Synthesis of polymer-immobilized TsDPEN ligand and its application in asymmetric transfer hydrogenation of cyclic sulfonimine

Abstract

Crosslinked polymers containing chiral N-sulfonylated diamine (TsDPEN) structure were synthesized by radical polymerization of chiral N1-(4-vinylbenzenesulfonyl)-1,2-diphenylethylene-1,2-diamine, divinylbenzene and achiral vinyl monomer. The polymer-immobilized chiral complex was prepared from the polymeric TsDPEN with ruthenium dichloride p-cymene. Asymmetric transfer hydrogenation of cyclic sulfonimine was performed using the polymer-immobilized TsDPEN–Ru (II) complex. The hydrophobic–hydrophilic balance of the polymers was tuned by means of the incorporation of the achiral vinyl monomers, which strongly influenced on the catalytic activity of the polymeric catalyst. In most cases the amphiphilic polymer-immobilized chiral catalysts are highly active in the asymmetric transfer hydrogenation. Enantioenriched sultam with up to 98% ee was obtained by using polymer-immobilized chiral catalysts containing quaternary ammonium salt in CH2Cl2. Some of the polymer-immobilized chiral catalysts containing quaternary ammonium salt were successfully used in water. Up to 95% ee was obtained by using the polymeric catalyst in water. Most of the quaternized polymeric catalysts showed sufficient reactivity and higher enantioselectivities compared with that of low-molecular-weight catalyst in water.