What is "diphosphenes"

In chemistry, a diphosphene is an organophosphorus compound that has a phosphorus-phosphorus double bond, denoted by R-P=P-R'. These compounds are not common but are of theoretical interest. Normally, compounds with the empirical formula RP exist as rings. However, when the organic substituent is very large, the diphosphene becomes stable. The parent compound, called diphosphene (diphosphaethylene), has the formula PH, but is not stable near room temperature.