Role of Water, CO<sub>2</sub>, and Noninnocent Ligands in the CO<sub>2</sub> Hydrogenation to Formate by an Ir(III) PNP Pincer Catalyst Evaluated by Static-DFT and ab Initio Molecular Dynamics under Reaction Conditions

Reaction pathways relevant to the CO<sub>2</sub> hydrogenation to formate using a homogeneous Ir<sup>III</sup>H<sub>3</sub>(PNP) pincer catalyst have been investigated using static DFT calculations and ab initio molecular dynamics simulations under reaction conditions. The role of a base, solvent, and the noninnocent ligand are demonstrated. Static DFT calculations with an implicit solvent highlight the importance of selecting a highly polar solvent. The insertion of CO<sub>2</sub> and regeneration of the catalyst are identified as the key steps in the reaction mechanism. Unlike in the static DFT calculations, the AIMD simulations show that an additional CO<sub>2</sub> molecule and explicit water molecules can expedite the direct cleavage of the H<sub>2</sub> coordinated to the metal center to regenerate the catalyst. In addition, the AIMD simulations indicate that the pyridine ring does not participate in the hydrogenation mechanism, while the α-carbon at the pyridine ring is very acidic and participates in off-cycle reactions.