New small-ring cyclogermanes: Syntheses and X-ray crystal structures

Reaction of GeCl2 . dioxane with 2 equiv of Li(THF)(2.5)Ge(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 R(3) over barc$ space group (rhombohedral) with a 19.294(3) Angstrom, alpha = 31.89(1)degrees, V = 1781 Angstrom(3), and Z = 2. The Ge-3 core consisted of an equilateral triangle with a Ge-Ge distance of 2.460(1) Angstrom, the shortest so far measured in cyclotrigermanes. The second product was tentatively identified by its NMR spectra as a cyclotetragermane, ((Me3Si)(3)GeGeCl)(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 F2(3) (cubic) space group with a = 22.7731(3) Angstrom, V = 11 810.5 Angstrom(3), and Z = 8. The Ge-4 core consisted of a nonplanar four-membered ring (fold angle = 18.7 degrees) disordered over three positions related by 3-fold symmetry. In the assumed ordered structure, ring Ge-Ge distances averaged 2.503 Angstrom. When the reaction was repeated with GeCl2 . dioxane and 2 equiv of Li(THF)(3)Si(SiMe3)(3), the known disilagermirane, (Me3Si)(2)Ge(Si(SiMe3)(2))(2), was isolated (66% yield) along with a small yield of the known cyclotetragermane, ((Me3Si)(3)SiGeCl)(4). Reaction of GeI2 with Li(THF)(2.5)Ge(SiMe3)(3) gave only traces of the cyclotrigermane.