Catalytic oxidation of a thioether and dibenzothiophenes using an oxorhenium(V) dithiolate complex tethered on silica

Abstract

A silica-tethered version of the oxorhenium(V) dithiolate oxidation catalyst [–S(CH 2) 3S–]Re(O)(Me)(PPh 3) was prepared and characterized by solid state 13C and 31P NMR spectroscopy. This tethered complex (SiO 2-RTA)Re(O)(Me)(PPh 3) ( Fig. 2) catalyzes the selective oxidation of methyl( p-tolyl)sulfide (MTS), dibenzothiophene (DBT) and 4,6-dimethyldibenzothiophene (4,6-Me 2DBT)) to their corresponding sulfoxides and sulfones by tert-butylhydroperoxide (TBHP) and can be recycled at least four times without loss in activity. Although the rate of oxidation catalyzed by the immobilized catalyst is about a factor of three times lower than the homogeneous analog [–S(CH 2) 3S–]Re(O)(Me)(PPh 3), the supported catalyst is much more long-lived achieving approximately 3000 turnovers in the oxidation of DBT at 100 °C. The immobilized catalyst effectively catalyzes the oxidation of DBT and the hindered 4,6-Me 2DBT to their sulfoxides or sulfones in simulated petroleum feedstocks.