Synthesis and characterization of phosphine-(thio)phenolate-based half-zirconocenes and their application in ethylene (co-)polymerization

Abstract

A series of novel half-zirconocenes containing phosphine-(thio)phenolate chelating ligands of the type Cp′Zr(thf)Cl₂[X-2-R¹-4-R²-6-(PPh₂)C₆H₂] (Cp′ = C₅Me₅, 2a: X = O, R¹ = Ph, R² = H; 2b: X = O, R¹ = ^tBu, R² = H; 2c: X = O, R¹ = R² = ^tBu; 2d: X = O, R¹ = SiMe₃, R² = H; 2e: X = S, R¹ = SiMe₃, R² = H; Cp′ = C₅H₅, 3b: X = O, R¹ = ^tBu, R² = H; 3c: X = O, R¹ = R² = ^tBu; 3d: X = O, R¹ = SiMe₃, R² = H; 3e: X = S, R¹ = SiMe₃, R² = H) have been synthesized in high yields (74–85%). These complexes were identified by ¹H, ¹³C and ³¹P NMR as well as elemental analyses. Structural analysis for 2a–b and 2d revealed that these complexes adopt six-coordinate, distorted octahedral geometry around the zirconium center. These novel half-zirconocenes possessed high catalytic performance for ethylene polymerization at high temperature in the presence of MMAO. The phosphine-phenolate-based Cp* complexes produced high molecular weight polymers (M_W > 400 000), while the Cp analogues displayed much higher activities at high temperature. Complex 3c with MMAO showed a maximum ethylene polymerization activity of 17 580 kg mol_Zr⁻¹ h⁻¹ at 75 °C. In addition, the Cp based complexes 3b–e could promote ethylene and 1-hexene copolymerization with high activities.