Understanding the acrylates formation from CO2 and ethylene over Ni- and Pd-based catalysts: A DFT study on the effects of solvents, methyl halides, and ligands

• High polarity solvents can effectively promote both the M-O bond cleavage reaction and the β -H elimination. • All the transition states and the intermediates in Ni-mediated systems can be greatly stabilized in the presence of CH 3 I. • The energy barrier for M-O bond cleavage increases with the enhancement of the ligand steric hindrance in the O1 attack mechanism, while the corresponding O2 mechanism shows the opposite trend. In this work, two methylation reaction pathways were investigated to explore the role of solvent and I − on the formation of methyl acrylate from coupling of CO 2 and ethylene catalyzed by nickel and palladium catalysts in the presence of MeI. The stabilization of non-productive intermediates is inhibited in the gas phase as well as in low-polar solvents, which explains the requirement of high excess of MeI to obtain high yields of methyl acrylate. The energy barrier for M-O bond cleavage as well as the stability of the overall reaction intermediates is consistent with the corresponding halogen electron-donating ability. The different catalytic behaviors of various bidentate ligands on Ni- and Pd-based catalysts were systematically investigated, mainly including dmpe(1,2-bis(dimethylphosphino)ethane), tmeda(tetramethylethylenediamine), dppe(1,2-bis(diphenylphosphino)ethane), dcpe(1,2-bis(dicyclohexylphosphino)ethane) and dtbpe(1,2-bis(di-tert-butylphosphino)ethane). The energy barrier of M-O bond cleavage increases with the enhancement of ligand steric hindrance in the O1 (ester sp 3 O atom) attack mechanism, while the corresponding O2 (carboxylic sp 2 O atom) attack mechanism shows an opposite trend. The energy barrier of β -H elimination in both catalytic systems is strongly related to the electron-donating ability of the diphosphine ligand substituents. The dcpp(1,3-bis(dicyclohexylphosphino)propane) ligand shows relatively good performance for β -H elimination among all the investigated ligands in Pd-mediated system. In general, diphosphine ligands are superior to diamine ligands in Pd-mediated system in terms of efficiency.