Haloperoxidase Activity of Oxovanadium(V) Thiobisphenolates

By employing the 2,2′-thiobis(2,4-di-tert-butylphenolate) ligand (SL2−) a novel oxovanadium(V) complex, (PPh4)2[SLV(O)(μ2-O)2V(O)SL] (1), was synthesised that exhibits haloperoxidase activity: on addition of H2O2 a sequence of successive peroxide formation and intramolecular thioether oxidation events (sulfoxide and sulfone) led to a mixture of five products, which were all identified unambiguously, partly through an independent synthesis and characterisation. It was shown that internal thioether oxidation proceeds through peroxide formation, but the sulfoxidation of external thioether functions requires further activation of the peroxide function by protons or alkyl cations. Consistently, the employment of tBuOOH instead of H2O2 led to a very active system for the catalytic sulfoxidation of thioethers.