Syndioselective Ring-Opening Polymerization of β-Lactones Enabled by Dimethylbiphenyl-Salen Yttrium Complexes

Polyhydroxyalkanoates (PHAs) have served as promising alternatives to traditional petroleum-based plastics. Chemical synthesis of stereoregular PHAs via stereocontrolled ring-opening polymerization (ROP) of racemic β-lactones was a desired strategy with a formidable challenge. Herein, we developed a class of DiMeBiPh-salen yttrium complexes that adopted a <i>cis</i>-α configuration for stereoselective ROP of <i>rac</i>-β-butyrolactones (<i>rac</i>-BBL) and <i>rac</i>-β-valerolactone (<i>rac</i>-BVL). Notably, catalyst <b>Y5</b> promoted robust polymerization with TOF up to 10⁴ h^-1 and furnished syndiotactic P3HB, P3HV, and P(3HB)-<i>co</i>-P(3HV) copolymers with <i>P</i>_r values of up to 0.95. Varying the compositions in P(3HB)-<i>co</i>-P(3HV) copolymers offered an intriguing opportunity to fine tune the thermal properties. Our kinetic study supported a polymeryl exchange mechanism. This work demonstrated that the DiMeBiPh-salen system could serve as a new catalytic framework for the stereoselective ROP of β-lactones, which leverages the catalyst design for stereoselective polymerization.