Two new moisture- and air-stable bis(β-ketoamino)nickel(II) complexes Ni[R1C(O)CHC(NAr)R2]2 (Ar ≡ 2,6-iPr2C6H3; R1 = R2 = CH3, 1; R1 = C6H5, R2 = CH3, 2), together with the moderately stable complex Ni2[CH3C(O)CHC(O)CH3]4[H2NtBu]2 (3), which bears a monoanionic O,O-chelate bidentate β-diketone and an sp3-N atom of tBuNH2 mixed ligands, were synthesized and characterized. The solid-state structures of the complexes have been determined by single-crystal X-ray diffractions. Additionally, these new complexes act as catalyst precursors for methyl methacrylate polymerization after activation with methylaluminoxane (MAO). The polymers obtained by 1 and 2 show broader polydispersity than that obtained by 3. 13C NMR analyses indicate that these catalytic systems initiate MMA polymerization to yield PMMA with rich syndiotacticity microstructure.

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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.