N-Heterocyclic Germylidenide and Stannylidenide Anions: Group 14 Metal(II) Cyclopentadienide Analogues

The reaction of a sterically bulky β-diketiminato lithium complex [Li( Bu t Nacnac)] ( Bu t Nacnac = [{N(Dip)C(Bu t )} 2 CH] −, Dip = C 6 H 3 Pr i 2 -2,6) with GeCl 2 ·dioxane has given the germanium(II) chloride complex [( Bu t Nacnac)GeCl] ( 3 ). Both it and its known tin analogue, [( Bu t Nacnac)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{η 5 -EC(Bu t )C(H)C(Bu t )N(Dip)}] (E = Ge, 5; Sn, 6 ). The reduction of the germanium(II) precursor, 3, also afforded the germanium(II) amide complex [( Bu t Nacnac)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{η 5 -EC(Bu t )C(H)C(Bu t )N(Dip)}] indicate a significant degree of aromatic π-delocalization within their heterocycles.