The development of transition-metal heterogeneous catalysts for economical and effective synthesis of N-methylamine, especially for the monomethylation of amines, is still challenging. Herein, two Rh-supported covalent organic framework (COF) heterogeneous catalysts Rh/MelCOF were facile-synthesized by a Schiff base reaction using melamine as a precursor, and, for the first time, it was successfully applied to the effective and high selective tandem reaction of transfer hydrogenation and monomethylation of nitroaromatic hydrocarbons, with methanol as a C1 and hydrogenation source. A series of nitroaromatic hydrocarbons, including heterocyclic or sterically hindered derivatives, can be well tolerated, and the catalyst could also be reused four times without losing significant reactivity. At the same time, the study of the Rh/MelCOF mechanism supports the hydrogen-borrowing mechanism and puts forward the reaction pathway of azobenzene as an intermediate, which is better than the hydrogen-transfer pathway from N-phenylhydroxylamine to aniline directly. This work expands the application of COF catalysts and provides an effective way to obtain mono-N-methylated amines from nitroaromatic hydrocarbons, as well as the detailed mechanism of Rh/COF-catalyzed tandem transfer hydrogenation and monomethylation of amines.

中文翻译：

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新型多相Rh/COF催化剂的简便合成及其在甲醇串联选择性转移氢化和硝基化合物单甲基化中的应用

开发用于经济有效地合成N-甲胺，特别是胺的单甲基化的过渡金属非均相催化剂仍然具有挑战性。在此，两个 Rh 负载的共价有机以三聚氰胺为前驱体，通过席夫碱反应简便合成了骨架（COF）非均相催化剂Rh/MelCOF，并首次成功应用于硝基芳烃转移加氢和单甲基化的高效、高选择性串联反应。碳氢化合物，以甲醇为 C1 和加氢源。一系列硝基芳烃，包括杂环或空间位阻衍生物，具有良好的耐受性，催化剂也可以重复使用四次而不会失去显着的反应性。同时，Rh/MelCOF机理的研究支持了借氢机理，提出了以偶氮苯为中间体的反应途径，优于N的氢转移途径。-苯基羟胺直接转化为苯胺。该工作拓展了COF催化剂的应用，为从硝基芳烃制备单N-甲基化胺提供了一种有效途径，以及Rh/COF催化的串联转移加氢和胺单甲基化的详细机理。