Silicon-hydrogen Bonds Research Articles

Carbenoid insertions into the siliconhydrogen bond catalyzed by chiral copper (I) schiff base complexes

An asymmetric insertion reaction of α-diazoesters derived from methyl arylacetates into the silicon-hydrogen bond of silanes was achieved using a copper (I) catalyst associated with a chiral, C 2 symmetric Schiff base. Addition of the diazoesters 1 (1 equiv) to the Cu·Lig complex (R,R)- 3 (0.1 equiv) in the presence of the silane reagent (1.5 equiv) at −40° C yielded the corresponding insertion products 2 or 4 in good yields with varying levels of selectivity (up to 84% ee).

Reaction studies on hypervalent silicon hydride compounds

The versatile reaction chemistry of penta-coordinated silanes of type [C 6H 4CH 2N(CH 3) 22](H 2CCH)(CH 3)SiH ( 1a) and [C 6H 4CH 2N(CH 3) 22](H 2CCH)SiH 2 ( 1b) with different substrates is described. The reaction behavior along with the structure and bonding of the compounds obtained is compared with tetravalent silicon molecules. Hypervalent 1a and 1b react, without added catalysts, with alcohols, water and benzoylic acid to produce alcoxysilanes, siloxanes and carboxysilanes, respectively. Compounds [C 6H 4CH 2N(CH 3) 22](H 2CCH)(CH 3)Si(OCH 3) ( 3), [C 6H 4CH 2N(CH 3) 22](H 2CCH)Si(OR) 2 ( 4a: R=CH 3, 4b: R=C 2H 5, 4c: R= i C 3H 7, 4d: R=CH 2CCH), {[C 6H 4CH 2N(CH 3) 22](H 2CCH)(CH 3)Si} 2O ( 5a), {[C 6H 4CH 2N(CH 3) 22](H 2CCH)SiO} n ( 5b) as well as [C 6H 4CH 2N(CH 3) 22](H 2CCH)Si(H)[OC(O)C 6H 5] ( 8) are formed in quantitative yields. The carboxysilane 8 reacts with C 6H 5CO 2H ( 7) further to give the polymeric siloxane 5b and benzoylic anhydride. Moreover, H 2PtCl 6-catalyzed head–tail polymerization of 1b yields the oligomeric carbosilane {[C 6H 4CH 2N(CH 3) 22](H)SiCH 2CH 2} n ( 6). Due to the intramolecular nitrogen–silicon interaction in hypervalent 1a as well as 1b, the hydrosilylation reaction with C 6H 5NCX ( 11a: X=S, 11b: X=O) takes place without a catalyst added, whereas hydrosilylation of isocyanates and isothiocyanates does not occur with tetravalent silanes. The obtained products [C 6H 4CH 2N(CH 3) 22](H 2CCH)(R)Si(C 6H 5NCHX) ( 12a: R=CH 3, X=S; 12b: R=H, X=S; 12c: R=H, X=O) are suitable catalysts for the cyclooligomerization of isocyanates and isothiocyanates. While compounds 12a– 12c are stable in the solid state, 12c starts to rearrange in solution to afford oligomeric 5b along with 1,3,5-triphenylhexahydro-1,3,5-triazine ( 13). A possible mechanism for the formation of the latter compounds is discussed. An example for an insertion–elimination process of compound 1b is given by the insertion of sulfur into the silicon–hydrogen bonds, yielding [C 6H 4CH 2N(CH 3) 22](H 2CCH)Si(SH) 2 ( 15) as an intermediate first; elimination of H 2S affords the intermolecular donor-stabilized silanethion [C 6H 4CH 2N(CH 3) 22](H 2CCH)SiS ( 16). The X-ray structure analysis of compound 12b is reported. Crystals of 12b are monoclinic, space group P2 1/ n with the cell constants a=9.356(3), b=10.890(4), c=17.236(6) Å, β=99.80(3)°, V=1730(1) Å 3 and Z=4.

