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.