A series of 2-(1-(arylimino)ethyl)-8-arylimino-5,6,7-trihydroquinolylcobalt dichloride (aryl = 2,6-R-1-4-R-2 C-6 H-2) pre-catalysts were synthesized and structurally characterized by FT-IR and elemental analyses. The molecular structures of Col (R-1 = Me, R-2 = H), Co2 (R-1 = Et, R-2 = H) and CoS (R-1 = Et, R-2 = Me) were determined by single-crystal X-ray diffraction analysis, and confirmed Col as a distorted trigonal bipyramidal geometry at the metal, whilst in Co2 and Co5 the metal is square-pyramidal. Upon treatment with either MAO or MMAO, all cobalt pre-catalysts exhibited highest activities at 60 degrees C for ethylene polymerization. The resultant polyethylenes, under optimization reaction parameters, possessed low molecular weight (waxes) and narrow polydispersity. (c) 2012 Elsevier B.V. All rights reserved.