σ-Bond electron delocalization of branched oligogermanes and germanium containing oligosilanes

Characterization of Germanium Nanoparticles from Arylgermanium Trihydrides

Germanium is a promising basis for nanomaterials due to its low toxicity and valuable optical and electronic properties. However, germanium nanomaterials have seen little research compared to other group 14 elements due to unpredictable chemical behavior and high costs. Here, we report the dehydrocoupling of o-tolylgermanium trihydride to amorphous nanoparticles. The reaction is facilitated through reflux at 162 °C and can be accelerated with an amine base catalyst. Through cleavage of both H2 and toluene, new Ge-Ge bonds form. This results in nanoparticles consisting of crosslinked germanium with o-tolyl termination. The particles are 2-6 nm in size and have masses above approximately 3500 Da. The organic substituents are promising for further functionalization. Combined with strong absorption up to 600 nm and moderate solubility and air stability, there are numerous possibilities for future applications.

1,2-Bis(triazolyl)tetraphenyldigermanes: Synthesis, Structure and Properties

Using the [3+2] cycloaddition reaction of [HC≡C-GePh2 -]2 (1) and a number of RCH2 N3 , this work described the synthesis of a series of novel heterocyclic digermanes, bitriazoles [1,4-C2 HN3 (CH2 R)GePh2 -]2 , 2-12 (R=Ph, p-Tol, p-C6 H4 NMe2 , p-C6 H4 OMe, p-C6 H4 Br, m-C6 H4 NO2 , 2-Naphth, CH2 -p-OC6 H4 CHO, CH2 -p-OC6 H4 COOMe, CH2 P(O)(OEt)2 , COOEt), difficult to produce by other methods. The structural peculiarities of these compounds were studied in detail by NMR spectroscopy and by XRD analysis (for 6, 9 and 10). The properties of 1-12 were studied by UV/vis and luminescence emission spectroscopy, electrochemistry and DFT calculations, indicating an effective conjugation in their molecules.

Iterative Synthesis of Oligosilanes Using Methoxyphenyl- or Hydrogen-Substituted Silylboronates as Building Blocks: A General Synthetic Method for Complex Oligosilanes

Organosilanes have attracted the attention of researchers for more than 150 years due to their unique properties, and they have become indispensable industrial assets. However, many synthesized oligosilanes with multiple Si-Si bonds are relatively simple, i.e., they often only contain a single repeating unit. More laborious customized synthetic routes can lead to more complex oligosilanes, but compared to carbon-based molecules, their structural diversity remains limited. The development of effective and practical synthetic routes to complex oligosilanes that contain mixed substituents constitutes a long-standing challenge. Here, we describe an iterative synthesis of oligosilanes using methoxyphenyl- or hydrogen-substituted silylboronates, which were obtained via transition-metal-catalyzed Si-H borylation reactions. The first key reaction is a cross-Si-Si bond-forming reaction between chloro(oligo)silanes and silylboronates activated by MeLi. The second key reaction is the selective chlorination of the methoxyphenyl group or the hydrogen atom at the terminal of the oligosilanes. Iteration of these two key reactions enables the synthesis of various oligosilanes that are otherwise difficult to access. As a demonstration of the synthetic utility of this iterative synthetic approach, oligosilanes with different sequences were prepared by simply changing the order of the reaction of four different silicon units. Furthermore, a bespoke tree-shaped oligosilane is easily obtained via the present iterative synthesis. The solid-state structures of several of these oligosilanes were unequivocally determined using single-crystal X-ray diffraction analysis.

