Eccentricities in Spectroscopy and Reactivity of Non‐Heme Metal Intermediates Contained in Bispidine Scaffolds

Mukherjee, Gourab; Sastri, Chivukula V.

doi:10.1002/ijch.202000045

Cited by 11 publications

(10 citation statements)

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“…[13][14][15][16] Bispidine-iron(IV)-oxido complexes have been studied extensively. [17][18][19][20][21][22][23][24][25][26] An interesting feature is the rigidity of the bispidine scaffold that is too large for Fe IV = O and therefore enforces high redox potentials of the ferryl species. [27] A range of easily accessible ligands with differing denticity and donor sets allows to fine-tune the reactivities of the bispidine-ferryl oxidants.…”

Section: Introductionmentioning

confidence: 99%

Pathways of the Extremely Reactive Iron(IV)‐oxido complexes with Tetradentate Bispidine Ligands

Abu-Odeh

Bleher

Britto³

et al. 2021

Chemistry A European J

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The nonheme iron(IV)-oxido complex trans-N3-[(L 1 ) Fe IV = O(Cl)] + , where L 1 is a derivative of the tetradentate bispidine 2,4-di(pyridine-2-yl)-3,7-diazabicyclo[3.3.1]nonane-1one, is known to have an S = 1 electronic ground state and to be an extremely reactive oxidant for oxygen atom transfer (OAT) and hydrogen atom abstraction (HAA) processes. Here we show that, in spite of this ferryl oxidant having the "wrong" spin ground state, it is the most reactive nonheme iron model system known so far and of a similar order of reactivity as nonheme iron enzymes (CÀ H abstraction of cyclohexane, À 90°C (propionitrile), t 1/2 = 3.5 sec). Discussed are spectroscopic and kinetic data, supported by a DFT-based theoretical analysis, which indicate that substrate oxidation is significantly faster than self-decay processes due to an intramolecular demethylation pathway and formation of an oxido-bridged diiron(III) intermediate. It is also shown that the iron(III)-chlorido-hydroxido/cyclohexyl radical intermediate, resulting from CÀ H abstraction, selectively produces chlorocyclohexane in a rebound process. However, the lifetime of the intermediate is so long that other reaction channels (known as cage escape) become important, and much of the CÀ H abstraction therefore is unproductive. In bulk reactions at ambient temperature and at longer time scales, there is formation of significant amounts of oxidation product -selectively of chlorocyclohexane -and it is shown that this originates from oxidation of the oxido-bridged diiron (III) resting state.

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Section: Introductionmentioning

confidence: 99%

Pathways of the Extremely Reactive Iron(IV)‐oxido complexes with Tetradentate Bispidine Ligands

Abu-Odeh

Bleher

Britto³

et al. 2021

Chemistry A European J

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“…In biomimetic systems, a number of mononuclear non-heme iron(III)–peroxo complexes have been synthesized and characterized spectroscopically and structurally; − a notable example is an X-ray crystal structure of an iron(III)–peroxo complex bearing a macrocyclic 14-TMC ligand, [Fe(III)(O 2 )(14-TMC)] + . In many of the iron(III)–peroxo complexes, the ν Fe–O and ν O–O stretches have been observed at ∼490 and ∼820 cm –1 , respectively, in resonance Raman (rRaman) experiments. ,,,, In reactivity studies, non-heme iron(III)–peroxo complexes have shown nucleophilic reactivities, such as in aldehyde deformylation reactions, , as reported in heme models . Herein we report for the first time the synthesis, characterization, and reactivity studies of a mononuclear non-heme iron(III)–peroxo complex bearing a macrocyclic 13-TMC ligand, [Fe(III)(O 2 )(13-TMC)] + ( 1 ), with an unusual high O–O stretching mode and unprecedented electrophilic reactivity in oxidation reactions (see Scheme ).…”

