Dinuclear gold(i) complexes of bridging bidentate carbene ligands: synthesis, structure and spectroscopic characterisation

Abstract

Eight dinuclear Au(I)-carbene complexes have been synthesized from various imidazolium-linked cyclophanes and related acyclic bis(imidazolium) salts, by treatment of the imidazolium salts with [Au(I)(SMe₂)Cl] in the presence of a carboxylate base. Single crystal structural studies showed that the Au(I)-carbene compounds contain dinuclear (AuL)₂ cations in which a pair of gold(I) centres are linked by a pair of bridging dicarbenoid ligands. Interestingly, the structural studies revealed short Au⋯Au contacts of 3.0485(3) Å and 3.5425(6) Å in two of these complexes. NMR studies showed that the (AuL)₂ cations constructed from the cyclophane-based ligands retain a relatively rigid structure in solution, whilst those of the non-cyclophane ligand systems are fluxional in solution. The electronic absorption and emission spectra of the complexes in solution at room temperature were recorded and the complex with the shortest Au⋯Au contact was found to emit intensely at 400 nm and more weakly at 780 nm upon excitation at 260 nm. The compounds with longer Au⋯Au separations were not emissive under these conditions.