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 d10–d10 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° in the Cu complex 4 and by 31° 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.