Nickel and Cobalt-Catalyzed Hydrofunctionalization Reaction of Alkene

DISSERTATION

Presented in Partial Fulfillment of the Requirements for the Degree Doctor of Philosophy in the Graduate School of The Ohio State University

Balaram Raya, M. S.

Graduate Program in Chemistry

The Ohio State University

2016

Dissertation Committee:

Professor T. V. RajanBabu, Advisor

Professor Craig Forsyth

Professor Jovica Badjic

Copyrighted by

Balaram Raya

2016

Abstract

Organic reactions catalyzed by metal complexes are an effective way to improve atom economy and environmental friendliness for many synthetic transformations.

Among the various synthetic transformations, hydrosilylation reaction has huge industrial applications for manufacturing consumer goods. The alkylsilanes from alkene hydrosilylation are widely used as raw materials in manufacturing silicon rubbers, molding implants and adhesive. The hydrosilylation reactions can also produce various organosilicon reagents, which are used in fine chemical synthesis for stereospecific oxidation and cross coupling reaction. Over the long decades, numerous reports on metal- catalyzed hydrosilylations include the use of platinum, palladium, rhodium, ruthenium, iridium, lanthanides and actinides, early transition metals, iron, cobalt to a limited extent

iPr nickel. This work has shown that readily accessible ( PDI)CoCl2 reacts with 2

o equivalents NaEt3BH at -78 C in toluene to generate a catalyst that effects highlyselective anti-Markovnikov hydrosilylation of the terminal double bond in alkene,

1,3- and 1,4-dienes. Primary and secondary silanes such as PhSiH3, Ph2SiH2 and

PhSi(Me)H2 react with a broad spectrum of dienes without affecting the configuration of the other double bond. A slight modification of the reaction conditions using a less reactive silane (OEt)2Si(Me)H leads to unprecedented and highly selective reduction of the terminal double bond with no contamination from the silane or reduction products of

ii the more substituted double bond. The major limitation for cobalt catalyzed hydrosilylation reaction using redox active PDI ligand is its terminal selectivity.

However, this active catalyst did not work for 1,1-disubstituted alkenes. In this connection, we also observed efficient cobalt catalyst system for hydrosilylation of 1,1- disubstituted alkenes using chelating phosphine ligand at room temperature, which is able to do hydrosilylation for numerous substrates such as alkene, vinyl arene, conjugated diene, 1,4-skipped diene and 1,1-disubstituted alkenes.

Carbocyclizations of α,ω-π-systems are extremely important and useful reactions for the synthesis of a variety of carbocyclic and heterocyclic compounds. Although metal catalyzed cyclization has been long known, controlling the selectivity (chemo- and regio-

) remains an important challenge in this field. Nickel complexes have been known to be specifically effective for cyclic homo-and co-oligomerization of alkenes, alkynes and dienes. During the past few years, through an approach that relied mostly on mechanistic insights and systematic examination of ligand effects, RajanBabu group has discovered a number of protocols for Ni(II)-catalyzed heterodimerization reactions of vinylarenes, selected 1,3-dienes and strained olefins. Substitution of one of the phenyl groups of triphenylphosphine with a 2-benzyloxy-(e.g., L18), 2-benzyloxy-methyl-(L19) or 2- benzyloxyethyl-(L20) phenyl moiety results in a set of simple ligands, which exhibit strikingly different behavior in various nickel (II)-catalyzed olefin dimerization reactions including related cycloisomerization of 1,6-dienes. Nickel(II)-catalyzed cycloisomerization of 1,6-dienes into methylenecyclopentanes, a reaction mechanistically related to the other heterodimerization reactions, is also uniquely affected by nickel(II)

iii complexes of L18, but not of L19 or L20. In an attempt to prepare authentic samples of the methylenecyclohexane products, nickel(II) complexes of N-heterocyclic carbene ligands were examined. In contrast to the phosphine, which gives the methylenecyclopentanes, methylenecyclohexanes are the major products in the N- heterocyclic carbine ligated nickel (II)-mediated reaction.

This dissertation discusses the ligand effect on hydrofuctionalization of alkenes using nickel or cobalt metal complexes.

This dissertation is dedicated to my parents (Khadga Bd. Raya Chhetri and Indra Kumari

Raya Chhetri) and my family who always supported my academic aspirations

Acknowledgments

I am grateful to my respectable advisor Prof. T.V RajanBabu, for his invaluable assistance, guidance, innovative ideas and encouragement throughout my Ph.D. Under his guidance, I learned how to identify and pursue meaningful goals.

I would like to thank the members of my committee, Professor Craig Forsyth and

Professor Jovica D Badjic for their time and valuable comments, and the faculty of department of chemistry for constructive suggestions. I am grateful to Professor David J

Hart for his candid feedback and for his mentorship while teaching the graduate organic course.

I would like to thank my parents, Mr. Khadga Bahadur Raya (Chhetri) and Mrs.

Indra Kumari Raya (Chhetri) for their constant encouragement and financial support.

Specific thanks to my beloved wife Mrs. Sulakshana Ghimire and my son Zenil Jung

Raya for their support and encouragement during my tough time. Sulakshana has supported me through some of my difficult moments and helped me to enjoy some of the best moment of my life. I am grateful for my wife and son for their love and kindness. In addition, I would like to thank my brothers (Junga and Rudra) and sisters (Durga,

Mamata and Sabitra) family for their constant encouragement.

I would acknowledge Dr. Tanya Whitmer, NMR lab manager, Mrs. Rebecca

Patton and Mrs. Jennifer Hambach, office support specialist for their consistent help.

I am grateful for my colleagues, Dr Souvagya Biswas, Stanley Jing and Dr Vagulejan

Balasanthiran sharing their insights and instruction on cobalt chemistry.

Last but not least, I would like to thank all the past and present RajanBabu group members specifically Dr. Yam N Timsina, Dr. Kendra Dewese, Krishnaja, Bryan,

Milauni for their help and encouragement.

I am in debated to my father-in-law Narendra Kumar Ghimire and mother-in-law

Sita Devi Chauhan for their words of encouragement during my tough times. I am grateful for my sister-in-laws (Srijana and Namuna) and their family, brother-in-law

(Anurodh and Anupam) for their love and encouragement.

I would like to acknowledge financial support by National Science Foundation and National Institute of Health, for supporting our research endeavors. I would also like to acknowledge The Ohio State University Department of Chemistry and Biochemistry for giving me the opportunity to enrich my educational goals.

I am deeply thankful for the friends I have made here at The Ohio State

University and Nepalese Community in Columbus

vii

Vita

November 2000 ...... M.Sc. in Chemistry,

Tribhuvan University,

Kathmandu, Nepal

2001-2009 ...... Lecturer

Damak Multiple Campus, Nepal

2009-2011 ...... Teaching and Research Assistant

Western Illinois University, IL

2011-2015 ...... Graduate Teaching Assistant, Department of

Chemistry and Biochemistry, The Ohio

State University

2016 ...... Graduate Research Assistant, Department of

Chemistry and Biochemistry, The Ohio

State University

Publications

Raya, B.; Jing, S.; RajanBabu, T. V. “ Control of Selectivity through Synergy between

Catalysts, Silanes and Reaction Conditions in Cobalt-Catalyzed Hydrosilylation of

Dienes and Terminal Alkenes.” Manuscript Submitted . viii

Raya, B.; Biswas, S.; RajanBabu, T. V. “Selective Cobalt-Catalyzed Reduction of

Terminal Alkenes and Alkynes using (EtO)2Si(Me)H.”ACS Catal.; 2016, 6, 6318-6323.

Biswas, S.; Zhang, A.; Raya, B.; RajanBabu, T. V. “Triarylphosphine Ligands With

Hemilabile Alkoxy Groups: Ligands for Nickel (II)-Catalyzed Olefin Dimerization

Reactions. Hydrovinylation of Vinylarenes, 1,3-Dienes, and Cycloisomerization of 1,6-

Dienes.” Adv. Synth. Catal. 2014, 356, 2281-2292.

Raya, B.; Jing, S.; Balasanthiran, V.; RajanBabu, T. V. “Novel Cobalt-Catalyst for

Hydrosilylation of 1,1-disubstituted Alkenes.” Manuscript in Preparation.

Balaram Raya; “Synthesis of Diol and Triol Substrate to Investigate Selective oxidation of Alcohols using Hypervalent Iodine Compounds.” MS Dissertation, 2011, Western

Illinois University, Macomb, IL.

Fields of Study

Major Field: Chemistry

Table of Contents

Abstract ...... ii

Dedication ...... v

Acknowledgement ...... vi

Vita ...... viii

Publication ...... viii

Fields of Study ...... ix

List of Schemes ...... xiv

List of Tables ...... xvi

List of Figures ...... xx

List of Abbreviations ...... xxiv

CHAPTER 1A: Cobalt-Catalyzed Hydrosilylation of Alkenes ...... 1

1.1. Introduction ...... 1

1.2. Background and Significance ...... 3

1.3. Results and Discussion ...... 10

1.4. Optimizing Cobalt-Catalyst for Hydrosilylation of 4-Methylstrene ...... 11

1.5. Development of Cobalt-Catalyst for Selective Hydrosilylation of Alkenes ...... 16

1.5.1. Catalyst Discovery ...... 16

1.6. Proposed Mechanism for Hydrosilylation Reaction ...... 40

1.7. Conclusions ...... 43

1.8. General Experimentals ...... 43

1.9. References ...... 73

CHAPTER 1B: Cobalt-Catalyzed Hydrosilylation of 1,3-and 1,4-Dienes ...... 77

1B.1. Introduction ...... 77

1B.2. Background and Significance ...... 79

1B.3. Results and Discussion ...... 84

1B. 4. Optimizing Cobalt Catalyst for Hydrosilylation of (E)-Dodeca-1,3-Dienes ...... 85

1B.5. Proposed Mechanism for Hydrosilylation Reaction of 1,3-Dienes ...... 107

1B.6. Conclusions ...... 109

1B.7. General Experimental ...... 110

1B.8. References ...... 129

CHAPTER 2: Cobalt-Catalyzed Reduction of Terminal Alkenes and Alkynes using

(EtO)2Si(Me)H as a Stoichiometric Reductant ...... 131

2.1. Backgrounds and Significance ...... 131

2.2. Results and Discussion ...... 132

2.3. Development of Cobalt Catalysts for Selective Hydrogenation of Alkenes ...... 133

2.4. Proposed Mechanism for Hydrogenation Reaction ...... 155

2.5. Conclusions ...... 157

2.6. General methods ...... 158

2.7. References ...... 181

CHAPTER 3: Novel Cobalt-Catalyzed for Chemo and Regioselective Hydrosilylation of

1-1-disubstituted Alkenes ...... 182

3.1. Backgrounds and Significance ...... 182

3.2. Results and Discussion ...... 184

3.3. Development of Cobalt Catalysts for Selective Hydrosilylation of Alkenes ...... 190

3.3.1. Catalyst Discovery ...... 190

3.4. Hydrosilylation of Prochiral 1,1-Disubstituted Alkene ...... 207

3.5. Proposed Mechanism for Hydrosilylation Reaction ...... 211

3.6. Conclusions ...... 212

3.7. General methods ...... 213

3.8. References ...... 232

CHAPTER 4: Cobalt-Catalyzed Hydrovinylation of Silyl 1,3-Dienes ...... 233

4.1. Introduction ...... 233

4.2. Results and Discussion ...... 237

xii

4.3. Proposed Mechanism for Cobalt Catalyzed Hydrovinylation of 1,3-Diene ...... 248

4.4. Conclusions ...... 251

4.5. General methods ...... 251

4.6. References ...... 264

CHAPTER 5: Triarylphosphines Ligands with Hemilabile Alkoxy Groups: Ligands for

Nickel(II)-Catalyzed Olefin Dimerization Reactions. Hydrovinylation of Vinylarenes,

1,3-Dienes, and Cycloisomerization of 1,6-Dienes ...... 266

5.1. Introduction ...... 266

5.2. Results and Discussion ...... 269

5.2.1. Ligands Effects on Hydrovinylation of Vinylarenes ...... 269

5.3. Ligands Effects on Cycloisomerization of 1,6-Dienes ...... 273

5.4. Identification of the Minor Methylene Cyclohexane Products (262) via Use of Nickel

N-Heterocyclic Carbene (NHC) Complexes ...... 275

5.5. Proposed Mechanism for Regioselectivity in the Cationic Metal Hydride mediated

Cyclization of 1,6-Dienes ...... 277

5.6. Conclusions ...... 279

5.7. General methods ...... 279

5.8. References ...... 307

Bibliography ...... 309

Appendices: Supplemental Files ...... 319 xiii

List of Schemes

Scheme 1.1. Reaction of Olefins with Hydrosilane ...... 5

Scheme 1.2. Cobalt Carbonyl Catalyzed Hydrosilylation of Alkene ...... 9

Scheme 1.3. Reduction of (iPrPDI)FeCl2(1-Cl2) ...... 17

Scheme 1.4. Sakurai Allylation ...... 78

Scheme 1.5. Peterson Olefination ...... 79

Scheme 1.6. Tamao-Fleming Oxidation ...... 79

Scheme 1.7. Common Products and Byproducts of 1,3-Diene Hydrosilylation ...... 80

Scheme 1.8. Products of Hydrosilylation of Isoprene ...... 81

Scheme 1.9. Synthesis of 1,3-Diene Substrates ...... 99

Scheme 2.1. Reaction of Silyl Enol Ether 194 using Standard Hydrogenation Condition and Under Optimized Condition ...... 149

Scheme 2.2. Proposed Catalytic Cycle for Hydrogenation Reaction ...... 157

Scheme 4.1. Synthesis of 1,3-Diene Substrates Contain Allylsilane ...... 242

Scheme 4.2. Synthesis of 1,3-Diene Substrates Contain Vinylsilane ...... 243

Scheme 4.3. Synthesis of 1,3-Diene Substrates Contain only E Vinylsilane ...... 243

Scheme 4.4. New Proposed Mechanism for Cobalt Catalyzed Hydrovinylation ...... 250

xiv

Scheme 5.1. Selected Examples of Asymmetric Hydrovinylation of Alkenes ...... 268

Scheme 5.2. Possible Control of RegioSelectivity in the Cationic Metal Hydride

Mediated Cyclization of 1,6-Dienes ...... 278

List of Tables

Table 1.0. Effect of Activators on Hydrosilylation of 4-Methylstyrene ...... 12

Table 1.1. Effect of Activators (Stoichiometric Amount) in Hydrosilylation of 13 ...... 13

Table 1.2. Cobalt (II) Acetate for Hydrosilylation of 4-MethylStyrene, 13 ...... 15

Table 1.3. Control Experiments for Hydrosilylation of 13 ...... 20

Table 1.4. Ligand Scan for Hydrosilylation of 4-MethylStyrene, 13 ...... 22

Table 1.5. Effects of Solvents for Hydrosilylation of 13 ...... 28

Table 1.6. Effect of Activator in Hydrosilylation of 4-MethylStyrene, 13 ...... 29

Table 1.7. Effect of Silane in Hydrosilylation of 4-MethylStyrene, 13 ...... 31

Table 1.8. Scope of Hydrosilylation of Activated Alkenes ...... 33

Table 1.9. Scope of Hydrosilylation of Unactivated Alkenes ...... 35

Table 1.10. Scope of Hydrosilylation of Alkenes Under Neat Condition ...... 36

Table 1.11. Scope of Hydrosilylation of Alkenes Using Pybox Ligand ...... 37

Table 1.12. Scope of Hydrosilylation of Alkenes Using Secondary Silane ...... 38

Table 1.13. Preparative Run (0.5 g) Hydrosilylation of Alkenes using Primary Silane ... 39

xvi

Table 1.14. Preparative Run (0.5 g) Hydrosilylation of Alkenes Using 1 mol% Catalyst with Phenylsilane ...... 40

Table 1.15. Effect of Ligand in Hydrosilylation of (E)-Dodeca-1,3-Diene, 98 ...... 89

Table 1.16. Effects of Solvents in Hydrosilylation of (E)-Dodeca-1,3-Diene, 98 ...... 91

Table 1.17. Effect of Activator in Hydrosilylation of (E)-Dodeca-1,3-Diene, 98 ...... 93

Table 1.18. Effect of Silane in Hydrosilylation of (E)-Dodeca-1,3-Diene, 98 ...... 95

Table 1.19. Effect of Counter Ion in Hydrosilylation of (E)-Dodeca-1,3-Diene, 98 ...... 97

Table 1.20. Scope of Hydrosilylation of 1,3-Diene ...... 102

Table 1.20. Scope of Hydrosilylation of 1,3-Diene Contd...... 103

Table 1.21. Scope of Hydrosilylation of 1,3-Diene Using 1mol% Catalyst ...... 105

Table 1.22. Scope of Hydrosilylation of 1,4-Skipped Diene Using Cobalt Catalyst ..... 106

Table 2.1. Effect of Silane in Hydrogenation of 4-MethylStyrene, 13 ...... 136

Table 2.2. Effect of Ligand in Hydrogenation of 4-MethylStyrene, 13 ...... 139

Table 2.3. Activator Scan for Hydrogenation of 4-MethylStyrene, 13 ...... 140

Table 2.4. Solvents Scan in Hydrogenation of 4-MethylStyrene, 13 ...... 141

Table 2.5. Scope of Hydrogenation of Activated Alkenes ...... 144

Table 2.6. Scope of Hydrogenation of Unactivated Alkenes ...... 142

Table 2.7. Scope of Hydrogenation Reaction of 1,3-Diene ...... 146

Table 2.8. Scope of Hydrogenation Reaction using 1 mol% Catalyst ...... 152

xvii

Table 2.9. Scope of Hydrogenation Reaction of 1,3-Alkyne ...... 154

Table 2.10. Hydrogenation Reaction of 33 Using Stoichiometric Amount of Silane ..... 156

Table 3.1. Effect of Activator for Hydrosilylation of 4-Methylstyrene, 13 ...... 185

Table 3.2. Activator Scan Contd. for Hydrosilylation of 4-Methylstyrene, 13 ...... 186

Table 3.3. Scanning Result of Cobalt Bromide Complex for Hydrosilylation of 13 ..... 188

Table 3.4. Scanning Result of Cobalt Acetate for Hydrosilylation of 13 ...... 189

Table 3.5. Ligand Scan in Hydrosilylation of 13 ...... 193

Table 3.6. Effect of Activator for Hydrosilylation of 13 ...... 194

Table 3.7. Effect of Solvents for Hydrosilylation of 13 ...... 196

Table 3.8. Scope of Hydrosilylation Reaction of Alkenes ...... 198

Table 3.9. Scope of Hydrosilylation Reaction of Alkenes Using 1 mol% Catalyst ...... 199

Table 3.10. Scope of Hydrosilylation Reaction of Alkenes Using Neat Substrate ...... 201

Table 3.11. Scope of Hydrosilylation Reaction of 1,1-Disubstituted Alkenes ...... 202

Table 3.12. Scope of Hydrosilylation Reaction of 1,1-Disubstituted Alkenes Using

Secondary Silanes ...... 204

Table 3.13. Scope of Hydrosilylation Reaction of 1,3- and 1,4-Dienes ...... 205

Table 3.14. Scope of Hydrosilylation Reaction of 200 Using Chiral Ligands ...... 209

Table 3.15. Scope of Hydrosilylation Reaction(Using Ph2SiH2) of 200 Using Chiral

Ligands ...... 208

xviii

Table 4.1. Ligand Scan in Hydrovinylation of 230 ...... 240

Table 4.2. Scope of Hydrovinylation of 1,3-Diene ...... 245

Table 4.3. Scope of Hydrovinylation of 1,3-Diene Using Chiral Ligands ...... 247

Table 4.4. Scope of Hydrovinylation of 1,3-Diene 242 Using Chiral Ligands ...... 248

Table 5.1. Effect of Ligands on Ni (II)-Catalyzed Hydrovinylation of 4-MethylStyrene 13

...... 272

Table 5.2. Cyclization of 1,6-Dienes Using (allyl)Ni(NHC)BARF ...... 276

xix

List of Figures

Figure 1.1. Karstedt's Catalyst ...... 4

Figure 1.2. Structure of New Pt(0) Catalyst ...... 6

Figure 1.3. Cobalt Catalyzed Hydrosilylation of 13 using iPrPDI Ligand ...... 17

Figure 1.4. Gas Chromatogram of Hydrosilylation of 13 using iPrPDI Ligand at RT ...... 18

Figure 1.5. Gas Chromatogram for Cobalt Catalyzed Hydrosilylation of 13 using iPrPDI

Ligand at -78 oC to RT ...... 19

Figure 1.6. Ligand Used for Hydrosilylation ...... 22

Figure 1.7. Cobalt Complexes Used for Hydrosilylation ...... 22

Figure 1.8. Gas Chromatogram of Hydrosilylated Products of 13 using L1-L3 Ligands . 23

Figure 1.9. Gas Chromatogram of Hydrosilylated Products of 1 using L1-L3 Ligands

(Effect of Ligands) ...... 24

Figure 1.10. Gas Chromatogram of Dehydrogenative Silylation Products of 1 using

MesPDICo-Me at 23 oC ...... 26

Mes Figure 1.11. Gas Chromatogram of Reduction Products of 1 using PDICoCl2 from -78 oC to RT ...... 26

Mes Figure 1.12. Gas Chromatogram of Hydrosilylated Obtained from 1 using PDICoCl2 from -78 oC to RT ...... 27 xx

Figure 1.13. Alkenes Tested in the Cobalt Catalyzed Hydrosilylation ...... 32

Figure 1.14. Proposed Catalytic Cycle for Hydrosilylation ...... 42

Figure 1.15. Gas Chromatogram of Products Obtained from 98 at RT ...... 86

Figure 1.16. Gas Chromatogram of Products Obtained from 98 at -78 oC to RT ...... 87

Figure 1.17. Ligands in Co-Complexes Used for Diene Hydrosilylation ...... 89

Figure 1.18. Cobalt Complexes Used for Diene Hydrosilylation ...... 90

Figure 1.19. Cobalt Complexes with Different Counter Ions for Hydrosilylation of Diene

95 ...... 96

Figure 1.20. Dienes Tested in the Cobalt Catalyzed Hydrosilylation ...... 100

Figure 1.21. Dienes Tested in Hydrosilylation Using 1 mol% Catalyst ...... 104

Figure 1.22. Proposed Catalytic Cycle for Hydrosilylation ...... 109

Figure 2.1. Gas Chromatogram of Products 28 ...... 137

Figure 2.2. Ligand Used for Hydrogenation ...... 139

Figure 2.3. Cobalt Complexes Used for Hydrogenation ...... 139

Figure 2.4. Functionalized Alkenes Tested for Cobalt catalyzed Hydrogenation ...... 142

Figure 2.5. Functionalized Dienes Tested for Cobalt catalyzed Hydrogenation ...... 146

Figure 2.6. Selective Hydrogenation of 1,4-Skipped Diene ...... 147

Figure 2.7. Gas Chromatogram of Reduction Products Using H2 Ballon ...... 148

Figure 2.8. Gas Chromatogram of Reduction Products Using 50 psi Pressure ...... 148

xxi

Figure 2.9. Gas Chromatogram of Reduction Product 195 ...... 151

Figure 2.10. Gas Chromatogram of Reduction Product 178 ...... 153

Figure 2.11. Gas Chromatogram of Reduction Product 189 ...... 153

Figure 2.12. Substrates did not Work Under the Optimized Condition ...... 155

Figure 3.1. Substrates did not Work for Hydrosilylation Using Cobalt(PDI)Complex .. 183

Figure 3.2. Ligand Used for Hydrosilylation of Alkene ...... 187

Figure 3.3. Gas Chromatogram of Hydrosilylated Product 14 ...... 192

Figure 3.4. Ligand Used for Hydrosilylation of 13 ...... 192

Figure 3.5. Alkenes Tested for Hydrosilylation ...... 197

Figure 3.6. Gas Chromatogram of Hydrosilylated Product 14 ...... 200

Figure 3.7. 1,1-Disubstituted Alkenes Tested for Hydrosilylation ...... 202

Figure 3.8. 1,3-Diene and 1,4-Skipped Diene Tested for Hydrosilylation ...... 205

Figure 3.9. Chiral Ligands Used for Hydrosilylation of 1,1-Disubstituted Alkene ...... 208

Figure 3.10. HPLC Chromatogram for Hydrosilylation of 200 ...... 210

Figure 3.11. Chiral Ligands(PHOX) Used for Hydrosilylation ...... 210

Figure 3.12. Proposed Mechanism for Hydrosilylation ...... 212

Figure 4.1. Ligand Used for Hydrovinylation of 230 ...... 239

Figure 4.2. Dienes Tested for Hydrovinylation ...... 241

Figure 4.3. Chiral Ligands Tested for Hydrovinylation ...... 247

xxii

Figure 4.4. Original proposed mechanism for Hydrovinylation of 1,3-Diene ...... 250

Figure 5.1. Ligands for Asymmetric Hydrovinylation Reaction ...... 269

xxiii

List of Abbreviations

α alpha

Ac acetyl acac acetylacetonate aq aqueous

β beta

BARF tetrakis[(3,5-trifluoromethyl)phenyl]borate

BDPP 2,4-bis(diphenylphosphino)pentane br broad (NMR) n-butyl normal-butyl t-butyl tertiary-butyl tert-butyl tertiary-butyl

°C degrees centigrade/Celsius cod 1,5-cyclooctadiene conv. conversion

CSP-GC chiral stationary phase gas chromatography

δ chemical shift in parts per million d doublet (NMR)

DCM dichloromethane xxiv dd doublet of doublets (NMR) ddd doublet of doublet of doublets (NMR)

DIOP [2,2-dimethyl-1,3-dioxalane-4,5-

diylbismethylene]bisdiphenylphosphine

DMF N,N-dimethylformamide dppb 1,4-bis(diphenylphosphino)butane dppe 1,2-bis(diphenylphosphino)ethane dppm 1,1-bis(diphenylphosphino)methane dppp 1,3-bis(diphenylphosphino)propane dpppent 1,5-bis(diphenylphosphino)pentane dt doublet of triplets (NMR)

η eta ee enantiomeric excess

E entgegen (trans) equiv/eq equivalent

Et ethyl

EtOAc ethyl acetate g gram

GC gas chromatography h hour

HV hydrovinylation

Hz Hertz

xxv iPr isopropyl

J coupling constant in Hertz (NMR)

LAH lithium aluminum hydride m meter (SI)/ milli- (SI)/ multiplet (NMR)

M molarity (moles/liter)

Me methyl

MAO methylaluminoxane

MeO methoxy min minute mol moles

NBS N-bromosuccinimide

NMR nuclear magnetic resonance

Ph phenyl psi pounds per square inch

π pi q quartet (NMR) rt room temperature

Rt retention time (GC) s singlet (NMR) t triplet (NMR) temp temperature

THF tetrahydrofuran

xxvi

TLC thin layer chromatography

TMS trimethylsilyl

TMSO trimethylsiloxy

TBDMS tert-butyl(dimethyl)silyl

Ts para-toluenesulfonyl

Z zusammen (cis)

xxvii

Chapter 1A: Cobalt-Catalyzed Hydrosilylation of Alkenes

Portions of this chapter appear in the following publication

Raya, B.; Jing, S.; RajanBabu, T.V. (Manuscript Submitted)

1.1 Introduction

The addition of silicon hydride (Si-H) across carbon-carbon multiple bonds is called hydrosilylation. Hydrosilylation reaction has huge industrial applications for manufacturing consumer goods.[1] The hydrosilylation reaction can also produce various organosilicon reagents, which are used in fine chemical synthesis for stereospecific oxidation and cross coupling reaction.[2] Among the various synthetic transformations, hydrosilylation is one of the most mild and functional group-tolerant reactions catalyzed by transition metals and is widely used in the synthesis of fine chemicals and complex organic molecules, as well as on large scale for the production of organosilane building blocks for material synthesis. Organosilanes are used in applications ranging from electronics manufacturing to in-vivo drug delivery.[3] Organosilanes are commonly incorporated to increase hydrophobicity in sol-gel synthesis.[4] Functionalized organosilanes called coupling agent that covalently bind to both silicate and organic materials have widely used in polymer industries to make organic polymers.[5]

Organofunctionalized silicates are used for the immobilization of peptides and as metal complex catalyst on inorganic supports,[6] as coating material for polycarbonate lenses,[7] as hydrophobic coatings for industrial and automobile glass,[8] as vehicles for pharmaceutical preparations,[9] and as chromatographic separation solid- and liquid- supports.[10]

Though natural products do not contain silicon, organosilanes have becomes invaluable in organic synthesis[11] for forming carbon-carbon bonds, carbon-oxygen bonds, reduction of ketones to chiral secondary alcohols, protection of functional groups and many more synthetic transformation.[12] Although elemental silicon is relatively inert to many reagents, it forms strong bonds with more electronegative elements such as oxygen and fluorine. This property of silicon allows silicon-carbon and silicon-oxygen bonds to be robust functional groups that react chemo selectively under verities of reaction conditions. Organosilanes utilized in organic transformations are synthesized by transition metal-catalyzed hydrosilylation and organosilicon reagents are widely used for carbon-carbon bond formation by a variety of transformations such as cross-couplings,[13] olefinations,[14] allylations,[15] rearrangements,[16] and cycloadditions.[17] Out of many useful carbon-carbon bond-forming reactions of organosilicon reagents are the Sakurai allylation[18] and the Peterson olefination reactions.[19] The carbon-silicon bond present in organosilane product produced by transition metal catalyzed hydrosilylation reaction can be transform to carbon-oxygen bond using Tamao-Fleming oxidation.[2, 20] This oxidation reaction is useful for the preparation of enantiomerically enriched alcohols because the oxidation proceeds stereo selectively with retention of configuration at carbon. So, the

2 development of diverse methods for hydrosilylation has greatly benefitted industries as well as synthetic organic chemistry.

1.2 Backgrounds and Significance

Olefin hydrosilylation is among the most important and widely used methods for the synthesis of organosilanes (Eq. 1.1).[21]

H SiR'3 HSiR' 3 SiR'3 H (Eq. 1.1) R R R

In 1947 Sommer[22] reported first alkene hydrosilylation reaction using trichlorosilane in the presence of peroxide (Eq. 1.2). The reaction proceeds via free-radical mechanism and thus proceeding with only moderate selectivity across different alkenes. Despite the first report of alkene hydrosilylation by Sommer, the synthetic transformation was not widely accepted until the discovery of transition metal catalyzed hydrosilylation by Speier in

1957 (Eq. 1.3).[21a] In Speier’s original report that hexachloroplatinic acid is a very effective homogeneous transition metal catalyst for hydrosilylation led to improved methods for selective reactions.

O O Ph Ph O H O SiCl3 (Eq. 1.2) SiHCl3 o o C4H9 Neat, 45 C - 63 C C4H9 1 9 h 2 99%

H H2PtCl6.H2O6 (1ppm) SiCl3 (Eq. 1.3) SiHCl3 o H3C Neat, 100 C H3C 3 15 min 4 95%

A major breakthrough on hydrosilylation has been made in 1973 by Karstedt.[23] Karstedt developed the Pt(0) complex catalyst containing vinyl-siloxane ligands (Fig. 1.1) and this catalyst exhibits highly improved activity and selectivity as well as high solubility on polysiloxane compositions. This important finding lead to the wider application of this method in the silicon chemistry for the manufacturing of diverse consumer goods including lubricating oils, coating materials etc.

O Si Si Si Si O O Pt Pt Si Si

Figure 1.1.: Karstedt’s Catalyst

Although numerous reports on hydrosilylation appeared in recent decades, Karstedt’s catalyst is still the most general and widely used catalyst for hydrosilylation of olefins, especially in industry. However, this catalyst decomposes upon dissociation of the weakly bound vinylsiloxane ligands to form Pt(0) colloids. This decomposition of catalyst reduces the catalyst turnover number and increases the cost of hydrosilylation reaction.[21c, 24] Despite the high utility of platinum catalyzed hydrosilylation reaction in industries, it is well known that the platinum catalyst still suffer from a number of side

4 reactions such as dehydrogenative silylation, hydrogenation of olefins, isomerization of olefins, olefin oligomerization and redistribution of silanes (Scheme 1.1). Cost of precious metal such as platinum is another concern for large-scale preparation. These side reactions lead to significant yield losses of the required product. Therefore, development of a well-defined and efficient catalytic system with higher selectivity is still an intensive research topic to attain more economical production of silicon material with high quality.

R3Si Isomerization Hydrosilylation

Cat. R3SiH Cat. R3Si n Dehydrogenative silylation Oligomerization H

R4Si, R2SiH2 H Redistribution of Silane Hydrogenation

Scheme 1.1 Reaction of Olefins with Hydrosilane

Recently many new efficient Pt(0) complexes (Fig. 1.2) supported by the N-heterocyclic carbene (NHC) as a σ-donor ligand has been reported for alkene hydrosilylation (Eq.

1.4).[25] Although these new platinum catalysts are slightly less active than Karstedt’s catalyst, they are able to reduce the amount of undesired side reactions. Furthermore, no colloidal platinum species was formed in the use of these new platinum catalysts.

R Si N O Pt Si N R = methyl, cyclohexyl, tert butyl R

Figure 1.2.: Structure of New Pt(0) Catalyst

Me OTMS catalyst 30 ppm Si Me H OTMS (Eq. 1.4) Si 72 oC TMSO OTMS O MD'M O 5 6 92%

Besides platinum catalyst, numerous reports on hydrosilylation using various noble metal catalysts appeared recently. Now, transition metal catalysis has become the method of choice for the synthesis of allyl- and vinyl silanes. Although platinum catalysts are the most commonly used catalyst for the large-scale synthesis of organosilanes, many other metals can catalyze hydrosilylation. Noble metal catalysts such as palladium,[26] rhodium,[27] ruthenium,[28] iridium,[29] early transition metals,[30] and lanthanide and actinides[31] all show high activity and selectivity for hydrosilylation of multiple bonds.

After the discovery of efficient transition metal catalyzed hydrosilylation reaction with high selectivity, various carbon-carbon multiple bonds as well as carbon-heteroatom multiple bonds are now common substrates for hydrosilylation.[21b, c, 32] For decades, hydrosilylation reaction has relied on precious noble metals (Pt, Pd, Rh, Ru or Ir) catalyst, early transition metals, lanthanide and actinide. Although the cost of noble metals is high, most industrial hydrosilylation process still utilize noble metal catalysts for hydrosilylation reaction because of their high efficiency and long life. However, due

to economic, competing side reaction and environmental concerns there has been an ever-increasing demand for efficient hydrosilylation methods with base-metal catalysts.

Nesmeyanov et al. [33] in 1962 reported the first base metal catalyzed hydrosilylation reaction of alkene using iron catalyst (Eq. 1.5). Since the discovery of iron carbonyl catalyzed hydrosilylation reaction several studies on this field have been done over half a century, leading to the finding of several iron carbonyl system.[34] However, these iron carbonyl systems require high temperature to generate the active catalyst and often compete hydrosilylation with undesired side reactions such as dehydrogenative silylation.

Cl3Si

Fe(CO) 8 50% Cl SiH 5 (Eq. 1.5) 3 H 140 oC 7 Cl3Si 9 50% Yield = 85%

In addition to side reaction, iron carbonyl system often exhibits complex reactivity, which is difficult to control due to their electronic structures of several possible Fe(Co)n- intermediates. Lappert et al. reported hydrosilylation of conjugated dienes using nickel,[35] cobalt[36] and iron.[35a] These reports are limited to substrates such as isoprene,

1,3-pentadiene, 2,3-dimethylbuta-1,3-diene and 1,3-cyclohexadiene and gave the mixture of 1,2- and 1,4-addition products in modest yield. The detail study of Lappert work is described in chapter 1B of this dissertation. Therefore, examples of efficient and well- defined non precious metal catalyst system still remained scarce. Chirik et al.[37] in 2004 have made a major breakthrough on hydrosilylation using iron catalyst. They reported

7 efficient hydrosilylation reaction of olefin with different silanes using iron complex [1-

[37] (N2)2] with redox-active bis(imino)pyridine (PDI) ligand (Eq. 1.6).

H 0.3% 1-(N2)2 C H PhSiH PhH2Si (Eq. 1.6) 4 9 3 o 22 C, 12 min C4H9 1 10

N N N Fe N N2 2

1-(N2)2

After the discovery of efficient iron catalyzed hydrosilylation reaction by Chirik group, numerous reports came on hydrosilylation using base metal catalyst such as iron,[38] and nickel.[39] Even though, hydrosilylation reaction using first-row transition metal catalysts have been known for decades, reports on cobalt catalyzed hydrosilylation are limited.[40]

The traditional cobalt-catalyzed hydrosilylations using cobalt carbonyl catalyst requires high temperatures and suffers from side reactions such as dehydrogenative silylation and isomerization (Scheme 1.2).

Dehydrogenative R3Si Silylation Co(CO)8 HSiR3

R' Hydrosilylation R SiCo(CO) SiR3 3 4 HSiR3 R'

(CO)n Co H HCo(CO)n R' R' SiR3 Isomerization R' HSiR3

HCo(CO)n Co(CO)n R' Co(CO)n R' R'

Scheme 1.2 Cobalt Carbonyl Catalyzed Hydrosilylation of Alkene

Recently, cobalt catalysts reported by Chirik,[41] Deng,[42] Holland and Weix, [43] Huang,

[44] Lu,[45], Fout,[46] have addressed some of these limitations but these reports are limited to alkene and alkyne substrates. In spite of long decades of development of hydrosilylation reaction, significant challenges still remain, such as selective hydrosilylation of unactivated alkenes and alkynes, with certain types of functional groups, vinylarenes, conjugated diene and a variety of other potentially useful substrate using a broad range of primary, secondary and tertiary silanes.

In summary, numerous reports on metal-catalyzed hydrosilylations include the use of platinum, palladium, rhodium, ruthenium, iridium, lanthanides and actinides, early transition metals, iron, cobalt to a limited extent nickel. These reports have recorded limitations such as substrates scope, functional group tolerance, variability in the silanes used. Thus there is always room for further improvements in this important

9 hydrofunctionalization method. In this chapter we report efficient cobalt catalyst systems for hydrosilylation using air stable cobalt complexes of well-known ligands activated under specific set of conditions. The modifications relay on a synergy between appropriate pyridine 2,6-bis-aryliminoyl ligands, activating agent, solvents and reaction parameters such as temperature to effect highly selective hydrosilylations of different kinds of substrates, which include alkenes, alkynes, vinylarenes and conjugated dienes.

1.3 Results and Discussion

The aim of this research was the development of a general method for cobalt catalyzed hydrosilylation of alkene, alkyne, vinylarene and conjugated diene. In a search of new reactions to further functionalize 1,4-skipped dienes (12) obtained from hydrovinylation of 1,3-dienes (11) (Eq. 1.7),[47] hydrosilylation was considered as a possible reaction. This chapter describes the development of PDI (2,6-iminopyridine) complexes of Co(II) that catalyze the hydrosilylation reaction at room temperature. The first part of this chapter describes the strategy we employed in our investigation to optimize the catalyst for selective hydrosilylation. Next we describe the scope of the discovery of cobalt catalyst for selective hydrosilylation. The last section discusses possible mechanism for this selective hydrosilylation.

Z R Hydrovinylation (Eq. 1.7) Z R = Alkyl, Z = H or OTMS R 11 12

Inspired by the success of cobalt in the hydrovinylation for dienes, the cobalt catalytic system developed for the hydrovinylation of dienes was initially applied to the hydrosilylation of alkenes. Using the optimized condition for hydrovinylation

(dppp)CoCl2 with TMA or MAO as activator, we attempted to do hydrosilylation of prototypical substrate 4-methylstyrene, 13 for our initial scouting experiments. The details of the study of the optimization of hydrosilylation reaction will be discussed below in the section 1.4.

1.4 Optimizing Cobalt Catalysis for Hydrosilylation of 4-Methylstyrene, 13

The initial substrate for hydrosilylation reaction to be tested was the prototypical alkene 4-methylstyrene (13). Under the optimized condition for hydrovinylation

([dppp]CoCl2 with methylaluminoxane (MAO) or trimethyl aluminium, (TMA) as an activator,[47a] catalyst for hydrovinylation did not give any hydrosilylated products as confirmed by GC-MS and 1HNMR. Furthermore, the optimized cobalt catalysts for hydrovinylation ([dppp]CoCl2) with different activator were tested as precatalyst for hydrosilylation with phenylsilane under a variety of conditions and the results are summarized in Table 1. During the scanning of cobalt precatalyst in chlorinated solvents such as dichloromethane and dichloroethane with different activator, no hydrosilylation product was detected; instead, redistribution of silane product along with starting material was observed using various activators. In contrast, the reaction with protic solvent such as ethanol exclusively gave the redistribution of silane product PhSi(OEt)3 from metathesis reaction with phenylsilane (PhSiH3). Thus, a combination of cobalt precatalyst, activator, silane and ethanol as solvent was found to be critical for the

11 formation of redistribution of silane product, but not suitable for the formation of hydrosilylated product.

SiH2Ph

(dppp)CoCl2 10 mol% SiH2Ph PhSiH Activator 20 mol% 3 (Eq. 1.8) 1.1 eq RT, Solvent, 5 h 13 14 15 1,2 linear 1,2 branched

Ph2P PPh2 (dppp)

Table 1.0 Effect of Activators on Hydrosilylation of 4-Methylstyrene, 13a

Entry Activator Solvent 14 15b 13b Silane Formed (%)c

1 Zn DCM - - 100% -

2 Et2Zn DCM - - 57% PhSiHEt2 (43%) 16

3 TMA DCM - - 100% -

4 MAO DCM - - 100% -

5 CH3LI DCM - - 21% PhSiHMe2 (79%) 17

6 nBuLi DCM - - 34% PhSiHnBu2 (66%) 18

7 Zn EtOH - - - PhSi(OEt)3 (100%) 19

o 8 Zn(80 C) DCE - 5% 50% Ph2SiH2 (45%) 20 a see eq. 1.8 for reaction scheme, 10 mol% catalyst, 20 mol% activator, solvent (2 mL), rt, 5 h, bGC ratio,c

Silanes formed were detected by GC and GC-MS

Consistent with the trend observed using catalytic amount of activator, reaction of cobalt precatalyst with phenylsilane in presence of stoichiometric amount of activator (Eq. 1.9) exclusively gave various redistribution products (Table 1.1).

(dppp)CoCl2 5 mol% PhSiHR'R'' (Eq. 1.9) PhSiH2R' PhSiH 3 Activator 1 eq. DCM, RT 3 h - 5 h 13

Table 1.1 Effect of Activator (Stoichiometric Amount)) in Hydrosilylation of 13 (Eq.

1.9)a

Entry Activator Silane Formed Yield(%)b

1 PhMgBr (1eq.) Ph2SiH2 20 95%

2 nBuLi (1eq.) PhSiH2nBu 21 92%

3 EtMgBr (1eq.) PhSiH2Et 22 93%

4 MeMgBr (1eq.) PhSiH2Me 23 89%

5 nBuLi (2eq.) PhSiHnBu2 18 91%

aSee eq. 1.9 for reaction scheme, bIsolated yield after purification

After determining that the cobalt precatalyst ([dppp]CoCl2) with different activator

(either catalytic or stoichiometric amount) was not suitable for hydrosilylation, we further investigated other catalyst for hydrosilylation. In this connection, we screened cobalt (II) acetate tetrahydrate with different phosphine ligand without using any activator. Cobalt

(II) acetate is perhaps the most attractive because it is among the most inexpensive source

[41b] of cobalt and is bench stable. The treatment of phosphine–Co(OAc)2 mixtures with pinacolborane generates active catalyst for the hydroboration of alkenes,[48] suggests the silane activation may also be possible. Although cobalt (II) acetate precatalyst is bench stable, it proved essentially inactive for hydrosilylation at room temperature using both monodentate (tricyclohexyl phosphine, PCy3) and bidentate ligand [1,3-bis

(diphenylphosphino)propane, dppp]. Performing the catalytic hydrosilylation at 80 oC resulted in complete conversion of 4-methylstyrene, 13 to 1,2-branched hydrosilylated product 15 along with accompanying redistribution silane product, generating diphenylsilane (Ph2SiH2, 20) as a minor (upto 33%) byproduct (Eq.1.10). Since Cobalt

(II) acetate precatalyst exhibit Markovnikov selectivity for hydrosilylation reaction, the hydrosilylated product obtained from the prototypical substrate 4-methylstyrene 13, is a chiral product. So, we attempted to do asymmetric hydrosilylation reaction using commercially available chiral bisphosphine ligands. Based on the optimized chiral catalyst for hydrovinylation, [47a] 2,3–O-isopropylidene-2,3-dihydroxy-1,4- bis(diphenylphosphino)butane (+DIOP) and 2,3bis-(diphenylphosphino)pentane (BDPP) were chosen for asymmetric hydrosilylation reaction. The reaction conditions were same as those that were established for the non-asymmetric reactions described above. The reaction of 13 with (+) DIOP gave the Markovnikov addition product 15 (67%) along with 33% of Ph2SiH2, 20 products detected by GC. The enantioselectivity of

Markovnikov addition product was 8% ee using (+) DIOP ligand. Furthermore, the reaction of 13 with 2,3 bis-(diphenylphosphino)pentane (BDPP) gave the Markovnikov

14 addition product 15 (79%) along with 21% of Ph2SiH2, 20 product detected by GC and the enantioselectivity was 7% ee. Guided by these results, we concluded that cobalt (II) acetate catalyzed reaction using phosphine ligand is slower and requires high temperature to complete the reaction. In addition to this, diphenylsilane (Ph2SiH2, 20) was also formed along with hydrosilylated product. The results of above reactions are shown in Table 1.2.

SiH2Ph

Co(OAc)2 10 mol% SiH2Ph Ligand 20 mol% (Eq. 1.10) PhSiH3 1.1 eq DCE, 80 oC, Time 13 14 15

Table 1.2 Cobalt (II) Acetate Complexes for Hydrosilylation of 4-Methylstyrene, 13a

b c Entry Ligand Time 14 15 Ph2SiH2 (%) 20 ee%

1 PCy3 26 h - 77% 23%

2 Dppp 28 h - 74% 26%

3 (+) DIOP 30 h - 67% 33% 8%

4 BDPP 28 h - 79% 21% 7% a o See Eq 1.10 reaction scheme. 10 mol% catalyst Co(OAc)2, 20 mol% ligand, dichloroethane, 80 C,

b c PhSiH3. Ratios of products determined by areas under the peaks in GC.. Significant amounts of Ph2SiH2 also observed;

In summary, guided by these disappointing results using Co(II)- phosphine complexes for the hydroslilylation reaction, we sought to develop more efficient and selective catalysts.

1.5 Development of Cobalt Catalysts for Selective Hydrosilylation of Alkenes

1.5.1 Catalyst Discovery

A collection of bis (imino) pyridine (PDI) ligands 1a-f and pybox ligand 1g were synthesized[49] and tested for the hydrosilylation of alkenes. Although many PDI complexes of iron known to be efficient for hydrosilylation,[38] no cobalt catalyzed hydrosilylation using bis (imino) pyridine (PDI) ligands and pybox ligands had been reported prior to our work. Since we initiated this work, there has been considerable effort in the cobalt-catalyzed hydrosilylation of alkene and alkyne from other groups.

After synthesizing various bis (imino) pyridine (PDI) ligands and pybox ligands, we treated these ligands with CoX2 (X = Cl, Br or I) to give Co(ligand)X2 complex in good yields. The catalytic activity of these cobalt complexes was then examined. The reactions of phenylsilane (PhSiH3) with prototypical substrate 4-methylstyrene, 13 were examined in the presence of catalytic amount (0.05 equivalents) of the cobalt complexes, but no reaction was observed at room temperature. Using the conditions reported for the

iPr [50] reduction of ( PDI)FeCl2 with NaEt3BH as an activator (Scheme 1.3), the

iPr hydrosilylation of 13 was attempted using ( PDI)CoCl2 1b with NaEt3BH at room temperature. To our delight, we were able to isolate mixture of 1,2- branched adduct 15 and 1,2-linear adduct 14 hydrosilylated products in 91% isolated yield (Fig. 1.3).

N 1 eq. NaEt3BH N N Fe N Toluene, RT N Fe N Cl Cl - NaCl Cl

1-Cl2 1-Cl

iPr Scheme 1.3 Reduction of ( PDI)FeCl2 (1-Cl2)

In addition to hydrosilylated product, neither the corresponding dehydrogenative silylation nor redistribution of silane products were formed. The GC trace of the products is shown in figure 1.4, which clearly shows the mixture of two products (14 and 15) in

iPr the ratio of 43: 57. This preliminary result revealed that the PDI (CoCl2) complex is better than phosphine (CoCl2) complex for alkene hydrosilylation.

SiH2Ph iPr ( PDI)CoCl2 5 mol% SiH2Ph NaEt BH 10 mol% PhSiH3 3 1.1 eq RT, Toluene, 5 h 13 14 43:57 GC ratio 15 91% yield

Figure 1.3.: Cobalt Catalyzed Hydrosilylation of 13 using iPrPDI Ligand

SiH2Ph

14 43:57 GC ratio 15 91% yield

Figure 1.4.: Gas Chromatogram of Hydrosilylation of 13 using iPrPDI Ligand

at Room Temperature

Next, we examined the effect of temperature to control the regioisomer of the product. The catalytic activity of this cobalt iPrPDI complex 1b was then examined at low temperature. The reaction of phenylsilane (PhSiH3) with 13 was examined in the presence of a catalytic amount (0.05 equivalents) of the cobalt complex 1b. Addition of

o NaEt3BH at -78 C to the reaction system and allow to warm up the reaction mixture at room temperature (Eq. 1.11). This led to the formation of exclusive (>99%) 1,2 linear hydrosilylated product 14 in 92 % isolated yield. GC-MS and NMR identified the hydrosilylated product 14. The GC trace of the product 14 is shown in figure 1.5

SiH2Ph iPr ( PDI)CoCl2 5 mol% SiH2Ph PhSiH NaEt3BH 10 mol% 3 (Eq. 1.11) 1.1 eq -78 oC - RT, Toluene, 5 h 13 14 99:1 GC ratio 15 92% yield

N N Co N Cl Cl

iPr PDI)CoCl2 1b

SiH2Ph

14 99:1 GC ratio 15 92% yield

Figure 1.5.: GC Trace for Cobalt Catalyzed Hydrosilylation of 13 Using iPrPDI

Ligand from -78 oC to RT

We attempted several control experiments (Table 1.3) to confirm the requirement of both

iPr catalyst PDICoCl2 1b and activator NaEt3BH are required for the hydrosilylation activity. Even after almost 48 h, no more than 2% hydrosilylation product was observed

iPr without the combination of catalyst PDICoCl2 and the activator NaEt3BH.

Table 1.3 Control Experiments for Hydrosilylation of 13

Entry Catalyst Activator Time 14:15a Conversiona

1 none NaEt3BH 48 h - -

iPr 2 PDICoCl2 none 48 h 2:0 2%

aGC ratio

Next, we examined the effect of ligands (Figure 1.6 for ligands used for hydrosilylation) on the regioselectivity of hydrosilylation. Bis (imino) pyridine (PDI) ligands (L1-L5) and pybox ligand (L6) across a range of different substituents on aromatic backbone of imine were tested after making the complex with cobalt dichloride

(Figure 1.7) to examine the effect of steric properties of the reaction (Table 1.4, entries 1-

6). Cobalt complex 1e with unsubstituted imine gave mixture of hydrosilylated products

14 and 15 in the ratio of 90:10 by GC integrations (Table 1.4, entries 4) whereas cobalt complex 1f with 2,6 disubstituted imine yielded more branched product 15 than the linear product 14 in the ratio of 60:40 by GC integrations (Table 1.4, entries 5). Since these cobalt complexes 1e and 1f have given promising result in the hydrosilylation of 13, we attempted to do further scanning of more substituted imine cobalt complex 1d and more sterically demanding cobalt complex 1c to observe the effect of ligand on hydrosilylation

20 of 13. The cobalt complex 1d having trisubstituted imine backbone gave more branched product 15 (Table 1.4, entries 3) than any other cobalt complexes where as cobalt complex 1c having 2,6-diethyl substituted imine gave the mixture of linear 14 and branched 15 hydrosilylated product in the ratio of 60:40 by GC integration (Entries 2).

Bryan Cunningham synthesized pybox ligand L6 and applied them to the cobalt catalyzed hydrosilylation reaction after making complex 1g with cobalt chloride (CoCl2).

The cobalt complex 1g exhibit similar result produced (more 1,2-linear product) by cobalt complex 1a and showed the hydrosilylated products 14 and 15 in the ratio of 70:30 by GC integration (Table 1.4, entries 6). The cobalt complex 1h showed reduced catalytic activity for hydrosilylation and gave only 4% (by GC integration) linear hydrosilyalted product 14 (Table 1.4, entries 7). Comparisons of all entries (Table 1.4) revealed that cobalt complex 1b with more sterically demanding diisopropyl substituents on imine showed the best catalytic activity for hydrosilylation of 13 compared to the other complexes (Fig.1.8).

SiH2Ph

(Ligand)CoCl2 5 mol% SiH2Ph NaEt BH 10 mol% PhSiH3 3 (Eq. 1.12) 1.1 eq -78 oC - RT, Toluene, 5 h 13 14 15

Table 1.4 Ligand Scan for Hydrosilylation of 4-Methylstyrene, 13a

Entry Ligand Complex 1,2 linear 14b 1,2 branched 15b 1 L1 1b 98% 2% 2 L2 1c 40% 60% 3 L3 1d 24% 76% 4 L4 1e 90% 10% 5 L5 1f 40% 60% 6 L6 1g 70% 30% 1h 4% - 7 L7 a iPr o See Eq 1.12 for reaction scheme. 5 mol% catalyst ( PDI)CoCl2.10 mol% NaEt3BH, -78 C to RT, PhSiH3. bRatios of products determined by areas under the peaks in GC

O O N N N N N N N N N Ar Ar PDI L1 Ar = 2,6-di-iPr Pybox Cy(PDI) L2 Ar = 2,6-di-Et L6 L7 L3 Ar = 2,4,6-tri-Me L4 Ar = Ph L5 Ar = 2,6-di-Me Bryan Cunningham Synthesized Pybox Ligand L6

Figure 1.6.: Ligand Used for Hydrosilylation

O O N N N N N N N N N Co Co Ar Co Ar Cl Cl Cl Cl Cl Cl PDI Pybox Cy(PDI) 1b Ar = 2,6-di-iPr 1e Ar = Ph 1c Ar = 2,6-di-Et 1f Ar = 2,6-di-Me 1g 1h 1d Ar = 2,4,6-tri-Me

Figure 1.7.: Cobalt Complexes Used for Hydrosilylation

MesPDI, L3 EtPDI, L2 iPrPDI, L1

76:24 60:40 2:98

Figure 1.8.: Gas Chromatogram of Hydrosilylated Products of 13 using L1-L3

Ligands (Ligand Effect)

Similarly 1-octene 1 also showed the similar ligand effect (Fig. 1.9) with PhSiH3 using

L1-L3 ligands under the same condition used for the hydrosilylation of 13.

SiH2Ph (Ligand)CoCl2 5 mol% NaEt BH 10 mol% SiH Ph C H PhSiH3 3 2 6 13 C6H13 C6H13 (Eq. 1.13) 1.1 eq -78 oC - RT, Toluene, 5 h 1 24 25

Mes PDI Et PDI IPr PDI 47:53 40:60 2:98

SiH2Ph SiH2Ph C6H13 C6H13

26 25

Figure 1.9.: Gas Chromatograms of Hydrosilylated Products of 1 using L1-L3

(Ligands Effect)

We also compare the temperature effect on the hydrosilylation reaction of 1 with

[41a] (OTMS)2MeSiH using L3 ligand. Chirik et al. reported structurally related Co(I)- complexes [(MesPDI)Co-Me] give only dehydrogenative silylation of 1-alkenes with several silanes including PhSiH3 and (TMSO)2Si(Me)H (Eq.1.14). They also note that

Mes similar catalytic performance using PDICoCl2 (0.02 equivalents) and NaEt3BH (0.04

24 equivalents) and substrate 1 also gave mixture of reduction product 27 and

Mes dehydrogenative silylation 26 at room temperature. Using ( PDI)CoCl2, the reaction of

0 1 with PhSiH3 at -78 C allows to slowly warm to room temperature gave mixture of hydrosilylated product 24 and 25 in the ratio of 53:47 by GC integration after 5 h (Eq.

1.16). However, the reaction of 1 with (OTMS)2SiMeH gave only mixture of reduction

Mes product 27 and starting material 1 using PDICoCl2 (0.02 equivalents) and NaEt3BH

(0.04 equivalents) for 5 h (Eq.1.15). No dehydrogenative silylation was observed under such conditions. The GC traces of the three different reactions are shown in figures 1.10,

1.11 and 1.12.

(OTMS) SiMeH Mes C H SiMe(OTMS) C6H13 2 ( PDI)Co-Me 0.5 mol% 5 11 2 (Eq. 1.14) 1 eq 0.5 eq Neat, 23 oC, 15 min 1-Octene, 1 26 (Dehydrogenative Silylation) -Octane

Mes ( PDI)CoCl2 2 mol% C6H13 (OTMS)2SiMeH NaEt3BH 4 mol% C H (Eq. 1.15) 1 eq 0.5 eq 6 13 Neat, -78 oC - RT, 5 h 1-Octene, 1 Octane, 27

30% by GC integration

C5H11 SiMe(OTMS)2

Figure 1.10.: Gas Chromatogram of Dehydrogenative Silylation Products of 1 using

MesPDICo-Me at 23 oC

C6H13

Mes Figure 1.11.: Gas Chromatogram of Reduction Products of 1 using PDICoCl2 from -78 oC to RT

Mes SiH2Ph ( PDI)CoCl2 5 mol% NaEt BH 10 mol% SiH Ph C H PhSiH3 3 2 (Eq. 1.16) 6 13 C6H13 C6H13 1.1 eq -78 oC - RT, Toluene, 5 h 1 24 53:47 GC Ratio 25 86% Yield

SiH2Ph SiH2Ph C6H13

C6H13 25 26

Figure 1.12.: Gas Chromatogram of Hydrosilylated Product Obtained from 1 using

Mes o (PDI)CoCl2 from -78 C to RT

Having identified a successful ligand to promote the selective hydrosilylation, attention was devoted to test various solvents for hydrosilylation of 13. An examination of various common solvents (Table 1.5, entries 1-7) revealed toluene (Table 1.5, entries 1) to be the best solvent for the hydrosilylation reaction. Hexane (Table 1.5, entries 4) and chlorinated solvent such as CH2Cl2 (Table 1.5, entries 2) and ClCH2CH2Cl (Table 1.5,

27 entries 6) lead to unsatisfactory results whereas THF (Table 1.5, entries 3), diethylether

(Table 1.5, entries 5) and benzene (Table 1.5, entries 7) gave modest to low yields.

