Photoinduced reactivity of Au–H intermediates in alcohol oxidation by gold nanoparticles supported on ceria

Abstract

H-Au-np/CeO 2 species, that are important intermediates in the alcohol oxidation by gold nanoparticles, show a photoinduced reactivity. UV-visible photoexcitation in deaerated conditions causes a hydride transfer from gold to the spin trap DMPO. The photoassisted breaking of the Au-H bond restores the catalyst in its active form. As a consequence, photochemical excitation has a positive effect on the catalytic oxidation of 2-pentanol under anaerobic conditions, demonstrating that light can be used in place of oxygen. This new photocatalytic activity of H-Au-np/CeO 2 species is of general interest in the field of catalysis with gold nanoparticles, since the photoinduced hydride shift from gold surface to organic substrates opens up exciting possibilities to use alcohols for hydrogenation reactions.Scheme 1 Mechanism of alcohol oxidation by supported Au-np.

Direct Photocatalysis for Organic Synthesis by Using Plasmonic‐Metal Nanoparticles Irradiated with Visible Light

“…The HÀAu NP reacts with NÀO bonds to produce a HOÀAu NP species, which subsequently decomposes to produce oxygen molecules and HÀAu NP species. [66] They conducted electron paramagnetic resonance (EPR) spin trapping experiments to confirm that the HÀAu NPs species are important intermediates that govern alcohol oxidation by Au NPs, and that the photoexcitation influences the stability of AuÀH bonds. Photocatalytic deoxygenation of epoxides to alkenes, reduction of ketones to alcohols, and hydrogenation of azobenzene to hydroazobenzene with Au NPs under visible-light irradiation.…”

A Highly Efficient Gold‐Catalyzed Oxidative CC Coupling from CH Bonds Using Air as Oxidant

“…[6a] The AuH species may be different from the CuH and AgH species, [13] and it could form the iminium ion/AuOOH complex 14 in the presence of air (O 2 ) in a similar way to PdH and RuH. [14] The iminium species 14 can be trapped with nitromethane quickly to afford the desired product 9 a, H 2 O and the gold(III) oxo complex 15.…”

Free‐radical‐mediated copper‐catalyzed triazole formation under UV‐irradiation

“…Metal oxide‐supported gold nanoparticle, plasmonic photocatalyst, is an excellent example of heterogeneous catalysis for the aerobic oxidation of alcohols in toluene under the irradiation of natural sunlight . Cerium oxide‐supported gold particles have been reported for the selective oxidation of 4‐aminobenzyl alcohol to 4‐aminobenzaldehyde through the photo‐induced Au–H intermediate under UV and visible light irradiation . The free‐standing gold particles could also act as a photocatalyst for the oxidation of alcohols to the corresponding carbonyl compounds in the presence of peroxide under LED irradiation (530 nm) …”

“…[9] Cerium oxide-supported gold particles have been reported for the selective oxidation of 4-aminobenzyl alcohol to 4aminobenzaldehyde through the photo-induced Au-H intermediate under UV and visible light irradiation. [10] The free-standing gold particles could also act as a photocatalyst for the oxidation of alcohols to the corresponding carbonyl compounds in the presence of peroxide under LED irradiation (530 nm). [11] Organic coupling reactions with high activation barriers of the substrates are mostly dependent on relatively high temperatures for activation.…”