Noncovalent immobilization of pyrene-terminated hyperbranched triazole-based polymeric ionic liquid onto graphene for highly active and recyclable catalysis of CO₂/epoxide cycloaddition

The first examples of bifunctional hyperbranched polymers (HBP) with high density ionic liquid (IL) moieties in the main chain and controllable amount of pyrene groups at the chain ends (Py-HBPIL) have been synthesized via a facile three-step procedure, which were then immobilized onto reduced graphene oxide (rGO) via π-π stacking interactions. Py-HBPIL(Br) bearing pyrene groups at 10% of the chain ends allowed the highest immobilization loading of 73% in weight. The resultant Py-HBPIL(Br)@rGO hybrid material displayed much better catalytic activity than ever reported for immobilized IL catalysts for coupling reaction between CO₂ and propylene oxide (PO), and it could be reused up to 6 times by simple filtration process without significant decline in activity. Furthermore, the combination of bifunctional HBP and π-π stacking immobilization may provide a general and versatile platform to design highly active, selective and recyclable catalysts for various chemical transformations.