Acceder

Bibliografías temáticas / Carbeni / Artículos de revistas

Siga este enlace para ver otros tipos de publicaciones sobre el tema: Carbeni.

Artículos de revistas sobre el tema "Carbeni"

Autor: Grafiati

Publicado: 10 de marzo de 2023

Crea una cita precisa en los estilos APA, MLA, Chicago, Harvard y otros

Elija tipo de fuente:

Consulte los 50 mejores artículos de revistas para su investigación sobre el tema "Carbeni".

Junto a cada fuente en la lista de referencias hay un botón "Agregar a la bibliografía". Pulsa este botón, y generaremos automáticamente la referencia bibliográfica para la obra elegida en el estilo de cita que necesites: APA, MLA, Harvard, Vancouver, Chicago, etc.

También puede descargar el texto completo de la publicación académica en formato pdf y leer en línea su resumen siempre que esté disponible en los metadatos.

Explore artículos de revistas sobre una amplia variedad de disciplinas y organice su bibliografía correctamente.

1

Poirel, Laurent, Michele Guibert, Samuel Bellais, Thierry Naas y Patrice Nordmann. "Integron- and Carbenicillinase-Mediated Reduced Susceptibility to Amoxicillin-Clavulanic Acid in Isolates of Multidrug-ResistantSalmonella enterica Serotype Typhimurium DT104 from French Patients". Antimicrobial Agents and Chemotherapy 43, n.º 5 (1 de mayo de 1999): 1098–104. http://dx.doi.org/10.1128/aac.43.5.1098.

Texto completo

Resumen

ABSTRACT Fifty-seven Salmonella enterica serotype Typhimurium (S. typhimurium) isolates were collected from human patients in two French hospitals, Hôpital Antoine Béclère (Clamart, France) and Hôpital Bicêtre (Le Kremlin-Bicêtre, France), between 1996 and 1997. Thirty of them (52 percent) were resistant to amino-, carbeni-, and ureidopenicillins, had reduced susceptibility to amoxicillin-clavulanic acid, were susceptible to cephalothin, and were resistant to sulfonamides, streptomycin, chloramphenicol, and tetracyclines. All these strains possessed a bla PSE-1-like gene and were of phage type DT104. Ten of them were studied in more detail, which revealed that bla PSE-1 is located on the variable region of a class 1 integron. This integron was found to be chromosomally located, as was another class 1 integron containingaadA2, a streptomycin-spectinomycin resistance gene. The reduced susceptibility to amoxicillin-clavulanic acid (and to ticarcillin-clavulanic acid) may result from the high level of hydrolysis of the β-lactam rather than to the clavulanic acid resistance properties of PSE-1 in these clonally related S. typhimurium isolates.

Los estilos APA, Harvard, Vancouver, ISO, etc.

2

KOROTKIKH, Nikolai, Gennady RAYENKO, Vagiz SABEROV, Vasyl YENYA, Nataliya GLINYANAYA, Alexandr AVKSENTIEV y Oles SHVAIKA. "PHILICITY OF CARBENES. A NEW VIEW". Proceedings of the Shevchenko Scientific Society. Series Сhemical Sciences 2020, n.º 60 (25 de febrero de 2020): 85–106. http://dx.doi.org/10.37827/ntsh.chem.2020.60.085.

Texto completo

Resumen

The electronic properties of carbenes including thermodynamic parameters such as new electronic philicity indices Ie, Ph, and for comparizon chemical hardnesses η, proton affinities (РA) calculated by DFT method (B3LYP5/6-31G*/RHF for definition of electronic indices and B3LYP5/3-21G/RHF, B3LYP5/3-21G/UHF for definition of chemical hard¬nesses) have been discussed in the paper. With their help, the estimation of philicities, electron-donating and electron-withdrawing abilities of a wide range of carbenes of both nucleophilic and electrophilic type was carried out. It was established that the philicities of carbenes according to electronic indices Іе, Ph depend on the carbenic structure (the backbone of the molecule and steric effects of substituents) and also on the reagent structure, particularly its steric effect. For typical nucleophilic carbenes, the Ph is in the range of 1–3,0, for neutral carbenes 1–1,5, IeH 8,5–22,2 eV, for neutral carbenes IeH 8,5–10,5, for typical electrophilic – in the intervals of PhH –0,3–0,5, IeH –3,4–3,4 eV. The intermediate values (Ph 0,5–1,0, IeH 3,4–8,5 eV) are characteristic for typical ambiphilic carbenes. In the evaluation of electron-donating and electron-withdrawing properties, the values of ED and EA should be taken into account (maximal EDH values were found for neutral carbene 20 (13,8 eV) and for superbasic anionic carbenes (for 22 18,4 eV)). The highest electron acceptability EAH was found for cationic carbene 29 (11,8 eV). In the reactions with carbon ions, the values of the IeH, PhH indices decrease significantly, and the electron acceptability increases. Increasing the steric effects leads to «inversion» of philicities for nucleophilic carbenes (Ph up to 0,1), and the properties of electrophilic carbenes become even more pronounced (Ph up to –2,7). The found dependences of the electronic properties of carbenes allow regulating the structure of carbenes to achieve certain characteristics, which together with stability factors can be used in the design of structures for synthesis and practical application.

Los estilos APA, Harvard, Vancouver, ISO, etc.

3

Frański, Rafał, Błażej Gierczyk, Grzegorz Schroeder, Stefan Pieper, Andreas Springer y Michael Linscheid. "Electrospray ionization mass spectrometric study of mercury complexes of N-heterocyclic carbenes derived from 1,2,4-triazolium salt precursors". Open Chemistry 5, n.º 1 (1 de marzo de 2007): 316–29. http://dx.doi.org/10.2478/s11532-006-0050-0.

Texto completo

Resumen

AbstractBy mixing 1,2,4-triazolium salts (precursors of N-heterocyclic carbenes 1–6) with mercury acetate, a number of complexes have been obtained under electrospray ionization condition. Carbenes 1 and 2 contain one carbene center; therefore, they are able to bond only one mercury cation. Carbenes 3–5 contain two carbene centers; therefore, they can bond two mercury cations. Mercury complexes of 1–5 always contain an acetate anion attached to a mercury cation. Carbene 6 also contains two carbene centers; however, its structure allows formation of a complex containing mercury bonded simultaneously to both centers, therefore, the complex that does not contain an acetate anion. The MS/MS spectra taken for complexes of carbenes 1–5 have shown formation of a cation corresponding to N1 substituent (adamantyl or benzyl), and those of complexes of carbenes 3–5 (doubly charged ions) have also shown the respective complementary partner ions. Mercury complex of 2 has yielded some other interesting fragmentation pathways, e.g. a loss of the HHgOOCCH3 molecule. The fragmentation pathway of the mercury complexes of 6 was found to be complicated.

Los estilos APA, Harvard, Vancouver, ISO, etc.

4

Andrada, Diego M., Nicole Holzmann, Thomas Hamadi y Gernot Frenking. "Direct estimate of the internal π-donation to the carbene centre within N-heterocyclic carbenes and related molecules". Beilstein Journal of Organic Chemistry 11 (24 de diciembre de 2015): 2727–36. http://dx.doi.org/10.3762/bjoc.11.294.

