Photochemical Reduction of Carbon Dioxide to Formic Acid using Ruthenium(II)‐Based Catalysts and Visible Light

Abstract A photocatalytic system that consists of an Ir‐based photosensitizer and a Ru II bipyridine catalyst was developed for the selective reduction of CO 2 to formic acid using triethanolamine as the electron donor. Catalyst turnover numbers up to 526 and a selectivity of 80 % towards formic acid were observed if the photocatalytic reaction was performed with [Ir(ppy) 2 (bpy)]PF 6 (ppy=2‐(pyridine‐2‐yl)benzene‐1‐ide, bpy=2,2′‐bipyridine) as the photosensitizer and [Ru(bpy) 2 (Cl)(CO)]PF 6 as the catalyst under visible‐light irradiation ( λ =400–700 nm). Interestingly, this photocatalytic system showed activity for the photoreduction of Na 2 CO 3 to formic acid as well. The investigation of different ruthenium(II) catalysts revealed the positive influence of carbonyl ligands coordinated to the metal center. The enhancement of the catalytic activity is explained by a more favorable electron transfer from the photosensitizer to the catalyst, which is supported by the redox potentials of the complexes.