cThe chiral vanadyl salen complex was immobilized into mesoporous silica by a covalent grafting method using 3-aminopropyltriethoxysilane as a reactive surface modifier. The formation and integrity of the complex have been confirmed by FT-IR, UV-vis and BET measurements and the complex was tested in the asymmetric oxidation of sulfide to sulfoxide using H 2 O 2 as oxidant. The immobilized complex showed better catalytic activity than the neat complex, while the neat complex has deactivated in the reaction. The combination of the heterogenized catalyst, H 2 O 2 and CH 2 Cl 2 as solvent offers a selective catalytic system for oxidation of sulfide to sulfoxide with a low but significant enantioselectivity in the range of 8-10% ee. In addition, the heterogenized catalyst could be easily separated from the products and reused.

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V/MCM-41 was prepared by impregnation of MCM-41, calcined at two different temperatures (550 and 750 °C), with vanadium (V) oxytriisopropoxide (VO(OiPr)3). The calcination temperature of the support controls the surface silanol density, leading to different surface organometallic species, as shown by different characterisation techniques, such as 29Si CP-MAS NMR, UV-Vis and FT-IR. Monopodal ≡SiO–VO(OiPr)2 and bipodal (≡SiO)2–VO(OiPr) species are the major ones in V-MCM750, whereas bipodal and tripodal (≡SiO)3–VO are the major ones in V-MCM550. Monopodal and bipodal species are more active in the oxidation of methyl phenyl sulfide with alkyl hydroperoxides, with higher selectivity to sulfoxide than tripodal ones, but at the same time they are more easily deactivated. It is possible to perform the enantioselective oxidation using (S,S)-(+)-N,N‘-bis(3,5-di-tert-butylsalicylidene)-1,2-cyclohexanediamine as chiral ligand, with the monopodal species being the most efficient.

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