Electronic and steric effects of ligands as control elements for rhodium-catalyzed asymmetric hydrogenation

Electronic and steric effects in the rhodium diphosphinite catalyzed asymmetric hydrogenation were investigated. A series of electronically and sterically modified (S)-BINOL and (S)-H8-BINOL ligands was synthesized and effects on the catalytic performance were studied. Phosphinite basicity was varied by using p-CH3O, p-CH3, p-H, p-CF3, 3,5-(CH3)2, 3,5-(CF3)2 substituents on the diphenylphosphine moieties. In the hydrogenation of dimethyl itaconate and methyl (Z)-α-acetamido cinnamate an increase in enantioselectivity and activity was observed with increasing phosphine basicity.