Novel Insight for Acrylate Formation Using CO2/Ethylene Coupling

Abstract

The acrylic acid formation through CO₂/ethylene coupling has significant industrial interest. The nickel complexed with a 1,2-bis(dicyclohexylphosphino)ethane ligand with acid/base pair additives is a proven catalyst for this chemistry. However, the role of additives is under debate. This study highlights the mechanistic aspects of catalyst activation and product formation and the specific role of each additive components using density functional theory calculations. The experimental and theoretical studies indicate that a LnNethylene complex (M1) is the active form of the catalyst and captures a CO₂ molecule, which reductively couples with ethylene to produce a metallalactone (M2). Conceptually, several reaction pathways can emerge from this metallalactone intermediate. However, in terms of energy efficiency, the preferred pathway seems to be a base-assisted enolization (keto-enol transformation) involving a direct proton transfer from β-carbon to carbonyl oxygen, without metallic interference. This finding contrasts with the classical notion of a β-hydride transfer to a metal. In this transformation, a Lewis acid also plays a crucial role of weakening the metal–oxygen bond, while new ethylene coordination facilitates product elimination. The theoretical and experimental evidence highlights the specific roles of the Lewis acid/base pair. This novel mechanism provides anintriguing opportunity to reevaluate this chemistry.