A series of unsymmetrical α-diimine compounds L1–L5 bearing the dibenzhydryl substituent (−CH(Ph)₂) has been prepared and characterized by IR and NMR (¹H/¹³C) spectroscopy as well as by elemental analysis. Their corresponding nickel dibromide complexes (Ni1–Ni5) were synthesized and characterized, and single crystal X-ray diffraction studies on Ni4 and Ni5 were conducted. Upon activation with either MAO or MMAO, all nickel complexes exhibited high activity toward ethylene polymerization producing polyethylene of high molecular weight and with a high degree of branching. The polyethylene obtained using MAO possessed bimodal characteristics, whereas that resulting from the use of MMAO exhibited unimodal characteristics. Such observations indicate that the behavior of the active species can be readily controlled via the use of different co-catalysts.