Selective Generation of Formamides through Photocatalytic CO 2 Reduction Catalyzed by Ruthenium Carbonyl Compounds

The selective formation of dialkyl formamides through photochemical CO 2 reduction was developed as a means of utilizing CO 2 as a C 1 building block. Photochemical CO 2 reduction catalyzed by a [Ru(bpy) 2 (CO) 2 ] 2+ (bpy: 2,2′‐bipyridyl)/[Ru(bpy) 3 ] 2+ /Me 2 NH/Me 2 NH 2 + system in CH 3 CN selectively produced dimethylformamide. In this process a ruthenium carbamoyl complex ([Ru(bpy) 2 (CO)(CONMe 2 )] + ) formed by the nucleophilic attack of Me 2 NH on [Ru(bpy) 2 (CO) 2 ] 2+ worked as the precursor to DMF. Thus Me 2 NH acted as both the sacrificial electron donor and the substrate, while Me 2 NH 2 + functioned as the proton source. Similar photochemical CO 2 reductions using R 2 NH and R 2 NH 2 + (R=Et, nPr, or n Bu) also afforded the corresponding dialkyl formamides (R 2 NCHO) together with HCOOH as a by‐product. The main product from the CO 2 reduction transitioned from R 2 NCHO to HCOOH with increases in the alkyl chain length of the R 2 NH. The selectivity between R 2 NCHO and HCOOH was found to depend on the rate of [Ru(bpy) 2 (CO)(CONR 2 )] + formation.