Catalytic peroxide oxidation: The structure of key intermediates in the VV/H2O2 system according to quantum chemical data

The inner-sphere isomerization of the peroxo complexes of vanadium(V) with the general formula [VO₆]^? was studied using approximations based on the density functional theory (B3LYP/6-31G**) and the Møller-Plesset perturbation theory (MP2/6-31G**). It was found that the complex [V(=O)(ηO₂)(O₃)]^? containing the O₃ group as a bidentate ligand was the most stable isomer. The transition state region of a rear-rangement of the triperoxo complex [V(ηO₂)₃]^? into [V(=O)(ηO₂)(O₃)]^? was localized. It was found that the activation barrier (～30 kcal/mol) was mainly due to O-O bond cleavage in the peroxo ligand. According to calculations, the reaction proceeds through two intermediate complexes whose structure can be interpreted as that containing coordinated singlet dioxygen (especially in the limiting case) because of noticeably shortened O-O bonds in the ηO₂ ligand. The calculated reaction scheme of the conversion of [V(ηO₂)₃]^? into [V(=O)(ηO₂)(O₃)]^? is qualitatively consistent with the previously found kinetics of the formation of ozone and the oxidation of alkanes, olefins, arenes, and singlet dioxygen traps.