Unusual Phosphorus−Phosphorus Double Bond Contraction upon Mono- and Di-auration of a Diphosphene

The diphosphene Mes*PMes* (Mes* = 2,4,6-tri-tert-butylphenyl; 1) reacted with 1 or 2 equiv of Au(tht)Cl (tht = tetrahydrothiophene) to produce the stable monoaurated adduct Mes*{AuCl}PPMes* (2) or diaurated adduct Mes*{AuCl}PP{AuCl}Mes* (3) respectively. The products were characterized by X-ray crystallography, UV−visible, IR, Raman, and multinuclear NMR spectroscopies, as well as by density functional theory calculations. The crystallographic and Raman spectroscopic data provide physical evidence that the PP bond grows shorter and increases in strength upon auration; these observations are further examined by DFT calculations for a series of model compounds CH3{AuCl}nPP{AuCl}n′CH3 1′−3′ (n, n′ = 0 or 1). Compounds 1−3 represent a rare series of crystallographically characterized diphosphenes bearing zero, one, or two AuCl units on each phosphorus atom, allowing for a systematic analysis of the impact of Lewis acids on the phosphorus−phosphorus double bond.