Formation of T‐Shaped versus Charge‐Transfer Molecular Adducts in the Reactions Between Bis(thiocarbonyl) Donors and Br2 and I2

The reactions of 4,5,6,7‐tetrathiocino‐[1,2‐b:3,4‐b′]‐1,3,8,10‐tetrasubstituted‐diimidazolyl‐2,9‐dithiones (R₂,R′₂‐todit; 1 : R=R′=Et; 2 : R=R′=Ph; 3 : R=Et, R′=Ph) with Br₂ exclusively afforded 1:1 and 1:2 “T‐shaped” adducts, as established by FT‐Raman spectroscopy and single‐crystal X‐ray diffraction in the case of complex 1? 2 Br₂. On the other hand, the reactions of compounds 1 – 3 with molecular I₂ provided charge‐transfer (CT) “spoke” adducts, among which the solvated species 3? 2 I₂ ? (1?x)I₂ ? x CH₂Cl₂ (x=0.94) and ( 3 )₂ ? 7 I₂ ? x CH₂Cl_2, (x=0.66) were structurally characterized. The nature of all of the reaction products was elucidated based on elemental analysis and FT‐Raman spectroscopy and supported by theoretical calculations at the DFT level.     

From Disilene (SiSi) to Phosphasilene (SiP) and Phosphacumulene (PCN)

The generation of heavier double‐bond systems without by‐ or side‐product formation is of considerable importance for their application in synthesis. Peripheral functional groups in such alkene homologues are promising in this regard owing to their inherent mobility. Depending on the steric demand of the N‐alkyl substituent R, the reaction of disilenide Ar₂Si?Si(Ar)Li (Ar=2,4,6‐iPr₃C₆H₂) with ClP(NR₂)₂ either affords the phosphinodisilene Ar₂Si?Si(Ar)P(NR₂)₂ (for R=iPr) or P‐amino functionalized phosphasilenes Ar₂(R₂N)Si? Si(Ar)?P(NR₂) (for R=Et, Me) by 1,3‐migration of one of the amino groups. In case of R=Me, upon addition of one equivalent of tert‐butylisonitrile a second amino group shift occurs to yield the 1‐aza‐3‐phosphaallene Ar₂(R₂N)Si? Si(NR₂)(Ar)? P?C?NtBu with pronounced ylidic character. All new compounds were fully characterized by multinuclear NMR spectroscopy as well as single‐crystal X‐ray diffraction and DFT calculations in selected cases.     

A theoretical study of the dependence of the ASxSi6−x cluster structures and properties on composition

The effect of the composition ratio between arsenic and silicon atoms on the structures and properties of As_xSi_6?x (x = 0–6) have been systematically investigated using the density functional theory at the B3LYP/6‐311+G* level. The As_xSi_6?x clusters prefer substitutional rather than attaching structures; the Si‐rich clusters favor Si₆‐like structures, whereas the As‐rich clusters prefer As₆‐like structures. The As atoms locating at the framework may explain the difficulty of removal of arsenic impurities from polycrystalline silicon. In general, the average binding energies gradually decrease, implying the As_xSi_6?x clusters become increasingly unstable as x increases. Both the HOMO‐LUMO gaps and the As‐dissociation energies present a strong even–odd alternation, implying alternating chemical stability, with the even x members being more stable than the odd ones. The dissociation energies of an As atom from As_xSi_6?x are: 3.07, 2.84, 1.84, 2.52, 1.86, and 2.85 eV, for x = 1–6, respectively, and 3.80, 3.08, 2.64, 3.01, 2.93, 3.16 eV for Si (x = 0–5). These dissociation energy results should provide a useful reference for further experimental investigations. © 2011 Wiley Periodicals, Inc. Int J Quantum Chem, 2012     

Density Functional Investigations of Electronic Structure and Dehydrogenation Reactions of Al‐ and Si‐Substituted Magnesium Hydride

