Highly Selective and Catalytic Oxygenations of C−H and C=C Bonds by a Mononuclear Nonheme High‐Spin Iron(III)‐Alkylperoxo Species

Ghosh, Ivy; Banerjee, Sridhar; Paul, S.; Corona, Teresa; Paine, Tapan Kanti

doi:10.1002/ange.201906978

Cited by 7 publications

(3 citation statements)

References 79 publications

(52 reference statements)

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“…It is our hypothesis that both of these components belong to the same intermediate and reflect a microheterogeneity in the sample. There is literature precendence for such a situation in which a single Fe(III) S = 5/2 species gives rise to two different subspectra due to site-to-site disorder. , Based on the Mössbauer spectra shown in the next section, the S t = 5/2 spectra of Int I can be assigned to high spin Fe(III) with closed-shell ligands, in agreement with the literature. − Finally, a sample frozen after 90 min incubation was EPR-silent again (Figure c) and assigned to Int II (also confirmed from the UV–vis measurements).…”

Section: Experimental and Spectroscopic Resultssupporting

confidence: 82%

“…Int II subsequently participates in the N -transfer reaction; the detailed mechanism of aminomethoxylation of styrenyl olefin has been delineated in the subsequent section via DFT calculations ( vide infra ). Similar to metal–alkyl/acyl peroxide chemistry, ,− product analyses from PivONH 3 OTf may be used as an indirect mechanistic probe, to differentiate between the proposed homolytic and heterolytic N–O bond cleavage pathways. In fact, GC-MS analysis of the headspace of the reaction after decay of Int II reveals formation of CO 2 and isobutene (Scheme S1, Figure S15 and S16, SI).…”

Section: Implications For the Reaction Mechanismmentioning

confidence: 99%

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A Combined Spectroscopic and Computational Study on the Mechanism of Iron-Catalyzed Aminofunctionalization of Olefins Using Hydroxylamine Derived N–O Reagent as the “Amino” Source and “Oxidant”

et al. 2022

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Herein, we study the mechanism of iron-catalyzed direct synthesis of unprotected aminoethers from olefins by a hydroxyl amine derived reagent using a wide range of analytical and spectroscopic techniques (Mössbauer, Electron Paramagnetic Resonance, Ultra-Violet Visible Spectroscopy, X-ray Absorption, Nuclear Resonance Vibrational Spectroscopy, and resonance Raman) along with high-level quantum chemical calculations. The hydroxyl amine derived triflic acid salt acts as the “oxidant” as well as “amino” group donor. It activates the high-spin Fe(II) ( S t = 2) catalyst [Fe(acac) 2 (H 2 O) 2 ] ( 1 ) to generate a high-spin ( S t = 5/2) intermediate ( Int I ), which decays to a second intermediate ( Int II ) with S t = 2. The analysis of spectroscopic and computational data leads to the formulation of Int I as [Fe(III)(acac) 2 - N -acyloxy] (an alkyl-peroxo-Fe(III) analogue). Furthermore, Int II is formed by N–O bond homolysis. However, it does not generate a high-valent Fe(IV)(NH) species (a Fe(IV)(O) analogue), but instead a high-spin Fe(III) center which is strongly antiferromagnetically coupled ( J = −524 cm –1 ) to an iminyl radical, [Fe(III)(acac) 2 -NH·], giving S t = 2. Though Fe(NH) complexes as isoelectronic surrogates to Fe(O) functionalities are known, detection of a high-spin Fe(III)- N -acyloxy intermediate ( Int I ), which undergoes N–O bond cleavage to generate the active iron–nitrogen intermediate ( Int II ), is unprecedented. Relative to Fe(IV)(O) centers, Int II features a weak elongated Fe–N bond which, together with the unpaired electron density along the Fe–N bond vector, helps to rationalize its propensity for N -transfer reactions onto styrenyl olefins, resulting in the overall formation of aminoethers. This study thus demonstrates the potential of utilizing the iron-coordinated nitrogen-centered radicals as powerful reactive intermediates in catalysis.

