Carbon dioxide reduction by pincer rhodium η²-dihydrogen complexes: Hydrogen-binding modes and mechanistic studies by density functional theory calculations

Density functional theory (DFT) calculations using the KMLYP method on a series of pincer PCP-rhodium dihydrogen complexes have been employed to model and examine the proposed mechanisms for the pincer PCP-rhodium complexes mediated hydrogenation of carbon dioxide (CO₂). The relative energies of dihydrogen rotamers and dihydride isomers were evaluated together with T₁ values to determine the molecular structures of these complexes. We have investigated possible pathways for the CO₂ reduction processes involving the formation of rhodium dihydride species. Although the dihydrogen complexes are more stable than the corresponding dihydride isomers, the reduction of CO₂ has to proceed through the dihydride structures.