Sterically hindered iron(II) complex of a new tripodal polyimidazole ligand: structure and reactivity toward superoxide

Abstract

The new tripodal potentially heptadentate ligand N(CH 2CH 2NCHR) 3 (L) with R = 1-triphenylmethyl-4-imidazolyl containing three 4-substitutes imidazole functions, where Nτ nitrogen atoms are protected with highly aromatic triphenylmethyl (trityl) groups, was synthesized. The corresponding iron(II) complex [Fe(L)](PF 6) 2 was prepared and characterized. Its molecular structure was determined by X-ray crystallography (monoclinic space group P2 1 n with a = 21.148(9), b = 23.484(9), c = 14.668(6) A ̊ , β = 97.44(4)°, Z = 4), and R = 0.0787). The Fe(II) ions is hexa-coordinated from three imine and three imidazole nitrogens. The tripodal bridging N atom is not bonded to the iron (3.1 Å). The complex is high spin as shown by NMR and electron paramagnetic resonance studies. UV-Vis and electrochemical properties are also reported. The reactivity of the complex with superoxide was investigated. A new species was discovered as ultimate product of the reaction with potassium superoxide in DMSO solution, which confirms effective superoxide scavenging by the complex despite the steric hindrance of the ligand.