Synthesis of the First 2H‐1‐Aza‐2‐phosphirene Complexes

A novel compound with an unsaturated three-membered ring, 2H-1-aza-2-phosphirene, is present in complex 1. This unusual ligand is formed in a surprisingly simple way in the reaction of the corresponding amino(aryl)carbenepentacarbonyltungsten(0) complex with [bis(trimethylsilyl)methylene]chlorophosphane. The crucial step is the rearrangement of 2-aza-1-phospha-4-tungsta-1,3-butadiene to give the 2H-1-aza-2-phosphirene tungsten complex.