SiH2Ph iPr ( PDI)CoCl2 5 mol% SiH2Ph NaEt BH 10 mol% PhSiH3 3 (Eq. 1.17) 1.1 eq -78 oC - RT, Solvent 13 5 h 14 15 28

Table 1.5 Effects of Solvents for Hydrosilylation of 13a

Entry Solvent 14b 15b 28b 13b Silane formedc

1 Toluene >98% <2% - - -

2 DCM 4% - 49% 47% -

3 THF 75% 2% 23% - -

4 Hexane 18% 12% 63% - 7% (20)

5 Ether 37% 34% 22% - 7% (20) 6 DCE - - 9% 91% -

7 Benzene 68% 20% 12% - -

a iPr o See Eq 1.17 for reaction scheme. 5 mol% catalyst ( PDI)CoCl2.10 mol% NaEt3BH, -78 C to RT, PhSiH3. b c Ratios of products determined by areas under the peaks in GC, Significant amounts of Ph2SiH2 also observed; Silane formed was detected by GC and GC-MS. 20 = Ph2SiH2.

A quick survey of most commonly used activators (trimethylaluminium, MeLi,

0 EtMgBr, PhMgBr, n-BuLi, NaEt3BH) confirmed that NaEt3BH at -78 C is the best

iPr reagent for reduction of cobalt complex ( PDI)CoCl2 1b. The only activators that showed any reactivity were PhMgBr, EtMgBr and MeLi (Table 1.6, entries 2-4). nBuLi or Me3Al (Table 1.6, entries 5-6) were not successful for hydrosilylation.

SiH2Ph iPr ( PDI)CoCl2 5 mol% SiH2Ph PhSiH Activator 10 mol% 3 (Eq. 1.18) 1.1 eq -78 oC - RT, 13 Toluene, 5 h 14 15 28

Table 1.6 Effect of Activator for Hydrosilylation of 4-Methylstyrene, 13a

Entry Activator 14b 15b 28b 13b Silane Formedc

1 NaEt3BH 98% 2% - - -

2 PhMgBr 42% 26% 20% - 12% (20)

3 EtMgBr 49% 23% 18% - 10% (22)

4 MeLi 53% 15% 16% - 16% (23) 5 nBuLi 10% 3% 22% 26% 39% (21)

6 Me Al - 4% - 71% 25% (20) 3 a iPr o See Eq 1.18 for reaction scheme. 5 mol% catalyst ( PDI)CoCl2.10 mol% NaEt3BH, -78 C to RT, PhSiH3. bRatios of products determined by areas under the peaks in GC, cSignificant amounts of different silanes are also observed; Silane formed was detected by GC and GC-MS. 20 = Ph2SiH2, 21 = PhSiH2nBu, 22 =

PhSiH2Et, 23 = PhSiH2Me.

Several commercially available silanes (Table 1.7) were screened in the presence of the

iPr cobalt precatalyst [( PDI)CoCl2, 1b activated by NaEt3BH] for the hydrosilylation of 4-

29 methylstyrene 13. In a typical procedure, the cobalt complex (0.05 equivalent) and the 4- methylstyrene 13 (1 equivalent) are dissolved in toluene (2 mL) under argon and the reaction mixture was cooled to -78 oC. To this cold solution was added a toluene solution of NaEt3BH (0.1 equivalent) followed by the addition of silane (1.1 equivalent). The mixture was warmed to room temperature and the reaction was monitored by gas chromatography and GC-mass spectrometry. Among the silane tested, phenylsilane

(Table 1.7, entries 1), diphenylsilane (Table 1.7, entries 2) and phenylmethylsilane (Table

1.7, entries 3) gave good yields of hydrosilylated products. Neither triethylsilane nor triphenylsilane displayed any significant reaction. A careful examination of the data in

Table 1.7 suggests that two kinds of products can be obtained in useful yield. Primary silane such as phenylsilane PhSiH3 gave an excellent yield of the linear silane 14.

Secondary silanes such as diphenylsilane Ph2SiH2 (Table 1.7, entries 2) and phenylmethyl silane MePhSiH2 (Table 1.7, entries 3) gave linear silane as major component along with varying amounts of branched hydrosilylated products and a reduction product 28.

Tertiary silanes such as triphenylsilane Ph3SiH (Tablble 1.7, entries 6), triethoxysilane

(EtO)3SiH (Table 1.7, entries 7) and bis (trimethylsiloxy) methylsilane (TMSO)2SiMeH

(Table 1.7, entries 8) are much less reactive, and the starting material 13 remains mostly unreacted at room temperature. In sharp contrast, methyldiethoxysilane (OEt)2MeSiH

(Table 1.7, entries 9), which is another tertiary silane, gave nearly quantitative yield of the reduction product 28.

SiH3-nRn

SiH3-nRn IPr ( PDI)CoCl25mol% RnSiH4-n (Eq. 1.19) NaEt3BH 10 mol% Toluene, 1,2 linear 1,2 branched Reduction 13 1.1 eq. -78 oC - RT, 5 h 14 15 28

Table 1.7 Effect of Silane for Hydrosilylation of 4-Methylstyrene, 13a

b Entry Silane 1,2 linear 1,2 branchedb Reduction(28)c Product Yieldd SMb

SiH2Ph 92% - 1 PhSiH3 >98% <2% - 14

- SiHPh2 - 2 Ph2SiH2 96% 4% 86%

29 SiHMePh 89% - 3 PhMeSiH2 89% 2% 9%

4 Ph3SiH - - 34% - 66% 5 Cl3SiH - - 16% - 84%

6 Et3SiH - - 36% - 64%

7 (EtO)3SiH - - 42% - 58%

- 57% 8 (OTMS)2SiMeH - - 43%

9 (EtO)2MeSiH - - 100% 97% 28

a iPr o See Eq 1.19 for reaction scheme. 5 mol% catalyst ( PDI)CoCl2.10 mol% NaEt3BH, Silane -78 C to RT, bRatios of products determined by areas under the peaks in GC, cSignificant amounts of reduction product is also observed; dYield of products were determined after purification.

After extensive screening of the ligand, solvent, activator and silane, the optimized procedure for the reaction is shown in equation 1.20 and the full scope of the reaction is 31 illustrated by examining the other substrates with varying degrees of steric effects and sensitive functional groups (Fig. 1.13).

SiH2Ph iPr ( PDI)CoCl2 5 mol% SiH2Ph PhSiH NaEt3BH 10 mol% 3 (Eq. 1.20) 1.1 eq Toluene, -78 oC - RT, 13 5 h 14 15

Cl 13 31 32 33 34 O F Br

O Ph AcO OPh 35 36 37 38 39

MeO MeO

40 41 42 43 44

C6H13 C8H17 TMS

43 45 1 46 47 48 43

Figure 1.13.: Alkenes Tested in the Cobalt Catalyzed Hydrosilylation

All of these substrates (Fig. 1.13) were purchased from commercial vendors or synthesized using the reported literature method.[51]. Under the optimized conditions [1

iPr equivalent of alkene, 1.1 equivalent of silane, PDICoCl2 (0.05 equivalent), NaEt3BH

(0.1 equivalent), toluene (2 mL)], the reactions of activated alkenes 13, 31-43 (Fig. 1.13) proceed at room temperature giving good yields and excellent selectivity for the linear

32 hydrosilylated product. GC, GC-MS and spectroscopic techniques have established the structure of all the hydrosilylated products. In all cases, the hydrosilylation favors the linear selectivity (anti Markovnikov’s product) in which the silicon is attached to the terminal carbon.

Table 1.8. Scope of Hydrosilylation of Activated Alkenesa

Entry Substrate Product Yield (%)b

SiH2Ph

R R

1 R = CH3 13 R = CH3 14 92% 2 R = -CH2CH(CH3)2 31 R = -CH2CH(CH3)2 49 89% 3 R = Cl 34 R = Cl 50 89% 4 R = OAc 39 R = OAc 51 91%

R R SiH2Ph

5 R = Br 38 R = Br 52 87% 6 R = OPh 36 R = OPh 53 86%

n n SiH2Ph

7 n = 1 32 n = 1 54 91% 8 n = 2 33 n = 2 55 97%

a iPr o See Eq 1.20 for reaction scheme. 5 mol% catalyst ( PDI)CoCl2.10 mol% NaEt3BH, Silane -78 C to RT, bYield of products were determined after purification.

Continued

Table 1.8. Contd. Scope of Hydrosilylation of Activated Alkenesa

Entry Substrate Product Yield (%)b

SiH2Ph 92% 9 O O 35 56 F F SiH2Ph 91% 10 Ph 37 Ph 57

I I 91% SiH2Ph 11 42 58

93% SiH2Ph

12 MeO MeO 43 59

SiH2Ph 13 R R 14 R = H 40 R = H 60 92% R = OMe 15 41 R = OMe 61 89% a iPr o See Eq 1.20 for reaction scheme. 5 mol% catalyst ( PDI)CoCl2.10 mol% NaEt3BH, Silane -78 C to RT, bYield of products were determined after purification

We further explored the scope of hydrosilylation reaction of unactivated alkene under the

iPr optimized conditions [1.1 equivalents of silane, PDICoCl2 (0.05 equivalents), NaEt3BH

(0.1 equivalents), toluene (2 mL)]. The reaction of unactivated alkenes 1, 44-48 (Table

1.9, entries 1-6) proceeds at room temperature giving good yields of hydrosilylated product. GC, GC-MS and spectroscopic techniques have established the structure of all the hydrosilylated products. In all cases, the hydrosilylation favors anti Markovnikov’s selectivity in which the silicon is attached to the terminal carbon (Table 1.9). No

34 contamination of any dehydrogenated silylation product or disubstituted silane 20

(Ph2SiH2) was detected on GC and GC-MS in all of the hydrosilylated products.

Table 1.9. Scope of Hydrosilylation of unactivated Alkenesa

Entry Substrate Product Yield (%)b

SiH2Ph R R

1 R = CH TMS 62 91% R = CH2TMS 48 2 2 R = -CH2CH(CH3)2 46 R = -CH2CH(CH3)2 63 94% 3 R = C8H17 47 R = C8H17 64 86% 4 R = C6H13 1 R = C6H13 24 84%

SiH2Ph 88% 5 44 65

SiH2Ph 6 77% 45 66

a iPr o See Eq 1.20 for reaction scheme. 5 mol% catalyst ( PDI)CoCl2.10 mol% NaEt3BH, Silane -78 C to RT, bYield of products were determined after purification

The new protocol developed for cobalt catalyzed hydrosilylation reaction of alkenes is also useful for hydrosilylation of alkene in the absence of any solvent. Several alkenes were tested for hydrosilylation under neat condition and gave linear adduct with good yield and excellent selectivity.

iPr SiH2Ph PDICoCl2 5 mol% PhSiH NaEt3BH 10 mol% SiH2Ph (Eq. 1.21) R 3 R R 1.1 eq Neat, -78 oC - RT, 5 h

Table 1.10. Scope of Hydrosilylation of Alkenes Under Neat Conditiona

Entry Substrate Product Yield (%)b SiH2Ph

R R

1 R = CH3 13 R = CH3 14 92% 2 R = Cl 34 R = Cl 50 89% 3 R = OAc 39 R = OAc 51 91%

Br Br SiH2Ph 87% 4 38 52

SiH2Ph 5 33 55 96%

SiH2Ph 6

MeO MeO 89% 41 61

SiH2Ph R R

7 R = C8H17 47 R = C8H17 64 86%

8 R = CH2TMS 48 R = CH TMS 62 86% 2 a iPr o See Eq 1.21 for reaction scheme.. 5 mol% catalyst ( PDI)CoCl2.10 mol% NaEt3BH, Silane -78 C to RT, bYield of products were determined after purification

We further screened the substrate scope (Table 1.11) of hydrosilylation reaction using cobalt complex 1g and observed the similar trends (mixture of linear adduct and branched adduct) similar to for all substrates.

1g 5 mol% SiH2Ph PhSiH NaEt3BH 10 mol% SiH2Ph (Eq. 1.22) R 3 R R 1.1 eq Toluene, -78 oC - RT, 5 h

Table 1.11 Scope of Hydrosilylation of Alkenes Using Pybox Liganda

Entry Substrate Productb Yield (%)c

SiH2Ph SiH2Ph

R R R 1 R = CH3 13 R = CH3 (70%) 14 R = CH3 (30%) 15 87% 2 R = Cl 34 R = Cl (67%) 50 R = Cl (33%) 67 85% 3 R = H 68 R = H (72%) 69 R = H (28%) 70 89% SiH2Ph

Br Br SiH2Ph Br 82% 4 37 52 71 66% 34%

91% SiH2Ph 5 SiH2Ph 72 73 74 80% 20%

SiH2Ph SiH2Ph R R R R = C H 75 88% 6 R = C8H17 47 R = C8H17 64 8 17

67% 33%

37 a o See Eq 1.22 for reaction scheme.. 5 mol% catalyst (pybox)CoCl2.10 mol% NaEt3BH, Silane -78 C to RT, bRatios of products determined by areas under the peaks in GC cYield of products were determined after purification

Among the silane tested (Table 1.7), phenylsilane (Table 1.7, entries 1), diphenylsilane

(Table 1.7, entries 2) and phenylmethylsilane (Table 1.7, entries 3) gave good yields and excellent selectivity of hydrosilylated products. So we further explored the scope of hydrosilylation reaction of activated and unactivated alkene (Table 1.12) using the secondary silanes. Under the optimized conditions [1 equivalent of alkene, 1.1 equivalent

iPr of silane, PDICoCl2 (0.05 equivalent), NaEt3BH (0.1 equivalent), toluene (2 mL)] substrate 13 and 44 gave exclusively anti Markovnikov’s products 29, 30, 76 and 77 using Ph2SiH2 and PhMeSiH2.

Table 1.12 Scope of Hydrosilylation of Alkenes using Secondary Silane

Entry Substrate Silane Product Yield (%)b

SiHPh2 Ph SiH 1 2 2 86%

H3C 13 H3C 29 SiHMePh 89% 2 PhMeSiH2 H C H3C 3 13 30 SiHPh2 85% 3 Ph2SiH2 44 76 SiHMePh 87% 4 44 PhMeSiH2 77

38 a iPr See Eq 1.20 for reaction scheme.. 5 mol% catalyst ( PDI)CoCl2.10 mol% NaEt3BH, secondary silane -78 oC to RT, bYield of products were determined after purification

These optimized cobalt catalyzed hydrosilylation reactions can be accomplished in neat substrate and on large scale (0.5 g) using as little as 0.01 equiv. (substrate/catalyst = 100) of the catalyst. Examples of large-scale hydrosilylation reaction using primary silane

(PhSiH3) for substrate 13 (Table 1.13, entries 1) and 33 (Table 1.13, entries 2) are shown in Table 1.13

iPr SiH2Ph PDICoCl2 5 mol% PhSiH NaEt3BH 10 mol% SiH2Ph (Eq. 1.23) R 3 R R 1.1 eq Neat, -78 oC - RT, 5 h

Table 1.13 Preparative Run (0.5 g) Hydrosilylation of Alkenes using Primary Silanea

Entry Substrate Product Yield (%)b

SiH2Ph 1 94% H C H3C 13 3 14

SiH Ph 2 97% 2 33 55

a iPr o See Eq 1.23 for reaction scheme, 5 mol% catalyst ( PDI)CoCl2.10 mol% NaEt3BH, Silane -78 C to RT, bYield of products were determined after purification

iPr SiH2Ph PDICoCl2 1 mol% PhSiH NaEt3BH 2 mol% SiH2Ph (Eq. 1.24) R 3 R R 1.1 eq Neat, -78 oC - 40oC (Oil bath), 2 h

Hydroslylation of Alkene Using 1 mol% Catalyst

Table 1.14 Preparative Run (0.5 g) Hydrosilylation of Alkenes Using 1 mol%

Catalyst with Phenylsilanea

Entry Substrate Product Yield (%)b

SiH2Ph 1 93% H C H3C 13 3 14

SiH Ph 2 96% 2 33 55

a iPr o See Eq 1.24 for reaction scheme. 1 mol% catalyst ( PDI)CoCl2.2 mol% NaEt3BH, Silane -78 C to RT, bYield of products were determined after purification

1.6 Proposed Mechanism for Hydrosilylation Reaction

The proposed catalytic cycle for hydrosilylation reaction is shown in Figure 1.14. On the basis of available literature the proposed mechanism for hydrosilylation is shown in

iPr( 1 Figure 14. Reduction of [ PDI)CoCl2] with 2 equivalents of NaEt3BH generates Co -H

78 intermediate.[52] Reduced Co(I) species [iPr(PDI)CoCl][53] by itself in toluene solvent or in dichloromethane solvent does not catalyze the hydrosilylation reaction.

N Zn N N Co N THF, RT, 12 h N Co N Cl Cl Cl

Isolated and fully characterized

iPrPDI(Co)-Cl 5 mol% PhSiH3 No reaction (Eq. 1.25) Toluene, RT, 24 h 13

iPrPDI(Co)-Cl 5 mol% PhSiH No reaction (Eq. 1.26) 3 DCM, RT, 24 h 13

However, in presence of Lewis acid such as triethylborane (Et3B), B(C6F5)3 or NaEt3BH

(5 mol%), the (iPrPDI)Co-Cl complex catalyzes the hydrosilylation reaction and gave excellent yield and selectivity.

iPrPDI(Co)-Cl 5 mol% SiH2Ph PhSiH3

NaEt3BH 5 mol%, (Eq. 1.27) 13 Toluene,-78 oC - RT, 2 h 14 94% Yield

IPrPDI(Co)-Cl 5 mol% SiH2Ph PhSiH 3 (Eq. 1.28) Et3B 15 mol%, Toluene, -78 oC-RT, 2 h 96% Yield 13 14

iPrPDI(Co)-Cl 5 mol% SiH2Ph PhSiH3 B(C6F5)3 15 mol%, (Eq. 1.29) Toluene, RT, 2 h 96% Yield 13 14

The Co1-H 78 intermediate inserts to the alkene give a Cobalt-alkyl complex 79, which upon reaction with silane give the hydrosilylated product and regenerates the Co1-H 78 intermediate.

N N Co N Ar Cl Cl Ar iPr Ar = (2,6-iPr)-phenyl) [ PDI]CoCl2

2 NaEt3BH 2 NaCl, 2 Et3B,1/2 H2

SiH2Ph R R LnCo H 78

SiH2Ph [iPr PDI]Co H [iPr PDI]Co H H R R

[iPr PDI]Co H PhSiH3 79 R

Figure 1.14.: Proposed Catalytic Cycle for Hydrosilylation

iPr Furthermore, reaction of 1with PhSiD3 in the presence of [( PDI)CoCl2] and NaEt3BH gives exclusively 2-d1-n-octylphenylsilane-(Si)d2 (25) with > 96% incorporation of D as determined NMR and GC-MS (Eq 1.30). No D-incorporation was seen at other sites

(D-NMR) which also support the proposed mechanism shown in figure 1.14

iPr D ( PDI)CoCl2 5 mol% NaEt BH 10 mol% SiD Ph (Eq. 1.30) PhSiD3 3 2 C6H13 C6H13 1.1 eq -78 oC - RT, Toluene, 5 h 1 80

1.7 Conclusion: In conclusion, we have discovered a new efficient cobalt catalyst for selective hydrosilylation of monosubstituted alkenes. Under the optimized conditions [1

iPr equivalent of alkene, 1.1 equivalent of silane, PDICoCl2 (0.05 equivalent), NaEt3BH

(0.1 equivalent), toluene (2 mL)], we are able to do hydrosilylation of variety of substartates bearing functional group such as aryl bromide, aryl iodide, protected alcohols and trisubstituted double bond.

1.8 General Experimentals

All air- and moisture sensitive manipulations were carried out using standard vacuum line and Schlenk techniques, or in a dry box containing a purified nitrogen. Solvents were distilled from the appropriate drying agents under nitrogen. All glassware was cleaned using base (KOH in i-PrOH) then acid (HClaq) baths. Analytical TLC was performed on

E. Merck pre-coated (0.25 mm) silica gel 60 F254 plates. Flash column chromatography was carried out on silica gel 40 (Sorbtech Chemicals), gas chromatographic analysis was 43 conducted on an Agilent 7820A using hydrogen as the carrier gas, equipped with a methyl silicone column (30 m x 0.32 mm, 0.25 µm film thickness). GC-MS was carried out on a HP-5MS 5% methyl phenylsiloxane (30 m x 0.25 mm, 0.25 µm film thickness) using He as carrier gas. Cobalt (II) chloride and phosphine ligands were purchased from

Strem Chemicals. All silanes were purchased from Sigma Aldrich, Oakwood, Alfa Aesar or Apollo Scientific. All activating reagents were purchased from Sigma Aldrich. 1H, 13C

NMR spectra were recorded on Bruker 400 and 600 MHz, spectrometers. All spectra were obtained at ambient temperature. The chemical shifts (δ) were recorded in parts per million (ppm) and the coupling constants (J) in Hertz (Hz). 1H and 13C NMR multiplicity and coupling constants are reported where applicable. 1H and 13C spectra were referenced to the residual deuterated solvent peak (CHCl3 7.26 ppm, 77.32 ppm).

Ligand preparation. Bis1,6-(diaryliminoyl)pyridine ligands L1-L5 and L7 were prepared by an Schiff’s base reaction using a modified literature methodology.

Bis(imino)pyridine ligand L1, was prepared by a Schiff’s base reaction using a previously reported literature procedure.[49] 2,6-diacetylpyridine (5.00 g, 30.64 mmol, 1.0 equivalents) and p-tolunesulfonic acid (0.59 g, 3.07 mmol, 0.1 equivalents) were added to the 250 mL round bottom flask with a magnetic stirrer bar and toluene (150 mL) was added via syringe. Distilled 2,6-diisopropylaniline (11.94 g, 67.41 mmol, 2.2 equivalents) was added to the reaction mixture via syringe. The reaction mixture was stirred at reflux for 72 h under argon in a Dean-Starke apparatus and then allowed to cool down to room temperature. The crude product precipitated as a yellow powder and was filtered using

Buchner funnel and washed with cold ethanol (0 °C). Pure L1 was obtained in upon recrystallization from ethanol as a yellow crystalline solid (13.12 g, 89% yield). 1H and

13C NMR matched with the reported literature.[54]

Bis(imino)pyridine ligand L2, was prepared from 2,6-diacetylpyridine (5.00 g, 30.64 mmol, 1.0 equivalents) and p-tolunesulfonic acid (0.59 g, 3.07 mmol, 0.1 equivalents) and distilled 2,6-diethylaniline (10.06 g, 67.41 mmol, 2.2 equivalents) according to the procedure described for L1 to afford L2 as a yellow crystalline solid (11.61 g, 87% yield). 1H and 13C NMR matched with the reported literature.[55]

Bis(imino)pyridine ligand L3, was prepared from 2,6-diacetylpyridine (5.00 g, 30.64 mmol, 1.0 equivalents), p-tolunesulfonic acid (0.59 g, 3.07 mmol, 0.1 equivalents) and distilled 2,4,6-trimethylaniline (9.11 g, 67.41 mmol, 2.2 equivalents) according to the procedure described for L1 with the following work-up and isolation modification. After

72 h reflux in a Dean-Starke apparatus, the resultant brown reaction mixture was cooled and washed with a saturated solution of Na2CO3 (~100 mL) and then with water (2 X 50 mL). The organic layer was separated and the combined aqueous layer was extracted with diethyl ether (2 X 50 mL). All organic layers were combined and dried with MgSO4 and concentrated in a rotary evaporator to afford a yellowish powder. The yellow powder was dissolved in hot ethanol, cooled to R.T and kept in a freezer at -25 oC overnight to afford a pure L3 as a yellow crystalline solid (9.25 g, 76% yield). 1H and 13C NMR matched with reported literature. [56]

Bis(imino)pyridine ligand L4, was prepared from 2,6-diacetylpyridine (5.00 g, 30.64 mmol, 1.0 equivalents), p-tolunesulfonic acid (0.59 g, 3.07 mmol, 0.1 equivalents) and

45 distilled aniline (6.27 g, 67.41 mmol, 2.2 equivalents) according to the procedure described for L1 to afford L4 as a yellowish brown crystalline solid (8.25 g, 86% yield).

1H and 13C NMR matched with the reported literature.[54]

Bis(imino)pyridine ligand L5, was prepared from 2,6-diacetylpyridine (5.00 g, 30.64 mmol, 1.0 equivalents), p-tolunesulfonic acid (0.59 g, 3.07 mmol, 0.1 equivalents) and distilled 2,6-dimethylaniline (8.16 g, 67.41 mmol, 2.2 equivalents) according to the procedure described for L3 to afford L5 as a yellowish brown crystalline solid (11.31 g,

83% yield). 1H and 13C NMR matched with the reported literature.[54]

Ligand L6 was prepared according to reported literature.[57]

Bis(imino)pyridine ligand L7, was prepared from 2,6-diacetylpyridine (5.00 g, 30.64 mmol, 1.0 equivalents), p-tolunesulfonic acid (0.59 g, 3.07 mmol, 0.1 equivalents) and distilled cyclohexylamine (17.34 g, 67.41 mmol, 2.2 equivalents) according to the procedure described for L1 to afford L7 a white crystalline solid (8.58 g, 86% yield) 1H and 13C NMR matched with reported literature.[58]

Synthesis of PDI-cobalt complexes: Modified literature methods were used for the

iPr Et Me Cy preparation of complexes ( PDI)CoCl2, ( PDI)CoCl2, ( PDI)CoCl2, ( PDI)CoCl2.

Anhydrous CoCl2 (48.5 mg, 0.37 mmol) and PDI ligand were taken in a flame dried 100 mL Schlenk flask and magnetic stir-bar was loaded inside the glove box. The flask was removed from the glove box and purged with dry argon. Freshly distilled, degassed THF

(13 mL) was added, and upon stirring at room temperature for 10 min, a brown solution was formed. The mixture was then stirred under argon for 72 h. After 72 h stirring at room temperature, freshly distilled diethyl ether (15 mL) and pentane (15 mL) were

added via syringe. The solid was filtered in air and washed with cold pentane (5 X 5 mL). The brown solid complex was dried under reduced pressure (0.3 mmHg) overnight to afford a brown powdery solid. (82 to 90% yield).

(DPPP)CoCl2 complex was prepared as follows. Anhydrous CoCl2 (50.5 mg, 0.390 mmol) was added to a previously flame-dried 50-mL 3-neck round bottom flask fitted with a flow control gas inlet and magnetic stir-bar loaded in a glove box under nitrogen.

The nitrogen atmosphere was removed and the flask purged with dry argon. Freshly distilled, degassed THF (5 mL) was added, and upon stirring at room temperature for 15 min, a clear deep blue solution formed. A solution of DPPP (181 mg, 0.410 mmol) in freshly distilled, degassed ether (5 mL) was added drop wise to yield a blue turbid solution. After stirring at room temperature for 15 h, 20 mL freshly distilled, degassed hexane was added in one portion to yield a blue precipitate. The resulting precipitate was filtered on a sintered glass fret under argon atmosphere, and washed with diethyl ether and hexane (1:1) mixture (3 X 5 mL) to remove any unreacted DPPP, resulting in quantitative yield of a light blue solid, which was used with no further purification.

(Cyhex)3PCoCl2 complex was prepared as follows. Anhydrous CoCl2 (46.7 mg, 0.36 mmol) was added to a previously flame-dried 50-mL round two-necked bottom flask fitted with a flow control gas inlet and magnetic stir-bar loaded in a glove box under nitrogen. The nitrogen atmosphere was removed and the flask purged with dry argon.

Freshly distilled, degassed THF (5 mL) was added, and upon stirring at room temperature for 15 min, a clear deep blue solution formed. A solution of (Cyhex)3P(200 mg, 0.71 mmol) in freshly distilled, degassed ether (5 mL) was added drop wise to yield a blue

47 turbid solution. After stirring at room temperature for 15 h, 20 mL freshly distilled, degassed hexane was added in one portion to yield a blue precipitate. The resulting precipitate was filtered on a sintered glass fret under argon atmosphere, and washed with diethyl ether and hexane (1:1) mixture (3 X 5 mL) to remove any unreacted DPPP, resulting in quantitative yield of a light blue solid, which was used with no further purification

Synthesis of Isolated PDI-Cobalt(I) complexes

iPrPDI-Cobalt(I) chloride: A mixture iPrPDI-Cobalt(II) chloride (3.00 g, 4.91 mmol,

1.0 equivalents), activated Zinc dust (1.60 g, 24.47 mmol, 5.0 equivalents) and distilled anhydrous THF (100 mL) was stirred overnight under inert atmosphere. The quality of the zinc dust is very important for this reduction to work properly; appearance of a purple color solution indicates successfully reduction. The solvent was removed under reduced pressure to afford crude product which was extracted with toluene and filtered inside the dry-box. The filtrate was concentrated and the product crystallized from a hexane/toluene

(1:1) to afford iPrPDI-Cobalt(I) chloride as reddish-pink crystals. 1H and 13C NMR matched with the reported literature. [59]

Mes Mes PDI-Cobalt(I) chloride: was prepared from PDI-CoCl2 complex (3.57 g, 6.77 mmol, 1.0 equivalents), activated Zinc powder (2.7 g, 41.5 mmol, 6.0 equivalents) and distilled anhydrous THF (100 mL) according to the procedure described for iPrPDI-

Cobalt(I) chloride to afford MesPDI-Cobalt(I) chloride as a dark pink crystalline solid. 1H and 13C NMR matched with the reported literature.[59]

Mes(PDI)Co(I)-Me: was prepared according to previously reported procedure[59]. To a

500-mL schlenk flask wad added MesPDI-Cobalt(I) chloride (1.21 g, 2.45 mmol 1.0 equivalents) and distilled anhydrous toluene (100 mL), the flask was cooled in dry-ice bath (~ -40 oC) and stirred for 30 min. Methyl lithium (1.31 ml, 1.6 M, 2.09 mmol) was added dropwise and the mixture allowed to warm to r.t and stirred overnight. All volatiles were removed and the crude product extracted in toluene. Pure Mes(PDI)Co(I)-Me was obtained by crystallization in toluene/THF/hexane mixture to afford 0.99 g (85 % yield).

The 1H NMR matches that previously reported in literature.[59]

Synthesis of starting materials (Alkenes)

All the alkenes were purchased from commercial vendors or synthesized using the reported literature method.[51]

General procedure cobalt-catalyzed hydrosilylation of alkene (Eq 1.20)

An alkene (0.3 mmol) was added to a solution of cobalt (II) chloride iPrPDI complex (9.2 mg, 0.015 mmol, 0.05 equivalents) in anhydrous toluene (0.16 M) at -78 oC (bath temperature) under an atmosphere of argon. At -78 oC, toluene solution of sodium triethyl borohydride (0.03 mmol, 0.1 equivalents) was added, followed by a silane (0.33 mmol,

1.1 equivalents). The reaction mixture was removed from the cold bath and was further stirred at room temperature for 5 h. The reaction was monitored by GC and GCMS. After completion the reaction (~ 5 h), it was filtered through the pad of silica by adding hexane and was concentrated under vacuum. Isolated yields were determined after purification by silica chromatography using hexane as eluent.

Cobalt-catalyzed hydrosilylation procedure of 1-octene 1 using EtPDI complex

The above experiment was repeated with 1 (0.9 mmol) and cobalt (II) chloride EtPDI complex (25 mg, 0.044 mmol, and 0.05 equivalents) in anhydrous toluene (0.16 M) at -78 oC (bath temperature) under an atmosphere of argon. Isolated yield of mixture 24 and 25

(60:40, 89%) was determined after purification by silica chromatography using hexane as eluent.

Mes Cobalt-catalyzed hydrosilylation procedure of 1-octene 1 using ( PDI)CoCl2 complex

An alkene (0.9 mmol) was added to a solution of cobalt (II) chloride MesPDI complex

(23.5 mg, 0.044 mmol, and 0.05 equivalents) in anhydrous toluene (0.16 M) at -78 oC

(bath temperature) under an atmosphere of argon. At -78 oC, toluene solution of sodium triethyl borohydride (0.09 mmol, 0.1 equivalents) was added, followed by phenylsilane

(0.98 mmol, 1.1 equivalents). The reaction mixture was removed from the cold bath and was further stirred at room temperature for 5 h. The reaction was monitored by GC and

GCMS. After completion the reaction, it was filtered through the pad of silica by adding hexane and was concentrated under vacuum. Isolated yield of mixture 24 and 25 (53:47,

86%) was determined after purification by silica chromatography using hexane as eluent.

Cobalt-catalyzed hydrosilylation procedure of 1-octene 1 using iPrPDI complexes

The above experiment was repeated with 1 (0.9 mmol) and cobalt (II) chloride iPrPDI complex (27.5 mg, 0.045 mmol, and 0.05 equivalents) in anhydrous toluene (0.16 M) at -

78 oC (bath temperature) under an atmosphere of argon. Isolated yield of mixture 24 and

25 (98:2, 87%) was determined after purification by silica chromatography using hexane as eluent.

Procedure for cobalt-catalyzed dehydrogenative hydrosilylation of 1-octene 1 using

Mes ( PDI)CoCl2 complex and (OTMS)2SiMeH

A 50 mL Schlenk flask was charged with 1-octene (0.1 g, 0.9 mmol, 1 equivalents),

Mes bis(trimethylsiloxy)methylsilane (0.45 mmol, 0.5 equivalents), PDI (CoCl2) complex

(9.5 mg, 0.018 mmol, 0.02 equivalents) at room temperature. At rt, toluene solution of sodium triethylborohydride (0.036 mmol, 0.04 equivalents) was added to the reaction mixture. The reaction was stirred for 1 h at room temperature. The reaction was quenched by exposure to air and the addition of hexane. Finally, it was filtered through the pad of silica by adding hexane and was concentrated under vacuum. The product

(dehydrogenative silylation+ octane) was confirmed by GC-MS and NMR.

Cobalt-Catalyzed Dehydrogenative hydrosilylation Procedure of 1-octene 1 using

MesPDI –Me complex (Eq 1.14)

A 50 mL schlenk flask was charged with MesPDI (Co-Me) complex (5 mg, 0.009 mmol,

0.005 equivalents), bis(trimethylsiloxy)methylsilane (0.45 mmol) and 1-octene (0.1 g, 0.9 mmol, 1 equivalents. The reaction was stirred for 15 min at room temperature. The reaction was quenched by exposure to air and the addition of hexane. Finally, it was

51 filtered through the pad of silica by adding hexane and was concentrated under vacuum.

The product (dehydrogenative silylation+ octane) was confirmed by GC-MS and NMR

Hydrosilylation of 4-methylstyrene 14 using isolated iPrPDI-Co(I)Cl (Eq 1.25)

4-Methylstyrene (0.43 mmol) was added to a solution of iPrPDI-cobalt(I) chloride complex (12.3 mg, 0.021 mmol, 0.05 equivalents) in anhydrous toluene (0.16 M) at -78 oC (bath temperature) under an atmosphere of argon. At -78 oC, phenylsilane (0.46 mmol,

1.1 equivalents) was added. The reaction mixture was removed from the cold bath and was further stirred at room temperature for 24 h. The reaction was monitored by GC and

GCMS. After 24 h, it was filtered through the pad of silica by adding hexane and was concentrated under vacuum. GC, GC-MS and NMR confirm the presence of only starting material. No hydrosilylated product was formed under such condition.

Hydrosilylation of 4-methylstyrene using isolated iPrPDI-Co(I)Cl and sodium triethylborohydride (Eq 1.27).

4-Methylstyrene (0.43 mmol) was added to a solution of (iPrPDI)Co(I)Cl complex (12.3 mg, 0.021 mmol, 0.05 equivalents) in anhydrous toluene (0.16 M) at -78 oC (bath temperature) under an atmosphere of argon. At -78 oC, toluene solution of sodium triethyl borohydride (0.021 mmol, 0.05 equivalents) was added followed by the addition of phenylsilane (0.46 mmol, 1.1 equivalents) was added. The reaction mixture was removed from the cold bath and was further stirred at room temperature for 2 h. The reaction was monitored by GC and GCMS. After 2 h, it was filtered through the pad of silica by

adding hexane and was concentrated under vacuum. The product was confirmed by GC-

MS and NMR. Isolated yield of 15 (94%) was determined after purification by silica chromatography using hexane as eluent.

Hydrosilylation of 4-methylstyrene using isolated iPrPDI-Co(I)Cl and triethylborane

(Et3B) (Eq 1.28)

The above experiment was repeated except 5 mol% cobalt catalyst and 15 mol% of Et3B

(in THF) was used. Isolated yield of 15 (96%) was determined after purification by silica chromatography using hexane as eluent. Purity was ascertained by GC and 1H

NMR.

iPr Hydrosilylation of 4-methylstyrene using isolated PDI-Co(I)Cl and B(C6F5)3 (Eq

1.29)

4-Methylstyrene (0.43 mmol) was added to a solution of iPrPDI-cobalt(I) chloride complex (12.3 mg, 0.021 mmol, 0.05 equivalents) and B(C6F5)3 (0.06 mmol, 33 mg, 0.15 equivalents) in anhydrous toluene (2.5 mL) at -78 oC (bath temperature) under an atmosphere of argon. At -78 oC phenylsilane (0.46 mmol, 1.1 equivalents) was added via syringe. The reaction mixture was removed from the cold bath and was further stirred at room temperature for 2 h. The reaction was monitored by GC and GCMS. After completion the reaction, it was filtered through the pad of silica by adding hexane and was concentrated under vacuum. Isolated yield (96%) was determined after purification

53 by silica chromatography using hexane as eluent. Purity was ascertained by GC and 1H

NMR

General procedure for hydrosilylation reaction using neat substrate (Eq 1.21)

An alkene (0.5 g, 4.23 mmol) was added to Cobalt (II) chloride iPrPDI complex (129.2 mg, 0.21 mmol, 0. 05 equivalents) at -78 oC under an atmosphere of argon. At -78 oC, toluene solution of sodium triethyborohydride (0.42 mmol, 0.1 equivalents, 1 M in toluene) was added, followed by an addition of phenylsilane (4.65 mmol, 1.1 equivalents,

0.57 mL). The flask was removed from the cold bath and allow to warming to room temperature. The reaction mixture was stirred at room temperature for 4 h – 5 h. After completion of the reaction, it was filtered through the pad of silica by adding hexane and was concentrated under vacuum. Isolated yield was determined after purification by silica chromatography using hexane as eluent.

Procedure for hydrosilylation reaction under low catalyst loading (1 mol%)

Hydrosilylation of 4-phenyl-1-butene 33 (with 1 mol% catalyst). The alkene (4-phenyl-1- butene, 0.5 g, 3.79 mmol) was added to a solution of iPrPDI-cobalt(II) chloride complex

(23.1 mg, 0.04 mmol, 0. 01 equivalents) at -78 oC under an atmosphere of argon. At -78 oC, toluene solution of sodium triethyborohydride (0.07 mmol, 0.02 equivalents, 1 M in toluene) was added, followed by a addition of phenylsilane (4.17 mmol, 1.1 equivalents,

0.51 mL). The flask was removed from the cold bath and placed in an oil bath preheated to 40 oC (~ in 2-3 min). The reaction mixture was stirred at 40 oC for 2 h. After

54 completion (GC) of the reaction, it was filtered through the pad of silica by adding hexane and was concentrated under vacuum. Isolated yield (96%) was determined after purification by silica chromatography using hexane as eluent.

Hydrosilylation of 4-methylstyrene 13 (with 1 mol% catalyst). The alkene (4- methylstyrene, 0.5 g, 4.23 mmol) was added to a solution of iPrPDI-cobalt(II) chloride complex (25.9 mg, 0.04 mmol, 0. 01 equivalents) at -78 oC under an atmosphere of argon. At -78 oC, toluene solution of sodium triethyborohydride (0.08 mmol, 0.02 equivalents, 1 M in toluene) was added, followed by an addition of phenylsilane (4.65 mmol, 1.1 equivalents, 0.57 mL). The flask was removed from the cold bath and placed in an oil bath preheated to 40 oC (~ in 2-3 min). The reaction mixture was stirred at 40 oC for 2 h. After completion (GC) of the reaction, it was filtered through the pad of silica by adding hexane and was concentrated under vacuum. Isolated yield (93%) was determined after purification by silica chromatography using hexane as eluent

Procedure for hydrosilylation reaction of 1-octene 1 using iPrPDI complexes under low catalyst loading (1 mol%)

1-Octene (0.5 g, 4.46 mmol) was added to a solution of iPrPDI-cobalt(II) chloride complex (27.3 mg, 0.044 mmol, 0. 01 equivalents) at -78 oC (bath temperature) under an atmosphere of argon. At -78 oC, toluene solution of sodium triethyborohydride (0.09 mmol, 0.02 equivalents) was added, followed by phenylsilane (1.32 mmol, 1.1 equivalents, 0.16 mL). The flask was removed from the cold bath and placed in an oil bath preheated to 40 oC (~ in 2-3 min). The reaction mixture was stirred at 40 oC for 2 h.

The reaction was monitored by GC and GCMS. After completion of the reaction, it was filtered through the pad of silica by adding hexane and was concentrated under vacuum.

Isolated yield of 24 and 25 (89%, 97:3) was determined after purification by silica chromatography using hexane as eluent

Procedure for deuterium labeling studies

An alkene (0.9 mmol) was added to a solution of cobalt (II) chloride iPrPDI complex (5 mg, 0.09 mmol, and 0.01 equivalents) in anhydrous toluene (0.16 M) at -78 oC (bath temperature) under an atmosphere of argon. At -78 oC, toluene solution of sodium triethyl borohydride (0.17 mmol, 0.02 equivalents) was added followed by addition of PhSiD3

(0.98 mmol, 1.1 equivalents). The flask was removed from the cold bath and placed in an oil bath preheated to 40 oC (~ in 2-3 min). The reaction mixture was stirred at 40 oC for 2 h. The reaction was monitored by GC and GCMS. After completion the reaction, it was filtered through the pad of silica by adding hexane and was concentrated under vacuum.

Isolated yield (88%) was determined after purification by silica chromatography using hexane as eluent. GC-MS and 1H NMR and 2H NMR established the structure of the product

Analytical Data for Products of Hydrosilylation of Alkenes

2-(4-Methylphenyl)(ethyl)silane 14

SiH2Ph

1 H NMR (600 MHz, CDCl3) δ 7.60-7.59 (m, 2H), 7.42-7.37 (m,

3 3H), 7.11 (s, 4H), 4.35 (t, JH,H = 3.6 Hz, 2H), 2.77-2.74 (m, 2H), 2.34 (s, 3H), 1.33-1.29

(m,2H)

13 C NMR (150 MHz, CDCl3) δ 141.1, 135.5, 135.4, 132.4, 129.8, 129.2, 128.2, 127.9,

127.9, 30.9, 21.2, 12.4.

GC (methyl silicone column, 80 0 C/ 5 min, rate = 20 oC, 250 oC = 40 min) RT for product = 11.23 min.

GC (methyl silicone column, 200 0 C/ Isotherm) RT for product = 2.14 min.

GC-MS m/z [M+] 226.12; exact mass calculated for C15H18Si 226.10.

Octyl(phenyl) silane 24

SiH2Ph C H 1 6 13 H NMR (400 MHz, CDCl3) δ 7.61-7.59 (m, 2H), 7.42-7.36 (m, 3H),

4.31 (t, 3J H, H= 3.7 Hz, 2H), 1.51-1.45 (m, 2H), 1.40-1.34 (m, 2H), 1.33- 1.26 (m, 8H),

1.00-0.94 (m, 2H), 0.91 (t, 3JH, H, J = 6.9 Hz, 3H).

13 C NMR (100 MHz, CDCl3) δ 135.2, 132.8, 129.5, 127.9, 32.8, 31.9, 29.3, 29.2, 25.1,

22.7, 14.1, 10.0.

GC (methyl silicone column, 180 0 C/Isotherm) RT for product = 3.09 min.

GC-MS m/z [M+] 220.10; exact mass calculated for C14H24Si 220.16.

Octyl(phenyl)silane 24 and 25 (obtained as a mixture Eq 1.16)

SiH2Ph

PhH2Si C H C H 1 6 13 6 13 H NMR (400 MHz, CDCl3) δ 7.58-7.55 (m, 4H), 7.39-

3 7.33 (m, 6H), 4.29-4.17 (m, 4H), 1.52-1.41 (m, 4H), 1.36-1.25 (m, 20H), 1.05 (d, JH, H =

3 6.8 Hz, 3H), 0.96-0.90 (m, 2H), 0.88 (t, JH, H = 6.7 Hz, 6H).

13 C NMR (100 MHz, CDCl3) δ 135.8, 135.4, 133.1, 132.5, 129.7, 129.7, 128.2, 128.1,

33.7, 33.1, 32.1, 32.0, 29.6, 29.4, 29.4, 28.7, 25.3, 22.9, 16.5, 16.4, 14.3, 10.2.

GC (methylsilicone column, 150 0 C/Isotherm) RT for product = 8.35 min and 8.82 min.

GC-MS m/z [M+] 220.10; exact mass calculated for C17H28 Si 220.16.

1-ethyl-4-methylbenzene 28

1 3 H NMR (600 MHz, CDCl3) δ 7.23 (s, 4H), 2.75 (q, JH, H = 7.6 Hz, 2H),

3 2.46 (s, 3H), 1.36 (t, JH, H = 7.6 Hz, 3H).

13 C NMR (150 MHz, CDCl3) δ 141.3, 135.0, 129.1, 127.8, 28.5, 21.0, 15.8.

GC (methyl silicone column, 80 0 C/ Isotherm) RT for product = 3.55 min.

GC-MS m/z ([M+) 120.10; exact mass calculated for C9H12 = 120.09.

(4-Methylphenethyl)diphenylsilane 29

SiHPh2

1 H NMR (600 MHz, CDCl3) δ 7.78-7.76 (m, 4H), 7.59-7.54 (m,

6H), 7.27 (s, 4H), 5.10 (t, 3 JH, H = 3.6 Hz, 2H), 2.94-2.91 (m, 2H), 2.50 (s, 3H), 1.71-

1.68 (m, 2H). 58

13 C NMR (150 MHz, CDCl3) δ 141.9, 138.4, 135.7, 135.7, 135.4, 134.7, 130.2, 129.6,

128.8, 128.6, 128.3, 125.9, 30.5, 21.5, 15.0.

GC (methyl silicone column, 230 0 C/ Isotherm) RT for product = 8.51 min.

GC-MS m/z [M+] 302.10; exact mass calculated for C21H22Si 302.15.

Methyl(4-methylphenethyl)(phenyl) silane 30

SiHMePh

1 H NMR (400 MHz, CDCl3) δ 7.63-7.61 (m, 2H), 7.45-7.41 (m,

3H), 7.14 (s, 4H), 4.49-4.45 (m, 1H), 2.74 (t, 3 JH, H = 3.6 Hz, 2H), 2.37 (s, 3H), 1.30 -

1.23 (m, 2H), 0.42 (d, 3 JH, H = 3.8 Hz, 3H).

13 C NMR (100 MHz, CDCl3) δ 141.7, 136.5, 135.3, 134.6, 129.5, 129.3, 128.2, 127.9,

30.2, 21.2, 15.8, -5.4.

GC (methyl silicone column, 140 0 C/ Isotherm) RT for product = 6.65 min.

GC-MS m/z [M+] 240.10; exact mass calculated for C16H20Si 240.13.

2-[(4-Isobutylphenyl)ethyl)](phenyl)silane 49

SiH2Ph

1 H NMR (600 MHz, CDCl3) δ 7.62-7.60 (m, 2H), 7.44-7.38

3 3 (m, 3H), 7.16-7.09 (m, 4H), 4.37 (t, JH,H = 3.6 Hz, 2H), 2.82-2.78 (m, 2H), 2.49 (t, JH,H

3 = 7.2 Hz, 2H), 1.94-1.86 (m, 1H), 1.38-1.32 (m, 2H), 0.95 (d, JH,H = 6.6 Hz, 6H).

13 C NMR (125 MHz, CDCl3) δ 141.8, 139.7, 135.8, 132.9, 130.2, 129.7, 128.6, 128.2,

45.7, 31.3, 30.9, 23.0, 12.7.

GC (methyl silicone column, 200 0 C/ Isotherm) RT for product = 5.90 min.

GC-MS m/z [M+] 268.10; exact mass calculated for C18H24Si 268.18.

(4-Chlorophenethyl)(phenyl) silane 50

SiH2Ph

1 Cl H NMR (400 MHz, CDCl3) δ 7.41-7.39 (m, 2H), 7.27-7.19 (m,

3 3H), 7.09-7.06 (m, 2H), 6.96-6.93 (m, 2H), 4.17 (t, JH,H = 3.6 Hz, 2H), 2.60-2.55 (m,

2H), 1.15-1.09 (m, 2H).

13 C NMR (100 MHz, CDCl3) δ 142.5, 135.4, 132.1, 131.7, 129.9, 129.4, 128.6, 128.3,

30.7, 12.3.

GC (methyl silicone column, 180 0 C/ Isotherm) RT for product = 4.51 min.

GC-MS m/z [M+] 246.10; exact mass calculated for C14H15ClSi 246.06.

4-(2-(Phenylsilyl)ethyl)phenyl acetate 51

SiH2Ph

1 AcO H NMR (400 MHz, CDCl3) δ 7.58-7.56 (m, 2H), 7.43-7.35 (m,

3 3H), 7.20-7.18 (m, 2H), 7.00-6.97 (m, 2H), 4.33 (t, JH,H = 3.6 Hz, 2H), 2.78-2.74 (m,

2H), 2.29 (s, 3H), 1.33-1.27 (m, 2H).

13 C NMR (100 MHz, CDCl3) δ 169.7, 148.8, 141.6, 135.3, 132.0, 129.7, 128.8, 128.1,

121.4, 30.6, 21.2, 12.1.

GC (methyl silicone column, 180 0 C/ Isotherm) RT for product = 8.35 min.

GC-MS m/z [M+] 270.10; exact mass calculated for C16H18O2Si 270.11.

(3-Bromophenethyl)(phenyl) silane 52

Br SiH2Ph

1 H NMR (400 MHz, CDCl3) δ 7.57-7.55 (m, 2H), 7.41-7.34 (m,

3 3H), 7.33-7.29 (m, 2H), 7.15-7.10 (m, 2H), 4.31 (t, JH,H = 3.6 Hz, 2H), 2.75-2.71 (m,

2H), 1.31-1.26 (m, 2H).

13 C NMR (100 MHz, CDCl3) δ 146.5, 135.5, 132.0, 131.2, 130.1, 130.0, 129.2, 128.3,

126.8, 122.7, 31.0, 12.2.

GC (methyl silicone column, 200 0 C/ Isotherm) RT for product = 3.57 min.

GC-MS m/z [M+] 290.10; exact mass calculated for C14H15BrSi 290.01.

(3-Phenoxyphenethyl) (phenyl) silane 53

SiH2Ph

1 OPh H (400 MHz, CDCl3) δ 7.55-7.53 (m, 2H), 7.40-7.33 (m, 3H), 7.32-

7.27 (m, 3H), 7.24-7.18 (m, 1H), 7.10-7.06 (m, 1H), 6.99-6.91 (m, 2H), 6.86- 6.74 (m,

2H), 6.31-6.22 (m, 1H), 4.29 (t, 3J H, H= 3.6 Hz, 2H), 2.76-2.71 (m, 2H), 1.30-1.22 (m,

2H).

13 C (100 MHz, CDCl3) δ 157.4, 157.2, 146.0, 135.6, 135.2, 133.6, 131.9, 129.6, 128.0,

123.0, 122.9, 118.7, 118.5, 116.4, 30.9, 11.9.

GC (methyl silicone column, 230 0 C/ Isotherm) RT for product = 8.51 min.

GC-MS m/z [M+] 304.13; exact mass calculated for C20H20OSi 304.12.

Phenyl (3-phenylpropyl) silane 54

SiH2Ph 1 H NMR (600 MHz, CDCl3) δ 7.43-7.41 (m, 2H), 7.27-7.20 (m,

3 3 3H), 7.15-7.13 (m, 2H), 7.06-7.02 (m, 3H), 4.19 (t, J H,H = 3.7 Hz, 2H), 2.54 (t, JH,H =

7.6 Hz, 2H), 1.69-1.64 (m, 2H), 0.87-0.84 (m, 2H,).

13 C NMR (100 MHz, CDCl3) δ142.5, 135.6, 132.8, 129.9, 128.8, 128.6, 128.4, 126.1,

39.3, 27.4, 10.1.

GC (methyl silicone column, 170 0 C/ isothermal) RT for product = 6.71 min.

GC-MS m/z ([M+) 226.10; exact mass calculated for C15H18Si 226.12.

Phenyl (4-phenylbutyl) silane 55

SiH2Ph

1 H NMR (400 MHz, CDCl3) δ 7.78-7.76 (m, 2H), 7.58-7.52 (m,

3H), 7.49-7.45 (m, 2H), 7.39-7.35 (m, 3H), 4.54 (t, 3J H,H = 3.7 Hz, 2H), 2.81 (t, 3J H,H

= 7.7 Hz, 2H), 1.94-1.87 (m, 2H), 1.77- 1.69 (m, 2H), 1.21-1.16 (m, 2H).

13 C NMR (100 MHz, CDCl3) δ 142.6, 135.3, 132.7, 129.6, 128.5, 128.4, 128.1, 125.7,

35.7, 34.7, 24.9, 10.1.

GC (methyl silicone column, 180 0 C/ Isotherm) RT for product = 6.85 min.

GC-MS m/z ([M+) 240.13; exact mass calculated for C16H20Si 240.10.

[(2-(Benzo[d][1,3]dioxol-5-yl)ethyl](phenyl)silane 56

O SiH2Ph

1 O H NMR (400 MHz, CDCl3) δ 7.59-7.56 (m, 2H), 7.42-7.36 (m,

3H), 6.74-6.70 (m, 2H), 6.66-6.63 (m, 1H), 5.92 (s, 2H), 4.32 (t, 3J, H, H = 3.6 Hz, 2H),

2.73-2.69 (m, 2H), 1.31-1.25 (m, 2H).

13 C NMR (100 MHz, CDCl3) 147.9, 145.9, 138.2, 135.5, 132.4, 129.9, 128.3, 120.8,

108.7, 108.4, 101.0, 31.2, 12.7.

GC (methyl silicone column, 180 0 C/ Isotherm) RT for product = 10.86 min.

GC-MS m/z [M+] 256.10; exact mass calculated for C15H16O2Si 256.09.

(2-(2-Fluoro-[1, 1’-biphenyl]-4-yl)ethyl)(phenyl)silane 57

F SiH2Ph

1 Ph H NMR (400 MHz, CDCl3) δ 7.60-7.54 (m, 4H), 7.47-7.32 (m,

7H), 7.05-6.98 (m, 2H), 4.37 (t, 3J H, H= 3.6 Hz, 2H), 2.83-2.79 (m, 2H), 1.38-1.32 (m,

2H).

13 C NMR (100 MHz, CDCl3) δ 161.1, 158.6, 146.0, 136.1, 130.6, 129.1, 129.0, 128.5,

127.5, 126.4, 126.3, 124.0, 115.6, 115.4, 28.5, 15.4.

GC (methyl silicone column, 180 0 C/ 10 min, rate = 15oC, 250 oC = 40 min) RT for product = 18.97.

GC-MS m/z [M+] 306.10; exact mass calculated for C20H19FSi 306.12.

(3-(3-Iodophenyl)butyl)(phenyl)silane 58

I SiH2Ph 1 H NMR (400 MHz, CDCl3) δ 7.54 -7.50 (m, 3H), 7.40-7.28

3 (m, 4H), 7.18-7.10 (m, 1H), 7.02 (t, JH,H = 7.6 Hz, 1H), 4.27-4.26 (m, 2H), 2.71-2.59 (m,

3 1H), 1.74 -1.66 (m, 2H), 1.22 (d, JH,H = 6.9 Hz, 3H), 0.89-0.77 (m, 2H).

13 C NMR (100 MHz, CDCl3) δ 150.1, 136.7, 135.7, 130.6, 130.1, 128.8, 128.5, 127.6,

126.9, 95.1, 42.8, 34.0, 22.1, 8.5.

GC (methyl silicone column, 180 0 C/ 5 min, rate = 15 oC, 230 oC = 40 min) RT for product = 10.01 min.

GC-MS m/z [M+] 366.10; exact mass calculated for C16H19ISi 366.03.

(3-(6-Methoxynaphthalen-2-yl)butyl)(phenyl)silane 59

SiH2Ph

O 1 H NMR (400 MHz, CDCl3) δ 7.61-7.55 (m, 2H), 7.41-7.39

3 (m, 3H), 7.29-7.16 (m, 4H), 7.04-7.01 (m, 2H), 4.18 (t, JH,H = 3.6 Hz, 2H), 3.79 (s, 3H),

3 2.73-2.68(m, 1H), 1.75-1.66 (m, 2H), 1.21(d, JH,H = 6.9 Hz, 3H), 0.82-0.68 (m, 2H).

13 C NMR (100 MHz, CDCl3) δ 157.4, 142.3, 135.4, 133.4, 132.6, 129.7, 129.2, 129.2,

128.1, 127.0, 126.5, 125.5, 118.8, 105.9, 55.4, 42.7, 33.8, 22.1, 8.31.

GC (methyl silicone column, 240 0 C/ Isotherm) RT for product = 10.37 min.

GC-MS m/z [M+] 320.10; exact mass calculated for C21H24OSi 320.16.

. (2-naphthalen-2-yl)ethyl)(phenyl)silane 60

SiH2Ph

1 H NMR (400 MHz, CDCl3) δ 7.84-7.78 (m, 2H), 7.64-7.61 (m,

3 3H), 7.50-7.35 (m, 7H), 4.39 (t, JH,H = 3.6 Hz, 2H), 2.99-2.95 (m, 2H), 1.46-1.40 (m,

2H).

13 C NMR (100 MHz, CDCl3) δ 141.5, 135.4, 133.7, 132.2, 132.1, 129.8, 128.1, 128.0,

127.7, 127.6, 127.0, 126.0, 125.8, 125.2, 31.4,12.1.

GC (methyl silicone column, 200 0 C/ Isotherm) RT for product = 6.56 min.

GC-MS m/z ([M+) 262.10; exact mass calculated for C18H18Si 262.12.

