Use of ring-expanded diamino- and diamidocarbene ligands in copper catalyzed azide-alkyne "click" reactions

The two-coordinate ring-expanded N-heterocyclic carbene copper(I) complexes [Cu(RE-NHC)(2)](+) (RE-NHC = 6-Mes, 7-o-Tol, 7-Mes) have been prepared and shown to be effective catalysts under neat conditions for the 1,3-dipolar cycloaddition of alkynes and azides. In contrast, the cationic diamidocarbene analogue [Cu(6-MesDAC)(2)](+) and the neutral species [(6-MesDAC)CuCl](2) and [(6-MesDAC)(2)(CuCl)(3)] show good activity when the catalysis is performed on water.