We report Fe porphyrins bearing different meso-substituents for the electrocatalytic CO₂ reduction reaction (CO₂RR). By replacing two and four meso-phenyl groups of Fe tetraphenylporphyrin (FeTPP) with strong electron-withdrawing pentafluorophenyl groups, we synthesized FeF₁₀TPP and FeF₂₀TPP, respectively. We showed that FeTPP and FeF₁₀TPP are active and selective for CO₂-to-CO conversion in dimethylformamide with the former being more active, but FeF₂₀TPP catalyzes hydrogen evolution rather than the CO₂RR under the same conditions. Experimental and theoretical studies revealed that with more electron-withdrawing meso-substituents, the Fe center becomes electron-deficient and it becomes difficult for it to bind a CO₂ molecule in its formal Fe⁰ state. This work is significant to illustrate the electronic effects of catalysts on binding and activating CO₂ molecules and provide fundamental knowledge for the design of new CO₂RR catalysts.

中文翻译：

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Fe卟啉的介观取代基电子效应对电催化CO2还原反应的影响


我们报道了带有不同内消旋取代基的铁卟啉用于电催化 CO ₂ 还原反应（CO ₂ RR）。通过用强吸电子五氟苯基取代四苯基卟啉铁（FeTPP）的两个和四个中间苯基，分别合成了FeF ₁₀ TPP和FeF ₂₀ TPP。我们发现 FeTPP 和 FeF ₁₀ TPP 对二甲基甲酰胺中的 CO ₂ 转化为 CO 具有活性和选择性，其中前者活性更高，但 FeF ₂₀ 在相同条件下，TPP 催化析氢而不是 CO ₂ RR。实验和理论研究表明，随着吸电子内消旋取代基的增多，Fe中心变得缺电子，其形式Fe ⁰ 分子的电子效应具有重要意义，并为新型CO ₂ RR催化剂的设计提供基础知识。