Catecholate and Phenolate Iron Complexes as Models for the Dioxygenases

Article abstract of DOI:10.1021/ja00374a016

The syntheses and physical properties of a series of Fe(salen)X and Fe(saloph)X complexes where X is phenolate or catecholate are reported.Magnetic susceptibility measurements as well as electronic, infrared, and NMR spectra indicate that the catecholate in Fe(salen)catH behaves very much like a phenolate and is concluded to be monodentate in its coordination to the iron.The abstraction of a proton from Fe(salen)catH results in an anionic complex, (-), with markedly different properties; the catecholate in this complex is chelated.Both monodentate and chelated catecholate complexes are high-spin ferric, demonstrating that catecholate coordination to a bis(phenolato)iron(III) complex does not result in the reduction of the ferric center.This is in agreement with observations made on dioxygenase-substrate complexes.In addition, studies on a series of Fe(salen)X complexes where X is a phenolate, thiophenolate, benzoate, and catecholate show that the dominant salen-to-Fe(III) charge-transfer interaction is modulated by the coordination of these ligands.Comparisons with corresponding dioxygenase complexes show that the tyrosinate-to-iron(III) charge-transfer interactions are similarly affected, thus indicating that the salen ligand provides a reasonable approximation of the iron environment in the dioxygenases.