Mechanism of [γ-H2SiV2W10O40]4--Catalyzed Epoxidation of Alkenes with Hydrogen Peroxide

摘要: The mechanism of [γ-H2SiV2W10O40]4--catalyzed epoxidation alkenes with hydrogen peroxide in acetonitrile/tert-butyl alcohol was investigated. negative Hammett ρ+ (−0.88) for the competitive oxidation p-substituted styrenes and low XSO (XSO = (nucleophilic oxidation)/(total oxidation)) value <0.01 thianthrene-5-oxide reveal that strong electrophilic oxidant species is formed on [γ-H2SiV2W10O40]4- (I). preferable formation trans-epoxide 3-substituted cyclohexenes shows steric constraints active I. 51V NMR, 183W CSI−MS spectroscopy show reaction I leads to reversible a hydroperoxo [γ-HSiV2W10O39OOH]4- (II). successive dehydration II forms III, which possibly has an oxygen μ-η2:η2-peroxo group. kinetic spectroscopic studies present proceeds via III. ene...