Synthesis, characterization and catalytic performance in enantioselective reactions by mesoporous silica materials functionalized with chiral thiourea-amine ligand

Abstract

Chiral heterogeneous catalysts have been synthesized by grafting of silyl derivatives of (1R, 2R)- or (1S, 2S)-1,2-diphenylethane-1,2-diamine on SBA-15 mesoporous support. The mesoporous material SBA-15 and so-prepared chiral heterogeneous catalysts were characterized by a combination of different techniques such as X-ray diffractometry (XRD), Fourier transform infrared (FT-IR), thermogravimetric analysis (TGA), field emission scanning electron microscopy (FESEM), and Brunauer–Emmett–Teller (BET) surface area. Results showed that (1R, 2R)- and (1S, 2S)-1,2-diphenylethane-1,2-diamine were successively immobilized on SBA-15 mesoporous support. Chiral heterogeneous catalysts and their homogenous counterparts were tested in enantioselective transfer hydrogenation of aromatic ketones and enantioselective Michael addition of acetylacetone to β-nitroolefin derivatives. The catalysts demonstrated notably high catalytic conversions (up to 99%) with moderate enantiomeric excess (up to 30% ee) for the heterogeneous enantioselective transfer hydrogenation. The catalytic performances for enantioselective Michael reaction showed excellent activities (up to 99%) with poor enantioselectivities. Particularly, the chiral heterogeneous catalysts could be readily recycled for Michael reaction and reused in three consecutive catalytic experiments with no loss of catalytic efficacies.