Peroxovanadium complexes as radical oxidants in organic solvents and in aqueous solutions

Radical oxidations carried out by peroxovanadium complexes, both in CH3CN and in water, are presented. A detailed mechanism for the decomposition of, and benzene hydroxylation by, the peroxocomplex [PicVO(O2)] (Pic = picolinic acid anion) is provided. A very good agreement between calculated and experimental data is observed. Data aimed at establishing a relationship between the nature of peroxovanadium complexes and their reactivity in water are also presented. These include 51V-NMR chemical shifts, Hammett-type and Ramsey-type correlations. Preliminary data obtained from ab initio calculations are also included. A radical chain mechanism, slightly different from that taking place in CH3CN, is presented for the decomposition of peroxovanadium complexes in water. Also in this case a good agreement between calculated and experimental data is found. Both in CH3CN, in water and in CH3CN/water mixtures, the oxidizing agent appears to be the species resulting from the one-electron reduction of the peroxovanadium complexes. Thus, the possible involvement of the HO radical is at least questionable.