There is an intriguing, current controversy on the involvement of multiple oxidizing species in oxygen transfer reactions by cytochromes P450 and iron porphyrin complexes. The primary evidence for the "multiple oxidants" theory was that products and/or product distributions obtained in the catalytic oxygenations were different depending on reaction conditions such as catalysts, oxidants, and solvents. In the present work, we carried out detailed mechanistic studies on competitive olefin epoxidation, alkane hydroxylation, and C=C epoxidation versus allylic C-H hydroxylation in olefin oxygenation with in situ generated oxoiron(IV) porphyrin pi-cation radicals (1) under various reaction conditions. We found that the products and product distributions were markedly different depending on the reaction conditions. For example, 1 bearing different axial ligands showed different product selectivities in competitive epoxidations of cis-olefins and trans-olefins and of styrene and para-substituted styrenes. The hydroxylation of ethylbenzene by 1 afforded different products, such as 1-phenylethanol and ethylbenzoquinone, depending on the axial ligands of 1 and substrates. Moreover, the regioselectivity of C=C epoxidation versus C-H hydroxylation in the oxygenation of cyclohexene by 1 changed dramatically depending on the reaction temperatures, the electronic nature of the iron porphyrins, and substrates. These results demonstrate that 1 can exhibit diverse reactivity patterns under different reaction conditions, leading us to propose that the different products and/or product distributions observed in the catalytic oxygenation reactions by iron porphyrin models might not arise from the involvement of multiple oxidizing species but from 1 under different circumstances. This study provides strong evidence that 1 can behave like a "chameleon oxidant" that changes its reactivity and selectivity under the influence of environmental changes.

The reactions of manganese(III) porphyrin complexes with terminal oxidants, such as mchloroperbenzoic acid, iodosylarenes, and H 2 O 2 , produced high-valent manganese(V)-oxo porphyrins in the presence of base in organic solvents at room temperature. The manganese(V)-oxo porphyrins have been characterized with various spectroscopic techniques, including UV-vis, EPR, 1 H and 19 F NMR, resonance Raman, and X-ray absorption spectroscopy. The combined spectroscopic results indicate that the manganese(V)-oxo porphyrins are diamagnetic low-spin (S = 0) species with a longer, weaker Mn-O bond than in previously reported Mn(V)-oxo complexes of non-porphyrin ligands. This is indicative of double bond character between the manganese(V) ion and the oxygen atom, and may be attributed to the presence of a trans-axial ligand. The Figure S2), UV-vis spectrum of (TM-2-PyP)Mn V =O ( Figure S3), UV-vis and EPR spectra of (TDCPP)Mn IV =O (2a) (Figure S4), time traces for the natural decay of 1a in the presence of different amounts of base ( Figure S5), and LC-ESI MS of PPh 3 O obtained in isotope labeling experiment ( Figure S6). NIH Public Access