Unmasking the constitution and bonding of the proposed lithium nickelate "Li 3 NiPh 3 (solv) 3 ": revealing the hidden C 6 H 4 ligand.

More than four decades ago, a complex identified as the planar homoleptic lithium nickelate "Li ₃ NiPh ₃ (solv) ₃ " was reported by Taube and co-workers. This and subsequent reports involving this complex have lain dormant since; however, the absence of an X-ray diffraction structure leaves questions as to the nature of the Ni-PhLi bonding and the coordination geometry at Ni. By systematically evaluating the reactivity of Ni(COD) ₂ with PhLi under different conditions, we have found that this classical molecule is instead a unique octanuclear complex, [{Li ₃ (solv) ₂ Ph ₃ Ni} ₂ (μ-η ² :η ² -C ₆ H ₄ )] (5). This is supported by X-ray crystallography and solution-state NMR studies. A theoretical bonding analysis from NBO, QTAIM, and ELI perspectives reveals extreme back-bonding to the bridging C ₆ H ₄ ligand resulting in dimetallabicyclobutane character, the lack of a Ni-Ni bond, and pronounced σ-bonding between the phenyl carbanions and nickel, including a weak σ _C-Li → s _Ni interaction with the C-Li bond acting as a σ-donor. Employing PhNa led to the isolation of [Na ₂ (solv) ₃ Ph ₂ NiCOD] ₂ (7) and [Na ₂ (solv) ₃ Ph ₂ (NaC ₈ H ₁₁ )Ni(COD)] ₂ (8), which lack the benzyne-derived ligand. These findings provide new insights into the synthesis, structure, bonding and reactivity of heterobimetallic nickelates, whose prevalence in organonickel chemistry and catalysis is likely greater than previously believed.
Competing Interests: There are no conflicts to declare.
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