An efficient biomimetic Fe-catalyzed epoxidation of olefins using hydrogen peroxide

Bromine and oxygen redox species mediated highly selective electro-epoxidation of styrene

Olefin epoxidation is an essential transformation and arouses great interest among the scientific community for the key role of epoxide in the chemical industry.

Methyltrioxorhenium (MTO) catalysis in the epoxidation of alkenes: a synthetic overview

Epoxides are biologically important moiety that is also used as synthetic intermediates. This review aims to present the up-to-date advancements in methyltrioxorhenium (MTO)-catalyzed epoxidation of alkenes using diverse oxidizing agents.

A Bottom Up Approach Towards Artificial Oxygenases by Combining Iron Coordination Complexes and Peptides

The combination of peptides and a chiral iron coordination complex catalyzes high yield highly asymmetric epoxidation with aqueous hydrogen peroxide.

Supramolecular systems resulting from the combination of peptides and a chiral iron coordination complex catalyze asymmetric epoxidation with aqueous hydrogen peroxide, providing good to excellent yields and high enantioselectivities in short reaction times. The peptide is shown to play a dual role; the terminal carboxylic acid assists the iron center in the efficient H₂O₂ activation step, while its β-turn structure is crucial to induce high enantioselectivity in the oxygen delivering step. The high level of stereoselection (84–92% ee) obtained by these supramolecular catalysts in the epoxidation of 1,1′-alkyl ortho-substituted styrenes, a notoriously challenging class of substrates for asymmetric catalysis, is not attainable with any other epoxidation methodology described so far. The current work, combining an iron center ligated to N and O based ligands, and a peptide scaffold that shapes the second coordination sphere, may be seen as a bottom up approach towards the design of artificial oxygenases.

Identifying active sites of CoNC/CNT from pyrolysis of molecularly defined complexes for oxidative esterification and hydrogenation reactions

Cobalt chelate complexes bonded to 2 to 3 nitrogens in the graphene lattice are the active sites for the oxidative esterification of benzyl alcohol by molecular oxygen, the selective reduction of nitrobenzene by hydrogen and the hydrogenated coupling of nitrobenzene and benzaldehyde.

Biologically inspired non-heme iron-catalysts for asymmetric epoxidation; design principles and perspectives

Iron coordination complexes with nitrogen and oxygen donor ligands have long since been known to react with peroxides producing powerful oxidizing species. These compounds can be regarded as simple structural and functional models of the active sites of non-heme iron dependent oxygenases. Research efforts during the last decade have uncovered basic principles and structural coordination chemistry motifs that permit us to control the chemistry that evolves when these iron complexes react with peroxides, in order to provide powerful metal-based, but at the same time selective, oxidising agents. Oxidation methodologies with synthetic value are currently emerging from this approach. The current review focuses on asymmetric epoxidation, a reaction which has large value in synthesis, and where iron/H2O2 based methodologies may represent not only a sustainable choice, but may also expand the scope of state-of-the-art oxidation methods. Basic principles that underlay catalyst design as well as H2O2 activation are discussed, whilst limitations and future perspectives are also reviewed.

Asymmetric epoxidation with H2O2 by manipulating the electronic properties of non-heme iron catalysts

A non-heme iron complex that catalyzes highly enantioselective epoxidation of olefins with H2O2 is described. Improvement of enantiomeric excesses is attained by the use of catalytic amounts of carboxylic acid additives. Electronic effects imposed by the ligand on the iron center are shown to synergistically cooperate with catalytic amounts of carboxylic acids in promoting efficient O-O cleavage and creating highly chemo- and enantioselective epoxidizing species which provide a broad range of epoxides in synthetically valuable yields and short reaction times.

Fe(II)-Catalysed Homocoupling of Arenediazonium Tetrafluoroborates

An efficient procedure for the synthesis of biaryls was catalysed by Fe(acac)2 and zinc powder in carbon tetrachloride solution at 60 °C using arenediazonium salts is reported. Symmetrical bi-aryl molecules with various substituents on the phenyl ring (methyl, trifluoromethyl, halogen, nitro, methoxyl) were synthesised in good yields in a short time under air. Zinc powder was used as reductant in the reaction to facilitate the regeneration of the iron(II) catalyst.

Practical iron-catalyzed atom/group transfer and insertion reactions

Iron-catalyzed reactions are receiving a surge of interest owing to the natural abundance and biocompatibility of Fe and the urge to develop practically useful sustainable catalysis for fine chemical industries. This article is a brief account of our studies on the C–O and C–N bond formation reactions catalyzed by Fe complexes supported by oligopyridine, macrocyclic tetraaza, and fluorinated porphyrin ligands. The working principle is the in situ generation of reactive Fe=O and Fe=NR intermediates supported by these oxidatively robust N-donor ligands for oxygen atom/nitrogen group transfer and insertion reactions. The catalytic reactions include C–H bond oxidation of saturated hydrocarbons (up to 87 % yield), epoxidation of alkenes (up to 96 % yield), cis-dihydroxylation of alkenes (up to 99 % yield), epoxidation–isomerization (E–I) reaction of aryl alkenes (up to 94 % yield), amination of C–H bonds (up to 95 % yield), aziridination of alkenes (up to 95 % yield), sulfimidation of sulfides (up to 96 % yield), and amide formation from aldehydes (up to 89 % yield). Many of these catalytic reactions feature high regio- and diastereoselectivity and/or high product yields and substrate conversions, and recyclability of the catalyst, demonstrating the applicability of Fe-catalyzed oxidative organic transformation reactions in practical organic synthesis.

Ionically tagged iron complex-catalyzed epoxidation of olefins in imidazolium-based ionic liquids

A new ionophilic ligand and a new ionically tagged imidazolium-based iron(III) complex were synthesized and applied in the air oxidation (also hydrogen peroxide) of alkenes in imidazolium-based ionic liquids. At least ten recycling reactions were performed. The epoxidized olefin was obtained in very good yields of 84-91 %. Some important mechanistic insights are also provided based on electrospray ionization quadrupole-time of flight mass spectrometry for the oxidation reaction. These results indicate that oxidations can take place by two different pathways, depending on the reaction condition: a radical or a concerted mechanism. These results contribute towards a better understanding of iron-catalyzed oxidation mechanisms.