Mesoporous SBA-15-supported chiral catalysts: preparation, characterization and asymmetric catalysis

Two mesoporous silica-supported chiral Rh and Ru catalysts 5 and 6 with ordered two-dimensional hexagonal mesostructures were prepared by directly postgrafting organometallic complexes RhCl[(R)-MonoPhos(CH2)3Si(OMe)3][(R,R)-DPEN] and RuCl2[(R)-MonoPhos(CH2)3Si(OMe)3][(R,R)-DPEN] (DPEN = 1,2-diphenylethylenediamine) on SBA-15. During the asymmetric hydrogenation of various aromatic ketones under 40 atm H2, both catalysts exhibited high catalytic activities (more than 97% conversions) and moderate enantioselectivities (33-54% ee). Furthermore, the chiral Rh catalyst 5 could be easily recovered and used repetitively five times without significantly affecting its catalytic activity and enantioselectivity. A catalytic comparison of the mesoporous silica-supported chiral Rh catalyst 4 prepared by a postmodification method is also discussed.