Investigation of heterogeneous asymmetric dihydroxylation over OsO 4–(QN) 2PHAL catalysts of functionalized bimodal mesoporous silica with ionic liquid

Abstract

A novel synthesis of the functionalized bimodal mesoporous silica with ionic liquid (FBMMs) was performed. After grafting 1-methyl-3-(trimethoxysilyl)propylimidazolium chloride onto the surface of bimodal mesoporous silicas, 1,4-bis(9-O-quininyl)phthalazine ((QN) 2-PHAL) and K 2Os(OH) 4·2H 2O were immobilized onto the modified FBMMs by adsorption or ionic exchange methods, and then, the asymmetric dihydroxylation reaction was carried out by using solid catalysts. Techniques such as X-ray diffraction, Fourier Transform Infrared spectroscopy, N 2 adsorption and desorption were employed to characterize their structure and properties. The results showed that the mesoporous ordering degree of bimodal mesoporous silica decreased after functionalization and immobilization of OsO 4–(QN) 2PHAL. Being very effective in asymmetric dihydroxylation with high yield and enantioselectivity, the prepared heterogeneous solid catalyst could be recycled for five times with little loss of enantioselectivity, with comparison of those results obtained in homophase system. Moreover, the effect of Osmium catalyst on asymmetric dihydroxylation was investigated.