Air oxidation of divanadium(IV) complexes

Abstract

The dinuclear V^IVO complex of 2,6-bis{[N,N-bis(2-pyridylmethyl)amino]methyl}-4-tert-butylphenolato (bpbp⁻), [(VO)₂bpbp(OH₂)₂](ClO₄)₃·H₂O, 1 is oxidised by air. Two products have been characterised in the solid state, namely a V^VV^Vdiperoxido complex, [(VO)₂bpbp(η²-O₂)₂](ClO₄), 2 and a V^VV^IVtrioxido complex, [V(O)₂V(O)bpbp(OH₂)](ClO₄)₂·2H₂O·EtOH, 3. The rate of formation of 2 is solvent-dependent and is fastest in 2-propanol, compared to methanol or tetrahydrofuran. A transient species postulated to be a V^V hydroperoxido species was detected during the course of this relatively slow reaction, which takes place on a timescale of hours to days. Concentration appears to be the factor determining whether complex 2 or complex 3 is obtained from reactions of 1 with air: at higher complex concentrations formation of 3 rather than 2 is presumed to occur via a bimolecular reaction between the starting V^IV complex and a reactive oxidized adduct.