Room-Temperature Direct Spectroscopic Observation of High-Valent Terminal Iron-Oxo Species of a µ-Nitrido-Bridged Iron Phthalocyanine Dimer Deposited on a Highly Oriented Pyrolytic Graphite Surface

High-valent metal-oxo species, such as iron(IV)-oxo porphyrin π-cation radical, are known to be involved in a variety of oxidative CH bond activation by metal complexes in the presence of oxidants. Although spectroscopic observations of these high-valent metal-oxo species are important for understanding reaction mechanisms, their high reactivities sometimes hamper direct observations, especially at ambient temperature. Herein, a high-valent iron-oxo species, involved in catalytic CH₄ oxidation by a µ-nitrido-bridged iron phthalocyanine dimer in an aqueous solution in the presence of excess H₂O₂, was successfully investigated by X-ray photoelectron spectroscopy (XPS), X-ray absorption spectroscopy (XAS), Raman, and matrix-assisted laser desorption and ionization-time-of-flight mass spectroscopy (MALDI-TOF MS) studies after deposition on a highly oriented pyrolytic graphite (HOPG) surface at room temperature. XPS study indicated the formation of a species with high oxidation states after treatment of the µ-nitrido-bridged iron phthalocyanine dimer attached on a HOPG with H₂O₂. Raman and O K-edge XAS studies, in combination with MALDI-TOF MS results, indicated the evidence for the formation of a species containing an oxygen atom with a double-bond character.