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New Small-Ring Cyclogermanes:  Syntheses and X-ray Crystal Structures

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journal contribution
posted on 31.12.1997, 00:00 by Siva P. Mallela, Sven Hill, R. A. Geanangel
Reaction of GeCl2·dioxane with 2 equiv of Li(THF)2.5Ge(SiMe3)3 in hexane afforded moderate yields of two cyclopolygermanes. A cyclotrigermane, (Ge(SiMe3)2)3, was characterized by NMR spectra, elemental analyses, and an X-ray crystal structure determination. It crystallized from pentane in the Rc space group (rhombohedral) with a = 19.294(3) Å, α = 31.89(1)°, V = 1781 Å3, and Z = 2. The Ge3 core consisted of an equilateral triangle with a Ge−Ge distance of 2.460(1) Å, the shortest so far measured in cyclotrigermanes. The second product was tentatively identified by its NMR spectra as a cyclotetragermane, ((Me3Si)3GeGeCl)4, and this was confirmed by elemental analyses and an X-ray structure determination on the yellow crystals formed from pentane. The product was found to crystallize as a complex with two molecules of Ge(SiMe3)4 in the F23 (cubic) space group with a = 22.7731(3) Å, V = 11 810.5 Å3, and Z = 8. The Ge4 core consisted of a nonplanar four-membered ring (fold angle = 18.7°) disordered over three positions related by 3-fold symmetry. In the assumed ordered structure, ring Ge−Ge distances averaged 2.503 Å. When the reaction was repeated with GeCl2·dioxane and 2 equiv of Li(THF)3Si(SiMe3)3, the known disilagermirane, (Me3Si)2Ge(Si(SiMe3)2)2, was isolated (66% yield) along with a small yield of the known cyclotetragermane, ((Me3Si)3SiGeCl)4. Reaction of GeI2 with Li(THF)2.5Ge(SiMe3)3 gave only traces of the cyclotrigermane.