(2-(6-Methoxynaphthalen-2-yl)ethyl)(phenyl)silane 61

SiH2Ph

O 1 3 H NMR (400 MHz, CDCl3) δ 7.68 (d, JH,H = 8.4 Hz, 2H),

3 7.62-7.56 (m, 3H), 7.43-7.36 (m, 3H), 7.33-7.31 (m, 1H), 7.16-7.13 (m, 2H), 4.38 (t, JH,H

= 3.6 Hz, 2H), 3.92 (s, 3H), 2.95-2.91 (m, 2H), 1.44-1.38 (m, 2H).

13 C NMR (125 MHz, CDCl3) δ 157.5, 139.5, 135.6, 133.3, 132.5, 129.9, 129.4, 129.2,

128.4, 127.7, 127.1, 125.9, 118.9, 106.0, 55.6, 31.4, 12.4.

GC (methyl silicone column, 210 0 C/ Isotherm) RT for product = 12.72 min.

GC-MS m/z [M+] 292.10; exact mass calculated for C19H20OSi 292.13.

Trimethyl(3-(phenylsilyl)propyl) silane 62

Me Me PhH2Si Si 1 Me H NMR (600 MHz, CDCl3) δ 7.65-7.64 (m, 2H), 7.46-7.41 (m,

3H,), 4.39 (t, 3 JH, H = 3.6 Hz, 2H), 1.63 -1.57 (m, 2H), 1.11-1.07 (m, 2H), 0.72-0.69 (m,

2H), 0.05 (s, 9H).

13 C NMR (150 MHz, CDCl3) δ 135.5, 133.1, 129.7, 128.3, 20.8, 20.1, 14.7, -1.3.

GC (methyl silicone column, 120 0 C/ Isotherm) RT for product = 7.13 min.

HRMS (EI), m/z calculated for C12H22Si2 (M+) 222.1260, found: 222.1256.

(4-methylpentyl)(phenyl) silane 63

SiH2Ph 1 H (400 MHz, CDCl3) δ 7.45-7.42 (m, 2H), 7.25-7.19 (m, 3H), 4.16

3 (t, JH,H = 3.7 Hz, 2H), 1.46 -1.37 (m, 1H), 1.36-1.29 (m, 2H), 1.15-1.09 (m, 2H), 0.82-

3 0.76 (m, 2H), 0.72 (d, JH,H = 6.6 Hz, 6H).

13 C NMR (100 MHz, CDCl3) δ 135.9, 133.5, 130.1, 128.6, 42.9, 28.3, 23.5, 23.2, 10.8.

GC (methyl silicone column, 100 0 C/ Isotherm) RT for product = 5.57 min.

GC-MS m/z [M+] 192.10; exact mass calculated for C12H20Si 192.13.

Decyl(phenyl) silane 64

SiH2Ph C H 1 8 17 H NMR (400 MHz, CDCl3) δ 7.58-7.56 (m, 2H), 7.39-7.34 (m, 3H),

4.29 (t, 3J H, H= 3.7 Hz, 2H), 1.50-1.42 (m, 2H), 1.37-1.26 (m, 14H), 0.97- 0.92 (m, 2H),

0.89 (t, 3JH, H, J = 6.8 Hz, 3H).

13 C NMR (100 MHz, CDCl3) δ 135.6, 133.2, 129.8, 128.3, 33.2, 32.3, 29.9, 29.9, 29.7,

29.6, 25.4, 23.0, 14.5, 10.4

GC (methyl silicone column, 155 0 C/Isotherm) RT for product = 7.59 min.

GC-MS m/z [M+] 248.10; exact mass calculated for C16H28Si 248.20.

(2-cyclohexylethyl)(phenyl) silane 65

SiH2Ph

1 H NMR (600 MHz, CDCl3) δ 7.60-7.58 (m, 2H), 7.42-7.36 (m, 3H),

4.31 (t. 3J H, H= 3.6 Hz, 2H), 1.77-1.70 (m, 4H), 1.68-1.65 (m, 1H), 1.38-1.34 (m, 2H),

1.27-1.12 (m, 4H), 0.98- 0.94 (m, 2H), 0.90- 0.84 (m, 2H)

13 C NMR (100 MHz, CDCl3) δ 135.4, 133.0, 129.6, 128.1, 40.4, 33.1, 32.8, 26.9, 26.5,

7.3.

GC (methyl silicone column, 160 0 C/Isotherm) RT for product = 5.57 min.

GC-MS m/z ([M+) 218.10; exact mass calculated for C14H22Si 218.15.

Cyclooctyl(phenyl)silane 66

SiH2Ph

1 H NMR (400 MHz, CDCl3) δ 7.60-7.57 (m, 2H), 7.41-7.34 (m, 3H),

4.21 (d, J= 3.3 Hz, 2H), 1.86-1.80 (m, 2H), 1.73-1.67 (m, 2H), 1.62-1.40 (m, 10H), 1.30-

1.27 (m, 1H).

13 C NMR (100 MHz, CDCl3) δ 135.6, 132.6, 129.4, 127.9, 28.7, 27.4, 26.9, 26.6, 20.2

GC (methyl silicone column, 180 o C = 5 min, rate = 15oC, 250oC = 40 min) RT for product = 4.71 min.

HRMS (EI) calculated for C14H22Si = 218.1485. Exact mass found = 218.1490.

(1-(4-chlorophenyl)ethyl)(phenyl)silane 67 (obtained as a mixture with 50, Table

1.11 entry 2)

SiH2Ph

1 Cl H NMR (400 MHz, CDCl3) δ 7.41-7.38 (m, 3H), 7.34-7.32 (m, 2H),

3 7.22- 7.19 (m, 2H), 7.01-6.99 (m, 2H), 4.31 (d, JH,H = 3.1 Hz, 2H), 2.62-2.57 (m, 1H),

3 1.43 (d, JH,H = 7.4 Hz, 3H).

13 C NMR (100 MHz, CDCl3) δ 143.6, 136.2, 136.1, 130.4, 128.9, 128.9, 128.6, 128.4,

25.5, 16.8.

GC (methyl silicone column, 180 0 C/ Isotherm) RT for product = 5.22 min.

GC-MS m/z ([M+) 246.10; exact mass calculated for C14H15ClSi 246.06.

Phenyl(1-phenylethyl)silane and phenethyl(phenyl)silane 70 & 69 (Table 1.11, entry

SiH2Ph

1 H NMR (400 MHz, CDCl3) δ 7.58-7.52 (m, 1H), 7.38

-7.31 (m, 5H), 7.29-7.20 (m, 5H), 7.11-7.05 (m, 4H), 4.38-4.24 (m, 4H), 2.76-2.72(m,

3 2H), 2.62-2.56 (m, 1H), 1.43 (d, JH,H = 7.5 Hz, 3H), 1.31-1.25 (m, 2H).

13 C NMR (100 MHz, CDCl3) δ 144.9, 144.3, 136.0, 135.6, 131.7, 130.2, 130.1, 130.0,

128.7, 128.5, 128.4, 128.2, 128.2, 127.5, 126.1, 125.4, 31.4, 25.7, 16.7, 12.4.

GC (methyl silicone column, 140 0 C/ Isotherm) RT for products = 8.02 min and 10.88 min.

GC-MS m/z ([M+) 212.12; exact mass calculated for C14H16Si 212.10.

(1-(3-bromophenyl)ethyl)(phenyl)silane 71 (obtained as a mixture with 52, Table

1.11 entry 4)

SiH2Ph Br

1 H NMR (400 MHz, CDCl3) δ 7.33-7.27 (m, 3H), 7.26-7.20 (m, 2H),

3 7.17-7.11 (m, 2H), 7.04 -6.98 (m, 1H), 6.90-6.89 (m, 1H), 4.22 (d, JH,H = 3.6 Hz, 2H),

3 2.52-2.46 (m, 1H), 1.34 (d, JH,H = 7.4 Hz, 3H).

13 C NMR (100 MHz, CDCl3) δ 147.2, 135.7, 135.2, 130.1, 130.0, 129.9, 128.1, 128.0,

125.8, 122.6, 25.4, 16.2.

GC (methyl silicone column, 180 0 C/ Isotherm) RT for product = 6.78 min.

GC-MS m/z ([M+) 290.10; exact mass calculated for C14H15BrSi 290.01.

(1-cyclohexylpropan-2-yl)(phenyl)silane and (3-cyclohexylpropyl)(phenyl)silane 74

& 73

SiH2Ph

SiH2Ph 1 H NMR (600 MHz, CDCl3) δ 7.59-7.57 (m,

4H), 7.40-7.35 (m, 6H), 4.24 (t, 3JH, H, J = 3.6 Hz, 4H), 1.70-1.67 (m, 8H), 1.66-1.63 (m,

2H), 1.51-1.45 (m, 4H), 1.28-1.17 (m, 12H), 1.16-1.13 (m, 1H), 1.05 (d, 3JH, H, J = 7.1

Hz, 3H), 0.95- 0.91 (m, 2H), 0.89-0.83 (m, 2H).

13 C NMR (100 MHz, CDCl3) δ 136.4, 135.9, 133.6, 133.0, 130.2, 129.9, 128.7, 128.6,

41.9, 41.5, 38.1, 36.3, 34.7, 34.1, 33.5, 27.5, 27.1, 27.0, 23.1, 16.9, 13.6, 11.0

GC (methyl silicone column, 160 0 C/Isotherm) RT for products = 9.01 min and 11.66 min.

GC-MS (methyl silicone): m/z ([M+) 232.10; exact mass calculated for C15H24Si 232.16.

Decan-2-yl(phenyl)silane and decyl(phenyl)silane 75 & 64

SiH2Ph

SiH2Ph C H C H 1 6 13 6 13 H NMR (400 MHz, CDCl3) δ 7.58-7.56

(m, 4H), 7.39-7.35 (m, 6H), 4.28 (t, 3J H, H= 3.7 Hz, 4H), 1.47-1.42 (m, 2H), 1.36-

1.35(m, 1H), 1.34-1.25 (m, 28H), 1.06-1.05 (m, 3H), 0.96-0.91 (m, 2H), 0.88 (t, 3JH, H, J

= 6.9 Hz, 6H).

13 C NMR (100 MHz, CDCl3) δ 136.2, 135.8, 133.4, 132.9, 130.0, 130.0, 128.5, 128.4,

34.0, 33.4, 32.5, 30.3, 30.2, 30.1, 29.9, 29.9, 29.8, 29.1, 25.6, 23.2, 16.8, 16.7, 14.7, 10.6.

GC (methyl silicone column, 200 0 C/Isotherm) RT for products = 3.10 min and 3.43 min.

GC-MS (methyl silicone): m/z ([M+) 248.10; exact mass calculated for C16H28Si 248.20.

(2-cyclohexylethyl)diphenyl) silane 76

SiHPh2

1 H NMR (600 MHz, CDCl3) δ 7.57-7.56 (m, 4H), 7.39-7.35 (m, 6H),

4.86- 4.84 (m, 1H), 1.76-1.68 (m, 4H), 1.66-1.64 (m, 1H), 1.36-1.34 (m, 2H), 1.23-1.12

(m, 6H), 0.85 (q, 3 JH, H = 12.0 Hz, 2H).

13 C NMR (100 MHz, CDCl3) δ 135.5, 135.1, 129.8, 128.3, 40.9, 33.3, 32.2, 27.1, 26.8, -

9.6.

GC (methyl silicone column, 160 0 C/Isotherm) RT for product = 5.77 min.

GC-MS m/z ([M+) 294.10; exact mass calculated for C20H26Si 294.18.

(2-cyclohexylethyl)(methyl)(phenyl) silane 77 SiHMePh

1 H NMR (600 MHz, CDCl3) δ 7.56-7.54 (m, 2H), 7.37-7.36 (m,

3H), 4.31 (m, 1H), 1.76-1.69 (m, 4H), 1.67-1.64 (m, 1H), 1.30-1.27 (m, 2H), 1.23-1.13

(m, 4H), 0.88- 0.82 (m, 4H), 0.34 (d, 3 JH, H = 3.8 Hz, 3H).

13 C NMR (150 MHz, CDCl3) δ 137.4, 134.9, 129.7, 128.4, 41.1, 33.6, 32.4, 27.4, 27.0,

11.0, -5.0.

GC (methyl silicone column, 160 0 C/Isotherm) RT for product = 5.77 min.

GC-MS (methyl silicone): m/z ([M+) 232.10; exact mass calculated for C15H24Si 232.16.

(Octyl-2-d)(phenyl)silane-d2 and Octane-2-yl-1-d)(phenyl)silane-d2 80

D SiD2Ph + SiD2Ph D C H 6 13 C6H13 85% 15% 1 H NMR (400 MHz, CDCl3) δ 7.62-7.56 (m, 2H),

7.42-7.33 (m, 3H), 4.29-4.27 (m, PhSi(H/D)3), 1.44-1.42 (m, 1H), 1.35-1.1.26 (m, 9H),

1.18- 1.10 (m, 0.2H), 1.08-1.017 (m, 0.3H), 0.93-0.86 (m, 4.2H).

2 2 2 H NMR (92.1 MHz, 5%CDCl3/CHCl3), δ 4.4 (2 H), 1.5 (1 H).

13 C NMR (100 MHz, CDCl3) δ 135.9, 135.5, 133.1, 130.2, 129.8, 128.4, 128.2, 128, 33.7,

2 33.04, 32.2, 32.1, 29.7, 29.5, 28.8, 24.9 (t, JC-D = 19.2 Hz), 22.9, 16.4, 16.3, 16.1, 15.9,

14.4, 10.1, 10.1.

GC-MS m/z [M+] 223.10; exact mass calculated for C14H21D3Si 223.18.

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Chapter 1B: Cobalt-Catalyzed Hydrosilylation of 1,3- and 1,4-Dienes

1B.1 Introduction:

1,3-Diene motifs is one of the most important and ubiquitous structural units in organic chemistry. Diene is also present in numerous natural products and drug candidates.[1] Dienes have been used for various synthetic transformations (e.g., Diels-

Alder, pericyclic transformations).[2] 1,3-Dienes have been attracting considerable interest as a key intermediate that are widely used in organic synthesis.[3] 1,3-Diene moiety can also be found in a variety of bioactive natural products including terpenoids, lipids and polyketides.[4] Dienes are readily accessible or can be synthesized by Witting reaction (Eq. 1.31) from their corresponding aldehydes.

MePPh3Br, nBuLi R O R (Eq. 1.31) THF, 0 oC - RT

Dienes are potentially desirable substrates for hydrosilylation because hydrosilylation reaction of 1,3-diene can produce a wider range of products than olefins. However, hydrosilylation of a diene is less studied than the hydrosilylation of other unsaturated substrates such as an alkene or alkyne. Hydrosilylation reaction is practiced on large scale as an industrial applications of homogeneous catalysis and is widely used for the production of various consumer goods and fine chemical synthesis.[5] The alkylsilanes

77 from alkene hydrosilylation are widely used as raw materials in manufacturing silicon rubbers, molding implants, releasing coatings and adhesive.[6] Organosilane are used for various synthetic transformations and many useful carbon-carbon bonds forming reaction. Among the various organic synthetic transformations, hydrosilylation is one of the most mild and functional group-tolerant reactions catalyzed by transition metals and is widely used in the synthesis of fine chemicals and complex organic molecules, as well as on large scale for the production of organosilane building blocks for material synthesis. Out of many useful carbon-carbon bond-forming reactions of organosilicon reagents are the Sakurai allylation (Scheme 1.4)[7] and the Peterson olefination reactions

(Scheme 1.5).[8]

R 3 R1 R O R3 R2 SiMe3 HO R R 1 Lewis Acid R2

LA LA R1 O O R SiMe3 SiMe3 LAO R R1 R R1 X

R1 R LAO

Scheme 1.4 Sakurai Allylation

OH R4 2 R3 R2 Acid R3 R2 R3Si R1 R R R4 4 1 R Si 3 OH O R4 Nuc R3 R3 R2 R1 R2 R3Si R1

R3Si O R4 R2 Base R4 R2

R3 R1 R3 R1

Scheme 1.5 Peterson Olefination

The carbon-silicon bond present in organosilane product produced by transition metal catalyzed hydrosilylation reaction can be transformed into carbon-oxygen bond using

Tamao-Fleming oxidation (Scheme 1.6).[5a, 9] A detail introduction to hydrosilylation reaction is given in chapter 1A.

SiMe2Ph OH 1. HBF4.OEt2 m R R1 2. CPBA, NEt3 R R1

Scheme 1.6 Tamao-Fleming Oxidation

1B.2 Backgrounds and Significance:

Dienes are readily accessible and hydrosilylation reaction of 1,3-diene can produce a wider range of products. Selectivity for 1,3-diene hydrosilylation is unpredictable and highly dependent on the catalyst structure, substrate and reaction conditions. There are only a limited number of reports on selective hydrosilylation of dienes and most known 79 catalysts generate mixture of isomers that are difficult to separate. Diene hydrosilylation usually give 1,2- and 1,4-addition products. In addition to the hydrosilylated product, side reaction can generate diene oligomers and redistribution of silane products (Scheme 1.7).

4 2 1 M (Cat.) SiR'3 SiR'3 R R R 3 HSiR' 3 1,2-addition 1,4-addition

SiR'3 R R'3Si SiR'3

oligomerization/ hydrosilylation Redistribution of Silane

Scheme 1.7 Common Products and Byproducts of 1,3-Diene Hydrosilylation

One principal goal in this area is to design efficient catalyst to do selective hydrosilylation of diene. Lappert et al. reported hydrosilylation of conjugated diene using nickel,[10] cobalt[11] and iron.[10a] These reports are limited to substrates such as isoprene,

1,3-pentadiene, 2,3-dimethylbuta-1,3-diene and 1,3-cyclohexadiene and gave the mixture of 1,2- and 1,4-addition products in modest yield (Scheme 1.8).

X3Si M(acac)3 Activator HSiX3 Neat, 2 h- 6 h SiX 81 3 X = OC2H5, C2H5, CH 3 1,4-addition 1,2-addition X3 = Cl2CH3 M = Ni, Co, Fe Activator = Et3Al 41-97% Yield

1,4-addition 1,2-addition

X = OC2H5, 82 X = OC2H5, 86 X = C2H5, 83 X = C2H5, 87 X = CH3, 84 X = CH3, 88 X = Cl CH , 89 X3 = Cl2CH3, 85 3 2 3

Scheme 1.8 Products of Hydrosilylation of Isoprene

Early report on platinum catalyzed diene hydrosilylation came before 1954 using Speier’s catalyst (H2PtCl6) but the reaction was not optimized for yield or selectivity.

Hydrosilylation of butadiene using hexachloroplatinic acid gave the mixture of mono and dihydrosilylation product (Eq. 1.32). 1,4-addition products were formed in preference to

1,2-product.

H2PtCl6 HSiMeCl2 H3C SiMeCl2 SiMeCl2 200 oC major minor 90 91 92

Cl2MeSi (Eq. 1.32) SiMeCl2 minor 93

Takahashi et al[12] reported first palladium-catalyzed hydrosilylation of butadiene in 1969 using a low valent palladium-phosphine complex. Palladium phosphine complex gave a

2:1 adduct of butadiene:trimethylsilane in nearly quantitative yield (Eq. 1.33) using

81 trimethylsilane. Palladium phosphine complex and butadiene gave a 1:1 adduct with selectivity for 1,4-addition using trichlorosilane (Eq. 1.34).

Ph3P Pd O Ph3P (Cat.) O HSiMeCl 2 H3C SiMe3 (Eq. 1.33) PhH, 85 oC, 4.5 h 90 94 98% Yield

0 Pd , PPh3 HSiCl 3 H3C SiCl3 (Eq. 1.34) PhH, 100 oC, 6 h 87 95 93.5% Yield

These early attempts on diene hydrosilylation demonstrates that selectivity is not only challenge in the diene hydrosilylation, but also the reaction depends upon number of variables including the catalyst, substrate, silane and reaction conditions. Early reports on diene hydrosilylation are limited to the few commercially available substrates and a very limited set of others. Out of many substrates, isoprene 81 is one of most common substrates used for hydrosilylation. Reports on substrate scope and functional group tolerance of many diene hydrosilylation are still limited and this aspect has not been fully evaluated. Therefore, development of a well-designed catalytic system with higher selectivity and activity is still an intensive research topic. More recently transition metal catalysis has become the method of choice for the synthesis of organosilane. From long decades, hydrosilylation reactions of alkene using first-row transition metal catalysts

82 have been known but report on selective hydrosilylation of diene are few.[13] Recently, cobalt catalyst reported by Hilt (Eq. 1.35),[14] iron catalyst reported by Ritter (Eq.

1.36),[15] nickel catalyst reported by Shimada (Eq. 1.37)[16] and platinum catalyst reported by Ritter (Eq. 1.38),[17] have addressed some of these limitations but these reports are still limited to few substrates like isoprene or myrcene

Si(OEt)3 CoBr2, 2PnBu

Bu4NBH4, ZnI2 HSi(OEt)3 (Eq. 1.35) CH2Cl2, RT

81 82, 90% yield

Cobalt Catalyzed 1,4-Hydrosilylation of Diene

(EtO)3 Si Cat. 5 mol% (Eq. 1.36) HSi(OEt)3 Toluene, 23 oC, 6 h 81 82

Ar N N N Ar = Fe N N Ar 91% yield

Iron Catalyzed 1,4-Hydrosilylation of Diene

Cat. 0.5 mol% Si(OEt)3 (EtO)3Si HSi(OEt)3 NaEt3BH (0.5 mol%) (Eq. 1.37) 81 THF, RT, 2 h 96 82 1,4-branched 1,4-linear

R R 79: 21, 79% Yield O O Ni O O R R

R = Me, CF3 or tBu Catalyst

Nickel Catalyzed 1,4-Hydrosilylation of Diene

Cat. 0.25 mol% (EtO)3Si (EtO) Si MeMgCl 1mol% 3 HSi(OEt) (Eq. 1.38) 3 o o -45 C - 50 C, CH2Cl2, 1 h 81 97 82 1,2 : 1,4 = 16 : 1 89% Yield

tBu tBu CH3 Cl P Pt H3C Pt P CH3 Cl tBu tBu H3C Catalyst

Platinum Catalyzed 1,2 and 1,4-Hydrosilylation of Diene

In this chapter we are report efficient hydrosilylation of 1,3-diene and 1,4-skipped diene using well-known air stable Co(II)-catalysts which are activated by reducing agents. redox active ligand at room temperature, and enable hydrosilylation of a wide variety of substrates.

1B.3 Results and Discussion

The aim of this research was the development of a general method for cobalt- catalyzed hydrosilylation of conjugated diene. In a search of new reactions to further

84 functionalize 1,4- skipped dienes (12) obtained from hydrovinylation of 1,3-dienes (11)

(Eq. 7),[18] hydrosilylation was considered as a possible target. This chapter describes the discovery and development of cobalt(II) complexes that catalyze the hydrosilylation reaction at room temperature. This chapter describes the strategy we employed in our investigation to optimize the catalyst for selective hydrosilylation.

Z R Hydrovinylation (Eq. 1.7) Z R = Alkyl, Z = H or OTMS R 11 12

iPr Inspired by the success of cobalt catalyst ( PDI)CoCl2 with NaEt3BH as activator in the hydrosilylation of alkenes, this system was applied to the hydrosilylation of dienes.

iPr Using the condition [1 equivalent of alkene, 1.1 equivalent of silane, PDICoCl2 (0.05 equivalent), NaEt3BH (0.1 equivalent), toluene (2 mL)] optimized for hydrosilylation of alkenes, we attempted to do hydrosilylation of prototypical substrate, (E)-dodeca-1,3- diene 98 for our initial scouting experiments.

1B.4 Optimizing Cobalt Catalyst for Hydrosilylation of (E)-Dodeca-1,3-Diene 98

Under the optimized condition for hydrosilylation of alkene [1 equivalent of alkene, 1.1

IPr equivalent of silane, PDICoCl2 (0.05 equivalent), NaEt3BH (0.1 equivalent), toluene (2 mL)], we attempted to do hydrosilylation of prototypical substrate, (E)-dodeca-1,3-diene

98 at room temperature. To our delight, we were able to isolate mixture of 1,2-addition

85 product 99 and 100 (> 87%), reduction product 101 (7%) and left over starting material

98 (4%) by GC integration. GC-MS and NMR readily confirms the identities of the hydrosilylated product 99 and 100. The GC trace of the products is shown in figure 1.15.

H SiH2Ph CoCl iPr(PDI) 5 mol% SiH Ph H PhSiH3 2 2 R R R (Eq. 1.39) NaEt BH 10 mol% 1,2 branched (R = C H ) 3 1,2 linear-E 8 17 Toluene, RT, 5 h (>83%) 4%

98 99 100 iPr CoCl2 (PDI) H N H N Co N R Cl Cl (8%) Reduction 101

C 8 H 17 H SiH Ph C 2

8 C8H17 H H 17 1,2 linear-E

H (>82% by GC)

C8H17 SiH 2 Ph H

Figure 1.15.: Gas Chromatogram of Products Obtained from 98 at Room

Temperature 86

Next, we examined the effect of temperature to control the side reaction such as reduction. The catalytic activity of this cobalt iPrPDI complex 1a was then examined at low temperature. The reaction of phenylsilane (PhSiH3) with 98 was examined in the presence of a catalytic amount (0.05 equivalents) of the cobalt complex 1a. Addition of

o NaEt3BH at -78 C to the reaction system and allowing to warm reaction mixture at room temperature resulted in a cleaner reaction leading to the formation of exclusive (>98%)

1,2 linear addition product 99 with 91 % isolated yield. The hydrosilylated product 99 was identified by GC-MS and NMR. The GC trace of the product 99 is shown in figure

1.16

SiH2Ph C8H17 1,2 linear-E (98% by GC)

Figure 1.16.: Gas Chromatogram of Products Obtained From 98 at -78 oC to Room

Temperature

Next, we examined the effect of ligands (Figure 1.17, for ligands used for diene hydrosilylation) on the regioselectivity of hydrosilylation. Bis(imino)pyridine (PDI) ligands (L1-L3, L5)) across a range of different substituents on aromatic backbone of imine, pybox ligand (L4) and chelating phosphine ligand (L6-L7) were tested after making the complex with cobalt dichloride (Figure 1.18) to examine the effect of steric properties on the reaction (Table 1.15). Cobalt N-mesityl-imine complex 1c gave no hydrosilylated products 99 or 100 (Table 1.15, entry 3) whereas cobalt complexes 1b

(Table 1.15, entry 2), 1d-1g (Table 1.15, entries 4-7) showed moderate reactivity.

Comparisons of all entries (Table 1.15) revealed that cobalt complex 1a with more sterically demanding diisopropyl substituents on the imine showed best catalytic activity for hydrosilylation of 98.

H SiH2Ph SiH Ph H PhSiH3 CoCl2 (Ligand) 5 mol% 2 C8H17 C8H17 C8H17 NaEt3BH 10 mol% Toluene, RT, 5 h 1,2 linear-E 1,2 branched

98 99 100

(Eq. 1.40) H H C8H17 Reduction 101

Table 1.15 Ligand Scan for Hydrosilylation of (E)-Dodeca-1,3-Diene 98a

Entry Ligand Complex 99b 100b 101, 20, Isomerizationc 98b 1 L1 1b 96% 4% - - 2 L2 1c 14% 6% 80% - 3 L3 1d - - 100% - 4 L4 1e 1% 7% 54% 38% 5 L5 1f 2% 3% 13% 82% 6 L6 1g 9% 18% 46% 27% 7 L7 1h 15% 5% - 80%

a iPr o See Eq 1.40 for reaction scheme. 5 mol% catalyst ( PDI)CoCl210 mol% NaEt3BH, Silane -78 C to RT, bGC ratio, cSignificant amount of reduction of terminal double bond, isomerization of terminal double bond to internal double bond and Ph2SiH2(20) were formed.

O O N N N N N N N Ar Ar N N PDI Pybox L4 Cy(PDI) L5 L1 Ar = 2,6-di-iPr L2 Ar = 2,6-di-Et L3 Ar = 2,4,6-tri-Me

Ph P PPh P 2 2

L6 L7

Figure 1.17.: Ligands in Co-Complexes Used for Diene Hydrosilylation

O O N N N N N N N N N Co Ar Co Ar Co Cl Cl Cl Cl Cl Cl

PDI Pybox Cy(PDI) 1a Ar = 2,6-di-iPr 1d 1e 1b Ar = 2,6-di-Et 1c Ar = 2,4,6-tri-Me

CoCl2 P Ph2P PPh2 CoCl2 1f 1g

Figure 1.18.: Cobalt Complexes Used for Diene Hydrosilylation

Having identified a successful ligand to promote the 1,2-selective hydrosilylation, attention was devoted to test various solvents for hydrosilylation of 98. An examination of various common solvents (Table 1.16) revealed toluene (Table 1.16, entry 1) was the best solvent for the formation of the 1,2-linear hydrosilylated product. Hexane (Table

1.16, entry 5), benzene (Table 1.16, entry 6), THF (Table 1.16, entry 3), diethyl ether

(Table 1.16, entry 4) and chlorinated solvent such as CH2Cl2 (Table 1.16, entry 2) lead to unsatisfactory results whereas ClCH2CH2Cl (Table 1.16, entry 7) and CH3CN (Table

1.16, entry 8) lead to moderate conversion to the desired 1,2-linear product along with reduction, isomerization of starting material and silane redistribution product 20

(Ph2SiH2). In parallel runs using these solvents, the best solvent for the reaction was identified as toluene.

H SiH2Ph iPr SiH Ph H PhSiH3 CoCl2 (PDI) 5 mol% 2 C8H17 C8H17 C8H17 NaEt3BH 10 mol% Solvent, RT, 5 h 1,2 linear-E 1,2 branched 98 99 100

H (Eq. 1.41) H Ph SiH R 2 2 Reduction Dipenylsilane 101 20

Table 1.16 Effect of Solvents for Hydrosilylation of (E)-Dodeca-1,3-Diene, 98a

Entry Solvent 99b 100b 101c +Isomerization 98b 20c 1 Toluene >98% <2% - - -

2 DCM 12% 5% 54% - -

3 THF 2% 1% 63% 6% 4%

4 Ether 6% 9% 80% - 4%

5 Hexane 6% 5% 63% - 7%

6 Benzene 7% 13% 27% 2% 1% 7 DCE 21% 1% 34% - 2%

8 CH CN 54% 1% 27% - 6% 3 a iPr o See Eq 1.41 for reaction scheme. 5 mol% catalyst ( PDI)CoCl210 mol% NaEt3BH, Silane -78 C to RT, bGC ratio, cSignificant amount of reduction of terminal double bond, isomerization of terminal double bond to internal double bond and Ph2SiH2(20) were formed.

A quick survey of most commonly used activators (trimethylaluminium, Et2Zn, MeLi,

MeMgBr, EtMgBr, PhMgBr, n-BuLi, NaEt3BH, MAO) confirmed that NaEt3BH at -78

0 iPr C is the best reagent for reduction of cobalt complex ( PDI)CoCl2 (Table 1.17, entry 1).

The only activators that showed any reactivity were, EtMgBr, MeLi and Et2Zn (Table

1.17, entries 3, 4 and 7). We attempted to the hydrosilylation reaction without using any activators but the reaction was unsuccessful and did not give any desired products or side reactions such as reduction or redistribution of silane. We observed only starting material

98 after 12 h.

H SiH2Ph iPr SiH Ph H PhSiH3 CoCl2 (PDI) 5 mol% 2 C8H17 C8H17 C8H17 Activator 10 mol% Toluene, -78 oC - RT, 5 h 1,2 linear-E 1,2 branched 98 99 100

(Eq. 1.42)

H H Ph SiH R 2 2 Reduction Dipenylsilane 101 20

Table 1.17 Effect of Activator for Hydrosilylation of (E)-Dodeca-1,3-Diene, 98a

Entry Activator 99b 100b 101c + Isomerization 98b Silane Formedc

1 - NaEt3BH 98% 2% - - 100% 2 PhMgBr - - - -

3 EtMgBr 6% - 12% 67% 15%(20)

4 MeLi 16% 11% 23% 2% 17%(20)

5 nBuLi 2% 3% 50% 4% 39% (21)

6 Me3Al - 4% - 71% 25% (20)

7 - Et2Zn 27% 20% - 38% (20)

8 MAO - - - 100% - 9 MeMgBr - - - 100% -

100% - 10 No Activator - - -

a iPr o See Eq 1.42 for reaction scheme. 5 mol% catalyst ( PDI)CoCl210 mol% NaEt3BH, Silane -78 C to RT, bGC ratio, cSignificant amount of reduction of terminal double bond, isomerization of terminal double bond to internal double bond, Ph2SiH2(20) and PhSiH2nBu (21) were formed

We attempted to broaden the scope of our methodology by screening different silanes.

Several commercially available silanes (Table 1.18) were screened in the presence of the

iPr cobalt precatalyst [( PDI)CoCl2 1a activated by NaEt3BH] for the hydrosilylation of (E)- dodeca-1,3-diene 98. In a typical procedure, the cobalt complex (0.05 equivalent) and the

(E)-dodeca-1,3-diene 98 (1 equivalent) are dissolved in toluene (2 mL) under argon and the reaction mixture was cooled to -78 oC. To this cold solution was added a toluene solution of NaEt3BH (0.1 equivalent) followed by the addition of silane (1.1 equivalent).

The mixture was warmed to room temperature and the reaction was monitored by gas chromatography and GC-mass spectrometry. Among the silane tested, phenylsilane

(Table 1.18, entry 1), diphenylsilane (Table 1.18, entry 2) and phenylmethylsilane (Table

1.18, entry 3) gave good yields of hydrosilylated products. Neither triethylsilane nor triphenylsilane display any reaction. A careful examination of the data in Table 1.18 suggests that two kinds of products can be obtained in useful yield. Primary silane such as phenylsilane (PhSiH3) gave an excellent yield of the linear silane 99. Secondary silanes such as diphenylsilane (Ph2SiH2) and phenylmethyl silane (MePhSiH2) (Table

1.18, entries 2-3) gave linear silane as major component along with varying amounts of branched hydrosilylated products and a reduction product 101. Tertiary silanes such as triphenylsilane (Ph3SiH), trichlorosilane (Cl3SiH), triethylsilane (Et3SiH), triethoxysilane

[(EtO)3SiH] and bis (trimethylsiloxy) methylsilane (TMSO)2SiMeH are much less reactive, and the starting material 98 remains mostly unreacted at room temperature. In sharp contrast, methyldimethoxysilane [(OMe)2MeSiH] (Table 1.18, entries 10) and methyldiethoxysilane [(OEt)2MeSiH] (table 1.18, entries 11), which are tertiary silane, gave nearly quantitative yield of the reduction product 101.

H SiRnH3-n CoCl iPr(PDI) 5 mol% 2 SiRnH3-n H RnSiH4-n C8H17 C8H17 C8H17 NaEt3BH 10 mol% Toluene, -78 oC-RT, 5 h 1,2 linear-E 1,2 branched 98 1.1 eq 99 100

(Eq. 1.43) H H Ph SiH R 2 2 Reduction Dipenylsilane 101 20

Table 1.18 Effect of Silane for Hydrosilylation of (E)-Dodeca-1,3-Diene, 98a

Entry Silane 99b 100b Reduction(101)c Yieldd SM(98)b

1 PhSiH3 >94% 4% - 91% -

2 Ph2SiH2 92% 4% 4% 88% -

- 3 PhMeSiH2 94% 6% - 86%

34% 4 Ph3SiH - - - 66%

5 Cl3SiH - - - - 100%

- 6 Et3SiH - - - 100%

- 4% 7 (EtO)3SiH - - 65%

- - 8 (OTMS)2SiMeH - - 100%

89% - 9 (EtO)2MeSiH - - 100%

91% - 10 (MeO)2MeSiH - - 100%

a iPr o See Eq 1.43 for reaction scheme 5 mol% catalyst ( PDI)CoCl210 mol% NaEt3BH, Silane -78 C to RT, bGC ratio, cSignificant amount of selective reduction of terminal double bond, dIsolated yield after purification.

Our studies also focused on the counter ion effect on cobalt for hydrosilylation of (E)- dodeca-1,3-diene, 98 Bis(imino)pyridine complexes (Figure 1.19) across a range of different counter ion on cobalt (1a, 1h, 1i, 1j and 1k) were synthesized and tested for

95 hydrosilylation of (E)-dodeca-1,3-diene, 98. Cobalt complex 1a gave hydrosilylated product in quantitative yield within 5 h at room temperature. Complexes 1h-1k showed minimal catalytic activity. By testing various counter ions on cobalt (Table 1.19), we confirmed that CoCl2 (Table 1.19, entry 1) was the most optimal salt for the 1,2-anti-

Markovnikov hydrosilylation of diene.

N N N N N Co N N N N Ar Ar Co Co Cl Cl Ar Ar Ar Ar Br Br I I 1a 1h 1i

N N N N N N Ar Co Ar Ar Co Ar AcO OAc AcO OAc .4H2O 1j 1k Ar = 2,6-di-iPr

Figure 1.19.: Cobalt Complexes with Different Counter Ions for Hydrosilylation of

Dienes

H SiH2Ph iPr SiH Ph H PhSiH3 CoX2 (PDI) 5 mol% 2 C8H17 C8H17 C8H17 NaEt3BH 10 mol% Toluene, -78 oC - RT, 5 h 1,2 linear-E 1,2 branched 98 99 100

H (Eq. 1.44)

H Ph2SiH2 C8H17 Reduction Dipenylsilane 101 20

Table 1.19 Effect of Counter Ion for Hydrosilylation of (E)-Dodeca-1,3-Diene, 98a

Entry Counter Ion 99b 100b 101c +Isomerization SM 98b 20c 1 CoCl2 >94% <4% - - -

2 CoBr2 13% 5% 43% - 39%

3 CoI2 15% 5% 41% - 39%

4 - Co(OAc)2 10% 13% 47% 30% 5 Co(OAc) .4H 0 14% - 11% 31% 2 2 44% a iPr o See Eq 1.44 for reaction scheme. 5 mol% catalyst ( PDI)CoCl210 mol% NaEt3BH, Silane -78 C to RT, bGC ratio, cSignificant amount of reduction of terminal double bond, isomerization of terminal double bond to internal double bond and Ph2SiH2(20) were formed

After extensive study of the ligand, solvent, activator, silane and counter ion, the optimized procedure for the reaction is shown in equation 1.45 and the full scope of the reaction is illustrated by examining the other substrates with varying degrees of steric effects and sensitive functional groups (Fig. 1.20). Under the optimized conditions [1

iPr equivalent of diene, 1.1 equivalents of silane, PDICoCl2 (0.05 equivalents), NaEt3BH

(0.1 equivalents), toluene (2 mL)], the reaction of 1,3-diene 98, 102-120 (Fig. 1.20) proceeds at room temperature giving good yields of hydrosilylated products. GC, GC-MS and spectroscopic techniques have established the structure of all the hydrosilylated products. In all cases, the hydrosilylation favors the linear selectivity (to give the anti

Markovnikov’s product) in which the silicon is attached to the terminal carbon (Table

1.20).

H SiH2Ph iPr SiH Ph H PhSiH3CoCl2 (PDI) 5 mol% 2 C8H17 C8H17 C8H17 NaEt3BH 10 mol% (Eq. 1.45) Toluene, 1,2 linear-E 1,2 branched -78 oC - RT, 5 h 98 99 100

To examine the utility of this optimized system, all of the 1,3-diene substrates (98, 102-

120) with varying degrees of steric effects and sensitive functional groups were explored.

Many of these 1,3-dienes were easily synthesized from their corresponding aldehyde by a

Wittig reaction (Scheme 1.9). Substrates 98, 102, 103, 111, 114 and 115 were made by using the corresponding unsaturated aldehyde and methyltriphenylphosphonium bromide

(Scheme 1.9a). Another set of dienes, 112 and 113 having E and Z isomers were also made by a Wittig reaction of allyltriphenylphosphonium bromide with the corresponding aldehyde (Scheme 1.9b). However, these conditions yield a mixture of E and Z isomers in varying ratio. To make selective the (E) only isomer, substrates 104 and 106 were made by a Horner-Wadsworth-Emmons reaction using diethyl allylphosphonate anion in hexamethylphosphoramide at low temperature (Scheme 3c).[19] 1-Vinylcycloalkenes 107 was synthesized by a Grignard addition of vinylmagnesium bromide to the corresponding cyclic ketone followed by dehydration using phosphoryl chloride (Scheme 1.9d). The functionalized diene 120 was synthesized using procedures reported by Morken et al

(Scheme 2e).[20] All the vinylcycloalkenes 108-110 were produced from the respective cyclic ketone using the original method reported by RajanBabu et al. [21] The simple synthetic route to vinylcycloalkenes start the addition of vinylmagnesium bromide to the respective ketone to generate the tertiary allyl alcohols. Thus formed

98 tertiary allyl alcohols after elimination gave the 1-vinylcycloalkenes in the presence of phosphoryl chloride and pyridine (Scheme 1.9f). The diene containing silyl enol ether

119 was prepared from the corresponding unsaturated ketone trans-3-octen-2-one. The α,

β unsaturated ketone (trans-3-octen-2-one) was subjected to kinetic deprotonation

(Scheme 1.9g) by using LDA (lithium diisopropylamine) and trapping of the resulting enolate by TMSCl (chlorotrimethyl silane). The crude product obtained from the reaction was further purified by bulb-to-bulb distillation after workup to get the clean diene product 119. Diene substrate 105 was synthesized according to the reported literature.[22]

Dienes substrates such as 116 and 118 are commercially available dienes. They were used as it was obtained from commercial vendors.

MePPh3Br, nBuLi 1.9a R O R THF, 0 oC - RT

allylPPh3Br, nBuLi 1.9b R O R THF, 0 oC - RT O P OEt OEt 1.9c R O R nBuLi, HMPA THF, -78 oC - RT O

1. VinylMgBr, THF, 0 oC to RT

1.9d o 2. Pyridine, POCl3, 0 C - RT n n

Scheme 1.9 Synthesis of 1,3-Diene Substrates

Continued

1. trimethylorthoacetate, Propionic acid, Toluene, 2HBr 1.9e OH o 120 OH 2. LiAlH4, Et2O, 0 C

PoCl3 (4 eq) O MgBr (1.1 eq) OH Pyridine, 0 oC, 2 h R 1.9f R o R THF, 0 C, 2 h Followed by RT, 12 h Followed by rt, 2 h

1. Diisopropylamine (1.1 eq) OTMS O nBuLi (1.1 eq)

1.9g THF, -78 oC, 1 h C4H9 C4H9 2. TMSCl, Rt, 2 h 119

Scheme 1.9 Contd. Synthesis of 1,3-Diene Substrates

R C3H7 Si

R = C8H17, 98 103 104 105 106 R= C5H11, 102

112 113

107 R 111 R = Me, 108 R = tBu,109 R = Ph, 110

C4H9

114 115 116 117 118

OTMS OH C4H9 119 120

Figure 1.20.: Dienes Tested in Cobalt Catalyzed Hydrosilylation

100

Under the optimized conditions [1 equivalent of diene, 1.1 equivalents of silane, iPr PDICoCl2 (0.05 equivalents), NaEt3BH (0.1 equivalents), toluene (2 mL)], the reaction of 1,3-dienes 98, 102-115) (Fig. 1.20) proceeds at room temperature giving good yields of hydrosilylated product. GC, GC-MS and spectroscopic techniques have established the structure of all the hydrosilylated products. In all cases, the hydrosilylation favors the linear selectivity (anti Markovnikov’s product) in which the silicon is attached to the terminal carbon (Table 1.20). Neither dehydrogenated silylation nor disubstituted silane

(Ph2SiH2) 20 was detected on GC and GC-MS.

101

Table 1.20. Scope of Hydrosilylation of 1,3-Diene

Entry Substrate 1,2-linearb 1,2-branchedb Yield (%)c

SiH2Ph SiH2Ph R R R GC Ratio

1 R = C8H17 R = C8H17 98% R = C8H17 2% 91% 98 99 100 R = C H 98% R = C H 2 5 11 R = C5H11 5 11 <1% 89% 102 121 122

3 R = Cy R = Cy 99% R = Cy <1% 93% 104 123 124

4 R = Si(iPr)3 R = Si(iPr)3 95% R = Si(iPr)3 <5% 92% 105 125 126

SiH2Ph SiH2Ph 5 C3H7 C3H7 C3H7 87% 96% 4% 103 127 128 SiH2Ph

SiH2Ph

R R R GC Ratio

6 R = Me R = Me 98% R = Me <2% 85% 108 129 130 7 R = tBu R = tBu 98% R = tBu <2% 91% 109 131 132 8 R = Ph R = Ph 99% R = Ph <1% 87% 110 133 134

a iPr o See Eq 1.45 for reaction scheme. 5 mol% catalyst ( PDI)CoCl210 mol% NaEt3BH, Silane -78 C to RT, bGC ratio, cIsolated yield after purification.

Continued

102

Table 1.20 Scope of Hydrosilylation of 1,3-Diene Contd.

Entry Substrate 1,2-linearb 1,2-branchedb Yield (%)c

SiH2Ph SiH2Ph 9 88%

111 135 136 GC Ratio 98% 2%

SiH2Ph SiH2Ph 10 R R R 86% R = CH2CH2Ph R = CH2CH2Ph R = CH2CH2Ph 113 137 138 GC Ratio 47:49, E:Z 4%

11 SiH2Ph 91% 106 139 >98%

12 SiH2Ph 91%

112 42:58 140 >98% 41: 59, E:Z

SiH2Ph 13 93%

SiH2Ph 107 141 >99% 142 SiH2Ph

SiH2Ph

R R R

14 R = H 114 R = H 143 34% R = H 144 66% 89% 15 R = Me 115 R = Me 145 42% R = Me 146 58% 84%

16 SiH2Ph SiH2Ph 1,2-linear 1,4 linear 116 147 GC Ratio 148 67% 33% 87%

103

Cobalt catalyzed 1,2-selective hydrosilylation of 1,3-dienes using phenylsilane gave excellent yield and selectivity. This method is broadly applicable for the formation of the anti-Markovnikov adduct. All of the examples of terminal dienes either having E or Z- geometry or a mixture illustrate the formation of the anti-Markovnikov product with retention of the diene configuration. The configuration of the double bond was confirmed by proton decupling experiments. Dienes that are conjugated to an aromatic ring (114

&115) gave mixture of 1,2-linear and 1,2-branched products. Out of all dienes we have examined only β-myrcene 116 gave a mixture of 1,4-linear 147 and 1,2-linear 148 hydrosilylated products. Diene 117 only show 8% conversion under the optimized condition confirmed by GC and GC-MS. Dienes (118-120) did not give any of the hydrosilylated products under the optimized conditions.

The optimized condition for hydrosilylation of 1,3-diene is also useful for the large-scale reaction and even in the neat condition. Several dienes (Figure 1.21) were tested in preparative scale for hydrosilylation using 1 mol% catalyst at 40 oC and gave exclusively linear product within 2h with excellent yield.

C8H17

98 104 131

112 106 42:58, E:Z GC Ratio

Figure 1.21.: Dienes Tested in Hydrosilylation Using 1mol% Catalyst

104

H SiH2Ph iPr PhSiH CoCl2 (PDI) 1 mol% SiH2Ph H R 3 R R NaEt BH 2 mol% (Eq. 1.46) 3 1,2 linear 1,2 branched Neat, -78 oC - 40 oC (oil bath), 2 h

Table 1.21 Scope of Hydrosilylation of 1,3-Diene Using 1 mol% Catalyst

Entry Substrate 1,2-linearb 1,2-branchedb Yield (%)c

SiH2Ph SiH2Ph R R R GC Ratio 1 R = Cy 104 R = Cy 123 99% R = Cy 124 1% 92% 100 2 R = C8H17 98 R = C8H17 99 98% R = C8H17 2% 91% SiH2Ph

SiH2Ph 3 92%

109 131 132 98% 2%

4 SiH2Ph 90% 106 >98% 139

5 SiH2Ph 88% 42:58, E:Z Ratio >98% 112 140 a iPr o o See Eq 1.46 for reaction scheme. 1 mol% catalyst ( PDI)CoCl2, 2 mol% NaEt3BH, Silane -78 C to 40 C oil bath, 2 h, bGC ratio, cIsolated yield after purification.

The optimized condition for cobalt catalyzed selective hydrosilylation of 1,3-diene [1

IPr equivalent of diene, 1.1 equivalents of silane, PDICoCl2 (0.05 equivalents), NaEt3BH

(0.1 equivalents), toluene (2 mL)] is also applicable for the hydrosilylation of skipped

1,4- dienes. The skipped 1,4-diene having highly sensitive silyl enol ether group is not

105 affected under our optimized condition for hydrosilylation and gave exclusively 1,2- linear product.

Z R Hydrovinylation (Eq. 1.7) Z R = Alkyl, Z = H or OTMS R 11 12

Table 1.22 Scope of Hydrosilylation of Skipped 1,4-diene using Cobalt Catalyst

Entry Substrate 1,2-linearb 1,2-branchedb Yield (%)c

SiH2Ph

PhH2Si

R R R GC Ratio

1 R = C5H11 149 R = C5H11 152 >99% R = C5H11 153 <1% 91%

2 R = C8H17 150 R = C8H17 154 >98% R = C8H17 155 <2% 89%

SiH2Ph

PhH2Si 89%

3 C4H9 OTMS C4H9 OTMS C4H9 OTMS 151 156 157 >99% <1% a iPr o See Eq 1.45 for reaction scheme. 5 mol% catalyst ( PDI)CoCl2, 10 mol% NaEt3BH, Silane -78 C to, 5 h, bGC ratio, cIsolated yield after purification.

106

We further tested the optimized conditions [1 equivalent of diene, 1.1 equivalents of

iPr silane, PDICoCl2 (0.05 equivalents), NaEt3BH (0.1 equivalents), toluene (2 mL)] for the substrates 98 and 102 using secondary silane such as Ph2SiH2 and PhMeSiH2 and gave exclusively anti Markovnikov’s product 158 and 159.

SiHPh2 SiHPhMe C5H11 C8H17 81% Yield 86% Yield 158 159

1B. 5 Proposed Mechanism for Hydrosilylation Reaction

The proposed catalytic cycle for hydrosilylation reaction of alkene was shown in figure

1.14 of chapter 1A. On the basis of various reports in the literature the proposed mechanism for hydrosilylation of 1,3-diene is shown in figure 1.22. Reduction of cobalt

iPr( 1 complex 1a [ PDI)CoCl2] with 2 equivalents of NaEt3BH generates Co -H 78 intermediate.[23] Reduced low valent Co(I) species [iPr(PDI)CoCl][24] by itself in toluene solvent does not catalyze the hydrosilylation reaction.

N Zn N N Co N THF, RT, 12 h N Co N Cl Cl Cl

Isolated and fully characterized

107

IPr PDI(Co)-Cl 5 mol% (Eq. 1.47) C8H17 PhSiH3 No reaction Toluene, -78 oC-RT 98 5 h

However, in presence of Lewis acid such as triethylborane (Et3B), B(C6F5)3 or NaEt3BH

(5 mol%), the (iPrPDI)Co-Cl complex catalyzes the hydrosilylation reaction and gave excellent yield and selectivity

IPr SiH2Ph PDI(Co)-Cl 5 mol% C H C8H17 PhSiH3 8 17 (Eq. 1.48)

98 NaEt3BH 5 mol%, 99 Toluene,-78oC - RT, 2 h >98% GC Ratio 89% Yield

Due to the steric of iPrPDI ligand, the incoming diene 98 is restricted to η2 – coordination.[17] The Co1-H intermediate 78 migratory inserts to the diene 98 give a cobalt-alkyl complex 160, which upon reaction with silane give the hydrosilylated product and regenerate the Co1-H 78 intermediate.

108

N N Co N Ar Cl Cl Ar iPr Ar = (2,6-iPr)-phenyl) [ PDI]CoCl2

2 NaEt3BH 2 NaCl, 2 Et3B,1/2 H2

SiH2Ph R R LnCo H 78

SiH2Ph iPr [ PDI]Co H η2-diene coordination [iPr PDI]Co H R R

[iPr PDI]Co H PhSiH3 160

Figure 1.22: Proposed Catalytic Cycle for Hydrosilylation

1B.6 Conclusion: We have discovered a new efficient cobalt catalyst system for selective hydrosilylation of 1,3-diene and 1,4-skipped dienes. Under the optimized

iPr conditions [1 equivalent of diene, 1.1 equivalents of silane, PDICoCl2 (0.05 equivalents), NaEt3BH (0.1 equivalents), toluene (2 mL)], we are able to do hydrosilylation of variety of substartates bearing sensitive functional groups. All the terminal dienes are converted to linear hydrosilylated product. This protocol is also useful

109 for reactions in neat substrates and for reactions using little as 0.01 equiv.

(substrate/catalyst = 100) of the catalyst.

1B.7 General Experimental

E. Merck pre-coated (0.25 mm) silica gel 60 F254 plates. Flash column chromatography was carried out on silica gel 40 (Sorbtech Chemicals), gas chromatographic analysis was conducted on an Agilent 7820A using hydrogen as the carrier gas, equipped with a methyl silicone column (30 m x 0.32 mm, 0.25 µm film thickness). GC-MS was carried out on a HP-5MS 5% methyl phenylsiloxane (30 m x 0.25 mm, 0.25 µm film thickness) using He as carrier gas. Cobalt (II) chloride and phosphine ligands were purchased from

Strem Chemicals. All silanes were purchased from Sigma Aldrich, Oakwood, Alfa Aesar or Apollo Scientific. All activating reagents were purchased from Sigma Aldrich. 1H, 13C

110

Ligand Preparation

Bis1,6-(diaryliminoyl)pyridine ligands L1-L3 and L5, were prepared by a Schiff’s base reaction using a modified literature methodology.[25] The detail experimental procedure for the synthesis of ligand L1-L3 and L5 is described in chapter 1A. 1H and 13C NMR of ligands matched what are the reported literature. Ligand L4 was prepared according to reported literature mentioned on chapter 1A.

Synthesis of Cobalt Complexes: Modified literature methods were used for the

iPr Et Me Cy preparation of complexes ( PDI)CoCl2, ( PDI)CoCl2, ( PDI)CoCl2, ( PDI)CoCl2. The experimental procedure for the synthesis of cobalt(PDI)complexes is described in chapter

For all other cobalt complexes (PCy3)2CoCl2, (DPPP)CoCl2 a procedure modified from

[18a] RajanBabu and co-workers was used: Anhydrous CoCl2 (50.5 mg, 0.390 mmol) was added to a previously flame-dried 50-mL round two-necked bottom flask fitted with a flow control gas inlet and magnetic stir-bar loaded in a glove box under nitrogen. The nitrogen atmosphere was removed and the flask purged with dry argon. Freshly distilled, degassed THF (5 mL) was added, and upon stirring at room temperature for 15 min, a clear deep blue solution formed. A solution of DPPP (181 mg, 0.410 mmol) in freshly distilled, degassed ether (5 mL) was added dropwise to yield a blue turbid solution. After stirring at room temperature for 15 h, 20 mL freshly distilled, degassed hexane was added in one portion to yield a blue precipitate. The resulting precipitate was filtered on a sintered glass fret under argon atmosphere, and washed with diethyl ether and hexane

111

(1:1) mixture (3 X 5 mL) to remove any unreacted DPPP, resulting in quantitative yield of a light blue solid, which was used with no further purification.

General Procedure to Synthesize Diene Substrates. General scheme for synthesis of diene substrates included in the scheme 1.9 of this chapter. All dienes used were synthesized using the reported literature methods. Many of these

1,3-dienes were easily synthesized from their corresponding aldehyde by a Wittig reaction. Diene substrates 98, 102, 103, 111, 114 and 115 were made by using the corresponding unsaturated aldehyde and methyltriphenylphosphonium bromide. Another set of dienes substrates, 112 and 113 having E and Z isomers were also made by a Wittig reaction of allyltriphenylphosphonium bromide with the corresponding aldehyde.

However, these conditions yield a mixture of E and Z isomers in varying ratio. To make selective the (E) only isomer, substrates 104 and 106 were made by a Horner-

Wadsworth-Emmons reaction using diethyl allylphosphonate anion in hexamethylphosphoramide at low temperature. 1-Vinylcycloalkenes 107-110 was synthesized by a Grignard addition of vinylmagnesium bromide to the corresponding cyclic ketone followed by dehydration using phosphoryl chloride. Diene substrate 105 is known in the literature. Diene substrate 116 (β-myrcene) is commercially available.

General Procedure to Synthesize 4-Substituted-1-Vinylcycloalkenes. A 100 mL schlenk flask equipped with a magnetic stir bar, septum stopper, and gas inlet was flame dried and purged with argon. The flask was cooled to 0 oC and 20 mL of a 1 M solution

(20.0 mmol, 1 equivalent) of vinyl magnesium bromide in THF was introduced. The

112 respective cyclic ketone (20. 0 mmol, 1 equivalent) was dissolved in 10 mL dry, distilled

THF, and added slowly to the Grignard solution over a period of one hour using a syringe pump to aid in the addition. The solution was then allowed to warm slowly to room temperature by removing the ice bath, and subsequently stirred for 2 hours at room temperature. The yellowish solution was quenched with saturated NH4Cl (aq), and the aqueous layer extracted with (3 x 25 mL) ether. The combined organic extracts were dried with anhydrous MgSO4, the solids were filtered off, and the solvent removed in vacuum, yielding a crude alcohol.

A new 100 mL schlenk flask was flame dried and purged with argon. The crude alcohol was introduced as a solution in 20 mL dry, distilled pyridine. The mixture was cooled to

0 oC and 2.80 mL (4.60 g, 30. 0 mmol) phosphoryl chloride was introduced drop wise.

The solution was kept in the ice bath and allowed to warm to room temperature overnight. The brown mixture was carefully transferred slowly to a 125 mL Erlenmeyer flask containing crushed ice to quench the remaining phosphoryl chloride. The ice was allowed to melt, and then the resulting aqueous mixture was extracted by (3 x 30 mL) pentane. The combined aqueous layers was washed with 10% CuSO4 (aq) until no discoloration of the aqueous layer was seen to remove any extracted pyridine, and then washed with distilled water, dried over MgSO4, the solids filtered off, and the solvent removed very carefully in vacuum without the use of a water bath to prevent loss of the volatile products. The crude product was purified by bulb-to-bulb distillation using a dry ice/acetone cooling bath to give the product as clear oil.

