A hybrid imidazolylidene/imidazolium nickel NHC complex: an isolated intermediate.

Macrocyclic ligand systems with a variety of (different) donor sites oftentimes give rise to very exciting and unexpected multinuclear metal complexes. We report herein the structure of a trinuclear mixed imidazolylidene/imidazolium nickel N-heterocyclic carbene (NHC) complex, namely di-μ-chlorido-bis{μ-calix[2]imidazolium[2]imidazolylidene[2]pyrazolate}trinickel(II) tetrakis(hexafluoridophosphate) acetonitrile tetrasolvate, [Ni(CHN)Cl](PF)·4CHCN or [Ni(L)Cl](PF)·4CHCN, that can be understood as a trapped reaction intermediate during the synthesis of the respective [NiL](PF) product. The structure not only contains protonated next to deprotonated imidazole heterocycles, but also Ni ions with fundamentally different coordination modes within one molecule. Two of the three metal atoms are coordinated in a square-pyramidal fashion by half a ligand molecule and one chloride ligand, whereas the third Ni ion is bound octahedrally by four pyrazolate moieties and two chloride anions.