The new neutral nickel complexes PhC(NSiMe3)2Ni(acac) (3), PhC(NSiMe3)2Ni(acac)-(TMEDA) (4), [PhC(NSiMe 3)2]2Ni2 (5), [PhC(NSiMe 3)2]2Ni·Li2Br 2(TMEDA)2 (6), (TMEDA)2Ni (7), p-MePhC(NSiMe3)2Ni(acac) (8), p-MePhC(NSiMe 3)2Ni(acac)(TMEDA) (9), [p-MePhC-(NSiMe3) 2]2Ni (10), NiMe2Py2 (11) and [p-MePhC(NSiMe3)]2Ni(Py) (14) have been synthesized and characterized. The solid-state molecular structures of all complexes have been confirmed by low-temperature X-ray diffraction analysis. The methyl complex p-MePhC(NSiMe3)2Ni(Me)(Py) (13) is not stable and rapidly decomposes, forming the complex [p-MePhC(NSiMe3)]2-Ni(Py) (14). Complex 3 activated with MAO has been shown to be an efficient catalytic system for the norbornene vinyl-type polymerization. The activity of the catalyst and the molecular weights of the resulting polynorbornenes were found to be dependent on the reaction time, the MAO/precatalyst ratio, and the reaction temperature. In addition, this catalytic system has been found to dimerize propylene to a mixture of hexenes with a high turnover frequency of η = 9040 h-1 and oligomerize ethylene to either a mixture of C4-C6 or/and C4-C14 products, depending on the temperature and the solvent, extremely rapidly (η = 83 500 h-1).