Oxygen Rebound Mechanism Research Articles

Five-coordinate carbon hydroxylation mechanism

Oxygen rebound mechanism for hydrocarbon hydroxylation by high-valent metal complexes is critically analyzed and is shown to be contradictory in certain aspects. The synchronous insertion of O atom mechanism is found to be significantly less contradictory (at least for the most interesting cases of strong CH bonds, for example in methane) if it is supplemented by the stage of formation of the five-coordinate carbon intermediate complex of a hydrocarbon molecule via oxygen atom of an active center.

Free-radicals in the oxidation and halogenation of alkanes by dimethyldioxirane: an oxygen rebound mechanism

The oxidation of alkanes by dimethyldioxirane (DMD) in the presence of CBrCl 3 provides strong evidence that free-radicals are involved in the reaction; enthalpic and polar effects and an “oxygen rebound” mechanism are suggested to explain the exceptional oxidation selectivity.

Syntheses, electrochemistry and reactivities of pyridine amide complexes of chromium(III) and manganese(III)

Reactions of anhydrous CrCl3 with H2bpb and H2bpc [H2bpb = 1,2-bis(pyridine-2-carboxamido)benzene; H2bpc = 4,5-dichloro-1,2-bis(pyridine-2-carboxamido)benzene] in dimethylformamide and manganese(III) acetate with H2bpc in methanol, yielded the respective [CrIII(bpb)Cl]·xH2O, [CrIII(bpc)Cl]·H2O and [MnIII(bpc)(O2CMe)] complexes. The electrochemistry of the chromium(III) amide complexes has been studied by cyclic voltammetry. They exhibit reversible oxidation couples with E° values ranging from 0.28 to 0.80 V vs. ferrocenium–ferrocene. Except for [CrIII(bpb)(CN)2]– which has a quasireversible reduction couple at –1.97 V, the electrochemical reductions are irreversible. The complexes [CrIII(bpb)(H2O)2]ClO4, [CrIII(bpb)Cl(MeOH)] and [MnIII(bpc)(O2CMe)] have been shown to catalyse olefin epoxidation by iodosobenzene. With [Mn(bpc)(O2CMe)], catalytic oxidation of alkanes by PhIO has also been observed. An oxygen-rebound mechanism involving a MnvO or a CrvO intermediate is proposed for the PhIO oxidation reactions.

Dual pathways for manganese catalysis of olefin oxidation with alkyl hydroperoxides

The catalytic oxidation of various olefins with t-butyl hydroperoxide as the terminal oxidant is effectively carried out with cationic manganese(III) complexes of the salen ligand [ N, N'-ethylenebis(salicylideneaminato)] in the presence of pyridine or imidazole as the cocatalyst. Two concurrent processes have been identified with cyclohexene as the olefinic substrate, which affords both cyclohexenyl t-butyl peroxide and cyclohexene oxide within 5 min at 25 °C in acetonitrile solutions. The pathway leading to cyclohexenyl t-butyl peroxide (allylic peroxidation) involves a free radical chain mechanism which is completely inhibited by the hindered phenol ionol. The presence of ionol allows various olefins to be cleanly epoxidized with t-butyl hydroperoxide-pyridine and catalytic amounts of salenMn III. Olefin epoxidation occurs by an oxygen-rebound mechanism involving a reactive oxomanganese(V) species similar to that obtained with iodosylbenzene as the terminal oxidant. Both systems yield the same spectral transients with λ max ~ 550 nm and show the same reactivity patterns of various olefins. Homolysis and heterolysis of an alkylperoxomanganese(III) intermediate is considered to be the common precursor responsible for the radical chain initiation of allylic peroxidation and for the reactive oxomanganese(V) species in olefin epoxidation.

Key elements of the chemistry of cytochrome P-450: The oxygen rebound mechanism

Diagnostic substrates for cytochrome P-450, synthetic models of the active site, and oxidations with synthetic metalloporphyrins. From the "State of the Art Symposium: Bioinorganic Chemistry", held at the ACS meeting, Miami, 1985.