds through the liberation of CO2 and transfer of the chloride to the Ru center

as the ethylidene is formed.

30

2.2 Results and Discussion

2.2.1 Synthesis of Ru-Hydride Complexes

In recent communications37,38

we described a synthetic strategy to the species of the general

formula (Im(OMe)2)(SIMes)(PPh3)RuHCl (Im(OMe)2 = (C3H2(NCH2CH2OMe)2). In a similar

fashion a series of related compounds with different NHC derivatives were synthesized. The

reaction of (Im(OMe)2)(PPh3)2RuHCl37

with IMes in THF at 60 oC proceeds overnight yielding

2-1 as a red solid in 73% yield (Scheme 2.2.1).

Scheme 2.2.1 Synthesis of 2-1 to 2-3.

The 1H NMR spectrum of 2-1 shows a doublet at -28.12 ppm, with a coupling constant of 26 Hz,

indicative of a hydride coupled to a single phosphorus center which was observed at 43.9 ppm in

the 31

P{1H} NMR spectrum. Single crystal X-ray analysis of 2-1 confirmed its formulation as

(IMes)(Im(OMe)2)(PPh3)RuHCl (Figure 2.2.1) with a five-coordinate square-pyramidal Ru

center where the two NHCs, chloride, and phosphine form the base of the pyramid and the

hydride occupies the apex. The Ru-C distances for IMes and Im(OMe)2 are 2.077(2) and

1.969(2) Å, respectively. The trans influence of these carbene ligands is reflected in the

elongated Ru-P and Ru-Cl distances of 2.2880(6) and 2.4509(6) Å, respectively. The hydride

31

was located from the difference map with a Ru-H distance of 1.50(3) Å and the cis disposition of

the carbene ligands in 2-1 results in a C-Ru-C angle of 91.27(9)°.

Figure 2.2.1 POV-ray depiction of the molecular structure of 2-1. Ru: dark green, O: red, Cl:

green, N: aquamarine, P: orange, C: black, H: gray. H-atoms except for Ru-H and IMes-CH

omitted for clarity.

Similarly, reaction of (Im(OMe)2)(PPh3)2RuHCl37

with IMes-Cl2 in THF at 60 °C for 48 hours

resulted in the formation of 2-2 in 65% yield. The 1H NMR spectrum of 2-2 reveals a doublet at

28.11 ppm with 2JPH of 25 Hz and the

31P{

1H} NMR spectrum shows a singlet at 43.2 ppm.

X-ray analysis of single crystals of 2-2 revealed a 5-coordinate square-pyramidal Ru center

where the base of the pyramid is formed by the two NHCs, chloride, and phosphine ligands and

the hydride occupies the apex: thus, the formulation is (IMes-Cl2)(Im(OMe)2)(PPh3)RuHCl

(Figure 2.2.2). The Ru-C distances for IMes-Cl2 and Im(OMe)2 are 2.058(5) and 1.976(5) Å,

respectively. The Ru-P and Ru-Cl distances are 2.314(1) and 2.452(1) Å, respectively, and the

Ru-H distance is 1.51(4) Å. Similar to 2-1, the cis disposition of the carbene ligands in 2-2

results in a C-Ru-C angle of 97.3(2)°.

32


green, N: aquamarine, P: orange, C: black, H: gray. H-atoms except for Ru-H omitted for clarity.

In an analogous reaction, (Me2Im(OMe)2)(PPh3)2RuHCl38

reacted with SIMes in THF at 50 oC

for 24 hours to give 2-3 in 73% yield. The hydride and phosphorus signals in the 1H and

31P{

1H}

NMR spectra for 2-3 are observed at -27.43 ppm and 36.5 ppm, respectively. Single crystal of

compound 2-3 were grown and an X-ray analysis confirmed its formulation as

(SIMes)(Me2Im(OMe)2)(PPh3)RuHCl (Figure 2.2.3).


green, N: aquamarine, P: orange, C: black, H: gray. H-atoms except for Ru-H omitted for clarity.

33

The Ru-C distances for SIMes and Me2Im(OMe)2 are 2.077(3) and 1.985(3) Å, respectively,

similar to those in 2-1. The Ru-P and Ru-Cl distances are 2.3384(8) and 2.4583(9) Å,

respectively, while the Ru-H distance is 1.50(3) Å. Similar to 2-1 and 2-2, the cis disposition of

the carbene ligands in 2-3 results in a C-Ru-C angle of 92.1(1)°.

2.2.2 Synthesis of Ru-Alkylidene Complexes Using Aryl-Alkenyl Sulfides

With a series of bis-carbene Ru-hydride species in hand, reactions with aryl alkenyl sulfides

were explored. Reaction of (Im(OMe)2)(SIMes)(PPh3)RuHCl37,38

with phenyl vinyl sulfide

(Scheme 2.2.2) in CH2Cl2, for four hours at 25 °C, yielded a new red solid 2-4 in 92% yield. The

1H NMR spectrum of 2-4 reveals signals arising from carbene and thiolate ligands as well as a

broad singlet at 18.29 ppm corresponding to one proton which was assigned to the Ru=CH

fragment with the corresponding carbon signal in the 13

C{1H} NMR spectrum at 313.7 ppm.


A single crystal X-ray analysis of compound 2-4 confirmed its formulation as

(Im(OMe)2)(SIMes)(PhS)RuCl(=CHCH3) (Figure 2.2.4). The geometry at the metal center is

distorted square pyramidal in nature and similar to related bis-carbene Ru-alkylidene

complexes,22-26

the two carbenes are positioned trans to each other with a C-Ru-C angle of

158.23(6)o. The two anionic groups are also in a trans disposition with the alkylidene fragment

occupying the pseudo-axial position. The Ru-C distances for the NHCs are 2.084(2) and

2.100(2) Å for SIMes and Im(OMe)2, respectively, while the Ru-C distance for the alkylidene is

34

1.820(2) Å. The corresponding Ru-Cl distance is 2.4744(4) Å while the Ru-S distance is

2.3595(5) Å.


green, N: aquamarine, S: yellow, C: black. H-atoms omitted for clarity.

Compound 2-5 was, analogously, prepared by the addition of phenyl vinyl sulfide to a solution

of 2-1 in CH2Cl2, and stirring for five hours at 25 °C, where it was isolated as a red solid in a

modest 59% yield. The 1H NMR spectrum of 2-5 reveals a quartet at 19.09 ppm, with a

3JHH of

6 Hz, which integrates to one proton and is assigned to the Ru=CH fragment. The corresponding

carbon signal for this fragment was derived from a two dimensional NMR experiment (HSQC)

and is present at 313.6 ppm. A single X-ray analysis of compound 2-5 confirmed its formulation

as (Im(OMe)2)(IMes)Ru(=CHCH3)Cl(SPh) where the geometry around the Ru center is best

described as distorted square pyramidal (Figure 2.2.5).

35


green, N: aquamarine, S: yellow, C: black, H: gray. H-atoms except for IMes-CH omitted for

clarity.

The two carbenes are trans with a C-Ru-C angle of 158.15(13)o, the two anionic groups are also

in a trans disposition while the alkylidene fragment occupies the pseudo-axial position. The

Ru-C distances for the NHCs are 2.102(3) and 2.086(3) Å for IMes and Im(OMe)2, respectively.

The Ru-C distance for the alkylidene is 1.818(4) Å and the corresponding Ru-Cl distance is

2.4783(9) Å while the Ru-S distance is 2.3592(9) Å.

The effect of having an electron withdrawing group on the thiolate ligand was probed using

electron poor aryl vinyl sulfides. The addition of p-fluorophenyl vinyl sulfide to a solution of

(Im(OMe)2)(SIMes)(PPh3)RuHCl37

in CH2Cl2, and stirring for four hours at room temperature,

resulted in the isolation of 2-6 as a red solid in 80% yield (Scheme 2.2.2). The 1H and

13C{

1H}

NMR spectra of 2-6 reveal a broad singlet at 18.34 ppm, which integrates to one proton, and a

signal at 313.5 ppm, respectively, which are assigned to the Ru=CH fragment. The 19

F{1H}

NMR spectrum shows a broad singlet at 124.49 which corresponds to the p-fluorophenyl

thiolate moiety.

36


green, N: aquamarine, S: yellow, C: black, F: deep pink. H-atoms omitted for clarity.

A single crystal X-ray analysis of compound 2-6 confirmed its formulation as

Ru(S(pFC6H4))(Cl)=CHCH3(Im(OMe)2)(SIMes) where the geometry around the metal center is

distorted square pyramidal (Figure 2.2.6). The geometry of 2-6 is related to that seen in 2-4 and

2-5 where the two carbenes are trans with a C-Ru-C angle of 158.59(14)o, the two anionic

groups are also in a trans disposition while the alkylidene fragment occupies the pseudo-axial

position. The Ru-C distances for the carbenes are 2.089(3) and 2.101(3) Å for SIMes and

Im(OMe)2, respectively, while the Ru-C distance for the alkylidene is 1.807(4) Å. The

corresponding Ru-Cl distance is 2.5009(9) Å while the Ru-S distance is 2.3494(9) Å.

In a similar fashion, 2-7 was isolated as a purple solid in 75% yield from the addition of

p-nitrophenyl vinyl sulfide to a solution of (Im(OMe)2)(SIMes)(PPh3)RuHCl in CH2Cl2. The 1H

NMR spectrum of 2-7 reveals signals arising from both carbene and thiolate ligands as well as a

quartet at 18.42 ppm, with a 3JHH of 6 Hz, which integrates to one proton and could be assigned

to the Ru=CH fragment. The corresponding carbon signal for this fragment is seen at 314.2 ppm

in the 13

C{1H} NMR spectrum.

The effect of having a more strongly donating carbene was probed by the addition of phenyl

vinyl sulfide to a solution of 2-3 in CH2Cl2, and stirring for one hour at room temperature, to

form 2-8 which was isolated as a red solid in 80% yield. The 1H NMR spectrum of 2-8 reveals

signals arising from carbene and thiolate ligands as well as a broad singlet at 19.05 ppm which

37

integrates to one proton and is assigned to the Ru=CH fragment. The corresponding carbon

signal for this fragment is at 312.0 ppm in the 13

C{1H} NMR spectrum. Single crystals suitable

for an X-ray diffraction study were grown and the formulation of 2-8 was confirmed as

(Me2Im(OMe)2)(SIMes)Ru(=CHCH3)Cl(SPh) where the geometry around the metal center is

distorted square pyramidal (Figure 2.2.7).


green, N: aquamarine, S: yellow, C: black. H-atoms omitted for clarity.

Similar to 2-4, 2-5 and 2-6, the two carbenes are trans with a C-Ru-C angle of 158.15(13)o, the

two anionic groups are also in a trans disposition while the alkylidene fragment occupies the

pseudo-axial position. The Ru-C distances for the NHCs are 2.070(5) and 2.114(5) Å for SIMes

and Me2Im(OMe)2, respectively. The Ru-C distance for the alkylidene is 1.811(5) Å and the

corresponding Ru-Cl distance is 2.4685(14) Å while the Ru-S distance is 2.3663(14) Å.

Analogues incorporating pentafluorophenylthiolate groups are accessible as the E and Z isomers

of pentafluorophenyl alkenyl sulfides are readily prepared employing a modification of literature

procedures described by Peach and co-workers39

(2-9) and by Ranu and co-workers.40

In a

similar method, (C6F5)SCH=CHR (R = n-Pr 2-10, n-Bu 2-11) were prepared (Scheme 2.2.3).

Scheme 2.2.3 Synthesis of 2-10 and 2-11.

38

The addition of 2-9 to a solution of (Im(OMe)2)(SIMes)(PPh3)RuHCl in C6H5Br at 25 °C gave

rise to a brown solution upon stirring overnight. Isolation of compound 2-12 as a pink/red solid

was achieved in 70% yield (Scheme 2.2.4) and the 1H NMR spectrum of 2-12 displays a doublet

of doublets at 15.65 ppm with coupling constants of 8 and 3 Hz. This signal integrates to one

proton and is assigned to the Ru=CH fragment and the corresponding carbon signal was

identified via a 2-D NMR experiment (HSQC) at 309.6 ppm. The 19

F{1H} NMR spectrum of

2-12 shows five signals indicating a dissymmetric environment of the (C6F5)S- moiety.


A single X-ray analysis of compound 2-12 confirmed its formulation as

(Im(OMe)2)(SIMes)(F5C6S)RuCl(=CH(CH2Ph)) where the geometry around the metal center is

best described as distorted square pyramidal (Figure 2.2.8). In contrast to 2-4 to 2-8, the two

carbenes adopt a cis-arrangement, similar to that observed in compounds where a tridentate

bis-carbene ligand is used.41

The SIMes ligand is trans to the chloride whereas the Im(OMe)2

carbene is trans to the thiolate moiety. The alkylidene occupies the pseudo-axial position of the

square pyramidal coordination sphere. The Ru-C distances for the NHCs are 2.047(4) and


1.815(4) Å. The corresponding Ru-Cl distance is 2.4660(9) Å while the Ru-S distance is

2.360(1) Å.

39


green, N: aquamarine, S: yellow, F: deep pink, C: black. H-atoms omitted for clarity.

Similarly, the subsequent reactions of 2-10 and 2-11 with Im(OMe)2(SIMes)(PPh3)RuHCl

afforded orange/brown solids Im(OMe)2(SIMes)(F5C6S)RuCl(=CHC4H9) 2-13 and

Im(OMe)2(SIMes)(F5C6S)RuCl(=CHC5H11) 2-14 in 73% and 71% yield, respectively. The 1H

NMR spectra reveal a triplet at 16.37 ppm, with a coupling constant of 5 Hz, for 2-13 and a

triplet at 16.44 ppm, with a coupling constant of 5 Hz, for 2-14 which correspond to the Ru=CH

fragments. The corresponding carbon signals for these fragments were derived from two

dimensional NMR experiments (HSQC) and are present at 315.2 and 315.3 ppm, for 2-13 and

2-14, respectively. Both 19

F{1H} NMR spectra of 2-13 and 2-14 show five signals, each,

indicating dissymmetric environments of the (C6F5)S- moieties.

40





Repeated crystallization attempts of these compounds yielded crystals of poor quality,

nonetheless, preliminary X-ray studies (Figure 2.2.9 for 2-13 and Figure 2.2.10 for 2-14)

confirmed their formulations. Similar to 2-12, the two carbenes in 2-13 and 2-14 adopt a cis

orientation.

41

2.3 Reactions of Ru-Hydride Species with Ethyl Vinyl Sulfide

The effect of introducing a more electron rich vinyl sulfide was probed by reacting the

corresponding Ru-hydride species with ethyl vinyl sulfide. The Ru-hydride precursors

(Im(OMe)2)(PPh3)2RuHCl (2-15) and (Me2Im(OMe)2)(PPh3)2RuHCl (2-16), were prepared using

previously published methodologies37,38

and subsequently reacted with ethyl vinyl sulfide. In the

case of 2-15, the mixture of ethyl vinyl sulfide with a benzene solution of 2-15 was stirred for six

hours resulting in an orange solution. After workup, 2-17 was isolated as a light orange solid in

80% yield (Scheme 2.3.1).


The presence of diethyl sulfide as a by-product was confirmed by GC-MS analysis of the

reaction mixture. The 31

P{1H} NMR spectrum shows two doublets at 41.9 and 35.7 ppm with a

coupling constant of 319 Hz indicative of two phosphines in a trans disposition. A multiplet at

6.29 ppm in the 1H NMR spectrum, which integrates to one proton, is assigned to the

Ru-CHOMe proton. The 13

C{1H} NMR spectrum displays a triplet at 82.5 ppm with a

2JPC of

42

6 Hz which corresponds to the Ru-alkyl carbon. In addition to these NMR spectra, single crystals

of 2-17 afforded the molecular structure determination (Figure 2.3.1) which affirmed its

formulation as ((MeOCH2CH2)C3H2N2(CH2CH(OMe))RuCl(PPh3)2.


green, N: aquamarine, P: orange, C: black. H-atoms omitted for clarity.

The distorted square pyramidal geometry about the Ru center consists of a square plane of two

phosphine donors, the chloride and the carbene carbon with an alkyl carbon fragment occupying

the pseudo-axial position. The corresponding Ru-Cl bond length is 2.4468(8) Å and the Ru-P

bond lengths are 2.3407(8) and 2.3515(8) Å. A Ru-C bond length of 1.961(3) Å is observed for

the NHC carbon which is similar to previously reported bond lengths for Ru complexes

employing similar ligands. The Ru-C bond length for the alkyl fragment of 2.061(7) Å is slightly

shorter than typical Ru-C single bonds.42-45

Chelation of the two carbons to the Ru center leads to

the formation of a 5-member metalla-ring with a C-Ru-C angle of 78.2(2)°. It is interesting to

note that subjecting a solution of 2-17 in C6D6 to 4 atm of H2 at room temperature leads to the

quantitative reformation of 2-15.

The corresponding reaction of 2-16 with ethyl vinyl sulfide in CH2Cl2 at room temperature

results in the isolation of 2-18 as a red solid in 69% yield (Scheme 2.3.1). Similar to 2-17, the

31P{

1H} NMR spectrum of 2-18 reveals two doublets at 40.8 and 33.0 ppm with a coupling

constant of 315 Hz, while the 1H NMR spectrum shows a doublet of doublet of doublets at

43

6.35 ppm (3JHH = 11 Hz,

3JHH = 7 Hz,

3JPH = 4 Hz) and the corresponding carbon shift is a triplet

at 80.6 ppm (2JPC = 6 Hz) in the

13C{

1H} NMR spectrum. A single crystal X-ray analysis (Figure

2.3.2) confirmed 2-18 to be ((MeOCH2CH2)C3Me2N2(CH2CH(OMe))RuCl(PPh3)2, the analogue

of 2-17. The geometry about the ruthenium center in 2-18 is directly analogous to 2-17 with a

Ru-CNHC distance of 1.986(3) Å and the Ru-Calkyl bond length of 2.066(4) Å and the C-Ru-C

angle of 79.2(2)°.


green, N: aquamarine, P: orange, C: black. H-atoms omitted for clarity.

Interestingly, dissolution of 2-18 in C6D6 prompts the formation of a new product, 2-19, which is

identified by a singlet in the 31

P{1H} NMR spectrum at 36.7 ppm. Stirring a solution of 2-18 in

benzene at 25 °C for 24 hours resulted in the formation of 2-19 as a yellow solid which was

isolated in 77% yield. Loss of methanol from 2-18 was confirmed by the 1H NMR spectrum

which also shows a doublet at 7.67 ppm with a coupling constant of 5 Hz and a doublet of triplet

at 5.66 with 3JHH of 5 Hz and

4JPH of 3 Hz. As each of these signals integrated to one proton, they

are assigned to the Ru-vinyl protons (RuCHCHN). The corresponding carbon signals are present

in the 13

C{1H} NMR spectrum as a triplet at 135.6 ppm (

2JPC = 19 Hz) and a broad singlet at

124.6 ppm. These data are consistent with the formulation of 2-19 as

((MeOCH2CH2)C5H6N2(CHCH)RuCl(PPh3)2 (Scheme 2.3.1).

44

We were interested in the reactivity differences of the bis-carbene Ru-hydride systems in

comparison to the mono-carbene systems. As such, the addition of ethyl vinyl sulfide to a

benzene solution of 2-2037

and stirring for 16 hours followed by workup resulted in the isolation

of 2-21 as a purple solid in 76% yield (Scheme 2.3.2). The presence of diethyl sulfide as a

by-product was determined through GC-MS analysis of the reaction mixture and the presence of

methanol was observed in the 1H NMR of the reaction mixture. The

31P{

1H} NMR spectrum of

2-21 shows a singlet at 37.0 ppm which indicates the presence of PPh3 bound to the Ru center. A

doublet at 7.70 ppm with a coupling constant of 5 Hz and a doublet of doublet at 6.10 with a 3JHH

of 5 Hz and a 4JPH of 2 Hz in the

1H NMR spectrum are observed which integrate to one proton

each and are assigned to the Ru-vinyl protons (RuCHCHN). The 13

C{1H} NMR spectrum

displays two doublets at 159.6 ppm with a 2JPC of 15 Hz and at 124.2 ppm with a

4JPC of 2 Hz

which correspond to the Ru-vinyl carbons.

Scheme 2.3.2 Synthesis of 2-21.

In addition to NMR spectra, single crystals of 2-21 were obtained and the molecular structure

(Figure 2.3.3) was determined allowing for its formulation as ((MeOCH2CH2)C3H2N2(CHCH)

RuCl(PPh3)(SIMes). There is a distorted square pyramidal geometry about the Ru center with the

square plane made up of PPh3, SIMes, the chloride as well as the vinylic carbon, with the

carbene carbon of the NHC occupying the pseudo-axial position. A Ru-C bond length of

1.940(2) Å is observed for the NHC carbon while the Ru-C bond length of SIMes is 2.113(2) Å.

The Ru-C bond length for the vinyl fragment is 2.031(3) Å, which is in the range of typical

Ru-Cvinyl bonds.46-51

The C-C bond length of the vinyl fragment is consistent with a C=C double

bond with a distance of 1.328(4) Å. Chelation of the two carbons to the Ru center leads to the

45

formation of a 5-member metalla-ring with a C-Ru-C angle of 75.68(11)°. The corresponding

Ru-Cl bond length is 2.4589(7) Å and the Ru-P bond length is 2.3164(6) Å.


green, N: aquamarine, P: orange, C: black. H-atoms except for vinylic protons omitted for

clarity.

Similarly, the reaction of ethyl vinyl sulfide with 2-1 in C6H6 and stirring for 48 hours resulted in

the isolation of 2-22 as red crystals in 79% yield (Scheme 2.3.3). The 31

P{1H} NMR spectrum of

2-22 reveals a singlet at 38.4 ppm. A doublet of doublets at 7.75 ppm, with 3JHH of 5 Hz and

3JPH

of 1 Hz, and a doublet of doublets at 6.09 with a 3JHH of 5 Hz and a

4JPH of 2 Hz are observed in

the 1H NMR spectrum which integrate to one proton each and are assigned to the Ru-vinyl

protons (RuCHCHN). The 13

C{1H} NMR spectrum displays two doublets at 160.2 ppm with a

2JPC of 12 Hz and at 124.4 ppm with a

4JPC of 2 Hz which correspond to the Ru-vinyl carbons.

46


In addition to NMR spectra, single-crystal X-ray analysis of 2-22 was used to confirm its

formulation as ((MeOCH2CH2)C3H2N2(CHCH)RuCl(PPh3)(IMes) (Figure 2.3.4). There is a

distorted square pyramidal geometry about the Ru center with the square plane made up of PPh3,

IMes, the chloride as well as the vinylic carbon, with the carbene carbon of the NHC occupying

the pseudo-axial position. A Ru-C bond length of 1.940(3) Å is observed for the NHC carbon

while the Ru-C bond length of IMes is 2.114(2) Å. The Ru-C bond length for the vinyl fragment

is 2.033(3) Å and the C-C bond length of the vinyl fragment is 1.325(4) Å, consistent with a

C=C bond. Similar to 2-21, chelation of the two carbons to the Ru center leads to the formation

of a 5-member metalla-ring with a C-Ru-C angle of 75.72(12)°. The corresponding Ru-Cl bond

length is 2.4528(8) Å and the Ru-P bond length is 2.3104(7) Å.

47


green, N: aquamarine, P: orange, C: black. H-atoms except for vinylic and IMes-CH protons


The addition of ethyl vinyl sulfide to a benzene solution of 2-2 and stirring for 48 hours followed

by workup afforded 2-23 as red crystals in 82% yield. The 31

P{1H} NMR spectrum shows a

singlet at 38.4 ppm which indicates the presence of PPh3. The 1H NMR spectrum reveals a

doublet of doublets at 7.66 ppm, with 3JHH of 5 Hz and

3JPH of 1 Hz, and a doublet of doublets at

6.04 with a 3JHH of 5 Hz and a

4JPH of 2 Hz which integrate to one proton each and are assigned

to the Ru-vinyl protons (RuCHCHN). The 13

C{1H} NMR spectrum displays two doublets at

159.2 ppm with a 2JPC of 12 Hz and at 124.4 ppm with a

4JPC of 2 Hz which correspond to the

Ru-vinyl carbons. The NMR data allowed for the formulation of 2-23 as

((MeOCH2CH2)C3H2N2(CHCH)RuCl(PPh3)(IMes-Cl2).

The formation of compounds 2-17 to 2-23 is thought to be initiated through the initial insertion

of the vinyl-fragment into the Ru-H (Scheme 2.3.1). Donation from the thioether sulfur enhances

electron density at Ru and prompts C-H activation of the pendant ether arm affording loss of

diethyl sulfide. In this fashion compounds 2-17 and 2-18 are generated. Loss of methanol from

2-18 gives the bis-phosphine Ru-vinyl species 2-19. Compounds 2-21 to 2-23 are thought to

form in a similar fashion, although the increased electron density on Ru derived from the

additional carbene ligand facilitates loss of both Et2S and MeOH.

48

2.4 Conclusion

In conclusion, a new method of preparing ruthenium alkylidenes from bis-carbene RuHCl

starting materials and alkenyl sulfides has been developed. This new method is safe, high

yielding, and uses inexpensive starting materials. This provides a route to bis-mixed carbene

ruthenium alkylidene complexes with a hemilabile tridentate carbene and it conveniently installs

the alkylidene fragment as well as transfers a thiolate in one simple step. The use of ethyl vinyl

sulfide, on the other hand, results in the formation of Ru-alkyl and Ru-vinyl species.

2.5 Experimental Section

2.5.1 General Considerations

All manipulations were carried out under an atmosphere of dry, O2-free N2 employing a Vacuum

Atmospheres glove box and a Schlenk vacuum line. Solvents were purified with a Grubbs-type

column system manufactured by Innovative Technology, dispensed into thick-walled Schlenk

glass flasks equipped with Teflonvalve stopcocks (pentane, hexanes, CH2Cl2) and stored over

molecular sieves. Some solvents were dried over the appropriate agents, vacuum-transferred into

storage flasks with Teflon stopcocks and degassed accordingly (C6H6, C6H5Br, C6D5Br, C6D6,

CD2Cl2). 1H,

13C,

19F, and

31P NMR spectra were recorded at 25

oC on a Bruker 400 MHz

spectrometer. Chemical shifts were given relative to SiMe4 and referenced to the residual solvent

signal (1H,

13C) or relative to an external standard (

31P: 85% H3PO4,

19F: CFCl3). In some

instances, signal and/or coupling assignment was derived from two dimensional NMR

experiments (HSQC). Chemical shifts are reported in ppm and coupling constants as scalar

values in Hz. Combustion analyses were performed in house employing a Perkin-Elmer CHN

analyzer. Phenyl vinyl sulfide and ethyl vinyl sulfide were purchased from Sigma Aldrich and

used as received. SIMes,52

IMes,52

IMes-Cl2,53

p-fluorophenyl vinyl sulfide,54

p-nitrophenyl

vinyl sulfide,55

(C6F5)SC8H7,40

(C6F5)SC6H11,40

(C6F5)SC5H9,40

(Im(OMe)2)(PPh3)2RuHCl,37

(Me2Im(OMe)2)(PPh3)2RuHCl,38

and (Im(OMe)2)(SIMes)(PPh3)RuHCl37

were prepared

according to literature procedures.

2.5.2 Synthetic Procedures

Synthesis of 2-1: IMes (0.105 g, 0.354 mmol) in 5 mL THF was added to a solution of

(Im(OMe)2)(PPh3)2RuHCl (0.150 g, 0.177 mmol) in 5 mL of THF and the mixture was heated at

49

60 °C for 24 h. All volatiles were removed in vacuum. The product was extracted with toluene

(10 mL) and filtered through celite. The solution was concentrated to 2 mL and pentane (15 mL)

was added to the red solution to precipitate the product. The red solid was collected on a frit and

dried under vacuum (0.114 g, 73%). X-ray quality crystals were grown from toluene/pentane at

25 oC.

1H NMR (400 MHz, C6D6): δ 7.54 (t,

3JHH = 8 Hz, 6H, PPh3), 7.39 (m, 1H, IMes-CH),

7.04 (m, 2H, Mes-CH), 6.99-6.90 (m, 13H, (9H) PPh3 + (1H) IMes-CH + (2H) Mes-CH + (1H)

Im(OMe)2-CH), 6.66 (d, 3JHH = 2 Hz, 1H, Im(OMe)2-CH), 4.68 (dd,

2JHH = 15 Hz,

3JHH = 3 Hz,

1H, Im(OMe)2-CH2), 3.90 (m, 1H, Im(OMe)2-CH2), 2.92-2.10 (br m, 30 H, Im(OMe)2-CH3 +

Im(OMe)2-CH2 + Mes-CH3), -28.12 (d, 2

JPH = 26 Hz, 1H, Ru-H). 31

P{1H} NMR (161 MHz,

C6D6): δ 43.9 (s, PPh3). 13

C{1H} NMR (101 MHz, C6D6): δ 141.3 (d,

1JPC = 30 Hz, Cipso, PPh3),

137.3 (br, Cipso), 134.9 (d, 2JPC = 11 Hz, o-C, PPh3), 134.3 (IMes-CH), 134.1 (IMes-CH), 130.3

(br, Cipso) 128.9 (d, 4JPC = 2 Hz, p-C, PPh3), 128.8 (Mes-CH), 128.4 (Mes-CH), 127.6 (d,

3JPC =

8 Hz, m-C, PPh3), 119.9 (Im(OMe)2-CH), 118.4 (Im(OMe)2-CH), 72.6 (Im(OMe)2-CH2), 71.4

(Im(OMe)2-CH2), 58.2 (Im(OMe)2-CH3), 57.9 (Im(OMe)2-CH3), 48.0 (Im(OMe)2-CH2), 47.5

(Im(OMe)2-CH2), 21.3 (br s, Mes-CH3), 19.7 (br s, Mes-CH3). Elemental Analysis for

C48H56ClN4O2PRu: C, 64.89; H, 6.35; N, 6.31. Found: C, 65.08; H, 6.59; N, 6.13.

Synthesis of 2-2: IMes-Cl2 (0.174 g, 0.472 mmol) in 5 mL THF was added to a solution of

(Im(OMe)2)(PPh3)2RuHCl (0.200 g, 0.236 mmol) in 5 mL of THF and the mixture was heated at

60 °C for 48 h. All volatiles were removed in vacuum. The product was extracted with toluene

(10 mL) and filtered through celite. The solution was concentrated to 2 mL and pentane (15 mL)

was added to the red solution to precipitate the product. The red solid was collected on a frit and

dried under vacuum (0.147 g, 65%). X-ray quality crystals were grown from toluene/pentane at

25 oC.

1H NMR (500 MHz, C6D6): δ 7.48 (t,

3JHH = 8 Hz, 6H, PPh3), 6.96 (m, 5H, PPh3 +

Mes-CH), 6.90 (m, 8H, PPh3 + Mes-CH), 6.68 (br s, 1H, Im(OMe)2-CH), 6.67 (d, 3JHH = 2 Hz,

1H, Im(OMe)2-CH), 4.61 (ddd, 2JHH = 15 Hz,

3JHH = 4 Hz,

3JHH = 2 Hz, 1H, Im(OMe)2-CH2),

3.88 (m, 1H, Im(OMe)2-CH2), 2.91 (s, 3H, Im(OMe)2-CH3), 2.87 (m, 1H, Im(OMe)2-CH2), 2.81-

2.57 (m, 13H, Im(OMe)2-CH3 + Mes-CH3 + Im(OMe)2-CH2) 2.36-2.15 (m, 10H, Im(OMe)2-CH2

+ Mes-CH3), 2.05 (br s, 3H, Mes-CH3), 28.11(d, 2

JPH = 25 Hz, 1H, Ru-H). 31

P{1H} NMR (161

MHz, C6D6): δ 43.2 (s, PPh3). 13

C{1H} NMR (126 MHz, C6D6, partial): δ 140.7 (d,

1JPC = 31 Hz,

Cipso, PPh3), 134.9 (d, 2JPC = 11 Hz, o-C, PPh3), 129.4 (br s, Cipso)128.3 (Mes-CH), 128.2 (d,

4JPC = 2 Hz, p-C, PPh3), 127.6 (d,

3JPC = 8 Hz, m-C, PPh3), 120.0 (Im(OMe)2-CH), 118.8

50

(Im(OMe)2-CH), 72.4 (Im(OMe)2-CH2), 71.3 (Im(OMe)2-CH2), 58.2 (Im(OMe)2-CH3), 57.9

(Im(OMe)2-CH3), 48.1 (Im(OMe)2-CH2), 47.4 (Im(OMe)2-CH2), 21.3 (br s, Mes-CH3), 18.2

(br s, Mes-CH3). Elemental Analysis for C48H54Cl3N4O2PRu•C6H14: C, 62.15; H, 6.57; N, 5.37.

Found: C, 62.64; H, 6.43; N, 5.45.

