Chiral Recognition in Catalytic Hydrogenation of α-Acylaminoacrylic Acids by Cationic Rhodium(I) Complexes of Chiral Aminophosphines Derived from (R,R)-1,2-Cyclohexanediamine or (R)-1,2-Propanediamine

Article abstract of DOI:10.1246/bcsj.53.2275

Four chiral diphosphines, (R,R)-1,2-biscyclohexane, (R,R)-1,2-bis-<(diphenylphosphino)amino>cyclohexane, (R)-1,2-bispropane, and (R)-1,2-bis<(diphenylphosphino)amino>propane have been prepared from the corresponding optically active diamines.The cationic 1,5-cyclooctadiene rhodium(I) complexes with these diphosphines act as effective homogeneous catalysts for the stereoselective hydrogenation of α-acylaminoacrylic acids.The optical yields and the absolute configurations of the products depend on the kind of diphosphine ligands.The (R,R)-1,2-biscyclohexane complex catalyst yields N-benzoyl-(S)-leucine, N-benzoyl-(S)-phenylalanine, and N-acetyl-(S)-phenylalanine in 94, 92, and 89percent e.e., respectively.The other three catalysts are less effective (6-74percent e.e.).The aminophosphine complexes with methyl groups on the nitrogen atoms always give (S)-amino acids, those with no methyl group (R)-amino acids.Such a difference in the chiral recognition has been discussed on the basis of circular dichroism spectra and Dreiding molecular models of the rhodium (I) complexes.