Liberation of acrylates from nickelalactones via Ni─O ring opening with alkyl iodides

Mechanistic study on the formation of the alkyl acrylates from CO2, ethylene and alkyl iodides over nickel-based catalyst

The catalytic conversion of carbon dioxide (CO2) and olefins into acrylates has been a long standing target, because society attempts to synthesize commodity chemicals in a more economical and sustainable fashion. In this work, two alkylation reaction pathways were investigated to explore the role of methylene linkage (-CH2-) on the formation of alkyl acrylate from coupling of CO2 and ethylene, catalyzed by a nickel catalyst in the presence of different alkyl iodides. The energy barrier of Ni-O bond cleavage decreases with increasing methylene linkage of alkyl iodides, which may be due to NPA charge transfer of alkyl iodides. Meanwhile, the O1 (ester sp3 O atom) attack route leading to the formation of alkyl acrylate competes with the O2 (carboxylic sp2 O atom) attack route in terms of energy barriers. Further studies on the fluoro-substituted alkyl acrylates show that neither CF3I nor CF3CH2I is effective in releasing trifluoroalkyl acrylates from the nickellacycle, which explains why only negligible amounts of the desired product were detected in the experiment. In addition, we investigated the non-productive pathways leading to byproducts, such as propionic acid, propionates and ion pair complexes, etc. By comparing the results obtained with CH3I, the use of C2H5I as an electrophilic reagent may stabilize the non-productive intermediates. The methylene linkage has little effect on the main productive pathway. However, it has a significant influence on the side reactions, which is detrimental to the formation of alkyl acrylate in competing with the main productive pathway.