Improving the cooperation of co-catalysts by locating them on different units of a copolymer

Abstract

Linear bifunctional copolymers were prepared by the free radical copolymerization in solution of a phosphine ligand (3- and 4-vinylbenzyl-biphenylphosphine (VBBP) or 3,4-bis(diphenylphosphine)-1-butene (BDPB) with an excess amount of a quaternary onium salt (vinylbenzyl tributyl ammonium chloride (VBAC)). The copolymer bicatalysts P(VBBP-Pd-VBAC) or P(BDPB-Pd-VBAC) were prepared by attaching palladium complexes to the pendant phosphine ligands. The Heck coupling reactions of iodobenzene with acrylate esters in DMF were employed to investigate the cooperation of the catalysts located on the copolymer by comparing their catalytic activities to those obtained with systems in which the two catalytic groups are not assembled together. It was found that the former exhibit higher catalytic activities than the latter, and that the P(VBBP-Pd-VBAC) system provides a higher product yield than P(BDPB-Pd-VBAC). The results also suggest that the polymer blocks of quaternary ammonium groups in the copolymers constitute receptors for the reactants. The amounts of phosphine, onium salt and palladium in the copolymer catalysts were determined by elemental analysis; 31P NMR experiments were carried out to investigate the distribution of phosphine in the copolymer chain.