Formation of Acrylates from Ethylene and CO2 on Ni Complexes: A Mechanistic Viewpoint from a Hybrid DFT Approach
Résumé
The most challenging step in the production of acrylates from
ethylene and CO2 mediated by transition-metal complexes is the release of
the acrylate from the metallalactone intermediate formed by coupling of
ethylene and CO2. Recently, methyl acrylate formation was achieved from
nickelalactones by using methyl iodide (MeI) as the electrophile, and the
yield was tuned with different amine and phosphine ligands. Modeling
organometallic catalysts with such large ligands accurately is a challenge for
computational chemistry. A hybrid approach has been designed here by
coupling the double hybrid XYG3 and the hybrid B3LYP exchange
correlation functionals, using the extended ONIOM scheme. This approach
was then applied to explore the role of the MeI electrophile for the formation
of methyl acrylate from the initial nickelalactone complex and to rationalize
the effect of the ligands on the yield of methyl acrylate. We show that the
choice of ligand has little effect on the main productive pathway. However, it has a significant influence on side reactions, which compete with the productive pathway and are detrimental to methyl acrylate formation. Finally, the need for a very large overstoichiometry of MeI for a good yield of methyl acrylate is explained by the lower polarity of MeI, which avoids the stabilization of nonproductive intermediates. The nature of the limiting intermediates has been validated by comparing calculated and experimental vibrational spectra.