Silylation partielle et réduction de composés gem-polychlorés fonctionnels

The trimethylchlorosilane/magnesium/hexamethylphosphoric triamide (HMPT) system reacts with some functional polychlorinated compounds (chloral, hexachloroacetone, acetone chloroform) affording a partial reduction accompanied by silylation and leads to new functional silylated derivatives.These reactions exhibit reductive properties of magnesium, in HMPT, towards the CCl bond.     

High conversion synthesis of pyrene end functionalized polyrotaxane based on poly(ethylene oxide) and alpha-cyclodextrins

We describe the quantitative synthesis of new pyrene labeled cyclodextrin-based polyrotaxane starting from pseudopolyrotaxane of alpha,omega-dimethacrylate poly(ethylene oxide) (PEO) and alpha-cyclodextrins (alpha-CDs). Using a solvent mixture (H2O/dimethyl sulfoxide (DMSO)), an almost quantitative conversion in polyrotaxane can be achieved using the coupling reaction between methacrylic functions and 1-pyrene butyric acid N-hydroxysuccinimide ester. This result is due to the fast blocking reaction of the pseudopolyrotaxane telechelic functions. The polyrotaxanes are characterized by NMR, size exclusion chromatography (SEC), and small-angle neutron scattering (SANS). A rodlike structure of the polyrotaxane is evidenced by SANS, and a persistence length of 70 A is determined. This result corresponds to an almost completely stretched PEO chain of 1000 g.mol(-1) molecular weight. We furthermore studied the opposite case of low packing density polyrotaxanes that were also silylated to suppress interactions between cyclodextrins. We observed a random coil structure only for silylated low packed polyrotaxane. This result demonstrates that both hydrogen bonding and packing density can explain the rodlike structure of cyclodextrin-based polyrotaxane.     

Synthese regiospecifique,d'alcenylfluorosilanes et de cetones β, γ- et γ, δ-ethyleniques siliciees a partir de sila-1 cyclopentenes-3 et de sila-3 bicyclo[3.1.0] Hexanes

Studies of the electrophilic substitution on two 1-sila-3-cyclopentenes and their cyclopropane homologues revealed the important role of silicon and provided a new route to alkenylfluorosilanes and novel β,γ or especially γ,δ-unsaturated silylated ketones.     

Migration 1,2 d''un groupe triméthylsilyle au niveau d''un cation vinylique: synthèse de diènes conjugués silylés à partir de bis(triméthylsilyl)-1,4 alcynes-2

Alkyl -substituted 1,4-bis(trimethylsilyl)-2-alkynes react with electrophilic reagents to give silylated conjugated dienes, which result from a 1,2-shift of a trimethylsilyl group to a vinylic cationic center.     

Direct Trimethylsilylation of Phenanthrene and its Products—An Abnormal Silylation of Phenanthrene

Direct trimethylsilylation¹⁾ of phenanthrene in different molar ratio of phenanthrene/sodium/trimethylchlorosilane is reported and discussed. Instead of the aromatic silyl compounds, such as 9-trimethylsilylphenanthrene (V), the hydroaromatic silyl compounds, such as 9, 10–bis (trimethylsilyl)-9, 10-dihydrophenanthrene (I) were obtained preferentially. Structure of these compounds are characterized and discussed. These silylated products have a general trend to change their properties during long time storage in the atmosphere under exposure to light. A significant difference of chemical shifts between silylated aromatic compound (V) and silylated hydroaromatic compound (I-IV) was observed.     

Diisobutylaluminum hydride-promoted cyclization of silylated 1,3-dien-5-ynes: Application to total synthesis of a 20-norabietane derivative

The diisobutylaluminum hydride (DIBAL-H)-promoted benzocyclization, recently developed by this group, was adopted for the synthesis of a natural product containing a 9,10-dihydrophenanthrene skeleton to demonstrate its synthetic utility. One of the extracts from the roots of Salvia hydrangea DC. ex Bentham (Lamiaceae), a 20-norabietane derivative, was selected as the target molecule. The key step forming the 9,10-dihydrophenanthrene skeleton was achieved by the DIBAL-H-promoted cyclization of a silylated 1,3-dien-5-yne easily accessible from a substituted α-tetralone.     

硅烷化对Ti/HMS分子筛催化性能的影响

分别用水热法和气相沉积法制备了Ti/HMS分子筛,采用三甲基氯硅烷(TMCS)和六甲基二硅氮烷(HMDSZ)对Ti/HMS样品进行了气相硅烷化,并用X射线衍射、N2吸附、红外光谱、29Si核磁共振和紫外-可见光谱对样品进行了表征.丙烯环氧化反应的测定结果表明,硅烷化可显著提高环氧化催化活性.水热法制备的Ti/HMS经HMDSZ硅烷化后的催化活性比经TMCS硅烷化后的稍高;气相沉积法制备的Ti/HMS经HMDSZ硅烷化后的催化活性远高于经TMCS硅烷化后的催化活性.这是由于TMCS不但能与分子筛表面的硅羟基反应,而且能破坏分子筛骨架中的Si-O-Ti甚至Si-O-Si键,形成新的羟基,导致样品的亲水性较强,同时还能对气相沉积法制备的Ti/HMS中的四配位骨架钛产生破坏作用.     