Synthesis of 2-3: SIMes (0.070 g, 0.228 mmol) in 5 mL THF was added to a solution of

(Me2Im(OMe)2)(PPh3)2RuHCl (0.100 g, 0.114 mmol) in 5 mL of THF and the mixture was

heated at 50 °C for 24 h. All volatiles were removed in vacuum. The product was extracted with

toluene (10 mL) and filtered through celite. The solution was concentrated to 2 mL and pentane

(15 mL) was added to the red solution to precipitate the product. The red solid was collected on a

frit and dried under vacuum (0.076 g, 73%). 1H NMR (400 MHz, C6D6): δ 7.52 (t,

3JHH = 8 Hz,

6H, PPh3), 6.94 (m, 11H, (9H) PPh3 + (2H) Mes-CH), 6.82 (s, 1H, Mes-CH), 6.51 (s, 1H,

Mes-CH), 4.43 (dt, 2JHH = 16 Hz,

3JHH = 4 Hz, 1H, Me2Im(OMe)2-CH2), 3.60 (m, 1H,

Me2Im(OMe)2-CH2), 3.39-3.16 (m, 8H, (4H) Me2Im(OMe)2-CH2 + (4H) SIMes-CH2), 2.99 (s,

6H, Me2Im(OMe)2-CH3 + Mes-CH3), 2.83 (br s, 5H, Mes-CH3 + Me2Im(OMe)2-CH2), 2.64 (s,

6H, Me2Im(OMe)2-CH3 + Mes-CH3), 2.33 (s, 3H, Mes-CH3), 2.13 (s, 3H, Mes-CH3), 1.92 (s,

3H, Me2Im(OMe)2-4,5-CH3), 1.83 (s, 3H, Me2Im(OMe)2-4,5-CH3), 1.59 (s, 3H, Mes-CH3), -

27.43 (d, 2JPH = 27 Hz, 1H, Ru-H).

31P{

1H} NMR (161 MHz, C6D6): δ 36.5 (s, PPh3).

13C{

1H}

NMR (101 MHz, C6D6, partial): δ 141.2 (d, 1JPC = 29 Hz, Cipso, PPh3), 139.7 (Cipso), 135.0 (d,

2JPC = 11 Hz, o-C, PPh3), 129.4 (Mes-CH), 128.9 (d,

4JPC = 2 Hz, p-C, PPh3), 128.8 (Mes-CH),

127.5 (d, 3JPC = 8 Hz, m-C, PPh3), 125.7 (Cipso), 124.5 (Me2Im(OMe)2-4,5-Cipso), 122.2

(Me2Im(OMe)2-4,5-Cipso), 72.9 (Me2Im(OMe)2-CH2), 71.0 (Me2Im(OMe)2-CH2), 58.4

(Me2Im(OMe)2-CH3), 57.8 (Me2Im(OMe)2-CH3), 51.5 (SIMes-CH2), 50.8 (SIMes-CH2), 46.5

(Me2Im(OMe)2-CH2), 45.9 (Me2Im(OMe)2-CH2), 21.4 (Mes-CH3), 21.2 (Mes-CH3), 21.0

(Mes-CH3), 20.9 (Mes-CH3), 19.6 (Mes-CH3), 17.1 (Mes-CH3), 10.3 (Me2Im(OMe)2-4,5-CH3),

9.8 (Me2Im(OMe)2-4,5-CH3). Elemental Analysis for C50H62ClN4O2PRu•C5H12: C, 66.68; H,

7.53; N, 5.66. Found: C, 66.24; H, 7.46; N, 5.85.

Synthesis of 2-4: Phenyl vinyl sulfide (16.7 μL, 0.128 mmol) was added to a solution of

(Im(OMe)2)(SIMes)(PPh3)RuHCl (0.100 g, 0.112 mmol) in 5 mL CH2Cl2 at room temperature.

The solution was then stirred for 5 hours before the solvent was concentrated to 0.5 mL and

15 mL of pentane was added and the resulting mixture was filtered over a pad of celite. The

pentane was then removed in vacuo and the resulting residue was layered with 10 mL of pentane

51

and left standing overnight. The free triphenylphosphine is taken up into the pentane layer

yielding a red solid (0.079 g, 92%). X-ray quality crystals were grown by slow evaporation of a

hexane solution. 1

H NMR (400 MHz, CD2Cl2): δ 18.29 (br s, 1H, Ru=CH), 7.01(s, 2H, Mes-CH),

6.96 (s, 1H, Mes-CH), 6.94 (s, 1H, Mes-CH), 6.85 (s, 1H, Im(OMe)2-CH), 6.69 (br s, 1H,

Im(OMe)2-CH), 6.60 (m, 3H, S(C6H5)), 6.56 (m, 2H, S(C6H5)), 3.93 (m, 4H, Mes-CH2), 3.32

(br s, 4H, Im(OMe)2-CH2), 3.19 (br s, 4H, Im(OMe)2-CH2 + Im(OMe)2-CH3), 3.16 (s, 3H,

Im(OMe)2-CH3), 3.06 (br s, 2H, Im(OMe)2-CH2), 2.74 (s, 3H, Mes-CH3), 2.62 (s, 3H, Mes-CH3),

2.50 (s, 3H, Mes- CH3), 2.42 (s, 3H, Mes- CH3), 2.35 (s, 3H, Mes- CH3), 2.31 (s, 3H, Mes- CH3),

1.63 (d, 3JHH = 5 Hz, 3H, Ru=CHCH3).

13C{

1H} NMR (101 MHz, CD2Cl2): δ 313.7

(Ru=CHCH3), 223.6 (NCN), 188.8 (NCN), 139.9 (Cipso), 139.03 (Cipso), 138.3 (S(C6H5)), 137.9

(S(C6H5)), 135.5 (Cipso), 130.0 (Mes-CH), 129.9 (Mes-CH), 129.7 (Mes-CH), 129.6 (Mes-CH),

126.9 (S(C6H5)), 121.6 (Im(OMe)2-CH), 121.2 (Im(OMe)2-CH), 72.2 (Im(OMe)2-CH2), 58.7

(Im(OMe)2-CH3), 58.6 (Im(OMe)2-CH3), 51.8 (SIMes-CH2), 51. 7 (SIMes-CH2), 49.1

(OCO-CH2), 48.7 (Ru=CHCH3), 21.2 (Mes-CH3), 20.3 (Mes-CH3), 19.0 (Mes-CH3), 18.8

(Mes-CH3). Elemental Analysis for C38H51ClN4O2RuS: C, 59.69; H, 6.73; N, 7.33. Found: C,

59.89; H, 6.96; N, 7.35.

Synthesis of 2-5: Phenyl vinyl sulfide (16.7 μL, 0.128 mmol) was added to a solution of 2-1

(0.100 g, 0.112 mmol) in 5 mL CH2Cl2 at room temperature. The solution was then stirred for 5

hours before the solvent was concentrated to 0.5 mL and 15 mL of pentane was added and the

resulting mixture was filtered over a pad of celite. The pentane was then removed in vacuo and

the resulting residue was layered with 10 mL of pentane and left standing overnight. The free

triphenylphosphine is taken up into the pentane layer yielding a red solid (0.050 g, 59%). X-ray

quality crystals were grown from benzene/pentane at 25 oC.

1H NMR (500 MHz, C6D6): δ 19.09

(q, 3JHH = 6 Hz, 1H, Ru=CH), 7.03(br m, 1H, S(C6H5)), 7.01 (br m, 1H, S(C6H5)), 6.94 (d,

3JHH = 2 Hz, 1H, Im(OMe)2-CH), 6.85-6.73 (br m, 7H, (3H) S(C6H5), (4H) Mes-CH), 6.65 (s,

1H, d, 3JHH = 2 Hz, 1H, Im(OMe)2-CH), 6.24 (d,

3JHH = 2 Hz, 1H, Mes-CH), 6.23 (d,

3JHH =

2 Hz, 1H, Mes-CH), 3.84 (br s, 2H, Im(OMe)2-CH2), 3.56 (m, 1H, Im(OMe)2-CH2), 3.46 (m, 1H,

Im(OMe)2-CH2), 3.21 (m, 2H, Im(OMe)2-CH2), 3.08 (m, 1H, Im(OMe)2-CH2), 2.96 (s, 3H,

Im(OMe)2-CH3), 2.85 (m, 1H, Im(OMe)2-CH2), 2.77 (s, 3H, Im(OMe)2-CH3), 2.73 (s, 3H,

Mes-CH3), 2.67 (s, 3H, Mes-CH3), 2.48 (s, 6H, Mes-CH3), 2.16 (s, 3H, Mes-CH3), 2.15 (s, 3H,

Mes-CH3), 2.08 (d, 3JHH = 5 Hz, 3H, Ru=CHCH3).

13C{

1H} NMR (126 MHz, C6D6): δ 313.6

52

(Ru=CHCH3), 193.9 (NCN), 189.8 (NCN), 139.4 (Cipso), 139.2 (Cipso), 138.7 (Cipso), 137.8

(Cipso), 137.2 (Cipso), 135.9 (S(C6H5)), 133.0 (S(C6H5)), 129.6 (Mes-CH), 129.4 (Mes-CH), 129.3

(Mes-CH), 129.2 (Mes-CH), 127.0 (S(C6H5)), 124.0 (IMes-CH), 123.6 (IMes-CH), 121.8

(Im(OMe)2-CH), 121.2 (Im(OMe)2-CH), 73.5 (Im(OMe)2-CH2), 72.4 (Im(OMe)2-CH2), 58.3


(Ru=CHCH3), 21.1 (Mes-CH3), 21.0 (Mes-CH3), 20.4 (Mes-CH3), 20.3 (Mes-CH3), 19.1

(Mes-CH3), 19.0 (Mes-CH3). Elemental Anal.: C38H49ClN4O2RuS: C, 59.86; H, 6.48; N, 7.35.

Found: C, 60.02; H, 6.20; N, 7.22.

Synthesis of 2-6: p-Fluorophenyl vinyl sulfide (0.017 g, 0.224 mmol) was added to a solution of


The solution was then stirred for 4 h before the solvent was concentrated to 0.5 mL and 15 mL of

pentane was added and the resulting mixture was filtered over a pad of celite. The pentane was

then removed in vacuo and the resulting residue was layered with 10 mL of pentane and left

standing overnight. The free triphenylphosphine is taken up into the pentane layer yielding a red

solid (0.070 g, 80%). X-ray quality crystals were grown from benzene/pentane at 25 oC.

1H NMR

(400 MHz, CD2Cl2): δ 18.34 (br s, 1H, Ru=CH), 7.01(s, 2H, Mes-CH), 6.96 (s, 1H, Mes-CH),

6.93 (s, 1H, Mes-CH), 6.86 (d, 3JHH = 2 Hz, 1H, Im(OMe)2-CH), 6.68 (br s, 1H, Im(OMe)2-CH),

6.51 (m, 2H, p-F-C6H5), 6.34 (app t, 3JHH = 9 Hz, 2H, p-F-C6H5), 3.92 (m, 4H, SIMes-CH2),

3.44-3.26 (br s, 4H, Im(OMe)2-CH2), 3.23 (br s, 3H, Im(OMe)2-CH3), 3.16 (s, 3H,

Im(OMe)2-CH3), 3.13-3.00 (br s, 4H, Im(OMe)2-CH2), 2.74 (s, 3H, Mes-CH3), 2.61 (s, 3H,


Mes-CH3), 1.63 (d, 3JHH = 5 Hz, Ru=CHCH3).

19F{

1H} NMR (178 MHz, CD2Cl2): δ -124.49

(br s). 13

C{1H} NMR (101 MHz, C6D6): δ 313.5 (Ru=CHCH3), 223.9 (NCN), 188.8 (NCN),

159.7 (d, 1JFF = 239 Hz, S(C6H4F)), 147.0 (d,

4JFC = 3 Hz, S(C6H4F)), 140.5 (Cipso), 139.9 (Cipso),

138.6 (Cipso), 138.5 (Cipso), 138.1 (Cipso), 137.9 (Cipso), 137.8 (Cipso), 135.6 (Cipso), 133.9 (br d,

3JFC = 7 Hz, S(C6H4F)), 129.8 (Mes-CH), 129.6 (Mes-CH), 121.7 (Im(OMe)2-CH), 121.1

(Im(OMe)2-CH), 113.7 (d, 2JFC = 21 Hz, S(C6H4F)), 73.6 (Im(OMe)2-CH2), 72.2

(Im(OMe)2-CH2), 58.4 (Im(OMe)2-CH3), 58.2 (Im(OMe)2-CH3), 51.3 (SIMes-CH2), 51.1

(SIMes-CH2), 49.7 (Im(OMe)2-CH2), 48.9 (Im(OMe)2-CH2), 46.8 (Ru=CHCH3), 21.1

(Mes-CH3), 21.0 (Mes-CH3), 20.7 (Mes-CH3), 20.5 (Mes-CH3), 19.3 (Mes-CH3), 19.2

53

(Mes-CH3). Elemental Anal.: C38H50ClFN4O2RuS: C, 58.33; H, 6.44; N, 7.16. Found: C, 58.27;

H, 6.87; N, 7.13.

Synthesis of 2-7: p-Nitrophenyl vinyl sulfide (0.041 g, 0.224 mmol) was added to a solution of


The solution was then stirred for 4 h before the solvent was concentrated to 0.5 mL and 15 mL of

pentane was added and the resulting mixture was filtered over a pad of celite. The pentane was

then removed in vacuo and the resulting residue was layered with 10 mL of pentane and left

standing overnight. The free triphenylphosphine is taken up into the pentane layer yielding a

purple solid (0.068 g, 75%). 1

H NMR (400 MHz, C6D6): δ 18.42 (q, 3JHH = 6 Hz, 1H, Ru=CH),

7.71 (d, 3JHH = 9 Hz, 2H, p-NO2(C6H4)), 6.75 (m, 7H, p-NO2(C6H4), Mes-CH, Im(OMe)2-CH),

6.49 (s, 1H, Im(OMe)2CH), 3.44 (m, 3H, Im(OMe)2-CH2), 3.32-3.21 (m, 4H, SIMesCH2), 3.13-

2.94 (m, 3H, Im(OMe)2CH2), 2.86 (s, 3H, Im(OMe)2CH3), 2.76 (s, 5H, Im(OMe)2CH2,

Mes-CH3), 2.73 (s, 3H, Im(OMe)2-CH3), 2.64 (s, 6H, Mes-CH3), 2.49 (s, 3H, Mes-CH3), 2.12 (s,

3H, Mes-CH3), 2.09 (s, 3H, Mes-CH3), 1.87 (d, 3JHH = 6 Hz, Ru=CHCH3).

13C{

1H} NMR

(101 MHz, C6D6): δ 314.2, (Ru=CH), 222.0 (NCN), 186.9 (NCN), 141.6 (Cipso), 139.8 (Cipso),

139.0 (Cipso), 138.6 (Cipso), 138.1 (Cipso), 137.7 (Cipso), 137.3 (Cipso), 137.2 (Cipso), 133.9 (Cipso),

133.7 (Cipso), 130.7 (p-NO2-C6H4) 129.7 (Mes-CH), 129.5 (Mes-CH), 129.2 (Mes-CH), 128.8

(Mes-CH), 121.5 (Im(OMe)2-CH), 121.3 (Im(OMe)2-CH), 121.1 (p-NO2-C6H4), 72.7


(SIMes-CH2), 50.7 (SIMes-CH2), 49.5 (Im(OMe)2-CH2), 46.3 (Ru=CHCH3), 20.6 (Mes-CH3),

20.5 (Mes-CH3), 20.1 (Mes-CH3), 19.5 (Mes-CH3), 18.7 (Mes-CH3), 18.6 (Mes-CH3). Elemental

Analysis for C38H50ClN5O4RuS•C5H12: C, 58.58; H, 7.09; N, 7.94. Found: C, 58.21; H, 6.76; N,

7.72.

Synthesis of 2-8: Phenyl vinyl sulfide (17.0 μL, 0.131 mmol) was added to a solution of 2-3

(0.100 g, 0.109 mmol) in 5 mL CH2Cl2 at room temperature. The solution was then stirred for

1 h before the solvent was concentrated to 0.5 mL and 15 mL of pentane was added and the

resulting mixture was filtered over a pad of celite. The pentane was then removed in vacuo and

the resulting residue was layered with 10 mL of pentane and left standing overnight. The free

triphenylphosphine is taken up into the pentane layer yielding a red solid (0.069 g, 80%). X-ray

quality crystals were grown from benzene/pentane at 25 oC.

1H NMR (400 MHz, C6D6): δ 19.05

(br s, 1H, Ru=CH), 7.05(m, 2H, S(C6H5)), 6.97 (s, 1H, Mes-CH), 6.94 (s, 1H, Mes-CH), 6.82 (s,

54

2H, Mes-CH), 6.67 (m, 3H, S(C6H5)), 3.73-3.03 (br m, 12H, SIMes-CH2 + Me2Im(OMe)2-CH2),

2.99 (s, 3H, Me2Im(OMe)2-CH3), 2.94 (s, 3H, Mes-CH3), 2.91 (s, 3H, Mes-CH3), 2.78 (s, 3H,

Me2Im(OMe)2-CH3), 2.68 (s, 3H, Mes-CH3), 2.66 (s, 3H, Mes-CH3), 2.25 (s, 3H, Mes-CH3),

2.13 (s, 3H, Mes-CH3), 2.07 (d, 3JHH = 6 Hz, 3H, Ru=CHCH3), 1.70 (s, 3H,

Me2Im(OMe)2-4,5-CH3), 1.44 (s, 3H, Me2Im(OMe)2-4,5-CH3). 13

C{1H} NMR (101 MHz, C6D6):

δ 312.0 (Ru=CHCH3), 223.7 (NCN), 186.3 (NCN), 152.1 (Cipso), 140.1 (Cipso), 139.7 (Cipso),

138.6 (Cipso), 138.5 (Cipso), 138.2 (Cipso), 137.9 (Cipso), 137.7 (Cipso), 136.0, 133.4 (S(C6H5)) 130.3

(Mes-CH), 129.9 (Mes-CH), 129.7 (Mes-CH), 129.6 (Mes-CH), 126.3 (S(C6H5)), 126.1

(Me2Im(OMe)2-Cipso), 125.5 (Me2Im(OMe)2-Cipso), 121.1 (S(C6H5)), 74.5 (Me2Im(OMe)2-CH2),

72.7 (Me2Im(OMe)2-CH2), 58.3 (Me2Im(OMe)2-CH3), 58.2 (Me2Im(OMe)2-CH3), 51.3

(SIMes-CH2), 51.1 (SIMes-CH2), 47.7 (Me2Im(OMe)2-CH2) 46.5 (Ru=CHCH3), 46.0

(Me2Im(OMe)2-CH2), 20.9 (Mes-CH3), 20.6 (Mes-CH3), 20.5 (Mes-CH3), 19.2 (Mes-CH3), 19.1

(Mes-CH3), 9.3 (Me2Im(OMe)2-4,5-CH3), 8.9 (Me2Im(OMe)2-4,5-CH3). Elemental Analysis for

C40H55ClN4O2RuS: C, 60.62; H, 7.00; N, 7.07. Found: C, 60.86; H, 7.11; N, 6.78.

Synthesis of 2-10: A mixture of 1-pentyne (0.74 mL, 7.50 mmol) and pentafluorothiophenol

(1.00 mL, 7.50 mmol) was stirred in 6 mL of H2O at room temperature for 4 hours. The reaction

mixture was extracted with Et2O (3 x 20 mL) and the ether extract was dried over MgSO4.

Solvent removal in vacuo gave a mixture of the (E)- and (Z)- isomers as a clear colorless liquid

(1.61 g, 80%). 1H NMR (400 MHz, C6D6): Isomer 1: δ 5.91-5.84 (m, 2H, (C6F5)SCHCH(C3H7)),

2.00 (m, 2H, (C6F5)SCHCH(C3H7)), 1.34 (m, 2H, (C6F5)SCHCH(C3H7)), 0.82 (m, 3H,

(C6F5)SCHCH(C3H7)). Isomer 2: δ 5.84 (d, 3JHH = 9 Hz, 1H, (C6F5)SCHCH(C3H7)), 5.76 (m,

1H, (C6F5)SCHCH(C3H7)), 2.21 (m, 2H, (C6F5)SCHCH(C3H7)), 1.41 (m, 2H,

(C6F5)SCHCH(C3H7)), 0.89 (m, 3H, (C6F5)SCHCH(C3H7)). 19

F{1H} NMR (178 MHz, C6D6): δ -

132.99 (m, 2F, o-F), -153.05 (t, 3JFF

= 21 Hz, 1F, p-F), -161.00 (m, 2F, m-F).

13C{

1H} NMR

(101 MHz, C6D6): δ 147.2 (dm, 1JCF = 247 Hz, C6F5), 141.2 (dm,

1JCF = 252 Hz, C6F5), 137.7

(dm, 1JCF = 252 Hz, C6F5). Isomer 1: 134.2 ((C6F5)SCHCH(C3H7)), 120.8

((C6F5)SCHCH(C3H7)), 34.7 ((C6F5)SCHCH(C3H7)), 22.1 ((C6F5)SCHCH(C3H7)), 13.4

((C6F5)SCHCH(C3H7)). Isomer 2: 137.7 ((C6F5)SCHCH(C3H7)), 118.7 ((C6F5)SCHCH(C3H7)),

35.0 ((C6F5)SCHCH(C3H7)), 21.9 ((C6F5)SCHCH(C3H7)), 13.3 ((C6F5)SCHCH(C3H7)).

HRMS-ESI+ m/z [M+H]

+ calculated for C11H10F5S: 269.04191, found: 269.04179.

55

Synthesis of 2-11: A mixture of 1-hexyne (0.86 mL, 7.48 mmol) and pentafluorothiophenol (1.00

mL, 7.50 mmol) was stirred in 6 mL of H2O at room temperature for 4 hours. The reaction

mixture was extracted with Et2O (3 x 20 mL) and the ether extract was dried over MgSO4.

Solvent removal in vacuo gave a mixture of the (E)- and (Z)- isomers as a clear colorless liquid

(1.92 g, 91%). 1H NMR (400 MHz, C6D6): Isomer 1: δ 5.80-5.74 (m, 2H, (C6F5)SCHCH(C4H9)),

1.81 (m, 2H, (C6F5)SCHCH(C4H9)), 1.13 (m, 4H, (C6F5)SCHCH(C4H9)), 0.79 (m, 3H,

(C6F5)SCHCH(C4H9)). Isomer 2: δ 5.69 (d, 3JHH = 9 Hz, 1H, (C6F5)SCHCH(C4H9)), 5.55 (dt,

3JHH = 9 Hz,

3JHH = 7 Hz, 1H, (C6F5)SCHCH(C4H9)), 2.19 (m, 2H, (C6F5)SCHCH(C4H9)), 1.26

(m, 4H, (C6F5)SCHCH(C4H9)), 0.84 (m, 3H, (C6F5)SCHCH(C4H9)). 19

F{1H} NMR (178 MHz,

C6D6): δ 133.94 (m, 2F, o-F), -154.03 (t, 3JFF

= 21 Hz, 1F, p-F), -161.80 (m, 2F, m-F).

13C{

1H}

NMR (101 MHz, C6D6): δ 146.9 (dm, 1JCF = 247 Hz, C6F5), 141.2 (dm,

1JCF = 252 Hz, C6F5),

137.6 (dm, 1JCF = 252 Hz, C6F5). Isomer 1: 134.1 ((C6F5)SCHCH(C4H9)), 120.5

((C6F5)SCHCH(C4H9)), 31.0 ((C6F5)SCHCH(C4H9)), 28.6 ((C6F5)SCHCH(C4H9)), 22.3

((C6F5)SCHCH(C4H9)), 13.7 ((C6F5)SCHCH(C4H9)). Isomer 2: 138.0 ((C6F5)SCHCH(C4H9)),

118.0 ((C6F5)SCHCH(C4H9)), 32.5 ((C6F5)SCHCH(C4H9)), 30.9 ((C6F5)SCHCH(C4H9)), 22.2

((C6F5)SCHCH(C4H9)), 13.7 ((C6F5)SCHCH(C4H9)). HRMS-ESI+ m/z [M+H]

+ calculated for

C12H12F5S: 283.05847, found: 283.05744.

Synthesis of 2-12: To a solution of (OCO)(SIMes)(PPh3)RuHCl (0.100 g, 0.112 mmol) in 2 mL

C6H5Br was added 2-9 (0.068 g, 0.224 mmol) at room temperature. The solution was then stirred

for 24 hours before the solution was added drop wise to 15 mL of cold pentane, while stirring, to

precipitate the product. The pink/red solid was collected on a frit and dried under vacuum

(0.073 g, 70%). X-ray quality crystals were grown from tetrahydrofuran/pentane at 25 oC.

1H

NMR (400 MHz, C6D5Br): δ 15.65 (dd, 3JHH = 8 Hz,

3JHH = 3 Hz, 1H, Ru=CH), 7.06 (s, 1H,

Mes-CH), 7.05 (s, 1H, Mes-CH), 6.95 (br s, 1H, Im(OMe)2-CH), 6.87 (s, 2H, Mes-CH), 6.84 (d,

3JHH = 2 Hz, 1H, Im(OMe)2-CH), 6.80 (br s, 1H, C6H5), 6.75 (br s, 2H, C6H5), 6.68 (br s, 2H,

C6H5), 4.08 (dd, 2JHH = 15 Hz,

3JHH = 3 Hz, 1H, Im(OMe)2-CH2), 4.00 (dt,

2JHH = 15 Hz,

3JHH =

3 Hz, 1H, Im(OMe)2-CH2), 3.64 (m, 4H, SIMes-CH2), 3.49 (m, 4H, Im(OMe)2-CH2), 3.32 (m,

2H, Im(OMe)2-CH2), 3.04 (s, 3H, Im(OMe)2-CH3), 2.87 (s, 2H, Ru=CHCH2), 2.72 (s, 3H,

Im(OMe)2-CH3), 2.61 (s, 3H, Mes-CH3), 2.23 (s, 6H, 2 x Mes-CH3), 2.15 (s, 9H, 3 x Mes-CH3).

19F{

1H} NMR (376 MHz, C6D5Br): δ 131.72 (br s, 1F, o-S(C6F5)), 132.36 (br s, 1F, o-

S(C6F5)), 162.33 (t, 3JFF = 22 Hz, 1F, p-S(C6F5)), 166.25 (br s, 1F, m-S(C6F5)), 166.68 (br s,

56

1F, m-S(C6F5)). 13

C{1H} NMR (101 MHz, C6D5Br, partial): δ 309.6 (Ru=CH), 138.0 (Cipso),

137.5 (Cipso), 137.1 (Cipso), 130.0 (C6H5), 129.8 (Mes-CH), 129.6 (Mes-CH), 129.4 (C6H5), 123.5

(C6H5), 122.5 (Im(OMe)2-CH), 121.0 (Im(OMe)2-CH), 72.9 (Im(OMe)2-CH2), 72.6

(Im(OMe)2-CH2), 58.2 (Im(OMe)2-CH3), 58.1 (Im(OMe)2-CH3), 58.0 (Ru=CHCH2), 52.1

(SIMes-CH2), 49.7 (Im(OMe)2-CH2), 49.4 (Im(OMe)2-CH2), 21.0 (Mes-CH3), 19.6 (Mes-CH3),

18.7 (Mes-CH3). Elemental Analysis for C44H50ClF5N4O2RuS•C6H5Br: C, 55.22; H, 5.10; N,

5.15. Found: C, 55.18; H, 5.03; N, 5.54.

Synthesis of 2-13: To a solution of (Im(OMe)2)(SIMes)(PPh3)RuHCl (0.100 g, 0.112 mmol) in

2 mL C6H5Br was added 2-10 (0.060 g, 0.224 mmol) at room temperature. The solution was then

stirred for 24 hours before the solution was added drop wise to 15 mL of cold pentane to

precipitate the product. The orange/brown solid was collected on a frit and dried under vacuum

(0.073 g, 73%). X-ray quality crystals were grown from bromobenzene/pentane at 25 oC.

1H

NMR (400 MHz, C6D5Br): δ 16.37 (t, 3JHH = 5 Hz, 1H, Ru=CH), 7.04 (d,

3JHH = 2 Hz, 1H,

Im(OMe)2-CH), 6.85 (s, 2H, Mes-CH), 6.83 (d, 3JHH = 2 Hz, 1H, Im(OMe)2-CH), 6.71 (s, 2H,

Mes-CH), 4.16 (m, 1H, Im(OMe)2-CH2), 3.69 (m, 3H, Im(OMe)2-CH2), 3.59 (m, 1H,

Im(OMe)2-CH2), 3.55 (m, 4H, SIMes-CH2), 3.37 (m, 1H, Im(OMe)2-CH2), 3.15 (m, 2H,

Im(OMe)2-CH2), 2.92 (s, 3H, Im(OMe)2-CH3), 2.90 (s, 3H, Im(OMe)2-CH3), 2.66 (s, 6H, 2 x

Mes-CH3), 2.23 (s, 6H, 2 x Mes-CH3), 2.16 (s, 6H, 2 x Mes-CH3), 1.31 (m, 2H,

pentylidene-CH2), 1.13 (m, 2H, pentylidene-CH2), 1.05 (m, 2H, pentylidene-CH2), 0.83 (t,

3JHH = 7 Hz, 3H, pentylidene-CH3) .

19F{

1H} NMR (376 MHz, C6D5Br): δ -131.87 (br s, 1F, o-

S(C6F5)), -132.41 (br s, 1F, o-S(C6F5)), -162.70 (t, 3JFF = 22 Hz, 1F, p-S(C6F5)), -166.45 (br s,

1F, m-S(C6F5)), -166.98 (br s, 1F, m-S(C6F5)). 13

C{1H} NMR (101 MHz, C6D5Br, partial): δ

315.2 (Ru=CH), 212.6 (NCN), 181.8 (NCN), 137.9 (Cipso), 137.4 (Cipso), 129.9 (Mes-CH), 129.6

(Mes-CH), 122.6 (Im(OMe)2-CH), 121.3 (Im(OMe)2-CH), 73.0 (Im(OMe)2-CH2), 71.4


(Im(OMe)2-CH2), 48.3 (Im(OMe)2-CH2), 29.3 (pentylidene-CH2), 22.9 (pentylidene-CH2), 21.0

(Mes-CH3), 19.6 (Mes-CH3), 18.7 (Mes-CH3), 14.3 (pentylidene-CH3). Elemental Analysis for

C41H52ClF5N4O2RuS•(C6H5Cl): C, 55.47; H, 5.77; N, 5.88. Found: C, 55.78; H, 5.87; N, 6.06.

Synthesis of 2-14: To a solution of (Im(OMe)2)(SIMes)(PPh3)RuHCl (0.100 g, 0.112 mmol) in

2 mL C6H5Br was added 2-11 (0.063 g, 0.224 mmol) at room temperature. The solution was then

stirred for 24 hours before the solution was added drop wise to 15 mL of cold pentane, while

57

stirring, to precipitate the product. The orange/brown solid was collected on a frit and dried

under vacuum (0.072 g, 71%). X-ray quality crystals were grown from bromobenzene/pentane at

25 oC.

1H NMR (400 MHz, C6D5Br): δ 16.44 (t,

3JHH = 5 Hz, 1H, Ru=CH), 7.00 (s, 1H,

Im(OMe)2-CH), 6.85 (s, 2H, Mes-CH), 6.82 (d, 3JHH = 2 Hz, 1H, Im(OMe)2-CH), 6.71 (s, 2H,

Mes-CH), 4.15 (dd, 2JHH = 14 Hz,

3JHH = 4 Hz, 1H, Im(OMe)2-CH2), 3.67 (m, 2H,

Im(OMe)2-CH2), 3.59 (m, 1H, Im(OMe)2-CH2), 3.50 (m, 4H, SIMes-CH2), 3.33 (m, 1H,

Im(OMe)2-CH2), 3.12 (m, 1H, Im(OMe)2-CH2), 2.92 (s, 4H, Im(OMe)2-CH2 + Im(OMe)2-CH3),

2.89 (s, 4H, Im(OMe)2-CH2 + Im(OMe)2-CH3), 2.66 (s, 7H, hexylidene-CH2 + 2 x Mes-CH3),

2.22 (s, 6H, 2 x Mes-CH3), 2.15 (s, 7H, hexylidene-CH2 + 2 x Mes-CH3), 1.21 (m, 3H,

hexylidene-CH2), 1.07 (m, 3H, hexylidene-CH2), 0.85 (t, 3JHH = 7 Hz, 3H, hexylidene-CH3).

19F{

1H} NMR (376 MHz, C6D5Br): δ -131.83 (br s, 1F, o-S(C6F5)), -132.44 (br s, 1F,

o-S(C6F5)), -162.69 (t, 3JFF = 22 Hz, 1F, p-S(C6F5)), -166.42 (br s, 1F, m-S(C6F5)), -166.96 (br s,

1F, m-S(C6F5)). 13

C{1H} NMR (101 MHz, C6D5Br, partial): δ 315.3 (Ru=CH), 212.3 (NCN),

181.8 (NCN), 137.7 (Cipso), 137.2 (Cipso), 129.3 (Mes-CH), 129.0 (Mes-CH), 122.0


(Im(OMe)2-CH3), 58.0 (Im(OMe)2-CH3), 52.3 (SIMes-CH2), 49.4 (Im(OMe)2-CH2), 48.3

(Im(OMe)2-CH2), 32.0 (hexylidene-CH2), 26.7 (hexylidene-CH2), 22.8 (hexylidene-CH2), 21.05

(hexylidene-CH2), 21.0 (Mes-CH3), 19.5 (Mes-CH3), 18.7 (Mes-CH3), 14.2 (hexylidene-CH3).

Elemental Analysis for C42H54ClF5N4O2RuS•(C6H5Cl): C, 55.91; H, 5.89; N, 5.80. Found: C,

56.27; H, 5.83; N, 6.19.

Synthesis of 2-17: Ethyl vinyl sulfide (24 μL, 0.236 mmol) was added to a solution of 2-15

(0.100 g, 0.118 mmol) in 5 mL C6H6 at room temperature. The solution was then stirred for 6 h

before the solvent was concentrated to 1 mL and 15 mL of pentane was added which caused a

light orange precipitate to form. The solid was collected by filtration, washed with pentane and

dried under high vacuum (0.080 g, 80%). X-ray quality crystals were grown from

benzene/pentane at 25 oC.

