Catalytic HO Activation by a Diiron Complex for Methanol Oxidation.

In nature, C-H bond oxidation of CH involves a peroxo intermediate that decays to the high-valent active species of either a "closed" {Fe(μ-O)Fe} core or an "open" {Fe(O)(μ-O)Fe(O)} core. To mimic and to obtain more mechanistic insight in this reaction mode, we have investigated the reactivity of the bioinspired diiron complex [(susan){Fe(OH)(μ-O)Fe(OH)}] [susan = 4,7-dimethyl-1,1,10,10-tetrakis(2-pyridylmethyl)-1,4,7,10-tetraazadecane], which catalyzes CHOH oxidation with HO to HCHO and HCOH. The kinetics is faster in the presence of a proton. O-labeling experiments show that the active species, generated by a decay of the initially formed peroxo intermediate [(susan){Fe(μ-O)(μ-O)Fe}], contains one reactive oxygen atom from the μ-oxo and another from the μ-peroxo bridge of its peroxo precursor. Considering an FeFe active species, a "closed" {Fe(μ-O)Fe} core explains the observed labeling results, while a scrambling of the terminal and bridging oxo ligands is required to account for an "open" {Fe(O)(μ-O)Fe(O)} core.