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.