Preparation of linear α-olefins to high-molecular weight polyethylenes using cationic α-diimine nickel(II) complexes containing chloro-substituted ligands

A series of α-diimine nickel(II) complexes containing chloro-substituted ligands, [(Ar)N=C(C₁₀H ₆)C=N(Ar)]NiBr₂ (4a, Ar = 2,3-C₆H ₃Cl₂; 4b, Ar = 2,4-C₆H₃C1 ₂; 4c, Ar = 2,5-C₆H₃Cl₂; 4d, Ar = 2,6-C₆H₃Cl₂; 4e, Ar = 2,4,6-C₆H ₂Cl₃) and [(Ar)N=C(C₁₀H ₆)C=N(Ar)]₂NiBr₂ (5a, Ar = 2,3-C ₆H₃Cl₂; 5b, Ar = 2,4-C₆H ₃Cl₂; 5c, Ar = 2,5-C₆H₃Cl ₂), have been synthesized and investigated as precatalysts for ethylene polymerization. In the presence of modified methylaluminoxane (MMAO) as a cocatalyst, these complexes are highly effective catalysts for the oligomerization or polymerization of ethylene under mild conditions. The catalyst activity and the properties of the products were strongly affected by the aryl-substituents of the ligands used. Depending on the catalyst structure, it is possible to obtain the products ranging from linear α-olefins to high-molecular weight polyethylenes.