The mechanistic details of the oxidative coupling of compounds with a number of different redox centers are investigated using N-(quinolin-8-yl)-benzamide (L) as a model substrate. The control of the chemical or electrooxidation parameters in the absence or presence of a cobalt catalyst makes it possible to obtain regioselectively different oxidative coupling products (ortho- vs para-C–H/C–H vs C–H/N–H vs N–H/N–H). The results indicate that the operative mechanism depends on the type of oxidized reaction center and the oxidant nature. Oxidation affects the para-C–H bond in quinoline or the N–H fragment or the ortho-C–H bond in the benzene substituent in the molecule. The intermediate Co(II)[L^–H]₂ complex and C–H-activated Co^III metallacycle with benzamide ligands, which are shown to oxidize at close potentials, have been isolated and characterized by various techniques, including X-ray diffraction and voltammetry. The strength of the oxidizing agent affects the formation of a particular product, though not acting as the determining factor. Two-electron oxidation of Co(II)[L^–H]₂ yields to C–N coupling, but one-electron oxidation of Co(III) leads to ortho-C–C coupling. All electrochemical reactions are performed under mild conditions at room temperature without adding special reagents (oxidants, halides, phosphines, etc.).

中文翻译：

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通过 C–H 或 N–H 激活的 N-(喹啉-8-基)-苯甲酰胺偶联反应的机制驱动发展

使用N- (喹啉-8-基)-苯甲酰胺 (L) 作为模型底物，研究了具有多个不同氧化还原中心的化合物氧化偶联的机制细节。在不存在或存在钴催化剂的情况下控制化学或电氧化参数，可以获得区域选择性不同的氧化偶联产物（邻位-对位-C–H/C–H vs C–H/N–H vs N –H/N–H)。结果表明，其作用机制取决于氧化反应中心的类型和氧化剂的性质。氧化影响喹啉中的对位-C-H键或分子中苯取代基中的N-H片段或邻位-C-H键。中间体Co(II)[L ^–H] ₂配合物和带有苯甲酰胺配体的C-H 激活的 Co ^{III金属环，显示出在接近电位下氧化，已通过各种技术（包括 X 射线衍射和伏安法）进行分离和表征。}氧化剂的强度影响特定产物的形成，但不是决定因素。^{Co(II)[L –H} ] ₂的双电子氧化产生 C–N 偶联，但 Co(III) 的单电子氧化导致邻位-C–C 偶联。所有电化学反应均在室温温和条件下进行，无需添加特殊试剂（氧化剂、卤化物、膦等）。