Helical silica immobilizing ruthenium complexes for highly asymmetric addition of diethylzinc to aldehydes

Abstract

A new series of helical silica were synthesized by doping of l-sodium hydrogen glutamate in a sol–gel procedure. Characterizations revealed doping of l-sodium hydrogen glutamate improved porosity, morphology, hydrolysis resistance and internal chirality of silica matrix. Meanwhile, chiral ruthenium complexes were synthesized and immobilized into helical silica in order to catalyze asymmetric addition of diethylzinc to aryl aldehydes. Catalysis revealed chiral induction synergy of multiple chiral centers on one ruthenium complex was existent. Ruthenium complexes immobilized over the glutamate-doped helical silica showed much better ee values and yields than those over blank-doped one. Immobilization of helical silica-supported ruthenium complex into imidazolium ionic liquid was efficiently recycled during three times. This work not only provided new chiral silica, but also studied their application in asymmetric catalysis.