Photocatalysis with TiO2 Applied to Organic Synthesis

Hoffmann, Norbert

doi:10.1071/ch15322

Cited by 57 publications

(28 citation statements)

References 104 publications

(100 reference statements)

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“…Heterogeneous photoredox catalysis is also applied to organic synthesis . Most frequently, inorganic semiconductors such as TiO 2 , ZnO, ZnS, CdS, etc.…”

Section: Proton‐coupled Electron Transfer In Heterogeneous Photoredoxmentioning

confidence: 99%

Proton‐Coupled Electron Transfer in Photoredox Catalytic Reactions

Hoffmann

2017

Eur J Org Chem

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104

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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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“…Heterogeneous photoredox catalysis is also applied to organic synthesis . Most frequently, inorganic semiconductors such as TiO 2 , ZnO, ZnS, CdS, etc.…”

Section: Proton‐coupled Electron Transfer In Heterogeneous Photoredoxmentioning

confidence: 99%

Proton‐Coupled Electron Transfer in Photoredox Catalytic Reactions

Hoffmann

2017

Eur J Org Chem

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104

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“…These reports successfully fulfilled the organic transformations with high yield, excellent selectivity, mild conditions, and wide substrate scope. Corresponding to this new field, a number of excellent reviews have focused on TiO2 photocatalysis in organic synthesis [39,40,42,43,47,50,52,56,57,63,[86][87][88]. However, the incredible potential of C-H bond functionalization by TiO2 photocatalysis for C-C coupling reactions has not been fully tapped yet.…”

Section: Introductionmentioning

confidence: 99%

TiO2 Photocatalyzed C–H Bond Transformation for C–C Coupling Reactions

Wang

Liu

et al. 2018

Catalysts

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Fulfilling the direct inert C–H bond functionalization of raw materials that are earth-abundant and commercially available for the synthesis of diverse targeted organic compounds is very desirable and its implementation would mean a great reduction of the synthetic steps required for substrate prefunctionalization such as halogenation, borylation, and metalation. Successful C–H bond functionalization mainly resorts to homogeneous transition-metal catalysis, albeit sometimes suffering from poor catalyst reusability, nontrivial separation, and severe biotoxicity. TiO2 photocatalysis displays multifaceted advantages, such as strong oxidizing ability, high chemical stability and photostability, excellent reusability, and low biotoxicity. The chemical reactions started and delivered by TiO2 photocatalysts are well known to be widely used in photocatalytic water-splitting, organic pollutant degradation, and dye-sensitized solar cells. Recently, TiO2 photocatalysis has been demonstrated to possess the unanticipated ability to trigger the transformation of inert C–H bonds for C–C, C–N, C–O, and C–X bond formation under ultraviolet light, sunlight, and even visible-light irradiation at room temperature. A few important organic products, traditionally synthesized in harsh reaction conditions and with specially functionalized group substrates, are continuously reported to be realized by TiO2 photocatalysis with simple starting materials under very mild conditions. This prominent advantage—the capability of utilizing cheap and readily available compounds for highly selective synthesis without prefunctionalized reactants such as organic halides, boronates, silanes, etc.—is attributed to the overwhelmingly powerful photo-induced hole reactivity of TiO2 photocatalysis, which does not require an elevated reaction temperature as in conventional transition-metal catalysis. Such a reaction mechanism, under typically mild conditions, is apparently different from traditional transition-metal catalysis and beyond our insights into the driving forces that transform the C–H bond for C–C bond coupling reactions. This review gives a summary of the recent progress of TiO2 photocatalytic C–H bond activation for C–C coupling reactions and discusses some model examples, especially under visible-light irradiation.

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“…For generating radicals, photoredox catalysts (PCs) of several types that require only visible light (sometimes UVA) have been developed. Heterogeneous PCs are mainly inorganic semiconductors, particularly titania (TiO 2 ), which has found numerous applications in conjunction with allylic alkenes, alkyl amines, carboxylic acids and other compounds [42,43,44,45]. Development of the alternative homogeneous type PCs has flourished exceptionally well.…”

Section: Oxime Esters and Related Carbonyl Oximesmentioning

confidence: 99%

Functionalised Oximes: Emergent Precursors for Carbon-, Nitrogen- and Oxygen-Centred Radicals

Walton

2016

Molecules

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Oxime derivatives are easily made, are non-hazardous and have long shelf lives. They contain weak N-O bonds that undergo homolytic scission, on appropriate thermal or photochemical stimulus, to initially release a pair of N-and O-centred radicals. This article reviews the use of these precursors for studying the structures, reactions and kinetics of the released radicals. Two classes have been exploited for radical generation; one comprises carbonyl oximes, principally oxime esters and amides, and the second comprises oxime ethers. Both classes release an iminyl radical together with an equal amount of a second oxygen-centred radical. The O-centred radicals derived from carbonyl oximes decarboxylate giving access to a variety of carbon-centred and nitrogen-centred species. Methods developed for homolytically dissociating the oxime derivatives include UV irradiation, conventional thermal and microwave heating. Photoredox catalytic methods succeed well with specially functionalised oximes and this aspect is also reviewed. Attention is also drawn to the key contributions made by EPR spectroscopy, aided by DFT computations, in elucidating the structures and dynamics of the transient intermediates.

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Photocatalysis with TiO2 Applied to Organic Synthesis

Cited by 57 publications

References 104 publications

Proton‐Coupled Electron Transfer in Photoredox Catalytic Reactions

Proton‐Coupled Electron Transfer in Photoredox Catalytic Reactions

TiO2 Photocatalyzed C–H Bond Transformation for C–C Coupling Reactions

Functionalised Oximes: Emergent Precursors for Carbon-, Nitrogen- and Oxygen-Centred Radicals

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