Electron paramagnetic resonance spectroscopic studies of the electron transfer reaction of Hantzsch ester and a pyrylium salt

Sebők-Nagy, Krisztina; Rózsár, D.; Puskás, L. G.; Balázs, Árpád; Páli, Tibor

doi:10.1039/c8ra05693e

Cited by 4 publications

(4 citation statements)

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“…Upon the addition of DMPO, the positive-ion electrospray ionization mass spectrum of the product mixture unequivocally confirmed the presence of a C α * major mass peak (MW, 386.2) and a HEH radical major mass peak (MW, 365.2) (Figure 3b and Figures S10-11). [37] Furthermore, the EPR results confirmed the generation of carbon radicals (Figure 3c), aligning with the result of LCMS. [38] Notably, the radical-mediated CÀ O bond cleavage can lower the BDE of the CÀ O bond from 274 to 66.9 kJ/ mol.…”

Section: Mechanistic Studiessupporting

confidence: 81%

“…The formation of the C α ⋅ intermediate was verified through liquid chromatography‐mass spectrometry (LCMS). Upon the addition of DMPO, the positive‐ion electrospray ionization mass spectrum of the product mixture unequivocally confirmed the presence of a C α ⋅ major mass peak (MW, 386.2) and a HEH radical major mass peak (MW, 365.2) (Figure 3b and Figures S10–11) [37] . Furthermore, the EPR results confirmed the generation of carbon radicals (Figure 3c), aligning with the result of LCMS [38] .…”

Section: Resultssupporting

confidence: 63%

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CsPbBr₃ Quantum Dots Promoted Depolymerization of Oxidized Lignin via Photocatalytic Semi‐Hydrogenation/Reduction Strategy

Jiang,

Liu,

Lian

et al. 2024

Angewandte Chemie

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Due to the demanding depolymerization conditions and limited catalytic efficiency, enhancing lignin valorization remains challenging. Therefore, lowering the bond dissociation energy (BDE) has emerged as a viable strategy for achieving mild yet highly effective cleavage of bonds. In this study, a photocatalytic semi‐hydrogenation/reduction strategy utilizing CsPbBr3 quantum dots (CPB‐QDs) and Hantzsch ester (HEH2) as a synergistic catalytic system was introduced to reduce the BDE of Cβ‐O‐Ar, achieving effective cleavage of the Cβ‐O‐Ar bond. This strategy offers a wide substrate scope encompassing various β‐O‐4 model lignin dimers, preoxidized β‐O‐4 polymers, and native oxidized lignin, resulting in the production of corresponding ketones and phenols. Notably, this approach attained a turnover frequency (TOF) that is 17 times higher than that of the reported Ir‐catalytic system in the photocatalytic depolymerization of the lignin model dimers. It has been observed via meticulous experimentation that HEH2 can be activated by CPB‐QDs via single electron transfer (SET), generating HEH2•+ as a hydrogen donor while also serving as a hole quencher. Moreover, HEH2•+ readily forms an active transition state with the substrates via hydrogen bonding. Subsequently, the proton‐coupled electron transfer (PCET) from HEH2•+ to the carbonyl group of the substrate generates a Cα• intermediate.

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Section: Mechanistic Studiessupporting

confidence: 81%

Section: Resultssupporting

confidence: 63%

CsPbBr₃ Quantum Dots Promoted Depolymerization of Oxidized Lignin via Photocatalytic Semi‐Hydrogenation/Reduction Strategy

Jiang,

Liu,

Lian

et al. 2024

Angewandte Chemie

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“…Such pyrylium derivatives, for example, 2,4,6‐triphenylpyrylium salts, show strong fluorescence and anion–π interactions . They have been successfully utilized for electron‐transfer reactions, (photo)organocatalysis, white‐light fluorophores and laser dyes …”

Section: Introductionmentioning

confidence: 99%

Flavylium Salts: A Blooming Core for Bioinspired Ionic Liquid Crystals

Forschner

Knelles

Bader

et al. 2019

Chemistry A European J

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Thermotropic ionic liquid crystals based on the flavylium scaffold have been synthesized and studied for their structure‐properties relationship for the first time. The mesogens were probed by differential scanning calorimetry (DSC), polarizing optical microscopy (POM), and X‐ray diffraction (XRD). Low numbers of alkoxy side chains resulted in smectic (SmA) and lamello‐columnar (LamCol) phases, whereas higher substituted flavylium salts showed Colro as well as ordered and disordered columnar (Colho, Colhd) mesophases. Mesophase width ranged from 13 K to 220 K, giving access to room temperature liquid crystals. The optical properties of the synthesized compounds were probed towards absorption and emission properties. Strong absorption with maxima between 444 and 507 nm was observed, and some chromophores were highly emissive with quantum yields up to 99 %. Ultimately, mesogenic and dye properties were examined by temperature‐dependent emissive experiments in the solid state.

