Trihydrogermyl-substituted thiophenes

Abstract

Treatment of 2-bromo- or 2,5-dibromo-thiophene with equivalent quantities of n-butyllithium at low temperature, followed by bromogermane, afforded 2-germyl- 2 and 2,5-di(germyl)-thiophene 3 in 44 and 82% yields, respectively. The in situ Grignard reaction of 2-bromothiophene with tetra(ethoxy)germane and magnesium gave low yields of 2-[tri(ethoxy)germyl]thiophene 1. Attempts to convert this product into the trihydride using LiAlH₄ yielded only traces of 2. Bis(2-thienyl)germane 4 is available from 2-lithiothiophene and dibromogermane (molar ratio 2∶1, 64% yield). The products have been characterized by analytical and spectroscopic methods. The ⁷³Ge NMR spectra show only broad resonances without discernible ⁷³Ge–¹H coupling owing to the low symmetry of the substituents. The molecular geometries of 2 and 3 have been calculated using standard ab initio quantum chemical methods. The results are similar to those for analogous silylthiophenes reported recently. There is no evidence for significant intramolecular Ge⋯S interactions.