113

General Cobalt-Catalyzed Hydrosilylation Procedure for Diene (Eq 1.45)

A diene (0.3 mmol) was added to a solution of cobalt (II) chloride iPrPDI complex (9.2 mg, 0.015 mmol, 0.05 equivalents) in anhydrous toluene (2 mL) at -78 oC (bath temperature) under an atmosphere of argon. At -78 oC, toluene solution of sodium triethyborohydride (0.03 mmol, 0.1 equivalents) was added, followed by the silane (0.33 mmol, 1.1 equivalents) addition. The color of solution turns to reddish brown and the reaction mixture was removed from the cold bath and was further stirred at room temperature (or 40 oC for low catalyst loadings) for prescribed time. The reaction was monitored by GC and GCMS. After completion the reaction, it was filtered through the pad of silica by adding hexane and was concentrated under vacuum. Isolated yields were determined after purification by silica chromatography using hexane as eluent.

Procedure for Hydrosilylation Reaction Using iPrPDI-Cobalt (I) Chloride Without

Adding Sodium Triethylborohydride (Eq 1.47)

A diene (0.3 mmol) was added to a solution of isolated cobalt (I) chloride PDI complex

(8.6 mg, 0.015 mmol, 0.05 equivalents) in anhydrous toluene (2 mL) at -78 oC (bath temperature) under an atmosphere of argon. At -78 oC, silane (0.33 mmol, 1.1 equivalents) was added to the cold solution of reaction mixture. The reaction mixture was removed from the cold bath and was further stirred at room temperature for 24 h. After

24 h reaction, it was filtered through the pad of silica by adding hexane and was concentrated under vacuum. GC, GC-MS and NMR confirm the presence of only starting material. No hydrosilylated product was formed under such condition.

114

Procedure for Hydrosilylation Reaction Using iPrPDI-Cobalt (I) Chloride and

Sodium Triethylborohydride at -78 oC to RT (Eq 1.45)

A diene (0.3 mmol) was added to a solution of isolated cobalt (I) chloride PDI complex

(8.6 mg, 0.015 mmol, 0.05 equivalents) in anhydrous toluene (2 mL) at -78 oC (bath temperature) under an atmosphere of argon. At -78 oC, toluene solution of sodium triethyborohydride (0.015 mmol, 0.05 equivalents) was added, followed by a silane (0.33 mmol, 1.1 equivalents) addition. The color of solution turns to reddish brown and the reaction mixture was removed from the cold bath and was further stirred at room temperature for prescribed time. The reaction was monitored by GC and GCMS. After completion the reaction, it was filtered through the pad of silica by adding hexane and was concentrated under vacuum. Isolated yields were determined after purification by silica chromatography using hexane as eluent.

Procedure for Hydrosilylation Reaction Using iPrPDI-Cobalt (I) Chloride and

Sodium Triethylborohydride at Room Temperature (Eq 1.39)

A diene (0.3 mmol) was added to a solution of isolated cobalt (I) chloride PDI complex

(8.6 mg, 0.015 mmol, 0.05 equivalents) in anhydrous toluene (2 mL) at room temperature under an atmosphere of argon. At room temperature, toluene solution of sodium triethyborohydride (0.015 mmol, 0.05 equivalents) was added, followed by a silane (0.33 mmol, 1.1 equivalents) addition. The reaction mixture was stirred at room temperature for 5 h. After 5 h the reaction, it was filtered through the pad of silica by adding hexane and was concentrated under vacuum. Isolated yields were determined after purification by silica chromatography using hexane as eluent.

115

General Procedure for Hydrosilylation Reaction Under Low Catalyst Loading (Neat

Substrate (Eq. 1.46).

Hydrosilylation of (E)-Dodeca-1,3-Diene (with 1 mol% catalyst). The (E)-dodeca-1,3- diene (0.2 g, 1.20 mmol) was added to a solution of PDI-cobalt(II) chloride complex (7.3 mg, 0.012 mmol, 0. 01 equivalents) at -78 oC (bath temperature) under an atmosphere of argon. At -78 oC, toluene solution of sodium triethyborohydride (0.24 mmol, 0.02 equivalents) was added, followed by a silane (1.32 mmol, 1.1 equivalents, 0.16 mL). The flask was removed from the cold bath and placed in an oil bath preheated to 40 oC (~ in

2-3 min). The reaction mixture was stirred at 40 oC for 2 h. After completion (GC) of the reaction, it was filtered through the pad of silica by adding hexane and was concentrated under vacuum. Isolated yield was determined after purification by silica chromatography using hexane as eluent.

Analytical Data for Hydrosilylation Products

(E)-dodec-3-en-1-yl) (phenyl) silane 99

SiH2Ph C H 1 8 17 H NMR (400 MHz, CDCl3) δ 7.59-7.57 (m, 2H), 7.40-7.34 (m,

3 3H), 5.49-5.38(m, 2H), 4.31(t, JH,H = 3.7 Hz, 2H, SiH2), 2.19-2.14 (m, 2H), 2.00-1.95

3 (m, 2H), 1.36-1.25 (m, 12H), 1.06-1.01 (m, 2H, SiCH2), 0.90 (t, JH,H = 6.9 Hz, 3H).

13 C NMR (100 MHz, CDCl3) δ 135.7, 133.1, 131.9, 130.6, 130.0, 128.4, 32.9, 32.4, 30.0,

30.0, 29.8, 29.7, 28.4, 23.1, 14.5, 10.6.

GC (methylsilicone column, 120 0 C/ 10 min, rate = 20oC, 250 oC = 40 min) RT for product = 15.49 min.

116

+ GC-MS (m/z [M ] 274.10; exact mass calculated for C18H30Si 274.21.

(E)-non-3-en-1-yl) (phenyl) silane 121

SiH2Ph C H 1 5 11 H NMR (400 MHz, CDCl3) δ 7.59-7.56 (m, 2H), 7.40-7.34 (m,

3 3H), 5.49-5.39(m, 2H), 4.31(t, JH,H = 3.7 Hz, 2H, SiH2), 2.19-2.14 (m, 2H), 1.99-1.95

3 (m, 2H), 1.36-1.25 (m, 6 H), 1.05-1.01 (m, 2H, SiCH2), 0.90 (t, JH,H = 6.9 Hz, 3H).

13 C NMR (100 MHz, CDCl3) δ 135.5, 132.8, 131.7, 130.3, 129.7, 128.1, 32.6, 31.6, 29.4,

28.1, 22.7, 14.2, 10.3.

GC (methylsilicone column, 180 0 C/ Isotherm) RT for product = 2.79 min.

GC-MS m/z [M+] 232.10; exact mass calculated for C15H24Si 232.16.

(E)-(4-cyclohexylbut-3-en-1-yl)(phenyl)silane 123

SiH2Ph

1 H NMR (400 MHz, CDCl3) δ 7.59-7.57 (m, 2H), 7.40-7.34 (m,

3 3H), 5.46-5.34 (m, 2H), 4.31 (t, JH,H = 3.6 Hz, 2H), 2.19-2.13 (m, 2H), 1.94-1.86 (m,

1H), 1.74-1.62 (m, 4H), 1.32-1.08 (m, 4H), 1.06-1.03 (m, 2H), 1.03-1.00 (m, 2H).

13 C NMR (100 MHz, CDCl3) 136.3, 135.5, 132.9, 129.7, 129.1, 128.2, 40.8, 33.4, 28.2,

26.5, 26.4, 10.4.

GC (methylsilicone column, 210 0 C/Isotherm) RT for product = 3.14 min.

GC-MS m/z [M+] 244.10; exact mass calculated for C16H24Si 244.16.

117

(E)-triisopropyl(4-(phenylsilyl)but-1-en-1-yl)silane 125

SiH2Ph Si 1 H NMR (400 MHz, CDCl3) δ 7.57-7.55 (m, 2H), 7.39-7.33 (m,

3 3 3H), 6.11(dt, t, JH,H = 18.7 Hz, 6.0 Hz, 1H), 5.51 (dt, t, JH,H = 18.7 Hz, 1.5 Hz, 1H),

3 4.31(t, JH,H = 3.7 Hz, 2H), 2.32-2.26 (m, 2H), 1.27-1.19 (m, 3H), 1.08-1.03 (m, 2H),

1.02-0.99 (m, 18H).

13 C NMR (100 MHz, CDCl3) δ 150.6, 135.7, 133.1, 130.4, 128.4, 123.1, 32.7, 19.1, 11.3,

9.7.

GC (methylsilicone column, 230 0 C/ Isotherm) RT for product = 2.33 min.

GC-MS m/z [M+] 318.10; exact mass calculated for C19H34Si2 318.22.

(E)- (3-ethylhept-3-en-1-yl) (Phenyl) silane 127

SiH2Ph C3H7 1 H NMR (400 MHz, CDCl3) δ 7.58-7.56 (m, 2H), 7.40-7.34 (m,

3 3 3H), 5.14-5.10 (t, JH,H = 7.1 Hz, 1H), 4.31 (t, JH,H = 3.7 Hz, 2H, SiH2), 2.17-2.12 (m,

3 2H), 2.06-1.94 (m, 4H) 1.38-1.32(q, JH,H = 7.3 Hz, 2H), 1.08-1.02 (m, 2H), 0.99-0.92 (t,

3 3 JH,H = 7.6 Hz, 3H), 0.92-0.88 (t, JH,H = 7.6 Hz, 3H).

13 C NMR (100 MHz, CDCl3) 142.5, 135.5, 133.0, 129.7, 1 28.2, 123.9, 31.8, 29.9, 23.4,

23.1, 14.1, 13.4, 8.9.

GC (methylsilicone column, 50 0 C/ 10 min, rate = 20 oC, 250 oC = 40 min) RT for product = 17.20 min.

GC-MS m/z [M+] 232.10; exact mass calculated for C15H24Si 232.16.

118

2-(4-methylcyclohex-1-en-1-yl) ethyl) (phenyl) silane 129

SiH2Ph

1 H NMR (400 MHz, CDCl3) δ 7.57-7.55 (m, 2H), 7.39-7.33 (m,

3 3 3 3H), 5.38 (t, JH,H = 1.3 Hz, 1H), 4.28 (t, JH,H = 3.6 Hz, 2H), 2.09 (t, JH,H = 8.42 Hz,

2H), 2.03-1.92 (m, 2H), 1.70-1.65(m, 1H), 1.60-1.55 (m, 4H), 1.09-1.03 (m, 2H), 0.93 (d,

3 JH,H = 6.2 Hz, 3H).

13 C NMR (100 MHz, CDCl3) δ 138.9, 135.5, 133.0, 131.2, 129.8, 120.3, 34.1, 33.0, 31.5,

28.8, 28.4, 22.1, 8.5.

GC (methylsilicone column, 160 0 C/Isotherm) RT for product = 5.03 min.

GC-MS m/z ([M+) 230.10; exact mass calculated for C15H22Si 230.15.

(2-(4-(tert-butyl) cyclohex-1-en-1-yl) ethyl (Phenyl) silane 131

SiH2Ph

1 H (400 MHz, CDCl3) δ 7.57-7.55 (m, 2H), 7.39-7.33 (m, 3H),

3 3 3 5.42 (q, JH,H = 1.7 Hz, 1H), 4.28 (t, JH,H = 3.6 Hz, 2H), 2.09 (t, JH,H = 7.9 Hz, 2H),

1.97-1.95 (m, 2H), 1.80-1.73 (m, 2H), 1.26 (m, 1H), 1.19-1.11 (m, 2H), 1.09-1.03 (m,

2H), 0.85 (s, 9H).

13 C NMR (100 MHz, CDCl3) δ 138.2, 134.8, 132.2, 129.0, 127.4, 120.2, 43.7, 32.1, 31.7,

29.0, 26.7, 26.2, 23.7, 7.8.

GC (methylsilicone column, 200 0 C/ Isotherm) RT for product = 3.93 min.

HRMS (ESI-MS): m/z 295.1852 ([M + Na]); exact mass calculated for C18H28SiNa

295.1838. 119

Phenyl (2-(1, 2, 3, 6-tetrahydro-(1, 1-’biphenyl-4-yl) ethyl) silane 133

SiH2Ph

1 Ph H NMR (400 MHz, CDCl3) δ 7.59-7.57 (m, 2H), 7.40-7.34 (m,

3 3 3H), 7.31-7.27 (m, 2H), 7.25-7.17 (m, 3H), 5.51 (t, JH,H = 2.4Hz, 1H), 4.31(t, JH,H = 3.7

Hz, 2H, SiH2), 2.65-2.27 (m, 1H), 2.29-1.89 (m, 6H), 1.75-1.65 (m, 1H), 1.36-1.25 (m,

1H), 1.14-1.08 (m, 2H).

13 C NMR (400 MHz, CDCl3) δ 147.7, 139.2, 135.6, 133.0, 129.9, 128.7, 128.4, 127.3,

126.3, 120.6, 40.6, 33.9, 33.1, 30.4, 29.1, 8.6.

GC (methylsilicone column, 100 0 C/ 10 min, rate = 20oC, 250 oC = 40 min) RT for product = 18.89 min.

GC-MS m/z [M+] 292.10; exact mass calculated for C20H24Si 292.16.

Phenyl (2-(4-(prop-1-en-2-yl) cyclohex-1-en-1-yl) ethyl)silane 135

SiH2Ph

1 H NMR (400 MHz, CDCl3) δ 7.59-7.56 (m, 2H), 7.40-7.34 (m,

3 3H), 5.46 (t, JH,H = 1.1 Hz, 1H), 4.72-4.70 (m, 2H), 4.30 (t, J= 3.6 Hz, 2H), 2.13-1.76

(m, 8H), 1.73 (s, 3H), 1.47-1.37 (m, 1H), 1.1-1.05 (m, 2H).

13 C NMR (100 MHz, CDCl3) δ 150.2, 138.6, 135.2, 132.6, 129.4, 127.9, 119.9, 108.3,

41.2, 32.6, 30.7, 28.5, 27.8, 20.7, 8.2.

GC (methylsilicone column, 150 0 C/ Isotherm) RT for product = 15.73 min.

HRMS (ESI-MS): m/z 279.1539 ([M + Na]); exact mass calculated for C17H24SiNa

279.1520. 120

(E, Z) phenyl (6-phenylhex-3-en-1-yl) (Phenyl) silane 137

SiH2Ph

1 H NMR (400 MHz, CDCl3) δ 7.44-7.41 (m, 4H), 7.28-

7.20 (m, 6H), 7.16-7.11 (m, 4H), 7.06-7.02 (m, 6H), 5.40-5.21(m, 4H), 4.16-4.13 (m,

4H), 2.54-2.49 (m, 4H), 2.21-2.13 (m, 4H), 2.04-1.97(m, 4H), 0.90-0.85 (m, 2H), 0.82-

0.76 (m, 2H).

13 C NMR (100 MHz, CDCl3) 142.1, 142.0, 135.7, 135.2, 135.2, 132.5, 132.4, 132.3,

132.0, 129.5, 129.5, 128.9, 128.4, 128.4, 128.2, 128.2, 128.0, 127.9, 125.7, 125.7, 36.5,

35.9, 34.3, 29.1, 27.9, 22.5, 10.2, 10.0.

GC (methylsilicone column, 100 0 C/ 10 min, rate = 20oC, 250 oC = 40 min) RT for product = 17.04 min and 17.17 min.

LC-MS m/z 289.0480([M+Na]); exact mass calculated for C18H22SiNa 289.14.

(S,E)-(6,10-dimethylundeca-3,9-dien-1-yl)(phenyl)silane 139

SiH2Ph 1 H NMR (400 MHz, CDCl3) δ 7.58-7.56 (m, 2H),

3 7.40-7.36 (m, 3H), 5.48-5.35 (m, 2H), 5.13-5.09 (m, 1H), 4.30 (t, JH,H = 3.7 Hz, 2H),

3 2.20-2.14 (m, 2H), 2.03-1.93 (m, 3H), 1.86-1.79 (m, 1H), 1.69 (d, JH,H = 1.0 Hz, 3H),

1.61 (s, 3H), 1.50-1.41 (m, 1H), 1.38-1.30 (m, 1H), 1.19-1.10 (m, 1H), 1.06-1.00 (m,

3 2H), 0.86 (d, JH,H = 6.6 Hz, 3H).

13 C NMR (100 MHz, CDCl3) δ 135.6, 133.2, 132.9, 131.4, 129.8, 128.7, 128.3, 125.3,

40.2, 37.0, 33.1, 28.3, 26.1, 26.0, 19.8, 18.0, 10.5.

GC (methylsilicone column, 200 0 C/ isothermal) RT for product = 3.78 min. 121

GC-MS m/z [M+] 286.10; exact mass calculated for C19H30Si 286.21.

(S (E&Z)-(6,10-dimethylundeca-3,9-dien-1-yl)(phenyl)silane 140

SiH2Ph 1 H NMR (400 MHz, CDCl3) δ 7.59-7.56 (m, 4H),

7.40-7.34 (m, 6H), 5.49-5.34(m, 4H), 5.13-5.09 (m, 2H), 4.40-4.30(m, 4H), 2.23-2.15 (m,

4H), 2.04-1.94 (m, 6H), 1.89-1.79 (m, 2H), 1.70 (s, 6H), 1.61 (s, 6H), 1.50-1.44 (m, 2H),

3 1.39-1.30 (m, 2H), 1.19-1.10 (m, 2H), 1.07-0.98 (m, 4H), 0.88 (d, JH,H = 1.0 Hz, 3H),

3 0.86 (d, JH,H = 1.0 Hz, 3H).

13 C NMR (100 MHz, CDCl3) δ 136.4, 135.7, 135.7, 133.3, 133.0, 132.9, 132.4, 131.5,

131.5, 130.0, 128.8, 128.5, 128.4, 128.4, 125.4, 125.4, 40.4, 40.3, 37.2, 37.1, 34.8, 33.5,

33.3, 28.4, 26.2, 26.1, 26.1, 23.1, 20.0, 19.9, 18.1, 18.1.

GC (methylsilicone column, 160 0 C/Isotherm) RT for products = 13.35 min and 14.26 min.

GC-MS m/z [M+] 286.10; exact mass calculated for C19H30Si 286.21.

(2- (cyclohept-1-en-1-yl) ethyl (Phenyl) silane 141

SiH2Ph

1 H NMR (400 MHz, CDCl3) δ 7.60-7.57 (m, 4H), 7.41-7.34 (m, 6H),

3 5.57-5.56(m, 1H), 5.26-5.23 (m, 1 H), 4.30 (q, JH,H = 3.9 Hz, 4H), 2.21-2.17 (m, 4H),

2.14-2.05 (m, 2H) 2.10-2.05 (m, 4H), 1.80-1.78 (m, 2H), 1.75-1.71 (m, 2H), 1.56-1.51

(m, 4H), 1.50-1.44 (m, 8H), 1.07-1.03(m, 2H).

122

13 C NMR (100 MHz, CDCl3) δ 145.9, 140.9, 135.3, 132.7, 129.5, 128.0, 125.2, 118.8,

37.9, 35.3, 32.7, 30.0, 29.9, 29.8, 29.4, 28.3, 27.3, 26.9, 26.8, 14.1, 11.7, 8.6.

GC (methylsilicone column, 50 0 C/ 10 min, rate = 20 oC, 250 oC = 40 min) RT for product = 16.07 min.

HRMS (ESI-MS): m/z 253.1383 ([M + Na]); exact mass calculated for C15H22SiNa

253.1370.

E-Phenyl (4-phenylbut-3-en-1-yl) silane 143

SiH2Ph

1 H NMR (600 MHz, CDCl3) δ 7.60-7.58 (m, 2H), 7.40-7.17 (m,

3 8H), 6.40-6.23 (m, 2H), 4.36 (t, JH,H = 3.6 Hz, 2H), 2.40-2.36 (m, 2H), 1.17-1.13 (m,

2H).

13 C NMR (100 MHz, CDCl3) 137.0, 133.3, 132.6, 131.4, 129.9, 129.4, 128.7, 128.3,

127.1, 126.3, 28.7, 10.2.

GC (methylsilicone column, 100 0 C/ 10 min, rate = 20oC, 250 oC = 40 min) RT for product = 16.43 min.

HRMS (ESI-MS): m/z 261.1070 ([M + Na]); exact mass calculated for C16H18SiNa

261.1035.

123

E- Phenyl (4-phenylbut-3-en-2-yl) silane 144

SiH2Ph

1 H NMR (600 MHz, CDCl3) δ 7.60-7.58 (m, 2H), 7.40-7.17 (m, 8H),

6.40- 6.32 (m, 1H), 6.29-6.23(m, 1H), 4.33-4.29 (m, 2H), 2.30-2.25 (m, 1H), 1.31 (d,

3 JH,H = 7.1 Hz, 3H).

13 C NMR (100 MHz, CDCl3) δ 138.4, 136.0, 133.3, 132.6, 130.1, 128.7, 128.3, 127.6,

126.8, 126.0, 23.1, 15.4.

GC (methylsilicone column, 100 0 C/ 10 min, rate = 20oC, 250 oC = 40 min) RT for product = 15.93 min.

HRMS (ESI-MS): m/z 261.1070 ([M + Na]); exact mass calculated for C16H18SiNa

261.1035.

E- (3-methyl-4-phenylbut-3-en-1-yl) (Phenyl) silane 145

SiH2Ph

1 H (400 MHz, CDCl3) δ 7.64-7.58 (m, 2H), 7.47-7.17 (m, 8H),

6.43- 6.36 (m, 1H), 4.38 (t, J= 3.6 Hz, 2H), 2.45-2.36 (m, 2H), 1.87 (s, 3H), 1.21-1.13

(m, 2H).

13 C (100 MHz, CDCl3) reported as mixture on 146.

GC (methylsilicone column, 100 0 C/ 10 min, rate = 20oC, 250 oC = 40 min) RT for product = 18.21 min.

GC-MS m/z [M+] 252.10; exact mass calculated for C17H20Si 252.

124

E- (3-methyl-4-phenylbut-3-en-2-yl) (phenyl) silane 146

SiH2Ph

1 H NMR (400 MHz, CDCl3) δ 7.65-7.59 (m, 2H), 7.48-7.18 (m, 8H),

6.40-6.28 (m, 1H), 4.35-4.29 (m, 2H), 2.34-2.23 (m, 1H), 1.87 (s, 3H), 1.32 (d, J= 7.2 Hz,

3H).

13 C NMR (100 MHz, CDCl3) δ 141.3, 140.8, 140.5, 139.1, 138.8, 135.5, 132.6, 130.0,

129.8, 129.1, 129.0, 128.3, 128.2, 128.1, 127.7, 126.4, 126.1, 126.0, 124.6, 123.4, 50.7,

48.2, 36.1, 26.4,17.8, 8.9 (mixture of 145 and 146).

GC (methylsilicone column, 100 0 C/ 10 min, rate = 20oC, 250 oC = 40 min) RT for product = 16.71 min.

GC-MS m/z [M+] 252.10; exact mass calculated for C17H20Si 252.

(7-methyl-3-methylene-oct-6-en-1-yl)(Phenyl) silane 147

SiH Ph 1 2 H NMR (400 MHz, CDCl3) δ 7.59-7.56 (m, 2H), 7.40-7.33

3 3 (m, 3H), 5.24-5.20 (m, 1H), 4.76 (dd, JH,H = 5.9 Hz, 1 Hz, 2H), 4.32 (t, JH,H = 3.6 Hz,

2H), 2.19-2.14 (m, 2H), 2.11-2.01 (m, 4H) 1.70-1.69 (m, 3H), 1.61 (s, 3H), 1.12-1.06(m,

2H).

13 C NMR (100 MHz, CDCl3) reported as mixture on 148.

GC (methylsilicone column, 120 0 C/ isothermal) RT for product = 26.25 min.

GC-MS m/z [M+] 244.10; exact mass calculated for C16H24Si 244.16.

125

E-(3, 7-dimethylocta-2, 6-diene-yl)(Phenyl) silane 148

SiH Ph 1 2 H NMR (400 MHz, CDCl3) δ 7.59-7.56 (m, 2H), 7.40-7.33

3 (m, 3H), 5.24-5.20 (m, 1H), 5.14-5.09 (m, 1H), 4.28 (t, JH,H = 3.8 Hz, 2H), 2.19-2.05 (m,

4H), 1.84-1.80 (m, 2H), 1.71-1.69 (m, 6H), 1.61 (s, 3H).

13 C NMR (100 MHz, CDCl3) δ 151.6, 135.9, 135.8, 135.5, 135.2, 135.1, 133.1, 132.2,

132.1, 130.3, 130.2, 128.6, 128.6, 125.0, 124.8, 119.8, 109.0, 36.45, 32.4, 32.0, 27.1,

26.3, 24.0, 18.3, 12.4, 8.9. (As a mixture of 147 and 148)

GC (methylsilicone column, 120 0 C/ isothermal) RT for product = 22.80 min.

GC-MS m/z [M+] 244.10; exact mass calculated for C16H24Si 244.16.

(Z)-phenyl(3-(prop-1-en-1-yl)octyl)silane 152

SiH2Ph

C H 1 5 11 H NMR (400 MHz, CDCl3) δ 7.58-7.56 (m, 2H), 7.40-7.36 (m, 3H),

3 5.56-5.48 (m, 1H), 5.08-5.02 (m, 1H), 4.28 (t, JH, H = 3.6 Hz, 2H), 2.37-2.29 (m, 1H),

3 1.61 (dd, JH, H = 6.7 Hz, 1.7 Hz, 3H), 1.57-1.50 (m, 1H), 1.40-1.21 (m, 10H), 1.04-0.95

3 (m, 1H), 0.88 (t, JH, H = 6.9 Hz, 3H).

13 C NMR (100 MHz, CDCl3) δ 135.6, 135.3, 132.8, 129.5, 128.0, 124.1, 39.5, 35.5, 32.1,

31.1, 27.0, 22.7, 14.1, 13.4, 7.7.

GC (methylsilicone column, 150 0 C/Isotherm) RT for product = 10.37 min.

GC-MS m/z [M+] 260.10; exact mass calculated for C17H28 Si 260.20.

126

(Z)-phenyl(3-(prop-1-en-1-yl)undecyl)silane 154

SiH2Ph

C H 1 8 17 H NMR (400 MHz, CDCl3) δ 7.56-7.55 (m, 2H), 7.40-7.34 (m, 3H),

3 5.56-5.48 (m, 1H), 5.08-5.01 (m, 1H), 4.28 (t, JH, H = 3.6 Hz, 2H), 2.35-2.29 (m, 1H),

3 3 1.60 (dd, JH, H = 6.7 Hz, 1.7 Hz, 3H), 1.31-1.26 (m, 18H), 0.89 (t, JH, H = 6.8 Hz, 3H).

13 C NMR (100 MHz, CDCl3) δ 135.8, 135.4, 133.0, 129.7, 128.2, 124.3, 39.7, 35.8, 32.1,

31.3, 30.1, 29.9, 29.6, 27.5, 22.9, 14.3, 13.6, 7.8.

GC (methylsilicone column, 230 0 C/Isotherm) RT for product = 2.61 min.

GC-MS m/z [M+] 302.10; exact mass calculated for C20H34 Si 302.24.

(E)-trimethyl((4-(2-(phenylsilyl)ethyl)oct-2-en-2-yl)oxy)silane 156

1H NMR (400 MHz, CDCl ) δ 7.56-7.53 (m, 2H), 7.38-7.32 (m, SiH2Ph 3

3 3 3H), 4.33 (d, JH, H = 10.1 Hz, 1H), 4.26 (t, JH, H = 3.6 Hz, 2H), 2.01-

C4H9 OTMS 3 1.94 (m, 1H), 1.71 (d, JH, H = 0.7 Hz, 3H), 1.27-1.25 (m, 10H), 0.86

3 (t, JH, H = 7.0 Hz, 3H), 0.17 (s, 9H).

13 C NMR (100 MHz, CDCl3) δ 148.3, 135.6, 133.1, 129.8, 128.3, 114.1, 40.9, 36.4, 32.2,

30.1, 30.0, 23.2, 18.7, 14.5, 8.1.

GC (methylsilicone column, 200 0 C/Isotherm) RT for product = 4.98 min.

GC-MS m/z [M+] 334.10; exact mass calculated for C19H34 OSi2 334.2.

127

(E)-dodec-3-en-1-yldiphenysilane 158

SiHPh2 C H 1 5 11 H NMR (400 MHz, CDCl3) δ 7.58-7.54 (m, 4H), 7.39-7.33 (m,

3 6H), 5.46-5.29(m, 2H), 4.83(t, JH, H = 3.5 Hz, 1H), 2.09-2.02 (m, 2H), 1.94-1.89 (m, 2H),

1.28-1.16 (m, 8H), 0.88-0.84 (m, 3H).

13 C NMR (400 MHz, CDCl3) δ 135.4, 135.4, 134.3, 132.0, 131.5, 129.7, 128.1, 128.1,

124.5, 123.7, 32.9, 31.9, 29.8, 28.9, 22.8, 18.0, 14.2.

GC (methylsilicone column, 230 0 C/Isotherm) RT for product = 3.64 min.

GC-MS m/z ([M+) 308.10; exact mass calculated for C21H28Si 308.20.

(E)-dodec-3-en-1-yl (methyl) (phenyl) silane 159

SiHMePh C H 1 8 17 H NMR (400 MHz, CDCl3) δ 7.5 7-7.51 (m, 2H), 7.38-7.33

(m, 3H), 5.45-5.26 (m, 2H), 4.38-4.34 (m, 1H), 1.97-1.91 (m, 2H), 1.82-1.72 (m, 2H), 1.

3 26 (m, 14 H), 0.90 (t, JH, H = 6.8 Hz, 3H), 0.37-0.34 (m, 3H).

13 C NMR (100 MHz, CDCl3) δ 134.3, 129.3, 129.1, 127.8, 124.7, 123.9, 32.7, 32.4, 31.9,

29.6, 29.3, 27.1, 22.7, 19.0, 15.0, 14.1, - 5.9.

GC (methylsilicone column, 180 0 C/Isotherm) RT for product = 6.78 min.

GC-MS m/z ([M+) 288.10; exact mass calculated for C19H32Si 288.23.

128

1B.8 References

[1] A. Deagostino, C. Prandi, C. Zavattaro and P. Venturello, Eur. J. Org. Chem. 2006, 2463. [2] a) O. Diels and K. Alder, Liebigs Ann. Chem. 1928, 460, 98; b) J. Sauer and R. Sustmann, Angew. Chem. Int. Ed. Engl. 1980, 19, 779; c) K. C. Nicolaou, S. A. Snyder, T. Montagnon and G. Vassilikogiannakis, Angew. Chem. Int. Ed. 2002, 41, 1668; d) S. Reymond and J. Cossy, Chem. Rev. 2008, 108, 5359. [3] a) B. Tarnchompoo, C. Thebtaranonth and Y. Thebtaranonth, Tetrahedron Lett. 1987, 28, 6671; b) B. Tarnchompoo, C. Thebtaranonth and Y. Thebtaranonth, Tetrahedron Lett. 1987, 28, 6675; c) M. Kotera, J.-M. Lehn and J.-P. Vigneron, Tetrahedron 1995, 51, 1953; d) W. J. Bailey, R. L. Hudson and E. T. Yates, J. Org. Chem 1963, 28, 828. [4] a) X. Zhang and R. C. Larock, Org. Lett. 2003, 5, 2993; b) C. C. Yu, D. K. P. Ng, B.-L. Chen and T.-Y. Luh, Organometallics 1994, 13, 1487; c) B. E. Simes, B. Rickborn, J. M. Flournoy and I. B. Berlman, J. Org. Chem 1988, 53, 4613; d) E.-i. Negishi, Z. Huang, G. Wang, S. Mohan, C. Wang and H. Hattori, Acc. Chem. Res. 2008, 41, 1474; e) Y. Cheng, B. Schneider, U. Riese, B. Schubert, Z. Li and M. Hamburger, J. Nat. Prod. 2004, 67, 1854; f) M. DellaGreca, C. Di Marino, A. Zarrelli and B. D'Abrosca, J. Nat. Prod. 2004, 67, 1492; g) F. Lv, Z. Deng, J. Li, H. Fu, R. W. M. van Soest, P. Proksch and W. Lin, J. Nat. Prod. 2004, 67, 2033; h) A. R. Pereira and J. A. Cabezas, J. Org. Chem 2005, 70, 2594; i) R. M. de Figueiredo, R. Berner, J. Julis, T. Liu, D. Türp and M. Christmann, J. Org. Chem 2007, 72, 640. [5] a) K. Tamao, N. Ishida, T. Tanaka and M. Kumada, Organometallics 1983, 2, 1694; b) W. Bernhard, I. Fleming and D. Waterson, Chem. Soc. Chem. Commun. 1984, 28. [6] L. N. Lewis, J. Stein, Y. Gao, R. E. Colborn and G. Hutchins, Platin. Met. Rev. 1997, 41, 66. [7] a) D. Schinzer, Synthesis 1988, 263; b) I. Fleming, J. Dunoguès and R. Smithers, Org.React. 1989, 37, 57; c) Y.-R. L. L.-X. Dai, X.-L. Hou, Y.-G. Zhou, Pure Appl. Chem. 1999, 71, 1033. [8] a) T.-H. Chan, Acc. Chem. Res. 1977, 10, 442; b) D. J. Anger, Org. React. 1990, 38. [9] a) K. Tamao, M. Kumada and K. Maeda, Tetrahedron Lett. 1984, 25, 321; b) I. Fleming and P. E. J. Sanderson, Tetrahedron Lett. 1987, 28, 4229. [10] a) M. F. Lappert, T. A. Nile and S. Takahashi, J. Organomet. Chem. 1974, 72, 425; b) A. J. Cornish, M. F. Lappert and T. A. Nile, J. Organomet. Chem. 1977, 132, 133. [11] A. J. Cornish, M. F. Lappert and T. A. Nile, J. Organomet. Chem. 1977, 136, 73. [12] a) S. Takahashi, T. Shibano and N. Hagihara, Chem. Commun. 1969, 161; b) M. Hara, K. Ohno and J. Tsuji, Journal of the Chemical Society D: Chemical 129

Communications 1971, 247; c) J. Tsuji, M. Hara and K. Ohno, Tetrahedron 1974, 30, 2143. [13] a) A. J. Chalk and J. F. Harrod, J. Am. Chem. Soc 1965, 87, 1133; b) N. J. Archer, R. N. Haszeldine and R. V. Parish, J. Chem. Soc. Dalton Trans. 1979, 695; c) C. L. Reichel and M. S. Wrighton, Inorg. Chem. 1980, 19, 3858; d) F. Seitz and M. S. Wrighton, Angew. Chem. Int. Ed. Eng. 1988, 27, 289; e) M. Brookhart and B. E. Grant, Journal of the American Chemical Society 1993, 115, 2151. [14] G. Hilt, S. Lüers and F. Schmidt, Synthesis 2004, 634. [15] J. Y. Wu, B. N. Stanzl and T. Ritter, J. Am. Chem. Soc. 2010, 132, 13214. [16] V. Srinivas, Y. Nakajima, W. Ando, K. Sato and S. Shimada, J. Organomet. Chem. 2016, 809, 57. [17] S. E. Parker, J. Börgel and T. Ritter, J. Am. Chem. Soc 2014, 136, 4857. [18] a) R. K. Sharma and T. V. RajanBabu, J. Am. Chem. Soc 2010, 132, 3295; b) J. P. Page and T. V. RajanBabu, J. Am. Chem. Soc 2012, 134, 6556; c) Y. N. Timsina, R. K. Sharma and T. V. RajanBabu, Chem. Sci 2015, 6, 3994; d) S. Biswas, J. P. Page, K. R. Dewese and T. V. RajanBabu, J. Am. Chem. Soc 2015, 137, 14268. [19] Y. Wang and F. G. West, Synthesis 2002, 0099. [20] R. J. Ely and J. P. Morken, J. Am. Chem. Soc 2010, 132, 2534. [21] A. Zhang and T. V. RajanBabu, J. Am. Chem. Soc 2006, 128, 54. [22] T. P. Meagher, L. Yet, C.-N. Hsiao and H. Shechter, J. Org, Chem. 1998, 63, 4181. [23] S. C. Bart, K. Chłopek, E. Bill, M. W. Bouwkamp, E. Lobkovsky, F. Neese, K. Wieghardt and P. J. Chirik, J. Am. Chem. Soc. 2006, 128, 13901-13912. [24] T. M. Kooistra, Q. Knijnenburg, J. M. M. Smits, A. D. Horton, P. H. M. Budzelaar and A. W. Gal, Angew. Chem. Int. Ed. 2001, 40, 4719-4722. [25] B. Raya, S. Biswas and T. V. RajanBabu, ACS Catal. 2016, 6318-6323

130

Chapter 2

Cobalt-Catalyzed Reduction of Terminal Alkenes and Alkynes Using

(EtO)2SiMeH as a Stoichiometric Reductant

Portions of this chapter appear in the following publication

Raya, B.; Biswas, S.; RajanBabu, T.V. ACS Catal. 2016, 6, 6318-6323

2.1 Backgrounds and Significance

Hydrogenation reaction (Eq. 2.1) is widely used in the chemical and petrochemical industries including pharmaceutical and agrochemical industries to make value-added products from alkene precursors.[1]

H2 H R R (Eq. 2.1)

From decades, numerous transition metal-based catalysts have been developed for hydrogenation using group 8, 9, 10 metals. Among the various transition-metal based catalysts, Rh, Ir, Pd, Pt or Ru catalysts are most oftenly used in the synthetic contexts.

Although alkene hydrogenation reaction is well-known with Rh,[2] Ir,[3] Ru,[4] catalyst, due to high cost, uncertainty in supply and environmental concerns have prompted an ever-increasing search for efficient hydrogenation methods with base-metal catalysts. 131

Recently, many efforts has been reported for hydrogenation reaction of alkenes using base metal catalysts based on Fe,[5] Co,[5-6] and Ni.[6a, 7] Among the base metal catalysts, iron and cobalt are attractive for hydrogenation reaction due to their eco-friendly nature and lesser cost then other transition metals. In these cobalt and iron catalyzed hydrogenations, a large number of alkenes substrates of varying structures have been reduced with high yields using hydrogen as the stoichiometric reagent. Despite decades of development of hydrogenation reaction, however, significant challenges still remain, such as selective hydrogenation of conjugated diene and a variety of other potentially useful substrate such as 1,4-skipped dienes. In this chapter we are reporting efficient cobalt catalyst system for hydrogenation using cobalt complexes at room temperature.

This system is capable of hydrogenation for verities of substrates such as alkenes, alkynes, vinyl arenes and conjugated dienes using a silane as stoichiometric reagent.

2.2 Results and Discussion

The aim of this research was the development of a general method for cobalt catalyzed selective reduction of alkene, alkyne, vinylarene and conjugated diene using silyl hydride. In a search of new reactions to further functionalize 1,4- skipped dienes

(12) obtained from hydrovinylation of 1,3-dienes (11) (Eq. 1.7),[8] selective hydrogenation was considered as a possible target. This chapter describes the discovery and development of PDI (iminopyridine) complexes of Co(II) that catalyze the reduction reaction at room temperature. The first part of this chapter describes the strategy we employed in our investigation to optimize the catalyst for selective reduction. Next we

132 describe the use of the optimized cobalt catalysts for chemo-selective reduction reactions of various substrates. The last section discusses possible mechanism for the selective reduction.

Z R Hydrovinylation (Eq. 1.7) Z R = Alkyl, Z = H or OTMS R 11 12

Z Z Cobalt Catalyst (Eq. 2.2)

R R R = Alkyl, Z = H or OTMS

Inspired by the success of cobalt in the hydrosilylation for alkene, the cobalt catalytic system developed for the hydrosilylation of alkenes and dienes was initially applied to the reduction of alkenes. Using the optimized condition for hydrosilylation [1.0

iPr equivalent of alkene, 1.1 equivalent of silane, PDICoCl2 (0.05 equivalent), NaEt3BH

(0.1 equivalent), toluene (2 mL)], we attempted to do reduction of prototypical substrate

4-methylstyrene, 13 for our initial scouting experiments.

2.3 Development of Cobalt Catalysts for Selective Hydrogenation of Alkenes

The reactions of phenylsilane (PhSiH3) with 13 in the presence of a catalytic amount (0.05 equivalents) of the cobalt complex 2a followed by the addition of toluene

133

o solution of NaEt3BH (0.1 equivalent) at -78 C and allowing the reaction to warm up the reaction mixture to room temperature. This led to the formation of exclusive (>99%) 1,2 linear hydrosilylated product 14 with 92 % isolated yield (Eq. 2.3). GC-MS and NMR identified the hydrosilylated product 14. The GC trace of the product 14 is shown in figure 1.5 of Chapter 1A.

SiH2Ph IPr ( PDI)CoCl2,2a 5 mol% SiH2Ph NaEt BH 10 mol% PhSiH3 3 1.1 eq -78 oC - RT, (Eq. 2.3) 13 Toluene, 5 h 14 99:1 GC ratio 15 92% yield

Several commercially available silanes (Table 2.1) were screened in the presence of the

iPr cobalt precatalyst [( PDI)CoCl2 2a activated by NaEt3BH] for the hydrogenation of 4- methylstyrene 13. In a typical procedure, the cobalt complex (0.05 equivalent) and the 4- methylstyrene 13 (1 equivalent) are dissolved in toluene (2 mL) under argon and the reaction mixture was cooled to -78 oC. To this cold solution was added a toluene solution of NaEt3BH (0.1 equivalent) followed by the addition of silane (1.1 equivalent). The mixture was warmed to room temperature and the reaction was monitored by gas chromatography and GC-mass spectrometry. Among the various silane tested, phenylsilane (Table 2.1, entries 1), diphenylsilane (Table 2.1, entries 2) and phenylmethylsilane (Table 2.1, entries 3) gave good yields of hydrosilylated products 14,

29, 30. Diethylsilane (Table 2.1, entries 4) also gave the hydrosilylated product (80% by

GC integration) along with 17% hydrogenated product 28 by GC integration. 134

Triethylsilane (Table 2.1, entries 6), trichlorosilane (Table 2.1, entries 5) and triphenylsilane (Table 2.1, entries 4) displayed no reaction in hydrosilylation but gave hydrogenated product 28 36%, 16% and 34% respectively by GC integration. A careful examination of the data in Table 2.1 suggests that two kinds of products can be obtained in useful yields. Primary silane such as phenylsilane (PhSiH3) gave an excellent yield of the linear silane 14. Secondary silanes such as diphenylsilane (Ph2SiH2) and phenylmethyl silane (MePhSiH2) (Table 2.1, entries 2-3) gave linear silane as major component along with varying amounts of branched hydrosilylated products and a reduction product 28. Tertiary silanes such as triphenylsilane (Ph3SiH), trichlorosilane

(Cl3SiH), triethylsilane (Et3SiH), triethoxysilane [(EtO)3SiH] and bis (trimethylsiloxy) methylsilane (TMSO)2SiMeH are much less reactive (Table 2.1, entries 4-8), and gave mixture of hydrogenated product 28 and starting material 13 remains mostly unreacted at room temperature. In sharp contrast, methyldiethoxysilane [(OEt)2MeSiH] and methyldimethoxysilane [(OMe)2MeSiH] (Table 2.1, entries 9-10), which are other tertiary silanes, gave nearly quantitative yield of the reduction product 28.

SiH3-nRn

SiH3-nRn IPr PDICoCl2 5mol% R SiH n 4-n (Eq. 2.4) 1.1 eq. NaEt3BH 10 mol% Toluene, 1,2 linear 1,2 branched Reduction o 13 -78 C - RT, 5 h 14 15 28

135

Table 2.1 Effect of Silane for Hydrogenation of 4-Methylstyrene, 13a

Entry Silane 1,2 linearb 1,2 branchedb Reduction(27)c Productb Yieldd SMb

GC Ratio SiH2Ph 92% - - 1 PhSiH3 >98% <2% 14

- SiHPh2 - 2 Ph2SiH2 96% 4% 86%

SiHMePh 89% - 3 PhMeSiH2 89% 2% 9%

4 Ph3SiH - - 34% - 66%

5 Cl3SiH - - 16% - 84%

6 Et3SiH - - 36% - 64%

7 (EtO)3SiH - - 42% - 58%

- 57% 8 (OTMS)2SiMeH - - 43%

9 (EtO)2MeSiH - - 100% 97% - 28

10 (MeO)2MeSiH - - 100% 95% 28

a iPr o See Eq 2.4 for reaction scheme. 5 mol% catalyst ( PDI)CoCl2.10 mol% NaEt3BH, Silane -78 C to RT, bRatios of products determined by areas under the peaks in GC, cSignificant amounts of reduction product was observed; dYield of products were determined after purification.

136

Thus, combination of methyldiethoxysilane [(OEt)2MeSiH] or methyldimethoxysilane

[(OMe)2MeSiH], cobalt (PDI) catalyst and toluene solvent was found to be most effective catalyst for hydrogenation of alkene. The GC trace of hydrogenated product 28 is shown in figure 2.1.

Figure. 2.1: Gas Chromatogram of Product 28

Next, we examined the effect of ligands (Figure 2.2 for ligand used for hydrogenation) on hydrogenation reaction using prototypical substrate 13. Bis(imino)pyridine (PDI) ligands

(L1-L4) and pybox ligand (L5) across a range of different substituents on aromatic backbone of imine and 1,n-bis (diphenylphosphino)-alkanes (n=1-4) were tested after

137 making the complex with cobalt dichloride (Figure 2.3) to examine the effect of steric properties of the ligands on the reaction (Table 2.2, entries 1-5). Cobalt complex 2e

(Table 2.2, entries 5) with cyclohexyl imine backbone gave unsatisfactory result and the starting material 13 remains mostly unreacted for several hours at room temperature whereas cobalt complex 2f (Table 2.2, entries 6) with chelating phosphine backbone showed some catalytic activity and gave 28% hydrogenated product 28 by GC integration. Since the cobalt complexes 2d showed no catalytic activity in the hydrosilylation of 13, we attempted to do hydrogenation reaction using cobalt complexes

2d and showed the moderate reactivity for hydrogenation (Table 2.2, entries 4). Further scanning of more substituted imine cobalt complex 2c (Table 2.2, entries 3) and sterically demanding cobalt complex 2b (Table 2.2, entries 4) gave 47 % and 67 % yield of hydrogenated product 28 by GC integration. During the study of these ligands (L1-L6),

iPr we found that cobalt complex 2a [ PDI(CoCl2)] to be the most useful in the hydrogenation reaction. During our investigation, we have identified the 2,6-bis(imino) pyridine ligands (L1-l4), in particular more sterically demanding 2,6-diisopropyl derivative (L1), to be the most optimal ligand for the hydrogenation reaction.

(Ligand)CoCl2 5 mol% (OEt)2MeSiH NaEt3BH 10 mol% (Eq. 2.5) o 1.1 eq -78 C - RT, Toluene, 5 h 13 28

138

Table 2.2 Effect of Ligand for Hydrogenation of 4-Methylstyrene, 13a

Entry Ligand Complex Reduction 28b SM 13b 1 L1 2a 100% - 2 L2 2b 47% 53% 3 L3 2c 67% 33% 4 L4 2d 36% 64%

5 L5 2e 4% 96% L6 72% 6 2f 28% a iPr o See Eq 2.5 for reaction scheme. 5 mol% catalyst ( PDI)CoCl2.10 mol% NaEt3BH, Silane -78 C to RT, bRatios of products determined by areas under the peaks in GC

O O N N N Ph P PPh N N N N N N 2 2 Ar Ar PDI L1 Ar = 2,6-di-iPr Cy(PDI) Pybox DPPP L2 Ar = 2,6-di-Et L3 Ar = 2,4,6-tri-Me L4 L5 L6

Figure 2.2: Ligand Used for Hydrogenation

N O O N N N N Co N N N N Co Ar Co Ar Cl Cl Cl Cl Cl Cl

PDI Cy(PDI) Pybox 2a Ar = 2,6-di-iPr 2d 2e 2b Ar = 2,6-di-Et 2c Ar = 2,4,6-tri-Me Ph2P PPh2 CoCl2

[dppp(CoCl2)] 2f

Figure 2.3: Cobalt Complexes Used for Hydrogenation

139

We also confirmed that NaEt3BH (Table 2.3, entries 1) was the required activator for hydrogenation reaction by testing various activators (Table 2.3). A quick scan of most commonly used activators (NaEt3BH, trimethylaluminium, MeLi, EtMgBr and n-BuLi)

0 confirmed that NaEt3BH at -78 C is the best reagent for reduction of cobalt complex iPr ( PDI)CoCl2 2a. The only activators that showed any activity were MeLi and nBuLi

(Table 2.3, entries 3 and 5). EtMgBr (Table 2.3, entries 4) or TMA (Table 2.3, entries 2) were moderately successful for hydrogenation. We attempted to do hydrogenation reaction of 13 without using any activator but the reaction was not successful and only gave the starting material 13 even after 24 h.

IPr ( PDI)CoCl2 5 mol% (OEt)2MeSiH Activator 10 mol% (Eq. 2.6) o 1.1 eq -78 C - RT, Toluene, 5 h 13 28

Table 2.3 Activator Scan for Hydrogenation of 4-Methylstyrene, 13a

Entry Activator Reduction 28b SM 13b

1 NaEt3BH 100% -

2 TMA 20% 80% 3 MeLi 85% 15%

4 EtMgBr 13% 87%

5 nBuLi 43% 57% 6 - - 100%

a iPr o See Eq 2.6 for reaction scheme. 5 mol% catalyst ( PDI)CoCl2.10 mol% NaEt3BH, Silane -78 C to RT, bRatios of products determined by areas under the peaks in GC. TMA = Trimethylaluminium

140

Having identified a successful ligand, activator and silane to promote the selective hydrogenation, attention was devoted to test various solvents for hydrogenation of 13. An examination of various common solvents (Table 2.4) demonstrated toluene (Table 2.4, entries 1) to be the best solvent for the hydrogenation reaction. Hexane (Table 2.4, entries

4) and chlorinated solvent such as CH2Cl2 (Table 2.4, entries 2) and ClCH2CH2Cl (Table

2.4, entries 6) lead unsatisfactory result whereas THF (Table 2.4, entries 3), diethylether

(Table 2.4, entries 5) and benzene (Table 2.4, entries 7) lead to acceptable yields. In a parallel run using these solvents, the best solvent for the reaction was identified as toluene.

IPr ( PDI)CoCl2 5 mol% (OEt)2MeSiH NaEt BH 10 mol% 3 (Eq. 2.7) o 1.1 eq -78 C - RT, Solvent, 5 h 13 28

Table 2.4 Solvents Scan for Hydrogenation of 13a

Entry Solvent 28b 13b 1 Toluene 100% - 2 DCM 4% 96%

3 THF 87% 13%

4 Hexane 12% 88%

5 Ether 90% 10% 6 DCE 9% 91%

7 Benzene 80% 20%

a iPr o See Eq 2.7 for reaction scheme. 5 mol% catalyst ( PDI)CoCl2.10 mol% NaEt3BH, Silane -78 C to RT, bRatios of products determined by areas under the peaks in GC. DCE = dichloroethane

141

After extensive screening of the ligand, solvent, activator and silane, the optimized procedure for the hydrogenation reaction that was arrived at is shown in equation 2.8. To investigate the limitation and the full scope of the reaction, optimized cobalt catalyst 2a for hydrogenation was examined for other substrates with varying degrees of steric effects and sensitive functional groups (Figure 2.4).

IPr ( PDI)CoCl2 5 mol% (OEt)2MeSiH NaEt BH 10 mol% 3 (Eq. 2.8) o 1.1 eq -78 C - RT, Toluene, 5 h 13 28

O F Br O Ph OPh 13 35 36 37 38

MeO F Cl

MeO O Ph 41 161 162 163

C6H13 C6H13 Br

164 33 47 43 1 165

O NH2 OH C4H9 O 166 167 5 168

Figure 2.4: Functionalized Alkenes Tested in Cobalt Catalyzed Hydrogenation

142

iPr To investigate the limitation of cobalt catalyst 2a [( (PDI)CoCl2], we examined various functionalized alkene (Figure 2.4) for hydrogenation. Functionalized alkenes bearing –

OH, epoxide, halide, amine, silyl enolether, β-vinyl ketone, arene, and ether were hydrogenated at room temperature using the optimized condition. Under the optimized

iPr conditions [1 equivalent of alkene, 1.1 equivalents of silane, PDICoCl2 (0.05 equivalents), NaEt3BH (0.1 equivalents), toluene (2 mL)], the reaction of vinylarenes 13,

35-38, 41, 161-164 (Figure 2.4) proceeds at room temperature giving quantitative yields of corresponding hydrogenated product 28, 172, 169, 171, 170, 173, 174, 177, 175, 176.

GC, GC-MS and spectroscopic techniques have established the structure of all the hydrogenated products.

It is noteworthy that retention of bromine in the aromatic ring in the example 38 under the optimized condition suggests the absence of Co(0) intermediate.[9] Substrates like 4- phenyl-1-butene 33 prone to isomerization of terminal double bond to internal double bond in a reaction that generates metal hydrides to give the products.[10] Under the optimized conditions compound 33 gave clean hydrogenated product 178 without any isomerization product. All of the terminal alkenes bearing carbonyl 168, bromide 165, hydroxyl 166, amine 167, and epoxy 5 functionalities are reduced to their corresponding saturated compounds 184, 180, 181, 182 and 183 respectively in nearly quantitative yield.

All of the hydrogenated products were isolated by simple filtration of the crude product through silica to remove the left over residue from the catalyst. The scope of hydrogenation reaction of activated alkenes and unactivated alkenes are shown is table

2.5 and 2.6.

143

Table 2.5. Scope of Hydrogenation of Activated Alkenesa

Entry Substrate Product Yield (%)b

R R

1 R = 4-CH3 13 R = 4-CH3 28 97% 2 R = 3-OPh 36 R = 3-OPh 169 94% 3 R = 3-Br 38 R = 3-Br 170 92%

F F 4 37 171 96% Ph Ph

5 O O 98%

35 172

6 99% MeO MeO 41 173

MeO MeO 7 89% O O 161 174

X X

8 X = 3-Cl 163 X = 3-Cl 175 91% 9 X = 4-i-Bu 164 X = 4-i-Bu 176 93%

96% 10 F F

162 177 Ph Ph

144 a iPr o See Eq 2.8 for reaction scheme. 5 mol% catalyst ( PDI)CoCl2.10 mol% NaEt3BH, Silane -78 C to RT, bIsolated yield after purification.

Table 2.6 Scope of Hydrogenation of Unactivated Alkenes

Entry Substrate Product Yield (%)b

R R

11 R = Ph 33 R = Ph 178 96%

12 R = C6H13 47 R = C6H13 179 92%

13 R = C4H9 1 R = C4H9 27 96% 14 R = Br 165 R = Br 180 96% 15 R = OH 166 R = OH 181 98%

NH2 NH2 16 167 182 97%

5 183 95% 17 O O

C4H9 O 168 C4H9 O 184 99%

a iPr o See Eq 2.8 for reaction scheme. 5 mol% catalyst ( PDI)CoCl2.10 mol% NaEt3BH, Silane -78 C to RT, bIsolated yield after purification

Another significant discovery using this protocol is the highly selective reduction of terminal double bond in conjugated dienes and skipped dienes. Under the optimized conditions, the reaction of 1,3-dienes 98, 102-103, 108-110, 120 (Figure 2.5) proceeds at room temperature giving excellent yields of reduction product. In all cases, the

145

hydrogenation favors the terminal selectivity in which the hydrogens are attached to the terminal double bond (Table 2.7).

C8H17 C5H11 C3H7 HO

98 102 103 120

Ph 108 109 110

Figure 2.5: Functionalized Dienes Tested in Cobalt Catalyzed Hydrogenations

Table 2.7 Scope of Hydrogenation Reaction of 1,3-Dienes

Entry Substrate Product Yield (%)b

R R

1 R = C8H17 98 R = C8H17 101 89%

2 R = C5H11 102 R = C5H11 185 91%

3 R = CH2CH2OH 120 R = CH2CH2OH 186 93%

4 C3H7 103 C3H7 187 92%

R R 5 R = CH3 108 R = CH3 188 94% 6 R = tBu 109 R = tBu 189 91% 7 R = Ph 110 R = Ph 190 92% a iPr o See Eq 2.8 for reaction scheme. 5 mol% catalyst ( PDI)CoCl2.10 mol% NaEt3BH, Silane -78 C to RT, bIsolated yield after purification

146

Furthermore, we observed a selective reduction of terminal double bond in presence of the additional disubstituted double bond. Using the optimized conditions, the reaction of

1,4-skipped diene 191 (Figure 2.6) proceeds at room temperature giving excellent yields of reduction product 192.

IPr ( PDI)CoCl2 5 mol% (OEt)2SiMeH NaEt BH 10 mol% C5H11 1.1 eq 3 C5H11 Toluene, -78 oC -RT, 5 h 191 192 89% Yield

Figure 2.6: Selective Hydrogenation of 1,4-Skipped Diene

We attempted to do selective hydrogenation reaction of 1,3-diene (Eq. 2.9) under hydrogenation conditions using hydrogen gas as stoichiometric reductant.[11] Using the optimized condition, Co(PDI) precatalyst and hydrogen gas gave complete reduction of both bond of diene using 50-psi pressure of H2. Our attempt to do selective hydrogenation of diene using 1 atm of hydrogen gas was unsuccessful and gave the mixture of reduction products 101 and 193. The GC traces of products 101 and 193 are shown in figure 2.7 and 2.8.

IPr ( PDI)CoCl2 5 mol% C8H17 C8H17 C8H17 98 101 193 NaEt3BH 10 mol% Toluene, -78 oC -RT, 5 h GC Ratio (Eq. 2.9) 0% 100% H2 (50 psi, RT)

H2 (1 atm, ballon, RT) 22% 78%

147

C8H17 C8H17 101 193 22% 78%

Figure 2.7: Gas Chromatogram of Reduction Products Using H2 Balloon

C8H17 193 100%

Figure 2.8: Gas Chromatogram of Reduction Product Using 50 psi Pressure 148

Other attempts aimed at selective reduction of a vinyl group over the other substituted double bond present in highly sensitive β-vinyl silyl enolate derivatives 194 were unsuccessful using standard hydrogenation conditions (Scheme 2.1). We found that reduction of terminal double bond in 194 using standard hydrogenation conditions using

+ - Wilkinson catalyst (PPh3)3RhCl, Crabtree catalyst [(COD)Ir(Py)-(PCy3)] [PF6] or

Prerlman’s catalyst gave the mixture of products including ketone product 168

Me3SiO Me3SiO

H C4H9 168 Wilkinson Cat. 10 mol% H C4H9 195 C H H 4 9 H (35 PSi), 24 h [R-(-)] 2 >96% ee 96% unreacted SM [(PDICoX ] 5 mol% 194 2 (NaEt3BH 10 mol%, RT) Wilkinson Cat. 10 mol% (OEt)2SiMeH H ballon, DCM 2 Me3SiO 24 h

H C4H9 194 [R-(-)] Crabtree Cat. 10 mol% >99% ee O H2 (35 PSi), 24 h O Pearlman's Cat. 10 mol% 168 92 % by GC H2 (35 PSi), 24 h H C4H9 168 58 H C4H9 % by GC

Scheme 2.1: Reaction of Silyl enol ether 194 Using Standard Hydrogenation

Condition.

