Molecular cobalt(III) complexes of bis-amidate-bis-alkoxide ligands, (Me₄N)[Co^III(L₁)] (1) and (Me₄N)[Co^III(L₂)] (2), are synthesized and assessed through a range of characterization techniques. Electrocatalytic water oxidation activity of the Co complexes in a 0.1 M phosphate buffer solution revealed a ligand-centered 2e^–/1H⁺ transfer event at 0.99 V followed by catalytic water oxidation (WO) at an onset overpotential of 450 mV. By contrast, 2 reveals a ligand-based oxidation event at 0.9 V and a WO onset overpotential of 430 mV. Constant potential electrolysis study and rinse test experiments confirm the homogeneous nature of the Co complexes during WO. The mechanistic investigation further shows a pH-dependent change in the reaction pathway. On the one hand, below pH 7.5, two consecutive ligand-based oxidation events result in the formation of a Co^III(L^2–)(OH) species, which, followed by a proton-coupled electron transfer reaction, generates a Co^IV(L^2–)(O) species that undergoes water nucleophilic attack to form the O–O bond. On the other hand, at higher pH, two ligand-based oxidation processes merge together and result in the formation of a Co^III(L^2–)(OH) complex, which reacts with OH^– to yield the O–O bond. The ligand-coordinated reaction intermediates involved in the WO reaction are thoroughly studied through an array of spectroscopic techniques, including UV–vis absorption spectroscopy, electron paramagnetic resonance, and X-ray absorption spectroscopy. A mononuclear Co^III(OH) complex supported by the one-electron oxidized ligand, [Co^III(L^3–)(OH)]⁻, a formal Co^IV(OH) complex, has been characterized, and the compound was shown to participate in the hydroxide rebound reaction, which is a functional mimic of Compound II of Cytochrome P450.

中文翻译：

---

参与钴分子络合物水氧化反应的反应中间体的表征

双酰胺-双醇盐配体的分子钴 (III) 配合物，(Me ₄ N)[Co ^III (L ₁ )] ( 1 ) 和 (Me ₄ N)[Co ^III (L ₂ )] ( 2 )，通过一系列表征技术进行合成和评估。Co 络合物在 0.1 M 磷酸盐缓冲溶液中的电催化水氧化活性表明在 0.99 V 时发生以配体为中心的 2e ^– /1H ⁺转移事件，随后在 450 mV 的起始过电势下发生催化水氧化 (WO)。相比之下，2揭示了 0.9 V 的基于配体的氧化事件和 430 mV 的 WO 起始过电势。恒电位电解研究和漂洗测试实验证实了 WO 期间 Co 配合物的均匀性。机理研究进一步表明反应途径中的 pH 依赖性变化。一方面，在 pH 7.5 以下，两个连续的基于配体的氧化事件导致 Co ^III (L ^2– )(OH) 物种的形成，随后发生质子耦合电子转移反应，生成 Co ^IV (L ^2– )(O) 物种经历水亲核攻击形成 O–O 键。另一方面，在较高的 pH 值下，两个基于配体的氧化过程合并在一起并导致形成 Co ^III(L ^2– )(OH) 络合物，与 OH ^–反应生成O–O 键。通过一系列光谱技术，包括紫外-可见吸收光谱、电子顺磁共振和 X 射线吸收光谱，对 WO 反应中涉及的配体配位反应中间体进行了深入研究。由单电子氧化配体 [Co ^III (L ^3– )(OH)] ⁻支持的单核 Co ^III (OH) 络合物，一种正式的 Co ^IV (OH) 络合物，已被表征，并且该化合物显示参与氢氧化物回弹反应，是细胞色素 P450 化合物 II 的功能模拟物。