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

Abstract

Reaction of GeCl 2 ‚dioxane with 2 equiv of Li(THF) 2.5 Ge(SiMe 3 ) 3 in hexane afforded moderate yields of two cyclopolygermanes. A cyclotrigermane, (Ge(SiMe 3 ) 2 ) 3 , was characterized by NMR spectra, elemental analyses, and an X-ray crystal structure determination. It crystallized from pentane in the R3 hc space group (rhombohedral) with a ) 19.294(3) Å, R ) 31.89(1)°, V ) 1781 Å 3 , and Z ) 2. The Ge 3 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, ((Me 3 Si) 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(SiMe 3 ) 4 in the F2 3 (cubic) space group with a ) 22.7731(3) Å, V ) 11 810.5 Å 3 , and Z ) 8. The Ge 4 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 GeCl 2 ‚dioxane and 2 equiv of Li(THF) 3 Si(SiMe 3 ) 3 , the known disilagermirane, (Me 3 Si) 2 Ge(Si(SiMe 3 ) 2 ) 2 , was isolated (66% yield) along with a small yield of the known cyclotetragermane, ((Me 3 Si) 3 SiGeCl) 4 . Reaction of GeI 2 with Li(THF) 2.5 Ge(SiMe 3 ) 3 gave only traces of the cyclotrigermane.

Cyclic Disilylated and Digermylated Germylenes

“…The first step of this reaction sequence is likely analogous to what happened in the reactions described by Stalke, 9 Klinkhammer, 10 and Mallela. 11 However, the acyclic examples can react by another 1,2-trimethylsilyl shift to give an isomeric silylene, which eventually inserts into the Si–Si bond, thus forming a three-membered ring. While the cyclic silagermene 4 and digermene 4a could also undergo an additional 1,2-trimethylsilyl shift, final insertion of the thus formed silylene or germylene into a Si–Si or Si–Ge bond is not likely, due to the cyclic nature of the molecule.…”

“…Using (Me 3 Si) 3 GeLi as the nucleophile, Mallela et al reported similar chemistry leading to hexakis(trimethylsilyl)germirane. 11 …”

Germanium Coordination Compounds: Classification and Analysis of Crystallographic and Structural Data

“…A yellow-orange derivative [128] contains a [Ge(SiBu)]3 + cation and a tfpb anion. The three Si atoms are nearly coplanar with the central triangle, and the overall structure is essentially the same as for two other derivatives [129,130], In the dark red derivative [129] the Ge-Ge bond distances in the Ge3 triangle are 223.9(4) and 252.2(4) pm (x2) (average 242.8(4) pm). The Ge-Ge bond distances of the three membered ring are almost equal, ranging from 232.9(2) to 234.3(2) pm (average 233.5(2) pm).…”

MOLECULAR STRUCTURE OF ORGANOSILICON COMPOUNDS WITH Si-M (M = Ge, Sn, Pb, Ti, Zr, Hf) BONDS

“…The structure of tris(trimethylsilyl)silylcyclotetragermane 7 (M=Si [22]) closely resembles that of its tris(trimethylsilyl)germyl counterpart 7 (M=Ge, [15]). Both compounds have all frans-geometry.…”

“…The cyclotrigermane 2 [15] crystallizes as a very hygroscopic, transparent, hexagonal slabs. Three germanium atoms form a regular triangle with a short Ge-Ge distance of 2.460 A.…”