Insights into the generation of high-valent copper-oxo species in ligand-modulated catalytic system for oxidizing organic pollutants

Abstract The development of coordination complexes to activate hydrogen peroxide (H 2 O 2 ) selectively is a goal that has long been pursued. As highly reactive intermediates, the high-valent metal-oxo species play important roles in many biological and industrial catalytic oxidation processes. To improve the catalytic efficiency of metal complexes, the peroxide O O bond should be cleaved heterolytically to decrease the decomposition of H 2 O 2 into O 2 and H 2 O. In this work, we provide a simple method to obtain coordination complex catalysts based on iminodiacetic acid (IDA), copper(II) ions and pyridine derivatives. Catalytic activity tests showed that the introduction of 4-aminopyridine ligands resulted in an enhanced catalytic activity of the IDA/Cu(II)/4-ampy complex. A series of designed experiments proved that high-valent copper-oxo species ([ O Cu III (IDA)(4-ampy) 2 ] species) were formed in the IDA/Cu(II)/4-ampy complex system in the presence of hydrogen peroxide. The [ O Cu III (IDA)(4-ampy) 2 ] species were detected by in-situ high-definition electrospray ionization mass spectrometry, and has been considered as the possible active species during H 2 O 2 activation catalyzed by the IDA/Cu(II)/4-ampy complex (with the molar ratio of IDA/Cu(II)/4-ampy being greater than 1:1:2). A mechanism has been proposed based on the results of electron paramagnetic resonance and density functional theory calculations.