Symmetric and asymmetric Ni(II) diimine complexes such as 2-[(2,6-diisopropylphenylimino)methyl]pyridine nickel(II) dibromide (a), 2-[1-(2,6-diisopropylphenylimino)ethyl]pyridine nickel(II) dibromide (b) and [1,2-bis(2,6-
diisopropylphenylimino)]acenaphthene nickel(II) dibromide (c) were synthesized. For olefin homopolymerization, asymmetric Ni(II) diimine complexes [(a) & (b)] were compared with symmetric system (c). Asymmetric Ni(II) diimine complexes exhibited less catalytic activity and thermal stability as well as more b-hydride elimination than a symmetric diimine complex (c). The activity of (a) was larger than that of (b), which indicates that methyl group has a contribution
to the instability of catalyst by s bond vibration rather than the stabilization of the active site by electron releasing property.
Brookhart M, Killian CM, Johnson LK, Tempel DJ, "New Ni(II)-Based Catalysts for the Preparation of Polyolefins," 6th International Business Forum on Specialty Polyolefins, SPO '96, Houston, 1996
Brookhart M, Killian CM, Johnson LK, Tempel DJ, "Ni(II) Catalysts for the Polymerization and Copolymerization of Olefins: A New Generation of Polyolefins," Metcon'97: Polymers in Transition Proceedings, 1997