Syntheses, Structures, and Electronic Properties of the Branched Oligogermanes (Ph₃Ge)₃GeH and (Ph₃Ge)₃GeX (X = Cl, Br, I)

Abstract

The branched oligogermanium hydride (Ph3Ge)3GeH was synthesized via a hydrogermolysis reaction from GeH4 and Ph3GeNMe2 and was converted to the halide series of compounds (Ph3Ge)3GeX (X = Cl, Br, I) upon reaction with [Ph3C][PF6] in CH2X2 solvent (X = Cl, Br, I). These species were fully characterized by NMR (1H and 13C) and UV/visible spectroscopy, cyclic voltammetry, and elemental analysis. In addition, (Ph3Ge)3GeH was analyzed by 73Ge NMR spectroscopy and exhibits two resonances at δ −56 and −311 ppm. A Ge−H coupling constant of 191 Hz was observed in the proton-coupled 73Ge NMR spectrum of (Ph3Ge)3GeH. The X-ray crystal structures of (Ph3Ge)3GeH and (Ph3Ge)3GeX (X = Cl, Br, I) were obtained and represent the first examples of branched oligogermane hydrides or halides to be characterized in this fashion. The Ge−Ge bond distances in (Ph3Ge)3GeH are short (average value 2.4310(5) Å), while those in the halide compounds (Ph3Ge)3GeX are similar to one another and range from 2.4626(7) to 2.4699(5) Å. The UV/visible and cyclic voltammetry data for these species have been correlated with DFT computations, and excellent agreement was found between the experimental and theoretical data.

Absorption, electrochemical, theoretical, and 73Ge NMR spectral characterization of the germanium neo-pentane analogue (Me3Ge)4Ge

“…Compound 3 exhibits a l max at 212 nm (ε ¼ 3.3 Â 10 4 L mol À1 cm À1 ) [3] that is considerably blue-shifted relative to those for 1 and 2 that were observed at 251 [4,5] and 256 nm [2] (respectively). A similar trend was observed among the related branched oligosilanes (Ph 3 Si) 3 SiH, (PhMe 2 Si) 3 SiPh and (Me 3 Si) 4 Si, where (Ph 3 Si) 3-SiH and (PhMe 2 Si) 3 SiPh exhibit a l max values at 240 and 243 nm (respectively) in their UV/visible spectra, both of which are significantly red-shifted relative to that for (Me 3 Si) 4 Si observed at 210 nm [12].…”

“…Linear oligogermanes that are completely devoid of aryl substituents or have aryl substituents attached only to the terminal germanium atoms typically exhibit only one irreversible oxidation wave [10,13,14], while those having aryl substituents at the internal germanium atoms exhibit n À 1 oxidation waves, where n is equal to the number of germanium atoms bonded together in the chain [11]. However, all of the branched oligogermanes we have analyzed using this method also exhibit one irreversible oxidation wave, even if aryl substituents are present [4,5].…”

“…The preparation of (Ph 3 Ge) 3 GeH (1) and (Ph 3 Ge) 3 GeMe was first reported in 1963 [6], and the compounds (PhCl 2 Ge) 3 GePh [7] and (PhX 2 Ge) 3 GePh (X ¼ Me, MeO, MeS, Me 2 N, Et 2 P) [8] were reported in the early 1970s. In light of the successful use of the hydrogermolysis reaction for the stepwise synthesis of linear oligogermanes, we have used this method for the synthesis of the branched oligogermanes (Ph 3 Ge) 3 GeH (1) [4,5] and (Ph 3 Ge) 3 GePh (2) [2]. The former compound was converted into the halide-substituted branched oligogermanes (Ph 3 Ge) 3 GeX (X ¼ Cl, Br, I) but neither the hydride 1 nor the amide (Ph 3 Ge) 3 GeNMe 2 that was obtained from (Ph 3 Ge) 3 GeCl could be employed for the synthesis of the neo-pentane analogue (Ph 3 Ge) 4 Ge via the hydrogermolysis reaction due to the steric effects of the four triphenylgermyl-groups [4,5].…”

“…In light of the successful use of the hydrogermolysis reaction for the stepwise synthesis of linear oligogermanes, we have used this method for the synthesis of the branched oligogermanes (Ph 3 Ge) 3 GeH (1) [4,5] and (Ph 3 Ge) 3 GePh (2) [2]. The former compound was converted into the halide-substituted branched oligogermanes (Ph 3 Ge) 3 GeX (X ¼ Cl, Br, I) but neither the hydride 1 nor the amide (Ph 3 Ge) 3 GeNMe 2 that was obtained from (Ph 3 Ge) 3 GeCl could be employed for the synthesis of the neo-pentane analogue (Ph 3 Ge) 4 Ge via the hydrogermolysis reaction due to the steric effects of the four triphenylgermyl-groups [4,5]. However, the reaction of Me 3 GeCl with GeBr 4 in the presence of lithium metal was recently shown to provide the neo-pentyl analogue (Me 3 Ge) 4 Ge (3), which could be further converted into a variety of other branched oligogermane species [3].…”

“…We have probed the electronic properties of both linear and branched oligogermanes using cyclic voltammetry and UV/visible spectroscopy and have also coupled these investigations with density functional theory (DFT) calculations [4,5,10,11]. We wish to report here the characterization of 3 using these methods as well as the details of its 73 Ge NMR spectrum.…”