A molecularly defined copper acetylide cluster with ancillary N‐heterocyclic carbene (NHC) ligands was prepared under acidic reaction conditions. This cluster is the first molecular copper acetylide complex that features high activity in copper‐catalyzed azide–alkyne cycloadditions (CuAAC) with added acetic acid even at −5 °C. Ethyl propiolate protonates the acetate ligands of the dinuclear precursor complex to release acetic acid and replaces one out of four ancillary ligands. Two copper(I) ions are thereby liberated to form the core of a yellow dicationic C₂‐symmetric hexa‐NHC octacopper hexaacetylide cluster. Coalescence phenomena in low‐temperature NMR experiments reveal fluxionality that leads to the facile interconversion of all of the NHC and acetylide positions. Kinetic investigations provide insight into the influence of copper acetylide coordination modes and the acetic acid on catalytic activity. The interdependence of “click” activity and copper acetylide aggregation beyond dinuclear intermediates adds a new dimension of complexity to our mechanistic understanding of the CuAAC reaction.

中文翻译：

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CuAAC催化中的乙酰铜助熔剂簇。

在酸性反应条件下，制备了具有辅助N-杂环卡宾（NHC）配体的分子定义的乙炔铜簇。该簇是第一个分子乙炔铜复合物，即使在-5°C时，在铜催化的叠氮化物-炔烃环加成反应（CuAAC）中，也具有添加的乙酸，具有很高的活性。丙酸乙酯使双核前体复合物的乙酸盐配体质子化，释放出乙酸，并取代了四个辅助配体中的一个。由此释放出两个铜（I）离子，以形成黄色指示性C ₂的核心对称的NHC八铜六乙炔基对称簇。低温NMR实验中的聚结现象显示出通量性，导致所有NHC和乙炔键位置之间都易于转换。动力学研究提供了对铜乙炔铜配位模式和乙酸对催化活性的影响的见解。双核中间物以外的“点击”活性和乙炔铜聚集之间的相互依赖性为我们对CuAAC反应的机理理解增加了复杂性的新维度。