Molecular Structure of a 1,3‐Diphosphaallene: (2,4,6‐tBu3C6H2)PCP(2,4,6‐tBu3C6H2), a Phosphorus Analogue of Carbon Disulfide

The first structure determination of a phosphacumulene by X‐ray diffraction indicates that the 1,3‐diphosphaallene 1, synthesized independently, is a genuine allene analogue. Isolated molecules are present in the crystal and the bulky substituents are arranged othogonally. The PC bonds of the almost linear PCP moiety are markedly shorter (1.63 Å) than “normal” PC double bonds (1.68–1.72 Å); the CS bonds in CS2 are also shorter than the CS bonds in thioketones equation image