WorldWideScience
1

Nickel N-heterocyclic carbene complexes in homogeneous catalysis  

OpenAIRE

Described in this thesis are the investigations into the chemistry of N-heterocyclic carbene (NHC) ligands and transition-metal complexes thereof. Specifically, a variety of N-heterocyclic carbene complexes of nickel were prepared, characterized and used as catalysts in three types of homogeneous catalytic processes. First, nickel(II) complexes of monodentate NHC ligands were successfully used as catalysts in the hydrosilylation of internal alkynes. Second, nickel(II) complexes bearing bident...

Berding, Joris

2009-01-01

2

N-heterocyclic carbene bonding to cobalt porphyrin complexes  

OpenAIRE

N-heterocyclic carbene (NHC) coordination to a cobalt(III) center embedded in a porphyrin scaffold has been accomplished by decarboxylation from N,N’-dimethylimidazolium-2-carboxylate in the presence of Co(TPP)Cl (TPP = 5,10,15,20-tetraphenylporphyrin). The distal chloride ligand in the resulting complexes Co(NHC)(TPP)Cl was successfully substituted with imidazoles and alcohols. Single crystal X-ray diffraction of the latter complexes Co(NHC)(TPP)(ROH) (R = Me, Et) revealed a pronounced ruf...

Albrecht, Martin; Maji, Pathik; Ha?usl, Christina; Monney, Ange?le; Mu?ller-bunz, Helge

2012-01-01

3

N-Heterocyclic carbene metal complexes: photoluminescence and applications.  

Science.gov (United States)

This review covers the advances made in the synthesis of luminescent transition metal complexes containing N-heterocyclic carbene (NHC) ligands. The presence of a high field strength ligand such as an NHC in the complexes gives rise to high energy emissions, and consequently, to the desired blue colour needed for OLED applications. Furthermore, the great versatility of NHC ligands for structural modifications, together with the use of other ancillary ligands in the complex, provides numerous possibilities for the synthesis of phosphorescent materials, with emission colours over the entire visible spectra and potential future applications in fields such as photochemical water-splitting, chemosensors, dye-sensitised solar cells, oxygen sensors, and medicine. PMID:24604135

Visbal, Renso; Gimeno, M Concepción

2014-05-21

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Synthesis and antimicrobial studies of silver N-heterocyclic carbene complexes bearing a methyl benzoate substituent  

OpenAIRE

Due to the properties of silver as an antimicrobial, our research group has synthesized many different silver carbene complexes. Two new silver N-heterocyclic carbene complexes derived from 4,5-dichloroimidazole and theobromine bearing methyl benzoate substituents were synthesized by in situ carbene formation using silver acetate as the base in the reaction. The new compounds were fully characterized by several methods including NMR spectroscopy and X-ray crystallography. Preliminary antimicr...

Knapp, Amanda R.; Panzner, Matthew J.; Medvetz, Doug A.; Wright, Brian D.; Tessier, Claire A.; Youngs, Wiley J.

2010-01-01

5

The Potential of N-Heterocyclic Carbene Complexes as Components for Electronically Active Materials  

OpenAIRE

The application of N-heterocyclic carbene complexes as active sites in materials other than catalysis has been remarkably scarce. Inspired by the — often misleading — ‘carbene’ label, which implies a substantial degree of M=C ? bonding, we have been interested in evaluating the potential of N-heterocylclic carbene complexes as building blocks for constructing electronically active materials. Electron mobility via the metal-carbon bond has been investigated in monometallic imidazol-2-...

Schuster, Oliver; Mercs, Laszlo; Albrecht, Martin

2010-01-01

6

Direct functionalisation of group 10 N-heterocyclic carbene complexes for diversity enhancement.  

Science.gov (United States)

The synthesis of alkyne-substituted N-heterocyclic carbene complexes of Pd(II) and Pt(II) is reported. Catalyzed 1,3-dipolar cycloaddition with azides has been applied as a modular way of functionalisation of group 10 transition metal NHC complexes to generate potentially new metallodrugs. PMID:21503314

Chardon, Edith; Puleo, Gian Luigi; Dahm, Georges; Guichard, Gilles; Bellemin-Laponnaz, Stéphane

2011-05-28

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Gold(I Complexes of N-Heterocyclic Carbene Ligands Containing Benzimidazole: Synthesis and Antimicrobial Activity  

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Full Text Available Gold(I N-heterocyclic carbene (NHC complexes were obtained in good yields from the corresponding silver complexes by treatment with [AuCl(PPh3] following the commonly used silver carbene transfer route. The silver complexes were synthesized from the benzimidazolium halide salts by the in situ reactions with Ag2O in dichloromethane as a solvent at room temperature. All gold complexes have been characterized by 1H-NMR, 13C-NMR and IR spectroscopy and elemental analysis. Au-NHC complexes were evaluated for their in vitro antimicrobial activity against a variety of Gram-positive and Gram-negative bacteria and fungal species.

?lknur Özdemir

2010-03-01

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Gold(I) complexes of N-heterocyclic carbene ligands containing benzimidazole: synthesis and antimicrobial activity.  

Science.gov (United States)

Gold(I) N-heterocyclic carbene (NHC) complexes were obtained in good yields from the corresponding silver complexes by treatment with [AuCl(PPh3)] following the commonly used silver carbene transfer route. The silver complexes were synthesized from the benzimidazolium halide salts by the in situ reactions with Ag2O in dichloromethane as a solvent at room temperature. All gold complexes have been characterized by 1H-NMR, 13C-NMR and IR spectroscopy and elemental analysis. Au-NHC complexes were evaluated for their in vitro antimicrobial activity against a variety of Gram-positive and Gram-negative bacteria and fungal species. PMID:20428038

Ozdemir, Ilknur; Temelli, Nazan; Günal, Selami; Demir, Serpil

2010-04-01

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Gold(I) Complexes of N-Heterocyclic Carbene Ligands Containing Benzimidazole: Synthesis and Antimicrobial Activity  

OpenAIRE

Gold(I) N-heterocyclic carbene (NHC) complexes were obtained in good yields from the corresponding silver complexes by treatment with [AuCl(PPh3)] following the commonly used silver carbene transfer route. The silver complexes were synthesized from the benzimidazolium halide salts by the in situ reactions with Ag2O in dichloromethane as a solvent at room temperature. All gold complexes have been characterized by 1H-NMR, 13C-NMR and IR spectroscopy and elemental analysis. Au-NHC complexes were...

?lknur Özdemir; Nazan Temelli; Selami Günal; Serpil Demir

2010-01-01

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Synthesis and Properties of Chelating N-Heterocyclic Carbene Rhodium(I) Complexes: Synthetic Experiments in Current Organometallic Chemistry  

Science.gov (United States)

The preparation and characterization of two air-stable Rh(I) complexes bearing a chelating N-heterocyclic carbene (NHC) ligand is described. The synthesis involves the preparation of a Ag(I)-NHC complex and its use as carbene transfer agent to a Rh(I) precursor. The so obtained complex can be further reacted with carbon monoxide to give the…

Mata, Jose A.; Poyatos, Macarena; Mas-Marza, Elena

2011-01-01

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Ruthenium(II) complexes of N-heterocyclic carbenes derived from imidazolium-linked cyclophanes.  

Science.gov (United States)

The present work seeks to characterize, in the light of electronic structure calculations, an unusual metal-[(?(1)-NHC)2:(?(6)-arene)] bonding situation in a set of ruthenium(ii) complexes containing the ortho-xylylene-linked-bis(NHC)cyclophane ligand (NHC-cyclophane) (), which binds to the ruthenium center through two carbene carbons and one of the arene rings. The nature of ruthenium(ii)-[(?(1)-NHC)2:(?(6)-arene)] bonding was investigated in the light of EDA-NOCV, NBO and QTAIM analyses by adopting as a model compound. The interplay between the ortho-cyclophane scaffold with different families of five-membered carbenes, such as imidazole, , triazole-based NHCs (Enders' carbenes), , and P-heterocyclic carbenes (PHCs), , was investigated. The metal-[(?(1)-NHC)2:(?(6)-arene)] bonding situation was also extended to heavier analogues, such as N-heterocyclic silylenes (NHSi) and N-heterocyclic germylenes (NHGe), in order to address how the basicity of NHC, NHSi and NHGe is affected by the cyclophane framework. The results reveal that ruthenium(ii)-[(?(1)-NHC)2:(?(6)-arene)] is more covalently than electrostatically bonded and that the degree of covalence is larger in PHCs than in NHCs or Enders' carbenes. It is also revealed that the covalent character in the ruthenium(ii)-[(?(1)-NHGe)2:(?(6)-arene)] and ruthenium(ii)-[(?(1)-NHSi)2:(?(6)-arene)] bonds is larger than in ruthenium(ii)-[(?(1)-NHC)2:(?(6)-arene)]. PMID:25144142

Caramori, Giovanni F; Garcia, Leone C; Andrada, Diego M; Frenking, Gernot

2014-10-21

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Application of silver N-heterocyclic carbene complexes in O-glycosidation reactions  

OpenAIRE

We report the efficient O-glycosidation of glycosyl bromides with therapeutically relevant acceptors facilitated by silver N-heterocyclic carbene (Ag-NHC) complexes. A set of four Ag-NHC complexes was synthesized and evaluated as promoters for glycosidation reactions. Two new bis-Ag-NHC complexes derived from ionic liquids 1-benzyl-3-methyl-1H-imidazolium chloride and 1-(2-methoxyethyl)-3-methyl-1H-imidazolium chloride were found to efficiently promote glycosidation, whereas known mono-Ag com...

Talisman, Ian J.; Kumar, Vineet; Deschamps, Jeffrey R.; Frisch, Mark; Malhotra, Sanjay V.

2011-01-01

13

Backbone tuning in indenylidene–ruthenium complexes bearing an unsaturated N-heterocyclic carbene  

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Full Text Available The steric and electronic influence of backbone substitution in IMes-based (IMes = 1,3-bis(2,4,6-trimethylphenylimidazol-2-ylidene N-heterocyclic carbenes (NHC was probed by synthesizing the [RhCl(CO2(NHC] series of complexes to quantify experimentally the Tolman electronic parameter (electronic and the percent buried volume (%Vbur, steric parameters. The corresponding ruthenium–indenylidene complexes were also synthesized and tested in benchmark metathesis transformations to establish possible correlations between reactivity and NHC electronic and steric parameters.

César A. Urbina-Blanco

2010-11-01

14

N-heterocyclic carbene and phosphine complexes of osmium and ruthenium carbonyls  

OpenAIRE

1,3-bis-(2,4,6-trimethylphenyl)imidazol-2-ylidene-silver(I)chloride ([IMes]AgCl), a carbene transfer agent, was employed in the reaction with various osmium clusters. Reaction of ([IMes]AgCl) with [Os3(µ-H)2(CO)10] gave [Os3(µ-H)(µ-Cl)(CO)9(IMes)] (1), an osmium N-heterocyclic carbene complex. The reaction of ([IMes]AgCl) with the cluster [Os3(CO)10(CH3CN)2] yielded two products, [Os3(µ-Cl)(CO)10(µ-Ag(IMes)] (2) and [(IMes-H)][Os3(µ-Cl)(CO)10](µ4-Ag)[Os3(µ-Cl)(CO)10] (3). Compound (2)...

Cooke, Craig E.

2008-01-01

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Exploring nitrogen ligand diversity in trans-N-heterocyclic carbene-amine platinum complexes: synthesis, characterization, and application to fluorescence.  

Science.gov (United States)

Expand and diversify your Ptfolio: N-Heterocyclic carbene-Pt-pyridine complexes have been used to generate an expanded and diversified set of trans NHC-Pt complexes with various amines, polyamines, hydroxylamines, or hydrazine as ligands. Attachment of a fluorophore moiety has also been successfully achieved. PMID:23559499

Chardon, Edith; Dahm, Georges; Guichard, Gilles; Bellemin-Laponnaz, Stéphane

2013-06-01

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Photofunctional Platinum Complexes Featuring N-heterocyclic Carbene-Based Pincer Ligands.  

Science.gov (United States)

Photoactive platinum complexes of stoichiometry [Pt((R) CCC(R) )L](0/+) (R=Me, nBu and L=?CN, ?C?CPh, ?N?CCH3 , ?Py, ?CO) featuring pincer-type bis N-heterocyclic carbene (NHC) ligands ((R) CCC(R) ) were synthesized. Organometallic syntheses of these complexes are facile and achievable through standard laboratory procedures. Control of intermolecular Pt???Pt interaction, ?-? stacking, and emission tuning is achieved through suitable choice of the NHC-wingtip substituent (R) and the auxiliary ligand (L). Exposure to specific volatile organic compounds (VOCs) or mechanical grinding triggers changes in emission colors, which render these complexes photofunctional. Solid-state structures and photoluminescence results are described herein. PMID:25663631

Lin, Wan-Jung; Naziruddin, Abbas Raja; Chen, Yu-Hsuan; Sun, Bian-Jian; Chang, A Hsiu Hwa; Wang, Wen-Jwu; Hwang, Wen-Shu

2015-03-01

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Nanofiber composites containing N-heterocyclic carbene complexes with antimicrobial activity  

Directory of Open Access Journals (Sweden)

Full Text Available Ahmed A Elzatahry1,4, Abdullah M Al-Enizi1, Elsayed Ahmed Elsayed2,5, Rachel R Butorac3, Salem S Al-Deyab1, Mohammad AM Wadaan2, Alan H Cowley31Petrochemical Research Chair, Department of Chemistry, 2Chair of Advanced Proteomics & Cytomics Research, Faculty of Science, King Saud University, Riyadh, Kingdom of Saudi Arabia; 3Department of Chemistry and Biochemistry, University of Texas at Austin, Austin, TX, USA; 4Institute of Advanced Technology and New Materials, City for Scientific Research and Technology Applications, New Borg Alrab, Alexandria, Egypt; 5Natural & Microbial Products Department, National Research Centre, Dokki, Cairo, EgyptAbstract: This report concerns nanofiber composites that incorporate N-heterocyclic carbenes and the use of such composites for testing antimicrobial and antifungal activities. The nanofiber composites were produced by electrospinning mixtures of the gold chloride or gold acetate complexes of a bis(iminoacenaphthene (BIAN-supported NHC with aqueous solutions of polyvinyl alcohol (PVA. The products were characterized by scanning-electron microscopy, which revealed that nanofibers in the range of 250–300 nm had been produced. The biological activities of the nanofiber composites were tested against two Gram-positive bacteria, six Gram-negative bacteria, and two fungal strains. No activity was evident against the fungal strains. However, the gold chloride complex was found to be active against all the Gram-positive pathogens and one of the Gram-negative pathogens. It was also found that the activity of the produced nanofibers was localized and that no release of the bioactive compound from the nanofibers was evident. The demonstrated antimicrobial activities of these novel nanofiber composites render them potentially useful as wound dressings.Keywords: nanofiber, electrospinning, N-Heterocyclic carbene, biopolymer, antimicrobial

Elzatahry AA

2012-06-01

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Pyridine versus acetonitrile coordination in rhodium-N-heterocyclic carbene square-planar complexes.  

Science.gov (United States)

Experimental and theoretical studies on the factors that control the coordination chemistry of N-donor ligands in square-planar complexes of the type RhCl(NHC)L(1)L(2) (NHC = N-heterocyclic carbene) are presented. The dinuclear complexes [Rh(?-Cl)(IPr)(?(2)-olefin)]2 {IPr = 1,3-bis-(2,6-diisopropylphenyl)imidazol-2-carbene} have been reacted with different combinations of ligands including pyridine, acetonitrile, 2-pyridylacetonitrile, triphenylphosphine, tricyclohexylphosphine, carbon monoxide or molecular oxygen. In addition, the reactivity of RhCl(IPr)(PPh3)2 has also been studied. Pyridine preferentially coordinates trans to the carbene ligand whereas ?-acceptor ligands (olefin, CO or PPh3) are prone to bind cis to IPr and trans to chlorido, unless steric bulk hinders the coordination of the ligand (PCy3). In contrast, acetonitrile is more labile than pyridine but is able to form complexes coordinated cis-to-IPr. Molecular dioxygen also displaces the labile cyclooctene ligand in RhCl(IPr)(?(2)-coe)(py) to give a square-planar dioxygen adduct which can be transformed into a peroxo derivative by additional coordination of pyridine. Charge decomposition analysis (CDA) shows that ?-donation values are similar for coordination at cis- or trans-IPr positions, whereas efficient ?-backbonding is significantly observed at cis position being the favoured coordination site for ?-acceptor ligands. The Rh-IPr rotational barrier in a series of square-planar complexes has been analysed. It has been found that the main contribution is the steric hindrance of the ancillary ligand. The presence of a ?-donor ligand such as chlorido slows down the dynamic process. PMID:25714797

Palacios, Laura; Di Giuseppe, Andrea; Castarlenas, Ricardo; Lahoz, Fernando J; Pérez-Torrente, Jesús J; Oro, Luis A

2015-03-10

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An overview of N-heterocyclic carbenes  

Science.gov (United States)

The successful isolation and characterization of an N-heterocyclic carbene in 1991 opened up a new class of organic compounds for investigation. From these beginnings as academic curiosities, N-heterocyclic carbenes today rank among the most powerful tools in organic chemistry, with numerous applications in commercially important processes. Here we provide a concise overview of N-heterocyclic carbenes in modern chemistry, summarizing their general properties and uses and highlighting how these features are being exploited in a selection of pioneering recent studies.

Hopkinson, Matthew N.; Richter, Christian; Schedler, Michael; Glorius, Frank

2014-06-01

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Novel platinum-N-heterocyclic carbene complex is more cardiotoxic than cis-platin in rats.  

Science.gov (United States)

Cis-platin and other platinum complexes are important chemotherapeutic agents useful in the treatment of several cancers. However, therapeutic usage of cis-platin and other platinum complex are limited by their undesirable side effects including cardiotoxicity. In this context, we aimed to compare the damage caused in heart by cis-platin and novel platinum-N-heterocyclic carbene (Pt-NHC) complex. For this purpose, 35 Sprague-Dawley rats were divided randomly into five equal groups (n = 7 for each group). Cis-platin and novel Pt-NHC complex were intraperitoneally administered at a single dose of 5 mg/kg and 10 mg/kg and then sacrificed 10 days after this treatment. The heart tissues were taken from all rats for determination of oxidative and myocardial damage. Cis-platin and novel Pt-NHC complex caused oxidative and histological damage in the heart tissue in a dose-dependent manner (p cis-platin caused lower oxidative and histological damage in heart tissue compared to novel Pt-NHC complex. These results suggest that novel Pt-NHC complex is more cardiotoxic than cis-platin. PMID:21075807

Ciftci, Osman; Ozdemir, Ilknur; Vardi, Nigar; Gurbuz, Nevin

2011-09-01

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N-heterocyclic carbene (NHC) complexes of group 4 transition metals.  

Science.gov (United States)

Since the discovery of a stable N-heterocyclic carbene (NHC), the use of NHCs in chemistry has developed rapidly over the past two decades. These interesting compounds are predominantly employed in organometallic chemistry as ligands for various metal centers, and as organocatalysts for a variety of transformations. In particular, the NHC transition metal complexes have received widespread attention, and significant progress has been made in the development of group 4 NHC-complexes in the last few years. These group 4 NHC-complexes are of interest because of their unique structural properties, and their potential application in organic transformations and catalysis. This review covers the superior design strategies for NHC ligands to stabilize early transition metals and well-defined group 4 metal complexes with mono- and multi-dentate NHC ligands. In this context, four types of NHC-complexes, i.e., carbon-functionalized NHCs, nitrogen-functionalized NHCs, oxygen-functionalized NHCs and nitrogen/oxygen-functionalized unsymmetric NHCs, are described. In addition, the use of group 4 NHC-complexes as catalysts in olefin (co)polymerization, ring-opening polymerization of rac-lactide, copolymerization of epoxides and CO2, as well as hydroamination/cyclization of aminoalkenes, is presented. Furthermore, limitations and challenges are discussed. PMID:25608933

Zhang, Dao; Zi, Guofu

2015-04-01

22

Application of silver N-heterocyclic carbene complexes in O-glycosidation reactions.  

Science.gov (United States)

We report the efficient O-glycosidation of glycosyl bromides with therapeutically relevant acceptors facilitated by silver N-heterocyclic carbene (Ag-NHC) complexes. A set of four Ag-NHC complexes was synthesized and evaluated as promoters for glycosidation reactions. Two new bis-Ag-NHC complexes derived from ionic liquids 1-benzyl-3-methyl-1H-imidazolium chloride and 1-(2-methoxyethyl)-3-methylimidazolium chloride were found to efficiently promote glycosidation, whereas known mono-Ag complexes of 1,3-bis(2,4,6-trimethylphenyl)imidazolium chloride and 1,3-bis(2,6-di-isopropylphenyl)imidazolium chloride failed to facilitate the reaction. The structures of the promoters were established by X-ray crystallography and these complexes were employed in the glycosidation of different glycosyl bromide donors with biologically valuable acceptors, such as estrone, estradiol, and various flavones. The products were obtained in yields considered good to excellent, and all reactions were highly selective for the ? isomer regardless of neighboring group effects. PMID:21911215

Talisman, Ian J; Kumar, Vineet; Deschamps, Jeffrey R; Frisch, Mark; Malhotra, Sanjay V

2011-11-01

23

Preparation of a N-Heterocyclic Carbene Nickel(II) Complex: Synthetic Experiments in Current Organic and Organometallic Chemistry  

Science.gov (United States)

A four-part experiment that leads to the synthesis of a cyclopentadienyl chloro-nickel(II) complex bearing a N-heterocyclic carbene (NHC) ligand is presented. In the first part, the preparation of 1,3-bis-(2,4,6-trimethylphenyl)imidazolium chloride (IMes[middle dot]HCl) in a one-pot procedure by reaction of 2,4,6-trimethylaniline with…

Ritleng, Vincent; Brenner, Eric; Chetcuti, Michael J.

2008-01-01

24

N-Heterocyclic carbenes: versatile second cyclometalated ligands for neutral iridium(III) heteroleptic complexes.  

Science.gov (United States)

With 2-(2,4-difluorophenyl)pyridine (dfppy) as the first cyclometalated ligand and different monoanionic N-heterocyclic carbenes (NHCs) as the second cyclometalated ligands, 16 blue or greenish-blue neutral iridium(III) phosphorescent complexes, (dfppy)2Ir(NHC), were synthesized efficiently. The obtained Ir(III) complexes display typical phosphorescence of 455-485 nm with quantum yields up to 0.73. By modifying the phenyl moiety in the NHCs with electron-withdrawing substituents (e.g., -F or -CF3) or replacing it with N-heteroaromatic rings (pyridine or pyrimidine), the HOMO-LUMO gaps are broadened, and the emissions shift to the more blue region accordingly. Furthermore, to extend the application scope of NHCs as the second cyclometalated ligands, five other Ir(III) complexes from blue to red were synthesized with different first cyclometalated ligands. Finally, the organic light-emitting diodes using one blue emitter exhibit a maximum current efficiency of 37.83 cd A(-1), an external quantum efficiency of 10.3%, and a maximum luminance of 8709 cd m(-2). Our results demonstrate that NHCs as the second cyclometalated ligands are good candidates for the achievement of efficient phosphorescent Ir(III) complexes and corresponding devices. PMID:25495711

Li, Tian-Yi; Liang, Xiao; Zhou, Liang; Wu, Chen; Zhang, Song; Liu, Xuan; Lu, Guang-Zhao; Xue, Li-Sha; Zheng, You-Xuan; Zuo, Jing-Lin

2015-01-01

25

Amide Synthesis from Alcohols and Amines Catalyzed by Ruthenium N-Heterocyclic Carbene Complexes  

DEFF Research Database (Denmark)

The direct synthesis of amides from alcohols and amines is described with the simultaneous liberation of dihydrogen. The reaction does not require any stoichiometric additives or hydrogen acceptors and is catalyzed by ruthenium N-heterocyclic carbene complexes. Three different catalyst systems are presented that all employ 1,3-diisopropylimidazol-2-ylidene (IiPr) as the carbene ligand. In addition, potassium tert-butoxide and a tricycloalkylphosphine are required for the amidation to proceed. In the first system, the active catalyst is generated in situ from [RuCl2(cod)] (cod = 1,5-cyclooctadiene), 1,3-diisopropylimidazolium chloride, tricyclopentylphosphonium tetrafluoroborate, and base. The second system uses the complex [RuCl2(IiPr)(p-cymene)] together with tricyclohexylphosphine and base, whereas the third system employs the Hoveyda-Grubbs 1st-generation metathesis catalyst together with 1,3-diisopropylimidazolium chloride and base. A range of different primary alcohols and amines have been coupled in thepresence of the three catalyst systems to afford the corresponding amides in moderate to excellent yields. The best results are obtained with sterically unhindered alcohols and amines. The three catalyst systems do not show any significant differences in reactivity, which indicates that the same catalytically active species is operating. The reaction is believed to proceed by initial dehydrogenation of the primary alcohol to the aldehyde that stays coordinated to ruthenium and is not released into the reaction mixture. Addition of the amine forms the hemiaminal that undergoes dehydrogenation to the amide. A catalytic cycle is proposed with the {(IiPr)Ru-II} species as the catalytically active components.

Dam, Johan Hygum; Osztrovszky, Gyorgyi

2010-01-01

26

Lipophilicity-dependent ruthenium N-heterocyclic carbene complexes as potential anticancer agents.  

Science.gov (United States)

Five Ru(ii)-N-heterocyclic carbenes (NHC) () were synthesized by reacting the appropriately substituted imidazolium chlorides with Ag2O, forming the NHC-silver chloride in situ followed by transmetalation with dimeric p-cymene ruthenium(ii) dichloride. All the complexes were characterized by NMR and ESI-MS, and complex was also characterized by single-crystal X-ray diffraction. The IC50 values of these five complexes were determined by the MTT-based assay on four human cancer cell lines, SKOV-3 (ovarian), PC-3 (prostate), MDA-MB-231 (breast) and EC109 (esophagus). The cytotoxicities of these complexes changed from a moderate effect to a fine one, corresponding to the increasing lipophilicity order of the complex of Complex showed the most cytotoxicity with the IC50 values 10.3 ± 0.3 ?M for SKOV-3, 2.9 ± 0.1 ?M for PC-3, 8.2 ± 0.6 ?M for MDA-MB-231, 6.4 ± 0.2 ?M for EC109 cell lines. Due to the superior cytotoxicity of complex against the PC-3 cell lines, further biological evaluations were carried out to elucidate its action mechanism. The morphologic changes and cell cycle analysis showed that complex can inhibit PC-3 cell lines by inducing cell cycle arrest at the G2/M phase. The DNA binding experiments further demonstrate that complex has a better binding ability for DNA (Kb = 2.2 × 10(6) M(-1)) than complexes (3.8 × 10(5), 7.0 × 10(5), 5.7 × 10(5), and 1.9 × 10(5) respectively). PMID:25797411

Lv, Gaochao; Guo, Liubin; Qiu, Ling; Yang, Hui; Wang, Tengfei; Liu, Hong; Lin, Jianguo

2015-04-01

27

Electrochemiluminescent ruthenium(II) N-heterocyclic carbene complexes: a combined experimental and theoretical study.  

Science.gov (United States)

A series of four Ru(II) complexes of the form [Ru(bpy)2(C(^)N)](2+) (where C(^)N is a bidentate pyridine-functionalized imidazolylidene- or benzimidazolylidene-based N-heterocyclic carbene (NHC) ligand and bpy is 2,2'-bipyridine) have been synthesized using a Ag(I) transmetalation protocol from the Ru(II) precursor compound, Ru(bpy)2Cl2. The synthesized azolium salts and Ru(II) complexes were characterized by elemental analysis, (1)H and (13)C NMR spectroscopy, cyclic voltammetry, and electronic absorption and emission spectroscopy. The molecular structures for two benzimidazolium salts and three Ru(II) complexes were determined by single crystal X-ray diffraction. The complexes display photoluminescence within the range 611-629 nm, with the emission wavelength of the benzimidazolylidene containing structures, slightly blue-shifted relative to the imidazolylidene containing complexes. All complexes exhibited a reversible, one-electron oxidation, which is assigned to the Ru(2+/3+) redox couple. When compared to [Ru(bpy)3](2+), complexes of imidazolylidene containing ligands were oxidized at more negative potentials, while those of the benzimidazolylidene containing ligands were oxidized at more positive potentials. All four complexes exhibited moderately intense electrochemiluminescence (ECL) with the obtained ECL spectra closely resembling the photoluminescence spectra. The ability to predictably fine-tune the highest occupied molecular orbital (HOMO) level of the Ru(II) complexes via the flexible synthetic strategy offered by NHCs is valuable for the design of ECL-based multiplexed detection strategies. PMID:23772555

Barbante, Gregory J; Francis, Paul S; Hogan, Conor F; Kheradmand, Peyman R; Wilson, David J D; Barnard, Peter J

2013-07-01

28

Chelated bis-N-heterocyclic carbene platinum and palladium units as tunable components of multinuclear complexes.  

Science.gov (United States)

Heterometallic trinuclear M2M' complexes (M = Rh, Ir; M' = Pt, Pd) containing a platinum or palladium moiety with chelated bis-N-heterocyclic carbene ligands, [(MCp*)2{M'(bisNHC-Cn-R)}(?3-S)2](BPh4)2 (M = Rh, Ir; M' = Pt, Pd; bisNHC-Cn-R = methylene-, ethylene-, or propylene-bridged bis(N-alkyl-imidazolylidene)), were synthesized by reacting bis(hydrosulfido)platinum(II) or palladium(II) complexs with bisNHC-Cn-R and hydroxo-bridged dinuclear complexes [(MCp*)2(?-OH)3](BPh4), whose dinuclear structures remained intact during the formation of the trinuclear complexes, which was confirmed by using electrospray mass spectrometry and NMR spectroscopy. The heterometallic trinuclear M2M' complexes with a variety of alkylene bridges in bisNHC-Cn-R showed two reversible reduction waves in the cyclic voltammogram, and the second reduction potentials were affected by the alkylene chain lengths, which caused different dihedral angles between the imidazolylidene rings and the coordination plane of the platinum or palladium center. The M2M' complexes, except for those containing the platinum unit with the ethylene-bridged bisNHC ligands, showed dynamic behavior in solution due to the flapping wing motion of the NHC ligand moieties. Although activation parameters obtained from line-shape analyses on variable-temperature NMR spectra of the complexes suggested that the flapping wing motion occurred without bond cleavage, large negative ?S(‡) values were obtained for the complexes with the palladium unit with the ethylene-bridged ligand, suggesting that the Pd-Ccarbene bond cleavage, accompanied by coordination of solvent molecules, occurred. PMID:25563064

Maeda, Yuri; Hashimoto, Hideki; Kinoshita, Isamu; Nishioka, Takanori

2015-01-20

29

Rhenium and technetium tricarbonyl complexes of N-heterocyclic carbene ligands.  

Science.gov (United States)

A strategy for the conjugation of N-heterocyclic carbene (NHC) ligands to biomolecules via amide bond formation is described. Both 1-(2-pyridyl)imidazolium or 1-(2-pyridyl)benzimidazolium salts functionalized with a pendant carboxylic acid group were prepared and coupled to glycine benzyl ester using 1-ethyl-3-(3-(dimethylamino)propyl)carbodiimide. A series of 10 rhenium(I) tricarbonyl complexes of the form [ReX(CO)3(?N)] (?N is a bidentate NHC ligand, and X is a monodentate anionic ligand: Cl(-), RCO2(-)) were synthesized via a Ag2O transmetalation protocol from the Re(I) precursor compound Re(CO)5Cl. The synthesized azolium salts and Re(I) complexes were characterized by elemental analysis and by (1)H and (13)C NMR spectroscopy, and the molecular structures for one imidazolium salt and seven Re(I) complexes were determined by single-crystal X-ray diffraction. (1)H NMR and mass spectrometry studies for an acetonitrile-d3 solution of [ReCl(CO)3(1-(2-pyridyl)-3-methylimidazolylidene)] show that the monodentate chloride ligand is labile and exchanges with this solvent yielding a cationic acetonitrile adduct. For the first time the labeling of an NHC ligand with technetium-99m is reported. Rapid Tc-99m labeling was achieved by heating the imidazolium salt 1-(2-pyridyl)-3-methylimidazolium iodide and Ag2O in methanol, followed by the addition of fac-[(99m)Tc(OH2)3(CO)3](+). To confirm the structure of the (99m)Tc-labeled complex, the equivalent (99)Tc complex was prepared, and mass spectrometric studies showed that the formed Tc complexes are of the form [(99m/99)Tc(CH3CN)(CO)3(1-(2-pyridyl)-3-methylimidazolylidene)](+) with an acetonitrile molecule coordinated to the metal center. PMID:25280253

Chan, Chung Ying; Pellegrini, Paul A; Greguric, Ivan; Barnard, Peter J

2014-10-20

30

Dehydrogenative Synthesis of Imines from Alcohols and Amines Catalyzed by a Ruthenium N-Heterocyclic Carbene Complex  

OpenAIRE

A new method for the direct synthesis of imines from alcohols and amines is described where hydrogen gas is liberated. The reaction is catalyzed by the ruthenium N-heterocyclic carbene complex [RuCl2(IiPr)(p-cymene)] in the presence of the ligand DABCO and molecular sieves. The imination can be applied to a variety of primary alcohols and amines and can be combined with a subsequent addition reaction. A deuterium labeling experiment indicates that the catalytically active species is a rutheni...

Maggi, Agnese; Madsen, Robert

2011-01-01

31

N-benzyl substituted N-heterocyclic carbene complexes of iridium(I): assessment in transfer hydrogenation catalyst.  

Science.gov (United States)

Iridium(I) complexes of N-heterocyclic carbenes (NHCs) (1a-3a) were obtained by transmetalation reactions from the corresponding Ag(I)-NHC complexes. These complexes have been fully characterized by (1)H, (13)C, heteronuclear multiple-bond correlation NMR spectroscopies, and elemental analysis. X-ray diffraction studies on single crystals of 1a and 2a confirm the square planar geometry at the metal center. [IrCl(CO)2(NHC)] complexes 1b-3b were also synthesized to compare ?-donor/?-acceptor strength of NHC ligands. Transfer hydrogenation (TH) reactions of various ketones and imines have been studied using complexes 1a-3a as precatalysts. N-Benzyl substituted NHC complexes of Ir(I) proved to be highly efficient precatalysts in the reduction of aromatic and aliphatic ketones to afford the corresponding alcohol products with turnover frequencies values up to 24,000 h(-1). PMID:24004417

Gülcemal, Süleyman; Gökçe, Aytaç Gürhan; Cetinkaya, Bekir

2013-09-16

32

Sulfur-Functionalized N-Heterocyclic Carbene Complexes of Pd(II: Syntheses, Structures and Catalytic Activities  

Directory of Open Access Journals (Sweden)

Full Text Available N-heterocyclic carbenes (NHCs can be easily modified by introducing functional groups at the nitrogen atoms, which leads to versatile coordination chemistry as well as diverse catalytic applications of the resulting complexes. This article summarizes our contributions to the field of NHCs bearing different types of sulfur functions, i.e., thioether, sulfoxide, thiophene, and thiolato. The experimental evidence for the truly hemilabile coordination behavior of a Pd(II thioether-NHC complex has been reported as well. In addition, complexes bearing rigid CSC-pincer ligands have been synthesized and the reasons for pincer versus pseudo-pincer formation investigated. Incorporation of the electron-rich thiolato function resulted in the isolation of structurally diverse complexes. The catalytic activities of selected complexes have been tested in Suzuki-Miyaura, Mizoroki-Heck and hydroamination reactions.

Dan Yuan

2012-03-01

33

N-heterocyclic carbene, high oxidation state molybdenum alkylidene complexes: functional-group-tolerant cationic metathesis catalysts.  

Science.gov (United States)

We synthesized the first N-heterocyclic carbene (NHC) complexes of Schrock's molybdenum imido alkylidene bis(triflate) complexes. Unlike existing bis(triflate) complexes, the novel 16-electron complexes represent metathesis active, functional-group-tolerant catalysts. Single-crystal X-ray structures of two representatives of this novel class of Schrock catalysts are presented and reactivity is discussed in view of their structural peculiarities. In the presence of monomer (substrate), these catalysts form cationic species and can be employed in ring-closing metathesis (RCM), ring-opening metathesis polymerization (ROMP), as well as in the cyclopolymerization of ?,?-diynes. Monomers containing functional groups, which are not tolerated by the existing variations of Schrock's catalyst, e.g., sec-amine, hydroxy, and carboxylic acid moieties, can be used. These catalysts therefore hold great promise in both organic and polymer chemistry, where they allow for the use of protic monomers. PMID:25123961

Buchmeiser, Michael R; Sen, Suman; Unold, Jörg; Frey, Wolfgang

2014-08-25

34

Forward molecular design for highly efficient OLED emitters: a theoretical analysis of photophysical properties of platinum(II) complexes with N-heterocyclic carbene ligands.  

Science.gov (United States)

The electronic structures and photophysical properties of eight Pt-complexes with different N-heterocyclic carbene ligands and potential to serve as light emitting diode materials were investigated by density functional theory and time-dependent density functional theory, employing the BP86 functional for geometry optimisations, SAOP potential for excited state calculations and all-electron TZ2P basis set throughout. Non-radiative and radiative decay rate constants were determined for each system through analyses of the geometric relaxations, d-orbital splitting and spin-orbit couplings at the optimised S(0) and T(1) geometries. Three Pt-systems bound to two N-heterocyclic carbenes were shown to be nonemissive, while a fourth was shown to be emissive from the T(1) excited state. Similar T(1)-initated emission was observed for three other Pt-systems investigated, each bound to four N-heterocyclic carbenes, while a fourth similarly tetra-ligated system showed T(2)-initation of emission. The results highlight the coupling of ligand-identity to photophysical properties and more importantly, the potential for rational optimisation and tuning of emission wavelengths and phosphorescent efficiencies. Encouragingly, two of the tetra-N-heterocyclic carbene ligated systems show strong potential to serve as highly-efficient blue and green light emitting materials, respectively. PMID:21409240

Wu, Yong; Wu, Shui-Xing; Li, Hai-Bin; Geng, Yun; Su, Zhong-Min

2011-05-01

35

An efficient N-heterocyclic carbene-ruthenium complex: application towards the synthesis of polyesters and polyamides.  

Science.gov (United States)

The ruthenium benzimidazolylidene-based N-heterocyclic carbene (NHC) complex 4 catalyzes the direct dehydrogenative condensation of primary alcohols into esters and primary alcohols in the presence of amines to the corresponding amides in high yields. This efficient new catalytic system shows a high selectivity towards the conversion of diols to polyesters and of a mixture of diols and diamines to polyamides. The only side product formed in this reaction is molecular hydrogen. Remarkable is the conversion of hydroxytelechelic polytetrahydrofuran (M¯n = 1000 g mol(-1) )-a polydispers starting material-into a hydrolytically degradable polyether with ester linkages (M¯n = 32 600 g mol(-1) ) and, in the presence of aliphatic diamines, into a polyether with amide linkages in the back bone (M¯n = 16 000 g mol(-1) ). PMID:25653190

Malineni, Jagadeesh; Keul, Helmut; Möller, Martin

2015-03-01

36

Dehydrogenative Synthesis of Imines from Alcohols and Amines Catalyzed by a Ruthenium N-Heterocyclic Carbene Complex  

DEFF Research Database (Denmark)

A new method for the direct synthesis of imines from alcohols and amines is described where hydrogen gas is liberated. The reaction is catalyzed by the ruthenium N-heterocyclic carbene complex [RuCl2(IiPr)(p-cymene)] in the presence of the ligand DABCO and molecular sieves. The imination can be applied to a variety of primary alcohols and amines and can be combined with a subsequent addition reaction. A deuterium labeling experiment indicates that the catalytically active species is a ruthenium dihydride. The reaction is believed to proceed by initial dehydrogenation of the alcohol to the aldehyde, which stays coordinated to ruthenium. Nucleophilic attack of the amine affords the hemiaminal, which is released from ruthenium and converted into the imine.

Maggi, Agnese; Madsen, Robert

2012-01-01

37

Stereoelectronic effects in C-H bond oxidation reactions of Ni(I) N-heterocyclic carbene complexes.  

Science.gov (United States)

Activation of O2 by the three-coordinate Ni(I) ring-expanded N-heterocyclic carbene complexes Ni(RE-NHC)(PPh3)Br (RE-NHC = 6-Mes, 1; 7-Mes, 2) produced the structurally characterized dimeric Ni(II) complexes Ni(6-Mes)(Br)(?-OH)(?-O-6-Mes')NiBr (3) and Ni(7-Mes)(Br)(?-OH)(?-O-7-Mes')NiBr (4) containing oxidized ortho-mesityl groups from one of the carbene ligands. NMR and mass spectrometry provided evidence for further oxidation in solution to afford bis-?-aryloxy compounds; the 6-Mes derivative was isolated, and its structure was verified. Low-temperature UV-visible spectroscopy showed that the reaction between 1 and O2 was too fast even at ca. -80 °C to yield any observable intermediates and also supported the formation of more than one oxidation product. Addition of O2 to Ni(I) precursors containing a less electron-donating diamidocarbene (6-MesDAC, 7) or less bulky 6- or 7-membered ring diaminocarbene ligands (6- or 7-o-Tol; 8 and 9) proceeded quite differently, affording phosphine and carbene oxidation products (Ni(O?PPh3)2Br2 and (6-MesDAC)?O) and the mononuclear Ni(II) dibromide complexes (Ni(6-o-Tol)(PPh3)Br2 (10) and (Ni(7-o-Tol)(PPh3)Br2 (11)) respectively. Electrochemical measurements on the five Ni(I) precursors show significantly higher redox potentials for 1 and 2, the complexes that undergo oxygen atom transfer from O2. PMID:24972307

Poulten, Rebecca C; López, Isidoro; Llobet, Antoni; Mahon, Mary F; Whittlesey, Michael K

2014-07-21

38

Triazole-functionalized N-heterocyclic carbene complexes of palladium and platinum and efficient aqueous Suzuki-Miyaura coupling reaction.  

Science.gov (United States)

Imidazolium salts bearing triazole groups are synthesized via a copper catalyzed click reaction, and the silver, palladium, and platinum complexes of their N-heterocyclic carbenes are studied. [Ag(4)(L1)(4)](PF(6))(4), [Pd(L1)Cl](PF(6)), [Pt(L1)Cl](PF(6)) (L1=3-((1-benzyl-1H-1,2,3-triazol-4-yl)methyl)-1-(pyrimidin-2-yl)-1H-imidazolylidene), [Pd(2)(L2)(2)Cl(2)](PF(6))(2), and [Pd(L2)(2)](PF(6))(2) (L2=1-butyl-3-((1-(pyridin-2-yl)-1H-1,2,3-triazol-4-yl)methyl)imidazolylidene) have been synthesized and fully characterized by NMR, elemental analysis, and X-ray crystallography. The silver complex [Ag(4)(L1)(4)](PF(6))(4) consists of a Ag(4) zigzag chain. The complexes [Pd(L1)Cl](PF(6)) and [Pt(L1)Cl](PF(6)), containing a nonsymmetrical NCN' pincer ligand, are square planar with a chloride trans to the carbene donor. [Pd(2)(L2)(2)Cl(2)](PF(6))(2) consists of two palladium centers with CN(2)Cl coordination mode, whereas the palladium in [Pd(L2)(2)](PF(6))(2) is surrounded by two carbene and two triazole groups with two uncoordinated pyridines. The palladium compounds are highly active for Suzuki-Miyaura cross coupling reactions of aryl bromides and 1,1-dibromo-1-alkenes in neat water under an air atmosphere. PMID:20503220

Gu, Shaojin; Xu, Hui; Zhang, Na; Chen, Wanzhi

2010-07-01

39

Preparation of a series of Ru(II) complexes with N-heterocyclic carbene ligands for the catalytic transfer hydrogenation of aromatic ketones.  

Science.gov (United States)

The reaction of [RuCl(2)(p-cymene](2) with Ag-N-heterocyclic carbene (NHC) complexes yields a series of [(p-cymene)Ru(NHC)] complexes (2a-f). All synthesised compounds were characterized by elemental analysis, NMR spectroscopy and the molecular structure of 2a was determined by X-ray crystallography. All complexes have been tested as catalysts for the transfer hydrogenation of aromatic ketones, showing excellent activity in this reaction. PMID:22182973

Gürbüz, Nevin; Özcan, Emine Özge; Özdemir, ?smail; Çetinkaya, Bekir; ?ahin, Onur; Büyükgüngör, Orhan

2012-02-28

40

Electronic Structure Determination of Pyridine N-Heterocyclic Carbene Iron Dinitrogen Complexes and Neutral Ligand Derivatives.  

Science.gov (United States)

The electronic structures of pyridine N-heterocyclic dicarbene ((iPr)CNC) iron complexes have been studied by a combination of spectroscopic and computational methods. The goal of these studies was to determine if this chelate engages in radical chemistry in reduced base metal compounds. The iron dinitrogen example ((iPr)CNC)Fe(N2)2 and the related pyridine derivative ((iPr)CNC)Fe(DMAP)(N2) were studied by NMR, Mössbauer, and X-ray absorption spectroscopy and are best described as redox non-innocent compounds with the (iPr)CNC chelate functioning as a classical ? acceptor and the iron being viewed as a hybrid between low-spin Fe(0) and Fe(II) oxidation states. This electronic description has been supported by spectroscopic data and DFT calculations. Addition of N,N-diallyl-tert-butylamine to ((iPr)CNC)Fe(N2)2 yielded the corresponding iron diene complex. Elucidation of the electronic structure again revealed the CNC chelate acting as a ? acceptor with no evidence for ligand-centered radicals. This ground state is in contrast with the case for the analogous bis(imino)pyridine iron complexes and may account for the lack of catalytic [2? + 2?] cycloaddition reactivity. PMID:25328270

Darmon, Jonathan M; Yu, Renyuan Pony; Semproni, Scott P; Turner, Zoë R; Stieber, S Chantal E; DeBeer, Serena; Chirik, Paul J

2014-10-13

41

Luminescent Ruthenium(II) Complex Bearing Bipyridine and N-Heterocyclic Carbene-based C?N?C Pincer Ligand for Live-Cell Imaging of Endocytosis  

Science.gov (United States)

Luminescent ruthenium(II)-cyanide complex with N-heterocyclic carbene pincer ligand C?N?C = 2,6-bis(1-butylimidazol-2-ylidene)pyridine and 2,2'-bipyridine (bpy) shows minimal cytotoxicity to both human breast carcinoma cell (MCF-7) and human retinal pigmented epithelium cell (RPE) in a wide range of concentration (0.1-500 ?M), and can be used for the luminescent imaging of endocytosis of the complex in these cells.

Tsui, Wai-Kuen; Chung, Lai-Hon; Wong, Matthew Man-Kin; Tsang, Wai-Him; Lo, Hoi-Shing; Liu, Yaxiang; Leung, Chung-Hang; Ma, Dik-Lung; Chiu, Sung-Kay; Wong, Chun-Yuen

2015-03-01

42

Luminescent Ruthenium(II) Complex Bearing Bipyridine and N-Heterocyclic Carbene-based C?N?C Pincer Ligand for Live-Cell Imaging of Endocytosis  

Science.gov (United States)

Luminescent ruthenium(II)-cyanide complex with N-heterocyclic carbene pincer ligand C?N?C = 2,6-bis(1-butylimidazol-2-ylidene)pyridine and 2,2?-bipyridine (bpy) shows minimal cytotoxicity to both human breast carcinoma cell (MCF-7) and human retinal pigmented epithelium cell (RPE) in a wide range of concentration (0.1–500??M), and can be used for the luminescent imaging of endocytosis of the complex in these cells. PMID:25765974

Tsui, Wai-Kuen; Chung, Lai-Hon; Wong, Matthew Man-Kin; Tsang, Wai-Him; Lo, Hoi-Shing; Liu, Yaxiang; Leung, Chung-Hang; Ma, Dik-Lung; Chiu, Sung-Kay; Wong, Chun-Yuen

2015-01-01

43

Luminescent Ruthenium(II) Complex Bearing Bipyridine and N-Heterocyclic Carbene-based C(?)N(?)C Pincer Ligand for Live-Cell Imaging of Endocytosis.  

Science.gov (United States)

Luminescent ruthenium(II)-cyanide complex with N-heterocyclic carbene pincer ligand C(?)N(?)C = 2,6-bis(1-butylimidazol-2-ylidene)pyridine and 2,2'-bipyridine (bpy) shows minimal cytotoxicity to both human breast carcinoma cell (MCF-7) and human retinal pigmented epithelium cell (RPE) in a wide range of concentration (0.1-500??M), and can be used for the luminescent imaging of endocytosis of the complex in these cells. PMID:25765974

Tsui, Wai-Kuen; Chung, Lai-Hon; Wong, Matthew Man-Kin; Tsang, Wai-Him; Lo, Hoi-Shing; Liu, Yaxiang; Leung, Chung-Hang; Ma, Dik-Lung; Chiu, Sung-Kay; Wong, Chun-Yuen

2015-01-01

44

Redox and luminescent properties of robust and air-stable N-heterocyclic carbene group 4 metal complexes.  

Science.gov (United States)

Robust and air-stable homoleptic group 4 complexes of the type M(L)2 [1-3; M = Ti, Zr, Hf; L = dianionic bis(aryloxide) N-heterocyclic carbene (NHC) ligand] were readily synthesized from the NHC proligand 1,3-bis(3,5-di-tert-butyl-2-hydroxyphenyl)imidazolinium chloride (H3L,Cl) and appropriate group 4 precursors. As deduced from cyclic voltammetry studies, the homoleptic bis-adduct zirconium and hafnium complexes 2 and 3 can also be oxidized, with up to four one-electron-oxidation signals for the zirconium derivative 2 (three reversible signals). Electron paramagnetic resonance data for the one-electron oxidation of complexes 1-3 agree with the formation of ligand-centered species. Compounds 2 and 3 are luminescent upon excitation in the absorption band at 362 nm with emissions at 485 and 534 nm with good quantum yields (? = 0.08 and 0.12) for 2 and 3, respectively. In contrast, the titanium complex 1 does not exhibit luminescent properties upon excitation in the absorption band at 310 and 395 nm. Complexes 2 and 3 constitute the first examples of emissive nonmetallocene group 4 metal complexes. PMID:24957272

Romain, Charles; Choua, Sylvie; Collin, Jean-Paul; Heinrich, Martine; Bailly, Corinne; Karmazin-Brelot, Lydia; Bellemin-Laponnaz, Stéphane; Dagorne, Samuel

2014-07-21

45

Synthesis and Characterization of Ag(I) and Pd(II) Complexes with a Pyridine Substituted N-Heterocyclic Carbene Ligand  

International Nuclear Information System (INIS)

We have used our new tridentate pyridine substituted N-heterocyclic carbene to generate an interesting trinuclear [((MepyCH2)2-Im)3Ag3]3+ complex, displaying very short Ag-Ag separations. A Pd(II)-NHC complex was prepared from [((MepyCH2)2-Im)3Ag3]3+ via a facile transmetallation, leading to a dimeric [(MepyCH2)2-ImPdCl]22+ complex. Future plans are underway for the survey of the potential applications of these new NHC complexes as luminesent materials or homogeneous catalysts. Since Arduengo's discovery of the first isolable free carbene in 1991, N-heterocyclic carbenes (NHC) have been extensively utilized as ligands for transition metals. NHC are generally more stable than two extreme types of carbenes, the Fischer and the Schrock carbenes. They are good ? donors like most tertiary phosphins, PR3, but the ?-bonding with the metal is rather weak. The thriving studies of NHC-coordinated metal complexes produced a wide range of applications from homogeneous catalysts to materials science

46

Synthesis and luminescent properties of cis bis-N-heterocyclic carbene platinum(II) bis-arylacetylide complexes.  

Science.gov (United States)

A series of luminescent N-heterocyclic carbene platinum(II) complexes, [(pmim)Pt(C?C-R)(2)] (R = C(6)H(5) (2), C(6)H(4)OMe (3), C(6)H(2)(OMe)(3) (4), C(6)H(4)NMe(2) (5), C(4)H(3)S (6), C(6)H(4)C?CC(6)H(5) (7), 1-pyrenyl (8), and C(6)H(4)F (9)), were successfully synthesized using the precursor (pmim)PtI(2), 1 (pmim = 1,1'-dipentyl-3,3'-methylene-diimidazoline-2,2'-diylidene). The X-ray crystal structures of 1, 4, 5, and 7 have been determined. These complexes showed long-lived emission in solution at room temperature. The emission origin of the complexes is tentatively assigned to be from triplet states of predominantly intraligand (IL) character with some mixing of metal-to-ligand charge-transfer (MLCT) character. TD-DFT and DFT calculations have been performed on most of the complexes to ascertain the nature of the excited state. Changes in the alkynyl ligands lead to a change in the absorption and emission maxima seen for these complexes in a potentially predictable way. PMID:21244032

Zhang, Yuzhen; Garg, Jai Anand; Michelin, Clement; Fox, Thomas; Blacque, Olivier; Venkatesan, Koushik

2011-02-21

47

Preparation of Ti(IV) fluoride N-heterocyclic carbene complexes.  

Science.gov (United States)

1,3,4,5-Tetramethylimidazol-2-ylidene (L(Me)) and 1,3-diisopropyl-4,5-dimethylimidazol-2-ylidene (L(iPr )) readily form complexes of trans-TiF4(L(Me))2 (1) and of trans-TiF4(L(iPr))2 (4) with TiF4 in THF, respectively. Complex 1 has been used as a precursor for preparing the Ti(IV) fluoride carbene complexes [{TiF2(L(Me))(NEt 2)}2(mu-F)2] (2) and (TiF4(L(Me))2)(NacNacLi) (3) (NacNac = HC(CMeN(2,6- iPr2C6H3))2). Complex 2 was prepared from the reaction of 1-3 equiv of 1 and 1 equiv of Ti(NEt2)4 or by reacting TiF4 with Ti(NEt2)4 and L(Me) in toluene. Complex 3 has been prepared from 1 and NacNacLi in toluene. Reaction of 1 and AlMe3 in toluene results in ligand transfer and formation of AlMe3(L(Me)). Complex 4 is unstable in solution at room temperature and degrades with formation of [HL(iPr)][TiF5(L(iPr))] (5). Complexes 1, 2.2CH2Cl2, 4, and 5 were characterized by single crystal X-ray structural analysis, elemental analysis, IR and NMR spectroscopy, and mass spectrometry. The relative basicities of L(Me), L (iPr), and the donor ligands THF, pyridine, DMSO, and H2O as well as [Cl](-) and [F](-) toward the Ti(IV) pentafluoride anion were established by NMR and confirmed by density functional theory (DFT) calculations. L(Me) and L(iPr ) are more basic than the mentioned molecular donors and more basic than chloride, however less basic than fluoride. PMID:18260620

Nikiforov, Grigory B; Roesky, Herbert W; Jones, Peter G; Magull, Jörg; Ringe, Arne; Oswald, Rainer B

2008-03-17

48

"Decarbonization" of an imino-N-heterocyclic carbene ligand via triple benzyl migration from hafnium.  

Science.gov (United States)

An imino-N-heterocyclic carbene underwent three sequential benzyl migrations upon reaction with tetrabenzylhafnium, resulting in complete removal of the carbene carbon from the ligand. The resulting eneamido-amidinato hafnium complex showed alkene polymerization activity comparable to that of a precatalyst containing the intact iminocarbene ligand. PMID:25790221

Prema, Dipesh; Mathota Arachchige, Yohan L N; Murray, Rex E; Slaughter, LeGrande M

2015-04-01

49

Iridium(I) N-heterocyclic carbene complexes of benzimidazol-2-ylidene: effect of electron donating groups on the catalytic transfer hydrogenation reaction.  

Science.gov (United States)

Two new [Ir(NHC)(COD)Cl] (NHC = N-heterocyclic carbene; COD = 1,5-cyclooctadiene) iridium complexes (2a,b) have been prepared by the reaction of [Ir(COD)Cl]2 with in situ prepared NHC-Ag carbene transfer agents in dichloromethane at ambient temperature. They have been fully characterized by (1)H, (13)C NMR, and elemental analysis. X-ray diffraction studies on single crystals of 2a and 2b confirm the square planar geometry. Complexes of type [Ir(NHC)(CO)2Cl] [NHC = 1,3-diisopropyl(5,6-dimethyl)benzimidazol-2-ylidene] 3 were also synthesized to compare ?-donor/?-acceptor strength of NHC ligands. Transfer hydrogenation (TH) reactions of various aldehydes and ketones have been studied using complexes 2a and 2b as catalysts. The 5,6-dimethyl substituted iridium complex (2b) showed the highest catalytic activity for the TH reaction. PMID:23223682

Gülcemal, Süleyman; Gökçe, Aytaç Gürhan; Çetinkaya, Bekir

2013-05-28

50

Synthesis, characterization and catalytic activity of novel N-heterocyclic carbene-palladium complexes.  

Science.gov (United States)

The reaction of Pd(OAc)2 with 1-(benzhydryl)-3-(alkyl)benzimidazolium salts 1a-d yields trans-bis[1-(benzhydryl)-3-(alkyl)benzimidazolin-2-ylidene]dibromopalladium(II) complexes (2a-d) which were characterized by elemental analysis, NMR spectroscopy and the molecular structures of 2b, and 2d were determined by X-ray crystallography. The catalytic activity of PdBr2bis(benzimidazolin-2-ylidene) complexes 2a-d was evaluated in the direct arylation reaction of benzothiazole with bromobenzene derivatives. PMID:20449152

Do?an, Oznur; Gürbüz, Nevin; Ozdemir, Ismail; Cetinkaya, Bekir; Sahin, Onur; Büyükgüngör, Orhan

2009-09-21

51

Synthesis of Silver (I Complexes of Iminoalkyl Functionalised N-Heterocyclic Carbenes  

Directory of Open Access Journals (Sweden)

Full Text Available A range of silver iminoalkyl imidazol-2-ylidene complexes have been isolated in good yield (50%–85% and characterised by 1H and 13C NMR spectroscopy. A single crystal X-ray diffraction structure determination of 1-{2-(benzylhydrylidene-amino-ethyl}-3-benzyl imidazol-2-ylidene silver bromide indicated monodentate coordination of the ligand.

Peter B. Hitchcock

2010-01-01

52

Alkyne hydroarylation with Au N-heterocyclic carbene catalysts  

Directory of Open Access Journals (Sweden)

Full Text Available Mono- and dinuclear gold complexes with N-heterocyclic carbene (NHC ligands have been employed as catalysts in the intermolecular hydroarylation of alkynes with simple unfunctionalised arenes. Both mono- and dinuclear gold(III complexes were able to catalyze the reaction; however, the best results were obtained with the mononuclear gold(I complex IPrAuCl. This complex, activated with one equivalent of silver tetrafluoroborate, exhibited under acidic conditions at room temperature much higher catalytic activity and selectivity compared to more commonly employed palladium(II catalysts. Moreover, the complex was active, albeit to a minor extent, even under neutral conditions, and exhibited lower activity but higher selectivity compared to the previously published complex AuCl(PPh3. Preliminary results on intramolecular hydroarylations using this catalytic system indicate, however, that alkyne hydration by traces of water may become a serious competing reaction.

Cristina Tubaro

2013-02-01

53

N-Heterocyclic Carbene Bound Nickel(I) Complexes and Their Roles in Catalysis  

OpenAIRE

New paramagnetic NiI(IMes)2X (IMes: 1,3-bis-(2,4,6-trimethylphenyl)-imidazol-2-ylidene) were prepared from the reaction of Ni(IMes)2 with aryl halides. Products that would arise from oxidative addition were not observed. In contrast, NiII(tmiy)2(X)(Ar) was formed from the oxidative addition of aryl halides to Ni bound by a sterically-less hindered NHC ligand, tmiy (tetramethylimidazol-2-ylidene). The paramagnetic NiI(IMes)2X complexes were compared to known Ni(0) and Ni(II) catalysts for Kuma...

Zhang, Kainan; Conda-sheridan, Martin; Cooke, Shayna; Louie, Janis

2011-01-01

54

N-heterocyclic carbene gold(I) and copper(I) complexes in C-H bond activation.  

Science.gov (United States)

Environmental concerns have and will continue to have a significant role in determining how chemistry is carried out. Chemists will be challenged to develop new, efficient synthetic processes that have the fewest possible steps leading to a target molecule, the goal being to decrease the amount of waste generated and reduce energy use. Along this path, chemists will need to develop highly selective reactions with atom-economical pathways producing nontoxic byproduct. In this context, C-H bond activation and functionalization is an extremely attractive method. Indeed, for most organic transformations, the presence of a reactive functionality is required. In Total Synthesis, the "protection and deprotection" approach with such reactive groups limits the overall yield of the synthesis, involves the generation of significant chemical waste, costs energy, and in the end is not as green as one would hope. In turn, if a C-H bond functionalization were possible, instead of the use of a prefunctionalized version of the said C-H bond, the number of steps in a synthesis would obviously be reduced. In this case, the C-H bond can be viewed as a dormant functional group that can be activated when necessary during the synthetic strategy. One issue increasing the challenge of such a desired reaction is selectivity. The cleavage of a C-H bond (bond dissociation requires between 85 and 105 kcal/mol) necessitates a high-energy species, which could quickly become a drawback for the control of chemo-, regio-, and stereoselectivity. Transition metal catalysts are useful reagents for surmounting this problem; they can decrease the kinetic barrier of the reaction yet retain control over selectivity. Transition metal complexes also offer important versatility in having distinct pathways that can lead to activation of the C-H bond. An oxidative addition of the metal in the C-H bond, and a base-assisted metal-carbon bond formation in which the base can be coordinated (or not) to the metal complexes are possible. These different C-H bond activation modes provide chemists with several synthetic options. In this Account, we discuss recent discoveries involving the versatile NHC-gold(I) and NHC-copper(I) hydroxide complexes (where NHC is N-heterocyclic carbene) showing interesting Brønsted basic properties for C-H bond activation or C-H bond functionalization purposes. The simple and easy synthesis of these two complexes involves their halide-bearing relatives reacting with simple alkali metal hydroxides. These complexes can react cleanly with organic compounds bearing protons with compatible pK(a) values, producing only water as byproduct. It is a very simple protocol indeed and may be sold as a C-H bond activation, although the less flashy "metalation reaction" also accurately describes the process. The synthesis of these complexes has led us to develop new organometallic chemistry and catalysis involving C-H bond activation (metalation) and subsequent C-H bond functionalization. We further highlight applications with these reactions, in areas such as photoluminescence and biological activities of NHC-gold(I) and NHC-copper(I) complexes. PMID:22166092

Gaillard, Sylvain; Cazin, Catherine S J; Nolan, Steven P

2012-06-19

55

Synthesis of the first radiolabeled 188Re N-heterocyclic carbene complex and initial studies on its potential use in radiopharmaceutical applications.  

