Readily accessible mesoporous silica nanoparticles supported chiral urea‐amine bifunctional catalysts for enantioselective reactions

Abstract

The main objective of this study is to develop readily accessible and recyclable solid catalysts for enantioselective reactions. To achieve this, magnetic MCM‐41 and non‐magnetic SBA‐15 mesoporous supports were prepared, then mesoporous silica supported chiral urea‐amine bifunctional catalysts were synthesized by grafting of chiral urea‐amine ligand onto SBA‐15 and magnetic MCM‐41. The magnetic and non‐magnetic supports and so‐prepared solid catalysts were characterized by using different methods such as N2 sorption measurements, Fourier transform infrared spectroscopy (FT‐IR), field emission scanning electron microscope‐energy dispersive X‐ray analysis (FESEM‐EDX), X‐ray diffraction (XRD), and thermogravimetric analysis (TGA). Results showed that (1R, 2R) or (1S, 2S)‐1,2‐diphenylethane‐1,2‐diamine was successively immobilized onto magnetic MCM‐41 and SBA‐15 pores. The heterogeneous chiral solid catalysts and their homogenous counterparts exhibited high activities both enantioselective transfer hydrogenation reaction (up to 99% conversion and 65% ee) and enantioselective Michael reaction (up to 98% conversion and 26% ee). Moreover, the SBA‐15 supported solid catalysts were separated from the reaction mixture by simple filtration, whereas the magnetic MCM‐41 supported solid catalysts were separated by simple magnetic decantation and reused in three consecutive catalytic experiments.