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

A silica-tethered version of the oxorhenium(V) dithiolate oxidation catalyst [–S(CH2)3S–]Re(O)(Me)(PPh3) was prepared and characterized by solid state 13C and 31P NMR spectroscopy. This tethered complex (SiO2-RTA)Re(O)(Me)(PPh3) (Fig. 2) catalyzes the selective oxidation of methyl(p-tolyl)sulfide (MTS), dibenzothiophene (DBT) and 4,6-dimethyldibenzothiophene (4,6-Me2DBT)) 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(CH2)3S–]Re(O)(Me)(PPh3), 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-Me2DBT to their sulfoxides or sulfones in simulated petroleum feedstocks.

Graphical abstractThe oxorhenium(V) dithiolate catalyst [S(CH2)3S]Re(O)(Me)(PPh3) tethered to silica was characterized by 13C and 31P CPMAS NMR spectroscopy and shown to catalyze the oxidation of methyl(p-tolyl)sulfide and dibenzothiophenes to their sulfoxides and sulfones at rates that are slightly slower than those of its homogeneous analog. The immobilized catalyst, however, offers the additional advantages of recyclability, extended stability and increased resistance to deactivation over the homogeneous catalyst. Figure optionsDownload full-size imageDownload as PowerPoint slide