Vanadium(v) complexes in carboxylic acid medium catalyze the oxidation with H2O2 of alkanes, fatty acid esters, alkenes, perfluoroalkenes, anthracene and the decomposition of hydrogen peroxide to singlet dioxygen and ozone. Kinetics of these reactions suggests the formation of a vanadium(v) triperoxo complex in the rate-determining step.
The inner-sphere transformations of the vanadium(v) peroxo complexes were studied by DFT methods to reveal the nature of intermediates of the vanadium catalyzed peroxide oxidations. It was found that the triperoxo complex [V(η-O2)3]− undergoes isomerization to the unexpectedly stable complex [V(=O)(η-O2)(O3)]− containing the O3 bidentate ligand. The reaction proceeds via two intermediates with uncommon electron structure and a rather short O–O distance in the peroxo ligands. These intermediates can transfer both the singlet dioxygen and oxygen atom to the substrate molecule. The reaction scheme proposed based on the DFT calculations is in good agreement with the experimental kinetic data for the singlet dioxygen and ozone formation, oxidation of alkanes, alkenes, arenes and singlet dioxygen acceptors in the VV/H2O2/RCOOH catalytic system.