| Popis: |
The oxygen reduction reaction (ORR) is catalyzed by manganese(II) tetraphenyl porphyrin (Mn(II)TPP) in the presence of Brønsted acids (HAs). Analysis of the catalytic wave in the cyclic voltammogram of the ORR reaction leads to the proposal two equivalents of HA drives the formation of the initial oxygen adduct, followed by oxygen-oxygen bond activation. An analogous hangman Mn(II) TPP compound has been prepared and characterized. For this ORR catalyst, an acidic proton is provided intramolecularly, and the HA order is reduced to one equivalent. Our data supports a model where one HA is used to stabilize the oxygen bound to the reduced hangman Mn(II) porphyrin platform; one HA is not needed as an internal hydrogen bond may be formed with the hanging acid group. The O–O bond cleavage requires an external HA for the rate-determining step, thus offering a rare example where the O–O bond activation of an ORR process is isolated and captured. |
