Polyoxotungstates incorporated organophosphonate and nickel: synthesis, characterization and efficient catalysis for epoxidation of allylic alcohols

Three new sandwich-type organophosphonate-functionalized polyoxotungstate clusters, [{Ni(H2O)5}x(AsW6O21)2{Ni(OOCCH2NCH2PO3)2}3] (x = 0 (Ni1), 1 (Ni2 and Ni3)), were successfully isolated via a "top-down" synthetic strategy. Compounds (Ni1-Ni3) were characterized by single crystal X-ray analysis, X-ray powder diffraction (XRPD), IR spectroscopy, UV-vis spectroscopy, and thermogravimetric analyses (TGA). Magnetic properties provide evidence for antiferromagnetic coupling in Ni2 and Ni3 and ferromagnetic interaction in Ni1. Catalytic studies of the three polyoxotungstates for the oxidation of allylic alcohols to epoxides have been investigated in water with H2O2 as the oxidant. All three polyoxotungstates exhibit efficient catalytic performance with excellent conversion and high selectivity at room temperature.