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Exploring New Synthetic Routes to Frustrated Lewis Pairs

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Exploring New Synthetic Routes to Frustrated Lewis Pairs Exploring New Synthetic Routes to Frustrated Lewis Pairs by Cheryl Anne Tanur A thesis submitted in conformity with the requirements for the degree of Master of Science Department of Chemistry University of Toronto © Copyright by Cheryl Anne Tanur 2011 Exploring New Synthetic Routes to Frustrated Lewis Pairs Cheryl Anne Tanur Master of Science Department of Chemistry University of Toronto 2011 Abstract Gold(I) and copper(I) imidazolium complexes were synthesized and probed for use as bulky Lewis acids in frustrated Lewis pairs (FLPs) with bulky phosphines and amines. Their reactivity with small molecules was investigated and the compounds were fully characterized by multinuclear NMR spectroscopy, elemental analysis and X-ray crystallography. Secondly, a new methylene-linked boron sulfur Lewis acid was synthesized. Its thermodynamic properties were determined and its reactivity with terminal and internal alkynes was demonstrated. Adducts and heterocycles of this boron sulfur system were fully characterized by multinuclear NMR spectroscopy, elemental analysis and X-ray crystallography. The application of these new systems for the activation of small molecules is described in this thesis. ii Acknowledgments First and foremost I would like to thank my supervisor, Prof. Doug Stephan, for presenting me with this wonderful opportunity to perform research in his lab. I immensely enjoyed my time at the University of Toronto and learned a lot with the aid of his ideas and suggestions about my projects. I would also like to thank Gabriel Menard and Shokei Zhao for all of their help in the lab and their willingness to help me. Moreover, I would like to thank Dr. Sharonna Greenberg, Rebecca Neu and Dr. Clinton Lund for their chemistry knowledge, Christopher Brown and Michael Sgro for their endless help with X-ray crystallography, and Dr. Zachariah Heiden for his help with the Van’t Hoff calculations. The editing help of Dr. Renan Cariou, Dr. Sharonna Greenberg, Fatme Dahcheh, Stephanie Granville, and Christopher Cap uto is also greatly appreciated. In addition, thanks to Prof. Doug Stephan and Prof. Datong Song for their final edits of this thesis. I would also like to thank everyone in the Stephan Research Group for their moral support and all of the laughs. Lastly, I want to thank my parents, my older brother Luke and my older sister Adrienne for their unwavering support throughout my life. Without them, I would not be the person I am today. iii Table of Contents Acknowledgments.......................................................................................................................... iii Table of Contents ............................................................................................................................iv List of Tables ................................................................................................................................ vii List of Figures ............................................................................................................................... vii List of Schemes ................................................................................................................................x List of Abbreviations and Symbols.............................................................................................. xiii 1 Introduction .................................................................................................................................1 1.1 Overview of Frustrated Lewis Pairs ....................................................................................1 1.2 Frustrated Lewis Pairs: Hydrogenation ...............................................................................3 1.3 Frustrated Lewis Pairs: Small Molecule Activation ............................................................5 1.4 Frustrated Lewis Pairs: New Directions ..............................................................................7 2 Gold(I) and Copper(I) Imidazolium Complexes .......................................................................10 2.1 Introduction ........................................................................................................................10 2.2 Results and Discussion ......................................................................................................13 2.2.1 Gold(I) and Copper(I) Imidazolium Complexes....................................................13 2.2.2 Reactions with Small Molecules............................................................................24 2.3 Conclusions ........................................................................................................................27 2.4 Experimental ......................................................................................................................27 2.4.1 General Considerations ..........................................................................................27 2.4.2 Synthesis and Characterization of Gold(I) Imidazolium Complexes ....................28 2.4.3 Synthesis and Characterization of Copper(I) Imidazolium Complexes ................31 2.4.4 Experimental Considerations for Imidazolium Complexes ...................................35 2.4.5 X-ray Data Collection, Reduction, Solution and Refinement................................35 3 Boron-Sulfur Linked Lewis Acid..............................................................................................40 iv 3.1 Introduction ........................................................................................................................40 3.2 Results and Discussion ......................................................................................................43 3.2.1 Synthetic Routes to Boron-Sulfur Linked Lewis Acid ..........................................43 3.2.2 Thermodynamics of Boron-Sulfur Linked Lewis Acid .........................................47 3.2.3 FLP Reactivity .......................................................................................................49 3.2.4 Adduct Formations.................................................................................................50 3.2.5 Reactions of Internal and Terminal Alkynes .........................................................52 3.3 Conclusions ........................................................................................................................61 3.4 Experimental ......................................................................................................................61 3.4.1 General Considerations ..........................................................................................61 3.4.2 Synthesis and Characterization of Boron-Sulfur Linked Lewis Acid ...................62 3.4.3 Thermodynamic Calculations for (11) ...................................................................65 3.4.4 Synthesis and Characterization of Phosphine Adducts..........................................66 3.4.5 Synthesis and Characterization of Five-membered Boron-Sulfur Heterocycles ...68 3.4.6 X-ray Data Collection, Reduction, Solution and Refinement................................71 4 Summary and Conclusions........................................................................................................74 Appendix A: Thermodynamic studies of B(C6F5)3·SMe2 ..............................................................75 A.1 Introduction ........................................................................................................................75 A.2 Experimental ......................................................................................................................75 A.2.1 General Considerations ..........................................................................................75 A.2.2 Synthesis of B(C6F5)3·SMe2 ...................................................................................76 A.3 Results and Discussion ......................................................................................................76 A.3.1 Reactions with Hydrogen.......................................................................................76 A.3.2 Thermodynamics of B(C6F5)3·SMe2 ......................................................................78 A.4 Conclusion .........................................................................................................................82 v References ......................................................................................................................................83 vi List of Tables Table 2.1 Selected bond lengths (Å) and bond angles ( ) of (1)....................................................17 Table 2.2 Selected bond lengths (Å) and bond angles ( ) of (2) and (3) .......................................18 Table 2.3 Bond lengths (Å) and bond angles ( ) involved in anagostic interactions in (2) and (7) ........................................................................................................................................................19 Table 2.4 Selected bond lengths (Å) and bond angles ( ) of (7)....................................................20 Table 2.5 Selected bond lengths (Å) and bond angles ( ) of (4) and (9) .......................................22 Table 2.6 Selected bond lengths (Å) and bond angles ( ) of (10)..................................................23 Table 2.7 Crystallographic data for compounds (1)–(3)................................................................37
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