Activation of Dioxygen by a Mononuclear Nonheme Iron Complex: Sequential Peroxo, Oxo, and Hydroxo Intermediates.

The activation of dioxygen by Fe(MeTACN)(SSiMe) () is reported. Reaction of with O at -135 °C in 2-MeTHF generates a thiolate-ligated (peroxo)diiron complex Fe(O)(MeTACN)(SSiMe) () that was characterized by UV-vis (λ = 300, 390, 530, 723 nm), Mössbauer (δ = 0.53, |Δ| = 0.76 mm s), resonance Raman (RR) (ν(O-O) = 849 cm), and X-ray absorption (XAS) spectroscopies. Complex is distinct from the outer-sphere oxidation product (UV-vis (λ = 435, 520, 600 nm), Mössbauer (δ = 0.45, |Δ| = 3.6 mm s), and EPR ( = 5/2, = [6.38, 5.53, 1.99])), obtained by one-electron oxidation of . Cleavage of the peroxo O-O bond can be initiated either photochemically or thermally to produce a new species assigned as an Fe(O) complex, Fe(O)(MeTACN)(SSiMe) (), which was identified by UV-vis (λ = 385, 460, 890 nm), Mössbauer (δ = 0.21, |Δ| = 1.57 mm s), RR (ν(Fe═O) = 735 cm), and X-ray absorption spectroscopies, as well as reactivity patterns. Reaction of at low temperature with H atom donors gives a new species, Fe(OH)(MeTACN)(SSiMe) (). Complex was independently synthesized from by the stoichiometric addition of a one-electron oxidant and a hydroxide source. This work provides a rare example of dioxygen activation at a mononuclear nonheme iron(II) complex that produces both Fe-O-O-Fe and Fe(O) species in the same reaction with O. It also demonstrates the feasibility of forming Fe/O intermediates with strongly donating sulfur ligands while avoiding immediate sulfur oxidation.