IRON(III) COMPLEXES OF PHENOLATE LIGANDS AS MODELS FOR CATECHOL DIOXYGENASES

Catechol 1,2-dioxygenase (CTD) and protocatechuate 3,4-dioxygenase (PC D) enzymes catalyse the oxidative cleavage of catechols to cis, cis-mu conic acids with the incorporation of molecular oxygen. In our laborat ory two series of iron(III) complexes of linear tridentate and tripoda l tetradentate phenolate ligands have been characterised using IR, UV- Vis and EPR spectral and electrochemical techniques. The X-ray crystal structure of a few of the complexes have been determined. The interac tions of the complexes with a variety of monodentate and bidentate het erocyclic bases as well as phenols have been investigated. The interac tions with catecholate anions reveal changes in the phenolate-to-iron( III) charge transfer band, which are remarkably similar to catechol di oxygenase-substrate complexes. The redox behaviour of the complexes an d their 1:1 adducts with 3,5-di-t-butyl-catechol (H2DBC) has been inve stigated. All the complexes catalyse the oxidative cleavage of H(2)DEC by molecular oxygen to yield cis,cis-muconic anhydride. The structure , redox and catalytic activities of the iron(III) complexes have been discussed vis-a-vis those of the enzymes.