Direct comparison of electrochemical and spectrochemical kinetics for catalytic oxygen reduction.

We describe here a direct comparison of electrochemical and spectrochemical experiments to determine rates and selectivity of oxygen reduction catalyzed by iron 5,10,15,20-meso-tetraphenylporphyrin chloride. Good agreement was found between the two methods, suggesting the same mechanism is occurring under both conditions, with the same third-order rate law, similar selectivity, and the derived rate constants agreeing within a factor of at most 4, with k(cat) ≅ 2 × 10(6) M(-2) s(-1). This Communication provides a rare example of a redox catalytic process characterized by two common but very different methods.