Photohydrogenation of Acetophenone Using Coumarin  Dye-Sensitized Titanium Dioxide under Visible  Light Irradiation

Kohtani, Shigeru; Mori, Mizuho; Yoshioka, Eito; Miyabe, Hideto

doi:10.3390/catal5031417

Cited by 14 publications

(9 citation statements)

References 26 publications

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“…Kohtani’s group has conducted a series of excellent work on TiO 2 photocatalytic transfer hydrogenations of aryl carbonyl compounds using alcohols as hydrogen donors [55,85,86,87,88,89,90]. In their most recent work, even moderate enantioselectivity for aryl ketones’ conversion to chiral secondary aryl alcohols was realized (as shown in Scheme 8) [56].…”

Section: Transfer Hydrogenation Of C=o and C=n Bondsmentioning

confidence: 99%

“…Furthermore, the efficiency of this visible-light-sensitized protocol was greatly increased by the introduction of more absorptive dyes. A series of pristine and thiophene-modified coumarin derivatives were chosen as the photosensitizers for visible-light driven TiO 2 photocatalytic transformation of acetophenone to 1-phenyl-ethanol [88]. The irradiation time to reach the same conversion was greatly shortened compared with the previous dye-sensitized system when appropriate hydrogen donor was chosen.…”

Section: Transfer Hydrogenation Of C=o and C=n Bondsmentioning

confidence: 99%

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TiO2 Photocatalysis for Transfer Hydrogenation

Zhai

Wang

et al. 2019

Molecules

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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.

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Section: Transfer Hydrogenation Of C=o and C=n Bondsmentioning

confidence: 99%

Section: Transfer Hydrogenation Of C=o and C=n Bondsmentioning

confidence: 99%

TiO2 Photocatalysis for Transfer Hydrogenation

Zhai

Wang

et al. 2019

Molecules

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“…Adapted with permission from reference [72]. Kohtani et al also reported the photohydrogenation of AP derivatives on P25 TiO2, modified with metal-free organic dyes such as rhodamine B, fluorescein, and coumarin derivatives [77,78]. The use of these organic dyes successfully extended the UV response of TiO2 to the visible light region, though these reaction rates were much slower than the hydrogenation rate using UV excitation of Kohtani et al also reported the photohydrogenation of AP derivatives on P25 TiO2, modified with metal-free organic dyes such as rhodamine B, fluorescein, and coumarin derivatives [77,78].…”

Section: Hydrogenation Of Carbonyl Compoundsmentioning

confidence: 99%

“…The use of these organic dyes successfully extended the UV response of TiO2 to the visible light region, though these reaction rates were much slower than the hydrogenation rate using UV excitation of non-modified TiO2. In this dye-sensitized system, the electron injection from dye into TiO2 can take Kohtani et al also reported the photohydrogenation of AP derivatives on P25 TiO 2, modified with metal-free organic dyes such as rhodamine B, fluorescein, and coumarin derivatives [77,78]. The use of these organic dyes successfully extended the UV response of TiO 2 to the visible light region, though these reaction rates were much slower than the hydrogenation rate using UV excitation of non-modified TiO 2 .…”

Section: Hydrogenation Of Carbonyl Compoundsmentioning

confidence: 99%

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Reactivity of Trapped and Accumulated Electrons in Titanium Dioxide Photocatalysis

2017

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Electrons, photogenerated in conduction bands (CB) and trapped in electron trap defects (Ti ds ) in titanium dioxide (TiO 2 ), play crucial roles in characteristic reductive reactions. This review summarizes the recent progress in the research on electron transfer in photo-excited TiO 2 . Particularly, the reactivity of electrons accumulated in CB and trapped at Ti ds on TiO 2 is highlighted in the reduction of molecular oxygen and molecular nitrogen, and the hydrogenation and dehalogenation of organic substrates. Finally, the prospects for developing highly active TiO 2 photocatalysts are discussed.

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