Facile Synthesis of Syndiotactic Polyhydroxyalkanoates Enabled by Stereoselective Copolymerization of <i>Rac</i> -epoxides with Carbon Monoxide

Polyhydroxyalkanoates (PHAs) have served as promising alternatives to traditional petroleum-based plastics. Chemical synthesis of stereoregular PHAs via stereoselective copolymerization of <i>racemic</i>-epoxides with carbon monoxide (CO) has not yet been achieved. Here, the design of trimetallic ligand platform featuring various electronic nature and steric demand enables Cr^III-catalyzed stereoselective copolymerization of <i>racemic</i>-epoxides with CO, yielding 9 types of functionalized PHA products having 0.70 syndiotacticity. Kinetic study has revealed that trimetallic complex favored the intramolecular chain propagation for the preparation of high molecular weight PHAs with high reactivity and moderate syndiotacticity, while monometallic complex promoted the intermolecular chain propagation toward isotactic-enriched PHAs.