Ligand-Acceleration By A Chiral Modifier In The Enantioselective Hydrogenation Of Methyl Acetoacetate On A Raney Nickel Catalyst: Effect Of A Modifier Configuration

Reaction rate and enantioselectivity of asymmetric hydrogenation of methyl acetoacetate were studied over Raney nickel catalysts modified with (R,R)-tartaric acid, malic acid, or succinic acid to reveal the impacts of the modifier configuration. Catalysts comodified with two different acids were also examined to confirm the conclusions. From analysis of the enantiomer ratio of the hydrogenation product and initial reaction rate, tartaric acid (TA) was found to have dual functions as the modifier during the hydrogenation; effective suppression of the racemic catalysis on bare Ni surface and extensive enantiodifferentiating ligand acceleration by adsorbed TA. It was demonstrated that each adsorbed chiral modifier molecule independently takes part in the enantiospecific hydrogenation.