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)₂ (COD, 1,5-cyclooctadiene) onto Brønsted acidic sulfated alumina (AlS) yields a highly electrophilic Ni(I) precatalyst, AlS/Ni(COD)₂, which is converted under H₂ to the active AlS/Ni^IIH 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/Ni^IIH remains highly selective and active for hydrogenolysis of iPP admixed with polyvinyl chloride, and the spent catalyst can be repeatedly regenerated by AlEt₃ 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.