One-pot reduction-hydrophobization of heterogenized platinum with 1,1,3,3-tetramethyldisiloxane

An original approach for the design of hydrophobized heterogeneous platinum-based catalytic systems is reported here. Heterogenization was performed by depositing the platinum precursor (H2PtCl6) on macroporous styrene-divinylbenzene (SDVB) beads with a high surface area, similar to 330 m(2) g(-1), as determined by N-2 sorption data, followed by treating with 1,1,3,3-tetramethyldisiloxane (TMDS) as Pt(IV) reducing agent without the need of special conditions. Simultaneously, the coupling by Si-O-Si bonds of the TMDS oxidation or hydrolysis intermediates endowed the SDVB-Pt systems with an enhanced hydrophobicity (up to 10 times higher than that of SDVB support). In addition, to obtain an optimum catalytic system, which stabilize the supported platinium against leaching, several mixtures of TMDS with other methylsiloxane precursors, namely, methyltrimethoxysilane (MTMS), alpha,omega-bis(trimethylsiloxy)poly(dimethylsiloxane-H-methylsiloxane) (PDMHS), and alpha,omega-bis(trimethylsiloxy)poly(dimethylsiloxane-co-vinylmethylsiloxane) (PDMVS), have been systematically investigated. The reduction of platinum, visible by an instant change in the color from yellow to black, was confirmed by X-ray photoelectron spectroscopy analysis, while its total content in the samples was determined quantitatively by atomic absorption spectroscopy. The obtained systems have been preliminarily assessed for catalytic activity in the hydrosilylation of 1,3-bis(vinyl)tetramethyldisiloxane and allyl alcohol with TMDS, and 1-hexene with trimethoxysilane, as model reactions. The results indicate the high suitability of these systems as catalysts for the selective anti-Markovnikov hydrosilylation of alkenes, as well as for the very fast oxidation-condensation homocoupling of H-silanes in presence of a green oxidation agent (air), under mild conditions, with the release of hydrogen and its in situ addition to the double bond.