Hexafluorophosphate ionic liquids have been applied as catalyst phase in the selective, biphasic oligomerization of ethylene to 1-olefins with the cationic Ni-complex (eta(3)-methallyl)[bis(diphenylphosphino)methane-monoxide-kappa(2)-P,O]n ickel(II) hexafluoroantimonate [(mall)Ni(dppmO)][SbF6]. The biphasic reaction mode opens up the possibility for effective catalyst recycling and offers additionally an interesting way to enhance catalytic activity. Moreover, a remarkable influence of the biphasic reaction mode-which is enabled for the first time using the ionic liquid catalyst phase-on the product selectivity is observed. Interestingly, slight modifications of the ionic liquid's cation give access to a further tuning of the product distribution. Moreover, the results of our efforts to optimize the reactor design for the specific needs of this biphasic reactions and some recycling experiments are presented. (C) 2004 Elsevier B.V. All rights reserved.