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Section: Experimental and Spectroscopic Resultssupporting

confidence: 82%

Section: Implications For the Reaction Mechanismmentioning

confidence: 99%

A Combined Spectroscopic and Computational Study on the Mechanism of Iron-Catalyzed Aminofunctionalization of Olefins Using Hydroxylamine Derived N–O Reagent as the “Amino” Source and “Oxidant”

et al. 2022

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“…The measured kobs was normalized by the number of abstractable C-H bonds of cyclic ethers, for example, 4 for THF and 1 for methyl 1,3-dioxlane. 57 The plot of log(normalized kobs) and calculated C-H BDEs exhibited a good linear correlation, giving a Brønsted slope α = 0.5 (Figure 4e). A value of α close to 0.5 is predicted by most rate/driving force relations for reactions with a transition state near the midpoint of the reaction coordinate, 58 including sets of similar HAT reactions with small reaction free energy changes.…”

Section: Correlation Between Reaction Kinetics and Bond Dissociation ...mentioning

confidence: 81%

CdS Quantum Dot Gels as a Direct Hydrogen Atom Transfer Photocatalyst for C-H Functionalization

Liu,

Hazra,

Liu

et al. 2024

Preprint

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Here, we report CdS quantum dot (QD) gels, a three-dimensional network of interconnected CdS QDs, as a new type of direct hydrogen atom transfer (d-HAT) photocatalyst for C-H functionalization. We discovered that the photoexcited CdS QD gel could generate various neutral radicals, including α-amido, heterocyclic, acyl, and benzylic radicals, from their correspond-ing stable molecular substrates, including amides, thio/ethers, aldehydes, and benzylic compounds. Its C-H activation ability imparts a broad substrate and reaction scope. The mechanistic study reveals that this reactivity is intrinsic to CdS materials, and the neutral radical generation did not proceed via the conventional sequential electron transfer and proton transfer pathway. Instead, the C-H bonds are activated by the photoexcited CdS QD gel via a d-HAT mechanism. This d-HAT mechanism is supported by the linear correlation between the logarithm of the C-H bond activation rate constant and the C-H bond dissociation energy with a Brønsted slope α = 0.5. Our findings expand the currently limited direct hydrogen atom transfer photocatalysis toolbox and provide new possibilities for photocatalytic C-H functionalization.

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CdS Quantum Dot Gels as a Direct Hydrogen Atom Transfer Photocatalyst for C−H Activation

Liu,

Hazra,

Liu

et al. 2024

Angewandte Chemie

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Here, we report CdS quantum dot (QD) gels, a three‐dimensional network of interconnected CdS QDs, as a new type of direct hydrogen atom transfer (d‐HAT) photocatalyst for C‐H activation. We discovered that the photoexcited CdS QD gel could generate various neutral radicals, including α‐amido, heterocyclic, acyl, and benzylic radicals, from their corresponding stable molecular substrates, including amides, thio/ethers, aldehydes, and benzylic compounds. Its C‐H activation ability imparts a broad substrate and reaction scope. The mechanistic study reveals that this reactivity is intrinsic to CdS materials, and the neutral radical generation did not proceed via the conventional sequential electron transfer and proton transfer pathway. Instead, the C‐H bonds are activated by the photoexcited CdS QD gel via a d‐HAT mechanism. This d‐HAT mechanism is supported by the linear correlation between the logarithm of the C‐H bond activation rate constant and the C‐H bond dissociation energy (BDE) with a Brønsted slope α = 0.5. Our findings expand the currently limited direct hydrogen atom transfer photocatalysis toolbox and provide new possibilities for photocatalytic C‐H activation.

show abstract

Highly Selective and Catalytic Oxygenations of C−H and C=C Bonds by a Mononuclear Nonheme High‐Spin Iron(III)‐Alkylperoxo Species

Cited by 7 publications

References 79 publications

A Combined Spectroscopic and Computational Study on the Mechanism of Iron-Catalyzed Aminofunctionalization of Olefins Using Hydroxylamine Derived N–O Reagent as the “Amino” Source and “Oxidant”

A Combined Spectroscopic and Computational Study on the Mechanism of Iron-Catalyzed Aminofunctionalization of Olefins Using Hydroxylamine Derived N–O Reagent as the “Amino” Source and “Oxidant”

CdS Quantum Dot Gels as a Direct Hydrogen Atom Transfer Photocatalyst for C-H Functionalization

CdS Quantum Dot Gels as a Direct Hydrogen Atom Transfer Photocatalyst for C−H Activation

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