N-Heterocyclic carbene gold(I) and silver(I) adducts of [Pt2(μ-S)2(PPh3)4]

Reaction of the metalloligand [Pt2(μ-S)2(PPh3)4] with the N-heterocyclic carbene (NHC) complexes IPrAuCl, IMesAuCl and IMesAgCl in methanol gave the first examples of metal adducts of [Pt2(μ-S)2(PPh3)4] that contain NHC ligands, namely [Pt2(μ-S)2(PPh3)4AuL]+ (L = IPr, IMes) and [Pt2(μ-S)2(PPh3)4AgIMes]+. The complexes were isolated as hexafluorophosphate salts. Reaction of [Pt2(μ-S)2(PPh3)4] with excess IPrAuCl in refluxing methanol yielded only the mono-adduct, in contrast to the behaviour with the gold(I) phosphine complex Ph3PAuCl, which undergoes double addition giving [Pt2(μ-SAuPPh3)2(PPh3)4]2+. The X-ray structure of [Pt2(μ-S)2(PPh3)4AuIPr]PF6 was determined and reveals that the ‘free’ sulfide is substantially sterically protected by the IPr ligand, accounting for the low reactivity towards addition of a second AgIPr+ moiety.