Oxidation of 3,5-di-tert-butylcatechol by molecular oxygen catalysed by a copper(I) complex, Cu2(bdpdz)Cl2, bdpdz=3,6-bis-(di-2-pyridilmethyl) pyridazine

New unsymmetric dinuclear CuIICuII complexes and their relevance to copper(II) containing metalloenzymes and DNA cleavage

The new homodinuclear complexes, [Cu(2)(II)(HLdtb)(mu-OCH(3))](ClO(4))(2) (1) and [Cu(2)(II)(Ldtb)(mu-OCH(3))](BPh(4)) (2), with the unsymmetrical N(5)O(2) donor ligand (H(2)Ldtb) - {2-[N,N-Bis(2-pyridylmethyl)aminomethyl]-6-[N',N'-(3,5-di-tert-butylbenzyl-2-hydroxy)(2-pyridylmethyl)]aminomethyl}-4-methylphenol have been synthesized and characterized in the solid state by X-ray crystallography. In both cases the structure reveals that the complexes have a common {Cu(II)(mu-phenoxo)(mu-OCH(3))Cu(II)} structural unit. Magnetic susceptibility studies of 1 and 2 reveal J values of -38.3 cm(-1) and -2.02 cm(-1), respectively, and that the degree of antiferromagnetic coupling is strongly dependent on the coordination geometries of the copper centers within the dinuclear {Cu(II)(mu-OCH(3))(mu-phenolate)Cu(II)} structural unit. Solution studies in dichloromethane, using UV-Visible spectroscopy and electrochemistry, indicate that under these experimental conditions the first coordination spheres of the Cu(II) centers are maintained as observed in the solid state structures, and that both forms can be brought into equilibrium ([Cu(2)(HLdtb)(mu-OCH(3))](2+)=[Cu(2)(Ldtb)(mu-OCH(3))](+)+H(+)) by adjusting the pH with Et(3)N (Ldtb(2-) is the deprotonated form of the ligand). On the other hand, potentiometric titration studies of 1 in an ethanol/water mixture (70:30 V/V; I=0.1M KCl) show three titrable protons, indicating the dissociation of the bridging CH(3)O(-) group.The catecholase activity of 1 and 2 in methanol/water buffer (30:1 V/V) demonstrates that the deprotonated form is the active species in the oxidation of 3,5-di-tert-butylcatechol and that the reaction follows Michaelis-Menten behavior with k(cat)=5.33 x 10(-3)s(-1) and K(M)=3.96 x 10(-3)M. Interestingly, 2 can be electrochemically oxidized with E(1/2)=0.27 V vs.Fc(+)/Fc (Fc(+)/Fc is the redox pair ferrocinium/ferrocene), a redox potential which is believed to be related to the formation of a phenoxyl radical. Since these complexes are redox active species, we analyzed their activity toward the nucleic acid DNA, a macromolecule prone to oxidative damage. Interestingly these complexes promoted DNA cleavage following an oxygen dependent pathway.

Dimetallic complexes of acyclic pyridine-armed ligands derived from 3,6-diformylpyridazine

A bis(pyridine-armed) acyclic Schiff base ligand L1 has been synthesised from 3,6-diformylpyridazine and two equivalents of 2-(2-aminoethyl)pyridine. Reduction of this ligand using NaBH(4) resulted in the formation of the amine analogue L2. Complexes of the form [M(2)L1(mu-X)]Y(2)ClO(4)[where: M = Cu(II), X = OH(-) and Y = ClO(4)(-) 1, Cl(-) 2, Br(-) 3 or I(-) 4; M = Co(II), X = OH(-) and Y = ClO(4)(-) 5; M = Ni(II), X = SCN(-) 6 or X = N(3)(-) 7 and Y = ClO(4)(-)], and [Cu(2)L2(mu-OH)](ClO(4))(3) 8 were prepared and characterised. The complexes 1 and 5-7 have been characterised by single-crystal X-ray diffraction. The acyclic L1 ligand provides three nitrogen donor atoms per metal centre, including a pyridazine bridge between the metal centres, and the anion X also bridges the two metal centres. As required, coordinating solvent molecules or additional anions make up the remainder of the coordination sphere. The two copper centres of 1 are very strongly antiferromagnetically coupled (2J=-1146 cm(-1))via the pyridazine and hydroxide ion bridges, whereas the competing antiferromagnetic pyridazine bridging pathway and ferromagnetic 1,1-bridging azide pathway resulted in the observation of weak antiferromagnetic exchange in the dinickel(II) complex 7 (2J=-14 cm(-1)). Electrochemical examination of L1, L2 and complexes 1 and 5-8 revealed multiple redox processes. These have been tentatively assigned to a mixture of metal centred and ligand centred redox processes on the basis of cyclic voltammetry and coulometry results and comparisons with literature examples.