A μ2-(η1,η2)-dinuclear diphosphene complex having two W(CO)5 groups with dimethyl acetylenedicarboxylate, 4-phenyl-1,2,4-triazoline-3,5-dione and diethyl azodicarboxylate was applied to P-heterocyclic synthesis, i.e., using a singlet carbene-type reactivity of a homonuclear π-system assisted by a haptotropic shift thus rendering a more nucleophilic β phosphorus and, hence, a subsequent ring expansion.