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Permanent link (DOI): https://doi.org/10.7939/R33776137

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Mixed-Valence First-Row Metal Clusters for Catalytic Hydrodesulfurization and Hydrodeoxygenation Open Access

Descriptions

Other title
Subject/Keyword
Catalysis
First-Row Metal
Mixed-Valence
Hydrodeoxygenation
Cluster
Hydrodesulfurization
Type of item
Thesis
Degree grantor
University of Alberta
Author or creator
Brown, Houston J. S.
Supervisor and department
Stryker, Jeffrey (Chemistry)
Examining committee member and department
Heinekey, D. Michael (Chemistry, University of Washington)
Stryker, Jeffrey (Chemistry)
Takats, Josef (Chemistry)
West, Frederick (Chemistry)
de Klerk, Arno (Chemical and Materials Engineering)
Department
Department of Chemistry
Specialization

Date accepted
2013-09-30T11:51:50Z
Graduation date
2013-11
Degree
Doctor of Philosophy
Degree level
Doctoral
Abstract
Salt metathesis between CoCl2 and [KNPEt3]n provides a new route to the halide-substituted cobalt phosphoranimide cluster [CoCl(NPEt3)]4. This cluster is a useful precursor for the preparation of alkyl-capped cobalt phosphoranimide complexes. The methylated heterocubane [CoMe(NPEt3)]4 was synthesized in high yield by transmetallation of [CoCl(NPEt3)]4 with Me2Mg•dioxane in dioxane. The structural, magnetic, and electrochemical properties of the cluster have been rigorously evaluated. The type (III) mixed-valence cluster [CoMe(NPEt3)]4PF6 was prepared from [CoMe(NPEt3)]4 by outer-sphere electron transfer with Cp2FePF6. The cationic cluster has been fully characterized. Both [CoMe(NPEt3)]4 and [CoMe(NPEt3)]4PF6 are active precatalysts for reductive C–S bond cleavage. The catalytic activity of [CoMe(NPEt3)]4PF6 has been investigated in more detail. Under basic conditions, the mixed-valence cluster catalyzes the complete hydrodesulfurization of a number of organosulfur compounds under mild conditions (110–170°C, 1 atm H2): dibenzothiophene, 4,6-diethyldibenzothiophene, benzothiophene, 3-hexylthiophene, diphenyl sulfide, benzyl phenyl sulfide, and phenoxathiin. In all instances no products indicative of aromatic ring hydrogenation were noted. The desulfurization of dibenzothiophene was investigated over a range of temperatures. A preliminary mechanistic ‗road map‘ for the reaction was proposed. The mixed valence cluster [CoMe(NPEt3)]4PF6 also catalyzes C–O bond hydrogenolysis of unstrained ethers. Aromatic, benzyl, and aliphatic C–O bonds are all cleaved under mild conditions. The substrate scope includes diphenyl ether, 4-methoxybiphenyl, 2,3- dihydrobenzofuran, 1,3-bis(4-methoxyphenoxy)benzene, dibenzofuran, and benzofuran. In no case were products indicative of aromatic ring hydrogenation noted. Catalytic hydrogenolysis in the presence of the Lewis acid AlMe3 results in higher turnover frequencies than those not including AlMe3. The presence of the Lewis acid also promoted further C–O bond reductions to give complete hydrodeoxygenation of resistant substrates.
Language
English
DOI
doi:10.7939/R33776137
Rights
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. 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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