Effect of annealing in an atomic-hydrogen atmosphere on the properties of amorphous hydrated silicon films and the parameters of p-i-n structures based on them

The decrease in the density of dangling silicon-silicon bonds in a-Si:H films as a result of annealing in an atomic-hydrogen atmosphere is determined by their density in the initial (nonannealed) film. The change in the total hydrogen density in a-Si:H films, annealed in an atomic-hydrogen atmosphere, is determined by the type of silicon-hydrogen bonds and the impurity content: The hydrogen content can decrease to 1 at. % in the presence of monohydride bonds (2020 cm−1) and no change is observed in the hydrogen content in the presence of oxygen (≲0.1 at. %). A decrease in the defect density as a result of annealing in an atomic-hydrogen atmosphere is observed for all films. The Staebler-Wronski effect — AM-1 irradiation for 10 h — is observed for all films irrespective of the total hydrogen density, the type of silicon-hydrogen bonds, and the presence of oxygen.

Effect of deposition temperature on the structural properties of n+ μc-Si:H films

The role of the deposition temperature (Td) on the structural properties of doped hydrogenated microcrystalline silicon (n+ μc-Si:H) has been studied through grazing incidence x-ray diffraction, Raman spectroscopy, and Fourier transform infrared spectroscopy measurements. The deposition temperature was varied from 200 to 400 °C to observe the crystalline and amorphous phase formations in these films. The results show that the films deposited at low temperatures are more crystalline in nature than their high temperature counterparts. The elimination of the hydrogen atoms from the growing surface of the film seems to be correlated with the transition from the amorphous to the crystalline phase. This may be attributed to the following. At low deposition temperatures, the impinging H atoms from H2 dilution interact with a silicon-hydrogen bond on the grown surface, forming a volatile H2 molecule, to leave a Si–Si network. The result of this interaction may be responsible for the increased crystallinity. At high deposition temperatures, a transition between the hydrogen out-diffusion from Si–H bonds and the hydrogen incorporation by H2 dilution may lead to formation of Si–H bonds, again on the surface at a particular chemical equilibrium. This causes the film to remain amorphous.

Femtosecond Infrared Studies of Silane Silicon−Hydrogen Bond Activation

Cleavage, or activation, of the silicon-hydrogen bond of a silane by a metal center has been the focus of many recent studies.1-6 Knowledge of this type of reaction is relevant to the central ideas of chemical bonding in general and is essential to the development of catalytic reactions such as hydrosilation. It is commonly accepted that the photochemical reaction for the oxidative addition of Et3SiH (Et ) C2H5) to CpMn(CO)3 (Cp ) C5H5) begins with the loss of a CO ligand as the result of UV irradiation, producing a coordinatively unsaturated dicarbonyl species7,8 which further reacts to activate the Si-H bond to form CpMn(CO)2(H)(SiEt3). Due to the fast reaction rates, however, the detailed reaction mechanism including the initial solvation of the nascent photogenerated chemical species has remained unclear. With the advent of ultrafast spectroscopy, especially in the infrared, it is now possible to identify such events which occur on a time scale shorter than diffusion to reveal the underlying elementary reaction steps.9 In this communication, we report the first ultrafast infrared study on silicon-hydrogen bond cleavage by CpMn(CO)3. As a result of photodissociating one CO ligand,10 the kinetics of the parent molecule recorded at 2028 cm-1 (A, Figure 1) shows an instrument limited bleach, 31% of which recovers in 32 ( 7.4 ps (Figure 2A).12 This rapid recovery of the parent bleach is due to vibrational relaxation in the ground electronic manifold of the parent molecule.9,13,14 The 31% recovery is in good agreement with reported CO loss quantum yields of 0.65 measured at 313-nm excitation.15 Subsequent spectral evolution suggests that photolysis of the parent molecules leads to two transient species including η-CpMn(CO)2 and a previously unreported intermediate. These reactive intermediates are solvated within a few picoseconds.16 The initial solvation of the nascent species through either the ethyl moiety or the Si-H bond of the solvent partitions the reaction into two channels of

Densely crosslinked polycarbosiloxanes. I. synthesis

Novel densely crosslinked polycarbosiloxanes were obtained by using functional branched prepolymers. Two types of soluble prepolymers were prepared from di- and trifunctional alkoxysilane monomers via cohydrolysis/condensation and for both final crosslinking occurred via hydrosilylation. The prepolymers having only vinyl functionalities (poly[phenylmethylvinyl]siloxanes, system A) were crosslinked by using a crosslinking agent with reactive silicon–hydrogen bonds. In the prepolymers having both silicon–vinyl and silicon–hydrogen functionalities (poly[phenylmethyl-vinylhydro]siloxanes, system B) crosslinking took place intermolecularly. For the characterization of the prepolymers 1H-NMR, 29Si–NMR, FT–IR spectroscopy, analytical SEC and VPO were employed. The prepolymers were fractionated with preparative SEC and the fractions analyzed with 1H-NMR and analytical SEC. The crosslinking reaction was followed by FT–IR spectroscopy. The polymer networks were fully transparent homogeneous materials and are promising for future optical applications. © 1997 John Wiley & Sons, Inc.

