Photocatalytic C–H Carboxylation of 1,3-Dicarbonyl Compounds with Carbon Dioxide Promoted by Nickel(II)-Sensitized α-Fe2O3 Nanoparticles

Abstract

Insertion of carbon dioxide into C–H bonds under mild conditions is an industrially important yet highly challenging task. In the present study, we report the synthesis of an efficient photocatalyst consisting of a Ni(bpy)3Cl2 sensitizer supported on α-Fe2O3 nanoparticles for the CO2 insertion into C–H bonds, particularly carboxylation of 1,3-dicarbonyl compounds like acetyl acetone, methyl acetoacetate, and ethyl acetoacetate with CO2 under visible light irradiation using carbon tetrachloride as a solvent. The carboxylation of these compounds afforded the predominant formation of a single isomeric acid as confirmed by 13C NMR spectroscopy. Based on the computational studies, a possible reaction mechanism suggested the generation of CO2 radical anions at the conduction band of α-Fe2O3 through single electron transfer mediated by the nickel(II) complex that coupled with acetyl acetone cation radicals at the valence band of α-Fe2O3 to give the corresponding carboxylic acid. The protocol described in the present study presents a light-assisted approach and a low-cost material for the synthesis of carboxylic acids utilizing CO2 under mild reaction conditions.