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]­(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.

本文报道了三脚架状三唑配体三(苄基三唑基甲基)胺（tris(benzyltriazolylmethyl)amine, TBTA, L1）的银配合物的合成与表征，该配体作为助促进剂可强化一价铜催化的叠氮-炔环加成（CuI-catalyzed azide–alkyne cycloaddition, CuAAC）反应。对该配体L1的银(I)配合物进行X射线分析后发现，其存在双核阳离子结构[Ag₂(L1)₂]²⁺，该结构与对应的铜(I)配合物基本同构。尽管[Ag₂(L1)₂](BF₄)₂配合物对叠氮-炔环加成过程表现出催化活性，但相关实验证据表明，其催化活性实际来源于痕量铜杂质。本文同时报道了第二种三脚架状配体三(2-苯并咪唑基甲基)胺（tris(2-benzimidazolymethyl)amine, L2）的银(I)、铜(II)及铜(I)配合物的合成，该配体可用于提升CuAAC反应的反应速率。对铜(I)配合物[Cu₃(L2)₂(CH₃CN)₂](BF₄)₃进行X射线晶体学分析，为此前关于该配体在CuAAC反应中作用机制的推测提供了结构层面的实验佐证。