Syndioselective Coordination (Co)Polymerization of Alkyne-Substituted Styrenes Using Rare-Earth Metal Catalysts

Developing convenient methods to introduce functional groups into syndiotactic polystyrene has gained increasing attention in recent years. Herein, we report the coordination polymerization of 4-(1-hexynyl)­styrene (HES), 4-(phenylethynyl)­styrene (PES), and 4-(trimethylsilyl)­ethynylstyrene (TES) with half-sandwich scandium precursor C₅Me₄PhSc­(CH₂C₆H₄NMe₂-o)₂ (1) and constrained-geometry-configuration (CGC) precursors C₁₃H₈CH₂PySc­(CH₂SiMe₃)₂ (2, Py = C₅H₄N) and 2,7-(^tBu)₂C₁₃H₈CH₂PyLn­(CH₂SiMe₃)₂(THF)_n (Ln = Sc (3a), n = 0; Y (3b), Lu (3c), n = 1). Under mild conditions, perfect syndiotactic products (rrrr > 99%) are produced by homopolymerizations of HES, PES, and TES. The random copolymerizations of TES and styrene (St) proceed smoothly with 3b, and the insertion fractions of TES are tuned in the range of 0–100 mol % via changing the TES-to-St feed ratio. The trimethylsilyl groups are facilely eliminated from the TES-based polymers by tetrabutylammonium fluoride to give terminal ethynyl-containing polystyrenes, the reactions of which with an azide compound, carbon dioxide, and anthracene-9-aldehyde afford a series of functional syndiotactic polystyrenes.