Iron complexes [((S,S)-PDP*)FeIII(μ-OH)2FeIII((S,S)-PDP*)](OTf)4 (6), (S,S)-PDP* = N,N′-bis(3,5-dimethyl-4-methoxypyridyl-2-methyl)-(S,S)-2,2′-bipyrrolidine, and [(TPA*)FeIII(μ-OH)2FeIII(TPA*)](OTf)4 (7), TPA* = tris(3,5-dimethyl-4-methoxypyridyl-2-methyl)amine, catalyze the selective hydroxylation of alkanes with H2O2 and peroxycarboxylic acids. Using in situ EPR spectroscopy, direct kinetic data on the reactivity of the iron-oxo intermediates formed in the catalyst systems 6,7/oxidant/RCOOH (RCOOH = acetic acid (AA) or 2-ethylhexanoic acid (EHA)) toward cyclohexane have been obtained for the first time, thus corroborating their key role in the selective CH oxidation. Intermediates 6aAA, 6aEHA and 7a2EHA with proposed structures [((S,S)-PDP*)FeVO(OC(O)CH3)]2+, [((S,S)-PDP*)FeVO(OC(O)R)]2+ and [(TPA*)FeVO(OC(O)R)]2+ (RCOOH = EHA) display similar EPR spectra (g1 = 2.07, g2 = 2.01, g3 = 1.96) and have close reactivities toward cyclohexane at −70 °C (k2 = 2–3 × 10−3 M−1 s−1).