Highly efficient solid catalysts for asymmetric hydrogenation fabricated via facile adsorption of Rh–MonoPhos on porous silicas

Abstract

Via very simple and facile adsorption, Rh–MonoPhos was successfully immobilized on mesoporous silicas with channel-like and cage-like pores. The resulting solid catalyst showed higher activity (TOF: 4800 vs. 936 h⁻¹) and enantioselectivity (96.0% vs. 94% ee) than its homogeneous counterpart in the asymmetric hydrogenation of itaconic acid dimethyl ester under similar conditions, probably due to the high dispersion of Rh–MonoPhos on mesoporous silicas. Significant rate enhancement was observed with Rh–MonoPhos immobilized on mesoporous silicas with cage-like pores in comparison with channel-like pores, reflecting that cage-like pores could facilitate the mass transport. The solid catalyst could be recycled several times without an obvious decrease in both activity and enantioselectivity.