New functional models for catechol oxidases

The new dinuclear copper(II) complexes [Cu2(L1)(μ-OAc)](ClO4)2·CH3CN (1), [Cu2(L2)(CH3CN)2](ClO4)4·C2H5OH (2), [Cu2(L3)2(CH3CN)2](PF6)2 (3) and [Cu2(L4)2](PF6)2·2CH2Cl2 (4) were prepared with the ligands N,N,N′,N′-tetrakis( (N-2-hydroxyethyl)-2-benzimidazolylmethyl)-2-hydroxy-1,3-diaminopropane HL1, N,N,N′,N′-tetrakis (2-methylimidazolyl)-2-hydroxy-1,3-diaminopropane HL2, (2-pyridylmethyl)(1-hydroxypropyl)amine HL3 and (2-hydroxybenzyl)(N,N-dimethylpropyl)amine HL4. All complexes were characterized by X-ray structure determination, revealing dinuclear cations and perchlorate or hexafluorophosphate counter ions. In the complex cations the two copper(II) atoms show different coordination spheres with N4O, N3O2 or N2O2 donor sets and different bridging systems. The Cu⋯Cu distances vary from 2.918(2) to 4.756(2) Å. The catalytic performance of the oxidation of 3,5-di-tert-butylcatechol to quinone was studied using UV–Vis absorption spectra methods. Complex 3 exhibits the highest activity with a turnover number of 32 h−1 while the other compounds show lower rates of oxidation. A kinetic treatment on the basis of the Michaelis–Menten model was applied.