Insights into the mechanism of selective olefin epoxidation catalyzed by [γ-(SiO4)W10O32H4] 4-. A computational study

Rajeev Prabhakar, Keiji Morokuma, Craig L. Hill, Djamaladdin G. Musaev

Research output: Contribution to journalArticle

46 Scopus citations

Abstract

A mechanism for the H2O2-based epoxidation of olefins catalyzed by the lacunary polyoxometalate (POM) [γ-(SiO 4)-W10O32H4]4- (1) has been investigated at the DFT level. In this study, for the first time a "hydroperoxy" mechanism for this important process has been proposed. It is divided into two steps and investigated using the whole lacunary compound as a model. In the first step, a hydroperoxy (W-OOH) species and a water molecule are generated. The formation of this nonradical oxidant (W-OOH), consistent with the experimental suggestions, occurs with a barrier of 4.4 (7.2) kcal/mol (the number without parenthesis includes solvent effects in benzene, while the one with parenthesis is in the gas phase). In the second step, the O-O bond of the W-OOH species is cleaved, and an epoxide is formed. This step has a barrier of 38.7 (40.0) kcal/mol. It was found that the presence of one and two (CH3)4N+ countercations significantly reduces the rate-limiting barrier by 7.6 (8.3) and 11.9 (12.6) kcal/mol, respectively, and makes this lacunary POM a very efficient catalyst for epoxidation of olefins by hydrogen peroxide. It was demonstrated that the lacunary polyoxometalate basically acts as a mononuclear W(VI) complex in activating the oxidant, a conceptually noteworthy finding.

Original languageEnglish (US)
Pages (from-to)5703-5709
Number of pages7
JournalInorganic Chemistry
Volume45
Issue number14
DOIs
StatePublished - Jul 10 2006
Externally publishedYes

ASJC Scopus subject areas

  • Physical and Theoretical Chemistry
  • Inorganic Chemistry

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