The effect on the hydrogen storage attributes of magnesium hydride (MgH₂) of the substitution of Mg by varying fractions of Al and Si is investigated by an ab initio plane‐wave pseuodopotential method based on density functional theory. Three supercells, namely, 2×2×2, 3×1×1 and 5×1×1 are used for generating configurations with varying amounts (fractions x=0.0625, 0.1, and 0.167) of impurities. The analyses of band structure and density of states (DOS) show that, when a Mg atom is replaced by Al, the band gap vanishes as the extra electron occupies the conduction band minimum. In the case of Si‐substitution, additional states are generated within the band gap of pure MgH₂—significantly reducing the gap in the process. The reduced band gaps cause the Mg? H bond to become more susceptible to dissociation. For all the fractions, the calculated reaction energies for the stepwise removal of H₂ molecules from Al‐ and Si‐substituted MgH₂ are much lower than for H₂ removal from pure MgH₂. The reduced stability is also reflected in the comparatively smaller heats of formation (ΔH_f) of the substituted MgH₂ systems. Si causes greater destabilization of MgH₂ than Al for each x. For fractions x=0.167 of Al, x=0.1, 0.167 of Si (FCC) and x=0.0625, 0.1 of Si (diamond), ΔH_f is much less than that of MgH₂ substituted by a fraction x=0.2 of Ti (Y. Song, Z. X. Guo, R. Yang, Mat. Sc. & Eng. A 2004 , 365, 73). Hence, we suggest the use of Al or Si instead of Ti as an agent for decreasing the dehydrogenation reaction and energy, consequently, the dehydrogenation temperature of MgH₂, thereby improving its potential as a hydrogen storage material.     

Oxo(trisyl)boran (Me3Si)3C?BO als Zwischenstufe

Oxo(trisyl)borane (Me₃Si)₃C? B?O as an Intermediate The acyclic trisylboranes R? B(OSiMe₃)? Cl ( 4 a ) and R? B(OH)? H ( 5 a ) and the cyclic boranes (? RB? O? CO? CO? O? ) ( 1 a ) and (? RB? O? RB? O? SO₂? O? ) ( 6 a ) [R = (Me₃Si)₃C, “Trisyl”] are thermolyzed in the gasphase to give well-defined products. The tris(trisyl)boroxine (? RB? O? )₃ ( 2 a ) is formed from 4 a and 5 a at 140 and 160°C, respectively, besides Me₃SiCl and H₂, respectively, whereas the six-membered ring [? BMe? CH(SiMe₃)? SiMe₂? O? SiMe₂? CH₂? ] ( 8 ) is the product from 1 a and 6 a at 600 and 700°C, respectively, besides CO/CO₂ and SO₃, respectively. The oxoborane R? B?O is presumably a common intermediate. It is stabilized at the lower temperature by cyclotrimerization to give 2 and at the higher temperature by a sequence of several intramolecular steps: a 1,3-silyl shift along the chain C? B? O, an exchange of Me and Me₃SiO along the chain Si? C? B, and a C? H addition to the B?C double bond; the steps can be rationalized by analogous known reactions. The gas-phase thermolysis at 600°C of the dioxaboracyclohexenes (? BR? O? CR′ = CH? CRR′? O? ) ( 7 b? d ; R = Me, iPr, tBu; R′ = Me) yields the boroxines (RBO)₃ and the enones Me? CO? CH?CHR? Me; the cyclohexene 7 e (R = Me; R′ = CF₃) is not decomposed at 600°C.     

