Dioxygen activation at a mononuclear Cu(I) center embedded in the calix[6]arene-tren core.
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 DbetaH 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.
Izzet
Guillaume
G
Laboratoire de Chimie et Biochimie Pharmacologiques et Toxicologiques, UMR CNRS 8601, Université Paris Descartes (Paris 5), 45 rue des Saints Pères, 75006 Paris, France.
Zeitouny
Joceline
J
Akdas-Killig
Huriye
H
Frapart
Yves
Y
Ménage
Stéphane
S
Douziech
Bénédicte
B
Jabin
Ivan
I
Le Mest
Yves
Y
Reinaud
Olivia
O
D047250:Calixarenes / Q000737:chemistry*; D003300:Copper / Q000737:chemistry*; D004563:Electrochemistry / Q000379:methods; D004578:Electron Spin Resonance Spectroscopy; D008958:Models, Molecular; D009942:Organometallic Compounds / Q000737:chemistry*; D010100:Oxygen / Q000737:chemistry*; D010636:Phenols / Q000737:chemistry*; D017550:Spectroscopy, Fourier Transform Infrared
D009942:Organometallic Compounds; D010636:Phenols; C476540:calix(6)arene; D047250:Calixarenes; D003300:Copper; D010100:Oxygen