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

A mu-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 mu-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 mu-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)-Fe-= 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 degrees 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 mu-nitrido-bridged iron porphycene dimer was so unstable that it decomposed quickly in the same reaction conditions.

Automated summary

A mu-nitrido-bridged dimer of iron phthalocyanine is an effective molecule-based CH4 oxidation catalyst. In this study, a novel mu-nitrido-bridged heterodimer of iron phthalocyanine and iron porphycene was synthesized, and its CH4 oxidation activity was examined. The heterodimer showed catalytic activity, while the mu-nitrido-bridged iron porphycene dimer decomposed quickly under the same reaction conditions.