Evolving Cyclopropenium Derivatives into Highly Active and Air-Stable Bifunctional Organoborane Catalysts towards Ring-Opening Alternating Copolymerization.
C. Wu, X. Song, Q. Han, R. Zhong*, X. Wang*, Z. Li*, Y. Liu*
CCS Chem. 2025, DOI:10.31635/ccschem.025.202505613.
Abstract： Bifunctional catalysts, known for their superior activity and selectivity compared to binary systems, hold great promise for ring-opening copolymerization (ROCOP). Here, we present our recent advancements in developing high-performance bifunctional organocatalysts by integrating borane with triaminocyclopropenium (TAC) derivatives. Specifically, we developed a bifunctional catalyst by conjugating 9-borabicyclo[3.3.1]nonane (9-BBN) with TAC-Cl through an optimized alkyl linker ( TB-3). This catalyst exhibited outstanding performance in the controlled ROCOP of epoxides and anhydrides, demonstrating high activity, selectivity, and thermal stability, and outperforming both binary catalytic systems and quaternary ammonium-borane analogues. Notably, further transformation of the TAC moiety into its cyclopropenimine (CPI) derivative led to the creation of a cyclopropenimine-borane bifunctional organocatalyst ( CPI-B). The strong yet dissociative intramolecular N-B coordination between the CPI and BBN units imparts exceptional air stability to CPI-B, effectively addressing the challenging issue of air sensitivity commonly associated with conventional organoborane catalysts. Additionally, the N/B Lewis pair in CPI-B effectively activates protic initiators, enabling precise control over end-group functionality and polymer topology in ROCOP. These advancements significantly broaden the practical utility of CPI-B in polymer synthesis.
