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.