Journal article

Publication year: 2008

Pages: 9714-9729

Journal: Chemistry - A European Journal

Volume number: 14

Issue number: 31

ISSN: 0947-6539

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

Publisher: 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 Citation style: 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 Citation style: 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