Structure of novel N-fluorosilylmethyl-N-isopropylureas

Novel N-isopropyl-N',N'-dimethyl-N-(silylmethyl)ureas Me₂NC(O)N(Prⁱ)CH₂SiMe_nX_3–n (X = OEt, F; n = 0–2) were synthesized, and their structure was confirmed by ¹H, ¹³C and ²⁹Si NMR spectroscopy. According to NMR data, the silicon atom of the fluorosilanes (X = F) is pentacoordinated. The X-ray diffraction analysis of the (trifluorosilyl)methylcontaining urea showed that it exists as (O–Si) chelate with intramolecular dative bond C=O→Si (1.880 Å).     

Quantum-chemical calculations of NMR chemical shifts of organic molecules: X. Dynamic equilibrium effects in the 29Si NMR spectra of silacycloalkanes

Dynamic equilibria related to change of the coordination number of the silicon atom in bis[N-(dimethylamino) imidato-N′,O]silacycloalkanes in solution were studied by theoretical calculations and experimental measurement of the ²⁹Si NMR chemical shifts. Silacyclopentane derivatives were found to exist in solution as mixtures of species with six- and five-coordinate silicon atoms, and silacyclohexane derivatives, as mixtures of five- and four-coordinate silicon compounds.     

29Si and 13C NMR spectra of permethylpolysilanes

²⁹Si, ¹³C and ¹H NMR spectra are reported for the series of linear permethylpolysilanes Me(SiMe₂)_nMe where n = 1 to 6, for the cyclic permethylpolysilanes (Me₂Si)_n where n = 5 to 8, and for a few related compounds. For linear polysilanes the ²⁹Si and ¹³C chemical shifts can be accurately calculated from simple additivity relationships based on the number of silicon atoms in α, β, γ and δ positions. Adjacent (α) silicon atoms lead to upfield shifts in the ²⁹Si and ¹³C resonances, whereas more remote silicon atoms lead to downfield shifts. The ²⁹Si chemical shifts of the polysilane chains are linearly related to the ¹³C shifts of the carbon atoms attached to the silicon. The ²⁹Si and ¹³C resonances of the cyclic silanes deviate from this relationship. Ring current effects arising from σ delocalization are suggested as an explanation for the deviations. Proton-coupled ²⁹Si NMR spectra are reported for Me₃SiSiMe₃ and for (Me₂Si)_n, n = 5 to 7.     

Reaction of tetrafluorosilane with tris(2-hydroxyethyl)amine, tris(2-trimethylsiloxyethyl)amine and bis(2-trimethylsiloxyethyl)amine and its N-methyl derivative. 1,1-difluoroquasisilatranes

Reaction of tetrafluorosilane with tris(2-hydroxyethyl)-and tris(2-trimethylsiloxyethyl)amine results in formation of 1-fluorosilatrane and fluorosilatrane in 75 and 53% yield, respectively. Reaction of tetrafluorosilane with bis(2-trimethylsiloxyethyl)amine and its N-methyl derivative leads to the hitherto unknown 1,1-difluoroquasisilatranes (N → Si) F₂Si(OCH₂CH₂)₂NR (R = H, Me) containing donor-acceptor bond N → Si and pentacoordinate silicon atom. The structure of the synthesized compounds was proved by ¹H, ¹³C, ¹⁵N, ¹⁹F, ²⁹Si NMR and IR spectroscopy.     

Reaction of transsilylation of <Emphasis Type="Italic">N</Emphasis>-methyl-<Emphasis Type="Italic">N</Emphasis>-trimethylsilylacetamide with silanes ClCH<Subscript>2</Subscript>SiR<Superscript>1</Superscript>R<Superscript>2</Superscript>Cl

The reaction of N-methyl-N-trimethylsilylacetamide with silanes ClCH₂SiR¹R²Cl (R¹, R² = H, Me; H, Ph; Ph₂) leads to the formation of (O→Si) chelate compounds with pentacoordinate silicon: N-[chloro(methyl)-silyl]methyl-, N-[chloro(phenyl)silyl]methyl-, and N-[chloro(diphenyl)silyl]methyl-N-methylacetamides. From the data of multinuclear NMR spectroscopy, the intermediates of the reaction of N-methyl-N-trimethylsilylacetamide with ClCH₂SiPhHCl and ClCH₂SiPh²Cl are stable in CDCl₃ solution at room temperature during several days and slowly rearrange to the final (O–Si) chelate compounds.     

