Grafting Reaction of Platinum Organometallic Complexes on Silica-Supported or Unsupported Heteropolyacids

Silica-supported Keggin-type heteropolyacids react with platinum(II) complexes displaying a Pt-CH3 group, leading to the evolution of methane and the formation of an organometallic fragment grafted on the polyacid. This species has been characterized by various physicochemical methods such as microanalyses, infrared spectroscopy, solid-state 1D and 2D MAS NMR, and EXAFS. Molecular models were also prepared by reaction of the nonsupported anhydrous polyacid with the platinum(II) methyl complexes. These compounds were characterized in solution by multinuclear NMR (H-1, C-13, W-183, and Pt-195) and in the solid state by X-ray diffraction on monocrystals. All data indicate that the interaction between the platinum complex and the polyoxometalate is weak and that this system is better expressed as an organometallic platinum salt of the supported heteropolyacid. This complex can be seen as one of the intermediates in the partial oxidation of methane to methanol, its synthesis being the reverse reaction of the methane activation.