共查询到20条相似文献,搜索用时 0 毫秒
1.
Ab initio electronic structure calculations using MP2 wavefunctions have been used to investigate a reaction path for the
hydrosilation reaction catalyzed by divalent titanium [modeled by TiH2, TiCl2, and Ti(C5H5)2]. Optimized structures and energies are presented. All model reactions predict a barrierless reaction path compared to a
barrier of 78 kcal/mol for the uncatalyzed reaction.
Received: 11 August 1998 / Accepted: 3 September 1998 / Published online: 23 February 1999 相似文献
2.
A hydrosilation reaction was used to bind four compounds with one or more alkyne groups or two alkene functionalities. The diffuse reflectance infrared Fourier transform, the 29Si cross-polarization magic-angle spinning (CP-MAS) NMR, and the 13C CP-MAS NMR spectra were used to characterize the various bonded materials. The bonded phase density was determined from carbon elemental analysis. The two ten-carbon hydrophobic stationary phases were characterized chromatographically and static stability tests were run in acidic and basic solutions. 相似文献
3.
Yuji Naruse 《Tetrahedron letters》2007,48(5):817-820
We predicted that uncatalyzed Mukaiyama aldol reactions are under the control of the geminal bond participation. At the transition state of the model reaction, addition of CH2O and CH2CH(OSiH3), the interbond energy IBE is negative between the σ-bonding orbital at the Z-position of the enolate terminal and , and positive between that at the E-position and . These results led us to predict that the electron-donating σ-bond at the Z-position enhances the reactivity. We calculated the enthalpies of activation of the reactions of a variety of the R-substituted silyl enolates and confirmed the prediction by showing that the reactivity of the Z-isomers relative to that of the E-isomers increases with the energy of the bonding orbital of the σ bond at the Z-position (the axial position at the transition state of the chair form). We demonstrate that the geminal bond participation is general not only to the pericyclic reactions but also to the aldol reaction, which is one of the most fundamental C-C bond forming reactions. 相似文献
4.
Scully NM Ashu-Arrah BA Nagle AP Omamogho JO O'Sullivan GP Friebolin V Dietrich B Albert K Glennon JD 《Journal of chromatography. A》2011,1218(15):1974-1982
Investigations into the preparation of silica hydride intermediate in supercritical carbon dioxide (sc-CO(2)) that avoids the use of organic solvents such as toluene or dioxane are described. The effects of reaction temperature, pressure and time on the surface coverage of the supercritical fluid generated silica hydride intermediate were studied. Under optimised supercritical conditions of 120°C, 483 bar and 3 h reaction time, silica hydride (Si-H) conversion efficiencies of ca. 40% were achieved for the hydride intermediate prepared from a monofunctional silane reagent (dimethylmethoxysilane). Si-H conversion efficiencies (as determined from (29)Si CP-MAS NMR spectral analysis) for the hydride intermediate prepared from triethoxysilane (TES) in sc-CO(2) were found to be comparable to those obtained using a TES silanisation approach in an organic solvent. (13)C and (29)Si CP-MAS-NMR spectroscopy was employed to provide a complete structural assignment of the silica hydride intermediates. Furthermore, supercritical CO(2) was subsequently employed as a reaction medium for the heterogenous hydrosilation of silica hydride with octadecene and with styrene, in the presence of a free radical initiator. These supercritical fluid generated reversed-phase materials were prepared in a substantially reduced reaction time (3 h) compared to organic solvent based methods (100 h reaction time). Silica functionalisation in sc-CO(2) presents an efficient and clean alternative to organic solvent based methods for the preparation of important silica hydride intermediate and silica bonded stationary phases via a hydrosilation approach. 相似文献
5.
Synthesis and characterization of a novel hydroxypolyether blocked polydimethylsiloxane PEO-b-PDMS-b-PEO 总被引:1,自引:0,他引:1
A novel hydroxypolyether blocked polydimethylsiloxane, poly(ethylene oxide) propyl-b-polydimethylsiloxane-b-propyl poly(ethylene oxide) (PEO-b-PDMS-b-PEO) was synthesized by simple hydrosilation reaction of poly(ethylene glycol) monoallyl ether with α,ω-dihydrogen terminated PDMS (HPDMS). Fourier transform infrared spectroscopy (FTIR) and IH NMR were used to identify the structure of PEO-b-PDMS-b-PEO and intermediate product HPDMS. Based on the effect investigations of temperature, reactant molar ratio, catalyst and time on the hydrosilation, it was found that the conversion of Si-H bond to SiC bond increased with the increase of catalyst and time, and the reaction completed when the content of catalyst was 22μg/g and the time was 5 h, respectively. Urethane reaction of OH and NCO group confirms that PEO-b-PDMS-b-PEO is more reactive toward to diisocyanate than α,ω-dihydroxylbutyl terminated PDMS. 相似文献
6.
The dendritic macromolecule with 4, 8, 16 and 32 bicyclo end groups on the periphery has been created by the Diels-Alder reaction of anthracene and maleimide. The dendritic skeleton with triple bonds has been prepared by the hydrosilation and the alkynylation of bis(phenylethynyl)dimethylsilane as a core. The peripheral anthracene on dendrimers has been substituted by the reaction of chlorosilyl groups containing dendritic generations and 9-anthracenecarbinol. NMR and MALDI-TOF mass spectrum has characterized these Diels-Alder products. 相似文献
7.
AbstractHeterocyclic compounds have a wide range of applications: they are predominant among the type of compounds used as pharmaceuticals, agrochemicals, fine chemicals, electronic components, polymers, and veterinary products. There is a vast scope to develop new heterocyclic compounds considering the high yield, low waste, and green synthesis. In this review, we have described the synthesis of heterocycles via insertion and cyclization which is achieved in recent years with the ideas, challenges, and milestone reactions. 相似文献
8.
