N-heterocyclic germylidenide and stannylidenide anions: group 14 metal(II) cyclopentadienide analogues

The reaction of a sterically bulky I?-diketiminato lithium complex [Li(ButNacnac)] (ButNacnac = [ N(Dip)C(But) 2CH]-, Dip = C6H3Pri 2-2,6) with GeCl2 3 dioxane has given the germanium(II) chloride complex [(ButNacnac)GeCl] (3). Both it and its known tin analogue, [(ButNacnac)SnCl] (4), were crystallographically characterized and found to be monomeric in the solid state. The reduction of both complexes with elemental lithium in THF led to lithium complexes of N-heterocyclic germylidenide and stannylidenide anions, viz., [(THF)Li I?5-EC(But)C(H)C(But)N(Dip) (E=Ge, 5; Sn, 6). The reduction of the germanium(II) precursor, 3, also afforded the germanium(II) amide complex [(ButNacnac)Ge N(H)(Dip) (7). The mechanisms of formation of the complexes are thought to involve a number of steps, including reductive ring contraction reactions. The crystallographic and spectroscopic data for [(THF)Li I?5-EC(But)C(H)C(But)N(Dip) indicate a significant degree of aromatic I?-delocalization within their heterocycles.