2,6-Dimethoxyphenylphosphirane Oxide and Sulfide and their Thermolysis to Phosphinidene Chalcogenides—Kinetic and Mechanistic Studies

2,6-Dimethoxyphenylphosphirane is readily converted to its oxide and sulfide whose pyrolysis and (perhaps) photolysis lead to the generation of phosphinidene chalcogenides Ar–PZ (Z=O,S). Trapping experiments were carried out under conditions similar to the kinetic studies of the phosphirane chalcogenide pyrolyses that confirmed the formation of free Ar–PZ. The trapping experiments were in accord with carbene-like character for Ar–PZ, and the activation parameters suggest a non-least motion pathway for the addition of Ar–PZ to olefins. This represents quantitative evidence for the validity of the predictions of frontier-orbital theory for species that undergo reactions with small (or no) enthalpic barriers.