Reversible Tautomeric Transformation between a Bis(amino)cyclodiphosph(V)azene and a Bis(imino)cyclodiphosph(V)azane.

The tautomeric four-membered-ring P-N heterocycles 1, 2, and 3 can be interconverted; the formation of the cyclodiphosph(V)azene 1 is enthalpically and entropically favored. The crystal structures of the tautomers 1 and 3 have been determined and indications are given regarding the mechanism of the interconversion.