Selective Synthesis and Derivatization of Germasilicon Hydrides

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Selective Synthesis and Derivatization of Germasilicon Hydrides Harald Stueger,*,† Viktor Christopoulos,† Andrea Temmel,† Michael Haas,† Roland Fischer,† Ana Torvisco,† Odo Wunnicke,‡ Stephan Traut,‡ and Susanne Martens‡ †

Institute of Inorganic Chemistry, Graz University of Technology, Stremayrgasse 9, A-8010 Graz, Austria Evonik Creavis GmbH, Paul-Baumann-Straße 1, D-45772 Marl, Germany

‡

S Supporting Information *

ABSTRACT: Mixed Si/Ge hydrides SixGeyHz are valuable precursors for the deposition of binary Si−Ge alloys. This work describes the synthesis and full characterization of the previously unknown germaisotetrasilane Ph3GeSi(SiH3)3 (2) on a multigram scale from the reaction of the lithium silanide LiSi(SiH3)3 with Ph3GeCl. The stability of the Si−Ge bond in 2 versus electrophiles and nucleophiles has been investigated with the primary aim of developing new approaches to mixed sila-H-germanes (H3Ge)xSi(SiH3)4−x. With 1 equiv of MeLi, 2 reacted cleanly under cleavage of one Si−Si bond to give Ph3GeSi(SiH3)2Li, which is a valuable synthon for further derivatization. In contrast, the dephenylation reaction of 2 with 1 or 2 equiv of CF3SO3H/iBu2AlH proceeded much less selectively and afforded the desired Ph/H-germasilanes Ph2HGeSi(SiH3)3 and PhH2GeSi(SiH3)3 along with considerable amounts of Si−Ge scission products.

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of H3GeK with silyl triflates (TfO)xSiH4−x (OTf = CF3SO3).3 Sundermeyer et al. synthesized the silylgermanes (H3Si)2GeH2, (H3Si)3GeH, and (H3Si)4Ge from the corresponding silylgermanides (H3Si)xGeH4−xNa (x = 2−4) and C4F9SO3SiH3 and isolated the individual products by preparative gas chromatography.7 The same group presented an alternative approach to H3GeSiH3 by halodephenylation of H3GeSiH2Ph with anhydrous HBr followed by hydrogenation of the bromosilane intermediate with LiAlH4.8 Hoefler et al., finally, investigated the reaction of Ph3GeSiPh3 with excess anhydrous HCl or HBr and observed the predominant scission of the Si−Ge bond.9 To the best of our knowledge, the latter two studies are the only examples in the literature of chemical transformations involving mixed Si/Ge hydrides. In a recent paper, we presented a novel method for the selective synthesis of alkali metal silanides MSi(SiH3)3 (M = Li, Na, or K) (1), which allows the straightforward preparation of isotetrasilane derivatives in multigram quantities.10 Now we report on the previously unknown germaisotetrasilane Ph3GeSi(SiH3)3 (2) and on the investigation of the stability of the Si− Ge bonds present in 2 versus MeLi and CF3SO3H/H−, with a primary aim of developing new approaches to mixed sila-Hgermanes (H3Ge)xSi(SiH3)4−x.

INTRODUCTION The combination of the chemical and physical properties of Si and Ge is a well-established strategy for the engineering of innovative materials. As a consequence, Si/SiGe heterostructures are today used in a wide range of electronics and optoelectronic devices.1 However, conventional growth of Si1−xGex films on Si is complicated by the inherent lattice mismatch between the films and the substrate. The development of suitable low-temperature pathways to the preparation of device quality Ge-rich layers on Si, thus, is one of the ongoing challenges in material science. For industrial applications, Si/Ge films are most abundantly deposited by reduced pressure−chemical vapor deposition (RP-CVD) of gaseous precursors such as SiH4, Si2H6, SiH2Cl2, and GeH4.2 This process, however, is complicated by the different thermal stabilities of the educts, which leads to nonuniform deposition rates, and frequently, segregation of either Ge or Si is observed. A more recent approach uses single-source hydrides with direct Si−Ge bonds as low-temperature (300−450 °C) precursors for the growth of binary Si−Ge alloys.3 Mixed Si/ Ge hydrides SixGeyHz, however, are not easily accessible from a synthetic point of view.4 The most common methods for their preparation, the impact of silent electric discharges on SiH4/ GeH4 mixtures5 and the acid hydrolysis of Mg(Ca)xSiyGez alloys or SiO/GeO mixtures,6 afford complex product mixtures, and individual Si/Ge/H species were never isolated and characterized in a pure state in these studies. Only scattered reports of the selective synthesis of sila-H-germanes can be found in the literature. Kouvetakis et al. prepared and isolated the entire family of silicon−germanium hydrides (H3Ge)xSiH4−x (x = 1−4), including H3GeSiH3 by the reaction © XXXX American Chemical Society

