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 CH(3){AuCl}(n)P=P{AuCl}(n')CH(3) 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.