Dioxygen activation at a mononuclear Cu(I) center embedded in the calix[6]arene-tren core


Izzet G., Zeitouny J., Akdas-Killig H. , Frapart Y., Menage S., Douziech B., ...More

JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, vol.130, no.29, pp.9514-9523, 2008 (Journal Indexed in SCI) identifier

  • Publication Type: Article / Article
  • Volume: 130 Issue: 29
  • Publication Date: 2008
  • Doi Number: 10.1021/ja8019406
  • Journal Name: JOURNAL OF THE AMERICAN CHEMICAL SOCIETY
  • Journal Indexes: Science Citation Index Expanded, Scopus
  • Page Numbers: pp.9514-9523

Abstract

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 O-2, 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 O-2 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 DOH and PHM activate O-2 at the Cum center to produce such an intermediate capable of C-H breaking before the electron input provided by the noncoupled Cu-H center.