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

Abstract

We present the synthesis of alkyl-substituted germylenes GeFlu2, Ge(FluTMS)2, and FluTMSGeCl (Flu = 9H-fluorenyl, FluTMS = 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 LiFluTMS, Ge(FluTMS)2 could be isolated in good yields in a further reaction. The homoleptic Ge(FluTMS)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 [FluTMSGeCl]4 during an unselective reaction. However, FluTMSGeCl undergoes significant stabilization through the formation of the monomeric phosphane adduct FluTMSGeCl·PEt3, which greatly increases the selectivity of the reaction. During further reactions of Ge(FluTMS)2 with a GeBr solution (toluol/nPr3P), 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 (FluTMS)2GeBr2.