2-(2-Pyridyl)phospholes have been evaluated as ligands for the nickel-catalyzed oligomerization of ethylene. Under mild homogeneous reaction conditions, high catalytic activities (> 15 cycles per second) were recorded. The selectivity depends on the ethylene pressure. At 41 bar, high C-4 fraction contents (until 97%) and high 1-butene selectivities (80% of the C4 fraction) were reached. This behavior is interpreted as a consequence of the steric hindrance of the intermediate cationic 2-pyridylphosphole nickel hydrides. (C) 2004 Elsevier Inc. All rights reserved.