13C and 29Si chemical shifts and coupling constants involving tris[(trimethylsilyl)methyl] silicon compounds

Silicon-29(δ²⁹Si) NMR chemical shifts are reported for the first time of tris[(trimethylsilyl)methyl] silicon compounds (disilylated derivatives) (Me₃Si^A)₃ C_αL, where L = Si^BR₁R₂R₃ and where R varies widely in electronegativity. ²⁹Si chemical shifts exhibit good correlation with the electronegativities of the groups bonded to the silicon atom. The ¹³C NMR spectra of these compounds have been recorded and assigned. δ¹³C_α is shown to depend on the type of substitutent on Si^B. The variation of ²⁹SiH coupling constants with electronegativity of R is studied.     

N-Isopropyl-N&#x27;,N&#x27;-diphenyl-N-(silylmethyl)ureas: Synthesis and structure

New N-isopropyl-N',N'-diphenyl-N-(silylmethyl)ureas were obtained, and their structure was explored by ¹H, ¹³C, ²⁹Si NMR spectroscopy and X-ray analysis. These results have shown that N-isopropyl-N', N'-diphenyl-N-[(fluorosilyl)-methyl]ureas exist as (O–Si) chelates with intramolecular dative bond C=O→Si.     

Silyl modification of biologically active compounds. 11. Synthesis,physico‐chemical and biological evaluation of N‐(trialkoxysilylalkyl)tetrahydro(iso,silaiso) quinoline derivatives

N‐(trialkoxysilylalkyl) derivatives of 1,2,3,4‐tetrahydroquinoline, 1,2,3,4‐tetrahydroisoquinoline and 4,4‐dimethyl‐4‐sila‐1,2,3,4‐tetrahydroisoquinoline were prepared and characterized by elemental analysis, ¹H, ¹³C and ²⁹Si NMR spectroscopy. In vivo psychotropic properties and in vitro cytotoxic effects of 3‐[N‐(1,2,3,4‐tetrahydroisoquinolyl)]propyltriethoxysilane methiodide and 3‐[N‐(1,2,3,4‐tetrahydroisoquinolyl)]propylsilatrane are reported. Comparative study of ²⁹Si shifts in newly synthesized compounds suggested donor–acceptor interaction between nitrogen and silicon atom, which increased electron density at Si nuclei, revealing a stronger increment of N → Si transannular bond in comparison with N → Si α‐effect. The molecular structure of 3‐[N‐(1,2,3,4‐tetrahydroisoquinolyl)]propylsilatrane features a penta‐coordinate silicon atom having CSiO₃ pattern and Si…N intramolecular interaction. Copyright © 2005 John Wiley & Sons, Ltd.     

Synthesis of N-(trifluorosilylmethyl)glutarimide. Alternate intramolecular coordination of the silicon atom to two oxygen atoms

A new representative of draconoids, N-(trifluorosilylmethyl)glutarimide, was synthesized by reaction of N-(trimethyoxysilylmethyl)glutarimide with boron trifluoride-ether complex. According to the IR and ¹H, ¹³C, ¹⁵N, ¹⁹F, and ²⁹Si NMR data, this compound molecule is characterized by intramolecular coordination between the silicon and carbonyl oxygen atoms (alternate coordination of the silicon atom to each oxygen atom).     

