Solvent effect on mechanistic pathways in Rh-catalyzed hydroformylation of formaldehyde

The homogeneous catalytic hydroformylation of formaldehyde to glycolaldehyde is a key intermediate step for one-step synthesis of ethylene glycol from syngas. The effect of solvent nature on the catalytic response and mechanistic pathway has been rarely studied. A group of parameters (e.g., er, p, alpha, beta) describing the solvent electronic features were achieved for a descriptor database and correlated with the hydroformylation activity. The net electron donating ability has been found to govern the selectivity to glycolaldehyde. The DFT calculation demonstrates the stronger electron-donating solvents serve to lower the energy required for the dissociation of Rh-H to form the anionic rhodium species, which induces the anion mechanism that preferentially facilitates the glycolaldehyde generation. The polar aprotic solvents can be protonated in the dissociation of Rh-H to the anionic species and participate in the HCHO activation through the proton transfer from solvent molecules to HCHO, resulting in the formation of hydroxymethyl species.

Automated summary

The nature of the solvent has a significant impact on the activity and selectivity of the hydroformylation reaction. Solvents with stronger electron-donating ability lower the energy barrier for the reaction and promote the formation of glycolaldehyde. Polar aprotic solvents can participate in the reaction through proton transfer, leading to the formation of hydroxymethyl species.