Synthesis, characterization, and reactivity of furan- and thiophene-functionalized bis(n-heterocyclic carbene) complexes of iron(II)

KAUST Repository

Rieb, Julia

2014-09-15

The synthesis of iron(II) complexes bearing new heteroatom-functionalized methylene-bridged bis(N-heterocyclic carbene) ligands is reported. All complexes are characterized by single-crystal X-ray diffraction (SC-XRD), nuclear magnetic resonance (NMR) spectroscopy, and elemental analysis. Tetrakis(acetonitrile)-cis-[bis(o-imidazol-2-ylidenefuran)methane]iron(II) hexafluorophosphate (2a) and tetrakis(acetonitrile)-cis-[bis(o-imidazol-2-ylidenethiophene)methane]iron(II) hexafluorophosphate (2b) were obtained by aminolysis of [Fe{N(SiMe3)2}2(THF)] with furan- and thiophene-functionalized bis(imidazolium) salts 1a and 1b in acetonitrile. The SC-XRD structures of 2a and 2b show coordination of the bis(carbene) ligand in a bidentate fashion instead of a possible tetradentate coordination. The four other coordination sites of these distorted octahedral complexes are occupied by acetonitrile ligands. Crystallization of 2a in an acetone solution by the slow diffusion of Et2O led to the formation of cisdiacetonitriledi[ bis(o-imidazol-2-ylidenefuran)methane]iron(II) hexafluorophosphate (3a) with two bis(carbene) ligands coordinated in a bidentate manner and two cis-positioned acetonitrile molecules. Compounds 2a and 2b are the first reported iron(II) carbene complexes with four coordination sites occupied by solvent molecules, and it was demonstrated that those solvent ligands can undergo ligand-exchange reactions.

Alkyne hydroarylation with Au N-heterocyclic carbene catalysts

Directory of Open Access Journals (Sweden)

Cristina Tubaro

2013-02-01

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.

N-heterocyclic carbene metal complexes as bio-organometallic antimicrobial and anticancer drugs.

Science.gov (United States)

Patil, Siddappa A; Patil, Shivaputra A; Patil, Renukadevi; Keri, Rangappa S; Budagumpi, Srinivasa; Balakrishna, Geetha R; Tacke, Matthias

2015-01-01

Late transition metal complexes that bear N-heterocyclic carbene (NHC) ligands have seen a speedy growth in their use as both, metal-based drug candidates and potentially active homogeneous catalysts in a plethora of C-C and C-N bond forming reactions. This review article focuses on the recent developments and advances in preparation and characterization of NHC-metal complexes (metal: silver, gold, copper, palladium, nickel and ruthenium) and their biomedical applications. Their design, syntheses and characterization have been reviewed and correlated to their antimicrobial and anticancer efficacies. All these initial discoveries help validate the great potential of NHC-metal derivatives as a class of effective antimicrobial and anticancer agents.

C-N Bond Activation and Ring Opening of a Saturated N-Heterocyclic Carbene by Lateral Alkali-Metal-Mediated Metalation.

Science.gov (United States)

Hernán-Gómez, Alberto; Kennedy, Alan R; Hevia, Eva

2017-06-01

Combining alkali-metal-mediated metalation (AMMM) and N-heterocyclic carbene (NHC) chemistry, a novel C-N bond activation and ring-opening process is described for these increasingly important NHC molecules, which are generally considered robust ancillary ligands. Here, mechanistic investigations on reactions of saturated NHC SIMes (SIMes=[:C{N(2,4,6-Me 3 C 6 H 2 )CH 2 } 2 ]) with Group 1 alkyl bases suggest this destructive process is triggered by lateral metalation of the carbene. Exploiting co-complexation and trans-metal-trapping strategies with lower polarity organometallic reagents (Mg(CH 2 SiMe 3 ) 2 and Al(TMP)iBu 2 ), key intermediates in this process have been isolated and structurally defined. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Enantioselective [3+3] atroposelective annulation catalyzed by N-heterocyclic carbenes

KAUST Repository

Zhao, Changgui; Guo, Donghui; Munkerup, Kristin; Huang, Kuo-Wei; Li, Fangyi; Wang, Jian

2018-01-01

on the transition-metal-catalyzed transformations. Here, we report the enantioselective NHC-catalyzed (NHC: N-heterocyclic carbenes) atroposelective annulation of cyclic 1,3-diones with ynals. In the presence of NHC precatalyst, base, Lewis acid and oxidant, a

In Silico Olefin Metathesis with Ru-Based Catalysts Containing N-Heterocyclic Carbenes Bearing C60Fullerenes

KAUST Repository

Martínez, Juan Pablo

2016-04-10

Density functional theory calculations have been used to explore the potential of Ru-based complexes with 1,3-bis(2,4,6-trimethylphenyl)imidazolin-2-ylidene (SIMes) ligand backbone (A) being modified in silico by the insertion of a C60 molecule (B and C), as olefin metathesis catalysts. To this end, we investigated the olefin metathesis reaction catalyzed by complexes A, B, and C using ethylene as the substrate, focusing mainly on the thermodynamic stability of all possible reaction intermediates. Our results suggest that complex B bearing an electron-withdrawing N-heterocyclic carbene improves the performance of unannulated complex A. The efficiency of complex B is only surpassed by complex A when the backbone of the N-heterocyclic carbene of complex A is substituted by two amino groups. The particular performance of complexes B and C has to be attributed to electronic factors, that is, the electronic-donating capacity of modified SIMes ligand rather than steric effects, because the latter are predicted to be almost identical for complexes B and C when compared to those of A. Overall, this study indicates that such Ru-based complexes B and C might have the potential to be effective olefin metathesis catalysts. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

In Silico Olefin Metathesis with Ru-Based Catalysts Containing N-Heterocyclic Carbenes Bearing C60Fullerenes

KAUST Repository

Martí nez, Juan Pablo; Vummaleti, Sai V. C.; Falivene, Laura; Nolan, Steven P.; Cavallo, Luigi; Solà , Miquel; Poater, Albert

2016-01-01

Density functional theory calculations have been used to explore the potential of Ru-based complexes with 1,3-bis(2,4,6-trimethylphenyl)imidazolin-2-ylidene (SIMes) ligand backbone (A) being modified in silico by the insertion of a C60 molecule (B and C), as olefin metathesis catalysts. To this end, we investigated the olefin metathesis reaction catalyzed by complexes A, B, and C using ethylene as the substrate, focusing mainly on the thermodynamic stability of all possible reaction intermediates. Our results suggest that complex B bearing an electron-withdrawing N-heterocyclic carbene improves the performance of unannulated complex A. The efficiency of complex B is only surpassed by complex A when the backbone of the N-heterocyclic carbene of complex A is substituted by two amino groups. The particular performance of complexes B and C has to be attributed to electronic factors, that is, the electronic-donating capacity of modified SIMes ligand rather than steric effects, because the latter are predicted to be almost identical for complexes B and C when compared to those of A. Overall, this study indicates that such Ru-based complexes B and C might have the potential to be effective olefin metathesis catalysts. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Theoretical NMR spectroscopy of N-heterocyclic carbenes and their metal complexes

KAUST Repository

Falivene, Laura; Cavallo, Luigi

2016-01-01

Recent theoretical analysis of the NMR properties of free N-heterocyclic carbenes (NHC) and Metal-NHC complexes has complemented experiments, allowing the establishment of structure/property relationships and the rationalization of otherwise

Structure and spectroscopic properties of the dimeric copper(I) N-heterocyclic carbene complex [Cu₂(CNC(t-Bu))₂](PF₆)₂.

Science.gov (United States)

Riener, Korbinian; Pöthig, Alexander; Cokoja, Mirza; Herrmann, Wolfgang A; Kühn, Fritz E

2015-08-01

In recent years, the use of copper N-heterocyclic carbene (NHC) complexes has expanded to fields besides catalysis, namely medicinal chemistry and luminescence applications. In the latter case, multinuclear copper NHC compounds have attracted interest, however, the number of these complexes in the literature is still quite limited. Bis[μ-1,3-bis(3-tert-butylimidazolin-2-yliden-1-yl)pyridine]-1κ(4)C(2),N:N,C(2');2κ(4)C(2),N:N,C(2')-dicopper(I) bis(hexafluoridophosphate), [Cu2(C19H25N5)2](PF6)2, is a dimeric copper(I) complex bridged by two CNC, i.e. bis(N-heterocyclic carbene)pyridine, ligands. Each Cu(I) atom is almost linearly coordinated by two NHC ligands and interactions are observed between the pyridine N atoms and the metal centres, while no cuprophilic interactions were observed. Very strong absorption bands are evident in the UV-Vis spectrum at 236 and 274 nm, and an emission band is observed at 450 nm. The reported complex is a new example of a multinuclear copper NHC complex and a member of a compound class which has only rarely been reported.

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

DEFF Research Database (Denmark)

Dam, Johan Hygum; Osztrovszky, Gyorgyi; Nordstrøm, Lars Ulrik Rubæk

2010-01-01

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...... chloride and base. A range of different primary alcohols and amines have been coupled in the presence 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...

Masked N-Heterocyclic Carbene-Catalyzed Alkylation of Phenols with Organic Carbonates.

Science.gov (United States)

Lui, Matthew Y; Yuen, Alexander K L; Masters, Anthony F; Maschmeyer, Thomas

2016-09-08

An easily prepared masked N-heterocyclic carbene, 1,3-dimethylimidazolium-2-carboxylate (DMI-CO2 ), was investigated as a "green" and inexpensive organocatalyst for the alkylation of phenols. The process made use of various low-toxicity and renewable alkylating agents, such as dimethyl- and diethyl carbonate, in a focused microwave reactor. DMI-CO2 was found to be a very active catalyst and excellent yields of a range of aryl alkyl ethers were obtained under relatively benign conditions. The observed difference in the conversion behavior of phenol methylation, in the presence of either the carbene or 1,8-diazabicycloundec-7-ene (DBU) catalyst, was rationalized on the basis of mechanistic investigations. The primary mode of action for the N-heterocyclic carbene is nucleophilic catalysis. Activation of the dialkyl carbonate electrophile results in concomitant evolution of an organo-soluble alkoxide, which deprotonates the phenolic starting material. In contrast, DBU is initially protonated by the phenol and thus consumed. Subsequent regeneration and participation in nucleophilic catalysis only becomes significant after some phenolate alkylation occurs. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

N-Heterocyclic carbene functionalized goup 7-9 transition metal

NARCIS (Netherlands)

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

2009-01-01

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

Enantioselective [3+3] atroposelective annulation catalyzed by N-heterocyclic carbenes

KAUST Repository

Zhao, Changgui

2018-02-05

Axially chiral molecules are among the most valuable substrates in organic synthesis. They are typically used as chiral ligands or catalysts in asymmetric reactions. Recent progress for the construction of these chiral molecules is mainly focused on the transition-metal-catalyzed transformations. Here, we report the enantioselective NHC-catalyzed (NHC: N-heterocyclic carbenes) atroposelective annulation of cyclic 1,3-diones with ynals. In the presence of NHC precatalyst, base, Lewis acid and oxidant, a catalytic C–C bond formation occurs, providing axially chiral α-pyrone−aryls in moderate to good yields and with high enantioselectivities. Control experiments indicated that alkynyl acyl azoliums, acting as active intermediates, are employed to atroposelectively assemble chiral biaryls and such a methodology may be creatively applied to other useful NHC-catalyzed asymmetric transformations.

Bis-ligated Ti and Zr complexes of chelating N-heterocyclic carbenes

KAUST Repository

El-Batta, Amer; Waltman, Andrew W.; Grubbs, Robert H.

2011-01-01

In this communication we report the synthesis of novel titanium and zirconium complexes ligated by bidentate "salicylaldimine-like" N-heterocyclic carbenes (NHC). Double addition of the NHC chelate to either TiCl4(thf)2 or ZrCl4 forms bis

Auranofin and N-heterocyclic carbene gold-analogs are potent inhibitors of the bacteria Helicobacter pylori.

Science.gov (United States)

Owings, Joshua P; McNair, Nina N; Mui, Yiu Fung; Gustafsson, Tomas N; Holmgren, Arne; Contel, Maria; Goldberg, Joanna B; Mead, Jan R

2016-07-01

Auranofin is an FDA-approved gold-containing compound used for the treatment of rheumatoid arthritis. Recent reports of antimicrobial activity against protozoa and bacteria indicate that auranofin targets the reductive enzyme thioredoxin reductase (TrxR). We evaluated auranofin as well as five auranofin analogs containing N-heterocyclic carbenes (instead of the triethylphosphane present in auranofin) and five gold-carbene controls for their ability to inhibit or kill Helicobacter pylori in vitro Auranofin completely inhibited bacterial growth at 1.2 μM. Purified H. pylori TrxR was inhibited by auranofin in a cell-free assay (IC50 ∼88 nM). The most active gold(I)-N-heterocyclic carbene compounds exhibited MICs comparable to auranofin against H. pylori (2 μM), while also exhibiting lower toxicities for human embryonic kidney cells (HEK-293T cells). Median toxic concentrations (TC50) were 13-20-fold higher compared to auranofin indicating that they were less cytotoxic. The N-heterocyclic carbene analogs maybe well tolerated, but further evaluation is needed in vivo Finally, auranofin was synergistic with the antibiotic amoxicillin, suggesting that targeting both the reductive enzyme TrxR and cell wall synthesis may be effective against H. pylori infections. © FEMS 2016. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com.

Synthesis and anticancer activity of silver(I)-N-heterocyclic carbene complexes derived from the natural xanthine products caffeine, theophylline and theobromine.

Science.gov (United States)

Mohamed, Heba A; Lake, Benjamin R M; Laing, Thomas; Phillips, Roger M; Willans, Charlotte E

2015-04-28

A new library of silver(I)-N-heterocyclic carbene complexes prepared from the natural products caffeine, theophylline and theobromine is reported. The complexes have been fully characterised using a combination of NMR spectroscopy, mass spectrometry, elemental analysis and X-ray diffraction analysis. Furthermore, the hydrophobicity of the complexes has been measured. The silver(I)-N-heterocyclic carbenes have been evaluated for their antiproliferative properties against a range of cancer cell lines of different histological types, and compared to cisplatin. The data shows different profiles of response when compared to cisplatin in the same panel of cells, indicating a different mechanism of action. Furthermore, it appears that the steric effect of the ligand and the hydrophobicity of the complex both play a role in the chemosensitivity of these compounds, with greater steric bulk and greater hydrophilicity delivering higher cytotoxicity.

N-heterocyclic carbene complexes of silver and gold as novel tools against breast cancer progression.

Science.gov (United States)

Saturnino, Carmela; Barone, Ines; Iacopetta, Domenico; Mariconda, Annaluisa; Sinicropi, Maria Stefania; Rosano, Camillo; Campana, Antonella; Catalano, Stefania; Longo, Pasquale; Andò, Sebastiano

2016-12-01

Metal carbenic complexes have received considerable attention in both the catalysis and biological fields for their potential applications in cancer and antimicrobial therapies. A small series of new silver and gold N-heterocyclic carbene complexes has been designed and synthesized. Among the tested complexes, one compound was particularly active in inhibiting anchorage-dependent and -independent breast cancer proliferation, and inducing cell apoptosis via a mitochondria-related process. The antitumor activity was associated to the transcriptional activation of the tumor suppressor gene p53 in an Sp1-dependent manner, as evidenced by biological and docking studies. Our results highlight the importance and the versatility of N-heterocyclic carbene complexes of gold and silver as useful tools against breast cancer progression.

Unexpected rearrangements in the synthesis of an unsymmetrical tridentate dianionic N-heterocyclic carbene

KAUST Repository

Despagnet-Ayoub, Emmanuelle; Miqueu, Karinne; Sotiropoulos, Jean-Marc; Henling, Lawrence M.; Day, Michael W.; Labinger, Jay A.; Bercaw, John E.

2013-01-01

Starting from the same ethylenediamine species, three valuable carbene precursors were synthesized under differing conditions: a tridentate dianionic N-heterocyclic carbene bearing an aniline, a phenol and a central dihydroimidazolium salt, its benzimidazolium isomer by intramolecular rearrangement and a dicationic benzimidazolium-benzoxazolium salt by changing the Brønsted acid from HCl to HBF4. A DFT study was performed to understand the rearrangement pathway. The structure of a bis[(NCO)carbene] zirconium complex was determined. © 2013 The Royal Society of Chemistry.

Reduction of the Work Function of Gold by N-Heterocyclic Carbenes

KAUST Repository

Kim, Hye Kyung

2017-04-12

N-Heterocyclic carbenes (NHCs) bind strongly to gold and other metals. This work experimentally probes the effect of NHCs on the work function (WF) of gold for the first time, theoretically analyzes the origin of this effect, and examines the effectiveness of NHC-modified gold as an electron-injecting electrode. UV photoelectron spectroscopy shows the WF of planar gold is reduced by nearly 2 eV to values of 3.3–3.5 eV. This effect is seen for NHCs with various heterocyclic cores, and with either small or large N,N′-substituents. DFT calculations indicate the WF reduction results from both the interface dipole formed between the NHC and the gold and from the NHC molecular dipole. For N,N′-diisopropyl-NHCs, an important contributor to the former is charge transfer associated with coordination of the carbene carbon atom to gold. In contrast, the carbene carbon of N,N′-2,6-diisopropylphenyl-NHCs is not covalently bound to gold, resulting in a lower interface dipole; however, a larger molecular dipole partially compensates for this. Single-layer C60 diodes with NHC-modified gold as the bottom electrode demonstrate high rectification ratios and show that these electrodes can act as effective electron-injecting contacts, suggesting they may be useful for a variety of materials applications.

Reduction of the Work Function of Gold by N-Heterocyclic Carbenes

KAUST Repository

Kim, Hye Kyung; Hyla, Alexander; Winget, Paul; Li, Hong; Wyss, Chelsea M.; Jordan, Abraham J.; Larrain, Felipe A.; Sadighi, Joseph P.; Fuentes-Hernandez, Canek; Kippelen, Bernard; Bredas, Jean-Luc; Barlow, Stephen; Marder, Seth R.

2017-01-01

N-Heterocyclic carbenes (NHCs) bind strongly to gold and other metals. This work experimentally probes the effect of NHCs on the work function (WF) of gold for the first time, theoretically analyzes the origin of this effect, and examines the effectiveness of NHC-modified gold as an electron-injecting electrode. UV photoelectron spectroscopy shows the WF of planar gold is reduced by nearly 2 eV to values of 3.3–3.5 eV. This effect is seen for NHCs with various heterocyclic cores, and with either small or large N,N′-substituents. DFT calculations indicate the WF reduction results from both the interface dipole formed between the NHC and the gold and from the NHC molecular dipole. For N,N′-diisopropyl-NHCs, an important contributor to the former is charge transfer associated with coordination of the carbene carbon atom to gold. In contrast, the carbene carbon of N,N′-2,6-diisopropylphenyl-NHCs is not covalently bound to gold, resulting in a lower interface dipole; however, a larger molecular dipole partially compensates for this. Single-layer C60 diodes with NHC-modified gold as the bottom electrode demonstrate high rectification ratios and show that these electrodes can act as effective electron-injecting contacts, suggesting they may be useful for a variety of materials applications.

In Situ Generated Ruthenium-Arene Catalyst for Photoactivated Ring-Opening Metathesis Polymerization through Photolatent N-Heterocyclic Carbene Ligand.

Science.gov (United States)

Pinaud, Julien; Trinh, Thi Kim Hoang; Sauvanier, David; Placet, Emeline; Songsee, Sriprapai; Lacroix-Desmazes, Patrick; Becht, Jean-Michel; Tarablsi, Bassam; Lalevée, Jacques; Pichavant, Loïc; Héroguez, Valérie; Chemtob, Abraham

2018-01-09

1,3-Bis(mesityl)imidazolium tetraphenylborate (IMesH + BPh 4 - ) can be synthesized in one step by anion metathesis between the corresponding imidazolium chloride and sodium tetraphenylborate. In the presence of 2-isopropylthioxanthone (sensitizer), an IMes N-heterocyclic carbene (NHC) ligand can be photogenerated under irradiation at 365 nm through coupled electron/proton transfer reactions. By combining this tandem NHC photogenerator system with metathesis inactive [RuCl 2 (p-cymene)] 2 precatalyst, the highly active RuCl 2 (p-cymene)(IMes) complex can be formed in situ, enabling a complete ring-opening metathesis polymerization (ROMP) of norbornene in the matter of minutes at room temperature. To the best of our knowledge, this is the first example of a photogenerated NHC. Its exploitation in photoROMP has resulted in a simplified process compared to current photocatalysts, because only stable commercial or easily synthesized reagents are required. © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

N-heterocyclic carbene copper(I) catalysed N-methylation of amines using CO2

KAUST Repository

Santoro, Orlando

2015-09-30

The N-methylation of amines using CO2 and PhSiH3 as source of CH3 was efficiently performed using a N-heterocyclic carbene copper(I) complex. The methodology was found compatible with aromatic and aliphatic primary and secondary amines. Synthetic and computational studies have been carried out to support the proposed reaction mechanism for this transformation.

N-heterocyclic carbene copper(I) catalysed N-methylation of amines using CO2

KAUST Repository

Santoro, Orlando; Lazreg, Faï ma; Minenkov, Yury; Cavallo, Luigi; Cazin, Catherine S. J.

2015-01-01

The N-methylation of amines using CO2 and PhSiH3 as source of CH3 was efficiently performed using a N-heterocyclic carbene copper(I) complex. The methodology was found compatible with aromatic and aliphatic primary and secondary amines. Synthetic and computational studies have been carried out to support the proposed reaction mechanism for this transformation.

π-face donation from the aromatic N-substituent of N-heterocyclic carbene ligands to metal and its role in catalysis

KAUST Repository

Credendino, Raffaele

2012-05-16

In this work, we calculate the redox potential in a series of Ir and Ru complexes bearing a N-heterocyclic carbene (NHC) ligand presenting different Y groups in the para position of the aromatic N-substituent. The calculated redox potentials excellently correlate with the experimental ΔE 1/2 potentials, offering a handle to rationalize the experimental findings. Analysis of the HOMO of the complexes before oxidation suggests that electron-donating Y groups destabilize the metal centered HOMO. Energy decomposition of the metal-NHC interaction indicates that electron-donating Y groups reinforce this interaction in the oxidized complexes. Analysis of the electron density in the reduced and oxidized states of representative complexes indicates a clear donation from the C ipso of the N-substituents to an empty d orbital on the metal. In case of the Ru complexes, this mechanism involves the Ru-alkylidene moiety. All of these results suggest that electron-donating Y groups render the aromatic N-substituent able to donate more density to electron-deficient metals through the C ipso atom. This conclusion suggests that electron-donating Y groups could stabilize higher oxidation states during catalysis. To test this hypothesis, we investigated the effect of differently donating Y groups in model reactions of Ru-catalyzed olefin metathesis and Pd-catalyzed C-C cross-coupling. Consistent with the experimental results, calculations indicate an easier reaction pathway if the N-substituent of the NHC ligand presents an electron-donating Y group. © 2012 American Chemical Society.

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

DEFF Research Database (Denmark)

Maggi, Agnese; Madsen, Robert

2012-01-01

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...

Room-temperature hydrohydrazination of terminal alkynes catalyzed by saturated abnormal N-heterocyclic carbene-gold(I) complexes.

Science.gov (United States)

Manzano, Rubén; Wurm, Thomas; Rominger, Frank; Hashmi, A Stephen K

2014-06-02

A number of saturated abnormal N-heterocyclic carbene (NHC) complexes of gold, in combination with KBAr(F) 4 as activator, were successfully applied in the chemoselective addition of hydrazine to alkynes. The reaction proceeds even at room temperature, which was not possible to date with gold catalysts. The reaction can be applied to a number of substituted arylalkynes. With alkylalkynes the yields are low. The saturated abnormal NHC ligands are resistant to isomerization to the saturated normal NHC coordination mode under basic reaction conditions. Under acidic conditions, a simple protonation at the nitrogen atom not neighboring the carbene center was observed and unambiguously characterized by an X-ray crystal-structure analysis. Computational studies confirm that such an isomerization would be highly exothermic, the observed kinetic stability probably results from the need to shift two protons in such a process. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Theoretical NMR spectroscopy of N-heterocyclic carbenes and their metal complexes

KAUST Repository

Falivene, Laura

2016-12-26

Recent theoretical analysis of the NMR properties of free N-heterocyclic carbenes (NHC) and Metal-NHC complexes has complemented experiments, allowing the establishment of structure/property relationships and the rationalization of otherwise surprising experimental results. In this review, the main conclusions from recent literature are discussed, with the aim to offer a vision of the potential of theoretical analyses of NMR properties.

Synthesis, characterization and antimicrobial activities of novel silver(I) complexes with coumarin substituted N-heterocyclic carbene ligands.

Science.gov (United States)

Karataş, Mert Olgun; Olgundeniz, Begüm; Günal, Selami; Özdemir, İlknur; Alıcı, Bülent; Çetinkaya, Engin

2016-02-15

Eight new coumarin substituted silver(I) N-heterocyclic carbene (NHC) complexes were synthesized by the interaction of the corresponding imidazolium or benzimidazolium chlorides and Ag2O in dichloromethane at room temperature. Structures of these complexes were established on the basis of elemental analysis, (1)H NMR, (13)C NMR, IR and mass spectroscopic techniques. The antimicrobial activities of carbene precursors and silver NHC complexes were tested against standard strains: Enterococcus faecalis, Staphylococcus aureus, Escherichia coli, Pseudomonas aeruginosa and the fungi Candida albicans and Candida tropicalis. Results showed that all the compounds inhibited the growth of the all bacteria and fungi strains and some complexes performed good activities against different microorganisms. Among all the compounds, the most lipophilic complex bis[1-(4-methylene-6,8-dimethyl-2H-chromen-2-one)-3-(naphthalene-2-ylmethyl)benzimidazol-2-ylidene]silver(I) dichloro argentate (5e) was found out as the most active one. Copyright © 2015 Elsevier Ltd. All rights reserved.

Rare-earth- and uranium-mesoionic carbenes. A new class of f-block carbene complex derived from an N-heterocyclic olefin

Energy Technology Data Exchange (ETDEWEB)

Seed, John A.; Gregson, Matthew; Chilton, Nicholas F.; Wooles, Ashley J.; Liddle, Stephen T. [School of Chemistry, The University of Manchester (United Kingdom); Tuna, Floriana; McInnes, Eric J.L. [School of Chemistry and Photon Science Institute, The University of Manchester (United Kingdom)

2017-09-11

Neutral mesoionic carbenes (MICs) have emerged as an important class of carbene, however they are found in the free form or ligated to only a few d-block ions. Unprecedented f-block MIC complexes [M(N''){sub 3}{CN(Me)C(Me)N(Me)CH}] (M=U, Y, La, Nd; N''=N(SiMe{sub 3}){sub 2}) are reported. These complexes were prepared by a formal 1,4-proton migration reaction when the metal triamides [M(N''){sub 3}] were treated with the N-heterocyclic olefin H{sub 2}C=C(NMeCH){sub 2}, which constitutes a new, general way to prepare MIC complexes. Quantum chemical calculations on the 5f{sup 3} uranium(III) complex suggest the presence of a U=C donor-acceptor bond, composed of a MIC→U σ-component and a U(5f)→MIC(2p) π-back-bond, but for the d{sup 0}f{sup 0} Y and La and 4f{sup 3} Nd congeners only MIC→M σ-bonding is found. Considering the generally negligible π-acidity of MICs, this is surprising and highlights that greater consideration should possibly be given to recognizing MICs as potential π-acid ligands when coordinated to strongly reducing metals. (copyright 2017 The Authors. Published by Wiley-VCH Verlag GmbH and Co. KGaA.)

-Heterocyclic Carbene Complexes of Mineral Acids

KAUST Repository

Brill, Marcel; Nahra, Fady; Gó mez-Herrera, Alberto; Zinser, Caroline; Cordes, David B.; Slawin, Alexandra M. Z.; Nolan, Steven P.

2016-01-01

We have synthesized and characterized new gold-N-heterocyclic carbene (NHC) complexes derived from the deprotonation of mineral acids. The use of sulfuric acid was a particularly interesting case. These complexes were tested in known gold-catalyzed reactions, such as the hydration of alkynes and the Meyer–Schuster rearrangement. They proved to be highly efficient in both reactions.

-Heterocyclic Carbene Complexes of Mineral Acids

KAUST Repository

Brill, Marcel

2016-11-08

We have synthesized and characterized new gold-N-heterocyclic carbene (NHC) complexes derived from the deprotonation of mineral acids. The use of sulfuric acid was a particularly interesting case. These complexes were tested in known gold-catalyzed reactions, such as the hydration of alkynes and the Meyer–Schuster rearrangement. They proved to be highly efficient in both reactions.

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

DEFF Research Database (Denmark)

Makarov, Ilya; Fristrup, Peter; Madsen, Robert

2012-01-01

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...

Olefin Metathesis with Ru-Based Catalysts Exchanging the Typical N-Heterocyclic Carbenes by a Phosphine–Phosphonium Ylide

Directory of Open Access Journals (Sweden)

Laia Arnedo

2017-03-01

Full Text Available Density functional theory (DFT calculations have been used to describe the first turnover of an olefin metathesis reaction calling for a new in silico family of homogenous Ru-based catalysts bearing a phosphine–phosphonium ylide ligand, with ethylene as a substrate. Equal to conventional Ru-based catalysts bearing an N-heterocyclic carbene (NHC ligand, the activation of these congeners occurs through a dissociative mechanism, with a more exothermic first phosphine dissociation step. In spite of a stronger electron-donating ability of a phosphonium ylide C-ligand with respect to a diaminocarbene analogue, upper energy barriers were calculated to be on average ca. 5 kcal/mol higher than those of Ru–NHC standards. Overall, the study also highlights advantages of bidentate ligands over classical monodentate NHC and phosphine ligands, with a particular preference for the cis attack of the olefin. The new generation of catalysts is constituted by cationic complexes potentially soluble in water, to be compared with the typical neutral Ru–NHC ones.

Synthesis and characterization of new N-heterocyclic carbene ligands: 1,3-Bis(acetamide)imidazol-3-ium bromide and 3-(acetamide)-1-(3-aminopropyl)-1H-imidazol-3-ium bromide

Science.gov (United States)

Turkyilmaz, Murat; Uluçam, Gühergül; Aktaş, Şaban; Okan, S. Erol

2017-05-01

Two new pincer type N-heterocyclic carbene ligands were synthesized. The compounds were characterized by FTIR, NMR (1H, 13C) GC-MS and elemental analyses. They were also both modelled by DFT calculations as the crystal structure of 1,3-bis(acetamide)imidazol-3-ium bromide was determined by XRD which is an orthorhombic system with space group P21212. The structural analyses in gas phase were realized by comparing the experimental NMR and IR spectra with those of the theoretical calculations. In vitro biological activities of the molecules were determined and found that one of them exhibits significant cytotoxic activity.

Enantioselective N-Heterocyclic Carbene Catalysis via the Dienyl Acyl Azolium.

Science.gov (United States)

Gillard, Rachel M; Fernando, Jared E M; Lupton, David W

2018-04-16

Herein we report the enantioselective N-heterocyclic carbene catalyzed (4+2) annulation of the dienyl acyl azolium with enolates. The reaction exploits readily accessible acyl fluorides and TMS enol ethers to give a range of highly enantio- and diastereo-enriched cyclohexenes (most >97:3 er and >20:1 dr). The reaction was found to require high nucleophilicity NHC catalysts with mechanistic studies supporting a stepwise 1,6-addition/β-lactonization. © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Asymmetric Reduction of tert-Butanesulfinyl Ketimines by N-Heterocyclic Carbene Boranes.

Science.gov (United States)

Liu, Tao; Chen, Ling-yan; Sun, Zhihua

2015-11-20

N-heterocyclic carbene borane (NHC-borane) based on a triazole core is demonstrated for the first time to be efficient for reduction of a variety of tert-butanesulfinyl ketimines. Up to 95% yield and up to >99% diastereomeric excess were achieved. NHC-borane exhibited excellent activities that are more efficient than or comparable to commonly used reductive reagents such as NaBH4, NaBH3CN, l-selectride, Ru catalyst, or BH3-THF.

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)

Ison, Elon A.; Ison, Ana

2012-01-01

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…

From betaines to anionic N-heterocyclic carbenes. Borane, gold, rhodium, and nickel complexes starting from an imidazoliumphenolate and its carbene tautomer

Directory of Open Access Journals (Sweden)

Ming Liu

2016-12-01

Full Text Available The mesomeric betaine imidazolium-1-ylphenolate forms a borane adduct with tris(pentafluorophenylborane by coordination with the phenolate oxygen, whereas its NHC tautomer 1-(2-phenolimidazol-2-ylidene reacts with (triphenylphosphinegold(I chloride to give the cationic NHC complex [Au(NHC2][Cl] by coordination with the carbene carbon atom. The anionic N-heterocyclic carbene 1-(2-phenolateimidazol-2-ylidene gives the complexes [K][Au(NHC−2], [Rh(NHC−3] and [Ni(NHC−2], respectively. Results of four single crystal analyses are presented.

Bimacrocyclic concave N-heterocyclic carbenes (NHCs): synthesis, structure, and application in catalyses

OpenAIRE

Lüning , Ulrich; Winkelmann , Ole

2009-01-01

Abstract Imidazolinium moieties have been incorporated into bimacrocycles to generate precursors for concave N-heterocyclic carbenes (NHCs). Starting from 2-nitroresorcinol and alkenols, symmetric concave imidazolinium salts 1 were obtained. Bimacrocyclization was achieved via ring closing metathesis (RCM). In an analogous fashion, axially chiral concave imidazolinium salts 2 were obtained by using a naphthalene bridgehead devoid of local C2-symmetry. The concave NHCs derived from ...

The reactions of anthronylidene carbene with some heterocyclic compounds

International Nuclear Information System (INIS)

Divisia, Bernadette

1970-01-01

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) [fr

N-Heterocyclic Carbene-Catalysed Diastereoselective Vinylogous Michael Addition Reaction of gamma-Substituted deconjugated Butenolides

KAUST Repository

Guo, Hao

2015-11-16

An efficient N-heterocyclic carbene (NHC)-catalysed vinylogous Michael addition of deconjugated butenolides was developed. In the presence of 5 mol% of the NHC catalyst, both γ-alkyl and aryl-substituted deconjugated butenolides undergo vinylogous Michael addition with various α, β-unsaturated ketones, esters, or nitriles to afford γ,γ-disubstituted butenolides containing adjacent quaternary and tertiary carbon centers in good to excellent yields with excellent diastereoselectivities. In this process, the free carbene is assumed to act as a strong Brønsted base to promote the conjugate addition.

N-Heterocyclic Carbene-Catalysed Diastereoselective Vinylogous Michael Addition Reaction of gamma-Substituted deconjugated Butenolides

KAUST Repository

Guo, Hao; Xing, Fen; Du, Guang-Fen; Huang, Kuo-Wei; Dai, Bin; He, Lin

2015-01-01

An efficient N-heterocyclic carbene (NHC)-catalysed vinylogous Michael addition of deconjugated butenolides was developed. In the presence of 5 mol% of the NHC catalyst, both γ-alkyl and aryl-substituted deconjugated butenolides undergo vinylogous Michael addition with various α, β-unsaturated ketones, esters, or nitriles to afford γ,γ-disubstituted butenolides containing adjacent quaternary and tertiary carbon centers in good to excellent yields with excellent diastereoselectivities. In this process, the free carbene is assumed to act as a strong Brønsted base to promote the conjugate addition.

Biological Screening of Newly Synthesized BIAN N-Heterocyclic Gold Carbene Complexes in Zebrafish Embryos

Science.gov (United States)

Farooq, Muhammad; Abu Taha, Nael; Butorac, Rachel R.; Evans, Daniel Anthony; Elzatahry, Ahmed A.; Elsayed, Elsayed Ahmed; Wadaan, Mohammad A. M.; Al-Deyab, Salem S.; Cowley, Alan H.

2015-01-01

N-Heterocyclic carbene (NHC) metal complexes possess diverse biological activities but have yet to be extensively explored as potential chemotherapeutic agents. We have previously reported the synthesis of a new class of NHC metal complexes N-heterocyclic with acetate [IPr(BIAN)AuOAc] and chloride [IPr(BIAN)AuCl] ligands. In the experiments reported herein, the zebrafish embryos were exposed to serial dilutions of each of these complexes for 10–12 h. One hundred percent mortality was observed at concentrations ≥50 µM. At sub-lethal concentrations (10–30 µM), both compounds influenced zebrafish embryonic development. However, quite diverse categories of abnormalities were found in exposed embryos with each compound. Severe brain deformation and notochord degeneration were evident in the case of [IPr(BIAN)AuOAc]. The zebrafish embryos treated with [IPr(BIAN)AuCl] exhibited stunted growth and consequently had smaller body sizes. A depletion of 30%–40% glutathione was detected in the treated embryos, which could account for one of the possible mechanism of neurotoxicity. The fact that these compounds are capable of both affecting the growth and also compromising antioxidant systems by elevating intracellular ROS production implies that they could play an important role as a new breed of therapeutic molecules. PMID:26501273

Anticancer Gold N-Heterocyclic Carbene Complexes: A Comparative in vitro and ex vivo Study.

Science.gov (United States)

Estrada-Ortiz, Natalia; Guarra, Federica; de Graaf, Inge A M; Marchetti, Lorella; de Jager, Marina H; Groothuis, Geny M M; Gabbiani, Chiara; Casini, Angela

2017-09-07

A series of organometallic Au I N-heterocyclic carbene (NHC) complexes was synthesized and characterized for anticancer activity in four human cancer cell lines. The compounds' toxicity in healthy tissue was determined using precision-cut kidney slices (PCKS) as a tool to determine the potential selectivity of the gold complexes ex vivo. All evaluated compounds presented cytotoxic activity toward the cancer cells in the nano- or low micromolar range. The mixed Au I NHC complex, (tert-butylethynyl)-1,3-bis-(2,6-diisopropylphenyl)imidazol-2-ylidene gold(I), bearing an alkynyl moiety as ancillary ligand, showed high cytotoxicity in cancer cells in vitro, while being barely toxic in healthy rat kidney tissues. The obtained results open new perspectives toward the design of mixed NHC-alkynyl gold complexes for cancer therapy. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

A multi-target caffeine derived rhodium(i) N-heterocyclic carbene complex: evaluation of the mechanism of action.

Science.gov (United States)

Zhang, Jing-Jing; Muenzner, Julienne K; Abu El Maaty, Mohamed A; Karge, Bianka; Schobert, Rainer; Wölfl, Stefan; Ott, Ingo

2016-08-16

A rhodium(i) and a ruthenium(ii) complex with a caffeine derived N-heterocyclic carbene (NHC) ligand were biologically investigated as organometallic conjugates consisting of a metal center and a naturally occurring moiety. While the ruthenium(ii) complex was largely inactive, the rhodium(i) NHC complex displayed selective cytotoxicity and significant anti-metastatic and in vivo anti-vascular activities and acted as both a mammalian and an E. coli thioredoxin reductase inhibitor. In HCT-116 cells it increased the reactive oxygen species level, leading to DNA damage, and it induced cell cycle arrest, decreased the mitochondrial membrane potential, and triggered apoptosis. This rhodium(i) NHC derivative thus represents a multi-target compound with promising anti-cancer potential.

Cyclopentadienyl molybdenum(II/VI) N-heterocyclic carbene complexes: Synthesis, structure, and reactivity under oxidative conditions

KAUST Repository

Li, Shenyu; Kee, Choonwee; Huang, Kuo-Wei; Hor, Andy Sum Andy; Zhao, Jin

2010-01-01

A series of N-heterocyclic carbene (NHC) complexes CpMo(CO) 2(NHC)X (NHC = IMe = 1,3-dimethylimidazol-2-ylidene, X = Br, 1; NHC = 1,3-dipropylimidazol-2-ylidene, X = Br, 2; NHC = IMes = 1,3-bis(2,4,6- trimethylphenyl)imidazol-2-ylidene, X = Br, 3

N-Heterocyclic-Carbene-Catalysed Diastereoselective Vinylogous Mukaiyama/Michael Reaction of 2-(Trimethylsilyloxy)furan and Enones

KAUST Repository

Wang, Ying; Du, Guang Fen; Xing, Fen; Huang, Kuo-Wei; Dai, Bin; He, Lin

2015-01-01

N-heterocyclic carbenes have been utilised as highly efficient nucleophilic organocatalysts to mediate vinylogous Mukaiyama/Michael reactions of 2-(trimethylsilyloxy)furan with enones to afford γ-substituted butenolides in 44-99% yield with 3:1-32:1 diastereoselectivity. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

N-Heterocyclic-Carbene-Catalysed Diastereoselective Vinylogous Mukaiyama/Michael Reaction of 2-(Trimethylsilyloxy)furan and Enones

KAUST Repository

Wang, Ying

2015-10-15

N-heterocyclic carbenes have been utilised as highly efficient nucleophilic organocatalysts to mediate vinylogous Mukaiyama/Michael reactions of 2-(trimethylsilyloxy)furan with enones to afford γ-substituted butenolides in 44-99% yield with 3:1-32:1 diastereoselectivity. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Cascade olefin isomerization/intramolecular Diels-Alder reaction catalyzed by N-heterocyclic carbenes.

Science.gov (United States)

Kowalczyk, Marcin; Lupton, David W

2014-05-19

The addition of an N-heterocyclic carbene to the carbonyl group of an α,β,γ,δ-unsaturated enol ester affords a hemiacetal azolium intermediate that enables a cascade olefin isomerization/Diels-Alder reaction, for which mechanistic studies implicate Lewis base catalysis. Preliminary studies into the utility of the products have been undertaken with reductive and oxidative cleavage, giving materials for potential use in complex-target synthesis. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

A chemical-biological evaluation of rhodium(I) N-heterocyclic carbene complexes as prospective anticancer drugs.

Science.gov (United States)

Oehninger, Luciano; Küster, Laura Nadine; Schmidt, Claudia; Muñoz-Castro, Alvaro; Prokop, Aram; Ott, Ingo

2013-12-23

Rhodium(I) complexes bearing N-heterocyclic carbene (NHC) ligands have been widely used in catalytic chemistry, but there are very few reports of biological properties of these organometallics. A series of Rh(I)-NHC derivatives with 1,5-cyclooctadiene and CO as secondary ligands were synthesized, characterized, and biologically investigated as prospective antitumor drug candidates. Pronounced antiproliferative effects were noted for all complexes, along with moderate inhibitory activity of thioredoxin reductase (TrxR) and efficient binding to biomolecules (DNA, albumin). Biodistribution studies showed that the presence of albumin lowered the cellular uptake and confirmed the transport of rhodium into the nuclei. Changes in the mitochondrial membrane potential (MMP) were observed as well as DNA fragmentation in wild-type and daunorubicin- or vincristine-resistant Nalm-6 leukemia cells. Overall, these studies indicated that Rh(I)-NHC fragments could be used as partial structures of new antitumor agents, in particular in those drugs designed to address resistant malignant tissues. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Bis-ligated Ti and Zr complexes of chelating N-heterocyclic carbenes

KAUST Repository

El-Batta, Amer

2011-07-01

In this communication we report the synthesis of novel titanium and zirconium complexes ligated by bidentate "salicylaldimine-like" N-heterocyclic carbenes (NHC). Double addition of the NHC chelate to either TiCl4(thf)2 or ZrCl4 forms bis-ligated organometallic fragments with a distorted octahedral geometry. These complexes are rare examples of group IV transition-metal NHC adducts. Preliminary catalytic tests demonstrate that in the presence of methylaluminoxane (MAO) these complexes are useful initiators for the polymerization of ethylene and the copolymerization of ethylene with norbornene and 1-octene. © 2011 Elsevier B.V. All rights reserved.

Application of Chan-Lam cross coupling for the synthesis of N-heterocyclic carbene precursors bearing strong electron donating or withdrawing groups

Science.gov (United States)

Huang, Liliang; He, Chengxiang; Sun, Zhihua

2015-07-01

Chan-Lam cross coupling allowed efficient synthesis of N,N’-disubstituted ortho-phenylene diamines bearing strong electron donating or withdrawing groups, such as nitro or methoxy groups, with moderate to high yields. These diamines can then be turned into N-heterocyclic carbene precursors after condensation with trimethyl orthoformate. The same strategy can also be utilized for the synthesis of N-monosubstituted aniline derivatives containing a functionalized ortho-aminomethyl group as intermediates for chiral 6-membered ring carbene precursors.

Alkyne-Azide Cycloaddition Catalyzed by Silver Chloride and “Abnormal” Silver N-Heterocyclic Carbene Complex

Directory of Open Access Journals (Sweden)

Aldo I. Ortega-Arizmendi

2013-01-01

Full Text Available A library of 1,2,3-triazoles was synthesized from diverse alkynes and azides using catalytic amounts of silver chloride instead of copper compounds. In addition, a novel “abnormal” silver N-heterocyclic carbene complex was tested as catalyst in this process. The results suggest that the reaction requires only 0.5% of silver complex, affording 1,2,3-triazoles in good yields.

1,2,4-Triazole-based N-heterocyclic carbene complexes of gold(I): synthesis, characterization and biological activity

Czech Academy of Sciences Publication Activity Database

Turek, J.; Růžičková, Z.; Tloušťová, Eva; Mertlíková-Kaiserová, Helena; Günterová, Jana; Rulíšek, Lubomír; Růžička, A.

2016-01-01

Roč. 30, č. 5 (2016), s. 318-322 ISSN 0268-2605 R&D Projects: GA ČR(CZ) GA14-31419S; GA MŠk LO1302 Institutional support: RVO:61388963 Keywords : gold(I) complexes * N-heterocyclic carbenes * cytotoxicity * apoptosis Subject RIV: CC - Organic Chemistry Impact factor: 2.319, year: 2016

Cyclopentadienyl molybdenum(II/VI) N-heterocyclic carbene complexes: Synthesis, structure, and reactivity under oxidative conditions

KAUST Repository

Li, Shenyu

2010-04-26

A series of N-heterocyclic carbene (NHC) complexes CpMo(CO) 2(NHC)X (NHC = IMe = 1,3-dimethylimidazol-2-ylidene, X = Br, 1; NHC = 1,3-dipropylimidazol-2-ylidene, X = Br, 2; NHC = IMes = 1,3-bis(2,4,6- trimethylphenyl)imidazol-2-ylidene, X = Br, 3; NHC = IBz = 1,3-dibenzylimidazol- 2-ylidene, X = Br, 4a, and X = Cl, 4b; NHC = 1-methyl-3-propylimidazol-2- ylidene, X = Br, 5) and [CpMo(CO)2(IMes)(CH3CN)][BF 4] (6) have been synthesized and fully characterized. The stability of metal-NHC ligand bonds in these compounds under oxidative conditions has been investigated. The thermally stable Mo(VI) dioxo NHC complex [CpMoO 2(IMes)][BF4] (9) has been isolated by the oxidation of the ionic complex 6 by TBHP (tert-butyl hydrogen peroxide). Complex 6 can be applied as a very active (TOFs up to 3400 h-1) and selective olefin epoxidation catalyst. While under oxidative conditions (in the presence of TBHP), compounds 1-5 decompose into imidazolium bromide and imidazolium polyoxomolybdate. The formation of polyoxomolybdate as oxidation products had not been observed in a similar epoxidation catalyzed by Mo(II) and Mo(VI) complexes. DFT studies suggest that the presence of Br- destabilizes the CpMo(VI) oxo NHC carbene species, consistent with the experimental observations. © 2010 American Chemical Society.

N-Heterocyclic Carbene-Catalyzed Vinylogous Mukaiyama Aldol Reaction of α-Keto Esters and α-Trifluoromethyl Ketones

KAUST Repository

Du, Guang-Fen; Wang, Ying; Xing, Fen; Xue, Mei; Guo, Xu-Hong; Huang, Kuo-Wei; Dai, Bin

2015-01-01

© Georg Thieme Verlag Stuttgart · New York · Synthesis 2016. N-Heterocyclic carbene (NHC)-catalyzed vinylogous Mukaiyama aldol reaction of ketones was developed. Under the catalysis of 5 mol% NHC, α-keto esters and α-trifluoromethyl ketones reacted with 2-(trimethysilyloxy)furan efficiently to produce γ-substituted butenolides containing adjacent quaternary and tertiary carbon centers in high yields with good diastereoselectivities.

Synthesis and characterization of a cationic phthalimido-functionalized N-heterocyclic carbene complex of palladium(II) and its catalytic activity

KAUST Repository

Goh, Li Min Serena; Hogerl, Manuel Peter; Jokic̈, Nadežda B.; Tanase, Alexandrina D.; Bechlars, Bettina; Baratta, Walter; Mí nk, Já nos; Kü hn, Fritz

2014-01-01

A cationic phthalimido-functionalized N-heterocyclic carbene (NHC) palladium(II) complex has been synthesized from [3-methyl-1-(2′- phthalimidoethyl)imidazolium] hexafluorophosphate ([NHCMe,PhtH] PF6) by transmetalation and isolated in 67 % yield. The title complex has been applied as catalyst in the Suzuki-Miyaura cross-coupling reaction under benign aqueous conditions. The catalyst is active without any observable initiation period. High average turnover frequencies (TOFs) of up to 55000 h-1 have been reached with catalyst concentrations as low as 0.01 mol-%. A cationic phthalimido-functionalized N-heterocyclic carbene (NHC) palladium(II) complex has been prepared in high yield. The complex was activated instantly, without an initiation period, in the Suzuki-Miyaura cross-coupling reaction under benign aqueous aerobic conditions. Turnover frequencies (TOFs) up to 55000 h-1, were achieved with 0.01 mol-% of the complex. Copyright © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Synthesis and characterization of a cationic phthalimido-functionalized N-heterocyclic carbene complex of palladium(II) and its catalytic activity

KAUST Repository

Goh, Li Min Serena

2014-01-29

A cationic phthalimido-functionalized N-heterocyclic carbene (NHC) palladium(II) complex has been synthesized from [3-methyl-1-(2′- phthalimidoethyl)imidazolium] hexafluorophosphate ([NHCMe,PhtH] PF6) by transmetalation and isolated in 67 % yield. The title complex has been applied as catalyst in the Suzuki-Miyaura cross-coupling reaction under benign aqueous conditions. The catalyst is active without any observable initiation period. High average turnover frequencies (TOFs) of up to 55000 h-1 have been reached with catalyst concentrations as low as 0.01 mol-%. A cationic phthalimido-functionalized N-heterocyclic carbene (NHC) palladium(II) complex has been prepared in high yield. The complex was activated instantly, without an initiation period, in the Suzuki-Miyaura cross-coupling reaction under benign aqueous aerobic conditions. Turnover frequencies (TOFs) up to 55000 h-1, were achieved with 0.01 mol-% of the complex. Copyright © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

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

Science.gov (United States)

Panzner, Matthew J.; Hindi, Khadijah M.; Wright, Brian D.; Taylor, Jane B.; Han, Daniel S.

2009-01-01

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 silver acetate produces the highly hydrophilic silver carbene complex SCC8. The in vitro antimicrobial efficacy of this newly synthesized complex was evaluated with excellent results on a variety of virulent and MDR pathogens isolated from CF patients. A comparative in vivo study between the known caffeine derived silver carbene SCC1 and SCC8 demonstrated the ability of both complexes to improve the survival rates of mice in a pneumonia model utilizing the clinically isolated infectious strain of Pseudomonas aeruginosa PA M57-15. PMID:20449175

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

Science.gov (United States)

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

2009-09-21

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 N(1) nitrogen atom with an ethanol substituent followed by the methylation of the N(9) nitrogen atom gives the N-heterocyclic carbene precursor 1-(2-hydroxyethyl)-3,7,9-trimethylxanthinium iodide. The reaction of this xanthinium salt with silver acetate produces the highly hydrophilic silver carbene complex SCC8. The in vitro antimicrobial efficacy of this newly synthesized complex was evaluated with excellent results on a variety of virulent and MDR pathogens isolated from CF patients. A comparative in vivo study between the known caffeine derived silver carbene SCC1 and SCC8 demonstrated the ability of both complexes to improve the survival rates of mice in a pneumonia model utilizing the clinically isolated infectious strain of Pseudomonas aeruginosa PA M57-15.

N-Heterocyclic Carbene-Catalyzed Olefination of Aldehydes with Vinyliodonium Salts To Generate α,β-Unsaturated Ketones.

Science.gov (United States)

Rajkiewicz, Adam A; Kalek, Marcin

2018-04-06

An organocatalyzed metal-free, direct olefination of aldehydes with vinyliodonium salts has been achieved by an N-heterocyclic carbene-promoted C-H bond activation. The reaction proceeds under very mild conditions, delivering a range of (hetero)aryl-vinyl ketones in good yields. The retention of the double bond configuration is uniformly observed, and the application of 2-methoxyphenyl auxiliary group in iodonium salts secures a complete selectivity of the vinyl transfer.

Immobilization of N-Heterocyclic Carbene Compounds: A Synthetic Perspective.

Science.gov (United States)

Zhong, Rui; Lindhorst, Anja C; Groche, Florian J; Kühn, Fritz E

2017-02-08

Over the course of the past 15 years the success story of N-heterocyclic carbene (NHC) compounds in organic, inorganic, and organometallic chemistry has been extended to another dimension. The immobilization of NHC compounds, undergoing continuous diversification, broadens their range of applications and leads to new solutions for challenges in catalytic and synthetic chemistry. This review intends to present a synthetic toolkit for the immobilization of NHC compounds, giving the reader an overview on synthetic techniques and strategies available in the literature. By individually summarizing and assessing the synthetic steps of the immobilization process, a comprehensive picture of the strategies and methodologies for the immobilization of NHC compounds is presented. Furthermore, the characterization of supported NHC compounds is discussed in detail in order to set up necessary criteria for an in-depth analysis of the immobilized derivatives. Finally, the catalytic applications of immobilized NHC compounds are briefly reviewed to illustrate the practical use of this technique for a broad variety of reaction types.

Dimerisation, rhodium complex formation and rearrangements of N-heterocyclic carbenes of indazoles

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Zong Guan

2014-04-01

Full Text Available Deprotonation of indazolium salts at low temperatures gives N-heterocyclic carbenes of indazoles (indazol-3-ylidenes which can be trapped as rhodium complexes (X-ray analysis. In the absence of Rh, the indazol-3-ylidenes spontaneously dimerize under ring cleavage of one of the N,N-bonds and ring closure to an indazole–indole spiro compound which possesses an exocyclic imine group. The E/Z isomers of the imines can be separated by column chromatography when methanol is used as eluent. We present results of a single crystal X-ray analysis of one of the E-isomers, which equilibrate in solution as well as in the solid state. Heating of the indazole–indole spiro compounds results in the formation of quinazolines by a ring-cleavage/ring-closure sequence (X-ray analysis. Results of DFT calculations are presented.

A Catalyst-Enabled Diastereodivergent Aza-Diels-Alder Reaction: Complementarity of N-Heterocyclic Carbenes and Chiral Amines.

Science.gov (United States)

Rong, Zi-Qiang; Wang, Min; Chow, Chi Hao Eugene; Zhao, Yu

2016-07-04

Highly efficient and diastereodivergent aza-Diels-Alder reactions have been developed to access either diastereomeric series of benzofuran-fused δ-lactams and dihydropyridines in nearly perfect stereoselectivity (d.r. >20:1, >99 % ee for all examples). The complementarity of N-heterocyclic carbene and chiral amine as the catalyst was demonstrated for the first time, together with an excellent level of catalytic efficiency (1 mol % loading). © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

α-Diazo oxime ethers for N-heterocycle synthesis.

Science.gov (United States)

Choi, Subin; Ha, Sujin; Park, Cheol-Min

2017-06-01

This Feature Article introduces the preparation and synthetic utility of α-diazo oxime ethers. α-Oximino carbenes are useful synthons for N-heterocycles, and can be easily prepared from α-diazo oxime ethers as precursors. We begin with the preparation of α-diazo oxime ethers and their application in [3+2] cycloaddition. It turns out that the nature of metals bound to carbenes plays a crucial role in modulating the reactivity of α-oximino carbenes, in which copper carbenes smoothly react with enamines, whereas the less reactive enol ethers and nitriles require gold carbenes. In Section 3.2, a discussion on N-O and C-H bond activation is presented. Carbenes derived from diazo oxime ethers show unique reactivity towards N-O and C-H bond activation, in which the proximity of the two functionalities, carbene and oxime ether, dictates the preferred reaction pathways toward pyridines, pyrroles, and 2H-azirines. In Section 3.3, the development of tandem reactions based on α-diazo oxime ethers is discussed. The nature of carbenes in which whether free carbenes or metal complexes are involved dissects the pathway and forms different types of 2H-azirines. The 2H-azirine formation turned out to be an excellent platform for the tandem synthesis of N-heterocycles including pyrroles and pyridines. In the last section, we describe the electrophilic activation of 2H-azirines with vinyl carbenes and oximino carbenes. The resulting azirinium species undergo rapid ring expansion rearrangements to form pyridines and pyrazines.

N-Heterocyclic carbenes on close-packed coinage metal surfaces: bis-carbene metal adatom bonding scheme of monolayer films on Au, Ag and Cu.

