Pentamethylcyclopentadienyltitanium aryl(pyridyl)amide complexes: Synthesis, characterization and catalytic performance for olefin polymerization

Abstract

A series of new half-sandwich pentamethylcyclopentadienyl titanium (IV) aryl(pyridyl)amide complexes, Cp*TiCl2[N(Ar)(2-Py)] [Ar = 2,6-iPr2Ph (1), 2,6-Et2Ph (2), 2,6-Me2Ph (3), 4-MePh (4)], have been synthesized from the reactions of Cp*TiCl3 with the lithium salts of the corresponding aryl(pyridyl)amido ligands in toluene. A byproduct with two aryl(pyridyl)amido ligands, Cp*TiCl[N(4-MePh)(2-Py)]2 (5) was also obtained from the synthetic reaction of complex 4 in a small amount. The new titanium complexes 1–4 were characterized by 1H and 13C NMR and elemental analyses. The molecular structures of complexes 1, 2, 4 and 5 were determined by single-crystal X-ray diffraction analysis. X-ray crystallographic analysis on complexes 1, 2, 4 demonstrates that these complexes possess a relatively crowded hepta-coordinating environment surrounding the central titanium atom. Upon activation with AliBu3 and Ph3CB(C6F5)4, complexes 1–4 exhibited moderate to high catalytic activity for ethylene and propylene polymerization, producing high molecular weight linear polyethylene and atactic polypropylene. It was found that complex 1 shows the highest catalytic activity for ethylene polymerization while complex 4 shows the highest catalytic activity for propylene polymerization among these complexes under similar conditions.