Revealing the Role of Ligand Dissociation in Ru(II) Pincer-Catalyzed CO2 Hydrogenation to Methanol.

The hydrogenation of CO2 to methanol is a key transformation for sustainable carbon utilization and energy conversion. Although metal-ligand cooperation has been widely explored in catalyst design, the mechanistic role of dynamic ligand dissociation in CO2 hydrogenation remains insufficiently understood. In this work, density functional theory calculations are performed to investigate the pathway selectivity in Ru-catalyzed CO2 hydrogenation. The results show that the ligand-dissociation pathway is energetically more favorable than the ligand-retained metal-ligand cooperative pathway throughout the catalytic cycle. This kinetic preference originates from a consistent enhancement of metal-substrate electronic interactions upon ligand dissociation. During H2 activation, ligand dissociation promotes stronger Ru-H2 orbital interactions, facilitating H-H bond cleavage with reduced structural distortion of both the catalyst and H2. In subsequent CO2 activation and hydride transfer steps, the unsaturated Ru center further strengthens orbital interactions and stabilizes key transition states through charge redistribution effects, as supported by distortion-interaction analysis, IGMH analysis, and energy decomposition analysis based on the sobEDA scheme. Overall, dynamic ligand dissociation enables persistent modulation of the electronic structure of the Ru center, leading to uniformly reduced activation barriers for H2 activation, CO2 conversion, and hydride transfer steps. These findings establish a unified mechanistic framework for understanding ligand-controlled pathway selectivity and provide design principles for efficient CO2 hydrogenation catalysts.