Texto completo

Resumen

Fifteen cyclic and acylic carbenes have been calculated with density functional theory at the BP86/def2-TZVPP level. The strength of the internal X→p(π) π-donation of heteroatoms and carbon which are bonded to the C(II) atom is estimated with the help of NBO calculations and with an energy decomposition analysis. The investigated molecules include N-heterocyclic carbenes (NHCs), the cyclic alkyl(amino)carbene (cAAC), mesoionic carbenes and ylide-stabilized carbenes. The bonding analysis suggests that the carbene centre in cAAC and in diamidocarbene have the weakest X→p(π) π-donation while mesoionic carbenes possess the strongest π-donation.

Los estilos APA, Harvard, Vancouver, ISO, etc.

5

Cui, Peng, Melissa R. Hoffbauer, Mariya Vyushkova y Vlad M. Iluc. "Heterobimetallic Pd–K carbene complexes via one-electron reductions of palladium radical carbenes". Chemical Science 7, n.º 7 (2016): 4444–52. http://dx.doi.org/10.1039/c6sc00948d.

Texto completo

Resumen

Unprecedented sequential substitution/reduction synthetic strategy on the Pd radical carbenes afforded heterobimetallic Pd–K carbene complexes, which features novel Pd–C_carbene–K structural moieties.

Los estilos APA, Harvard, Vancouver, ISO, etc.

6

Chen, Kai, Xiongyi Huang, Shuo-Qing Zhang, Andrew Zhou, S. B. Jennifer Kan, Xin Hong y Frances Arnold. "Engineered Cytochrome c-Catalyzed Lactone-Carbene B–H Insertion". Synlett 30, n.º 04 (14 de enero de 2019): 378–82. http://dx.doi.org/10.1055/s-0037-1611662.

Texto completo

Resumen

Previous work has demonstrated that variants of a heme protein, Rhodothermus marinus cytochrome c (Rma cyt c), catalyze abiological carbene boron–hydrogen (B–H) bond insertion with high efficiency and selectivity. Here we investigated this carbon–boron bond-forming chemistry with cyclic, lactone-based carbenes. Using directed evolution, we obtained a Rma cyt c variant BORLAC that shows high selectivity and efficiency for B–H insertion of 5- and 6-membered lactone carbenes (up to 24,500 total turnovers and 97.1:2.9 enantiomeric ratio). The enzyme shows low activity with a 7-membered lactone carbene. Computational studies revealed a highly twisted geometry of the 7-membered lactone carbene intermediate relative to 5- and 6-membered ones. Directed evolution of cytochrome c together with computational characterization of key iron-carbene intermediates has allowed us to expand the scope of enzymatic carbene B–H insertion to produce new lactone-based organoborons.

Los estilos APA, Harvard, Vancouver, ISO, etc.

7

García, Lucía, Khalidah H. M. Al Furaiji, David J. D. Wilson, Jason L. Dutton, Michael S. Hill y Mary F. Mahon. "Ring expansion of a ring expanded carbene". Dalton Transactions 46, n.º 36 (2017): 12015–18. http://dx.doi.org/10.1039/c7dt03046k.

Texto completo

Los estilos APA, Harvard, Vancouver, ISO, etc.

8

Hollóczki, Oldamur. "Unveiling the peculiar hydrogen bonding behavior of solvated N-heterocyclic carbenes". Physical Chemistry Chemical Physics 18, n.º 1 (2016): 126–40. http://dx.doi.org/10.1039/c5cp05369b.

Texto completo

Resumen

After fitting a molecular mechanical force field for imidazol-2-ylidenes, MD simulations revealed carbene–carbene and three-center hydrogen bonds of carbenes. The practical importance of these structures is also highlighted.

Los estilos APA, Harvard, Vancouver, ISO, etc.

9

Dong, Zhaowen, Cristian Pezzato, Andrzej Sienkiewicz, Rosario Scopelliti, Farzaneh Fadaei-Tirani y Kay Severin. "SET processes in Lewis acid–base reactions: the tritylation of N-heterocyclic carbenes". Chemical Science 11, n.º 29 (2020): 7615–18. http://dx.doi.org/10.1039/d0sc01278e.

Texto completo

Los estilos APA, Harvard, Vancouver, ISO, etc.

10

Pezacki, John Paul. "Normal acid/base behaviour in proton transfer reactions to alkoxy substituted carbenes: estimates for intrinsic barriers to reaction and pKa values". Canadian Journal of Chemistry 77, n.º 7 (1 de julio de 1999): 1230–40. http://dx.doi.org/10.1139/v99-087.

Texto completo

Resumen

Theoretical Eigen curves can be drawn through Brønsted data for dimethoxycarbene (1), phenyltrimethyl-siloxycarbene (3a), 4-methylphenyl(trimethylsiloxy)carbene (3b), 4-methoxyphenyl(trimethylsiloxy)carbene (3c), and β-naphthyl(trimethylsiloxy)carbene (3d). The Brønsted plots for these data are clearly curved with α values near 1 when proton transfer is thermodynamically unfavourable and α values near 0 when proton transfer is thermodynamically favourable, suggesting that these carbenes behave as "normal" Brønsted bases. Estimates of the intrinsic barriers (ΔG0‡) for proton transfer reactions and of the pKa values for the conjugate acids of the carbenes, extracted from these theoretical curves, have been made. The magnitudes of the intrinsic barriers (ΔG0‡) for these proton transfer reactions determined by Eigen and Marcus theories are all 1-5 kcal mol-1, suggesting that these reactions are intrinsically fast. Small intrinsic barriers also imply "normal" acid/base behaviour. Extrapolated pKa values are also the first estimates for the pKa values of the conjugate acids of carbenes 1 and 3a-3d. Key words: carbenes, proton transfer reactions, carbocations, Marcus theory, Brønsted plots.

Los estilos APA, Harvard, Vancouver, ISO, etc.

11

Mehta, Meera, Timothy C. Johnstone, Jolie Lam, Bidraha Bagh, André Hermannsdorfer, Matthias Driess y Douglas W. Stephan. "Synthesis and oxidation of phosphine cations". Dalton Trans. 46, n.º 41 (2017): 14149–57. http://dx.doi.org/10.1039/c7dt03175k.

Texto completo

Resumen

Cationic phosphines of the form [(L)PPh₂]⁺ are prepared from Ph₂PCl and carbenes (L), including a chiral bis(oxazoline)-based carbene, a cyclic(alkyl)(amino) carbene, and a 1,2,3-triazolium-derived carbene. A related dication was prepared from PhPCl₂ and a bis-carbene. The monocations, but not the dication, can be oxidized with XeF₂.

Los estilos APA, Harvard, Vancouver, ISO, etc.

12

Šumanovac, Tatjana, Marija Alešković, Marina Šekutor, Marija Matković, Thibaut Baron, Kata Mlinarić-Majerski, Cornelia Bohne y Nikola Basarić. "Photoelimination of nitrogen from adamantane and pentacycloundecane (PCU) diazirines: a spectroscopic study and supramolecular control". Photochemical & Photobiological Sciences 18, n.º 7 (2019): 1806–22. http://dx.doi.org/10.1039/c9pp00124g.

