Chemistry An Asian Journal 2010-05-03

(R)-(+)-Binol-functionalized mesoporous organosilica as a highly efficient pre-chiral catalyst for asymmetric catalysis.

Xiao Liu, Peiyuan Wang, Yan Yang, Peng Wang, Qihua Yang

Index: Chem. Asian J. 5(5) , 1232-9, (2010)

Full Text: HTML

Abstract

(R)-(+)-Binol-functionalized chiral periodic mesoporous organosilicas (PMOs) with different framework compositions were successfully synthesized by cocondensation of (R)-2,2'-di(methoxymethyl)oxy-6,6'-di(1-propyltrimethoxysilyl)-1,1'-binaphthyl (BSBinol) with 1,2-bis(trimethoxysilyl)ethane (BTME) and tetramethoxysilane (TMOS) using triblock copolymer P123 as a template in acidic solution. The mixture of BTME and BSBinol can result in a highly ordered mesostructure in an acidic medium but the mesoporous materials synthesized using a mixture of TMOS and BSBinol can only be obtained in a weak acidic buffer solution. All the materials are efficient catalysts (coordinated with Ti) for asymmetric addition of diethylzinc to aldehydes. The chiral PMO with ethane and (R)-(+)-Binol in the framework exhibits an enantioselectivity as high as 90% with a turnover frequency (TOF) of 104 h(-1), which is even higher than the homogeneous (R)-(+)-Binol catalyst (83% ee with TOF of 96 h(-1)) using toluene as solvent under similar conditions. This work demonstrates the positive effect of the rigid pore wall in increasing the enantioselectivity of the chiral PMOs.