CO electro-oxidation by carbon-supported Rh tetraphenylporphyrins that have o-methyl groups on meso-phenyl substituents

The ortho-methyl groups on meso-phenyl substituents were shown to strongly inhibit CO oxidation by Rh tetraphenylporphyrins. When both of the ortho-positions were occupied by methyl groups, CO oxidation was dramatically inhibited. The CO adduct was characterized by spectroscopy. O2 reduction by Rh tetraphenylporphyrins with ortho-methyl groups on meso phenyl substituents was also examined. The effects of ortho-methyl groups on CO oxidation are discussed in terms of steric hindrance.

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► We investigated electrochemical CO oxidation activity of Rh tetraphenylporphyrins.
► Ortho-methyl groups on meso phenyl groups strongly inhibit CO oxidation activity.
► The effect of ortho-methyl groups was also examined by spectroscopy.
► O2 reduction is not strongly inhibited by ortho-methyl groups.
► The results suggest that steric hindrance of ortho-methyl groups is important.