Hydrogenations without Hydrogen: Titania Photocatalyzed Reductions of Maleimides and Aldehydes

Manley, David W.; Buzzetti, Luca; MacKessack-Leitch, Andrew; Walton, John C.

doi:10.3390/molecules190915324

Cited by 13 publications

(11 citation statements)

References 44 publications

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“…Similar reactions have been carried out with ketimines or with diazo compounds , . Similar reaction steps have also been discussed in the cases of photoredox‐catalyzed radical addition of tertiary amines,, , radical addition involving decarboxylation, or reductions with inorganic semiconductors.…”

Section: Proton‐coupled Electron Transfer In Heterogeneous Photoredoxmentioning

confidence: 87%

Proton‐Coupled Electron Transfer in Photoredox Catalytic Reactions

Hoffmann

2017

Eur J Org Chem

109

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Proton-coupled electron transfer (PCET) is studied in different research domains of chemistry. Many reports involve biochemical processes. Although related phenomena have often been investigated in photochemical electron-and hydrogen-transfer processes, only recently have a larger variety of such steps come to be discussed under the comprehensive concept of PCET. In photoredox catalytic reactions applied to

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Section: Proton‐coupled Electron Transfer In Heterogeneous Photoredoxmentioning

confidence: 87%

Proton‐Coupled Electron Transfer in Photoredox Catalytic Reactions

Hoffmann

2017

Eur J Org Chem

109

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“…In the case of p ‐nitrobenzaldehyde, mainly the nitro group was reduced. Manley et al recently expanded this study to reduction of more highly substituted aromatic aldehydes to alcohols on TiO 2 Degussa P25 …”

Section: Reaction Typesmentioning

confidence: 99%

Heterogeneous Photoredox Catalysis: Reactions, Materials, and Reaction Engineering

Bloh

Marschall

2017

Eur J Org Chem

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This microreview briefly summarizes recent developments in heterogeneous photoredox catalysis, with a special focus on materials, reactors, and reaction design to optimize IntroductionThe use of inorganic semiconductor light absorbers to generate charge carriers for electrochemical surface reactions is a viable strategy for conversion of solar energy into fuel.[1] Besides prominent applications in water splitting, waste water/air depollution, and CO 2 reduction, the preparation of organic compounds has drawn a lot of attention in recent years, for synthesis of organic compounds through either oxidative or reductive pathways, or through coupled photoredox reactions to result in one reaction product. Moreover, the use of visible-light-absorbing materials for such reactions is a very important development in this field of heterogeneous photocatalysis.[a] DECHEMA Research Institute 60486 Frankfurt am Main, 35392 Giessen, yields. New areas such as the integration of enzymatic processes are also presented, together with an extended overview of materials, reactors, and engineering.Upon light irradiation of a semiconductor with photon energy larger than the band gap, electrons are excited from the valence band (VB) of the semiconductor into its conduction band (CB). At that point, the resulting charge carriers [electrons in the CB (e -CB ) and holes in the VB (h + VB )] have to diffuse to the surface of the semiconductor for surface redox reactions; however, many of them recombine at an earlier stage before reaching it.[2] Thus, materials scientists are looking into ways to optimize semiconductor materials for optimum charge carrier transport by reducing charge carrier diffusion lengths.[3] After reaching the surface, electrons and holes can react with acceptors ( . Such acceptors or donors could be protons, water, or other adsorbed molecules. For the oxidation of alcohols, for example, it is generally accepted that the alcohol needs to be adsorbed before reaction. [4] Photocatalytic reactions/syntheses can be divided, according to Kisch et al., into two kinds of reactions: into type A or type B photocatalysis, with the generation either of two reaction products or of one reaction product, respectively.[5] Whereas some Microreview industrial processes might require harsh reaction conditions or potentially health-impairing solvents, photocatalysis can generate organic products under relatively mild conditions, thanks to the high potential energy provided by the energy of the photons. One of the very first reported organic syntheses on a semiconductor surface was the photo-Kolbe reaction, in which acetate was converted into ethane on a TiO 2 electrode. [6] At that time, evolution of hydrogen as reduction product could not be detected. Other early oxidation reactions include oxidative cleavages [7] and oxidation of aromatic olefins, [8] but also oxidation reactions of lactams and N-acylamines, [9] all in the presence of air/oxygen. Kisch et al. showed in 1982 that, in addition to an oxidative C-C coupling react...

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“…A systematic study of the reduction of a variety of maleimide derivatives has been published (Scheme 12). [72] N-Phenylmaleimide 76 was readily reduced to N-phenylsuccinimide 77 using non-modified TiO 2 . Methanol is used as sacrificial electron donor and hole scavenger.…”

Section: Oxidationsmentioning

confidence: 99%

Photocatalysis with TiO2 Applied to Organic Synthesis

Hoffmann

2015

Aust. J. Chem.

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Titanium dioxide is a versatile heterogeneous catalyst. Absorption of light by a TiO2 particle leads to the formation of an electron–hole pair. Electron transfer from or to the particle induces redox reactions. Although mainly applied in the context of environmental chemistry, these processes are also used to selectively transform organic compounds. Oxidations and reductions have been carried out. Applications to the synthesis of heterocycles have been reported. Many C–C bond formation reactions have been performed. Owing to adsorption of the substrates or by different surface modifications, visible light can be used to excite the catalytic system, which generates mild reaction conditions.

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Hydrogenations without Hydrogen: Titania Photocatalyzed Reductions of Maleimides and Aldehydes

Cited by 13 publications

References 44 publications

Proton‐Coupled Electron Transfer in Photoredox Catalytic Reactions

Proton‐Coupled Electron Transfer in Photoredox Catalytic Reactions

Heterogeneous Photoredox Catalysis: Reactions, Materials, and Reaction Engineering

Photocatalysis with TiO2 Applied to Organic Synthesis

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