Rhenium and ruthenium catalyzed processes involving organosilanes 1

I would also like to thank Mdm Han Yanhui from the Chemistry Department NMR Laboratory, Mdm Patricia Tan from the Physical Chemistry Laboratory, and also to the various staffs of the Che

Acknowledgement

Firstly, I would like to thank both of my supervisors and mentors, Assoc Prof Ang Siau Gek and Assoc Prof Fan Wai Yip for their patience, dedication and guidance from the initial to the final stages of my project Without their guidance,

it would not be possible for me to be able to understand and develop this project I

am grateful for their constant encouragements and patience which they have given

me through the years

My research experience in NUS would not have been as enjoyable and fulfilling without my fellow group members; Tan Sze Tat, Kee Jun Wei, Tan Kheng Yee Desmond, Fong Wai Kit, Chong Che Chang, Sum Yin Ngai, Lim Ching Si, Sim Bai Ting, Lim Xiao Zhi, Tan Yong Yao and Goh Wei Bin It is a pleasure to be able to work in the same lab as them, and I sincerely thank them for their help and support through these years

I would also like to thank Mdm Han Yanhui from the Chemistry Department NMR Laboratory, Mdm Patricia Tan from the Physical Chemistry Laboratory, and also to the various staffs of the Chemistry Department who have helped me in one way or another

Most importantly, I would like to acknowledge the continuous support that my family has given me Of which without their persistent encouragements, I would not be able to persevere through this course of study

Thesis Declaration

The work in this thesis is the original work of Toh Chun Keong, performed

independently under the supervision of A/P Fan Wai Yip, (in the IR and Laser

Research Laboratory), Chemistry Department, National University of Singapore,

between 3 August 2009 and 2 August 2012

Toh Chun Keong

Table of Contents

1.1 Organometallic Compounds in Catalysis 2

1.3.1 Catalytic Hydrosilylation of Carbonyls via Re(CO)5Cl Photolysis 12

1.3.2 Ruthenium Carbonyl-Catalyzed Si-X Coupling (X = S, O, N) 13

CHAPTER 2 Catalytic Hydrosilylation of Carbonyls via

19

2.2.1 Hydrosilylation of Silanes with Aldehydes and Ketones 21 2.2.2 Hydrosilylation of Esters and Carbonates 24 2.2.3 Comparison of Hydrosilylation Rates for Different Carbonyls 26

CHAPTER 3 Ruthenium Carbonyl-Catalyzed Si-X Coupling (X

= S, O, N)

45

3.2.1 Reactive Intermediates and Mechanism 51

3.2.2 Calculations 56

Summary

The hydrosilylation reaction between silanes and various carbonyl substrates has been catalysed by Re(CO)5Cl uv-photolysis Kinetic studies have shown that the reaction is favoured for the least sterically-hinderd silanes with aldehydes The IR spectrum of a rhenium carbonyl dimer HRe2(CO)9(SiR3) has been recorded in the reaction mixture and is believed to be the resting state of the active catalyst Re(CO)4SiR3 A catalytic mechanism has been proposed and supported by computational studies, which can also be used to explain relative hydrosilylation rates among various carbonyl substrates

Ru3(CO)12 has been shown to catalyze the coupling of silanes with thiols, alcohols and amines with turnover number and turnover frequency of up to 200 and

50 hr-1 at 80oC IR, NMR and mass spectroscopic studies have identified a ruthenium dimer complex, [Ru(CO)4(SiEt3)]2 as a likely resting state of the catalyst

A mechanism involving this complex has been proposed for the silicon-thiol coupling process with supporting evidence from computational studies