Texto completo

Resumen

Nitrogen photoelimination delivers carbenes from diazirines. Protonation of singlet carbenes was detected based on the PCU skeleton rearrangement. Complexation of diazirines changes the relative singlet/triplet ratio of carbene products.

Los estilos APA, Harvard, Vancouver, ISO, etc.

13

Er, Hui-Teng, David L. Pole y John Warkentin. "(Alkylthio)- and (phenylthio)methoxycarbenes from oxadiazolines". Canadian Journal of Chemistry 74, n.º 8 (1 de agosto de 1996): 1480–89. http://dx.doi.org/10.1139/v96-165.

Texto completo

Resumen

Four 2-methoxy-5,5-dimethyl-Δ3-1,3,4-oxadiazolines bearing an alkylthio or arylthio group at C2 were prepared. The oxadiazolines undergo thermolysis at 60–80 °C in solution to afford the corresponding oxythiocarbene intermediates. In the absence of carbene traps, dimers of the carbenes were formed. The carbenes were trapped with ethyl crotonate, with dichloromaleic anhydride, with dimethyl acetylenedicarboxylate, and with phenyl isocyanate. Phenyl isocyanate traps methoxy(methylthio)carbene to form two types of adducts, both fundamentally different from the product obtained from reaction of dimethoxycarbene with phenyl isocyanate. All of the adducts have structures consistent with nucleophilic behaviour of the carbenes. Key words: oxythiocarbene, oxadiazoline, thermolysis, nucleophilic.

Los estilos APA, Harvard, Vancouver, ISO, etc.

14

Saá, Carlos, Damián Padín y Jesús A. Varela. "Recent Advances in Ruthenium-Catalyzed Carbene/Alkyne Metathesis (CAM) Transformations". Synlett 31, n.º 12 (31 de marzo de 2020): 1147–57. http://dx.doi.org/10.1055/s-0039-1690861.

Texto completo

Resumen

Carbene intermediates have shown versatile applications in modern synthetic chemistry. Catalytic ruthenium carbene/alkyne metathesis (CAM) with readily available substrates renders an efficient procedure for the in situ generation of ruthenium vinyl carbene intermediates. Here, recent advances in synthetic applications of ruthenium-catalyzed carbene/alkyne metathesis (CAM) are highlighted.1 Introduction2 Ruthenium Vinyl Carbenes through Carbene/Alkyne Metathesis (CAM)3 Nonpolar Transformations of Ruthenium Vinyl Carbenes4 Polar Transformations of Ruthenium Vinyl Carbenes4.1 Intramolecular Ruthenium-Catalyzed [1,5]- and [1,6]-Hydride Transfer/Cyclization4.2 Heterocyclizations of Alkynals and Alkynones4.3 Heterocyclizations of ortho-(Alkynyloxy)benzylamines5 DFT Studies on the Stereoselectivity of the CAM Reaction6 Conclusions

Los estilos APA, Harvard, Vancouver, ISO, etc.

15

Jawiczuk, Magdalena, Angelika Janaszkiewicz y Bartosz Trzaskowski. "The influence of the cationic carbenes on the initiation kinetics of ruthenium-based metathesis catalysts; a DFT study". Beilstein Journal of Organic Chemistry 14 (20 de noviembre de 2018): 2872–80. http://dx.doi.org/10.3762/bjoc.14.266.

Texto completo

Resumen

Cationic carbenes are a relatively new and rare group of ancillary ligands, which have shown their superior activity in a number of challenging catalytic reactions. In ruthenium-based metathesis catalysis they are often used as ammonium tags, to provide water-soluble, environment-friendly catalysts. In this work we performed computational studies on three cationic carbenes with the formal positive charge located at different distances from the carbene carbon. We show that the predicted initiation rates of Grubbs, indenylidene, and Hoveyda–Grubbs-like complexes incorporating these carbenes show little variance and are similar to initiation rates of standard Grubbs, indenylidene, and Hoveyda–Grubbs catalysts. In all investigated cases the partial charge of the carbene carbon atom is similar, resulting in comparable Ccarbene–Ru bond strengths and Ru–P/O dissociation Gibbs free energies.

Los estilos APA, Harvard, Vancouver, ISO, etc.

16

Muchall, Heidi M., Nick H. Werstiuk y Biswajit Choudhury. "Article". Canadian Journal of Chemistry 76, n.º 2 (1 de febrero de 1998): 221–27. http://dx.doi.org/10.1139/v98-002.

Texto completo

Resumen

Photoelectron (PE) spectra of two stable carbenes 7 and 8 have been recorded and the spectra have been interpreted with the aid of eigenvalues and eigenvectors taken from Becke3LYP calculations. For the carbene series 6-8, the lone pair on the carbene carbon atom is the HOMO. The first adiabatic ionization potential (IP) of eight electronically quite different carbenes has been calculated using semiempirical PM3 and ab initio HF, Becke3LYP, and Becke3PW91 methods (3-21G(*) and 6-31+G* basis sets) as well as the CBS-4 model. For the first vertical IP, the HAM/3, Becke3LYP, and Becke3PW91 methods have been employed. CBS-4 and DFT calculations show excellent agreement with experimental values. Considering both accuracy and speed, the method of choice for the prediction of first ionization potentials of carbenes seems to be Becke3LYP/6-31+G*//Becke3LYP/3-21G(*).Key words: carbenes, electronic structure, first ionization potential, photoelectron spectroscopy, quantum chemical calculations.

Los estilos APA, Harvard, Vancouver, ISO, etc.

17

Blanch, Rodney J. y Curt Wentrup. "Trifluoromethylphenylcarbenes. Carbene-Carbene Interconversion on the Singlet Energy Surface and Rearrangement to Trifluorobenzocyclobutene, Trifluorostyrene, and Trifluoromethylfulvenallenes". Australian Journal of Chemistry 68, n.º 1 (2015): 36. http://dx.doi.org/10.1071/ch14097.

Texto completo

Resumen

The four isomeric α-, ortho-, meta-, and para-trifluoromethylphenylcarbenes were generated by photolysis of the corresponding 3-phenyl-3-trifluoromethyldiazirene 1 or the four isomeric trifluoromethylphenyldiazomethanes 2 and 4–6. The four corresponding triplet trifluoromethylphenylcarbenes 3 and 7–9 were observed by electron spin resonance (ESR) spectroscopy in Ar matrices at 14 K. The α- and ortho-carbenes 3 and 7 and the ortho- and para-carbenes 7 and 9 interconvert partially when generated by short-wavelength photolysis (350 nm) before intersystem crossing to the triplet states. The triplet states do not undergo further Carbene-Carbene interconversion. The interconversions are assumed to take place via the meta-trifluoromethylphenylcarbene 8. When the ortho- and para-carbenes are generated by long-wavelength photolysis (>450 nm), the discrete, non-interconverting triplet carbenes are observed in the ESR spectra. Flash vacuum thermolysis of the diazirene 1 at 500°C afforded a mixture of bis(trifluoromethyl)heptafulvalenes 11, bis(trifluoromethyl)stilbenes 12, and bis(trifluoromethyl)anthracenes 13, and the presence of their likely precursor(s), trifluoromethylcycloheptatetraene(s), was confirmed by a peak at 1830 cm–1 in the Ar matrix IR spectrum. In addition, at 700°C, four monomeric carbene rearrangement products were isolated and characterised, viz. 1,1,2-trifluorobenzocyclobutene 14, 1′,2′,2′-trifluorostyrene 15, and 1- and 2-trifluoromethylfulvenallenes 16 and 17.

