Stepwise Protonation and Electron-Transfer Reduction of a Primary Copper–Dioxygen Adduct.
In: Journal of the American Chemical Society, Jg. 135 (2013-11-06), Heft 44, S. 16454-16467
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Zugriff:
The protonation–reduction of a dioxygen adduct with [LCuI][B(C6F5)4], cupric superoxo complex [LCuII(O2•–)]+ (1) (L = TMG3tren (1,1,1-tris[2-[N2-(1,1,3,3-tetramethylguanidino)]ethyl]amine)) has been investigated. Trifluoroacetic acid (HOAcF) reversibly associates with the superoxo ligand in ([LCuII(O2•–)]+) in a 1:1 adduct [LCuII(O2•–)(HOAcF)]+ (2), as characterized by UV–visible, resonance Raman (rR), nuclear magnetic resonance (NMR), and X-ray absorption (XAS) spectroscopies, along with density functional theory (DFT) calculations. Chemical studies reveal that for the binding of HOAcF with 1 to give 2, Keq = 1.2 × 105 M–1 (−130 °C) and ΔHo = −6.9(7) kcal/mol, ΔSo = −26(4) cal mol–1 K–1). Vibrational (rR) data reveal a significant increase (29 cm–1) in vO–O (= 1149 cm–1) compared to that known for [LCuII(O2•–)]+ (1). Along with results obtained from XAS and DFT calculations, hydrogen bonding of HOAcF to a superoxo O-atom in 2 is established. Results from NMR spectroscopy of 2 at −120 °C in 2-methyltetrahydrofuran are also consistent with 1/HOAcF = 1:1 formulation of 2 and with this complex possessing a triplet (S = 1) ground state electronic configuration, as previously determined for 1. The pre-equilibrium acid association to 1 is followed by outer-sphere electron-transfer reduction of 2 by decamethylferrocene (Me10Fc) or octamethylferrocene (Me8Fc), leading to the products H2O2, the corresponding ferrocenium salt, and [LCuII(OAcF)]+. Second-order rate constants for electron transfer (ket) were determined to be 1365 M–1 s–1 (Me10Fc) and 225 M–1 s–1 (Me8Fc) at −80 °C. The (bio)chemical relevance of the proton-triggered reduction of the metal-bound dioxygen-derived fragment is discussed. [ABSTRACT FROM AUTHOR]
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Stepwise Protonation and Electron-Transfer Reduction of a Primary Copper–Dioxygen Adduct.
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Autor/in / Beteiligte Person: | Peterson, Ryan L. ; Ginsbach, Jake W. ; Cowley, Ryan E. ; Qayyum, Munzarin F. ; Himes, Richard A. ; Siegler, Maxime A. ; Moore, Cathy D. ; Hedman, Britt ; Hodgson, Keith O. ; Fukuzumi, Shunichi ; Solomon, Edward I. ; Karlin, Kenneth D. |
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Zeitschrift: | Journal of the American Chemical Society, Jg. 135 (2013-11-06), Heft 44, S. 16454-16467 |
Veröffentlichung: | 2013 |
Medientyp: | academicJournal |
ISSN: | 0002-7863 (print) |
DOI: | 10.1021/ja4065377 |
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