Evaluation of CH4 oxidation activity of high-valent iron-oxo species of a μ-nitrido-bridged heterodimer of iron porphycene and iron phthalocyanine

Abstract

A μ-nitrido-bridged dimer of iron phthalocyanine is one of the most potent molecule-based CH₄ oxidation catalysts reported to date. The reactive intermediate is a high-valent iron-oxo species generated through reaction with H₂O₂ in an acidic aqueous solution. However, there are few reports on the synthesis and catalytic CH₄ oxidation activity of a μ-nitrido-bridged heterodimer of two different iron porphyrinoids, despite that there are a variety of iron porphyrinoids with coordination and electronic structures different from those of iron phthalocyanines or iron porphyrins. Herein, we report the synthesis of a novel μ-nitrido-bridged heterodimer of an iron phthalocyanine and iron porphycene and examine its CH₄ oxidation activity. Porphycenes are an important class of porphyrinoids with a smaller coordination sphere than phthalocyanines or porphyrins. Single crystal structural analyses revealed that the heterodimer possessed a Fe–NFe core structure similar to that of the phthalocyanine homodimer. The heterodimer showed catalytic CH₄ oxidation activity in an acidic aqueous solution in the presence of H₂O₂ at 60 °C through the high-valent iron-oxo species as in the case with the phthalocyanine homodimer. This was in clear contrast to the result that the high-valent iron-oxo species of a μ-nitrido-bridged iron porphycene dimer was so unstable that it decomposed quickly in the same reaction conditions.