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 sulfid e whose pyrolysis and (perhaps) photolysis lead to the generation of phosph inidene chalcogenides Ar-P=Z (Z=O,S). Trapping experiments were carried out under conditions similar to the kinetic studies of the phosphirane chalcog enide pyrolyses that confirmed the formation of free Ar-P=Z. The trapping e xperiments were in accord with carbene-like character for Ar-P=Z, and the a ctivation 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 reac tions with small (or no) enthalpic barriers. (C) 1999 Elsevier Science Ltd. All rights reserved.