Ethylene polymerization and oligomerization catalyzed by bulky β-diketiminato Ni(II) and β-diimine Ni(II) complexes/methylaluminoxane systems

Abstract β-Diketiminato complexes Ni{(N(Ar)C(Me)) 2 CH}Br ( 9 ), Ni{(N(Ar)C(Me)) 2 CH} Pph 3 Br ( 10 ) and β-diimine complexes Ni{(N(Ar)C(Me)) 2 CH 2 }Br 2 ( 5 ) (Ar = 2,6-iPr 2 C 6 H 3 ( a ), 2,6-Me 2 C 6 H 3 ( b )) were used as catalyst precursors for ethylene polymerization in the presence of methylaluminoxane (MAO). High molecular weight ethylene polymers as well as short chain oligomers (C4–C8) were simultaneously produced from the catalysis reactions. Ethylene polymers obtained by using these β-N–N Ni(II)/MAO catalyst systems are mainly methyl branched. Small amounts of even number branches were also observed in the 13 C NMR spectra of the obtained ethylene polymers, which are believed generating from the incorporation of simultaneously produced α-olefins. Except methyl branch and the branches derived from the incorporation of α-olefin oligomers, the formation of other branch types via the chain walking process is not favored in β-diketiminato Ni(II) systems.