1H NMR (400 MHz, C6D6): δ 7.71(br s, 10H, PPh3), 7.39 (m, 1H,

PPh3), 7.03 (br s, 19H, PPh3), 6.33 (d, 3

JHH = 2 Hz, 1H, Im-CH), 6.29 (m, 1H, Ru-CHOMe), 5.83

(d, 3

JHH = 2 Hz, 1H, Im-CH), 3.54 (br s, 4H, NCH2CH2OMe + O(CH3)), 3.45 (m, 1H,

NCH2CH2OMe), 2.77 (s, 3H, O(CH3)), 2.55 (dd, 2JHH = 12 Hz,

3JHH = 5 Hz, 1H, NCH2CHOMe),

2.48 (m, 2H, NCH2CH2OMe), 2.37 (dd, 2JHH = 12 Hz,

3JHH = 5 Hz, 1H, NCH2CHOMe).

31P{

1H}

NMR (161 MHz, C6D6): δ 41.9 (d, 2JPP = 319 Hz, PPh3), 35.7 (d,

2JPP = 319 Hz, PPh3).

13C{

1H}

58

NMR (101 MHz, C6D6): δ 192.8 (t, 2JPC = 14 Hz, NCN), 138.0 (d,

2JPC = 12 Hz, PPh3), 134.7 (br

s, PPh3), 134.1 (d, 1JPC = 20 Hz, PPh3), 129.0 (PPh3), 128.8 (d,

3JPC = 7 Hz, PPh3), 128.5 (PPh3),

120.4 (Im-CH), 116.7 (Im-CH), 82.5 (t, 2JPC = 6 Hz, NCH2CHOMe), 71.1 (NCH2CH2OMe), 58.8

(O(CH3)), 58.1 (O(CH3)), 57.9 (NCH2CHOMe), 49.2 (NCH2CH2OMe). Elemental Analysis for

C45H45ClN2O2P2Ru: C, 64.01; H, 5.37; N, 3.32. Found: C, 63.90; H, 5.71; N, 3.45.

Synthesis of 2-18: Ethyl vinyl sulfide (24 μL, 0.234 mmol) was added to a solution of 2-16

(0.140 g, 0.161 mmol) in 5 mL CH2Cl2 at room temperature. The solution was then stirred for

6 h before the solution was filtered over celite and the solvent was concentrated to 1 mL. Pentane

(15 mL) was added while stirring to precipitate a red solid which was collected on a frit and


benzene/hexane at 25 oC.

1H NMR (400 MHz, C6D6): δ 7.90(br s, 6H, PPh3), 7.11-6.88 (br m,

24H, PPh3), 6.35 (ddd, 3JHH = 11 Hz,

3JHH = 7 Hz,

3JPH = 4 Hz, 1H, Ru-CHOMe), 3.59 (m, 2H,

NCH2CH2OMe), 3.42 (s, 3H, O(CH3)), 2.76 (s, 3H, O(CH3)), 2.73-2.64 (m, 2H, NCH2CH2OMe

+ NCH2CHOMe), 2.61 (dt, 2JHH = 10 Hz,

3JHH = 5 Hz, 1H, NCH2CHOMe), 2.22 (dd,

2JHH = 12 Hz,

3JHH = 7 Hz, 1H, NCH2CHOMe), 1.47 (s, 3H, Me2Im(OMe)2-4,5-CH3), 1.27 (s,

3H, Me2Im(OMe)2-4,5-CH3). 31

P{1H} NMR (161 MHz, C6D6): δ 40.8 (d,

2JPP = 315 Hz, PPh3),

33.0 (d, 2JPP = 315 Hz, PPh3).

13C{

1H} NMR (101 MHz, CD2Cl2): δ 134.6 (t,

2JPC = 6 Hz, PPh3),

134.2 (d, 1JPC = 18 Hz, PPh3), 129.2 (PPh3), 127.7 (t,

3JPC = 4 Hz, PPh3), 124.6 (Im-4,5-Cipso),

122.6 (Im-4,5-Cipso), 80.6 (t, 2JPC = 6 Hz, NCH2CHOMe), 71.3 (NCH2CH2OMe), 58.5 (O(CH3)),

58.1 (O(CH3)), 56.1 (NCH2CHOMe), 46.4 (NCH2CH2OMe), 9.2 (Me2Im-4,5-CH3), 8.9

(Me2Im-4,5-CH3), NCN peak not observed. Elemental Analysis for

C47H49ClN2O2P2Ru•(CH2Cl2)0.5: C, 62.36; H, 5.51; N, 3.06. Found: C, 62.14; H, 5.76; N, 3.28.

Synthesis of 2-19: A solution of 2-18 (0.060 g, 0.068 mmol) in 3 mL C6H6 was left stirring for

24 h before the solvent was concentrated to 1 mL and pentane was added while stirring to

precipitate a yellow solid which was collected on a frit and dried under high vacuum (0.045 g,

77%).1H NMR (400 MHz, CD2Cl2): δ 7.67 (d,

3JHH = 5 Hz, 1H, RuCHCHN),7.44 (br s, 12H,

PPh3), 7.29 (br m, 6H, PPh3), 7.23 (br m, 12H, PPh3), 5.66 (dt, 3JHH = 5 Hz,

4JPH = 3 Hz, 1H,

RuCHCHN), 3.63 (t, 3JHH = 6 Hz, 2H, NCH2CH2OMe), 3.01 (t,

3JHH = 6 Hz, 2H,

NCH2CH2OMe) 2.93 (s, 3H, O(CH3)), 1.71 (s, 3H, Me2Im(OMe)2-4,5-CH3), 1.42 (s, 3H,

Me2Im(OMe)2-4,5-CH3). 31

P{1H} NMR (161 MHz, CD2Cl2): δ 36.7 (s, PPh3).

13C{

1H} NMR

(101 MHz, CD2Cl2): δ 135.6 (t, 2JPC = 19 Hz, RuCHCHN), 134.6 (t,

2JPC = 6 Hz, PPh3), 134.2 (d,

59

1JPC = 18 Hz, PPh3), 129.2 (PPh3), 127.6 (t,

3JPC = 4 Hz, PPh3), 125.2 (Im-4,5-Cipso), 124.6 (br s,

RuCHCHN), 122.6 (Im-4,5-Cipso), 71.8 (NCH2CH2OMe), 58.7 (O(CH3)), 46.4 (NCH2CH2OMe),

9.2 (Me2Im-4,5-CH3), 8.9 (Me2Im-4,5-CH3), NCN peak not observed. Elemental Analysis for

C46H45ClN2OP2Ru•(C5H12)0.5: C, 66.47; H, 5.87; N, 3.20. Found: C, 66.49; H, 6.18; N, 2.98.

Synthesis of 2-21: Ethyl vinyl sulfide (13.0 μL, 0.128 mmol) was added to a solution of 2-20


before the solvent was concentrated to 1 mL and 15 mL of pentane was added to which caused a

purple precipitate to form. The purple solid was collected by filtration, washed with pentane and



1H NMR (400 MHz, C6D6): δ 7.70 (d,

3JHH = 5 Hz, 1H, RuCHCHN),

7.27 (t, 3

JHH = 8 Hz, 6H, C6H5, PPh3 ), 7.04-6.90 (m, 13H, C6H5, PPh3 + Mes-CH), 6.61 (d,

3JHH = 2 Hz, 1H, Im-CH), 6.42 (d,

3JHH = 2 Hz, 1H, Im-CH), 6.10 (dd,

3JHH = 5 Hz,

4JPH = 2 Hz,

1H, RuCHCHN), 4.95 (dt, 2JHH = 14 Hz,

3JHH = 3 Hz, 1H, NCH2CH2OMe), 3.44 (br m, 1H,

SIMes-CH2), 3.29 (br m, 1H, SIMes-CH2), 3.09-2.96 (br m, 4H, SIMes-CH2 + NCH2CH2OMe),

2.90 (dt, 2JHH = 11 Hz,

3JHH = 3 Hz, 1H, NCH2CH2OMe), 2.83 (s, 3H, O(CH3)), 2.74 (s, 3H,


Mes-CH3). 31

P{1H} NMR (161 MHz, C6D6): δ 37.0 (s, PPh3).

13C{

1H} NMR (101 MHz, C6D6): δ

202.6 (NCN), 184.9 (d, 2JPC = 15 Hz, NCN), 159.6 (d,

2JPC = 15 Hz, RuCHCHN), 137.6 (Cipso),

137.3 (Cipso), 136.3 (br, Cipso), 134.6 (d, 2JPC = 11 Hz, PPh3), 130.4 (br, Cipso), 129.7 (Mes-CH),

128.6 (Mes-CH), 127.6 (d, 3JPC = 9 Hz, PPh3), 124.2 (d,

4JPC = 2 Hz, RuCHCHN), 118.9

(Im-CH), 114.5 (Im-CH), 72.9 (NCH2CH2OMe), 58.0 (O(CH3)), 51.3 (br s, NCH2CH2N), 48.6

(NCH2CH2OMe), 21.3 (Mes-CH3), 21.0 (Mes-CH3), 20.4 (Mes-CH3), 20.1 (Mes-CH3), 19.9

(Mes-CH3), 17.9 (Mes-CH3). Elemental Analysis for C47H52ClN4OPRu•(C6H6)0.5: C, 67.06; H,

6.19; N, 6.26. Found: C, 66.69; H, 6.65; N, 6.25.



before the solvent was concentrated to 1 mL. Pentane (15 mL) was layered and left overnight at

room temperature yielding red crystals. The pentane was decanted and the crystals were dried

under high vacuum (0.076 g, 79%). X-ray quality crystals were grown from benzene/hexane at

25 oC.

1H NMR (400 MHz, C6D6): δ 7.75 (dd,

3JHH = 5 Hz,

3JPH = 1 Hz, 1H, RuCHCHN), 7.32

(ddd, 3JPH = 10 Hz,

3JHH = 8 Hz,

4JHH = 2 Hz, 6H, C6H5, PPh3 ), 7.06-6.92 (m, 11H, (9H) PPh3 +

60

(2H) Mes-CH), 6.86 (br s, 2H, Mes-CH), 6.69 (d, 3

JHH = 2 Hz, 1H, Im-CH), 6.45 (d, 3

JHH = 2 Hz,

1H, Im-CH), 6.12 (br s, 2H, IMes-CH), 6.09 (dd, 3JHH = 5 Hz,

4JPH = 2 Hz, 1H, RuCHCHN),

4.97 (m, 1H, NCH2CH2OMe), 2.97 (m, 1H, NCH2CH2OMe), 2.91 (m, 1H, NCH2CH2OMe), 2.84

(s, 3H, O(CH3)), 2.47 (app dt, 2JHH = 10 Hz,

3JHH = 2 Hz, 1H, NCH2CH2OMe), 2.79-2.05 (br s,

18H, Mes-CH3). 31

P{1H} NMR (161 MHz, C6D6): δ 38.4 (s, PPh3).

13C{

1H} NMR (101 MHz,

C6D6): δ 185.9 (d, 2JPC = 16 Hz, NCN), 160.2 (d,

2JPC = 12 Hz, RuCHCHN), 137.8 (Cipso), 137.5

(Cipso), 134.6 (d, 2JPC = 11 Hz, PPh3), 134.2 (d,

1JPC = 20 Hz, PPh3), 129.3 (Mes-CH), 128.6

(Mes-CH), 127.6 (d, 3JPC = 9 Hz, PPh3), 124.4 (d,

4JPC = 2 Hz, RuCHCHN), 122.9 (IMes-CH),

122.8 (IMes-CH), 118.7 (Im-CH), 114.5 (Im-CH), 73.0 (NCH2CH2OMe), 58.0 (O(CH3)), 48.5

(NCH2CH2OMe), 21.2 (br s, Mes-CH3), 19.8 (br s, Mes-CH3). Elemental Analysis for

C47H50ClN4OPRu•(C6H6)0.5: C, 67.21; H, 5.98; N, 6.27. Found: C, 66.90; H, 6.28; N, 6.22.



before the solvent was concentrated to 1 mL. Pentane (15 mL) was layered and left overnight at

room temperature yielding red crystals. The pentane was decanted and the crystals were dried

under high vacuum (0.079 g, 82%). X-ray quality crystals were grown from benzene/hexane at

25 oC.

1H NMR (400 MHz, C6D6): δ 7.66 (dd,

3JHH = 5 Hz,

3JPH = 1 Hz, 1H, RuCHCHN), 7.27

(m, 6H, C6H5, PPh3 ), 6.99 (m, 3H, C6H5, PPh3), 6.94 (m, 6H, C6H5, PPh3), 6.83 (br s, 2H,

Mes-CH), 6.75 (br s, 2H, Mes-CH), 6.63 (d, 3

JHH = 2 Hz, 1H, Im-CH), 6.40 (d, 3

JHH = 2 Hz, 1H,

Im-CH), 6.04 (dd, 3JHH = 5 Hz,

4JPH = 2 Hz, 1H, RuCHCHN), 4.89 (ddd,

2JHH = 10 Hz,

3JHH =

4 Hz, 3JHH = 3 Hz, 1H, NCH2CH2OMe), 2.99 (m, 1H, NCH2CH2OMe), 2.86 (ddd,

2JHH = 14 Hz,

3JHH = 4 Hz,

3JHH = 2 Hz, 1H, NCH2CH2OMe), 2.82 (s, 3H, O(CH3)), 2.44 (app dt,

2JHH = 10 Hz,

3JHH = 3 Hz, 1H, NCH2CH2OMe), 2.16 (br s, 9H, Mes-CH3), 2.11 (br s, 9H, Mes-CH3).

31P{

1H}

NMR (161 MHz, C6D6): δ 38.4 (s, PPh3). 13

C{1H} NMR (101 MHz, C6D6): δ 184.8 (d,

2JPC =

16 Hz, NCN), 159.2 (d, 2JPC = 12 Hz, RuCHCHN), 137.2 (Cipso), 136.9 (Cipso), 134.4 (d,

2JPC =

11 Hz, PPh3), 128.9 (Mes-CH), 128.8 (Mes-CH), 127.5 (d, 3JPC = 9 Hz, PPh3), 124.4 (d,

4JPC =

2 Hz, RuCHCHN), 118.8 (Im-CH), 114.5 (Im-CH), 72.6 (NCH2CH2OMe), 57.9 (O(CH3)), 48.5

(NCH2CH2OMe), 21.1 (Mes-CH3), 20.9 (Mes-CH3), 17.8 (Mes-CH3). Elemental Analysis for

C47H48Cl3N4OPRu: C, 61.14; H, 5.24; N, 6.07. Found: C, 56.84; H, 5.74; N, 6.08.

61

2.5.3 X-ray Data Collection and Reduction

Crystals were coated in Paratone-N oil in the glove-box, mounted on a MiTegen Micromount

and placed under an N2 stream, thus maintaining a dry, O2-free environment for each crystal. The

data for crystals were collected on a Bruker Apex II diffractometer employing Mo Kα radiation

(λ = 0.71073 Å). The data were collected at 150(±2) K for all crystals. The frames were

integrated with the Bruker SAINT software package using a narrow-frame algorithm. Data were

corrected for absorption effects using the empirical multi-scan method (SADABS).56

2.5.4 X-ray Data Solution and Refinement

Non-hydrogen atomic scattering factors were taken from the literature tabulations.57

The heavy

atom positions were determined using direct methods employing the SHELXTL direct methods

routine. The remaining non-hydrogen atoms were located from successive difference Fourier

map calculations. The refinements were carried out by using full-matrix least squares techniques

on F, minimizing the function (Fo–Fc)2 where the weight is defined as 4Fo2/2 (Fo

2) and Fo

and Fc are the observed and calculated structure factor amplitudes, respectively. In the final

cycles of each refinement, all non-hydrogen atoms were assigned anisotropic temperature factors

in the absence of disorder or insufficient data. In the latter cases atoms were treated isotropically.

C-H atom positions were calculated and allowed to ride on the carbon to which they are bonded

assuming a C-H bond length of 0.95 Å. H-atom temperature factors were fixed at 1.10 times the

isotropic temperature factor of the C-atom to which they are bonded. The H-atom contributions

were calculated, but not refined. The locations of the largest peaks in the final difference Fourier

map calculation as well as the magnitude of the residual electron densities in each case were of

no chemical significance.

62

Table 2.5.1 Select crystallographic parameters for 2-1 to 2-4.

2-1 2-2 2-3•1.5(C7H8)•0.5(C5H12) 2-4

Formula C48H56ClN4O2PRu C48H54Cl3N4O2PRu C63H80ClN4O2PRu C38H51ClN4O2RuS

Wt 888.46 957.34 1092.80 764.42

Cryst. syst. Monoclinic Monoclinic Monoclinic Triclinic

Space group P21/n P21 P21/n P-1

a(Å) 13.9645(12) 9.9860(6) 14.687(2) 8.7915(3)

b(Å) 17.4923(14) 19.2471(12) 16.729(2) 11.7773(4)

c(Å) 18.6694(18) 24.3594(16) 24.285(3) 19.4743(7)

(deg) 90.00 90.00 90.00 79.623(2)

(deg) 107.017(3) 90.793(2) 101.749(8) 88.313(2)

(deg) 90.00 90.00 90.00 68.932(2)

V(Å3) 4360.7(7) 4681.5(5) 5841.9(14) 1849.44(11)

Z 4 4 4 2

d(calc) gcm–3

1.353 1.358 1.243 1.373

R(int) 0.0431 0.0831 0.0870 0.0303

, mm–1

0.501 0.582 0.387 0.591

Total data 10004 19065 13365 12822

>2(FO2) 7963 10494 8756 10894

Variables 518 1085 704 421

R (>2) 0.0338 0.0460 0.0479 0.0342

Rw 0.0836 0.0656 0.1244 0.0930

GOF 1.019 0.662 1.010 1.032

63

Table 2.5.2 Select crystallographic parameters for 2-5, 2-6, 2-8 and 2-12.

2-5 2-6 2-8 2-12•(C4H8O)

Formula C38H49ClN4O2RuS C38H50ClFN4O2RuS C40H55ClN4O2RuS C48H58ClF5N4O3RuS

wt 762.39 782.41 792.46 1002.56

Cryst. syst. Triclinic Triclinic Orthorhombic Orthorhombic

Space group P-1 P-1 Pbca Pbca

a(Å) 8.7968(3) 8.8552(11) 25.5160(18) 20.6520(7)

b(Å) 11.7375(4) 11.8620(15) 8.8783(6) 21.0587(7)

c(Å) 19.4493(7) 19.312(3) 38.627(3) 21.6212(7)

(deg) 79.242(2) 80.115(7) 90.00 90.00

(deg) 88.387(1) 89.229(6) 90.00 90.00

(deg) 68.968(1) 69.025(6) 90.00 90.00

V(Å3) 1839.81(11) 1863.5(4) 8750.6(11) 9403.2(5)

Z 2 2 8 8

d(calc) gcm–3

1.376 1.394 1.203 1.416

R(int) 0.0608 0.0646 0.1370 0.1100

, mm–1

0.594 0.592 0.502 0.500

Total data 8388 8517 7699 10790

>2(FO2) 6011 6283 5084 6457

Variables 421 430 439 568

R (>2) 0.0480 0.0486 0.0655 0.0491

Rw 0.1107 0.1172 0.1399 0.1116

GOF 1.024 1.032 1.082 1.003

64

Table 2.5.3 Select crystallographic parameters for 2-17, 2-18, 2-21 and 2-22.

2-17 2-18•(C6H6)•(C5H12) 2-21•(C6H6) 2-22•0.5(C6H6)

Formula C45H45ClN2O2P2Ru C50.5H58ClN2O2P2Ru C50H55ClN4OPRu C50H53ClN4OPRu

wt 844.29 947.47 895.47 893.45

Cryst. syst. Triclinic Monoclinic Monoclinic Monoclinic

Space group P-1 P21/n I2/a C2/c

a(Å) 10.2192(4) 13.009(3) 21.7335(12) 34.768(5)

b(Å) 13.8275(6) 18.484(4) 14.9240(6) 14.8467(17)

c(Å) 14.7190(6) 20.315(5) 26.9039(13) 21.575(4)

(deg) 105.817(2) 90.00 90.00 90.00

(deg) 93.474(2) 104.490(12) 91.324(4) 128.344(9)

(deg) 101.154(2) 90.00 90.00 90.00

V(Å3) 1949.13(14) 4729.5(19) 8726.2(7) 8735(2)

Z 2 4 8 8

d(calc) gcm–3

1.439 1.331 1.363 1.359

R(int) 0.0453 0.0407 0.0443 0.0699

, mm–1

0.594 0.497 0.499 0.499

Total data 8958 10871 10073 10076

>2(FO2) 6406 8829 7770 7422

Variables 475 528 523 523

R (>2) 0.0434 0.0505 0.0363 0.0384

Rw 0.0966 0.1463 0.0906 0.0903

GOF 1.006 1.068 1.015 1.013

65

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(42) Corrochano, A. E.; Jalon, F. A.; Otero, A.; Kubicki, M. M.; Richard, P. Organometallics

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68

Chapter 3 Catalytic Olefin Metathesis

3.1 Introduction

3.1.1 Types of Olefin Metathesis Reactions

Olefin metathesis has become a synthetic tool for the modification of organic substrates that is

exploited across the discipline in natural product synthesis, polymer, pharmaceutical and

industrial chemistry.1-7

The most common olefin metathesis reactions are typically grouped into

three specific types (Scheme 3.1.1). These types include ring opening metathesis polymerization

(ROMP) which is used to synthesize polymers.8-10

This is an example of a living polymerization

where the continuous opening of cyclic olefinic monomers results in a growing polymer attached

to the metal center. The driving force for this reaction is typically from the relief of ring strain in

the monomer. A number of interesting polymers can be obtained through ROMP including

polydicyclopentadiene11

and polynorbornene12,13

which are used for body panels of vehicles and

anti-vibration, anti-impact and grip improvement, respectively. The second reaction type is ring

closing metathesis (RCM) where two terminal olefinic functionalities that are contained within

the same molecule are linked together creating a cyclic product with the elimination of

ethylene.14

This transformation is applied for the synthesis of heterocycles, bicycles and

cycloalkenes15-17

where the equilibrium can be driven to the cyclic product by the removal of

ethylene from the system. Pressurizing the system with ethylene drives the equilibrium to the

ring opened product in a process called ring opening metathesis (ROM). Cross metathesis (CM)

of two olefinic substrates results in the formation of a coupled product with the liberation of

ethylene as a byproduct.18-20

Similar to RCM, this equilibrium is driven to the coupled product

by the liberation of ethylene. The reverse reaction can be accomplished by applying an ethylene

pressure which results in cleavage of the carbon-carbon double bond resulting in two terminal

olefinic products.21,22

This process is called ethenolysis and is used for the production of

biodiesel from unsaturated fatty acids.23

69

Scheme 3.1.1 Common olefin metathesis reactions.

3.1.2 Catalyst Screening

3.1.2.1 Standard Test Reactions

Due to the lack of standard test reactions for catalytic olefin metathesis, assessing the activity of

new catalytic systems and comparing them to existing catalysts was highly inconsistent. To this

end, Grubbs and co-workers developed a series of standard transformations to serve as an easily

applicable platform for catalyst comparison.24

The three standard tests provide insight into a

catalyst’s ability to perform the three most common reactions described above (ROMP, RCM,

and CM).

To investigate the effectiveness of a catalyst to accomplish ROMP, 1,5-cyclooctadiene is

polymerized using the catalyst of choice (Scheme 3.1.2), typically as a solution in CD2Cl2.

70

Scheme 3.1.2 Standard test reaction for ROMP.

The standard test for RCM is the ring closing of diethyl diallylmalonate (Scheme 3.1.3) again as

a CD2Cl2 solution with the catalyst of choice.

Scheme 3.1.3 Standard test reaction for RCM.

The standard metathesis test for CM involves the coupling of 5-hexenyl acetate and methyl

acrylate in a CD2Cl2 solution (Scheme 3.1.4). This reaction can give the desired heterocoupled

product as shown below and also the homocoupled 5-hexenyl acetate product.

Scheme 3.1.4 Standard test reaction for CM.

3.1.2.2 Activity of Common Catalysts

The activity of some common olefin metathesis catalysts is presented in Table 3.1.124

to provide

a comparison with activities presented in this chapter. For ROMP, Grubbs II and 2nd Generation

Hoveyda-Grubbs Catalyst (HG II) (see Figure 2.1.1 for structures) are the most active achieving

99% conversion in 6 and 5 min respectively. After 90 min Grubbs I achieves 40% conversion

and after 100 min 1st Generation Hoveyda-Grubbs Catalyst (HG I) achieves 4% conversion.

Grubbs I converts diethyl diallylmalonate to the ring closed product in 66% yield after 30 min

whereas Grubbs II, HG I, and HG II can accomplish RCM of diethyl diallylmalonate to over

90% in 30 min. For CM Grubbs II and HG II achieve 90% conversion after 70 min with 97 and

99% consumption of 5-hexenyl acetate respectively. Grubbs I achieves 8% conversion to the

71

heterocoupled product with 87% consumption of 5-hexenyl acetate and HG I achieves 3%

conversion with 73% consumption of 5-hexenyl acetate. The consumption of 5-hexenyl acetate

in this reaction is due to both the formation of the heterocoupled product and the 5-hexenyl

acetate homocoupling product.

Table 3.1.1 Standard olefin metathesis reactions using common catalysts.

Catalyst ROMPa

RCMb CM

c

Grubbs I 40% (90 min) 66% 8% (87%)

Grubbs II 99% (6 min) 96% 90% (97%)

HG I 4% (100 min) 90% 3% (73%)

HG II 99% (5 min) 99.5% 90% (99%)

aMaximum conversions at the respective reaction times. Conditions: 0.1 mol% cat., 0.5 M, 30 °C.

bConversions at 30 min reaction time under standard conditions. Conditions: 1 mol% cat., 0.1 M, 30 °C.

cConversion to heterocoupled product at 70 min. In brackets, consumption of 5-hexenyl acetate. Conditions: 2.5

mol% cat., 0.4 M, 30 °C.

3.1.3 Acid Assisted Olefin Metathesis

There are a number of reports on the use of Brønsted or Lewis acids as additives in olefin

metathesis reactions. Their role is different depending on the catalyst and/or metathesis

transformation being studied. Lewis acids could be used to increase yields for transformations

that utilize substrates with a reactive or Lewis basic functional group. For example, it has been

shown that the use of Lewis acids, such as Ti(OiPr)4, for RCM reactions involving substrates

with a nucleophilic nitrogen results in increased yield of the ring closed product (Scheme

3.1.5).25

It is believed that the Lewis acid binds to the nucleophilic N atom to prevent it from

binding to the Ru center and thus shutting off metathesis.

Scheme 3.1.5 Lewis acid assisted RCM.

72

Alternatively, and more relevant to this thesis, acids could activate the catalysts by protonation of

a ligand, ligand abstraction via coordination of a ligand to the Lewis acid or via halide

abstraction. In these cases, the acid activation of olefin metathesis catalysts creates a vacant

coordination site which results in a coordinatively unsaturated metal center for substrate to bind.

Grubbs and co-workers have reported the use of HCl as an additive to enhance the activity of

Grubbs II in CM reactions (Scheme 3.1.6).26

The acid acts as a phosphine scavenger to generate

the active 4-coordinate catalyst and prevents the phosphine from competing with substrate for

coordination to the ruthenium center.

Scheme 3.1.6 Use of acid as a phosphine scavenger.

BCl3 has recently been shown to activate Ru alkylidene complexes with tridentate, dianionic

thiolate ligands for olefin metathesis (Scheme 3.1.7).27

Scheme 3.1.7 Activation of metathesis catalysts with BCl3.

The first equivalent results in a chloride being transferred to the metal center and the remaining

BCl2 fragment bridges the two anionic donors. The second equivalent of BCl3 abstracts the

73

chloride from the metal center resulting in a cationic ruthenium species which is active in

standard metathesis tests.

3.1.4 Halide Abstraction for Activation of Metathesis Catalysts

Hofmann and co-workers showed that Ru-based alkylidene species could be activated for olefin

metathesis through halide abstraction (Scheme 3.1.8).28

The addition of TMS-OTf abstracts a

halide and results in the formation of a chloride bridged Ru dimer.

Scheme 3.1.8 Activation of metathesis catalyst through halide abstraction.

This species exists in equilibrium with the monomeric form which is metathesis active. This is an

example of a metathesis active Ru-alkylidene species that is attained through halide abstraction

and not phosphine dissociation. More recently, Cazin and co-workers reported a 4-coordinate

cationic olefin metathesis catalyst29

that is formed through halide abstraction using AgSbF6

(Scheme 3.1.9).

Scheme 3.1.9 Synthesis of a 4-coordinate olefin metathesis catalyst by halide abstraction.

74

Both the neutral parent species and the cationic species are active for ring closing metathesis and

cross metathesis at 140 °C. Interestingly, even though the cationic species is more active for

olefin metathesis than the parent neutral complex, it is slower initiating.

3.1.5 Cross Metathesis of NBR and 1-Hexene

As mentioned in Section 1.3, a lower molecular weight polymer can be obtained by performing

cross metathesis of NBR with 1-hexene.5,30

This process is conceptually similar to ethenolysis

where the polymer is cut into smaller chains through cross metathesis of the internal olefins in

the polymer structure with a small olefinic substrate (1-hexene). Industrially this is accomplished

by employing Grubbs II where, depending on the catalyst loading and reaction times, polymers

of varying molecular weights and viscosities can be obtained.


With a number of ruthenium alkylidene species prepared, their activity for catalytic olefin

metathesis was probed. To do this, the standard system of characterization for olefin metathesis

catalysts was followed using the three specific reactions outlined above. As for the CM of NBR

with 1-hexene, only one example is shown below. Shown in Scheme 3.2.1 is a list of compounds

tested for catalytic olefin metathesis in this chapter.

75

Scheme 3.2.1 List of catalysts used for catalytic olefin metathesis.

3.2.1 ROMP of 1,5-Cyclooctadiene

Compound 2-4 was ineffective as a catalyst for ROMP at room temperature, but upon heating to

45 °C conversion to the product was achieved in 93% after 24 hours. The addition of one

equivalent of BCl3 to 2-4 resulted in increased activity in ROMP affording 100% product yield

after 6 hours at room temperature (Figure 3.2.1). This reaction was accelerated at 45 °C affording

98% conversion after 2 hours.

76

Figure 3.2.1 ROMP of 1,5-cyclooctadiene using 2-4. Conditions: 1 mol% cat., 0.1 M in CD2Cl2.

Similarly, using 2-5, ROMP activity was only observed at 45 °C with product yields of 69% after

24 hours. In the presence of one equivalent of BCl3, conversion of 92% was observed after 24

hours at room temperature and complete conversion after 8 hours at 45 °C.

Compound 2-6 was more effective than 2-5 with complete conversion after 24 hours at 45 °C

and upon the addition of BCl3, at room temperature, product yields of 100% were observed after

8 hours. At 45 °C the same conversion was achieved after 2 hours. Compound 2-7 effected

ROMP catalysis with complete conversion after 2 hours both at room temperature and at 45 °C

upon using one equivalent of BCl3. Minimal activity is shown in the absence of BCl3 (58% after

24 hours at 45 °C).

Better rates are observed using 2-8 where, at 45 °C in the absence of BCl3, ROMP was achieved

in 100% yield after 4 hours. Upon the addition of BCl3, the same conversion was obtained after 6

hours at room temperature or 30 min at 45 °C (Figure 3.2.2).

77

Figure 3.2.2 ROMP of 1,5-cyclooctadiene using 2-8. Conditions: 1 mol% cat., 0.1 M in CD2Cl2.

ROMP activity at room temperature, in the absence of a Lewis acid, was obtained using 2-12

with conversions of 79% after 24 hours. This was enhanced to 93% after 6 hours at 45 °C. Upon

the addition of BCl3, complete conversion was obtained after 8 hours at room temperature or

after 30 minutes at 45 °C (Figure 3.2.3).

Figure 3.2.3 ROMP of 1,5-cyclooctadiene using 2-12. Conditions: 1 mol% cat., 0.1 M in

CD2Cl2.

78

Using 2-13, product yields for ROMP of 95% were achieved at room temperature without the

addition of BCl3. Complete conversion was obtained at room temperature upon the addition of

BCl3 after 2 hours and similar conversions were obtained with 2-14.

3.2.2 RCM of Diethyl Diallylmalonate

In the case of RCM of diethyl diallylmalonate, 2-4 was ineffective both at room temperature and

at 45 °C in the absence of a Lewis acid. Upon the addition of BCl3, moderate conversion to the

ring-closed product (14%) was achieved after 24 hours at room temperature. Conversion was

enhanced at 45 °C to 88% when BCl3 was added (Figure 3.2.4). Adding two equivalents of BCl3

did not enhance catalysis and at elevated temperatures lower conversions were obtained.

Figure 3.2.4 RCM of diethyl diallylmalonate using 2-4. Conditions: 5 mol% cat., 0.16 M in

CD2Cl2.

Compound 2-5 was only effective as a catalyst for RCM at 45 °C upon the addition of BCl3

(100% after 24 hours). Slightly enhanced conversions were obtained with 2-6 where upon the

addition of BCl3, at room temperature, product yields of 33% were observed after 24 hours. At

45 °C complete conversion was obtained after 6 hours for 2-6 while compound 2-7 showed

moderate activities with 52% product yield after 24 hours, under similar conditions.

79

Better rates were observed using 2-8 as the catalyst where upon the addition of BCl3 at room

temperature product yields of 79% were observed after 24 hours. This is further enhanced at

45 °C where complete conversion was obtained after 2 hours (Figure 3.2.5).


CD2Cl2.

Minimal RCM activity at room temperature, in the absence of a Lewis acid, was obtained using

2-12 with conversions of 17% after 24 hours. Upon the addition of BCl3, enhanced activity was

observed with conversions of 93% after 24 hours at room temperature and 100% after 2 hours at

45 °C (Figure 3.2.6).

80


CD2Cl2.

