Tuning of the redox potential and catalytic activity of a new Cu(ii) complex by o-iminobenzosemiquinone as an electron-reservoir ligand

Abstract

The synthesis and characterization of a new Cu(II) complex, L^NIS₂Cu^II (L^NIS = o-iminobenzosemiquinone), are reported. X-ray crystallography studies showed that two o-iminobenzosemiquinone radicals form a distorted square-planar geometry around the Cu(II) center of L^NIS₂Cu^II. Magnetic measurements revealed the paramagnetic character of the complex caused by the presence of three unpaired electrons located on the o-iminobenzosemiquinonate ligands and the Cu^II center. Magnetochemical experiments, and EPR and DFT studies prove that the ground state of the complex is a doublet, which is consistent with the ferromagnetic coupling between Cu(II) and o-iminobenzosemiquinone centers and stronger antiferromagnetic coupling between the iminobenzosemiquinone moieties. The ligand-centered redox reactions of the complex were studied by cyclic voltammetry. Aerobic oxidation of alcohols to aldehydes with TEMPO was studied in the presence of L^NIS₂Cu^II. Furthermore, L^NIS₂Cu^II was found to be an efficient catalyst in homo-coupling of terminal alkynes.