Lewis Acid Activated Olefin Metathesis Catalysts by Adam Michael McKinty A thesis submitted in conformity with the requirements for the degree of Doctor of Philosophy Department of Chemistry University of Toronto © Copyright by Adam Michael McKinty 2014 Lewis Acid Activated Olefin Metathesis Catalysts Adam Michael McKinty Doctor of Philosophy Department of Chemistry University of Toronto 2014 Abstract Since its discovery, catalytic olefin metathesis has been used as a powerful tool for the synthesis of a variety of molecules. Over the last 20 years research in this area has received enormous attention in the development of new catalysts and applications. The vast majority of the ruthenium based catalysts developed have been modifications to the Grubbs Catalyst type architecture. The research presented herein focuses on the development of new olefin metathesis catalysts bearing tridentate, dianionic ligands and their activation with Lewis acids. Complexes [(PPh3)2Ru(SCH2CH2)2O] and [(PPh3)2Ru(SC6H4)2O] were synthesized from (PPh3)3RuCl2 and the corresponding dilithio-dithiolate salt or from (PPh3)4RuH2 and the corresponding dithiol. These complexes were shown to react with BCl3 forming complexes [(PPh3)2RuCl(Cl2B(SCH2CH2)2O)] and [(PPh3)2RuCl(Cl2B(SC6H4)2O)]. Complexes of the general structure [LRu(CHPh)(SC6H4)2O] and [LRu(CHPh)(XCH2CH2)2E] where L = PCy3, SIMes, X = O, S, and E = O, S, PPh were prepared by ligand exchange with Grubbs I and II. Alternatively, complexes [LRu(CHPh)(SC6H4)2O] and [LRu(CHPh)(SCH2CH2)2E] where L = PCy3, SIMes and E = O, S were synthesized independently of Grubbs Catalyst by the reaction of dithioacetals with Ru(0) sources. These complexes proved to be inactive for catalytic olefin metathesis. ii The addition of BCl3 to these complexes resulted in the formation of new 6-coordinate ruthenium alkylidene complexes of the general formula [LRuCl(CHPh)(Cl2B(SC6H4)2O)] and [LRuCl(CHPh)(Cl2B(XCH2CH2)2E)] where L = PCy3, SIMes, X = O, S, and E = O, S, PPh. These complexes also proved to be inactive for olefin metathesis. The addition of a second equivalent of BCl3 results in the formation of 5-coordinate cationic ruthenium species of the general formula [LRu(CHPh)(Cl2B(SC6H4)2O)][BCl4] and [LRu(CHPh)(Cl2B(XCH2CH2)2E)][BCl4] where L = PCy3, SIMes, X = O, S, and E = O, PPh. These cationic species proved to be active for a variety of olefin metathesis reactions including ring closing metathesis (RCM), ring opening metathesis polymerization (ROMP) and cross metathesis (CM). iii Acknowledgments First and foremost I would like to thank Professor Doug Stephan for giving me the opportunity to complete my degree in his group. His contagious enthusiasm, vast knowledge and continuous support were invaluable in the completion and success of my degree. My grad school experience has been nothing but a positive one. I am truly grateful for the experiences and opportunities Doug gave me and I will always look back on my time in his group as a great chapter in my life. I would also like to thank the Stephan group members, past and present, for their helpful discussions, advice and friendship. I learned a lot from each one of them and they made a huge contribution to my success. Outside of the lab I am thankful I could always count on them to keep a healthy work-life balance. I would like to thank my best friend and partner, Sanja for all her support and patience throughout my degree. Her love and encouragement provided me with the strength and determination to succeed and I could always count on her to provide support during difficult times. Thank you so much. Finally, I would like to thank my family for their unconditional support over the years. Specifically I would like to thank my parents, Mike and Shirley McKinty. Without their encouragement, support and love none of this would have been possible. I am extremely grateful for the opportunities they've given me and the sacrifices they've made to enable me to pursue my education. iv Table of Contents Acknowledgments .......................................................................................................................... iv Table of Contents ............................................................................................................................ v List of Tables ................................................................................................................................. ix List of Schemes .............................................................................................................................. xi List of Figures .............................................................................................................................. xiv List of Abbreviations ................................................................................................................. xviii Chapter 1 Introduction .................................................................................................................... 1 1.1 Catalysis .............................................................................................................................. 1 1.2 Catalytic Olefin Metathesis ................................................................................................. 1 1.2.1 Heterogenous Catalysis ........................................................................................... 1 1.2.2 Well-Defined Homogenous Catalysts ..................................................................... 2 1.2.3 Mechanism of Catalytic Olefin Metathesis ............................................................. 4 1.2.4 Variations of Grubbs Catalyst ................................................................................. 6 1.2.5 Z-selective Olefin Metathesis ................................................................................. 7 1.3 Lewis Acid Activation of Catalysts .................................................................................... 9 1.4 Nitrile Butadiene Rubber .................................................................................................... 9 1.5 Lanxess Project ................................................................................................................. 11 1.6 Scope of this Thesis .......................................................................................................... 11 Chapter 1 References .................................................................................................................... 14 Chapter 2 Coordination Chemistry of Tridentate, Dithiolate Ligands ......................................... 18 2.1 Introduction ....................................................................................................................... 18 2.1.1 Thiolate Ligands in Metal Complexes .................................................................. 18 2.2 Results and Discussion ..................................................................................................... 22 2.2.1 Synthesis of Ru Complexes .................................................................................. 22 v 2.2.2 Reactivity of Complexes with BCl3 ...................................................................... 25 2.3 Conclusion ........................................................................................................................ 27 2.4 Experimental Section ........................................................................................................ 28 2.4.1 General Considerations ......................................................................................... 28 2.4.2 Synthetic Procedures ............................................................................................. 28 Chapter 2 References .................................................................................................................... 31 Chapter 3 Ruthenium Alkylidene Complexes with Tridentate, Dianionic Ligands ..................... 33 3.1 Introduction ....................................................................................................................... 33 3.1.1 Modifications to Grubbs Catalyst ......................................................................... 33 3.1.2 Halide Variations in Grubbs Catalyst ................................................................... 34 3.1.3 Pseudo-halides as Ligands on Ruthenium Metathesis Catalysts .......................... 35 3.1.4 Bidentate Monoanionic Ligands on Ruthenium Metathesis Catalysts ................. 36 3.1.5 Bidentate Dianionic Ligands on Ruthenium Metathesis Catalysts ....................... 37 3.1.6 Tridentate Ligands on Ruthenium Alkylidene Complexes ................................... 38 3.2 Results and Discussion ..................................................................................................... 38 3.2.1 Synthesis of Ruthenium Alkylidene Complexes .................................................. 38 3.3 Conclusions ....................................................................................................................... 48 3.4 Experimental Section ........................................................................................................ 49 3.4.1 General Considerations ......................................................................................... 49 3.4.2 Synthetic Procedures ............................................................................................. 49 3.4.3 X-ray Crystallography .........................................................................................