Sulfoxidation with hydrogen peroxide catalyzed by [SeO4{WO(O2)2}2]2-

The selenium-containing dinuclear peroxotungstate, [(n-C4H9)(4)N](2)[SeO4{WO(O-2)(2)}(2)] (I), acts as a homogeneous catalyst for the selective oxidation of various kinds of cyclic mono- and disulfides with 30% aqueous H2O2. The cyclic disulfides were selectively oxidized to the corresponding monosulfoxides with one equivalent of H2O2 with respect to the sulfides. In the presence of two equivalents of H2O2, the oxidation of dibenzothiophene gave the corresponding sulfone in 98% yield under the mild conditions. The negative Hammett rho value (-0.62) for the competitive oxidation of p-substituted thioanisoles and the low X-SO (X-SO = (nucleophilic oxidation)/(total oxidation)) value of 0.14 for the I-catalyzed oxidation of thianthrene 5-oxide (SSO) revealed that I is a strong electrophilic oxidant. The reactivities of the di- and tetranuclear peroxotungstates with XO4n- ligands (X = Se(VI), As(V), P(V), S(VI), and Si(IV)) were strongly dependent on the kinds of hetcro atoms. The reaction rates for the sulfoxidation decreased with an increase in the X-SO values and a peroxotungstate with a stronger electrophilicity was more active for the sulfoxidation. The kinetic and mechanistic investigations showed that the electrophilic attack of the peroxo oxygen at the sulfur atom is a key step in the sulfoxidation. The computational investigation supported the high chemoselectivitiy for the sulfoxidation of diallyl sulfide.