Electrochemical Implication of a Hydrogen‐Bonded Imidazole on a Redox‐Active‐Bound Phenolate Group

We report the synthesis of a pentadentate N4O ligand with an imidazole group in the ortho position of the phenol group. The syntheses and crystallographic structures are reported for zinc(II) complexes by using the previously reported tert-butyl-substituted ligand and the imidazole-substituted ligand in two different protonation states. We describe the influence of the ortho substituent (tert-butyl, imidazole, and imidazolium) on the electrochemical behavior of the zinc(II) complexes. The substitution of the tert-butyl group in the ortho position by an imidazole group shifts the oxidation potential of the phenolate by more than 300 mV. The o-tert-butyl-substituted ligand allows the formation of a stable radical phenoxylzinc(II) complex upon electrochemical oxidation, but it is unstable in the case of the imidazole-substituted complex. The imidazole-substituted ligand can be reversibly protonated without altering the electrochemical properties of the phenolate group.