A Mechanistic Study of Ni‐catalyzed Carbon Dioxide Coupling with Ethylene towards the Manufacture of Acrylic Acid

Abstract

Abstract The reaction mechanism of CO 2 coupling with C 2 H 4 by homogeneous Ni‐complexes bearing bidentate phosphorous ligands was studied by means of density functional theory calculations. The reaction is initiated by sequential coordination of C 2 H 4 and CO 2 to the Ni center, followed by a facile coupling step, which results in a stable nickelalactone intermediate. Subsequent decomposition of this intermediate through β ‐H transfer is the rate‐determining step. Together with the following reductive elimination step to form acrylic acid they represent a strongly kinetically‐hampered process. Destabilization of the nickelalactone intermediate in the presence of large bite angle bidentate ligands has only a minor effect on the overall reaction energetics. Modifying the electronic properties of ligands is also not effective to drive the reaction in a catalytic manner. These studies indicate that the coupling reaction has to be enforced through an alternative route. It is predicted here that a base‐assisted decomposition of the nickelalactone intermediate represents a favorable reaction channel. The factors affecting the reactivity of this route are investigated. The best reactivity corresponds to the CH 3 OH‐solvated CH 3 ONa that allows the β ‐H transfer step to proceed with a barrier of only 49 kJ mol −1 .