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RESULTS AND DISCUSSION Synthesis of Ph3GeSi(SiH3)3 (2). As shown in Scheme 1, the reaction of LiSi(SiH3)3 with 1 equiv of Ph3GeCl cleanly afforded the germasilane 2, although care had to be taken to Received: February 10, 2016

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DOI: 10.1021/acs.inorgchem.6b00349 Inorg. Chem. XXXX, XXX, XXX−XXX

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distances and a slightly distorted tetrahedral geometry around Si1. The Si−Ge bond in 2 of 2.380 Å is somewhat longer than that measured in Me3SiGePh3 (2.384 Å)12 but shorter than the elongated Si−Ge bond in (Me3Si)3SiGePh3 (2.416 Å).13 Reaction of 2 with MeLi/Ph3ECl (E = Si or Ge). To assess the stability of the Si−Ge bond versus bases, 2 was reacted with MeLi. It has been found that the addition of 0.95 equiv of MeLi to a diethyl ether solution of 2 at −30 °C selectively affords the triphenylgermyl-substituted silanide anion 3 after a reaction time of 1 h at room temperature as indicated by the presence of only two characteristic resonances in the decoupled 29Si NMR spectrum of the resulting solution. Upon anion formation, the SiH3 signal in the spectrum of 2 near −90 ppm is shifted downfield by ∼8 ppm to −82.8 ppm while the resonance line of the central silicon atom exhibits a pronounced upfield shift of ∼75 ppm, from −151.2 to −225.4 ppm. 3 turned out to be thermally unstable. When the anion solution was stored overnight at room temperature under inert gas, 29Si NMR spectroscopy showed the formation of ∼50% of (Ph3Ge)2(SiH3)SiLi (4) along with residual 3 and insoluble pyrophoric hydrosilane oligomers of unknown structure. Storage for longer periods afforded increasing amounts of the solid material. 4 unequivocally was identified by a comparison of its 29Si chemical shift values with the corresponding data obtained for 4 prepared independently from 6 and MeLi (for details, consult the Experimental Section). Freshly prepared solutions of 3, however, can be used successfully for further derivatization reactions on a multigram scale. Thus, 3 cleanly reacted in the expected way with Ph3ECl (E = Si or Ge) to give the previously unknown germa-H-silanes 5 and 6 (Scheme 2).

