Tetraphosphatricyclo[4.2.0.02,5]octadienes; New Phosphaalkyne Cyclotetramers Derived from λ3σ2‐Diphosphetes

Two new tetrameric phosphaalkynes, the isomers 1 and 3, have been synthesized. The cyclotetramer 1 with a “central” P4 unit forms in high yield by the demetalation of the zirconium compound 2 with [(Ph3P)2NiCl2]. The isomer 3, which contains two PC double bonds, is obtained as a by-product in the reaction of 2 with hexachloroethane; the major product is the tetraphosphacubane 4.