Nickel-Based Heterometallic Catalysts for Ethylene-Acrylate Copolymerization: Interrogating Effects of Secondary Metal Additives

A class of in situ-generated Ni-based multimetallic complexes based on a bisphosphine phenoxide ligand (POP) was studied for ethylene-acrylate copolymerization. Starting from a previously prepared Ni-POP complex, addition of several metal precursors results in coordination involving the second phosphine not bound to Ni. These isolated complexes show lower copolymerization activity compared to Ni-POP. Structural characterization of relevant bimetallic complexes shows ancillary ligand binding in a PO-bidentate fashion to each metal with phenoxide bridging. Additionally, halide bridges are observed in several complexes, highlighting a potential inhibition mechanism by binding to Ni. In contrast, in situ addition of Al(OiPr)3 as a secondary metal results in an increase in activity for ethylene/acrylate copolymerization while maintaining high levels of acrylate incorporation. Overall, these results demonstrate various effects in bimetallic systems for polymerization catalysis relevant to future catalyst design.