Asymmetric Transfer Hydrogenation of Aromatic Ketones in Water using a Polymer-Supported Chiral Catalyst Containing a Hydrophilic Pendant Group

Hydrophilic polymers having pendant groups of carboxylates or sulfonates have been used as a polymer support for chiral 1,2-diamine monosulfonamides. ne polymeric chiral complex prepared from the polymer-supported chiral ligand with ruthenium dichloride-p-cymene was used in the asymmetric transfer hydrogenation of prochiral ketones in water. The balance between hydrophilicity and hydrophobicity of the polymer support influenced both the reactivity and the enantioselectivity of the reaction in water. The chiral polymeric complex having a quaternary ammonium salt structure as the pendant group worked well in water. In most cases the polymer-supported catalyst having a quaternary ammonium sulfonate pendant group showed superior enantioselectivity compared to the corresponding nonsupported model catalyst in the solution system. The polymeric catalysts can be reused without loss of catalytic activity.