Highly-efficient N-arylation of imidazole catalyzed by Cu(II) complexes with quaternary ammonium-functionalized 2-acetylpyridine acylhydrazone

Abstract The reaction of ( E )- N , N , N -trimethyl-2-oxo-2-(2-(1-(pyridin-2-yl)ethylidene)hydrazinyl)ethan-1-aminium-chloride ( HL Cl) with copper(II) perchlorate led to mononuclear [Cu L Cl]ClO 4 complex ( 1 ). The same reaction with excess of sodium azide gives dinuclear azido double end-on bridged Cu(II) complex [Cu 2 L 2 (μ- 1,1 -N 3 ) 2 ](ClO 4 ) 2 ( 2 ). In both complexes hydrazone ligand is NNO coordinated in monodeprotonated formally neutral zwitter-ionic form. Complexes were characterized by elemental analysis, IR spectroscopy and single-crystal X-ray crystallography. Variable‐temperature magnetic susceptibility measurements for dinuclear Cu(II) complex showed intra-dimer ferromagnetic coupling between Cu(II) ions ( J  = 7.4 cm −1 ). DFT-BS calculations provided explanation for magnetic properties of dinuclear Cu(II) complex. Both complexes were shown to highly efficiently catalyze the N -arylation of imidazole and benzimidazole with electron-poor or electron-rich aryl iodides, under user-friendly and sustainable conditions.