Synthesis of chiral iridium complexes immobilized on amphiphilic polymers and their application to asymmetric catalysis
This article details the enantioselective catalytic performance of crosslinked, polymer immobilized, Ir-based, chiral complexes for transfer hydrogenation of cyclic imines to chiral amines. Polymerization of the achiral vinyl monomer, divinylbenzene, and
Asymmetric transfer hydrogenation of imines catalyzed by a polymer-immobilized chiral catalyst
The asymmetric transfer hydrogenation of imines was performed with the use of a polymer-immobilized chiral catalyst. The chiral catalyst, prepared from crosslinked polystyrene-immobilized chiral 1,2-diamine monosulfonamide, was effective in the asymmetric transfer hydrogenation of N-benzyl imines in CH 2Cl2 to give a chiral amine in high yield and good enantioselectivity. Furthermore, an amphiphilic polymeric catalyst prepared from crosslinked polystyrene containing sulfonated groups successfully catalyzed the asymmetric transfer hydrogenation of cyclic imines in water. Enantioenriched secondary amines with up to 94% ee were obtained by using a polymeric catalyst.
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. The 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 non-supported model catalyst in the solution system. The polymeric catalysts can be reused without loss of catalytic activity.