Los estilos APA, Harvard, Vancouver, ISO, etc.

18

Tang, Xiang-Ting, Fan Yang, Ting-Ting Zhang, Yi-Fan Liu, Si-Yu Liu, Tong-Fu Su, Dong-Can Lv y Wen-Bo Shen. "Recent Progress in N-Heterocyclic Carbene Gold-Catalyzed Reactions of Alkynes Involving Oxidation/Amination/Cycloaddition". Catalysts 10, n.º 3 (20 de marzo de 2020): 350. http://dx.doi.org/10.3390/catal10030350.

Texto completo

Resumen

Recent rapid development in homogeneous gold catalysis affords an alternative and particularly thriving strategy for the generation of gold carbenes through gold-catalyzed oxidation/amination/cycloaddition of alkynes, while it avoids the employment of hazardous and potentially explosive diazo compounds as starting materials for carbene generation. In addition to facile and secure operation, gold carbenes generated in this strategy display good chemoselectivity distinct from other metal carbenes produced from the related diazo approach. N-heterocyclic carbene (NHC) gold is a special metal complex that can be used as ancillary ligands, which provides enhanced stability and can also act as an efficient chiral directing group. In this review, we will present an overview of these recent advances in alkyne oxidation/amination/cycloaddition by highlighting their specificity and applicability, aiming to facilitate progress in this very exciting area of research.

Los estilos APA, Harvard, Vancouver, ISO, etc.

19

Tomioka, H. "Triplet carbenes: From fleeting existence to attractive molecular units". Pure and Applied Chemistry 75, n.º 8 (1 de enero de 2003): 1041–47. http://dx.doi.org/10.1351/pac200375081041.

Texto completo

Resumen

Attempts to stabilize the triplet state of carbenes to the extent that they can survive under normal conditions were made, in which triplet carbenes having a half-life of 19 min are realized. A way to use the resulting persistent carbene as a unit to construct photosensitive magnetic materials is also discussed.

Los estilos APA, Harvard, Vancouver, ISO, etc.

20

Zhao, Shixian, Feifei Wu, Yuyu Ma, Wanzhi Chen, Miaochang Liu y Huayue Wu. "Enhancement of N-heterocyclic carbenes on rhodium catalyzed olefination of triazoles". Organic & Biomolecular Chemistry 14, n.º 8 (2016): 2550–55. http://dx.doi.org/10.1039/c5ob02397a.

Texto completo

Los estilos APA, Harvard, Vancouver, ISO, etc.

21

Klys, Arkadiusz, Malgorzata Dawid y John Warkentin. "Synthesis and spectra of aldehyde- and ketone-O-(2,5-dihydro-2-methoxy-5,5-dimethyl-1,3,4-oxadiazol-2-yl)oximes Thermal sources of some methoxy(oximino)carbenes". Canadian Journal of Chemistry 83, n.º 5 (1 de mayo de 2005): 443–48. http://dx.doi.org/10.1139/v05-061.

Texto completo

Resumen

Ten new oxadiazoline sources of methoxy(oximino)carbenes were synthesized by exchanging the acetoxy group of 2-acetoxy-2-methoxy-Δ3-1,3,4-oxadiazoline with an oximino group. The new compounds were characterized by means of spectroscopy and the formation of carbenes upon thermolysis of a few was demonstrated by means of interception with tert-butyl alcohol. The carbenes fragmented to form methoxycarbonyl and iminyl radicals.Key words: 2,2-dioxyoxadiazoline, methoxy(oximino)carbene, oxadiazole, radical pair, rearrangement.

Los estilos APA, Harvard, Vancouver, ISO, etc.

22

Popik, Vladimir V. "The role of molecular geometry in the Wolff rearrangement of α-diazocarbonyl compounds Conformational control or structural constraints?" Canadian Journal of Chemistry 83, n.º 9 (1 de septiembre de 2005): 1382–90. http://dx.doi.org/10.1139/v05-152.

Texto completo

Resumen

Relaxed scans of potential energy surfaces for the loss of nitrogen from four different diazocarbonyl compounds: 3-diazo-2-butanone (1), 2-diazocyclohexanone (2), methyl diazomalonate (3), and diazo Meldrum's acid (4), were conducted at the B3LYP/6-31+G(d,p) level. The geometries of species and transition states involved in the process were optimized at the B3LYP/6-311+G(3df,2p) level, while electronic energies were computed using the MP2(full)/aug-cc-pVTZ method. These calculations suggest that the rigidity of cyclic molecules, rather than the conformational structure of the starting diazocarbonyl compounds, defines the pathway of the dediazotization reaction. In acyclic diazocarbonyl compounds, loss of nitrogen results in the formation of a carbene, which is stabilized by the overlap of the system of carbonyl group and the unshared electron pair of a singlet carbene. On the contrary, in small- to medium-sized cyclic systems, carbonyl carbenes are unable to attain a stabilizing orthogonal conformation. Consequently, cyclic carbonyl carbenes are less stable, and the concerted Wolff rearrangement becomes the predominant process. Transition states for the concerted Wolff rearrangement and for the formation of carbonyl carbenes have a very similar geometry.Key words: diazocarbonyl compounds, Wolff rearrangement, conformation, carbene, ketene.

Los estilos APA, Harvard, Vancouver, ISO, etc.

23

DeAngelo, Joseph D., Sayaka Hatano y Dasan M. Thamattoor. "Generation and Rearrangement of (1-Hydroxycyclopropyl)- and (1-Hydroxycyclobutyl)carbene". Australian Journal of Chemistry 72, n.º 11 (2019): 890. http://dx.doi.org/10.1071/ch19379.

Texto completo

Resumen

Photolysis of exo-1-(1a,9b-dihydro-1H-cyclopropa[l]phenanthren-1-yl)cyclopropan-1-ol and exo-1-(1a,9b-dihydro-1H-cyclopropa[l]phenanthren-1-yl)cyclobutan-1-ol in benzene-d6 produces (1-hydroxycyclopropyl)- and (1-hydroxycyclobutyl)carbene respectively. It was observed that (1-hydroxycyclopropyl)carbene rearranges to cyclobutanone whereas (1-hydroxycyclobutyl)carbene forms cyclopentanone. Formation of both ketones is attributed to tautomerization of the corresponding enols that arise from ring expansion of the carbenes. Products assignable to intramolecular C–H insertions were not detected in the photolysates.

Los estilos APA, Harvard, Vancouver, ISO, etc.

24

Wang, Hanghang, Pengcheng Lian, Yonggao Zheng, Jingjing Li y Xiaobing Wan. "Cross coupling of sulfonyl radicals with silver-based carbenes: a simple approach to β-carbonyl arylsulfones". Organic & Biomolecular Chemistry 18, n.º 11 (2020): 2163–69. http://dx.doi.org/10.1039/d0ob00091d.

