Oxidation of Aldehydes into Carboxylic Acids by a Mononuclear Manganese(III) Iodosylbenzene Complex through Electrophilic C–H Bond Activation,Journal of the American Chemical Society

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Oxidation of Aldehydes into Carboxylic Acids by a Mononuclear Manganese(III) Iodosylbenzene Complex through Electrophilic C–H Bond Activation
Journal of the American Chemical Society ( IF 14.4 ) Pub Date : 2023-01-04 , DOI: 10.1021/jacs.2c09274
Donghyun Jeong ₁ , Hyokyung Kim ₁ , Jaeheung Cho _{1,

2}

Affiliation

The oxidation of aldehyde is one of the fundamental reactions in the biological system. Various synthetic procedures and catalysts have been developed to convert aldehydes into corresponding carboxylic acids efficiently under ambient conditions. In this work, we report the oxidation of aldehydes by a mononuclear manganese(III) iodosylbenzene complex, [Mn^III(TBDAP)(OIPh)(OH)]²⁺ (1), with kinetic and mechanistic studies in detail. The reaction of 1 with aldehydes resulted in the formation of corresponding carboxylic acids via a pre-equilibrium state. Hammett plot and reaction rates of 1 with 1°-, 2°-, and 3°-aldehydes revealed the electrophilicity of 1 in the aldehyde oxidation. A kinetic isotope effect experiment and reactivity of 1 toward cyclohexanecarboxaldehyde (CCA) analogues indicate that the reaction of 1 with aldehyde occurs through the rate-determining C–H bond activation at the formyl group. The reaction rate of 1 with CCA is correlated to the bond dissociation energy of the formyl group plotting a linear correlation with other aliphatic C–H bonds. Density functional theory calculations found that 1 electrostatically interacts with CCA at the pre-equilibrium state in which the C–H bond activation of the formyl group is performed as the most feasible pathway. Surprisingly, the rate-determining step is characterized as hydride transfer from CCA to 1, affording an (oxo)methylium intermediate. At the fundamental level, it is revealed that the hydride transfer is composed of H atom abstraction followed by a fast electron transfer. Catalytic reactions of aldehydes by 1 are also presented with a broad substrate scope. This novel mechanistic study gives better insights into the metal oxygen chemistry and would be prominently valuable for development of transition metal catalysts.

中文翻译：

单核锰 (III) 碘苯配合物通过亲电 C-H 键活化将醛氧化成羧酸

醛的氧化是生物系统中的基本反应之一。已经开发了各种合成程序和催化剂以在环境条件下有效地将醛转化为相应的羧酸。在这项工作中，我们报告了单核锰 (III) 碘代苯络合物 [Mn ^III (TBDAP)(OIPh)(OH)] ²⁺ ( 1 ) 对醛的氧化作用，并进行了详细的动力学和机理研究。1与醛的反应导致通过预平衡状态形成相应的羧酸。哈米特图和1与 1°-、2°- 和 3°- 醛的反应速率揭示了1的亲电子性在醛氧化中。动力学同位素效应实验和1对环己烷甲醛 (CCA) 类似物的反应性表明1与醛的反应是通过甲酰基上的 C-H 键活化来发生的。1与 CCA的反应速率与甲酰基的键解离能相关，与其他脂肪族 C-H 键呈线性相关。密度泛函理论计算发现，1在预平衡状态下与 CCA 发生静电相互作用，其中甲酰基的 C-H 键激活是最可行的途径。令人惊讶的是，速率决定步骤的特征是氢化物从 CCA 转移到1, 提供 (oxo)methylium 中间体。在基本层面上，揭示氢化物转移由 H 原子提取和随后的快速电子转移组成。1对醛的催化反应也具有广泛的底物范围。这项新颖的机理研究可以更好地了解金属氧化学，并且对于过渡金属催化剂的开发具有重要价值。

更新日期：2023-01-04

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