Scheme 1. Synthesis of 2

prevent any excess of lithium silanide in the reaction mixture to suppress undesired side reactions. Similar tendencies for the formation of increased amounts of byproducts in the presence of excess metal silanide have been observed before for the reaction of KSiH3 with MeI or Me3EX (E = Si, Ge, or Sn; X = Cl or Br)11 or for the reaction of 1 with PhH2SiCl or PhMe2SiCl.10 Thus, 2 only could be synthesized and isolated by crystallization in only >80% yield, if the metal silanide solution was slowly added to the chlorogermane dissolved in diethyl ether at −30 °C. Structural assignment is easily accomplished as shown by the analytical and spectroscopic data of 2 given in the Experimental Section. In the 1H NMR spectrum, one sharp signal appears at 3.53 ppm in the range typical for SiH3 groups along with the multiplet of the aromatic protons between 7.1 and 7.6 ppm in an integral ratio of 9:15. Chemical shifts and splitting patterns apparent in the coupled 29Si spectrum are also consistent with the proposed structure. A quartet of heptets centered at −90.4 ppm appears due to 29Si−1H couplings within the Si(SiH3) moiety (1JSi−H = 200.1 Hz; 3JSi−H = 3.7 Hz), while the signal of the central silicon atom at −151.2 ppm is split into a multiplet because of long-range coupling of the silicon nucleus to the nine hydrogen atoms of the attached SiH3 groups (2JSi−H = 5.5 Hz). The molecular structure of 2 as determined by single-crystal X-ray crystallography is depicted in Figure 1 together with selected bond lengths and bond and torsion angles. 2 is isostructural to the corresponding silyl derivative Ph3SiSi(SiH3)3.10 Both compounds crystallize in the trigonal space group R3̅ with nearly identical and unexceptional Si−SiH3

Scheme 2. Reaction of 2 with MeLi/Ph3ECl

5 and 6 were obtained in isolated yields of >90% as colorless and moderately air stable crystals. Analytical and spectroscopic data are given in the Experimental Section together with experimental details. Compound 6 was also characterized by Xray crystallography. Figure 2 shows the obtained molecular structure along with selected structural data. 6 crystallizes in the monoclinic space group P21/c. Compared to those of 2, the Si−Ge bonds are slightly elongated and the geometry around Si1 is somewhat more distorted because of the presence of the second sterically demanding Ph3Ge group. Reaction of 2 with CF3SO3H/iBu2AlH. The stability of the Si−Ge bond under acidic conditions was studied by reacting 2 with triflic acid followed by the hydrogenation of the resulting products with iBu2AlH. CF3SO3H has been shown before to be excellently suitable for the substitution of phenyl groups in organopolysilanes, -polygermanes, and -polysilagermanes under preservation of the element−element bonds.14 If one assumes

Figure 1. ORTEP diagram for compound 2. Thermal ellipsoids are depicted at the 50% probability level. Hydrogen atoms have been omitted for the sake of clarity. Selected bond lengths (angstroms) and bond and torsion angles (degrees) with estimated standard deviations: Si1−Si2, 2.329(2); Si1−Ge1, 2.380(2); Si2−Si1−Si2, 112.6(2); Si2− Si1−Ge1, 106.1(2). B

DOI: 10.1021/acs.inorgchem.6b00349 Inorg. Chem. XXXX, XXX, XXX−XXX

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Figure 2. ORTEP diagram for compound 6. Thermal ellipsoids are depicted at the 50% probability level. Hydrogen atoms have been omitted for the sake of clarity. Selected bond lengths (angstroms) and bond and torsion angles (degrees) with estimated standard deviations: Si1−Si2, 2.336(1); Si1−Si3, 2.337(1); Si1−Ge1, 2.393(1); Si1−Ge2, 2.406(1); Si2−Si1−Si3, 104.4(1); Si2−Si1−Ge1, 115.3(1); Si3−Si1− Ge1, 105.8(1); Si3−Si1−Ge2, 108.8(1); Ge2−Si1−Ge1, 111.7(1).

Figure 3. 1H NMR spectra (hydride region) of 2 after addition of (A) 1 and (B) 2 equiv of CF3SO3H/iBu2AlH.