Texto completo

Los estilos APA, Harvard, Vancouver, ISO, etc.

25

Empel, Claire y Rene M. Koenigs. "Sustainable Carbene Transfer Reactions with Iron and Light". Synlett 30, n.º 17 (26 de junio de 2019): 1929–34. http://dx.doi.org/10.1055/s-0037-1611874.

Texto completo

Resumen

Carbenes are versatile, highly reactive intermediates with great importance in chemistry. We recently reported on our findings on safe and scalable applications of hazardous diazoacetonitrile using cheap and commercially available iron catalysts in efficient carbene transfer reactions, ranging from cyclopropanation towards C–H functionalization reactions for the synthesis of biologically important building blocks. More lately, we uncovered the reactivity of diazoalkanes under photochemical conditions using visible light and were able to demonstrate a variety of different, metal-free carbene transfer reactions, which now open up new sustainable ways for the construction of small functional molecules.1 Introduction2 Iron-Catalyzed Carbene Transfer Reactions of Diazoacetonitrile3 Metal-free Carbene Transfer Reaction with Visible Light4 Summary

Los estilos APA, Harvard, Vancouver, ISO, etc.

26

Bakhonsky, Vladyslav V., Jonathan Becker, Grzegorz Mlostoń y Peter R. Schreiner. "N-Alkoxyimidazolylidines (NOHCs): nucleophilic carbenes based on an oxidized imidazolium core". Chemical Communications 58, n.º 10 (2022): 1538–41. http://dx.doi.org/10.1039/d1cc05696d.

Texto completo

Los estilos APA, Harvard, Vancouver, ISO, etc.

27

Iversen, Kalon J., David J. D. Wilson y Jason L. Dutton. "Activation of the C–N bond of N-heterocyclic carbenes by inorganic elements". Dalton Trans. 43, n.º 34 (2014): 12820–23. http://dx.doi.org/10.1039/c4dt00946k.

Texto completo

Los estilos APA, Harvard, Vancouver, ISO, etc.

28

Mamantov, Andrew. "Halocarbenes May Deplete Atmospheric Ozone". Progress in Reaction Kinetics and Mechanism 42, n.º 4 (diciembre de 2017): 307–33. http://dx.doi.org/10.3184/146867817x14954764850360.

Texto completo

Resumen

Photooxidation of tetrachloroethylene (PERC) and trichloroethylene (TCE) in simulated tropospheric smog chamber studies occurs with a time delay, accelerating simultaneous decreasing O3/chlorinated ethylene (CE) concentrations along with increasing CCl2O, which is attributed to CCl2 in the case of PERC and CCl2 or CHCl for TCE. The carbenes, chlorinated acetyl chlorides and CCl2O products may result from the rearrangement of the oxidised and/or excited oxidised CE, e.g. an epoxide. Analyses indicate scavenging experiments have not proved the existence of Cl atoms as being responsible for chlorinated acetyl chloride formation. Halocarbenes may form complexes with O3 which can undergo electron transfer (ET) and lead to dissociation of O3 to O2 and O and regeneration of carbene, resulting in a chain reaction. The direction of ET may be determined by the smallest differential HOMO–LUMO energy between the carbene and O3 which results in greater transition state stabilisation. Similarities in the reactions of O3 with carbenes and simple alkenes, nucleophilic carbenes with electron-poor alkenes and electrophilic carbene PhCCl with alkyl-substituted alkenes, i.e. (1) complex formation, (2) very low or negative activation energies and (3) the ability to undergo ET reactions with alkylalkenes are discussed. The possibility of the world-wide used perhalocarbons, e.g. perfluorinated carbons, hydroperhalocarbons, their halogenated replacements and starting materials degrading to halocarbenes which may degrade O3, is analysed.

Los estilos APA, Harvard, Vancouver, ISO, etc.

29

Wang, Jianbo y Kang Wang. "Transition-Metal-Catalyzed Cross-Coupling with Non-Diazo Carbene Precursors". Synlett 30, n.º 05 (16 de octubre de 2018): 542–51. http://dx.doi.org/10.1055/s-0037-1611020.

Texto completo

Resumen

Transition-metal-catalyzed cross-coupling reactions through metal carbene migratory insertion have emerged as powerful methodology for carbon–carbon bond constructions. Typically, diazo compounds (or in situ generated diazo compounds from N-tosylhydrazones) have been employed as the metal carbene precursors for this type of cross-coupling reactions. Recently, cross-coupling reactions employing non-diazo carbene precursors, such as conjugated ene-yne-ketones, allenyl ketones, alkynes, cyclopropenes, and Cr(0) Fischer carbenes, have been developed. This account will summarize our efforts in the development of transition-metal-catalyzed cross-coupling reactions with these non-diazo carbene precursors.1 Introduction2 Cross-Coupling with Ene-yne-ketones, Allenyl Ketones, and Alkynes3 Cross-Coupling Involving Ring-Opening of Cyclopropenes4 Palladium-Catalyzed Cross-Coupling with Chromium(0) Fischer Carbenes5 Conclusion

Los estilos APA, Harvard, Vancouver, ISO, etc.

30

Arduengo, Anthony J., Jens R. Goerlicha, Fredric Davidson y William J. Marshall. "Carbene Adducts of Dimethylcadmium". Zeitschrift für Naturforschung B 54, n.º 11 (1 de noviembre de 1999): 1350–56. http://dx.doi.org/10.1515/znb-1999-1102.

Texto completo

Resumen

The first examples of carbene-cadmium complexes are reported from the reactions of a variety of imidazol-2-ylidenes or imidazolin-2-ylidenes with dimethylcadmium. Four new carbene complexes are characterized by NMR spectroscopy (1H , 13C and 113Cd). The cadmium centers are strongly shifted downfield (100 -150 ppm) by interaction with the carbenes. X-ray structures are reported for three carbene-cadmium 1:1 adducts. The cadmium centers exhibit distorted trigonal-planar geometries in which the carbene ligands have an average 18.2 pm longer bond distance to cadmium compared to the methyl groups. The planes of cadmium coordination are twisted with respect to the plane of the imidazole ring. The more basic imidazolin-2-ylidene is shown to displace imidazol-2-ylidenes from the cadmium center.

Los estilos APA, Harvard, Vancouver, ISO, etc.

31

Azizi, Zahra, Mehdi Ghambarian, Mohammad A. Rezaei y Mohammad Ghashghaee. "Saturated N,X-Heterocyclic Carbenes (X=N, O, S, P, Si, C, and B): Stability, Nucleophilicity, and Basicity". Australian Journal of Chemistry 68, n.º 9 (2015): 1438. http://dx.doi.org/10.1071/ch14715.

