An efficient catalytic oxygenation of hydrocarbons using iodosobenzene diacetate-metalloporphyrin systems as oxidants: A model for cytochrome P-450 monooxygenation enzyme

Iodosobenzene diacetate (IBDA) is shown to effect the hydroxylation of alkanes and the epoxidation of alkenes in the presence of simple metalloporphyrins in homogeneous acetone: water solvent systems. Good to excellent yields of hydrocarbon oxidation products are obtained. Olefin reactivity seems to follow the ease of ionization of the pi bond in the substrates, terminal olefins being the least reactive; however, good to excellent yields of epoxides are obtained from all the alkenes studied with meso-tetrakis (2,4,6-trimethoxyphenyl)- and meso-tetrakis(halogenophenyl)-porphyrinato manganese(III) acetate. In alkane hydroxylation reactivity follows the bond dissociation energy with the order: benzylic $\u3e$ tertiary $\u3e$ secondary $\u3e$ primary hydrogen. Kinetic results show that generation of the hypervalent oxomanganese(V) porphyrin intermediate is a fast step during oxygenation of both alkane and alkene substrates and that the reaction of this intermediate with hydrocarbons is the rate-limiting step of the catalytic cycle. The stereochemistry of the starting aliphatic olefin is retained in the epoxide product except for aromatic cis-olefins which suffer some isomerization about the alkene double bond. Use of nitrogenous bases (e.g., pyridine, 4$\sp\prime$-(imidazol-1-yl)acetophenone) as axial ligands affects favorably on (1) the stability of the catalysts, (2) yields of oxidation product(s), (3) the overall efficiency of the catalytic reaction (turnover rate), (4) isomerization of the carbon skeleton in aromatic cis-olefins. Olefin shape-selectivity, alkane regioselectivity, N-alkylation and O-demethylation reactions were also examined in the respective epoxidation and hydroxylation reactions. A rapid, facile one-pot synthesis of chlorin-free vanadyl(IV) meso-tetraarylporphyrins from pyrrole and the corresponding aldehyde using vanadyl-bis(acetylacetonate) as a template in propionic acid or phenol medium gave complete metallation and up to 40% yields of pure product. The catalytic behavior of vanadyl(IV) meso-tetraarylporphyrin in the autooxidation of olefins and the catalytic activity of iron(III) porphyrins in the oxidative reactions of olefins were investigated