The Sialons MLn[Si4−xAlxOxN7−x] with M = Eu,Sr, Ba and Ln = Ho‐Yb – Twelve Substitution Variants with the MYb[Si4N7] Structure Type

The oxonitridoalumosilicates (so‐called sialons) MLn[Si_4?xAl_xO_xN_7?x] with M = Eu, Sr, Ba and Ln =Ho, Er, Tm, Yb were obtained by the reaction of the respective lanthanoid metal, the alkaline earth carbonates or europium carbonate, resp., AlN, “Si(NH)₂” and MCl₂ as a flux in a radiofrequency furnace at temperatures around 2100 °C. The compounds MLn[Si_4?xAl_xO_xN_7?x] are relevant for the investigation of substitutional effects on the materials properties due to their ability of tolerating a comparatively large phase width up to x ≈ 2.0(5). The crystal structures of the twelve compounds were refined from X‐ray single crystal data and X‐ray powder data and are found to be isotypic to the MYb[Si₄N₇] structure type. The compounds crystallize in space group P6₃mc (no. 186, hexagonal) and are made up of chains of so‐called starlike units [N^[4](SiN₃)₄] or [N^[4]((Si,Al)(O,N)₃)₄], respectively. These units are formed by four (Si,Al)(N/O)₄ tetrahedra sharing a common central nitrogen atom. The structure refinement was performed utilizing an O/N‐distribution model according to Paulings rules, i.e. nitrogen was positioned on the four‐fold bridging site and nitrogen and oxygen were distributed equally on both of the two‐fold bridging sites, resulting in charge neutrality of the compound. The Si and Al atoms were distributed equally on their two crystallographic sites, referring to their elemental proportion in the compound, due to being poorly distinguishable by X‐ray methods. The chemical compositions of the compounds were derived from electron probe micro analyses (EPMA).     

Magnetotransport Properties and Kondo Effect Observed in a Ferromagnetic Single‐Crystalline Fe1−xCoxSi Nanowire

We report unconventional magnetotransport properties of an individual Fe_1?xCo_xSi nanowire. We have studied the dependence of the resistivity on the angle between the directions of the magnetization and electrical current below the Curie temperature (T_C). The observed anisotropic magnetoresistance (MR) ratio is negative, thereby indicating that the conduction electrons in a minority spin band of the Fe_1?xCo_xSi nanowire dominantly contribute to the transport. Unlike typical ferromagnets, positive MR is observed in the overall temperature range. MR curves are linear below T_C and show a quadratic form above T_C, which can be explained by the change of density of states that arises as the band structures of the Fe_1?xCo_xSi nanowire shift under a magnetic field. The temperature dependence of the resistivity curve is sufficiently explained by the Kondo effect. The Kondo temperature of the Fe_1?xCo_xSi nanowire is lower than that of the bulk state due to suppression of the Kondo effect. The high single crystallinity of Fe_1?xCo_xSi nanowires allowed us to observe and interpret quite subtle variations in the prominent intrinsic transport properties.     

Synthese,Kristallstruktur und Festkörper‐NMR‐spektroskopische Untersuchung des Oxonitridosilicates BaSi6N8O

Synthesis, Crystal Structure and Solid‐State NMR Spectroscopic Investigation of the Oxonitridosilicate BaSi₆N₈O The phase‐pure oxonitridosilicate BaSi₆N₈O has been synthesized starting from BaCO₃ and silicon diimide Si(NH)₂ in a radiofrequency furnace at temperatures below 1630 °C as a coarsely crystalline colorless material. The structure has been determined by single‐crystal X‐ray diffraction analysis (BaSi₆N₈O, space group Imm2 (no. 44), a = 810.5(2), b = 967.8(2), c = 483.7(1) pm, V = 379.4(2)·10⁶ pm³, Z = 2, R1 = 0.014, 618 independent reflections, 44 parameters). The oxonitridosilicate comprises a three‐dimensional network structure of corner sharing SiN₄ and SiON₃ tetrahedra with Ba²⁺ located in the resulting voids. BaSi₆N₈O is isostructural with the oxonitridoalumosilicate (sialon) Sr₂Al_xSi_12?xN_16?xO_2+x (x ≈ 2) that previously has been described in the literature. Furthermore, the anionic network of BaSi₆N₈O derives from that of the homeotypic reduced nitridosilicate SrSi₆N₈ by a topotactic insertion of oxygen into the Si–Si single bonds. In the ²⁹Si MAS‐NMR spectrum two sharp isotropic signals have been observed at ?54.0 and ?56.3 ppm, respectively. With respect to their observed intensity ratio of 1 : 2.1(1) these two signals have to be attributed to the central atoms of SiON₃ and SiN₄ tetrahedra, respectively, which is in accordance with the X‐ray crystal structure determination (Si at Wyckoff positions 4d (SiON₃) and 8e (SiN₄)).     

