Ruthenium Olefin Metathesis Complexes: Catalyst Development and Mechanistic Studies

Citation

Anderson, Donde R. (2008) Ruthenium Olefin Metathesis Complexes: Catalyst Development and Mechanistic Studies. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/6B6N-2V77. https://resolver.caltech.edu/CaltechETD:etd-08142007-151304

Abstract

The field of olefin metathesis has grown to include organometallic chemists who strive to develop more efficient catalysts and to understand their mechanism of activity and decomposition, synthetic organic chemists who construct complex molecules utilizing existing catalysts and continually find challenging reactions in need of more efficient catalysts, and polymer chemists who utilize current catalysts to synthesize polymers with an ever-widening array of functional groups and structures in a controlled manner. This thesis describes the exploration of new ligands for olefin metathesis catalysts and the investigation of the model compounds of olefin metathesis reaction intermediates.

Chapter 2 describes the synthesis, characterization, activity and kinetic selectivity of ruthenium olefin metathesis complexes bearing cyclic (alkyl)(amino)carbenes (CAACs). The activity of phosphine-free CAAC-ruthenium complexes is significantly affected by steric interactions. By decreasing the steric bulk of the ligand, a new catalyst with activity comparable to that of existing NHC-ruthenium (N-heterocyclic carbene) complexes has been synthesized. Additionally, these complexes exhibit unusual E/Z-diastereoselectivity and ethenolysis selectivity relative to previously studied NHC-ruthenium complexes.

Chapter 3 describes the exploration of 3- and 6-membered carbenes as ligands for ruthenium olefin metathesis complexes. Stable silver-cyclopropenylidene adducts were synthesized and utilized as carbene transfer reagents in the presence of ruthenium precursors. Although good conversions were observed, isolation of cyclopropenylidene-ruthenium complexes was unsuccessful. Ruthenium complexes of 6-membered ‘borazine’-like carbenes were isolated, characterized and evaluated for ring-closing metathesis activity.

Chapter 4 describes the development of a model system to study ruthenium-olefin complexes relevant to the mechanism of olefin metathesis. Upon addition of the ligand precursor 1,2-divinylbenzene to (H₂IMes)(py₂)(Cl)₂Ru=CHPh (H₂IMes = 1,3-dimesityl-4,5-dihydroimidazol-2-ylidene), two ruthenium-olefin adducts are formed. Based on ¹H NMR spectroscopy experiments and X-ray crystallographic analysis, the solution phase and solid-state structure of these complexes is assigned. Exploration of the generality of these observations through variation of the N-heterocyclic carbene ligand and the ligand precursor are also presented.

Appendix 1 describes the screening of transitional-metal salts and ligands for the non-oxidative hydration of styrene. Appendix 2 describes the investigation of a prior report of intramolecular olefin hydroalkoxylation with ruthenium, copper and silver salts. Appendix 3 describes the evaluation of chiral NHCs as ligands for ruthenium and rhodium hydrosilylation catalysts. Appendix 4 describes the investigation of tin(II) halides as ligands for ruthenium olefin metathesis catalysts. Appendix 5 contains X-ray crystallographic analysis parameters of the structures presented in this thesis.

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