Periodic mesoporous organosilicas with trans-(1R,2R)-diaminocyclohexane in the framework: A potential catalytic material for asymmetric reactions

With benzyl group as a linker, trans-(1R,2R)-diaminocyclohexane was incorporated into the framework of mesoporous silica through one-step co-condensation of tetramethoxysilane with N,N′-bis[4-(trimethoxysilyl)benzyl]-(−)-(1R,2R)-diaminocyclohexane using cetyltrimethylammonium bromide as a structure-directing agent under basic conditions. All materials were fully characterized by X-ray diffraction, N2 sorption isotherms, transmission electron microscopy, and 13C and 29Si cross-polarization magic-angle spinning nuclear magnetic resonance spectroscopy. Coordinated with [Rh(cod)Cl]2, the material exhibited a TOF up to ∼414 h−1 with 30% ee for the asymmetric transfer hydrogenation of acetophenone. Various ketones were hydrogenated with different activities and enantioselectivities. An enantioselectivity of about 61% ee was observed in the case of 2-acetylnaphthalene. Moreover, a comparison of the catalytic properties of the materials with benzyl and propyl groups as linkers indicates the importance of the rigidity and electron-withdrawing ability of the linker in the high reaction rate of the catalysts.