WorldWideScience
1

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

2

Nickel N-heterocyclic carbene complexes in homogeneous catalysis  

OpenAIRE

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

Berding, Joris

2009-01-01

3

N-Heterocyclic Carbene Complexes in Additions to Multiple Bonds  

Science.gov (United States)

The use of N-heterocyclic carbene (NHC) complexes as homogeneous catalysts in addition reactions across carbon-carbon double and triple bonds and carbon-heteroatom double bonds is described. The discussion is focused on the description of the catalytic systems, their current mechanistic understanding and occasionally the relevant organometallic chemistry. The reaction types covered include hydrogenation, transfer hydrogenation, hydrosilylation, hydroboration and diboration, hydroamination, hydrothiolation, hydration, hydroarylation, allylic substitution, addition, chloroesterification and chloroacylation.

Danopoulos, Andreas A.

4

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

5

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

OpenAIRE

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

Schuster, Oliver; Mercs, Laszlo; Albrecht, Martin

2010-01-01

6

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

OpenAIRE

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

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

2010-01-01

7

Sterically driven synthesis of ruthenium and ruthenium-silver N-heterocyclic carbene complexes.  

Science.gov (United States)

A straightforward and efficient synthetic route to novel Ru N-heterocyclic carbene (NHC) complexes by transmetallation of non-bulky silver NHC to ruthenium dicarbonyl tetraarylcyclopentadienone is described. The same procedure with sterically demanding NHC leads to unprecedented heterobimetallic Ru-Ag(NHC) complexes. PMID:25338159

Cesari, C; Conti, S; Zacchini, S; Zanotti, V; Cassani, M C; Mazzoni, R

2014-12-14

8

Electrochemical flow-reactor for expedient synthesis of copper-N-heterocyclic carbene complexes.  

Science.gov (United States)

An electrochemical flow-cell for highly efficient and selective generation of Cu(I)-N-heterocyclic carbene complexes under neutral and ambient conditions is reported. The feasibility of the flow-cell is demonstrated through the electrochemical synthesis of [Cu(IMes)Cl] and subsequent in situ flow directly into hydrosilylation reactions, with equal efficiency to the purified catalyst. PMID:25476754

Chapman, Michael R; Shafi, Yarseen M; Kapur, Nikil; Nguyen, Bao N; Willans, Charlotte E

2014-12-23

9

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

Science.gov (United States)

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). PMID:17283796

Kluser, Evelyne; Neels, Antonia; Albrecht, Martin

2006-11-21

10

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

OpenAIRE

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

11

Synthesis and characterization of N-heterocyclic carbene complexes of uranium(III).  

Science.gov (United States)

Reaction of [(((Ad)ArO)(3)tacn)U(III)] (1) or [((Me(3)Si)(2)N)(3)U(III)] (3) with tetramethylimidazol-2-ylidene (Me(4)IMC:) yields novel N-heterocyclic carbene complexes [(((Ad)ArO)(3)tacn)U(III)(Me(4)IMC:)] (2) and [((Me(3)Si)(2)N)(3)U(III)(Me(4)IMC:)] (4). Uranium complexes 2 and 4 represent the first examples of compounds with an N-heterocyclic carbene ligand coordinated to a low-valent uranium center. The paramagnetic complexes 1, 2, and 4 were characterized by (1)H NMR, UV-vis-NIR, and EPR spectroscopy as well as SQUID magnetization measurements and X-ray diffraction analyses. DFT studies indicate a significant degree of pi-bonding in the U(III)-carbene entity. PMID:14753804

Nakai, Hidetaka; Hu, Xile; Zakharov, Lev N; Rheingold, Arnold L; Meyer, Karsten

2004-02-01

12

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

OpenAIRE

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

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

2010-01-01

13

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

OpenAIRE

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

Ortega-arizmendi, Aldo I.; Eugenia Aldeco-Pérez; Erick Cuevas-Yañez

2013-01-01

14

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

Science.gov (United States)

Due to the properties of silver as an antimicrobial, our research group has synthesized many different silver carbene complexes. Two new silver N-heterocyclic carbene complexes derived from 4,5-dichloroimidazole and theobromine bearing methyl benzoate substituents were synthesized by in situ carbene formation using silver acetate as the base in the reaction. The new compounds were fully characterized by several methods including NMR spectroscopy and X-ray crystallography. Preliminary antimicrobial efficacy studies against Pseudomonas aeruginosa, Staphylococcus aureus, and Escherichia coli were conducted. The results of this study demonstrated antimicrobial efficacy of the two complexes comparable to silver nitrate, showing their potential for use in the treatment of bacterial infections. PMID:21218156

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

2010-01-01

15

N-Heterocyclic Carbene Complexes of Rh: Reaction With Dioxygen Without Oxidation  

Energy Technology Data Exchange (ETDEWEB)

The reaction of oxygen with rhodium complexes containing N-heterocyclic carbenes was found to give dioxygen complexes with rare square planar geometries and unusually short O-O bond lengths. Analysis of the bonding in these complexes by Rh L-edge X-ray absorption spectroscopy (XAS), Raman spectroscopy, and DFT calculations provides evidence for a bonding model in which singlet oxygen is bound to a Rh(I) d{sup 8} metal complex, rather than the more common Rh(III) d{sup 6} peroxo species with octahedral geometry and O-O bond lengths in the 1.4-1.5 {angstrom} range.

Praetorius, J.M.; Allen, D.P.; Wang, R.; Webb, J.D.; Grein, F.; Kennepohl, P.; Crudden, C.M.

2009-05-21

16

N-heterocyclic carbene complexes of Rh: reaction with dioxygen without oxidation.  

Science.gov (United States)

The reaction of oxygen with rhodium complexes containing N-heterocyclic carbenes was found to give dioxygen complexes with rare square planar geometries and unusually short O-O bond lengths. Analysis of the bonding in these complexes by Rh L-edge X-ray absorption spectroscopy (XAS), Raman spectroscopy, and DFT calculations provides evidence for a bonding model in which singlet oxygen is bound to a Rh(I) d8 metal complex, rather than the more common Rh(III) d6 peroxo species with octahedral geometry and O-O bond lengths in the 1.4-1.5 A range. PMID:18321109

Praetorius, Jeremy M; Allen, Daryl P; Wang, Ruiyao; Webb, Jonathan D; Grein, Friedrich; Kennepohl, Pierre; Crudden, Cathleen M

2008-03-26

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Catalytic homogeneous hydrogenation of olefins using N-heterocyclic carbene complexes of rhodium and iridium  

OpenAIRE

A synthesis of a small library of rhodium(I) and iridium(I) complexes that combine different types of N-heterocyclic carbenes with pyridines and phosphines was developed. The complexes were tested for the hydrogenation of the simple olefins, 1-octene, cyclohexene, 1-methyl-1-cyclohexene and 2,3-dimethyl-2-butene. Three major trends were observed: first, complexes having iridium and a combination of a phosphine and a NHC prove to be more effective than those with a combination of a pyridine an...

Vazquez-serrano, Leslie D.

2004-01-01

18

Complexes of borane and N-heterocyclic carbenes: a new class of radical hydrogen atom donor.  

Science.gov (United States)

Calculations suggest that complexes of borane with N-heterocyclic carbenes (NHC) have B-H bond dissocation energies more then 20 kcal/mol less than free borane, diborane, borane-THF, and related complexes. Values are in the range of popular radical hydrogen atom donors like tin hydrides (70-80 kcal/mol). The resulting prediction that NHC borane complexes could be used as radical hydrogen atom donors was verified by radical deoxygenations of xanthates by using either AIBN or triethylborane as initiator. PMID:18611014

Ueng, Shau-Hua; Brahmi, Malika Makhlouf; Derat, Etienne; Fensterbank, Louis; Lacôte, Emmanuel; Malacria, Max; Curran, Dennis P

2008-08-01

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N-heterocyclic carbene complexes of au, pd, and pt as effective catalysts in organic synthesis.  

