Structural control of mesoporous ethane-silicas with trans-(1 R,2 R)-diaminocyclohexane in the pore and asymmetric catalysis

Abstract

Design and synthesis of periodic mesoporous materials containing chiral functionalities remain to be a challenging and interesting research topic. In this study, the mesostructures of the ethane-silicas with trans-(1 R,2 R)-diaminocyclohexane in the pore were controlled in acidic medium using KCl and 1,3,5-trimethylbenzene (TMB) as additives in the presence of triblock copolymer P123. It was observed that an increase in Si/P123 molar ratio leads to a gradual increase in the pore diameter. Simultaneously, the 2-D hexagonal mesostructure gradually transforms from open pore system into plugged pore system. The addition of TMB not only expands the pore diameter but also induces the mesophase transformation from 2-D hexagonal mesostructure into mesostructured cellular foam (MCF). Inorganic salt KCl plays a key role in the formation of ordered pore structure. Through adjusting the amount of KCl and TMB, the mesoporous materials with bimodal pore structure can be obtained. Increasing the amount of KCl can increase the pore diameter of the material in the presence of TMB. After complexed with [Rh(cod)Cl] 2, the catalytic properties of the trans-(1 R,2 R)-diaminocyclohexane functionalized mesoporous ethane-silicas with various pore structures were tested in the asymmetric transfer hydrogenation of acetophenone. The catalysts show medium enantioselectivity and high activity. The catalyst with plugged pore structure exhibits the highest catalytic activity among all the catalysts investigated.