Dioxygen reactivity of new bispidine-copper complexes

摘要

The reactivity of copper complexes of three different 2^nd generation bispidine-based ligands (bispidine = 3,7-diazabicyclo[3.3.1]nonane; mono- and bis-tetradentate; exclusively tertiary amine donors) with dioxygen [(reversible) binding of dioxygen by copper(I)] is reported. The UV-vis, electrospray ionization mass spectra (ESI-MS), electron paramagnetic resonance (EPR) and vibrational spectra (resonance Raman,rR) of the dioxygen adducts indicate that, depending on the ligand and reaction conditions, several different species (mono- and dinuclear, superoxo, peroxo and hydroperoxo), partially in equilibrium with each other, are formed. Minor changes in the ligand structure and/or experimental conditions (solvent, temperature, relative concentrations) allow switching between the different forms. With one of the ligands, an end-on-peroxo-dicopper(II) and a mononuclear copper(II)-hydroperoxo complex could be characterized. With another ligand, reversible dioxygen binding was observed, leading to a meta-stable copper(II)-superoxo complex, and the amount of dioxygen involved in the reversible binding to Cu^I was determined quantitatively. The mechanism of dioxygen binding as well as the preference of each of the three ligands for a particular dioxygen adduct is discussed on the basis of a computational (DFT) analysis.