Imidovanadium( V ) Complexes as Reaction Partners for Kinetically Stabilized Phosphaalkynes: Synthesis of 1,2,4‐Azaphosphavanada( V )‐cyclobutenes, 1,3,5‐Triphosphabenzenes, and 1 H ‐1,2,4‐Azadiphospholes

Abstract Cycloaddition reactions of the kinetically stabilized phosphaalkynes 1 with the imidovanadium( V ) trihalides 9 furnish the 1,2,4‐azaphosphavanada( V )cyclobutenes 10 . The stability of these novel metallacyclic compounds depends solely on the substitutents of the imido unit. Thus, the imidovanadium( V ) species 9 with tertiary alkyl groups on the N atom form stable addition products with 1 while in the cases of compounds 9 with a lower degree of substitution at N (primary and secondary alkyl groups) the primarily formed adducts 10 undergo irreversible decomposition to afford the 1 H ‐1,2,4‐azadiphospholes 13 . Reactions of an excess of the phosphaaalkyne 1 with the vanadium complexes 9 furnish the corresponding triphosphabenzenes 8 in good yields (36–68 %). A catalytic reaction course has been demonstrated for the all‐ tert‐ butyl system 1 a/9 a in which the metallacyclic species 10 a serves as the catalytically active species. Poisoning of the catalyst leads to a second reaction pathway, which results in formation of the azatetraphosphaquadricyclanes 16 . By means of the stepwise use of different phosphaalkynes 1 a , b this methodology provides the first access to the differently substituted triphosphabenzenes through cyclotrimerization.