A Functional Model of Extradiol-Cleaving Catechol Dioxygenases: Mimicking the 2-His-1-Carboxylate Facial Triad

The synthesis and characterization of an iron−catecholate model complex of a tridentate 2-N-1-carboxylate ligand derived from l-proline are reported. The X-ray crystal structure of the complex [(L)3Fe3(DBC)3] (1) (where L is 1-(2-pyridylmethyl)pyrrolidine-2-carboxylate and DBC is the dianion of 3,5-di-tert-butyl catechol) reveals that the tridentate ligand binds to the iron center in a facial manner and mimics the 2-his-1-carboxylate facial triad motif observed in extradiol-cleaving catechol dioxygenases. The iron(III)−catecholate complex (1) reacts with dioxygen in acetonitrile in ambient conditions to cleave the C−C bond of catecholate. In the reaction, an equal amount of extra- and intradiol cleavage products are formed without any auto-oxidation product. The iron−catecholate complex is a potential functional model of extradiol-cleaving catechol dioxygenases.