Synthesis, Molecular Structure, and Solution-Dependent Behavior of Nickel Complexes Chelating Anilido−Imine Donors and Their Catalytic Activity toward Olefin Polymerization

A series of novel nickel complexes (1−4) bearing anilido−imine ligands, [(Ar1NCHC6H4NAr2)NiBr]2 (Ar1 = Ar2 = 2,6-dimethylphenyl, 1; Ar1 = 2,6-dimethylphenyl, Ar2 = 2,6-diisopropylphenyl, 2; Ar1 = Ar2 = 2,6-diisopropylphenyl, 3; Ar1 = 2,6-diisopropylphenyl, Ar2
= 2,6-dimethylphenyl, 4), have been synthesized and characterized. The solid-state structures
of the complexes 1, 2, and 4 were confirmed by X-ray single-crystal analyses to be in the
form of a dinuclear and bromine-bridged structure. However, there is an equilibrium that
shifts between the monomer and dimer in solution, which has been monitored using 1H
NMR and UV−vis spectrophotometry. The themodynamic parameters for the equilibriums
were calculated to be ΔH = +13.68 kJ/mol and ΔS = 40.32 J/(mol K) for 1 and ΔH = +8.35
kJ/mol and ΔS = 15.21 J/(mol K) for 3. All nickel complexes show low activities for ethylene
oligomerization with MAO as cocatalyst but high catalytic activities for norbornene
polymerization in the presence of MAO.