Dioxygen Activation at a Mononuclear Cu(I) Center Embedded in the Calix[6]arene-Tren Core

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• 作者：Guillaume Izzet ; Joceline Zeitouny ; Huriye Akdas-Killig ; Yves Frapart ; Ste&#x301 ; phane Me&#x301 ; nage ; Be&#x301 ; ne&#x301 ; dicte Douziech ; Ivan Jabin ; Yves Le Mest ; Olivia Reinaud
• 刊名：Journal of the American Chemical Society
• 出版年：2008
• 出版时间：July 23, 2008
• 年：2008
• 卷：130
• 期：29
• 页码：9514 - 9523
• 全文大小：1595K
• 年卷期：v.130,no.29(July 23, 2008)
• ISSN：1520-5126

文摘

The reaction of a cuprous center coordinated to a calix[6]arene-based aza-cryptand with dioxygen has been studied. In this system, Cu(I) is bound to a tren unit that caps the calixarene core at the level of the small rim. As a result, although protected from the reaction medium by the macrocycle, the metal center presents a labile site accessible to small guest ligands. Indeed, in the presence of O₂, it reacts in a very fast and irreversible redox process, leading, ultimately, to Cu(II) species. In the coordinating solvent MeCN, a one electron exchange occurs, yielding the corresponding [CalixtrenCu–MeCN]²⁺ complex with concomitant release of superoxide in the reaction medium. In a noncoordinating solvent such as CH₂Cl₂, the dioxygen reaction leads to oxygen insertions into the ligand itself. Both reactions are proposed to proceed through the formation of a superoxide-Cu(II) intermediate that is unstable in the Calixtren environment due to second sphere effects. The transiently formed superoxide ligand either undergoes fast substitution for a guest ligand (in MeCN) or intramolecular redox evolutions toward oxygenation of Calixtren. Interestingly, the latter process was shown to occur twice on the same ligand, thus demonstrating a possible catalytic activation of O₂ at a single cuprous center. Altogether, this study illustrates the oxidizing power of a [CuO₂]⁺ adduct and substantiates a mechanism by which copper mono-oxygenases such as DβH and PHM activate O₂ at the Cu_M center to produce such an intermediate capable of C−H breaking before the electron input provided by the noncoupled Cu_H center.