Diphosphene

In chemistry, diphosphene is a molecule that has a phosphorus-phosphorus double bond, indicated by R-P=P-R'. Diphosphenes are heavier analogues of azo compounds.

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In 1887, H. Köhler and A. Michaelis reported the isolation of a compound that was thought to be the phosphorus analogue of azobenzene, "Ph-P=P-Ph", but it later turned out to be wrong.

In 1981, Masaaki Yoshifuji reported the first stable diphosphene, which is kinetically stabilized by very bulky two substituents attached to the phosphorus atoms. Numerous other diphosphenes with a variety of substituents have been synthesized and structurally characterized. In addition, there are several transition metal complexes where the diphosphene behaves as an end-on donor through one or both phosphorus atoms.

Most uncomplexed diphosphenes have trans-bent structures, in which the angles to the phosphorus are strongly influenced by the electronic effects of the substituents. The P-P distances are in the range 195.4 to 204.4 pm (1.954 to 2.044 Å) (compared to the single P-P bond length of 222 pm).