- Direct cross-coupling between alkenes and tetrahydrofuran with a platinum-loaded titanium oxide photocatalyst
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A Pt-loaded TiO2 photocatalyst successfully catalyzed the direct cross-coupling between various alkenes and tetrahydrofuran (THF) without any additional oxidizing agent. The reaction between cyclohexene and THF gave three cross-coupling products, namely, 2-cyclohexyltetrahydrofuran (A), 2-(cyclohex-2-en-1-yl)tetrahydrofuran (B) and 2-(cyclohex-1-en-1-yl)tetrahydrofuran (C), along with gaseous hydrogen. The mechanistic study revealed that these products were formed through different individual mechanisms: successive addition of two radical species, a 2-tetrahydrofuranyl radical and a hydrogen radical, to the double bond of cyclohexene for A, coupling of a 3-cyclohexenyl radical and a 2-tetrahydrofuranyl radical for B, and 2-tetrahydrofuranyl radical addition and hydrogen radical elimination at the double bond of cyclohexene for C. Among these three mechanisms, those for B and C are dehydrogenative. In this photocatalytic reaction system, since the cyclohexene molecule has enough reactivity, due to the localized π electron density, the Pt nanoparticles loaded on the TiO2 function not as a metal catalyst but as an electron receiver to enhance the charge separation, although the dehydrogenative cross-coupling of benzene with THF requires Pd metal catalysis.
- Tyagi, Akanksha,Yamamoto, Akira,Yamamoto, Muneaki,Yoshida, Tomoko,Yoshida, Hisao
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p. 2546 - 2556
(2018/06/01)
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- Bifunctional property of Pt nanoparticles deposited on TiO2 for the photocatalytic sp3C-sp3C cross-coupling reactions between THF and alkanes
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The photocatalytic sp3C-sp3C cross-coupling between tetrahydrofuran (THF) and various alkanes was accomplished with Pt loaded titanium oxide (Pt/TiO2) photocatalysts. The cross-coupling between THF and cyclohexane was systematically studied, which revealed that the reaction followed two routes: the main course was the photooxidation of both substrates on a Pt/TiO2 photocatalyst to generate radical species followed by their successive coupling; meanwhile, the minor one was a hybrid of photocatalysis by Pt/TiO2 and thermocatalysis by Pt metal nanoparticles. The activity of the Pt catalysis was suggested to consist in the activation of an sp3C-H bond in THF or alkane molecules adsorbed on its surface and promote the reaction between the activated molecules and photogenerated radical species. Thus, the Pt nanoparticles on TiO2 were believed to play a bifunctional role of an electron receiver as well as a metal catalyst.
- Tyagi, Akanksha,Yamamoto, Akira,Kato, Tatsuhisa,Yoshida, Hisao
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p. 2616 - 2623
(2017/07/25)
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- Tandem redox mediator/Ni(II) trihalide complex photocycle for hydrogen evolution from HCl
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Photoactivation of M-X bonds is a challenge for photochemical HX splitting, particularly with first-row transition metal complexes because of short intrinsic excited state lifetimes. Herein, we report a tandem H2 photocycle based on combination of a non-basic photoredox phosphine mediator and nickel metal catalyst. Synthetic studies and time-resolved photochemical studies have revealed that phosphines serve as photochemical H-atom donors to Ni(II) trihalide complexes to deliver a Ni(I) centre. The H2 evolution catalytic cycle is closed by sequential disproportionation of Ni(I) to afford Ni(0) and Ni(II) and protolytic H2 evolution from the Ni(0) intermediate. The results of these investigations suggest that H2 photogeneration proceeds by two sequential catalytic cycles: a photoredox cycle catalyzed by phosphines and an H2-evolution cycle catalyzed by Ni complexes to circumvent challenges of photochemistry with first-row transition metal complexes.
- Hwang, Seung Jun,Powers, David C.,Maher, Andrew G.,Nocera, Daniel G.
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p. 917 - 922
(2015/02/05)
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- Radical addition of tetrahydrofuran and tetrahydro-2-furanone to alkenylsilanes in the presence of di(t-butyl)peroxide
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β-(Silylethyl)- and γ-(silylpropyl)-tetrahydrofurans and tetrahydro-2-furanones containing alkyl and phenyl groups at the Si atom were obtained by the reactions of tetrahydrofuran (THF) and tetrahydro-2-furanone with vinyl- and allylsilanes in the presence of di(t-butyl) peroxide (DTBP).To reduce the amount of bis-products, the ratio : : = 80 : 4 : 1 was used.
