Ge-H Bond Research Articles

Construction of Ge-Stereogenic Center by Desymmetric Carbene Insertion of Dihydrogermanes.

We developed a method for the enantioselective synthesis of germanium-stereogenic compounds by the desymmetric carbene insertion of dihydrogermanes. A chiral rhodium phosphate catalyst decomposes diaryldiazo-methanes to generate rhodium carbenes that insert enantioselectively into one of the two Ge-H bonds of dihydrogermanes to form germanium-stereogenic compounds under mild reaction conditions. By this method, a variety of chiral germanes with germanium-stereogenic centers were synthesized in high yields and excellent enantioselectivities. Kinetic studies of the reaction showed that the diazo decomposition process was the rate-determining step. The remaining Ge-H bond of the chiral germane products provides a possibility for preparing chiral tetra-substituted germanium-stereogenic compounds.

Heterobimetallic Hydrides with a Germanium(II)-Zinc Bond.

In the presence of TMEDA (TMEDA=N,N,N',N'-tetramethylethylenediamine), zinc dihydride reacted with germanium(II) compounds (BDI-H)Ge (1) and [(BDI)Ge][B(3,5-(CF3 )2 C6 H3 )4 ] (3) (BDI-H = HC{(C=CH2 )(CMe)(NAr)2 }, BDI = [HC(CMeNAr)2 ]; Ar = 2,6-i Pr2 C6 H3 ) by formal insertion of the germanium(II) center into the Zn-H bond of polymeric [ZnH2 ]n to give neutral and cationic zincagermane with a H-Ge-Zn-H core [(BDI-H)Ge(H)-(H)Zn(tmeda)] (2) and [(BDI)Ge(H)-(H)Zn(tmeda)][B(3,5-(CF3 )2 C6 H3 )4 ] (4), respectively. Compound 2 eliminated [ZnH2 ] giving diamido germylene 1 at 60 °C. Compound 2 and deuterated analogue 2-d2 exchanged with [ZnH2 ]n and [ZnD2 ]n in the presence of TMEDA to give a mixture of 2 and 2-d2 . Compounds 2 and 4 reacted with carbon dioxide (1 bar) at room temperature to form zincagermane diformate [(BDI-H)Ge(OCHO)-(OCHO)Zn(tmeda)] (5) and formate bridged digermylene [({BDI}Ge)2 (μ-OCHO)]+ [B(C6 H3 (CF3 )2 )4 ] (6) along with zinc formate [(tmeda)Zn(μ-OCHO)3 Zn(tmeda)][B(C6 H3 (CF3 )2 )4 ] (7), respectively. The hydridic nature of the Ge-H and Zn-H bonds in 2 and 4 was probed by reactions with Brönsted and Lewis acids.

Gas-Phase Preparation of 1-Germavinylidene (H2CGe; X1A1), the Isovalent Counterpart of Vinylidene (H2CC; X1A1), via Non-adiabatic Dynamics through the Elementary Reaction of Ground State Atomic Carbon (C; 3P) with Germane (GeH4; X1A1).

1-Germavinylidene (H2CGe; X1A1), the germanium analogue of vinylidene (H2CC; X1A1), was prepared via a directed gas-phase synthesis through the bimolecular reaction of ground state atomic carbon (C; 3P) with germane (GeH4; X1A1) under single-collision conditions. The reaction commences with the barrierless insertion of carbon into the Ge-H bond followed by intersystem crossing from the triplet to singlet surface and migration of atomic hydrogen to germylene (H2GeCH2), which predominantly decomposes via molecular hydrogen loss to 1-germavinylidene (H2CGe; X1A1). Therefore, the replacement of a single carbon atom in the acetylene-vinylidene system by germanium critically impacts the chemical bonding, molecular structure, and thermodynamic stability of the carbene-type structures favoring 1-germavinylidene (H2CGe) over germyne (HGeCH) by 160 kJ mol-1. Hence, the carbon-germane system represents a benchmark in the exploration of the chemistries of main group 14 elements with germanium-bearing systems showing few similarities with the isovalent carbon system.

Activation of Ge-H and Sn-H Bonds with N-Heterocyclic Carbenes and a Cyclic (Alkyl)(amino)carbene.