Using 2-13, product yields for RCM of 60% were achieved at 45 °C without the addition of BCl3

and 88% upon the addition of BCl3 after 24 hours at 25 °C. At 45 °C, in the presence of BCl3,

complete conversion was obtained after 2 hours. Under similar conditions, using 2-14,

conversions of 56, 93 and 100% were obtained, respectively.

3.2.3 CM of 5-Hexenyl Acetate and Methyl Acrylate

For the CM of 5-hexenyl acetate and methyl acrylate, 2-4 was ineffective both at room

temperature and at 45 °C in the absence of a Lewis acid. Upon the addition of BCl3, minimal

conversion to the heterocoupled product (26%) was achieved after 24 hours at 25 °C. Conversion

was enhanced at 45 °C to 51% when BCl3 was added (Figure 3.2.7). Adding two equivalents of

BCl3 enhanced the conversions slightly at room temperature (41% after 24 hours) and at 45 °C

(61% after 8 hours). It is worth noting that although conversions to the heterocoupled product

were not very high, the homocoupled product was also observed.

81

Figure 3.2.7 CM of methyl acrylate and 5-hexenyl acetate using 2-4. Conditions: 2 mol% cat.,

0.4 M in CD2Cl2.

Compound 2-5 was only minimally effective as a catalyst for CM at 45 °C upon the addition of

BCl3 (28% after 2 hours). Slightly enhanced conversions were obtained with 2-6 with the

addition of BCl3, at 45 °C, where 48% of the heterocoupled product was obtained after 2 hours

while compound 2-7 showed conversions of 32% after 24 hours, under similar conditions.

Better rates were observed using 2-8, with the addition of BCl3 at room temperature, where

product yields of 50% were obtained after 6 hours. This is further enhanced at 45 °C where

conversion of 72% was obtained after 4 hours (Figure 3.2.8).

82


0.4 M in CD2Cl2.

No CM activity at 25 °C, in the absence of a Lewis acid, was observed using 2-12. Upon the

addition of BCl3, enhanced activity was observed with conversions to the heterocoupled product

of 40% after 6 hours at 25 °C and 50% after 4 hours at 45 °C (Figure 3.2.9).


0.4 M in CD2Cl2.

83

Using 2-13, product yields for CM of 21%, at room temperature upon the addition of BCl3 after 6

hours, were obtained while at 45 °C, in the presence of BCl3, 60% conversion was obtained after

4 hours. The best CM conversions were obtained with 2-14 where, at room temperature with one

equivalent of BCl3, conversions of 79% were observed after 6 hours. Similar conversions were

obtained after 2 hours at 45 °C.

3.2.4 Trends in Catalytic Olefin Metathesis

Pentafluorophenyl thiolate-containing compounds (2-12, 2-13, and 2-14) were shown to be more

active for ROMP, RCM, and CM than phenyl thiolate analogues (2-4, 2-5, 2-6, 2-7, and 2-8).

Pseudo-halides have been studied by Fogg and co-workers who reported substitution of chlorides

with catecholate31

or phenoxide32,33

based anionic ligands in Grubbs type systems. Most of the

systems reported showed slow initiation, but very good activities, where metathesis was done at

elevated temperatures. It is also observed that compounds with more electron donating carbenes

(i.e. Me2Im(OMe)2 > Im(OMe)2 and SIMes > IMes) show better activity with 2-8 being the most

active. It has been demonstrated that Ru-alkylidene complexes with more electron donating

NHCs tend to be more active for olefin metathesis. This is presumably because they enhance the

rate of oxidative addition needed for metallacyclobutane formation during catalysis.34

The

addition of BCl3 as an additive enhanced the activity of all the pre-catalysts tested both at room

temperature and at 45 oC. The role of the BCl3 as an activator was probed by monitoring

reactions of several of the compounds discussed above with BCl3 by 11

B{1H} NMR

spectroscopy. The products showed resonances at 6.9 ppm attributable to the formation of the

[BCl4] anion.35

Nonetheless, efforts to either isolate the corresponding cation or its complex with

a series of donor molecules were unsuccessful. In spite of this, these data suggest that the borane

abstracts the halide to generate a site of unsaturation on ruthenium, presumably accounting for

the enhanced catalytic activity.

3.2.5 Cross Metathesis of NBR and 1-Hexene

The systems described above were developed with the ultimate goal of catalyzing the cross

metathesis of NBR and 1-hexene to decrease to molecular weight and PDI (Ð) of the polymer.

The NBR tested had an initial Mw of 275 000 Da and a Mn of 82 000 Da with a PDI of 3.4. Only

catalysts that displayed activity for CM of 5-hexenyl acetate and methyl acrylate were tested for

CM of NBR and 1-hexene and only one example is provided in this chapter. Several parameters

84

were probed including changing the catalyst loading, using either no BCl3 or one or two

equivalents of the Lewis acid, as well as running the reactions at room temperature, 45 °C and

60 °C. For comparison purposes, Grubbs II was tested under similar conditions.

After one hour at 25 °C, using Grubbs II with a catalyst loading of 0.07 phr, a decrease in Mw

and Mn to 80 000 and 38 000 Da, respectively, was observed. The Ð was also reduced to 2.1

After 24 hours, Mw, Mn and Ð are further lowered to 33 000 Da, 20 000 Da, and 1.6,

respectively. Using 0.07 phr catalyst loading with 2-4 at room temperatures resulted in no

considerable CM where after 24 hours the Mw, Mn and Ð were essentially unchanged at 231 000

Da, 76 000 Da, and 3.0, respectively. Upon the addition of one or two equivalents of BCl3, at

room temperature, minimal CM is observed. In the case of one equivalent of BCl3, the Mw, Mn

and Ð are 207 000 Da, 68 000 Da, and 3.0 respectively, after 24 hours. In the case of two

equivalents of BCl3, the Mw, Mn and Ð are 191 000 Da, 70 000 Da, and 2.7 respectively, after 24

hours.

Using Grubbs II at a catalyst loading of 0.07 phr at 45 °C resulted in very effective CM of NBR

with 1-hexene where, after one hour, the Mw, Mn and Ð are 23 000 Da, 16 000 Da, and 1.5

respectively. These numbers remain essentially unchanged after 24 hours. On the other hand,

using 2-4 under the same reaction conditions resulted in no tangible metathesis where, after 24

hours, the Mw, Mn and Ð are 235 000 Da, 76 000 Da, and 3.1 respectively. Slightly enhanced

metathesis was observed upon the addition of one or two equivalents of BCl3. In the case of one

equivalent of BCl3, after 24 hours at 45 °C, the Mw, Mn and Ð are 170 000 Da, 64 000 Da, and

2.6 respectively. In the case of two equivalents of BCl3, after 24 hours at 45 °C, the Mw, Mn and

Ð are 176 000 Da, 66 000 Da, and 2.7 respectively (Figure 3.2.10).

85

Figure 3.2.10 CM of NBR and 1-hexene using 2-4 and Grubbs II at 45 °C.

Increasing the catalyst loading of 2-4 to 0.14 phr at 45 °C significantly enhanced the CM of NBR

and 1-hexene. With no BCl3 added, after 24 hours, the Mw, Mn and Ð are 221 000 Da,

75 000 Da, and 2.9 respectively. Upon the addition of one equivalent of BCl3, after 24 hours at

45 °C, the Mw, Mn and Ð are 157 000 Da, 63 000 Da, and 2.5 respectively. In the case of two

equivalents of BCl3, after 24 hours at 45 °C, the Mw, Mn and Ð are 76 000 Da, 39 000 Da, and

2.0 respectively (Fig. 3.2.10).

Increasing the temperature to 60 °C enhanced catalysis slightly compared to runs at 45 °C with

2-4 (Figure 3.2.11). At a catalyst loading of 0.07 phr with one equivalent of BCl3, after 24 hours,

the Mw, Mn and Ð are 147 000 Da, 59 000 Da, and 2.5 respectively. With two equivalents of

BCl3, after 24 hours at 60 °C, the Mw, Mn and Ð are 119 000 Da, 52 000 Da, and 2.3

respectively. At a catalyst loading of 0.14 phr with one equivalent of BCl3, after 24 hours, the

Mw, Mn and Ð arere 126 000 Da, 54 000 Da, and 2.3 respectively. With two equivalents of BCl3,

after 24 hours at 60 °C, the Mw, Mn and Ð are 88 000 Da, 43 000 Da, and 2.1 respectively.

86

Figure 3.2.11 CM of NBR and 1-hexene using 2-4 at 60 °C.

There is no enhancement to catalysis at 60 °C both with one and two equivalents of BCl3. This is

presumably because the generated species upon adding two equivalents of BCl3 is less stable

than the one generated upon addition of just one equivalent of BCl3.

3.3 Conclusion

Ruthenium alkylidene complexes bearing the hemilabile tridentate NHC 2-4 to 2-14 are either

inactive or minimally active for RCM, ROMP and CM. The species generated by the addition of

one equivalent of BCl3 show improved activity for RCM, ROMP and CM either at room

temperature or at 45 °C. In general, the catalysts which contain more electron donating carbenes

are more active than those containing less donating NHCs. The catalysts with S(C6F5), as one of

the anionic ligands, are most active compared to the catalysts with the PhS- ligand. Complex 2-4

is chosen as an example to demonstrate the activity in the cross metathesis of NBR and 1-hexene

at different conditions. This system was active but higher catalyst loadings and elevated

temperatures were required to achieve similar conversions as Grubbs II catalyst at room

temperature.

87



All synthetic manipulations were carried out under an atmosphere of dry, O2-free N2 employing

a VAC Atmospheres glove box. Dichloromethane-d2 was dried over CaH2 and vacuum

transferred into a Young bomb. All solvents were thoroughly degassed after purification (three

freeze-pump-thaw cycles). NMR spectra were recorded at 25 °C on a Bruker Avance 400 MHz

spectrometer. Commercially available substrates were obtained from Sigma-Aldrich and used

without further purification. NBR was obtained from Lanxess and stored at -40 ºC. GPC data

was collected using Styragel HR 5E-THF columns at 45 °C using a Waters 2414 RI Detector.

Data was processed using Empower Pro software and Mw and Mn data were determined against a

polystyrene calibration curve.


3.4.2.1 Standard Metathesis Reaction Tests

All standard metathesis reaction tests were performed employing a modified procedure of

Grubbs and co-workers.24

The standard procedure for the ring opening metathesis polymerization of 1,5-cyclooctadiene is

as follows: The required amount of the catalyst (1 mol%), was weighed out and dissolved in

0.5 mL CD2Cl2. For the tests that involved the use of an additive (i.e. BCl3, 1M in hexane) the

required volume was added and the mixture was allowed to stand for 5 min. The solutions were

placed in an NMR tube, 1,5-cyclooctadiene (60 μL, 0.50 mmol) was added, the NMR tube was

capped and the solution was mixed at the desired temperature. Reaction progress was monitored

by 1H NMR every 2 hours (unless otherwise noted). Reaction progress was determined by

integration of the peaks corresponding to the starting material versus the product.

88

Table 3.4.1 ROMP of 1,5-cyclooctadiene with 2-4.

Compound 2-4

Additive Temperature (oC) Time (h) Conversion (%)

None 25 24 0

None 45 2 4

4 8

6 14

24 93

1 mol% BCl3 25 2 54

4 96

6 100

1 mol% BCl3 45 2 98

4 100

2 mol% BCl3 25 2 53

3 71

2 mol% BCl3 45 2 100


Compound 2-5


None 25 24 0

None 45 2 6

4 11

6 16

8 21

24 69

1 mol% BCl3 25 2 11

4 16

6 21

8 30

89

24 92

1 mol% BCl3 45 2 26

4 64

6 90

8 100

2 mol% BCl3 25 2 70

4 92

6 100

2 mol% BCl3 45 2 100


Compound 2-6


None 25 24 0

None 45 2 5

4 13

6 23

8 36

24 100

1 mol% BCl3 25 2 30

4 56

6 83

8 100

1 mol% BCl3 45 2 100


Compound 2-7


None 25 24 0

None 45 2 3

90

4 9

6 14

24 58

1 mol% BCl3 25 2 100

1 mol% BCl3 45 2 100


Compound 2-8


None 25 24 0

None 45 2 54

4 100

1 mol% BCl3 25 0.5 21

2 61

4 92

6 100

1 mol% BCl3 45 0.5 100


Compound 2-12


None 25 2 14

4 23

6 30

8 37

24 79

None 45 2 79

4 89

6 93

91

1 mol% BCl3 25 2 64

4 83

6 95

8 100

1 mol% BCl3 45 0.5 100

2 mol% BCl3 25 2 42

4 73

6 89

8 97


Compound 2-13


None 25 2 38

4 58

6 71

8 80

24 95

1 mol% BCl3 25 2 100


Compound 2-14


None 25 2 71

4 62

6 84

8 90

24 93

1 mol% BCl3 25 2 100

92

2 mol% BCl3 25 2 77

4 93

6 100

A standard procedure for the ring closing metathesis of diethyl diallylmalonate is as follows. The

required amount of catalyst (5 mol%) was weighed out and dissolved in 0.5 mL CD2Cl2. For the

tests that involved the use of an additive (i.e. BCl3, 1M in hexane) the required volume was

added and the mixture was allowed to stand for 5 min. The solution was placed in an NMR tube,

diethyl diallylmalonate (20 μL, 0.50 mmol) was added, the NMR tube was capped and the

solution was mixed at the desired temperature. Reaction progress was monitored by 1H NMR

every 2 hours (unless otherwise noted). Reaction progress was determined by integration of the

olefinic peaks of the starting material versus the product.

Table 3.4.9 RCM of diethyl diallylmalonate with 2-4.

Compound 2-4


None 25 24 0

None 45 24 0

5 mol% BCl3 25 24 14

5 mol% BCl3 45 2 5

4 16

6 34

8 47

24 88

10 mol% BCl3 25 2 4

4 6

6 10

8 12

24 28

10 mol% BCl3 45 2 17

4 41

6 54

93

8 59

24 67


Compound 2-5


None 25 24 0

None 45 24 0

5 mol% BCl3 25 24 0

5 mol% BCl3 45 2 5

4 11

6 14

8 21

24 100

10 mol% BCl3 25 2 3

4 7

6 12

8 17

24 46

10 mol% BCl3 45 2 19

4 44

6 49

8 51

24 75

94


Compound 2-6


None 25 24 0

None 45 2 6

4 10

6 13

8 16

5 mol% BCl3 25 2 0

4 3

6 7

8 15

24 33

5 mol% BCl3 45 2 63

4 91

6 100


Compound 2-7


None 25 24 0

None 45 24 0

5 mol% BCl3 25 8 3

24 10

5 mol% BCl3 45 2 16

4 24

6 28

8 29

24 52

.

95


Compound 2-8


None 25 24 0

None 45 2 7

4 12

5 mol% BCl3 25 2 5

4 13

6 28

8 47

24 79

5 mol% BCl3 45 0.5 42

2 100


Compound 2-12


None 25 2 0

24 4

None 45 2 2

4 4

6 6

8 8

24 17

5 mol% BCl3 25 2 15

4 51

6 72

8 81

24 93

5 mol% BCl3 45 2 100

10 mol% BCl3 25 2 3

96

4 7

6 13

8 22

24 57

10 mol% BCl3 45 2 67

4 87

6 92


Compound 2-13


None 25 24 7

None 45 2 10

4 16

6 24

8 30

24 60

5 mol% BCl3 25 2 12

4 20

6 32

8 52

24 88

5 mol% BCl3 45 2 100

97


Compound 2-14


None 25 2 1

24 15

None 45 2 9

4 14

6 19

8 25

24 56

5 mol% BCl3 25 2 28

4 62

6 85

8 90

24 93

5 mol% BCl3 45 2 100

10 mol% BCl3 25 2 6

4 17

6 28

8 41

24 86

10 mol% BCl3 45 2 83

4 100

A standard procedure for cross metathesis of 5-hexenyl acetate and methyl acrylate is as follows.

The required amount of catalyst (2 mol%) was weighed out and dissolved in 0.5 mL CD2Cl2. For

the tests that involved the use of an additive (i.e. BCl3, 1M in hexane) the required volume was

added and the mixture was allowed to stand for 5 min. The solution was placed in an NMR tube

and a mixture of 5-hexenyl acetate (20 μL, 0.12 mmol) and methyl acrylate (10 μL, 0.11 mmol)

was added and the solution was mixed at the desired temperature. Reaction progress was

monitored by 1H NMR every 2 hours (unless otherwise noted). Reaction progress was

determined by integration of the olefinic peaks of the starting material versus the product.

98

Table 3.4.17 CM of 5-hexenyl acetate and methyl acrylate with 2-4.

Compound 2-4


None 25 24 0

None 45 24 0

2 mol% BCl3 25 2 0

6 13

8 24

24 26

2 mol% BCl3 45 2 24

4 43

6 49

8 51

4 mol% BCl3 25 2 15

4 20

6 24

8 31

24 41

4 mol% BCl3 45 2 35

4 47

6 56

8 61


Compound 2-5


None 25 24 0

None 45 24 0

2 mol% BCl3 25 24 0

2 mol% BCl3 45 2 28

99

4 mol% BCl3 25 24 0

4 mol% BCl3 45 2 20


Compound 2-6


None 25 24 0

None 45 24 0

2 mol% BCl3 25 2 48

2 mol% BCl3 45 2 42


Compound 2-7


None 25 24 0

None 45 24 0

2 mol% BCl3 25 24 0

2 mol% BCl3 45 4 21

6 23

8 28

24 32


Compound 2-8


None 25 24 0

None 45 24 0

2 mol% BCl3 25 2 38

100

4 46

6 50

2 mol% BCl3 45 2 65

4 72


Compound 2-12


None 25 24 0

None 45 24 0

2 mol% BCl3 25 2 32

4 37

6 40

2 mol% BCl3 45 2 47

4 50

4 mol% BCl3 25 2 0

4 28

6 33

4 mol% BCl3 45 2 65


Compound 2-13


None 25 24 0

None 45 24 0

2 mol% BCl3 25 2 15

4 18

6 21

2 mol% BCl3 45 2 55

4 60

101


Compound 2-14


None 25 24 0

None 45 24 0

2 mol% BCl3 25 2 20

4 50

6 79

2 mol% BCl3 45 2 80

4 mol% BCl3 25 2 18

4 28

6 32

8 36

24 53

4 mol% BCl3 45 2 61

4 75

3.4.2.2 Cross Metathesis of NBR and 1-hexene

A standard procedure for the cross metathesis of nitrile butadiene rubber (NBR) and 1-hexene is

as follows. NBR (1.5 g) were placed in 13.5 g of chlorobenzene and placed on a shaker for 48 h

to give a 10 wt% NBR solution. 1-Hexene (60 mg, 90 μL) was added to the solution and shaken

for 1 h. The catalysts were prepared by dissolving the required mass of precatalyst in CH2Cl2

(2 mL) in a glove box and the appropriate amount of BCl3 was then added and the solutions were

stirred for 5 min before being taken out of the glove box and added to the NBR solutions. The

solutions were then stirred at the desired temperature for a total of 24 h. Samples were taken at 1,

2, 3, 4, and 24 h. The catalysts were poisoned with ethyl vinyl ether (0.1 mL) to stop the

metathesis. All volatiles were removed from the samples. GPC samples were made by preparing

a 1 mg/mL THF solution of the resulting NBR. The samples were passed through a microporous

filter and the Mn, Mw, and Ð were determined by GPC using a polystyrene calibration curve. The

102

Mw and Mn for NBR used with 2-4 and Grubbs II are 275 000 and 82 000 Da, respectively, and

the Ð is 3.3.

Table 3.4.25 GPC data for CM of NBR and 1-hexene using 2-4 and Grubbs II at 25 °C.

Catalyst 2-4 2-4 2-4 Grubbs II

Catalyst loading (phr) 0.07 0.07 0.07 0.07

BCl3 (equiv.) None 1 2 None

1 h

Mw 251 000 240 000 257 000 80 000

Mn 82 000 88 000 92 000 38 000

Ð 3.0 2.7 2.8 2.1

2 h

Mw 255 000 242 000 235 000 58 000

Mn 81 000 80 000 78 000 30 000

Ð 3.1 3.0 3.0 1.9

3 h

Mw 242 000 236 000 221 000 48 000

Mn 79 000 79 000 77 000 27 000

Ð 3.0 3.0 2.9 1.8

4 h

Mw 248 000 233 000 - 42 000

Mn 84 000 79 000 - 24 000

Ð 3.0 3.0 - 1.7

24 h

Mw 231 000 207 000 191 000 33 000

Mn 76 000 68 000 70 000 20 000

Ð 3.0 3.0 2.7 1.6

103

Table 3.4.26 GPC data for CM of NBR and 1-hexene using 2-4 and Grubbs II at 45 °C.

Catalyst 2-4 2-4 2-4 Grubbs II


BCl3 (equiv.) None 1 2 None

1 h

Mw 240 000 204 000 220 000 24 000

Mn 87 000 80 000 80 000 15 000

Ð 2.8 2.6 2.7 1.5

2 h

Mw 236 000 209 000 231 000 23 000

Mn 90 000 76 000 81 000 15 000

Ð 2.6 2.7 2.9 1.5

3 h

Mw 261 000 205 000 231 000 24 000

Mn 82 000 69 000 77 000 16 000

Ð 3.2 3.0 3.0 1.5

4 h

Mw 251 000 207 000 217 000 23 000

Mn 85 000 73 000 81 000 15 000

Ð 2.9 2.8 2.7 1.5

24 h

Mw 235 000 170 000 176 000 23 000

Mn 76 000 64 000 66 000 15 000

Ð 3.1 2.6 2.7 1.5

104

Table 3.4.27 GPC data for CM of NBR and 1-hexene using 0.14 phr of 2-4 at 45 °C.

Catalyst 2-4 2-4 2-4

Catalyst loading (phr) 0.14 0.14 0.14

BCl3 (equiv.) None 1 2

1 h

Mw 232 000 175 000 103 000

Mn 79 000 66 000 48 000

Ð 2.9 2.6 2.1

2 h

Mw 239 000 170 000 88 000

Mn 89 000 67 000 43 000

Ð 2.6 2.6 2.1

3 h

Mw 230 000 173 000 85 000

Mn 77 000 64 000 42 000

Ð 3.0 2.7 2.0

4 h

Mw 238 000 169 000 82 000

Mn 76 000 66 000 41 000

Ð 3.1 2.6 2.0

24 h

Mw 221 000 157 000 76 000

Mn 75 000 63 000 39 000

Ð 3.0 2.5 2.0

105

Table 3.4.28 GPC data for CM of NBR and 1-hexene using 2-4 at 60 °C.

Catalyst 2-4 2-4 2-4 2-4


BCl3 (equiv.) 1 2 1 2

1 h

Mw 161 000 159 000 144 000 97 000

Mn 72 000 61 000 58 000 45 000

Ð 2.3 2.6 2.5 2.1

2 h

Mw 168 000 146 000 141 000 94 000

Mn 64 000 58 000 56 000 45 000

Ð 2.7 2.5 2.5 2.1

3 h

Mw 162353 145277 134695 93700

Mn 62 000 58 000 54 000 44 000

Ð 2.6 2.5 2.5 2.1

4 h

Mw 164 000 140 000 137 000 95 000

Mn 63 000 57 000 56 000 45 000

Ð 2.6 2.4 2.4 2.0

24 h

Mw 147 000 119 000 126 000 88 000

Mn 59 000 52 000 54 000 43 000

Ð 2.5 2.3 2.3 2.0

106

References

(1) Astruc, D. New J. Chem. 2005, 29, 42.

(2) Dragutan, I.; Dragutan, V.; Demonceau, A. Rsc. Adv. 2012, 2, 719.

(3) Grubbs, R. H.; Chang, S. Tetrahedron 1998, 54, 4413.

(4) Meek, S. J.; O'Brien, R. V.; Llaveria, J.; Schrock, R. R.; Hoveyda, A. H. Nature 2011,

471, 461.

(5) Ong, C.; Mueller, J. M.; Soddemann, M.; Koenig, T. Metathesis of nitrile rubbers in the

presence of transition metal catalysts. WO2011023763A1, 2011.

(6) Pederson, R. L.; Fellows, I. M.; Ung, T. A.; Ishihara, H.; Hajela, S. P. Adv. Synth. Catal.

2002, 344, 728.

(7) Grubbs, R. H. Handbook of Metathesis; WILEY-VCH Verlag GmbH and Co.: Germany,

2003; Vol. 1.

(8) Schrock, R. R. Acc. Chem. Res. 1990, 23, 158.

(9) Buchmeiser, M. R. In Materials Science and Technology; Wiley-VCH Verlag GmbH &

Co. KGaA: 2006.

(10) Piotti, M. E. Curr. Opin. Solid State Mater. Sci. 1999, 4, 539.

(11) Kessler, M. R.; White, S. R. J. Polym. Sci., Part A: Polym. Chem. 2002, 40, 2373.

(12) Bazan, G. C.; Khosravi, E.; Schrock, R. R.; Feast, W. J.; Gibson, V. C.; O'Regan, M. B.;

Thomas, J. K.; Davis, W. M. J. Am. Chem. Soc. 1990, 112, 8378.

(13) Bielawski, C. W.; Benitez, D.; Morita, T.; Grubbs, R. H. Macromolecules 2001, 34,

8610.

(14) Grubbs, R. H.; Miller, S. J.; Fu, G. C. Acc. Chem. Res. 1995, 28, 446.

(15) Deiters, A.; Martin, S. F. Chem. Rev. 2004, 104, 2199.

(16) Maier, M. E. Angew. Chem. Int. Ed. 2000, 39, 2073.

(17) Fu, G. C.; Nguyen, S. T.; Grubbs, R. H. J. Am. Chem. Soc. 1993, 115, 9856.

(18) Chatterjee, A. K.; Choi, T.-L.; Sanders, D. P.; Grubbs, R. H. J. Am. Chem. Soc. 2003,

125, 11360.

(19) Connon, S. J.; Blechert, S. Angew. Chem. Int. Ed. 2003, 42, 1900.

(20) Chatterjee, A. K.; Grubbs, R. H. Org. Lett. 1999, 1, 1751.

107

(21) Marinescu, S. C.; Levine, D. S.; Zhao, Y.; Schrock, R. R.; Hoveyda, A. H. J. Am. Chem.

Soc. 2011, 133, 11512.

(22) Schrodi, Y.; Ung, T.; Vargas, A.; Mkrtumyan, G.; Lee, C. W.; Champagne, T. M.;

Pederson, R. L.; Hong, S. H. CLEAN – Soil, Air, Water 2008, 36, 669.

(23) Thomas, R. M.; Keitz, B. K.; Champagne, T. M.; Grubbs, R. H. J. Am. Chem. Soc. 2011,

133, 7490.

(24) Ritter, T.; Hejl, A.; Wenzel, A. G.; Funk, T. W.; Grubbs, R. H. Organometallics 2006,

25, 5740.

(25) Yang, Q.; Xiao, W.-J.; Yu, Z. Org. Lett. 2005, 7, 871.

(26) Morgan, J. P.; Grubbs, R. H. Org. Lett. 2000, 2, 3153.


(28) Hansen, S. M.; Volland, M. A. O.; Rominger, F.; Eisentrager, F.; Hofmann, P. Angew.

Chem. Int. Ed. 1999, 38, 1273.

(29) Songis, O.; Slawin, A. M. Z.; Cazin, C. S. J. Chem. Commun. 2012, 48, 1266.

(30) Ong, C.; Mueller, J. M. Process for the preparation of low molecular weight

hydrogenated nitrile rubber. WO2011023788A1, 2011.

(31) Monfette, S.; Camm, K. D.; Gorelsky, S. I.; Fogg, D. E. Organometallics 2009, 28, 944.

(32) Kotyk, M. W.; Gorelsky, S. I.; Conrad, J. C.; Carra, C.; Fogg, D. E. Organometallics

2009, 28, 5424.

(33) Conrad, J. C.; Parnas, H. H.; Snelgrove, J. L.; Fogg, D. E. J. Am. Chem. Soc. 2005, 127,

11882.


(35) Hartman, J. S.; Yuan, Z.; Fox, A.; Nguyen, A. Can. J. Chem. 1996, 74, 2131.

108

Chapter 4 Synthesis of Bis-Mixed-Carbene Ruthenium-Alkylidene

Complexes Through Anion Exchange

4.1 Introduction

4.1.1 Halide Variation in Grubbs Catalyst

Modifications to the NHC ligand in Grubbs Catalyst have received considerable attention while,

by comparison, modification of the anionic ligands has received very little.1 To study the effect

of replacing the chloride ligands in Grubbs I and II for other halides on catalytic activity, Grubbs

and co-workers synthesized (PCy3)2RuX2(CHPh) and SIMes(PCy3)RuX2(CHPh) where X=Cl,

Br, I.2 In terms of initiation it was found that systems with X = I were the fastest initiating

followed by X = Br and X = Cl. Increasing the size of the halide from Cl- to I

- lowers the barrier

to phosphine dissociation due to steric congestion at the metal center which results in faster

initiation rates. The activity of the catalysts, however, decreased from X=Cl to X=Br to X=I.

This is, again, due to the size of the halide preventing the coordination of the incoming olefin.

4.1.2 Pseudo-halides as Ligands in Ruthenium Metathesis Catalysts

In addition to halides, a number of other X-type ligands have been investigated and the effect of

the resulting complexes on metathesis activity studied. Typical ligands have included alkoxides,3

aryloxides,4-8

carboxylates,9-11

and more recently, thiolates12-14

and nitrates.15

A common

decomposition pathway for most Grubbs-type systems is through the formation of inactive halide

bridged dimers.16-18

This was successfully avoided by changing the halides for different anionic

groups when Grubbs and co-workers reported the synthesis of the 4-coordinate species

(PCy3)Ru(OtBu)2(CHPh) (A in Figure 4.1.1).3 Although these complexes are 4-coordinate, the

ability of the alkoxide to act as an XL-type ligand and donate 3 electrons to the metal center

results in low activity for olefin metathesis even at elevated temperatures. Fogg and co-workers

successfully overcame this problem through the use of electron deficient, perhalogenated

aryloxides as ligands (B and C in Figure 4.1.1).4,6

These catalysts showed slower initiation rates

but had activities similar to or better than Grubbs II.

109

Figure 4.1.1 Alkoxide and electron deficient aryloxides as ligands on olefin metathesis catalysts.

Changing the anionic groups not only affects activity and stability of catalysts, it also induces

unprecedented reactivity. More recently, Jensen and co-workers have prepared an olefin

metathesis catalyst with a bulky arylthiolate ligand (Figure 4.1.2).13

The large aryl group on the

thiolate induces Z-selectivity on the resulting product olefin with up to 96% selectivity.

Figure 4.1.2 Z-selective olefin metathesis catalyst with a thiolate ligand.

This compound is formed through chloride exchange in Grubbs-Hoveyda II with the sterically

demanding 2,4,6-triphenylbenzenethiolate ligand.


4.2.1 Synthesis of Ru Complexes

Based on the results presented in Chapters 2 and 3, we were interested in probing the effect of

the anionic ligands on metathesis activity, especially on initiation. Therefore, a series of

complexes featuring other halides were synthesized. The addition of trimethylsilyl iodide to a

solution of 2-4 in C6H6 and stirring for one hour at room temperature followed by workup

afforded the isolation of compound 4-1 as a red solid in 87% yield (Scheme 4.2.1). The 1H NMR

110

spectrum of 4-1 reveals a broad singlet at 18.82 ppm which integrates to one proton and is

assigned to the Ru=CH fragment. The corresponding carbon signal was derived from two

dimensional NMR experiments (HSQC) and is observed at 314.2 ppm.


Single crystal X-ray analysis of 4-1 confirmed its formulation as

(Im(OMe)2)(SIMes)Ru(=CHCH3)I(SPh). The geometry around the Ru center is distorted square

pyramid (Figure 4.2.1) where the two carbenes are trans disposed with a C-Ru-C angle of

158.22(14)o. The two anionic groups in 4-1 are also mutually trans while the alkylidene fragment

occupies the pseudo-apical position. The Ru-C distances for the carbenes are 2.082(3) Å and


1.826(4) Å. The corresponding Ru-I distance is 2.7781(4) Å and the Ru-S distance is

2.3860(10) Å.

111

Figure 4.2.1 POV-ray depiction of the molecular structure of 4-1. Ru: dark green, O: red, I:

magenta, N: aquamarine, S: yellow, C: black. H-atoms omitted for clarity.

A similar reaction utilizing 2-8 resulted in the isolation of 4-2 as a red solid in a modest 53%

yield. The 1H NMR spectrum of 4-2 reveals a diagnostic broad singlet at 19.04 ppm which

integrates to one proton and is assigned to the Ru=CH fragment. Single crystal X-ray analysis of

4-2 confirmed the formulation as (Me2Im(OMe)2)(SIMes)Ru(=CHCH3)I(SPh) where the

geometry around the metal center is best described as distorted square pyramid (Figure 4.2.2).


magenta, N: aquamarine, S: yellow, C: black. H-atoms omitted for clarity.

Similar to 4-1, the two carbenes are trans disposed with a C-Ru-C angle of 160.20(15)o. The two

anionic groups in 4-2 are also mutually trans while the alkylidene fragment occupies the

pseudo-apical position. The Ru-C distances for the carbenes are 2.087(4) Å and 2.120(4) Å for

112

SIMes and Me2Im(OMe)2, respectively, while the Ru-C distance for the alkylidene is 1.827(4) Å.

The Ru-I distance is 2.7599(7) Å and the Ru-S distance is 2.3783(11) Å.

