Mechanism of [gamma-H2SiV2W10O40](4-)-catalyzed epoxidation of alkenes with hydrogen peroxide.
The mechanism of [gamma-H2SiV2W10O40]4--catalyzed epoxidation of alkenes with hydrogen peroxide in acetonitrile/tert-butyl alcohol was investigated. The negative Hammett rho+ (-0.88) for the competitive oxidation of p-substituted styrenes and the low XSO (XSO = (nucleophilic oxidation)/(total oxidation)) value of <0.01 for the [gamma-H2SiV2W10O40]4--catalyzed oxidation of thianthrene-5-oxide reveal that the strong electrophilic oxidant species is formed on [gamma-H2SiV2W10O40]4- (I). The preferable formation of trans-epoxide for the epoxidation of 3-substituted cyclohexenes shows the steric constraints of the active oxidant on I. The 51V NMR, 183W NMR, and CSI-MS spectroscopy show that the reaction of I with hydrogen peroxide leads to the reversible formation of a hydroperoxo species [gamma-HSiV2W10O39OOH]4- (II). The successive dehydration of II forms III, which possibly has an active oxygen species of a mu-eta2:eta2-peroxo group. The kinetic and spectroscopic studies show that the present epoxidation proceeds via III. The energy diagram of the epoxidation with density functional theory (DFT) supports the idea.
Nakagawa
Yoshinao
Y
Department of Applied Chemistry, School of Engineering, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656, Japan.
Mizuno
Noritaka
N
D000475:Alkenes / Q000138:chemical synthesis* / Q000737:chemistry; D002384:Catalysis; D006861:Hydrogen Peroxide / Q000737:chemistry*; D007700:Kinetics; D008956:Models, Chemical; D015394:Molecular Structure; D017646:Organosilicon Compounds / Q000138:chemical synthesis / Q000737:chemistry*; D010084:Oxidation-Reduction; D011789:Quantum Theory; D017640:Silicates / Q000737:chemistry*; D012997:Solvents / Q000737:chemistry; D013237:Stereoisomerism; D013997:Time Factors; D017973:Tungsten Compounds / Q000737:chemistry*; D014639:Vanadium / Q000737:chemistry*
D000475:Alkenes; D017646:Organosilicon Compounds; D017640:Silicates; D012997:Solvents; D017973:Tungsten Compounds; D014639:Vanadium; D006861:Hydrogen Peroxide