A study of the reactivity of several N-heterocyclic carbenes (NHCs) and the cyclic (alkyl)(amino)carbene 1-(2,6-di-iso-propylphenyl)-3,3,5,5-tetramethyl-pyrrolidin-2-ylidene (cAACMe ) with the group 14 hydrides GeH2 Mes2 and SnH2 Me2 (Me=CH3 , Mes=1,3,5-(CH3 )3 C6 H2 ) is presented. The reaction of GeH2 Mes2 with cAACMe led to the insertion of cAACMe into one Ge-H bond to give cAACMe H-GeHMes2 (1). If 1,3,4,5-tetramethyl-imidazolin-2-ylidene (Me2 ImMe ) was used as the carbene, NHC-mediated dehydrogenative coupling occurred, which led to the NHC-stabilized germylene Me2 ImMe ⋅GeMes2 (2). The reaction of SnH2 Me2 with cAACMe also afforded the insertion product cAACMe H-SnHMe2 (3), and reaction of two equivalents Me2 ImMe with SnH2 Me2 gave the NHC-stabilized stannylene Me2 ImMe ⋅SnMe2 (4). If the sterically more demanding NHCs Me2 ImMe , 1,3-di-isopropyl-4,5-dimethyl-imidazolin-2-ylidene (iPr2 ImMe ) and 1,3-bis-(2,6-di-isopropylphenyl)-imidazolin-2-ylidene (Dipp2 Im) were employed, selective formation of cyclic oligomers (SnMe2 )n (5; n=5-8) in high yield was observed. These cyclic oligomers were also obtained from the controlled decomposition of cAACMe H-SnHMe2 (3).

Взаимодействие сквалена с некоторыми гидросиланами и гидрогерманами

Squalene hydrosilylation by a number of organohydrosilanes R3SiH and Me3GeH, including a mixture of α- and β-isomers of adducts of vinyltrimethylsilane addition to tetramethyldisiloxane: HSi(Me2)O(Me2)Si-C(Me)-SiMe3 and HSi(Me2)O(Me2)Si-(CH2)2-SiMe3, formed both according to Markovnikov's rule and against it, is discussed. We pay attention to the mismatch of values between the electronegativities of carbon, silicon, germanium and hydrogen atoms and the reactivity of C-H, Si-H, and Ge-H bonds. A spectral study of a mixture of α- and β-isomers was carried out. The effect of substituents at elements on its reactivity is discussed: hydrosilanes with chlorine atoms, alkyl and alkoxy groups on silicon are not active in the squalene hydrosilylation. In contrast to them, the α- and β-adducts and their mixture add well to squalene with an unambiguously unknown regioselectivity. The results obtained indicate the special behavior of squalene in electrophilic addition reactions catalyzed by metal complexes, in contrast to substituted ethylenes.

Structural stabilities and optical properties of SixGeyHz nanocrystals

Based on the high-throughput first-principles calculations with structural recognition, we have ystematically investigated the structural stabilities and optical properties of SixGeyHz nanocrystals(H-SiGeNCs), including various sizes, shapes and compositions. The total energies of H-SiGeNCs can be simply estimated by the bond energy model in high accuracy, where the error of test set is less than 0.5 meV per atom. According to the energy difference of Si/Ge in various bonding environments, we have determined the ground state structures by the geometry analysis, as is confirmed the convex hulls of formation enthalpy from the first-principles calculations. In addition, the energy gaps of H-SiGeNCs are modulated by the atomic distributions, as well as the vibrations of Si-H and Ge-H bonds at room temperature which is revealed by ab initio molecular dynamics simulations.

Chemistry of Germanene: Surface Modification of Germanane Using Alkyl Halides.

Two-dimensional materials attract enormous attention across several scientific fields. The current demands in nano- and optoelectronics, semiconductors, or in catalysis have been accelerating the research process in the field of 2D materials. Among the 14th group 2D materials besides graphene and silicene, layered germanium represents a promising candidate for another class of materials, and its functionalization represents a way to tune either its electronic or optical properties. Here, the exfoliation and functionalization of germanane surface is achieved via abstraction of hydrogen from Ge-H bond and its subsequent alkylation utilizing n-alkyl halides or trifluoromethyl (CF3) group containing benzyl halides. Composition of materials is confirmed by several methods including FT-IR, Raman, X-ray photoelectron, and energy-dispersive X-ray spectroscopy as well as X-ray powder diffraction. Scanning and transmission electron spectroscopy is used to reveal the layered morphology of functionalized germananes.

