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1

Olefin Metathesis With Ruthenium-Arene Catalysts Bearing N-Heterocyclic Carbene Ligands  

Science.gov (United States)

In this chapter, we summarize the main results of our investigations on the ring-opening metathesis polymerization (ROMP) of cyclooctene catalyzed by various ruthenium (Ru)-arene complexes bearing imidazolin-2-ylidene, imidazolidin- 2-ylidene, or triazolin-5-ylidene ligands. Three major findings emerged from this study. First, we underscored the intervention of a photochemical activation step due to visible light illumination. Second, we established that the presence of an endocyclic double bond in the carbene ligand central heterocycle was not crucial to achieve high catalytic efficiencies. Third, we demonstrated that ortho-metallation of the N-heterocyclic carbene (NHC) ligand by the Ru center led to inactive catalysts.

Delaude, Lionel; Demonceau, Albert

2

Photoluminescent organoplatinum (II) complexes containing N-heterocyclic carbene (NHC) ligands  

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?The syntheses, structures, photophysical properties and applications of three types of photoluminescent organoplatinum(II) complexes containing N-heterocyclic carbene (NHC) ligands are described. The tetradentate dianionic bis(phenolate-NHC) type ligands provide a superior scaffold for constructing thermally stable and efficient deep-blue phosphorescent Pt(II) complexes with ?max of ~440-460 nm and solid-state emission quantum yields of ~30%. Highly efficient blue OLEDs with CIEx, y o...

Li, Kai; ??

2013-01-01

3

Catalysts containing n-heterocyclic carbenes as ligands: properties, syntheses, applications and comparison with other catalysts  

International Nuclear Information System (INIS)

N-heterocyclic carbenes (NHCs) have become of considerable importance in modern organometallic chemistry and homogeneous catalysis. There are several advantages in the use NHCs over their phosphorus analogues, which explains the enormous development of NHC ligands in the field of organometallic catalysis in the past few years. In this article, we present an overview of the importance of the catalysts containing NHC ligands, their synthesis, some pertinent synthetic applications, and a brief comparison with other catalysts. (author)

4

T-Shaped Platinum(II) Complexes Stabilised by Bulky N-Heterocyclic Carbene Ligands  

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Pt to a T! Treating bulky N-heterocyclic carbene (NHC) ligands with [PtMe3I]4 results in rapid elimination of ethene and formation of [PtMeI(NHC)2] complexes. These complexes are suitable materials for the synthesis of T-shaped platinum(II) complexes stabilised by agostic interactions. X-ray structure determination of one of these complexes shows a rather long ? agostic interaction.

Rivada-wheelaghan, Orestes; Donnadieu, Bruno; Maya, Celia; Conejero Iglesias, Salvador

2010-01-01

5

Functionalised N-heterocyclic carbene complexes  

CERN Document Server

N-heterocyclic carbenes (NHCs) have found increasing use as reagents for a range of organic transformations and in asymmetric organocatalysis. The performance of these molecules can be improved and tuned by functionalisation. Functionalised carbenes can anchor free carbenes to the metal site, introduce hemilability, provide a means to immobilise transition metal carbene catalysts, introduce chirality, provide a chelate ligand or bridge two metal centres. NHC can be attached to carbohydrates and campher, derived from amino acids and purines, they can be used as organocatalysts mimicking vitamin

Kühl, Olaf

2010-01-01

6

Synthesis and biological assays on cancer cells of dinuclear gold complexes with novel functionalised di(N-heterocyclic carbene) ligands.  

Science.gov (United States)

New dinuclear di(N-heterocyclic carbene) silver(I), gold(I) and gold(III) complexes have been synthesised and their antiproliferative effects towards various cancer cell lines have been screened. The di(N-heterocyclic carbene) ligands have a propylene linker between the carbene moieties and the imidazole backbone has been functionalised with a 1-benzyl- or 1-PEG-1,2,3-triazole ring (PEG=poly(ethylene glycol)) via a CuAAC (copper azido alkyne cycloaddition) reaction. The resulting gold(I) and gold(III) complexes display an antiproliferative activity superior to that of the unfunctionalised pristine complexes together with a higher selectivity towards cancerous cells with respect to healthy cells. PMID:25226437

Baron, Marco; Bellemin-Laponnaz, Stéphane; Tubaro, Cristina; Basato, Marino; Bogialli, Sara; Dolmella, Alessandro

2014-12-01

7

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

Directory of Open Access Journals (Sweden)

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

?lknur Özdemir

2010-03-01

8

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

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

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

2010-01-01

9

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

Science.gov (United States)

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

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

2014-10-20

10

Photophysical properties of trans-platinum acetylide complexes featuring N-heterocyclic carbene ligands.  

Science.gov (United States)

A series of trans-N-heterocyclic carbene (NHC) platinum(ii) acetylide complexes of the form (ICy)2Pt(R)2 (where ICy = 1,3-bis-(cyclohexyl)imidazol-2-ylidene and R = 1-Ethynyl-4-(phenylethynyl)benzene (PE2), 2-(9,9-Diethyl-9H-fluoren-7-yl)benzo[d]thiazole (BTF), and 9,9-Diethyl-7-ethynyl-N,N-diphenyl-9H-fluoren-2-amine (DPAF), respectively), were synthesized via Hagihara reaction of the unprotected aryl-acetylide ligands with trans-(ICy)2PtCl2 () in 47-73% yield. Precursor was generated in a one-pot synthesis via formation of a silver carbene precursor followed by transmetallation, and was obtained in high yield (95%). The single-crystal X-ray structures of , were determined and analyzed. The photophysical properties of were compared to their respective tributyl phosphine (PBu3) analogues. The optical properties of the series were studied by UV-Vis spectroscopy, photoluminescence spectroscopy, nanosecond transient absorption spectroscopy, and open aperture nanosecond z-scan. Coupling of the organic chromophores to the platinum center affords efficient intersystem crossing as concluded by the complexes' low fluorescence quantum yields, efficient phosphorescence and intense T1 - Tn absorption. Open aperture z-scan with 606 nm, 10 ns laser pulses showed comparable optical attenuation relative to a standard sample of (PBu3)2Pt(DPAF)2 (). Pulse limiting was achieved via a dual-mechanism of two-photon absorption (2PA) coupled with excited-state absorption (ESA). TD-DFT Computations were also employed for to give greater insight into the nature of the singlet-singlet electronic transitions. PMID:25019204

Winkel, Russell W; Dubinina, Galyna G; Abboud, Khalil A; Schanze, Kirk S

2014-11-12

11

N,N'-dialkyl- and N-alkyl-N-mesityl-substituted N-heterocyclic carbenes as ligands in Grubbs catalysts.  

Science.gov (United States)

Various symmetrically and asymmetrically substituted N-heterocyclic carbene (NHC) ligands bearing aliphatic nitrogen-containing side groups have been synthesised. In our attempts to isolate the corresponding second-generation Grubbs catalysts, we were unsuccessful when using the symmetrical aliphatic NHC ligands. For the asymmetrical ligands bearing an aliphatic moiety on one side and an aromatic mesityl group on the other side, substitution of a phosphine ligand was achieved. The performance of a so-formed series of Ru-based metathesis initiators has been evaluated for the ring-opening metathesis polymerisation (ROMP) of cycloocta-1,5-diene and the ring-closing metathesis (RCM) of diethyl diallylmalonate. PMID:16538690

Ledoux, Nele; Allaert, Bart; Pattyn, Siegfried; Vander Mierde, Hans; Vercaemst, Carl; Verpoort, Francis

2006-06-01

12

An N-Heterocyclic Carbene as a Bidentate Hemilabile Ligand: A Synchrotron X-ray Diffraction and Density Functional Theory Study  

International Nuclear Information System (INIS)

The N-heterocyclic carbene ligand IMes was shown by synchrotron crystallography and DFT computations to adopt a hemilabile bidentate coordination mode in CpM(CO)2(IMes)+B(C6F5)4- (M = Mo, W), with a C=C bond of one mesityl weakly coordinated to the metal.

13

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

Science.gov (United States)

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

Cooke, Jason; Lightbody, Owen C.

2011-01-01

14

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

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

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

2013-01-01

15

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

International Nuclear Information System (INIS)

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

16

Solvent-dependent switch of ligand donor ability and catalytic activity of ruthenium(II) complexes containing pyridinylidene amide (PYA) N-heterocyclic carbene hybrid ligands.  

Science.gov (United States)

Chelating ligands incorporating both N-[1-alkylpyridin-4(1H)-ylidene]amide (PYA) and N-heterocyclic carbene (NHC) donor sites were prepared and used for the synthesis of ruthenium(II) complexes. Cyclic voltammetry, NMR, and UV-vis spectroscopy of the complexes indicate a solvent-dependent contribution of the limiting resonance structures associated with the ligand in solution. The neutral pyridylidene imine structure is more pronounced in apolar solvents (CH2Cl2), while the mesoionic pyridinium amide form is predominant in polar solvents (MeOH, DMSO). The distinct electronic properties of these hybrid PYA-NHC ligands in different solvents have a direct influence on the catalytic activity of the ruthenium center, e.g., in the dehydrogenation of benzyl alcohol to benzaldehyde. The activity in different solvents qualitatively correlates with the solvent permittivity. PMID:25046249

Leigh, Vivienne; Carleton, Daniel J; Olguin, Juan; Mueller-Bunz, Helge; Wright, L James; Albrecht, Martin

2014-08-01

17

Noninnocent behavior of ancillary ligands: apparent trans coupling of a saturated N-heterocyclic carbene unit with an ethyl ligand mediated by nickel.  

Science.gov (United States)

Oxidative addition of the tridentate N-heterocyclic carbene (NHC) diphosphine ligand precursor ([PCP]H)PF(6) (1) {[PCP] = o-(i)Pr(2)PC(6)H(4)(NC(3)H(4)N)o-C(6)H(4)P(i)Pr(2)} to Ni(COD)(2) results in the formation of the nickel(II) hydride complex ([PCP]NiH)PF(6) (2). This hydride undergoes a rapid reaction with ethylene to generate a nickel(0) complex in which an ethyl group has been transferred to the carbene carbon of the original NHC-diphosphine ligand. If the first intermediate is the anticipated square-planar nickel(II) ethyl species, then the formation of the product would require a process that involves a trans C-C coupling of the NHC carbon and a presumed Ni-ethyl intermediate. Deuterium-labeling studies provide evidence for migratory insertion of the added ethylene into the Ni-H bond rather than into the Ni-carbene linkage; this is based on the observed deuterium scrambling, which requires reversible beta-elimination, alkene rotation, and hydride readdition. However, density functional theory studies suggest that a key intermediate is an agostic ethyl species that has the Ni-C bond cis to the NHC unit. A possible transition state containing two cis-disposed carbon moieties was also identified. Such a process represents a new pathway for catalyst deactivation involving NHC-based metal complexes. PMID:19585991

Steinke, Tobias; Shaw, Bryan K; Jong, Howard; Patrick, Brian O; Fryzuk, Michael D; Green, Jennifer C

2009-08-01

18

Nickel-catalyzed enantio- and diastereoselective three-component coupling of 1,3-dienes, aldehydes, and silanes using chiral N-heterocyclic carbenes as ligands.  

Science.gov (United States)

Nickel(0)-catalyzed asymmetric three-component coupling of 1,3-dienes, aldehydes, and silanes has been realized utilizing a chiral N-heterocyclic carbene as a ligand. On the basis of the screening of various NHC precursors, an imidazolium salt having 1-(2,4,6-trimethylphenyl)propyl groups on the nitrogen was designed and synthesized. In this reaction, various coupling products were produced in good yields with high regio-, diastereo- (anti selective in the case of the internal 1,3-diene), and enantioselectivities (up to 97% ee). PMID:18020355

Sato, Yoshihiro; Hinata, Yu; Seki, Reiko; Oonishi, Yoshihiro; Saito, Nozomi

2007-12-20

19

Conformations of N-Heterocyclic Carbene Ligands in Ruthenium Complexes Relevant to Olefin Metathesis  

Science.gov (United States)

The structure of ruthenium-based olefin metathesis catalyst 3 and model ?-complex 5 in solution and in the solid state are reported. The N-tolyl ligands, due to their lower symmetry than the traditional N-mesityl substituents, complicate this analysis, but ultimately provide explanation for the enhanced reactivity of 3 relative to standard catalyst 2. The tilt of the N-tolyl ring provides additional space near the ruthenium center, which is consistent with the enhanced reactivity of 3 towards sterically demanding substrates. Due to this tilt, the more sterically accessible face bears the two methyl substituents of the N-aryl rings. These experimental studies are supported by computational studies of these complexes by DFT. The experimental data provides a means to validate the accuracy of the B3LYP and M06 functionals. B3LYP provides geometries that match X-ray crystal structural data more closely, though it leads to slightly less (?0.5 kcal mol?1) accuracy than M06 most likely because it underestimates attractive non-covalent interactions. PMID:19146414

Stewart, Ian C.; Benitez, Diego; O'Leary, Daniel J.; Tkatchouk, Ekaterina; Day, Michael W.; Goddard, William A.; Grubbs, Robert H.

2009-01-01

20

Gold(I) N-heterocyclic carbene complexes with naphthalimide ligands as combined thioredoxin reductase inhibitors and DNA intercalators.  

Science.gov (United States)

Organometallic conjugates consisting of a gold(I) N-heterocyclic carbene (NHC) moiety and a naphthalimide were prepared and investigated as cytotoxic agents that interact with both DNA and the disulfide reductase enzyme thioredoxin reductase (TrxR). The complexes were potent DNA intercalators related to their naphthalimide partial structure, inhibited TrxR as a consequence of the incorporation of the gold(I) moiety, and triggered efficient cytotoxic effects in MCF-7 breast and HT-29 colon adenocarcinoma cells. Strong effects on tumor cell metabolism were noted for the most cytotoxic complex, chlorido[1-(3'-(4''-ethylthio-1'',8''-naphthalimid-N''-yl))-propyl-3-methyl-imidazol-2-ylidene]gold(I) (4?d). In conclusion, the conjugation of naphthalimides with gold(I) NHC moieties provided a useful strategy for the design of bioorganometallic anticancer agents with multiple modes of action. PMID:24803348

Meyer, Andreas; Oehninger, Luciano; Geldmacher, Yvonne; Alborzinia, Hamed; Wölfl, Stefan; Sheldrick, William S; Ott, Ingo

2014-08-01

 
 
 
 
21

Theoretical study on the effect of annelation and carbonylation on the electronic and ligand properties of N-heterocyclic silylenes and germylenes: carbene comparisons begin to break down.  

Science.gov (United States)

Quantum chemical calculations have been carried out to investigate the effect of annelation and carbonylation on the electronic and ligand properties of N-heterocyclic silylenes and germylenes. The thermodynamic stability of these ligands has been found to increase with annelation, while the reverse is true for carbonylation. This is in sharp contrast to N-heterocyclic carbenes (NHCs) where annelation leads to a decrease in their thermodynamic stabilities. Compared to nonannelated derivatives, annelated and carbonylated ones are found to be weaker ? donors but better ? acceptors. The effect of carbonylation is more pronounced than annelation toward increasing the ? acidity of these ligands. Carbonylation at the ?-position with respect to the N atom attached to the Si/Ge center has been found to be the most effective way of enhancing the ? acidity of these ligands. The computed natural charges reveal that electrophilicity increases upon both annelation and carbonylation. The calculated values of (31)P NMR chemical shifts of corresponding phosphinidene adducts of these ligands have been found to correlate well with the ? acidity of these Si/Ge centers. PMID:24738711

Guha, Ankur Kanti; Phukan, Ashwini K

2014-05-01

22

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

Science.gov (United States)

Density functional theory (DFT) calculations were used to predict and rationalize the effect of the modification of the structure of the prototype 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene) N-heterocyclic carbene (NHC) ligand. The modification consists in the substitution of the methyl groups of ortho isopropyl substituent with phenyl groups, and here we plan to describe how such significant changes affect the metal environment and therefore the related catalytic behaviour. Bearing in mind that there is a significant structural difference between both ligands in different 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. PMID:23455458

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

2013-05-28

23

N-Heterocyclic carbene metal complexes: photoluminescence and applications.  

Science.gov (United States)

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

Visbal, Renso; Gimeno, M Concepción

2014-05-21

24

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

DEFF Research Database (Denmark)

Two novel tripodal ligands, (BIMPNMes,Ad,Me)? and (MIMPNMes,Ad,Me)2–, combining two types of donor atoms, namely, NHC and phenolate donors, were synthesized to complete the series of N-anchored ligands, ranging from chelating species with tris(carbene) to tris(phenolate) chelating arms. 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. Zero-field 57Fe Mo?ssbauer spectroscopy of the Fe(II) complexes 3, 4, 8, and 11 shows isomer shifts ? that increase gradually as carbenes are substituted for phenolates in the series of ligands. From the single-crystal structure determinations of the complexes, the different steric demand of the ligands is evident. Particularly, the molecular structure of 1?in which a pyridine molecule is situated next to the Mn–Cl bond?and those of azide complexes 2, 4, and 6 demonstrate the flexibility of these mixed-ligand derivatives, which, in contrast to the corresponding symmetrical TIMENR ligands, allow for side access of, e.g., organic substrates, to the reactive metal center.

Ka?ß, Martina; Hohenberger, Johannes

2014-01-01

25

Synthesis, characterization, and photophysical study of luminescent rhenium(I) diimine complexes with various types of N-heterocyclic carbene ligands.  

Science.gov (United States)

A series of luminescent Re(I) diimine complexes with various types of N-heterocyclic carbene (NHC) ligands has been synthesized through the reaction between isocyano Re(I) diimine complexes with different nucleophiles. These Re(I) NHC complexes were characterized by (1)H and (13)C NMR and IR spectroscopy, mass spectrometry, and elemental analysis. One of the precursor complexes fac-{Re(CO)3[CN(H)C6H4-2-O]2Br} and five of the Re(I) diimine complexes with different types of NHC ligands were also structurally characterized by X-ray crystallography. In the preparation of these Re(I) NHC complexes, it is found that the reactivity of the isocyanide ligands in the synthetic complex precursors is significantly affected by the electronic nature of the trans ligand. All these complexes displayed (3)MLCT [d?(Re) ? ?*(N-N)] phosphorescence in degassed CH2Cl2 and CH3CN solutions at room temperature. Through the study of the photophysical and electrochemical properties of these Re(I) NHC complexes, the electronic properties of different types of NHC ligands were investigated. PMID:24592975

Ng, Chi-On; Yiu, Shek-Man; Ko, Chi-Chiu

2014-03-17

26

Catalysts containing n-heterocyclic carbenes as ligands: properties, syntheses, applications and comparison with other catalysts; Catalisadores contendo carbenos N-Heterociclicos como ligantes: propriedades, sinteses, aplicacoes e comparacao o com outros ligantes  

Energy Technology Data Exchange (ETDEWEB)

N-heterocyclic carbenes (NHCs) have become of considerable importance in modern organometallic chemistry and homogeneous catalysis. There are several advantages in the use NHCs over their phosphorus analogues, which explains the enormous development of NHC ligands in the field of organometallic catalysis in the past few years. In this article, we present an overview of the importance of the catalysts containing NHC ligands, their synthesis, some pertinent synthetic applications, and a brief comparison with other catalysts. (author)

Pastre, Julio Cezar; Correia, Carlos Roque Duarte [Universidade Estadual de Campinas (UNICAMP), Campinas, SP (Brazil). Inst. de Quimica]. E-mail: roque@iqm.unicamp.br

2008-07-01

27

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

Digital Repository Infrastructure Vision for European Research (DRIVER)

N-heterocyclic carbenes (NHCs) have become of considerable importance in modern organometallic chemistry and homogeneous catalysis. There are several advantages in the use NHCs over their phosphorus analogues, which explains the enormous development of NHC ligands in the field of organometallic catalysis in the past few years. In this article, we present an overview of the importance of the catalysts containing NHC ligands, their synthesis, some pertinent synthetic ap...

Julio Cezar Pastre; Carlos Roque Duarte Correia

2008-01-01

28

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

Directory of Open Access Journals (Sweden)

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

Julio Cezar Pastre

2008-01-01

29

Synthesis of Tridentate 2,6-Bis(imino)pyridyl Ruthenium(II) Complexes with N-Heterocyclic Carbene Ligands: Activation of Imidazolium Salts.  

Science.gov (United States)

Low-valent Ru(0) complexes, [?(2)-N3]Ru(?(6)-Ar) (1) or {[N3]Ru}2(?-N2) (2), where Ar = C6H6 or C6H5Me, and [N3] = 2,6-(2,4,6-(CH3)3C6H2N?CCH3)2C5H3N, activate C-H bonds in imidazolium salts to produce bis(imino)pyridyl ruthenium-(imidazolidin-2-ylidene) complexes, [N3]Ru(H)(X)(NHC) (4) (X = halides and tosylate). Formation of 4 is most likely to proceed via C-H oxidative addition, followed by anion coordination, which is expected to be a useful pathway in synthesizing new complexes with both N-heterocyclic carbene (NHC) and hydride ligands. A zwitterionic ruthenium complex with an ylidic ligand, bis(imino)pyridyl ruthenium-(2-methyleneimidazoline) complex, 7, was also successfully isolated and fully characterized. The (1)H NMR spectra and the solid-state structure confirm that complex 7 is an ylidic transition-metal complex with both NHC and hydride ligands, which was formed through the activation of imidazolium salts. PMID:25337998

Yoo, Hyojong; Berry, Donald H

2014-11-01

30

Alkyne hydroarylation with Au N-heterocyclic carbene catalysts  

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

Cristina Tubaro

2013-02-01

31

An Electronic Rationale for Observed Initiation Rates in Ruthenium-Mediated Olefin Metathesis: Charge Donation in Phosphine And N-Heterocyclic Carbene Ligands  

Energy Technology Data Exchange (ETDEWEB)

Ru K-edge XAS data indicate that second generation ruthenium-based olefin metathesis precatalysts (L = N-heterocyclic carbene) possess a more electron-deficient metal center than in the corresponding first generation species (L = tricyclohexylphosphine). This surprising effect is also observed from DFT calculations and provides a simple rationale for the slow phosphine dissociation kinetics previously noted for second-generation metathesis precatalysts.

Getty, K.; Delgado-Jaime, M.U.; Kennepohl, P.

2009-06-01

32

Synthesis and unexpected reactivity of germyliumylidene hydride [:GeH]+ stabilized by a bis(N-heterocyclic carbene)borate ligand.  

Science.gov (United States)

Employing the potassium salt of the monoanionic bis(NHC)borate 1 (NHC = N-Heterocyclic Carbene) enables the synthesis and isolation of the bis(NHC)borate-stabilized chlorogermyliumylidene precursor 2 in 61% yield. A Cl/H exchange reaction of 2 using potassium trisec.-butylborhydride as a hydride source leads to the isolation of the first germyliumylidene hydride [HGe:(+)] complex 3 in 91% yield. The Ge(II)-H bond in the latter compound has an unexpected reactivity as shown by the reaction with the potential hydride scavenger [Ph3C](+)[B(C6F5)4](-), furnishing the corresponding HGe: ? CPh3 cation in the ion pair 4 as initial product. Compound 4 liberates HCPh3 in the presence of 3 to give the unusual dinuclear HGe: ? Ge: cation in 5. The latter represents the first three-coordinate dicationic Ge(II) species stabilized by an anionic bis(NHC) chelate ligand and a Ge(II) donor. All novel compounds were fully characterized, including X-ray diffraction analyses. PMID:25073089

Xiong, Yun; Szilvási, Tibor; Yao, Shenglai; Tan, Gengwen; Driess, Matthias

2014-08-13

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N-heterocyclic carbene-main-group chemistry: a rapidly evolving field.  

Science.gov (United States)

This Award Article targets the evolving, yet surprisingly fruitful, chemistry of N-heterocyclic carbenes with low-oxidation-state main-group elements. Specifically, the chemistry of carbene-stabilized diatomic allotropes, diborenes, gallium octahedra, beryllium borohydride, and a host of related compounds will be presented. Providing a valuable historical perspective, the foundational work concerning the organometallic chemistry of gallium with sterically demanding m-terphenyl ligands from this laboratory will also be discussed. PMID:25343222

Wang, Yuzhong; Robinson, Gregory H

2014-11-17

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Enantioselective N-heterocyclic carbene catalyzed annulation reactions with imidazolidinones.  

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Add acetic acid: A highly stereoselective N-heterocyclic carbene (NHC)-catalyzed formal [4+2] annulation between ?,?-unsaturated aldehydes and imidazolidinones for the synthesis of imidazoles has been developed. Acetic acid serves as a key additive to achieve high chemoselectivity for the formal [4+2]?annulation product. PMID:24249661

McCusker, Elizabeth O'Bryan; Scheidt, Karl A

2013-12-16

35

N-heterocyclic carbenes in porous networks  

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Ziel dieser Arbeit war die Darstellung sowie Charakterisierung N-heterocyclischer Carbene in porösen Netzwerken. Es konnte gezeigt werden, dass ein direkter Nachweis der Carbene durch gängige spektroskopische Nachweismethoden nicht eindeutig gegeben ist. Durch die Verwendung verschiedener Aminoverbindungen (1,4-Diaminobenzol, Melamin, Tetra(4-aminophenyl)methan und Meso- tetra-p-aminophenylporphyrin) mit unterschiedlichen Geometrien, wurde der Versuch unternommen N-heterocyclische Carbene i...

Thiel, Kerstin

2012-01-01

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N-Heterocyclic Carbene-Catalyzed Conjugate Additions of Alcohols  

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An efficient intermolecular conjugate addition of alcohols to activated alkenes catalyzed by N-heterocyclic carbenes has been developed. With 5 mol % of the free carbene derived from IMes•HCl, unsaturated ketones and esters are competent substrates and a variety of primary and secondary alcohols can be employed as the nucleophile. No oligomerization is observed under these mild conditions for effective hydroalkoxylation. In addition to reactions with activated alkenes, IMes catalyzes the formation of vinyl ethers through the 1,4-addition of alcohols to ynones and promotes tandem conjugate addition/Michael cascade reactions. Preliminary data supports a Brønsted base mechanism with the free carbene. PMID:20809579

Phillips, Eric M.; Riedrich, Matthias; Scheidt, Karl A.

2010-01-01

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

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

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

2011-01-01

38

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

Scientific Electronic Library Online (English)

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

Julio Cezar, Pastre; Carlos Roque Duarte, Correia.

39

DFT prediction of multitopic N-heterocyclic carbenes using Clar's aromatic sextet theory.  

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Existence of several multitopic N-heterocyclic carbene (NHC) ligands with up to four carbene centers have been predicted on the basis of Clar's aromatic sextet theory. Assessment on stability and reactivity of NHCs was made by quantifying aromaticity, aromatic stabilization energy (E(aroma)), strength of carbene lone pair, proton affinity, and CuCl binding energy. On NICS(0) and HOMA scales of aromaticity, several NHCs showed high aromaticity, while E(aroma) (17.2-19.4 kcal/mol) indicated substantial stability for the N-heterocycle. Homodesmotic reactions suggested that heat of formation of most of the newly designed carbenes is very close to that of the existing bis-NHCs. Designing a multitopic ligand through branching via C(sp3) linkage was very effective as it improved the stability of the carbene. Electrostatic potential minimum (V(min)) at the carbene lone pair suggested that annelation of heterocycle to a benzenoid ring or branching through C(sp3) linkage can only marginally influence the electron donating power of the ligand. Hence, all multitopic NHCs showed proton affinity (252.3-267.4 kcal/mol) and CuCl binding energy (62.9-66.6 kcal/mol) very close to those of 1,3-dimethylimidazolidine-2-ylidene (1). It has also been demonstrated that branched multitopic 3-dimensional NHCs are attractive for designing metal-organic framework with narrow (1-1.5 nm) cage/pore size. PMID:23461408

Suresh, Cherumuttathu H; Ajitha, Manjaly J

2013-04-19

40

N-heterocyclic carbene-catalyzed rearrangements of vinyl sulfones†  

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N-heterocyclic carbenes catalyze the rearrangement of 1,1-bis(arylsulfonyl)ethylene to the corresponding trans-1,2-bis(phenylsulfonyl) under mild conditions. Tandem rearrangement/cycloadditions have been developed to capitalize on this new process and generate highly substituted isoxazolines and additional heterocyclic compounds. Preliminary mechanistic studies support a new conjugate addition/Umpolung process involving the ejection and subsequent unusual re-addition of a sulfinate ion.

Atienza, Roxanne L.; Roth, Howard S.; Scheidt, Karl A.

2011-01-01

 
 
 
 
41

N-heterocyclic carbene-catalyzed rearrangements of vinyl sulfones†  

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N-heterocyclic carbenes catalyze the rearrangement of 1,1-bis(arylsulfonyl)ethylene to the corresponding trans-1,2-bis(phenylsulfonyl) under mild conditions. Tandem rearrangement/cycloadditions have been developed to capitalize on this new process and generate highly substituted isoxazolines and additional heterocyclic compounds. Preliminary mechanistic studies support a new conjugate addition/Umpolung process involving the ejection and subsequent unusual re-addition of a sulfinate ion. PMID:22448316

Atienza, Roxanne L.; Roth, Howard S.

2012-01-01

42

N-heterocyclic carbene-catalyzed rearrangements of vinyl sulfones.  

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N-heterocyclic carbenes catalyze the rearrangement of 1,1-bis(arylsulfonyl)ethylene to the corresponding trans-1,2-bis(phenylsulfonyl) under mild conditions. Tandem rearrangement/cycloadditions have been developed to capitalize on this new process and generate highly substituted isoxazolines and additional heterocyclic compounds. Preliminary mechanistic studies support a new conjugate addition/Umpolung process involving the ejection and subsequent unusual re-addition of a sulfinate ion. PMID:22448316

Atienza, Roxanne L; Roth, Howard S; Scheidt, Karl A

2011-01-01

43

Synthesis of functionalised N-heterocyclic carbene ligands bearing a long spacer and their use in olefin metathesis.  

Science.gov (United States)

A synthetic route to backbone functionalised imidazolinium salts-NHC ligand precursors has been developed. These tagged NHC ligands can be used to obtain a homogeneous Hoveyda-type catalyst (19) containing a quaternary ammonium group on a C-8 long spacer. Products of olefin metathesis reactions promoted by complex 19 can be readily purified from Ru-residues by filtration of the reaction mixture through a small amount of silica gel. PMID:23463014

Ko?nik, Wioletta; Grela, Karol

2013-05-28

44

Homobimetallic Ruthenium-N-Heterocyclic Carbene Complexes For Olefin Metathesis  

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In this chapter, the synthesis and catalytic activity towards olefin metathesis of homobimetallic ruthenium (Ru)-alkylidene, -cyclodiene or -arene complexes bearing phosphine or N-heterocyclic carbene (NHC) ligands are reviewed. Emphasis is placed on the last category of bimetallic compounds. Three representatives of this new type of molecular scaffold were investigated. Thus, [(p-cymene)Ru(m-Cl)3RuCl (h2-C2H4)(L)] complexes with L = PCy3 (15a), IMes (16a), or IMesCl2 (16b) were prepared. They served as catalyst precursors for cross-metathesis (CM) of various styrene derivatives. These experiments revealed the outstanding aptitude of complex 16a (and to a lesser extent of 16b) to catalyze olefin metathesis reactions. Contrary to monometallic Ru-arene complexes of the [RuCl2(p-cymene)(L)] type, the new homobimetallic species did not require the addition of a diazo compound nor visible light illumination to initiate the ring-opening metathesis of norbornene or cyclooctene. When diethyl 2,2-diallylmalonate and N,N-diallyltosylamide were exposed to 16a,b, a mixture of cycloisomerization and ring-closing metathesis (RCM) products was obtained in a nonselective way. Addition of phenylacetylene enhanced the metathetical activity while completely repressing the cycloisomerization process.

Sauvage, Xavier; Demonceau, Albert; Delaude, Lionel

45

Modular synthesis of bidentate triazolyl-functionalized N-heterocyclic carbenes and their palladium complexes  

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New heterobidentate N-heterocyclic carbene-triazolyl ligands and several of their palladium(II) complexes have been synthesized in a modular fashion using click chemistry. These complexes are the first examples where triazolyl-substituted NHCs exhibit bidentate behavior, which was confirmed by NMR and X-ray diffraction studies. The synthesis of the complexes could be achieved in relatively few steps by introducing the diversity at a late stage in the synthesis.The complexes are ac...

Warsink, Stefan; Drost, R. M.; Lutz, M.; Spek, A. L.; Elsevier, C. J.

2010-01-01

46

Cyclopentadienyl-functionalised N-heterocyclic carbenes: synthesis, coordination to Mo, Ru, Rh  

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This thesis deals with the synthesis of cyclopentadienyl-functionalised N-heterocyclic carbenes and its coordination to both middle and late transition metals. One of the goals was to gain chemical knowledge on the reactivity patterns of these complexes, and explore their potential applications in catalysis. The imidazolium salts synthesised in the course of this thesis represent a series containing changes in the electronic and steric parameters. The ligand precursors we...

Costa, Andre? Pontes Da

2011-01-01

47

N-donor functionalized N-heterocyclic carbene nickel(II) complexes in the Kumada coupling  

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The synthesis and characterization of novel nickel(II) complexes bearing two bidentate N-heterocyclic carbene ligands functionalized with anionic N-donor moieties are described. Two different N-donor groups are employed, namely amido and benzimidazolato moieties. The solid-state structures of three of these complexes have been determined by X-ray crystallography. The amido-functionalized low-spin, square-planar Ni(II) complexes exhibit a cis geometry around the metal centre, while...

Berding, Joris; Dijkman, Thomas F.; Lutz, M.; Spek, A. L.; Bouwman, E.

2009-01-01

48

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

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

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

2011-09-21

49

Hydroboration of arynes with N-heterocyclic carbene boranes.  

Science.gov (United States)

Arynes were generated in situ from ortho-silyl aryl triflates and fluoride ions in the presence of stable N-heterocyclic carbene boranes (NHC?BH3 ). Spontaneous hydroboration ensued to provide stable B-aryl-substituted NHC-boranes (NHC?BH2 Ar). The reaction shows good scope in terms of both the NHC-borane and aryne components and provides direct access to mono- and disubstituted NHC-boranes. The formation of unusual ortho regioisomers in the hydroboration of arynes with an electron-withdrawing group supports a hydroboration process with hydride-transfer character. PMID:25346015

Taniguchi, Tsuyoshi; Curran, Dennis P

2014-11-24

50

Cationic Bis-N-Heterocyclic Carbene (NHC) Ruthenium Complex: Structure and Application as Latent Catalyst in Olefin Metathesis.  

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An unexpected cationic bis-N-heterocyclic carbene (NHC) benzylidene ether based ruthenium complex (2?a) was prepared through the double incorporation of an unsymmetrical unsaturated N-heterocyclic carbene (U2 -NHC) ligand that bore an N-substituted cyclododecyl side chain. The isolation and full characterization (including X-ray diffraction studies) of key synthetic intermediates along with theoretical calculations allowed us to understand the mechanism of the overall cationization process. Finally, the newly developed complex 2?a displayed interesting latent behavior during ring-closing metathesis, which could be "switched on" under acidic conditions. PMID:25212827

Rouen, Mathieu; Queval, Pierre; Falivene, Laura; Allard, Jessica; Toupet, Loïc; Crévisy, Christophe; Caijo, Frédéric; Baslé, Olivier; Cavallo, Luigi; Mauduit, Marc

2014-10-13

51

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

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

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

2010-01-01

52

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

Science.gov (United States)

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

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

2014-11-24

53

Piano-stool iron(ii) complexes as probes for the bonding of n-heterocyclic carbenes: indications for -acceptor ability  

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A series of new piano-stool iron(II) complexes comprising mono- and bidentate chelating N-heterocyclic carbene ligands [Fe(cp)(CO)(NHC)(L)]X have been prepared and analyzed by spectroscopic, electrochemical, crystallographic, and theoretical methods. Selectively substituting the L site with a series of ligands going from carbene to pyridine to CO suggests that CO is the strongest ? acceptor, while the behavior of pyridine and carbene is nearly identical. This suggests that in these co...

Mercs, Laszlo; Labat, Gae?l; Neels, Antonia; Ehlers, Andreas; Albrecht, Martin

2008-01-01

54

N-Heterocyclic carbene functionalized goup 7-9 transition metal  

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

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

2009-01-01

55

Luminescence Studies of the Intracellular Distribution of a Dinuclear Gold(I) N-Heterocyclic Carbene Complex  

Energy Technology Data Exchange (ETDEWEB)

A bidentate cyclophane N-heterocyclic carbene ligand has been used to synthesize a new dinuclear Au{sup I} complex of the formula [Au{sub 2}L{sub 2}]{sup 2+}. The short Au {hor_ellipsis} Au distance imposed by the rigid cyclophane ligand leads to a red-shifted luminescence profile that enables the complex to be used as a luminescent probe for distribution studies in single living cancer cells.

Barnard, Peter J.; Wedlock, Louise E.; Baker, Murray V.; Berners-Price, Susan J.; Joyce, David A.; Skelton, Brian W.; Steer, James H. (UWA)

2008-10-03

56

Antimicrobial Properties of Some Bis(Iminoacenaphthene (BIAN-Supported N-Heterocyclic Carbene Complexes of Silver and Gold  

Directory of Open Access Journals (Sweden)

Full Text Available The AgCl, AgOAc, AuCl, and AuOAc complexes of the new bis(iminoacenaphthene(BIAN-supported N-heterocyclic carbene ligand and the precursor imidazolium salt have been investigated with respect to their antimicrobial activities against Staphylococcus aureus, Bacillus subtilis, Escherichia coli and Psudomonas aeruginosa. The most active antimicrobial is the precursor imidazolium salt, which has a minimum inhibitory concentration (MIC value of

Rachel R. Butorac

2011-03-01

57

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

Science.gov (United States)

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

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

2008-01-01

58

Stable N-heterocyclic carbene (NHC)-palladium(0) complexes as active catalysts for olefin cyclopropanation reactions with ethyl diazoacetate.  

Science.gov (United States)

The Pd(0) complexes [(NHC)PdL(n)] (NHC=N-heterocyclic carbene ligand; L=styrene for n=2 or PR(3) for n=1) efficiently catalyse olefin cyclopropanation by using ethyl diazoacetate (EDA) as the carbene source with activities that improve on previously described catalytic systems based on this metal. Mechanistic studies have shown that all of these catalyst precursors deliver the same catalytic species in solution, that is, [(IPr)Pd(sty)], a 14e(-) unsaturated intermediate that further reacts with EDA to afford [(IPr)Pd(=CHCO(2)Et)(sty)], from which the cyclopropane is formed. PMID:22139750

Martín, Carmen; Molina, Francisco; Alvarez, Eleuterio; Belderrain, Tomás R

2011-12-23

59

Ultra stable self-assembled monolayers of N-heterocyclic carbenes on gold.  

Science.gov (United States)

Since the first report of thiol-based self-assembled monolayers (SAMs) 30 years ago, these structures have been examined in a huge variety of applications. The oxidative and thermal instabilities of these systems are widely known, however, and are an impediment to their widespread commercial use. Here, we describe the generation of N-heterocyclic carbene (NHC)-based SAMs on gold that demonstrate considerably greater resistance to heat and chemical reagents than the thiol-based counterparts. This increased stability is related to the increased strength of the gold-carbon bond relative to that of a gold-sulfur bond, and to a different mode of bonding in the case of the carbene ligand. Once bound to gold, NHCs are not displaced by thiols or thioethers, and are stable to high temperatures, boiling water, organic solvents, pH extremes, electrochemical cycling above 0 V and 1% hydrogen peroxide. In particular, benzimidazole-derived carbenes provide films with the highest stabilities and evidence of short-range molecular ordering. Chemical derivatization can be employed to adjust the surface properties of NHC-based SAMs. PMID:24755592

Crudden, Cathleen M; Horton, J Hugh; Ebralidze, Iraklii I; Zenkina, Olena V; McLean, Alastair B; Drevniok, Benedict; She, Zhe; Kraatz, Heinz-Bernhard; Mosey, Nicholas J; Seki, Tomohiro; Keske, Eric C; Leake, Joanna D; Rousina-Webb, Alexander; Wu, Gang

2014-05-01

60

Ultra stable self-assembled monolayers of N-heterocyclic carbenes on gold  

Science.gov (United States)

Since the first report of thiol-based self-assembled monolayers (SAMs) 30 years ago, these structures have been examined in a huge variety of applications. The oxidative and thermal instabilities of these systems are widely known, however, and are an impediment to their widespread commercial use. Here, we describe the generation of N-heterocyclic carbene (NHC)-based SAMs on gold that demonstrate considerably greater resistance to heat and chemical reagents than the thiol-based counterparts. This increased stability is related to the increased strength of the gold-carbon bond relative to that of a gold-sulfur bond, and to a different mode of bonding in the case of the carbene ligand. Once bound to gold, NHCs are not displaced by thiols or thioethers, and are stable to high temperatures, boiling water, organic solvents, pH extremes, electrochemical cycling above 0 V and 1% hydrogen peroxide. In particular, benzimidazole-derived carbenes provide films with the highest stabilities and evidence of short-range molecular ordering. Chemical derivatization can be employed to adjust the surface properties of NHC-based SAMs.

Crudden, Cathleen M.; Horton, J. Hugh; Ebralidze, Iraklii I.; Zenkina, Olena V.; McLean, Alastair B.; Drevniok, Benedict; She, Zhe; Kraatz, Heinz-Bernhard; Mosey, Nicholas J.; Seki, Tomohiro; Keske, Eric C.; Leake, Joanna D.; Rousina-Webb, Alexander; Wu, Gang

2014-05-01

 
 
 
 
61

Isolation of an Imino-N-heterocyclic Carbene/Germanium(0) Adduct: A Mesoionic Germylene Equivalent.  

Science.gov (United States)

An autoionization of germanium dichloride/dioxane complex with an imino-N-heterocyclic carbene ligand (L) afforded a novel germyliumylidene ion, [(L)GeCl](+) [GeCl3 ](-) , which was fully characterized. Reduction of the germyliumylidene ion with potassium graphite produced a cyclic species [(L)Ge], which can be viewed as both a Ge(0) species and a mesoionic germylene. X-ray diffraction analysis and computational studies revealed one of the lone pairs on the Ge atom is involved in the ??system on the GeC2 N2 five-membered ring. It was also confirmed that the nucleophilic behavior of [(L)Ge] as a two lone-pair donor. PMID:25283638

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

2014-11-24

62

N-Heterocyclic carbene/Brønsted acid cooperative catalysis as a powerful tool in organic synthesis  

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Full Text Available The interplay between metals and N-heterocyclic carbenes (NHCs has provided a window of opportunities for the development of novel catalytic strategies within the past few years. The recent successful combination of Brønsted acids with NHCs has added a new dimension to the field of cooperative catalysis, enabling the stereoselective synthesis of functionalized pyrrolidin-2-ones as valuable scaffolds in heterocyclic chemistry. This Commentary will briefly highlight the concept of N-heterocyclic carbene/Brønsted acid cooperative catalysis as a new and powerful methodology in organic chemistry.

Rob De Vreese

2012-03-01

63

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

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

Morgan, John P.; Shrimp, Jonathan H.

2014-01-01

64

Mild and rational synthesis of palladium complexes comprising C(4)-bound N-heterocyclic carbenes  

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Oxidative addition of pyridyl-functionalised 4-iodoimidazolium salts to palladium(0) gives catalytically active complexes in which the N-heterocyclic carbene is bound to the palladium(II) centre in a non-classical bonding mode via C(4).

Kluser, Evelyne; Neels, Antonia; Albrecht, Martin

2007-01-01

65

N-heterocyclic carbene catalysed asymmetric cross-benzoin reactions of heteroaromatic aldehydes with trifluoromethyl ketones.  

