Mononuclear Nonheme High‐Spin (<i>S</i>=2) versus Intermediate‐Spin (<i>S</i>=1) Iron(IV)–Oxo Complexes in Oxidation Reactions

Bae, Seong Hee; Seo, Mi Sook; Lee, Yong Min; Cho, Kyung‐Bin; Kim, Won‐Suk; Nam, Wonwoo

doi:10.1002/ange.201603978

Cited by 15 publications

(5 citation statements)

References 45 publications

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“…On the basis of the above results, we conclude that iron-oxygen intermediate(s) that prefers C=C cis-dihydroxylation to allylic S; bond activation was generated in this catalytic system exhibiting excellent chemoselectivity, which is different from the preference of the allylic C-H bond activation of cycloalkenes by nonheme metal-oxo complexes. 56,57 It is noteworthy that the enantioselective cisdihydroxylation of acrylates catalyzed by 11 delivered most of the corresponding cis-diols with comparable or even higher enantioselectivities than that of the well-established osmium-based SAD (Figure S5), thus demonstrating that our biologically inspired nonheme iron-based catalysis could serves as a complementary approach to the SAD to some extent.…”

Section: Scope Of Alkenesmentioning

confidence: 90%

Nonheme Iron-Catalyzed Enantioselective cis -Dihydroxylation of Aliphatic Acrylates as Mimics of Rieske Dioxygenases

et al. 2022

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Enantioselective cis-dihydroxylation of alkenes represents an ideal route to synthesize enantioenriched syn-2,3-dihydroxy esters that are important structural motifs in numerous biologically and pharmaceutically relevant molecules. Bioinspired nonheme iron-catalyzed enantioselective cis-dihydroxylation meets the requirement of the modern synthetic chemistry from atomic economy, green chemistry and sustainable development perspectives. However, nonheme iron-catalyzed enantioselective cis-dihydroxylation is much underdeveloped because of the formidable challenges of controlling chemo-and enantioselectivities and product selectivity caused from the competitive epoxidation, cis-dihydroxylation and overoxidation reactions.Herein, we disclose a biologically inspired nonheme iron complex-catalyzed enantioselective cisdihydroxylation of multi-substituted acrylates using hydrogen peroxide (H 2 O 2 ) as a terminal oxidant by controlling the non-ligating or weakly ligating counterions of iron(II) complexes; we have demonstrated a dramatic counteranion effect on the enantioselective cis-dihydroxylation of olefins by H 2 O 2 catalyzed by nonheme iron complexes. A range of structurally disparate alkenes are transformed to the corresponding syn-2,3-dihydroxy esters in practically useful yields with exquisite chemo-and enantioselectivities (up to 99% ee).Given the mild and benign nature of this biologically inspired oxidation system and the ubiquity and synthetic utility of enantioenriched syn-2,3-dihydroxy esters in pharmaceuticals candidates and natural products, we

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Section: Scope Of Alkenesmentioning

confidence: 90%

Nonheme Iron-Catalyzed Enantioselective cis -Dihydroxylation of Aliphatic Acrylates as Mimics of Rieske Dioxygenases

et al. 2022

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“…63,94 It should however be mentioned that the recent study of Bae et al revealed similar reactivity features of S = 1 and S = 2 structurally similar iron(IV)oxo complexes. 95 There is no high versus low spin dilemma for iron(V)oxo complexes derived from TAML activators, which are S = 1/2 species, and their S = 3/2 state is practically unattainable due to a large gap in the lowest energy, doubly occupied d xy and HOMO d xz orbitals of 18 500 cm −1 . 31 Our major inspiration for probing the ability of Fe V O TAMLs to cleave C−H bonds of hydrocarbons stemmed from their high reactivity in the oxidation of thioanisoles and persistent micropollutants of water (see previous sections).…”

