Pyrolysis and photolysis of 3,4,5-triphenyl-4-phosphabicyclo[3.1.0]hex-2-ene-4-oxide and the 1:1 adduct of diazomethane with 1,2,5-triphenylphosphole oxide lead to the formation of compounds of formula C46H36O2P2, andC46H34O2P2, respectively. These compounds are shown to be derivatives of the 4,4′-diphosphabi(cyclohexa-1,5-dienyl) and 4,4′-diphosphabi(cyclohexa-2,5-dienylidene) systems, respectively, and possible mechanisms for the formation of these systems are briefly discussed.