Syntheses, Characterization, and Ethylene Polymerization of Titanium Complexes with Double-Duty Tridentate [ONN] Ligands

A series of titanium complexes containing the tridentate [ONN] ligands LaLf were synthesized and characterized. The ligands Lb (8-quinolinolato-CH2NHAr; Ar = 2,6-diisopropylphenyl) has been prepared by the reduction of the corresponding imino-quinolinol compound La (8-quinolinolato-CHNAr; Ar = 2,6-diisopropylphenyl) with LiAlH4 in high yield. Ligands Lc–Lf were synthesized by a procedure similar to that used to prepare ligand Lb. Reaction of TiCl4 with imino-quinolinol ligand La affords the six-coordinate trichloride titanium complex 1. The selective synthesis of tri- and dichlorotitanium complexes containing ligand Lb was achieved by changing the base for deprotonation. When it is deprotonated by NaH, ligand Lb can be used as a tridentate monoanionic ligand to synthesize trichlorotitanium complex 2. While deprotonated by nBuLi, it can be used as a tridentate dianionic ligand to synthesize dichlorotitanium complex 3. Other dichlorotitanium complexes 47 were synthesized by a procedure similar to that used to prepare complex 3. All complexes have been characterized by 1H NMR spectra and elemental analysis. The molecular structures of ligand Lb and complex 1 have been characterized by single-crystal X-ray diffraction analyses. XANES and EXAFS spectroscopy performed on the representative complexes 2 and 3 reveals the different coordination geometries. When they are activated by excess methylaluminoxane (MAO), all of the titanium complexes can be used as catalysts for ethylene polymerization and exhibit moderate to good activities. It was found that the catalytic behaviors of the title complexes were highly affected by the coordination entironment of the metal center and the effect of substituent groups on ligands.