Highly electron-withdrawing pentafluorosulfanyl groups were probed as substituents in an organometallic catalyst. In Ni(II) salicylaldiminato complexes as an example case, these highly electron-withdrawing substituents allow for polymerization of ethylene to higher molecular weights with reduced branching due to significant reductions in beta-hydrogen elimination. Combined with the excellent functional group tolerance of neutral Ni(II) complexes, this suppression of beta-hydrogen elimination allows for the direct polynierizatiori of ethylene in water to nanocrystal dispersions of disentangled, ultrahigh-molecular-weight linear polyethylene.