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First-Row Transition Metal-Mediated Reactions: Catalytic Ester Hydrogenolysis, Aerobic Alkane Oxidation, and [5+2] Ring-Expansion Reactions Open Access


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Type of item
Degree grantor
University of Alberta
Author or creator
Yu, Shaohui
Supervisor and department
Stryker, Jeffrey (Chemistry)
Examining committee member and department
Clive, Derrick (Chemistry)
Arndtsen, Bruce (Chemistry)
Rivard, Eric (Chemistry)
West, Frederick (Chemistry)
McCaffrey, William (Engineering)
Department of Chemistry

Date accepted
Graduation date
Doctor of Philosophy
Degree level
The research described in this dissertation focuses on first-row transition metal catalyzed and mediated organic reactions. The first part of the thesis involves the exploration of the catalytic reactivity of phosphoranimide-supported tetrametallic nickel and cobalt clusters, while the second part focuses on the development of stoichiometric cobalt/iron-mediated ring-expansion reactions. The ester hydrogenolysis reactions catalyzed by the new nickel cluster proceeded under remarkably mild conditions. Both nickel and cobalt catalysts show unique selectivity for ester sp3 C–O bond activation, affording the corresponding carboxylic acids and alkanes by simple hydrogenolysis. Other relevant reactions catalyzed by this cluster include ketone hydrogenation and an unprecedented new reduction of benzyl aldehyde, in which sequential Tishchenko and ester reduction reactions are involved. The catalytic aerobic alkane oxidation reactions were developed, remarkably, using the same nickel and cobalt clusters. Despite the air-sensitive nature of the clusters, the air-oxidized catalysts mediate aerobic oxidation, activating sp3 C–H bonds in hydrocarbons and functionalized organics to afford mainly ketones at elevated temperatures. The investigated substrates include alkyl arenes, ethers and non-functionalized hydrocarbons. Oxidation occurs selectively at the methylene positions α to the activating groups, which include either phenyl groups or oxygen atoms. For alkanes, tertiary C–H bonds appear to be more reactive than secondary C–H bonds, suggesting a free radical process, at least at some point(s) in the overall transformation. For cobalt-mediated [5+2] cyclopentenyl/alkyne ring-expansion reactions, the narrow substrate scope defined in previous studies limits the potential for developing applications. Two synthetic routes for preparing unsymmetrical cobalt(I) cyclopentadiene precursors were examined, including reduction of unsymmetrical cobaltocenium compounds and replacement of ethylene ligands with cyclopentadiene in cobalt(I) bisethylene complexes. The attempted [5+2] ring-expansion reactions afford unsymmetrical cobaltocenium compounds as the major products, instead of the desired seven-membered ring formation. Based on DFT calculations conducted by Salai and Nakamura, a new strategy for [5+2] ring-expansion reaction was proposed. Instead of η4-cyclopentadiene cobalt (I) complexes, an α-diimine iron(0) alkyne complex is protonated in the presence of cyclic alkene. However, the reaction generates an ammonium derivative from ligand reduction and no ring-expansion products are obtained. New ligand design is required for the further investigations.
Permission is hereby granted to the University of Alberta Libraries to reproduce single copies of this thesis and to lend or sell such copies for private, scholarly or scientific research purposes only. Where the thesis is converted to, or otherwise made available in digital form, the University of Alberta will advise potential users of the thesis of these terms. The author reserves all other publication and other rights in association with the copyright in the thesis and, except as herein before provided, neither the thesis nor any substantial portion thereof may be printed or otherwise reproduced in any material form whatsoever without the author's prior written permission.
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