Science.gov (United States)

N-Heterocyclic carbenes (NHC) have been developed in the last 20 years as effective alternatives to classical tertiary phosphines in transition metal-catalyzed transformations. The rapid development of this area is a result of synergistic interactions between experimental and computational chemists. Indeed, computer modeling has proven extremely useful in rationalizing large amount of experimental data, and thus has permitted to accelerate the pace at which this chemistry has been developed. In this review, we will discuss catalytic transformations involving NHC-containing gold, platinum, and palladium complexes. Particular attention is drawn to the fundamental insights that computational chemistry provided to rationalize mechanistic aspects of these processes. PMID:21290215

Correa, Andrea; Nolan, Steven P; Cavallo, Luigi

2011-01-01

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Electronic structure and ionization energies of palladium and platinum N-heterocyclic carbene complexes.  

OpenAIRE

Density functional methods have been used to calculate the geometries, electronic structure and ionization energies (IE) of N-heterocyclic carbene complexes of palladium and platinum, [M(CN2R2C2H2)2](M = Pd, Pt; R = H, Me, Bu t). Agreement with X-ray structures (R = Bu t) was good. Calculated IE agreed well with the photoelectron (PE) spectra (R = Bu t); metal bands were calculated to be within 0.25 eV of the experimental values, whereas the higher lying ligand bands deviated by up to 0.9 eV....

Green, Jc; Herbert, Bj

2005-01-01

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'Classical' and 'Abnormal' Bonding in Tin (II) N-Heterocyclic Carbene Complexes  

OpenAIRE

Reaction of Sn(OTf)2 (OTf-?OSO2CF3-) with one and two equivalents of the N-heterocyclic carbene (NHC) 1,3-bis(2,6-diisopropylphenyl)-imidazol-2-ylidene (IPr) yielded the complexes [Sn(IPr)(OTf)2] (1) and [Sn(IPr)(aIPr)(OTf)][OTf] (2), respectively. Both species were characterised by single crystal X-ray diffraction, multi-element NMR spectroscopy, and elemental analysis. Both compounds display an NHC ligand bonded to the tin(ii) metal centre via the C2 carbon in a 'classical' mode, while 2 ...

Turbervill, Rsp; Goicoechea, Jm

2013-01-01

22

N-Heterocyclic Carbene Complexes in Dehalogenation Reactions  

Science.gov (United States)

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

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

23

Electrocatalytic Reduction of CO2 with Palladium Bis-N-heterocyclic Carbene Pincer Complexes.  

Science.gov (United States)

A series of pyridine- and lutidine-linked bis-N-heterocyclic carbene (NHC) palladium pincer complexes were electrochemically characterized and screened for CO2 reduction capability with 2,2,2-trifluoroethanol, acetic acid, or 2,2,2-trifluoroacetic acid (TFA) as proton sources. The lutidine-linked pincer complexes electrocatalytically reduce CO2 to CO at potentials as low as -1.6 V versus Ag/AgNO3 in the presence of TFA. The one-electron reduction of these complexes is shown to be chemically reversible, yielding a monometallic species, with density functional theory studies indicating charge storage on the redox-active ligand, thus addressing a major source of deactivation in earlier triphosphine electrocatalysts. PMID:25337973

Therrien, Jeffrey A; Wolf, Michael O; Patrick, Brian O

2014-12-15

24

Proton-induced generation of remote N-heterocyclic carbene-ru complexes.  

Science.gov (United States)

The proton-induced Ru?C bond variation, which was previously found to be relevant in the water oxidation, has been investigated by using cyclometalated ruthenium complexes with three phenanthroline (phen) isomers. The designed complexes, [Ru(bpy)2 (1,5-phen)](+) ([2](+) ), [Ru(bpy)2 (1,6-phen)](+) ([3](+) ), and [Ru(bpy)2 (1,7-phen)](+) ([4](+) ) were newly synthesized and their structural and electronic properties were analyzed by various spectroscopy and theoretical protocols. Protonation of [4](+) triggered profound electronic structural change to form remote N-heterocyclic carbene (rNHC), whereas protonation of [2](+) and [3](+) did not affect their structures. It was found that changes in the electronic structure of phen beyond classical resonance forms control the rNHC behavior. The present study provides new insights into the ligand design of related ruthenium catalysts. PMID:25382152

Fukushima, Takashi; Fukuda, Ryoichi; Kobayashi, Katsuaki; Caramori, Giovanni F; Frenking, Gernot; Ehara, Masahiro; Tanaka, Koji

2015-01-01

25

Group 12 Metal Complexes of N-Heterocyclic Ditopic Carbanionic Carbenes  

OpenAIRE

Reaction of the N-heterocyclic carbene 1,3-bis(2,6-diisopropylphenyl) imidazol-2-ylidene (IPr) with M(mes)2 (M = Zn, Cd) in diethyl ether afforded the Lewis acid-base adducts [M(IPr)(mes)2] (M = Zn (1), Cd (2)) in quantitative yields. An analogous reaction between Hg(mes)2 and IPr failed to form the desired 1:1 adduct, [Hg(IPr)(mes)2], as evidenced by NMR spectroscopy. Reduction of 1 and 2 with KC8 afforded K+ salts of the anionic complexes [{:C[N(2,6-iPr 2C6H3)]2(CH)C}2M(mes)] - (M = Zn (3),...

Waters, Jb; Turbervill, Rsp; Goicoechea, Jm

2013-01-01

26

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

Science.gov (United States)

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. PMID:23209531

Gao, Ting-Ting; Jin, Ai-Ping; Shao, Li-Xiong

2012-01-01

27

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

OpenAIRE

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.

Gao, Ting-ting; Jin, Ai-ping; Shao, Li-xiong

2012-01-01

28

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

Science.gov (United States)

Summary 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. PMID:23209531

Gao, Ting-Ting; Jin, Ai-Ping

2012-01-01

29

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

Directory of Open Access Journals (Sweden)

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

30

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

Directory of Open Access Journals (Sweden)

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

31

N-Heterocyclic Carbenes: Versatile Second Cyclometalated Ligands for Neutral Iridium(III) Heteroleptic Complexes.  

Science.gov (United States)

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

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

2015-01-01

32

Cytotoxic gold(I) N-heterocyclic carbene complexes with phosphane ligands as potent enzyme inhibitors.  

Science.gov (United States)

Organometallic gold complexes with N-heterocyclic carbene (NHC) ligands have been demonstrating promising properties as novel anticancer agents. Gold(I) NHC complexes containing different phosphanes as secondary ligands were shown to trigger strong cytotoxic effects in cancer cells, and their effective uptake into the cells was quantified by atomic absorption spectroscopy. Moreover, the new compounds strongly inhibited the activity of the seleno-enzyme thioredoxin reductase (TrxR) and of the zinc-finger enzyme poly(ADP-ribose) polymerase?1 (PARP-1). In the case of TrxR inhibition, their activity depended clearly on the size of the alkyl/aryl residues of phosphorus atoms. Density functional theory (DFT) calculations showed that the Au-P bond of the triphenylphosphane complex [Au(I) (NHC)(PPh3 )]I had a lower bond dissociation energy compared to trialkylphosphane complexes [Au(I) (NHC)(PR3 )]I, indicating a higher kinetic reactivity of this particular compound. In fact, [Au(I) (NHC)(PPh3 )]I triggered an enhanced inhibitory activity against PARP-1. PMID:24677779

Rubbiani, Riccardo; Salassa, Luca; de Almeida, Andreia; Casini, Angela; Ott, Ingo

2014-06-01

33

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

2014-12-21

34

Chelated Bis-N-heterocyclic Carbene Platinum and Palladium Units as Tunable Components of Multinuclear Complexes.  

Science.gov (United States)

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

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

2015-01-20

35

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

36

Carbene rearrangements in three-coordinate N-heterocyclic carbene complexes of cobalt(II) bis(trimethylsilyl)amide.  

Science.gov (United States)

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

37

A chiral 6-membered N-heterocyclic carbene copper(I) complex that induces high stereoselectivity.  

Science.gov (United States)

A chiral 6-membered annulated N-heterocyclic (6-NHC) copper complex that catalyzes ?-borylations with high yield and enantioselectivity was developed. The chiral 6-NHC copper complex is easy to prepare on the gram scale and is very active, showing 10,000 turnovers at 0.01 mol % of catalyst without significant decrease of enantioselectivity and with useful reaction rates. PMID:20919706

Park, Jin Kyoon; Lackey, Hershel H; Rexford, Matthew D; Kovnir, Kirill; Shatruk, Michael; McQuade, D Tyler

2010-11-01

38

A benzimidazole-based N-heterocyclic carbene derived from 1,10-phenanthroline.  

