Computational Insight into the Ligand Effect on the Original Activity of Rh-Catalyzed Formaldehyde Hydroformylation

This study performs a computational examination of the effect of the ligand nature on the Rh–L interaction and of the formaldehyde hydroformylation for substituted rhodium–carbonyl catalysts using a range of realistic mono- and bidentate ligands (CO, P­(OMe)₃, PPh₃, DMI, and DPPE). The energy decomposition analysis of the Rh–L bond suggests the bidentate ligand, DPPE, shows the strongest interaction with Rh. The π-accepting capacity of monodentate ligands follows the sequence CO > P­(OMe)₃ > PPh₃ > DMI. Analysis of the potential energy surface reveals the σ-donor ligands serve to increase the energy of the active anionic complex [Rh­(CO)₃L]⁻. No clear correlation has been found between the CO insertion/hydrogenolysis energy barrier and electronic properties of ligands, while the H₂ oxidative addition barrier increases with increasing the ligand’s electron donating capacity. The investigation on the effect of the ligand (PPh₃) coordination number demonstrates that the three-coordinated catalyst exhibits the highest energy barrier, and the influence of ligand steric hindrance on the H₂ oxidative addition can be ignorable.