Science.gov (United States)

A novel approach towards the synthesis of radiolabeled organometallic rhenium complexes is presented. We successfully synthesized and analyzed the first (188)Re-labeled N-heterocyclic biscarbene complex, trans-dioxobis(1,1'-methylene-bis(3,3'-diisopropylimidazolium-2-ylidene))(188)rhenium(V) hexafluorophosphate ((188)Re-4) via transmetalation using an air-stable and moisture-stable silver(I) biscarbene complex. In order to assess the viability of this complex as a potential lead structure for in vivo applications, the stability of the (188)Re-NHC complex was tested in physiologically relevant media. Ultimately, our studies illustrate that the complex we synthesized dissociates rapidly and is therefore unsuitable for use in radiopharmaceuticals. However, it is clear that the transmetalation approach we have developed is a rapid, robust, and mild method for the synthesis of new (188)Re-labeled carbene complexes. PMID:24889257

Wagner, Thomas; Zeglis, Brian M; Groveman, Sam; Hille, Claudia; Pöthig, Alexander; Francesconi, Lynn C; Herrmann, Wolfgang A; Kühn, Fritz E; Reiner, Thomas

2014-06-15

56

Synthesis of Well-Defined Copper "N"-Heterocyclic Carbene Complexes and Their Use as Catalysts for a "Click Reaction": A Multistep Experiment that Emphasizes the Role of Catalysis in Green Chemistry  

Science.gov (United States)

A multistep experiment for an advanced synthesis lab course that incorporates topics in organic-inorganic synthesis and catalysis and highlights green chemistry principles was developed. Students synthesized two "N"-heterocyclic carbene ligands, used them to prepare two well-defined copper(I) complexes and subsequently utilized the complexes as…

Ison, Elon A.; Ison, Ana

2012-01-01

57

Influence of pyrazolate vs N-heterocyclic carbene ligands on the slow magnetic relaxation of homoleptic trischelate lanthanide(III) and uranium(III) complexes.  

Science.gov (United States)

Two isostructural series of trigonal prismatic complexes, M(Bp(Me))3 and M(Bc(Me))3 (M = Y, Tb, Dy, Ho, Er, U; [Bp(Me)](-) = dihydrobis(methypyrazolyl)borate; [Bc(Me)](-) = dihydrobis(methylimidazolyl)borate) are synthesized and fully characterized to examine the influence of ligand donor strength on slow magnetic relaxation. Investigation of the dynamic magnetic properties reveals that the oblate electron density distributions of the Tb(3+), Dy(3+), and U(3+) metal ions within the axial ligand field lead to slow relaxation upon application of a small dc magnetic field. Significantly, the magnetization relaxation is orders of magnitude slower for the N-heterocyclic carbene complexes, M(Bc(Me))3, than for the isomeric pyrazolate complexes, M(Bp(Me))3. Further, investigation of magnetically dilute samples containing 11-14 mol % of Tb(3+), Dy(3+), or U(3+) within the corresponding Y(3+) complex matrix reveals thermally activated relaxation is favored for the M(Bc(Me))3 complexes, even when dipolar interactions are largely absent. Notably, the dilute species U(Bc(Me))3 exhibits Ueff ? 33 cm(-1), representing the highest barrier yet observed for a U(3+) molecule demonstrating slow relaxation. Additional analysis through lanthanide XANES, X-band EPR, and (1)H NMR spectroscopies provides evidence that the origin of the slower relaxation derives from the greater magnetic anisotropy enforced within the strongly donating N-heterocyclic carbene coordination sphere. These results show that, like molecular symmetry, ligand-donating ability is a variable that can be controlled to the advantage of the synthetic chemist in the design of single-molecule magnets with enhanced relaxation barriers. PMID:24650296

Meihaus, Katie R; Minasian, Stefan G; Lukens, Wayne W; Kozimor, Stosh A; Shuh, David K; Tyliszczak, Tolek; Long, Jeffrey R

2014-04-23

58

A new library of arsine, stibine-stabilized N-heterocyclic carbene palladium complexes: synthesis, structures and activities in C-C and C-N coupling reactions.  

Science.gov (United States)

A series of new N-heterocyclic carbene palladium complexes bearing AsPh3 and SbPh3 functions PdCl2(IMes)(AsPh3) (1a), PdCl2(IMes)(SbPh3) (1b), PdCl2(IPr)(AsPh3) (1c), PdCl2(IPr)(SbPh3) (1d), PdCl2(SIMes)(AsPh3) (2a), PdCl2(SIMes)(SbPh3) (2b), PdCl2(SIPr)(AsPh3) (2c), and PdCl2(SIPr)(SbPh3) (2d) (IMes = N,N'-bis-(2,4,6-trimethylphenyl)imidazol-2-ylidene; IPr = N,N'-bis-(2,6-di(iso-propyl)phenyl)imidazol-2-ylidene; SIMes = N,N'-bis-(2,4,6-trimethylphenyl)imidazolidin-2-ylidene; SIPr = N,N'-bis-(2,6-di(iso-propyl)phenyl)imidazolidin-2-ylidene) was synthesized and fully characterized by (1)H NMR, (13)C NMR, and FT-IR spectroscopy, elemental analysis and single-crystal X-ray crystallography. The catalytic potential of these arsine and stibine-stabilized carbene palladium complexes for Pd-mediated transformations was investigated with various substrates in the Hiyama cross-coupling reactions and Buchwald-Hartwig aminations. The results demonstrate that these complexes show high catalytic activity and good tolerance to various chemical functions. PMID:25133960

Yang, Jin; Li, Pinhua; Zhang, Yicheng; Wang, Lei

2014-10-01

59

Direct amination of homoenolates catalyzed by N-heterocyclic carbenes.  

Science.gov (United States)

N-Heterocyclic carbenes derived from N-mesityl-N-methyltriazolium salts are effective catalysts for generating homoenolate species from alpha,beta-unsaturated aldehydes. The unique intermediate adds to the electrophilic nitrogen of 1-acyl-2-aryldiazenes, and the resulting activated carbonyl unit undergoes an intramolecular acylation event. This formal [3+2] cycloaddition between alpha,beta-unsaturated aldehydes and acylaryldiazenes, catalyzed by an N-heterocyclic carbene, produces substituted pyrazolidinones in good yields. This new NHC-catalyzed reaction accommodates aromatic and alkyl alpha,beta-unsaturated aldehydes and various aromatic diazenes. A chiral triazolium salt catalyzes the formation of the pyrazolidinone product in moderate yield and good enantioselectivity. The pyrazolidinones can undergo reductive N-N bond cleavage to give beta-amino acid derivatives. PMID:18260665

Chan, Audrey; Scheidt, Karl A

2008-03-01

60

A Cooperative N-Heterocyclic Carbene/Palladium Catalysis System.  

Science.gov (United States)

N-heterocyclic carbenes (NHC) have been extensively studied as organocatalysts and ligands for transition metals, but the successful integration of NHCs and late transition metals in cooperative catalysis remains an underexplored area. We have developed a cooperative palladium-catalyzed allylation of NHC-activated aldehydes to access a variety of 3-allyl dihydrocoumarin derivatives. Kinetic experiments support a cooperative pathway for this transformation. PMID:25364496

Liu, Kun; Hovey, M Todd; Scheidt, Karl A

2014-10-01

61

Modulating reactivity in iridium bis(N-heterocyclic carbene) complexes: influence of ring size on E-H bond activation chemistry.  

Science.gov (United States)

The changes in the steric and electronic properties of N-heterocyclic carbenes (NHCs) as a function of ring size have a profound effect on the reactivity of their late transition metal complexes. Comparison of closely related complexes featuring either a saturated 5- or 6-membered NHC, reveals that the larger ring is associated with an increased propensity towards intramolecular C-H activation, but with markedly lower reactivity towards external substrates. Thus, systems of the type [IrL2(H)2](+) give rise to contrasting chemical behaviour, primarily reflecting the differing possibilities for secondary stabilization of the metal centre by the N-bound aryl substituents: highly labile [Ir(5-Mes)2(H)2](+) can only be studied by trapping experiments, while [Ir(6-Mes)2(H)2](+) is air and moisture stable, and unreactive towards many external reagents. With appropriate substrates, this heightened reactivity can be exploited, and in situ generated [Ir(5-Mes)2(H)2](+) is capable of intermolecular B-H and N-H activation chemistry. In the case of H3B·NMe2H, this affords a rare opportunity to study amine/aminoborane coordination via single crystal neutron diffraction methods. PMID:24986367

Phillips, Nicholas; Tang, Christina Y; Tirfoin, Rémi; Kelly, Michael J; Thompson, Amber L; Gutmann, Matthias J; Aldridge, Simon

2014-08-28

62

Macrophage and colon tumor cells as targets for a binuclear silver(I) N-heterocyclic carbene complex, an anti-inflammatory and apoptosis mediator.  

Science.gov (United States)

Chronic inflammation intensifies the risk for malignant neoplasm, indicating that curbing inflammation could be a valid strategy to prevent or cure cancer. Cancer and inflammation are inter-related diseases and many anti-inflammatory agents are also used in chemotherapy. Earlier, we have reported a series of novel ligands and respective binuclear Ag(I)-NHC complexes (NHC=N-heterocyclic carbene) with potential anticancer activity. In the present study, a newly synthesized salt (II) and respective Ag(I)-NHC complex (III) of comparable molecular framework were prepared for a further detailed study. Preliminarily, II and III were screened against HCT-116 and PC-3 cells, wherein III showed better results than II. Both the compounds showed negligible toxicity against normal CCD-18Co cells. In FAM-FLICA caspase assay, III remarkably induced caspase-3/7 in HCT-116 cells most probably by tumor necrosis factor-alpha (TNF-?) independent intrinsic pathway and significantly inhibited in vitro synthesis of cytokines, interleukin-1 (IL-1) and TNF-? in human macrophages (U937 cells). In a cell-free system, both the compounds inhibited cyclooxygenase (COX) activities, with III being more selective towards COX-2. The results revealed that III has strong antiproliferative property selectively against colorectal tumor cells which could be attributed to its pro-apoptotic and anti-inflammatory abilities. PMID:25699476

Iqbal, Muhammad Adnan; Umar, Muhammad Ihtisham; Haque, Rosenani A; Khadeer Ahamed, Mohamed B; Asmawi, Mohd Zaini Bin; Majid, Amin Malik Shah Abdul

2015-05-01

63

Visible-Light Photoredox Catalysis: Selective Reduction of Carbon Dioxide to Carbon Monoxide by a Nickel N-Heterocyclic Carbene-Isoquinoline Complex  

Energy Technology Data Exchange (ETDEWEB)

The solar-driven reduction of carbon dioxide to value-added chemical fuels is a longstanding challenge in the fields of catalysis, energy science, and green chemistry. In order to develop effective CO2 fixation, several key considerations must be balanced, including (1) catalyst selectivity for promoting CO2 reduction over competing hydrogen generation from proton reduction, (2) visible-light harvesting that matches the solar spectrum, and (3) the use of cheap and earth-abundant catalytic components. In this report, we present the synthesis and characterization of a new family of earth-abundant nickel complexes supported by N-heterocyclic carbene amine ligands that exhibit high selectivity and activity for the electrocatalytic and photocatalytic conversion of CO2 to CO. Systematic changes in the carbene and amine donors of the ligand have been surveyed, and [Ni(Prbimiq1)]2+ (1c, where Prbimiq1 = bis(3-(imidazolyl)isoquinolinyl)propane) emerges as a catalyst for electrochemical reduction of CO2 with the lowest cathodic onset potential (Ecat = 1.2 V vs SCE). Using this earth-abundant catalyst with Ir(ppy)3 (where ppy = 2-phenylpyridine) and an electron donor, we have developed a visible-light photoredox system for the catalytic conversion of CO2 to CO that proceeds with high selectivity and activity and achieves turnover numbers and turnover frequencies reaching 98,000 and 3.9 s1, respectively. Further studies reveal that the overall efficiency of this solar-to-fuel cycle may be limited by the formation of the active Ni catalyst and/or the chemical reduction of CO2 to CO at the reduced nickel center and provide a starting point for improved photoredox systems for sustainable carbon-neutral energy conversion.

Thoi, VanSara; Kornienko, Nick; Margarit, C; Yang, Peidong; Chang, Christopher

2013-06-07

64

The Depolymerization of Poly(Ethylene Terephthalate) (PET) Using N-Heterocyclic Carbenes from Ionic Liquids  

Science.gov (United States)

The depolymerization of the plastic polyethylene terephthalate (PET or PETE) is described in this laboratory procedure. The transesterification reaction used to depolymerize PET employs a highly efficient N-heterocyclic carbene catalyst derived from a commercially available imidazolium ionic liquid. N-heterocyclic carbenes are potent nucleophilic…

Kamber, Nahrain E.; Tsujii, Yasuhito; Keets, Kate; Waymouth, Robert M.; Pratt, Russell C.; Nyce, Gregory W.; Hedrick, James L.

2010-01-01

65

Mixed N-Heterocyclic Carbene-Bis(oxazolinyl)borato Rhodium and Iridium Complexes in Photochemical and Thermal Oxidative Addition Reactions  

Energy Technology Data Exchange (ETDEWEB)

In order to facilitate oxidative addition chemistry of fac-coordinated rhodium(I) and iridium(I) compounds, carbene–bis(oxazolinyl)phenylborate proligands have been synthesized and reacted with organometallic precursors. Two proligands, PhB(OxMe2)2(ImtBuH) (H[1]; OxMe2 = 4,4-dimethyl-2-oxazoline; ImtBuH = 1-tert-butylimidazole) and PhB(OxMe2)2(ImMesH) (H[2]; ImMesH = 1-mesitylimidazole), are deprotonated with potassium benzyl to generate K[1] and K[2], and these potassium compounds serve as reagents for the synthesis of a series of rhodium and iridium complexes. Cyclooctadiene and dicarbonyl compounds {PhB(OxMe2)2ImtBu}Rh(?4-C8H12) (3), {PhB(OxMe2)2ImMes}Rh(?4-C8H12) (4), {PhB(OxMe2)2ImMes}Rh(CO)2 (5), {PhB(OxMe2)2ImMes}Ir(?4-C8H12) (6), and {PhB(OxMe2)2ImMes}Ir(CO)2 (7) are synthesized along with ToMM(?4-C8H12) (M = Rh (8); M = Ir (9); ToM = tris(4,4-dimethyl-2-oxazolinyl)phenylborate). The spectroscopic and structural properties and reactivity of this series of compounds show electronic and steric effects of substituents on the imidazole (tert-butyl vs mesityl), effects of replacing an oxazoline in ToM with a carbene donor, and the influence of the donor ligand (CO vs C8H12). The reactions of K[2] and [M(?-Cl)(?2-C8H14)2]2 (M = Rh, Ir) provide {?4-PhB(OxMe2)2ImMes?CH2}Rh(?-H)(?-Cl)Rh(?2-C8H14)2 (10) and {PhB(OxMe2)2ImMes}IrH(?3-C8H13) (11). In the former compound, a spontaneous oxidative addition of a mesityl ortho-methyl to give a mixed-valent dirhodium species is observed, while the iridium compound forms a monometallic allyl hydride. Photochemical reactions of dicarbonyl compounds 5 and 7 result in C–H bond oxidative addition providing the compounds {?4-PhB(OxMe2)2ImMes?CH2}RhH(CO) (12) and {PhB(OxMe2)2ImMes}IrH(Ph)CO (13). In 12, oxidative addition results in cyclometalation of the mesityl ortho-methyl similar to 10, whereas the iridium compound reacts with the benzene solvent to give a rare crystallographically characterized cis-[Ir](H)(Ph) complex. Alternatively, the rhodium carbonyl 5 or iridium isocyanide {PhB(OxMe2)2ImMes}Ir(CO)CNtBu (15) reacts with PhSiH3 in the dark to form the silyl compound {PhB(OxMe2)2ImMes}RhH(SiH2Ph)CO (14) or {PhB(OxMe2)2ImMes}IrH(SiH2Ph)CNtBu (17). These examples demonstrate the enhanced thermal reactivity of {PhB(OxMe2)2ImMes}-supported iridium and rhodium carbonyl compounds in comparison to tris(oxazolinyl)borate, tris(pyrazolyl)borate, and cyclopentadienyl-supported compounds.

Xu, Songchen [Ames Laboratory; Manna, Kuntal [Ames Laboratory; Ellern, Arkady [Ames Laboratory; Sadow, Aaron D [Ames Laboratory

2014-12-08

66

Silver(I) complexes of mono- and bidentate N-heterocyclic carbene ligands: synthesis, crystal structures, and in vitro antibacterial and anticancer studies.  

Science.gov (United States)

A series of benzimidazole-based N-heterocyclic carbene (NHC) proligands {1-benzyl-3-(2-methylbenzyl)-benzimidazolium bromide/hexafluorophosphate (1/4), 1,3-bis(2-methylbenzyl)-benzimidazolium bromide/hexafluorophosphate (2/5) and 1,3-bis(3-(2-methylbenzyl)-benzimidazolium-1-ylmethylbenzene dibromide/dihexafluorophosphate (3/6)} has been synthesized by the successive N-alkylation method. Ag complexes {1-benzyl-3-(2-methylbenzyl)-benzimidazol-2-ylidenesilver(I) hexafluorophosphate (7), 1,3-bis(2-methylbenzyl)-benzimidazol-2-ylidenesilver(I) hexafluorophosphate (8) and 1,3-bis(3-(2-methylbenzyl)-benzimidazol-2-ylidene)-1-ylmethylbenzene disilver(I) dihexafluorophosphate (9)} of NHC ligands have been synthesized by the treatment of benzimidazolium salts with Ag2O at mild reaction conditions. Both, NHC proligands and Ag-NHC complexes have been characterized by (1)H and (13)C{(1)H} NMR and FTIR spectroscopy and elemental analysis technique. Additionally, the structure of the NHC proligand 5 and the mononuclear Ag complexes 7 and 8 has been elucidated by the single crystal X-ray diffraction analysis. Both the complexes exhibit the same general structural motif with linear coordination geometry around the Ag centre having two NHC ligands. Preliminary in vitro antibacterial potentials of reported compounds against a Gram negative (Escherichia coli) and a Gram positive (Bacillus subtilis) bacteria evidenced the higher activity of mononuclear silver(I) complexes. The anticancer studies against the human derived colorectal cancer (HCT 116) and colorectal adenocarcinoma (HT29) cell lines using the MTT assay method, revealed the higher activity of Ag-NHC complexes. The benzimidazolium salts 4-6 and Ag-NHC complexes 7-9 displayed the following IC50 values against the HCT 116 and HT29 cell lines, respectively, 31.8 ± 1.9, 15.2 ± 1.5, 4.8 ± 0.6, 10.5 ± 1.0, 18.7 ± 1.6, 1.20 ± 0.3 and 245.0 ± 4.6, 8.7 ± 0.8, 146.1 ± 3.1, 7.6 ± 0.7, 5.5 ± 0.8, 103.0 ± 2.3 ?M. PMID:25461313

Haque, Rosenani A; Choo, Sze Yii; Budagumpi, Srinivasa; Iqbal, Muhammad Adnan; Al-Ashraf Abdullah, Amirul

2015-01-27

67

N-Heterocyclic carbene functionalized goup 7-9 transition metal  

OpenAIRE

The N-heterocyclic carbene (NHC) functionalized phosphinidene complexes [(pCy)(IiPr2Me2)- RudPMes*] (4), [(pCy)(IiPr2Me2)OsdPMes*] (6), and [(Cp*)(IiPr2Me2)RhdPMes*] (7) were generated by a double-dehydrohalogenation-ligation sequence of the corresponding primary phosphine complexes with 3 equiv of NHC. The effect of the NHC ligand on the electronic properties of the phosphinidene complexes [(Ring)(NHC)MdPH] (8-16), bearing group 7-9 transition metals and cycloheptatrienyl (Cht...

Aktas, H.; Slootweg, J. C.; Ehlers, A. W.; Lutz, M.; Spek, A. L.; Lammertsma, K.

2009-01-01

68

Dehydrogenative Coupling of Primary Alcohols To Form Esters Catalyzed by a Ruthenium N-Heterocyclic Carbene Complex  

DEFF Research Database (Denmark)

The ruthenium complex [RuCl2(IiPr)(p-cymene)] catalyzes the direct condensation of primary alcohols into esters and lactones with the release of hydrogen gas. The reaction is most effective with linear aliphatic alcohols and 1,4-diols and is believed to proceed with a ruthenium dihydride as the catalytically active species.

SØlvhØj, Amanda Birgitte; Madsen, Robert

2011-01-01

69

Highly stable water-soluble platinum nanoparticles stabilized by hydrophilic N-heterocyclic carbenes.  

Science.gov (United States)

Controlling the synthesis of stable metal nanoparticles in water is a current challenge in nanochemistry. The strategy presented herein uses sulfonated N-heterocyclic carbene (NHC) ligands to stabilize platinum nanoparticles (PtNPs) in water, under air, for an indefinite time period. The particles were prepared by thermal decomposition of a preformed molecular Pt?complex containing the NHC ligand and were then purified by dialysis and characterized by TEM, high-resolution TEM, and spectroscopic techniques. Solid-state NMR studies showed coordination of the carbene ligands to the nanoparticle surface and allowed the determination of a (13)C-(195)Pt?coupling constant for the first time in a nanosystem (940?Hz). Additionally, in one case a novel structure was formed in which platinum(II) NHC complexes form a second coordination sphere around the nanoparticle. PMID:25267410

Baquero, Edwin A; Tricard, Simon; Flores, Juan Carlos; de Jesús, Ernesto; Chaudret, Bruno

2014-11-24

70

Comproportionation of Cationic and Anionic Tungsten Complexes Having an N-Heterocyclic Carbene Ligand to Give the Isolable 17-Electron Tungsten Radical, CpW(CO)2(IMes)•  

Energy Technology Data Exchange (ETDEWEB)

A series consisting of a tungsten anion, radical and cation, supported by the N-heterocyclic carbene IMes (1,3-bis(2,4,6-trimethylphenyl)imidazol-2-ylidene) and spanning formal oxidation states W(0), W(I) and W(II), has been synthesized, isolated, and characterized. Reaction of the hydride CpW(CO)2(IMes)H with KH and 18 crown 6 gives the tungsten anion [CpW(CO)2(IMes)]-[K(18 crown 6)]+. The crystal structure of this complex shows that the K+ interacts not only with the oxygen atoms in the crown ether, but also with the carbonyl oxygens. The electrochemical oxidation of [CpW(CO)2(IMes)]- in acetonitrile is fully reversible (E½ = ?1.65 V vs Cp2Fe+•/0) at all scan rates, indicating that CpW(CO)2(IMes)• is a persistent radical. Hydride transfer from CpW(CO)2(IMes)H to Ph3C+PF6 affords [cis-CpW(CO)2(IMes)(MeCN)]+PF6 . Comproportionation of [CpW(CO)2(IMes)]- with [CpW(CO)2(IMes)(MeCN)]+ gives the 17-electron tungsten radical CpW(CO)2(IMes)•. This complex shows paramagnetically shifted resonances in 1H NMR spectra and has been characterized by IR spectroscopy, low-temperature EPR spectroscopy, and X-ray diffraction. CpW(CO)2(IMes)• is very stable with respect to disproportionation and dimerization. NMR studies of degenerate electron transfer between CpW(CO)2(IMes)• and [CpW(CO)2(IMes)]- are reported. DFT calculations were carried out on CpW(CO)2(IMes)H, as well as on related complexes bearing NHC ligands with N,N´ substituents Me [CpW(CO)2(IMe)H] or H [CpW(CO)2(IH)H] to compare to the experimentally studied IMes complexes with mesityl substituents. These calculations reveal W H homolytic bond dissociation energies (BDEs) to decrease with increasing steric bulk of the NHC ligand, from 67 for CpW(CO)2(IH)H to 64 for CpW(CO)2(IMe)H to 63 kcal/mol for CpW(CO)2(IMes)H. The calculated spin density at W for CpW(CO)2(IMes)• is 0.63. The W radicals CpW(CO)2(IMe)• and CpW(CO)2(IH)• are calculated to form weak W W bonds. The weakly bonded complexes [CpW(CO)2(IMe)]2 and [CpW(CO)2(IH)]2, are predicted to have W-W BDEs of 6 and 18 kcal/mol, respectively, and to dissociate readily to the W-centered radicals CpW(CO)2(IMe)• and CpW(CO)2(IH)•. This work was supported by the US Department of Energy Basic Energy Sciences' Chemical Sciences, Geosciences & Biosciences Division. Pacific Northwest National Laboratory is operated by Battelle for the US Department of Energy.

Roberts, John A.; Franz, James A.; van der Eide, Edwin F.; Walter, Eric D.; Petersen, Jeffrey L.; DuBois, Daniel L.; Bullock, R. Morris

2011-09-21

71

Calix[4]arenes with one and two N-linked imidazolium units as precursors of N-heterocyclic carbene complexes. Coordination chemistry and use in Suzuki-Miyaura cross-coupling.  

Science.gov (United States)

The calix[4]arene-imidazolium salts 5-(3-butyl-1-imidazolylium)-25,26,27,28-tetrabenzyloxy-calix[4]arene bromide (cone) (2), and 5,11-bis(3-alkyl-1-imidazolylium)-25,26,27,28-tetrabenzyloxycalix[4]arene diiodide (cone) (R = methyl, 3a; R = n-butyl, 3b) have been synthesised. Reaction of 2 in dioxane with PdCl(2) in the presence of CsCO(3) and KBr (80 °C, 24 h) gives the carbene complex trans-[PdBr(2)(calix-monocarbene)(2)] (14), containing two N-heterocyclic carbene ligands derived from 2 (yield: 63%). Repeating the reaction in pyridine instead of dioxane gives the mixed pyridine-carbene complex trans-[PdBr(2)(calix-carbene)(pyridine)] (15) in 75% yield. Treatment of the bis-imidazolium salt 3a with [Pd(OAc)(2)] affords a chelate complex, trans-[PdI(2){calix-bis(carbene)}] (16), in which a metallo-(bis-carbene) fragment caps the upper rim of the calixarene basket. Complex 16, as well as its analogue 17, obtained from 3b, display apparent C(s)-symmetry in solution. This is not the case in the solid state, a single X-ray diffraction study carried out for 16 revealing a pinced cone structure for the calixarene skeleton, which reduces the symmetry to C(1). The chelate complex 17 shows poor activity in Suzuki-Miyaura cross-coupling of phenyl boronic acid and p-tolyl halides, an observation that suggests the presence of a strained metallocyclic unit preventing easy stereochemical rearrangement to an active species. Unlike 17, complexes 14 and 15 show good activities in cross-coupling. A comparative study using the carbene precursor 1-butyl-3-(2,6-diisopropylphenyl)imidazolium bromide (18), which is devoid of the receptor fragment, strongly suggests that the carbene ligands of 14 and 15 operate typically as bulky NHC-ligands. PMID:21879086

Brenner, Eric; Matt, Dominique; Henrion, Mickaël; Teci, Matthieu; Toupet, Loïc

2011-10-14

72

Evaluation of an olefin metathesis pre-catalyst with a bulky and electron-rich N-heterocyclic carbene  

KAUST Repository

The commercially-available metathesis pre-catalyst M23 has been evaluated alongside new complex [RuCl2((3-phenyl)indenylidene)(PPh3)(SIPrOMe)] (1), which bears a para-methoxy-substituted N-heterocyclic carbene ligand. Several model metathesis reactions could be conducted using only parts-per-million levels of ruthenium catalyst. The effects of the different NHC ligands on reactivity have been explored.

Manzini, Simone

2015-03-01

73

Practical Heck-Mizoroki coupling protocol for challenging substrates mediated by an N-heterocyclic carbene-ligated palladacycle.  

Science.gov (United States)

A highly active, N-heterocyclic carbene-palladacycle precatalyst for the Heck-Mizoroki reaction was rationally designed. The complex can be synthesized on a large scale in excellent yield by a novel, one-pot, three-component reaction and is tolerant to air, moisture, and long-term storage. A wide range of challenging substrates is successfully coupled under a simple and user-friendly reaction protocol. PMID:18710241

Kantchev, Eric Assen B; Peh, Guang-Rong; Zhang, Chi; Ying, Jackie Y

2008-09-18

74

A Tungsten Complex with a Bidentate, Hemilabile N-Heterocyclic Carbene Ligand, Facile Displacement of the Weakly Bound W-(C=C) Bond, and the Vulnerability of the NHC Ligand Toward Catalyst Deactivation During Ketone Hydrogenation  

Energy Technology Data Exchange (ETDEWEB)

The initial reaction observed between N-heterocyclic carbene IMes (IMes = 1,3-bis(2,4,6-trimethylphenyl)-imidazol-2-ylidene) and molybdenum and tungsten hydride complexes CpM(CO)2(PPh3)H (M = Mo, W) is deprotonation of the metal hydride by IMes, giving [(IMes)H]+[CpM(CO)2(PPh3)]– . At longer reaction times and higher temperatures, the reaction of IMes with CpM(CO)2(PR3)H (M = Mo, W; R = Me, Ph) produces CpM(CO)2(IMes)H. Hydride transfer from CpW(CO)2(IMes)H to Ph3C+B(C6F5)4- gives CpW(CO)2(IMes)+B(C6F5)4- which was crystallographically characterized using x-ray radiation from a synchrotron. The IMes is bonded as a bidentate ligand, through the carbon of the carbene as well as forming a weak bond from the metal to a C=C bond of one mesityl ring. The weakly bound C=C ligand is hemilabile, being readily displaced by H2, THF, ketones or alcohols. Reaction of CpW(CO)2(IMes)+ with H2 gives the dihydride complex [CpW(CO)2(IMes)(H)2]+. Addition of Et2CH–OH to CpW(CO)2(IMes)+B(C6F5)4- gives the alcohol complex [CpM(CO)2(IMes)(Et2CH–OH)]+[B(C6F5)4]– which was characterized by crystallography and exhibits no evidence for hydrogen bonding of the bound OH group. Addition of H2 to the ketone complex [CpW(CO)2(IMes)(Et2C=O)]+[B(C6F5)4]– produces an equilibrium with the dihydride [CpW(CO)2(IMes)(H)2]+ (Keq = 1.1 ? 103 at 25 °C). The tungsten ketone complex [CpW(CO)2(IMes)(Et2C=O)]+[B(C6F5)4]– serves as a modest catalyst for hydrogenation of Et2C=O to Et2CH–OH in neat ketone solvent. Decomposition of the catalyst produces [H(IMes)]+B(C6F5)4-, indicating that these catalysts with N-heterocyclic carbenes ligands are vulnerable to decomposition by a reaction that produces a protonated imidazolium cation.

Wu, Fan; Dioumaev, Vladimir K.; Szalda, David J.; Hanson, Jonathan; Bullock, R. Morris

2007-09-24

75

N?Heterocyclic Carbene and Brønsted Acid Cooperative Catalysis: Asymmetric Synthesis of trans???Lactams  

OpenAIRE

An efficient enantioselective approach to form trans-?-lactams in up to 99% yield, 93% ee and >20/1 dr using unactivated imines has been developed. The cyclohexyl-substituted azolium and the weak base sodium o-chlorobenzoate are most suitable for this transformation. Notably, the process involves cooperative catalysis by N-heterocyclic carbene and Brønsted acid.

Zhao, Xiaodan; Dirocco, Daniel A.; Rovis, Tomislav

2011-01-01

76

N-Heterocyclic Carbene-Catalyzed Alcohol Acetylation: An Organic Experiment Using Organocatalysis  

Science.gov (United States)

Undergraduate students in the teaching laboratory have successfully used N-heterocyclic carbenes (NHCs) as organocatalysts for the acetylation of primary alcohols, despite the high water sensitivity of uncomplexed ("free") NHCs. The free NHC readily reacted with chloroform, resulting in an air- and moisture-stable adduct that liberates…

Morgan, John P.; Shrimp, Jonathan H.

2014-01-01

77

Isolation of an imino-N-heterocyclic carbene/germanium(0) adduct: a mesoionic germylene equivalent.  

Science.gov (United States)

An autoionization of germanium dichloride/dioxane complex with an imino-N-heterocyclic carbene ligand (L) afforded a novel germyliumylidene ion, [(L)GeCl](+)[GeCl3](-), which was fully characterized. Reduction of the germyliumylidene ion with potassium graphite produced a cyclic species [(L)Ge], which can be viewed as both a Ge(0) species and a mesoionic germylene. X-ray diffraction analysis and computational studies revealed one of the lone pairs on the Ge atom is involved in the ??system on the GeC2N2 five-membered ring. It was also confirmed that the nucleophilic behavior of [(L)Ge] as a two lone-pair donor. PMID:25283638

Su, Bochao; Ganguly, Rakesh; Li, Yongxin; Kinjo, Rei

2014-11-24

78

Injection, transport, absorption and phosphorescence properties of a series of platinum (II) complexes with N-heterocyclic carbenes: a DFT and time-dependent DFT study.  

Science.gov (United States)

The ground and excited states, charge injection/transport, and phosphorescence properties of five N?heterocyclic carbine-functionalized Pt(II) complexes were investigated by using the DFT method. By analyzing the nonradiative (k nr) rate constant and energies at [Formula: see text] and [Formula: see text] states, it is possible to forecast that BC5 with the pyrrole ligand has a higher phosphorescence quantum yield than any of the other four complexes. Thus, we consider that BC5 will be an efficient phosphorescent material that has balanced electron/hole-transport performance as well as high phosphorescence quantum yield. The calculated results indicate that, for the studied complexes, the nature of the ligand strongly affected the energy of the emissive state and was able to tune the emission color. We hope that our study will aid better understanding of the structure-property relationship of phosphorescent Pt (II) complexes and provide constructive information for designing novel and highly efficient OLED materials in the future. PMID:25227448

Li, Leijiao; Liu, Xiaojuan; Feng, Jing; Song, Shuyan; Zhang, Hongjie

2014-10-01

79

Syntheses and characterizations of thiolato-functionalized N-heterocyclic carbene Pd(II) complexes with normal and mesoionic binding modes.  

Science.gov (United States)

The thiolato-bridged dimeric Pd(II) NHC complex 1 has been synthesized from the reaction of thioester-functionalized imidazolium salt B and Pd(OAc)(2). The isolation of its interesting constitutional isomer 2 bearing both classical C(2)-bound and mesoionic C(4)-bound ligands coordinating to two different metal centers in the same complex allowed for a direct comparison of these isomeric carbenes. Reactivity studies of 1 with NaSCH(CH(3))(2) and NaBF(4) afforded the tetranuclear compound 3 with a [Pd(4)S(4)] macrocycle. All complexes have been fully characterized by multinuclei NMR spectroscopies, ESI mass spectrometry and X-ray diffraction analysis. PMID:21833400

Yuan, Dan; Huynh, Han Vinh

2011-11-28

80

1,2-migration in N-phosphano functionalized N-heterocyclic carbenes.  

Science.gov (United States)

1,2-Migration of the phosphano-group to the carbene center in N-phosphano functionalized N-heterocyclic carbenes has been studied by density functional theory (DFT) calculations. An intramolecular mechanism with a three-center transition state structure seems to be most plausible for the isolated carbenes, while an intermolecular pathway catalyzed by azolium salts may be preferable for a migration proceeding in the course of generating the carbenes in situ. Our calculations show that amino-substitution at the phosphorus atom and an enhanced nucleophilicity of the heterocycle scaffold facilitate the phosphorus shift. Calculated singlet-triplet energy gaps do not correlate with thermodynamic stability of the studied carbenes and their disposition toward the 1,2-rearrangement. PMID:25363134

Kirilchuk, Andrey A; Yurchenko, Aleksandr A; Kostyuk, Aleksandr N; Rozhenko, Alexander B

2015-01-01

81

O-Glycosidation reactions promoted by in situ generated silver N-heterocyclic carbenes in ionic liquids.  

Science.gov (United States)

We herein report O-glycosidation reactions promoted via silver N-heterocyclic carbene complexes formed in situ in ionic liquids. Seven different room temperature ionic liquids were screened for the glycosidation reaction of 4-nitrophenol with tetra-O-acetyl-?-d-galactopyranosyl bromide. Good to excellent yields were obtained using Ag-NHC complexes derived from imidazolium halide salts to promote the glycosidation reaction, whereas yields considered moderate to low were obtained without use of the silver carbene complex. Anion metathesis of the ionic liquids with inexpensive alkylammonium halides also resulted in silver N-heterocyclic carbene formation and subsequent O-glycosidation in the presence of silver carbonate. Effective utility of this methodology has been demonstrated with biologically relevant acceptors (including flavones and steroids) where O-?-glycoside products were obtained selectively in moderate to good yields. We have also demonstrated that the Ag-NHC complex is a superior promoter to traditionally used silver carbonate for the glycosidation of polyphenolic acceptors. The ionic liquids used in the study could be recycled three times without apparent loss in activity. PMID:21459367

Talisman, Ian Jamie; Kumar, Vineet; Razzaghy, Jacqueline; Malhotra, Sanjay V

2011-05-15

82

N-Heterocyclic carbene-catalyzed cyclocondensation of 2-aryl carboxylic acids and enones: highly enantioselective synthesis of ?-lactones.  

Science.gov (United States)

The enantioselective N-heterocyclic carbene-catalyzed [4 + 2] cyclocondensation of 2-aryl carboxylic acids and enones was developed, affording the corresponding chiral ?-lactones in good yields with good diastereo- and high enantioselectivities. PMID:25485768

Cheng, Jin-Tang; Chen, Xiang-Yu; Ye, Song

2015-02-01

83

Structural diversity of copper(I)-N-heterocyclic carbene complexes; ligand tuning facilitates isolation of the first structurally characterised copper(I)-NHC containing a copper(I)-alkene interaction.  

Science.gov (United States)

The preparation of a series of imidazolium salts bearing N-allyl substituents, and a range of substituents on the second nitrogen atom that have varying electronic and steric properties, is reported. The ligands have been coordinated to a copper(I) centre and the resulting copper(I)-NHC (NHC=N-heterocyclic carbene) complexes have been thoroughly examined, both in solution and in the solid-state. The solid-state structures are highly diverse and exhibit a range of unusual geometries and cuprophilic interactions. The first structurally characterised copper(I)-NHC complex containing a copper(I)-alkene interaction is reported. An N-pyridyl substituent, which forms a dative bond with the copper(I) centre, stabilises an interaction between the metal centre and the allyl substituent of a neighbouring ligand, to form a 1D coordination polymer. The stabilisation is attributed to the pyridyl substituent increasing the electron density at the copper(I) centre, and thus enhancing the metal(d)-to-alkene(?*) back-bonding. In addition, components other than charge transfer appear to have a role in copper(I)-alkene stabilisation because further increases in the Lewis basicity of the ligand disfavours copper(I)-alkene binding. PMID:24203461

Lake, Benjamin R M; Willans, Charlotte E

2013-12-01

84

A Tungsten Complex with a Bidentate, Hemilabile N-Heterocyclic Carbene Ligand, Facile Displacement of the Weakly Bound W-(C=C) Bond, and the Vulnerability of the NHC Ligand Towards Catalyst Deactivation During Ketone Hydrogenation  

Energy Technology Data Exchange (ETDEWEB)

The initial reaction observed between the N-heterocyclic carbene IMes (IMes = 1,3-bis(2,4,6-trimethylphenyl)imidazol-2-ylidene) and molybdenum and tungsten hydride complexes CpM(CO){sub 2}(PPh{sub 3})H (M = Mo, W) is deprotonation of the metal hydride by IMes, giving [(IMes)H]{sup +}[CpM(CO){sub 2}(PPh{sub 3})]{sup -}. At longer reaction times and higher temperatures, the reaction of IMes with CpM(CO){sub 2}(PR{sub 3})H (M = Mo, W; R = Me, Ph) produces CpM(CO){sub 2}(IMes)H. Hydride transfer from CpW(CO)2(IMes)H to Ph{sub 3}C{sub +}B(C{sub 6}F{sub 5}){sub 4}{sup -} gives CpW(CO){sub 2}(IMes){sup +}B(C{sub 6}F{sub 5}){sub 4}{sup -}, which was crystallographically characterized using X-ray radiation from a synchrotron. The IMes is bonded as a bidentate ligand, through the carbon of the carbene as well as forming a weak bond from the metal to a C=C bond of one mesityl ring. The weakly bound C=C ligand is hemilabile, being readily displaced by H{sub 2}, THF, ketones, or alcohols. Reaction of CpW(CO){sub 2}(IMes){sup +} with H{sub 2} gives the dihydride complex [CpW(CO){sub 2}(IMes)(H){sub 2}]{sup +}. Addition of Et{sub 2}CH-OH to CpW(CO){sub 2}(IMes){sup +}B(C{sub 6}F{sub 5}){sub 4}{sup -} gives the alcohol complex [CpW(CO){sub 2}(IMes)(Et{sub 2}CH-OH)]{sup +}[B(C{sub 6}F{sub 5}){sub 4}]{sup -}, which was characterized by crystallography and exhibits no evidence for hydrogen bonding of the bound OH group. Addition of H{sub 2} to the ketone complex [CpW(CO){sub 2}(IMes)(Et{sub 2}C=O)]{sup +}[B(C{sub 6}F{sub 5}){sub 4}]{sup -} produces an equilibrium with the dihydride [CpW(CO){sub 2}(IMes)(H){sub 2}]{sup +} (K{sub eq} = 1.1 x 10{sup 3} at 25 {sup o}C). The tungsten ketone complex [CpW(CO){sub 2}(IMes)(Et{sub 2}C=O)]{sup +}[B(C{sub 6}F{sub 5}){sub 4}]{sup -}- serves as a modest catalyst for hydrogenation of Et{sub 2}C=O to Et{sub 2}CH-OH in neat ketone solvent. Decomposition of the catalyst produces [H(IMes)]{sup +}B(C{sub 6}F{sub 5}){sub 4}{sup -}, indicating that these catalysts with N-heterocyclic carbene ligands are vulnerable to decomposition by a reaction that produces a protonated imidazolium cation.

Wu,F.; Dioumaev, V.; Szalda, D.; Hanson, J.; Bullock, R.

2007-01-01

85

New stable aryl-substituted acyclic imino-N-heterocyclic carbene: synthesis, characterisation and coordination to early transition metals.  

Science.gov (United States)

The synthesis of the bulky 1-(1-arylimino-2,2-dimethylpropyl)-3-(aryl)imidazolium salt from the corresponding imidazole and the activated imidoyl chloride is presented. The absence of acidic protons adjacent to the iminic carbon allowed for the first isolation of an imino-N-heterocyclic carbene of this ligand class. The free carbene was isolated, structurally characterised, and coordinated to titanium, zirconium, hafnium and chromium. The resulting metal halide complexes were fully characterised and were tested at room temperature and atmospheric pressure for their activity as ethylene polymerisation catalysts. The Zr(IV) complex was found to be the most active with a productivity of 140 kg PE mol M(-1) h(-1). PMID:22006062

Larocque, Timothy G; Badaj, Anna C; Dastgir, Sarim; Lavoie, Gino G

2011-12-21

86

Estimating ? binding energy of N-Heterocyclic carbenes: The role of polarization.  

Science.gov (United States)

In this work, the tuneability of the ? acceptor or donor properties of a set of N-heterocyclic carbenes (NHCs) with a wide spectrum of electronic characteristics is established by means of density functional theory and energy decomposition analysis (EDA) tools. Even though the main orbital interaction contribution to the NHC coordination is the ? donation, a significant contribution of the ? interactions to the bond is observed. By means of carefully selected coordination sites, different contributions to the ? interactions could be identified and isolated. It includes not only the well known back donation and donation interactions, but also the intrafragment polarization, which has not been considered in previous studies. This can be obtained through the use of the extended transition state method for EDA combined with the natural orbitals for chemical valence and the constrained space orbital variation analysis. The contributions vary with the position of the heteroatoms and the presence of exocyclic substituents; the donation/backdonation ? interactions between NHC and the coordination site can range between 2 and 61% of the total ? orbital interactions, while the rest is owed to intrafragment polarization. Our results do not only contribute to the understanding of the electronic structure of NHC-based complexes, giving ways to improve their catalytic properties, but also provide comprehension on the modelization methods used to study their donor-acceptor interactions. © 2015 Wiley Periodicals, Inc. PMID:25708019

Rezabal, Elixabete; Frison, Gilles

2015-03-30

87

Systematic strategy for designing immidazolium containing precursors to produce N-heterocyclic carbenes: a DFT study.  

Science.gov (United States)

A series of cationic N-heterocyclic carbene (NHC) precursors that can be utilized as fluorescent chemosensors for carbon dioxide capture were investigated by density functional theory (DFT) calculations. Activation energy barriers for the reactions of the cationic NHC precursors and hydrogen carbonate (HCO3(-)) based on intrinsic reaction coordinate (IRC) profiles as well as proton affinity of the precursors were compared. The calculated proton affinity of 1-ethyl-3-methylimidazol-2-yliene was in good agreement with experimental one within the margin of error. We clarified main factors to lower the activation energy barrier based on the correlation among the number of N-heterocyclic functional group, aromatic ring size, and structural characteristics for the candidate compounds. On the basis of the results, it was verified that some of our model systems spontaneously generate NHCs without any specific catalyst. PMID:25594878

Baek, Kyung Yup; Jo, Ji Hye; Moon, Jong Hun; Yoon, Juyoung; Lee, Jin Yong

2015-02-01

88

Synthesis of chiral mono(N-heterocyclic carbene) palladium and gold complexes with a 1,1'-biphenyl scaffold and their applications in catalysis  

OpenAIRE

Axially chiral mono(NHC)–Pd(II) and mono(NHC)–Au(I) complexes with one side shaped 1,1'-biphenyl backbone have been prepared from chiral 6,6'-dimethoxybiphenyl-2,2'-diamine. The complexes were characterized by X-ray crystal structure diffraction. The Pd(II) complex showed good catalytic activities in the Suzuki–Miyaura and Heck–Mizoroki coupling reactions, and the (S)-Au(I) complexes also showed good catalytic activities in the asymmetric intramolecular hydroamination ...

Min Shi; Mei-xin Zhao; Wenfeng Wang; Lian-jun Liu; Feijun Wang

2011-01-01

89

One-pot synthesis of unsymmetrical N-heterocyclic carbene ligands from N-(2-iodoethyl)arylamine salts.  

Science.gov (United States)

An approach that provides symmetrical, unsymmetrical, and asymmetric N-heterocyclic carbene (NHC) ligands is reported. Reaction of iodoethanol with aniline provides N-(2-iodoethyl)arylamine salts that are then converted to the corresponding iodide. Reaction with aliphatic or aromatic amines followed by triethyl orthoformate was used to provide 26 different NHC ligands. PMID:19624103

Prasad, B A Bhanu; Gilbertson, Scott R

2009-08-20

90

Optimized Syntheses of Cyclopentadienyl Nickel Chloride Compounds Containing "N"-Heterocyclic Carbene Ligands for Short Laboratory Periods  

Science.gov (United States)

Experiments are described for the preparation of imidazolium chloride precursors to "N"-heterocyclic carbenes and their cyclopentadienyl nickel chloride derivatives. The syntheses have been optimized for second- and third-year undergraduate laboratories that have a maximum programmed length of three hours per week. The experiments are flexible and…

Cooke, Jason; Lightbody, Owen C.

2011-01-01

91

[CNN]-pincer nickel(II) complexes of N-heterocyclic carbene (NHC): synthesis and catalysis of the Kumada reaction of unactivated C-Cl bonds.  

Science.gov (United States)

Three novel [CNN]-pincer nickel(ii) complexes with NHC-amine arms were synthesized in three steps. Complex was proven to be an efficient catalyst for the Kumada coupling of aryl chlorides or aryl dichlorides under mild conditions. PMID:24828414

Sun, Yunqiang; Li, Xiaoyan; Sun, Hongjian

2014-07-01

92

Amino Group Functionalized N-Heterocyclic 1,2,4-Triazole-Derived Carbenes: Structural Diversity of Rhodium(I) Complexes.  

Czech Academy of Sciences Publication Activity Database

Ro?. 32, ?. 23 (2013), s. 7234-7240. ISSN 0276-7333 Institutional support: RVO:61388955 Keywords : TRANSITION-METAL COMPLEXES * BIFUNCTIONAL MECHANISM * TRANSFER HYDROGENATION Subject RIV: CF - Physical ; Theoretical Chemistry Impact factor: 4.253, year: 2013

Turek, J.; Panov, I.; Horá?ek, Michal; ?ernošek, Z.; Pad?lková, Z.; R?ži?ka, A.

2013-01-01

93

Suzuki–Miyaura cross-coupling reaction of 1-aryltriazenes with arylboronic acids catalyzed by a recyclable polymer-supported N-heterocyclic carbene–palladium complex catalyst  

Directory of Open Access Journals (Sweden)

Full Text Available The Suzuki–Miyaura cross-coupling reaction of 1-aryltriazenes with arylboronic acids catalyzed by a recyclable polymer-supported Pd–NHC complex catalyst has been realized for the first time. The polymer-supported catalyst can be re-used several times still retaining high activity for this transformation. Various aryltriazenes were investigated as electrophilic substrates at room temperature to give biaryls in good to excellent yields and showed good chemoselectivity over aryl halides in the reactions.

Guangming Nan

2010-06-01

94

Theoretical investigation on the chemoselective N-heterocyclic carbene-catalyzed cross-benzoin reactions.  

Science.gov (United States)

A density functional theory study was performed to understand the detailed mechanisms of the cross-benzoin reactions catalyzed by N-heterocyclic carbene (NHC) species. Our theoretical study predicted that the first H-transfer operates with water in solution as a mediator, and the second H-transfer undergoes a concerted mechanism rather than a stepwise one. In addition, the chemoselectivity of the reactions studied in this work has been explored. was obtained as a major product mainly due to the more stable intermediate formed by reaction of NHC with reactant . Different steric effects resulting from the fused six-membered ring in transition state TS7 and the fused five-membered ring in transition state TS13 are the origin leading to the chemoselectivity. PMID:25672268

Liu, Tao; Han, Shu-Min; Han, Ling-Li; Wang, Lu; Cui, Xiang-Yang; Du, Chong-Yang; Bi, Siwei

2015-03-11

95

Intramolecular c?n bond activation and ring-expansion reactions of N-heterocyclic carbenes.  

Science.gov (United States)

Intramolecular ring-expansion reactions (RER) of the N-heterocyclic carbene 1,3-dimethylimidazolin-2-ylidene were observed upon vacuum ultraviolet (VUV) photoexcitation. Similarly to RERs reported in the solvent phase, for the reaction of NHCs with main-group-element hydrides, hydrogen transfer to the NHC carbon atom is the crucial initial step. In an ionization-mediated protonation, 1,3-dimethylimidazolin-2-ylidene forms an imidazolium ion, which is the rate-limiting step on the pathway to two six-membered ring products, namely, methylpyrimidinium and -pyrazinium ions. To unravel the reaction path, we have used imaging photoelectron photoion coincidence spectroscopy with VUV synchrotron radiation, as well as high-level composite method calculations. Similarities and differences between the mechanism in the gas phase and in the condensed phase are discussed. PMID:25430962

Hemberger, Patrick; Bodi, Andras; Berthel, Johannes H J; Radius, Udo

2015-01-19

96

Zwitterionic dithiocarboxylates derived from N-heterocyclic carbenes: coordination to gold surfaces.  

Science.gov (United States)

The zwitterionic dithiocarboxylates 1(+)-CS(2)(-)-4(+)-CS(2)(-) were prepared by reacting the corresponding N-heterocyclic carbenes 1,3-bis(2,6-diisoproylphenyl)imidazol-2-ylidene (1), 1,3-diisopropylimidazol-2-ylidene (2), 1,3-dibenzylimidazol-2-ylidene (3) and 1,3-diethylbenzimidazol-2-ylidene (4) with CS(2). In the latter two cases, the corresponding N-heterocylic carbene was generated in situ. Compounds 2(+)-CS(2)(-)-4(+)-CS(2)(-) were structurally characterised by single-crystal X-ray diffraction studies. The chemisorption of these zwitterionic dithiocarboxylates on solid gold substrates was investigated in situ and in real time by optical second harmonic generation (SHG). The resulting thin films were exemplarily characterised by near-edge X-ray absorption fine structure (NEXAFS) spectroscopy and X-ray photoelectron spectroscopy (XPS) in the case of 1(+)-CS(2)(-) and 2(+)-CS(2)(-), revealing the formation of almost contamination-free self-assembled monolayers, which exhibit a remarkable degree of orientational order. PMID:22274745

Siemeling, Ulrich; Memczak, Henry; Bruhn, Clemens; Vogel, Florian; Träger, Frank; Baio, Joe E; Weidner, Tobias

2012-03-14

97

Efficient electronic communication of two ruthenium centers through a rigid ditopic N-heterocyclic carbene linker  

OpenAIRE

A ditopic benzobis(carbene) ligand precursor was prepared that contained a chelating pyridyl moiety to ensure co-planarity of the carbene ligand and the coordination plane of a bound octahedral metal center. Bimetallic ruthenium complexes comprising this ditopic ligand [L?Ru-C,N-bbi-C,N-RuL?] were obtained by a transmetalation methodology (C,N-bbi-C,N=benzobis(N-pyridyl-N?-methyl-imidazolylidene). The two metal centers are electronically decoupled when the ruthenium is in a pseudotetrah...

Nussbaum, Michael; Schuster, Oliver; Albrecht, Martin

2014-01-01

98

A theobromine derived silver N-heterocyclic carbene: synthesis, characterization, and antimicrobial efficacy studies on cystic fibrosis relevant pathogens†  

OpenAIRE

The increasing incidence of multidrug-resistant (MDR) pulmonary infections in the cystic fibrosis (CF) population has prompted the investigation of innovative silver based therapeutics. The functionalization of the naturally occurring xanthine theobromine at the N1 nitrogen atom with an ethanol substituent followed by the methylation of the N9 nitrogen atom gives the N-heterocyclic carbene precursor 1-(2-hydroxyethyl)-3,7,9-trimethylxanthinium iodide. The reaction of this xanthinium salt with...

Panzner, Matthew J.; Hindi, Khadijah M.; Wright, Brian D.; Taylor, Jane B.; Han, Daniel S.; Youngs, Wiley J.; Cannon, Carolyn L.

2009-01-01

99

Investigation of the Role of Electrogenerated N-Heterocyclic Carbene in the Staudinger Synthesis in Ionic Liquid  

OpenAIRE

Electrogenerated N-heterocyclic carbene (NHC), obtained by cathodic reduction of Bmim-BF4, behaves as organocatalyst and base in the Staudinger synthesis from an acyl chloride and a deactivated imine in ionic liquid to yield ?-lactams. The effect of many parameters (temperature, amount of electricity, substituents, presence of an external base) has been evaluated and a tentative mechanism for the Staudinger synthesis in a very polar medium like the ionic liquid reported. The yields of isolate...

Marta Feroci

2011-01-01

100

Palladium-catalyzed direct c2-arylation of an N-heterocyclic carbene: an atom-economic route to mesoionic carbene ligands.  

Science.gov (United States)

Blocking the C2 position of an imidazole-derived classical N-heterocyclic carbene (NHC) with an aryl group is an essential strategy to establish a route to mesoionic carbenes (MICs), which coordinate to the metal via the C4 (or C5) carbon atom. An efficient catalytic route to MIC precursors by direct arylation of an NHC is reported. Treatment of 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene (IPr) with an aryl iodide (RC6 H4 I) in the presence of 0.5?mol?% of [Pd2 (dba)3 ] (dba=dibenzylideneacetone) precatalyst affords the C2-arylated imidazolium salts {IPr(C6 H4 R)}I (R=H, 4-Me, 2-Me, 4-OMe, 4-COOMe) in excellent (up to 92?%) yields. Treatment of {IPr(C6 H5 )}I with CuI and KN(SiMe3 )2 exclusively affords the MIC-copper complex [(IPrPh)CuI]. PMID:25639790

Ghadwal, Rajendra S; Reichmann, Sven O; Herbst-Irmer, Regine

2015-03-01

101

Spherical core-shell magnetic particles constructed by main-chain palladium N-heterocyclic carbenes  

Science.gov (United States)

The encapsulation of the functional species on magnetic core is a facile approach for the synthesis of core-shell magnetic materials, and surface encapsulating matrices play crucial roles in regulating their properties and applications. In this study, two core-shell palladium N-heterocyclic carbene (NHC) particles (Fe3O4@PNP1 and Fe3O4@PNP2) were prepared by a one-pot reaction of semi-rigid tripodal imidazolium salts and palladium acetate in the presence of magnetite nanoparticles. The magnetite nanoparticles are encapsulated inside the main-chain palladium, which act as cores. The conjugated effects of triphenyltriazine and triphenylbenzene in the imidazolium salts have important influence on their physical properties and catalytic performances. Fe3O4@PNP2 shows better recyclability than Fe3O4@PNP1. Unexpectedly, Pd(ii) is well maintained after six consecutive catalytic runs in Fe3O4@PNP2, and Pd(0) and Pd(ii) coexist in Fe3O4@PNP1 under the same conditions; moreover, the morphologies of these spherical core-shell particles show no significant variation after six consecutive catalytic runs.The encapsulation of the functional species on magnetic core is a facile approach for the synthesis of core-shell magnetic materials, and surface encapsulating matrices play crucial roles in regulating their properties and applications. In this study, two core-shell palladium N-heterocyclic carbene (NHC) particles (Fe3O4@PNP1 and Fe3O4@PNP2) were prepared by a one-pot reaction of semi-rigid tripodal imidazolium salts and palladium acetate in the presence of magnetite nanoparticles. The magnetite nanoparticles are encapsulated inside the main-chain palladium, which act as cores. The conjugated effects of triphenyltriazine and triphenylbenzene in the imidazolium salts have important influence on their physical properties and catalytic performances. Fe3O4@PNP2 shows better recyclability than Fe3O4@PNP1. Unexpectedly, Pd(ii) is well maintained after six consecutive catalytic runs in Fe3O4@PNP2, and Pd(0) and Pd(ii) coexist in Fe3O4@PNP1 under the same conditions; moreover, the morphologies of these spherical core-shell particles show no significant variation after six consecutive catalytic runs. Electronic supplementary information (ESI) available: The additional SEM images, IR spectra, TG-MS curves, Solid state 13C NMR spectra, XPS spectra and XRD spectra of palladium NHC particles. See DOI: 10.1039/c4nr07330d

Zhao, Huaixia; Li, Liuyi; Wang, Jinyun; Wang, Ruihu

2015-02-01

102

Mechanistic Investigation of the Ruthenium–N-Heterocyclic-Carbene-Catalyzed Amidation of Alcohols and Amines  

DEFF Research Database (Denmark)

The mechanism of the ruthenium–N-heterocyclic-carbene-catalyzed formation of amides from alcohols and amines was investigated by experimental techniques (Hammett studies, kinetic isotope effects) and by a computational study by using dispersion-corrected density functional theory (DFT/ M06). The Hammett study indicated that a small positive charge builds-up at the benzylic position in the transition state of the turnover-limiting step. The kinetic isotope effect was determined to be 2.29ACHTUNGTRENUNG(!0.15), which suggests that the breakage of the C"H bond is not the rate-limiting step, but that it is one of several slow steps in the catalytic cycle. Rapid scrambling of hydrogen and deuterium at the a position of the alcohol was observed with deuterium-labeled substrates, which implies that the catalytically active species is a ruthenium dihydride. The experimental results were supported by the characterization of a plausible catalytic cycle by using DFT/M06. Both cisdihydride and trans-dihydride intermediates were considered, but when the theoretical turnover frequencies (TOFs) were derived directly from the calculated DFT/M06 energies, we found that only the trans-dihydride pathway was in agreement with the experimentally determined TOFs.

Makarov, Ilya; Fristrup, Peter

2012-01-01

103

Shape-Controllable Formation of Poly-imidazolium Salts for Stable Palladium N-Heterocyclic Carbene Polymers  

Science.gov (United States)

The imidazolium-based main-chain organic polymers are one of promising platforms in heterogeneous catalysis, the size and outer morphology of polymer particles are known to have important effects on their physical properties and catalytic applications, but main-chain ionic polymers usually generate amorphous or spherical particles. Herein, we presented a versatile and facile synthetic route for size- and shape-controllable synthesis of main-chain poly-imidazolium particles. The wire-shaped, spherical and ribbon-shaped morphologies of poly-imidazolium particles were readily synthesized through quaternization of bis-(imidazol-1-yl)methane and 2,4,6-tris(4-(bromomethyl)phenyl)-1,3,5-triazine, and the modification of their size and morphology were realized through adjusting solvent polarity, solubility, concentration and temperatures. The direct complexation of the particles with Pd(OAc)2 produced ionic polymers containing palladium N-heterocyclic carbene units (NHCs) with intactness of original morphologies. The particle morphologies have a significant effect on catalytic performances. Wire-shaped palladium-NHC polymer shows excellent catalytic activity and recyclabilty in heterogeneous Suzuki-Miyaura cross-coupling reaction.

Zhao, Huaixia; Li, Liuyi; Wang, Yangxin; Wang, Ruihu

2014-06-01

104

Investigation of the Role of Electrogenerated N-Heterocyclic Carbene in the Staudinger Synthesis in Ionic Liquid  

Directory of Open Access Journals (Sweden)

Full Text Available Electrogenerated N-heterocyclic carbene (NHC, obtained by cathodic reduction of Bmim-BF4, behaves as organocatalyst and base in the Staudinger synthesis from an acyl chloride and a deactivated imine in ionic liquid to yield ?-lactams. The effect of many parameters (temperature, amount of electricity, substituents, presence of an external base has been evaluated and a tentative mechanism for the Staudinger synthesis in a very polar medium like the ionic liquid reported. The yields of isolated ?-lactams are good, starting from non-electrophilic imines, and predominantly trans lactams are obtained with a good diastereomeric ratio.

Marta Feroci

2011-12-01

105

Efficient electronic communication of two ruthenium centers through a rigid ditopic N-heterocyclic carbene linker.  