Synthesis, structure and dynamic stereochemistry of (O → Si)-chelate N-(trifluorosilylmethyl)-[N-(S)-(1-phenylethyl)]acetamide and 1-(trifluorosilylmethyl)-2-oxoperhydroazepine: Retention of the O → Si coordination in the adduct with KF and 18-crown-6

The novel compounds, N-(trifluorosilylmethyl)-[N-(S)-(1-phenylethyl)]-acetamide (1a) and 1-(trifluorosilylmethyl)-2-oxoperhydroazepine (1b) have been prepared from the corresponding NH-compounds using ClCH₂SiCl₃/Et₃N or ClCH₂SiCl₃/(Me₃Si)₂NH followed by methanolysis or hydrolysis of the reaction mixture in the presence of Lewis bases, and then BF₃ etherate. Potassium-(18-crown-6)-(2-oxoperhydroazepinomethyl)tetrafluorosilicate (2) was synthesized by reaction of the trifluoride (1b) with KF in the presence of 18-crown-6. Using ¹⁹F, ²⁹Si NMR and X-ray diffraction techniques it was established that the silicon atom is pentacoordinate in the trifluorides (1a, b) and hexacoordinate in the adduct 2. Thus the internal coordination of the O → Si bond present in the trifluoride (1b) is retained in the adduct 2.The stereochemical non-rigidity of the trifluorides (1a, b) and the N-(trifluorosilylmethyl)-N-methylacetamide (1c) was investigated using dynamic ¹⁹F NMR spectroscopy. The activation barriers for permutational isomerization are in the range 9.5-10 kcal mol⁻¹. Lower values of ΔG^# for permutation of trifluorides (1a-c) compared to the monofluorides with the coordination core OSiC₃F together with small negative values for the activation entropy implies a non-dissociative mechanism. Quantum-chemical analysis suggests a mechanism involving a turnstile rotation.     

Synthesis, structure, and spatial arrangement of Si-substituted N-(dimethylsilylmethyl)imides

The synthesis of N-(chlorodimethylsilylmethyl)succinimide and N-(chlorodimethylsilylmethyl)-glutarimide by the reaction of the corresponding N-trimethylsilylimides with chlorodimethylsilane and by the reaction of unsubstituted imides with a mixture of hexamethyldisilazane with dimethylchloromethylchlorosilane is described. The formation of N-(chlorodimethylsilylmethyl)succinimide is followed by substitution by the silicon atom, which, depending on the reagent ratio, provides N-(dimethylsuccinimidomethyl)succinimide as the major or minor product. ¹H, ¹³C, and ²⁹Si NMR spectroscopy and X-ray diffraction analysis showed that the silicon atom in N-(chlorodimethylsilylmethyl)glutarimide is five-coordinate. By contrast, in N-(chlorodimethylsilylmethyl)succinimide and N-(dimethylsuccinimidomethyl)succinimide, according to NMR and X-ray diffraction data, the silicon atom is four-coordinate. Quantumchemical calculations by the AM1 method show that the molecular conformations of N-(chlorodimethylsilylmethyl)imides containing an intramolecular OSi bond are not energetically most favorable in the gas phase.Translated from Zhurnal Obshchei Khimii, Vol. 74, No. 10, 2004, pp. 1617–1623.Original Russian Text Copyright © 2004 by Pogozhikh, Ovchinnikov, Kramarova, Negrebetskii, Shipov, Albanov, Voronkov, Pestunovich, Baukov.This revised version was published online in April 2005 with a corrected cover date.     

Reactions of silicon-, germanium- and tin-containing carbene complexes of tungsten Ph3E-CW(OBu)3 (E=Si, Ge, Sn) with hydrogen chloride: crystal structures of carbene complexes Ph3E-CHWCl2(OBu)2 (E=Si, Ge)

The novel organosilicon, -germanium and -tin-containing carbene complexes of tungsten of the type Ph₃E-CHWCl₂(OBu^t)₂ (E=Si, Ge, Sn) have been prepared by the reaction of heteroelement-containing carbene complexes of tungsten Ph₃E-CW(OBu^t)₃ (E=Si, Ge, Sn) with hydrogen chloride. The tin-containing carbene complex was identified in solution by ¹H NMR spectroscopy. Silicon- and germanium-containing carbene complexes were isolated in high yields as crystalline solids and characterized by elemental analysis, IR, ¹H NMR, ¹³C NMR and ²⁹Si NMR spectroscopy and X-ray diffraction studies. The geometry of the W atoms in the compounds can be described as a distorted square pyramid.     

