Inorganic Chemistry, Vol.53, No.13, 6503-6511, 2014
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, L-1), that is used as promoter to enhance Cu-I-catalyzed azide-alkyne cycloaddition (CuAAC) reactions is reported. X-ray analysis of the silver(I) complex with L-1 reveals a dinuclear cation, [Ag-2(L-1)(2)](2+), that is essentially isostructural to the copper(I) analogue. While the [Ag-2(L-1)(2)](BF4)(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 (1,2), which is used to enhance the rate of CuAAC reactions, is also reported. X-ray crystallography of the Cu-I complex [Cu-3(I)(L-2)(2)(CH3CN)(2)](BF4)(3) offers structural insight into previous mechanistic speculation about the role of this ligand in the CuAAC reaction.