Oxidation of 2-aminophenol by iron(III) isoindoline complexes

• Synthesis of the 1,3-bis(5′-methyl-2′-thiazolylimino)isoindoline.
• Iron(III)-isoindoline-catalyzed oxidation of 2-aminophenol with dioxygen.
• Iron(III)-isoindoline-catalyzed oxidation of 2-aminophenol with H2O2.
• Correlation of the reaction rates on the redox potential of the iron centers.

Series of dichloroiron(III) complexes of 1,3-bis(2′-arylimino)isoindoline, including a new structurally characterized ligand 1,3-bis(5′-methyl-2′-thiazolylimino)isoindoline and its complex, have been used as catalysts for the oxidative coupling of 2-aminophenol (OAPH) to 2-aminophenoxazine-3-one (APX) in DMF solution at ambient temperature. The complexes were suitable as catalyst, and depending on the oxidant used, two different mechanisms can be proposed, namely a metal-based oxidation for dioxygen, and a hydroxyl radical mediated process, including zero-order dependence on the concentration of the substrate, for H2O2. In the former case a mechanism on the basis of kinetic data was proposed assuming ternary complex formation between catalyst, substrate and dioxygen, and a nice correlation was found between the reaction rate and the oxidation potential, E°′paE°′pa of the iron center in the precursor complexes.

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