The nickel-substituted quasi-Wells-Dawson-type polyfluoroxometalate, [Ni^II(H₂O)H₂F₆NaW₁₇O ₅₅]^9-, as a uniquely active nickel-based catalyst for the activation of hydrogen peroxide and the epoxidation of alkenes and alkenols

A series of transition metal substituted polyfluorooxometalates (PFOM) [M(L)H₂F₆NaW₁₇O₅₅]^q-, M = Zn²⁺, Co²⁺, Mn²⁺, Fe²⁺, Ru²⁺, Ni²⁺ and V⁵⁺ and L = H₂O, O^2-, of quasi-Wells -Dawson structure, was synthesized. In the series prepared, only the nickel-substituted polyfluorooxometalate was capable of catalytic activation of hydrogen peroxide in biphasic reaction media, the reaction leading mainly to the selective epoxidation of alkenes and alkenols. The manganese-, cobalt-, ruthenium-, iron-, vanadium-, and zinc-substituted polyfluorooxometalates were catalytically inactive, although, except for the zinc polyfluorooxometalate, very significant catalase activity was observed. Oxidation of thianthrene showed that sulfoxides were oxidized more easily than sulfides. Kinetic profiles of cyclooctene epoxidation showed that the reaction was zero order in both cyclooctene and hydrogen peroxide. Hydrogen peroxide was consumed at a rate 40% higher than the rate of epoxidation of cyclooctene. The reaction appears to proceed through an intermediate peroxo/hydroperoxo species that was observed in the IR spectrum. Atomic absorption, IR and ¹⁹F NMR spectroscopy indicated that the [Ni(H₂O)-H₂F₆NaW₁₇O ₅₅]^9- compound was stable under reaction conditions.