Science.gov (United States)

[reaction: see text] A catalytically active palladium-complexed tetracyclic N-heterocyclic carbene (NHC) was prepared in three steps from commercially available 1,10-phenanthroline by using a reduction-cyclization-deprotonation sequence. The new carbene framework is a prototype for the development of a series of chiral N-heterocyclic carbenes. PMID:15387568

Metallinos, Costa; Barrett, Fred B; Chaytor, Jennifer L; Heska, Mary E A

2004-09-30

39

C?C coupling of ketones with methanol catalyzed by a N-heterocyclic carbene-phosphine iridium complex.  

Science.gov (United States)

An N-heterocyclic carbene-phosphine iridium complex system was found to be a very efficient catalyst for the methylation of ketone via a hydrogen transfer reaction. Mild conditions together with low catalyst loading (1?mol?%) were used for a tandem process which involves the dehydrogenation of methanol, C?C bond formation with a ketone, and hydrogenation of the new generated double bond by iridium hydride to give the alkylated product. Using this iridium catalyst system, a number of branched ketones were synthesized with good to excellent conversions and yields. PMID:25589169

Quan, Xu; Kerdphon, Sutthichat; Andersson, Pher G

2015-02-23

40

Activation of carbon dioxide and carbon disulfide by a scandium N-heterocyclic carbene complex.  

Science.gov (United States)

A Sc NHC complex readily activates three equivalents of CO2 showing 'Frustrated Lewis Pair' type reactivity with each metal-carbene bond, but whilst CS2 is also activated by the labile carbenes, no metal involvement is observed. PMID:24162511

Arnold, Polly L; Marr, Isobel A; Zlatogorsky, Sergey; Bellabarba, Ronan; Tooze, Robert P

2014-01-01

41

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

Science.gov (United States)

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

42

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

Directory of Open Access Journals (Sweden)

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

Dan Yuan

2012-03-01

43

Phosphorescent iridium(III)-bis-N-heterocyclic carbene complexes as mitochondria-targeted theranostic and photodynamic anticancer agents.  

Science.gov (United States)

Mitochondria-targeted compounds represent a promising approach to target tumors selectively and overcome resistance to current anticancer therapies. In this work, three cyclometalated iridium(III) complexes (1-3) containing bis-N-heterocyclic carbene (NHC) ligands have been explored as theranostic and photodynamic agents targeting mitochondria. These complexes display rich photophysical properties, which greatly facilitates the study of their intracellular fate. All three complexes are more cytotoxic than cisplatin against the cancer cells screened. 1-3 can penetrate into human cervical carcinoma (HeLa) cells quickly and efficiently, and they can carry out theranostic functions by simultaneously inducing and monitoring the morphological changes in mitochondria. Mechanism studies show that these complexes exert their anticancer efficacy by initiating a cascade of events related to mitochondrial dysfunction. Additionally, they display up to 3 orders of magnitude higher cytotoxicity upon irradiation at 365 nm, which is so far the highest photocytotoxic responses reported for iridium complexes. PMID:25477176

Li, Yi; Tan, Cai-Ping; Zhang, Wei; He, Liang; Ji, Liang-Nian; Mao, Zong-Wan

2015-01-01

44

Sterically Encumbered Iridium Bis(N-heterocyclic carbene) Systems: Multiple C-H Activation Processes and Isomeric Normal/Abnormal Carbene Complexes  

OpenAIRE

The reaction of [Ir(coe)2Cl]2 (coe = cyclooctene) with the N-heterocyclic carbene N,N?-bis(2,6diisopropylphenyl)imidazol-2- ylidene (IPr) in tetrahydrofuran under anaerobic conditions leads to the formation of two main products, the planar four-coordinate Ir(I) complex Ir(IPr)(IPr?)Cl (1) formed by dehydrogenation of one of the IPr isopropyl substituents (to give the mixed NHC/alkene donor IPr?) and the trigonal bipyramidal Ir(III) system Ir(IPr)(aIPr)(H)2Cl (6), which features both "no...

Tang, Cy; Smith, W.; Vidovic, D.; Thompson, Al; Chaplin, Ab; Aldridge, S.

2009-01-01

45

N-Heterocyclic Carbene-Catalyzed Oxidations  

OpenAIRE

N-Heterocyclic carbenes catalyze the oxidation of allylic and benzylic alcohols as well as saturated aldehydes to esters with manganese(IV) oxide in excellent yields. A variety of esters can be synthesized, including protected carboxylates. The oxidation proceeds under mild conditions, with low loadings of a simple triazolium salt pre-catalyst in the presence of base. Substrates containing potentially epimerizable centers are oxidized while preserving stereochemical integrity. The acyl triazo...

Maki, Brooks E.; Chan, Audrey; Phillips, Eric M.; Scheidt, Karl A.

2009-01-01

46

Mixed phosphine/N-heterocyclic carbene palladium complexes: synthesis, characterization and catalytic use in aqueous Suzuki-Miyaura reactions.  

Science.gov (United States)

A series of N-heterocyclic carbene (NHC)/PR3 palladium(II) and palladium(0) complexes has been synthesized and fully characterized. X-ray crystallographic data have allowed comparison of ligand steric properties. The NHC ligand was found to vary its steric properties as a function of the phosphine co-ligand. These complexes display interesting catalytic properties in the Suzuki-Miyaura reaction performed in aqueous media. The pre-catalyst [PdCl2(IPr)(XPhos)] (IPr = N,N'-bis-(2,6-diisopropylphenyl)imidazol-2-ylidene; XPhos = 2-dicyclohexylphosphino-2',4',6'-triisopropylbiphenyl) was found to be the most efficient system, promoting the coupling of a wide range of aryl chlorides with boronic acids in aqueous media with a typical catalyst loading of 0.03 mol%. PMID:23348096

Schmid, Thibault E; Jones, Dale C; Songis, Olivier; Diebolt, Olivier; Furst, Marc R L; Slawin, Alexandra M Z; Cazin, Catherine S J

2013-05-28

47

On the electronic impact of abnormal C4-bonding in N-heterocyclic carbene complexes  

OpenAIRE

Sterically similar palladium dicarbene complexes have been synthesized that comprise permethylated dicarbene ligands which bind the metal center either in a normal coordination mode via C2 or abnormally via C4. Due to the strong structural analogy of the complexes, differences in reactivity patterns may be attributed to the distinct electronic impact of normal versus abnormal carbene bonding, while stereoelectronic effects are negligible. Unique reactivity patterns have been identified for th...

Heckenroth, M.; Neels, A.; Garnier, M. G.; Aebi, P.; Ehlers, A. W.; Albrecht, M.

2009-01-01

48

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

Science.gov (United States)

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

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

2014-07-21

49

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

Science.gov (United States)

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

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

2014-10-13

50

Novel benzyl-substituted N-heterocyclic carbene-silver acetate complexes: synthesis, cytotoxicity and antibacterial studies.  

Science.gov (United States)

From the reaction of 1-methylimidazole (1a), 4,5-dichloro-1H-imidazole (1b(I)) and 1-methylbenzimidazole (1c) with p-cyanobenzyl bromide (2a), non-symmetrically substituted N-heterocyclic carbene (NHC) [(3a-c)] precursors, 5,6-dimethyl-1H-benzimidazole (1d) and 4,5-diphenyl-1H-imidazole (1e) with p-cyanobenzyl bromide (2a) and benzyl bromide (2b), symmetrically substituted N-heterocyclic carbene (NHC) [(3d-f)] precursors were synthesised. These NHC-precursors were then reacted with silver(i) acetate to yield the NHC-silver complexes (1-methyl-3-(4-cyanobenzyl)imidazole-2-ylidene)silver(i)acetate (4a), (4,5-dichloro-1-(4-cyanobenzyl)-3-methyl)imidazole-2-ylidene)silver(i)acetate (4b), (1-methyl-3-(4-cyanobenzyl)benzimidazole-2-ylidene)silver(i)acetate (4c), (1,3-bis(4-cyanobenzyl)5,6-dimethylbenzimidazole-2-ylidene) silver(i) acetate (4d), (1,3-dibenzyl-5,6-dimethylbenzimidazole-2-ylidene) silver(i) acetate (4e) and (1,3-dibenzyl-4,5-diphenylimidazol-2-ylidene) silver(i) acetate (4f) respectively. Three NHC-precursors 3c-e and four NHC-silver complexes 4b and 4d-f were characterised by single crystal X-ray diffraction. Preliminary in vitro antibacterial activity of the NHC-precursors and NHC-silver complexes was investigated against Gram-positive bacteria Staphylococcus aureus, and Gram-negative bacteria Escherichia coli using the qualitative Kirby-Bauer disk-diffusion method. NHC-silver complexes have shown very high antibacterial activity compared to the NHC-precursors. All six NHC-silver complexes were tested for their cytotoxicity through MTT based in vitro tests on the human renal-cancer cell line Caki-1 in order to determine their IC?? values. NHC-silver complexes 4a-f were found to have IC?? values of 6.2 (±1.0), 7.7 (±1.6), 1.2 (±0.6), 10.8 (±1.9), 24.2 (±1.8) and 13.6 (±1.0) ?M, respectively. These values represent improved cytotoxicity against Caki-1, most notably for 4c, which is a three times more cytotoxic than cisplatin (IC?? value = 3.3 ?M) itself. PMID:21135954

