Abstract
V/MCM-41 was prepared by impregnation of MCM-41, calcined at two different temperatures (550 and 750 °C), with vanadium (V) oxytriisopropoxide (VO(O i Pr)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(O i Pr)2 and bipodal (≡SiO)2–VO(O i Pr) 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.