Investigations of ligand backbone effects on bulky diarylmethyl-based nickel(II) and palladium(II) catalyzed ethylene polymerization and copolymerization

Recently, the sterically hindered ortho-dibenzhydryl or diarylmethyl-derived (CHPh2 or CHAr2 on the N-aryl ring) alpha-diimine nickel(II) and palladium(II) catalysts have received much attention due to their unique catalytic properties for olefin (co)polymerization. In this work, the synthesis and characterization of bulky diarylmethyl-derived Ni(II) and Pd(II) ethylene (co)polymerization catalysts containing a series of backbone substituents (H, CH3 and acenaphthene) were described. Substituent effect of the backbone on catalyst activity and stability, polymer molecular weight, polymer branching density and polar monomer incorporation were investigated in detail. Overall, acenaphthene-based Ni3 showed the highest catalytic activity and produced the polymer with the highest molecular weight in Ni(II) system, while CH3-based Pd2 showed the best catalytic property in Pd(II) system. The H-substituted Ni(II) and Pd(II) catalyst was notable in its low activity or no activity compared to the other substituted Ni(II) and Pd(II) catalyst. Most interestingly, Pd2 demonstrated highest polymerization activities under gas-phase conditions through the self-supported catalytic mechanism. (C) 2021 Elsevier B.V. All rights reserved.