Organophosphorus compounds Part 164. 2,4-Disubstituted 1,3-diphosphacyclobutadienes: generation and trapping reactions

1λ3,3λ3-Diphosphacyclobutadienes have been specifically generated for the first time through hexachloroethane-induced extrusion of the organophosphorus ligands from dimeric zirconocene–phosphaalkyne complexes. The species were chemically characterized indirectly by reactions with appropriate trapping reagents. Thus, the use of bis(acceptor)-substituted alkynes gave rise to 2,5-diphosphabenzvalenes, whereas reactions with N-methylmaleinimide and donor-substituted alkynes such as bis(diethylamino)acetylene resulted in the formation of 1,3-diphospha-Dewar-benzenes. Representatives of both classes of compounds were analyzed by X-ray crystallography. Kinetically stabilized phosphaalkynes reacted similarly to furnish tetraphosphabishomoprismanes through a sequence of [4+2] and [2+2+2] cycloaddition processes.