Unraveling Metal/Pincer Ligand Effects in the Catalytic Hydrogenation of Carbon Dioxide to Formate

The hydrogenation of carbon dioxide to formate is an intriguing reaction from both an environmental and an energy perspective, primarily due to the prospective uses of the product as a platform chemical in numerous applications such as an organic hydrogen carrier. Although several transition-metal-based catalysts have been shown to facilitate this chemical transformation, few guidelines exist on how best to tune the catalysts in order to achieve maximum activity. Here, we use linear scaling relationships and molecular volcano plots to gauge the potential of different metal-pincer catalysts for the aforementioned reaction. Analysis of combinations of five metals (Ru, Os, Co, Rh, and Ir) and seven tridentate pincer-type ligands reveals several complexes lying near the volcano top, suggesting that these species have nearly ideal energetic profiles for facilitating the hydrogenation reaction. In particular, catalysts bearing group 9 metal centers (Ir, Rh, Co) with pi-acidic ligands provide a clear route to improving catalytic activity. Overall, these findings highlight how linear scaling relationships and molecular volcano plots provide unique insight into the underlying stereoelectronic factors that make specific metal-ligand combinations highly efficient catalysts.