Dinuclear Coinage-Metal Complexes of Bis(NHC) Ligands: Structural Features and Dynamic Behavior of a Cu-Cu Complex

Binuclear complexes of copper, silver, and gold bearing a 2,2'-bipyridine analogue, the pyridazine annelated bis(N-heterocyclic carbene) ligand (vegi) 1, were prepared and structurally characterized. They all feature the shortest metal-metal distances that have been measured so far in complexes with this structural motif bearing neutral bidentate ligands, indicative of d(10)-d(10) interactions. While in the silver complex the linear coordination of each silver atom with two carbene ligands results in a planar complex, the ligand planes are twisted by 70 degrees in the Cu complex 4 and by 31 degrees in the gold complex 3. The copper complex shows a solvent-dependent equilibrium between the [Cu2L2](2+) complex and a [Cu2L3](2+) complex along with solvated CuPF6.