When trimethylsilyl iodide was added to a solution of 2-13 in C6D6, the 19

F{1H} NMR displayed

signals corresponding to 2-13 and another set of signals consistent with Me3SiS(C6F5) in a 1:1

ratio. Thus, when the reaction was repeated using two equivalents of trimethylsilyl iodide, 4-3

was isolated as a red solid in 88% yield (Scheme 4.2.2). The 1H NMR spectrum of 4-3 reveals a

triplet at 18.81 ppm, with 3JHH of 4 Hz, which integrates to one proton and is assigned to the

Ru=CH fragment with the corresponding carbon signal being present at 323.5 ppm in the

13C{

1H} NMR spectrum. The

19F{

1H} NMR shows an absence of signals which indicates the

loss of the S(C6F5) moiety.


Single crystals of 4-3 suitable for X-ray analysis were grown and the study confirmed its

formulation as (Im(OMe)2)(SIMes)Ru(=CHC4H9)I2 where the geometry around the ruthenium

center is distorted square pyramid (Figure 4.2.3) and the two carbenes are trans disposed with a

C-Ru-C angle of 160.7(3)o. The two iodide ligands in 4-3 are mutually trans while the alkylidene

fragment occupies the pseudo-apical position. The Ru-C distances for the carbenes are

2.089(6) Å and 2.100(7) Å for SIMes and Im(OMe)2, respectively, while the Ru-C distance for

the alkylidene is 1.826(7) Å. The corresponding Ru-I distances are 2.7156(7) Å and 2.7224(7) Å.

113


magenta, N: aquamarine, C: black. H-atoms omitted for clarity.

Similarly, adding two equivalents of trimethylsilyl iodide to a solution of 2-14 in C6H6 results in

the formation of 4-4 in 90% yield. The 1H NMR spectrum of 4-4 reveals a triplet at 18.81 ppm,

with 3JHH of 4 Hz, which is assigned to the Ru=CH fragment and the corresponding carbon

signal was derived from two dimensional NMR experiments (HSQC) and is observed at

324.0 ppm. The 19

F{1H} NMR displays an absence of signals which indicates the loss of the

S(C6F5) moiety and these NMR data lead to the formulation of 4-4 as

(Im(OMe)2)(SIMes)Ru(=CHC5H11)I2.

Upon observing the facile exchange of the S(C6F5) ligand for an iodide, we targeted the synthesis

of the bis-chloride analogue of 4-4. As such, the addition of trimethylsilyl chloride to a solution

of 2-14 in CH2Cl2 and stirring for two days at room temperature followed by workup afforded

the isolation of compound 4-5 as a red solid in 85% yield (Scheme 4.2.3). The 1H NMR

spectrum of 4-5 reveals a broad singlet at 19.11 ppm which integrates to one proton and is

assigned to the Ru=CH fragment and the corresponding carbon signal is observed at 321.7 ppm

in the 13

C{1H} NMR spectrum. The

19F{

1H} NMR shows an absence of signals which again

indicates the loss of the S(C6F5) moiety.

114


Single crystal X-ray analysis of 4-5 confirmed its formulation as

(Im(OMe)2)(SIMes)Ru(=CHC5H11)Cl2. The geometry around the metal center is distorted square

pyramid (Figure 4.2.4) and the two carbenes are cis disposed with a C-Ru-C angle of 95.7(3)o.

The two chloride ligands groups in 4-5 are also mutually cis while the alkylidene fragment

occupies the pseudo-apical position.


green, N: aquamarine, C: black. H-atoms omitted for clarity.

The Ru-C distances for the carbenes are 2.051(7) Å and 2.064(7) Å for SIMes and Im(OMe)2,

respectively, while the Ru-C distance for the alkylidene is 1.809(7) Å. The corresponding Ru-Cl

distances are 2.3681(17) and 2.4983(18) Å. This is a rare example of bis-carbene bis-halide Ru-

alkylidene complexes where the halides are in a cis disposition.19

We were interested in comparing the metathesis activity of 4-5 to a system where the chlorides

would be trans. Such a system is accessible through the reaction of (Im(OMe)2)AgCl with

115

Grubbs II where a green solid was isolated in 78% yield (Scheme 4.2.4). The 1H NMR spectrum

of 4-6 reveals a broad singlet at 19.10 ppm which integrates to one proton and is assigned to the

Ru=CH fragment with the corresponding carbon signal being observed at 299.0 ppm in the

13C{

1H} NMR spectrum.


Single crystals suitable for an X-ray diffraction study were grown and the formulation of 4-6 was

confirmed as (Im(OMe)2)(SIMes)Ru(=CHPh)Cl2. The geometry around the metal center is

square pyramid (Figure 4.2.5) and the two carbenes are trans disposed with a C-Ru-C angle of

164.51(10)o. The two chloride ligands groups in 4-6 are also mutually trans while the alkylidene

fragment occupies the pseudo-apical position. The Ru-C distances for the carbenes are 2.089(2)

and 2.114(2) Å for SIMes and Im(OMe)2, respectively, while the Ru-C distance for the

alkylidene is 1.830(3) Å. The corresponding Ru-Cl distances are 2.4000(8) and 2.4118(7) Å.

116


green, N: aquamarine, C: black. H-atoms omitted for clarity.

4.2.2 Standard Olefin Metathesis Tests

Similar to previous examples (Chapter 3) these alkylidene complexes were also subjected to the

standard olefin metathesis standard tests to gauge their catalytic activity for this process.

Compound 4-1 was effective as a catalyst for ROMP of 1,5-cyclooctadiene at room temperature,

at 1 mol% catalyst loading, where conversion to the product was achieved in 100% after 24

hours. The addition of one equivalent of BCl3 to 4-1 resulted in increased activity for the ROMP

of this substrate, affording 100% product yield after 20 minutes at room temperature (Figure

4.2.6). Using 4-2, ROMP of 1,5-COD was accomplished with product yields of 68% after 24

hours at room temperature and 100% after 2 hours upon the addition of BCl3.

117

Figure 4.2.6 ROMP of 1,5-cyclooctadiene with 4-1.

The bis-halide systems showed increased activity in the absence of BCl3 where 4-3, 4-4 and 4-6

showed complete conversion to the product, at room temperature, after 30, 45, and 20 minutes,

respectively. Reducing the catalyst loading of 4-4 to 0.5 mol% still effects complete conversion

after 45 minutes.

Compound 4-1 was ineffective for the RCM of diethyl diallylmalonate in the absence of a Lewis

acid at room temperature, with 5 mol% catalyst loading, but complete conversion to the

ring-closed product was achieved, after 6 hours, upon the addition of one equivalent of BCl3

(Figure 4.2.7). Similarly, using 4-2 as the catalyst resulted in 100% conversion to the ring closed

product of diethyl diallylmalonate at room temperature, with one equivalent of BCl3, after 2

hours. Similar to 4-1, compound 4-2 was ineffective in the absence of BCl3 at room temperature.

118

Figure 4.2.7 RCM of diethyl diallylmalonate with 4-1.

The bis-halide systems showed increased activity in the absence of BCl3 where 4-3, at room

temperature, achieved RCM of diethyl diallylmalonate in 97% conversion after 2 hours.

Similarly, compound 4-4 resulted in 92% conversion of the same substrate after 2 hours while

4-6 showed complete conversion to the product, at room temperature, after 2.25 hours (Figure

4.2.8).

Figure 4.2.8 RCM of diethyl diallylmalonate with 4-3, 4-4 and 4-6.

119

For the CM of 5-hexenyl acetate and methyl acrylate, 4-1 was ineffective at room temperature in

the absence of a Lewis acid. Upon the addition of BCl3, at room temperature, conversion to the

heterocoupled product in a 72% yield was achieved after 6 hours (Figure 4.2.9). Using 4-2 with

one equivalent of BCl3 as the catalyst resulted in 70% conversion to the heterocoupled product at

25 °C after 2 hours. Just like 4-1, 4-2 was ineffective for CM in the absence of BCl3 at room

temperature.

Figure 4.2.9 CM of 5-hexenyl acetate and methyl acrylate with 4-1.

Similar to ROMP and RCM, the bis-halide systems showed increased activity in the absence of

BCl3 for CM. Compound 4-3, at 25 °C, showed CM of 5-hexenyl acetate and methyl acrylate to

the heterocoupled product in 54% conversion after 4 hours. Similarly, compound 4-4 resulted in

56% conversion after 4 hours while 4-6 showed conversion of 66% to the product, at room

temperature, after 2.25 hours (Figure 4.2.10).

120

Figure 4.2.10 CM of 5- hexenyl acetate and methyl acrylate with 4-3, 4-4 and 4-6.

It is worth noting that although conversions to the heterocoupled were not very high, the

homocoupled product was also observed.

4.2.3 Cross Metathesis of NBR with 1-Hexene

The systems described above were developed with the ultimate goal of effecting the cross

metathesis of NBR and 1-hexene at room temperature to make them industrially viable. The

NBR used in the following tests has an initial Mw of 274 000 Da and a Mn of 76 000 Da with a Ð

of 3.6. Only one example using 4-1 as a catalyst for CM of NBR and 1-hexene is provided in this

chapter. Several parameters were probed including changing the catalyst loading and using either

one or two equivalents of the Lewis acid, BCl3.

Using 0.07 phr catalyst loading of 4-1, at room temperature with one equivalent of BCl3, the

resulting Mw, Mn and Ð, after 4 hours, are 106 000 Da, 41 000 Da, and 2.6 respectively. After 24

hours the polymer was further metathesized to give Mw, Mn and Ð values of 51 000 Da, 23 000,

and 2.2, respectively. In the case of two equivalents of BCl3, after 24 hours, the Mw, Mn and Ð

are 1156 000 Da, 45 000 Da, and 2.6 respectively (Figure 4.2.11).

121

Figure 4.2.11 CM of NBR and 1-hexene with 4-1 at 25 °C.

Using 0.14 phr catalyst loading with 4-1, at 25 °C with one equivalent of BCl3, the resulting Mw,

Mn and Ð, after 4 hours, are 51 000 Da, 23 000 Da, and 2.2 respectively. After 24 hours the

polymer was further metathesized to give Mw, Mn and Ð values of 20 000 Da, 11 000, and 1.8

respectively. In the case of two equivalents of BCl3, after 24 hours, the Mw, Mn and Ð are 35 000

Da, 17 000 Da, and 2.0 respectively.

4.3 Conclusion

In conclusion, it was demonstrated that exchanging a chloride for an iodide to form 4-1 and 4-2

resulted in enhanced metathesis activity for the standard tests as well as for the CM of NBR with

1-hexene. Catalytic olefin metathesis was observed for both systems at room temperature and

elevated temperatures were not necessary. The bis-halide containing complexes (4-3, 4-4 and

4-6) showed the highest activity for all standard metathesis tests without the need for a Lewis

acid to initiate. This is presumably due to the presence of the bulky iodides on the metal center

which results in faster initiation. These systems, however, too closely resemble Grubbs’ catalysts

and were therefore not patented and not tested further for the CM of NBR with 1-hexene.

122



All manipulations were carried out under an atmosphere of dry, O2-free N2 employing a Vacuum

Atmospheres glove box and a Schlenk vacuum line. Solvents were purified with a Grubbs-type

column system manufactured by Innovative Technology, dispensed into thick-walled Schlenk

glass flasks equipped with Teflonvalve stopcocks (pentane, hexanes, CH2Cl2) and stored over

molecular sieves. Some solvents were dried over the appropriate agents, vacuum-transferred into

storage flasks with Teflon stopcocks and degassed accordingly (C6H6, C6D6, CD2Cl2). 1H,

13C,

and 19

F spectra were recorded at 25 oC on a Bruker 400 MHz spectrometer. Chemical shifts were

given relative to SiMe4 and referenced to the residual solvent signal (1H,

13C) or relative to an

external standard (19

F: CFCl3). In some instances, signal assignment was derived from two

dimensional NMR experiments (HSQC). Chemical shifts are reported in ppm and coupling

constants as scalar values in Hz. Combustion analyses were performed in house employing a

Perkin-Elmer CHN analyzer. Trimethylsilyl iodide, trimethylsilyl chloride and Grubbs II were

purchased from Sigma Aldrich and used as received. 1,5-Cyclooctadiene, diethyl

diallylmalonate, 5-hexenyl acetate, and methyl acrylate were purchased from Sigma Aldrich or

Alfa Aesar and used as received.


Synthesis of 4-1: Trimethylsilyl iodide (10.0 µL, 0.071 mmol) was added to a solution of 2-4

(0.050 g, 0.065 mmol) in 2 mL C6H6 at room temperature. The solution was then stirred for one

hour before the solvent was removed and the residue washed with pentane. The pentane was then

decanted to yield a red solid (0.048 g, 87%). X-ray quality crystals were grown from


1H NMR (400 MHz, C6D6): δ 18.82 (br s, 1H, Ru=CH), 7.09 (m, 2H,

S(C6H5)), 6.90 (d, 3JHH = 2 Hz, 1H, Im(OMe)2-CH), 6.84 (s, 1H, Mes-CH), 6.82 (s, 1H, Mes-

CH), 6.78 (m, 6H, Mes-CH + S(C6H5) + Im(OMe)2-CH), 3.44 (m, 4H, SIMes-CH2 + Im(OMe)2-

CH2), 3.30 (m, 4H, SIMes-CH2 + Im(OMe)2-CH2), 3.19-2.99 (m, 4H, Im(OMe)2-CH2), 2.95 (s,

3H, Im(OMe)2-CH3), 2.89 (s, 3H, Mes-CH3), 2.85 (s, 3H, Mes-CH3), 2.81 (s, 3H, Im(OMe)2-

CH3), 2.75 (s, 3H, Mes-CH3), 2.71 (s, 3H, Mes-CH3), 2.14 (s, 3H, Mes-CH3), 2.13 (s, 3H, Mes-

CH3), 2.00 (d, 3JHH = 6 Hz, 3H, Ru=CHCH3).

13C{

1H} NMR (101 MHz, C6D6): δ 314.2

(Ru=CHCH3), 223.7 (NCN), 188.5 (NCN), 139.8 (Cipso), 139.6 (Cipso), 138.4 (Cipso), 138.3

123

(Cipso), 138.3 (Cipso), 137.9 (S(C6H5)), 133.5 (S(C6H5)), 130.2 (Mes-CH), 129.9 (Mes-CH), 129.7

(Mes-CH), 127.2 (S(C6H5)), 122.1 (Im(OMe)2-CH), 121.0 (Im(OMe)2-CH), 72.5 (Im(OMe)2-

CH2), 71.7 (Im(OMe)2-CH2), 58.3 (Im(OMe)2-CH3), 58.2 (Im(OMe)2-CH3), 51.6 (SIMes-CH2),

51.5 (SIMes-CH2), 49.3 (Ru=CHCH3), 49.0 (Im(OMe)2-CH2), 23.2 (Mes-CH3), 21.3 (Mes-CH3),

21.1 (Mes-CH3), 20.9 (Mes-CH3), 20.7 (Mes-CH3), 19.6 (Mes-CH3). Elemental Analysis for

C38H51IN4O2RuS: C, 53.33; H, 6.01; N, 6.55. Found: C, 52.59; H, 5.66; N, 6.51.


(0.065 g, 0.095 mmol) in 2 mL C6H6 at room temperature. The solution was then stirred for one

hour before the solvent was removed and the residue washed with pentane. The pentane was then

decanted to yield a red solid (0.038 g, 53%). X-ray quality crystals were grown from


1H NMR (400 MHz, C6D6): δ 19.04 (br s, 1H, Ru=CH), 7.13(br s, 2H,

S(C6H5)), 6.94 (s, 1H, Mes-CH), 6.91 (s, 1H, Mes-CH), 6.84 (s, 1H, Mes-CH), 6.77 (s, 1H, Mes-

CH), 6.72 (m, 1H, S(C6H5)), 6.64 (br m, 2H, S(C6H5)), 3.70-3.17 (br m, 12H, SIMes-CH2 +

Me2Im(OMe)2-CH2), 2.98 (s, 3H, Me2Im(OMe)2-CH3), 2.95 (br s, 6H, Mes-CH3), 2.88 (s, 3H,

Me2Im(OMe)2-CH3), 2.74 (s, 6H, Mes-CH3), 2.23 (s, 3H, Mes-CH3), 2.13 (s, 3H, Mes-CH3),

2.09 (d, 3JHH = 6 Hz, 3H, Ru=CHCH3),1.69 (s, 3H, Me2Im(OMe)2-4,5-CH3), 1.47 (s, 3H,

Me2Im(OMe)2-4,5-CH3). 13

C{1H} NMR partial (101 MHz, C6D6): δ 185.2 (NCN), 139.6 (Cipso),

139.3 (Cipso), 138.8 (Cipso), 138.6 (Cipso), 138.3 (Cipso), 136.7 (S(C6H5)), 134.3 (br s, S(C6H5)),

130.6 (Mes-CH), 130.1 (Mes-CH), 129.9 (Mes-CH), 129.8 (Mes-CH), 126.6 (S(C6H5)), 126.4

(Me2Im(OMe)2-Cipso), 126.1 (Me2Im(OMe)2-Cipso), 122.6 (S(C6H5)), 73.5 (Me2Im(OMe)2-CH2),

71.7 (Me2Im(OMe)2-CH2), 58.6 (Me2Im(OMe)2-CH3), 58.3 (Me2Im(OMe)2-CH3), 51.8 (SIMes-

CH2), 47.7 (Me2Im(OMe)2-CH2), 46.1 (Ru=CHCH3), 23.0 (Mes-CH3), 21.4 (Mes-CH3), 21.1

(Mes-CH3), 20.6 (Mes-CH3), 19.6 (Mes-CH3), 9.55 (Me2Im(OMe)2-4,5-CH3), 9.05

(Me2Im(OMe)2-4,5-CH3).


(0.075 g, 0.084 mmol) in 2 mL C6H6 at room temperature. The solution was then stirred

overnight before the solvent was removed and the residue washed with pentane. The pentane was

then decanted to yield a red solid (0.068 g, 88%). X-ray quality crystals were grown from


1H NMR (400 MHz, C6D6): δ 18.81 (t,

3JHH = 4 Hz, 1H, Ru=CH),

7.14 (d, 3JHH = 2 Hz, 1H, Im(OMe)2-CH), 6.91 (d,

3JHH = 2 Hz, 1H, Im(OMe)2-CH), 6.78 (s, 2H,

Mes-CH), 6.76 (s, 2H, Mes-CH), 3.50 (m, 4H, Im(OMe)2-CH2), 3.40 (br s, 2H, Im(OMe)2-CH2),

124

3.31 (br s, 6H, (2H) Im(OMe)2-CH2, (4H) SIMes-CH2), 2.99 (s, 3H, Im(OMe)2-CH3), 2.83 (br s,

6H, 2 x Mes-CH3), 2.82 (s, 3H, Im(OMe)2-CH3), 2.71 (br s, 6H, 2 x Mes-CH3), 2.16 (s, 3H, Mes-

CH3), 2.10 (s, 3H, Mes-CH3), 1.26-1.12 (br m, 6H, pentylidene-CH2), 0.91 (app t, 3JHH = 7 Hz,

3H, pentylidene-CH3). 13

C{1H} NMR (101 MHz, C6D6): δ 323.5 (Ru=CH), 226.4 (NCN), 187.3

(NCN), 139.4 (Cipso), 138.5 (Cipso), 138.04 (Cipso), 138.02 (Cipso), 137.9 (Cipso), 135.9 (Cipso),

130.1 (Mes-CH), 129.9 (Mes-CH), 122.7 (Im(OMe)2-CH), 121.7 (Im(OMe)2-CH), 72.7


(SIMes-CH2), 51.5 (SIMes-CH2), 49.9 (Im(OMe)2-CH2), 48.5 (Im(OMe)2-CH2), 33.6

(pentylidene-CH2), 23.1 (pentylidene-CH2), 22.9 (Mes-CH3), 21.0 (Mes-CH3), 20.9 (Mes-CH3),

20.6 (Mes-CH3), 14.5 (pentylidene-CH3). Elemental Analysis for C35H52I2N4O2Ru: C, 45.91; H,

5.72; N, 6.12. Found: C, 45.65; H, 5.64; N, 6.03. Repeated attempts to obtain EA were

unsuccessful and as such the NMR spectra of 4-3 are attached at the end of this section.


(0.075 g, 0.082 mmol) in 2 mL C6H6 at room temperature. The solution was then stirred

overnight before the solvent was removed and the residue washed with pentane. The pentane was

then decanted to yield a red solid (0.069 g, 90%). 1H NMR (400 MHz, C6D6): δ 18.81 (t,

3JHH = 4

Hz, 1H, Ru=CH), 7.14 (d, 3JHH = 2 Hz, 1H, Im(OMe)2-CH), 6.91 (d,

3JHH = 2 Hz, 1H,

Im(OMe)2-CH), 6.78 (s, 2H, Mes-CH), 6.75 (s, 2H, Mes-CH), 3.52 (m, 4H, Im(OMe)2-CH2),

3.40 (br s, 2H, Im(OMe)2-CH2), 3.31 (br s, 6H, (2H) Im(OMe)2-CH2, (4H) SIMes-CH2), 2.98 (s,

3H, Im(OMe)2-CH3), 2.83 (br s, 9 H, (6H) Mes-CH3, (3H) Im(OMe)2-CH3), 2.71 (br s, 6H, 2 x

Mes-CH3), 2.17 (s, 3H, Mes-CH3), 2.10 (s, 3H, Mes-CH3), 1.34-1.10 (br m, 8H, hexylidene-

CH2), 0.92 (app t, 3JHH = 7 Hz, 3H, hexylidene-CH3).

13C{

1H} NMR (101 MHz, C6D6): δ 324.0

(Ru=CH), 226.4 (NCN), 187.4 (NCN), 139.4 (Cipso), 138.5 (Cipso), 138.1 (Cipso), 137.9 (Cipso),

135.9 (Cipso), 130.1 (Mes-CH), 129.9 (Mes-CH), 122.7 (Im(OMe)2-CH), 121.7 (Im(OMe)2-CH),

72.7 (Im(OMe)2-CH2), 72.1 (Im(OMe)2-CH2), 58.3 (Im(OMe)2-CH3), 58.2 (Im(OMe)2-CH3),

52.0 (SIMes-CH2), 51.5 (SIMes-CH2), 49.9 (Im(OMe)2-CH2), 48.5 (Im(OMe)2-CH2), 32.2

(hexylidene-CH2), 31.3 (hexylidene-CH2), 23.4 (hexylidene-CH2), 23.1 (Mes-CH3), 21.0 (Mes-

CH3), 20.9 (Mes-CH3), 20.6 (Mes-CH3), 14.5 (hexylidene-CH3). Elemental Analysis for

C36H54I2N4O2Ru: C, 46.51; H, 5.85; N, 6.03. Found: C, 46.56; H, 5.86; N, 6.01.

Synthesis of 4-5: Trimethylsilyl chloride (139.0 µL, 1.099 mmol) was added to a solution of

2-14 (0.100 g, 0.109 mmol) in 2 mL CH2Cl2 at room temperature. The solution was then stirred

125

for 48 hours before the solvent was removed and the residue was layered with 10 mL of pentane

and was left at room temperature for 16 hours. The pentane was then decanted to yield a

red/brown solid which was dried under high vacuum (0.070 g, 85%). X-ray quality crystals were

grown from benzene/pentane at 25 oC.

1H NMR (400 MHz, C6D6): δ 19.11 (br s, 1H, Ru=CH),

6.97 (s, 1H, Mes-CH), 6.94 (s, 1H, Im(OMe)2-CH), 6.88 (s, 1H, Mes-CH), 6.83 (s, 1H, Mes-

CH), 6.77 (s, 1H, Mes-CH), 6.35 (d, 3JHH = 2 Hz, 1H, Im(OMe)2-CH), 3.77 (m, 2H, Im(OMe)2-

CH2), 3.45-3.10 (m, 10H, (4H) SIMes-CH2 + (6H) Im(OMe)2-CH2), 3.01 (s, 3H, Mes-CH3), 2.98

(s, 3H, Im(OMe)2-CH3), 2.73 (s, 3H, Mes-CH3), 2.71 (s, 3H, Im(OMe)2-CH3), 2.69 (s, 3H, Mes-

CH3), 2.43 (s, 3H, Mes-CH3), 2.19 (s, 3H, Mes-CH3), 2.18 (s, 3H, Mes-CH3), 1.37-1.08 (br m,

8H, hexylidene CH2), 0.92 (t, 3JHH = 7 Hz, 3H, hexylidene-CH3).

13C{

1H} NMR (101 MHz,

C6D6): δ 321.7 (Ru=CH), 222.2 (NCN), 188.2 (NCN), 139.9 (Cipso), 139.7 (Cipso), 138.6 (Cipso),

137.7 (Cipso), 137.6 (Cipso), 137.5 (Cipso), 135.4 (Cipso), 129.9 (Mes-CH), 129.8 (Mes-CH), 129.6

(Mes-CH), 121.5 (Im(OMe)2-CH), 121.1 (Im(OMe)2-CH), 73.6 (Im(OMe)2-CH2), 71.6


(SIMes-CH2), 49.4 (Im(OMe)2-CH2), 48.4 (Im(OMe)2-CH2), 32.3 (hexylidene-CH2), 30.3

(hexylidene-CH2), 23.2 (hexylidene-CH2), 22.6 (Mes-CH3), 21.0 (Mes-CH3), 20.8 (Mes-CH3),

20.4 (Mes-CH3), 19.1 (Mes-CH3), 18.9 (Mes-CH3), 14.5 (hexylidene-CH3). Repeated attempts to

obtain EA were unsuccessful and as such the NMR spectra of 4-5 are attached at the end of this

section.

Synthesis of 4-6: A solution of (PCy3)(SIMes)Ru(=CHPh)Cl2 (0.274 g, 0.323 mmol) in 5 mL

toluene was added to a suspension of AgCl(Im(OMe)2) (0.117 g, 0.357 mmol) in 5 mL toluene.

The mixture was stirred at 25 °C for 72 hours to give a green solution. The AgCl precipitate was

filtered through celite and the solution was concentrated to 2 mL and 15 mL of pentane was

added to precipitate a green solid. The solution was decanted yielding a green solid

(0.190 g, 78%). 1H NMR (400 MHz, CD2Cl2): δ 19.10 (s, 1H, Ru=CH), 7.68 (d,

3JHH = 8 Hz, 2H,

Ru=CH(C6H5)), 7.45 (t, 3

JHH = 7 Hz, 1H, Ru=CH(C6H5)), 7.11-7.02 (m, 7H, Ru=CH(C6H5) +

Mes-CH + Im(OMe)2-CH), 6.89 (d, 3JHH = 2 Hz, 1H, Im(OMe)2-CH), 4.05 (br m, 2H, SIMes-

CH2), 3.93 (br m, 2H, SIMes-CH2), 3.69 (br m, 2H, Im(OMe)2-CH2), 3.49 (br m, 2H, Im(OMe)2-

CH2), 3.38 (s, 3H, Im(OMe)2-CH3), 3.09 (br s, 2H, Im(OMe)2-CH2), 2.96 (s, 3H, Im(OMe)2-

CH3), 2.70 (br s, 11H, Mes-CH3 + Im(OMe)2-CH2), 2.38 (s, 3H, Mes-CH3), 2.23 (s, 3H, Mes-

CH3), 1.97 (br s, 3H, Mes-CH3). 13

C NMR (400 MHz, CD2Cl2): δ 299.0 (Ru=CH), 223.3 (NCN),

126

186.4 (NCN), 140.2 (Cipso), 139.0 (Cipso), 138.0 (Cipso), 137.5 (Cipso), 135.4 (Cipso), 122.2


(Im(OMe)2-CH3), 58.4 (Im(OMe)2-CH3), 52.1 (SIMes-CH2), 51.7 (SIMes-CH2), 49.5

(Im(OMe)2-CH2), 49.1 (Im(OMe)2-CH2), 21.2 (Mes-CH3), 21.1 (Mes-CH3), 20.3 (Mes-CH3),

18.5 (br s, Mes-CH3). Elemental Analysis for C37H48Cl2RuN4O2: C, 59.03; H, 6.43; N, 7.44.

Found: C, 59.58; H,6.73; N, 7.90.

Figure 4.4.1 1H NMR spectrum of 4-3 in C6D6.

127

Figure 4.4.2 13

C{1H} NMR spectrum of 4-3 in C6D6.


128

Figure 4.4.4 13


4.4.3 Standard Metathesis Reaction Tests

All standard metathesis reaction tests were performed employing a modified procedure of

Grubbs and co-workers.20

The standard procedure for the ring opening metathesis polymerization of 1,5-cyclooctadiene is

as follows: The required amount of the catalyst (1 mol%), was weighed out and dissolved in 0.5

mL CD2Cl2. For the tests that involved the use of an additive (i.e. BCl3, 1M in hexane) the

required volume was added and the mixture was allowed to stand for 5 min. The solutions were

placed in an NMR tube, 1,5-cyclooctadiene (60 μL, 0.50 mmol) was added, the NMR tube was

capped and the solution was mixed at the desired temperature. Reaction progress was monitored

by 1H NMR every 2 hours (unless otherwise noted). Reaction progress was determined by

integration of the peaks corresponding to the starting material versus the product.

129


Compound 4-1


None 25 2 6

4 8

6 39

8 55

24 100

1 mol% BCl3 25 0.33 100


Compound 4-2


None 25 2 0

4 3

6 9

8 15

24 68

1 mol% BCl3 25 0.25 85

2 100

Table 4.4.3 ROMP of 1,5-cyclooctadiene with 4-3, 4-4, and 4-6.

Catalyst Time (h) Conversion (%)

4-3 0.5 96

2 100

4-4 0.75 100

4-4 (0.5 mol%) 0.75 100

4-6 0.3 100

130

A standard procedure for the ring closing metathesis of diethyl diallylmalonate is as follows. The

required amount of catalyst (5 mol%) was weighed out and dissolved in 0.5 mL CD2Cl2. For the

tests that involved the use of an additive (i.e. BCl3, 1M in hexane) the required volume was

added and the mixture was allowed to stand for 5 min. The solution was placed in an NMR tube,

diethyl diallylmalonate (20 μL, 0.50 mmol) was added, the NMR tube was capped and the

solution was mixed at the desired temperature. Reaction progress was monitored by 1H NMR

every 2 hours (unless otherwise noted). Reaction progress was determined by integration of the

olefinic peaks of the starting material versus the product.


Compound 4-1


None 25 24 0

5 mol% BCl3 25 2 81

4 95

6 100


Compound 4-2


None 25 24 0

5 mol% BCl3 25 2 100


Compound 4-3


None 25 0.5 87

2 97

4 100

131


Compound 4-4


None 25 0.5 80

2 92

4 100


Compound 4-6


None 25 0.3 39

0.6 54

2.25 100

A standard procedure for cross metathesis of 5-hexenyl acetate and methyl acrylate is as follows.

The required amount of catalyst (2 mol%) was weighed out and dissolved in 0.5 mL CD2Cl2. For

the tests that involved the use of an additive (i.e. BCl3, 1M in hexane) the required volume was

added and the mixture was allowed to stand for 5 min. The solution was placed in an NMR tube

and a mixture of 5-hexenyl acetate (20 μL, 0.12 mmol) and methyl acrylate (10 μL, 0.11 mmol)

was added and the solution was mixed at the desired temperature. Reaction progress was

monitored by 1H NMR every 2 hours (unless otherwise noted). Reaction progress was

determined by integration of the olefinic peaks of the starting material versus the product.

Table 4.4.9 CM of 5- hexenyl acetate and methyl acrylate with 4-1.

Compound 4-1


None 25 24 0

2 mol% BCl3 25 2 47

4 63

6 72

132


Compound 4-2


None 25 24 0

2 mol% BCl3 25 2 70


Compound 4-3


None 25 0.5 37

2 47

4 54


Compound 4-4


None 25 0.5 37

2 46

4 52

6 56


Compound 4-6


None 25 0.4 56

2.25 66

133

4.4.4 Cross Metathesis of NBR and 1-hexene

A standard procedure for the cross metathesis of nitrile butadiene rubber (NBR) and 1-hexene is

as follows. NBR (1.5 g) were placed in 13.5 g of chlorobenzene and placed on a shaker for 48 h

to give a 10 wt% NBR solution. 1-Hexene (60 mg, 90 μL) was added to the solution and shaken

for 1 h. The catalysts were prepared by dissolving the required mass of precatalyst in CH2Cl2

(2 mL) in a glove box and the appropriate amount of BCl3 was then added and the solutions were

stirred for 5 min before being taken out of the glove box and added to the NBR solutions. The

solutions were then stirred at the desired temperature for a total of 24 h. Samples were taken at 1,

2, 3, 4, and 24 h. The catalysts were poisoned with ethyl vinyl ether (0.1 mL) to stop the

metathesis. All volatiles were removed from the samples. GPC samples were made by preparing

a 1 mg/mL THF solution of the resulting NBR. The samples were passed through a microporous

filter and the Mn, Mw, and Ð were determined by GPC using a polystyrene calibration curve. The

Mw and Mn for NBR used with 4-1 for are 274 000 and 76 000 Da, respectively, and the Ð is 3.6.

134

Table 4.4.14 GPC data for CM of NBR and 1-hexene using 4-1 at 25 °C.

