Photocatalytic Hydrodehalogenation for the Removal of Halogenated Aromatic Contaminants

Wang, Yuanyuan; Yan, Wei; Song, Wenjing; Chen, Chuncheng; Zhao, Jincai

doi:10.1002/cctc.201801222

Cited by 38 publications

(21 citation statements)

References 124 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…In this article, according to the unsaturated bond being reduced by TiO 2 photocatalyst, this review is mainly divided into the following parts: (1) Transfer hydrogenation of C=C and C≡C (2) C=O and C=N (3) N=O. As the hydrodehalogenation by TiO 2 photocatalysis has been recently reviewed by Zhao et al [64], this review would not cover this section.…”

Section: Introductionmentioning

confidence: 99%

TiO2 Photocatalysis for Transfer Hydrogenation

Zhai

Wang

et al. 2019

Molecules

Self Cite

View full text Add to dashboard Cite

Catalytic transfer hydrogenation reactions, based on hydrogen sources other than gaseous H2, are important processes that are preferential in both laboratories and factories. However, harsh conditions, such as high temperature, are usually required for most transition-metal catalytic and organocatalytic systems. Moreover, non-volatile hydrogen donors such as dihydropyridinedicarboxylate and formic acid are often required in these processes which increase the difficulty in separating products and lowered the whole atom economy. Recently, TiO2 photocatalysis provides mild and facile access for transfer hydrogenation of C=C, C=O, N=O and C-X bonds by using volatile alcohols and amines as hydrogen sources. Upon light excitation, TiO2 photo-induced holes have the ability to oxidatively take two hydrogen atoms off alcohols and amines under room temperature. Simultaneously, photo-induced conduction band electrons would combine with these two hydrogen atoms and smoothly hydrogenate multiple bonds and/or C-X bonds. It is heartening that practices and principles in the transfer hydrogenations of substrates containing C=C, C=O, N=O and C-X bond based on TiO2 photocatalysis have overcome a lot of the traditional thermocatalysis’ limitations and flaws which usually originate from high temperature operations. In this review, we will introduce the recent paragon examples of TiO2 photocatalytic transfer hydrogenations used in (1) C=C and C≡C (2) C=O and C=N (3) N=O substrates and in-depth discuss basic principle, status, challenges and future directions of transfer hydrogenation mediated by TiO2 photocatalysis.

show abstract

Section: Introductionmentioning

confidence: 99%

TiO2 Photocatalysis for Transfer Hydrogenation

Zhai

Wang

et al. 2019

Molecules

Self Cite

View full text Add to dashboard Cite

show abstract

“…Substituting CdS QDs for Ir(ppy) 3 , among the most-reducing of commonly used molecular photocatalysts, resulted in only trace product formation (entry 10), despite exhibiting a similar reduction potential to CdS QDs (E 1/2 III/II = -2.19 V vs SCE for Ir(ppy) 3 ; E pc QD/QD-= -2.15 V vs SCE for 3.9 nm CdS QDs) 82 and a much longer excited state lifetime (τ = 1.3 µs for Ir(ppy) 3 vs. ~10 ns for Cd chalcogenide QDs). [85][86][87] While bulk semiconductors have seen increasing utility in photoredox catalysis, [88][89][90] in this case CdS QDs outperformed an equal mass of bulk CdS powder (entry 11), showing that the catalyst morphology and quantum properties play a role in dehalogenation activity. Auger processes are vanishingly inefficient in bulk semiconductors, 91,92 consistent with the inactivity of bulk CdS powder for photoreduction beyond its reduction potential.…”

Section: Resultsmentioning

confidence: 99%

CdS Quantum Dots as Potent Photoreductants for Organic Chemistry Enabled by Auger Recombination

Widness

Enny

McFarlane-Connelly

et al. 2022

Preprint

View full text Add to dashboard Cite

Strong reducing agents (< -2.0 V vs SCE) enable a wide array of useful organic chemistry, but suffer from a variety of limitations. Stoichiometric metallic reductants such as alkali metals and SmI2 are commonly employed for these reactions, however considerations including expense, ease of use, safety, and waste generation limit the practicality of these methods. Recent approaches utilizing energy from multiple photons or electron-primed photoredox catalysis have accessed reduction potentials equivalent to Li0 and shown how this enables selective transformations of aryl chlorides via aryl radicals. However, in some cases low stability of catalytic intermediates can limit turnover numbers. Herein we report the ability of CdS nanocrystal quantum dots (QDs) to function as strong photoreductants and present evidence that a highly reducing electron is generated from two consecutive photoexcitations of CdS QDs with intermediate reductive quenching. Mechanistic experiments suggest that Auger recombination, a photophysical phenomenon known to occur in photoexcited anionic QDs, generates transient thermally excited electrons to enable the observed reductions. Using blue LEDs and sacrificial amine reductants, aryl chlorides and phosphate esters with reduction potentials up to -3.4 V vs. SCE are photo-reductively cleaved to afford hydrodefunctionalized or functionalized products. In contrast to small molecule catalysts, the QDs are stable under these conditions and turnover numbers up to 47500 have been achieved. These conditions can also effect other challenging reductions, such as tosylate protecting group removal from amines, debenzylation of alcohols, and reductive ring-opening of cyclopropanecarboxylic acid derivatives.

show abstract

“…Nowadays, photoredox catalysis [7] attracts significant attention in the community of organic synthesis in terms of the unique reactivity and environmental sustainability. There have been many photoredox catalysts suitable for hydrodehalogenation of haloarenes because of their highly reducing abilities upon excitation [1b] . For instance, iodo‐ and bromoarenes are easily reducible by combination of common Ir photocatalysts and tertiary amines [8] .…”

Section: Introductionmentioning

confidence: 99%

Metal‐Free Photoredox‐Catalyzed Hydrodefluorination of Fluoroarenes Utilizing Amide Solvent as Reductant

Toriumi

Yamashita

Iwasawa

2021

Chemistry A European J

View full text Add to dashboard Cite

A metal-free photoredox-catalyzed hydrodefluorination of fluoroarenes was achieved by using N,N,N',N'tetramethyl-para-phenylenediamine (1) as a strong photoreduction catalyst. This reaction was applicable not only to electron-rich monofluoroarenes but also to polyfluoroarenes to afford non-fluorinated arenes. The experimental mechanistic studies indicated that the amide solvent NMP plays an important role for regeneration of the photocatalyst, enabling additive-free photoreduction catalysis.

show abstract

Photocatalytic Hydrodehalogenation for the Removal of Halogenated Aromatic Contaminants

Cited by 38 publications

References 124 publications

TiO2 Photocatalysis for Transfer Hydrogenation

TiO2 Photocatalysis for Transfer Hydrogenation

CdS Quantum Dots as Potent Photoreductants for Organic Chemistry Enabled by Auger Recombination

Metal‐Free Photoredox‐Catalyzed Hydrodefluorination of Fluoroarenes Utilizing Amide Solvent as Reductant

Contact Info

Product

Resources

About