Immobilization of rhodium complexes with chiral cationic water soluble ligands on Nafion-H and other strongly acidic cation exchange resins

Abstract

Abstract Rhodium complexes of the chiral cationic water soluble ligands, [(S, S)-2,4-bis[-bis(-p-N, N-dimethylammoniumphenyl)phosphino]pentane]4+, [(S, S)-2,3-bis[-bis(-p-N, N-dimethylammoniumphenyl)phosphino]butane]4+, and [(S, S)-2,4-bis[-bis(-p-N, N, N-trimethylammoniumphenyl)phosphino]pentane]4+, were immobilized on several cation exchange resins. All of these supported complexes catalyze the asymmetric hydrogenation of dehydroaminoacid derivatives at the appropriate conditions with no detectable loss of rhodium into the substrate phase. The rates and enantioselectivities of these hydrogenations depend not only on the ligand used but also on the nature of the exchange resin upon which the complex is immobilized. When the complexes were supported onto the acidic Nafion-H cation exchange resin the resulting catalysts were easy to handle and gave optical yields comparable to those obtained with the non-supported complexes in homogeneous solution. The results presented here show that ion exchange resins may be used in the immobilization of asymmetric catalysts with no detectable rhodium leaching under batch conditions.