A highly useful, visible-light-driven carboxylation of aryl bromides and chlorides with CO was realized using a combination of Pd(OAc) as a carboxylation catalyst and Ir(ppy)(dtbpy)(PF) as a photoredox catalyst. This carboxylation reaction proceeded in high yields under 1 atm of CO with a variety of functionalized aryl bromides and chlorides without the necessity of using stoichiometric metallic reductants.

A visible light driven catalytic cycle for hydrocarboxylation of alkenes with CO was established using a combination of a Rh(i) complex as a carboxylation catalyst and [Ru(bpy)] (bpy = 2,2'- bipyridyl) as a photoredox catalyst. Two key steps, the generation of Rh(i) hydride species and nucleophilic addition of π-benzyl Rh(i) species to CO, were found to be mediated by light.

A visible-light-driven carboxylation of aryl and alkenyl triflates with CO 2 is developed by using a combination of Pd and photoredox catalysts. This reaction proceeds under mild conditions and can be applied to a wide range of substrates including acyclic alkenyl triflates.

The improved catalytic conditions and detailed reaction mechanism of the visible-light driven hydrocarboxylation of alkenes with CO 2 by the Rh(I) and photoredox dual catalysts were investigated. The use of the benzimidazoline derivative, BI(OH)H, as a sacrificial electron donor was found to increase the yield of the hydrocarboxylated product by accelerating the reduction process. In addition, the incorporation of the cyclometalated Ir(III) complex as a second photosensitizer with [Ru(bpy) 3 ] 2+ photosensitizer also resulted in the promotion of the reduction process, supporting that the catalytic cycle includes two photochemical elementary processes: photoinduced electron and energy transfers.

The reaction mechanism of palladium-catalyzed visible light-driven carboxylation of aryl halides and triflates with a photoredox catalyst was examined in detail. Experimental and theoretical studies indicated that the active species for photoredox-catalyzed reduction was cationic ArPd(II)+ species to generate nucleophilic ArPd(I) or its further reduced ArPd(0)− species, which reacted with CO2 to give carboxylic acids. Hydrodehalogenated compounds, main byproducts in this carboxylation, were thought to be generated by protonation of these reduced species.