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 [LCup>I p>][B(C6F5)4], cupric superoxo complex [LCup>II p>(O2p>鈥⑩€?/sup>)]p>+ p> (1) (L = TMG3tren (1,1,1-tris[2-[Np>2 p>-(1,1,3,3-tetramethylguanidino)]ethyl]amine)) has been investigated. Trifluoroacetic acid (HOAcF) reversibly associates with the superoxo ligand in ([LCup>II p>(O2p>鈥⑩€?/sup>)]p>+ p>) in a 1:1 adduct [LCup>II p>(O2p>鈥⑩€?/sup>)(HOAcF)]p>+ p> (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 10p>5 p> Mp>鈥? p> (鈭?30 掳C) and 螖Hp>o p> = 鈭?.9(7) kcal/mol, 螖Sp>o p> = 鈭?6(4) cal molp>鈥? p> Kp>鈥? p>). Vibrational (rR) data reveal a significant increase (29 cmp>鈥? p>) in vO鈥揙 (= 1149 cmp>鈥? p>) compared to that known for [LCup>II p>(O2p>鈥⑩€?/sup>)]p>+ p> (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 [LCup>II p>(OAcF)]p>+ p>. Second-order rate constants for electron transfer (ket) were determined to be 1365 Mp>鈥? p> sp>鈥? p> (Me10Fc) and 225 Mp>鈥? p> sp>鈥? p> (Me8Fc) at 鈭?0 掳C. The (bio)chemical relevance of the proton-triggered reduction of the metal-bound dioxygen-derived fragment is discussed.