Synthesis and structure characterization of ladder-like polymethylsilsesquioxane (PMSQ) by isolation of stereoisomer

The stereo cyclic siloxane compounds having tetra hydroxyl and tetra methyl group were synthesized by hydrolysis of tetrahydrido tetramethyl cyclosiloxane consisting of four stereoisomers. Among the stereo cyclic isomers, cis-trans-cis tetrahydroxyl tetramethyl cyclosiloxane (2) was separated by recrystallization and was used as a monomer species for preparation of ladder-like polymethylsilsesquioxane (PMSQ). The isolated isomer was directly polymerized in THF with potassium carbonate (K₂CO₃) by systematic ring condensation. The hydrolyzed stereoisomers were characterized by ¹H and ²⁹Si NMR, and HPLC. The structure of the synthesized PMSQs were characterized by size exclusion chromatography (SEC), MALDI-TOF mass, ²⁹Si NMR, and small angle X-ray scattering (SAXS).     

Intra- and intermolecular coordination reactions in solution involving pentacoordinated fluorosilanes based on proline

NMR spectroscopy was used to study a series of C,O-monochelate N′-(fluorodimethyl-silylmethyl)-N′-methyl-N-(organosulfonyl)proline amides in the solid state and in solutions in chloroform, pyridine, and acetone. The structure of one of the complexes was established by X-ray crystallography. Quantum chemical calculations were performed to interpret the spectral data obtained. The molecular conformation observed in crystal was found to be retained in solutions. The coordination bonds of silicon atom with acetone and pyridine are very weak and cannot stabilize the acyclic form (without the Si-O coordination bond). The ²⁹Si chemical shift was found to be directly dependent on the Si-O bond distance. The mutual influence of organosulfonyl group and chelate ring was described in terms of polarization effects.     

Nmr study of the VixSiX4−x compounds with X = Cl,Br; x = 0, 1, 2, 3

¹H, ¹³C and ²⁹Si NMR data for the compounds Vi_xSiX_4?x are reported. While the ¹H and ¹³C resonances from the π system are indicative of the electron-withdrawing inductive effect (-I) of the halogens, the ²⁹Si chemical shift data reveal not only a shift contribution originating from this inductive effect but also the important influence of a {d, σ^*-π} hyperconjugation [1]. This back-donation originates from the vinyl π system and not from the halogens. The chemical shift data and the coupling constants also show an important influence from steric interaction and even from an electric field effect caused by polarization of the silicon—halogen bond.     

Structural studies of sialon ceramics by high-resolution solid-state NMR

High-resolution solide-state ²⁷Al NMR with magic-angle spinning (MASNMR) readily monitors the quantity and coordination (four- and six-fold) of aluminium in two ceramic materials of the SiAlON system. Sialon X-phase, of approximate composition Si₃Al₆O₁₂N₂, contains aluminium-centred octahedra and tetrahedra in the ratio ca. 1.9:1.0, while another sample containing a mixture of sialon polytypoids shows AlO₆ octahedra and a large quantity of what is most probably nitrogen-coordinated tetrahedral aluminium. In addition, ²⁹Si MASNMR detects two different kinds of silicon in the latter sample in a 2:1 ratio. These observations are interpreted satisfactorily in terms of the crystal structures of the compounds and provide further examples of the potential of MASNMR in the investigation of complex ceramic systems.     