Science.gov (United States)

A ditopic benzobis(carbene) ligand precursor was prepared that contained a chelating pyridyl moiety to ensure co-planarity of the carbene ligand and the coordination plane of a bound octahedral metal center. Bimetallic ruthenium complexes comprising this ditopic ligand [L4Ru-C,N-bbi-C,N-RuL4] were obtained by a transmetalation methodology (C,N-bbi-C,N=benzobis(N-pyridyl-N'-methyl-imidazolylidene). The two metal centers are electronically decoupled when the ruthenium is in a pseudotetrahedral geometry imparted by a cymene spectator ligand (L4=[(cym)Cl]). Ligand exchange of the Cl(-)/cymene ligands for two bipyridine or four MeCN ligands induced a change of the coordination geometry to octahedral. As a consequence, the ruthenium centers, separated through space by more than 10 Å, become electronically coupled, which is evidenced by two distinctly different metal-centered oxidation processes that are separated by 134 mV (L4=[(bpy)2]; bpy=2,2'-bipyridine) and 244 mV (L4=[(MeCN)4]), respectively. Hush analysis of the intervalence charge-transfer bands in the mixed-valent species indicates substantial valence delocalization in both complexes (delocalization parameter ?=0.41 and 0.37 in the bpy and MeCN complexes, respectively). Spectroelectrochemical measurements further indicated that the mixed-valent Ru(II)/Ru(III) species and the fully oxidized Ru(III)/Ru(III) complexes gradually decompose when bound to MeCN ligands, whereas the bpy spectators significantly enhance the stability. These results demonstrate the efficiency of carbenes and, in particular, of the bbi ligand scaffold for mediating electron transfer and for the fabrication of molecular redox switches. Moreover, the relevance of spectator ligands is emphasized for tailoring the degree of electronic communication through the benzobis(carbene) linker. PMID:24218243

Nussbaum, Michael; Schuster, Oliver; Albrecht, Martin

2013-12-16

106

Palladium, iridium and ruthenium complexes with acyclic imino-N-heterocyclic carbenes and their application in aqua-phase Suzuki-Miyaura cross-coupling reaction and transfer hydrogenation.  

Science.gov (United States)

Palladium (4a–4c), iridium (5a–5c) and ruthenium (6a–6c) complexes have been prepared by in situ transmetalation from the corresponding silver complexes of acyclic imino-functionalized imidazolium chlorides [1-(Me)-imidazolium-3-{C(p-CH(3)-Ph)=N(Ar)}]Cl (3) (Ar = 2,4,6-trimethylphenyl (3a), 2,6-diisopropylphenyl (3b) and phenyl (3c)) with [Pd(COD)Cl(2)], [Cp*IrCl(2)](2) or [Ru(p-cymene)Cl(2)](2), respectively. Iridium and ruthenium complexes, 5a[PF(6)]–5c[PF(6)], 6a[PF(6)]–6c[PF(6)], 6c[BF(4)], 6c[BPh(4)] and 6c[NTf(2)], were obtained directly from 5a–5c and 6a–6c through an anion-exchange process with KPF(6), NaBF(4), NaBPh(4) and LiNTf(2) (bis(trifluoromethylsulfonyl)imide lithium), respectively. All complexes were characterized by FT-IR, (1)H and (13)C NMR spectroscopy and elemental analysis. Crystal structures of 4a, 5a and 6c[NTf(2)], and show that five-membered chelate ring is formed in these complexes by the coordination of the carbene carbon and the imino nitrogen atom, and the latter two are cationic compounds with Cl(-) and NTf(2)(-) as counteranion respectively. The catalytic performance of Pd complexes for Suzuki-Miyaura cross-coupling reactions in pure water and Ir and Ru complexes for transfer hydrogenation of ketones and imines was tested in a wide scope of substrates. Pd complex 4b with the largest steric hinder exhibited the best performance to gain moderate to excellent yields on catalyzing Suzuki-Miyaura cross-coupling of aryl chlorides and arylboronic acids in water. While in transfer hydrogenation of various ketones, all the Ir and Ru complexes were effective with good to excellent yields. Among all these complexes, 6c[PF(6)] was found most effective, and moderate yields could be obtained even in the transfer hydrogenation of imines. Moreover, different counteranions of Ru complexes are influential on catalyzing the transfer hydrogenation, with the sequence of PF(6)(-) ? BF(4)(-) > BPh(4)(-) > Cl(-) > NTf(2)(-). PMID:23132042

Guo, Xu-Qing; Wang, Ya-Nong; Wang, Dong; Cai, Li-Hua; Chen, Zhen-Xia; Hou, Xiu-Feng

2012-12-28

107

Systematic investigation of the ring-expansion reaction of N-heterocyclic carbenes with an iminoborane dihydride.  

Science.gov (United States)

Conversions of iminoboranes with an N-heterocyclic carbene (NHC) result in borane dihydride formation (BDF) concomitant with dihydrogenated NHC. The iminoborane dihydrides are prone to a hydride-mediated ring-expansion reaction (RER) at elevated temperature, that is, the insertion of the boron atom into the adjacent C?N bond of the NHC to yield boracycles. Upon conversion of a saturated-backbone NHC with respective iminoborane precursors RER yet occurs at ambient temperature to yield the ring-expanded products. When a less bulky iminoborane is brought in contact with sterically unhindered NHC neither the iminoborane dihydride is stable at room temperature nor is the RER observed to take place upon heating. The conversions of iminoboranes with very bulky NHC do not show BDF at ambient temperature and only in the case of the less hindered borane precursor the RER is found to proceed in a controlled fashion upon heating. PMID:24938679

Franz, Daniel; Inoue, Shigeyoshi

2014-08-01

108

How does the addition of steric hindrance to a typical N-heterocyclic carbene ligand affect catalytic activity in olefin metathesis?  

OpenAIRE

Density functional theory (DFT) calculations were used to predict and rationalize the effect of the modification of the structure of the prototype 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene) N-heterocyclic carbene (NHC) ligand. The modification consists in the substitution of the methyl groups of ortho isopropyl substituent with phenyl groups, and here we plan to describe how such significant changes affect the metal environment and therefore the related catalytic behaviour. Bearing in ...

Poater Teixidor, Albert; Falivene, Laura; Urbina-blanco, Cesar A.; Manzini, Simone; Nolan, Steven P.; Cavallo, Luigi

2013-01-01

109

N-Heterocyclic carbene-catalyzed annulation of cyclic ?-enamino esters with enals: access to functionalized indolo[2,3-a]quinolizidines.  

Science.gov (United States)

A novel synthetic approach to functionalized indolo[2,3-a]quinolizidines is developed via an N-heterocyclic carbene (NHC)-catalyzed annulation of cyclic ?-enamino esters with enals . This methodology offers a pathway for quick and efficient construction of an indolo[2,3-a]quinolizidine skeleton which is a core structure of many natural products with diverse bioactivities. PMID:25799005

Hu, Shihe; Wang, Bingyang; Zhang, Yu; Tang, Weifang; Fang, Mengyuan; Lu, Tao; Du, Ding

2015-04-01

110

A N-heterocyclic carbene derived highly regioselective ambident C-C-S and C-C-N 1,3-dipolar system.  

Science.gov (United States)

N-Heterocyclic carbene derived 2-phenylthiocarbamoyl benzimidazolium and imidazolinium inner salts are a unique ambident C-C-S and C-C-N 1,3-dipolar system able to undergo highly efficient and regioselective cycloaddition with dimethyl acetylenedicarboxylate and ethyl propiolate to furnish, respectively, spiro[imidazole-2,3'-thiophene] and spiro[imidazole-2,3'-pyrrole] derivatives in good to excellent yields. PMID:16518495

Liu, Mei-Fang; Wang, Bo; Cheng, Ying

2006-03-21

111

Synthesis and in vitro Efficacy Studies of Silver Carbene Complexes on Biosafety Level 3 Bacteria  

OpenAIRE

A series of N-heterocyclic carbene silver complexes have been synthesized and tested against the select group of bio-safety level 3 bacteria Burkholderia pseudomallei, Burkholderia mallei, Bacillus anthracis, methicillin-resistant Staphylococcus aureus and Yersinia pestis. Minimal inhibitory concentrations, minimal bactericidal and killing assays demonstrated the exceptional efficacy of the complexes against these potentially weaponizable pathogens.

Panzner, Matthew J.; Deeraksa, Arpaporn; Smith, Alyssa; Wright, Brian D.; Hindi, Khadijah M.; Kascatan-nebioglu, Aysegul; Torres, Alfredo G.; Judy, Barbara M.; Hovis, Christine E.; Hilliard, Julia K.; Mallett, Rebekah J.; Cope, Emily; Estes, D. Mark; Cannon, Carolyn L.; Leid, Jeff G.

2009-01-01

112

A comparative study on dinuclear and multinuclear Ni(II), Pd(II), and Pt(II) complexes of a thiolato-functionalized, benzannulated N-heterocyclic carbene ligand.  

Science.gov (United States)

Dimeric thiolato-bridged Ni(II) and Pt(II) NHC complexes 2 and 4 have been synthesized from ligand precursor A through a combined and in situ deprotonation/hydrolysis protocol of a thioester-functionalized benzimidazolium salt in the presence of the respective metal salts. Reactivity studies of 2 and 4, and their previously reported Pd(II) analogue 1a toward either Me3OBF4, NaOH, or Na2S·9H2O revealed clear differences. Complex 2 decomposed when treated with Me3OBF4. On the other hand, its reaction with aqueous NaOH solution in the presence of NaBF4 yielded trinuclear [Ni3S3O] complex 6, which possesses an interesting [Ni3S3] triangle with a capping ?3-oxido ligand. Pt(II) analogue 4 was converted to the tetranuclear [Pt4S4] macrocycle 5 when treated with Me3OBF4, in analogy to the result from 1a, while no defined products could be isolated when 4 was treated with either NaOH or Na2S·9H2O. Pd(II) analogue 1a reacted with Na2S·9H2O to give the tripalladium [Pd3S3S] complex 7 bearing a capping ?3-sulfido ligand. PMID:23679658

Yuan, Dan; Huynh, Han Vinh

2013-06-01

113

Catalytic hydrodechlorination of benzyl chloride promoted by Rh-N-heterocyclic carbene catalysts.  

Science.gov (United States)

The rhodium(I) complexes [Rh(Cl)(COD)(R-NHC-(CH2 )3 Si(OiPr)3 )] [COD=cyclooctadiene; R=2,6-diisopropylphenyl (1?a); n-butyl (1?b)] are effective catalyst precursors for the homogeneous hydrodechlorination of benzyl chloride using HSiEt3 as hydrogen source. This reaction is selective to the formation of toluene. However, in presence of a stoichiometric amount of potassium tert-butoxide (KtBuO) the formation of mixtures containing toluene together with 17-19?mol?% of the C--C homocoupling product, namely PhCH2 CH2 Ph, is observed. A mechanism proposal based on experimental insights and theoretical calculations at the DFT level that allows explanation of the experimental findings is included. Moreover, the heterogeneous catalytic system based on catalyst 1?a supported on MCM-41 has been demonstrated to be effective for the solvent-free hydrodechlorination of benzyl chloride using HSiEt3 and HSiMe(OSiMe3 )2 . PMID:25504980

Lázaro, Guillermo; Polo, Víctor; Fernández-Alvarez, Francisco J; García-Orduña, Pilar; Lahoz, Fernando J; Iglesias, Manuel; Pérez-Torrente, Jesús J; Oro, Luis A

2015-02-01

114

Effect of chelating ring size in catalytic ketone hydrogenation: facile synthesis of ruthenium(II) precatalysts containing an N-heterocyclic carbene with a primary amine donor for ketone hydrogenation and a DFT study of mechanisms.  

Science.gov (United States)

A half-sandwich ruthenium(II) complex, [Ru(?(6)-p-cymene)(C-NH(2))Cl]PF(6) (4·PF(6)), containing an N-heterocyclic carbene (NHC) with a primary amine donor (C-NH(2)) which chelates through the carbene carbon and the amine nitrogen to form a 6-membered ring was synthesized in a one-pot reaction starting from a primary-amine functionalized imidazolium salt 2. Complex 4·PF(6) catalyzed the hydrogenation of ketones using 2-propanol or H(2) as the reductant. A maximum turnover frequency of 1062 h(-1) and a turnover number of 1140 at 5 h were achieved for the transfer hydrogenation of 3'-chloroacetophenone in 2-propanol at 75 °C. A cationic hydride-amine complex 5, [Ru(?(6)-p-cymene)(C-NH(2))H]PF(6), was synthesized, and this reacted very slowly with acetophenone unless first activated by an alkoxide base. Computational studies by DFT methods suggested that the poor reactivity of the hydride-amine complex 5 was attributed to a large barrier for the transfer of its H(+)/H(-) couple to a ketone for bifunctional catalysis. An inner-sphere mechanism, which involves a decoordinated amine group of the C-NH(2) ligand, was computed to be a feasible energetic pathway in comparison to the computed outer-sphere bifunctional mechanism. This explains the catalytic activity and selectivity that is observed for the newly synthesized ruthenium(II) catalysts. PMID:22728720

Ohara, Hisashi; O, Wylie W N; Lough, Alan J; Morris, Robert H

2012-08-01

115

Mechanism of Ni N-heterocyclic carbene catalyst for C-O bond hydrogenolysis of diphenyl ether: a density functional study.  

Science.gov (United States)

Catalysts for aromatic C-O bond activation can potentially be used for the lignin degradation process. We investigated the mechanisms of C-O bond hydrogenolysis of diphenyl ether (PhOPh) by the nickel N-heterocyclic carbene (Ni-SIPr) complex to produce benzene and phenol as products. Our calculations revealed that diphenyl ether is not only a substrate, but also serves as a ligand to stabilize the Ni-SIPr complex. The Ni(SIPr)(?(6)-PhOPh) complex is initially formed before rearranging to Ni(SIPr)(?(2)-PhOPh), the active species for C-O bond activation. The catalytic reaction has three steps: (i) oxidative addition of Ni(SIPr)(?(2)-PhOPh) to form [Ni(SIPr)(OPh)(Ph)](0), (ii) ?-complex-assisted metathesis, in which H2 binds to the nickel to form [Ni(SIPr)(OPh)(Ph)(H2)](0), and then benzene (or phenol) is eliminated, and (iii) reductive elimination of phenol (or benzene) and the binding of PhOPh to regenerate Ni(SIPr)(?(2)-PhOPh). As the rate determining step is the oxidative addition step (+24 kcal mol(-1)), we also calculated the free energy barriers for the oxidative addition of diaryl ether containing a trifluoromethyl electron withdrawing group (PhOC6H4CF3) and found that C-O bond activation at the carbon adjacent to the aryl ring that contains the electron withdrawing substituent is preferred. This is in agreement with the experimental results, in that the major products are phenol and trifluoromethylbenzene. Moreover, the hydrogenation of benzene via Ni(SIPr)(?(2)-C6H6) requires a high energy barrier (+39 kcal mol(-1)); correspondingly, the hydrogenation products, e.g. cyclohexane and cyclohexadiene, were not observed in the experiment. Understanding the reaction mechanisms of the nickel catalysts for C-O bond hydrogenolysis of diphenyl ether will guide the development of catalytic systems for aromatic C-O bond activation to achieve the highest possible selectivity and efficiency. PMID:25355042

Sawatlon, Boodsarin; Wititsuwannakul, Taveechai; Tantirungrotechai, Yuthana; Surawatanawong, Panida

2014-12-28

116

N-heterocyclic carbene-catalyzed domino ring-opening/redox amidation/cyclization reactions of formylcyclopropane 1,1-diesters: direct construction of a 6-5-6 tricyclic hydropyrido[1,2-a]indole skeleton.  

Science.gov (United States)

Catalyzed by N-heterocyclic carbenes (NHCs), domino ring-opening/redox amidation/cyclization reactions of the readily available formylcyclopropane 1,1-diesters with 2-chloro-1H-indole-3-carboaldehydes were reported. This methodology provides an efficient and direct construction of a 6-5-6 tricyclic hydropyrido[1,2-a]indole skeleton, which can be potentially applied for the synthesis of several types of polycyclic indole alkaloids. PMID:19476395

Du, Ding; Li, Linxia; Wang, Zhongwen

2009-06-01

117

Stabilities of Immonium Ions Derived from N-Heterocyclic Carbenes Probed by Collision-Induced Dissociation Mass Spectrometry.  

Czech Academy of Sciences Publication Activity Database

-, ?. 20 (2012), s. 3852-3862. ISSN 1434-193X Grant ostatní: European Research Council(XE) AdG HORIZOMS Institutional support: RVO:61388963 Keywords : carbenes * cations * collision-induced dissociation * density functional calculations * electrospray ionization * lipophilic cations * mass spectrometry * phase-transfer catalysis Subject RIV: CC - Organic Chemistry Impact factor: 3.344, year: 2012

Polyakova, Svetlana; Kunetskiy, Roman Alexejevi?; Schröder, Detlef

118

Copper- and copper-N-heterocyclic carbene-catalyzed C-H activating carboxylation of terminal alkynes with CO2 at ambient conditions.  

Science.gov (United States)

The use of carbon dioxide as a renewable and environmentally friendly source of carbon in organic synthesis is a highly attractive approach, but its real world applications remain a great challenge. The major obstacles for commercialization of most current protocols are their low catalytic performances, harsh reaction conditions, and limited substrate scope. It is important to develop new reactions and new protocols for CO(2) transformations at mild conditions and in cost-efficient ways. Herein, a copper-catalyzed and copper-N-heterocyclic carbene-cocatalyzed transformation of CO(2) to carboxylic acids via C?H bond activation of terminal alkynes with or without base additives is reported. Various propiolic acids were synthesized in good to excellent yields under ambient conditions without consumption of any organometallic or organic reagent additives. This system has a wide scope of substrates and functional group tolerances and provides a powerful tool for the synthesis of highly functionalized propiolic acids. This catalytic system is a simple and economically viable protocol with great potential in practical applications. PMID:21059950

Yu, Dingyi; Zhang, Yugen

2010-11-23

119

An experimental and theoretical study on the interaction of N-heterocyclic carbene-derived 1,3-dipoles with methoxycarbonylallenes: highly regio- and stereoselective [3+2]-cycloadditions controlled by the structures of N-heterocycles of 1,3-dipoles.  

Science.gov (United States)

The reactions of N-heterocyclic carbene-derived 1,3-dipoles with methoxycarbonylallenes were studied systematically by means of experimental and theoretical approach. The regioselectivity of [3+2]-cycloaddition of 1,3-dipoles toward the ester-substituted (activated) or alkyl-substituted (less activated) carbon-carbon double bond of methoxycarbonylallenes was strongly governed by the structures of N-heterocycles of 1,3-dipoles. In addition, the reaction temperature played an important part in regulating the regioselectivity of [3+2]-cycloaddition in some cases. While the reaction between benzimidazole carbene-derived 2-thiocarbamoyl benzimidazolium inner salts 5 and methoxycarbonylallenes 6 with or without heating gave predominantly adducts of C(+)-C-S(-) moiety to the alkyl-substituted double bond of methoxycarbonylallenes, triazole carbene-derived triazolium salts 14 underwent mainly its [3+2]-cycloaddition of C(+)-C-S(-) dipoles to the ester-substituted double bond of methoxycarbonylallenes. In the case of imidazoline carbene-derived 1,3-dipoles 10, the cycloaddition occurred between the C(+)-C-S(-) fragment and the activated double bond at room temperature, while in refluxing benzene, however, the same reaction yielded cycloadducts from the addition of 10 to the less activated double bond of methoxycarbonylallenes. DFT calculation revealed asynchronous cycloaddition mechanisms for the reactions of benzimidazole and imidazoline carbene-derived 1,3-dipoles with methoxycarbonylallenes, and a concerted mechanism for the reaction of triazole carbene-derived dipoles. The different regioselectivity of the reaction originated from the combination of electronic and steric effects of the reactants and the stability of the final products. PMID:19231834

Cheng, Ying; Wang, Bo; Wang, Xiao-Rong; Zhang, Jian-Hong; Fang, De-Cai

2009-03-20

120

Substrate-controlled and site-selective [3+2] cycloadditions of N-heterocyclic carbene derived ambident dipoles.  

Science.gov (United States)

2-aryl thiocarbamoyl benzimidazolium and imidazolinium inner salts derived from benzimidazole and imidazoline carbenes are unique ambident C-C-S and C-C-N 1,3-dipolar systems, which undergo highly efficient and site-selective cycloaddition reactions with dimethyl acetylenedicarboxylate or dibenzoylacetylene to furnish spiro(imidazole-2,3'-thiophene) derivatives in excellent yields. When treated with ethyl propiolate, methyl acrylate or acrylonitrile, spiro(imidazole-2,3'-pyrrole) derivatives were formed in good yields. Theoretical studies revealed an asynchronous concerted mechanism for both the C-C-S and C-C-N 1,3-dipolar cycloaddition reactions. The site selectivity in the [3+2] cycloaddition reaction of ambident 1,3-dipoles was predictably regulated by both the electronic and steric effects of dipolarophiles. PMID:17323390

Cheng, Ying; Liu, Mei-Fang; Fang, De-Cai; Lei, Xue-Mei

2007-01-01

121

Catalisadores contendo carbenos n-heterocíclicos como ligantes: propriedades, sínteses, aplicações e comparação com outros ligantes / Catalysts containing n-heterocyclic carbenes as ligands: properties, syntheses, applications and comparison with other catalysts  

Scientific Electronic Library Online (English)

Full Text Available SciELO Brazil | Language: Portuguese Abstract in portuguese [...] Abstract in english N-heterocyclic carbenes (NHCs) have become of considerable importance in modern organometallic chemistry and homogeneous catalysis. There are several advantages in the use NHCs over their phosphorus analogues, which explains the enormous development of NHC ligands in the field of organometallic cata [...] lysis in the past few years. In this article, we present an overview of the importance of the catalysts containing NHC ligands, their synthesis, some pertinent synthetic applications, and a brief comparison with other catalysts.

Julio Cezar, Pastre; Carlos Roque Duarte, Correia.

122

Two 2-D Cd(II) complexes constructed from N-heterocyclic and aromatic polycarboxylate ligands  

Science.gov (United States)

Two new complexes, {[Cd(bimt)(bdc)(H 2O)]·2H 2O} n ( 1) and [Cd(bimt)(Hbtc)] n ( 2) have been synthesized through the self-assembly of Cd(NO 3) 2·4H 2O with unsymmetrical N-heterocyclic ligand 2-((benzoimidazol-yl)methyl)-1H-tetrazole (bimt) and aromatic polycarboxylate acid 1,3-benzenedicarboxylic acid (H 2bdc) or 1,3,5-benzenetricarboxylic acid (H 3btc). Single crystal X-ray diffraction determination shows that complex 1 possesses an infinite 2-D layered structure with parallelogram grid units. Complex 2 is a 2-D layered structure containing 1-D ladder-like chains linked by the Hbtc 2- anions in tridentate bridging fashion. Both complexes are stacked into complicated 3-D frameworks by coordinating bonds and hydrogen bonds in the solid state. In addition, the luminescent properties of both complexes have been investigated in the solid state at room temperature.

Zhang, Jun; Li, Baoding; Wu, Xinjuan; Yang, Huaixia; Zhou, Wan; Meng, Xiangru; Hou, Hongwei

2010-12-01

123

Synthesis, spectroscopic studies and reactivity of triphenylphosphine ruthenium (II) complexes with N-heterocyclic ligands  

International Nuclear Information System (INIS)

Reported is the chemistry of triphenylphosphine ruthenium (II) complexes of general formula RuCl2(PPh3)2L2 and RuCl2(PPh3)2A, obtained from the reaction of RuCl2(PPh3)3 with N-heterocyclic ligands L, or A (of ambidentate nature). The electronic spectra exhibit two strong metal-to-ligand charge-transfer bands, ascribed to the b1(dxz)->b1(pi) and a2(dxy)->a2(pi) transitions, and a third, weak band ascribed to the b2(dyz)->a2(pi) transition. The electronic states and the vibrational modes of the complexes were characterized by means of their resonance Raman and infrared absorption spectra. Thermogravimetric and thermodifferential analysis indicated that the melting process is succeeded by an exothermic reaction, and that the weigh loss starts to occur only after this step. The complexes dissociated in CHCl3 solution, showing preferential labilization of the phosphine ligands, as in the case of the hydrogenation catalyst Ru(PPh3)3Cl2. In the presence of CO, RuCl2(CO)2L2 complexes were gennerated. Several derivatives were isolated and characterized. (author)

124

N-heterocycle carbene (NHC)-ligated cyclopalladated N,N-dimethylbenzylamine: a highly active, practical and versatile catalyst for the Heck-Mizoroki reaction.  

Science.gov (United States)

The wide dissemination of catalytic protocols in academic and industrial laboratories is facilitated by the development of catalysts that are not only highly active but also user-friendly, stable to moisture, air and long term storage and easy to prepare on a large scale. Herein we describe a protocol for the Heck-Mizoroki reaction mediated by cyclopalladated N,N-dimethylbenzylamine (dmba) ligated with a N-heterocyclic carbene, 1,3-bis(mesityl)imidazol-2-ylidene (IMes), that fulfils these criteria. The precatalyst can be synthesized on approximately 100 g scale by a tri-component, sequential, one-pot reaction of N,N-dimethylbenzylamine, PdCl2 and IMes.HCl in refluxing acetonitrile in air in the presence of K2CO3. This single component catalyst is stable to air, moisture and long term storage and can be conveniently dispensed as a stock solution in NMP. It mediates the Heck-Mizoroki reaction of a range of aryl- and heteroaryl bromides in reagent grade NMP at the 0.1-2 mol% range without the need for rigorous anhydrous techniques or a glovebox, and is active even in air. The catalyst is capable of achieving very high levels of catalytic activity (TON of up to 5.22 x 10(5)) for the coupling of a deactivated arylbromide, p-bromoanisole, with tBu acrylate as a benchmark substrate pair. A wide range of aryl bromides, iodides and, for the first time with a NHC-Pd catalyst, a triflate was coupled with diverse acrylate derivatives (nitrile, tert-butyl ester and amides) and styrene derivatives. The use of excess (>2 equiv.) of the aryl bromide and tert-butyl acrylate leads to mixture of tert-butyl beta,beta-diarylacrylate and tert-butyl cinnamate derivatives depending on the substitution pattern of the aryl bromide. Electron rich m- and p-substituted arylbromides give the diarylated products exclusively, whereas electron-poor aryl bromides give predominantly mono-arylated products. For o-substituted aryl bromides, no doubly arylated products could be obtained under any conditions. Overall, the active catalyst (IMes-Pd) shows higher activity with electron-rich aryl halides, a marked difference compared with the more commonly used phosphane-Pd or non-ligated Pd catalysts. PMID:19421449

Peh, Guang-Rong; Kantchev, Eric Assen B; Zhang, Chi; Ying, Jackie Y

2009-05-21

125

N-Heterocyclic carbene–palladium catalysts for the direct arylation of pyrrole derivatives with aryl chlorides  

Directory of Open Access Journals (Sweden)

Full Text Available New Pd–NHC complexes have been synthesized and employed for palladium-catalyzed direct arylation of pyrrole derivatives by using electron-deficient aryl chlorides as coupling partners. The desired coupling products were obtained in moderate to good yields by using 1 mol % of these air-stable palladium complexes. This is an advantage compared to the procedures employing air-sensitive phosphines, which have been previously shown to promote the coupling of aryl chlorides with heteroarenes.

Ismail Özdemir

2013-02-01

126

What can NMR spectroscopy of selenoureas and phosphinidenes teach us about the ?-accepting abilities of N-heterocyclic carbenes?  

KAUST Repository

The electronic nature of the interaction of NHCs with metal centres is of interest when exploring their properties, how these properties influence those of metal complexes, and how these properties might depend on ligand structure. Selenourea and phosphinidene complexes have been proposed to allow the measurement of the ?-accepting ability of NHCs, independent of their ?-donating ability, via the collection of 77Se or 31P NMR spectra, respectively. Herein, the synthesis and characterisation of selenoureas derived from a range of imidazol-2-ylidenes, 4,5-dihydroimidazol-2-ylidenes and triazol-2-ylidenes are documented. Computational studies are used to explore the link between the shielding of the selenium centre and the electronic properties of the NHCs. Results show that ?Se is correlated to the energy gap between a filled lone pair orbital on Se and the empty ?* orbital corresponding to the Se–NHC bond. Bond energy decomposition analysis indicated no correlation between the orbital ?-contribution to bonding and the chemical shielding, while a good correlation was found between the ?-contribution to bonding and the chemical shielding, confirming that this technique is indeed able to quantify the ability of NHCs to accept ?-electron density. Calculations conducted on phosphinidene adducts yielded similar results. With the link between ?Se and ?P and ?-back bonding ability clearly established, these compounds represent useful ways in which to fully understand and quantify this aspect of the electronic properties of NHCs.

Nelson, David J.

2015-01-02

127

A Facile Route to Backbone-Tethered N-Heterocyclic Carbene (NHC) Ligands via NHC to aNHC Rearrangement in NHC Silicon Halide Adducts.  

Science.gov (United States)

The reaction of 1,3-diisopropylimidazolin-2-ylidene (iPr2 Im) with diphenyldichlorosilane (Ph2 SiCl2 ) leads to the adduct (iPr2 Im)SiCl2 Ph2 1. Prolonged heating of isolated 1 at 66?°C in THF affords the backbone-tethered bis(imidazolium) salt [((a) HiPr2 Im)2 SiPh2 ](2+) ?2?Cl(-) 2 ("(a) " denotes "abnormal" coordination of the NHC), which can be synthesized in high yields in one step starting from two equivalents of iPr2 Im and Ph2 SiCl2 . Imidazolium salt 2 can be deprotonated in THF at room temperature using sodium hydride as a base and catalytic amounts of sodium tert-butoxide to give the stable N-heterocyclic dicarbene ((a) iPr2 Im)2 SiPh2 3, in which two NHCs are backbone-tethered with a SiPh2 group. This easy-to-synthesize dicarbene 3 can be used as a novel ligand type in transition metal chemistry for the preparation of dinuclear NHC complexes, as exemplified by the synthesis of the homodinuclear copper(I) complex [{(a) (ClCu?iPr2 Im)}2 SiPh2 ] 4. PMID:25534013

Schneider, Heidi; Schmidt, David; Radius, Udo

2015-02-01

128

Contrasting reactivities of silicon and germanium complexes supported by an N-heterocyclic guanidine ligand.  

Science.gov (United States)

We report the synthesis of an acyclic two-coordinate germylene supported by two bulky and electron donating N-heterocyclic guanidine [IPr?N](-) ligands (IPr = [(HCNDipp)2C:]; Dipp = [2,6-(i)Pr2C6H3]), and its reactivity with molecular hydrogen to form IPr?NH, which presumably proceeds via the unstable intermediate [H2Ge(N?IPr)2]. Our attempts to isolate the corresponding silylene [:Si(N?IPr)2] led to an unexpected ligand activation/rearrangement process involving N-C(aryl) bond cleavage within the N-heterocyclic guanidine ligand; this transformation was also studied by computational methods. PMID:25621845

Lui, Melanie W; Merten, Christian; Ferguson, Michael J; McDonald, Robert; Xu, Yunjie; Rivard, Eric

2015-02-16

129

Cyclometalated Pd(II) and Ir(III) 2-(4-bromophenyl)pyridine complexes with N-heterocyclic carbenes (NHCs) and acetylacetonate (acac): synthesis, structures, luminescent properties and application in one-pot oxidation/Suzuki coupling of aryl chlorides containing hydroxymethyl.  

Science.gov (United States)

A series of cyclopalladated 2-(4-bromophenyl)pyridine (bpp) complexes [Pd(bpp)(NHC)Cl] 1-3, [Pd(bpp)(acac)] 4, cyclometalated iridium(iii) complexes [Ir(bpp)2Cl]25 and [Ir(bpp)2(acac)] 6 have been synthesized and characterized. Their detailed structures have been determined by X-ray diffraction and many intermolecular C-HX (Cl, Br, ?) and ?? interactions were found in their crystals. Cyclometalated complexes 1-4 and 6 exhibit luminescence with emission peaks of 390-543 nm in dichloromethane solution under UV irradiation. Their application to coupling reactions of aryl chlorides containing hydroxymethyl was also investigated. An efficient 3/Cu cocatalyzed oxidation/Suzuki reaction for the synthesis of biarylaldehydes from chloro-phenylmethanol and arylboronic acids in air has been developed. In addition, a 6/3-cocatalyzed one-pot reaction of acetylferrocene, (2-amino-5-chlorophenyl)methanol, and arylboronic acids provided 6-aryl-2-ferrocenylquinolines in moderate to good yields. PMID:24878778

Xu, Chen; Li, Hong-Mei; Xiao, Zhi-Qiang; Wang, Zhi-Qiang; Tang, Si-Fu; Ji, Bao-Ming; Hao, Xin-Qi; Song, Mao-Ping

2014-07-14

130

Enyne Metathesis Catalyzed by Ruthenium Carbene Complexes  

DEFF Research Database (Denmark)

Enyne metathesis combines an alkene and an alkyne into a 1,3-diene. The first enyne metathesis reaction catalyzed by a ruthenium carbene complex was reported in 1994. This review covers the advances in this transformation during the last eight years with particular emphasis on methodology development and synthetic applications.

Poulsen, Carina Storm; Madsen, Robert

2003-01-01

131

N-Heterocyclic Carbene-Catalyzed Diastereoselective and Enantioselective Reaction of 2-Aroylvinylcinnamaldehydes with ?,?-Unsaturated Imines: Complete Control and Switch of Diastereoselectivity by N-Substituents of Catalysts.  

Science.gov (United States)

Highly diastereoselective and enantioselective reactions between 2-aroylvinylcinnamaldehydes and ?,?-unsaturated imines were achieved under asymmetric catalysis of chiral triazole carbene catalysts. In the presence of N-anisylindeno[2,1-b]triazolo[4,3-d][1,4]oxazinium salt, the reaction of 2-aroylvinylcinnamaldehydes with ?,?-unsaturated imines afforded indeno[2,1-c]pyran-1-one derivatives 4 with 90%-99% ee, while enantiopure indenocyclopentan-1-ones 5 (>99% ee) were obtained under the catalysis of N-mesitylindeno[2,1-b]triazolo[4,3-d][1,4]oxazinium salt. A slight variation of an N-substituent on triazole carbenes was found to switch completely the diastereoselectivity of the reaction for the formation of indeno[2,1-c]pyran-1-ones. PMID:25584883

Wang, Zi-Tian; Zhao, Yuan; Wang, Zhan-Yong; Cheng, Ying

2015-02-01

132

Uranium(IV) nucleophilic carbene complexes  

International Nuclear Information System (INIS)

The mono-, bis-, and tris-carbene uranium complexes [Li(THF)2U(SCS)Cl3(THF)] (2a), [U(SCS)2(THF)2] (3a), and [{Li(OEt2)}2U(SCS)3] (1) were synthesized in good yields by reactions of UCl4 and the stoichiometric amount of Li2(SCS) [(SCS)2 = [Ph2P(dS)]2C2]. Complex 3a was also obtained by comproportionation reaction of 1 and 0.5 molar equiv of UCl4 and further reacted with 1 molar equiv of UCl4 to give the neutral mono-carbene [U(SCS)Cl2(THF)2] (5a). Treatment of U(NEt2)4 with H2C(Ph2PS)2 in THF led to a mixture of 3a and [U(SCS)(NEt2)2] (6), while the same reaction in Et2O gave the mixed alkyl-carbene compound [U(SCS)(SCHS)(NEt2)] (7) in 85% yield. The cationic uranium carbene complex [U(SCS)(NEt2)(THF)3][BPh4] (9) was isolated in almost quantitative yield from reaction of [U(NEt2)3][BPh4] and H2C(Ph2PS)2. Mono-carbenes 2a, 5a, and 9 were used as precursors for the synthesis of Cp and COT derivatives (Cp = C5H5, COT=C8H8). Treatment of 2a with 1 or 2 molar equiv of TlCp gave [Tl{U(Cp)(SCS)}2(?-Cl)3] (10) and [U(Cp)2(SCS)] (11) in 90% and 79% yield, respectively, whereas [U(Cp*)2(SCS)] (12) (Cp* = C5Me5) was obtained only by reaction of [U(Cp*)2Cl2] and Li2(SCS). Reactions of 5a or 9 with K2COT gave [U(COT)(SCS)(THF)] (13) in 78% and 99% yield, respectively. 2a, [Li(THF)(Et2O)U(SCS)(?-Cl)3]2 (2b), [U(SCS)2(py)2] 3 1.5py 3 0.5THF (3b 3 1.5py 3 0.5THF), [U(SCS){CS(Ph2PS)2}(py)] (4), 7.toluene, [Li(THF)2U(SCS)(NEt2)(?-O)]2 (8), 10.2 toluene, 11, 12, and 13.0.5 pentane were characterized by X-ray diffraction. The crystal data revealed that, in contrast to transition metal complexes, changes in the coordination sphere of the U(IV) center have little influence on the U(double bond)C bond. This feature was explained by DFT analysis of analogous U(IV) and Zr(IV) compounds [M(SCS1)Cl2(py)2] and [M(SCS1)(Cp)2] [M = U, Zr; SCS1 = C(H2PS)2]. Although the 5f orbitals are more radially contracted than the 6d atomic orbitals, the 5f AOs are lower in energy in uranium and can lead to greater angular overlaps in symmetry-constrained systems. As a result, the seven 5f orbitals play a 'buffer' role by engaging in covalent interactions with the carbon center to stabilize the nucleophilic carbene lone pairs. (authors)

133

Facile Thermal W-W Bond Homolysis in the N-Heterocyclic Carbene-Containing Tungsten Dimer [CpW(CO)2(IMe)]2  

Energy Technology Data Exchange (ETDEWEB)

The thermal W-W bond homolysis in [CpW(CO)2(IMe)]2 (IMe = 1,3-dimethylimidazol-2-ylidene) was investigated and was found to occur to a large extent compared to other tungsten dimers such as [CpW(CO)3]2. CpW(CO)2(IMe)H was prepared by heating a solution of [IMeH]+[CpW(CO)2(PMe3)]?, and exists in solution as a mixture of interconverting cis and trans isomers. The carbene rotation in CpW(CO)2(IMe)H was explored by DFT calculations, and low enthalpic barriers (< 3.5 kcal mol?1) are predicted. CpW(CO)2(IMe)H has pKaMeCN = 31.5(3) and deprotonation with KH gives K+[CpW(CO)2(IMe)]? (• MeCN). Hydride abstraction from CpW(CO)2(IMe)H with Ph3C+PF6? in the presence of a coordinating ligand L (MeCN or THF) gives [CpW(CO)2(IMe)(L)]+PF6?. Electrochemical measurements on the anion [CpW(CO)2(IMe)]? in MeCN, together with digital simulations, give an E1/2 of ?1.54(2) V vs Cp2Fe+/0 for the [CpW(CO)2(IMe)]•/? couple. A thermochemical cycle provides the solution bond dissociation free energy of the W-H bond of CpW(CO)2(IMe)H as 61.3(6) kcal mol?1. In the electrochemical oxidation of [CpW(CO)2(IMe)]?, reversible dimerization of the electrogenerated radical CpW(CO)2(IMe)• occurs, and digital simulation provides kinetic and thermodynamic parameters for the monomer-dimer equilibrium: kdimerization ~ 2.5 ? 104 M?1 s?1, khomolysis ~ 0.5 s?1 (i.e., Kdim ~ 5 ? 104 M?1). Reduction of [CpW(CO)2(IMe)(MeCN)]+PF6? with cobaltocene gives the dimer [CpW(CO)2(IMe)]2, which in solution exists as a mixture of anti and gauche rotomers. As expected from the electrochemical experiments, the dimer is in equilibrium with detectable amounts of CpW(CO)2(IMe)•. This species was observed by IR spectroscopy, and its presence in solution is also in accordance with the observed reactivity toward 2,6-di-tert-butyl-1,4-benzoquinone, chloroform and dihydrogen. This work was supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, Division of Chemical Sciences, Biosciences and Geosciences. Pacific Northwest National Laboratory is a multiprogram national laboratory operated for DOE by Battelle. The EPR studies were performed at EMSL, a national scientific user facility sponsored by the Department of Energy’s Office of Biological and Environmental Research located at Pacific Northwest National Laboratory.

van der Eide, Edwin F.; Liu, Tianbiao L.; Camaioni, Donald M.; Walter, Eric D.; Bullock, R. Morris

2012-03-05

134

N-heterocycle chelated oxomolybdenum(VI and V) complexes with bidentate citrate.  

Science.gov (United States)

A 1,10-phenanthroline (phen) chelated molybdenum(VI) citrate, [(MoO2)2O(H2cit)(phen)(H2O)2] x H2O (1) (H4cit = citric acid), is isolated from the reaction of citric acid, ammonium molybdate and phen in acidic media (pH 0.5-1.0). A citrato oxomolybdenum(V) complex, [(MoO)2O(H2cit)2(bpy)2] x 4H2O (2), is synthesized by the reduction of citrato molybdate with hydrazine hydrochloride in the presence of 2,2'-bipyridine (bpy), and a monomeric molybdenum(VI) citrate [MoO2(H2cit)(bpy)] x H2O (6) is also isolated and characterized structurally. The citrate ligand in the three neutral compounds uses the alpha-alkoxy and alpha-carboxy groups to chelate as a bidentate leaving the two beta-carboxylic acid groups free, that is different from the tridentate chelated mode in the citrato molybdate(VI and V) complexes. 1 and in solution show obvious dissociation based on 13C NMR studies. PMID:18461203

Zhou, Zhao-Hui; Chen, Can-Yu; Cao, Ze-Xing; Tsai, Khi-Rui; Chow, Yuan L

2008-05-14

135

Intramolecular cyclopropanation reactions of chromium (alkenyloxy)carbene complexes  

Energy Technology Data Exchange (ETDEWEB)

Chromium (aryl)(alkenyloxy)carbene complexes underwent intramolecualr cyclopropanation reactions under mild conditions. Evidence for the intervention of metathesis/readdition and for twist' addition followed by {beta}-hydride elimiantion/reductive elimination was obtained. Carbenes of this class, sufficiently stable to isolate, underwent facile photochemical intramolecualr cyclobutanone formation. Molecular structures were determined by {sup 1}H and {sup 13}C NMR spectroscopy.

Soederberg, B.C.; Hegedus, L.S. (Colorado State Univ., Fort Collins (United States))

1990-12-01

136

The Synthesis of Some Perhydrobenzimidazolinium Salts and Their Application in Pd-Carbene Catalyzed Heck and Suzuki Reactions  

Directory of Open Access Journals (Sweden)

Full Text Available Novel 1,3-dialkylperhydrobenzimidazolinium chloride salts were prepared as precursors of N-heterocyclic carbenes 3a-e by reacting N,N’-dialkylcyclohexandiamine, triethyl orthoformate and ammonium chloride. The salts were characterized spectroscopically and the complexes formed in situ from Pd(OAc2 and 3 have been tested as catalysts in homogenous Heck and Suzuki reactions.

Murat Yi?it

2009-06-01

137

The synthesis of some perhydrobenzimidazolinium salts and their application in pd-carbene catalyzed heck and suzuki reactions.  

Science.gov (United States)

Novel 1,3-dialkylperhydrobenzimidazolinium chloride salts were prepared as precursors of N-heterocyclic carbenes 3a-e by reacting N,N'-dialkylcyclohexandiamine, triethyl orthoformate and ammonium chloride. The salts were characterized spectroscopically and the complexes formed in situ from Pd(OAc)2 and 3 have been tested as catalysts in homogenous Heck and Suzuki reactions. PMID:19513003

Yi?it, Murat

2009-01-01

138

The Synthesis of Some Perhydrobenzimidazolinium Salts and Their Application in Pd-Carbene Catalyzed Heck and Suzuki Reactions  

OpenAIRE

Novel 1,3-dialkylperhydrobenzimidazolinium chloride salts were prepared as precursors of N-heterocyclic carbenes 3a-e by reacting N,N’-dialkylcyclohexandiamine, triethyl orthoformate and ammonium chloride. The salts were characterized spectroscopically and the complexes formed in situ from Pd(OAc)2 and 3 have been tested as catalysts in homogenous Heck and Suzuki reactions.

Murat Yi?it

2009-01-01

139

Ring-closing olefin metathesis on ruthenium carbene complexes: model DFT study of stereochemistry.  

Science.gov (United States)

Ring-closing metathesis (RCM) is the key step in a recently reported synthesis of salicylihalamide and related model compounds. Experimentally, the stereochemistry of the resulting cycloolefin (cis/trans) depends strongly on the substituents that are present in the diene substrate. To gain insight into the factors that govern the observed stereochemistry, density functional theory (DFT) calculations have been carried out for a simplified dichloro(2-propylidene)(imidazole-2-ylidene)ruthenium catalyst I, as well as for the real catalyst II with two mesityl substituents on the imidazole ring. Four model substrates are considered, which are closely related to the systems studied experimentally, and in each case, two pathways A and B are possible since the RCM reaction can be initiated by coordination of either of the two diene double bonds to the metal center. The first metathesis yields a carbene intermediate, which can then undergo a second metathesis by ring closure, metallacycle formation, and metallacycle cleavage to give the final cycloolefin complex. According to the DFT calculations, the stereochemistry is always determined in the second metathesis reaction, but the rate-determining step may be different for different catalysts, substrates, and pathways. The ancillary N-heterocyclic carbene ligand lies in the Ru-Cl-Cl plane in the simplified catalyst I, but is perpendicular to it in the real catalyst II, and this affects the relative energies of the relevant intermediates and transition states. Likewise, the introduction of methyl substituents in the diene substrates influences these relative energies appreciably. Good agreement with the experimentally observed stereochemistry is only found when using the real catalyst II and the largest model substrates in the DFT calculations. PMID:15838859

Vyboishchikov, Sergei F; Thiel, Walter

2005-06-20

140

Directional properties of fluorenylidene moieties in unsymmetrically substituted N-heterocyclic carbenes. Unexpected CH activation of a methylfluorenyl group with palladium. Use in palladium catalysed Suzuki-Miyaura cross coupling of aryl chlorides.  

Science.gov (United States)

Benzimidazolium salts having their two nitrogen atoms substituted by different 9-alkylfluorenyl groups ( and , alkyl(1)/alkyl(2) = Me/Et, Me/Pr, Me/n-Bu, Me/i-Pr, Me/Bn, Me/CH2SMe have been synthesised in high yields in two or three steps from N,N'-bis(9H-fluoren-9-ylidene)benzene-1,2-diamine (). The imidazolium salts were converted readily into the corresponding PEPPSI-type palladium complexes (PEPPSI = pyridine-enhanced precatalyst preparation stabilisation and initiation), while reaction of the methylthioether-substituted salt with PdCl2/K2CO3/pyridine afforded the palladacycle resulting from metallation of the methyl group attached to the fluorenylidene moiety. NMR and X-ray diffraction studies revealed that the carbene ligands in behave as clamp-like ligands, the resulting metal confinement arising from a combination of the orientational properties of the fluorenylidene moieties that push the alkyl groups towards the metal centre and attractive anagostic interactions involving CH2(fluorenyl) groups. Complexes were assessed in Suzuki-Miyaura cross-coupling reactions. Like their symmetrical analogues they displayed high activity in the coupling of phenyl boronic acid with p-tolylchloride but their performance remained slightly inferior to that of the related, symmetrical Et/Et complex . PMID:24927082

Teci, Matthieu; Brenner, Eric; Matt, Dominique; Gourlaouen, Christophe; Toupet, Loïc

2014-08-28

141

Carbene generation by cytochromes and electronic structure of heme-iron-porphyrin-carbene complex: a quantum chemical study.  

Science.gov (United States)

Carbene-heme-iron-porphyrin complexes generated from cytochrome P450 (CYP450)-mediated metabolism of compounds containing methylenedioxyphenyl (MDP) moiety lead to the mechanism-based inhibition (MBI) of CYPs. This coordination complex is termed as the metabolic-intermediate complex (MIC). The bioinorganic chemistry of MDP carbenes has been studied using quantum chemical methods employing density functional theory (B3LYP functional with implicit solvent corrections) to (i) analyze the characteristics of MDP-carbene in terms of singlet-triplet energy difference, protonation, and dimerization energies, etc.; (ii) determine the electronic structure and analyze the Fe-carbene interactions; and (iii) elucidate the potential reaction pathways for the generation of carbene, using Cpd I (iron(IV)-oxo-porphine with SH(-) as the axial ligand) as the model oxidant to mimic the activity of CYP450. The results show that MDP-carbenes are sufficiently stable and nucleophilic, leading to the formation of stable MIC (-40.35 kcal/mol) on the doublet spin state, formed via interaction between ?(LP) of carbene and empty dz(2) orbital of heme-iron. This was aided by the back-bonding between filled d(xz) orbital of heme-iron and the empty p orbital of carbene. The mechanistic pathway proposed in the literature for the generation of MDP-carbene (CH hydroxylation followed by water elimination) was studied, and observed to be unfavorable, owing to the formation of highly stable hydroxylated product (-57.12 kcal/mol). An intriguing pathway involving hydride ion abstraction and proton transfer followed by water elimination step was observed to be the most probable pathway. PMID:23560646

Taxak, Nikhil; Patel, Bhargav; Bharatam, Prasad V

2013-05-01

142

Modulation of the stacking interaction of MN4 (M=Pt, Pd, Au) complexes with tryptophan through N-heterocyclic ligands.  

Science.gov (United States)

A survey of selected N-heterocycle ligands showed that platination of 4-N-dimethylaminopyridine (DMAP) in [Pt(dien)L](2+) (dien=diethylenetriamine) gave especially strong ?-? stacking interactions with tryptophan and the tryptophan-containing C-terminal zinc finger (ZF) of the HIV (human immunodeficiency virus) nucleocapsid protein NCp7. The association constants (all at 10(3)M(-1)) were significantly stronger (25.0 and 28.1 for tryptophan and ZF respectively) than those previously measured for the purine nucleobase 9-ethylguanine (9EtG) in [Pt(dien)(9EtG)](2+) (6.88 and 7.55 for tryptophan and ZF respectively). Extension to Pd and Au complexes also confirmed the utility of DMAP in assisting stacking interactions. The results confirm the utility of a "bioinorganic" approach to targeting and inactivation of medicinal chemistry targets using the dual approach of target recognition (non-covalent) followed by target fixation (covalent). PMID:24206773

Tsotsoros, Samantha D; Bate, Aaron B; Dows, Martina G; Spell, Sarah R; Bayse, Craig A; Farrell, Nicholas P

2014-03-01

143

Exploiting Acyl and Enol Azolium Intermediates via NHeterocyclic Carbene Catalyzed Reactions of Alpha-Reducible Aldehydes  

OpenAIRE

N-heterocyclic carbenes are well known for their role in catalyzing benzoin and Stetter reactions: the generation of acyl anion equivalents from simple aldehydes to react with a variety of electrophiles. However, when an aldehyde bearing a leaving group or unsaturation adjacent to the acyl anion equivalent is subjected to an NHC, a new avenue of reactivity is unlocked, leading to a number of novel transformations which can generate highly complex products from simple starting materials, many ...

Vora, Harit U.; Wheeler, Philip; Rovis, Tomislav

2012-01-01

144

Exceptionally efficient catalytic hydrodechlorination of persistent organic pollutants: application of new sterically shielded palladium carbene complexes.  

Science.gov (United States)

A new sterically shielded carbene with branched aromatic substituents (9a) and two palladium halogenide complexes (11a,b) have been prepared. The single crystal X-ray structures of free carbene 9a and palladium carbene complexes 10b and 11a were determined. Very high catalytic efficiencies were evident for the sterically shielded palladium carbene complexes 10b and 11a,b when the latter complexes were employed as catalysts for hydrodechlorination of the chloroarenes p-dichlorobenzene and hexachlorobenzene. When optimized, the foregoing approach is significantly more effective than those of currently known transition metal carbene complexes. The most active catalysts were found to be the monocarbene complexes of palladium chloride and iodide, both of which feature highly branched aromatic substituents (11a,b). PMID:25355459

Saberov, Vagiz Sh; Evans, Daniel A; Korotkikh, Nikolai I; Cowley, Alan H; Pekhtereva, Tatyana M; Popov, Anatolii F; Shvaika, Oles P

2014-12-28

145

Synthesis and Structure-Activity Correlation Studies of Metal Complexes of ?-N-heterocyclic Carboxaldehyde Thiosemicarbazones in Shewanella oneidensis  

OpenAIRE

This investigation involved the synthesis of metal complexes to test the hypothesis that structural changes and metal coordination in pyridine thiosemicarbazones affect cell growth and cell proliferation in vitro. Thiosemicarbazones are well known to possess antitumor, antiviral, antibacterial, antimalarial, and other activities. Extensive research has been carried out on aliphatic, aromatic, heterocyclic and other types of thiosemicarbazones and their metal complexes. Due to the pronounced r...

Wilson, Barbara A.; Venkatraman, Ramaiyer; Whitaker, Cedrick; Tillison, Quintell

2005-01-01

146

Synthesis, structure and thermal stability of ternary metal complexes based on polycarboxylate and N-heterocyclic ligands  

Science.gov (United States)

The reactions of metal salts with pyrazine-2,3-dicarboxylic acid (H 2pzdc), pyridine-2,5-dicarboxylic acid (H 2pydc), pyrazine-2,3,5,6-tetracarboxylic acid (H 4pztc), 4,4'-bipyridine (bipy) and 1,10-phenanthroline (phen) afforded four new ternary complexes, namely [Co 2(pzdc) 2(bipy)(H 2O) 2] n·3 nH 2O ( 1), [Zn 2(pzdc) 2(bipy)(H 2O) 2] n·3 nH 2O ( 2), [Co(pydc) 2(H 2O) 2](H 2bipy) ( 3) and [Cu 2(pztc)(phen) 2(H 2O) 2]·2HNO 3·2H 2O ( 4). The metal centers are all six-coordinated. Compounds 1 and 2 are 2D coordination polymers exhibiting wave-like polymeric networks. The 2D layers are stacked in an interpenetrating mode to form double-layered frameworks, which possess ˜8 Å×6 Å tunnels occupied by (H 2O) 6 clusters. Compound 3 is a mononuclear supramolecular compound in which 4,4'-bipyridine is protonated and acted as a cationic building block. Compound 4 is a centro-symmetric binuclear complex. Pztc 4- as a hexadentate ligand coordinates to two Cu(II) ions to form four chelating rings. Phen are arranged in an ABAB parallel fashion to form a supramolecular architecture incorporating HNO 3 lattice molecule. The thermal stabilities of 1- 4 and luminescence of zinc complex 2 were also investigated.

Fang, Ming-Jin; Li, Ming-Xing; He, Xiang; Shao, Min; Pang, Wei; Zhu, Shou-Rong

2009-03-01

147

Assignment of the charge-transfer excited states of bis(N-heterocyclic) complexes of copper(I)  

International Nuclear Information System (INIS)

Four title complexes were investigated spectroscopically to ascertain the natures of their singlet and triplet excited-state manifolds. Absorption (room temperature, RT) and luminescence (77 K) spectra were measured for all the species. Augmented by additional measurements for the bis(2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline)copper(I) ion [MCD (RT), excitation polarization measurements (100 K), and variations of both the emission spectra and the lifetimes as a function of temperature], group theoretical assignments of both the low-lying singlet and triplet charge-transfer states have been made. The model invokes a lowering of the symmetry from D2d to D2 to account for the experimental observations

148

Fischer carbene complexes with two chromium centers as potential molecular wires.  

Czech Academy of Sciences Publication Activity Database

Lausanne : International Society of Electrochemistry, 2014. ise142050. [Annual Meeting of the International Society of Electrochemistry /65./. 31.08.2014-05.09.2014, Lausanne] Institutional support: RVO:61388955 Keywords : Fiescher carbene complexes * electron transfer * electrochemistry Subject RIV: CG - Electrochemistry

Metelková, R.; Tobrman, T.; Hoskovcová, I.; Ludvík, Ji?í

149

A rhodium IBiox[(-)-menthyl] complex as a highly selective catalyst for the asymmetric hydroarylation of azabicyles: an alternative route to epibatidine.  

Science.gov (United States)

The synthesis and characterization of a new chiral rhodium N-heterocyclic carbene complex, Rh(IBiox[(-)-menthyl](CO)(2)Cl, is reported. In addition, the very high enantioselectivity exhibited by this complex, as a catalyst for the asymmetric hydroarylation of azabicycles, is demonstrated and applied to the synthesis of epibatidine. PMID:20550216

Bexrud, Jason; Lautens, Mark

2010-07-16

150

{alpha},{beta}-Unsaturated Fischer carbene complexes as chemical multitalents  

Energy Technology Data Exchange (ETDEWEB)

The well established reaction of {alpha},{beta}-unsaturated Fischer carbenechromium complexes 6(R{sup 1} = H) with alkynes normally proceeds with carbonyl insertion to yield 4-alkoxyphenols 9. Led by the incidental formation of a cyclopentadiene 3 from certain {beta}-aminosubstituted complexes 6(X = NR{sub 2}{sup 3}, R{sup 1} = cPr) the authors have studied the influences of the nature of substituents (R{sup 1}, X on 6; R{sub L}, R{sub S} in the alkyne; R{sup 3} in the amino group), solvents, and temperature on the outcome of the reaction. Imino substitution on complexes 6 leads to 2H-pyrroles 1, a free primary amino group (X = NH{sub 2}) to pyridines 5, and bulky substituents R{sup 1} to cyclopenta[b]pyrans 8 with double insertion of an alkyne. Eventually, appropriate conditions have been developed which permit to selectively prepare either 3-alkoxy-5-(dialkylamino)cyclopentadienes 3 (as synthetic equivalents of cyclopentenones 4), 5-(dialkylaminomethylene)cyclopent-2-enones 7, 3-alkoxy-2-(1{prime}-morpholino-1{prime}-alkenyl)cyclopent-2-enones 10, and 2-acyl-3-(dialkylamino)cyclopent-2-enones 11 from easily accessible carbene complexes 6 (X = NR{sub 2}{sup 3}) in high yields. Mechanistic aspects and implications of these novel transformations will be discussed.

Meijere, A. de [Institut fuer Organische Chemie der George-August-Universitaet Goettingen (Germany)

1995-12-31

151

Insights on the mechanism of thioredoxin reductase inhibition by gold N-heterocyclic carbene compounds using the synthetic linear selenocysteine containing C-terminal peptide hTrxR(488-499): an ESI-MS investigation.  

Science.gov (United States)

Gold-based drugs typically behave as strong inhibitors of the enzyme thioredoxin reductase (hTrxR), possibly as the consequence of direct Gold(I) coordination to its active site selenocysteine. To gain a deeper insight into the molecular basis of enzyme inhibition and prove gold-selenocysteine coordination, the reactions of three parent Gold(I) NHC compounds with the synthetic C-terminal dodecapeptide of hTrxR containing Selenocysteine at position 498, were investigated by electrospray ionization mass spectrometry (ESI-MS). Formation of 1:1 Gold-peptide adducts, though in highly different amounts, was demonstrated in all cases. In these adducts the same [Au-NHC](+) moiety is always associated to the intact peptide. Afterward, tandem MS experiments, conducted on a specific Gold-peptide complex, pointed out that Gold is coordinated to the selenolate group. The relatively large strength of the Gold-selenolate coordinative bond well accounts for potent enzyme inhibition typically afforded by these Gold(I) compounds. In a selected case, the time course of enzyme inhibition was explored. Interestingly, enzyme inhibition turned out to show up very quickly and reached its maximum just few minutes after mixing. Overall, the present results offer some clear insight into the process of thioredoxin reductase inhibition by Gold-based compounds. PMID:24524917

Pratesi, Alessandro; Gabbiani, Chiara; Michelucci, Elena; Ginanneschi, Mauro; Papini, Anna Maria; Rubbiani, Riccardo; Ott, Ingo; Messori, Luigi

2014-07-01

152

Substitution effects on the formation of T-shaped palladium carbene and thioketone complexes from Li/Cl carbenoids.  

Science.gov (United States)

The preparation of palladium thioketone and T-shaped carbene complexes by treatment of thiophosphoryl substituted Li/Cl carbenoids with a Pd(0) precursor is reported. Depending on the steric demand, the anion-stabilizing ability of the silyl moiety (by negative hyperconjugation effects) and the remaining negative charge at the carbenic carbon atom, isolation of a three-coordinate, T-shaped palladium carbene complex is possible. In contrast, insufficient charge stabilization results in the transfer of the sulfur of the thiophosphoryl moiety and thus in the formation of a thioketone complex. While the thioketones are stable compounds the carbene complexes are revealed to be highly reactive and decompose under elimination of Pd metal. Computational studies revealed that both complexes are formed by a substitution mechanism. While the ketone turned out to be the thermodynamically favored product, the carbene is kinetically favored and thus preferentially formed at low reaction temperatures. PMID:24664573

Molitor, Sebastian; Feichtner, Kai-Stephan; Kupper, Claudia; Gessner, Viktoria H

2014-08-18

153

Ring contraction of six-membered metallabenzynes to five-membered metal-carbene complexes: a comparison with organic analogues.  

Science.gov (United States)

The ring contraction of six-membered metallabenzynes to five-membered metal-carbene complexes in comparison with the corresponding rearrangement of benzyne to cyclopentadienylidene carbene have been studied by computational quantum mechanical calculations. The rearrangement of benzyne to a cyclopentadienylidene carbene is endothermic by 27.8 kcal mol(-1). The instability of the cyclopentadienylidene carbene is attributed to the electron deficient singlet carbene carbon atom. However, the isolobal replacement of a sp-hybridized carbon atom in benzyne by a 14 valence electron transition metal fragment (M(PH3)2Cl2, M = Fe, Ru and Os) makes the corresponding rearrangement feasible. The first row transition metal iron shows thermodynamic (exothermic by 19.1 kcal mol(-1)) and kinetic preference (energy barrier of 1.8 kcal mol(-1)) towards the carbene complex. However, the preference reduces down the group. The coordination number of the metal as well as the low-lying in-plane M-C ?*-MO play a crucial role for this rearrangement. The conversion of metallabenzynes to metal-carbene complexes is also associated with a ring plane rotation to attain an effective overlap between the metal d-orbital and the p-orbital on the carbene carbon atom. PMID:23907353

Anusha, Chakkittakandiyil; De, Susmita; Parameswaran, Pattiyil

2013-10-01

154

Synthetic, structural and spectroscopic studies of (pseudo)halo(1,3-di-tert-butylimidazol-2-ylidine)gold complexes.  

Science.gov (United States)

A series of (pseudo)halo(1,3-di-tert-butylimidazol-2-ylidine)gold complexes [(But2Im)AuX](X = Cl, Br, I, CN, N3, NCO, SCN, SeCN, ONO2, OCOCH3, CH3) have been synthesized and characterised spectroscopically and structurally. 13C NMR chemical shifts for the carbene carbon vary widely with differing ancillary anion, correlating well with the sigma-donor ability of the latter and with the M-C(carbene) bond distance. These results reinforce the notion that N-heterocyclic carbene ligands are primarily sigma-donor ligands with little pi-acceptor ability. PMID:15605145

Baker, Murray V; Barnard, Peter J; Brayshaw, Simon K; Hickey, James L; Skelton, Brian W; White, Allan H

2005-01-01

155

N-heterocyclic donor- and acceptor-type ligands based on 2-(1H-[1,2,3]triazol-4-yl)pyridines and their ruthenium(II) complexes.  

