The catalytic systems NiBr₂(DPP-DAB) + 20 MAO and NiBr₂(DPP-BIAN) + 20 MAO (DPP-BIAN = bis(2,6-diisopropylphenyl)-bis(imino)-acenaphtene, MAO = methylaluminoxane), as well as a number of model systems, are studied under conditions of their activation and functioning. There are paramagnetic nickel complexes and radical-anion aluminum complexes in the systems under real conditions of activation and functioning. The highest activity is observed when the Ni(I) signal intensity in the ESR spectrum is maximal. A mechanism of paramagnetic species formation is proposed.