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Flower-like mesoporous silica: a bifunctionalized catalyst for rhodium-catalyzed asymmetric transfer hydrogenation of aromatic ketones in aqueous medium†
Fei Gao,Ronghua Jin,Dacheng Zhang,Quanxi Liang,Qunqun Ye,Guohua Liu
Green Chemistry Pub Date : 05/13/2013 00:00:00 , DOI:10.1039/C3GC40547H
Abstract

Functionalized flower-like mesoporous silica with a chiral organorhodium functionality incorporated within its silica framework is prepared through an assembly of chiral 4-((trimethoxysilyl)ethyl)phenylsulfonyl-1,2-diphenylethylenediamine and tetraethoxysilane under a cooperative dual-template approach followed by complexation with organorhodium complexes. Structural characterization discloses its mesostructure and well-defined single-site chiral organorhodium functionality, while electron microscopy analyses reveal the uniformly distributed three-dimensional spherical flowers constructed by the stacking of leaf-shaped nanoflakes. In particular, as a bifunctionalized heterogeneous catalyst, it shows excellent catalytic activity and high enantioselectivity in the asymmetric transfer hydrogenation of aromatic ketones in aqueous medium (more than 99% conversion and up to 97% ee). The superior catalytic performance is attributed to the synergistic effect of the salient cetyltrimethylammonium bromide phase-transfer function and confined chiral organorhodium catalytic nature. Furthermore, this heterogeneous catalyst could be recovered easily and reused repeatedly (ten times) without affecting its ee value, showing a practical application in asymmetric synthesis.

Graphical abstract: Flower-like mesoporous silica: a bifunctionalized catalyst for rhodium-catalyzed asymmetric transfer hydrogenation of aromatic ketones in aqueous medium
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