Patil, Siddappa; Deally, Anthony; Gleeson, Brendan; Müller-Bunz, Helge; Paradisi, Francesca; Tacke, Matthias

2011-01-01

51

Metal Complexes of a Boron-Dipyrromethene (BODIPY)-Tagged N-Heterocyclic Carbene (NHC) as Luminescent Carbon Monoxide Chemodosimeters.  

Science.gov (United States)

Several metal complexes with a boron dipyrromethene (BODIPY)-functionalized N-heterocyclic carbene (NHC) ligand 4 were synthesized. The fluorescence in [(4)(SIMes)RuCl2 (ind)] complex is quenched (?=0.003), it is weak in [(4)PdI2 (Clpy)] (?=0.033), and strong in [(4)AuI] (?=0.70). The BODIPY-tagged complexes can experience pronounced changes in the brightness of the fluorophore upon ligand-exchange and ligand-dissociation reactions. Complexes [(4)MX(1,5-cyclooctadiene)] (M=Rh, Ir; X=Cl, I; ?=0.008-0.016) are converted into strongly fluorescent complexes [(4)MX(CO)2 ] (?=0.53-0.70) upon reaction with carbon monoxide. The unquenching of the Rh and Ir complexes appears to be a consequence of the decreased electron density at Rh or Ir in the carbonyl complexes. In contrast, the substitution of an iodo ligand in [(4)AuI] by an electron-rich thiolate decreases the brightness of the BODIPY fluorophore, rendering the BODIPY as a highly sensitive probe for changes in the coordination sphere of the transition metal. PMID:25487747

Kos, Pavlo; Plenio, Herbert

2015-01-12

52

Copper(i), silver(i) and gold(i) complexes of N-heterocyclic carbene-phosphinidene.  

Science.gov (United States)

N-heterocyclic carbene stabilized phosphinidene IMes·PPh has been used as a bridging ligand to isolate a group of closely related molecules involving all three coinage metal ions. The bis-copper(i) chloride, bis-silver(i) chloride and bis-copper(i) bromide adducts of IMes·PPh crystallize as halide ion bridged octanuclear molecules while the [IMes·PPh](AuCl)2 adduct remains monomeric. These molecules feature long P-C(carbene) bonds in the range 1.822(3)-1.843(4) Å, near the typical P-C single bond length region. PMID:25410496

Adiraju, Venkata A K; Yousufuddin, Muhammed; Rasika Dias, H V

2014-11-20

53

N-heterocyclic carbene gold(i) and silver(i) complexes bearing functional groups for bio-conjugation.  

Science.gov (United States)

This work describes several synthetic approaches to append organic functional groups to gold and silver N-heterocyclic carbene (NHC) complexes suitable for applications in biomolecule conjugation. Carboxylate appended NHC ligands (3) lead to unstable Au(I) complexes that convert into bis-NHC species (4). A benzyl protected carboxylate NHC-Au(I) complex was synthesized but deprotection to produce the carboxylic acid functionality could not be achieved. A small library of new alkyne functionalized NHC proligands were synthesized and used for subsequent silver and gold metalation reactions. The alkyne appended NHC gold complex readily reacts with benzyl azide in a copper catalyzed azide-alkyne cycloaddition reaction to form the triazole appended NHC gold complex . Cell cytotoxicity studies were performed on DLD-1 (colorectal adenocarcinoma), Hep-G2 (hepatocellular carcinoma), MCF-7 (breast adenocarcinoma), CCRF-CEM (human T-Cell leukemia), and HEK (human embryonic kidney). Complete spectroscopic characterization of the ligands and complexes was achieved using (1)H and (13)C NMR, gHMBC, ESI-MS, and combustion analysis. PMID:25490699

Garner, Mary E; Niu, Weijia; Chen, Xigao; Ghiviriga, Ion; Abboud, Khalil A; Tan, Weihong; Veige, Adam S

2014-12-23

54

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

Directory of Open Access Journals (Sweden)

Full Text Available The title complex, aqua[1,3-bis(2,6-diisopropylphenylimidazol-2-ylidene](?4-cycloocta-1,5-dienerhodium(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 between the aqua ligand H atoms and the BF4? F atoms.

Ashley L. Huttenstine

2011-09-01

55

Tungsten(VI) N-Heterocyclic Carbene Complexes: Synthetic, Structural, and Computational Study  

Science.gov (United States)

The reaction of WOCl4 with 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene (Idipp) leads to an orange solid whose spectroscopic data are consistent with the 1:1 adduct [WOCl4(Idipp)]. Computational studies at the DFT level further support this formulation. Exposure of this compound to the atmosphere results in rapid hydrolysis to various imidazolium salts. If air diffuses very slowly into solutions of [WOCl4(Idipp)], it also undergoes slow hydrolysis to form [WO2Cl2(Idipp)]. This has been crystallographically characterized and is the first five-coordinate, 1:1 adduct of WO2Cl2. This complex has also been subject to DFT calculations, and its metal–ligand bonding has been explored. The carbene–metal interaction is primarily ?-donor in nature. The mechanism of the hydrolysis has also been probed by computational methods, revealing a plausible, low-energy reaction pathway. PMID:24882916

2011-01-01

56

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

Science.gov (United States)

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

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

2008-03-17

57

Quinone-annulated N-heterocyclic carbene-transition-metal complexes: observation of pi-backbonding using FT-IR spectroscopy and cyclic voltammetry.  

Science.gov (United States)

A new N-heterocyclic carbene architecture comprising a 1,4-naphthoquinone annulated to 1,3-dimesitylimidazolylidene (NpQ-NHC) was synthesized in two high yielding steps from commercially available starting materials. The free NpQ-NHC was characterized (solution and solid-state) and was used to synthesize various Rh and Ag complexes that ranged in pi-electron density. Enabled by the quinone moiety, the pi-systems of these complexes were analyzed using infrared spectroscopy and cyclic voltammetry. In contrast to previous reports, pi-backbonding was found to be non-negligible and was directly influenced by the metal's electronic character. PMID:17177396

Sanderson, Matthew D; Kamplain, Justin W; Bielawski, Christopher W

2006-12-27

58

Monomeric bis(anilido)iron(II) Complexes with N-heterocyclic carbene ligation: synthesis, characterization, and redox reactivity toward aryl halides.  

Science.gov (United States)

Using monodentate N-heterocyclic carbenes as the ancillary ligands, seven monomeric bis(anilido)iron(II) complexes [(IPr(2)Me(2))(2)Fe(NHAr)(2)] (IPr(2)Me(2) = 2,5-diisopropyl-3,4-dimethylimidazol-1-ylidene; Ar = Ph, C(6)H(4)-2-Pr(i), Mes, C(6)H(3)-2,6-Cl(2), Dipp) and [(IPr)Fe(NHAr)(2)] (IPr = 2,5-di(2,6-diisopropylphenyl)imidazol-1-ylidene; Ar = C(6)H(3)-2,6-Cl(2), Dipp) have been prepared by the one-pot reactions of [Fe(Mes)(2)](2) with the corresponding N-heterocyclic carbenes, and anilines. These high-spin diamido complexes have been fully characterized by (1)H NMR, solution magnetic susceptibility, UV-vis, IR, X-ray diffraction, cyclic voltammetry, as well as elemental analysis. The strong affinity of the N-heterocyclic carbene ligands toward ferrous centers, and the steric protection exerted by the NHC ligands are the key factors to stabilize these bis(anilido)iron complexes in a monomeric manner. Reactivity studies revealed the four-coordinate complex [(IPr(2)Me(2))(2)Fe(NHMes)(2)] can react with 1 equiv of 1-iodo-3,5-dimethylbenzene or 1-bromo-3,5-dimethylbenzene in C(6)D(6) and THF-d(8) to furnish 1-C(6)D(5)-3,5-Me(2)C(6)H(3), and 5-D-1,3-Me(2)C(6)H(3), respectively. Under similar conditions, the three-coordinate compound [(IPr)Fe(NHDipp)(2)] is inert toward these halides. PMID:23249144

Wang, Xiaojie; Mo, Zhenbo; Xiao, Jie; Deng, Liang

2013-01-01

59

N-Heterocyclic carbene-palladium(II)-1-methylimidazole complex catalyzed Suzuki-Miyaura coupling of benzylic chlorides with arylboronic acids or potassium phenyltrifluoroborate in neat water.  

