A P₂C₂ Four‐Membered Ring with Unusual Bonding—Synthesis, Structure, and Ring Opening of a 1,3‐Diphosphacyclobutane‐2,4‐diyl

An open form of a 2,4-diphosphabicyclobutane is one way to describe the unprecedented structure of the P2C2 heterocycle 1 (Ar = 2,4,6-tBu3C6H2). Ab initio calculations on 1 show that a partially delocalized π system exists with a considerable diradical contribution. Dark red 1 is accessible from ArP  CCl2 and nBuLi.