STERICALLY HINDERED IRON(II) COMPLEX OF A NEW TRIPODAL POLYIMIDAZOLE LIGAND - STRUCTURE AND REACTIVITY TOWARD SUPEROXIDE

The new tripodal potentially heptadentate ligand N(CH2-CH2-N=CH-R)(3) (L) with R = 1-triphenylmethyl-4-imidazolyl containing three LF-substi tuted imidazole functions, where N tau nitrogen atoms are protected wi th highly aromatic triphenylmethyl (trityl) groups, was synthesized. T he corresponding iron(II) complex [Fe(L)](PF,), was prepared and chara cterized. Its molecular structure was determined by X-ray crystallogra phy (monoclinic space group P2(1)/n with a=21.148(9), b=23.484(9), c=1 4.668(6) Angstrom, beta=97.44(4)degrees, Z=4, and R = 0.0787). The Fe( II) ion is hexa-coordinated from three imine and three imidazole nitro gens. The tripodal bridging N atom is not bonded to the iron (3.1 Angs trom). The complex is high spin as shown by NMR and electron paramagne tic resonance studies. W-Vis and electrochemical properties are also r eported. The reactivity of the complex with superoxide was investigate d. A new species was discovered as ultimate product of the reaction wi th potassium superoxide in DMSO solution, which confirms effective sup eroxide scavenging by the complex despite the steric hindrance of the ligand. (C) 1998 Elsevier Science S.A. All rights reserved.