New substituents for the stabilization of low-coordinate germanium species: Use in access to diazogermylenes

The reactions of the P-bis(trimethylsilyl)amino-N-(trimethylsilyl)iminophosphine with various dialkoxydichlorogermanes (alkoxy: OR = OMe, OEt and Oi-Pr) at 0 °C led to the stable dichlorogermylene-complexes [(RO)2P(NSiMe3)(N(SiMe3)2)]GeCl2 [R = Me (1), Et (2) and R = i-Pr (3)]. The solid-state structure of (2) has been determined by X-ray crystallography. A mechanism for the formation of these compounds is proposed, based on the transient species observed in the case of the isopropoxy derivatives. At room temperature in benzene solution, compounds (1) and (2) eliminate chlorotrimethylsilane without side reactions leading to the corresponding 2,4-diaza-3-phosphagermatidines [(RO)2P(NSiMe3)2]GeCl (4) and (5), respectively. At the opposite, complex (3) showed a modulated behavior: at room temperature, (3) still slowly eliminates mainly chlorotrimethylsilane with the formation of [(i-PrO)2P(NSiMe3)2]GeCl (6). Structure of this chlorinated germanium(II) compound which can also be seen as a germyl anion has been evidenced by an X-ray analysis. But at higher temperature (40–50 °C) (3) mainly decomposes with elimination of isopropylchloride leading to the formation of [(i-PrO)(Me3SiO)P(NSiMe3)2]GeCl (7) as a mixture of Z- and E-isomers. The mechanism of this reaction is discussed. The Z-isomer of (7) was successfully isolated after a selective crystallization, and investigated by an X-ray analysis. The interconversion mechanism of the two diastereoisomers is also discussed. Reaction of compound (5) with the lithio derivative of the trimethylsilyldiazomethane leads to the diazogermylene (8), a potential precursor of germa-alkyne.

Graphical abstractThis study focuses on the synthesis, the characterization and the crystal structures of new low-coordinate germanium species stabilized by donor ligands. The mechanisms involved are also discussed.Figure optionsDownload full-size imageDownload as PowerPoint slide