Mono-, tri- and polynuclear copper(ii) complexes of Schiff-base ligands: synthesis, characterization and catalytic activity towards alcohol oxidation

Abstract

Three new copper(II) complexes with different Schiff-base ligands, namely, [Cu(L¹)Cl₂] (1), [Cu₃(L²)₂Cl₄] (2) and [Cu(L³)N₃]_n (3) where L¹ = 2-morpholino-N-(pyridin-2-ylmethylene)ethanamine, HL² = 4-bromo-2-((2-morpholinoethylimino)methyl)phenol and HL³ = 4-chloro-2-((2-(dimethylamino)ethylimino)methyl)phenol, have been synthesized and characterized by elemental analysis, standard spectroscopic methods, cyclic voltammometry and single crystal X-ray diffraction analysis. The X-ray diffraction analysis confirms the formation of mononuclear (1), trinuclear (2) and polynuclear (3) complexes. These complexes have been applied as catalysts for alcohol oxidation reactions using tert-butyl hydroperoxide (TBHP) as the terminal oxidant under mild conditions. The catalytic reaction mixture has been analyzed by gas chromatography and it shows that the mononuclear complex has the highest conversion while the other two complexes exhibit moderate catalytic activities. The corresponding aldehyde has been obtained as the sole product. The obtained catalysis results have been corroborated with electrochemical studies.