1,1‐Ethylboration of alkyn‐1‐yl‐chloro(methyl)silanes: alkenes with chloro(methyl)silyl and diethylboryl groups in cis positions

The 1,1‐ethylboration of alkyn‐1‐yl‐chloro(methyl)silanes, Me₂Si(Cl)? C?C? R ( 1 ) and Me(H)Si(Cl)? C?C? R ( 2 ) [R = Bu ( 2a ), CH₂NMe₂ ( 2b )] requires harsh reaction conditions (up to 20 days in boiling triethylborane), and leads to alkenes in which the boryl and silyl groups occupy cis ((E)‐isomers: 3a , 3b , 5a , 5b ) or trans positions ((Z)‐isomers in smaller quantities: 4b and 6b ). The alkenes are destabilized in the presence of SiH(Cl) and CH₂NMe₂ units ( 5b , 6b ). NMR data indicate hyper‐coordinated silicon by intramolecular N? Si coordination in 3b and 5b , by which, at the same time, weak Si? Cl? B bridges are favoured. Copyright © 2005 John Wiley & Sons, Ltd.     

Darstellung SiH-haltiger Silylphosphine und Untersuchung ihrer PMR-Spektren

The preparation of SiH-containing silylphosphines from SiH-containing chlorosilanes is successful by using an excess of chlorosilans. Chemical shift data and coupling constants of the compounds H_xSi[P(C₂H₅)₂]_4?x and (CH₃)_xSi[P(C₂H₅)₂]_4?x are communicated and compared with those of H_xSiX_4?x and (CH₃)_xSiX_4?x (X = halogen or H).     

Imino‐Bridged Bisphosphaalkenes (2,4‐Diphospha‐3‐azapentadienes)

Deprotonation of aminophosphaalkenes (RMe₂Si)₂C?PN(H)(R′) (R=Me, iPr; R′=tBu, 1‐adamantyl (1‐Ada), 2,4,6‐tBu₃C₆H₂ (Mes*)) followed by reactions of the corresponding Li salts Li[(RMe₂Si)₂C?P(M)(R′)] with one equivalent of the corresponding P‐chlorophosphaalkenes (RMe₂Si)₂C?PCl provides bisphosphaalkenes (2,4‐diphospha‐3‐azapentadienes) [(RMe₂Si)₂C?P]₂NR′. The thermally unstable tert‐butyliminobisphosphaalkene [(Me₃Si)₂C?P]₂NtBu ( 4 a ) undergoes isomerisation reactions by Me₃Si‐group migration that lead to mixtures of four‐membered heterocyles, but in the presence of an excess amount of (Me₃Si)₂C?PCl, 4 a furnishes an azatriphosphabicyclohexene C₃(SiMe₃)₅P₃NtBu ( 5 ) that gave red single crystals. Compound 5 contains a diphosphirane ring condensed with an azatriphospholene system that exhibits an endocylic P?C double bond and an exocyclic ylidic P⁽⁺⁾? C^(?)(SiMe₃)₂ unit. Using the bulkier iPrMe₂Si substituents at three‐coordinated carbon leads to slightly enhanced thermal stability of 2,4‐diphospha‐3‐azapentadienes [(iPrMe₂Si)₂C?P]₂NR′ (R′=tBu: 4 b ; R′=1‐Ada: 8 ). According to a low‐temperature crystal‐structure determination, 8 adopts a non‐planar structure with two distinctly differently oriented P?C sites, but ³¹P NMR spectra in solution exhibit singlet signals. ³¹P NMR spectra also reveal that bulky Mes* groups (Mes*=2,4,6‐tBu₃C₆H₂) at the central imino function lead to mixtures of symmetric and unsymmetric rotamers, thus implying hindered rotation around the P? N bonds in persistent compounds [(RMe₂Si)₂C?P]₂NMes* ( 11 a , 11 b ). DFT calculations for the parent molecule [(H₃Si)₂C?P]₂NCH₃ suggest that the non‐planar distortion of compound 8 will have steric grounds.     

