In this work, the complex 2,6-bis [1-(2-isopropyl-6-methylphenylimino)ethyl]-pyridineiron(II)dichloride was used for propylene polymerization. Activation with Ph3C [B(C6F5)(4)] and subsequent treatment with triisobutylaluminium or triethylaluminium generated a very active polymerization catalyst for propylene, The kinetics of this polymerization reaction were investigated with mass-flowmeters. Further we show propagation-time-profiles of this reaction. Depending on the nature of the aluminiumalkyl we are able to determine different aliphatic endgroups in the polymer using C-13 NMR spectroscopy. Addition of hydrogen to the polymerization leads to higher activities and allows us to formulate a complete catalytic reaction cycle containing an iron hydride species, This cycle comprises one starting cycle and two propagation cycles which can be controlled with the aluminiumtrialkyl-propylene ratio. (C) 2002 Elsevier Science B.V. All rights reserved.