Science.gov (United States)

Jiang, Li; Zhang, Bodong; Médard, Guillaume; Seitsonen, Ari Paavo; Haag, Felix; Allegretti, Francesco; Reichert, Joachim; Kuster, Bernhard; Barth, Johannes V; Papageorgiou, Anthoula C

2017-12-01

By means of scanning tunnelling microscopy (STM), complementary density functional theory (DFT) and X-ray photoelectron spectroscopy (XPS) we investigate the binding and self-assembly of a saturated molecular layer of model N -heterocyclic carbene (NHC) on Cu(111), Ag(111) and Au(111) surfaces under ultra-high vacuum (UHV) conditions. XPS reveals that at room temperature, coverages up to a monolayer exist, with the molecules engaged in metal carbene bonds. On all three surfaces, we resolve similar arrangements, which can be interpreted only in terms of mononuclear M(NHC) 2 (M = Cu, Ag, Au) complexes, reminiscent of the paired bonding of thiols to surface gold adatoms. Theoretical investigations for the case of Au unravel the charge distribution of a Au(111) surface covered by Au(NHC) 2 and reveal that this is the energetically preferential adsorption configuration.

N-BUTYL SUBSTITUTED N-HETEROCYCLIC CARBENE-PD(II-PYRIDINE (PEPPSI COMPLEXES: SYNTHESIS, CHARACTERIZATION AND CATALYTIC ACTIVITY IN THE SUZUKI-MIYAURA REACTION

Directory of Open Access Journals (Sweden)

Rukiye Fırıncı

2016-08-01

Full Text Available A series of N-butyl substituted imidazolium salts, (1a-c and their pyridine enhanced precatalyst preparation stabilization and initiation (PEPPSI themed palladium N-heterocyclic carbene complexes (2a-c were synthesized and characterized. Pd-NHC complexes were fully determined by elemental analysis and spectroscopic. The synthesized complexes were tested in Suzuki-Miyaura cross-coupling reaction. These complexes were found to be efficient catalysts for the Suzuki-Miyaura reaction of phenylboronic acid with aryl bromides.

Ballbot-type motion of N-heterocyclic carbenes on gold surfaces

Science.gov (United States)

Wang, Gaoqiang; Rühling, Andreas; Amirjalayer, Saeed; Knor, Marek; Ernst, Johannes Bruno; Richter, Christian; Gao, Hong-Jun; Timmer, Alexander; Gao, Hong-Ying; Doltsinis, Nikos L.; Glorius, Frank; Fuchs, Harald

2017-02-01

Recently, N-heterocyclic carbenes (NHCs) were introduced as alternative anchors for surface modifications and so offered many attractive features, which might render them superior to thiol-based systems. However, little effort has been made to investigate the self-organization process of NHCs on surfaces, an important aspect for the formation of self-assembled monolayers (SAMs), which requires molecular mobility. Based on investigations with scanning tunnelling microscopy and first-principles calculations, we provide an understanding of the microscopic mechanism behind the high mobility observed for NHCs. These NHCs extract a gold atom from the surface, which leads to the formation of an NHC-gold adatom complex that displays a high surface mobility by a ballbot-type motion. Together with their high desorption barrier this enables the formation of ordered and strongly bound SAMs. In addition, this mechanism allows a complementary surface-assisted synthesis of dimeric and hitherto unknown trimeric NHC gold complexes on the surface.

A facile route to ruthenium-carbene complexes and their application in furfural hydrogenation

NARCIS (Netherlands)

Strassberger, Z.; Mooijman, M.; Ruijter, E.; Alberts, A.H.; de Graaff, C.; Orru, R.V.A.; Rothenberg, G.

2010-01-01

A number of new N-heterocyclic carbene (NHC) ligands were synthesized via a multicomponent reaction, wherein an aldehyde or ketone, a primary amine and an α-acidic isocyanide were reacted, giving the corresponding 2H-2-imidazolines. These were easily alkylated with an alkyl halide at position N-3,

Variation of the Sterical Properties of the N-Heterocyclic Carbene Coligand in Thermally Triggerable Ruthenium-Based Olefin Metathesis Precatalysts/Initiators

KAUST Repository

Pump, Eva

2015-11-09

A series of ruthenium complexes based on the κ(C,N)-(2-(benzo[h]quinolin-10-yl)methylidene ruthenium dichloride fragment featuring different neutral coligands L (L = 1,3-bis(2,6-diisopropylphenyl)-4,5-dihydroimidazol-2-ylidene (SIPr), 1,3-bis(2,4,6-trimethylphenyl)-4,5-dihydroimidazol-2-ylidene (SIMes), 1,3-bis(2,4-dimethylphenyl)-4,5-dihydroimidazol-2-ylidene (SIXyl), and 1,3-bis(2-methylphenyl)-4,5-dihydroimidazol-2-ylidene (SITol)) was prepared, characterized, and tested in the thermally induced ring-opening metathesis polymerization of dicyclopentadiene. In addition, the corresponding tricyclohexylphosphine derivative was investigated for comparison. All compounds were isolated as their trans-dichloro isomers. NMR spectroscopic features as well as structural features are, particularly within the NHC-bearing complexes, very similar, but their polymerization activity at elevated temperatures is distinctly different. While the SIMes derivative shows the desired properties, i.e., latency at room temperature and pronounced polymerization activity at elevated temperature, all other preinitiators do not. The preinitiator featuring the SIPr coligand is the most latent one, needing temperatures > 140 °C to show moderate activity in the polymerization of dicyclopentadiene. Compounds bearing the smaller N-heterocyclic carbene congeners are stable and latent at room temperature, but decompose upon heating, diminishing the polymerization activity at elevated temperatures. Density functional calculations show that the SIMes derivative is the easiest to activate and yields the most stable 14-electron intermediate. Finally calculations reveal a distinct influence of the nature of the N-heterocyclic carbene ligand on the position of the equilibrium of cis- and trans-dichloro isomers of the complexes. While the SIPr and the SIMes derivatives prefer the cis-configuration, all other derivatives favor, at least in solvents with low dielectric constants, the trans

Anti-trypanosomal activity of cationic N-heterocyclic carbene gold(I) complexes.

Science.gov (United States)

Winter, Isabel; Lockhauserbäumer, Julia; Lallinger-Kube, Gertrud; Schobert, Rainer; Ersfeld, Klaus; Biersack, Bernhard

2017-06-01

Two gold(I) N-heterocyclic carbene complexes 1a and 1b were tested for their anti-trypanosomal activity against Trypanosoma brucei parasites. Both gold compounds exhibited excellent anti-trypanosomal activity (IC 50 =0.9-3.0nM). The effects of the gold complexes 1a and 1b on the T. b. brucei cytoskeleton were evaluated. Rapid detachment of the flagellum from the cell body occurred after treatment with the gold complexes. In addition, a quick and complete degeneration of the parasitic cytoskeleton was induced by the gold complexes, only the microtubules of the detached flagellum remained intact. Both gold compounds 1a and 1b feature selective anti-trypanosomal agents and were distinctly more active against T. b. brucei cells than against human HeLa cells. Thus, the gold complexes 1a and 1b feature promising drug candidates for the treatment of trypanosome infections such as sleeping sickness (human African Trypanosomiasis caused by Trypanosoma brucei parasites). Copyright © 2017 Elsevier B.V. All rights reserved.

Redox noninnocence of carbene ligands: carbene radicals in (catalytic) C-C bond formation

NARCIS (Netherlands)

Dzik, W.I.; Zhang, X.P.; de Bruin, B.

2011-01-01

In this Forum contribution, we highlight the radical-type reactivities of one-electron-reduced Fischer-type carbenes. Carbene complexes of group 6 transition metals (Cr, Mo, and W) can be relatively easily reduced by an external reducing agent, leading to one-electron reduction of the carbene ligand

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)

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

2015-01-27

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 μM. Copyright �

Oxidative N-Heterocyclic Carbene-Catalyzed γ-Carbon Addition of Enals to Imines: Mechanistic Studies and Access to Antimicrobial Compounds.

Science.gov (United States)

Zheng, Peng-Cheng; Cheng, Jiajia; Su, Shihu; Jin, Zhichao; Wang, Yu-Huang; Yang, Song; Jin, Lin-Hong; Song, Bao-An; Chi, Yonggui Robin

2015-07-06

The reaction mechanism of the γ-carbon addition of enal to imine under oxidative N-heterocyclic carbene catalysis is studied experimentally. The oxidation, γ-carbon deprotonation, and nucleophilic addition of γ-carbon to imine were found to be facile steps. The results of our study also provide highly enantioselective access to tricyclic sulfonyl amides that exhibit interesting antimicrobial activities against X. oryzae, a bacterium that causes bacterial disease in rice growing. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Mechanistic Insights into the Organopolymerization of N-Methyl N-Carboxyanhydrides Mediated by N-Heterocyclic Carbenes

KAUST Repository

Falivene, Laura

2016-10-04

We report on a DFT investigation of initiation, propagation, and termination in the organopolymerization of N-methyl N-carboxyanhydrides toward cyclic poly(N-substituted glycine)s, promoted by N-heterocyclic carbenes (NHC). Calculations support the experimentally based hypothesis of two competing initiation pathways. The first leading to formation of a zwitterionic adduct by nucleophilic addition of the NHC to one of the carbonyl groups of monomer. The second via acid–base reactivity, starting with the NHC promoted abstraction of a proton from the methylene group of the monomer, leading to an ion-pair-type adduct, followed by nucleophilic attack of the adduct to a new monomer molecule. Chain elongation can proceed from both the initiation adducts via nucleophilic attack of the carbamate chain-end to a new monomer molecule via concerted elimination of CO2 from the carbamate chain-end. Energy barriers along all the considered termination pathways are remarkably higher that the energy barrier along the chain elongation pathways, consistent with the quasi-living experimental behavior. Analysis of the competing termination pathways suggests that the cyclic species determined via MALDI-TOF MS experiments consists of a zwitterionic species deriving from nucleophilic attack of the N atom of the carbamate chain-end to the C═O group bound to the NHC moiety.

Effect of tert-Butyl Functionalization on the Photoexcited Decay of a Fe(II)-N-Heterocyclic Carbene Complex

DEFF Research Database (Denmark)

Pápai, Mátyás Imre; Penfold, Thomas J.; Møller, Klaus Braagaard

2016-01-01

-vibronic quantum dynamics simulations on the Fe-N-heterocyclic carbene complex, [Fe(btbip)2]2+ (btbip = 2,6-bis(3-tert-butyl-imidazole-1-ylidene)pyridine). The results demonstrate that a relatively minor structural change compared to its parent complex, [Fe(bmip)2]2+ (bmip = 2,6-bis(3-methyl-imidazole-1-ylidene....... This occurs because the tert-butyl functionalization stabilizes the 1MC states, enabling the 1,3MLCT → 1MC population transfer to occur close to the Franck-Condon geometry, making the conversion very efficient. Subsequently, a spin cascade occurs within the MC manifold, leading to the population of triplet...

Synthesis of a 1-Aryl-2,2-chlorosilyl(phosphasilene Coordinated by an N-Heterocyclic Carbene

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Andreas Wolfgang Kyri

2016-09-01

Full Text Available Phosphasilenes, P=Si doubly bonded compounds, have received considerable attention due to their unique physical and chemical properties. We report on the synthesis and structure of a chlorophosphasilene coordinated by an N-heterocyclic carbene (NHC, which has the potential of functionalization at the Si–Cl moiety. Treatment of a silylphosphine, ArPH–SiCl2RSi (Ar = bulky aryl group, RSi = Si(SiMe33 with two equivalents of Im-Me4 (1,3,4,5-tetramethylimidazol-2-ylidene afforded the corresponding NHC-coordinated phosphasilene, ArP=SiClRSi(Im-Me4 as a stable compound. Bonding properties of the P=Si bond coordinated to an NHC will be discussed on the basis of theoretical calculations.

Synthesis and Antimicrobial Activity of Novel Ag-N-Hetero-cyclic Carbene Complexes

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İlknur Özdemir

2010-04-01

Full Text Available A series of imidazolidinium ligand precursors are metallated with Ag2O to give silver(I N-heterocyclic carbene complexes. All compounds were fully characterized by elemental analyses, 1H-NMR, 13C-NMR and IR spectroscopy techniques. All compounds studied in this work were screened for their in vitro antimicrobial activities against the standard strains: Enterococcus faecalis (ATCC 29212, Staphylococcus aureus (ATCC 29213, Escherichia coli (ATCC 25922, Pseudomonas aeruginosa (ATCC 27853 and the fungi Candida albicans and Candida tropicalis. The new imidazolidin-2-ylidene silver complexes have been found to display effective antimicrobial activity against a series of bacteria and fungi.

N-Heterocyclic Carbene Capture by Cytochrome P450 3A4

Science.gov (United States)

Jennings, Gareth K.; Ritchie, Caroline M.; Shock, Lisa S.; Lyons, Charles E.

2016-01-01

Cytochrome P450 3A4 (CYP3A4) is the dominant P450 enzyme involved in human drug metabolism, and its inhibition may result in adverse interactions or, conversely, favorably reduce the systemic elimination rates of poorly bioavailable drugs. Herein we describe a spectroscopic investigation of the interaction of CYP3A4 with N-methylritonavir, an analog of ritonavir, widely used as a pharmacoenhancer. In contrast to ritonavir, the binding affinity of N-methylritonavir for CYP3A4 is pH-dependent. At pH UV-visible spectroscopy binding studies with molecular fragments narrows the source of this pH dependence to its N-methylthiazolium fragment. The C2 proton of this group is acidic, and variable-pH resonance Raman spectroscopy tentatively assigns it a pKa of 7.4. Hence, this fragment of N-methylritonavir is expected to be readily deprotonated under physiologic conditions to yield a thiazol-2-ylidene, which is an N-heterocyclic carbene that has high-affinity for and is presumed to be subsequently captured by the heme iron. This mechanism is supported by time-dependent density functional theory with an active site model that accurately reproduces distinguishing features of the experimental UV-visible spectra of N-methylritonavir bound to CYP3A4. Finally, density functional theory calculations support that this novel interaction is as strong as the tightest-binding azaheterocycles found in P450 inhibitors and could offer new avenues for inhibitor development. PMID:27126611

Guidelines To Select the N-Heterocyclic Carbene for the Organopolymerization of Monomers with a Polar Group

KAUST Repository

Falivene, Laura

2017-02-13

We report on the DFT stability of zwitterion and spirocycle adducts of five polar monomers with nine N-heterocyclic carbenes (NHC), covering the most typical classes of monomers and NHCs used in organopolymerization. Results indicate that the relative stability of the two adducts is dominated by the singlet-triplet energy gap of the free NHC, with low energy gaps favoring the spirocycle adduct, while high energy gaps favor the zwitterionic adduct. This basic structure/property relationship can be tuned by the hindrance of the NHC and the nature of the monomer. In addition to rationalize existing systems, the 45 NHC/monomer combinations we examined can be used as a guideline to predict the behavior of a new NHC/monomer combination.

Synthesis, Structural Analysis and Antimicrobial Activities of Novel Water Soluble Ionic Liquids Derived from N-Heterocyclic Carbene Salts

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Ahmet Kunduracıoğlu

2016-06-01

Full Text Available Six N-heterocyclic Carbene based Ionic Liquids (ILs have been synthesized by conventional methods. The ILs were spectroscopically characterized by NMR and FT-IR techniques. Their in vitro antimicrobial activities were determined towards gram-positive and gram-negative bacterias and yeast strains using minimum inhibition concentration (MIC assay. The best inhibition performances were obtained with compound 1 due to its more hydrophilic nature compared with the others. It exhibited 1 mg L–1 MIC value against to the most bacteria while the others showed 4 mg L–1. This work is licensed under a Creative Commons Attribution 4.0 International License.

Oxygen Atom Transfer Using an Iron(IV)-Oxo Embedded in a Tetracyclic N-Heterocyclic Carbene System: How Does the Reactivity Compare to Cytochrome P450 Compound I?

Science.gov (United States)

Cantú Reinhard, Fabián G; de Visser, Sam P

2017-02-24

N-Heterocyclic carbenes (NHC) are commonly featured as ligands in transition metal catalysis. Recently, a cyclic system containing four NHC groups with a central iron atom was synthesized and its iron(IV)-oxo species, [Fe IV (O)(cNHC 4 )] 2+ , was characterized. This tetracyclic NHC ligand system may give the iron(IV)-oxo species unique catalytic properties as compared to traditional non-heme and heme iron ligand systems. Therefore, we performed a computational study on the structure and reactivity of the [Fe IV (O)(cNHC 4 )] 2+ complex in substrate hydroxylation and epoxidation reactions. The reactivity patterns are compared with cytochrome P450 Compound I and non-heme iron(IV)-oxo models and it is shown that the [Fe IV (O)(cNHC 4 )] 2+ system is an effective oxidant with oxidative power analogous to P450 Compound I. Unfortunately, in polar solvents, a solvent molecule will bind to the sixth ligand position and decrease the catalytic activity of the oxidant. A molecular orbital and valence bond analysis provides insight into the origin of the reactivity differences and makes predictions of how to further exploit these systems in chemical catalysis. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

In situ Generated Ruthenium Catalyst Systems Bearing Diverse N-Heterocyclic Carbene Precursors for Atom-Economic Amide Synthesis from Alcohols and Amines.

Science.gov (United States)

Cheng, Hua; Xiong, Mao-Qian; Cheng, Chuan-Xiang; Wang, Hua-Jing; Lu, Qiang; Liu, Hong-Fu; Yao, Fu-Bin; Chen, Cheng; Verpoort, Francis

2018-02-16

The transition-metal-catalyzed direct synthesis of amides from alcohols and amines is herein demonstrated as a highly environmentally benign and atom-economic process. Among various catalyst systems, in situ generated N-heterocyclic carbene (NHC)-based ruthenium (Ru) halide catalyst systems have been proven to be active for this transformation. However, these existing catalyst systems usually require an additional ligand to achieve satisfactory results. In this work, through extensive screening of a diverse variety of NHC precursors, we discovered an active in situ catalyst system for efficient amide synthesis without any additional ligand. Notably, this catalyst system was found to be insensitive to the electronic effects of the substrates, and various electron-deficient substrates, which were not highly reactive with our previous catalyst systems, could be employed to afford the corresponding amides efficiently. Furthermore, mechanistic investigations were performed to provide a rationale for the high activity of the optimized catalyst system. NMR-scale reactions indicated that the rapid formation of a Ru hydride intermediate (signal at δ=-7.8 ppm in the 1 H NMR spectrum) after the addition of the alcohol substrate should be pivotal in establishing the high catalyst activity. Besides, HRMS analysis provided possible structures of the in situ generated catalyst system. © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Insights Into the Carbene-Initiated Aggregation of [Fe(cot)2

KAUST Repository

Lavallo, Vincent; El-Batta, Amer; Bertrand, Guy; Grubbs, Robert H.

2010-01-01

Carbenes attack! Stable carbenes react with [Fe(cot)2] in very different ways. Whereas the classical N-heterocyclic carbenes induce the formation of tetra- and trimetallic iron clusters, abnormal NHCs and carbocyclic carbenes (BACs) form mono- and bimetallic iron complexes. Cyclic (alkyl)(amino)carbenes (CAACs) react with [Fe(cot)2] in a completely different manner, namely through outersphere [4+1] cycloaddition.

Insights Into the Carbene-Initiated Aggregation of [Fe(cot)2

KAUST Repository

Lavallo, Vincent

2010-11-25

Carbenes attack! Stable carbenes react with [Fe(cot)2] in very different ways. Whereas the classical N-heterocyclic carbenes induce the formation of tetra- and trimetallic iron clusters, abnormal NHCs and carbocyclic carbenes (BACs) form mono- and bimetallic iron complexes. Cyclic (alkyl)(amino)carbenes (CAACs) react with [Fe(cot)2] in a completely different manner, namely through outersphere [4+1] cycloaddition.

Steric Maps to Evaluate the Role of Steric Hindrance on the IPr NHC Ligand

KAUST Repository

Poater, Albert; Falivene, Laura; Urbina-Blanco, Cé sar A.; Manzini, Simone; Nolan, Steven P.; Cavallo, Luigi

2013-01-01

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) (IPr) N-heterocyclic carbene (NHC) ligand

Ligand-Controlled Synthesis of Azoles via Ir-Catalyzed Reactions of Sulfoxonium Ylides with 2-Amino Heterocycles.

Science.gov (United States)

Phelps, Alicia M; Chan, Vincent S; Napolitano, José G; Krabbe, Scott W; Schomaker, Jennifer M; Shekhar, Shashank

2016-05-20

An iridium-catalyzed method was developed for the synthesis of imidazo-fused pyrrolopyrazines. The presence or absence of a nitrogenated ligand controlled the outcome of the reaction, leading to simple β-keto amine products in the absence of added ligand and the cyclized 7- and 8-substituted-imidazo[1,2-a]pyrrolo[2,3-e]pyrazine products in the presence of ligand. This catalyst control was conserved across a variety of ylide and amine coupling partners. The substrate was shown to act as a ligand for the iridium catalyst in the absence of other ligands via NMR spectroscopy. Kinetic studies indicated that formation of the Ir-carbene was reversible and the slow step of the reaction. These mechanistic investigations suggest that the β-keto amine products form via an intramolecular carbene N-H insertion, and the imidazopyrrolopyrazines form via an intermolecular carbene N-H insertion.

N-Heterocyclic-Carbene-Treated Gold Surfaces in Pentacene Organic Field-Effect Transistors: Improved Stability and Contact at the Interface.

Science.gov (United States)

Lv, Aifeng; Freitag, Matthias; Chepiga, Kathryn M; Schäfer, Andreas H; Glorius, Frank; Chi, Lifeng

2018-04-16

N-Heterocyclic carbenes (NHCs), which react with the surface of Au electrodes, have been successfully applied in pentacene transistors. With the application of NHCs, the charge-carrier mobility of pentacene transistors increased by five times, while the contact resistance at the pentacene-Au interface was reduced by 85 %. Even after annealing the NHC-Au electrodes at 200 °C for 2 h before pentacene deposition, the charge-carrier mobility of the pentacene transistors did not decrease. The distinguished performance makes NHCs as excellent alternatives to thiols as metal modifiers for the application in organic field-effect transistors (OFETs). © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Ruthenium(II) Complexes Containing Lutidine-Derived Pincer CNC Ligands: Synthesis, Structure, and Catalytic Hydrogenation of C-N bonds.

Science.gov (United States)

Hernández-Juárez, Martín; López-Serrano, Joaquín; Lara, Patricia; Morales-Cerón, Judith P; Vaquero, Mónica; Álvarez, Eleuterio; Salazar, Verónica; Suárez, Andrés

2015-05-11

A series of Ru complexes containing lutidine-derived pincer CNC ligands have been prepared by transmetalation with the corresponding silver-carbene derivatives. Characterization of these derivatives shows both mer and fac coordination of the CNC ligands depending on the wingtips of the N-heterocyclic carbene fragments. In the presence of tBuOK, the Ru-CNC complexes are active in the hydrogenation of a series of imines. In addition, these complexes catalyze the reversible hydrogenation of phenantridine. Detailed NMR spectroscopic studies have shown the capability of the CNC ligand to be deprotonated and get involved in ligand-assisted activation of dihydrogen. More interestingly, upon deprotonation, the Ru-CNC complex 5 e(BF4 ) is able to add aldimines to the metal-ligand framework to yield an amido complex. Finally, investigation of the mechanism of the hydrogenation of imines has been carried out by means of DFT calculations. The calculated mechanism involves outer-sphere stepwise hydrogen transfer to the C-N bond assisted either by the pincer ligand or a second coordinated H2 molecule. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Sequential Functionalization of Alkynes and Alkenes Catalyzed by Gold(I) and Palladium(II) N-Heterocyclic Carbene Complexes

KAUST Repository

Gó mez-Herrera, Alberto; Nahra, Fady; Brill, Marcel; Nolan, Steven P.; Cazin, Catherine S. J.

2016-01-01

The iodination of terminal alkynes for the synthesis of 1-iodoalkynes using N-iodosuccinimide in the presence of a AuI-NHC (NHC=N-heterocyclic carbene) catalyst is reported. A series of aromatic alkynes was transformed successfully into the corresponding 1-iodoalkynes in good to excellent yields under mild reaction conditions. The further use of these compounds as organic building blocks and the advantageous choice of metal-NHC complexes as catalysts for alkyne functionalization were further demonstrated by performing selective AuI-catalyzed hydrofluorination to yield (Z)-2-fluoro-1-iodoalkenes, followed by a Suzuki–Miyaura cross-coupling with aryl boronic acids catalyzed by a PdII-NHC complex to access trisubstituted (Z)-fluoroalkenes. All methodologies can be performed sequentially with only minor variations in the optimized individual reaction conditions, maintaining high efficiency and selectivity in all cases, which therefore, provides straightforward access to valuable fluorinated alkenes from commercially available terminal alkynes.

Sequential Functionalization of Alkynes and Alkenes Catalyzed by Gold(I) and Palladium(II) N-Heterocyclic Carbene Complexes

KAUST Repository

Gómez-Herrera, Alberto

2016-08-22

The iodination of terminal alkynes for the synthesis of 1-iodoalkynes using N-iodosuccinimide in the presence of a AuI-NHC (NHC=N-heterocyclic carbene) catalyst is reported. A series of aromatic alkynes was transformed successfully into the corresponding 1-iodoalkynes in good to excellent yields under mild reaction conditions. The further use of these compounds as organic building blocks and the advantageous choice of metal-NHC complexes as catalysts for alkyne functionalization were further demonstrated by performing selective AuI-catalyzed hydrofluorination to yield (Z)-2-fluoro-1-iodoalkenes, followed by a Suzuki–Miyaura cross-coupling with aryl boronic acids catalyzed by a PdII-NHC complex to access trisubstituted (Z)-fluoroalkenes. All methodologies can be performed sequentially with only minor variations in the optimized individual reaction conditions, maintaining high efficiency and selectivity in all cases, which therefore, provides straightforward access to valuable fluorinated alkenes from commercially available terminal alkynes.

Interpretation of electronic spectra of ruthenium nitroso complexes with N-heterocyclic ligands

International Nuclear Information System (INIS)

Sizova, O.V.; Ivanova, N.V.; Lyubimova, O.O.; Nikol'skij, A.B.

2004-01-01

Relaying on ab initio and semiempirical CINDO/CI calculations of free ligands L and complexes trans-[Ru(NO)(NH 3 ) 4 (L)] 3+ (L=pyridine, pyrazine, nicotinamide, l-histidine, imidazole), electronic absorption spectra of nitroso complexes with nitrogen-containing heterocyclic ligands L have been analyzed. Spectral manifestations of strong covalent bond Ru-NO was pointed out and the conclusion was made about advisability of presentation of Ru and NO oxidation states in grouping RuNO 3+ as Ru(III) and NO 0 . Introduction of nitroso group into inner coordination sphere of Ru(II) complexes with nitrogen-containing heterocyclic ligands results in essential rearrangement of the entire structure and deprives ligands L of their ability to manifest chromophore properties [ru

Steric and electronic parameters of a bulky yet flexible N-heterocyclic carbene: 1,3-bis(2,6-bis(1-ethylpropyl)phenyl)imidazol-2-ylidene (IPent)

KAUST Repository

Collado, Alba; Balogh, Já nos; Meiries, Sé bastien; Slawin, Alexandra M. Z.; Falivene, Laura; Cavallo, Luigi; Nolan, Steven P.

2013-01-01

The free N-heterocyclic carbene IPent (1; IPent = 1,3-bis(2,6-bis(1- ethylpropyl)phenyl)imidazol-2-ylidene) was prepared from the corresponding imidazolium chloride salt (2). The steric and electronic parameters of 1 were determined by synthesis of the gold(I) chloride complex [Au(IPent)Cl] (3) and the nickel-carbonyl complex [Ni(IPent)(CO)3] (4), respectively. 3 and 4 were fully characterized by NMR spectroscopy, elemental analysis, and X-ray diffraction studies on single crystals. © 2013 American Chemical Society.

Steric and electronic parameters of a bulky yet flexible N-heterocyclic carbene: 1,3-bis(2,6-bis(1-ethylpropyl)phenyl)imidazol-2-ylidene (IPent)

KAUST Repository

Collado, Alba

2013-06-10

The free N-heterocyclic carbene IPent (1; IPent = 1,3-bis(2,6-bis(1- ethylpropyl)phenyl)imidazol-2-ylidene) was prepared from the corresponding imidazolium chloride salt (2). The steric and electronic parameters of 1 were determined by synthesis of the gold(I) chloride complex [Au(IPent)Cl] (3) and the nickel-carbonyl complex [Ni(IPent)(CO)3] (4), respectively. 3 and 4 were fully characterized by NMR spectroscopy, elemental analysis, and X-ray diffraction studies on single crystals. © 2013 American Chemical Society.

Direct Functionalization of Nitrogen Heterocycles via Rh-Catalyzed C-H Bond Activation

Energy Technology Data Exchange (ETDEWEB)

Lewis, Jared; Bergman, Robert; Ellman, Jonathan

2008-02-04

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

Alkali-Metal-Mediated Magnesiations of an N-Heterocyclic Carbene: Normal, Abnormal, and "Paranormal" Reactivity in a Single Tritopic Molecule.

Science.gov (United States)

Martínez-Martínez, Antonio J; Fuentes, M Ángeles; Hernán-Gómez, Alberto; Hevia, Eva; Kennedy, Alan R; Mulvey, Robert E; O'Hara, Charles T

2015-11-16

Herein the sodium alkylmagnesium amide [Na4Mg2(TMP)6(nBu)2] (TMP=2,2,6,6-tetramethylpiperidide), a template base as its deprotonating action is dictated primarily by its 12 atom ring structure, is studied with the common N-heterocyclic carbene (NHC) IPr [1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene]. Remarkably, magnesiation of IPr occurs at the para-position of an aryl substituent, sodiation occurs at the abnormal C4 position, and a dative bond occurs between normal C2 and sodium, all within a 20 atom ring structure accommodating two IPr(2-). Studies with different K/Mg and Na/Mg bimetallic bases led to two other magnesiated NHC structures containing two or three IPr(-) monoanions bound to Mg through abnormal C4 sites. Synergistic in that magnesiation can only work through alkali-metal mediation, these reactions add magnesium to the small cartel of metals capable of directly metalating a NHC. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Antibacterial and DNA cleavage activity of carbonyl functionalized N-heterocyclic carbene-silver(I) and selenium compounds

Science.gov (United States)

Haque, Rosenani A.; Iqbal, Muhammad Adnan; Mohamad, Faisal; Razali, Mohd R.

2018-03-01

The article describes syntheses and characterizations of carbonyl functionalized benzimidazolium salts, I-IV. While salts I-III are unstable at room temperature, salt IV remained stable and was further utilised to form N-heterocyclic carbene (NHC) compounds of silver(I), V and VI, and selenium compound, VII respectively. Compounds IV-VII were tested for their antibacterial potential against Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus). Salt IV shows a very low inhibition potential (minimum inhibitory concentration, MIC 500 μg/mL) compared to the respective silver(I)-NHC, V and VI (MIC 31.25 μg/mL against both, E. coli and S. aureus) and selenium compound, VII (MIC 125 μg/mL against E. coli and 62.50 μg/mL against S. aureus). In DNA cleavage abilities, all the test compounds cleave DNA in which the VII cleaves the DNA at the faster rate. Meanwhile, the silver(I)-NHC complexes V and VI act at the same mode and pattern of DNA cleavage while VII is similar to IV.

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

International Nuclear Information System (INIS)

Cunha, C.J. da.

1989-01-01

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)

Synthesis of axially chiral oxazoline-carbene ligands with an N-naphthyl framework and a study of their coordination with AuCl·SMe(2).

Science.gov (United States)

Wang, Feijun; Li, Shengke; Qu, Mingliang; Zhao, Mei-Xin; Liu, Lian-Jun; Shi, Min

2012-01-01

Axially chiral oxazoline-carbene ligands with an N-naphthyl framework were successfully prepared, and their coordination behavior with AuCl·SMe(2) was also investigated, affording the corresponding Au(I) complexes in moderate to high yields.

Unraveling the synthesis of homoleptic [Ag(N,N-diaryl-NHC)2]Y (Y = BF4, PF6) complexes by ball-milling.

Science.gov (United States)

Beillard, Audrey; Bantreil, Xavier; Métro, Thomas-Xavier; Martinez, Jean; Lamaty, Frédéric

2016-11-28

A user-friendly and general mechanochemical method was developed to access rarely described NHC (N-heterocyclic carbene) silver(i) complexes featuring N,N-diarylimidazol(idin)ene ligands and non-coordinating tetrafluoroborate or hexafluorophosphate counter anions. Comparison with syntheses in solution clearly demonstrated the superiority of the ball-milling conditions.

Partitioning-separation of metal ions using heterocyclic ligands

International Nuclear Information System (INIS)

Hudson, M.J.; Drew, M.G.B.; Iveson, P.B.; Russell, M.L.

2001-01-01

Some guidelines are proposed for the effective design of heterocyclic ligands for partitioning because there is no doubt that the correct design of a molecular extractant is required for the effective separation of metal ions such as actinides(III) from lanthanides(III). Heterocyclic ligands with aromatic ring systems have a rich chemistry, which is only now becoming sufficiently well understood in relation to the partitioning process. The synthesis, characterisation and structures of some chosen molecules will be introduced in order to illustrate some important features. For example, the molecule N-carboxy-butyl-2-amino-4,6-di (2-pyridyl)-1,3,5-triazine (BADPTZ), which is an effective solvent extraction reagent for actinides and lanthanides, has been synthesised, characterised and its interaction with lanthanide ions studied. The interesting and important features of this molecule will be compared with those of other heterocyclic molecules such as 2,6-bis(5-butyl-1,2,4-triazole-3-yl) pyridine (DBTZP), which is a candidate molecule for the commercial separation of actinides and lanthanide elements. (author)

A dual Lewis base activation strategy for enantioselective carbene-catalyzed annulations.

Science.gov (United States)

Izquierdo, Javier; Orue, Ane; Scheidt, Karl A

2013-07-24

A dual activation strategy integrating N-heterocyclic carbene (NHC) catalysis and a second Lewis base has been developed. NHC-bound homoenolate equivalents derived from α,β-unsaturated aldehydes combine with transient reactive o-quinone methides in an enantioselective formal [4 + 3] fashion to access 2-benzoxopinones. The overall approach provides a general blueprint for the integration of carbene catalysis with additional Lewis base activation modes.

Cycloalkyl-based unsymmetrical unsaturated (U2)-NHC ligands: Flexibility and dissymmetry in ruthenium-catalysed olefin metathesis

KAUST Repository

Rouen, Mathieu

2014-01-01

Air-stable Ru-indenylidene and Hoveyda-type complexes bearing new unsymmetrical unsaturated N-heterocyclic carbene (U2-NHC) ligands combining a mesityl unit and a flexible cycloalkyl moiety as N-substituents were synthesised. Structural features, chemical stabilities and catalytic profiles in olefin metathesis of this new library of cycloalkyl-based U2-NHC Ru complexes were studied and compared with their unsymmetrical saturated NHC-Ru homologues as well as a set of commercially available Ru-catalysts bearing either symmetrical SIMes or IMes NHC ligands. © 2014 the Partner Organisations.

Synthesis and Characterization of New Silver (I N-Heterocyclic Ccarbene Ccomplex Dderived from Imidazol-2-ylidene salt

Directory of Open Access Journals (Sweden)

Mohammedl Mujbe Hasson

2018-04-01

Full Text Available A new N, N'-imidazolium salt 1-(2,6-diisopropylphenyl-3- (4,6-dimorpholino -1,3,5-traizine-2-yl-1H-imidazol-3-ium chloride as a precursor of N - heterocyclic carbene ligand was prepared via the reaction of 1 - (2, 6 - diisopropyl phenyl - 1H - imidazole with 1, 3, 5 - triazine derivative bearing morpholine substituent (2, 6 -dimorpholine - 6- chloro-1, 3, 5-triaziazine. Linear coordi-nated Ag (І NHC complex was synthesised via deprotonation of the imidazolium salt and reac-tion with Ag2O in darkness at room temperature by in situ method. The complex was synthesised for using as transfer agent to prepare another transition metals complexes by transmetallation method in the future. The imidazolium salt and their silver complex have been characterized by 1 H and 13C NMR spectroscopy as well as mass spectrometry.

Rhenium carbene complexes and their applications; Rhenium-Carben-Komplexe und ihre Anwendungen

Energy Technology Data Exchange (ETDEWEB)

Hille, Claudia Heidi

2016-01-25

New pharmaceutically suitable metal complexes play an important role in the development of diagnostic and therapeutic agents for cancer treatment. One option concerning new radiopharmaceuticals, is the application of the rhenium isotopes {sup 186}Re and {sup 188}Re. Therefore, water soluble but at the same time stable complexes, which can be synthesized straightforward, are required. In this thesis, several synthetic pathways to such rhenium complexes bearing Nheterocyclic carbenes are presented and applicability tests of literature known complexes conducted. The selected target structures based on monocarbenes turned out to be inappropriate for use in radiopharmaceutical applications, due to their long reaction times and purification issues. Additionally, sterical and electronical effects of the carbene ligands concerning complex formation have been investigated. Possibilities of functionalization at different positions on the heterocycle as well as hydrophilic wingtips - to achieve a better stability in an aqueous media - have been examined to gain information about chemical and physical properties of the resulting complexes. Furthermore, experiments regarding the coordination of various biscarbene ligands, which provides besides the stable chelatisation additionally the possibility of varying the linking bridge, to rhenium(I/V) precursors, have been performed. Dioxo-bis-(1,1{sup '}-methylene-bis(3,3{sup '}-diisopropylimidazolium-2-ylidene)) rhenium(V )-hexafluorophosphate was synthesized via a transmetalation reaction of the corresponding silver carbene with ReOCl{sub 3}(PPh{sub 3}){sub 2} and silver hexafluorophosphate. This complex provided the basis for the first radiolabeled {sup 188}Rhenium NHC complex later on. An enhancement of the kinetic and thermodynamic stability of potential rhenium biscarbene complexes based on modifications concerning the length and character of the bridging moiety between the chelating NHC rings as well as the nature of

Coordination behavior of bis-phenolate saturated and unsaturated N-heterocyclic carbene ligands to zirconium: reactivity and activity in the copolymerization of cyclohexene oxide with CO2.

Science.gov (United States)

Lalrempuia, Ralte; Breivik, Frida; Törnroos, Karl W; Le Roux, Erwan

2017-06-27

Tetravalent zirconium complexes supported by tridentate bis-phenolate imidazolidin-2-ylidene (L1), imidazol-2-ylidene (L2) and benzimidazol-2-ylidene (L3) NHC ligands were synthesized and evaluated as precursors for the copolymerization of cyclohexene oxide (CHO) with CO 2 . While the reactivity of the imidazolidinium [H 3 L1] chloride salt with Zr(OiPr) 4 (HOiPr), and subsequent ligand exchanges with either (CH 3 ) 3 SiCl or LiOiPr lead to a series of heteroleptic compounds (κ 3 -O,C,O-L1)Zr(X) 2 (THF) (X = Cl, OiPr), both imidazolium [H 3 L2] and benzimidazolium [H 3 L3] chloride salts give a mixture of homoleptic (κ 3 -O,C,O-NHC) 2 Zr and zwitterionic (κ 2 -O,O-HL)ZrCl 2 (OiPr) compounds along with traces or the absence of the heteroleptic intermediate (κ 3 -O,C,O-NHC)Zr(Cl)(OiPr)(THF). Such dissimilar reactivity between the unsaturated and saturated NHC ligands is predominantly ascribed to the increased acidity of azolium salts along with the π-donor strength of the C carbene in L2 and L3-Zr moieties. The reactivity with the more acidic azolium salts (H 3 L2/3) and the destabilized Zr-X trans to NHC carbene bond results in a significant increase in the amount of homoleptic compounds generating HCl. The released HCl reacts preferentially with the heteroleptic intermediates having non-planar NHC ligands (i.e. L2/3) promoting the formation of zwitterionic complexes. The in situ deprotonation of the isolated zwitterionic (κ 2 -O,O-HL3)ZrCl 2 (OiPr) compound by using Ag 2 O gives the homoleptic complex as the major component along with a bimetallic hydroxo-bridged [(κ 3 -O,C,O-L3)Zr(μ-OH)(OiPr)] 2 compound. Of particular interest is that only the heteroleptic NHC-Zr(iv) complexes were identified to be active and highly selective towards the copolymerization of CHO with CO 2 independently of the co-catalysts used (both anionic and neutral) under mild conditions (P CO 2 < 1 bar, T = 60 °C), and gave atactic and completely alternating copolymers in a

Supporting Information Palladium Complexes of a New Type of N ...

Indian Academy of Sciences (India)

Prasenjit Ghosh

Palladium Complexes of a New Type of N-heterocyclic Carbene. Ligand Derived From a Tricyclic Triazolooxazine Framework. Manoj Kumar Gangwar, Alok Ch. Kalita and Prasenjit Ghosh*. Department of Chemistry,. Indian Institute of Technology Bombay, ... 2. Figure S1. 1. H NMR spectrum of the compound 1a in CDCl3.

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

Science.gov (United States)

Yu, Dingyi; Zhang, Yugen

2010-01-01

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, a copper-catalyzed and copper–N-heterocyclic carbene-cocatalyzed transformation of CO2 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

Metal–organic coordination architectures of tetrazole heterocycle ligands bearing acetate groups: Synthesis, characterization and magnetic properties

International Nuclear Information System (INIS)

Hu, Bo-Wen; Zheng, Xiang-Yu; Ding, Cheng

2015-01-01

Two new coordination complexes with tetrazole heterocycle ligands bearing acetate groups, [Co(L) 2 ] n (1) and [Co 3 (L) 4 (N 3 ) 2 ·2MeOH] n (2) (L=tetrazole-1-acetate) have been synthesized and structurally characterized. Single crystal structure analysis shows that the cobalt-complex 1 has the 3D 3,6-connected (4 2 .6) 2 (4 4 .6 2 .8 8 .10)-ant topology. By introducing azide in this system, complex 2 forms the 2D network containing the [Co 3 ] units. And the magnetic properties of 1 and 2 have been studied. - Graphical abstract: The synthesis, crystal structure, and magnetic properties of the new coordination complexes with tetrazole heterocycle ligands bearing acetate groups are reported. - Highlights: • Two novel Cobalt(II) complexes with tetrazole acetate ligands were synthesized. • The magnetic properties of two complexes were studied. • Azide as co-ligand resulted in different structures and magnetic properties. • The new coordination mode of tetrazole acetate ligand was obtained.

Proton-Transfer Polymerization by N-Heterocyclic Carbenes: Monomer and Catalyst Scopes and Mechanism for Converting Dimethacrylates into Unsaturated Polyesters

KAUST Repository

Hong, Miao

2016-01-18

This contribution presents a full account of experimental and theoretical/computational investigations into the N-heterocyclic carbene (NHC)-catalyzed proton-transfer polymerization (HTP) that converts common dimethacrylates (DMAs) containing no protic groups into unsaturated polyesters. This new HTP proceeds through the step-growth propagation cycles via enamine intermediates, consisting of the proposed conjugate addition–proton transfer–NHC release fundamental steps. This study examines the monomer and catalyst scopes as well as the fundamental steps involved in the overall HTP mechanism. DMAs having six different types of linkages connecting the two methacrylates have been polymerized into the corresponding unsaturated polyesters. The most intriguing unsaturated polyester of the series is that based on the biomass-derived furfuryl dimethacrylate, which showed a unique self-curing ability Four MeO– and Cl–substituted TPT (1,3,4-triphenyl-4,5-dihydro-1H-1,2,4-triazol-5-ylidene) derivatives as methanol insertion products, RxTPT(MeO/H) (R = MeO, Cl; x = 2, 3), and two free carbenes (catalysts), OMe2TPT and OMe3TPT, have been synthesized, while OMe2TPT(MeO/H) and OMe2TPT have also been structurally characterized. The structure/reactivity relationship study revealed that OMe2TPT, being both a strong nucleophile and a good leaving group, exhibits the highest HTP activity and also produced the polyester with the highest Mn, while the Cl–substituted TPT derivatives are least active and efficient. Computational studies have provided mechanistic insights into the tail-to-tail dimerization coupling step as a suitable model for the propagation cycle of the HTP. The extensive energy profile was mapped out and the experimentally observed unicity of the TPT-based catalysts was satisfactorily explained with the thermodynamic formation of key spirocyclic species.

Hydrogen Production and Storage on a Formic Acid/Bicarbonate Platform using Water-Soluble N-Heterocyclic Carbene Complexes of Late Transition Metals.

Science.gov (United States)

Jantke, Dominik; Pardatscher, Lorenz; Drees, Markus; Cokoja, Mirza; Herrmann, Wolfgang A; Kühn, Fritz E

2016-10-06

The synthesis and characterization of two water-soluble bis-N-heterocyclic carbene (NHC) complexes of rhodium and iridium is presented. Both compounds are active in H 2 generation from formic acid and in hydrogenation of bicarbonate to formate. The rhodium derivative is most active in both reactions, reaching a TOF of 39 000 h -1 and a TON of 449 000 for H 2 production. The catalytic hydrogenation reactions were carried out in an autoclave system and analyzed using the integrated peak areas in the 1 H NMR spectra. Decomposition of formic acid was investigated using a Fisher-Porter bottle equipped with a pressure transducer. Long-term stability for hydrogen evolution was tested by surveillance of the gas flow rate. The procedure does not require any additives like amines or inert gas conditions. Density functional theory calculations in agreement with experimental results suggest a bicarbonate reduction mechanism involving a second catalyst molecule, which provides an external hydride acting as reducing agent. © 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Synthesis, structure and DFT conformation analysis of CpNiX(NHC) and NiX2(NHC)2 (X = SPh or Br) complexes

Science.gov (United States)

Malan, Frederick P.; Singleton, Eric; van Rooyen, Petrus H.; Conradie, Jeanet; Landman, Marilé

2017-11-01

The synthesis, density functional theory (DFT) conformational study and structure analysis of novel two-legged piano stool Ni N-heterocyclic carbene (NHC) complexes and square planar Ni bis-N-heterocyclic carbene complexes, all containing either bromido- or thiophenolato ligands, are described. [CpNi(SPh)(NHC)] complexes were obtained from the neutral 18-electron [CpNiBr(NHC)] complexes by substitution of a bromido ligand with SPh, using NEt3 as a base to abstract the proton of HSPh. The 16-electron biscarbene complexes [Ni(SPh)2{NHC}2] were isolated when an excess of HSPh was added to the reaction mixture. Biscarbene complexes of the type [NiBr2(NHC)2] were obtained in the reaction of NiCp2 with a slight excess of the specific imidazolium bromide salt. The molecular and electronic structures of the mono- and bis-N-heterocyclic carbene complexes have been analysed using single crystal diffraction and density functional theory (DFT) calculations, to give insight into their structural properties.

Human colon cancer targeted pro-apoptotic, anti-metastatic and cytostatic effects of binuclear Silver(I)-N-Heterocyclic carbene (NHC) complexes.

Science.gov (United States)

Asif, Muhammad; Iqbal, Muhammad Adnan; Hussein, Mouayed A; Oon, Chern Ein; Haque, Rosenani A; Khadeer Ahamed, Mohamed B; Abdul Majid, Aman Shah; Abdul Majid, Amin Malik Shah

2016-01-27

The current mechanistic study was conducted to explore the effects of increased lipophilicity of binuclear silver(I)-NHC complexes on cytotoxicity. Two new silver(I)-N-Heterocyclic Carbene (NHC) complexes (3 and 4), having lypophilic terminal alkyl chains (Octyl and Decyl), were derived from meta-xylyl linked bis-benzimidazolium salts (1 and 2). Each of the synthesized compounds was characterized by microanalysis and spectroscopic techniques. The complexes were tested for their cytotoxicity against a panel of human cancer c as well normal cell lines using MTT assay. Based on MTT assay results, complex 4 was found to be selectively toxic towards human colorectal carcinoma cell line (HCT 116). Complex 4 was further studied in detail to explore the mechanism of cell death and findings of the study revealed that complex 4 has promising pro-apoptotic and anti-metastatic activities against HCT 116 cells. Furthermore, it showed pronounced cytostatic effects in HCT 116 multicellular spheroid model. Hence, binuclear silver(I)-NHC complexes with longer terminal aliphatic chains have worth to be further studied against human colon cancer for the purpose of drug development. Copyright © 2015 Elsevier Masson SAS. All rights reserved.

Synthesis and characterization of nitrile functionalized silver(I)-N-heterocyclic carbene complexes: DNA binding, cleavage studies, antibacterial properties and mosquitocidal activity against the dengue vector, Aedes albopictus.

Science.gov (United States)

Asekunowo, Patrick O; Haque, Rosenani A; Razali, Mohd R; Avicor, Silas W; Wajidi, Mustafa F F

2018-04-25

A series of four benzimidazolium based nitrile-functionalized mononuclear-Ag(I)-N-heterocyclic carbene and binuclear-Ag(I)-N-heterocyclic carbene (Ag(I)-NHC) hexafluorophosphate complexes (5b-8b) were synthesized by reacting the corresponding hexafluorophosphate salts (1b-4b) with Ag 2 O in acetonitrile, respectively. These compounds were characterized by 1 H NMR, 13 C NMR, IR, UV-visible spectroscopic techniques, elemental analyses and molar conductivity. Additionally, 8b was structurally characterized by single crystal X-ray diffraction technique. Preliminary in vitro antibacterial evaluation was conducted for all the compounds against two standard bacteria; gram-positive (Staphylococcus aureus) and gram-negative (Escherichia coli) bacterial strains. Most of the Ag(I)-NHC complexes (5b-8b) showed moderate to good antibacterial activity with MIC values in the range of 12.5-100 μg/mL. Especially, compound 8b exhibited promising anti-Staphylococcus aureus activity with a low MIC value (12.5 μg/mL). However, all the hexafluorophosphate salts (1b-4b) were inactive against the bacteria strains. The preliminary interactive investigation revealed that the most active compound, 8b, could effectively intercalate into DNA to form 8b-DNA complex which shows a better binding ability for DNA (K b  = 3.627 × 10 6 ) than the complexes 5b-7b (2.177 × 10 6 , 8.672 × 10 5 and 6.665 × 10 5 , respectively). Nuclease activity of the complexes on plasmid DNA and Aedes albopictus genomic DNA was time-dependent, although minimal. The complexes were larvicidal to the mosquito, with 5b, 6b and 8b being highly active. Developmental progression from the larval to the adult stage was affected by the complexes, progressively being toxic to the insect's development with increasing concentration. These indicate the potential use of these complexes as control agents against bacteria and the dengue mosquito Ae. albopictus. Copyright © 2018 Elsevier Masson SAS. All

Enhanced π-Back-Donation as a Way to Higher Coordination Numbers in d10 [M(NHC)n] Complexes: A DFT Study

NARCIS (Netherlands)

Nitsch, J.; Wolters, L.P.; Fonseca Guerra, C.; Bickelhaupt, F.M.; Steffen, A.

2016-01-01

We aim to understand the electronic factors determining the stability and coordination number of d10 transition-metal complexes bearing N-heterocyclic carbene (NHC) ligands, with a particular emphasis on higher coordinated species. In this DFT study on the formation and bonding of Group 9–12 d10

Enhanced pi-Back-Donation as a Way to Higher Coordination Numbers in d10 [M(NHC)n] Complexes: A DFT Study

NARCIS (Netherlands)

Nitsch, J.S.; Wolters, L.P.; Fonseca Guerra, C.; Bickelhaupt, F.M.; Steffen, A.

2017-01-01

We aim to understand the electronic factors determining the stability and coordination number of d10 transition-metal complexes bearing N-heterocyclic carbene (NHC) ligands, with a particular emphasis on higher coordinated species. In this DFT study on the formation and bonding of Group 9–12 d10

Water oxidation catalyzed by mononuclear ruthenium complexes with a 2,2'-bipyridine-6,6'-dicarboxylate (bda) ligand: how ligand environment influences the catalytic behavior.

Science.gov (United States)

Staehle, Robert; Tong, Lianpeng; Wang, Lei; Duan, Lele; Fischer, Andreas; Ahlquist, Mårten S G; Sun, Licheng; Rau, Sven

2014-02-03

A new water oxidation catalyst [Ru(III)(bda)(mmi)(OH2)](CF3SO3) (2, H2bda = 2,2'-bipyridine-6,6'-dicarboxylic acid; mmi = 1,3-dimethylimidazolium-2-ylidene) containing an axial N-heterocyclic carbene ligand and one aqua ligand was synthesized and fully characterized. The kinetics of catalytic water oxidation by 2 were measured using stopped-flow technique, and key intermediates in the catalytic cycle were probed by density functional theory calculations. While analogous Ru-bda water oxidation catalysts [Ru(bda)L2] (L = pyridyl ligands) are supposed to catalyze water oxidation through a bimolecular coupling pathway, our study points out that 2, surprisingly, undergoes a single-site water nucleophilic attack (acid-base) pathway. The diversion of catalytic mechanisms is mainly ascribed to the different ligand environments, from nonaqua ligands to an aqua ligand. Findings in this work provide some critical proof for our previous hypothesis about how alternation of ancillary ligands of water oxidation catalysts influences their catalytic efficiency.

Poly-N-Heterocyclic Carbene Ligands with Polyaromatic Linkers. Self-Assembly and Host-Guest Chemistry

OpenAIRE

Mejuto Nieblas, Carmen

2017-01-01

In summary, a series of polytopic ligands based on NHC and MIC ligands have been synthesized in this Doctoral Thesis by means of different synthetic routes that gave rise to systems with very sophisticated architectures. A large variety of metal complexes have been formed based on these salt precursors that allowed the preparation of homo and heteroleptic mono-, di- and tri-metal complexes with different geometries. The luminescence properties of various imidazolium salts, the catalytic activ...

Nickel(0)-catalyzed enantioselective annulations of alkynes and arylenoates enabled by a chiral NHC ligand: efficient access to cyclopentenones.

Science.gov (United States)

Ahlin, Joachim S E; Donets, Pavel A; Cramer, Nicolai

2014-11-24

Cyclopentenones are versatile structural motifs of natural products as well as reactive synthetic intermediates. The nickel-catalyzed reductive [3+2] cycloaddition of α,β-unsaturated aromatic esters and alkynes constitutes an efficient method for their synthesis. Here, nickel(0) catalysts comprising a chiral bulky C1-symmetric N-heterocyclic carbene ligand were shown to enable an efficient asymmetric synthesis of cyclopentenones from mesityl enoates and internal alkynes under mild conditions. The bulky NHC ligand provided the cyclopentenone products in very high enantioselectivity and led to a regioselective incorporation of unsymmetrically substituted alkynes. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

The effect of heterocyclic S,S’-ligands on the electrochemical properties of some cobalt(III complexes in acid

Directory of Open Access Journals (Sweden)

V. M. JOVANOVIC

2005-02-01

Full Text Available Eight mixed-ligand cobalt(III complexes with the macrocyclic amine 1,4,8,11-tetraazacyclotetradecane (cyclam and a heterocyclic dithiocarbamate (Rdtc- i.e., morpholine- (Morphdtc, thiomorpholine- (Timdtc, piperazine- (Pzdtc, N-methylpiperazine-(Mepzdtc, piperidine- (Pipdtc, 2-, 3- or 4-methylpiperidine- (2-, 3- and 4-Mepipdtc carbodithionato-S,S ions, of the general formula [Co(cyclamRdtc](ClO42, were investigated in deoxygenated 0.1MHClO4 solutions. Cyclic voltammetry data at a glassy carbon (GC electrode demonstrate a redox reaction of cobalt(III from the complexes at potentials strongly influenced by the presence of different heterocyclic Rdtc- ligands. In this respect, the complexes were separated into two groups: the first, with a heteroatom O, S or N in the heterocyclic ring, and the second, with a methyl group on the piperidine ring of the Rdtc- ligand. Anodic polarization of an Fe electrode in the presence of the complexes shows their influence not only on the dissolution of iron but also on the hydrogen evolution reactions and on this basis complexes the complexes could be divided into the same two groups. It was found that the weaker the inhibiting effect of the free heterocyclic amines is, the significantly higher is the efficiency of the corresponding complexes.

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

International Nuclear Information System (INIS)

Rivera, A.B.

1989-01-01

Reported is the chemistry of triphenylphosphine ruthenium (II) complexes of general formula RuCl 2 (PPh 3 ) 2 L 2 and RuCl 2 (PPh 3 ) 2 A, obtained from the reaction of RuCl 2 (PPh 3 ) 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 b 1 (dxz)->b 1 (pi) and a 2 (dxy)->a 2 (pi) transitions, and a third, weak band ascribed to the b 2 (dyz)->a 2 (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 CHCl 3 solution, showing preferential labilization of the phosphine ligands, as in the case of the hydrogenation catalyst Ru(PPh 3 ) 3 Cl 2 . In the presence of CO, RuCl 2 (CO) 2 L 2 complexes were gennerated. Several derivatives were isolated and characterized. (author) [pt

Cis/trans Coordination in olefin metathesis by static and molecular dynamic DFT calculations

KAUST Repository

Poater, Albert; Correa, Andrea; Pump, Eva; Cavallo, Luigi

2014-01-01

In regard to [(N-heterocyclic carbene)Ru]-based catalysts, it is still a matter of debate if the substrate binding is preferentially cis or trans to the N-heterocyclic carbene ligand. By means of static and molecular dynamic DFT calculations, a simple olefin, like ethylene, is shown to be prone to the trans binding. Bearing in mind the higher reactivity of trans isomers in olefin metathesis, this insight helps to construct small alkene substrates with increased reactivity. © 2014 Springer Science+Business Media New York.

