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. © 2014 American Chemical Society.