Stepwise Protonation and Electron-Transfer Reduction of a Primary Copper–Dioxygen Adduct
In: Journal of the American Chemical Society, Jg. 135 (2013-10-28), S. 16454-16467
Online
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Zugriff:
The protonation–reduction of a dioxygen adduct with [LCu(I)][B(C6F5)4], cupric superoxo complex [LCu(II)(O2(•–))]+ (1) (L = TMG3tren (1,1,1-tris[2-[N(2)-(1,1,3,3-tetramethylguanidino)]ethyl]amine)) has been investigated. Trifluoroacetic acid (HOAcF) reversibly associates with the superoxo ligand in ([LCu(II)(O2(•–))]+) in a 1:1 adduct [LCu(II)(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 × 10(5) M(–1) (−130 °C) and ΔH° = −6.9(7) kcal/mol, ΔS° = −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 [LCu(II)(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 [LCu(II)(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.
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Stepwise Protonation and Electron-Transfer Reduction of a Primary Copper–Dioxygen Adduct
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Autor/in / Beteiligte Person: | Hedman, Britt ; Hodgson, Keith O. ; Cowley, Ryan E. ; Fukuzumi, Shunichi ; Peterson, Ryan L. ; Himes, Richard A. ; Solomon, Edward I. ; Qayyum, Munzarin F. ; Siegler, Maxime A. ; Ginsbach, Jake W. ; Karlin, Kenneth D. ; Moore, Cathy D. |
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Zeitschrift: | Journal of the American Chemical Society, Jg. 135 (2013-10-28), S. 16454-16467 |
Veröffentlichung: | American Chemical Society (ACS), 2013 |
Medientyp: | unknown |
ISSN: | 1520-5126 (print) ; 0002-7863 (print) |
DOI: | 10.1021/ja4065377 |
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