New homo- and hetero-alkali metal alkoxide cages; crystal structures of [Me2N(CH2)2OLi]8 and [{Me2N(CH2)2O}12Li8K6]O

Abstract

The reaction of N,N′-dimethylaminoethanol (DMAEH), (Me)₂N(CH₂)₂OH, with ⁿBuLi and ⁿBuLi/ⁿBuK respectively results in the formation of the homo- and hetero-metallic alkoxides [Me₂N(CH₂)₂OLi]₈, 1, and [{Me₂N(CH₂)₂O}₁₂Li₈K₆]O, 2, rather than mixed alkyl–alkoxide species. From single crystal X-ray diffraction studies the two complexes are shown to be highly aggregated cage structures. Complex 1 (monoclinic, C2/c) adopts a rare octameric structure constructed from a ring stacked hexamer fused with a (LiO)₂ dimer creating a sixteen vertex Li–O cluster. Complex 2, which crystallises (rhombohedral, R) with thf and cyclohexane molecules in the lattice, forms a highly symmetrical, almost spherical, cage with an unprecedented Li ∶ K ratio of 8 ∶ 6.