Role of Water, CO2, and Noninnocent Ligands in the CO2 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 CO2 hydrogenation to formate using a homogeneous IrIIIH3(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 CO2 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 CO2 molecule and explicit water molecules can expedite the direct cleavage of the H2 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.