Oligoorganogermanes: Interplay between Aryl and Trimethylsilyl Substituents

Derivatives of main group elements containing element-element bonds are characterized by unique properties due to σ-conjugation, which is an attractive subject for investigation. A novel series of digermanes, Ar₃Ge-Ge(SiMe₃)₃, containing aryl (Ar = p-C₆H₄Me (1), p-C₆H₄F (2), C₆F₅ (3)) and trimethylsilyl substituents, was synthesized by the reaction of germyl potassium salt, [(Me₃Si)₃GeK*THF], with triarylchlorogermanes, Ar₃GeCl. The optical and electronic properties of such substituted oligoorganogermanes were investigated spectroscopically by UV/vis absorption spectroscopy and theoretically by DFT calculations. The molecular structures of compounds 1 and 2 were studied by XRD analysis. Conjugation between all structural fragments (Ge-Ge, Ge-Si, Ge-Ar, where Ar is an electron-donating or withdrawing group) was found to affect the properties.

Subvalent mixed SixGey oligomers: (Cl3Si)4Ge and Cl2(Me2EtN)SiGe(SiCl3)2

(Cl₃Si)₄Ge (1; 91%) is accessible from GeCl₄, the Si₂Cl₆/[nBu₄N]Cl silylation system, and excess SiCl₄. A key intermediate step involves Cl^- sequestration with AlCl₃ in the course of the reaction between the first-formed germanide [(Cl₃Si)₃Ge]^- and SiCl₄. The related adduct Cl₂(Me₂EtN)SiGe(SiCl₃)₂ (2; quantitative conversion) was prepared either by amine-induced cleavage of 1 or by a bottom-up synthesis starting from GeCl₄ and Si₂Cl₆.

Indirect and Direct Grafting of Transition Metals to Siliconoids

Unsaturated charge‐neutral silicon clusters (siliconoids) are important as gas‐phase intermediates between molecules and the elemental bulk. With stable zirconocene‐ and hafnocene‐substituted derivatives, we here report the first examples containing directly bonded transition‐metal fragments that are readily accessible from the ligato‐lithiated Si₆ siliconoid (1Li) and Cp₂MCl₂ (M=Zr, Hf). Charge‐neutral siliconoid ligands with pending tetrylene functionality were prepared by the reaction of amidinato chloro tetrylenes [PhC(NtBu)₂]ECl (E=Si, Ge, Sn) with 1Li, thus confirming the principal compatibility of such low‐valent functionalities with the unsaturated Si₆ cluster scaffold. The pronounced donor properties of the tetrylene/siliconoid hybrids allow for their coordination to the Fe(CO)₄ fragment.

The Bicyclo[2.2.2]octane Motif: A Class of Saturated Group 14 Quantum Interference Based Single-Molecule Insulators

The electronic transmission through σ-conjugated molecules can be fully suppressed by destructive quantum interference, which makes them potential candidates for single-molecule insulators. The first molecule with clear suppression of the single-molecule conductance due to σ-interference was recently found in the form of a functionalized bicyclo[2.2.2]octasilane. Here we continue the search for potential single-molecule insulators based on saturated group 14 molecules. Using a high-throughput screening approach, we assess the electron transport properties of the bicyclo[2.2.2]octane class by systematically varying the constituent atoms between carbon, silicon, and germanium, thus exploring the full chemical space of 771 different molecules. The majority of the molecules in the bicyclo[2.2.2]octane class are found to be highly insulating molecules. Though the all-silicon molecule is a clear-cut case of σ-interference, it is not unique within its class and there are many potential molecules that we predict to be more insulating. The finding of this class of quantum interference based single-molecule insulators indicates that a broad range of highly insulating saturated group 14 molecules are likely to exist.

