Fine modulation of the ligand structure of metal-complex-based homogeneous water oxidation catalysts is a feasible method to realize efficient electrochemical oxygen evolution. Herein, the synthesis and electrocatalytic water oxidation activity of two novel mononuclear N₄-coordinated Ni complexes, [Ni(dmabpy)](ClO₄)₂ (1, dmabpy = 6,6′-bis(dimethylamino methyl)-2,2′-bipyridine) and [Ni(mabpy)](ClO₄)₂ (2, mabpy = 6,6′-bis(methylamino methyl)-2,2′-bipyridine), are reported for the first time. Both the Ni complexes are capable of accelerating water oxidation to oxygen with low onset overpotential under neutral conditions. Combined experiment and measurement prove that the two complexes are genuine homogeneous water oxidation catalysts. Besides, they maintain their molecular structure during long-term catalytic cycles. Catalytic activity tests indicate that, though they are stabilized by similar bipyridine-based ligands, complex 1 shows lower overpotential and higher catalytic current for water oxidation than complex 2, revealing that methyl groups on the coordinated N atoms of the organic ligand obviously benefit the water oxidation catalytic activity. Detailed electrochemical measurements reveal that the water oxidation process was accomplished with the assistance of Ni^IV species generated by two successive e⁻/H⁺ proton coupled electron transfer (PCET) processes of the Ni^II center for both the Ni complexes. The facilitation effect of methyl on the catalytic activity of the Ni complex is realized by modulating the redox potential of the metal center via an electronic effect.

中文翻译：

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中性条件下 N4 配位镍配合物催化高效电化学水氧化

金属配合物基均相水氧化催化剂配体结构的精细调控是实现高效电化学析氧的可行方法。在此，研究了两种新型单核N ₄配位Ni配合物[Ni(dmabpy)](ClO ₄ ) ₂ ( 1 , dmabpy = 6,6′-bis(二甲氨基甲基)-2,2)的合成及其电催化水氧化活性。 '-联吡啶）和[Ni(mabpy)](ClO ₄ ) ₂ ( 2 , mabpy = 6,6'-双(甲氨基甲基)-2,2'-联吡啶)为首次报道。这两种镍配合物都能够在中性条件下以低起始过电势加速水氧化成氧气。结合实验和测量证明这两种配合物是真正的均相水氧化催化剂。此外，它们在长期催化循环中保持其分子结构。催化活性测试表明，虽然它们都被类似的联吡啶基配体稳定，但配合物1比配合物2表现出更低的过电势和更高的水氧化催化电流，表明有机配体配位N原子上的甲基对水有明显的好处。氧化催化活性。详细的电化学测量表明，水氧化过程是在两种 Ni 配合物的 Ni ^{II中心的两个连续e-} /H ⁺质子耦合电子转移 (PCET) 过程产生的Ni ^IV物质的帮助下完成的。甲基对Ni配合物催化活性的促进作用是通过电子效应调节金属中心的氧化还原电位来实现的。