Catalysis Letters, Vol.150, No.1, 31-38, 2020
Metal Cocatalyst Directing Photocatalytic Acetonylation of Toluene via Dehydrogenative Cross-Coupling with Acetone
A heterogeneous metal-loaded titanium oxide photocatalyst provided an efficient route to bring out direct dehydrogenative cross-coupling between toluene and acetone without consuming any additional oxidizing agent. The nature of the metal nanoparticle cocatalyst deposited on TiO2 photocatalyst dictated the product selectivity for the cross-coupling. Pd nanoparticles on TiO2 photocatalyst allowed a C-C bond formation between the aromatic ring of toluene and acetone to give 1-(o-tolyl)propan-2-one (1a1) with high regioselectivity, while Pt nanoparticles on TiO2 photocatalyst promoted the cross-coupling between the methyl group of toluene and acetone to give 4-phenylbutan-2-one (1b) as the acetonylated product. These results demonstrated that the selection of the metal cocatalyst on TiO2 photocatalyst could determine which C-H bonds in toluene, aromatic or aliphatic, can react with acetone. Two kinds of reaction mechanisms were proposed for the photocatalytic dehydrogenative cross-coupling reaction, depending on the property of the metal nanoparticles, i.e., only Pd nanoparticles can catalyze the reaction between aromatic ring and the acetonyl radical species. [GRAPHICS] .