Synthesis and characterization of phosphine-(thio)phenolate-based half-zirconocenes and their application in ethylene (co-)polymerization
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 (MW > 400000), while the Cp analogues displayed much higher activities at high temperature. Complex 3c with MMAO showed a maximum ethylene polymerization activity of 17580 kg molZr−1 h−1 at 75 °C. In addition, the Cp based complexes 3b–e could promote ethylene and 1-hexene copolymerization with high activities.