On the origins of the mechanistic variants in the thermal reactions of S ( = 1-3) with benzene

The S-π interaction between sulfur atom(s) and aromatic ring prevails in chemical and biochemical processes. The thermal gas-phase reactions of the S n + ( n = 1-3) ions with benzene have been explored by using Quadrupole-Ion Trap (Q-IT) mass spectrometry complemented by quantum chemical calculations. Charge transfer was found to be the only reaction channel for S 2 + /C 6 H 6 , while both charge transfer and bond activation are available for the S + /C 6 H 6 and S 3 + /C 6 H 6 couples. Upon interrogating the associated electronic origins, multiple factors were found to matter for these processes. In contrast to the σ-type two-center three-electron (2c-3e) S-π hemibond as reported previously, unusual S-π hemibonds were addressed for the S n + /C 6 H 6 couples, i.e. the 2c-3e π(S061Eπ) and the three-center three-electron (3c-3e) σ(S 2 061Eπ) hemibonds. Such S-π interaction was found to be responsible for the charge transfer processes in S + /C 6 H 6 and S 2 + /C 6 H 6 , but uninvolved in any transformation for S 3 + /C 6 H 6 . The various transformations upon thermal interactions of the S + , S 2 + and S 3 + ions with benzene.