Science.gov (United States)

An easily available N-heterocyclic carbene-palladium(II)-1-methylimidazole complex showed efficient catalytic activity in the Suzuki-Miyaura coupling of benzylic chlorides with arylboronic acids or potassium phenyltrifluoroborate in neat water under mild conditions, providing an alternative method for the synthesis of diarylmethane derivatives, which widely exist in molecules with pharmaceutical activities and are also frequently found as subunits in supramolecules. Under the optimal conditions, all reactions performed well to give the desired products in moderate to almost quantitative yields in an environmentally benign medium within 12 h, extending their applications toward potentially industrial processes. PMID:23381388

Zhang, Yun; Feng, Meng-Ting; Lu, Jian-Mei

2013-04-14

60

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

61

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

Science.gov (United States)

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

62

Gold(III) N-heterocyclic carbene complexes mediated synthesis of ?-enaminones from 1,3-dicarbonyl compounds and aliphatic amines.  

Science.gov (United States)

A series of gold(III) N-heterocyclic carbene complexes [1-(R(1))-3-(R(2))imidazol-2-ylidene]AuBr(3) [R(1) = i-Pr, R(2) = CH(2)Ph (1c); R(1) = mesityl, R(2) = CH(2)Ph (2c); R(1) = i-Pr, R(2) = CH(2)COt-Bu (3c), and R(1) = t-Bu, R(2) = CH(2)COt-Bu (4c)] act as effective precatalysts in the synthesis of ?-enaminones from 1,3-dicarbonyl compounds and primary amines under ambient conditions. Specifically the 1c-4c complexes efficiently catalyzed the condensation of a variety of cyclic as well as acyclic 1,3-dicarbonyl compounds, namely, acetyl acetone, benzoylacetone, 2-acetylcyclopentanone, and ethyl-2-oxocyclopentanecarboxylate with primary aliphatic amines, viz., methylamine, ethylamine, n-propylamine, i-propylamine, and n-butylamine, yielding ?-enamines at room temperature. Interestingly enough, the more electrophilic gold(III) 1c-4c complexes exhibited superior activity in comparison to the gold(I) counterparts 1b-4b. A comparison along a representative 4a-c series further underscored the importance of gold in the reaction as both the gold(I) 4b and gold(III) 4c complexes were more effective than the silver analogue 4a. The density functional theory (DFT) study revealed that the strong ?-donating nature of the N-heterocyclic carbene ligand results in a strong C(carbene)-Au(III) interaction in the 1c-4c complexes. PMID:21254751

Samantaray, Manoja K; Dash, Chandrakanta; Shaikh, Mobin M; Pang, Keliang; Butcher, Ray J; Ghosh, Prasenjit

2011-03-01

63

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

64

Dual reactivity of N-heterocyclic carbenes towards copper(II) salts.  

Science.gov (United States)

Complexes of N-heterocyclic carbenes (NHCs) with copper(II) halogenides are unstable. Upon formation, these complexes decompose to give haloamidinium salts. Contrastingly, O-substituted copper(II) NHC complexes are fairly stable. A series of new five-, six- and seven-membered ring NHC complexes of Cu(OAc)(2) have been synthesised and characterised in the solid state. PMID:21327287

Kolychev, Eugene L; Shuntikov, Viacheslav V; Khrustalev, Victor N; Bush, Alexander A; Nechaev, Mikhail S

2011-03-28

65

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

Science.gov (United States)

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

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

2014-04-23

66

N-heterocyclic carbenes in porous networks  

OpenAIRE

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

67

Synthesis and Isolation of a Stable, Axially-Chiral Seven-Membered N-Heterocyclic Carbene  

OpenAIRE

A chiral seven-membered N-heterocyclic carbene (NHC) has been synthesized from its phenol adduct (NHC-HOPh) by a novel base-induced ?-elimination method, and its donor strength has been determined from the IR stretching frequencies of the NHC-Rh(CO)2Cl complex.

Scarborough, Christopher C.; Guzei, Ilia A.; Stahl, Shannon S.

2009-01-01

68

Stepwise Strategy to Cyclometallated Pt(II) Complexes with N-Heterocyclic Carbene Ligands: A Luminescence Study on New ?-Diketonate Complexes.  

Science.gov (United States)

The imidazolium salt 3-methyl-1-(naphthalen-2-yl)-1H-imidazolium iodide (2) has been treated with silver(I) oxide and [{Pt(?-Cl)(?(3) -2-Me-C3 H4 )}2 ] (?(3) -2-Me-C3 H4 =?(3) -2-methylallyl) to give the intermediate N-heterocyclic carbene complex [PtCl(?(3) -2-Me-C3 H4 )(H$\\widehat{CC}$*-?C*)] (3) (H$\\widehat{CC}$*-?C*=3-methyl-1-(naphthalen-2-yl)-1H-imidazol-2-ylidene). Compound 3 undergoes regiospecific cyclometallation at the naphthyl ring of the NHC ligand to give the five-membered platinacycle compound [{Pt(?-Cl)($\\widehat{CC}$*)}2 ] (4). Chlorine abstraction from 4 with ?-diketonate Tl derivatives rendered the corresponding neutral compounds [Pt($\\widehat{CC}$*)(L-O,O')] {L=acac (HL=acetylacetone) 5, phacac (HL=1,3-diphenyl-1,3-propanedione) 6, hfacac (HL=hexafluoroacetylacetone) 7}. All of the compounds (3-7) were fully characterized by standard spectroscopic and analytical methods. X-ray diffraction studies were performed on 5-7, revealing short Pt?Pt and ?-? interactions in the solid-state structure. The influence of the R-substituents of the ?-diketonate ligand on the photophysical properties and the use of the most efficient emitter, 5, as phosphor converter has also been studied. PMID:25412763

Fuertes, Sara; García, Hector; Perálvarez, Mariano; Hertog, Wim; Carreras, Josep; Sicilia, Violeta

2014-11-20

69

Water-soluble luminescent cyclometalated gold(III) complexes with cis-chelating bis(N-heterocyclic carbene) ligands: synthesis and photophysical properties.  

Science.gov (United States)

A new class of cyclometalated Au(III) complexes containing various bidentate C-deprotonated C^N and cis-chelating bis(N-heterocyclic carbene) (bis-NHC) ligands has been synthesized and characterized. These are the first examples of Au(III) complexes supported by cis-chelating bis-NHC ligands. [Au(C^N)(bis-NHC)] complexes display emission in solutions under degassed condition at room temperature with emission maxima (?max ) at 498-633?nm and emission quantum yields of up to 10.1?%. The emissions are assigned to triplet intraligand (IL) ???* transitions of C^N ligands. The Au(III) complex containing a C^N (C-deprotonated naphthalene-substituted quinoline) ligand with extended ?-conjugation exhibits prompt fluorescence and phosphorescence of comparable intensity with ?max at 454 and 611?nm respectively. With sulfonate-functionalized bis-NHC ligand, four water-soluble luminescent Au(III) complexes, including those displaying both fluorescence and phosphorescence, were prepared. They show similar photophysical properties in water when compared with their counterparts in acetonitrile. The long phosphorescence lifetime of the water-soluble AuIII complex with C-deprotonated naphthalene-substituted quinoline ligand renders it to function as ratiometric sensor for oxygen. Inhibitory activity of one of these water-soluble Au(III) complexes towards deubiquitinase (DUB) UCHL3 has been investigated; this complex also displayed a significant inhibitory activity with IC50 value of 0.15??M. PMID:24957269

Hung, Faan-Fung; To, Wai-Pong; Zhang, Jing-Jing; Ma, Chensheng; Wong, Wai-Yeung; Che, Chi-Ming

2014-07-01

70

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

71

Reactivity of coordinatively unsaturated bis(N-heterocyclic carbene) Pt(II) complexes toward H(2). Crystal structure of a 14-electron Pt(II) hydride complex.  

