Silicon Derivatives Research Articles

Stabilizing the silicon fullerene Si24 by La and Gd encapsulation

Using gradient-corrected spinpolarized density-functional theory (DFT) for electronic structure calculations，we study the fullerene of silicon Si24 with Th and D2d symmetries in the neutral state stabilized by lanthanum and gadolinium encapsulation. The electronic and magnetic properties of La@Si24 and Gd@Si24 are calculated using spin unrestricted DFT. The higher spin magnetic moment is achieved for Gd@Si24 and the magnetic moment of La@Si24 is completely quenched. These results could possibly lead to new phases and derivatives of silicon.

Hypervalent and binuclear silicon and germanium derivatives from bis-(3,5-di- tert-butyl-2-phenol)-oxamide

The reactions of bis-(3,5-di- tert-butyl-2-phenol)oxamide ( 1) with Cl 2SiR 2 (Me or Ph) or Cl 2GeR 2 (Me, nBu or Ph) in THF provided binuclear pentacoordinated silicon and germanium compounds: bis-(3,5-di- tert-butyl-2-oxo-phenyl)-oxamido-bis-dimethylsilane ( 2), bis-(3,5-di- tert-butyl-2-oxo-phenyl)-oxamido-bis-diphenylsilane ( 3), bis-(3,5-di- tert-butyl-2-oxo-phenyl)-oxamido-bis-dimethylgermane ( 4), bis-(3,5-di- tert-butyl-2-oxo-phenyl)-oxamido-bis-di- n-butylgermane ( 5) and bis-(3,5-di- tert-butyl-2-oxo-phenyl)-oxamido-bis-diphenylgermane ( 6). The mono-nuclear tetracoordinated silicon compounds N-acetyl-bis-(3,5-di- tert-butyl-2-oxo-phenyl)-amide-bis-(dimethylsilane) ( 8) and N-acetyl-bis-(3,5-di- tert-butyl-2-oxo-phenyl)-amide-bis-(diphenylsilane) ( 9) were synthesized from N-( 3, 5- di- tert- butyl- 2- phenol) acetamide ( 7) and Cl 2SiR 2 (R = Me and Ph). Comparison of the 29Si NMR chemical shifts of the penta- ( 2 and 3) and tetracoordinated ( 8 and 9) silicon compounds provided information about the intramolecular coordination of the carbonyl group to the silicon atom. Compounds 3 and 6 were characterized by single-crystal X-ray analyses. They have planar hexacyclic structures where the central atoms present distorted tbp geometries with one nitrogen and two carbon atoms in equatorial positions and two oxygen atoms in apical positions.

Metallocanes of Group 14 Elements. Part 1. Derivatives of Silicon and Germanium

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Biomechanical In Vitro Testing of Human Osteoporotic Lumbar Vertebrae Following Prophylactic Kyphoplasty With Different Candidate Materials

Biomechanical study of human osteoporotic lumbar vertebrae following prophylactic kyphoplasty. To evaluate the potential benefits of different resorbable candidate materials for use in prophylactic kyphoplasty compared with the behavior of polymethylmethacrylate cement. Kyphoplasty using PMMA bone cement for the stabilization of fractured osteoporotic vertebrae has been established as a useful clinical tool. In several studies, consecutive compression fractures have been reported in vertebrae caudal or cranial to those augmented with bone cement. Consequently, some physicians have begun to treat adjacent vertebrae by means of prophylactic augmentation. Biomechanical in vitro testing was performed on 40 human osteoporotic nonfractured lumbar vertebrae. Three types of bone cement (PMMA, 2 different calcium phosphate cements) and one silicon derivative were assessed during compressive and cyclic sinusoidal testing. Each candidate material was applied bipedicularly under fluoroscopic control. Differing processing qualities of the materials led to substantial differences during cement injection, in particular in the amount of cement filling of the vertebrae. However, in comparison to native vertebrae, augmented specimens showed significantly higher compressive failure. No significant differences between vertebral bodies treated with PMMA and those treated with either type of calcium phosphate cement were documented. The biomechanical properties of the vertebrae could not be significantly improved by the silicon derivative. This study demonstrated that calcium phosphate cements displayed identical behavior to PMMA cement with respect to in vitro mechanical qualities. Consequently, from a mechanical viewpoint, calcium phosphate cements may be used in addition to PMMA cement for kyphoplasty and prophylactic kyphoplasty. Silicon derivatives are apparently not recommendable as candidate materials for kyphoplasty.

