While activation of tungsten bis(imido) complexes [WCl2(NAr)2(dme)] with EtAlCl2 affords active, and moderately selective ethylene dimerization catalysts, addition of Et3N or Oct4NCl leads to a doubling in productivity and activity, along with increased selectivity (e.g., >93% C4, >99% 1-C4). The performance of the resulting tungsten-based catalyst package is competitive with that of Axens' commercialised Ti-based AlphaButol process and exemplifies the wide potential of similar additives in selective oligomerization.