On the origins of the mechanistic variants in the thermal reactions of Sx+ (x = 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 Sn+ (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 S2+/C6H6, while both charge transfer and bond activation are available for the S+/C6H6 and S3+/C6H6 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 Sn+/C6H6 couples, i.e. the 2c-3e π(S061Eπ) and the three-center three-electron (3c-3e) σ(S2061Eπ) hemibonds. Such S-π interaction was found to be responsible for the charge transfer processes in S+/C6H6 and S2+/C6H6, but uninvolved in any transformation for S3+/C6H6.