Densely crosslinked polycarbosiloxanes. I. synthesis

Novel densely crosslinked polycarbosiloxanes were obtained by using functional branched prepolymers. Two types of soluble prepolymers were prepared from di- and trifunctional alkoxysilane monomers via cohydrolysis/condensation and for both final crosslinking occurred via hydrosilylation. The prepolymers having only vinyl functionalities (poly[phenylmethylvinyl]siloxanes, system A) were crosslinked by using a crosslinking agent with reactive silicon–hydrogen bonds. In the prepolymers having both silicon–vinyl and silicon–hydrogen functionalities (poly[phenylmethyl-vinylhydro]siloxanes, system B) crosslinking took place intermolecularly. For the characterization of the prepolymers 1H-NMR, 29Si–NMR, FT–IR spectroscopy, analytical SEC and VPO were employed. The prepolymers were fractionated with preparative SEC and the fractions analyzed with 1H-NMR and analytical SEC. The crosslinking reaction was followed by FT–IR spectroscopy. The polymer networks were fully transparent homogeneous materials and are promising for future optical applications. © 1997 John Wiley & Sons, Inc.

Formation of Silicon Nanocrystallites by Electron Cyclotron Resonance Chemical Vapor Deposition and Ion Beam Assisted Electron Beam Deposition

AbstractNano-crystalline silicon (nc-Si) thin films were directly deposited by electron cyclotron resonance chemical vapor deposition (ECR-CVD) and ion beam assisted electron beam deposition (IBAED) method. In the sample deposited by ECR-CVD, the room temperature photoluminescence originated from the nc-Si and the silicon-hydrogen bond were appeared. It was confirmed that the size of the nc-Si could be controlled up to about 3 nm with the low substrate temperature during the deposition process and then the hydrogen atoms play a very important role in the formation of the nc-Si. The IBAED method was also found to an useful technique for nc-Si formation by the control of ion beam power.

Electrical characterization of radio frequency sputtered hydrogenated amorphous silicon carbide films

The electrical results of rf sputtered hydrogenated amorphous silicon carbide (a-Si1−xCx:H) films prepared under different sputtering conditions are presented. It was found that hopping and Poole–Frenkel effects are the conduction mechanisms for low and high applied fields, respectively. From the capacitance versus voltage measurements, the fixed charge density (Qf) and the interface trapped charge density (Dit) were found to be in the range of 5.5–6.81×1010 cm−2 and 5–13×1011 eV−1 cm−2, respectively. Dit decreases with either an increase in the total sputtering pressure, the partial hydrogen pressure, or the substrate temperature, but increases with an increase in the rf sputtering power. The decrease in Dit was found to be closely related to the increase in the number of silicon–hydrogen bonds.

High-Mobility Thin-Film Transistor Fabricated Using Hydrogenated Amorphous Silicon Deposited by Discharge of Disilane

Plasma-enhanced chemical vapor deposition of hydrogenated amorphous silicon (a-Si:H) film was investigated with emphasis on the effect of disilane flow rate. A coplanar thin-film transistor (TFT) was fabricated using this a-Si:H film. Silicon-hydrogen bond content in the a-Si:H film was measured by infrared absorption spectroscopy. With decrease in the disilane flow rate from 3.0 cm3/min to 1.5 cm3/min, the maximum field-effect electron mobility (µ FE) of the TFT which depends on the gate voltage increased from 3.3 cm2/( V·s) to 4.9 cm2/( V·s), accompanied by a reduction in the silicon-hydrogen bond content. There was a negative correlation between µ FE and the silicon-hydrogen bond content in the a-Si:H film. The improvement mechanism of µ FE was discussed in terms of the chemical structure of the a-Si:H film.