Science.gov (United States)

The reactivity toward H2 of coordinatively unsaturated Pt(II) complexes, stabilized by N-heterocyclic carbene (NHC) ligands, is herein analyzed. The cationic platinum complexes [Pt(NHC')(NHC)](+) (where NHC' stands for a cyclometalated NHC ligand) react very fast with H2 at room temperature, leading to hydrogenolysis of the Pt-CH2 bond and concomitant formation of hydride derivatives [PtH(NHC)2](+) or hydrido-dihydrogen complexes [PtH(H2)(NHC)2](+). The latter species release H2 when these compounds are subjected to vacuum. The X-ray structure of complex [PtH(IPr)2][SbF6] revealed its unsaturated nature, exhibiting a true T-shaped structure without stabilization by agostic interactions. Density functional theory calculations indicate that the binding and reaction of H2 in complexes [PtH(H2)(NHC)2](+) is more favored for derivatives bearing aryl-substituted NHCs (IPr, 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene and IMes = 1,3-dimesityl-1,3-dihydro-2H-imidazol-2-ylidene) than for those containing tert-butyl groups (I(t)Bu). This outcome is related to the higher close-range steric effects of the I(t)Bu ligands. Accordingly, H/D exchange reactions between hydrides [PtH(NHC)2](+) and D2 take place considerably faster for IPr and IMes* derivatives than for I(t)Bu ones. The reaction mechanisms for both H2 addition and H/D exchange processes depend on the nature of the NHC ligand, operating through oxidative addition transition states in the case of IPr and IMes* or by a ?-complex assisted-metathesis mechanism in the case of I(t)Bu. PMID:24716606

Rivada-Wheelaghan, Orestes; Roselló-Merino, Marta; Ortuño, Manuel A; Vidossich, Pietro; Gutiérrez-Puebla, Enrique; Lledós, Agustí; Conejero, Salvador

2014-04-21

72

Synthesis and characterization of divalent manganese, iron, and cobalt complexes in tripodal phenolate/N-heterocyclic carbene ligand environments.  

Science.gov (United States)

Two novel tripodal ligands, (BIMPN(Mes,Ad,Me))(-) and (MIMPN(Mes,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 (1)H 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 (57)Fe Mössbauer 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 TIMEN(R) ligands, allow for side access of, e.g., organic substrates, to the reactive metal center. PMID:24299260

Käß, Martina; Hohenberger, Johannes; Adelhardt, Mario; Zolnhofer, Eva M; Mossin, Susanne; Heinemann, Frank W; Sutter, Jörg; Meyer, Karsten

2014-03-01

73

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

74

An N-heterocyclic carbene phenanthroline ligand: synthesis, multi-metal coordination and spectroscopic studies.  

Science.gov (United States)

Dimetal complexes of a new N-heterocyclic carbene/phenanthroline ligand have been synthesized. Coordination of both ruthenium and rhenium to the phenanthroline moiety in combination with platinum at the carbene moiety are reported. Steady-state and time-resolved optical absorption and photoluminescence spectra were obtained for the complexes. These results illustrate significant changes occur with the incorporation of the second metal, and that the specific metal bound to the phenanthroline moiety is important to the photophysical characteristics of this system. PMID:25604044

Webster, Alyssa A; Prasad, Shyamal K K; Hodgkiss, Justin M; Hoberg, John O

2015-02-10

75

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

Science.gov (United States)

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

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

2010-01-01

76

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

Energy Technology Data Exchange (ETDEWEB)

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

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

2014-12-08

77

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

Science.gov (United States)

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

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

2015-01-27

78

Highly enantioselective [4 + 2] cyclization of chloroaldehydes and 1-azadienes catalyzed by N-heterocyclic carbenes.  

Science.gov (United States)

Highly functionalized dihydropyridinones were synthesized via the N-heterocyclic carbene-catalyzed enantioselective [4 + 2] annulation of ?-chloroaldehydes and azadienes. Hydrogenation of the resulted dihydropyridinones afforded the corresponding piperidinones with high enantiopurity. PMID:23023792

Jian, Teng-Yue; Sun, Li-Hui; Ye, Song

2012-11-14

79

N-heterocyclic carbene-palladium(II)-1-methylimidazole complex catalyzed amination between aryl chlorides and amides.  

Science.gov (United States)

We report herein that amides are excellent N-sources in the NHC-Pd(II)-Im complex 1 catalyzed amination of aryl chlorides. In the presence of KO(t)Bu, various aryl chlorides and amides can react smoothly to give the corresponding aminated products in moderate to almost quantitative yields at room temperature within 6 h. PMID:23020672

Chen, Wen-Xin; Shao, Li-Xiong

2012-10-19

80

Asymmetric catalysis with N-heterocyclic carbenes as non-covalent chiral templates.  

Science.gov (United States)

N-heterocyclic carbenes are a class of persistent carbenes stabilized by adjacent heteroatoms that are part of a heterocycle. They play a central role in multiple enzymatic biosynthetic reactions that involve thiamine diphosphate. Inspired by this biocatalysis machinery, N-heterocyclic carbenes have emerged as one of the most versatile classes of organocatalysts for organic reactions. However, the asymmetric synthesis of carbon-carbon bonds through a non-covalent interaction mechanism has not been previously established for chiral carbenes. Here, we report an N-heterocylic carbene-catalysed, highly enantioselective process that uses weak hydrogen bonds to relay asymmetric bias. We find that catalytic amounts of hexafluoroisopropanol are the critical proton shuttle that facilitates hydrogen transfer to provide high-reaction rates and high enantioselectivity. We demonstrate that a successful asymmetric reaction of this type can be accomplished through a rational design that balances the pKa values of the substrate, the carbene precursor and the product. PMID:24599089

Chen, Jiean; Huang, Yong

2014-01-01

81

Helical metal cage of silver(I) and mercury(II)-N-heterocyclic carbene complexes of 1,4-phenylene-bis{imidazo[1,5-a]pyridine-4-iumhexaflurophosphate}  

Science.gov (United States)

Novel N-heterocyclic carbene (NHC) architecture of 1,4-phenylene-bis{imidazo[1,5-a]pyridine-4 iumhexaflurophosphate}, [1(HPF6)2] has been synthesized in two steps from commercially available starting materials. The p-phylene bridged free annulated imidazolium salt has been synthesized and characterized both in solution and solid-state and has been used to synthesize silver(I) and mercury(II)-NHC complexes using the basic metal precursors. The [Ag2(1)2][PF6]2 (2) was synthesized using [1(HPF6)2] by Ag2O method in acceptable yield. The dinuclear Hg(II) complex [Hg2(1)2][PF6]4 (3) consisting of two biscarbene ligand has been synthesized from Hg(OAc)2 and [1(HPF6)2]. The helical nature of Hg(II)-NHC (3) has been established from solid state X-ray structure.

Rana, Bidyut Kumar; Bertolasi, Valerio; Pal, Satyanarayan; Mitra, Partha; Dinda, Joydev

2013-10-01

82

Catalytic boracarboxylation of alkynes with diborane and carbon dioxide by an N-heterocyclic carbene copper catalyst.  

Science.gov (United States)

By the use of an N-heterocyclic carbene copper(I) complex as a catalyst, the boracarboxylation of various alkynes (e.g., diaryl alkynes, aryl/alkyl alkynes, and phenylacetylene) with a diborane compound and carbon dioxide has been achieved for the first time, affording the ?,?-unsaturated ?-boralactone derivatives regio- and stereoselectively via a borylcupration/carboxylation cascade. Some important reaction intermediates were isolated and structurally characterized to clarify the reaction mechanism. PMID:22909063

Zhang, Liang; Cheng, Jianhua; Carry, Béatrice; Hou, Zhaomin

2012-09-01

83

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

Directory of Open Access Journals (Sweden)

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

84

N-Heterocyclic Carbene-Promoted Rauhut]Currier Reactions between Vinyl Sulfones and ?,?-Unsaturated Aldehydes  

OpenAIRE

N-heterocyclic carbenes (NHCs) promote the addition of 1,1-bis(phenylsulfonyl)ethylene to the ?-position of ?,?-unsaturated aldehydes. The proposed reaction pathway for this Rauhut-Currier-type reaction includes an unusual conjugate addition of an NHC to a bis-vinyl sulfone.

