Evolving Cyclopropenium Derivatives into High-Performance Bifunctional Organocatalysts towards Ring-Opening Alternating Copolymerization

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 triamino-cyclopropenium (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 remarkable air stability to CPI-B. 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.