Michael Merkel

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

Abstract 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.

Four isotypic highly coordinated lanthanide complexes of the tripodal ligand bis[(2-pyridyl)methyl][(1-methylimidazol-2-yl)methyl]amine

The Ln(III) complexes (Ln = Pr, Nd, Sm and Tb) of the tripodal ligand bis[(2-pyridyl)methyl][(1- methylimidazol-2-yl)methyl]amine (bpia) have been synthesized and characterized by single crystal X-ray structure determination as well as vibrational spectroscopy. The coordination spheres of the lanthanide cations are completed by three chelating nitrate anions yielding neutral complexes with a tenfold coordination of the metal ions. All four compounds are found to be isotypic, crystallizing in space group P1̄ (No. 2) with Z = 2. On comparing the IR-spectra of the new complexes to the spectra of the free ligands a shift to higher wave numbers is observed for corresponding bands in both, bpia and nitrate ligands.