Catalyst loading (phr) 0.07 0.07 0.14 0.14 0.28 0.28 0.28

BCl3 (equiv.) 1 2 1 2 1 2 10

1 hour

Mw 193 000 - 131 000 148 000 94 000 91 000 50 000

Mn 56 000 - 46 000 57 000 36 000 38 000 24 000

Ð 3.4 - 2.9 2.6 2.6 2.4 2.1

2 hours

Mw 144 000 196 000 89 000 121 000 75 000 59 000 40 000

Mn 53 000 64 000 37 000 50 000 30 000 27 000 19 000

Ð 2.7 3.1 2.4 2.4 2.5 2.3 2.1

3 hours

Mw 131 000 171 000 62 000 112 000 65 000 48 000 32 000

Mn 46 000 58 000 29 000 44 000 26 000 22 000 16 000

Ð 2.8 2.9 2.1 2.5 2.5 2.2 2.0

4 hours

Mw 106 000 160 000 51 000 93 000 45 000 37 000 35 000

Mn 41 000 58 000 23 000 39 000 21 000 18 000 17 000

Ð 2.6 2.8 2.2 2.4 2.1 2.0 2.0

24 hours

Mw 51 000 116 000 20 000 35 000 10 000 19 000 23 000

Mn 23 000 45 000 11 000 17 000 6 000 10 000 12 000

Ð 2.2 2.6 1.8 2.0 1.6 1.9 1.9

135

4.4.5 X-ray Crystallography

4.4.5.1 X-ray Data Collection and Reduction







4.4.5.2 X-ray Data Solution and Refinement


The heavy





2) and Fo










136


4-1 4-2 4-3

Formula C38H51IN4O2RuS C40H55IN4O2RuS C35H52I2N4O2Ru

wt 855.86 883.91 915.68

Cryst. syst. Triclinic Triclinic Triclinic

Space group P-1 P-1 P-1

a(Å) 9.1565(4) 8.747(2) 9.3246(4)

b(Å) 11.7895(5) 11.097(3) 11.9304(5)

c(Å) 19.3652(8) 21.731(6) 17.6952(8)

(deg) 97.521(2) 95.845(12) 74.445(2)

(deg) 93.603(2) 95.823(11) 77.912(2)

(deg) 112.499(2) 105.936(10) 89.472(2)

V(Å3) 1900.14(14) 1999.3(9) 1852.07(14)

Z 2 2 2

d(calc) gcm-3

1.496 1.468 1.642

R(int) 0.0403 0.0503 0.0357

, mm–1

1.317 1.254 2.125

Total data 8624 6720 6287

>2(FO2) 6652 5308 5147

Variables 461 442 397

R (>2) 0.0380 0.0358 0.0461

Rw 0.0841 0.0810 0.1079

GOF 1.023 1.046 1.105

137

Table 4.4.16 Select crystallographic parameters for 4-5 and 4-6.

4-5 4-6

Formula C36H54Cl2N4O2Ru C37H48Cl2N4O2Ru

wt 746.80 752.76

Cryst. syst. Orthorhombic Monoclinic

Space group Pca2(1) P21/c

a(Å) 17.2005(13) 12.7136(17)

b(Å) 13.0632(10) 14.8473(18)

c(Å) 16.3886(12) 21.807(3)

(deg) 90.00 90.00

(deg) 90.00 118.462(8)

(deg) 90.00 90.00

V(Å3) 3682.4(5) 3618.8(8)

Z 4 4

d(calc) gcm-3

1.347 1.382

R(int) 0.1451 0.0876

, mm–1

0.607 0.618

Total data 7186 8277

>2(FO2) 4570 6082

Variables 406 415

R (>2) 0.0622 0.0377

Rw 0.1371 0.0828

GOF 1.010 1.004

138

References


(2) Dias, E. L.; Nguyen, S. T.; Grubbs, R. H. J. Am. Chem. Soc. 1997, 119, 3887.

(3) Sanford, M. S.; Henling, L. M.; Day, M. W.; Grubbs, R. H. Angew. Chem. Int. Ed. 2000,

39, 3451.

(4) Conrad, J. C.; Amoroso, D.; Czechura, P.; Yap, G. P. A.; Fogg, D. E. Organometallics

2003, 22, 3634.

(5) Monfette, S.; Fogg, D. E. Organometallics 2006, 25, 1940.

(6) Conrad, J. C.; Parnas, H. H.; Snelgrove, J. L.; Fogg, D. E. J. Am. Chem. Soc. 2005, 127,

11882.

(7) Conrad, J. C.; Camm, K. D.; Fogg, D. E. Inorg. Chim. Acta 2006, 359, 1967.

(8) Conrad, J. C.; Snelgrove, J. L.; Eeelman, M. D.; Hall, S.; Fogg, D. E. J. Mol. Catal. A:

Chem. 2006, 254, 105.

(9) Zhang, W. Z.; Liu, P.; Jin, K.; He, R. J. Mol. Catal. A: Chem. 2007, 275, 194.

(10) Samec, J. S. M.; Grubbs, R. H. Chem. Eur. J. 2008, 14, 2686.

(11) Endo, K.; Grubbs, R. H. J. Am. Chem. Soc. 2011, 133, 8525.

(12) Khan, R. K. M.; Torker, S.; Hoveyda, A. H. J. Am. Chem. Soc. 2013, 135, 10258.

(13) Occhipinti, G.; Hansen, F. R.; Törnroos, K. W.; Jensen, V. R. J. Am. Chem. Soc. 2013,

135, 3331.


(15) Cannon, J. S.; Grubbs, R. H. Angew. Chem. Int. Ed. 2013, 52, 9001.

(16) Hong, S. H.; Day, M. W.; Grubbs, R. H. J. Am. Chem. Soc. 2004, 126, 7414.

(17) Leitao, E. M.; Dubberley, S. R.; Piers, W. E.; Wu, Q.; McDonald, R. Chem. Eur. J. 2008,

14, 11565.

(18) Amoroso, D.; Yap, G. P. A.; Fogg, D. E. Organometallics 2002, 21, 3335.

(19) Lund, C. L.; Sgro, M. J.; Stephan, D. W. Organometallics 2012, 31, 580.

(20) Ritter, T.; Hejl, A.; Wenzel, A. G.; Funk, T. W.; Grubbs, R. H. Organometallics 2006,

25, 5740.

139



140

Chapter 5 Carbene Stabilized Iminoboranes

5.1 Introduction

5.1.1 Iminoboranes and Iminoboryl Transition Metal Complexes

Iminoboranes, X-B≡N-R, are isoelectronic to alkynes; a relationship that has inspired significant

experimental1-6

and theoretical7,8

studies, particularly by the research groups of Paetzold1-4

and

Nöth5,6

. Such systems are commonly generated by the vacuum gas-phase pyrolysis of

(trimethylsilylamino)boron halides, a forcing procedure that has subsequently been adopted for

the synthesis of amino iminoboranes (Scheme 5.1.1).1

Scheme 5.1.1 Synthesis of iminoboranes via thermally induced elimination of Me3SiX.

The polarity and relative weakness of the B≡N moiety leads to increased reactivity of

iminoboranes compared to alkynes. This, however, also results in their thermodynamic

instability towards cyclooligomerization and therefore low temperature, high dilution, and the

presence of sterically demanding substituents are typically needed for the isolation of monomeric

species. The reactivity of such systems was heavily studied and they were shown to undergo

several transformations. Some of these reactions include 1,2-additions of polar reagents across

the B≡N multiple bond where, for example, hydrometallations with [Cp2Zr(H)Cl] afforded

examples of N-metallated aminoboranes.9,10

Amino iminoboranes were also shown to undergo

[2+2] cycloaddition reactions, across the B≡N linkage, with substrates (Scheme 5.1.2) such as

formaldehyde or tetracyanoethylene.5,11

141

Scheme 5.1.2 [2+2] Cycloaddition reactions of amino iminoboranes.

Nöth and co-workers also reported the [2+2] cycloaddition reactions between molecules of the

form CX2 (X = O, S, Se) and an amino iminoborane (Scheme 5.1.3).12

The corresponding

products decompose under thermal duress to form (CH3)3CN=C=X (X = O, S, Se) and the

dimers of the (tetramethylpiperidino)boron chalcogenides.

Scheme 5.1.3 Reaction of an amino iminoborane with CX2.

Over the last decade, transition metal iminoboryl complexes have garnered more attention as

metal centers can be used to stabilize the iminoboryl moiety. Braunschweig and co-workers have

reported the synthesis and characterization of (trimethylsilyl)iminoboryl complexes

trans-[(PCy3)2M(B≡N-SiMe3)(Br)] (M = Pd, Pt) obtained through the oxidative addition of the

B-Br bond in (Me3Si)2NBBr2 to a metal precursor followed by a facile intramolecular

elimination of Me3SiBr (Scheme 5.1.4).13

These reactions occur at room temperature and provide

a much gentler route to iminoboryl fragments. However, while the products of these reactions

were isolated and characterized, the intermediates in these transformations were not.

142

Scheme 5.1.4 Synthesis of iminoboryl transition metal complexes.

Notably, the transition metal iminoboryl systems were found to be reactive towards a variety of

substrates14

(Scheme 5.1.5). For example, when in the presence of a Lewis acid such as AlCl3, a

classical Lewis acid-base adduct forms leading to a shortening of the Pt-B bond and lengthening

of the B-N bond. Furthermore, these systems undergo 1,2-dipolar addition reactions with protic

reagents such as CH3OH, as well as the regiospecific addition of B-H bonds to the B≡N moiety.

Scheme 5.1.5 Reactions of an iminoboryl complex with various substrates.

These systems can also undergo substitution reactions through the bromide on the metal center.15

5.1.2 Carbenes in Stabilizing Low Valent Boron Species and Boron Centered Radicals

Since their discovery in the late 1980s, stable singlet carbenes have been utilized as ligands for

transition metal based catalysts16

, in addition to being organocatalysts17

on their own. They have

also been shown to coordinate and stabilize main group elements in low oxidation states, and

even activate small molecules.18

143

Carbenes have been traditionally viewed as strong σ-donors with negligible π-accepting

properties.16,19-21

This view has changed over the last few years as recent reports demonstrated

that modifications to the carbene influence both the donor ability and the electron accepting

properties.22-30

It was shown that the empty p-orbital on the carbene carbon can engage in π-back

donation and thus delocalize electron density. This observation has been used to stabilize

reactive species and has allowed for their detection spectroscopically and in some cases their

isolation.31,32

A few examples of main group systems stabilized by carbenes were discussed in

Chapter 1 and only select boron based systems will be discussed here.

Robinson and co-workers employed NHCs to stabilize and isolate a neutral diborene containing

a B=B double bond which was evidenced by the short distance in the molecular structure (Figure

5.1.1).33

Figure 5.1.1 Carbene stabilized neutral diborene.

More recently, Braunschweig and co-workers have reported the synthesis of the first example of

a compound with a triple bond between two boron atoms that is stable at room temperature,

using an IDipp as the stabilizing ligand (A in Figure 5.1.2).34

The importance of the NHC in the

stabilization and isolation of A indicated that the central diboron moiety is sensitive to the

electronic structure of the carbene. More recently, the same research group has isolated an

analogous complex utilizing a CAAC as the stabilizing ligand. Interestingly, the diboron species

that was isolated showed an elongated B-B bond distance that falls between a B≡B triple and

double bond and B-C bonds that fall in the range of B-C single and double bonds (B in Figure

5.1.2).35

The resulting compound is an example of an organic/inorganic analogue of butatriene

which is formed because CAACs are superior π acceptors compared to NHCs.

144

Figure 5.1.2 Carbene stabilized diboryne and diborabutatriene.

Carbenes have also been used to stabilize and allow for the isolation of boron centered radicals.

Curran and Lacôte have shown that tert-butoxy radicals abstract hydrogen atoms from

NHC-boranes to form NHC-boryl radicals (A-C in Figure 5.1.3).36,37

Gabbaï and co-workers

were also able to synthesize and spectroscopically characterize a carbene-BR2 radical

(D in Figure 5.1.3).38

Figure 5.1.3 Examples of carbene stabilized boron centered radicals.

More recently, Braunschweig and co-workers reported the synthesis of the first neutral borolyl

radical which is stabilized by an NHC (Scheme 5.1.6).39

The radical is formed through

single-electron-transfer between a borolyl anion, based on the borole framework, with

triorganotetrel halides.

Scheme 5.1.6 Synthesis of a neutral borolyl radical.

145

Since stable carbenes have been shown to activate small molecules as well as stabilize highly

reactive intermediates18

, two tasks previously exclusive to transition metals, we wanted to study

their ability to replace transition metals and stabilize iminoboranes.


5.2.1 Synthesis of Iminoborane species

To study the use of CAACs as a means of stabilizing iminoboranes, a series of boranes of the

general formula (Me3Si)2NBX2, where X = Cl, Br, I, were synthesized. The boranes

(Me3Si)2NBCl2 and (Me3Si)2NBBr2 were prepared according to literature procedures.13,40

Compound 5-1 was prepared according to a modified literature procedure and was isolated in

78% yield (Scheme 5.2.1). The NMR data indicate the formation of 5-1 where the 11

B{1H} NMR

spectrum shows a singlet at 7.9 ppm and a signal at 7.1 ppm is observed in the 29

Si{1H} NMR

spectrum corresponding to the Me3Si groups which have a signal at 0.28 ppm in the 1H NMR

spectrum. Complementary to NMR data, a single crystal X-ray diffraction study was performed

confirming the formulation of 5-1 as (Me3Si)2NBI2 (Figure 5.2.1).


The geometry around boron is perfectly planar with the sum of angles at B being 360°. The B-I

bond lengths are each 2.1809(19) Å and the B-N distance is 1.385(4) Å which is typical of a BN

double bond indicating the donation of the N lone pair into the empty p orbital on boron.

146

Figure 5.2.1 POV-ray depiction of the molecular structure of 5-1. C: black, N: aquamarine, Si:

blue, B: yellow-green, I: magenta. H-atoms omitted for clarity.

Adding one equivalent of Cy-CAAC to a solution of 5-1 in benzene results in the formation of a

new product in less than 50% yield along with unreacted 5-1. When the same reaction was

repeated using two equivalents of Cy-CAAC and 5-1, compound 5-2 was obtained as an orange

solid in 95% yield (Scheme 5.2.2). The 11

B{1H} NMR spectrum of 5-2 shows a singlet at 6.5

ppm, similar to 5-1, and the 29

Si{1H} NMR spectrum shows a signal at -8.9 ppm. The

1H NMR

spectrum reveals a peak at 0.33 ppm corresponding to the trimethylsilyl group and it integrates to

9H which indicates a loss of Me3SiI. The second equivalent of Cy-CAAC traps the released

trimethylsilyl iodide and forms [Cy-CAAC-TMS][I] which was identified in the 1H NMR

spectrum.

147


A single crystal X-ray study was performed which further confirmed the formulation of 5-2 as

[(Cy-CAAC)BN(SiMe3)][I] (Figure 5.2.2). The geometry around boron is slightly bent where the

C-B-N angle is 170.6(3)° and the iodide counter anion is outersphere. The B-C distance is

1.543(3) Å which lies between typical B-C single (1.59 Å) and double (1.44 Å) bonds.41,42

The

B-N distance is 1.229(3) Å which is indicative of a B-N triple bond and is similar to reported

XB≡NR, (Me3Si)3SiB≡NtBu, and (Me3Si)N≡BM(PCy3)2Br systems.1,2,4-6,13,43

The B-N-Si bond

angle is found to be 164.4(2)° which deviates from linearity.

148

Figure 5.2.2 POV-ray depiction of the molecular structure of the cation of 5-2. C: black, N:

aquamarine, Si: blue, B: yellow-green. H-atoms omitted for clarity.

Similarly, the addition of two equivalents of Cy-CAAC to a benzene solution of (Me3Si)2NBBr2

resulted in the isolation of compound 5-3 as a yellow solid in 95% yield. The 11

B{1H} NMR

spectrum of 5-3 shows a singlet at 12.6 ppm, which is more downfield compared to 5-2,

suggesting a different environment around the boron center and the 29

Si{1H} NMR shows a

signal at -10.5 ppm. A single crystal X-ray study was performed confirming the formulation of

5-3 as (Cy-CAAC)BBrN(SiMe3) (Figure 5.2.3). The geometry around boron is trigonal planar

(sum of angles at B is 360°). The B-C distance is 1.606(4) Å which is typical of a B-C single

bond and the B-Br and B-N distances are 2.078(3) and 1.304(3) Å, respectively. The shortened

B-N bond length is indicative of double bond character and the B-N-Si is 133.3(2) ° which

indicates that the lone pair on nitrogen is accessible and not involved in bonding with the boron

center.

149


blue, B: yellow-green, Br: maroon. H-atoms omitted for clarity.

An iminoborane similar to 5-2 could conceivably be accessed through halide abstraction from

5-3. As such, the addition of NaBPh4 to a solution of 5-3 in C6H5Br was undertaken, and

following workup, resulted in the isolation of 5-4 in 75% yield (Scheme 5.2.2). The

11B{

1H} NMR of 5-4 shows a singlet at 7.7 ppm, which is upfield from 5-3 and similar to 5-2,

and a second singlet at -6.5 ppm corresponding to the BPh4 counter anion. The 29

Si{1H} NMR

spectrum shows a signal at 1.7 ppm, while the signal corresponding to the trimethylsilyl group

shifts upfield to 0.00 ppm in the 1H NMR spectrum. An X-ray analysis of single crystals of 5-4

was performed which showed an analogous geometry to that observed for 5-2 and confirmed the

formulation as [(Cy-CAAC)BN(SiMe3)][BPh4] (Figure 5.2.4). The geometry around boron is

slightly bent as the C-B-N angle is 173.4(4)°. The B-C distance of 1.545(5) Å is similar to that in

5-2 and the B-N distance is 1.218(4) Å, indicative of a B-N triple bond and similar to 5-2 as well

as reported systems containing a BN triple bond.1,2,4-6,13,40,43

The B-N-Si bond angle is 175.8(3)°

which deviates slightly from linearity.

150


blue, B: yellow-green. H-atoms omitted for clarity.

While the addition of one equivalent of Cy-CAAC to either 5-1 or (Me3Si)2NBBr2 resulted in a

50:50 mixture of 5-2 or 5-3, respectively, and the starting borane, the addition of one equivalent

of Cy-CAAC in pentane to a solution of (Me3Si)2NBCl2 afforded 5-5 as a white solid in 65%

yield (Scheme 5.2.3). The 11

B{1H} NMR spectrum of 5-5 shows a singlet at 4.3 ppm, which is

indicative of a 4-coordinate boron center, and the 29

Si{1H} NMR shows a signal at -0.49 ppm.

The 1H and

13C{

1H} NMR spectra show signals belonging to the carbene and the

bis-trimethylsilyl amide moieties with a peak at 0.56 ppm in the 1H NMR integrating to 18H

corresponding to the Me3Si groups.

151


X-ray analysis of single crystals of 5-5 confirmed its formulation as (Cy-CAAC)BCl2N(SiMe3)2

(Figure 5.2.5). The geometry around the boron center is tetrahedral but further discussion of

metric parameters is prevented due to severe disorder. Interestingly, over time in solution, 5-5

loses trimethylsilyl chloride and forms a new product, 5-6. The same result is observed when a

solid sample is left at room temperature for prolonged periods of time (over one month) or when

a solid sample is heated under vacuum.

152


blue, B: yellow-green, Cl: green. H-atoms omitted for clarity.

Compound 5-6 was also obtained as a yellow solid in 70% yield when two equivalents of

Cy-CAAC were added to a benzene solution of (Me3Si)2NBCl2. The 11

B{1H} NMR spectrum of

5-6 shows a singlet at 17.4 ppm, which is indicative of a three coordinate boron center, and the

29Si{

1H} NMR shows a signal at -11.9 ppm. The

1H NMR spectrum reveals a peak at 0.45 ppm

corresponding to the trimethylsilyl group which integrates to 9H indicating the loss of Me3SiCl.

An X-ray analysis of single crystals of 5-6 showed an analogous geometry to that observed for

5-3 and confirmed its formulation as (Cy-CAAC)BClN(Me3Si) (Figure 5.2.6).



153

The geometry around boron is trigonal planar (sum of angles at B is 360°) and the B-C distance

is 1.612(3) Å which is similar to that observed for 5-3. The B-Cl and B-N distances are 1.881(2)

and 1.300(3) Å, respectively. The shortened B-N bond length is indicative of a double bond and

the B-N-Si angle is 139.21(16)°.

Similar to 5-3, the addition of KB(C6F5)4 to a solution of 5-6 in C6H5Br resulted in the isolation

of 5-7 as pale yellow crystals in 74% yield (Scheme 5.2.3). The 11

B{1H} NMR spectrum of 5-7

shows a singlet at 7.4 ppm, and a second singlet at -16.7 ppm corresponding to the B(C6F5)4

counter anion and the 29

Si{1H} NMR shows a signal at 0.96 ppm. The

19F{

1H} NMR spectrum

of 5-7 shows three peaks at -133.09, -163.80, and -167.62 ppm corresponding to the B(C6F5)4

moiety and the signal corresponding to the trimethylsilyl group shifts upfield to -0.02 ppm in the

1H NMR spectrum. Single crystals suitable for X-ray diffraction were obtained and the study

performed which confirmed the formulation of 5-7 as [(Cy-CAAC)BN(SiMe3)][B(C6F5)4]

(Figure 5.2.7).


blue, B: yellow-green, F: deep pink. H-atoms omitted for clarity.

The geometry around boron is approximately linear with a C-B-N angle of 175.0(4)° and the

B-C distance is 1.550(5) Å which is similar to that in 5-2 and 5-4. The B-N distance is

1.192(5) Å, indicative of a BN triple bond, and is similar to 5-2 and 5-4. The B-N-Si bond angle

is 169.8(3)° which deviates from linearity.

As cyclic(alkylamino)carbenes often show reactivity that is not attained with NHCs we were

interested in probing whether this reactivity could be extended to NHCs. No reaction was

154

observed when the carbene SIMes was used, but the addition of two equivalents of IDipp to 5-1

resulted in the isolation of 5-8 as a pale yellow solid in 76% yield (Scheme 5.2.4). The second

equivalent of IDipp traps the released trimethylsilyl iodide and forms [IDipp-SiMe3][I] which

was identified in the 1H NMR spectrum. The

11B{

1H} NMR of 5-8 shows a singlet at 2.9 ppm

and the 29

Si{1H} NMR shows a signal at -9.1 ppm. The signal corresponding to the trimethylsilyl

group is found at 0.19 ppm in the 1H NMR spectrum and it integrates to 9H which indicates a

loss of Me3SiI.


In addition to the NMR data, a single crystal X-ray study was performed which further

confirmed the formulation of 5-8 as (IDipp)B(I)N(SiMe3) (Figure 5.2.8). The geometry around

boron is trigonal planar (sum of angles at B is 360°), the B-C distance is 1.581(8) Å which is

typical of a B-C single bond,33,44

and the B-I and B-N distances are 2.361(6) and 1.282(7) Å,

respectively. The shortened B-N bond length is indicative of a double bond and the B-N-Si angle

is 145.5(4)°.

155


blue, B: yellow-green, I: magenta. H-atoms omitted for clarity.

In a similar fashion, 5-9 was isolated as a pale yellow solid in 87% yield when two equivalents

of IDipp were added to a benzene solution of (Me3Si)2NBBr2. The 11

B{1H} NMR of 5-9 shows a

singlet at 10.9 ppm, and the 29

Si{1H} NMR spectrum shows a signal at -10.8 ppm. Along with

peaks corresponding to IDipp in the 1H NMR spectrum, a singlet at 0.20 ppm which integrates to

9H is present corresponding to the trimethylsilyl group. Based on the NMR data, the formulation

of 5-9 is (IDipp)BBrN(SiMe3).

Similar to the reactivity observed with Cy-CAAC, the addition of one equivalent of IDipp in

pentane to a solution of (Me3Si)2NBCl2 resulted in the formation of 5-10 as a white solid in 65%

yield (Scheme 5.2.4). The 11

B{1H} NMR spectrum of 5-10 shows a singlet at 3.7 ppm and the

29Si{

1H} NMR shows a signal at 0.04 ppm. The

1H and

13C{

1H} NMR spectra show signals

corresponding to the carbene and the bis-trimethylsilyl amide moieties. Single crystal X-ray

analysis of 5-10 confirmed its formulation as (IDipp)B(Cl)2N(SiMe3)2 (Figure 5.2.9). The

geometry around boron is tetrahedral with a B-C distance of 1.665(2) Å which is in the range of

B-C single bonds. The B-N distance is 1.507(2) Å which is in line with a typical B-N single bond

and the B-Cl bond lengths are 1.9080(17) and 1.9026(16) Å. Similar to 5-5, over time in

solution, 5-10 loses trimethylsilyl chloride and forms a new product, 5-11.

156



Compound 5-11 was also obtained as colorless crystals in 71% yield when one equivalent of

IDipp was added to a benzene solution of (Me3Si)2NBCl2 (Scheme 5.2.4). The 11

B{1H} NMR of

5-11 shows a singlet at 15.8 ppm and the 29

Si{1H} NMR spectrum shows a signal at -12.2 ppm.

The 1H NMR spectrum reveals a peak at 0.21 ppm corresponding to the trimethylsilyl group

integrating to 9H which indicates the loss of Me3SiCl. Based on the NMR data, the formulation

of 5-11 is (IDipp)B(Cl)N(SiMe3). In an effort to generate an iminoborane stabilized by IDipp,

NaBPh4 was added to a solution of 5-11 in C6H5Br and NMR data of the reaction mixture

showed several products. Upon workup, however, poor quality single crystals were formed and a

preliminary crystal structure indicated the formation of 5-11a (Figure 5.2.10).

157

Figure 5.2.10 POV-ray depiction of the molecular structure of the cation of 5-11a. C: black, N:

aquamarine, Si: blue, B: yellow-green, Cl: green. H-atoms and iPr groups omitted for clarity.

The molecular structure indicates the formation of the IDipp stabilized iminoborane but the

compound undergoes further reactivity including the generation of a bridging normal-abnormal

carbene, loss of [IDipp][HCl], and migration of one Me3Si group to another N atom resulting in

the formation of (Me3Si)2N and a bridging N moiety (Scheme 5.2.5).

Scheme 5.2.5 Reaction of 5-11 with NaBPh4.

158

At this time, it is unclear how this transformation proceeds and further studies are needed to

elucidate the reactivity including attempting to make the saturated version of IDipp (SIDipp) to

prevent the formation of an abnormal carbene.

5.2.2 Reactivity of Iminoboranes with CO2

We were interested in testing the reactivity of the iminoborane systems synthesized with CO2. To

that end, solutions of 5-2, 5-3, 5-4, 5-6, and 5-7 were exposed to 1 atm of CO2. While there was

no observed reactivity between 5-4 or 5-7 and CO2, both at room temperature and upon heating,

the reaction of 5-2, 5-3, and 5-6 with CO2 in C6H6 led to the isolation of 5-12, 5-13, and 5-14 as

white solids in 86, 83 and 91% yields, respectively (Scheme 5.2.6). The lack of reactivity

observed with 5-4 and 5-7 is attributed to the unavailability of the lone pair on N to react with

CO2. This is evidenced in the shortened B-N distances in 5-4 and 5-7 (BN triple bonds) which

indicates donation of the lone pair on N into the empty p orbital on the boron center, preventing

further reactivity.


159

The 11

B{1H} NMR spectrum of 5-12 shows a singlet at -1.9 ppm, which is indicative of a

4-coordinate boron center, and the 29

Si{1H} NMR shows a signal at 2.6 ppm. A signal at

157.1 ppm in the 13

C{1H} NMR spectrum, which falls in the carbamate region, is assigned to the

CO2 carbon. A single crystal X-ray study was performed and confirmed the formulation of 5-12

as (Cy-CAAC)B(CO2)N(SiMe3)I (Figure 5.2.11) which is a result of [2+2] cycloaddition

between CO2 and the BN fragment in 5-2.

Figure 5.2.11 POV-ray depiction of the molecular structure of 5-12. C: black, N: aquamarine,

Si: blue, B: yellow-green, O: red, I: magenta. H-atoms omitted for clarity.

The geometry around boron is distorted tetrahedral where the N-B-O angle is 88.6 (4)° which is

significantly smaller than typically observed angles. This is presumably due to the chelation of

the CO2 molecule and formation of a tight 4-member ring. The B-C distance is 1.619(9) Å which

is similar to 5-3 and the B-I distance is 2.331(6) Å. The B-N and B-O bond distances are

1.524(8) and 1.480(7) Å, respectively, which are in line with typical B-N and B-O single

bonds.45-47

The C-OB and C-O bond lengths are 1.371(7) and 1.200(8) Å, which are typical of

CO single and double bonds, respectively.

The 11

B{1H} NMR of 5-13 shows a singlet at 0.49 ppm, which is indicative of a 4-coordinate

boron center, and the 29

Si{1H} NMR spectrum shows a signal at 2.2 ppm. Similar to 5-12, the

13C{

1H} NMR shows a signal at 158.9 ppm which is assigned to the CO2 carbon. X-ray analysis

of single crystals of 5-13 showed an analogous geometry to that observed for 5-12 and confirmed

160

the formulation as (Cy-CAAC)B(CO2)N(SiMe3)Br (Figure 5.2.12). The geometry around B is

distorted tetrahedral where the N-B-O angle is 88.6(3)° due to the formation of a tight 4-member

ring. The B-C distance is 1.633(6) Å which is similar to 5-12 and the B-Br distance is

2.082(5) Å. The B-N and B-O bond distances are 1.525(6) and 1.483(6) Å, respectively, which

are in line with typical B-N and B-O single bonds and the C-OB and C-O bond lengths are

1.353(6) and 1.211(5) Å.


Si: blue, B: yellow-green, O: red, Br: maroon. H-atoms omitted for clarity.

Similar to 5-12 and 5-13, the 11

B{1H} NMR spectrum of 5-14 shows a singlet at 1.6 ppm and the

29Si{

1H} NMR shows a signal at 0.8 ppm. Similar to 5-12 and 5-13, the

13C{

1H} NMR shows a

signal at 159.1 ppm which is assigned to the CO2 carbon. Single crystals suitable for an X-ray

study were obtained and confirmed the formulation of 5-14 as (Cy-CAAC)B(CO2)N(Me3Si)Cl

(Figure 5.2.13). The geometry around boron is distorted tetrahedral and the N-B-O angle is

87.81(18)°. The B-C distance is 1.635(4) Å which is similar to 5-12 and 5-13 and the B-Cl

distance is 1.885(3) Å. The B-N and B-O bond distances are 1.534(3) and 1.507(3) Å,

respectively and the C-OB and C-O bond lengths are 1.357(3) and 1.204(3) Å, respectively.

161


Si: blue, B: yellow-green, O: red, Cl: green. H-atoms omitted for clarity.

These results are consistent with a recent report by Cui and co-workers where they described the

intermolecular [2+2] cycloaddition of CO2 with a π-conjugated iminoborane stabilized by an

intramolecular imine group (Scheme 5.2.7).48

This system, however, loses CO2, regenerating the

iminoborane, upon heating under vacuum at 180 °C.

Scheme 5.2.7 Reaction of a π-conjugated iminoborane with CO2.

Efforts to further functionalize the CO2 moiety either with triaryl- or trialkylsilane or H2 were

unsuccessful. While compounds 5-2, 5-3, and 5-6 reacted with CO2, they were unreactive

towards other small molecules such as H2, CO, and small olefins.

162

5.3 Conclusion

Cyclic (alkylamino)carbenes have been shown to stabilize iminoboryl moieties which have only

been previously stabilized in the coordination sphere of transition metals. These species were

characterized crystallographically and, depending on the halide size, can be directly formed

through elimination of TMS-X (X = I), or through halide exchange for a non-coordinating anion

after TMS-X elimination (X = Br, Cl). The analogous species using IDipp instead of a CAAC

could not be isolated as further reactivity with the carbene backbone is observed. Some of the

species were shown to undergo [2+2] cycloaddition with CO2.




a VAC Atmospheres glove box and a Schlenk vacuum-line. Hexanes and pentane were purified

with a Grubbs-type column system manufactured by Innovative Technology and dispensed into

thick-walled glass Schlenk bombs equipped with Young-type Teflon valve stopcocks.

Anhydrous benzene was purchased from Sigma Aldrich and stored over molecular sieves.

Dichloromethane-d2 and toluene-d8 were dried over CaH2 and benzene-d6 was dried over Na

metal and vacuum-transferred into a Young bomb. All solvents were thoroughly degassed after

purification (three freeze-pump-thaw cycles). NMR spectra were recorded at 25 °C on a Bruker

Avance 400 MHz spectrometer or Agilent 500 MHz. BI3, BBr3, BCl3 (1 M in hexane),

K(N(SiMe3)2), and CO2, were obtained from Sigma-Aldrich and used without further

purification. IDipp49

, Cy-CAAC50

, Cl2B(N(SiMe3)2)40

and Br2B(N(SiMe3)2)13

were prepared

according to literature procedures. Chemical shifts are given relative to SiMe4 and referenced to

the residual solvent signal (1H,


29Si: Me4Si,

11B: BF3

.Et2O,

19F: CFCl3). In some instances, signal assignment was derived from two-

dimensional NMR experiments. Chemical shifts are reported in ppm and coupling constants as

scalar values in Hz. Combustion analyses were performed in house employing a Perkin-Elmer

CHN Analyzer.

163


Synthesis of 5-1: A solution of KHMDS (0.112 g, 0.561 mmol) in 5 mL toluene was added at

room temperature to a stirring solution of BI3 (0.200 g, 0.511 mmol) in 5 mL toluene. A white

solid instantaneously starts to precipitate. The reaction mixture was left stirring overnight and

then filtered to remove the white solid. The solvent was then removed in vacuo to yield an oily

solid (0.170 g, 0.400 mmol, 78%). X-ray quality crystals were grown from toluene and melt at

room temperature. 1H NMR (400 MHz, C6D6): δ 0.28 (s, 18H, (CH3)3Si).

13C{

1H} NMR (101

MHz, C6D6): δ 4.2 (s, (CH3)3Si). 11

B{1H} NMR (96 MHz, C6D6): δ 7.9 (s).

