LAUSR

Abstract The aldehyde hydroformylation is of critical importance for synthesis of higher aldehydes and polyhydric alcohols, but the reaction mechanism has not been clearly resolved in the existing literature. In this paper, we have established the dissociation and anion mechanism for formaldehyde hydroformylation using DFT calculation and experimental study. In the dissociation mechanism, HCHO insertion into the Rh-H bond is the rate-controlling step and CH3OH, HCOOCH3 are preferentially produced via the CH3O-Rh route. The CO coordination reaction of CH3O-Rh(CO)2(PPh3) is not favored energetically leading to facile generation of CH3OH relative to HCOOCH3. In the anion mechanism, the nucleophilic addition of HCHO to the HOCH2-Rh species is more energetically favorable and the rate-determining step turns to H2 oxidation addition. The effective energy barrier of hydrogenolysis for CH3OH is higher than that for HOCH2CHO, accounting for higher selectivity of HOCH2CHO than CH3OH observed in the reaction. The calculations also predict the strong electron-donating ligand serves to give rise to higher reactivity in the anion mechanism.