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A new triazolium salt derived N-heterocyclic carbene catalyses an asymmetric cross-benzoin-type reaction of heteroaromatic aldehydes and various trifluoromethyl ketones in good to excellent yields (69-96%) and moderate to good enantioselectivities (ee = 39-85%). Up to 99% ee can be achieved by recrystallisation. PMID:20694237

Enders, Dieter; Grossmann, André; Fronert, Jeanne; Raabe, Gerhard

2010-09-14

66

Catalytic dynamic kinetic resolutions with N-heterocyclic carbenes: asymmetric synthesis of highly substituted ?-lactones.  

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New DKR type: An N-heterocyclic carbene (NHC)-catalyzed dynamic kinetic resolution of racemic ?-substituted ?-keto esters has been developed. This method relies on the epimerization of an NHC-enol intermediate before subsequent aldol/acylation events. Highly substituted ?-lactones are produced in good yield with good to excellent selectivities (see scheme). PMID:22700327

Cohen, Daniel T; Eichman, Chad C; Phillips, Eric M; Zarefsky, Emily R; Scheidt, Karl A

2012-07-16

67

N-heterocyclic carbene-catalyzed internal redox reaction of alkynals: an efficient synthesis of allenoates.  

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An efficient N-heterocyclic carbene (NHC)-catalyzed internal redox reaction of alkynals that bear a ? leaving group has been developed. This process provides a new access to a range of allenoates in good yields. Preliminary results demonstrate that the enantioselective variant can also be achieved. PMID:22352302

Zhao, Yu-Ming; Tam, Yik; Wang, Yu-Jie; Li, Zigang; Sun, Jianwei

2012-03-16

68

N-heterocyclic carbene catalysed aerobic oxidation of aromatic aldehydes to aryl esters using boronic acids.  

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The organocatalytic behavior of N-heterocyclic carbenes in the aerobic oxidation of aromatic aldehydes to esters with boronic acids has been explored. This transition metal-free protocol allows access to a wide variety of aromatic esters in good to excellent yields under mild reaction conditions. PMID:22134382

Arde, Panjab; Ramanjaneyulu, B T; Reddy, Virsinha; Saxena, Apurv; Anand, R Vijaya

2012-01-28

69

N-heterocyclic carbene-catalyzed enantioselective annulation of indolin-3-ones with bromoenals.  

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N-Heterocyclic carbene-catalyzed reactions of indolin-3-ones with 2-bromoenals opened an asymmetric access to 3,4-dihydropyrano[3,2-b]indol-2(5?H)-ones in good yields and with good to excellent enantioselectivities. This protocol tolerates a broad substrate scope. In addition, a possible mechanism for the annulation reaction is presented. PMID:24729588

Ni, Qijian; Song, Xiaoxiao; Raabe, Gerhard; Enders, Dieter

2014-06-01

70

Coordination Chemistry of Highly Hemilabile Bidentate Sulfoxide N-Heterocyclic Carbenes with Palladium(II).  

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Imidazolium salts, [RS(O)?CH2 (C3 H3 N2 )Mes]Cl (R=Me (L1?a), Ph (L1?b)); Mes=mesityl), make convenient carbene precursors. Palladation of L1?a affords the monodentate dinuclear complex, [(PdCl2 {MeS(O)CH2 (C3 H2 N2 )Mes})2 ] (2?a), which is converted into trans-[PdCl2 (NHC)2 ] (trans-4?a; N-heterocyclic carbene) with two rotamers in anti and syn configurations. Complex trans-4?a can isomerize into cis-4?a(anti) at reflux in acetonitrile. Abstraction of chlorides from 4?a or 4?b leads to the formation of a new dication: trans-[Pd{RS(O)CH2 (C3 H2 N2 )Mes}2 ](PF6 )2 (R=Me (5?a), Ph (5?b)). The X-ray structure of 5?a provides evidence that the two bidentate SO?NHC ligands at palladium(II) are in square-planar geometry. Two sulfoxides are sulfur- and oxygen-bound, and constitute five- and six-membered chelate rings with the metal center, respectively. In acetonitrile, complexes 5?a or 5?b spontaneously transform into cis-[Pd(NHC)2 (NCMe)2 ](PF6 )2 . Similar studies of thioether-NHCs have also been examined for comparison. The results indicate that sulfoxides are more labile than thioethers. PMID:25263615

Yu, Kuo-Hsuan; Wang, Chia-Ching; Chang, I-Hsin; Liu, Yi-Hung; Wang, Yu; Elsevier, Cornelis J; Liu, Shiuh-Tzung; Chen, Jwu-Ting

2014-12-01

71

Synthesis, Characterization, and Reactivity of Furan- and Thiophene-Functionalized Bis(N-heterocyclic carbene) Complexes of Iron(II).  

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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 cis-diacetonitriledi[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. PMID:25188636

Rieb, Julia; Raba, Andreas; Haslinger, Stefan; Kaspar, Manuel; Pöthig, Alexander; Cokoja, Mirza; Basset, Jean-Marie; Kühn, Fritz E

2014-09-15

72

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

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

Maggi, Agnese; Madsen, Robert

2011-01-01

73

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

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1,2-Migration of the phosphano-group to the carbene center in N-phosphano functionalized N-heterocyclic carbenes has been studied by density functional theory (DFT) calculations. An intramolecular mechanism with a three-center transition state structure seems to be most plausible for the isolated carbenes, while an intermolecular pathway catalyzed by azolium salts may be preferable for a migration proceeding in the course of generating the carbenes in situ. Our calculations show that amino-substitution at the phosphorus atom and an enhanced nucleophilicity of the heterocycle scaffold facilitate the phosphorus shift. Calculated singlet-triplet energy gaps do not correlate with thermodynamic stability of the studied carbenes and their disposition toward the 1,2-rearrangement. © 2014 Wiley Periodicals, Inc. PMID:25363134

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

2015-01-01

74

Accesses to electronic structures and the excited states of blue luminescent copper(I) complexes containing N-heterocyclic carbene ligands: a DFT/TDDFT exploitation.  

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The ground electronic states and photophysical properties of three designed Cu(I) complexes [Cu(ImNHC)(POP)](+) (1), [Cu(methyl-ImNHC)(POP)](+) (2), and [Cu(BenzImNHC)(POP)](+) (3); where [ImNHC?=?3-methyl-1-(pyridin-2-yl)-1H-imidazol-2-ylidene; methyl-ImNHC?=?3-methyl-1-(pyridin-2-ylmethyl)-1H-imidazol-2-ylidene; BenzImNHC?=?3-methyl-1-(pyridin-2-yl)-1H-benzimidazol-2-ylidene], have been investigated using density functional theory (DFT) and time-dependent density functional theory (TDDFT). The results reveal that the presence of the methylene spacer in the NHC ligands has a more direct effect on the distribution of frontier molecular orbitals while the elongation of ? conjugation provided by the fused imidazole in the NHC ligands has a negligible effect. The UV-vis absorption spectra of all the complexes are well produced by TD-DFT calculations based on the charge transfer amount calculations and the corresponding band assignments are discussed. Importantly, the triplet energy calculations demonstrated that complex 2 would be a highly efficient blue emitter with the deep-blue of 440 nm. PMID:25123713

Li, Qiang; Zhao, Feng; Xu, Shengxian; Xia, Hongying; Wang, Jinglan; Wang, Yibo

2014-09-01

75

Unsymmetrical N-heterocyclic carbenes with a 1,1'-ferrocenediyl backbone.  

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This paper focuses on ferrocene-based expanded-ring N-heterocyclic carbenes (NHCs) of the type [Fe(C5H4-NR-C-NR'-C5H4)] (), which contain two different N-substituents. Three combinations were addressed, with R = neopentyl (Np) in each case and R' being either 2-adamantyl (Ad), phenyl (Ph) or 9-anthracenylmethyl (Acm). The NHCs were generated by reaction of the corresponding formamidinium tetrafluoroborates [H-][BF4] with lithium diisopropylamide (LDA). While only was sufficiently stable for isolation, and could be efficiently trapped in situ by complexation reactions. Two series of Rh(I) complexes were prepared, viz. [RhCl(cod)()] (cod = 1,5-cyclooctadiene) by reacting [{Rh(?-Cl)(cod)}2] with and cis-[RhCl(CO)2()] by reacting [RhCl(cod)(')] with CO. All complexes exhibit pronounced anagostic ?-CHRh interactions, both in solution and in the solid state, in accord with a strong influence of the N-substituents on the steric ligand properties, as is chemically illustrated by the huge reactivity difference of [RhCl(cod)()] (R = R' = Ad) and [RhCl(cod)()] towards CO, the former complex being inert. Tolman electronic parameter (TEP) values are 2050 ± 1 cm(-1) for the unsymmetrical NHCs studied, indicating only a weak influence of the N-substituents on the electronic ligand properties. PMID:24424525

Rittinghaus, Stefan; Färber, Christian; Bruhn, Clemens; Siemeling, Ulrich

2014-03-01

76

N-Heterocyclic carbene/Brønsted acid cooperative catalysis as a powerful tool in organic synthesis  

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The interplay between metals and N-heterocyclic carbenes (NHCs) has provided a window of opportunities for the development of novel catalytic strategies within the past few years. The recent successful combination of Brønsted acids with NHCs has added a new dimension to the field of cooperative catalysis, enabling the stereoselective synthesis of functionalized pyrrolidin-2-ones as valuable scaffolds in heterocyclic chemistry. This Commentary will briefly highlight the concept of N-heterocyc...

Vreese, Rob; D’hooghe, Matthias

2012-01-01

77

Small molecule activation using electropositive metal N-heterocyclic carbene complexes  

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The versatility of N-heterocyclic carbenes (NHCs) is demonstrated by numerous practical applications in homogeneous transition metal catalysis, organocatalysis and materials science. There remains a paucity of electropositive metal NHC complexes and so this chemistry is poorly developed with respect to that of the late transition metal and main group elements. This thesis describes the synthesis of new alkoxy-tethered NHC proligands, their use in the synthesis of reactive metal...

Turner, Zoe Rose

2011-01-01

78

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

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

Dam, Johan Hygum; Osztrovszky, Gyorgyi

2010-01-01

79

N-heterocyclic-carbene-catalyzed synthesis of 2-aryl indoles.  

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A convergent and efficient transition-metal-free catalytic synthesis of 2-aryl-indoles has been developed. The interception of a highly reactive and transient aza-ortho-quinone methide by an acyl anion equivalent generated through N-hetereocyclic carbene catalysis is central to this successful strategy. High yields and a wide scope as well as the streamlined synthesis of a kinase inhibitor are reported. PMID:25044815

Hovey, M Todd; Check, Christopher T; Sipher, Alexandra F; Scheidt, Karl A

2014-09-01

80

Photophysical and photochemical trends in tricarbonyl rhenium(I) N-heterocyclic carbene complexes.  

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A family of tricarbonyl Re(I) complexes of the formulation fac-[Re(CO)3(NHC)L] has been synthesized and characterized, both spectroscopically and structurally. The NHC ligand represents a bidentate N-heterocyclic carbene species where the central imidazole ring is substituted at the N3 atom by a butyl, a phenyl, or a mesityl group and substituted at the N1 atom by a pyridyl, a pyrimidyl, or a quinoxyl group. On the other hand, the ancillary L ligand alternates between chloro and bromo. For the majority of the complexes, the photophysical properties suggest emission from the lowest triplet metal-to-ligand charge transfer states, which are found partially mixed with triplet ligand-to-ligand charge transfer character. The nature and relative energy of the emitting states appear to be mainly influenced by the identity of the substituent on the N3 atom of the imidazole ring; thus, the pyridyl complexes have blue-shifted emission in comparison to the more electron deficient pyrimidyl complexes. The quinoxyl complexes show an unexpected blue-shifted emission, possibly occurring from ligand-centered excited states. No significant variations were found upon changing the substituent on the imidazole N3 atom and/or the ancillary ligand. The photochemical properties of the complexes have also been investigated, with only the complexes bound to the pyridyl-substituted NHC ligands showing photoinduced CO dissociation upon excitation at 370 nm, as demonstrated by the change in the IR and NMR spectra as well as a red shift in the emission profile after photolysis. Temperature-dependent photochemical experiments show that CO dissociation occurs at temperatures as low as 233 K, suggesting that the Re-C bond cleaves from excited states of metal-to-ligand charge transfer nature rather than thermally activated ligand field excited states. A photochemical mechanism that takes into account the reactivity of the complexes bound to the pyridyl-NHC ligand as well as the stability of those bound to the pyrimidyl- and quinoxyl-NHC ligands is proposed. PMID:24665819

Vaughan, Jamila G; Reid, Brodie L; Wright, Phillip J; Ramchandani, Sushil; Skelton, Brian W; Raiteri, Paolo; Muzzioli, Sara; Brown, David H; Stagni, Stefano; Massi, Massimiliano

2014-04-01

 
 
 
 
81

Selective C-F bond activation of tetrafluorobenzenes by nickel(0) with a nitrogen donor analogous to N-heterocyclic carbenes.  

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N, not NHC: A neutral, basic, strong sigma-donor nitrogen ancillary ligand with properties analogous to those of N-heterocyclic carbenes (NHCs) was developed to aid in the oxidative additions of challenging substrates to late transition metals. Selective, room-temperature C-F bond activation was observed with hexa-, penta-, and all three isomers of tetrafluorobenzene using a nickel(0) source in the presence of this donor. PMID:19199307

Doster, Meghan E; Johnson, Samuel A

2009-01-01

82

Carbene Rearrangements in Three-Coordinate N-Heterocyclic Carbene Complexes of Cobalt(II) Bis(trimethylsilyl)amide.  

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The synthesis and molecular structures of the cobalt(II) N-heterocyclic carbene (NHC) complexes [(NHC)Co{N(SiMe3)2}2], where NHC = 1,3-bis(diisopropylphenyl)imidazolylidene (IPr) (6), 1,3-bis(mesityl)imidazolylidene (IMes) (7), and 1,3-bis(tert-butyl)imidazol-2-ylidene (I(t)Bu) (8), are reported. Complexes 6-8 are rare examples of three-coordinate cobalt NHC complexes. The steric congestion within the coordination environments of the cobalt(II) centers in 6 and 7 results in the longest Co-C(NHC) distances currently known. Investigating the thermal stability of 6-8, we have found that the steric congestion in 6 is such that heating the complex to reflux in toluene prompts a rearrangement from the normal, C2-bonding mode of the IPr ligand to the corresponding "abnormal" or mesoionic bonding mode. The rearrangement results in formation of [(aIPr)Co{N(SiMe3)2}2] (9), which is the first cobalt complex of an abnormal NHC ligand. The Co-C bond in 9 is 0.06 Å shorter than the analogous bond in 6, suggesting that, although the rearrangement occurs due to the spatial demands of the IPr ligand, there is also a thermodynamic driving force in terms of the Co-C bond. In contrast to the case for 6, complex 7 is stable with respect to the normal-to-abnormal rearrangement. Refluxing complex 8 in toluene results in activation of a tert-butyl substituent, which is eliminated as isobutene, followed by formation of the 1-tert-butylimidazole complex [((t)BuIm)Co{N(SiMe3)2}2] (10). PMID:25203858

Day, Benjamin M; Pal, Kuntal; Pugh, Thomas; Tuck, Jessica; Layfield, Richard A

2014-10-01

83

N-heterocyclic carbene coordinated neutral and cationic heavier cyclopropylidenes.  

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Cyclopropylidene is a transient intermediate of the allene-propyne-cyclopropene isomerization. The incorporation of heavier Group?14 elements into the cyclopropylidene scaffold has to date been restricted to the formal replacement of the carbenic carbon atom by a base-coordinated silicon(II) center. Herein we report the synthesis and characterization of NHC-coordinated heavier cyclopropylidenes (Si2 GeR3 X, and Si3 R3 Br; X=Cl, Mes; R=Tip=2,4,6-iPr3 C6 H2 ) in which the three-membered ring is exclusively formed by silicon and germanium. In case of the chloro-substituted Si2 Ge-cyclopropylidene, a stable heavier cycloprop-1-yl-2-ylidene cation is obtained by NHC-induced chloride dissociation. PMID:25060704

Jana, Anukul; Omlor, Isabell; Huch, Volker; Rzepa, Henry S; Scheschkewitz, David

2014-09-01

84

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

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

César A. Urbina-Blanco

2010-11-01

85

A dihydrodisilene transition metal complex from an N-heterocyclic carbene-stabilized silylene monohydride.  

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Through the use of an N-heterocyclic carbene (NHC) and the super-silyl group (tBu3Si), the novel silylene hydride 2 could be synthesized and isolated in 41% yield. The reaction of 2 with bis(1,5-cyclooctadiene)nickel(0) afforded complex 3, which represents the first example of a dihydrodisilene transition metal complex. Compounds 2 and 3 were fully characterized, including single-crystal X-ray diffraction analysis. The reaction mechanism for the formation of 3 from 2 was investigated by density functional theory calculations, which showed that migration of the NHC from silicon to nickel takes place in this reaction. PMID:24252067

Inoue, Shigeyoshi; Eisenhut, Carsten

2013-12-11

86

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

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

Dan Yuan

2012-03-01

87

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

DEFF Research Database (Denmark)

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

Maggi, Agnese; Madsen, Robert

2012-01-01

88

N-Heterocyclic Carbene Complexes in Olefin Metathesis  

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Olefin metathesis is now a synthetic tool found ubiquitously in various fields involving synthesis. Of its many variations, three are prominently used: (1) catalytic ring closing metathesis (RCM) is an extremely powerful method for the construction of carbon-carbon double bonds in organic chemistry; (2) ring opening metathesis polymerisation (ROMP) where polymers are formed by use of the energy released from cyclic strain; and (3) cross metathesis (CM) where non-cyclic partners are coupled through C-C double bond formation. These important transformations and variations on these themes mediated by second generation ruthenium complexes bearing a NHC ligand will be presented in the following sections.

Luan, Xinjun; Dorta, Reto; Leitgeb, Anita; Slugovc, Christian; Tiede, Sascha; Blechert, Siegfried

89

An Efficient Synthesis of Achiral and Chiral 1,2,4-Triazolium Salts: Bench Stable Precursors for N-Heterocyclic Carbenes  

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The promising utility of triazolyl N-heterocyclic carbene catalysts in umpolung aldehyde chemistry requires a straightforward reliable synthesis from readily available materials. Herein we describe the synthesis of a variety of triazolyl N-heterocyclic carbene precursors. The reactions commence from commercially available amino acids and proceed in 44-68% overall yields. The N-heterocyclic salts are air stable crystalline solids that can be stored with no special precaution and can generate t...

Kerr, Mark S.; Alaniz, Javier Read; Rovis, Tomislav

2005-01-01

90

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

Science.gov (United States)

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

Ison, Elon A.; Ison, Ana

2012-01-01

91

Designing N-heterocyclic carbenes: simultaneous enhancement of reactivity and enantioselectivity in the asymmetric hydroacylation of cyclopropenes.  

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Faster, higher, stronger! The N-heterocyclic carbene (NHC) catalyzed diastereo- and enantioselective hydroacylation of cyclopropenes affords structurally valuable acylcyclopropanes. A new family of electron-rich, 2,6-dimethoxyphenyl-substituted NHCs induces excellent reactivity and enantioselectivity. Preliminary kinetic studies unambiguously demonstrated the superiority of this family of catalysts over known NHCs in this challenging transformation. PMID:22058006

Liu, Fan; Bugaut, Xavier; Schedler, Michael; Fröhlich, Roland; Glorius, Frank

2011-12-23

92

Pd-N-Heterocyclic Carbene (NHC) Organic Silica: Synthesis and Application in Carbon-Carbon Coupling Reactions  

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The first Pd-N-heterocyclic carbene (NHC) complex in the form of organic silica was prepared using sol-gel method and its application in Heck and Suzuki reaction were demonstrated. These C-C coupling reactions proceeded efficiently under the influence of microwave irradiation, wi...

93

Nickel N-heterocyclic carbene catalyst for cross-coupling of neopentyl arenesulfonates with methyl and primary alkyl grignard reagents.  

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Nickel N-heterocyclic carbene (NHC) catalytic system prepared in situ by the reaction of Ni(acac)(2) with NHC precursor efficiently catalyzed the cross-coupling reaction of alkoxysulfonylarenes with methyl, neopentyl, and benzyl Grignard reagents at ambient temperature. PMID:19924892

Kim, Chul-Bae; Jo, Hyunjong; Ahn, Bo-Kyoung; Kim, Chang Keun; Park, Kwangyong

2009-12-18

94

Non-covalent interactions in coinage metal complexes of 1,2,4-triazole-based N-heterocyclic carbenes.  

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Seven coinage metal(I) complexes bearing two different triazole-based N-heterocyclic carbene (NHC) ligands, [1-tert-butyl-4-{2-[(N,N-dimethylamino)methyl]phenyl}-3-phenyl-1H-1,2,4-triazol-4-ium-5-ide and 1-tert-butyl-4-(4-methylphenyl)-3-phenyl-1H-1,2,4-triazol-4-ium-5-ide], were synthesized and fully characterized in solution by NMR spectroscopy as well as in the solid state by X-ray diffraction techniques. Furthermore, the XRD analysis showed that the bidentate coordination of the amino group substituted NHC ligand, previously observed for rhodium and palladium complexes, does not take place in the solid state structure of Au(I) complexes with various halide ligands. Nevertheless, the formation of sets of two head-to-tail oriented monomers aggregated via a weak metallophilic contact was revealed for both NHC ligands as well as for all three coinage metals with different halides. These experimental data correlate quite well with the previously published theoretical study on related complexes. PMID:25189129

Turek, Jan; Panov, Illia; Švec, Petr; R?ži?ková, Zde?ka; R?ži?ka, Aleš

2014-11-01

95

The Crystallographic and Quantum Mechanical Analysis of some Pd(II) N-heterocyclic carbene Complexes  

International Nuclear Information System (INIS)

Because of their extraordinary properties, N-heterocyclic carbenes (NHC) have found access to a great variety of catalytic processes which include C-C coupling reactions, formation of furans, cyclopropanation, olefin metathesis, hydroformylation, polymerization and hydrosilylation reactions. In this study, molecular and crystal structures of Pd(II) NHC complexes have been determined by single crystal x-ray diffraction technique. In addition, molecular geometries of all complexes under study were optimized at the B3LYP level of density functional theory (DFT) and the effective core potentials of Hay and Wadt with LanL2DZ basis set were used. In order to investigate binding orbitals of metal and charge transfer mechanism occurred in NHC ring, natural bond orbital (NBO) analyses were performed at the B3LYP/LanL2DZ level on the basis of the optimized ground state for complexes

96

Toward molecular rotors: tetra-N-heterocyclic carbene Ag(I)-halide cubane-type clusters.  

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1,3-Bis(3'-butylimidazol-1'-yl)benzene diiodide (2a), 1,3-bis(3'-but-3''-enyl-imidazolium-3'-yl)benzene diiodide (2b), 1,3-bis(3'-pent-4''-enyl-imidazolium-3'-yl)benzene diiodide (2c), 1,3-bis(4'-butyl-1',2',4'-triazolium-1'-yl)benzene diiodide (2d), or 1,3-bis(4'-butyl-1',2',4'-triazolium-1'-yl)benzene dibromide (2e) was reacted with Ag2O yielding unprecedented tetra-N-heterocyclic carbene-Ag(I)-X cubane-type clusters. These were characterized by (1)H and (13)C NMR spectroscopy, ESI-TOF MS, elemental analysis, and X-ray crystallography. Results from VT (13)C NMR spectroscopy and cross-over experiments are consistent with intramolecular exchange suggesting that the Ag(I) complexes are molecular rotors. PMID:23389555

Clark, Wesley D; Tyson, Ginger E; Hollis, T Keith; Valle, Henry U; Valente, Edward J; Oliver, Allen G; Dukes, Matthew P

2013-05-28

97

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

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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. PMID:24778738

Guan, Zong; Namyslo, Jan C; Drafz, Martin H H; Nieger, Martin; Schmidt, Andreas

2014-01-01

98

Tunneling assists the 1,2-hydrogen shift in N-heterocyclic carbenes.  

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At room temperature, 1,2-hydrogen-transfer reactions of N-heterocyclic carbenes, like the imidazol-2-ylidene to give imidazole is shown to occurr almost entirely (>90?%) by quantum mechanical tunneling (QMT). At 60?K in an Ar matrix, for the 2, 3-dihydrothiazol-2-ylidene?thiazole transformation, QMT is shown to increase the rate about 10(5) ?times. Calculations including small-curvature tunneling show that the barrier for intermolecular 1,2-hydrogen-transfer reaction is small, and QMT leads to a reduced rate of the forward reaction because of nonclassical reflections even at room temperature. A small barrier also leads to smaller kinetic isotope effects because of efficient QMT by both H and D. QMT does not always lead to faster reactions or larger KIE values, particularly when the barrier is small. PMID:25044956

Karmakar, Sharmistha; Datta, Ayan

2014-09-01

99

Nanofiber composites containing N-heterocyclic carbene complexes with antimicrobial activity  

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

Elzatahry AA

2012-06-01

100

Expedient syntheses of the N-heterocyclic carbene precursor imidazolium salts IPr·HCl, IMes·HCl and IXy·HCl  

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Abstract The 1,3-diaryl-imidazolium chlorides IPr·HCl (aryl = 2,6-diisopropylphenyl), IMes·HCl (aryl = 2,4,6-trimethylphenyl) and IXy·HCl (aryl = 2,6-dimethylphenyl), precursors to widely used N-heterocyclic carbene (NHC) ligands and catalysts, were prepared in high yields (81%, 69% and 89%, respectively) by the reaction of 1,4-diaryl-1, 4-diazabutadienes, paraformaldehyde and chlorotrimethylsilane in dilute ethyl acetate solution. A reaction mechanism involving a 1,5-dipolar ele...

Hintermann Lukas

2007-01-01

 
 
 
 
101

Expedient syntheses of the N-heterocyclic carbene precursor imidazolium salts IPr·HCl, IMes·HCl and IXy·HCl  

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Full Text Available Abstract The 1,3-diaryl-imidazolium chlorides IPr·HCl (aryl = 2,6-diisopropylphenyl, IMes·HCl (aryl = 2,4,6-trimethylphenyl and IXy·HCl (aryl = 2,6-dimethylphenyl, precursors to widely used N-heterocyclic carbene (NHC ligands and catalysts, were prepared in high yields (81%, 69% and 89%, respectively by the reaction of 1,4-diaryl-1, 4-diazabutadienes, paraformaldehyde and chlorotrimethylsilane in dilute ethyl acetate solution. A reaction mechanism involving a 1,5-dipolar electrocyclization is proposed.

Hintermann Lukas

2007-08-01

102

Imidazolium hydrogen carbonates versus imidazolium carboxylates as organic precatalysts for N-heterocyclic carbene catalyzed reactions.  

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Imidazolium-2-carboxylates (NHC-CO(2) adducts, 3) and (benz)imidazolium hydrogen carbonates ([NHC(H)][HCO(3)], 4) were independently employed as organic precatalysts for various molecular N-heterocyclic carbene (NHC) catalyzed reactions. NHC-CO(2) adducts were obtained by carboxylation in THF of related free NHCs (2), while the synthesis of [NHC(H)][HCO(3)] precursors was directly achieved by anion metathesis of imidazolium halides (1) using potassium hydrogen carbonate (KHCO(3)) in methanolic solution, without the need for the prior preparation of free carbenes. Thermogravimetric analysis (TGA) and TGA coupled with mass spectrometry (TGA-MS) of most [NHC(H)][HCO(3)] precursors 4 showed a degradation profile in stages, with either a concomitant or a stepwise release of H(2)O and CO(2), between 108 and 280 °C, depending on the nature of the azolium and substituents. In solution, NHC generation from both [NHC(H)][HCO(3)] salts and NHC-CO(2) adducts could be achieved at room temperature, most likely by a simple solvation effect. Both types of precursors proved efficient for organocatalyzed molecular reactions, including cyanosilylation, benzoin condensation, and transesterification reactions. The catalytic efficiencies of NHC-CO(2) adducts 3 were found to be approximately 3 times higher than those of their [NHC(H)][HCO(3)] counterparts 4. PMID:23092332

Fèvre, Maréva; Coupillaud, Paul; Miqueu, Karinne; Sotiropoulos, Jean-Marc; Vignolle, Joan; Taton, Daniel

2012-11-16

103

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

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

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

2014-07-21

104

Cationic gold(I) heteroleptic complexes bearing a pyrazole-derived N-heterocyclic carbene: syntheses, characterizations, and cytotoxic activities.  

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A series of cationic gold(I) heteroleptic complexes bearing the pyrazole-derived N-heterocyclic carbene (NHC) FPyr (1,2,3,4,6,7,8,9-octahydropyridazino[1,2-a]indazolin-11-ylidene), and either a 1,3-disubstituted benzimidazole-derived NHC of the type RR'-bimy (3: R = R' = CHPh2; 4: R = CHPh2, R' = (i)Pr; 5: R = R' = CH2Ph; 6: R = R' = (i)Bu; 7: R = R' = n-Pr; 8: R = R' = Et; 9: R = R' = 2-propenyl) or a non-NHC co-ligand L (10: L = PPh3; 11: L = P(OPh)3; 12: L = DMAP) (DMAP = 4-dimethylaminopyridine) have been synthesized from [AuCl(FPyr)] (1). Complexes 3-12 have been characterized using multinuclei NMR spectroscopies, ESI mass spectrometry, and elemental analysis. X-ray diffraction analyses have been performed on complexes 5, 6, and 9-11. To the best of our knowledge, 11 represents the first gold-NHC complex to bear the P(OPh)3 ligand. The cytotoxic activities of complexes 3-12 have been studied in vitro with the NCI-H1666 non-small cell lung cancer cell line. PMID:23860905

Sivaram, Haresh; Tan, Jackie; Huynh, Han Vinh

2013-09-14

105

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

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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. PMID:24243420

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

2013-12-23

106

Copolymerization of ethylene with norbornene catalyzed by cationic rare earth metal fluorenyl functionalized N-heterocyclic carbene complexes.  

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Rare earth metal bis(alkyl) complexes attached by fluorenyl modified N-heterocyclic carbene (NHC) (Flu-NHC)Ln(CH(2)SiMe(3))(2) (Flu-NHC = (C(13)H(8)CH(2)CH(2)(NCHCCHN)C(6)H(2)Me(3)-2,4,6); Ln = Sc (2a); Y (2b); Ho (2c); Lu (2d)), ((tBu)Flu-NHC)Ln(CH(2)SiMe(3))(2) ((tBu)Flu-NHC = 2,7-(t)Bu(2)C(13)H(6)CH(2)CH(2)(NCHCCHN)C(6)H(2)Me(3)-2,4,6; Ln = Sc (1a); Lu (1d)) and attached by indenyl modified N-heterocyclic carbene (Ind-NHC)Ln(CH(2)SiMe(3))(2) (Ind-NHC = C(9)H(6)CH(2)CH(2)(NCHCCHN)C(6)H(2)Me(3)-2,4,6; Ln = Sc (3a); Lu (3d)), under the activation of Al(i)Bu(3) and [Ph(3)C][B(C(6)F(5))(4)], showed varied catalytic activities toward homo- and copolymerization of ethylene and norbornene. Among which the scandium complexes, in spite of ligand type, exhibited medium to high catalytic activity for ethylene polymerization (10(5) g mol(Sc)(-1) h(-1) atm(-1)), but all were almost inert to norbornene polymerization. Remarkably, higher activity was found for the copolymerization of ethylene and norbornene when using Sc based catalytic systems, which reached up to 5 x 10(6) g mol(Sc)(-1) h(-1) atm(-1) with 2a. The composition of the isolated copolymer was varying from random to alternating according to the feed ratio of the two monomers (r(E) = 4.1, r(NB) = 0.013). The molecular structure of complex 1d was characterized by X-ray analysis. The influences of structural factors of complexes and polymerization conditions on both the catalytic activity and the norbornene content in the copolymer were discussed. PMID:19826729

Wang, Baoli; Tang, Tao; Li, Yuesheng; Cui, Dongmei

2009-11-01

107

N-Heterocyclic carbene-catalyzed direct cross-aza-benzoin reaction: Efficient synthesis of ?-amino-?-keto esters  

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Full Text Available An efficient catalytic synthesis of ?-amino-?-keto esters has been newly developed. Cross-coupling of various aldehydes with ?-imino ester, catalyzed by N-heterocyclic carbene, leads chemoselectively to ?-amino-?-keto esters in moderate to good yields with high atom efficiency. The reaction mechanism is discussed, and it is proposed that the ?-amino-?-keto esters are formed under thermodynamic control.

Takuya Uno

2012-09-01

108

N-Heterocyclic carbene–palladium(II-1-methylimidazole complex catalyzed Mizoroki–Heck reaction of aryl chlorides with styrenes  

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Full Text Available A well-defined N-heterocyclic carbene–palladium(II-1-methylimidazole [NHC-Pd(II-Im] complex 1 was found to be an effective catalyst for the Mizoroki–Heck reaction of a variety of aryl chlorides with styrenes. Both activated and deactivated aryl chlorides work well to give the corresponding coupling products in good to excellent yields by using tetrabutylammonium bromide (TBAB as the ionic liquid.

Ting-Ting Gao

2012-11-01

109

Suzuki-Miyaura Reactions Catalyzed by C2-Symmetric Pd-Multi-Dentate N-Heterocyclic Carbene Complexes  

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Full Text Available Suzuki-Miyaura coupling reactions are promoted by Pd complexes ligated with C2-symmetric multi-dentate N-heterocyclic carbenes derived in situ from Pd(OAc2 and imidazolium salts. Good to excellent yields were obtained for aryl bromides as substrates. Turnover numbers of up to 105 could be achieved with 5 × 10?4 mol% of Pd(OAc2/1 × 10?3 mol% NHC precatalyst in 24 h.

Zhengning Li

2012-10-01

110

N-heterocyclic carbene boryl radicals: a new class of boron-centered radical.  

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Reduction of xanthates by N-heterocyclic carbene boranes (NHC-boranes) has been suggested to occur by a radical chain mechanism involving heretofore unknown NHC-boryl radicals. In support of this suggestion, both the expected borane dithiocarbonate product and an unexpected borane xanthate product have now been isolated. These are the first NHC-boranes with boron-sulfur bonds, and their structures have been secured by spectroscopic and crystallographic means. The first rate constants for H-atom transfer from an NHC borane complex were determined by using the ring opening of a substituted cyclobutylcarbinyl radical as a clock reaction. The rate constant for reaction of the NHC-borane with a secondary alkyl radical at ambient temperature is 4 x 10(4) M(-1) s(-1), and the Arrhenius function displayed an entropic term (log A term) that was typical for a bimolecular reaction. The B-H bond dissociation energy of an NHC-borane complex has been estimated at 88 kcal/mol. The putative NHC-boryl radical in these transformations has been detected by EPR spectroscopy. Spectral analysis suggests that it is a pi-radical, analogous to the benzyl radical. PMID:19606860

Ueng, Shau-Hua; Solovyev, Andrey; Yuan, Xinting; Geib, Steven J; Fensterbank, Louis; Lacôte, Emmanuel; Malacria, Max; Newcomb, Martin; Walton, John C; Curran, Dennis P

2009-08-12

111

Synthesis, structural characterization and properties of new N-heterocyclic carbene Ag(I) complexes  

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The syntheses and properties of new N-heterocyclic carbene complexes [{1-(2,3,5,6-tetra methyl benzyl)-3-benzylbimy}AgCl] (2a), [{1-(benzyl)-3-benzylbimy}2Ag][BF4] (2b), [{1-(benzyl)-3-butylbimy}AgBr]2 (2c), [{1-(benzyl)-3-(4-nitro-benzyl)bimy}AgBr] (2d), [{1-(benzyl)-3-(4-bromo-benzyl)bimy}AgBr] (2e), [{1-(benzyl)-3-(4-nitro-benzyl)bimy}2Ag][BF4] (2f), [{1-(benzyl)-3-(4-bromo-benzyl)bimy}2Ag][BF4] (2g) (bimy = benzimidazol-2-ylidene), and [{1-(10-bromo-9-anthracenylmethyl)-3-butylimy}AgBr] (2h) (imy = imidazol-2-ylidene) have been described. Compounds 2a-2h have been characterized by 1H NMR-, UV-vis- LC/MS-spectral studies and elemental analysis. Compounds 2a-2c and 2h are unambiguously characterized by single crystal X-ray crystallography. Compound 2h shows solution emission at room temperature.

Kishore, Ravada; Das, Samar K.

2013-12-01

112

Recent advances in carbon dioxide capture, fixation, and activation by using N-heterocyclic carbenes.  

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In the last two decades, CO2 emission has caused a lot of environmental problems. To mitigate the concentration of CO2 in the atmosphere, various strategies have been implemented, one of which is the use of N-heterocyclic carbenes (NHCs) and related complexes to accomplish the capture, fixation, and activation of CO2 effectively. In this review, we summarize CO2 capture, fixation, and activation by utilizing NHCs and related complexes; homogeneous reactions and their reaction mechanisms are discussed. Free NHCs and NHC salts can capture CO2 in both direct and indirect ways to form imidazolium carboxylates, and they can also catalyze the reaction of aromatic aldehydes with CO2 to form carboxylic acids and derivatives. Moreover, associated with transition metals (TMs), NHCs can form NHC-TM complexes to transform CO2 into industrial acid or esters. Non-metal-NHC complexes can also catalyze the reactions of silicon and boron complexes with CO2 . In addition, catalytic cycloaddition of epoxides with CO2 is another effective function of NHC complexes, and NHC ionic liquids perform excellently in this aspect. PMID:24644039

Yang, Longhua; Wang, Hongming

2014-04-01

113

A cationic rhodium(I) N-heterocyclic carbene complex isolated as an aqua adduct  

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The title complex, aqua[1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene](?4-cycloocta-1,5-diene)rhodium(I) tetrafluoridoborate, [Rh(C8H12)(C27H36N2)(H2O)]BF4, exihibits a square-planar geometry around the Rh(I) atom, formed by a bidentate cycloocta-1,5-diene (cod) ligand, an N-heterocylcic carbene and an aqua ligand. The complex is cationic and a BF4? anion balances the charge. The structure exists as a hydrogen-bonded dimer in the solid state, formed via interactions betw...

2011-01-01

114

Synthesis and structural investigation of R2Si (R = Me, Ph) bridged di-N-heterocyclic carbenes.  

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Functionalization of the C4 carbon of an imidazol-derived N-heterocyclic carbene (NHC) may allow fine-tuning of the electronic and steric properties of the C2 carbene center. A facile route to silyl-functionalized di-N-heterocyclic carbenes (Di-NHCs) is described. Treatment of the polymeric lithiated NHC, {Li(IPrH)}n (1) (Li(IPrH) = {(N-2,6-iPr2C6H3)2CHCLi}C:) with a dichlorosilane affords monomeric silyl-functionalized Di-NHCs, R2Si(IPrH)2 (R = Ph, 2; Me, 3). Interestingly, silyl-functionalized mono-NHC, Ph2(Cl)Si(IPrH) (4) with a pendant chloro-substituent can also be exclusively isolated maintaining the reactants 1 and Ph2SiCl2 ratio. NHCs 2 and 4 readily form copper complexes, Ph2Si{(IPrH)CuCl}2 (5) and Ph2(Cl)Si{(IPrH)CuCl} (6), on reaction with CuCl. Straightforward conversion of an NHC to a Di-NHC (2 or 3) via C4 functionalization is reported for the first time. Molecular structures of 2, 4, 5 and 6 have been established by single crystal X-ray diffraction studies. PMID:25101953

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

2014-09-28

115

N-heterocyclic carbene catalyzed carba-, sulfa-, and phospha-Michael additions with NHC·CO? adducts as precatalysts.  

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N-heterocyclic carbene catalyzed Michael additions have been revisited with 1,3-dialkyl- or 1,3-diarylimidazol(in)ium-2-carboxylates, that is, NHC·CO2 adducts, as the source of the free NHC catalysts in solution. Using these precatalysts, a number of efficient carba-, sulfa-, and phospha-Michael additions were achieved very conveniently, without the need for an external strong base to generate the NHC by deprotonation of an azolium salt. To further expand the scope of the procedure, some NHC-catalyzed sulfa-Michael/aldol organocascades were also investigated. PMID:24568358

Hans, Morgan; Delaude, Lionel; Rodriguez, Jean; Coquerel, Yoann

2014-03-21

116

Palladium-N-Heterocyclic Carbene (NHC)-Catalyzed Asymmetric Synthesis of Indolines through Regiodivergent C(sp(3) )?H Activation: Scope and DFT Study.  

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Two bulky, chiral, monodentate N-heterocyclic carbene ligands were applied to palladium-catalyzed asymmetric C?H arylation to incorporate C(sp(3) )?H bond activation. Racemic mixtures of the carbamate starting materials underwent regiodivergent reactions to afford different trans-2,3-substituted indolines. Although this CAr ?Calkyl coupling requires high temperatures (140-160?°C), chiral induction is high. This regiodivergent reaction, when carried out with enantiopure starting materials, can lead to single structurally different enantiopure products, depending on the catalyst chirality. The C?H activation at a tertiary center was realized only in the case of a cyclopropyl group. No C?H activation takes place alpha to a tertiary center. A detailed DFT study is included and analyses of methyl versus methylene versus methine C?H activation is used to rationalize experimentally observed regio- and enantioselectivities. PMID:25262613

Katayev, Dmitry; Larionov, Evgeny; Nakanishi, Masafumi; Besnard, Céline; Kündig, E Peter

2014-11-10

117

Unsymmetrical pincer-type ruthenium complex containing ?-protic pyrazole and N-heterocyclic carbene arms: comparison of Brønsted acidity of NH groups in second coordination sphere.  

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A reaction of a 2-(imidazol-1-yl)methyl-6-(pyrazol-3-yl)pyridine with [RuCl2 (PPh3 )3 ] resulted in tautomerization of the imidazole unit to afford the unsymmetrical pincer-type ruthenium complex 2 containing a protic pyrazole and N-heterocyclic carbene (NHC) arms. Deprotonation of 2 with one equivalent of a base led to the formation of the NHC-pyrazolato complex 3, indicating that the protic NHC arm is less acidic. When 2 was treated with two equivalents of a base under H2 or in 2-propanol, the hydrido complex 4 containing protic NHC and pyrazolato groups was obtained through metal-ligand cooperation. PMID:24965086

Toda, Tatsuro; Kuwata, Shigeki; Ikariya, Takao

2014-07-28

118

Iridium(III) hydrido N-heterocyclic carbene-phosphine complexes as catalysts in magnetization transfer reactions.  

