Nafion as a support for transition metal catalysis

Abstract

The properties of the perfluoropolymer sulphonic acid resin, sold under the trade name of Nafion have been examined. The use of Nafion as a support for transition metal catalysts has been studied in the context of alternative support systems. It has been demonstrated that transition metal complexes are readily incorporated into Nafion, provided they are either ionic in nature or contain ligands which are organic acid anions or ligands which can be protonated. Nafion used as a support has been successfully recycled and forms of Nafion with modified functional groups have been successfully synthesised. In order to explore the scope of Nafion as a catalyst support, a range of reactions has been investigated, the main purpose being comparison between the performance of a catalyst used homogeneously to its performance supported in Nafion. The hydroesterification of ethene to methyl propanoate was studied using several palladium complexes as catalysts. The ejects of temperature, CO pressure, catalyst loading and ligand to metal ratio on yields of product were recorded, using the most effective of the supported palladium catalyst systems. Yields of methyl propanoate using Nafion supported complex as catalyst were higher than the same catalyst used unsupported under comparable conditions. The hydrogenation of cyclohexene, dimethyl maleate and nitrotoluene was accomplished using the complexes [Ir(COD)(PPh(_2)Me)]PF(_6), [Rh(NBD)]BF(_4) and [RhCl(Ph(_2)P-NC(_5)H(_10))(_3)]. Yields of hydrogenation products using Nafion supported complexes were comparable or higher than yields obtained homogeneously. The hydrofonnylati n of hexene was carried out using a series of complexes of the form [Rh(NBD)L(_2)]BF(_4) where L represents a phosphine. Yields of aldehydes and normal to branched ratios were slightly lower using Nafion supported complexes in comparison to the homogeneous case. The production of substituted pyridines from propyne and acetonitrile was attempted using cobalt complexes coordinated to modified cyclopentadiene rings without success.