Two New Sandwich-Type Polyoxomolybdates Functionalized with Diphosphonates: Efficient and Selective Oxidation of Sulfides to Sulfones

Two sandwich-type polyoxomolybdates Na(8)[MO(2){Mo(2)O(5)(O(3)PCH(3)C(O)PO(3))}(2)] (M = Ni(2+) (1); Co(2+) (2)) were synthesized by one-pot reaction of Na(2)HPMo(12)O(40)·14H(2)O, 1-hydroxy ethidene diphosphonic acid (HEDP=HOC(CH(3))(PO(3)H(2))(2)), and (1) NiCl(2)/CoCl(2) (2). Compounds 1 and 2 were characterized by single crystal X-ray analysis, X-ray powder diffraction (XRPD), IR spectroscopy, (31)P NMR spectra, UV-vis spectroscopy, and thermogravimetric analyses (TGA). Structural analysis reveals that 1 and 2 exhibit similar centrosymmetric structure, which consists of one transition metal (TM) ion sandwiched by two same subunits {Mo(2)O(5)(O(3)PCH(3)C(O)PO(3))}. The clusters 1 and 2 show efficient catalytic activities for oxidation of thioanisole. Moreover, they are catalytically selective for oxidizing thioanisole. Both resuable polyoxomolybdates 1 and 2 catalysts show good thermo- and hydrolytic stability. It is noted that compound 1 shows outstanding catalytic activity for oxidation of various sulfides to corresponding sulfones with 93–100% selectivity at 97–100% conversion in one hour under mild conditions, which is potentially valuable to the removal of organic sulfides.