Homogeneous Catalytic Reduction of O 2 to H 2 O by a Terpyridine-Based FeN 3 O Complex.

We report a new terpyridine-based FeN 3 O catalyst, Fe(tpy tbu pho)Cl 2 , which reduces O 2 to H 2 O. Variable concentration and variable temperature spectrochemical studies with decamethylferrocene as a chemical reductant in acetonitrile solution enabled the elucidation of key reaction parameters for the catalytic reduction of O 2 to H 2 O by Fe(tpy tbu pho)Cl 2 . These mechanistic studies suggest that a 2 + 2 mechanism is operative, where hydrogen peroxide is produced as a discrete intermediate, prior to further reduction to H 2 O. Consistent with this proposal, the spectrochemically measured first-order rate constant k (s -1 ) value for H 2 O 2 reduction is larger than that for O 2 reduction. Further, significant H 2 O 2 production is observed under hydrodynamic conditions in rotating ring-disk electrode measurements, where the product can be swept away from the cathode surface before further reduction occurs.