Texto completo

Resumen

Various saturated five-membered N,X-heterocyclic carbenes (X = N, O, S, P, Si, C, and B) have been studied by ab initio and density functional theory (DFT) methods. The substitutions alter the properties of the reference carbene from the viewpoint of electronic structure, stability, nucleophilicity, and basicity. Our study shows that the oxygen containing carbene (X = O) induces the highest HOMO–LUMO energy gap (ΔEHOMO–LUMO), while carbene with X = N has the widest singlet–triplet energy difference (ΔEs–t). The nucleophilicity of the carbene derivatives increased upon replacement of C, Si, and B, with the effect of the boron substituent being more pronounced. In addition, the basicity of the structure increased for the carbene derivatives with X = C and B with the latter substitution imposing a remarkably higher effect. Moreover, the substitution of boron at the α-position of the carbene increased the nucleophilicity and basicity, while inducing a reduction in the values of ΔEs–t and ΔEHOMO–LUMO.

Los estilos APA, Harvard, Vancouver, ISO, etc.

32

Longevial, Jean-François, Mamadou Lo, Aurélien Lebrun, Danielle Laurencin, Sébastien Clément y Sébastien Richeter. "Molecular complexes and main-chain organometallic polymers based on Janus bis(carbenes) fused to metalloporphyrins". Dalton Transactions 49, n.º 21 (2020): 7005–14. http://dx.doi.org/10.1039/d0dt00594k.

Texto completo

Resumen

Janus bis(N-heterocyclic carbenes) composed of a porphyrin core with two N-heterocyclic carbene (NHC) heads fused to opposite pyrroles were used as bridging ligands for the preparation of metal complexes.

Los estilos APA, Harvard, Vancouver, ISO, etc.

33

Rozhenko, Alexander B., Yuliia S. Horbenko, Andrii A. Kyrylchuk, Evgenij V. Zarudnitskii, Sergiy S. Mykhaylychenko, Yuriy G. Shermolovich y Andriy V. Grafov. "Stable Carbenes as Structural Components of Partially Saturated Sulfur-Containing Heterocycles". Molecules 27, n.º 5 (22 de febrero de 2022): 1458. http://dx.doi.org/10.3390/molecules27051458.

Texto completo

Resumen

Recently, an unusual elongation of the C-S bond was observed experimentally for some sulfur-containing heterocycles. Using a superior ab initio (SCS-MP2/cc-pVTZ) level of theory, we showed that the phenomenon can be explained by a contribution of a donor–acceptor adduct of a carbene with an unsaturated ligand. One may achieve further elongation of the C-S bond, eventually turning it to a coordinate one, by increasing the stability of each part of the system as, e.g., in the utmost case of spiro adducts with Arduengo carbenes. The effect of carbene stability was quantified by employing the isodesmic reactions of carbene exchange.

Los estilos APA, Harvard, Vancouver, ISO, etc.

34

Bencze, L., N. Bíró, B. Szabó-Ravasz y L. Mihichuk. "Chemical transformations of cis-W(CO)4(C5H5N)2 in the ring-opening metathesis polymerization of norbornene". Canadian Journal of Chemistry 82, n.º 4 (1 de abril de 2004): 499–503. http://dx.doi.org/10.1139/v04-007.

Texto completo

Resumen

The six-coordinate W0 complex cis-W(CO)4(C5H5N)2 has been found to be active in the in situ formation of a carbene species from norbornene, which generates a typical ring-opening metathesis product (ROMP). A proposed mechanism of initiation suggests that the reaction involves a 2,3-hydrogen shift in the coordinated norbornene (η2 → η1). The initiating carbenoid group is identified from the products of the spontaneous carbeneCO coupling and Wittig reactions test. Formation of W(CO)3(η6-C6H5CH3) when toluene is the solvent, followed by reaction with the carbene, is blamed for catalyst deactivation.Key words: bis-pyridine-tetracarbonyl-tungsten, ROMP, olefin metathesis, norbornene.

Los estilos APA, Harvard, Vancouver, ISO, etc.

35

Gehrke, Sascha y Oldamur Hollóczki. "A molecular mechanical model for N-heterocyclic carbenes". Physical Chemistry Chemical Physics 18, n.º 32 (2016): 22070–80. http://dx.doi.org/10.1039/c6cp02624a.

Texto completo

Resumen

In this work a set of force fields for nine synthetically relevant and/or structurally interesting N-heterocyclic carbenes is presented, allowing facile substitution and the simulation of numerous carbene catalysts in solution by classical MD.

Los estilos APA, Harvard, Vancouver, ISO, etc.

36

Stenner, Richard, Jack W. Steventon, Annela Seddon y J. L. Ross Anderson. "A de novo peroxidase is also a promiscuous yet stereoselective carbene transferase". Proceedings of the National Academy of Sciences 117, n.º 3 (2 de enero de 2020): 1419–28. http://dx.doi.org/10.1073/pnas.1915054117.

Texto completo

Resumen

By constructing an in vivo-assembled, catalytically proficient peroxidase, C45, we have recently demonstrated the catalytic potential of simple, de novo-designed heme proteins. Here, we show that C45’s enzymatic activity extends to the efficient and stereoselective intermolecular transfer of carbenes to olefins, heterocycles, aldehydes, and amines. Not only is this a report of carbene transferase activity in a completely de novo protein, but also of enzyme-catalyzed ring expansion of aromatic heterocycles via carbene transfer by any enzyme.

Los estilos APA, Harvard, Vancouver, ISO, etc.

37

Le, Nguyen Nhat Thu, Josefine Just, Jonathan M. Pankauski, Paul R. Rablen y Dasan M. Thamattoor. "Ring Expansion of Alkylidenecarbenes Derived from Lactams, Lactones, and Thiolactones into Strained Heterocyclic Alkynes: A Theoretical Study". Molecules 24, n.º 3 (7 de febrero de 2019): 593. http://dx.doi.org/10.3390/molecules24030593.

Texto completo

Resumen

Strained cycloalkynes are of considerable interest to theoreticians and experimentalists, and possess much synthetic value as well. Herein, a series of cyclic alkylidenecarbenes—formally obtained by replacing the carbonyl oxygen of four-, five-, and six-membered lactams, lactones, and thiolactones with a divalent carbon—were modeled at the CCSD(T)/cc-pVTZ//B3LYP/6-311+G** and CCSD(T)/cc-pVTZ//CCSD/6-311+G** levels of theory. The singlet carbenes were found to be more stable than the triplets. The strained heterocyclic alkynes formed by ring expansion of these singlet carbenes were also modeled. Interestingly, the C≡C bonds in the five-membered heterocycles, obtained from the rearrangement of β-lactam- and β-lactone-derived alkylidenecarbenes, displayed lengths intermediate between formal double and triple bonds. Furthermore, 2-(1-azacyclobutylidene)carbene was found to be nearly isoenergetic with its ring-expanded isomer, and 1-oxacyclopent-2-yne was notably higher in energy than its precursor carbene. In all other cases, the cycloalkynes were lower in energy than the corresponding carbenes. The transition states for ring-expansion were always lower for the 1,2-carbon shifts than for 1,2-nitrogen or oxygen shifts, but higher than for the 1,2-sulfur shifts. These predictions should be verifiable using carbenes bearing appropriate isotopic labels. Computed vibrational spectra for the carbenes, and their ring-expanded isomers, are presented and could be of value to matrix isolation experiments.

