Polymeric monolith supported Pt-nanoparticles as ligand-free catalysts for olefin hydrosilylation under batch and continuous conditions

Pt-nanoparticles were generated within the mesopores of polymeric monolithic supports. These monoliths were prepared via ring-opening metathesis polymerization (ROMP) from (Z)-9-oxabicyclo[6.1.0] non-4-ene (OBN) and tris(cyclooct-4-en-1-yloxy) methylsilane (CL) using the 3rd-generation Grubbs-initiator RuCl2(pyridine)(2)(IMesH(2))(CHPh) (1) in the presence of a macro-and microporogen. To generate the Pt nanoparticles inside the porous system, the epoxy-groups of the monolithic supports were hydrolyzed into the corresponding vic-diol with the aid of 0.1 N sulfuric acid. Loading with Pt4+ and reduction with NaBH4 resulted in the formation of Pt nanoparticles <7 nm in diameter that were exclusively located within the mesopores of the support as demonstrated by transmission electron microscopy/EDX spectrometry. The nanoparticles were stabilized by both the vic-diols and the polymeric double bonds as evidenced by control experiments with poly(glycidylmethacrylate)-based monoliths that lack the double bonds. Typical metal loadings of around 1.7 mg g(-1) (8.7 mu mol g(-1)) were obtained. Pt(0)-loaded monoliths were used in the hydrosilylation of terminal alkenes, norborn-2-ene and norbornadiene applying both batch and continuous flow conditions. Hydrosilylation of olefins under continuous flow conditions resulted in constant product formation in 98% yield at T = 45 degrees C applying a linear flow of 12.0 mm min(-1). Metal leaching was very low, resulting in Pt-contamination in the addition products of less than 4 ppm throughout.