Solid state and solution structures of 2-halophenolate complexes of lithium

Solvent-free 2-halophenolate complexes of lithium, LiOC₆H₄-2-X)]_n (X = F, Cl, Br), were synthesized by treating the corresponding 2-halophenols with n-butyllithium. ortho-Lithiation was avoided by cooling the reaction mixture to −78 °C and using n-hexane as solvent. Recrystallization from THF/n-hexane lead to tetrameric Li(THF)(μ₃-OC₆H₄-2-X)]₄ (X = F, 1; X = Cl, 2; X = Br, 3), which was verified by X-ray crystallography for 1 and 2 and derived for 3 by the strong similarities in the ¹H, ¹³C and ⁷Li NMR data for 1, 2 and 3. Cubane structures were revealed for the Li₄O₄ core of 1 and 2. While complex salt 2 possesses only slight distortions within its cubane core, complex salt 1 has an unusual C_2v distortion towards a butterfly shape. Additionally, dimeric Li(H₂O)₂(μ-OC₆H₄-2-Br)]₂ was obtained containing an extensive network of hydrogen bonding between water molecules. Upfield shifts in the ¹H NMR spectra for the coordinated THF molecules as well as ¹³C and ⁷Li NMR spectra are interpreted as indicating the tetrameric form observed in the X-ray crystal structure is preserved in solution.