Phosphine-Mediated Cleavage of Sulfur–Sulfur Bonds

A series of phosphine-mediated reactions resulting in the cleavage of sulfur–sulfur bonds in the imidazole-based dithione dimer (1) have been investigated. 2, the first X-ray structurally characterized 1,2,5-trithiepin, was synthesized through triphenylphosphine-mediated thermal extrusion of sulfur from 1. While reaction of 1 with P(NMe2)3 gave a zwitterionic phosphine–dithiolene complex (3), through heterolytic cleavage of the sulfur–sulfur bonds in 1, the thiophosphonate 4 was obtained when P(OMe)3 was combined with 1. Reaction of 2 with NHCiPr produced 5, containing a unique S+–C═C–S–C=C–S– zwitterionic core.