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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

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posted on 07.07.2014, 00:00 by Timothy U. Connell, Christine Schieber, Ilaria Proietti Silvestri, Jonathan M. White, Spencer J. Williams, Paul S. Donnelly
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]­(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 (L2), which is used to enhance the rate of CuAAC reactions, is also reported. X-ray crystallography of the CuI complex [CuI3(L2)2(CH3CN)2]­(BF4)3 offers structural insight into previous mechanistic speculation about the role of this ligand in the CuAAC reaction.