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.