Immobilization of rhodium diphosphine complexes on mesoporous Al-MCM-41 materials:: Catalysts for enantioselective hydrogenation

Heterogeneous chiral catalysts for the enantioselective hydrogenation of prochiral alkenes are prepared from chiral rhodium diphosphine complexes and Al-MCM-41. Impregnation of the mesoporous carrier Al-MCM-41 with the organometallic complexes in dichloromethane leads to strong and not leaching hydrogenation catalysts. The catalysts are characterized by spectroscopic methods such as FT-IR and MAS-NMR as well as thermoprogrammed desorption of ammonia, thermogravimetric analysis, and nitrogen sorption experiments. The hydrogenation of dimethylitaconate was studied as a test reaction. The immobilized catalysts showed high activity and excellent regio- and enantioselectivity. Up to 92% ee, 100% conversion, and 99% regioselectivity were observed for the hydrogenation of dimethyl (R)-methylsuccinate. The catalysts could be reused without any regeneration procedure and with no loss of catalytic acitivity. Leaching of the homogeneous complex out of the MCM-41 framework was not observed. (C) 2001 Academic Press.