Factors affecting the efficiency of hybrid chiral mesoporous silicas used as heterogeneous inorganic-organic catalysts in the enantioselective alkylation of benzaldehyde

Chiral hybrid organic-inorganic materials were prepared by anchoring optically active beta-aminoalcohols such as (-)-ephedrine on MCM-41 type silica as a member of micelle-templated silicas (MTS). Silylation of the surface was performed with halogenopropyltrimethoxysilane. Then, (-)-ephedrine was anchored through halogen substitution. These materials were used as chiral auxiliaries in the heterogeneous enantioselective catalysis of the alkylation of benzaldehyde by diethylzinc. This work deals with the study of the various factors such as accessibility to the catalytic sites and coverage of the inorganic surface, which affect their efficiency (activity, selectivity and enantioselectivity). (C) 1999 Elsevier Science Ltd. All rights reserved.