Highly Syndioselective Polymerization of 2-Vinylpyridine Catalyzed by Rare-Earth Precursors and Its Mechanistic Aspects

Precise control over stereoselective polymerization is crucial for regulating polymer properties. Poly(2-vinylpyridine) (P(2-VP)) represents an important class of polymeric materials. Despite extensive research on stereoregular P(2-VP)s driven by their potential outstanding properties, studies on highly syndiotactic P(2-VP) remain limited. Herein, we report the 2-vinylpyridine (2-VP) syndioselective polymerization catalyzed by quinolyl anilido-ligated rare-earth metal complexes. The stereoselectivity of the 2-VP polymerization is strongly influenced by the types of central metal. While scandium and lutetium complexes afford atactic P(2-VP), the yttrium analog could efficiently yield highly syndiotactic P(2-VP) (rr > 99%) with high molecular weights (2.2 × 104 to 31.8 × 104 g mol–1) and narrow molecular weight distributions (Mw/Mn = 1.2–2.4) for the first time. Density functional theory (DFT) calculations reveal that the syndioselectivity arises from the combined influence of ligand steric hindrance and the nature of the Y+ center, leading to the thermodynamically preferred formation of syndiotactic P(2-VP). We expect that these findings will provide valuable insights for the design of stereoselective catalysts and the synthesis of stereoregular polymers.