New Structural Motifs Resulting from Internal Constraints in Chelating Bis(NHC) Ligands: A Dinuclear Ruthenium(II) Complex Featuring an η²‑Arene Binding Mode and a Remarkable New Tetrameric Silver(I) Halide Form

A novel dinuclear ruthenium­(II) complex containing two ortho-xylylene-linked bis­(NHC) ligands (NHC = N-heterocyclic carbene) has been synthesized via transmetalation from a silver-NHC complex. Each ruthenium atom in the dinuclear complex is chelated through the two carbene carbon atoms and, unusually, an η²-bound xylylene ring, two separate bis­(NHC) units being linked by a Ru­(μ-Cl)₃Ru core. The same bis­(NHC) ligand has yielded a neutral tetranuclear 4:2 AgBr:bis­(NHC) complex, where ligand steric constraints seemingly inhibit formation of structures derivative of the more familiar “cubane” or “step” forms, resulting in an interesting new structural type.