Nickel(0)/Phosphine-Catalyzed Copolymerization of CO₂ and Cyclohexylallene to Degradable Long-Chain Polyesters

Developing efficient strategies to copolymerize carbon dioxide (CO₂) with unsaturated hydrocarbon monomers, such as olefins, to produce CO₂-based polyesters is highly desirable but remains challenging owing to thermodynamic and kinetic barriers. Herein, we demonstrate that allenes, specifically cyclohexylallene (CA), serve as effective comonomers for one-pot copolymerization with CO₂. Using a nickel(0)-bidentate diarylphosphine complex, we achieve the statistical copolymerization of CA and CO₂ to deliver long-chain polyester P(CA-co-CO₂) with widely spaced ester linkages, via a classical sequence of oxidative addition, coordination-insertion, and reductive elimination. Systematic tuning of both phosphine ligand and solvent reveals their crucial roles in facilitating CO₂ insertion into the Ni-C bond and subsequent allene insertion into the Ni-O bond, thereby driving efficient chain propagation. Notably, incorporation of a small amount of CO₂ into the polymer backbone enhances the degradability of P(CA-co-CO₂) while preserving its high thermal stability and glass-transition temperature, compared with the allene homopolymer.