Dioxygen Reactivity of Biomimetic Iron-Catecholate and Iron-o-Aminophenolate Complexes of a Tris(2-pyridylthio)methanido Ligand: Aromatic C-C Bond Cleavage of Catecholate versus o-Iminobenzosemiquinonate Radical Formation

An iron(III)catecholate complex [L1FeIII(DBC)] (2) and an iron(II)o-aminophenolate complex [L1FeII(HAP)] (3; where L1=tris(2-pyridylthio)methanido anion, DBC=dianionic 3,5-di-tert-butylcatecholate, and HAP=monoanionic 4,6-di-tert-butyl-2-aminophenolate) have been synthesised from an iron(II)acetonitrile complex [L1FeII(CH3CN)2](ClO4) (1). Complex 2 reacts with dioxygen to oxidatively cleave the aromatic C?C bond of DBC giving rise to selective extradiol cleavage products. Controlled chemical or electrochemical oxidation of 2, on the other hand, forms an iron(III)semiquinone radical complex [L1FeIII(SQ)](PF6) (2ox-PF6; SQ=3,5-di-tert-butylsemiquinonate). The iron(II)o-aminophenolate complex (3) reacts with dioxygen to afford an iron(III)o-iminosemiquinonato radical complex [L1FeIII(ISQ)](ClO4) (3ox-ClO4; ISQ=4,6-di-tert-butyl-o-iminobenzosemiquinonato radical) via an iron(III)o-amidophenolate intermediate species. Structural characterisations of 1, 2, 2ox and 3ox reveal the presence of a strong iron?carbon bonding interaction in all the complexes. The bond parameters of 2ox and 3ox clearly establish the radical nature of catecholate- and o-aminophenolate-derived ligand, respectively. The effect of iron?carbon bonding interaction on the dioxygen reactivity of biomimetic ironcatecholate and irono-aminophenolate complexes is discussed.