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Selective Formation (selective + formation)
Selected AbstractsCopper(I)-Assembled Pseudorotaxanes Bearing Bis(nitrile) Ligands: Selective Formation of Large Chelate RingsEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 3 2004Efstathia G. Sakellariou Abstract The syntheses of two novel CuI -bis(benzonitrile) complexes of the type [Cu(dCNn)2][PF6] {where dCNn = NCPhO(CH2)nOPhCN, n = 3, 4} are described. Both compounds have been characterized by X-ray crystallography. To our surprise, and although the two complexes were quite similar, two very distinct structures were obtained. For the [Cu(dCN4)2][PF6] complex, a tetrahedral geometry was observed whereas for [Cu(dCN3)2][PF6], a polymeric assembly was formed. A further extension of this work involved the syntheses of two threaded species bearing the M30 macrocycle, Cu metal and a dCNn ligand. The formation of the desired complexes was confirmed by means of mass spectrometry as well as 1-D and 2-D 1H NMR spectroscopy. Finally, the cyclic voltammograms of all 4 new species were recorded giving rise to redox potentials ranging from +0.88 to +1.25 V. These new threaded complexes are of particular interest since they can form the basis of novel rotaxane structures. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004) [source] Supramolecular Architectures: Selective Formation of Bi-Component Arrays Through H-Bonding of Multivalent Molecular Modules (Adv. Funct.ADVANCED FUNCTIONAL MATERIALS, Issue 8 2009Mater. Molecular recognition occurs at dynamic interfaces too! The cover shows a donor,acceptor,donor hydrogen-bond moiety, incorporated in a tailor-made monovalent molecular module (in blue), that is able to recognize both complementary monovalent (in red) and tetravalent (in green) molecular modules at interfaces. This finding, described by P. Samori and co-workers on page 1207, paves the way towards the formation of robust multicomponent 2D functional nanostructures with tunable size and geometries. [source] Selective Formation of Bi-Component Arrays Through H-Bonding of Multivalent Molecular ModulesADVANCED FUNCTIONAL MATERIALS, Issue 8 2009Luc Piot Abstract Here, the formation of discrete supramolecular mono- and bi-component architectures from novel and multivalent molecular modules bearing complementary recognition moieties that are prone to undergo multiple H-bonds, such as 2,6-di(acetylamino)pyridine and uracil residues, is described. These nanostructured H-bonded arrays, including dimeric and pentameric species, are thoroughly characterized in solution by NMR, in the solid state by FT-IR, and at the solid,liquid interface by means of scanning tunneling microscopy. The employed strategy is extremely versatile as it relies on the tuning of the valency, size, and geometry of the molecular modules; thus, it may be of interest for the bottom-up fabrication of nanostructured functional materials with sub-nanometer precision. [source] Selective Formation of Dihydropyran Derivatives by a Tandem Domino Ring-Closing Metathesis/Cross-Metathesis.CHEMINFORM, Issue 21 2007Marie-Alice Virolleaud Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF. [source] Highly Selective Formation of Propargyl- and Allenyltrichlorosilanes and Their Regiospecific Addition to Various Types of Aldehydes: Preparation of Both Allenic and Homopropargylic Alcohols.CHEMINFORM, Issue 21 2006Uwe Schneider Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF. [source] A One-Pot, Metathesis,Hydrogenation Sequence for the Selective Formation of Carbon,Carbon Bonds.CHEMINFORM, Issue 11 2006Andrea J. Robinson Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF. [source] Titanocene(II)-Promoted Reactions of Thioacetals with Ethylene: Selective Formation of Terminal Olefins with One- or Two-Carbon Homologation.CHEMINFORM, Issue 47 2002Akira Tsubouchi Abstract For Abstract see ChemInform Abstract in Full Text. [source] ChemInform Abstract: Selective Formation of C60F18(g) and C60F36(g) by Reaction of [60]Fullerene with Molecular Fluorine.CHEMINFORM, Issue 26 2002N. S. Chilingarov Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source] ChemInform Abstract: Ytterbium Trifluoromethanesulfonate Yb(OTf)3: An Efficient, Reusable Catalyst for Highly Selective Formation of ,-Alkoxy Alcohols via Ring-Opening of 1,2-Epoxides with Alcohols.CHEMINFORM, Issue 37 2001Pravin R. Likhar Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source] Mapping the Mechanism of Nickel-Ferrophite Catalysed Methylation of Baylis,Hillman-Derived SN2, ElectrophilesEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 6 2009Andrew Novak Abstract Enantioselective Ni-catalysed methylation of Baylis,Hillman-derived allylic electrophiles in the presence of ferrophite ligands has been investigated computationally and experimentally. The sense and degree of enantioselectivity attained is independent of both the leaving group and the isomeric structure of the initial allylic halide. DFT studies support the selective formation of a limited number of energetically favoured anti and syn ,-allyl intermediates. The observed regio- and enantioselectivity can be rationalised based on the energetics of these structures. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009) [source] Regio- and Stereoselective Intermolecular Hydroalkoxylation of Alkynes Catalysed by Cationic Gold(I) ComplexesADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 10 2010Avelino Corma Abstract Vinyl ethers and ketals are obtained from the reaction of phenylacetylene derivatives and dimethyl acetylenedicarboxylate (DMAD) with alcohols in good yields and levels of stereoselectivity by using cationic gold(I)-phosphine complexes as catalysts. By choosing the appropriate phosphine, the selective formation of the Z or the E isomer of the vinyl ether can be tuned, and the undesired formation of the ketal can be controlled. The isomerisation of fumarates (Z -isomer) to maleates (E -isomer) is a gold-catalysed process that can be conducted in one-pot. When using polyols, 5-membered cyclic ketals are easily isolated by extraction with hexane and the gold complex can be reused. [source] Hydrogenation of Phenol in Supercritical Carbon Dioxide Catalyzed by Palladium Supported on Al-MCM-41: A Facile Route for One-Pot Cyclohexanone FormationADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 11-12 2009M. Chatterjee Abstract The hydrogenation of phenol has been carried out in supercritical carbon dioxide (scCO2) under very mild reaction conditions at the temperature of 50,°C over palladium supported Al-MCM-41 (metal loading ,1%). This palladium catalyst is shown to be highly active and promotes the selective formation of cyclohexanone (,98%), an industrially important compound, in a "one-pot" way. The effects of different variables like carbon dioxide and hydrogen pressure, reaction time and also silica/alumina ratio of the MCM-41 support along with palladium dispersion are presented and discussed. The pressure effect of carbon dioxide is significantly prominent in terms of conversion and cyclohexanone selectivity. Moreover, the silica/alumina ratio was also found to be an important parameter to enhance the effectiveness of the catalyst as it exhibits a remarkable increase in phenol conversion from 20.6% to 98.4% as the support changes from only silica MCM-41 to Al-MCM-41. A plausible mechanism for the hydrogenation of phenol to cyclohexanone over the palladium catalyst has been proposed. The proposition is validated by transition state calculations using density functional theory (DFT), which reveal that cyclohexanone is a favorable product and stabilized by <19,kcal,mol,1 over cyclohexanol in scCO2 medium. Under similar reaction conditions, phenol hydrogenation was also carried out with rhodium, supported on Al-MCM-41. In contrast to the palladium catalyst, a mixture of cyclohexanone (57.8%) and cyclohexanol (42.2%) was formed. Detailed characterization by X-ray diffraction and transmission electron microscopy confirmed the presence of metal nanoparticles (palladium and rhodium) between 10,20,nm. Both the catalysts exhibit strikingly different product distributions in solventless conditions compared to scCO2. This method can also be successfully applied to the other hydroxylated aromatic compounds. [source] The influence of organic solvent and ionic liquids on the selective formation of 2-(2-ethylhexyl)-3-phenyl-1,2-oxaziridine mediated by lipases,JOURNAL OF PHYSICAL ORGANIC CHEMISTRY, Issue 10 2010Thiago Bergler Bitencourt Abstract This paper describes the influence of the addition of ionic liquids (ILs) based on [BMIm][X], where [X],=,SCN, Cl, BF4, and PF6, on the chemo-enzymatic oxidation of N -benzyliden-2-ethylhexylamine to form the corresponding E- and Z -isomers of oxaziridines mediated by Pseudomonas sp. (PSL) and Candida antarctica (CAL-B) lipases in various organic solvents at room temperature (25,°C) with urea hydrogen peroxide (UHP). The results showed that the use of different organic solvents in the presence of ILs, critically changes the conversions (5,99%) and the isomeric ratio E:Z, (50,100% E -isomer) of the products formed. Copyright © 2010 John Wiley & Sons, Ltd. [source] Bifunctional Heterogeneous Catalysis of Silica,Alumina-Supported Tertiary Amines