共查询到20条相似文献,搜索用时 15 毫秒
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Prof. Dr. Christer B. Aakeröy Dr. Michele Baldrighi Dr. John Desper Prof. Dr. Pierangelo Metrangolo Prof. Dr. Giuseppe Resnati 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(48):16240-16247
Through a combination of structural chemistry, vibrational spectroscopy, and theory, we have systematically examined the relative structure‐directing importance of a series of ditopic halogen‐bond (XB) donors. The molecular electrostatic potential surfaces of six XB donors were evaluated, which allowed for a charge‐based ranking. Each molecule was then co‐crystallized with 21 XB acceptors and the results have made it possible to map out the supramolecular landscape describing the competition between I/Br–ethynyl donors, perfluorinated I/Br donors, and I/Br–phenyl based donors. The results offer practical guidelines for synthetic crystal engineering driven by robust and directional halogen bonds. 相似文献
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An amine mono(phenolate) ligand bearing two side-arm donors led to octahedral trialkoxo and trialkyl group IV metal complexes, in which one of the donors was unbound, and to exceptionally stable cationic complexes in which the two side-arm donors were tightly bound. 相似文献
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Maria Carmela Sacchi Fabrizio Forlini Incoronata Tritto Paolo Locatelli 《Macromolecular Symposia》1995,89(1):91-100
The results of a study on a new generation of MgCl2 supported Ziegler-Natta catalysts that contain dialkyl propane diethers as internal donors and produce highly stereospecific polypropene even without any external donor are presented. The results concerning three different catalysts containing 2,2-diisobutyl-1,3-dimethoxy propane (DIBDMP), 2,2-dicyclopentyl-1,3-dimethoxy propane (DCPDMP) and 2-ethyl,2-butyl-1,3-dimethoxy propane (EBDMP) as internal donors are compared. The same donors have also been studied by using them as external donors with a catalyst contaning diisobutyl phthalate as internal donor. The present results, along with previously obtained findings on traditional supported Ziegler-Natta catalysts, permit a general comprehension of the role of internal and external donors. 相似文献
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N'-Glycopyranosylsulfonohydrazides are introduced as glycosyl donors for protecting group free synthesis of O-glycosides, glycosyl azides, and oxazolines. Mono- and disaccharides containing a reducing terminal N-acetylglucosamine residue were condensed with p-toluenesulfonylhydrazide to give the desired beta- d-pyranose donors. These donors can be activated with NBS and then glycosidated with the desired alcohol or transformed to the oxazoline or glycosyl azide. 相似文献
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Grayson EJ Ward SJ Hall AL Rendle PM Gamblin DP Batsanov AS Davis BG 《The Journal of organic chemistry》2005,70(24):9740-9754
[reaction: see text] Glycosyl disulfides have been shown for the first time to be effective glycosyl donors. Glucosylation and galactosylation of a panel of representative alcohol acceptors allowed the formation of 28 simple glycosides, disaccharides, and glycoamino acids in yields of up to 90%. As well as providing a novel class of effective glycosyl donors, the ability to easily alter the nature of the aglycon and the ability to differently activate donors that differ only in their aglycon simply through altering conditions lends glycosyl disulfide donors to their use in latent-active reactivity tuning strategies. 相似文献
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The role of electron donors in propylene polymerization using Ziegler-Natta model catalyst [TiCl2CH3]+ has been investigated using density functional calculations at B3LYP/6-31G* level. Methyl benzoate (MBz) and para-methoxy methyl benzoate (p-OMe-MBz) are the electron donors considered in this study. We have found two major roles of these electron donors that match well with the corresponding experimental results. First, for both the catalysts having different electron donors, the propylene insertion in Ti-CH3 bond in syn-fashion rather than anti-fashion has lower activation barriers (Eact). This indicates that the regioselectivity of propylene insertion is maintained in the presence of the electron donors. Secondly, co-ordination of electron donors is found to increase the activation barriers of propylene insertion, which explains the experimentally observed drop in catalytic activity of [TiCl2Me]+ on adding electron donors. 相似文献
