Stable single-site organonickel catalyst preferentially hydrogenolyses branched polyolefin C-C bonds.

Current methods of processing accumulated polyolefin waste typically require harsh conditions, precious metals or high metal loadings to achieve appreciable activities. Here we examined supported, single-site organonickel catalysts for polyolefin upcycling. Chemisorption of Ni(COD) (COD, 1,5-cyclooctadiene) onto Brønsted acidic sulfated alumina (AlS) yields a highly electrophilic Ni(I) precatalyst, AlS/Ni(COD), which is converted under H to the active AlS/NiH catalyst. This single-site system exhibits unique hydrogenolysis selectivity that favours cleaving branched polyolefin C-C linkages, enabling the hydrogenolytic separation of polyethylene and isotactic polypropylene (iPP) mixtures. Moreover, AlS/NiH remains highly selective and active for hydrogenolysis of iPP admixed with polyvinyl chloride, and the spent catalyst can be repeatedly regenerated by AlEt treatment. Experimental mechanistic analysis and density functional theory modelling reveal a turnover-limiting C-C scission pathway featuring β-alkyl transfer and strong olefin binding. These results highlight the potential of nickel-based systems for the selective upcycling of complex plastic waste streams.