Oligothienyl catenated germanes and silanes: synthesis, structure, and properties

The synthesis of two new groups of oligothienyl catenated silanes and germanes, Me5M2Thn (1a-b), Me5M2ThnM2Me5 (2a-c) (terminal), and ThnM2Me4Thn (3a-d) (internal) (M = Si, Ge; n = 2, 3; Th = 2- or 2,5-thienyl), is reported. The study of their structural parameters as well as of their spectral (NMR), electrochemical (CV) and optical (UV/vis absorbance, luminescence) properties has been performed in detail; in addition, the unexpected compound [Th2Si2Me4Th]2 (3a') is also studied. Theoretical investigations have been performed for model compounds in order to establish structure-property relationships. The molecular structures of 2a (Me5Si2Th2Si2Me5), 2b (Me5Ge2Th2Ge2Me5), 3a (Th2Si2Me4Th2) and 3b (Th2Ge2Me4Th2) have been investigated by X-ray diffraction analysis. An effective conjugation with flattening of both Th planes in terminal 2a and 2b was observed. The main trends in the dependence of the optical and electrochemical properties on the structural parameters have been established. All of the compounds studied exhibit a strong emission within the 378-563 nm range, and the maximal quantum yield (up to 77%) is observed for the Si derivative 3a'. For the majority of the compounds, the quantum yields (20-30%) are significantly larger than for 2,2'-bi- and 2,2':5',5''-terthiophenes. Due to their good emission properties, these compounds could be used to develop new materials with specific spectral properties.

Incorporating Methyl and Phenyl Substituted Stannylene Units into Oligosilanes. The Influence on Optical Absorption Properties

Molecules containing catenated heavy group 14 atoms are known to exhibit the interesting property of σ-bond electron delocalization. While this is well studied for oligo- and polysilanes the current paper addresses the UV-absorption properties of small tin containing oligosilanes in order to evaluate the effects of Sn–Si and Sn–Sn bonds as well as the results of substituent exchange from methyl to phenyl groups. The new stannasilanes were compared to previously investigated oligosilanes of equal chain lengths and substituent pattern. Replacing the central SiMe₂ group in a pentasilane by a SnMe₂ unit caused a bathochromic shift of the low-energy band (λ_max = 260 nm) of 14 nm in the UV spectrum. If, instead of a SnMe_2, a SnPh₂ unit is incorporated, the bathochromic shift of 33 nm is substantially larger. Keeping the SnMe₂ unit and replacing the two central silicon with tin atoms causes shift of the respective band (λ = 286 nm) some 26 nm to the red. A similar approach for hexasilanes where the model oligosilane [(Me₃Si)₃Si]₂(SiMe₂)₂ (λ_max = 253 nm) was modified in a way that the central tetramethyldisilanylene unit was exchanged for a tetraphenyldistannanylene caused a 50 nm bathochromic shift to a low-energy band with λ_max = 303 nm.

Molecular Oligogermanes and Related Compounds: Structure, Optical and Semiconductor Properties

The optical (UV/Vis absorbance, fluorescence in the solid state and in solution) and semiconducting properties of a number of di- and trigermanes as well as related silicon- and tin-containing germanes, 1-6 ((p-Tol)₃ GeGeMe₃ (1), Ph₃ SnGe(SiMe₃ )₃ (2), (C₆ F₅ )₃ GeGePh₃ (3), (p-Tol)₃ GeSiMe₂ SiMe₃ (4), (p-Tol)₃ GeGeMe₂ Ge(p-Tol)₃ (5), (p-Tol)₃ GeSiMe₂ SiMe₂ Ge(p-Tol)₃ (6)) were investigated. Molecular structures of 5 and 6 were studied by X-ray diffraction analysis. All compounds displayed luminescence properties. In addition, a band gap (of about 3.3 eV) was measured for compounds 1-6 showing that those molecules display semiconductor properties.

σ-Bond Electron Delocalization in Oligosilanes as Function of Substitution Pattern, Chain Length, and Spatial Orientation

Polysilanes are known to exhibit the interesting property of σ-bond electron delocalization. By employing optical spectroscopy (UV-vis), it is possible to judge the degree of delocalization and also differentiate parts of the molecules which are conjugated or not. The current study compares oligosilanes of similar chain length but different substitution pattern. The size of the substituents determines the spatial orientation of the main chain and also controls the conformational flexibility. The chemical nature of the substituents affects the orbital energies of the molecules and thus the positions of the absorption bands.