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

Two sandwich-type polyoxomolybdates Na₈[MO₂{Mo₂O₅(O₃PCH₃C(O)PO₃)}₂] (M = Ni (); Co ()) were synthesized by one-pot reaction of Na₂HPMoO·14H₂O, 1-hydroxy ethidene diphosphonic acid (HEDP=HOC(CH₃)(PO₃H₂)₂), and (1) NiCl₂/CoCl₂ (2). Compounds and were characterized by single crystal X-ray analysis, X-ray powder diffraction (XRPD), IR spectroscopy, P NMR spectra, UV-vis spectroscopy, and thermogravimetric analyses (TGA). Structural analysis reveals that and exhibit similar centrosymmetric structure, which consists of one transition metal (TM) ion sandwiched by two same subunits {Mo₂O₅(O₃PCH₃C(O)PO₃)}. The clusters 1 and 2 show efficient catalytic activities for oxidation of thioanisole. Moreover, they are catalytically selective for oxidizing thioanisole. Both resuable polyoxomolybdates and catalysts show good thermo- and hydrolytic stability. It is noted that compound 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.