Cis/trans Coordination in olefin metathesis by static and molecular dynamic DFT calculations

KAUST Repository

Poater, Albert

2014-05-25

In regard to [(N-heterocyclic carbene)Ru]-based catalysts, it is still a matter of debate if the substrate binding is preferentially cis or trans to the N-heterocyclic carbene ligand. By means of static and molecular dynamic DFT calculations, a simple olefin, like ethylene, is shown to be prone to the trans binding. Bearing in mind the higher reactivity of trans isomers in olefin metathesis, this insight helps to construct small alkene substrates with increased reactivity. © 2014 Springer Science+Business Media New York.

Tip-induced gating of molecular levels in carbene-based junctions

Czech Academy of Sciences Publication Activity Database

Foti, Giuseppe; Vázquez, Héctor

2016-01-01

Roč. 27, č. 12 (2016), 1-8, č. článku 125702. ISSN 0957-4484 R&D Projects: GA ČR GA15-19672S Institutional support: RVO:68378271 Keywords : single molecule transport * N-heterocyclic carbene * tip-induced gating * DFT-NEGF * metal-molecule charge rearrangement Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 3.440, year: 2016

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)

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

2009-05-21

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

Mixed ligand complexes of uranyl lactate with some simple and heterocyclic amines

International Nuclear Information System (INIS)

Jaiswal, S.R.; Rupainwar, D.C.

1984-01-01

Mixed ligand complexes of uranyl lactate with simple and heterocyclic amines having a general formula UO 2 (C 3 H 5 O 3 ).nL.xH 2 O, were prepared, where n=1 and x=1 for L=ethylenediamine (En), dimethyl aniline (DMAn), diethyl amine (DEA), orthophenylenediamine (OPDA), pyridine (Py), 2-picoline(2-Pic), 3-picoline(3-Pic), 4-Picoline(4-Pic), piperidine (Pipy), 2,4-lutidine (2,4 Lut), 2-Aminopyridine (2 APy), quinoline (Quin), isoquinoline (Isoquin) but x=0 for the ligands 2,2'-bipyrldyl (Bipy) and 1,10-phenenthroline (Phen). All the compounds are bright yellow coloured with high decomposition temp. (>200deg) and were characterized by electronic and infrared spectral data. (author)

Journal of Chemical Sciences | Indian Academy of Sciences

Indian Academy of Sciences (India)

functionalized N-heterocyclic carbene ligands: Synthesis, structure and catalytic application over amide synthesis. MUTHUKUMARAN NIRMALA PERIASAMY VISWANATHAMURTHI. Regular Article Volume 128 Issue 11 November 2016 pp 1725-1735 ...

Water-soluble tetrapodal N, O ligands incorporating soft N-heterocycles for the selective complexation of Am(III) over Ln(III)

Energy Technology Data Exchange (ETDEWEB)

Heitzmann, M.; Gateau, Ch.; Delangle, P. [CEA Grenoble, Inac, Service de Chimie Inorganique et Biologique, UMR E 3 CEA UJF, FRE CNRS 3200, F-38054 Grenoble (France); Chareyre, L.; Miguirditchian, M.; Charbonnel, M.Ch. [CEA Marcoule, DEN, DRCP, SCPS, F-30207, Bagnols-sur-Ceze (France)

2010-07-01

A series of four water-soluble N, O-tetrapodal ligands derived from ethylenediamine, bearing hard acetate groups and soft N-heterocycles, either pyridine or pyrazine, was developed to study the impact of the softness of N-donors on the complexation properties with trivalent f ions. Two novel ligands of enhanced soft character, bearing three pyridines (L{sup 3py}) or three pyrazines (L{sup 3pz}), were synthesized and the related lanthanide complexes were studied in solution. The ligand containing three pyridyl-methyl moieties L{sup 3py} gives complexes with a coordination similar to EDTA, i.e. a hexa-dentate coordination mode as indicated by NMR and luminescence decays (q = 3) and stability constants in the range log {beta}{sub 110} = 6.99-9.3 (La-Lu). On the other hand, the softest molecule L{sup 3pz} forms much less stable complexes with log {beta}{sub 110} = 4.0-4.4 (La-Eu). The selective back-extraction of Am(III) from organic solutions containing 4f and 5f elements was tested with the four water-soluble complexing agents. The ligand L{sup 3pz} demonstrates poor stripping ability and selectivity. In contrast, the three ligands L{sup py}, L{sup pz} and L{sup 3py} give interesting back-extraction results with Eu/Am separation factors ranging from 36 to 46, which are significantly higher than with HEDTA. This exemplifies the role of the N-hetero-cycle softness in enhancing the separation between Am(III) and Eu(III). Interestingly, the pyrazine-based ligand, L{sup pz}, demonstrates the best stripping properties, with a distribution factor that approaches that of HEDTA in the same conditions (D{sub Am{approx}}0.3). This molecule is a good compromise between softness and hardness and forms complexes still stable at pH 3 due to its low basicity. (authors)

Asymmetric Hydrogenation of Seven-Membered C=N-containing Heterocycles and Rationalization of the Enantioselectivity.

Science.gov (United States)

Balakrishna, Bugga; Bauzá, Antonio; Frontera, Antonio; Vidal-Ferran, Anton

2016-07-18

Iridium(I) complexes with phosphine-phosphite ligands efficiently catalyze the enantioselective hydrogenation of diverse seven-membered C=N-containing heterocyclic compounds (eleven examples; up to 97 % ee). The P-OP ligand L3, which incorporates an ortho-diphenyl substituted octahydrobinol phosphite fragment, provided the highest enantioselectivities in the hydrogenation of most of the heterocyclic compounds studied. The observed stereoselection was rationalized by means of DFT calculations. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Tungsten(VI) Carbyne/Bis(carbene) Tautomerization Enabled by N-Donor SBA15 Surface Ligands: A Solid-State NMR and DFT Study

KAUST Repository

Bendjeriou-Sedjerari, Anissa

2016-08-11

Designing supported well-defined bis(carbene) complexes remains a key challenge in heterogeneous catalysis. The reaction of W(CtBu)(CH(2)tBu)(3) with amine-modified mesoporous SBA15 silica, which has vicinal silanol/silylamine pairs [(SiOH)(SiNH2)], leads to [(SiNH2-)(SiO-)W(CHtBu)(CH(2)tBu)(2)] and [(SiNH2-)(SiO-)W(=CHtBu)(2)(CH(2)tBu). Variable temperature, H-1-H-1 2D double-quantum, H-1-C-13 HETCOR, and HETCOR with spin diffusion solid-state NMR spectroscopy demonstrate tautomerization between the alkyl alkylidyne and the bis(alkylidene) on the SBA15 surface. Such equilibrium is possible through the coordination of W to the surface [(Si-OH)(Si-NH2)] groups, which act as a [N,O] pincer ligand. DFT calculations provide a rationalization for the surface-complex tautomerization and support the experimental results. This direct observation of such a process shows the strong similarity between molecular mechanisms in homogeneous and heterogeneous catalysis. In propane metathesis (at 150 degrees C), the tungsten bis(carbene) tautomer is favorable, with a turnover number (TON) of 262. It is the highest TON among all the tungsten alkyl-supported catalysts.

Tungsten(VI) Carbyne/Bis(carbene) Tautomerization Enabled by N-Donor SBA15 Surface Ligands: A Solid-State NMR and DFT Study

KAUST Repository

Bendjeriou-Sedjerari, Anissa; Sofack-Kreutzer, Julien; Minenkov, Yury; Abou-Hamad, Edy; Hamzaoui, Bilel; Werghi, Baraa; Anjum, Dalaver H.; Cavallo, Luigi; Huang, Kuo-Wei; Basset, Jean-Marie

2016-01-01

Designing supported well-defined bis(carbene) complexes remains a key challenge in heterogeneous catalysis. The reaction of W(CtBu)(CH(2)tBu)(3) with amine-modified mesoporous SBA15 silica, which has vicinal silanol/silylamine pairs [(SiOH)(SiNH2)], leads to [(SiNH2-)(SiO-)W(CHtBu)(CH(2)tBu)(2)] and [(SiNH2-)(SiO-)W(=CHtBu)(2)(CH(2)tBu). Variable temperature, H-1-H-1 2D double-quantum, H-1-C-13 HETCOR, and HETCOR with spin diffusion solid-state NMR spectroscopy demonstrate tautomerization between the alkyl alkylidyne and the bis(alkylidene) on the SBA15 surface. Such equilibrium is possible through the coordination of W to the surface [(Si-OH)(Si-NH2)] groups, which act as a [N,O] pincer ligand. DFT calculations provide a rationalization for the surface-complex tautomerization and support the experimental results. This direct observation of such a process shows the strong similarity between molecular mechanisms in homogeneous and heterogeneous catalysis. In propane metathesis (at 150 degrees C), the tungsten bis(carbene) tautomer is favorable, with a turnover number (TON) of 262. It is the highest TON among all the tungsten alkyl-supported catalysts.

Unusual NHC-Iridium(I) Complexes and Their Use in the Intramolecular Hydroamination of Unactivated Aminoalkenes

KAUST Repository

Sipos, Gellé rt; Ou, Arnold; Skelton, Brian W.; Falivene, Laura; Cavallo, Luigi; Dorta, Reto

2016-01-01

N-heterocyclic carbene (NHC) ligands with naphthyl side chains were employed for the synthesis of unsaturated, yet isolable [(NHC)Ir(cod)]+ (cod=1,5-cyclooctadiene) complexes. These compounds are stabilised by an interaction of the aromatic wingtip that leads to a sideways tilt of the NHC-Ir bond. Detailed studies show how the tilting of such N-heterocyclic carbenes affects the electronic shielding properties of the carbene carbon atom and how this is reflected by significant upfield shifts in the 13CNMR signals. When employed in the intramolecular hydroamination, these [(NHC)Ir(cod)]+ species show very high catalytic activity under mild reaction conditions. An enantiopure version of the catalyst system produces pyrrolidines with excellent enantioselectivities. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Unusual NHC-Iridium(I) Complexes and Their Use in the Intramolecular Hydroamination of Unactivated Aminoalkenes

KAUST Repository

Sipos, Gellért

2016-04-10

N-heterocyclic carbene (NHC) ligands with naphthyl side chains were employed for the synthesis of unsaturated, yet isolable [(NHC)Ir(cod)]+ (cod=1,5-cyclooctadiene) complexes. These compounds are stabilised by an interaction of the aromatic wingtip that leads to a sideways tilt of the NHC-Ir bond. Detailed studies show how the tilting of such N-heterocyclic carbenes affects the electronic shielding properties of the carbene carbon atom and how this is reflected by significant upfield shifts in the 13CNMR signals. When employed in the intramolecular hydroamination, these [(NHC)Ir(cod)]+ species show very high catalytic activity under mild reaction conditions. An enantiopure version of the catalyst system produces pyrrolidines with excellent enantioselectivities. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

A general access to organogold(iii) complexes by oxidative addition of diazonium salts.

Science.gov (United States)

Huang, Long; Rominger, Frank; Rudolph, Matthias; Hashmi, A Stephen K

2016-05-11

At room temperature under mild photochemical conditions, namely irradiation with a simple blue light LED, gold(i) chloro complexes of both phosphane and carbene ligands in combination with aryldiazonium salts afford arylgold(iii) complexes. With chelating P,N-ligands cationic six- or five-membered chelate complexes were isolated in the form of salts with weakly coordinating counter anions that were brought in from the diazonium salt. With monodentate P ligands or N-heterocyclic carbene ligands and diazonium chlorides neutral arylgold(iii) dichloro complexes were obtained. The coordination geometry was determined by X-ray crystal structure analyses of representative compounds, a cis arrangement of the aryl and the phosphane ligand at the square planar gold(iii) center is observed.

JCSC_128_11_1725_1735_SI.docx

Indian Academy of Sciences (India)

Windows7

Ruthenium(II) complexes bearing pyridine-functionalized N-heterocyclic carbene ligands: Synthesis, structure and catalytic application over amide synthesis. MUTHUKUMARAN NIRMALA and PERIASAMY VISWANATHAMURTHI*. Department of Chemistry, Periyar University, Salem, Tamil Nadu 636 011, India. e-mail: ...

Elution behavior of N-heterocyclic derivatives of mixed ruthenium(II)-sulfoxide complexes in reversed-phase high-performance liquid chromatography

International Nuclear Information System (INIS)

Toma, H.E.; Silva, D.O.

1991-01-01

The elution behaviour of a series of dichlorobis-(dimethylsulfoxide)bis(N-heterocyclic) ruthenium(II) complexes has been investigated using reversed-phase HPLC. Similar trends as those displayed by the free N-heterocyclic bases have been observed for the complexes, essentially reflecting the hydrophobic properties of the aromatic ligands. (orig.)

Insights into the catalytic activity of [Pd(NHC)(cin)Cl] (NHC = IPr, IPrCl, IPrBr) complexes in the Suzuki-Miyaura reaction

KAUST Repository

Nolan, Steven Patrick; Izquierdo, Frederic; Zinser, Caroline; Minenkov, Yury; Cordes, David; Slawin, Alexandra; Cavallo, Luigi; Nahra, Fady; Cazin, Catherine

2017-01-01

The influence of C4,5-halogenation on palladium N-heterocyclic carbene complexes and their activity in the Suzuki-Miyaura reaction have been investigated. Two [Pd(NHC)(cin)Cl] complexes bearing IPrCl and IPrBr ligands were synthesized. After

Stereoselective 1,3-Insertions of Rhodium(II) Azavinyl Carbenes

Science.gov (United States)

Chuprakov, Stepan; Worrell, Brady T.; Selander, Nicklas; Sit, Rakesh K.; Fokin, Valery V.

2014-01-01

Rhodium(II) azavinyl carbenes, conveniently generated from 1-sulfonyl-1,2,3-triazoles, undergo a facile, mild and convergent formal 1,3-insertion into N–H and O–H bonds of primary and secondary amides, various alcohols, and carboxylic acids to afford a wide range of vicinally bis-functionalized Z-olefins with perfect regio- and stereoselectively. Utilizing the distinctive functionality installed through these reactions, a number of subsequent rearrangements and cyclizations expand the repertoire of valuable organic building blocks constructed by reactions of transition metal carbene complexes, including α-allenyl ketones and amino-substituted heterocycles. PMID:24295389

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

International Nuclear Information System (INIS)

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

2007-01-01

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 Rh 2 (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)

New Gold(I) Organometallic Compounds with Biological Activity in Cancer Cells

NARCIS (Netherlands)

Bertrand, Benoit; de Almeida, Andreia; van der Burgt, Evelien P. M.; Picquet, Michel; Citta, Anna; Folda, Alessandra; Rigobello, Maria Pia; Le Gendre, Pierre; Bodio, Ewen; Casini, Angela

N-Heterocyclic carbene gold(I) complexes bearing a fluorescent coumarin ligand were synthesized and characterized by various techniques. The compounds were examined for their antiproliferative effects in normal and tumor cells in vitro; they demonstrated moderate activity and a certain degree of

Building new discrete supramolecular assemblies through the interaction of iso-tellurazole N-oxides with Lewis acids and bases.

Science.gov (United States)

Ho, Peter C; Jenkins, Hilary A; Britten, James F; Vargas-Baca, Ignacio

2017-10-13

The supramolecular macrocycles spontaneously assembled by iso-tellurazole N-oxides are stable towards Lewis bases as strong as N-heterocyclic carbenes (NHC) but readily react with Lewis acids such as BR 3 (R = Ph, F). The electron acceptor ability of the tellurium atom is greatly enhanced in the resulting O-bonded adducts, which consequently enables binding to a variety of Lewis bases that includes acetonitrile, 4-dimethylaminopyridine, 4,4'-bipyridine, triphenyl phosphine, a N-heterocyclic carbene and a second molecule of iso-tellurazole N-oxide.

Steric Maps to Evaluate the Role of Steric Hindrance on the IPr NHC Ligand

KAUST Repository

Poater, Albert

2013-06-01

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) (IPr) 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 effect the metal environment and therefore the related catalytic behaviour by simple steric maps. Bearing in mind that there is a significant structural difference between IPr and IPr* ligands, that translated in different reactivity for several olefin metathesis reactions, here by means of DFT we characterize where the NHC ligand plays a more active role and where it is a simple spectator, or at least its modification does not significantly change its catalytic role/performance. Furthermore, this communication endeavours to modify further the skeleton of the IPr NHC ligand. The optimization of these bulky new systems go to the limits of the DFT computational method.

Ruthenium sulfoxides structure and reactivity with nitrogen heterocyclic bases

International Nuclear Information System (INIS)

Oliveira, Denise de.

1990-01-01

Ruthenium (II) sulfoxides are compounds of great interest in oxidative catalysis and in chemotherapy. In order to contribute for the understanding of the chemistry and electronic structure of this class of compounds, it has been studied a series of [Ru Cl 2 (S-DMSO) 2 L x ] complexes, where x = 1 (polymeric compounds) or 2 (monomers) and L N-heterocyclic ligands (pyridine, pyrazine and imidazole derivatives). The nature of N-heterocyclic ligand and their coordination are of great relevance to the stability, spectroscopic and electrochemical characteristics of the complexes. The trans-interactions are extremely important in this series, influencing the strength of the Ru(II)-> S-DMSO and Ru(II)-> L π-back donation. The DMSO and L ligands are π-acceptors. The metal-> ligand π-back donation is strengthened when the ligand is trans to chloride, which is π-donor, due to trans-cooperative interactions of the type: π-donor -> Ru(II) π-acceptor. Another interesting aspect in the series of [Ru Cl 2 (S-DMSO) 2 L 2 ] complexes is the occurrence of dissociative equilibria in the solution, due to the existence of three types of ligands. It was observed that the trans-N isomer of 2,6-dimethyl pyrazine derivative undergoes thermal substitution, with preferential liabilization of the N-heterocyclic ligand. Chloride ion is the most inert ligand in this complex. (author). 145 refs., 76 figs., 21 tabs

Catalytic hydrogenation of CO2 to formates by lutidine-derived Ru-CNC pincer complex : theoretical insight into unrealized potential

NARCIS (Netherlands)

Filonenko, G.; Smykowski, D.; Szyja, B.M.; Li, G.; Szczygiel, J.; Hensen, E.J.M.; Pidko, E.A.

2015-01-01

Metal-ligand cooperative properties of a bis-N-heterocyclic carbene ruthenium CNC-pincer catalyst and its activity in CO2 hydrogenation to formates were studied by DFT calculations complemented by NMR spectroscopy and kinetic measurements. The dearomatized Ru-CNC* pincer (1*) is significantly more

Metal-organic coordination architectures of tetrazole heterocycle ligands bearing acetate groups: Synthesis, characterization and magnetic properties

Science.gov (United States)

Hu, Bo-Wen; Zheng, Xiang-Yu; Ding, Cheng

2015-12-01

Two new coordination complexes with tetrazole heterocycle ligands bearing acetate groups, [Co(L)2]n (1) and [Co3(L)4(N3)2·2MeOH]n (2) (L=tetrazole-1-acetate) have been synthesized and structurally characterized. Single crystal structure analysis shows that the cobalt-complex 1 has the 3D 3,6-connected (42.6)2(44.62.88.10)-ant topology. By introducing azide in this system, complex 2 forms the 2D network containing the [Co3] units. And the magnetic properties of 1 and 2 have been studied.

Chiral PEPPSI Complexes: Synthesis, Characterization, and Application in Asymmetric Suzuki–Miyaura Coupling Reactions

KAUST Repository

Benhamou, Laure

2014-01-13

PEPPSI complexes incorporating chiral N-heterocyclic carbene (NHC) ligands based on 2,2-dimethyl-1-(o-substituted aryl)propan-1-amines were synthesized. Two complexes, with one saturated and one unsaturated NHC ligand, were structurally characterized. The chiral PEPPSI complexes were used in asymmetric Suzuki-Miyaura reactions, giving atropisomeric biaryl products in modest to good enantiomeric ratios. © 2013 American Chemical Society.

Chiral PEPPSI Complexes: Synthesis, Characterization, and Application in Asymmetric Suzuki–Miyaura Coupling Reactions

KAUST Repository

Benhamou, Laure; Besnard, Cé line; Kü ndig, E. Peter

2014-01-01

PEPPSI complexes incorporating chiral N-heterocyclic carbene (NHC) ligands based on 2,2-dimethyl-1-(o-substituted aryl)propan-1-amines were synthesized. Two complexes, with one saturated and one unsaturated NHC ligand, were structurally characterized. The chiral PEPPSI complexes were used in asymmetric Suzuki-Miyaura reactions, giving atropisomeric biaryl products in modest to good enantiomeric ratios. © 2013 American Chemical Society.

3,3′-Di-n-butyl-1,1′-(p-phenylenedimethylenediimidazolium bis(hexafluorophosphate

Directory of Open Access Journals (Sweden)

Rosenani A. Haque

2010-04-01

Full Text Available The asymmetric unit of the title N-heterocyclic carbene compound, C22H32N42+·2PF6−, consists of one half of the N-heterocyclic carbene dication and one hexafluorophosphate anion. The dication lies across a crystallographic inversion center. The imidazole ring is twisted away from the central benzene ring, making a dihedral angle of 76.23 (6°. The hexafluorophosphate anions link the cations into a three-dimensional network via intermolecular C—H...F hydrogen bonds. A weak C—H...π interaction further stabilizes the crystal structure.

Enthalpies of ligand substitution for [Mo(η5C5H5)(CO)2(NO)] – The role of π-bonding effects in metal–ligand bond strengths

International Nuclear Information System (INIS)

Majumdar, Subhojit; Captain, Burjor; Cazin, Catherine S.J.; Nolan, Steven P.; Hoff, Carl D.

2014-01-01

Graphical abstract: - Highlights: • Enthalpies of ligand substitution are measured for Mo(C 5 H 5 )(CO) 2 (NO). • Phosphines and N-heterocyclic carbenes are stronger ligands and displace CO. • Backbonding to π ∗ orbitals is an important part of complex stability. • FTIR studies show shifts to lower wavenumbers of ν-CO and ν-NO. • Structural studies show lengthening of the C-O and N-O bonds. - Abstract: Enthalpies of ligand substitution for [Mo(η 5 -C 5 H 5 )(CO) 2 (NO)] producing [Mo(η 5 -C 5 H 5 )Mo(CO)(L)(NO)] have been measured by solution calorimetry at 30 °C in THF for L = P(OMe) 3 2 2 Ph 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(η 5 -C 5 H 5 )(CO)(NO)] has a vacant site containing strongly π-accepting carbonyl and nitrosyl ligands and this is shown to influence the stability of the product complex. Infrared studies of both ν CO and ν NO show that metal-to-ligand backbonding increases in the order P(OMe) 3 3 5 -C 5 H 5 )(CO)(IPr)(NO)] and [Mo(η 5 -C 5 H 5 )(CO)(SIPr)(NO)] are reported

Azido, triazolyl, and alkynyl complexes of gold(I): syntheses, structures, and ligand effects.

Science.gov (United States)

Robilotto, Thomas J; Deligonul, Nihal; Updegraff, James B; Gray, Thomas G

2013-08-19

Gold(I) triazolyl complexes are prepared in [3 + 2] cycloaddition reactions of (tertiary phosphine)gold(I) azides with terminal alkynes. Seven such triazolyl complexes, not previously prepared, are described. Reducible functional groups are accommodated. In addition, two new (N-heterocyclic carbene)gold(I) azides and two new gold(I) alkynyls are described. Eight complexes are crystallographically authenticated; aurophilic interactions appear in one structure only. The packing diagrams of gold(I) triazolyls all show intermolecular hydrogen bonding between N-1 of one molecule and N-3 of a neighbor. This hydrogen bonding permeates the crystal lattice. Density-functional theory calculations of (triphenylphosphine)gold(I) triazolyls and the corresponding alkynyls indicate that the triazolyl is a stronger trans-influencer than is the alkynyl, but the alkynyl is more electron-releasing. These results suggest that trans-influences in two-coordinate gold(I) complexes can be more than a simple matter of ligand donicity.

Uranium nucleophilic carbene complexes

International Nuclear Information System (INIS)

Tourneux, Jean-Christophe

2012-01-01

The only stable f-metal carbene complexes (excluding NHC) metals f present R 2 C 2- groups having one or two phosphorus atoms in the central carbon in alpha position. The objective of this work was to develop the chemistry of carbenes for uranium (metal 5f) with the di-anion C{Ph 2 P(=S)} 2 2- (SCS 2- ) to extend the organometallic chemistry of this element in its various oxidation states (+3-+6), and to reveal the influence of the 5f orbitals on the nature and reactivity of the double bond C=U. We first isolated the reactants M(SCHS) (M = Li and K) and demonstrated the role of the cation M + on the evolution of the di-anion M 2 SCS (M = Li, K, Tl) which is transformed into LiSCHS in THF or into product of intramolecular cyclization K 2 [C(PhPS) 2 (C 6 H 4 )]. We have developed the necessary conditions mono-, bis- and tris-carbene directly from the di-anion SCS 2- and UCl 4 , as the precursor used in uranium chemistry. The protonolysis reactions of amides compounds (U-NEt 2 ) by the neutral ligand SCH 2 S were also studied. The compounds [Li(THF)] 2 [U(SCS)Cl 3 ] and [U(SCS)Cl 2 (THF) 2 ] were then used to prepare a variety of cyclopentadienyl and mono-cyclo-octa-tetra-enyliques uranium(IV) carbene compounds of the DFT analysis of compounds [M(SCS)Cl 2 (py) 2 ] and [M(Cp) 2 (SCS)] (M = U, Zr) reveals the strong polarization of the M=C double bond, provides information on the nature of the σ and π interactions in this binding, and shows the important role of f orbitals. The influence of ancillary ligands on the M=C bond is revealed by examining the effects of replacing Cl - ligands and pyridine by C 5 H 5 - groups. Mulliken and NBO analyzes show that U=C bond, unlike the Zr=C bond, is not affected by the change in environment of the metal center. While the oxidation tests of carbene complexes of U(IV) were disappointing, the first carbene complex of uranium (VI), [UO 2 (SCS)(THF) 2 ], was isolated with the uranyl ion UO 2 2+ . The reactions of compounds UO 2 X 2

Versatile deprotonated NHC: C,N-bridged dinuclear iridium and rhodium complexes

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Albert Poater

2016-01-01

Full Text Available Bearing the versatility of N-heterocyclic carbene (NHC ligands, here density functional theory (DFT calculations unravel the capacity of coordination of a deprotonated NHC ligand (pNHC to generate a doubly C2,N3-bridged dinuclear complex. Here, in particular the discussion is based on the combination of the deprotonated 1-arylimidazol (aryl = mesityl (Mes with [M(cod(μ-Cl] (M = Ir, Rh generated two geometrical isomers of complex [M(cod{µ-C3H2N2(Mes-κC2,κN3}]2. The latter two isomers display conformations head-to-head (H-H and head-to-tail (H-T of CS and C2 symmetry, respectively. The isomerization from the H-H to the H-T conformation is feasible, whereas next substitutions of the cod ligand by CO first, and PMe3 later confirm the H-T coordination as the thermodynamically preferred. It is envisaged the exchange of the metal, from iridium to rhodium, confirming here the innocence of the nature of the metal for such arrangements of the bridging ligands.

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)

Nuno R. Candeias

2007-01-01

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.

Journal of Chemical Sciences | Indian Academy of Sciences

Indian Academy of Sciences (India)

Coordination chemistry of bonds between main group elements and electron donating ligands as in L→E (where E is electron acceptor centre like C⁰, Si⁰, N¹, P¹, As¹, B¹ and L is an electron donating N-heterocyclic carbene) have been recently gaining attention. Many important drugs have nitrogen atom as an electron ...

Synthesis of 3-fluoro-3-aryl oxindoles: Direct enantioselective α arylation of amides

KAUST Repository

Wu, Linglin; Falivene, Laura; Drinkel, Emma E.; Grant, Sharday; Linden, Anthony; Cavallo, Luigi; Dorta, Reto

2012-01-01

Modus operandi: Catalytic access to the title compounds through a new asymmetric α-arylation protocol is reported (see scheme). These products are formed in good yields and excellent enantioselectivities by using a new and easily synthesized chiral N-heterocyclic carbene (NHC) ligand. Advanced DFT calculations reveal the properties of the NHC ligand and the mode of operation of the catalyst. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Synthesis of 3-fluoro-3-aryl oxindoles: Direct enantioselective α arylation of amides

KAUST Repository

Wu, Linglin

2012-02-06

Modus operandi: Catalytic access to the title compounds through a new asymmetric α-arylation protocol is reported (see scheme). These products are formed in good yields and excellent enantioselectivities by using a new and easily synthesized chiral N-heterocyclic carbene (NHC) ligand. Advanced DFT calculations reveal the properties of the NHC ligand and the mode of operation of the catalyst. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Discovering protein-ligand chalcogen bonding in the protein data bank using endocyclic sulfur-containing heterocycles as ligand search subsets.

Science.gov (United States)

Mitchell, Miguel O

2017-09-24

The chalcogen bond, the noncovalent, electrostatic attraction between covalently bonded atoms in group 16 and Lewis bases, is present in protein-ligand interactions based on X-ray structures deposited in the Protein Data Bank (PDB). Discovering protein-ligand chalcogen bonding in the PDB employed a strategy that focused on searching the database for protein complexes of five-membered, heterocyclic ligands containing endocyclic sulfur with endo electron-withdrawing groups (isothiazoles; thiazoles; 1,2,3-, 1,2.4-, 1,2,5-, 1,3,4-thiadiazoles) and thiophenes with exo electron-withdrawing groups, e.g., 2-chloro, 2-bromo, 2-amino, 2-alkylthio. Out of 930 ligands investigated, 33 or 3.5% have protein-ligand S---O interactions of which 31 are chalcogen bonds and two appear to be S---HO hydrogen bonds. The bond angles for some of the chalcogen bonds found in the PDB are less than 90°, and an electrostatic model is proposed to explain this phenomenon.

Organocatalytic conjugate-addition polymerization of linear and cyclic acrylic monomers by N-heterocyclic carbenes: Mechanisms of chain initiation, propagation, and termination

KAUST Repository

Zhang, Yuetao

2013-11-27

This contribution presents a full account of experimental and theoretical/computational investigations into the mechanisms of chain initiation, propagation, and termination of the recently discovered N-heterocyclic carbene (NHC)-mediated organocatalytic conjugate-addition polymerization of acrylic monomers. The current study specifically focuses on three commonly used NHCs of vastly different nucleophilicity, 1,3-di-tert-butylimidazolin-2-ylidene (ItBu), 1,3- dimesitylimidazolin-2-ylidene (IMes), and 1,3,4-triphenyl-4,5-dihydro-1H-1,2,4- triazol-5-ylidene (TPT), and two representative acrylic monomers, the linear methyl methacrylate (MMA) and its cyclic analog, biomass-derived renewable γ-methyl-α-methylene-γ-butyrolactone (MMBL). For MMA, there exhibits an exquisite selectivity of the NHC structure for the three types of reactions it promotes: enamine formation (single-monomer addition) by IMes, dimerization (tail-to-tail) by TPT, and polymerization by ItBu. For MMBL, all three NHCs promote no dimerization but polymerization, with the polymerization activity being highly sensitive to the NHC structure and the solvent polarity. Thus, ItBu is the most active catalyst of the series and converts quantitatively 1000-3000 equiv of MMBL in 1 min or 10 000 equiv in 5 min at room temperature to MMBL-based bioplastics with a narrow range of molecular weights of Mn = 70-85 kg/mol, regardless of the [MMBL]/[ItBu] ratio employed. The ItBu-catalyzed MMBL polymerization reaches an exceptionally high turnover frequency up to 122 s -1 and a high initiator efficiency value up to 1600%. Unique chain-termination mechanisms have been revealed, accounting for the production of relative high-molecular-weight linear polymers and the catalytic nature of this NHC-mediated conjugate-addition polymerization. Computational studies have provided mechanistic insights into reactivity and selectivity between two competing pathways for each NHC-monomer zwitterionic adduct, namely enamine

Organocatalytic conjugate-addition polymerization of linear and cyclic acrylic monomers by N-heterocyclic carbenes: Mechanisms of chain initiation, propagation, and termination

KAUST Repository

Zhang, Yuetao; Schmitt, Meghan L.; Falivene, Laura; Caporaso, Lucia; Cavallo, Luigi; Chen, Eugene You Xian

2013-01-01

This contribution presents a full account of experimental and theoretical/computational investigations into the mechanisms of chain initiation, propagation, and termination of the recently discovered N-heterocyclic carbene (NHC)-mediated organocatalytic conjugate-addition polymerization of acrylic monomers. The current study specifically focuses on three commonly used NHCs of vastly different nucleophilicity, 1,3-di-tert-butylimidazolin-2-ylidene (ItBu), 1,3- dimesitylimidazolin-2-ylidene (IMes), and 1,3,4-triphenyl-4,5-dihydro-1H-1,2,4- triazol-5-ylidene (TPT), and two representative acrylic monomers, the linear methyl methacrylate (MMA) and its cyclic analog, biomass-derived renewable γ-methyl-α-methylene-γ-butyrolactone (MMBL). For MMA, there exhibits an exquisite selectivity of the NHC structure for the three types of reactions it promotes: enamine formation (single-monomer addition) by IMes, dimerization (tail-to-tail) by TPT, and polymerization by ItBu. For MMBL, all three NHCs promote no dimerization but polymerization, with the polymerization activity being highly sensitive to the NHC structure and the solvent polarity. Thus, ItBu is the most active catalyst of the series and converts quantitatively 1000-3000 equiv of MMBL in 1 min or 10 000 equiv in 5 min at room temperature to MMBL-based bioplastics with a narrow range of molecular weights of Mn = 70-85 kg/mol, regardless of the [MMBL]/[ItBu] ratio employed. The ItBu-catalyzed MMBL polymerization reaches an exceptionally high turnover frequency up to 122 s -1 and a high initiator efficiency value up to 1600%. Unique chain-termination mechanisms have been revealed, accounting for the production of relative high-molecular-weight linear polymers and the catalytic nature of this NHC-mediated conjugate-addition polymerization. Computational studies have provided mechanistic insights into reactivity and selectivity between two competing pathways for each NHC-monomer zwitterionic adduct, namely enamine

Aminomethylation of enals through carbene and acid cooperative catalysis: concise access to β(2)-amino acids.

Science.gov (United States)

Xu, Jianfeng; Chen, Xingkuan; Wang, Ming; Zheng, Pengcheng; Song, Bao-An; Chi, Yonggui Robin

2015-04-20

A convergent, organocatalytic asymmetric aminomethylation of α,β-unsaturated aldehydes by N-heterocyclic carbene (NHC) and (in situ generated) Brønsted acid cooperative catalysis is disclosed. The catalytically generated conjugated acid from the base plays dual roles in promoting the formation of azolium enolate intermediate, formaldehyde-derived iminium ion (as an electrophilic reactant), and methanol (as a nucleophilic reactant). This redox-neutral strategy is suitable for the scalable synthesis of enantiomerically enriched β(2) -amino acids bearing various substituents. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

synthesis and characterisation of quinoline functionalised

African Journals Online (AJOL)

DR. AMINU

. Accepted: ... Department of Chemistry, Kano University of Science and Technology Wudil. Email: aahmedte64@yahoo.com, ... Keywords: Nucleophilic heterocyclic carbene (NHC), Imidazolium salt, ligand, ring closure. Barf. INTRODUCTION.

Study of physicochemical properties of zinc(II) butyrate complex compounds with some heterocyclic ligands

Czech Academy of Sciences Publication Activity Database

Szakácsová, M.; Györová, K.; Szunyogová, E.; Kovářová, Jana

2002-01-01

Roč. 96, - (2002), s. 383 ISSN 0009-2770. [Meeting of Chemical Societies /54./. 30.06.2002-04.07.2002, Brno] R&D Projects: GA AV ČR KSK4050111; GA MŠk VEGA 1/9247/02; GA MŠk VEGA 047/074 Keywords : butyrate complex compounds * heterocyclic ligands Subject RIV: CD - Macromolecular Chemistry

Mixed-ligand complexes of zirconium (IV) and uranium with salicylaldehyde and some heterocyclic azopyrazolones

International Nuclear Information System (INIS)

Amrallahi, A.H.

1994-01-01

Mixed-ligand complexes of Zr(IV) and U(IV) with salicylaldehyde (SA) and some heterocyclic azopyrazolenes have been studied spectrophotometrically. All formed chelates have ratio 1:1:1. The stoichiometry and stability of the binary mixed chelates been evaluated. Elemental analysis, molar conductance and IR spectra have been used for identification of solid mixed complexes. (author)

Mixed-ligand complexes of copper (II with ditiolfenols and heterocyclic diamines

Directory of Open Access Journals (Sweden)

K. A. Kuliev

2017-01-01

Full Text Available By the methods spectrophotometric methods was investigated complex formation of copper with 2,6-ditiolphenol and its derivatives (2,6-ditiol-4-methylphenol, 2,6-ditiol-4-ethylphenol and 2,6-ditiol-4-tert-buthylphenol in the presence of heterocyclic diamines. As heterocyclic diamines phenantroline (Fen, batophenantroline and dipyridile were used. It was established, that mixedligand complex were formed in weak acidic medium (pHop=6,0-8,5. Maximum of light absorption observed at (=522–550 nm. Molar coefficient of light absorption was ( = (3.08–4.92?104. The stoichiometry of complexes had been discovered using shift the equilibrium and relative yield methods. During the extraction of copper(II complexes with ditiol-phenols with the presence of heterocyclic diamines there was discovered that there is no chlorophorm molecules in the composition of the extracted complexes. IR spectra shows that hydroxyl group is involved to the formation of a bond with the metal and that phenantroline is included in the composition of the copper complex. In the organic phase mixed-ligand complexes have the monomeric form and can’t polymerize; that fact can be proved by calculations. By dint of spectrophotometric, IR-spectroscopic, thermogravimetric experiments and some published data we were able to determine the structural formula of complexes. Also had been determined main spectrophotometric characteristics of copper(II mixed-ligand complexes: pH of the beginning of the deposition, optimal pH, detection limit and sensivity. For separation and finding copper, we studied the effect of interfering foreign ions: alkali, alkaline earth and rare earth elements, as well as acid anions selected masking reagents. On the base of the results was offered photometric method for determination of copper in steel different trade-marks and in food. This method characterized by good reproduction (relatively standard deviation no more 0.05 and low limit of discovery.

Metal-Free Catalytic Enantioselective C–B Bond Formation: (Pinacolato)boron Conjugate Additions to α,β-Unsaturated Ketones, Esters, Weinreb Amides and Aldehydes Promoted by Chiral N-Heterocyclic Carbenes

Science.gov (United States)

Wu, Hao; Radomkit, Suttipol; O’Brien, Jeannette M.; Hoveyda, Amir H.

2012-01-01

The first broadly applicable metal-free enantioselective method for boron conjugate addition (BCA) to α,β-unsaturated carbonyls is presented. The C–B bond forming reactions are promoted in the presence of 2.5–7.5 mol % of a readily accessible C1-symmetric chiral imidazolinium salt, which is converted, in situ, to the catalytically active diastereo- and enantiomerically pure N-heterocyclic carbene (NHC) by the common organic base 1,8-diazabicyclo[5.4.0]undec-7-ene (dbu). In addition to the commercially available bis(pinacolato)diboron [B2(pin)2], and in contrast to reactions with the less sterically demanding achiral NHCs, the presence of MeOH is required for high efficiency. Acyclic and cyclic α,β-unsaturated ketones, as well as acyclic esters, Weinreb amides and aldehydes can serve as suitable substrates; the desired β-boryl carbonyls are isolated in up to 94% yield and >98:2 enantiomer ratio (er). Transformations are often carried out at ambient temperature. In certain cases, such as when the relatively less reactive unsaturated amides are used, elevated temperatures are required (50–66 °C); nonetheless, reactions remain highly enantioselective. The utility of the NHC-catalyzed method is demonstrated through comparison with the alternative Cu-catalyzed protocols; in cases involving a polyfunctional substrate, unique profiles in chemoselectivity are exhibited by the metal-free approach (e.g., conjugate addition vs reaction with an alkyne, allene or aldehyde). PMID:22559866

Synthesis, Crystal Structure and Luminescent Property of A Novel Cd(II) Coordination Polymer with Bis-imidazole Ligand

International Nuclear Information System (INIS)

Zhou, Yong Hong

2013-01-01

The key to the successful design of metal-organic coordination polymers is the judicious selection of organic ligand. Recently, polydentate aromatic nitrogen heterocyclic ligands with five-membered rings have been well-studied in the construction of supramolecular structure for their N-coordinated sites apt to coordinating to transition metals. Similar to six-membered N-heterocyclic ligands, the azole-based five-membered N-heterocyclic ligands, such as imidazoles, triazoles and tetrazoles have been extensively employed in the construction of various coordination polymers with diverse topologies and interesting properties. The bis(azole) ligands in which N-donor azole rings (imidazole, triazole, or tetrazole) are separated by alkyl, (CH 2 ) n , spacers are good choices for flexible bridging ligands. The conformational flexibility of the spacers makes the ligands adaptable to various coordination networks with one-, two-, and three dimensional structures

Synthesis of heterocycles: Indolo (2,1-a) isoquinolines, renewables, and aptamer ligands for cellular imaging

Energy Technology Data Exchange (ETDEWEB)

Beasley, Jonathan [Ames Laboratory (AMES), Ames, IA (United States)

2013-01-01

In this thesis, we explore both total syntheses and methodologies of several aromatic heterocyclic molecules. Extensions of the Kraus indole synthesis toward 2-substituted and 2,3-disubstituted indoles, as well as biologically attractive indolo[2,1-a]isoquinolines are described. Recent renewable efforts directed to commodity maleic acid and the first reported furan-based ionic liquids are described. Our total synthesis of mRNA aptamer ligand PDC-Gly, and its dye coupled forms, plus aminoglycoside dye coupled ligands used in molecular imaging, are described.

N-Heterocyclic Carbene Coinage Metal Complexes of the Germanium-Rich Metalloid Clusters [Ge9R3]− and [Ge9RI2]2− with R = Si(iPr3 and RI = Si(TMS3

Directory of Open Access Journals (Sweden)

Felix S. Geitner

2017-07-01

Full Text Available We report on the synthesis of novel coinage metal NHC (N-heterocyclic carbene compounds of the germanium-rich metalloid clusters [Ge9R3]− and [Ge9RI2]2− with R = Si(iPr3 and RI = Si(TMS3. NHCDippCu{η3Ge9R3} with R = Si(iPr3 (1 represents a less bulky silyl group-substituted derivative of the known analogous compounds with R = Si(iBu3 or Si(TMS3. The coordination of the [NHCDippCu]+ moiety to the cluster unit occurs via one triangular face of the tri-capped trigonal prismatic [Ge9] cluster. Furthermore, a series of novel Zintl cluster coinage metal NHC compounds of the type (NHCM2{η3Ge9RI2} (RI = Si(TMS3 M = Cu, Ag and Au; NHC = NHCDipp or NHCMes is presented. These novel compounds represent a new class of neutral dinuclear Zintl cluster coinage metal NHC compounds, which are obtained either by the stepwise reaction of a suspension of K12Ge17 with Si(TMS3Cl and the coinage metal carbene complexes NHCMCl (M = Cu, Ag, Au, or via a homogenous reaction using the preformed bis-silylated cluster K2[Ge9(Si(TMS32] and the corresponding NHCMCl (M = Cu, Ag, Au complex. The molecular structures of NHCDippCu{η3Ge9(Si(iPr33} (1 and (NHCDippCu2{η3-Ge9(Si(TMS32} (2 were determined by single crystal X-ray diffraction methods. In 2, the coordination of the [NHCDippCu]+ moieties to the cluster unit takes place via both open triangular faces of the [Ge9] entity. Furthermore, all compounds were characterized by means of NMR spectroscopy (1H, 13C, 29Si and ESI-MS.

Proton-Transfer Polymerization by N-Heterocyclic Carbenes: Monomer and Catalyst Scopes and Mechanism for Converting Dimethacrylates into Unsaturated Polyesters

KAUST Repository

Hong, Miao; Tang, Xiaoyan; Falivene, Laura; Caporaso, Lucia; Cavallo, Luigi; Chen, Eugene Y.-X.

2016-01-01

as methanol insertion products, RxTPT(MeO/H) (R = MeO, Cl; x = 2, 3), and two free carbenes (catalysts), OMe2TPT and OMe3TPT, have been synthesized, while OMe2TPT(MeO/H) and OMe2TPT have also been structurally characterized. The structure

Effects of histidin-2-ylidene vs. imidazol-2-ylidene ligands on the anticancer and antivascular activity of complexes of ruthenium, iridium, platinum, and gold

Czech Academy of Sciences Publication Activity Database

Schmitt, F.; Donnelly, K.; Muenzner, J.K.; Rehm, T.; Novohradský, Vojtěch; Brabec, Viktor; Kašpárková, Jana; Albrecht, M.; Schobert, R.; Mueller, T.

2016-01-01

Roč. 163, OCT2016 (2016), s. 221-228 ISSN 0162-0134 R&D Projects: GA ČR(CZ) GA14-21053S Institutional support: RVO:68081707 Keywords : n-heterocyclic carbene * human cancer-cells * metal-complexes Subject RIV: BO - Biophysics Impact factor: 3.348, year: 2016

Formation of quinones, indanones and furans by the reaction of molybdenum carbene complexes with alkynes

International Nuclear Information System (INIS)

Doetz, K.H.; Larbig, H.

1992-01-01

(Alkoxy)carbene complexes of molybdenum react with terminal alkynes to give carbene annulation of cycloaddition products, the skeleton of which depends on the carbene substitution pattern and the alkyne used. (CO) 5 Mo=C(OMe)-p-tol undergoes carbene annulation upon reaction with trimethylsilylacetylene leading to naphthoquinone after oxidative work-up. Similar products are obtained from (CO) 5 Mo=C(OMe)2-furyl and hex-1-yne or oct-1-yne. The reaction of these alkynes results in the formation of indanones as five-membered annulation products. In the presence of 3.3-dimethylbut-1-yne the (phenyl) carbene ligands act as a C 1 -synthon, which is incorporated into the furan cycloaddition products

Synthesis and Characterization of Divalent Manganese, Iron, and Cobalt Complexes in Tripodal Phenolate/N-Heterocyclic Carbene Ligand Environments

DEFF Research Database (Denmark)

Käß, Martina; Hohenberger, Johannes; Adelhardt, Mario

2014-01-01

. The complete ligand series offers a convenient way of tuning the electronic and steric environment around the metal center, thus, allowing for control of the complex’s reactivity. This series of divalent complexes of Mn, Fe, and Co was synthesized and characterized by 1H NMR, IR, and UV/vis spectroscopy...... as well as by single-crystal X-ray diffraction studies. Variable-temperature SQUID magnetization measurements in the range from 2 to 300 K confirmed high-spin ground states for all divalent complexes and revealed a trend of increasing zero-field splitting |D| from Mn(II), to Fe(II), to Co(II) complexes...

Synthesis and crystal structure of the iridium(I) carbene complex with a pair of hydrogen wing tips

Energy Technology Data Exchange (ETDEWEB)

Huang, H.-Y.; Chen, Z.-M.; Wang, Y.; Wu, E.-M.; Wang, G. [Jiangsu Institute of Nuclear Medicine, Ministry of Health, Key Laboratory of Molecular Nuclear Medicine (China); Jiang, M.-J., E-mail: jmj16888@126.com [Nanjing Medical University, Affiliated Wuxi Peoples Hospital, Wuxi Institute of Translational Medicine, Department of Clinical Laboratory Science (China)

2016-12-15

The iridium(I) cyclooctadiene complex with two (3-tert-butylimidazol-2-ylidene) ligands [(H-Im{sup t}Bu){sub 2}Ir(COD)]{sup +}PF{sub 6}{sup −} (C{sub 22}H{sub 32}PF{sub 6}IrN{sub 4}) has been prepared, and its crystal structure is determined by X-ray diffraction. Complex exhibits slightly distorted square planar configurations around the metal atom, which is coordinated by two H-Im{sup t}Bu ligands and one cyclooctadiene group. The new iridium carbene complex has a pair of hydrogen wing tips. The Ir−C{sub carbene} bond lengths are 2.066(5) and 2.052(5) Å, and the bond angle C−Ir−C between these bonds is 95.54(19)°. The dihedral angle between two imidazol-2-ylidene rings is 86.42°.

Artificial Diels–Alderase based on the transmembrane protein FhuA

Directory of Open Access Journals (Sweden)

Hassan Osseili

2016-06-01

Full Text Available Copper(I and copper(II complexes were covalently linked to an engineered variant of the transmembrane protein Ferric hydroxamate uptake protein component A (FhuA ΔCVFtev. Copper(I was incorporated using an N-heterocyclic carbene (NHC ligand equipped with a maleimide group on the side arm at the imidazole nitrogen. Copper(II was attached by coordination to a terpyridyl ligand. The spacer length was varied in the back of the ligand framework. These biohybrid catalysts were shown to be active in the Diels–Alder reaction of a chalcone derivative with cyclopentadiene to preferentially give the endo product.

Synthesis, Structure and Catalytic Activity of NHC-AgICarboxylate Complexes

KAUST Repository

Wong, Valerie H. L.; Vummaleti, Sai V. C.; Cavallo, Luigi; White, Andrew J. P.; Nolan, Steven P.; Hii, King Kuok Mimi

2016-01-01

A general synthetic route was used to prepare 15 new N-heterocyclic carbene (NHC)–AgI complexes bearing anionic carboxylate ligands [Ag(NHC)(O2CR)], including a homologous series of complexes of sterically flexible ITent ligands, which permit a systematic spectroscopic and theoretical study of the structural and electronic features of these compounds. The complexes displayed a significant ligand-accelerated effect in the intramolecular cyclisation of propargylic amides to oxazolidines. The substrate scope is highly complementary to that previously achieved by NHC–Au and pyridyl–AgI complexes. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Synthesis, Structure and Catalytic Activity of NHC-AgICarboxylate Complexes

KAUST Repository

Wong, Valerie H. L.

2016-08-03

A general synthetic route was used to prepare 15 new N-heterocyclic carbene (NHC)–AgI complexes bearing anionic carboxylate ligands [Ag(NHC)(O2CR)], including a homologous series of complexes of sterically flexible ITent ligands, which permit a systematic spectroscopic and theoretical study of the structural and electronic features of these compounds. The complexes displayed a significant ligand-accelerated effect in the intramolecular cyclisation of propargylic amides to oxazolidines. The substrate scope is highly complementary to that previously achieved by NHC–Au and pyridyl–AgI complexes. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Synthesis, characterization, and reactivity of a uranium(VI) carbene imido oxo complex

Energy Technology Data Exchange (ETDEWEB)

Lu, Erli; Cooper, Oliver J.; McMaster, Jonathan; Lewis, William; Blake, Alexander J.; Liddle, Stephen T. [Nottingham Univ. (United Kingdom). School of Chemistry; Tuna, Floriana; McInnes, Eric J.L. [Manchester Univ. (United Kingdom). School of Chemistry and Photon Science Inst.

2014-06-23

We report the uranium(VI) carbene imido oxo complex [U(BIPM{sup TMS})(NMes)(O)(DMAP){sub 2}] (5, BIPM{sup TMS}=C(PPh{sub 2}NSiMe{sub 3}){sub 2}; Mes=2,4,6-Me{sub 3}C{sub 6}H{sub 2}; DMAP=4-(dimethylamino)pyridine) which exhibits the unprecedented arrangement of three formal multiply bonded ligands to one metal center where the coordinated heteroatoms derive from different element groups. This complex was prepared by incorporation of carbene, imido, and then oxo groups at the uranium center by salt elimination, protonolysis, and two-electron oxidation, respectively. The oxo and imido groups adopt axial positions in a T-shaped motif with respect to the carbene, which is consistent with an inverse trans-influence. Complex 5 reacts with tert-butylisocyanate at the imido rather than carbene group to afford the uranyl(VI) carbene complex [U(BIPM{sup TMS})(O){sub 2}(DMAP){sub 2}] (6).

Silylene-Nickel Promoted Cleavage of B-O Bonds: From Catechol Borane to the Hydroborylene Ligand.

Science.gov (United States)

Hadlington, Terrance J; Szilvási, Tibor; Driess, Matthias

2017-06-19

The first 16 valence electron [bis(NHC)](silylene)Ni 0 complex 1, [( TMS L)ClSi:→Ni(NHC) 2 ], bearing the acyclic amido-chlorosilylene ( TMS L)ClSi: ( TMS L=N(SiMe 3 )Dipp; Dipp=2,6-Pr i 2 C 6 H 4 ) and two NHC ligands (N-heterocyclic carbene=:C[(Pr i )NC(Me)] 2 ) was synthesized in high yield and structurally characterized. Compound 1 is capable of facile dihydrogen activation under ambient conditions to give the corresponding HSi-NiH complex 2. Most notably, 1 reacts with catechol borane to afford the unprecedented hydroborylene-coordinated (chloro)(silyl)nickel(II) complex 3, {[cat( TMS L)Si](Cl)Ni←:BH(NHC) 2 }, via the cleavage of two B-O bonds and simultaneous formation of two Si-O bonds. The mechanism for the formation of 3 was rationalized by means of DFT calculations, which highlight the powerful synergistic effects of the Si:→Ni moiety in the breaking of incredibly strong B-O bonds. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Oxidative degradation of the organometallic iron(II) complex [Fe{bis[3-(pyridin-2-yl)-1H-imidazol-1-yl]methane}(MeCN)(PMe3)](PF6)2: structure of the ligand decomposition product trapped via coordination to iron(II).

Science.gov (United States)

Haslinger, Stefan; Pöthig, Alexander; Cokoja, Mirza; Kühn, Fritz E

2015-12-01

Iron is of interest as a catalyst because of its established use in the Haber-Bosch process and because of its high abundance and low toxicity. Nitrogen-heterocyclic carbenes (NHC) are important ligands in homogeneous catalysis and iron-NHC complexes have attracted increasing attention in recent years but still face problems in terms of stability under oxidative conditions. The structure of the iron(II) complex [1,1'-bis(pyridin-2-yl)-2,2-bi(1H-imidazole)-κN(3)][3,3'-bis(pyridin-2-yl-κN)-1,1'-methanediylbi(1H-imidazol-2-yl-κC(2))](trimethylphosphane-κP)iron(II) bis(hexafluoridophosphate), [Fe(C17H14N6)(C16H12N6)(C3H9P)](PF6)2, features coordination by an organic decomposition product of a tetradentate NHC ligand in an axial position. The decomposition product, a C-C-coupled biimidazole, is trapped by coordination to still-intact iron(II) complexes. Insights into the structural features of the organic decomposition products might help to improve the stability of oxidation catalysts under harsh conditions.

Neutral bidentate N-heterocyclic ligands - phase transfer reagents improving the kinetics of solvent extraction of Am(III) and Eu(III) ions with tetradentate 6,6'-bis-(diethyl-1,2,4-triazin-3-yl)-2,2'-bipyridine

International Nuclear Information System (INIS)

Narbutt, J.; Krejzler, J.

2008-01-01

Poor kinetics of solvent extraction of Am(III) and Eu(III) ions from 1 M HNO 3 with 6,6'-bis-(diethyl-1,2,4-triazin-3-yl)-2,2'-bipyridine (etBTBP) has been improved by adding an auxiliary bidentate N-heterocyclic ligand to the extraction system. Two such ligands were studied, derivatives of bis-triazine and pyridine-triazine, which alone poorly extract the metal ions, but together with etBTBP they act as phase transfer reagents, improving the extraction kinetics to a different degree. The ability to transfer the metal ions from aqueous to organic phase depends on lipophilicity and acid/base properties of these auxiliary ligands, as well as on the mode of shaking the two liquid phases - gentle or vigorous. (orig.)

A simple building-block route to (phosphanyl-carbene)palladium complexes via intermolecular addition of functionalised phosphanes to isocyanides

NARCIS (Netherlands)

Eberhard, M.R.; van Vliet, B.; Durán Páchon, L.; Rothenberg, G.; Eastham, G.; Kooijman, H.; Spek, A.L.; Elsevier, C.J.

