Preparation, structure, and 73Ge NMR spectroscopy of arylgermanes ArGeH3, Ar2GeH2, and Ar3GeH

Arylgermanes of the types ArGeH3, Ar2GeH2, and Ar3GeH are important precursors for the preparation of oligo- and polygermanes. These precursors are readily prepared in good yields via an in situ Grignard reaction employing tetra(ethoxy)germane, an aryl halide, and magnesium metal in tetrahydrofuran as the reaction medium. The aryl-tri(ethoxy)germanes obtained were reduced to the germane hydrides with LiAlH4. This method is also applicable for aryl groups with sensitive substituents, as demonstrated for (4-methoxyphenyl)germane (p-anisylgermane, MeOC6H4GeH3). With modified stoichiometry, bis(p-anisyl)germane is also available. The insertion of GeCl2 into the C-Br bond of arylbromides using catalytic amounts of anhydrous AlCl3 proved to bean efficient alternative if the reaction was carried out in the absence of a solvent. After LiAlH4 reduction of the aryltrihalogermanes, phenyl-, p-tolyl-, and mesitylgermane were obtained in good yields. The arylgermanes have been identified by their analytical and spectroscopic data, including Ge-73 (s = 9/2) NMR spectroscopy. Very surprisingly, sharp multiplet signals were observed with well-resolved (1)J(Ge,H) couplings. The molecular structure of p-MeOC6H4GeH3 was determined from low-temperature X-ray diffraction data collected from a single-crystal grown "in situ" from the melt (mp: 15 degrees C). The significant distortions observed in the anisyl part of the structure and the conformation of the molecule are in excellent agreement with results of ab initio quantum chemical calculations (MP2/6-31G*) of this compound.