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Date Permissions Signed

5-28-2021

Date of Award

Spring 2021

Document Type

Masters Thesis

Department or Program Affiliation

Chemistry

Degree Name

Master of Science (MS)

Department

Chemistry

First Advisor

O'Neil, Gregory (Gregory W.)

Second Advisor

Vyvyan, James R.

Third Advisor

Scheuermann, Margaret Louise

Abstract

Olefin metathesis is a reaction that creates new carbon-carbon double bonds by rearranging two alkenes. The reaction has undergone significant development since its discovery in the 1950s, from first reports to new catalysts and industrial uses, culminating in the 2005 Nobel Prize in chemistry. Grubbs ruthenium-based catalysts are widely used for such reactions, including ring closing metathesis (RCM) that involves the rearrangement of two alkenes on a single molecule to form a ring. During the course of investigating RCM reactions to produce eight-membered ring silyl ethers, we observed double bond isomerization when using the second-generation Grubbs catalyst and the Hoveyda-Grubbs catalyst but not the first-generation Grubbs catalyst. Isomerization during metathesis reactions can be problematic, giving undesired products and signaling catalyst degradation. If controllable, however, tandem metathesis/isomerization can be of value to make compounds that would otherwise be difficult to prepare. For this reason, the RCM/isomerization we observed was studied in detail. The impact of temperature, solvent, time, and additives on the distribution of isomerized and non-isomerized products were investigated. By monitoring the reaction via nuclear magnetic resonance (NMR) at different reaction times, we were able to conclude that ring closure generally occurs first, followed by isomerization of the double bond in the ring. For systems where a single isomerization event results in formation of a silyl enol ether, this was the major product obtained (which we explain as being driven by thermodynamics). However, the direction of isomerization when using the Grubbs second-generation catalyst was not entirely selective, giving a mixture of regioisomers representing both kinetic and thermodynamic products. This thesis describes investigations aimed at understanding what drives the isomerization (e.g. the catalyst species responsible, substrate structure considerations, reaction conditions) and whether we can control the direction of isomerization.

Type

Text

Keywords

Olefin metathesis, ring closing metathesis, isomerization, Grubbs catalyst

Publisher

Western Washington University

OCLC Number

1254087312

Subject – LCSH

Alkenes; Isomerization; Metathesis (Chemistry); Ruthenium catalysts

Format

application/pdf

Genre/Form

masters theses

Language

English

Rights

Copying of this document in whole or in part is allowable only for scholarly purposes. It is understood, however, that any copying or publication of this document for commercial purposes, or for financial gain, shall not be allowed without the author’s written permission.

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