Iron(III) complexes with a tripodal N3O ligand containing an internal base as a model for catechol intradiol-cleaving dioxygenases

• A bis(mu-alkoxo)-bridged dinuclear iron(III) complex [Fe(L)(NO3)](2)(NO3)(2) [1; HL = NN-bis(2-pyridylmethyl)-N-(2hydroxyethyl)amine] of the tripodal N3O ligand was prepared as a biomimetic model for the intradiol-cleaving dioxygenase enzymes. The reaction of 1 and catechol in the presence of excess triethylamine gave the catecholate (CAT) chelate b is(u -al koxo) -bridged dinuclear iron(Ill) complex [Fe(L)(CAT)12 (2). The molecular structures of complexes 1 and 2 were determined by X-ray crystallography. Diiron complexes 1 and 2 contain the same bis(u-alkoxo)diiron diamond core. All heteroatoms (N3O) of the ligand are coordinated to the iron center in complex 1 with two pyridine nitrogen atoms on the axial bonds, while one of the pyridyl arms of the ligand is left uncoordinated in complex 2. The interaction of the diiron complex 1 and 3,5-di-tert-butylcatechol (H2DBC) was investigated by electronic and mass spectroscopy. Complex 1 displays the intradiol-cleaving dioxygenase activity, and the coordinate ethoxyl arm of the ligand is capable of accepting the proton from catechol, which mimics the function of Tyr447 in the. protocatechuate 3,4-dioxygenase as an internal base. The spectrop h oto metric titration experiment indicates the relatively low demand of the external base (0.8 equiv based on Fe3+) for attaining the highest dioxygenase activity of complex 1. The reaction rate of the reactive intermediate [Fe(HL)(DBC)](+) with dioxygen is 0.38 M-1 s(-1) determined by kinetic studies.

Nyckelord

reactive functional-model

nonheme iron enzymes

protocatechuate 3,4-dioxygenase

crystal-structure

active-sites

(catecholato)iron(iii) complexes

tetradentate ligands

angstrom resolution

oxidative cleavage

1,2-dioxygenase

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