Effect of porphyrin ligands on the catalytic CH oxidation activity of monocationic μ-nitrido-bridged iron porphyrinoid dimers by using HO as an oxidant

The μ-nitrido-bridged iron phthalocyanine homodimer is a potent molecule-based CH 4 oxidation catalyst that can effectively oxidize chemically stable CH 4 under mild reaction conditions in an acidic aqueous solution including an oxidant such as H 2 O 2 . The reactive intermediate is a high-valent iron-oxo species generated upon reaction with H 2 O 2 . However, a detailed comparison of the CH 4 oxidation activity of the μ-nitrido-bridged iron phthalocyanine dimer with those of μ-nitrido-bridged iron porphyrinoid dimers containing one or two porphyrin ring(s) has not been yet reported, although porphyrins are the most important class of porphyrinoids. Herein, we compare the catalytic CH 4 and CH 3 CH 3 oxidation activities of a monocationic μ-nitrido-bridged iron porphyrin homodimer and a monocationic μ-nitrido-bridged heterodimer of an iron porphyrin and an iron phthalocyanine with those of a monocationic μ-nitrido-bridged iron phthalocyanine homodimer in an acidic aqueous solution containing H 2 O 2 as an oxidant. It was demonstrated that the CH 4 oxidation activities of monocationic μ-nitrido-bridged iron porphyrinoid dimers containing porphyrin ring(s) were much lower than that of a monocationic μ-nitrido-bridged iron phthalocyanine homodimer. These findings suggested that the difference in the electronic structure of the porphyrinoid rings of monocationic μ-nitrido-bridged iron porphyrinoid dimers strongly affected their catalytic light alkane oxidation activities. Catalytic methane and ethane oxidation activities by μ-nitrido-bridged iron porphyrinoid dimers containing one or two porphyrins in aqueous solutions containing excess H 2 O 2 were compared with those by a μ-nitrido-bridged iron phthalocyanine dimer.