Synthese neuer Aminofluorsilane,sowie Alkoxylierung von Bis (trimethylsilyl)-amino-fluorsilanen

The reaction of aminofluorsilanes of the type (R=H,F) (Me ₃Si)₂N?SiF₂R with two moles of ammonia, or of a mono- or dialkylamine, yields the corresponding amino-compounds, e.g. (Me ₃Si)₂N?Si(F)R?NH₂, (Me ₃Si)₂N?Si(F)R?NHR′ and (Me ₃Si)₂N?Si(F)R?NR₂′ (R′=Me, Et). Analogous products are obtained by reaction of the aminofluorosilanes with lithium salts of amines with bulky organic substituents in a 1 : 1 molar ratio. Alkoxy- and aryloxyaminofluorosilanes are prepared by the reaction of sodium alcoholates and sodium phenolate with (Me ₃Si)₂N?Si(F₂)R (R=H, C₂H₃, C₂H₅, C₆H₅). The i.r.-, mass-,¹H- and¹⁹F-NMR spectra of the above compounds are reported.     

Whitlockite solid solutions Ca9?xMxR(PO4)7 (x = 1, 1.5; M = Mg, Zn, Cd; R = Ln, Y) with antiferroelectric properties

Whitlockite solid solutions Ca_9−x M _x R(PO₄)₇ (M = Mg, Zn, Cd; R = Ln, Y) were synthesized as powders and ceramics using solid-phase synthesis. Dielectric investigations and second harmonic generation (SHG) tests showed that ferroelectric (FE) phase transitions existing in samples with x = 0 change to antiferro-electric (AFE) transitions between two centrosymmetrical phases in samples with x = 1 or 1.5. The calcium-ion solid electrolyte conductivity in Ca_9−x M _x R(PO₄)₇ at high temperatures appears either as a result of an antiferroelectric-paraelectric (AFE-PE) phase transition (for x = 1) or as a result of a separate phase transition near 1173 K (for x = 1.5). The appearance of dielectric properties in whitlockites is discussed with reference to the features of their polar and centrosymmetrical structures. Original Russian Text ? A.V. Teterskii, S.Yu. Stefanovich, B.I. Lazoryak, D.A. Rusakov, 2007, published in Zhurnal Neorganicheskoi Khimii, 2007, Vol. 52, No. 3, pp 357–363.     

Ring Opening and Bidentate Coordination of Amidinate Germylenes and Silylenes on Carbonyl Dicobalt Complexes: The Importance of a Slight Difference in Ligand Volume

