Arylhydrazone Cd(II) and Cu(II) complexes as catalysts for secondary alcohol oxidation

Reaction of cadmium acetate hydrate with sodium 2-[2-(4,4-dimethyl-2,6-dioxocyclohexylidene)hydrazinyl]terephthalate (Na2HL), in the presence of imidazole (im), leads to the polymeric species [Cd(im)3(µ,η-HL-1κOO′:2κO″O‴)]n (1) that is characterized by IR spectroscopy, elemental analysis, UV–Vis absorption spectroscopy and X-ray diffraction analysis. Complex 1 was successfully tested as catalyst for the peroxidative oxidation of alcohols (1-phenylethanol and cyclohexanol) to the corresponding ketones under microwave irradiation, with no added solvent and under mild conditions. The use of tert-butylhydroperoxide as oxidant, of TEMPO as additive, and a temperature of 80 °C leads in 1 h to a yield of acetophenone (from 1-phenylethanol) of nearly 70% or to a cyclohexanone yield (from cyclohexanol) of 66%. A comparison between the catalytic activity of 1 with those (also studied in this work) shown by Cu(II) complexes bearing the same or related hydrazo ligand is presented. © 2017 Elsevier Ltd