Science.gov (United States)

New 2-(1H-[1,2,3]triazol-4-yl)pyridine bidentate ligands were synthesized as bipyridine analogs, whereas different phenylacetylene moieties of donor and acceptor nature were attached at the 5-position of the pyridine unit. The latter moieties featured a crucial influence on the electronic properties of those ligands. The N-heterocyclic ligands were coordinated to ruthenium(II) metal ions by using a bis(4,4'-dimethyl-2,2'-bipyridine)ruthenium(II) precursor. The donor or acceptor capability of the 2-(1H-[1,2,3]triazol-4-yl)pyridine ligands determined the quantum yield of the resulting ruthenium(II) complexes remarkably. Separately, 2-([1,2,3]triazol-4-yl)pyridine ligands are known to be potential quenchers, but using these new ligand systems led to room temperature emission of the corresponding ruthenium(II) complexes. The compounds have been fully characterized by elemental analysis, high-resolution ESI mass spectrometry, (1)H and (13)C NMR spectroscopy, and X-ray crystallography. Theoretical calculations for two ruthenium(II) complexes bearing a donor and acceptor unit, respectively, were performed to gain a deeper understanding of the photophysical behavior. PMID:20496945

Happ, Bobby; Escudero, Daniel; Hager, Martin D; Friebe, Christian; Winter, Andreas; Görls, Helmar; Altunta?, Esra; González, Leticia; Schubert, Ulrich S

2010-06-18

156

Helicene-grafted vinyl- and carbene-osmium complexes: an example of acid-base chiroptical switching.  

Science.gov (United States)

The first helicene-based carbene-osmium complex has been prepared from a vinyl-osmium derivative and this system has been shown to behave as a potential acid-base triggered chiroptical switch. PMID:24322581

Anger, Emmanuel; Srebro, Monika; Vanthuyne, Nicolas; Roussel, Christian; Toupet, Loïc; Autschbach, Jochen; Réau, Régis; Crassous, Jeanne

2014-03-18

157

Covalent immobilization of active lysozyme on Si/glass surface using alkoxy Fischer carbene complex on SAM.  

Science.gov (United States)

A cross-metathesis reaction between an alkene terminated self-assembled monolayer (SAM) on glass/Si wafer and an alkene tethered Fischer carbene complex yielded a functionalized surface. Rapid aminolysis of the Fischer carbene moieties permit efficient anchoring of amine containing molecules on such a surface. Attachment of 1-pyrenemethylamine was thus monitored by ATR-IR spectroscopy and fluorescence microscopy. Similarly, BSA and lysozyme were individually grafted to such Fischer carbene modified surfaces using their pendant lysine residues. It has been demonstrated that the anchored lysozyme retains its bactericidal property. PMID:21629886

Dutta, Piyali; Ray, Namrata; Roy, Sarita; Dasgupta, Anjan Kr; Bouloussa, Othman; Sarkar, Amitabha

2011-07-21

158

Phosphorus-stabilized titanium carbene complexes: synthesis, reactivity and DFT studies.  

Science.gov (United States)

The synthesis of two novel titanium carbene complexes from the bis(thiophosphinoyl)methanediide geminal dianion 1 (SCS(2-) ) is described. Dianion 1 reacts cleanly with 0.5 equivalents of [TiCl4 (thf)2 ] to afford the bis-carbene complex [(SCS)2 Ti] (2) in 86?% yield. The mono-carbene complex [(SCS)TiCl2 (thf)] (3) can also be obtained by using an excess of [TiCl4 (thf)2 ]. The structures of 2 and 3 are confirmed by X-ray crystallography. A strong nucleophilic reactivity towards various electrophiles (ketones and aldehydes) is observed. The reaction of 3 with N,N'-dicyclohexylcarbodiimide (DCC) and phenyl isocyanate leads to the formation of two novel diphosphinoketenimines 8?a and 8?b. The bis-titanium guanidinate complex 9 is trapped as the by-product of the reaction with DCC. The X-ray crystal structures of 8?a and 9 are presented. The mechanism of the reaction between complex 3 and DCC is rationalized by DFT studies. PMID:25339253

Lafage, Mathieu; Heuclin, Hadrien; Le Goff, Xavier-Frédéric; Saffon-Merceron, Nathalie; Mézailles, Nicolas

2014-12-15

159

Electrochemical behaviour and structure of novel phosphine- and phosphite-substituted tungsten(0) Fischer carbene complexes  

International Nuclear Information System (INIS)

Highlights: • Synthesis and crystal structure of novel phosphine- and phosphite-substituted Fischer ethoxy-W-carbenes. • DFT understanding of oxidation and reduction centre of W-carbenes. • Relationship between redox potentials and DFT calculated energies of W-carbenes. - Abstract: The electrochemical behaviour of a series of sixteen novel Fischer ethoxy- and aminocarbene complexes of the type [(CO)4(PPh3)W = C(X)R] with R = 2-thienyl or 2-furyl and X = OEt or NHCy, (1-4), [(CO)3(dppe)W = C(X)R] with R = 2-thienyl or 2-furyl and X = OEt or NHCy, (5-8) (dppe = 1,2-bis(diphenylphosphino)ethane) and [(CO)4P(OPh)3W = C(X)R] with R = 2-thienyl or 2-furyl and X = OEt or NHCy, (9-12) is investigated by means of cyclic voltammetry. The complexes all exhibit a two-electron oxidation process that is W-based and a one-electron reduction that is mainly localized on the carbene ligand. Complexes 1-4 and 9-12 are considerably more difficult to oxidize than 5-8 due to the better ?-acceptor ability of the (CO)4(PR?3) (R? = Ph or OPh) ligand combination than that of (CO)3(dppe). Density functional theory calculations on the neutral, reduced and oxidized complexes confirmed the role of the frontier orbitals in the oxidation and reduction processes and enabled formulation of mathematical relationships that can be used to predict experimental measured potentials. X-ray crystal structures of 2cis, 3 and 5 are discussed

160

Salicylaldimine Ruthenium Alkylidene Complexes: Metathesis Catalysts Tuned for Protic Solvents  

OpenAIRE

Tuning the electronic and steric environment of olefin metathesis catalysts with specialized ligands can adapt them to broader applications, including metathesis in aqueous solvents. Bidentate salicylaldimine ligands are known to stabilize ruthenium alkylidene complexes, as well as allow ring-closing metathesis in protic media. Here, we report the synthesis and characterization of exceptionally robust olefin metathesis catalysts bearing both bidentate salicylaldimine and N-heterocyclic carben...

Binder, Joseph B.; Guzei, Ilia A.; Raines, Ronald T.

2007-01-01

161

Synthesis and Structure-Activity Correlation Studies of Metal Complexes of α-N-heterocyclic Carboxaldehyde Thiosemicarbazones in Shewanella oneidensis  

OpenAIRE

This investigation involved the synthesis of metal complexes to test the hypothesis that structural changes and metal coordination in pyridine thiosemicarbazones affect cell growth and cell proliferation in vitro. Thiosemicarbazones are well known to possess antitumor, antiviral, antibacterial, antimalarial, and other activities. Extensive research has been carried out on aliphatic, aromatic, heterocyclic and other types of thiosemicarbazones and their metal complexes. Due to the pronounced r...

Quintell Tillison; Cedrick Whitaker; Ramaiyer Venkatraman; Wilson, Barbara A.

2005-01-01

162

Synthesis and bonding in carbene complexes of an unsymmetrical dilithio methandiide: a combined experimental and theoretical study.  

Science.gov (United States)

Herein, we report the preparation of a new unsymmetrical, bis(thiophosphinoyl)-substituted dilithio methandiide and its application for the synthesis of zirconium- and palladium-carbene complexes. These complexes were found to exhibit remarkably shielded (13)C NMR shifts, which are much more highfield-shifted than those of "normal" carbene complexes. DFT calculations were performed to determine the origin of these observations and to distinguish the electronic structure of these and related carbene complexes compared with the classical Fischer and Schrock-type complexes. Various methods show that these systems are best described as highly polarized Schrock-type complexes, in which the metal-carbon bond possesses more electrostatic contributions than in the prototype Schrock systems, or even as "masked" methandiides. As such, geminal dianions represent a kind of "extreme" Schrock-type ligands favoring the ionic resonance structure M(+)-CR2(-) as often used in textbooks to explain the nucleophilic nature of Schrock complexes. PMID:24150833

Gessner, Viktoria H; Meier, Florian; Uhrich, Diana; Kaupp, Martin

2013-12-01

163

Synthesis and Structure-Activity Correlation Studies of Metal Complexes of α-N-heterocyclic Carboxaldehyde Thiosemicarbazones in Shewanella oneidensis  

Directory of Open Access Journals (Sweden)

Full Text Available This investigation involved the synthesis of metal complexes to test the hypothesis that structural changes and metal coordination in pyridine thiosemicarbazones affect cell growth and cell proliferation in vitro. Thiosemicarbazones are well known to possess antitumor, antiviral, antibacterial, antimalarial, and other activities. Extensive research has been carried out on aliphatic, aromatic, heterocyclic and other types of thiosemicarbazones and their metal complexes. Due to the pronounced reactivity exhibited by metal complexes of heterocyclic thiosemicarbazones, synthesis and structural characterization of di-2-pyridylketone 4N-phenyl thiosemicarbazone and diphenyl tin (Sn and platinum (Pt complexes were undertaken. Shewanella oneidensis MR-1, a metal ion-reducing bacterium, was used as a model organism to explore the biological activity under aerobic conditions. A comparision of the cytotoxic potential of selected ligand and metal-complex thiosemicarbazones on cell growth in wild type MR-1 and mutant DSP-010 Shewanella oneidensis strains at various concentrations (0, 5, 10, 15, 20 or 25 ppm was performed. The wild type (MR-1 grown in the presence of increasing concentrations of Sn- thiosemicarbazone complexes was comparatively more sensitive (mean cell number = 4.8 X 108 + 4.3 X 107 SD than the DSP-010, a spontaneous rifampicillin derivative of the parent strain (mean cell number = 5.6 x 108 + 6.4 X 107 SD under comparable aerobic conditions (p=0.0004. No differences were observed in the sensitivity of the wild and mutant types when exposed to various concentrations of diphenyl Pt- thiosemicarbazone complex (p= 0.425 or the thiosemicarbazone ligand (p=0.313. Growth of MR-1 in the presence of diphenyl Sn- thiosemicarbazone was significantly different among treatment groups (p=0.012. MR-1 cell numbers were significantly higher at 5ppm than at 10 to 20ppm (p = 0.05. The mean number of DSP-010 variant strain cells also differed among diphenyl Sn- thiosemicarbazone complex treated groups (p=0.051. In general, there was an increasing trend in the number of cells from about 5.0 X 108 cells (methanol control group to about 6.0 X 108 cells (25ppm. The number of cells in methanol control group was significantly lower than cell numbers at 20ppm and 25ppm (p = 0.05, and numbers at 5ppm treatment were lower than at 20 and 25ppm (p = 0.05. Furthermore, a marginally significant difference in the number of MR-1 cells was observed among diphenyl Pt- thiosemicarbazone complex treatment groups (p = 0.077, and an increasing trend in the number of cells was noted from ~5.0 X 108 cells (methanol control group to ~5.8 X 108 cells (20ppm. In contrast, the DSP-010 variant strain showed no significant differences in cell numbers when treated with various concentrations of diphenyl Pt- thiosemicarbazone complex (p = 0.251. Differences in response to Sn- metal complex between MR-1 and DSP-010 growing cultures indicate that biological activity to thiosemicarbazone metal complexes may be strain specific.

Quintell Tillison

2005-04-01

164

Mutagenic activity of some platinum and ruthenium complexes with N-heterocyclic ligands in salmonella typhimurium Ta 1530 and Ta 98  

International Nuclear Information System (INIS)

The mutagenic activity of some platinum and ruthenium complexes with 2,2'-biquinoline (b iq) and 2-(2' -pyridyl) quinoline (p q) was examined in strains of salmonella typhimurium Ta 1530 and Ta 98. The complexes cis-[Pt(Nn)X2)] (Nn=b iq, X=CI; Nn=p q, X=CI, Br), Pt3(b iq)2I6 and me r-[Ru(b iq)2CI3].2H2O exhibit significant mutagenic activity while me r-[Ru(p q)CI3(C2H5OH)], [Ru(p q)CI4]. 3a-2a and [Ru(p q) (DMSO)2CI2].0.5H2O show much weaker mutagenic activity. the platinum complexes appear to be more active via induction of frameshift than base substitution mutation while me r-[Ru(b iq)2CI3].2H2O is highly mutagenic via base substitution. (authors). 16 refs., 2 tabs

165

Regioselective Allene Hydrosilylation Catalyzed by NHC Complexes of Nickel and Palladium  

OpenAIRE

Regioselective methods for allene hydrosilylation have been developed, with regioselectivity being governed primarily by choice of metal. Alkenylsilanes are produced via nickel catalysis with larger N-heterocyclic carbene ligands, and allylsilanes are produced via palladium catalysis with smaller N-heterocyclic carbene ligands. These complementary methods allow either regioisomeric product to be obtained with exceptional regiocontrol.

Miller, Zachary D.; Li, Wei; Belderrain, Toma?s R.; Montgomery, John

2013-01-01

166

The Orientation and Stereodynamic Paths of Planar Monodentate Ligands in Square Planar Nickel N2S Complexes  

OpenAIRE

The well-established presence of histidine donors in binding sites of Ni-containing biomolecules prompts the study of orientational preference and stereodynamic nature of flat monodentate ligands (L = imidazoles, pyridine and an N-heterocyclic carbene) bound to planar N2SNi moieties. Square planar [N2SNiL]n+ complexes are accessed through bridge-splitting reactions of dimeric, thiolate-S bridged [N2SNi]2 complexes. The solid state molecular structures of three mononuclear products, and three ...

Jenkins, Roxanne M.; Singleton, Michael L.; Leamer, Lauren A.; Reibenspies, Joseph H.; Darensbourg, Marcetta Y.

2010-01-01

167

Palladium(0) pre-catalysts with heteroditopic NHC-amine ligands by transmetallation from their silver(I) complexes  

OpenAIRE

The synthesis of an air-stable series of Pd0 complexes with dissymmetric bidentate N-heterocyclic carbene-amine ligands has been performed. The key step is an unprecedented carbene transfer from AgI to obtain electron-rich zero-valent palladium precatalysts. The coordination behavior of the ligands was determined with X-ray crystallography. Surprising results were obtained in the catalysis of transfer semi-hydrogenation, where the addition of base appeared not to be necessary to obtain the de...

Warsink, S.; Hauwert, P.; Siegler, M. A. M.; Spek, A. L.; Elsevier, C. J.

2009-01-01

168

Cationic Iridium(III) Complexes with Two Carbene-Based Cyclometalating Ligands: Cis Versus Trans Isomers.  

Science.gov (United States)

A series of cationic iridium(III) complexes with two carbene-based cyclometalating ligands and five different N^N bipyridine and 1,10-phenanthroline ancillary ligands is presented. For the first time-in the frame of a rarely studied class of bis(heteroleptic) iridium complexes with two carbene-based cyclometalating ligands-a pair of cis and trans isomers has been isolated. All complexes (trans-1-5 and cis-3) were characterized by (1)H NMR, (13)C NMR, (31)P NMR, and HRMS (ESI-TOF); in addition, crystal structures of cis-3 and trans-4 are reported and discussed. Cyclic voltammetric studies show that the whole series exhibits highly reversible oxidation and reduction processes, suggesting promising potential for optoelectronic applications. Ground-state DFT and TD-DFT calculations nicely predict the blue shift experimentally observed in the room-temperature absorption and emission spectra of cis-3, compared to the trans complexes. In CH3CN, cis-3 displays a 4-fold increase in photoluminescence quantum yield (PLQY) with respect to trans-3, as a consequence of drastically slower nonradiative rate constant. By contrast, at 77 K, the emission properties of all the compounds, including the cis isomer, are much more similar, with a pronounced hypsochromic shift for the trans complexes. A similar behavior is found in solid state (1% w/w poly(methyl methacrylate) matrix), with all complexes displaying PLQY of ?70-80%, comparable emission lifetimes (? ? 1.3 ?s), and a remarkable rigidochromic shift. To rationalize the more pronounced nonradiative deactivation (and smaller PLQY) observed for photoexcited trans complexes, comparative temperature-dependent emission studies in the range of 77-450 K for cis-3 and trans-3 were made in propylene glycol, showing that solvation effects are primarily responsible for the observed behavior. PMID:25741900

Monti, Filippo; La Placa, Maria Grazia I; Armaroli, Nicola; Scopelliti, Rosario; Grätzel, Michael; Nazeeruddin, Mohammad Khaja; Kessler, Florian

2015-03-16

169

Synthesis of hydronaphthalenes through coupling of enyne carbonyl compounds that contain pendant alkene groups with Fischer carbene complexes  

OpenAIRE

The coupling of enyne carbonyl compounds that contain pendant alkene groups with Fischer carbene complexes to afford furans that contain pendant alkene groups is described. Subsequent intramolecular Diels-Alder reactions are effective in select cases, resulting in hydronaphthalene systems after dehydration. Although the Diels-Alder event is thermodynamically unfavorable, the overall transformation of alkene-furans to dihydronaphthalenes is a favorable process.

Kumar-patti, Rajesh; Duan, Shaofeng; Camacho-davila, Alejandro; Waynant, Kris; Dunn, Kenneth A.; Herndon, James W.

2010-01-01

170

Cyclodehydrations leading to indene products having N-heterocyclic substituents.  

Science.gov (United States)

In this Note, we describe superacid-promoted cyclodehydrations leading to functionalized indenes. The product indenes are synthesized having N-heterocyclic substituents, including pyridyl, imidazolyl, pyrimdyl, and other groups. A mechanism is proposed involving dicationic, superelectrophilic intermediates. The protonated N-heterocyclic rings are shown to dramatically lower the LUMO energy level of the carboxonium electrophile (compared to that of a similar uncharged system). PMID:24841486

Boblak, Kenneth N; Klumpp, Douglas A

2014-06-20

171

Bis-mixed-carbene ruthenium-thiolate-alkylidene complexes: synthesis and olefin metathesis activity.  

Science.gov (United States)

A series of bis-carbene Ru-hydride species, including (IMes)(Im(OMe)2)(PPh3)RuHCl (1) and (SIMes)(Me2Im(OMe)2)(PPh3)RuHCl (2) were prepared and subsequently shown to react with aryl-vinyl-sulfides to give the bis-carbene-alkylidene complexes: Im(OMe)2(SIMes)RuCl(SR)(=CHCH3) (R = p-FC6H4 (3), p-(NO2)C6H4 (4)), Im(OMe)2(IMes)RuCl(=CHCH3)(SPh) (5), Me2Im(OMe)2(SIMes)RuCl(=CHCH3)(SPh) (6), Im(OMe)2(SIMes)(F5C6S)RuCl(=CHR) (R = C4H9 (9), C5H11 (10)). The activity of these species in the standard Grubbs' tests for ring-opening metathesis polymerization, ring-closing and cross-metathesis are reported. Although these thiolate derivatives are shown to exhibit modest metathesis activities, the reactivity is enhanced in the presence of BCl3. PMID:25462569

Dahcheh, Fatme; Stephan, Douglas W

2015-01-28

172

Synthesis, structure and reactivity of novel pyridazine-coordinated diiron bridging carbene complexes.  

Science.gov (United States)

[{mu-(Pyridazine-N(1):N(2))}Fe(2)(mu-CO)(CO)(6)](1) reacts with aryllithium reagents, ArLi (Ar = C(6)H(5), m-CH(3)C(6)H(4)) followed by treatment with Me(3)SiCl to give the novel pyridazine-coordinated diiron bridging siloxycarbene complexes [(C(4)H(4)N(2))Fe(2){mu-C(OSiMe(3))Ar}(CO)(6)](2, Ar = C(6)H(5); 3, Ar =m-CH(3)C(6)H(4)). Complex 2 reacts with HBF(4).Et(2)O at low temperature to yield a cationic bridging carbyne complex [(C(4)H(4)N(2))Fe(2)(mu-CC(6)H(5))(CO)(6)]BF(4)(4). Cationic 4 reacts with NaBH(4) in THF at low temperature to afford the diiron bridging arylcarbene complex [(C(4)H(4)N(2))Fe(2){mu-C(H)C(6)H(5)}(CO)(6)](5). Unexpectedly, the reaction of 4 with NaSCH(3) under similar conditions gave the bridging arylcarbene complex 5 and a carbonyl-coordinated diiron bridging carbene complex [Fe(2){mu-C(SCH(3))C(6)H(5)}(CO)(7)](6), while the reaction of NaSC(6)H(4)CH(3)-p with 4 affords the expected bridging arylthiocarbene complex [(C(4)H(4)N(2))Fe(2){mu-C(SC(6)H(4)CH(3)-p)C(6)H(5)}(CO)(6)](7), which can be converted into a novel diiron bridging carbyne complex with a thiolato-bridged ligand, [Fe(2)(mu-CC(6)H(5))(mu-SC(6)H(4)CH(3)-p)(CO)(6)](8). Cationic can also react with the carbonylmetal anionic compound Na(2)[Fe(CO)(4)] to yield complex 5, while the reactions of 4 with carbonylmetal anionic compounds Na[M(CO)(5)(CN)](M = Cr, Mo, W) produce the diiron bridging aryl(pentacarbonylcyanometal)carbene complexes [(C(4)H(4)N(2))Fe(2)-{mu-C(C(6)H(5))NCM(CO)(5)}(CO)(6)](9, M = Cr; 10, M = Mo; 11, M = W). The structures of complexes 2, 5, 6, 8, and 9 have been established by X-ray diffraction studies. PMID:16172652

Xiao, Nu; Xu, Qiang; Sun, Jie; Chen, Jiabi

2005-10-01

173

One-pot three-component synthesis of quinoxaline and phenazine ring systems using Fischer carbene complexes  

Directory of Open Access Journals (Sweden)

Full Text Available One-pot three-component coupling of o-alkynylheteroaryl carbonyl derivatives with Fischer carbene complexes and dienophiles leading to the synthesis of quinoxaline and phenazine ring systems has been investigated. This involves the generation of furo[3,4-b]pyrazine and furo[3,4-b]quinoxaline as transient intermediates, which were trapped with Diels–Alder dienophiles. This is the first report on furo[3,4-b]pyrazine intermediates.

Priyabrata Roy

2010-05-01

174

Formation and crystallographic elucidation of stable [4 + 2]-coordinate nickel(II) N,S-heterocyclic carbene (NSHC) complexes.  

Science.gov (United States)

A series of square-planar N,S-heterocyclic carbene (NSHC) complexes trans-[NiX(2)(N-RBzTh)(2)] (BzTh = benzothiazolin-2-ylidene) (R/X = Bz/Br; Me/I; Et/I; Pr(i)/I; Bu(i)/I) have been synthesized and characterized by X-ray single-crystal diffraction analysis. These are the first crystallographically established NSHC complexes of nickel in the literature. The N,S-heterocyclic carbene (NSHC) rings invariably twist away from co-planarity with the metal coordination plane such that the N-substituent moves on top and below the metal to facilitate electrostatic gamma-hydride interaction, thus giving an essentially [4 + 2] coordination at the Ni(ii) center. These compounds are active toward reductive Ullmann-type coupling reactions in Bu(4)NBr showing higher activities towards bromoanisole or bromotoluene than bromobenzene. The complex trans-[NiI(2)(N-Pr(i)BzTh)(2)] with the shortest NiH anagostic separation and a near-ideal orthogonal orientation between the carbene and metal planes gives the highest yields. PMID:19240921

Ding, Nini; Zhang, Jun; Hor, T S Andy

2009-03-14

175

Conformation analysis of triphenylphosphine in trans and cis triphenylphosphine-substituted Fischer carbene complexes  

Science.gov (United States)

The synthesis and selected crystal structures of novel (M = Cr or Mo) and known (M = W) [(CO)4(PPh3)M = C(OEt)R] complexes, M = Cr, R = 2-thienyl (1), 2-furyl (2); M = Mo, R = 2-thienyl (3), 2-furyl (4); M = W, R = 2-thienyl (5), 2-furyl (6), are presented. Experimental crystal structures and DFT calculations of selected trans- and cis-triphenylphosphine-substituted Fischer carbene complexes, illustrate that the minimum energy conformation of triphenylphosphine (PPh3) in octahedral [(CO)4(PPh3)ML]-complexes generally have distinct features that can be described in terms of the "plane of nadir energy", a plane linking all points of minimum steric compression between the ligands. The generally observed orientation of PPh3 involves a correlated feathering of the phenyl groups with the PCipso bond of one phenyl group orientated near parallel to the nadir plane, and a meta carbon (Cm) of the other two phenyl groups orientated as near as possible to the nadir plane, orthogonal to the first. Although the orientation of PPh3 in 6-trans, [(CO)4(PPh3)W = C(OEt)2-furyl], deviates from this, DFT correctly calculated the unexpected and not generally observed PPh3 orientation.

Landman, Marilé; Levell, Tamzyn; van Rooyen, Petrus H.; Conradie, Jeanet

2014-05-01

176

Carbene-transition metal complexes formed by double C-H bond activation.  

Science.gov (United States)

The activation of a single sp(3) C-H bond of alkanes and their derivatives by electron-rich transition metal complexes has been a topic of interest since the landmark work by Bergman and Graham in 1982. Ten years later, it was shown that compounds of 5d elements, such as osmium and iridium, even enable a double alpha-C-H bond activation of alkane or cycloalkane derivatives containing an OR or NR(2) functional group, thus opening up a new route to obtain Fischer-type transition metal carbene complexes. Subsequent work focused in particular on the conversion of methyl alkyl and methyl aryl ethers into bound oxocarbenes and also of dimethyl amines to bound aminocarbenes. In the context of this work, it was recently shown that square-planar oxocarbene-iridium(I) complexes prepared in this way exhibit an unusual mode of reactivity: They react with CO(2), CS(2), COS, PhNCO, and PhNCS by an atom- or group-transfer metathesis, which has no precedent. Organic azides RN(3) and N(2)O behave similarly. Recent results confirm that this novel type of metathesis can be made catalytic, thus offering a novel possibility for C-H bond functionalization. PMID:20512826

Werner, Helmut

2010-06-28

177

Coinage-metal mediated ring opening of cis-1,2-dimethoxycyclopropane: trends from the gold, copper, and silver Fischer carbene bond strength.  

Science.gov (United States)

N-heterocyclic carbene (NHC) supported coinage metal cations proved to react in the gas phase with the electron-rich cis-1,2-dimethoxycyclopropane. Upon Collision Induced Dissociation (CID), several spectrometric fragment-ion signals were observed, one corresponding to the recovery of the bare cation IMes-M(+) (IMes = 1,3-bis(2,4,6-trimethylphenyl)imidazol-2-ylidene) and the second to the methoxymethylidene metal complex IMes-M-[HCOCH3](+). The gold and copper complexes appear to stabilize the carbene sufficiently enough to promote the latter channel. On the contrary, the silver complex binds weakly to the methoxymethylidene moiety as observed by the predominance of the bare cation IMes-M(+) channel. Density Functional Theory (DFT) investigations of the Potential Energy Surface and Bond Energy Decomposition Analyses provided results that correlate well with the experimental data. In the case of the bare cation channel, two distinct reaction pathways were found: a straightforward decoordination of the cyclopropane and a cationic rearrangement of the three-membered ring into a dimethoxypropylene isomer before dissociation. However, for the abstraction of the methoxymethylidene moiety by the metal cation, only one pathway was found. In analogy to earlier studies by other groups, we found the trend Au > Cu > Ag for the metal-carbene bond strength. PMID:24911627

Batiste, Laurent; Chen, Peter

2014-07-01

178

Late metal carbene complexes generated by multiple C-H activations: examining the continuum of M=C bond reactivity.  

Science.gov (United States)

Unactivated C(sp(3))-H bonds are ubiquitous in organic chemicals and hydrocarbon feedstocks. However, these resources remain largely untapped, and the development of efficient homogeneous methods for hydrocarbon functionalization by C-H activation is an attractive and unresolved challenge for synthetic chemists. Transition-metal catalysis offers an attractive possible means for achieving selective, catalytic C-H functionalization given the thermodynamically favorable nature of many desirable partial oxidation schemes and the propensity of transition-metal complexes to cleave C-H bonds. Selective C-H activation, typically by a single cleavage event to produce M-C(sp(3)) products, is possible through myriad reported transition-metal species. In contrast, several recent reports have shown that late transition metals may react with certain substrates to perform multiple C-H activations, generating M=C(sp(2)) complexes for further elaboration. In light of the rich reactivity of metal-bound carbenes, such a route could open a new manifold of reactivity for catalytic C-H functionalization, and we have targeted this strategy in our studies. In this Account, we highlight several early examples of late transition-metal complexes that have been shown to generate metal-bound carbenes by multiple C-H activations and briefly examine factors leading to the selective generation of metal carbenes through this route. Using these reports as a backdrop, we focus on the double C-H activation of ethers and amines at iridium complexes supported by Ozerov's amidophosphine PNP ligand (PNP = [N(2-P(i)Pr(2)-4-Me-C(6)H(3))(2)](-)), allowing isolation of unusual square-planar iridium(I) carbenes. These species exhibit reactivity that is distinct from the archetypal Fischer and Schrock designations. We present experimental and theoretical studies showing that, like the classical square-planar iridium(I) organometallics, these complexes are best described as nucleophilic at iridium. We discuss the classification of this reactivity in the context of a scheme originally delineated by Roper. These "Roper-type" carbenes perform a number of multiple-bond metatheses leading to atom and group transfer from electrophilic heterocumulene (e.g., CO(2), CS(2), PhNCS) and diazo (e.g., N(2)O, AdN(3)) reagents. In one instance, we have extended this methodology to a process for catalytic C-H functionalization by a double C-H activation-group transfer process. Although the scope of these reactions is currently limited, these new pathways may find broader utility as the reactivity of late-metal carbenes continues to be explored. Examination of alternative transition metals and supporting ligand sets will certainly be important. Nonetheless, our findings show that carbene generation by double C-H activation is a viable strategy for C-H functionalization, leading to products not accessible through traditional C(sp(3))-H activation pathways. PMID:19624162

Whited, Matthew T; Grubbs, Robert H

2009-10-20

179

Simple synthesis of neutral and cationic Cu-NHC complexes.  

Science.gov (United States)

A direct and practical synthetic route to N-heterocyclic carbene copper complexes of [(NHC)CuX] (X = halide) and [(NHC)2Cu]PF6 types using commercially available copper powder is described. A number of copper-NHC complexes have been obtained in a range of yields from 26 to 99%. The reactions take place in air without removal of moisture and oxygen, and the excess of copper powder can be easily removed via simple filtration after completion. The direct reactions of imidazolium salts and copper powder can also be performed in aqueous media avoiding tedious purification processes. The procedure is also suitable for gram-scale preparation. PMID:25479082

Liu, Bo; Ma, Xueji; Wu, Feifei; Chen, Wanzhi

2015-01-28

180

Methandiide as a non-innocent ligand in carbene complexes: from the electronic structure to bond activation reactions and cooperative catalysis.  

Science.gov (United States)

The synthesis of a ruthenium carbene complex based on a sulfonyl-substituted methandiide and its application in bond activation reactions and cooperative catalysis is reported. In the complex, the metal-carbon interaction can be tuned between a Ru-C single bond with additional electrostatic interactions and a Ru=C double bond, thus allowing the control of the stability and reactivity of the complex. Hence, activation of polar and non-polar bonds (O-H, H-H) as well as dehydrogenation reactions become possible. In these reactions the carbene acts as a non-innocent ligand supporting the bond activation as nucleophilic center in the 1,2-addition across the metal-carbon double bond. This metal-ligand cooperativity can be applied in the catalytic transfer hydrogenation for the reduction of ketones. This concept opens new ways for the application of carbene complexes in catalysis. PMID:25047390

Becker, Julia; Modl, Tanja; Gessner, Viktoria H

2014-09-01

181

Density functional computations of the cyclopropanation of ethene catalyzed by iron (II) carbene complexes Cp(CO)(L)Fe?CHR, L D CO, PMe3, R D Me, OMe, ph, CO2Me  

Science.gov (United States)

Density functional theory has been used to study the Fe-catalyzed cyclopropanation of Fe-carbene complexes with ethene. All the intermediates and transition states were optimized completely at the B3LYP/6-31+G(d,p) level. Calculation results confirm that the cyclopropanation of Fe-carbene complexes with ethene involves the two reaction paths I and II. In the reaction path I, the double bond of ethene attacks directly on the carbene carbon of Fe-carbene complexes to generate the cyclopropane. In the reaction path II, ethene substitution for PMe3 or CO in the Fe-carbene complexes leads to the complexes M2; and the attack of one carbon of ethene on the carbene carbon results in the complexes M3 with a Fe bond C bond C bond C four-membered ring, and then generates the cyclopropane via the elimination reaction. For Fe-carbene complexes A, C, D, E, and H, the main reaction mode is the reaction path I; for Fe-carbene complexes B, F, and G, the main reaction mode is the reaction path II.0

Wang, Fen; Meng, Qingxi; Li, Ming

182

Aerosolized Antimicrobial Agents Based on Degradable Dextran Nanoparticles Loaded with Silver Carbene Complexes  

Science.gov (United States)

Degradable acetalated dextran (Ac-DEX) nanoparticles were prepared and loaded with a hydrophobic silver carbene complex (SCC) by a single-emulsion process. The resulting particles were characterized for morphology and size distribution using scanning electron microscopy (SEM), transmission electron microscopy (TEM), and dynamic light scattering (DLS). The average particle size and particle size distribution were found to be a function of the ratio of the organic phase to the surfactant containing aqueous phase with a 1:5 volume ratio of Ac-DEX CH2Cl2 (organic): PBS (aqueous) being optimal for the formulation of nanoparticles with an average size of 100 ± 40 nm and a low polydispersity. The SCC loading was found to increase with an increase in the SCC quantity in the initial feed used during particle formulation up to 30% (w/w); however, the encapsulation efficiency was observed to be the best at a feed ratio of 20% (w/w). In vitro efficacy testing of the SCC loaded Ac-DEX nanoparticles demonstrated their activity against both Gram-negative and Gram-positive bacteria; the nanoparticles inhibited the growth of every bacterial species tested. As expected, a higher concentration of drug was required to inhibit bacterial growth when the drug was encapsulated within the nanoparticle formulations compared with the free drug illustrating the desired depot release. Compared with free drug, the Ac-DEX nanoparticles were much more readily suspended in an aqueous phase and subsequently aerosolized, thus providing an effective method of pulmonary drug delivery. PMID:23025592

Ornelas-Megiatto, Cátia; Shah, Parth N.; Wich, Peter R.; Cohen, Jessica L.; Tagaev, Jasur A.; Smolen, Justin A.; Wright, Brian D.; Panzner, Matthew J.; Youngs, Wiley J.; Fréchet, Jean M. J.; Cannon, Carolyn L.

2012-01-01

183

Carbene complexes of zirconium. Synthesis, structure, and reactivity with carbon monoxide to affort coordinated ketene  

International Nuclear Information System (INIS)

Treatment of Cp2Zr(L)(CO) (Cp = C5H5; L = PMe3, CO) with Cp*2ZrH2 (Cp* = C5Me5) affords zirconium oxycarbene complexes, Cp2(L)Zr double bond CHO single bond Zr(X)Cp*2 (L = PMe3, X = H, I; L = CO, X = H), that represent some of the first examples of group 4 metal-to-carbon multiple bonding. The first X-ray diffraction structure determination of a zirconium carbene complex, that of Cp(PMe3)Zr double bond CHO single bond Zr(H)Cp*2.C6H6, is reported (C2/c, a = 27.318 (4) A, b = 19.895 (3) A, c = 19.932 (5) A ? = 132.188 (10)0, Z = 8) and shows a very short Zr-C bond length of 2.117 (7) A. Treatment of Cp2(CO)Zr double bond CHO single bond Zr(H)Cp*2 with CH3 I or Cp2(PMe3)Zr double bond CHO single bond Zr(I)Cp*2 with CO affords the zirconium substituted enediolate zirconacycle, Cp*2ZrOCH double bond C(Zr(I)Cp2)O, which has been characterized by an X-ray diffraction study (P21/c, a = 15.866 (4) A, b = 10.673 (3) A, c = 20.561 (4) A, ? = 105.5 (2)0, Z = 4). This complex most likely forms by coupling of the zirconoxycarbene and a carbonyl to give a metal-coordinated ketene intermediate that subsequently rearranges to the isolated product. An isotopic crossover experiment has demonstrated that ssover experiment has demonstrated that the new carbon-carbon bond is formed in an intramolecular coupling step. The ketene intermediate can be trapped by dissolving Cp2(CO)Zr double bond CHO single bond Zr(H)Cp*2 in pyridine, giving Cp2(py)Zr(O double bond C double bond CHOZr(I)Cp*2). Treatment of the isolated ketene complex with CH3I in benzene gives the enediolate zirconocycle; in pyridine Cp2(py)Zr(O double bond C double bond CHOZr(I)Cp*2) can be observed spectroscopically. 38 references, 4 figures, 5 tables

184

Z- and enantioselective ring-opening/cross-metathesis with enol ethers catalyzed by stereogenic-at-Ru carbenes: reactivity, selectivity, and Curtin-Hammett kinetics.  

Science.gov (United States)

The first instances of Z- and enantioselective Ru-catalyzed olefin metathesis are presented. Ring-opening/cross-metathesis (ROCM) reactions of oxabicyclic alkenes and enol ethers and a phenyl vinyl sulfide are promoted by 0.5-5.0 mol % of enantiomerically pure stereogenic-at-Ru complexes with an aryloxy chelate tethered to the N-heterocyclic carbene. Products are formed efficiently and with exceptional enantioselectivity (>98:2 enantiomer ratio). Surprisingly, the enantioselective ROCM reactions proceed with high Z selectivity (up to 98% Z). Moreover, reactions proceed with the opposite sense of enantioselectivity versus aryl olefins, which afford E isomers exclusively. Preliminary DFT calculations in support of Curtin-Hammett kinetics as well as initial models that account for the stereoselectivity levels and trends are provided. PMID:22823567

Khan, R Kashif M; O'Brien, Robert V; Torker, Sebastian; Li, Bo; Hoveyda, Amir H

2012-08-01

185

Investigation of the properties of 4,5-dialkylated N-heterocyclic carbenes  

DEFF Research Database (Denmark)

The investigation of the electronic and steric properties of 4,5-disubstituted imidazolylidenes is reported, as well as their successful application as organocatalysts in the formation of gamma-butyrolactones by conjugate Umpolung.

Urban, S.; Tursky, Matyas

2009-01-01

186

CAAC Boranes. Synthesis and characterization of cyclic (alkyl (amino carbene borane complexes from BF3 and BH3  

Directory of Open Access Journals (Sweden)

Full Text Available In situ formation of two cyclic (alkyl (amino carbenes (CAACs followed by addition of BF3•Et2O provided the first two examples of CAAC–BF3 complexes: 1-(2,6-diisopropylphenyl-3,5,5-trimethyl-3-phenylpyrrolidin-2-ylidene trifluoroborane, and 2-(2,6-diisopropylphenyl-3,3-dimethyl-2-azaspiro[4.5]decan-1-ylidene trifluoroborane. These CAAC–BF3 complexes are robust compounds that are stable to ambient laboratory conditions and silica gel chromatography. They were characterized by spectroscopy and X-ray crystallography. In contrast, a CAAC complex with borane (BH3 was readily formed in situ according to 1H and 11B NMR analysis, but did not survive the workup conditions. These results set the stage for further studies of the chemistry of CAAC boranes.

Julien Monot

2010-08-01

187

Traditional and ion-pair halogen-bonded complexes between chlorine and bromine derivatives and a nitrogen-heterocyclic carbene.  

Science.gov (United States)

A theoretical study of the halogen-bonded complexes (A-X···C) formed between halogenated derivatives (A-X; A = F, Cl, Br, CN, CCH, CF3, CH3, H; and X = Cl, Br) and a nitrogen heterocyclic carbene, 1,3-dimethylimidazole-2-ylidene (MeIC) has been performed using MP2/aug'-cc-pVDZ level of theory. Two types of A-X:MeIC complexes, called here type-I and -II, were found and characterized. The first group is described by long C-X distances and small binding energies (8-54 kJ·mol(-1)). In general, these complexes show the traditional behavior of systems containing halogen-bonding interactions. The second type is characterized by short C-X distances and large binding energies (148-200 kJ·mol(-1)), and on the basis of the topological analysis of the electron density, they correspond to ion-pair halogen-bonded complexes. These complexes can be seen as the interaction between two charged fragments: A(-) and (+)[X-CIMe] with a high electrostatic contribution in the binding energy. The charge transfer between lone pair A(LP) to the ?* orbital of C-X bond is also identified as a significant stabilizing interaction in type-II complexes. PMID:25188812

Donoso-Tauda, Oscar; Jaque, Pablo; Elguero, José; Alkorta, Ibon

2014-10-01

188

A Theoretical Study of Uranium(IV) Bis-Methyl Complexes: Towards the Predictive Formation of a Transient Uranium(IV) Carbene Complex  

Energy Technology Data Exchange (ETDEWEB)

In summary, we have shown that the first step of ortho C-H activation of pyridine N-oxide mediated by L{sub 2}U(IV)-(CH{sub 3}){sub 2} can occur with the three ligands L (Cp, CpTMS, and Cp*) to form an {eta}{sup 2}(C, O) ortho-metallated complex. Also, we have shown that for L=Cp and CpTMS it is possible to form a very stable uranium (VI) formaldehyde complex going through an uranium(IV) Schrock-type carbene intermediate. This is in contrast with the ligand Cp*: the formation of uranium(IV) formaldehyde complex is not possible with the Cp* owing to a high barrier at the H{sub 2}C-O repulsive coupling transition state. This high barrier can be explained by the steric hindrance of Cp* compared with Cp and CpTMS. Moreover, the electronic repulsion between the two negative charges (carbene and oxygen) is enhanced in the case of Cp*. (authors)

Yahia, A.; Castro, L.; Maron, L. [Univ Toulouse 3, Lab Phys and Chim Nanoobjets, INSA, F-31077 Toulouse (France); Yahia, A. [Univ Montpellier 2, Inst Chim Separat and Marcoule, UMR 5257, CEA, CNRS, ENSCM, Ctr Marcoule, F-30207 Bagnols Sur Ceze (France)

2010-07-01

189

Dihydrogen activation by frustrated carbene-borane Lewis pairs: an experimental and theoretical study of carbene variation.  

Science.gov (United States)

A variety of Lewis acid-base pairs consisting of tris(pentafluorophenyl)borane, B(C(6)F(5))(3), in combination with sterically demanding five- and six-membered N-heterocyclic carbenes (NHCs) of the imidazolin-2-ylidene, imidazolidin-2-ylidene, and tetrahydropyrimidin-2-ylidene types were investigated with respect to their potential to act as frustrated Lewis pairs (FLP) by reaction with dihydrogen (H(2)) and tetrahydrofuran (THF). A sufficient degree of "frustration" was usually established by introduction of a 1,3-di-tert-butyl or 1,3-diadamantyl carbene substitution pattern, which allows an unquenched acid-base reactivity and thus leads to heterolytic dihydrogen activation and ring-opening of THF. In contrast, 1,3-bis(2,6-diisopropylphenyl)-substituted carbenes showed ambiguous behavior, and the corresponding five-membered imidazolin-2-ylidene formed a stable carbene-B(C(6)F(5))(3) adduct, whereas fast C-F activation and formation of a zwitterionic pyrimidinium-fluoroborate was observed for the six-membered tetrahydropyrimidin-2-ylidene. A stable adduct was also isolated for the combination of the acyclic carbene bis(diisopropylamino)methylene with B(C(6)F(5))(3), and consequently no reactivity toward H(2) and THF was observed. To rationalize the reactivity of the carbene-borane Lewis pairs, the thermodynamics of adduct formation with B(C(6)F(5))(3) were calculated for 10 different carbenes; the stability (or instability) of these adducts can be used as a good measure of the degree of "frustration". PMID:21718018

Kronig, Sabrina; Theuergarten, Eileen; Holschumacher, Dirk; Bannenberg, Thomas; Daniliuc, Constantin G; Jones, Peter G; Tamm, Matthias

2011-08-01

190

Conversion of alpha,beta-unsaturated aldehydes into saturated esters: an Umpolung reaction catalyzed by nucleophilic carbenes.  

Science.gov (United States)

N-Heterocyclic carbenes derived from benzimidazolium salts are effective catalysts for generating homoenolate species from alpha,beta-unsaturated aldehydes. These nucleophilic intermediates can be protonated, and the resulting activated carbonyl unit is trapped with an alcohol nucleophile, thereby promoting a highly efficient conversion of an alpha,beta-unsaturated aldehyde into a saturated ester. A kinetic resolution of secondary alcohols can be achieved using chiral imidazoylidene catalysts. [reaction: see text] PMID:15727471

Chan, Audrey; Scheidt, Karl A

2005-03-01

191

Redox Non–innocence of a N–heterocyclic Nitrenium Cation Bound to a Nickel–Cyclam Core  

OpenAIRE

The redox properties of Ni complexes bound to a new ligand [DMC–nit]+, where a N–heterocyclic nitrenium group is anchored on a 1,4,8,11–tetraazacyclotetradecane backbone, have been examined using spectroscopic and DFT methods. Ligand based [Ni(DMC–nit)]2+/+ reduction and metal based [Ni(DMC–nit)]2+/3+ oxidation processes have been established for the [Ni(DMC–nit)]+/2+/3+ redox series, which represents the first examples of nitrenium nitrogen (Nnit) bound first row transition metal...

Heims, Florian; Pfaff, Florian Felix; Abram, Sarah-luise; Farquhar, Erik R.; Bruschi, Maurizio; Greco, Claudio; Ray, Kallol

2013-01-01

192

Confocal and fluorescence lifetime imaging sheds light on the fate of a pyrene-tagged carbon monoxide-releasing Fischer carbene chromium complex.  

Science.gov (United States)

The synthesis of a new pyrene-containing Fischer carbene complex is described. The complex has a broad absorbance spectrum between 300 and 400 nm and, on excitation at 345 nm in CH2Cl2 solution, emission is observed at 395 and 415 nm. Emission is also observed in PBS buffer, but in this case the resulting spectra are much broader. Confocal and fluorescence lifetime imaging indicate that emission occurs on treating HeLa cells with the complex and co-localisation studies demonstrate that this is from the mitochondria and lipid-rich regions of the cell. PMID:25553721

Arrowsmith, Rory L; Atkin, Anthony J; Botchway, Stanley W; Fairlamb, Ian J S; Lynam, Jason M; Moir, James W B; Pascu, Sofia I; Ward, Jonathan S; Zhang, Wei-Qiang

2015-03-01

193

Redox non-innocence of a N-heterocyclic nitrenium cation bound to a nickel-cyclam core.  

Science.gov (United States)

The redox properties of Ni complexes bound to a new ligand, [DMC-nit](+), where a N-heterocyclic nitrenium group is anchored on a 1,4,8,11-tetraazacyclotetradecane backbone, have been examined using spectroscopic and DFT methods. Ligand-based [(DMC-nit)Ni](2+/+) reduction and metal-based [(DMC-nit)Ni](2+/3+) oxidation processes have been established for the [(DMC-nit)Ni](+/2+/3+) redox series, which represents the first examples of nitrenium nitrogen (N(nit))-bound first-row transition-metal complexes. An unprecedented bent binding mode of N(nit) in [(DMC-nit)Ni](2+) is observed, which possibly results from the absence of any N(nit)?Ni ?-donation. For the corresponding [(DMC-nit)Ni(F)](2+) complex, ?-donation is dominant, and hence a coplanar arrangement at N(nit) is predicted by DFT. The binding of the triazolium ion to Ni enables new chemistry (formate oxidation) that is not observed in a derivative that lacks this functional group. Thus the N-heterocyclic nitrenium ligand is a potentially useful and versatile reagent in transition-metal-based catalysis. PMID:24380589

Heims, Florian; Pfaff, Florian Felix; Abram, Sarah-Luise; Farquhar, Erik R; Bruschi, Maurizio; Greco, Claudio; Ray, Kallol

2014-01-15

194

Synthesis of binuclear gold (I) biscarbene complexes by carbene transfers from tungsten to gold  

Energy Technology Data Exchange (ETDEWEB)

The binuclear tungsten (0) biscarbene complexes 3 and 4 react with tetrachloroauric acid (stoichiometric ratio 1:2) to give the corresponding gold (I) complexes 5 and 6 involving the transfer of biscarbene ligands from two tungsten to two gold fragments. Preparation and spectroscopic data are described.

Fischer, E.O.; Boeck, M. (Technische Univ. Muenchen (Germany, F.R.). Anorganisch-Chemisches Lab.)

1984-01-01

195

The ketimide ligand is not just an inert spectator: heteroallene insertion reactivity of an actinide-ketimide linkage in a thorium carbene amide ketimide complex.  

Science.gov (United States)

The ketimide anion R2C=N(-) is an important class of chemically robust ligand that binds strongly to metal ions and is considered ideal for supporting reactive metal fragments due to its inert spectator nature; this contrasts with R2N(-) amides that exhibit a wide range of reactivities. Here, we report the synthesis and characterization of a rare example of an actinide ketimide complex [Th(BIPM(TMS)){N(SiMe3)2}(N=CPh2)] [2, BIPM(TMS)=C(PPh2NSiMe3)2]. Complex 2 contains Th=C(carbene), Th-N(amide) and Th-N(ketimide) linkages, thereby presenting the opportunity to probe the preferential reactivity of these linkages. Importantly, reactivity studies of 2 with unsaturated substrates shows that insertion reactions occur preferentially at the Th-N(ketimide) bond rather than at the Th=C(carbene) or Th-N(amide) bonds. This overturns the established view that metal-ketimide linkages are purely inert spectators. PMID:25044515

Lu, Erli; Lewis, William; Blake, Alexander J; Liddle, Stephen T

2014-08-25

196

Gold complexes as antimicrobial agents: an overview of different biological activities in relation to the oxidation state of the gold ion and the ligand structure.  

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Interest in antimicrobial gold complexes originated from the work of Robert Koch at the end of 19th century, who demonstrated that potassium dicyanidoaurate(I), K[Au(CN)2], showed activity against Mycobacterium tuberculosis, a causative agent of tuberculosis. Subsequently, a large number of gold(I) and gold(III) complexes have been evaluated as possible antimicrobial agents against a broad spectrum of bacteria, fungi and parasites. The first part of the present review article summarizes the results achieved in the field of antibacterial and antifungal activity of gold(I) and gold(III) complexes. The represented gold(I) complexes have been divided into three distinct classes based on the type of coordinated ligand: (i) complexes with phosphine-type ligands, (ii) complexes with N-heterocyclic carbene ligands and (iii) various other gold(I) complexes, while the results related to the antibacterial and antifungal gold(III) complexes have been mainly focused on the organometallic-type of complexes. The second section of this article represents findings obtained from the evaluation of antimalarial activity of gold complexes against chloroquine-sensitive and chloroquine-resistant strains of Plasmodium falciparum parasite. Antimalarial gold(I) and gold(III) complexes have been divided into the following classes, based on the nature of the coordinated ligand: (i) complexes with chloroquine and its derivatives, (ii) complexes with N-heterocyclic carbene ligands, (iii) complexes containing functionalised alkynes and (iv) thiosemicarbazonato ligands, as well as (v) other gold(I) and gold(III) complexes. In the last section of the review, gold(I) and gold(III) complexes have been reported to be potential agents against parasites that cause amoebiasis, leishmaniasis and trypanosomiasis. A systematic summary of these results could contribute to the future design of new gold(I) and gold(III) complexes as potential antimicrobial agents. PMID:24598838

Gliši?, Biljana ?; Djuran, Miloš I

2014-04-28

197

Ruthenium(II) carbonyl complexes bearing CCC-pincer bis-(carbene) ligands: synthesis, structures and activities toward recycle transfer hydrogenation reactions.  

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A new series of ruthenium(II) carbonyl complexes with benzene-based CCC-pincer bis-(carbene) ligands, [((R)CCC(R))Ru(CO)2(X)](0/+) and [((R)CCC(R))Ru(CO)(NN)](+) ((R)CCC(R) = 2,6-bis-(1-alkylimidazolylidene)benzene, R = Me or (n)Bu; X = I, Br, CH3CN, or 6-(aminomethyl)pyridine (ampy); NN = 2·CH3CN, or chelating ampy or bipyridine), was synthesized and fully characterized. X-Ray structure determinations revealed that these eight complexes have pseudo-octahedral configurations around the ruthenium center with the pincer ligand occupying three meridional sites. These complexes prove to be efficient precatalysts demonstrating very good activity and reusability for the transfer hydrogenation of ketones. PMID:23880878

Naziruddin, Abbas Raja; Huang, Zhao-Jiunn; Lai, Wei-Chih; Lin, Wan-Jung; Hwang, Wen-Shu

2013-09-28

198

Ring opening of donor-acceptor cyclopropanes with the azide ion: a tool for construction of N-heterocycles.  

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A general method for ring opening of various donor-acceptor cyclopropanes with the azide ion through an SN 2-like reaction has been developed. This highly regioselective and stereospecific process proceeds through nucleophilic attack on the more-substituted C2 atom of a cyclopropane with complete inversion of configuration at this center. Results of DFT calculations support the SN 2 mechanism and demonstrate good qualitative correlation between the relative experimental reactivity of cyclopropanes and the calculated energy barriers. The reaction provides a straightforward approach to a variety of polyfunctional azides in up to 91?% yield. The high synthetic utility of these azides and the possibilities of their involvement in diversity-oriented synthesis were demonstrated by the developed multipath strategy of their transformations into five-, six-, and seven-membered N-heterocycles, as well as complex annulated compounds, including natural products and medicines such as (-)-nicotine and atorvastatin. PMID:25573783

Ivanov, Konstantin L; Villemson, Elena V; Budynina, Ekaterina M; Ivanova, Olga A; Trushkov, Igor V; Melnikov, Mikhail Ya

2015-03-23

199

Syntheses of sterically shielded stable carbenes of the 1,2,4-triazole series and their corresponding palladium complexes: efficient catalysts for chloroarene hydrodechlorination.  

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The new sterically shielded 1,3,4-trisubstituted 1,2,4-triazol-5-ylidenes 8b–d were synthesized by a three step method starting from 2-phenyl-1,3,4-oxadiazole. The syntheses of palladium complexes 9a–d and 10a–d (including the sterically shielded derivatives 9c,d and 10a–d) were carried out via the reactions of the stable carbenes 8a–d with palladium halogenide salts in THF or toluene solution. Complexes 9c,d and 10a–d were found to be excellent catalysts for the reductive dechlorination (hydrodechlorination) of p-dichlorobenzene. The structures of 8c, 9a,b, and 10a were determined by single-crystal X-ray diffraction. PMID:25030067

Glinyanaya, Nataliya V; Saberov, Vagiz Sh; Korotkikh, Nikolai I; Cowley, Alan H; Butorac, Rachel R; Evans, Daniel A; Pekhtereva, Tatyana M; Popov, Anatolii F; Shvaika, Oles P

2014-11-21

200

Synthesis of tricyclic silicon-, germanium- and tin-containing tungsten carbene complexes [ButO)2(Cl)2W=CH]2EPh2 (E=Si, Ge, Sn). Crystal structure of [ButO)2(Cl)2W=CH]2SiPh2 complex  

International Nuclear Information System (INIS)

Tungsten carbene complexes [ButO)2(Cl)2W=CH]2EPh2 (E=Si, Ge, Sn) were synthesized by the reaction of tricyclic carbin complexes Ph2E[C?W(OBu1)3]2 with HCl. Tin-containing carbene complex is not thermally stable and identified in solution by 1H and 13C NMR spectroscopy. Silicon- and germanium-containing carbene complexes of tungsten were separated with high yields in the individual crystal state were identified by element analysis, IR- and 1H, 13C NMR-spectroscopy. Structure of silicon-containing complex [ButO)2(Cl)2W=CH]2SiPh2 were determined by X-ray diffraction. Silicon and tungsten atoms are deformed according to tetrahedral and tetragonal-pyramidal coordinations correspondingly

201

2-Alkynylbenzaldoxime: a versatile building block for the generation of N-heterocycles.  

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2-Alkynylbenzaldoxime as a versatile building block has been applied widely for the construction of N-heterocycles in organic synthesis. Since it could be easily transferred to isoquinoline N-oxide via intramolecular 6-endo cyclization in the presence of metal catalysts or electrophiles, the subsequent [3 + 2] cycloaddition/nucleophilic addition and rearrangement could be expected. On the other hand, a Beckmann rearrangement could occur first since an oxime moiety is present in the molecule, which would then undergo an intramolecular cyclization to furnish nitrogen-containing heterocycles. This review reports the recent advancement in the generation of N-heterocycles starting from 2-alkynylbenzaldoximes via tandem reactions based on different reaction types. PMID:25297655

He, Linman; Nie, Hongming; Qiu, Guanyinsheng; Gao, Yueqiu; Wu, Jie

2014-12-01

202

Enantioselective construction of quaternary N-heterocycles by palladium-catalysed decarboxylative allylic alkylation of lactams  

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The enantioselective synthesis of nitrogen-containing heterocycles (N-heterocycles) represents a substantial chemical research effort and resonates across numerous disciplines, including the total synthesis of natural products and medicinal chemistry. In this Article, we describe the highly enantioselective palladium-catalysed decarboxylative allylic alkylation of readily available lactams to form 3,3-disubstituted pyrrolidinones, piperidinones, caprolactams and structurally related lactams. Given the prevalence of quaternary N-heterocycles in biologically active alkaloids and pharmaceutical agents, we envisage that our method will provide a synthetic entry into the de novo asymmetric synthesis of such structures. As an entry for these investigations we demonstrate how the described catalysis affords enantiopure quaternary lactams that intercept synthetic intermediates previously used in the synthesis of the Aspidosperma alkaloids quebrachamine and rhazinilam, but that were previously only available by chiral auxiliary approaches or as racemic mixtures.

Behenna, Douglas C.; Liu, Yiyang; Yurino, Taiga; Kim, Jimin; White, David E.; Virgil, Scott C.; Stoltz, Brian M.

2012-02-01

203

Interaction of carbene and olefin donors with [Cl2PN]3: exploration of a reductive pathway toward (PN)3.  

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The iminophosphine-phosphazene [P(III)-P(V)] heterocyclic adduct [IPr·PN(PCl(2)N)(2)] was prepared via reduction of the cyclic phosphazene [Cl(2)PN](3) in the presence of the carbene donor IPr {IPr = [(HCNDipp)(2)C:], where Dipp = 2,6-(i)Pr(2)C(6)H(3)}. By contrast, the treatment of [Cl(2)PN](3) with the N-heterocyclic olefin IPr?CH(2) yielded the olefin-grafted phosphazene ring [(IPr?CH)P(Cl)N(PCl(2)N)(2)]. PMID:21981136

Al-Rafia, S M Ibrahim; Ferguson, Michael J; Rivard, Eric

2011-11-01

204

Influence of solvent on carbene intersystem crossing rates.  

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The influence of coordinating solvents on singlet-to-triplet carbene intersystem crossing (ISC) rates has been studied with diphenylcarbene (DPC) and para-biphenyltrifluoromethylcarbene (BpCCF 3) by using ultrafast time-resolved spectroscopy. DPC has a triplet ground state in all of the solvents considered, and the concentration of singlet carbene at equilibrium is too small to be measured. It is found that the lifetime of (1)DPC is extended in acetonitrile, benzene, tetrahydrofuran, dichloromethane, and halobenzene solvents relative to cyclohexane. The solvent effect does not well correlate with bulk measures of solvent polarity. The singlet-triplet energy separation of BpCCF 3 is close to zero. The data demonstrates that BpCCF 3 has a triplet ground state in benzene, fluorobenzene, and hexafluorobenzene. Halogenated solvents are found to dramatically retard the rate of ISC in (1)BpCCF 3. We postulate that the empty p orbital of a singlet carbene coordinates with a nonbonding pair of electrons of a halogen atom of the solvent to form a pseudoylide solvent complex, stabilize the singlet carbene, and decrease the singlet-triplet (S-T) energy gap. The "golden rule" of radiationless transitions posits that the smaller the energy gap between the two states, the faster their rate of interconversion. To explain the apparent violation of the golden rule of radiationless transitions for the carbene ISC processes monitored in this study, we propose that the significantly different specific solvation of the singlet and triplet carbenes imposes a Franck-Condon-like factor on the ISC process. Those solvents that most solvate the singlet carbene will also have the greatest structural difference between singlet carbene-solvent complex and their triplet spin isomer-solvent complex, the smallest S-T gap, and the slowest ISC rate. Alternatively, one can propose that a highly solvated singlet carbene must desolvate prior to ISC, and that this requirement decelerates the radiationless transition. PMID:18433130

Wang, Jin; Kubicki, Jacek; Peng, Huolei; Platz, Matthew S

2008-05-21

205

Synthesis of Aryliron Complexes [CpFe(CO2Ar] by Palladium-Catalyzed Reactions of [CpFe(CO2I] with Arylzinc, -Boron, or -Indium Reagents  

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Full Text Available Transmetalation between [CpFe(CO2I] and arylzinc iodide-lithium chloride complexes proceeds in the presence of catalytic amounts of palladium acetate and N,N,N’,N’-tetramethyl-1,2-cyclohexanediamine to yield the corresponding aryliron complexes [CpFe(CO2Ar]. Phenylation of [CpFe(CO2I] also takes place when triphenylindium is used under similar conditions. Arylboronic acids undergo arylation in the presence of cesium carbonate and a palladium-N-heterocyclic carbene complex, PEPPSI. The present methods are useful for the facile synthesis of various functionalized [CpFe(CO2Ar]. The products [CpFe(CO2Ar] represent an interesting class of aryl metals that undergo several transformation.

Koichiro Oshima

2009-08-01

206

Application of open chain tetraimidazolium salts as precursors for the synthesis of silver tetra(NHC) complexes.  

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The synthesis of 3-((1H-imidazol-1-yl)methyl)-1-methyl-1H-imidazol-3-ium iodide 1 for the synthesis of multidentate tetra-N-heterocyclic carbene (NHC) structures is described. Two acyclic open chain tetra(NHC) precursors are synthesized together with their corresponding silver complexes. On the basis of nuclear magnetic resonance (NMR) spectroscopy and single crystal X-ray diffraction (XRD) data, the coordination geometry of the silver complexes is discussed. Dependent on the length of the alkyl bridge of the tetradentate ligand either a double helix structure with four linear-coordinated silver cations or a twisted geometry with two linear-coordinated silver cations is obtained. PMID:25551583

Weiss, Daniel T; Haslinger, Stefan; Jandl, Christian; Pöthig, Alexander; Cokoja, Mirza; Kühn, Fritz E

2015-01-20

207

Ru(II) , Os(II) , and Ir(III) Complexes with Chelating Pyridyl-Mesoionic Carbene Ligands: Structural Characterization and Applications in Transfer Hydrogenation Catalysis.  