2009-01-01

We present a straightforward protocol for making (phosphanyl-carbene)PdII complexes. These complexes have bidentate ligands containing an acyclic diamino- or aminooxy-carbene and a phosphane. The synthesis gives good yields (typically 70-90 %) for a variety of complexes (22 compounds). Moreover, it

Rhodium (II) carbene C-H insertion in water and catalyst reuse; Insercao C-H de carbenoides de rodio em agua e reutilizacao do catalisador

Energy Technology Data Exchange (ETDEWEB)

Candeias, Nuno R.; Gois, Pedro M.P.; Afonso, Carlos A.M. [Instituto Superior Tecnico, Lisboa (Portugal)]. E-mail: carlosafonso@ist.utl.pt

2007-07-01

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 Rh{sub 2}(OAc){sub 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)

Synthesis, characterization, and reactivity of a uranium(VI) carbene imido oxo complex

Energy Technology Data Exchange (ETDEWEB)

Lu, Erli; Cooper, Oliver J.; McMaster, Jonathan; Lewis, William; Blake, Alexander J.; Liddle, Stephen T. [School of Chemistry, University of Nottingham (United Kingdom); Tuna, Floriana; McInnes, Eric J.L. [School of Chemistry and Photon Science Institute, University of Manchester (United Kingdom)

2014-06-23

We report the uranium(VI) carbene imido oxo complex [U(BIPM{sup TMS})(NMes)(O)(DMAP){sub 2}] (5, BIPM{sup TMS}=C(PPh{sub 2}NSiMe{sub 3}){sub 2}; Mes=2,4,6-Me{sub 3}C{sub 6}H{sub 2}; DMAP=4-(dimethylamino)pyridine) which exhibits the unprecedented arrangement of three formal multiply bonded ligands to one metal center where the coordinated heteroatoms derive from different element groups. This complex was prepared by incorporation of carbene, imido, and then oxo groups at the uranium center by salt elimination, protonolysis, and two-electron oxidation, respectively. The oxo and imido groups adopt axial positions in a T-shaped motif with respect to the carbene, which is consistent with an inverse trans-influence. Complex 5 reacts with tert-butylisocyanate at the imido rather than carbene group to afford the uranyl(VI) carbene complex [U(BIPM{sup TMS})(O){sub 2}(DMAP){sub 2}] (6). (copyright 2014 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

Heterocyclic N-Oxides – An Emerging Class of Therapeutic Agents

Science.gov (United States)

Mfuh, Adelphe M.; Larionov, Oleg V.

2016-01-01

Heterocyclic N-oxides have emerged as potent compounds with anticancer, antibacterial, antihypertensive, antiparasitic, anti-HIV, anti-inflammatory, herbicidal, neuroprotective, and procognitive activities. The N-oxide motif has been successfully employed in a number of recent drug development projects. This review surveys the emergence of this scaffold in the mainstream medicinal chemistry with a focus on the discovery of the heterocyclic N-oxide drugs, N-oxide-specific mechanisms of action, drug-receptor interactions and synthetic avenues to these compounds. As the first review on this subject that covers the developments since 1950s to date, it is expected that it will inspire wider implementation of the heterocyclic N-oxide motif in the rational design of new medicinal agents. PMID:26087764

Catalytic α-arylation of imines leading to N-unprotected indoles and azaindoles

KAUST Repository

Marelli, Enrico

2016-03-30

A Palladium-N-heterocyclic carbene-catalyzed methodology for the synthesis of substituted, N-unprotected indoles and azaindoles is reported. The protocol permits access to various, highly substituted members of these classes of compounds. Although two possible reactions pathways (deprotonative and Heck-like) can be proposed, control experiments, supported by computational studies, point towards a deprotonative mechanism being operative.

Catalytic α-arylation of imines leading to N-unprotected indoles and azaindoles

KAUST Repository

Marelli, Enrico; Corpet, Martin; Minenkov, Yury; Neyyappadath, Rifahath; Bismuto, Alessandro; Buccolini, Giulia; Curcio, Massimiliano; Cavallo, Luigi; Nolan, Steven P.

2016-01-01

A Palladium-N-heterocyclic carbene-catalyzed methodology for the synthesis of substituted, N-unprotected indoles and azaindoles is reported. The protocol permits access to various, highly substituted members of these classes of compounds. Although two possible reactions pathways (deprotonative and Heck-like) can be proposed, control experiments, supported by computational studies, point towards a deprotonative mechanism being operative.

Electronic bond tuning with heterocyclic carbenes

KAUST Repository

Falivene, Laura; Caporaso, Lucia; Cavallo, Luigi; Jacobsen, Heiko

2013-01-01

have a propensity to increase the bonding of the labile ligand and of the substrate in Ru-promoted olefin metathesis, whereas negligible impact is expected on the stability of the ruthenacycle intermediate. In the case of Pd cross-coupling reactions

Exploring new generations of ruthenium olefin metathesis catalysts: The reactivity of a bis-ylidene ruthenium complex by DFT

KAUST Repository

Poater, Albert; Credendino, Raffaele; Slugovc, Christian; Cavallo, Luigi

2013-01-01

Density functional theory calculations were used to predict the behaviour of a potential novel architecture of olefin metathesis catalysts, in which one of the neutral ligands of classical Ru-based catalysts, e.g. a phosphine or an N-heterocyclic carbene, is replaced by an alkylidene group. Introduction of a second alkylidene ligand favors dissociation of the remaining phosphine and the overall energy profile for the metathesis using ethylene as the probe substrate reveals that the proposed bis-alkylidene complexes might match the requirements of a good performing olefin metathesis catalyst. © 2013 The Royal Society of Chemistry.

Reactions of Fischer carbene complexes with Electron-deficient olefins: Scope and limitations of this route to donor-acceptor-substituted cyclopropanes

Energy Technology Data Exchange (ETDEWEB)

Wienand, A.; Reissig, H.U. (Inst. fuer Organische Chemie der Technischen Hochschule Darmstadt (West Germany))

1990-12-01

The Fischer carbene complex ((CO){sub 5}Cr{double bond}C(OMe)Ph) (1) is able to transfer its carbene ligand to a variety of electron-deficient olefins and provides donor-acceptor-substituted cyclopropanes in good yields. Apt activating groups with respect to the alkene are ester, amide, nitrile, sulfone, and dialkyl phosphonate functions. Methyl vinyl ketone (19) affords products in low yield that may arise from an intermediate cyclopropane derivative. Phenyl vinyl sulfoxide (24) mainly acts as an oxidizing agent, transforming 1 into methyl benzoate. for olefin 24 and {alpha}-(N-methylanilino)acrylonitrile the authors found products that should be formed on an olefin metathesis pathway. The methyl-substituted carbene complex 48 also affords the expected donor-acceptor-substituted cyclopropanes; however, acyclic isomers are formed in higher amounts. The molybdenum and tungsten complexes 55 and 56, respectively, also furnish cyclopropane derivatives, but the yields are lower than with the chromium compound 1. Disubstituted olefins and complex 1 still give the cyclopropanes in moderate yields, while all trisubstituted and most of the difunctionalized alkenes do not react with this Fischer carbene complex. The cyclopropanes synthesized can be deprotonated and alkylated or transformed into ring-opened products. These model reactions demonstrate the synthetic potentials of donor-acceptor-substituted cyclopropanes prepared via Fischer carbene complexes.

Journal of Chemical Sciences | Indian Academy of Sciences

Indian Academy of Sciences (India)

Home; Journals; Journal of Chemical Sciences; Volume 128; Issue 1 ... Ruthenium(II) complexes (1-3) bearing bis-phenolate--heterocyclic carbene ligand were synthesized in good yields by the reaction of imidazolinium proligand (HL) with ... Department of Chemistry, Periyar University, Salem 636 011, Tamil Nadu, India ...

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

Science.gov (United States)

Whited, Matthew T; Grubbs, Robert H

2009-10-20

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

Investigation of the structure and properties of heterocyclic compounds and their complexes

International Nuclear Information System (INIS)

Shejnker, V.N.; Troilina, V.S.; Merinova, E.G.; Garnovskij, A.D.; Osipov, O.A.

1988-01-01

Complexing of acetyl derivatives of azoles with iodine and bromine iodide is investigated using UV-spectroscopy and dipole moment methods. In bimolecular complexes σ-acceptor coordination occurs by heterocycle pyridine type nitrogen atom and is not accompanied by the ligand conformation change. The complex stability increases in agreement with azole basicity. For N-acetyltriazole ligand, conformation reversal occurs in its trimolecular complex with IBr

Structural, spectral and magnetic studies of two Co(II)-N-heterocyclic diphosphonates based on multinuclear units

Science.gov (United States)

Zhao, Chen; Ma, Kui-Rong; Zhang, Yu; Kan, Yu-He; Li, Rong-Qing; Hu, Hua-You

2016-01-01

Two examples of Co(II)-N-heterocyclic coordination polymers based on 1-hydroxyethylidenediphosphonic acid (H5L = CH3C(OH)(PO3H2)2), namely 0.5(H3NCH2CH2NH3)·[Co6(Cl2)(H3L)2(H2L)(HL)(2,2‧-bipy)6] 1 and 2(NH4)·[Co3(HL)2(H2O)2(phen)2]·2(H2O) 2, have been solvothermally obtained by introducing the second ligands 2,2‧-bipyridine/1,10-phenanthroline (2,2‧-bipy/phen) and characterized by powder X-ray diffraction (PXRD), elemental analysis, IR, TG-DSC. The single-crystal X-ray diffractions show that compound 1 possesses a 0-D structure with hexa-nuclear cluster [Co6(O-P-O)8] built through single/double O-P-O bridges and compound 2 displays a 1-D ladder-like chain structure with magnetic topology building blocks [Co4(O-P-O)4]n. Then H-bonding and π-π stacking interactions further expand the two low-dimensional structures into three-dimensional supramolecular frameworks. Fluorescent measurements reveal that both the maximum emission peaks of 1-2 are centered at 423 nm, mainly deriving from intraligand π*-π transition state of N-heterocyclic ligand 2,2‧-bipy/phen, respectively. Magnetism data indicate that 1 exhibits antiferromagnetic behavior within hexa-nuclear Co(II) clusters, while 2 shows weak ferromagnetic interactions in 1-D topology Co(II)-chain, showing promising potential as magnetic materials.

Multidentate Di-N-heterocyclic carbene ligands for transition metal catalyzed hydrogenation reactions

NARCIS (Netherlands)

Sluijter, S.N.

2015-01-01

Synthetic catalysts play an important role in creating a more sustainable society. The use of catalysts has environmental as well as economic advantages. They speed up reactions without being consumed in the reaction itself. Moreover, they reduce the amount of byproducts and waste significantly.

Highly photoluminescent europium tetraphenylimidodiphosphinate ternary complexes with heteroaromatic co-ligands. Solution and solid state studies

Energy Technology Data Exchange (ETDEWEB)

Pietraszkiewicz, Marek, E-mail: mpietraszkiewicz@ichf.edu.pl [Institute of Physical Chemistry, Polish Academy of Sciences, Kasprzaka 44/52, 01-224 Warsaw (Poland); Pietraszkiewicz, Oksana; Karpiuk, Jerzy; Majka, Alina [Institute of Physical Chemistry, Polish Academy of Sciences, Kasprzaka 44/52, 01-224 Warsaw (Poland); Dutkiewicz, Grzegorz; Borowiak, Teresa [Adam Mickiewicz University, Faculty of Chemistry, Department of Crystallography, Grunwaldzka 6, 60-780 Poznań (Poland); Kaczmarek, Anna M. [L3–Luminescent Lanthanide Lab, f-element coordination chemistry, Ghent University, Department of Inorganic and Physical Chemistry, Krijgslaan 281, Building S3, 9000 Gent (Belgium); Van Deun, Rik, E-mail: rik.vandeun@ugent.be [L3–Luminescent Lanthanide Lab, f-element coordination chemistry, Ghent University, Department of Inorganic and Physical Chemistry, Krijgslaan 281, Building S3, 9000 Gent (Belgium)

2016-02-15

Tetraphenylimidodiphosphinate (tpip) forms neutral 3:1 complexes with lanthanide ions. These complexes can accommodate one ancillary planar heterocyclic ligand to complement their coordination sphere of Eu{sup 3+} to coordination number 8. Several co-ligands were tested to form new complexes: 1,10-phenanthroline, bathophenanthroline, 2,4,6-tris(2-pyridyl)-1,3,5-triazine, dipyrido[3,2-f:2′,3′-h]quinoxaline and 2,2′:6′,2′′-terpyridine. The addition of heterocyclic N,N-bidentate co-ligands to the coordination sphere results in a dramatic (by a factor of 45–50) luminescence enhancement of the parent Eu(tpip){sub 3}. The solid-state measurements confirmed that the ancillary ligands strongly increased the photoluminescence quantum yield (PLQY) of the investigated complexes. - Highlights: • We have disovered highly photoluminescent ternary Eu(III) complexes. • They consist of Eu(III) tetraphenylimidodiphosphinate, and planar heterocyclic ligands. • The increase in photoluminescence quantum yields in solution is enhanced up to 50 times in solution. • The solid-state photoluminescence exceeds 80% at room temperature.

Highly photoluminescent europium tetraphenylimidodiphosphinate ternary complexes with heteroaromatic co-ligands. Solution and solid state studies

International Nuclear Information System (INIS)

Pietraszkiewicz, Marek; Pietraszkiewicz, Oksana; Karpiuk, Jerzy; Majka, Alina; Dutkiewicz, Grzegorz; Borowiak, Teresa; Kaczmarek, Anna M.; Van Deun, Rik

2016-01-01

Tetraphenylimidodiphosphinate (tpip) forms neutral 3:1 complexes with lanthanide ions. These complexes can accommodate one ancillary planar heterocyclic ligand to complement their coordination sphere of Eu 3+ to coordination number 8. Several co-ligands were tested to form new complexes: 1,10-phenanthroline, bathophenanthroline, 2,4,6-tris(2-pyridyl)-1,3,5-triazine, dipyrido[3,2-f:2′,3′-h]quinoxaline and 2,2′:6′,2′′-terpyridine. The addition of heterocyclic N,N-bidentate co-ligands to the coordination sphere results in a dramatic (by a factor of 45–50) luminescence enhancement of the parent Eu(tpip) 3 . The solid-state measurements confirmed that the ancillary ligands strongly increased the photoluminescence quantum yield (PLQY) of the investigated complexes. - Highlights: • We have disovered highly photoluminescent ternary Eu(III) complexes. • They consist of Eu(III) tetraphenylimidodiphosphinate, and planar heterocyclic ligands. • The increase in photoluminescence quantum yields in solution is enhanced up to 50 times in solution. • The solid-state photoluminescence exceeds 80% at room temperature.

A non-diazo approach to α-oxo gold carbenes via gold-catalyzed alkyne oxidation.

Science.gov (United States)

Zhang, Liming

2014-03-18

intermolecular approach offers excellent synthetic flexibility because no tethering of the oxidant is required, and its reduced form is not tangled with the product. We were the first research group to develop this strategy, through the use of pyridine/quinolone N-oxides as the external oxidants. In this manner, we can effectively make a C-C triple bond a surrogate of an α-diazo carbonyl moiety in various gold catalyses. With terminal alkynes, we demonstrated that we can efficiently trap exclusively formed terminal carbene centers by internal nucleophiles en route to the formation of cyclic products, including strained oxetan-3-ones and azetidin-3-ones, and by external nucleophiles when a P,N-bidentate ligand is coordinated to gold. With internal alkynes, we generated synthetically useful regioselectivities in the generation of the α-oxo gold carbene moiety, which enables expedient formation of versatile enone products. Other research groups have also applied this strategy en route to versatile synthetic methods. The α-oxo gold carbenes appear to be more electrophilic than their Rh counterpart, which many chemists have focused on in a large array of excellent work on metal carbene chemistry. The ease of accessing the reactive gold carbenes opens up a vast area for developing new synthetic methods that would be distinctively different from the known Rh chemistry and promises to generate a new round of "gold rush".

A Non-Diazo Approach to α-Oxo Gold Carbenes via Gold-Catalyzed Alkyne Oxidation

Science.gov (United States)

2015-01-01

intermolecular approach offers excellent synthetic flexibility because no tethering of the oxidant is required, and its reduced form is not tangled with the product. We were the first research group to develop this strategy, through the use of pyridine/quinolone N-oxides as the external oxidants. In this manner, we can effectively make a C–C triple bond a surrogate of an α-diazo carbonyl moiety in various gold catalyses. With terminal alkynes, we demonstrated that we can efficiently trap exclusively formed terminal carbene centers by internal nucleophiles en route to the formation of cyclic products, including strained oxetan-3-ones and azetidin-3-ones, and by external nucleophiles when a P,N-bidentate ligand is coordinated to gold. With internal alkynes, we generated synthetically useful regioselectivities in the generation of the α-oxo gold carbene moiety, which enables expedient formation of versatile enone products. Other research groups have also applied this strategy en route to versatile synthetic methods. The α-oxo gold carbenes appear to be more electrophilic than their Rh counterpart, which many chemists have focused on in a large array of excellent work on metal carbene chemistry. The ease of accessing the reactive gold carbenes opens up a vast area for developing new synthetic methods that would be distinctively different from the known Rh chemistry and promises to generate a new round of “gold rush”. PMID:24428596

N-(2,4,6-Trimethylphenylformamide

Directory of Open Access Journals (Sweden)

David C. Liles

2011-01-01

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.

Insights into the catalytic activity of [Pd(NHC)(cin)Cl] (NHC = IPr, IPrCl, IPrBr) complexes in the Suzuki-Miyaura reaction

KAUST Repository

Nolan, Steven Patrick

2017-09-06

The influence of C4,5-halogenation on palladium N-heterocyclic carbene complexes and their activity in the Suzuki-Miyaura reaction have been investigated. Two [Pd(NHC)(cin)Cl] complexes bearing IPrCl and IPrBr ligands were synthesized. After determining electronic and steric properties of these ligands, their properties were compared to those of [Pd(IPr)(cin)Cl]. The three palladium complexes were studied using DFT calculations to delineate their behaviour in the activation step leading to the putative 12-electron active catalyst. Experimentally, their catalytic activity in the Suzuki-Miyaura reaction involving a wide range of coupling partners (30 entries) at low catalyst loading was studied.

Half -sand wish ruthenium complexes of heterocyclic-dithio carboxylato ligands

International Nuclear Information System (INIS)

El-khateeb, M.; Al-Noaimi, M.; Harb, M.; Gorls, H.; Weigand, W.

2008-01-01

The heterocyclic-dithio carboxylato complexes Cp Ru(PPh 3 )(κ 2 S,S-S 2 C-h et) [h et= 2-C 4 H 3 O (1), 2-C 4 H 3 S (2), 1-C 4 H 8 N (3)] are obtained by the reaction of the ruthenium chloride, Cp Ru(PPh 3 ) 2 CI, with the anions, h et-CS 2 . The X-ray structure of Cp Ru(PPh 3 )(κ 2 S, S-S 2 C-1- C 4 H 8 N) (3) is determined by single crystal X-ray diffraction.

Comparing Ru and Fe-catalyzed olefin metathesis

KAUST Repository

Poater, Albert; Chaitanya Vummaleti, Sai Vikrama; Pump, Eva; Cavallo, Luigi

2014-01-01

Density functional theory calculations have been used to explore the potential of Fe-based complexes with an N-heterocyclic carbene ligand, as olefin metathesis catalysts. Apart from a less endothermic reaction energy profile, a small reduction in the predicted upper energy barriers (≈ 2 kcal mol -1) is calculated in the Fe catalyzed profile with respect to the Ru catalysed profile. Overall, this study indicates that Fe-based catalysts have the potential to be very effective olefin metathesis catalysts. This journal is © the Partner Organisations 2014.

Complexes of Th(IV) perchlorates, nitrates and thiocyanates with some heterocyclic bases

International Nuclear Information System (INIS)

Agarwal, R.K.; Srivastava, A.K.; Srivastava, M.; Bhakru, N.; Srivastava, T.N.

1980-01-01

Some Th(IV) perchlorate complexes of heterocyclic bases have been reported previously. Adducts of Th(IV) nitrates and thiocyanates with some heterocyclic N-oxides have been prepared and physico-chemical properties investigated. Comparatively little is known about the complexes of Th(IV) ion with the ligands containing nitrogen atom acting as electron donating centres. In view of this, the adducts of Th(IV) ion with certain nitrogen heterocyclic bases such as pyridine (Py), α-picoline (Pic), 2-amino pyridine (NH 2 Py), 2:4-lutidine (2,4LN), 2:6-lutidine, (2,6LN), quinoline (Q), isoquinoline (Isoq), 2,2'-bipyridine (Bipy) and 1,10-phenanthroline (Phen) were synthesised and characterised by analysis and IR absorption spectra. The results are presented and discussed. (author)

Making oxidation potentials predictable: Coordination of additives applied to the electronic fine tuning of an iron(II) complex

KAUST Repository

Haslinger, Stefan

2014-11-03

This work examines the impact of axially coordinating additives on the electronic structure of a bioinspired octahedral low-spin iron(II) N-heterocyclic carbene (Fe-NHC) complex. Bearing two labile trans-acetonitrile ligands, the Fe-NHC complex, which is also an excellent oxidation catalyst, is prone to axial ligand exchange. Phosphine- and pyridine-based additives are used for substitution of the acetonitrile ligands. On the basis of the resulting defined complexes, predictability of the oxidation potentials is demonstrated, based on a correlation between cyclic voltammetry experiments and density functional theory calculated molecular orbital energies. Fundamental insights into changes of the electronic properties upon axial ligand exchange and the impact on related attributes will finally lead to target-oriented manipulation of the electronic properties and consequently to the effective tuning of the reactivity of bioinspired systems.

Making oxidation potentials predictable: Coordination of additives applied to the electronic fine tuning of an iron(II) complex

KAUST Repository

Haslinger, Stefan; Kü ck, Jens W.; Hahn, Eva M.; Cokoja, Mirza; Pö thig, Alexander; Basset, Jean-Marie; Kü hn, Fritz

2014-01-01

This work examines the impact of axially coordinating additives on the electronic structure of a bioinspired octahedral low-spin iron(II) N-heterocyclic carbene (Fe-NHC) complex. Bearing two labile trans-acetonitrile ligands, the Fe-NHC complex, which is also an excellent oxidation catalyst, is prone to axial ligand exchange. Phosphine- and pyridine-based additives are used for substitution of the acetonitrile ligands. On the basis of the resulting defined complexes, predictability of the oxidation potentials is demonstrated, based on a correlation between cyclic voltammetry experiments and density functional theory calculated molecular orbital energies. Fundamental insights into changes of the electronic properties upon axial ligand exchange and the impact on related attributes will finally lead to target-oriented manipulation of the electronic properties and consequently to the effective tuning of the reactivity of bioinspired systems.

C-C coupling of N-heterocycles at the fac-Re(CO)(3) fragment: synthesis of pyridylimidazole and bipyridine ligands.

Science.gov (United States)

Viguri, Maialen Espinal; Pérez, Julio; Riera, Lucía

2014-05-05

A new family of cationic rhenium tricarbonyl complexes with either two N-alkylimidazole (N-RIm) and one pyridine (Py) ligand, or two pyridine and one N-RIm ligand, [Re(CO)3 (N-RIm)(3-x) (Py)x ](+) , has been prepared. The reaction of these complexes with a strong base, followed by an oxidant, selectively afforded 2,2'-pyridylimidazole complexes as the result of intramolecular dehydrogenative CC coupling reactions. For tris(pyridine) complexes [Re(CO)3 (Py)3 ](+) the reaction pattern upon a deprotonation/oxidation sequence is maintained, which allows the generation of complexes with 2,2'-bipyridine ligands. In the particular combination of two different types of pyridine ligand in the cationic fac-Re(CO)3 complexes only the cross-coupling products with asymmetric 2,2'-bipyridine ligands were obtained; the homocoupling products were not observed. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Highvalent and organometallic technetium and rhenium compounds

International Nuclear Information System (INIS)

Oehlke, Elisabeth

2010-01-01

Diagnostic methods in nuclear medicine allow a detailed description of morphological organ structures and their function. The beta emitting isotope Tc-99 has optimal physical properties (140 keV gamma rays, half-life 6 h) and is therefore used for radiopharmaceuticals. The thesis is concerned with the search for new technetium complexes and their reproducible production. The (TcO3) core is of main interest. The second part of the thesis deals with organometallic technetium and rhenium complexes with carbonyl ligands and N-heterocyclic carbenes that show stability in aerobic aqueous solutions.

The Ligand Substitution Reactions of Hydrophobic Vitamin B ...

African Journals Online (AJOL)

NJD

Vitamin B. 12. Derivatives. Reaction of Cobyric Acid. Heptapropyl Ester with Heterocyclic N-donor Ligands. Mohamed S.A. .... RESEARCH ARTICLE. M.S.A. Hamza ..... neutralized with NaHCO3 and treated with excess KCN to give. DCCbs-Pr.

Carbene Transfer Reactions Catalysed by Dyes of the Metalloporphyrin Group

Directory of Open Access Journals (Sweden)

Mário M. Q. Simões

2018-03-01

Full Text Available Carbene transfer reactions are very important transformations in organic synthesis, allowing the generation of structurally challenging products by catalysed cyclopropanation, cyclopropenation, carbene C-H, N-H, O-H, S-H, and Si-H insertion, and olefination of carbonyl compounds. In particular, chiral and achiral metalloporphyrins have been successfully explored as biomimetic catalysts for these carbene transfer reactions under both homogeneous and heterogeneous conditions. In this work the use of synthetic metalloporphyrins (MPorph, M = Fe, Ru, Os, Co, Rh, Ir, Sn as homogeneous or heterogeneous catalysts for carbene transfer reactions in the last years is reviewed, almost exclusively focused on the literature since the year 2010, except when reference to older publications was deemed to be crucial.

Heterocyclic N-oxides - A Promising Class of Agents Against Tuberculosis, Malaria and Neglected Tropical Diseases.

Science.gov (United States)

Dos Santos Fernandes, Guilherme Felipe; Pavan, Aline Renata; Dos Santos, Jean Leandro

2018-04-17

Heterocyclic N-oxides have emerged as promising agents against a number of diseases and disorders, especially infectious diseases. This review analyzes the emergence and development of this scaffold in the medicinal chemistry, focusing mainly on the discovery of new heterocyclic N-oxide compounds with potent activity against tuberculosis, malaria and neglected tropical diseases (i.e. leishmaniasis and Chagas disease). A number of heterocyclic N-oxide are described herein, nevertheless, the following chemical classes deserve to be highlighted due to the large number of reports in the literature about their promising pharmacological effects: furoxan, benzofuroxan, quinoxaline 1,4-di-N-oxide, indolone N-oxide and benzimidazole N-oxide. In order to describe those most promising compounds, we included in this review only those most biologically active heterocyclic N-oxide published since 2000. Copyright© Bentham Science Publishers; For any queries, please email at epub@benthamscience.org.

Hydrofluorination of Alkynes Catalysed by Gold Bifluorides.

Science.gov (United States)

Nahra, Fady; Patrick, Scott R; Bello, Davide; Brill, Marcel; Obled, Alan; Cordes, David B; Slawin, Alexandra M Z; O'Hagan, David; Nolan, Steven P

2015-01-01

We report the synthesis of nine new N -heterocyclic carbene gold bifluoride complexes starting from the corresponding N -heterocyclic carbene gold hydroxides. A new methodology to access N,N' -bis(2,6-diisopropylphenyl)imidazol-2-ylidene gold(I) fluoride starting from N,N' -bis(2,6-diisopropylphenyl)imidazol-2-ylidene gold(I) hydroxide and readily available potassium bifluoride is also reported. These gold bifluorides were shown to be efficient catalysts in the hydrofluorination of symmetrical and unsymmetrical alkynes, thus affording fluorinated stilbene analogues and fluorovinyl thioethers in good to excellent yields with high stereo- and regioselectivity. The method is exploited further to access a fluorinated combretastatin analogue selectively in two steps starting from commercially available reagents.

Basic deuteroexchange in transition metal complexes with nitrogen-containing aromatic heterocycles

International Nuclear Information System (INIS)

Tupitsyn, I.F.

1986-01-01

Kinetics of deuteroexchange in the methyl group of nitrate complexes of a metal - nickel (2) - with different methyl-substituted aromatic heterocycles and isostructural complexes of a ligand - 2 - methyl quinoline - with different central metal atoms (Mn(2), Ni(2), Cu(2), Zn(2)) is studied. Series for influence of ligand structure on deuteroexchange rate in complexes doesn't correspond qualitatively to series for deuteroexchange rate increase in noncoordinated ligands. Deuteroexchange rate is weakly subjected to influence of exchange in metal-complexing agent. Deuteroexchange mechanism is suggested and discussed. According to this mechanism the structure developed in the course of the exchange process with electron density transfer from the heterocyclic ligand to a metal ion is a transition state of the reaction

Sacrificial spacer and non-covalent routes toward the molecular imprinting of 'poorly-functionalized' N-heterocycles

International Nuclear Information System (INIS)

Kirsch, N.; Alexander, C.; Davies, S.; Whitcombe, M.J.

2004-01-01

A comparison of three different methods for the imprinting of small aromatic heterocycles containing only a single nitrogen atom, for the preparation of specific analytical phases, was carried out. A conventional non-covalent approach to the imprinting of pyridine using methacrylic acid as the functional monomer was compared with two sacrificial spacer methods, in which heterocycles were imprinted as covalent template analogues. The results of binding experiments showed that discrimination based on ligand size was possible when polymers were prepared using a silyl ester-based template. The most selective polymer was able to bind pyridine in preference to quinoline or acridine which is opposite to the trend predicted by the pK HB values for the three ligands. Curve fitting of the isotherm for pyridine binding to this polymer to the Langmuir model gave an approximate K d of 1.1±0.1 mM and a binding site concentration of 57±2 mmol g -1 . Acridine binding did not show saturation behaviour and was non-specific and cooperative in nature

Regio- and Enantioselective N-Allylations of Imidazole, Benzimidazole, and Purine Heterocycles Catalyzed by Single-Component Metallacyclic Iridium Complexes

Science.gov (United States)

Stanley, Levi M.

2010-01-01

Highly regio- and enantioselective iridium-catalyzed N-allylations of benzimidazoles, imidazoles, and purines have been developed. N-Allylated benzimidazoles and imidazoles were isolated in high yields (up to 97%) with high branched-to-linear selectivity (up to 99:1) and enantioselectivity (up to 98% ee) from the reactions of benzimidazole and imidazole nucleophiles with unsymmetrical allylic carbonates in the presence of single component, ethylene-bound, metallacyclic iridium catalysts. N-Allylated purines were also obtained in high yields (up to 91%) with high N9:N7 selectivity (up to 96:4), high branched-to-linear selectivity (98:2), and high enantioselectivity (up to 98% ee) under similar conditions. The reactions encompass a range of benzimidazole, imidazole, and purine nucleophiles, as well as a variety of unsymmetrical aryl, heteroaryl, and aliphatic allylic carbonates. Competition experiments between common amine nucleophiles and the heterocyclic nitrogen nucleophiles studied in this work illustrate the effect of nucleophile pKa on the rate of iridium-catalyzed N-allylation reactions. Kinetic studies on the allylation of benzimidazole catalyzed by metallacyclic iridium-phosphoramidite complexes, in combination with studies on the deactivation of these catalysts in the presence of heterocyclic nucleophiles, provide insight into the effects of the structure of the phosphoramidite ligands on the stability of the metallacyclic catalysts. The data obtained from these studies has led to the development of N-allylations of benzimidazoles and imidazoles in the absence of an exogenous base. PMID:19480431

Natural bond orbital analysis of molecular interactions: Theoretical study of W(CO)5 complexes with E(PH3)2 and NHEMe ligands (E=C, Si, Ge, Sn, Pb)

International Nuclear Information System (INIS)

Nguyen Thi Ai Nhung; Huynh Thi Phuong Loan; Duong Tuan Quang; Pham Van Tat

2014-01-01

The complexes with ligands carbodiphosphorane-analogues (called tetrylones) [(CO) 5 W-{E(PH 3 ) 2 }] (W5-EP 2 ) and N-heterocyclic carbene-analogues (called tetrylenes) [(CO) 5 W-{NHE Me }] (W5-NHE Me ) when E=C-Pb have been studied using natural bond orbital (NBO) method. The NBO analysis provides a consistent picture of the chemical bonding is two entire families of transition metal complexes of tetrylone and tetrylene ligands in term of donor-acceptor interactions, showing the correlation of these interactions with Wiberg bond indies (WBI), natural partial charges, and the energetically highest lying occupied molecular orbitals for σ and π orbitals of free ligands E(PH 3 ) 2 and NHE Me . Analysis of the bonding situation reveals that in E(PH 3 ) 2 and NHE Me ligands, the energy level of the π orbital rises, whereas that of the σ orbital decreases as atom E becomes heavier. The complexes with head-on-bonded ligands have (CO) 5 W←E donation which comes from the σ-lone-pair orbital of E(PH 3 ) 2 and NHE Me where E=C for tetrylones and E=C, Si, Ge for tetrylenes, whereas the (CO) 5 W←E donation in the side-on bonded complexes when E becomes heavier arises from the π-lone-pair orbital of E(PH 3 ) 2 and NHE Me ligands which is the HOMO of the free ligands. This makes the heavier adducts of tetrylones and tetrylenes become stronger donors than the lighter systems. The NBO analysis suggests that the E(PH 3 ) 2 ligands are strong σ-donors and strong π-acceptors while the NHE Me ligands are strong σ-donors and weak π-acceptors. This is possible for tetrylones that have two lone-pair orbitals available for donation, whereas the tetrylenes have only one lone-pair orbital available for donation. (author)

Simple building-block route to (Phosphanyl-carbene)palladium complexes via intermolecular addition of functionalised phosphanes to isocyanides

NARCIS (Netherlands)

Eberhard, M.R.; van Vliet, Bart; Durán Páchon, L.; Rothenberg, G.; Eastham, G.; Kooijman, H.; Spek, A.L.; Elsevier, C.J.

2009-01-01

We present a straightforward protocol for making (phosphanyl- carbene)PdII complexes. These complexes have bidentate ligands containing an acyclic diamino- or aminooxycarbene and a phosphane. The synthesis gives good yields (typically 70–90%) for a variety of complexes (22 compounds). Moreover, it

Comparative reactivity of different types of stable cyclic and acyclic mono- and diamino carbenes with simple organic substrates.

Science.gov (United States)

Martin, David; Canac, Yves; Lavallo, Vincent; Bertrand, Guy

2014-04-02

A series of stable carbenes, featuring a broad range of electronic properties, were reacted with simple organic substrates. The N,N-dimesityl imidazolylidene (NHC) does not react with isocyanides, whereas anti-Bredt di(amino)carbene (pyr-NHC), cyclic (alkyl)(amino)carbene (CAAC), acyclic di(amino)carbene (ADAC), and acyclic (alkyl)(amino)carbene (AAAC) give rise to the corresponding ketenimines. NHCs are known to promote the benzoin condensation, and we found that the CAAC, pyr-NHC, and ADAC react with benzaldehyde to give the ketone tautomer of the Breslow intermediate, whereas the AAAC first gives the corresponding epoxide and ultimately the Breslow intermediate, which can be isolated. Addition of excess benzaldehyde to the latter does not lead to benzoin but to a stable 1,3-dioxolane. Depending on the electronic properties of carbenes, different products are also obtained with methyl acrylate as a substrate. The critical role of the carbene electrophilicity on the outcome of reactions is discussed.

Sacrificial spacer and non-covalent routes toward the molecular imprinting of 'poorly-functionalized' N-heterocycles

Energy Technology Data Exchange (ETDEWEB)

Kirsch, N.; Alexander, C.; Davies, S.; Whitcombe, M.J

2004-02-16

A comparison of three different methods for the imprinting of small aromatic heterocycles containing only a single nitrogen atom, for the preparation of specific analytical phases, was carried out. A conventional non-covalent approach to the imprinting of pyridine using methacrylic acid as the functional monomer was compared with two sacrificial spacer methods, in which heterocycles were imprinted as covalent template analogues. The results of binding experiments showed that discrimination based on ligand size was possible when polymers were prepared using a silyl ester-based template. The most selective polymer was able to bind pyridine in preference to quinoline or acridine which is opposite to the trend predicted by the pK{sub HB} values for the three ligands. Curve fitting of the isotherm for pyridine binding to this polymer to the Langmuir model gave an approximate K{sub d} of 1.1{+-}0.1 mM and a binding site concentration of 57{+-}2 mmol g{sup -1}. Acridine binding did not show saturation behaviour and was non-specific and cooperative in nature.

Fullerene–Carbene Lewis Acid–Base Adducts

KAUST Repository

Li, Huaping; Risko, Chad; Seo, Jung Hwa; Campbell, Casey; Wu, Guang; Brédas, Jean-Luc; Bazan, Guillermo C.

2011-01-01

The reaction between a bulky N-heterocylic carbene (NHC) and C60 leads to the formation of a thermally stable zwitterionic Lewis acid-base adduct that is connected via a C-C single bond. Low-energy absorption bands with weak oscillator strengths

Basic deuteroexchange in complexes of transition metals with nitrogen-containing aromatic heterocycles

International Nuclear Information System (INIS)

Tupitsyn, I.F.

1986-01-01

A study was made of the kinetics of deuteroexchange in the methyl group in complexes of one metal [nickel(II)] with different methyl-substituted aromatic heterocycles and in isostructural complexes of one ligand (2-methylquinoline) with different central metal atoms (Mn 2+ , Ni 2+ , Cu 2+ , Zn 2+ ). The order in which the structures of the ligands influence the rate of deuteroexchange in the complexes does not correspond qualitatively with the order of increase in the rate of deuteroexchange in the noncoordinated ligands. The rate of deuteroexchange is only weakly influenced by change in the identity of the metal complex former. A deuteroexchange mechanism is proposed and discussed. A structure arising in the course of the exchange process with transfer of electron density from the heterocyclic ligand to the metal ion forms the transition state of the reaction

Diphenylcarbene Protected by Four ortho-Iodine Groups: An Unusually Persistent Triplet Carbene

Directory of Open Access Journals (Sweden)

Katsuyuki Hirai

2016-11-01

Full Text Available Diphenyldiazomethane with four iodine groups at the ortho positions and two tert-butyl groups at the para positions, i.e., bis(4-tert-butyl-2,6-diiodophenyldiazomethane (1a-N2, was synthesized as a sterically hindered triplet carbene precursor. Irradiation of 1a-N2 in solution effectively generated the corresponding triplet diphenylcarbene 31a, which was characterized by UV-vis spectroscopy at low temperature, along with laser flash photolysis techniques at room temperature. The UV-vis spectrum of 31a was obtained by irradiating 1a-N2 in a 2-methyltetrahydrofuran matrix at 77 K. The ESR spectrum showed no triplet carbene signals, while a radical species was observed at the anticipated temperature of the decomposition of triplet carbene 31a. Transient absorption bands ascribable to 31a were observed by laser flash photolysis of 1a-N2 in a degassed benzene solution and decayed very slowly with a second-order rate constant (2k/εl of 5.5 × 10−3·s−1. Steady-state irradiation of 1a-N2 in degassed benzene afforded 9,10-diarylphenanthrene derivative 2a in a 31% yield. Triplet carbene 31a was also trapped by either oxygen (kO2 = 6.5 × 105 M−1·s−1 or 1,4-cyclohexadiene (kCHD = 1.5 M−1·s−1 to afford the corresponding ketone 1a-O or the diarylmethane 1a-H2. The carbene was shown to be much less reactive than the triplet diphenylcarbene that is protected by two ortho-iodo and two ortho-bromo groups, 31b.

Improve the biodegradability of post-hydrothermal liquefaction wastewater with ozone: conversion of phenols and N-heterocyclic compounds.

Science.gov (United States)

Yang, Libin; Si, Buchun; Martins, Marcio Arêdes; Watson, Jamison; Chu, Huaqiang; Zhang, Yuanhui; Tan, Xiaobo; Zhou, Xuefei; Zhang, Yalei

2017-04-01

Hydrothermal liquefaction is a promising technology to convert wet biomass into bio-oil. However, post-hydrothermal liquefaction wastewater (PHWW) is also produced during the process. This wastewater contains a high concentration of organic compounds, including phenols and N-heterocyclic compounds which are two main inhibitors for biological treatment. Thus, proper treatment is required. In this work, ozone was used to convert phenols and N-heterocyclic compounds with a dosage range of 0-4.64 mg O 3 /mL PHWW. After ozone treatment, the phenols were fully converted, and acids were produced. However, N-heterocyclic compounds were found to have a low conversion rate (21.7%). The kinetic analysis for the degradation of phenols and N-heterocyclic compounds showed that the substitute played an important role in determining the priority of ozone reactions. The OH moiety in the ring compounds (phenols and pyridinol) may form hydroxyl radical, which lead to an efficient reaction. A substantial improved biodegradability of PHWW was observed after ozone treatment. The ratio of BOD 5 /COD was increased by about 32.36%, and reached a maximum of 0.41. The improved biodegradability of PHWW was justified by the conversion of phenols and N-heterocyclic compounds.

A two-dimensional layered Cd(II) coordination polymer with a three-dimensional supramolecular architecture incorporating mixed multidentate N- and O-donor ligands.

Science.gov (United States)

Huang, Qiu-Ying; Su, Ming-Yang; Meng, Xiang-Ru

2015-06-01

The combination of N-heterocyclic and multicarboxylate ligands is a good choice for the construction of metal-organic frameworks. In the title coordination polymer, poly[bis{μ2-1-[(1H-benzimidazol-2-yl)methyl]-1H-tetrazole-κ(2)N(3):N(4)}(μ4-butanedioato-κ(4)O(1):O(1'):O(4):O(4'))(μ2-butanedioato-κ(2)O(1):O(4))dicadmium], [Cd(C4H4O4)(C9H8N6)]n, each Cd(II) ion exhibits an irregular octahedral CdO4N2 coordination geometry and is coordinated by four O atoms from three carboxylate groups of three succinate (butanedioate) ligands and two N atoms from two 1-[(1H-benzimidazol-2-yl)methyl]-1H-tetrazole (bimt) ligands. Cd(II) ions are connected by two kinds of crystallographically independent succinate ligands to generate a two-dimensional layered structure with bimt ligands located on each side of the layer. Adjacent layers are further connected by hydrogen bonding, leading to a three-dimensional supramolecular architecture in the solid state. Thermogravimetric analysis of the title polymer shows that it is stable up to 529 K and then loses weight from 529 to 918 K, corresponding to the decomposition of the bimt ligands and succinate groups. The polymer exhibits a strong fluorescence emission in the solid state at room temperature.

The activation mechanism of Fe-based olefin metathesis catalysts

KAUST Repository

Poater, Albert; Pump, Eva; Vummaleti, Sai V. C.; Cavallo, Luigi

2014-01-01

Density functional theory calculations have been used to describe the first turnover for olefin metathesis reaction of a homogenous Fe-based catalyst bearing a N-heterocyclic carbene ligand with methoxyethene as a substrate. Equal to conventional Ru-based catalysts, the activation of its Fe congener occurs through a dissociative mechanism, however with a more exothermic reaction energy profile. Predicted upper energy barriers were calculated to be on average ∼2 kcal/mol more beneficial for Fe catalyzed metathesis. Overall, this present computational study emphasises on advantages of Fe-based metathesis and gives a potential recipe for the design of an efficient Fe-based olefin metathesis catalysts. © 2014 Elsevier B.V.

The activation mechanism of Fe-based olefin metathesis catalysts

KAUST Repository

Poater, Albert

2014-08-01

Density functional theory calculations have been used to describe the first turnover for olefin metathesis reaction of a homogenous Fe-based catalyst bearing a N-heterocyclic carbene ligand with methoxyethene as a substrate. Equal to conventional Ru-based catalysts, the activation of its Fe congener occurs through a dissociative mechanism, however with a more exothermic reaction energy profile. Predicted upper energy barriers were calculated to be on average ∼2 kcal/mol more beneficial for Fe catalyzed metathesis. Overall, this present computational study emphasises on advantages of Fe-based metathesis and gives a potential recipe for the design of an efficient Fe-based olefin metathesis catalysts. © 2014 Elsevier B.V.

Expedient Syntheses of Neutral and Cationic Au(I)–NHC Complexes

KAUST Repository

Veenboer, Richard M. P.

2017-09-08

The synthesis and isolation of gold(I) precatalysts often requires the generation of several isolable intermediates as well as numerous purification steps. New protocols for the expedient synthesis of neutral [Au(OH)(NHC)] and [Au(CH2COCH3)(NHC)] species from [AuCl(NHC)] or [AuCl(DMS)] precursors bearing a variety of N-heterocyclic carbene (NHC) ligands are presented. These methods can be employed in a telescoping manner for the synthesis of catalytically relevant [Au(NTf2)(NHC)] and [Au(NHC)(NCCH3)][BF4] complexes. These attractive methods are straightforward and practical leading to various complexes in high isolated yields and purity.

Expedient Syntheses of Neutral and Cationic Au(I)–NHC Complexes

KAUST Repository

Veenboer, Richard M. P.; Gasperini, Danila; Nahra, Fady; Cordes, David B.; Slawin, Alexandra M. Z.; Cazin, Catherine S. J.; Nolan, Steven P.

2017-01-01

The synthesis and isolation of gold(I) precatalysts often requires the generation of several isolable intermediates as well as numerous purification steps. New protocols for the expedient synthesis of neutral [Au(OH)(NHC)] and [Au(CH2COCH3)(NHC)] species from [AuCl(NHC)] or [AuCl(DMS)] precursors bearing a variety of N-heterocyclic carbene (NHC) ligands are presented. These methods can be employed in a telescoping manner for the synthesis of catalytically relevant [Au(NTf2)(NHC)] and [Au(NHC)(NCCH3)][BF4] complexes. These attractive methods are straightforward and practical leading to various complexes in high isolated yields and purity.

Dinuclear NHC-palladium complexes containing phosphine spacers: synthesis, X-ray structures and their catalytic activities towards the Hiyama coupling reaction.

Science.gov (United States)

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

2014-05-21

Six dinuclear N-heterocyclic carbene (NHC) palladium complexes, [PdCl2(IMes)]2(μ-dppe) (1), [PdCl2(IPr)]2(μ-dppe) (2), [PdCl2(IMes)]2(μ-dppb) (3), [PdCl2(IPr)]2(μ-dppb) (4), [PdCl2(IMes)]2(μ-dpph) (5), and [PdCl2(IPr)]2(μ-dpph) (6) [IMes = N,N'-bis-(2,4,6-trimethylphenyl)imidazol-2-ylidene; IPr = N,N'-bis-(2,6-di(iso-propyl)phenyl)imidazol-2-ylidene; dppe = 1,2-bis(diphenylphosphino)ethane, dppb = 1,4-bis(diphenylphosphino)butane; and dpph = 1,6-bis(diphenylphosphino)hexane], have been synthesized through bridge-cleavage reactions of chloro-bridged dimeric compounds, [Pd(μ-Cl)(Cl)(NHC)]2, with the corresponding diphosphine ligands. The obtained compounds were fully characterized by (1)H NMR, (13)C NMR and (31)P NMR spectroscopy, FT-IR, elemental analysis and single-crystal X-ray crystallography. Moreover, further explorations of the catalytic potential of the dinuclear carbene palladium complexes as catalysts for the Pd-catalyzed transformations have been performed under microwave irradiation conditions, and the complexes exhibited moderate to good catalytic activity in the Hiyama coupling reaction of trimethoxyphenylsilane with aryl chlorides.

Journal of Chemical Sciences | Indian Academy of Sciences

Indian Academy of Sciences (India)

Reactions of B(C6F5)3 with abnormal N-heterocyclic carbene (NHC), L1 and cyclic (alkyl)(amino) carbene (AAC), L2 in the presence of moisture as well as in its absence, have been investigated in toluene. Reaction of NHC with 1 equivalent of B(C6F5)3 under inert condition produced classical Lewis acid-base adduct ...

Journal of Chemical Sciences | Indian Academy of Sciences

Indian Academy of Sciences (India)

Ruthenium complexes of chelating amido-functionalized N-heterocyclic carbene .... Axial phenoxide coordination on di-iron(III) bisporphyrin: Insights from .... Synthesis of azamacrocycle stabilized palladium nanoparticles: Controlled size and ...

Formation and ecotoxicity of N-heterocyclic compounds on ammoxidation of mono- and polysaccharides.

Science.gov (United States)

Klinger, Karl Michael; Liebner, Falk; Fritz, Ines; Potthast, Antje; Rosenau, Thomas

2013-09-25

Ammoxidation of technical lignins under mild conditions is a suitable approach to artificial humic substances. However, carbohydrates as common minor constituents of technical lignins have been demonstrated to be a potential source of N-heterocyclic ecotoxic compounds. Ethyl acetate extracts of ammoxidation mixtures of the monosaccharides glucose and xylose exhibited considerable growth inhibiting activity in the OECD 201 test, with 4-methyl-1H-imidazole, 4-(hydroxymethyl)-1H-imidazole, and 3-hydroxypyridine being the most active compounds. The amount of N-heterocyclic compounds formed at moderate ammoxidation conditions (70 °C, 0.2 MPa O2, 3 h) was significantly lower for the polysaccharides cellulose and xylan (16-30 μg/g of educt) compared to glucose (15.4 mg). Ammoxidation at higher temperature is not recommendable for carbohydrate-rich materials as much higher amounts of N-heterocyclic compounds were formed from both monosaccharides (100 °C: 122.4-160.5 mg/g of educt) and polysaccharides (140 °C: 5.52-16.03 mg/g of educt).

Chemistry of Stable Carbenes and «Green» Technologies

Directory of Open Access Journals (Sweden)

Korotkikh, N.I.

2015-11-01

Full Text Available Brief analysis of fundamental research in the chemistry of stable carbenes and applications in the field of «green» chemistry on their basis carried out at the L.M. Litvinenko Institute of Physical Organic & Coal Chemistry of NAS of Ukraine over the last decade is given. Carbene versions of ester Claisen condensation to form zwitterionic compounds, the Leuckart-Wallach reaction with the autoreduction of carbenoid azolium salts, Hofmann cleavage of aminocarbene insertion products, an induced tandem autotransformation of 1,2,4-triazol-5-ylidenes into 5-amidino-1,2,4-triazoles were found. New carbene reactions of ad dition, deesterification, oxidation and complexation were revealed. Effective methods of obtaining stable carbenes and carbenoids were suggested. New types of carbenes, namely benzimidazolylidenes, superstable conjugated biscarbenes and new types of carbenoids were synthesized. The existence of hypernucleophilic carbenes was theoretically predicted and experimentally confirmed. The prospects of the use of carbenes and their derivatives, in particular, carbene complexes of transition metals in catalysis of organic reactions and the search of biologically active compounds were shown.

Synthesis of Fischer carbene complexes of iridium by C-H bond activation of methyl and cyclic ethers: Evidence for reversible {alpha}-hydrogen migration

Energy Technology Data Exchange (ETDEWEB)

Luecke, H.F.; Arndtsen, B.A.; Burger, P.; Bergman, R.G. [Lawrence Berkeley Lab., CA (United States)]|[Univ. of California, Berkeley, CA (United States)

1996-03-13

We report here a mild and versatile route to Fischer carbene complexes of iridium via the activation of C-H bonds of methyl and cyclic ethers, along with our preliminary studies of this rare family of carbene complexes. Theoretical studies suggest that {alpha}-hydrogen migrations can be kinetically favorable if a coordinatively unsaturated species can be accessed. Thus, the lability of the triflate ligand presumably facilitates this process. Further evidence for the rapidity, as well as reversibility, of this rearrangement was obtained by NMR analysis. 20 refs.

Crystal and molecular structure of three molybdenum (6) dioxocomplexes with heterocyclic hydrazones

International Nuclear Information System (INIS)

Ilyukhin, A.B.; Sergienko, V.S.

1994-01-01

The X-ray diffraction investigation into three Mo(6) dioxocomplexes with heterocyclic hydrazones has been made. In all compounds the Mo atom has a deformed octahedral coordination by two O atoms of cis-dioxogroups, N atoms (azomethane), N (heterocyclie), O (phenol) of tridentate organic ligand. Sixth position in Mo coordination octahedron is due to O atom of methanol solvated molecule in the 1,3 structures or N atom of γ-picoline molecule in the 2 structure. The packing of structural units in the crystals of the 1-3 compounds is under consideration. 12 refs., 5 figs., 3 tabs

Chemistry of Iron N -heterocyclic carbene complexes: Syntheses, structures, reactivities, and catalytic applications

KAUST Repository

Riener, Korbinian

2014-05-28

Iron is the most abundant transition metal in Earth\\'s crust. It is relatively inexpensive, not very toxic, and environmentally benign. Undoubtedly, due to the involvement in a multitude of biological processes, which heavily rely on the rich functionalities of iron-containing enzymes, iron is one of the most important elements in nature. Additionally, three-coordinate iron complexes have been reported during the past several years. In this review, the mentioned iron NHC complexes are categorized by their main structure and reactivity attributes. Thus, monocarbene and bis-monocarbene complexes are presented first. This class is subdivided into carbonyl, nitrosyl, and halide compounds followed by a brief section on other, more unconventional iron NHC motifs. Subsequently, donor-substituted complexes bearing bi-, tri-, tetra-, or even pentadentate ligands and further pincer as well as scorpionato motifs are described.

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

KAUST Repository

Behenna, Douglas C.

2011-12-18

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. © 2012 Macmillan Publishers Limited. All rights reserved.

: Recyclable, ligand free palladium(II) catalyst for Heck reaction

Indian Academy of Sciences (India)

well as heterogeneous palladium catalysts, generated from either palladium(0) compounds or palladium(II) acetate or chloride salts.6 Several ligands such as phosphines, phoshites, carbenes, thioethers have been successfully employed for this reaction.7 However, homogeneous catalysis results in problems of recovery.

Asymmetric NHC-catalyzed aza-Diels-Alder reactions: Highly enantioselective route to α-amino acid derivatives and DFT calculations

KAUST Repository

Yang, Limin; Wang, Fei; Lee, Richmond; Lv, Yunbo; Huang, Kuo-Wei; Zhong, Guofu

2014-01-01

A facile N-heterocyclic carbene catalytic enantioselective aza-Diels-Alder reaction of oxodiazenes with α-chloroaldehydes as dienophile precursors is reported, with excellent enantioselectivity (ee > 99%) and excellent yield (up to 93%). DFT study

Synthesis, characterization and luminescence studies of gold(I–NHC amide complexes

Directory of Open Access Journals (Sweden)

Adrián Gómez-Suárez

2013-10-01

Full Text Available A flexible, efficient and straightforward methodology for the synthesis of N-heterocyclic carbene gold(I–amide complexes is reported. Reaction of the versatile building block [Au(OH(IPr] (1 (IPr = 1,3-bis(2,6-diisopropylphenylimidazol-2-ylidene with a series of commercially available (heteroaromatic amines leads to the synthesis of several [Au(NRR’(IPr] complexes in good yields and with water as the sole byproduct. Interestingly, these complexes present luminescence properties. UV–vis and fluorescence measurements have allowed the identification of their excitation and emission wavelengths (λmax. These studies revealed that by selecting the appropriate amine ligand the emission can be easily tuned to achieve a variety of colors, from violet to green.

Interfacial charge separation and photovoltaic efficiency in Fe(ii)-carbene sensitized solar cells.

Science.gov (United States)

Pastore, Mariachiara; Duchanois, Thibaut; Liu, Li; Monari, Antonio; Assfeld, Xavier; Haacke, Stefan; Gros, Philippe C

2016-10-12

The first combined theoretical and photovoltaic characterization of both homoleptic and heteroleptic Fe(ii)-carbene sensitized photoanodes in working dye sensitized solar cells (DSSCs) has been performed. Three new heteroleptic Fe(ii)-NHC dye sensitizers have been synthesized, characterized and tested. Despite an improved interfacial charge separation in comparison to the homoleptic compounds, the heteroleptic complexes did not show boosted photovoltaic performances. The ab initio quantitative analysis of the interfacial electron and hole transfers and the measured photovoltaic data clearly evidenced fast recombination reactions for heteroleptics, even associated with un unfavorable directional electron flow, and hence slower injection rates, in the case of homoleptics. Notably, quantum mechanics calculations revealed that deprotonation of the not anchored carboxylic function in the homoleptic complex can effectively accelerate the electron injection rate and completely suppress the electron recombination to the oxidized dye. This result suggests that introduction of strong electron-donating substituents on the not-anchored carbene ligand in heteroleptic complexes, in such a way of mimicking the electronic effects of the carboxylate functionality, should yield markedly improved interfacial charge generation properties. The present results, providing for the first time a detailed understanding of the interfacial electron transfers and photovoltaic characterization in Fe(ii)-carbene sensitized solar cells, open the way to a rational molecular engineering of efficient iron-based dyes for photoelectrochemical applications.

Synthesis and reactions of cyclovalence isomers of azo-keto-carbenes

International Nuclear Information System (INIS)

Rettenbacher, A.S.