149

** The reaction of silyl enol ether 194 using standard hydrogenation condition and under optimed condition was done in collaboration with Dr. Souvagya Biswas.

In sharp contrast, in the cobalt-catalyzed hydrogenation, diethoxymethylsilane

(OEt)2SiMeH effects highly selective reduction of the 1,4-skip diene 194, giving an excellent yield of hydrogenated product 195 without any contamination of ketone product

167. Under our optimized condition, the enantimeric purity of the starting material 194 is not affected (Shown in Eq. 2.10).

Me3SiO Me3SiO

iPr (Eq. 2.10) [( PDICoCl2] 5 mol% (NaEt BH 10 mol%, RT) H C4H9 3 H C4H9 194 (OEt)2SiMeH 1.1 Eq. 195 [R-(-)] [R-(-)] 94% yield >99% ee >96% ee

150

Figure 2.9: Gas Chromatogram of Reduction Product 195

Our optimized catalyst is also applicable for the reduction of terminal alkyne to the 1- alkene or to the completely reduced alkane on the basis of the stoichiometry of the silane used for the reaction (Table 2.9). Variety of terminal alkynes 196-199 are reduced to corresponding alkenes within 1 h by using 1 equiv of (EtO)2SiMeH and 0.01 equiv of the catalyst at 40 oC (oil bath temperature). Under the same condition, varieties of alkynes

196-199 are directly reduced to alkanes by using 2 equiv of (EtO)2SiMeH. The rate of second reduction (alkene to alkane) is slow enough to allow us to isolate the intermediate alkene in excellent yields. The reduction reaction from alkyne to alkane via alkene is compatible with a variety of functional groups.

151

Several alkenes-reactions were scaled up without loss of yield and selectivity. These optimized cobalt catalyzed hydrogenation reactions can be accomplished in neat substrate and large scale (0.5 g) reaction using little as 0.01 equiv. (substrate/catalyst = 100) of the catalyst. Examples of hydrogenation reaction using tertiary silane [(EtO)2MeSiH] for substrate 32 and 106 to give respective hydrogenated product 177 and 189 (Table 2.8, entries 1 and 2)) are shown in Table 2.8.

iPr ( PDI)CoCl2 1 mol% NaEt BH 2 mol% R (OEt)2SiMeH 3 R (Eq. 2.11) o o 1.1 eq -78 C - 40 C (oil bath), 1 h

Table 2.8 Scope of Hydrogenation Reaction Using 1 mol% Catalysta

Entry Substrate Product Yield (%)b

1 Ph Ph 93% 33 178

2 109 189 96%

a iPr o o See Eq 2.11 for reaction scheme. 1 mol% catalyst ( PDI)CoCl2.2 mol% NaEt3BH, Silane -78 C to 40 C oil bath, 1 h, bIsolated yield after purification

152

Figure 2.10: Gas Chromatogram of Reduction Product 178

Figure 2.11: Gas Chromatogram of Reduction Product 189

153

IPr ( PDI)CoCl2 1mol% 1 equiv. (OEt)2SiMeH R (OEt)2SiMeH R R o NaEt3BH 2 mol% 40 C 1.0 equiv. Neat, -78 oC - 40 oC, 1h no additional cat. Alkene Alkane

-CH CH Ph R = -C6H13 -CH2NH2 2 2 -CH2CH2OH

1 equiv. silane, 1 h 95% 96% 94 % 97%

2 equiv. silane, 2 h 95% 93% 97 % 96%

Table 2.9 Scope of Hydrogenation Reaction of Alkyne

Entry Substrate Product Yield (%)a

R R

1 R = C6H13 196 R = C6H13 1 95%

2 R = CH2NH2 197 R = CH2NH2 167 96% 3 94% R = CH2CH2Ph 198 R = CH2CH2Ph 33

4 R = CH2CH2OH 199 R = CH2CH2OH 166 97%

R R

5 R = C H 95% 6 13 196 R = C6H13 27 6 R = CH2NH2 197 R = CH2NH2 182 93%

7 R = CH2CH2Ph 198 R = CH2CH2Ph 178 97% R = CH CH OH 199 R = CH CH OH 181 96% 8 2 2 2 2

iPr o o For reaction scheme. 1 mol% catalyst ( PDI)CoCl2.2 mol% NaEt3BH, Silane -78 C to 40 C oil bath, 1 h, aIsolated yield after purification

154

Finally, our optimized cobalt catalyst failed to react with substrates 200-205 shown in figure 2.12. Under the variety of conditions, the reaction showed only starting material after prolonged reaction time as confirmed by GC and GC-MS.

Br Br Et C4H9 200 201 202 203 204 205 cis or trans

Figure. 2.12: Substrates did not Work under the Optimized Condition

2.4 Proposed Mechanism for Hydrogenation Reaction

The proposed catalytic cycle for hydrogenation reaction is shown in Scheme 2.2. The origin of both hydrogen from 1 equivalent of silane has not been fully established. Our attempts to test the mechanism of hydrogenation reaction by deuterium labeling experiment were hampered by difficulties in preparing the completely deuterated silane

[(CD2CD3O)2SiDCD3]. However we did following experiments that provide strong evidence to suggest that both hydrogen came from silane. Using the optimized deuterated solvents such as toluene-d8 or THF-d8 for the reduction reaction did not show any deuterium incorporation in the products. GC, GC-MS and NMR spectroscopy confirms the structure of the products. Furthermore, we did the reduction reactions of 3-phenoxy styrene using excess deuterium oxide and 4 0A MS. Under the optimized condition, the

0 presence of either D2O or 4 A MS has no effect on the product composition. This experiment rules out H2O in our reaction medium as a possible source of hydrogen. 155

Finally we carried out a series of reduction reactions of 33 using different stoichiometric amount of the silane. By changing the stoichiometry of the silane, we were able to measure the yield of the reduction product 178 from preoperatively scale runs using 4- phenylbutene 33. The results are shown on Table 2.10. Careful analysis of these results suggests that the reaction is stoichiometric in the silane and further that the silane is the sole source of both hydrogen.

Table 2.10 Hydrogenation Reaction of 33 Using Stoichiometric Amount of Silane

IPr ( PDI)CoCl2 (0.01 equiv.) Ph (OEt)2SiMeH Ph 33 NaEt3BH (0.02 equiv.) 178 Neat, 40 oC, 1h

Silane (equiv.) Yield of 54% 0.1 11 0.2 22 0.4 43 0.8 83 1.1 >97%

On the basis of above evidence the proposed mechanism for hydrogenation is shown in

iPr( 1 Scheme 2.2. Reduction of [ PDI)CoCl2] with 2 equivalents of NaEt3BH generates Co -

H intermediate 78.[12] The Co1-H intermediate inserts to the alkene give a cobalt-alkyl complex 79, which on reaction with silane give the hydrogenated product. Isolated

iPr( [13] species [ PDI)CoCl] itself or on treatment with Lewis acid such as Et3B does not show any catalytic activity for hydrogenation. However [iPr(PDI)CoCl], upon treatment

156 with 1 equivalent of NaEt3BH reduced the alkenes and proved to be an efficient catalyst for hydrogenation reaction.

N N Co N Ar Cl Cl Ar iPr Ar = (2,6-iPr)-phenyl) [ PDI]CoCl2

2 NaEt3BH 2 NaCl, 2 Et3B,1/2 H2

Polymeric Silicon R Compounds LnCo H 78

Me [iPr PDI]Co H [iPr PDI]Co Si OEt OEt H H R

[iPr PDI]Co H (OEt)2SiMeH 79 R

Scheme 2.2: Proposed Catalytic Cycle for Hydrogenation Reaction

2.5 Conclusion: In conclusion, we have discovered a new efficient cobalt catalyst system for selective reduction of monosubstituted alkenes, alkynes, 1,3-dienes and 1,4-skipped dienes. Under the optimized conditions [1 equivalent of alkene or alkyne, 1.1 equivalent

iPr of silane, PDICoCl2 (0.05 equivalent), NaEt3BH (0.1 equivalent), toluene (2 mL)], we

157 are able to reduce the terminal double bond in variety of substrates include the dienes bearing sensitive functional group such as silyl enol ether. Substrates carrying carbonyl group, alcohol, epoxide, amine, bromides, di or trisubstituted alkenes are well tolerated.

All the terminal akynes are converted to alkenes or alkanes depending upon the stoichiometry amount of the silane. This protocol is also useful for the neat substrate and gave the quantitative yield for various substrates. Our initial mechanistic studies suggest that both of the hydrogens come from the silane.

2.6 Experimental Procedures

General methods All air- and moisture sensitive manipulations were carried out using standard vacuum line and Schlenk techniques, or in a dry box containing a purified nitrogen. Solvents were distilled from the appropriate drying agents under nitrogen. All glassware was cleaned using base (KOH in i-PrOH) then acid (HClaq) baths. Analytical

TLC was performed on E. Merck pre-coated (0.25 mm) silica gel 60 F254 plates. Flash column chromatography was carried out on silica gel 40 (Sorbtech Chemicals), gas chromatographic analysis was conducted on an Agilent 7820A using hydrogen as the carrier gas, equipped with a methyl silicone column (30 m x 0.32 mm, 0.25 µm film thickness). GC-MS was carried out on a HP-5MS 5% methyl phenylsiloxane (30 m x

0.25 mm, 0.25 µm film thickness) using He as carrier gas. Cobalt (II) chloride and phosphine ligands were purchased from Strem Chemicals. All silanes were purchased from Sigma Aldrich, Oakwood, Alfa Aesar or Apollo Scientific. All activating reagents were purchased from Sigma Aldrich. 1H, 13C NMR spectra were recorded on Bruker 400

158

and 600 MHz, spectrometers. All spectra were obtained at ambient temperature. The chemical shifts (δ) were recorded in parts per million (ppm) and the coupling constants

(J) in Hertz (Hz). 1H and 13C NMR multiplicity and coupling constants are reported where applicable. 1H and 13C spectra were referenced to the residual deuterated solvent peak (CHCl3 7.26 ppm, 77.32 ppm).

Ligand preparation. Bis1,6-(diaryliminoyl) pyridine ligands L1-L4, were prepared by a

Schiff’s base reaction using a modified literature methodology.[14]. The detail experimental procedure for the synthesis of ligand L1-L4 is described in chapter 1A. 1H and 13C NMR of ligands matched what are the reported literature. Ligand L5 was prepared according to reported literature.[15]

Synthesis of Cobalt Complexes: All the cobalt complexes used for this chapter were synthesized according to the procedure described in the chapter 1A.

General Procedure for Cobalt-Catalyzed Reductions (Eq 2.8). An alkene (0.3 mmol) was added to a solution of cobalt (II) chloride PDI complex (9.2 mg, 0.015 mmol, 0. 05 equivalents) in anhydrous freshly distilled toluene (0.16 M) at -78 oC under an atmosphere of argon. At -78 oC (outside bath temperature), toluene solution of sodium triethyborohydride (0.03 mmol, 0.1 equivalents) was added, followed by a silane (0.33 mmol, 1.1 equivalents) and the reaction mixture was removed from the cold bath. The

159 reaction mixture was further stirred at room temperature (or 40 oC for low catalyst loadings) for prescribed time. The reaction was monitored by GC and GCMS. After completion the reaction, it was filtered through the pad of silica by adding hexane and was concentrated under vacuum. Isolated yields were determined after purification by silica chromatography using hexane as eluent and removal of the solvent.

Procedure for Reduction Reaction Under Low Catalyst Loading (Neat Substrate).

Reduction of 4-phenyl-1-butene (with 0.1 mol% catalyst). The alkene (4-phenyl-1-butene,

0.5 g, 3.8 mmol) was added to a solution of PDI-cobalt(II) chloride complex (2.3 mg,

0.003 mmol, 0. 001 equivalent) at -78 oC under an atmosphere of argon. At -78 oC, toluene solution of sodium triethyborohydride (0.007 mmol, 0.002 equivalent) was added, followed by a silane (4.17 mmol, 1.1 equivalents, 0.56 mL). The flask was removed from the cold bath and placed in an oil bath preheated to 40 oC (~ in 2-3 min).

The reaction mixture was stirred at 40 oC for 1 h. After completion (GC) of the reaction, it was filtered through the pad of silica by adding hexane and was concentrated under vacuum. Isolated yield (93%) was determined after purification by silica chromatography using hexane as eluent. The product was 98% by GC with the remaining <2% identified

(GC-MS) as the isomerized 4-phenyl-2-butene, originally present in the starting material.

A parallel reaction done exactly as the previous one was evaporated to dryness and the white residue (~ 129 mg) was identified as higher molecular weight (up to MW 544) compounds by MALDI.

160

Reduction of 4-tert-butyl-1-vinylcyclohexene (0.1 mol% catalyst). The alkene (0.5 g, 3.05 mmol) was added to a solution of PDI- cobalt (II) chloride complex (2.0 mg, 0.003 mmol, 0. 001 equivalent) at -78 oC under an atmosphere of argon. At -78 oC toluene solution of sodium triethyborohydride (0.006 mmol, 0.002 equivalent) was added, followed by a (EtO)2MeSiH (3.35 mmol, 0.45 mL, 1.1 equivalent). The flask was removed from the cold bath and placed in an oil bath preheated to 40 oC (~ in 2-3 min).

The reaction mixture was stirred at 40 oC for 1 h. After completion the reaction

(monitored by GC), it was filtered through the pad of silica by adding hexane and was concentrated under vacuum. Isolated yield (96%) was determined after purification by silica chromatography using hexane as eluent.

Cobalt-Catalyzed Reduction of Dodecadiene at 50 psi H2. The diene (1.21 mmol) was added to a solution of cobalt (II) chloride PDI complex (36.8 mg, 0.06 mmol, 0. 05 equivalents) in anhydrous toluene (0.16 M) at -78 oC under an atmosphere of argon. At -

78 oC toluene solution of sodium triethyborohydride (0.12 mmol, 0.1 equivalents) was added to the reaction mixture. The reaction mixture was then transferred to the 20 mL white cap vial equipped with magnetic stir bar and the vial was placed inside a Fisher-

Porter tube. The tube was sealed, evacuated and purged three times with hydrogen gas and then filled to 50 psi. A glass shield was placed in front of the tube and mixture was stirred for 5 h (monitor by GC, opening of the tube should be done very carefully releasing the pressure and the tube was sealed, evacuated and purged every single time).

After 5 h, the solution was filtered through a short pad of silica with pentane to get the

161 hydrogenated products(s) identified by NMR and GC-MS.

Reduction of Dodeca-1,3-Diene at 1 atm of Hydrogen Using an H2-Filled Balloon. A

50 mL Schlenk flask equipped with magnetic stirring bar was flame dried and purged with argon. The flask was charged with Cobalt (II) chloride PDI complex (36.8 mg, 0.06 mmol, 0. 05 equivalents). Anhydrous toluene (0.16 M) was added via syringe and the flask was cooled at -78 oC under an atmosphere of argon. Diene (1.21 mmol) followed by sodium triethyborohydride (0.12 mmol, 0.1 equivalents) was added to a solution at -78 oC. The flow control valve was closed to argon and hydrogen balloon was placed through the rubber septum. The flask was then removed from the bath and allowed to stirrer at room temperature for 5 h. The progress of reaction was monitored by GC. After 5 h, the solution was filtered through a short pad of silica with pentane to get the hydrogenated product.

Cobalt-Catalyzed Reduction of the Silyl Enol Ether Under 50 psi H2. The diene (0.08 mmol) was added to a solution of cobalt (II) chloride PDI complex (2.8 mg, 0.05 mmol,

0. 05 equivalents) in anhydrous toluene (0.16 M) at -78 oC under an atmosphere of argon.

Toluene solution of sodium triethyborohydride (0.09 mmol, 0.1 equivalent) was added to the reaction mixture. The reaction mixture was then transferred to the 20 mL white cap vial equipped with magnetic stir bar through cannula transfer and the vial was placed inside a Fisher-Porter tube. The tube was sealed, evacuated and purged three times with hydrogen gas and then filled to 50 psi. A glass shield was placed in front of the tube and mixture was stirred for 5 h (monitor by GC, opening of the tube should be done very

162 carefully releasing the pressure and the tube was sealed, evacuated and purged every single time). After 5 h, the solution was filtered through a short pad of silica with pentane to get the hydrogenated product, which was analyzed by GC and NMR.

Cobalt-Catalyzed Reduction of Alkyne to Alkene with 1 Equivalents of

(EtO)2SiMeH. A 50 mL Schlenk flask equipped with magnetic stirring bar was flame dried and purged with argon. The flask was charged with cobalt (II) chloride PDI complex (16.6 mg, 0.03 mmol, 0. 01 equivalent). The flask was cooled at -78 oC under an atmosphere of argon. At -78 oC alkyne (3.63 mmol) was added to the solution. Toluene solution of sodium triethyborohydride (0.07 mmol, 0.02 equivalent) and silane (3.99 mmol, 1.1 equivalent) was added to a solution at -78 oC. The reaction mixture was transferred to the pre heated oil bath (40 oC). The reaction mixture was stirred at 40 oC for 1h. The progress of reaction was monitored by GC and GC-MS. The solution was then filtered through the pad of silica by adding hexane and was concentrated under vacuum. Isolated yield was determined after purification by silica chromatography using hexane as eluent. With 2 equivalents of silane the alkanes are produced in quantitative yield.

Cobalt-Catalyzed Reduction of Alkyne to Alkane with 2 Equivalents of

(EtO)2SiMeH.

A 50 mL Schlenk flask equipped with magnetic stirring bar was flame dried and purged with argon. The flask was charged with cobalt (II) chloride PDI complex (16.6 mg, 0.03

163

mmol, 0. 01 equivalents). The flask was cooled at -78 oC under an atmosphere of argon.

Alkyne (3.63 mmol) was added to the solution. Toluene solution of sodium triethyborohydride (0.07 mmol, 0.02 equivalent) and silane (3.99 mmol, 1.1 equivalent) was added to a solution at -78 oC. The flask was removed from the cold bath and placed in an oil bath preheated to 40 oC (~ in 2-3 min) for 1h. The progress of reaction was monitored by GC and GC-MS, revealing only the alkene. After 1 h, additional silane

(3.99 mmol, 1.1 equivalent) was added via syringe and the reaction mixture was further stirred at 40 oC for 90 minutes. The solution was then filtered through the pad of silica by adding hexane and was concentrated under vacuum. Isolated yield was determined after purification by silica chromatography using hexane as eluent.

Procedure for the Attempted Reduction in the Presence of Triethyl Borane (Et3B) and (iPrPDI)Co(I)Cl. 3-Phenoxystyrene (0.26 mmol) was added to a solution of PDI-

Cobalt(I)chloride complex (7.8 mg, 0.01 mmol, 0.05 equivalents) in anhydrous toluene

(0.16 M) at -78 oC under an atmosphere of argon. At -78 oC, hexane solution of triethylborane (0.02 mmol, 0.1 equivalent) was added, followed by a (EtO)2MeSiH (0.30 mmol, 1.1equivalent). The flask was removed from the cold bath and the reaction mixture was stirred at room temperature for 12 h. At the end of 12 h, it was filtered through the pad of silica by adding hexane and was concentrated under vacuum. No product was detected by GC.

Attempted Reduction of Alkene Using iPrPDI-Co(I)Cl. 3-Phenoxystyrene (0.26 mmol)

164 was added to a solution of PDI-Cobalt(I) chloride complex (prepared by reduction of the

Co(II) complex with Zn) in anhydrous toluene (0.16 M) at -78 oC under an atmosphere of argon. At -78 oC, toluene solution of sodium triethyborohydride (0.01 mmol, 0.05 equivalent) was added, followed by a (EtO)2MeSiH (0.30 mmol, 1.1 equivalent). The flask was removed from the cold bath and the reaction mixture was stirred at room temperature for 4 h. After completion the reaction, it was filtered through the pad of silica by adding hexane and was concentrated under vacuum. Isolated yield (96%) was determined after purification by silica chromatography using hexane as eluent. Purity was ascertained by GC and 1H NMR.

Procedure for Deuterium Labeling Studies. An alkene (0.26 mmol) was added to a solution of Cobalt (II) chloride PDI complex (7.8 mg, 0.01 mmol, 0. 05 equivalents) in anhydrous deuterated toluene (0.16 M) at -78 oC under an atmosphere of argon. At -78 oC, toluene solution of sodium triethyborohydride (0.03 mmol, 0.1 equivalent) was added followed by (EtO)2MeSiH (0.30 mmol, 1.1 equivalent). The flask was removed from the cold bath and the reaction mixture was stirred at room temperature for 5 h. After completion the reaction, it was filtered through the pad of silica by adding hexane and was concentrated under vacuum. Isolated yield (97%) was determined after purification by silica chromatography using hexane as eluent. There was no D-incorporation as judged by NMR and mass spectrometry.

A similar experiment was conducted in THF-d8. The converted product (~ 34%) was isolated and analyzed by GC and GC-MS and showed similar results.

165

Cobalt-Catalyzed Reduction of 3-Phenoxystyrene in the Presence of D2O. A 50 mL

At -78 oC, alkene (0.51 mmol), toluene solution of sodium triethyborohydride (0.01 mmol, 0.02 equivalent) and silane (0.56 mmol, 1.1 equivalent) were added. D2O (0.51 mmol, 1 equivalents) was finally added to the reaction mixture at -78 oC and the reaction mixture was transferred to the pre-heated oil bath (40 oC). The reaction mixture was stirred at 40 oC for 1h. After 1 h, it was filtered through the pad of silica by adding hexane and was concentrated under vacuum. Isolated yield (98%) was determined after purification by silica chromatography using hexane as eluent. There was no D- incorporation as judged by NMR and mass spectrometry.

Reduction of 3-Phenoxystyrene in the Presence of 4 Å Molecular Sieves. A 50 mL

Schlenk flask equipped with magnetic stirring bar was flame dried and purged with argon. The flask was charged with cobalt (II) chloride PDI complex (3.2 mg, 0.005 mmol, 0. 01 equivalents) and 4 Å MS. The flask was cooled at -78 oC under an atmosphere of argon. At -78 oC Alkene (0.51 mmol), toluene solution of sodium triethyborohydride (0.01 mmol, 0.02 equivalent) and silane (0.56 mmol, 1.1 equivalent) were added. The flask was removed from the cold bath and was transferred to the pre heated oil bath (40 oC). The reaction mixture was stirred at 40 oC for 1h. After 1 h, it was filtered through the pad of silica by adding hexane and was concentrated under vacuum.

166

Isolated yield (97%) was determined after purification by silica chromatography using hexane as eluent.

Reduction of 4-Phenyl-1-Butene Using Various Equivalents of Silanes. Six 50 mL

Schlenk flask equipped with magnetic stirring bar were flame dried and purged with argon. Each flask was charged with cobalt (II) chloride PDI complex (9.3 mg, 0.01 mmol, 0. 01 equivalents). The flask was cooled at -78 oC under an atmosphere of argon.

At -78 oC, Alkene (1.51 mmol), toluene solution of sodium triethyborohydride (0.03 mmol, 0.02 equivalent) and silane (0.15 mmol for 10 mol%, 0.30 mmol for 20 mol%,

0.60 mmol for 40 mol%, 0.90 mmol for 60 mol%, 1.20 mmol for 80 mol% and 1.66 mmol for 0.11 equivalent) were added to each solution. The reaction mixtures were transferred to the pre heated oil bath (40 oC) and the reaction mixtures were stirred at 40 oC for 1h. The progress of reaction was monitored by GC and GC-MS. The reactions were quenched and the product mixture in each case was then filtered through the pad of silica by adding hexane and was concentrated under vacuum. Isolated yield was determined after purification by silica chromatography using hexane as eluent. The product(s) was analyzed by GC.

167

Analytical Data for Reduction Products

Oct-1-ene 1

1 H NMR (400 MHz, CDCl3) δ 5.85-5.75 (m, 1H), 5.01-4.89 (m, 2H)

3 2.06-2.00 (m, 2H), 1.39-1.27 (m, 8H), 0.88 (t, JH, H = 7.9Hz, 3H).

13 C NMR (100 MHz, CDCl3) δ 139.6, 114.5, 34.3, 32.2, 29.4, 29.3, 23.1, 14.4.

GC (methyl silicone column, 50 0 C/ Isotherm) RT for product = 2.20 min.

GC-MS m/z ([M+) 112.10; exact mass calculated for C8H16 = 112.13.

Octane 27

1 3 H NMR (400 MHz, CDCl3) δ 1.36-1.29 (m, 12H), 0.90 (t, JH, H = 6.8

Hz, 6H).

13 C NMR (100 MHz, CDCl3) δ 32.4, 29.8, 23.1, 14.4.

GC (methyl silicone column, 50 0 C/ Isotherm) RT for product = 1.67 min.

GC-MS m/z ([M+) 114.10; exact mass calculated for C8H18 = 114.14.

1-ethyl-4-methylbenzene 28

1 3 H NMR (600 MHz, CDCl3) δ 7.23 (s, 4H), 2.75 (q, JH, H = 7.6 Hz, 2H),

3 2.46 (s, 3H), 1.36 (t, JH, H = 7.6 Hz, 3H).

13 C NMR (150 MHz, CDCl3) δ 141.3, 135.0, 129.1, 127.8, 28.5, 21.0, 15.8.

GC (methyl silicone column, 80 0 C/ Isotherm) RT for product = 3.55 min.

GC-MS m/z ([M+) 120.10; exact mass calculated for C9H12 = 120.09.

168

But-3-en-1-ylbenzene 33

1 H NMR (400 MHz, CDCl3) δ 7.12-7.08 (m, 2H), 7.03-6.96 (m, 3H),

3 5.76-5.66 (m, 1H), 4.97-4.89 (m, 2H) 2.48 (t, JH, H = 8.2 Hz, 2H), 2.22-2.16 (m, 2H).

13 C NMR (100 MHz, CDCl3) δ 141.9, 138.2, 128.6, 128.5, 126.0, 114.9, 35.8, 35.7.

GC (methyl silicone column, 80 0 C/ Isotherm) RT for product = 2.75 min.

GC-MS m/z ([M+) 132.10; exact mass calculated for C10H12 = 132.09.

(E)-dodec-3-ene 101

C H 1 8 17 H NMR (400 MHz, CDCl3) δ 5.47-5.35 (m, 2H), 2.03-1.94(m, 4H), 1.34-

1.27 (m, 12 H), 0.98-0.94 (m, 3H), 0.90-0.84(m, 3H).

13 C NMR (100 MHz, CDCl3) δ 132.1, 129.7, 32.9, 32.2, 30.0, 29.8, 29.6, 29.5, 25.9, 23.0,

14.4, 14.3.

GC (methyl silicone column, 100oC/Isotherm) RT for product = 3.66 min.

GC-MS m/z ([M+) 168.10; exact mass calculated for C12H24 168.16.

But-3-en-1-ol 166

1 OH H NMR (400 MHz, CDCl3) δ 5.76-5.66 (m, 1H), 5.05-4.96 (m, 2H) 3.54 (t,

3 JH, H = 6.6 Hz, 2H), 3.28 (s, 1H), 2.24-2.19 (m, 2H).

13 C NMR (100 MHz, CDCl3) δ 135.0, 117.0, 61.5, 37.0.

GC (methyl silicone column, 40 0 C/ Isotherm) RT for product = 1.81 min.

GC-MS m/z ([M+) 72.10; exact mass calculated for C4H8O = 72.06.

169

Prop-2-en-1-amine 167

NH2 1 H NMR (400 MHz, CDCl3) δ 5.55-5.45 (m, 1H), 4.71-4.55 (m, 2H), 2.83-

2.81 (m, 2H), 0.72 (s, 2H).

13 C NMR (100 MHz, CDCl3) δ 139.2, 112.4, 43.9.

GC (methyl silicone column, 35 0 C/ Isotherm) RT for product = 2.52 min.

GC-MS m/z ([M+) 57.10; exact mass calculated for C3H7N = 57.06.

1-ethyl-3-phenoxybenzene 169

1 3 OPh H NMR (400 MHz, CDCl3) δ 7.36-7.31 (m, 2H), 7.24 (t, J H, H = 7.6 Hz,

1H), 7.11-7.07 (m, 1H), 7.03-7.00 (m, 2H), 6.96-6.94 (m, 1H), 6.88-6.87 (m, 1H), 6.83-

6.80 (m, 1H), 2.63 (q, 3J H, H = 7.6 Hz, 2H), 1.23 (t, 3J H, H = 7.6 Hz, 3H).

13 C NMR (100 MHz, CDCl3) δ 158.0, 157.8, 146.9, 130.3, 130.1, 123.6, 123.4, 119.4,

119.1, 116.7, 29.4, 15.9.

GC (methyl silicone column, 140 0 C/) RT for product = 5.88 min.

GC-MS m/z ([M+) 198.12; exact mass calculated for C14H14O 198.10.

1-bromo-3-ethylbenzene 170

1 H NMR (400 MHz, CDCl3) δ 7.34-7.29 (m, 2H), 7.16-7.11 (m, 2H),

2.62(q, 3J H, H = 7.6 Hz, 2H), 1.23 (t, 3J H, H = 7.6 Hz, 3H).

170

13 C NMR (100 MHz, CDCl3) δ 146.9, 131.2, 130.1, 128.9, 126.7, 122.5, 28.7, 15.5.

GC (methyl silicone column, 100 0 C/) RT for product = 3.52 min.

GC-MS m/z ([M+) 184.12; exact mass calculated for C8H9Br 183.99.

4-ethyl-2-fluoro-1, 1’-biphenyl 171

F 1 Ph H NMR (400 MHz, CDCl3) δ 7.57-7.55 (m, 2H), 7.46-7.42 (m, 2H), 7.38-7.34

(m, 2H), 7.07-6.99 (m, 2H), 2.70 (q, 3J H, H = 7.6 Hz, 2H), 1.29 (t, 3J H, H = 7.6 Hz,

3H).

13 C NMR (100 MHz, CDCl3) δ 161.2, 158.8, 146.1, 136.2, 130.7, 129.2, 128.6, 127.6,

124.0, 115.4, 28.6, 15.4.

GC (methyl silicone column, 140 0 C/ Isotherm) RT for product = 9.28 min.

GC-MS m/z ([M+) 200.12; exact mass calculated for C14H13F 200.10.

5-ethylbenzo[d][1,3]dioxole 172

1 O H NMR (600 MHz, CDCl3) δ 6.74- 6.72 (m, 1H), 6.70-6.69 (m, 1H), 6.65-

6.63 (m, 1H), 5.92 (s, 2H), 2.57 (q, 3J, H, H = 7.6 Hz, 2H), 1.20 (t, 3J, H, H = 7.6 Hz,

3H).

13 C NMR (150 MHz, CDCl3) 147.6, 145.5, 138.3, 120.5, 108.5, 108.2, 100.8, 28.7, 16.1.

GC (methyl silicone column, 100 0 C/ Isotherm) RT for product = 6.24 min. 171

GC-MS m/z ([M+) 150.10; exact mass calculated for C9H10O2 =150.07.

2-ethyl-6-methoxynaphthalene 173

O 1 H (400 MHz, CDCl3) δ 7.69-7.56 (m, 3H), 7.33-7.31 (m, 1H), 7.14-

7.11 (m, 2H), 3.91 (s, 3H), 2.79 (q, 3J H, H= 7.6 Hz, 2H), 1.32 (t, 3J H, H= 7.6 Hz, 3H).

13 C (100 MHz, CDCl3) δ 157.3, 139.6, 133.1, 129.4, 129.1, 127.7, 126.9, 125.6, 118.8,

105.9, 55.5, 29.0, 15.8.

GC (methyl silicone column, 140 0 C/Isotherm) RT for product = 7.48 min.

GC-MS m/z ([M+) 186.12; exact mass calculated for C13H14O 186.10.

2-ethyl-5-methoxybenzofuran 174

MeO

1 3 O H NMR (400 MHz, CDCl3) δ 7.28 (d, JH,H = 8.9 Hz 1H), 6.96-6.95

3 3 3 (d, JH,H = 2.5 Hz 1H), 6.81-6.78 (dd, JH,H = 8.8 Hz, 3.8 Hz 1H), 6.31-6.30 (d, JH,H =

3 1.0 Hz 1H), 3.82 (s, 3H), 2.80-2.74 (m, 2H), 1.31 (t, JH,H = 7.5 Hz, 3H).

13 C NMR (100 MHz, CDCl3) δ 162.0, 155.8, 149.7, 129.7, 111.4, 111.1, 103.3, 101.3,

65.9, 56.0, 22.0, 12.0.

GC (methyl silicone column, 120 0 C/ Isotherm) RT for product = 7.85 min.

GC-MS m/z ([M+) 176.10; exact mass calculated for C11H12O2 176.08.

172

1-(sec-butyl)-3-chlorobenzene 175

Cl 1 H NMR (400 MHz, CDCl3) δ 7.24-7.14 (m, 4H), 2.62-2.53 (m, 1H),

3 3 1.62-1.55 (m, 2H), 1.30 (d, JH, H = 6.9 Hz, 3H), 0.90 (t, JH, H = 7.4 Hz, 3H).

13 C NMR (100 MHz, CDCl3) δ 149.9, 134.2, 129.6, 127.4, 126.1, 125.5, 41.7, 31.2, 21.8,

12.3.

GC (methyl silicone column, 100 0 C/Isotherm) RT for product = 3.52 min.

GC-MS m/z ([M+) 168.10; exact mass calculated for C10H13Cl 168.07.

1-(sec-butyl)-4-isobutylbenzene 176

1 H NMR (400 MHz, CDCl3) δ 7.14-7.07 (m, 4H), 2.64-2.55 (m,

3 3 1H), 2.47 (d, JH,H = 7.5 Hz, 2H), 1.93-1.83 (m, 1H), 1.65-1.57 (m, 2H), 1.26 (d, JH,H =

3 3 6.9 Hz, 3H), 0.93 (d, JH,H = 6.6 Hz, 6H), 0.85 (t, JH,H = 7.4 Hz, 3H).

13 C NMR (100 MHz, CDCl3) δ 145.1, 139.2, 129.2, 127.0, 45.4, 41.5, 31.5, 30.5, 22.7,

22.1, 12.5.

GC (methyl silicone column, 100 0 C/Isotherm) RT for product = 7.15 min.

GC-MS m/z ([M+) 190.10; exact mass calculated for C14H22 190.17.

173

4-(sec-butyl)-2-fluoro-1, 1’-biphenyl 177

1 Ph H NMR (400 MHz, CDCl3) δ 7.60-7.57 (m, 2H), 7.48-7.44 (m, 2H),

3 7.40-7.35 (m, 2H), 7.07-6.99 (m, 2H), 2.71-2.62 (m, 1H), 1.69-1.62 (m, 2H), 1.30 (d, JH,

3 H = 6.9 Hz, 3H), 0.90 (t, JH, H = 7.4 Hz, 3H).

13 C NMR (100 MHz, CDCl3) δ 161.1, 158.6, 149.6, 136.1, 130.5, 129.0, 128.5, 127.4,

123.2, 114.4, 41.4, 31.1, 21.7, 12.3.

GC (methyl silicone column, 180 0 C/Isotherm) RT for product = 3.14 min.

GC-MS m/z ([M+) 228.10; exact mass calculated for C16H17F 228.13.

Butylbenzene 178

1 H NMR (400 MHz, CDCl3) δ 7.26-7.19 (m, 3H), 7.15-7.12 (m, 2H),

2.58 (t, 3J H, H = 7.7 Hz, 2H), 1.61-1.54 (m, 2H), 1.37-1.28 (m, 2H), 0.90 (t, 3JH, H = 7.3

Hz, 3H).

13 C NMR (100 MHz, CDCl3) δ143.0, 128.6, 128.4, 125.7, 35.8, 33.8, 22.5, 14.1.

GC (methyl silicone column, 80 0 C/ Isotherm) RT for product = 3.27 min.

GC-MS m/z ([M+) 134.10; exact mass calculated for C10H14 134.11.

Decane 179

C H 1 3 6 13 H NMR (400 MHz, CDCl3) δ 1.37-1.26 (m, 16H), 0.92 (t, JH, H = 6.9 Hz,

6H).

174

13 C NMR (100 MHz, CDCl3) δ 32.0, 29.7, 29.4, 22.7, 14.1.

GC (methyl silicone column, 70 0 C/ Isotherm) RT for product = 2.87 min.

GC-MS m/z ([M+) 142.10; exact mass calculated for C10H22 = 142.17.

1-bromobutane 180

1 3 Br H NMR (400 MHz, CDCl3) δ 3.39 (t, JH, H = 6.8 Hz, 2H), 1.85-1.78 (m,

3 2H), 1.49-1.40 (m, 2H), 0.91 (t, JH, H = 7.4 Hz, 3H).

13 C NMR (100 MHz, CDCl3) δ 34.9, 33.7, 21.4, 13.3.

GC (methyl silicone column, 60 0 C/ Isotherm) RT for product = 1.87 min.

GC-MS m/z ([M+) 135.10; exact mass calculated for C4H9 Br = 135.99.

Butan-1-ol 181

1 3 OH H NMR (400 MHz, CDCl3) δ 3.53 (t, JH, H = 6.7 Hz, 2H), 2.91 (s, 1H),

3 1.50-1.43 (m, 2H), 1.35- 1.25 (m, 2H), 0.85 (t, JH, H = 7.3 Hz, 3H).

13 C NMR (100 MHz, CDCl3) δ 62.6, 35.0, 19.2, 14.1.

GC (methyl silicone column, 40 0 C/ Isotherm) RT for product = 1.55 min.

GC-MS m/z ([M+) 74.10; exact mass calculated for C4H10O = 74.07.

Propan-1-amine 182

NH2 1 3 H NMR (400 MHz, CDCl3) δ 2.34 (t, JH, H = 7.4 Hz, 2H), 1.20-1.10 (m, 2H),

3 0.80 (s, 2H), 0.85 (t, JH, H = 7.4 Hz, 3H).

13 C NMR (100 MHz, CDCl3) δ 43.5, 26.2, 10.5.

175

GC (methyl silicone column, 35 0 C/ Isotherm) RT for product = 2.22 min.

GC-MS m/z ([M+) 59.10; exact mass calculated for C3H9N = 59.07.

(cis, trans) 3-ethyl-7-oxabicyclo[4.1.0]heptane 183

O 1 H NMR (400 MHz, CDCl3) δ 3.79-3.69 (m, 4H), 1.19-1.1.42 (m, 16H),

0.83-0.78 (m, 2H), 0.12-0.04 (m, 6H).

13 C NMR (100 MHz, CDCl3) δ 36.3, 34.8, 34.7, 31.8, 29.2, 27.1, 25.5, 22.8, 21.6, 20.9,

18.9, 14.2, 11.6 (mixture of two products).

GC (methyl silicone column, 100 0 C/ Isotherm) RT for product = 4.01 min and 4.06 min in the ratio of 59: 41.

GC-MS m/z ([M+) 126.19; exact mass calculated for C8H14O = 126.10.

4-ethyloctan-2-one 184

C H O 1 4 9 H NMR (400 MHz, CDCl3) δ 2.32 (d, J = 6.8 Hz, 2H), 2.11 (s, 3H),

1.80(q, J = 6.4 Hz, 1H), 1.32-1.20 (m, 8H), 0.89-0.81(two triplets superimposed, 3H each).

13 C NMR (100 MHz, CDCl3) δ 209.4, 48.4, 35.3, 33.1, 30.3, 29.7, 28.8, 26.3, 22.9, 14.0,

10.8.

GC (methyl silicone column, 100 0 C/Isotherm) RT for product = 2.56 min.

GC-MS m/z 156.30 ([M+]); exact mass calculated for C10H20O 156.27.

176

(E)-non-3-ene 185

C H 1 5 11 H NMR (400 MHz, CDCl3) δ 5.46-5.35 (m, 2H), 2.02-1.94(m, 4H),

1.34-1.27 (m, 6 H), 0.98-0.86(m, 6H).

13 C NMR (100 MHz, CDCl3) δ 131.8, 129.3, 32.5, 31.9, 29.7, 29.3, 25.5, 22.6, 13.9.

GC (methyl silicone column, 50 o C/ Isotherm) RT for product = 2.97 min.

GC-MS m/z ([M+) 126.05; exact mass calculated for C9H18 126.14.

(E)-hex-3-en-1-ol 186

1 OH H NMR (400 MHz, CDCl3) δ 5.53-5.46 (m, 1H), 5.33-5.26 (m, 1H)

3 3.58 (t, JH, H = 6.6 Hz, 2H), 2.30-2.25 (m, 2H), 2.22 (s, 1H), 2.07-2.00 (m, 2H), 0.93 (t,

3 JH, H = 7.5 Hz, 3H).

13 C NMR (100 MHz, CDCl3) δ 134.9, 124.7, 62.4, 30.9, 20.8, 14.5.

GC (methyl silicone column, 140 0 C/ Isotherm) RT for product = 3.99 min.

GC-MS m/z ([M+) 100.10; exact mass calculated for C6H12O = 100.09.

3-ethylhept-3-ene 187

C3H7 1 3 H NMR (400 MHz, CDCl3) δ 5.08 (t, J H, H= 7.1 Hz, 1H), 2.09-1.95(m,

6H), 1.43-1.29(m, 2H), 0.95 (t, 3J H, H= 7.4 Hz, 6H), 0.91(t, 3J H, H= 7.4 Hz, 3H).

13 C NMR (100 MHz, CDCl3) δ 143.1, 123.0, 31.9, 30.0, 29.9, 23.0, 22.9, 14.4.

GC (methyl silicone column, 50 0 C/Isotherm) RT for product = 3.27 min.

GC-MS m/z ([M+) 220.10; exact mass calculated for C9H18 126.14.

177

1-ethyl-4-methylcyclohex-1-ene 188

1 H NMR (400 MHz, CDCl3) δ 5.32-5.31 (m, 1H), 2.05-1.88(m, 6H), 1.68-1.63 (m,

1H), 1.60-1.54 (m, 2H), 0.95 (t, 3J H, H= 7.4 Hz, 3H), 0.91(d, 3J H, H= 6.3 Hz, 3H).

13 C NMR (100 MHz, CDCl3) δ 139.3, 119.0, 34.0, 31.5, 30.4, 29.8, 28.7, 28.5, 12.5

GC (methyl silicone column, 40 0 C/ Isotherm) RT for product = 4.97 min.

GC-MS m/z ([M+) 124.13; exact mass calculated for C9H16 124.10.

4-(tert-butyl)-1-ethylcyclohex-1-ene 189

1 tBu H NMR (400 MHz, CDCl3) δ 5.39-5.38 (m, 1H), 2.04-1.92 (m, 4H,), 1.83-1.72(m,

2H), 1.32-1.26 (m, 1H), 1.23-1.11 (m, 2H), 0.98 (t, 3JH, H = 7.5 Hz, 3H), 0.86 (s, 9H).

13 C NMR (100 MHz, CDCl3) δ 139.6, 119.8, 44.6, 32.5, 30.4, 30.1, 27.5, 27.0, 24.6, 12.7.

GC (methyl silicone column, 100 0 C/ Isotherm) RT for product = 3.56 min.

GC-MS m/z ([M+) 166.17; exact mass calculated for C12H22 166.10.

178

4-ethyl-1, 2, 3, 6-tetrahydro-1, 1’-biphenyl 190

1 Ph H (400 MHz, CDCl3) δ 7.31-7.27 (m, 2H), 7.23-7.16 (m, 3H), 5.48-5.47 (m, 1H),

2.78-2.70 (m, 1H,), 2.19-1.92 (m, 6H), 1.81-1.70 (m, 2H), 1.02 (t, 3 JH, H = 7.5 Hz, 3H).

13 C NMR (100 MHz, CDCl3) δ 147.5, 139.5, 128.4, 127.0, 125.9, 119.1, 53.5, 40.4, 33.6,

30.3, 29.1, 12.4.

GC (methyl silicone column, 100oC/ 10 min, rate = 20 oC, 250 oC = 40 min) RT for product = 12.97 min.

GC-MS m/z ([M+) 186.10; exact mass calculated for C14H18 186.14.

(Z)-4-ethylnon-2-ene 192

C H 1 5 11 H NMR (400 MHz, CDCl3) δ 5.59-5.55 (m, 1H), 5.18-512 (m, 1H), 2.38-

2.21(m, 1H), 1.70-1.67 (m, 3H), 1.47-1.22 (m, 10H), 1.07-0.94 (m, 6H).

13 C NMR (100 MHz, CDCl3) δ 136.2, 123.7, 38.8, 35.9, 32.4, 31.9, 28.9, 27.3, 22.9, 14.4,

12.0.

GC (methyl silicone column, 50 0 C/Isotherm) RT for product = 6.42 min.

GC-MS m/z ([M+) 154.10; exact mass calculated for C11H22 154.17.

179

Dodecane 193

C H 1 3 8 17 H NMR (400 MHz, CDCl3) δ 1.36-1.24 (m, 20H), 0.90 (t, JH, H = 6.8 Hz,

6H).

13 C NMR (100 MHz, CDCl3) δ 32.4, 30.2, 30.1, 29.9, 23.1, 14.4.

GC (methyl silicone column, 100 0 C/ Isotherm) RT for product = 3.22 min.

GC-MS m/z ([M+) 170.10; exact mass calculated for C12H26 = 170.20.

(E)-((4-ethyloct-2-en-2-yl)oxy)trimethylsilane 195

C H OTMS 1 3 4 9 H NMR (400 MHz, CDCl3) δ 4.35 (dq, JH, H = 0.8 Hz, 10.1 Hz,

1H), 1.95-1.84 (m, 1H), 1.72 (d, 3J H, H= 0.9 Hz, 3H), 1.44-1.21 (m, 5H), 1.18-1.08 (m,

3H), 0.90-0.82 (m, 6H), 0.18 (s, 9H).

13 C NMR (100 MHz, CDCl3) δ 147.4, 114.2, 39.7, 36.1, 29.7, 29.4, 22.9, 18.3, 14.1, 11.9,

0.3.

GC (methyl silicone column, 100 0 C/ Isotherm) RT for product = 4.56 min.

GC-MS m/z ([M+) 228.10; exact mass calculated for C10H12 228.19.

180

2.7 References

[1] a) N. B. Johnson, I. C. Lennon, P. H. Moran and J. A. Ramsden, Acc. Chem. Res. 2007, 40, 1291; b) C. S. Shultz and S. W. Krska, Acc. Chem. Res. 2007, 40, 1320; c) H.- U. Blaser, B. Pugin, F. Spindler and M. Thommen, Acc. Chem. Res. 2007, 40, 1240. [2] J. A. Osborn, F. H. Jardine, J. F. Young and G. Wilkinson, J. Chem. Soc. A 1966, 1711. [3] R. Crabtree, Acc. Chem. Res. 1979, 12, 331. [4] R. Noyori, M. Yamakawa and S. Hashiguchi, J. Org. Chem. 2001, 66, 7931. [5] P. J. Chirik, Acc. Chem. Res. 2015, 48, 1687. [6] a) T.-P. Lin and J. C. Peters, J. Am. Chem. Soc 2014, 136, 13672; b) M. R. Friedfeld, G. W. Margulieux, B. A. Schaefer and P. J. Chirik, J. Am. Chem. Soc 2014, 136, 13178; c) M. R. Friedfeld, M. Shevlin, J. M. Hoyt, S. W. Krska, M. T. Tudge and P. J. Chirik, Science 2013, 342, 1076. [7] K. V. Vasudevan, B. L. Scott and S. K. Hanson, Eur. J. Inorg. Chem. 2012, 2012, 4898. [8] a) R. K. Sharma and T. V. RajanBabu, J. Am. Chem. Soc 2010, 132, 3295; b) J. P. Page and T. V. RajanBabu, J. Am. Chem. Soc 2012, 134, 6556; c) Y. N. Timsina, R. K. Sharma and T. V. RajanBabu, Chem. Sci 2015, 6, 3994; d) S. Biswas, J. P. Page, K. R. Dewese and T. V. RajanBabu, J. Am. Chem. Soc 2015, 137, 14268. [9] D. Zhu and P. H. M. Budzelaar, Organometallics 2010, 29, 5759-5761. [10] a) T. V. RajanBabu, N. Nomura, J. Jin, M. Nandi, H. Park and X. F. Sun, J. Org. Chem. 2003, 68, 8431-8446; b) H. J. Lim, C. R. Smith and T. V. RajanBabu, J. Org. Chem. 2009, 74, 4565-4572; c) S. Biswas, A. Zhang, B. Raya and T. V. RajanBabu, Adv. Synth. Catal. 2014, 356, 2281-2292. [11] Q. Knijnenburg, A. D. Horton, H. v. d. Heijden, T. M. Kooistra, D. G. H. Hetterscheid, J. M. M. Smits, B. d. Bruin, P. H. M. Budzelaar and A. W. Gal, J. Mol. Catal. A. Chem. 2005, 232, 151-159. [12] S. C. Bart, K. Chłopek, E. Bill, M. W. Bouwkamp, E. Lobkovsky, F. Neese, K. Wieghardt and P. J. Chirik, J. Am. Chem. Soc. 2006, 128, 13901-13912. [13] T. M. Kooistra, Q. Knijnenburg, J. M. M. Smits, A. D. Horton, P. H. M. Budzelaar and A. W. Gal, Angew. Chem. Int. Ed. 2001, 40, 4719-4722. [14] G. J. P. Britovsek, M. Bruce, V. C. Gibson, B. S. Kimberley, P. J. Maddox, S. Mastroianni, S. J. McTavish, C. Redshaw, G. A. Solan, S. Strömberg, A. J. P. White and D. J. Williams, J. Am. Chem. Soc. 1999, 121, 8728-8740. [15] H.-J. Kim, R. Asif, D. S. Chung and J.-I. Hong, Tetrahedron Lett. 2003, 44, 4335.

181

Chapter 3: Novel Cobalt Catalysts for Chemo and Regioselective

Hydrosilylation of 1,1-disubstituted Alkenes

3.1 Backgrounds and Significance:

To attain more economical production of silicon-containing industrial materials, development of a well-defined and efficient catalytic system based on more-abundant and economical metals with higher selectivity is still an intensive research topic. As outlined in the previous chapter, numerous reports can be found on hydrosilylation using base metal catalyst such as iron,[1] and nickel.[2] From decades, hydrosilylation reaction using first-row transition metal catalysts have been known, but report on cobalt-catalyzed hydrosilylations have been limited.[3] Recently, cobalt catalysts reported by Chirik,[4]

Deng,[5] Holland and Weix, [6] Huang, [7] Lu,[8], Fout,[9] have addressed some of these limitations but these reports are limited to simple alkene and alkyne substrates. In spite of long decades of development of hydrosilylation reaction, significant challenges remain, in the selective hydrosilylation of unactivated alkene, alkyne, vinylarenes, conjugated diene and a variety of other potentially useful functionalized substrates using different primary, secondary and tertiary silanes. In this connection, we have discovered a new efficient cobalt catalyst for selective hydrosilylation of monosubstituted alkenes, alkyne, vinylarenes, conjugated dienes and 1,4-skipped dienes.[10] Under the optimized conditions

iPr [1 equivalent of alkene, 1.1 equivalents of silane, PDICoCl2 (0.05 equivalents),

182

NaEt3BH (0.1 equivalents), toluene (0.16 M)], we are able to do hydrosilylation of variety of substartates bearing sensitive functional groups such as bromide, silyl enol ether, β-vinyl ketone etc. Substrates carrying ether, chloride, and acetate are well tolerated. All the terminal alkenes and dienes are converted to linear hydrosilylated product. This protocol is also useful for the neat substrate and reactions using little as

0.01 equiv. (substrate/catalyst = 100) of the catalyst, which gave the quantitative yield for various substrates. Although this protocol is highly efficient for hydrosilylation of terminal alkenes and dienes, failed in reactions of substrates 200, 206-208 shown in

Figure 3.1. Under a variety of conditions, the reaction showed only starting material after prolonged reaction time.

200 206 207 208

Figure 3.1: Substrates that Failed in Hydrosilylation Using Cobalt(PDI) Complex

The major limitation (and in some sense, advantage) for cobalt catalyzed hydrosilylation reaction using the PDI ligand is its terminal selectivity. However, this active catalyst did not work for 1,1-disubstituted alkenes. In this chapter we report an efficient cobalt catalyst system for room temperature hydrosilylation of 1,1-disubstituted alkenes using chelating phosphines as ligand for cobalt. This reaction is more general than the ones

183 described in the previous chapters and effect hydrosilylation of numerous substrates such as alkene, vinyl arene, conjugated diene, 1,4-skipped diene and 1,1-disubstituted alkenes.

3.2 Results and Discussion:

The aim of this research was the development of a general method for cobalt- catalyzed hydrosilylation of 1,1-disubstituted alkenes. This chapter describes the discovery and development of phosphine complex of cobalt that catalyze these hydrosilylation reactions at room temperature. This chapter describes the strategy we employed in our investigation to optimize the catalyst for selective hydrosilylation of these demanding substrates. In our initial attempts to find a new catalyst for hydrosilylation reaction of 13, a cobalt catalysts used for hydrovinylation ([dppp]CoCl2) with different activators were tested using phenylsilane under the varities of conditions.[11] The preliminary study of hydrosilylation using the cobalt precatalyst

([dppp]CoCl2) with different activator (either catalytic or stoichiometric amount) was discussed in chapter 1A. It was found that this precatalyst ([dppp]CoCl2) is not suitable for hydrosilylation. All the preliminary result is summarized in Table 3.1. In this chapter we will present the detail studies of alternate cobalt catalysts for hydrosilylation reaction of alkenes using phosphine ligands.

SiH2Ph

(dppp)CoCl2 10 mol% SiH2Ph PhSiH Activator 20 mol% 3 (Eq. 3.1) 1.1 eq RT, Solvent, 5 h 13 14 15 1,2 linear 1,2 branched

Ph2P PPh2 (dppp) 184

Table 3.1 Effect of Activator for Hydrosilylation of 4-Methylstyrene, 13 Using a

Bisphosphine Ligand dpppa

Entry Activator Solvent 14 15b 13b Silane Formed (%)c

1 Zn DCM - - 100% -

2 Et2Zn DCM - - 57% PhSiHEt2 (43%) 16

3 TMA DCM - - 100% -

4 MAO DCM - - 100% -

5 CH3LI DCM - - 21% PhSiHMe2 (79%) 17

6 nBuLi DCM - - 34% PhSiHnBu2 (66%) 18

7 Zn EtOH - - - PhSi(OEt)3 (100%) 19

o 8 Zn(80 C) DCE - 5% 50% Ph2SiH2 (45%) 20 a See Eq 3.1 for reaction scheme. 10 mol% catalyst [dppp]CoCl2, 20 mol% activator, dichloromethane, rt,

b c PhSiH3. Ratios of products determined by areas under the peaks in GC. Significant amounts of different silanes were also observed; Rest percentage for mass balance is reduction product 28.

The bisphosphine ligands (e.g., dppp, dppb, dpppent, and dppf) across a range of bite angles (Figure 3.2) were tested to examine the effects of steric properties on the reaction

(Table 3.2, entries 1-6). Since NaEt3BH was proven to be the most selective activator attempted to reduce the (PDI) CoCl2 complex, sodium triethylborohydride was the initial choice to reduce the cobalt phosphine complex. Neither sodium triethylborohydride nor trimethylalumunium (TMA) exclusively favored the formation of hydrosilylated product

185

(Table 3.2). However several bisphophine ligands showed limited catalytic activity along with redistribution of silane 20 and, reduction of alkene.

SiH2Ph

(Ligand)CoCl2 10 mol% SiH2Ph PhSiH Activator 20 mol% 3 (Eq. 3.2) 1.1 eq RT, DCM, 5 h 13 14 15 1,2 linear 1,2 branched

Table 3.2 Activator Scan (contd). for Hydrosilylation of 4-Methylstyrene, 13a

Entry Activator Ligand 14b 15b 13b Silane Formed (%)c

1 NaEt3BH dppf 5% 2% 50% 3% 20

2 TMA dppf 15% 2% 61% 10% 20

3 NaEt3BH dpppent 1% 1% 94% -

4 NaEt3BH dppm 8% 2% 55% 7% 20

5 NaEt3BH dppb 28% 5% 36% 4% 20

6 NaEt3BH dppe 19% 20% 34% 8% 20 a See Eq 3.2 for reaction scheme. 10 mol% catalyst [ligand]CoCl2, 20 mol% activator, dichloromethane, rt,

b c PhSiH3. Ratios of products determined by areas under the peaks in GC. Significant amounts of Ph2SiH2 also observed; 20 = Ph2SiH2

186

PPh2 Ph2P PPh2 Ph2P Ph2P PPh2

dppm dppe dppp L1 L2 L3

PPh2 Fe PPh2 Ph2P PPh2 Ph2P Ph2P dppb dpppent dppf L4 L5 L6

Figure 3.2.: Ligand Used for Hydrosilylation of Alkene

Furthermore, our studies also focused on the counter ion effect on cobalt for hydrosilylation of 13. So we screened cobalt (II) bromide phosphine complexes using different phosphine ligands (L1-L6). Performing the catalytic hydrosilylation at 23 oC

(RT) using different activators (Table 3.3) resulted in incomplete conversion of 4- methylstyrene, 13 to 1,2-linear hydrosilylated product 14 and 1,2-branched hydrosilylated product 15 along with accompanying redistribution silane product, generating diphenylsilane (Ph2SiH2, 20) as a minor byproduct (Table 3.3). Among the activators,

B(C6F5)3 (Table 3.3, entries 8) showed moderate catalytic activity. Sodium triethylborohydride (Table 3.3, entries 1-4) and trimethylaluminium (TMA) (Table 3.3, entries 5-7) showed the less catalytic activity compared to B(C6F5)3.