Science.gov (United States)

The hyperpolarization (HP) method signal amplification by reversible exchange (SABRE) uses para-hydrogen to sensitize substrate detection by NMR. The catalyst systems [Ir(H)2(IMes)(MeCN)2(R)]BF4 and [Ir(H)2(IMes)(py)2(R)]BF4 [py = pyridine; R = PCy3 or PPh3; IMes = 1,3-bis(2,4,6-trimethylphenyl)imidazol-2-ylidene], which contain both an electron-donating N-heterocyclic carbene and a phosphine, are used here to catalyze SABRE. They react with acetonitrile and pyridine to produce [Ir(H)2(NCMe)(py)(IMes)(PPh3)]BF4 and [Ir(H)2(NCMe)(py)(IMes)(PCy3)]BF4, complexes that undergo ligand exchange on a time scale commensurate with observation of the SABRE effect, which is illustrated here by the observation of both pyridine and acetonitrile HP. In this study, the required symmetry breaking that underpins SABRE is provided for by the use of chemical inequivalence rather than the previously reported magnetic inequivalence. As a consequence, we show that the ligand sphere of the polarization transfer catalyst itself becomes hyperpolarized and hence that the high-sensitivity detection of a number of reaction intermediates is possible. These species include [Ir(H)2(NCMe)(py)(IMes)(PPh3)]BF4, [Ir(H)2(MeOH)(py)(IMes)(PPh3)]BF4, and [Ir(H)2(NCMe)(py)2(PPh3)]BF4. Studies are also described that employ the deuterium-labeled substrates CD3CN and C5D5N, and the labeled ligands P(C6D5)3 and IMes-d22, to demonstrate that dramatically improved levels of HP can be achieved as a consequence of reducing proton dilution and hence polarization wastage. By a combination of these studies with experiments in which the magnetic field experienced by the sample at the point of polarization transfer is varied, confirmation of the resonance assignments is achieved. Furthermore, when [Ir(H)2(pyridine-h5)(pyridine-d5)(IMes)(PPh3)]BF4 is examined, its hydride ligand signals are shown to become visible through para-hydrogen-induced polarization rather than SABRE. PMID:24215616

Fekete, Marianna; Bayfield, Oliver W; Bayfield, Oliver; Duckett, Simon B; Hart, Sam; Mewis, Ryan E; Pridmore, Natalie; Rayner, Peter J; Whitwood, Adrian

2013-12-01

119

Synthesis of Pd-N-heterocyclic carbene Pd-catalyst and its application in MW-assisted Heck and Suzuki reaction  

Science.gov (United States)

The first Pd-N-heterocyclic carbene (NHC) complex in the form of organic silica is prepared using sol-gel method and its application in Heck and Suzuki reactions are demonstrated. These C-C coupling reactions proceeded efficiently under the influence of microwave irradiation, wit...

120

N-heterocyclic carbene catalyzed formal [3+2] annulation reaction of enals: an efficient enantioselective access to spiro-heterocycles.  

Science.gov (United States)

A highly enantioselective N-heterocyclic carbene (NHC) catalyzed formal [3+2] annulation of ?,?-unsaturated aldehydes with azaaurones or aurone generating spiro-heterocycles has been developed. The protocol represents a unique NHC-activation-based approach to access spiro-heterocyclic derivatives bearing a quaternary stereogenic center with high optical purity (up to 95%?ee). PMID:25130870

Guo, Chang; Schedler, Michael; Daniliuc, Constantin G; Glorius, Frank

2014-09-15

 
 
 
 
121

On the mechanism of N-heterocyclic carbene-catalyzed reactions involving acyl azoliums.  

Science.gov (United States)

Catalytic reactions promoted by N-heterocyclic carbenes (NHCs) have exploded in popularity since 2004 when several reports described new fundamental reactions that extended beyond the long-studied generation of acyl anion equivalents. These new NHC-catalyzed reactions allow chemists to generate unique reactive species from otherwise inert starting materials, all under simple, mild reaction conditions and with exceptional selectivities. In analogy to transition metal catalysis, the use of NHCs has introduced a new set of elementary steps that operate via discrete reactive species, including acyl anion, homoenolate, and enolate equivalents, usually generated by oxidation state reorganization ("redox neutral" reactions). Nearly all NHC-catalyzed reactions offer operationally simple reactions, proceed at room temperature without the need for stringent exclusion of air, and do not generate reaction byproducts. Variation of the catalyst or reaction conditions can profoundly influence reaction outcomes, and researchers can tune the desired selectivities through careful choice of NHC precursor and base. The catalytically generated homoenolate and enolate equivalents are nucleophilic species. In contrast, the catalytically generated acyl azolium and ?,?-unsaturated acyl azoliums are electrophilic cationic species with unique and unprecedented chemistry. For example, when generated catalytically, these species transformed an ?-functionalized aldehyde to an ester under redox neutral conditions without coupling reagents or waste. In addition to providing new approaches to catalytic esterifications, acyl azoliums offer unique reactivities that chemists can exploit for selective reactions. This Account focuses on the discovery and mechanistic investigation of the catalytic generation of acyl azoliums and ?,?-unsaturated acyl azoliums. These chemical species are fascinating, and their catalytic generation is an important development. Studies of their unusual chemistry, however, date back to the intense investigation of thiamine-dependent enzymatic processes in the 1960s. Acyl azoliums are remarkably reactive in acylation chemistry and are unusually chemoselective. These two properties have led to a new wave of reactions such as redox esterification reaction (1) and the catalytic kinetic resolution of challenging substrates (i.e., 3). Our group and others have also developed methods to generate and exploit ?,?-unsaturated acyl azoliums, which have facilitated new C-C bond-forming annulations, including a catalytic, enantioselective variant of the Claisen rearrangement (2). From essentially one class of catalysts, the N-mesityl derived triazolium salts, researchers can easily prepare highly enantioenriched dihydropyranones and dihydropyridinones. Although this field is now one of the most explored areas of enantioselective C-C bond forming reactions, many mechanistic details remained unsolved and in dispute. In this Account, we address the mechanistic inquiries about the characterization of the unsaturated acyl triazolium species and its kinetic profile under catalytically relevant conditions. We also provide explanations for the requirement and effect of the N-mesityl group in NHC catalysis based on detailed experimental data within given specific reactions or conditions. We hope that our studies provide a roadmap for catalyst design/selection and new reaction discovery based on a fundamental understanding of the mechanistic course of NHC reactions. PMID:24410291

Mahatthananchai, Jessada; Bode, Jeffrey W

2014-02-18

122

Catalytic Asymmetric ?-Acylation of Tertiary Amines Mediated by a Dual Catalysis Mode: N-Heterocyclic Carbene and Photoredox Catalysis  

Science.gov (United States)

Cross-coupling reactions are some of the most widely utilized methods for C-C bond formation; however, the requirement for pre-activated starting materials still presents a major limitation. Methods that take direct advantage of the inherent reactivity of the C-H bond offer an efficient alternative to these methods, negating the requirement for substrate pre-activation. In this process two chemically distinct activation events culminate in the formation of the desired C-C bond with loss of H2 as the only by-product. Herein we report the catalytic asymmetric ?-acylation of tertiary amines with aldehydes facilitated by the combination of chiral N-heterocyclic carbene catalysis and photoredox catalysis. PMID:22548244

DiRocco, Daniel A.

2012-01-01

123

An abnormal N-heterocyclic carbene-carbon dioxide adduct from imidazolium acetate ionic liquids: the importance of basicity.  

Science.gov (United States)

In the reaction of 1-ethyl-3-methylimidazolium acetate [C2C1Im][OAc] ionic liquid with carbon dioxide at 125?°C and 10?MPa, not only the known N-heterocyclic carbene (NHC)-CO2 adduct I, but also isomeric aNHC-CO2 adducts II and III were obtained. The abnormal NHC-CO2 adducts are stabilized by the presence of the polarizing basic acetate anion, according to static DFT calculations and ab initio molecular dynamics studies. A further possible reaction pathway is facilitated by the high basicity of the system, deprotonating the initially formed NHC-CO2 adduct I, which can then be converted in the presence of the excess of CO2 to the more stable 2-deprotonated anionic abnormal NHC-CO2 adduct via the anionic imidazolium-2,4-dicarboxylate according to DFT calculations on model compounds. This suggests a generalizable pathway to abnormal NHC complex formation. PMID:25137312

Kelemen, Zsolt; Péter-Szabó, Barbara; Székely, Edit; Hollóczki, Oldamur; Firaha, Dzmitry S; Kirchner, Barbara; Nagy, József; Nyulászi, László

2014-09-26

124

Bis-N-heterocyclic carbene (NHC) stabilized ?6-arene iron(0) complexes: synthesis, structure, reactivity, and catalytic activity.  

Science.gov (United States)

Reaction of FeCl2 with the chelating bis-N-heterocyclic carbene (NHC) bis-(N-Dipp-imidazole-2-ylidene)methylene (abbreviated {((Dipp)C:)2CH2}) (Dipp = 2,6-di-isopropylphenyl) affords the complex [FeCl2{((Dipp)C:)2CH2}] (1) in high yield. Reduction of complex 1 with excess KC8 with a 10-fold molar excess of PMe3 affords the Fe(II) complex [FeH{((Dipp)C:)2CH2}(PMe3)(?(2)-PMe2CH2)] (2) as a mixture of three stereoisomers. Complex 2, the first example of any iron(II) complex bearing mutually an NHC and PMe3 ligand, is likely obtained from the in situ, reductively generated 16 VE Fe(0) complex, [Fe{((Dipp)C:)2CH2}(PMe3)2] (2'), following intramolecular C-H activation of one of the phosphorus-bound CH3 groups. Complex 2 is unstable in aromatic solvents and forms, via a novel synthetic transformation involving intramolecular reductive elimination and concomitant PMe3 elimination, the Fe (0) arene complex [Fe{((Dipp)C:)2CH2}(?(6)-C6D6)] (4-d6) in C6D6. Complex 4-d6 represents the first example of an NHC stabilized iron (0) arene complex. The transformation from 2 to 4-d6 can be accelerated at higher temperature and at 60 °C forms immediately. Alternatively, the reduction of 1 in the presence of toluene or benzene affords the complexes [Fe{((Dipp)C:)2CH2}(?(6)-C7H8)] (3) and [Fe{((Dipp)C:)2CH2}(?(6)-C6H6)] (4), selectively and in good yields. DFT calculations characterizing the bonding situation in 3 and 4 reveal similar energies of the HOMO and LUMO orbitals, with the LUMO orbital of both complexes located on the Dipp rings of the bis-NHC. The HOMO orbital reflects a ?-back-bonding interaction between the Fe(0) center and the chelating NHC ligand, while the HOMO-1 is associated with the arene interaction with the Fe(0) site. The calculations do not suggest any noninnocence of the coordinated arene in either complex. Moreover, the (57)Fe Mössbauer spectrum of 4 at 80K exhibits parameters (? = 0.43 mm·s(-1); ?EQ = 1.37 mm·s(-1)) which are consistent with a five-coordinate Fe(0) system, rendering 3 and 4 the first examples of well-defined authentic Fe(0)-?(6)-arene complexes of the type [Fe(?(6)-arene)L2] (L = ?(1 or 2) neutral ligand, mono or bidentate). Some reactivitiy studies of 3 are also reported: The reaction of 3 with excess CO selectively yields the five-coordinate piano-stool complex [Fe{((Dipp)C:)2CH2}(CO)3] (6) in near quantitative yields, while the reaction of complex 3 with C6D6 under heating affords by toluene elimination 4-d6. The catalytic ability of 4 was also investigated with respect to amide reduction to amines, for a variety of substrates using Ph2SiH2 as a hydride source. In all cases good to excellent yields to the corresponding amines were obtained. The use of 4 as a precatalyst represents the first example of a well-defined Fe(0) complex to effect this catalytic process. PMID:24195449

Blom, Burgert; Tan, Gengwen; Enthaler, Stephan; Inoue, Shigeyoshi; Epping, Jan Dirk; Driess, Matthias

2013-12-01

125

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

Energy Technology Data Exchange (ETDEWEB)

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

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

2013-06-07

126

Visible-light photoredox catalysis: selective reduction of carbon dioxide to carbon monoxide by a nickel N-heterocyclic carbene-isoquinoline complex.  

Science.gov (United States)

The solar-driven reduction of carbon dioxide to value-added chemical fuels is a longstanding challenge in the fields of catalysis, energy science, and green chemistry. In order to develop effective CO2 fixation, several key considerations must be balanced, including (1) catalyst selectivity for promoting CO2 reduction over competing hydrogen generation from proton reduction, (2) visible-light harvesting that matches the solar spectrum, and (3) the use of cheap and earth-abundant catalytic components. In this report, we present the synthesis and characterization of a new family of earth-abundant nickel complexes supported by N-heterocyclic carbene-amine ligands that exhibit high selectivity and activity for the electrocatalytic and photocatalytic conversion of CO2 to CO. Systematic changes in the carbene and amine donors of the ligand have been surveyed, and [Ni((Pr)bimiq1)](2+) (1c, where (Pr)bimiq1 = bis(3-(imidazolyl)isoquinolinyl)propane) emerges as a catalyst for electrochemical reduction of CO2 with the lowest cathodic onset potential (E(cat) = -1.2 V vs SCE). Using this earth-abundant catalyst with Ir(ppy)3 (where ppy = 2-phenylpyridine) and an electron donor, we have developed a visible-light photoredox system for the catalytic conversion of CO2 to CO that proceeds with high selectivity and activity and achieves turnover numbers and turnover frequencies reaching 98,000 and 3.9 s(-1), respectively. Further studies reveal that the overall efficiency of this solar-to-fuel cycle may be limited by the formation of the active Ni catalyst and/or the chemical reduction of CO2 to CO at the reduced nickel center and provide a starting point for improved photoredox systems for sustainable carbon-neutral energy conversion. PMID:24033186

Thoi, V Sara; Kornienko, Nikolay; Margarit, Charles G; Yang, Peidong; Chang, Christopher J

2013-09-25

127

Combining oxidative N-heterocyclic carbene catalysis with click chemistry: a facile one-pot approach to 1,2,3-triazole derivatives.  

Science.gov (United States)

A combination of the oxidative N-heterocyclic carbene catalysis and click chemistry has been explored for the direct, one-pot synthesis of 1,2,3-triazole derivatives from aromatic aldehydes. This procedure was found to be very efficient and a variety of 1,2,3-triazole derivatives could be accessed through their corresponding propargyl esters in moderate-to-good yields under mild conditions. PMID:23606655

Ramanjaneyulu, B T; Reddy, Virsinha; Arde, Panjab; Mahesh, Sriram; Anand, R Vijaya

2013-07-01

128

N-heterocyclic carbene (NHC)-stabilized silanechalcogenones: NHC-->Si(R2)=E (E=O, S, Se, Te).  

Science.gov (United States)

A series of N-heterocyclic carbene-stabilized silanechalcogenones 2 a,b (Si=O), 3 a,b (Si=S), 4 a,b (Si=Se), and 5 a,b (Si=Te) are described. The silanone complexes 2 a,b were prepared by facile oxygenation of the carbene-silylene adducts 1 a,b with N(2)O, whereas their heavier congeners were synthesized by gentle chalcogenation of 1 a,b with equimolar amounts of elemental sulfur, selenium, and tellurium, respectively. These novel compounds have been isolated in a crystalline form in high yields and have been fully characterized by a variety of techniques including IR spectroscopy, ESIMS, and multinuclear NMR spectroscopy. The structures of 2 b, 3 a, 4 a, 4 b, and 5 b have been confirmed by single-crystal X-ray crystallography. Due to the NHC-->Si donor-acceptor electronic interaction, the Si=E (E=O, S, Se, Te) moieties within these compounds are well stabilized and thus the compounds possess several ylide-like resonance structures. Nevertheless, these species also exhibit considerable Si=E double-bond character, presumably through a nonclassical Si=E pi-bonding interaction between the chalcogen lone-pair electrons and two antibonding Si-N sigma* orbitals, as evidenced by their high stretching vibration modes and the shortening of the Si-E distances (between 5.4 and 6.3%) compared with the corresponding Si-E single-bond lengths. PMID:20013763

Yao, Shenglai; Xiong, Yun; Driess, Matthias

2010-01-25

129

CO2 and Sn(II) adducts of N-heterocyclic carbenes as delayed-action catalysts for polyurethane synthesis.  

Science.gov (United States)

Catalytic rivals: Both CO(2)-protected tetrahydropyrimidin-2-ylidene-based N-heterocyclic carbenes (NHCs) and Sn(II)-1,3-dimesitylimidazol-2-ylidene, as well as Sn(II)-1,3-dimesitylimidazolin-2-ylidene complexes (example displayed), have been identified as truly latent catalysts for polyurethane (PUR) synthesis rivaling all existing systems both in activity and latency.A series of CO(2)-protected pyrimidin-2-ylidenes as well as 1,3-dimesitylimidazol-2-ylidene and dimesitylimidazolin-2-ylidene complexes of Sn(II) have been prepared. Selected single-crystal X-ray structures are reported. The new compounds were investigated for their catalytic behavior in polyurethane (PUR) synthesis. All compounds investigated showed excellent catalytic activity, rivaling the industrially most relevant catalyst dibutyltin dilaurate. Even more important, all compounds displayed pronounced latent behavior, in selected cases rivaling and exceeding the industrially relevant latent catalyst phenylmercury neodecanoate both in terms of latency and catalytic activity. This allows for creating one-component PUR systems with improved pot lifetimes. Pseudo-second-order kinetics were found for both CO(2)-protected tetrahyropyrimidin-2-ylidenes and for [SnCl(2)(1,3-dimesityldihydroimidazol-2-ylidene)], indicating a fast pre-catalyst decomposition prior to polyurethane formation. 1,3-Di(2-propyl)tetrahydropyrimidin-2-ylidene was additionally found to be active in the cyclotrimerization of various isocyanates, offering access to a broad variability in polymer structure, that is, creating both urethane and isocyanurate moieties within the same polymer. PMID:19212991

Bantu, Bhasker; Pawar, Gajanan Manohar; Decker, Ulrich; Wurst, Klaus; Schmidt, Axel M; Buchmeiser, Michael R

2009-01-01

130

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

Science.gov (United States)

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

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

2014-06-01

131

Experimental and computational studies on the mechanism of zwitterionic ring-opening polymerization of ?-valerolactone with N-heterocyclic carbenes.  

Science.gov (United States)

Experimental and computational investigations of the zwitterionic ring-opening polymerization (ZROP) of ?-valerolactone (VL) catalyzed by the N-heterocyclic carbenes (NHC) 1,3-diisopropyl-4,5-dimethyl-imidazol-2-ylidene (1) and 1,3,4,5-tetramethyl-imidazol-2-ylidene (2) were carried out. The ZROP of ?-valerolactone generates cyclic poly(valerolactone)s whose molecular weights are higher than predicted from [VL]0/[NHC]0. Kinetic studies reveal the rate of polymerization is first order in [VL] and first order in [NHC]. Density functional theory (DFT) calculations were carried out to elucidate the key steps involved in the ring-opening of ?-valerolactone and its subsequent oligomerization. These studies have established that the initial steps of the mechanism involve nucleophilic attack of the NHC on ?-valerolactone to form a zwitterionic tetrahedral intermediate. DFT calculations indicate that the highest activation barrier of the entire mechanism is associated with the ring-opening of the tetrahedral intermediate formed from the NHC and ?-valerolactone, a result consistent with inefficient initiation to generate reactive zwitterions. The large barrier in this step is due to the fact that ring-opening requires a partial positive charge to develop next to the directly attached NHC moiety which already bears a delocalized positive charge. PMID:24702523

Acharya, Ashwin K; Chang, Young A; Jones, Gavin O; Rice, Julia E; Hedrick, James L; Horn, Hans W; Waymouth, Robert M

2014-06-19

132

Electrogenerated N-heterocyclic carbene: N-acylation of chiral oxazolidin-2-ones in ionic liquids  

International Nuclear Information System (INIS)

An electrochemical procedure for the N-acylation of chiral oxazolidin-2-ones, in the absence of volatile molecular organic solvents, has been set up via electrolyses of ionic liquid [bmim]BF4 containing oxazolidin-2-ones followed by addition of saturated or unsaturated anhydrides. N-acyloxazolidin-2-ones were isolated in good to elevated yields. The electrochemically induced N-acylation of chiral oxazolidin-2-ones occurs with total retention of the absolute configuration of all the chiral atoms. The electrogenerated carbene (1-butyl-3-methyl-1H-imidazol-2-ylidene) has been indicated as the base involved in the deprotonation of chiral oxazolidin-2-ones

133

N-alkyl functionalised expanded ring N-heterocyclic carbene complexes of rhodium(I) and iridium(I): structural investigations and preliminary catalytic evaluation.  

Science.gov (United States)

A series of new N-alkyl functionalised 6- and 7-membered expanded ring N-heterocyclic carbene (NHC) pro-ligands 3-6 and their corresponding complexes of rhodium(I) and iridium(I), [M(NHC)(COD)Cl] 7-14 and [M(NHC)(CO)2Cl] 15-22 are described. The complexes have been characterised by (1)H and (13)C{(1)H} NMR, mass spectrometry, IR and X-ray diffraction. It is noted from X-ray diffraction studies that the N-alkyl substituents are found to orientate themselves away from the metal centre due to unfavourable steric interactions resulting in low percent buried volume (%V(bur)) values in the solid state. The heterocycle ring size is also found to dictate the spatial orientation of the N-alkyl substituents in the neopentyl functionalised derivatives 10 and 14. The 7-membered derivative 14 allows for a conformational 'twist' of the heterocycle ring with the N-alkyl substituents adopting a mutually trans configuration with respect to each other, while the more rigid 6-membered system 10 does not allow for this conformational 'twist' and consequently the N-alkyl substituents adopt a mutually cis configuration. The ?-donor function of this new class of expanded ring NHC ligand has also been probed by measured IR stretching frequencies of the [M(NHC)(CO)2Cl] complexes 15-22. A preliminary catalytic survey of the hydrogenation of functionalised alkenes with molecular hydrogen under mild conditions has also been undertaken with complex , affording an insight into the application of large ring NHC ancillary ligands bearing N-alkyl substituents in hydrogenation transformations. PMID:23292451

Dunsford, Jay J; Tromp, Dorette S; Cavell, Kingsley J; Elsevier, Cornelis J; Kariuki, Benson M

2013-05-28

134

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

Science.gov (United States)

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

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

2011-10-14

135

Cyclodimerization versus polymerization of methyl methacrylate induced by N-heterocyclic carbenes: a combined experimental and theoretical study.  

Science.gov (United States)

The activation behavior of two N-heterocyclic carbenes (NHCs), namely, 1,3-bis(isopropyl)imidazol-2-ylidene(NHCiPr) and 1,3-bis(tert-butyl) imidazol-2-ylidene (NHCtBu), as organic nucleophiles in the reaction with methyl methacrylate (MMA) is described. NHCtBu allows the polymerization of MMA in DMF at room temperature and in toluene at 50?°C, whereas NHCiPr reacts with two molecules of MMA, forming an unprecedented imidazolium-enolate cyclodimer (NHCiPr/MMA=1:2). It is proposed that the reaction mechanism occurs by initial 1,4-nucleophilic addition of NHCiPr to MMA, generating a zwitterionic enolate 2, followed by addition of 2 to a second MMA molecule, forming a linear imidazolium-enolate 3 (NHCiPr/MMA=1:2). Proton transfer, generating intermediate 5, followed by cyclization and release of methanol yielded the aforementioned zwitterionic cyclodimer 1:2 adduct 7, the molecular structure of which has been established by NMR spectroscopy, X-ray diffraction, and mass spectrometry. This unexpected difference between NHCtBu and NHCiPr in the reaction with MMA (polymerization and cyclodimerization, respectively) can be rationalized by using DFT calculations. In particular, the nature of the NHC strongly influences the cyclodimerization pathway, the cyclization of 5 and the release of methanol are the discriminating step and limiting step, respectively. In the case of NHCtBu, both steps are strongly disfavoured compared with that of NHCiPr (energetic difference of around 14 and 9?kcal?mol(-1), respectively), preventing the cyclization mechanism from a kinetic viewpoint. Moreover, addition of a third molecule of MMA in the polymerization pathway results in a lower activation barrier than that of the limiting step in the cyclodimerization pathway (difference of around 14?kcal?mol(-1)), in agreement with the formation of polymethyl methacrylate (PMMA) by using NHCtBu as nucleophile. PMID:24604823

Nzahou Ottou, Winnie; Bourichon, Damien; Vignolle, Joan; Wirotius, Anne-Laure; Robert, Fredéric; Landais, Yannick; Sotiropoulos, Jean-Marc; Miqueu, Karinne; Taton, Daniel

2014-04-01

136

Substituent-dependent structures and catalysis of benzimidazole-tethered N-heterocyclic carbene complexes of Ag(I), Ni(II) and Pd(II).  

Science.gov (United States)

Homoleptic cationic benzimidazole-imidazolin-2-ylidene N-heterocyclic carbene (NHC = L) complexes of Ni(II) and Pd(II) have been prepared directly from the ligand precursor in salt form [H.L]Cl and from the transmetallation route via Ag(I). The N-tether of the imidazolinylidene ring imposes a significant influence on the nuclearity of the intermediate Ag(I)-NHC complexes and the geometric isomer outcome of the d(8) products. Use of a benzyl-substituted NHC gives [Ag(4)(L(Bn))(2)Cl(4)], 2a (from [HL(Bn)]Cl, 1a, and Ag(2)O) (Bn = benzyl), which shows an alignment of four silver atoms bridged by the difunctional C-N ligands and chlorides. Its transmetallation with NiCl(2)(PPh(3))(4) and PdCl(2)(MeCN)(2) results in double-metal salts 2[M(L(Bn))(2)](2+)[Ag(4)Cl(8)](4-) (M = Ni (3a) and Pd (4a)). The nuclearity of the Ag(4) aggregate is maintained in the transmetallation process. Their Ag-free forms [M(L(Bn))(2)]Cl(2) (M = Ni (5) and Pd (6)) were prepared by direct deprotonation of 1a with M(OAc)(2). The two carbenic carbon donor are cis- to each other in both 3a and 4a, thus imposing the weaker sigma-benzimidazole nitrogen donor to be trans to them. A sterically demanding mesityl pendant however gives the dinuclear dissymmetic [Ag(2)(L(Mes))(2)Cl(2)], 2b (Mes = mesityl) that shows a 12-membered metallomacrocyclic ring with a 2-coordinated [Ag(I)(NHC)(2)] and 4-coordinated [Ag(I)(Imd)(2)Cl(2)] (Imd = imidazole). Transmetallation of the latter, or direct metallation from [HL(Mes)]Cl, 1b, gives [M(L(Mes))(2)]Cl(2) (M = Ni (3b) and Pd (4b)) with the two carbonic carbon trans to each other. The catalytic potential of 3b and 4b, which are more effective than 5 and 6, has been demonstrated by their high activities in Ni-catalyzed Kumada at room temperature and Pd-catalyzed Heck couplings of aryl and/or heteroaryl halides, respectively. PMID:20440424

Li, Fuwei; Hu, Jian Jin; Koh, Lip Lin; Hor, T S Andy

2010-06-14

137

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

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

Peter B. Hitchcock

2010-01-01

138

Water-soluble IrIII N-heterocyclic carbene based catalysts for the reduction of CO2 to formate by transfer hydrogenation and the deuteration of aryl amines in water.  

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Two new water-soluble [IrI(2)(AcO)(bis-NHC)] complexes (NHC=N-heterocyclic carbene) incorporating a sulfonate functionality have been synthesized. The two complexes have been tested in the reduction of CO(2) with H(2) and iPrOH, and their activity has been compared with similar species without the sulfonate moiety. In both reactions, the complex with the two abnormally bound NHCs shows the best catalytic efficiencies, due to the higher ?-electron-donor character of the ligand. Remarkably, the activities obtained for the reduction of CO(2) under the transfer hydrogenation conditions are the best reported to date in terms of TON value (max. TON=2700). The two new complexes have also shown very good activity in the selective deuteration of arylamines, a process that is known to proceed through a chelate assisted N-directed process. PMID:21365699

Azua, Arturo; Sanz, Sergio; Peris, Eduardo

2011-03-28

139

Antibacterial properties of water-soluble gold(I) N-heterocyclic carbene complexes.  

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The antibacterial properties of water-soluble gold(I) complexes [1-methyl-3-(3-sulfonatopropyl)imidazol-2-ylidene]gold(I) chloride (C1), [1-mesityl-3-(3-sulfonatopropyl)imidazol-2-ylidene]gold(I) chloride (C2), [1-(2,6-diisopropylphenyl)-3-(3-sulfonatopropyl)imidazol-2-ylidene]gold(I) chloride (C3) and [1,3-bis(2,6-diisopropyl-4-sodiumsulfonatophenyl)imidazol-2-ylidene]gold(I) chloride (C4) and the respective ligands were assessed by agar diffusion and broth macrodilution methods against Gram-positives Staphylococcus aureus, Enterococcus faecalis and Micrococcus luteus and the Gram-negative bacteria Yersinia ruckeri, Pseudomonas aeruginosa and Escherichia coli. Viability after treatments was determined by direct plate count. The bactericidal activity displayed by C1 and C3 was comparable to that of AgNO3. PMID:24662463

Fernández, Gabriela A; Vela Gurovic, María S; Olivera, Nelda L; Chopa, Alicia B; Silbestri, Gustavo F

2014-06-01

140

Highly efficient deep-blue emitters based on cis and trans N-heterocyclic carbene Pt(II) acetylide complexes: synthesis, photophysical properties, and mechanistic studies.  

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We have synthesized cis and trans N-heterocyclic carbene (NHC) platinum(II) complexes bearing ?-alkynyl ancillary ligands, namely [Pt(dbim)2 (C?CR)2 ] [DBIM=N,N'-didodecylbenzimidazoline-2-ylidene; R=C6 H4 F (4), C6 H5 (5), C6 H2 (OMe)3 (6), C4 H3 S (7), and C6 H4 C?CC6 H5 (8)] and [Pt(ibim)2 (C?CC6 H5 )2 ] (9) (ibim=N,N'-diisopropylbenzimidazoline-2-ylidene), starting from [Pt(cod)(C?CR)2 ] (COD=cyclooctadiene) and 2?equivalents of [dbimH]Br ([ibimH]Br for complexes 9) in the presence of tBuOK and THF. Mechanistic investigations aimed at uncovering the cis to trans isomerization reaction have been performed on the representative cis complex 5?a [Pt(dbim)2 (C?CC6 H5 )2 ] and revealed the isomerization to progress smoothly in good yield when 5?a was treated with catalytic amounts of [Pt(cod)(C?CR)2 ] at 75?°C in THF or when 5?a was heated at 200?°C in the solid state under an inert atmosphere. Detailed examination of the reactions points to the possible involvement, in a catalytic fashion, of a solvent-stabilized Pt(II) dialkyne complex in the former case and a Pt(0) NHC complex in the latter case, for the transformation of the cis isomer to the corresponding trans complex. Thermal stability and the isomerization process in the solid state have been further investigated on the basis of TGA and DSC measurements. X-ray diffraction studies have been carried out to confirm the solid-state structures of 4?b, 5?a, 5?b, and 9?b. All of the synthesized dialkyne complexes 4-9 exhibit phosphorescence in solution, in the solid state at room temperature (RT), and also in frozen solvent glasses at 77?K. The emission wavelengths and quantum yields have been found to be highly tunable as a function of the alkynyl ligand. In particular, the trans isomer of complex 9 in a spin-coated film (10?wt?% in poly(methyl methacrylate), PMMA) exhibits a high phosphorescence quantum yield of 80?%, which is the highest reported for Pt(II) -based deep-blue emitters. Experimental observations and time-dependent density functional theory (TD-DFT) calculations are strongly indicative of the emission being mainly governed by metal-perturbed interligand ((3) IL) charge transfer. PMID:24108420

Zhang, Yuzhen; Blacque, Olivier; Venkatesan, Koushik

2013-11-11

 
 
 
 
141

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

International Nuclear Information System (INIS)

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

142

Palladium complexes of abnormal N-heterocyclic carbenes as precatalysts for the much preferred Cu-free and amine-free Sonogashira coupling in air in a mixed-aqueous medium.  

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A series of new PEPPSI (Pyridine Enhanced Precatalyst Preparation Stabilization and Initiation) themed precatalysts of abnormal N-heterocyclic carbenes for the highly desirable Cu-free and amine-free Sonogashira coupling in air in a mixed-aqueous medium is reported. Specifically, the PEPPSI themed (NHC)PdI2(pyridine) type precatalysts, 1b-4b, efficiently carried out the highly convenient Cu-free and amine-free Sonogashira coupling of aryl bromides and iodides with terminal acetylenes in air in a mixed aqueous medium. Complexes, 1b-4b, were synthesized by the direct reaction of the corresponding imidazo[1,2-a]pyridinium iodide salts, 1a-4a, with PdCl2 in pyridine in the presence of K2CO3 as a base while the imidazo[1,2-a]pyridinium iodide salts, 1a-4a, were in turn synthesized by the alkylation reactions of the respective imidazo[1,2-a]pyridine derivatives with alkyl iodides. The density functional theory (DFT) studies revealed that these imidazol-3-ylidene[1,2-a]pyridine derived abnormal carbenes are strongly sigma-donating and consequently significantly weaken the catalytically important labile trans pyridine ligand in 1b-4b. PMID:20023883

John, Alex; Shaikh, Mobin M; Ghosh, Prasenjit

2009-12-21

143

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

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

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

2014-11-18

144

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

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

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

2014-06-15

145

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

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

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

2010-12-01

146

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

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

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

2014-10-01

147

A new, mild one-pot synthesis of iodinated heterocycles as suitable precursors for N-heterocyclic carbene complexes  

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The use of I2/AgOAc in dichloromethane constitutes a cheap, mild, and efficient method for the selective iodination of a variety of heterocycles. In a number of cases, this method provides superior yields than other literature methods and affords iodo-functionalized heterocycles that are suitable precursors for carbene complexes.

Iglesias, Manuel; Schuster, Oliver; Albrecht, Martin

2010-01-01

148

Total Syntheses of the Histone Deacetylase Inhibitors Largazole and 2-epi-Largazole: Application of N-Heterocyclic Carbene Mediated Acylations in Complex Molecule Synthesis  

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Details of the evolution of strategies toward convergent assembly of the histone deacetylase inhibiting natural product largazole exploiting ?,?-unsaturated-?,?-epoxy-aldehydes and a thiazole-thiazoline containing ?-amino-acid are described. The initial N-heterocyclic carbene mediated redox amidation exploying these two types of building blocks representing largazole’s structural domains of distinct biosynthetic origin directly afforded the seco-acid of largazole. This was accomplished without any protecting groups resident upon either thioester bearing epoxy-aldehyde or the tetrapeptide. However, the ineffective production of largazole via the final macrolactonization led to an alternative intramolecular esterification/macrolactamization strategy employing the established two building blocks. This provided largazole along with its C2-epimer via an unexpected inversion of the ?-stereocenter at the valine residue. The biological evaluation demonstrated that both largazole and 2-epi-largazole led to dose-dependent increases of acetylation of histone H3, indicating their potencies as class I histone deacetylase selective inhibitiors. Enhanced p21 expression was also induced by largazole and its C2 epimer. In addition, 2-epi-largazole displayed more potent activity than largazole in cell viability assays against PC-3 and LNCaP prostate cancer cell lines. PMID:21244075

Wang, Bo; Huang, Po-Hsien; Chen, Ching-Shih

2014-01-01

149

Highly emissive platinum(II) complexes bearing carbene and cyclometalated ligands.  

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A series of heteroleptic platinum(II) complexes (1a-3a and 1b-3b) bearing a dicarbene ligand and a cyclometalated bidentate ligand have been prepared. Two of the complexes (1a and 3a) were characterized by X-ray diffraction analyses, confirming the square-planar structures. Detailed spectroscopic properties of the complexes have been studied, and two complexes, 3a and 3b bearing a carbene chelate, which has a trimethylene group between the two N-heterocyclic carbene ligating groups, show intense luminescence (quantum yields >50%) in fluid solution at room temperature. Non-radiative rate constants of the emissive excited states of the complexes vary markedly among the 6 complexes, although radiative constants of them lie in a narrow range of values, so that the difference in the photophysical properties is ascribed to the difference in the non-radiative decay rates. The photophysical parameters have been discussed with the results of the quantum mechanical calculations. The DFT and TDDFT calculations show that the emissive excited states have mainly ligand-centered character with a slight contribution of MLCT. PMID:23411495

Uesugi, Haruka; Tsukuda, Toshiaki; Takao, Koichiro; Tsubomura, Taro

2013-05-28

150

Expanded-ring N-heterocyclic carbenes for the stabilization of highly electrophilic gold(i) cations.  

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Strategies for the synthesis of highly electrophilic Au(I) complexes from either hydride- or chloride-containing precursors have been investigated by employing sterically encumbered Dipp-substituted expanded-ring NHCs (Dipp=2,6-iPr2 C6 H3 ). Thus, complexes of the type (NHC)AuH have been synthesised (for NHC=6-Dipp or 7-Dipp) and shown to feature significantly more electron-rich hydrides than those based on ancillary imidazolylidene donors. This finding is consistent with the stronger ?-donor character of these NHCs, and allows for protonation of the hydride ligand. Such chemistry leads to the loss of dihydrogen and to the trapping of the [(NHC)Au](+) fragment within a dinuclear gold cation containing a bridging hydride. Activation of the hydride ligand in (NHC)AuH by B(C6 F5 )3 , by contrast, generates a species (at low temperatures) featuring a [HB(C6 F5 )3 ](-) fragment with spectroscopic signatures similar to the "free" borate anion. Subsequent rearrangement involves B?C bond cleavage and aryl transfer to the carbophilic metal centre. Under halide abstraction conditions utilizing Na[BAr(f) 4 ] (Ar(f) =C6 H3 (CF3 )2 -3,5), systems of the type [(NHC)AuCl] (NHC=6-Dipp or 7-Dipp) generate dinuclear complexes [{(NHC)Au}2 (?-Cl)](+) that are still electrophilic enough at gold to induce aryl abstraction from the [BAr(f) 4 ](-) counterion. PMID:25336057

Phillips, Nicholas; Dodson, Tristan; Tirfoin, Rémi; Bates, Joshua I; Aldridge, Simon

2014-12-01

151

Highly selective biaryl cross-coupling reactions between aryl halides and aryl Grignard reagents: a new catalyst combination of N-heterocyclic carbenes and iron, cobalt, and nickel fluorides.  

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Combinations of N-heterocyclic carbenes (NHCs) and fluoride salts of the iron-group metals (Fe, Co, and Ni) have been shown to be excellent catalysts for the cross-coupling reactions of aryl Grignard reagents (Ar(1)MgBr) with aryl and heteroaryl halides (Ar(2)X) to give unsymmetrical biaryls (Ar(1)-Ar(2)). Iron fluorides in combination with SIPr, a saturated NHC ligand, catalyze the biaryl cross-coupling between various aryl chlorides and aryl Grignard reagents in high yield and high selectivity. On the other hand, cobalt and nickel fluorides in combination with IPr, an unsaturated NHC ligand, exhibit interesting complementary reactivity in the coupling of aryl bromides or iodides; in contrast, with these substrates the iron catalysts show a lower selectivity. The formation of homocoupling byproducts is suppressed markedly to less than 5% in most cases by choosing the appropriate metal fluoride/NHC combination. The present catalyst combinations offer several synthetic advantages over existing methods: practical synthesis of a broad range of unsymmetrical biaryls without the use of palladium catalysts and phosphine ligands. On the basis of stoichiometric control experiments and theoretical studies, the origin of the unique catalytic effect of the fluoride counterion can be ascribed to the formation of a higher-valent heteroleptic metalate [Ar(1)MF(2)]MgBr as the key intermediate in our proposed catalytic cycle. First, stoichiometric control experiments revealed the stark differences in chemical reactivity between the metal fluorides and metal chlorides. Second, DFT calculations indicate that the initial reduction of di- or trivalent metal fluoride in the wake of transmetalation with PhMgCl is energetically unfavorable and that formation of a divalent heteroleptic metalate complex, [PhMF(2)]MgCl (M = Fe, Co, Ni), is dominant in the metal fluoride system. The heteroleptic ate-complex serves as a key reactive intermediate, which undergoes oxidative addition with PhCl and releases the biaryl cross-coupling product Ph-Ph with reasonable energy barriers. The present cross-coupling reaction catalyzed by iron-group metal fluorides and an NHC ligand provides a highly selective and practical method for the synthesis of unsymmetrical biaryls as well as the opportunity to gain new mechanistic insights into the metal-catalyzed cross-coupling reactions. PMID:19639999

Hatakeyama, Takuji; Hashimoto, Sigma; Ishizuka, Kentaro; Nakamura, Masaharu

2009-08-26

152

Axial ligand exchange of N-heterocyclic cobalt(III) Schiff base complexes: molecular structure and NMR solution dynamics.  

Science.gov (United States)

The kinetic and thermodynamic ligand exchange dynamics are important considerations in the rational design of metal-based therapeutics and therefore, require detailed investigation. Co(III) Schiff base complex derivatives of bis(acetylacetone)ethylenediimine [acacen] have been found to be potent enzyme and transcription factor inhibitors. These complexes undergo solution exchange of labile axial ligands. Upon dissociation, Co(III) irreversibly interacts with specific histidine residues of a protein, and consequently alters structure and causes inhibition. To guide the rational design of next generation agents, understanding the mechanism and dynamics of the ligand exchange process is essential. To investigate the lability, pH stability, and axial ligand exchange of these complexes in the absence of proteins, the pD- and temperature-dependent axial ligand substitution dynamics of a series of N-heterocyclic [Co(acacen)(X)(2)](+) complexes [where X = 2-methylimidazole (2MeIm), 4-methylimidazole (4MeIm), ammine (NH(3)), N-methylimidazole (NMeIm), and pyridine (Py)] were characterized by NMR spectroscopy. The pD stability was shown to be closely related to the nature of the axial ligand with the following trend toward aquation: 2MeIm > NH(3) ? 4MeIm > Py > Im > NMeIm. Reaction of each [Co(III)(acacen)(X)(2)](+) derivative with 4MeIm showed formation of a mixed ligand Co(III) intermediate via a dissociative ligand exchange mechanism. The stability of the mixed ligand adduct was directly correlated to the pD-dependent stability of the starting Co(III) Schiff base with respect to [Co(acacen)(4MeIm)(2)](+). Crystal structure analysis of the [Co(acacen)(X)(2)](+) derivatives confirmed the trends in stability observed by NMR spectroscopy. Bond distances between the Co(III) and the axial nitrogen atoms were longest in the 2MeIm derivative as a result of distortion in the planar tetradentate ligand, and this was directly correlated to axial ligand lability and propensity toward exchange. PMID:23282130

Manus, Lisa M; Holbrook, Robert J; Atesin, Tulay A; Heffern, Marie C; Harney, Allison S; Eckermann, Amanda L; Meade, Thomas J

2013-01-18

153

Luminescent square-planar platinum(II) complexes with tridentate 3-bis(2-pyridylimino)isoindoline and monodentate N-heterocyclic ligands.  

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A series of platinum(II) complexes with 1,3-bis(2-pyridylimino)isoindoline (BPI) derivatives were prepared by substitution of the coordinated Cl in the precursor complex Pt(BPI)Cl with a N-heterocyclic ligand such as pyridine, phthalazine or phenanthridine. These complexes display orange to red luminescence in fluid dichloromethane solutions and in the solid states at room temperature. The photophysical properties were tuned by introducing electron-withdrawing -NO(2) or electron-donating -NH(2) to the BPI ligand. The DFT computational studies suggest that the emission in the N-heterocyclic ligand substituted platinum(II) complexes originates mainly from the (3)[???*(BPI)] (3)IL triplet excited state, mixed with some (3)[d?(Pt)??*(BPI)] (3)MLCT character. Compared with the precursor Pt(BPI)Cl, both the low-energy absorption and the emission in the N-heterocyclic ligand substituted platinum(II) complexes exhibits a distinct blue-shift due to an obviously enhanced contribution from the (3)IL state and a reduced (3)MLCT character. PMID:21643611

Wen, Hui-Min; Wu, Yu-Hui; Xu, Liang-Jin; Zhang, Li-Yi; Chen, Chang-Neng; Chen, Zhong-Ning

2011-07-14

154

First Application of An Efficient and Versatile Ligand for Copper-Catalyzed Cross-Coupling Reactions of Vinyl Halides with N-Heterocycles and Phenols  

Science.gov (United States)

2-Pyridin-2-yl-1H-benzoimidazole L3 is presented as a new, efficient, and versatile bidentate N-donor ligand suitable for the copper-catalyzed formation of vinyl C-N and C-O bonds. This inexpensive and easily prepared ligand facilitates copper-catalyzed cross-coupling reactions of alkenyl bromides and iodides with N-heterocycles and phenols to afford the desired cross-coupled products in good to excellent yields with full retention of stereochemistry. This method is particularly noteworthy given its efficiency i.e., mild reaction conditions, low catalyst loading, simplicity, versatility, and exceptional level of functional group tolerance. PMID:20039699

Kabir, M. Shahjahan; Lorenz, Michael; Namjoshi, Ojas A.; Cook, James M.