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“…We envisaged that strongly oxidizing photoexcited 2,4,6-triphenyl pyrylium tetrafluoroborate (TPT) ( E red = +2.55 V vs SCE) , will not only oxidize 2 H -azirines but also may serve as dipolarophile in [3 + 2]-cycloaddition with the resulting 2-azaallenyl intermediate (Scheme b) . The pyrylium salts have been classically employed as photosensitizers in the photoinduced electron transfer (PET) mediated cycloadditions .…”

Section: Introductionmentioning

confidence: 99%

Redox-Neutral 1,3-Dipolar Cycloaddition of 2H-Azirines with 2,4,6-Triarylpyrylium Salts under Visible Light Irradiation

et al. 2021

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A novel visible light mediated redox-neutral 1,3-dipolar cycloaddition of 2H-azirines with 2,4,6-triarylpyrylium tetrafluoroborate salts providing tetrasubstituted pyrroles has been developed. The 2,4,6-triarylpyrylium salt acts as dipolarophile as well as photosensitizer in the reaction, under blue light irradiation. The control experiments indicated single electron oxidation of 2H-azirines by photoexcited pyrylium salts, followed by coupling between an azaallenyl radical cation and triarylpyranyl radical as the key mechanistic feature. The mild conditions, wide substrate scope, and complete regioselectivity are the noticeable attributes of the reaction.

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Electron paramagnetic resonance spectroscopic studies of the electron transfer reaction of Hantzsch ester and a pyrylium salt

Abstract: The oxidation of Hantzsch ester by a pyrylium cation takes 3 place via electron–proton–electron transfer. The present in-depth EPR study of the radical reactions of a NADH analogue indicate a complex electron transfer mechanism in the title reaction.

Cited by 4 publications

References 32 publications

CsPbBr₃ Quantum Dots Promoted Depolymerization of Oxidized Lignin via Photocatalytic Semi‐Hydrogenation/Reduction Strategy

CsPbBr₃ Quantum Dots Promoted Depolymerization of Oxidized Lignin via Photocatalytic Semi‐Hydrogenation/Reduction Strategy

Flavylium Salts: A Blooming Core for Bioinspired Ionic Liquid Crystals

Redox-Neutral 1,3-Dipolar Cycloaddition of 2H-Azirines with 2,4,6-Triarylpyrylium Salts under Visible Light Irradiation

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Electron paramagnetic resonance spectroscopic studies of the electron transfer reaction of Hantzsch ester and a pyrylium salt

Abstract: The oxidation of Hantzsch ester by a pyrylium cation takes 3 place via electron–proton–electron transfer. The present in-depth EPR study of the radical reactions of a NADH analogue indicate a complex electron transfer mechanism in the title reaction.

Cited by 4 publications

References 32 publications

CsPbBr3 Quantum Dots Promoted Depolymerization of Oxidized Lignin via Photocatalytic Semi‐Hydrogenation/Reduction Strategy

CsPbBr3 Quantum Dots Promoted Depolymerization of Oxidized Lignin via Photocatalytic Semi‐Hydrogenation/Reduction Strategy

Flavylium Salts: A Blooming Core for Bioinspired Ionic Liquid Crystals

Redox-Neutral 1,3-Dipolar Cycloaddition of 2H-Azirines with 2,4,6-Triarylpyrylium Salts under Visible Light Irradiation

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CsPbBr₃ Quantum Dots Promoted Depolymerization of Oxidized Lignin via Photocatalytic Semi‐Hydrogenation/Reduction Strategy

CsPbBr₃ Quantum Dots Promoted Depolymerization of Oxidized Lignin via Photocatalytic Semi‐Hydrogenation/Reduction Strategy