Copper and silver complexes of tris(triazole)amine and tris(benzimidazole) amine ligands: Evidence that catalysis of an azide-alkyne cycloaddition ("click") reaction by a silver tris(triazole)amine complex arises from copper impurities

The synthesis and characterization of a silver complex of the tripodal triazole ligand, tris(benzyltriazolylmethyl)amine (TBTA, L1), that is used as promoter to enhance CuI-catalyzed azide-alkyne cycloaddition (CuAAC) reactions is reported. X-ray analysis of the silver(I) complex with L1 reveals a dinuclear cation, [Ag2(L1) 2]2+, that is essentially isostructural to the copper(I) analogue. While the [Ag2(L1)2](BF 4)2 complex provides catalysis for the azide-alkyne cycloaddition process, evidence is presented that this arises from trace copper contamination. The synthesis of silver(I), copper(II), and copper(I) complexes of a second tripodal ligand, tris(2-benzimidazolymethyl)amine (L2), which is used to enhance the rate of CuAAC reactions, is also reported. X-ray crystallography of the CuI complex [CuI3(L 2)2(CH3CN)2](BF4) 3 offers structural insight into previous mechanistic speculation about the role of this ligand in the CuAAC reaction. © 2014 American Chemical Society.