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

摘要

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 CuIcatalyzed azide-alkyne cycloaddition (CuAAC) reactions is reported. X-ray analysis of the silver(I) complex with L1 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](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 (L~2), which is used to enhance the rate of CuAAC reactions, is also reported. X-ray crystallography of the CuI complex [Cu_3~I(L~2)_2(CH_3CN)_2](BF_4)_3 offers structural insight into previous mechanistic speculation about the role of this ligand in the CuAAC reaction.