ChemInform Abstract: Mixed Group 14-Group 14 Bonds. Part 5. Six Perphenylated Propane Analogues Ph3M-M′Ph2-M′′Ph3 (M, M′, M′′: Si/Ge): Electronegativity Differences Between Silicon and Germanium.

Über polygermane

Abstract The optimum conditions for selectively cleaving off two phenyl groups in Ge2Ph6 by trichloroacetic acid have been determined. Neither trihaloacetic acids nor HCl/AlCl3 nor reactive tetrahalides MCl4 are suitable reagents for cleaving one phenyl group alone. The 13C NMR chemical shifts of functional phenyl-mono- and -digermanes are given. The crystal structure of 1,2-bis(trichloroacetate)tetraphenyldigermane has been determined and refined to R = 0.048. The digermane bond is bridged by both acetates (distances GeGe 239.3(2), GeO 207.3(3) and 231.4(3) pm). The Ge atoms have trigonal bipyramidal coordination.

Über polygermane

Abstract The synthesis of GePh4 and Ge2Ph6 by Grignard reaction in THF or ether/toluene leads to the by-products Ge3Ph8 (up to 11%) and Ge4Ph10 (up to 18%) which is dependant on using an excess of Mg. A quantitative analysis of the resulting products by HPLC and a semipreparative separation by column, flash, and HPL chromatography is described. The crystal structures of Ge3Ph8 (R = 0.075) and Ge4Ph10 · 2C6H6 (R = 0.054) have been determined. Ge4Ph10 has Ci symmetry and both chain conformations are well staggered (49–70° for Ge3Ph8, 53–66° for Ge4Ph10). The GeGe distances and GeGeGe angles are 244 pm and 121° (Ge3Ph8), and 246 pm and 118° (Ge4Ph10).

Über polygermane

Abstract The optimum conditions for the synthesis of the trigermanes Ge3Ph8 and Ge3Me2Ph6 according to R2GeCl2 + 2 Ph3GeAk (Ak = Li, K) in HMPT have been determined. The main difficulty is to repress a nucleophilic attack of Ph3Ge− at newly formed GeGe bonds. The mass spectrum of Ge3Me2Ph6 shows rearrangements of the GePh3 and Ph/Me groups. The 13C NMR phenyl signals of di-, tri- and tetra-germanes are nearly identical. Ge3Ph8 and Ge4Ph10 transform to the plastically-crystalline state before melting (ΔH 45.3 and 54.9 kJ mol−1). The crystal structure of Ge3Me2Ph6 has been determined. The molecule has C2 symmetry (GeGe 242.9(1) pm, GeGeGe 120.3(1)°).

Über gemischte gruppe 14-gruppe 14-bindungen

Abstract The six title compounds have been synthesized from Li/KSi/GePh 3 and chloride precursors in THF, DME or diethyl ether at low temperature. The six compounds crystallize isomorphously in the space group Pbca with ordered arrangement for the four symmetrical cases (SiSi 2.394, SiGe 2.412, GeGe 2.440 A) and statistical alignment for the two asymmetrical chains; angle range 116.5–123.3°. Replacement of Si by Ge atoms leads to low field NMR chemical shifts for 13 C ipso atoms and for directly bonded 29 Si atoms. This is in accordance with an enhanced electronegativity of germanium in comparison with silicon. UV/Vis and IR/Raman data are given.