Synthesis, characterization and efficient catalytic ethylene polymerization reactions of phenylphosphine half-metallocene zirconium complexes

Abstract

A series of half-metallocene zirconium complexes with phenylphosphine ligands, CpZr(thf)Cl₂[O-2-R₁-4-R₂-6-(PPh₂)C₆H₂] (2a: R₁ = ^tBu, R₂ = ^tBu; 2b: R₁ = C(CH₃)₂CH₂CH₃, R₂ = C(CH₃)₂CH₂CH₃; 2c: R₁ = ^tBu, R₂ = OCH₃; and 2d: R₁ = cumenyl, R₂ = OCH₃), were synthesized. Density functional theory calculations were conducted to investigate the structure of the cationic active species, revealing the impact of the complex structure on catalytic performance. By designing the catalyst structure and controlling the polymerization conditions, all four complexes demonstrated efficient ethylene polymerization. Notably, complex 2c exhibited an exceptionally high activity of 58 000 kg mol_Zr⁻¹ h⁻¹ for the homopolymerization of ethylene at 100 °C. Furthermore, complex 2c also demonstrated impressive activity of over 10⁴ kg mol_Zr⁻¹ h⁻¹ in the copolymerization of ethylene with norbornene or 1-hexene, with monomer incorporation rates reaching 56.2% for norbornene and 8.0% for 1-hexene. These findings indicated that the catalyst possessed high-temperature stability, outstanding catalytic activity, and excellent comonomer incorporation capabilities, holding significant potential in the polyolefin industry.