2010-01-01

155

Cyclometalated N-heterocyclic carbene complexes of ruthenium for access to electron-rich silylene complexes that bind the Lewis acids CuOTf and AgOTf.  

Science.gov (United States)

The synthesis of the cyclometalated complexes Cp*Ru(IXy-H) (2) [IXy = 1,3-bis(2,6-dimethylphenyl)imidazol-2-ylidene; IXy-H = 1-(2-CH2C6H3-6-methyl)-3-(2,6-dimethylphenyl)imidazol-2-ylidene-1-yl (the deprotonated form of IXy); Cp* = ?(5)-C5Me5] and Cp*Ru(IXy-H)(N2) (3) was achieved by dehydrochlorination of Cp*Ru(IXy)Cl (1) with KCH2Ph. Complexes 2 and 3 activate primary silanes (RSiH3) to afford the silyl complexes Cp*(IXy-H)(H)RuSiH2R [R = p-Tol (4), Mes (5), Trip (6)]. Density functional theory studies indicated that these complexes are close in energy to the corresponding isomeric silylene species Cp*(IXy)(H)Ru?SiHR. Indeed, reactivity studies indicated that various reagents trap the silylene isomer of 6, Cp*(IXy)(H)Ru?SiHTrip (6a). Thus, benzaldehyde reacts with 6 to give the [2 + 2] cycloaddition product 7, while 4-bromoacetophenone reacts via C-H bond cleavage and formation of the enolate Cp*(IXy)(H)2RuSiH[OC(?CH2)C6H4Br]Trip (8). Addition of the O-H bond of 2,6-dimethylphenol across the Ru?Si bond of 6a gives Cp*(IXy)(H)2RuSiH(2,6-Me2C6H3O)Trip (9). Interestingly, CuOTf and AgOTf also react with 6 to provide unusual Lewis acid-stabilized silylene complexes in which MOTf bridges the Ru-Si bond. The AgOTf complex, which was crystallographically characterized, exhibits a structure similar to that of [Cp*((i)Pr3P)Ru(?-H)2SiHMes](+), with a three-center, two-electron Ru-Ag-Si interaction. Natural bond orbital analysis of the MOTf complexes supported this type of bonding and characterized the donor interaction with Ag (or Cu) as involving a delocalized interaction with contributions from the carbene, silylene, and hydride ligands of Ru. PMID:25050912

Liu, Hsueh-Ju; Raynaud, Christophe; Eisenstein, Odile; Tilley, T Don

2014-08-13

156

Rhodium(iii) complexes containing C4-bound N-heterocyclic carbenes: synthesis, coordination chemistry, and catalytic activity in transfer hydrogenation  

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Direct metalation of C2-protected diimidozolium salts with RhCl? or [RhCl(cod)]? and KI afforded a series of new rhodium(III) complexes with abnormally C4-bound, cis-chelating NHC ligands. The complexes were isolated as dimetallic species containing two (?²-I)?-bridged rhodium(III) centers. In the presence of coordinating ligands such as CH?CN, PPh?, or dppe, the dimeric structure is readily cleaved and yields monometallic complexes. Crystallographic analysis of representat...

Yang, Liangru; Kru?ger, Anneke; Neels, Antonia; Albrecht, Martin

2008-01-01

157

Uranium carbene compounds  

International Nuclear Information System (INIS)

This article gives an overview of the development of uranium carbene complexes. The first example of these compounds was reported in 1981 with the phospho-ylide complex Cp3U-CHPMe2Ph but nearly three decades passed before the area witnessed spectacular advances. During this time, actinide methylidene compounds were detected in solid argon, carbenoid uranium species were evidenced in McMurry type reactions, and a series of uranium complexes with N-heterocyclic carbene ligands was isolated. The recent developments in uranium carbene chemistry have to be related to the use of bis-phosphorus stabilized geminal carbon dianions as ligands. Homoleptic complexes and a series of mixed chloro-, tetrahydro-borato-, amido-, cyclopentadienyl- and cyclo-octa-tetra-enyl- carbene complexes of thorium(IV) and uranium in the +4, +5 and +6 oxidation states have been isolated and characterized. DFT calculations led to a good description of the U-C double bond that demonstrates a double ? and ? donation toward the metal atom with the involvement of the 5f orbitals. (author)

158

Hydride-rhodium(III)-N-heterocyclic carbene catalysts for vinyl-selective H/D exchange: a structure-activity study.  

Science.gov (United States)

A series of neutral and cationic Rh(III) -hydride and Rh(III) -ethyl complexes bearing a NHC ligand has been synthesized and evaluated as catalyst precursors for H/D exchange of styrene using CD(3)OD as a deuterium source. Various ligands have been examined in order to understand how the stereoelectronic properties can modulate the catalytic activity. Most of these complexes proved to be very active and selective in the vinylic H/D exchange, without deuteration at the aromatic positions, displaying very high selectivity toward the ?-positions. In particular, the cationic complex [RhClH(CH(3)CN)(3)(IPr)]CF(3)SO(3) showed excellent catalytic activity, reaching the maximum attainable degree of ?-vinylic deuteration in only 20?min. By modulation of the catalyst structure, we obtained improved ?/? selectivity. Thus, the catalyst [RhClH(?(2)-O,N-C(9)H(6)NO)(SIPr)], bearing an 8-quinolinolate ligand and a bulky and strongly electron-donating SIPr as the NHC, showed total selectivity for the ?-vinylic positions. This systematic study has shown that increased electron density and steric demand at the metal center can improve both the catalytic activity and selectivity. Complexes bearing ligands with very high steric hindrance, however, proved to be inactive. PMID:24895153

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

2014-07-01

159

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)

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)

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

160

N-Heterocyclic tridentate aromatic ligands bound to [Ln(hexafluoroacetylacetonate)3] units: thermodynamic, structural, and luminescent properties.  

Science.gov (United States)

Herein, we discuss how, why, and when cascade complexation reactions produce stable, mononuclear, luminescent ternary complexes, by considering the binding of hexafluoroacetylacetonate anions (hfac(-)) and neutral, semi-rigid, tridentate 2,6-bis(benzimidazol-2-yl)pyridine ligands (Lk) to trivalent lanthanide atoms (Ln(III)). The solid-state structures of [Ln(Lk)(hfac)(3)] (Ln=La, Eu, Lu) showed that [Ln(hfac)(3)] behaved as a neutral six-coordinate lanthanide carrier with remarkable properties: 1) the strong cohesion between the trivalent cation and the didentate hfac anions prevented salt dissociation; 2) the electron-withdrawing trifluoromethyl substituents limited charge-neutralization and favored cascade complexation with Lk; 3) nine-coordination was preserved for [Ln(Lk)(hfac)(3)] for the complete lanthanide series, whilst a counterintuitive trend showed that the complexes formed with the smaller lanthanide elements were destabilized. Thermodynamic and NMR spectroscopic studies in solution confirmed that these characteristics were retained for solvated molecules, but the operation of concerted anion/ligand transfers with the larger cations induced subtle structural variations. Combined with the strong red photoluminescence of [Eu(Lk)(hfac)(3)], the ternary system Ln(III)/hfac(-)/Lk is a promising candidate for the planned metal-loading of preformed multi-tridentate polymers. PMID:22549920

Zaïm, Amir; Nozary, Homayoun; Guénée, Laure; Besnard, Céline; Lemonnier, Jean-François; Petoud, Stéphane; Piguet, Claude

2012-06-01

 
 
 
 
161

An N-heterocyclic silylene-stabilized digermanium(0) complex.  

Science.gov (United States)

The synthesis of an N-heterocyclic silylene-stabilized digermanium(0) complex is described. The reaction of the amidinate-stabilized silicon(II) amide [LSiN(SiMe3 )2 ] (1; L=PhC(NtBu)2 ) with GeCl2 ?dioxane in toluene afforded the Si(II) -Ge(II) adduct [L{(Me3 Si)2 N}Si?GeCl2 ] (2). Reaction of the adduct with two equivalents of KC8 in toluene at room temperature afforded the N-heterocyclic carbene silylene-stabilized digermanium(0) complex [L{(Me3 Si)2 N}Si? Ge?Ge?Si{N(SiMe3 )2 }L] (3). X-ray crystallography and theoretical studies show conclusively that the N-heterocyclic silylenes stabilize the singlet digermanium(0) moiety by a weak synergic donor-acceptor interaction. PMID:25267490

Shan, Yu-Liang; Yim, Wai-Leung; So, Cheuk-Wai

2014-11-24

162

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

Science.gov (United States)

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

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

2014-08-28

163

Tuning the electronic and ligand properties of remote carbenes: a theoretical study.  

Science.gov (United States)

The effect of annulation and carbonylation on the electronic and ligating properties of remote N-heterocyclic carbenes (rNHCs) has been studied quantum-chemically. The thermodynamic stability of these complexes has been assessed on the basis of their hydrogenation and stabilization energies, while HOMO-LUMO gaps are used to measure the kinetic stabilities. Annulated/carbonylated rNHCs are found to be weaker ? donors but better ? acceptors compared with the parent rNHCs. The reactivity of these rNHCs has been studied by evaluating their nucleophilicity and electrophilicity indices. The nucleophilicity values are in good agreement with the ? basicities of all of the rNHCs. The (31)P NMR chemical shifts of the corresponding rNHC-phosphinidene adducts have been calculated and found to correlate well with the ? acidities of these rNHCs. PMID:25340967

Borthakur, Bitupon; Rahman, Taskia; Phukan, Ashwini K

2014-11-21

164

A ligand knowledge base for carbenes (LKB-C): maps of ligand space.  

Science.gov (United States)

We describe the development of a ligand knowledge base designed to capture the properties of C-donor ligands coordinating to transition metal centres, LKB-C. This knowledge base has been developed to describe both singlet (Arduengo and Fischer) and triplet (Schrock) carbenes, as well as related neutral monodentate C-donor ligands. The descriptors evaluated and used have been derived from a range of coordination environments to maximise their transferability and hence utility for the investigation of such ligands. These descriptors have been analysed with different statistical approaches, both individually to determine their chemical context, and collectively by principal component analysis thereby allowing the derivation of maps of ligand space for different ligand sets. The utility of such maps for investigating ligand similarity and identification of target areas for future ligand designs has been discussed. In addition, linear regression models have been fitted for the prediction of a calculated response variable, highlighting further potential applications of such a knowledge base. PMID:19789771

Fey, Natalie; Haddow, Mairi F; Harvey, Jeremy N; McMullin, Claire L; Orpen, A Guy

2009-10-21

165

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

Science.gov (United States)

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. PMID:24692049

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

2014-05-01

166

Photophysical properties of ternary rare earth (Sm3+, Eu3+) centered hybrids with N-heterocyclic modified Si-O bridge and terminal ligands.  

Science.gov (United States)

5-Amino-1,10-phenanthroline (Phen-NH(2)) is grafted to 3-(triethoxysilyl)-propyl isocyanate (TESPIC) to achieve the organic precursor Phen-Si, which is coordinated to rare earth ions (Sm(3+) or Eu(3+)) and formed Si-O networks with tetraethoxysilane (TEOS) (Phen-Si-RE) after hydrolysis and polycondensation processes to obtain the hybrids Phen-Si-Ln. To investigate the influence of the second ligands to the photophysical properties of the hybrid material Phen-Si-RE, the organic ligand nicotinic acid (NA) and the polymers polyvinylpyrrolidone (PVP) (or PMMA) are further introduced into the above system to assemble the ternary hybrid materials Phen-Si-RE-NA and Phen-Si-RE-PVP (or Phen-Si-RE-PMMA), respectively. These hybrids are amorphous and especially the photophysical properties of them indicate that the introduction of the second ligands is favorable for the luminescence lifetime and quantum efficiency. PMID:21253658

Wang, Xiao-Long; Yan, Bing; Liu, Jin-Liang

2011-04-01

167

Carbene based photochemical molecular assemblies for solar driven hydrogen generation.  

Science.gov (United States)

Novel photocatalysts based on ruthenium complexes with NHC (N-heterocyclic carbene)-type bridging ligands have been prepared and structurally and photophysically characterised. The identity of the NHC-unit of the bridging ligand was established unambiguously by means of X-ray structural analysis of a heterodinuclear ruthenium-silver complex. The photophysical data indicate ultrafast intersystem crossing into an emissive and a non-emissive triplet excited state after excitation of the ruthenium centre. Exceptionally high luminescence quantum yields of up to 39% and long lifetimes of up to 2 ?s are some of the triplet excited state characteristics. Preliminary studies into the visible light driven photocatalytic hydrogen formation show no induction phase and constant turnover frequencies that are independent on the concentration of the photocatalyst. In conclusion this supports the notion of a stable assembly under photocatalytic conditions. PMID:25100041

Peuntinger, Katrin; Pilz, T David; Staehle, Robert; Schaub, Markus; Kaufhold, Simon; Petermann, Lydia; Wunderlin, Markus; Görls, Helmar; Heinemann, Frank W; Li, Jing; Drewello, Thomas; Vos, Johannes G; Guldi, Dirk M; Rau, Sven

2014-09-28

168

Fischer and N-heterocyclic carbene complexes of tungsten(0)  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Access to this dissertation is restricted until 2014-09-07 Copyright © 2012, University of Pretoria. All rights reserved. The copyright in this work vests in the University of Pretoria. No part of this work may be reproduced or transmitted in any form or by any means, without the prior written permission of the University of Pretoria E12/9/111/gm

Pretorius, Rene

2012-01-01

169

Carbohydrate-based N-heterocyclic carbenes for enantioselective catalysis.  

Science.gov (United States)

Versatile syntheses of C2-linked and C2-symmetric carbohydrate-based imidazol(in)ium salts from functionalised amino-carbohydrate derivatives are reported. The novel NHCs were ligated to [Rh(COD)Cl]2 and evaluated in Rh-catalysed asymmetric hydrosilylation of ketones with good yields and promising enantioselectivities. PMID:25296562

Henderson, Alexander S; Bower, John F; Galan, M Carmen

2014-10-29

170

Uranyl(VI) complexes in and from imidazolium acetate ionic liquids: carbenes versus acetates?  

Science.gov (United States)

Formation of uranyl(VI)-N-heterocyclic carbene complexes from 1-alkyl-3-methylimidazolium acetate ionic liquid carbene sources was investigated by theoretical methods, combining classical molecular dynamics ab initio molecular dynamics and static DFT calculations. The interaction between the UO2(2+) cation and the acetate anion was found to be very strong, in accordance with the hard and soft acids and bases principle. The calculations, however, indicate that the preference of the acetate anions to coordinate monodentately, together with the Coulombic repulsion between these anionic ligands, provides accessible sites for the carbene in the corresponding uranyl-acetato complexes. According to the calculations the carbene is bound to the uranium atom of the [UO2(OAc)3](-) complex with significant strength; ?E value of -79.4 kJ mol(-1) was obtained. Comparison with the analogous, but experimentally confirmed, reaction between the present ionic liquid and CO2 indicates that this binding strength should be enough for the reaction to occur. The analogous aqua complexes exhibit lower stability, showing that traces of moisture should not prohibit the reaction via competitive coordination. The results obtained suggest a mild and very convenient method for preparing carbene complexes of metals in general, including those with the uranyl cation, which have been so far limited to a few exotic examples. PMID:24377752

Hollóczki, Oldamur

2014-01-21

171

Dearomatization Reactions of N-Heterocycles Mediated by Group 3 Complexes  

Energy Technology Data Exchange (ETDEWEB)

Group 3 (Sc, Y, Lu, La) benzyl complexes supported by a ferrocene diamide ligand are reactive toward aromatic N-heterocycles by mediating their coupling and, in a few cases, the cleavage of their C?N bonds. When these complexes reacted with 2,2?-bipyridine or isoquinoline, they facilitated the alkyl migration of the benzyl ligand onto the pyridine ring, a process accompanied by the dearomatization of the N-heterocycle. The products of the alkyl-transfer reactions act as hydrogen donors in the presence of aromatic N-heterocycles, ketones, and azobenzene. Experimental and computational studies suggest that the hydrogen transfer takes place through a concerted mechanism. An interesting disproportionation reaction of the dearomatized, alkyl-substituted isoquinoline complexes is also reported.

Miller, Kevin L; Williams, Bryan N; Benitez, Diego; Carver, Colin T; Ogilby, Kevin R; Tkatchouk, Ekaterina; Goddard, William A; Diaconescu, Paula L

2010-01-01

172

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)

Poor kinetics of solvent extraction of Am(III) and Eu(III) ions from 1 M HNO3 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.)

173

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  

Energy Technology Data Exchange (ETDEWEB)

Poor kinetics of solvent extraction of Am(III) and Eu(III) ions from 1 M HNO{sub 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.)

Narbutt, J.; Krejzler, J. [Dept. of Radiochemistry, Inst. of Nuclear Chemistry and Technology, Warsaw (Poland)

2008-07-01

174

Diverse reactions of PhI(OTf)2 with common 2-electron ligands: complex formation, oxidation, and oxidative coupling.  

Science.gov (United States)

The crystal structures of bis-pyridine stabilized iodine dications [PhI(pyr)(2)](2+) are reported as triflate salts, representing the first ligand supported iodine dications to be structurally characterized. The pyridine complexes are susceptible to ligand exchange in reaction with stronger N-based donors such as 4-dimethylaminopyridine. Attempts to extend this reactivity to N-heterocyclic carbene and phosphine ligands, as has been accomplished in the earlier p-block groups, resulted in redox chemistry, with oxidation of the ligands rather than coordination. PMID:23148595

Pell, Thomas P; Couchman, Shannon A; Ibrahim, Sara; Wilson, David J D; Smith, Brian J; Barnard, Peter J; Dutton, Jason L

2012-12-01

175

A new aspect of nickel-catalyzed Grignard cross-coupling reactions: selective synthesis, structure, and catalytic behavior of a T-shape three-coordinate nickel(I) chloride bearing a bulky NHC ligand.  

Science.gov (United States)

Novel T-shape three-coordinate nickel(I) chlorides bearing an N-heterocyclic carbene ligand, NiCl(IPr)(2) (IPr = 1,3-bis(2,6-diisopropylphenyl)imidazolin-2-ylidene), were isolated by a reaction of Ni(0)(NHC)(2) with aryl chlorides. This Ni(I) complex was shown to act as a catalyst in a cross-coupling reaction of aryl halides with phenylmagnesium chloride. PMID:20198257

Miyazaki, Satoshi; Koga, Yuji; Matsumoto, Taisuke; Matsubara, Kouki

2010-03-21

176

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

Science.gov (United States)

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

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

2014-09-01

177

Rhodium and iridium complexes of a new ferrocene-derived chelating bis(NHC) ligand.  

Science.gov (United States)

Rhodium and iridium complexes of a new ferrocene-derived bis(N-heterocyclic carbene) ligand, [M(cod){1,2-(MeNCHCHNCCH(2))(2)C(5)H(3)}Fe(C(5)H(5))]BF(4) (M = Rh, 8a; M = Ir, 8b; cod = 1,5-cyclooctadiene), were synthesized from the corresponding bis(imidazolium) salt 6. The molecular structure of 8a was determined by single-crystal X-ray diffraction. Complexes 8a and 8b smoothly react with CO with displacement of the chelating cod ligand to give the corresponding dicarbonyl derivatives 9a and 9b. PMID:22772354

Panov, Dmitriy M; Petrovskii, Pavel V; Ezernitskaya, Mariam G; Smol'yakov, Alexander F; Dolgushin, Fedor M; Koridze, Avthandil A

2012-08-28

178

Chelation assistance as a tool for the selective preparation of an imidazole-based mesoionic palladium carbene complex.  

Science.gov (United States)

A C(4)-bound palladium-N-heterocyclic carbene (4) was selectively obtained from the C(2)-unsubstituted imidazolium salt 3. The higher stability of the C(4) versus the C(2)-bound carbene complex due to pyridine chelation assistance allowed this mesoionic compound to be obtained. PMID:25347320

Juzgado, Arturo; Lorenzo-García, M Mercedes; Barrejón, Myriam; Rodríguez, Ana M; Rodríguez-López, Julián; Merino, Sonia; Tejeda, Juan

2014-12-18

179

Cycloalkyl-based unsymmetrical unsaturated (U?)-NHC ligands: flexibility and dissymmetry in ruthenium-catalysed olefin metathesis.  

Science.gov (United States)

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. PMID:24647372

Rouen, Mathieu; Borré, Etienne; Falivene, Laura; Toupet, Loic; Berthod, Mikaël; Cavallo, Luigi; Olivier-Bourbigou, Hélène; Mauduit, Marc

2014-05-21

180

Nickel(0)-Catalyzed Enantioselective Annulations of Alkynes and Arylenoates Enabled by a Chiral NHC Ligand: Efficient Access to Cyclopentenones.  

Science.gov (United States)

Cyclopentenones are versatile structural motifs of natural products as well as reactive synthetic intermediates. The nickel-catalyzed reductive [3+2] cycloaddition of ?,?-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. PMID:25258104

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

2014-11-24

 
 
 
 
181

Physicochemical analysis of ruthenium(II) sensitizers of 1,2,3-triazole-derived mesoionic carbene and cyclometalating ligands.  

Science.gov (United States)

A series of heteroleptic bis(tridentate) ruthenium(II) complexes bearing ligands featuring 1,2,3-triazolide and 1,2,3-triazolylidene units are presented. The synthesis of the C^N^N-coordinated ruthenium(II) triazolide complex is achieved by direct C-H activation, which is enabled by the use of a 1,5-disubstituted triazole. By postcomplexation alkylation, the ruthenium(II) 1,2,3-triazolide complex can be converted to the corresponding 1,2,3-triazolylidene complex. Additionally, a ruthenium(II) complex featuring a C^N^C-coordinating bis(1,2,3-triazolylidene)pyridine ligand is prepared via transmetalation from a silver(I) triazolylidene precursor. The electronic consequences of the carbanion and mesoionic carbene donors are studied both experimentally and computationally. The presented complexes exhibit a broad absorption in the visible region as well as long lifetimes of the charge-separated excited state suggesting their application in photoredox catalysis and photovoltaics. Testing of the dyes in a conventional dye-sensitized solar cell (DSSC) generates, however, only modest power conversion efficiencies (PCEs). PMID:24467434

Sinn, Stephan; Schulze, Benjamin; Friebe, Christian; Brown, Douglas G; Jäger, Michael; Altunta?, Esra; Kübel, Joachim; Guntner, Oliver; Berlinguette, Curtis P; Dietzek, Benjamin; Schubert, Ulrich S

2014-02-17

182

Synthesis and structure of ruthenium(IV) complexes featuring N-heterocyclic ligands with an N-H group as the hydrogen-bond donor: hydrogen interactions in solution and in the solid state.  

Science.gov (United States)

The synthesis and characterization of novel ruthenium(IV) complexes [Ru(?(3):?(3)-C(10)H(16))Cl(2)L] [L = 3-methylpyrazole (2b), 3,5-dimethylpyrazole (2c), 3-methyl-5-phenylpyrazole (2d), 2-(1H-pyrazol-5-yl)phenol (2e), 6-azauracile (3), and 1H-indazol-3-ol (4)] are reported. Complex 2e is converted to the chelated complex [Ru(?(3):?(3)-C(10)H(16))Cl(?(2)-N,O-2-(1H-pyrazol-3-yl)phenoxy)] (5) by treatment with an excess of NaOH. All of the ligands feature N-H, O-H, or C?O as the potential hydrogen-bonding group. The structures of complexes 2a-2c, 2e, 3, and 5 in the solid state have been determined by X-ray diffraction. Complexes 2a-2c and 3, which contain the pyrazole N-H group, exhibit intra- and intermolecular hydrogen bonds with chloride ligands [N-H···Cl distances (Å): intramolecular, 2.30-2.78; intermolecular, 2.59-2.77]. Complexes 2e and 3 bearing respectively O-H and C?O groups also feature N-H···O interactions [intramolecular (2e), 2.27 Å; intermolecular (3), 2.00 Å]. Chelated complex 5, lacking the O-H group, only shows an intramolecular N-H···Cl hydrogen bonding of 2.42 Å. The structure of complex 3, which turns out to be a dimer in the solid state through a double intermolecular N-H···O hydrogen bonding, has also been investigated in solution (CD(2)Cl(2)) by NMR diffusion studies. Diffusion-ordered spectroscopy experiments reveal an equilibrium between monomer and dimer species in solution whose extension depends on the temperature, concentration, and coordinating properties of the solvent. Preliminary catalytic studies show that complex 3 is highly active in the redox isomerization of the allylic alcohols in an aqueous medium under very mild reaction conditions (35 °C) and in the absence of a base. PMID:21557560

Díez, Josefina; Gimeno, José; Merino, Isabel; Rubio, Eduardo; Suárez, Francisco J

2011-06-01

183

A molecular iron catalyst for the acceptorless dehydrogenation and hydrogenation of N-heterocycles.  

Science.gov (United States)

A well-defined iron complex (3) supported by a bis(phosphino)amine pincer ligand efficiently catalyzes both acceptorless dehydrogenation and hydrogenation of N-heterocycles. The products from these reactions are isolated in good yields. Complex 3, the active catalytic species in the dehydrogenation reaction, is independently synthesized and characterized, and its structure is confirmed by X-ray crystallography. A trans-dihydride intermediate (4) is proposed to be involved in the hydrogenation reaction, and its existence is verified by NMR and trapping experiments. PMID:24877556

Chakraborty, Sumit; Brennessel, William W; Jones, William D

2014-06-18

184

Structural characterization of 6,6?-bis(substituted)-5,5?-bi-1,2,4-triazines as potential N-heterocyclic ligands for the extraction of nuclear waste  

Science.gov (United States)

Novel disubstituted 5,5'-bi-1,2,4-triazines bearing pyridine (1), furan (2) and thiophene (3) rings at 6 and 6'-positions of the parent bitriazine were prepared as potential extractants of nuclear waste. The compounds were easily obtained by Stille coupling starting from 6,6'-bisbromo-3,3'-bis( N,N-dimethylamine)-5,5'-bi-1,2,4-triazine and the corresponding tin reagents. The molecular and crystal structures of the ligands 1- 3 were determined by the X-ray analysis. The X-ray investigations show different conformations of the molecules described as gauche- gauche- gauche for 1 and gauche- cis- cis for 2 and 3. Each of the molecules resides on a twofold axis that passes through the middle of the central C5-C5' bond. The molecular packing in 1 is influenced by the ?⋯ ? and weak C-H⋯ ? interactions. The crystal structures of 2 and 3 are governed by a combination of a weak C-H⋯N hydrogen bonds and C-H⋯ ? interactions. Theoretical calculations using semi-empirical AM1 and DFT/B3LYP/6-311++G(d,p) ab initio methods were carried out to find correlation between conformational and electronic parameters of the molecules and their preferences to metal ions complexations.

Branowska, Danuta; Karczmarzyk, Zbigniew; Rykowski, Andrzej; Wysocki, Waldemar; Olender, Ewa; Urba?czyk-Lipkowska, Zofia; Kalicki, Przemys?aw

2010-08-01

185

The influence of anionic ligands on stereoisomerism of Ru carbenes and their importance to efficiency and selectivity of catalytic olefin metathesis reactions.  

Science.gov (United States)

Investigations detailed herein provide insight regarding the mechanism of stereochemical inversion of stereogenic-at-Ru carbene complexes through a nonolefin metathesis-based polytopal rearrangement pathway. Computational analyses (DFT) reveal that there are two key factors that generate sufficient energy barriers that are responsible for the possibility of isolation and characterization of high-energy, but kinetically stable, intermediates: (1) donor-donor interactions that involve the anionic ligands and the strongly electron donating carbene groups and (2) dipolar effects arising from the syn relationship between the anionic groups (iodide and phenoxide). We demonstrate that a Brønsted acid lowers barriers to facilitate isomerization, and that the positive influence of a proton source is the result of its ability to diminish the repulsive electronic interactions originating from the anionic ligands. The implications of the present studies regarding a more sophisticated knowledge of the role of anionic units on the efficiency of Ru-catalyzed olefin metathesis reactions are discussed. The electronic basis for the increased facility with which allylic alcohols participate in olefin metathesis processes will be presented as well. Finally, we illustrate how a better understanding of the role of anionic ligands has served as the basis for successful design of Ru-based Z-selective catalysts for alkene metathesis. PMID:24533571

Torker, Sebastian; Khan, R Kashif M; Hoveyda, Amir H

2014-03-01

186

A general synthetic route to [Cu(X)(NHC)] (NHC = N-heterocyclic carbene, X = Cl, Br, I) complexes† †Electronic supplementary information (ESI) available: Optimisation details and full characterisation data. CCDC 940850–940853. For ESI and crystallographic data in CIF or other electronic format see DOI: 10.1039/c3cc45488f Click here for additional data file.  

Science.gov (United States)

A one-pot procedure for the synthesis of [Cu(X)(NHC)] (X = Cl, Br, I) is reported. The reaction is applicable to a wide range of saturated and unsaturated NHC ligands, is scalable and proceeds under mild conditions using technical grade solvents in air. PMID:24087835

Santoro, Orlando; Collado, Alba; Slawin, Alexandra M. Z.; Nolan, Steven P.

2013-01-01

187

Synthetic and Thermodynamic Investigations of Ancillary Ligand Influence on Catalytic Organometallic Systems. Final Report  

Energy Technology Data Exchange (ETDEWEB)

During the grant period we have been involved in synthesizing and experimentally determining solution enthalpy values associated with partially fluorinated ligands. This has lead to the publication of manuscripts dealing with synthetic, calorimetric and catalytic behavior of partially fluorinated ligands. The collaboration with Los Alamos researchers has lead to the publication of catalytic results in sc CO{sub 2} which have proven very interesting. Furthermore, we have also examined ligands that behave as phosphine mimics. The N-heterocyclic carbenes have been explored as alternatives for tertiary phosphines and have resulted in the design and construction of efficient palladium and nickel system capable of performing C-C and C-N cross coupling reactions. The initial studies in this areas were made possible by exploratory work conducted under the DOE/EPSCoR grant.

Nolan, Steven

2003-03-20

188

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

Science.gov (United States)

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

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

2014-08-25

189

Electronic structure of transition metal carbene complexes  

International Nuclear Information System (INIS)

The analysis of the electronic structure of transition metal (V, Nb, Ta) carbene complexes is given. The properties and peculaiarities of the electronic structure of Fischer and Schrock type complexes are compared. The results of the most accurate nonempirical calculations of the simplest systems simulating the transition metal-carbene ligand and some less strict semiempirical and nonempirical calculations which permit to find out the regularities of the electronic structure of carbene complexes, depending on position of the metal in the Periodic system and the nature of ligand surrounding, are discussed. Main factors causing the stabilization of covalently bound or donor-acceptor systems are singled out

190

A large perturbation on electronic and photophysical properties of Ir(III) carbene complexes caused by the variation of N-substitution in N,N?-heteroaromatic ligands  

Science.gov (United States)

DFT/TDDFT investigation was performed on the electronic and photophysical properties of blue-emitting Ir(III) carbene complexes (fpmi)3-xIr(N^N?)x (x = 1, 2) [fpmi = 1-(4-fluorophenyl)-3-methylimidazolin-2-ylidene-C,C2?, N^N? = 2-(1H-pyrazol-5-yl)pyridinato (1a(x = 1)/1a?(x = 2)); 2-(1H-imidazol-5-yl)pyridinato (1b/1b?); 2-(1H-imidazol-2-yl)pyridinato (1c/1c?); 2-(1H-1,2,4-triazol-5-yl)pyridinato (2a/2a?); 2-(1H-1,2,3-triazol-5-yl)pyridinato (2b/2b?); 2-(4H-1,2,4-triazol-3-yl)pyridinato (2c/2c?)]. The absorption intensities and band positions are obviously affected by the variation of N substitution in N^N? ligand. The emission properties show an apparent dependence on the solvent effects, and the N^N? ligand plays an important role in governing the emissive state. The pyrazolyl-pyridyl-based N^N? ligand is considered to be more beneficial for blue OLEDs emitters.

Liu, Yuqi; Si, Yanling; Wang, Ying; Wu, Zhijian

2014-08-01

191

Ruthenium Olefin Metathesis Catalysts Bearing Carbohydrate-Based N-Heterocyclic Carbenes  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Ru-based olefin metathesis catalysts containing carbohydrate-derived NHCs from glucose and galactose were synthesized and characterized by NMR spectroscopy. 2D-NMR spectroscopy revealed the presence of Ru-C (benzylidene) rotamers at RT and the rate of rotation was measured using magnetization transfer and VT-NMR spectroscopy. The catalysts were found to be effective at ring-opening metathesis polymerization (ROMP), ring closing metathesis (RCM), cross metathesis (CM), and asymmetric ring open...

Keitz, Benjamin K.; Grubbs, Robert H.

2010-01-01

192

Ruthenium Olefin Metathesis Catalysts Bearing Carbohydrate-Based N-Heterocyclic Carbenes  

Science.gov (United States)

Ru-based olefin metathesis catalysts containing carbohydrate-derived NHCs from glucose and galactose were synthesized and characterized by NMR spectroscopy. 2D-NMR spectroscopy revealed the presence of Ru-C (benzylidene) rotamers at RT and the rate of rotation was measured using magnetization transfer and VT-NMR spectroscopy. The catalysts were found to be effective at ring-opening metathesis polymerization (ROMP), ring closing metathesis (RCM), cross metathesis (CM), and asymmetric ring opening cross metathesis (AROCM) and showed surprising selectivity in both CM and AROCM. PMID:21603126

Keitz, Benjamin K.; Grubbs, Robert H.

2010-01-01

193

N-heterocyclic carbene-silver complex as a novel reference electrode in electrochemical applications.  

Science.gov (United States)

We demonstrate a novel reference electrode material namely an organometallic silver complex e.g., silver (I) tetramethylbis(benzimidazolium) diiodide [1a] for both acid and alkaline electrolysis. The potential usage of the silver complex as a reference electrode with at least equal electrochemical capabilities compared to those of the conventional electrode materials (e.g., Hg/HgO in alkaline media and Ag/AgCl in acidic media) are also demonstrated using cyclic voltammetry. In addition, the well dispersed surface morphology and fine crystalinity of the silver complex is investigated using field-emission scanning electron microscopy (FE-SEM) and X-ray diffraction (XRD). PMID:20188950

Park, Won Jin; Yi, Youngmi; Lee, Jaeyoung; Lee, Byung Cheol; Park, Ok Kyung; Lee, Hye Jin; Lee, Hyosun

2010-04-15

194

Nanofiber composites containing N-heterocyclic carbene complexes with antimicrobial activity  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Ahmed A Elzatahry1,4, Abdullah M Al-Enizi1, Elsayed Ahmed Elsayed2,5, Rachel R Butorac3, Salem S Al-Deyab1, Mohammad AM Wadaan2, Alan H Cowley31Petrochemical Research Chair, Department of Chemistry, 2Chair of Advanced Proteomics & Cytomics Research, Faculty of Science, King Saud University, Riyadh, Kingdom of Saudi Arabia; 3Department of Chemistry and Biochemistry, University of Texas at Austin, Austin, TX, USA; 4Institute of Advanced Technology and New Materials, City for Scientific ...

Aa, Elzatahry; Am, Al-enizi; Ea, Elsayed; Rr, Butorac; Ss, Al-deyab; Mam, Wadaan; Ah, Cowley

2012-01-01

195

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

DEFF Research Database (Denmark)

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

Tursky, Matyas

2009-01-01

196

[3 + 2]-dipolar cycloaddition reactions of an N-heterocyclic carbene boryl azide.  

Science.gov (United States)

Thermal 1,3-dipolar cycloaddition reactions of 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene dihydridoboron azide occur smoothly with alkynes, nitriles, and alkenes bearing electron-withdrawing groups. New, stable NHC-boryl-substituted triazoles, tetrazoles, and triazolidines are formed in good to excellent yields. PMID:22616557

Merling, Everett; Lamm, Vladimir; Geib, Steven J; Lacôte, Emmanuel; Curran, Dennis P

2012-06-01

197

A cooperative N-heterocyclic carbene/chiral phosphate catalysis system for allenolate annulations.  

Science.gov (United States)

The highly enantioselective NHC-catalyzed [3+2] annulation reaction with ?,?-alkynals and ?-ketoesters has been developed. A new mode of cooperative catalysis involving the combination of a chiral Brønsted acid and a C1-symmetric biaryl saturated-imidazolium precatalyst was required to generate the desired ?-crotonolactones in high yields and levels of enantioselectivity. PMID:24895280

Lee, Anna; Scheidt, Karl A

2014-07-14

198

Arrested catalysis: controlling Kumada coupling activity via a redox-active N-heterocyclic carbene.  

Science.gov (United States)

Optimized syntheses for 1,3-dimesitylnaphthoquinimidazolium chloride [1H][Cl] and the corresponding silver-NHC complex [AgCl(1)] (2) were developed, enabling access to this versatile reagent in near-quantitative yield. Transmetalation from 2 to [NiCl(2)(PPh(3))(2)], trans-[PdCl(2)(PhCN)(2)], or trans-[PtCl(2)(PhCN)(2)] afforded the Group 10 complexes trans-[MCl(2)(1)(2)] (3a-c, M = Ni, Pd, and Pt, respectively) in excellent overall yield (>95%) after three steps from commercially available starting materials. Electrochemical measurements indicated that the E(1/2) and DeltaE(1/2) values for the quinone reduction couples were independent of the identity of the bridging transition metal in these complexes. Whereas attempts to isolate the reduced complexes were unsuccessful, UV/vis spectroelectrochemical analysis confirmed that electrochemical reduction of 3a-c in situ afforded optical difference spectra consistent with the formation of the expected reduced species. Complex 3a was found to catalyze the Kumada cross-coupling reaction between PhMgCl and a range of bromoarenes at room temperature. Addition of 2 equiv of cobaltocene (with respect to 3a) to the coupling reaction with bromotoluene caused a decrease in catalytic activity (from 4.7 x 10(-5) to 2.7 x 10(-6) s(-1)), which was attributed to the conversion of 3a to an arrested state. Subsequent introduction of ferrocenium tetrafluoroborate (2 equiv with respect to 3a) restored a significant degree of catalytic activity (k(obs) = 1.2 x 10(-5) s(-1)). Redox-switching experiments performed over different time scales revealed that the catalyst was stable in the reduced/inactive state and that extended durations in this state did not impede catalytic reactivation upon subsequent oxidation. PMID:20560593

Tennyson, Andrew G; Lynch, Vincent M; Bielawski, Christopher W

2010-07-14

199

N-Heterocyclic carbene-catalyzed enantioselective synthesis of functionalized cyclopentenes via ?,?-unsaturated acyl azoliums.  

Science.gov (United States)

Highly enantioselective NHC-organocatalyzed synthesis of functionalized cyclopentenes proceeding via ?,?-unsaturated acyl azolium intermediates is reported. The organocascade reaction of modified enals with malonic ester derivatives having a ?-benzoyl group involves the Michael-intramolecular aldol-?-lactonization-decarboxylation sequence to deliver cyclopentenes in good yields and excellent ee values. PMID:25307503

Mondal, Santigopal; Yetra, Santhivardhana Reddy; Patra, Atanu; Kunte, Sunita S; Gonnade, Rajesh G; Biju, Akkattu T

2014-10-28

200

N-heterocyclic carbene catalyzed activation of esters: a new option for asymmetric domino reactions.  

Science.gov (United States)

Esters-what else! A new strategy in NHC organocatalysis allows the ?-, ?- and ?-activation of saturated and unsaturated esters. The resulting acyl azolium intermediates efficiently participate in domino reactions with suitable substrates to generate synthetically valuable carbo- and heterocycles with very good diastereo- and excellent enantioselectivities. PMID:24492969

Chauhan, Pankaj; Enders, Dieter

2014-02-01

 
 
 
 
201

Alkali metal salts of ditopic carbanionic carbenes as reagents for the synthesis of novel complexes of group 12 and 14 metals.  

Science.gov (United States)

Reaction of the lithiated N-heterocyclic carbene [:C[N(2,6-(i)Pr2C6H3)]2(CH)CLi]n () with KO(t)Bu in diethylether (Et2O) afforded the novel organo-potassium compound [:C[N(2,6-(i)Pr2C6H3)]2(CH)CK(THF)2] (·2THF). Both and can be interpreted as ditopic carbanionic carbenes (or alkali metal salts of anionic "dicarbenes") and are interesting precursors for the synthesis of novel metal complexes bearing carbanionic carbenes as ligands. Reaction of with M[N(SiMe3)2]2 (M = Zn, Sn) afforded salts of the anionic three coordinate complexes [M{C(CH)[N(2,6-(i)Pr2C6H3)]2C:}{N(SiMe3)2}2](-) (M = Zn () and Sn ()). Contrasting reactivity was observed for the other group 14 bis-amide compounds M[N(SiMe3)2]2 (M = Ge, Pb), which initially appear to yield analogous 1?:?1 complexes (M = Ge () and Pb ()), however over time give rise to compounds bearing two ditopic carbanionic carbenes ([M{C(CH)[N(2,6-(i)Pr2C6H3)]2C:}2{N(SiMe3)2}](-); Ge () and Pb ()) and the tris-amide anions ([M{N(SiMe3)3}](-)), presumably via a Schlenk-type equilibrium. Compounds and can be directly synthesized by reacting M[N(SiMe3)2]2 (M = Ge, Pb) with two equivalents of , respectively. PMID:24827736

Waters, Jordan B; Goicoechea, Jose M

2014-09-10

202

Organosulphur and related ligands in Suzuki-Miyaura C-C coupling.  

Science.gov (United States)

Suzuki-Miyaura C-C cross coupling (SMC), an important synthetic strategy for many organic molecules, has several advantages such as mild reaction conditions, high tolerance toward various functional groups and ease in isolation of the product. Palladium(II) ligated with phosphines (particularly bulky and electron-rich) and N-heterocyclic carbenes (NHCs) has been found to be efficient in the catalysis of SMC. The drawback with many of these catalysts is their air/moisture sensitivity. Since 2000, palladium(II) complexes of organosulphur and related ligands have emerged as viable alternatives to palladium-phosphine/carbene complexes as they have sufficient thermal stability, air and moisture insensitivity. Moreover synthesis of complexes of such ligands is easy. In this perspective Suzuki-Miyaura C-C coupling reactions catalyzed with palladium(II)-complexes of organosulphur ligands have been reviewed. Catalysis of SMC with palladium(II) complexes of organoselenium and tellurium ligands, studied much less in comparison to those of organosulphur ligands, is also included. PMID:23340712

Kumar, Arun; Rao, Gyandshwar Kumar; Kumar, Satyendra; Singh, Ajai K

2013-04-21

203

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

Science.gov (United States)

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

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

2014-01-15

204

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

Science.gov (United States)

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

Gliši?, Biljana ?; Djuran, Miloš I

2014-04-28

205

N-heterocyclic amine-directed structures and properties of two Cu(II) diphosphonates.  

