Alkaline earth metal-assisted dinitrogen activation at nickel

Rare examples of trinuclear [Ni-N₂-M-N₂-Ni] core (M = Ca, Mg) with linear bridged dinitrogen ligands are reported in this work. The reduction of [ⁱPr₂NN]Ni(μ-Br)₂Li(thf)₂ (1) (ⁱPr₂NN = 2,4-bis-(2,6-diisopropylphenylimido)pentyl) with elemental Mg or Ca in THF under an atmosphere of dinitrogen yields the complex {ⁱPr₂NNNi(μ-N₂)}₂M (thf)₄ (M = Mg, complex 2 and M = Ca, complex 3). The bridging end-on (μ-N₂)₂M(thf)₄ moiety connects the two [ⁱPr₂NNNi]^- nickelate fragments. A combination of X-ray crystallography, solution and solid-state spectroscopy have been applied to characterize complexes 2 and 3, and DFT studies have been used to help explain the bonding and electronic structure in these unique Ni-N₂-Mg and Ni-N₂-Ca complexes.