Section: Oxidation Of Hydrocarbons: C−h Bond Cleavage Versus Electron...mentioning

confidence: 99%

Targeting of High-Valent Iron-TAML Activators at Hydrocarbons and Beyond

2017

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TAML activators of peroxides are iron(III) complexes. The ligation by four deprotonated amide nitrogens in macrocyclic motifs is the signature of TAMLs where the macrocyclic structures vary considerably. TAML activators are exceptional functional replicas of the peroxidases and cytochrome P450 oxidizing enzymes. In water, they catalyze peroxide oxidation of a broad spectrum of compounds, many of which are micropollutants, compounds that produce undesired effects at low concentrations-as with the enzymes, peroxide is typically activated with near-quantitative efficiency. In nonaqueous solvents such as organic nitriles, the prototype TAML activator gave the structurally authenticated reactive iron(V)oxo units (FeO), wherein the iron atom is two oxidation equivalents above the Fe resting state. The iron(V) state can be achieved through the intermediacy of iron(IV) species, which are usually μ-oxo-bridged dimers (FeFe), and this allows for the reactivity of this potent reactive intermediate to be studied in stoichiometric processes. The present review is primarily focused at the mechanistic features of the oxidation by FeO of hydrocarbons including cyclohexane. The main topic is preceded by a description of mechanisms of oxidation of thioanisoles by FeO, because the associated studies provide valuable insight into the ability of FeO to oxidize organic molecules. The review is opened by a summary of the interconversions between Fe, FeFe, and FeO species, since this information is crucial for interpreting the kinetic data. The highest reactivity in both reaction classes described belongs to FeO. The resting state Fe is unreactive oxidatively. Intermediate reactivity is typically found for FeFe; therefore, kinetic features for these species in interchange and oxidation processes are also reviewed. Examples of using TAML activators for C-H bond cleavage applied to fine organic synthesis conclude the review.

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“…Oxidation of C-H and C=C bonds is a main topic in chemistry and specifically in catalysis research [31]. Even though highvalent iron systems excel at both of these transformations [32,33], non-heme iron(IV)-oxo species generally prefer C-H over the C=C bond oxidation [34,35]. The epoxidation has been achieved by additives such as acids [36], or using iodosylarene-based oxidants, instead of iron-oxo species [37] or using substrates with deuterated C-H bonds [38].…”

Section: Electronic Supplementary Materialsmentioning

confidence: 99%

Chemoselectivity in the Oxidation of Cycloalkenes with a Non-Heme Iron(IV)-Oxo-Chloride Complex: Epoxidation vs. Hydroxylation Selectivity

Terencio

Andris

Gamba

et al. 2019

J. Am. Soc. Mass Spectrom.

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We report and analyze chemoselectivity in the gas phase reactions of cycloalkenes (cyclohexene, cycloheptene, cis-cyclooctene, 1,4cyclohexadiene) with a non-heme iron(IV)-oxo complex [(PyTACN)Fe(O)(Cl)] + , which models the active species in iron-dependent halogenases. Unlike in the halogenases, we did not observe any chlorination of the substrate. However, we observed two other reaction pathways: allylic hydrogen atom transfer (HAT) and alkene epoxidation. The HAT is clearly preferred in the case of 1,4-cyclohexadiene, both pathways have comparable reaction rates in reaction with cyclohexene, and epoxidation is strongly favored in reactions with cycloheptene and cis-cyclooctene. This preference for epoxidation differs from the reactivity of iron(IV)-oxo complexes in the condensed phase, where HAT usually prevails. To understand the observed selectivity, we analyze effects of the substrate, spin state, and solvation. Our DFT and CASPT2 calculations suggest that all the reactions occur on the quintet potential energy surface. The DFT-calculated energies of the transition states for the epoxidation and hydroxylation pathways explain the observed chemoselectivity. The SMD implicit solvation model predicts the relative increase of the epoxidation barriers with solvent polarity, which explains the clear preference of HAT in the condensed phase.

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Mononuclear Nonheme High‐Spin (S=2) versus Intermediate‐Spin (S=1) Iron(IV)–Oxo Complexes in Oxidation Reactions

Cited by 15 publications

References 45 publications

Nonheme Iron-Catalyzed Enantioselective cis -Dihydroxylation of Aliphatic Acrylates as Mimics of Rieske Dioxygenases

Nonheme Iron-Catalyzed Enantioselective cis -Dihydroxylation of Aliphatic Acrylates as Mimics of Rieske Dioxygenases

Targeting of High-Valent Iron-TAML Activators at Hydrocarbons and Beyond

Chemoselectivity in the Oxidation of Cycloalkenes with a Non-Heme Iron(IV)-Oxo-Chloride Complex: Epoxidation vs. Hydroxylation Selectivity

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