Los estilos APA, Harvard, Vancouver, ISO, etc.

38

Merkley, Nadine, Manal El-Saidi y John Warkentin. "Radicals from fragmentation of benzyloxymethoxycarbenes in solution". Canadian Journal of Chemistry 78, n.º 3 (1 de marzo de 2000): 356–61. http://dx.doi.org/10.1139/v00-021.

Texto completo

Resumen

2-Benzyloxy-2-methoxy-5,5-dimethyl-Δ3-1,3,4-oxadiazolines, including the parent as well as p-substituted analogues, undergo thermolysis at 100°C in benzene to afford a mixture of products. Two primary fragmentations of the oxadiazolines were identified. The major pathway involves 1,3-dipolar cycloreversion to N2 and the corresponding carbonyl ylides. The latter dissociate to acetone and the corresponding benzyloxy(methoxy)carbenes, which undergo fragmentation to ArCH2 and MeOCO radical pairs that recombine to afford methyl arylacetates. Carbene dimers were not observed, showing that the fragmentation process is faster than carbene dimerization. A second fragmentation pathway observed for the oxadiazolines is an alternative cycloreversion to the corresponding benzyl methyl carbonate and 2-diazopropane. Products from diazopropane included acetone azine and, in some instances, traces of propene.Key words: benzyloxy(methoxy)carbene, carbene, radical pair, rearrangement.

Los estilos APA, Harvard, Vancouver, ISO, etc.

39

Wilhelm, René, Eduard Rais y Ulrich Flörke. "Reactivity of Grubbs–Hoveyda II Complexes Including Extended N-Heterocyclic Carbenes with a Bicyclic Camphor-Based Framework". Synthesis 49, n.º 13 (7 de junio de 2017): 2852–64. http://dx.doi.org/10.1055/s-0036-1588849.

Texto completo

Resumen

This feature article discusses the synthesis of new asymmetric Grubbs–Hoveyda II complexes with extended N-heterocyclic carbenes containing a bicyclic camphor-based framework. The new enantiopure complexes can be prepared in a short route from the chiral pool. The extended carbene-based catalyst shows high activity in olefin metathesis reactions. The new complexes exhibited enantioselectivity in an asymmetric ROCM desymmetrization. Depending on the substituents on the nitrogen atoms of the carbenes, the opposite enantiomer was formed in excess.

Los estilos APA, Harvard, Vancouver, ISO, etc.

40

Shen, Wen-Bo y Xiang-Ting Tang. "Recent advances in catalytic asymmetric intermolecular oxidation of alkynes". Organic & Biomolecular Chemistry 17, n.º 30 (2019): 7106–13. http://dx.doi.org/10.1039/c9ob01096c.

Texto completo

Resumen

In recent years, gold-metal-catalyzed intermolecular alkyne oxidation by an N-oxide oxidant, which presumably involves a gold carbenoid intermediate, has attracted increasing attention because it circumvents the employment of hazardous and potentially explosive diazocarbonyl compounds as starting materials for carbene generation.

Los estilos APA, Harvard, Vancouver, ISO, etc.

41

Chalifoux, Wesley A. y Rik R. Tykwinski. "Polyyne synthesis using carbene/carbenoid rearrangements". Chemical Record 6, n.º 4 (2006): 169–82. http://dx.doi.org/10.1002/tcr.20081.

Texto completo

Los estilos APA, Harvard, Vancouver, ISO, etc.

42

Dong, Kuiyong, Mengting Liu y Xinfang Xu. "Recent Advances in Catalytic Alkyne Transformation via Copper Carbene Intermediates". Molecules 27, n.º 10 (11 de mayo de 2022): 3088. http://dx.doi.org/10.3390/molecules27103088.

Texto completo

Resumen

As one of the abundant and inexpensive metals on the earth, copper has demonstrated broad applications in synthetic chemistry and catalysis. Among these copper-catalyzed advances, copper carbenes are versatile and reactive intermediates that can mediate a variety of transformations, which have attracted much attention in the past decades. The present review summarizes two different reaction models that take place between a copper carbene intermediate and alkyne species, including the cross-coupling reaction of copper carbene intermediate with terminal alkyne, and the addition of copper carbene intermediate onto the C–C triple bond. This article will cover the profile from 2010 to 2021 by placing emphasis on the detailed catalytic models and highlighting the synthetic applications offered by these practical and mild methods.

Los estilos APA, Harvard, Vancouver, ISO, etc.

43

Merkley, Nadine y John Warkentin. "Benzyloxy(4-substituted benzyloxy)carbenes. Generation from oxadiazolines and fragmentation to radical pairs in solution". Canadian Journal of Chemistry 78, n.º 7 (1 de julio de 2000): 942–49. http://dx.doi.org/10.1139/v00-078.

Texto completo

Resumen

Thermolysis of 2,2-dibenzyloxy-5,5-dimethyl-Δ3-1,3,4-oxadiazoline in benzene at 110°C leads to dibenzyloxycarbene. The carbene was trapped with tert-butyl alcohol to afford dibenzyl-tert-butyl orthoformate. In the absence of a trapping agent for the carbene, it fragmented to benzyloxycarbonyl and benzyl radicals, as shown by trapping the latter with TEMPO. In the absence of both TEMPO and tert-butyl alcohol, the radicals were partitioned between coupling to benzyl phenylacetate and decarboxylation, with subsequent formation of bibenzyl. The preferred sense of fragmentation of the analogous carbenes from benzyloxy-(p-substituted-benzyloxy)carbenes was determined by comparing the yields of the two possible esters, ArCH2O(CO)CH2Ph and PhCH2O(CO)CH2Ar. It was found that an electron-withdrawing group in the para position favoured fragmentation to the benzylic radical containing that group. A Hammett plot of the data gave a best fit with σ- substituent constants (r = 0.994, ρ(PhH, 110°C) = 0.7) suggesting that the fragmentation involves charge separation in the sense that increases electron density on the group that is becoming a benzylic radical and decreases electron density on the carbonyl group that is becoming the benzyloxycarbonyl radical.Key words: carbene, dibenzyloxycarbene, fragmentation, substituent effect, radical pair, TEMPO.

Los estilos APA, Harvard, Vancouver, ISO, etc.

44

Nonnenmacher, Michael, Dominik M. Buck y Doris Kunz. "Experimental and theoretical investigations on the high-electron donor character of pyrido-annelated N-heterocyclic carbenes". Beilstein Journal of Organic Chemistry 12 (23 de agosto de 2016): 1884–96. http://dx.doi.org/10.3762/bjoc.12.178.