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[reaction: see text] A new method for the synthesis of alpha(2 --> 9) oligosialic acids is developed using phosphite sialyl donors that are protected with a C-5 N-trifluoroacetyl (NHTFA) substituent. Compared with conventional donors, these donors gave a higher degree of alpha-anomeric selectivity during glycosidic bond formation and better yields during iterative sialylation in the synthesis of oligosialic acids. 相似文献
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5-Thioglucosylation of a 1,6-anhydro-2-azido-2-deoxy-β-d-glucopyranose derivative was carried out with various 1,5-dithioglucosyl donors. The use of per-O-acetyl donors resulted in poor yields of an α-disaccharide. On the other hand, per-O-benzyl donors selectively gave an α-disaccharide in good to excellent yields regardless of the anomeric configuration of the donors. To study the relevance of the glycosylation results to the pre-equilibrium of exo- versus endocyclic sulfide activation, the relative nucleophilicities of exo- and endocyclic sulfides were estimated from the regioselectivities in the electrophilic oxidation of the per-O-benzyl donors with m-chloroperbenzoic acid. The results obeyed stereoelectronic effects and the endocyclic sulfides were more nucleophilic than the exocyclic sulfides for both anomers of per-O-benzyl-1,5-dithioglucosyl donors, the relative nucleophilicities of the endocyclic over exocyclic sulfides being 67% and 100%, respectively, for the α- and β-anomers. The results of the glycosidation and oxidation suggest that the glycosidation proceeded through an exocyclic cleavage mechanism despite the preferential endocyclic activation of 1,5-dithioglucosides. 相似文献
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B. Strehlitz B. Gründig K. -D. Vorlop P. Bartholmes H. Kotte U. Stottmeister 《Fresenius' Journal of Analytical Chemistry》1994,349(8-9):676-678
Various nitrate and nitrite reductases are capable of accepting electrons from artificial donors. Combining these redox active donors with an amperometric redox electrode which is covered with an immobilized layer of such a nitrate or nitrite reductase, new enzyme sensors can be created for the detection of nitrate or nitrite, respectively. A range of suitable electron donors for nitrate reductases and nitrite reductase from different sources have been selected and characterized by electrochemical methods. 相似文献
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Kwang Bo Chung Masao Tomoi 《Journal of polymer science. Part A, Polymer chemistry》1992,30(6):1089-1097
Crown ethers bound to microporous polystyrene resins by oxyethylene spacers were prepared by the reaction of monoazacrown ethers with 2-tosyloxyethoxymethylated or 2-(2-tosyloxyethoxy)ethoxymethylated polystyrene resins crosslinked with 2 mol % of divinylbenzene. The activity of the immobilized lariat crowns for halogen exchange reactions under triphase conditions has been studied as a function of catalyst structure, loading, substrate structure, reagent structure, and solvent. The lariat catalysts with extra oxygen donors in the spacer chain exhibited higher activity than the corresponding immobilized catalysts without the donors in the spacer. The increased activity of the catalyst containing 15-crown-5 unit and two extra donors for the reaction of 1-bromooctane with KI was concluded to result from the enhanced complexation with the K+ ion, induced by the cooperative coordination of the crown unit donors and the donors in the spacer chain. The recovered catalysts could be re-used without decrease in activity. 相似文献
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[reaction: see text] Three pairs of primary-secondary diol acceptors have been exposed to armed, disarmed, and n-pentenyl ortho ester glycosyl donors in glycosidation reactions. It is shown that the regioselectivity of those glycosylations is greatly influenced by the armed, disarmed, or ortho ester nature of the glycosyl donors. The selectivities observed have been used to devise efficient in situ three-component glycosylations involving two donors and one acceptor. 相似文献
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Simon Rohrbach Dr. Rushabh S. Shah Prof. Dr. Tell Tuttle Prof. Dr. John A. Murphy 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2019,131(33):11576-11580
Neutral organic super electron donors (SEDs) display impressive reducing power but, until now, it has not been possible to use them catalytically in radical chain reactions. This is because, following electron transfer, these donors form persistent radical cations that trap substrate‐derived radicals. This paper unlocks a conceptually new approach to super electron donors that overcomes this issue, leading to the first catalytic neutral organic super electron donor. 相似文献