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Chelating ligands with one pyridine donor and one mesoionic carbene donor are fast establishing themselves as privileged ligands in homogeneous catalysis. The synthesis of several new Ir(III) -Cp*- and Os(II) -Cym complexes (Cp*=pentamethylcyclopentadienyl, Cym=p-cymene=4-isopropyl-toluene) derived from chelating pyridyltriazolylidenes where the additional pyridine donor was incorporated via the azide part of the triazole is presented. Furthermore, different 4-substituted phenylacetylene building blocks have been used to introduce electronic fine-tuning in the ligands. The ligands thus can be generally described as 4-(4-R-phenyl)-3-methyl-1-(pyridin-2-yl)-1H-1,2,3-triazol-5-ylidene (with R being H (L(1) ), Me (L(2) ), OMe (L(3) ), CN (L(4) ), CF3 (L(5) ), Br (L(6) ) or NO2 (L(7) )). The corresponding complexes (Ir-1 to Ir-7 and Os-1 to Os-7) were characterized by standard spectroscopic methods, and the expected three-legged, piano-stool type coordination was unambiguously confirmed by X-ray diffraction analysis of selected compounds. Together with Ru(II) analogues previously reported by us, a total of 21 complexes were tested as (pre)catalysts for the transfer hydrogenation of carbonyl groups, showing a remarkable reactivity even at very low catalyst loadings. The electronic effects of the ligands as well as different substrates were investigated. Some mechanistic elucidations are also presented. PMID:25752929

Bolje, Aljoša; Hohloch, Stephan; van der Meer, Margarethe; Košmrlj, Janez; Sarkar, Biprajit

2015-04-27

208

Spectroscopic and electrochemical correlations in triangular ruthenium clusters containing N-heterocyclic ligands  

International Nuclear Information System (INIS)

A series of clusters of general formula [Ru sub(3) O (OOCCH sub(3)) sub(6) L sub(3)] sup(+), where L = N-heterocyclic ligands, were synthesized and characterized based on elemental analysis. UV-VIS and IR spectra. Voltametric studies revealed the existence of up to six acessible oxidation states, with a high degree of electronic delocalization. The Ru sub(3) O trigonal center possesses many delocalized electrons and can be visualized as a source of electrons. The ligands coordinated to the clusters tune their redox potentials, determine the differences in their electronic spectra, and are responsible for the special conditions required for their synthesis. (author)

209

Self-assembly of N-heterocyclic derivatives of divalent germanium, tin, and lead.  

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A new class of exceptionally stable asymmetric N-heterocyclic germylenes, stannylenes, and plumbylenes has been successfully isolated and characterized by single-crystal X-ray diffraction analysis and multinuclear NMR spectroscopy. Their stability results from tetrameric supramolecular aggregation through strong intermolecular Npy ?E(II) (E=Ge, Sn, Pb) interactions involving the nitrogen atom of a neighboring pyridine moiety. The electronic structures and stabilities of the prepared divalent derivatives of Ge, Sn, and Pb in monomeric and aggregated forms are discussed based on theoretical investigations. PMID:25346531

Zabula, Alexander V; Rogachev, Andrey Yu; West, Robert

2014-12-01

210

Enantioselective synthesis of dialkylated N-heterocycles by palladium-catalyzed allylic alkylation.  

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The enantioselective synthesis of ?-disubstituted N-heterocyclic carbonyl compounds has been accomplished using palladium-catalyzed allylic alkylation. These catalytic conditions enable access to various heterocycles, such as morpholinone, thiomorpholinone, oxazolidin-4-one, 1,2-oxazepan-3-one, 1,3-oxazinan-4-one, and structurally related lactams, all bearing fully substituted ?-positions. Broad functional group tolerance was explored at the ?-position in the morpholinone series. We demonstrate the utility of this method by performing various transformations on our useful products to readily access a number of enantioenriched compounds. PMID:25714704

Numajiri, Yoshitaka; Jiménez-Osés, Gonzalo; Wang, Bo; Houk, K N; Stoltz, Brian M

2015-03-01

211

Chemistry of diruthenium and dirhodium analogues of pentaborane(9): synthesis and characterization of metal n,s-heterocyclic carbene and B-agostic complexes.  

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Building upon our earlier results on the synthesis of electron-precise transition-metal-boron complexes, we continue to investigate the reactivity of pentaborane(9) and tetraborane(10) analogues of ruthenium and rhodium towards thiazolyl and oxazolyl ligands. Thus, mild thermolysis of nido-[(Cp*RuH)2 B3 H7 ] (1) with 2-mercaptobenzothiazole (2-mbtz) and 2-mercaptobenzoxazole (2-mboz) led to the isolation of Cp*-based (Cp*=?(5) -C5 Me5 ) borate complexes 5?a,b [Cp*RuBH3 L] (5?a: L=C7 H4 NS2 ; 5?b: L=C7 H4 NOS)) and agostic complexes 7?a,b [Cp*RuBH2 (L)2 ], (7?a: L=C7 H4 NS2 ; 7?b: L=C7 H4 NOS). In a similar fashion, a rhodium analogue of pentaborane(9), nido-[(Cp*Rh)2 B3 H7 ] (2) yielded rhodaboratrane [Cp*RhBH(L)2 ], 10 (L=C7 H4 NS2 ). Interestingly, when the reaction was performed with an excess of 2-mbtz, it led to the formation of the first structurally characterized N,S-heterocyclic rhodium-carbene complex [(Cp*Rh)(L2 )(1-benzothiazol-2-ylidene)] (11) (L=C7 H4 NS2 ). Furthermore, to evaluate the scope of this new route, we extended this chemistry towards the diruthenium analogue of tetraborane(10), arachno-[(Cp*RuCO)2 B2 H6 ] (3), in which the metal center possesses different ancillary ligands. PMID:25537367

Roy, Dipak Kumar; Mondal, Bijan; Anju, R S; Ghosh, Sundargopal

2015-02-23

212

[Au(dien)(N-heterocycle)](3+): reactivity with biomolecules and zinc finger peptides.  

Science.gov (United States)

The reaction of [Au(dien)(N-heterocycle)](3+) (AuN4) coordination compounds with simple amino acids and zinc finger proteins is reported. Compared to [AuCl(dien)](2+), NMR studies show that the presence of a more substitution-inert N-donor as the putative leaving group slows the reaction with the sulfur-containing amino acids N-acetylmethionine (NAcMet) and N-acetylcysteine (NAcCys). Lack of ligand dissociation upon reaction with NAcCys indicates, to our knowledge, the first long-lived N-heterocycle-Au-S species in solution. Reactions with zinc finger proteins show a higher reactivity with the Cys3His zinc finger than with Cys2His2, likely due to the presence of fewer aurophilic cysteines in the latter. Of the Au(III) compounds studied, [Au(dien)(DMAP)](3+) (DMAP = 4-dimethylaminopyridine) appears to be the least reactive, with ESI-MS studies showing the presence of intact zinc fingers at initial reaction times. These results, in combination with previously reported characterization and pH dependency studies, will further aid in optimizing the structure of these AuN4 species to obtain a substitution-reactive yet selective compound for targeting zinc finger proteins. PMID:25531886

Spell, Sarah R; Farrell, Nicholas P

2015-01-01

213

Low-spin hexacoordinate Mn(III): synthesis and spectroscopic investigation of homoleptic tris(pyrazolyl)borate and tris(carbene)borate complexes.  

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Three complexes of Mn(III) with "scorpionate" type ligands have been investigated by a variety of physical techniques. The complexes are [Tp(2)Mn]SbF(6) (1), [Tp(2)*Mn]SbF(6) (2), and [{PhB(MeIm)(3)}(2)Mn](CF(3)SO(3)) (3a), where Tp(-) = hydrotris(pyrazolyl)borate anion, Tp*(-) = hydrotris(3,5-dimethylpyrazolyl)borate anion, and PhB(MeIm)(3)(-) = phenyltris(3-methylimidazol-2-yl)borate anion. The crystal structure of 3a is reported; the structures of 1 and 2 have been previously reported, but were reconfirmed in this work. The synthesis and characterization of [{PhB(MeIm)(3)}(2)Mn]Cl (3b) are also described. These complexes are of interest in that, in contrast to many hexacoordinate (pseudo-octahedral) complexes of Mn(III), they exhibit a low-spin (triplet) ground state, rather than the high-spin (quintet) ground state. Solid-state electronic absorption spectroscopy, SQUID magnetometry, and high-frequency and -field electron paramagnetic resonance (HFEPR) spectroscopy were applied. HFEPR, in particular, was useful in characterizing the S = 1 spin Hamiltonian parameters for complex 1, D = +19.97(1), E = 0.42(2) cm(-1), and for 2, D = +15.89(2), E = 0.04(1) cm(-1). In addition, frequency domain Fourier-transform THz-EPR spectroscopy, using coherent synchrotron radiation, was applied to 1 only and gave results in good agreement with HFEPR. Variable-temperature dc magnetic susceptibility measurements of 1 and 2 were also in good agreement with the HFEPR results. This magnitude of zero-field splitting (zfs) is over 4 times larger than that in comparable hexacoordinate Mn(III) systems with S = 2 ground states. Complexes 3a and 3b (i.e., regardless of counteranion) have a yet much larger magnitude zfs, which may be the result of unquenched orbital angular momentum so that the spin Hamiltonian model is not appropriate. The triplet ground state is rationalized in each complex by ligand-field theory (LFT) and by quantum chemistry theory, both density functional theory and unrestricted Hartree-Fock methods. This analysis also shows that spin-crossover behavior is not thermally accessible for these complexes as solids. The donor properties of the three different scorpionate ligands were further characterized using the LFT model that suggests that the tris(carbene)borate is a strong ?-donor with little or no ?-bonding. PMID:23259486

Forshaw, Adam P; Smith, Jeremy M; Ozarowski, Andrew; Krzystek, J; Smirnov, Dmitry; Zvyagin, S A; Harris, T David; Karunadasa, Hemamala I; Zadrozny, Joseph M; Schnegg, Alexander; Holldack, Karsten; Jackson, Timothy A; Alamiri, Ahmad; Barnes, Diane M; Telser, Joshua

2013-01-01

214

Enzymatic hydrolysis of long-chain N-heterocyclic fatty esters.  

Science.gov (United States)

Incubation of a 1-pyrroline ester [viz. methyl 8-(5-hexyl-1-pyrroline-2-yl)octanoate, 1] with bakers' yeast (Saccharomyces cerevisiae) gave the corresponding free fatty acid (1a, 52%). The C = N bond of the 1-pyrroline was not reduced by the yeast. Complete hydrolysis of compound 1 was successful using lipase of Candida cylindracea (CCL) or Lipolase (Rhizomucor miehei) under stirred or ultrasound condition. Fatty esters containing a pyrrolidine [viz. methyl 8-(cis/trans-5-hexyl-pyrrolidine-2-)octanoate, 2] or N-methyl pyrrolidine [viz. methyl 8-(cis-5-hexyl-N-methyl-pyrrolidine-2-)octanoate, 3] system in the alkyl chain were not hydrolyzed by either CCL or Lipolase, unless conducted in an ultrasonic bath. The hydrolytic activities of the enzymes appeared to be strongly affected by the stereochemistry of the N-heterocyclic ring system. Chemical hydrolysis of compounds 1-3 gave the corresponding fatty acid N-HCl salts. PMID:8569439

Lie Ken Jie, M S; Syed-Rahmatullah, M S

1995-11-01

215

Cyclic (Alkyl)(Amino)Carbenes (CAACs): Stable Carbenes on the Rise.  

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Conspectus Carbenes are compounds that feature a divalent carbon atom with only six electrons in its valence shell. In the singlet state, they possess a lone pair of electrons and a vacant orbital and therefore exhibit Lewis acidic and Lewis basic properties, which explains their very high reactivity. Following the preparation by our group in 1988 of the first representative, a variety of stable carbenes are now available, the most popular being the cyclic diaminocarbenes. In this Account, we discuss another class of stable cyclic carbenes, namely, cyclic (alkyl)(amino)carbenes (CAACs), in which one of the electronegative and ?-donor amino substituents of diaminocarbenes is replaced by a ?-donating but not ?-donating alkyl group. As a consequence, CAACs are more nucleophilic (?-donating) but also more electrophilic (?-accepting) than diaminocarbenes. Additionally, the presence of a quaternary carbon in the position ? to the carbene center provides steric environments that differentiate CAACs dramatically from all other ligands. We show that the peculiar electronic and steric properties of CAACs allow for the stabilization of unusual diamagnetic and paramagnetic main group element species. As examples, we describe the preparation of room temperature stable phosphorus derivatives in which the heteroatom is in the zero oxidation state, nucleophilic boron compounds, and phosphorus-, antimony-, boron-, silicon-, and even carbon-centered neutral and cationic radicals. CAACs are also excellent ligands for transition metal complexes. The most recent application is their use for the stabilization of paramagnetic complexes, in which the metal is often in a formal zero oxidation state. Indeed, bis(CAAC)M complexes in which the metal is gold, copper, cobalt, iron, nickel, manganese, and zinc have been isolated. Depending on the metal, the majority of spin density can reside either on the metal or on the carbene carbons and the nitrogen atoms of the CAAC ligand. In contrast to diaminocarbenes, the higher basicity of CAACs makes them poor leaving groups, and thus they cannot be used for classical organocatalysis. However, because of their superior electrophilicity and smaller singlet-triplet gap, CAACs can activate small molecules at room temperature, such as CO, H2, and P4, as well as enthalpically strong bonds, such as B-H, Si-H, N-H, and P-H. Lastly, excellent results have been obtained in palladium, ruthenium, and gold catalysis. CAAC-metal complexes are extremely thermally robust, which allows for their utilization in harsh conditions. This property has been used to perform a variety of gold-catalyzed reactions in the presence of basic amines, including ammonia and hydrazine, which usually deactivate catalysts. PMID:25515548

Soleilhavoup, Michèle; Bertrand, Guy

2015-02-17

216

Theoretical studies of the effective exchange interactions and photoinduced magnetism in manganese and copper di(4-pyridyl)carbene complexes  

Science.gov (United States)

UHF, UMP n ( n=2,4), UCC and DFT (UBLYP and UB3LYP) calculations using several basis sets were performed in order to elucidate the sign and magnitudes of the effective exchange interactions ( Jab) of models of 1:1 complex of Mn(hfac) 2 or Cu(hfac) 2 with (4-pryidyl)methylene. The Jab value between Mn(II) and divalent carbon (:C) through 4-pyridyl group by the UMP and UCCSD(T)/triple-zeta basis set was antiferromagnetic, while it was ferromagnetic between Cu(II) and :C. This is wholly consistent with the experiments. The signs of Jab values are explained by mechanisms of spin-exchange couplings through the configuration interaction pictures.

Takano, Yu; Soda, Tomohisa; Kitagawa, Yasutaka; Yoshioka, Yasunori; Yamaguchi, Kizashi

1999-02-01

217

New thiocyanatocadmates templated by multi-dentate N-heterocyclic/diamine molecules.  

Science.gov (United States)

With diverse multi-dentate N-heterocyclic/diamine molecules as the cations, the reactions between Cd(2+) and SCN(-) in C2H5OH/H2O solution acidified by H2SO4 created five new thiocyanatocadmates [H2(bim)][Cd(SCN)2(H2O)2]SO4 (bim = 2,2'-biimidazole) 1, [H2(pympip)]2[Cd2(SCN)4(SO4)2(H2O)4]·2H2O (pympip = 1-(2-pyrimidyl)piperazine) 2, [H2(tdpy)]2[Cd3(SCN)10] (tdpy = 4,4'-thiodipyridine) 3, [H2(badpm)][Cd(SCN)4] (badpm = 4,4'-biaminodiphenylmethane) 4 and [H2(pdma)][Cd2(SCN)4(SO4)] (pdma = 1,4-phenylenedimethanamine) 5. It is noteworthy that (i) in compounds 1, 2 and 5, SO4(2-) was incorporated into the organically templated thiocyanatocadmate frameworks; (ii) compound is a rare example, in which two types of chained thiocyanatocadmates are found, and (iii) compound shows an interesting layer structure, constructed up from the ribboned thiocyanatocadmates by ?2-mode SO4(2-). Photoluminescence analysis revealed that compounds 1, 2 and 5 in solid state emit blue light with the maximum at 425 nm for 1, 405 nm for 2 and 445 nm for 5, respectively. PMID:23467616

Jia, Hong-Li; Jia, Ming-Jun; Li, Guang-Hua; Wang, Yan-Ning; Yu, Jie-Hui; Xu, Ji-Qing

2013-05-14

218

Unexpected ring expansion of an enantiopure imidazoline carbene ligand.  

Science.gov (United States)

[reaction: see text] We report an unexpected ring expansion reaction of an enantiopure fenchone-derived imidazolinium salt during attempts to form copper complexes of the corresponding imidazoline carbene ligand. A N,N'-difenchyl piperazinone was formed in low yield together with the difenchyl-substituted five-membered urea. PMID:16805549

Pelegrí, Adela Sanchez; Elsegood, Mark R J; McKee, Vickie; Weaver, George W

2006-07-01

219

Protonolysis of a Ruthenium-Carbene Bond and Applications in Olefin Metathesis  

OpenAIRE

The synthesis of a ruthenium complex containing an N-heterocylic carbene (NHC) and a mesoionic carbene (MIC) is described wherein addition of a Brønsted acid results in protonolysis of the Ru-MIC bond to generate an extremely active metathesis catalyst. Mechanistic studies implicate a rate-determining protonation step to generate the metathesis active species. The NHC/MIC catalyst was found to have activity exceeding current commercial ruthenium catalysts.

Keitz, Benjamin K.; Bouffard, Jean; Bertrand, Guy; Grubbs, Robert H.

2011-01-01

220

Novel Synthesis of 3-Phenyl-chromen-4-ones Using N-Heterocyclic Carbene as Organocatalyst: An Efficient Domino Catalysis Type Approach  

International Nuclear Information System (INIS)

Herein is reported a simple and efficient synthesis of isoflavones starting from various substituted phenacyl bromides and salicylaldehydes in presence of NHC. The mechanism involved domino catalysis type approach with consumption and regeneration of catalyst in two catalytic cycles. This method proved to be very lucrative and gives very good yield. The method described here represents an environmentally benign alternative to classical approach

221

Copper- and copper–N-heterocyclic carbene-catalyzed C?H activating carboxylation of terminal alkynes with CO2 at ambient conditions  

OpenAIRE

The use of carbon dioxide as a renewable and environmentally friendly source of carbon in organic synthesis is a highly attractive approach, but its real world applications remain a great challenge. The major obstacles for commercialization of most current protocols are their low catalytic performances, harsh reaction conditions, and limited substrate scope. It is important to develop new reactions and new protocols for CO2 transformations at mild conditions and in cost-efficient ways. Herein...

Yu, Dingyi; Zhang, Yugen

2010-01-01

222

N-Heterocyclic carbene-catalyzed [4 + 2] cyclization of 2-bromo-2-enal with 3-alkylenyloxindoles: efficient assembly of spirocarbocyclic oxindole.  

Science.gov (United States)

A NHC-catalyzed [4 + 2] cyclization of 2-bromo-2-enal bearing ?-H with 3-alkylenyloxindoles under mild reaction conditions gives spirocarbocyclic oxindoles containing one quaternary carbon in moderate to good yields with high diastereoselectivities. The easy availability of the starting materials, the concise assembly and the potential utilization value of the products make this strategy attractive in molecular biology and pharmacy. PMID:25501791

Xie, Yuanwei; Que, Yonglei; Li, Tuanjie; Zhu, Ling; Yu, Chenxia; Yao, Changsheng

2015-02-14

223

Novel Synthesis of 3-Phenyl-chromen-4-ones Using N-Heterocyclic Carbene as Organocatalyst: An Efficient Domino Catalysis Type Approach  

Energy Technology Data Exchange (ETDEWEB)

Herein is reported a simple and efficient synthesis of isoflavones starting from various substituted phenacyl bromides and salicylaldehydes in presence of NHC. The mechanism involved domino catalysis type approach with consumption and regeneration of catalyst in two catalytic cycles. This method proved to be very lucrative and gives very good yield. The method described here represents an environmentally benign alternative to classical approach.

Mishra, Priya; Singh, Sarita; Ankit, Preyas; Fatma, Shahin; Singh, Divya; Singh, Jagdamba [Univ. of Allahabad, Allahabad (India)

2013-04-15

224

Quantitative description of structural effects on the stability of gold(I) carbenes.  

Science.gov (United States)

The gas-phase bond-dissociation energies of a SO2 -imidazolylidene leaving group of three gold(I) benzyl imidazolium sulfone complexes are reported (E0 =46.6±1.7, 49.6±1.7, and 48.9±2.1?kcal?mol(-1) ). Although these energies are similar to each other, they are reproducibly distinguishable. The energy-resolved collision-induced dissociation experiments of the three [L]-gold(I) (L=ligand) carbene precursor complexes were performed by using a modified tandem mass spectrometer. The measurements quantitatively describe the structural and electronic effects a p-methoxy substituent on the benzyl fragment, and trans [NHC] and [P] gold ligands, have towards gold carbene formation. Evidence for the formation of the electrophilic gold carbene in solution was obtained through the stoichiometric and catalytic cyclopropanation of olefins under thermal conditions. The observed cyclopropane yields are dependent on the rate of gold carbene formation, which in turn is influenced by the ligand and substituent. The donation of electron density to the carbene carbon by the p-methoxy benzyl substituent and [NHC] ligand stabilizes the gold carbene intermediate and lowers the dissociation barrier. Through the careful comparison of gas-phase and solution chemistry, the results suggest that even gas-phase leaving-group bond-dissociation energy differences of 2-3?kcal?mol(-1) enormously affect the rate of gold carbene formation in solution, especially when there are competing reactions. The thermal decay of the gold carbene precursor complex was observed to follow first-order kinetics, whereas cyclopropanation was found to follow pseudo-first-order kinetics. Density-functional-theory calculations at the M06-L and BP86-D3 levels of theory were used to confirm the observed gas-phase reactivity and model the measured bond-dissociation energies. PMID:25236486

Ringger, David H; Kobylianskii, Ilia J; Serra, Daniel; Chen, Peter

2014-10-27

225

Study of the factors supporting the selective complexation of the trivalent lanthanide and actinide ions  

International Nuclear Information System (INIS)

In order to obtain clear-cut information on the factors which favour the discrimination between trivalent actinides and lanthanides, we investigated the complexation of the tris(cyclopentadienyl) Ce(III) and U(III) compounds, (RCp)3M (R = tBu, SiMe3), with a series of monocyclic azines with distinct Lewis basicity and reduction potential. Coordination of pyrazine and 4,4' and 2,2'-bipyridines on the (RCp)3M complexes has also been studied. Of major interest is the reversible oxidation of the (RCp)3U species into the uranium(IV) [(RCp)3U]2(pyz) complexes by pyrazine. The presence of cooperativity in the binding of the cyclopentadienyl groups by U(III), due to late appearance of back-bonding, leads to a greater stabilization of the uranium(III) complexes. Complexation of the species Cp*2MI (M = Ce, U) by 2,2'-bipyridine, phenanthroline and ter-pyridine affords the adducts [Cp*2M(L)]I. For L = bipy and terpy, these compounds are reduced into Cp*2M(L). The magnetic data for [Cp*2M(terpy)]I and Cp*2M(terpy) are consistent with Ce(III) and U(III) species, with the formulation Cp*2MIII(terpy). An electron transfer reaction between these species was observed in NMR. Reactions of the [Cp*2M(terpy)]I and Cp*2M(terpy) complexes with H and H+ donor reagents lead to a clear differentiation of these trivalent ions. We studied the coordination of the stable N-heterocyclic carbene and isonitrile molecules on (RCp)3M and Cp*2MI; competition reactions and comparison of the crystal structures of the carbene compounds reveal the much better affinity of the NHC and tBuNC ligands for the 5f rather than for the 4f ion. (authors)

226

Hemilabile and bimetallic coordination in Rh and Ir complexes of NCN pincer ligands.  

Science.gov (United States)

Two new pincer ligands have been developed that contain a central N-heterocyclic carbene (NHC) moiety linked to two pendant pyrazole groups by either a methylene (NCN(me)) or ethylene (NCN(et)) chain. The coordination of these two ligands to rhodium and iridium resulted in a variety of binding modes. Tridentate coordination of the ligands was observed in the complexes [Rh(NCN(me))(COD)]BPh4 (8), [Ir(NCN(me))(COD)]BPh4 (10), [Rh(NCN(et))(CO)2]BPh4 (13), and [Ir(NCN(me))(CO)2]BPh4 (14), and monodentate NHC coordination was observed for [Ir(NCN(me))2(COD)]BPh4 (11) and [Ir(NCN(et))2(COD)]BPh4 (12). Both tridentate and bidentate coordination modes were characterized for [Rh(NCN(et))(COD)]BPh4 (9) in the solution and solid state, respectively, while an unusual bridging mode was observed for the bimetallic complex [Rh(?-NCN(me))(CO)]2(BPh4)2 (15). The impact of this diverse coordination chemistry on the efficiency of the complexes as catalysts for the addition of NH, OH, and SiH bonds to alkynes was explored. PMID:25252249

Mancano, Giulia; Page, Michael J; Bhadbhade, Mohan; Messerle, Barbara A

2014-10-01

227

Exotic noble gas carbene-like ions  

Science.gov (United States)

Using a combination of theoretical techniques, this work studies the Kr2C2+ species, which has electronic, structural, and some typical chemical characteristics of carbenes, and whose ground state is singlet. Similarly to the case of traditional carbenes, Kr2C2+ is metastable and appears to be a candidate for a reactive intermediate.

Echeverri, Andrea; Moreno, Norberto; Restrepo, Albeiro; Hadad, C. Z.

2014-11-01

228

Luminescent pillared LnIII–ZnII heterometallic coordination frameworks with two kinds of N-heterocyclic carboxylate ligands  

International Nuclear Information System (INIS)

In our efforts toward rational design and systematic synthesis of ‘pillar-layer’ structure coordination frameworks, four new LnIII–ZnII heterometallic coordination polymers (CPs) based on two kinds of N-heterocyclic carboxylic ligands with formula ([LnZn(L1)2(L2)(H2O)m]·nH2O)? (Ln=La (1), Eu (2), Gd (3) and Dy (4), m=3 (for 1) and 2 (for 2–4), n=8 (for 1) and 7 (for 2–4), H2L1=pyridine-2,3-dicarboxylate acid, HL2=isonicotinic acid), have been synthesized under hydrothermal reaction of Ln2O3, ZnO, H2L1 and HL2. CP 1 has a three-dimensional (3D) structure with a (3,6)-connected sit topology network, while CPs 2–4 are isostructural with 3D single-node pcu alpha-Po topology network. Also, luminescent properties of these CPs have also been investigated. The emission of 1 and 3 should be attributed to the coordination-perturbed ligand-centered luminescence and the emission spectra of 2 and 4 show the characteristic bands of the corresponding LnIII ions. - Graphical abstract: Four new 3D LnIII–ZnII coordination frameworks with “pillar-layer” sit or pcu alpha-Po topology have been successfully obtained. Moreover, the photoluminescent properties of compounds 1–4 have also been investigated. - Highlights: • Four new LnIII–ZnII heterometallic coordination frameworks with two types of topologies have been synthesized. • Metal oxides and two kinds of N-heterocyclic carboxylate ligands were used for the construction of targeted coordination polymers. • The luminescent properties of the coordination polymers are investigated

229

A Heteroleptic Ferrous Complex with Mesoionic Bis(1,2,3-triazol-5-ylidene) Ligands: Taming the MLCT Excited State of Iron(II).  

Science.gov (United States)

Strongly ?-donating N-heterocyclic carbenes (NHCs) have revived research interest in the catalytic chemistry of iron, and are now also starting to bring the photochemistry and photophysics of this abundant element into a new era. In this work, a heteroleptic Fe(II) complex (1) was synthesized based on sequentially furnishing the Fe(II) center with the benchmark 2,2'-bipyridine (bpy) ligand and the more strongly ?-donating mesoionic ligand, 4,4'-bis(1,2,3-triazol-5-ylidene) (btz). Complex?1 was comprehensively characterized by electrochemistry, static and ultrafast spectroscopy, and quantum chemical calculations and compared to [Fe(bpy)3 ](PF6 )2 and (TBA)2 [Fe(bpy)(CN)4 ]. Heteroleptic complex?1 extends the absorption spectrum towards longer wavelengths compared to a previously synthesized homoleptic Fe(II) NHC complex. The combination of the mesoionic nature of btz and the heteroleptic structure effectively destabilizes the metal-centered (MC) states relative to the triplet metal-to-ligand charge transfer ((3) MLCT) state in 1, rendering it a lifetime of 13?ps, the longest to date of a photochemically stable Fe(II) complex. Deactivation of the (3) MLCT state is proposed to proceed via the (3) MC state that strongly couples with the singlet ground state. PMID:25504660

Liu, Yizhu; Kjaer, Kasper S; Fredin, Lisa A; Chábera, Pavel; Harlang, Tobias; Canton, Sophie E; Lidin, Sven; Zhang, Jianxin; Lomoth, Reiner; Bergquist, Karl-Erik; Persson, Petter; Wärnmark, Kenneth; Sundström, Villy

2015-02-23

230

Coinage metals binding as main group elements: structure and bonding of the carbene complexes [TM(cAAC)2] and [TM(cAAC)2](+) (TM = Cu, Ag, Au).  

Science.gov (United States)

Quantum chemical calculations using density functional theory have been carried out for the cyclic (alkyl)(amino)carbene (cAAC) complexes of the group 11 atoms [TM(cAAC)2] (TM = Cu, Ag, Au) and their cations [TM(cAAC)2](+). The nature of the metal-ligand bonding was investigated with the charge and energy decomposition analysis EDA-NOCV. The calculations show that the TM-C bonds in the charged adducts [TM(cAAC)2](+) are significantly longer than in the neutral complexes [TM(cAAC)2], but the cations have much higher bond dissociation energies than the neutral molecules. The intrinsic interaction energies ?Eint in [TM(cAAC)2](+) take place between TM(+) in the (1)S electronic ground state and (cAAC)2. In contrast, the metal-ligand interactions in [TM(cAAC)2] involve the TM atoms in the excited (1)P state yielding strong TM p(?) ? (cAAC)2 ? backdonation, which is absent in the cations. The calculations suggest that the cAAC ligands in [TM(cAAC)2] are stronger ? acceptors than ? donors. The trends of the intrinsic interaction energies and the bond dissociation energies of the metal-ligand bonds in [TM(cAAC)2] and [TM(cAAC)2](+) give the order Au > Cu > Ag. Calculations at the nonrelativistic level give weaker TM-C bonds, particularly for the gold complexes. The trend for the bond strength in the neutral and charged adducts without relativistic effects becomes Cu > Ag > Au. The EDA-NOCV calculations suggest that the weaker bonds at the nonrelativistic level are mainly due to stronger Pauli repulsion and weaker orbital interactions. The NBO picture of the C-TM-C bonding situation does not correctly represent the nature of the metal-ligand interactions in [TM(cAAC)2]. PMID:25394669

Jerabek, Paul; Roesky, Herbert W; Bertrand, Guy; Frenking, Gernot

2014-12-10

231

Palladium-catalyzed carbene migratory insertion using conjugated ene-yne-ketones as carbene precursors.  

Science.gov (United States)

Palladium-catalyzed cross-coupling reactions between benzyl, aryl, or allyl bromides and conjugated ene-yne-ketones lead to the formation of 2-alkenyl-substituted furans. This novel coupling reaction involves oxidative addition, alkyne activation-cyclization, palladium carbene migratory insertion, ?-hydride elimination, and catalyst regeneration. Palladium (2-furyl)carbene is proposed as the key intermediate, which is supported by DFT calculations. The palladium carbene character of the key intermediate is validated by three aspects, including bond lengths, Wiberg bond order indices, and molecular orbitals, by comparison to those reported for stable palladium carbene species. Computational studies also revealed that the rate-limiting step is ene-yne-ketone cyclization, which leads to the formation of the palladium (2-furyl)carbene, while the subsequent carbene migratory insertion is a facile process with a low energy barrier (<5 kcal/mol). PMID:23947689

Xia, Ying; Qu, Shuanglin; Xiao, Qing; Wang, Zhi-Xiang; Qu, Peiyuan; Chen, Li; Liu, Zhen; Tian, Leiming; Huang, Zhongxing; Zhang, Yan; Wang, Jianbo

2013-09-11

232

Cyclometallated platinum(ii) complexes containing NHC ligands: synthesis, characterization, photophysics and their application as emitters in OLEDs.  

Science.gov (United States)

A series of square planar [Pt(N^C)(NHC)L] complexes containing cyclometallated N^C ligands (phenylpyridine and benzoquinoline) and N-heterocyclic carbene (NHC) - N^C = 2-phenylpyridine, 7,8-benzoquinoline; NHC = 1,3-dibenzylbenzimidazolium, 1,3-diethylbenzimidazolium, 1,3-dibenzylimidazolium; L = Cl, Br, -C2Ph - have been synthesized in moderate to good yields. The complexes obtained were characterized using chemical analysis, MS-ESI spectrometry, NMR spectroscopy and X-ray crystallography. The complexes display moderate to strong phosphorescence in solution (Q.Y. 0.3-7.9%) and in the solid state (Q.Y. 2.7-16.0%), which is related to metal modulated intraligand ?-?* transitions located at the aromatic system of cyclometallated ligands with some contribution of the MLCT excited state. Emission lifetimes fall in the range of 0.2-1.5 ?s in solution and amount up to 13 ?s in the solid state. Analysis of the spectroscopic data together with the density functional theory (DFT) and time-dependent density functional theory (TDDFT) calculations clearly support this assignment and show negligible contribution of the auxiliary ligands to the emissive excited states. The compounds obtained were also used to prepare organic light emitting diode (OLED) devices, which display good luminance efficiency emitting in the green area of the visible spectrum. PMID:25482398

Solomatina, A I; Krupenya, D V; Gurzhiy, V V; Zlatkin, I; Pushkarev, A P; Bochkarev, M N; Besley, N A; Bichoutskaia, E; Tunik, S P

2015-04-01

233

Unsaturated carbenes from primary vinyl triflates. IX. Intramolecular rearrangement via free carbenes  

International Nuclear Information System (INIS)

The mechanism and exact nature of the intermediates in the base-initiated rearrangement of arylvinyl triflates were examined to determine if the reaction proceeds via a carbenoid or the unencumbered carbene. A clear-cut difference was noted in the intramolecular rearrangement of aryl-substituted unsaturated carbenes, with the reaction proceeding via a carbenoid in the case of arylvinyl halides and via the free carbene in the case of arylvinyl triflates

234

Experimental determination of redox cooperativity and electronic structures in catalytically active Cu-Fe and Zn-Fe heterobimetallic complexes.  

Science.gov (United States)

Complexes of the type (NHC)M-Fp (NHC = N-heterocyclic carbene, M = Cu or ZnCl, Fp = FeCp(CO)2) have been used recently as replacements for noble metal C-H functionalization catalysts and for small molecule activation studies. The promising reactivity of these systems has been linked to the use of the late metal electrophiles Cu and Zn in place of early metal electrophiles, and also to the ability of the M-Fe pairs to cooperate during catalytically relevant multielectron redox processes such as bimetallic oxidative addition and bimetallic reductive elimination. Using Mössbauer spectroscopy and metal K-edge XANES analysis, a detailed electronic structure description of these complexes is presented. One unusual feature of the late-metal M-Fp interactions is the presence of significant M ? Fe ?-backdonation in addition to Fe ? M ?-donation; this ?-backdonation is absent in early metal analogues and is apparent from analysis of Mössbauer data and Fe K-edge data. Multi-edge XANES analysis of C-I bimetallic oxidative addition at a Cu-Fe reaction center reveals little change in metal effective nuclear charges during the two-electron redox process. IR spectroscopy indicates that the supporting carbonyl ligands participate to a large extent in the redox process. PMID:25100199

Karunananda, Malkanthi K; Vázquez, Francisco X; Alp, E Ercan; Bi, Wenli; Chattopadhyay, Soma; Shibata, Tomohiro; Mankad, Neal P

2014-09-28

235

Syntheses, characterizations and photoluminescent properties of two novel coordination polymers constructed by poly-carboxylate and N-heterocyclic ligands  

Science.gov (United States)

Two novel coordination compounds constructed from aromatic acid and N-heterocyclic ligands, namely, [Mn(dipt)2(n-BDC)]n (1) [dipt = 2-(2,4-dichlorophenyl)-1H-imidazo[4,5-f][1,10]phenanthroline, n-BDC = 5-nitrobenzene-1,3-dioic acid] and [Cu2(bip)2(m-BDC)2(H2O)3]?2H2O (2) [bip = 2-(4-bromophenyl)-1H-imidazo[4,5-f][1,10]phenanthroline, m-BDC = isophthalic acid] have been synthesized by hydrothermal reaction: compounds 1 and 2 were characterized by elemental analysis, infrared spectrum (IR), single crystal X-ray diffraction and thermogravimetric analysis (TGA). In 1, n-BDC anions link the adjacent Mn(II) centers to generate a one-dimensional (1D) zigzag chain. Furthermore, unprecedented intersections of C-H⋯O bonds lead 1D chain into 2D sheet supra-molecular architecture. Differed from 1, 2 exhibits 0D structure, and displays a 2D topology via strong H-bond and ?-? stacking interactions. TG analysis shows clear courses of weight loss, which corresponds to the decomposition of different ligands. The structure-related solid-state fluorescence spectra of compounds 1 and 2 have been determined, and the result displays that compounds 1 and 2 are potential luminescent material.

Yan, Li; Li, Chuanbi; Wang, Yifei

2013-03-01

236

Microwave-assisted synthesis of N-heterocycles and their evaluation using an acetylcholinesterase immobilized capillary reactor  

Scientific Electronic Library Online (English)

Full Text Available SciELO Brazil | Language: English Abstract in portuguese Os etenoditioacetais polarizados são conhecidos como importantes intermediários em muitos processos de síntese. Neste trabalho, reporta-se a anelação livre de metal de transição de 1,1-bis(tiometil)-2-nitroetileno com hidroxilalquilaminas e alquildiaminas. Esta metodologia permite a síntese direta d [...] e N-heterociclos tais como imidazolidinas, oxazolidinas e benzoxazóis sob irradiação de micro-ondas. Estes compostos foram avaliados como inibidores da acetilcolinesterase usando um reator capilar contendo a enzima imobilizada acoplado a um espectrômetro de massas. Abstract in english Polarized ketene dithioketals have been recognized as useful building blocks in many synthetic operations. In this work, a transition-metal-free annulations of 1,1-bis(thiomethyl)-2-nitroethylene with hydroxylalkylamines or alkyldiamines have been reported. This methodology provides a directed appro [...] ach to N-heterocycles, e.g., imidazolidines, oxazolidines and benzoxazoles under microwave conditions. These compounds were evaluated as acetylcholinesterase inhibitors by using an enzyme immobilized capillary reactor-tandem mass spectrometry.

Diego P., Sangi; Julia L., Monteiro; Kenia L., Vanzolini; Quezia B., Cass; Marcio W., Paixão; Arlene G., Corrêa.

2014-05-01

237

Effects of halogenated aromatics/aliphatics and nitrogen(N)-heterocyclic aromatics on estimating the persistence of future pharmaceutical compounds using a modified QSAR model.  

Science.gov (United States)

The effects of halogenated aromatics/aliphatics and nitrogen(N)-heterocyclic aromatics on estimating the persistence of future pharmaceutical compounds were investigated using a modified half life equation. The potential future pharmaceutical compounds investigated were approximately 2000 pharmaceutical drugs currently undergoing the United States Food and Drug Administration (US FDA) testing. EPI Suite (BIOWIN) model estimates the fates of compounds based on the biodegradability under aerobic conditions. While BIOWIN considered the biodegradability of a compound only, the half life equation used in this study was modified by biodegradability, sorption and cometabolic oxidation. It was possible that the potential future pharmaceutical compounds were more accurately estimated using the modified half life equation. The modified half life equation considered sorption and cometabolic oxidation of halogenated aromatic/aliphatics and nitrogen(N)-heterocyclic aromatics in the sub-surface, while EPI Suite (BIOWIN) did not. Halogenated aliphatics in chemicals were more persistent than halogenated aromatics in the sub-surface. In addition, in the sub-surface environment, the fates of organic chemicals were much more affected by halogenation in chemicals than by nitrogen(N)-heterocyclic aromatics. PMID:24144939

Lim, Seung Joo; Fox, Peter

2014-02-01

238

Electron pairing analysis of the Fischer-type chromium-carbene complexes (CO)5Cr=C(X)R (X=H, OH, OCH3, NH2, NHCH3 and R=H, CH3, CH=CH2, Ph, C-CH )  

International Nuclear Information System (INIS)

The electron-pair density distributions of a series of 25 Fischer carbene complexes of the type (CO)5Cr=C(X)R (X=H, OH, OCH3, NH2, NHCH3 and R=H, CH3, CH=CH2, Ph, C-CH) are analyzed using the Atoms in Molecules theory. Localization and delocalization indices are used to characterize the electron pairing taking place in the Cr=C---X moiety in these complexes. Electron delocalization between the Cr and C atoms and between the C atom and the X group are related to the ?-donor strength of the X group and the degree of back-donation between the chromium pentacarbonyl and the carbene fragments. The results obtained with the Atoms in Molecules theory complement those obtained in a previous study by means of energy and charge decomposition analyses. Electron delocalization between the Cr atom and the X group is consistent with the hypothesis of a weak 3-center 4-electron bonding interaction in the Cr=C-X group of atoms. Except for X=H, ?(Cr,X) increases with the decrease of the ?-donor character of the X group

239

Syntheses and molecular structures of some saturated N-heterocyclic plumbylenes.  

Science.gov (United States)

Cyclic diamino plumbylenes derived from saturated heterocycles are obtained from deprotonation of diamines and subsequent reaction with PbCl(2), or by reaction of a suitable diamine with Pb[N(SiMe(3))(2)](2). Single crystal X-ray studies have been used to probe the solid state structures of a range of these complexes and have shown the fine balance between monomer and dimer formation which is related to the bulk of the organic group attached to the nitrogen atoms. Dimerisation is also shown to effect structural changes within the core of the heterocyclic plumbylene. PMID:19082063

Charmant, Jonathan P H; Haddow, Mairi F; Hahn, F Ekkehardt; Heitmann, Dennis; Fröhlich, Roland; Mansell, Stephen M; Russell, Christopher A; Wass, Duncan F

2008-11-21

240

Uranyl(VI)-acetylacetonate coordination compounds with various N-heterocyclic ligands  

International Nuclear Information System (INIS)

Seven uranyl(VI) complexes, [UO2(acac)2(L)] [L=4-methylpyridine (1), 4-ethylpyridine (2), 2,4-dimethylpyridine (3), (-)-nicotine (4), and imidazole (5)], [{UO2(acac)2}2-(4,4'-bipyridine)] (6), and [(2,2'-bipyridine)2H][UO2(acac)(NO3)2] (7) have been synthesized and characterized crystallographically. The coordination geometry of U has a UNO6 pentagonal-bipyramidal coordination in 1-6, and a UO8 hexagonal-bipyramidal coordination in 7. (author)

241

Frontispiece: a simple iridicycle catalyst for efficient transfer hydrogenation of N-heterocycles in water.  

Science.gov (United States)

Transfer hydrogenation Transfer hydrogenation is a simple safe way for reduction reactions and using water as a solvent has the additional benefit of being "green". In their Full paper on page?5370?ff., J. Xiao et?al. report that a cyclometalated iridium complex catalyzes the transfer hydrogenation of various nitrogen heterocycles in an aqueous solution of formate under mild conditions. The catalyst shows excellent functional-group compatibility and high turnover number, with loadings as low as 0.01?mol?% being feasible. A mechanistic study of quinoline reduction suggests that the reaction proceeds via both 1,2- and 1,4-addition pathways, with the catalytic turnover limited by hydride transfer. PMID:25787753

Talwar, Dinesh; Li, Ho Yin; Durham, Emma; Xiao, Jianliang

2015-03-27

242

Novel insertions of carbene homologs into Metal-Eta-5-Cp bonds : sandwich complexes with Ge2Ni and Sn2Ni cores  

OpenAIRE

An unsymmetrical bridging Cp(~)ligand is the striking structural element in 1. Compound 1 can be considered as an intermediate of the reaction in which GeMe2Si(NtBu)2 attacks [Cp2Ni] as a Lewis acid, and inserts into the Ni-Cp bond. The analogous Sn complex has a symmetric structure.(~)

Veith, Michael; Stahl, Lothar

1993-01-01

243

Thiophene decorated with Fischer carbene ligands  

OpenAIRE

The activation of a section, or of all the carbons of thiophene by bromine in lithium–halogen exchange reactions, was implemented in a step-wise manner to facilitate the preparation of novel multiple Fischer carbene-bearing thiophene compounds.

Jaarsveld, Nina A.; Liles, David C.; Lotz, Simon

2010-01-01

244

Unusual solvation through both p-orbital lobes of a carbene carbon  

Science.gov (United States)

As a result of a configurational space search done to explain the experimental evidence of transient specific solvation of singlet fluorocarbene amide with tetrahydrofuran, we found that the most stable structures consist in a group in which each oxygen of two tetrahydrofuran molecules act as electron donor to its respective empty p-orbital lobe of the carbene carbon atom, located at each side of the carbene molecular plane. This kind of species, which to our knowledge has not been reported before, explains very well the particular experimental characteristics observed for the transient solvation of this system. We postulate that the simultaneous interaction to both p-orbital lobes seems to confer a special stability to the solvation complexes, because this situation moves away the systems from the proximity of the corresponding transition states for the ylide products. Additionally, we present an analysis of other solvation complexes and a study of the nature of the involved interactions.

Hadad, C. Z.; Jenkins, Samantha; Flórez, Elizabeth

2015-03-01

245

N, N?-Olefin Functionalized Bis-Imidazolium Gold(I) Salt Is an Efficient Candidate to Control Keratitis-Associated Eye Infection  

OpenAIRE

Keratitis treatment has become more complicated due to the emergence of bacterial or fungal pathogens with enhanced antibiotic resistance. The pharmaceutical applications of N-heterocyclic carbene complexes have received remarkable attention due to their antimicrobial properties. In this paper, the new precursor, 3,3?-(p-phenylenedimethylene) bis{1-(2- methyl-allyl)imidazolium} bromide (1a) and its analogous PF6 salt (1b) were synthesized. Furthermore, silver(I) and gold(I) -N-heterocyclic ...

Samanta, Tapastaru; Roymahapatra, Gourisankar; Porto, William F.; Seth, Saikat; Ghorai, Sudipta; Saha, Suman; Sengupta, Jayangshu; Franco, Octa?vio L.; Dinda, Joydev; Mandal, Santi M.

2013-01-01

246

alpha-Addition von Aminen, Iminen und Hydrazinen an Allenyliden-Komplexe : Bildung von Carben-, Azetidinyliden- und Nitril-Komplexen  

OpenAIRE

Diarylallenylidene(pentacarbonyl)-chromium and -tungsten complexes, (CO)5M=C=C=CR2 (M = W (1), Cr (2)), react with amines, imines and hydrazines by addition of the nitrogen nucleophile to the C?allenylidene atom. With NEt3 the adduct formation is reversible. With secondary and primary amines, imines and hydrazines, the initially formed N-ylide complexes react readily further to give carbene, azetidinylidene and nitrile complexes, respectively. For example the reaction of (a) 1 and 2 with HNE...

Fischer, Helmut; Roth, Gerhard; Reindl, David; Troll, Carsten

1993-01-01

247

Transition metal complexes with unsaturated carbones: synthesis, structure and reactivity  

International Nuclear Information System (INIS)

Review of studies, performed by domestric and foreign authors for the last five years deals with methods for preparation, composition, physicochemical properties and reactivity of transition metal complexes (Mo, W, Re, Ru), containing unsaturated carbene ligands: vinylidenes, allenylidenes, hetorocumulenylidenes. Particular affention is paid to heterometallic compounds. Prospect of development of unsaturated carbene complex chemistry and their application in organic and organometallic synthesis are discussed

248

Adsorbed States of phosphonate derivatives of N-heterocyclic aromatic compounds, imidazole, thiazole, and pyridine on colloidal silver: comparison with a silver electrode.  

Science.gov (United States)

Here, we report a systematic surface-enhanced Raman spectroscopy (SERS) study of the structures of phosphonate derivatives of the N-heterocyclic aromatic compounds imidazole (ImMeP ([hydroxy(1H-imidazol-5-yl)methyl]phosphonic acid) and (ImMe)(2)P (bis[hydroxy-(1H-imidazol-4-yl)-methyl]phosphinic acid)), thiazole (BAThMeP (butylaminothiazol-2-yl-methyl)phosphonic acid) and BzAThMeP (benzylaminothiazol-2-yl-methyl)phosphonic acid)), and pyridine ((PyMe)(2)P (bis[(hydroxypyridin-3-yl-methyl)]phosphinic acid)) adsorbed on nanometer-sized colloidal particles. We compared these structures to those on a roughened silver electrode surface to determine the relationship between the adsorption strength and the geometry. For example, we showed that all of these biomolecules interact with the colloidal surface through aromatic rings. However, for BzAThMeP, a preferential interaction between the benzene ring and the colloidal silver surface is observed more so than that between the thiazole ring and this substrate. The PC(OH)C fragment does not take part in the adsorption process, and the phosphonate moiety of ImMeP and (ImMe)(2)P, being removed from the surface, only assists in this process. PMID:19670840

Podstawka, Edyta; Olszewski, Tomasz K; Boduszek, Bogdan; Proniewicz, Leonard M

2009-09-01

249

An unusual norcaradiene/tropylium rearrangement from a persistent amino-phosphonio-carbene  

OpenAIRE

An amino-phosphonio-carbene featuring a bromobiphenyl backbone was prepared and spectroscopically characterized at low temperature. This carbene was found to readily rearrange upon warm up, affording an original tricyclic phospholium derivative, presumably via a norcaradiene/tropylium isomerization.

Vignolle, Joan; Donnadieu, Bruno; Bourissou, Didier; Bertrand, Guy

2007-01-01

250

Thermodynamic, kinetic, and mechanistic study of oxygen atom transfer from mesityl nitrile oxide to phosphines and to a terminal metal phosphido complex.  

Science.gov (United States)

The enthalpies of oxygen atom transfer (OAT) from mesityl nitrile oxide (MesCNO) to Me(3)P, Cy(3)P, Ph(3)P, and the complex (Ar[(t)Bu]N)(3)MoP (Ar = 3,5-C(6)H(3)Me(2)) have been measured by solution calorimetry yielding the following P-O bond dissociation enthalpy estimates in toluene solution (±3 kcal mol(-1)): Me(3)PO [138.5], Cy(3)PO [137.6], Ph(3)PO [132.2], (Ar[(t)Bu]N)(3)MoPO [108.9]. The data for (Ar[(t)Bu]N)(3)MoPO yield an estimate of 60.2 kcal mol(-1) for dissociation of PO from (Ar[(t)Bu]N)(3)MoPO. The mechanism of OAT from MesCNO to R(3)P and (Ar[(t)Bu]N)(3)MoP has been investigated by UV-vis and FTIR kinetic studies as well as computationally. Reactivity of R(3)P and (Ar[(t)Bu]N)(3)MoP with MesCNO is proposed to occur by nucleophilic attack by the lone pair of electrons on the phosphine or phosphide to the electrophilic C atom of MesCNO forming an adduct rather than direct attack at the terminal O. This mechanism is supported by computational studies. In addition, reaction of the N-heterocyclic carbene SIPr (SIPr = 1,3-bis(diisopropyl)phenylimidazolin-2-ylidene) with MesCNO results in formation of a stable adduct in which the lone pair of the carbene attacks the C atom of MesCNO. The crystal structure of the blue SIPr·MesCNO adduct is reported, and resembles one of the computed structures for attack of the lone pair of electrons of Me(3)P on the C atom of MesCNO. Furthermore, this adduct in which the electrophilic C atom of MesCNO is blocked by coordination to the NHC does not undergo OAT with R(3)P. However, it does undergo rapid OAT with coordinatively unsaturated metal complexes such as (Ar[(t)Bu]N)(3)V since these proceed by attack of the unblocked terminal O site of the SIPr·MesCNO adduct rather than at the blocked C site. OAT from MesCNO to pyridine, tetrahydrothiophene, and (Ar[(t)Bu]N)(3)MoN was found not to proceed in spite of thermochemical favorability. PMID:21875050

Cai, Xiaochen; Majumdar, Subhojit; Fortman, George C; Frutos, Luis Manuel; Temprado, Manuel; Clough, Christopher R; Cummins, Christopher C; Germain, Meaghan E; Palluccio, Taryn; Rybak-Akimova, Elena V; Captain, Burjor; Hoff, Carl D

2011-10-01

251

A highly efficient dual catalysis approach for C-glycosylation: addition of (o-azaaryl)carboxaldehyde to glycals.  

Science.gov (United States)

A novel and efficient dual catalysis approach by concurrent activation of glycals and (o-azaaryl)-carboxaldehydes using palladium and N-heterocyclic carbene has been developed. The two electrophiles could react after activation through formation of the Breslow intermediate and a ?-allyl Pd complex, widening the scope of reacting glycosylation partners and opening up possibilities for future glycosylation. PMID:25236260

Bai, Yaguang; Leng, Wei Lin; Li, Yongxin; Liu, Xue-Wei

2014-11-11

252

Microwave-assisted syntheses of N-heterocycles using alkenone-, alkynone- and aryl-carbonyl O-phenyl oximes: formal synthesis of neocryptolepine.  

Science.gov (United States)

This research aimed to provide a new and "clean" synthetic method that would enable both known and novel N-heterocycles to be prepared efficiently. O-Phenyl oximes were found to be excellent precursors for iminyl radicals with a variety of acceptor side chains. Dihyropyrroles were made in good yields from O-phenyl oximes containing pent-4-ene acceptors. The analogous process with a hex-5-enyl acceptor did not yield a dihydropyridine, probably because the 6-exo-trig ring closure of the iminyl radical was too slow to compete with H-atom abstraction. The iminyl radical from a precursor with a pent-4-yne type side chain underwent ring closure followed by rearrangement to afford a pyrrole derivative. Suitably substituted iminyl radicals ring closed readily onto aromatic acceptors, thus enabling several polycyclic systems to be accessed. Quinolines were made from 3-phenylpropanones via their O-phenyl oximes. Syntheses of phenanthridines starting from 2-formylbiphenyls were particularly efficient, and this approach enabled the natural product trisphaeridine to be made. Starting from 2-phenylnicotinaldehyde derivatives, ring closures of the derived iminyl radicals onto the phenyl rings yielded benzo[h][1,6]naphthyridines. Similarly, ring closure onto a phenyl ring from a benzothiophene-based iminyl yielded a benzo[b]thieno[2,3-c]quinoline. By way of contrast, iminyl radical ring closure onto pyridine rings was not observed. However, iminyl radicals did cyclize onto indoles, enabling indolopyridines to be prepared. The latter route was exploited in a short formal synthesis of neocryptolepine starting from 2-((1H-indol-3-yl)methyl)cyclohexanone. PMID:18549288

Portela-Cubillo, Fernando; Scott, Jackie S; Walton, John C

2008-07-18

253

The reactions of anthronylidene carbene with some heterocyclic compounds  

International Nuclear Information System (INIS)

The action of the anthronylidene carbene, generated by photochemical decomposition of 9-diazo 10-anthron, on four heterocyclic compounds (furan, thiophene, 1-methyl-pyrrole and 2,5-dihydrofuran) has been examined. Two classical carbene reactions have been observed: the addition on double bond (furan, thiophene, 1-methylpyrrole) and hydrogen atom abstraction of the heterocyclic compound (2,5-dihydrofuran). In the case of furan and thiophene, the cyclo-propanic compound resulting from the addition is spontaneously transformed into an ethylenic derivative by valence isomerization. The furan derivative undergoes a cis-trans isomerization, while the thiophene one undergoes an extra carbene attack. In the case of 1-methylpyrrole, the corresponding cyclo-propanic compound undergoes a ring cleavage, followed by a hydrogen atom migration leading to the formation of a substituted anthron. Only an allylic hydrogen atom selective abstraction of heterocyclic compound takes place in the reaction of anthronylidene carbene with 2,5-dihydrofuran. The asymmetrical coupling of radicals so obtained yields the corresponding substituted anthron. (author)

254

Three-dimensional supramolecular networks constructed from Keggin anions and metal-organic complex with unpredicted oxidation of an N-heterocycle ligand  

Science.gov (United States)

Two novel Keggin polyoxometalate compounds, [Cu 2(PCA) 4(H 2O) 2][SiW 12O 40]·8H 2O ( 1) and [Cu(PCA) 2(H 2O) 4][Cu(PCA) 3(H 2O)][SiW 12O 40]·H 2O ( 2) (PCA = pyridine-4-carboxylic acid), were synthesized by in situ generation of pyridine-4-carboxylic acid ligand from 1,3-bis(4-pyridyl)propane precursor under hydrothermal conditions. Compounds 1 and 2 were structurally characterized by elemental analysis, IR and UV spectrography, TGA and single-crystal X-ray diffraction analysis. The variable-temperature magnetic susceptibility was measured at 2-300 K for 1. The compound 1 consists of polyoxoanions [?-SiW 12O 40] 4-, dimer cations [Cu 2(PCA) 4(H 2O) 2] 4+ and lattice water molecules. The water molecules link [?-SiW 12O 40] 4- and [Cu 2(PCA) 4(H 2O) 2] 4+ into three-dimensional (3D) architecture via hydrogen bonds. Polyoxoanions of 2 are linked into 1D chains through hydrogen bonds. Moreover, 1D chains are further extended into 3D supramolecular networks by hydrogen bonds and ?···? stacking interactions of pyridine-4-carboxylic acid molecules. The variable-temperature magnetic measurement of 1 shows an antiferromagnetic interaction in the 2-300 K temperature range.

Li, Jia; Chen, Ya-Guang; Zhang, Chun-Jing; Kong, Qing-Jiao

2009-03-01

255

An anionic phosphenium complex as an ambident nucleophile.  

Science.gov (United States)

A unique anionic phosphenium complex was prepared from reaction of an N-heterocyclic chlorophosphine with Collman's reagent or K[HFe(CO)4]/NaH and characterized by spectral and XRD data. The complex behaves as an ambident nucleophile. Reactions with acetic acid, ClSnPh3, and a further equivalent of an N-heterocyclic chlorophosphine proceed via electrophilic functionalization at the metal site to yield appropriate mono- or bis-phosphenium complexes. Reaction with MeI at -70 °C produces a P-alkylation product as the first spectroscopically detectable intermediate, which decays at a higher temperature to give a mixture of free P-methylated N-heterocyclic phosphine and its Fe(CO)4 complex. The different reaction products were characterized by spectral and XRD data. Computational studies indicate that the NHP units in all complexes display ?-acceptor behaviour but show no disposition to adopt phosphide-like character or formally oxidize the metal centre. PMID:25722043

Stadelmann, B; Bender, J; Förster, D; Frey, W; Nieger, M; Gudat, D

2015-03-17

256

The C-H activation of methane by laser-ablated zirconium atoms: CH2=ZrH2, the simplest carbene hydride complex, agostic bonding, and (CH3)2ZrH2.  

Science.gov (United States)

Reaction of laser-ablated Zr with CH(4) ((13)CH(4), CD(4), and CH(2)D(2)) in excess neon during condensation at 5 K forms CH(2)=ZrH(2), the simplest alkylidene hydride complex, which is identified by infrared absorptions at 1581.0, 1546.2, 757.0, and 634.5 cm(-)(1). Density functional theory electronic structure calculations using a large basis set with polarization functions predict a C(1) symmetry structure with agostic C-H- - -Zr bonding and distance of 2.300 A. Identification of the agostic CH(2)=ZrH(2) methylidene complex is confirmed by an excellent match of calculated and observed isotopic frequencies particularly for the four unique CHD=ZrHD isotopic modifications. The analogous reactions in excess argon give two persistent photoreversible matrix configurations for CH(2)=ZrH(2). Finally, methane activation by CH(2)=ZrH(2) gives the new (CH(3))(2)ZrH(2) molecule. PMID:15631498

Cho, Han-Gook; Wang, Xuefeng; Andrews, Lester

2005-01-12

257

Boron nitride nanotubes functionalized by a series of carbenes.  

Science.gov (United States)

We systematically studied the structural, energetic and electronic properties of zigzag boron nitride nanotubes (BNNTs) functionalized by a class of substituted carbenes (CR(2)) where R = H, F, Cl, CH(3), CN and NO(2) on different absorption sites using density functional theory. For R = H, F and Cl, the open structure is preferred with a BNNT sidewall bond cleavage, while for R = CH(3) and CN, a competition between the open and closed cyclopropane-like three-membered ring (3MR) structure occurs. Interestingly, for R = NO(2) we find a novel double five-membered ring (5MR) structure with high reaction stability. This new structure cannot be found in BNNTs' alternative carbon nanotubes (CNTs). In addition, the electronic properties of BNNTs functionalized with carbenes are hardly changed for R = H, F, Cl, CH(3) and CN, but are significantly affected when R = NO(2) due to the heterocyclic double 5MR structure. PMID:19606337

Cao, Fenglei; Ren, Wei; Xu, Xianyan; Ji, Yue-meng; Zhao, Cunyuan

2009-08-01

258

Singlet 2-adamantylidene--an ambiphilic foiled carbene stabilized by hyperconjugation.  

Science.gov (United States)

The EDA-NOCV analysis shows that the singlet 2-adamantylidene is a foiled-type carbene stabilized by the hyperconjugative interaction of one pair of the vicinal C-C ?-MOs with the empty p-orbital on the carbene carbon atom. The high proton affinity and hydride affinity indicate the ambiphilic nature of 2-adamantylidene. PMID:23939037

Rojisha, Vallyanga Chalil; Nijesh, Karikkeeriyil; De, Susmita; Parameswaran, Pattiyil

2013-10-01

259

How does the nickel pincer complex catalyze the conversion of CO2 to a methanol derivative? A computational mechanistic study.  

