Enantioselective Hydrogenation over Chiral Cobalt Complexes with (+)-(1S,2S,5R)-Neomenthyldiphenylphosphine and (-)-(R,R)-2,2-Dimethyl-4,5-bis(diphenylphosphinomethyl)-1,3-dioxolane

The optical yield in enantioselective hydrogenation of methyl -acetamidocinnamate over mono- and diphosphine cobalt(II) complexes CoX₂L₂ where X = Cl or CF₃SO₃, L = (+)-(1S,2S,5R)-neomenthyl-diphenylphosphine or L2' = (-)-(R,R)-2,2-dimethyl-4,5-bis(diphenylphosphinomethyl)-1,3-dioxolane], which are generated in situ, in the presence of sodium tetrahydridoborate increases with rise in the phosphine-to-metal ratio and hydrogen pressure. The maximal optical yields of (+)-(S)-N-acetylphenylalanine methyl ester attain 40% (CoX₂L₂) and 42% (CoX₂L₂').