Catalytic oxygenation of alkenes and alkanes by oxygen donors catalyzed by cobalt-substituted polyoxotungstate

The cobalt-substituted polyoxotungstate [(CoPW₁₁O₃₉)^5-] has been used as a catalyst in olefin epoxidation and alkane hydroxylation reactions. The epoxidation of olefins by iodosylbenzene in CH₃CN yielded epoxides predominantly with trace amounts of allylic oxidation products. cis-Stilbene was streoselectively oxidized to cis-stilbene oxide with small amounts of trans-stilbene oxide and benzaldehyde formation. The epoxidation of carbamazepine (CBZ) by potassium monopersulfate in aqueous solution gave the corresponding CBZ 10,11-oxide product. Other transition metal-substituted polyoxotungstates (M = Mn²⁺, Fe²⁺, Ni²⁺, and Cu²⁺) were inactive in the CBZ epoxidation reaction. The cobalt-substituted polyoxotungstate also catalyzed the oxidation of alkanes with m-chloroperbenzoic acid to give the corresponding alcohols and ketones. The presence of CH₂Br₂ in the hydroxylation of cyclohexane afforded the formation of bromocyclohexane, suggesting the participation of cyclohexyl radical. In the ¹⁸O-labeled water experiment, there was no incorporation of ¹⁸O into the cyclohexanol product when the hydroxylation of cyclohexane by MCPBA was carried out in the presence of H₂¹⁸O. Some mechanistic aspects are discussed as well.