A diazadiphosphapentalene derivative 5 featuring a bent geometry with two phosphorus atoms at the bridgehead has been synthesized. Under mild conditions, compound 5 readily activated ammonia to afford 1-aza-2,3-diphospholene derivative 6 bearing an enamine group. The reaction is therefore viewed as a formal σ-bond metathesis between an N-H bond of ammonia and an endocyclic P-N bond of 5. Details of the reaction mechanism for ammonia activation as well as subsequent isomerization were explored by density functional theory calculations.

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The reactivity of diazadiphosphapentalene 1 towards various substrates was investigated. Reaction of 1 with ammonia-borane resulted in transfer hydrogenolysis concomitantly with the cleavage of a P-N bond. By treatment of 1 with 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO), oxidation took place at one of the phosphorus atoms of 1, and a P(V) /P(III) mixed-valence derivative was isolated. At the same time, it was demonstrated that only one of the phosphorus atoms in 1 behaves as an electron donor for electrophiles and Lewis acids. The former afforded an intramolecularly coordinated phosphine-phosphenium species, whereas the latter demonstrates the ligand property of 1. UV irradiation induced rearrangement of 1 into another example of another diazadiphosphapentalene.

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