Aggregate Catalysts: Regulating Multimetal Cooperativity for CO₂/Epoxide Copolymerization

Biomimetic aggregates have flourished in various fields, particularly in small-molecule catalysis, but their application in polymer synthesis remains understudied. Herein, we propose a strategy for constructing aggregate catalysts based on aggregation-regulating cooperativity to enhance the copolymerization of CO2/propylene oxide (PO). The key design strategy involves constructing polymeric aluminum porphyrin catalysts (PAPCs) with varied stacking modes induced by substituents' electronic effects, enabling effective modulation of metal synergism. PAPCs with -Cl and -Br substitution exhibit H-aggregates of porphyrin units, leading to a strong metal synergy effect and stability at high temperatures. The H-aggregate catalysts show high activity (TOF > 10,000 h(-1)) and high selectivity (>98%). Meanwhile, the activity was maintained at a very low catalyst loading ([Al]/PO = 1/100,000), with the number-average molecular weight of the resulting copolymer over 480 kg/mol. Contrarily, -CH3- and -CH2CH3-substituted PAPCs display J-aggregates with a weak metal synergy effect (unstable at a high temperature). The J-aggregate catalysts show low activity (TOF < 2500 h(-1)) and polymer selectivity (<90%). The present strategy of designing aggregate catalysts provides a new perspective to regulate metal cooperativity, suitable not only for CO2/epoxide or anhydride/epoxide copolymerization but also for lactone ring-opening polymerizations.