Montgomery Charlotte L, Ertem Mehmed Z, Claytor Zoe H, Dempsey Jillian L
Department of Chemistry, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599-3290, United States.
Chemistry Division, Brookhaven National Laboratory, Upton, New York 11973, United States.
Inorg Chem. 2025 May 26;64(20):10139-10149. doi: 10.1021/acs.inorgchem.5c00767. Epub 2025 May 15.
We report the role of pendant amine basicity on the proton-coupled electron transfer (PCET) reactivity for the conversion of [CoCp(PN)(CHCN)] complexes to [HCoCp(PN)], which is a key transformation involved in catalytic CO conversion to formate and in H evolution. Three complexes were studied, where the amine substituent (R) varies from benzyl, methoxyphenyl, or phenyl. In previous work on the benzyl system, we showed that the amine on the PN ligand serves as a kinetically accessible protonation site and enables three participating hydride formation mechanisms. In this work, a combination of electrochemical measurements and theoretical calculations were used to show that the electronic donation at the pendant amine influences the accessible PCET mechanism and proton transfer kinetics related to cobalt hydride formation under analogous reaction conditions. Notably, the amine with the most electron-donating substituent correlates to the lowest barrier for amine protonation, and specific cobalt hydride formation mechanisms can be shut off for the amine with the least electron-donating substituent. The mechanistic and kinetic changes upon modulation of the amine substituent have great implications for overall catalytic efficiency and selectivity, especially to generate the cobalt hydride intermediate involved in selective CO reduction to formate. This work shows how to exploit kinetic basicity using ligand-cooperative design to facilitate PCET reactions involved in energy related transformations.
我们报道了 pendant 胺的碱性对质子耦合电子转移（PCET）反应活性的作用，该反应活性涉及[CoCp(PN)(CHCN)]配合物转化为[HCoCp(PN)]，这是催化 CO 转化为甲酸盐以及析氢过程中的关键转变。研究了三种配合物，其中胺取代基（R）分别为苄基、甲氧基苯基或苯基。在之前关于苄基体系的工作中，我们表明 PN 配体上的胺作为一个动力学上可及的质子化位点，并促成了三种参与氢化物形成的机制。在这项工作中，结合电化学测量和理论计算表明，在类似反应条件下，pendant 胺上的电子给予作用影响了可及的 PCET 机制以及与钴氢化物形成相关的质子转移动力学。值得注意的是，具有最强供电子取代基的胺与胺质子化的最低势垒相关，而对于具有最弱供电子取代基的胺，特定的钴氢化物形成机制可能会被阻断。胺取代基调节后发生的机理和动力学变化对整体催化效率和选择性有重大影响，特别是对于生成参与选择性 CO 还原为甲酸盐的钴氢化物中间体。这项工作展示了如何利用配体协同设计来利用动力学碱性，以促进与能量相关转化中涉及的 PCET 反应。
