Visible Light Uranyl Photocatalysis: Direct C–H to C–C Bond Conversion

Capaldo, Luca; Merli, Daniele; Fagnoni, Maurizio; Ravelli, Davide

doi:10.1021/acscatal.9b00287

Cited by 106 publications

(104 citation statements)

References 44 publications

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“…A recent example deals with the use of uranyl nitrate, UO 2 (NO 3 ) 2 , as photocatalyst to promote the C–H to C–C bond conversion in alkanes and other simple aliphatic derivatives (ethers, acetals, and amides) in the presence of electron‐poor olefins . The process was demonstrated to proceed through a direct HAT step promoted upon visible light irradiation, confirming the typical reactivity profile previously reported for this photocatalyst …”

Section: Catalytic Cycle Being Closed By a Reaction Intermediatesupporting

confidence: 73%

“…In particular, a correlation between the redox potential of the 5.5 • / 5.5 – couple and the efficiency of the overall reaction was found. In other words, 5.5 • had to be reducible enough to accept an electron from the (weakly reducing) deactivated form of the uranyl cation ( E ([U V O 2 ] + /[U VI O 2 ] 2+ ) = +0.32 V vs. SCE; non‐reversible behavior) …”

Section: Catalytic Cycle Being Closed By a Reaction Intermediatementioning

confidence: 99%

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The Dark Side of Photocatalysis: One Thousand Ways to Close the Cycle

Capaldo

Ravelli

2020

Eur J Org Chem

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Photocatalytic strategies have recently revolutionized the field of organic synthesis. However, while the progress has been impressive in terms of reported methodologies, less attention has been devoted to mechanistic aspects. In this regard, key to the development of efficient strategies is the recovery of the exhausted photocatalyst formed upon quenching of the excited state. This review summarizes the different ways available to turn over the photocatalyst and classifies them according to the species responsible for this step, being a reaction intermediate, a co‐catalyst, a reaction partner or an electrode. Finally, an analysis of the common aspects of the described alternatives is offered, also showcasing how the tuning of the photocatalyst turn‐over step can completely divert the reaction outcome.

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Section: Catalytic Cycle Being Closed By a Reaction Intermediatesupporting

confidence: 73%

Section: Catalytic Cycle Being Closed By a Reaction Intermediatementioning

confidence: 99%

The Dark Side of Photocatalysis: One Thousand Ways to Close the Cycle

Capaldo

Ravelli

2020

Eur J Org Chem

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“…Uranyl nitrate hexahydrate ([UO 2 ](NO 3 ) 2 .6H 2 O) is proven to be an efficient photocatalyst for activation of C−H bond in alkanes to form C−C bond . The photophysical and photochemical properties of uranyl cation [UO 2 ] 2+ with the uranium oxidation state of +6 have been reported .…”

Section: Metal Complexes As Photocatalystsmentioning

confidence: 99%

Photoinduced Generation of Superoxidants for the Oxidation of Substrates with High C−H Bond Dissociation Energies

et al. 2019

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Oxidation of substrates, such as methane, with large C−H bond dissociation energies usually requires harsh reaction conditions, such as high temperature and pressure. The use of photoexcited states of oxidants enables the oxidation of substrates which would otherwise be unable to react thermally. This Review focuses on photoinduced generation of strong inorganic and organic oxidants, which enables the oxidation of substrates with strong C−H bonds. For example, photoexcitation of a CeIV‐alkoxide complex results in the cleavage of Ce−O bond to produce an alkoxyl radical, which can abstract a hydrogen atom from methane to afford a methyl radical, leading to amination of methane with tert‐butyloxycarbonyl (Boc)‐protected monomethylhydrazine. Hydrogen atom abstraction from alkanes also occurs induced by the photoexcited state of tetrabutylammonium decatungstate, leading to alkylations and acylation of both aromatic and aliphatic N‐tosylimines. Photoexcitation of Bi‐ and V‐containing beta zeolites also results in hydrogen atom abstraction from methane to produce methanol at ambient temperature. The photoexcited state of a manganese(IV)‐oxo complex binding with two Sc3+ ions has a surprisingly long lifetime (6.4 μs), and is able to oxidize benzene to produce phenol. Chlorine radicals, that can be generated by photoinduced oxidation of chloride ion by the photoexcited states of oxidants or by photoexcitation of a chlorine dioxide radical, abstracts a hydrogen atom from alkanes including methane to produce alkyl radicals, which can be converted to the oxygenated products. Photoinduced oxidation of methane was also made possible by mixing photosystem II (PSII) and the membrane fraction of a particular form of methane monooxygenase. A PSII model reaction has been achieved by using p‐benzoquinone derivatives as plastoquinone analogues with a non‐heme FeII catalyst in the presence of H2O under photoirradiation, to yield dioxygen with the corresponding hydroquinone derivatives.

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“… 1 Among the various photocatalytic methods, hydrogen atom transfer (HAT) processes are particularly useful for the functionalization of substrates containing unreactive C–H bonds without recurring to metal catalysis or strong oxidants. 2 Light-induced HAT catalysis can proceed via three different pathways: direct HAT, 3 indirect HAT, 4 and proton-coupled electron transfer (PCET) processes. 5 Among these, direct HAT processes are the most reagent-economical, as the other two approaches require the addition of additives to the reaction.…”

Section: Introductionmentioning

confidence: 99%

Optimization of a Decatungstate-Catalyzed C(sp³)–H Alkylation Using a Continuous Oscillatory Millistructured Photoreactor

Wen

Maheshwari

Sambiagio

et al. 2020

Org. Process Res. Dev.

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Tetrabutylammonium decatungstate (TBADT) has emerged as an efficient and versatile photocatalyst for hydrogen atom transfer (HAT) processes that enables the cleavage of both activated and unactivated aliphatic C–H bonds. Using a recently developed oscillatory millistructured continuous-flow photoreactor, investigations of a decatungstate-catalyzed C(sp 3 )–H alkylation protocol were carried out, and the results are presented here. The performance of the reactor was evaluated in correlation to several chemical and process parameters, including residence time, light intensity, catalyst loading, and substrate/reagent concentration. In comparison with previously reported batch and flow protocols, conditions were found that led to considerably higher productivity, achieving a throughput up to 36.7 mmol/h with a residence time of only 7.5 min.

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Visible Light Uranyl Photocatalysis: Direct C–H to C–C Bond Conversion

Cited by 106 publications

References 44 publications

The Dark Side of Photocatalysis: One Thousand Ways to Close the Cycle

The Dark Side of Photocatalysis: One Thousand Ways to Close the Cycle

Photoinduced Generation of Superoxidants for the Oxidation of Substrates with High C−H Bond Dissociation Energies

Optimization of a Decatungstate-Catalyzed C(sp³)–H Alkylation Using a Continuous Oscillatory Millistructured Photoreactor

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Visible Light Uranyl Photocatalysis: Direct C–H to C–C Bond Conversion

Cited by 106 publications

References 44 publications

The Dark Side of Photocatalysis: One Thousand Ways to Close the Cycle

The Dark Side of Photocatalysis: One Thousand Ways to Close the Cycle

Photoinduced Generation of Superoxidants for the Oxidation of Substrates with High C−H Bond Dissociation Energies

Optimization of a Decatungstate-Catalyzed C(sp3)–H Alkylation Using a Continuous Oscillatory Millistructured Photoreactor

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Product

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Optimization of a Decatungstate-Catalyzed C(sp³)–H Alkylation Using a Continuous Oscillatory Millistructured Photoreactor