Vorawit Banphavichit 《Tetrahedron》2007,63(36):8727-8734
A one-step, multicomponent Mannich-type reaction between phenols, paraformaldehyde, and β-aminoalcohols in the presence of LiCl afforded N-2-hydroxybenzyloxazolidines with high ortho-selectivity. Hydrolytic or reductive ring opening of the oxazolidines provided a series of N-salicyl-β-aminoalcohols in 84-92% overall yield. The synthesized compounds were evaluated as ligands for a titanium-catalyzed catalytic asymmetric Strecker reaction. The reaction employing 10 mol % of catalyst provided the Strecker products in excellent yields and up to 98% ee. 相似文献
9.
10.
Reactions of (bromophenylethenyl)diethoxysilanes with magnesium in THF gave poly[(ethoxysilylene)phenylenevinylene]s. The ethoxy group of the polymers could be readily replaced with other substituents by treating them with nucleophiles. Optical properties of the resulting poly(silylenephenylenevinylene)s were examined with respect to their UV absorption and emission spectra. Of those, pyrenylethynyl-substituted one exhibited energy transfer from the backbone to the substituent in the photo-excited state. 相似文献
11.
Abdol R. Hajipour Kazem Karami Arnold E. Ruoho 《Journal of organometallic chemistry》2009,694(16):2548-529
The [Pd{C6H2(CH2CH2NH2)-(OMe)2,3,4} (μ-Br)]2 complex of homoveratrylamine was synthesized and its application in the Heck coupling reaction was studied. This complex had been demonstrated to be active and efficient catalyst for the Heck reaction of aryl iodides, bromides and even chlorides. The cross-coupled products were produced in excellent yields in a short reaction time using catalytic amounts of [Pd{C6H2(CH2CH2NH2)-(OMe)2,3,4} (μ-Br)]2 complex in N-methyl-2-pyrrolidinone (NMP at 130 °C). 相似文献
12.
Catalysts have been found for the selective reaction of aliphatic isocyanates with carboxylic acids giving amides after carbon dioxide extrusion. Magnesium and calcium salts lead to a dramatic increase in reaction rates while improving the selectivity when sterically hindered isocyanates and/or carboxylic acids are used. 相似文献
13.
Lynch B Müller GH Healy LO Glennon JD Pursch M Albert K 《Analytical and bioanalytical chemistry》2003,377(6):1014-1019
29Si and 13C CP-MAS NMR spectroscopy was used to follow the conversion of native silica to a p-chlorobenzamide bonded silica material. The benzamide bonded phase was prepared via a hydrosilation reaction of a hydride silica intermediate with p-chloro-N-allylbenzamide. Solid-state NMR was used to show the disappearance of reactive surface hydride species (MH) and to identify newly formed bonded chemical species on the silica surface. DRIFT spectroscopy, elemental analysis, and specific surface-area determinations (BET) of the prepared phases are also reported. 相似文献
14.
Friedel-Crafts acylation catalyzed by niobium pentachloride with silver salt is described. Aromatic compounds with Ac2O or Bz2O were smoothly converted into the corresponding ketones in good to excellent yields. This system was also applied to the Sakurai-Hosomi reaction using acetals. The reaction proceeded quite rapidly to give the desired products in excellent yields. 相似文献
15.
Study of catalytic effect of ammonium molybdate on the bisphthalonitrile resins curing reaction with aromatic amine 总被引:1,自引:0,他引:1
A kind of catalyst, ammonium molybdate was developed in this paper to promote the curing reaction of bisphthalonitrile resins with aromatic amine as curing agent, and the catalytic effect was studied by differential scanning calorimetry (DSC), rheometric measurements and thermogravimetric analysis (TGA). The results indicated that the catalyst could improve the curing rate and increase the curing degree, which could be regulated by the content of the catalyst used in the reaction. 相似文献
16.
The activity of [Pd{C6H4(CH2N(CH2Ph)2)} (μ-Br)]2 complex was investigated in the Heck-Mizoroki C-C cross-coupling reaction. This complex is an active and efficient catalyst for the Heck reaction of aryl iodides, bromides and even chlorides and also arenesulfonyl chlorides. The cross-coupled products were produced in excellent yields in short reaction time using a catalytic amount of [Pd{C6H4(CH2N(CH2Ph)2) (μ-Br)]2 complex in NMP at 130 °C. 相似文献
17.
18.
Selective two-electron (2 e?) pathway oxygen reduction reaction (ORR) has gained prominence for enabling small-scale, on-site electrochemical H2O2 production and has emerged as a promising alternative to the conventional anthraquinone process. The rational design of catalysts that can suppress the competing four-electron pathway ORR is critical. This review highlights catalyst design strategies for promoting the selective 2 e? pathway ORR, including alloying with inert metals, partial surface poisoning, and generating atomically dispersed sites. The major results and advances, as well as unresolved challenges are summarized. 相似文献
19.
Tomoko Mineno Rie Tsukagoshi Tsubasa Iijima Kazuki Watanabe Hiroyuki Miyashita Hitoshi Yoshimitsu 《Tetrahedron letters》2014
A reductive coupling reaction was effectively developed to convert an aldehyde to its symmetrical ether. The successful reactions required Et3SiH and CH2Cl2 as the suitable solvent in the presence of a catalytic amount of In(OTf)3. Various aldehydes were subjected to the method, and each afforded the expected ethers in good to excellent yields. 相似文献