Novel iron(III) complexes with phenolate containing tripodal tetradentate ligands as model systems for catechol 1,2-dioxygenases

The iron(III) complexes HNEt3[Fe(L1)(tbc)]·0.5Me2CO·0.5Et2O (1), HNEt3[Fe(L2)(tbc)]·0.25H2O (2) and HNEt3[Fe(L3)(tbc)] (3) containing the new tripodal tetradentate ligands H2L1, H2L2 and H2L3 (H2L1: (3,5-dibromo-2-hydroxybenzyl)(2-hydroxybenzyl)(2-pyridylmethyl)amine, H2L2: (3,5-dichloro-2-hydroxybenzyl)(2-hydroxybenzyl)(2-pyridylmethyl)amine, H2L3: (3,5-dichloro-2-hydroxybenzyl)(2-hydroxy-5-nitrobenzyl)(2-pyridylmethyl)amine, H2tbc: tetrabromocatechol) were synthesized. They are structural models for inhibitor substrate adducts of catechol 1,2-dioxygenases. All complexes were characterized by spectroscopic methods and X-ray structure analysis. The coordination sphere of all Fe(III) cores is distorted octahedral with the inhibitor substrate tbc occupying two cis positions whereas the ligand with its N2O2 donor set represents the endogenous protein ligands. The in situ prepared iron(III) complexes in absence of tbc show one of the highest intradiol catechol dioxygenase activities with respect to the cleavage of 3,5-di-tert-butylcatechol (dbc) reported for model compounds containing phenolate donors.