Science.gov (United States)

By introducing the second organic N-heterocyclic ligands 4'-(4-pyridyl)-4,2':6',4''-terpyridine (pyterpy) and 4,4'-bipyridyl (4,4'-bipy), two examples of Cu(II)-diphosphonates, [Cu(3)(HL)(2)(Hpyterpy)(2)]·2H(2)O 1 and [Cu(4)(HL)(2)(4,4'-bipy)(H(2)O)(5)] 2 based on 1-hydroxyethylidenediphosphonic acid (H(5)L = CH(3)C(OH)(PO(3)H(2))(2)), have been hydrothermally obtained and characterized by powder X-ray diffraction, elemental analysis, IR, TG-DSC. The single-crystal X-ray diffractions reveal that compound 1 has a one-dimensional fishbone-like chain constructed by anions [Cu(3)(HL)(2)(2-)](n) while simultaneously organic cations [Hpyterpy(+)](n) suspending both sides, and compound 2 exhibits two-dimensional inorganic-organic alternate arrangement layer built from 1-D ladder-like inorganic chain with tetranuclear cluster [Cu(4)O(10)] via 4,4'-bipy linkage. The results of electrochemical measurements indicate half-wave potential of 1 (E(1/2)(1) = 1.01 V) is less than that of 2 (E(1/2)(2) = 1.20 V), indicating a good D-A system in ICT for 1. Moreover fluorescent measurements reveal that emission intensity of 1 centered at 422 nm is larger than that of 2 emitted at 420 nm, caused by intraligand ?*-? emission state of organic N-heterocyclic amine (?(ex) = 233 nm). Magnetism data indicate that compound 1 exhibits ferrimagnetic interactions between metal centers, while compound 2 has antiferromagnetic property. PMID:21869977

Ma, Kui-Rong; Ma, Feng; Zhu, Yu-Lan; Yu, Lin-Juan; Zhao, Xiao-Min; Yang, Yin; Duan, Wei-He

2011-10-14

206

Stereoelectronic basis for the kinetic resolution of N-heterocycles with chiral acylating reagents.  

Science.gov (United States)

The kinetic resolution of N-heterocycles with chiral acylating agents reveals a previously unrecognized stereoelectronic effect in amine acylation. Combined with a new achiral hydroxamate, this effect makes possible the resolution of various N-heterocycles by using easily prepared reagents. A transition-state model to rationalize the stereochemical outcome of this kinetic resolution is also proposed. PMID:24839065

Hsieh, Sheng-Ying; Wanner, Benedikt; Wheeler, Philip; Beauchemin, André M; Rovis, Tomislav; Bode, Jeffrey W

2014-06-10

207

(C^C*) Cyclometalated binuclear N-heterocyclic biscarbene platinum(II) complexes--highly emissive phosphorescent emitters.  

Science.gov (United States)

A series of bimetallic N-heterocyclic carbene (NHC) platinum(II) complexes with the general formula [Pt(NHC)(L)]2Ph were synthesized, which are composed of two [Pt(NHC)(L)] (L = acetylacetone, dipivaloylmethane or dimesitoylmethane; NHC = 3-methylimidazole or 3-benzylimidazole) fragments. Both fragments are cyclometalated to the same central phenyl ring in the para- or meta-position. All complexes have been fully characterized by standard techniques, two of them additionally by solid-state structures. Photoluminescence properties were investigated and very high quantum yields of 76-93% at room temperature have been observed. For a single-matrix device with an emitter concentration of 30%, a current efficiency of 25 cd A(-1), an external quantum efficiency of 8.5%, and a luminance efficiency of 10 lm W(-1) were achieved at 300 cd m(-2). Density functional theory (DFT) calculations were performed to support experimental data and gain further insight into the photoluminescence behaviour. PMID:23689316

Tronnier, Alexander; Strassner, Thomas

2013-07-21

208

Ruthenium(II) and osmium(II) 1,2,3-triazolylidene organometallics: a preliminary investigation into the biological activity of 'click' carbene complexes.  

Science.gov (United States)

Taking advantage of the facile and versatile synthetic properties of 'click' 1,2,3-triazolylidene N-heterocyclic carbenes (tzNHC's), a range of new organometallic Ru(II) and Os(II) arene complexes containing functionalised tzNHC ligands, [M(?(6)-p-cymene)(tzNHC)Cl2] [M = Ru(II), Os(II)], have been synthesised and fully characterised, including the X-ray crystal structure of one of the Os(II) complexes. The tzNHC ligands remain coordinated to the metal centres under relevant physiological conditions, and following binding to the model protein, ubiquitin. The in vitro cytotoxicity of the compounds towards human ovarian cancer cells is dependent on the substituent on the tzNHC ligand but is generally <50 ?M and in some cases <1 ?M, whilst still retaining a high degree of selectivity towards cancer cells over healthy cells (1.85 ?M in A2780 ovarian cancer cells versus 435 ?M in human embryonic kidney cells in one case). PMID:24201979

Kilpin, Kelly J; Crot, Stéphanie; Riedel, Tina; Kitchen, Jonathan A; Dyson, Paul J

2014-01-21

209

A Diruthenium ?-Carbido Complex That Shows Singlet-Carbene-like Reactivity.  

Science.gov (United States)

Low-temperature deprotonation of the cationic ?-methylidyne complex [(Cp*Ru)2(?-NPh)(?-CH)][BF4] (Cp* = ?(5)-C5Me5) with KN(SiMe3)2 affords a thermally unstable ?-carbido complex [(Cp*Ru)2(?-NPh)(?-C)] (2), as evidenced by trapping experiments with elemental S or Se and (13)C NMR spectroscopic observation. The reactivity of 2 toward CO2, Ph2S(+)CH2(-), EtOH, and an intramolecular C-H bond indicates that the ?-carbido carbon in 2 has an ambiphilic (nucleophilic and electrophilic) nature consistent with the formulation of 2 as the first example of a transition-metal-substituted singlet carbene. DFT study suggests that the Ru substituents in 2 are stronger ?-donor and weaker ?-donor to the carbene center than amino substituents in N-heterocyclic carbenes. PMID:25365114

Takemoto, Shin; Ohata, Jun; Umetani, Kento; Yamaguchi, Masahiro; Matsuzaka, Hiroyuki

2014-11-12

210

Expanding the steric coverage offered by bis(amidosilyl) chelates: isolation of low-coordinate N-heterocyclic germylene complexes.  

Science.gov (United States)

The synthesis and coordination chemistry of a series of dianionic bis(amido)silyl and bis(amido)disilyl, [NSiN] and [NSiSiN], chelates with N-bound aryl or sterically modified triarylsilyl (SiAr(3)) groups is reported. In order to provide a consistent comparison of the steric coverage afforded by each ligand construct, various two-coordinate N-heterocyclic germylene complexes featuring each ligand set were prepared and oxidative S-atom transfer chemistry was explored. In the cases where clean oxidation transpired, sulfido-bridged centrosymmetric germanium(IV) dimers of the general form [LGe(?-S)](2) (L = bis(amidosilyl) ligands) were obtained in lieu of the target monomeric germanethiones with discrete Ge?S double bonds. These results indicate that the reported chelates possess sufficient conformational flexibility to allow for the dimerization of LGe?S units to occur. Notably, the new triarylsilyl groups (4-RC(6)H(4))(3)Si- (R = (t)Bu and (i)Pr) still offer considerably expanded degrees of steric coverage relative to the parent congener, -SiPh(3,) and thus the use of substituted triarylsilyl groups within ligand design strategies should be a generally useful concept in advancing low-coordination main group and transition-metal chemistry. PMID:22530833

Liew, Sean K; Al-Rafia, S M Ibrahim; Goettel, James T; Lummis, Paul A; McDonald, Sean M; Miedema, Leah J; Ferguson, Michael J; McDonald, Robert; Rivard, Eric

2012-05-01

211

Copper(I)-catalyzed nucleophilic addition of ynamides to acyl chlorides and activated N-heterocycles.  

Science.gov (United States)

The addition of ynamides to acyl chlorides and N-heterocycles activated in situ with ethyl chloroformate has been accomplished at room temperature using copper iodide as catalyst. This economical and practical carbon-carbon bond formation provides convenient access to a variety of 3-aminoynones from aliphatic and aromatic acyl chlorides in up to 99% yield. The addition to pyridines and quinolines occurs under almost identical conditions and proceeds with good to high regioselectivity, producing the corresponding 1,2-dihydro-N-heterocycles in up to 95% yield. PMID:24724797

Zhang, Peng; Cook, Andrea M; Liu, Yang; Wolf, Christian

2014-05-01

212

Visualizing carbene equilibria.  

Science.gov (United States)

Reviewed herein are equilibria between halocarbenes and halocarbanions, carbenes and carbene complexes and carbenes and O-ylides. The transient species were visualized by laser flash photolysis coupled with UV-Visible spectroscopy. This methodology enabled the determination of equilibrium constants and the extraction of associated thermodynamic parameters. Parallel computational studies provided anticipated structures and energies for the transient species, as well as electronic absorption wavelengths and oscillator strengths. PMID:23800012

Moss, Robert A; Wang, Lei; Hoijemberg, Pablo A; Krogh-Jespersen, Karsten

2014-01-01

213

Fischer carbene complexes remain favourite targets, and vehicles for new discoveries.  

Science.gov (United States)

Exciting new variations in Fischer-type carbene complex composition and reactivity have been realised by following or modifying well-established synthetic approaches such as metal carbonyl functionalization and modification of existing carbene ligands. The formation of targeted complexes for organic synthesis, carbene-containing chelates, and polynuclear carbene complexes, by employing 'click chemistry', warrants discussion. Transmetallation and ?,?-dehydrogenation of ethers and amines have come into their own as viable synthetic methods to access carbene complexes with unique properties and activities. Successful mediation of carbene complex formation with pincer ligands has proved its worth. Quantum chemistry has become essential for supporting or initiating mechanistic proposals, but heuristic approaches such as invoking the vinylology principle to describe substituted phenylcarbene complexes are still valuable in the interpretation of bonding properties and the classification of complex types. Electrochemical studies now also constitute a powerful part of the experimental characterization tool kit. PMID:25325879

Raubenheimer, H G

2014-10-28

214

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

International Nuclear Information System (INIS)

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)

215

Two-Step Synthesis of Aza- and Diazaindoles from Chloroamino-N-heterocycles Using Ethoxyvinylborolane  

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An efficient two-step route to a broad range of aza- and diazaindoles was established, starting from chloroamino-N-heterocycles, without the need for protecting groups. The method involves an optimized Suzuki-Miyaura coupling with (2-ethoxyvinyl)borolane followed by acetic acid-catalyzed cyclization.

Whelligan, Dk; Thomson, Dw; Taylor, D.; Hoelder, S.

2010-01-01

216

Lewis basicity modulation of N-heterocycles: a key for successful cross-metathesis.  

Science.gov (United States)

Cross-metathesis involving N-heteroaromatic olefinic derivatives is disclosed. The introduction of an appropriate substituent on the heteroaromatic ring decreases the Lewis basicity of the nitrogen atom, thus preventing the deactivation of the ruthenium-centered catalyst. The reaction is quite general in terms of both N-heterocycles and olefinic partners. PMID:25243368

Lafaye, Kevin; Nicolas, Lionel; Guérinot, Amandine; Reymond, Sébastien; Cossy, Janine

2014-10-01

217

On the reactivity and stability of electrogenerated N-heterocyclic carbene in parent 1-butyl-3-methyl-1H-imidazolium tetrafluoroborate: Formation and use of N-heterocyclic carbene-CO2 adduct as latent catalyst  

International Nuclear Information System (INIS)

A simple electrolysis (under galvanostatic conditions) of the room temperature ionic liquid 1-butyl-3-methyl-1H-imidazolium tetrafluoroborate, BMIm-BF4, yields, after bubbling CO2 into the catholyte, the adduct NHC-CO2. The considerable stability of this NHC-CO2 adduct, at room temperature, in the parent ionic liquid as solvent, has been compared with the one of free NHC in the same BMIm-BF4. The BMIm-BF4 solution containing NHC-CO2 adduct, suitably triggered (US irradiation or 120 °C), is able to release free NHC. The NHC-CO2 adduct usefulness has been demonstrated using it as efficient latent catalyst, in BMIm-BF4 as solvent, in the benzoin condensation and in the oxidative esterification of cinnamaldehyde with benzyl alcohol

218

Synthesis and structure of ruthenium-silylene complexes: activation of Si-Cl bonds in N-heterocyclic silanes.  

Science.gov (United States)

Ru(0) complexes of bis(imino)pyridine ligands, [eta2-N3]Ru(eta6-Ar) and {[N3]Ru}2(mu-N2), where Ar = C6H6 or C6H5Me and [N3] = 2,6-(MesN=CMe)2C5H3N, react with N-heterocyclic silicon(IV) compounds to yield Ru(II) silylene complexes of the type [N3]Ru(X)(Cl){Si(NN)} (X = H, Cl, and Si(NN) = N,N'-bis(neopentyl)-1,2-phenylenedi(amino)silylene). The activation of two groups on the silane occurs in a stepwise fashion: initial oxidative addition of a Si-X bond, followed by 1,2-migration (alpha-elimination) of the Si-Cl group to the metal. Reversible dissociation from the Ru(II) center leads to free silylene, which can be preferentially trapped with Ru(0) complexes to generate a zero-valent silylene complex, [N3]Ru(N2){Si(NN)}, which also contains a terminal dinitrogen ligand. PMID:16669664

Yoo, Hyojong; Carroll, Patrick J; Berry, Donald H

2006-05-10

219

Mechanistic and preparative studies of radical chain homolytic substitution reactions of N-heterocyclic carbene boranes and disulfides.  

Science.gov (United States)

Reactions of 1,3-dimethylimidazol-2-ylidene-borane (diMe-Imd-BH3) and related NHC-boranes with diaryl and diheteroaryl disulfides provide diverse NHC-boryl monosulfides (diMe-Imd-BH2SAr) and NHC-boryl disulfides (diMe-Imd-BH(SAr)2). Heating in the dark with 1 equiv of disulfide favors monosulfide formation, while irradiation with 2 equiv disulfide favors disulfide formation. With heteroaryl disulfides, the NHC-borane in the primary NHC-boryl sulfide product migrates from sulfur to nitrogen to give new products with a thioamide substructure. Most substitution reactions are thought to proceed through radical chains in which homolytic substitution of a disulfide by an NHC-boryl radical is a key step. However, with electrophilic disulfides under dark conditions, a competing ionic path may also be possible. PMID:23718209

Pan, Xiangcheng; Vallet, Anne-Laure; Schweizer, Stéphane; Dahbi, Karim; Delpech, Bernard; Blanchard, Nicolas; Graff, Bernadette; Geib, Steven J; Curran, Dennis P; Lalevée, Jacques; Lacôte, Emmanuel

2013-07-17

220

A cationic zinc hydride cluster stabilized by an N-heterocyclic carbene: synthesis, reactivity, and hydrosilylation catalysis.  

Science.gov (United States)

The trinuclear cationic zinc hydride cluster [(IMes)3 Zn3 H4 (THF)](BPh4 )2 (1) was obtained either by protonation of the neutral zinc dihydride [(IMes)ZnH2 ]2 with a Brønsted acid or by addition of the putative zinc dication [(IMes)Zn(THF)](2+) . A triply bridged thiophenolato complex 2 was formed upon oxidation of 1 with PhS?SPh. Protonolysis of 1 by methanol or water gave the corresponding trinuclear dicationic derivatives. At ambient temperature, 1 catalyzed the hydrosilylation of aldehydes, ketones, and nitriles. Carbon dioxide was also hydrosilylated under forcing conditions when using (EtO)3 SiH, giving silylformate as the main product. PMID:25257989

Rit, Arnab; Zanardi, Alessandro; Spaniol, Thomas P; Maron, Laurent; Okuda, Jun

2014-11-24

 
 
 
 
221

Substitution reactions at tetracoordinate boron: synthesis of N-heterocyclic carbene boranes with boron-heteroatom bonds.  

Science.gov (United States)

Boryl halide, carboxylate and sulfonate complexes of 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene (dipp-Imd-BH(2)X, X = halide or sulfonate) have been prepared from the parent borane dipp-Imd-BH(3) by (1) substitution reactions with R-X (X = halide or sulfonate), (2) reactions with electrophiles (like I(2) or NIS), or (3) acid/base reactions with HX (provided that HX has a pK(a) of about 2 or less). Dipp-Imd-BH(2)I is most conveniently prepared by reaction with diiodine while dipp-Imd-BH(2)OTf is best prepared by reaction with triflic acid. These and other less reactive complexes behave as electrophiles and can be substituted by a wide range of heteroatom nucleophiles including halides, thiolates and other sulfur-based nucleophiles, isocyanate, azide, nitrite, and cyanide. The resulting products are remarkably stable, and many have been characterized by X-ray crystallography. Several are members of very rare classes of functionalized boron compounds (boron azide, nitro compound, nitrous ester, etc.). PMID:20886852

Solovyev, Andrey; Chu, Qianli; Geib, Steven J; Fensterbank, Louis; Malacria, Max; Lacôte, Emmanuel; Curran, Dennis P

2010-10-27

222

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

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

Ismail Özdemir

2013-02-01

223

Asymmetric homoenolate additions to acyl phosphonates through rational design of a tailored N-heterocyclic carbene catalyst.  

Science.gov (United States)

A highly selective NHC-catalyzed synthesis of ?-butyrolactones from the fusion of enals and ?-ketophosphonates has been developed. Computational modeling of competing transition states guided a rational design strategy to achieve enhanced levels of enantioselectivity with a new tailored C1-symmetric biaryl-saturated imidazolium-derived NHC catalyst. PMID:24299299

Jang, Ki Po; Hutson, Gerri E; Johnston, Ryne C; McCusker, Elizabeth O; Cheong, Paul H-Y; Scheidt, Karl A

2014-01-01

224

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

DEFF Research Database (Denmark)

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

SØlvhØj, Amanda Birgitte; Madsen, Robert

2011-01-01

225

Tandem ammonia borane dehydrogenation/alkene hydrogenation mediated by [Pd(NHC)(PR3)] (NHC = N-heterocyclic carbene) catalysts.  

Science.gov (United States)

[Pd(NHC)(PR(3))] complexes were shown to be active catalysts in the dehydrogenation of ammonia borane and the subsequent hydrogenation of unsaturated compounds at very low catalyst loadings (0.05 mol% for some substrates). PMID:23254388

Hartmann, Caroline E; Jur?ík, Václav; Songis, Olivier; Cazin, Catherine S J

2013-02-01

226

Anionic N-heterocyclic carbenes (NHCs): a versatile route to saturated NHCs bearing pendant weakly coordinating anions.  

Science.gov (United States)

A versatile methodology is reported for the synthesis of anionic NHCs featuring a 5-, 6-, or 7-membered saturated heterocyclic core. Lewis acid promoted exocyclic ring closure generates systems in which the pendant borate functionality is incorporated via a CH2 linker, allowing for electronic and steric isolation of the anionic component. Hence, a library of NHCs can be accessed which incorporate metal binding environments essentially identical to the neutral parent donors, but with significantly altered solubility profiles. PMID:25198297

Phillips, Nicholas; Tirfoin, Rémi; Aldridge, Simon

2014-11-01

227

Access to oxoquinoline heterocycles by N-heterocyclic carbene catalyzed ester activation for selective reaction with an enone.  

Science.gov (United States)

Organocatalytic ester activation is developed for a highly selective cascade reaction between saturated esters and amino enones. The reaction involves activation of the ?-carbon atom of the ester as a key step. This method allows a single-step access to multicyclic oxoquinoline-type heterocycles with high enantiomeric ratios. PMID:24839111

Fu, Zhenqian; Jiang, Ke; Zhu, Tingshun; Torres, Jaume; Chi, Yonggui Robin

2014-06-16

228

Can an ancillary ligand lead to a thermodynamically stable end-on 1 : 1 Cu-O2 adduct supported by a beta-diketiminate ligand?  

Science.gov (United States)

The finding that dioxygen binds end-on to the Cu(B) site in the crystal structure of a precatalytic complex of peptidylglycine alpha-hydroxylating monooxygenase has spurred the search for biomimetic model complexes exhibiting the same dioxygen coordination. Recent work has not only indicated that sterically hindered beta-diketiminate ligands (L(1)) could support side-on 1 : 1 Cu-O(2) adducts, but also that an end-on L(1)Cu(THF)O(2) structure occurs as an unstable intermediate in the oxygenation mechanism of the Cu(I) complex. In this work, density functional theory and multireference methods are used to determine the potential of ancillary ligands, X, other than THF to yield thermodynamically stable end-on L(1)CuXO(2) species. A diverse set of ligands X, comprising phosphines, thiophene, cyclic ethers, acetonitrile, para-substituted pyridines, N-heterocyclic carbenes, and ligands bearing hydrogen bond donors, has been considered in order to identify ligand characteristics which energetically favor end-on L(1)CuXO(2) over: a) reversion to the Cu(I) complex and dioxygen, b) isomerization to side-on L(1)CuXO(2), and c) decay to L(1)CuO(2) and X. Ancillary ligands with judiciously chosen degrees and orientation of steric bulk and which bear potential hydrogen bond donors to an end-on bound dioxygen moiety most favor oxygenation of L(1)CuX to yield end-on L(1)CuXO(2). Conversion to the side-on isomer can be deterred through the use of a sufficiently bulky ligand X, such as one that is at least the size of a 5-membered ring. Loss of X to give L(1)CuO(2) can be made prohibitively endergonic by employing ligands X which are highly electron donating and which backbond strongly with and sigma-donate significantly to copper. PMID:17033702

Heppner, David E; Gherman, Benjamin F; Tolman, William B; Cramer, Christopher J

2006-10-28

229

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

Science.gov (United States)

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

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

2014-10-01

230

Springloaded porphyrin NHC hybrid rhodium(III) complexes: carbene dissociation and oxidation catalysis.  

Science.gov (United States)

Porphyrin rhodium(III) complexes accommodate one or two NHC ligands in the apical position, which leads to severe porphyrin distortion and dearomatization. The strain in the bis(carbene) complex induces facile carbene dissociation and the formation of a catalytically active site for alcohol oxidation. PMID:24553627

Olguín, Juan; Müller-Bunz, Helge; Albrecht, Martin

2014-04-01

231

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

Science.gov (United States)

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

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

2012-02-01

232

Enantioselective Construction of Quaternary N-Heterocycles by Palladium-Catalyzed Decarboxylative Allylic Alkylation of Lactams  

Science.gov (United States)

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 manuscript, we describe the highly enantioselective palladium-catalyzed 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 envision 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 employed in the synthesis of the Aspidosperma alkaloids quebrachamine and rhazinilam, but that were previously only available by chiral auxiliary approaches or as racemic mixtures. PMID:22270628

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

2011-01-01

233

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

Science.gov (United States)

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

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

2014-10-29

234

ESI HRMSn fragmentation payhways of some N-heterocyclic drug compounds  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Title (20) ESI HRMSn fragmentation payhways of some N-heterocyclic drug compounds . Introduction (120) The large amount of bibliography about EI mass spectra of organic compounds constitutes the support on which spectral databases were built. The huge diffusion of atmospheric pressure ionization methods does not correlate at present with a similar extent of work. The number of papers about gas phase fragmentation is not so large and sometimes useful pathways in spectral characteri...

Medana, Claudio

2010-01-01

235

Fluorocarbon and hydrocarbon N-heterocyclic (c5-c7) imidazole-based liquid crystals.  

Science.gov (United States)

By using three synthetic protocols, a series of fluorocarbon and hydrocarbon N-heterocyclic imidazole-based liquid crystals (LCs) and related imidazolium-based ionic liquid crystals (ILCs) have been prepared. The ring size of the N-heterocycle and the length of the N-terminal chain (on the imidazolium unit in the ILCs) were modified, and the influence of these structural parameters on liquid-crystal phases was investigated by means of polarizing optical microscopy (POM), differential scanning calorimetry (DSC), and X-ray diffraction (XRD). These new ILCs exhibit a disordered smectic phase (SmA), good thermal stabilities, a broad smectic phase range, a high dipole moment, relatively low melting points, but high clearing points and strong emission fluorescence relative to imidazole-based LCs. These encouraging results have led us to believe these fluorocarbon and hydrocarbon N-heterocyclic imidazole-based LCs and related imidazolium-based ILCs could be used as new liquid-crystalline materials. PMID:25256069

Chen, Hongren; Hong, Fengying; Shao, Guang; Hang, Deyu; Zhao, Lei; Zeng, Zhuo

2014-12-01

236

Supramolecular hydrogen-bonded structures between melamine and N-heterocycles  

Science.gov (United States)

Melamine (M) forms hydrogen bonded adducts with the N-heterocycles tris(2-pyridyl)-triazine (TPTZ) and tetrakis(4-N-methylpyridinumyl)porphyrin tetratosylate (TMPyP-Tos). The 4:3 adduct 4M·3TPTZ was obtained under solvent-free conditions and the 3:1 adduct 3M·TMPyP-Tos·9H2O in aqueous solution. In both adduct phases N-heterocycles are arranged in ?-? stacks and melamine molecules are arranged perpendicular to these stacks. Whereas cohesion between the extended ?-systems of N-heterocycles is mainly achieved by dispersive interactions no stacking interactions between melamine molecules occur. Melamine units are orientated in such a way to be located most suitable as donors and acceptors, respectively, for a dense hydrogen bonding network. In 4M·3TPTZ all molecules are involved in hydrogen bonding, whereas in 3M·TMPyP-Tos·9H2O hydrogen bridges are primarily formed between melamine, tosylate and water units and the macrocycle TMPyP is mainly bound by electrostatic interactions.

Makowski, Sophia J.; Lacher, Monika; Lermer, Claudia; Schnick, Wolfgang

2012-04-01

237

Metallocene carbene chemistry  

International Nuclear Information System (INIS)

A review of chemical properties of group IV element chamfered metallocenes Cp2M (M=Ti, Zr, Hf) is presented. It is shown that specific features of their stereoelectronic structure and clearly pronounced oxophily of M metals permit using the complexes as components of reaction systems involving carbenes. The use of ruthenium carbene complexes for realizing the catalytic metathesis of lateral olefin substituents in the chamfered metallocenes is described by way of example

238

Azavinylidenephosphoranes: a class of cyclic push-pull carbenes.  

Science.gov (United States)

The synthesis of a novel family of cyclic push-pull carbenes, namely, azavinylidene phosphoranes, is described. The methodology is based on a formal [3+2] cycloaddition between terminal alkynes and phosphine-imines followed by an oxidation/deprotonation step. Carbenes 6, obtained by simple deprotonation, exhibit typical transient carbene reactivity like the intramolecular C?H insertion reaction and a pronounced ambiphilic character exemplified by [2+1] cycloaddition with electron-poor methyl acrylate. Owing to the cyclic structure, carbenes 6 also exhibit an excellent coordination ability toward transition metals. Rh(I) complex 10 was obtained in excellent yield and was fully characterized by multinuclear NMR spectroscopy and X-ray crystallography. The corresponding Rh(I) -carbonyl complex was also prepared; this indicates that carbenes 6 belong to the strongest ?-donating ligands to date. DFT calculations confirmed the high ?-donation ability of 6 and their classification as push-pull carbenes with a relatively small singlet-triplet energy gap of 23.2-24.3?kcal?mol(-1) . PMID:25123091

Lavigne, Florie; Kazzi, Aimée El; Escudié, Yannick; Maerten, Eddy; Kato, Tsuyoshi; Saffon-Merceron, Nathalie; Branchadell, Vicenç; Cossío, Fernando P; Baceiredo, Antoine

2014-09-22

239

Synthesis of P,N-Heterocycles from ?-Amino-H-Phosphinates: Conformationally Restricted ?-Amino Acid Analogs  

Science.gov (United States)

P,N-Heterocycles (3-hydroxy-1,3-azaphospholane and 3-hydroxy-1,3-azaphosphorinane-3-oxide) are synthesized in moderate yield from readily available ?-amino-H-phosphinates and aldehydes or ketones via an intramolecular Kabachnik-Fields reaction. The products are conformationally restricted phosphinic analogs of ?-amino acids. The multi-gram scale syntheses of the H2N(CH2)nPO2H2 phosphinic precursors (n = 1, 2, 3) and some derivatives are also described. PMID:18855477

Queffelec, Clemence; Ribiere, Patrice; Montchamp, Jean-Luc

2009-01-01

240

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

International Nuclear Information System (INIS)

(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)5Mo=C(OMe)-p-tol undergoes carbene annulation upon reaction with trimethylsilylacetylene leading to naphthoquinone after oxidative work-up. Similar products are obtained from (CO)5Mo=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 C1-synthon, which is incorporated into the furan cycloaddition products

 
 
 
 
241

Metal-free aerobic oxidative C-N bond cleavage of tertiary amines for the synthesis of N-heterocycles with high atom efficiency.  

Science.gov (United States)

An efficient metal-free aerobic oxidative C-N bond cleavage of tertiary amines has been developed to construct N-heterocycles using molecular oxygen as the sole oxidant with high atom efficiency, in which all of the three alkyl groups in tertiary amines can be utilized and transformed into N-heterocycles. PMID:24788750

Chen, Xiuling; Chen, Tieqiao; Zhou, Yongbo; Han, Daoqing; Han, Li-Biao; Yin, Shuang-Feng

2014-06-21

242

Relationship between Antifungal Activity against Candida albicans and Electron Parameters of Selected N-Heterocyclic Thioamides  

Science.gov (United States)

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.

Stachowicz, Jadwiga; Krajewska-Kulak, Elzbieta; Lukaszuk, Cecylia; Niewiadomy, A.

2014-01-01

243

Carbenes as catalysts for transformations of organometallic iron complexes.  

Science.gov (United States)

Compared with the enormous arsenal of catalysts used to produce organic compounds, complementary species that are able to mediate sophisticated organometallic transformations are virtually nonexistent. We found that stable N-heterocyclic carbenes (NHCs) can mediate unusual organometallic transformations in solution at room temperature. Depending on the choice of NHC initiator, stoichiometric or catalytic reactions of bis(cyclooctatetraene)iron [Fe(COT)2] ensue. The stoichiometric reaction leads to the isolation of a previously unknown mixed-valent species, featuring distinct and directly bonded Fe(0) and Fe(I) centers. In the catalytic process, three iron atoms are fused to afford the tri-iron cluster Fe3(COT)3, which is a hydrocarbon analog of Dewar's classic Fe3(CO)12 complex. The key step in both of these processes is proposed to involve the NHC's ability to induce metal-metal bond formation. These NHC-mediated reactions provide a foundation on which to develop future organometallic transformations that are catalyzed by organic species. PMID:19900894

Lavallo, Vincent; Grubbs, Robert H

2009-10-23

244

An additional structure and property study on polymeric haloplumbates(II) with aromatic N-heterocyclic organic molecules  

Science.gov (United States)

Three new haloplumbates(II)/aromatic N-heterocyclic organic hybrids, [(nmp)(PbI3)]n (nmp = N-methylpyrazine)(1), [(dhpp)(Pb2Cl6)]n (dhpp = 6,12-dihydrodipyrido[1,2-a:1',2'-d] pyrazinium)(2), [(dedp)3(Pb6I18)]n (dedp = N,N'-diethyl-4,4'-dipyridinium)(3) have been synthesized and structurally determined. These polymeric haloplumbates exhibit different model type structures, including one-dimensional linear chain (for 1), ribbonlike arrangement based on face- and edge-sharing PbXn tetragonal pyramids or octahedra (for 2 and 3), and N-heterocyclic organic cations weakly interact with inorganic haloplumbates to present 3-D supramolecular networks. Three compounds posses semiconducting properties with Eg ranging among 2.07-2.71 eV. Photoluminescence and third-order nonlinear optical (NLO) activity of 3 were also discussed.

Li, Hao-Hong; Wang, Yun-Jie; Lian, Zhao-Xun; Xu, Yong-Fu; Wang, Min; Huang, Shu-Wei; Chen, Zhi-Rong

2012-05-01

245

Antiradiation compounds XVII: binding ability of radiation-protective N-heterocyclic aminoethyl disulfides and thiosulfides to DNA  

International Nuclear Information System (INIS)

Binding parameters for a series of N-heterocyclic aminoethyl disulfides and thiosulfates to DNA were determined at different ionic strengths and pH values. None of the thiosulfates showed any binding ability, but the disulfides revealed DNA binding abilities that were suppressed both by increased ionic strength and hydrogen-ion concentration. No correlation between DNA binding ability and radiation protective activity in mice was evident

246

Cyclization of ?(3)-Benzylpalladium Intermediates Derived from Carbene Insertion.  

Science.gov (United States)

Migratory insertion of benzylidene carbene ligands into arylpalladium(II) species generates ?(3)-benzylpalladium intermediates that can cyclize to generate five- and six-membered rings with new sp(3) centers. The reaction tolerates a range of arene functional groups and stabilized enolates. The products generated through this reaction are 1-arylindanes and 1-aryltetralins that are common to a range of natural products. PMID:25279856

Gutman, Eugene S; Arredondo, Vanessa; Van Vranken, David L

2014-10-17

247

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

Energy Technology Data Exchange (ETDEWEB)

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

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

2013-04-15

248

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

International Nuclear Information System (INIS)

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

249

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

Directory of Open Access Journals (Sweden)

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

Guangming Nan

2010-06-01

250

Cellulose-supported N-heterocyclic carbene-palladium catalyst: synthesis and its applications in the Suzuki cross-coupling reaction.  

Science.gov (United States)

A cellulose-supported N-methylimidazole-palladium catalyst (Cell-NHC-Pd) was synthesized and used for Suzuki cross-coupling reactions between aryl halides and phenylboronic acids to create the corresponding coupling products in good to excellent yields. Moreover, the catalyst is easily recovered using only a few cycles of simple filtration. PMID:25263916

Wang, Xiaoxia; Hu, Peibo; Xue, Fengjun; Wei, Yuping

2014-12-19

251

Carbene transfer from triazolylidene gold complexes as a potent strategy for inducing high catalytic activity.  

Science.gov (United States)

A series of gold(I) complexes [AuCl(trz)] were synthesized that contain 1,2,3-triazolylidene (trz) ligands with variable wingtip groups. In the presence of AgBF4, these complexes undergo ligand redistribution to yield cationic complexes [Au(trz)2]BF4 in high yields as a result of efficient carbene transfer. Identical reactivity patterns were detected for carbene gold complexes comprised of Arduengo-type IMes ligands (IMes = N,N'-dimesityl-imidazol-2-ylidene). Reaction of cationic complexes [Au(trz)2](+) with [AuCl(trz')] afforded the heteroleptic complex [Au(trz)(trz')](+) and [AuCl(trz)] (trz, trz' = triazolylidene ligands with different wingtip groups). Carbene transfer occurs spontaneously, yet is markeldy rate-enhanced in the presence of Ag(+). The facile carbene transfer was exploited as a catalyst activation process to form active gold species for the aldol condensation of isocyanides and aldehydes to form oxazolines. The catalytic activity is strongly dependent on the presence of Ag(+) ions to initiate catalyst activation. High turnovers (10(5)) and turnover frequencies (10(4) h(-1)) were accomplished. Structural analysis at early stages of the reaction support the critical role of triazolylidene dissociation to activate the precatalyst and dynamic light scattering revealed the presence of nanoparticles (±100 nm diameter) as potential catalytically active species. Furthermore, the triazolylidene scaffold had no impact on the diastereoselectivity of the oxazoline formation, and chiral triazolylidenes did not induce any asymmetry in the product. The facile dissociation of carbenes from [AuCl(carbene)] in the presence of Ag(+) ions suggests a less stable Au-Ccarbene interaction than often assumed, with potential implications for gold-catalyzed reactions that employ a silver salt as (putative) halide scavenger. PMID:23902160

Canseco-Gonzalez, Daniel; Petronilho, Ana; Mueller-Bunz, Helge; Ohmatsu, Kohsuke; Ooi, Takashi; Albrecht, Martin

2013-09-01

252

Rh-Catalyzed rearrangement of vinylcyclopropane to 1,3-diene units attached to N-heterocycles  

Science.gov (United States)

Summary Dienes embedded in quinolizidine and indolizidine structures can be prepared in four steps from cyclic nitrones and bicyclopropylidene. The key intermediates ?-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%). PMID:21448251

Vurchio, Carolina; Cicchi, Stefano; de Meijere, Armin

2011-01-01

253

Rh-Catalyzed rearrangement of vinylcyclopropane to 1,3-diene units attached to N-heterocycles  

Directory of Open Access Journals (Sweden)

Full Text Available Dienes embedded in quinolizidine and indolizidine structures can be prepared in four steps from cyclic nitrones and bicyclopropylidene. The key intermediates ?-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%.

Alberto Brandi

2011-03-01

254

Synthesis, structure and properties of 2D lanthanide coordination polymers based on N-heterocyclic arylpolycarboxylate ligands.  

Science.gov (United States)

The reaction of 3-(2,4-dicarboxyphenyl)-2,6-pyridinedicarboxylic acid (H4dppd) with rare earth nitrates under hydrothermal conditions generated a series of new two-dimensional (2D) coordination polymers, namely {[La(Hdppd)(H2O)2·(H2O)2]n (), [Ln2(Hdppd)2(H2O)4·(H2O)3]n [Ln = Sm (), Eu ()] and [Ln(Hdppd)(H2O)3·H2O]n [Ln = Gd (), Tb (), Dy (), Ho (), Er ()] [Hdppd = 3-(2,4-dicarboxyphenyl)-2,6-pyridinedicarboxylic trivalent anion]}. The complexes were characterized by X-ray single-crystal diffraction, infrared spectroscopy, elemental analysis and thermogravimetric analysis. Luminescence spectroscopy of and showed bright red and green luminescences due to the 4f(n)-4f(n) transitions in Eu(3+) and Tb(3+) respectively, although the luminescence lifetime is shortened by non-radiative decay due to the presence of coordinating water molecules. The magnetic properties of were measured and discussed. Compound exhibits frequency dependent out-of-phase signals, and ferromagnetic coupling exists in . PMID:25331555

You, Li-Xin; Wang, Shu-Ju; Xiong, Gang; Ding, Fu; Meert, Katrien W; Poelman, Dirk; Smet, Philippe F; Ren, Bao-Yi; Tian, Yan-Wen; Sun, Ya-Guang

2014-11-01

255

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

Science.gov (United States)

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

Batiste, Laurent; Chen, Peter

2014-07-01

256

The inhibition of mild steel corrosion in phosphoric acid solutions by some N-heterocyclic compounds in the salt form  

International Nuclear Information System (INIS)

The effect of some quaternary N-heterocyclic compounds on the corrosion of mild steel in solutions of phosphoric acid (H3PO4) has been investigated in relation to the concentration of the inhibitor and acid as well as temperature by various monitoring corrosion techniques. Surface morphology was studied by scanning electron microscopy (SEM). Results obtained revealed that these compounds are good mixed-type inhibitors without changing the mechanism of the corrosion process. In general, at constant acid concentration, inhibitor efficiency increased with concentration of the inhibitor. On the other hand, at constant inhibitor concentration, inhibitor efficiency decreased with concentration of the acid up to a critical concentration above which it started to increase. The studied compounds appeared to function through general adsorption following the thermodynamic-kinetic adsorption isotherm. The thermodynamic parameters were determined and discussed. A quantitative correlation between inhibitor structure and inhibition efficiency was discussed

257

Highly enantioselective synthesis of chiral 7-ring O- and N-heterocycles by a one-pot nitro-Michael-cyclization tandem reaction.  

Science.gov (United States)

A concise enantioselective approach to synthesise medium-sized 7-ring O- and N-heterocycles has been developed. The synthetic strategy relies on an organocatalytic nitro-Michael-nitrile oxide cycloaddition tandem reaction, leading to the corresponding chiral benzoxe- and benzazepine derivatives containing an additional fused dihydroisoxazoline ring in good yields and excellent enantioselectivities (up to 97% ee). PMID:24190160

Rohlmann, Renate; Daniliuc, Constantin-Gabriel; Mancheño, Olga García

2013-12-25

258

NaSH in the construction of thiophene ring fused with N-heterocycles: a rapid and inexpensive synthesis of novel small molecules as potential inducers of apoptosis.  

Science.gov (United States)

A facile construction of a thiophene ring fused with N-heterocycles has been achieved via the reaction of NaSH with 2-chloro-3-alkynyl quinoxalines/pyrazines leading to novel 2-substituted thieno[2,3-b]pyrazine/quinoxaline derivatives as potential inducers of apoptosis. Some of them showed encouraging pharmacological properties when tested in zebrafish. PMID:25168747

Kolli, Sunder Kumar; Nakhi, Ali; Medishetti, Raghavender; Yellanki, Swapna; Kulkarni, Pushkar; Ramesh Raju, R; Pal, Manojit

2014-09-15

259

Strain-promoted oxidative annulation of arynes and cyclooctynes with benzamides: palladium-catalyzed C-h/n-h activation for the synthesis of N-heterocycles.  

Science.gov (United States)

Strained alkynes include arynes and cyclooctynes reacted with N-methoxyamides through palladium-catalyzed C-H/N-H activation for the first time. A variety of important N-heterocycles such as phenanthridinones and isoquinolones were constructed in one step with high efficiency. PMID:25275617

Peng, Xianglong; Wang, Weiguo; Jiang, Chao; Sun, Di; Xu, Zhenghu; Tung, Chen-Ho

2014-10-17

260

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

International Nuclear Information System (INIS)

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, (CH2)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

 
 
 
 
261

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

Energy Technology Data Exchange (ETDEWEB)

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{sub 2}){sub 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.

Zhou, Yong Hong [Huaibei Normal Univ., Huaibei (China)

2013-04-15

262

Direct synthesis of cis-dihalido-bis(NHC) complex of nickel(II) and catalytic application in olefin addition polymerization: effect of halogen co-ligands and density functional theory study.  

Science.gov (United States)

Two novel amine-containing N-heterocyclic carbene ligand precursors [H(1a-b)]Br have been prepared in good yield and fully characterized. Direct syntheses of cis- and trans-dihalido-bis(NHC) nickel complexes [Ni(NHC)2X2] (X = Cl, Br) are reported. The solid structures of trans-[Ni(1a-b)2Br2] (2a-b) and cis-[Ni(1a)2Cl2] (3) were determined by single-crystal X-ray analysis and 3 was found to be the first example of cis-configuration coordination of monodentate NHC ligands to a metal center for dihalido-bis(NHC) nickel complexes. DFT calculations were conducted to determine the energy difference between cis- and trans-isomers of complexes 2a and 3 bearing bromide and chloride co-ligands. The cis-[Ni(1a)2Cl2] (cis-3) is 1.77-1.55 kcal mol(-1) lower in energy than its trans-isomer in polar solvents including CH2Cl2 and THF, while the trans-[Ni(1a)2Br2] (trans-2a) is more stable than the cis-isomer similarly in the gas phase. The cis nickel complex 3 with two coordinated monodentate NHCs was tested for olefin addition polymerization at standard conditions. It was found that cis-3 was inactive in ethylene polymerization but showed moderate catalytic activities (0.5-3.0 × 10(6) g of PNB (mol of Ni)(-1) h(-1)) in the addition polymerization of norbornene in the presence of methylaluminoxane (MAO) as cocatalyst. PMID:23838704

Zhang, Dao; Zhou, Sen; Li, Zhiming; Wang, Quanrui; Weng, Linhong

2013-09-01

263

Assessing the ligand properties of 1,3-dimesitylbenzimidazol-2-ylidene in ruthenium-catalyzed olefin metathesis.  

Science.gov (United States)

The deprotonation of 1,3-dimesitylbenzimidazolium tetrafluoroborate with a strong base afforded 1,3-dimesitylbenzimidazol-2-ylidene (BMes), which was further reacted in situ with rhodium or ruthenium complexes to afford three new organometallic products. The compounds [RhCl(COD)(BMes)] (COD is 1,5-cyclooctadiene) and cis-[RhCl(CO)2(BMes)] were used to probe the steric and electronic parameters of BMes. Comparison of the percentage of buried volume (%V(Bur)) and of the Tolman electronic parameter (TEP) of BMes with those determined previously for 1,3-dimesitylimidazol-2-ylidene (IMes) and 1,3-dimesitylimidazolin-2-ylidene (SIMes) revealed that the three N-heterocyclic carbenes (NHCs) had very similar profiles. Nonetheless, changes in the hydrocarbon backbone subtly affected the stereoelectronic properties of these ligands. Accordingly, the corresponding [RuCl2(PCy3)(NHC)(=CHPh)] complexes displayed different catalytic behaviors in the ring-closing metathesis (RCM) of ?,?-dienes. In the benchmark cyclization of diethyl 2,2-diallylmalonate, the new [RuCl2(PCy3)(BMes)(=CHPh)] compound (1d) performed slightly better than the Grubbs second-generation catalyst (1a), which was in turn significantly more active than the related [RuCl2(PCy3)(IMes)(=CHPh)] initiator (1b). For the formation of a model trisubstituted cycloolefin, complex 1d ranked in-between catalyst precursors 1a and 1b, whereas in the RCM of tetrasubstituted cycloalkenes it lost its catalytic efficiency much more rapidly. PMID:22990296

Borguet, Yannick; Zaragoza, Guillermo; Demonceau, Albert; Delaude, Lionel

2013-05-28

264

Mechanism of ultrasound scission of a silver-carbene coordination polymer.  

