A molecular pre-catalyst complex, [Cu^II(indH)(OClO₃)(NCCH₃)](ClO₄)·CH₃CN (1·CH₃CN) with the 3N pincer ligand 1,3-bis(2′-pyridyl)iminoisoindoline (indH) was immobilized on indium tin oxide (ITO) transparent conducting substrate to generate O₂ electrocatalytically for over 20 hours at pH 10 in a carbonated buffer, reaching a turnover of 139 with no signs of CuO_x/Cu(OH)₂ formation at the surface. Further electrolysis experiments revealed that the catalyst was present in the aqueous phase, despite the poor initial solubility of the pre-catalyst (1). In order to identify the actual form responsible for this important catalytic reaction, the aquo complex [Cu^II(ind)(OClO₃)(OH₂)]·CH₃OH (2·CH₃OH) was structurally characterized. Spectroscopic investigations of a solid isolated from the buffer used in the electrolysis reaction and solution equilibrium studies using 2 indicated that the [Cu^II(ind)(OH)] form occurs at pH 10. Electron paramagnetic resonance (EPR) spectroscopy and DFT calculations confirmed a distorted {3N,O}_eq coordination plane in solution, as found in 2. The buffer (i.e. bicarbonate/carbonate) may affect reactivity in two ways: as an external base facilitating the proton-coupled electron transfer steps; and/or displacing the inner-sphere solvent molecules from the favourable quasi-equatorial position, thus inhibiting the catalysis. Structural features of a tri-nuclear cluster [Cu^II₃(ind)₃(μ₃-CO₃)(CH₃OH)(OClO₃)] (3) isolated under basic conditions confirmed that beside acting as an external base, the inhibiting effect of carbonate anions may also play a role. In acetonitrile-water solutions, where both 1 and 2 exhibit reasonable solubility, experimental findings supported by DFT calculations suggest that it is the ind⁻ ligand which is being oxidized while the cupric ion remains redox-inactive which is very unusual yet of great significance for the creation of a new generation of low-cost Cu-based water oxidation catalysts as well as potentially other 1st row transition metals.

中文翻译：

---

氧化还原惰性金属单中心分子复合物：新一代析氧电催化剂？

分子前催化剂复合物，[Cu ^II (indH)(OClO ₃ )(NCCH ₃ )](ClO ₄ )·CH ₃ CN ( 1 ·CH ₃ CN) 与 3N 钳状配体 1,3- bis (2' -吡啶基）亚氨基异二氢吲哚（indH）固定在氧化铟锡（ITO）透明导电基材上，在碳酸化缓冲液中，在 pH 10 下电催化产生 O ₂超过 20 小时，达到 139 的周转率，没有 CuO _x /Cu（ OH) ₂在表面形成。进一步的电解实验表明，尽管前催化剂的初始溶解度很差，但催化剂存在于水相中（1）。为了确定负责这一重要催化反应的实际形式，对水络合物 [Cu ^II (ind)(OClO ₃ )(OH ₂ )]·CH ₃ OH ( 2 ·CH ₃ OH) 进行了结构表征。从电解反应中使用的缓冲液中分离出的固体的光谱研究和使用2 的溶液平衡研究表明 [Cu ^II (ind)(OH)] 形式出现在 pH 10。电子顺磁共振 (EPR) 光谱和 DFT 计算证实解中扭曲的 {3N,O} _eq坐标平面，如2 所示。缓冲区（即碳酸氢盐/碳酸盐）可能以两种方式影响反应性：作为促进质子耦合电子转移步骤的外部碱；和/或从有利的准赤道位置置换内球溶剂分子，从而抑制催化作用。在碱性条件下分离的三核簇 [Cu ^II ₃ (ind) ₃ (μ ₃ -CO ₃ )(CH ₃ OH)(OClO ₃ )] ( 3 ) 的结构特征证实，除了作为外部碱外，碳酸根阴离子的抑制作用也可能起作用。在乙腈-水溶液中，其中1和2表现出合理的溶解度，由 DFT 计算支持的实验结果表明，正是 ind ^-配体被氧化，而铜离子保持氧化还原活性，这是非常不寻常的，但对于创造新一代低成本铜具有重要意义基于水氧化催化剂以及潜在的其他第一行过渡金属。