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

Abstract

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.

Toward a Porphyrin-Style NHC: A 16-Atom Ringed Dianionic Tetra-NHC Macrocycle and Its Fe(II) and Fe(III) Complexes

“…Macrocyclic N-heterocyclic carbenes (NHCs) have gained considerable attention in organometallic chemistry for a wide variety of applications, ranging from catalysis to fluorescence. − Since their structure inherently resembles naturally occurring porphyrins, a main emphasis for research has been on their heme-analogue Fe complexes. ,,, Indeed, several of those Fe-NHC complexes are more effective catalysts than heme analogues for oxidation reactions like aziridination and epoxidation. − Combining those traits with other known advantages of iron, such as very low toxicity, natural abundance, and low cost, the current effort put into the investigation of this type of organometallic systems is highly rational …”