Metallocanes of group 14 elements. 1. Derivatives of silicon and germanium. (Review)

Results on the synthesis of silocanes and germocanes, eight-membered heterocycles with the general formula D(CH2CH2Z)2MXY are analyzed and classified. The chemical behavior of these compounds and the characteristics of the element-nitrogen transannular bond are studied.

Synthesis and solid state structures of tri- t-butyl-cyclopropenyl derivatives of main group elements: Cyp*MPh 3 (M = Si, Ge, Sn)

The reaction of Ph 3MLi (M = Si, Ge, and Sn) with tri- t-butylcyclopropenium tetrafluoroborate ( Cyp ∗ BF 4 - ) gives the cyclopropenyl compounds Cyp*MPh 3 as air and moisture stable solids in 11%, 74%, and 77% yields, respectively. Attempts to prepare Cyp*PbPh 3 by this method were unsuccessful. The X-ray crystal structures of all three of these compounds were obtained. The M–C(Cyp*) bond distances increase with the order: Sn–C (2.19 Å) > Ge–C (2.00 Å) > Si–C (1.91 Å). A high degree of steric strain is evidenced for the silicon derivative which forms an exocyclic bond angle (Si–C(Cyp*)–C( t Bu)) of 121.6°. The high degree of steric strain for the silicon analog is believed to be responsible for the low yields for its synthesis.

Reaction of N-trimethylsilyl derivatives of amides and lactams with chloro(chloromethyl)dimethylstannane: Crystal and molecular structure of 1-(chlorodimethylstannylmethyl)-2-piperidone

A general scheme of reactions between chloro(chloromethyl)dimethylstannane and N-trimethylsilylamides and -lactams was established by NMR and IR techniques. The reactions proceed via transmetallation followed by transformation of the N-stannylated intermediate ( 1) into (N–Sn)-coordinated O-stannylmethyl ( 2) and (O–Sn)-coordinated N-stannylmethyl ( 3) derivatives. In the cases of 2-piperidone and 2-hexahydroazepinone these products were isolated as individual compounds ( 2b, c and 3b, c). X-ray diffraction study of 1-(chlorodimethylstannylmethyl)-2-piperidone ( 3b) confirmed (3 + 2)-coordination state of the tin atom and axial positions of oxygen and halogen atoms. The experimental and quantum-chemically calculated structural parameters are discussed in comparison with those of related trigonal bipyramidal (TBP) silicon, germanium and tin derivatives. Calculation at the MP2/LanL2DZ/D95 level reveals that the stability of the (O–M)chelates increases in the following order: (O–Si) < (O–Ge) < (O–Sn).

Isobaric vapor-liquid equilibrium for methyldichlorosilane-dimethyldichlorosilane-benzene system.

The elucidation of vapor-liquid equilibrium (VLE) of the halogenated silane was necessary for the production of silicon derivatives, especially for methylvinyldichlorosilane, due to the lack of the relevant reports. Isobaric VLE for the system methyldichlorosilane-dimethyldichlorosilane-benzene and isobaric VLE of the three binary systems were measured with a new pump-ebulliometer at the pressure of 101.325 kPa. These binary compositions of the equilibrium vapor were calculated according to the Q function of molar excess Gibbs energy by the indirect method and the resulted VLE data agreed well with the thermodynamic consistency. Moreover, the experimental data were correlated with the Wilson, NRTL, Margules and van Laar equations by means of the least-squares fit, the acquired optimal interaction parameters were fitted to experimental vapor-liquid equilibrium data for binary systems. The binary parameters of Wilson equation were also used to calculate the bubble point temperature and the vapor phase composition for the ternary mixtures without any additional adjustment. The predicted vapor-liquid equilibrium for the ternary system was in a good agreement with the experimental results. The VLE of binary and multilateral systems provided essential theory for the production of the halogenated silane.

Functions Containing at Least One As, Sb, or Bi with or Without a Metalloid (Si or Ge) or a Metal

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Synthesis of Silicon Derivatives with Ruthenium Catalysts

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Stabilizing the silicon fullereneSi20by thorium encapsulation

We show using ab initio electronic structure calculations that the dodecahedral fullerene of silicon ${\mathrm{Si}}_{20}$ is stabilized by thorium encapsulation. Thorium is found to be the only element in the Periodic Table that stabilizes this fullerene with icosahedral symmetry in the neutral state. The preference for $s{p}^{3}$ bonding in silicon makes it an optimal cage with all pentagonal faces in contrast to carbon for which ${\mathrm{C}}_{20}$ is difficult to stabilize. Similar to ${\mathrm{C}}_{60}$, this is the highest symmetry cluster of silicon and should be abundant. It could lead to the possibilities of novel new phases and derivatives of silicon.

