Synthesis, structure and ethylene (co)polymerization behavior of new nonbridged half-metallocene-type titanium complexes based on bidentate β-enaminoketonato ligands

A series of novel half-metallocene-type titanium complexes CpTiCl2[PhNC(R2)CHC(R1)O] (2a, R1 = Cy, R2 = CF3; 2b, R1 = tBu, R2 = CF3; 2c, R1 = Ph, R2 = CF3; 2d, R1 = Ph, R2 = CH3) have been synthesized by treating CpTiCl3 with the corresponding bidentate β-enaminoketonato ligands PhNC(R2)CHC(R1)OH in the presence of triethylamine. Single crystal X-ray diffraction revealed that complex 2b adopts distorted square-pyramid geometry around the titanium center. The complexes 2a–d were investigated as the catalysts for ethylene polymerization and the copolymerization of ethylene with norbornene. All the complexes were active towards ethylene (co)polymerization in the presence of modified methylaluminoxane, and produced high molecular weight (co)polymers. The catalytic activity and the norbornene incorporation were highly dependent upon catalyst and reaction conditions employed. Among four complexes, 2c exhibited both high catalytic activity and efficient norbornene incorporation under the same conditions, affording high molecular weight copolymers with unimodal molecular weight distributions.