Preparation of metal ion-planted mesoporous silica by template ion-exchange method and its catalytic activity for asymmetric oxidation of sulfide

For the preparation of metal ion-planted MCM-41 we have developed a template ion-exchange method, in which the template ions of as-synthesized MCM-41 are exchanged for the mete ions in aqueous media. The cations of Al, Ti, Cr, Mn, Zn, and Zr could be incorporated with high dispersion, while those of Fe, Co, Ni, Cu, Ga, Pd, and Pt formed small particles on the outside of the MCM-41 particles. Investigation on the time course of the template ion-exchange process suggested that the exchange proceeded first between the template ion and a proton and subsequently between the proton and a metal cation. Among the resulting metal ion-planted MCM-41s, Mn-MCM-41 showed excellent activity for the epoxidation of aromatic olefins. Trans-stilbene oxide was obtained in 93% yield from stilbene in MeCN-DMF solution at 328 K for 96 h. Ti-MCM-41 was the most suitable catalyst for the oxidation of sulfide with H2O2. It should be noted that the oxidation proceeded asymmetrically on Ti-MCM-41 in the presence of optically active tartaric acid in a CH2Cl2 solution. The chemical yield and optical yield of sulfoxide reached 54 and 30% ee, respectively.