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

Abstract

A series of novel nickel complexes ( 1 − 4 ) bearing anilido−imine ligands, [(Ar 1 N CHC 6 H 4 NAr 2 )NiBr] 2 (Ar 1 = Ar 2 = 2,6-dimethylphenyl, 1; Ar 1 = 2,6-dimethylphenyl, Ar 2 = 2,6-diisopropylphenyl, 2; Ar 1 = Ar 2 = 2,6-diisopropylphenyl, 3; Ar 1 = 2,6-diisopropylphenyl, Ar 2 = 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 1 H NMR and UV−vis spectrophotometry. The themodynamic parameters for the equilibriums were calculated to be Δ H = +13.68 kJ/mol and Δ S = 40.32 J/(mol K) for 1 and Δ H = +8.35 kJ/mol and Δ S = 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.