29Si{

1H} NMR (80

MHz, C6D6): δ 7.1 (s, (CH3)3Si). Elemental Analysis for C6H18BI2NSi2: C, 16.96; H, 4.27; N,

3.30. Found: C, 17.81; H, 4.65; N, 3.58. NMR spectra are attached at the end of this section.

Synthesis of 5-2: A solution of Cy-CAAC (0.300 g, 0.921 mmol) in 10 mL of C6H6 was added at

room temperature to a stirring solution of 5-1 (0.196 g, 0.461 mmol) in 5 mL of C6H6. The

solution turns bright orange and a white solid instantaneously starts to precipitate. The reaction

mixture was left stirring overnight and then filtered to remove the white solid. The solvent was

then removed in vacuo to yield an orange solid (0.205 g, 0.372 mmol, 95%). X-ray quality

crystals were grown from pentane at -35 oC.

1H NMR (400 MHz, C6D6): δ 7.08 (m, 1H, C6H3),

7.00 (m, 2H, C6H3), 2.83 (septet, 3JHH = 7 Hz, 2H, CH(CH3)2), 2.74 (dt,

2JHH = 13 Hz,

3JHH =

4 Hz, 2H, C6H10), 1.83 (s, 1H, Dipp-NCCH2), 1.80 (s, 1H, Dipp-NCCH2), 1.66 (d, 3JHH = 7 Hz,

6H, CH(CH3)2), 1.60 (s, 2H, C6H10), 1.49 (m, 2H, C6H10), 1.36 (m, 2H, C6H10), 1.07 (d, 3JHH =

7 Hz, 6H, CH(CH3)2), 0.98 (br s, 2H, C6H10), 0.94 (s, 6H, Dipp-NC(CH3)2), 0.33 (s, 9H,

(CH3)3Si). 11

B{1H} NMR (96 MHz, C6D6): δ 6.5 (s).

13C{

1H} NMR (101 MHz, C6D6, Dipp-

NCC-Cy not observed): δ 146.1 (C6H3), 130.5 (C6H3), 128.2 (C6H3), 127.9 (C6H3), 125.8 (C6H3),

78.7 (Dipp-NC(CH3)2), 56.6 (C6H10), 46.4 (C6H10), 39.5 (C6H10 + Dipp-NCCH2), 29.5

(CH(CH3)2), 27.8 (Dipp-NC(CH3)2), 27.4 (CH(CH3)2), 25.4 (CH(CH3)2), 24.7 (C6H10), 22.8

(C6H10), 2.5 (s, (CH3)3Si). 29

Si{1H} NMR (99 MHz, C6D6): δ -8.9 (s, (CH3)3Si). Elemental

Analysis for C26H44BIN2Si: C, 56.73; H, 8.06; N, 5.09. Found: C, 56.69; H, 8.05; N, 5.28.


room temperature to a stirring solution of (Me3Si)2NBBr2 (0.152 g, 0.461 mmol) in 5 mL of

C6H6. The solution turns bright yellow and a white solid instantaneously starts to precipitate. The

reaction mixture was left stirring overnight and then filtered to remove the white solid. The

164

solvent was then removed in vacuo to yield a yellow solid (0.190 g, 0.377 mmol, 95%). X-ray

quality crystals were grown from pentane at -35 oC.

1H NMR (400 MHz, C6D6): δ 7.09 (m, 1H,

C6H3), 7.01 (m, 2H, C6H3), 2.77 (m, 4H, CH(CH3)2 + C6H10), 1.68 (br s, 2H, Dipp-NCCH2), 1.65

(d, 3JHH = 7 Hz, 6H, CH(CH3)2), 1.55 (s, 2H, C6H10), 1.51 (m, 2H, C6H10), 1.40 (m, 2H, C6H10),

1.10 (d, 3JHH = 7 Hz, 6H, CH(CH3)2), 0.99 (m, 2H, C6H10), 0.88 (s, 6H, Dipp-NC(CH3)2), 0.42 (s,

9H, (CH3)3Si). 11

B{1H} NMR (128 MHz, C6D6): δ 12.6 (s).

13C{

1H} NMR (101 MHz, C6D6,

Dipp-NCC-Cy not observed): δ 146.0 (C6H3), 130.3 (C6H3), 128.2 (C6H3), 127.9 (C6H3), 125.6

(C6H3), 79.3 (Dipp-NC(CH3)2), 56.9 (C6H10), 45.6 (C6H10), 37.6 (C6H10 + Dipp-NCCH2), 29.6


(C6H10), 3.7 (s, (CH3)3Si). 29


Analysis for C26H44BBrN2Si: C, 62.03; H, 8.81; N, 5.56. Found: C, 61.71; H, 9.19; N, 5.62.

Synthesis of 5-4: Solid NaBPh4 (0.075 g, 0.219 mmol) was added to a stirring solution of 5-3

(0.100 g, 0.199 mmol) in 5 mL of C6H5Cl. The mixture was left stirring at room temperature

overnight and was then filtered over a pad of celite and the filtrate concentrated to 3 mL. The

solution was layered with 15 mL of pentane and left standing overnight. The solvent was then

decanted and the product was isolated as pale yellow crystals which were dried under high

vacuum (0.110 g, 75%). X-ray quality crystals were grown from C6H5Cl/pentane. 1H NMR

(400 MHz, CD2Cl2): δ 7.66 (m, 1H, C6H3), 7.46 (s, 1H, C6H3), 7.44 (s, 1H, C6H3), 7.34 (m, 8H,

o-H, BPh4), 7.05 (m, 8H, m-H, BPh4), 6.90 (m, 4H, p-H, BPh4), 2.50 (septet, 3JHH = 7 Hz, 2H,

CH(CH3)2), 2.33 (s, 2H, C6H10), 1.94 (m, 4H, C6H10 + Dipp-NCCH2), 1.82 (m, 4H, C6H10), 1.48

(br s, 8H, C6H10 + Dipp-NC(CH3)2), 1.39 (d, 3JHH = 7 Hz, 6H, CH(CH3)2), 1.25 (d,

3JHH = 7 Hz,

6H, CH(CH3)2), 0.00 (s, 9H, (CH3)3Si). 11

B{1H} NMR (128 MHz, CD2Cl2): δ 7.7 (br, CBN), -6.5

(sharp s, BPh4). 13

C{1H} NMR (101 MHz, CD2Cl2): δ 164.6 (q,

1JCB = 50 Hz, Cipso BPh4), 144.8

(C6H3), 136.5 (q, 2JCB = 1 Hz, o-C BPh4), 133.4 (C6H3), 130.3 (C6H3), 129.0 (C6H3), 126.9

(C6H3), 126.1 (q, 3JCB = 3 Hz, m-C BPh4), 122.2 (s, p-C BPh4), 87.1 (Dipp-NC(CH3)2), 57.9

(C6H10), 45.4 (C6H10), 35.8 (C6H10 + Dipp-NCCH2), 30.4 (CH(CH3)2), 29.6 (Dipp-NC(CH3)2),

26.6 (CH(CH3)2), 24.6 (CH(CH3)2), 23.4 (C6H10), 21.6 (C6H10), 0.8 (s, (CH3)3Si). 29

Si{1H} NMR

(99 MHz, CD2Cl2): δ 1.7 (s, (CH3)3Si). Elemental Analysis51

for C50H64B2N2Si: C, 80.85; H,

8.68; N, 3.77. Found: C, 79.6; H, 9.10; N, 3.87.

Synthesis of 5-5: A solution of Cy-CAAC (0.300 g, 0.921 mmol) in 10 mL pentane was added to

a solution of (Me3Si)2NBCl2 (0.223 g, 0.921 mmol) in 5 mL hexane. A white solid precipitates

165

instantaneously. The reaction mixture was stirred for 3 more hours before it was filtered through

a frit. The white solid was washed with 10 mL pentane and dried under high vacuum (0.348 g,

65%). X-ray quality crystals were grown from layering a hexane solution of Cy-CAAC over a

benzene solution of (Me3Si)2NBCl2 at room temperature. Single crystals were grown at the

interface. 1H NMR (400 MHz, Tol-d8): δ 7.08-6.99 (m, 3H, C6H3), 2.99 (m, 2H, CH(CH3)2), 2.94

(m, 2H, C6H10), 1.75 (br s, 1H, Dipp-NCCH2), 1.72 (br s, 1H, Dipp-NCCH2), 1.68-1.58 (m, 6H,

C6H10), 1.44 (d, 3JHH = 7 Hz, 6H, CH(CH3)2), 1.17 (d,

3JHH = 7 Hz, 6H, CH(CH3)2), 1.13 (m, 2H,

C6H10), 0.88 (s, 6H, Dipp-NC(CH3)2), 0.56 (s, 18H, (CH3)3Si). 11

B{1H} NMR (96 MHz, Tol-d8):

δ 4.3 (s). 13

C{1H} NMR (101 MHz, Tol-d8, Dipp-NCC-Cy not observed): δ 145.6 (C6H3), 135.6

(C6H3), 129.1 (C6H3), 128.2 (C6H3), 125.8 (C6H3), 80.4(Dipp-NC(CH3)2), 59.9 (C6H10), 45.4

(C6H10), 37.8 (C6H10 + Dipp-NCCH2), 29.9 (CH(CH3)2), 29.7 (Dipp-NC(CH3)2), 29.3

(CH(CH3)2), 25.5 (CH(CH3)2), 25.3 (C6H10), 22.8 (C6H10), 7.7 (s, (CH3)3Si). 29

Si{1H} NMR

(99 MHz, Tol-d8): δ -0.49 (s, (CH3)3Si). Elemental Analysis for C30H55BCl2N2Si2: C, 61.95; H,

9.53; N, 4.82. Found: C, 61.66; H, 9.65; N, 5.11.


room temperature to a stirring solution of (Me3Si)2NBCl2 (0.111 g, 0.461 mmol) in 5 mL of

C6H6. The solution turns orange/yellow. The reaction mixture was left stirring overnight and the

solvent was then removed in vacuo. The product was extracted into 15 mL of pentane and

filtered over a pad of celite. The yellow pentane solution was cooled to -35 oC, overnight,

yielding the product as yellow crystals (0.148 g, 70%). X-ray quality crystals were grown from

pentane at -35 oC.

1H NMR (400 MHz, C6D6): δ 7.10 (m, 1H, C6H3), 7.02 (br s, 1H, C6H3), 7.00

(m, 1H, C6H3), 2.75 (m, 4H, C6H10 + CH(CH3)2), 1.61 (d, 3JHH = 7 Hz, 6H, CH(CH3)2), 1.55-1.44

(br m, 8H, C6H10 + NCCH2), 1.12 (d, 3JHH = 7 Hz, 6H, CH(CH3)2), 1.01 (m, 2H, C6H10), 0.87 (s,

6H, Dipp-NC(CH3)2), 0.45 (s, 9H, (CH3)3Si). 11

B{1H} NMR (96 MHz, C6D6): δ 17.4 (s).

13C{

1H} NMR (101 MHz, C6D6, Dipp-NCC-Cy not observed): δ 145.8 (C6H3), 132.1 (C6H3),

130.2 (C6H3), 128.3 (C6H3), 125.5 (C6H3), 79.4 (Dipp-NC(CH3)2), 57.2 (C6H10), 45.3 (C6H10),

36.8 (C6H10 + Dipp-NCCH2), 29.6 (CH(CH3)2), 29.0 (Dipp-NC(CH3)2), 27.4 (CH(CH3)2), 25.2

(CH(CH3)2), 24.9 (C6H10), 22.4 (C6H10), 4.2 (s, (CH3)3Si). 29

Si{1H} NMR (99 MHz, C6D6): δ

-11.9 (s, (CH3)3Si). Elemental Analysis for C26H44BClN2Si: C, 68.04; H, 9.66; N, 6.10. Found:

C, 67.46; H, 9.63; N, 6.14.

166

Synthesis of 5-7: Solid KB(C6F5)4 (0.156 g, 0.218 mmol) was added to a stirring solution of 5-5

(0.100 g, 0.218 mmol) in 10 mL of C6H5Cl. The mixture was left stirring at room temperature

overnight and was then filtered over a pad of celite and the filtrate concentrated to 5 mL. The

solution was layered with 15 mL of pentane and left standing overnight. The solvent was then

decanted and the product was isolated as pale yellow crystals which were dried under vacuum

(0.178 g, 74%). X-ray quality crystals were grown from C6H5Cl/pentane. 1H NMR (400 MHz,

CD2Cl2): δ 7.65 (apparent t, 3JHH = 8 Hz, 1H, C6H3), 7.46 (s, 1H, C6H3), 7.44 (s, 1H, C6H3), 2.53

(septet, 3JHH = 7 Hz, 2H, CH(CH3)2), 2.49 (s, 2H, C6H10), 1.95 (m, 4H, C6H10 + Dipp-NCCH2),

1.85 (m, 4H, C6H10), 1.58 (s, 6H, Dipp-NC(CH3)2), 1.49 (m, 2H, C6H10), 1.37 (d, 3JHH = 7 Hz,

6H, CH(CH3)2), 1.24 (d, 3JHH = 7 Hz, 6H, CH(CH3)2), -0.02 (s, 9H, (CH3)3Si).

19F NMR (376

MHz, CD2Cl2): δ -133.09 (m, 8F, o-C6F5), -163.80 (t, 3JFF = 20 Hz, 4F, p-C6F5),

-167.62 (apparent t, 3JFF = 20 Hz, 8F, m-C6F5).

11B{

1H} NMR (128 MHz, CD2Cl2): δ 7.4 (br,

CBN), -16.7 (sharp s, B(C6F5)4). 13

C{1H} NMR (101 MHz, CD2Cl2): δ 148.7 (dm,

1JCF = 241 Hz,

o-C6F5), 144.9 (C6H3), 138.8 (dm, 1JCF = 244 Hz, p-C6F5), 136.9 (dm,

1JCF = 245 Hz, m-C6F5),

133.5 (C6H3), 130.4 (C6H3), 129.1 (C6H3), 126.9 (C6H3), 86.9 (Dipp-NC(CH3)2), 58.0 (C6H10),

45.6 (C6H10), 35.9 (C6H10 + Dipp-NCCH2), 30.4 (CH(CH3)2), 29.7 (Dipp-NC(CH3)2), 26.6

(CH(CH3)2), 24.6 (CH(CH3)2), 23.3 (C6H10), 21.5 (C6H10), 0.7 (s, (CH3)3Si). 29

Si{1H} NMR (99

MHz, CD2Cl2): δ 0.96. Elemental Analysis for C50H44B2F20N2Si: C, 54.47; H, 4.02; N, 2.54.

Found: C, 54.14; H, 3.73; N, 2.88.

Synthesis of 5-8: A solution of IDipp (0.150 g, 0.386 mmol) in 5 mL of C6H6 was added at room

temperature to a stirring solution of 5-1 (0.082 g, 0.193 mmol) in 5 mL of C6H6. The solution

turns pale orange and a white solid instantaneously starts to precipitate. The reaction mixture was

left stirring overnight and then filtered to remove the white solid. The solvent was then removed

in vacuo and the residue was washed with 3 mL of cold pentane. The pentane was decanted and

the product dried under high vacuum to yield a pale yellow solid (0.090 g, 76%). X-ray quality

crystals were grown from pentane at -35 oC.

1H NMR (400 MHz, C6D6): δ 7.21 (m, 2H, C6H3),

7.09 (br s, 2H, C6H3), 7.07 (br s, 2H, C6H3), 6.37 (s, 2H, IDipp-4,5-CH), 2.89 (septet, 3JHH = 7

Hz, 4H, CH(CH3)2), 1.49 (d, 3JHH = 7 Hz, 12H, CH(CH3)2), 1.00 (d,

3JHH = 7 Hz, 12H,

CH(CH3)2), 0.19 (s, 9H, (CH3)3Si). 11

B{1H} NMR (96 MHz, C6D6): δ 2.9 (s).

13C{

1H} NMR

(101 MHz, C6D6, NCN not observed ): δ 145.7 (C6H3), 133.0 (C6H3), 131.2 (C6H3), 128.6

(C6H3), 128.3 (C6H3), 124.5 (C6H3), 122.6 (IDipp-4,5-CH), 29.2 (CH(CH3)2), 25.7 (CH(CH3)2),

167

23.4 (CH(CH3)2), 2.5 (s, (CH3)3Si). 29

Si{1H} NMR (99 MHz, C6D6): δ -9.1 (s, (CH3)3Si).

Elemental Analysis for C30H45BIN3Si: C, 58.73; H, 7.39; N, 6.85. Found: C, 58.29; H, 7.87; N,

6.75.

Synthesis of 5-9: A solution of IDipp (0.150 g, 0.386 mmol) in 5 mL of C6H6 was added at room

temperature to a stirring solution of (Me3Si)2NBBr2 (0.064 g, 0.193 mmol) in 5 mL of C6H6. The

solution turns pale yellow and a white solid instantaneously starts to precipitate. The reaction

mixture was left stirring overnight and then filtered to remove the white solid. The solvent was

then removed in vacuo and the residue was washed with 3 mL of cold pentane. The pentane was

decanted and the product dried under high vacuum to yield a pale yellow solid (0.095 g, 87%).

1H NMR (400 MHz, C6D6): δ 7.21 (m, 2H, C6H3), 7.09 (br s, 2H, C6H3), 7.07 (br s, 2H, C6H3),

6.33 (s, 2H, IDipp-4,5-CH), 2.80 (septet, 3JHH = 7 Hz, 4H, CH(CH3)2), 1.47 (d,

3JHH = 7 Hz, 12H,

CH(CH3)2), 1.02 (d, 3JHH = 7 Hz, 12H, CH(CH3)2), 0.20 (s, 9H, (CH3)3Si).

11B{

1H} NMR (96

MHz, C6D6): δ 10.9 (s). 13

C{1H} NMR (101 MHz, C6D6, NCN not observed ): δ 145.6 (C6H3),

133.4 (C6H3), 130.9 (C6H3), 129.0 (C6H3), 128.3 (C6H3), 124.4 (C6H3), 122.4 (IDipp-4,5-CH),

29.2 (CH(CH3)2), 25.4 (CH(CH3)2), 23.3 (CH(CH3)2), 3.3 (s, (CH3)3Si). 29

Si{1H} NMR (99

MHz, C6D6): δ -10.8 (s, (CH3)3Si). Repeated attempts to obtain EA were unsuccessful and as

such the NMR spectra of 5-9 are attached at the end of this section.

Synthesis of 5-10: To a solution of (Me3Si)2NBCl2 (0.124 g, 0.512 mmol) in 15 mL pentane was

added a solution of IDipp (0.200 g, 0.515 mmol) in 0.5 mL benzene. A white solid precipitates

within minutes. The reaction mixture was stirred for 6 more hours before it was filtered through

a frit. The white solid was washed with 10 mL pentane and dried under high vacuum (0.210 g,

65%). X-ray quality crystals were grown from C6H5Cl/pentane at -35 °C. 1H NMR (400 MHz,

C6D6): δ 7.20-7.10 (m, 6H, C6H3), 6.34 (s, 2H, IDipp-4,5-CH), 3.00 (br s, 4H, CH(CH3)2), 1.43

(d, 3JHH = 7 Hz, 12H, CH(CH3)2), 0.91 (d,

3JHH = 7 Hz, 12H, CH(CH3)2), 0.35 (s, 18H,

(CH3)3Si).11

B{1H} NMR (96 MHz, C6D6): δ 3.7 (s).

13C{

1H} NMR (101 MHz, C6D6, NCN not

observed ): δ 145.4 (C6H3), 133.9 (C6H3), 130.7 (C6H3), 128.3 (C6H3), 124.6 (C6H3), 122.5

(IDipp-4,5-CH), 29.1 (CH(CH3)2), 25.2 (CH(CH3)2), 23.4 (CH(CH3)2), 7.3 (s, (CH3)3Si).

29Si{

1H} NMR (99 MHz, C6D6): δ 0.04 (s, (CH3)3Si). Elemental Analysis for C33H54BCl2N3Si2:

C, 62.84; H, 8.63; N, 6.66. Found: C, 62.96; H, 9.07; N, 6.86.

168

Synthesis of 5-11: A solution of IDipp (0.185 g, 0.386 mmol) in 5 mL of C6H6 was added at

room temperature to a stirring solution of (Me3Si)2NBCl2 (0.114 g, 0.386 mmol) in 5 mL of

C6H6. The solution was left stirring overnight and then filtered over a pad of celite. The solvent

was then removed in vacuo and the residue extracted with 5 mL pentane which was left at -35 °C

for 24 hours to yield colorless crystals (0.174 g, 71%). 1H NMR (400 MHz, C6D6): δ 7.21 (m,

2H, C6H3), 7.08 (br s, 2H, C6H3), 7.06 (br s, 2H, C6H3), 6.24 (s, 2H, IDipp-4,5-CH), 2.72 (septet,

3JHH = 7 Hz, 4H, CH(CH3)2), 1.45 (d,

3JHH = 7 Hz, 12H, CH(CH3)2), 1.03 (d,

3JHH = 7 Hz, 12H,

CH(CH3)2), 0.21 (s, 9H, (CH3)3Si). 11

B{1H} NMR (96 MHz, C6D6): δ 15.8 (s).

13C{

1H} NMR

(101 MHz, C6D6, NCN not observed ): δ 145.4 (C6H3), 133.9 (C6H3), 130.7 (C6H3), 129.0

(C6H3), 124.3 (C6H3), 122.5 (IDipp-4,5-CH), 29.2 (CH(CH3)2), 25.2 (CH(CH3)2), 23.4

(CH(CH3)2), 3.7 (s, (CH3)3Si). 29


Analysis for C30H45BClN3Si: C, 69.02; H, 8.69; N, 8.05. Found: C, 68.84; H, 8.75; N, 8.18.

Synthesis of 5-12: A solution of 5-2 (0.100 g, 0.182 mmol) in 5 mL C6H6 was degassed and put

under 1 atm of CO2. The orange solution turns pale yellow within two minutes. The solution was

left stirring under an atmosphere of CO2 for 2 hours before the solvent was concentrated to 1 mL

and 15 mL of pentane were added to precipitate the product as an off-white solid which was

dried under high vacuum (0.093 g, 86%). X-ray quality crystals were grown from C6H6/pentane.

1H NMR (400 MHz, C6D6): δ 7.03 (m, 2H, C6H3), 6.87 (dd,

3JHH = 8 Hz,

4JHH = 1 Hz, 1H, C6H3),

3.19 (septet, 3JHH = 7 Hz, 1H, CH(CH3)2), 2.84 (dt,

2JHH = 14 Hz,

3JHH = 4 Hz, 1H, C6H10), 2.43

(dt, 2JHH = 14 Hz,

3JHH = 4 Hz, 1H, C6H10), 2.34 (septet,

3JHH = 7 Hz, 1H, CH(CH3)2), 2.12 ( br

m, 1H, Dipp-NCCH2), 1.62 (d, 3JHH = 7 Hz, 3H, CH(CH3)2), 1.54 (m, 2H, C6H10), 1.43 (m, 2H,

C6H10), 1.36 (m, 2H, C6H10), 1.20 (d, 3JHH = 7 Hz, 3H, CH(CH3)2), 1.16 (d,

3JHH = 7 Hz, 3H,

CH(CH3)2), 1.13 (s, 3H, Dipp-NC(CH3)2), 1.07 (m, 2H, C6H10), 0.99 (d, 3JHH = 7 Hz, 3H,

CH(CH3)2), 0.64 (s, 3H, Dipp-NC(CH3)2), 0.58 (s, 9H, (CH3)3Si). 11

B{1H} NMR (128 MHz,

C6D6): δ -1.9 (s). 13

C{1H} NMR (101 MHz, C6D6): δ 157.1 (BOCN), 145.0 (C6H3), 144.6

(C6H3), 134.0 (C6H3), 130.3 (C6H3), 126.4 (C6H3), 124.6 (C6H3), 80.0 (Dipp-NC(CH3)2), 57.9

(C6H10), 46.0 (Dipp-NCCH2), 37.1 (C6H10), 29.8 (Dipp-NC(CH3)2), 29.2 (CH(CH3)2), 29.1

(CH(CH3)2), 28.7 (CH(CH3)2), 25.7 (Dipp-NC(CH3)2), 25.4 (C6H10), 24.6 (CH(CH3)2), 24.1

(C6H10), 24.0 (CH(CH3)2), 23.7 (CH(CH3)2), 21.5 (C6H10), 1.2 ((CH3)3Si). 29

Si{1H} NMR (99

MHz, C6D6): δ 2.6 (s, (CH3)3Si). Elemental Analysis for C27H44BIN2O2Si: C, 54.55; H, 7.46; N,

4.71. Found: C, 54.40; H, 7.95; N, 4.93.

169


under 1 atm of CO2. The yellow solution turns colorless within two minutes. The solution was

left stirring under an atmosphere of CO2 for 1 hour before the solvent was concentrated to 1 mL

and 15 mL of pentane were added to precipitate the product as a white solid which was dried

under high vacuum (0.091 g, 83%). X-ray quality crystals were grown from C6H6/pentane. 1H

NMR (400 MHz, CD2Cl2): δ 7.45 (t, 3JHH = 8 Hz, 1H, C6H3), 7.32 (dd,

3JHH = 8 Hz,

4JHH = 1 Hz,

1H, C6H3), 7.24 (dd, 3JHH = 8 Hz,

4JHH = 1 Hz, 1H, C6H3), 2.99 (septet,

3JHH = 7 Hz, 1H,

CH(CH3)2), 2.55 (m, 1H, C6H10), 2.48 (septet, 3JHH = 7 Hz, 1H, CH(CH3)2), 2.32 (d,

2JHH = 13

Hz, 1H, Dipp-NCCH2), 2.29 (m, 1H, C6H10), 2.15 (d, 2JHH = 13 Hz, 1H, Dipp-NCCH2), 2.06 (m,

1H, C6H10), 1.91 (m, 1H, C6H10), 1.85 (m, 1H, C6H10), 1.74 (m, 1H, C6H10), 1.55 (s, 3H, Dipp-

NC(CH3)2), 1.49 (m, 4H, C6H10), 1.31 (m, 9H, CH(CH3)2), 1.21 (s, 3H, Dipp-NC(CH3)2), 1.03

(d, 3JHH = 7 Hz, 3H, CH(CH3)2), 0.29 (s, 9H, (CH3)3Si).

11B{

1H} NMR (128 MHz, CD2Cl2): δ

0.49 (s). 13

C{1H} NMR (101 MHz, CD2Cl2): δ 158.9 (BOCN), 145.1 (C6H3), 145.0 (C6H3),

134.0 (C6H3), 130.3 (C6H3), 126.3 (C6H3), 125.0 (C6H3), 81.1 (Dipp-NC(CH3)2), 58.7 (C6H10),

45.9 (Dipp-NCCH2), 37.9(C6H10), 37.3 (C6H10), 31.5 (Dipp-NC(CH3)2), 29.9 (CH(CH3)2), 29.6

(CH(CH3)2), 27.7 (CH(CH3)2), 26.7 (Dipp-NC(CH3)2), 25.5 (C6H10), 24.7 (CH(CH3)2), 24.4

(C6H10), 24.0 (CH(CH3)2), 23.6 (CH(CH3)2), 21.8 (C6H10), 1.1 ((CH3)3Si). 29

Si{1H} NMR (99

MHz, CD2Cl2): δ 2.2 (s, (CH3)3Si). Elemental Analysis for C27H44BBrN2O2Si•(C6H6)0.25: C,

60.37; H, 8.09; N, 4.94. Found: C, 60.37; H, 8.57; N, 5.34.


under 1 atm of CO2. The yellow solution turns colorless instantaneously. The solution was left

stirring under an atmosphere of CO2 for 1 hour before the solvent was concentrated to 1 mL and

15 mL of pentane were added to precipitate the product as a white solid which was dried under

high vacuum (0.100 g, 91%). X-ray quality crystals were grown from C6H6/pentane. 1H NMR

(400 MHz, C6D6): δ 7.08 (t, 3JHH = 8 Hz, 1H, C6H3), 7.03 (dd,

3JHH = 8 Hz,

4JHH = 2 Hz, 1H,

C6H3), 6.95 (dd, 3JHH = 8 Hz,

4JHH = 2 Hz, 1H, C6H3), 2.86 (septet,

3JHH = 7 Hz, 1H, CH(CH3)2),

2.67 (dt, 2JHH = 14 Hz,

3JHH = 4 Hz, 1H, C6H10), 2.49 (m, 2H, Dipp-NCCH2 + CH(CH3)2), 1.76

(m, 1H, C6H10), 1.62 (m, 7H, Dipp-NCCH2 + C6H10), 1.50 (d, 3JHH = 7 Hz, 3H, CH(CH3)2), 1.44

(m, 2H, C6H10), 1.34 (d, 3JHH = 7 Hz, 3H, CH(CH3)2), 1.15 (d,

3JHH = 7 Hz, 3H, CH(CH3)2), 1.06

(d, 3JHH = 7 Hz, 3H, CH(CH3)2), 0.97 (s, 3H, Dipp-NC(CH3)2), 0.79 (s, 3H, Dipp-NC(CH3)2),

0.54 (s, 9H, (CH3)3Si). 11

B{1H} NMR (128 MHz, C6D6): δ 1.6 (s).

13C{

1H} NMR (101 MHz,

170

C6D6): δ 159.1 (BOCN), 144.6 (C6H3), 144.5 (C6H3), 130.2 (C6H3), 125.6 (C6H3), 125.0 (C6H3),

124.8 (C6H3), 80.4 (Dipp-NC(CH3)2), 58.4 (C6H10), 45.2 (Dipp-NCCH2), 36.3 (C6H10), 35.9

(C6H10), 30.2 (Dipp-NC(CH3)2), 29.7 (CH(CH3)2), 29.4 (CH(CH3)2), 27.3 (CH(CH3)2), 27.2

(Dipp-NC(CH3)2), 25.3 (C6H10), 24.9 (CH(CH3)2), 24.5 (C6H10), 24.2 (CH(CH3)2), 22.6

(CH(CH3)2), 21.7 (C6H10), 1.3 ((CH3)3Si). 29

Si{1H} NMR (99 MHz, C6D6): δ 0.8 (s, (CH3)3Si).

Elemental Analysis for C27H44BClN2O2Si: C, 64.47; H, 8.82; N, 5.57. Found: C, 63.98; H, 9.32;

N, 5.49.


171

Figure 5.4.2 11

B{1H} NMR spectrum of 5-1 in C6D6.

Figure 5.4.3 13


172

Figure 5.4.4 29

Si{1H} NMR spectrum of 5-1 in C6D6.

Figure 5.4.5 11


173


Figure 5.4.7 13


174

Figure 5.4.8 29












The heavy



175



2) and Fo










176


5-1 5-2 5-3 5-4

Formula C6H18BI2NSi2 C26H44BIN2Si C26H44BBrN2Si C50H64B2N2Si

wt 425.00 550.43 503.44 742.74


Space group C2/c P2/c P21/n P-1

a(Å) 15.6776(10) 14.3428(5) 9.8668(6) 12.4924(11)

b(Å) 8.5777(5) 10.6121(4) 16.8993(11) 13.0727(11)

c(Å) 12.6262(13) 21.2246(7) 16.6423(12) 15.2439(14)

(deg) 90.00 90.00 90.00 92.753(5)

(deg) 118.583(2) 94.641(1) 91.432(2) 94.776(4)

(deg) 90.00 90.00 90.00 113.285(4)

V(Å3) 1491.0(2) 3219.9(2) 2774.1(3) 2269.8(3)

Z 4 4 4 2

d(calc) gcm

–3

1.893 1.135 1.205 1.087

R(int) 0.0177 0.0379 0.0634 0.0589

, mm–1

4.342 1.045 1.540 0.086

Total data 1712 7377 6377 7891

>2(FO2) 1584 5527 3915 4441

Variables 59 289 280 506

R (>2) 0.0183 0.0339 0.0449 0.0649

Rw 0.0408 0.0821 0.1008 0.1977

GOF 1.126 1.047 1.015 1.031

177


5-5 5-6 5-7 5-8

Formula C70H118B2Cl4N4Si4 C26H44BClN2Si C50H44B2F20N2Si C60H90B2I2N6Si2

wt 1291.46 458.98 1102.58 1226.98


Space group P21/c P21/n P2/c P-1

a(Å) 19.4594(16) 11.1637(7) 19.594(2) 12.6172(12)

b(Å) 18.5314(13) 10.1237(6) 15.6615(18) 16.7229(17)

c(Å) 22.2381(19) 23.8515(14) 17.5583(17) 18.938(2)

(deg) 90.00 90.00 90.00 90.760(3)

(deg) 114.504(2) 97.853(3) 110.206(3) 106.310(3)

(deg) 90.00 90.00 90.00 111.827(3)

V(Å3) 7297.0(10) 2670.4(3) 5056.5(9) 3528.9(6)

Z 4 4 4 2

d(calc) gcm–3

1.176 1.142 1.448 1.155

R(int) 0.0928 0.0462 0.0420 0.0775

, mm–1

0.270 0.204 0.158 0.961

Total data 12845 6153 8904 12384

>2(FO2) 7651 4405 6096 7519

Variables 837 280 707 649

R (>2) 0.0667 0.0497 0.0543 0.0506

Rw 0.1836 0.1270 0.1583 0.1178

GOF 1.007 1.027 1.017 0.910

178

Table 5.4.3 Select crystallographic parameters for 5-10, 5-12 to 5-14.

