Dinuclear gold(I) and gold(III) complexes of bridging functionalized bis(N-heterocyclic carbene) ligands: synthesis, structural, spectroscopic and electrochemical characterizations

We report the synthesis of Au(I) and Au(III) complexes, involving alcohol functionalized bis(N-heterocyclic carbene) ligands. Two short reaction pathways lead to the diimidazolium precursors, namely 1,1'-(2,6-pyridinediyl) bis[3-(2-hydroxyethyl)-1H-imidazol-3-ium] diiodide (2), 3,3'(methanediyl) bis[1-(2-hydroxy-2-methylpropyl)-1H-imidazol-3-ium] dibromide (4) and 3,3'-(1,3-propanediyl) bis[1-(2-hydroxy-2-methylpropyl)-1H-imidazol-3-ium] bis(4-methylbenzenesulfonate) (6), in which the two azolium rings are bridged by a rigid pyridine unit or an aliphatic chain (C1 or C3). The Au(I) complexes [Au-I(L-py)](2)(2+)[PF6-](2) (11) and [Au-I(L-C1)](2)(2+)[PF6-](2) (13) were obtained by direct metallation of the salts 2 and 4, respectively, in the presence of sodium acetate with Au(SMe2) Cl, followed by an anionic metathesis in the presence of KPF6. The trimethylene compound [Au-I(L-C3)](2)(2+)[PF6-](2) (15) was prepared by transmetallation between the related precursor [Ag-I(L-C3)](2) (2+)[PF6-](2) (10) andAu(SMe2)Cl. The Au(III) complexes, [Au-III(L-py) Br-2](2)(2+)[PF6-](2) (16), [Au-III(L-C1)Br-2](2)(2+)[PF6-](2) (17) and [Au-III(L-C3)Br-2](2)(2+)[PF6-](2) (18) were generated by oxidation of the corresponding Au(I) species with an excess of elemental bromine. Complexes 11, [Au-I(L-C1)](2)(2+)[Br-](2) (12) and 15 have been characterized by single-crystal X-ray diffraction analyses. The electrochemical and luminescence properties of the Au(I) andAu(III) compounds have been studied.