The reactions of [Co₂(CO)₈] with one equiv of the benzamidinate (R₂bzam) group‐14 tetrylenes [M(R₂bzam)(HMDS)] (HMDS=N(SiMe₃)₂; 1 : M=Ge, R=iPr; 2 : M=Si, R=tBu; 3 : M=Ge, R=tBu) at 20 °C led to the monosubstituted complexes [Co₂{κ¹M?M(R₂bzam)(HMDS)}(CO)₇] ( 4 : M=Ge, R=iPr; 5 : M=Si, R=tBu; 6 : M=Ge, R=tBu), which contain a terminal κ¹M–tetrylene ligand. Whereas the Co₂Si and Co₂Ge tert‐butyl derivatives 5 and 6 are stable at 20 °C, the Co₂Ge isopropyl derivative 4 evolved to the ligand‐bridged derivative [Co₂{μ‐κ²Ge,N‐Ge(iPr₂bzam)(HMDS)}(μ‐CO)(CO)₅] ( 7 ), in which the Ge atom spans the Co?Co bond and one arm of the amidinate fragment is attached to a Co atom. The mechanism of this reaction has been modeled with the help of DFT calculations, which have also demonstrated that the transformation of amidinate‐tetrylene ligands on the dicobalt framework is negligibly influenced by the nature of the group‐14 metal atom (Si or Ge) but is strongly dependent upon the volume of the amidinate N?R groups. The disubstituted derivatives [Co₂{κ¹M?M(R₂bzam)(HMDS)}₂(CO)₆] ( 8 : M=Ge, R=iPr; 9 : M=Si, R=tBu; 10 : M=Ge, R=tBu), which contain two terminal κ¹M–tetrylene ligands, have been prepared by treating [Co₂(CO)₈] with two equiv of 1 – 3 at 20 °C. The IR spectra of 8 – 10 have shown that the basicity of germylenes 1 and 3 is very high (comparable to that of trialkylphosphanes and 1,3‐diarylimidazol‐2‐ylidenes), whereas that of silylene 2 is even higher.     

Etude thermochimique de carboxylates de cuivresolvates par des amines aromatiques

The carboxylates (formate, acetate, propionate, isobutyrate) of copper(II) solvated by aromatic amines (pyridine; α, β and γ picolines) corresponding to the formula Cu(R?COO)₂(H₂O)_x(Am)_y(x = 0,1 or 2, and γ = 1 or 2) have been prepared. The thermal decomposition has been studied by TG and DTA methods. The standard enthalpies of formation have been determined and a relation has been proposed for the estimation of these values.     

Über die Darstellung der Bis(triphenylsilyl)-sulfane (C6H5)3Si?Sx?Si(C6H5)3 (x = 3, 4) und die Kristallstruktur von (C6H5)3Si?S4?Si(C6H5)3

On the Preparation of Bis(triphenylsilyl)sulfanes (C₆H₅)₃Si? S_x? Si(C₆H₅)₃ (x = 3, 4) and the Crystal Structure of (C₆H₅)₃Si? S₄? Si(C₆H₅)₃ The preparation of the bis(triphenylsilyl)sulfanes Ph₃Si? S_x? SiPh₃ (x = 3, 4) from Ph₃SiSNa and SCl₂ resp. S₂Cl₂ is reported. They are characterized by vibrational, NMR and UV-VIS spectroscopic measurements. Ph₃Si? S₄? SiPh₃ crystallizes in space group P1 with a = 943.6(6) pm, b = 945.7(5) pm, c = 1 881.7(12) pm, α = 82.11(5)°, β = 78.95(5)°, γ = 83.15(5)° and Z = 2.     

Pr10[Si10−xAlxO9+xN17−x]Cl with x ≈ 1 – an Oxonitridoaluminosilicate Chloride

The oxonitridoaluminosilicate chloride Pr₁₀[Si_10?xAl_xO_9+xN_17?x]Cl was obtained by the reaction of praseodymium metal, the respective chloride, AlN and Al(OH)₃ with “Si(NH)₂” in a radiofrequency furnace at temperatures around 1900 °C. The crystal structure was determined by single‐crystal X‐ray diffraction (Pbam, no. 55, Z = 2,a = 10.5973(8) Å, b = 11.1687(6) Å, c = 11.6179(7) Å, R1 = 0.0337). The sialon crystallizes isotypically to the oxonitridosilicate halides Ce₁₀[Si₁₀O₉N₁₇]Br, Nd₁₀[Si₁₀O₉N₁₇]Br and Nd₁₀[Si₁₀O₉N₁₇]Cl, which represent a new layered structure type. The structure refinement was performed utilizing an O/N‐distribution model according to Paulings rules, i.e. nitrogen was positioned on all bridging sites and mixed O/Noccupation was assumed on the terminal sites resulting in charge neutrality of the compounds. The Si and Al atoms were refined equally distributed on their three crystallographic sites, due to their poor distinguishability by X‐ray analysis. The tetrahedra layers of the structure consist of condensed [(Si,Al)N₂(O,N)₂] and [(Si,Al)N₃(O,N)] tetrahedra of Q² and Q³ type. The chemical composition of the compound was derived from electron probe micro analyses (EPMA).     