Divalent Silicon, Germanium, and Tin Compounds with Element—Heteroatom Bonds

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Intra-molecular dihydrogen bond in the amino acid

There has been much attention on unconventional hydrogen bond in literature, particularly on intermolecular dihydrogen bond. But there is less attention on intra-molecular dihydrogen bond. In this research, we have tried to find some rules in these types of interactions. Since, the investigations around life sciences are helpful, amino acids have chosen. There are important molecules in biology, biochemistry and medicine. In order to investigate the behavior of silicon atom in comparison with carbon, silicon derivatives of amino acids are taken into considerations. All ab initio calculations are done at B3lyp/6-311G** level of theory. The existences of dihydrogen bond in above species are also investigated by donor–acceptor interactions of Natural Bond Orbital analysis. We have found that some amino acids with intra-molecular dihydrogen bond are stable than original compound between 0.5 and 5 kcal/mole.

Reaction of N,N'-Bis(trimethylsilyl)-N-methyl-N'-arylureas with Chloro(chloromethyl)dimethylsilane

We previously showed that the reaction of chloro(chloromethyl)dimethylsilane with bis(N-methyl-N-trimethylsilylamido)methylphosphonate is accompanied by separation of 2 equiv of chlorotrimethylsilane and provides 1,2,3,4,4-pentamethyl-1,3-diaza-2-phospha4-silolidin-2-one [1]. With the purpose of investigate the possibility of formation of new silacyclanes on the basis of chloromethyl derivatives of silicon we turned to reaction of N,N -bis(trimethylsilyl)-N-methylN -phenylurea (Ia) and N,N -bis(trimethylsilyl)N-methyl-N -p-chlorophenylurea (Ib) with chloro(chloromethyl)dimethylsilane. Silylated urea Ib was prepared from heptamethyldisilazane and p-chlorophenyl isocyanate.

Divalent silicon, germanium, and tin compounds with element—heteroatom bonds

Principal results and trends in chemistry of organic derivatives of divalent silicon, germanium, and tin containing bonds between these elements and the halogen, nitrogen, oxygen, and sulfur atoms are briefly surveyed. Selected characteristics of compounds with the element--phosphorus and element--arsenic bonds are discussed for comparison. Data on the synthesis and structures of new types of these compounds, viz., germanium(ii) diacylates, the alkoxy derivatives E14(OR)2 and E14(OR)Y (E14 = Ge, Sn; R = Me2NCH2CH2; Y = Cl, AcO, (Me3Si)2N), and the ate-complexes Li(+)[E14(OCH2CH2NMe2)3](–) and [Li(thf)2](+)[TsiE14(SBu)2](–) (E14 = Ge, Sn; Tsi = (Me3Si)3C), are presented. It was established for the first time that germanium(ii) and tin(ii) derivatives can be stabilized in the monomeric form only through the intramolecular Nsp3→E14 coordination bonds and the σ-acceptor effect of the oxygen atoms without introduction of bulky substituents.

Exchange Reactions in Alkoxy Derivatives of Silicon and Germanium

Reaction SiCl4+ Ge(OR)4 → GeCl4+ Si(OR)4 was carried out for the first time. Triethoxysilane reduces tetraethoxygermane via intermediate formation of unstable GeH(OEt)3 that transforms into GeO·Et2O or Ge(OH)2.

Synthesis and neurotropic activity of silyl propargyl alcohols and sulfides

AbstractNew silicon derivatives of hetaryl propargyl sulfides and propargyl alcohols were synthesized using phase‐transfer catalytic and organometallic methods. These compounds were tested for acute toxicity and neurotropic activity in the pentylenetetrazole test, and for phenamine hypothermia, phenamine hyperactivity and passive avoidance response tests. We have found that the silyl propargyl alcohols and sulfides are low toxicity compounds, the LD50 being 700–1300 mg kg−1. In the PAR test, the synthesized compounds exerted some memory‐improving activity. For di‐1‐(3‐methyl‐3‐hydroxybutyn‐1‐yl)methyl(3‐iodopropyl)silane (16) the effect was statistically significant and amounted to 250% of the control level. In the pentylenetetrazole test, all compounds possessed anticonvulsant activity, the most active compounds being 3‐(benzoxazolylthio)‐1‐propynyl(trimethyl)silane (6) and di‐[2‐(1‐hydroxycyclohexyl)ethynyl]methyl(3‐iodopropyl)silane (17). The phenamine‐induced hyperactivity was significantly elevated after treatment with (3‐trimethylsilyl‐2‐propynyl)thiobenzene (1) or di‐[1‐(3‐methyl‐3‐hydroxybutyn‐1‐yl)diphenylsilane (12). Our data show that these silicon derivatives of hetaryl propargyl sulfides and propargyl alcohols possess certain memory improving and anticonvulsant activity that should be studied in detail to evaluate the receptor systems involved. Copyright © 2004 John Wiley &amp; Sons, Ltd.

