New titanium complexes having two pyrrolide-imine chelate ligands: Syntheses, structures, and ethylene polymerization behavior

New titanium complexes 1-4 having two nonsymmetric bidentate pyrrolide-imin e chelate ligands, [2-(RNCH)C4H3N](2)TiCl2 (1, R = Ph; 2, R = Et; 3, R = n- hexyl; 4, R = cyclohexyl), are prepared in good yields from the lithium sal t of the corresponding ligands and TiCl4. Complex I is suggested by DFT cal culations to adopt a distorted-octahedral structure in which the two pyrrol ide-N atoms are situated in trans positions, while the two imine-N atoms an d the two Cl atoms are located cis to one another. The spatial disposition elucidated by X-ray crystallographic analysis of complex 1 is consistent wi th the preferred structure predicted by DFT calculations. The molecular str uctures of complexes 2 and 4 established by X-ray analyses are very similar to that of complex 1. DFT calculations suggest that an active species deri ved from complex 1, for ethylene polymerization, possesses cis-located acti ve sites trans to the imine-N atoms. These complexes were investigated as e thylene polymerization catalysts. Using methylalumoxane (MAO) as a cocataly st, these complexes display very high activities and produce high-molecular -weight polyethylenes. Among them, complex 4 exhibits the highest activity (14 100 kg of polymer/((mol of Ti) h) comparable to that of Cp2TiCl2 with a very high molecular weight (M-v) value of 2 601 000. Alternatively, using Ph3CB(C6F5)(4)/i-Bu3Al as a cocatalyst, these complexes produce ultrahigh-m olecular-weight polyethylenes (M-v > 4 000 000) with high activities (1500- 2000 kg of polymer/((mol of Ti)/h).