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ZHAO Shu-min GU Hai-ning ZHOU Qi-zhong . Key Laboratory for Molecular Design Nutrition Engineering of Ningbo Ningbo Institute of Technology of Zhejiang University Ningbo P. R. China 《高等学校化学研究》2009,25(3)
The authors synthesized the electron-rich 1,5-dioxonaphthyl group incorporated foldamers,and linear donors and electron-deficient pyromellitic diimide incorporated foldamers,which were investigated in organic solvents. There is an evident charge transfer process from the donors to the electron-deficient foldamers,due to the donor-acceptor interaction of the heteroduplexes formed from the donors and the electron-deficient foldamers in chloroform,observed by using the ultraviolet(UV) visible method. The charg... 相似文献
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Oakes DC Kimberley BS Gibson VC Jones DJ White AJ Williams DJ 《Chemical communications (Cambridge, England)》2004,(19):2174-2175
Group 4 metal complexes containing phenoxy-amide ligands bearing soft pendant donors are shown to give more highly active ethylene polymerisation catalysts than counterparts containing hard donors or systems without a pendant donor. 相似文献
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Reported herein is a new protocol for glycosidation of alkyl and aryl thioglycosides in the presence of copper(II) bromide. While the activation with CuBr2 alone was proven suitable for reactive glycosyl donors, the activation of less reactive donors was more efficient in the presence of triflic acid as an additive. A variety of thioglycoside donors in reactions with different glycosyl acceptors were investigated to determine the initial scope of this reaction. 相似文献
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Multiple Multidentate Halogen Bonding in Solution,in the Solid State,and in the (Calculated) Gas Phase
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Stefan H. Jungbauer Severin Schindler Dr. Eberhardt Herdtweck Prof. Dr. Sandro Keller Prof. Dr. Stefan M. Huber 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(39):13625-13636
The binding properties of neutral halogen‐bond donors (XB donors) bearing two multidentate Lewis acidic motifs toward halides were investigated. Employing polyfluorinated and polyiodinated terphenyl and quaterphenyl derivatives as anion receptors, we obtained X‐ray crystallographic data of the adducts of three structurally related XB donors with tetraalkylammonium chloride, bromide, and iodide. The stability of these XB complexes in solution was determined by isothermal titration calorimetry (ITC), and the results were compared to X‐ray analyses as well as to calculated binding patterns in the gas phase. Density functional theory (DFT) calculations on the gas‐phase complexes indicated that the experimentally observed distortion of the XB donors during multiple multidentate binding can be reproduced in 1:1 complexes with halides, whereas adducts with two halides show a symmetric binding pattern in the gas phase that is markedly different from the solid state structures. Overall, this study demonstrates the limitations in the transferability of binding data between solid state, solution, and gas phase in the study of complex multidentate XB donors. 相似文献
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S. K. Patil V. V. Ramakrishna 《Journal of Radioanalytical and Nuclear Chemistry》1979,54(1-2):123-135
Formation of adducts between U(TTA)4 and several neutral donors was studied by spectrophotometry and it was shown that each of the neutral donors forms only 1∶1 adduct with U(TTA)4. The adduct formation constants with some neutral donors were determined for benzene and chloroform media. As these adducts are involved in the synergistic extraction of U(IV) from aqueous media by mixtures of HTTA and neutral donors dissolved in organic solvents, the extraction equilibrium constants were estimated, The adduct formation was found to result in an increase of the co-ordination number of U(IV) from 8 in U(TTA)4 to 9 in the adducts it forms with the neutral donors. Similar absorption spectral studies with U(DBM)4 revealed that it forms much weaker adducts than the corresponding ones with U(TTA)4. 相似文献
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[reaction: see text] The new class of glycosyl donors with a methyl 3,5-dinitrosalicylate (DISAL) anomeric leaving group has proved efficient for glycosylation under strictly neutral, mildly basic, or mildly acidic conditions. Here, we report the synthesis of novel DISAL disaccharide glycosyl donors prepared by easy nucleophilic aromatic substitution. These DISAL donors proved efficient in the synthesis of a starch-related hexasaccharide under very mild conditions. Glycosylations proceeded with alpha-selectivity and were compatible with Trt protecting groups. 相似文献