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

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(ButO)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(ButO)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.