2-Fluorenyl benzoates were recently shown to undergo C–H bond oxidation through intramolecular proton transfer coupled with electron transfer to an external oxidant. Kinetic analysis revealed unusual rate-driving force relationships. Our analysis indicated a mechanism of multi-site concerted proton–electron transfer (MS-CPET) for all of these reactions. More recently, an alternative interpretation of the kinetic data was proposed to explain the unusual rate-driving force relationships, invoking a crossover from CPET to a stepwise mechanism with an initial intramolecular proton transfer (PT) (Costentin, Savéant, Chem. Sci., 2020, 11, 1006). Here, we show that this proposed alternative pathway is untenable based on prior and new experimental assessments of the intramolecular PT equilibrium constant and rates. Measurement of the fluorenyl 9-C–H pK_a, H/D exchange experiments, and kinetic modelling with COPASI eliminate the possibility of a stepwise mechanism for C–H oxidation in the fluorenyl benzoate series. Implications for asynchronous (imbalanced) MS-CPET mechanisms are discussed with respect to classical Marcus theory and the quantum-mechanical treatment of concerted proton–electron transfer.

中文翻译：

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芴基苯甲酸酯中的 C-H 氧化不是通过逐步途径进行的：重新审视异步质子耦合电子转移

最近显示 2-芴基苯甲酸酯通过分子内质子转移和电子转移到外部氧化剂进行 C-H 键氧化。动力学分析揭示了不寻常的速率驱动力关系。我们的分析表明了所有这些反应的多位点协同质子 - 电子转移（MS-CPET）机制。最近，提出了对动力学数据的另一种解释来解释不寻常的速率驱动力关系，调用从 CPET 到具有初始分子内质子转移 (PT) 的逐步机制的交叉 (Costentin, Savéant, Chem. Sci. , 2020, 11, 1006)。在这里，我们表明，基于分子内 PT 平衡常数和速率的先前和新的实验评估，这种提议的替代途径是站不住脚的。芴基 9-C-H p Ka 的测量_、 H/D 交换实验和使用COPASI的动力学建模消除了苯甲酸芴基系列中 C-H 氧化逐步机制的可能性。就经典马库斯理论和协同质子-电子转移的量子力学处理讨论了异步（不平衡）MS-CPET 机制的含义。