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−imine chelate ligands, [2-(RNCH)C 4 H 3 N] 2 TiCl 2 ( 1, R = Ph; 2, R = Et; 3, R = n -hexyl; 4, R = cyclohexyl), are prepared in good yields from the lithium salt of the corresponding ligands and TiCl 4 . Complex 1 is suggested by DFT calculations to adopt a distorted-octahedral structure in which the two pyrrolide-N atoms are situated in trans positions, while the two imine-N atoms and the two Cl atoms are located cis to one another. The spatial disposition elucidated by X-ray crystallographic analysis of complex 1 is consistent with the preferred structure predicted by DFT calculations. The molecular structures 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 derived from complex 1, for ethylene polymerization, possesses cis-located active sites trans to the imine-N atoms. These complexes were investigated as ethylene polymerization catalysts. Using methylalumoxane (MAO) as a cocatalyst, 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 Cp 2 TiCl 2 with a very high molecular weight ( M v ) value of 2 601 000. Alternatively, using Ph 3 CB(C 6 F 5 ) 4 / i- Bu 3 Al as a cocatalyst, these complexes produce ultrahigh-molecular-weight polyethylenes ( M v > 4 000 000) with high activities (1500−2000 kg of polymer/((mol of Ti)/h).