Selective Generation of Formamides through Photocatalytic CO2 Reduction Catalyzed by Ruthenium Carbonyl Compounds

Angewandte Chemie International Edition by Katsuaki Kobayashi, Takashi Kikuchi, Susumu Kitagawa, Koji Tanaka  /  7d  //  keep unread  //  hide  //  preview Abstract The selective formation of dialkyl formamides through photochemical CO2 reduction was developed as a means of utilizing CO2 as a C1 building block. Photochemical CO2 reduction catalyzed by a [Ru(bpy)2(CO)2]2+ (bpy: 2,2′-bipyridyl)/[Ru(bpy)3]2+/Me2NH/Me2NH2+system in CH3CN selectively produced dimethylformamide. In this process a ruthenium carbamoyl complex ([Ru(bpy)2(CO)(CONMe2)]+) formed by the nucleophilic attack of Me2NH on [Ru(bpy)2(CO)2]2+ worked as the precursor to DMF. Thus Me2NH acted as both the sacrificial electron donor and the substrate, while Me2NH2+ functioned as the proton source. Similar photochemical CO2 reductions using R2NH and R2NH2+ (R=Et, nPr, or nBu) also afforded the corresponding dialkyl formamides (R2NCHO) together with HCOOH as a by-product. The main product from the CO2 reduction transitioned from R2NCHO to HCOOH with increases in the alkyl chain length of the R2NH. The selectivity between R2NCHO and HCOOH was found to depend on the rate of [Ru(bpy)2(CO)(CONR2)]+ formation. Formamide generation: Photochemical CO2 reduction in the presence of a dialkyl amine and its ammonium salt affords a dialkyl formamide when a ruthenium carbonyl compound, [Ru(bpy)2(CO)2]2+, is used as a catalyst. Fast nucleophilic attack of the dialkyl amine on the RuCO scaffold with resulting formamide generation takes priority over the competing formation of formic acid. Visit Website