Mechanism of Electrochemical Generation and Decomposition of Phthalimide-N‑oxyl

Phthalimide N-oxyl (PINO) is a potent hydrogen atom transfer (HAT) catalyst that can be generated electrochemically from N-hydroxyphthalimide (NHPI). However, catalyst decomposition has limited its application. This paper details mechanistic studies of the generation and decomposition of PINO under...

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Bibliographic Details
Published in:Journal of the American Chemical Society 2021-07, Vol.143 (27), p.10324-10332
Main Authors: Yang, Cheng, Farmer, Luke A, Pratt, Derek A, Maldonado, Stephen, Stephenson, Corey R. J
Format: Article
Language:English
Subjects:
Chemistry
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Summary:Phthalimide N-oxyl (PINO) is a potent hydrogen atom transfer (HAT) catalyst that can be generated electrochemically from N-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 pK a’s in the range of ∼11–15, which strikes a balance between promoting PINO formation and minimizing its decay.
ISSN:0002-7863
1520-5126
DOI:10.1021/jacs.1c04181