Synthesis and structural characterization of metal complexes with macrocyclic tetracarbene ligands

Fourteen Ag(I), Au(I), Ni(II), Pd(II), and Pt(II) complexes with macrocyclic tetradentate N-heterocyclic carbene (NHC) ligands were prepared via reactions between three macrocyclic tetrabenzimidazolium salts and metal precursors. All except two Au complexes were characterized using single-crystal X-ray diffraction. Three different structures, including a trinuclear one containing a NHC-Ag-(H2O) moiety and a hexanuclear propeller-like supramolecular assembly, are found for Ag-NHC complexes. Nine complexes of group 10 metal ions adopt square-planar geometry, in which the different ring-sizes of the macrocyclic tetracarbene ligands lead to a variation of metal-carbene bond lengths. pi-pi stackings are observed between the rigid aromatic benzimidazole rings in the nickel group complexes.