Diverse copper(II) complexes with simple nitrogen ligands: Structural characterization and applications in aerobic alcohol oxidations in water

Four copper(II) complexes based on simple mono- or bi-dentate nitrogen ligands 2–5 were synthesized and structurally characterized by X-ray crystallography. Structural analysis revealed that diverse solid state structures of these Cu(II) complexes were formed, depending on the ligands used. The new copper(II) assembles include dinuclear tetra-ligand complex (6), mononuclear bis-ligand complex (7), one-dimensional (1-D) polymeric chain (8) and two-dimensional (2-D) hydrogen-bonded network composed of mononuclear bis-ligand complexes (9). In continuation with our previous findings of an efficient Cu/DMAP catalysis system for aerobic alcohol oxidation in water (DMAP = 4-dimethylaminopyridine), we tested the catalytic activity of newly synthesized copper(II) complexes 6–9 under similar conditions. Both the isolated complexes and in-situ combinations of ligands with copper(I) or copper(II) salts were examined as catalysts toward aerobic oxidations of both primary and secondary alcohols in water in the presence of nitroxyl radicals (TEMPO or ABNO) and the results confirmed that complex 6 showed high catalytic activity, similar to the previously reported Cu/DMAP catalyst, while other complexes were less efficient catalysts. The remarkable differences on catalytic activity were tentatively attributed to their diverse molecular structures, in comparison with previous results in relevant systems.

Four new copper(II) complexes with diverse structures were isolated and structurally characterized by X-ray diffraction analysis. The catalytic activity of these complexes towards nitroxyl radical-mediated aerobic alcohol oxidations was tested in water and the structure–catalytic activity relationship was discussed.Figure optionsDownload as PowerPoint slide