2-Aldiminophenoxytitanium chloride complexes: Synthesis, characterization, and ethylene (co-)polymerization behavior

A series of trichlorotitanium 2-aldiminophenoxylate complexes (C1–C6) was synthesized by the stoichiometric reaction of TiCl4(THF)2 with the potassium salts of 6-alkyl-2-aldiminophenolates derived from ligands (L1–L6) bearing a bulky benzhydryl substituent, whereas the bis(2-aldiminophenoxy)titanium dichloride (C7) was isolated in the reaction of a ligand L6 with 0.5 equivalents of TiCl4(THF)2. All titanium complexes were characterized by 1H/13C NMR spectroscopy and elemental analysis. Single-crystal X-ray diffraction revealed distorted octahedron geometries around the titanium center for complexes C2, C4 and C7. Upon activation with the co-catalyst MAO, all titanium pre-catalysts exhibited good to high activities (up to 1.3 × 106 g mol (Ti)−1 h−1) for ethylene polymerization at 70 °C, producing polyethylene products with high molecular weights. Furthermore, co-polymerization of ethylene with either α-olefins or norbornene was achieved with activities in the range of 105 g mol (Ti)−1 h−1 by these titanium pre-catalysts along with good incorporation of co-monomer, typically 4.5 mol % for 1-hexene or 13.5 mol % for norbornene, respectively.

Graphical abstractA series of 2-aldiminophenoxylate titanium complexes containing the bulky CHPh2 group were prepared and fully characterized. The bulky ligands enhanced the stability of their mono-ligated titanium complexes, which exhibited good activities toward both ethylene homo-polymerization and co-polymerization.Figure optionsDownload full-size imageDownload as PowerPoint slideHighlights► Bulky ligands stabilize 2-aldiminophenoxytitanium chloride. ► Mono-ligated and bis-ligated N,O-bidentate titanium chlorides. ► Good activity for ethylene homo-polymerization. ► Good activity for ethylene co-polymerization. ► High incorporation of norbornene in the copolymer.