Catalyst Design for Highly Efficient Base-Free Carbon Dioxide Hydrogenation to Formic Acid

We report on new ruthenium complexes as catalysts for the efficient transformation of CO2 into formic acid as a high-value chemical and fuel. Remarkably, these complexes catalyze the hydrogenation of CO2 selectively and without employing any base, which improves the sustainability of the process when compared the common base-assisted technologies. The molecular catalyst design relies on donor-flexible and synthetically versatile pyridylidene amide (PYA) ligands which allows the ligand architecture to be varied in a controlled manner to gain valuable insights for the improvement of catalyst performance. Modification of the ligand properties directly influence the catalytic process by shifting the turnover limiting step, the reaction mechanism and the stability upon the acidification of the reaction media and provide access to high-performance systems reaching turnover numbers of several thousands and turnover frequencies up to 350 h–1.