Department of Chemistry, National Tsing Hua University, 101, Sec 2, Kuang-Fu Rd., 30013, Hsinchu, Taiwan.
Department of Chemistry, National Chung Hsing University, 145, Xingda Rd., South Dist., 402, Taichung, Taiwan.
ChemSusChem. 2022 Nov 8;15(21):e202201317. doi: 10.1002/cssc.202201317. Epub 2022 Sep 27.
In this study, dinuclear cobalt complexes (1 and 2) featuring bis(benzimidazole)pyrazolide-type ligands (H L and Me L) were prepared and evaluated as molecular electrocatalysts for water oxidation. Notably, 1 bearing a non-innocent ligand (H L) displayed faster catalytic turnover than 2 under alkaline conditions, and the base dependence of water oxidation and kinetic isotope effect analysis indicated that the reaction mediated by 1 proceeded by a different mechanism relative to 2. Spectroelectrochemical, cold-spray ionization mass spectrometric and computational studies found that double deprotonation of 1 under alkaline conditions cathodically shifted the catalysis-initiating potential and further altered the turnover-limiting step from nucleophilic water attack on (H L)Co (superoxo) to deprotonation of (L)Co (OH) . The rate-overpotential analysis and catalytic Tafel plots showed that 1 exhibited a significantly higher rate than previously reported Ru-based dinuclear electrocatalysts at similar overpotentials. These observations suggest that using non-innocent ligands is a valuable strategy for designing effective metal-based molecular water oxidation catalysts.
在这项研究中，制备了具有双（苯并咪唑）吡唑啉酮型配体（H L 和 Me L ）的双核钴配合物（1 和 2），并将其评估为水氧化的分子电催化剂。值得注意的是，在碱性条件下，带有非中性配体（H L ）的 1 比 2 显示出更快的催化周转率，水氧化的碱依赖性和动力学同位素效应分析表明，1 介导的反应具有与 2 不同的机制。光谱电化学、冷喷雾电离质谱和计算研究发现，1 在碱性条件下的双重去质子化阴极将引发催化的电位向更低的方向移动，并进一步将限速步骤从亲核水分子攻击（H L ）Co （超氧）改变为（L）Co （OH）的去质子化。速率过电势分析和催化塔菲尔图表明，在类似过电势下，1 的速率比以前报道的基于 Ru 的双核电催化剂高得多。这些观察结果表明，使用非中性配体是设计有效金属基分子水氧化催化剂的一种有价值的策略。