similar behavior of the Si−Ge bond in 2, this route might provide an easy approach to sila-H-germanes PhnH3−nGeSi(SiH3)3 (n = 1 or 2), which otherwise are not readily available. However, as shown in Scheme 3, 2 reacted with 1 equiv of CF3SO3H/iBu2AlH under formation of Ph2HGeSi(SiH3)3 (7) along with ∼20% of Ph3GeH and minor amounts of unidentified poly-H-silanes, indicating Si−Ge bond scission at least to a certain extent. Besides the multiplets of the aromatic protons between 7 and 7.5 ppm and some low-intensity signals around 3.50 ppm due to the presence of minor amounts of further poly-H-silanes, the 1H NMR spectrum of the resulting crude mixture (compare Figure 3A) showed singlets at 5.80, 5.31, and 3.50 ppm with an intensity ratio of approximately 0.2:1:9, which can be assigned to the hydridic hydrogen atoms present in Ph3GeH15 and in the Ph2HGe and H3Si groups of 7, respectively. Consistent with this picture, only two resonance lines appeared in the proton-decoupled 29Si spectrum of 7 arising from the SiH3 group (δ29Si = −91.0 ppm) and from the quaternary silicon atom (δ29Si = −151.9 ppm). 7 and Ph3GeH were also identified by GC/MS analysis as the major products with an intensity ratio of ∼4:1. Attempts to isolate pure 7 from the crude material by crystallization under various conditions or by distillation at reduced pressure were not successful.

When we tried to substitute a second phenyl group by hydrogen at the germanium center in 7, we observed even more pronounced scission of the Si−Ge bond (compare to Scheme 3). The 1H NMR spectrum of the oily residue obtained after the addition of an additional 1 equiv of CF3SO3H/iBu2AlH to a toluene solution of 7 at −30 °C and removal of the solvent in vacuo (Figure 3B) clearly indicated the presence of residual Ph3GeH (δ1H = 5.80 ppm), already present in the starting material, of the Ge−Ph substitution product 8 [δ1H = 4.43 ppm (2H, PhH2Ge), 3.45 ppm (9H, SiH3)] and of the Ge−Si bond scission product Ph2GeH2 (δ1H = 5.11 ppm).16 The remaining signals around 3.5 and 4.5 ppm arise from further oligo-Ph/Ge/ H-silanes of unidentified structure formed by additional and presumably complex side reactions. After distillation of this crude material at 0.05 mbar, a small amount of a 1:2 mixture of 8 and Ph2GeH2 was isolated, which could not be separated further. Reaction of 1 with CF3SO3GeH3. Because silyl triflates (TfO)xSiH4−x recently were shown to react with H3GeK under formation of Si−Ge bonds,3 we attempted to synthesize