Quantum chemical study of the Si–C bond photodissociation in benzylsilane derivatives: a specific ‘excited-state’ silicon effect

Structure and properties of the ground ( S 0) and lowest excited triplet ( T 1) states of benzylsilane derivatives bearing the benzophenone chromophore group, p-PhCO-C 6H 4-CR″R‴-SiR′ 3 (R′, R″, R‴=H, H, H; Me, H, H; Me, H, Me; Me, Me, Me; Me, H, Ph; Me, Me, Ph; Me, Ph, Ph), were calculated using the semiempirical PM3 method. The bond dissociation energy (BDE) of the Si–C bond in the S 0 state and the heat of the bond dissociation reaction (Δ H r) in the T 1 state were found to decrease with increasing substitution at silicon and/or benzylic carbon atom. There exists a straight-line dependence between the BDE and Δ H r values in the series of the compounds studied. Minimal energy paths for the ‘heterobenzylic’ Si–C bond dissociation in benzylsilane PhCH 2-SiH 3 and for the benzylic C–C bond dissociation in the carbon analogue ethylbenzene PhCH 2-CH 3 in T 1 states were calculated using PM3 and B3LYP/6-31G**. The activation energies obtained are 13.3 and 36.7 kcal/mol (PM3), and 6.3 and 19.6 kcal/mol (B3LYP/6-31G** with ZPE correction) for benzylsilane and ethylbenzene, respectively. Both methods predict much lower activation barrier for benzylsilane compared to ethylbenzene. The difference in activation energies explains the experimentally observed high quantum yields (up to 0.9) of the Si–C bond photodissociation in silicon derivatives of benzophenone as compared to the C–C bond photodissociation in the corresponding carbon analogues (quantum yields <0.17).

Synthesis, psychotropic and anticancer activity of 2,2‐dimethyl‐5‐[5′‐trialkylgermyl(silyl)‐2′‐hetarylidene]‐1,3‐dioxane‐4,6‐diones and their analogues

AbstractA series of 2,2‐dimethyl‐5‐(5′‐R‐hetarylidene)‐1,3‐dioxane‐4,6‐diones has been synthesized for examing a structure–activity relationship. Furyl and thienyl derivatives of Meldrum's acid possess neurotropic activity comprising both depriming and activating components. Comparison of acute toxicity of carbon, silicon and germanium analogues in the furan series of the compounds has demonstrated that the germanium derivative is 11.5 times less toxic than the carbon analogue and four times less toxic than the silicon derivative. 2,2‐Dimethyl‐5‐(5′‐triethylsilyl‐2′‐thenylidene)‐1,3‐dioxane‐4,6‐dione has moderate toxicity with the highest neurotropic and cytotoxic activity Copyright © 2003 John Wiley &amp; Sons, Ltd.

Novel pentacoordinate silicon compounds bearing [Si-N-C-N-C-N] chelate ring derived from biguanide ligands

The reactions between secondary carbosilanes 1– 3 and 1-propylbiguanide/1-phenylbiguanide, H 6bigR proceed via SiH/NH dehydrocoupling and afford 1,4-bis(silyl)-5-propyl/phenylbiguanides with the general formula (R 1R 2 2SiCH 2CH 2SiMeH) 2·H 4bigR, [R 1=Ph, R 2=Me, R= n Pr ( 4), R=Ph ( 5); R 1=Me, R 2=Ph, R= n Pr ( 6), R 1=R 2=Et, R=Ph ( 7)]. These compounds represent a new family of pentacoordinate silicon derivatives comprising of [Si-N-C-N-C-N] chelate ring and have been characterized by elemental analysis, FAB mass, IR and multinuclear ( 1H, 13C and 29Si) NMR spectral studies.