Science.gov (United States)

Scission of a supramolecular polymer-metal complex can be carried out using collapsing cavitation bubbles created by ultrasound. Although the most plausible scission mechanism of the coordinative bonds is through mechanical force, the influence of radicals and high hot-spot temperatures on scission has to be considered. A silver(I)-N-heterocyclic carbene complex was exposed to 20 kHz ultrasound in argon, nitrogen, methane, and isobutane saturated toluene. Scission percentages were almost equal under argon, nitrogen, and methane. Radical production differs by a factor of 10 under these gases, indicating that radical production is not a significant contributor to the scission process. A model to describe the displacement of the bubble wall, strain rates, and temperature in the gas shows that critical strain rates for coil-to-stretch transition, needed for scission, are achieved at reactor temperatures of 298 K, an acoustic pressure of 1.2 × 10(5) Pa, and an acoustic frequency of 20 kHz. Lower scission percentages were measured under isobutane, which also shows lower strain rates in model simulations. The activation of the polymer-metal complexes in toluene under the influence of ultrasound occurs through mechanical force. PMID:21827184

Rooze, Joost; Groote, Ramon; Jakobs, Robert T M; Sijbesma, Rint P; van Iersel, Maikel M; Rebrov, Evgeny V; Schouten, Jaap C; Keurentjes, Jos T F

2011-09-29

265

Nonempirical investigation of electronic structure of simple model alkyl and carbene complexes of metals of the first transition period beginning  

International Nuclear Information System (INIS)

The nonempirical LCAO MO SCF method in small bases of groupped Gauss functions is used to calculate electronic structure of model complexes of the Hsub(n)MCHsub(3) and Hsub(m)MCHsub(2) composition, where M=Ti, V, Cr. The character of the metal-carbon bond depending on the nature of metal and hydrocarbon ligand is analyzed. The energetics of some processes accompanied by the breaking of ?- or ?-component of the metal-carbon bond is considered. The growth of relative ability to the formation of carbene complex from initial alkyl in the process od ?-elimination in the Ti< V< Cr series is established, which is explained by relative ?-component strengthening of metal-carbon bond in carbene complex as compared with the initial alkyl one. Carbene complexes with increased coordination of the transition metal are characterized by resuced populations of the 2psub(?)-AO of C atom of carbene ligand. On the basis of obtained results some general regularities of the M=C bond nature and the problems of stabilization of carbene complexes are discussed

266

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

Science.gov (United States)

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

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

2013-09-11

267

Base-mediated selective synthesis of diversely substituted N-heterocyclic enamines and enaminones by the hydroamination of alkynes.  

Science.gov (United States)

Regio- and stereoselective alkynylation of various N-heterocycles 1a-l using potassium and cesium salts in DMSO is described. Terminal alkynes 2a-k and internal alkynes 4a-f provided the kinetically stable Z-enamines 3a-l and 5a-i in good to excellent yields using KOH at 120 °C. Addition of heterocyclic amines to 1,3- and 1,4-diethynylbenzene 6a-b provided the mixture of E/Z isomers with KOH; however, with Cs(2)CO(3) selectively Z-isomers 7ab-db were obtained by the hydroamination at one triple bond. This developed methodology also provides an easy and novel access for the synthesis of enaminones 10a-c. The detailed work also supports the formation of cis-isomer by preferential addition of o-haloarylalkynes followed by intramolecular C2 arylation in the copper-catalyzed tandem synthesis of indolo and pyrrolo[2,1-a]isoquinolines. PMID:22708683

Joshi, Megha; Patel, Monika; Tiwari, Rakesh; Verma, Akhilesh K

2012-07-01

268

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

Scientific Electronic Library Online (English)

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

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

269

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

Scientific Electronic Library Online (English)

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

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

2014-05-01

270

Retention or inversion in stereospecific nickel-catalyzed cross-coupling of benzylic carbamates with arylboronic esters: control of absolute stereochemistry with an achiral catalyst.  

Science.gov (United States)

Stereospecific coupling of benzylic carbamates and pivalates with aryl- and heteroarylboronic esters has been developed. The reaction proceeds with selective inversion or retention at the electrophilic carbon, depending on the nature of the ligand. Tricyclohexylphosphine ligand provides the product with retention, while an N-heterocyclic carbene ligand provides the product with inversion. PMID:23414579

Harris, Michael R; Hanna, Luke E; Greene, Margaret A; Moore, Curtis E; Jarvo, Elizabeth R

2013-03-01

271

Transition metal free hydrolysis/cyclization strategy in a single pot: synthesis of fused furo N-heterocycles of pharmacological interest.  

Science.gov (United States)

A transition metal free tandem two-step strategy has been developed involving hydrolysis of 2-chloro-3-alkynyl quinoxalines/pyrazines followed by in situ cyclization of the corresponding 2-hydroxy-3-alkynyl intermediates in a single pot leading to fused furo N-heterocycles as potential inhibitors of sirtuins. A representative compound showed promising pharmacological properties in vitro and in vivo. PMID:23824158

Nakhi, Ali; Rahman, Md Shafiqur; Seerapu, Guru Pavan Kumar; Banote, Rakesh Kumar; Kumar, Kummari Lalith; Kulkarni, Pushkar; Haldar, Devyani; Pal, Manojit

2013-08-14

272

Amides of gold(I) diphosphines prepared from N-heterocyclic sources and their in vitro and in vivo screening for anticancer activity  

Digital Repository Infrastructure Vision for European Research (DRIVER)

A series of new neutral mononuclear or dinuclear gold(I) complexes and a cyclic cationic tetranuclear amidogold(I) complex comprising of the phosphines 1,2- bis(dimethylphosphino)ethane (dmpe), ?-1,2–bis(diphenylphosphino)ethane (dppe), ?-1,3- bis(diphenylphosphino)propane (dppp), ?-1,5-bis(diphenylphosphino)pentane (dpppe), ?-1,6- bis(diphenylphosphino)hexane (dpph) or trimethylphosphine, and several N-heterocyclic ring systems (imidazolate, pyrazolate, 1,2,3-triazolate,...

Horvath, Ulrike E. I.; Dobrzan?ska, Liliana; Strasser, Christoph E.; Bouwer, Wilna; Joone, Gisela; Jansen Rensburg, Constance E.; Cronje, Stephanie; Raubenheimer, Helgard G.

2012-01-01

273

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

Science.gov (United States)

For the past dozen years, homogeneous gold catalysis has evolved from a little known topic in organic synthesis to a fully blown research field of significant importance to synthetic practitioners, due to its novel reactivities and reaction modes. Cationic gold(I) complexes are powerful soft Lewis acids that can activate alkynes and allenes toward efficient attack by nucleophiles, leading to the generation of alkenyl gold intermediates. Some of the most versatile aspects of gold catalysis involve the generation of gold carbene intermediates, which occurs through the approach of an electrophile to the distal end of the alkenyl gold moiety, and their diverse transformations thereafter. On the other hand, ?-oxo metal carbene/carbenoids are highly versatile intermediates in organic synthesis and can undergo various synthetically challenging yet highly valuable transformations such as C-H insertion, ylide formation, and cyclopropanation reactions. Metal-catalyzed dediazotizations of diazo carbonyl compounds are the principle and most reliable strategy to access them. Unfortunately, the substrates contain a highly energetic diazo moiety and are potentially explosive. Moreover, chemists need to use energetic reagents to prepare them, putting further constrains on operational safety. In this Account, we show that the unique access to the gold carbene species in homogeneous gold catalysis offers an opportunity to generate ?-oxo gold carbenes if both nucleophile and electrophile are oxygen. Hence, this approach would enable readily available and safer alkynes to replace hazardous ?-diazo carbonyl compounds as precursors in the realm of gold carbene chemistry. For the past several years, we have demonstrated that alkynes can indeed effectively serve as precursors to versatile ?-oxo gold carbenes. In our initial study, we showed that a tethered sulfoxide can be a suitable oxidant, which in some cases leads to the formation of ?-oxo gold carbene intermediates. The 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 ?-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 ?-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 ?-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

Zhang, Liming

2014-03-18

274

A study of the resistance of some N-heterocycles (BTPS) to radiolysis  

International Nuclear Information System (INIS)

Full text of publication follows. One option for the selective extraction of trivalent minor actinides within highly active effluents coming from the PUREX process could be as follows: firstly, to co-extract trivalent actinides [An(III)Am(III) and Cm(III)] and also lanthanides [Ln(III)] from the PUREX raffinates; secondly, to separate An(III) from Ln(III) by means of selective extractants. Although efficient extractants for the co-extraction of An(III) and Ln(III) have been developed, selective extractants for An(III) are still required. The various tetra-alkyl substituted BTP molecules, which have been studied within the FP5 European integrated project PARTNEW have been shown to be too sensitive towards acidic hydrolysis and alpha-radiolysis for the development of an An(III)/Ln(III) separation process. Other extracting molecules have been developed within the framework of the FP6 European Integrated Project EUROPART. These molecules include some nitrogen heterocycles. This paper presents some of the basic research carried out in order to improve the resistance of the chosen molecules towards radiolytic degradation. Attempts to improve their extraction properties by the addition of synergists, which usually avoid third-phase formation and improve the kinetics of extraction, will be outlined. It appears that some reagents are not only more selective towards An(III) than tetra-alkyl substituted BTPs, but also more resistant to radiolysis. The carbon atoms on the alpha positions of their triazinyl rings are fully substituted, thus preventing oxidation and nitration of the alkyl groups. Although none of the presently studied ligands has yet met the requirements of a process development strategy, huge improvements have been made in the field of nitrogen heterocycles since the first reference molecule, tetra-n-propyl-bis-triazinyl-pyridine (nPr-BTP), was first chosen in 1998 to demonstrate the scientific feasibility of An(III)/Ln(III) separation from highly active waste of medium acidity ([HNO3] > 0.5 mol/L). Many of these developments have taken place within European research programmes. (authors)

275

Ruthenium Vinyl Carbene Intermediates in Enyne Metathesis  

Digital Repository Infrastructure Vision for European Research (DRIVER)

This review provides an overview of ruthenium vinyl carbene reactivity as it relates to enyne metathesis. Methods for the synthesis of metathesis-active and metathesis-inactive complexes are also summarized. Some of the early hypotheses about vinyl carbene intermediates in enyne metatheses were tested in the arena of synthetic chemistry and subsequently led to mechanistic studies. In these two areas, studies from the author's labs are described. There are still many unresolved questions in en...

Diver, Steven T.

2007-01-01

276

3-Trimethylsilylcyclobutylidene. The ?-effect of silicon on carbenes.  

Science.gov (United States)

3-Trimethylsilylcyclobutylidene was generated by pyrolysis of the sodium salt of the tosylhydrazone derivative of 3-trimethylsilylcyclobutanone. This carbene converts to 1-trimethylsilylbicyclobutane as the major product. A labeling study shows that this intramolecular rearrangement product comes from 1,3-hydrogen migration to the carbenic center and not 1,3-silyl migration. Computational studies show two carbene minimum energy conformations, with the lower energy conformation displaying a large stabilizing interaction of the carbene center with the rear lobe of the C3-Si bond. In this conformation, the trimethylsilyl group cannot migrate to the carbene center, and the most favorable process is 1,3-hydrogen migration. When the carbene is generated photochemically in methanol, it reacts by a protonation mechanism giving the highly stabilized 3-trimethylsilylcyclobutyl carbocation as an intermediate. When generated in dimethylamine as solvent, the carbene undergoes preferred attack of this nucleophilic solvent from the back of this C-Si rear lobe stabilized carbene. PMID:23527580

Creary, Xavier

2013-05-01

277

?-Silyl-substituted norbornyl carbocations and carbenes.  

Science.gov (United States)

endo-2-Trimethylsilyl-anti-7-norbornyl triflate undergoes solvolysis reactions 1.8 × 10(4) faster than 7-norbornyl triflate in CD3CO2D and 1.3 × 10(5) times faster in CF3CH2OH. The exclusive substitution products with retained stereochemistry point to a significantly stabilized ?-trimethylsilyl carbocation intermediate. The endo-2-trimethylsilyl-7-norbornyl carbene gives a major rearrangement product where the trimethylsilyl-activated hydrogen migrates to the carbenic center. This rearrangement product implies stabilization of the carbene by the ?-trimethylsilyl group. Isodesmic computational studies (M062X/6-311+G**) indicate that the endo-2-trimethylsilyl-7-norbornyl cation is stabilized by 16.2 kcal/mol and that the endo-2-trimethylsilyl-7-norbornyl carbene is stabilized by a smaller factor of 1.8 kcal/mol. By way of contrast, anti-7-trimethylsilyl-endo-2-norbornyl mesylate undergoes solvolysis in CD3CO2D only 2.6 times faster than endo-2-norbornyl mesylate and 9.4 times faster in CF3CH2OH. The substitution products have only partially retained stereochemistry, and significant rearrangements are observed. The anti-7-trimethylsilyl-2-norbornyl carbene gives a rearrangement product via 1,3-hydrogen migration of the C6 hydrogen, which is completely analogous to the behavior of the unsubstituted 2-norbornyl carbene. Isodesmic calculations show that the anti-7-trimethylsilyl-2-norbornyl cation is stabilized by only 3.2 kcal/mol relative to the 2-norbornyl cation, and the corresponding anti-7-trimethylsilyl-2-norbornyl carbene is stabilized by a negligible 0.9 kcal/mol. PMID:24548109

Creary, Xavier; Heffron, Anna

2014-03-21

278

Properties and reactions of manganese methylene complexes in the gas phase. The importance of strong metal: carbene bonds for effective olefin metathesis catalysts  

Energy Technology Data Exchange (ETDEWEB)

In this communication the formation, properties and reactions of the gas phase carbenes MnCH/sub 2//sup +/, (CO)/sub 5/MnCH/sub 2//sup +/, and (CO)/sub 4/MnCH/sub 2//sup +/ are described. Reported results include observation of metathesis and abstraction reactions of the methylene ligand with olefins and the first experimental determination of metal-carbene bond dissociation energies. Important points are that: (a) metal-methylene bond energies are extremely strong; and (b) the Mn/sup +/-methylene bond energy is decreased substantially on addition of five carbonyls to the metal center. If the metal-carbene bond energy exceeds 100 kcal/mol, then transfer of the carbene to an olefin to give a cyclopropane or new olefin will be endothermic and thus will not compete with the metathesis reaction. In order to avoid low turnover numbers resulting from consumption of carbene intermediates, strong metal-carbene bonds are a desirable feature of practical metathesis catalysts. (DP)

Stevens, A.E.; Beauchamp, J.L.

1979-10-10

279

Enyne Metathesis Catalyzed by Ruthenium Carbene Complexes  

DEFF Research Database (Denmark)

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

Poulsen, Carina Storm; Madsen, Robert

2003-01-01

280

High-resolution mapping of carbene-based protein footprints.  

Science.gov (United States)

Carbene chemistry has been used recently in structural mass spectrometry as a labeling method for mapping protein surfaces. The current study presents a method for quantitating label distribution at the amino acid level and explores the nature and basis for an earlier observation of labeling bias. With the use of a method based on liquid chromatography-tandem mass spectrometry (LC-MS/MS) applied to digests of holo-calmodulin, we developed a quantitation strategy to map site-specific incorporation of carbene, generated from photolysis of ionic label precursors 2-amino-4,4-azipentanoic acid and 4,4-azipentanoic acid. The approach provides reliable incorporation data for fragments generated by electron-transfer dissociation, whereas high-energy collisional dissociation leads to energy and sequence-dependent loss of the label as a neutral. However, both can produce data suitable for mapping residues in the interaction of holo-calmodulin with M13 peptide ligand. Site-specific labeling was monitored as a function of reagent, ionic strength, and temperature, demonstrating that electrostatic interactions at the protein surface can "steer" the distribution of label precursors to sites of surface charge and favor label insertion into residues in the vicinity of the surface charge. A further preference for insertion into carboxylates was observed, based on chemical reactivity. We suggest that decoupling surface partitioning from the chemistry of insertion offers a flexible, tunable labeling strategy for structural mass spectrometry that can be applied to a broad range of protein surface compositions and promotes the design of reagents to simplify the workflow. PMID:22480364

Jumper, Chanelle C; Bomgarden, Ryan; Rogers, John; Etienne, Chris; Schriemer, David C

2012-05-15

 
 
 
 
281

Novel N-heterocyclic ylideneamine gold(I) complexes : synthesis, characterisation and screening for antitumour and antimalarial activity  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Ylideneamine functionalised heterocyclic ligands, 1,3-dimethyl-1,3-dihydro-benzimidazol-2-ylideneamine (I), 3-methyl-3H-benzothiazol-2-ylideneamine (II) or 3,4-dimethyl-3H-thiazol-2-ylideneamine (III), were employed in the preparation of a series of both charged and neutral gold(I) complexes consisting either of a Au(C6F5) fragment (1–3), a [Au(PPh3)]+ unit (4–6) or a [Au(NHC)]+ unit (7) coordinated to the imine nitrogen of the neutral ylideneamine ligand. These complexes were fully chara...

Coetzee, Jacorien; Cronje, Stephanie; Dobrzanska, Liliana; Raubenheimer, Helgard G.; Joone, Gisela; Nell, Margo J.; Hoppe, Heinrich C.

2011-01-01

282

Isolation of a neutral boron-containing radical stabilized by a cyclic (alkyl)(amino)carbene.  

Science.gov (United States)

Utilizing a cyclic (alkyl)(amino)carbene (CAAC) as a ligand, neutral CAAC-stabilized radicals containing a boryl functionality could be prepared by reduction of the corresponding haloborane adducts. The radical species with a duryl substituent was fully characterized by single-crystal X-ray structural analysis, EPR spectroscopy, and DFT calculations. Compared to known neutral boryl radicals, the isolated radical species showed larger spin density on the boron atom. Furthermore, the compound that was isolated is extraordinarily stable to high temperatures under inert conditions, both in solution and in the solid state. Electrochemical investigations of the radical suggest the possibility to generate a stable formal boryl anion species. PMID:24917474

Bissinger, Philipp; Braunschweig, Holger; Damme, Alexander; Krummenacher, Ivo; Phukan, Ashwini K; Radacki, Krzysztof; Sugawara, Shun

2014-07-01

283

Copper(I) complexes based on five-membered P^N heterocycles: structural diversity linked to exciting luminescence properties.  

Science.gov (United States)

Bridging P(^)N ligands bearing five-membered heterocyclic moieties such as tetrazoles, 1,2,4-triazoles, oxadiazoles, thiadiazoles, and oxazoles have been investigated regarding their complexation behavior with copper(I) iodide as metal salts. Different complex structures were found, depending either on the ligand itself or on the ligand-to-metal ratios used in the complexation reaction. Two different kinds of luminescent dinuclear complex structures and a kind of tetranuclear complex structure were revealed by X-ray single-crystal analyses and were further investigated for their photophysical properties. The emission maxima of these complexes are in the blue to yellow region of the visible spectrum for the dinuclear complexes and in the yellow to orange region for the tetranuclear complexes. Further investigations using density functional theory (DFT) show that the highest occupied molecular orbital (HOMO) is located mainly on the metal halide cores, while the lowest unoccupied molecular orbital (LUMO) resides mostly in the ligand sphere of the complexes. The emission properties were further examined in different environments such as neat powders, neat films, PMMA matrices, or dichloromethane solutions, revealing the high potential of these complexes for their application in organic light-emitting diodes. Especially complexes with 1,2,4-triazole moieties feature emission maxima in the blue region of the visible spectrum and quantum yields up to 95% together with short decay times of about 1-4 ?s and are therefore promising candidates for blue-emitting materials in OLEDs. PMID:24205840

Zink, Daniel M; Baumann, Thomas; Friedrichs, Jana; Nieger, Martin; Bräse, Stefan

2013-12-01

284

Synthesis, spectroscopic, structural and conformational study of some tri-substituted ureas derived from N-methylpiperazine containing phenyl and N-heterocyclic substituents  

Science.gov (United States)

A series of tri-substituted ureas containing an N-methylpiperazine moiety as well as phenyl and N-heterocyclic substituents were synthesized and studied by 1H, 13C NMR and IR spectroscopies. From 1H and 13C NMR data, in CDCl3 solution at room temperature, a fast inter-conversion of the piperazine ring with the N-CH3 group in equatorial position can be proposed. Amino-imino tautomerism is observed for both thiazole and benzothiazole derivatives. Moreover, with the exception of the imino form of the thiazole derivative, the aryl substituted N-carbamoyl group rotates freely. IR data show that the compounds adopt a planar trans conformation of the CONH moiety.

Iriepa, I.; Bellanato, J.

2013-07-01

285

A theoretical study on the mechanisms of the reactions between 1,3-dialkynes and ammonia derivatives for the formation of five-membered N-heterocycles.  

Science.gov (United States)

The reactions between 1,3-dialkynes and ammonia derivatives (such as hydrazine and hydroxylamine) for the formation of five-membered N-heterocycles (i.e. 3,5-disubstituted pyrazole and 3,5-disubstituted isoxazole) have been investigated using the density functional theory (DFT) method. The calculated results indicate that the favorable mechanism of this kind of reaction generally contains four processes: (1) the Cope-type hydroamination reaction between the reactants coupled with the hydrazine/hydroxylamine-assisted proton transfer process or the trimolecular hydroamination reaction via a six-membered transition state, (2) the bimolecular proton transfer process for the formation of an allenyl oxime intermediate, (3) the cyclization process, and (4) another bimolecular or hydrazine/hydroxylamine-assisted proton transfer process to afford the final products (3,5-disubstituted pyrazole and 3,5-disubstituted isoxazole). The computational results demonstrate that the novel bimolecular proton transfer process occurs in a stepwise manner and the first step of the novel bimolecular proton transfer process is calculated to be the rate-determining step in both the reactions, and their energy barriers are 28.45 kcal mol(-1) associated with the formation of 3,5-disubstituted pyrazole and 31.07 kcal mol(-1) associated with the formation of 3,5-disubstituted isoxazole. In particular, the novel bimolecular proton transfer process has reasonably explained in detail on how and why this kind of reaction occurs, and this would provide valuable clues for the rational design of Brønsted acid/base catalysts to promote the synthesis of the five-membered N-heterocyclic compounds. PMID:24999759

Wang, Yang; Wei, Donghui; Zhang, Wenjing; Wang, Yanyan; Zhu, Yanyan; Jia, Yu; Tang, Mingsheng

2014-10-14

286

The synthesis of an aryl alkyl ionic liquid and its application in catalyzing Suzuki-Miyaura coupling reaction  

Science.gov (United States)

An aryl alkyl ionic liquids with a tertiary amino group (N(CH3)2) in the cation were synthesized. As a ligand, the synthesized ionic liquids can coordinate with palladium to form N-heterocyclic carbene (NHC)-Pd complex which exhibited high efficiency in catalyzing Suzuki-Miyaura coupling reaction.

Chen, Guochang; Ye, Mingfu; Qiao, Hongbin; Qiu, Xiaoning

2014-08-01

287

Direct C-H bond arylation of fluorenes with aryl chlorides catalyzed by N-heterocyclic carbene-palladium(II)-1-methylimidazole complex and further transformation of the products in a one-pot procedure.  

Science.gov (United States)

We report here the NHC-Pd(II)-Im complex 1-catalyzed direct C-H bond functionalization of the C9 position of fluorenes with aryl chlorides and further transformation of the resulting products in a one-pot procedure. Under the optimal conditions, arylated fluorenes can be obtained in moderate to almost quantitative yields using various activated and unactivated (hetero)aryl chlorides as the arylating reagents. Furthermore, if the mixture from the arylation reaction is exposed to air, the C9-oxidized products can be obtained in acceptable to good yields in a one-pot procedure. In addition, alkyl groups can also be efficiently introduced to the above mixture from the arylation reaction, producing further C9-alkylated products in good to almost quantitative yields in a one-pot procedure, thus providing an expedient, inexpensive and practical strategy for the mono- and di-functionalization of fluorenes. PMID:25231668

Ji, Ya-Yun; Lu, Li-Li; Shi, Yu-Chun; Shao, Li-Xiong

2014-11-14

288

Three-Coordinate Cobalt(IV) and Cobalt(V) Imido Complexes with N-Heterocyclic Carbene Ligation: Synthesis, Structure, and Their Distinct Reactivity in C-H Bond Amination.  

Science.gov (United States)

The reaction of the cobalt(0) alkene complex [(IMes)Co(?(2):?(2)-dvtms)] (1) (IMes = 1,3-bis(1',3',5'-trimethylphenyl)imidazol-2-ylidene, dvtms = divinyltetramethyldisiloxane) with 2 equiv of DippN3 (Dipp = 2,6-diisopropylphenyl) afforded the cobalt(IV) imido complex [(IMes)Co(NDipp)2] (2), which could be oxidized by [Cp2Fe][BAr(F)4] (Ar(F) = 3,5-di(trifluoromethyl)phenyl) to give the cobalt(V) imido species [(IMes)Co(NDipp)2][BAr(F)4] (3). The molecular structures of all these complexes were established by single-crystal X-ray diffraction studies. Characterization data and theoretical calculations suggest ground spin states of S = (1)/2 and S = 0 for the cobalt(IV) and cobalt(V) species, respectively. When heated, the cobalt(IV) imido species was converted to a cobalt(II) diamido complex via an intramolecular C-H bond amination reaction, but the cobalt(V) species was stable under similar conditions. The different outcomes suggest that a high oxidation state does not guarantee C-H bond activation reactivity of late-transition-metal imido species. PMID:25330361

Zhang, Long; Liu, Yuesheng; Deng, Liang

2014-11-01

289

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

Energy Technology Data Exchange (ETDEWEB)

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.

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

2004-02-16

290

Uranium(IV) nucleophilic carbene complexes  

International Nuclear Information System (INIS)

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

291

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

Science.gov (United States)

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

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

2009-09-01

292

Improved Ruthenium Catalysts for Z-Selective Olefin Metathesis  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Several new C-H activated ruthenium catalysts for Z-selective olefin metathesis have been synthesized. Both the carboxylate ligand and the aryl group of the N-heterocyclic carbene have been altered and the resulting catalysts were evaluated using a range of metathesis reactions. Substitution of bidentate with monodentate X-type ligands led to a severe attenuation of metathesis activity and selectivity, while minor differences were observed between bidentate ligands within the same family (e.g...

Keitz, Benjamin K.; Endo, Koji; Patel, Paresma R.; Herbert, Myles B.; Grubbs, Robert H.

2012-01-01

293

Chelated Ruthenium Catalysts for Z-Selective Olefin Metathesis  

Digital Repository Infrastructure Vision for European Research (DRIVER)

We report the development of ruthenium-based metathesis catalysts with chelating N-heterocyclic carbene (NHC) ligands which catalyze highly Z-selective olefin metathesis. A very simple and convenient synthetic procedure of such a catalyst has been developed. An intramolecular C-H bond activation of the NHC ligand, which is promoted by anion ligand substitution, forms the appropriate chelate for stereo- controlled olefin metathesis.

Endo, Koji; Grubbs, Robert H.

2011-01-01

294

Chelated Ruthenium Catalysts for Z-Selective Olefin Metathesis  

Science.gov (United States)

We report the development of ruthenium-based metathesis catalysts with chelating N-heterocyclic carbene (NHC) ligands which catalyze highly Z-selective olefin metathesis. A very simple and convenient synthetic procedure of such a catalyst has been developed. An intramolecular C-H bond activation of the NHC ligand, which is promoted by anion ligand substitution, forms the appropriate chelate for stereo- controlled olefin metathesis. PMID:21563826

Endo, Koji; Grubbs, Robert H.

2011-01-01

295

Cyclometalated mono- and dinuclear Ir(III) complexes with "click"-derived triazoles and mesoionic carbenes.  

Science.gov (United States)

Orthometalation at Ir(III) centers is usually facile, and such orthometalated complexes often display intriguing electronic and catalytic properties. By using a central phenyl ring as C-H activation sites, we present here mono- and dinuclear Ir(III) complexes with "click"-derived 1,2,3-triazole and 1,2,3-triazol-5-ylidene ligands, in which the wingtip phenyl groups in the aforementioned ligands are additionally orthometalated and bind as carbanionic donors to the Ir(III) centers. Structural characterization of the complexes reveal a piano stool-type of coordination around the metal centers with the "click"-derived ligands bound either with C^N or C^C donor sets to the Ir(III) centers. Furthermore, whereas bond localization is observed within the 1,2,3-triazole ligands, a more delocalized situation is found in their 1,2,3-triazol-5-ylidene counterparts. All complexes were subjected to catalytic tests for the transfer hydrogenation of benzaldehyde and acetophenone. The dinuclear complexes turned out to be more active than their mononuclear counterparts. We present here the first examples of stable, isomer-pure, dinuclear cyclometalated Ir(III) complexes with poly-mesoionic-carbene ligands. PMID:25044321

Maity, Ramananda; Hohloch, Stephan; Su, Cheng-Yong; van der Meer, Margarethe; Sarkar, Biprajit

2014-08-01

296

Homo- and Heteroleptic Bismuth(III/V) Thiolates from N-Heterocyclic Thiones: Synthesis, Structure and Anti-Microbial Activity.  

Science.gov (United States)

Homo- and heteroleptic bismuth thiolato complexes have been synthesised and characterised from biologically relevant tetrazole-, imidazole-, thiadiazole- and thiazole-based heterocyclic thiones (thiols): 1-methyl-1H-tetrazole-5-thiol (1-MMTZ(H)); 4-methyl-4H-1,2,4-triazole-3-thiol (4-MTT(H)); 1-methyl-1H-imidazole-2-thiol (2-MMI(H)); 5-methyl-1,3,4-thiadiazole-2-thiol (5-MMTD(H)); 1,3,4-thiadiazole-2-dithiol (2,5-DMTD(H)2 ); and 4-(4-bromophenyl)thiazole-2-thiol (4-BrMTD(H)). Reaction of BiPh3 with 1-MMTZ(H) produced the rare Bi(V) thiolato complex [BiPh(1-MMTZ)4 ], which undergoes reduction in DMSO to give [BiPh(1-MMTZ)2 {(1-MMTZ(H)}2 ]. Reactions with PhBiCl2 or BiPh3 generally produced monophenylbismuth thiolates, [BiPh(SR)2 ]. The crystal structures of [BiPh(1-MMTZ)2 {1-MMTZ(H)}2 ], [BiPh(5-MMTD)2 ], [BiPh{2,5-DMTD(H)}2 (Me2 C?O)] and [Bi(4-BrMTD)3 ] were obtained. Evaluation of the bactericidal properties against M. smegmatis, S. aureus, MRSA, VRE, E. faecalis and E. coli showed complexes containing the anionic ligands 1- MMTZ, 4-MTT and 4-BrMTD to be most effective. The dithiolato dithione complexes [BiPh(4-MTT)2 {4-MTT(H)}2 ] and [BiPh(1-MMTZ)2 {1-MMTZ(H)}2 ] were most effective against all the bacteria: MICs 0.34??M for [BiPh(4-MTT)2 {4-MTT(H)}2 ] against VRE, and 1.33??M for [BiPh(1-MMTZ)2 {1-MMTZ(H)}2 ] against M. smegmatis and S. aureus. Tris-thiolato Bi(III) complexes were least effective overall. All complexes showed little or no toxicity towards mammalian COS-7 cells at 20??g?mL(-1) . PMID:25224757

Luqman, Ahmad; Blair, Victoria L; Brammananth, Rajini; Crellin, Paul K; Coppel, Ross L; Andrews, Philip C

2014-10-27

297

Structurally Characterized Cationic Silver(I) and Ruthenium(II)carbene complexes of 1,2,3-Triazol-5-ylidenes.  

Science.gov (United States)

A novel 1,3,4-substituted 1,2,3-triazolium salt was found to function as an effective precursor for the synthesis of the first structurally characterized cationic silver(I) and ruthenium(II)carbene complexes of overall 1:2 ligand-to-metal stoichiometry. The Ag(I) complex crystallized in the form of an eight silver atom-containing cluster, whereas the Ru(II) complex proved to be a discrete species and was found to be capable of initiating the ring-opening metathesis polymerization of norbornene upon activation with (trimethylsilyl)diazomethane. PMID:22140293

Cai, Jiajia; Yang, Xiaoping; Arumugam, Kuppuswamy; Bielawski, Christopher W; Sessler, Jonathan L

2011-09-26

298

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

Digital Repository Infrastructure Vision for European Research (DRIVER)

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

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

2009-01-01

299

Design and Synthesis of Ruthenium based Olefin Metathesis Catalysts  

Digital Repository Infrastructure Vision for European Research (DRIVER)

The present Master thesis seeks to develop new unsymmetrical ruthenium-based olefin metathesis catalysts and therein a better understanding of olefin metathesis catalysis with unsymmetrical active complexes. Such catalysts have a potential for chemoselectivity and in best case, stereoselectivity. Two different classes of catalysts, coordinated by a hemilabile amine ligand and by a novel N-heterocyclic carbene (NHC) ligand respectively, have been investigated. Two new amine-based olefin metath...

Singstad, A?smund

2010-01-01

300

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

Digital Repository Infrastructure Vision for European Research (DRIVER)

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 ...

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

2013-01-01

 
 
 
 
301

Salicylaldimine Ruthenium Alkylidene Complexes: Metathesis Catalysts Tuned for Protic Solvents  

Digital Repository Infrastructure Vision for European Research (DRIVER)

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

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

2007-01-01

302

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

International Nuclear Information System (INIS)

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 ?-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.

303

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

Energy Technology Data Exchange (ETDEWEB)

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.

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

304

The reactions of anthronylidene carbene with some heterocyclic compounds  

International Nuclear Information System (INIS)

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

305

Fundamental spectroscopic studies of carbenes and hydrocarbon radicals  

Energy Technology Data Exchange (ETDEWEB)

Determination of bond dissociation energies and heats of formation of hydrocarbon radicals and carbenes requires knowledge of their structures, but this is not provided by standard mass spectrometric studies; what is needed is high-resolution spectroscopy, often best achieved at centimeter and millimeter wavelengths. Nearly 60 reactive organic molecules were investigated in the period from 1988--1998.

None

1999-03-12

306

Fundamental spectroscopic studies of carbenes and hydrocarbon radicals  

Energy Technology Data Exchange (ETDEWEB)

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.

Gottlieb, C.A.; Thaddeus, P. [Harvard Univ., Cambridge, MA (United States)

1993-12-01

307

Z-Selectivity in olefin metathesis with chelated Ru catalysts: computational studies of mechanism and selectivity.  

Science.gov (United States)

The mechanism and origins of Z-selectivity in olefin metathesis with chelated Ru catalysts were explored using density functional theory. The olefin approaches from the "side" position of the chelated Ru catalysts, in contrast to reactions with previous unchelated Ru catalysts that favor the bottom-bound pathway. Steric repulsions between the substituents on the olefin and the N-substituent on the N-heterocyclic carbene ligand lead to highly selective formation of the Z product. PMID:22229694

Liu, Peng; Xu, Xiufang; Dong, Xiaofei; Keitz, Benjamin K; Herbert, Myles B; Grubbs, Robert H; Houk, K N

2012-01-25

308

Comparing Ru and Fe-catalyzed olefin metathesis.  

Science.gov (United States)

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. PMID:24821502

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

2014-08-01

309

Thermally Stable, Latent Olefin Metathesis Catalysts  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Highly thermally stable N-aryl,N-alkyl N-heterocyclic carbene (NHC) ruthenium catalysts were designed and synthesized for latent olefin metathesis. These catalysts showed excellent latent behavior toward metathesis reactions, whereby the complexes were inactive at ambient temperature and initiated at elevated temperatures, a challenging property to achieve with second generation catalysts. A sterically hindered N-tert-butyl substituent on the NHC ligand of the ruthenium complex was found to i...

Thomas, Renee M.; Fedorov, Alexey; Keitz, Benjamin K.; Grubbs, Robert H.

2011-01-01

310

Regioselective Allene Hydroarylation via One-Pot Allene Hydrosilylation/Pd-Catalyzed Cross-Coupling.  

Science.gov (United States)

Advances in hydroarylation have been achieved by the development of a one-pot regioselective allene hydrosilylation/Pd(0)-catalyzed cross-coupling protocol. The regioselectivity is primarily governed by N-heterocyclic carbene (NHC) ligand identity in the hydrosilylation step and is preserved in the subsequent cross-coupling reaction. This methodology affords streamlined access to functionalized 1,1-disubstituted alkenes with excellent regiocontrol. PMID:25275880

Miller, Zachary D; Montgomery, John

2014-10-17

311

Stereoselective synthesis of 5-substituted pyrrolo[1,2-c]imidazol-3-ones: access to annulated chiral imidazol(in)ium salts.  

Science.gov (United States)

A two-step synthesis of N-heterocyclic carbene (NHC) precatalysts by diastereoselective or enantioselective lithiation of pyrrolo[1,2-c]imidazol-3-ones followed by POCl(3)-induced salt formation is described. The resulting 3-chloro-pyrroloimidazol(in)ium salts may be coordinated to palladium(II) upon NHC generation with t-BuLi at low temperature. The method may facilitate exploitation of these compounds as chiral organocatalysts or ligands in metal catalysis. PMID:19961188

Metallinos, Costa; Xu, Shufen

2010-01-01

312

Transfer Hydrogenation of Ketones and Activated Olefins Using Chelating NHC Ruthenium Complexes  

Digital Repository Infrastructure Vision for European Research (DRIVER)

N-Heterocyclic carbene (NHC) ruthenium complexes consisting of different donor substituents attached to the NHC ligand efficiently catalyse the transfer hydrogenation of ketones and of activated olefins in ?,?-unsaturated ketones to give saturated alcohols. The most active catalyst precursor contains a tethered olefin as a hemilabile donor site. This complex also converts nitriles and, depending on the reaction conditions, either benzylamines are produced by means of transfer hydro...

Horn, Sabine; Gandolfi, Claudio; Albrecht, Martin

2011-01-01

313

Selective C-4 alkylation of pyridine by nickel/Lewis acid catalysis.  

Science.gov (United States)

Direct C-4-selective addition of pyridine across alkenes and alkynes is achieved for the first time by nickel/Lewis acid cooperative catalysis with an N-heterocyclic carbene ligand. A variety of substituents on both alkenes and pyridine are tolerated to give linear 4-alkylpyridines in modest to good yields. The addition across styrene, on the other hand, gives branched 4-alkylpyridines. A single example of C-4-selective alkenylation is also described. PMID:20822182

Nakao, Yoshiaki; Yamada, Yuuya; Kashihara, Natsuko; Hiyama, Tamejiro

2010-10-01

314

Copper-catalyzed borylation of ?-alkoxy allenes with bis(pinacolato)diboron: efficient synthesis of 2-boryl 1,3-butadienes.  

Science.gov (United States)

Something solid to build on: 2-Boryl 1,3-butadienes with various substitution patterns were formed in good to high yields in a copper-catalyzed borylation of ?-alkoxy allenes with bis(pinacolato)diboron (see scheme; Bn=benzyl, pin=pinacolate, L is an N-heterocyclic carbene ligand). The products were found to be useful intermediates for the synthesis of cyclic vinyl boranes, ?,?-unsaturated ketones, and functionalized multisubstituted dienes. PMID:24123693

Semba, Kazuhiko; Fujihara, Tetsuaki; Terao, Jun; Tsuji, Yasushi

2013-11-18

315

Assembly and tunable luminescence of lanthanide-organic frameworks constructed from 4-(3,5-dicarboxyphenyl)pyridine-2,6-dicarboxylate ligand  

International Nuclear Information System (INIS)

Highlights: ? A new N-heterocycle muticarboxylate ligand 4-(3,5-dicarboxyphenyl)pyridine-2,6-dicarboxylic acid (H4dpda) was developed. ? Several lanthanide metal–organic frameworks (Ln = Eu, Gd, Tb, Dy) and Eu/Tb mixed MOFs were synthesized. ? The ligand H4dpda can provide efficient sensitization for the lanthanide ion Tb(III) and Eu(III). ? Luminescence color of the mixed MOFs can be easily tuned by varying the molar ratios of Eu(III)/Tb(III). - Abstract: A novel N-heterocycle multicarboxylate ligand 4-(3,5-dicarboxyphenyl)pyridine-2,6-dicarboxylic acid (H4dpda) was synthesized, and then reacted with lanthanide salts to yield a series of lanthanide metal–organic frameworks, [Ln(Hdpda)(H2O)4]·0.5(H2O) (Ln = Eu(1), Gd(2), Tb(3), Dy(4)) and [Tb1?xEux(Hdpda)(H2O)4]·0.5(H2O) (x = 0.1–10 mol%). Single crystal X-ray diffraction and powder XRD patterns confirm these MOFs are isostructural. Luminescent measurements suggest that the ligand can provide efficient sensitization for the lanthanide ion Tb(III) and Eu(III) in the mixed lanthanide MOFs. Additionally, the luminescence color of the mixed MOFs can be easily tuned from green to green–yellow, yellow, orange, red–orange and red by varying the molar ratio of Eu(III)/Tb(III).

316

Ferrocene phosphane-heteroatom/carbon bidentate ligands in asymmetric catalysis.  

Science.gov (United States)

Chiral ferrocene derivatives belong to privileged ligand classes for asymmetric transition metal catalysed reactions. Hetero-bidentate phosphane ligands are hybrid ligands, which combine the properties of phosphorus with those of other donor atoms. This feature creates further asymmetry around the metal centre, which may be helpful for increasing the stereoinduction. Therefore, hetero-bidentate ligands are useful alternatives to homo-bidentate ligands. Ligands featuring phosphorus and nitrogen or sulphur are quite common. From among ferrocene catalysts, ferrocenyl amino phosphanes and phosphane oxazolines serve as excellent examples. Fesulphos and ThioClickFerrophos are notable P,S-ligand examples. On the other hand, combinations of phosphorus with oxygen or carbon are only beginning to show their potential in asymmetric catalysis. Another useful feature in ligands of this type is the markedly different coordination properties of donor atoms, resulting in interesting opportunities for catalysis. Ferrocenyl MOP-analogues or a fascinating combination of phosphane and secondary phosphane-oxide would represent this ligand class. The last section of the review focuses on phosphanes combined with carbon-based donor atoms that are phosphane-alkene and phosphane-carbene ligands. This review focuses on the applications of these hetero-bidentate ferrocene ligands in asymmetric catalysis with a special emphasis on the most recent and influential literature reports. PMID:25307172

Toma, Stefan; Csizmadiová, Jana; Me?iarová, Mária; Sebesta, Radovan

2014-10-22

317

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

Science.gov (United States)

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

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

2014-11-18

318

Actinide metals with multiple bonds to carbon: synthesis, characterization, and reactivity of U(IV) and Th(IV) bis(iminophosphorano)methandiide pincer carbene complexes.  

