Controlling the coordination modes of a new and highly flexible ligand bearing two N-heterocyclic carbene moieties at a bipyridine backbone

A new and highly flexible biscarbene ligand with two imidazolin-2-ylidene moieties in 6,6'-position of a 2,2'-bipyridine was prepared and structurally characterised by X-ray analysis. Various silver complexes were prepared from the imidazolium salts. Depending on the counterion, the coordination mode of the ligand can be mono-or bidentate. Pd complexes are feasible directly from the imidazolium salt using palladium(II)-acetate or via transmetallation from silver carbene complexes with [PdCl2(CH3CN)(2)] or [PdCl2(COD)]. Controlled by the structure of the silver complexes the biscarbenebipyridine ligand is a di-or tetracoordinating ligand forming mono-or dinuclear complexes. The high flexibility of this ligand is confirmed by transmetallation from silver to copper, which results in formation of a dinuclear copper complex with two bridging biscarbene ligands.