Dodecatungsto-silicic H(4)SiW(12)O(40) and -phosphoric acids H(3)PW(12)O(40) were deposited on silica by a classical impregnation technique. The resulting materials were studied by in situ Raman and infrared spectroscopy, XPS and by solid-state (1)H MAS NMR as a function of their dehydroxylation temperature. The data show that in the case of H(3)PW(12)O(40) three silanol groups are protonated while in the case of H(4)SiW(12)O(40) at least one acidic proton remains. Upon heating this proton reacts leading to a disordered structure and a broadening of the W-O Raman bands.

The Pd(TPPTS)3 complex (TPPTS is the sodium salt of tris(m-sulfophenyl)phosphine) easily ionizes allyl alcohol in water over a wide range of pH: OH− and TPPTS are released, and [Pd(η3-allyl)(TPPTS)2]+ is formed. The released TPPTS further reacts with the palladium cationic complex to reversibly produce both the allylphosphonium salt of TPPTS [(allyl)Ar3P]+ and Pd(TPPTS)3, the latter acting as the catalyst of the allylation of TPPTS by allyl alcohol. Primary allylic alcohols, such as butenol (trans-2-buten-1-ol), prenol (3-methyl-2-buten-1-ol), geraniol, and cinnamyl alcohol, react with Pd(TPPTS)3 to produce hydroxide ion, the corresponding hydrosoluble cationic palladium complex, and allylic phosphonium salts. At room temperature, [Pd(η3-allyl)(TPPTS)2]+ is stable up to pH 12, but beyond this value, palladium precipitates. The temperature has an adverse effect on the complex stability: palladium precipitates at 80 °C, even at pH 7, with the formation of a small amount of propylene. The addition of [(allyl)Ar3P]+ increases the stability of [Pd(η3-allyl)(TPPTS)2]+. Above pH 10, [(allyl)Ar3P]+ decomposes into OTPPTS and propylene by reaction with OH−. At lower pH, [(allyl)Ar3P]+ is slowly isomerized into [(propenyl)Ar3P]+, which further reduces its stability toward pH and temperature. These consecutive reactions of the TPPTS ligand could explain most of the catalyst instability. This study outlines the basis for a better understanding of the instability phenomenon of the catalytic system Pd(0)−TPPTS in reactions with allylic intermediates, e.g. the Tsuji−Trost reaction, and in the reaction of dienes in aqueous media in which palladium often precipitates.

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 (1H, 13C, 183W, and 195Pt) 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.