Reactivity of Monomeric N→Ge Coordinated Germanium(II) Hydrides

Monomeric organogermanium(II) hydrides {(LGeH)M(CO)5} (M = Cr (1), W (2), L = [2‐(CH2NEt2)‐4,6‐tBu2‐C6H2]–) were treated with ortho‐quinones and terminal alkyne HC≡CCO2Me to give {[(LH)Ge(κ2‐O2‐3,5‐tBu2C6H2)]M(CO)5} (M = Cr (3), W (4)), {[(LH)Ge(κ2‐O2‐3,4,5,6‐Cl4C6)]M(CO)5} (M = Cr (5), W (6)) and {[LGeCH=CH(COOMe)]Cr(CO)5} (11). These reactions proceeded as catalyst‐free reductions of C=O and C≡C bonds. Experimental data demonstrated zwitterionic character of Ge(II) complexes 3–6, where the 1,3,2‐benzodioxagermylenolato anion involving the GeO2C2 five membered ring coordinates the M(CO)5 fragment. This anionic part is compensated by the NHEt2 counter cation that is part of ligand L. Reactions of 1 and 2 differ mutually in the case of reduction of HC≡CCO2Me. The experimental and theoretical data suggest that compound 1 reacts with HC≡CCO2Me to give vinyl germylene 11 as the product of the anti‐Markovnikov cis‐1,2‐addition, while complex 2 is inactive. These results thus suggest that the reactivity of the terminal GeH bond may be tuned by its coordination to various transition metals.

Visible-Light-Initiated Manganese-Catalyzed E-Selective Hydrosilylation and Hydrogermylation of Alkynes.

Manganese-photocatalyzed activation of the Si-H bond in silanes for the hydrosilylation of alkynes has been developed. The mild protocol operates efficiently with high regioselectivity ( anti-Markovnikov) and stereoselectivity ( Z/ E ratio ranges from 92:8 to >99:1), providing a wide range of Z-vinylsilanes in high yields. Moreover, visible-light-induced manganese-catalyzed activation of the Ge-H bond for E-selective alkyne hydrogermylation is reported for the first time.

Vegard's-law-like dependence of the activation energy of blistering on the x composition in hydrogenated a-SixGe1-x

Surface quality is a key issue in semiconductor structures for device applications. Typical surface defects are blisters. Here we investigate on the relationship between the activation energy of blistering and the composition x in hydrogenated amorphous a-SixGe1-x by employing layers deposited by Radio Frequency sputtering. To this aim the blistering activation energy was determined by means of Arrhenius plots in several samples with different compositions, including x = 0 and x = 1. Each sample was submitted to heat treatment up to the temperature where the onset of blistering was observed by change of the surface reflectivity. It is found that a linear dependence of the activation energy on x similar to the Vegard's law holds. The experimental result is supported by reaction kinetics modeling. It is suggested that the key step for the formation of blisters is the scission of the SiH and GeH bonds. The related energetic reaction leading to the formation of H2 molecules in a-SixGe1-x follows a linear law as a function of the x composition similarly to the activation energy.

Zinc-Catalyzed Synthesis of Allylsilanes by Si-H Bond Insertion of Vinyl Carbenoids Generated from Cyclopropenes.

Allylsilanes have long been recognized as valuable building blocks for organic synthesis. A zinc-catalyzed reaction of cyclopropenes and hydrosilanes provides a convenient route to these versatile unsaturated organosilanes. In this transformation, ZnBr2 serves as an efficient catalyst, allowing the generation of a zinc vinyl carbenoid intermediate, which is subsequently involved in a Si-H bond insertion. The process shows broad scope, and is amenable to substituted and functionalized cyclopropenes or the functionalization of polysiloxanes. Moreover, zinc-catalyzed carbene insertion into a Ge-H bond is reported for the first time.

