Atmospheric ethylene reactions were studied with backbone fluorinated β-diketiminato Ni(II) complexes CH{C(CF3)NAr}2NiBr (1, Ar = 2,6-Me2C6H3, and 2 2,6-iPr2C6H3) activated by methylaluminoxane (MAO). The catalytic systems exhibit the characteristics of catalyzing simultaneously of ethylene, indicating different active species involved in the reaction system. In an effort to investigate the species involved in the β-diketiminato nickel (II)/MAO system, the reaction of 1 with methylaluminoxane were studied. With 19F{1H NMR} spectra, two sets of new signals different from 1 were presented. Two products were proposed precursors of active species for producing oligomer and polymer of ethylene in the β-diketiminato Ni(II)/MAO system. Copyright © 2014 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]