Nickel(II) complexes with imino-imidazole chelating ligands bearing pendant donor groups (SR, OR, NR2, PR2) as precatalysts in ethylene oligomerization

New imino-imidazole ligands bearing a pendant donor function L were synthesized in excellent yields. The corresponding nickel(II) complexes [NiCl2(imino-imidazole-L)]n (L = (CH2)2SMe (2a), (CH2)2OMe (2b), (CH2)2NEt2 (2c), (CH2)2PPh2 (2d), (C6H4)-p-OMe (2e), (CH2)3OMe (2f), (CH2)3CH3 (2g); n = 1, 2) were prepared and characterized by FT-IR spectroscopy and elemental analysis. Furthermore, the coordination geometry around the metal center in the dinuclear complex 2a and the mononuclear complexes 2c and 2e was unambiguously established by single crystal X-ray diffraction. All complexes have been evaluated for the oligomerization of ethylene in the presence of EtAlCl2 or MAO (methylaluminoxane) as cocatalyst, and mostly dimers and trimers were produced. Better activities were observed with EtAlCl2 as cocatalyst than with MAO.