Synthesis and Surface Functionalization of Hydride-Terminated Ge Nanocrystals Obtained from the Thermal Treatment of Ge(OH)2.

The synthesis of germanium nanocrystals (GeNCs) with well-defined surface chemistry is of considerable interest because of their potential applications in the optoelectronic, battery, and semiconductor industries. Modifying and tailoring GeNC surface chemistry provides an avenue by which reactivity, environmental compatibility (e.g., solubility, resistance to oxidation), and electronic properties may be tailored. Hydride-terminated GeNCs (H-GeNCs) are of particular interest because the reactivity of surface Ge-H bonds toward alkenes and alkynes via hydrogermylation affords the potential for convenient modification; however, these reactions and their scope have not been widely explored. This report describes a straightforward route for preparing a GeNC/GeO2 composite via disproportionation of heretofore-unexplored Ge(II) oxide-based precursor from which the H-GeNCs were freed by subsequently chemical etching. The H-GeNCs were derivatized using a series of hydrogermylation approaches (i.e., thermally activated, radical-initiated, and borane-catalyzed). The presented findings indicate surface functionalization occurs under all conditions investigated; however the nature of surface species (i.e., monolayers vs multilayers) and surface coverage varies depending upon the conditions employed.

The Induced Electrochemical Codeposition of Cu-Ge Alloy Films

Various examples of induced codeposition have been over time reported in the literature and partly understood. In particular, Brenner discussed as early as 1963 in his book “Electrodeposition of alloys” evidence of the induced deposition of Germanium; attempts to understand such mechanism however are lacking. In this work, the electrochemical co-deposition of Cu-Ge thin films from an alkaline tartrate-complexing electrolyte was investigated by combined cyclic voltammetry and quartz crystal microbalance of the unitary and alloy electrolytes. Ge undergoes reduction from Ge4+ (GeO32−) to Ge1− (GeH) in a two-step process and forms a self-limiting deposit, the thickness of which is a function of the Ge ion concentration and pH. Cu2+ deposition is strongly inhibited by the presence of Ge species above −1.2 V Ag/AgCl, while at more negative potentials a signature of alloy codeposition is present, in parallel with hydrogen evolution. Oxygen deposition is significant when Ge is at or above 25 at%. Induced codeposition is rationalized in terms of the activation of the Ge-H bond by Cu, resulting possibly in the formation of adsorbed species containing H-Cu-Ge, whereby H is dissociated, resulting in alloy growth in parallel with formation of a significant amount of H2 gas.

The low temperature epitaxy of Ge on Si (1 0 0) substrate using two different precursors of GeH4 and Ge2H6

We have investigated the initial stage of low temperature epitaxy (LTE) of Ge on 8″-dia. Si (100) substrate using a rapid thermal chemical vapor deposition (RTCVD) with two different precursors of GeH4 and Ge2H6. The quality of LTE Ge films such as surface morphology, defects and crystallinity were analyzed using SEM, AFM and TEM. Experimental results confirmed that the LTE Ge using Ge2H6 precursor was much more beneficial than the LTE using GeH4 in terms of growth rate (×10), stress relaxation (85% at surface), and crystal quality (low TDDs). The discrepancy looks originated from the weak GeGe bonds requiring their dissociation energy small compared to the GeH bonds in GeH4 precursors, and the abundant supply of GeH3 molecules should stimulate chemical reactions at free surface sites. Our LTE technology would be promising for very thin Ge virtual substrate as well as be beneficial for nano-micro electronic devices in need of low temperature processes below 300–500°C.

Optical vibrational modes of Ge nanowires: A computational approach

Although Ge nanowires (GeNWs) have been extensively studied in the last decade the information about their vibrational modes is still scarce, their correct comprehension could hasten the development of new microelectronic technologies, therefore, in this work we aimed to study the vibrational properties, Raman and IR and spectrum of GeNWs using the first principles density functional perturbation theory. The nanowires are modelled in the [001] direction and all dangling bonds are passivated with H and Cl atoms. Results show that the vibrational modes can be classified in three frequency intervals, a low frequency one (between 0 and 300cm−1) of mainly GeGe vibrations, and two of GeH bending and stretching vibrations (400–500cm−1 and 2000cm−1, respectively). There is a shift of the highest optical modes of GeGe vibrations compared to their bulk counterparts due to phonon confinement effects, however it is masked by some GeH bond bending modes as demonstrated by the IR and Raman responses. The Cl passivated case shows a larger number of modes at lower frequencies due to the higher mass of Cl compared to H, which in turn reduces the red shift of the highest optical modes frequencies. These results could be important for the characterization of GeNWs with different surface passivations.

