A Kinetic Study of the Electron-Transfer Reaction of the Phthalimide-N-oxyl Radical (PINO) with Ferrocenes

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• 作者：Enrico Baciocchi ; Massimo Bietti ; Massimo Di Fusco ; Osvaldo Lanzalunga
• 刊名：Journal of Organic Chemistry
• 出版年：2007
• 出版时间：November 9, 2007
• 年：2007
• 卷：72
• 期：23
• 页码：8748 - 8754
• 全文大小：148K
• 年卷期：v.72,no.23(November 9, 2007)
• ISSN：1520-6904

文摘

1211qn00001>A kinetic study of the one-electron oxidation of a series of ferrocenes (FcX: X = H, CO₂Et, CONH₂,CH₂CN, CH₂OH, Et, and Me₂) by PINO generated in CH₃CN by reaction of N-hydroxyphthalimide(NHPI) with the cumyloxyl radical produced by 355 nm laser flash photolysis of dicumyl peroxide hasbeen carried out. Ferrocenium cations were formed, and the reaction rate was determined by followingthe decay of PINO radical at 380 nm as a function of the FcX concentration. Rate constants were verysensitive to the oxidation potential of the substrates and exhibited a good fit with the Marcus equation,from which a value of 38.3 kcal mol^-1 was calculated for the reorganization energy required in thePINO/ferrocenes electron-transfer process. Knowing the ferrocene/ferrocenium self-exchange reorganizationenergy it was possible to calculate a value of 49.1 kcal mol^-1 for the PINO/PINO^- self-exchange reactionin CH₃CN. Moreover, from the Marcus cross relation and the self-exchange rates of ferrocene anddimethylferrocene, the intrinsic reactivity of PINO in electron-transfer reactions has been calculated as7.6 × 10² M^-1 s^-1. The implications of these values and the comparison with the electron-transfer self-exchange reorganization energies of peroxyl radicals are briefly discussed.