Nonheme iron mediated oxidation of light alkanes with oxone: characterization of reactive oxoiron(IV) ligand cation radical intermediates by spectroscopic studies and DFT calculations.

The oxidation of light alkanes that is catalyzed by heme and nonheme iron enzymes is widely proposed to involve highly reactive {Fe(V)=O} species or {Fe(IV)=O} ligand cation radicals. The identification of these high-valent iron species and the development of an iron-catalyzed oxidation of light alkanes under mild conditions are of vital importance. Herein, a combination of tridentate and bidentate ligands was used for the generation of highly reactive nonheme {Fe=O} species. A method that employs [Fe(III)(Me3tacn)(Cl-acac)Cl](+) as a catalyst in the presence of oxone was developed for the oxidation of hydrocarbons, including cyclohexane, propane, and ethane (Me3tacn=1,4,7-trimethyl-1,4,7-triazacyclononane; Cl-acac=3-chloro-acetylacetonate). The complex [Fe(III)(Tp)2](+) and oxone enabled stoichiometric oxidation of propane and ethane. ESI-MS, EPR and UV/Vis spectroscopy, (18)O labeling experiments, and DFT studies point to [Fe(IV)(Me3tacn)({Cl-acac}(.+))(O)](2+) as the catalytically active species.

Practical manganese-catalysed highly enantioselective cis-dihydroxylation of electron-deficient alkenes and detection of a cis-dioxomanganese(V) intermediate by high resolution ESI-MS analysis.

A practical protocol has been developed for asymmetric cis-dihydroxylation of electron-deficient alkenes with Oxone catalysed by a manganese complex bearing a chiral tetradentate N(4)-donor ligand affording cis-diols in up to 95% yield with up to 96% ee. Analysis of the reaction mixture by high resolution ESI-MS revealed the formation of a cis-dioxomanganese(V) intermediate.

cis-Dihydroxylation of alkenes with oxone catalyzed by iron complexes of a macrocyclic tetraaza ligand and reaction mechanism by ESI-MS spectrometry and DFT calculations.

[Fe(III)(L-N(4)Me(2))Cl(2)](+) (1, L-N(4)Me(2) = N,N'-dimethyl-2,11-diaza[3.3](2,6)pyridinophane) is an active catalyst for cis-dihydroxylation of various types of alkenes with oxone at room temperature using limiting amounts of alkene substrates. In the presence of 0.7 or 3.5 mol % of 1, reactions of electron-rich alkenes, including cyclooctene, styrenes, and linear alkenes, with oxone (2 equiv) for 5 min resulted in up to >99% substrate conversion and afforded cis-diol products in up to 67% yield, with cis-diol/epoxide molar ratio of up to 16.8:1. For electron-deficient alkenes including α,ß-unsaturated esters and α,ß-unsaturated ketones, their reactions with oxone (2 equiv) catalyzed by 1 (3.5 mol %) for 5 min afforded cis-diols in up to 99% yield with up to >99% substrate conversion. A large-scale cis-dihydroxylation of methyl cinnamate (9.7 g) with oxone (1 equiv) afforded the cis-diol product (8.4 g) in 84% yield with 85% substrate conversion. After catalysis, the L-N(4)Me(2) ligand released due to demetalation can be reused to react with newly added Fe(ClO(4))(2)·4H(2)O to generate an iron catalyst in situ, which could be used to restart the catalytic alkene cis-dihydroxylation. Mechanistic studies by ESI-MS, isotope labeling studies, and DFT calculations on the 1-catalyzed cis-dihydroxylation of dimethyl fumarate with oxone reveal possible involvement of cis-HO-Fe(V)═O and/or cis-O═Fe(V)═O species in the reaction; the cis-dihydroxylation reactions involving cis-HO-Fe(V)═O and cis-O═Fe(V)═O species both proceed by a concerted but highly asynchronous mechanism, with that involving cis-HO-Fe(V)═O being more favorable due to a smaller activation barrier.