A neutral hybrid macrocycle with two trans-positioned N-heterocyclic carbenes (NHCs) and two pyridine donors hosts copper in three oxidation states (+I-+III) in a series of structurally characterized complexes (1-3). Redox interconversion of [LCu]+/2+/3+ is electrochemically (quasi)reversible and occurs at moderate potentials (E1/2 =-0.45 V and +0.82 V (vs. Fc/Fc+ )). A linear CNHC -Cu-CNHC arrangement and hemilability of the two pyridine donors allows the ligand to adapt to the different stereoelectronic and coordination requirements of CuI versus CuII /CuIII . Analytical methods such as NMR, UV/Vis, IR, electron paramagnetic resonance, and Cu Kβ high-energy-resolution fluorescence detection X-ray absorption spectroscopies, as well as DFT calculations, give insight into the geometric and electronic structures of the complexes. The XAS signatures of 1-3 are textbook examples for CuI , CuII , and CuIII species. Facile 2-electron interconversion combined with the exposure of two basic pyridine N sites in the reduced CuI form suggest that [LCu]+/2+/3+ may operate in catalysis via coupled 2 e- /2 H+ transfer.

中文翻译：

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一种适应性强的 N-杂环卡宾大环，其具有三种氧化态的铜。

具有两个转位 N-杂环卡宾 (NHC) 和两个吡啶供体的中性杂化大环在一系列结构特征配合物 (1-3) 中以三种氧化态 (+I-+III) 承载铜。[LCu]+/2+/3+ 的氧化还原相互转化是电化学（准）可逆的，并且发生在中等电位（E1/2 =-0.45 V 和 +0.82 V（相对于 Fc/Fc+））。线性 CNHC -Cu-CNHC 排列和两个吡啶供体的半性允许配体适应 CuI 与 CuII /CuIII 的不同立体电子和配位要求。NMR、UV/Vis、IR、电子顺磁共振和 Cu Kβ 高能分辨率荧光检测、X 射线吸收光谱以及 DFT 计算等分析方法可以深入了解配合物的几何和电子结构。1-3 的 XAS 特征是 CuI 、 CuII 和 CuIII 物种的教科书示例。容易的 2-电子互变与还原 CuI 形式中两个碱性吡啶 N 位点的暴露相结合表明 [LCu]+/2+/3+ 可能通过耦合的 2 e-/2 H+ 转移在催化中起作用。