Selective Synthesis of a Phosphine Sulfide-Capped Hexasulfide by the Reaction of a Stable Dialkylphosphinyl Radical with Elemental Sulfur

Sulfur-sulfur bond activation by a stable phosphinyl radical was investigated. Treatment of the radical with di-p-tolyl disulfide afforded a p-tolylthiophosphine via an SH2 process followed by radical coupling. Reaction of the phosphinyl radical with S8 selectively provided a 1,6-bis(thiophosphoryl)hexasulfide as the initial product.The formation of the hexasulfide suggests that both radical and nucleophilic S-S bond activation processes drive this reaction. The hexasulfide gradually decomposed into phosphorus-sulfur heterocycles such as 2,3-thiaphosphirane 1-sulfide, dithiaphosphetane 1-sulfide, and 2,3,4-trithiaphospholane 1-sulfide.Based on the structures of products, silyl migration from carbon to sulfur atoms is proposed as the key step in the formation of the phosphorus-sulfur heterocycles.