Herein, we examine the electronic and geometric structural properties of O2-derived aliphatic thiolate-ligated Fe-peroxo, Fe-hydroxo, and Fe­(IV) oxo compounds. The latter cleaves strong C–H bonds (96 kcal mol–1) on par with the valine C–H bond cleaved by isopencillin N synthase (IPNS). Stopped-flow kinetics studies indicate that the barrier to O2 binding to [FeII(SMe2N4(tren))]+ (3) is extremely low (E a = 36(2) kJ mol–1), as theoretically predicted for IPNS. Dioxygen binding to 3 is shown to be reversible, and a superoxo intermediate, [FeIII(SMe2N4(tren))­(O2)]+ (6), forms in the first 25 ms of the reaction at −40 °C prior to the rate-determining (E a = 46(2) kJ mol–1) formation of peroxo-bridged [(SMe2N4(tren))­Fe­(III)]2(μ-O2)2+ (7). A log­(k obs) vs log­([Fe]) plot for the formation of 7 is consistent with the second-order dependence on iron, and H2O2 assays are consistent with a 2:1 ratio of Fe/H2O2. Peroxo 7 is shown to convert to ferric-hydroxo [FeIII(SMe2N­(tren))­(OH)]+ (9, g ⊥ = 2.24, g ∥ = 1.96), the identity of which was determined via its independent synthesis. Rates of the conversion 7 → 9 are shown to be dependent on the X–H bond strength of the H-atom donor, with a k H/k D = 4 when CD3OD is used in place of CH3OH as a solvent. A crystallographically characterized cis thiolate-ligated high-valent iron oxo, [FeIV(O)­(SMe2N4(tren))]+ (11), is shown to form en route to hydroxo 9. Electronic structure calculations were shown to be consistent with 11 being an S = 1 Fe­(IV)O with an unusually high ν Fe–O stretching frequency at 918 cm–1 in line with the extremely short Fe–O bond (1.603(7) Å).