Synthesis and characterization of fluoro-substituted β-enaminoketonato titanium complexes and their catalytic behavior of regioselective ethylene/cyclopentadiene copolymerization

The ethylene/cyclopentadiene (CPD) copolymerization behavior by using fluoro-substituted bis(beta-enaminoketonato) titanium complexes [FC6H4NC(CH3)CHCO(CF3)](2)TiCl2 (1a-1c) has been investigated in detail. Upon utilizing MMAO as a cocatalyst, complexes 1a-1c exhibit high catalytic activities, affording the copolymers with high molecular weight and unimodal molecular weight distribution. Compared with non-substituted complex [C6H5NC(CH3)CHCO(CF3)](2)TiCl2 (1), complexes 1a-1c can produce the copolymers with CPD incorporation adjusted in a wide range due to the enhancement of electrophilicity of metal center caused by introducing electron-withdrawing groups. Especially complex 1c bearing fluorine at the para-position of N-aryl moiety provides the highest CPD incorporation, which is nearly two times (18.5 mol%) higher than the non-substituted complex 1 (8.9 mol%) under the same conditions. The highest CPD incorporation up to 24.6 mol% can be easily achieved using this complex. H-1- and C-13-NMR spectra demonstrate that these fluoro-substituted complexes possess regioselective nature with exclusive 1,2-insertion fashion, and alternating ethylene-CPD sequence can be detected at high CPD incorporation.