o&o-Nitrophenyl meso-substituted ironporphyrins (FeP) and their corresponding ~-0x0 dimers were studied as catalyst in the oxidation of cyclohexane by iodosylbenzene (PhIO). The cyclohexanol yield versus FeP concentration plot indicate the nature of active species. For ( FeTNPP) Cl and (FeDNPP)Cl the active species is Fe'"( O)P+ . (1). For unhindered ( FeMNPP) Cl, the involvement of PFe'"-O-Fe'"( O)P+ ( ) explains the results. The catalytic activity of dimeric species (FeMNPP),O and (FeDNPP),O were surprisingly high, being as good as the monomeric ones. There is evidence of species 2 for these dimer catalysts. The oxidation reaction conditions were studied. We observed that the concentration of the catalyst, stirring method, ratio of iodosylbenzene/catalyst and presence of air can affect the cyclohexanol yields. (FeMNPP)Cl and (FeMNPP),O as catalysts can be seen as good P-450 model systems due to their stability, efficiency and selectivity toward cyclohexanol. The electron withdrawing effect of the substituents on the meso-phenyl rings of the porphyrin overwhelms the steric one in the catalytic activity, since only one or&o-nitro group is almost as efficient as the tetra-orrho-nitro substituted FeP. This work contributes to the understanding of the catalytic activities of unhindered ironporphyrins.