Electrochemical behavior and dioxygen reactivity of tripodal dinuclear copper complexes linked by unsaturated rigid spacers

New dinucleating ligands based on two tripodal tris(2-pyridylmethyl) amine (TMPA) units linked by a series of delocalized pi-electrons spacers have been synthesized. Their di-Cu-II complexes have been prepared and structurally characterized. As compared to the corresponding monotopic complexes, these dinuclear Cu-II complexes reveal spectroscopic and voltammetric features ascribable to weakly perturbed electronic interactions. In the case of the anthracenyl spacer, observation both in the solid and in solution suggests that the existence of intramolecular pi-pi stacking interactions influences the geometry of the complex and hence its electronic properties. The bis-Cu-I complexes were prepared electrochemically. In the specific case of the complex bearing a mono-alkyne spacer, addition of dioxygen in acetonitrile leads to the slow formation of a trans-mu-1,2 peroxo Cu-2 complex which shows good stability at 268 K (t(1/2) = 240 s). Analysis of the kinetics of the peroxo formation by UV-vis spectroscopy suggests that the increased activation barrier for intramolecular binding of dioxygen is due to the rigidity of the spacer.