Science.gov (United States)

Treatment of ThCl(4)(DME)(2) or UCl(4) with 1 equiv of dilithiumbis(iminophosphorano) methandiide, [Li(2)C(Ph(2)P?NSiMe(3))(2)] (1), afforded the chloro actinide carbene complexes [Cl(2)M(C(Ph(2)P?NSiMe(3))(2))] (2 (M = Th) and 3 (M = U)) in situ. Stable PCP metal-carbene complexes [Cp(2)Th(C(Ph(2)P?NSiMe(3))(2))] (4), [Cp(2)U(C(Ph(2)P?NSiMe(3))(2))] (5), [TpTh(C(Ph(2)P?NSiMe(3))(2))Cl] (6), and [TpU(C(Ph(2)P?NSiMe(3))(2))Cl] (7) were generated from 2 or 3 by further reaction with 2 equiv of thallium(I) cyclopentadienide (CpTl) in THF to yield 4 or 5 or with 1 equiv of potassium hydrotris(pyrazol-1-yl) borate (TpK) also in THF to give 6 or 7, respectively. The derivative complexes were isolated, and their crystal structures were determined by X-ray diffraction. All of these U (or Th)-carbene complexes (4-7) possess a very short M (Th or U)?carbene bond with evidence for multiple bond character. Gaussian 03 DFT calculations indicate that the M?C double bond is constructed by interaction of the 5f and 6d orbitals of the actinide metal with carbene 2p orbitals of both ? and ? character. Complex 3 reacted with acetonitrile or benzonitrile to cyclo-add C?N to the U?carbon double bond, thereby forming a new C-C bond in a new chelated quadridentate ligand in the bridged dimetallic complexes (9 and 10). A single carbon-U bond is retained. The newly coordinated uranium complex dimerizes with one equivalent of unconverted 3 using two chlorides and the newly formed imine derived from the nitrile as three connecting bridges. In addition, a new crystal structure of [CpUCl(3)(THF)(2)] (8) was determined by X-ray diffraction. PMID:21667978

Ma, Guibin; Ferguson, Michael J; McDonald, Robert; Cavell, Ronald G

2011-07-18

319

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

International Nuclear Information System (INIS)

In summary, we have shown that the first step of ortho C-H activation of pyridine N-oxide mediated by L2U(IV)-(CH3)2 can occur with the three ligands L (Cp, CpTMS, and Cp*) to form an ?2(C, O) ortho-metallated complex. Also, we have shown that for L=Cp and CpTMS it is possible to form a very stable uranium (VI) formaldehyde complex going through an uranium(IV) Schrock-type carbene intermediate. This is in contrast with the ligand Cp*: the formation of uranium(IV) formaldehyde complex is not possible with the Cp* owing to a high barrier at the H2C-O repulsive coupling transition state. This high barrier can be explained by the steric hindrance of Cp* compared with Cp and CpTMS. Moreover, the electronic repulsion between the two negative charges (carbene and oxygen) is enhanced in the case of Cp*. (authors)

320

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

Science.gov (United States)

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

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

2012-01-01

 
 
 
 
321

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

Science.gov (United States)

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

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

2014-05-01

322

Isolation of a non-heteroatom-stabilized gold-carbene complex.  

Science.gov (United States)

Gold-carbene complexes are essential intermediates in many gold-catalyzed organic-synthetic transformations. While gold-carbene complexes with direct, vinylogous, or phenylogous heteroatom substitution have been synthesized and characterized, the observation in the condensed phase of electronically non-stabilized gold-carbenes has so far remained elusive. The sterically extremely shielded, emerald-green complex [IPr**Au=CMes2](+)[NTf2](-) has now been synthesized, isolated, and fully characterized. Its absorption maximum at 642?nm, in contrast to 528?nm of the red-purple carbocation [Mes2CH](+), clearly demonstrates that gold is more than just a "soft proton". PMID:24953223

Hussong, Matthias W; Rominger, Frank; Krämer, Petra; Straub, Bernd F

2014-08-25

323

Cyclic (Alkyl)(amino)carbene Gold(I) complexes: A Synthetic and Structural Investigation  

Digital Repository Infrastructure Vision for European Research (DRIVER)

A series of mono- and dicarbene gold(I) complexes of types Au(CAAC)(Cl) [CAAC = cyclic (alkyl)(amino)carbene] (1) and [Au(CAAC)2]+[X]- (X = Cl, AuCl2) (2) have been prepared through reaction of AuCl(SMe2) with free carbenes a-e, and structurally characterized by single X-ray diffraction studies (1a, 1b, 2d, 2e). In addition two new free cyclic (alkyl)(amino)carbenes (c and e) have been synthesized.

Frey, Guido D.; Dewhurst, Rian D.; Kousar, Shazia; Donnadieu, Bruno; Bertrand, Guy

2008-01-01

324

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

Directory of Open Access Journals (Sweden)

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

Quintell Tillison

2005-04-01

325

Structural and spectroscopic comparison of methylaminophenylcarbenepentacarbonyltungsten(0) with tungsten carbonyl carbene complexes lacking a heteroatom  

International Nuclear Information System (INIS)

Crystallographic and spectroscopic data for (CO)5WC(NHCH3)C6H5 provide evidence that there is comparatively little metal-carbene ?-bonding in this and other zerovalent tungsten carbonyl carbene complexes. The W-Csub(car) bond length of 2.19(2) A indicates that its bond order is significantly lower than 2.0. Resonances in the 13C n.m.r. spectrum for CO w.r.t. tetramethylsilane at 195 and 215 ppm and an asymmetric CO stretching frequency of 2060 cm-1, in addition to structural similarities, imply analogous bonding in other zero-valent tungsten carbonyl carbene complexes, including those lacking a heteroatom bonded to the carbene carbon. (orig.)

326

Reaction of trisubstituted alkenes with iron porphyrin carbenes: facile synthesis of tetrasubstituted dienes and cyclopentadienes.  

Science.gov (United States)

The unprecedented reaction of trisubstituted alkenes with iron porphyrin carbenes has been successfully developed. Both multiply substituted 1,3-butadiene and cyclopentadiene products are readily accessible with high efficiency and selectivity in good yields. PMID:23857008

Wang, Peng; Liao, Saihu; Wang, Sunewang R; Gao, Run-Duo; Tang, Yong

2013-08-28

327

Chelating alkylidene ligands as pacifiers for ruthenium catalysed olefin metathesis.  

Science.gov (United States)

Olefin metathesis catalysed by ruthenium has emerged at the frontier of modern synthetic chemistry. The desire to enhance catalyst stability, gain control over the catalytic process and deepen the understanding of the mechanisms of metathesis has yielded a class of latent ruthenium precatalysts of delayed initiation and with switchable activity. One of the main methodologies developed for this purpose has been the introduction of tethered carbene ligands. Herein we track the evolution of ruthenium based metathesis catalysts bearing chelated alkylidenes, from the early oxygen Hoveyda type benzylidenes to the latent sulphur containing complexes. PMID:22020679

Vidavsky, Yuval; Anaby, Aviel; Lemcoff, N Gabriel

2012-01-01

328

(Aminocarbene)(divinyltetramethyldisiloxane)iron(0) compounds: a class of low-coordinate iron(0) reagents.  

Science.gov (United States)

The combined use of aminocarbene and divinyltetramethyldisiloxane (dvtms) as supporting ligands enables the access of unprecedented low-coordinate iron(0) alkene compounds [L(n)Fe(?(2):?(2)-dvtms)] (L=N-heterocyclic carbene (NHC) or cyclic (alkyl)(amino)carbene (CAAC), n=1 or 2) from the reactions of FeCl2 with alkali-metal reducing agents, free aminocarbene ligands, and dvtms. The iron(0) species deliver their {L(n)Fe(0)} fragments to perform redox reactions with Ph2SiH2, S8, Se, and DippN3, furnishing novel aminocarbene-supported iron(IV) silylene, all-ferrous iron-sulfur/selenium cubanes, and bis(imido)iron(IV) compounds. These conversions demonstrate the potential synthetic utility of the carbene-supported iron(0) complexes as a valuable class of low-coordinate iron(0) reagents. PMID:24961207

Zhang, Hezhong; Ouyang, Zhenwu; Liu, Yuesheng; Zhang, Qiang; Wang, Lei; Deng, Liang

2014-08-01

329

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

Science.gov (United States)

The synthesis of a ruthenium complex containing an N-heterocylic carbene (NHC) and a mesoionic carbene (MIC) is described wherein addition of a Brønsted acid results in protonolysis of the Ru-MIC bond to generate an extremely active metathesis catalyst. Mechanistic studies implicate a rate-determining protonation step to generate the metathesis active species. The NHC/MIC catalyst was found to have activity exceeding current commercial ruthenium catalysts. PMID:21574621

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

2011-01-01

330

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

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

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

2011-01-01

331

Thermodynamics of Ylide Formation from Carbenes and Carbonyl Compounds  

Scientific Electronic Library Online (English)

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

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

1998-04-01

332

Thermodynamics of Ylide Formation from Carbenes and Carbonyl Compounds  

Scientific Electronic Library Online (English)

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

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

333

Diastereoselective cyclopropanation of ketone enols with Fischer carbene complexes.  

Science.gov (United States)

Treatment of aryl/heteroaryl methoxycarbene complexes of chromium with -substituted ketone lithium enolates between -78 degrees C and room temperature resulted in the diastereoselective synthesis of 1,2,2,3-tetrasubstituted cyclopropanols. An exception has been observed in the reaction with cyclohexanone lithium enolate that yielded a bicyclic 2-buten-4-olide. 1,2-Dimethoxycyclopropanes and 1-methoxy-2-trimethylsilyloxycyclopropanes were isolated by quenching the reactions with MeOTf or Me3SiCl, respectively. This novel cyclopropanation process involves formation of lithium (3-oxoalkyl)pentacarbonylchromate intermediates which on warming undergo intramolecular addition to the carbonyl group. This cyclization is equivalent to the cyclopropanation in smooth conditions of electron-rich alkenes with Fischer carbene complexes. PMID:18257560

Barluenga, José; Suero, Marcos G; Pérez-Sanchez, Ivan; Flórez, Josefa

2008-03-01

334

Complexation of trivalent cationic lanthanides by N.O donor ligands: physico-chemical studies of the association and selectivity in solution  

International Nuclear Information System (INIS)

The aim of this work is to study the complexation of f-elements in solution by ligands incorporating N-heterocyclic donors. These ligands display interesting properties for the selective separation of An(III)/Ln(III) have been studied to obtain a better understanding of the coordination properties with f-elements and to develop more selective extractants. The hepta-dentate ligand tpaam shows an affinity for Ln(III) similar to the tetradentate ligand tpa in water even when the three additional amide groups are bonded to the metal. Even though the complexation with tpa is exothermic, that with tpaam is endothermic with a more positive entropy. The dehydration of the cation disfavours the formation of Ln(III) complexes with ligands containing weak donors. The analysis of the solution paramagnetic relaxation times of the tpaam complexes is in agreement with data in the solid-state. There is little difference between the formation constants of the Ln3+ complexes with different ligands (tpaam, tpzen, tpa and tpza) as determined by UV-vis spectrophotometry in anhydrous acetonitrile. The limitations encountered during this study are intrinsic to the ligands studied. The preliminary study of two tetrapodal ligands containing acid and pyridine groups (Lpy)or pyrazine (Lpz) show the formation of 1:1 complexes in water. Analysis of the formation constants of the corresponding Gd(III) complexes shows that replacement of a pyridine group by pyrazine result in a loss of stability of 1.6 logarithmic units. (author)

335

Identification of carbene particles forming during decomposition of molybdenum neopentyl derivatives  

International Nuclear Information System (INIS)

Method of chromatomass-spectrometry was used to study MoCl5 interaction with neopentylmagnesium bromide at -78 and 20 deg C in the medium of dibutyl ether with successive addition of benzaldehyde to the system. It is shown that the main products of reactions are tetramethylhexane with 45-47 and 3-7% yield respectively, as well as ?-neopentylstyrene and ?-neopentylbutyl ether. If reaction is conducted at -78 deg C the major part of formed carbenes is used for reaction with benzaldehyde. The yield of ?-neopentylstyrene decreases at 20 degC. This is conditioned by carbene reactions with the solvent or other system components. The obtained data are the direct experimental corroboration of carbene particle formation during decomposition of molybdenum neopentyl derivatives

336

Intermolecular crosslinking of fatty acyl chains in phospholipids: use of photoactivable carbene precursors.  

Science.gov (United States)

Phospholipids containing photolysable carbene precursors (beta-trifluoro-alpha-diazopropionoxy and m-diazirinophenoxy groups) in omega-positions of sn-2 fatty acyl chains were prepared. Photolysis of their vesicles produced crosslinked products in 40-60% yields. Crosslinking was mostly intermolecular and occurred by carbene insertion into the C-H bonds of a second fatty acyl chain. Crosslinking products were characterized by (i) their gel permeation behavior, (ii) analysis of products formed by base-catalyzed transesterification, (iii) degradation with phospholipases A2 and C, (iv) gas chromatography/mass spectrometry, and (v) use of mixtures of phospholipids carrying the carbene precursors and a phospholipid containing radioactively labeled fatty acyl groups. Nitrenes generated from the aliphatic or aromatic azido groups in phospholipids were unsatisfactory for forming crosslinks by insertion in C-H bonds. PMID:288050

Gupta, C M; Radhakrishnan, R; Gerber, G E; Olsen, W L; Quay, S C; Khorana, H G

1979-06-01

337

Assembly and tunable luminescence of lanthanide-organic frameworks constructed from 4-(3,5-dicarboxyphenyl)pyridine-2,6-dicarboxylate ligand  

Energy Technology Data Exchange (ETDEWEB)

Highlights: Black-Right-Pointing-Pointer A new N-heterocycle muticarboxylate ligand 4-(3,5-dicarboxyphenyl)pyridine-2,6-dicarboxylic acid (H{sub 4}dpda) was developed. Black-Right-Pointing-Pointer Several lanthanide metal-organic frameworks (Ln = Eu, Gd, Tb, Dy) and Eu/Tb mixed MOFs were synthesized. Black-Right-Pointing-Pointer The ligand H{sub 4}dpda can provide efficient sensitization for the lanthanide ion Tb(III) and Eu(III). Black-Right-Pointing-Pointer Luminescence color of the mixed MOFs can be easily tuned by varying the molar ratios of Eu(III)/Tb(III). - Abstract: A novel N-heterocycle multicarboxylate ligand 4-(3,5-dicarboxyphenyl)pyridine-2,6-dicarboxylic acid (H{sub 4}dpda) was synthesized, and then reacted with lanthanide salts to yield a series of lanthanide metal-organic frameworks, [Ln(Hdpda)(H{sub 2}O){sub 4}]{center_dot}0.5(H{sub 2}O) (Ln = Eu(1), Gd(2), Tb(3), Dy(4)) and [Tb{sub 1-x}Eu{sub x}(Hdpda)(H{sub 2}O){sub 4}]{center_dot}0.5(H{sub 2}O) (x = 0.1-10 mol%). Single crystal X-ray diffraction and powder XRD patterns confirm these MOFs are isostructural. Luminescent measurements suggest that the ligand can provide efficient sensitization for the lanthanide ion Tb(III) and Eu(III) in the mixed lanthanide MOFs. Additionally, the luminescence color of the mixed MOFs can be easily tuned from green to green-yellow, yellow, orange, red-orange and red by varying the molar ratio of Eu(III)/Tb(III).

Zhang, Wenqian; Yu, Jiancan [State Key Lab of Silicon Materials, Cyrus Tang Center for Sensor Materials and Applications, Department of Materials Science and Engineering, Zhejiang University, Hangzhou 310027 (China); Cui, Yuanjing, E-mail: cuiyj@zju.edu.cn [State Key Lab of Silicon Materials, Cyrus Tang Center for Sensor Materials and Applications, Department of Materials Science and Engineering, Zhejiang University, Hangzhou 310027 (China); Rao, Xingtang; Yang, Yu [State Key Lab of Silicon Materials, Cyrus Tang Center for Sensor Materials and Applications, Department of Materials Science and Engineering, Zhejiang University, Hangzhou 310027 (China); Qian, Guodong, E-mail: gdqian@zju.edu.cn [State Key Lab of Silicon Materials, Cyrus Tang Center for Sensor Materials and Applications, Department of Materials Science and Engineering, Zhejiang University, Hangzhou 310027 (China)

2013-02-25

338

Stereoselective 1,3-insertions of rhodium(II) azavinyl carbenes.  

Science.gov (United States)

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 bisfunctionalized (Z)-olefins with perfect regio- and stereoselectivity. 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 ?-allenyl ketones and amino-substituted heterocycles. PMID:24295389

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

2014-01-01

339

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

International Nuclear Information System (INIS)

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

340

Reactions of ligands similar to molecular nitrogen and being capable to take its coordination place in complexes  

International Nuclear Information System (INIS)

Reactions of ligands similar relative to molecular nitrogen in complexes of transition metals are djscussed. Isonitriles, carbon monoxide, carbon dioxide, olefins, acetylenes, cyanide, nitrils, nitrogen monoxide, azide are considered as investigated ligands. It is concluded that, as a rule, both for coordination of N2 and its analogs metal complexes rich with electrons and able to stabilize even sUch unstable particles as carbenes or carbynes formed under the effect of electrophilic reagents on coordinated isonitrils are most suitable. Reactions of introduction and oxidation of complexes with N2 analogs are considered

 
 
 
 
341

The formation of carbenes during interaction of Mo, W, and Co chlorides with lithium alkyls  

International Nuclear Information System (INIS)

Ethyl derivatives of Mo and W and amyl derivatives of Mo underwent not only ?-cleavage to give equimolar quantities of corresponding alkane and alkene, but also ?-cleavage, which was accompanied by generation of carbenes. It was shown that the latter pathway of cleavage is assumed also for ethyl and amyl derivatives of Co

342

A comparison of the bonding in the second-row transition-metal oxides and carbenes  

Science.gov (United States)

Calculations including electron correlation of all valence electrons have been performed for the sequence of second-row transition-metal oxides and carbenes. For the atoms to the right the bond strengths of the carbenes and the oxides are similar while for the atoms to the left the oxide bond strengths are much larger. The origin of this difference is the interaction between the oxygen lone pairs and empty 4d orbitals on the metal. With the large donation of electrons from the oxygen lone pair to the metal for the atoms to the left, the bonding can almost be described as triple bond formation for YO, ZrO and NbO. For MoO, where a 4d ? orbital is singly occupied on the metal, the bond strength is much smaller than for the oxides to the left. For the metal carbenes two covalent bonds are formed. The ground state spin for the oxides to the right is higher than for the corresponding carbenes, which can be explained by the presence of the ? degeneracy for the oxides. The relevance of the present results for the epoxidation and the olefin metathesis reactions are discussed.

Siegbahn, Per E. M.

1993-01-01

343

Pd-carbene migratory insertion: application to the synthesis of trifluoromethylated alkenes and dienes.  

Science.gov (United States)

Pd-catalyzed cross-coupling of halides with CF3-substituted diazo compounds or N-tosylhydrazones has been explored for the synthesis of CF3-substituted alkenes and 1,3-butadienes. Pd-carbene migratory insertion plays the key role in these transformations. PMID:24425676

Wang, Xi; Xu, Yan; Deng, Yifan; Zhou, Yujing; Feng, Jiajie; Ji, Guojing; Zhang, Yan; Wang, Jianbo

2014-01-20

344

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

Science.gov (United States)

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

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

2014-03-18

345

Luminescent goldI carbenes from 2-pyridylisocyanide complexes: structural consequences of intramolecular versus intermolecular hydrogen-bonding interactions.  

Science.gov (United States)

Isocyanide [AuX(CNPy-2)] (X = Cl, C6F5, fluoromesityl, 1/2 octafluorobiphenyl) and carbene [AuX{C(NR1R2)(NHPy-2)}] (R1R2NH = primary or secondary amines or 1/2 primary diamine) gold(I) complexes have been synthesized and characterized. For X = Cl, the carbene complexes show aurophilic interactions. The fragment NHPy-2, formed in the carbenes, can give rise to intra- (for primary amines) or intermolecular (for secondary amines) hydrogen bonds, depending on the amine used. These bonds and contacts have been studied in the solid state and in solution. The intermolecular hydrogen bonds are split in an acetone solution, but the intramolecular ones, which close a six-membered ring, survive in solution. Except for the fluoromesityl derivatives, the carbene complexes display luminescent properties. PMID:18237121

Bartolomé, Camino; Carrasco-Rando, Marta; Coco, Silverio; Cordovilla, Carlos; Martín-Alvarez, Jose M; Espinet, Pablo

2008-03-01

346

Well-defined NHC-rhodium hydroxide complexes as alkene hydrosilylation and dehydrogenative silylation catalysts.  

Science.gov (United States)

Alkene hydrosilylation and dehydrogenative silylation reactions, mediated by [Rh(cod)(NHC)(OH)] complexes (cod = 1,5-cyclooctadiene; NHC = N-heterocyclic carbene) are described. The study details a comparison of the catalytic activity and steric characteristics of four rhodium complexes bearing different NHC ligands. The novel [Rh(cod)(Ii-PrMe)(OH)] complex (Ii-PrMe = 1,3-diisopropyl-4,5-dimethylimidazol-2-ylidine) was designed to improve the reactivity of Rh(I)-hydroxides and proved to be a successful promoter of hydrosilylation and dehydrogenative silylation, displaying good stereo- and regiocontrol. PMID:23108177

Truscott, Byron J; Slawin, Alexandra M Z; Nolan, Steven P

2013-01-01

347

Highvalent and organometallic technetium and rhenium compounds  

Digital Repository Infrastructure Vision for European Research (DRIVER)

This thesis contains synthesis and characterization of mixed anhydrides of pertechnetic acid which may possibly serve as precursors for [TcO3]+ complexes, and the synthesis of new organometallic technetium complexes containing carbonyl ligands and N-heterocyclic carbenes as well as the first syntheses of technetium aryls. In the first section, the synthesis, characterization and stability of [R3EOTcO3] (E = C, Si, Ge, Sn, Pb; R = Me, iPr, tBu, Ph) and related compounds are discussed. The ...

Oehlke, Elisabeth

2010-01-01

348

Phosphine modified cobalt hydroformylation  

Energy Technology Data Exchange (ETDEWEB)

An ongoing challenge in phosphine modified cobalt hydroformylation is the fundamental understanding of the electronic and steric properties of phosphine ligands that influence the selectivity and activity of the catalytic reaction. A series of acyclic and cyclic phosphines have been prepared and tested in phosphine modified cobalt hydroformylation of 1-octene. Molecular modelling on a series of phospholanes showed some interesting theoretical and experimental correlations. We also evaluated the use of N-heterocyclic carbenes as an alternative for phosphines in modified cobalt hydroformylation. (orig.)

Rensburg, H. van; Tooze, R.P.; Foster, D.F. [Sasol Technology UK, St. Andrews (United Kingdom); Janse van Rensburg, W. [Sasol Technology, Sasolburg (South Africa)

2006-07-01

349

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

Digital Repository Infrastructure Vision for European Research (DRIVER)

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

Monassier, Antoine

2013-01-01

350

Highvalent and organometallic technetium and rhenium compounds  

International Nuclear Information System (INIS)

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.

351

Tandem isomerization/telomerization of long chain dienes  

Directory of Open Access Journals (Sweden)

Full Text Available The first example of a tandem reaction involving double-bond migration in combination with telomerization is reported. Homogeneous and heterogeneous Ru catalysts were employed as isomerisation catalysts, and telomerization was realized using a homogeneous Pd(0 precursor complex with a N-heterocyclic carbene (IMes ligand. Overall conversions approaching 60 % were achieved with the best selectivity to telomerization products of 91% attained at 11 % conversion. Conversion was markedly higher in the presence of longer-chain alcohol (1-butanol as the nucleophile (telogen.

AlexeiLapkin

2014-06-01

352

Polymer complexes.. XXXX. Supramolecular assembly on coordination models of mixed-valence-ligand poly[1-acrylamido-2-(2-pyridyl)ethane] complexes  

Science.gov (United States)

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.

El-Sonbati, A. Z.; El-Bindary, A. A.; Diab, M. A.

2003-02-01

353

The photochemical reaction of vinylaziridines and vinylazetidines with chromium(0) and molybdenum(0) (Fischer) carbene complexes.  

Science.gov (United States)

The [5+2] and [6+2] cycloaddition reactions of vinylaziridines and vinylazetidines with ketenes generated photochemically from chromium(0) and molybdenum(0) Fischer carbene complexes have been investigated. These processes constitute a straightforward and efficient route to azepanones and azocinones, respectively. The peculiar electronic properties of the metalated ketenes allow for the introduction of electron-rich substituents in the final cycloadducts, a difficult task using conventional organic chemistry procedures. The versatility of the process is demonstrated by using Cr(0) Fischer bis(carbene) complexes as metalated bis(ketene) precursors. These species produce tethered bis(azepanone)s in a single step under mild reaction conditions. Density functional theory calculations point to a stepwise reaction pathway through the initial nucleophilic attack of the nitrogen atom of the aziridine on the metalated ketene, followed by ring closure of the zwitterionic intermediate formed. PMID:24375694

Rivero, Alexandra R; Fernández, Israel; Sierra, Miguel A

2014-01-27

354

Supported ruthenium-carbene catalyst on ionic magnetic nanoparticles for olefin metathesis.  

Science.gov (United States)

The Grubbs-Hoveyda ruthenium-carbene complex has been covalently immobilized on ionic magnetic nanoparticles utilizing an imidazolium salt linker. The supported catalyst exhibited excellent catalytic activity for ring-closing metathesis (RCM) and cross-metathesis (CM) in the presence of less than 1 mol % of ruthenium. The catalysts can easily be recovered magnetically and reused up to seven times with minimal leaching of ruthenium species. PMID:25215600

Chen, Shu-Wei; Zhang, Zhi-Cheng; Ma, Miaofeng; Zhong, Chong-Min; Lee, Sang-gi

2014-10-01

355

Steady state and laser flash photolysis studies of ferrocenyl group VI fischer-carbenes and metalloporphyrins  

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Chapter one begins with a theoretical description of the electronic structure of the various compounds studied in this thesis, which includes group VI Fischer carbenes, ferrocene and meso-substituted porphyrins. This is followed by an introduction to the principles of photophysics and non-lmear optics. Chapter one finishes with an outline of the experimental techniques of laser flash photolysis and electric field induced second harmonic generation (EFISHG). Chapter two opens with a litera...

Rochford, Jonathan

2005-01-01

356

Carbene synthesis and chemical reactions of cyclopropene-3-carboxylate esters — promising intermediates for organic synthesis  

Science.gov (United States)

The data on the methods of synthesis and chemical reactions of cyclopropene-3-carboxylate esters have been correlated and classified. Particular attention has been given to the direct carbene synthesis of cyclopropene esters, which provides an accessible route to compounds of this series. In studying the chemical reactions particular attention has been given to selective reactions that provide the opportunity of using cyclopropene-3-carboxylate esters in organic synthesis to obtain various types of compounds. The bibliography includes 112 references.

Protopopova, Marina N.; Shapiro, Evgenii A.

1989-07-01

357

Computational evaluation of tris(carbene)borate donor properties in {NiNO}(10) complexes.  

Science.gov (United States)

Electronic structure calculations are performed to characterise the structures, energies, and spectroscopic data for a series of four-coordinate tris(carbene)borate {NiNO}(10) complexes. There is excellent agreement between the computational and experimental results for known complexes, allowing for structure-function relationships to be delineated. Calculations that provide insights into the synthetic accessibility of nickel(iv) nitrides by oxygen atom abstraction from these complexes are also reported. PMID:25142086

Juarez, Ruth A; Lee, Wei-Tsung; Smith, Jeremy M; Wang, Haobin

2014-10-21

358

Towards New Generations of Metathesis Metal-Carbene Pre-catalysts  

Science.gov (United States)

: A short general introduction combined with some historical milestones in the field of olefin metathesis is presented followed by an overview of recent representatives of metal carbene initiators. This paper attempts to relief the many superb contributions and overwhelming work invested in intelligent design and innovative synthesis in this area. Despites of recent advances there is still a great interest in the generation of new, better performing, and more environment friendly metathesis.

Allaert, Bart; Dieltiens, Nicolai; Stevens, Chris; Drozdzak, Renata; Dragutan, Ileana; Dragutan, Valerian; Verpoort, Francis

359

Role of quantum mechanical tunneling on the ?-effect of silicon on carbenes in 3-trimethylsilylcyclobutylidene.  

Science.gov (United States)

Quantum mechanical tunneling (QMT) is increasingly being realized as an important phenomenon that can enhance the rate of reactions even at room temperature. Recently, the ability of a trimethylsilane (TMS) group to activate 1,3-H shift to a carbene from a ?-position has been demonstrated. Direct dynamical calculations (using canonical varitational transition state theory) inclusive of small curvature tunneling (CVT-SCT) show that QMT plays a decisive role in such 1,3-hydrogen migration in both the presence and absence of TMS. The presence of a TMS group reduces the activation energy of 1,3-H shift reaction via 1,3-equatorial interaction of the TMS group with the carbene. Tunneling across the smaller barrier enhances the overall forward rate of the reaction. The Arrhenius plot for the reaction shows substantial curvature in comparison to the CVT mechanism at room temperature. Arrhenius plots for the kinetic isotope effects (KIEs) for the ?-deuterated and per deuterated 3-trimethylsilylcyclobutylidene also show strong deviations from the classical over the barrier mechanism. The magnitude of the KIE is suggestive of QMT from the vibrational excited states of the carbenes. PMID:24467461

Karmakar, Sharmistha; Datta, Ayan

2014-03-01

360

Quantum-chemical investigation of electronic nature of metal-carbene and metal-alkyl bonds in series of isoelectronic complexes (C5H5)2M(CH2)CH3 (M=V,Nb,Ta)  

International Nuclear Information System (INIS)

The electron nature, of M=CH2 and M-CH3 bonds depending on metal in (C5H5)2M(CH2)CH3 complexes (M=V, Nb, Ta) is comparatively studied. It is shown that intensification of covalent nature and strength increase of M=CH3 bonds in the V2 bond compared with M-CH3 bond also grows as well as the barrier of CH2 rotation around M=CH2 bond. The supposition is made that stability increase of carbene structures can be expected for systems with covalent bonds M=L, where L is electron-seeking ligand (L=Csub(n), Hsub(2n+2), C5H2, CO)

 
 
 
 
361

Efficient Removal of Ruthenium Byproducts from Olefin Metathesis Products by Simple Aqueous Extraction  

Science.gov (United States)

Simple aqueous extraction removed ruthenium byproducts efficiently from ring-closing metathesis (RCM) reactions catalyzed by a PEG-supported N-heterocyclic carbene-based ruthenium complex. PMID:17428062

Hong, Soon Hyeok; Grubbs, Robert H.

2008-01-01

362

Gold(I)-Catalyzed Hydration of Allenes  

Digital Repository Infrastructure Vision for European Research (DRIVER)

A gold(I) N-heterocyclic carbene complex catalyzes the intermolecular hydration of allenes to form allylic alcohols in modest yield with selective delivery of water to the terminal carbon atoms of the allenyl moiety.

Zhang, Zhibin; Du Lee, Seong; Fisher, Aaron S.; Widenhoefer, Ross A.

2009-01-01

363

Synthesis and reactivity of heterodinuclear iron, ruthenium, and cobalt compounds containing bridging dithiomethylene ligands. Attempted synthesis of the iron carbyne compound Cp(CO)Fe triple bond CSCH3  

Energy Technology Data Exchange (ETDEWEB)

Part I of this dissertation involves studying the reactivity of cationic dithiocarbene complexes of iron and ruthenium toward metal carbonyl anions. The cationic terminal dithiocarbene complex (Cp(CO)(NCCH3)Fe(C(SCH3)2))PF6 reacts with Na(Co(CO)4) in THF to yield the bridging heterodinuclear -dithioalkoxymethylene compound Cp(CO)Fe( -CO)( -C(SCH3)2)Co(CO)2. An X-ray structure of this compound indicates a sulfur atom of the -methylene ligand is bonded to Co forming a three-membered metallothiocyclopropane ring. Part II of this dissertation describes attempts to synthesize the thiocarbyne compound Cp(CO)Fe triple bond CSCH3 by deprotonation of the etaS-carbene compounds Cp(CO)Fe(etaS-CHSCH3) . The etaS-carbene is obtained from the acid induced cleavage of a mercaptide group from the cyclic dithioketal Cp(CO)Fe(C(SCH3)(SCH3)H). Reactions of the etaS-carbene with the bases NaH, KSCO3, OR (R = CH3, t-butyl), NMe3, or proton sponge failed to yield Cp(CO)Fe triple bond CSCH3. Reaction of the eta2-carbene with SCH3 in the presence of CS2 lead to the formation of the previously known trithiocarbonate complex Cp(CO)Fe(S2C(SCH3)) in 49% yield.

Matachek, J.R.

1984-01-01

364

Synthesis of an imidazolium phosphanide zwitterion and its conversion into anionic imidazol-2-ylidene derivatives.  

Science.gov (United States)

Matter of opinion: The novel zwitterion 1 has been synthesized and studied theoretically and also converted into anionic NHCs 2. The former can also be described as a phosphinidene adduct of an abnormal N-heterocyclic carbene (1') and, in the same vein, the latter represents a phosphinidene adduct of an anionic N-heterocyclic dicarbene (2'). PMID:23929541

Majhi, Paresh K; Schnakenburg, Gregor; Kelemen, Zsolt; Nyulaszi, Laszlo; Gates, Derek P; Streubel, Rainer

2013-09-16

365

?(3)-Chlorido-tris-(bis-{1-[2-(dimethyl-amino)-eth-yl]-3-methyl-imidazol-2-yl-idene}silver(I)) dichloride.  

Science.gov (United States)

In the crystal structure of the title compound, [Ag(3)Cl(C(8)H(15)N(3))(6)]Cl(2), the Ag(I) ion, which is located on a twofold rotation axis, exists in a T-shape coordination environment. Two carbene C atoms of the N-heterocyclic carbene (NHC) ligands are bonded tightly forming a slightly bent [Ag(NHC)(2)](+) cation [C-Ag-C angle = 162.80?(18)°]. Three of these complex cations are further aggregated by one bridging chloride anion, which is lying on a threefold rotoinversion axis and is only loosely binding to the Ag(+) ions. The N atom of the amine group is not engaged in any coordinative bond. PMID:22412422

Topf, Christoph; Leitner, Sebastian; Monkowius, Uwe

2012-03-01

366

?3-Chlorido-tris(bis{1-[2-(dimethylaminoethyl]-3-methylimidazol-2-ylidene}silver(I dichloride  

Directory of Open Access Journals (Sweden)

Full Text Available In the crystal structure of the title compound, [Ag3Cl(C8H15N36]Cl2, the AgI ion, which is located on a twofold rotation axis, exists in a T-shape coordination environment. Two carbene C atoms of the N-heterocyclic carbene (NHC ligands are bonded tightly forming a slightly bent [Ag(NHC2]+ cation [C—Ag—C angle = 162.80?(18°]. Three of these complex cations are further aggregated by one bridging chloride anion, which is lying on a threefold rotoinversion axis and is only loosely binding to the Ag+ ions. The N atom of the amine group is not engaged in any coordinative bond.

Sebastian Leitner

2012-03-01

367

?3-Chlorido-tris­(bis­{1-[2-(dimethyl­amino)­eth­yl]-3-methyl­imidazol-2-yl­idene}silver(I)) dichloride  

Science.gov (United States)

In the crystal structure of the title compound, [Ag3Cl(C8H15N3)6]Cl2, the AgI ion, which is located on a twofold rotation axis, exists in a T-shape coordination environment. Two carbene C atoms of the N-heterocyclic carbene (NHC) ligands are bonded tightly forming a slightly bent [Ag(NHC)2]+ cation [C—Ag—C angle = 162.80?(18)°]. Three of these complex cations are further aggregated by one bridging chloride anion, which is lying on a threefold rotoinversion axis and is only loosely binding to the Ag+ ions. The N atom of the amine group is not engaged in any coordinative bond. PMID:22412422

Topf, Christoph; Leitner, Sebastian; Monkowius, Uwe

2012-01-01

368

{3,3?-Bis[(anthracen-9-ylmethyl]-1,1?-[(ethane-1,2-diyldioxybis(ethane-1,2-diyl]bis(imidazol-2-ylidene}mercury(II bis(hexafluoridophosphate acetonitrile disolvate  

Directory of Open Access Journals (Sweden)

Full Text Available In the title compound, [Hg(C42H38N4O2](PF62·2CH3CN, the HgII cation lies on a twofold axis which is also the internal symmetry element of the complete cationic complex. The HgII cation is coordinated by two symmetry-related C(carbene atoms [Hg—C = 2.058?(9?Å] in a nearly linear geometry, with a C—Hg—C angle of 175.8?(5°. There are weak intermolecular C—H...F interactions in the crystal packing between an F atom of a hexafluoridophosphate anion and a –CH2– group of the bis-N-heterocyclic carbene ligand.

Di-Si Bai

2012-03-01

369

Improved ruthenium catalysts for Z-selective olefin metathesis.  

Science.gov (United States)

Several new C-H-activated ruthenium catalysts for Z-selective olefin metathesis have been synthesized. Both the carboxylate ligand and the aryl group of the N-heterocyclic carbene have been altered and the resulting catalysts evaluated using a range of metathesis reactions. Substitution of bidentate with monodentate X-type ligands led to a severe attenuation of metathesis activity and selectivity, while minor differences were observed between bidentate ligands within the same family (e.g., carboxylates). The use of nitrato-type ligands in place of carboxylates afforded a significant improvement in metathesis activity and selectivity. With these catalysts, turnover numbers approaching 1000 were possible for a variety of cross-metathesis reactions, including the synthesis of industrially relevant products. PMID:22097946

Keitz, Benjamin K; Endo, Koji; Patel, Paresma R; Herbert, Myles B; Grubbs, Robert H

2012-01-11

370

Making Oxidation Potentials Predictable: Coordination of Additives Applied to the Electronic Fine Tuning of an Iron(II) Complex.  

Science.gov (United States)

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. PMID:25333790

Haslinger, Stefan; Kück, Jens W; Hahn, Eva M; Cokoja, Mirza; Pöthig, Alexander; Basset, Jean-Marie; Kühn, Fritz E

2014-11-01

371

Kinetic Selectivity of Olefin Metathesis Catalysts Bearing Cyclic (Alkyl)(Amino)Carbenes  

Digital Repository Infrastructure Vision for European Research (DRIVER)

The evaluation of ruthenium olefin metathesis catalysts 4–6 bearing cyclic (alkyl)(amino)carbenes (CAACs) in the cross-metathesis of cis-1,4-diacetoxy-2-butene (7) with allylbenzene (8) and the ethenolysis of methyl oleate (11) is reported. Relative to most NHC-substituted complexes, CAAC-substituted catalysts exhibit lower E/Z ratios (3:1 at 70% conversion) in the cross-metathesis of 7 and 8. Additionally, complexes 4–6 demonstrate good selectivity for the formation of terminal olefins v...

Anderson, Donde R.; Ung, Thay; Mkrtumyan, Garik; Bertrand, Guy; Grubbs, Robert H.; Schrodi, Yann

2008-01-01

372

The solvation of carbenes: ? and O-ylidic complexes of p-nitrophenylchlorocarbene.  

Science.gov (United States)

p-Nitrophenylchlorocarbene (PNPCC) was studied by laser flash photolysis with UV-vis detection in solution at ambient temperature. The ? ? p (316 nm) and ? ? p (628 nm) absorptions of PNPCC were replaced in ?- or O-donor solvents by absorptions due to ?- or O-ylidic complexes or O-ylides. Donors included anisole, 1,3-dimethoxybenzene, 1,3,4,5-tetramethoxybenzene, diethyl ether, 18-crown-6, and dibenzo-18-crown-6. Suggestive evidence was also obtained for weak ?-complexation of PNPCC by benzene. Computational studies aided in understanding the carbene complex and O-ylide absorption spectra, and they provided structures and energetics for these species. PMID:18433110

Moss, Robert A; Wang, Lei; Weintraub, Elon; Krogh-Jespersen, Karsten

2008-05-22

373

Palladium-Catalyzed Heck Coupling Reaction of Aryl Bromides in Aqueous Media Using Tetrahydropyrimidinium Salts as Carbene Ligands  

Directory of Open Access Journals (Sweden)

Full Text Available An efficient and stereoselective catalytic system for the Heck cross coupling reaction using novel 1,3-dialkyl-3,4,5,6-tetrahydropyrimidinium salts (1, LHX and Pd(OAc2 loading has been reported. The palladium complexes derived from the salts 1a-f prepared in situ exhibit good catalytic activity in the Heck coupling reaction of aryl bromides under mild conditions.

?smail Özdemir

2010-01-01

374

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

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

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

2010-01-01

375

C-H activation by multiply bonded complexes with potentially noninnocent ligands: a computational study.  

Science.gov (United States)

Second- and third-row (typically precious metals) transition metal complexes are known to possess certain electronic features that define their structure and reactivity and are usually not observed in their first-row (base metal) congeners. Can these electronic features be conferred onto first-row transition metals with the aid of noninnocent and/or very high-field ligands? In this research, the impact upon methane C-H bond activation was modeled using the dipyridylazaallyl (smif) supporting ligand for late, first-row transition metal (M) imide, oxo, and carbene complexes (M = Fe, Co, Ni, or Cu; E = O, NMe, or CMe2). Density functional theory calculations suggest that the combination of smif with iron and the oxo activating ligand is the most energetically favorable complex for methane C-H activation. A change in the preferred transition state for methane C-H activation from [2+2] addition to hydrogen atom abstraction was observed upon going from Fe to Cu and for Fe as compared to precious metals. Contrary to expectations, it was the imide ligand rather than the dipyridylazaallyl ligand that was found to possess redox "noninnocent" characteristics. PMID:23802880

Olatunji-Ojo, Olayinka A; Cundari, Thomas R

2013-07-15

376

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

Scientific Electronic Library Online (English)

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

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

2009-09-01

377

A photodimerizable ditopic ligand  

Digital Repository Infrastructure Vision for European Research (DRIVER)

The synthesis, photophysical properties, and structural characterization of a photodimerizable ditopic ligand are described. Upon irradiation at 366 nm, ligand 1 dimerizes to the head-to-tail tetra-bpy ligand 2. This thermally stable photodimer can be dissociated back to 1 using higher energy irradiation (254 nm).

Jouvenot, Damien; Glazer, Edith C.; Tor, Yitzhak

2006-01-01

378

Synthesis, isolation, characterization, and reactivity of high-energy stereogenic-at-Ru carbenes: stereochemical inversion through olefin metathesis and other pathways.  

