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

The synthesis and characterization of a new Cu(II) complex, LNIS2CuII (LNIS = 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 LNIS2CuII. 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 CuII 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 LNIS2CuII. Furthermore, LNIS2CuII was found to be an efficient catalyst in homo-coupling of terminal alkynes.