2001-09-01

Novel types of cycloaddition products with an azomethine imine functionality have been prepared from ω-azo-α'-diazo ketones with a carbon chain of variable length between the azo- and the keto-group; the reaction is induced by catalytical amounts of rhodium(II) acetate and occurs with the concomitant extrusion of dinitrogen. The synthesis of these cyclic azomethine imines succeeded in the course of the intramolecular reaction of the azo nitrogen atoms with a carbene/carbenoid carbon atom, in situ generated from the α-diazoketone functionality; this is a novel cyclization reaction. Some of the resulting cyclization products are stable and have been isolated, others could only be trapped with dipolarophiles as [3+2] cycloadducts. The ring-size of the heterocyclic products depends on the one hand on the length of the carbon-chain (for n = 0, 1, 2) between the carbonyl carbon atom and the quaternary aliphatic or aromatic carbon atom that blocks the tautomerization of the azo-group in the starting material. On the other hand, the ring size depends on which of the two nitrogen atoms of the azo-group undergoes the ring closure with the carbene/carbenoid carbon atom generated from the α-diazoketon functionality in the course of the reaction. By far the most serious problem in the preparation of the cyclic azomethine imines is the synthesis of the required ω-azo-α'-diazo ketones. A so far unknown property of the azo-group is its intramolecularly directed nucleophilicity toward ketenes, which emerge from acid chlorides and anhydrides, or from α-diazo ketones in the course of the Wolff rearrangement. This complicated the approach to the required ω-azo-α'-diazo ketones via these functionalities as precursors and with the desired chain length between the azo- and diazo-keto-groups. Nevertheless, these problems could be overcome by using alternative strategies. Utilizing ω-azo-α'-diazo ketones a largely commonly applicable approach to endocyclic and N

Hexacoordinate Ru-based olefin metathesis catalysts with pH-responsive N-heterocyclic carbene (NHC and N-donor ligands for ROMP reactions in non-aqueous, aqueous and emulsion conditions

Directory of Open Access Journals (Sweden)

Shawna L. Balof

2015-10-01

Full Text Available Three new ruthenium alkylidene complexes (PCy3Cl2(H2ITapRu=CHSPh (9, (DMAP2Cl2(H2ITapRu=CHPh (11 and (DMAP2Cl2(H2ITapRu=CHSPh (12 have been synthesized bearing the pH-responsive H2ITap ligand (H2ITap = 1,3-bis(2’,6’-dimethyl-4’-dimethylaminophenyl-4,5-dihydroimidazol-2-ylidene. Catalysts 11 and 12 are additionally ligated by two pH-responsive DMAP ligands. The crystal structure was solved for complex 12 by X-ray diffraction. In organic, neutral solution, the catalysts are capable of performing standard ring-opening metathesis polymerization (ROMP and ring closing metathesis (RCM reactions with standard substrates. The ROMP with complex 11 is accelerated in the presence of two equiv of H3PO4, but is reduced as soon as the acid amount increased. The metathesis of phenylthiomethylidene catalysts 9 and 12 is sluggish at room temperature, but their ROMP can be dramatically accelerated at 60 °C. Complexes 11 and 12 are soluble in aqueous acid. They display the ability to perform RCM of diallylmalonic acid (DAMA, however, their conversions are very low amounting only to few turnovers before decomposition. However, both catalysts exhibit outstanding performance in the ROMP of dicyclopentadiene (DCPD and mixtures of DCPD with cyclooctene (COE in acidic aqueous microemulsion. With loadings as low as 180 ppm, the catalysts afforded mostly quantitative conversions of these monomers while maintaining the size and shape of the droplets throughout the polymerization process. Furthermore, the coagulate content for all experiments stayed <2%. This represents an unprecedented efficiency in emulsion ROMP based on hydrophilic ruthenium alkylidene complexes.

Expedient Access to an N -phenylpyrrolidin-2-yl Heterocycle via a ...

African Journals Online (AJOL)

Expedient Access to an N -phenylpyrrolidin-2-yl Heterocycle via a Base-Induced Intramolecular aza -Michael Reaction. ... in good overall yield when employing a stoichiometric amount of base to facilitate the intramolecular aza-Michael reaction. Keywords: aza Michael, intramolecular, catalysed, piperidine, pyrrolidine, base ...

Group 4 Transition-Metal Complexes of an Aniline–Carbene–Phenol Ligand

KAUST Repository

Despagnet-Ayoub, Emmanuelle

2013-05-24

Attempts to install a tridentate aniline-NHC-phenol (NCO) ligand on titanium and zirconium led instead to complexes resulting from unexpected rearrangement pathways that illustrate common behavior in carbene-early- transition-metal chemistry. © 2013 American Chemical Society.

N-Heterocyclic Carbene Complexes in Dehalogenation Reactions

Science.gov (United States)

Mas-Marzá, Elena; Page, Michael J.; Whittlesey, Michael K.

Catalytic dehalogenation represents an underdeveloped transformation in M-NHC chemistry with a small number of reports detailing the reactivity of Co, Ru, Ni and Pd catalysts. In situ generated nickel and palladium NHC complexes catalyse the hydrodechlorination of aryl chlorides. Lower coordinate Ni complexes are proposed to operate in the hydrodefluorination of mono- and poly-fluorinated substrates. The single example of Ru-NHC catalysed hydrodefluorination of fully and partially fluorinated aromatic substrates is characterised by an unusual regioselectivity. The highly regioselective dehydrohalogenation of relatively unreactive alkyl halide substrates is achieved with a cobalt NHC catalyst.

Arrested α-hydride migration activates a phosphido ligand for C–H insertion

Energy Technology Data Exchange (ETDEWEB)

Hickey, Anne K. [Indiana Univ., Bloomington, IN (United States); Muñoz, Salvador B. [Indiana Univ., Bloomington, IN (United States); Lutz, Sean A. [Indiana Univ., Bloomington, IN (United States); Pink, Maren [Indiana Univ., Bloomington, IN (United States); Chen, Chun-Hsing [Indiana Univ., Bloomington, IN (United States); Smith, Jeremy M. [Indiana Univ., Bloomington, IN (United States)

2016-12-05

Bulky tris(carbene)borate ligands provide access to high spin iron(II) phosphido complexes. The complex PhB(MesIm)₃FeP(H)Ph is thermally unstable, and we observed [PPh] group insertion into a C–H bond of the supporting ligand. An arrested α-hydride migration mechanism suggests increased nucleophilicity of the phosphorus atom facilitates [PPh] group transfer reactivity.

Rhodium, iridium and nickel complexes with a 1,3,5-triphenylbenzene tris-MIC ligand. Study of the electronic properties and catalytic activities

Directory of Open Access Journals (Sweden)

Carmen Mejuto

2015-12-01

Full Text Available The coordination versatility of a 1,3,5-triphenylbenzene-tris-mesoionic carbene ligand is illustrated by the preparation of complexes with three different metals: rhodium, iridium and nickel. The rhodium and iridium complexes contained the [MCl(COD] fragments, while the nickel compound contained [NiCpCl]. The preparation of the tris-MIC (MIC = mesoionic carbene complex with three [IrCl(CO2] fragments, allowed the estimation of the Tolman electronic parameter (TEP for the ligand, which was compared with the TEP value for a related 1,3,5-triphenylbenzene-tris-NHC ligand. The electronic properties of the tris-MIC ligand were studied by cyclic voltammetry measurements. In all cases, the tris-MIC ligand showed a stronger electron-donating character than the corresponding NHC-based ligands. The catalytic activity of the tri-rhodium complex was tested in the addition reaction of arylboronic acids to α,β-unsaturated ketones.

Synthesis of Heavy Fluorous Ruthenium Metathesis Catalysts Using the Stereoselective Addition of Polyfluoroalkyllithium to Sterically Hindered Diimines

Czech Academy of Sciences Publication Activity Database

Hošek, J.; Rybáčková, M.; Čejka, J.; Cvačka, Josef; Kvíčala, J.

2015-01-01

Roč. 34, č. 13 (2015), s. 3327 -3334 ISSN 0276-7333 Institutional support: RVO:61388963 Keywords : ring-closing metathesis * form tetrasubstituted olefins * N-heterocyclic carbene Subject RIV: CC - Organic Chemistry Impact factor: 4.186, year: 2015

Binding of molecular oxygen by an artificial heme analogue: investigation on the formation of an Fe–tetracarbene superoxo complex

KAUST Repository

Anneser, Markus R.; Haslinger, Stefan; Pö thig, Alexander; Cokoja, Mirza; D'Elia, Valerio; Hö gerl, Manuel P.; Basset, Jean-Marie; Kü hn, Fritz E.

2016-01-01

The dioxygen reactivity of a cyclic iron(II) tetra–NHC-complex (NHC: N-heterocyclic carbene) is investigated. Divergent oxidation behavior is observed depending on the choice of the solvent (acetonitrile or acetone). In the first case, exposure

Synthesis and electrochemical study of iron, chromium and tungsten aminocarbenes: Role of ligand structure and central metal nature

Energy Technology Data Exchange (ETDEWEB)

Hoskovcova, Irena [Department of Inorganic Chemistry, Institute of Chemical Technology, Technicka 5, 166 28 Prague 6 (Czech Republic); Rohacova, Jana; Dvorak, Dalimil; Tobrman, Tomas [Department of Organic Chemistry, Institute of Chemical Technology, Technicka 5, 166 28 Prague 6 (Czech Republic); Zalis, Stanislav [J. Heyrovsky Institute of Physical Chemistry, Academy of Science of the Czech Republic, Dolejskova 3, 182 23 Prague 8 (Czech Republic); Zverinova, Radka [Department of Inorganic Chemistry, Institute of Chemical Technology, Technicka 5, 166 28 Prague 6 (Czech Republic); J. Heyrovsky Institute of Physical Chemistry, Academy of Science of the Czech Republic, Dolejskova 3, 182 23 Prague 8 (Czech Republic); Ludvik, Jiri, E-mail: jiri.ludvik@jh-inst.cas.c [J. Heyrovsky Institute of Physical Chemistry, Academy of Science of the Czech Republic, Dolejskova 3, 182 23 Prague 8 (Czech Republic)

2010-11-30

Several series of Fischer-type aminocarbene complexes with central Fe, Cr or W atoms and with various carbene substitution were synthesized and electrochemically investigated by dc-polarography and cyclic voltammetry. The shifts and changes of reduction and oxidation potentials were evaluated using the linear free energy relationship (LFER) approach with respect to (a) the type of coordination, (b) the substitution on the carbene ligand and (c) the nature of the central metal atom. The analysis of measured data confirms that the reduction center is localized on the carbene moiety and is strongly influenced by both electronic and sterical properties of its substituents. The oxidation proceeds on the metal and depends mainly on its nature and on the {pi}-acidity of the ligands. Electrochemistry thus represents an important experimental approach to the description and understanding of the molecular electronic structure and redox properties. Experimental results are supported by DFT calculation of HOMO and LUMO orbitals shape and composition.

Exceptionally Stable and Efficient Solid Supported Hoveyda-Type Catalyst

Czech Academy of Sciences Publication Activity Database

Skowerski, K.; Pastva, J.; Czarnocki, S. J.; Janošcová, Jana

2015-01-01

Roč. 19, č. 7 (2015), s. 872-877 ISSN 1083-6160 Institutional support: RVO:61388955 Keywords : OLEFIN-METATHESIS CATALYSTS * RING-CLOSING METATHESIS * N-HETEROCYCLIC CARBENES Subject RIV: CF - Physical ; Theoretical Chemistry Impact factor: 2.922, year: 2015

Tuning and Quantifying Steric and Electronic Effects of N-Heterocyclic Carbenes

KAUST Repository

Falivene, Laura; Poater, Albert; Cavallo, Luigi

2014-01-01

This chapter states that the main handles for tuning steric and electronic effects are the substituents on N atoms, the nature of the C4-C5 bridge (either saturated or unsaturated), and the substituents on the C4 and C5 atoms. The initial intuition

An unprecedented chemospecific and stereoselective tandem nucleophilic addition/cycloaddition reaction of nucleophilic carbenes with ketenimines.

Science.gov (United States)

Cheng, Ying; Ma, Yang-Guang; Wang, Xiao-Rong; Mo, Jun-Ming

2009-01-16

The first study of the reaction between nucleophilic carbenes and ketenimines is reported. The interaction of thiazole and benzothiazole carbenes with ketenimines proceeded in a chemospecific and stereoselective manner to produce thiazole- and benzothiazole-spiro-pyrrole derivatives generally in good yields. The reaction was proposed to proceed via a tandem nucleophilic addition of carbene to the C=N bond of ketenimine followed by a stepwise [3+2] cycloaddition of the 1,3-dipolar intermediate with the C=C bond of ketenimine. This reaction provides a powerful protocol for the construction of novel polyfunctional thiazole-spiro-pyrrole or benzothiazole-spiro-pyrrole compounds that are not readily accessible by other methods.

Reversible alkyne insertion in the benzannulation reaction of Fischer carbene complexes with alkynes

Energy Technology Data Exchange (ETDEWEB)

Waters, M.L.; Bos, M.E.; Wulff, W.D. [Univ. of Chicago, IL (United States)

1995-12-31

The benzannulation reaction of Fischer carbene complexes with alkynes to give phenols is highly regioselective with terminal alkynes, and reasonably regioselective with internal alkynes. This has been attributed to steric factors in intermediates, where one form is favored due to close contact between the R substituent and a cis-CO ligand. Whether alkyne insertion is kinetically or thermodynamically controlled has not been determined. The authors now have evidence from regioselectivity studies that alkyne insertion into the metal-carbon bond is reversible. Implications of these results and further mechanistic considerations will be presented.

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

Energy Technology Data Exchange (ETDEWEB)

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

2014-12-08

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(η4-C8H12) (3), {PhB(OxMe2)2ImMes}Rh(η4-C8H12) (4), {PhB(OxMe2)2ImMes}Rh(CO)2 (5), {PhB(OxMe2)2ImMes}Ir(η4-C8H12) (6), and {PhB(OxMe2)2ImMes}Ir(CO)2 (7) are synthesized along with ToMM(η4-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(μ-Cl)(η2-C8H14)2]2 (M = Rh, Ir) provide {κ4-PhB(OxMe2)2ImMes'CH2}Rh(μ-H)(μ-Cl)Rh(η2-C8H14)2 (10) and {PhB(OxMe2)2ImMes}IrH(η3-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 {κ4-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

Journal of Chemical Sciences | Indian Academy of Sciences

Indian Academy of Sciences (India)

(±)Methanodibenzodiazocine tethered [C-H]+ functional site: Study towards benzoin condensation and Baylis-Hillman reactions ... Tröger's base; Imidazolium salt; N-Heterocyclic carbenes; C-H bond activation. ... The possible applications of these newly prepared salts were investigated in homogeneous catalysis.

The inverse-trans-influence in tetravalent lanthanide and actinide bis(carbene) complexes

Science.gov (United States)

Gregson, Matthew; Lu, Erli; Mills, David P.; Tuna, Floriana; McInnes, Eric J. L.; Hennig, Christoph; Scheinost, Andreas C.; McMaster, Jonathan; Lewis, William; Blake, Alexander J.; Kerridge, Andrew; Liddle, Stephen T.

2017-02-01

Across the periodic table the trans-influence operates, whereby tightly bonded ligands selectively lengthen mutually trans metal-ligand bonds. Conversely, in high oxidation state actinide complexes the inverse-trans-influence operates, where normally cis strongly donating ligands instead reside trans and actually reinforce each other. However, because the inverse-trans-influence is restricted to high-valent actinyls and a few uranium(V/VI) complexes, it has had limited scope in an area with few unifying rules. Here we report tetravalent cerium, uranium and thorium bis(carbene) complexes with trans C=M=C cores where experimental and theoretical data suggest the presence of an inverse-trans-influence. Studies of hypothetical praseodymium(IV) and terbium(IV) analogues suggest the inverse-trans-influence may extend to these ions but it also diminishes significantly as the 4f orbitals are populated. This work suggests that the inverse-trans-influence may occur beyond high oxidation state 5f metals and hence could encompass mid-range oxidation state actinides and lanthanides. Thus, the inverse-trans-influence might be a more general f-block principle.

Biochemical interpretation of quantitative structure-activity relationships (QSAR) for biodegradation of N-heterocycles: a complementary approach to predict biodegradability.

Science.gov (United States)

Philipp, Bodo; Hoff, Malte; Germa, Florence; Schink, Bernhard; Beimborn, Dieter; Mersch-Sundermann, Volker

2007-02-15

Prediction of the biodegradability of organic compounds is an ecologically desirable and economically feasible tool for estimating the environmental fate of chemicals. We combined quantitative structure-activity relationships (QSAR) with the systematic collection of biochemical knowledge to establish rules for the prediction of aerobic biodegradation of N-heterocycles. Validated biodegradation data of 194 N-heterocyclic compounds were analyzed using the MULTICASE-method which delivered two QSAR models based on 17 activating (OSAR 1) and on 16 inactivating molecular fragments (GSAR 2), which were statistically significantly linked to efficient or poor biodegradability, respectively. The percentages of correct classifications were over 99% for both models, and cross-validation resulted in 67.9% (GSAR 1) and 70.4% (OSAR 2) correct predictions. Biochemical interpretation of the activating and inactivating characteristics of the molecular fragments delivered plausible mechanistic interpretations and enabled us to establish the following biodegradation rules: (1) Target sites for amidohydrolases and for cytochrome P450 monooxygenases enhance biodegradation of nonaromatic N-heterocycles. (2) Target sites for molybdenum hydroxylases enhance biodegradation of aromatic N-heterocycles. (3) Target sites for hydratation by an urocanase-like mechanism enhance biodegradation of imidazoles. Our complementary approach represents a feasible strategy for generating concrete rules for the prediction of biodegradability of organic compounds.

Studies of coal structure using carbene chemistry

Energy Technology Data Exchange (ETDEWEB)

1990-01-01

The object of this grant was to react coal, derivatized forms of coal, and solvent swelled coal with carbenes (divalent carbon species) under mild conditions. These carbenes were to be prepared by treating the coal with several diazo compounds and then thermally decomposing them at relatively low temperatures (80--130{degree}C). The carbenes were to be chosen to show varying selectively toward aromatic rings containing heteroatom functionalities and toward polynuclear aromatic systems. In some instances, where selectivities toward aromatic and heteroaromatic ring systems were not known, model studies were to be carried out. Because of the generally mild conditions employed and the good selectivity anticipated, and actually observed with one particular system, it was expected that this methodology would provide structural information about the coal, along with data on the extent of occurrence and type of aromatic systems. After carbene reactions, treatment of the coal samples was to include extractions and thermolysis. Physical studies included thermogravimetric analysis, diffuse reflectance FT-IR spectroscopy, NMR ({sup 1}H and {sup 13}C) spectroscopy, gas chromatography, GC/MS and GC/FT-IR. 7 figs., 10 tabs.

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)

Bravard, F.

2004-01-01

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 Ln 3+ 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 (L py )or pyrazine (L pz ) 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) [fr

Construction of a monoanionic S,N,S-pincer ligand with a pyrrole core by sequential [1,2] phospho-Fries rearrangement. Characterization of palladium and silver coordination complexes

NARCIS (Netherlands)

Fraix, A.; Lutz, M.; Spek, A.L.; Klein Gebbink, R.J.M.; van Koten, G.; Salaun, J. -Y; Jaffrès, P. -A

2010-01-01

The synthesis of an S,NH,S-pincer ligand possessing a pyrrole core and two O,O-diethylthiophosphonyl groups to design PS lateral coordination sites is reported. The synthetic procedure to produce this ligand makes use of the nitrogen atom of the pyrrole heterocycle to successively functionalize the

Lutidine-derived Ru-CNC hydrogenation pincer catalysts with versatile coordination properties

NARCIS (Netherlands)

Filonenko, Georgy A.; Cosimi, Elena; Lefort, Laurent; Conley, Matthew P.; Copéret, Christophe; Lutz, Martin; Hensen, Emiel J M; Pidko, Evgeny A.

2014-01-01

Lutidine-derived bis-N-heterocyclic carbene (NHC) ruthenium CNC-pincer complexes (Ru-CNC's) were prepared. Depending on the synthetic procedure, normal (1, 2) or mixed normal/abnormal NHC-complexes (3) are formed. In the presence of phosphazene base, Ru-CNC complexes activate nitriles to give

Complexes of uranyl with N-oxides of heterocyclic amines. Electron-vibrational absorption spectra

International Nuclear Information System (INIS)

Jezowska-Trzebiatowska, B.; Wieczorek, M.

1977-01-01

A number of coordination compounds formed by uranyl chloride and nitrate with N-oxides of heterocyclic amines have been prepared and characterized by spectral measurements in the absorption region 20000-50000 cm -1 . The electrons and vibronic transitions have been determined and discussed. (author)

Functional (co)polymers from carbenes: scope, mechanism & polymer properties

NARCIS (Netherlands)

Franssen, N.M.G.

2012-01-01

Polymerization of carbenes is a valuable alternative to traditional olefin polymerization with regard to the formation of high molecular-weight functional copolymers in a stereoregular way. The versatility of this reaction with respect to different carbene precursors allows the formation of a large

Mechanochemical activation of latent N-heterocyclic carbene catalysts

NARCIS (Netherlands)

Groote, R.

2013-01-01

The use of mechanical forces to activate chemical bonds and carry out chemical transformations is called "mechanochemistry". Mechanochemistry is an alternative method for the activation of chemical reactions, next to activation by heat or by means of (photo)chemical stimuli. Although being

Engineering of RuMb: Toward a Green Catalyst for Carbene Insertion Reactions.

Science.gov (United States)

Wolf, Matthew W; Vargas, David A; Lehnert, Nicolai

2017-05-15

The small, stable heme protein myoglobin (Mb) was modified through cofactor substitution and mutagenesis to develop a new catalyst for carbene transfer reactions. The native heme was removed from wild-type Mb and several Mb His64 mutants (H64D, H64A, H64V), and the resulting apoproteins were reconstituted with ruthenium mesoporphyrin IX (RuMpIX). The reconstituted proteins (RuMb) were characterized by UV-vis and circular dichroism spectroscopy and were used as catalysts for the N-H insertion of aniline derivatives and the cyclopropanation of styrene derivatives. The best catalysts for each reaction were able to achieve turnover numbers (TON) up to 520 for the N-H insertion of aniline, and 350 TON for the cyclopropanation of vinyl anisole. Our results show that RuMb is an effective catalyst for N-H insertion, with the potential to further increase the activity and stereoselectivity of the catalyst in future studies. Compared to native Mb ("FeMb"), RuMb is a more active catalyst for carbene transfer reactions, which leads to both heme and protein modification and degradation and, hence, to an overall much-reduced lifetime of the catalyst. This leads to lower TONs for RuMb compared to the iron-containing analogues. Strategies to overcome this limitation are discussed. Finally, comparison is also made to FeH64DMb and FeH64AMb, which have not been previously investigated for carbene transfer reactions.

Far IR spectra of Th(IV) halide complexes of some heterocyclic bases

International Nuclear Information System (INIS)

Srivastava, A.K.; Agarwal, R.K.; Srivastava, M.; Kapoor, V.; Srivastava, T.N.

1981-01-01

The synthesis and IR spectra of Th(IV) perchlorato, nitrato and thiocyanato complexes of some heterocyclic bases have been reported. Halogens are common ligands in coordination chemistry forming coordinate bonds with metals readily. Metal halogen (M-X) stretching bands show a strong absorption in the far-IR region. Very little information is available on Th-X stretching frequencies. In the present communication, adducts of Th(IV) halide with certain nitrogen heterocyclic bases such as pyridine, α-picoline, 2-amino pyridine, 2:4-lutidine, 2:6-lutidine, quinoline, 2,2'-bipyridine and 1,10-phenanthroline were synthesised and characterised. Experimental details are given. Results are presented and discussed. (author)

Palladium-catalyzed allylation of tautomerizable heterocycles with alkynes.

Science.gov (United States)

Lu, Chuan-Jun; Chen, Dong-Kai; Chen, Hong; Wang, Hong; Jin, Hongwei; Huang, Xifu; Gao, Jianrong

2017-07-21

A method for the allylic amidation of tautomerizable heterocycles was developed by a palladium catalyzed allylation reaction with 100% atom economy. A series of structurally diverse N-allylic substituted heterocycles can be synthesized in good yields with high chemo-, regio-, and stereoselectivities under mild conditions.

2-(2′-Pyridyl)-4,6-diphenylphosphinine versus 2-(2′-Pyridyl)-4,6-diphenylpyridine: Synthesis, Characterization, and Reactivity of Cationic RhIII and IrIII Complexes Based on Aromatic Phosphorus Heterocycles

NARCIS (Netherlands)

de Krom, I.; Broeckx, L.E.E.; Lutz, M.; Müller, Christian

2013-01-01

The bidentate P,N hybrid ligand 1 allows access for the first time to novel cationic phosphinine-based RhIII and IrIII complexes, broadening significantly the scope of low-coordinate aromatic phosphorus heterocycles for potential applications. The coordination chemistry of 1 towards RhIII and IrIII

Improving cytotoxic properties of ferrocenes by incorporation of saturated N-heterocycles

Czech Academy of Sciences Publication Activity Database

Hodík, Tomáš; Lamač, Martin; Červenková Šťastná, Lucie; Cuřínová, Petra; Karban, Jindřich; Skoupilová, H.; Hrstka, R.; Císařová, I.; Gyepes, Robert; Pinkas, Jiří

2017-01-01

Roč. 846, OCT 2017 (2017), s. 141-151 ISSN 0022-328X R&D Projects: GA ČR(CZ) GAP207/12/2368; GA ČR(CZ) GA17-05838S Institutional support: RVO:61388955 ; RVO:67985858 Keywords : metallodrugs * ferrocene derrivatives * N-heterocycles Subject RIV: CF - Physical ; Theoretical Chemistry; CF - Physical ; Theoretical Chemistry (UCHP-M) OBOR OECD: Inorganic and nuclear chemistry; Physical chemistry (UCHP-M) Impact factor: 2.184, year: 2016

Crystal structure of bis(azido-κNbis[2,5-bis(pyridin-2-yl-1,3,4-thiadiazole-κ2N2,N3]nickel(II

Directory of Open Access Journals (Sweden)

Abdelhakim Laachir

2015-02-01

Full Text Available Reaction of 2,5-bis(pyridin-2-yl-1,3,4-thiadiazole and sodium azide with nickel(II triflate yielded the mononuclear title complex, [Ni(N32(C12H8N4S2]. The NiII ion is located on a centre of symmetry and is octahedrally coordinated by four N atoms of the two bidentate heterocyclic ligands in the equatorial plane. The axial positions are occupied by the N atoms of two almost linear azide ions [N—N—N = 178.8 (2°]. The thiadiazole and pyridine rings of the heterocyclic ligand are almost coplanar, with a maximum deviation from the mean plane of 0.0802 (9 Å. The cohesion of the crystal structure is ensured by π–π interactions between parallel pyridine rings of neighbouring molecules [centroid-to-centroid distance = 3.6413 (14 Å], leading to a layered arrangement of the molecules parallel to (001.

Correlations between electrochemical and spectrochemical parameters of ruthenium sulfoxides series with N-heterocyclic

International Nuclear Information System (INIS)

Oliveira, D. de; Toma, H.E.

1990-01-01

A systematic study of Ru Cl sub(2) (DMSO) sub(2) L sub(2) derivates, where L = N-heterocyclic base is described, contributing for a best understanding of chemical behaviour and electronic structure of the ruthenium sulfoxides. The correlations between the electrochemical and the spectroscopical parameters of the serie are presented with more emphasis. (author)

Aryl-NHC-group 13 trimethyl complexes: structural, stability and bonding insights

KAUST Repository

Wu, Melissa M.; Gill, Arran M.; Yunpeng, Lu; Yongxin, Li; Ganguly, Rakesh; Falivene, Laura; Garcí a, Felipe

2016-01-01

Treatment of aromatic N-substituted N-heterocyclic carbenes (NHCs) with trimethyl-gallium and -indium yielded the new Lewis acid-base adducts, IMes·GaMe3 (1), SIMes·GaMe3 (2), IPr·GaMe3 (3), SIPr·GaMe3 (4), IMes·InMe3 (5), SIMes·InMe3 (6), IPr·InMe3 (7), and SIPr·InMe3 (8), with all complexes being identified by X-ray diffraction, IR, and multinuclear NMR analyses. Complex stability was found to be largely dependent on the nature of the constituent NHC ligands. Percent buried volume (%VBur) and topographic steric map analyses were employed to quantify and elucidate the observed trends. Additionally, a detailed bond snapping energy (BSE) decomposition analysis focusing on both steric and orbital interactions of the M-NHC bond (M = Al, Ga and In) has been performed.

Aryl-NHC-group 13 trimethyl complexes: structural, stability and bonding insights

KAUST Repository

Wu, Melissa M.

2016-12-14

Treatment of aromatic N-substituted N-heterocyclic carbenes (NHCs) with trimethyl-gallium and -indium yielded the new Lewis acid-base adducts, IMes·GaMe3 (1), SIMes·GaMe3 (2), IPr·GaMe3 (3), SIPr·GaMe3 (4), IMes·InMe3 (5), SIMes·InMe3 (6), IPr·InMe3 (7), and SIPr·InMe3 (8), with all complexes being identified by X-ray diffraction, IR, and multinuclear NMR analyses. Complex stability was found to be largely dependent on the nature of the constituent NHC ligands. Percent buried volume (%VBur) and topographic steric map analyses were employed to quantify and elucidate the observed trends. Additionally, a detailed bond snapping energy (BSE) decomposition analysis focusing on both steric and orbital interactions of the M-NHC bond (M = Al, Ga and In) has been performed.

Coordinatively unsaturated ruthenium complexes as efficient alkyneazide cycloaddition catalysts

KAUST Repository

Lamberti, Marina

2012-01-23

The performance of 16-electron ruthenium complexes with the general formula Cp*Ru(L)X (in which L = phosphine or N-heterocyclic carbene ligand; X = Cl or OCH2CF3) was explored in azidealkyne cycloaddition reactions that afford the 1,2,3- triazole products. The scope of the Cp*Ru(PiPr 3)Cl precatalyst was investigated for terminal alkynes leading to new 1,5-disubstituted 1,2,3-triazoles in high yields. Mechanistic studies were conducted and revealed a number of proposed intermediates. Cp*Ru- (PiPr3)(2-HCCPh)Cl was observed and characterized by 1H, 13C, and 31P NMR at temperatures between 273 and 213 K. A rare example of N,N-κ2-phosphazide complex, Cp*Ru(κ2- iPr3PN3Bn)Cl, was fully characterized, and a single-crystal X-ray diffraction structure was obtained. DFT calculations describe a complete map of the catalytic reactivity with phenylacetylene and/or benzylazide. © 2012 American Chemical Society.

Coordinatively unsaturated ruthenium complexes as efficient alkyneazide cycloaddition catalysts

KAUST Repository

Lamberti, Marina; Fortman, George C.; Poater, Albert; Broggi, Julie; Slawin, Alexandra M. Z.; Cavallo, Luigi; Nolan, Steven P.

2012-01-01

The performance of 16-electron ruthenium complexes with the general formula Cp*Ru(L)X (in which L = phosphine or N-heterocyclic carbene ligand; X = Cl or OCH2CF3) was explored in azidealkyne cycloaddition reactions that afford the 1,2,3- triazole products. The scope of the Cp*Ru(PiPr 3)Cl precatalyst was investigated for terminal alkynes leading to new 1,5-disubstituted 1,2,3-triazoles in high yields. Mechanistic studies were conducted and revealed a number of proposed intermediates. Cp*Ru- (PiPr3)(2-HCCPh)Cl was observed and characterized by 1H, 13C, and 31P NMR at temperatures between 273 and 213 K. A rare example of N,N-κ2-phosphazide complex, Cp*Ru(κ2- iPr3PN3Bn)Cl, was fully characterized, and a single-crystal X-ray diffraction structure was obtained. DFT calculations describe a complete map of the catalytic reactivity with phenylacetylene and/or benzylazide. © 2012 American Chemical Society.

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

Energy Technology Data Exchange (ETDEWEB)

Bergman, Roberg G.; Gribble, Jr., Michael W.; Ellman, Jonathan A.

2008-01-30

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(PCy{sub 3}){sub 2} fragment to induce NHC-forming tautomerization of heterocycles possessing a single carbene-stabilizing heteroatom. Implications for the synthesis of benzodiazepines and related pharmacophores via C-H functionalization are discussed.

Handbook of heterocyclic chemistry

National Research Council Canada - National Science Library

Katritzky, Alan R

2010-01-01

... Heterocyclic Chemistry I (1984) Comprehensive Heterocyclic Chemistry II (1996) Comprehensive Heterocyclic Chemistry III (2008) Comprehensive Organic Functional Group Transformations I (1995) Compreh...

Ligand-Promoted C(sp(3) )-H Olefination en Route to Multi-functionalized Pyrazoles.

Science.gov (United States)

Yang, Weibo; Ye, Shengqing; Schmidt, Yvonne; Stamos, Dean; Yu, Jin-Quan

2016-05-17

A Pd-catalyzed/N-heterocycle-directed C(sp(3) )-H olefination has been developed. The monoprotected amino acid ligand (MPAA) is found to significantly promote Pd-catalyzed C(sp(3) )-H olefination for the first time. Cu(OAc)2 instead of Ag(+) salts are used as the terminal oxidant. This reaction provides a useful method for the synthesis of alkylated pyrazoles. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Kappa-receptor selective binding of opioid ligands with a heterocyclic bicyclo[3.3.1]nonan-9-one structure.

Science.gov (United States)

Benyhe, S; Márki, A; Nachtsheim, Corina; Holzgrabe, Ulrike; Borsodi, Anna

2003-01-01

Previous pharmacological results have suggested that members of the heterocyclic bicyclo[3.3.1]nonan-9-one-like compounds are potent kappa-opioid receptor specific agonists. One lead molecule of this series. called compound 1 (dimethyl 7-methyl-2,4-di-2-pyridyl-3.7-diazabicyclo[3.3.1]nonan-9-one-1,5-dicarboxylate) exhibited high affinity for [3H]ethylketocyclazocine and [3H]U-69.593 binding sites in guinea pig cerebellar membranes which known to be a good source for kappa1 receptors. It was shown by molecular modelling that heterocyclic bicyclo[3.3.1]nonan-9-ones fit very well with the structure of ketazocine, a prototypic kappa-selective benzomorphan compound; when compared to the arylacetamide structure of U-69.593, a specific kappa1-receptor agonist, a similar geometry was found with a slightly different distribution of the charges. It is postulated, that the essential structural skeleton involved in the opioid activity is an aryl-propyl-amine element distributed along the N7-C6-C5-C4-aryl bonds.

N- AND O-HETEROCYCLES PRODUCED FROM THE IRRADIATION OF BENZENE AND NAPHTHALENE IN H2O/NH3-CONTAINING ICES

International Nuclear Information System (INIS)

Materese, Christopher K.; Nuevo, Michel; Sandford, Scott A.

2015-01-01

Aromatic heterocyclic molecules are an important class of molecules of astrophysical and biological significance that include pyridine, pyrimidine, and their derivatives. Such compounds are believed to exist in interstellar and circumstellar environments, though they have never been observed in the gas phase. Regardless of their presence in the gas phase in space, numerous heterocycles have been reported in carbonaceous meteorites, which indicates that they are formed under astrophysical conditions. The experimental work described here shows that N- and O-heterocyclic molecules can form from the ultraviolet (UV) irradiation of the homocyclic aromatic molecules benzene (C 6 H 6 ) or naphthalene (C 10 H 8 ) mixed in ices containing H 2 O and NH 3 . This represents an alternative way to generate aromatic heterocycles to those considered before and may have important implications for astrochemistry and astrobiology

Atmospheric CO2 promoted synthesis of N-containing heterocycles over B(C6F5)3 catalyst

International Nuclear Information System (INIS)

Xiang Gao; Bo Yu; Qingqing Mei; Zhenzhen Yang; Yanfei Zhao; Hongye Zhang; Leiduan Hao, Zhimin Liu

2016-01-01

B(C 6 F 5 ) 3 combined with atmospheric CO 2 was found to be highly effective for the cyclization of ortho substituted aniline derivatives with N,N-dimethylformamide (DMF), and a series of N-containing heterocycles including benzothiazoles, benzimidazoles, quinazolinone and benzoxazole were obtained in good to excellent yields. (authors)

Aurophilic Interactions in [(L)AuCl](center dot center dot center dot)[(L')AuCl] Dimers: Calibration by Experiment and Theory

Czech Academy of Sciences Publication Activity Database

Andris, E.; Andrikopoulos, Prokopis C.; Schulz, J.; Turek, J.; Růžička, A.; Roithová, J.; Rulíšek, Lubomír

2018-01-01

Roč. 140, č. 6 (2018), s. 2316-2325 ISSN 0002-7863 R&D Projects: GA ČR(CZ) GA17-24155S Institutional support: RVO:61388963 Keywords : N-heterocyclic carbenes * approximate coulomb potentials * auxiliary basis sets Subject RIV: CF - Physical ; Theoretical Chemistry OBOR OECD: Physical chemistry Impact factor: 13.858, year: 2016

QSAR studies of multidentate nitrogen ligands used in lanthanide and actinide extraction processes

International Nuclear Information System (INIS)

Drew, Michael G.B.; Hudson, Michael J.; Youngs, Tristan G.A.

2004-01-01

Quantitative structure activity relationships (QSARs) have been developed to optimise the choice of nitrogen heterocyclic molecules that can be used to separate the minor actinides such as americium(III) from europium(III) in the aqueous PUREX raffinate of nuclear waste. Experimental data on distribution coefficients and separation factors (SFs) for 47 such ligands have been obtained and show SF values ranging from 0.61 to 100. The ligands were divided into a training set of 36 molecules to develop the QSAR and a test set of 11 molecules to validate the QSAR. Over 1500 molecular descriptors were calculated for each heterocycle and the Genetic Algorithm was used to select the most appropriate for use in multiple regression equations. Equations were developed fitting the separation factors to 6-8 molecular descriptors which gave r 2 values of >0.8 for the training set and values of >0.7 for the test set, thus showing good predictive quality. The descriptors used in the equations were primarily electronic and steric. These equations can be used to predict the separation factors of nitrogen heterocycles not yet synthesised and/or tested and hence obtain the most efficient ligands for lanthanide and actinide separation

Investigations on organogermanium compounds; III. N-tributylgermyl-substituted aliphatic and heterocyclic amines

NARCIS (Netherlands)

Rijkens, F.; Janssen, M.J.; Kerk, G.J.M. van der

1965-01-01

A series of new organogermanium compounds containing a germanium‐nitrogen bond, in many of which the nitrogen atom forms part of an heterocyclic ring, are prepared, in some cases by new methods: transamination reactions and reactions of germoxanes with heterocyclic amines. Striking differences in

Magnetic Study of the Novel Polynuclear Compound [Cu(II)(6-Mercaptopurinolate 2-)] n

Science.gov (United States)

Acevedo-Chávez, Rodolfo; Costas, María. Eugenia; Escudero, Roberto

1997-08-01

Chemical reactions between Cu(II) and 6-mercaptopurine, both in aqueous and in methanolic media, yield the novel amorphous polynuclear compound [Cu(II)(6-mercaptopurinolate)2-]n, which is also obtained from diverse Cu(II)-heterocyclic ligand competitive reactions. The kinetic and thermodynamic stabilities associated with the formation of this compound are inferred as remarkable. The spectroscopic data let us suggest the involvement of the exocyclic S(6) donor site and the N atoms in the imidazolic moiety of the deprotonated heterocyclic ligand in the coordination to Cu(II) atoms, forming a distorted bidimensional metallic network. The magnetic studies show the existence of very weak antiferromagnetic coupling in the solid sample. This system represents the first example of a 1 : 1 metal : 6-mercaptopurinolate2-system with ad-type open shell metallic center. The magnetic study carried out also represents the first example of magnetic characterization for this type of polynuclear Cu(II) systems with the dianionic 6-mercaptopurine ligand.

Ruthenium catalysts bearing a benzimidazolylidene ligand for the metathetical ring-closure of tetrasubstituted cycloolefins

KAUST Repository

Borguet, Yannick

2015-01-01

© The Royal Society of Chemistry. Deprotonation of 1,3-di(2-tolyl)benzimidazolium tetrafluoroborate with a strong base afforded 1,3-di(2-tolyl)benzimidazol-2-ylidene (BTol), which dimerized progressively into the corresponding dibenzotetraazafulvalene. The complexes [RhCl(COD)(BTol)] (COD is 1,5-cyclooctadiene) and cis-[RhCl(CO)2(BTol)] were synthesized to probe the steric and electronic parameters of BTol. Comparison of the percentage of buried volume (%VBur) and of the Tolman electronic parameter (TEP) of BTol with those determined previously for 1,3-dimesitylbenzimidazol-2-ylidene (BMes) revealed that the two N-heterocyclic carbenes displayed similar electron donicities, yet the 2-tolyl substituents took a slightly greater share of the rhodium coordination sphere than the mesityl groups, due to a more pronounced tilt. The anti,anti conformation adopted by BTol in the molecular structure of [RhCl(COD)(BTol)] ensured nonetheless a remarkably unhindered access to the metal center, as evidenced by steric maps. Second-generation ruthenium-benzylidene and isopropoxybenzylidene complexes featuring the BTol ligand were obtained via phosphine exchange from the first generation Grubbs and Hoveyda-Grubbs catalysts, respectively. The atropisomerism of the 2-tolyl substituents within [RuCl2(=CHPh)(PCy3)(BTol)] was investigated by using variable temperature NMR spectroscopy, and the molecular structures of all four possible rotamers of [RuCl2(=CH-o-OⁱPrC6H4)(BTol)] were determined by X-ray crystallography. Both complexes were highly active at promoting the ring-closing metathesis (RCM) of model α,ω-dienes. The replacement of BMes with BTol was particularly beneficial to achieve the ring-closure of tetrasubstituted cycloalkenes. More specifically, the stable isopropoxybenzylidene chelate enabled an almost quantitative RCM of two challenging substrates, viz., diethyl 2,2-bis(2-methylallyl)malonate and N,N-bis(2-methylallyl)tosylamide, within a few hours at 60°C.

Arylation of Rhodium(II) Azavinyl Carbenes with Boronic Acids

Science.gov (United States)

Selander, Nicklas; Worrell, Brady T.; Chuprakov, Stepan; Velaparthi, Subash; Fokin, Valery V.

2013-01-01

A highly efficient and stereoselective arylation of in situ generated azavinyl carbenes affording 2,2-diaryl enamines at ambient temperatures has been developed. These transition metal carbenes are directly produced from readily available and stable 1-sulfonyl-1,2,3-triazoles in the presence of a rhodium carboxylate catalyst. In several cases, the enamines generated in this reaction can be cyclized into substituted indoles employing copper catalysts. PMID:22913576

Pincer-CNC mononuclear, dinuclear and heterodinuclear Au(III) and Pt(II) complexes supported by mono- and poly-N-heterocyclic carbenes: synthesis and photophysical properties.

Science.gov (United States)

Gonell, S; Poyatos, M; Peris, E

2016-04-07

A family of cyclometallated Au(iii) and Pt(ii) complexes containing a CNC-pincer ligand (CNC = 2,6-diphenylpyridine) supported by pyrene-based mono- or bis-NHC ligands have been synthesized and characterized, together with the preparation of a Pt-Au hetero-dimetallic complex based on a Y-shaped tris-NHC ligand. The photophysical properties of all the new species and of two related Ru(ii)-arene complexes were studied and compared. Whereas the pyrene-based complexes only exhibit emission in solution, those containing the Y-shaped tris-NHC ligand are only luminescent when dispersed in poly(methyl methacrylate) (PMMA). In particular, the pyrene-based complexes were found to be emissive in the range of 373-440 nm, with quantum yields ranging from 3.1 to 6.3%, and their emission spectra were found to be almost superimposable, pointing to the fluorescent pyrene-centered nature of the emission. This observation suggests that the emission properties of the pyrene fragment may be combined with some of the numerous applications of NHCs as supporting ligands allowing, for instance, the design of biological luminescent agents.

Catalytic Asymmetric C–H Insertions of Rhodium(II) Azavinyl Carbenes

OpenAIRE

Chuprakov, Stepan; Malik, Jamal A.; Zibinsky, Mikhail; Fokin, Valery V.

2011-01-01

A highly efficient enantioselective C–H insertion of azavinyl carbenes into unactivated alkanes has been developed. These transition metal carbenes are directly generated from readily available and stable 1-sulfonyl-1,2,3-triazoles in the presence of chiral Rh(II) carboxylates and are used for C–H functionalization of alkanes to access a variety of β-chiral sulfonamides.

Bis(acetylacetonato-κ2O,O′(2-amino-1-methyl-1H-benzimidazole-κN3oxidovanadium(IV

Directory of Open Access Journals (Sweden)

Zukhra Ch. Kadirova

2009-07-01

Full Text Available The title mixed-ligand oxidovanadium(IV compound, [VO(C5H7O22(C8H9N3], contains a VIV atom in a distorted octahedral coordination, which is typical for such complexes. The vanadyl group and the N-heterocyclic ligand are cis to each other. The coordination bond is located at the endocyclic N atom of the benzimidazole ligand. Intramolecular hydrogen bonds between the exo-NH2 group H atoms and acetylacetonate O atoms stabilize the crystal structure.

Novel synthetic route to molybdenum hydrido-thiocarbamoyl and hydrosulfido-carbyne complexes by reactions of trans-Mo(N{sub 2}){sub 2}(R{sub 2}PC{sub 2}H{sub 4}PR{sub 2}){sub 2} with N,N-dimethylthioformamide

Energy Technology Data Exchange (ETDEWEB)

Luo, X.L.; Kubas, G.J.; Burns, C.J.; Butcher, R.J. [Los Alamos National Lab., NM (United States)

1995-07-01

The reactions of bis(dinitrogen)molybdenum complexes trans-Mo(N{sub 2}){sub 2}(R{sub 2}PC{sub 2}H{sub 4}PR{sub 2}){sub 2} (R = Ph, Et) with N,N-dimethylthioformamide (HC(S)NMe{sub 2}) in refluxing benzene under argon give the molybdenum hydrido-thiocarbamoyl complexes MoH({eta}{sup 2}-C(S)NMe{sub 2})(R{sub 2}PC{sub 2}H{sub 4}PR{sub 2}){sub 2} (R = Ph (1a), Et (1b)). On heating at 125{degree}C in toluene solutions, compounds 1a and 1b rearrange to form the molybdenum hydrosulfido-aminocarbyne complexes trans-Mo(SH)-(=CNMe{sub 2})(R{sub 2}PC{sub 2}H{sub 4}PR{sub 2}){sub 2} (R = Ph (2a), Et (2b)). A mechanism is proposed for this thermal rearrangement which involves migration of the hydride ligand from molybdenum to the sulfur atom of the thiocarbamoyl ligand to give the 16-electron Fischer carbene intermediate Mo-(=C(SH)NMe{sub 2})(R{sub 2}PC{sub 2}H{sub 4}PR{sub 2}){sub 2}, followed by migration of the hydrosulfido group from the carbene carbon to molybdenum. The molecular structures of compounds 1a and 2a have been determined by single-crystal X-ray diffraction studies. 30 refs., 4 figs., 4 tabs.

π-face donation from the aromatic N-substituent of N-heterocyclic carbene ligands to metal and its role in catalysis

KAUST Repository

Credendino, Raffaele; Falivene, Laura; Cavallo, Luigi

2012-01-01

excellently correlate with the experimental ΔE 1/2 potentials, offering a handle to rationalize the experimental findings. Analysis of the HOMO of the complexes before oxidation suggests that electron-donating Y groups destabilize the metal centered HOMO

Synthesis and Crystal Structure of Di-μ-chlorido-bis{chlorido[4-ethyl- N-(pyridin-2-ylmethylidene-κ N)aniline-κ N]mercury(II)}

Science.gov (United States)

Khalaj, M.; Seftejani, F. B.; Ghazanfarpour-Darjani, M.; Lalegani, A.

2017-12-01

The centrosymmetric dinuclear title complex [Hg2Cl4(dip)2] was synthesized using the Schiff base bidentate ligand (E)-4-ethyl- N-(pyridine-2-ylmethylene)benzeneamine ( dip) and mercury(II) chloride salts. It has been characterized by elemental analysis, X-ray diffraction, and UV-Visible and infrared spectroscopic techniques. The X-ray analysis shows that the title compound crystallizes in the monoclinic sp. gr. P21/n, Z = 2 with a = 7.8233(17) Å, b = 15.178(3) Å, c = 12.559(3) Å, β = 97.021(3)°. The Hg(II) ion has a distorted trigonal-bipyramidal coordination environment formed by the bischelating N-heterocyclic ligands, two bridging Cl atoms and one terminal Cl atom.

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)

Høj, Martin; Kvaskoff, David; Wentrup, Curt

2014-01-01

). 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....

General and efficient one-pot synthesis of novel sugar/heterocyclic(aryl) 1,2-diketones from sugar terminal alkynes by Sonogashira/tetra-n- butylammonium permanganate oxidation.

Science.gov (United States)

Zhang, Fuyi; Wu, Xiaopei; Wang, Liming; Liu, Hong; Zhao, Yufen

2015-11-19

A new approach for one-pot synthesis of novel sugar/heterocyclic(aryl) 1,2-diketones has been achieved by the reaction of various sugar terminal alkynes with heterocyclic(aryl) iodides at room temperature. This one-pot protocol includes Sonogashira coupling and mild n-Bu4NMnO4 oxidation reaction. This method is mild, general and efficient. Fifty-six examples have been given and the sugar/heterocyclic(aryl) 1,2-diketones were obtained in 71-94% yields. The sugar terminal alkynes include 9 structurally different sugars in pyranose, furanose, and acyclic form which have various protecting groups, sensitive groups, and sterically bulky substituents. The heterocyclic(aryl) iodides include sterically bulky heterocyclic compounds and iodobenzenes with electron-donating, electron-neutral, and electron-withdrawing substituents. Copyright © 2015 Elsevier Ltd. All rights reserved.

Single-catalyst high-weight% hydrogen storage in an N-heterocycle synthesized from lignin hydrogenolysis products and ammonia.

Science.gov (United States)

Forberg, Daniel; Schwob, Tobias; Zaheer, Muhammad; Friedrich, Martin; Miyajima, Nobuyoshi; Kempe, Rhett

2016-10-20

Large-scale energy storage and the utilization of biomass as a sustainable carbon source are global challenges of this century. The reversible storage of hydrogen covalently bound in chemical compounds is a particularly promising energy storage technology. For this, compounds that can be sustainably synthesized and that permit high-weight% hydrogen storage would be highly desirable. Herein, we report that catalytically modified lignin, an indigestible, abundantly available and hitherto barely used biomass, can be harnessed to reversibly store hydrogen. A novel reusable bimetallic catalyst has been developed, which is able to hydrogenate and dehydrogenate N-heterocycles most efficiently. Furthermore, a particular N-heterocycle has been identified that can be synthesized catalytically in one step from the main lignin hydrogenolysis product and ammonia, and in which the new bimetallic catalyst allows multiple cycles of high-weight% hydrogen storage.

N- AND O-HETEROCYCLES PRODUCED FROM THE IRRADIATION OF BENZENE AND NAPHTHALENE IN H{sub 2}O/NH{sub 3}-CONTAINING ICES

Energy Technology Data Exchange (ETDEWEB)

Materese, Christopher K.; Nuevo, Michel; Sandford, Scott A., E-mail: christopher.k.materese@nasa.gov [NASA Ames Research Center, Moffett Field, CA 94035 (United States)

2015-02-20

Aromatic heterocyclic molecules are an important class of molecules of astrophysical and biological significance that include pyridine, pyrimidine, and their derivatives. Such compounds are believed to exist in interstellar and circumstellar environments, though they have never been observed in the gas phase. Regardless of their presence in the gas phase in space, numerous heterocycles have been reported in carbonaceous meteorites, which indicates that they are formed under astrophysical conditions. The experimental work described here shows that N- and O-heterocyclic molecules can form from the ultraviolet (UV) irradiation of the homocyclic aromatic molecules benzene (C{sub 6}H{sub 6}) or naphthalene (C{sub 10}H{sub 8}) mixed in ices containing H{sub 2}O and NH{sub 3}. This represents an alternative way to generate aromatic heterocycles to those considered before and may have important implications for astrochemistry and astrobiology.

Structure, bonding and energetics of N-heterocyclic carbene (NHC ...

Indian Academy of Sciences (India)

... of Science Education and Research (NISER), Bhubaneswar, 751 005 India .... out with Gaussian software with the default conver- .... with Multiwfn software.67 The FBO bond order has ... free energy ( G) of bond dissociation are given in.

Insight into π-hole interactions containing the inorganic heterocyclic compounds S2N2/SN2P2.

Science.gov (United States)

Lu, Bo; Zhang, Xueying; Meng, Lingpeng; Zeng, Yanli

2017-08-01

Similar to σ-hole interactions, the π-hole interaction has attracted much attention in recent years. According to the positive electrostatic potentials above and below the surface of inorganic heterocyclic compounds S 2 N 2 and three SN 2 P 2 isomers (heterocyclic compounds 1-4), and the negative electrostatic potential outside the X atom of XH 3 (X = N, P, As), S 2 N 2 /SN 2 P 2 ⋯XH 3 (X = N, P, As) complexes were constructed and optimized at the MP2/aug-cc-pVTZ level. The X atom of XH 3 (X = N, P, As) is almost perpendicular to the ring of the heterocyclic compounds. The π-hole interaction energy becomes greater as the trend goes from 1⋯XH 3 to 4⋯XH 3 . These π-hole interactions are weak and belong to "closed-shell" noncovalent interactions. According to the energy decomposition analysis, of the three attractive terms, the dispersion energy contributes more than the electrostatic energy. The polarization effect also plays an important role in the formation of π-hole complexes, with the contrasting phenomena of decreasing electronic density in the π-hole region and increasing electric density outside the X atom of XH 3 (X = N, P, As). Graphical abstract Computed density difference plots for the complexes 3⋯NH 3 (a 1 ), 3⋯PH 3 (b 1 ), 3⋯AsH 3 (c 1 ) and electron density shifts for the complexes 3⋯NH 3 (a 2 ), 3⋯PH 3 (b 2 ),3⋯AsH 3 (c 2 ) on the 0.001 a.u. contour.

13C GIAO DFT calculation as a tool for configuration prediction of N-O group in saturated heterocyclic N-oxides

Czech Academy of Sciences Publication Activity Database

Pohl, Radek; Potmischil, F.; Dračínský, Martin; Vaněk, Václav; Slavětínská, Lenka; Buděšínský, Miloš

2012-01-01

Roč. 50, č. 6 (2012), s. 415-423 ISSN 0749-1581 R&D Projects: GA ČR GA203/09/1919 Institutional research plan: CEZ:AV0Z40550506 Keywords : NMR * 13C * 1H * saturated heterocyclic N-oxides * chemical shift calculations * DFT Subject RIV: CC - Organic Chemistry Impact factor: 1.528, year: 2012

Chemical functionalization of graphene by carbene cycloaddition: A density functional theory study

International Nuclear Information System (INIS)

Zan, Wenyan

2014-01-01

Graphical abstract: - Highlights: • The reaction process of graphene functionalization with CCl 2 group in atomic scales was studied. • The potential candidate carbenes CR 2 (R = H, F, CN, NO 2 0 , NO 2 90 , CH 3 , OCH 3 , CCH, C 6 H 5 ) were separately combined with graphene. • The functionalization of graphene nanoribbon with dichlorocarbene group was investigated. • The electronic properties of graphene functionalized by carbene groups were discussed. - Abstract: In this work, we have systematically studied the structural, energetic and electronic properties of graphene functionalized with carbene groups by using density functional theory. Introducing a low concentration of CCl 2 group in graphene was studied in detail by DFT, and closed cyclopropane-like three-membered ring structure was formed, meanwhile, the potential candidate carbene groups CR 2 (R = H, F, CH 3 , CN, NO 2 , OCH 3 , CCH, C 6 H 5 ) were added to graphene sheet, and CR 2 (R = H, NO 2 , CH 3 ) groups were expected to be good reactive species to covalently modify graphene. The graphene functionalization with carbene groups above can open graphene's band gap. More CCl 2 molecules were added to graphene, and different concentrations of CCl 2 group can tune graphene's band gap. In addition, the addition of CCl 2 group to graphene edges was investigated, and the stronger binding energy was found. Multiple CCl 2 molecules preferred to be bound with the same edge of graphene nanoribbon. This work provides an insight into the detailed molecular mechanism of graphene functionalization with carbene groups

Bis[1,3-bis(2,4,6-trimethylphenyl-2,3-dihydro-1H-imidazol-2-ylidene]dinitrosyl(tetrahydroborato-κ2H,H′tungsten(0

Directory of Open Access Journals (Sweden)

Heinz Berke

2011-01-01

Full Text Available In the title paramagnetic 19-electron neutral complex, [W(BH4(C21H24N22(NO2], the W(0 atom is coordinated by two 1,3-bis(2,4,6-trimethylphenylimidazol-2-ylidene (IMes carbene ligands, two NO groups and two H atoms of an η2-tetrahydroborate ligand. Depending on the number of coordination sites (n assigned to the BH4− ligand, the coordination geometry of the W atom may either be described as approximately trigonal–bipyramidal (n = 1 or as very distorted octahedral with the bridging H atoms filling two coordination positions (n = 2. In the latter case, the coplanar NO groups and bridging H atoms (r.m.s. deviation = 0.032 Å form one octahedral plane, with mutually trans-oriented carbene ligands. In the crystal, molecules are connected via C—H...O interactions.

Synthesis and structure of the unligated carbene of chromium

Energy Technology Data Exchange (ETDEWEB)

Billups, W.E.; Souchan Chang; Hauge, R.H.; Margrave, J.L. (Rice Univ., Houston, TX (United States))

1993-04-14

Complexes with metal-carbon double bonds have found applications as intermediates in many important catalytic reactions including cyclopropanation of alkenes by diazoalkanes, Fischer-Tropsch synthesis, olefin metathesis, Ziegler-Natta polymerization, alkane activation, and in the decomposition of transition metal alkyl complexes. However, complexes with the simplest carbene, CH[sub 2], coordinated to the metal center are relatively rare. In this paper the authors report the synthesis and characterization of the simple unligated carbene of chromium by FTIR matrix isolation spectroscopy. 7 refs., 3 figs., 4 tabs.

