Dinuclear Copper(I) Complexes of Phenanthrolinyl-Functionalized NHC Ligands

We have prepared a number of phenanthroline-functionalized imidazolium and triazolium salts from 2-iodo-1,10-phenanthroline and imidazole and triazole derivatives. Simple reactions of these imidazolium salts with copper powder at room temperature have afforded a series of dinuclear copper­(I)-NHC complexes doubly bridged by N-(1,10-phenanthrolin-2-yl)­imidazolylidene ligands in excellent yields. The two phen-NHC ligands are either head-to-head or head-to-tail arranged depending upon the steric repulsion of the substituents. Reactions of imidazolium halides and copper yielded dinuclear complexes [Cu2(μ-X)­(L6)2]­X (X = Cl, Br, I) in nearly quantitative yields. The dinuclear [Cu2(L10)2(μ-MeCN)]2+ was similarly obtained through 1,2,4-triazolium salts and copper, and the compound consists of a bridging CH3CN molecule, representing the first example of Cu-NHC complexes with a 3c–2e bond. These Cu­(I) complexes have been characterized by NMR spectra and elemental analysis and further confirmed by X-ray diffraction analysis. These dinuclear copper-NHC complexes are highly active for cycloaddition reaction of alkynes and azides at room temperature. [Cu2(μ-X)­(L6)2]­X are the most efficient catalysts among these dinuclear complexes in acetonitrile, which are superior to the commonly used copper catalysts for click reaction.