A new dinuclear unsymmetric copper(II) complex as model for the active site of catechol oxidase

The crystal structure, magnetic, redox and spectroscopic properties of a no vel unsymmetrical dinuclear copper(II) complex, prepared by the reaction be tween copper(II) perchlorate, sodium acetate and the unsymmetrical, binucle ating ligand HTPPNOL, where HTPPNOL is NNN ' -tris-(2-pyridylmethyl)-1,3-di aminopropan-2-ol, is reported. HTPPNOL (I equiv.) reacted with I equiv. of copper(II) ion, in methanol, and produced the mononuclear copper complex [C u(TPPNOL)](ClO4)(BPh4) (1). On the other hand, the reaction of I equiv. of HTPPNOL with 2 equiv. each of copper (II) ion and acetate, in methanol, pro duced the dinuclear complex [Cu-2(TPPNOL)(OOCCH3)](ClO4)(2) (2), whose stru cture has been determined by X-ray diffraction. In complex 2, as a result o f the inherent asymmetry of the ligand HTPPNOL, one copper ion is five-coor dinated (distorted trigonal-bipyramidal) while the other copper is four-coo rdinated (distorted square-planar). Then, as a result of the presence of di stinct geometries for the metal centres, complex 2 exhibits a ferromagnetic coupling (J = + 25.41 cm (1)). Titration experiments carried out on the di nuclear complex suggest a pK(a) = 8.0, which was related to the aquo/hydrox o equilibrium. Complex 2 is able to oxidise 3,5-di-tert-butylcatechol to th e respective o-quinone. The oxidation reaction was studied by following the appearance of the quinone spectrophotometrically, at pH 8.0 and 25 degrees C. (C) 2001 Elsevier Science B.V. All rights reserved.