Asymmetric hydrogenation of alpha,beta-unsaturated carboxylic acid esters by rhodium(I)-phosphine complexes supported on smectites

Hectorite(HT)-supported Rh complex catalysts were prepared by the intercalation of [Rh(P*-P*)(COD)](+) (P*-P*=(S)-BINAP and (S)-(R)-BPPFA, COD=cyclooctadiene) into sodium hectorites (NaHT) in acetonitrile/H2O. The basal spacing of each modified clay was 2.94 nm (BINAP) and 2.72 nm (BPPFA), respectively. Asymmetric hydrogenation of alpha,beta-unsaturated carboxylic acid esters containing ester groups of various chain lengths was studied on these modified hectorites. The dependence of selectivity on employed solvents and bulkiness of the ester groups suggested that the interaction between substrates and the active sites increased in the interlayer space, thus enhancing the asymmetric selectivity.