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

Abstract

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)]₂²⁺[PF₆⁻]₂ (11) and [Au^I(L_C1)]₂²⁺[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)]₂²⁺[PF₆⁻]₂ (15) was prepared by transmetallation between the related precursor [Ag^I(L_C3)]₂²⁺[PF₆⁻]₂ (10) and Au(SMe₂)Cl. The Au(III) complexes, [Au^III(L_py)Br₂]₂²⁺[PF₆⁻]₂ (16), [Au^III(L_C1)Br₂]₂²⁺[PF₆⁻]₂ (17) and [Au^III(L_C3)Br₂]₂²⁺[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)]₂²⁺[Br⁻]₂ (12) and 15 have been characterized by single-crystal X-ray diffraction analyses. The electrochemical and luminescence properties of the Au(I) and Au(III) compounds have been studied.