Stable Au complexes with four N-heterocyclic carbene groups can be prepared in high yield directly from KAuCl.

Gold(iii) N-heterocyclic carbene (NHC) complexes of form [Au(NHC)Cl]Cl were synthesized by reaction of KAuCl with bis- and tetrakis(imidazolium) salts in the presence of a mild base. Treatment of these complexes with KPF afforded four-coordinate Au complexes of form Au(NHC). X-Ray crystallography showed the [Au(NHC)] cations in the hexafluorophosphate salts to have a square planar Au(NHC) moiety [AuC 2.024(4)-2.082(7) Å]. In the [Au(NHC)Cl] cations in the chloride salts, coordination about Au was tetragonally-distorted octahedral, the axial Au-Cl bonds being substantially longer [AuCl 3.148(2)-3.693(1) Å] than the equatorial Au-C bonds [AuC 2.024(4)-2.082(7) Å]. NMR and conductance studies suggested that the structures of the complexes seen in the solid state persisted in DMSO solution, except in one case where a chlorido ligand dissociated from [Au(NHC)Cl] to form [Au(NHC)Cl]. The Au(NHC) unit was surprisingly robust. An Au complex was found to undergo H/D exchange reactions in DO solution at 100 °C with no signs of decomposition detectable by H NMR spectroscopy. H NMR studies showed that various complexes containing Au(NHC) moieties underwent little or no decomposition when heated at 120 °C in DMSO-d for extended periods.