Mechanistic Insights into the C-S Bond Breaking in Dibenzothiophene Sulfones

The reactivity of Grignard reagents in the presence of nickel catalysts is known to be highly efficient in the deoxydesulfurization of dibenzothiophene sulfone (DBTO2), 4-methyldibenzothiophene (4-MeDBTO2), and 4,6-dimethyldibenzothiophene (4,6-Me2DBTO2), to yield sulfur-free biphenyls via cross-coupling reactions. However, the mechanistic details involved in the process remained unknown. In this report the reactivity of [(dippe)Pt(mu-H)](2) with DBTO2 turned out to be catalytically less efficient compared with [(dippe)Ni(mu-H)](2), but the first allowed the isolation and full characterization of several reaction intermediates, such as [(dippe)Pt(kappa(2)-C,S-DBTO2)]. It was demonstrated that this is a key intermediate in all the deoxydesulfurization reactions of the above-mentioned aromatic sulfones (DBTsO2).