187

SiH2Ph

(Ligand)CoBr2 10 mol% SiH2Ph PhSiH Activator 20 mol% 3 (Eq. 3.3) 1.1 eq RT, DCM, 5 h 13 14 15 1,2 linear 1,2 branched

Table 3.3 Scanning Result of Cobalt Bromide Complex for Hydrosilylation of 13a

Entry Activator Ligand 14b 15b 13b Silane Formed (%)c

1 NaEt3BH L1 8% 4% 52% 12% 20

2 NaEt BH L2 13% 7% 49% 15% 20 3

3 NaEt3BH L3 18% 4% 45% 18% 20

4 NaEt3BH L4 18% 3% 42% 10% 20

5 TMA L2 19% 2% 54% 9% 20

6 TMA L3 19% 20% 2% 46% 20

7 TMA L4 14% 3% 34% 15% 20

8 B(C6F5)3 L3 38% 4% 41% 4% 20

a See Eq 3.3 for reaction scheme. 10 mol% catalyst [ligand]CoBr2, 20 mol% activator, dichloromethane, rt,

b c PhSiH3. Ratios of products determined by areas under the peaks in GC. Significant amounts of Ph2SiH2

(20) also observed; Rest percentage for mass balance is reduction product 28.

Next we screened cobalt (II) acetate tetrahydrate with different phosphine ligand without using any activator. Cobalt (II) acetate is perhaps the most attractive because they are among the most inexpensive source of cobalt and are bench stable.[4b] Although cobalt

188

(II) acetate precatalyst is bench stable, it proved essentially inactive for hydrosilylation at room temperature using both monodentate (tricyclohexyl phosphine, PCy3) and bidentate ligand [1,3-bis (diphenylphosphino) propane, dppp]. Performing the catalytic hydrosilylation at 80 oC resulted in complete conversion of 4-methylstyrene, 13 to 1,2- branched hydrosilylated product 15 along with accompanying redistribution of silane product, generating diphenylsilane (Ph2SiH2, 20) as a byproduct.

SiH2Ph Co(OAc) 10 mol% 2 SiH2Ph PhSiH Ligand 20 mol% 3 (Eq. 3.4) 1.1 eq 80 oC, DCE, Time 13 14 15 1,2 linear 1,2 branched

Table 3.4 Scanning result of Cobalt Acetate for Hydrosilylation of 13a

d e Entry Ligand Time 14 15 Ph2SiH2 (%) 20

b 1 PCy3 26 h - 77% 23%

2 Dpppc 28 h - 74% 26% a b c See Eq 3.4 for reaction scheme. 10 mol% catalyst Co(OAc)2. 20 mol% ligand (PCy3), 10 mol% dppp,

o d 1,2-dichloroethane, 80 C, PhSiH3. Ratios of products determined by areas under the peaks in GC. e Significant amounts of Ph2SiH2 also observed; Silane formed was detected by GC and GC-MS.

Guided by these negative results with phosphine ligands for hydroslilylation reaction, we pushed forward to search for more efficient catalyst for hydrosilylation with improved selectivity.

189

3.3 Development of Cobalt Catalysts for Selective Hydrosilylation of Alkenes

3.3.1 Catalyst Discovery: Recently, Stanley Jing and Vagulejan Balasanthiran in our group, while investigating the mechanism for cobalt-catalyzed hydrovinylation reaction

(Eq. 3.5), isolated several cobalt(I) phosphine complexes [(P~P)Co-X]. They were able to synthesize varities of cobalt (I) phosphine complexes using different phosphine ligand and found that hydrovinylation reaction can be done by using the mixture of isolated cobalt(I) phosphine complex and catalytic amount of various activators (Eq. 3.6).

Ph2P Ethylene, [(+)-DIOP]CoCl2 (5 mol%), Additives (Stoichiometric amount) Z (Eq. 3.5) 4 DCM, Temp, Time O * R 2 R Z 1 O PPh2 Z = H, OSiR'3 1,4 -Z (S,S)-DIOP (Original Protocal for Hydrovinylation) Z = H,96% yield, >94% ee, Z = OSiR'3, 95% yield, 99% ee

4 2 Ethylene, [dppp]CoBr 5 mol% (Eq. 3.6) R * 3 R 1 NABARF 10 mol% DCM, 0 oC -Rt, 2 h R = C8H17 1,4 -Z

F3C CF3

Na B

F3C CF3

F3C CF3 NaBARF

190

All cobalt(I) phosphine complexes were synthesized by reduction of cobalt(II) phosphine complex with zinc, the cobalt(I) species shows better catalytic activity under the same hydrovinylation conditions. Inspired by the success of isolated cobalt (I) phosphine complex in the hydrovinylation for dienes, we sought to develop more efficient cobalt catalyst for hydrosilylation with improved selectivity. The reactions of phenylsilane

(PhSiH3) with prototypical substrate 4-methylstyrene, 13 were examined in the presence of catalytic amount (0.05 equivalents) of the cobalt (I) phosphine complexes alone but no reaction was observed at room temperature without adding any activator. Using the conditions optimized for the cobalt (I) catalyst for the hydrovinylation of diene; the hydrosilylation of 13 was attempted. Thus using (dppp)CoBr with B(C6F5)3 at room temperature, we were able to isolate exclusively 1,2 linear hydrosilylated products 15 having 96% isolated yield (Eq. 3.7). The GC traces of the product 14 is shown in Figure

3.3

SiH2Ph

(dppp)CoBr 5 mol% SiH2Ph PhSiH B(C6F5)3 15 mol% 3 (Eq. 3.7) 1.1 eq RT, DCM, 10 min 13 14 15 1,2 linear 1,2 branched > 98% <1% 96% Yield

A quick screening of effect of ligands (Figure 3.4 for ligand used for hydrosilylation) on the regioselectivity of hydrosilylation using isolated cobalt (I) complex revealed that dppp (L3) is the best ligand for the hydrosilylation of 13 (Table 3.5, entries 6 and 7).

191

SiH2Ph

Figure 3.3: Gas Chromatogram of Hydrosilylated Product 14

PPh2 PPh2 Ph2P PPh2 Ph2P Ph2P PPh2 PPh2 dppm dppe dppp BISBI

L1 L2 L3 L8

PPh 2 Ph P PPh PPh Ph2P 2 2 2 PPh2 dppb dpppent

L4 L5 BINAP L7

Figure 3.4: Ligand Used for Hydrosilylation of 13

192

SiH2Ph

(Ligand)CoX 5 mol% SiH2Ph PhSiH B(C6F5)3 15 mol% 3 (Eq. 3.8) 1.1 eq RT, DCM, 5 h 13 14 15 1,2 linear 1,2 branched

Table 3.5 Ligand Scan for Hydrosilylation of 13a

Entry CoX Ligand 14b 15b 13b Silane Formed (%)c

1 CoBr L1 60% 2% 24% 9% 20

2 CoBr L2 45% 2% 22% 26% 20

3 CoBr L4 51% 8% - 20% 20

4 CoBr L5 30% 12% - 45% 20

5 CoBr L7 57% 8% - 30% 20

6 CoEt L3 98% 2% - - (2 h)

7 CoBr L3 100% - - - (10 min)

8 CoCl L3 67% 3% - 25% 20

9 CoCl L8 55% 2% - 23% 20 a b See Eq 3.8 for reaction scheme. 5 mol% catalyst (P~P)Co-X. 15 mol% B(C6F5)3, rt, PhSiH3. Ratios of

c products determined by areas under the peaks in GC. Significant amounts of Ph2SiH2 also observed; Silane formed was detected by GC and GC-MS. 20 = Ph2SiH2, Rest percentage for mass balance is 1-ethyl-4- methylbenzene (28).

By testing various activators (Table 3.6), we confirmed that B(C6F5)3 (Table 3.6, entries

7) was the required activator for hydrosilylation of 13. A quick survey of most commonly

193 used activators [NaBARF, Ph3B, Et3B, NaBPh4, NaEt3BH and B(C6F5)3] confirmed that

B(C6F5)3 is the best reagent for hydrosilylation of 13. Sodium triethylborohydride (Table

3.6, entries 1) and NaBPh4 (Table 3.6, entries 6) did not show any catalytic activity and the starting material 13 remains mostly unreacted for several hours at room temperature.

All other activators (Table 3.6, entries 3-6) showed moderate activity and gave the mixture of linear product 14 and branched product 15.

SiH2Ph

(dppp)CoX 5 mol% SiH2Ph PhSiH Activator 15 mol% 3 (Eq. 3.9) 1.1 eq RT, DCM, 5 h 13 14 15 1,2 linear 1,2 branched

Table 3.6 Effect of Activator for Hydrosilylation of 13a

Entry CoX Activator 14b 15b 13b Silane Formed (%)c

1 CoCl NaEt3BH - - 94% -

2 CoBr NaEt3BH - - 86% -

3 CoBr NaBARF 28% 5% 36% 4% 20

4 CoBr Ph3B 19% 20% 48% 8% 20

5 CoBr Et3B 15% 15% 52% 6% 20

d 6 CoBr NaBPh4 98% 2% - -

7 CoBr B(C6F5)3 100% - - - (10 min)

194 a b See Eq 3.9 for reaction scheme. 5 mol% catalyst (dppp)Co-X. 15 mol% B(C6F5)3, rt, PhSiH3. Ratios of

c products determined by areas under the peaks in GC. Significant amounts of Ph2SiH2 also observed; Silane

d formed was detected by GC and GC-MS. reaction was completed after 2 h. 20 = Ph2SiH2, Rest percentage for mass balance is 1-ethyl-4-methylbenzene (28)

Having identified a successful ligand and activator to promote the selective hydrosilylation, attention was devoted to test various solvents for hydrosilylation of 13.

An examination of various common solvents (Table 3.7, entries 1-7) revealed CH2Cl2

(Table 3.7, entries 1) was identified as best solvent for the hydrosilylation reaction. Ether

(Table 3.7, entries 2) and THF (Table 3.7, entries 5) lead unsatisfactory result whereas hexane (Table 3.7, entries 3), ClCH2CH2Cl (Table 3.7, entries 4) and Toluene (Table 3.7, entries 6) lead to moderate yields. In a parallel run using these solvents, the best solvent for the reaction was identified as CH2Cl2.

SiH2Ph

(dppp)CoBr 5 mol% SiH2Ph PhSiH B(C6F5)3 15 mol% 3 (Eq. 3.10) 1.1 eq RT, Solvent, 5 h 13 14 15 1,2 linear 1,2 branched

195

Table 3.7 Effect of Solvents for Hydrosilylation of 13a

Entry Solvent 14b 15b 13b Silane Formed (%)c

1 DCM 100 - - - (10 min)

2 Ether 3% 1% 68% 27% 20

3 Hexane 43% 1% 38% 8% 20

4 DCE 56% - - 24% 20

5 THF 3% 1% 83% 3% 20

6 Toluene 41% 1% 36% 8% 20 a b See Eq 3.10 for reaction scheme. 5 mol% catalyst (dppp)Co-Br. 15 mol% B(C6F5)3, rt, PhSiH3. Ratios of

After extensive screening of the ligand, solvent, activator, the optimized procedure for the reaction is shown in equation 3.11 and the full scope of the reaction is illustrated by examining the other substrates with varying degrees of steric effects and sensitive functional groups (Figure 3.5).

SiH2Ph

(dppp)CoBr 5 mol% SiH2Ph PhSiH B(C6F5)3 15 mol% 3 (Eq. 3.11) 1.1 eq RT, DCM, 30 Min 13 14 15 1,2 linear 1,2 branched

196

All of the substrates (Figure 3.5) were scanned using optimized condition shown in Eq.

3.11. Under the optimized conditions [1 equivalent alkene, 1.1 equivalents of PhSiH3,

(dppp)CoBr (0.05 equivalents), B(C6F5)3 (0.15 equivalents), dcm (0.16 M)], the reaction of activated and unactivated alkenes 13, 33-34, 40, 44, 200 (Fig.3.5) proceeds at room temperature giving good yields and excellent selectivity of hydrosilylated product. GC,

GC-MS and spectroscopic techniques have established the structure of all the hydrosilylated products. In all cases, the hydrosilylation favors the linear selectivity (anti

Markovnikov’s product) in which the silicon is attached to the terminal carbon (Table

3.8). Neither dehydrogenated silylation nor disubstituted silane 20 (Ph2SiH2) was detected on GC and GC-MS.

Cl 13 33 34 40

200 44

Figure 3.5.: Alkenes Tested for Hydrosilylation

197

Table 3.8. Scope of Hydrosilylation Reaction of Alkenesa

Entry Substrate Product Yield (%)b

SiH2Ph

R R 1 R = CH3 13 R = CH3 14 97% 2 R = Cl 34 R = Cl 50 91%

SiH2Ph 3 33 55 98%

SiH2Ph

4 40 60 94%

SiH2Ph

5 200 209 98%

SiH2Ph

6 44 65 95% a b See Eq 3.11 for reaction scheme. 5 mol% catalyst (dppp)Co-Br. 15 mol% B(C6F5)3, rt, PhSiH3, isolated yield after purification.

These optimized cobalt catalyzed hydrosilylation reactions can be accomplished in neat substrate and large scale (0.5 g) reaction using little as 0.01 equiv. (substrate/catalyst =

100) of the catalyst. Examples of hydrosilylation reaction using primary silane (PhSiH3) for substrate 13 (Table 3.9, entries 1), 33 (Table 3.9, entries 4), 34 (Table 3.9, entries 2),

39 (Table 3.9, entries 4), 41 (Table 3.9, entries 5), 44 (Table 3.9, entries 6), and 47 (Table

3.9, entries 7) are shown in Table 3.9.

198

(dppp)CoBr 1 mol% SiH2Ph PhSiH B(C6F5)3 3 mol% SiH2Ph (Eq. 3.12) R 3 R R 1.1 eq RT, DCM, 1 h 1,2 linear 1,2 branched

Table 3.9. Scope of Hydrosilylation Reaction of Alkenes using 1mol% Catalysta

Entry Substrate Product Yield (%)b

SiH2Ph

R R

1 R = CH3 13 R = CH3 14 97% 2 R = Cl 34 R = Cl 50 91% 3 R = OAc 39 R = OAc 51 94%

SiH2Ph 4 33 55 98%

SiH2Ph

5 MeO 41 MeO 61 96%

SiH2Ph

6 44 65 93%

SiH2Ph C8H17 7 C8H17 47 64 89%

a b See Eq 3.12 for reaction scheme. 1 mol% catalyst (dppp)Co-Br. 3 mol% B(C6F5)3, rt, PhSiH3, isolated yield after purification.

199

SiH2Ph

Figure 3.6.: Gas Chromatogram for Hydrosilylated Product 14 (Using 1mol%

Catalyst)

The new protocol [Co(I)phosphine complex] developed for cobalt catalyzed hydrosilylation reaction of alkenes is also useful for hydrosilylation of alkene in the absence of any solvent. Several alkenes were tested for hydrosilylation under neat condition and gave linear adduct with good yield and excellent selectivity.

200

(dppp)CoBr 1 mol% SiH2Ph B(C F ) 3 mol% 6 5 3 SiH2Ph (Eq. 3.13) R PhSiH3 R R 1.1 eq RT, Neat, 1 h 1,2 linear 1,2 branched

Table 3.10. Scope of Hydrosilylation Reaction of Alkenes using Neat Substratea

Entry Substrate Product Yield (%)b

SiH2Ph 1

13 14 95%

SiH2Ph 2 33 55 96%

SiH2Ph 3 40 60 97%

SiH2Ph 4 44 65 95% a See Eq 3.13 for reaction scheme. 1 mol% catalyst (dppp)Co-Br. 3 mol% B(C6F5)3, neat, rt, PhSiH3, bisolated yield after purification.

We further explored the scope of hydrosilylation reaction of 1,1-disubstituted alkene under the optimized conditions [1 equivalent of alkene, 1.1 equivalent of silane,

(dppp)CoBr(0.01 equivalent), B(C6F5)3 (0.03 equivalents, DCM (0.16 M)]. The reaction of 1,1-disubstituted alkenes 206, 210-212 (Table 3.11, entries 1-4) proceeds at room temperature giving excellent yields of hydrosilylated product. In all cases, the

201 hydrosilylation favors anti Markovnikov’s selectivity in which the silicon is attached to the terminal carbon (Table 3.11).

206 210 211 212

Figure 3.7.: 1,1-Disubstituted Alkenes Tested for Hydrosilylation

R' (dppp)CoBr 1 mol% R'

B(C6F5)3 3 mol% SiH2Ph R PhSiH3 R (Eq. 3.14) 1.1 eq RT, DCM, 1 h 1,2 linear

Table 3.11. Scope of Hydrosilylation Reaction of 1,1-Disubstituted Alkenesa

Entry Substrate Product Yield (%)b

SiH2Ph

1 206 213 96%

SiH Ph 2 2 95% 210 214

SiH2Ph

3 211 215 98%

Ph Ph

SiH2Ph

4 212 216 96% 202 a See Eq 3.14 for reaction scheme. 1 mol% catalyst (dppp)Co-Br, 3 mol% B(C6F5)3, dcm, rt, PhSiH3, bisolated yield after purification.

Among the silane tested, phenylsilane (PhSiH3), diphenylsilane (Ph2SiH2) and phenylmethylsilane (PhSiMeH2) gave good yields and excellent selectivity of hydrosilylated products. So we further explored the scope of hydrosilylation reaction of alkene (Table 3.12). Under the optimized conditions [1 equivalent of alkene, 1.1 equivalents of silane, dppp (Co) Cl (0.01 equivalents), B(C6F5)3 (0.03 equivalents), DCM

(0.16 M)] substrates 200, 210-211, gave exclusively anti Markovnikov’s product 217,

218-220.

R' (dppp)CoBr 1 mol% R'

B(C6F5)3 3 mol% SiRnH3-n R RnSiH4-n R (Eq. 3.15) 1.1 eq RT, DCM, 1 h 1,2 linear

203

Table 3.12. Scope of Hydrosilylation Reaction of 1,1-Disubstituted Alkenes Using

Secondary Silanes

Entry Substrate Product Yield (%)b

SiHPh2

1 200 217 92%

SiHPh 2 2 96%

210 218

SiHPhMe

3 211 219 94%

SiHPhMe 4 200 220 92%

a See Eq 3.15 for reaction scheme. 1 mol% catalyst (dppp)Co-Br, 3 mol% B(C6F5)3, dcm, rt, silane, bisolated yield after purification.

Triethylsilane did not display any hydrosilylation activity using iPrPDI (Co) complex 1b but under the optimized condition using [1 equivalent of alkene, 1.1 equivalents of silane, dppp (Co)-Br (0.01 equivalents), B(C6F5)3 (0.03 equivalents), DCM (0.16 M)] substrates

200 gave exclusively anti Markovnikov’s product 221.

204

(dppp)CoBr 1 mol% SiEt3 B(C F ) 3 mol% Et3SiH 6 5 3 (Eq. 3.16) 1.1 eq RT, DCM, 1 h 200 221 97% yield

Furthermore, under the optimized conditions, the reaction of 1,3-dienes and 1,4-skipped diene 95, 106, 147 (Figure 3.8) proceeds at room temperature giving good yields of hydrosilylated product.. In all cases, the hydrosilylation favors the linear selectivity (anti

Markovnikov’s product) in which the silicon is attached to the terminal carbon (Table

3.13).

C H 8 17 C8H17 98 109 150

Figure 3.8: 1,3-Diene and 1,4-Skipped Diene Tested for Hydrosilylation

Table 3.13. Scope of Hydrosilylation Reaction of 1,3- and 1,4-Dienesa

Entry Substrate Product Yield (%)b SiHPh C8H17 2 1 C8H17 94% 98 99 SiHPh 2 96% 2 109 131 SiH2Ph

3 150 154 94% C H C8H17 8 17 a See Eq 3.14 for reaction scheme. 1 mol% catalyst (dppp)Co-Br, 3 mol% B(C6F5)3, dcm, rt, PhSiH3, bisolated yield after purification.

205

Several alkenes reactions were scaled up without loss of yield and selectivity. These optimized cobalt catalyzed hydrosilylation reactions can be accomplished in neat substrate and large scale (0.5 g) reaction using little as 0.001 equiv. (substrate/catalyst =

1000) of the catalyst. Examples of hydrosilylation reaction using primary silane PhSiH3 for substrate 13 and 200 to give respective hydrosilylated product 14 and 209 (Eq. 3.17,

3.18, 3.19and 3.20) with good yield and excellent regioselectivity.

(dppp)CoBr 1 mol% SiH2Ph PhSiH B(C6F5)3 3 mol% 3 (Eq. 3.17) 1.1 eq RT DCM, 3 h 13 14 500 mg 1,2 linear 92% yield

(dppp)CoBr 1 mol% SiH2Ph PhSiH B(C6F5)3 3 mol% 3 (Eq. 3.18) 1.1 eq RT Neat, 2 h 200 209 1,2 linear 94% yield 300 mg

(dppp)CoBr 0.1 mol% SiH2Ph PhSiH B(C6F5)3 0.3 mol% 3 (Eq. 3.19) 1.1 eq RT DCM, 2 h 13 14 1,2 linear 91% yield

206

(dppp)CoBr 0.1 mol% SiH2Ph PhSiH B(C6F5)3 0.3 mol% 3 (Eq. 3.20) 1.1 eq RT Neat, 1.30 h 200 209 1,2 linear 93 yield

3.4 Hydrosilylation of Prochiral 1,1-disubstituted Alkene

Because the 1,2-linear product was the major product observed with every substrate when dppp was employed as the ligand, the next challenge was to install a substituent at C2 carbon of the 1,1-disubstituted alkene to form a chiral center upon hydrosilylation. 1,1-disubstituted alkene 200 was subjected to the optimized cobalt- catalyzed hydrosilylation conditions to examine the enantioselectivity of the reaction.

When substrate 200 was subjected for hydrosilylation using optimized conditions with dppp as a ligand, the expected regioselectivity was observed with the 1,2-addition leading to the linear silane 209 as a final product (Eq. 3.21) and as expected the racemic product was observed by chiral stationary phase gas chromatography (CSP-GC).

(dppp)CoBr 1 mol% SiH2Ph B(C F ) 3 mol% PhSiH3 6 5 3 (Eq. 3.21) 1.1 eq RT, DCM, 1 h 200 209 97% yield

Next we screened substrate 200 for the hydrosilylation reaction to examine the enantioselectivity of the reaction using (Ligand) Co-Et complex with L9-L11 as a 207 ligands. The expected regioselectivity was observed with the 1,2-addition leading to the linear silane 209 as a final product (Eq. 3.22). However, a completely racemic product was observed by chiral stationary phase gas chromatography (CSP-GC).

O PPh2 PPh2 PPh2

PPh2 PPh2 O PPh2

(S)-BINAP (R,R)-DIOP (S,S)-BDPP L9 L10 L11

Figure 3.9: Chiral Ligand Used for Hydrosilylation of 1,1-Disubstituted Alkene

(Ligand)CoEt 5 mol% SiH2Ph B(C F ) 15 mol% PhSiH3 6 5 3 (Eq. 3.22) 1.1 eq RT, DCM, 2 h 200 209 >95% yield

Table 3.13. Scope of Hydrosilylation Reaction of 200 Using Chiral Ligandsa

Entry Ligand Yieldb ee (%)c

1 L11 95% 2%

2 L9 97% 2%

96% 2% 3 L10 a See Eq 3.22 and Supporting Information for details. 5 mol% catalyst (ligand)Co-Et, 15 mol% B(C6F5)3,

b c dcm, rt, PhSiH3, isolated yield after purification, %ee was determined using csp-gc

208

An examination of secondary silane (Ph2SiH2 20) was performed (Eq. 3.23) to determine if the enantioselectivity could be optimized (Table 3.14). When alkene 209 is submitted to hydrosilylation using L9-L11 chiral ligand, 1,2-linear product 217 was produced respectively (Eq. 3.23). These chiral products (Table 3.14, entries 2-4) were only found to have the low enantioselectivities of 15% ee, 21% ee and 23% ee. CSP-HPLC was used to determine the enantioselectivity and 1H-NMR analysis identified the product 217 as a

1,2-addition linear product.

(Ligand)CoEt 1 mol% SiHPh2 B(C F ) 3 mol% Ph2SiH2 6 5 3 (Eq. 3.23) 1.1 eq RT, DCM, 3 h 200 217 >93% yield

Table 3.14. Scope of Hydrosilylation Reaction (using Ph2SiH2) of 200 using Chiral

Ligandsa

Entry Ligand Yieldb ee (%)c

1 L3 97% - 2 L9 95% 15%

3 L10 96% 21% 4 L11 93% 23% a See Eq 3.23 for reaction scheme. 1 mol% catalyst (ligand)Co-Et, 3 mol% B(C6F5)3, dcm, rt, PhSiH3, bisolated yield after purification, c%ee was determined using csp-hplc

209

Figure 3.10: HPLC Chromatogratogram for Hydrosilylation of 200

Furthermore, an examination of various chiral ligands L12-L13 was performed to determine if the enantioselctivity could be further optimized. When alkene 200 is submitted to hydrosilylation using L12-L13 chiral ligand using optimized condition (Eq.

3.24), unfortunately, no hydrosilylated product was observed and starting material 200 remains mostly unreacted at room temperature.

O O

PPh2 N PPh2 N Ph L12 L13

Figure 3.11: Chiral Ligand (PHOX) Used for Hydrosilylation 210

(Ligand)CoBr 5 mol% Ph SiH B(C6F5)3 15 mol% 2 2 No Reaction (Eq. 3.24) 1.1 eq RT, DCM, 3 h 200

Proposed Mechanism for Hydrosilylation Reaction

On the basis of various reported literature precedents the proposed mechanism for hydrosilylation is shown in figure 3.12. We propose a Co(I/III) catalytic cycle to rationalize the selectivity for 1,2-linear hydrosilylated product. (Ligand) Co-X precatalyst was activated by Lewis acid B(C6F5)3 to provide an cationic cobalt(I) complex 222. cobalt(I) complex 222 that can undergo oxidative addition of phenylsilane to form coordinatively unsaturated cobalt(III) intermediate 223. Because of 223, which is coordinatively unsaturated, alkene is coordinated to the 223, which forms the linear alkyl complex 224 by 1,2-migratory insertion. Finally linear alkyl complex 224 undergoes reductive elimination to give the desired 1,2-hydrosilylation products and regeneration of active catalyst 222.

211

LnCo(I)-X (X= Br, Cl, Et)

B(C6F5)3 XB(C6F5)3

SiH2Ph R PhSiH3 225 LnCo(I) 222 Oxidative Addition Reductive Elimination Cationic Cobalt

H SiH2Ph Co(III)Ln SiH Ph Ln(III)Co 223 2

224 H R H Ln(III)Co Migratory Insertion SiH2Ph R

R Coordination

Figure 3.12: Proposed Catalytic Cycle for Hydrosilylation

Conclusion: In conclusion, we have discovered a new efficient novel cobalt catalyst for selective hydrosilylation of monosubstituted alkenes, 1,1-disubstituted alkenes, 1,3- conjugated diene and 1,4-skipped dienes. Under the optimized conditions, we are able to do hydrosilylation of variety of substartates. Substrates carrying ether, chloride, acetate, are well tolerated. All the terminal alkenes are converted to linear hydrosilylated product.

This protocol is also useful for the neat substrate and reaction using little as 0.001 equiv.

(substrate/catalyst = 1000) of the catalyst, which gave the quantitative yield for various

212 substrates. Primary, secondary and tertiary silanes were used for the hydrosilylation of terminal and 1,1-disubstituted alkenes. This methodology was extended to operate hydrosilylation reaction under neat condition. A series of asymmetric hydrosilylation reaction was performed using different chiral ligands, which exhibit the moderate enantioselectivity.

Experimental Procedures

General methods All air- and moisture sensitive manipulations were carried out using standard vacuum line and Schlenk techniques, or in a dry box containing a purified argon atmosphere. Solvents were distilled from the appropriate drying agents under nitrogen.

All glassware was cleaned using base (KOH, iPrOH) then acid (HClaq) baths. Analytical

TLC was performed on E. Merck pre-coated (0.25 mm) silica gel 60 F254 plates. Flash column chromatography was carried out on silica gel 40 (Sorbtech Chemicals). Cobalt

(II) chloride and Phosphine ligands were purchased from Strem Chemicals Inc. All dienes and ligands used were synthesized within the laboratory. All silanes were purchased from Sigma Aldrich, Oakwood, Alfa Aesar and Apollo Scientific. Gas chromatographic analysis was done on an Agilent 7820A using hydrogen as the carrier gas, equipped with a methyl silicone column (30 m X 0.32mm, 0.25 µm film thickness).

GC-MS was carried out on a HP-5MS 5% methyl phenylsiloxane (30 m x 0.25 mm, 0.25

µm film thickness) using He as carrier gas. Enantiomeric excess of chiral compounds were measured by chiral stationary phase gas chromatographic analysis, which were performed on Agilent 7820A using hydrogen as the carrier gas, equipped with a Cyclosil-

213

B (30 m X 0.25 mm, 0.25 µm film thickness) and Cyclodex-B (60 m X 0.25 mm, 0.25

µm film thickness), capillary GC columns purchased from Agilent. Each GC was equipped with FID detectors and integrators on a computer. Enantiomeric excess of chiral compounds obtained by using Ph2SiH2 were measured by chiral stationary phase high performance liquid chromatographic analysis (HPLC). All activating reagents were purchased from Sigma Aldrich. 1H, 13C NMR spectra were recorded on Bruker 400 and

600MHz, spectrometers. All spectra were obtained at ambient temperature. The chemical shifts (δ) were recorded in parts per million (ppm) and the coupling constants (J) in Hertz

(Hz). 1H and 13C NMR multiplicity and coupling constants are reported where applicable.

1H and 13C spectra were referenced to the residual deuterated solvent peak (CHCl3

7.26ppm, 77.32ppm).

The bis-phosphine Cobalt (II)-complexes were prepared as described earlier.[11]

Anhydrous CoCl2 (50.5 mg, 0.390 mmol) was added to a previously flame-dried 50-mL round two-necked bottom flask fitted with a flow control gas inlet and magnetic stir-bar loaded in a glove box under nitrogen. The nitrogen atmosphere was removed and the flask purged with dry argon. Freshly distilled, degassed THF (5 mL) was added, and upon stirring at room temperature for 15 min, a clear deep blue solution formed. A solution of diphenylphosphinopropane (DPPP, 181mg, 0.410 mmol) in freshly distilled, degassed ether (5 mL) was added drop wise to yield a blue turbid solution. After stirring at room temperature for 15 h, 20 mL freshly distilled, degassed hexane was added in one portion to yield a blue precipitate. The resulting precipitate was filtered on a sintered

214 glass fret under argon atmosphere, and washed with diethyl ether and hexane (1:1) mixture (3 X 5 mL) to remove any unreacted DPPP, resulting in quantitative yield of a light blue solid, which was used with no further purification.

Synthesis of Bis-Phosphine Cobalt (I)-Complex

In a 100 mL flame dried round bottom flask equipped with magnetic stirrer, dppp(Co)Br2

(1.3 g, 2 mmol) and activated Zn (0.65 g, 10 mmol) were added inside the glove box.

Approximately, 30 mL of anhydrous THF was added to the flask and stirred at room temperature for an overnight. After overnight stirring, all the volatile components were removed under vacuum. The resulting crude product was dissolved in anhydrous toluene and filtrated. The filtrate solution was dried under vacuum for an overnight and green color solid product was obtained with 87% yield. All the other bis-phosphine cobalt(I)- complex was synthesized using similar method described above.

General Cobalt-Catalyzed Hydrosilylation Procedure using Bis-phosphine Cobalt

(II) Complex (Eq 3.1)

An alkene (0.43 mmol) was added to a solution of cobalt (II) chloride phosphine complex (11.5 mg, 0.02 mmol, 0.05 equivalents) in anhydrous dichloromethane (0.16 M) at room temperature under an atmosphere of argon. Activator (0.04 mmol, 0.1 equivalents) was added, followed by a silane (0.46 mmol, 1.1 equivalents) and the reaction mixture was stirred at room temperature for 5 h-9 h. After completion the reaction, it was filtered through the pad of silica by adding hexane and was concentrated

215 under vacuum. Isolated yields were determined after purification by silica chromatography using hexane as eluent.

General Cobalt-Catalyzed Hydrosilylation Procedure Using Cobalt (II) Acetate and

Phosphine Ligand (Eq 3.4)

An alkene (0.43 mmol) was added to a solution of cobalt (II) acetate (10.5 mg, 0.04 mmol, 0.1 equivalents) and phosphine ligand (17.4 mg, 0.04 mmol, 0.1 equivalents) in anhydrous dichloroethane (0.16 M) at room temperature under an atmosphere of argon.

The reaction mixture was transferred to the preheated oil bath (80 oC) followed by a addition of silane (0.46 mmol, 1.1 equivalents) and the reaction mixture was stirred at 80 oC temperature for 30 h. After completion the reaction, it was filtered through the pad of silica by adding hexane and was concentrated under vacuum. Isolated yields were determined after purification by silica chromatography using hexane as eluent.

General Cobalt-Catalyzed Hydrosilylation Procedure Using Bis-Phosphine Cobalt

(I) Bromide Complex and B(C6F5)3 (Eq 3.7)

An alkene (0.43 mmol) was added to a solution of bis-phosphine cobalt (I) bromide complex (32 mg, 0.02 mmol, 0.05 equivalents) in anhydrous dichloromethane (0.16 M) at room temperature under an atmosphere of argon. B(C6F5)3 (21.6 mg, 0.04 mmol, 0.1 equivalents) was added, followed by a silane (0.46 mmol, 1.1 equivalents) and the reaction mixture was stirred at room temperature for 10 min. After completion the 216 reaction, it was filtered through the pad of silica by adding hexane and was concentrated under vacuum. Isolated yields were determined after purification by silica chromatography using hexane as eluent.

General Cobalt-Catalyzed Hydrosilylation Procedure Using Bis-Phosphine Cobalt

(I)- Et Complex and B(C6F5)3 (Eq 3.22)

An alkene (0.43 mmol) was added to a solution of bis-phosphine cobalt (I)-Et complex

(10.6 mg, 0.02 mmol, 0.05 equivalents) in anhydrous dichloromethane (0.16 M) at room temperature under an atmosphere of argon. B(C6F5)3 (21.6 mg, 0.04 mmol, 0.1 equivalents) was added, followed by a silane (0.46 mmol, 1.1 equivalents) and the reaction mixture was stirred at room temperature for 2 h. After completion the reaction, it was filtered through the pad of silica by adding hexane and was concentrated under vacuum. Isolated yields were determined after purification by silica chromatography using hexane as eluent.

Procedure for Hydrosilylation Reaction Under Low Catalyst Loading (1 mol%

Catalyst) (Eq 3.17)

217 reaction mixture was stirred at room temperature for 10 min. After completion the reaction, it was filtered through the pad of silica by adding hexane and was concentrated under vacuum. Isolated yields were determined after purification by silica chromatography using hexane as eluent.

Procedure for Hydrosilylation Reaction Using Neat Substrate (5 mol% catalyst) (Eq

3.13)

An alkene (1.7 mmol) was added to a mixture of bis-phosphine cobalt (I) bromide complex (128 mg, 0.08 mmol, 0.05 equivalents) and B(C6F5)3 (130 mg, 0.26 mmol, 0.15 equivalents) at room temperature under an atmosphere of argon, followed by a addition of silane (1.87 mmol, 1.1 equivalents) and the reaction mixture was stirred at room temperature for 2 h. After completion the reaction, it was filtered through the pad of silica by adding hexane and was concentrated under vacuum. Isolated yields were determined after purification by silica chromatography using hexane as eluent.

Procedure for Hydrosilylation Reaction Using Neat Substrate (1 mol% Catalyst)

(Eq 3.18)

An alkene (1.7 mmol) was added to a mixture of bis-phosphine cobalt (I) bromide complex (25 mg, 0.02 mmol, 0.01 equivalents) and B(C6F5)3 (26 mg, 0.05 mmol, 0.03 equivalents) at room temperature under an atmosphere of argon, followed by a addition of silane (1.87 mmol, 1.1 equivalents) and the reaction mixture was stirred at room temperature for 3 h. After completion the reaction, it was filtered through the pad of silica

218 by adding hexane and was concentrated under vacuum. Isolated yields were determined after purification by silica chromatography using hexane as eluent.

Procedure for Hydrosilylation Reaction Using Large Scale Reaction (5 mol% catalyst)

An alkene (4.23 mmol) was added to a solution of bis-phosphine cobalt (I) bromide complex (320 mg, 0.21 mmol, 0.05 equivalents) in anhydrous dichloromethane (0.16 M) at room temperature under an atmosphere of argon. B(C6F5)3 (324 mg, 5.13 mmol, 0.15 equivalents) was added, followed by a silane (1.87 mmol, 1.1 equivalents) and the reaction mixture was stirred at room temperature for 3 h. After completion the reaction, it was filtered through the pad of silica by adding hexane and was concentrated under vacuum. Isolated yields were determined after purification by silica chromatography using hexane as eluent

Procedure for Hydrosilylation Reaction Using Secondary Silane (Ph2SiH2) (Eq 3.15)

An alkene (1.69 mmol) was added to a solution of bis-phosphine cobalt (I) bromide complex (26 mg, 0.016 mmol, 0.01 equivalents) in anhydrous dichloromethane (0.16 M) at room temperature under an atmosphere of argon. B(C6F5)3 (25.9 mg, 0.05 mmol, 0.03 equivalents) was added, followed by a silane (1.35 mmol, 0.8 equivalents) and the reaction mixture was stirred at room temperature for 2 h. After completion the reaction, it was filtered through the pad of silica by adding hexane and was concentrated under

219

vacuum. Isolated yields were determined after purification by silica chromatography using hexane as eluent

Procedure for hydrosilylation reaction using tertiary silane (Et3SiH) (Eq 3.16)

An alkene (0.43 mmol) was added to a solution of bis-phosphine cobalt (I) bromide complex (6.5 mg, 0.004 mmol, 0.01 equivalents) in anhydrous dichloromethane (0.16 M) at room temperature under an atmosphere of argon. B(C6F5)3 (6.6 mg, 0.013 mmol, 0.1 equivalents) was added, followed by a silane (0.46 mmol, 1.1 equivalents) and the reaction mixture was stirred at room temperature for 1 h. After completion the reaction, it was filtered through the pad of silica by adding hexane and was concentrated under vacuum. Isolated yields were determined after purification by silica chromatography using hexane as eluent

Analytical Data Hydrosilylated Products

(4-methylphenyl)(Phenyl) silane 14

SiH2Ph

1 H NMR (600 MHz, CDCl3) δ 7.60-7.59 (m, 2H), 7.42-7.37 (m,

3 3H), 7.11 (s, 4H), 4.35 (t, JH,H = 3.6 Hz, 2H), 2.77-2.74 (m, 2H), 2.34 (s, 3H), 1.33-1.29

(m, 2H).

13 C NMR (125 MHz, CDCl3) δ 141.1, 135.5, 135.4, 132.4, 129.8, 129.2, 128.2, 127.9,

127.9, 30.9, 21.2, 12.4.

220

GC (methyl silicone column, 80 0 C/ 5 min, rate = 20 oC, 250 oC = 40 min) RT for product = 11.23 min.

GC (methyl silicone column, 200 0 C/ Isotherm) RT for product = 2.14 min.

GC-MS m/z ([M+) 226.12; exact mass calculated for C15H18Si 226.10.

(4-chlorophenethyl)(phenyl) silane 50

SiH2Ph

1 Cl H NMR (400 MHz, CDCl3) δ 7.41-7.39 (m, 2H), 7.27-7.19 (m,

3 3H), 7.09-7.06 (m, 2H), 6.96-6.93 (m, 2H), 4.17 (t, JH,H = 3.6 Hz, 2H), 2.60-2.55 (m,

2H), 1.15-1.09 (m, 2H).

13 C NMR (100 MHz, CDCl3) δ 142.5, 135.4, 132.1, 131.7, 129.9, 129.4, 128.6, 128.3,

30.7, 12.3.

GC (methyl silicone column, 180 0 C/ Isotherm) RT for product = 4.51 min.

GC-MS m/z ([M+) 246.10; exact mass calculated for C14H15ClSi 246.06.

4-(2-(phenylsilyl)ethyl)phenyl acetate 51

SiH2Ph

1 AcO H NMR (400 MHz, CDCl3) δ 7.58-7.56 (m, 2H), 7.43-7.35 (m,

3 3H), 7.20-7.18 (m, 2H), 7.00-6.97 (m, 2H), 4.33 (t, JH,H = 3.6 Hz, 2H), 2.78-2.74 (m,

2H), 2.29 (s, 3H), 1.33-1.27 (m, 2H).

221

13 C NMR (100 MHz, CDCl3) δ 169.7, 148.8, 141.6, 135.3, 132.0, 129.7, 128.8, 128.1,

121.4, 30.6, 21.2, 12.1.

GC (methyl silicone column, 180 0 C/ Isotherm) RT for product = 8.35 min.

GC-MS m/z ([M+) 270.10; exact mass calculated for C16H18O2Si 270.11.

Phenyl (4-phenylbutyl) silane 55

SiH2Ph

1 H NMR (400 MHz, CDCl3) δ 7.78-7.76 (m, 2H), 7.58-7.52 (m,

3H), 7.49-7.45 (m, 2H), 7.39-7.35 (m, 3H), 4.54 (t, 3J H,H = 3.7 Hz, 2H), 2.81 (t, 3J H,H

= 7.8 Hz, 2H), 1.94-1.87 (m, 2H), 1.77- 1.69 (m, 2H), 1.21-1.16 (m, 2H).

13 C NMR (100 MHz, CDCl3) δ 142.6, 135.3, 132.7, 129.6, 128.5, 128.4, 128.1, 125.7,

35.7, 34.7, 24.9, 10.1.

GC (methyl silicone column, 180 0 C/ Isotherm) RT for product = 6.85 min.

GC-MS (methyl silicone): m/z ([M+) 240.13; exact mass calculated for C16H20Si 240.10.

(2-naphthalen-2-yl)ethyl)(phenyl)silane 60

SiH2Ph

1 H NMR (400 MHz, CDCl3) δ 7.84-7.78 (m, 2H), 7.64-7.61 (m,

3 2H), 7.50-7.35 (m, 7H), 4.39 (t, JH,H = 3.6 Hz, 2H), 2.99-2.95 (m, 2H), 1.46-1.40 (m,

2H).

13 C NMR (100 MHz, CDCl3) δ 141.5, 135.4, 133.7, 132.2, 132.1, 129.8, 128.1, 128.0,

127.7, 127.6, 127.0, 126.0, 125.8, 125.2, 31.4,12.1.

GC (methyl silicone column, 200 0 C/ Isotherm) RT for product = 6.56 min. 222

GC-MS m/z ([M+) 262.10; exact mass calculated for C18H18Si 262.12

(2-(6-methoxynaphthalen-2-yl)ethyl)(phenyl)silane 61

SiH2Ph

O 1 3 H NMR (400 MHz, CDCl3) δ 7.68 (d, JH,H = 8.4 Hz, 2H),

3 7.62-7.56 (m, 3H), 7.43-7.36 (m, 3H), 7.33-7.31 (m, 1H), 7.16-7.13 (m, 2H), 4.38 (t, JH,H

= 3.6 Hz, 2H), 3.92 (s, 3H), 2.95-2.91 (m, 2H), 1.44-1.38 (m, 2H).

13 C NMR (125 MHz, CDCl3) δ 157.5, 139.5, 135.6, 133.3, 132.5, 129.9, 129.4, 129.2,

128.4, 127.7, 127.1, 125.9, 118.9, 106.0, 55.6, 31.4, 12.4.

GC (methyl silicone column, 210 0 C/ Isotherm) RT for product = 12.72 min.

GC-MS m/z ([M+) 292.10; exact mass calculated for C19H20OSi 292.13.

Decyl(phenyl) silane 64

SiH2Ph C H 1 8 17 H NMR (400 MHz, CDCl3) δ 7.58-7.56 (m, 2H), 7.39-7.34 (m, 3H),

4.29 (t, 3J H, H= 3.7 Hz, 2H), 1.50-1.42 (m, 2H), 1.37-1.26 (m, 14H), 0.97- 0.92 (m, 2H),

0.89 (t, 3JH, H, J = 6.8 Hz, 3H).

13 C NMR (100 MHz, CDCl3) δ 135.6, 133.2, 129.8, 128.3, 33.2, 32.3, 29.9, 29.9, 29.7,

29.6, 25.4, 23.0, 14.5, 10.4.

GC (methyl silicone column, 155 0 C/Isotherm) RT for product = 7.59 min.

GC-MS m/z ([M+) 248.10; exact mass calculated for C16H28Si 248.20.

223

(2-cyclohexylethyl)(phenyl) silane 65

SiH2Ph

1 H NMR (600 MHz, CDCl3) δ 7.60-7.58 (m, 2H), 7.42-7.36 (m, 3H),

4.31 (t. 3J H, H= 3.6 Hz, 2H), 1.77-1.70 (m, 4H), 1.68-1.65 (m, 1H), 1.38-1.34 (m, 2H),

1.27-1.12 (m, 4H), 0.98-0.94 (m, 2H), 0.90-0.84 (m, 2H).

13 C NMR (100 MHz, CDCl3) δ 135.4, 133.0, 129.6, 128.1, 40.4, 33.1, 32.8, 26.9, 26.5,

7.3.

GC (methyl silicone column, 160 0 C/Isotherm) RT for product = 5.57 min.

GC-MS m/z ([M+) 218.10; exact mass calculated for C14H22Si 218.15.

(E)-dodec-3-en-1-yl) (Phenyl) silane 99

SiH2Ph C H 1 8 17 H NMR (400 MHz, CDCl3) δ 7.59-7.57 (m, 2H), 7.40-7.34 (m,

3 3H), 5.49-5.38(m, 2H), 4.31(t, JH,H = 3.7 Hz, 2H), 2.19-2.14 (m, 2H), 2.00-1.95 (m, 2H),

3 1.36-1.25 (m, 12H), 1.06-1.01 (m, 2H), 0.90 (t, JH,H = 6.9 Hz, 3H).

13 C NMR (100 MHz, CDCl3) δ 135.7, 133.1, 131.9, 130.6, 130.0, 128.4, 32.9, 32.4, 30.0,

30.0, 29.8, 29.7, 28.4, 23.1, 14.5, 10.6.

GC (methylsilicone column, 200 0 C/ Isotherm) RT for product = 3.72 min.

GC-MS m/z ([M+) 274.10; exact mass calculated for C18H30Si 274.21.

224

(2-(4-(tert-butyl) cyclohex-1-en-1-yl) ethyl (Phenyl) silane 131

SiH2Ph

1 3 H (400 MHz, CDCl3) δ 7.57-7.55 (m, 2H), 7.39-7.33 (m, 3H), 5.42 (q, JH,H =

3 3 1.7 Hz, 1H), 4.28 (t, JH,H = 3.6 Hz, 2H), 2.09 (t, JH,H = 7.9 Hz, 2H), 1.97-1.95 (m, 2H),

1.80-1.73 (m, 2H), 1.26 (m, 1H), 1.19-1.11 (m, 2H), 1.19-1.11 (m, 2H), 1.09-1.03 (m,

2H), 0.85 (s, 9H).

13 C NMR (100 MHz, CDCl3) δ 138.2, 134.8, 132.2, 129.0, 127.4, 120.2, 43.7, 32.1, 31.7,

29.0, 26.7, 26.2, 23.7, 7.8.

GC (methylsilicone column, 200 0 C/ Isotherm) RT for product = 3.93 min.

HRMS (ESI-MS): m/z 295.1852 ([M + Na]); exact mass calculated for C18H28SiNa

295.1838.

(Z)-phenyl(3-(prop-1-en-1-yl)undecyl)silane 151

SiH2Ph

C H 1 8 17 H NMR (400 MHz, CDCl3) δ 7.56-7.55 (m, 2H), 7.40-7.34 (m, 3H),

3 5.56-5.48 (m, 1H), 5.08-5.01 (m, 1H), 4.28 (t, JH, H = 3.6 Hz, 2H), 2.35-2.29 (m, 1H),

3 3 1.60 (dd, JH, H = 6.7 Hz, 1.7 Hz, 3H), 1.31-1.26 (m, 18H), 0.89 (t, JH, H = 6.8 Hz, 3H).

13 C NMR (100 MHz, CDCl3) δ 135.8, 135.4, 133.0, 129.7, 128.2, 124.3, 39.7, 35.8, 32.1,

31.3, 30.1, 29.9, 29.6, 27.5, 22.9, 14.3, 13.6, 7.8.

GC (methylsilicone column, 230 0 C/Isotherm) RT for product = 2.61 min. 225

GC-MS m/z ([M+) 302.10; exact mass calculated for C20H34 Si 302.24.

Phenyl(2-phenylbutyl)silane 209

SiH2Ph

1 H NMR (400 MHz, CDCl3) δ 7.51-7.48 (m, 2H), 7.40-7.38 (m, 3H),

7.33-7.28 (m, 2H), 7.23-7.17 (m, 3H), 4.21-4.14 (m, 2H), 2.71-2.64 (m, 1H), 1.82-1.74

3 (m, 1H), 1.72-1.64 (m, 1H), 1.48-1.40 (m, 1H), 1.35-1.30 (m, 1H), 0.80 (t, JH,H = 7.4 Hz,

3H).

13 C NMR (100 MHz, CDCl3) δ 146.0, 134.9, 132.2, 129.1, 127.9, 127.6, 127.1, 125.7,

43.9, 32.0, 18.1, 11.8.

GC (methyl silicone column, 180 0 C/ Isotherm) RT for product = 3.30 min.

GC (cyclodex-B, 60 °C): Rt from dppp: 127.953 min and 129.115 min; from (S,S-BDPP):

127.997 min and 129. 146; (-) DIOP: 127.998 min and 129.155; BINAP: 128.09 min and

129.214.

GC-MS m/z ([M+) 240.10; exact mass calculated for C16H20Si 240.13.

(2-cyclohexylbutyl)(phenyl)silane 213

SiH2Ph

1 H NMR (400 MHz, CDCl3) δ 7.60-7.58 (m, 2H), 7.42-7.36 (m, 3H),

4.31 (t. 3J H, H= 3.6 Hz, 2H), 1.77-1.70 (m, 4H), 1.68-1.65 (m, 1H), 1.38-1.34 (m, 2H),

226

1.27-1.12 (m, 4H), 0.98- 0.94 (m, 2H), 0.90- 0.84 (m, 2H), 0.83-0.82 (m, 1H), 0.80 (t,

3 JH,H = 7.4 Hz, 3H).

13 C NMR (100 MHz, CDCl3) δ 135.4, 133.0, 129.6, 128.1, 42.4, 39.4, 32.8, 29.0, 26.1,

26.0, 11.9, 5.5.

GC (methyl silicone column, 160 0 C/Isotherm) RT for product = 5.57 min.

GC-MS m/z ([M+) 218.10; exact mass calculated for C14H22Si 218.15.

Phenyl(2-(p-tolyl)butyl)silane 214

SiH2Ph

1 H NMR (400 MHz, CDCl3) δ 7.46-7.44 (m, 2H), 7.36-7.30 (m, 3H),

7.08-7.01 (m, 4H), 4.15-4.08 (m, 2H), 2.63-2.56 (m, 1H), 2.31 (s, 3H), 1.75-1.66 (m,

3 1H), 1.65-1.57 (m, 1H), 1.41-1.34 (m, 1H), 1.29-1.21 (m, 1H), 0.75 (t, JH,H = 7.4 Hz,

3H).

13 C NMR (100 MHz, CDCl3) δ 143.3, 135.5, 135.2,132.7, 129.4, 128.9, 127.9, 127.3,

43.9, 32.4, 21.0, 18.1, 12.2.

GC (methyl silicone column, 180 0 C/ Isotherm) RT for product = 3.35 min.

GC-MS m/z ([M+) 254.10; exact mass calculated for C17H22Si 254.15.

227

Phenyl(2-phenylpropyl)silane 215

SiH2Ph

1 H NMR (400 MHz, CDCl3) δ 7.56-7.50 (m, 2H), 7.46-7.29 (m, 5H),

3 7.25-7.19 (m, 3H), 4.29-4.20 (m, 2H), 2.97 (m, 1H), 1.42-1.31 (m, 2H), 0.25 (d, JH,H =

7.6 Hz, 3H).

13 C NMR (100 MHz, CDCl3) δ 148.5, 135.1, 132.3, 129.4, 128.3, 127.8, 126.5, 125.9,

36.6, 24.8, 20.2.

GC (methyl silicone column, 200 0 C/ Isotherm) RT for products = 3.21 min.

GC-MS m/z ([M+) 226.10; exact mass calculated for C16H20Si 226.12.

(2-cyclohexyl-2-phenylethyl)diphenylsilane 216

SiH2Ph

1 H NMR (400 MHz, CDCl3) δ 7.41-7.38 (m, 2H), 7.36-7.28 (m, 3H),

7.27-7.22 (m, 2H), 7.19-7.15 (m, 1H), 7.09-7.07 (m, 2H), 4.02-3.95 (m, 2H), 2.51-2.45

(m, 1H), 1.94-1.91 (m, 1H), 1.74-1.70 (m, 1H), 1.60-1.49 (m, 4H), 1.47-1.41 (m, 2H),

1.28-1.13 (m, 1H), 1.11-1.02 (m, 2H), 0.93-0.83 (m, 1H), 0.79-0.73 (m, 1H).

13 C NMR (100 MHz, CDCl3) δ 145.3, 135.6, 133.3, 129.8, 128.9, 128.4, 128.3, 126.5,

49.1, 45.7, 31.7, 31.2, 27.0, 15.1.

GC (methyl silicone column, 100 0 C/ 5 min, rate = 20 oC, 250 oC = 40 min) RT for product = 14.91 min.

GC-MS m/z ([M+) 294.10; exact mass calculated for C20H26Si 294.18.

228

Diphenyl(2-phenylbutyl)silane 217

SiHPh2

1 H NMR (400 MHz, CDCl3) δ 7.43-7.41 (m, 2H), 7.38-7.35 (m, 2H),

3 7.31-7.22 (m, 5H), 7.20-7.13 (m, 3H), 7.09-7.05 (m, 1H), 7.02-7.00 (m, 2H), 4.58 (t, JH,H

= 7.8 Hz, 1H), 2.59-2.52 (m, 1H), 1.71-1.61 (m, 1H), 1.59-1.55(m, 1H), 1.54-1.50(m,

3 1H), 1.45-1.38 (m, 1H), 0.64 (t, JH,H = 7.3 Hz, 3H).

13 C NMR (100 MHz, CDCl3) δ 146.6, 135.2, 135.0, 134.7, 134.6, 129.5, 129.4, 128.2,

127.9, 127.9, 127.6, 126.0, 43.6, 32.5, 20.7, 12.1.

GC (methyl silicone column, 180 0 C/ Isotherm) RT for product = 20.64 min

HPLC conditions: Chiralcel OJ-H, n-hexane/i-PrOH = 98/2, 0.5 mL/min, η = 220 nm, tr for enantiomers =10.5 (major), 14.1 (minor).

Diphenyl(2-(p-tolyl)butyl)silane 218

SiHPh2

1 H NMR (400 MHz, CDCl3) δ 7.27-7.18 (m, 3H), 7.16-7.10 (m, 2H),

7.04-7.02 (m, 1H), 6.85-6.82 (m, 4H), 6.74-6.69 (m, 4H), 5.15 (s, 1H), 2.26-2.20 (m,

1H), 2.17 (s, 3H), 1.32-1.08 (m, 4H), 0.46-0.41 (m, 3H).

13 C NMR (100 MHz, CDCl3) δ 144.3, 144.0, 137.3, 137.0, 136.9, 135.2, 135.1,134.8,

128.8, 128.8, 127.7, 127.6, 42.9, 33.2, 32.9, 21.1, 12.3.

GC (methyl silicone column, 180 0 C/ Isotherm) RT for product = 22.76 min

GC-MS m/z ([M+) 330.10; exact mass calculated for C23H26Si 330.18.

229

Methyl(phenyl)(2-phenylpropyl)silane 219

SiHMePh

1 H NMR (400 MHz, CDCl3) δ 7.51-7.49 (m, 4H), 7.38-7.33 (m, 6H),

7.30-7.26 (m, 4H), 7.22-7.17 (m, 6H), 4.33-4.29 (m, 2H), 2.97-2.88 (m, 2H), 1.33-1.32

3 3 (m, 2H), 1.31-1.30 (m, 2H), 0.65-0.61 (m, 6H), 0.25 (d, JH,H = 3.8 Hz, 3H), 0.20 (d, JH,H

= 3.8 Hz, 3H).

13 C NMR (100 MHz, CDCl3) δ 149.1, 149.1, 136.7, 136.4, 134.3, 134.3, 133.8, 129.1,

128.3, 128.3, 127.8, 127.6, 126.6, 126.6, 125.9, 125.8, 36.6, 36.2 25.5, 25.4, 23.8, 23.7, -

5.2, -5.2.

GC (methyl silicone column, 150 0 C/ Isotherm) RT for products = 7.57 min and 7.78 min.

GC-MS m/z ([M+) 240.10; exact mass calculated for C16H20Si 240.13.

Methyl(phenyl)(2-phenylbutyl)silane 220

SiHMePh

1 H NMR (400 MHz, CDCl3) δ 7.36-7.33 (m, 4H), 7.25-7.20 (m, 6H),

7.18-7.13 (m, 6H), 7.09-7.01 (m, 4H), 4.13-4.08 (m, 2H), 2.54-2.45 (m, 2H), 1.65-1.43

3 (m, 4H), 1.26-1.02 (m, 4H), 0.65-0.61 (m, 6H), 0.08 (d, JH,H = 3.8 Hz, 3H), -0.00 (d,

3 JH,H = 3.8 Hz, 3H).

230

13 C NMR (100 MHz, CDCl3) δ 147.2, 147.2, 137.3, 137.0, 134.7, 134.7, 129.5, 128.6,

128.6, 128.5, 128.4, 128.2, 128.0, 128.0, 126.4, 126.4, 44.6, 44.1, 33.2, 22.4, 22.1, 12.6,

12.5, -4.7, -4.9.

GC (methyl silicone column, 180 0 C/ Isotherm) RT for products = 8.88 min and 9.16 min.

GC-MS m/z ([M+) 254.10; exact mass calculated for C17H22Si 254.15

Triethyl(2-phenylbutyl)silane 221

SiEt3

1 H NMR (400 MHz, CDCl3) δ 7.39-7.35 (m, 2H), 7.29-7.25 (m, 3H), 2.68-

3 2.61 (m, 1H), 1.81-1.65 (m, 2H), 1.08-1.04 (m, 2H), 0.96 (t, JH,H = 7.9 Hz, 9H), 0.85 (t,

3 JH,H = 7.3 Hz, 3H), 0.53-0.41 (m, 6H).

13 C NMR (100 MHz, CDCl3) δ 148.0, 128.3, 127.7, 126.0, 43.9, 34.0, 19.8, 12.5, 7.6, 3.9.

GC (methyl silicone column, 160 0 C/ Isotherm) RT for product = 5.50 min.