Highly Luminescent Dinuclear Platinum(II) Complexes Incorporating Bis-Cyclometallating Pyrazine-Based Ligands: A Versatile Approach to Efficient Red Phosphors

OpenAIRE

Culham, Stacey; Lanoe, Pierre-Henri; Whittle, Victoria; Durrant, Marcus; Williams, Gareth; Kozhevnikov, Valery

2013-01-01

A series of luminescent dinuclear platinum(II) complexes incorporating diphenylpyrazine-based bridging ligands ((LH2)-H-n) has been prepared. Both 2,5-diphenylpyrazine ((LH2)-H-2) and 2,3-diphenylpyrazine ((LH2)-H-3) are able to undergo cyclometalation of the two phenyl rings, with each metal ion binding to the two nitrogen atoms of the central heterocycle, giving, after treatment with the anion of dipivaloyl methane (dpm), complexes of formula \\{Pt(dpm)\\}(2)L-n. These compounds are isomers o...

Synthesis of New Chiral Benzimidazolylidene–Rh Complexes and Their Application in Asymmetric Addition Reactions of Organoboronic Acids to Aldehydes

Directory of Open Access Journals (Sweden)

Weiping He

2016-09-01

Full Text Available A series of novel chiral N-heterocyclic carbene rhodium complexes (NHC–Rh based on benzimidazole have been prepared, and all of the NHC–Rh complexes were fully characterized by NMR and mass spectrometry. These complexes could be used as catalysts for the asymmetric 1,2-addition of organoboronic acids to aldehydes, affording chiral diarylmethanols with high yields and moderate enantioselectivities.

Spectroscopic properties and antimicrobial activity of dioxomolybdenum(VI complexes with heterocyclic S,S’-ligands

Directory of Open Access Journals (Sweden)

Sovilj Sofija P.

2012-01-01

Full Text Available Five new dioxomolybdenum(VI complexes of the general formula[MoO2(Rdtc2], 1-5, where Rdtc-refer to piperidine- (Pipdtc, 4-morpholine-(Morphdtc, 4-thiomorpholine-(Timdtc, piperazine- (Pzdtc or Nmethylpiperazine- (N-Mepzdtc dithiocarbamates, respectively, have been prepared. Elemental analysis, conductometric measurements, electronic, IR and NMR spectroscopy have been employed to characterize them. Complexes 1-5 contain a cis-MoO2 group and are of an octahedral geometry. Two dithiocarbamato ions join as bidentates with both the sulphur atoms to the molybdenum atom. The presence of different heteroatom in the piperidinо moiety influences the v(C----N and v(C----S vibrations, which decrease in the order of the complexes with: Pipdtc > N-Mepipdtc > Morphdtc > Pzdtc > Timdtc ligands. On the basis of spectral data, molecular structures of complexes 1-5 were optimized on semiempirical molecular-orbital level, and the geometries, as obtained from calculations, described. Antimicrobial activity was tested against nine different laboratory control strains of bacteria and two strains of yeast Candida albicans. All tested strains were sensitive. Complexes bearing heteroatom in position 4 of piperidine moiety are significantly more potent against bacteria tested comparing to corresponding ligands.

Adsorptive stripping voltammetric behaviour of copper complexes of some heterocyclic azo compounds.

Science.gov (United States)

Farias, P A; Ferreira, S L; Ohara, A K; Bastos, M B; Goulart, M S

1992-10-01

Controlled adsorptive accumulation of copper complexed with TAN, TAC, TAR and TAM (heterocyclic azo-compounds) on a static mercury drop electrode provides the basis for the direct stripping measurement of this element in the nanomolar concentration level. The ligand TAN exhibited great sensitivity and better separation of the peak current of the ligand in relation to the complex. The reduction current of adsorbed complex ions of copper is measured by linear scan cathodic stripping voltammetry, preceded by a period of accumulation of a few minutes. The peak potential is at approximately -0.37 V vs. Ag/AgCl. Optimal experimental parameters were found to be a TAN concentration of 1 x 10(-5)M, an accumulation potential of -0.22 V, and a solution pH of 3.7 (acetate buffer). The detection limit is 0.8nM after a 5-min accumulation with a stirred solution, and the response is linear up to 50 mug/l. Many common cations and anions do not interfere in the determination of copper. The interference of titanium is eliminated by addition of fluoride ion. Results are reported for a fresh water sample.

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)

Lim, Seung Joo; Fox, Peter

2014-02-01

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. © 2013.

Electrochemistry of chromium(0)-aminocarbene complexes

International Nuclear Information System (INIS)

Hoskovcova, Irena; Rohacova, Jana; Meca, Ludek; Tobrman, Tomas; Dvorak, Dalimil; Ludvik, Jiri

2005-01-01

Two series of chromium(0)-(aryl)aminocarbene complexes substituted on the ligand phenyl ring were prepared and electrochemically investigated: pentacarbonyl((N,N-dimethylamino)(phenyl)carbene(chromium(0) (Ia-e) and chelated tetracarbonyl((η 2 -N-allyl-N-allylamino)(phenyl)carbene(chromium(0) (IIa, c-e). For comparison, a tungsten analogue of IIc (III) and a chromium chelate bearing a methyl substituent instead of the phenyl group IV were taken into the study. The intramolecular interactions of p-substituents on the ligand phenyl ring with the reduction and oxidation centres of the molecule of complex (followed electrochemically using LFER [P. Zuman, Substituent Effects in Organic Polarography, Plenum Press, New York, 1967]) enabled to localize the corresponding electron transfer. The influence of the type of coordination, the substituent on the ligand phenyl ring and the central metal atom on oxidation and reduction potentials is discussed

Nitrenes, carbenes, diradicals, and ylides. Interconversions of reactive intermediates.

Science.gov (United States)

Wentrup, Curt

2011-06-21

Rearrangements of aromatic and heteroaromatic nitrenes and carbenes can be initiated with either heat or light. The thermal reaction is typically induced by flash vacuum thermolysis, with isolation of the products at low temperatures. Photochemical experiments are conducted either under matrix isolation conditions or in solution at ambient temperature. These rearrangements are usually initiated by ring expansion of the nitrene or carbene to a seven-membered ring ketenimine, carbodiimide, or allene (that is, a cycloheptatetraene or an azacycloheptatetraene when a nitrogen is involved). Over the last few years, we have found that two types of ring opening take place as well. Type I is an ylidic ring opening that yields nitrile ylides or diazo compounds as transient intermediates. Type II ring opening produces either dienylnitrenes (for example, from 2-pyridylnitrenes) or 1,7-(1,5)-diradicals (such as those formed from 2-quinoxalinylnitrenes), depending on which of these species is better stabilized by resonance. In this Account, we describe our achievements in elucidating the nature of the ring-opened species and unraveling the connections between the various reactive intermediates. Both of these ring-opening reactions are found, at least in some cases, to dominate the subsequent chemistry. Examples include the formation of ring-opened ketenimines and carbodiimides, as well as the ring contraction reactions that form five-membered ring nitriles (such as 2- and 3-cyanopyrroles from pyridylnitrenes, N-cyanoimidazoles from 2-pyrazinyl and 4-pyrimidinylnitrenes, N-cyanopyrazoles from 2-pyrimidinylnitrenes and 3-pyridazinylnitrenes, and so forth). The mechanisms of formation of the open-chain and ring-contraction products were unknown at the onset of this study. In the course of our investigation, several reactions with three or more consecutive reactive intermediates have been unraveled, such as nitrene, seven-membered cyclic carbodiimide, and open-chain nitrile ylide

synthesis and characterization of some poly functionalized heterocyclic derivatives of expected biological activity

International Nuclear Information System (INIS)

El-sayed, M.S.

2001-01-01

The present work was aimed and designed to fulfil The following objectives : 1- Continuation of the effort done by our research group in the field of chemistry of pyridinethione derivatives and their biological activities. 2- Synthesis of several new heterocyclic derivatives containing N and/or S using the laboratory available reagents. 3- Establishment of the structures of the newly synthesized heterocyclic compounds by the data of IR, 1 H-NMR, mass spectra in addition to the elemental analysis. 4- Synthesis of some of these heterocyclic derivatives via alternative routs and this used as a tool to confirm the structures of the newly synthesized heterocyclic derivatives. 5- study of the most probable mechanisms leading to the formation of the new heterocyclic derivatives. 6- The antimicrobial activity of some of the newly synthesized heterocyclic derivatives was tested against several types of organisms

Mode of action of nifurtimox and N-oxide-containing heterocycles against Trypanosoma cruzi: is oxidative stress involved?

Science.gov (United States)

Boiani, Mariana; Piacenza, Lucia; Hernández, Paola; Boiani, Lucia; Cerecetto, Hugo; González, Mercedes; Denicola, Ana

2010-06-15

Chagas disease is caused by the trypanosomatid parasite Trypanosoma cruzi and threatens millions of lives in South America. As other neglected diseases there is almost no research and development effort by the pharmaceutical industry and the treatment relies on two drugs, Nifurtimox and Benznidazole, discovered empirically more than three decades ago. Nifurtimox, a nitrofurane derivative, is believed to exert its biological activity through the bioreduction of the nitro-group to a nitro-anion radical which undergoes redox-cycling with molecular oxygen. This hypothesis is generally accepted, although arguments against it have been presented. In the present work we studied the ability of Nifurtimox and five N-oxide-containing heterocycles to induce oxidative stress in T. cruzi. N-Oxide-containing heterocycles represent a promising group of new trypanosomicidal agents and their mode of action is not completely elucidated. The results here obtained argue against the oxidative stress hypothesis almost for all the studied compounds, including Nifurtimox. A significant reduction in the level of parasitic low-molecular-weight thiols was observed after Nifurtimox treatment; however, it was not linked to the production of reactive oxidant species. Besides, redox-cycling is only observed at high Nifurtimox concentrations (>400microM), two orders of magnitude higher than the concentration required for anti-proliferative activity (5microM). Our results indicate that an increase in oxidative stress is not the main mechanism of action of Nifurtimox. Among the studied N-oxide-containing heterocycles, benzofuroxan derivatives strongly inhibited parasite dehydrogenase activity and affected mitochondrial membrane potential. The indazole derivative raised intracellular oxidants production, but it was the least effective as anti-T. cruzi. Copyright 2010 Elsevier Inc. All rights reserved.

catena-Poly[[[dichloridozinc(II]-μ-1,4-bis(1H-benzimidazol-2-yl-κN3butane] 1,4-bis(1H-benzimidazol-2-ylbutane solvate

Directory of Open Access Journals (Sweden)

Yan-Ling Zhou

2010-01-01

Full Text Available In the crystal structure of the title coordination polymer/co-crystal, {[ZnCl2(C18H18N4]·C18H18N4}n, the tetrahedrally coordinated ZnII ions are linked by the N-heterocycle into a linear chain. Another N-heterocycle present is not coordinated to the metal atom but interacts with the chain through N—H...N and N—H...Cl hydrogen bonds. The butyl chain of the uncoordinated ligand is disordered over three positions in a 0.511 (4:0.289 (5:0.200 (5 ratio.

Carbenes and Nitrenes: Recent Developments in Fundamental Chemistry.

Science.gov (United States)

Wentrup, Curt

2018-05-29

There has been significant progress in the direct observation of carbenes, nitrenes, and many other reactive intermediates in recent years due to the application of matrix photolysis and flash vacuum pyrolysis linked with matrix isolation at cryogenic temperatures. Our understanding of singlet and triplet states has improved through the interplay of spectroscopy and computations. Bistable carbenes and nitrenes as well as many examples of tunneling have been discovered. Numerous rearrangements and fragmentations have been documented. This minireview aims to give an overview of some of these developments but will not generally cover laser flash photolysis and chemical reactions in liquid solution. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Fullerene–Carbene Lewis Acid–Base Adducts

KAUST Repository

Li, Huaping

2011-08-17

The reaction between a bulky N-heterocylic carbene (NHC) and C60 leads to the formation of a thermally stable zwitterionic Lewis acid-base adduct that is connected via a C-C single bond. Low-energy absorption bands with weak oscillator strengths similar to those of n-doped fullerenes were observed for the product, consistent with a net transfer of electron density to the C60 core. Corroborating information was obtained using UV photoelectron spectroscopy, which revealed that the adduct has an ionization potential ∼1.5 eV lower than that of C60. Density functional theory calculations showed that the C-C bond is polarized, with a total charge of +0.84e located on the NHC framework and -0.84e delocalized on the C 60 cage. The combination of reactivity, characterization, and theoretical studies demonstrates that fullerenes can behave as Lewis acids that react with C-based Lewis bases and that the overall process describes n-doping via C-C bond formation. © 2011 American Chemical Society.

Iron(III) complexes of certain tetradentate phenolate ligands as ...

Indian Academy of Sciences (India)

non-heme iron enzymes, which catalyse the oxidative cleavage of catechols to cis, cis-muconic acids with the incorporation of ... nature of heterocyclic rings of the ligands and the methyl substituents on them regulate the electronic spectral features .... and simple substitution reactions.19,21 The complexes of [H2(L5)] and ...

Entangled zinc-ditetrazolate frameworks involving in situ ligand synthesis and topological modulation by various secondary N-donor ligands

International Nuclear Information System (INIS)

Li Yunwu; Chen Weilin; Wang Yonghui; Li Yangguang; Wang Enbo

2009-01-01

The introduction of various secondary N-donor ligands into an in situ ditetrazolate-ligand synthesis system of terephthalonitrile, NaN 3 and ZnCl 2 led to the formation of three new entangled frameworks Zn(pdtz)(4,4'-bipy).3H 2 O (1), [Zn(pdtz)(bpp)] 2 .3H 2 O (2) and Zn(pdtz) 0.5 (N 3 )(2,2'-bipy) (3) (4,4'-bipy=4,4'-bipyridine; bpp=1,3-bis(4-pyridyl)propane; 2,2'-bipy=2,2'-bipyridine; H 2 pdtz=5,5'-1,4-phenylene-ditetrazole). The formation of pdtz 2- ligand involves the Sharpless [2+3] cycloaddition reaction between terephthalonitrile and NaN 3 in the presence of Zn 2+ ion as a Lewis-acid catalyst under hydrothermal conditions. Compound 1 exhibits a fivefold interpenetrating 3D framework based on the diamondoid topology. Compound 2 displays a twofold parallel interpenetrating framework based on the wavelike individual network. Compound 3 possesses a 2D puckered network. These new Zn-ditetrazolate frameworks are highly dependent on the modulation of different secondary N-donor ligands. Their luminescent properties were investigated. - Graphical abstract: Three new entangled frameworks were prepared by an in situ ditetrazolate-ligand synthesis system assisted with various auxiliary N-donor ligands. The entangled structures can be modulated by different secondary ligands.

Asymmetric NHC-catalyzed aza-Diels-Alder reactions: Highly enantioselective route to α-amino acid derivatives and DFT calculations

KAUST Repository

Yang, Limin

2014-08-01

A facile N-heterocyclic carbene catalytic enantioselective aza-Diels-Alder reaction of oxodiazenes with α-chloroaldehydes as dienophile precursors is reported, with excellent enantioselectivity (ee > 99%) and excellent yield (up to 93%). DFT study showed that cis-TSa, formed from a top face approach of oxodiazene to cis-IIa, is the most favorable transition state and is consistent with the experimental observations. © 2014 American Chemical Society.

Zinc-Catalyzed Synthesis of Conjugated Dienoates through Unusual Cross-Couplings of Zinc Carbenes with Diazo Compounds.

Science.gov (United States)

Mata, Sergio; González, María J; González, Jesús; López, Luis A; Vicente, Rubén

2017-01-23

Zinc-catalyzed selective cross-coupling of two carbene sources, such as vinyl diazo compounds and enynones, enabled the synthesis of conjugated dienoate derivatives. This reaction involved the unprecedented coupling of a zinc furyl carbene with vinyl diazo compounds through the γ-carbon. Alternatively, dienoates were also prepared by a commutative cross-coupling of zinc vinyl carbenes generated from cyclopropenes and simple diazo compounds. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Flow chemistry and polymer-supported pseudoenantiomeric acylating agents enable parallel kinetic resolution of chiral saturated N-heterocycles

Science.gov (United States)

Kreituss, Imants; Bode, Jeffrey W.

2017-05-01

Kinetic resolution is a common method to obtain enantioenriched material from a racemic mixture. This process will deliver enantiopure unreacted material when the selectivity factor of the process, s, is greater than 1; however, the scalemic reaction product is often discarded. Parallel kinetic resolution, on the other hand, provides access to two enantioenriched products from a single racemic starting material, but suffers from a variety of practical challenges regarding experimental design that limit its applications. Here, we describe the development of a flow-based system that enables practical parallel kinetic resolution of saturated N-heterocycles. This process provides access to both enantiomers of the starting material in good yield and high enantiopurity; similar results with classical kinetic resolution would require selectivity factors in the range of s = 100. To achieve this, two immobilized quasienantiomeric acylating agents were designed for the asymmetric acylation of racemic saturated N-heterocycles. Using the flow-based system we could efficiently separate, recover and reuse the polymer-supported reagents. The amide products could be readily separated and hydrolysed to the corresponding amines without detectable epimerization.

N-Heterocyclic Olefins as Initiators for the Polymerization of (Meth)Acrylic Monomers: A Combined Experimental and Theoretical Approach

KAUST Repository

Naumann, Stefan

2017-08-25

The zwitterionic organopolymerization of four different acrylic monomers (N,N-dimethylacrylamide, methyl acrylate, methyl methacrylate and tert-butyl methacrylate) based on neutral initiators, so-called N-heterocyclic olefins (NHOs), is presented. Scope and underlying (deactivation-)mechanisms where studied in a combined experimental and computational effort. From a range of differently structured NHOs it emerged that imidazole-, in contrast to imidazoline- and benzimidazole-derivatives, readily polymerize the selected monomers. While the additive-free reactions proceed with a relatively low degree of control to yield largely atactic material, for the acrylamide the addition of LiCl as µ-type ligand has been shown to result in a rapid and quantitative monomer consumption. The thus generated poly(N,N-dimethyl acrylamide) was found to be highly isotactic (>90% isotactic dyads) with high molecular weight (Mn = 250 000 – 650 000 g/mol, ÐM = 1.3- 1.6). Complementing DFT calculations considered the zwitterionic chain growth with respect to competing side reactions, namely spirocycles and enamine formation. It was found that NHOs with unsaturated backbone better support the zwitterionic chain growth, with the spirocycles acting as dormant species that slow down but do not quench the polymerization process. Contrasting this, enamine formation irreversibly terminates the polymerization and is found to be energetically favored. This pathway can be blocked by introduction of substituents on the exocyclic carbon of the NHO, resulting in structures like 2-isopropylidene-1,3,4,5-tetramethylimidazoline (4) which consequently deliver the most controlled polymerizations. Finally, a good correlation of the initiation energy barrier with the buried volume (%VBur) and the Parr electrophilicity index is described, allowing for a quick and reliable screening of potential monomers based on these two readily accessible parameters.

A theoretical investigation on the neutral Cu(I) phosphorescent complexes with azole-based and phosphine mixed ligand

Science.gov (United States)

Ding, Xiao-Li; Shen, Lu; Zou, Lu-Yi; Ma, Ming-Shuo; Ren, Ai-Min

2018-04-01

A theoretical study on a series of neutral heteroleptic Cu(I) complexes with different azole-pyridine-based N^N ligands has been presented to get insight into the effect of various nitrogen atoms in the azole ring on photophysical properties. The results reveal that the highest occupied molecular orbital (HOMO) levels and the emission wavelengths of these complexes are mainly governed by the nitrogen atom number in azole ring. With the increasing number of nitrogen atom , the electron density distribution of HOMO gradually extend from the N^N ligand to the whole molecule, meanwhile, the improved contribution from Cu(d) orbits in HOMO results in an effective mixing of various charge transfermodes, and hence, the fast radiative decay(kr) and the slow non-radiative decay rate(knr) are achieved. The photoluminescence quantum yield (PLQY) show an apparent dependence on the nitrogen atom number in the five-membered nitrogen heterocycles. However, the increasing number of nitrogen atoms is not necessary for increasing PLQY. The complex 3 with 1,2,4-triazole-pyridine-based N^N ligands is considered to be a potential emitter with high phosphorescence efficiency. Finally, we hope that our investigations will contribute to systematical understanding and guiding for material molecular engineering.

Pd(OAc)2/Ph3P-catalyzed dimerization of isoprene and synthesis of monoterpenic heterocycles.

Science.gov (United States)

Kellner, Dominik; Weger, Maximilian; Gini, Andrea; Mancheño, Olga García

2017-01-01

The palladium-catalyzed dimerization of isoprene is a practical approach of synthesizing monoterpenes. Though several highly selective methods have been reported, most of them still required pressure or costly ligands for attaining the active system and desired selectivity. Herein, we present a simple and economical procedure towards the tail-to-tail dimer using readily available Pd(OAc) 2 and inexpensive triphenylphosphine as ligand. Furthermore, simple screw cap vials are employed, allowing carrying out the reaction at low pressure. In addition, the potential of the dimer as a chemical platform for the preparation of heterocyclic terpenes by subsequent (hetero)-Diels-Alder or [4 + 1]-cycloadditions with nitrenes is also depicted.

N-heterocyclic carbene gold hydroxide complexes as bond activation reagents

OpenAIRE

Dupuy, Stéphanie

2014-01-01

Although known since the 1930s, organogold chemistry has been dormant until recently, primarily due to preconceptions about the inertness of gold in transformations. However, this last decade has witnessed the emergence of a Golden Age with the development of a wealth of reports on gold in a plethora of reactions. In recent years, the drive for more atom- and step-economical and environmentally friendly reactions has become a field of intense research. In our on-going research on well-defined...

Spectroscopic study of cadmium (II) complexes with heterocyclic dithiocarbamate ligands

International Nuclear Information System (INIS)

Garcia-Fontan, S.; Rodriguez-Seoane, P.; Casas, J.S.; Sordo, J.; Jones, M.M.

1993-01-01

Cadmium(II) dithiocarbamates [Cd(dtc) 2 ] (dtc=4-carboxamidopiperidine-1-carbodithioate, morpholine-1-carbodithioate or 4-(2-hydroxyethyl)piperazine-1-carbodithioate) and [Cd(dtc) 2 ].H 2 O (dtc=4-hydroxypiperidine-1-carbodithioate} have been prepared and characterized by thermal analysis and IR and NMR ( 13 C, 113 Cd) spectrometry. Two of these ligands have previously been shown capable of removing cadmium from its aged in vivo storage sites. The use of solid state 13 C NMR measurements to establish the coordination mode of the dithiocarbomate ligands is also examined and the difficulties which arise are discussed. (orig.)

A latent ruthenium based olefin metathesis catalyst with a sterically demanding NHC ligand

KAUST Repository

Leitgeb, Anita; Abbas, Mudassar E.; Fischer, Roland C.; Poater, Albert; Cavallo, Luigi; Slugovc, Christian

2012-01-01

An olefin metathesis catalyst featuring a SIPr NHC and an ester chelating carbene ligand is introduced. In contrast to its previously published SIMes analogue, only the trans dichloro configurated isomer was obtained. The two counterparts are tested in various olefin metathesis reactions, revealing a striking superiority of the new complex in the cross metathesis of olefins with methyl vinyl ketone allowing for full conversion with only 500 ppm catalyst loading. © 2012 The Royal Society of Chemistry.

Theoretical study of ionization and one-electron oxidation potentials of N-heterocyclic compounds.

Science.gov (United States)

Sviatenko, Liudmyla K; Gorb, Leonid; Hill, Frances C; Leszczynski, Jerzy

2013-05-15

A number of density functionals was utilized to predict gas-phase adiabatic ionization potentials (IPs) for nitrogen-rich heterocyclic compounds. Various solvation models were applied to the calculation of difference in free energies of solvation of oxidized and reduced forms of heterocyclic compounds in acetonitrile (AN) for correct reproduction of their standard oxidation potentials. We developed generally applicable protocols that could successfully predict the gas-phase adiabatic ionization potentials of nitrogen-rich heterocyclic compounds and their standard oxidation potentials in AN. This approach is supported by a MPW1K/6-31+G(d) level of theory which uses SMD(UA0) approximation for estimation of solvation energy of neutral molecules and PCM(UA0) model for ionized ones. The mean absolute derivation (MAD) and root mean square error (RMSE) of the current theoretical models for IP are equal to 0.22 V and 0.26, respectively, and for oxidation potentials MAD = 0.13 V and RMSE = 0.17. Copyright © 2013 Wiley Periodicals, Inc.

Abstraction of methyl from neutral Fischer-type carbene complexes: A new site for nucleophilic attack

Energy Technology Data Exchange (ETDEWEB)

Toomey, L.M.; Atwood, J.D. [State Univ. of New York, Buffalo, NY (United States)

1997-02-04

Reactions of Fischer-type carbene complexes, M(CO){sub 5}(C(OMe)pH) (M = Cr, W), with metal carbonyl anions (M`{sup -} = CpFe(CO){sub 2}{sup -@}, Re(CO){sub 5}{sup -}, Mn(CO){sub 4}PPh{sub 3}{sup -}, Co(CO){sub 3}PPh{sub 3}{sup -}, Cp{sup *}Cr(CO){sub 3}{sup -}, CpMo(CO){sub 3}{sup -}) result in demethylation of the carbene complexes. The products are M(CO){sub 5}C(O)Ph{sup -} and M`-Me, characterized by infrared and NMR spectroscopy. A slower rate for reaction with W(CO){sub 5}(C(OEt)Ph) in comparison to the methyl analogue is consistent with nucleophilic attack of the metal carbonyl anion on the methyl of the methoxy group of the carbene. This is a new type of nucleophilic attack of a Fischer-type carbene. 22 refs., 1 fig., 1 tab.

The tert-Amino Effect in Heterocyclic Chemistry. Synthesis of Spiro Heterocycles

Directory of Open Access Journals (Sweden)

Y. Morzherin

2005-09-01

Full Text Available The tert-amino reaction effect was examined. A new method to synthesize spiro heterocycles is presented. It was shown that the “tert-amino effect” could be applied to the formation of spiro-fused heterocycles. The formation of spiro compounds proceeds in most cases in good yields in a one-pot reaction.

Heterocyclic Scaffolds: Centrality in Anticancer Drug Development.

Science.gov (United States)

Ali, Imran; Lone, Mohammad Nadeem; Al-Othman, Zeid A; Al-Warthan, Abdulrahman; Sanagi, Mohd Marsin

2015-01-01

Cancer has been cursed for human beings for long time. Millions people lost their lives due to cancer. Despite of the several anticancer drugs available, cancer cannot be cured; especially at the late stages without showing any side effect. Heterocyclic compounds exhibit exciting medicinal properties including anticancer. Some market selling heterocyclic anticancer drugs include 5-flourouracil, methortrexate, doxorubicin, daunorubicin, etc. Besides, some natural products such as vinblastine and vincristine are also used as anticancer drugs. Overall, heterocyclic moeities have always been core parts in the expansion of anticancer drugs. This article describes the importance of heterocyclic nuclei in the development of anticancer drugs. Besides, the attempts have been made to discuss both naturally occurring and synthetic heterocyclic compounds as anticancer agents. In addition, some market selling anticancer heterocyclic compounds have been described. Moreover, the efforts have been made to discuss the mechanisms of actions and recent advances in heterocyclic compounds as anticancer agents. The current challenges and future prospectives of heterocyclic compounds have also been discussed. Finally, the suggestions for syntheses of effective, selective, fast and human friendly anticancer agents are discussed into the different sections.

Synthesis of heterocyclic compounds through palladium-catalyzed C-H cyclization processes.

Science.gov (United States)

Inamoto, Kiyofumi

2013-01-01

Herein, we describe our development of synthetic methods for heterocyclic compounds based on the palladium-catalyzed carbon-hydrogen bond (C-H) functionalization/intramolecular carbon-heteroatom (nitrogen or sulfur) bond formation process. By this C-H cyclization method, we efficiently prepared various N-heterocycles, including indazoles, indoles, and 2-quinolinones, as well as S-heterocycles such as benzothiazoles and benzo[b]thiophenes. Yields are typically good to high and good functional-group tolerance is observed for each process, thereby indicating that the method provides a novel, highly applicable synthetic route to the abovementioned biologically important heterocyclic frameworks. As an application of this approach, an auto-tandem-type, one-pot process involving the oxidative Heck reaction and subsequent C-H cyclization using cinnamamides and arylboronic acids as starting materials in the presence of a palladium catalyst was also developed for the rapid construction of the 2-quinolinone nucleus.

Enyne Metathesis Catalyzed by Ruthenium Carbene Complexes

DEFF Research Database (Denmark)

Poulsen, Carina Storm; Madsen, Robert

2003-01-01

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...

Metal coordination by sterically hindered heterocyclic ligands, including 2-vinylpyridine, assessed by investigation of cobaloximes.

Science.gov (United States)

Siega, Patrizia; Randaccio, Lucio; Marzilli, Patricia A; Marzilli, Luigi G

2006-04-17

Structural and 1H NMR data have been obtained for cobaloximes with the bulkiest substituted pyridines reported so far. We have isolated in noncoordinating solvents the complexes CH3Co(DH)2L (methylcobaloxime, where DH = the monoanion of dimethylglyoxime) with L = sterically hindered N-donor ligands: quinoline, 4-CH3quinoline, 2,4-(CH3)2pyridine, and 2-R-pyridine (R = CH3, OCH3, CH2CH3, CH=CH2). We have found that the Co-N(ax) bond is very long in the structurally characterized complexes. In particular, CH3Co(DH)2(4-CH3quinoline) has a longer Co-N(ax) bond (2.193(3) A) than any reported for methylcobaloximes. The main cause of the long bonds is unambiguously identified as the steric bulk of L by the fairly linear relationship found for Co-N(ax) distance vs CCA (calculated cone angle, CCA, a computed measure of bulk) over an extensive series of methylcobaloximes. The linear relationship improves if L basicity (quantified by pKa) is taken into account. In anhydrous CDCl3 at 25 degrees C, all complexes except the 2-aminopyridine adduct exhibit 1H NMR spectra consistent with partial dissociation of L to form the methylcobaloxime dimer. 1H NMR experiments at -20 degrees C allowed us to assess qualitatively the relative binding ability of L as follows: 2,4-(CH3)2pyridine > 4-CH3quinoline approximately = quinoline approximately = 2-CH3pyridine > 2-CH3Opyridine > 2-CH3CH2pyridine > 2-CH2=CHpyridine. The broadness of the 1H NMR signals at 25 degrees C suggests a similar order for the ligand exchange rate. The lack of dissociation by 2-aminopyridine is attributed to an intramolecular hydrogen bond between the NH2 group and an oxime O atom. The weaker than expected binding of 2-vinylpyridine relative to the Co-N(ax) bond length is attributed to rotation of the 2-vinyl group required for this bulky ligand to bind to the metal center, a conclusion supported by pronounced changes in 2-vinylpyridine signals upon coordination.

Synthesis of heterocycles through transition-metal-catalyzed isomerization reactions

DEFF Research Database (Denmark)

Ishøy, Mette; Nielsen, Thomas Eiland

2014-01-01

of structurally complex and diverse heterocycles. In this Concept article, we attempt to cover this area of research through a selection of recent versatile examples. A sea of opportunities! Transition-metal-catalyzed isomerization of N- and O-allylic compounds provides a mild, selective and synthetically...... versatile method to form iminium and oxocarbenium ions. Given the number of reactions involving these highly electrophilic intermediates, this concept provides a sea of opportunities for heterocycle synthesis, (see scheme; Nu=nucleophile). © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim....

Synthesis and Characterization of a New Heterocyclic Azo Pigment

International Nuclear Information System (INIS)

Asniza, M.; Issam, A.M.; Khalil, H.P.S.A.

2011-01-01

A new heterocyclic coupling agent has been produced from the reaction of maleic anhydride and p-aminophenol, namely N-(4-hexahydrophenol)maleimide. The coupling agent underwent azo coupling reaction with aromatic amine, which is p-aminophenol to produce a new heterocyclic azo pigment. The pigment was then subjected to solubility, hiding power and light fastness test. Fourier Transform Infrared Spectroscopy (FTIR), Ultraviolet/ Visible (UV/Vis) Spectroscopy, and Nuclear Magnetic Resonance Spectroscopy ( 1 H-NMR, 13 C-NMR) were used to obtain the characteristics and structural features of the pigment. (author)

One-Pot Two-Step Multicomponent Process of Indole and Other Nitrogenous Heterocycles or Amines toward α-Oxo-acetamidines.

Science.gov (United States)

Martinez-Ariza, Guillermo; McConnell, Nicholas; Hulme, Christopher

2016-04-15

A cesium carbonate promoted three-component reaction of N-H containing heterocycles, primary or secondary amines, arylglyoxaldehydes, and anilines is reported. The key step involves a tandem sequence of N-1 addition of a heterocycle or an amine to preformed α-iminoketones, followed by an air- or oxygen-mediated oxidation to form α-oxo-acetamidines. The scope of the reaction is enticingly broad, and this novel methodology is applied toward the synthesis of various polycyclic heterocycles.

Generation of N-Heterocycles via Tandem Reactions of N '-(2-Alkynylbenzylidene)hydrazides.

Science.gov (United States)

Qiu, Guanyinsheng; Wu, Jie

2016-02-01

As a powerful synthon, N '-(2-alkynylbenzylidene)hydrazides have been utilized efficiently for the construction of N-heterocycles. Since N '-(2-alkynylbenzylidene)hydrazides can easily undergo intramolecular 6-endo cyclization promoted by silver triflate or electrophiles, the resulting isoquinolinium-2-yl amides can proceed through subsequent transformations including [3 + 2] cycloaddition, nucleophilic addition, and [3 + 3] cycloaddition. Several unexpected rearrangements via radical processes were observed in some cases, which afforded nitrogen-containing heterocycles with molecular complexity. Reactive partners including internal alkynes, arynes, ketenimines, ketenes, allenoates, and activated alkenes reacted through [3 + 2] cycloaddition and subsequent aromatization, leading to diverse H-pyrazolo[5,1-a]isoquinolines with high efficiency. Nucleophilic addition to the in situ generated isoquinolinium-2-yl amide followed by aromatization also produced H-pyrazolo[5,1-a]isoquinoline derivatives when terminal alkynes, carbonyls, enamines, and activated methylene compounds were used as nucleophiles. Isoquinoline derivatives were obtained when indoles or phosphites were employed as nucleophiles in the reactions of N '-(2-alkynylbenzylidene)hydrazides. A tandem 6-endo cyclization and [3 + 3] cycloaddition of cyclopropane-1,1-dicarboxylates with N '-(2-alkynylbenzylidene)hydrazides was observed as well. Small libraries of these compounds were constructed. Biological evaluation suggested that some compounds showed promising activities for inhibition of CDC25B, TC-PTP, HCT-116, and PTP1B. © 2015 The Chemical Society of Japan & Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Pd(OAc2/Ph3P-catalyzed dimerization of isoprene and synthesis of monoterpenic heterocycles

Directory of Open Access Journals (Sweden)

Dominik Kellner

2017-08-01

Full Text Available The palladium-catalyzed dimerization of isoprene is a practical approach of synthesizing monoterpenes. Though several highly selective methods have been reported, most of them still required pressure or costly ligands for attaining the active system and desired selectivity. Herein, we present a simple and economical procedure towards the tail-to-tail dimer using readily available Pd(OAc2 and inexpensive triphenylphosphine as ligand. Furthermore, simple screw cap vials are employed, allowing carrying out the reaction at low pressure. In addition, the potential of the dimer as a chemical platform for the preparation of heterocyclic terpenes by subsequent (hetero-Diels–Alder or [4 + 1]-cycloadditions with nitrenes is also depicted.

N,S,O-Heterocycles in Aged Champagne Reserve Wines and Correlation with Free Amino Acid Concentrations.

Science.gov (United States)

Le Menn, Nicolas; Marchand, Stephanie; de Revel, Gilles; Demarville, Dominique; Laborde, Delphine; Marchal, Richard

2017-03-22

Champagne regulations allow winegrowers to stock still wines to compensate for quality shifts in vintages, mainly due to climate variations. According to their technical requirements and house style, Champagne producers use these stored wines in their blends to enhance complexity. The presence of lees and aging at low pH (2.95-3.15), as in Champagne wines, lead to several modifications in wine composition. These conditions, combined with extended aging, result in the required environment for the Maillard chemical reaction, involving aromatic molecules, including sulfur, oxygen, and nitrogen heterocycles (such as thiazole, furan, and pyrazine derivatives), which may have a sensory impact on wine. Some aromatic heterocycles in 50 monovarietal wines aged from 1 to 27 years provided by Veuve Clicquot Ponsardin Champagne house were determined by the SPME-GC-MS method. The most interesting result highlighted a strong correlation between certain heterocycle concentrations and wine age. The second revealed a correlation between heterocyclic compound and free amino acid concentrations measured in the wines, suggesting that these compounds are potential aromatic precursors when wine is aged on lees and, thus, potential key compounds in the bouquet of aged Champagnes. The principal outcome of these assays was to reveal, for the first time, that aromatic heterocycle concentrations in Champagne base wines are correlated with wine age.

Double stabilization of nanocrystalline silicon: a bonus from solvent

Energy Technology Data Exchange (ETDEWEB)

Kolyagin, Y. G.; Zakharov, V. N.; Yatsenko, A. V.; Paseshnichenko, K. A.; Savilov, S. V.; Aslanov, L. A., E-mail: aslanov.38@mail.ru [Lomonosov Moscow State University (Russian Federation)

2016-01-15

Double stabilization of the silicon nanocrystals was observed for the first time by {sup 29}Si and {sup 13}C MAS NMR spectroscopy. The role of solvent, 1,2-dimethoxyethane (glyme), in formation and stabilization of silicon nanocrystals as well as mechanism of modification of the surface of silicon nanocrystals by nitrogen-heterocyclic carbene (NHC) was studied in this research. It was shown that silicon nanocrystals were stabilized by the products of cleavage of the C–O bonds in ethers and similar compounds. The fact of stabilization of silicon nanoparticles with NHC ligands in glyme was experimentally detected. It was demonstrated that MAS NMR spectroscopy is rather informative for study of the surface of silicon nanoparticles but it needs very pure samples.

Ru(II)-Catalyzed Cross-Coupling of Cyclopropenes with Diazo Compounds: Formation of Olefins from Two Different Carbene Precursors.

Science.gov (United States)

Wang, Bo; Yi, Heng; Zhang, Hang; Sun, Tong; Zhang, Yan; Wang, Jianbo

2018-01-19

Formal carbene dimerization is a convergent method for the synthesis of alkenes. Herein, we report a Ru(II)-catalyzed carbene dimerization of cyclopropenes and diazo compounds. The yields are up to 97% and the stereoselectivity are up to >20:1. Mechanistically, it has been experimentally demonstrated that the catalyst reacts with cyclopropene first to generate a Ru(II)-carbene species, which is attacked by nucleophilic diazo substrate, followed by dinitrogen extrusion to form the double bond.

Antiradiation compounds XV: condensations of carbon disulfide with amino, chloro, cyanomethyl, and sulfonamido heterocycles

International Nuclear Information System (INIS)

Foye, W.O.; Kauffman, J.M.; Lanzillo, J.J.; LaSala, E.F.

1975-01-01

Condensations of carbon disulfide were carried out with amino, chloro, and diamino heterocycles to give condensed ring thiazoline-2-thiones and imidazoline-2-thiones, with cyanomethyl heterocycles to give dithio acid derivatives, and with heterocyclic sulfonamides to give sulfonyldithiocarbamates. Of several examples tested, pyrido[3,2-d]thiazoline-2-thione, disodium 2-(5-chloro-2-thienyl)-3,3-dimercaptoacrylonitrile, triethylammonium 4-sulfamoylphenyldithiocarbamate, ammonium β-phenethyldithiocarbamate, and methyl N-(thiophene-2-sulfonyl)dithiocarbamate, only the last-named compound showed any radiation protection for mice. Several compounds gave negative tests for antimalarial activity

Synthesis and characterisation of nitrogen poly-heterocyclic molecules using as selective complexing agents of metallic cations

International Nuclear Information System (INIS)

Alphonse, F.A.

2003-12-01

Separation of actinides (III) from lanthanides (III) is a crucial problem in the reprocessing of used nuclear fuels. Experimental results shown that soft donor extractants such as nitrogen polydentate heterocycles containing a NCCNCCN coordination site are potentials ligands for selective extraction of actinides (III). In those cases, two types of liquid-liquid extractions are employed: synergistic combination with lipophilic acid extractants and direct extraction. On the basis of the Hard and Soft Acids and Bases theory and basicity evaluation, new extractants were defined. We have first studied the synthesis of potential 1,3,5-triazine ligands designed for extraction in synergy with α-bromodecanoic acid. Secondly, we have examined the synthesis of bis-triazinyl-pyridine ligands for direct extraction studies. Extraction tests were carried out and perspectives of synthesis were deducted from those extraction results. (author)

Polymer complexes.. XXXX. Supramolecular assembly on coordination models of mixed-valence-ligand poly[1-acrylamido-2-(2-pyridyl)ethane] complexes

Science.gov (United States)

El-Sonbati, A. Z.; El-Bindary, A. A.; Diab, M. A.

2003-02-01

The build-up of polymer metallic supramolecules based on homopolymer (1-acrylamido-2-(2-pyridyl)ethane (AEPH)) and ruthenium, rhodium, palladium as well as platinum complexes has been pursued with great interest. The homopolymer shows three types of coordination behaviour. In the mixed valence paramagnetic trinuclear polymer complexes [( 11)+( 12)] in the paper and in mononuclear polymer complexes ( 1)-( 5) it acts as a neutral bidentate ligand coordinating through the N-pyridine and NH-imino atoms, while in the mixed ligand diamagnetic poly-chelates, which are obtained from the reaction of AEPH with PdX 2 and KPtCl 4 in the presence of N-heterocyclic base consisting of polymer complexes ( 9)+( 10), and in monouclear compounds ( 6)-( 8), it behaves as a monobasic bidentate ligand coordinating through the same donor atoms. In mononuclear compounds ( 13)+( 14) it acts as a monobasic and neutral bidentate ligand coordinating only through the same donor atoms. Monomeric distorted octahedral or trimeric chlorine-bridged, approximately octahedral structures are proposed for these polymer complexes. The poly-chelates are of 1:1, 1:2 and 3:2 (metal-homopolymer) stoichiometry and exhibit six coordination. The values of ligand field parameters were calculated. The homopolymer and their polymer complexes have been characterized physicochemically.

Transition metal-catalyzed carbocyclization of nitrogen and oxygen-tethered 1,n-enynes and diynes: synthesis of five or six-membered heterocyclic compounds.

Science.gov (United States)

Zhang, Di-Han; Zhang, Zhen; Shi, Min

2012-10-25

Cycloisomerization of 1,n-enynes and diynes is a powerful method in organic synthesis to access heterocyclic compounds and has drawn increasing attention from organic chemists. In this paper, we attempted to summarize our recent results on the transition metal-catalyzed cycloisomerization to synthesize five or six-membered heterocyclic compounds using 1,n-enynes and diynes having a propargylic ester moiety. First, we will describe the synthesis of 2,3-disubstituted 3-pyrrolines via gold catalyzed cycloisomerization of 1,6-diynes. In addition, we will also disclose a novel silver catalyzed tandem 1,3-acyloxy migration/Mannich-type addition/elimination of the sulfonyl group of N-sulfonylhydrazone-propargylic esters to 5,6-dihydropyridazin-4-one derivatives. Furthermore, we will introduce three interesting examples of the synthesis of bicyclic compounds via titanium or rhodium catalyzed carbocyclization of enynes. In this context, we have presented that 1,n-enynes and diynes containing propargylic esters are highly reactive and useful starting materials for the cycloisomerization catalyzed by a transition metal catalyst.

3,6-Bis(2-pyrazinyl)-1,2,4,5-tetrazin: Ein neuer mehrfunktioneller Ligand und sein syn,fac-konfigurierter Bis(tricarbonylchlororhenium)-Komplex

Czech Academy of Sciences Publication Activity Database

Sarkar, B.; Kaim, W.; Schleid, T.; Hartenbach, I.; Fiedler, Jan

2003-01-01

Roč. 629, - (2003), s. 1353-1357 ISSN 0044-2313 R&D Projects: GA MŠk OC D14.20; GA MŠk OC D15.10 Institutional research plan: CEZ:AV0Z4040901 Keywords : carbonyl ligands * heterocyclic ligands * rhenium Subject RIV: CF - Physical ; Theoretical Chemistry Impact factor: 1.127, year: 2003

HARNESSING THE CHEMISTRY OF CO2

Energy Technology Data Exchange (ETDEWEB)

Louie, Janis

2010-05-11

Our research program is broadly focused on activating CO{sub 2} through the use of organic and organometallic based catalysts. Some of our methods have centered on annulation reactions of unsaturated hydrocarbons (and carbonyl substrates) to provide a diverse array of carbocycles and heterocycles. We use a combination of catalyst discovery and optimization in conjunction with classical physical organic chemistry to elucidate the key mechanistic features of the cycloaddition reactions such that the next big advances in catalyst development can be made. Key to all of our cycloaddition reactions is the use of a sterically hindered, electron donating N heterocyclic carbene (NHC) ligand, namely IPr (or SIPr), in conjunction with a low valent nickel pre-catalyst. The efficacy of this ligand is two-fold: (1) the high {delta}-donating ability of the NHC increases the nucleophilicity of the metal center which thereby facilitates interaction with the electrophilic carbonyl and (2) the steric hindrance prevents an otherwise competitive side reaction involving only the alkyne substrate. Such a system has allowed for the facile cycloaddition to prepare highly functionalized pyrones, pyridones, pyrans, as well as novel carbocycles. Importantly, all reactions proceed under extremely mild conditions (room temperature, atmospheric pressures, and short reaction times), require only catalytic amounts of Ni/NHC and readily available starting materials, and afford annulated products in excellent yields. Our current focus revolves around understanding the fundamental processes that govern these cycloadditions such that the next big advance in the cyclization chemistry of CO{sub 2} can be made. Concurrent to our annulation chemistry is our investigation of the potential for imidazolylidenes to function as thermally-actuated CO{sub 2} sequestering and delivery agents.

Radical C-H functionalization to construct heterocyclic compounds.

Science.gov (United States)

Yu, Jin-Tao; Pan, Changduo

2016-02-07

Heterocyclic compounds are widely present in natural products, pharmaceuticals and bioactive molecules. Thus, organic and pharmaceutical chemists have been making extensive efforts to construct those heterocyclic frameworks through developing versatile and efficient synthetic strategies. The direct C-H functionalization via the radical pathway has emerged as a promising and dramatic approach towards heterocycles with high atom- and step-economy. Heterocyclic compounds such as coumarins, furans, benzofurans, xanthones, benzothiazoles, indoles, indolines, oxindoles, quinolines, isoquinolines, quinoxaline, and phenanthridines have been successfully synthesized by C-H functionalization through the radical pathway. In this review, recent advances on radical C-H functionalization to construct heterocyclic compounds are highlighted with discussions.

Studies on the selectivity of the reaction of (CO){sub 5}W=C(aryl)H with enynes: transfer of the carbene ligand to the C=C Bond versus insertion of the C triple bond C into the W=C Bond

Energy Technology Data Exchange (ETDEWEB)

Fischer, H.; Volkland, H.P.; Stumpf, R.

1996-10-01

The strongly electrophilic monophenylcarbene complex [(CO){sub 5}W=C(Ph)H] (2a) reacts with the enynes H-C triple bond C-R(R=-C(Me)=CH{sub 2})(3), -C{sub 6}H{sub 4}-CH=CH{sub 2}-p (5) and subsequently with PMe{sub 3} to form the C{sub a}lpha-PMe{sub 3} adducts of the vinylidene complexes [(CO){sub 5}W-{l_brace}C(PMe{sub 3})=CH-C{sub 3}H{sub 3}(Me)Ph{r_brace}] (4) and [(CO){sub 5}W {l_brace}C(PMe{sub 3})=CH-C{sub 6}H{sub 4}-C{sub 3}H{sub 4}Ph{r_brace}] (6). The reaction very likely proceeds by transfer of the carbene ligand to the C=C bond of the enyne to form a cyclopropyl-substituted alkyne complex which is in equilibrium with its vinylidene isomer.

Self-association and infrared spectres of some heterocyclic compounds based on pyrrol in solid state

International Nuclear Information System (INIS)

Mulloev, N.; Nurulloev, M.; Narziev, B.N.

1993-01-01

Present article is devoted to self-association and infrared spectres of some heterocyclic compounds based on pyrrol in solid state. The study results of self-association specified by molecular hydrogen bonds of some heterocyclic compounds based on pyrrol on spectres of infrared absorption of stretching vibrations of N-H group were considered.

Fundamental spectroscopic studies of carbenes and hydrocarbon radicals

Energy Technology Data Exchange (ETDEWEB)

Gottlieb, C.A.; Thaddeus, P. [Harvard Univ., Cambridge, MA (United States)

1993-12-01

Highly reactive carbenes and carbon-chain radicals are studied at millimeter wavelengths by observing their rotational spectra. The purpose is to provide definitive spectroscopic identification, accurate spectroscopic constants in the lowest vibrational states, and reliable structures of the key intermediates in reactions leading to aromatic hydrocarbons and soot particles in combustion.

Copper(I)-catalyzed olefination of N-sulfonylhydrazones with sulfones.

Science.gov (United States)

Xu, Shuai; Gao, Yunpeng; Chen, Ri; Wang, Kang; Zhang, Yan; Wang, Jianbo

2016-03-25

The Cu(I)-catalyzed olefination of N-sulfonylhydrazones with sulfones via metal carbene intermediates is reported. This reaction uses readily available starting materials and is operationally simple, thus representing a practical method for the construction of carbon-carbon double bonds. Mechanistically, Cu(I) carbene formation and subsequent carbene migratory insertion are proposed as the key steps.

Comparisons Between Tridentate Bis(benzazoles-pyridine and Bis(benzazolestriazine Ligands: a Theoretical Study

Directory of Open Access Journals (Sweden)

Mihaiela Andoni

2015-12-01

Full Text Available Twelve bis(benzazole structures with potential ligand character were investigated by means of computational chemistry. Global and local reactivity descriptors within DFT (Density Functional Theory theory (Fukui functions, chemical potential, hardness, electrophilicity index have been computed at B3LYP/6-31G(d,p level of theory. NICS(0 (Nucleus Independent Chemical Shift index computations were employed for the evaluation of the local aromatic character of each heterocyclic moiety. Best results have been reported for the bis(benzimidazole derivatives. Copper and zinc complexes of the investigated tridentate ligands have been proposed.

Rh-Catalyzed rearrangement of vinylcyclopropane to 1,3-diene units attached to N-heterocycles

Directory of Open Access Journals (Sweden)

Alberto Brandi

2011-03-01

Full Text Available Dienes embedded in quinolizidine and indolizidine structures can be prepared in four steps from cyclic nitrones and bicyclopropylidene. The key intermediates α-spirocyclopropanated N-heterocyclic ketones, generated via a domino 1,3-dipolar cycloaddition/thermal rearrangement sequence, were converted by Wittig methylenation to the corresponding vinylcyclopropanes (VCPs, which underwent rearrangement to 1,3-dienes in the presence of the Wilkinson Rh(I complex under microwave heating. The previously unexplored Rh(I-catalyzed opening of the VCP moiety embedded in an azapolycyclic system occurs at high temperature (110–130 °C to afford the corresponding 1,3-dienes in moderate yield (34–53%.

Ternary complexes of Zn(II) and Cu(II) with 1-((2-hydroxynaphthalen-1-yl)methylene)-4-phenylthiosemicarbazide in the presence of heterocyclic bases as auxiliary ligands: Synthesis, spectroscopic and structural characterization and antibacterial activity

Science.gov (United States)

Azarkish, Mohammad; Akbari, Alireza; Sedaghat, Tahereh; Simpson, Jim

2018-03-01

The new ternary complexes, ZnLL‧ [L = 1-((2-hydroxynaphthalen-1-yl)methylene)-4-phenylthiosemicarbazide and L‧ = imidazole (1), 2, 2‧-bipyridine (2) and 2-methyimidazole (3)], Zn2L2L‧ [L‧ = 4, 4‧-bipy (4)] and CuLL‧ [L‧ = 2, 2‧-bipy (5)] have been synthesized by the reaction of a metal(II) acetate salt with the thiosemicarbazone and in presence of heterocyclic bases as auxiliary ligands. The synthesized compounds were investigated by elemental analysis and IR, 1H NMR, and 13C NMR spectroscopy and complex 5 was structurally characterized by X-ray crystallography. The results indicate the thiosemicarbazone doubly deprotonated and coordinates to metal through the thiolate sulfur, imine nitrogen and phenolic oxygen atoms. The nitrogen atom(s) of the auxiliary ligand complete the coordination sphere. Complex 4 is binuclear with 4, 4‧-bipy acting as a bridging ligand. The structure of 5 is a distorted square pyramid with one of the bipyridine nitrogen atoms in the apical position. This compound creates an inversion dimer in solid state by intermolecular hydrogen bonds of Nsbnd H⋯S type. The in vitro antibacterial activity of the synthesized compounds were evaluated against Gram-positive (B. subtilis and S. aureus) and Gram-negative (P. aeruginosa) bacteria and is compared to that of standard antibacterial drugs. All complexes exhibit good inhibitory effects and are significantly more effective than the parent ligand.

Carbynes and carbenes in coordination chemistry: A new class of pentaammine and tetraammine complexes of osmium(II)

Energy Technology Data Exchange (ETDEWEB)

Hodges, L.M.; Sabat, M.; Harman, W.D. (Univ. of Virginia, Charlottesville (United States))

1993-02-17

Since their discovery by Fischer and co-workers in 1973, the study of transition-metal carbyne complexes and their role in alkyne metathesis has rapidly developed into a mature field. Although carbyne complexes are known for a diverse set of early- and mid-transition metals, the vast majority of these complexes contain carbon or phosphine [pi]-acids, or bulky alkoxide ligands, which limit the coordination number. We wish to report the first example of a carbyne species, as well as several heteroatom-carbene derivatives, in which the metal fragment, Os[sup II](NH[sub 3])[sub 5], provides a classical octahedral coordination environment. The carbyne [Os(NH[sub 3])[sub 5]([equivalent to]CPh)](OTf)[sub 3] (2) is synthesized in two steps from Os(NH[sub 3])[sub 5](OTf)[sub 3] and benzaledhyde dimethyl acetal.

Stereoselective synthesis of organosulfur compounds incorporating N-aromatic heterocyclic motifs and quaternary carbon centers via a sulfa-Michael triggered tandem reaction.

Science.gov (United States)

Qin, Tianyou; Cheng, Lu; Zhang, Sean Xiao-An; Liao, Weiwei

2015-06-14

A novel sulfa-Michael addition (SMA)-triggered tandem reaction was developed by combining a SMA reaction with a simultaneous rearomatization process utilizing a less reactive carbonyl group as an intramolecular electrophile partner, which provided a unique synthetic route to access various organosulfur compounds incorporating an N-aromatic heterocyclic motif and quaternary carbon centers.

Alkoxy(alkyl)silylalkyl derivatives of nitrogen-containing heterocycles

International Nuclear Information System (INIS)

Trofimova, Ol'ga M; Voronkov, Mikhail G; Chernov, Nikolai F

1999-01-01

The published data on the synthesis, properties and transformations of alkoxy(alkyl)silylalkyl derivatives of nitrogen-containing heterocycles of the general formula Het(CH 2 ) n SiX 3 are surveyed and systematised. Data on the biological activities and applications of these compounds are presented. The bibliography includes 255 references.

Synthesis of 2-arylidenebenzocycloalkanones containing N-donor heterocyclic rings

Energy Technology Data Exchange (ETDEWEB)

Sun, S.-W., E-mail: sunsw0819@163.com [Yuncheng University, Department of Applied Chemistry (China); Zhang, X., E-mail: zhangx@hit.edu.cn [Harbin Institute of Technology, Academy of Fundamental and Interdisciplinary Science (China); Wang, G.-F. [Yuncheng University, Department of Applied Chemistry (China)

2016-12-15

A series of 2-arylidenebenzocycloalkanones containing heterocyclic rings 1–8 were prepared and characterized by IR, {sup 1}H NMR and elemental analyses. X-ray diffraction study of 6 reveals that the cyclohexyl ring of the 3,4-dihydronaphthalen-1(2H)-one adopts a chair conformation with a maximum deviation of 0.547(3) Å and makes dihedral angles of 52.24(17)° and 11.23(16)°, respectively, with the benzene plane and the mean plane of the benzimidazole ring.

