Catalytic Role of Multinuclear Palladium鈥揙xygen Intermediates in Aerobic Oxidation Followed by Hydrogen Peroxide Disproportionation
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- 作者：Andrew J. Ingram ; Katherine L. Walker ; Richard N. Zare ; Robert M. Waymouth
- 刊名：Journal of the American Chemical Society
- 出版年：2015
- 出版时间：October 28, 2015
- 年：2015
- 卷：137
- 期：42
- 页码：13632-13646
- 全文大小：877K
- ISSN：1520-5126
文摘
Aerobic oxidation of alcohols are catalyzed by the Pd鈥揳cetate compound [LPd(OAc)]2(OTf)2 (L = neocuproine = 2,9-dimethyl-1,10-phenanthroline) to form ketones and the release of hydrogen peroxide, but the latter rapidly undergoes disproportionation. We employ a series of kinetic and isotope labeling studies made largely possible by electrospray ionization mass spectrometry to determine the role of intermediates in causing this complex chemical transformation. The data suggested that multiple catalytic paths for H2O2 disproportionation occur, which involve formation and consumption of multinuclear Pd species. We find that the trinuclear compound [(LPd)3(渭3-O)2]2+, which we have identified in a previous study, is a product of dioxygen activation that is formed during aerobic oxidations of alcohols catalyzed by [LPd(OAc)]2(OTf)2. It is also a product of hydrogen peroxide activation during disproportionation reactions catalyzed by [LPd(OAc)]2(OTf)2. The results suggest that this trinuclear Pd compound is involved in one of the simultaneous mechanisms for the reduction of oxygen and/or the disproportionation of hydrogen peroxide during oxidation catalysis. Electrospray ionization mass spectrometry of hydrogen peroxide disproportionation reactions suggested the presence of other multinuclear Pd鈥揙2 species in solution. Theoretical calculations of these compounds yield some insight into their structure and potential chemistry.