Chen Haoqing, Cai Chengzhi, Li Siheng, Ma Yong, Luozhong Sijin, Zhu Zhiling
Department of Chemistry, University of Houston, 3585 Cullen Blvd., Houston, Texas, 77204-5003, USA.
Department of Pharmacological and Pharmaceutical Sciences, University of Houston, 1441 Moursund St., Houston, Texas, 77030, USA.
Chemistry. 2017 Apr 3;23(19):4730-4735. doi: 10.1002/chem.201700555. Epub 2017 Mar 15.
Tris(triazolylmethyl)amine ligands (TL) are widely used to accelerate the Cu -catalyzed azide-alkyne cycloaddition (CuAAC) reaction, but its mechanistic role remains unclear. Using electrospray ionization mass spectrometry, we detected for the first time the trinuclear TL-Cu -acetylide and the dinuclear TL-Cu -acetylide complexes in aqueous solution. The apparent second-order rate constants of their reaction with an azide were 27 and 783 m ⋅s when the alkyne was tethered to TL. In the catalytic system without the tether, the rate constant increased to >146 m ⋅s for the TL-Cu -acetylide, but dropped about 14-fold to approximately 55 m ⋅s for the TL-Cu -acetylide. The results indicated that TL accelerated the reaction by stabilizing the Cu - and Cu -acetylide and their azide-adduct intermediates, but this role is largely weakened by excess alkyne and other competing ligands under catalytic conditions.
三（三唑基甲基）胺配体（TL）被广泛用于加速铜催化的叠氮化物-炔烃环加成反应（CuAAC），但其作用机制仍不清楚。利用电喷雾电离质谱，我们首次在水溶液中检测到了三核TL-Cu-乙炔化物和双核TL-Cu-乙炔化物配合物。当炔烃连接到TL上时，它们与叠氮化物反应的表观二级速率常数分别为27和783 m·s。在没有连接基团的催化体系中，TL-Cu-乙炔化物的速率常数增加到>146 m·s，但TL-Cu-乙炔化物的速率常数下降了约14倍，降至约55 m·s。结果表明，TL通过稳定Cu-和Cu-乙炔化物及其叠氮化物加合物中间体来加速反应，但在催化条件下，过量的炔烃和其他竞争配体会大大削弱这种作用。
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