Unveiling the Role of Ligand Assistance in H2 Activation and CO2 Hydrogenation Catalyzed by an Iridium Complex: A DFT Study.

Density functional theory (DFT) calculations were employed to elucidate the mechanistic pathways of hydrogen activation and CO2 addition mediated by a novel iridium catalyst. The results demonstrate that hydrogen activation proceeds efficiently via an oxidative addition mechanism at the Ir(I) center, followed by ligand-assisted heterolysis. Detailed distortion-interaction and energy decomposition analyses indicate that the oxidative addition at the Ir(I) center exhibits stronger orbital interactions, which are key determinants of the selectivity in hydrogen activation. In the CO2 addition reaction, the trihydride complex reacts with DBU, inducing a redox transition from Ir(III) to an Ir(I) dihydride intermediate, which undergoes ligand-assisted stepwise hydride transfer. This dynamic reduction pathway significantly lowers the reaction barrier and facilitates hydride transfer. Compared to the direct hydrogenation pathway involving Ir(III) species, this route exhibits a substantially lower energy barrier. Energy decomposition and noncovalent interaction analyses further reveal that the reduced Pauli repulsion in the Ir(I)-centered pathway is a critical factor contributing to its lower activation energy and higher selectivity. These findings highlight the significance of the Ir(I)/Ir(III) dynamic redox transition in catalytic processes, providing valuable theoretical insights for the development of efficient catalysts for hydrogen activation and CO2 conversion.