Imidazolium-based organoiridium-functionalized periodic mesoporous organosilica boosts enantioselective reduction of alpha-cyanoacetophenones, alpha-nitroacetophenones, and beta-ketoesters

摘要

An imidazolium-based, organoiridium-functionalized periodic mesoporous organosilica is developed through complexation of chiral pentafluorophenylsulfonyl-1,2-diphenylethylenediamine and organoiridium-functionalized periodic mesoporous organosilica. Structural analyses and characterizations of catalyst reveal well-defined single-site iridium active species within its organosilicate network. Electron microscopy confirms a highly ordered dimensional-hexagonal mesostructure. This bifunctional heterogeneous catalyst displays excellent catalytic performance in the enantioselective reduction of a-cyano and alpha-nitroacetophenones. As expected, incorporation of imidazolium-functionality within hydrophobic periodic mesoporous organosilica promotes catalytic activity and enantioselectivity. In addition, this heterogeneous catalyst can be recovered and reused for at least eight times without loss of its catalytic activity. Furthermore, the approach described here can also construct another organoiridium-functionalized periodic mesoporous organosilica through postcoordination of chiral methylsulfonyl-1,2-diphenylethylenediamine, which provides excellent catalytic activity and enantioselectivity in the enantioselective reduction of beta-ketoesters. The method presented here offers a potential way for immobilizing various chiral ligands to construct chiral organometal-functionalized periodic mesoporous organosilicas. (C) 2014 Elsevier Inc. All rights reserved.