Willard Henry Dow Laboratory, Department of Chemistry, University of Michigan, 930 North University Avenue, Ann Arbor, Michigan 48109, United States.
Department of Chemistry and Biomolecular Sciences, University of Ottawa, Ottawa, Ontairo K1N 6N5, Canada.
J Am Chem Soc. 2021 Jul 14;143(27):10324-10332. doi: 10.1021/jacs.1c04181. Epub 2021 Jul 2.
Phthalimide -oxyl (PINO) is a potent hydrogen atom transfer (HAT) catalyst that can be generated electrochemically from -hydroxyphthalimide (NHPI). However, catalyst decomposition has limited its application. This paper details mechanistic studies of the generation and decomposition of PINO under electrochemical conditions. Voltammetric data, observations from bulk electrolysis, and computational studies suggest two primary aspects. First, base-promoted formation of PINO from NHPI occurs via multiple-site concerted proton-electron transfer (MS-CPET). Second, PINO decomposition occurs by at least two second-order paths, one of which is greatly enhanced by base. Optimal catalytic efficiency in PINO-catalyzed oxidations occurs in the presence of bases whose corresponding conjugate acids have p's in the range of ∼11-15, which strikes a balance between promoting PINO formation and minimizing its decay.
邻苯二甲酰亚胺-氧自由基（PINO）是一种有效的氢原子转移（HAT）催化剂，可以通过电化学从 -羟基邻苯二甲酰亚胺（NHPI）生成。然而，催化剂的分解限制了其应用。本文详细介绍了电化学条件下 PINO 的生成和分解的机理研究。伏安数据、体相电解观察和计算研究表明有两个主要方面。首先，NHPI 通过多位点协同质子-电子转移（MS-CPET）生成 PINO 是由碱促进的。其次，PINO 的分解至少通过两条二级反应途径进行，其中一条在碱的存在下大大增强。在具有相应共轭酸的 p 值在 ∼11-15 范围内的碱的存在下，PINO 催化氧化的最佳催化效率达到，这在促进 PINO 的形成和最小化其衰减之间取得了平衡。