Synthese „anorganischer”︁ Tintenfisch-Moleküle. II

Synthesis of “Inorganic” Pode-type Molecules. II The reaction of the amino compounds Me_yB? NMe₂ (B ? As, y ? 2; B ? Si, y ? 3) with 1, n-dioles results in the formation of the compounds HO(CH₂)_nOBMe_y. These compounds can be used as the arms of pode-type molecules Me_xA[? O(CH₂)_nOBMe_y]_z with A ? Si, As. The influence of A, B, n, and z in the rearrangement of these molecules is examined. A second type of pode molecules can be prepared by the reaction of Me₂As? R? OH (R ? CH₂CH₂, CH₂CH₂(OCH₂CH₂)₂) with the amino compounds Me_x(NMe₂)_z (A ? As, Si). These reactions result in the formation of molecules as Me_xA(ORAsMe₂)_z.     

An Alternative Mechanistic Paradigm for the β‐Z Hydrosilylation of Terminal Alkynes: The Role of Acetone as a Silane Shuttle

The β‐Z selectivity in the hydrosilylation of terminal alkynes has been hitherto explained by introduction of isomerisation steps in classical mechanisms. DFT calculations and experimental observations on the system [M(I)₂{κ‐C,C,O,O‐(bis‐NHC)}]BF₄ (M=Ir ( 3 a ), Rh ( 3 b ); bis‐NHC=methylenebis(N‐2‐methoxyethyl)imidazole‐2‐ylidene) support a new mechanism, alternative to classical postulations, based on an outer‐sphere model. Heterolytic splitting of the silane molecule by the metal centre and acetone (solvent) affords a metal hydride and the oxocarbenium ion [R₃Si? O(CH₃)₂]⁺, which reacts with the corresponding alkyne in solution to give the silylation product [R₃Si? CH?C? R]⁺. Thus, acetone acts as a silane shuttle by transferring the silyl moiety from the silane to the alkyne. Finally, nucleophilic attack of the hydrido ligand over [R₃Si? CH?C? R]⁺ affords selectively the β‐(Z)‐vinylsilane. The β‐Z selectivity is explained on the grounds of the steric interaction between the silyl moiety and the ligand system resulting from the geometry of the approach that leads to β‐(E)‐vinylsilanes.     

Synthesis of alkoxysilanes as starting substances for preparation of new materials by the sol-gel procedure. Silanes with urea functional group

New bis(triethoxysilanes) containing a urea functional group >NC(O)N< and having the composition (C₂H₅O)₃Si(CH₂)₃NHC(O)NRR [R = R = n-C₃H₇; R = H, R = (CH₂)₃Si(CH₃)(OC₂H₅)₂] and [(C₂H₅O)₃Si(CH₂)₃NHC(O)NH]₂(C_nA_m)_x (A = H, x = 2, 4, 12, n = 1, m = 2; A = H, CH₃, x = 1, n = 6, m = 4; A = H, x = 1, n = 10, m = 6) were prepared in high yields and with satisfactory purity by reactions of primary amines (or diamines) with 3-(triethoxysilyl)propyl isocyanate.Translated from Zhurnal Obshchei Khimii, Vol. 74, No. 11, 2004, pp. 1782–1788.Original Russian Text Copyright © 2004 by Melnik, Lyashenko, Zub, Chuiko, Cauzzi, Predieri.This revised version was published online in April 2005 with a corrected cover date.