Stability of the number of silicon-hydrogen bonds upon photoillumination of undoped amorphous hydrogenated silicon

Deuteron magnetic resonance measurements on high quality a-Si:H,D films reveal three principal features: a sharp 66 kHz quadrupolar Pake doublet corresponding to silicon-bonded D passivating dangling bonds, a broad central line which has been shown to arise primarily from relatively isolated D 2 and HD molecules in nanovoids, and a small narrow central line arising from mobile molecular D 2 and HD in greater than 3 Å microvoids. The results of measurements on high quality plasma-deposited partially deuterated amorphous silicon cyclically exposed to a 2 h 150°C dark anneal and a 36 h photoillumination at 0.5 W/cm 2 with a 400–700 nm xenon are lamp are described. The spectra show that, following an initial spin-lattice relaxation-related transient, the intensities of all three components of the deuterium may vary by less than 1% upon illumination or dark anneal. The broad central line, primarily from isolated molecules, shows a small diamagnetic shift upon illumination. The shift becomes strongly paramagnetic at short magnetization recovery times following radio frequency saturation. The SiD doublet and the small narrow central line do not shift appreciably. This absence strongly suggests that Staebler-Wronski magnetic changes are remote from the environments of most of the silicon bonded hydrogen.

Effects of hot carrier induced interface state generation in submicron LDD MOSFET's

A two-dimensional numerical simulation including a new interface state generation model has been developed to study the performance variation of a LDD MOSFET after a dc voltage stress. The spatial distribution of hot carrier induced interface states is calculated with a breaking silicon-hydrogen bond model. Mobility degradation and reduction of conduction charge due to interface traps are considered. A 0.6 /spl mu/m LDD MOSFET was fabricated. The drain current degradation and the substrate current variation after a stress were characterized to compare the simulation. A reduction of the substrate current at V/sub g//spl sime/0.5 V/sub d/ in a stressed device was observed from both the measurement and the simulation. Our study reveals that the reduction is attributed to a distance between a maximum channel electric field and generated interface states.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Silicon-hydrogen (Si-H) bond activation on copper: reaction of silane on Cu(111)

The activation and decomposition of silane on Cu(111) have been studied using Fourier transform infrared (FTIR), Auger electron (AES), and temperature-programmed reaction (TPRS) spectroscopies, as well as low-energy electron diffraction (LEED). Silane dissociatively chemisorbs on Cu(111) at 90 K. Cleavage of the Si-H bond yields two structurally distinct adsorbed silyl fragments. Infrared spectroscopy identifies the predominant intermediates formed under these conditions as being adsorbed SiH[sub 2] and SiH species. The relative and absolute concentrations of these intermediates depend sensitively on the surface coverage of both Si and H, which themselves depend upon the silane exposure. SiH[sub 2] is stable over a wide range of coverage up to 180 K, where it then undergoes Si-H bond cleavage to form surface bound SiH. At higher temperatures, bond scission in the Si-H moiety results in the formation of adsorbed silicon atoms and the desorption of dihydrogen in a peak centered at [approximately]330 K. Auger electron spectra show that the amount of silicon deposited on the Cu(111) surface in this way is approximately one-third of the amount deposited on a stable Cu[sub 3]Si surface. This latter surface is readily formed by carrying out the silane exposure at temperatures above 300 K. 39 refs., 15more » figs., 1 tab.« less

Facile intermolecular activation of carbon-hydrogen bonds in methane and other hydrocarbons and silicon-hydrogen bonds in silanes with the iridium(III) complex Cp*(PMe3)Ir(CH3)(OTf)

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTFacile intermolecular activation of carbon-hydrogen bonds in methane and other hydrocarbons and silicon-hydrogen bonds in silanes with the iridium(III) complex Cp*(PMe3)Ir(CH3)(OTf)Peter Burger and Robert G. BergmanCite this: J. Am. Chem. Soc. 1993, 115, 22, 10462–10463Publication Date (Print):November 1, 1993Publication History Published online1 May 2002Published inissue 1 November 1993https://doi.org/10.1021/ja00075a113RIGHTS & PERMISSIONSArticle Views1814Altmetric-Citations236LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (276 KB) Get e-AlertsSupporting Info (2)»Supporting Information Supporting Information Get e-Alerts

