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.