GC-MS m/z ([M+) 248.10; exact mass calculated for C16H28Si 248.20

231

3.8 References

[1] a) A. M. Tondreau, E. Lobkovsky and P. J. Chirik, Org. Lett. 2008, 10, 2789; b) A. M. Tondreau, J. M. Darmon, B. M. Wile, S. K. Floyd, E. Lobkovsky and P. J. Chirik, Organometallics 2009, 28, 3928; c) J. Y. Wu, B. N. Stanzl and T. Ritter, J. Am. Chem. Soc. 2010, 132, 13214; d) K. Kamata, A. Suzuki, Y. Nakai and H. Nakazawa, Organometallics 2012, 31, 3825; e) D. Peng, Y. Zhang, X. Du, L. Zhang, X. Leng, M. D. Walter and Z. Huang, J. Am. Chem. Soc. 2013, 135, 19154; f) M. D. Greenhalgh, D. J. Frank and S. P. Thomas, Adv. Synth. Catal. 2014, 356, 584; g) J. Chen, B. Cheng, M. Cao and Z. Lu, Angew. Chem. Int. Ed. 2015, 54, 4661; h) G. I. Nikonov, ChemCatChem 2015, 7, 1918; i) Y. Sunada, D. Noda, H. Soejima, H. Tsutsumi and H. Nagashima, Organometallics 2015, 34, 2896-2906. [2] a) F.-G. Fontaine, R.-V. Nguyen and D. Zargarian, Can. J. Chem. 2003, 81, 1299; b) L. González-Sebastián, M. Flores-Alamo and J. J. Garcı́a, Organometallics 2013, 32, 7186; c) J. Zheng, C. Darcel and J.-B. Sortais, Catal. Sci. Tech 2013, 3, 81; d) I. Buslov, J. Becouse, S. Mazza, M. Montandon-Clerc and X. Hu, Angew. Chem. Int. Ed. 2015, 54, 14523–14526. [3] a) A. J. Chalk and J. F. Harrod, J. Am. Chem. Soc 1965, 87, 1133; b) N. J. Archer, R. N. Haszeldine and R. V. Parish, J. Chem. Soc. Dalton Trans. 1979, 695; c) C. L. Reichel and M. S. Wrighton, Inorg. Chem. 1980, 19, 3858; d) F. Seitz and M. S. Wrighton, Angew. Chem. Int. Ed. Eng. 1988, 27, 289; e) M. Brookhart and B. E. Grant, Journal of the American Chemical Society 1993, 115, 2151. [4] a) C. C. H. Atienza, T. Diao, K. J. Weller, S. A. Nye, K. M. Lewis, J. G. P. Delis, J. L. Boyer, A. K. Roy and P. J. Chirik, J. Am. Chem. Soc 2014, 136, 12108; b) C. H. Schuster, T. Diao, I. Pappas and P. J. Chirik, ACS Catal. 2016, 6, 2632-2636. [5] a) Z. Mo, J. Xiao, Y. Gao and L. Deng, J. Am. Chem. Soc 2014, 136, 17414; b) J. Sun and L. Deng, ACS Catal. 2016, 6, 290. [6] C. Chen, M. B. Hecht, A. Kavara, W. W. Brennessel, B. Q. Mercado, D. J. Weix and P. L. Holland, J. Am. Chem. Soc 2015, 137, 13244. [7] a) X. Y. Du, Y. L. Zhang, D. J. Peng and Z. Huang, Angew. Chem. Int. Ed. 2016, 55, 6670; b) Z. Zuo, J. Yang and Z. Huang, Angew. Chem. Int. Ed. 2016, 55, 10839. [8] J. Guo and Z. Lu, Angew. Chem. Int. Ed. 2016, 55, 10835. [9] A. D. Ibrahim, S. W. Entsminger, L. Zhu and A. R. Fout, ACS Catal. 2016, 6, 3589. [10] B. Raya, S. Biswas and T. V. RajanBabu, ACS Catal. 2016, 6, 6318-6323. [11] R. K. Sharma and T. V. RajanBabu, J. Am. Chem. Soc 2010, 132, 3295.

232

Chapter 4:Cobalt Catalyzed Hydrovinylation of Silyl 1,3-Dienes

4.1. Introduction

The carbon-carbon bond forming reactions are among the most important reactions in organic chemistry. The formation of many carbon-carbon bonds by traditional methods often requires reactive or complex starting material that are not often eco-friendly. A large number of carbon-carbon bonds forming reaction such as Wittig,

Friedel-Crafts and many cross coupling reactions are not efficient and cost effective in real synthetic situations due to significant generation of side products. Because of the global emphasis to move towards green chemistry, use of neutral feedstock chemicals

[1] such as CO/H2, HCN and ethylene shows enormous potential for the formation of new carbon-carbon bonds.[2] Although, there are numerous approaches for the creation of carbon-carbon bonds, efficient method for the asymmetric incorporation of ethylene that form new carbon-carbon bond are still limited. The addition of ethylene molecule across a carbon-carbon multiple bonds is called hydrovinylation reaction (Eq. 4.1).[3]

Hydrovinylation R H H (Eq. 4.1) R *

233

Numerous reports has been published on hydrovinylation using metal catalyst such as iron,[4] nickel, [5], ruthenium,[6] rhodium,[6a] palladium, [7] and cobalt[8] . RajanBabu group has focused on base metals such as nickel and cobalt catalyzed hydrovinylation reactions and this chapter will focus on the chemistry of cobalt-complexes for these reactions. In the early work on hydrovinylation, some of the first reactions were developed as the codimerization of ethylene and 1,3-butadiene. Early reports on hydrovinylation by

Hata,[4] Su,[9] Tolman,[5b] Hashimoto,[8a] and Alderson, Jenner, and Lindsey[6a] and others used a variety of metals with heat and high pressures of ethylene to produce the hydrovinylation products. These pioneering works on hydrovinylation established the catalytic addition of ethylene across carbon-carbon multiple bond using various metal catalysts at high pressure. In addition to the extreme conditions, which do not tolerate many functional groups, another major limitation of these early experiments was a relatively high frequency of observed side reactions such as isomerization or polymerization of the olefins. The original asymmetric hydrovinylation report by

Wilke[10] established the catalytic addition of ethylene across carbon-carbon bond of styrene molecule (Eq. 4.2).

Ethylene (10-15 atm) (L13) NiCl2, Et2AlCl H3C P CH Cl , -70 oC Eq. 4.2) 2 2 226 H C N 66 3 H 96% Yield, 95%ee Ph H 2 L13 234

After the discovery of efficient nickel catalyzed hydrovinylation reaction by Wilke group, numerous reports came on hydrovinylation using base metal catalyst such as nickel[5, 11] and cobalt[12]. The detail study of metal-catalyzed hydrovinylation reaction is described on RajanBabu’s reviews.[11, 13] Despite numerous report on hydrovinylation, limited report on the cobalt catalyzed hydrovinylation of functionalized dienes. From last two decades, RajanBabu group has spent a good portion to optimize hydrovinylation reaction and its application to natural product synthesis that utilizes nickel(II) as a precatalyst and examining the effects of various ligands and counter-anions.[14] Although, nickel catalyzed hydrovinylation works best for vinylarenes and strained olefins, major limitation to the chemistry of nickel-catalyzed hydrovinylation is reactions of 1,3-dienes.

Linear 1,3-dienes especially were unsuccessful, giving complex mixtures of 1,2- products with both (E) and (Z) geometry (Eq. 4.3).

1 1 ethylene (1 atm) 4 R 1 [(allyl)NiBr]2 R 4 R 4 R NaBARF, PPh3 1,4-Z 1,4-E 1,4-linear Z DCM, -55 oC (Eq. 4.3)

2 4 R R 1 R 1 1,2-E 1,2-Z 1,4-linear E

In 2010 RajanBabu et al.[12d] reported cobalt catalyzed hydrovinylation reaction of linear

1,3-dienes 102 by using bisphosphine ligands [e.g., 1,4-bis-diphenylphosphinobutane

235

(dppb)] and trimethylaluminum as an activator at -10 oC - 0 °C, yielding the (Z)-1,4- hydrovinylation product (227) in 96% purity in a half hour (Eq. 4.4).

1 1 ethylene (1 atm) 4 C5H11 C H (Eq. 4.4) (dppb)CoCl2 5 mol% C5H11 4 5 11 AlMe3 15 mol% 1,4-Z 1,4-linear Z DCM, -10 oC, 6 h 93% by GC 7% by GC 102 227 228

Similarly, RajanBabu et al.[15] in 2012 reported successful cobalt-catalyzed hydrovinylation of 1-vinylcycloalkenes 107 (Eq. 4.5) using MAO (methylaluminoxane) as an activator. The 1,4-hydrovinylation product 229 was formed and this reaction was performed enantioselectively with (S,S)-BDPP ligand to achieve an enantiometic excess of >99% ee. Recently Prof RajanBabu group reported detail study on effect of ligand for cobalt catalyzed hydrovinylation reaction of conjugated diene (Eq. 4.6) and hydrovinylation of functionalized dienes (Eq. 4.7).[16]

ethylene (1 atm) (Eq. 4.5) [(S, S)-BDPP]CoCl2 5 mol% MAO 2 eq. 107 DCM, RT, 6 h 229 > 98% regioselectivity >99% ee

236

H 1 ethylene (1 atm) R (Eq. 4.6) [(S, S)-BDPP]CoCl 10 mol% R 4 2 1,4-Z R = alkyl, TMA 50 mol% CH2CO2Et DCM, -45 oC to RT 90% Yeld CH OBn 2 90-99% ee

H 1 R SiO R3SiO 3 ethylene (1 atm) (Eq. 4.7) (dppp)CoCl2 5 mol% 4 MAO 2 equiv. C4H9 C4H9 DCM, RT, 1 h 116 194 1,4-Z

R3 = Me3, >95% R3 = Et3 R3 = tBu(Me)2

As an extension of this work, we have been interested in pursuing the hydrovinylation of substituted dienes that would result in functional group handles for further synthetic transformation. We decided to investigate the hydrovinylation of 1,3-dienes containing allyl and vinyl silanes, which could be a useful as cross coupling partners for further synthetic transformations. In this chapter report an efficient cobalt catalyst system for hydrovinylation at room temperature, which is able to do hydrovinylation for diene substrate containing allyl and vinyl silanes.

4.2 Results and Discussion

The aim of this research is the development of a general method for cobalt- catalyzed hydrovinylation of conjugated diene containing vinyl and allylsilane. The first

237 part of this chapter describes the strategy we employed in our investigation to optimize the catalyst for selective hydrovinylation. Inspired by the success of cobalt catalyst

(dppb)CoCl2 with TMA as activator in the hydrovinylation of linear 1,3-diene, the cobalt catalytic system developed in RajanBabu group[12d] for the hydrovinylation of 1,3-diene was initially applied to the hydrovinylation of dienes containing vinyl and allylsilane.

Using the optimized condition [1 equivalent of diene, 1 atm ethylene, (dppb)CoCl2 (0.05 equivalents), TMA (0.25 equivalents), DCM: Toluene (4:1) (0.15 M)] for hydrovinylation of linear 1,3-diene, we attempted to do hydrovinylation of prototypical substrate, (E)-trimethyl(4-methyl-2-vinylhept-3-en-1-yl)silane 230 for our initial scouting experiments at -15 oC temperature. The hydrovinylation reaction of 230 at -15 oC gave

51% of 1,4-E hydrovinylated product 231, 19% 1,4 linear product 232 and 14 % Z isomer of 230 by GC integration as left over starting material after 18 h. GC-MS and NMR identified the hydrovinylated product 231.

TMS (Etylene 1atm) TMS TMS (Eq. 4.8) C3H7 C3H7 C3H7 (dppb)CoCl2 5 mol% 1,4-E 1,4-linear 230 TMA 25 mol% 231 232 o -15 C, 18 h 51 % by GC 19 % by GC

The (dppb)CoCl2/TMA-mediated reaction gave almost 70 % conversion of starting material 230 by GC integration and was found exclusively to be the 1,4- adduct. We also identified MAO as a better reagent to activate the cobalt precatalyst compared to TMA for diene containing vinyl and allylsilane. 238

Next, we examined the effects of steric properties of the ligand on the reaction. A quick scan of commonly used bisphosphine ligands L1-L4 (Table 4.1, entries 1-4) confirmed that L3 (dppp, Table 4.1, entries 3) at room temperature is the best ligand for hydrovinylation of 230. Bisphosphine ligand across a range of bite angles (figure 4.1) was tested to examine the effects of steric properties on the reaction (Table 4.1, entries 1-

4). Several ligands with varying bite angles were tested for the hydrovinylation reaction of 230 (Eq. 4.9). Ligand L1 (Table 4.1, entries 1) gave more linear product 232 than branched product 231 where as ligand L2-L4 (Table 4.1, entries 2-4) gave more branched adduct 231 than linear adduct 232.

Ph P PPh PPh2 2 2 Ph2P dppm dppe L1 L2

PPh2 Ph2P PPh2 Ph2P dppp dppb L3 L4

Figure 4.1: Ligand Used for Hydrovinylation of 230

239

TMS (Etylene 1atm) TMS TMS (Eq. 4.9) C3H7 C3H7 C3H7 (Ligand)CoCl2 5 mol% 1,4-E 1,4-linear 230 MAO 2 equiv. 231 232 RT, Time

Table 4.1 Ligand Scan for Hydrovinylation of 230

Entry Ligand Time 231b 232b 230b

1 L1 40 min 41% 59% - 2 L2 35 min 75% 13% - 3 L3 50 min 87% 13% -

4 L4 45 min 62% 25% -

a b See Eq 4.9 for reaction scheme. 5 mol% catalyst (ligand)CoCl2. 2 eq. MAO, rt, ethylene. Ratios of products determined by areas under the peaks in GC, Rest percentage for mass balance is regioisomers

Having identified a successful ligand (L3) and activator (MAO) to promote the 1,4- selective hydrovinylation, attention was devoted to test various substrates for hydrovinylation. The full scope of the reaction is illustrated by examining the other diene substrates with varying degree of vinyl and allyl silanes (Fig. 4.2). To examine the utility of this optimized system, all of the 1,3-diene substrates (230, 233-242) with varying degrees of steric effects and sensitive functional groups were explored.

240

SiMe3 R Me3Si R1

R1 = CH2SiMe3, 237

R = C3H7, 230

R1 = CH2CH(CH3)2, 238

R = C6H13, 233

R = CH NHTs, 234 H 2 R = 2 1 C 239

R = CH2CH2OBz, 235

R1 = CH2CH(CO2Me)2, 240 R = C4H9, 236

Me Si Br 3 Me3Si 241 (E only) 242 (E only)

Figure 4.2 Dienes Tested for Hydrovinylation

Many of these 1,3-dienes were easily synthesized from their corresponding alkyne and alkene by enyne metathesis reaction using Grubb’s first generation and second-generation catalysts (Scheme 4). Substrates 230, 233, 234, 235 and 236 were made from their corresponding alkyne and alkene by using the corresponding Grubb’s first generation catalyst (Scheme 4.1). Another set of dienes, 237-240 having E and Z isomers were also made from their corresponding alkyne and alkene by using Grubb’s second generation catalyst (Scheme 4.2). However, these conditions yield a mixture of E and Z isomers in varying ratio. To make selective the (E) only isomer, substrates 241 and 242 were made

241 from their corresponding alkyne and alkene by enyne metathesis reaction using Grubb’s second-generation catalyst in presence of ethylene atmosphere (Scheme 4.3).

SiMe3 Grubb's I catalyst 6.7% R TMS DCM (0.16 M) R Z/E (Eq. 4.10) 1 eq. 3 eq. RT, 18 h - 22 h

R = C3H7, C6H13, CH2NHTs, CH2CH2OBz, C4H9 Me3Si SiMe3 Cy Cy Cy P Cl (homodimerized product), 243 Grubb's I Catalyst Ru Cl P Ph Cy Cy Cy Z:E ratio (% by GC) 243 Cy = Cyclohexyl

R = C3H7, 230, 89% Yield 50:42 8%

R = C6H13, 233, 86% Yield 50:42 8%

R = CH2NHTs, 234, 83% Yield 72:27 -

R = CH2CH2OBz, 235, 72% Yield 45:36 18% R = C4H9, 236, 90% Yield 53:40 7%

Scheme 4.1 Synthesis of 1,3-Diene Substrates Contain Allylsilane 230, 233-236

242

Grubb's II catalyst 5 mol% Me3Si R1 DCM (0.2 M) Me3Si R1 1 eq. 3 eq. E/Z (Eq. 4.11) RT, 18 h - 24 h

R1 = CH2SiMe3, CH2CH(CH3)2, R1 R1

R1 = CH2CH(CH2)4, CH2CH(CO2Me)2 (homodimerized product) HDP

N N E:Z ratio (% by GC) HDP

R1 = CH2SiMe3, 237, 86% Yield 60:12 28% Cl R1 = CH2CH(CH3)2, 238, 88% Yield Ru 61:6 33% Cl P Ph R1 = CH2CH(CH2)4, 239, 89% Yield Cy Cy 71:29 - Cy R1 = CH2CH(CO2Me)2, 240, 91% Yield Grubb's II Catalyst 62:38 -

Scheme 4.2 Synthesis of 1,3-Diene Substrates Contain Vinylsilane 237-240

Etylene 1 atm Grubb's II catalyst 5 mol% Me3Si R3 DCM (0.2 M) Me3Si R3 1 eq. 3 eq. E only (Eq. 4.12) RT, 24 h

R3 R3 N N

(homodimerized product) HDP Grubb's II Catalyst Cl Ru Cl P Ph Cy Cy Cy E only (% by GC) HDP

R3 = C4H9, 241, 78% Yield 90 10% 100 R = CH2CHCH2CH2Br, 242, 92% Yield -

Scheme 4.3 Synthesis of 1,3-Diene Substrates Contain only E Vinylsilane 241-242

243

Using the optimized condition [1 equivalent of diene, 1 atm ethylene, (dppp)CoCl2 (0.05 equivalents), MAO (2 equivalents), DCM (0.15 M)] the hydrovinylation reaction of 1,3- dienes 230, 233, 241 containing vinyl and allylsilane (Scheme 4) proceeds at room temperature giving good yields of hydrovinylated product. GC, GC-MS and spectroscopic techniques have established the structure of all the hydrovinylated products. In all cases, the hydrovinylation favors the 1,4-E branched product than 1,4- linear product (Table 4.2). Diene 237 showed moderate reactivity and gave only 20 % by

GC integration of 1,4-E branched hydrovinylated product after 3 h. However, dienes 234,

235, 240 and 242 did not show any reactivity under the optimized condition. The starting material got decomposed under the optimized condition.

TMS (Etylene 1atm) TMS TMS (Eq. 4.13) R R R (dppp)CoCl 5 mol% 2 1,4-E 1,4-linear MAO 2 equiv. RT, 30 - 50 min

244

Table 4.2 Scope of Hydrovinylation of 1,3-Diene

Entry Substrate 1,4-E branchedb 1,4-linearb Yield (%)c

TMS

SiMe3 SiMe3 R R R 1,4-E branched

GC Ratio

1 R = C3H7 R = C3H7 87% R = C3H7 13% 96% 230 231 232 R = C H R = C H 2 6 13 R = C6H13 >98% 6 13 <1% 94% 233 244 245 a b See Eq 4.13 for reaction scheme. 5 mol% catalyst (dppp)CoCl2. 2 eq. MAO, rt, ethylene. Ratios of products determined by areas under the peaks in GC, cisolated yield after purification

C4H9 (Etylene 1atm) (Eq. 4.14) Me3Si C4H9 Me3Si C4H9 Me3Si (dppp)CoCl 5 mol% 2 1,4-E 1,4-linear MAO 2 equiv. RT, 1 h

Entry Substrate 1,4-E branchedb 1,4-linearb Yield (%)c

SiMe3 1 97% Me3Si C4H9 Me3Si C4H9 Me3Si >99% GC Ratio <1% 242 246 247 a b See Eq 4.14 for reaction scheme. 5 mol% catalyst (dppp)CoCl2. 2 eq. MAO, rt, ethylene. Ratios of products determined by areas under the peaks in GC, cisolated yield after purification

245

Because the 1,4-E branched product was the major product observed with every substrate when dppp was employed as the ligand, the next aim was to examine the enantioselectivity of the reaction using chiral ligands. Dienes 230 and 242 form a chiral center upon hydrovinylation. Diene 230 and 242 was subjected to the optimized cobalt- catalyzed hydrovinylation conditions to examine the enantioselectivity of the reaction.

When substrate 230 was subjected for hydrovinylation using optimized conditions with dppp as a ligand, the expected regioselectivity was observed with the 1,4-addition leading to the branched product 231 as a final product (Eq. 4.9) and a completely racemic product was observed by chiral stationary phase gas chromatography (CSP-GC). Next we screened substrate 230 for hydrovinylation reaction to examine the enantioselectivity of the reaction using chiral ligand L10-L11, the expected regioselectivity was observed with the 1,4-addition leading to the branched product 231 as a major product (Eq. 4.14).

However, only low enantioselectivity (21% ee and 22% ee) was observed by chiral stationary phase gas chromatography (CSP-GC).

TMS (Etylene 1atm) TMS TMS (Eq. 4.15) C3H7 C3H7 C3H7 (Ligand)CoCl2 5 mol% 1,4-E 1,4-linear 230 MAO 2 equiv. 231 232 RT, 1 h

246

Table 4.3 Scope of Hydrovinylation of 1,3-diene using Chiral Ligand

d Entry Substrate 1,4-E branchedb 1,4-linearb Yield (%)c %ee

TMS

SiMe3 SiMe3 C3H7 C3H7 C3H7 1,4-E branched 1,4-linear 230 231 232 GC Ratio

1 L10 60% 20% 97% 21%

2 L11 78% <1% 95% 22% a b See Eq 4.15 for reaction scheme. 5 mol% catalyst (ligand)CoCl2. 2 eq. MAO, rt, ethylene. Ratios of products determined by areas under the peaks in GC, cisolated yield after purification, d% ee was determined using csp-gc

O PPh2 PPh2

PPh2 O PPh2

(R,R)-DIOP (S,S)-BDPP L10 L11

Figure 4.3 Chiral Ligand Tested for Hydrovinylation

We further screened substrate 242 for asymmetric hydrovinylation reaction using chiral ligand L10-L11., The expected regioselectivity was observed with the 1,4-addition leading to the branched product 246 as a major product (Eq. 4.14). Only modest enantioselectivity was observed upon analysis by chiral stationary phase gas chromatography (CSP-GC). 247

C4H9 (Etylene 1atm) (Eq. 4.16) Me3Si C4H9 Me3Si C4H9 Me3Si (ligand)CoCl 5 mol% 2 1,4-E 1,4-linear MAO 2 equiv. DCM, RT, 1 h

Table 4.4 Scope of Hydrovinylation of 1,3-Diene 242 Using Chiral Ligand

d Entry Substrate 1,4-E branchedb 1,4-linearb Yield (%)c %ee

C4H9

Me3Si C4H9 Me3Si C4H9 Me3Si 1,4-E branched 1,4-linear 242 246 247 GC Ratio

1 L10 >90% <2% 96% 24%

2 L11 >98% <2% 94% 29% a b See Eq 4.16 for reaction scheme. 5 mol% catalyst (ligand)CoCl2. 2 eq. MAO, rt, ethylene. Ratios of products determined by areas under the peaks in GC, cisolated yield after purification, d% ee was determined using csp-gc

4.3 Proposed Mechanism for Cobalt Catalyzed Hydrovinylation of 1,3-Diene

The initially proposed mechanism for hydrovinylation of 1,3-diene is shown in figure 4.4.

This involves the formation of a cationic cobalt hydride. However, recent mechanistic investigation of hydrovinylation has provided further insight that changes the original hypothesis. Cobalt(I) isolated species made by reduction of cobalt(II) chloride with zinc maintains same catalytic activity under the same hydrovinylation conditions. This

248 isolated cobalt(I) catalyst is also active with strong Lewis acids such as B(C6F5)3 which are not reducing or alkylating agents. On the basis of our preliminary observation using isolated cobalt(I) species for hydrovinylation, it is currently thought that TMA or MAO may first act as a reducing agent to provide a cobalt(I) species and then act as a Lewis acid to remove the chloride. The next step is the diene coordination to the open sites on cobalt followed by oxidative addition to make a cobalt cycle into which ethylene can insert. In the final step of catalytic cycle, β-hydride elimination followed by reductive elimination that would afford the 1,4-branched hydrovinylation product and regenerate a cationic cobalt species. The detail study of new proposed mechanism (Scheme 4.4) is currently under investigation.

Me AlCl Me3Al 2 Me2AlCl P Cl P Me Me3Al P Co Co Co Me Cl Cl P P P

P P P Co H Co Co Me P P R P R

249

R R P Hydrovinylated Co H Product P H 1 P P Co Co P R P 4 R

1 1 P P Co Co P P 4 4 R R

Figure 4.4.: Originally Proposed Mechanism for Hydrovinylation of 1,3-Diene

(P-P)nCoCl2

(P-P)nCoCl Me3Al

[Me3Al Cl] R Hydrovinylated R (P-P) Co Product n

(P-P)nCo H n(P-P)Co

R 4 R

R n(P-P)Co n(P-P)Co

Scheme 4.4 New Proposed Mechanism for Cobalt-Catalyzed Hydrovinylation

250

4.4 Conclusion: In conclusion, we are able to synthesized functionalized 1,3-diene bearing vinyl and allylsilane by using enyne metathesis reaction and we have identified efficient cobalt catalyst for 1,4-selective hydrovinylation of functionalized 1,3-diene.

Under the optimized conditions, we are able to do hydrovinylation of functionalized 1,3- diene bearing vinyl and allylsilane group. The functionalized 1,3-diene is converted to

1,4-E branched hydrovinylated product. This protocol is also useful for asymmetric hydrovinylation of functionalized 1,3-diene, which gave the only low enantioselectivity of the product even though quantitative yields substrates are obtained.

4.5 Experimental Procedures

All glassware was cleaned using base (KOH, iPrOH) then acid (HClaq) baths. Analytical

TLC was performed on E. Merck pre-coated (0.25 mm) silica gel 60 F254 plates. Flash column chromatography was carried out on silica gel 40 (Sorbtech Chemicals), Gas chromatographic analysis was conducted on Agilent 7820A using hydrogen as the carrier gas, equipped with a methyl silicone column (30 m X 0.32 mm, 0.25 µm film thickness).

Cobalt (II) chloride and Phosphine ligands were purchased from Strem Chemicals Inc.

All dienes used were synthesized within the laboratory. All silanes were purchased from

Sigma Aldrich, Oakwood, Alfa Aesar and Apollo Scientific. Gas chromatographic analysis was done on an Agilent 7820A using hydrogen as the carrier gas, equipped with

251 a methyl silicone column (30 m X 0.32mm, 0.25 µm film thickness). GC-MS was carried out on a HP-5MS 5% methyl phenylsiloxane (30 m x 0.25 mm, 0.25 µm film thickness) using He as carrier gas. Enantiomeric excess of chiral compounds were measured by chiral stationary phase gas chromatographic analysis, which were performed on Agilent

7820A using hydrogen as the carrier gas, equipped with a Cyclosil-B (30 m X 0.25 mm,

0.25 µm film thickness) and Cyclodex-B (60 m X 0.25 mm, 0.25 µm film thickness), capillary GC columns purchased from Agilent. Each GC was equipped with FID detectors and integrators on a computer. All activating reagents were purchased from

Sigma Aldrich. 1H, 13C NMR spectra were recorded on Bruker 400 and 600MHz, spectrometers. All spectra were obtained at ambient temperature. The chemical shifts (δ) were recorded in parts per million (ppm) and the coupling constants (J) in Hertz (Hz). 1H and 13C NMR multiplicity and coupling constants are reported where applicable. 1H and

13C spectra were referenced to the residual deuterated solvent peak (CHCl3 7.26ppm,

77.32ppm).

Typical Procedure for Synthesis of bis-phosphine Cobalt (II)-complexes

The bis-phosphine Cobalt (II)-complexes were prepared as described earlier.[12d]

Anhydrous CoCl2 (50.5 mg, 0.390 mmol) was added to a previously flame-dried 50-mL round two-necked bottom flask fitted with a flow control gas inlet and magnetic stir-bar loaded in a glove box under nitrogen. The nitrogen atmosphere was removed and the flask purged with dry argon. Freshly distilled, degassed THF (5 mL) was added, and upon stirring at room temperature for 15 min, a clear deep blue solution formed. A 252 solution of diphenylphosphinopropane (DPPP, 181mg, 0.410 mmol) in freshly distilled, degassed ether (5 mL) was added drop wise to yield a blue turbid solution. After stirring at room temperature for 15 h, 20 mL freshly distilled, degassed hexane was added in one portion to yield a blue precipitate. The resulting precipitate was filtered on a sintered glass fret under argon atmosphere, and washed with diethyl ether and hexane (1:1) mixture (3 X 5 mL) to remove any unreacted DPPP, resulting in quantitative yield of a light blue solid, which was used with no further purification

Typical Procedure for Synthesis of Methylaluminoxane (MAO)

A 500 mL three-necked, flame dried round-bottomed flask equipped with a septum, flow- control inlet, reflux condenser, and magnetic stir bar was purged with argon. Under argon atmosphere, hydrous aluminum sulfate (5.90 g, 9.5 mmol) was suspended in 19 mL freshly distilled toluene. The suspension is then cooled to 0 °C in an ice bath and a 2M solution of trimethylaluminum (28 mL, 55 mmol) in toluene was added slowly by syringe. The reaction was then slowly warmed to room temperature and stirred for eight hours, then heated gradually to 61 °C in a silicone oil bath and maintained at that temperature for nine hours. The mixture was then cooled to room temperature and filtered using an Schlenck filter (12” column fitted with two male ground joints and a micro porous fret in the center) into a flame-dried 250 mL single-necked round-bottomed flask, using a positive pressure of argon. The filtrate was then submitted to vacuum pump (<0.1 mm Hg) equipped with a liquid nitrogen trap to remove the toluene. White crystalline solid was formed and was left on vacuum pump overnight to dry completely, then

253

transferred to a glove box under argon to provide methylaluminoxane (MAO) as free- flowing, white crystals. Finally, MAO was stored in the glove box in a freezer (-15 °C).

General Procedure for Enyne Metathesis using Grubb First Generation Catalyst:

To a 100 mL flame dried schlenk flask equipped with magnetic stirrer was added

Grubb Ist generation catalyst (40 mg, 0.04 mmol, 0.06 eq) inside the glove box and the flask was removed from glove box and kept under vacuum for 10 minutes. The flask was then purged with argon. Grubb Ist generation catalyst was then dissolved in degassed dichloromethane (18 mL). The catalyst was stirred for 10 minutes and alkene (44 mg,

2.20 mmol, 3 eq) was added via syringe. Finally alkyne (50 mg, 0.73 mmol, 1 eq) was added to the reaction mixture and the reaction mixture was stirred at room temperature for 24 h. Progress of reaction was monitored by GC. After completion of reaction, it was filtered through silica (1 inch plug elution with CH2Cl2) and concentrated in vacuo to yield a desired crude product. The product was further purified by flash column chromatography (elution with hexane) to yield a pure product.

General Procedure for Enyne Metathesis using Grubb Second Generation Catalyst:

To a 100 mL flame dried schlenk flask equipped with magnetic stirrer was added Grubb

2nd generation catalyst (34 mg, 0.04 mmol, 0.05 eq) inside the glove box and the flask was removed from glove box and kept under vacuum for 10 minutes. The flask was then purged with argon. Grubb 2nd generation catalyst was then dissolved in degassed dichloromethane (18 mL). The catalyst was stirred for 10 minutes and alkene (44 mg,

254

General Procedure for Enyne Metathesis using Grubb Second Generation Catalyst in Presence of Ethylene Filled Balloon:

To a 100 mL flame dried schlenk flask equipped with magnetic stirrer was added Grubb

2nd generation catalyst (173 mg, 0.20 mmol, 0.1 eq) inside the glove box and the flask was removed from glove box and kept under vacuum for 10 minutes. The flask was then purged with argon. Grubb 2nd generation catalyst was then dissolved in degassed dichloromethane (13 mL). The catalyst was stirred for 10 minutes and alkene (1.7 g, 20.3 mmol, 10 eq) was added via syringe. Finally alkyne (0.2 g, 2.03 mmol, 1 eq) was added to the reaction mixture. The flow control valve was closed to argon and ethylene balloon was placed through the rubber septum and the reaction mixture was stirred at room temperature for 24 h. Progress of reaction was monitored by GC. After completion of reaction, it was filtered through silica (1 inch plug elution with CH2Cl2) and concentrated in vacuo to yield a desired crude product. The product was further purified by flash column chromatography (elution with hexane) to yield a pure product.

255

General Procedure for Cobalt Catalyzed Hydrovinylation Reaction of 1,3-Diene

A flame-dried schlenk flask equipped with a magnetic stir bar, and rubber septum was charged with cobalt catalyst (5 mg, 0.008 mmol, 0.05 eq) and MAO (20 mg, 0.38 mmol,

2 eq) under argon. Dry distilled dichloromethane (2 mL) was then added and the solution turned red and was allowed to stir for 5 minutes. The schlenk flask was closed to argon and an ethylene filled balloon was inserted through rubber septum. Air present inside the schlenk flask was removed via syringe (3 x volume of headspace) to cover the reaction with an atmosphere of ethylene and the solution was stirred under ethylene for 1 h. The

1,3-diene (30 mg, 0.16 mmol, 1 eq) was then added in one portion and the reaction was monitored by GC. After completion of reaction, the reaction was quenched with 0.1 mL

MeOH, diluted with hexane and filtered over silica. The filtrate solution was removed on a rotovap and gave the pure product as colorless oil.

Analytic Data for Synthesis of 1,3-Diene Products

(E,Z) trimethyl(4-methylenehept-2-en-1-yl)silane 230

TMS C H 1 3 7 H NMR (400 MHz, CDCl3) δ 5.93- 5.89 (m, 1H), 5.74- 5.66 (m,

2H), 5.53- 5.46 (m, 1H), 4.92- 4.75 (m, 4H), 2.17- 2.13 (m, 2H), 2.06(t, 3J, H, H = 7.5

Hz, 2H), 1.73 (dd, J, H, H = 8.8 Hz, 2H), 1.74- 1.71 (m, 2H), 1.50- 1.41 (m, 4H), 0.94-

0.87 (m, 6H), 0.03 (s, 9H), 0.00 (s, 9H).

13 C NMR (100 MHz, CDCl3) δ 146.7, 145.8, 130.8, 128.2, 128.1, 126.9, 112.5, 111.6,

39.8, 34.7, 23.7, 21.7, 21.5, 20.0, 14.2, 13.9, -1.4, -1.7.

256

GC (methyl silicone column, 80 0 C/ Isotherm) RT for product (E:Z) = 8.23 min and 7.80 min.

GC-MS (methyl silicone): m/z ([M+) 182.10; exact mass calculated for C11H22Si 182.15.

(E,Z) trimethyl(4-methylenedec-2-en-1-yl)silane 233

TMS C H 1 6 13 H NMR (400 MHz, CDCl3) δ 5.92- 5.88 (m, 1H), 5.74- 5.66 (m,

2H), 5.53- 5.46 (m, 1H), 4.91- 4.75 (m, 4H), 2.18- 2.15 (m, 2H), 2.07(t, 3J, H, H = 14.7

Hz, 2H), 1.72(dd, J, H, H = 8.8 Hz, 2H), 1.53(dd, J, H, H = 8.2 Hz, 2H), 1.42- 1.39 (m,

4H), 1.32- 1.26 (m, 12H), 0.89- 0.86 (m, 6H), 0.02 (s, 9H), 0.00 (s, 9H).

13 C NMR (100 MHz, CDCl3) δ 147.3, 146.4, 131.0, 128.4, 128.4, 127.1, 112.6, 111.7,

38.0, 32.9, 32.2, 32.1, 29.7, 29.4, 28.9, 28.7, 23.9, 23.1, 23.0, 20.3, 18.2, 14.5, -1.2, -1.4.

GC (methyl silicone column, 100 0 C/ Isotherm) RT for product (E:Z) = 18.89 min and

18.30 min.

GC-MS (methyl silicone): m/z ([M+) 224.10; exact mass calculated for C14H28Si 224.20.

(E,Z)4-methyl-N-(2-methylene-5-(trimethylsilyl)pent-3-en-1-yl)benzenesulfonamide

234

TsHN TMS 1 H NMR (400 MHz, CDCl3) δ 7.76- 7.73 (m, 4H), 7.32- 7.28 (m,

4H), 5.67- 5.52 (m, 4H), 5.07-4.95 (m, 4H), 4.46-4.39 (m, 2H), 3.57 (d, 3J, H, H = 6.1

Hz, 4H), 2.42 (s, 6H), 1.62- 1.58 (m, 4H), 0.00 (s, 18H).

257

13 C NMR (100 MHz, CDCl3) δ 143.0, 140.4, 139.8, 138.4, 136.5, 134.9, 132.6, 130.9,

129.9, 129.2, 128.7, 127.1, 126.8, 123.6, 114.4, 113.7, 48.2, 44.7, 23.5, 21.1, 19.9, 0.6, -

2.0, -2.2.

GC (methyl silicone column, 200 0 C/ Isotherm) RT for product (E:Z) = 17.06 min and

16.63 min.

(E,Z) 3-methylene-6-(trimethylsilyl)hex-4-en-1-ylbenzoate 235

TMS 1 BzO H NMR (400 MHz, CDCl3) δ 8.07-8.02 (m, 5H), 7.46- 7.40

(m, 5H), 5.97 (d, 3J, H, H = 16.0 Hz, 1H), 5.86- 5.73 (m, 2H), 5.62- 5.54 (m, 1H), 5.08-

4.90 (m, 4H), 4.46- 4.38 (m, 4H), 2.68- 2.64 (m, 2H), 2.56 (t, 3J, H, H = 6.8 Hz, 2H), 1.74

(dd, J, H, H = 8.8 Hz, 2H), 1.57- 1.56 (m, 2H), 0.02 (s, 9H), 0.02 (s, 9H).

13 C NMR (100 MHz, CDCl3) δ 166.7, 142.3, 141.5, 133.2, 132.9, 130.6, 130.6, 130.2,

129.8, 129.7, 129.7, 129.5, 128.5, 128.4, 127.7, 127.0, 114.9, 113.7, 63.9, 63.7, 36.8,

31.8, 23.7, 20.1, -1.48, -1.71.

GC (methyl silicone column, 140 0 C/ 10 min, rate = 15 oC, 250 oC/ 40 min) RT for product (E:Z) = 13.96 min and 13.72 min.

GC-MS (methyl silicone): m/z ([M+) 288.15; exact mass calculated for C17H24O2Si

288.10.

258

(E,Z)trimethyl(4-methyleneoct-2-en-1-yl)silane 236

TMS C H 1 4 9 H NMR (400 MHz, CDCl3) δ 5.92- 5.88 (m, 1H), 5.74- 5.66 (m,

2H), 5.53- 5.46 (m, 1H), 4.92- 4.75 (m, 4H), 2.19- 2.15 (m, 2H), 2.08(t, 3J, H, H = 14.5

Hz, 2H), 1.74- 1.71 (m, 2H), 1.54- 1.51 (m, 2H), 1.47- 1.27 (m, 8H), 0.92-0.87 (m, 6H),

0.02 (s, 9H), 0.00 (s, 9H).

13 C NMR (100 MHz, CDCl3) δ 147.1, 146.2, 130.9, 128.3, 128.2, 127.0, 112.5, 111.6,

37.6, 32.5, 31.1, 30.8, 23.8, 22.9, 22.7, 20.2, 14.3, 14.2, -1.3, -1.6.

GC (methyl silicone column, 80 0 C/ Isotherm) RT for product (E:Z) = 12.30 min and

11.71 min.

GC-MS (methyl silicone): m/z ([M+) 196.20; exact mass calculated for C12H24Si 196.16.

(E,Z) penta-2,4-diene-1,4-diylbis(trimethylsilane) 237

TMS 1 3 TMS H NMR (400 MHz, CDCl3) δ 6.18-6.14 (m, 1H), 6.00 (d, J, H, H =

15.8 Hz, 1H), 5.87- 5.83 (m, 1H), 5.74- 5.66 (m, 1H), 5.64-5.56 (m, 1H), 5.53 (d, 3J, H, H

= 3.3 Hz, 1H), 5.47- 5.40 (m, 1H), 5.20 (d, 3J, H, H = 3.3 Hz, 1H), 1.59- 1.57 (m, 2H),

1.52- 1.50 (m, 2H), 0.15 (s, 18H), 0.07 (s, 18H).

13 C NMR (100 MHz, CDCl3) δ 149.9, 149.7, 134.0, 129.9, 129.0, 126.3, 125.6, 124.8,

24.3, 19.3, -0.3, -1.5.

GC (methyl silicone column, 80 0 C/ Isotherm) RT for product (E:Z) = 9.68 min and 8.58 min.

GC-MS (methyl silicone): m/z ([M+) 212.10; exact mass calculated for C11H24Si2 212.14.

259

(E,Z)trimethyl(6-methylhepta-1,3-dien-2-yl)trimethylsilane 238

1 3 TMS H NMR (400 MHz, CDCl3) δ 6.13 (d, J, H, H = 15.8 Hz, 2H),

5.74- 5.62 (m, 2H), 5.63 (d, 3J, H, H = 3.2 Hz, 2H), 5.31 (d, 3J, H, H = 3.2 Hz, 2H), 1.99-

1.96 (m, 4H), 1.69- 1.55 (m, 2H), 0.91- 0.87 (m, 12H), 0.71 (s, 18H).

13 C NMR (100 MHz, CDCl3) δ 149.5, 136.1, 132.0, 126.3, 42.8, 28.9, 22.6, -0.5.

GC (methyl silicone column, 80 0 C/ Isotherm) RT for product (E:Z) = 5.63 min and 4.79 min.

GC-MS (methyl silicone): m/z ([M+) 182.10; exact mass calculated for C11H22Si 182.15.

(E,Z)(5-cyclopentylpenta-1,3-dien-2-yl)trimethylsilane 239

1 3 TMS H NMR (400 MHz, CDCl3) δ 6.34- 6.30 (m, 1H), 6.15(d, J, H, H

= 15.8 Hz, 1H), 6.00- 5.96 (m, 1H), 5.76- 5.69 (m, 1H), 5.62 (d, 3J, H, H = 15.8 Hz, 1H),

5.53- 5.52 (m, 1H), 5.49- 5.43 (m, 1H), 5.32 (d, 3J, H, H = 3.2 Hz, 1H), 2.23- 2.08 (m,

4H), 1.92- 1.81 (m, 2H), 1.77- 1.71 (m, 4H), 1.63- 1.49 (m, 8H), 1.18- 1.12 (m, 4H), 0.17

(s, 9H), 0.09 (s, 9H).

13 C NMR (100 MHz, CDCl3) δ 149.6, 149.2, 135.1, 132.3, 130.8, 129.7, 125.8, 125.5,

40.7, 40.1, 39.5, 33.9, 32.2, 32.1, 25.1, 24.9, -0.9, -2.4.

GC (methyl silicone column, 120 0 C/ Isotherm) RT for product (E:Z) = 6.23 min and

5.44 min.

GC-MS (methyl silicone): m/z ([M+) 208.16; exact mass calculated for C13H24Si 208.10.

260

(E, Z)dimethyl 2-(4-(trimethylsilyl)penta-2,4-dien-1-yl)malonate 240

CO2Me

TMS CO Me 1 3 2 H NMR (400 MHz, CDCl3) δ 6.21(d, J, H, H = 15.8 Hz, 1H),

6.10- 6.05 (m, 1H), 5.79- 5.58 (m, 2H), 5.53- 5.47 (m, 2H), 5.38-5.03 (m, 2H), 3.72 (s,

3H), 3.71 (s, 3H), 3.45 (t, 3J, H, H = 7.62 Hz, 1H), 3.36 (t, 3J, H, H = 7.64 Hz, 1H), 2.73-

2.64 (m, 4H), 0.13 (s, 9H), 0.07 (s, 9H).

13 C NMR (100 MHz, CDCl3) δ 169.3, 169.1, 149.1, 148.5, 137.7, 134.1, 127.5, 126.8,

126.1, 124.4, 52.4, 52.1, 51.8, 51.3, 32.4, 27.2, -1.1, -2.1.

GC (methyl silicone column, 140 0 C/ Isotherm) RT for product (E:Z) = 10.00 min and

9.09 min.

GC-MS (methyl silicone): m/z ([M+) 270.10; exact mass calculated for C13H22O4Si

270.13.

(E)-trimethyl(octa-1,3-dien-2-yl)silane 241

TMS C H 1 3 4 9 H NMR (400 MHz, CDCl3) δ 6.14 (d, J, H, H = 15.8 Hz, 1H), 1.73

(dt, J, H, H = 15.8 Hz, 1H), 5.61 (d, 3J, H, H = 3.2 Hz, 1H), 5.29 (d, 3J, H, H = 3.3 Hz,

1H), 2.10- 2.05 (m, 2H), 1.40- 1.29 (m, 4H), 0.89 (t, 3J, H, H = 7.1 Hz, 3H), 0.15 (s, 9H).

13 C NMR (100 MHz, CDCl3) δ 149.5, 135.0, 133.3, 126.2, 33.2, 31.9, 22.5, 14.2, -0.5.

GC (methyl silicone column, 80 0 C/ Isotherm) RT for product = 7.59 min.

GC-MS (methyl silicone): m/z ([M+) 182.10; exact mass calculated for C11H22Si 182.15.

261

(E)-(6-bromohexa-1,3-dien-2-yl)trimethylsilane 242

1 TMS Br H NMR (400 MHz, CDCl3) δ 6.24-6.20 (m, 1H), 5.71- 5.64 (m,

2H), 5.37(d, 3J, H, H = 3.1 Hz, 1H), 3.39(t, 3J, H, H = 7.1 Hz, 2H), 2.64- 2.62 (m, 2H),

0.16 (s, 9H).

13 C NMR (100 MHz, CDCl3) δ 149.6, 138.5, 129.3, 128.5, 37.3, 33.4, -0.0.

GC (methyl silicone column, 80 0 C/ Isotherm) RT for product = 19.17 min.

GC-MS (methyl silicone): m/z ([M+) 232.10; exact mass calculated for C9H17BrSi 232.03.

Analytical Data for Hydrovinylated Products

(E)-trimethyl(4-methyl-2-vinylhept-3-en-1-yl)silane 231

TMS C H 1 3 7 H NMR (400 MHz, CDCl3) δ 5.75- 5.67 (m, 1H), 4.93- 4.88 (m,

2H), 4.82- 4.79 (m, 1H), 3.06- 3.02 (m, 1H), 1.95- 1.91 (m, 2H), 1.58 (d, 3J, H, H = 1.3

Hz, 3H), 1.43- 1.38 (m, 2H), 0.86 (t, 3J, H, H = 7.3 Hz, 3H), 0.75- 0.60 (m, 2H), -0.02 (s,

9H).

13 C NMR (100 MHz, CDCl3) δ 145.0, 134.2, 129.6, 111.2, 42.3, 38.7, 24.0, 21.3, 16.5,

14.3, -0.28.

GC (methyl silicone column, 80 0 C/ Isotherm) RT for product = 13.98 min.

GC-MS (methyl silicone): m/z ([M+) 210.10; exact mass calculated for C16H32Si 210.18.

262

(E)-trimethyl(4-methyl-2-vinyldec-3-en-1-yl)silane 244

TMS C H 1 6 13 H NMR (400 MHz, CDCl3) δ 5.74- 5.66 (m, 1H), 4.91- 4.86 (m,

2H), 4.81- 4.78 (m, 1H), 3.06- 2.99 (m, 1H), 1.95- 1.91 (m, 2H), 1.35 (d, 3J, H, H = 6.8

Hz, 3H), 1.38- 1.23 (m, 8H), 0.87- 0.84 (m, 3H), 0.73- 0.68 (m, 2H), -0.03 (s, 9H).

13 C NMR (100 MHz, CDCl3) δ 145.0, 134.4, 129.4, 111.1, 40.1, 38.7, 32.2, 29.5, 28.2,

23.9, 23.0, 16.6, 14.5, -0.29.

GC (methyl silicone column, 120 0 C/ Isotherm) RT for product = 11.38 min.

GC-MS (methyl silicone): m/z ([M+) 252.20; exact mass calculated for C16H32Si 252.23.

(E)-trimethyl(4-vinyloct-2-en-2-yl)silane 246

TMS C H 1 4 9 H NMR (400 MHz, CDCl3) δ 5.73- 5.64 (m, 1H), 5.50- 5.48 (m, 1H),

4.97- 4.90 (m, 2H), 3.11- 3.04 (m, 1H), 2.22- 2.06 (m, 2H), 1.67 (d, 3J, H, H = 1.7 Hz,

3H), 1.30- 1.26 (m, 4H), 0.90- 0.86 (m, 3H), 0.05 (s, 9H).

13 C NMR (100 MHz, CDCl3) δ 141.9, 141.6, 136.2, 113.2, 42.7, 35.1, 29.7, 23.0, 14.9,

14.4, -1.7.

GC (methyl silicone column, 80 0 C/ Isotherm) RT for product = 11.29 min.

GC-MS (methyl silicone): m/z ([M+) 210.10; exact mass calculated for C13H26Si 210.18.

263

4.6 Reference [1] T. V. RajanBabu, G. A. Cox, H. J. Lim, N. Nomura, R. K. Sharma, C. R. Smith and A. Zhang in Hydrovinylation Reactions in Organic Synthesis, Vol. 5 Eds.: G. A. Molander and P. Knochel), Elsevier, Oxford, 2014, pp. 1582-1620. [2] a) F. Agbossou, J.-F. Carpentier and A. Mortreux, Chem. Rev. 1995, 95, 2485; b) A. L. Casalnuovo, T. V. RajanBabu, T. A. Ayers and T. H. Warren, J. Am. Chem. Soc 1994, 116, 9869; c) K. Nozaki, N. Sakai, T. Nanno, T. Higashijima, S. Mano, T. Horiuchi and H. Takaya, J. Am. Chem. Soc 1997, 119, 4413. [3] S. M. Pillai, M. Ravindranathan and S. Sivaram, Chem. Rev. 1986, 86, 353-399. [4] G. Hata, J. Am. Chem. Soc 1964, 86, 3903. [5] a) K. Noboru, M. Ken-ichi, M. Tsutomu and O. Atsumu, Bull. Chem. Soc. Jpn. 1971, 44, 3217; b) C. A. Tolman, J. Am. Chem. Soc 1970, 92, 6777. [6] a) T. Alderson, E. L. Jenner and R. V. Lindsey, J. Am. Chem. Soc 1965, 87, 5638; b) C. S. Yi, Z. He and D. W. Lee, Organometallics 2001, 20, 802. [7] M. G. Barlow, M. J. Bryant, R. N. Haszeldine and A. G. Mackie, J. Organomet. Chem. 1970, 21, 215. [8] a) T. I. Kagawa, Y.; Hashimoto, H., Bull. Chem. Soc. Jpn. 1970, 43, 1250; b) M. Y. Iwamoto, S., Bull. Chem. Soc. Jpn. 1968, 41, 150. [9] A. C. L. Su, In Advances in Organometallic Chemistry, F. G. A. Stones and Robert West, Ed.; Academic Press, 1979, p. 269-318. [10] G. Wilke, B. Bogdanović, P. Hardt, P. Heimbach, W. Keim, M. Kröner, W. Oberkirch, K. Tanaka, E. Steinrücke, D. Walter and H. Zimmermann, Angew. Chem. Int. Ed. Eng. 1966, 5, 151. [11] T. V. RajanBabu, Chem. Rev. 2003, 103, 2845. [12] a) M. M. P. Grutters, C. Müller and D. Vogt, J. Am. Chem. Soc 2006, 128, 7414; b) M. Arndt, A. Reinhold and G. Hilt, J. Org. Chem 2010, 75, 5203; c) M. M. P. Grutters, J. I. van der Vlugt, Y. Pei, A. M. Mills, M. Lutz, A. L. Spek, C. Müller, C. Moberg and D. Vogt, Adv. Synth. Catal. 2009, 351, 2199; d) R. K. Sharma and T. V. RajanBabu, J. Am. Chem. Soc 2010, 132, 3295. [13] a) T. V. RajanBabu, Synlett 2009, 2009, 853; b) T. V. A. C. RajanBabu, G.; Lim, H. J.; Nomura, N.; Sharma, R. K.; Smith, C. R.; Zhang, A, In Comprehensive Organic Synthesis II, Elsevier: Amsterdam,, 2014, p. [14] a) C. R. Smith and T. V. RajanBabu, Org Lett 2008, 10, 1657; b) A. Zhang and T. V. RajanBabu, Org. Lett. 2004, 6, 1515; c) A. Zhang and T. V. RajanBabu, J. Am. Chem. Soc 2006, 128, 5620; d) C. R. Smith and T. V. RajanBabu, J. Org. Chem 2009, 74, 3066; e) D. J. Mans, G. A. Cox and T. V. RajanBabu, J. Am. Chem. Soc 2011, 133, 5776; f) W. Liu, H. J. Lim and T. V. RajanBabu, J. Am. Chem. Soc 2012, 134, 5496; g) N. Nomura, J.

264

Jin, H. Park and T. V. RajanBabu, J. Am. Chem. Soc 1998, 120, 459; h) M. Nandi, J. Jin and T. V. RajanBabu, J. Am. Chem. Soc 1999, 121, 9899. [15] J. P. Page and T. V. RajanBabu, J. Am. Chem. Soc 2012, 134, 6556. [16] a) Y. N. Timsina, R. K. Sharma and T. V. RajanBabu, Chem. Sci 2015, 6, 3994; b) S. Biswas, J. P. Page, K. R. Dewese and T. V. RajanBabu, J. Am. Chem. Soc 2015, 137, 14268

265

Chapter 5: Triarylphosphine Ligands with Hemilabile Alkoxy Groups: Ligands for Nickel (II)-Catalyzed Olefin Dimerization Reactions. Hydrovinylation of Vinylarenes, 1-3-Dienes, and Cycloisomerization of 1,6-Dienes. Portions of this chapter appear in the following publication

Biswas, S.; Zhang, A.; Raya, B.; RajanBabu, T.V. Adv. Synth. Catal. 2014, 356, 2281

5.1 Introduction

The carbon-carbon bond forming reactions are the most important reactions in organic chemistry. Carbon-carbon bond forming reaction has emerged as attractive tools for the synthesis of various types of organic compounds.[1] Although, there are numerous approaches for the creation of carbon-carbon bonds, efficient catalytic methods for making new carbon-carbon bonds starting from neutral precursors are still limited.

Hydrovinylation reactions[2] and cycloisomerization reactions[3] are among the various carbon-carbon bonds forming reactions, have emerged as attractive tools for the synthesis of various types of organic compounds in an easy one-pot process. A wide range of transition-metal complexes can be used in these reactions. Here in this chapter we will report the nickel catalyzed cycloisomerization reaction of 1,6-diene. Cycloisomerization reaction using transition metals represent a versatile approach to a variety of products by a simple manipulation of the catalyst.[1] Our initial efforts to find new protocals for the efficient nickel catalyzed asymmetric hydrovinylation.[2, 4] of activated alkenes such as

266 vinylarenes,[5] conjugated 1,3-dienes[5d] and bicyclo[2.2.1]-heptenes[6] have resulted in the identification of different types of ligands that are capable of effecting these remarkable transformation with very high efficiency and selectivity (Scheme 5.1).

These several ligands include 2’-alkoxy-1-diarylphosphino-1,1’-binaphthyl derivatives

(L14),[7] 1-aryl-2,5-dialkylphospholanes (L15)[8], phosphoramidites derived from 1,1’- biaryl-2,2’-dihydroxy compounds (L16),[9] and, diarylphosphinites,(L17)[10] derived from carbohydrate and these are shown in figure 5.1.

During these investigations for efficient asymmetric hydrovinylation reaction, we focused most of our efforts on enantio-pure ligands. For the synthesis of racemic mixtures of the hydrovinylated products, we often resorted to the original protocol that was developed for the hydrovinylation of vinylarenes. The original protocol involved the

[7a] use of a combination of [(allyl)NiBr]2, Ph3P and AgOTf (Eq 5.1), or, in some cases, the use of the more expensive 1:1 mixture of the enantiopure ligands with a Ni(II) precursor. While these have been reliable procedures for hydrovinylation reaction and served our purpose well, occasionally we faced difficulties with the former protocol (Eq

5.1) due to the sensitivity of the reaction to temperature, especially in the case of reactions of vinylarenes. Unless the temperature is rigorously maintained (– 50 oC to –

56 oC) in this moderately exothermic reaction, in addition to the expected product 226, varying amounts of an isomerization product, 248,[7b] and a dimer, 249[11] are formed as impurities. We wondered whether we could design a simple and more robust phosphine ligand based on our recognition[9a] of the role of a hemilabile atom in this reaction.

Accordingly, we prepared a series of 2-alkoxyaryl and 2-(alkoxyalkyl)aryl-

267 diphenylphosphines (Eq 5.2, L18, L19, L20) in which the hemilabile oxygen atom is placed on β, γ or δ- carbon in relation to the chelating phosphine.[9a] This subtle variation in the ligand has a dramatic effect on the efficiency and selectivity of several hydrovinylation reactions. Such ligand effects extend to a mechanistically related cycloisomerization reaction of 1,6-dienes. Nickel catalyzed cycloisomerization of 1,6- dienes into methylenecyclopentanes is uniquely effected by nickel (II) complexes of L18.

Furthermore, in our attempt to prepare authentic samples of the methylenecyclohexane products, nickel (II) complexes of N-heterocyclic carbene ligands were examined. Here in this chapter we will report the detail results of these studies.

(all C-quateranry center) (vinylarenes) H3C Ar R Ar = 4-i-Bu-styrene (1 atm.) (72% yield; 99 %ee) (97 % yield; 96% ee) [(allyl)Ni-L] X (cat.)

