The nature of nickel species formed upon the activation of α-diimine nickel(II) pre-catalyst with alkylaluminum sesquichlorides

The nature of nickel(II) species, formed upon the activation of α-diiminonickel pre-catalyst L_NNi^IIBr₂ (L_N = 1,2-Bis[(2,4,6-trimethylphenyl)imino]acenaphthene) with Al₂Et₃Cl₃ and Al₂Me₃Cl₃, has been studied using ¹H and ²H NMR spectroscopy. The paramagnetic heterobinuclear ion pairs of the type [L_NNi^II(μ-Cl)₂AlRCl]⁺[A]^– (where R = Et or Me, [A]^- = counter anion) have been observed in the catalyst systems L_NNi^IIBr₂/Al₂Et₃Cl₃ and L_NNi^IIBr₂/Al₂Me₃Cl₃. At room temperature, both ion pairs gradually transform into EPR-active complexes of Ni(I). Their possible role in ethylene polymerization is discussed.