An eight-member cyclic bis(iminophosphorane) was synthesized by treatment of 2,2′-bis(phosphino)azobenzene with pentachlorophenol via NN bond cleavage of the azobenzene. The crystal structure of the cyclic bis(iminophosphorane) was determined by the X-ray crystallographic analysis. A study on the reaction mechanism showed that both protonation of the azo moiety and intramolecular nucleophilic attacks