Bis(imino)pyridine ligands, L [where L=2,6-(ArNCR1)(2)C5H3N R-1=Et, Pr-i, CH2CH2Ph or CH(CH2Ph)(2) and Ar=2,4,6-(Me)(3)C6H2 (MES) or 2,6-(Pr-i)(2)C6H3 (DIPP)] have been prepared by deprotonation of the parent ketimine ligand (R-l =Me) using lithium diisopropylamide (LDA), followed by alkylation with the appropriate alkylhalide. The corresponding iron dichloride complexes LFeCl2 are highly active ethylene polymerisation catalysts upon treatment with methylaluminoxane (MAO), with activities in the range of 3000-18,000 g/mmol bar h. The molecular weights (M-n) of the resultant polyethylenes lie in the range of 6500-24,000 with broad molecular weight distributions (16.5-38.0). The nature of the imine carbon substituent has a marked effect on the polymer molecular weight whereas the catalyst activity is largely unaffected by changes to this substituent. (c) 2006 Elsevier B.V. All rights reserved.