Synthesis, crystal and molecular structures, and steroechemical nonrigidity ofN-(chlorodimethylgermylmethyl)-andN-(bromodimethylgermylmethyl)-N-[(S)-1-phenylethyl]acetamides andN-(chlorodimethylgermylmethyl)-4-phenyl-2-pyrrolidone

RacemicN-(chlorodimethylgermylmethyl)-4-phenyl-2-pyrrolidone and the first optically active amide derivatives containing the asymmetrical carbon atom and the five-coordinate germanium atom,viz.,N-(chlorodimethylgermylmethyl)- andN-(bromodimethylgermyl-methyl)-N-[(S)-1-phenylethyl] acetamides, were synthesized. Their structures were established by X-ray diffraction analysis. The geometric characteristics of the trigonal-bipyramidal valence environment about the germanium atoms are compared with those of analogous enantiomeric silicon compounds and the related five-coordinate germanium compounds. The barriers to permutational isomerization of the title compounds were determined by dynamic¹H NMR spectroscopy. It was found that these barriers are higher than those of the corresponding silicon analogs. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 137–144, January, 2000.     

Fourier transform NMR studies of organometallic compounds. II—synthesis and NMR spectroscopy of propenyl and isopropenyl derivatives of silicon and lead

Isomeric mixtures of compounds Me_nM(CH?CHMe)_4?n (M=Si, Pb; n=0?3) have been prepared and studied, as well as pure Me₃M(CMe?CH₂) and mixtures containing propenyl isopropenyl residues bonded to silicon and lead. ¹H, ¹³C, ²⁹Si and ²⁰⁷Pb NMR data are presented; as previously observed for the corresponding tin compounds, the ²⁹Si and ²⁰⁷Pb shifts for the Me₃MC₃H₅ isomers can be used to calculate the shifts expected for the other isomers; while for lead the agreement is good, calculated and observed values for silicon diverge with decreasing n due, at least in part, to steric factors.     

Synthesis, crystal and molecular structures, and steroechemical nonrigidity ofN-(chlorodimethylgermylmethyl)-andN-(bromodimethylgermylmethyl)-N-[(S)-1-phenylethyl]acetamides andN-(chlorodimethylgermylmethyl)-4-phenyl-2-pyrrolidone

RacemicN-(chlorodimethylgermylmethyl)-4-phenyl-2-pyrrolidone and the first optically active amide derivatives containing the asymmetrical carbon atom and the five-coordinate germanium atom,viz.,N-(chlorodimethylgermylmethyl)- andN-(bromodimethylgermyl-methyl)-N-[(S)-1-phenylethyl] acetamides, were synthesized. Their structures were established by X-ray diffraction analysis. The geometric characteristics of the trigonal-bipyramidal valence environment about the germanium atoms are compared with those of analogous enantiomeric silicon compounds and the related five-coordinate germanium compounds. The barriers to permutational isomerization of the title compounds were determined by dynamic¹H NMR spectroscopy. It was found that these barriers are higher than those of the corresponding silicon analogs. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 137–144, January, 2000.     

Hydrolytic vs. Nonhydrolytic Sol-Gel in Preparation of Mixed Oxide Silica–Alumina Catalysts for Esterification

The development of green and sustainable materials for use as heterogeneous catalysts is a growing area of research in chemistry. In this paper, mesoporous SiO₂-Al₂O₃ mixed oxide catalysts with different Si/Al ratios were prepared via hydrolytic (HSG) and nonhydrolytic sol-gel (NHSG) processes. The HSG route was explored in acidic and basic media, while NHSG was investigated in the presence of diisopropylether as an oxygen donor. The obtained materials were characterized using EDX, N₂-physisorption, powder XRD, ²⁹Si, ²⁷Al MAS-NMR, and NH₃-TPD. This approach offered good control of composition and the Si/Al ratio was found to influence both the texture and the acidity of the mesoporous materials. According to ²⁷Al and ²⁹Si MAS NMR analyses, silicon and aluminum were more regularly distributed in NHSG samples that were also more acidic. Silica–alumina catalysts prepared via NHSG were more active in esterification of acetic acid with n-BuOH.