Science.gov (United States)

The synthesis, isolation, purification (routine silica gel chromatography), and spectroscopic characterization of high-energy endo stereogenic-at-Ru complex isomers, generated by ring-opening/cross-metathesis (ROCM) reaction of the corresponding exo carbenes, are disclosed. We provide experimental evidence showing that an endo isomer can undergo thermal or Brønsted acid-catalyzed polytopal rearrangement, causing conversion to the energetically favored exo carbene. PMID:22816554

Khan, R Kashif M; Zhugralin, Adil R; Torker, Sebastian; O'Brien, Robert V; Lombardi, Pamela J; Hoveyda, Amir H

2012-08-01

379

Metal nanoparticles functionalized with metal-ligand covalent bonds  

Science.gov (United States)

Metal-organic contact has been recognized to play important roles in regulation of optical and electronic properties of nanoparticles. In this thesis, significant efforts have been devoted into synthesis of ruthenium nanoparticles with various metal-ligand interfacial linkages and investigation of their electronic and optical properties. Ruthenium nanoparticles were prepared by the self-assembly of functional group onto bare Ru colloid surface. As to Ru-alkyne nanoparticles, the formation of a Ru-vinylidene (Ru=C=CH--R) interfacial bonding linkage was confirmed by the specific reactivity of the nanoparticles with imine derivatives and olefin at the metal-ligand interface, as manifested in NMR, photoluminescence, and electrochemical measurements. Interestingly, it was found the electronic coupling coefficient (beta)for strongly depend upon such metal-ligand interfacial bonding. Next, such metal-ligand interfacial bonding was extended to ruthenium-nitrene pi bonds on ruthenium colloids, which were investigated by XPS. The nanoparticles exhibited a 1:1 atomic ratio of nitrogen to sulfur, consistent with that of sulfonyl nitrene fragments. In addition, the nanoparticle-bound nitrene moieties behaved analogously to azo derivatives, as manifested in UV-vis and fluorescence measurements. Further testimony of the formation of Ru=N interfacial linkages was highlighted in the unique reactivity of the nanoparticles with alkenes by imido transfer. Extensive conjugation between metal-ligand interfacial bond results in remarkable intraparticle charge delocalization on Ru-alkynide nanoparticles, which was manipulated by simple chemical reduction or oxidation. Charging of extra electrons into the nanoparticle cores led to an electron-rich metal core and hence red-shift of the triple bond stretching mode, lower binding energy of sp hybridized C 1s and dimmed fluorescence of nanoparticles. Instead, chemical oxidation resulted in the opposite impacts on these properties. By taking advantage of such extensively conjugated metal-ligand bonding and effective intraparticle charge delocalization of ruthenium nanoparticles, Ru=carbene nanoparticles functionalized with multiple moieties by olefin metathesis reactions was further exploited for metal ion sensing. When the nanoparticles were co-functionalized with 1-vinylpyrene and 4-vinylbenzo-18-crown-6, upon the binding of metal ions into the crown ether cavity, the emission intensity of the nanoparticle fluorescence from the conjugation of vinylpyrene was found to diminish, with the most significant effects observed with K+ ions. In the case of ruthenium nanoparticles co-functionalized with pyrene and histidine derivative moieties through Ru=carbene pi bonds. The selective complexation of the histidine moiety with transition metal ions led to marked diminishment of the emission intensity from conjugation of pyrene. Of all the metal ions tested, the impacts were much more drastic with Pb2+ , Co2+ and Hg2+ than with Li +, K+, Rb+, Mg2+ Ca 2+ and Zn2+ ions. These were ascribed to the selective binding of 18-crown-6 to potassium ions or complexation of histidine derivative to transition metal ions, where the metal ions led to polarization of the nanoparticle core electrons to the metal surface and hence impeded intraparticle charge delocalization. Functionalization of semiconductor with metal nanoparticles could be exploited to remarkably enhance their photo catalytic performance. Before this exploration, in the last chapter, the impacts of the TiO2 nanocrystalline structure on the photocatalytic activity were then examined by using the reduction of methylene blue in water. It was found that in the presence of anatase and brookite crystalline phase, TiO2 nanotube arrays exhibited the highest photo catalytic activity. This is ascribed to synergistic coupling of the anatase and brookite crystalline domains, which led to effective charge separation upon photoirradiation.

Kang, Xiongwu

380

Kinetic Selectivity of Olefin Metathesis Catalysts Bearing Cyclic (Alkyl)(Amino)Carbenes  

Science.gov (United States)

The evaluation of ruthenium olefin metathesis catalysts 4–6 bearing cyclic (alkyl)(amino)carbenes (CAACs) in the cross-metathesis of cis-1,4-diacetoxy-2-butene (7) with allylbenzene (8) and the ethenolysis of methyl oleate (11) is reported. Relative to most NHC-substituted complexes, CAAC-substituted catalysts exhibit lower E/Z ratios (3:1 at 70% conversion) in the cross-metathesis of 7 and 8. Additionally, complexes 4–6 demonstrate good selectivity for the formation of terminal olefins versus internal olefins in the ethenolysis of 11. Indeed, complex 6 achieved 35 000 TONs, the highest recorded to date. CAAC-substituted complexes exhibit markedly different kinetic selectivity than most NHC-substituted complexes. PMID:18584055

Anderson, Donde R.; Ung, Thay; Mkrtumyan, Garik; Bertrand, Guy; Grubbs, Robert H.; Schrodi, Yann

2008-01-01

 
 
 
 
381

CAAC Boranes. Synthesis and characterization of cyclic (alkyl) (amino) carbene borane complexes from BF? and BH?.  

Science.gov (United States)

In situ formation of two cyclic (alkyl) (amino) carbenes (CAACs) followed by addition of BF?•Et?O provided the first two examples of CAAC-BF? complexes: 1-(2,6-diisopropylphenyl)-3,5,5-trimethyl-3-phenylpyrrolidin-2-ylidene trifluoroborane, and 2-(2,6-diisopropylphenyl)-3,3-dimethyl-2-azaspiro[4.5]decan-1-ylidene trifluoroborane. These CAAC-BF? complexes are robust compounds that are stable to ambient laboratory conditions and silica gel chromatography. They were characterized by spectroscopy and X-ray crystallography. In contrast, a CAAC complex with borane (BH?) was readily formed in situ according to ¹H and ¹¹B NMR analysis, but did not survive the workup conditions. These results set the stage for further studies of the chemistry of CAAC boranes. PMID:20978616

Monot, Julien; Fensterbank, Louis; Malacria, Max; Lacôte, Emmanuel; Geib, Steven J; Curran, Dennis P

2010-01-01

382

Possible formation of crystalline sodium carbene carbonate Na2(CO)CO3 at high pressure  

International Nuclear Information System (INIS)

Combined experimental and ab-initio computational studies suggest that at pressures above 20 GPa and temperatures above 1500 K sodium formate deprotonizes under formation of Na+2 [C=O| CO32-]. This new compound involves mesomeric C-O bonds with carbonate plus carbene units as limiting states and CO2 chains as intermediate. Sodium is six-fold coordinated by O-atoms. The formation of this new compound implies nucleophilic addition as reaction mechanism which is consistent with previously observed reduced stability of the H-O bond at these high pressures. The findings suggest further that the sextet state of carbon is energetically less unfavourable at high pressure than at ambient pressure.

383

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

Energy Technology Data Exchange (ETDEWEB)

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

Zhang, Xianping.

1990-09-21

384

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

Directory of Open Access Journals (Sweden)

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

Priyabrata Roy

2010-05-01

385

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

Science.gov (United States)

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

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

2009-03-14

386

Ligand screening using NMR.  

Science.gov (United States)

NMR has proven to be an invaluable technique for identifying and characterizing ligand interactions with biomolecules. NMR-based detection of ligand binding to protein targets is described. Specifically, the use of the WaterLOGSY NMR experiment to screen mixtures of compounds from a fragment library for binding to influenza H5 hemagglutinin is detailed. PMID:24590726

Ramirez, Benjamin E; Antanasijevic, Aleksandar; Caffrey, Michael

2014-01-01

387

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

Science.gov (United States)

A series of ruthenium olefin metathesis catalysts bearing N-heterocyclic carbene (NHC) ligands with varying degrees of backbone and N-aryl substitution have been prepared. These complexes show greater resistance to decomposition through C–H activation of the N-aryl group, resulting in increased catalyst lifetimes. This work has utilized robotic technology to examine the activity and stability of each catalyst in metathesis, providing insights into the relationship between ligand architecture and enhanced efficiency. The development of this robotic methodology has also shown that, under optimized conditions, catalyst loadings as low as 25 ppm can lead to 100% conversion in the ring-closing metathesis of diethyl diallylmalonate. PMID:19351207

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

2009-01-01

388

Effects of NHC-backbone substitution on efficiency in ruthenium-based olefin metathesis.  

Science.gov (United States)

A series of ruthenium olefin metathesis catalysts bearing N-heterocyclic carbene (NHC) ligands with varying degrees of backbone and N-aryl substitution have been prepared. These complexes show greater resistance to decomposition through C-H activation of the N-aryl group, resulting in increased catalyst lifetimes. This work has utilized robotic technology to examine the activity and stability of each catalyst in metathesis, providing insights into the relationship between ligand architecture and enhanced efficiency. The development of this robotic methodology has also shown that, under optimized conditions, catalyst loadings as low as 25 ppm can lead to 100% conversion in the ring-closing metathesis of diethyl diallylmalonate. PMID:19351207

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

2009-04-15

389

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

Directory of Open Access Journals (Sweden)

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

Gregory J. Domski

2012-09-01

390

Synthesis and Characterization of Some N-Heterocyclic Carbohydrate Derivatives  

Directory of Open Access Journals (Sweden)

Full Text Available The nucleophilic bimolecular substitution on 1,2:3,4-di-O-isopropylidene-α-Dgalactopyranose with NH2-heterocyclic derivatives allows us to obtain some new compounds with potential biological activities. The characterization of them as well as a discussion of their reactivities toward sulfur analogues are present.

M. A. Martins Alho

2000-03-01

391

Magnetic nanoparticles catalyzed synthesis of diverse N-heterocycles.  

Science.gov (United States)

A large library of diversified compounds (pyrano [2,3-d]pyrimidines, pyrido[2,3-d] pyrimidines and a variety of spirooxindoles) were synthesized through a very efficient, economical and environmentally benign process utilizing magnetic nanoparticles. Ease of recovery using an external magnetic field is an additional ecofriendly attribute of this catalytic system. Most of the compounds are new; therefore, could be further explored for their pharmaceutical application. Moreover, column chromatography and recrystallisation of the products is not required as the crude products are already highly pure and hence can be used for target oriented synthesis on a wide scale. PMID:22057791

Kidwai, Mazaahir; Jain, Arti; Bhardwaj, Saurav

2012-02-01

392

Ligand modeling and design  

Energy Technology Data Exchange (ETDEWEB)

The purpose of this work is to develop and implement a molecular design basis for selecting organic ligands that would be used in the cost-effective removal of specific radionuclides from nuclear waste streams. Organic ligands with metal ion specificity are critical components in the development of solvent extraction and ion exchange processes that are highly selective for targeted radionuclides. The traditional approach to the development of such ligands involves lengthy programs of organic synthesis and testing, which in the absence of reliable methods for screening compounds before synthesis, results in wasted research effort. The author`s approach breaks down and simplifies this costly process with the aid of computer-based molecular modeling techniques. Commercial software for organic molecular modeling is being configured to examine the interactions between organic ligands and metal ions, yielding an inexpensive, commercially or readily available computational tool that can be used to predict the structures and energies of ligand-metal complexes. Users will be able to correlate the large body of existing experimental data on structure, solution binding affinity, and metal ion selectivity to develop structural design criteria. These criteria will provide a basis for selecting ligands that can be implemented in separations technologies through collaboration with other DOE national laboratories and private industry. The initial focus will be to select ether-based ligands that can be applied to the recovery and concentration of the alkali and alkaline earth metal ions including cesium, strontium, and radium.

Hay, B.P. [Pacific Northwest National Lab., Richland, WA (United States)

1997-10-01

393

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

International Nuclear Information System (INIS)

Novel types of cycloaddition products with an azomethine imine functionality have been prepared from ?-azo-?'-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 ?-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 ?-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 ?-azo-?'-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 ?-diazo ketones in the course of the Wolff rearrangement. This complicated the approach to the required ?-azo-?'-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 ?-azo-?'-diazo ketones a largely commonly applicable approach to endocyclic and N-exocyclic azomethine imines was worked out, which results from the so far unknown intramolecular reaction of azo-nitrogen atoms on carbenoids (rhodium-stabilized carbenes). Work up and isolation of the different reaction products turned out not to be without difficulty. Most of the novel and in solution partly unstable compounds that were characterized in this thesis would not have been isolable in the conventional manner (chemical separation processes, column chromatography). However, this has been managed by employing the radial chromatography upon optimizing some parameters; apparently, this is a not widely known chromatographic separation method that enables fast separations with high efficiency. To clarify the question, why only certain azomethine imines react with special dipolarophiles, quantum-mechanical calculations of the reactants' frontier orbitals have been carried out; this resulted in a satisfactory concordance with the FMO theory by Fukui. Likewise, molecular calculations rationalize the observed stereo- and regioselectivity as well as the kinetic and thermodynamic reaction control in the course of cycloaddition reactions of azomethine imines. (author)

394

Catalytic asymmetric syntheses of quinolizidines by dirhodium-catalyzed dearomatization of isoquinolinium/pyridinium methylides--the role of catalyst and carbene source.  

Science.gov (United States)

Convenient access to highly enantioenriched substituted quinolizidines has been achieved by chiral dirhodium(II) carboxylate-catalyzed dearomatizing formal [3 + 3]-cycloaddition of isoquinolinium/pyridinium methylides and enol diazoacetates. Coordination of Lewis basic methylides to dirhodium(II) prompts the rearrangement of the enol-carbene that is bound to dirhodium to produce a donor-acceptor cyclopropene. The donor-acceptor cyclopropene is in equilibrium with the dirhodium-bound enol-carbene and undergoes both enantioselective [3 + 3]-cycloaddition from the dirhodium-bound enol-carbene and diastereoselective [3 + 2]-cycloaddition by uncatalyzed reaction of the cyclopropene with isoquinolinium or pyridinium methylides. Increasing the mol % of catalyst loading suppresses the [3 + 2]-cycloaddition pathway. PMID:23889041

Xu, Xichen; Zavalij, Peter Y; Doyle, Michael P

2013-08-21

395

Ligand modeling and design  

International Nuclear Information System (INIS)

The purpose of this work is to develop and implement a molecular design basis for selecting organic ligands that would be used tin applications for the cost-effective removal of specific radionuclides from nuclear waste streams

396

Thin films of molecular materials synthesized from fisher's carbene ferrocenyl: Film formation and electrical properties  

International Nuclear Information System (INIS)

The synthesis of materials from Fisher's carbene ferrocenyl of the elements chromium, molybdenum and tungsten was carried out. The Fisher's compounds that were synthesized included the following combinations of two different metallic atoms: iron with chromium, iron with molybdenum and iron with tungsten. The molecular solids' preparation was done in electro-synthesis cells with platinum electrodes. Thin films were prepared by vacuum thermal evaporation on quartz substrates and crystalline silicon wafers. Pellets and thin films from these compounds were characterized by Fourier transform infrared spectroscopy, scanning electron microscopy, energy-dispersive spectroscopy, atomic force microscopy and ellipsometry. The powder and thin films synthesized from these materials show the same intra-molecular bonds shown by infrared spectroscopy results, suggesting that thermal evaporation does not alter these bonds in spite of the thin films being amorphous, in contrast with other bimetallic complexes where material decomposition occurs. The differences in the conductivity values of the prepared films are very small, so they may be attributed to the different metallic ions employed in each case. The tungsten complex exhibits a higher conductivity than the molybdenum and chromium complexes at room temperature. Electrical conductivity values found for thin films are higher than for pellets made of the same molecular materials

397

Iron porphyrin carbenes as catalytic intermediates: structures, Mössbauer and NMR spectroscopic properties, and bonding.  

Science.gov (United States)

Iron porphyrin carbenes (IPCs) are thought to be intermediates involved in the metabolism of various xenobiotics by cytochrome P450, as well as in chemical reactions catalyzed by metalloporphyrins and engineered?P450s. While early work proposed IPCs to contain Fe(II), more recent work invokes a double-bond description of the iron-carbon bond, similar to that found in Fe(IV) porphyrin oxenes. Reported herein is the first quantum chemical investigation of IPC Mössbauer and NMR spectroscopic properties, as well as their electronic structures, together with comparisons to ferrous heme proteins and an Fe(IV) oxene model. The results provide the first accurate predictions of the experimental spectroscopic observables as well as the first theoretical explanation of their electrophilic nature, as deduced from experiment. The preferred resonance structure is Fe(II)?{:C(X)Y}(0) and not Fe(IV)={C(X)Y}(2-), a result that will facilitate research on IPC reactivities in various chemical and biochemical systems. PMID:24910004

Khade, Rahul L; Fan, Wenchao; Ling, Yan; Yang, Liu; Oldfield, Eric; Zhang, Yong

2014-07-14

398

All-electron relativistic multireference configuration interaction investigation of fluoroiodo carbene.  

Science.gov (United States)

We present herein the first all-electron relativistic internally contracted multireference configuration interaction with Davidson correction (icMRCI+Q) study on the low-lying states of fluoroiodo carbene, CFI, which contains the most electronegative element (fluorine) and the heavy halogen (iodine). The potential energy surface (PES) of the first excited singlet state (Ã(1)A?) of CFI was carefully examined along the C-I bond distance at the icMRCI+Q/ANO-RCC level, while the other two geometric parameters were optimized at every C-I bond length in contrast to fixing them at the equilibrium values. A reliable barrier height of the Ã(1)A? state was determined to be 625 cm(-1) by our high-level icMRCI+Q calculations with large ANO-RCC basis set and with inclusion of the spin-orbit coupling, core-valence correlation, and zero-point-energy. Finally, the electronic states of CFI with vertical transition energy up to 6 eV were studied. The calculation presented here will provide more comprehensive results about the structure and behavior of electronic states of CFI radical. PMID:24611930

Sun, Erping; Lv, Hang; Shi, Dandan; Wei, Changli; Xu, Haifeng; Yan, Bing

2014-04-01

399

Molecular rectangles from platinum(II) and bridging dicarbene, diisocyanide and 4,4'-bipyridine ligands.  

Science.gov (United States)

A series of benzobisimidazolium salts have been prepared and treated with [PtCl2(dppe)] or [PtCl2(dmpe)] in the presence of sodium acetate to yield dinuclear dicarbene-bridged complexes of the type [(P^P)(X)Pt(benzodicarbene)Pt(X)(P^P)](X)2 [5]Br2-[11]I2. The reaction of compounds [7]Br2 and [11]I2 with AgPF6 in acetonitrile led to the exchange of the metal-bound bromo or iodo ligands for acetonitrile and the formation of complexes [(dmpe)(MeCN)Pt(benzodicarbene)Pt(MeCN)(dmpe)](PF6)4 [12](PF6)4 and [13](PF6)4. The dinuclear complex [13](PF6)4 reacts with 4,4'-bipyridine (4,4'-bipy) to give the molecular rectangle [15](PF6)8 featuring two bridging dicarbene and two bridging 4,4'-bipy ligands. Complex [13](PF6)4 also reacts with ?,?'-bis(triisopropylsiloxy)phenyl-1,4-diisocyanide 16 followed by hydrolysis of the Si-O bonds and intramolecular carbene formation to yield the molecular square [18](BF4)8 featuring bridging NR,NR- and NH,O-substituted dicarbene ligands. Reaction of the dinuclear complex [12](PF6)4 containing a sterically demanding N,N',N'',N'''-substituted dicarbene ligand under otherwise identical reaction conditions did not lead to any molecular rectangles. The molecular square [19](BF4)8 was synthesized from ?,?'-bis(triisopropylsiloxy)phenyl-1,4-diisocyanide 16 and [PtCl2(dmpe)] in the presence of AgBF4. It reacts to yield the molecular square [20](BF4)8 with four NH,O-substituted dicarbene ligands by Si-O bond cleavage and subsequent intramolecular cyclization. PMID:24022647

Schmidtendorf, Markus; Pape, Tania; Hahn, F Ekkehardt

2013-12-01

400

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

Digital Repository Infrastructure Vision for European Research (DRIVER)

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

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

2013-01-01

 
 
 
 
401

A concise route to pyridines from hydrazides by metal carbene N-H insertion, 1,2,4-triazine formation, and Diels-Alder reaction.  

Science.gov (United States)

A simple, new three-step sequence for the conversion of hydrazides into pyridines is reported in which the key steps are N-H insertion by a copper carbene intermediate derived from alpha-diazo-beta-ketoesters into the hydrazide, reaction with ammonium acetate to give 1,2,4-triazines, followed by Diels-Alder reaction with norbornadiene. PMID:19719202

Shi, Baolu; Lewis, William; Campbell, Ian B; Moody, Christopher J

2009-08-20

402

Nearly degenerate isomers of C(BH)2: cumulene, carbene, or carbone?  

Science.gov (United States)

The ground electronic state of C(BH)2 exhibits both a linear minimum and a peculiar angle-deformation isomer with a central B-C-B angle near 90°. Definitive computations on these species and the intervening transition state have been executed by means of coupled-cluster theory including single and double excitations (CCSD), perturbative triples (CCSD(T)), and full triples with perturbative quadruples (CCSDT(Q)), in concert with series of correlation-consistent basis sets (cc-pVXZ, X=D, T, Q, 5, 6; cc-pCVXZ, X=T, Q). Final energies were pinpointed by focal-point analyses (FPA) targeting the complete basis-set limit of CCSDT(Q) theory with auxiliary core correlation, relativistic, and non-Born-Oppenheimer corrections. Isomerization of the linear species to the bent form has a minuscule FPA reaction energy of 0.02 kcal mol(-1) and a corresponding barrier of only 1.89 kcal mol(-1). Quantum tunneling computations reveal interconversion of the two isomers on a timescale much less than 1 s even at 0 K. Highly accurate CCSD(T)/cc-pVTZ and composite c~CCSDT(Q)/cc-pCVQZ anharmonic vibrational frequencies confirm matrix-isolation infrared bands previously assigned to linear C(BH)2 and provide excellent predictions for the heretofore unobserved bent isomer. Chemical bonding in the C(BH)2 species was exhaustively investigated by the atoms-in-molecules (AIM) approach, molecular orbital plots, various population analyses, local mode vibrations and force constants, unified reaction valley analysis (URVA), and other methods. Linear C(BH)2 is a cumulene, whereas bent C(BH)2 is best characterized as a carbene with little carbone character. Weak B-B attraction is clearly present in the unusual bent isomer, but its strength is insufficient to form a CB2 ring with a genuine boron-boron bond and attendant AIM bond path. PMID:24123325

Barua, Shiblee R; Allen, Wesley D; Kraka, Elfi; Jerabek, Paul; Sure, Rebecca; Frenking, Gernot

2013-11-18

403

Stabilization of a cobalt-cobalt bond by two cyclic alkyl amino carbenes.  

Science.gov (United States)

(Me2-cAAC:)2Co2 (2, where Me2-cAAC: = cyclic alkyl amino carbene, :C(CH2)(CMe2)2N-2,6-iPr2C6H3)) was synthesized via the reduction of precursor (Me2-cAAC:Co(II)(?-Cl)Cl)2 (1) with KC8. 2 contains two cobalt atoms in the formal oxidation state zero. Magnetic measurement revealed that 2 has a singlet spin ground state S = 0. The cyclic voltammogram of 2 exhibits both one-electron oxidation and reduction, indicating the possible synthesis of stable species containing 2(•-) and 2(•+) ions. The latter was synthesized via reduction of 1 with required equivalents of KC8 and characterized as [(Me2-cAAC:)2Co2](•+)OTf(-) (2(•+)OTf(-)). Electron paramagnetic resonance spectroscopy of 2(•+) reveals the coupling of the electron spin with 2 equiv (59)Co isotopes, leading to a (Co(0.5))2 state. The experimental Co1-Co2 bond distances are 2.6550(6) and 2.4610(6) Å for 2 and 2(•+)OTf(-), respectively. Theoretical investigation revealed that both 2 and 2(•+)OTf(-) possess a Co-Co bond with an average value of 2.585 Å. A slight increase of the Co-Co bond length in 2 is more likely to be caused by the strong ?-accepting property of cAAC. 2(•+) is only 0.8 kcal/mol higher in energy than the energy minimum. The shortening of the Co-Co bond of 2(•+) is caused by intermolecular interactions. PMID:24437683

Mondal, Kartik Chandra; Samuel, Prinson P; Roesky, Herbert W; Carl, Elena; Herbst-Irmer, Regine; Stalke, Dietmar; Schwederski, Brigitte; Kaim, Wolfgang; Ungur, Liviu; Chibotaru, Liviu F; Hermann, Markus; Frenking, Gernot

2014-02-01

404

Theoretical insight into electronic spectra of carbon chain carbenes H2Cn (n = 3-10)  

Science.gov (United States)

Ground-state geometries of carbenes H2Cn (n = 3-10) have been fully optimized with the C2?-symmetry constraint at the density functional theory and restricted-spin coupled-cluster single-double plus perturbative triple excitation levels of theory, respectively. Comparison of structures corresponding to the X1A1 and B1B1 electronic states has been made by the complete active space self-consistent field calculations. Parity alternation effect on various properties of the ground-state geometries has been discovered in the present study, which generally gives illustration for the relative stabilities of the titled carbon chains. Further calculations on their electronic spectra have been carried out by means of the complete active space second-order perturbation theory method along with the cc-pVTZ basis set. It is found that the vertical excitation energies of the dipole-allowed B1B1 ? X1A1 transition in the gas phase are 2.28, 4.75, 1.69, 3.66, 1.30, 2.94, 1.12, and 2.49 eV, respectively, which agree very well with the available experimental result for H2C3 (2.27 eV). In addition, the vertical excitation energies for both transitions B1B1 ? X1A1 and A1A2 ? X1A1 are found to obey a nonlinear ?E-n relationship as a function of chain size by performing curves fitting.

Zhang, Yanxin; Wang, Li; Li, Yuanyuan; Zhang, Jinglai

2013-05-01

405

Transition metal-induced activation of alkynes leading to metal carbene species: synthetic application to new ?-conjugated molecules  

International Nuclear Information System (INIS)

The in situ generation of furylcarbene complexes by means of transition metals was applied to catalytic carbene reactions, such as Wittig-type olefination and cycloisomerization reactions. In the presence of [Rh(OAc)2]2 as a catalyst and triphenylphosphine as a carbene accepter, carbonyl-ene-ynes 1a reacted with benzaldehyde to give a 2-styrylfuran derivative 3a. The reaction involving phosphine-ylide formation followed by Wittig-type olefination with aldehydes was applied to synthesis of furfurylidene-containing p-extended conjugated molecules. A Ruthenium catalyst underwent cycloisomerization of 1,2-bis(carbonylenyl)acetylene 10a,b to afford 2,2'-bifuran structures. The crystal structure of 5,5'-diphenyl-2,2'-bifuran 11b was determined by X-ray crystallography. The ORTEP drawings of 11b exhibited transoid and highly planar structure. The emission bands of the bisfuran 11b were observed at 414 and 440 nm, its quantum yield (84%) was higher than that of a similar 5,5'-diphenyl-2,2'-bithiophene

406

Reactions of the cationic zinc thiolate model complex [Zn(Tab)4](PF6)2 with N-donor ligands and cobalt dichloride.  

Science.gov (United States)

Reactions of [Zn(Tab)(4)](PF(6))(2) (Tab = 4-(trimethylammonio)benzenethiolate) (1) with 2,2'-bipyridine (2,2'-bipy), 1,10-phenanthroline (phen), 2,9-dimethyl-1,10-phenanthroline (2,9-dmphen), N-methylimidazole (N-Meim), and 2,6-bis(pyrazol-3-yl)pyridine (bppy) or with CoCl(2)·6H(2)O at the presence of N-donor ligands (2,2'-bipy, phen, 4,4'-dimethyl-2,2'-bipyridine (4,4'-dmbpy), 2,6-bis(3,5-dimethyl-1H-pyrazol-1-yl)pyridine (bdmppy))gave rise to a family of zinc or cobalt thiolate complexes, [Zn(Tab)(2)(L)](PF(6))(2) (2: L = 2,2'-bipy, 3: L = phen, 4: L = 2,9-dmphen), [Zn(Tab)(2)(N-Meim)(2)](PF(6))(2) (5), [Zn(Tab)(2)(bppy)](PF(6))(2) (6), [Co(Tab)(2)(L)(2)](PF(6))(3) (7: L = 2,2'-bipy, 8: L = phen, 9: L = 4,4'-dmbpy), and [Co(Tab)(bdmppy)Cl](PF(6)) (10). These compounds were characterized by elemental analysis, IR spectra, UV-vis spectra,(1)H NMR, electrospray ionization (ESI) mass spectra, and single-crystal X-ray diffraction. The Zn(II) in [Zn(Tab)(2)L(n)](2+)dications of 2-5 is tetrahedrally coordinated by two Tab ligands and one L or two N-Meim ligands. In 6, the Zn(II) has a distorted trigonal-bipyramidal geometry, coordinated by two Tab ligands and one tridentate bppy ligand. The Co(III) in the [Co(Tab)(2)(L)(2)](3+) trications of 7-9 is octahedraly chelated by two bidentate L ligands and two Tab ligands. In 10, the Co(II) adopts a distorted trigonal-bipyramidal geometry, coordinated by one Cl(-), one Tab ligand, and one tridentate bdmppy. In the formation of 2-6, two Tab ligands are removed from the [Zn(Tab)(4)](2+) dication when it is attacked by L ligands, while in the cases of 7-9, the Zn(II) of the [Zn(Tab)(4)](2+) dication was replaced by Co(III) (derived from oxidation of Co(II) by O(2)) followed by the removal of two Tab ligands via L ligands. In the case of 10, the central Zn(II) of the [Zn(Tab)(4)](2+) dication was displaced by Co(II) followed by the removal of three Tab ligands via one Cl(-) and one tridentate bdmppy. These ligand and metal replacement reactions may provide some interesting information on the interactions of the [Zn(S-Cys)(4)](2-) unit of Zn-MTs with N-heterocyclic ligands and toxic metal ions encountered in a natural environment. PMID:22985442

Zheng, Ai-Xia; Si, Jing; Tang, Xiao-Yan; Miao, Li-Li; Yu, Miao; Hou, Kai-Peng; Wang, Fan; Li, Hong-Xi; Lang, Jian-Ping

2012-10-01

407

The doping effect of fluorinated aromatic solvents on the rate of ruthenium-catalysed olefin metathesis.  

Science.gov (United States)

A study concerning the effect of using a fluorinated aromatic solvent as the medium for olefin metathesis reactions catalysed by ruthenium complexes bearing N-heterocyclic carbene ligands is presented. The use of fluorinated aromatic hydrocarbons (FAH) as solvents for olefin metathesis reactions catalysed by standard commercially available ruthenium pre-catalysts allows substantially higher yields of the desired products to be obtained, especially in the case of demanding polyfunctional molecules, including natural and biologically active compounds. Interactions between the FAH and the second-generation ruthenium catalysts, which apparently improve the efficiency of the olefin metathesis transformation, have been studied by X-ray structure analysis and computations, as well as by carrying out a number of metathesis experiments. The optimisation of reaction conditions by using an FAH can be regarded as a complementary approach for the design of new improved ruthenium catalysts. Fluorinated aromatic solvents are an attractive alternative medium for promoting challenging olefin metathesis reactions. PMID:21956694

Samoj?owicz, Cezary; Bieniek, Micha?; Pazio, Aleksandra; Makal, Anna; Wo?niak, Krzysztof; Poater, Albert; Cavallo, Luigi; Wójcik, Jacek; Zdanowski, Konrad; Grela, Karol

2011-11-11

408

Mono- and Bimetallic Ruthenium—Arene Catalysts for Olefin Metathesis: A Survey  

Science.gov (United States)

In this chapter, we summarize the main achievements of our group toward the development of easily accessible, highly efficient ruthenium—arene catalyst precursors for olefin metathesis. Major advances in this field are presented chronologically, with an emphasis on catalyst design and mechanistic details. The first part of this survey focuses on monometallic complexes with the general formula RuCl2(p-cymene)(L), where L is a phosphine or N-heterocyclic carbene ancillary ligand. In the second part, we disclose recent developments in the synthesis and catalytic applications of homobimetallic ruthenium—arene complexes of generic formula (p-cymene)Ru(?-Cl)3RuCl(?2-C2H4)(L) and their derivatives resulting from the substitution of the labile ethylene moiety with vinylidene, allenylidene, or indenylidene units

Borguet, Yannick; Sauvage, Xavier; Demonceau, Albert; Delaude, Lionel

409

A golden future in medicinal inorganic chemistry: the promise of anticancer gold organometallic compounds.  

Science.gov (United States)

From wedding rings on fingers to stained glass windows, by way of Olympic medals, gold has been highly prized for millennia. Nowadays, organometallic gold compounds occupy an important place in the field of medicinal inorganic chemistry due to their unique chemical properties with respect to gold coordination compounds. In fact, several studies have proved that they can be used to develop highly efficient metal-based drugs with possible applications in the treatment of cancer. This Perspective summarizes the results obtained for different families of bioactive organometallic gold compounds including cyclometallated gold(iii) complexes with C,N-donor ligands, gold(I) and gold(I/III) N-heterocyclic (NHC) carbene complexes, as well as gold(I) alkynyl complexes, with promising anticancer effects. Most importantly, we will focus on recent developments in the field and discuss the potential of this class of organometallic compounds in relation to their versatile chemistry and innovative mechanisms of action. PMID:24225667

Bertrand, Benoît; Casini, Angela

2014-03-21

410

High-density monolayers of metal complexes: preparation and catalysis.  

Science.gov (United States)

Catalysts are one of the key materials for realizing a sustainable society. However, we may encounter problematic cases where conventional catalyst systems cannot provide effective solutions. We thus believe that the establishment of novel methods of catalyst preparation is currently necessary. Utilization of high-density monolayers of molecular metal complexes is our strategy, and we expect that this methodology will enable facile and systematic screening of unique and efficient catalysts. This Personal Account describes our challenges to establish such an immature method in catalyst preparation as well as the related background and perspective. Preparation and catalysis by high-density monolayers of Rh complexes with N-heterocyclic carbene, structurally compact phosphine and diisocyanide ligands on gold surfaces are presented. The catalytic application of a high-density Pd-bisoxazoline complex prepared on a single-crystal silicon surface is also shown. Uniquely high catalyst turnover numbers and high chemoselectivities were observed with these catalyst systems. PMID:25112780

Hara, Kenji; Sawamura, Masaya; Fukuoka, Atsushi

2014-10-01

411

Ligand efficiency metrics considered harmful.  

Science.gov (United States)

Ligand efficiency metrics are used in drug discovery to normalize biological activity or affinity with respect to physicochemical properties such as lipophilicity and molecular size. This Perspective provides an overview of ligand efficiency metrics and summarizes thermodynamics of protein-ligand binding. Different classes of ligand efficiency metric are critically examined and the study concludes with suggestions for alternative ways to account for physicochemical properties when prioritizing and optimizing leads. PMID:24899110

Kenny, Peter W; Leitão, Andrei; Montanari, Carlos A

2014-07-01

412

Ligand-Receptor Interactions  

CERN Document Server

The formation and dissociation of specific noncovalent interactions between a variety of macromolecules play a crucial role in the function of biological systems. During the last few years, three main lines of research led to a dramatic improvement of our understanding of these important phenomena. First, combination of genetic engineering and X ray cristallography made available a simultaneous knowledg of the precise structure and affinity of series or related ligand-receptor systems differing by a few well-defined atoms. Second, improvement of computer power and simulation techniques allowed extended exploration of the interaction of realistic macromolecules. Third, simultaneous development of a variety of techniques based on atomic force microscopy, hydrodynamic flow, biomembrane probes, optical tweezers, magnetic fields or flexible transducers yielded direct experimental information of the behavior of single ligand receptor bonds. At the same time, investigation of well defined cellular models raised the ...

Bongrand, Pierre

2008-01-01

413

Synthesis, in vitro and in vivo characterization of rhenium tricarbonyl complexes with different bifunctional tridentate ligands  

International Nuclear Information System (INIS)

Discovery of new chelating ligands that bind technetium/rhenium strongly is a priority in the quest toward the design and development of site specific radiopharmaceuticals. The current study on the application of Tc/Re carbonyls in radiopharmaceuticals has been focused on the utility of specific tridentate ligand systems for achieving kinetic inertness and in vivo stability. In this paper, (Bis (2-pyridylmethyl)-amino)-ethylamine(1) (Fig. 1), (Bis (2-pyridylmethyl)-amino)-acetic acid (2) (Fig. 1), L(6-amino-hexyl)-pyridyl-2-methyl- amino-acetic acid (3) (Fig. 2), and picolylamine diacetic acid (4) (Fig. 3) that possessed an NNN, NNO and NOO donor atom sets were synthesized, which can be a good selection for these requirements. The Re(I)-complexes of above four ligands were prepared in good yield with [NEt4]2[ReBr3(CO)3] in water at 75 degree C for 3 h. The complexes were characterized by elemental analysis and spectroscopic methods. The 188Re(I)-complexes of Four ligands were carried out by incubating the fac- [188Re(CO)3(H2O)3]+ fragment for 60 min at 75 degree C in PBS buffer (0.1 M NaCl/0.05 M sodium phosphate buffered, pH 7.4) under nitrogen. After cooling in ice bath, complexes formations were monitored by HPLC. The HPLC analysis demonstrated that the reaction produces in the complex 1 with yield greater than 95% and its retention times was 7.5 min, which is stable for more than 12 h in human serum, and the complex 2 with yield 93% is stable for more than 8 h in human serum, its retention times was 15.5 min, and the complex 3 with yield 90% is stable for more than 10 h in human serum, its retention times was 15.4 min, while the complex 4 with yields more than 92% can be stable 10 h in human serum and its retention time was 15.6 min respectively. The identity of the 188Re-complexes were proved by comparative HPLC studies using samples of the well characterized thenium(I) complexes as reference. In vivo biodistribution studies at 24 hour post-injection were carried out in normal, white mice. The biodistribution data are shown in table 1. The data show: the major part of the complexes cleared efficiently from the blood pool (0.09-0.67%); No organs (apart from liver and kidneys) or tissue was specifically targeted; Low activity (0.25-0.93%) found in the stomach indicated the good in vivo stability of the complexes. In conclusion, four ligands react with fac- [M(CO)3(H2O)3]+ (M=188Re, Re) fragment resulting in four single stable complexes, M(CO)3(1), M(CO)3(2), M(CO)3(3) and M(CO)3(4), containing aromatic N-heterocycles. These ligand systems are attractive for functionalization purposes of biological vectors since they are easy to synthesize. The corresponding complexes with fac-[M(CO)3(H2O)3]+ are in vivo and vitro stable. Thus the proposed strategy of attaching M(CO)3(1), M(CO)3(2), M(CO)3(3) and M(CO)3(4) complexes is promising for labeling of biomolecules. The approach is worthy of further investigation.

414

Radiobiology with DNA ligands  

International Nuclear Information System (INIS)

The paper deals with the following topics: labelling of DNA ligands and other tumour-affinic compounds with 4.15-d 124I, radiotoxicity of Hoechst 33258 and 33342 and of iodinated Hoechst 33258 in cell cultures, preparation of 76Br-, 123I-, and 221At-labelled 5-halo-2'-deoxyuridine, chemical syntheses of boron derivatives of Hoechst 33258.III., Gadolinium neutron capture therapy

415

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

Directory of Open Access Journals (Sweden)

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...? interaction further stabilizes the crystal structure.

Rosenani A. Haque

2010-04-01

416

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

International Nuclear Information System (INIS)

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

417

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

Scientific Electronic Library Online (English)

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

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

1021-10-01

418

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

Science.gov (United States)

Summary In situ formation of two cyclic (alkyl) (amino) carbenes (CAACs) followed by addition of BF3•Et2O provided the first two examples of CAAC–BF3 complexes: 1-(2,6-diisopropylphenyl)-3,5,5-trimethyl-3-phenylpyrrolidin-2-ylidene trifluoroborane, and 2-(2,6-diisopropylphenyl)-3,3-dimethyl-2-azaspiro[4.5]decan-1-ylidene trifluoroborane. These CAAC–BF3 complexes are robust compounds that are stable to ambient laboratory conditions and silica gel chromatography. They were characterized by spectroscopy and X-ray crystallography. In contrast, a CAAC complex with borane (BH3) was readily formed in situ according to 1H and 11B NMR analysis, but did not survive the workup conditions. These results set the stage for further studies of the chemistry of CAAC boranes. PMID:20978616

Monot, Julien; Geib, Steven J

2010-01-01

419

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

Directory of Open Access Journals (Sweden)

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

Julien Monot

2010-08-01

420

Electronic structure and slow magnetic relaxation of low-coordinate cyclic alkyl(amino) carbene stabilized iron(I) complexes.  

Science.gov (United States)

Cyclic alkyl(amino) carbene stabilized two- and three-coordinate Fe(I) complexes, (cAAC)2FeCl (2) and [(cAAC)2Fe][B(C6F5)4] (3), respectively, were prepared and thoroughly studied by a bouquet of analytical techniques as well as theoretical calculations. Magnetic susceptibility and Mössbauer spectroscopy reveal the +1 oxidation state and S = 3/2 spin ground state of iron in both compounds. 2 and 3 show slow magnetic relaxation typical for single molecule magnets under an applied direct current magnetic field. The high-frequency EPR measurements confirm the S = 3/2 ground state with a large, positive zero-field splitting (?20.4 cm(-1)) and reveal easy plane anisotropy for compound 2. CASSCF/CASPT2/RASSI-SO ab initio calculations using the MOLCAS program package support the experimental results. PMID:25072104

Samuel, Prinson P; Mondal, Kartik Chandra; Amin Sk, Nurul; Roesky, Herbert W; Carl, Elena; Neufeld, Roman; Stalke, Dietmar; Demeshko, Serhiy; Meyer, Franc; Ungur, Liviu; Chibotaru, Liviu F; Christian, Jonathan; Ramachandran, Vasanth; van Tol, Johan; Dalal, Naresh S

2014-08-27

 
 
 
 
421

Metal-metal interaction in Fischer carbene complexes: a study of ferrocenyl and biferrocenyl tungsten alkylidene complexes.  

Science.gov (United States)

A series of ferrocenyl (Fc = ferrocenyl; fc = ferrocen-1,1'-diyl) and biferrocenyl (Bfc = 1',1?-biferrocenyl; bfc = 1',1?-biferrocen-1,1?-diyl) mono- and biscarbene tungsten(0) complexes of the type [(CO)5W?C(OMe)R] (1, R = Fc; 3, R = Bfc) and [(CO)5W?C(OMe)-R'-(OMe)C?W(CO)5] (2, R' = fc; 4, R' = bfc) were synthesized according to the classical synthetic methodology by reacting W(CO)6 with LiR (R = Fc, fc, bfc), followed by a subsequent alkylation using methyl trifluoromethanesulfonate. Electrochemical investigations were carried out on these complexes to get a closer insight into the electronic properties of 1-4. The ferrocenyl and biferrocenyl moieties in 1-4 show reversible one-electron redox events. It was further found that the Fischer carbene unit is reducible in an electrochemical one-electron transfer process. For the tungsten carbonyl moieties, irreversible oxidation processes were found. In addition, charge transfer studies were performed on 1-4 using in situ UV-vis-NIR and infrared spectroelectrochemical techniques. During the UV-vis-NIR investigations, typical low energy transitions for the mixed-valent biferrocenyl unit were found. A further observed high energy NIR absorption is attributed to a metal-metal charge transfer transition between the tungsten carbonyl fragment and the ferrocenyl/biferrocenyl group in the corresponding oxidized states, which can be described as class II systems according to Robin and Day. This assignment was verified by infrared spectroelectrochemical studies. The electrochemical investigations are supported by density functional theory calculations. The structural properties of 1-4 in the solid state were investigated by single-crystal X-ray diffraction studies showing no substituent effects on bond lengths and angles. The biferrocenyl derivatives exhibit syn-conformation of the ferrocenyl and carbene building blocks. PMID:24299202

van der Westhuizen, Belinda; Speck, J Matthäus; Korb, Marcus; Friedrich, Joachim; Bezuidenhout, Daniela I; Lang, Heinrich

2013-12-16

422

Macrocyclic G-quadruplex ligands  

DEFF Research Database (Denmark)

G-quadruplex stabilizing compounds have recently received increased interest due to their potential application as anticancer therapeutics. A significant number of structurally diverse G-quadruplex ligands have been developed. Some of the most potent and selective ligands currently known are macrocyclic structures which have been modeled after the natural product telomestatin or from porphyrin-based ligands discovered in the late 1990s. These two structural classes of G-quadruplex ligands are reviewed here with special attention to selectivity and structure-activity relationships, and with focus on the recent developments.

Nielsen, M C; Ulven, Trond

2010-01-01

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