Mesoporous Ethane-Silicas Functionalized with trans-(1R,2R)-Diaminocyclohexane as Heterogeneous Chiral Catalysts

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• 作者：Dongmei Jiang ; Qihua Yang ; Jie Yang ; Lei Zhang ; Guiru Zhu ; Weiguang Su ; and Can Li
• 刊名：Chemistry of Materials
• 出版年：2005
• 出版时间：November 29, 2005
• 年：2005
• 卷：17
• 期：24
• 页码：6154 - 6160
• 全文大小：282K
• 年卷期：v.17,no.24(November 29, 2005)
• ISSN：1520-5002

文摘

Mesoporous ethane-silicas functionalized with trans-(1R,2R)-diaminocyclohexane were synthesizedby one-step co-condensation of 1,2-bis(trimethoxysilyl)ethane and N-[(triethoxysilyl)propyl]-(-)-(1R,2R)-diaminocyclohexane using octadecyltrimethylammonium chloride as the template under basic conditions.For comparison, the mesoporous silica containing trans-(1R,2R)-diaminocyclohexane was also synthesized.The structural characterizations (X-ray powder diffraction, transmission electron microscopy, and N₂sorption isotherms) show that the two materials have ordered two-dimensional-hexagonal mesostructureand wormhole-like structure, respectively. The integrity of the organic groups in the mesoporous materialsis confirmed by Fourier transform infrared and solid-state ¹³C and ²⁹Si cross-polarization magic-angle-spinning NMR spectroscopies. Mesoporous materials are used as catalysts for the asymmetric transferhydrogenation of acetophenone after complexing [Rh(cod)Cl]₂ to the chiral ligands, trans-(1R,2R)-diaminocyclohexane, in the mesopores. The catalyst with the ethane-bridged framework exhibits 82-96% conversion with 19-23% enantiomeric excess (ee), while the catalyst with pure-silica frameworkshows 48% conversion with 14% ee under identical reaction conditions. The enhanced catalytic activityof the mesoporous organosilicas is mainly caused by the specific adsorption and physical properties ofthe mesoporous network bridged with ethane groups, particularly the hydrophobic properties. Theenantioselectivity, albeit not yet high enough, demonstrates the possibility for synthesizing a new kindof chiral solid catalysts for potential applications in asymmetric reactions.