Metal–Ligand Cooperativity via Exchange Coupling Promotes Iron- Catalyzed Electrochemical CO2 Reduction at Low Overpotentials,Journal of the American Chemical Society

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Metal–Ligand Cooperativity via Exchange Coupling Promotes Iron- Catalyzed Electrochemical CO2 Reduction at Low Overpotentials
Journal of the American Chemical Society ( IF 14.4 ) Pub Date : 2020-11-18 , DOI: 10.1021/jacs.0c10664
Jeffrey S. Derrick _{1,

2} , Matthias Loipersberger ₁ , Ruchira Chatterjee ₃ , Diana A. Iovan ₁ , Peter T. Smith _{1,

2} , Khetpakorn Chakarawet ₁ , Junko Yano ₃ , Jeffrey R. Long _{1,

4,

5} , Martin Head-Gordon _{1,

2} , Christopher J. Chang _{1,

2,

6}

Affiliation

Biological and heterogeneous catalysts for the electrochemical CO2 reduction reaction (CO2RR) often exhibit a high degree of electronic delocalization that serves to minimize overpotential and maximize selectivity over the hydrogen evolution reaction (HER). Here, we report a molecular iron(II) system that captures this design concept in a homogeneous setting through the use of a redox non-innocent terpyridine-based pentapyridine ligand (tpyPY2Me). As a result of strong metal-ligand exchange coupling between the Fe(II) center and ligand, [Fe(tpyPY2Me)]2+ exhibits redox behavior at potentials 640 mV more positive than the isostructural [Zn(tpyPY2Me)]2+ analog containing the redox-inactive Zn(II) ion. This shift in redox potential is attributed to the requirement for both an open-shell metal ion and a redox non-innocent ligand. The metal-ligand cooperativity in [Fe(tpyPY2Me)]2+ drives the electrochemical reduction of CO2 to CO at low overpotentials with high selectivity for CO2RR (>90%) and turnover frequencies of 100 000 s-1 with no degradation over 20 h. The decrease in the thermodynamic barrier engendered by this coupling also enables homogeneous CO2 reduction catalysis in water without compromising selectivity or rates. Synthesis of the two-electron reduction product, [Fe(tpyPY2Me)]0, and characterization by X-ray crystallography, Mössbauer spectroscopy, X-ray absorption spectroscopy (XAS), variable temperature NMR, and density functional theory (DFT) calculations, support assignment of an open-shell singlet electronic structure that maintains a formal Fe(II) oxidation state with a doubly reduced ligand system. This work provides a starting point for the design of systems that exploit metal-ligand cooperativity for electrocatalysis where the electrochemical potential of redox non-innocent ligands can be tuned through secondary metal-dependent interactions.

中文翻译：

通过交换偶联的金属-配体协同促进低过电位下铁催化的电化学 CO2 还原

用于电化学 CO2 还原反应 (CO2RR) 的生物和非均相催化剂通常表现出高度的电子离域，这有助于最大限度地减少过电位并最大限度地提高析氢反应 (HER) 的选择性。在这里，我们报告了一种分子铁 (II) 系统，该系统通过使用氧化还原非纯三联吡啶基五吡啶配体 (tpyPY2Me) 在均质环境中捕捉此设计概念。由于 Fe(II) 中心和配体之间强金属-配体交换耦合，[Fe(tpyPY2Me)]2+ 在电位比同构 [Zn(tpyPY2Me)]2+ 类似物高 640 mV 时表现出氧化还原行为氧化还原惰性 Zn(II) 离子。氧化还原电位的这种变化归因于对开壳金属离子和氧化还原非无害配体的要求。[Fe(tpyPY2Me)]2+ 中的金属-配体协同驱动 CO2 在低过电位下电化学还原为 CO，对 CO2RR 具有高选择性 (>90%)，周转频率为 100 000 s-1，20 小时内无降解. 由这种耦合引起的热力学障碍的减少还能够在不影响选择性或速率的情况下在水中进行均相 CO2 还原催化。合成双电子还原产物 [Fe(tpyPY2Me)]0，并通过 X 射线晶体学、穆斯堡尔光谱、X 射线吸收光谱 (XAS)、变温 NMR 和密度泛函理论 (DFT) 计算表征，支持分配开壳单线态电子结构，该结构保持正式的 Fe(II) 氧化态和双还原配体系统。

更新日期：2020-11-18

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