Mechanism of Propylene Oxide Polymerization Promoted by N-Heterocyclic Olefins

KAUST Repository

Al-Ghamdi, Miasser

2017-01-11

We report a mechanistic DFT investigation of the organopolymerization of propylene oxide (PO) promoted by N-heterocyclic olefins (NHOs) in combination with benzylic alcohol (BnOH). Calculations support the experimentally based hypothesis of two competing pathways, namely, the anionic and zwitterionic pathways. The former is based on an acid–base cooperativity between BnOH and the NHO, promoting ring opening of PO by BnO–. The latter occurs through the formation of a zwitterionic adduct by nucleophilic attack of the exocyclic carbon atom of the NHO on the PO, with the concerted ring opening of PO. The two initiating species cannot interconvert, and chain elongation can proceed from both initiation adducts. Potential energy surfaces were computed for a set of NHOs to clarify the effects of the steric and electronic properties of the NHO on the system reactivity. The results achieved represent useful insight toward the synthesis of PPO with better properties with respect to the polymer obtained with the experimental tested systems because the computationally proposed NHO system is the only one that favors the mechanism leading to higher molecular weight.

Polymerization of Polar Monomers from a Theoretical Perspective

KAUST Repository

Alghamdi, Miasser

2016-10-11

Density functional theory calculations have been used to investigate catalytic mechanism of polymer formation containing polar groups, from the synthesis of the monomer to the synthesis of the macromolecule. In the spirit of a sustainable and green chemistry, we initially focused attention on the coupling of CO2 as economically convenient and recyclable C1 source with C2H4 to form acrylate and/or butirro-lactone, two important polar monomers. In this process formation of a mettallolactone via oxidative coupling of CO2 and C2H4 is an important intermediate. Given this background, we explored in detail (chapter-3) several Ni based catalysts for CO2 coupling with C2H4 to form acrylate. In this thesis we report on the competitive reaction mechanisms (inner vs outer sphere) for the oxidative coupling of CO2 and ethylene for a set of 11 Ni-based complexes containing bisphosphine ligands. In another effort, considering incorporation of a C=C bond into a metal-oxygen-Functional-Group moiety is a challenging step in several polymerization reactions, we explored the details of this reaction (chapter4) using two different catalysts that are capable to perform this reaction in the synthesis of heterocycles. Specifically, the [Rh]-catalyzed intramolecular alkoxyacylation ([Rh] = [RhI(dppp)+] (dppp, 1,3-Bis-diphenylphosphino-propane), and the [Pd]/BPh3 intramolecular alkoxyfunctionalizations. Rest of the thesis we worked on understanding the details of the polymerization of polar monomers using organocatalysts based on N-heterocyclic carbenes (NHC) or N-heterocyclic olefins (NHO). In particular (chapter-5) we studied the polymerization of N-methyl N-carboxy- anhydrides, towards cyclic poly(N-substituted glycine)s, promoted by NHC catalysts. In good agreement with the experimental findings, we demonstrated that NHC promoted ring opening polymerization of N-Me N-Carboxyanhydrides may proceed via two different catalytic pathways. In a similar effort we studied polymerization of

Greener Synthesis of N-Heterocycles via Sustainable Applications of Nano-Catalysts

Science.gov (United States)

A brief historic account of reactions involving microwave (MW) exposure of neat reactants or catalysis by mineral surfaces, such as alumina, silica, clay, or their ‘doped’ versions, for the rapid one-pot assembly of heterocyclic compounds from in situ generated reactive intermedi...

Gold(I)-catalyzed diazo coupling: strategy towards alkene formation and tandem benzannulation.

Science.gov (United States)

Zhang, Daming; Xu, Guangyang; Ding, Dong; Zhu, Chenghao; Li, Jian; Sun, Jiangtao

2014-10-06

A gold(I)-catalyzed cross-coupling of diazo compounds to afford tetrasubstituted alkenes has been developed by taking advantage of a trivial electronic difference between two diazo substrates. A N-heterocyclic-carbene-derived gold complex is the most effective catalyst for this transformation. Based on this new strategy, a gold(I)-initiated benzannulation has been achieved through a tandem reaction involving a diazo cross-coupling, 6π electrocyclization, and oxidative aromatization. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

[PdA (IPr*) (cinnamyl)Cl]: An efficient pre-catalyst for the preparation of tetra-ortho-substituted biaryls by Suzuki-Miyaura cross-coupling

KAUST Repository

Chartoire, Anthony

2012-03-13

The bigger the better: The new well-defined [Pd(IPr*)(cin)Cl] pre-catalyst is described (see scheme). This complex proves to be highly active in the Suzuki-Miyaura cross-coupling for the synthesis of tetra-ortho- substituted biaryls under mild conditions. IPr* is reported as the largest N-heterocyclic carbene (NHC) to date for [Pd(NHC)(cin)Cl] complexes, explaining the high reactivity observed for this complex in this challenging transformation. © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

[PdA (IPr*) (cinnamyl)Cl]: An efficient pre-catalyst for the preparation of tetra-ortho-substituted biaryls by Suzuki-Miyaura cross-coupling

KAUST Repository

Chartoire, Anthony; Lesieur, Mathieu; Falivene, Laura; Slawin, Alexandra M. Z.; Cavallo, Luigi; Cazin, Catherine S J; Nolan, Steven P.

2012-01-01

The bigger the better: The new well-defined [Pd(IPr*)(cin)Cl] pre-catalyst is described (see scheme). This complex proves to be highly active in the Suzuki-Miyaura cross-coupling for the synthesis of tetra-ortho- substituted biaryls under mild conditions. IPr* is reported as the largest N-heterocyclic carbene (NHC) to date for [Pd(NHC)(cin)Cl] complexes, explaining the high reactivity observed for this complex in this challenging transformation. © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Bond Energies and Thermochemical Properties of Ring-Opened Diradicals and Carbenes of exo-Tricyclo[5.2.1.0(2,6)]decane.

Science.gov (United States)

Hudzik, Jason M; Castillo, Álvaro; Bozzelli, Joseph W

2015-09-24

Exo-tricyclo[5.2.1.0(2,6)]decane (TCD) or exo-tetrahydrodicyclopentadiene is an interesting strained ring compound and the single-component high-energy density hydrocarbon fuel known as JP-10. Important initial reactions of TCD at high temperatures could cleave a strained carbon-carbon (C-C) bond in the ring system creating diradicals also constrained by the remaining ring system. This study determines the thermochemical properties of these diradicals (TCD-H2 mJ-nJ where m and n correspond to the cleaved carbons sites) including the carbon-carbon bond dissociation energy (C-C BDE) corresponding to the cleaved TCD site. Thermochemical properties including enthalpies (ΔH°f298), entropies (S(T)), heat capacities (Cp(T)), and C-H and C-C BDEs for the parent (TCD-H2 m-n), radical (TCD-H2 mJ-n and m-nJ), diradical (TCD-H2 mJ-nJ), and carbene (TCD-H2 mJJ-n and m-nJJ) species are determined. Structures, vibrational frequencies, moments of inertia, and internal rotor potentials are calculated at the B3LYP/6-31G(d,p) level of theory. Standard enthalpies of formation in the gas phase for the TCD-H2 m-n parent and radical species are determined using the B3LYP density functional theory and the higher level G3MP2B3 and CBS-QB3 composite methods. For singlet and triplet TCD diradicals and carbenes, M06-2X, ωB97X-D, and CCSD(T) methods are included in the analysis to determine ΔH°f298 values. The C-C BDEs are further calculated using CASMP2(2,2)/aug-cc-pvtz//CASSCF(2,2)/cc-pvtz and with the CASMP2 energies extrapolated to the complete basis set limit. The bond energies calculated with these methods are shown to be comparable to the other calculation methods. Isodesmic work reactions are used for enthalpy analysis of these compounds for effective cancelation of systematic errors arising from ring strain. C-C BDEs range from 77.4 to 84.6 kcal mol(-1) for TCD diradical singlet species. C-H BDEs for the parent TCD-H2 m-n carbon sites range from 93 to 101 kcal mol(-1) with a

A modular approach to neutral P,N-ligands: synthesis and coordination chemistry

Directory of Open Access Journals (Sweden)

Vladislav Vasilenko

2016-04-01

Full Text Available We report the modular synthesis of three different types of neutral κ2-P,N-ligands comprising an imine and a phosphine binding site. These ligands were reacted with rhodium, iridium and palladium metal precursors and the structures of the resulting complexes were elucidated by means of X-ray crystallography. We observed that subtle changes of the ligand backbone have a significant influence on the binding geometry und coordination properties of these bidentate P,N-donors.

Photo-cross-linked small-molecule microarrays as chemical genomic tools for dissecting protein-ligand interactions.

Science.gov (United States)

Kanoh, Naoki; Asami, Aya; Kawatani, Makoto; Honda, Kaori; Kumashiro, Saori; Takayama, Hiroshi; Simizu, Siro; Amemiya, Tomoyuki; Kondoh, Yasumitsu; Hatakeyama, Satoru; Tsuganezawa, Keiko; Utata, Rei; Tanaka, Akiko; Yokoyama, Shigeyuki; Tashiro, Hideo; Osada, Hiroyuki

2006-12-18

We have developed a unique photo-cross-linking approach for immobilizing a variety of small molecules in a functional-group-independent manner. Our approach depends on the reactivity of the carbene species generated from trifluoromethylaryldiazirine upon UV irradiation. It was demonstrated in model experiments that the photogenerated carbenes were able to react with every small molecule tested, and they produced multiple conjugates in most cases. It was also found in on-array immobilization experiments that various small molecules were immobilized, and the immobilized small molecules retained their ability to interact with their binding proteins. With this approach, photo-cross-linked microarrays of about 2000 natural products and drugs were constructed. This photo-cross-linked microarray format was found to be useful not merely for ligand screening but also to study the structure-activity relationship, that is, the relationship between the structural motif (or pharmacophore) found in small molecules and its binding affinity toward a protein, by taking advantage of the nonselective nature of the photo-cross-linking process.

Formation of Haloacetonitriles, Haloacetamides, and Nitrogenous Heterocyclic Byproducts by Chloramination of Phenolic Compounds.

Science.gov (United States)

Nihemaiti, Maolida; Le Roux, Julien; Hoppe-Jones, Christiane; Reckhow, David A; Croué, Jean-Philippe

2017-01-03

The potential formation of nitrogenous disinfection byproducts (N-DBPs) was investigated from the chloramination of nitrogenous and non-nitrogenous aromatic compounds. All molecules led to the formation of known N-DBPs (e.g., dichloroacetonitrile, dichloroacetamide) with various production yields. Resorcinol, a major precursor of chloroform, also formed di/trichloroacetonitrile, di/trichloroacetamide, and haloacetic acids, indicating that it is a precursor of both N-DBPs and carbonaceous DBPs (C-DBPs) upon chloramination. More detailed experiments were conducted on resorcinol to understand N-DBPs formation mechanisms and to identify reaction intermediates. Based on the accurate mass from high resolution Quadrupole Time-of-Flight GC-MS (GC-QTOF) and fragmentation patterns from electronic impact and positive chemical ionization modes, several products were tentatively identified as nitrogenous heterocyclic compounds (e.g., 3-chloro-5-hydroxy-1H-pyrrole-2-one with dichloromethyl group, 3-chloro-2,5-pyrroledione). These products were structurally similar to the heterocyclic compounds formed during chlorination, such as the highly mutagenic MX (3-chloro-4-(dichloromethyl)-5-hydroxy-2(5H)-furanone) or halogenated pyrroles. To our knowledge, this is the first time that the formation of halogenated nitrogenous heterocyclic compounds is reported from chloramination process. The formation of these nitrogenous byproducts during chloramination might be of concern considering their potential toxicity.

Insight into eukaryotic topoisomerase II-inhibiting fused heterocyclic compounds in human cancer cell lines by molecular docking.

Science.gov (United States)

Taskin, T; Yilmaz, S; Yildiz, I; Yalcin, I; Aki, E

2012-01-01

Etoposide is effective as an anti-tumour drug by inhibiting eukaryotic DNA topoisomerase II via establishing a covalent complex with DNA. Unfortunately, its wide therapeutic application is often hindered by multidrug resistance (MDR), low water solubility and toxicity. In our previous study, new derivatives of benzoxazoles, benzimidazoles and related fused heterocyclic compounds, which exhibited significant eukaryotic DNA topoisomerase II inhibitory activity, were synthesized and exhibited better inhibitory activity compared with the drug etoposide itself. To expose the binding interactions between the eukaryotic topoisomerase II and the active heterocyclic compounds, docking studies were performed, using the software Discovery Studio 2.1, based on the crystal structure of the Topo IIA-bound G-segment DNA (PDB ID: 2RGR). The research was conducted on a selected set of 31 fused heterocyclic compounds with variation in structure and activity. The structural analyses indicate coordinate and hydrogen bonding interactions, van der Waals interactions and hydrophobic interactions between ligands and the protein, as Topo IIA-bound G-segment DNA are responsible for the preference of inhibition and potency. Collectively, the results demonstrate that the compounds 1a, 1c, 3b, 3c, 3e and 4a are significant anti-tumour drug candidates that should be further studied.

Combinatorial Libraries of Bis-Heterocyclic Compounds with Skeletal Diversity

OpenAIRE

Soural, Miroslav; Bouillon, Isabelle; Krchňák, Viktor

2008-01-01

Combinatorial solid-phase synthesis of bis-heterocyclic compounds, characterized by the presence of two heterocyclic cores connected by a spacer of variable length/structure, provided structurally heterogeneous libraries with skeletal diversity. Both heterocyclic rings were assembled on resin in a combinatorial fashion.

Synthesis and research of benzylamides of some isocyclic and heterocyclic acids as potential anticonvulsants.

Science.gov (United States)

Strupińska, Marzanna; Rostafińska-Suchar, Grazyna; Pirianowicz-Chaber, Elzbieta; Stables, James P; Jiang, Jeff; Paruszewski, Ryszard

2013-01-01

A series of benzylamides of isocyclic and heterocyclic acids was synthesized and tested in Anticonvulsant Screening Project (ASP) of Antiepileptic Drug Development Program (ADDP) of NIH. Near all synthesized derivatives of heterocyclic acids showed activity. All obtained derivatives of mono- and bicyclic isocyclic acids were inactive. The power of action of heterocyclic acids derivatives seems does not depend upon kind of heteroatom (N, O or S). One of the compounds (2-furoic acid benzylamide (4)) appeared most promising. It showed in minimal clonic seizure (6Hz) test (ASP) in rats after i. p. administration: MES ED50 = 36.5 mg/kg, TOX TD50 = 269.75 mg/kg, and PI = 7.39.

Combinatorial Libraries of Bis-Heterocyclic Compounds with Skeletal Diversity

Science.gov (United States)

Soural, Miroslav; Bouillon, Isabelle; Krchňák, Viktor

2009-01-01

Combinatorial solid-phase synthesis of bis-heterocyclic compounds, characterized by the presence of two heterocyclic cores connected by a spacer of variable length/structure, provided structurally heterogeneous libraries with skeletal diversity. Both heterocyclic rings were assembled on resin in a combinatorial fashion. PMID:18811208

Aspects and prospects of the chemistry of organic heterocycles (review)

International Nuclear Information System (INIS)

Schroth, W.

1986-01-01

The systematics of heterocycles, their place in organic chemistry, and their significance for theory and practice are discussed. Problems of the chemistry of heterocycles are discussed on the examples of systems with various types of conjugation and ring sizes. The focus is on the principles of synthesis of heterocycles, in particular, those based on acetylene, various C 3 fragments, carbon disulfide, and maleic anhydride. Individual sections of the survey are devoted to the role of heterocycles in biosynthesis, as well as certain problems common to the chemistry of heterocycles, biochemistry, and macromolecular chemistry

Antioxidant evaluation of heterocyclic compounds by cytokinesis-block micronucleus assay.

Science.gov (United States)

Godevac, Dejan; Tesević, Vele; Vajs, Vlatka; Milosavljević, Slobodan; Stanković, Miroslava

2013-03-01

This article summarizes the results of using cytokinesis-block micronucleus (CBMN) assay to evaluate the antioxidant potential of heterocyclic compounds. Most studies were carried out with naturally occurring heterocyclic compounds such as plant polyphenols: flavonoids, xanthones, coumarins, and ellagitannins, or plant derived products (juices, extracts, supplements) rich in bioactive heterocyclic compounds. There are also some studies dealing with synthetic heterocyclic antioxidants. CBMN assay is an in vitro study that has been used to evaluate antioxidant and protective effects of heterocyclic compounds on induced chromosome aberration in human lymphocytes.

Molecular and polymeric uranyl and thorium hybrid materials featuring methyl substituted pyrazole dicarboxylates and heterocyclic 1,3-diketones

Science.gov (United States)

Carter, Korey P.; Kerr, Andrew T.; Taydakov, Ilya V.; Cahill, Christopher L.

2018-02-01

A series of seven novel f-element bearing hybrid materials have been prepared from either methyl substituted 3,4 and 4,5-pyrazoledicarboxylic acids, or heterocyclic 1,3- diketonate ligands using hydrothermal conditions. Compounds 1, [UO2(C6H4N2O4)2(H2O)], and 3, [Th(C6H4N2O4)4(H2O)5]·H2O feature 1-Methyl-1H-pyrazole-3,4-dicarboxylate ligands (SVI-COOH 3,4), whereas 2, [UO2(C6H4N2O4)2(H2O)], and 4, [Th(C6H5N2O4)(OH)(H2O)6]2·2(C6H5N2O4)·3H2O feature 1-Methyl-1H-pyrazole-4,5-dicarboxylate moieties (SVI-COOH 4,5). Compounds 5, [UO2(C13H15N4O2)2(H2O)]·2H2O and 6, [UO2(C11H11N4O2)2(H2O)]·4.5H2O feature 1,3-bis(4-N1-methyl-pyrazolyl)propane-1,3-dione and 1,3-bis(4-N1,3-dimethyl-pyrazolyl)propane-1,3-dione respectively, whereas the heterometallic 7, [UO2(C11H11N4O2)2(CuCl2)(H2O)]·2H2O is formed by using 6 as a metalloligand starting material. Single crystal X-ray diffraction indicates that all coordination to either [UO2]2+ or Th(IV) metal centers is through O-donation as anticipated. Room temperature, solid-state luminescence studies indicate characteristic uranyl emissive behavior for 1 and 2, whereas those for 5 and 6 are weak and poorly resolved.

Applications of ortho-phenylisonitrile and ortho-N-Boc aniline for the two-step preparation of novel bis-heterocyclic chemotypes.

Science.gov (United States)

Xu, Zhigang; Shaw, Arthur Y; Nichol, Gary S; Cappelli, Alexandra P; Hulme, Christopher

2012-08-01

Concise routes to five pharmacologically relevant bis-heterocyclic scaffolds are described. Significant molecular complexity is generated in a mere two synthetic operations enabling access to each scaffold. Routes are often improved by microwave irradiation and all utilize isocyanide-based multi-component reaction methods to incorporate the required diversity elements. Common reagents in all initial condensation reactions include 2-(N-Boc-amino)-phenyl-isocyanide 1, mono-Boc-phenylenediamine 2 and ethyl glyoxalate 3.

Pyrrole PMOs, incorporating new N-heterocyclic compounds on an ethene-PMO through Diels–Alder reactions

International Nuclear Information System (INIS)

Esquivel, Dolores; De Canck, Els; Jiménez-Sanchidrián, César; Romero-Salguero, Francisco J.; Van Der Voort, Pascal

2014-01-01

The ethenylene bridges on the walls of an ethenylene-bridged periodic mesoporous organosilica were successfully modified with a variety of pyrrole derivatives – pyrrole, methylpyrrole, dimethylpyrrole, trimethylpyrrole and 1-phenylpyrrole – through Diels–Alder reactions. X-ray diffraction measurements and N 2 adsorption–desorption analysis confirmed the preservation of the ordering and mesoporosity of the parent material as well as the decoration of the pores with the surface Diels–Alder adducts. Moreover, other techniques such as DRIFT, 13 C and 29 Si nuclear magnetic resonances revealed the formation of the surface N-heterocyclic compounds at the parent ethenylene sites. - Highlights: • Chemical modification of the double bonds on an ethene-PMO through the Diels–Alder reaction. • A family of pyrrole derivatives act as dienes in the Diels–Alder reaction. • Well-ordering and mesoporosity are retained after the post-functionalization. • N-containing compounds on the surface of ethene-PMO are present after the Diels–Alder reaction

Pyrrole PMOs, incorporating new N-heterocyclic compounds on an ethene-PMO through Diels–Alder reactions

Energy Technology Data Exchange (ETDEWEB)

Esquivel, Dolores; De Canck, Els [Center for Ordered Materials, Organometallics and Catalysis, Department of Inorganic and Physical Chemistry, Ghent University, Krijgslaan 281-S3, 9000 Ghent (Belgium); Jiménez-Sanchidrián, César [Department of Organic Chemistry, Nanochemistry and Fine Chemistry Research Institute (IUIQFN), Faculty of Sciences, University of Córdoba, Campus de Rabanales, Marie Curie Building, Ctra. Nnal. IV, km 396, 14071 Córdoba (Spain); Romero-Salguero, Francisco J., E-mail: qo2rosaf@uco.es [Department of Organic Chemistry, Nanochemistry and Fine Chemistry Research Institute (IUIQFN), Faculty of Sciences, University of Córdoba, Campus de Rabanales, Marie Curie Building, Ctra. Nnal. IV, km 396, 14071 Córdoba (Spain); Van Der Voort, Pascal, E-mail: pascal.vandervoort@ugent.be [Center for Ordered Materials, Organometallics and Catalysis, Department of Inorganic and Physical Chemistry, Ghent University, Krijgslaan 281-S3, 9000 Ghent (Belgium)

2014-11-14

The ethenylene bridges on the walls of an ethenylene-bridged periodic mesoporous organosilica were successfully modified with a variety of pyrrole derivatives – pyrrole, methylpyrrole, dimethylpyrrole, trimethylpyrrole and 1-phenylpyrrole – through Diels–Alder reactions. X-ray diffraction measurements and N{sub 2} adsorption–desorption analysis confirmed the preservation of the ordering and mesoporosity of the parent material as well as the decoration of the pores with the surface Diels–Alder adducts. Moreover, other techniques such as DRIFT, {sup 13}C and {sup 29}Si nuclear magnetic resonances revealed the formation of the surface N-heterocyclic compounds at the parent ethenylene sites. - Highlights: • Chemical modification of the double bonds on an ethene-PMO through the Diels–Alder reaction. • A family of pyrrole derivatives act as dienes in the Diels–Alder reaction. • Well-ordering and mesoporosity are retained after the post-functionalization. • N-containing compounds on the surface of ethene-PMO are present after the Diels–Alder reaction.

Facile insertion of a cyclic alkyl(amino) carbene carbon into the B-B bond of diboron(4) reagents.

Science.gov (United States)

Eichhorn, Antonius F; Kuehn, Laura; Marder, Todd B; Radius, Udo

2017-10-24

We report herein the room temperature insertion of the carbene carbon atom of the cyclic (alkyl)(amino) carbene cAAC Me into the B-B single bonds of the diboron(4) compounds B 2 pin 2 , B 2 cat 2 , B 2 neop 2 , and B 2 eg 2 (pin = pinacolato, cat = catecholato, neop = neopentylglycolato, eg = ethyleneglycolato).

Mechanistic Insights into the Organopolymerization of N-Methyl N-Carboxyanhydrides Mediated by N-Heterocyclic Carbenes

KAUST Repository

Falivene, Laura; Alghamdi, Miasser; Cavallo, Luigi

2016-01-01

the experimentally based hypothesis of two competing initiation pathways. The first leading to formation of a zwitterionic adduct by nucleophilic addition of the NHC to one of the carbonyl groups of monomer. The second via acid–base reactivity, starting with the NHC

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

KAUST Repository

Vummaleti, Sai V. C.

2015-01-02

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 π-accepting ability of NHCs, independent of their σ-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 δSe is correlated to the energy gap between a filled lone pair orbital on Se and the empty π* orbital corresponding to the Se–NHC bond. Bond energy decomposition analysis indicated no correlation between the orbital σ-contribution to bonding and the chemical shielding, while a good correlation was found between the π-contribution to bonding and the chemical shielding, confirming that this technique is indeed able to quantify the ability of NHCs to accept π-electron density. Calculations conducted on phosphinidene adducts yielded similar results. With the link between δSe and δP and π-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.

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

KAUST Repository

Vummaleti, Sai V. C.; Nelson, David J.; Poater, Albert; Gó mez-Suá rez, Adriá n; Cordes, David B.; Slawin, Alexandra M. Z.; Nolan, Steven P.; Cavallo, Luigi

2015-01-01

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 π-accepting ability of NHCs, independent of their σ-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 δSe is correlated to the energy gap between a filled lone pair orbital on Se and the empty π* orbital corresponding to the Se–NHC bond. Bond energy decomposition analysis indicated no correlation between the orbital σ-contribution to bonding and the chemical shielding, while a good correlation was found between the π-contribution to bonding and the chemical shielding, confirming that this technique is indeed able to quantify the ability of NHCs to accept π-electron density. Calculations conducted on phosphinidene adducts yielded similar results. With the link between δSe and δP and π-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.

A crystallographically isolated dimeric hydrolyzed chlorophosphazene dianion

Directory of Open Access Journals (Sweden)

Matthew J. Panzner

2009-01-01

Full Text Available Single crystals of the title compound bis[bis(1-ethyl-3-methyl-imidazol-2-ylidenesilver(I] 1,5,5,7,11,11-hexachloro-2,8-dioxa-4,6,10,12,13,14-hexaaza-1λ5,3,5λ5,7λ5,9,11λ5-hexaphosphatricyclo[7.3.1.13,7]tetradeca-1(13,4,7(14,10-tetraene-6,12-diide 3,9-dioxide, [Ag(C6H10N22](Cl6N6O4P60.5, were isolated from the reaction of the silver N-heteocyclic carbene complex [Ag(C6H10N22]Cl and hexachlorocyclotriphosphazene [NPCl2]3 in the presence of water. The asymmetric unit contains one silver carbene cation with the carbene ligands bound to the Ag(I in an almost linear arrangement and one half of a hydrolyzed phosphazene dianion. The second cation and additional half of the anion are generated by an inversion center.

Mitsunobu mischief: Neighbor-directed histidine N(π)–alkylation provides access to peptides containing selectively functionalized imidazolium heterocycles

Science.gov (United States)

Qian, Wen-Jian

2015-01-01

There are few methodologies that yield peptides containing His residues with selective N(π), N(π)-bis-alkylated imidazole rings. We have found that, under certain conditions, on-resin Mitsunobu coupling of alcohols with peptides having a N(π)-alkylated His residue results in selective and high-yield alkylation of the imidazole N(π) nitrogen. The reaction requires the presence of a proximal phosphoric, carboxylic or sulfonic acid, and proceeds through an apparent intramolecular mechanism involving Mitsunobu intermediates. These transformations have particular application to phosphopeptides, where “charge masking” of one phosphoryl anionic charge by the cationic histidine imidazolium ion is now possible. This chemistry opens selective access to peptides containing differentially functionalized imidazolium heterocycles, which provide access to new classes of peptides and peptide mimetics. PMID:25739367

Adsorbate-driven cooling of carbene-based molecular junctions

Czech Academy of Sciences Publication Activity Database

Foti, Giuseppe; Vázquez, Héctor

2017-01-01

Roč. 8, Oct (2017), s. 2060-2068 ISSN 2190-4286 R&D Projects: GA ČR GA15-19672S EU Projects: European Commission(XE) 702114 - HEATEXMOL Institutional support: RVO:68378271 Keywords : adsorbate * carbene * current-induced heating and cooling * molecular junction * vibrations Subject RIV: BM - Solid Matter Physics ; Magnetism OBOR OECD: Condensed matter physics (including formerly solid state physics, supercond.) Impact factor: 3.127, year: 2016

Spectrochemical study on different ligand neodymium complexes

International Nuclear Information System (INIS)

Khomenko, V.S.; Lozinskij, M.O.; Fialkov, Yu.A.; Krasovskaya, L.I.; Rasshinina, T.A.; AN Ukrainskoj SSR, Kiev. Inst. Organicheskoj Khimii)

1986-01-01

A series of new adducts of neodymium complexes with 1, 1, 1, 5, 5, 5-hexafluoropentadione - 2, 4 and 2-heptafluoropropoxy-1, 1, 1, 2-tetrafluoro-5-phenylpentadione-3, 5: Nd(HFPTFPhPD) 3 x2H 2 O, Nd(HFPTFPhPD) 3 xDipy, Nd(HFPTFPhPD) 3 xPhen, Nd(HFPTFPhPD) 3 xDphen, Nd(HFA) 3 x2H 2 O, Nd(HFA) 3 xDipy, Nd(HFA) 3 xPhen, Nd(HFA) 3 xDphen, have been synthesized. Ways of their fragmentation under electron impact are established. Bond strength of additional ligands with central atom in the complexes studied is evaluated. Data on decomposition mechanisms of bicharged ions have been obtained for the first time. Addition of bis-heterocycles to neodymium three-ligand complexes changes the properties of the complexes - their thermal stability and photochemical stability increase, in certain cases their volatility increases

Structural and spectral comparisons between isomeric benzisothiazole and benzothiazole based aromatic heterocyclic dyes

Science.gov (United States)

Wang, Yin-Ge; Wang, Yue-Hua; Tao, Tao; Qian, Hui-Fen; Huang, Wei

2015-09-01

A pair of isomeric heterocyclic compounds, namely 3-amino-5-nitro-[2,1]-benzisothiazole and 2-amino-6-nitrobenzothiazole, are used as the diazonium components to couple with two N-substituted 4-aminobenzene derivatives. As a result, two pairs of isomeric aromatic heterocyclic azo dyes have been produced and they are structurally and spectrally characterized and compared including single-crystal structures, electronic spectra, solvatochromism and reversible acid-base discoloration, thermal stability and theoretically calculations. It is concluded that both benzisothiazole and benzothiazole based dyes show planar molecular structures and offset π-π stacking interactions, solvatochromism and reversible acid-base discoloration. Furthermore, benzisothiazole based aromatic heterocyclic dyes exhibit higher thermal stability, larger solvatochromic effects and maximum absorption wavelengths than corresponding benzothiazole based ones, which can be explained successfully by the differences of their calculated isomerization energy, dipole moment and molecular band gaps.

Relationship between Antifungal Activity against Candida albicans and Electron Parameters of Selected N-Heterocyclic Thioamides

Science.gov (United States)

Stachowicz, Jadwiga; Krajewska-Kułak, Elżbieta; Łukaszuk, Cecylia; Niewiadomy, A.

2014-01-01

Due to the increasing demand for new pharmaceuticals showing biological activity against pathogenic microorganisms, there is increasing search for new compounds with predicted biological activity. Variously substituted thioamide derivatives with 1.3 and 1.2 ring of thiazole and 1,3,4-thiadiazole, as well as pyrazole were assessed for their activity against Candida albicans. Activity of majority of tested thioamides was larger as compared with that of the reference drugs. The electron parameters of obtained N-heterocyclic thioamides were determined and dependencies on their biological activity against Candida albicans were studied. The best electron compliance of produced bindings with the activity against Candida albicans was observed for the derivatives containing 1,3,4-thiadiazole ring. PMID:25284926

Recent advances in the electrochemical construction of heterocycles

Directory of Open Access Journals (Sweden)

Robert Francke

2014-12-01

Full Text Available Due to the fact that the major portion of pharmaceuticals and agrochemicals contains heterocyclic units and since the overall number of commercially used heterocyclic compounds is steadily growing, heterocyclic chemistry remains in the focus of the synthetic community. Enormous efforts have been made in the last decades in order to render the production of such compounds more selective and efficient. However, most of the conventional methods for the construction of heterocyclic cores still involve the use of strong acids or bases, the operation at elevated temperatures and/or the use of expensive catalysts and reagents. In this regard, electrosynthesis can provide a milder and more environmentally benign alternative. In fact, numerous examples for the electrochemical construction of heterocycles have been reported in recent years. These cases demonstrate that ring formation can be achieved efficiently under ambient conditions without the use of additional reagents. In order to account for the recent developments in this field, a selection of representative reactions is presented and discussed in this review.

Design, synthesis, antiviral activity and mode of action of phenanthrene-containing N-heterocyclic compounds inspired by the phenanthroindolizidine alkaloid antofine.

Science.gov (United States)

Yu, Xiuling; Wei, Peng; Wang, Ziwen; Liu, Yuxiu; Wang, Lizhong; Wang, Qingmin

2016-02-01

The phenanthroindolizidine alkaloid antofine and its analogues have excellent antiviral activity against tobacco mosaic virus (TMV). To simplify the structure and the synthesis of the phenanthroindolizidine alkaloid, a series of phenanthrene-containing N-heterocyclic compounds (compounds 1 to 33) were designed and synthesised, based on the intermolecular interaction of antofine and TMV RNA, and systematically evaluated for their anti-TMV activity. Most of these compounds exhibited good to reasonable anti-TMV activity. The optimum compounds 5, 12 and 21 displayed higher activity than the lead compound antofine and commercial ribavirin. Compound 12 was chosen for field trials of antiviral efficacy against TMV, and was found to exhibit better activity than control plant virus inhibitors. Compounds 5 and 12 were chosen for mode of action studies. The changes in fluorescence intensity of compounds 5 and 12 on separated TMV RNA showed that these small molecules can also bind to TMV RNA, but the mode is very different from that of antofine. The compounds combining phenanthrene and an N-heterocyclic ring could maintain the anti-TMV activity of phenanthroindolizidines, but their modes of action are different from that of antofine. The present study lays a good foundation for us to find more efficient anti-plant virus reagents. © 2015 Society of Chemical Industry.

Two novel mixed-ligand complexes containing organosulfonate ligands.

Science.gov (United States)

Li, Mingtian; Huang, Jun; Zhou, Xuan; Fang, Hua; Ding, Liyun

2008-07-01

The structures reported herein, viz. bis(4-aminonaphthalene-1-sulfonato-kappaO)bis(4,5-diazafluoren-9-one-kappa(2)N,N')copper(II), [Cu(C(10)H(8)NO(3)S)(2)(C(11)H(6)N(2)O)(2)], (I), and poly[[[diaquacadmium(II)]-bis(mu-4-aminonaphthalene-1-sulfonato)-kappa(2)O:N;kappa(2)N:O] dihydrate], {[Cd(C(10)H(8)NO(3)S)(2)(H(2)O)(2)].2H(2)O}(n), (II), are rare examples of sulfonate-containing complexes where the anion does not fulfill a passive charge-balancing role, but takes an active part in coordination as a monodentate and/or bridging ligand. Monomeric complex (I) possesses a crystallographic inversion center at the Cu(II) atom, and the asymmetric unit contains one-half of a Cu atom, one complete 4-aminonaphthalene-1-sulfonate (ans) ligand and one 4,5-diazafluoren-9-one (DAFO) ligand. The Cu(II) atom has an elongated distorted octahedral coordination geometry formed by two O atoms from two monodentate ans ligands and by four N atoms from two DAFO molecules. Complex (II) is polymeric and its crystal structure is built up by one-dimensional chains and solvent water molecules. Here also the cation (a Cd(II) atom) lies on a crystallographic inversion center and adopts a slightly distorted octahedral geometry. Each ans anion serves as a bridging ligand linking two Cd(II) atoms into one-dimensional infinite chains along the [010] direction, with each Cd(II) center coordinated by four ans ligands via O and N atoms and by two aqua ligands. In both structures, there are significant pi-pi stacking interactions between adjacent ligands and hydrogen bonds contribute to the formation of two- and three-dimensional networks.

Lanthanide and actinide complexation studies with tetradentate 'N' donor ligands

International Nuclear Information System (INIS)

Bhattacharyya, A.; Mohapatra, M.; Mohapatra, P.K.; Rawat, N.; Tomar, B.S.; Gadly, T.; Ghosh, S.K.; Manna, D.; Ghanty, T.K.

2014-01-01

Because of their similar charge and chemical behaviour separation of trivalent actinides and lanthanides is an important and challenging task in nuclear fuel cycle. Soft (S,N) donor ligands show selectivity towards the trivalent actinides over the lanthanides. Out of various 'N' donor ligands studied, bis(1,2,4)triazinyl bipyridine (BTBP) and bis(1,2,4)triazinyl phenanthroline (BTPhen) were found to be most promising. In order to understand the separation behaviour of these ligands, their complexation studies with these 'f' block elements are essential. In the present work, complexation studies of various lanthanide ions (La 3+ , Eu 3+ and Er 3+ ) was studied with ethyl derivatives of BTBP (C 2 BTBP) and BTBPhen (C 2 BTPhen) and pentyl derivative of BTBP (C 5 BTBP) in acetonitrile medium using UV-Vis spectrophotometry, fluorescence spectroscopy and solution calorimetry. Computational studies were also carried out to understand the experimental results

Activation of trans geometry in bifunctional mononuclear platinum complexes by a non-bulky methylamine ligand

Czech Academy of Sciences Publication Activity Database

Frýbortová, M.; Nováková, Olga; Štěpánková, Jana; Novohradský, Vojtěch; Gibson, D.; Kašpárková, Jana; Brabec, Viktor

2013-01-01

Roč. 126, SEP2013 (2013), s. 46-54 ISSN 0162-0134 R&D Projects: GA ČR(CZ) GAP301/10/0598; GA ČR(CZ) GA13-08273S Institutional research plan: CEZ:AV0Z50040702 Institutional support: RVO:68081707 Keywords : HETEROCYCLIC AMINE LIGAND * INTERSTRAND CROSS-LINKS * DNA-BINDING MODE Subject RIV: BO - Biophysics Impact factor: 3.274, year: 2013

Amide Synthesis from Alcohols and Amines by the Extrusion of Dihydrogen

DEFF Research Database (Denmark)

Nordstrøm, Lars Ulrik Rubæk; Vogt, Henning; Madsen, R.

2008-01-01

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...

Stereodivergent Synthesis of N-Heterocycles by Catalyst-Controlled, Activity-Directed Tandem Annulation of Diazo Compounds with Amino Alkynes.

Science.gov (United States)

Liu, Kai; Zhu, Chenghao; Min, Junxiang; Peng, Shiyong; Xu, Guangyang; Sun, Jiangtao

2015-10-26

A stereodivergent synthesis of five-membered N-heterocycles, such as 2,3-dihydropyrroles, and 2-methylene and 3-methylene pyrrolidines, has been developed through a tandem annulation of amino alkynes with diazo compounds and involves the trapping of in situ formed intermediates. Mechanistic investigations indicate that the copper-catalyzed tandem annulations proceed by allenoate formation and subsequent intramolecular hydroamination. In contrast, the rhodium-catalyzed protocol features a carbenoid insertion into the NH bond and subsequent Conia-ene cyclization. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Pentamethylcyclopentadienyl-rhodium and iridium complexes containing (N^N and N^O) bound chloroquine analogue ligands: synthesis, characterization and antimalarial properties.

Science.gov (United States)

Ekengard, Erik; Kumar, Kamlesh; Fogeron, Thibault; de Kock, Carmen; Smith, Peter J; Haukka, Matti; Monari, Magda; Nordlander, Ebbe

2016-03-07

The synthesis and characterization of twenty new pentamethylcyclopentadienyl-rhodium and iridium complexes containing N^N and N^O-chelating chloroquine analogue ligands are described. The in vitro antimalarial activity of the new ligands as well as the complexes was evaluated against the chloroquine sensitive (CQS) NF54 and the chloroquine resistant (CQR) Dd2 strains of Plasmodium falciparum. The antimalarial activity was found to be good to moderate; although all complexes are less active than artesunate, some of the ligands and complexes showed better activity than chloroquine (CQ). In particular, rhodium complexes were found to be considerably more active than iridium complexes against the CQS NF54 strain. Salicylaldimine Schiff base ligands having electron-withdrawing groups (F, Cl, Br, I and NO2) in para position of the salicyl moiety and their rhodium complexes showed good antiplasmodial activity against both the CQS-NF54 and the CQR-Dd2 strains. The crystal structures of (η(5)-pentamethylcyclopentadienyl){N(1)-(7-chloroquinolin-4-yl)-N(2)-(pyridin-2-ylmethyl)ethane-1,2-diamine)} chlororhodium(III) chloride and (η(5)-pentamethylcyclopentadienyl){(4-chloro-2-(((2-((7-chloroquinolin-4-yl)amino)ethyl)imino)methyl)phenolate)}chlororhodium(III) chloride are reported. The crystallization of the amino-pyridyl complex (η(5)-pentamethylcyclopentadienyl){(N(1)-(7-chloroquinolin-4-yl)-N(2)-(pyridin-2-ylmethyl)ethane-1,2-diamine)}chloroiridium(III) chloride in acetone resulted in the formation of the imino-pyridyl derivative (η(5)-pentamethylcyclopentadienyl){(N1-(7-chloroquinolin-4-yl)-N2-(pyridin-2-ylmethylene)ethane-1,2-diamine)}chloroiridium(III) chloride, the crystal structure of which is also reported.

Ring-Opening Polymerization of N-Carboxyanhydrides for Preparation of Polypeptides and Polypeptide-Based Hybrid Materials with Various Molecular Architectures

KAUST Repository

Pahovnik, David

2015-09-01

Different synthetic approaches utilizing ring-opening polymerization of N-carboxyanhydrides for preparation of polypeptide and polypeptide-based hybrid materials with various molecular architectures are described. An overview of polymerization mechanisms using conventional (various amines) as well as some recently developed initiators (hexamethyldisilazane, N-heterocyclic persistent carbenes, etc.) is presented, and their benefits and drawbacks for preparation of polypeptides with well-defined chain lengths and chain-end functionality are discussed. Recent examples from literature are used to illustrate different possibilities for synthesis of pure polypeptide materials with different molecular architectures bearing various functional groups, which are introduced either by modification of amino acids, before they are transformed into corresponding Ncarboxyanhydrides, or by post-polymerization modifications using protective groups and/or orthogonal functional groups. Different approaches for preparation of polypeptide-based hybrid materials are discussed as well using examples from recent literature. Syntheses of simple block copolymers or copolymers with more complex molecular architectures (graft and star copolymers) as well as modifications of nanoparticles and other surfaces with polypeptides are described.

Application of heterocyclic aldehydes as components in Ugi–Smiles couplings

Directory of Open Access Journals (Sweden)

Katelynn M. Mason

2016-09-01

Full Text Available Efficient one-pot Ugi–Smiles couplings are reported for the use of furyl-substituted aldehyde components. In the presence of these heterocyclic aldehydes, reactions tolerated variations in amine components and led to either isolated N-arylamide Ugi–Smiles adducts or N-arylepoxyisoindolines, products of tandem Ugi–Smiles Diels–Alder cyclizations, in moderate yields. A thienyl-substituted aldehyde was also a competent component for Ugi–Smiles adduct formation.

Synthesis in situ of gold nanoparticles by a dialkynyl Fischer carbene complex anchored to glass surfaces

International Nuclear Information System (INIS)

Bertolino, María Candelaria; Granados, Alejandro Manuel

2016-01-01

Highlights: • Fischer carbene 1-W reacts via cycloaddition without Cu(I) with azide terminal surface. • This reaction on the surface is regioselective to internal triple bond of 1-W. • 1-W bound to glass surface produce AuNps in situ fixed to the surface. • This ability is independent of how 1-W is bonded to the surface. • This hybrid surface can be valuable as SERS substrate or in heterogeneous catalysis. - Abstract: In this work we present a detailed study of classic reactions such as “click reaction” and nucleophilic substitution reaction but on glass solid surface (slides). We used different reactive center of a dialkynylalcoxy Fischer carbene complex of tungsten(0) to be anchored to modified glass surface with amine, to obtain aminocarbene, and azide terminal groups. These cycloaddition reaction showed regioselectivity to internal triple bond of dialkynyl Fischer carbene complex without Cu(I) as catalyst. Anyway the carbene anchored was able to act as a reducing agent to produce in situ very stable gold nanoparticles fixed on surface. We showed the characterization of modified glasses by contact angle measurements and XPS. Synthesized nanoparticles were characterized by SEM, XPS, EDS and UV–vis. The modified glasses showed an important enhancement Raman-SERS. This simple, fast and robust method to create a polifunctional and hybrid surfaces can be valuable in a wide range of applications such as Raman-SERS substrates and other optical fields.

Synthesis in situ of gold nanoparticles by a dialkynyl Fischer carbene complex anchored to glass surfaces

Energy Technology Data Exchange (ETDEWEB)

Bertolino, María Candelaria, E-mail: cbertolino@fcq.unc.edu.ar; Granados, Alejandro Manuel, E-mail: ale@fcq.unc.edu.ar

2016-10-15

Highlights: • Fischer carbene 1-W reacts via cycloaddition without Cu(I) with azide terminal surface. • This reaction on the surface is regioselective to internal triple bond of 1-W. • 1-W bound to glass surface produce AuNps in situ fixed to the surface. • This ability is independent of how 1-W is bonded to the surface. • This hybrid surface can be valuable as SERS substrate or in heterogeneous catalysis. - Abstract: In this work we present a detailed study of classic reactions such as “click reaction” and nucleophilic substitution reaction but on glass solid surface (slides). We used different reactive center of a dialkynylalcoxy Fischer carbene complex of tungsten(0) to be anchored to modified glass surface with amine, to obtain aminocarbene, and azide terminal groups. These cycloaddition reaction showed regioselectivity to internal triple bond of dialkynyl Fischer carbene complex without Cu(I) as catalyst. Anyway the carbene anchored was able to act as a reducing agent to produce in situ very stable gold nanoparticles fixed on surface. We showed the characterization of modified glasses by contact angle measurements and XPS. Synthesized nanoparticles were characterized by SEM, XPS, EDS and UV–vis. The modified glasses showed an important enhancement Raman-SERS. This simple, fast and robust method to create a polifunctional and hybrid surfaces can be valuable in a wide range of applications such as Raman-SERS substrates and other optical fields.

H-D exchange in metal carbene complexes: Structure of cluster (μ-H)(μ-OCD3)Os3(CO)9{:C(CD3)NC2H8O}

Science.gov (United States)

Savkov, Boris; Maksakov, Vladimir; Kuratieva, Natalia

2015-10-01

X-ray and spectroscopic data for the new complex (μ-H)(μ-OCH3)Os3(CO)9{:C(CD3)NC2H8O} (2) obtained in the reaction of the (μ-H)(μ-Cl)Os3(CO)9{:C(CH3)NC2H8O} (1) with NaOCD3 in CD3OD solution are reported. It is shown that cluster 1 has the property of CH-acidity inherent of Fisher type carbenes. This had demonstrated using hydrogen deuterium exchange reaction in the presence of a strong base. Bridging chlorine to metoxide ligand substitution takes place during the reaction. The molecular structure of 2 is compared with known analogues.

Alkynylation of heterocyclic compounds using hypervalent iodine reagent.

Science.gov (United States)

Kamlar, M; Císařová, I; Veselý, J

2015-03-14

The alkynylation of various nitrogen- and/or sulphur-containing heterocyclic compounds using hypervalent iodine TMS-EBX by utilization of tertiary amines under mild conditions is described. The developed metal-free methodology furnishes the corresponding alkynylated heterocycles bearing quaternary carbon in high yields.

Nitrogen-rich heterocycles as reactivity retardants in shocked insensitive explosives.

Science.gov (United States)

Manaa, M Riad; Reed, Evan J; Fried, Laurence E; Goldman, Nir

2009-04-22

We report the first quantum-based multiscale simulations to study the reactivity of shocked perfect crystals of the insensitive energetic material triaminotrinitrobenzene (TATB). Tracking chemical transformations of TATB experiencing overdriven shock speeds of 9 km/s for up to 0.43 ns and 10 km/s for up to 0.2 ns reveal high concentrations of nitrogen-rich heterocyclic clusters. Further reactivity of TATB toward the final decomposition products of fluid N(2) and solid carbon is inhibited due to the formation of these heterocycles. Our results thus suggest a new mechanism for carbon-rich explosive materials that precedes the slow diffusion-limited process of forming the bulk solid from carbon clusters and provide fundamental insight at the atomistic level into the long reaction zone of shocked TATB.

Role of β-h elimination in rhodium-mediated carbene insertion polymerization

NARCIS (Netherlands)

Finger, M.; Reek, J.N.H.; de Bruin, B.

2011-01-01

The importance of β-H elimination as a possible mechanism to induce chain termination/transfer and/or the formation of stereodefects in the Rh(diene)-mediated oligomerization and polymerization of carbenes has been studied by means of different approaches. As a remarkable feature, this reaction is

Biotinylated N-Acetyllactosamine- and N,N-Diacetyllactosamine-Based Oligosaccharides as Novel Ligands for Human Galectin-3

Directory of Open Access Journals (Sweden)

Sophia Böcker

2017-04-01

Full Text Available Galectin inhibitor design is an emerging research field due to the involvement of galectins in cancer. Galectin-3, in particular, plays an important role in tumor progression. To generate inhibitors, modifications of the glycan structure can be introduced. Conjugation of hydrophobic compounds to saccharides has proven to be promising as increased binding of galectin-3 can be observed. In the present study, we report on neo-glycans carrying hydrophobic biotin as novel ligands for human galectin-3. We modified N-acetyllactosamine- and N,N-diacetyllactosamine-based tetrasaccharides at the C6-position of the terminal saccharide unit using selective enzymatic oxidation and subsequent chemical conjugation of biotinamidohexanoic acid hydrazide. These neo-glycans were much better bound by galectin-3 than the unmodified counterparts. High selectivity for galectin-3 over galectin-1 was also proven. We generated multivalent neo-glycoproteins by conjugation of neo-glycans to bovine serum albumin showing high affinity for galectin-3. Compared to non-biotinylated neo-glycoproteins, we achieved high binding levels of galectin-3 with a lesser amount of conjugated neo-glycans. Multivalent ligand presentation of neo-glycoproteins significantly increased the inhibitory potency towards galectin-3 binding to asialofetuin when compared to free monovalent glycans. Our findings show the positive impact of 6-biotinylation of tetrasaccharides on galectin-3 binding, which broadens the recent design approaches for producing high-affinity ligands.

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

Energy Technology Data Exchange (ETDEWEB)

Hadad, C. Z., E-mail: cacier.hadad@udea.edu.co [Grupo de Química-Física Teórica, Instituto de Química, Universidad de Antioquia, A. A. 1226 Medellín (Colombia); Jenkins, Samantha [College of Chemistry and Chemical Engineering, Hunan Normal University, Changsha, Hunan 410081 (China); Flórez, Elizabeth [Departamento de Ciencias Básicas, Universidad de Medellín, Carrera 87 N° 30-65, Medellín (Colombia)

2015-03-07

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.

Explicit role of dynamical and nondynamical electron correlation on singlet-triplet splitting in carbenes

International Nuclear Information System (INIS)

Seal, Prasenjit; Chakrabarti, Swapan

2007-01-01

Density functional theoretical studies have been performed on carbene systems to determine the singlet-triplet splitting and also to explore the role of electron correlation. Using an approximate method of separation of dynamical and nondynamical correlation, it is found that dynamical and nondynamical electron correlation stabilizes the singlet state relative to the triplet for halo carbenes in both BLYP and B3LYP methods. Calculations performed on higher homologues of methylene suggest that beyond CH(CH 3 ), both the electron correlations have leveling effect in stabilizing the singlet state relative to the triplet. It has also been observed while dynamical electron correlation fails to provide any substantial degree of stabilization to the singlet states of higher homologues of methylene in B3LYP method, an opposite trend is observed for nondynamical counterpart. Among the larger systems studied (9-triptycyl)(α-naphthyl)-carbene has the highest stability of the triplet state whereas bis-imidazol-2-ylidenes has the most stable singlet state. Interestingly, the values of the dynamical electron correlation for each state of each system studied are different for the two methods used. The reason behind this apparent discrepancy lies in the fact that the coefficients of the LYP part in B3LYP and BLYP functionals are different

Copper-Catalyzed N-Arylation of Amides Using (S-N-Methylpyrrolidine-2-carboxylate as the Ligand

Directory of Open Access Journals (Sweden)

Dong-Sheng Ma

2010-03-01

Full Text Available (S-N-methylpyrrolidine-2-carboxylate, a derivative of natural L-proline, was found to be an efficient ligand for the copper-catalyzed Goldberg-type N-arylation of amides with aryl halides under mild conditions. A variety of N-arylamides were synthesized in good to high yields.

gem-Difluoroolefination of Diazo Compounds with TMSCF3 or TMSCF2Br: Transition-Metal-Free Cross-Coupling of Two Carbene Precursors.

Science.gov (United States)

Hu, Mingyou; Ni, Chuanfa; Li, Lingchun; Han, Yongxin; Hu, Jinbo

2015-11-18

A new olefination protocol for transition-metal-free cross-coupling of two carbene fragments arising from two different sources, namely, a nonfluorinated carbene fragment resulting from a diazo compound and a difluorocarbene fragment derived from Ruppert-Prakash reagent (TMSCF3) or TMSCF2Br, has been developed. This gem-difluoroolefination proceeds through the direct nucleophilic addition of diazo compounds to difluorocarbene followed by elimination of N2. Compared to previously reported Cu-catalyzed gem-difluoroolefination of diazo compounds with TMSCF3, which possesses a narrow substrate scope due to a demanding requirement on the reactivity of diazo compounds and in-situ-generated CuCF3, this transition-metal-free protocol affords a general and efficient approach to various disubstituted 1,1-difluoroalkenes, including difluoroacrylates, diaryldifluoroolefins, as well as arylalkyldifluoroolefins. In view of the ready availability of diazo compounds and difluorocarbene reagents and versatile transformations of 1,1-difluoroalkenes, this new gem-difluoroolefination method is expected to find wide applications in organic synthesis.

Mechanochemical synthesis and structural characterization of three novel cocrystals of dimethylglyoxime with N-heterocyclic aromatic compounds and acetamide

Science.gov (United States)

Abidi, Syed Sibte Asghar; Azim, Yasser; Gupta, Abhishek Kumar; Pradeep, Chullikkattil P.

2017-12-01

With an aim to explore the interactions of (RR'Cdbnd Nsbnd OH) oxime moiety of dimethylglyoxime (DMG) with pyridyl ring of N-heterocyclic aromatic compounds and acetamide, three novel cocrystals of dimethylglyoxime with acridine (ACR), 1,10-phenanthroline monohydrate (PT) and acetamide (ACT) are reported. These three cocrystals were obtained with a mechanochemical synthesis approach and were characterized by single crystal X-ray diffraction (SCXRD), powder X-ray diffraction (PXRD), fourier transform-infrared spectroscopy (FT-IR), differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). Additionally, Hirshfeld surface analysis is used to investigate the intermolecular interaction and the crystal packing of cocrystals.

In vitro disposition profiling of heterocyclic compounds.

Science.gov (United States)

Keemink, Janneke; Wuyts, Benjamin; Nicolaï, Johan; Jonghe, Steven De; Stella, Alessandro; Herdewijn, Piet; Augustijns, Patrick; Annaert, Pieter

2015-08-01

Compound libraries that are screened for biological activity commonly contain heterocycles. Besides potency, drug-like properties need to be evaluated to ensure in vivo efficacy of test compounds. In this context, we determined hepatic and intestinal disposition profiles for 17 heterocyclic compounds. All studied compounds showed rapid uptake in suspended rat hepatocytes, whereas metabolism was poor and the rate-limiting step in hepatic elimination. In vitro assays demonstrated a relatively low solubility and high intestinal permeability. Based on these in vitro data, heterocycles were categorized in the biopharmaceutics classification system (BCS) and the biopharmaceutics drug disposition classification system (BDDCS) to predict disposition characteristics before clinical data are available. Our findings emphasized the importance to use hepatocytes in addition to microsomes to study metabolism, since the latter lack non-microsomal enzymes and cellular context. Moreover, intracellular exposure should be considered to gain insight in the relevant fraction of the compound available at the enzymatic site. Finally, the study reveals discrepancies associated with the classification of heterocycles in BCS versus BDDCS. These probably originate from the binary character of both systems. Copyright © 2015 Elsevier B.V. All rights reserved.

Sulfur-Kβ /sub emission studies on sulfur-bearing heterocycles

International Nuclear Information System (INIS)

Phillips, D.R.; Andermann, G.G.; Fujiwara, F.

1986-01-01

Sulfur-K/β /sub x-ray fluorescence spectroscopy (XFS) has been used to study the electronic structure and bonding in sulfur-bearing heterocycles. XFS not only has the capability of experimentally measuring valence electron energies in molecular species, but can also provide intensity data which can help define the nature of the molecular orbitals defined by the electrons. This report discusses the feasibility of using XFS as an analytical tool for the determination of total and specific sulfur heterocycle content in samples. A variety of compounds were studied. These include thiophene, thiophene derivatives, tetranydrothiophene, several more complex saturated and unsaturated sulfur heterocycles, and heterocycles containing both sulfur and nitrogen. The sulfur-K/β /sub spectra were obtained using a double crystal spectrometer which provided an instrumental resolution of about 0.7 eV

Theoretical description of metal-ligand bonding within f-element complexes: A successful and necessary interplay between theory and experiment

International Nuclear Information System (INIS)

Maldivi, P.; Petit, L.; Vetere, V.; Petit, L.; Adamo, C.

