Reaction of three-coordinate phosphorus compounds with organophosphorus pseudohalogens 3. Phosphonium and phosphorane intermediates in the desulfurization and deoxygenation of bis(phosphinoyl) disulfides. Influence of Lewis acids on the reaction chemoselectivity

Abstract

The reactions of bis(phosphinoyl) disulfides RR¹P(O)S–S–P(O)RR¹1 with P^III compounds have been investigated and various mechanistic features have been elucidated by variable-temperature ³¹P NMR spectroscopy. These studies show that in most cases phosphonium intermediates [[graphic omitted]P(O)–S–[graphic omitted]^–O–P(S)[graphic omitted]]5 and [[graphic omitted]P(S)–O–[graphic omitted] ^–O–P(S)[graphic omitted]]6 are involved. In cases where ligands on P^III increase the stability of the five-coordinate structures phosphorane intermediates are observed. In the isomerization 5→6, the mode of decomposition (desulfurization, deoxygenation or dealkylation) to give stable end products is influenced by electronic and steric factors. The presence of the Lewis acid BF₃ influences considerably the stability of the transient species 5 and 6 and the chemoselectivity of the reaction.