Science.gov (United States)

The mechanistic details of nickel-catalyzed reduction of CO(2) with catecholborane (HBcat) have been studied by DFT calculations. The nickel pincer hydride complex ({2,6-C(6)H(3)(OP(t)Bu(2))(2)}NiH = [Ni]H) has been shown to catalyze the sequential reduction from CO(2) to HCOOBcat, then to CH(2)O, and finally to CH(3)OBcat. Each process is accomplished by a two-step sequence at the nickel center: the insertion of a C?O bond into [Ni]H, followed by the reaction of the insertion product with HBcat. Calculations have predicted the difficulties of observing the possible intermediates such as [Ni]OCH(2)OBcat, [Ni]OBcat, and [Ni]OCH(3), based on the low kinetic barriers and favorable thermodynamics for the decomposition of [Ni]OCH(2)OBcat, as well as the reactions of [Ni]OBcat and [Ni]OCH(3) with HBcat. Compared to the uncatalyzed reactions of HBcat with CO(2), HCOOBcat, and CH(2)O, the nickel hydride catalyst accelerates the H(?-) transfer by lowering the barriers by 30.1, 12.4, and 19.6 kcal/mol, respectively. In general, the catalytic role of the nickel hydride is similar to that of N-heterocyclic carbene (NHC) catalyst in the hydrosilylation of CO(2). However, the H(?-) transfer mechanisms used by the two catalysts are completely different. The H(?-) transfer catalyzed by [Ni]H can be described as hydrogen being shuttled from HBcat to nickel center and then to the C?O bond, and the catalyst changes its integrity during catalysis. In contrast, the NHC catalyst simply exerts an electronic influence to activate either the silane or CO(2), and the integrity of the catalyst remains intact throughout the catalytic cycle. The comparison between [Ni]H and Cp(2)Zr(H)Cl in the stoichiometric reduction of CO(2) has suggested that ligand sterics and metal electronic properties play critical roles in controlling the outcome of the reaction. A bridging methylene diolate complex has been previously observed in the zirconium system, whereas the analogous [Ni]OCH(2)O[Ni] is not a viable intermediate, both kinetically and thermodynamically. Replacing HBcat with PhSiH(3) in the nickel-catalyzed reduction of CO(2) results in a high kinetic barrier for the reaction of [Ni]OOCH with PhSiH(3). Switching silanes to HBcat in NHC-catalyzed reduction of CO(2) generates a very stable NHC adduct of HCOOBcat, which makes the release of NHC less favorable. PMID:21413735

Huang, Fang; Zhang, Chenggen; Jiang, Jinliang; Wang, Zhi-Xiang; Guan, Hairong

2011-04-18

260

Hydrogen radical abstraction by small ionized molecules, distonic ions and ionized carbenes in the gas phase  

Science.gov (United States)

In the gas phase and within ion-neutral complexes, H[radical sign] abstraction by the ion from the neutral moiety was studied by using FT-ICR experiments and molecular orbital calculations. Ionized methanol abstracts rapidly H[radical sign] from methane and other alkanes while its [alpha]-distonic counterpart, [radical sign]CH2OH2+, is completely unreactive. On the other hand, [beta]-distonic ions, such as [radical sign]CH2CH2XH+ (X=OCH3, NH2), are also unreactive towards methane but can abstract H[radical sign] from ketones and ethers. Finally, ionized carbenes, such as HO---C---NH2[radical sign]+, react with methane by a slow H[radical sign] abstraction. Ab initio molecular orbital calculations at the G3(MP2) level were performed in order to understand these behaviors. For ionized methanol and its [alpha]-distonic counterpart, the reacting structure that could lead to H[radical sign] abstraction is the highly stabilized complex between protonated methanol and a methyl radical, which yields the final state (CH3OH2++[radical sign]CH3) by simple cleavage. In the case of methanol the encounter complex with methane leads easily by rotation of the methane molecule to this reacting structure. In contrast, in the case of the [alpha]-distonic ion, the almost linear structure of the encounter complex [[radical sign]CH2OH2+...CH4] and the high energy required for its isomerization into the reacting structure prevent the reaction. Two factors are required to observe H[radical sign] abstraction in [beta]-distonic ions: the interaction energy of the encounter complex and the distance between the hydrogen to be transferred and the carbon radical. Reaction of the HO---C---NH2[radical sign]+ carbene with methane lies between these two extreme cases. The encounter complex is poorly stabilized (-8.7 kcal mol-1) and the transition state for H[radical sign] abstraction is very close to the reactants energy.

Nedev, Hristo; van der Rest, Guillaume; Mourgues, Philippe; Audier, Henri E.

2004-02-01

261

Gold(I-catalyzed synthesis of ?-vinylbutyrolactones by intramolecular oxaallylic alkylation with alcohols  

Directory of Open Access Journals (Sweden)

Full Text Available Gold(I-N-heterocyclic carbene (NHC complexes proved to be a reliable catalytic system for the direct synthesis of functionalized ?-vinylbutyrolactones by intramolecular oxaallylic alkylation with primary alcohols. Good isolated chemical yields were obtained for a range of malonyl and acetate derivatives. The good performance in reagent-grade solvents and the functional group/moisture tolerance make this catalytic process a promising route for the synthesis of architecturally complex polycyclic structures.

Michel Chiarucci

2011-09-01

262

Gold(I)-catalyzed synthesis of ?-vinylbutyrolactones by intramolecular oxaallylic alkylation with alcohols  

OpenAIRE

Gold(I)-N-heterocyclic carbene (NHC) complexes proved to be a reliable catalytic system for the direct synthesis of functionalized ?-vinylbutyrolactones by intramolecular oxaallylic alkylation with primary alcohols. Good isolated chemical yields were obtained for a range of malonyl and acetate derivatives. The good performance in reagent-grade solvents and the functional group/moisture tolerance make this catalytic process a promising route for the synthesis of architecturally complex po...

Michel Chiarucci; Mirko Locritani; Gianpiero Cera; Marco Bandini

2011-01-01

263

Synthesis and characterization of palladium(II) and nickel(II) alcoholate-functionalized NHC complexes and of mixed nickel(II)-lithium(I) complexes.  

Science.gov (United States)

The synthesis of Pd(II) and Ni(II) alcohol-functionalized N-heterocyclic carbene (NHC) complexes was explored to examine the possible influence of the functional arm attached to the NHC backbone on their structure and reactivity and, in the case of a Ni(II) complex, on its catalytic properties in ethylene oligomerization. Starting from the alcohol-functionalized imidazolium salt [ImDiPP(C2OH)]Cl (2), the new functionalized NHC palladium(II) complex [PdCl(acac){ImDiPP(C2OH)-CNHC}] (3) was synthesized and fully characterized. Two byproducts, [PdCl{?-ImDiPP(C2O)-CNHC,O}]2 (4) and trans-[PdCl2{ImDiPP(C2OH)-CNHC}2] (5), formed during the synthesis of 3, were also fully characterized. Acids promoted the transformation of 3 into the new CNHC-bound complex [PdCl(?-Cl){ImDiPP(C2OH)-CNHC}]2 (6), unveiling the lability of the acac ligand and the resistance of the Pd-NHC bond to acids. Complex 6 reacted with a base to afford complex 4, in which alkoxide coordination to Pd(II) has occurred to generate a CNHC,O chelate. The stability of 3 was also assessed under basic conditions, and the new complex [Pd(acac){ImDiPP(C2O)-CNHC,O}] (7) was characterized. The new nickel(II) alcoholate-functionalized NHC complex [NiCl{?-ImDiPP(C2O)-CNHC,O}]2 (8) was synthesized by the reaction of the imidazolium salt 2 with n-BuLi and [NiCl2(dme)]. The reaction of 8 with HCl regenerates the imidazolium and alcohol functions to give [ImDiPP(C2OH)]2[NiCl4] (9). The mixed-metal Ni(II)-Li(I) complexes [Ni2{?-ImDiPP(C2O)-CNHC,?-O}4Li]BF4 (10), [Ni2{?-ImDiPP(C2O)-CNHC,?-O}4Li]Cl (11), and [Ni{ImDiPP(C2O)-CNHC,?-O}2LiBr] (12) were isolated and characterized. However, it was not possible to synthesize a Ni(II) alcohol-functionalized NHC complex in high yield. Small amounts of the square-planar complex [NiCl2{ImDiPP(C2OH)-CNHC}2] (13) could be isolated, and this complex was characterized by single-crystal X-ray diffraction. In 13, only the CNHC atom of the alcohol-functionalized NHC ligand is bound to the metal. The structures of the imidazolium salt 2·2H2O and of the complexes 3, 4, 4-polymorph, 5, 6·CH2Cl2, and 8-13 were established by single-crystal X-ray diffraction. PMID:24766603

Hameury, Sophie; de Frémont, Pierre; Breuil, Pierre-Alain R; Olivier-Bourbigou, Hélène; Braunstein, Pierre

2014-05-19

264

Nitrene-carbene-carbene rearrangement. Photolysis and thermolysis of tetrazolo[5,1- a ]phthalazine with formation of 1-phthalazinylnitrene, o-cyanophenylcarbene, and phenylcyanocarbene  

DEFF Research Database (Denmark)

1-Azidophthalazine 9A is generated in trace amount by mild FVT of tetrazolo[5,1-a]phthalazine 9T and is observable by its absorption at 2121 cm-1 in the Ar matrix IR spectrum. Ar matrix photolysis of 9T/9A at 254 nm causes ring opening to generate two conformers of (o-cyanophenyl) diazomethane 11 (2079 and 2075 cm-1), followed by (o-cyanophenyl)carbene 312, cyanocycloheptatetraene 13, and finally cyano(phenyl)carbene 314 as evaluated by IR spectroscopy. The two carbenes 312 and 314 were observed by ESR spectroscopy (D|hc = 0.5078, E|hc = 0.0236 and D|hc = 0.6488, E|hc = 0.0195 cm-1, respectively). The rearrangement of 12 â., 13 â., 14 constitutes a carbene-carbene rearrangement. 1-Phthalazinylnitrene 310 is observed by means of its UV-vis spectrum in Ar matrix following FVT of 9 above 550 C. Rearrangement to cyanophenylcarbenes also takes place on FVT of 9 as evidenced by observation of the products of ring contraction, viz., fulvenallenes and ethynylcyclopentadienes 16-18. Thus the overall rearrangement 10 ?11 ? 12 â., 13 â., 14 can be formulated. © 2013 American Chemical Society.

HØj, Martin; Kvaskoff, David

2014-01-01

265

[4 + 1] cycloaddition of bis(alkylthio)carbenes with vinyl isocyanates. Total synthesis of (+/-)-mesembrine.  

Science.gov (United States)

[reaction: see text] The Sceletium alkaloid mesembrine has been synthesized in 13% overall yield by a sequence featuring a [4 + 1] cycloaddition of a bis(alkylthio)carbene with a functionalized vinyl isocyanate. PMID:10880198

Rigby, J H; Dong, W

2000-06-15

266

The Effects of NHC-Backbone Substitution on Efficiency in Ruthenium-based Olefin Metathesis  

OpenAIRE

A series of ruthenium olefin metathesis catalysts bearing N-heterocyclic carbene (NHC) ligands with varying degrees of backbone and N-aryl substitution have been prepared. These complexes show greater resistance to decomposition through C–H activation of the N-aryl group, resulting in increased catalyst lifetimes. This work has utilized robotic technology to examine the activity and stability of each catalyst in metathesis, providing insights into the relationship between ligand architectur...

Kuhn, Kevin M.; Bourg, Jean-baptiste; Chung, Cheol K.; Virgil, Scott C.; Grubbs, Robert H.

2009-01-01

267

Frustrated Lewis pair activation of an N-sulfinylamine: a source of sulfur monoxide.  

Science.gov (United States)

Inter- and intramolecular P/B frustrated Lewis pairs are shown to react with an N-sulfinylamine to form PNSOB linakages. These species can be regarded as phosphinimine-borane-stabilized sulfur monoxide complexes, and indeed these species act as sources of SO, effecting the oxidation of PPh3 and delivering SO to [RhCl(PPh3)3] and an N-heterocyclic carbene. PMID:25376102

Longobardi, Lauren E; Wolter, Vanessa; Stephan, Douglas W

2015-01-12

268

N-(2,4,6-Trimethylphenylformamide  

Directory of Open Access Journals (Sweden)

Full Text Available The title compound, C10H13NO, was obtained as the unexpected, almost exclusive, product in the attempted synthesis of a manganese(I–N-heterocyclic carbene (NHC complex. The dihedral angle between the planes of the formamide moiety and the aryl ring is 68.06?(10°. In the crystal, molecules are linked by N—H...O hydrogen bonds, forming infinite chains along the c axis.

David C. Liles

2011-01-01

269

Thermodynamics of Ylide Formation from Carbenes and Carbonyl Compounds  

Scientific Electronic Library Online (English)

Full Text Available Os parâmetros termodinâmicos para a reação dos carbenos CH2 (simpleto e tripleto), CF2 e C(OH)2 com formaldeído, acetaldeído e acetona foram determinados através de cálculos ab initio de alto nível. O metileno simpleto forma ilídeos estáveis com os três compostos carbonílicos, tendo um deltaHº de re [...] ação de -41.6 kcal/mol, -40.0 kcal/mol (isômero E), -44.5 kcal/mol (isômero Z) e -40.8 kcal/mol, respectivamente. O metileno tripleto também forma ilídeo com formaldeído, com um deltaE de reação de -15.7 kcal/mol, resultando que a formação do ilídeo neste estado eletrônico é reversível. Já os carbenos CF2 e C(OH)2 formam ilídeos com formaldeído com um deltaHº de 13.0 kcal/mol e 22.0 kcal/mol, e um deltaGº de 25.3 kcal/mol e 34.0kcal/mol, respectivamente. Estes valores positivos de energia livre indicam que estes ilídeos não devem ser formados a partir de carbenos e carbonilas, e possivelmente estes carbenos reagem com aldeídos e cetonas por cicloadição 1,2. Abstract in english Thermodynamic parameters for the reaction of CH2 (singlet and triplet), CF2 and C(OH)2 carbenes with formaldehyde, acetaldehyde and acetone, forming carbonyl ylides, were determined using high level ab initio molecular orbital calculations. Singlet methylene forms a stable ylide with the three carbo [...] nyl compounds, with a deltaHº of -41.6 kcal/mol, -40.0 kcal/mol (E isomer), -44.5 kcal/mol (Z isomer) and -40.8 kcal/mol, respectively. Triplet methylene also forms a y lide with formaldehyde with a deltaE of -15.7 kcal/mol, resulting in the triplet ylide being formed reversibly. For the reaction with formaldehyde, the CF2 and C(OH)2 carbenes have a positive deltaHº of 13.0 kcal/mol and 22.0 kcal/mol, and a deltaGº of 25.3 kcal/mol and 34.0 kcal/mol, respectively. Due to its unfavorable free energy of formation, and the potential competition of direct 1,2 cycloaddition of carbene to the C=O group, CF2 and C(OH)2 should not react with carbonyl compounds forming ylides.

Josefredo R., Pliego Jr.; Wagner B., De Almeida.

1998-04-01

270

Probing Protein Surface with a Solvent Mimetic Carbene Coupled to Detection by Mass Spectrometry  

Science.gov (United States)

Much knowledge into protein folding, ligand binding, and complex formation can be derived from the examination of the nature and size of the accessible surface area (SASA) of the polypeptide chain, a key parameter in protein science not directly measurable in an experimental fashion. To this end, an ideal chemical approach should aim at exerting solvent mimicry and achieving minimal selectivity to probe the protein surface regardless of its chemical nature. The choice of the photoreagent diazirine to fulfill these goals arises from its size comparable to water and from being a convenient source of the extremely reactive methylene carbene (:CH2). The ensuing methylation depends primarily on the solvent accessibility of the polypeptide chain, turning it into a valuable signal to address experimentally the measurement of SASA in proteins. The superb sensitivity and high resolution of modern mass spectrometry techniques allows us to derive a quantitative signal proportional to the extent of modification (EM) of the sample. Thus, diazirine labeling coupled to electrospray mass spectrometry (ESI-MS) detection can shed light on conformational features of the native as well as non-native states, not easily addressable by other methods. Enzymatic fragmentation of the polypeptide chain at the level of small peptides allows us to locate the covalent tag along the amino acid sequence, therefore enabling the construction of a map of solvent accessibility. Moreover, by subsequent MS/MS analysis of peptides, we demonstrate here the feasibility of attaining amino acid resolution in defining the target sites.

Gómez, Gabriela E.; Mundo, Mariana R.; Craig, Patricio O.; Delfino, José M.

2012-01-01

271

Carbene vs olefin products of C-H activation on ruthenium via competing alpha- and beta-H elimination.  

Science.gov (United States)

Bulky pincer complexes of ruthenium are capable of C-H activation and H-elimination from the pincer ligand backbone to produce mixtures of olefin and carbene products. To characterize the products and determine the mechanisms of the C-H cleavage, reactions of [RuCl(2)(p-cymene)](2) with N,N'-bis(di-tert-butylphosphino)-1,3-diaminopropane (L1) and 1,3-bis(di-tert-butylphosphinomethyl)cyclohexane (L2) were studied using a combination of X-ray crystallography, NMR spectroscopy, and DFT computational techniques. The reaction of L1 afforded a mixture of an alkylidene, a Fischer carbene, and two olefin isomers of the 16-e monohydride RuHCl[(t)Bu(2)PNHC(3)H(4)NHPBu(t)(2)] (2), whereas the reaction of L2 gave two olefin and two alkylidene isomers of 16-e RuHCl[2,6-(CH(2)PBu(t)(2))(2)C(6)H(8)] (3), all resulting from dehydrogenations of the ligand backbone of L1 and L2. The key intermediates implicated in the C-H activation reactions were identified as 14-electron paramagnetic species RuCl(PCP), where PCP = cyclometalated L1 or L2. Thus the alpha- and beta-H elimination reactions of RuCl(PCP) involved spin change and were formally spin-forbidden. Hydrogenation of 2 and 3 afforded 16-electron dihydrides RuH(2)Cl(PCP) distinguished by a large quantum exchange coupling between the hydrides. PMID:17076513

Kuznetsov, Vladimir F; Abdur-Rashid, Kamaluddin; Lough, Alan J; Gusev, Dmitry G

2006-11-01

272

Rhodium (II) carbene C-H insertion in water and catalyst reuse  

International Nuclear Information System (INIS)

A five-session laboratory experiment is described for the synthesis of a beta-lactam via Rh(II) catalysed intramolecular C-H insertion of a alpha-diazo-alpha-ethoxycarbonyl acetamide. The metallo-carbene, responsible for the C-H bond activation, was generated from the diazo substrate and the catalyst Rh2(OAc)4. The high stability and solubility of the catalyst and the exclusive C-H insertion of the Rh-carbene allows the synthesis of this important heterocycle in water and the catalyst reutilization. (author)

273

N-heterocycles from chromium aminocarbenes.  

Science.gov (United States)

The initial [2 + 2]-cycloadduct between a chromium aminocarbene and a tethered alkene undergoes a ?-hydrogen elimination very efficiently when triphenylphosphine is added as a ligand. The reaction gives cyclic enamines or homoenamines depending on the substitution on the alkene. PMID:25702700

Déry, Martin; Assouvie, Kevin; Heinrich, Nora; Rajotte, Isabelle; Lefebvre, Louis-Philippe D; Legault, Marc-André; Spino, Claude

2015-03-01

274

Intramolecular transannulation of alkynyl triazoles via alkyne-carbene metathesis step: access to fused pyrroles.  

Science.gov (United States)

An intramolecular Rh-catalyzed transannulation reaction of alkynyl triazoles has been developed. This method allows efficient construction of various 5,5-fused pyrroles, including tetrahydropyrrolo and spiro systems. The method demonstrates excellent functional group compatibility. A rhodium carbene-alkyne metathesis mechanism is proposed for this transformation. PMID:24093728

Shi, Yi; Gevorgyan, Vladimir

2013-10-18

275

A simple access to transition metal cyclopropenylidene complexes.  

Science.gov (United States)

We report the first example of BAC-Cu complex (BAC = bis(diisopropylamino)cyclopropenylidene) and its use as a carbene-transfer reagent, allowing access to Au-, Pd-, Ir- and Rh-BAC compounds. Catalytic experiments show the high activity of the [CuCl(BAC)] complex in Click chemistry. PMID:25621852

Bidal, Yannick D; Lesieur, Mathieu; Melaimi, Mohand; Cordes, David B; Slawin, Alexandra M Z; Bertrand, Guy; Cazin, Catherine S J

2015-03-01

276

Facile displacement of ?5-cyclopentadienyl ligands from half-sandwich alkyl,NHC-nickel complexes: an original route to robust cis-C,C-nickel square planar complexes.  

Science.gov (United States)

The ?(5)-cyclopentadienyl (Cp) ligands of 18-electron half-sandwich alkyl,NHC-nickel complexes are readily displaced under acidic conditions to afford a novel class of cis-C,C-nickel square planar complexes. Remarkably, the nickel-alkyl and nickel-carbene bonds are not ruptured in these unprecedented Cp acidolysis reactions. PMID:23752919

Henrion, Mickaël; Oertel, Anna Magdalena; Ritleng, Vincent; Chetcuti, Michael J

2013-07-21

277

Highly nucleophilic acetylide, vinyl, and vinylidene complexes. Progress report  

Energy Technology Data Exchange (ETDEWEB)

The research was divided into the following: studies of nucleophilic and chiral acetylide complex [Cp(CO)(PPh{sub 3})Mn-C{triple_bond}CR]{sup {minus}}; nucleophilic addition of carbene anions to organic ligands on electrophilic complexes; halide-promoted carbonylation of imido ligands; binuclear Fe{sub 2} complexes with bridging organonitrogen ligands; addition and cycloaddition reactions of carbyne complex [Cp(CO){sub 2}Re{triple_bond}CTol]{sup +}; addition and cycloaddition reactions of methylcarbyne complexes [Cp(CO){sub 2}M{triple_bond}CCH{sub 3}]{sup +} and vinylidene complexes Cp(CO){sub 2}M{double_bond}C{double_bond}CH{sub 2} (M=Mn, Re); studies of generation and reactivity of vinylcarbene complexes formed from reaction of manganese carbene anions and aldehydes; and addition of oxo ligands of nucleophilic oxo complexes to organic ligands on electrophilic metal centers.

1992-06-15

278

1,2,3-triazolylidenes as versatile abnormal carbene ligands for late transition metals  

OpenAIRE

The [3 + 2] cycloaddition of azides and acetylenes followed by nitrogen quaternization was applied for the generation of novel and highly modular triazolium salts. The selective substitution of the 1,3,4-substitution pattern presets such salts as precursors for a new class of abnormal carbene ligands, thus expanding the family of these high-impact ligands. Metalation of the triazolium salts is highly versatile and is illustrated by direct C?H bond activation as well as by applying a transme...

Mathew, Paulson; Neels, Antonia; Albrecht, Martin

2009-01-01

279

A theoretical study of the mechanism of the addition reaction between carbene and azacyclopropane  

Directory of Open Access Journals (Sweden)

Full Text Available The mechanism of the addition reaction between carbene and azacyclopropane was investigated using the second-order Moller–Plesset perturbation theory (MP2. By using the 6-311+G* basis set, geometry optimization, vibrational analysis and the energy properties of the involved stationary points on the potential energy surface were calculated. From the surface energy profile, it can be predicted that there are two reaction mechanisms. The first one (1 is carbene attack at the N atom of azacyclopropane to form an intermediate, 1a (IM1a, which is a barrier-free exothermic reaction. Then, IM1a can isomerize to IM1b via a transition state 1a (TS1a, in which the potential barrier is 30.0 kJ/mol. Subsequently, IM1b isomerizes to a product (Pro1 via TS1b with a potential barrier of 39.3 kJ/mol. The other one (2 is carbene attack at the C atom of azacyclopropane, firstly to form IM2 via TS2a, the potential barrier is 35.4 kJ/mol. Then IM2 isomerizes to a product (Pro2 via TS2b with a potential barrier of 35.1 kJ/mol. Correspondingly, the reaction energy for the reactions (1 and (2 is –478.3 and –509.9 kJ/mol, respectively. Additionally, the orbital interactions are also discussed for the leading intermediate.

XIAOJUN TAN

2010-05-01

280

Synthesis of a Benzodiazepine-derived Rhodium NHC Complex by C-H Bond Activation  

OpenAIRE

The synthesis and characterization of a Rh(I)-NHC complex generated by C-H activation of 1,4-benzodiazepine heterocycle are reported. This complex constitutes a rare example of a carbene tautomer of a 1,4-benzodiazepine aldimine stabilized by transition metal coordination and demonstrates the ability of the catalytically relevant RhCl(PCy3)2 fragment to induce NHC-forming tautomerization of heterocycles possessing a single carbene-stabilizing heteroatom. Implications for the synthesis of benz...

Gribble, Michael W.; Ellman, Jonathan A.; Bergman, Robert G.

2008-01-01

281

rac-cis-Dicarbonyl­chlorido{1-[2-(diphenyl­phosphanyl-?P)benz­yl]-3-(phenyl-?C 1)imidazol-2-yl­idene-?C 2}ruthenium(II) dichloro­methane monosolvate  

OpenAIRE

In the title compound, [Ru(C28H22N2P)Cl(CO)2]·CH2Cl2, the RuII atom exhibits a distorted octa­hedral coordination geometry. The N-phenyl group of the ligand has undergone orthometalation; as a result, the tridentate phosphane-functionalized N-heterocyclic carbene ligand is coordinating in a meridional fashion. This complex is of inter­est with respect to transfer hydrogenation catalysis and also provides an example of C—H activation behavior in late transition metal complexes. The dichlo...

Domski, Gregory J.; Pecak, Wiktoria H.; Swenson, Dale C.

2012-01-01

282

4-Oxo-2,3,5,6-tetrafluorocyclohexa-2,5-dienylidene--a highly electrophilic triplet carbene.  

Science.gov (United States)

The 4-oxocyclohexa-2,5-dienylidenes are an interesting class of highly electrophilic carbenes. We investigated the reactivity of the 2,3,5,6-tetrafluorinated and -tetrachlorinated derivatives 1b and 1c with small molecules under conditions of matrix isolation. The reactions with molecular oxygen and with carbon monoxide produce the expected carbonyl O-oxides and ketenes, respectively. As a result of the extreme electrophilicity of 1b and c both carbenes insert with no or very small activation barriers into H2 or the CH bonds of hydrocarbons. Obviously, spin restrictions for these formally spin-forbidden reactions do not result in substantial thermal activation barriers. PMID:11192090

Sander, W; Hübert, R; Kraka, E; Gräfenstein, J; Cremer, D

2000-12-15

283

Cycloaddition of azidoformic acid methylester to the metal carbon double bond of [eta][sup 2]-thiocarbene complexes of molybdenum and tungsten. Zur Cycloaddition von Azidoameisensaeuremethylester an die Metall-Carben-Doppelbindung in [eta][sup 2]-Thiocarbenkomplexes des Molybdaens und Wolframs  

Energy Technology Data Exchange (ETDEWEB)

Cationic [eta][sup 2]-thiocarbene complexes of molybdenum and tungsten Cp(CO)PMe[sub 3]M=C(R)SMeBF[sub 4] (R=Me, Ph, Tol) add N[sub 3]COOMe to the electron rich metal carbon double bond to yield the corresponding bicyclic system. The products have been characterized by [sup 1]H, [sup 13]C, [sup 31]P NMR, IR and mass spectra. The crystal structure of 4b has been determined: Space group P2[sub 1]/n with a=1749.9(7), b=827.9(1), c=1846.8(7) pm and Z=4. (orig.)

Kreissl, F.R. (Technische Univ. Muenchen (Germany). Anorganisch-Chemisches Inst.); Schuett, W. (Technische Univ. Muenchen (Germany). Anorganisch-Chemisches Inst.); Ostermeier, J. (Technische Univ. Muenchen (Germany). Anorganisch-Chemisches Inst.); Stegmair, C.M. (Technische Univ. Muenchen (Germany). Anorganisch-Chemisches Inst.); Ullrich, W. (Technische Univ. Muenchen (Germany). Anorganisch-Chemisches Inst.); Herdtweck, E. (Technische Univ. Muenchen (Germany). Anorganisch-Chemisches Inst.)

1993-11-01

284

Kinetische und mechanistische Studien über die Umwandlung von Kohlendioxid durch molekulare Katalysatoren  

OpenAIRE

A screening of different metal halides and nucleophilc co-catalysts, as well as a mechanistic study, were performed on the synthesis of propylene carbonate from propylene oxide and carbon dioxide (CO2). The system NbCl5/nBu4Br leads to high TOFs under mild conditions (r.t., 1 bar CO2). Different platinum and palladium complexes with phosphines or N-heterocyclic carbenes ligands were synthesized and their reactivity towards CO2 activation and CO2 insertion into metal-H or metal-CH3 bond was...

Monassier, Antoine

2013-01-01

285

Amide Synthesis from Alcohols and Amines by the Extrusion of Dihydrogen  

DEFF Research Database (Denmark)

An environmentally friendly method for synthesis of amides is presented where a simple ruthenium catalyst mediates the direct coupling between an alcohol and an amine with the liberation of two molecules of dihydrogen. The active catalyst is generated in situ from an easily available ruthenium complex, an N-heterocyclic carbene and a phosphine. The reaction allows primary alcohols to be coupled with primary alkyamines to afford the corresponding secondary amides in good yields. The amide formation presumably proceeds through a catalytic cycle where the intermediate aldehyde and hemiaminal are both coordinated to the metal catalyst.

NordstrØm, Lars Ulrik Rubæk; Vogt, Henning

2008-01-01

286

Quinoline beta-lactams by Rh(II)-catalyzed highly steroselective intramolecular carbene insertion into a carbon-hydrogen bond  

OpenAIRE

A convenient synthesis of tricyclic ?-lactams by chemo- and diastereoselective intramolecular CH insertion of metal carbenes generated by dirhodium(II) tetraacetate catalyzed decomposition of ?-diazoamides 1a-c is reported. In the case of reagent 1b, in the presence of the (+)-menthyl chiral auxiliary, the ?-lactam is obtained with 76% e.e.

Muroni, Daniele; Saba, Antonio

2005-01-01

287

Theoretical Predictions of Redox Potentials of Fischer-Type Chromium Anninocarbene Complexes.  

Czech Academy of Sciences Publication Activity Database

Ro?. 33, ?. 18 (2014), s. 4964-4972. ISSN 0276-7333 R&D Projects: GA MŠk LD14129; GA ?R GA13-04630S Institutional support: RVO:61388955 Keywords : standard hydrogen electrode * density functional theory * metal carbene complexes Subject RIV: CG - Electrochemistry Impact factor: 4.253, year: 2013

Kvapilová, Hana; Hoskovcová, Irena; Ludvík, Ji?í; Záliš, Stanislav

2014-01-01

288

Carbene Spin Multiplicity in Solution Probed Using Time-Resolved EPR Spectroscopy  

Scientific Electronic Library Online (English)

Full Text Available SciELO Mexico | Language: English Abstract in spanish Espectroscopia de resonancia paramagnética electrónica (EPR por las siglas en inglés) fue utilizada para detectar los radicales libres formados mediante reacciones de abstracción de átomos de hidrógeno de diversos carbenos generados fotoquímicamente en soluciones de n-hexano y a temperatura ambiente [...] . En particular, se describe el análisis de tres carbenos que fueron generados por fotoexcitación de un bifenilo con dos grupos diazo. Se identificaron señales EPR de dos radicales alquilo y uno bencílico. La estructura de dichos radicales se confirmó mediante un proceso de simulación computacional utilizando parámetros espectroscópicos (factores-g, constantes de acoplamiento hiperfino) reportados en la literatura. Experimentos previos de absorción óptica han llevado a la conclusión de que los carbenos estudiados presentan un estado basal de tipo triplete, lo que se confirma al observar las señales EPR de emisión a campo bajo pero de absorción a campo alto. Además, se encontró que los espectros presentan un espín fuertemente polarizado como consecuencia de un mecanismo CIDEP, y que la intensidad de las señales está relacionada con los rendimientos cuánticos asociados a la producción de los carbenos iniciales. Como era de esperarse, un tercer sustrato, que reacciona vía una reacción concertada de tipo Wolff a través de un reordenamiento del intermediario singulete producido en el estado excitado, no dio lugar a ninguna señal EPR. Así mismo, cuando las reacciones de los tres carbenos se llevan a cabo en acetonitrilo, la multiplicidad del espín se invierte de modo que se genera un estado basal.singulete, por lo que no se observan señales EPR. Los resultados descritos en este trabajo son consistentes con aquellos obtenidos mediante fotólisis láser. Abstract in english Time-resolved (CW) EPR spectroscopy at X-band has been used to detect free radicals created by H-atom abstraction reactions of photochemically generated carbenes in n-hexadecane solutions at room temperature. Three different carbenes were studied, formed via loss of nitrogen after photo-excitation o [...] f a substituted biphenyl diazo precursor. The TREPR signals from two different alkyl radicals and the benzylic-type radical from the carbene are detected for two of the three diazo substrates. The radicals were unambiguously identified by spectral simulation using literature parameters (g-factors and hyper-fine coupling constants). Previous transient optical absorption spectroscopy experiments have concluded that these two carbenes have triplet ground states, which is confirmed by the low field emissive, high field absorptive phase of the TREPR signals reported here. The spectra are strongly spin polarized by the Radical Pair Mechanism of CIDEP, and their overall intensities track with the measured quantum yields for carbene production. A third substrate, known to react via a concerted Wolff reaction or excited state rearrangement via a singlet state, showed no TREPR signal, as expected. Reactions run in acetonitrile, where the spin multiplicity is reversed to give a singlet ground state, did not lead to detectable TREPR signals for all three substrates. The observations are consistent with previously published laser flash photolysis results.

Jin, Wang; Natalia V., Lebedeva; Matthew S., Platz; Malcolm D. E., Forbes.

2009-09-01

289

Catalytic water splitting with an iridium carbene complex: a theoretical study.  

Science.gov (United States)

Catalytic water oxidation at Ir(OH)(+) (Ir = IrCp*(Me2NHC), where Cp* = pentamethylcyclopentadienyl and Me2NHC = N,N'-dimethylimidazolin-2-ylidene) can occur through various competing channels. A potential-energy surface showing these various multichannel reaction pathways provides a picture of how their importance can be influenced by changes in the oxidant potential. In the most favourable calculated mechanism, water oxidation occurs via a pathway that includes four sequential oxidation steps, prior to formation of the O-O bond. The first three oxidation steps are exothermic upon treatment with cerium ammonium nitrate and lead to formation of Ir(V) (=O)(O(·))(+), which is calculated to be the most stabile species under these conditions, whereas the fourth oxidation step is the potential-energy-determining step. O-O bond formation takes place by coupling of the two oxo ligands along a direct pathway in the rate-limiting step. Dissociation of dioxygen occurs in two sequential steps, regenerating the starting material Ir(OH)(+). The calculated mechanism fits well with the experimentally observed rate law: v = kobs[Ir][oxidant]. The calculated effective barrier of 24.6?kcal?mol(-1) fits well with the observed turnover frequency of 0.88?s(-1). Under strongly oxidative conditions, O-O bond formation after four sequential oxidation steps is the preferred pathway, whereas under milder conditions O-O bond formation after three sequential oxidation steps becomes competitive. PMID:24644093

Venturini, Alessandro; Barbieri, Andrea; Reek, Joost N H; Hetterscheid, Dennis G H

2014-04-25

290

Electronic Excitations in Fischer-Type Cr and W Aminocarbene Complexes: A Combined ab Initio and Experimental Study.  

Czech Academy of Sciences Publication Activity Database

Ro?. 117, ?. 45 (2013), s. 11456-11463. ISSN 1089-5639 R&D Projects: GA MŠk LD11086 Institutional support: RVO:61388955 Keywords : METAL CARBENE COMPLEXES * FLASH-PHOTOLYSIS * BASIS-SETS Subject RIV: CF - Physical ; Theoretical Chemistry Impact factor: 2.775, year: 2013

Kvapilová, Hana; Hoskovcová, Irena; Kayanuma, M.; Daniel, CH.; Záliš, Stanislav

2013-01-01

291

A search for thermal isomerization of olefins to carbenes: Thermal generations of the silicon-nitrogen double bond  

Energy Technology Data Exchange (ETDEWEB)

The first part of this thesis will search for the thermal isomerization of olefins to carbenes which is predicted to be a high energy process by calculations and has only been observed in a few strained olefins. The possibility of thermal isomerization of simple olefins to carbenes will be explored. Substitution of a silyl group on the double bond of an olefin allows a potential intermediate which has a {beta}-radical to the silyl group during the cis-trans isomerization. The effects of a trimethylsilyl group on this isomerization are the subject of this study. The second part of this thesis will include the generation and chemistry of intermediates containing a silicon-nitrogen double bond. The isomerization of parent silanimine to the aminosilylene was calculated to be a high energy process. New approaches to the silicon-nitrogen double bond will also be presented. 92 refs., 12 figs., 11 tabs.

Zhang, Xianping.

1990-09-21

292

The use of benzil to obtain functionalized N-heterocycles  

Scientific Electronic Library Online (English)

Full Text Available SciELO Brazil | Language: English Abstract in portuguese Neste trabalho foi estudada a reatividade da benzila, empregando-se C, N- e N, N-nucleófilos tais como 2-butenoatos de etila 3-amino substituidos 4a-c, (S, Z)-3-(1-etóxi-3-hidróxi-1-oxo-2-propanilamina)-2-butenoato de etila 6, semicarbazida 8 e tiossemicarbazida 10, para avaliar os centros eletrofíl [...] icos na formação de compostos heterocíclicos polifuncionalizados, obtendo-se pirrolinonas 5a-c, pirrol 7, triazinona 9 e triazintiona 11. A dibenzoila 3 empregada foi obtida pela oxidação da benzoina na ausência de solvente em um estudo comparativo entre diferentes protocolos de oxidação, utilizando suportes sólidos associados ou não a energia de microondas com bons rendimentos sem empregar reagentes agressivos. Abstract in english In this work, the reactivity of benzil was studied, employing C, N- and N, N-nucleophiles, such as ethyl(3-amino substituted) 2-butenoates 4a-c , (S, Z)-ethyl 3-(1-ethoxy-3-hydroxy-1-oxopropan-2-ylamino)but-2-enoate 6, semicarbazide 8 or thiosemicarbazide 10, to evaluate their electrophilic centers [...] as building blocks for the synthesis of the polyfunctionalized heterocyclic compounds, resulting in pyrrolinone 5a-c, pyrrole 7, triazinone 9 and triazinethione 11. The employed benzil 3 was obtained by the oxidation of the benzoin under solvent free conditions in a comparative study between different protocols of oxidation, using the methodology under mild reaction conditions and supported reagent associated to the microwave irradiation, with good results and without aggressive reagents.

Mara E. F., Braibante; Hugo T. S., Braibante; Marciana P., Uliana; Carla C., Costa; Marcelo, Spenazzatto.

293

Inserção C-H de carbenóides de ródio em água e reutilização do catalisador Rhodium (II) carbene C-H insertion in water and catalyst reuse  

OpenAIRE

A five-session laboratory experiment is described for the synthesis of a beta-lactam via Rh(II) catalysed intramolecular C-H insertion of a alpha-diazo-alpha-ethoxycarbonylacetamide. The metallo-carbene, responsible for the C-H bond activation, was generated from the diazo substrate and the catalyst Rh2(OAc)4. The high stability and solubility of the catalyst and the exclusive C-H insertion of the Rh-carbene allows the synthesis of this important heterocycle in water and the catalyst reutiliz...

Candeias, Nuno R.; Gois, Pedro M. P.; Afonso, Carlos A. M.

2007-01-01

294

Inserção C-H de carbenóides de ródio em água e reutilização do catalisador Rhodium (II carbene C-H insertion in water and catalyst reuse  

Directory of Open Access Journals (Sweden)

Full Text Available A five-session laboratory experiment is described for the synthesis of a beta-lactam via Rh(II catalysed intramolecular C-H insertion of a alpha-diazo-alpha-ethoxycarbonylacetamide. The metallo-carbene, responsible for the C-H bond activation, was generated from the diazo substrate and the catalyst Rh2(OAc4. The high stability and solubility of the catalyst and the exclusive C-H insertion of the Rh-carbene allows the synthesis of this important heterocycle in water and the catalyst reutilization.

Nuno R. Candeias

2007-01-01

295

Rapid Generation and Safe Use of Carbenes Enabled by a Novel Flow Protocol with In-line IR spectroscopy.  

Science.gov (United States)

A powerful new continuous process for the formation and use of donor/acceptor-substituted carbenes is described. The safety profile of diazo group transfer on methyl phenylacetate was determined including kinetic studies in batch and in flow using in-line IR analysis. Batch work-up and liquid chromatography were circumvented by developing an optimized liquid/liquid flow separation method providing aryl diazoacetates in high purity. Fast screening of reaction conditions in flow with in-line IR analysis allowed rapid reaction optimization. Finally, a multistep process of diazo group transfer, extraction, separation and subsequent diazo decomposition combined with multiple X?H insertion reactions was established. PMID:25808068

Müller, Simon T R; Murat, Aurélien; Maillos, Delphine; Lesimple, Patrick; Hellier, Paul; Wirth, Thomas

2015-05-01

296

Nucleophilic addition of amines to ruthenium carbenes: ortho-(alkynyloxy)benzylamine cyclizations towards 1,3-benzoxazines.  

Science.gov (United States)

A new ruthenium-catalyzed cyclization of ortho-(alkynyloxy)benzylamines to dihydro-1,3-benzoxazines is reported. The cyclization is thought to take place via the vinyl ruthenium carbene intermediates which are easily formed from [Cp*RuCl(cod)] and N2 CHSiMe3 . The mild reaction conditions and the efficiency of the procedure allow the easy preparation of a broad range of new 2-vinyl-2-substituted 1,3-benzoxazine derivatives. Rearrangement of an internal C(sp) in the starting material into a tetrasubstituted C(sp(3) ) atom in the final 1,3-benzoxazine is highly remarkable. PMID:25640908

González-Rodríguez, Carlos; Suárez, José Ramón; Varela, Jesús A; Saá, Carlos

2015-02-23

297

Copper, silver, and gold complexes in hydrosilylation reactions.  

Science.gov (United States)

The reduction of diverse functional groups is an essential protocol in organic chemistry. Transition-metal catalysis has been successfully applied to the reduction of olefins, alkynes, and many carbonyl compounds via hydrogenation or hydrosilylation; the latter presenting several advantages over hydrogenation. Notably, hydrosilylation generally occurs under mild reaction conditions, and consequently over-reduced products are rarely detected. Moreover, the great majority of hydrosilanes employed in this reaction are easily handled, inexpensive, or both. A large number of multiple bonds can be involved in this context, and the hydrosilylation reaction can be regarded as a useful method for the synthesis of silicon-containing organic molecules or a convenient way of reducing organic compounds. Furthermore, the silyl group can also be retained as a protecting group, a strategy that can be of great usefulness in organic synthesis. Since the first Wilkinson's catalyst-mediated hydrosilylation of ketones in 1972, metals such as rhodium and iridium have attracted most of the attention in this area. A wide array of catalytic systems for hydrosilylation reactions is nowadays available, which has allowed for a great expansion of the synthetic scope of this transformation. After having been overlooked in the early years, group 11 metals (Cu, Ag, and Au), especially copper, have emerged as appealing alternatives for hydrosilylation. The use of a stabilized form of copper hydride, the hexameric [(Ph3P)CuH]6, by Stryker represented a breakthrough in copper-catalyzed reduction reactions. Nowadays, several copper-based catalytic systems compare well with a variety of reported rhodium-based catalysts, which generally suffer from the high cost of the catalyst. Tertiary phosphine ligands are the most widely used in these transformations. However, other families such as N-heterocyclic carbenes (NHCs) have shown promising activities. Compared with copper, little attention has been paid to silver- or gold-based catalysts. Silver salts have been considered inert towards hydrosilylation, and they are often employed as innocent anion exchange reagents for the in situ generation of cationic transition metal catalysts. Despite the rare reports available, they have already shown interesting reactivity profiles, for example, in the chemoselective reduction of aldehydes in the presence of ketones. Furthermore, 1,2-hydride delivery is favored over 1,4-reductions for alpha,beta-unsaturated carbonyl compounds, in contrast with most copper-based systems. PMID:18281951

Díez-González, Silvia; Nolan, Steven P

2008-02-01

298

3,3′-Dimethyl-1,1′-(methylenedi-p-phenylene)diimidazolium bis(hexafluorophosphate)  

OpenAIRE

The title N-heterocyclic carbene compound, C21H22N42+·2PF6?, crystallizes as an inversion twin. There are two independent N-heterocyclic carbene dications (A and B) and four independent hexafluorophosphate anions in the asymmetric unit. The cations are L-shaped with the benzene rings being inclined to one another by 88.82?(16)° in cation A and 87.03?(16)° in cation B. The imidazole rings make dihedral angles of 35.7?(2) and 32...

Kun Huang; Ping Zhang; Da-Bin Qin

2010-01-01

299

Molecular electrocatalysts for the hydrogen production from iron based hydrogenases; Electrocatalyseurs moleculaires pour la production d'hydrogene inspires des hydrogenases a fer  

Energy Technology Data Exchange (ETDEWEB)

The complex type [Fe{sub 2}(CO){sub 6}({mu}-SRS)] are structural analogue of the active site of iron hydrogenases constituted of a dinuclear entity and diatomic ligands CO and CN. The today knowledge on the electrocatalytic activity of some of these organometallic complexes towards the proton reduction in hydrogen{sup 1,2,3}, makes possible the elaboration of bio inspired electrocatalysts. Studies must now be realized to better understand the reduction processes of the iron dinuclear complexes with and without acids. In this framework the authors synthesized series of complexes type [Fe{sub 2}(CO){sub 6-n} L{sub n}({mu}-E-CH{sub 2}-X-CH{sub 2}-E)] (n=0,1 or 2; L=carbene N-heterocyclic; E=S or P(Ph); X= CH{sub 2}, C{sub 6}H{sub 4} or NR). (A.L.B.)

Gloaguen, F.; Capon, J.F.; Schollhammer, Ph.; Talarmin, J. [Laboratoire de Chimie, Electrochimie Moleculaires et Chimie Analytique, UMR CNRS 6521 UBO, 29 - Brest (France)

2005-07-01

300

Molecular electrocatalysts for the hydrogen production from iron based hydrogenases  

International Nuclear Information System (INIS)

The complex type [Fe2(CO)6(?-SRS)] are structural analogue of the active site of iron hydrogenases constituted of a dinuclear entity and diatomic ligands CO and CN. The today knowledge on the electrocatalytic activity of some of these organometallic complexes towards the proton reduction in hydrogen1,2,3, makes possible the elaboration of bio inspired electrocatalysts. Studies must now be realized to better understand the reduction processes of the iron dinuclear complexes with and without acids. In this framework the authors synthesized series of complexes type [Fe2(CO)6-n Ln(?-E-CH2-X-CH2-E)] (n=0,1 or 2; L=carbene N-heterocyclic; E=S or P(Ph); X= CH2, C6H4 or NR). (A.L.B.)

301

Theoretical studies of the insertion of carbenes in the zeolite framework: modification of the acidity and creation of chiral sites  

Scientific Electronic Library Online (English)

Full Text Available Foi realizado um estudo teórico da inserção de carbenos (CH2 e CHCHO) na estrutura cristalina da zeólita Y. O método our own n-layered integrated molecular orbital and molecular mechanics (ONIOM) M062x/6-31G(d,p):PM6 foi utilizado para descrever a inserção do metileno (CH2) nas ligações T-O (T = Si [...] ou Al) da rede resultando em quatro estruturas isômeras. Em todos os casos os cálculos indicaram uma alta exotermicidade para a inserção do metileno na rede cristalina, independentemente da multiplicidade do carbeno (singlete ou triplete). A inserção na ligação O-H ácida para formar um grupo metóxi adsorvido foi o processo mais favorável, mas este caminho não ocorre se a inserção é feita na zeólita desprotonada. A inserção do formil-carbeno (CHCHO) cria centros quirais na estrutura cristalina. A acidez da zeólita após a inserção dos carbenos foi calculada usando a energia de desprotonação. Os cálculos predizem a possibilidade de desenvolver zeólitas ácidas com centros quirais, que poderiam imitar enzimas, especialmente para uso em processos de química fina e transformação de biomassa. Abstract in english A theoretical study of the insertion of carbenes (CH2, CHCHO) in the framework structure of zeolite Y was carried out. The "our own n-layered integrated molecular orbital and molecular mechanics" (ONIOM) scheme M062x/6-31G(d,p):PM6 was used to describe the insertion of methylene (CH2) in the T-O bon [...] ds (T = Si, Al) of the framework yielding four isomeric structures. In all cases, calculations indicated a high exothermic process for the insertion of methylene in the framework, regardless of the spin multiplicity of the carbene (singlet or triplet). Insertion into the acidic O-H bond to afford an adsorbed methoxy group was the most favourable process, but this pathway does not occur if insertion is carried out on the deprotonated zeolite. Insertion of formylcarbene (CHCHO) creates chiral sites in the framework. The acidity of the zeolite structures after carbene insertion was calculated by means of the deprotonation energy. The calculations predicted the possibility of designing acidic zeolites with chiral sites that could mimic enzymes, especially for uses in fine chemical processes and biomass transformations.

Maria Beatriz S., Mota; Nilton, Rosenbach Jr.; Claudio J. A., Mota.

1021-10-01

302

Density functional study of the first-row transition-metal complexes M-CH2, M-CHF, and M-CF2  

Science.gov (United States)

Carbenes and fluorocarbenes are important intermediates in the hydrodechlorination of CFCs catalyzed by metal surfaces. However, the reaction mechanism at a molecular level is not completely understood. In this work, density functional calculations have been performed for the first-row transition-metal complexes M-CH2, M-CHF, and M-CF2 aiming to conbribute to the understanding of the metal/carbene interaction mechanism. Relative energies, geometries, and frequencies of the M-CXY complexes in different electronic states are reported. The binding mechanism is described through an analysis of the molecular orbitals. The binding energy of the M-CF2 is about 30% smaller than the respective M-CH2 binding energy. The electronic configuration of all complexes studied is presented in a diagram that allows one to predict qualitatively properties such as geometries, multiplicities, charge transfers, and relative bond lengths.

Dalmázio, Ilza; Anderson Duarte, Hélio

2001-07-01

303

Copper-catalyzed domino rearrangement/dehydrogenation oxidation/carbene oxidation for one-pot regiospecific synthesis of highly functionalized polysubstituted furans.  

Science.gov (United States)

A novel and efficient method for the regiospecific synthesis of polysubstituted furan aldehydes/ketones has been developed via a copper(I)-catalyzed rearrangement/dehydrogenation oxidation/carbene oxidation sequence of 1,5-enynes in situ formed from alkynols and diethyl but-2-ynedioate under atmospheric pressure. The domino reaction proceeds smoothly under mild conditions with commercially available catalysts and affords highly functionalized furans in moderate to good yields. PMID:19323564

Cao, Hua; Jiang, Huanfeng; Yao, Wenjuan; Liu, Xiaohang

2009-05-01

304

Formation of organometallic compounds of carbene and carbine types in the interaction of RLi with neodymium and yttrium chlorides in solvating media  

International Nuclear Information System (INIS)

Studied is the interaction of neodymium and yttrium chlorides with benzyl lithium and neophyl lithium and shown is the formation of unusual organometallic compounds of the carbene and carbine types. The product yield is 60-100% from the theory (in calculation per RLi). On the basis of the data obtained by the method of infrared spectroscopy a conclusion is made that in synthesized compounds the benzyl grouping is connected with the metal by ternary bonds

305

Cooperativity of anion⋯? and ?⋯? interactions regulates the self-assembly of a series of carbene proligands: Towards quantitative analysis of intermolecular interactions with Hirshfeld surface  

Science.gov (United States)

The cooperative effect of weak non-covalent forces between anions and electron deficient aromatics by ?⋯? stacking of a series of carbene proligands (1-3) have been thoroughly explored by crystallographic studies. Structural analysis revealed that the anion⋯? and ?⋯? interactions along with intermolecular hydrogen bonding mutually cooperate to facilitate the assembling of the supramolecular framework. The ?⋯? and corresponding anion⋯? interactions have been investigated in the title carbene proligands despite their association with counter ions. The presence of the anion in the vicinity of the ?-system leads to the formation of anion⋯?/?⋯?/?⋯anion network for an inductive stabilization of the assemblies. To assess the dimensionality of the supramolecular framework consolidated by cooperative anion⋯?/?⋯? interactions and hydrogen bonding, different substituent effects in the carbene backbone have been considered to tune these interactions. These facts show that the supramolecular framework based on these cooperative weak forces may be robust enough for application in molecular recognition. The investigation of close intermolecular interactions between the molecules via Hirshfeld surface analyses is presented in order to reveal subtle differences and similarities in the crystal structures. The decomposition of the fingerprint plot area provides a percentage of each intermolecular interaction, allowing for a quantified analysis of close contacts within each crystal.

Samanta, Tapastaru; Dey, Lingaraj; Dinda, Joydev; Chattopadhyay, Shyamal Kumar; Seth, Saikat Kumar

2014-06-01

306

rac-cis-Dicarbonylchlorido{1-[2-(diphenylphosphanyl-?Pbenzyl]-3-(phenyl-?C1imidazol-2-ylidene-?C2}ruthenium(II dichloromethane monosolvate  

Directory of Open Access Journals (Sweden)

Full Text Available In the title compound, [Ru(C28H22N2PCl(CO2]·CH2Cl2, the RuII atom exhibits a distorted octahedral coordination geometry. The N-phenyl group of the ligand has undergone orthometalation; as a result, the tridentate phosphane-functionalized N-heterocyclic carbene ligand is coordinating in a meridional fashion. This complex is of interest with respect to transfer hydrogenation catalysis and also provides an example of C—H activation behavior in late transition metal complexes. The dichloromethane solvent molecule is disordered over two sets of sites with an occupancy ratio of 0.873?(14:0.127?(14.

Gregory J. Domski

2012-09-01

307

Formal synthesis of salinosporamide A via NHC-catalyzed intramolecular lactonization  

OpenAIRE

An N-heterocyclic carbene (NHC) catalyzed intramolecular lactonization to prepare densely functionalized bicyclic ?-lactam-?-lactone adducts from enals is reported. This method has been applied to the formal synthesis of salinosporamide A, a potent 20S proteasome inhibitor and anti-cancer therapeutic.

Struble, Justin R.; Bode, Jeffrey W.

2009-01-01

308

Acyl azolium fluorides for room temperature nucleophilic aromatic fluorination of chloro- and nitroarenes.  

Science.gov (United States)

The reaction of acid fluorides with N-heterocyclic carbenes (NHCs) produces anhydrous acyl azolium fluorides. With appropriate selection of acid fluoride and NHC, these salts can be used for the room temperature SNAr fluorination of a variety of aryl chlorides and nitroarenes. PMID:25822156

Ryan, Sarah J; Schimler, Sydonie D; Bland, Douglas C; Sanford, Melanie S

2015-04-17

309

A cryptand-encapsulated germanium(II) dication.  

Science.gov (United States)

Unlike cations of metals such as sodium or calcium, oxidized silicon and germanium centers generally require strongly bound covalent ligands. We report the synthesis and characterization of a germanium(II) dication in the form of the salt (Ge.cryptand[2.2.2])(O3SCF3)2. The salt is isolated in 88% yield from the reaction of cryptand [2.2.2] and an N-heterocyclic carbene complex of GeCl(O3SCF3) as an air-sensitive, white solid. The crystal structure of the salt shows minimal interaction between the cryptand-encapsulated germanium(II) ion and the two -O3SCF3 counterions. These results suggest a widely expanded role of cryptands and related molecules in stabilizing nonmetallic cations. PMID:19039131

Rupar, Paul A; Staroverov, Viktor N; Baines, Kim M

2008-11-28

310

Synthesis, structure, and catecholase activity of bispyrazolylacetate copper(II) complexes.  

Science.gov (United States)

A series of six-coordination copper(ii) complexes containing bis(3,5-di-t-butylpyrazol-1-yl)acetate (bdtbpza) and N-heterocycles or chelating aliphatic ligands have been synthesized. The steric bulkiness of bis(pyrazol-1-yl)acetate anchors two bdtbpza to situate a trans position and to adopt an O-bound monodentate coordination mode with other nitrogen bases occupying the basal plane. Five mononuclear mixed ligand complexes, [Cu(bdtbpza)2(py)4] , [Cu(bdtbpza)2(t-Bupy)4] , [Cu(bdtbpza)2(pym)2(MeOH)2] , [Cu(bdtbpza)2(eda)2] , [Cu(bdtbpza)2(tmeda)(H2O)2] , where py = pyridine, t-Bupy = tert-butylpyridine, pym = pyrimidine, eda = ethylenediamine, and tmeda = tetramethylethylenediamine, were isolated and thoroughly characterized. Intriguingly, the heteroleptic complex , which has two aquo-ligands oriented in the cis positions, demonstrates higher catecholase-like activity in performing aerial oxidation of 3,5-di-tert-butylcatechol (3,5-DTBC) to 3,5-di-tert-butylquinone (3,5-DTBQ) than other bis(pyrazolyl)acetate-embedded copper complexes reported herein, which suggests the essential role of labile cis-aquo ligands to promote the catalytic reaction. PMID:25146734

Gajewska, Ma?gorzata J; Ching, Wei-Min; Wen, Yuh-Sheng; Hung, Chen-Hsiung

2014-10-21

311

Unexpected reactivity of diaryl ?-diketones with thiazolium carbenes: discovery of a novel multicomponent reaction for the facile synthesis of 1,4-thiazin-3-ones.  

Science.gov (United States)

Diaryl ?-diketones do not undergo polarity reversal in the presence of (benzo)thiazolium carbenes but are engaged in a novel multicomponent reaction with water to efficiently give medicinally relevant 1,4-thiazin-3-one heterocycles. Three different sets of conditions have been optimized to furnish the title compounds in fair to excellent yields depending on the electronic properties of ?-diketone aromatic substituents and thiazolium or benzothiazolium substrate. A plausible reaction mechanism is also proposed based on the isolation and characterization of the postulated key intermediate and isotopic labeling experiments. PMID:22766681

Bertolasi, Valerio; Bortolini, Olga; Donvito, Adelaide; Fantin, Giancarlo; Fogagnolo, Marco; Giovannini, Pier Paolo; Massi, Alessandro; Pacifico, Salvatore

2012-08-28

312

Formation of the first derivatives of praseodymium-containing metallofullerenes via regioselective carbene addition to Pr rate at C{sub 2v}(9)-C{sub 82}  

Energy Technology Data Exchange (ETDEWEB)

The first derivatives of praseodymium-containing metallofullerenes are formed through regioselective cycloaddition of adamantylidene carbene to Pr rate at C{sub 2v}(9)-C{sub 82}, and two isomers out of the 35 possible monoadducts are successfully isolated. Optical adsorption and electrical chemistry characterizations indicate that the electronic property of Pr rate at C{sub 2v}(9)-C{sub 82} is largely pertained in these derivatives, since their ?-electron systems are not altered markedly. (copyright 2014 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

Zhou, Qin; Li, Hui; Wang, Yan; Lian, Yongfu [Key Laboratory of Functional Inorganic Material Chemistry, Ministry of Education, School of Chemistry and Materials Science, Heilongjiang University, Harbin (China)

2014-12-01

313

Formation of the first derivatives of praseodymium-containing metallofullerenes via regioselective carbene addition to Pr rate at C2v(9)-C82  

International Nuclear Information System (INIS)

The first derivatives of praseodymium-containing metallofullerenes are formed through regioselective cycloaddition of adamantylidene carbene to Pr rate at C2v(9)-C82, and two isomers out of the 35 possible monoadducts are successfully isolated. Optical adsorption and electrical chemistry characterizations indicate that the electronic property of Pr rate at C2v(9)-C82 is largely pertained in these derivatives, since their ?-electron systems are not altered markedly. (copyright 2014 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

314

Synthesis of novel synthetic intermediates from the reaction of benzimidazole and triazole carbenes with ketenimines and their application in the construction of spiro-pyrroles.  

Science.gov (United States)

2-(2-Alkoxycarbonyl-1-arylamino-1-propenyl)benzimidazolium and 5-(2-alkoxycarbonyl-1-arylamino-1-propenyl)triazolium salts were synthesized in good yields from the reaction of benzimidazole and triazole carbenes with ketenimines. Upon treatment with a base, both salts were converted into novel 1,3-dipoles which underwent [3+2] cycloaddition reactions with electron-deficient alkynes and allenes to produce benzimidazole-spiro-pyrroles or triazole-spiro-pyrroles. This work provides novel synthons for the construction of multifunctional spiro-pyrrole derivatives that are not easy accessible by other synthetic methods and are potentially amenable to further transformations. PMID:19907793

Mo, Jun-Ming; Ma, Yang-Guang; Cheng, Ying

2009-12-01

315

A new class of photoactivatable and carbene generating reagents with extremely high specific radioactivity. Synthesis, characterization and applications. Eine neue Klasse photoaktivierbarer, Carben-erzeugender Reagenzien extrem hoher spezifischer Radioaktivitaet. Synthese, Charakterisierung und Anwendungen  

Energy Technology Data Exchange (ETDEWEB)

The main objective of this work was the development of new photocrosslinking and labeling reagents which show favourable photochemical properties and can be synthesized in an extremely high specific radioactivity. A key compound in the synthesis of these reagents was 2-tributyltin-4-(3-trifluormethyl-3H-diazirin-3-yl)-benzyl alcohol. Esters of this alcohol can be easily radioiodinated at a specific radioactivity of >2000 Ci/mmol under mild conditions. By experiments with a model compound it was shown that 2-iodo-4-(3-trifluormethyl-3H-diazirin-3-yl)-benzyl esters, upon photolysis, generate highly reactive (singlet) carbenes capable of inserting into CH-bonds. Equally important, there is no indication of loss of iodine under the photolysis conditions applied. Therefore two key requirements for photolabeling reagents are fulfilled. Several photoactivatable radioiodinated phospholipids have been synthesized. Their properties have been evaluated by labeling of the the membranes of intact erythrocytes and influenza viruses. Currently these lipids are used to study the interaction of various proteins (shown are experiments with MARCKS) with membranes. Furthermore a new class of actual label transfer crosslinkers (two thiol specific and one amino specific) have been developed. The range of potentialities of these reagents is currently being investigated. Finally a photoactivatable radioiodinated ceramide analogue suitable as a photoaffinity crosslinker has been developed with the goal of identifying the putative receptor of this second messenger-like lipid. Preliminary studies towards this goal are described. We are convinced that the reagents and methods presented in this work are valuable tools, and that they will find widespread use in future cell-biological and biochemical research. (author) figs., tabs., refs.

Weber, T.

1994-01-01

316

Studies on complex compounds of uranium(IV) with pyridine and quinoline carboxylic acid. Part II  

Energy Technology Data Exchange (ETDEWEB)

The reactions between bis(pyridine-2,6-dicarboxylato)-uranium(IV), U(dip)/sub 2/ and N-heterocyclic bases (L) in methanol (L = pyridine, 2-methylpyridine, 3-methylpyridine and 4-methylpyridine) produce eight coordinate uranium(IV) complexes, U(dip)/sub 2/(H/sub 2/O)L which have been characterized by elemental analysis, ir studies, thermal analysis and magnetic susceptibility measurement. The anionic complex (Ph/sub 4/As)/sub 2/(U(dip)/sub 3/), 3H/sub 2/O has been isolated by reacting U(dip)/sub 2/ with pyridine-2,6-dicarboxylic acid in the presence of tetraphenyl arsonium chloride. Uranium(IV) complexes of the type U(quind)/sub 2/(acetate)/sub 2/, U(quin)(acetate)/sub 2/ (quindH = quinaldinic acid, quinH/sub 2/ = quinolinic acid, acetate = CH/sub 3/COO/sup -/) have also been prepared by the interaction of the methanolic solution of uranium tetraacetate and the respective acids.

