Photoinduced electron-transfer reaction of α-bromomethyl-substituted benzocyclic β-keto esters with amines: selective reaction pathways depending on the nature of the amine radical cations

Hasegawa, Eietsu; Tosaka, Emi; Yoneoka, Akira; Tamura, Y.; Takizawa, Shin‐ya; Tomura, Masaaki; Yamashita, Yoshiro

doi:10.1007/s11164-012-0646-2

Cited by 11 publications

(7 citation statements)

References 67 publications

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“…+0.35 V) to 2 and O 2 (eqs 2 and 3) are both highly endergonic and, thus, expected to be slow. As a moderately strong acid, , 1a •+ could transfer a proton to basic O 2 •– in a manner that should be more efficient than PT from 1a •+ to the bromide anion in the alternative pathway for this process (compare eq 3 with eq 2).…”

Section: Resultsmentioning

confidence: 99%

Sterically Regulated α-Oxygenation of α-Bromocarbonyl Compounds Promoted Using 2-Aryl-1,3-dimethylbenzimidazolines and Air

et al. 2020

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A debrominative oxygenation protocol has been developed for the conversion of α-bromo-α,α-dialkyl-substituted carbonyl compounds to their corresponding α-hydroxy analogues. For example, stirring a solution of α-bromoisobutyrophenone and 2-aryl-1,3-dimethylbenzimidazoline (BIH-Ar) at room temperature under an air atmosphere leads to the efficient formation of α-hydroperoxyisobutyrophenone, which can be converted to α-hydroxyisobutyrophenone using Me2S reduction. In contrast, reaction of α-bromoacetophenone under the same conditions produces the α-hydrogenated product acetophenone. α-Keto-alkyl and benzimidazolyl radicals (BI•-Ar), generated via dissociative electron transfer from BIH-Ar to α-bromoketone substrates, serve as key intermediates in the oxidation and reduction processes. The dramatic switch from hydrogenation to oxygenation is attributed to a steric effect of α-alkyl substituents, which causes hydrogen atom abstraction from sterically crowded BIH-Ar to α-keto-alkyl radicals to be slow and enable preferential reaction with molecular oxygen. Generation of the α-keto-alkyl radical and BI•-Ar intermediates in these process and their sterically governed hydrogen atom transfer reactions are supported by results arising from DFT calculations. Moreover, an electron spin resonance study showed that visible light irradiation of phenyl benzimidazoline (BIH-Ph) in the presence of molecular oxygen produces the benzimidazolyl radical (BI•-Ph). The addition of thiophenol into the reaction of α-bromoisobutyrophenone and BIH-Ph predominantly produced α-phenylthiolated isobutyrophenone even if a high concentration of molecular oxygen exists. Furthermore, the developed protocol was applied to other α-bromo-α,α-dialkylated carbonyl compounds.

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Section: Resultsmentioning

confidence: 99%

Sterically Regulated α-Oxygenation of α-Bromocarbonyl Compounds Promoted Using 2-Aryl-1,3-dimethylbenzimidazolines and Air

et al. 2020

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“…BIH and BI(OH)H have much stronger reducing power (BIH: E 1/2 ox = 0.33 V; BI(OH)H: E 1/2 ox = 0.31 V vs SCE) compared to that of the NADH model compounds. − Owing to this property, both compounds efficiently quenched the excited state of the Ru photosensitizer unit in the supramolecular photocatalysts (for example, k q = 9.7 × 10 8 M –1 s –1 , η q = 99% for RuRe12 with BIH (0.1 M)) (Process II). , Irradiation of a mixed solution of DMF-TEOA containing RuRe12 and BIH (0.1 M) induced the selective catalytic formation of CO with much greater efficiency, durability, and rate of CO formation (entry 23: Φ CO = 0.45, TON CO = 3029, TOF CO = 35.7 min –1 ) compared with those using BNAH (entry 22: Φ CO = 0.15, TON CO = 207, TOF CO = 4.7 min –1 ) . The efficiency and durability of the photocatalysis using RuRe15 were also much improved by using BIH (entry 27: Φ CO = 0.54, TON CO = 2915) instead of BNAH (entry 26: Φ CO = 0.13, TON CO = 233).…”

