Bi- and trinuclear copper(I) complexes of 1,2,3-triazole-tethered NHC ligands: synthesis, structure, and catalytic properties.

A series of copper complexes (3-6) stabilized by 1,2,3-triazole-tethered N-heterocyclic carbene ligands have been prepared via simple reaction of imidazolium salts with copper powder in good yields. The structures of bi- and trinuclear copper complexes were fully characterized by NMR, elemental analysis (EA), and X-ray crystallography. In particular, Cu2(L2)22 (3) and Cu2(L3)22 (4) were dinuclear copper complexes. Complexes Cu3(L4)23 (5) and Cu3(L5)23 (6) consist of a triangular Cu3 core. These structures vary depending on the imidazolium backbone and N substituents. The copper-NHC complexes tested are highly active for the Cu-catalyzed azide-alkyne cycloaddition (CuAAC) reaction in an air atmosphere at room temperature in a CH3CN solution. Complex 4 is the most efficient catalyst among these polynuclear complexes in an air atmosphere at room temperature.