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 optica lly active beta-aminoalcohols such as (-)-ephedrine on MCM-41 type silica a s a member of micelle-templated silicas (MTS). Silylation of the surface wa s performed with halogenopropyltrimethoxysilane. Then, (-)-ephedrine was an chored through halogen substitution. These materials were used as chiral au xiliaries in the heterogeneous enantioselective catalysis of the alkylation of benzaldehyde by diethylzinc. This work deals with the study of the vari ous factors such as accessibility to the catalytic sites and coverage of th e inorganic surface, which affect their efficiency (activity, selectivity a nd enantioselectivity). (C) 1999 Elsevier Science Ltd. All rights reserved.