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“…Intermediate 1 , which was metastable ( t 1/2 ∼ 30 min) at −10 °C, was characterized by various spectroscopic techniques, such as UV–vis spectrophotometry, cold-spray ionization mass spectrometry (CSI-MS), electron paramagnetic resonance (EPR) spectroscopy, rRaman, Mössbauer spectroscopy, and X-ray absorption spectroscopy (XAS). The UV–vis spectrum of 1 shows a broad absorption band at 705 nm (Figures a and S1), which is typically assigned to a ligand-to-metal charge transfer (LMCT) transition from the O 2 2– unit to Fe III in mononuclear non-heme iron(III)–peroxo complexes. − CSI-MS data show a mass peak at m / z 330.1 corresponding to [Fe( 16 O 2 )(13-TMC)] + . This shifted to m / z 334.1 (corresponding to [Fe( 18 O 2 )(13-TMC)] + ) when 1 was prepared with H 2 18 O 2 (Figure b), suggesting that 1 contains two oxygen atoms (i.e., an O 2 unit).…”

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confidence: 99%

“…The X-band EPR spectrum of 1 exhibits an intense signal centered at g = 4.3, typical of a high-spin ( S = 5 / 2 ) Fe(III) species (Figures S2 and S3). − …”

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A Mononuclear Non-heme Iron(III)–Peroxo Complex with an Unprecedented High O–O Stretch and Electrophilic Reactivity

et al. 2021

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A mononuclear non-heme iron(III)–peroxo complex, [Fe(III)(O2)(13-TMC)]+ (1), was synthesized and characterized spectroscopically; the characterization with electron paramagnetic resonance, Mössbauer, X-ray absorption, and resonance Raman spectroscopies and mass spectrometry supported a high-spin S = 5/2 Fe(III) species binding an O2 unit. A notable observation was an unusually high νO–O at ∼1000 cm–1 for the peroxo ligand. With regard to reactivity, 1 showed electrophilic reactivity in H atom abstraction (HAA) and O atom transfer (OAT) reactions. In the HAT reaction, a kinetic isotope effect (KIE) value of 5.8 was obtained in the oxidation of 9,10-dihydroanthracene. In the OAT reaction, a negative ρ value of −0.61 in the Hammett plot was determined in the oxidation of p-X-substituted thioanisoles. Another interesting observation was the electrophilic reactivity of 1 in the oxidation of benzaldehyde derivatives, such as a negative ρ value of −0.77 in the Hammett plot and a KIE value of 2.2. To the best of our knowledge, the present study reports the first example of a mononuclear non-heme iron(III)–peroxo complex with an unusually high νO–O value and unprecedented electrophilic reactivity in oxidation reactions.

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Iron Catalyzed CH Amination

Mukherjee

Visser

Sastri

2022

Handbook of CH-Functionalization

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Due to its large natural abundance, iron is the metal that is often utilized by metalloenzymes in Nature. Their unique catalytic properties have triggered the interest of chemists and hence many studies have explored synthetic analogues, for instance, for CH activation reactions. Herein, we show a number of examples where we describe how different iron‐based catalysts undergo CH activation reactions. In particular, several highlights on the functions of iron in synthetic models of heme and non‐heme complexes are discussed. In these catalytic cycles the active form of iron is often in a high‐valent state that gives it its oxidative abilities. Specifically, bio‐inspired CH hydroxylation reactions are at the forefront of chemistry as conducted and catalyzed by a number of iron‐oxo systems that are synthesized and stabilized in a variety of ligand frameworks. In recent years; however, the isolobal analogue, namely the high‐valent iron‐imido complex, has been studied as well and found to be able to undergo CH activation of organic substrates. In this chapter, we have compiled a comparative analysis of iron‐oxo and imido systems towards CH activation reactions, and the factors governing such changes.

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Eccentricities in Spectroscopy and Reactivity of Non‐Heme Metal Intermediates Contained in Bispidine Scaffolds

Cited by 11 publications

References 155 publications

Pathways of the Extremely Reactive Iron(IV)‐oxido complexes with Tetradentate Bispidine Ligands

Pathways of the Extremely Reactive Iron(IV)‐oxido complexes with Tetradentate Bispidine Ligands

A Mononuclear Non-heme Iron(III)–Peroxo Complex with an Unprecedented High O–O Stretch and Electrophilic Reactivity

Iron Catalyzed CH Amination

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