The vacuum ultraviolet photodissociation of silane at 125.1 nm

We observe the photodissociation of SiH4 in a pulsed molecular beam after excitation with 125.1 nm vacuum ultraviolet light generated via resonant four-wave mixing in mercury vapor. Ultraviolet radiation from a Nd:YAG/dye laser combination ionizes the neutral photodissociation fragments and a time-of-flight mass spectrometer detects the ions. The photodissociation signal consists entirely of silicon atoms and silylidyne (SiH) in its first electronically excited state. We see no silylene (SiH2) or silyl radicals (SiH3). Thus, the photodissociation cleaves almost all of the silicon–hydrogen bonds, but the energetics of the dissociation require the production of at least one hydrogen molecule per dissociation event. These results imply that the high energy content of the initially excited Rydberg state prevents formation of the silylene and silyl radicals in stable vibronic states and that dissociation pathways exist that connect the Rydberg state directly to the corresponding silicon atom and silylidyne asymptotes. These pathways are likely to exist because of Jahn–Teller distortion from the initial Td symmetry. Very little of the available energy appears as kinetic energy of the fragments but rather as electronic excitation of the products. Our results differ from those of earlier studies that concluded silylene and silyl are the principle products.

Silicon-hydrogen, silicon-silicon, and carbon-hydrogen bond activation by coordinatively unsaturated rhodium phosphine RhCl(PH3)2: ab initio molecular orbital study

SiH bond activation, oxidative addition of the SiH bond of SiH 4 to coordinatively unsaturated RhCl (PH 3 ) 2 , was theoretically investigated with an ab initio molecular orbital (MO) method, and its potential energy profile was compared with that for CH bond activation, oxidative addition of the CH bond of CH 4 . All the stationary point were determined at the MP2 level. While CH bond activation passes through an η 2 -CH 4 complex and a three-centered transition state, SiH bond activation is downhill and the η 2 -SiH 4 complex is a transition state for intramolecular rearrangement connecting two silyl hydride complexes, the product of SiH bond activation

Direct synthesis of bis(silyl)methanes containing silicon-hydrogen bonds

Direct synthesis of bis(silyl)methanes containing silicon-hydrogen bonds

Selective arylation of a silicon-hydrogen bond in o-bis(dimethylsilyl)benzene via carbon-hydrogen bond activation of arenes

Selective arylation of a silicon-hydrogen bond in o-bis(dimethylsilyl)benzene via carbon-hydrogen bond activation of arenes

Ab initio study of silylene and dimethylsilylene insertion mechanisms into the silicon-hydrogen bonds of silane and methylsilane

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTAb initio study of silylene and dimethylsilylene insertion mechanisms into the silicon-hydrogen bonds of silane and methylsilaneShogo Sakai and Masaya NakamuraCite this: J. Phys. Chem. 1993, 97, 19, 4960–4965Publication Date (Print):May 1, 1993Publication History Published online1 May 2002Published inissue 1 May 1993https://doi.org/10.1021/j100121a017RIGHTS & PERMISSIONSArticle Views129Altmetric-Citations16LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (3 MB) Get e-Alerts

Optical properties of μc-Si:H/α-Si:H layered structures: Influence of the hydrogen bonds, crystallite size, and thickness

Thin films of layered μc-Si:H/α-Si:H structures grown with rf magnetron sputtering have been studied with spectroscopic ellipsometry (SE) and Raman spectroscopy (RS). Analysis of the dielectric function spectra with the Si-centered tetrahedron model and deconvolution of the Raman spectra suggest that the silicon-hydrogen bonds are correlated with the microscopic voids in α-Si:H while the good quality α-Si:H films exhibit SiH3 bonds and small amount of SiH2 bonds. The quality of the surface and interface of the μc-Si:H/α-Si:H was analyzed by SE and transmission electron microscopy and the dependence of an interfacial amorphous layer at the initial stages of the μc-Si:H growth on the argon and hydrogen pressure was found. Furthermore, a correlation between the SE and RS results on μc-Si:H layers is shown and commented, while a dependence of the energy shift and the broadening of the interband transitions and the Raman transverse optical peak on the mean crystallite size has been found and discussed in view of the finite size and stress effects on the electronic structure of these materials. This analysis suggests that strain is one of the most important factors during the growth of μc-Si:H.