Design of mesoporous aluminosilicates supported (1R,2S)-(−)-ephedrine: evidence for the main factors influencing catalytic activity in the enantioselective alkylation of benzaldehyde with diethylzinc
作者:S Abramson、M Laspéras、D Brunel
DOI:10.1016/s0957-4166(02)00103-9
日期:2002.3
(-)-Ephedrine, used as a model beta-amino alcohol, was covalently anchored on mesoporous micelle templated aluminosilicates (Al-MTS) through nucleophilic substitution of halogenoalkyl(aryl)silane chains previously grafted on the surface. The covalent grafting was performed either by silylation (method a) or b Surface sol-gel (method 6). The latter method provided higher loading. However, the higher loading lowers the resulting mesoporous volume. The coupling alkyl halide moiety was then substituted with (1R,2S)-(-)-ephedrine. Used as chiral auxiliaries in the heterogeneous enantioselective catalysis of the alkylation of benzaldehyde by diethylzine, these materials showed properties which depend mainly on the grafting method. The best results (activity, enantioselectivity) were obtained with catalysts prepared from Supports featuring high initial pore diameter. The effect of the regular porosity on the efficiency and enantioselectivity was shown. Dilution of catalytic sites by alkyl groups and rigidification of the linker were also studied. (C) 2002 Elsevier Science Ltd. All rights reserved.
(-)-麻黄碱被用作模型β-氨基醇,通过卤代烷基(芳基)硅烷链之前接枝在介孔胶束模板铝硅酸盐(Al-MTS)表面的亲核取代反应,将其共价键合到介孔胶束模板铝硅酸盐上。共价接枝可以通过两种方法进行:方法a为硅烷化,方法b为表面溶胶-凝胶法。后者提供了更高的负载量,但较高的负载量会降低介孔体积。随后,将连接基的卤代烷基部分替换成(1R,2S)-(-)-麻黄碱。在异相手性选择性催化苯甲醛与二乙基锌的烷基化反应中,这些材料用作手性辅剂,显示的性能主要取决于接枝方法。具有高初始孔径的载体制备的催化剂表现出最佳的活性和对映选择性。研究表明介孔的规则孔结构对反应效率和对映选择性有显著影响。此外,还研究了烷基化对活性部位的稀释效应以及连接基的刚性化效应。©2002 Elsevier Science Ltd. 保留所有权利。