Metal-Free σ‑Bond Metathesis in Ammonia Activation by a Diazadiphosphapentalene

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.