Étude thermodynamique de la protonation de dérivés diméthylés de la pipérazine

The thermodynamic functions ΔG^o_n, ΔH^o_n and ΔS^o_n of the two steps of proton ionization of N,N′-dimethylpiperazine, 2,6-dimethylpiperazine, 2,5-dimethylpiperazine (cis) and 2,5-dimethylpiperazine (trans) are determined at 25°C in water and water—ethanol (52%, w/w) solvents, including 0.1 M KNO₃ as ionic strength.Free energies are calculated from the ionisation constants obtained by pH-metric method; enthalpies are determined from calorimetric measurements.The comparison of these functions and of the corresponding entropies is discussed in terms of the position of CH₃ groups in each molecule and takes account of previous results relative to piperazine and its monomethyl derivatives.     

硅烷化聚氨酯复合催化剂的研究

以聚丙二醇、TDI、N-正丁基-γ-氨丙基三甲氧基硅烷和蒙脱土为主要原料,采用原位聚合方法研究了蒙脱土和有机铋化合物对环境友好和储存稳定的硅烷化聚氨酯催化作用.通过滴定法测试了反应体系中异氰酸根(NCO)含量的变化,发现蒙脱土可以催化NCO与OH的反应,且与有机铋化合物具有协同效应,利用在线红外分析仪证实了蒙脱土的催化...     

Acid-catalysed isomerization of the tetraisopropyldisiloxane-1,3-diyl group. Simultaneous protection of two secondary alcoholic functions.

The reaction of 1,3-dichloro-1,1,3,3-tetraisopropyldisiloxane with ribonucleosides or sugar derivatives affords products containing one silyl-protected primary and secondary hydroxy function. Treatment of these products with MSA in DMF gives products having two silylated secondary hydroxy functions.     

Bis-ortho-metalation/silylation of unprotected o-phthalic acids. Straightforward access to new silylated N-hydroxyphthalimide (NHPI) analogs

The one pot, in situ ortho-metalation/silylation of unprotected o-phthalic acids using lithium tetramethylpiperidide (LiTMP) and chlorotrimethylsilane is described. This method gives a straightforward access to silylated phthalic anhydrides. These can be easily converted into the corresponding silylated N-hydroxyphthalimide (NHPI) analogs, which are promising new aerobic oxidation catalysts.     

Processing and thermal properties evaluation of silylated apophyllite–filled epoxy nanocomposite

The primary objective of the research was to evaluate the rheology and thermal properties of silylated apophyllite–filled epoxy nanocomposite. Several n‐octyldimethylsiloxy‐apophyllite with different grafting degrees were synthesized by controlling the ratio of the apophyllite and n‐octyldimethylchlorosilane. The thermal studies of silylated apophyllite have shown that the onset decomposition temperature of silylated apophyllite far exceeds the onset temperature of conventional organoclays (~260 °C). Chemorheological measurements of 1.8 wt% silylated apophyllite–filled tetra functional epoxy (MY720) and difunctional epoxy (DER661) resin mixture showed that the addition of the silylated apophyllite does not dramatically affect the cure profile of the epoxy resin with the availability of 40 min of processing window after the addition of apophyllite. Wide angle X‐ray diffraction and transmission electron microscopy results of the shear mixed and cured nanocomposite suggest that the apophyllite was well dispersed in the epoxy matrix. The thermal studies of epoxy nanocomposite showed an increase in the char yield on the addition of silylated apophyllite to the epoxy resin. In addition, an improvement in the onset decomposition temperature of the cyanopropyldimethylsiloxy‐apophyllite epoxy nanocomposite was observed compared with that of pure epoxy resin. Copyright © 2011 John Wiley & Sons, Ltd.     

Silylated cyclohexadienes as new radical chain reducing reagents: preparative and mechanistic aspects

Various silylated 1,4-cyclohexadienes are presented as superior tin hydride substitutes for the conduction of various radical chain reductions. Debrominations, deiodinations, and deselenations can be performed using these environmentally benign reagents. Furthermore, Barton-McCombie-type deoxygenations using silylated cyclohexadienes are described. Radical cyclizations, ring expansions, and Giese-type addition reactions with the new tin hydride substitutes are presented. The polymerization of styrene can be regulated using silylated cyclohexadienes. Rate constants for hydrogen atom abstraction from two 1-silyl-cyclohexadienes by primary C-radicals were determined. The effects of the cyclohexadiene substituents on the reaction outcomes are discussed. Finally, qualitative EPR experiments on silyl radical expulsion from silylated cyclohexadienyl radicals are presented.     

Gas chromatographic retention indices of trimethylsilyl derivatives of terpene alcohols

This paper presents the experimentally determined retention indices (RI(TMS)) for a set of 75 silylated terpenols (33 monoterpenols and 42 sesquiterpenols). The attempt was made to assess the dependence of RI(TMS) on RI (for non-silylated terpenols) and on RI(Ac) (for acetylated terpenols). Satisfactory linear regression parameters (RI(TMS)=b(0)+b(1)RI) were observed for tertiary substituted monoterpenols and primary or secondary substituted sesquiterpenols. The mass spectra of silylated terpenols that were not found in the available literature are in Supplementary information.     

