Synthesis and characterization of a ferric complex of the tripodal ligand tris(2-benzimidazolylmethyl)amine—a superoxide dismutase mimic

Abstract

The mononuclear iron complex 1 was synthesized using a tripodal ligand, tris(2-benzimidazolylmethyl)amine (ntb), where ntb served as a neutral tetradentate chelating ligand for the distorted octahedral ferric ion. Three benzimidazole groups of ntb and one chloride anion formed a base of octahedral geometry. One of the two axial positions was occupied by an apical nitrogen atom of ntb and the other site was occupied by another chloride anion. Two of the chloride anions in complex 1 are in a cis arrangement. The decay of the electrochemically generated superoxide radical (O 2 −) by complex 1 was observed using cyclic voltammetry. The superoxide dismutase (SOD) activity of complex 1 was also examined using a modified method of the light- and riboflavin-driven hydroxylaminenitrate assay. Reaction of complex 1 with an O 2 − radical in methanol gave the μ-oxo dinuclear iron complex 2. The μ-oxo group was substituted for the basal chloride anion of complex 1 in complex 2. Complex 2 could also be synthesized using weak bases instead of the O 2 − radical.