Highly Selective O -Phenylene Bisurea Catalysts for ROP: Stabilization of Oxyanion Transition State by a Semiflexible Hydrogen Bond Pocket

作者：Jia Zhang, Kai Hin Lui, Rachele Zunino, Jia Yuan, Romain Morodo, Niklas Warlin, James L. Hedrick, Giovanni Talarico, Robert M. Waymouth · 发表于：Journal of the American Chemical Society · 年份：2024 · DOI：10.1021/jacs.4c04740 · 被引用次数：22 · 研究领域：Carbon dioxide utilization in catalysis、biodegradable polymer synthesis and properties、Click Chemistry and Applications

Organocatalyzed ring-opening polymerization (ROP) is a versatile technique for synthesizing biodegradable polymers, including polyesters and polycarbonates. We introduce o -phenylene bisurea (OPBU) (di)anions as a novel class of organocatalysts that are fast, easily tunable, mildly basic, and exceptionally selective. These catalysts surpass previous generations, such as thiourea, urea, and TBD, in selectivity ( k p / k tr ) by 8 to 120 times. OPBU catalysts facilitate the ROP of various monomers, achieving high conversions (>95%) in seconds to minutes, producing polymers with precise molecular weights and very low dispersities ( Đ ≈ 1.01). This performance nearly matches the ideal distribution expected from living polymerization (Poisson distribution). Density functional theory (DFT) calculations reveal that the catalysts stabilize the oxyanion transition state via a hydrogen bond pocket similar to the “oxyanion hole” in enzymatic catalysis. Both experimental and theoretical analyses highlight the critical role of the semirigid o -phenylene linker in creating a hydrogen bond pocket that is tight yet flexible enough to accommodate the oxyanion transition state effectively. These new insights have provided a new class of organic catalysts whose accessibility, moderate basicity, excellent solubility, and unparalleled selectivity and tunability open up new opportunities for controlled polymer synthesis.