Cationic iron and cobalt acetonitrile cationic complexes were prepared and used as catalyst precursors in catalytic ethylene oligomerization. The effects of temperature and the nature and effects of the co-catalysts were evaluated. The iron and cobalt catalysts are less active, giving turnover frequencies of 20,000 to 30,000 h(-1) while the corresponding nickel analogs exhibit turnover frequencies of 215,000 h(-1). The iron and cobalt catalysts were more selective for the synthesis of 1-butene, especially at lower temperatures, compared to the nickel catalyst.