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-R(1)-4-R(2)-6-(PPh2)C6H2] (Cp' = C5Me5, 2a: X = O, R(1) = Ph, R(2) = H; 2b: X = O, R(1) = (t)Bu, R(2) = H; 2c: X = O, R(1) = R(2) = (t)Bu; 2d: X = O, R(1) = SiMe3, R(2) = H; 2e: X = S, R(1) = SiMe3, R(2) = H; Cp' = C5H5, 3b: X = O, R(1) = (t)Bu, R(2) = H; 3c: X = O, R(1) = R(2) = (t)Bu; 3d: X = O, R(1) = SiMe3, R(2) = H; 3e: X = S, R(1) = SiMe3, R(2) = H) have been synthesized in high yields (74-85%). These complexes were identified by (1)H, (13)C and (31)P 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.