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PNNP-iridium: A prototypical catalyst framework tailored for diverse hydrogenative depolymerization of polyesters
Summary
Chemists developed a family of iridium-based catalysts that can chemically break polyesters—including PET plastic from bottles—back into their building-block chemicals under mild, potentially solvent-free conditions, enabling chemical recycling rather than downcycling or landfill disposal. Preventing plastic from fragmenting into microplastics in the first place, by recycling it efficiently at the chemical level, is a complementary strategy to cleanup. While this is early-stage chemistry, it demonstrates a versatile platform for upcycling plastic waste into valuable feedstocks.
Abstract Growing concern over marine- and microplastic pollution has intensified the need for efficient polymer upcycling strategies. Herein, we report a family of iridium complexes bearing a PNNP tetradentate ligand, ((PNNP)Ir), as a versatile prototypical platform for the hydrogenative depolymerization of polyesters. Systematic modification of the bipyridine and phosphine substituents enables the conversion of a broad range of polyesters, including commodity plastics, into diols under mild and even solvent-free conditions. Notably, selective semi-hydrogenation of poly(ethylene terephthalate) (PET) is achieved through fine-tuning of the (PNNP)Ir framework. While fully hydrogenative depolymerization proceeds via direct H₂ addition, semi-hydrogenation operates through a H2-free, transfer-hydrogenation pathway. As a result, (PNNP)Ir complexes can utilize diverse hydrogen sources, and both reaction modes are readily extended to deuteration. These findings establish (PNNP)Ir as an exceptionally versatile and pertinent scaffold for the upcycling of polyesters into value-added chemical feedstocks.