- Gevorgyan, Vladimir,Priede, Einars,Liepins, Edvards,Gavars, Maris,Lukevics, Edmunds
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p. 333 - 338
(2007/10/02)
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- Alkane Functionalization on a Preparative Scale by Mercury-Photosensitized Cross-Dehydrodimerization
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Alkanes can be functionalized with high conversions and in high chemical and quantum yields on a multigram scale by mercury-photosensitized reaction between an alkane and alcohols, ethers, or silanes to give homodimers and cross-dehydrodimers.The separation of the product mixtures is often particulary easy because of a great difference in polarity of the homodimers and cross-dimers.It is also possible to bias the product composition when the ratio of the components in the vapor phase is adjusted by altering the liquid composition.This is useful either to maximize chemical yield or to ease separation by favoring the formation of the most easily separated pair of compounds.The mechanistic basis of the reaction is discussed and a number of specific types of syntheses, for example of 2,2-disubstituted carbinols, are described in detail.The selectivity of cross-dimerization is shown to exceed that for homodimerization and reasons are discussed.Relative reactivities of different compounds and classes of compound are MeOHp-dioxanecyclohexane1,3,5-trioxacyclohexaneethanolisobutaneTHFEt3SiH.The observed selectivities generally parallel those for homodimerization, reported in the preceding paper, but certain differences are noted, and reasons for the differences are proposed.The bond-dissociation energy of Et3SiH is estimated from the reactivity data to be 90 kcal/mol.Eleven new carbinols are synthesized.
- Brown, Stephen H.,Crabtree, Robert H.
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p. 2946 - 2953
(2007/10/02)
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- DEPLACEMENTS HOMOLYTIQUES INTRAMOLECULAIRES . 12 - DECOMPOSITION INDUITE DE PEROXYDES ETHYLENIQUES : INFLUENCE DE LA LONGUEUR DE LA CHAINE
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Products analyses of the thermolyses of the peroxides CH2=CH-(CH2)nOOtBu, 1, (n=1-5) showed that an induced decomposition of 1 occurred for n=1,2,3,4.Free radical additions of THF, carbon tetrachloride, bromotrichloromethane to 1 have been performed at lower temperature; they allowed, through the isolation of an adduct peroxide, at least in one case for each peroxide, to prove that a two-steps mechanism (addition of radical Z. to the double bond, intramolecular homolytic displacement) is involved in the induced decomposition of 1.The order of magnitude of the rate constants of these SHi reactions could be estimated.
- Bourgeois, M. J.,Maillard, B.,Montaudon, E.
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p. 5309 - 5320
(2007/10/02)
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- Photocatalytic Carbon-Carbon Bond Formation with Concurrent Hydrogen Evolution on Colloidal Zinc Sulphide
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In the photocatalytic system containing colloidal ZnS, water, and organic substrates such as triethylamine, tetrahydrofuran, or methanol, oxidative carbon-carbon bond formation occurs with efficient reductive H2 evolution, to give the dimeric products 2,3-bis(diethylamino)butane, 2,2'-bitetrahydrofuryl, or ethylene glycol, respectively.
- Yanagida, Shozo,Azuma, Takayuki,Kawakami, Horishi,Kizumoto, Hirotoshi,Sakurai, Hiroshi
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- Deplacements homolytiques intramoleculaires. 2. Decomposition du perpentene-4 oate de tert-butyle dans les ethers
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The thermolysis of tert-butyl perpent-4-enoate 1 in THF led to several compounds; the main product, 5-(2-tetrahydrofuryl)-4-pentanolide (yield 42percent) comes from an induced decomposition of the perester occuring with the addition of 2-tetrahydrofuryl radical to the double bond.A similar reaction was performed at a lower temperature, using butyl perdicarbonate as initiator, but did not define the mechanism (concerted or two-step).The thermolysis of 1 in ethers (THP, oxepane, 1,4-dioxane, dipropyl ether) appears to be a useful synthetic tool: several new γ-lactones have been obtained in this way.
- Kharrat, A.,Gardrat, C.,Maillard, B.
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p. 2385 - 2390
(2007/10/02)
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