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-(1 R,2 R)-diaminocyclohexane was incorporated into the framework of mesoporous silica through one-step co-condensation of tetramethoxysilane with N.N'-bis[4-(trimethoethoxysilyl)benzyl]-(-)-(1R,2R)-diaminocyclohexane using cetyltrimethylammonium bromide as a structure-directing agent under basic conditions. All materials were fully characterized by X-ray diffraction. N-2 sorption isotherms, transmission electron microscopy, and C-13 and Si-29 cross-polarization magic-angle spinning nuclear magnetic resonance spectroscopy. Coordinated with [Rh(cod)Cl](2,) the material exhibited a TOF Lip to similar 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. (c) 2006 Elsevier Inc. All rights reserved.