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

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) Angstrom and 3.5425(6) Angstrom 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.