Synthesis and Reactivity of Fluorenyl-Based Germanium(II) Compounds

We present the synthesis of alkyl-substituted germylenes GeFlu₂, Ge(Flu^TMS)₂, and Flu^TMSGeCl (Flu = 9H-fluorenyl, Flu^TMS = 9-trimethylsilyl-9H-fluorenyl) using bulky fluorenyl ring systems and modifications of that. GeFlu₂ can only be crystallized as its three-membered ring trimer, whereby the reaction is accompanied by the formation of several byproducts, such as [Li(THF)₄][Ge(Ge₃Flu₇H)]. These results led to the modification of the fluorenyl framework by substitution the one H atom in the 9-position by a TMS group. With the synthesis of the corresponding Li salt LiFlu^TMS, Ge(Flu^TMS)₂ could be isolated in good yields in a further reaction. The homoleptic Ge(Flu^TMS)₂ is found in its crystalline form as a monomer and thus belongs to the series of monomeric alkyl-substituted germylenes. Also, the corresponding monoalkyl-substituted halogenido germylene was isolated as a four-membered ring tetramer [Flu^TMSGeCl]₄ during an unselective reaction. However, Flu^TMSGeCl undergoes significant stabilization through the formation of the monomeric phosphane adduct Flu^TMSGeCl·PEt₃, which greatly increases the selectivity of the reaction. During further reactions of Ge(Flu^TMS)₂ with a GeBr solution (toluol/Pr₃P), more impressions of the reactivity of Ge(I)X solutions with germylenes were achieved, showing that those germylenes take part in the disproportionation reaction of metastable Ge(I) solutions to give oxidized Ge(IV) compounds like (Flu^TMS)₂GeBr₂.