Atienza, Roxanne L.; Scheidt, Karl A.

2011-01-01

85

N-Heterocyclic Carbene-Promoted Rauhut]Currier Reactions between Vinyl Sulfones and ?,?-Unsaturated Aldehydes.  

Science.gov (United States)

N-heterocyclic carbenes (NHCs) promote the addition of 1,1-bis(phenylsulfonyl)ethylene to the ?-position of ?,?-unsaturated aldehydes. The proposed reaction pathway for this Rauhut-Currier-type reaction includes an unusual conjugate addition of an NHC to a bis-vinyl sulfone. PMID:22399824

Atienza, Roxanne L; Scheidt, Karl A

2011-08-19

86

Bifunctional N-heterocyclic carbene-catalyzed highly enantioselective synthesis of spirocyclic oxindolo-?-lactams.  

Science.gov (United States)

The N-heterocyclic carbene-catalyzed Staudinger reaction of ketenes with isatin-derived ketimines was investigated. The bifunctional NHCs with a free hydroxyl group were demonstrated as efficient catalysts for the reaction, giving the corresponding spirocyclic oxindolo-?-lactams in high yields with excellent diastereo- and enantioselectivities. PMID:24856000

Zhang, Han-Ming; Gao, Zhong-Hua; Ye, Song

2014-06-01

87

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

Science.gov (United States)

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

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

2014-11-24

88

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

Science.gov (United States)

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

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

2014-10-01

89

Coordination chemistry of highly hemilabile bidentate sulfoxide N-heterocyclic carbenes with palladium(II).  

Science.gov (United States)

Imidazolium salts, [RS(O)-CH2 (C3 H3 N2 )Mes]Cl (R=Me (L1a), Ph (L1b)); Mes=mesityl), make convenient carbene precursors. Palladation of L1a affords the monodentate dinuclear complex, [(PdCl2 {MeS(O)CH2 (C3 H2 N2 )Mes})2 ] (2a), which is converted into trans-[PdCl2 (NHC)2] (trans-4a; N-heterocyclic carbene) with two rotamers in anti and syn configurations. Complex trans-4a can isomerize into cis-4a(anti) at reflux in acetonitrile. Abstraction of chlorides from 4a or 4b leads to the formation of a new dication: trans-[Pd{RS(O)CH2(C3H2N2)Mes}2](PF6)2 (R=Me (5a), Ph (5b)). The X-ray structure of 5a 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 5a or 5b 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

90

New N-Heterocyclic Carbene Ligands in Grubbs and Hoveyda-Grubbs Catalysts  

Science.gov (United States)

A series of N-heterocyclic carbene (NHC) ligands bearing aliphatic amino side groups were synthesized and reacted with the Grubbs first generation catalyst. Reactions involving symmetrical, aliphatic NHCs did not allow the isolation of any pure NHC substituted complexes due to their instability. Unsymmetrical NHCs having a planar mesityl group on one amino side reacted with Grubbs catalyst in a favorable manner, and the resulting complexes were stable enough to be isolated. X-ray crystallographic analysis demonstrated that the mesityl group is co-planar with the phenyl ring of the benzylidene, which indicates that a ?-? interaction between the mesityl arm and the benzylidene moiety might constitute an important structural element. Catalysts substituted with an NHC derived from a primary or secondary amino-group were found to surpass the parent-complex for the ROMP of cycloocta-1,5-diene. The catalyst substituted with an NHC derived from tBu-NH2 was considerably less metathesis active. Also new N-alkyl-N'-(2,6-diisopropylphenyl) heterocyclic carbenes were synthesized. These NHC ligands revealed a different reactivity towards Grubbs complexes than the hitherto reported imidazolinylidenes: (i) facile bis(NHC) coordination was found, and (ii) both NHCs on the bis(NHC) complexes can be exchanged with a phosphine, thereupon regenerating the Grubbs first generation complex. Furthermore, a comparison between the classical Hoveyda-Grubbs complexes and complexes substituted with N-alkyl-N'-(aryl) heterocyclic carbenes demonstrates that the introduction of one aliphatic group into the NHC framework does not improve the catalytic activity in any of the tested metathesis reactions. The introduction of two aliphatic amino side groups enhances the reactivity in the ROMP reaction while the increase of steric interactions lowers the CM activity. The lower activity of the N-alkyl-N'-(2,6-diisopropylphenyl) heterocyclic carbene complexes compared with the N-alkyl-N'-mesityl heterocyclic carbene complexes, may analogously be attributed to a more demanding steric environment. While small differences in donor capacities might cause a significantly different catalytic behavior, it is thus plausible that subtle steric differences exert a more determining influence on the activity of the catalysts. In addition, the obtained results confirm that the NHC's amino side groups play a pivotal role in determining the reactivity, selectivity as well as the stability of the corresponding catalysts.

Monsaert, Stijn; Ledoux, Nele; Drozdzak, Renata; van der Voort, Pascal; Verpoort, Francis

91

N-heterocyclic carbenes bearing two, one and no nitrogen atoms at the ylidene carbon: insight from theoretical calculations.  

Science.gov (United States)

Electronic structure, thermodynamic stability and ligand properties in LRh(CO)2Cl complexes of a series of N-heterocyclic carbenes (NHCs) were studied at the DFT level. The systems under study are: imidazolin-2-ylidene (1), imidazolidin-2-ylidene (2), cyclic(alkyl)(amino)carbene (CAAC, 3), pyrazolin-3-ylidene (4), pyridin-2-ylidene (5), and pyridin-4-ylidene (6). The main structural feature influencing the properties of these species is the number of nitrogen atoms at the ylidene carbon. A decrease of the number of nitrogen atoms on the one hand leads to an increase in donor ability and ligand-to-metal bond strength, but lowers the stability of the NHC on the other hand. The number of nitrogen atoms can be taken as a key parameter for the classification of carbenes into 2N-NHC, 1N-NHC and r-NHC (r = remote). PMID:20449144

Tukov, Aleksandr A; Normand, Adrien T; Nechaev, Mikhail S

2009-09-21

92

C(sp3)-H activation without a directing group: regioselective synthesis of N-ylide or N-heterocyclic carbene complexes controlled by the choice of metal and ligand.  

Science.gov (United States)

N-Ylide complexes of Ir have been generated by C(sp(3))-H activation of ?-pyridinium or ?-imidazolium esters in reactions with [Cp*IrCl2]2 and NaOAc. These reactions are rare examples of C(sp(3))-H activation without a covalent directing group, which-even more unusually-occur ? to a carbonyl group. For the reaction of the ?-imidazolium ester [3H]Cl, the site selectivity of C-H activation could be controlled by the choice of metal and ligand: with [Cp*IrCl2]2 and NaOAc, C(sp(3))-H activation gave the N-ylide complex 4; in contrast, with Ag2O followed by [Cp*IrCl2]2, C(sp(2))-H activation gave the N-heterocyclic carbene complex 5. DFT calculations revealed that the N-ylide complex 4 was the kinetic product of an ambiphilic C-H activation. Examination of the computed transition state for the reaction to give 4 indicated that unlike in related reactions, the acetate ligand appears to play the dominant role in C-H bond cleavage. PMID:25164979

Cross, Warren B; Razak, Sunnah; Singh, Kuldip; Warner, Andrew J

2014-10-01

93

N-heterocyclic carbene-catalyzed hydroacylation of unactivated double bonds.  