Ta, N.C.

1978-01-01

317

A new class of photoactivatable and carbene generating reagents with extremely high specific radioactivity. Synthesis, characterization and applications  

International Nuclear Information System (INIS)

The main objective of this work was the development of new photocrosslinking and labeling reagents which show favourable photochemical properties and can be synthesized in an extremely high specific radioactivity. A key compound in the synthesis of these reagents was 2-tributyltin-4-(3-trifluormethyl-3H-diazirin-3-yl)-benzyl alcohol. Esters of this alcohol can be easily radioiodinated at a specific radioactivity of >2000 Ci/mmol under mild conditions. By experiments with a model compound it was shown that 2-iodo-4-(3-trifluormethyl-3H-diazirin-3-yl)-benzyl esters, upon photolysis, generate highly reactive (singlet) carbenes capable of inserting into CH-bonds. Equally important, there is no indication of loss of iodine under the photolysis conditions applied. Therefore two key requirements for photolabeling reagents are fulfilled. Several photoactivatable radioiodinated phospholipids have been synthesized. Their properties have been evaluated by labeling of the the membranes of intact erythrocytes and influenza viruses. Currently these lipids are used to study the interaction of various proteins (shown are experiments with MARCKS) with membranes. Furthermore a new class of actual label transfer crosslinkers (two thiol specific and one amino specific) have been developed. The range of potentialities of these reagents is currently being investigated. Finally a photoactivatable radioiodinated ceramide analogue suitable as a photoaffinity crosslinker has been developed witffinity crosslinker has been developed with the goal of identifying the putative receptor of this second messenger-like lipid. Preliminary studies towards this goal are described. We are convinced that the reagents and methods presented in this work are valuable tools, and that they will find widespread use in future cell-biological and biochemical research. (author) figs., tabs., refs

318

Complexation of trivalent cationic lanthanides by N.O donor ligands: physico-chemical studies of the association and selectivity in solution  

International Nuclear Information System (INIS)

The aim of this work is to study the complexation of f-elements in solution by ligands incorporating N-heterocyclic donors. These ligands display interesting properties for the selective separation of An(III)/Ln(III) have been studied to obtain a better understanding of the coordination properties with f-elements and to develop more selective extractants. The hepta-dentate ligand tpaam shows an affinity for Ln(III) similar to the tetradentate ligand tpa in water even when the three additional amide groups are bonded to the metal. Even though the complexation with tpa is exothermic, that with tpaam is endothermic with a more positive entropy. The dehydration of the cation disfavours the formation of Ln(III) complexes with ligands containing weak donors. The analysis of the solution paramagnetic relaxation times of the tpaam complexes is in agreement with data in the solid-state. There is little difference between the formation constants of the Ln3+ complexes with different ligands (tpaam, tpzen, tpa and tpza) as determined by UV-vis spectrophotometry in anhydrous acetonitrile. The limitations encountered during this study are intrinsic to the ligands studied. The preliminary study of two tetrapodal ligands containing acid and pyridine groups (Lpy)or pyrazine (Lpz) show the formation of 1:1 complexes in water. Analysis of the formation constants of the corresponding Gd(III) complexes shows that replacement of a pyridine group by pyrazine result in a loss of stability of 1.6 logarithmic units. (author)

319

Equilibrium between a cyclotrisilene and an isolable base adduct of a disilenyl silylene  

Science.gov (United States)

In organic chemistry, compounds with adjacent alkene and carbene functionalities (vinyl carbenes) are studied widely as fleeting intermediates and in the coordination sphere of transition metals. Stable derivatives of vinyl carbenes remain elusive, including the corresponding heavier group 14 homologues. Here we report the isolation and full characterization of a base-stabilized silicon version of a vinyl carbene that features a silicon-silicon double bond as well as a silylene functionality, coordinated by an N-heterocyclic carbene (NHC). In solution, the intensely green disilenyl silylene adduct exists in equilibrium with the corresponding silicon analogue of a cyclopropene and free NHC, which was quantified by nuclear magnetic resonance spectroscopy and ultraviolet-visible spectroscopy. The reversibility of this process raises exciting possibilities for the preparation of extended conjugated ? systems of silicon.

Cowley, Michael J.; Huch, Volker; Rzepa, Henry S.; Scheschkewitz, David

2013-10-01

320

Highly efficient and site-selective [3 + 2] cycloaddition of carbene-derived ambident dipoles with ketenes for a straightforward synthesis of spiro-pyrrolidones.  

Science.gov (United States)

The [3 + 2] cycloaddition reaction of 2-arylthiocarbamoyl benzimidazolium, -imidazolinium, and -triazolium inner salts (the ambident C-C-N and C-C-S 1,3-dipoles derived from carbenes) with ketenes proceeded efficiently in a highly site-selective manner to produce the C-C-N cycloaddition products benzimidazoline-, imidazolidine-, or triazoline spiro-pyrrolidones in 58-93% yields. Theoretical calculation suggests a stepwise mechanism for the reaction and indicates that the C-C-N cycloaddition of the dipoles with ketenes is both a dynamically and thermodynamically favored reaction pathway. Their easy availability, high reactivity, and reaction selectivity render the benzimidazolium, -imidazolinium, and -triazolium inner salts powerful and versatile 1,3-dipoles in the construction of novel spiro heterocyclic systems, which are not easily accessible by other methods. PMID:17629341

Li, Jia-Qi; Liao, Rong-Zhen; Ding, Wan-Jian; Cheng, Ying

2007-08-01

321

Cu-catalyzed efficient synthetic methodology for ebselen and related Se-N heterocycles.  

Science.gov (United States)

An efficient copper-catalyzed method for the synthesis of biologically important ebselen and related analogues containing a Se-N bond has been developed. This is the first report of a catalytic process of selenation and Se-N bond formation reaction. Copper-catalyzed reaction tolerates functional groups such as amides, hydroxyls, ethers, nitro, fluorides, and chlorides. The best results are obtained by using a combination of potassium carbonate as a base, iodo- or bromo-arylamide substrates, selenium powder, and copper iodide catalyst. PMID:21053969

Balkrishna, Shah Jaimin; Bhakuni, Bhagat Singh; Chopra, Deepak; Kumar, Sangit

2010-12-01

322

A novel stereoselective synthesis of N-heterocycles by intramolecular hydrovinylation  

DEFF Research Database (Denmark)

A novel method for the synthesis of bicyclic amines has been developed. Cyclisation of 1,6-dienes by intramolecular hydrovinylation in the presence of catalytic amounts of allylpalladium chloride dimer afforded bicyclic amines in one step. Added phosphines, silver salts, as well as the nature of the N-protecting group influenced the yield and selectivity of the reactions. Most strikingly, intramolecular hydrovinylation allowed the preparation of diastereomerically pure bicyclic amines as e.g. hexahydroindoles 2a-2d.

Bothe, Ulrich; Rudbeck, H. C.

2001-01-01

323

ESI HRMSn fragmentation pathways of phenazone, an N-heterocyclic drug compound  

OpenAIRE

Determination of drug residues in the environment is currently a hot topic in analytical chemistry. It is thus absolutely necessary to develop analytical methodologies appropriate to determine both parent drug compounds and degradants formed from in vivo and environmental reactions. In this research we studied MS2 and MS3 fragmentations of phenazone, employing a high-mass-accuracy Orbitrap mass spectrometer, equipped with an ESI source. Tandem mass spectra (positive and negative ion mode) wer...

Medana, Claudio; Calza, Paola; Baiocchi, Claudio; Dal Bello, Federica; Deagostino, Annamaria

2011-01-01

324

Synthesis, characterization, and crystal structure of two ?,?-unsaturated ketones with N-heterocycle  

Science.gov (United States)

Two ?,?-unsaturated ketones: C22H16N2O ( 1), ( E)-3-(4-(1 H-benzo[d]imidazol-1-yl)phenyl)-1-phenylprop-2-en-1-one and C19H16N2O2 ( 2), ( E)-3-(4-(1 H-pyrazol-1-yl)phenyl)-1-(4-methoxyphenyl)prop-2-en-1-one were synthesized and characterized by X-ray diffraction analyses, EA, 1H NMR-, and IR-spectra. In the crystal structure of 1, molecules are linked through intermolecular hydrogen bonds, C-H⋯? and ?⋯? interactions forming a 3-D network, while in the crystal structures of 2, molecules are assembled by the C-H⋯O, C-H⋯N hydrogen bonds and C-H⋯? interactions into an infinite 3-D supramolecular structure. A particularly interesting feature of the packing in the structure of 2, is the extensive contribution of C-H⋯? interactions, involving two hydrogen atoms from each of the methyl groups of the methoxy substituents.

Wang, G.-F.; Sun, S.-W.; Gong, Q.-J.; Sun, H.

2014-12-01

325

Coupling Reactions of ?-Bromocarboxylate with Non-Aromatic N-Heterocycles  

OpenAIRE

The conditions for the C-N bond forming reaction (C-N coupling reaction) between ?-bromocarboxylate and nitrogen-containing non-aromatic heterocyclic rings under heterogeneous copper(I) oxide catalysis are investigated in this paper. All the generated compounds were fully characterized by IR, NMR and MS spectroscopy. Ab initio/DFT calculations of partial charges on nitrogen atoms in all the discussed heterocycles and on C(2) of carboxylate under applied conditions were predicted. These in si...

Jozef Csollei; Ivan Raich; Josef Jampilek; Lukas Placek; Barbora Slaba; Katerina Brychtova

2009-01-01

326

Coupling Reactions of ?-Bromocarboxylate with Non-Aromatic N-Heterocycles  

Directory of Open Access Journals (Sweden)

Full Text Available The conditions for the C-N bond forming reaction (C-N coupling reaction between ?-bromocarboxylate and nitrogen-containing non-aromatic heterocyclic rings under heterogeneous copper(I oxide catalysis are investigated in this paper. All the generated compounds were fully characterized by IR, NMR and MS spectroscopy. Ab initio/DFT calculations of partial charges on nitrogen atoms in all the discussed heterocycles and on C(2 of carboxylate under applied conditions were predicted. These in silico results correlate relatively with the experimental observations.

Jozef Csollei

2009-08-01

327

Coupling reactions of alpha-bromocarboxylate with non-aromatic N-heterocycles.  

Science.gov (United States)

The conditions for the C-N bond forming reaction (C-N coupling reaction) between alpha-bromocarboxylate and nitrogen-containing non-aromatic heterocyclic rings under heterogeneous copper(I) oxide catalysis are investigated in this paper. All the generated compounds were fully characterized by IR, NMR and MS spectroscopy. Ab initio/DFT calculations of partial charges on nitrogen atoms in all the discussed heterocycles and on C((2)) of carboxylate under applied conditions were predicted. These in silico results correlate relatively with the experimental observations. PMID:19701142

Brychtova, Katerina; Slaba, Barbora; Placek, Lukas; Jampilek, Josef; Raich, Ivan; Csollei, Jozef

2009-01-01

328

New cadmium(II) halides modified by N-heterocyclic molecules  

Science.gov (United States)

Under the solvothermal condition, the reaction of CdI2, bpp and KI at pH = 8 afforded compound [CdI2(bpp)] (bpp = 1,2-bis(4-pyridyl)propane) 1, while at the ambient conditions, the reactions of CdX2, dabco and KX at pH = 4-5 produced compounds [H2(dabco)][CdBr4]·H2O (dabco = 1,4-diazabicyclo[2,2,2]octane) 2 and [(Hdabco)CdI3] 3. X-ray single-crystal diffraction analysis reveals that (i) compound 1 possesses a one-dimensional (1-D) zigzag chain structure. The large volume bpp molecule controls the Cd2+ ion to adopt a tetrahedral geometric configuration; (ii) both compounds 2 and 3 are mononuclear. Interestingly, in the same pH environments, dabco was in situ diprotonated in compound 2, while dabco was in situ monoprotonated in compound 3. The templating effect as well as the X- ion maybe plays a key role in the protonated degree for dabco in an acidic environment. The photoluminescence analysis indicates that compound 1 emits the strong green light, which should be attributed to a combination of two types of charge transfers: the charge transfer between Cd2+ and I-; the charge transfer between Cd2+ and bpp.

Wang, Tie-Gang; Li, Su; Yu, Jie-Hui; Xu, Ji-Qing

2015-03-01

329

New iodocuprates(I) with N-heterocyclic molecules as the cations  

Energy Technology Data Exchange (ETDEWEB)

Under the hydrothermal conditions, the reactions between CuI, KI and bp/bpp (bp=4,4?-bipiperidine, bpp=1,3-bis(4-piperidyl)propane) in an acidic alcohol solution produced three new organically templated iodocuprates(I) as [H{sub 2}bp]{sub 2}[Cu{sub 2}I{sub 6}] 1, [tmbp][Cu{sub 2}I{sub 4}] 2 and [tmbpp] 2 [Cu{sub 4}I{sub 8}]·2H{sub 2}O 3 (tmbp{sup 2+}=N,N,N?,N?-tetramethyl-4,4?-bipiperidinium; tmbpp{sup 2+}=N,N,N?,N?-tetramethyl-1,3-bis(4-piperidyl)propane dication). X-ray analysis revealed that (i) tmbp{sup 2+} and tmbpp{sup 2+} in compounds 2 and 3 originated from the complete N-alklation of bp/bpp with CH{sub 3}OH; (ii) templated by H{sub 2}bp{sup 2+}, the inorganic anion [Cu{sub 2}I{sub 6}]{sup 2?} of 1 possesses a dinuclear structure, whereas templated by tmbp{sup 2+}, the inorganic anion [Cu{sub 2}I{sub 4}]{sup 2?} of 2 exhibits a one-dimensional (1D) chain structure; (iii) templated by tmbpp{sup 2+}, the inorganic anion [Cu{sub 4}I{sub 8}]{sup 4?} of 3 shows a cubane-like structure modified by four terminal I{sup ?} ions. The photoluminescence analysis indicates that compounds 1 and 2 emit blue light, while compound 3 emits green light. - Graphical abstract: By employing hydrothermal in situ N-alkylation of bp/bpp with CH{sub 3}OH, three new organically templated iodocuprates(I) were obtained. Display Omitted - Highlights: • Three new organically templated iodocuprates(I) were reported. • Cations tmbp{sup 2+} and tmbpp{sup 2+} originated from in situ alkylation of bp/bpp with CH{sub 3}OH. • H{sup +} and I{sup ?} play a key role in alkylation of bp/bpp with CH{sub 3}OH. • Photoluminescence emission for iodocuprates(I) is related to Cu···Cu interaction.

Zhao, Jin-Jing [College of Chemistry and State Key Laboratory of Inorganic Synthesis and Preparative Chemistry, Jilin University, Changchun, Jilin 130023 (China); Zhang, Xiao [State Key Lab of Urban Water Resource and Environment (SKLUWRE) and Academy of Fundamental and Interdisciplinary Science, Harbin Institute of Technology, Harbin, Heilongjiang 150080 (China); Wang, Yan-Ning; Jia, Hong-Li [College of Chemistry and State Key Laboratory of Inorganic Synthesis and Preparative Chemistry, Jilin University, Changchun, Jilin 130023 (China); Yu, Jie-Hui, E-mail: jhyu@jlu.edu.cn [College of Chemistry and State Key Laboratory of Inorganic Synthesis and Preparative Chemistry, Jilin University, Changchun, Jilin 130023 (China); Xu, Ji-Qing, E-mail: xjq@mail.jlu.edu.cn [College of Chemistry and State Key Laboratory of Inorganic Synthesis and Preparative Chemistry, Jilin University, Changchun, Jilin 130023 (China)

2013-11-15

330

New iodocuprates(I) with N-heterocyclic molecules as the cations  

International Nuclear Information System (INIS)

Under the hydrothermal conditions, the reactions between CuI, KI and bp/bpp (bp=4,4?-bipiperidine, bpp=1,3-bis(4-piperidyl)propane) in an acidic alcohol solution produced three new organically templated iodocuprates(I) as [H2bp]2[Cu2I6] 1, [tmbp][Cu2I4] 2 and [tmbpp] 2 [Cu4I8]·2H2O 3 (tmbp2+=N,N,N?,N?-tetramethyl-4,4?-bipiperidinium; tmbpp2+=N,N,N?,N?-tetramethyl-1,3-bis(4-piperidyl)propane dication). X-ray analysis revealed that (i) tmbp2+ and tmbpp2+ in compounds 2 and 3 originated from the complete N-alklation of bp/bpp with CH3OH; (ii) templated by H2bp2+, the inorganic anion [Cu2I6]2? of 1 possesses a dinuclear structure, whereas templated by tmbp2+, the inorganic anion [Cu2I4]2? of 2 exhibits a one-dimensional (1D) chain structure; (iii) templated by tmbpp2+, the inorganic anion [Cu4I8]4? of 3 shows a cubane-like structure modified by four terminal I? ions. The photoluminescence analysis indicates that compounds 1 and 2 emit blue light, while compound 3 emits green light. - Graphical abstract: By employing hydrothermal in situ N-alkylation of bp/bpp with CH3OH, three new organically templated iodocuprates(I) were obtained. Display Omitted - Highlights: • Three new organically templated iodocuprates(I) were reported. • Cations tmbp2+ and tmbpp2+ originated from in situ alkylation of bp/bpp with CH3OH. • H+ and I? play a key role in alkylation of bp/bpp with CH3OH. • Photoluminescence emission for iodocuprates(I) is related to Cu···Cu interaction

331

Transient negative ions in benzene. Some N-heterocyclic and mono-substituted derivatives  

International Nuclear Information System (INIS)

Electron transmission spectroscopy is used to study transient negative ions or shape resonances in various benzene derivatives. Because of the long lifetime of these ions (? > 10-14 S) the vibrational structure of their first two electronic states is observed superposed on the total electron cross section curves in the energy range 0-6 eV and the corresponding adiabatic electron affinities are determined. The comparison of the first electron affinity with the first ionization potential and the energy on the first excited state of each of the derivatives is used to characterize the 'donor' substituents on the benzene ring. As a complementary study, these derivatives are studied in the liquid phase using polarography (cyclic voltametry). The linear correlation established between polarographic potentials measured in dimethyl formamide and the electron affinities was used to deduce electron affinities for several molecules which are difficult to measure in the gas phase. (author)

332

Inhibition of oxidative metabolism of tocopherols with ?-N-heterocyclic derivatives of vitamin E  

OpenAIRE

The oxidative metabolism of tocopherols and tocotrienols by monooxygenases is a key factor in the plasma and tissue clearance of forms of vitamin E other than ?-tocopherol. It is well known that a commonly ingested form of vitamin E, ?-tocopherol, has greatly reduced plasma half life (faster clearance) than ?-tocopherol. The tocotrienols are metabolized even faster than ?-tocopherol. Both ?-tocopherol and ?- and ?-tocotrienol possess intriguing biological activities that are different ...

Ohnmacht, Stephan; Nava, Phillip; West, Ryan; Parker, Robert; Atkinson, Jeffrey

2008-01-01

333

Experimental and theoretical study of the kinetics of dissociation in cis-[RuCl2(P-P)(N-N)] type complexes  

International Nuclear Information System (INIS)

The substitution reactions [RuCl2(P-P)(N-N)] + L ? [RuCl(L)(P-P)(N-N)]+ + Cl-, where P.P = 1,4-bis(diphenylphosphino)butane and N-N = 2,2' -bipyridine, 4,4' L-dimethoxy-2,2' L- bipyridine, 4,4' L-dimethylpyridine-2,2' L-bipyridine and 4,4' L-dichloro-2,2' L-bipyridine, L = pyridine (py) or 4-methylpyridine (4-pic), were studied under pseudo-first order conditions. The reactions proceeded by means of a dissociative mechanism. The rate constants of the substitution reactions increased as the pKa of the N-heterocyclic ligands increased and as the oxidation potential of the metal center decreased. The greater the participation of the atomic d orbitals of the metal in the HOMO, according to DFT calculations, the easier is the dissociation of the chloride from the coordination sphere of the complex. In the 31P{1H} NMR spectra of the series of complexes of general formula [RuCl(L)(P-P)(N-N)]PF6, there are two doublets with ?? < 1. This is consistent with products formed by dissociation of the chloride trans to one of the phosphorus atoms in the precursors. (author)

334

Experimental and theoretical study of the kinetics of dissociation in cis-[RuCl{sub 2}(P-P)(N-N)] type complexes  

Energy Technology Data Exchange (ETDEWEB)

The substitution reactions [RuCl{sub 2}(P-P)(N-N)] + L {yields} [RuCl(L)(P-P)(N-N)]{sup +} + Cl{sup -}, where P.P = 1,4-bis(diphenylphosphino)butane and N-N = 2,2' -bipyridine, 4,4' L-dimethoxy-2,2' L- bipyridine, 4,4' L-dimethylpyridine-2,2' L-bipyridine and 4,4' L-dichloro-2,2' L-bipyridine, L = pyridine (py) or 4-methylpyridine (4-pic), were studied under pseudo-first order conditions. The reactions proceeded by means of a dissociative mechanism. The rate constants of the substitution reactions increased as the pK{sub a} of the N-heterocyclic ligands increased and as the oxidation potential of the metal center decreased. The greater the participation of the atomic d orbitals of the metal in the HOMO, according to DFT calculations, the easier is the dissociation of the chloride from the coordination sphere of the complex. In the {sup 31}P{l_brace}{sup 1}H{r_brace} NMR spectra of the series of complexes of general formula [RuCl(L)(P-P)(N-N)]PF{sub 6}, there are two doublets with {Delta}{sigma} < 1. This is consistent with products formed by dissociation of the chloride trans to one of the phosphorus atoms in the precursors. (author)

Monteiro, Marcos C.R.; Machado, Sergio de Paula, E-mail: sergiopm@iq.ufrj.b [Universidade Federal do Rio de Janeiro (UFRJ), RJ (Brazil). Inst. de Quimica; Nascimento, Fabio B.; Valle, Eliana M.A.; Batista, Alzir A. [Universidade Federal de Sao Carlos (UFSCAR), Sao Carlos, SP (Brazil). Dept. de Quimica; Ellena, Javier; Castellano, Eduardo E. [Universidade de Sao Paulo (IFSC/USP), Sao Carlos, SP (Brazil). Inst. de Fisica

2010-07-01

335

Synthesis of a carbene transfer organometallic polymer and application to forming a recyclable heterogeneous catalyst for the Suzuki reactions of aryl chlorides.  

Science.gov (United States)

An efficient and versatile synthetic approach to NHC-based organometallic polymers has been developed by a simple three-step synthesis. A novel brush polymer having imidazolium salt side chains (P2) was firstly synthesized through postpolymerization modification of P1, which permits access to Ag(I)-NHC-based side chain polymer (P3) at room temperature in high yield. P3 was applied as a carbene transfer agent to form a Pd-NHC-containing polymer (P4) by the transmetallation reaction of Ag(I)-NHCs in the side chains. Inductively coupled plasma atomic emission spectroscopy (ICP-AES) analysis indicated that 77% of Ag(I)-NHCs in the side chains of P3 were transmetallated. The resulting Pd-NHC-containing polymer (P4) showed high catalytic activity and reusability in the Suzuki reactions of aryl chlorides and aryl boronic acids. This novel Pd-NHC-containing polymeric catalyst was used five times and still remained active giving the desired biaryl products in 70% yield in the fifth run of the cross-coupling reaction of deactivated 4-chloroanisole with phenylboronic acid. PMID:19789786

Zeng, Xiaoming; Zhang, Tongxin; Qin, Yuancheng; Wei, Zhijun; Luo, Meiming

2009-10-21

336

THEORETICAL STUDY OF THE MECHANISM OF CYCLOADDITION REACTION BETWEEN DICHLORO-SILYLENE CARBENE(CL2SI=C:) AND ACETONE  

Scientific Electronic Library Online (English)

Full Text Available SciELO Chile | Language: English Abstract in english The mechanism of the cycloaddition reaction between singlet dichloro-silylene carbene and acetone has been investigated with DFT, including geometry optimization and vibrational analysis for the involved stationary points on the potential energy surface. The energies of the different conformations a [...] re calculated by CCSD(T)//B3LYP/6-31G* method. From the potential energy profile, it can be predicted that the reaction has two competitive dominant reaction pathways. The channel (I) consists of two steps: (1) the two reactants firstly form a four-membered ring intermediate through a barrier-free exothermic reaction of 307.1 kJ/mol; (2) four-membered ring intermediate then isomerizes to a CH3-transfer product via a transition state with energy barrier of 11.3 kJ/mol. The process of channel (II) is as following: on the basis of four-membered ring intermediate created between the two reactants, four-membered ring intermediate further reacts with acetone to form the intermediate through a barrier-free exothermic reaction of 165.8 kJ/mol; Then, intermediate isomerizes to a silicic bis-heterocyclic product via a transition state, for which the barrier is 57.6 kJ/mol.

XIUHUI, LU; PINGPING, XIANG; LEYI, SHI; JUNFENG, HAN; ZHENXIA, LIAN.

337

Drug-loaded, bivalent-bottle-brush polymers by graft-through ROMP  

OpenAIRE

Graft-through ring-opening metathesis polymerization (ROMP) using ruthenium N-heterocyclic carbene catalysts has enabled the synthesis of bottle-brush polymers with unprecedented ease and control. Here we report the first bivalent-brush polymers; these materials were prepared by graft-through ROMP of drug-loaded polyethylene-glycol (PEG) based macromonomers (MMs). Anticancer drugs doxorubicin (DOX) and camptothecin (CT) were attached to a norbornene-alkyne-PEG MM via a photocleavable linker. ...

Johnson, Jeremiah A.; Lu, Ying Y.; Burts, Alan O.; Xia, Yan; Durrell, Alec C.; Tirrell, David A.; Grubbs, Robert H.

2010-01-01

338

Asymmetric NHC-Catalyzed Addition of Enals to Nitroalkenes: Controlling Stereochemistry Via the Homoenolate Reactivity Pathway To Access ?-Lactams  

OpenAIRE

An asymmetric intermolecular reaction between enals and nitroalkenes to yield ?-nitroesters has been developed, catalyzed by a novel chiral N-heterocyclic carbene. Key to this work was the development of a catalyst that favors the ?-nitroester pathway over the established Stetter pathway. The reaction proceeds in high stereoselectivity and affords the previously unreported syn diastereomer. We also report an operationally facile two-step, one-pot procedure for the synthesis of ?-lactams.

White, Nicholas A.; Dirocco, Daniel A.; Rovis, Tomislav

2013-01-01

339

Asymmetric Pd-NHC*-catalyzed coupling reactions  

OpenAIRE

Very high asymmetric inductions result in the Pd-catalyzed intramolecular arylation of amides to give 3,3-disubstituted oxindoles when new in situ-generated chiral N?heterocyclic carbene (NHC*) ligands are employed. Structural studies show that conformational locking to minimize allylic strain is the key to understanding the function of these ligands. New applications of these ligands in the frontier area of asymmetric coupling reactions involving C(sp3)–H bonds are detailed. Highly enant...

Kundig, Ernst Peter; Jia, Yixia; Katayev, Dmitry; Nakanishi, Masafumi

2012-01-01

340

1-(1H-Benzimidazol-1-ylmeth­yl)-3-[2-(di­isopropyl­amino)eth­yl]-1H-benzimid­azolium bromide 0.25-hydrate  

OpenAIRE

The title N-heterocyclic carbene derivative, C23H30N5+·Br?·0.25H2O, was synthesized using microwave heating and was characterized by 1H and 13C NMR spectroscopy and a single-crystal X-ray diffraction study. The structure of the title compound are stabilized by a network of intra- and intermolecular C—H...Br hydrogen-bonding interactions. The crystal structure is further stabilized by ?–? stacking interactions between benzene an...

Hakan Arslan; Don VanDerveer; Serpil Demir; smail Özdemir; Bekir Çetinkaya

2009-01-01

341

Modelling fundamental arene-borane contacts: spontaneous formation of a dibromoborenium cation driven by interaction between a borane Lewis acid and an arene ? system.  

OpenAIRE

Reaction of 2,6-dimesityl pyridine (L(py)) with BBr(3) leads to the spontaneous formation of the trigonal dibromoborenium cation [L(py)·BBr(2)](+)via bromide ejection. Systematic structural and computational studies, and the reactivity displayed by a closely related N-heterocyclic carbene (NHC) donor, reveal the role played by arene-borane interactions in this chemistry. [L(py)·BBr(2)](+) features a structurally characterized (albeit weak) electrostatic interaction between the borane Lewis ...

Mansaray, Hb; Rowe, Ad; Phillips, N.; Niemeyer, J.; Kelly, M.; Addy, Da; Bates, Ji; Aldridge, S.

2011-01-01

342

Frontispiece: On the Reactivity of Tetrakis(trifluoromethyl)cyclopentadienone towards Carbon-Based Lewis Bases.  

Science.gov (United States)

Organic Lewis Acids Tetrakis(trifluoromethyl)cyclopentenedione has been described to form Lewis adducts with phosphines through the oxygen atom. This reactivity is quite counterintuitive as it requires the Umpolung of its carbonyl group. In their Communication on page?2744?ff., M. Alcarazo et al. investigate the mechanism of this and related transformations, in which N-heterocyclic carbenes and isonitriles are used as nucleophiles. PMID:25645899

Holle, Sigrid; Escudero, Daniel; Inés, Blanca; Rust, Jörg; Thiel, Walter; Alcarazo, Manuel

2015-02-01

343

Haloaurate and halopalladate imidazolium salts: structures, properties, and use as precursors for catalytic metal nanoparticles.  

OpenAIRE

The synthesis and characterisation of a series of new gold- and palladium-containing symmetrical imidazolium salts are described which display significant cation-dependent effects determined by the structure of the alkyl chains of the imidazolium motifs. Whereas direct reduction of the Pd salts can produce stable nanoparticles (NPs) coated by imidazolium salts, the addition of strong base to the Pd or Au salts before reduction gives stable NPs, potentially pacified by N-heterocyclic carbene u...

Serpell, Cj; Cookson, J.; Thompson, Al; Brown, Cm; Beer, Pd

2013-01-01

344

On the Reactivity of Tetrakis(trifluoromethyl)cyclopentadienone towards Carbon-Based Lewis Bases.  

Science.gov (United States)

The reactivitiy of tetrakis(trifluoromethyl)cyclopentadienone towards different C-based Lewis bases, such as N-heterocyclic carbenes (NHC), ylides and isonitriles, are reported. While sterically not hindered carbenes were found to yield kinetic adducts by regiospecific nucleophilic attack at the position adjacent to the carbonyl group of the ketone, bulkier nucleophiles afforded the thermodynamically more stable O-bridged zwitterions. Interestingly, isonitriles were found to dimerize and trimerize under the same reaction conditions, forming bicyclic products that evolve differently depending on the nature of the substituents. PMID:25504921

Holle, Sigrid; Escudero, Daniel; Inés, Blanca; Rust, Jörg; Thiel, Walter; Alcarazo, Manuel

2015-02-01

345

Organic-Inorganic Hybrid Silica Material Derived from a Monosilylated Grubbs-Hoveyda Ruthenium Carbene as a Recyclable Metathesis Catalyst  

Directory of Open Access Journals (Sweden)

Full Text Available The synthesis of a monosilylated Grubbs-Hoveyda ruthenium alkylidene complex is described, as well as the preparation and characterization of the corresponding material by sol-gel cogelification with tetraethoxysilane (TEOS and the assay of this recyclable supported catalyst in ring-closing diene and enyne metathesis reactions under thermal and microwave conditions.

Michel Wong Chi Man

2010-08-01

346

Designing the "search pathway" in the development of a new class of highly efficient stereoselective hydrosilylation catalysts.  

Science.gov (United States)

The direct coupling of oxazolines and N-heterocyclic carbenes leads to chelating C,N ancillary ligands for asymmetric catalysis that combine both an "anchor" unit and a stereodirecting element. Reacting various N-substituted imidazoles with 2-bromo-4(S)-tert-butyl- and 2-bromo-4(S)-isopropyloxazoline gave the imidazolium precursors of the stereodirecting ancillary ligands. A library of ten different ligand precursors was obtained by using this simple procedure (65-97 % yield). These protioligands were metalated in a subsequent step by reaction with [{Rh(mu-OtBu)(nbd)}2] (nbd=norbornadiene), generated in situ from KOtBu and [{RhCl(nbd)}2] giving the corresponding N-heterocyclic carbene complexes [RhBr(nbd)(oxazolinyl-carbene)] 4 a-j in good yields. X-ray diffraction studies of two of the rhodium complexes, 4 d and 4 j, established a distorted square-pyramidal coordination geometry with the bromo ligand occupying the apical position. The rhodium-carbene bond length was found to be 2.070(4) A (4 d) and 2.012(3) A (4 j). Complexes 4 a-j were treated with AgBF4 in dichloromethane, giving the active cationic square-planar catalysts for the hydrosilylation of ketones. As a reference reaction for the catalyst optimisation, the hydrosilylation of acetophenone with diphenylsilane was studied and the system optimised with respect to the counterion (BF(4) (-)), solvent (THF) and the silane reducing agent (diphenylsilane). The reaction product (1-phenylethanol) was obtained with the highest enantiomeric excess (ee) by carrying out the reaction at -60 degrees C, whilst the enantioselectivity drops upon going both to lower and higher temperatures. The observation that the temperature dependence of the ee values goes through a maximum indicated a change in the rate-determining step as the temperature is varied. The determination of the initial reaction rate in the hydrosilylation of acetophenone upon varying the catalyst (4 d) and substrate concentrations at -55 degrees C established a rate law for the initial conversion which is first-order in both substrates as well as the catalyst (Vi = k[4][PhCOMe][Ph2SiH2]). The catalytic system derived from complex 4 d was found to afford high yields and good enantioselectivities in the reduction of various aryl alkyl ketones (acetophenone: 92 % isolated yield and 90 % ee, 2-naphtyl methyl ketone: 99 % yield, 91 % ee). The selectivity for the reduction of prochiral dialkyl ketones is comparable or even superior to the best previously reported for prochiral nonaromatic ketones; whereas cyclopropyl methyl ketone is hydrosilylated with an enantioselectivity of 81 % ee, the increase of the steric demand of one of the alkyl groups leads to improved ee's, reaching 95 % ee in the case of tert-butyl methyl ketone. Linear chain n-alkyl methyl ketones, which are particularly challenging substrates, are reduced in good asymmetric induction, such as 2-octanone (79 % ee) and even 2-butanone (65 % ee). PMID:15744702

César, Vincent; Bellemin-Laponnaz, Stéphane; Wadepohl, Hubert; Gade, Lutz H

2005-04-22

347

Catalysts For Hydrogenation And Hydrosilylation Methods Of Making And Using The Same  

Science.gov (United States)

A compound is provided including an organometallic complex represented by the formula I: wherein M is an atom of molybdenum or tangsten, Cp is substituted or unsubstituted cyclopentadienyl radical represented by the formula [C.sub.5 Q.sup.1 Q.sup.2 Q.sup.3 Q.sup.4 Q.sup.5 ], wherein Q.sup.1 to Q.sup.5 are independently selected from the group consisting of H radical, C.sub.1-20 hydrocarbyl radical, substituted hydrocarbyl radical, halogen radical, halogen-substituted hydrocarbyl radical, --OR, --C(O)R', --CO.sub.2 R', --SiR'.sub.3 and --NR'R", wherein R' and R" are independently selected from the group consisting of H radical, C.sub.1-20 hydrocarbyl radical, halogen radical, and halogen-substituted hydrocarbyl radical, wherein said Q.sup.1 to Q.sup.5 radicals are optionally linked to each other to form a stable bridging group, NHC is any N-heterocyclic carbene ligand, L is either any neutral electron donor ligand, wherein k is a number from 0 to 1 or L is an anionic ligand wherein k is 2, and A.sup.- is an anion. Processes using the organometallic complex as catalyst for hydrogenation of aldehydes and ketones are provided. Processes using the organometallic complex as catalyst for the hydrosilylation of aldehydes, ketones and esters are also provided.

Dioumaev, Vladimir K. (Coram, NY); Bullock, R. Morris (Wading River, NY)

2004-05-18

348

Decomposition Complexes  

OpenAIRE

We introduce decomposition complexes of posets, which generalize order complexes. The main advantage of our construction is that decomposition complexes are closed under taking products. Other special instances of this theory include nested set complexes as well as Bergman complexes.

Dlugosch, Martin

2013-01-01

349

Enthalpies of ligand substitution for [Mo(?5C5H5)(CO)2(NO)] – The role of ?-bonding effects in metal–ligand bond strengths  

International Nuclear Information System (INIS)

Graphical abstract: - Highlights: • Enthalpies of ligand substitution are measured for Mo(C5H5)(CO)2(NO). • Phosphines and N-heterocyclic carbenes are stronger ligands and displace CO. • Backbonding to ?? orbitals is an important part of complex stability. • FTIR studies show shifts to lower wavenumbers of ?-CO and ?-NO. • Structural studies show lengthening of the C-O and N-O bonds. - Abstract: Enthalpies of ligand substitution for [Mo(?5-C5H5)(CO)2(NO)] producing [Mo(?5-C5H5)Mo(CO)(L)(NO)] have been measured by solution calorimetry at 30 °C in THF for L = P(OMe)3 2 2Ph 3 (SIPr = 1,3-bis(2,6-bis(diisopropylphenyl)imidazolinylidene; IPr = 1,3-bis(2,6-bis(diisopropylphenyl)-imidazol-2-ylidene)). The accepting metal fragment [Mo(?5-C5H5)(CO)(NO)] has a vacant site containing strongly ?-accepting carbonyl and nitrosyl ligands and this is shown to influence the stability of the product complex. Infrared studies of both ?CO and ?NO show that metal-to-ligand backbonding increases in the order P(OMe)3 3 5-C5H5)(CO)(IPr)(NO)] and [Mo(?5-C5H5)(CO)(SIPr)(NO)] are reported

350

Synthesis of a stable adduct of dialane(4) (Al2H4) via hydrogenation of a magnesium(I) dimer  

Science.gov (United States)

The desorption of dihydrogen from magnesium(II) hydride, MgH2 (containing 7.6 wt% H), is reversible. MgH2 therefore holds promise as a hydrogen storage material in devices powered by fuel cells. We believed that dimeric magnesium(I) dimers (LMgMgL, L = ?-diketiminate) could find use as soluble models to aid the study of the mechanisms and/or kinetics of the hydrogenation of magnesium and its alloys. Here, we show that LMgMgL can be readily hydrogenated to yield LMg(µ-H)2MgL by treatment with aluminium(III) hydride complexes. In one case, hydrogenation was reversed by treating LMg(µ-H)2MgL with potassium metal. The hydrogenation by-products are the first thermally stable, neutral aluminium(II) hydride complexes to be produced, one of which, [{(IPr)(H)2Al}2] (IPr = :C[{(C6H3-i-Pr2-2,6)NCH}2]), is an N-heterocyclic carbene adduct of the elusive parent dialane(4) (Al2H4). A computational analysis of this compound is presented.

Bonyhady, Simon J.; Collis, David; Frenking, Gernot; Holzmann, Nicole; Jones, Cameron; Stasch, Andreas

2010-10-01

351

Nickel-Triad Complexes of a Side-on Coordinating Distannene.  

Science.gov (United States)

NHC adducts of the stannylene Trip2 Sn (Trip=2,4,6-triisopropylphenyl) were reacted with zero-valent Ni, Pd, and Pt precursor complexes to cleanly yield the respective metal complexes featuring a three-membered ring moiety Sn-Sn-M along with carbene transfer onto the metal and complete substitution of the starting ligands. Thus the easily accessible NHC adducts to stannylenes are shown to be valuable precursors for transition-metal complexes with an unexpected Sn?Sn bond. The complexes have been studied by X-ray diffraction and NMR spectroscopy as well as DFT calculations. The compounds featuring the structural motif of a distannametallacycle comprised of a [(NHC)2 M(0) ] fragment and Sn2 Trip4 represent rare higher congeners of the well-known olefin complexes. DFT calculations indicate the presence of a ?-type Sn-Sn interaction in these first examples for acyclic distannenes symmetrically coordinating to a zero-valent transition metal. PMID:25656569

Sindlinger, Christian P; Weiß, Sebastian; Schubert, Hartmut; Wesemann, Lars

2015-03-23

352

Highly nucleophilic acetylide, vinyl, and vinylidene complexes. Final progress report, 1 January 1991--31 March 1994  

Energy Technology Data Exchange (ETDEWEB)

In the course of this research the authors found that the anionic alkynyl complex [Cp{prime}(CO)(PPh{sub 3})Mn-C{triple_bond}C-CH{sub 3}]{sup {minus}} can be generated in situ by the addition of two equivalents of n-BuLi to a solution of the carbene complex Cp{prime}(CO)(PPh{sub 3})Mn{double_bond}C(OMe)CH{sub 2}CH{sub 3}. It was also found that the highly nucleophilic propynyl complex [Cp(CO)(PPh{sub 3})Mn-C{triple_bond}C-Me]{sup {minus}} reacts with a variety of aldehydes and ketones in the presence of BF{sub 3}{center_dot}Et{sub 2}O to give, after quenching with MeOH, a series of cationic vinylcarbyne complexes of the general form [Cp(CO)(PPh{sub 3})Mn{triple_bond}C-C(Me){double_bond}C(R)(R{prime})]BF{sub 4}. The cationic alkylidyne complexes [Cp(CO){sub 2}M{triple_bond}C-CH{sub 2}R]{sup +} [M = Re, R = H, M = Mn, R = H, Me, Ph] have been found to undergo facile deprotonation to give the corresponding neutral vinylidene complexes Cp(CO){sub 2}M{double_bond}C{double_bond}C(H)R. The authors have also investigated reactions relevant to the halide promoted Fe and Ru catalyzed carbonylation of nitroaromatics. The final part of this work has involved investigations of metal-oxo complexes.

Geoffroy, G.L.

1994-10-04

353

Synthesis, in vitro and in vivo characterization of rhenium tricarbonyl complexes with different bifunctional tridentate ligands  

International Nuclear Information System (INIS)

Discovery of new chelating ligands that bind technetium/rhenium strongly is a priority in the quest toward the design and development of site specific radiopharmaceuticals. The current study on the application of Tc/Re carbonyls in radiopharmaceuticals has been focused on the utility of specific tridentate ligand systems for achieving kinetic inertness and in vivo stability. In this paper, (Bis (2-pyridylmethyl)-amino)-ethylamine(1) (Fig. 1), (Bis (2-pyridylmethyl)-amino)-acetic acid (2) (Fig. 1), L(6-amino-hexyl)-pyridyl-2-methyl- amino-acetic acid (3) (Fig. 2), and picolylamine diacetic acid (4) (Fig. 3) that possessed an NNN, NNO and NOO donor atom sets were synthesized, which can be a good selection for these requirements. The Re(I)-complexes of above four ligands were prepared in good yield with [NEt4]2[ReBr3(CO)3] in water at 75 degree C for 3 h. The complexes were characterized by elemental analysis and spectroscopic methods. The 188Re(I)-complexes of Four ligands were carried out by incubating the fac- [188Re(CO)3(H2O)3]+ fragment for 60 min at 75 degree C in PBS buffer (0.1 M NaCl/0.05 M sodium phosphate buffered, pH 7.4) under nitrogen. After cooling in ice bath, complexes formations were monitored by HPLC. The HPLC analysis demonstrated that the reaction produces in the complex 1 with yield greater than 95% and its retention times was 7.5 min, whichand its retention times was 7.5 min, which is stable for more than 12 h in human serum, and the complex 2 with yield 93% is stable for more than 8 h in human serum, its retention times was 15.5 min, and the complex 3 with yield 90% is stable for more than 10 h in human serum, its retention times was 15.4 min, while the complex 4 with yields more than 92% can be stable 10 h in human serum and its retention time was 15.6 min respectively. The identity of the 188Re-complexes were proved by comparative HPLC studies using samples of the well characterized thenium(I) complexes as reference. In vivo biodistribution studies at 24 hour post-injection were carried out in normal, white mice. The biodistribution data are shown in table 1. The data show: the major part of the complexes cleared efficiently from the blood pool (0.09-0.67%); No organs (apart from liver and kidneys) or tissue was specifically targeted; Low activity (0.25-0.93%) found in the stomach indicated the good in vivo stability of the complexes. In conclusion, four ligands react with fac- [M(CO)3(H2O)3]+ (M=188Re, Re) fragment resulting in four single stable complexes, M(CO)3(1), M(CO)3(2), M(CO)3(3) and M(CO)3(4), containing aromatic N-heterocycles. These ligand systems are attractive for functionalization purposes of biological vectors since they are easy to synthesize. The corresponding complexes with fac-[M(CO)3(H2O)3]+ are in vivo and vitro stable. Thus the proposed strategy of attaching M(CO)3(1), M(CO)3(2), M(CO)3(3) and M(CO)3(4) complexes is promising for labeling of biomolecules. The approach is worthy of further investigation.

354

Trianionic pincer and pincer-type metal complexes and catalysts.  

Science.gov (United States)

Trianionic pincer and pincer-type ligands are the focus of this review. Metal ions from across the periodic table, from main group elements, transition metals, and the rare earths, are combined with trianionic pincer ligands to produce some of the most interesting complexes to appear in the literature over the past decade. This review provides a comprehensive examination of the synthesis, characterization, properties, and catalytic applications of trianionic pincer metal complexes. Some of the interesting applications employing trianionic pincer and pincer-type complexes include: (1) catalyzed aerobic oxidation, (2) alkene isomerization, (3) alkene and alkyne polymerization, (4) nitrene and carbene group transfer, (5) fundamental transformations such as oxygen-atom transfer, (6) nitrogen-atom transfer, (7) O2 activation, (8) C-H bond activation, (9) disulfide reduction, and (10) ligand centered storage of redox equivalents (i.e. redox active ligands). Expansion of the architecture, type of donor atoms, chelate ring size, and steric and electronic properties of trianionic pincer ligands has occurred rapidly over the past ten years. This review is structured according to the type of pincer donor atoms that bind to the metal ion. The type of donor atoms within trianionic pincer and pincer-type ligands to be discussed include: NCN(3-), OCO(3-), CCC(3-), redox active NNN(3-), NNN(3-), redox active ONO(3-), ONO(3-), and SNS(3-). Since this is the first review of trianionic pincer and pincer-type ligands, an emphasis is placed on providing the reader with in-depth discussion of synthetic methods, characterization data, and highlights of these complexes as catalysts. PMID:24927219

O'Reilly, Matthew E; Veige, Adam S

2014-09-01

355

Facile synthetic access to rhenium(II) complexes: activation of carbon-bromine bonds by single-electron transfer.  

Science.gov (United States)

The five-coordinated Re(I) hydride complexes [Re(Br)(H)(NO)(PR(3))(2)] (R=Cy 1 a, iPr 1 b) were reacted with benzylbromide, thereby affording the 17-electron mononuclear Re(II) hydride complexes [Re(Br)(2)(H)(NO)(PR(3))(2)] (R=Cy 3 a, iPr 3 b), which were characterized by EPR, cyclic voltammetry, and magnetic susceptibility measurements. In the case of dibromomethane or bromoform, the reaction of 1 afforded Re(II) hydrides 3 in addition to Re(I) carbene hydrides [Re(=CHR(1))(Br)(H)(NO)(PR(3))(2)] (R(1)=H 4, Br 5; R=Cy a, iPr b) in which the hydride ligand is positioned cis to the carbene ligand. For comparison, the dihydrogen Re(I) dibromide complexes [Re(Br)(2)(NO)(PR(3))(2)(eta(2)-H(2))] (R=Cy 2 a, iPr 2 b) were reacted with allyl- or benzylbromide, thereby affording the monophosphine Re(II) complex salts [R(3)PCH(2)R'][Re(Br)(4)(NO)(PR(3))] (R'=-CH=CH(2) 6, Ph 7). The reduction of Re(II) complexes has also been examined. Complex 3 a or 3 b can be reduced by zinc to afford 1 a or 1 b in high yield. Under catalytic conditions, this reaction enables homocoupling of benzylbromide (turnover frequency (TOF): 3 a 150, 3 b 134 h(-1)) or allylbromide (TOF: 3 a 575, 3 b 562 h(-1)). The reaction of 6 a and 6 b with zinc in acetonitrile affords in good yields the monophosphine Re(I) complexes [Re(Br)(2)(NO)(MeCN)(2)(PR(3))] (R=Cy 8 a, iPr 8 b), which showed high catalytic activity toward highly selective dehydrogenative silylation of styrenes (maximum TOF of 61 h(-1)). Single-electron transfer (SET) mechanisms were proposed for all these transformations. The molecular structures of 3 a, 6 a, 6 b, 7 a, 7 b, and 8 a were established by single-crystal X-ray diffraction studies. PMID:20066700

Jiang, Yanfeng; Blacque, Olivier; Fox, Thomas; Frech, Christian M; Berke, Heinz

2010-02-15

356

Complex chemistry  

Energy Technology Data Exchange (ETDEWEB)

This book introduces complex chemistry with ten chapters, which include development of complex chemistry on history coordination theory and Warner's coordination theory and new development of complex chemistry, nomenclature on complex with conception and define, chemical formula on coordination compound, symbol of stereochemistry, stereo structure and isomerism, electron structure and bond theory on complex, structure of complex like NMR and XAFS, balance and reaction on solution, an organo-metallic chemistry, biology inorganic chemistry, material chemistry of complex, design of complex and calculation chemistry.

Kim, Bong Gon; Kim, Jae Sang; Kim, Jin Eun; Lee, Boo Yeon

2006-06-15

357

Alkane metathesis with the tantalum methylidene [(?SiO)Ta(?CH2)Me2]/[(?SiO)2Ta(?CH2)Me] generated from well-defined surface organometallic complex [(?SiO)Ta(V)Me4].  

Science.gov (United States)

By grafting TaMe5 on Aerosil700, a stable, well-defined, silica-supported tetramethyl tantalum(V) complex, [(?SiO)TaMe4], is obtained on the silica surface. After thermal treatment at 150 °C, the complex is transformed into two surface tantalum methylidenes, [(?SiO)2Ta(?CH2)Me] and [(?SiO)Ta(?CH2)Me2], which are active in alkane metathesis and comparable to the previously reported [(?SiO)2TaHx]. Here we present the first experimental study to isolate and identify a surface tantalum carbene as the intermediate in alkane metathesis. A systematic experimental study reveals a new reasonable pathway for this reaction. PMID:25557135

Chen, Yin; Abou-hamad, Edy; Hamieh, Ali; Hamzaoui, Bilel; Emsley, Lyndon; Basset, Jean-Marie

2015-01-21

358

Solid phase approaches to N-heterocycles using a sulfur linker cleaved by SmI2.  

Science.gov (United States)

A sulfur HASC (alpha-hetero-atom substituted carbonyl) linker has been utilized in solid-phase approaches to oxindoles and tetrahydroquinolones. The route to oxindoles employs the first Pummerer cyclizations on solid phase, whereas the route to tetrahydroquinolones involves a microwave-assisted Heck reaction followed by a Michael cyclization. In both cases, the linker is cleaved in a traceless fashion by electron transfer from samarium(II) iodide. The routes illustrate the compatibility of the linker system with a number of reaction types and its utility for library synthesis. PMID:16901135

McAllister, Laura A; Turner, Kristy L; Brand, Stephen; Stefaniak, Mark; Procter, David J

2006-08-18

359

Preparation of Second Generation Ionic Liquids by Efficient Solvent-Free Alkylation of N-Heterocycles with Chloroalkanes  

Directory of Open Access Journals (Sweden)

Full Text Available Non-conventional techniques, such as microwave (MW and power ultrasound(US as well as combined MW/US irradiation, have been used to promote one-potsynthesis of second-generation ionic liquids (ILs, cutting down reaction times andimproving yields. However, the use of chloroalkanes in the alkylation of N-heterocyclesrequires more drastic conditions if results are to match those obtained with more reactivealkyl halides. The present paper describes a series of MW- or MW/US-promoted ILpreparations starting from chloroalkanes and classic heterocycles (1-methylimidazole,pyridine and 1-methylpyrrolidine. When reactions were carried out under conventionalheating in an oil bath they required longer reaction times and gave poorer yields. 1H-NMRanalysis and ion-exchange chromatography showed that the present solventless procedureafforded ILs of satisfactory purity. The observed high yields (usually 70-98% isolated,and short reaction times showed that a straightforward access to ILs can be also achievedwith the use of alkyl chlorides, resulting in a considerable reduction of costs.

Werner Bonrath

2008-01-01

360

Oxidation of aromatic N-heterocyclic compounds to N-oxides by Verticillium sp. GF39 cells.  

Science.gov (United States)

Verticillium sp. GF39, catalyzing the oxidation of 1-methylisoquinoline to 1-methylisoquinoline N-oxide, was found to be the highest N-oxide producer. Under the optimized reaction conditions, the whole cells of Verticillium sp. GF39 formed 5 mM 1-methylisoquinoline N-oxide from 1-methylisoquinoline with a molar conversion yield of 100% after a 10-h incubation at 20°C. The whole cells also acted on pyridine, 2-methylpyridine, quinoline and isoquinoline and formed the corresponding N-oxides. PMID:23290448

Mitsukura, Koichi; Hayashi, Masafumi; Yoshida, Toyokazu; Nagasawa, Toru

2013-06-01

361

Bucolic Complexes  

CERN Document Server

In this article, we introduce and investigate bucolic complexes, a common generalization of systolic complexes and of CAT(0) cubical complexes. This class of complexes is closed under Cartesian products and amalgamations over some convex subcomplexes. We study various approaches to bucolic complexes: from graph-theoretic and topological viewpoints, as well as from the point of view of geometric group theory. Bucolic complexes can be defined as locally-finite simply connected prism complexes satisfying some local combinatorial conditions. We show that bucolic complexes are contractible, and satisfy some nonpositive-curvature-like properties. In particular, we prove a version of the Cartan-Hadamard theorem, the fixed point theorem for finite group actions, and establish some results on groups acting geometrically on such complexes. We also characterize the 1-skeletons (which we call bucolic graphs) and the 2-skeletons of bucolic complexes. In particular, we prove that bucolic graphs are precisely retracts of Ca...

Brešar, Bostjan; Chepoi, Victor; Gologranc, Tanja; Osajda, Damian

2012-01-01

362

Engaging complexity  

OpenAIRE

In this article, I discuss studies in complexity and its epistemological implications for systematic and practical theology. I argue that engagement with complexity does not necessarily assurea non-reductionist approach. However, if complexity is engaged transversally, it becomes possible to transcend reductionist approaches. Moreover, systematic and practical the ologians can draw on complexity in developing new ways of understanding and, therefore, new ways of describing the focus, epistemi...

Loubser, Gys M.

2014-01-01

363

An electrochemical alternative strategy to the synthesis of ?-lactams  

International Nuclear Information System (INIS)

Electrochemically induced cyclization of bromoamides to ?-lactams has been achieved in room-temperature ionic liquids (RTILs). The use of volatile, organic solvents (VOCs) and of supporting electrolytes may be avoided. Proton exchange reaction between amide substrates and suitable electrogenerated bases gives rise to a C4 carbanion which undergoes cyclization to ?-lactam via intramolecular nucleophilic substitution (C3-C4 bond formation). ?-Lactams have been isolated in good to elevated yields. The 'non innocent' nature of the RTILs (imidazolium-based salts) is considered. Proton exchange reaction between N-dialkylimidazolium cation and EGB yielding N-heterocyclic carbene is discussed

364

Phosphine modified cobalt hydroformylation  

Energy Technology Data Exchange (ETDEWEB)

An ongoing challenge in phosphine modified cobalt hydroformylation is the fundamental understanding of the electronic and steric properties of phosphine ligands that influence the selectivity and activity of the catalytic reaction. A series of acyclic and cyclic phosphines have been prepared and tested in phosphine modified cobalt hydroformylation of 1-octene. Molecular modelling on a series of phospholanes showed some interesting theoretical and experimental correlations. We also evaluated the use of N-heterocyclic carbenes as an alternative for phosphines in modified cobalt hydroformylation. (orig.)

Rensburg, H. van; Tooze, R.P.; Foster, D.F. [Sasol Technology UK, St. Andrews (United Kingdom); Janse van Rensburg, W. [Sasol Technology, Sasolburg (South Africa)

2006-07-01

365

Palladium-catalyzed ?-arylation of arylketones at low catalyst loadings.  

Science.gov (United States)

A general catalytic protocol for the ?-arylation of aryl ketones has been developed. It involves the use of a preformed, bench-stable Pd-N-heterocyclic carbene pre-catalyst bearing IHept as an ancillary ligand, and allows the coupling of various functionalized coupling partners at very low catalyst loading. Careful choice of the solvent/base system was crucial to obtain optimum catalyst performance. The pre-catalyst was also successfully tested in the synthesis of an industrially relevant compound. PMID:25414140

Marelli, Enrico; Corpet, Martin; Davies, Sian R; Nolan, Steven P

2014-12-22

366

Controlling complexity  

International Nuclear Information System (INIS)

Complex systems have the property that many competing behaviors are possible, and the system tends to alternate among them. In fact, the ability of a complex system to access many different states, combined with its sensitivity, offers great flexibility in manipulating the system's dynamics to select a desired behavior. By understanding dynamically how some of the complex features arise, we show that it is indeed possible to control a complex system's behavior. This is illustrated by using the noisy double rotor map as a paradigm. copyright 1995 The American Physical Society

367

Designing Complexity  

Science.gov (United States)

This article considers the nature of complexity and design, as well as relationships between the two, and suggests that design may have much potential as an approach to improving human performance in situations seen as complex. It is developed against two backgrounds. The first is a world view that derives from second order cybernetics and radical…

Glanville, Ranulph

2007-01-01

368

Hamiltonian complexity  

International Nuclear Information System (INIS)

In recent years we have seen the birth of a new field known as Hamiltonian complexity lying at the crossroads between computer science and theoretical physics. Hamiltonian complexity is directly concerned with the question: how hard is it to simulate a physical system? Here I review the foundational results, guiding problems, and future directions of this emergent field.

369

Complex derivatives  

Science.gov (United States)

The intrinsic complexity of the financial derivatives market has emerged as both an incentive to engage in it, and a key source of its inherent instability. Regulators now faced with the challenge of taming this beast may find inspiration in the budding science of complex systems.

Battiston, Stefano; Caldarelli, Guido; Georg, Co-Pierre; May, Robert; Stiglitz, Joseph

2013-03-01

370

Lutetium-methanediide-alkyl complexes: synthesis and chemistry.  

Science.gov (United States)

The first four-coordinate methanediide/alkyl lutetium complex (BODDI)Lu2 (CH2 SiMe3 )2 (?2 -CHSiMe3 )(THF)2 (BODDI=ArNC(Me)CHCOCHC(Me)NAr, Ar=2,6-iPr2 C6 H3 ) (1) was synthesized by a thermolysis methodology through ?-H abstraction from a Lu-CH2 SiMe3 group. Complex 1 reacted with equimolar 2,6-iPrC6 H3 NH2 and Ph2 C+O to give the corresponding lutetium bridging imido and oxo complexes (BODDI)Lu2 (CH2 SiMe3 )2 (?2 -N-2,6-iPr2 C6 H3 )(THF)2 (2) and (BODDI)Lu2 (CH2 SiMe3 )2 (?2 -O)(THF)2 (3). Treatment of 3 with Ph2 C=O (4?equiv) caused a rare insertion of Lu-?2 -O bond into theC=O group to afford a diphenylmethyl diolate complex 4. Reaction of 1 with PhN=C=O (2?equiv) led to the migration of SiMe3 to the amido nitrogen atom to give complex (BODDI)Lu2 (CH2 SiMe3 )2 -?-{PhNC(O)CHC(O)NPh(SiMe3 )-?(3) N,O,O}(THF) (5). Reaction of 1 withtBuN=C formed an unprecedented product (BODDI)Lu2 (CH2 SiMe3 ){?2 -[?(2) :?(2) -tBuN=C(=CH2 )SiMe2 CHC=NtBu-?(1) N]}(tBuN=C)2 (6) through a cascade reaction of N=C bond insertion, sequential cyclometalative ?-(sp(3) )-H activation, C=C bond formation, and rearrangement of the newly formed carbene intermediate. The possible mechanistic pathways between 1, PhN=C=O, and tBuN=C were elucidated by DFT calculations. PMID:25284379

Li, Shihui; Wang, Meiyan; Liu, Bo; Li, Lei; Cheng, Jianhua; Wu, Chunji; Liu, Dongtao; Liu, Jingyao; Cui, Dongmei

2014-11-17

371

Complexity International  

Science.gov (United States)

Complexity International (CI) is an electronic journal devoted to "the field of complex systems, the generation of complex behaviour from the interaction of multiple parallel processes." The journal covers a wide variety of topics, including genetic algorithms, neural networks, and chaos theory. Because much of the focus is based on technological imitation of biological processes, some of the papers are closely tied to the life sciences. Volumes are added to on a continual basis as papers are accepted. Due to the lengthy acceptance process, it is especially useful that the CI Web site offers drafts of current submissions.

372

Unusual carbon monoxide activation, reduction, and homologation reactions of 5f-element organometallics: the chemistry of carbene-like dihaptoacyls  

International Nuclear Information System (INIS)

This article reviews recent results on the chemical, spectral and structural properties of bis(pentamethylcyclopentadienyl) thorium and uranium dihaptoacyl complexes produced by migratory insertion of carbon monoxide into actinide-carbon sigma bonds. The high coordinative unsaturation and oxygen affinity of the ligation environment produces a marked perturbation of the bonding and reactivity toward that of a coordinated oxycarbene: M(eta2-OCR). Reactivity patterns observed include hydrogen atom and trimethylsilyl migration to the acyl carbon, as well as coupling with additional carbon monoxide to produce a dimeric complex of the enedionediolate ligand, OC(R)(anti O)C=C(anti O)(R)CO. The dihaptoacyls insert into the Th-H bond of ]Th[(CH3)5C5]2H2]2. For Th[(CH3)5C5]2[eta2-COCH2C(CH3)3]Cl, this results, via ?-hydride elimination, in catalytic isomerization to Th[(CH3)5C5]2-[trans-OC(H)=C(H)C(CH3)3]. In the presence of hydrogen gas, the hydride catalytically hydrogenates the dihaptoacyls to alkoxides (M(eta2-COR)?M-OCH2R). Mechanistic studies include kinetic measurements as well as isotopic labelling and stereochemical analysis. 102 references

373

Complex Numbers  

Science.gov (United States)

Written by Tony R. Kuphaldt and Jason Starck, this chapter of All About Circuit's second volume on Alternating Current describes complex numbers: "In order to successfully analyze AC circuits, we need to work with mathematical objects and techniques capable of representing these multi-dimensional quantities. Here is where we need to abandon scalar numbers for something better suited: complex numbers." In addition to the introduction and credits to contributors, the chapter has seven sections: Vectors and AC waveforms, Simple vector addition, Complex vector addition, Polar and rectangular notation, Complex number arithmetic, More on AC "polarity," and Some examples with AC circuits. Each section has clear illustrations and a concise, bulleted review of what was covered at the end.

