Improvement of Olefin Metathesis Efficiency through Understanding Catalyst Stability

Abstract

The recent development of ruthenium olefin metathesis catalysts, which show high activity and functional group tolerance, has expanded the scope of olefin metathesis. To improve efficiency of the ruthenium-catalyzed olefin metathesis, this dissertation describes: (1) mechanistic study to understand decomposition pathways of ruthenium olefin metathesis catalysts for the development of more stable and efficient catalysts, (2) a method to prevent an undesirable side reaction for the improvement of selectivity of ruthenium-catalyzed olefin metathesis, and (3) a novel ruthenium catalyst to increase olefin metathesis efficiency in aqueous media for potential biological applications and environmentally friendly approaches to this chemistry. Chapter 2 describes the first well-characterized decomposition products, dinuclear ruthenium hydride complex and methylphosphonium salt, from an N-heterocyclic carbene-based ruthenium catalyst under typical metathesis conditions. In Chapter 3, the decomposition study was expanded to other widely used ruthenium olefin metathesis catalysts. Phosphine-involvement in the decomposition was consistently observed whether or not an olefin was present. The presence of other decomposition modes for phosphine-free ruthenium catalysts was also described. Chapter 4 addresses another decomposition pathway of an N,N’-diphenylbenzimidazol-2-ylidene-based catalyst via C--H activation. Chapter 6 describes the development of a novel poly(ethylene glycol)-supported water-soluble catalyst, which is active and stable in aqueous media. Chapter 7 describes an efficient, practical, and environmentally friendly method to remove residual ruthenium-containing byproducts by simple aqueous workup from olefin metathesis products using the poly(ethylene glycol)-supported catalyst.