美国耶鲁大学Hailiang Wang及团队报道了分子催化剂催化使用CO₂的电化学还原N-甲基化反应。相关研究成果发表在2021年11月16日出版的《美国化学会杂志》。

利用CO₂作为一个单碳构件块的良性甲基化反应的开发将使化学工业更加可持续。电化学CO₂还原已被广泛研究，但其在还原甲基化反应中的应用仍不属于当前电催化的范围。

该文中，研究人员报道了第一个使用CO₂的电化学还原N-甲基化反应，并证明了其与胺、羟胺和肼的相容性。在碳纳米管上负载的酞菁钴分子的催化下，N-甲基化反应通过亲电碳中间体的化学缩合在水介质中进行，该亲电碳中间体拟被吸附或靠近由CO₂的四电子还原形成的甲醛电极，与亲核含氮反应物和随后的还原反应。通过比较各种胺，研究人员发现胺反应物的亲核性是C–N偶联效率的描述符。研究人员开发了一种级联还原过程，通过12个电子和12个质子的整体转移，同时还原CO₂和硝基化合物，生成具有高单甲基化选择性的N-甲胺，从而将反应范围扩展到与廉价且丰富的硝基化合物兼容。

附：英文原文

Title: Electrochemical Reductive N-Methylation with CO2 Enabled by a Molecular Catalyst

Author: Conor L. Rooney, Yueshen Wu, Zixu Tao, Hailiang Wang

Issue&Volume: November 16, 2021

Abstract: The development of benign methylation reactions utilizing CO2 as a one-carbon building block would enable a more sustainable chemical industry. Electrochemical CO2 reduction has been extensively studied, but its application for reductive methylation reactions remains out of the scope of current electrocatalysis. Here, we report the first electrochemical reductive N-methylation reaction with CO2 and demonstrate its compatibility with amines, hydroxylamines, and hydrazine. Catalyzed by cobalt phthalocyanine molecules supported on carbon nanotubes, the N-methylation reaction proceeds in aqueous media via the chemical condensation of an electrophilic carbon intermediate, proposed to be adsorbed or near-electrode formaldehyde formed from the four-electron reduction of CO2, with nucleophilic nitrogenous reactants and subsequent reduction. By comparing various amines, we discover that the nucleophilicity of the amine reactant is a descriptor for the C–N coupling efficacy. We extend the scope of the reaction to be compatible with cheap and abundant nitro-compounds by developing a cascade reduction process in which CO2 and nitro-compounds are reduced concurrently to yield N-methylamines with high monomethylation selectivity via the overall transfer of 12 electrons and 12 protons.

DOI: 10.1021/jacs.1c10863

Source: https://pubs.acs.org/doi/10.1021/jacs.1c10863