Journalartikel

Jahr der Veröffentlichung: 2008

Seiten: 9714-9729

Zeitschrift: Chemistry - A European Journal

Bandnummer: 14

Heftnummer: 31

ISSN: 0947-6539

DOI Link: https://doi.org/10.1002/chem.200800799

Verlag: Wiley

Abstract: 
Detailed mechanistic studies on the ligand hydroxylation reaction mediated by a copper bis(imine) complex are presented. Starting from a structural analysis of the CuI complex and the CuII product with a hydroxylated ligand, the optical absorption and vibrational spectra of starting material and product are analyzed. Kinetic analysis of the ligand hydroxylation reaction shows that O2 binding is the rate-limiting step. The reaction proceeds much faster in methanol than in acetonitrile. Moreover, an inverse kinetic isotope effect (KIE) is evidenced for the reaction in acetonitrile, which is attributed to a sterically congested transition state leading to the peroxo adduct. In methanol, however, no KIE is observed. A DFT analysis of the oxygenation reaction mediated by the micro-eta2:eta2 peroxo core demonstrates that the major barrier after O2 binding corresponds to electrophilic attack on the arene ring. The relevant orbital interaction occurs between the sigma* orbital of the Cu2O2 unit and the HOMO of the ligand. On the basis of the activation energy for the rate-limiting step (18.3 kcal mol(-1)) this reaction is thermally allowed, in agreement with the experimental observation. The calculations also predict the presence of a stable dienone intermediate which, however, escaped experimental detection so far. Reasons for these findings are considered. The implications of the results for the mechanism of tyrosinase are discussed.

Harvard-Zitierstil: Sander, O., Henss, A., Näther, C., Würtele, C., Holthausen, M., Schindler, S., et al. (2008) Aromatic Hydroxylation in a Copper Bis(imine) Complex Mediated by a μ‐η2:η2 Peroxo Dicopper Core: A Mechanistic Scenario, Chemistry - A European Journal, 14(31), pp. 9714-9729. https://doi.org/10.1002/chem.200800799

APA-Zitierstil: Sander, O., Henss, A., Näther, C., Würtele, C., Holthausen, M., Schindler, S., & Tuczek, F. (2008). Aromatic Hydroxylation in a Copper Bis(imine) Complex Mediated by a μ‐η2:η2 Peroxo Dicopper Core: A Mechanistic Scenario. Chemistry - A European Journal. 14(31), 9714-9729. https://doi.org/10.1002/chem.200800799