Kuphaldt, Tony R.

374

Complex Covariance  

Directory of Open Access Journals (Sweden)

Full Text Available According to some generalized correspondence principle the classical limit of a non-Hermitian quantum theory describing quantum degrees of freedom is expected to be the well known classical mechanics of classical degrees of freedom in the complex phase space, i.e., some phase space spanned by complex-valued space and momentum coordinates. As special relativity was developed by Einstein merely for real-valued space-time and four-momentum, we will try to understand how special relativity and covariance can be extended to complex-valued space-time and four-momentum. Our considerations will lead us not only to some unconventional derivation of Lorentz transformations for complex-valued velocities, but also to the non-Hermitian Klein-Gordon and Dirac equations, which are to lay the foundations of a non-Hermitian quantum theory.

Frieder Kleefeld

2013-01-01

375

Decomposition Complexity  

CERN Document Server

We consider a problem of decomposition of a ternary function into a composition of binary ones from the viewpoint of communication complexity and algorithmic information theory as well as some applications to cellular automata.

Shen, Alexander

2010-01-01

376

Complex Networks  

Science.gov (United States)

1. Introduction; Part I. Random Network Models: 2. The Erdos-Renyi models; 3. Observations in real-world networks; 4. Models for complex networks; 5. Growing network models; Part II. Structure and Robustness of Complex Networks: 6. Distances in scale-free networks - the ultra small world; 7. Self-similarity in complex networks; 8. Distances in geographically embedded networks; 9. The network's structure - the generating function method; 10. Percolation on complex networks; 11. Structure of random directed networks - the bow tie; 12. Introducing weights - bandwidth allocation and multimedia broadcasting; Part III. Network Function - Dynamics and Applications: 13. Optimization of the network structure; 14. Epidemiological models; 15. Immunization; 16. Thermodynamic models on networks; 17. Spectral properties, transport, diffusion and dynamics; 18. Searching in networks; 19. Biological networks and network motifs; Part IV. Appendices; References; Index.

Cohen, Reuven; Havlin, Shlomo

2010-07-01

377

Statistical Complexity  

CERN Document Server

The understanding of electron density as the carrier of all the information of a multielectronic system is implicit in the theorems of density functional theory. Information theoretical based measures giving a quantitative understanding of statistical complexity of such systems is shaping up as a new area of research in chemical physics. This book is the first monograph of its kind covering the aspects of complexity measure in atoms and molecules.

Sen, Kalidas D

2011-01-01

378

Gold-catalyzed cycloisomerization of 1,6-diyne esters to 1H-cyclopenta[b]naphthalenes, cis-cyclopenten-2-yl ?-diketones, and bicyclo[3.2.0]hepta-1,5-dienes.  

Science.gov (United States)

A synthetic method to chemoselectively prepare 1H-cyclopenta[b]naphthalenes, cis-cyclopenten-2-yl ?-diketones, and bicyclo[3.2.0]hepta-1,5-dienes efficiently by gold-catalyzed cycloisomerization of 1,6-diyne esters is described. These three product classes were accessed divergently by taking advantage of the electronic and steric differences between a phosphine and NHC (NHC = N-heterocyclic carbene) ligand in the respective gold(I) complexes and that of gold(III) complex combined with substrate substitution patterns and optimized reaction conditions. In the presence of [PhCNAuIPr](+)SbF6(-) (IPr = 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidine) as the catalyst, substrates with a pendant aryl group at the acetate alkynyl position were found to undergo preferential 1,3-acyloxy migration/5-exo-dig cyclization/Friedel-Crafts reaction to give 1H-cyclopenta[b]naphthalenes. In contrast, the analogous reactions with PicAuCl2 (Pic =2-picolinate) were found to proceed by selective 1,3-acyloxy migration/5-exo-dig cyclization/1,5-acyl migration to afford cis-cyclopenten-2-yl ?-diketones. Changing the catalyst to [MeCNAu(JohnPhos)](+)SbF6(-) (JohnPhos = (1,1'-biphenyl-2-yl)-di-tert-butylphosphine) and the acetate alkynyl position from an aryl to vinyl substituent in the starting ester led to 1,3-acyloxy migration/5-exo-dig cyclization/Prins-type [2 + 2]-cycloaddition to provide bicyclo[3.2.0]hepta-1,5-dienes. PMID:25263810

Li, Dan; Rao, Weidong; Tay, Guan Liang; Ayers, Benjamin James; Chan, Philip Wai Hong

2014-12-01

379

Gold-catalyzed cycloisomerization of 1,7-enyne esters to structurally diverse cis-1,2,3,6-tetrahydropyridin-4-yl ketones.  

Science.gov (United States)

A synthetic method that relies on gold(I)-catalyzed cycloisomerization of 1,7-enyne esters to prepare highly functionalized cis-1,2,3,6-tetrahydropyridin-4-yl ketone derivatives in good to excellent yields and as a single regio-, diastereo-, and enantiomer is described. By taking advantage of the distinctive differences in the electronic and steric properties between an NHC (NHC = N-heterocyclic carbene) and phosphine ligand in the respective gold(I) complexes, a divergence in product selectivity was observed. In the presence of [PhCNAuIPr](+)SbF6(-) (IPr = 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidine) as the catalyst, tandem 1,3-acyloxy migration/6-exo-trig cyclization/1,5-acyl migration of the substrate was found to selectively occur to give the ?-diketone-substituted 1,2,3,6-tetrahydropyridine adduct. In contrast, reactions with the gold(I) phosphine complex [MeCNAu(JohnPhos)](+)SbF6(-) (JohnPhos = (1,1'-biphenyl-2-yl)-di-tert-butylphosphine) as the catalyst was discovered to result in preferential 1,3-acyloxy migration/6-exo-trig cyclization/hydrolysis of the 1,7-enyne ester and formation of the cis-1,2,3,6-tetrahydropyridin-4-yl ketone derivative. The utility of this piperidine forming strategy as a synthetic tool that makes use of 1,7-enyne esters was exemplified by its application to the synthesis of an enantiopure analogue of the bioactive 2,3,4,4a,5,9b-hexahydroindeno[1,2-c]pyridine family of compounds. PMID:23458312

Rao, Weidong; Sally; Koh, Ming Joo; Chan, Philip Wai Hong

2013-04-01

380

Controlling complexity  

Science.gov (United States)

Complex systems and dynamics are present in many parts of daily life and branches of science. This participation is continuation of our previous research, that introduced a novelty method of visualization and possible control of complex networks, that are used to visualize dynamics of evolutionary algorithms. Selected evolutionary algorithms are used as an example in order to show how its behavior can be understood as complex network and controlled via conversion into CML system - a model based on mutually joined nonlinear n equations. The main aim of this investigation was to show that dynamics of evolutionary algorithms can be converted to CML system and then controlled. Selected results of evolutionary controlled CML system are discussed here.

Zelinka, Ivan; Skanderova, Lenka; Davendra, Donald D.; Senkerik, Roman; Oplatkova, Zuzana

2012-09-01

381

Communication Complexity  

OpenAIRE

The first section starts with the basic definitions following mainly the notations of the book written by E. Kushilevitz and N. Nisan. At the end of the first section I examine tree-balancing. In the second section I summarize the well-known lower bound methods and prove the exact complexity of certain functions. In the first part of the third section I introduce the random complexity and prove the basic lemmas about it. In the second part I prove a better lower bound...

Pa?lvo?lgyi, Do?mo?to?r

2010-01-01

382

Experimental and theoretical study of the kinetics of dissociation in cis-[RuCl2(P-P)(N-N)] type complexes  

Scientific Electronic Library Online (English)

Full Text Available SciELO Brazil | Language: English Abstract in portuguese As reações de substituição [RuCl2(P-P)(N-N)] + L ? [RuCl(L)(P-P)(N-N)]+ + Cl-, onde P-P = 1,4-bis(difenilfosfino)butano e N-N = 2,2´-bipiridina, 4,4´-dimetóxi-2,2´-bipiridina, 4,4´-dimetil-2,2´-bipiridina e 4,4´-dicloro-2,2´-bipiridina, L = piridina (py) ou 4-metilpiridina (4-pic), foram estudadas s [...] ob condições de pseudo-primeira ordem. As reações ocorrem por um mecanismo dissociativo e as constantes de velocidade nas reações de substituição aumentam com o aumento do pKa dos ligantes N-heterocíclicos e com a diminuição dos potenciais de oxidação do centro metálico. Quanto mais alta é a porcentagem de participação dos orbitais atômicos d do metal na formação do HOMO, conforme calculado pelo método DFT, mais fácil é a dissociação do cloreto da esfera de coordenação do complexo. Nos espectros de 31P{¹H} RMN da série de complexos de fórmula geral [RuCl(L)(P-P)(N-N)]PF6, há dois dubletos com ?? Abstract in english The substitution reactions [RuCl2(P-P)(N-N)] + L ? [RuCl(L)(P-P)(N-N)]+ + Cl-, where P-P = 1,4-bis(diphenylphosphino)butane and N-N = 2,2´-bipyridine, 4,4´-dimethoxy-2,2´-bipyridine, 4,4´-dimethylpyridine-2,2´-bipyridine and 4,4´-dichloro-2,2´-bipyridine, L = pyridine (py) or 4-methylpyridine (4-pic [...] ), were studied under pseudo-first order conditions. The reactions proceeded by means of a dissociative mechanism. The rate constants of the substitution reactions increased as the pKa of the N-heterocyclic ligands increased and as the oxidation potential of the metal center decreased. The greater the participation of the atomic d orbitals of the metal in the HOMO, according to DFT calculations, the easier is the dissociation of the chloride from the coordination sphere of the complex. In the 31P{¹H} NMR spectra of the series of complexes of general formula [RuCl(L)(P-P)(N-N)]PF6, there are two doublets with ??

Marcos C. R., Monteiro; Fabio B., Nascimento; Eliana M. A., Valle; Javier, Ellena; Eduardo E., Castellano; Alzir A., Batista; Sergio de Paula, Machado.

1992-19-01

383

Metal-Mediated Couplings of Primary Alcohols with Amines and Carbohydrates  

DEFF Research Database (Denmark)

The work presented in this thesis was performed at the Department of Chemistry of the Technical University of Denmark during a three year Ph.D. program. The thesis involves two distinct Projects related to organometallic and carbohydrate chemistry. Project 1: Dehydrogenative synthesis of imines from alcohols and amines catalyzed by a ruthenium N-heterocyclic carbene complex. The successful method development and application of a convenient and direct (one step) synthesis of imines from alcohols and amines is described. The developed method provides quick andextended access to structurally diverse and synthetically important imines. The reaction is catalyzed by the ruthenium N-heterocyclic carbene complex [RuCl2(IiPr)(p-cymene)] (3) and proceeds in the presence of the ligand DABCO and molecular sieves with concomitant extrusion of water and hydrogen. A range of different primary alcohols and amines have been coupled in the presence of the catalyst to afford the corresponding imines in moderate to good yields.Optically pure amines gave the corresponding imines without any sign of racemization. Moreover, the one-pot diastereoselective addition of different organometallic reagents to the imine, obtained from the coupling between benzyl alcohol and (R)-1-phenylethylamine, was performed. To address specifics of the reaction mechanism, different experiments with deuterium-labeled benzyl alcohol were carried out indicating that that the catalytically active species is a ruthenium dihydride. The reaction is proposed to proceed by initial dehydrogenation of the alcohol to the aldehyde, which stays coordinated to the ruthenium centre. Then, nucleophilic attack of the amine affords the hemiaminal, which is released from ruthenium and converted into the imine. Project 2: Tin-mediated regioselective 6-O-glycosylations of unprotected phenyl 1-thioglycopyranosides Chemical glycosylation is of outstanding importance to access biologically relevant carbohydrate structures, but classical methods suffer from the disadvantage of extensive protecting group manipulations. Thus, approaches to reduce the number of steps connected to chemical synthesis are highly important. In this thesis approaches to the regioselective glycosylation of fully unprotected phenyl 1-thio-glycopyranoside acceptors via tin activation are described. Tin-mediated Koenigs-Knorr glycosylation of phenyl 1-thio-?-D-glucopyranoside (28), phenyl 1-thio-?-Dgalactopyranoside (32) and phenyl 1-thio-?-D-mannopyranoside (33) with different bromide donors afforded the corresponding (1?6) linked disaccharides in good to moderate yields. The disaccharides obtained from the first coupling can be activated as donors for subsequent tinmediated glycosylation reactions. The activation has been performed following two different strategies. The first involved one-step activation with a thiophilic reagent, while the second employed a two-step activation which entailed first formation of a glycosyl halide, and then activation with a halophilic reagent. This last approach is of particular interest; in fact, thioglycosides can be used as acceptors enabling an iterative oligosaccharide synthesis. Following these strategies a number of different trisaccharides have been successfully synthesized.

Maggi, Agnese; Madsen, Robert

2012-01-01

384

Complex networks  

OpenAIRE

An outline of recent work on complex networks is given from the point of view of a physicist. Motivation, achievements and goals are discussed with some of the typical applications from a wide range of academic fields. An introduction to the relevant literature and useful resources is also given.

Evans, Ts

2004-01-01

385

Nucleophilic substitution in ionizable Fischer thiocarbene complexes: steric effect of the alkyl substituent on the heteroatom.  

Science.gov (United States)

A detailed kinetic study has been carried out for the aminolysis of ionizable Fischer thiocarbene complexes (CO)5M[double bond, length as m-dash]C(SR)CH3 (M = Cr, W; R = iPr, nBu, cHex, tBu) with five primary amines and one secondary amine in aqueous acetonitrile solutions (50% MeCN-50% water (v/v)). The observed rate constants for the reaction with primary amines showed a first-order dependence on the amine concentration, while with morpholine, the rate constant has second-order dependence. The general base catalysis process was confirmed by the variation of the rate constants with the concentration of an external catalyst and the pH. The results agree with a stepwise mechanism where the nucleophilic addition to the carbene carbon to produce a tetrahedral intermediate () is the first step, followed by a rapid deprotonation of to form the anion which leads to the products by general-acid catalysed leaving group (-SR) expulsion. In general, it was found that the chromium complexes are less reactive than the tungsten analogues. The obtained Brønsted parameters for the nucleophilic addition (?nuc) indicate that C-N bond formation has made little progress at the transition state. By using Charton's correlation, the role that the steric factor plays throughout the mechanism has been unraveled. The nucleophilic addition to the thiocarbenes is less sensitive to steric effects than the alkoxycarbenes regardless of the nature of the metal centre. Conversely, the steric effects on the general-base catalysis can be strong depending on the volume of the catalyst and the metal centre. On the basis of the structure-reactivity coefficients ? and ? and comparison with alkoxycarbene complexes, esters and thiolesters, insights into the main factors ruling the reactivity in terms of transition state imbalances are discussed. PMID:25698135

Andrada, Diego M; Zoloff Michoff, Martin E; de Rossi, Rita H; Granados, Alejandro M

2015-03-10

386

Time complexity and gate complexity  

Science.gov (United States)

We formulate and investigate the simplest version of time-optimal quantum computation theory (TO-QCT), where the computation time is defined by the physical one and the Hamiltonian contains only one- and two-qubit interactions. This version of TO-QCT is also considered as optimality by sub-Riemannian geodesic length. The work has two aims: One is to develop a TO-QCT itself based on a physically natural concept of time, and the other is to pursue the possibility of using TO-QCT as a tool to estimate the complexity in conventional gate-optimal quantum computation theory (GO-QCT). In particular, we investigate to what extent is true the following statement: Time complexity is polynomial in the number of qubits if and only if gate complexity is also. In the analysis, we relate TO-QCT and optimal control theory (OCT) through fidelity-optimal computation theory (FO-QCT); FO-QCT is equivalent to TO-QCT in the limit of unit optimal fidelity, while it is formally similar to OCT. We then develop an efficient numerical scheme for FO-QCT by modifying Krotov’s method in OCT, which has a monotonic convergence property. We implemented the scheme and obtained solutions of FO-QCT and of TO-QCT for the quantum Fourier transform and a unitary operator that does not have an apparent symmetry. The former has a polynomial gate complexity and the latter is expected to have an exponential one which is based on the fact that a series of generic unitary operators has an exponential gate complexity. The time complexity for the former is found to be linear in the number of qubits, which is understood naturally by the existence of an upper bound. The time complexity for the latter is exponential in the number of qubits. Thus, both the targets seem to be examples satisfyng the preceding statement. The typical characteristics of the optimal Hamiltonians are symmetry under time reversal and constancy of one-qubit operation, which are mathematically shown to hold in fairly general situations.

Koike, Tatsuhiko; Okudaira, Yosuke

2010-10-01

387

Time complexity and gate complexity  

International Nuclear Information System (INIS)

We formulate and investigate the simplest version of time-optimal quantum computation theory (TO-QCT), where the computation time is defined by the physical one and the Hamiltonian contains only one- and two-qubit interactions. This version of TO-QCT is also considered as optimality by sub-Riemannian geodesic length. The work has two aims: One is to develop a TO-QCT itself based on a physically natural concept of time, and the other is to pursue the possibility of using TO-QCT as a tool to estimate the complexity in conventional gate-optimal quantum computation theory (GO-QCT). In particular, we investigate to what extent is true the following statement: Time complexity is polynomial in the number of qubits if and only if gate complexity is also. In the analysis, we relate TO-QCT and optimal control theory (OCT) through fidelity-optimal computation theory (FO-QCT); FO-QCT is equivalent to TO-QCT in the limit of unit optimal fidelity, while it is formally similar to OCT. We then develop an efficient numerical scheme for FO-QCT by modifying Krotov's method in OCT, which has a monotonic convergence property. We implemented the scheme and obtained solutions of FO-QCT and of TO-QCT for the quantum Fourier transform and a unitary operator that does not have an apparent symmetry. The former has a polynomial gate complexity and the latter is expected to have an exponential one which is based on the fact that a series of generic unitary operators has an exponential gate compley operators has an exponential gate complexity. The time complexity for the former is found to be linear in the number of qubits, which is understood naturally by the existence of an upper bound. The time complexity for the latter is exponential in the number of qubits. Thus, both the targets seem to be examples satisfyng the preceding statement. The typical characteristics of the optimal Hamiltonians are symmetry under time reversal and constancy of one-qubit operation, which are mathematically shown to hold in fairly general situations.

388

Managing Complexity  

Energy Technology Data Exchange (ETDEWEB)

Physical analogs have shown considerable promise for understanding the behavior of complex adaptive systems, including macroeconomics, biological systems, social networks, and electric power markets. Many of today’s most challenging technical and policy questions can be reduced to a distributed economic control problem. Indeed, economically-based control of large-scale systems is founded on the conjecture that the price-based regulation (e.g., auctions, markets) results in an optimal allocation of resources and emergent optimal system control. This paper explores the state of the art in the use physical analogs for understanding the behavior of some econophysical systems and to deriving stable and robust control strategies for them. In particular we review and discussion applications of some analytic methods based on the thermodynamic metaphor according to which the interplay between system entropy and conservation laws gives rise to intuitive and governing global properties of complex systems that cannot be otherwise understood.

Chassin, David P.; Posse, Christian; Malard, Joel M.

2004-08-01

389

Complex mortgages  

OpenAIRE

Complex mortgages became a popular borrowing instrument during the bullish housing market of the early 2000s but vanished rapidly during the subsequent downturn. These non-traditional loans (interest only, negative amortization, and teaser mortgages) enable households to postpone loan repayment compared to traditional mortgages and hence relax borrowing constraints. At the same time, they increase household leverage and heighten dependence on mortgage refinancing to escape changes in contract...

Amromin, Gene; Huang, Jennifer; Sialm, Clemens; Zhong, Edward

2010-01-01

390

Managing Complexity  

OpenAIRE

Physical analogs have shown considerable promise for understanding the behavior of complex adaptive systems, including macroeconomics, biological systems, social networks, and electric power markets. Many of today's most challenging technical and policy questions can be reduced to a distributed economic control problem. Indeed, economically-based control of large-scale systems is founded on the conjecture that the price-based regulation (e.g., auctions, markets) results in a...

Chassin, David P.; Malard, Joel; Posse, Christian

2004-01-01

391

Time complexity and gate complexity  

CERN Document Server

We formulate and investigate the simplest version of time-optimal quantum computation theory (t-QCT), where the computation time is defined by the physical one and the Hamiltonian contains only one- and two-qubit interactions. This version of t-QCT is also considered as optimality by sub-Riemannian geodesic length. There two aims: one is to develop a t-QCT itself based on physically natural concept of time, and the other is to pursue the possibility of using t-QCT as a tool to estimate the complexity in conventional gate-optimal quantum computation theory (g-QCT). In particular, we investigate to what extent is true the statement: time complexity is polynomial in the number of qubits if and only if so is gate complexity. In the analysis, we relate t-QCT and optimal control theory (OCT) through fidelity-optimal computation theory (f-QCT); f-QCT is equivalent to t-QCT in the limit of unit optimal fidelity, while it is formally similar to OCT. We then develop an efficient numerical scheme for f-QCT by modifying ...

Koike, Tatsuhiko

2009-01-01

392

Theoretical research on the effect of regulated ?-conjugation on the photophysical properties of Ir(iii) complexes.  

Science.gov (United States)

In this work, the effect of regulated host and auxiliary ligand ?-conjugation on the photophysical properties of a series of Ir(iii) carbene complexes is examined by using the start-of-the-art theoretical methods. According to our results, all of the lowest-lying and strongest absorption peaks can be assigned as having a mixed ligand-to-ligand/metal-to-ligand charge transfer (LLCT/MLCT) character, but the different ways of introducing phenyl have a great effect on the absorption wavelength variation. In addition, the charge transfer characteristics of lowest-lying emission have some minute differences. In addition, when the extended ?-conjugation is broken, the emission wavelength can be effectively retained due to the similar emission charge transfer related electronic density distribution of occupied molecular orbitals and unoccupied molecular orbitals. However, the larger ?-conjugation can give rise to remarkably blue-shifted emission. This blue-shifted emission can be attributed to the alteration in the transition character due to intense interactions between nearly degenerate unoccupied molecular orbitals. Through the evaluation of the spin-orbit coupling (SOC) effect, we can gain a deeper understanding of the radiative decay rate processes. These results reveal that the larger ?-conjugation can also lead to higher quantum efficiency due to the larger radiative decay and the smaller nonradiative decay rate. Our theoretical studies highlight the role of ?-conjugation of the host and auxiliary ligand, and thus, can pave the way for the design of novel and efficient blue phosphorescent materials. PMID:25785669

Xie, Li-Ming; Bai, Fu-Quan; Li, Wei; Zhang, Zhi-Xiang; Zhang, Hong-Xing

2015-04-01

393

Complex variables  

CERN Document Server

A caution to mathematics professors: Complex Variables does not follow conventional outlines of course material. One reviewer noting its originality wrote: ""A standard text is often preferred [to a superior text like this] because the professor knows the order of topics and the problems, and doesn't really have to pay attention to the text. He can go to class without preparation."" Not so here-Dr. Flanigan treats this most important field of contemporary mathematics in a most unusual way. While all the material for an advanced undergraduate or first-year graduate course is covered, discussion

Flanigan, Francis J

2013-01-01

394

Cosmic Complexity  

Science.gov (United States)

What explains the extraordinary complexity of the observed universe, on all scales from quarks to the accelerating universe? My favorite explanation (which I certainty did not invent) ls that the fundamental laws of physics produce natural instability, energy flows, and chaos. Some call the result the Life Force, some note that the Earth is a living system itself (Gaia, a "tough bitch" according to Margulis), and some conclude that the observed complexity requires a supernatural explanation (of which we have many). But my dad was a statistician (of dairy cows) and he told me about cells and genes and evolution and chance when I was very small. So a scientist must look for me explanation of how nature's laws and statistics brought us into conscious existence. And how is that seemll"!gly Improbable events are actually happening a!1 the time? Well, the physicists have countless examples of natural instability, in which energy is released to power change from simplicity to complexity. One of the most common to see is that cooling water vapor below the freezing point produces snowflakes, no two alike, and all complex and beautiful. We see it often so we are not amazed. But physlc!sts have observed so many kinds of these changes from one structure to another (we call them phase transitions) that the Nobel Prize in 1992 could be awarded for understanding the mathematics of their common features. Now for a few examples of how the laws of nature produce the instabilities that lead to our own existence. First, the Big Bang (what an insufficient name!) apparently came from an instability, in which the "false vacuum" eventually decayed into the ordinary vacuum we have today, plus the most fundamental particles we know, the quarks and leptons. So the universe as a whole started with an instability. Then, a great expansion and cooling happened, and the loose quarks, finding themselves unstable too, bound themselves together into today's less elementary particles like protons and neutrons, liberating a little energy and creating complexity. Then, the expanding universe cooled some more, and neutrons and protons, no longer kept apart by immense temperatures, found themselves unstable and formed helium nuclei. Then, a little more cooling, and atomic nuclei and electrons were no longer kept apart, and the universe became transparent. Then a little more cooling, and the next instability began: gravitation pulled matter together across cosmic distances to form stars and galaxies. This instability is described as a "negative heat capadty" in which extracting energy from a gravitating system makes it hotter -- clearly the 2nd law of thermodynamics does not apply here! (This is the physicist's part of the answer to e e cummings' question: what is the wonder that's keeping the stars apart?) Then, the next instability is that hydrogen and helium nuclei can fuse together to release energy and make stars burn for billions of years. And then at the end of the fuel source, stars become unstable and explode and liberate the chemical elements back into space. And because of that, on planets like Earth, sustained energy flows support the development of additional instabilities and all kinds of complex patterns. Gravitational instability pulls the densest materials into the core of the Earth, leaving a thin skin of water and air, and makes the interior churn incessantly as heat flows outwards. And the heat from the sun, received mostly near the equator and flowing towards the poles, supports the complex atmospheric and oceanic circulations. And because or that, the physical Earth is full of natural chemical laboratories, concentrating elements here, mixing them there, raising and lowering temperatures, ceaselessly experimenting with uncountable events where new instabilities can arise. At least one of them was the new experiment called life. Now that we know that there are at least as many planets as there are stars, it is hard to imagine that nature's ceasess experimentation would not be able to produce life elsewhere

Mather, John C.

2012-01-01

395

Electrochemistry of Fischer alkoxycarbene complexes of chromium: The use of density functional theory to predict and understand oxidation and reduction potentials  

International Nuclear Information System (INIS)

Highlights: •Synthesis, crystal structure and electrochemical study of Fischer ethoxycarbenes. •Density functional theory (DFT) calculated energies of Fischer ethoxycarbenes. •DFT understanding of oxidation and reduction centre of Fischer ethoxycarbenes. •Relationship between first oxidation and first reduction potential and DFT calculated energies. -- Abstract: The electrochemical behaviour of a series of Fischer ethoxycarbene complexes of the type [(CO)5Cr=C(OEt)R] with R = 2-thienyl (1), 2-furyl (2), 2-(N-methylpyrrolyl) (3), N-methyl-2-(2?-thienyl)pyrrole) (4) and 2,2?-thienylfuran (5), is investigated by means of cyclic voltammetry. Results show that the first one electron reduction process is sensitive to the energy, shape and distribution of the LUMO orbital, leading to a linear relationship between the formal reduction potential and the LUMO energy: E0?(Ccarbene) = –0.70 ELUMO–3.44 (R2 = 1.00) which is valid over a large potential range. The dimeric heteroarene substituents of 4 and 5 lead to enhanced stabilization of the reduced complexes 4 and 5, making another one electron reduction possible. The formal reduction potential, E0?(Cr) of the first oxidation process of 1–5 lays within a narrow potential range of 0.43–0.50 V vs. Fc/Fc+, is Cr-based and is mainly sensitive to the electrophilic character of the heteroarene ring directly attached to the carbene carb

396

Complex silumins  

Directory of Open Access Journals (Sweden)

Full Text Available Purpose: The study presents the results of investigations carried out on silumins with additions of Mg, Ni, Cu, Cr, Mo and W. The silumins containing Mg, Cu and Ni are well-known and commonly used in construction of machines and equipment.Design/methodology/approach: Additions of Cr, Mo and W have not been thoroughly investigated yet. They are considered a new family of innovative cast aluminium alloys.Findings: In Al-Si systems they form silicides, like Cr3Si, Mo3Si, W3Si and intermetallic phases of Al13Cr4Si4, Al12Mo, Al12W and AlWSi. The silicides crystallise in cubic lattice of parameters similar to aluminium and silicon.Research limitations/implications: Therefore they can act as crystallisation substrates and occur as separate phases. The examinations under the microscope and X-ray microanalysis of the linear and point distribution of elements confirmed the presence of the above mentioned phases. A combination of two elements, e.g. Cr and Mo, or Cr and W, was observed to cause the formation of complex silicide layers of Mo3Si and (Cr, Mo3Si, or Cr3Si as well as (W, Cr3Si.Originality/value: The presence of the silicides has been indicated as a possible source of the refinement of ?(Al and ?(Si phases. The precipitations of these phases and of the intermetallic phases favour a high degree of the silumins hardening. A characteristic feature is the fact that nucleation and crystallisation of the successive phases takes place at the phase boundaries formed between the previously precipitated phase and solid solution ?. The studies carried out so far have indicated that in complex silumins at high temperatures crystallise the silicides and peritectic phases of Al12W, AlWSi, Al12Mo and Al13Cr4Si4. Phases ? or ? are the next ones to crystallise, followed by complex eutectic ? + ? +Al(Si, Cr, Mo, W, Fe. Further crystallise the phases of Mg2Si, Al3Ni and Al2Cu. The silumins presented here are characterised by high mechanical properties: Rp0,2=320-420MPa, Rm =400-520MPa, A5=0.5-5.0% and elevated hardness of 145-210HB. Further investigations will be carried out to optimise the chemical composition of silumins and the precipitation hardening process parameters to produce alloys characterised by optimum combination of strength, ductility and hardness.

S. Pietrowski

2007-09-01

397

Making oxygen with ruthenium complexes.  

Science.gov (United States)

Mastering the production of solar fuels by artificial photosynthesis would be a considerable feat, either by water splitting into hydrogen and oxygen or reduction of CO(2) to methanol or hydrocarbons: 2H(2)O + 4hnu --> O(2) + 2H(2); 2H(2)O + CO(2) + 8hnu --> 2O(2) + CH(4). It is notable that water oxidation to dioxygen is a key half-reaction in both. In principle, these solar fuel reactions can be coupled to light absorption in molecular assemblies, nanostructured arrays, or photoelectrochemical cells (PECs) by a modular approach. The modular approach uses light absorption, electron transfer in excited states, directed long range electron transfer and proton transfer, both driven by free energy gradients, combined with proton coupled electron transfer (PCET) and single electron activation of multielectron catalysis. Until recently, a lack of molecular catalysts, especially for water oxidation, has limited progress in this area. Analysis of water oxidation mechanism for the "blue" Ru dimer cis,cis-[(bpy)(2)(H(2)O)Ru(III)ORu(III)(OH(2))(bpy)(2)](4+) (bpy is 2,2'-bipyridine) has opened a new, general approach to single site catalysts both in solution and on electrode surfaces. As a catalyst, the blue dimer is limited by competitive side reactions involving anation, but we have shown that its rate of water oxidation can be greatly enhanced by electron transfer mediators such as Ru(bpy)(2)(bpz)(2+) (bpz is 2,2'-bipyrazine) in solution or Ru(4,4'-((HO)(2)P(O)CH(2))(2)bpy)(2)(bpy)(2+) on ITO (ITO/Sn) or FTO (SnO(2)/F) electrodes. In this Account, we describe a general reactivity toward water oxidation in a class of molecules whose properties can be "tuned" systematically by synthetic variations based on mechanistic insight. These molecules catalyze water oxidation driven either electrochemically or by Ce(IV). The first two were in the series Ru(tpy)(bpm)(OH(2))(2+) and Ru(tpy)(bpz)(OH(2))(2+) (bpm is 2,2'- bipyrimidine; tpy is 2,2':6',2''-terpyridine), which undergo hundreds of turnovers without decomposition with Ce(IV) as oxidant. Detailed mechanistic studies and DFT calculations have revealed a stepwise mechanism: initial 2e(-)/2H(+) oxidation, to Ru(IV)=O(2+), 1e(-) oxidation to Ru(V)=(3+), nucleophilic H(2)O attack to give Ru(III)-OOH(2+), further oxidation to Ru(IV)(O(2))(2+), and, finally, oxygen loss, which is in competition with further oxidation of Ru(IV)(O(2))(2+) to Ru(V)(O(2))(3+), which loses O(2) rapidly. An extended family of 10-15 catalysts based on Mebimpy (Mebimpy is 2,6-bis(1-methylbenzimidazol-2-yl)pyridine), tpy, and heterocyclic carbene ligands all appear to share a common mechanism. The osmium complex Os(tpy)(bpy)(OH(2))(2+) also functions as a water oxidation catalyst. Mechanistic experiments have revealed additional pathways for water oxidation one involving Cl(-) catalysis and another, rate enhancement of O-O bond formation by concerted atom-proton transfer (APT). Surface-bound [(4,4'-((HO)(2)P(O)CH(2))(2)bpy)(2)Ru(II)(bpm)Ru(II)(Mebimpy)(OH(2))](4+) and its tpy analog are impressive electrocatalysts for water oxidation, undergoing thousands of turnovers without loss of catalytic activity. These catalysts were designed for use in dye-sensitized solar cell configurations on TiO(2) to provide oxidative equivalents by molecular excitation and excited-state electron injection. Transient absorption measurements on TiO(2)-[(4,4'((HO)(2)P(O)CH(2))(2)bpy)(2)Ru(II)(bpm)Ru(II)(Mebimpy)(OH(2))](4+), (TiO(2)-Ru(II)-Ru(II)OH(2)) and its tpy analog have provided direct insight into the interfacial and intramolecular electron transfer events that occur following excitation. With added hydroquinone in a PEC configuration, APCE (absorbed-photon-to-current-efficiency) values of 4-5% are obtained for dehydrogenation of hydroquinone, H(2)Q + 2hnu --> Q + H(2). In more recent experiments, we are using the same PEC configuration to investigate water splitting. PMID:19817345

Concepcion, Javier J; Jurss, Jonah W; Brennaman, M Kyle; Hoertz, Paul G; Patrocinio, Antonio Otávio T; Murakami Iha, Neyde Yukie; Templeton, Joseph L; Meyer, Thomas J

2009-12-21

398

Complexes of clusters and complexes of stars  

OpenAIRE

Most star complexes are in fact complexes of stars, clusters and gas clouds; term "star complexes" was introduced as general one disregarding the preferential content of a complex. Generally the high rate of star formation in a complex is accompanied by the high number of bound clusters, including massive ones, what was explained by the high gas pressure in such regions. However, there are also complexes, where clusters seems to be more numerous in relation to stars than in ...

Efremov, Yu N.

2005-01-01

399

Synthesis, structure, and reactivity of thienyl-, benzothienyl-, and selenylcarbene complexes of rhenium. A new mechanicm of H/D exchange during hydrodesulfurization  

Energy Technology Data Exchange (ETDEWEB)

A series of [eta][sup 1](E)-coordinated (E = S or Se) thiophene, benzo[b]thiophene and selenophene complexes [Cp(NO)(PPh[sub 3])Re([eta][sup 1](E)-L)][sup +], Cp = C[sub 5]H[sub 5], L = thiophene (T), 2-methylthiophene (2-MeT), 2,5-dimethylthiophene (2,5-Me[sub 2]T), benzo[b]thiophene (BT), 3-methylbenzo[b]thiophene (3-MeBT), selenophene (Sel), 2-methylselenophene (2-MeSel), and 2,5-dimethylselenophene (2,5-Me[sub 2]Sel) are prepared by the reaction of [Cp(NO)(PPh[sub 3])Re(ClC[sub 6]H[sub 5])][sup +] with the appropriate ligand. The T, 2-MeT, BT, 3-MeBT, Sel, 2-MeSel complexes are deprotonated at C(2) by strong, non-nucleophilic bases to give the neutral Cp(NO)(PPh[sub 3])Re(2-L-yl) complexes, where 2-L-yl = 2-thienyl (2-Tyl), 2-5(methylthienyl) (2-(5-MeTyl), 2[minus]benzothienyl (2-BTyl), 2-(3-methylbenzothienyl) (2-3-MeBTyl)), 2-selenyl (2-Selyl), and 2-(5-methylselenyl) (2-5-MeSelyl). The pK[sub a] of the base required to effect this deprotonation increases with the L ligand in the complex in the following order: Sel < T < BT. The 2-Tyl, 2-BTyl and 2-Selyl complexes react with either HBF[sub 4][center dot]Et[sub 2]O or HO[sub 3]SCF[sub 3] at [minus]42[degrees]C to give the corresponding carbene complexes [Cp(NO)(PPh[sub 3])Re(2-L-ylcarbene)][sup +] resulting from protonation at C(3). 43 refs., 2 figs., 5 tabs.

White, C.J.; Angelici, R.J. (Iowa State Univ., Ames, IA (United States))

1994-12-01

400

Synthesis, characterization, and photophysical and electroluminescent properties of blue-emitting cationic iridium(III) complexes bearing nonconjugated ligands.  

Science.gov (United States)

The development of pure-blue-to-deep-blue-emitting ionic phosphors is an ultimate challenge for full-color displays and white-light sources. Herein we report two series of short-wavelength light-emitting cationic iridium(III) complexes with nonconjugated ancillary and cyclometalating ligands, respectively. In the first series, nonconjugated 1-[(diphenylphosphino)methyl]-3-methylimidazolin-2-ylidene-C,C2' (dppmmi) is used as the ancillary ligand and 2-phenylpyridine (ppy), 2-(2,4-difluorophenyl)pyridine (dfppy), and 1-(2,4-difluorophenyl)-1H-pyrazole (dfppz) are used as cyclometalating ligands. In the second one, nonconjugated 2,4-difluorobenzyl-N-pyrazole (dfbpz) is used as the cyclometalating ligand and 3-methyl-1-(2-pyridyl)benzimidazolin-2-ylidene-C,C(2)' (pymbi) as the ancillary ligand. The synthesis and photophysical and electrochemical properties, together with the X-ray crystal structures of these complexes, have been investigated. At room temperature, blue-emitting complexes [Ir(ppy)2(dppmmi)]PF6 (1) and [Ir(dfppy)2(dppmmi)]PF6 (2; PF6(-) is hexafluorophosphate) show much larger photoluminescence quantum yields of 24% and 46%, respectively. On the contrary, for complexes [Ir(dfppz)2(dppmmi)]PF6 (3) and [Ir(dfbpz)2(pymbi)]PF6 (4), deep-blue luminescence is only observed at low temperature (77 K). Density functional theory calculations are used to rationalize the differences in the photophysical behavior observed upon changes of the ligands. It is shown that the electronic transition dipoles of cationic iridium complexes 1 and 2 are mainly confined to cyclometalated ligands ((3)MLCT and LC (3)?-?*) and those of complex 3 are confined to all of the ligands ((3)MLCT, LC (3)?-?*, and (3)LLCT) because of the high LUMO energy level of dfppz. The emission of 4 mainly originates from the central iridium(III) ion and cyclometalated ligand to ancillary ligand charge transfer ((3)MLCT and (3)LLCT), in contrast to commonly designed cationic complexes using carbene-type ancillary ligands, where emission originates from the cyclometalated main ligands. Solution-processed organic light-emitting diodes based on complexes 1 and 2 gave blue-green (498 nm) and blue (478 nm) electroluminescence with maximum current efficiencies of 3.8 and 3.4 cd A(-1), respectively. The results indicate that introducing nonconjugated ligands into cationic iridium complexes is an effective means of achieving short-wavelength light-emitting phosphors. PMID:24914469

Zhang, Fuli; Ma, Dongxin; Duan, Lian; Qiao, Juan; Dong, Guifang; Wang, Liduo; Qiu, Yong

2014-07-01

401

Direct Functionalization of Nitrogen Heterocycles via Rh-Catalyzed C-H Bond Activation  

Energy Technology Data Exchange (ETDEWEB)

Nitrogen heterocycles are present in many compounds of enormous practical importance, ranging from pharmaceutical agents and biological probes to electroactive materials. Direct funtionalization of nitrogen heterocycles through C-H bond activation constitutes a powerful means of regioselectively introducing a variety of substituents with diverse functional groups onto the heterocycle scaffold. Working together, our two groups have developed a family of Rh-catalyzed heterocycle alkylation and arylation reactions that are notable for their high level of functional-group compatibility. This Account describes their work in this area, emphasizing the relevant mechanistic insights that enabled synthetic advances and distinguished the resulting transformations from other methods. They initially discovered an intramolecular Rh-catalyzed C-2-alkylation of azoles by alkenyl groups. That reaction provided access to a number of di-, tri-, and tetracyclic azole derivatives. They then developed conditions that exploited microwave heating to expedite these reactions. While investigating the mechanism of this transformation, they discovered that a novel substrate-derived Rh-N-heterocyclic carbene (NHC) complex was involved as an intermediate. They then synthesized analogous Rh-NHC complexes directly by treating precursors to the intermediate [RhCl(PCy{sub 3}){sub 2}] with N-methylbenzimidazole, 3-methyl-3,4-dihydroquinazolein, and 1-methyl-1,4-benzodiazepine-2-one. Extensive kinetic analysis and DFT calculations supported a mechanism for carbene formation in which the catalytically active RhCl(PCy{sub 3}){sub 2} fragment coordinates to the heterocycle before intramolecular activation of the C-H bond occurs. The resulting Rh-H intermediate ultimately tautomerizes to the observed carbene complex. With this mechanistic information and the discovery that acid co-catalysts accelerate the alkylation, they developed conditions that efficiently and intermolecularly alkylate a variety of heterocycles, including azoles, azolines, dihydroquinazolines, pyridines, and quinolines, with a wide range of functionalized olefins. They demonstrated the utility of this methodology in the synthesis of natural products, drug candidates, and other biologically active molecules. In addition, they developed conditions to directly arylate these heterocycles with aryl halides. The initial conditions that used PCy{sub 3} as a ligand were successful only for aryl iodides. However, efforts designed to avoid catalyst decomposition led to the development of ligands based on 9-phosphabicyclo[4.2.1]nonane (Phoban) that also facilitated the coupling of aryl bromides. They then replicated the unique coordination environment, stability, and catalytic activity of this complex using the much simpler tetrahydrophosphepine ligands and developed conditions that coupled aryl bromides bearing diverse functional groups without the use of a glovebox or purified reagents. With further mechanistic inquiry, they anticipate that researchers will better understand the details of the aforementioned Rh-catalyzed C-H bond functionalization reactions, resulting in the design of more efficient and robust catalysts, expanded substrate scope, and new transformations.

Lewis, Jared; Bergman, Robert; Ellman, Jonathan

2008-02-04

402

Direct functionalization of nitrogen heterocycles via Rh-catalyzed C-H bond activation.  

Science.gov (United States)

[Reaction: see text]. Nitrogen heterocycles are present in many compounds of enormous practical importance, ranging from pharmaceutical agents and biological probes to electroactive materials. Direct functionalization of nitrogen heterocycles through C-H bond activation constitutes a powerful means of regioselectively introducing a variety of substituents with diverse functional groups onto the heterocycle scaffold. Working together, our two groups have developed a family of Rh-catalyzed heterocycle alkylation and arylation reactions that are notable for their high level of functional-group compatibility. This Account describes our work in this area, emphasizing the relevant mechanistic insights that enabled synthetic advances and distinguished the resulting transformations from other methods. We initially discovered an intramolecular Rh-catalyzed C-2 alkylation of azoles by alkenyl groups. That reaction provided access to a number of di-, tri-, and tetracyclic azole derivatives. We then developed conditions that exploited microwave heating to expedite these reactions. While investigating the mechanism of this transformation, we discovered that a novel substrate-derived Rh- N-heterocyclic carbene (NHC) complex was involved as an intermediate. We then synthesized analogous Rh-NHC complexes directly by treating precursors to the intermediate [RhCl(PCy 3)2] with N-methylbenzimidazole, 3-methyl-3,4-dihydroquinazoline, and 1-methyl-1,4-benzodiazepine-2-one. Extensive kinetic analysis and DFT calculations supported a mechanism for carbene formation in which the catalytically active RhCl(PCy 3) 2 fragment coordinates to the heterocycle before intramolecular activation of the C-H bond occurs. The resulting Rh-H intermediate ultimately tautomerizes to the observed carbene complex. With this mechanistic information and the discovery that acid cocatalysts accelerate the alkylation, we developed conditions that efficiently and intermolecularly alkylate a variety of heterocycles, including azoles, azolines, dihydroquinazolines, pyridines, and quinolines, with a wide range of functionalized olefins. We demonstrated the utility of this methodology in the synthesis of natural products, drug candidates, and other biologically active molecules. In addition, we developed conditions to directly arylate these heterocycles with aryl halides. Our initial conditions that used PCy 3 as a ligand were successful only for aryl iodides. However, efforts designed to avoid catalyst decomposition led to the development of ligands based on 9-phosphabicyclo[4.2.1]nonane (phoban) that also facilitated the coupling of aryl bromides. We then replicated the unique coordination environment, stability, and catalytic activity of this complex using the much simpler tetrahydrophosphepine ligands and developed conditions that coupled aryl bromides bearing diverse functional groups without the use of a glovebox or purified reagents. With further mechanistic inquiry, we anticipate that researchers will better understand the details of the aforementioned Rh-catalyzed C-H bond functionalization reactions, resulting in the design of more efficient and robust catalysts, expanded substrate scope, and new transformations. PMID:18616300

Lewis, Jared C; Bergman, Robert G; Ellman, Jonathan A

2008-08-01

403

Di-, tri-, and tetranuclear copper(I) complexes of phenanthroline-linked dicarbene ligands.  

Science.gov (United States)

A family of 2,9-di(3-R-1H-imidazolium-1-yl)-1,10-phenanthroline iodides and hexafluorophosphates (R = allyl, benzyl, mesityl, picolyl) were synthesized from 2,9-diiodophenanthroline and imidazole or N-substituted imidazoles. Simple reactions of these diimidazolium salts with copper powder at room temperature have afforded a series of multinuclear copper(I)-NHC complexes in good yields. The structures vary depending on the N substituents and counterions. [Cu4(L1)2(MeCN)4](PF6)4 (R = allyl) exhibits a zigzag Cu4 chain with two terminal [Cu(NHC)(MeCN)2] and two internal [Cu(phen)(NHC)] moieties. [Cu3(L2)2](PF6)3 (R = benzyl) contains a strictly linear Cu3 framework with two [Cu(NHC)2] units and a [Cu(phen)2] located at the center. Both complexes [Cu3(L4)2](PF6)3 (R = mesityl) and [Cu3(L5)2](PF6)3 (R = picolyl) consist of a triangular Cu3 core in which two copper(I) ions are surrounded by a phen and a NHC group and the third copper(I) is coordinated by two NHC groups. [Cu3(L3)2](PF6)3 derived from 2,9-di(3-benzyl-1H-benzimidazolium-1-yl)-1,10-phenanthroline hexafluorophosphate can undergo transannulation of the benzimidazolylidene ring giving [Cu2(L3')2](PF6)2. The decomposition process might involve solvent-induced rearrangement of the ligand and hydrolysis of carbene moieties. Treatment of 2,9-di(3-mesityl-1H-benzimidazolium-1-yl)-1,10-phenanthroline iodide with copper powder generated dinuclear complex [Cu2(L4)2][Cu2(?-I)2I2] (R = mesityl) possessing a macrocyclic cation and [Cu2(?-I)2I2](2-) anion. Tetranuclear complex [Cu4(L5)2(?-I)2](CuI3) (R = picolyl) has been obtained from its diimidazolium iodide and copper powder. All Cu(I) complexes have been characterized by X-ray single diffraction analysis, elemental analysis, and NMR spectra. Their redox behavior and fluorescent properties have also been studied. PMID:25216090

Liu, Bo; Pan, Shanfei; Liu, Bin; Chen, Wanzhi

2014-10-01

404

Hydrolyses of 2- and 4-fluoro N-heterocycles. 3. Nucleophilic catalysis by buffer bases in the general acid catalyzed hydrolysis of 4-fluoroquinaldine  

International Nuclear Information System (INIS)

Pseudo-first-order rate constants and catalytic rate constants are reported for the buffer-catalyzed hydrolysis of 4-fluoroquinaldine (1) in carboxylic acid and phosphoric acid buffers. The buffer catalysis is consistent with specific acid, general base catalysis. Hydrolyses in 99% 18O-labeled acetate, indicate that the predominant catalytic mode for the acetic acid/acetate buffer system is nucleophilic catalysis by the acetate anion coupled with specific acid catalysis. The other buffers presumably react in a similar manner. A Broensted-type plot of the catalytic rate constants for hydrolysis of protonated 1 has a slope of 0.57, with formate deviating positively from the line determined by acetate, chloroacetate, monohydrogen phosphate, and water. This Broensted slope is less than that found for hydrolysis of the 2-fluoro-1-methylpyridinium ion, 2, but is still within the range expected for aromatic nucleophilic substitution. Rate constants and 18O-labeling results for hydrolysis in acetate buffer are also reported for 4-acetoxyquinaldine (3), the proposed intermediate in the acetate-catalyzed hydrolysis of 1. 15 references, 5 figures, 3 tables

405

AQUEOUS N-HETEROCYCLIZATION OF PRIMARY AMINES AND HYDRAZINES WITH DIHALIDES: MICROWAVE-ASSISTED SYNTHESES OF N-AZACYCLOALKANES, ISOINDOLE, PYRAZOLE, PYRAZOLIDINE AND PHTHALAZINE DERIVATIVES  

Science.gov (United States)

The synthesis of nitrogen-containing heterocycles from alkyl dihalides (ditosylates) and primary amines and hydrazines via a simple and efficient cyclocondensation in alkaline aqueous medium that occurs under microwave irradiation is described. This improved greener synthetic met...

406

A novel binuclear ruthenium complex: spectroscopic and electrochemical characterization, and formation of Langmuir and Langmuir-Blodgett films  

Scientific Electronic Library Online (English)

Full Text Available O complexo [{RuCl3(dppb)}2(µ-4,4'-bipy)] (dppb = PPh2(CH2)4PPh2; 4,4'-bipy= 4,4'-bipiridil) foi obtido por meio da reação entre 4,4'-bipiridina e mer-[RuCl3(dppb)].H2O, em bom rendimento. As características do complexo binuclear obtido, estudadas por medidas de FT-IR, UV-Vis, EPR e análise elementar [...] foram similares às do complexo [RuCl3(dppb)L] (L= N-heterociclo). [{RuCl3(dppb)}2(µ-4,4'-bipy)] é solúvel em solventes fracamente polares, facilitando a sua utilização para produzir filmes de Langmuir e Langmuir-Blodgett (LB). Enquanto que filmes cast e o complexo em solução são vermelhos, filmes LB são azul-esverdeados, provavelmente devido à oxidação da bisfosfina. A natureza nanoestruturada dos filmes LB, se manifestou nas medidas eletroquímicas, já que estes filmes exibem maior corrente de pico do que os filmes cast e dip-coated. As respostas eletroquímicas destes filmes são caracterizadas pelo processo RuIII RuIII/RuII RuII, o qual difere do complexo em solução. Neste último caso, um processo irreversível é observado devido à formação de novas espécies. A eletroatividade dos filmes LB/[{RuCl3(dppb)}2(µ-4,4' -bipy)] indica a possibilidade de utilização em dispositivos eletroquímicos. Abstract in english [{RuCl3(dppb)}2(µ-4,4'-bipy)] was prepared from the reaction of the 4,4'-bipyridine and mer-[RuCl3(dppb)].H2O, in good yield. The characteristics of the binuclear complex studied with FT-IR, UV-Vis, EPR and elemental analysis were similar to those of the [RuCl3(dppb)L] (L= N-heterocycle). [{RuCl3(dp [...] pb)}2(µ-4,4'-bipy)] is soluble in weakly polar organic solvents, facilitating its use in the production of Langmuir and Langmuir-Blodgett (LB) films production. While the cast films and the complex in solution were red, the LB films were green-bluish, probably due to oxidation of the bisphosphine. The nanostructured nature of the LB films was manifested in electrochemical measurements, as these films exhibited higher peak currents than cast or dip-coated films. For all films, the electrochemical response was dominated by the RuIII RuIII/RuII RuII process, which differed from that of the binuclear compound. For the latter, an irreversible process appeared due to formation of new species. The electroactivity of LB films from [{RuCl3(dppb)}2(µ-4,4'-bipy)] also pointed to their possible use in electrochemical devices.

Karen, Wohnrath; Poliana M. dos, Santos; B., Sandrino; Jarem R., Garcia; Alzir A., Batista; Osvaldo N., Oliveira Jr.

1634-16-01

407

Complexes of bipartite graphs, neighborhood complexes, and box complexes  

OpenAIRE

Neighborhood complexes and box complexes of graphs were constructed in the context of the graph coloring problem. In this paper, we investigate the relationships among graphs, their Hom complexes ${\\rm Hom}(K_2,G)$, and their neighborhood complexes. We prove that for graphs $G$ and $H$ having no isolated vertices, $K_2 \\times G \\cong K_2 \\times H$ if and only if ${\\rm Hom}(K_2,G) \\cong {\\rm Hom}(K_2,H)$ as posets. And $G \\cong H$ if and only if ${\\rm Hom}(G) \\cong {\\rm Hom}(...

Matsushita, Takahiro

2014-01-01

408

Complex analysis and geometry  

CERN Document Server

The papers in this wide-ranging collection report on the results of investigations from a number of linked disciplines, including complex algebraic geometry, complex analytic geometry of manifolds and spaces, and complex differential geometry.

Silva, Alessandro

1993-01-01

409

Generalization of neighborhood complexes  

OpenAIRE

We introduce the notion of r-neighborhood complex for a positive integer r, which is a natural generalization of Lovasz neighborhood complex. The topologies of these complexes give some obstructions of the existence of graph maps. We applied these complexes to prove the nonexistence of graph maps about Kneser graphs. We prove that the fundamental groups of r-neighborhood complexes are closely related to the (2r)-fundamental groups defined in the author's previous paper.

Matsushita, Takahiro

2013-01-01

410

Visualization of Complex Systems  

OpenAIRE

Complex systems are difficult to understand. To aid understanding of complex dynamic systems the field of system dynamics has developed a set of visualization methods for graphic representation of the simulation models of complex systems. The resulting visualizations, however, may sometimes be difficult to understand for audiences without a background in the scientific investigation of complex dynamic systems. It is therefore necessary to find new ways of representing complex s...

Viste, Magnhild

2008-01-01

411

Complex Systems + Systems Engineering = Complex Systems Engineeri  

CERN Document Server

One may define a complex system as a system in which phenomena emerge as a consequence of multiscale interaction among the system's components and their environments. The field of Complex Systems is the study of such systems--usually naturally occurring, either bio-logical or social. Systems Engineering may be understood to include the conceptualising and building of systems that consist of a large number of concurrently operating and interacting components--usually including both human and non-human elements. It has become increasingly apparent that the kinds of systems that systems engineers build have many of the same multiscale characteristics as those of naturally occurring complex systems. In other words, systems engineering is the engineering of complex systems. This paper and the associated panel will explore some of the connections between the fields of complex systems and systems engineering.

Abbott, R

2006-01-01

412

Complex networks analysis of language complexity  

CERN Document Server

Methods from statistical physics, such as those involving complex networks, have been increasingly used in quantitative analysis of linguistic phenomena. In this paper, we represented pieces of text with different levels of simplification in co-occurrence networks and found that topological regularity correlated negatively with textual complexity. Furthermore, in less complex texts the distance between concepts, represented as nodes, tended to decrease. The complex networks metrics were treated with multivariate pattern recognition techniques, which allowed us to distinguish between original texts and their simplified versions. For each original text, two simplified versions were generated manually with increasing number of simplification operations. As expected, distinction was easier for the strongly simplified versions, where the most relevant metrics were node strength, shortest paths and diversity. Also, the discrimination of complex texts was improved with higher hierarchical network metrics, thus point...

Amancio, Diego R; Oliveira, Osvaldo N; Costa, Luciano da F; 10.1209/0295-5075/100/58002

2013-01-01

413

[2-Butyl-4-(4-tert-butylbenzyl-1,2,4-triazol-3-ylidene]chlorido[(1,2,5,6-?-cycloocta-1,5-diene]iridium(I  

Directory of Open Access Journals (Sweden)

Full Text Available In the title compound, [IrCl(C8H12(C17H25N3], the IrI ion has a distorted square-planar coordination geometry. The N-heterocyclic carbene ligand has an extended S-shaped conformation. The butyl group was refined using a two-part 1:1 disorder model. In the crystal, three unique weak C—H...Cl contacts are present. Two of these form a motif described as R21(6 in graph-set notation, while a third forms an R22(8 motif about a crystallographic inversion center. The result is a chain structure which extends parallel to the crystallographic a axis.

Gary S. Nichol

2012-02-01

414

1-(4-tert-Butylbenzyl-3-(3,4,5-trimethoxybenzylbenzimidazolium bromide monohydrate  

Directory of Open Access Journals (Sweden)

Full Text Available A novel N-heterocyclic carbene derivative, C28H33N2O3+·Br?·H2O, was synthesized and characterized by elemental analysis, 1H and 13C-NMR and IR spectroscopy and a single-crystal X-ray diffraction study. Ions of the title compound are linked by ?...? stacking interactions (face–face separation 3.441?Å and C—H...Br and O—H...Br interactions. Intra- and intermolecular C—H...O interactions are also present. The C—N bond lengths for the compound [1.329?(3, 1.325?(3, 1.389?(3 and 1.391?(3?Å] are all shorter than the average single C—N bond length of 1.48?Å, thus showing varying degrees of double-bond character.

Hakan Arslan

2009-01-01

415

Latent and delayed action polymerization systems.  

Science.gov (United States)

Various approaches to latent polymerization processes are described. In order to highlight recent advances in this field, the discussion is subdivided into chapters dedicated to diverse classes of polymers, namely polyurethanes, polyamides, polyesters, polyacrylates, epoxy resins, and metathesis-derived polymers. The described latent initiating systems encompass metal-containing as well as purely organic compounds that are activated by external triggers such as light, heat, or mechanical force. Special emphasis is put on the different chemical venues that can be taken to achieve true latency, which include masked N-heterocyclic carbenes, latent metathesis catalysts, and photolatent radical initiators, among others. Scientific challenges and the advantageous application of latent polymerization processes are discussed. PMID:24519912

Naumann, Stefan; Buchmeiser, Michael R

2014-04-01

416

Divergent Reactivity of Homologue ortho-Allenylbenzaldehydes Controlled by the Tether Length: Chromone versus Chromene Formation.  

Science.gov (United States)

The divergent behavior of two homologue allenals, namely, 2-(buta-2,3-dienyloxy)- and 2-(propa-1,2-dienyloxy)benzaldehydes, as cyclization substrates is described. 2-(Buta-2,3-dienyloxy)benzaldehydes suffers a formal allenic carbocyclization reaction to afford chromenes, whereas 2-(propa-1,2-dienyloxy)benzaldehydes react to yield chromones. The formation of chromenes is strictly a formal hydroarylation process divided into two parts, namely, allenic Claisen-type rearrangement and oxycyclization. An unknown N-heterocyclic carbene (NHC)-catalyzed allenic hydroacylation reaction must be invoked to account for the preparation of chromones. ortho-Allenylbenzaldehydes bearing either electron-donating substituents or electron-withdrawing substituents worked well to afford both the hydroarylation and hydroacylation products. This unexpected difference in reactivity can be rationalized by means of density functional theory calculations. PMID:25418081

Alcaide, Benito; Almendros, Pedro; Fernández, Israel; Martínez Del Campo, Teresa; Naranjo, Teresa

2015-01-19

417

Vitamin B1-catalyzed acetoin formation from acetaldehyde: a key step for upgrading bioethanol to bulk C? chemicals.  

Science.gov (United States)

The production of bulk chemicals and fuels from renewable biobased feedstocks is of significant importance for the sustainability of human society. The production of ethanol from biomass has dramatically increased and bioethanol also holds considerable potential as a versatile building block for the chemical industry. Herein, we report a highly selective process for the conversion of ethanol to C4 bulk chemicals, such as 2,3-butanediol and butene, via a vitamin B1 (thiamine)-derived N-heterocyclic carbene (NHC)-catalyzed acetoin condensation as the key step to assemble two C2 acetaldehydes into a C4 product. The environmentally benign and cheap natural catalyst vitamin B1 demonstrates high selectivity (99%), high efficiency (97% yield), and high tolerance toward ethanol and water impurities in the acetoin reaction. The results enable a novel and efficient process for ethanol upgrading. PMID:25044300

Lu, Ting; Li, Xiukai; Gu, Liuqun; Zhang, Yugen

2014-09-01

418

Ambient stable zwitterionic perylene bisimide-centered radical.  

Science.gov (United States)

The unexpected introduction of a cationic imidazolium substituent in the 2-position of a tetrachloro-substituted perylene-3,4:9,10-tetracarboxylic acid bisimide (PBI) by the reaction of PBI-Cl4 1 with the N-heterocyclic carbene 1,3-di-iso-propyl-imidazolin-2-ylidene ((i) Pr2 Im 2) enables the isolation of an ambient stable zwitterionic radical. The remarkable stability of this unprecedented PBI-centered radical facilitates the complete characterization by several spectroscopic methods as well as single crystal structure analysis. Redox studies revealed that (i) Pr2 Im-PBI-Cl4 4 can be transferred reversibly to the corresponding anion and cation, respectively, even on a preparative scale. PMID:25393879

Schmidt, David; Bialas, David; Würthner, Frank

2015-03-16

419

1-(2-Phenylbenzyl-3-(2,4,6-trimethylbenzylimidazolidinium bromide  

Directory of Open Access Journals (Sweden)

Full Text Available In the title salt, C26H29N2+·Br?, which may serve as a precursor for N-heterocyclic carbenes, the imidazolidine ring adopts a twist conformation with a pseudo-twofold axis passing through the N—C—N carbon and the opposite C—C bond. The N—C—N bond angle [113.0?(4°] and C—N bond lengths [1.313?(6 and 1.305?(6?Å] confirm the existence of strong resonance in this part of the molecule. In the crystal, a C—H...Br interaction is present. The dihedral angle between the biphenyl rings is 64.3?(2° and the phenyl rings make angles of 76.6?(3 and 18.5?(3° with the plane of the imidazolidine ring.

Hakan Arslan

2009-01-01

420

Doxorubicin Lipid Complex Injection  

Science.gov (United States)

Doxorubicin lipid complex is used to treat ovarian cancer that has not improved or that has worsened after treatment with other medications. Doxorubicin lipid complex is also used to treat Kaposi's sarcoma ( ...