Mechanistic Studies of Rhodium Oxidation Catalysts
Nyberg, Eric David
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https://hdl.handle.net/2142/70202
Description
Title
Mechanistic Studies of Rhodium Oxidation Catalysts
Author(s)
Nyberg, Eric David
Issue Date
1982
Department of Study
Chemistry
Discipline
Chemistry
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Chemistry, Inorganic
Abstract
Over the past eight years a number of catalytic processes for the O(,2) oxidation of terminal olefins have been proposed to proceed through non-free radical, non-Wacker mechanisms involving the coordination of O(,2) and olefin to a rhodium(I) catalyst. One particularly promising system is the Rh/Cu co-catalyzed O(,2) oxidation of terminal olefins to almost exclusively 2-hexanone. The relatively short lifetimes of the homogeneous catalysts for this olefin oxidation encouraged us to seek a functionalized solid support to site-isolate the rhodium complexes. This approach is based on the assumption that the catalyst deactivation process is multi-ordered in rhodium. In chapter 2 is described the immobilization of {Rh(CO)(,2)S'(,n)}BF(,4) using a silica gel bound organosulfide ligand, {SG}-SH. When solid supports possessing site-isolated sulfide are employed, the monomeric rhodium carbonyl complexes, {SG}-SRh(CO)(,2)S'(,n), are formed. These produce catalysts for the oxidation of 1-hexene to 2-hexanone, and are more stable to deactivation than the analogous homogeneous reaction using {Rh(CO)(,2)S'(,n)}BF(,4). The O(,2) oxidation of {Rh(CO)(,2)Cl}(,2) was studied as part of an investigation to determine the character of the catalyst for the homogeneous Rh/Cu co-catalyzed oxidation of 1-hexene. In chapter 3 are presented the result of a detailed investigation of the mechanism of the O(,2) oxidation of {Rh(CO)(,2)Cl}(,2) to RhCl(,3)(H(,2)O)(,2)CH(,3)CH(,2)OH. This has been found to proceed by an unusual process involving the coordination of in situ generated HOOH to {Rh(CO)(,2)Cl}(,2), forming H(,2){Rh(CO)Cl(,2)(OOH)} as a stable intermediate. The observations that the O(,2) oxidation of {Rh(CO)(,2)Cl}(,2) produces rhodium(III) trichloride, and that this process corresponds to the initiation of the O(,2) oxidation of 1-hexene to 2-hexanone, has led to the characterization of the catalyst for the Rh/Cu co-catalyzed oxidation of 1-hexene at 40.C as RhCl(,2)S'(,4)('+). These results, and a general investigation of the mechanism of this catalytic 1-hexene oxidation, are presented in chapter 4. It has been found that RhCl(,3) 3 H(,2)O catalyzes the HOOH oxidation of 1-hexene to 2-hexanone, indicating peroxide is the direct oxidant in this system. Mechanisms for the Rh-only and Rh/Cu co-catalyzed oxidations of 1-hexene are proposed which are consistant with both the earlier reported results, and those presented in this study.
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