Texto completo

Resumen

Rh(CO)2Cl(NHC) complexes of dipyrido-annelated N-heterocyclic carbenes were prepared. From the C–H coupling constant of the respective imidazolium salts and the N–C–N angle of the N-heterocyclic carbene (NHC), a weaker σ-donor character than that of typical unsaturated NHCs is expected. However, the IR stretching frequencies of their Rh(CO)2Cl complexes suggest an electron-donor character even stronger than that of saturated NHCs. We ascribe this to the extremely weak π-acceptor character of the dipyrido-annelated NHCs caused by the conjugated 14 πe− system that thus allows for an enhanced Rh–CO backbonding. This extremely low π-acceptor ability is also corroborated by the 77Se NMR chemical shift of −55.8 ppm for the respective selenourea, the lowest value ever measured for imidazole derived selenoureas. DFT-calculations of the free carbene confirm the low σ-donor character by the fact that the σ-orbital of the carbene is the HOMO−1 that lies 0.58 eV below the HOMO which is located at the π-system. Natural population analysis reveals the lowest occupation of the pπ-orbital for the saturated carbene carbon atom and the highest for the pyrido-annelated carbene. Going from the free carbene to the Rh(CO)2Cl(NHC) complexes, the increase in occupancy of the complete π-system of the carbene ligand upon coordination is lowest for the pyrido-annelated carbene and highest for the saturated carbene.

Los estilos APA, Harvard, Vancouver, ISO, etc.

45

Fujita, Ken-ichi, Junichi Sato y Hiroyuki Yasuda. "Tautomerization of 5-Alkylidene-2-Oxazolidinone to 2-Oxazolone by Use of an N-Heterocyclic Carbene Catalyst". Synlett 26, n.º 08 (3 de marzo de 2015): 1106–10. http://dx.doi.org/10.1055/s-0034-1380274.

Texto completo

Resumen

By employing an N-heterocyclic carbene as a catalyst, the tautomerization of 5-alkylidene-2-oxazolidinone proceeded to afford the corresponding 2-oxazolone. Among N-heterocyclic carbenes, 1,3-di-tert-butylimidazol-2-ylidene was the most effective catalyst for the tautomerization of 5-alkylidene-2-oxazolidinone.

Los estilos APA, Harvard, Vancouver, ISO, etc.

46

Koch, Alexander, Helmar Görls, Sven Krieck y Matthias Westerhausen. "Coordination behavior of bidentate bis(carbenes) at alkali metal bis(trimethylsilyl)amides". Dalton Transactions 46, n.º 28 (2017): 9058–67. http://dx.doi.org/10.1039/c7dt01538k.

Texto completo

Resumen

Crystallization of LiN(SiMe₃)₂ from 2,2,5,5-tetramethyltetrahydrofuran yields the base-free tetramer. Strong carbenes monomerize the lithium bis(trimethylsilyl)amides, whereas the heavier congeners from carbene-stabilized dimers [AN(SiMe₃)₂]₂ with A = Na, K.

Los estilos APA, Harvard, Vancouver, ISO, etc.

47

Lin, Ivan JB y Chandra Sekhar Vasam. "Review of gold(I) N-heterocyclic carbenes". Canadian Journal of Chemistry 83, n.º 6-7 (1 de junio de 2005): 812–25. http://dx.doi.org/10.1139/v05-087.

Texto completo

Resumen

This review presents an overview of the work on Au(I)NHC chemistry. The efficiency of different synthetic strategies of Au(I)NHCs is discussed. Transmetallation of Ag(I)NHCs appears to be an easy method as compared with the others. The influence of aurophilicity "a traditional property of a Au(I) center" in making the supramolecular assemblies is also covered. The combination of the Au(I) center with NHCs has great potential in the fields of medicine, catalysis, liquid crystal, and optoelectronic.Key words: goldcarbenes, silvercarbenes, carbene transfer, aurophilicity.

Los estilos APA, Harvard, Vancouver, ISO, etc.

48

Zhang, Lumin, Bethany M. DeMuynck, Alyson N. Paneque, Joy E. Rutherford y David A. Nagib. "Carbene reactivity from alkyl and aryl aldehydes". Science 377, n.º 6606 (5 de agosto de 2022): 649–54. http://dx.doi.org/10.1126/science.abo6443.

Texto completo

Resumen

Carbenes are highly enabling reactive intermediates that facilitate a diverse range of otherwise inaccessible chemistry, including small-ring formation and insertion into strong σ bonds. To access such valuable reactivity, reagents with high entropic or enthalpic driving forces are often used, including explosive (diazo) or unstable ( gem -dihalo) compounds. Here, we report that common aldehydes are readily converted (via stable α-acyloxy halide intermediates) to electronically diverse (donor or neutral) carbenes to facilitate >10 reaction classes. This strategy enables safe reactivity of nonstabilized carbenes from alkyl, aryl, and formyl aldehydes via zinc carbenoids. Earth-abundant metal salts [iron(II) chloride (FeCl 2 ), cobalt(II) chloride (CoCl 2 ), copper(I) chloride (CuCl)] are effective catalysts for these chemoselective carbene additions to σ and π bonds.

Los estilos APA, Harvard, Vancouver, ISO, etc.

49

Graham, David C. y Brian F. Yates. "Increased Stability of NO and NS Heterocyclic Carbenes?" Australian Journal of Chemistry 57, n.º 4 (2004): 359. http://dx.doi.org/10.1071/ch03248.

Texto completo

Resumen

Density functional theory has been used to investigate the effects of alkylation and oxidation on the stability of NO and NS heterocyclic carbenes. While O- and S-alkylation leads to a dramatic increase in stability with respect to dimerization, oxidation of the NS heterocyclic carbene to form the sulphoxide appears to have the opposite effect.

Los estilos APA, Harvard, Vancouver, ISO, etc.

50

Leitão, Maria Inês P. S., Giulia Francescato, Clara S. B. Gomes y Ana Petronilho. "Synthesis of Platinum(II) N-Heterocyclic Carbenes Based on Adenosine". Molecules 26, n.º 17 (4 de septiembre de 2021): 5384. http://dx.doi.org/10.3390/molecules26175384.

Texto completo

Resumen

Organometallic derivatization of nucleosides is a highly promising strategy for the improvement of the therapeutic profile of nucleosides. Herein, a methodology for the synthesis of metalated adenosine with a deprotected ribose moiety is described. Platinum(II) N-heterocyclic carbene complexes based on adenosine were synthesized, namely N-heterocyclic carbenes bearing a protected and unprotected ribose ring. Reaction of the 8-bromo-2′,3′,5′-tri-O-acetyladenosine with Pt(PPh3)4 by C8−Br oxidative addition yielded complex 1, with a PtII centre bonded to C-8 and an unprotonated N7. Complex 1 reacted at N7 with HBF4 or methyl iodide, yielding protic carbene 2 or methyl carbene 3, respectively. Deprotection of 1 to yield 4 was achieved with NH4OH. Deprotected compound 4 reacted at N7 with HCl solutions to yield protic NHC 5 or with methyl iodide yielding methyl carbene 6. Protic N-heterocyclic carbene 5 is not stable in DMSO solutions leading to the formation of compound 7, in which a bromide was replaced by chloride. The cis-influence of complexes 1–7 was examined by 31P{1H} and 195Pt NMR. Complexes 2, 3, 5, 6 and 7 induce a decrease of 1JPt,P of more than 300 Hz, as result of the higher cis-influence of the N-heterocyclic carbene when compared to the azolato ligand in 1 and 4.

Los estilos APA, Harvard, Vancouver, ISO, etc.

Ofrecemos descuentos en todos los planes premium para autores cuyas obras están incluidas en selecciones literarias temáticas. ¡Contáctenos para obtener un código promocional único!