with Controlled Acid,Base Interactions for Efficient 1,4-Addition ReactionsCHEMISTRY - A EUROPEAN JOURNAL, Issue 41 2009Ken Motokura Dr. Abstract We report the first tunable bifunctional surface of silica,alumina-supported tertiary amines (SA,NEt2) active for catalytic 1,4-addition reactions of nitroalkanes and thiols to electron-deficient alkenes. The 1,4-addition reaction of nitroalkanes to electron-deficient alkenes is one of the most useful carbon,carbon bond-forming reactions and applicable toward a wide range of organic syntheses. The reaction between nitroethane and methyl vinyl ketone scarcely proceeded with either SA or homogeneous amines, and a mixture of SA and amines showed very low catalytic activity. In addition, undesirable side reactions occurred in the case of a strong base like sodium ethoxide employed as a catalytic reagent. Only the present SA-supported amine (SA,NEt2) catalyst enabled selective formation of a double-alkylated product without promotions of side reactions such as an intramolecular cyclization reaction. The heterogeneous SA,NEt2 catalyst was easily recovered from the reaction mixture by simple filtration and reusable with retention of its catalytic activity and selectivity. Furthermore, the SA,NEt2 catalyst system was applicable to the addition reaction of other nitroalkanes and thiols to various electron-deficient alkenes. The solid-state magic-angle spinning (MAS) NMR spectroscopic analyses, including variable-contact-time 13C cross-polarization (CP)/MAS NMR spectroscopy, revealed that acid,base interactions between surface acid sites and immobilized amines can be controlled by pretreatment of SA at different temperatures. The catalytic activities for these addition reactions were strongly affected by the surface acid,base interactions. [source] Regio- and Diastereoselective Synthesis of Bis- and Tetrakisadducts of C70 by Directed Remote Functionalization Using Tröger Base TethersCHEMISTRY - A EUROPEAN JOURNAL, Issue 13 2006Wallace W. H. Wong Dr. Abstract Double Bingel cyclopropanation of C70 with bismalonates featuring Tröger base derivatives as chiral spacers afforded bisadducts with almost perfect regio- and stereoselectivity. The excellent directing property of these rigidly folded spacers in the remote functionalization of the higher fullerene was further highlighted by the selective formation of a product with a novel bisaddition pattern involving the C(7)C(22) and C(33)C(34) bonds of C70. Enantiomerically pure bisadducts of C70 were prepared by highly diastereoselective transformations of bismalonates incorporating optically pure Tröger base tethers. The absolute configuration of these bisadducts was established by comparison of circular dichroism (CD) spectra with data reported in the literature. For the first time, optically active tetrakisadducts of a fullerene were prepared by two sequential chiral-spacer-controlled remote functionalizations. [source] Generation of Cationic [Zr-{tert -Butyl Enolate}] Reactive Species: Methyl Abstraction versus Hydride AbstractionCHEMISTRY - A EUROPEAN JOURNAL, Issue 17 2004Bing Lian Dr. Abstract Treatment of the neutral methyl,Zr,enolate [Cp2Zr(Me){O(tBuO)CCMe2}] (1) with one equivalent of B(C6F5)3 or [HNMe2Ph][B(C6F5)4] as a methyl abstractor in THF at 0,°C leads to the selective formation of the free ion pair complex [Cp2Zr(THF){O(tBuO)CCMe2}]+,[anion], (2) (anion=MeB(C6F5)3,, B(C6F5)4,), which is relevant to the controlled polymerization of methacrylates. Cation 2 rapidly decomposes at 20,°C in THF with release of one equivalent of isobutene to form the cationic Zr,carboxylate species [Cp2Zr(THF)(O2CiPr)]+ (3), through a proposed intramolecular proton transfer process from the tert -butoxy group to the enolate. The reaction of 1 with one equivalent of B(C6F5)3 or [HNMe2Ph][B(C6F5)4] in CH2Cl2 leads to the direct, rapid formation of the dimeric ,-isobutyrato,Zr dicationic species [{Cp2Zr[,-(O2CiPr)]}2]2+ (4), which gives 3 upon dissolution in THF. Contrastingly, when [Ph3C][B(C6F5)4] is used to generate the cationic Zr,enolate species from 1 in CD2Cl2, a 15:85 mixture of dicationic complexes 4 and [{Cp2Zr[, -(O2CC(Me)CH2)]}2]2+[B(C6F5)4] (5 -[B(C6F5)4]2) is obtained quantitatively. The formation of 5 is proposed to arise from initial hydride abstraction from a methyl enolate group by Ph3C+, as supported by the parallel production of Ph3CH, and subsequent elimination of methane and isobutene. In addition to standard spectroscopic and analytical characterizations for the isolated complexes 2,5, complexes 4 and 5 have also been structurally characterized by X-ray diffraction studies. [source] | ||||||||||