Section: Sacrificial Electron Donorsmentioning

confidence: 99%

Supramolecular Photocatalysts for the Reduction of CO₂

2017

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Photocatalytic reduction of CO2 into energy-rich compounds utilizing solar light as an energy source is expected to provide a solution to serious problems of the shortage of fossil resources and global warming. In this perspective, we summarize advances in supramolecular photocatalysts for the reduction of CO2, of which photosensitizer and catalyst units are connected via a bridging ligand. The first successful Ru(II)–Re(I) supramolecular photocatalysts reported in 2005 indicated molecular architecture for developing efficient supramolecular photocatalysts for CO2 reduction to CO with high selectivity and durability. On the basis of this architecture, both the bridging ligands and Re(I) catalyst unit were optimized to increase the photocatalytic activity. In addition, the compositional units of supramolecular photocatalytic systems were modified: (1) Ir(III) and Os(II) complexes, free- and metallo-porphyrins, and chlorophyll functioned as alternative or better photosensitizer units in comparison to the Ru(II) complexes, (2) Ru(II) carbonyl complexes reduced CO2 giving HCOOH selectively, and (3) dihydrobenzoimidazole derivatives were suitable sacrificial electron donors for evaluating the potential of supramolecular photocatalytic systems. These research studies have provided efficient photocatalytic systems for CO2 reduction with high selectivity, durability, and reaction rate under visible-light irradiation.

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“…1,3-Dimethyl-2-phenyl-2,3-dihydro-1 H -benzoimidazole (BIH) and BI(OH)H were found to be possessing a much better reducing power (BIH: E 1/2 ox = 0.33 V; BI(OH)H: E 1/2 ox = 0.31 V vs SCE) with respect to that of BNAH. − BIH undergoes oxidation quite differently from that of BNAH. It has been investigated that BIH gives two electrons on a photon excitation of the photocatalyst sequentially through electron transfer, deprotonation, and subsequent electron transfer.…”

Section: Resultsmentioning

confidence: 99%

Reticular-Chemistry-Inspired Supramolecule Design as a Tool to Achieve Efficient Photocatalysts for CO₂ Reduction

et al. 2021

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Photocatalytic CO2 reduction into C1 products is one of the most trending research subjects of current times as sustainable energy generation is the utmost need of the hour. In this review, we have tried to comprehensively summarize the potential of supramolecule-based photocatalysts for CO2 reduction into C1 compounds. At the outset, we have thrown light on the inert nature of gaseous CO2 and the various challenges researchers are facing in its reduction. The evolution of photocatalysts used for CO2 reduction, from heterogeneous catalysis to supramolecule-based molecular catalysis, and subsequent semiconductor–supramolecule hybrid catalysis has been thoroughly discussed. Since CO2 is thermodynamically a very stable molecule, a huge reduction potential is required to undergo its one- or multielectron reduction. For this reason, various supramolecule photocatalysts were designed involving a photosensitizer unit and a catalyst unit connected by a linker. Later on, solid semiconductor support was also introduced in this supramolecule system to achieve enhanced durability, structural compactness, enhanced charge mobility, and extra overpotential for CO2 reduction. Reticular chemistry is seen to play a pivotal role as it allows bringing all of the positive features together from various components of this hybrid semiconductor–supramolecule photocatalyst system. Thus, here in this review, we have discussed the selection and role of various components, viz. the photosensitizer component, the catalyst component, the linker, the semiconductor support, the anchoring ligands, and the peripheral ligands for the design of highly performing CO2 reduction photocatalysts. The selection and role of various sacrificial electron donors have also been highlighted. This review is aimed to help researchers reach an understanding that may translate into the development of excellent CO2 reduction photocatalysts that are operational under visible light and possess superior activity, efficiency, and selectivity.

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Photoinduced electron-transfer reaction of α-bromomethyl-substituted benzocyclic β-keto esters with amines: selective reaction pathways depending on the nature of the amine radical cations

Cited by 11 publications

References 67 publications

Sterically Regulated α-Oxygenation of α-Bromocarbonyl Compounds Promoted Using 2-Aryl-1,3-dimethylbenzimidazolines and Air

Sterically Regulated α-Oxygenation of α-Bromocarbonyl Compounds Promoted Using 2-Aryl-1,3-dimethylbenzimidazolines and Air

Supramolecular Photocatalysts for the Reduction of CO₂

Reticular-Chemistry-Inspired Supramolecule Design as a Tool to Achieve Efficient Photocatalysts for CO₂ Reduction

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Photoinduced electron-transfer reaction of α-bromomethyl-substituted benzocyclic β-keto esters with amines: selective reaction pathways depending on the nature of the amine radical cations

Cited by 11 publications

References 67 publications

Sterically Regulated α-Oxygenation of α-Bromocarbonyl Compounds Promoted Using 2-Aryl-1,3-dimethylbenzimidazolines and Air

Sterically Regulated α-Oxygenation of α-Bromocarbonyl Compounds Promoted Using 2-Aryl-1,3-dimethylbenzimidazolines and Air

Supramolecular Photocatalysts for the Reduction of CO2

Reticular-Chemistry-Inspired Supramolecule Design as a Tool to Achieve Efficient Photocatalysts for CO2 Reduction

Contact Info

Product

Resources

About

Supramolecular Photocatalysts for the Reduction of CO₂

Reticular-Chemistry-Inspired Supramolecule Design as a Tool to Achieve Efficient Photocatalysts for CO₂ Reduction