Alkylphenyl-Substituted Bis(salicylaldiminato) Titanium Catalysts in Ethene Polymerization

Titanium complexes bearing anionic [N,O-] bidentate salicylaldiminato ligands were synthesized with excellent yields via one- or two-step processes. The common feature of these catalyst precursors is the presence of aliphatic substituents (adamantyl, benzyl, (CH2)(2)Ph, (CH2)(3)Ph, and i-Pr) at the aldimino moieties. X-ray structure analysis of the benzyl-substituted complex revealed a distorted octahedral geometry, wherein nitrogen and chlorine atoms form the basal plane while the oxygen atoms of the phenoxy moieties complete the coordination sphere of the Ti center by occupying the axial positions. However, according to dynamic H-1 NMR measurements, these complexes can possess different structural isomers in solution, even at room temperature. After MAO activation, the catalysts displayed a range of catalytic activities [3-1700 kg(PE)/(mol(Ti).h.bar)]. The complex with ethylphenyl substituents was the most active in the series. In general, the (CH2)(2)Ph- and (CH2)(3)Ph-substituted catalysts produce PE with unimodal molar mass distribution, while the benzyl-, adamantyl-, and isopropyl-substituted catalysts tend to produce high molar mass bimodal PE with low activity. Computational methods were used to interpret the polymerization results, particularly the catalytic activity.