Scheme 3. Reaction of 2 with CF3SO3H/iBu2AlH

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7.3 Hz, SiH3), −259.1 (m, 2JSi−H = 6.2 Hz, SiSi3). Data consistent with the literature.10 Synthesis of Ph3GeSi(SiH3)3 (2). A solution of 1 in 40 mL of diethyl ether [freshly prepared from 1.0 g (6.6 mmol, 1 equiv) of Si(SiH3)4 and 6.3 mmol (0.95 equiv) of MeLi] was added slowly to a solution of 1.6 g (6.3 mmol, 0.95 equiv) of Ph3GeCl in 40 mL of diethyl ether at −30 °C. After the mixture had been stirred overnight and the solvent removed in vacuo, 50 mL of toluene was added and the salts were filtered off. After evaporation of the solvent in vacuo and crystallization of the semisolid residue from pentane at −30 °C, 1.8 g (82%) of pure 2 could be isolated as colorless and moderately air stable crystals: mp 108 °C; 29Si NMR (C6D6, TMS) δ −90.4 (q, 1JSi−H = 200.1 Hz; hep, 3JSi−H = 3.7 Hz, SiH3), −151.2 (m, 2JSi−H = 5.5 Hz, SiSi3Ge); 1H NMR (C6D6, TMS, relative intensity) δ 7.5 (m, 6H, oC6H5), 7.1 (m, m,p-C6H5), 3.53 (s, 9H, SiH3); IR (Nujol mull) ν(Si− H) 2144 (s) cm−1; HRMS calcd for [C18H24GeSi4]+ (M+) 426.0170, found 426.0170. Synthesis of Ph3Ge(H3Si)2SiLi (3). A volume of 1.5 mL of a 1.6 M solution of MeLi (2.5 mmol, 0.95 equiv) in diethyl ether was added slowly to a solution of 1.1 g (2.6 mmol, 1 equiv) of 2 in 20 mL of diethyl ether at −30 °C. After the mixture had been stirred for an additional 30 min at room temperature, 29Si NMR analysis of the resulting orange solution revealed quantitative formation of 3. 3 decomposes upon storage of the solution at room temperature for 24 h to give a 1:1 mixture of 3 and 4: 29Si NMR (Et2O/D2O, TMS) δ −82.8 (q, 1JSi−H = 173.0 Hz; hep, 3JSi−H = 6.9 Hz, SiH3), −225.4 (m, 2 JSi−H = 6.4 Hz, SiSi3Ge). Synthesis of (Ph3Ge)2(H3Si)SiLi (4). The same procedure that was used for 3 was followed with 0.7 g (1 mmol, 1 equiv) of 6 and 0.6 mL of a 1.6 M solution of MeLi (0.95 mmol, 0.95 equiv). 29Si NMR analysis of the resulting orange solution revealed quantitative formation of 4: 29Si NMR (Et2O/D2O, TMS) δ −85.2 (q, 1JSi−H = 175.3 Hz, SiH3), −181.6 (q, 2JSi−H = 6.9 Hz, SiSiGe2); 1H NMR (Et2O/D2O, TMS) δ 7.8−7.5 (m, 30 H, C6H5), 4.06 (s, 3H, SiH3). Synthesis of (Ph3Ge)(Ph3Si)Si(SiH3)2 (5). The same procedure that was used for the synthesis of 2 was followed with 2.02 g (4.8 mmol, 1 equiv) of 2, 4.5 mmol (0.95 equiv) of MeLi, and 1.33 g (4.5 mmol, 0.95 equiv) of Ph3SiCl. The solution of 3 was added to Ph3GeCl at 0 °C to prevent any excess of 3 in the reaction mixture. After crystallization from toluene at −30 °C, 2.9 g (93%) of pure, colorless, and air stable crystals of 5 could be isolated: mp 135 °C; 29Si NMR (C6D6, TMS) δ −11.5 (m, SiPh3), −89.1 (q, 1JSi−H = 197.8 Hz; q, 3JSi−H = 5.1 Hz, SiH3), −148.8 (m, 2JSi−H = 5.6 Hz, SiSi3Ge); 1H NMR (C6D6, TMS, relative intensity) δ 7.5 (m, 12H, o-C6H5), 7.1− 6.9 (m, m,p-C6H5), 3.61 (s, 6 H, SiH3); IR (Nujol mull) ν(Si−H) 2129 (s) cm−1; HRMS calcd for [C18H24GeSi4]+ (M+) 654.1114, found 654.1161. Synthesis of (Ph3Ge)2Si(SiH3)2 (6). The same procedure that was used for the synthesis of 2 was followed with 1.1 g (2.6 mmol, 1 equiv) of 2, 2.5 mmol (0.95 equiv) of MeLi, and 0.84 g (2.5 mmol, 0.95 equiv) of Ph3GeCl. The solution of 3 was added to Ph3GeCl at 0 °C to prevent any excess of 3 in the reaction mixture. After crystallization from toluene at −30 °C, 1.7 g (92%) of pure, colorless, and air stable crystals of 6 could be isolated: mp 120 °C; 29Si NMR (C6D6, TMS) δ −89.4 (q, 1JSi−H = 199.2 Hz; q, 3JSi−H = 4.3 Hz, SiH3), −135.4 (m, 2 JSi−H = 6.0 Hz, SiSi2Ge2); 1H NMR (C6D6, TMS, relative intensity) δ 7.5 (m, 12H, o-C6H5), 7.1−6.9 (m, m,p-C6H5), 3.65 (s, 6 H, SiH3); IR (Nujol mull) ν(Si−H) 2131 (s) cm −1 ; HRMS calcd for [C18H24GeSi4]+ (M+) 698.0571, found 698.0588. Reaction of 2 with CF3SO3H/iBu2AlH. A volume of 0.16 mL (1.8 mmol, 1 equiv) of triflic acid was added to a solution of 0.76 g (1.8 mmol, 1 equiv) of 2 in 15 mL of toluene at −30 °C. After the mixture had been stirred overnight at room temperature, 0.32 mL (1.8 mmol, 1 equiv) of iBu2AlH was added and the resulting mixture was stirred for an additional 1 h at room temperature. Workup was accomplished by the addition of 10% deoxygenated H2SO4, phase separation, drying of the organic layer with Na2SO4, and removal of the solvent in vacuo. 1H and 29Si NMR and GC/MS analysis of the resulting colorless and viscous oil showed the formation of 7 [HPh2GeSi(SiH3)3] along with ∼20% of Ph3GeCl. Separation of the crude material by crystallization