Structural evolution and optical properties of hydrogenated germanium carbonitride films

Although the control of bond structure and optical properties in hydrogenated amorphous germanium carbonitride films (a-GeC1−xNx:H) is important for technological applications, the composition dependence of chemical bonds, especially hydrogen-containing bonds, is not yet well explored. The evolution in refractive index (n) and Urbach tail width (E0) remains unclear. Here, we show that nitrogen content (CN) exerts a significant effect on bonding structure and optical properties of a-GeC1−xNx:H films. As CN increases, the fraction of NH increases, whereas that of CH and GeH bonds reduces, and GeN bonds form at expense of GeC bonds. The replacement of carbon by nitrogen induces a substantial decrease in n from 3.0 to 2.3 because of decrease in electronic polarizability. With increasing CN, a significant increase in E0 from 198.8 to 327.9 meV takes place. This behavior arises from decrease in dielectric coefficient (ε), rather than the change in the degree of disorder previously believed. The change in E0 is proportional to the variation in 1/ε2, which agrees well with hydrogen-like atom model. This study discovers that a-GeC1−xNx:H films have the apparent tunability of n and E0 over a wide range, which is useful in controlling the optical transmission and absorption characteristics of these films.

Synthesis and Characterization of Atomically Flat Methyl-Terminated Ge(111) Surfaces.

Atomically flat, terraced H-Ge(111) was prepared by annealing in H2(g) at 850 °C. The formation of monohydride Ge-H bonds oriented normal to the surface was indicated by angle-dependent Fourier-transform infrared (FTIR) spectroscopy. Subsequent reaction in CCl3Br(l) formed Br-terminated Ge(111), as shown by the disappearance of the Ge-H absorption in the FTIR spectra concomitant with the appearance of Br photoelectron peaks in X-ray photoelectron (XP) spectra. The Br-Ge(111) surface was methylated by reaction with (CH3)2Mg. These surfaces exhibited a peak at 568 cm(-1) in the high-resolution electron energy loss spectrum, consistent with the formation of a Ge-C bond. The absorption peaks in the FTIR spectra assigned to methyl "umbrella" and rocking modes were dependent on the angle of the incident light, indicating that the methyl groups were bonded directly atop surface Ge atoms. Atomic-force micrographs of CH3-Ge(111) surfaces indicated that the surface remained atomically flat after methylation. Electrochemical scanning-tunneling microscopy showed well-ordered methyl groups that covered nearly all of the surface. Low-energy electron diffraction images showed sharp, bright diffraction spots with a 3-fold symmetry, indicating a high degree of order with no evidence of surface reconstruction. A C 1s peak at 284.1 eV was observed in the XP spectra, consistent with the formation of a C-Ge bond. Annealing in ultrahigh vacuum revealed a thermal stability limit of ∼400 °C of the surficial CH3-Ge(111) groups. CH3-Ge(111) surfaces showed significantly greater resistance to oxidation in air than H-Ge(111) surfaces.

Cooperative Ge-N Bond activation in aluminium-functionalised aminogermanes and spontaneous imine elimination via an intermediate germyl cation.

