Synthesis, Staructure and Redox Properties of Cu(II) Chelate Complexes on the Basis of 2‐(Hydroxyphenyl)‐1H‐benzoimidazol‐1‐yl Phenol Ligands

A series of 2‐(hydroxyphenyl)‐1H‐benzo[d]imidazols bearing readily oxidizable 2,6‐di‐tert‐butyl‐phenol substituents and bis‐chelate Cu(II) complexes based on these ligands were synthesized. The structure of the compounds was characterized by NMR, IR, mass spectroscopy and X‐ray crystallographic analysis and redox behavior explored using ESR spectra and cyclic voltammetry. Under oxidation with PbO2 in toluene solution both the ligands and Cu(II) complexes form stable phenoxyl‐type radicals. As shown by ESR measurements and DFT calculations, no exchange interaction exists between unpaired electrons located on metal and oxygen centers in the biradical Cu (II) complexes. The ligands and complexes reveal antioxidant radical scavenging activity measured spectrophotometrically and using ESR and DPPH‐tests.