H3GeSi(SiH3)3 (9) directly from H3GeOTf and LiSi(SiH3)3 (Scheme 4). Scheme 4. Reaction of 1 with CF3SO3GeH3

As shown by GC/MS and 29Si NMR analysis, however, the volatile fraction obtained after the addition of 1 equiv of LiSi(SiH3)3 to a pentane solution of H3GeOTf at −30 °C contained ∼65% Si(SiH3)4 along with minor amounts of other silicon hydrides of unidentified structure. The additional formation of considerable amounts of insoluble polymeric material further indicates the unfavorable course of the reaction.

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CONCLUSION Previously unknown higher silicon hydrides containing Ph3Ge groups can be accessed in excellent yields on a multigram scale starting from neopentasilane using an easy-to-perform reaction pathway. With MeLi, the obtained products can be transformed to the corresponding lithium silanides, which are valuable educts for further derivatization. Dephenylation reactions at the Ge center with CF3SO3H/iBu2AlH, however, turned out to be unsuitable for the preparation of perhydrogermasilanes such as 9 because of the limited chemical stability of the Ge−Si bond. Attempts to synthesize 9 directly from LiSi(SiH3)3 and H3GeOTf also failed.

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EXPERIMENTAL SECTION

General Considerations. All experiments were performed under a nitrogen atmosphere using standard Schlenk techniques. Solvents were dried using a column solvent purification system.17 Commercial MeLi (1.6 M solution in ether, free of LiBr), Ph3SiCl (95−98%), CF3SO3H (95−98%), and iBu2AlH (95−98%) were used as purchased. 1H (299.95 MHz) and 29Si (59.59 MHz) NMR spectra were recorded on a Varian INOVA 300 spectrometer and referenced versus TMS using the internal 2H-lock signal of the solvent or of internal D2O capillaries. Neopentasilane [Si(SiH3)4]10,18 and Ph3GeCl19 were synthesized according to published procedures. Mass spectra were run on an HP 5971/A/5890-II GC/MS coupling [HP 1 capillary column, length of 25 m, diameter of 0.2 mm, 0.33 μm poly(dimethylsiloxane)] or on a Kratos Profile mass spectrometer equipped with a solid probe inlet (HRMS). Calculated masses are for the isotope peak with the highest intensity, typically containing mainly 74Ge. Infrared spectra were recorded on a Bruker Alpha-P Diamond ATR spectrometer from the solid sample. Melting points were determined using a Buechi 535 apparatus and are uncorrected. Elemental analyses of 2, 5, and 6 performed on a Hanau Vario Elementar EL apparatus gave experimental values considerably lower than the calculated ones due to incomplete combustion. Synthesis of (H3Si)3SiLi (1). A volume of 3.1 mL of a 1.6 M solution of MeLi (4.9 mmol, 0.95 equiv) in diethyl ether was added slowly to a solution of 0.78 g (5.13 mmol, 1 equiv) of Si(SiH3)4 in 20 mL of diethyl ether at −30 °C. After the mixture had been stirred for a further 30 min at room temperature 1H and 29Si NMR analysis of the resulting off-white solution revealed quantitative formation of 1: 29Si NMR (Et2O/D2O, TMS) δ −79.9 (q, 1JSi−H = 172.0 Hz; hep, 3JSi−H = D

