Optimisation of Polystyrene Resin-supported Pt Catalysts in Room Temperature, Solvent-less, Oct-l-ene Hydrosilylation using Methyldichlorosilane

R.      Drake; R.      Dunn; D.   C.   Sherrington; S.   J.   Thomson

Abstract

Six precursor resins with systematic variation of porous parameters were prepared by suspension polymerisation using specific compositions of divinylbenzene, styrene vinylbenzyl chloride (VBC) and 2- ethylhexan-l-ol (a porogen). Surface areas from N2 sorption and BET analysis were ∼2-170 m2g-1. The VBC content in each case was 38 mol% and these groups were aminated using the sodium salt of trimethylethylene diamine. Pt was introduced onto each resin at three different loadings (∼0.03, ∼ 0.2 and ∼ 0.4 mmol g-1) by appropriate manipulation of K2PtCl6. The matrix of 18 resin-supported Pt complexes was then assessed for catalytic activity in the room temperature, solvent-less, hydrosilylation of oct-l-ene using methyldichlorosilane such that alkene: silane: Pt ratio was fixed at 2:1:1x10-3. Though all the catalysts showed activity lower than that of homogeneous Speiers catalyst, most were sufficiently active to be potentially valuable heterogeneous catalysts in the laboratory, and indeed the plant. The most lightly loaded resins proved to be the least active. The remainder were recycled 5 times, and the best performers, the most highly loaded species, a further 5 times making 10 consecutive uses in all. A strong dependence on the porous structure of the resins was demonstrated with the activity rising systemically with the surface area. The two highest surface area highest loaded species displayed good activity even when used for the tenth time. The level of concurrent alkene isomerisation observed was very low throughout ( < 1%) making these heterogeneous species very selective as well as highly active. Overall the derived catalysts are excellent candidates for use in the research laboratory, and with further development could also be valuable in continuous processes.

Keywords: polystyrene resin-support, pt catalyst, solid support, solid phase peptide synthesis

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