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

A diazadiphosphapentalene derivative <b>5</b> featuring a bent geometry with two phosphorus atoms at the bridgehead has been synthesized. Under mild conditions, compound <b>5</b> readily activated ammonia to afford 1-aza-2,3-diphospholene derivative <b>6</b> 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 <b>5</b>. Details of the reaction mechanism for ammonia activation as well as subsequent isomerization were explored by density functional theory calculations