Catalytic Synthesis of a Methylmalonate Salt from Ethylene and Carbon Dioxide through Photoinduced Activation and Photoredox-Catalyzed Reduction of Nickelalactones

Catalytic 1,1-dicarboxylation of ethylene with CO₂ to form a methylmalonate salt was achieved by a Ni/Ir dual-catalyst system under photoirradiation conditions. In this reaction, photoenergy was utilized not only for the reduction of the methylmalonate Ni­(II) complex but also for the transformation of the nickelalactone to the methylmalonate complex. By careful mechanistic investigations, it was revealed that photoirradiation promotes not only isomerization of five-membered to four-membered nickelalactones but also insertion of the second molecule of CO₂ to form methylmalonate complexes via triplet excited states of the four-membered nickelalactones. This is an unprecedented example of catalytic methylmalonate synthesis from ethylene and CO₂.