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(μ-H)]2 with DBTO2 turned out to be catalytically less
efficient compared with [(dippe)­Ni­(μ-H)]2, but the
first allowed the isolation and full characterization of several reaction
intermediates, such as [(dippe)­Pt­(κ2-C,S-DBTO2)]. It was demonstrated that
this is a key intermediate in all the deoxydesulfurization reactions
of the above-mentioned aromatic sulfones (DBTsO2).