Mechanistic insight into formaldehyde hydroformylation catalyzed by rhodium complexes: A theoretical and experimental study

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 CH 3 OH, HCOOCH 3 are preferentially produced via the CH 3 O-Rh route. The CO coordination reaction of CH 3 O-Rh(CO) 2 (PPh 3 ) is not favored energetically leading to facile generation of CH 3 OH relative to HCOOCH 3 . In the anion mechanism, the nucleophilic addition of HCHO to the HOCH 2 -Rh species is more energetically favorable and the rate-determining step turns to H 2 oxidation addition. The effective energy barrier of hydrogenolysis for CH 3 OH is higher than that for HOCH 2 CHO, accounting for higher selectivity of HOCH 2 CHO than CH 3 OH observed in the reaction. The calculations also predict the strong electron-donating ligand serves to give rise to higher reactivity in the anion mechanism.