A closer look at the phosphorus–phosphorus double bond lengths in meta-terphenyl substituted diphosphenes

The single crystal X-ray structure of DmpPPDmp (1, Dmp = 2,6-Mes2C6H3), which was previously reported to have a relatively short PP bond distance of 1.985(2) Å at room temperature, has been reexamined at variable temperatures. Crystallographic analyses of 1 at 100 K allow for resolution of disorder of the two phosphorus atoms (which is unresolvable from room temperature diffraction data), and for determination of a more conventional PP bond length of 2.029(1) Å. Single crystals of the closely related diphosphene DxpPPDxp (2, Dxp = 2,6-(2,6-Me2C6H3)2C6H3) show similar disorder in one of two crystallographically independent molecules in the unit cell. A value of 2.0276(4) Å is found for the non-disordered PP bonds at 100 K for 2. A new diphosphene Ar′PPAr′ (3, Ar′ = 2,6-Mes2-4-OMe–C6H3) has been prepared and its structure has also been examined. The PP bond length for 3 was determined to be 2.0326(9) Å and relatively free of the effects of disorder.

Detailed X-ray structural analyses of some diphosphenes of the form Ar′PPAr′ (Ar′ = meta-terphenyl) reveal the phosphorus atoms to be disordered, giving the impression that the P atoms are rattling around in between the two well ordered ligands (as if “in a can”). The disorder, if unresolved, can give rise to erroneous PP bond distances.Figure optionsDownload as PowerPoint slide