Hydrometallation of iPr2 N-Ge(CMe3 )(C≡C-CMe3 )2 with H-M(CMe3 )2 (M=Al, Ga) affords alkenyl-alkynylgermanes in which the Lewis-acidic metal atoms are not coordinated by the amino N atoms but by the α-C atoms of the ethynyl groups. These interactions result in a lengthening of the Ge-C bonds by approximately 10 pm and a comparably strong deviation of the Ge-CC angle from linearity (154.3(1)°). This unusual behaviour may be caused by steric shielding of the N atoms. Coordination of the metal atoms by the amino groups is observed upon hydrometallation of Et2 N-Ge(C6 H5 )(C≡C-CMe3 )2 , bearing a smaller NR2 group. Strong M-N interactions lead to a lengthening of the Ge-N bonds by 10 to 15 pm and a strong deviation of the M atoms from the MC3 plane by 52 and 47 pm, for Al and Ga, respectively. Dual hydrometallation is achieved only with HAl(CMe3 )2 . In the product, there is a strong Al-N bond with converging Al-N and Ge-N distances (208 vs. 200 pm) and an interaction of the second Al atom to the phenyl group. Addition of chloride anions terminates the latter interaction while the activated Ge-N bond undergoes an unprecedented elimination of EtN=C(H)Me at room temperature, leading to a germane with a Ge-H bond. State-of-the-art DFT calculations reveal that the unique mechanism comprises the transfer of the amino group from Ge to Al to yield an intermediate germyl cation as a strong Lewis acid, which induces β-hydride elimination, with chloride binding being crucial for providing the thermodynamic driving force.

Synthesis and structures of new tetrairidium carbonyl clusters containing phenylgermanium ligands

The reaction of Ir4(CO)11(PPh3) with GePh3H in the presence of Me3NO at room temperature has yielded a new complex Ir4(CO)10(PPh3)(GePh3)(μ-H), 1 in 54% yield by decarbonylation and oxidative addition of the GeH bond of the GePh3H to the cluster. The structure of 1 consists of a tetrahedral Ir4 cluster with a terminal GePh3 ligand and a bridging hydrido ligand. Compound 1 was converted to the GePh2-bridged complex Ir4(CO)10(PPh3)(μ-GePh2), 2 in 95% yield when heated to 40 °C, by the cleavage of a phenyl ring from the GePh3 ligand and the elimination of a molecule of benzene. The reaction of 2 with GePh3H at 65 °C yielded the new tetrahedral Ir4 complex Ir4(CO)7(PPh3)(GePh2)(GePh3)(μ3-η2-GePhC6H4)(μ-H)2, 3 which contains an ortho-metallated bridging μ3-η2-GePh(C6H4) ligand, a terminal GePh3 ligand, a bridging GePh2 ligand and two bridging hydrido ligands. Compound 3 was converted to the complex Ir4(CO)7(PPh3)(GePh2)2(μ3-η2-GePhC6H4)(μ-H), 5 cleavage of a phenyl ring from the GePh3 ligand and the elimination of a molecule of benzene. The structure of 5 consists of a tetrahedral Ir4 cluster with an ortho-metallated bridging μ3-η2-GePh(C6H4) group, two bridging GePh2 ligands and one bridging hydrido ligand. The reaction of 2 with GePh2H2 at 40 °C yielded the tetrairidium complex Ir4(CO)6(PPh3)(GePh2)3(GePh2H)(μ-H)3, 6 with three bridging GePh2 ligands, a terminal GePh2H ligand and three bridging hydrido ligands. All new compounds were fully characterized by IR and 1H NMR spectroscopy, single-crystal X-ray diffraction analyses, and mass spectrometry.

Crystallization behavior of microcrystalline silicon germanium

Hydrogenated microcrystalline silicon germanium (μc-Si1−xGex:H) thin films were evaluated as a bottom cell absorber for multi-junction solar cells based on Si thin films. The crystallization behavior of μc-Si1−xGex:H was examined. Raman spectroscopy and grazing angle X-ray diffraction showed that the crystallinity of the μc-Si1−xGex:H films decreased with increasing Ge content. Fourier transform infrared spectroscopy revealed an increase in the intensity of the GeH and GeH2 bonds in μc-Si1−xGex:H due to the increased amorphous phase. The rapid GeH4 decomposition rate and preferential etching of Si bonds led to a decrease in crystallinity and an extremely high Ge content in the μc-Si1−xGex:H films. The dark conductivity of μc-Si1−xGex:H was affected by the internal crystallinity and an excessively high crystallinity deteriorated the electrical properties. The photo response increased from 102 to 103 with increasing Ge content. This study presents a comprehensive evaluation of the crystallization behavior of μc-Si1−xGex:H films for solar cell absorber applications.