ANALOGS OF THE IRON-BINDING SITE IN CATECHOL 1,2-DIOXYGENASE - IRON(III) COMPLEXES OF BENZIMIDAZOLE AND PYRIDINE-CONTAINING TRIDENTATE LIGANDS

A series of iron(III) complexes of the type [FeLCl(2)].H2O [HL = N-(pyridin-2-ylmethyl)salicylideneamine, (2-hydroxy-5-nitrobenzyl)(pyridin-2-ylmethyl)amine, (2-hydroxy-5-nitrobenzyl)(2-pyridin-2-ylethyl)-amine, N-(2-imidazol-4-ylethyl)salicylideneamine N-(benzimidazole-2-ylmethyl)salicylaldime (benzimidazol-2-ylmethyl)(2-hydroxybenzyl)amine, or (benzimidazol-2-ylmethyl) (2-hydroxy-5-nitrobenzyl)amine] have been prepared. Also [FeLCl(3)].H2O [L = bis(benzimidazol-2-ylmethyl)amine] has been isolated. These complexes have been characterised using IR, UV/VIS and EPR spectral and electrochemical techniques. Their interaction with a variety of mono- and bi-dentate heterocyclic bases as well as phenols has been investigated using electronic and EPR spectroscopy. Their interaction with 3,5-di-tert-butylcatechol (H(2)dbcat) and its anions reveals changes in the phenolate-to-iron(III) charge-transfer (c.t.) band similar to those for catechol dioxygenase-substrate complexes. The redox behaviour of the iron(III) complexes and their 1:1 adducts with dbcat anions generated in situ has been investigated in methanol. There is a linear correlation between the Fe-III-Fe-II] redox potential and the c.t. band energy of the complexes. All the complexes catalyse the oxidative cleavage of H(2)dbcat by molecular oxygen to yield cis,cis-muconic anhydride. The catalytic activity has been correlated with the Fe-III-Fe-II as well as dbsq'-H(2)dbcat (dbsq = 3,5-di-tert-butyl-1,2-benzosemiquinone) redox potentials of the dbcat adducts.