Determination de bases de gaussiennes optimales pour les molecules

Bases composed of one fixed linear combination ofn = 2 and 3 Gaussian functions have been investigated for the hydrogen molecule. It is shown that the scaling factor applied to Huzinaga's free atom exponents,which minimizes the total SCF energy, is independent of n and has the same value as forn = 1. This holds for every interatomic distanceD. From the energy variation as a function ofD, the force constant, the equilibrium distance and the bonding energy are deduced, for the different bases investigated, and compared with experimental values, and with values obtained by other authors by means of minimal bases of Slater orbitals.     

Coordination assembly and characterization of red-emitting europium (III) organic/inorganic polymeric hybrids

Novel luminescent ternary organic-inorganic-polymeric hybrid material has been assembled by Eu(3+) complex incorporating into poly (methyl methacrylate) (PMMA) matrix. The functionalized silylated precursor PDC-Si derived from PDC (2,6-pyridinedicarboxylic acid chloride) behaves as the coordination units of Eu(3+) ion. The organic polymer was introduced into the system by directly dissolving PMMA in solution of Eu(PDC-Si)(3) complex and N-N-Dimethyl Formamide (DMF) with subsequent addition of tetraethoxysilane to promote hydrolysis and condensation. The structure and photophysical properties of the resulting hybrids are characterized by Fourier transform infrared spectra, X-ray diffraction (XRD), scanning electronic microscopy and photoluminescence spectra. The luminescence quantum yield was calculated based on the emission spectra and luminescence lifetimes. XRD reveals its amorphous structure. Efficient energy transfer process occurs between PMMA and Eu(3+), and replacement of water molecule by PMMA in the first coordination sphere was confirmed by comparing with the binary hybrid.     

Prediction of retention indexes. III. Silylated derivatives of polar compounds.

Polar compounds containing hydroxyl, amino and carboxyl groups, singly or in combination, can be chromatographed after the polar functional groups are silylated. The silylated derivatives of acids, alcohols, amines, diols, amino alcohols, amino acids are shown to behave chromatographically as hydrocarbons, and their retention indexes can be readily predicted from their base values. The column difference, namely, the difference between the retention indexes of the analyte on polar and non-polar columns is minimal for the silylated derivatives in comparison to that observed for the underivatized analytes. This minimal column difference is attributed to the hydrocarbon-like chromatographic characteristics of the silylated derivatives. The retention indexes of the silyl derivatives appear to correlate with the atom number Z of the analyte.     

Preparation of silylated magadiite thin-film-containing covalently attached pyrene chromophores

Thin-film of magadiite (Mag) silylated by [2-(perfluorohexyl)-ethyl]trichlorosilane was prepared by casting the chloroform/ethylacetate nanosheet solution of it. The addition of alkylamine and perfluoroalkyl groups to silylated magadiite greatly changed the surface morphology of the resulting sample and the transparent thin-film with relatively smooth surface was obtained. Amino groups were introduced into it by using 3-aminopropyltriethoxysilane after removal of alkylamine. The reaction of 1-pyrenebutanoic acid succimidyl ester with the thin-film of silylated magadiite-containing amino groups in N,N-dimethylforamide (DMF) resulted in the covalent attachment of pyrene chromophores to it.     

Synthesis of carbobicyclic compounds via palladium-catalyzed cyclization/hydrosilylation: evidence for reversible silylpalladation

Cyclization/hydrosilylation of substituted 1-vinyl-1-(3-butenyl)cycloalkanes catalyzed by a 1:1 mixture of (phen)Pd(Me)Cl (1) and NaBAr(4) [phen = 1,10-phenanthroline; Ar = 3,5-C(6)H(3)(CF(3))(2)] formed silylated spirocycles in high yield with excellent regio and diastereoselectivity. Cyclization/hydrosilylation of substituted 3-(3-butenyl)cycloalkenes or 2,3-diallyl-5,6-dimethyl-1,4-hydroquinone diacetate (16) formed silylated fused bicyclic complexes in good yield. Reaction of substituted 1,6,11-nonatrienes with silane catalyzed by 1/NaBAr(4) led to cascade cyclization with hydrosilylation. This latter procedure was employed in the synthesis of silylated bicyclopentanes and a linear triquinane.     

Une fonction d'onde autocohérente (self-consistent) sans restriction de symétrie pour 1′état X3Π de la molécule BN

We give the self-consistent wave functions for the BN molecule in the …(5 σ) (1 π⁺)² (1 π^?), X³ Π state. These wave functions are obtained as linear combinations of SLATER orbitals of the atoms. In this openshell case the π⁺ and π^? orbitals belonging to the same symmetry species but to different subspecies are allowed to vary independently. Their coefficients are found rather different from one another; this seems to mean that the effect of the usual symmetry restriction could be relatively important in such cases.