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under various conditions was not successful. For 7: 29Si NMR (INEPT, bb-decoupled, toluene/D2O, TMS) δ −91.0 (s, SiH3), −151.9 (s, SiSi3Ge); 1H NMR (C6D6, TMS, relative intensity) δ 7.5− 7.1 (m, C6H5), 5.31 (s, 1H, GeHPh2), 3.50 (s, 9H, SiH3); MS [m/e (relative intensity)] 350.0 (3%, M+), 229.0 (100%, Ph2GeH). Reaction of 7 with CF3SO3H/iBu2AlH. The same procedure that is described above was followed with 0.24 g (0.7 mmol, 1 equiv) of 7, 0.062 mL (0.7 mmol, 1 equiv) of triflic acid, and 0.13 mL (0.7 mmol, 1 equiv) of iBu2AlH. 1H and 29Si NMR analysis of the resulting liquid residue showed the formation of 8, Ph2GeH2, and further products of unknown composition. Distillation of the crude material at 36−38 °C and 0.05 mbar afforded a 1:2 mixture of 8 and Ph2GeH2 that could not be separated. For 8: 29Si NMR (INEPT, bb-decoupled, toluene/D2O, TMS) δ −90.9 (s, SiH3), −153.4 (s, SiSi3Ge); 1H NMR (C6D6, TMS, relative intensity) 7.5−7.0 (m, C6H5), 4.43 (s, 2H, GeH2Ph), 3.45 (s, 9H, SiH3); MS [m/e (relative intensity)] 274.0 (2%, M+), 210.0 (100%, PhGeSiSiH3). Reaction of 1 with CF3SO3GeH3. A volume of 0.29 mL (3.3 mmol, 1 equiv) of triflic acid was added to a solution of 0.50 g (3.3 mmol, 1 equiv) of PhGeH3 in 5 mL of toluene at −30 °C. After the mixture had been stirred for 1 h at room temperature, the resulting mixture was cooled to 0 °C and a solution of 1 in 10 mL of diethyl ether [freshly prepared from 0.50 g (3.3 mmol, 1 equiv) of Si(SiH3)4 and 3.1 mmol (0.95 equiv) of MeLi] was added via a syringe. After the mixture had been stirred for an additional 1 h at room temperature, considerable amounts of insoluble polymeric material of unidentified structure were obtained. 29Si NMR and GC/MS analysis of the soluble fraction showed the formation of Si(SiH3)4 along with minor amounts of other silicon hydrides. X-ray Crystallography. For X-ray structure analysis, suitable crystals were mounted onto the tip of glass fibers using mineral oil. Data collection was performed on a Bruker Kappa Apex II CCD diffractometer at 100 K using graphite-monochromated Mo Kα (λ = 0.71073 Å) radiation. Details of the crystal data and structure refinement are provided in the Supporting Information. SHELX version 6.1 was used for the structure solution and refinement.20 Absorption corrections were applied using SADABS.21 All nonhydrogen atoms were refined with anisotropic displacement parameters. Hydrogen atoms were included in the refinement at calculated positions using a riding model as implemented in SHELXTL. Crystallographic data (excluding structure factors) have been deposited with the Cambridge Crystallographic Data Centre as supplementary publications CCDC-1450030 (2) and CCDC-1450031 (6). Copies of the data can be obtained free of charge on application to The Director, CCDC, 12 Union Road, Cambridge CB2 1EZ, UK (fax (internat.) + 44-1223/336-033; e-mail [email protected]).

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ACKNOWLEDGMENTS We thank the FFG (Austrian Research Promotion Agency, Wien, Austria) for financial support (Project 838476 “SILAVOLT”). We gratefully acknowledge support from NAWI Graz.

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REFERENCES

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ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.inorgchem.6b00349. Figures of 1H NMR spectra of 2, 5, and 6, figures of 29Si NMR spectra of 3, 4, and 7, and tables giving crystal, collection, and refinement data for the structures of compounds 2 and 6 (PDF) CIF files giving crystal, collection, and refinement data for the structures of compounds 2 and 6 (CIF)

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*E-mail: [email protected]. Notes

The authors declare no competing financial interest. E

DOI: 10.1021/acs.inorgchem.6b00349 Inorg. Chem. XXXX, XXX, XXX−XXX