Equilibria and catalytic properties of a chloro-bridged Diimine copper(II) complex in the N,N,N',N'-tetramethyl-p-phenylenediamine (TMPD) oxidation

Abstract

2 Cl 2 ]X 2 ·nH 2 O preparada como sais perclorato 3, nitrato 4 e cloreto 5, respectivamente, foram isoladas e caracterizadas por técnicas espectroscópicas (UV/Vis, IV e EPR). O composto 2 teve sua estrutura determinada por cristalografia de raios-X. Em solventes não-aquosos predomina a espécie dinuclear, enquanto em solução aquosa, ou solventes contendo água, um equilíbrio entre a espécie dinuclear e a mononuclear 1 foi observado. Estudos cinéticos, em metanol, da oxidação catalisada de TMPD indicaram uma dependência de primeira-ordem da velocidade inicial com a concentração de catalisador e um efeito de saturação com aumento da concentração de substrato. O composto dinuclear é mais reativo que o mono-, e experimentos adicionais mostraram que o contra-íon cloreto afeta significativamente os parâmetros cinéticos, deslocando o equilíbrio envolvendo as espécies 2 e 5, além de estabilizar um par iônico com o substrato.Some new copper(II) complexes with a tridentate imine ligand, bimpy (or 2-(benzimidazolyl)methylene-2-amino-1-ethylpyridine), were prepared, and had their catalytic activity in the N,N,N´,N´-tetramethyl-p-phenylenediamine (TMPD) oxidation compared. Mononuclear species, [Cu(bimpy)(H 2 O) 2 ](NO 3 ) 2 , (1) and [Cu(bimpy)Cl 2 ]·H 2 O, (2), as well as the dinuclear species containing chloro-bridges, [Cu 2 (bimpy) 2 Cl 2 ]X 2 ·nH 2 O as perchlorate 3, nitrate 4 and chloride 5 salts, respectively, were obtained and characterized by different techniques (UV/Vis, IR, EPR and X-ray crystallography). In non-aqueous solvents, the dinuclear species predominates; however, in aqueous solution or solvents containing water, equilibrium between dinuclear and correlated mononuclear species 1 was verified. Kinetic studies, in methanol solution, on the catalyzed TMPD oxidation indicated a first-order dependence of the initial rate with the catalyst concentration, and a saturation effect with increasing concentrations of the substrate. The dinuclear species was observed to be more reactive than the mononuclear one, and further experiments showed that the counter-ion chloride can significantly affect the kinetic parameters, mostly by shifting the mono-/dinuclear equilibrium, and stabilizing an ion-pair with the substrate.Keywords: copper(II) complexes, dinuclear species, equilibria, kinetics, catalytic activity IntroductionCopper complexes containing diimines have been extensively studied, and reported as good models for a variety of enzymes associated to the molecular oxygen metabolism. 1 Additionally some of them were used to construct exotic molecular architectures, sensitize photoelectrochemical cells, label biomaterials as the basis for selective sensors, and also to obtain new magnetic materials. 2 Copper-containing active sites are responsible, in vivo, for the catalyzed oxidation of phenols, and amines, where two-electron transfer occurs between the substrate and two metal centres, as in tyrosinase and catechol oxidases, 3 or 873 Equilibria and Catalytic Properties of a Chloro-Bridged Diimine Copper(II) Complex V...

Synthesis, crystal structure, spectroscopic and electrochemical characterization of the dinuclear complex {tetra-μ-[(±)-2-(p-methoxyphenoxy)-propionato-O,O′]bis(aqua)dicopper(II)}

“…On the contrary, ethanol seems to favor the mononuclear species. Similar equilibrium between mono-and dinuclear copper(II) species in solution, very dependent on the solvent used, has been observed with dinuclear copper-imine complexes containing chloride bridges [33].…”

Copper(II) complexes with tridentate pyrazole-based ligands: synthesis, characterization, DNA cleavage activity and cytotoxicity

“…In most cases, copper(II) centers have tetrahedral, or axially elongated octahedral geometry and their EPR spectra show axial symmetry with a more intense absorption at higher field (g ⊥ ) and a less intense one at lower field (g ∥ ). [34,35] Among other factors, the g ∥ and A ∥ values depend on the nature of the donor atoms, and therefore these can be used to confirm the binding mode around the metal ion. Spectroscopic studies by EPR were carried out for 1-3 in the solid state at 298 K. The EPR spectra of the complexes were also recorded in phosphate buffer (pH 7.4) at 77 K, in order to assess the coordination environment around copper, an important issue taking into consideration the in vitro biological evaluation that has been performed for 1 and 2.…”

Approaches for multicopper oxidases in the design of electrochemical sensors for analytical applications

“…Among the most studied copper ion ligands, imine compounds have deserved special attention [33][34][35][36][37][38][39], due to their flexibility, facility of preparation, and ability on stabilizing both oxidation states of this metal. These ligands can provide macroacyclic and macrocyclic structures, tripodal, compartmental, or dinucleating species [33][34][35][36][37][38][39].…”

“…These ligands can provide macroacyclic and macrocyclic structures, tripodal, compartmental, or dinucleating species [33][34][35][36][37][38][39]. Particularly, copper(II) complexes with imine ligands containing imidazolate-bridging groups have been used as precursors of assemblies based on supramolecular coordination chemistry, leading to highly ordered, symmetrical molecular or supramolecular structures [40,41].…”