5-10 5-12 5-13 5-14

Formula C33H54BCl2N3Si2 C27H44BIN2O2Si C27H44BBrN2O2Si C27H44BClN2O2Si

wt 630.68 594.44 547.45 502.99

Cryst. syst. Orthorhombic Monoclinic Monoclinic Monoclinic

Space group P212121 C2/c P21/n P21/n

a(Å) 12.7630(7) 40.906(4) 10.7506(9) 10.8576(10)

b(Å) 14.5858(8) 11.0189(8) 15.3661(12) 15.1405(14)

c(Å) 22.6290(11) 16.0649(14) 17.8097(14) 17.7482(17)

(deg) 90.00 90.00 90.00 90.00

(deg) 90.00 100.112(7) 104.526(3) 104.260(4)

(deg) 90.00 90.00 90.00 90.00

V(Å3) 4212.6(4) 7128.6(11) 2848.0(4) 2827.7(5)

Z 4 8 4 4

d(calc) gcm–3

0.994 1.108 1.277 1.182

R(int) 0.0215 0.0690 0.0652 0.0540

, mm–1

0.233 0.953 1.511 0.203

Total data 9595 6176 5014 4973

>2(FO2) 8844 4280 3830 3452

Variables 385 307 307 307

R (>2) 0.0329 0.0618 0.0593 0.0457

Rw 0.0821 0.1496 0.1295 0.1128

GOF 1.042 1.063 1.167 1.016

179

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182

Chapter 6 A Room Temperature Stable Organoboron Isoelectronic with

Singlet Carbenes

6.1 Introduction

6.1.1 Borylenes: Group 13 Carbene Analogues

Low-valent main-group element derivatives have been a subject of considerable interest. Among

them, singlet carbenes A have arguably been the most widely studied (Scheme 6.1.1). These

species feature a carbon center with a lone pair and a vacant orbital, and are therefore both Lewis

acids and bases. Despite their expected high reactivity, many types of carbenes1-5

, as well as their

higher group-14 counterparts6, are stable at room temperature. On the other hand, there is only

one nitrene B7, which has been isolated, and no borylenes C.

Scheme 6.1.1 Schematic representation of singlet carbenes A, nitrenes B, borylenes C, and

Lewis base-borylene adducts D.

Borylenes C have a lone pair, but also two vacant orbitals, which make them extremely unstable.

They are accessible under drastic reaction conditions such as the preparation of the

fluoroborylene BF at high temperatures as was reported by Timms and co-workers in 19678, and

no free borylene has been isolated under synthetically useful conditions. Although borylenes are

often considered as the group 13 element analogues of carbenes, they are not isoelectronic with

carbenes since they possess one lone pair but two vacant orbitals. To fulfill the isoelectronic

criteria, a Lewis base should be appended to borylenes C, as shown in D. All attempts to isolate

Lewis base stabilized borylenes D have so far failed. For example, Robinson and co-workers9

reported that the reduction of the IDipp-BBr3 adduct led to the formation of the neutral diborene

183

in very low yields, a compound that possesses a boron-boron double bond (Scheme 6.1.2). This

species could be regarded as the dimer of the IDipp-BH borylene.

Scheme 6.1.2 Synthesis of a stable diborene stabilized by NHCs.

Curran and co-workers10

have shown that the reduction of (IDipp)BHCl2 led to the formation of

the borane shown in Scheme 6.1.3, which formally results from the intramolecular insertion of a

transient borylene into the CH bond of the iPr group of the Dipp substituent.

Scheme 6.1.3 Formation of a borane through C-H activation of a transient borylene.

In an analogous reaction, Braunschweig and co-workers11

observed that the reduction of

(IMe)BHCl2, in the presence of naphthalene, afforded a borirane (Scheme 6.1.4) that is described

as the trapping product of the transient derivative borylene of type D. These reactions represent

the expected high reactivity of these electron deficient species.

Scheme 6.1.4 Formation of a borirane by trapping of a transient borylene.

184

More recently, Bertrand and co-workers12

have reported the synthesis of a bis-CAAC stabilized

borylene through the reduction of the (CAAC)BBr3 adduct (Scheme 6.1.5) and developed a more

general route to synthesize bis-carbene-BH species13

which are isoelectronic with amines.

Scheme 6.1.5 Synthesis of a bis-CAAC-borylene.

We believe that the borylene-Lewis base adducts of type D are accessible and could be isolated.

These compounds are isoelectronic with carbenes and therefore most of the stabilization modes

known for carbenes should be applicable for the borylene adducts (L)BR.

6.1.2 Transition Metal Borylene Complexes

While free borylenes have yet to be isolated, borylene fragments have been isolated in the

coordination sphere of transition metals where they are generated.14-16

While there are different

types of borylene metal complexes14

only terminal borylenes, which feature a 2-coordinate boron

center will be discussed here.

Borylenes bind to metal centers through σ as well as π-back donation (Figure 6.1.1) where, for

terminal transition metal borylene complexes, the sigma donation exceeds π acceptance.14

This

leads to a buildup of positive charge on boron making it more susceptible to nucleophilic attack

which results in its kinetic instability. This was lessened and in some cases eliminated through

the introduction of sterically encumbered substituents on the boron center.17,18

185

Figure 6.1.1 Orbital interaction between borylenes and metal fragments.

The same effect is achieved through the introduction of strong π-donor substituents (such as

amino groups) on the boron center.19,20

The first borylene complexes were prepared via double

salt elimination reactions using dihaloboranes (Scheme 6.1.6).17,18

Scheme 6.1.6 Synthesis of the first terminal borylene complexes.

The potential of using these complexes as borylene sources for organic synthesis under standard

conditions was shown in the reaction where the borylene fragment transfers to alkynes forming

borirenes.21,22

6.1.3 CO Adducts of Carbenes and of Boranes

Carbenes over the last ten years have been shown to mimic transition metals and activate small

molecules such as H2 and CO.23

In contrast with NHCs24

, more electrophilic stable singlet

carbenes, such as CAACs25

and diamidocarbenes (DACs)26

, readily react with CO to give the

corresponding adducts (Scheme 6.1.7).

186

Scheme 6.1.7 CO fixation to a CAAC and a DAC.

Boranes on the other hand do not form stable adduct with CO and have not been experimentally

shown to activate H2 on their own. Willner and co-workers reported in 2002 the formation of a

tris(trifluoromethyl)borane carbonyl adduct (Scheme 6.1.8) by the solvolysis of K[B(C6F5)4] in

concentrated sulfuric acid.27,28

This compound has a melting point of 9 °C and decomposes

rapidly above that temperature with CO dissociation being the first step. Poor quality single

crystals can only be grown near -70 °C.

Scheme 6.1.8 Synthesis of tris(trifluoromethyl)borane carbonyl adduct.

Another example was reported by the Piers group in 2012 where they isolated a CO adduct of

pentafluoropentaphenylborole (Scheme 6.1.9).29

This reaction is reversible and under vacuum

results in the rapid reformation of the free borole.

Scheme 6.1.9 Synthesis of pentaarylborole-CO adduct.

187

The most recent example was reported by Erker and co-workers where they isolate the CO

adduct of Piers borane, HB(C6F5)2, (Scheme 6.1.10).30

Single crystals of the adduct were

obtained under an atmosphere of CO at -40 °C and this system loses CO at room temperature

regenerating Piers borane.

Scheme 6.1.10 Synthesis of Piers borane-CO adduct.

To demonstrate the carbene-like and electrophilic character of borylenes, preliminary reactivity

studies with small molecules, like H2 and CO are of interest.


6.2.1 Reduction Route to Borylene Synthesis

The first successful isolation of a carbene31,32

followed the prediction in 1980 by Pauling33

that

substituents of opposing electronic properties (push-pull effect) should stabilize singlet carbenes

by preserving the electroneutrality of the carbon center. The same strategy utilized to prepare the

first carbene is used to synthesize the boron analogue. As the push-substituent, a

bis(trimethylsilyl)amino group was chosen because an amino group is arguably a better π-donor

than a phosphino moiety, and silyl groups were chosen to further stabilize the electron-deficiency

at boron via the well-known -effect. As a Lewis base, and the pull-substituent, a CAAC was

chosen as it is a strong -acceptor23

and therefore can withdraw excessive electron-density from

boron center. Having already made the CAAC adduct of the

bis(trimethylsilylamino)dichloroborane, namely 5-5, its reduction chemistry was probed.

Reactions with KC8 produced intractable mixtures and as such Co(Cp*)2 was used as the

reducing agent. The choice of solvent for the reduction is important since 5-5 in solution, over

time, converts to the CAAC stabilized iminoborane (5-6) as was discussed in the previous

chapter. This reaction is much faster in polar organic solvents and as such benzene was chosen as

the solvent for reduction. Thus, adding one equivalent of Co(Cp*)2 to a C6H6 suspension of 5-5

188

and after stirring for four hours, followed by workup, the radical 6-1 was isolated as a yellow

solid in 74% yield (Scheme 6.2.1).


Single crystals suitable for X-ray diffraction studies were grown and the formulation of 6-1 was

confirmed as [(Cy-CAAC)BClN(SiMe3)2]• (Figure 6.2.1). The geometry around boron is

perfectly planar where the sum of angles at B is 359.94°. The B-N distance is 1.460(3) Å which

falls within the range of B-N single bond lengths. The B-C distance is 1.527(3) Å which is

shortened and falls in the range of typical B-C single and double bonds (1.59-1.48 Å

respectively).34

The CAAC C-N distance is 1.378(3) Å which is slightly elongated compared to

typical CAAC adducts; similarly, the B-Cl distance is 1.831(3) Å which is shorter than that

typically observed.35

189

Figure 6.2.1 POV-Ray depiction of the molecular structure of 6-1. C: black, N: aquamarine, Si:


This indicates that the unpaired electron is delocalized on the Cy-CAAC ligand and the planar

geometry around the boron center indicates delocalization over a p orbital which makes this

species a π-type radical. The radical 6-1 was analyzed by EPR spectroscopy in toluene at 280 K

as well as by DFT calculations.

The SOMO of 6-1 (B3LYP/6-311+g** level of theory) formally results from the bonding

interaction of the LUMO of the Cy-CAAC moiety and the * orbital of the B-Cl fragment

(Figure 6.2.2). This indicates a spin delocalization across the -system, which was also

supported by a Mulliken analysis of the spin density (N: 26%; C: 42%; B: 28%; Cl: 2%). These

theoretical results are in line with the simulation of the pattern of the experimental EPR spectra

of 6-1 in solution, which requires the introduction of isotropic hyperfine coupling constants with

boron, as well as nitrogen and chlorine (Figure 6.2.3).

190

Figure 6.2.2 Representation of the SOMO of 6-1 with isovalue at 0.06 a.u.; hydrogen atoms are


Figure 6.2.3 Experimental X-band EPR spectrum of 6-1 in toluene at 280 K (green) and

simulated EPR spectrum (blue) with the following set of hyperfine coupling constants: a(B) =

4.7, a(N) = 18.4 and a(Cl) = 2.5 MHz.

This neutral CAAC-stabilized boron-centered radical is reminiscent to the arylboryl radical

recently prepared by Braunschweig and co-workers (Scheme 6.2.2).35

191

Scheme 6.2.2 Synthesis of a neutral boron-containing radical stabilized by a CAAC.

Thanks to the stability of 6-1 in solution the second reduction with one equivalent of Co(Cp*)2

was performed in benzene at 25 °C for 8 h where, upon workup, 6-2 was isolated as a red solid

in 86% yield. The 11

B{1H} NMR of 6-2 shows a broad singlet at 83.7 ppm and the

29Si{

1H}

NMR spectrum shows a signal at 7.2 ppm. The 1H NMR spectrum reveals a peak at 0.13 ppm

corresponding to the Me3Si group and it integrates to 18H which indicates that the N(SiMe3)2

moiety remains intact. The chemical shift observed in the 11

B{1H} NMR spectrum is more

downfield compared to aminoboraalkenes (R2C=BNR’2) (+ 59 to +71 ppm)36-39

and in the range

of transition metal stabilized terminal aminoborylenes (LnM=BNR2) (+ 67 to + 92 ppm).14

A

single crystal X-ray study was performed which confirmed the formulation of 6-2 as

(Cy-CAAC)BN(SiMe3) (Figure 6.2.4).

192


blue, B: yellow-green. H-atoms omitted for clarity.

The geometry around boron is slightly bent with a C-B-N angle of 174.8(3)°. The B-C distance

is 1.401(5) Å which is significantly shorter than those reported for compounds 5-6 and 6-1 and is

indicative of a B-C double bond. The B-N distance is 1.382(5) Å which is shorter than the B-N

bond in 6-1 and similar to that in 5-6 which indicates a double bond character.

DFT calculations at the 6-311g(d,p) level of theory well reproduce the solid state geometry of

6-2 [B-N: 1.383 Å; B-C: 1.412 Å; C-B-N angle 175.4°]. The highest occupied molecular orbital

(HOMO) results from a bonding interaction of the vacant * molecular orbital of the Cy-CAAC

moiety with the occupied p orbital of the boron atom, as expected from the stabilization of the

formal lone pair at the boron center by the -accepting Cy-CAAC ligand (Figure 6.2.5).

Similarly, the interaction of the lone pair at nitrogen with the formal empty p orbital at boron

results in a high-energy * molecular orbital (+0.16 eV). The latter is not even the lowest

unoccupied molecular orbital (LUMO), but the LUMO+2. However, a vibrational analysis

indicates that the C-B-N bending mode corresponds to an abnormally low energy frequency

(389 cm-1

). This suggests significant flexibility of the molecule along this coordinate and, indeed,

bending the C-B-N angle up to 155° has nearly no energetic cost (5.7 kcal.mol-1

). In marked

contrast with 6-2, the resulting bent structure 6-2* has pronounced electrophilicity, since the

formal empty p orbital at boron becomes sp2 hybridized, and is lower in energy. As a

193

consequence, the * orbital of the B-N moieties becomes the LUMO (Figure 6.2.5), its energy

being dramatically decreased by more than 0.6 eV. Consequently, although the minimum on the

energy hyper-surface of 6-2 corresponds to an apparently non-electrophilic molecule with a

nearly linear C-B-N alignment, organoboron 6-2 is expected to be highly electrophilic due to the

flexibility at the boron center.

Figure 6.2.5 a) and a’): highest occupied molecular orbital (HOMO) of 6-2, and of 6-2* with a

frozen C-B-N angle at 155°, respectively. b-d) and b’-d’) lowest unoccupied molecular orbitals

(LUMO) of 6-2 and 6-2*, respectively.

Based on these results small molecule activation with 6-2 which can easily bend to form 6-2*

was attempted.

194

6.2.2 Reactivity of Borylenes

Exposing a solution of 6-2 in pentane to 1 atm. of 13

CO, followed by workup, resulted in the

formation of 6-3 as a pink solid in 80% yield (Scheme 6.2.3). The 11

B{1H} NMR of 6-3 shows a

resonance with a significant upfield shift from 83.7 ppm for 6-2 to -3.4 ppm which is a doublet

with 1JBC of 87 Hz indicating a change to the coordination around the boron center. The

corresponding carbon of the 13

CO fragment is observed as a broad multiplet at 236.3 ppm in the

13C{

1H} NMR spectrum. A signal is observed at 3.01 ppm in the

29Si{

1H} NMR spectrum

indicating the presence of the (Me3Si)2N moiety and a single crystal X-ray diffraction study

confirmed the formulation of 6-3 as (Cy-CAAC)B(CO)[N(SiMe3)2] (Figure 6.2.6).


The geometry around boron is perfectly planar where the sum of angles at B is 360°. The

B-CCAAC distance is 1.506(4) Å which is lengthened compared to 6-2 but still shorter than a

typical B-C single bond. The linear B-C≡O unit (172.7(3)°) showed a B-CCO distance of

1.529(5) Å, which is significantly shorter than previously reported B-CO distances (1.609(3) to

1.601(2) Å),29,30

indicative of a B-C bond halfway between typical BC single and double bonds.

The C-O distance is 1.091(3) Å which is slightly shorter than previously reported BC≡O

distances (1.115(3) to 1.107(2) Å) and is shorter than that of free CO (1.1281 Å as determined by

microwave spectroscopy)40

. The IR spectrum of 6-3 in the solid state shows a 12

CO stretching

frequency of 1956 cm-1

which is much lower than free 12

CO (2143 cm-1

) and is consistent with

the IR stretching frequency predicted by DFT calculations. The B-N distance is 1.526(4) Å

which is longer than that observed in 6-2.

195


blue, B: yellow-green, O: red. H-atoms omitted for clarity.

Compound 6-3 is a rare example of a stable, isolable CO adduct of a borane with very few

reported examples of CO adducts of organoboranes.28-30,41

To our knowledge, 6-3 is the first

example of a CO adduct of a formally B(+1) species that is also stable both in the solid state and

in solution where this reaction is not reversible either under vacuum or upon heating to 100 °C.

Based on the observed reactivity with CO we were also interested in the reactivity of 6-2 with

H2. Exposing a solution of 6-2 in toluene to 4 atm of H2 followed by workup resulted in the

isolation of 6-5 as pale yellow crystals in 85% yield (Scheme 6.2.4).


196

The 11

B{1H} NMR of 6-5 shows a broad singlet at 51.2 ppm which is indicative of a three- and

not a four-coordinate boron center. The 1H NMR spectrum shows peaks corresponding to the

Cy-CAAC and N(SiMe3)2 moieties along with a singlet at 5.55 ppm and a doublet at 3.62 ppm

with 3JHH = 6 Hz. These signals were assigned to the BH and Dipp-NCHCCy, respectively, and

the corresponding carbon signal is observed at 67.3 ppm in the 13

C{1H} NMR spectrum.

A single crystal X-ray diffraction study confirmed that the isolated compound was not the boron

dihydride 6-4, but the monohydride 6-5 (Figure 6.2.7). The geometry around boron is perfectly

planar where the sum of angles at B is 360°. The B-CCAAC-H distance is 1.582(2) Å which is

typical of a B-C single bond and the B-N distance is 1.4243(19) Å, similar to that observed in

6-1. The hydride was located from the difference density map and the B-H distance is

1.118(16) Å.


blue, B: yellow-green. H-atoms other than B-H and Cy-CAAC-CH omitted for clarity.

The formation of 6-5 results from a formal 1,2-addition through the B-C bond of 6-2 but it has

been shown42,43

that CAAC-borohydride adducts, such as 6-4, can rearrange via 1,2-hydride

migration, and therefore it is quite likely that the first step of the reaction is an oxidative addition

of hydrogen at the boron center. Such a two-step process leading to 6-5 has been confirmed by

DFT calculations where both steps are strongly exergonic (G = -18 and -12 kcal.mol-1

,

197

respectively). Not surprisingly, the rate-limiting step is the oxidative addition

(Gǂ = +25 kcal.mol-1

) with hydride migration having a very low activation barrier

(Gǂ = +4.6 kcal.mol-1

). The first step corresponds to an early transition state (Figure 6.2.8)

which is reminiscent of the homolytic bond cleavage of H2 by electrophilic metals.44,45

Figure 6.2.8 Calculated transition state for the activation of H2 by 6-2.

Indeed, the approach of dihydrogen results in the primary interaction of the low-lying LUMO of

the bent 6-2* with the bonding σ orbital of H2 (Figure 6.2.9 a). The concomitant secondary back-

donation from the HOMO of 6-2* to the anti-bonding σ* orbital of H2 finally triggers the

cleavage of the activated H-H bond (Figure 6.2.9 b). Importantly, despite multiple attempts, a

transition state leading directly to 6-5 from 6-2 by direct addition of dihydrogen on the B-C bond

was not found.

Figure 6.2.9 a) Primary interaction between the LUMO of 6-2* and theorbital of H2. b)

Secondary interaction between the HOMO of 6-2* and the * orbital of H2.

Compound 6-2 shows reactivity unprecedented before with boron species where it forms a strong

adduct with CO and is capable of H2 activation.

198

6.3 Conclusion

The synthesis of a group-13 derivative, which is isoelectronic with singlet carbenes, namely a

borylene was described. This compound, which is stabilized by a push-pull effect, is formed by

the double reduction of a CAAC adduct of bis(trimethylsilylamino)dichloroborane, going

through a boron based radical. Similarly to singlet carbenes, it reacts with carbon monoxide and

hydrogen, but in contrast with the former, the latter acts as an electrophile and therefore mimics

the behavior of metals.




a VAC Atmospheres glove box and a Schlenk vacuum-line. Hexanes and pentane were purified

with a Grubbs-type column system manufactured by Innovative Technology and dispensed into

thick-walled glass Schlenk bombs equipped with Young-type Teflon valve stopcocks.

Anhydrous benzene was purchased from Sigma Aldrich and stored over molecular sieves.

Toluene-d8 was dried over CaH2 and benzene-d6 was dried over Na metal and vacuum-

transferred into a Young bomb. All solvents were thoroughly degassed after purification (three

freeze-pump-thaw cycles). NMR spectra were recorded at 25 °C on a Bruker Avance 400 MHz

spectrometer or Agilent 500 MHz. 13

CO was purchased from Sigma-Aldrich and used without

further purification. Chemical shifts are given relative to SiMe4 and referenced to the residual

solvent signal (1H,


29Si: Me4Si,

11B: BF3

.Et2O). In some

instances, signal assignment was derived from two-dimensional NMR experiments. Chemical

shifts are reported in ppm and coupling constants as scalar values in Hz. Combustion analyses

were performed in house employing a Perkin-Elmer CHN Analyzer.


Synthesis of 6-1: To a mixture of 5-5 (0.100 g, 0.176 mmol) and Co(Cp*)2 (0.058 g,

0.176 mmol) was added 10 mL of C6H6. The reaction mixture was left stirring at room

temperature for 6 hours before the volatiles were removed. The product was extracted into

pentane (15 mL) and filtered over a pad of celite. The solvent was then removed in vacuo

yielding a pale yellow solid (0.070 g, 74%). X-ray quality crystals were grown by slow

199

evaporation of a pentane solution at room temperature. Elemental Analysis for C29H53BClN2Si2:

C, 65.45; H, 10.04; N, 5.26. Found: C, 64.92; H, 10.21; N, 5.41.

Synthesis of 6-2: To a mixture of 6-1 (0.200 g, 0.376 mmol) and Co(Cp*)2 (0.124 g, 0.376

mmol) was added 15 mL of C6H6. The reaction mixture was left stirring at 25 °C for 8 hours it

was filtered over celite. The filtrate was concentrated to 1 mL and 15 mL of pentane was added

drop wise to precipitate residual [Co(Cp*)2][Cl]. The mixture was then filtered over a pad of

celite and the solvent was then removed in vacuo yielding a dark orange/red solid (0.150 g,

86%). X-ray quality crystals were grown by slow evaporation of a benzene solution at room

temperature. 1H NMR (400 MHz, C6D6): δ 7.14 (s, 1H, C6H3), 7.12 (s, 1H, C6H3), 7.10 (s, 1H,

C6H3), 3.72 (d, 3JHH = 7 Hz, 2H, CH(CH3)2), 2.28 (d,

2JHH = 12 Hz, 2H, C6H10), 1.94 (s, 2H,

Dipp-NCCH2), 1.72-1.63 (m, 4H, C6H10), 1.58-1.47 (m, 4H, C6H10), 1.36 (s, 6H, Dipp-

NC(CH3)2), 1.33 (d, 3JHH = 7 Hz, 6H, CH(CH3)2), 1.30 (d,

3JHH = 7 Hz, 6H, CH(CH3)2), 0.13 (s,

18H, (CH3)3Si). 11

B{1H} NMR (96 MHz, C6D6): δ 83.7 (br s).

13C{

1H} NMR (101 MHz, C6D6,

Dipp-NCC-Cy not observed ): δ 151.8 (C6H3), 142.3 (C6H3), 128.6 (C6H3), 126.7 (C6H3), 124.1

(C6H3), 64.0 (Dipp-NC(CH3)2), 53.9 (C6H10), 47.0 (C6H10), 43.7 (C6H10 + Dipp-NCCH2), 28.0


(C6H10), 2.7 (s, (CH3)3Si). 29

Si{1H} NMR (99 MHz, C6D6): δ 7.2 (s, (CH3)3Si). Repeated

attempts to obtain EA were unseccussful. NMR spectra are included at the end of this section.

Synthesis of 6-3: A solution of 6-2 (0.100 g, 0.201 mmol) was dissolved in 2 mL pentane and

transferred to a tube bomb and sealed. The solution was degassed using three freeze-pump-thaw

cycles before being warmed to room temperature and charged with 1 atm. 13

CO. The mixture

was stirred at room temperature for 18 h yielding a pale red solution and pink solid. The volatiles

were removed in vacuo and a pink solid was obtained (0.085 g, 80%). X-ray quality crystals

were grown from pentane at -35 °C. 1H NMR (400 MHz, C6D6): δ 7.23 (m, 1H, C6H3), 7.12

(br s, 1H, C6H3), 7.10 (m, 1H, C6H3), 2.94 (d, 3JHH = 7 Hz, 2H, CH(CH3)2), 2.52 (m, 2H, C6H10),

1.77 (s, 2H, NCCH2), 1.69 (m, 5H, C6H10), 1.45 (d, 3JHH = 7 Hz, 6H, CH(CH3)2), 1.31 (m, 3H,

C6H10), 1.18 (d, 3JHH = 7 Hz, 6H, CH(CH3)2), 1.00 (s, 6H, Dipp-NC(CH3)2), 0.37 (s, 18H,

(CH3)3Si). 11

B{1H} NMR (96 MHz, C6D6): δ -3.4 (d,

1JBC = 87 Hz).

13C{

1H} NMR (101 MHz,

C6D6, Dipp-NCC-Cy not observed ): δ 236.3 (br m, B-CO), 148.9 (C6H3), 133.6 (C6H3), 129.8

(C6H3), 127.9 (C6H3), 125.6 (C6H3), 68.1 (Dipp-NC(CH3)2), 48.4 (C6H10), 37.4 (C6H10 +

Dipp-NCCH2), 30.2 (CH(CH3)2), 27.9 (Dipp-NC(CH3)2), 27.2 (CH(CH3)2), 25.4 (CH(CH3)2),

200

25.0 (C6H10), 22.9 (C6H10), 4.2 (s, (CH3)3Si). 29

Si{1H} NMR (99 MHz, C6D6): δ 3.01 (s,

(CH3)3Si). IR (solid) 1904 cm-1

(13

CO). Elemental Analysis for C30H53BN2OSi2: C, 68.67; H,

10.18; N, 5.34. Found: C, 68.25; H, 10.74; N, 5.45.

Synthesis of 6-5: A solution of 6-2 (0.075 g, 0.151 mmol) was dissolved in 5 mL toluene and

transferred to a tube bomb and sealed. The solution was degassed using three freeze-pump-thaw

cycles before being put under 4 atm. of hydrogen. The mixture was stirred at room temperature

for 24 h yielding a pale orange solution. The mixture was filtered over a plug of silica yielding a

yellow solution. The volatiles were removed in vacuo and the residue was dissolved in 2 mL of

pentane and left at -35 °C for 24 h. Pale yellow crystals were formed, the solvent was decanted

and crystals dried under high vacuum (0.064 g, 0.85%). X-ray quality crystals were grown from

pentane at -35 °C. 1H NMR (400 MHz, C6D6): δ 7.18 (m, 2H, C6H3), 7.11 (dd,

3JHH = 6 Hz,

4JHH = 3 Hz, 1H, C6H3), 5.55 (br s, 1H, Dipp-NCH-BH), 4.27 (d,

3JHH = 7 Hz, 1H, CH(CH3)2),

3.62 (d, 3JHH = 6 Hz, 1H, Dipp-NCH-BH) 3.48 (d,

3JHH = 7 Hz, 1H, CH(CH3)2), 2.41 (d,

2JHH =

12 Hz, 1H, C6H10), 2.09 (d, 2JHH = 13 Hz, 1H, Dipp-NCCH2), 1.91 (d,

2JHH = 12 Hz, 1H, C6H10),

1.82 (d, 2JHH = 13 Hz, 1H, Dipp-NCCH2), 1.76-1.65 (m, 4H, C6H10), 1.50-1.41 (m, 4H, C6H10),

1.39 (s, 3H, Dipp-NC(CH3)2), 1.36 (d, 3JHH = 7 Hz, 3H, CH(CH3)2), 1.35 (d,

3JHH = 7 Hz, 3H,

CH(CH3)2), 1.30 (d, 3JHH = 7 Hz, 3H, CH(CH3)2), 1.29 (d,

3JHH = 7 Hz, 3H, CH(CH3)2), 1.19 (s,

3H, Dipp-NC(CH3)2), 0.23 (s, 9H, (CH3)3Si), 0.20 (s, 9H, (CH3)3Si). 11

B{1H} NMR (96 MHz,

C6D6): δ 51.2 (br s). 13

C{1H} NMR (101 MHz, C6D6, Dipp-NCC-Cy not observed): δ 153.2

(C6H3), 150.8 (C6H3), 141.2 (C6H3), 126.7 (C6H3), 124.6 (C6H3), 124.4 (C6H3), 67.3 (Dipp-NCH-

BH), 63.7 (Dipp-NC(CH3)2), 52.7 (C6H10), 48.2 (C6H10), 41.1 (Dipp-NCCH2), 37.4 (C6H10), 30.7

(Dipp-NC(CH3)2), 28.4 (CH(CH3)2), 27.8 (CH(CH3)2), 27.0 (CH(CH3)2), 26.9 (C6H10), 26.7

(Dipp-NC(CH3)2), 26.2 (CH(CH3)2), 25.2 (CH(CH3)2), 25.1 (CH(CH3)2), 24.8 (C6H10), 23.7

(C6H10), 4.8 ((CH3)3Si), 4.3 ((CH3)3Si). 29

Si{1H} NMR (99 MHz, C6D6): δ 8.6 (s, (CH3)3Si), 5.7

(s, (CH3)3Si). Elemental Analysis for C29H55BN2Si2: C, 69.84; H, 11.12; N, 5.62. Found: C,

69.39; H, 11.50; N, 5.80.

201


Figure 6.4.2 11


202

Figure 6.4.3 13


Figure 6.4.4 29


203











The heavy





2) and Fo










204


6-1 6-2 6-3 6-5

Formula C29H53BClN2Si2 C29H53BN2Si2 C30H53BN2OSi2 C29H55BN2Si2

Wt 532.17 496.72 524.73 498.74

Cryst. syst. Monoclinic Monoclinic Triclinic Monoclinic

Space group Cc P21/n P-1 P21/n

a(Å) 9.5806(7) 11.3825(12) 9.4580(8) 11.2220(8)

b(Å) 21.5850(19) 17.672(2) 11.4105(9) 17.4420(12)

c(Å) 15.5951(11) 15.5106(15) 16.9815(13) 15.9634(11)

(deg) 90.00 90.00 102.223(4) 90.00

(deg) 97.295(4) 92.331(6) 96.357(4) 95.365(2)

(deg) 90.00 90.00 114.021(4) 90.00

V(Å3) 3198.9(4) 3117.4(6) 1590.6(2) 3110.9(4)

Z 4 4 2 4

d(calc) gcm–3

1.105 1.058 1.096 1.065

R(int) 0.0255 0.1143 0.0635 0.0392

, mm–1

0.214 0.132 0.135 0.133

Total data 6923 5492 5595 7139

>2(FO2) 6421 3413 3616 5659

Variables 317 307 325 315

R (>2) 0.0446 0.0628 0.0593 0.0391

Rw 0.1111 0.1778 0.1492 0.1034

GOF 1.035 1.018 1.019 1.023

205

References

(1) Díez-González, S. N-Heterocyclic carbenes, from laboratory curiosities to efficient

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Chapter 7 Summary

7.1 Summary

A new method of preparing ruthenium alkylidene complexes starting with bis-carbene RuHCl

species and alkenyl sulfides was developed. This new method is safe, high yielding, and uses

inexpensive starting materials. It also provides a route to bis-mixed carbene ruthenium

alkylidene complexes with a hemilabile tridentate carbene and conveniently installs both an

alkylidene fragment and a thiolate in one simple step. The use of ethyl vinyl sulfide, on the other

hand, resulted in the formation of Ru-alkyl and Ru-vinyl species.

The Ru-alkylidene complexes bearing the hemilabile tridentate NHC were either inactive or

minimally active for the standard metathesis tests. The species generated by the addition of one

equivalent of BCl3, however, showed improved activity for RCM, ROMP and CM either at room

temperature or at slightly elevated temperatures. In general, the catalysts which contain more

electron donating carbenes were more active and the catalysts with S(C6F5), as one of the anionic

ligands, were most active compared to the catalysts with the PhS- ligand. These species showed

activity in the cross metathesis of NBR and 1-hexene at different conditions. While they were

active, higher catalyst loadings and elevated temperatures were required to achieve similar

conversions as Grubbs II catalyst at room temperature.

Exchanging a chloride for an iodide resulted in enhanced metathesis activity for the standard

tests as well as for the CM of NBR with 1-hexene where catalytic olefin metathesis was observed

at room temperature. The bis-halide containing complexes showed the highest activity for all

standard metathesis tests without the need for a Lewis acid to initiate. This is presumably due to

the presence of the bulky iodides on the metal center which results in faster initiation. These

systems, however, too closely resemble Grubbs’ catalysts and were therefore not patented and

not tested further for the CM of NBR with 1-hexene.

Cyclic (alkylamino)carbenes were shown to stabilize iminoboryl moieties which have only been

previously stabilized in the coordination sphere of transition metals. These species were

characterized crystallographically and, depending on the halide size, directly formed through

elimination of Me3SiI, or through halide exchange for a non-coordinating anion after Me3SiX

209

elimination (X = Br, Cl). Some of the species were also shown to undergo [2+2] cycloaddition

with CO2.

CAACs were also used for the synthesis of a group-13 derivative, which is isoelectronic with

singlet carbenes, namely a borylene. This compound, which is stabilized by a push-pull effect,

was formed by the double reduction of a CAAC adduct of bis(trimethylsilylamino)

dichloroborane, going through a stable boron based radical. Similarly to singlet carbenes, it

reacted with carbon monoxide and hydrogen, but in contrast with the former, the latter acts as an

electrophile and therefore mimics the behavior of metals.

carbenes in ruthenium based olefin metathesis catalysts and … · ii carbenes in ruthenium based...

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