Aggregate Catalysts: Regulating Multimetal Cooperativity for CO₂/Epoxide Copolymerization

Abstract

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 aggregationregulating cooperativity to enhance the copolymerization of CO 2 / 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, −CH 3 -and −CH 2 CH 3 -substituted PAPCs display J-aggregates with a weak metal synergy effect (unstable at a high temperature). The Jaggregate 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 CO 2 /epoxide or anhydride/epoxide copolymerization but also for lactone ring-opening polymerizations.

Rigid-Flexible Binuclear Catalysts: Boosting Activity for Copolymerization of CO2 and Propylene Oxide

“…An elevation in the reaction temperature from 70 to 100 °C, 120 °C, and then to 140 °C led to a notable enhancement in the catalytic activity from 5000 to 20000 h –1 , 19000 h –1 , and then to 25200 h –1 , respectively (Table , entries 2, 5–7). Furthermore, polymer selectivity was maintained at a high level (>90%), outperforming the previously reported polymeric aluminum catalyst (polymer selectivity% = 81%, TOF = 12600 h –1 , 130 °C) . Owing to the use of rigid skeleton and the π–π interactions between porphyrin units, the catalyst demonstrates resilience to elevated temperatures of up to 160 °C without significant activity drop (Figure c), but it displays limited selectivity toward polymers (76%).…”

“…As depicted in Figure b, the Soret band (400–440 nm) of RFBCs exhibits a significantly broader profile with a shoulder peak, in contrast to m-Al. This observation implies that the two porphyrin units are spatially conjugated and adopt a face-to-face configuration. ,, Significantly, when the distance between the porphyrin units is reduced, the Soret band absorption of RFBCs widens, suggesting an increasing synergy. Both UV–vis and 1 H NMR spectra demonstrated an enhancement in the intramolecular synergy of RFBCs as the proximity between the two porphyrins increased (Figure c).…”

Highly active aggregate catalysts for the synthesis of high-molecular-weight polyesters via copolymerization of epoxides and cyclic anhydrides

“…Previous research has indicated that electron-withdrawing/donating substituents on porphyrins influence π–π interactions and induce distinct stacking modes, such as H-aggregation (face-to-face arrangement) or J-aggregation (edge-to-edge arrangement). 35–37 In this study, using porphyrin monomers carrying –Cl and –Me substituents, we synthesized H-aggregate catalysts (PAPC-Cl) with strong interaction and J-aggregate catalysts (PAPC-Me) with weak interaction, respectively (Scheme S1 and Fig. S1–S13†).…”

“…Our recent studies have shown that interactions between the porphyrins in individual polymer chains are more efficient at ultra-dilute catalyst concentrations and high temperatures. 35 This insight is crucial for understanding synergistic effects in copolymerization reactions. In conclusion, the construction of these two aggregate catalysts (H- and J-aggregate) set the stage for investigating synergistic effects in polymerization reactions of cyclic anhydrides and epoxides.…”

“…Inspired by the multiple cooperative catalysis of enzymes, our group reported a series of aggregate catalysts featuring multiple active sites. 31–35 The key design concept of aggregate catalysts is to transform conventional monomeric aluminum porphyrin catalysts (MonoAl) into polymeric aluminum porphyrin catalysts (PAPCs). This transformation aims to achieve the aggregation of active centers, enhancing the synergistic effect.…”