Electron transfer studies on Cu(II) complexes bearing phenoxy-pincer ligands

Oxido-pincer ligands with phenolate-groups [2,6-bis(2-methoxyphenyl)pyridine (LOMe₂), 2,6-bis(2-hydroxyphenyl)-pyridine (LOH₂), 2,6-bis-(2,4-dimethoxyphenyl)-pyridine (LOMe₄)] coordinate to Cu^II forming binuclear complexes which can be easily and reliably converted into mononuclear species. Their physical properties were analysed using EPR, optical spectroscopy and (spectro-)electrochemical methods. The results were compared to those of related Ni^II complexes and discussed in view of Cu-containing metalloenzymes. Due to the ligands flexibility the Cu^II/Cu^I redox couple exhibits high reversibility, while the ligand-centred oxidation leads to highly reactive phenoxy radicals. Reduction of the LOH₂ complex leads to sequential deprotonation. The ligand LOMe₄ and the derived complexes show blue luminescence, which can be rationalised from its molecular structure (analysed by XRD).