Titanium-Imido Complexes with Pendant Groups - Synthesis, Characterization, and Evaluation of Their Role as Precatalysts for Ethylene Polymerization

The synthesis of several anilines ((ArNH2)-N-PG) substituted in the ortho position with pendant groups (PGs, terminated by potentially coordinative arene, thienyl, furanyl, or pyridyl functionalities) was accomplished by a two-to five-step synthesis in good yields. The (ArNH2)-N-PG proligands were used for the preparation of titanium complexes starting from Ti(NMe2)(4) in the presence of excess Me3SiCl. Complexes of the general formula [Ti(NArPG)Cl-2(NHMe2)(x)] (x = 1, 2), which are supported by a terminal imido functionality, were obtained in 60-95% yield. The nature of the pendant group influences the coordination mode of the ligand. Although only monodentate imido linkages have been observed with ligands where PG is arene, thiophene, and furan, ligands with substituted pyridine sidearms lead to chelating imido-donor functionalities. The potential hemilabile behavior of some imido-donor ligands, which results from the reversible coordination of the side arm, was studied by variable-temperature H-1 NMR spectroscopy. These compounds were evaluated as precatalysts for ethylene polymerization with various aluminum cocatalysts. Ultrahigh molecular-weight (UHMW) polyethylenes were obtained. All compounds were fully characterized by spectroscopic methods (H-1 and C-13 NMR), and elemental analysis and some were also characterized by single-crystal X-ray diffraction.