To compare approximate catalytic turnover frequencies of Fe and Ru catalysts, we apply the energetic span model 119 to the Fe and Ru variants of catalysts D and F (Figure ). For each catalyst/metal combination, we start from the ground state spin of the reactant species (R) and compute energetic spans for the cases where spin crossover is alternately allowed or disallowed (Supporting Information Table ). In each of these cases, the turnover-determining intermediate (TDI) is the ground state spin of the oxidant-bound reactant species (R) because the exchange of isopropanol with 2,6-dichloropyridine 1-oxide is exothermic for all catalyst/metal combinations.