The ruthenium(III) octaethylporphyrin complex, Ru(OEP)(PPh 3)Br, 1,has been prepared by the oxidation of Ru(OEP)(PPh 3) 2 [1] with excess bromine, and fully characterized by spectroscopic and crystallographic methods [2]. We have found that CH 2Cl 2 solutions of 1 (5 × 10 −3 M) containing iodosylbenzene (0.1 M) catalyze at 20 °C the oxidation of certain olefins and cyclohexane (0.2–20.5 M). Some of the oxidation data are summarized in Table I. Groves et al. [3] have reported on corresponding oxidations using iron(III) porphyrins, and have presented evidence for involvement of an oxoiron(IV) porphyrin cation-radical intermediate, OFe IV(porp +•). This is equivalent electronically to iron(III) plus the oxygen atom (from iodosylbenzene), and is overall at the same oxidation level as the active species in the cytochrome P-450 enzyme cycle; the enzyme systems utilize molecular O 2 for alkene epoxidation and hydrocarbon hydroxylation, and active OFe IV(porp +•) intermediates have been implicated [3–5]. Studies with our ruthenium(III) system have led to isolation of closely related cation-radical species. Thus, reaction of 1 with PhIO yields a green complex tentatively formulated as 0Ru IV (OEP +•)Br, 2. A strong ESR signal at g = 2.00 (at 77 K or 20 °C), and a broad Soret band at 384 nm coupled with bands at 502 and 604 nm, are typical of cation-radical species [1, 4]; a stoichiometric spectrophotometric titration with PPh 3 (complex 2: PPh 3 = 2.0) to give quantitatively OPPh 3 and [Ru IV(OEP)Br] 2O [6] (see Scheme), and detection of bromine as cyclohexylbromide in the hydrocarbon oxidations (close to stoichiometric based on Ru, up to 85%, see Table) are consistent with the oxygen and bromine content of 2, and with 2 being the active oxidizing species via free-radical reactions [1, 9, 10]: ▪ ▪ An inactive green complex, isolated at the end of the oxidations, and also formed by decomposition of 2 in solution, is believed to be a ORu(OEP) species, 3, since it reacts quantitatively with PPh 3(1:1) to give the phosphine oxide and [Ru(OEP)] 2 [8]. Species 3, which is rapidly converted by trace amounts of base into [Ru(OEP)(OH)] 2O [7, 8], may contain an axial water ligand in which case it would resemble ORu(bipyridine) 2(py), which is known to oxidize PPh 3 by an oxygen atom transfer mechanism [11]. Spectroscopic studies are in progress in attempts to characterize more fully the putative oxo species 2 and 3.