Highly Syndiotactic or Isotactic Polyhydroxyalkanoates by Ligand‐Controlled Yttrium‐Catalyzed Stereoselective Ring‐Opening Polymerization of Functional Racemic β‐Lactones

Reported herein is the first stereoselective controlled ROP of a specific family of racemic functional β‐lactones, namely 4‐alkoxymethylene‐β‐propiolactones (BPL OR s). This process is catalyzed by an yttrium complex stabilized by a nonchiral tetradentate amino alkoxy bisphenolate ligand {ONOO R′2 } 2− , which features both a good activity and a high degree of control over the molar masses of the resulting functional poly(3‐hydroxyalkanoate)s. A simple modification of the R′ substituents in ortho and para position on the ligand platform allows for a complete reversal from virtually pure syndioselectivity (P s up to 0.91 with R′=cumyl) to very high isoselectivity (P i up to 0.93 with R′=Cl), as supported by DFT insights. This is the first example of a highly isoselective ROP of a racemic chiral β‐lactone.