A new approach to lithium–heavier alkali metal interchange reactions: synthesis of a tetralithium pentasodium mixed alkoxide–amide dome-shaped cage compound with an encapsulated hydroxide molecule

Abstract

An investigation of metal–metal interchange reactions between alkali metal amides and alkali metal alkoxides, relevant to the area of ‘superbases’, has uncovered a novel adduct containing both components, which has been isolated from solution and crystallographically characterised. Formulated as [Li₄Na₄(Bu^tO)₄{PhN(H)}₄(NaOH)(4-Me-py)₄], this tetralithium pentasodium mixed alkoxide–amide can be synthesized either by reaction of lithium anilide with sodium t-butoxide or of sodium anilide with lithium t-butoxide, in the presence of the co-ordinating solvent 4-methylpyridine (4-Me-py). The single sodium hydroxide molecule in the formulation occurs adventitiously, but consistently. X-Ray crystallographic studies reveal a 17-vertex dome-shaped structure founded on a (NaN)₄ basal ring, above which lies a smaller (LiO)₄ ring then an apical Na atom: the OH⁻ ion occupies an internal position within the dome. Discussion focuses on the striking resemblance between this structure and that of the previously reported tetralithium pentapotassium mixed alkoxide–enolate [Li₄K₄(Bu^tO)₄(C₆H₁₁O)₄(KOH)(THF)₅], and it is pointed out that the dominant factor in their common architectural design appears to be the encapsulated hydroxide molecule.