OBn OBn OBn OBn O O (90% yield; 95% ee) (97% yield; 99% ee) (1,3-Diene) (strained alkenes)

Scheme 5.1. Selected Examples of Asymmetric Hydrovinylation of Alkenes

268

Me H R O O R Ph O Me Ar S O O c O R Me O Me HN O OBn R PPh2 S a P N P Ac P O Me Ar Sc Me S

L14 L15 L16 L17

Figure 5.1 Ligands for Asymmetric Hydrovinylation Reaction

5.2 Results and Discussion 5.2.1 Ligand Effects on Hydrovinylation of Vinylarenes Our initial investigations for hydrovinylation of styrene 68 and 4-methylstyrene 13 as a prototypical substrates using the previously disclosed catalyst system

[(allyl)NiBr]2/Ph3P/AgOTf showed the extreme sensitivity of the reaction to temperature changes (Eq 5.1). While at – 78 oC there is very low conversion of styrene 68 after 6 h, at room temperature, extensive isomerization of the initially formed product 226 to a mixture of 2-arylbutenes (248) and a styrene dimer (249)[11] are observed. Varying amounts of these side products are observed at intermediate temperatures, and the reaction was eventually optimized for a series of vinylarenes where these side products were found to be virtually absent around –55 oC.[7] We turned our attention to the hemilabile ligands L18, L19 and L20, each carrying hemilabile oxygen atom with the hope of finding a hydrovinylation protocol under ambient conditions, without the complications of isomerization of the double bond. These aryldiphenylphosphino-ligands were readily synthesized from the corresponding bromoaryl derivatives by lithium exchange reaction followed by treatment with Ph2PCl at low temperature (Eq 5.2). 269

Ligands L18, L19 and L20 were examined in the hydrovinylation of a number of vinylarenes including 4-methylstyrene 13, using the procedure we previously developed[9a] for ligands that carry a hemilabile group (Eq 5.3). The illustrative results are shown in Table 5.1.

ethylene (1 atm.)

[(allyl)NiBr] , AgOTf R 2 Ph3P, CH2Cl2 68 (0.007 equiv. cat.)

(R = H) (5.1) + + Ar Ar R R

temp. (oC) time conv. % 226 248 249

– 78 6 h <5 trace -- -- – 78 - 25 14 h 100 5 1 0 25 5 min 100 33 67 (trace)

–56 2 h 100 >99 0 0

Z 1. n-BuLi, – 78 oC Z (Eq. 5.2) o Br 2. Ph2PCl, – 78 C to rt PPh2

250a Z = OBn L18 Z = OBn (45%) 250b Z = CH2OBn L19 Z = CH2OBn (69%) 250c Z = CH2CH2OBn L20 Z = CH2CH2OBn (75%)

270

As seen from the entries 1-3 of table 5.1, the most striking difference between these ligands is the respective reactivities of the putative [(allyl)NiL][BARF] complexes as catalysts for the hydrovinylation reaction. The o-benzyloxyphenyldiphenylphosphine

(L18) is the most active ligand, even more active than the [(allyl)Ni(Ph3P)][OTf], presumably involved in the original protocol (Eq 5.1). This catalyst with L18 not only effects the hydrovinylation of 4-methylstyrene 13 at -55 oC, but it also promotes further isomerization of the primary product 252b at this low temperature (entry 1) giving upto

33% of a conjugated product 253b as a mixture of E- and Z-Isomers in a ratio of 2.0:1.2.

In sharp contrast, Hemilabile ligand L19 (o-benzyloxymethylphenyl ligand) promotes only a sluggish reaction at – 55 oC, thus requiring a prolonged period (~ 11 h) at room temperature for complete conversion of the starting material (Table 5.1, entry 2). To our delight, unlike many other ligand systems we have examined, there is no sign of dimerization of the vinylarene or isomerization of the primary product (252) to the conjugated derivative 253.

Hemilabile ligand L20, with an ethano-bridge between the oxygen and the aryl moiety, behaves like L19, except that the corresponding Ni(II) complex is much less reactive (Table 5.1, entries 3 and 4). However the selectivity for the primary product 252 is equally impressive (98%, Table 5.1, entry 3).

271

[(allyl)NiBr]2 ligand (L), NaBARF

[(allyl)NiL] [BARF] + (Eq. 5.3) Ar (0.007 equiv. cat.) Ar Ar CH2Cl2, RT

251 BARF = [3,5-(CF3)2C6H3]4 252 253

Table 5.1. Effect of Ligands on Ni(II)-Catalyzed Hydrovinylation of 4-

Methylstyrenea

Entry Ligand Temp. Time Conv. Product, yield(%) Selectivity oC (h) (% of 252)

Me Me 252b 253b

1a OBn -55 2 >99 67 33 67 1b rt 20 >99 0 >99 0 1c -55 2 <4b,c <4 - - PPh2 1d L18 -55 2 >99d 70 29 70

OBn 2 23 11 >99 >99 0 >99

PPh2 L19

OBn

3 -55 16 0 0 - - PPh2 23 2.5 48 48 0 >99 L20 [a] see Eq. 5.3 for procedure. [b] Using AgOTf [c] Rest Starting Material [d] Using AgSbF6

272

Having identified a successful ligand to promote the selective hydrovinylation reaction, attention was focused to test various hemilabile ligands for cycloisomerization of 1,6- diene.

5.3 Ligand Effects on Cycloisomerization of 1,6-Dienes

After the discovery of the original hydrovinylation protocol (Eq 5.1), we reported that these conditions can be modified to effect cycloisomerization of 1,6-dienes, examples of

[12] which are shown in Eq 5.4 and Eq 5.5. Both of the [(allyl)NiBr]2 and the corresponding [(allyl)PdCl]2 were used as precursors in otherwise identical conditions.

The palladium catalyzed [Pd(II)-catalyzed] reaction appear to be more compatible with broader set of substrates, even though isomerization of the primary product can be a serious problem in these reactions, and, occasionally regioselectivity ( e.g., formation of

259 in Eq 5.5b) can be different from the Ni(II)-catalyzed reactions.

MeO C MeO C MeO2C (0.05 equiv. cat.) 2 2 + (Eq. 5.4) MeO C MeO2C 2 MeO2C

254 255 256

[(allyl)NiBr]2, AgOTf 92% <2% [(4-OMe)C6H4]3P, CH2Cl2, 4 h

[(allyl)PdCl]2, AgOTf 20% 70% [(2-Me)C H ] P, CH Cl , 24 h 6 4 3 2 2

273

[(allyl)NiBr]2, AgOTf [(4-OMe)C6H4]3P, CH2Cl2 Ts N (Eq. 5.5a) 0.1 equiv. Ni(II)cat., 24 h Ts N 258 (10%)

[(allyl)PdCl]2, AgOTf 257 [(2-Me)C6H4]3P, CH2Cl2 Ts N + (Eq. 5.5b) N 0.1 equiv. Pd(II) cat., 24 h Ts 258 (35%) 259 (57%)

Since formally this cyclization reaction of dienes can be described as an intramolecular version of the hydrovinylation (strictly a hydroalkenylation) reaction,[13] we decided to examine the modified procedure using the hemilabile ligands L18-L20 for this reaction, and the results are shown in Eq 5.6.

[(allyl)NiBr]2 L18, Na BARF Z Z + Z (Eq.5.6) o CH2Cl2, 0 C to rt, 5 h Z 260 (0.1 equiv. cat.) 261 262 263 (no trace)

• No reaction with L19 or L20

a 260a C(CO2Et)2 261a (92) 262a (<5) a 260b C(CO2Me)2 261b (93) 262b (5) b 260c CH(CO2Et) 261c (>95) 262c (0)

260d PhSO2N 261d (99) 262d (0) 260e TolSO2N 261e (99) 262e (1) 260f PhCH2N (no reaction) 260g Ph(CO)N (no reaction) a rest starting material. b diasteromers 65:35.

The hamilabile ligands L18, L19 and L20 were tested in the Ni(II)-catalyzed cyclization reactions using essentially the same procedure used for the intermolecular reactions (Eq

5.6). The hamilabile ligand L19 and L20 were found to be totally 274 ineffective in the cyclization, where as ligand L18 gave excellent yields for the cyclization of the prototypical substrates 260a-e. These substrates shown under Eq. 5.6, gave the methylenecyclopentane (261a-e), along with traces of methylenecyclohexane

(262a-e), resulting from a different regioselectivity in the insertion (Eq. 5.6). Under these cyclization conditions, only small amounts (<5%) of isomerized products (e.g., 263) were detected by gas chromatography (GC). The product were analyzed by gas chromatography, and, subsequently purified by column chromatography to determine the yield of the reaction. The reaction works equally well for the formation of nitrogen containing heterocyclic compounds from the corresponding 1,6-dienes. As we have observed earlier, judicious choice of the protecting group on nitrogen is crucial for the success of the reaction. While an arylsufonyl (ArSO2) protecting group (e.g., 260d,

260e) is perfectly compatible with the reaction, leading to excellent yields of the cyclization product, Lewis basic centers present in the benzylamine 260f or the benzamide 260g totally inhibits the cyclization reaction and leaving behind unreacted starting materials even after prolonged reaction times.

5.4 Identification of the Minor Methylenecyclohexane Products (262) via Use of

Nickel N-Hetrocyclic Carbenes (NHC) Complexes

The observations based on the effect of phosphine ligands by differing steric demands in the Ni(II) and Pd(II)-catalyzed cyclization reactions of 1,6-dienes suggest that it might be possible to control the regio-selectivity of the initial metal-hydride addition (Scheme 2), and, hence the product distribution [in Eq 5.6: methylencyclopentane (261) vs

275 methylenecyclohexane (262)] by ligand tuning. Such a possibility for the formation of different regioisomers is further bolstered by the uncommon regioselectivity observed by

Ho in the tail-to-tail heterodimerization of styrene with a 1-alkenes.[14] In this reaction, which involves the addition of a metal hydride as a key step in mechanism, the larger size of an NHC ligand has been invoked to rationalize the selectivity of the product. Thus we decided to examine a series of the N-heterocyclic carbenes (NHC)[15] as ligands for the cyclization under our new protocol (Eq. 5.7) and results are shown in Table 5.2.

Table 5.2. Cyclization of 1,6-dienes using (allyl)Ni(NHC)BARF[a] entry substrate Ligand L21 (IMes) Ligand L22 (IPr) 261 (%) 262 (%) 261 (%) 262 (%) 1 260a 3 92 <1 >97 2 260b 6 82 trace >92 3 260cb 71c 29 9c 71e 4 260d 65 29f 35 59 5 260e 65 35 32 67h 6 260f, 260g 0 0 0 0 aSee Eq 5.7 for reaction scheme. bThe reaction mixture contains other products, the proportions shown are normalized with respect to the cyclized products to highlight the effect of NHC ligands on the cyclization. Phosphine ligands L18 gives only 261c (see Eq.

5.6), c dr = 2.2:1.0.

[16] The carbene complexes were prepared in situ starting from Ni(COD)2, allyl bromide and the NHC ligand[17] followed by addition of NaBARF.[9a] (Eq 5.7) As documented in entries 1-5, Table 5.3, NHC ligands L21 and L22 are competent ligands

276 to effect the cyclization, whereas larger NHC ligands L23 and L24 gave no products.

Substrates 260a and 260b, where Thorpe-Ingold effect is operative, gave excellent yields of the methyelenecyclohexane derivative 262, with the cyclopentane derivative 261 as a side-product (entries 1 and 2, columns 4 and 6). The larger of the two ligands (L21 and

L22), L22 gave almost exclusively the cyclohexane derivative 262. Other substrates

260c-260e gave varying proportions of the two cyclic products, in each case giving more of the six-membered product 262 with the larger NHC ligand L22.

Ni(COD)2/COD/CH2Cl2 (allyl)bromide, add NHC Z Z + Z (Eq. 5.7) NaBARF followed by 26 Z 263 (no trace) 260 (0.2 equiv. cat, rt, 5 h) 261 262

• No reaction with L23 or L24

L21 L22 L23 L24

Ligands: R N N R R = mesityl i-propyl adamantyl t-butyl •• a %Vbur 26 29 37 37 a proportional to size of the ligand, see: ref.[15]

5.5 Proposed Mechanism for Regioselectivity Control in the Cationic Metal Hydride

Mediated Cyclization of 1,6-Dienes

The proposed mechanism for nickel catalyzed 1,6-diene cyclization is shown in scheme

5.2. In this proposed mechanism, which involves the addition of a metal hydride as a key

277 step, the larger size of an NHC ligand than phosphine ligand has been invoked to rationalize the selectivity of the product.

[(allyl)NiBr] L X 2 NaBr R NaBARF Ni Ni R L L

X = BARF

'' '' L X Ni H Ni R L R F3C CF3 L-[M-H] F3C CF3

Na B NaBARF

F3C CF3

X X β-hydride elimina-on LNi H LNi H β-hydride elimina-on H NHC Carbene Phosphine H NiL NiL NiL NiL

migratory inser-on migratory inser-on

Scheme 5.2. Possible Control of Regioselectivity in the Cationic Metal Hydride Mediated Cyclization of 1,6-Dienes

278

5.6 Conclusion In conclusion, hemilabile ligand L18, L19 and L20, exhibit strikingly different behavior in various Ni(II)-catalyzed olefin dimerization reactions. Nickel complexes of ligands

L18 and L19 are most active for hydrovinylation of vinylarenes, with the former (L18) leading to extensive isomerization of the primary 3-aryl-1-butenes into the conjugated 2- aryl-2-butenes even at low temperature. Hemilabile ligand L19 is the most optimal for the hydrovinylation of vinylarenes, leading to up to quantitative yields of products at ambient temperature with no trace of isomerization. In sharp contrast, hydrovinylation of a variety of 1,3-dienes is best catalyzed by Ni(II)-complexes of hemilabile ligand L18.

Hemilabile ligands L19 and L20 are much less effective in the hydrovinylation of dienes.

Nickel(II)-catalyzed cycloisomerization of 1,6-dienes into methylenecyclopentanes, a reaction mechanistically related to the other hydrovinylation reactions, is also uniquely effected by Ni(II)-complexes of hemilabile ligand L18. Attempts to prepare authentic samples of the methyelencyclohexane products led to Ni(II)-complexes of NHC-ligands, which in sharp contrast to the phosphines, gave methylenecyclohexanes as the major product.

5.7 Experimental Procedures

General Methods. Reactions requiring air-sensitive manipulations were conducted under an inert atmosphere of nitrogen by using Schlenk techniques or a Vacuum Atmospheres glovebox. Dichloromethane was distilled from calcium hydride under nitrogen and stored over molecular sieves. Tetrahydrofuran was distilled under nitrogen from sodium/benzophenone ketyl. Catalyst precursors [(allyl)NiBr]2 and NaBARF were 279

[18] prepared according to the literature. The [(allyl)NiBr]2 was stored in a freezer in the drybox. Ethylene (99.5%) was purchased from Matheson Inc., and passed through a column of Drierite® before use. Analytical TLC was performed on E. Merck precoated

(0.25 mm) silica gel 60 F254 plates. Flash column chromatography was carried out on silica gel 40 (Scientific Adsorbents Incorporated, Microns Flash). Conversion of the products was determined by gas chromatographic analysis, which was performed on an

Agilent HP-5 column (30 m length X 0.325 mm diameter) using helium or hydrogen as a carrier gas (25 psi). Absence of polymeric impurities was ascertained by NMR, and, except for the volatile materials, the isolated yields of the products were not significantly different from the conversions.

Ligands L18, L19 and L20 were prepared according to literature procedures.[19]

Precursors for the NHC ligands, L21, L22, L24 were synthesized in laboratory and L23 was purchased as the corresponding imidazolium salts from Strem Chemicals. 2- and 3-

Vinylfurans were prepared by known methods.[20] All other precursors are described in the publications that deal with the synthesis of the HV products (see below).

Spectroscopic and gas chromatographic data for the HV products (including separations on chiral stationary phase gas or liquid chromatography of chiral materials) are described the publications cited below.

Preparation of Ligand L18.[19] A mixture of 2-bromophenol (1.73g, 10 mmol), benzyl bromide (1.20 mL, 1.71g, 10 mmol) and K2CO3 (2.2g, 16 mmol) in acetone (20 mL) was refluxed for 18 h under nitrogen. After removal of acetone, water was added and the

280

mixture was extracted with ether. The organic layers were washed with water, dried and concentrated under vacuum. The resulting residue was purified by flash column chromatography on silica gel (eluting with hexanes/ethyl acetate = 100/1) to afford 2.08 g

(79%) of 2-bromophenyl benzyl ether.

To the solution of 2-bromophenyl benzyl ether (789 mg, 3 mmol) in THF (5 mL) was added n-BuLi (1.9 mL, 1.6 M in hexanes, 3 mmol) at -78 oC under nitrogen. After the resulting solution was stirred at this temperature for 30 min, a solution of chlorodiphenylphosphine (696 mg, 3 mmol) in THF (5 mL) was added at -78 oC. Then the mixture was allowed to warm to room temperature and stirred for 1 h. Water was added to quench the reaction and the mixture was extracted with ether. The organic layers were combined, washed with brine, dried over MgSO4 and concentrated. The resulting residue was purified by column chromatography on silica gel (eluting with hexanes/ethyl acetate=100/1) to get 490 mg (45%) of L18. 1H NMR (500 MHz, CDCl3):

δ 7.55-7.30 (m, 11 H), 7.30-7.20 (m, 3 H), 7.15-7.05 (m, 2 H), 7.00-6.90 (m, 2 H), 6.90-

13 6.80 (m, 1 H), 5.10 (s, 2 H); C NMR (125.7 MHz, CDCl3): δ 159.97, 138.83,136.68,

134.21, 133.59, 130.21, 128.75, 128.48, 128.31, 127.55, 126.93, 126.54, 121.28, 111.47,

31 70.03; P NMR (202.4 MHz, CDCl3): δ -15.53; HRMS (ESI): m/z 407.1193

+ ([M+Na+O] , exact mass calcd for C25H21O2PNa 407.1171).

Preparation of Ligand L19.[19] A solution of 2-bromobenzaldhyde (2.34 mL, 3.7g, 20 mmol) in THF (20 mL) was slowly added to a stirred slurry of NaBH4 (760 mg, 20 mmol) in THF (40 mL) at room temperature. After 20 h, the mixture was cooled in an

281 ice-salt bath, and 1:1 concentrated HCl-water was added dropwise carefully until the resulting solution was acidic. The aqueous solution was saturated with NaCl and extracted with ether. The combined extracts were washed once with water, dried and concentrated. The crude product was used for the next step without further purification.

To the solution of the crude alcohol from the previous step in THF (20 mL) was added

KH (964 mg, 24 mmol) at 0 oC under nitrogen and the resulting mixture was stirred for

30 min at this temperature. Benzyl bromide (2.6 mL, 22 mmol) was added all at once via syringe. The mixture was stirred at 0 oC for 30 min and then allowed to warm to room temperature and stirred for 1 h. After the mixture was cooled to 0 oC, water was added to quench the reaction and the mixture was extracted with ether. The organic layers were washed with brine, dried and concentrated to give yellow oil, which was purified by column chromatography (eluting with hexanes/ethyl acetate=20/1) to afford 3.8 g (69% in two steps) of 1-bromo-2-benzyloxymethylbenzene.

To the solution of 1-bromo-2-benzyloxymethylbenzene (554 mg, 2 mmol) in THF (5 mL) was added n-BuLi (1.25 mL, 1.6 M in hexanes, 2 mmol) at -78 oC under nitrogen.

After the resulting solution was stirred at this temperature for 30 min, a solution of chlorodiphenylphosphine (696 mg, 3 mmol) in THF (5 mL) was added at -78 oC. Then the mixture was allowed to warm to room temperature and stirred for 1 h. Water was added to quench the reaction and the mixture was extracted with ether. The organic layers were combined, washed with brine, dried over MgSO4 and concentrated. The resulting yellow liquid was crystallized from methanol in the freezer to give 574 mg

(75%) of L19. 1H NMR (500 MHz, CDCl3): δ 7.80-7.70 (m, 1 H), 7.50-7.25 (m, 17 H),

282

7.10-7.00 (m, 1 H), 4.94 (s, 2 H), 4.59 (s, 2 H); 13CNMR (125.7 MHz, CDCl3): δ 142.80,

138.31, 136.71, 135.62, 133.95, 133.61, 129.06, 128.82, 128.72, 128.41, 128.22, 127.84,

127.79, 127.49, 72.47, 70.65; 31P NMR (202.4 MHz, CDCl3): δ -15.63; HRMS (ESI):

+ m/z 421.1310, ([M+Na+O] , exact mass calcd for C26H23O2PNa 421.1328).

Preparation of Ligand L20.[19] To a solution of 2-bromophenethylalcohol (905 mg, 4.5 mmol) in THF (5 mL) was added KH (200 mg, 5 mol) in one portion at 0 oC under argon.

The resulting suspension was stirred at 0 oC for 30 min and then benzyl bromide (0.54 mL, 4.5 mmol) was added dropwise at 0 oC. The mixture was allowed to warm to room temperature and stirred for 1 h. Water was added to quench the reaction and the mixture was extracted with ether and the organic layers were combined, washed with brine, dried and concentrated. The resulting residue was purified by column chromatography on silica gel (eluting with hexanes/ethyl acetate=20/1) to get 1.24 (95%) of 2-bromophenethyl benzyl ether.

To a solution of 2-bromophenethyl benzyl ether (1.24 g, 4.26 mmol) in THF (15 mL) was added n-BuLi (2.7 mL, 1.6 M in hexanes, 4.26 mmol) at -78 oC under argon. After the resulting solution was stirred at this temperature for 30 min, a solution of chlorodiphenylphosphine (988 mg, 4.26 mmol) in THF (5 mL) was added at -78 oC.

Then the mixture was allowed to warm to room temperature and stirred for 1 h. Water was added to quench the reaction and the mixture was extracted with ether. The organic layers were combined, washed with brine, dried over MgSO4 and concentrated. The resulting residue was purified by column chromatography on silica gel (eluting with

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hexanes/ethyl acetate=100/1) to get 1.09 (65%) of ligand L20. 1H NMR (500 MHz,

CDCl3): δ 7.40-7.20 (m, 17 H), 7.13 (td, J = 8.09, 1.74 Hz, 1 H), 6.88 (dd, J = 7.50, 4.20

Hz, 1 H), 4.41 (s, 2 H), 3.61 (t, J = 7.29 Hz, 2 H), 3.22 (t, J = 7.29 Hz, 2 H); 13C NMR

(125.7 MHz, CDCl3): δ 143.50, 138.62, 136.96, 136.09, 134.07, 133.88, 130.14, 129.04,

128.75, 128.61, 128.38, 127.66, 127.50, 126.73, 72.82, 70.79, 34.80; 31P NMR (202.4

MHz, CDCl3 δ -15.20; HRMS (ESI): m/z 435.1466 ([M+Na+O]+, exact mass calcd for

C27H25O2PNa 435.1484).

Typical Procedure for Hydrovinylation of Vinylarenes (Tables 5.1). To a solution of

[(allyl)NiBr]2 (2.5 mg, 0.007 mol) in CH2Cl2 (1 mL) at room temperature was added a solution of ligand 2-benzoxymethylphenyldiphenyl-phosphine (L18, 5.3 mg, 0.014 mmol) in CH2Cl2 (1 mL) in drybox. The resulting solution was added to a suspension of

NaBARF (12.9 mg, 0.0146 mmol) in CH2Cl2 (1 mL). Methylene chloride (1 mL) was used to rinse the vial and combined with the above mixture and the resulting mixture was stirred for 1.5 h at room temperature. The resulting catalyst was filtered through a small pad of celite into a dry Schlenk flask and taken out of drybox. Methyelene chloride (1 mL) was used facilitate complete transfer. For room temperature reactions, the catalyst solution was cooled to 0 oC, and was exposed to an ethylene atmosphere from an Schlenk line, and to the solution was added dropwise the solution of vinylarenes (2 mmol) in

CH2Cl2 (3 mL) under 1 atm of ethylene. After the addition was over, the mixture was allowed to warm to rt and stirred for the designated time in table. For low temperature

284

reactions (Table 1) the catalyst solution was maintained at the prescribed temperature and the substrate was added under ethylene at this temperature, and the reaction was maintained for the suggested period. The reaction was followed by GC for completion of reaction. The mixture was quenched with half-saturated aqueous NH4Cl solution and extracted three times with 10 mL portions of CH2Cl2. The combined organic layers were dried over anhydrous MgSO4 and concentrated and the residue was passed through a small plug of silica gel eluting with hexanes/ethyl acetate system (For styrene and 2- and

3-vinylfurans, pentane was used). The filtrate was concentrated to afford the crude products, which were analyzed by GC (for 2- and 3-vinylfuran, the solvent was removed by distillation during work-up). The product was analyzed by GC (attached) and NMR, the later to ascertain the absence of polymeric materials.

The procedure was repeated with ligands L19 and L20 under conditions described in

Table 1 and the exact ratio of products obtained were determined by gas chromatography.

These chromatograms are included later in this Supporting Information.

Experimental Procedure for Making Substrates

Diethyl 2,2-diallylmalonate 260a

EtO2C

In a flame dried 50 mL 3-neck flask equipped with a magnetic stir bar, NaH (60% in mineral oil, 0.90 g, 37.5 mmol) and dry THF (17 mL) were placed. After cooling to 0

°C, a solution of diethylmalonate (2.00 g, 12.5 mmol) in 8.3 mL of dry THF was slowly

285 added to the NaH suspension. The reaction was stirred at room temperature for 0.5 h, after which allyl bromide (3.2 mL, 37.5 mmol) was added at once. The mixture was then warmed to room temperature (~25 °C) and stirred for 3 h. Next, a saturated solution of

NH4Cl was carefully added until complete dissolution of the suspended solid. The aqueous phase was separated and washed with Et2O (3 × 20 mL). The organic layers were combined, washed with brine (3 × 20 mL), dried over Na2SO4, and the solvent removed under reduced pressure to provide an oily residue. This material was purified by column chromatography, using hexanes: EtOAc (4:1) as eluent, to provide the diallyldiethylmalonate in 1.90 g (92% yields).

Dimethyl 2,2-diallylmalonate 260b

MeO2C

MeO2C In a flame dried 50 mL 3-neck flask equipped with a magnetic stir bar,

NaH (60% in mineral oil, 1.09 g, 45.4 mmol) and dry THF (20 mL) were placed. The flask was then cooled to 0 °C. After cooling to 0 °C, a solution of dimethylmalonate (2.00 g, 15.1 mmol) in 10 mL of dry THF was slowly added to the NaH suspension. The reaction was stirred at room temperature for 0.5 h, after which allyl bromide (3.92 mL,

45.4 mmol) was added at once. The mixture was then warmed to room temperature (~25

°C) and stirred for 3 h. Next, a saturated solution of NH4Cl was carefully added until complete dissolution of the suspended solid. The aqueous phase was separated and washed with Et2O (3 × 25 mL). The organic layers were combined, washed with brine (3 286

× 25 mL), dried over Na2SO4, and the solvent removed under reduced pressure to provide an oily residue. This material was purified by column chromatography, using hexanes: EtOAc (4:1) as eluent, to provide the diallyldiethylmalonate in 1.82 g (87% yields).

N-allyl-N-benzylprop-2-en-1-amine 260f

PhH2C N

To a solution of benzyl amine (0.21 g, 2.0 mmol) and K2CO3 (1.38 g, 10.0 mmol) in CH3CN (26 mL) was added allyl bromide (0.43 mL, 5.0 mmol) in 50 mL flame dried 3-neck flame equipped with magnetic stirrer. The mixture was stirred for 10 h at room temperature. The solution was filtered through a celite pad and the filtrate was concentrated under reduced pressure. The residue was subjected to column chromatography (hexane: ethyl acetate = 10:1) on silica gel to give product as colorless oil in 0.29 g (93% yields).

N, N –diallyl benzene sulfonamide 260d

O S N O To a solution of p-benzene sulfonamide (0.63 g, 4.0 mmol) and

K2CO3 (1.38 g, 10.0 mmol) in CH3CN (40 mL) was added allyl bromide (0.87 mL, 10.0 mmol) in 50 mL flame dried 3-neck flame equipped with magnetic stirrer. The mixture was refluxed for 4 h at 70 oC. The solution was filtered through a celite pad and the 287 filtrate was concentrated under reduced pressure. The residue was subjected to column chromatography (hexane: ethyl acetate = 5:1) on silica gel to give product as colorless oil in 63% yield.

N, N –diallyl p-toluene sulfonamide 260e

O S N O Triethylamine (1.09 g, 10.7 mmol) and tosyl chloride (2.00 g, 10.5 mmol) were added to a solution of diallylamine (1.0 g, 10.3 mmol) in 35 mL of CH2Cl2 in

50 mL flame dried 3-neck flame equipped with magnetic stirrer. The mixture was stirred

o at 20 C for 16 h. The organic phase was washed twice by a 10 % aq. Solution of KHSO4

(30 mL) and twice by a saturated aq. Solution of NaHCO3 (30 mL) then by water (30 mL). The organic phase was dried over anhydrous MgSO4, concentrated under vacuum and purified through column chromatography (hexane: ethyl acetate = 4:1) on silica gel to give product as colorless oil in 76% yield.

Preparation of N, N –Diallyl benzamide 260g

O C N

In 250 mL flame dried 3-neck flask equipped with magnetic stirrer, benzoyl chloride (2.00 g, 15.8 mmol) was added in one portion to a solution of the diallylamine (1.68 g, 17.4 mmol), Et3N (2.00 g, 19.7 mmol) and dichloromethane (0.5M) at room temperature, resulting rapidly in a boiling solution. The reaction mixture was 288 stirred for 20 minute at room temperature and then was diluted with dichloromethane.

The solution was transferred to a separation funnel and was washed with 1N HCl. The organic layer was dried with Na2SO4, filtered and concentrated under reduced pressure.

The final product was then purified through column chromatography (hexane: ethyl acetate = 4:1) on silica gel to give product as colorless oil in 86% yield.

N, N –Diallyl methane Sulfonamide

H3C S N O In 250 mL flame dried 3-neck flask equipped with magnetic stirrer,

Triethylamine (1.78 g, 17.6 mmol) and methane sulfonyl chloride (2.00 g, 17.4 mmol) were added to a solution of diallylamine (0.17 g, 17.4 mmol) in 58 mL of CH2Cl2. The mixture was stirred at 20 oC for 16 h. The organic phase was washed twice by a 10 % aq.

Solution of KHSO4 (30 mL) and twice by a saturated aq. Solution of NaHCO3 (30 mL) then by water (30 mL). The organic phase was dried over anhydrous MgSO4, concentrated under vacuum and purified through column chromatography (hexane: ethyl acetate = 4:1) on silica gel to give product as colorless oil in 92% yield.

289

Making the Imidazolium Salt 1,3-Bis(2,6-Diisopropylphenyl)-1H-Imidazol-3-ium

Chloride

(1E,2E)-N1,N2-Bis(2,6-Diisopropylphenyl)Ethane-1,2-Diimine

N N

In air, to a solution of 2, 6-diisopropyl aniline (15.2 g, 86.1 mmol, 2 eq) and HOAc (0.1 mL, 1.5 mmol, 0.035 eq) in 21.5 mL of MeOH at 50 oC in a

250 mL flask was added a solution of glyoxal (2.5 g, 40 % in water, 43.0 mmol, 1 eq) in

21.5 mL of MeOH. The reaction mixture was stirred at 50 oC for 15 min and then stirred at 23 oC for 12h. The reaction mixture was filtered. The filter cake was washed with

MeOH (3x50 mL) and dried in vacuum to afford 12.7g of compound as a yellow solid.

1,3-Bis(2,6-Diisopropylphenyl)-1H-Imidazol-3-ium Chloride

N N

In air, to N, N1-1,4-bis (2,6-diisopropyl phenyl)-1,4- diazabutadiene (1 g, 2.7 mmol, 1 eq) and paraformaldehyde (0.082 g, 2.7 mmol, 1.03 eq) in 24 mL of EtOAc in a flask at 70 oC was added a solution of TMSCl (0.30 g, 2.7 mmol,

1.03 eq) in 0.4 mL of EtOAc drop wise over 15 min with vigorous stirring. The reaction mixture was refluxed at 70 oC for 2h. After cooling to 10 oC with stirring, the reaction mixture was filtered. The filter cake was washed with EtOAc (3x 20 mL) and dried on

290 vacuum to afford 0.75 g of compound as a colorless solid (86% yields).

1,3-Bis(1-Adamantyl)Imidazolium Tetrafluoroborate

N N Ad Ad BF4 In a 100 mL flame dried 3-neck flask, a mixture of 1-adamantanamine

(0.2 g, 1.4 mmol) and paraformaldehyde (0.04 g, 1.4 mmol) was stirred for 1 h at room

o temperature in CHCl3 (5mL) before being cooled to 0 C. After the addition of extra 1- adamantanamine (0.2 g, 1.3 mmol), a 48 % aqueous solution of HBF4 (0.12 g, 0.08 mL,

1.4 mmol) and a 40 % aq. solution of glyoxal (0.07 g, 1.3 mmol) and TMSCl (0.15 g, 1.3 mmol) were added slowly. After being stirred for 19 h at 60 oC, the mixture was cooled at RT and a saturated aqueous solution of Na2CO3 was added. The aq. phase was extracted with CH2Cl2 and the combined organic layers were dried over anhydrous

MgSO4, filtered and concentrated in vacuum. The residue was dissolved in least CH2Cl2 and diethyl ether was added to the solution. The precipitate thus obtained were filtered and dried under vacuum to give IAd.HBF4 as a white solid (87 % yield).

Making the Catalyst Nickel Allyl Bromide Dimer [(allyl)NiBr]2

Br Ni Ni Br A 100 ml 2-neck round-bottomed flask equipped with a rubber septum, a

Teflon-taped flow controlled nitrogen inlet, a thermometer and magnetic stirring bar is flame dried, purged with nitrogen and transferred into a glove box. The flask is then charged with nickel cyclooctadiene (0.5 g, 1.8 mmol) and is removed from the glove box under nitrogen from a schlenk line, the flask is charged with anhydrous diethyl ether (29 291 mL) and is cooled to -70 oC in a dry ice/acetone bath, at which time allyl bromide (0.15 mL, 0.22 g, 1.9 mmol, 1.0 eq) is added via syringe with stirring. The cold bath is removed and replaced by an ice-water bath. The reaction mixture is allowed to warm to 0 oC gradually (20 min), then to ambient temperature over another 15 minute by removing the cold bath. The reaction mixture is stirred at ambient temperature for another 1h and is then transferred into the glove box by evaporating the solvent by pump. The flask is rinsed with anhydrous ether (3x10 mL) and the resulting suspension is passed through a plug of dry celite in a fritted glass filter funnel. The celite pad is washed with an additional 40 mL of ether. The ether washings are transferred to a 250 mL pear shaped flask equipped with a magnetic stirrer bar. The ether is removed under vacuum with vigorous stirring to afford the product as a dark-red powder.

Preparation of Free Carbene form Imidazolium Salt (Carbene salt) Using Silver

Oxide

To a solution of imidazolium salt (2.02 mg, 0.01 mmol) in DCM (0.5 mL) was added silver oxide (27.3 mg, 0.12 mmol, 20 eq) and the mixture was stirred for 18 h inside the dry box. The solution was filtered through the celite pad to make the free carbene.

Preparation of Free Carbene form Imidazolium Salt (Carbene salt) Using Potassium tert Butoxide

In a 20 mL white cap vial, imidazolium salt (85 mg, 0.25 mmol) and KOtBu (42 mg, 0.38 mmol, 1.5 eq) were suspended in 2 mL of THF and stirred magnetically for 8 h. THF was

292 then removed in vacuum to yield a white solid. To the solid was added 0.5 mL of toluene, which dissolved most of the material. The resulting mixture was treated with 5 mL of hexanes to precipitate excess KOtBu and unreacted starting material and the mixture was filtered through a glass-fritted funnel. The precipitate was washed with two 0.5 mL portions of hexanes. The filtrate was concentrated and dried in vacuum to yield free carbene as a white solid.

Making the Nickel allyl carbene complex from IMes carbene

N N

Ni Br Ni (cod) 2 (72 mg, 0.27 mmol) was suspended in ca. 0.47 g 1,

5-cyclooctadiene. Allyl bromide (32 mg, 0.27 mmol) was then added drop wise. The resulting slurry was then stirred for 5 min, rapidly resulting in the formation of a blood- red ally nickel (II) bromide dimer. 0.2 mL of toluene was added to dissolve all material.

A solution of carbene (80 mg, 0.27 mmol) in 0.2 mL of toluene was then added and the mixture was stirred for 5 min. The solution rapidly changed from a dark maroon color to a dark orange-brown solution. The mixture was filtered over celite and concentrated in vacuum. The resulting orange solid was washed with 3 x 0.1 mL portions of cold hexanes and dried in vacuum to yield 123.4 mg of product.

293

Making the Nickel Allyl Carbene Complex from IPr Carbene

N N

Ni Br In a 20 mL white cap vial equipped with magnetic stirrer, nickel cyclooctadiene (140 mg, 0.51 mmol) was suspended in ca. 0.8 g 1, 5-cyclooctadiene.

Allyl bromide (62 mg, 0.51mmol) was then added drop wise. The resulting slurry was then stirred for 5 min, rapidly resulting in the formation of a blood-red ally nickel (II) bromide dimer. 1.5 mL of toluene was added to dissolve all material. A solution of carbene (0.19 g, 0.51 mmol) in 1.5 mL of toluene was then added and the mixture was stirred for 5 min. The solution rapidly changed from a dark maroon color to a dark orange-brown solution. The mixture was filtered over celite and concentrated in vacuum.

The resulting orange solid was washed with 3 x 0.5 mL portions of cold hexanes and dried in vacuum to yield 0.2 g of product.

General Procedure for 1, 6 -diene Cyclization Reaction using Phosphine Ligand

The solution of phosphine ligand (5 mg, 0.02 mmol, 10 mol%) in 0.3 mL of dichloromethane was transferred to a vial containing nickel allyl bromide dimer (2.3 mg,

0.007 mmol, 5 mol%). The vial was rinsed with the help of 0.3 mL of dichloromethane solution and again transferred to the vial containing Nickel allyl bromide dimer. The solution was stand for 15-20 min then the solution was transferred to the vial containing

NaBARF (11 mg, 0.013 mmol, 10 mol %) and the vial was further rinsed with the help of

0.3 mL of dichloromethane solution then the solution was stand for 2h inside the dry box. 294

After 2h the solution was transferred to the 3 -neck round bottomed flask equipped with magnetic stirrer with the help of cannula transfer at -35 oC (dry ice/acetone bath). After transferring the catalyst, diene (30 mg, 0.127 mmol) was injected with the help of syringe and the dry ice/acetone bath was removed. The reaction was stirred at room temperature and the progress of reaction was monitored by GC analysis. After completion the reaction the product was quenched by using 1:1 hexane/ether and passed through silica pad and the solvent was evaporated under reduced pressure to yield the product.

General Procedure for 1, 6 -diene Cyclization Reaction using Carbene Ligand

The solution of Nickel allyl carbene complex (8 mg, 0.014 mmol, 20 mol%) in 0.3 mL of dichloromethane was transferred to a vial containing NaBARF (12 mg, 0.014 mmol, 20 mol%) and the vial was again rinsed with the help of 0.3 mL of dichloromethane solution. Then the solution was stand for 2 h inside the dry box. After 2h the solution was transferred to the 3 neck round bottomed flask equipped with magnetic stirrer with the help of cannula transfer at -35 oC (dry ice/acetone bath). After transferring the catalyst the starting material (16 mg, 0.07 mmol) was injected with the help of syringe and the dry ice/acetone bath was removed. The reaction was stirred at room temperature and the progress of reaction was monitored by GC analysis. After completion the reaction, the product was quenched by using 1:1 hexane/ether and passed through silica pad and the solvent was evaporated under reduced pressure to yield the product.

295

Typical Procedure for 1,6-diene cyclization using [(allyl)NiBr]2 and L18 catalyst (Eq

5.6). In a glovebox, NaBARF (14.7 mg, 0.017 mmol, 10 mol%), ligand L18 (6.15 mg,

0.017 mmol, 10 mol%), and [(allyl)NiBr]2 (3.0 mg, 0.008 mmol, 5.0 mol%) were weighed into separate glass vials. The hemilabile ligand was dissolved in anhydrous

DCM (1.0 mL) and transferred to the vial containing [(allyl)NiBr]2, followed by 1.0 mL rinsing of the source vial. The resulting yellow solution of ligand L18 and [(allyl)NiBr]2 was transferred to the vial containing NaBARF, followed by 1.0 mL rinsing of the source vial. The resulting orange-yellow solution was diluted with DCM (1.0 mL) and allowed to stand for 1.5 h.

Cyclization procedure: A 25 mL three-necked flask equipped with a rubber septum, flow-controlled nitrogen inlet, thermometer, and magnetic stirring bar was flame-dried and purged with nitrogen. The catalyst solution prepared above was transferred to the reaction vessel via cannula, followed by 1.0 mL rinsing of the source vial. The system was cooled to 0 °C in an ice bath and diallyl malonate (260a, 34 mg, 0.16 mmol) was added in to the reaction mixture by microliter syringe. The reaction mixture was allowed to stir at rt for 5 h. The reaction was exposed to air and diluted with pentane to quench the reaction. The crude cyclized product that was then eluted through a plug of silica with pentane to remove any nickel salts was concentrated and further analyzed by NMR and

GC.

Typical Procedure for 1,6-diene cyclization using Ni(COD)2 and free carbene: In a glovebox, Ni(COD)2 (123 mg, 0.45 mmol) was dissolved in 1 mL 1,5-cyclooctadiene.

296

Allyl bromide (54.4 mg, 0.45 mmol) was then added dropwise. The resulting slurry was then stirred for 5 minutes, rapidly resulting in the formation of a blood-red allylnickel(II) bromide dimer. Toluene (2 mL) was added to dissolve all material. A solution of free the free IPr carbene L22 (175 mg, 0.45 mmol) in 2 mL of toluene was then added and the mixture was stirred for 5 min. The solution was filtered over celite and concentrated in vacuum. The resulting orange solid was washed with 3 1-mL portions of cold hexanes and dried under reduced pressure to yield ca. 210 mg of product (82% yield).

Cyclization procedure: In a glovebox, NaBARF (8.3 mg, 0.0094 mmol, 10 mol%) and [allyl)Ni(L22)Br] (5.3 mg, 0.0094 mmol, 10 mol%) were weighed into separate glass vials. The complex was dissolved in anhydrous DCM (1.0 mL). The resulting yellow solution of the complex was transferred to the vial containing NaBARF, followed by 1.0 mL rinsing of the source vial. The resulting orange-yellow solution was diluted with

DCM (1.0 mL) and allowed to stand for 1.5 h. A 25 mL three-necked flask equipped with a rubber septum, flow-controlled nitrogen inlet, thermometer, and magnetic stirring bar was flame-dried and purged with nitrogen. The catalyst solution prepared above was transferred to the reaction vessel via cannula, followed by 1.0 mL rinsing of the source vial. The system was cooled to 0 °C in an ice bath and diallyl malonate (260a, 10 mg,

0.047 mmol) was added in to the reaction mixture by microliter syringe. The reaction mixture was allowed to stir at rt for 5 h. The reaction was exposed to air and diluted with pentane to quench the reaction. The crude cyclized product that was then eluted through a

297 plug of silica with pentane to remove any nickel salts was concentrated and further analyzed by NMR and GC.

Analytical Data for Substrates

Diethyl 2,2-diallylmalonate 260a

EtO2C

EtO2C 1 H NMR (400 MHz, CDCl3) δ 5.64-5.54 (m, 2H), 5.06-5.01 (m, 4H), 4.11

3 3 (q, JH,H = 7.1 Hz, 4H), 2.58 (m, 4H), 1.27 (t, JH,H = 7.4 Hz, 6H).

13 C NMR (100 MHz, CDCl3) δ 170.8, 132.5, 119.2, 61.3, 57.4, 36.9, 14.3.

GC (methyl silicone column, 120 0 C/ Isotherm) RT for product = 8.59 min.

GC-MS m/z ([M+) 240.10; exact mass calculated for C13H20O4 = 240.14.

Dimethyl 2,2-diallylmalonate 260b

MeO2C

MeO2C 1 H NMR (400 MHz, CDCl3) δ 5.64-5.54 (m, 2H), 5.07-5.02 (m, 4H), 3.65

3 (s, 6H), 2.58-2.55 (m, 4H), 1.18 (t, JH,H = 7.1 Hz, 6H).

13 C NMR (100 MHz, CDCl3) δ 171.7, 132.8, 119.8, 58.2, 52.9, 37.5.

GC (methyl silicone column, 120 0 C/ Isotherm) RT for product = 5.08 min.

GC-MS m/z ([M+) 212.12; exact mass calculated for C11H16O4 = 212.10.

298

N-allyl-N-benzylprop-2-en-1-amine 260f

PhH2C N

1 H NMR (400 MHz, CDCl3) δ 7.37-7.31 (m, 4H), 7.28-7.25 (m, 1H),

3 5.96-5.86 (m, 2H), 5.24-5.15 (m, 4H), 3.60 (s, 2H), 3.12 (d, JH,H = 6.8 Hz, 4H).

13 C NMR (100 MHz, CDCl3) δ 140.0, 136.5, 129.5, 128.7, 127.4, 117.9, 58.1, 57.0.

GC (methyl silicone column, 180 0 C/ Isotherm) RT for product = 4.96 min.

GC-MS m/z ([M+) 187.10; exact mass calculated for C13H17N = 187.14.

N, N –diallyl benzene sulfonamide 260d

O S N O 1 H NMR (400 MHz, CDCl3) δ 7.81-7.79 (m, 2H), 7.55-7.46 (m, 3H),

3 5.63-5.53 (m, 2H), 5.14-5.10 (m, 4H), 3.80 (d, JH,H = 6.2 Hz, 4H).

13 C NMR (100 MHz, CDCl3) δ 140.0, 133.0, 132.9, 129.5, 127.6, 119.5, 49.8.

GC (methyl silicone column, 180 0 C/ Isotherm) RT for product = 12.49 min.

GC-MS m/z ([M+) 237.10; exact mass calculated for C12H15NO2S = 237.08.

299

N, N –diallyl p-toluene sulfonamide 261e

O S N O 1 3 H NMR (400 MHz, CDCl3) δ 7.69 (d, JH,H = 8.2 Hz, 2H), 7.28

3 3 (d, JH,H = 6.2 Hz, 2H), 5.65-5.55 (m, 2H), 5.15-5.11 (m, 4H), 3.79 (d, JH,H = 6.3 Hz,

4H), 2.41 (s, 3H).

13 C NMR (100 MHz, CDCl3) δ 143.4, 137.6, 132.8, 129.8, 127.3, 119.1, 49.5, 21.6.

GC (methyl silicone column, 180 0 C/ Isotherm) RT for product = 8.81 min.

GC-MS m/z ([M+) 251.12; exact mass calculated for C13H17NO2S = 251.10.

N, N –Diallyl benzamide 260g

O C N

1 H NMR (400 MHz, CDCl3) δ 7.42-7.39 (m, 2H), 7.38-7.32 (m, 3H),

3 5.85 (br, s, 1H), 5.70 (br, s, 1H), 5.26-5.14 (m, 4H), 3.96 (d, JH,H = 6.2 Hz, 4H).

13 C NMR (100 MHz, CDCl3) δ 171.4, 135.9, 132.9, 132.5, 129.3, 128.0, 126.2, 117.3,

50.4, 46.6.

GC (methyl silicone column, 180 0 C/ Isotherm) RT for product = 8.27 min.

GC-MS m/z ([M+) 201.10; exact mass calculated for C13H15NO = 201.12.

300

N, N –Diallyl methane Sulfonamide

H3C S N O 1 H NMR (400 MHz, CDCl3) δ 5.80-5.69 (m, 2H), 5.23-5.18 (m, 4H),

3 3.78 (d, JH,H = 6.2 Hz, 4H), 2.81 (s, 3H).

13 C NMR (100 MHz, CDCl3) δ 132.6, 119.3, 49.1, 40.0.

GC (methyl silicone column, 150 0 C/ Isotherm) RT for product = 1.63 min.

GC-MS (methyl silicone): m/z ([M+) 175.10; exact mass calculated for C7H13NO2S =

175.07.

(1E,2E)-N1,N2-Bis(2,6-Diisopropylphenyl)Ethane-1,2-Diimine

N N

1 H NMR (400 MHz, CDCl3) δ 8.08 (s, 2H), 7.19-7.13 (m, 6H),

3 2.96-2.89 (m, 4H), 1.19 (d, JH,H = 6.8 Hz, 24H).

13 C NMR (100 MHz, CDCl3) δ 163.2, 148.2, 136.9, 125.3, 123.3, 28.2, 23.5.

301

1,3-Bis(2,6-Diisopropylphenyl)-1H-Imidazol-3-ium Chloride

N N

1 H NMR (400 MHz, CDCl3) δ 10.00 (s, 1H), 8.10 (s, 2H), 7.55 (t,

3 3 3 JH,H = 7.8 Hz, 2H), 7.33 (d, JH,H = 7.8 Hz, 4H), 2.47-2.40 (m, 4H), 1.27 (d, JH,H = 6.8

3 Hz, 12H), 1.23 (d, JH,H = 6.8 Hz, 12H).

13 C NMR (100 MHz, CDCl3) δ 144.9, 138.0, 132.0, 129.7, 126.6, 124.6, 29.0, 24.5, 23.7.

1,3-Bis(1-Adamantyl)Imidazolium Tetrafluoroborate

N N Ad Ad BF 1 4 H NMR (400 MHz, CDCl3) δ 10.77 (s, 1H), 7.35 (s, 2H), 2.36 (s, 18H),

3 1.82 (q, JH,H = 13.6 Hz, 12H).

13 C NMR (125 MHz, CDCl3) δ 132.6, 119.0, 65.7, 47.1, 38.8, 38.3, 37.3, 36.2, 35.9, 32.2,

28.8, 24.3.

Analytical Data for Cyclized Products

261b MeO2C MeO C 1 [12] 2 H NMR (CDCl3, 400 MHz): δ 4.91 (q, J = 2.1 Hz, 1 H), 4.80 (q, J = 2.1

Hz, 1 H), 3.73 (s, 3 H), 3.72 (s, 3 H), 3.04-3.08 (m, 1 H), 2.92-2.97 (m, 1 H), 2.53-2.59

(m, 2 H), 1.72-1.80 (m, 1 H), 1.10 (d, J = 6.3 Hz, 3 H).

13 C NMR (CDCl3, 100 MHz): δ 172.6, 172.5, 153.4, 105.8, 58.4, 53.0, 53.0, 42.5, 40.8,

37.5, 18.2.

GC (methyl silicone 120 °C): Rt 6.76 min. 302

262b

CO2Me CO Me 1 [21] 2 H NMR (CDCl3, 400 MHz). δ 4.73 (s, 2 H), 3.71 (s, 6 H), 3.72 (s, 3

H), 2.68 (s, 2 H), 2.10-2.13 (m, 2 H), 2.04-2.07 (m, 2 H), 1.63-1.69 (m, 2 H).

13 C NMR (CDCl3, 100 MHz): δ 171.8, 144.3, 110.9, 57.0, 52.7, 39.9, 34.1, 31.8, 31.4,

24.4, 22.9.

GC (methyl silicone 120 °C): Rt 7.69 min.

261a

EtO2C EtO C 1 [22] 2 H NMR (CDCl3, 400 MHz): δ 4.89-4.90 (m, 1 H), 4.78-4.79 (m, 1 H),

4.14-4.21 (m, 4 H), 3.01-3.06 (m, 1 H), 2.90-2.96 (m, 1 H), 2.51-2.57 (m, 2 H), 1.74-1.78

(m, 1 H), 1.21-1.25 (m, 6 H), 1.10 (d, J = 6.3 Hz, 3 H).

13 C NMR (CDCl3, 100 MHz): δ 172.2, 172.1, 153.7, 105.6, 61.6, 58.5, 42.3, 40.7, 37.5,

18.2, 14.2.

GC (methyl silicone 120 °C): Rt 11.59 min.

262a

CO2Et CO Et 1 [23] 2 H NMR (CDCl3, 400 MHz): δ 4.74 (s, 2 H), 4.13-4.21 (m, 4 H), 2.67 (s, 2

H), 2.10-2.14 (m, 2 H), 2.04-2.06 (m, 2 H), 1.64-1.70 (m, 2 H) 1.24 (t, J = 8.7 Hz, 6 H).

13 C NMR (CDCl3, 100 MHz): δ 171.4, 144.5, 110.7, 61.4, 56.8, 39.8, 34.2, 31.3, 24.4,

303

14.3.

GC (methyl silicone 120 °C): Rt 13.76 min.

261c

EtO C 2 1 H NMR (CDCl3, 400 MHz): δ 4.88-4.89 (m, 1 H, diastereomers), 4.79-

4.80 (m, 1 H, diastereomers), 4.10-4.17 (m, 2 H, diastereomers), 2.84-2.91 (m, 0.27 H),

2.73-2.82 (m, 0.73 H), 2.57-2.69 (m, 2 H), 2.11-2.27 (m, 1 H), 1.64-1.71 (m, 1 H), 1.58-

1.60 (m, 1 H), 1.24-1.27 (m, 3 H, diastereomers), 1.12 (d, J = 6.6 Hz, 3 H, one diastereomer), 1.065 (d, J = 6.8 Hz, 3 H, one diastereomer).

13 C NMR (CDCl3, 100 MHz): δ 176.2, 175.7, 156.0, 155.3, 105.0, 105.0, 60.6, 42.6, 42.0,

41.6, 39.2, 39.1, 38.2, 37.5, 36.5, 36.4, 22.6, 19.6, 18.3, 14.5, 14.3, 13.7.

GC (methyl silicone 90 °C): Rt 7.099 mins & 7.395 min.

262c

CO Et 1 [24] 2 H NMR (CDCl3, 400 MHz): δ 4.68 (s, 2 H), 4.10-4.16 (s, 2 H), 2.47-2.51

(m, 1 H), 2.33-2.40 (m, 1 H), 2.17-2.29 (m, 2 H), 1.93-2.02 (m, 2 H), 1.82-1.89 (m, 1 H),

1.67-1.69 (m, 1 H), 1.54-1.60 (m, 1 H), 1.24-1.28 (m, 3 H).

13 C NMR (CDCl3, 100 MHz): δ 175.5, 147.2, 108.8, 60.5, 44.6, 43.6, 37.5, 34.6, 28.9,

26.8, 14.5.

GC (methyl silicone 90 °C): Rt 8.44 min.

304

261d

Ph O S N 2 1 13 H NMR (CDCl3, 400 MHz): δ 7.82-7.85 (m, 2 H), 7.59-7.63 (m, 1 H),

7.52-7.56 (m, 2 H), 4.90-4.92 (m, 1 H), 4.84-4.87 (m, 1 H), 3.94-3.99 (m, 1 H), 3.74-3.79

(m, 1 H), 3.58-3.62 (m, 1 H), 2.70-2.74 (m, 1 H), 2.64-2.68 (m, 1 H), 1.04 (d, J = 6.5 Hz,

3 H).

13 C NMR (CDCl3, 100MHz): δ 149.4, 136.3, 133.0, 129.3, 127.9, 106.3, 55.3, 52.3, 37.7,

16.3.

GC (methyl silicone 180 °C): Rt 9.131 min.

262d & 261d

N Ph SO2 + O S N 2 1 [25] Ph H NMR (CDCl3, 400 MHz): δ 7.78-7.84 (m, 2 H, 6 & 5 member ring), 7.49-7.62 (m, 2 H, 6 & 5 member ring), 4.90-4.92 (m, 1 H, 6 & 5 member ring), 4.84-4.87 (m, 1 H, 5 member ring), 4.81-4.82 (m, 1 H, 6 member ring), 3.94-3.99

(m, 1 H, 5 member ring), 3.74-3.79 (m, 1 H, 5 member ring), 3.58-3.62 (m, 1 H, 5 member ring), 3.54 (s, 2 H, 6 member ring), 3.10 (t, J = 5.5 Hz, 2 H, 6 member ring),

2.70-2.74 (m, 1 H), 2.64-2.68 (m, 1 H), 2.09-2.12 (m, 2 H, 6 member ring), 1.66-1.72 (m,

13 2 H, 6 member ring), 1.04 (d, J = 6.5 Hz, 3 H, 5 member ring). C NMR (CDCl3,

100MHz): 6 member ring: δ 140.7, 136.6, 132.9, 129.2, 128.0, 112.0, 52.6, 46.6, 32.2,

25.9. GC (methyl silicone 180 °C): Rt 9.131 mins (261d) and 9.978 mins (262d).

305

261e

4-Tol O S N 2 1 [12] H NMR (CDCl3, 400 MHz): δ 7.70-7.72 (m, 2 H), 7.32-7.34 (m, 2 H),

4.89-4.91 (m, 1 H), 4.84-4.86 (m, 1 H), 3.96-3.97 (m, 1 H), 3.72-3.76 (m, 1 H), 3.54-3.61

(m, 1 H), 2.66-2.72 (m, 2 H), 2.43 (s, 3 H), 1.04 (d, J = 6.5 Hz, 3 H).

13 C NMR (CDCl3, 100 MHz): δ 149.6, 143.8, 140.6, 133.2, 129.9, 128.0, 106.2, 55.3,

52.4, 37.7, 21.8, 16.3.

GC (methyl silicone 180 °C): Rt 13.350 mins

261e & 262e

4-Tol N + SO2 O2S N 4-Tol 1 7 H NMR (CDCl3, 400MHz): δ 7.68-7.72 (m, 2 H, 5 member ring), 7.65-7.68 (m, 2 H, 6 member ring), 7.32-7.33 (m, 2 H, 6 & 5 member ring), 4.89-

4.91 (m, 1 H, 6 & 5 member ring), 4.84-4.86 (m, 1 H, 5 member ring), 4.81-4.82 (m, 1 H,

6 member ring), 3.93-3.97 (m, 1 H, 5 member ring), 3.72-3.76 (m, 1 H, 5 member ring),

3.56-3.60 (m, 1 H, 5 member ring), 3.51 (s, 2 H, 6 member ring), 3.08 (t, J = 5.5 Hz, 2 H,

6 member ring), 2.65-2.72 (m, 2 H, 5 member ring), 2.43 (s, 3 H, 6 & 5 member ring),

2.09-2.12 (m, 2 H, 6 member ring), 1.66-1.72 (m, 2 H, 6 member ring), 1.04 (d, J = 6.5

Hz, 3 H, 5 member ring).

13 C NMR (CDCl3, 100 MHz): 6 member ring: δ 143.7, 140.9, 133.5, 129.0, 128.0, 112.0,

52.6, 46.6, 32.2, 25.9, 21.7.

GC (methyl silicone 180 °C): Rt 13.35 min (261e) and 14.667 min (262e). 306

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