Effect of cross-linking on catalytic performance of polystyrene supported platinum carbonyl clusters

Abstract

Commercial chlormethylated divinylbenzene cross-linked polystyrene resins (5.5% and 8%) have been functionalized by the reaction with triethylamine. The Chini cluster [Pt₁₅(CO)₃₀]^2- has been anchored onto the resultant materials by anion exchange. The degrees of functonalization in terms of chloromethyl and benzyltriethyl ammonium functionalities are found to be very high and high (> 85% and > 60%) respectively for both the polymers. The total platinum content of the 8% cross-linked polystyrene is a little (~13%) more than that of 5.5% cross-linked polymer. The catalytic activities of the resultant materials after mild thermal activation have been studied for the hydrogenation of a variety of unsaturated compounds. The substrates studied are: cyclohexanone, acetophenone, methyl pyruvate, ethyl acetoacetate and nitrobenzene. For most of the substrates the activity of the 5.5% cross-linked material is found to be a little more than that of the 8.8% cross-linked material. This is despite the fact that the latter has more platinum both in the bulk and on the surface as measured by atomic absorption and EDAX (SEM) techniques respectively. After functionalization with cinchonine and [Pt₁₅(CO)₃₀]^2- , both the polymers have been tested as possible asymmetric catalysts for the hydrogenation of methyl pyruvate. No enantioselection is observed and a tentative explanation is offered for the lack of enantioselection.