Hydrogenation of CO2 to CH3OH catalyzed by a ruthenium-triphos complex: Theoretical free energy profile and microkinetic modeling

Direct hydrogenation of carbon dioxide to methanol is an important goal for sustainability. The ruthenium-triphos complex was reported to be successful in achieving this transformation. However, a reliable free energy profile able to explain the experimental kinetics has not been published yet. This work presents a detailed investigation of this transformation using the accurate ωB97M-V functional, followed by a detailed microkinetic analysis. We have found two key intermediates. The first one is [(triphos)Ru(HCOO)(THF)]+, named MS5 and formed at the beginning of the catalyzed reaction. The second, and the most stable, is [(triphos)Ru(HCOO)(CH3OH)]+, named MS22 and formed later in the reaction time. The highest barrier in the catalytic cycle (28.1 kcal mol−1) corresponds to the steps MS22 → [(triphos)Ru(H)(H2)(THF)]+ → TS4, with TS4 being the hydride transfer to the coordinated formate. Formic acid released in the catalysis can participate in the important proton transfer steps along the catalytic cycle.