2007-01-01

The quantum chemical study presented here shows various aspects of the bonding of lanthanide (La 3+ , Gd 3+ ) and actinide (U 3+ , Am 3+ , Cm 3+ ) ions with N-heterocyclic ligands (poly-azines, BTP: bis(1,2,4-triazinyl)-2,6-pyridine). Several families of complexes, differing by their coordination sphere, have been examined. Clearly, the lanthanide complexes always show a purely ionic bonding. The behaviour of U(III) is also well defined with a more or less strong back bonding interaction whatever the complex is. In contrast, the heavy actinides (Am 3+ and Cm 3+ ) are changeable, with a weak covalent character, going from donation to back donation, depending on the coordination sphere of the complex. (authors)

New Acridine Thiourea Gold(I) Anticancer Agents: Targeting the Nucleus and Inhibiting Vasculogenic Mimicry

Czech Academy of Sciences Publication Activity Database

Perez, S.A.; de Haro, C.; Vicente, C.; Donaire, A.; Zamora, A.; Zajac, Juraj; Kostrhunová, Hana; Brabec, Viktor; Bautista, D.; Ruiz, J.

2017-01-01

Roč. 12, č. 6 (2017), s. 1524-1537 ISSN 1554-8929 R&D Projects: GA ČR(CZ) GA17-09436S Institutional support: RVO:68081707 Keywords : heterocyclic carbene complexes * inflammatory breast - cancer Subject RIV: CE - Biochemistry OBOR OECD: Biochemistry and molecular biology Impact factor: 4.995, year: 2016

Synthesis of Backfunctionalized Imidazolinium Salts and NHC Carbene Complexes

Science.gov (United States)

2017-04-02

Backfunctionalized Imidazolinium salts and NHC carbene complexes – Initial Research – Unintended Discovery – Survey chemistry of aromatic systems – Expansion of...survey chemistry to aliphatics • Conclusions and Future Directions Introduction 3 Distribution A: Approved for Public Release; Distribution Unlimited...AFRL – Tenant of Edwards AFB since late ‘50s – Full scale testing of the Atlas rockets (Gemini missions) – Initial testing of the F-1 engine (Apollo

Serotonergic 5-HT6 Receptor Antagonists: Heterocyclic Chemistry and Potential Therapeutic Significance.

Science.gov (United States)

Bali, Alka; Singh, Shalu

2015-01-01

The serotonin 5-HT(6) receptor (5- HT(6)R) is amongst the recently discovered serotonergic receptors with almost exclusive localization in the brain. Hence, this receptor is fast emerging as a promising target for cognition enhancement in central nervous system (CNS) diseases such as Alzheimer's disease (cognitive function), obesity, schizophrenia and anxiety. The last decade has seen a surge of literature reports on the functional role of this receptor in learning and memory processes and investigations related to the chemistry and pharmacology of 5-HT(6) receptor ligands, especially 5- HT(6) receptor antagonists. Studies show the involvement of multiple neurotransmitter systems in cognitive enhancement by 5-HT(6)R antagonists including cholinergic, glutamatergic, and GABAergic systems. Several of the 5-HT(6)R ligands are indole based agents bearing structural similarity to the endogenous neurotransmitter serotonin. Based on the pharmacophoric models proposed for these agents, drug designing has been carried out incorporating various heterocyclic replacements for the indole nucleus. In this review, we have broadly summarized the medicinal chemistry and current status of this fairly recent class of drugs along with their potential therapeutic applications.

Tripodal (N-alkylated) CMP(O) and malonamide ligands: synthesis, extraction of metal ions, and potentiometric studies

International Nuclear Information System (INIS)

Janczewski, D.; Reinhoudt, D.N.; Verboom, W.; Malinowska, E.; Pietrzak, M.; Hill, C.; Allignol, C.

2007-01-01

Tripodal ligands build on the C-pivot (9b-e, 13b-d, and 17a-d) and tri-alkyl-benzene platforms (10a,b, 11, 12, 14a,b, and 18a,b) bearing (N-alkylated) carbamoyl-methyl-phosphine oxide (CMPO), carbamoyl-methyl-phosphonate (CMP), and malonamide moieties were synthesized. Extraction studies with Am 3+ and Eu 3+ show that in general there is a positive influence of the N-alkyl substituents in C-pivot CMP(O) ligands on the D(distribution) coefficients. The tri-alkyl-benzene CMPO ligands 10a,b, 11, and 12 have considerably larger D coefficients than the corresponding C-pivot analogues 9a-e, although hardly having any selectivity, while N-alkylation gives rise to smaller D coefficients. Although less effective the extraction behavior of the C-pivot CMP analogues 13b-d shows more or less the same trend as the corresponding CMPO ligands 9b-e upon substitution of the carboxamide N-atom with different alkyl chains. The different malonamide ligands 17a-d and 18a,b are bad extractants, while N-alkylation makes them even worse. Potentiometric studies of CMP(O) and malonamide ligands in polymeric membranes on Pb 2+ , Cu 2+ , Ca 2+ , Mg 2+ , Na + , and K + salts revealed that N-alkyl substituents increase the stability constants of ion-ionophore complexes compared to unsubstituted ligands. In polymeric membrane electrodes the ligands induce a selectivity pattern that differs significantly from the so-called Hofmeister series, giving the highest selectivity coefficients for UO 2 2+ among all examined cations (Pb 2+ , Cu 2+ , Ca 2+ , Mg 2+ , Na + , K + ). (authors)

Analysis of heterocyclic amines in hair by on-line in-tube solid-phase microextraction coupled with liquid chromatography−tandem mass spectrometry

International Nuclear Information System (INIS)

Kataoka, Hiroyuki; Inoue, Tsutomu; Saito, Keita; Kato, Hisato; Masuda, Kazufumi

2013-01-01

Graphical abstract: Mutagenic and carcinogenic heterocyclic amines are accumulated in the hair of smoker. -- Highlights: •On-line in-tube solid-phase microextraction of heterocyclic amines was optimized. •Fourteen heterocyclic amines were simultaneously determined by LC–MS/MS. •Pico gram levels of heterocyclic amines could be easily analyzed within 15 min. •Heterocyclic amines could be quantitatively analyzed from several milligrams of hair. •The method is useful for the assessment of long-term exposure to heterocyclic amines. -- Abstract: Mutagenic and carcinogenic heterocyclic amines (HCAs) are formed during heating of various proteinaceous foods, but human exposure to HCAs has not yet been elucidated in detail. To assess long-term exposure to HCAs, we developed a simple and sensitive method for measuring HCAs in hair by automated on-line in-tube solid-phase microextraction (SPME) coupled with liquid chromatography–tandem mass spectrometry (LC–MS/MS). Using a Zorbax Eclipse XDB-C8 column, 16 HCAs were analyzed within 15 min. The optimum in-tube SPME conditions were 20 draw/eject cycles of 40 μL sample at a flow rate of 200 μL min −1 using a Supel-Q PLOT capillary column as an extraction device. The extracted HCAs were easily desorbed from the column by passage of the mobile phase, with no carryover observed. This in-tube SPME LC–MS/MS method showed good linearity for HCAs in the range of 10–2000 pg mL −1 , with correlation coefficients above 0.9989 (n = 18), using stable isotope-labeled HCA internal standards. The detection limits (S/N = 3) of 14 HCAs except for MeAαC and Glu-P-1 were 0.10–0.79 pg mL −1 . This method was successfully utilized to analyze 14 HCAs in hair samples without any interference peaks, with quantitative limits (S/N = 10) of about 0.17–1.32 pg mg −1 hair. Using this method, we evaluated the exposure to HCAs in cigarette smoke and the suitability of using hair HCAs as exposure biomarkers

Construction of porous cationic frameworks by crosslinking polyhedral oligomeric silsesquioxane units with N-heterocyclic linkers

Science.gov (United States)

Chen, Guojian; Zhou, Yu; Wang, Xiaochen; Li, Jing; Xue, Shuang; Liu, Yangqing; Wang, Qian; Wang, Jun

2015-06-01

In fields of materials science and chemistry, ionic-type porous materials attract increasing attention due to significant ion-exchanging capacity for accessing diversified applications. Facing the fact that porous cationic materials with robust and stable frameworks are very rare, novel tactics that can create new type members are highly desired. Here we report the first family of polyhedral oligomeric silsesquioxane (POSS) based porous cationic frameworks (PCIF-n) with enriched poly(ionic liquid)-like cationic structures, tunable mesoporosities, high surface areas (up to 1,025 m2 g-1) and large pore volumes (up to 0.90 cm3 g-1). Our strategy is designing the new rigid POSS unit of octakis(chloromethyl)silsesquioxane and reacting it with the rigid N-heterocyclic cross-linkers (typically 4,4‧-bipyridine) for preparing the desired porous cationic frameworks. The PCIF-n materials possess large surface area, hydrophobic and special anion-exchanging property, and thus are used as the supports for loading guest species PMo10V2O405- the resultant hybrid behaves as an efficient heterogeneous catalyst for aerobic oxidation of benzene and H2O2-mediated oxidation of cyclohexane.

Photometabolism of Heterocyclic Aromatic Compounds by Rhodopseudomonas palustris OU 11

Science.gov (United States)

Sasikala, C.; Ramana, C. V.; Rao, P. Raghuveer

1994-01-01

Rhodopseudomonas palustris OU 11 (ATCC 51186; DSM 7375) isolated from a pond of chemical industry effluent could anaerobically photometabolize heterocyclic aromatic compounds belonging to the pyridine and pyrazine groups only after a period of adaptation on pyrazinoic acid of 5 to 6 weeks. Growth on heterocyclic compounds was light dependent. The effects of various concentrations of heterocyclic compounds on growth suggest that higher concentrations of these compounds inhibit growth and are toxic. PMID:16349307

Bimolecular reactions of carbenes: Proton transfer mechanism

Science.gov (United States)

Abu-Saleh, Abd Al-Aziz A.; Almatarneh, Mansour H.; Poirier, Raymond A.

2018-04-01

Here we report the bimolecular reaction of trifluoromethylhydroxycarbene conformers and the water-mediated mechanism of the 1,2-proton shift for the unimolecular trans-conformer by using quantum chemical calculations. The CCSD(T)/cc-pVTZ//MP2/cc-pVDZ potential-energy profile of the bimolecular reaction of cis- and trans-trifluoromethylhydroxycarbene, shows the lowest gas-phase barrier height of 13 kJ mol-1 compared to the recently reported value of 128 kJ mol-1 for the unimolecular reaction. We expect bimolecular reactions of carbene's stereoisomers will open a valuable field for new and useful synthetic strategies.

Tripodal (N-alkylated) CMP(O) and malonamide ligands: synthesis, extraction of metal ions, and potentiometric studies

Energy Technology Data Exchange (ETDEWEB)

Janczewski, D.; Reinhoudt, D.N.; Verboom, W. [Twente Univ., Lab. of Supramolecular Chemistry and Technology, Mesa Research Institute for Nanotechnology, Enschede (Netherlands); Malinowska, E.; Pietrzak, M. [Warsaw Univ. of Technology, Dept. of Analytical Chemistry, Faculty of Chemistry (Poland); Hill, C.; Allignol, C. [CEA Valrho, 30 - Marcoule (France)

2007-01-15

Tripodal ligands build on the C-pivot (9b-e, 13b-d, and 17a-d) and tri-alkyl-benzene platforms (10a,b, 11, 12, 14a,b, and 18a,b) bearing (N-alkylated) carbamoyl-methyl-phosphine oxide (CMPO), carbamoyl-methyl-phosphonate (CMP), and malonamide moieties were synthesized. Extraction studies with Am{sup 3+} and Eu{sup 3+} show that in general there is a positive influence of the N-alkyl substituents in C-pivot CMP(O) ligands on the D(distribution) coefficients. The tri-alkyl-benzene CMPO ligands 10a,b, 11, and 12 have considerably larger D coefficients than the corresponding C-pivot analogues 9a-e, although hardly having any selectivity, while N-alkylation gives rise to smaller D coefficients. Although less effective the extraction behavior of the C-pivot CMP analogues 13b-d shows more or less the same trend as the corresponding CMPO ligands 9b-e upon substitution of the carboxamide N-atom with different alkyl chains. The different malonamide ligands 17a-d and 18a,b are bad extractants, while N-alkylation makes them even worse. Potentiometric studies of CMP(O) and malonamide ligands in polymeric membranes on Pb{sup 2+}, Cu{sup 2+}, Ca{sup 2+}, Mg{sup 2+}, Na{sup +}, and K{sup +} salts revealed that N-alkyl substituents increase the stability constants of ion-ionophore complexes compared to unsubstituted ligands. In polymeric membrane electrodes the ligands induce a selectivity pattern that differs significantly from the so-called Hofmeister series, giving the highest selectivity coefficients for UO{sub 2}{sup 2+} among all examined cations (Pb{sup 2+}, Cu{sup 2+}, Ca{sup 2+}, Mg{sup 2+}, Na{sup +}, K{sup +}). (authors)

An insight into the biological activities of heterocyclic-fatty acid hybrid molecules.

Science.gov (United States)

Venepally, Vijayendar; Reddy Jala, Ram Chandra

2017-12-01

Heterocyclic compounds are the interesting core structures for the development of new bioactive compounds. Fatty acids are derived from renewable raw materials and exhibit various biological activities. Several researchers are amalgamating these two bioactive components to yield bioactive hybrid molecules with some desirable features. Heterocyclic-fatty acid hybrid derivatives are a new class of heterocyclic compounds with a broad range of biological activities and significance in the field of medicinal chemistry. Over the last few years, many research articles emphasized the significance of heterocyclic-fatty acid hybrid derivatives. The present review article focuses the developments in designing and biological evaluation of heterocyclic-fatty acid hybrid molecules. Copyright © 2017. Published by Elsevier Masson SAS.

METHODS OF SYNTHESIS EIGHT-TELLURIUM-CONTAINING HETEROCYCLES WITH MORE HETEROATOMS

Directory of Open Access Journals (Sweden)

G. M. Abakarov

2013-01-01

Full Text Available In this article systematized and summarized data on the synthesis of neweight-embered tellurium-containing heterocycles and new preparative methods described above produce heterocyclic tellurium.

Novel 7-phenylsulfanyl-1,2,3,4,10,10a-hexahydro-pyrazino[1,2-a]indoles as dual serotonin 5-HT2C and 5-HT6 receptor ligands

DEFF Research Database (Denmark)

Krogsgaard-Larsen, Niels; Jensen, Anders A.; Kehler, Jan

2010-01-01

Novel 7-phenylsulfanyl-1,2,3,4,10,10a-hexahydro-pyrazino[1,2-a]indoles are synthesized using a six-step protocol. Notably, the synthesis route make use of a new and improved ring-closing methodology for the assembly of the hexahydro-pyrazino[1,2-a]indole scaffold, which is based on intramolecular......-H insertion of a carbene. The compounds act as dual serotonin 5-HT2C- and 5-HT6-ligands....

Structural mechanisms of photoeffect in polyimide structures containing heterocyclic fragments

International Nuclear Information System (INIS)

Aleksandrova, E. L.

2006-01-01

Trends in the variation in the quantum yields of charge-carrier photogeneration in polyimide structures containing heterocyclic fragments are studied. It is shown that the efficiency of sensitization of polyimides depends on the donor and acceptor properties of the fragments of monomeric units of the polyimide. It is established that the range of spectral sensitivity for heterocyclic fragments representing intramolecular complexes with charge transport is wider than that for heterocycles that do not represent such complexes

Anaerobic biodegradation of halogenated and nonhalogenated N-, s-, and o-heterocyclic compounds in aquifer slurries

Science.gov (United States)

Adrian, Neal R.; Suflita, Joseph M.

1994-01-01

The fate of several halogenated and nonhalogenated heterocyclic compounds in anoxic aquifer slurries was investigated Substrate depletion and methane formation were monitored in serum bottle incubations by HPLC and GC, respectively Pyridine, pyrimidine, thiophene, and furan were not mineralized following an 11-month incubation, but the corresponding carboxylated or oxygenated compounds were That is, >74% of the theoretically expected amount of methane was recovered from nicotinic acid, uracil, or 2-furoic acid Chlorinated derivatives, like 2 chloro- or 6-chloronicotinic acid, as well as 4 chloro- and 5-chlorouracil resisted mineralization However, 5-bromouracil was reductively dehalogenated to stoichiometric amounts of uracil, whereas 2-chloropyrimidine was metabolized to a more polar unidentified compound that resisted further anaerobic biodegradation Microorganisms acclimated to 5-bromouracil were unable to transform 4 chloro or 5 chlorouracil These findings illustrate how the structure of heterocyclic contaminants influences their susceptibility to anaerobic decay

Blue Chitin columns for the extraction of heterocyclic amines from urine samples

DEFF Research Database (Denmark)

Bang, J.; Frandsen, Henrik Lauritz; Skog, K.

2004-01-01

During normal cooking of meat, a class of mutagenic/carcinogenic compounds called heterocyclic amines is formed. Heterocyclic amines are rapidly absorbed and metabolised in the human body, and for estimation of the intake of heterocyclic amines, it is useful to determinate their levels in the uri...

Synthesis, characterization, and reactivity of ruthenium hydride complexes of N-centered triphosphine ligands.

Science.gov (United States)

Phanopoulos, Andreas; Brown, Neil J; White, Andrew J P; Long, Nicholas J; Miller, Philip W

2014-04-07

The reactivity of the novel tridentate phosphine ligand N(CH2PCyp2)3 (N-triphos(Cyp), 2; Cyp = cyclopentyl) with various ruthenium complexes was investigated and compared that of to the less sterically bulky and less electron donating phenyl derivative N(CH2PPh2)3 (N-triphos(Ph), 1). One of these complexes was subsequently investigated for reactivity toward levulinic acid, a potentially important biorenewable feedstock. Reaction of ligands 1 and 2 with the precursors [Ru(COD)(methylallyl)2] (COD = 1,5-cycloocatadiene) and [RuH2(PPh3)4] gave the tridentate coordination complexes [Ru(tmm){N(CH2PR2)3-κ(3)P}] (R = Ph (3), Cyp (4); tmm = trimethylenemethane) and [RuH2(PPh3){N(CH2PR2)3-κ(3)P}] (R = Ph (5), Cyp (6)), respectively. Ligands 1 and 2 displayed different reactivities with [Ru3(CO)12]. Ligand 1 gave the tridentate dicarbonyl complex [Ru(CO)2{N(CH2PPh2)3-κ(3)P}] (7), while 2 gave the bidentate, tricarbonyl [Ru(CO)3{N(CH2PCyp2)3-κ(2)P}] (8). This was attributed to the greater electron-donating characteristics of 2, requiring further stabilization on coordination to the electron-rich Ru(0) center by more CO ligands. Complex 7 was activated via oxidation using AgOTf and O2, giving the Ru(II) complexes [Ru(CO)2(OTf){N(CH2PPh2)3-κ(3)P}](OTf) (9) and [Ru(CO3)(CO){N(CH2PPh2)3-κ(3)P}] (11), respectively. Hydrogenation of these complexes under hydrogen pressures of 3-15 bar gave the monohydride and dihydride complexes [RuH(CO)2{N(CH2PPh2)3-κ(3)P}] (10) and [RuH2(CO){N(CH2PPh2)3-κ(3)P}] (12), respectively. Complex 12 was found to be unreactive toward levulinic acid (LA) unless activated by reaction with NH4PF6 in acetonitrile, forming [RuH(CO)(MeCN){N(CH2PPh2)3-κ(3)P}](PF6) (13), which reacted cleanly with LA to form [Ru(CO){N(CH2PPh2)3-κ(3)P}{CH3CO(CH2)2CO2H-κ(2)O}](PF6) (14). Complexes 3, 5, 7, 8, 11, and 12 were characterized by single-crystal X-ray crystallography.

Singlet-triplet energy differences in divalent five membered cyclic conjugated Arduengo-type carbenes XC2HN2M (M = C, Si, Ge, Sn, and Pb; X = F, Cl, Br, and I)

Science.gov (United States)

Vessally, Esmail; Dehbandi, Behnam; Ahmadi, Elaheh

2016-09-01

Singlet-triplet energy differences in Arduengo-type carbenes XC2HN2C compared and contrasted with their sila, germa, stana and plumba analogues; at B3LYP/6-311++G** level of theory. Free Gibbs energy differences between triplet (t) and singlet (s) states (Δ G(t-s)) change in the following order: plumbylenes > stannylenes > germylenes > silylenes > carbenes. The singlet states in XC2HN2C are generally more stable when the electron withdrawing groups such as-F was used at β-position. However, the singlet states in XC2N2HM (M = Si, Ge, Sn, and Pb) are generally more stable when the withdrawing groups such as-F was placed. The puckering energy is investigated for each the singlet and triplet states. The DFT calculations found the linear correlation to size of the group 14 divalent element (M), the ∠N-M-N angle, and the Δ(LUMO-HOMO) of XC2HN2M.

Binuclear complexes of technetium. Evidence for bis(terdentate)bidentate coordination by the bridging ligand 2,3,5,6-tetrakis(2-pyridyl)pyrazine to technetium(V)

International Nuclear Information System (INIS)

Du Preez, J.G.H.; Gerber, T.I.A.; Gibson, M.L.; Geyser, R.

1990-01-01

The authors have used the potentially bis(terdentate) nitrogen aromatic heterocyclic ligand 2,3,5,6-tetrakis(2-pyridyl)pyrazine (tppz) to prepare mono- and bimetallic technetium(V) complexes bound to tppz. The stimulus for the development of the coordination chemistry of the man-made element technetium is provided by the use of complexes of this element as anatomical imaging agents in nuclear medicine. Although the chemistry of technetium(V) with nitrogen donor ligands is well understood, no complexes have been prepared using potentially terdentate neutral nitrogen donor ligands of this metal in the +5 oxidation state

Theoretical studies of mechanisms of cycloaddition reaction between difluoromethylene carbene and acetone

Science.gov (United States)

Lu, Xiu Hui; Yu, Hai Bin; Wu, Wei Rong; Xu, Yue Hua

Mechanisms of the cycloaddition reaction between singlet difluoromethylene carbene and acetone have been investigated with the second-order Møller-Plesset (MP2)/6-31G* method, including geometry optimization and vibrational analysis. Energies for the involved stationary points on the potential energy surface (PES) are corrected by zero-point energy (ZPE) and CCSD(T)/6-31G* single-point calculations. From the PES obtained with the CCSD(T)//MP2/6-31G* method for the cycloaddition reaction between singlet difluoromethylene carbene and acetone, it can be predicted that path B of reactions 2 and 3 should be two competitive leading channels of the cycloaddition reaction between difluoromethylene carbene and acetone. The former consists of two steps: (i) the two reactants first form a four-membered ring intermediate, INT2, which is a barrier-free exothermic reaction of 97.8 kJ/mol; (ii) the intermediate INT2 isomerizes to a four-membered product P2b via a transition state TS2b with an energy barrier of 24.9 kJ/mol, which results from the methyl group transfer. The latter proceeds in three steps: (i) the two reactants first form an intermediate, INT1c, through a barrier-free exothermic reaction of 199.4 kJ/mol; (ii) the intermediate INT1c further reacts with acetone to form a polycyclic intermediate, INT3, which is also a barrier-free exothermic reaction of 27.4 kJ/mol; and (iii) INT3 isomerizes to a polycyclic product P3 via a transition state TS3 with an energy barrier of 25.8 kJ/mol.

Comprehensive database of Manufactured Gas Plant tars. Part C. Heterocyclic and hydroxylated polycyclic aromatic hydrocarbons.

Science.gov (United States)

Gallacher, Christopher; Thomas, Russell; Lord, Richard; Kalin, Robert M; Taylor, Chris

2017-08-15

Coal tars are a mixture of organic and inorganic compounds that were by-products from the manufactured gas and coke making industries. The tar compositions varied depending on many factors such as the temperature of production and the type of retort used. For this reason a comprehensive database of the compounds found in different tar types is of value to understand both how their compositions differ and what potential chemical hazards are present. This study focuses on the heterocyclic and hydroxylated compounds present in a database produced from 16 different tars from five different production processes. Samples of coal tar were extracted using accelerated solvent extraction (ASE) and derivatized post-extraction using N,O-bis(trimethylsilyl)trifluoroacetamide (BSTFA) with 1% trimethylchlorosilane (TMCS). The derivatized samples were analysed using two-dimensional gas chromatography combined with time-of-flight mass spectrometry (GCxGC/TOFMS). A total of 865 heterocyclic compounds and 359 hydroxylated polycyclic aromatic hydrocarbons (PAHs) were detected in 16 tar samples produced by five different processes. The contents of both heterocyclic and hydroxylated PAHs varied greatly with the production process used, with the heterocyclic compounds giving information about the feedstock used. Of the 359 hydroxylated PAHs detected the majority would not have been be detected without the use of derivatization. Coal tars produced using different production processes and feedstocks yielded tars with significantly different heterocyclic and hydroxylated contents. The concentrations of the individual heterocyclic compounds varied greatly even within the different production processes and provided information about the feedstock used to produce the tars. The hydroxylated PAH content of the samples provided important analytical information that would otherwise not have been obtained without the use of derivatization and GCxGC/TOFMS. Copyright © 2017 John Wiley & Sons, Ltd.

Transformation of saturated nitrogen-containing heterocyclic compounds by microorganisms.

Science.gov (United States)

Parshikov, Igor A; Silva, Eliane O; Furtado, Niege A J C

2014-02-01

The saturated nitrogen-containing heterocyclic compounds include many drugs and compounds that may be used as synthons for the synthesis of other pharmacologically active substances. The need for new derivatives of saturated nitrogen-containing heterocycles for organic synthesis, biotechnology and the pharmaceutical industry, including optically active derivatives, has increased interest in microbial synthesis. This review provides an overview of microbial technologies that can be valuable to produce new derivatives of saturated nitrogen-containing heterocycles, including hydroxylated derivatives. The chemo-, regio- and enantioselectivity of microbial processes can be indispensable for the synthesis of new compounds. Microbial processes carried out with fungi, including Beauveria bassiana, Cunninghamella verticillata, Penicillium simplicissimum, Aspergillus niger and Saccharomyces cerevisiae, and bacteria, including Pseudomonas sp., Sphingomonas sp. and Rhodococcus erythropolis, biotransform many substrates efficiently. Among the biological activities of saturated nitrogen-containing heterocyclic compounds are antimicrobial, antitumor, antihypertensive and anti-HIV activities; some derivatives are effective for the treatment and prevention of malaria and trypanosomiasis, and others are potent glycosidase inhibitors.

Utilization of mixed ligands to construct diverse Ni(II)-coordination polymers based on terphenyl-2,2′,4,4′-tetracarboxylic acid and varied N-donor co-ligands

International Nuclear Information System (INIS)

Wang, Chao; Zhao, Jun; Xia, Liang; Wu, Xue-Qian; Wang, Jian-Fang; Dong, Wen-Wen; Wu, Ya-Pan

2016-01-01

Three new coordination polymers, namely, {[Ni(H 2 L)(bix)(H 2 O) 2 ]·2h 2 O} n (1), {[Ni(HL)(Hdpa)(H 2 O) 2 ]·H 2 O} n (2), {[Ni(L) 0.5 (bpp)(H 2 O)]·H 2 O} n (3) (H 4 L=terphenyl-2,2′,4,4′-tetracarboxylic acid; bix=1,4-bis(imidazol-1-ylmethyl)benzene; dpa =4,4′-dipyridylamine; bpp=1,3-bis(4-pyridyl)propane), based on rigid H 4 L ligand and different N-donor co-ligands, have been synthesized under hydrothermal conditions. Compound 1 features a 3D 4-connected 6 6 -dia-type framework with H 4 L ligand adopts a μ 2 -bridging mode with two symmetry-related carboxylate groups in μ 1 -η 1 :η 0 monodentate mode. Compound 2 displays a 1D [Ni(HL)(Hdpa)] n ribbon chains motif, in which the H 4 L ligand adopts a μ 2 -bridging mode with two carboxylate groups in μ 1 -η 1 :η 1 and μ 1 -η 1 :η 0 monodentate modes, while 3 possesses a (4,4)-connected 3D frameworks with bbf topology, with H 4 L ligand displays a μ 4 -bridging coordination mode. The H 4 L ligand displays not only different deprotonated forms but also diverse coordination modes and conformations. The structural diversities among 1–3 have been carefully discussed, and the roles of N-donor co-ligands in the self-assembly of coordination polymers have been well documented. - Graphical abstract: Three nickel coordination polymers with different architectures based on mixed ligand system were synthesized and structurally characterized. Topology analyses indicate that 1 shows the 4-connected 6 6 -dia net, 1D ribbon chains for 2 and 3D (4,4)-connected bbf network for 3. Display Omitted - Highlights: • Three Ni-based coordination polymers with distinct features have been prepared. • Compound 1 features a 3D 4-connected 66-dia-type framework, 2 displays a 1D [Ni(HL)(Hdpa)] n ribbon chains motif, while 3 possesses a (4,4)-connected 3D frameworks with bbf topology. • The “mixed ligand assembled” strategy is significant potential for network design.

A DFT Study on Selected Physical Organic Aspects of the Fischer Carbene Intermediates [(M(CO4(C(OMeMe

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Tareq Irshaidat

2010-01-01

Full Text Available Fischer carbenes are important starting materials for C-C bond formation via coupling reactions between carbene and wide variety of substituted alkenes or alkynes. This DFT study shed light on unique fundamental organic/organometallic aspects for the C(OMeMe carbene in the free form and in case of bonding with M(CO4 (M= Cr, Mo, W. The data illustrate that the structures of the title intermediates include a unique structure stabilizing intramolecular M…C-H interaction (agostic interaction. This conclusion was made based on calculated NMR data (for carbon and hydrogen, structural parameters, energy calculations of conformers (C-C conformation, selected IR stretching frequencies (C-O, C-C, and C-H, and atomic charges. The agostic interaction is most efficient in case of chromium and in general is described as an overlap between the σ-bond electron pair of C-H with an empty d-orbital of the metal. These characterized examples are new addition to the orbital interaction theory.

Microwave-assisted synthesis of bio-active heterocycles in aqueous media

KAUST Repository

Polshettiwar, Vivek; Varma, Rajender S.

2010-01-01

Synthesis of bio-active heterocycles and fine chemicals in aqueous media are one of the best solutions for the development of green and sustainable protocols. To illustrate the advantages of aqueous MW chemistry in heterocycle synthesis

Spectrophotometric method for determination of bifunctional macrocyclic ligands in macrocyclic ligand-protein conjugates

International Nuclear Information System (INIS)

Dadachova, E.; Chappell, L.L.; Brechbiel, M.W.

1999-01-01

A simple spectrophotometric assay for determination of bifunctional polyazacarboxylate-macrocyclic ligands of different sizes that are conjugated to proteins has been developed for: 12-membered macrocycle DOTA (2-[4-nitrobenzyl]-1, 4, 7, 10-tetraazacyclododecane-N,N',N'',N'''-tetraacetic acid) and analogs, the 15-membered PEPA macrocycle (2-[4-nitrobenzyl]-1,4,7,10,13-pentaazacyclopentadecane-N,N',N'',N''',N'''' -pentaacetic acid), and the large 18-membered macrocycle HEHA (1,4,7,10,13,16-hexaazacyclooctadecane-N,N',N'',N''',N''''-hexaacetic acid). The method is based on titration of the blue-colored 1:1 Pb(II)-Arsenazo III (AAIII) complex with the polyazacarboxylate macrocyclic ligand in the concentration range of 0-2.5 μM, wherein color change occurring upon transchelation of the Pb(II) from the AAIII to the polyazamacrocyclic ligand is monitored at 656 nm. The assay is performed at ambient temperature within 20 min without any interfering interaction between the protein and Pb(II)-AA(III) complex. Thus, this method also provides a ligand-to-protein ratio (L/P ratio) that reflects the effective number of ligands per protein molecule available to radiolabeling. The method is not suitable for 14-membered TETA macrocycle (2-[4-nitrobenzyl]-1, 4, 8, 11-tetraazacyclotetradecane N,N',N'',N'''-tetraacetic acid) because of low stability constant of Pb(II)-TETA complex. The method is rapid, simple and may be customized for other polyazacarboxylate macrocyclic ligands

The formation of electronically excited fragments by the electron impact of furan and related five-membered heterocycles

International Nuclear Information System (INIS)

Tokue, Ikuo; Ikarashi, Masami; Takizawa, Sadachika; Ito, Yoshio

1983-01-01

In the wavelength region of 200-600 nm, photoemissions from electronically excited H, CH, C 2 , and CS (only from thiophene and tetrahydrothiophene) were observed when furan, tetrahydrofuran, thiophene, and tetrahydrothiophene were excited by electron impact (0-70 eV). Hydrogen atoms (n = 4) and CH(A 2 Δ) radicals were produced from these five-membered heterocycles via single collision excitations, while CS(A 1 PI) radicals from thiophene and tetrahydrothiophene were partly formed in secondary processes. The appearance potentials for the hydrogen Balmer β and the CH(A 2 Δ-X 2 PI) bands from these five-membered heterocycles are determined, and the dissociation processes forming H(n = 4) and CH(A) are discussed. (author)

Divergent Reactivity of Rhodium(I) Carbenes Derived from Indole Annulations.

Science.gov (United States)

Li, Xiaoxun; Li, Hui; Song, Wangze; Tseng, Po-Sen; Liu, Lingyan; Guzei, Ilia A; Tang, Weiping

2015-10-26

Rhodium(I) carbenes were generated from propargylic alcohol derivatives as the result of a dehydrative indole annulation. Depending on the choice of the electron-withdrawing group on the aniline nitrogen nucleophile, either a cyclopropanation product or dimerization product was obtained chemoselectively. Intramolecular hydroamidation occurred for the same type of propargylic alcohol derivatives when other transition-metal catalysts were employed. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Dirhodium(II Carbenes : The Chiral Product Cascade

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Gregory H. P. Roos

2000-12-01

Full Text Available The last decade has witnessed enormous growth in the spectrum of highly efficient asymmetric synthetic transformations. One prominent example of this progress is the application of dirhodium (II carbenes generated from diazo- precursors. Innovative construction of ‘designer’ catalysts has played a integral role in extending the breadth of the synthetic cascade of non-racemic products now available through the range of cyclopropanation, C-X insertion, aromatic cycloaddition-rearrangement, and ylide-based reaction types. This review deals briefly with an overview of the important catalytic systems and maintains as its primary focus the cascade of diverse optically enriched products that flow from their applications.

On the behaviour of biradicaloid [P(μ-NTer)]2 towards Lewis acids and bases.

Science.gov (United States)

Hinz, Alexander; Schulz, Axel; Villinger, Alexander

2016-05-07

The well-known diphosphadiazane-1,3-diyl [P(μ-NTer)]2 (Ter = 2,6-bis(2,4,6-trimethyl-phenyl)-phenyl) was treated with Lewis bases such as N-heterocyclic carbenes and Lewis acids e.g. gold(i) chloride complexes. In the reaction with the Lewis base, fragmentation of the P2N2 framework was observed, yielding a salt of the type [(NHC)2P](+)[(TerN)2P](-) in a clean reaction. The reaction of [P(μ-NTer)]2 with gold(i) chloride afforded 1 : 1 and 1 : 2 complexes. The dinuclear complex [(ClAu)2P(μ-NTer)2P] displays a bridging P atom between both gold centers, as has been observed for P based zwitterions.

The use of phosphite-type ligands in the Ir-catalyzed asymmetric hydrogenation of heterocyclic compounds.

Science.gov (United States)

Lyubimov, Sergey E; Ozolin, Dmitry V; Ivanov, Pavel Yu; Melman, Artem; Velezheva, Valeriya S; Davankov, Vadim A

2014-01-01

A series of chiral phosphite-type ligands was tested in asymmetric Ir-catalyzed hydrogenation of quinolines and 2,4,5,6-tetrahydro-1H-pyrazino(3,2,1-j,k)carbazole. Hydrogenation of quinaldine hydrochloride provided superior enantioselectivity up to 65% ee compared to quinaldine free base. The ligands were tested for the first time in the asymmetric Ir-Ircatalyzed hydrogenation of 2,4,5,6-tetrahydro-1H-pyrazino(3,2,1-j,k)carbazole yielding the antidepressant drug, pirlindole. © 2013 Wiley Periodicals, Inc.

Chemistry of Iron N -heterocyclic carbene complexes: Syntheses, structures, reactivities, and catalytic applications

KAUST Repository

Riener, Korbinian; Haslinger, Stefan; Raba, Andreas; Hogerl, Manuel Peter; Cokoja, Mirza; Herrmann, Wolfgang A.; Kü hn, Fritz

2014-01-01

Iron is the most abundant transition metal in Earth's crust. It is relatively inexpensive, not very toxic, and environmentally benign. Undoubtedly, due to the involvement in a multitude of biological processes, which heavily rely on the rich

Reductive Coupling of Carbon Monoxide in a Rhenium Carbonyl Complex with Pendant Lewis Acids

OpenAIRE

Miller, Alexander J. M.; Labinger, Jay A.; Bercaw, John E.

2008-01-01

Phosphinoborane ligands impart unique reactivity to a rhenium carbonyl cation relative to simple phosphine complexes. Addition of either triethylborohydride or a platinum hydride (that can be formed from H2) forms a rhenium boroxycarbene. This carbene, which crystallizes as a dimer, disproportionates over a period of days to afford the starting cation and a structurally unprecedented boroxy(boroxymethyl)carbene, in which a new C−C bond has been formed between two reduced CO ligands. This prod...

Kinetics of molybdenum(6) complexation with o,o'-dihydroxyazo compounds or heterocyclic azo compounds in the presence of hydroxylamine

International Nuclear Information System (INIS)

Kochelaeva, G.A.; Degtyarev, M.Yu.; Ivanov, V.M.; Prokhorova, G.V.; Figurovskaya, V.N.

1999-01-01

The kinetics of complexation in the system molybdenum(6)-azo compound-hydroxylamine was studied. Azo compounds of the types o,o'-dihydroxyazo compounds, such as Lyumogallion IREA and Magneson IREA, and heterocyclic azo compounds, such as 4-(2-pyridylazo)resorcinol and 2-(5-bromo-2-pyridylazo)-5-diethylaminophenol, were studied. The formation of mixed-ligand complexes with the ratio of component 1 : 1 : 1 was detected. Rate constants, activation energies, and stability constants of the forming compounds were evaluated. It was concluded that the reagents under study are promising for the analytical chemistry of molybdenum [ru

Sigma receptor ligand N,N'-di-(ortho-tolyl)guanidine inhibits release of acetylcholine in the guinea pig ileum.

Science.gov (United States)

Cambell, B G; Keana, J F; Weber, E

1991-11-26

The inhibition of stimulated contractions of the guinea pig ileum longitudinal muscle/myenteric plexus preparation by sigma receptor ligands has been previously described. In this study, the stimulated release of [3H]acetylcholine from cholinergic nerve terminals in this same preparation was monitored in the presence and absence of sigma receptor ligands. N,N'-Di-(orthotolyl)guanidine (DTG) and other compounds selective for the sigma receptor inhibited stimulated [3H]acetylcholine release. These results suggest that their inhibition of stimulated contractions in this preparation was mediated by inhibition of acetylcholine release.

Carbene Chemistry. I. Stereochemical Integrity at C Alpha in Ketone Tosylhydrazones. II. Hydrogen Migration in 2-Carbena-6,6-Dimethylnorbornane.

Science.gov (United States)

1978-02-01

H20, 10% Na2 CO3 , H20, and dried over MqSO 4 . Yields were typically ca. 75%. "! 33 CARBENE CHEMISTRY PART II. HYDROGEN MIGRATION IN 2-CARBENA-6,6...any a delocaliza- tion. Thus if one assumes a single product determining intermediate, carbene 54 is classical in the usual sense of the word. It has...placed in a refrigerator. The crystalline product was re- crystallized from methanol-O-d/D20 yielding purified tosylhydrazone with mp 156-1580. 58

Heterocyclic Dications as a New Class of Telomeric G-Quadruplex Targeting Agents

Science.gov (United States)

Nanjunda, Rupesh; Musetti, Caterina; Kumar, Arvind; Ismail, Mohamed A.; Farahat, Abdelbasset A.; Wang, Siming; Sissi, Claudia; Palumbo, Manlio; Boykin, David W.; Wilson, W. David

2013-01-01

Small molecules that can induce and stabilize G-quadruplex DNA structures represent a novel approach for anti-cancer and anti-parasitic therapy and extensive efforts have been directed towards discovering lead compounds that are capable of stabilizing quadruplexes. The purpose of this study is to explore conformational modifications in a series of heterocyclic dications to discover structural motifs that can selectively bind and stabilize specific G-quadruplexes, such as those present in the human telomere. The G-quadruplex has various potential recognition sites for small molecules; however, the primary interaction site of most of these ligands is the terminal tetrads. Similar to duplex-DNA groove recognition, quadruplex groove recognition by small molecules offers the potential for enhanced selectivity that can be developed into a viable therapeutic strategy. The compounds investigated were selected based on preliminary studies with DB832, a bifuryl-phenyl diamidine with a unique telomere interaction. This compound provides a paradigm that can help in understanding the optimum compound-DNA interactions that lead to quadruplex groove recognition. DNA recognition by the DB832 derivatives was investigated by biophysical experiments such as thermal melting, circular dichroism, mass spectrometry and NMR. Biological studies were also performed to complement the biophysical data. The results suggest a complex binding mechanism which involves the recognition of grooves for some ligands as well as stacking at the terminal tetrads of the human telomeric G-quadruplex for most of the ligands. These molecules represent an excellent starting point for further SAR analysis for diverse modes of quadruplex recognition and subsequent structure optimization for drug development. PMID:22380518

N6-Benzyladenosine Derivatives as Novel N-Donor Ligands of Platinum(II Dichlorido Complexes

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Ján Vančo

2013-06-01

Full Text Available The platinum(II complexes trans-[PtCl2(Ln2]∙xSolv 1–13 (Solv = H2O or CH3OH, involving N6-benzyladenosine-based N-donor ligands, were synthesized; Ln stands for N6-(2-methoxybenzyladenosine (L1, involved in complex 1, N6-(4-methoxy-benzyladenosine (L2, 2, N6-(2-chlorobenzyladenosine (L3, 3, N6-(4-chlorobenzyl-adenosine (L4, 4, N6-(2-hydroxybenzyladenosine (L5, 5, N6-(3-hydroxybenzyl-adenosine (L6, 6, N6-(2-hydroxy-3-methoxybenzyladenosine (L7, 7, N6-(4-fluoro-benzyladenosine (L8, 8, N6-(4-methylbenzyladenosine (L9, 9, 2-chloro-N6-(3-hydroxy-benzyladenosine (L10, 10, 2-chloro-N6-(4-hydroxybenzyladenosine (L11, 11, 2-chloro-N6-(2-hydroxy-3-methoxybenzyladenosine (L12, 12 and 2-chloro-N6-(2-hydroxy-5-methylbenzyladenosine (L13, 13. The compounds were characterized by elemental analysis, mass spectrometry, IR and multinuclear (1H-, 13C-, 195Pt- and 15N- and two-dimensional NMR spectroscopy, which proved the N7-coordination mode of the appropriate N6-benzyladenosine derivative and trans-geometry of the title complexes. The complexes 1–13 were found to be non-toxic in vitro against two selected human cancer cell lines (HOS and MCF7; with IC50 > 50.0 µM. However, they were found (by ESI-MS study to be able to interact with the physiological levels of the sulfur-containing biogenic biomolecule L-methionine by a relatively simple 1:1 exchange mechanism (one Ln molecule was replaced by one L-methionine molecule, thus forming a mixed-nitrogen/sulfur-ligand dichlorido-platinum(II coordination species.

Utilization of mixed ligands to construct diverse Ni(II)-coordination polymers based on terphenyl-2,2′,4,4′-tetracarboxylic acid and varied N-donor co-ligands

Energy Technology Data Exchange (ETDEWEB)

Wang, Chao [College of Materials and Chemical Engineering, Key Laboratory of Inorganic Nonmetallic Crystalline and Energy Conversion Materials, Hubei Provincial Collaborative Innovation Center for New Energy Microgrid, China Three Gorges University, Yichang 443002 (China); Zhao, Jun, E-mail: junzhao08@126.com [College of Materials and Chemical Engineering, Key Laboratory of Inorganic Nonmetallic Crystalline and Energy Conversion Materials, Hubei Provincial Collaborative Innovation Center for New Energy Microgrid, China Three Gorges University, Yichang 443002 (China); State Key Laboratory of Structural Chemistry, Fujian Institute of Research on the Structure of Matter, Chinese Academy of Sciences, Fuzhou, Fujian 35002 (China); Xia, Liang [College of Materials and Chemical Engineering, Key Laboratory of Inorganic Nonmetallic Crystalline and Energy Conversion Materials, Hubei Provincial Collaborative Innovation Center for New Energy Microgrid, China Three Gorges University, Yichang 443002 (China); State Key Laboratory of Structural Chemistry, Fujian Institute of Research on the Structure of Matter, Chinese Academy of Sciences, Fuzhou, Fujian 35002 (China); Wu, Xue-Qian; Wang, Jian-Fang; Dong, Wen-Wen; Wu, Ya-Pan [College of Materials and Chemical Engineering, Key Laboratory of Inorganic Nonmetallic Crystalline and Energy Conversion Materials, Hubei Provincial Collaborative Innovation Center for New Energy Microgrid, China Three Gorges University, Yichang 443002 (China)

2016-06-15

Three new coordination polymers, namely, {[Ni(H_2L)(bix)(H_2O)_2]·2h_2O}{sub n} (1), {[Ni(HL)(Hdpa)(H_2O)_2]·H_2O}{sub n} (2), {[Ni(L)_0_._5(bpp)(H_2O)]·H_2O}{sub n} (3) (H{sub 4}L=terphenyl-2,2′,4,4′-tetracarboxylic acid; bix=1,4-bis(imidazol-1-ylmethyl)benzene; dpa =4,4′-dipyridylamine; bpp=1,3-bis(4-pyridyl)propane), based on rigid H{sub 4}L ligand and different N-donor co-ligands, have been synthesized under hydrothermal conditions. Compound 1 features a 3D 4-connected 6{sup 6}-dia-type framework with H{sub 4}L ligand adopts a μ{sub 2}-bridging mode with two symmetry-related carboxylate groups in μ{sub 1}-η{sup 1}:η{sup 0} monodentate mode. Compound 2 displays a 1D [Ni(HL)(Hdpa)]{sub n} ribbon chains motif, in which the H{sub 4}L ligand adopts a μ{sub 2}-bridging mode with two carboxylate groups in μ{sub 1}-η{sup 1}:η{sup 1} and μ{sub 1}-η{sup 1}:η{sup 0} monodentate modes, while 3 possesses a (4,4)-connected 3D frameworks with bbf topology, with H{sub 4}L ligand displays a μ{sub 4}-bridging coordination mode. The H{sub 4}L ligand displays not only different deprotonated forms but also diverse coordination modes and conformations. The structural diversities among 1–3 have been carefully discussed, and the roles of N-donor co-ligands in the self-assembly of coordination polymers have been well documented. - Graphical abstract: Three nickel coordination polymers with different architectures based on mixed ligand system were synthesized and structurally characterized. Topology analyses indicate that 1 shows the 4-connected 6{sup 6}-dia net, 1D ribbon chains for 2 and 3D (4,4)-connected bbf network for 3. Display Omitted - Highlights: • Three Ni-based coordination polymers with distinct features have been prepared. • Compound 1 features a 3D 4-connected 66-dia-type framework, 2 displays a 1D [Ni(HL)(Hdpa)]{sub n} ribbon chains motif, while 3 possesses a (4,4)-connected 3D frameworks with bbf topology. • The “mixed ligand assembled�

Diverse Cd(II) compounds based on N-benzoyl-L-glutamic acid and N-donor ligands: Structures and photoluminescent properties

International Nuclear Information System (INIS)

Ma, Ning; Guo, Wei-Ying; Song, Hui-Hua; Yu, Hai-Tao

2016-01-01

Five new Cd(II) coordination polymers with N-benzoyl-L-glutamic acid (H_2bzgluO) and different N-donor ligands, [Cd(bzgluO)(2,2′-bipy)(H_2O)]_n (1), [Cd(bzgluO)(2,4′-bipy)_2(H_2O)·3H_2O]_n (2), [Cd(bzgluO)(phen)·H_2O]_n (3), [Cd(bzgluO)(4,4′-bipy)(H_2O)]_n (4), [Cd(bzgluO)(bpp)(H_2O)·2H_2O]_n (5) were synthesized (2,2′-bipy=2,2′-bipyridine, 2,4′-bipy=2,4′-bipyridine, phen=1,10-phenanthroline, 4,4′-bipy=4,4′-bipyridine, bpp=1,3-di(4-pyridyl)propane). Compounds 1–2 exhibit a 1D single-chain structure. Compound 1 generates a 2D supramolecular structure via π–π stacking and hydrogen bonding, 3D architecture of compound 2 is formed by hydrogen bonding. Compound 3 features a 1D double-chain structure, which are linked by π–π interactions into a 2D supramolecular layer. Compounds 4-5 display a 2D network structure. Neighboring layers of 4 are extended into a 3D supramolecular architecture through hydrogen bonding. The structural diversity of these compounds is attributed to the effect of ancillary N-donor ligands and coordination modes of H_2bzgluO. Luminescent properties of 1–5 were studied at room temperature. Circular dichroism of compounds 1, 2 and 5 were investigated. - Graphical abstract: Five new Cd(II) metal coordination compounds with H_2bzgluO and different N-donor ligands were synthesized and characterized. Compounds 1, 2 and 3 present 1D structures, compounds 4 and 5 display 2D networks. Results indicate that auxiliary ligands and coordination modes of H_2bzgluO play an important role in governing the formation of final frameworks, and the hydrogen-bonding and π–π stacking interactions contribute the formation of the diverse supramolecular architectures. Furthermore, the different crystal structures influence the emission spectra significantly. - Highlights: • It is rarely reported that complexes prepared with N-benzoyl-L-glutamic acid. • Each complex displays diverse structures and different supramolecular

Heterocyclic aramid nanoparticle-assisted graphene exfoliation for fabrication of pristine graphene-based composite paper

Energy Technology Data Exchange (ETDEWEB)

Mo, Yao; Liu, Qi; Fan, Jinchen, E-mail: Jinchen.fan@shiep.edu.cn; Shi, Penghui; Min, Yulin, E-mail: ahaqmylin@126.com; Xu, Qunjie [Shanghai University of Electric Power, Shanghai Key Laboratory of Materials Protection and Advanced Materials in Electric Power, College of Environmental and Chemical Engineering (China)

2015-07-15

Mechanically strong, electrically conductive, and flexible pristine graphene-based composite paper was prepared based on heterocyclic aramid nanoparticle-assisted liquid-phase exfoliation of graphite. The macroscopic heterocyclic aramid yarns were split and assembled into heterocyclic aramid nanoparticles with the size of ∼30 nm by deprotonation in dimethylsulfoxide in the presence of potassium hydroxide. The obtained heterocyclic aramid nanoparticles dimethylsulfoxide dispersion was used as good medium solvent for highly efficiency liquid-phase exfoliation of graphite. The results demonstrated that the concentration of exfoliated graphene can facile reaches ∼2.72 mg/mL after direct sonication of 7 h with assist of heterocyclic aramid nanoparticles. After exfoliation, the self-assembled pristine graphene-based composite paper was fabricated by vacuum-assisted filtration. Due to the introduction of heterocyclic aramid nanoparticles, the self-assembled pristine graphene/heterocyclic aramid nanoparticles composite paper exhibited good mechanical property with tensile strength of ∼129.7 MPa, meantime, has a high electrical conductivity of ∼1.42 × 10{sup 4} S/m.

Heterocyclic aramid nanoparticle-assisted graphene exfoliation for fabrication of pristine graphene-based composite paper

International Nuclear Information System (INIS)

Mo, Yao; Liu, Qi; Fan, Jinchen; Shi, Penghui; Min, Yulin; Xu, Qunjie

2015-01-01

Mechanically strong, electrically conductive, and flexible pristine graphene-based composite paper was prepared based on heterocyclic aramid nanoparticle-assisted liquid-phase exfoliation of graphite. The macroscopic heterocyclic aramid yarns were split and assembled into heterocyclic aramid nanoparticles with the size of ∼30 nm by deprotonation in dimethylsulfoxide in the presence of potassium hydroxide. The obtained heterocyclic aramid nanoparticles dimethylsulfoxide dispersion was used as good medium solvent for highly efficiency liquid-phase exfoliation of graphite. The results demonstrated that the concentration of exfoliated graphene can facile reaches ∼2.72 mg/mL after direct sonication of 7 h with assist of heterocyclic aramid nanoparticles. After exfoliation, the self-assembled pristine graphene-based composite paper was fabricated by vacuum-assisted filtration. Due to the introduction of heterocyclic aramid nanoparticles, the self-assembled pristine graphene/heterocyclic aramid nanoparticles composite paper exhibited good mechanical property with tensile strength of ∼129.7 MPa, meantime, has a high electrical conductivity of ∼1.42 × 10 4  S/m.

Antiferromagnetic Coupling in the Polynuclear Compound [Cu(II) (Allopurinolate) (OH-)] n

Science.gov (United States)

Acevedo-Chávez, Rodolfo; Costas, María. Eugenia; Escudero-Derat, Roberto

1994-11-01

Synthetic, spectral, and magnetic studies of the Cu(II) polynuclear coordination compound [Cu(HL(OH-)]n with bridging OH- and HL (allopurinolate; C5H3N4O-) ligands are reported. The compound is obtained from aqueous media (at several pH values and from CI-, Br-, NO-3, SO2-4, ClO-4, and CH3CO-2 Cu(II) salts), from DMSO at ca. 70°C using several of the above salts, and under refluxing methanol employing Cu(SO4) or Cu(CH3CO2)2. The results suggest that the compound [Cu(HL)(OH-)]n has a polynuclear form in which the bridging allopurinolate is coordinated through the N(1) and N(2) atoms of the pyrazolic moiety. All attempts to grow crystals suitable for X-ray studies were unsuccessful, and an amorphous compound was always obtained. Magnetic studies show the existence of a strong antiferromagnetic coupling, which may be associated with a favorable structural arrangement between the metallic centers and the bridging ligands. This magnetic behavior is remarkable for a Cu(II) polynuclear coordination compound. Spectral and magnetic results together with the coordination modes of the bridging groups let us postulate as a possible arrangement a cyclic polynuclear structure presenting the allopurinolate and OH- bridging ligands in a mutually trans configuration. This work is the first EPR spectral and magnetic study reported for a coordination compound with the allopurinol heterocycle as a ligand and, thus for the first example of a polynuclear coordination compound combining allopurinolate and OH- as bridging groups.

Gold-catalyzed heterocyclizations in alkynyl- and allenyl-β-lactams

Directory of Open Access Journals (Sweden)

Pedro Almendros

2011-05-01

Full Text Available New gold-catalyzed methods using the β-lactam scaffold have been recently developed for the synthesis of different sized heterocycles. This overview focuses on heterocyclization reactions of allenic and alkynic β-lactams which rely on the activation of the allene and alkyne component. The mechanism as well as the regio- and stereoselectivity of the cyclizations are also discussed.

Blue-emitting dinuclear N-heterocyclic dicarbene gold(I) complex featuring a nearly unit quantum yield

KAUST Repository

Baron, Marco

2012-02-06

Dinuclear N-heterocyclic dicarbene gold(I) complexes of general formula [Au 2(RIm-Y-ImR) 2](PF 6) 2 (R = Me, Cy; Y = (CH 2) 1-4, o-xylylene, m-xylylene) have been synthesized and screened for their luminescence properties. All the complexes are weakly emissive in solution whereas in the solid state some of them show significant luminescence intensities. In particular, crystals or powders of the complex with R = Me, Y = (CH 2) 3 exhibit an intense blue emission (λ max = 450 nm) with a high quantum yield (Φ em = 0.96). The X-ray crystal structure of this complex is characterized by a rather short intramolecular Au•••Au distance (3.272 Ǻ). Time dependent density functional theory (TDDFT) calculations have been used to calculate the UV/vis properties of the ground state as well as of the first excited state of the complex, the latter featuring a significantly shorter Au•••Au distance. © 2012 American Chemical Society.

Synthesis and catalytic activity of N-heterocyclic silylene (NHSi) cobalt hydride for Kumada coupling reactions.

Science.gov (United States)

Qi, Xinghao; Sun, Hongjian; Li, Xiaoyan; Fuhr, Olaf; Fenske, Dieter

2018-02-20

The electron-rich silylene Co(i) chloride 5 was obtained through the reaction of CoCl(PMe 3 ) 3 with chlorosilylene. Complex 5 reacted with 1,3-siladiazole HSiMe(NCH 2 PPh 2 ) 2 C 6 H 4 to give the silylene Co(iii) hydride 6 through chelate-assisted Si-H activation. To the best of our knowledge, complex 6 is the first example of Co(iii) hydride supported by N-heterocyclic silylene. Complexes 5 and 6 were fully characterized by spectroscopic methods and X-ray diffraction analysis. Complex 6 was used as an efficient precatalyst for Kumada cross-coupling reactions. Compared with the related complex 3 supported by only trimethylphosphine, complex 6 as a catalyst supported by both chlorosilylene and trimethylphosphine exhibits a more efficient performance for the Kumada cross-coupling reactions. A novel catalytic radical mechanism was suggested and experimentally verified. As an intermediate silylene cobalt(ii) chloride 6d was isolated and structurally characterized.