芳香胺及其衍生物是药物、染料、除草剂等的重要原料或关键中间体, 开发高效、低成本、高选择性的硝基芳烃还原催化剂具有重要的现实意义. 以常见的沸石类咪唑骨架材料为模板, 原位热解制备了一种Co单原子催化剂(Co-N-C), 并以乙醇作溶剂, 水合肼作氢源, 实现了多种硝基芳烃的高效氢化还原. 该Co-N-C材料制备简单, 催化活性优异, 所催化的硝基芳烃还原体系反应条件温和, 官能团兼容性优异. 天然产物应用实验、克级扩大实验、循环实验和抗浸出实验证实了Co-N-C的高效性和还原体系的实用性. 另外, 通过反应过程检测, 提出了Co-N-C催化硝基芳烃直接还原和缩合还原的两种反应机理.

Aromatic amines and their derivatives are widely used as important active intermediates in drugs, dyes and herbicides. Therefore, the development of highly efficient, low-cost, and highly selective catalysts for the hydrogenation of nitroaromatic hydrocarbons is desirable. In this study, Zn-Co metal-organic framework (MOF) materials were synthesized with Zn²⁺/Co²⁺ as the metal source and 2-methylimidazole as an organic ligand at room temperature. Then, a Co catalyst (Co-N-C) was prepared by in-situ pyrolysis using the Zn-Co MOF as a sacrificial template under a nitrogen atmosphere. Aromatic nitro compounds can be selectively converted to the corresponding aromatic amines using ethanol as solvent, hydrazine hydrate as a hydrogen source, and Co-N-C as catalyst. The Co-N-C synthesized by pyrolysis at 1000 ℃ possesses the best catalytic activity. The effects of solvent and reaction time and the amount of Co-N-C, ethanol, and hydrazine hydrate on the catalytic system were investigated. The catalytic effect was the best when 5 mg Co-N-C, 4 mL ethanol, and 4 mmol hydrazine hydrate were added to the system, and the yield of aniline reached 100% after 10 h. Thirty-one different types of nitro-aromatic compounds, including ortho-, meta-, and para-substituted nitroaromatics with electron-donating or electron-withdrawing substituents, nitrobenzene derivatives with other reducible functional groups, and heterocyclic and polycyclic aromatic compounds, were obtained in high yields under this system, which has a wide substrate scope. In addition, the flutamide and nilutamide derivatives and aminoglutethimide were prepared in excellent yields using the Co-N-C catalytic system. The feasibility of the Co-N-C catalytic system was demonstrated using a gram-scale reaction. Cycling and anti-leaching experiments demonstrated that the Co-N-C material has excellent stability and anti-leaching properties, and acts as a reusable heterogeneous catalyst, which can be easily separated and collected by centrifugation. In addition, two reaction mechanisms of direct reduction and condensation reduction of nitro-aromatics using a Co-N-C catalyzed system were proposed by testing the reaction process. This research provides an efficient, simple, and green method for the hydrogenation reduction of nitroaromatics.