Stepwise Protonation and Electron-Transfer Reduction of a Primary Copper鈥揇ioxygen Adduct
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- 作者：Ryan L. Peterson ; Jake W. Ginsbach ; Ryan E. Cowley ; Munzarin F. Qayyum ; Richard A. Himes ; Maxime A. Siegler ; Cathy D. Moore ; Britt Hedman ; Keith O. Hodgson ; Shunichi Fukuzumi ; Edward I. Solomon ; Kenneth D. Karlin
- 刊名：Journal of the American Chemical Society
- 出版年：2013
- 出版时间：November 6, 2013
- 年：2013
- 卷：135
- 期：44
- 页码：16454-16467
- 全文大小：659K
- 年卷期：v.135,no.44(November 6, 2013)
- ISSN：1520-5126
文摘
The protonation鈥搑eduction of a dioxygen adduct with [LCuI][B(C6F5)4], cupric superoxo complex [LCuII(O2鈥⑩€?/sup>)]+ (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鈥⑩€?/sup>)]+) in a 1:1 adduct [LCuII(O2鈥⑩€?/sup>)(HOAcF)]+ (2), as characterized by UV鈥搗isible, 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 脳 105 M鈥? (鈭?30 掳C) and 螖Ho = 鈭?.9(7) kcal/mol, 螖So = 鈭?6(4) cal mol鈥? K鈥?). Vibrational (rR) data reveal a significant increase (29 cm鈥?) in vO鈥揙 (= 1149 cm鈥?) compared to that known for [LCuII(O2鈥⑩€?/sup>)]+ (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 鈭?20 掳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鈥? s鈥? (Me10Fc) and 225 M鈥? s鈥? (Me8Fc) at 鈭?0 掳C. The (bio)chemical relevance of the proton-triggered reduction of the metal-bound dioxygen-derived fragment is discussed.
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