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

A series of titanium complexes containing the tridentate
[ONN]
ligands La–Lf 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 4–7 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.