Novel Diphosphetene Derivatives by Reactions of Di(isopropyl)aminophosphaethyne with Chalcogens or Halogens

The 1λ3σ2,3λ5σ4-diphosphetene derivatives 6a, 6b are formed in quantitative yields by reactions of di(isopropyl)aminophosphaethyne 1a with sulphur and selenium, respectively, at 25°C. 6a is also produced slowly from 1a and CS2. The tert-butylphosphaalkyne PC–tBu (1b), however, does not react with sulphur or selenium, but undergoes a slow reaction with CS2 to give the five-membered heterocycle 3,5-di-tert-butyl-1-thia-2,4-diphosphole as one of the main products. Halogenation of 1a using SO2Cl2, Br2 or I2 as reagents leads to the 1λ3σ2,3λ3σ3-diphosphetenium salts 9a–9c. X-ray diffraction studies of 6a and 6b prove that the easy formation of the four-membered diphospha-heterocycles is obviously governed by electronically delocalized phosphaallyl units within the unsaturated rings.