The inner-sphere transformations of vanadium(v) peroxo complexes with general formula [VO6] − were studied earlier by DFT methods to reveal the nature of the active intermediates of peroxide oxidation catalyzed by vanadium compounds. It was found that the triperoxo complex [V(η-O2)3]− undergoes isomerization to an unexpectedly stable complex [V(=O)(η-O2)(O3)]− containing the O3 bidentate ligand. This reaction proceeds via two intermediates that can transfer both the singlet dioxygen and oxygen atom to the substrate molecule. The reaction scheme proposed on the basis of calculations is in qualitative agreement with the kinetic regularities of ozone formation and oxidation of alkanes, alkenes, arenes and singlet dioxygen acceptors in the VV/H2O2/RCOOH catalytic system.
In this work, an oxygen atom transfer reactions from vanadium(v) peroxo complexes to ethylene and methyl vinyl ether have been studied using hybrid meta-GGA functional M06. Geometries of reactants, transition structures and products have been optimized with Ahlrichs def2-TZVP basis set. The IRC paths from transition states have been computed.
The activation barriers of reactions considered decreases upon peroxo group addition and achieves its minimum for triperoxo intermediate (16.0 and 10.5 kcal/mol, to ethylene and methyl vinyl ether, respectively). It can be explained by additional stabilization of the transition state structure with shortening remaining V–O bond of complex upon peroxo O–O bond breaking. Furthermore, the transfer of terminal oxygen atom from O3 group of complex [V(=O)(ηO2)(O3)]− was investigated. In this case we associate low activation energy (14.9 and 8.8 kcal/mol, to ethylene and methyl vinyl ether, respectively) with stabilization of leaving oxygen atom by interaction with former vacant dZ2 orbital of vanadium.