Science.gov (United States)

An intramolecular N-heterocyclic carbene (NHC)-catalyzed hydroacylation of unactivated double bonds is reported. Systematic variation of the catalyst structure revealed an N-mesitylthiazolylidene annulated with a seven-membered ring to be especially reactive. This NHC enables a unique C-C bond-forming reaction to afford substituted chroman-4-ones in moderate to excellent yields, even ones containing all-carbon quaternary centers. PMID:19807174

Hirano, Keiichi; Biju, Akkattu T; Piel, Isabel; Glorius, Frank

2009-10-14

94

Chiral N-heterocyclic carbene (NHC) ligands in Pd-catalyzed cross-coupling reactions  

OpenAIRE

New chiral N-heterocyclic carbene (NHC) ligands have been developed and applied in the asymmetric Pd-catalyzed intramolecular a-arylation of amides producing 3,3-disubstituted-, spiro-, and aza-spirooxindoles in high yields (up to 99%) and excellent enantioselectivities (up to 97% ee). For the first time a palladacycle intermediates were isolated and fully characterized including X-ray crystal structure determinations. Analysis of these solid state structures demonstrates the importance of bo...

Katayev, Dmitry

2012-01-01

95

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

OpenAIRE

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

Lu?ning, Ulrich; Winkelmann, Ole

2009-01-01

96

N-Heterocyclic Carbenes : catalys in the chemistry of silicones Cyclic Carbodiphosphoranes : synthesis, coordination and reactivity  

OpenAIRE

In a first chapter, we are interested in the use of N-Heterocyclic Carbenes like nucleophilic organic catalysts for ring opening polymerization of octamethylcyclosiloxane and for reactions of polycondensation.In a second chapter, we carry out a bibliographical review on coumpounds presenting two cumulated ylides functions : carbodiphosphoranes.In a third chapter, we present the synthesis and the coordination of new cyclic carbodiphosphoranes. They are recognized to be strong -dono...

Marrot, Se?bastien

2007-01-01

97

Oxidative Enantioselective ?-Fluorination of Aliphatic Aldehydes Enabled by N-Heterocyclic Carbene Catalysis.  

Science.gov (United States)

Described is the first study on oxidative enantioselective ?-fluorination of simple aliphatic aldehydes enabled by N-heterocyclic carbene catalysis. N-fluorobis(phenyl)sulfonimide serves as a an oxidant and as an "F" source. The C?F bond formation occurs directly at the ??position of simple aliphatic aldehydes, thus overcoming nontrivial challenges, such as competitive difluorination and nonfluorination, and proceeds with high to excellent enantioselectivities. PMID:25348753

Li, Fangyi; Wu, Zijun; Wang, Jian

2015-01-01

98

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

Science.gov (United States)

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

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

2011-12-21

99

Three-coordinate nickel(I) complexes stabilised by six-, seven- and eight-membered ring n-heterocyclic carbenes: synthesis, EPR/DFT studies and catalytic activity.  

Science.gov (United States)

Comproportionation of [Ni(cod)(2)] (cod = cyclooctadiene) and [Ni(PPh(3))(2)X(2)] (X = Br, Cl) in the presence of six-, seven- and eight-membered ring N-aryl-substituted heterocyclic carbenes (NHCs) provides a route to a series of isostructural three-coordinate Ni(I) complexes [Ni(NHC)(PPh(3))X] (X = Br, Cl; NHC = 6-Mes 1, 6-Anis 2, 6-AnisMes 3, 7-o-Tol 4, 8-Mes 5, 8-o-Tol 6, O-8-o-Tol 7). Continuous wave (CW) and pulsed EPR measurements on 1, 4, 5, 6 and 7 reveal that the spin Hamiltonian parameters are particularly sensitive to changes in NHC ring size, N substituents and halide. In combination with DFT calculations, a mixed SOMO of ?3d?z?2? and ?3d?x?2-y?2? character, which was found to be dependent on the complex geometry, was observed and this was compared to the experimental g values obtained from the EPR spectra. A pronounced (31)P superhyperfine coupling to the PPh(3) group was also identified, consistent with the large spin density on the phosphorus, along with partially resolved bromine couplings. The use of 1, 4, 5 and 6 as pre-catalysts for the Kumada coupling of aryl chlorides and fluorides with ArMgY (Ar = Ph, Mes) showed the highest activity for the smaller ring systems and/or smaller substituents (i.e., 1>4?6?5). PMID:23292787

Page, Michael J; Lu, Wei Y; Poulten, Rebecca C; Carter, Emma; Algarra, Andrés G; Kariuki, Benson M; Macgregor, Stuart A; Mahon, Mary F; Cavell, Kingsley J; Murphy, Damien M; Whittlesey, Michael K

2013-02-01

100

Expanded ring N-heterocyclic carbene adducts of group 15 element trichlorides: synthesis and reduction studies.  

Science.gov (United States)

Reactions of the expanded ring N-heterocyclic carbene, 6-Dip (:C{N(Dip)CH2}2CH2, Dip = 2,6-diisopropylphenyl), with group 15 element trichlorides have yielded the monomeric complexes, [(6-Dip)ECl3] (E = P, As or Sb), two examples of which (E = P and Sb) have been crystallographically characterised. Reduction of [(6-Dip)PCl3] with KC8 yielded the unusual tetraphosphorus dicationic complex, [(6-Dip)2(?-P4)]Cl2, the X-ray crystal structure of which shows it to be an ion-separate salt. The compound can also be prepared from the direct reaction of excess 6-Dip with PCl3. Treatment of the cyclic amidinium salt, [6-MesH]Br (6-MesH = [HC{N(Mes)CH2}2CH2](+), Mes = mesityl) with KC8, leads to reductive coupling of the heterocycle and formation of the hindered bis(hexahydropyrimidine), (6-MesH)2. An X-ray crystallographic analysis of (6-MesH)2 shows the compound to have a long central C-C bond, while an electrochemical analysis reveals it to undergo an irreversible two-electron oxidation in dichloromethane solutions. PMID:25166429

Sidiropoulos, Anastas; Osborne, Brooke; Simonov, Alexandr N; Dange, Deepak; Bond, Alan M; Stasch, Andreas; Jones, Cameron

2014-10-21

101

End-on and side-on ?-acid ligand adducts of gold(I): carbonyl, cyanide, isocyanide, and cyclooctyne gold(I) complexes supported by N-heterocyclic carbenes and phosphines.  

Science.gov (United States)

N-heterocyclic carbene ligand SIDipp (SIDipp = 1,3-bis(2,6-diisopropylphenyl)imidazolin-2-ylidene) and trimesitylphosphine ligand have been used in the synthesis of gold(I) cyanide, t-butylisocyanide, and cyclooctyne complexes (SIDipp)Au(CN) (3), (Mes(3)P)Au(CN) (4), [(Mes(3)P)(2)Au][Au(CN)(2)] (5), [(SIDipp)Au(CN(t)Bu)][SbF(6)] ([6][SbF(6)]), [(SIDipp)Au(cyclooctyne)][SbF(6)] ([8][SbF(6)]), and [(Mes(3)P)Au(cyclooctyne)][SbF(6)] ([9][SbF(6)]). A detailed computational study has been carried out on these and the related gold(I) carbonyl adducts [(SIDipp)Au(CO)][SbF(6)] ([1][SbF(6)]), [(Mes(3)P)Au(CO)][SbF(6)] ([2][SbF(6)]), and [(Mes(3)P)Au(CN(t)Bu)](+) ([7](+)). X-ray crystal structures of 3, 5, [6][SbF(6)], [8][SbF(6)], and [9][SbF(6)] revealed that they feature linear gold sites. Experimental and computational data show that the changes in ?-acid ligand on (SIDipp)Au(+) from CO, CN(-), CN(t)Bu, cyclooctyne as in [1](+), 3, [6](+), and [8](+) did not lead to large changes in the Au-C(carbene) bond distances. A similar phenomenon was also observed in Au-P distance in complexes [2](+), 4, [7](+), and [9](+) bearing trimesitylphosphine. Computational data show that the Au-L bonds of "naked" [Au-L](+) or SIDipp and Mes(3)P supported [Au-L](+) (L = CO, CN(-), CN(t)Bu to cyclooctyne) have higher electrostatic character than covalent character. The Au?L ?-donation and Au?L ?-back-donation contribute to the orbital term with the former being the dominant component, but the latter is not negligible. In the Au-CO adducts [1](+)and [2](+), the cationic gold center causes the polarization of the C-O ? and ? orbitals toward the carbon end making the coefficients at the two atoms more equal which is mainly responsible for the large blue shift in the CO stretching frequency. The SIDipp and Mes(3)P supported gold(I) complexes of cyanide and isocyanide also exhibit a significant blue shift in ?(CN) compared to that of the free ligands. Calculated results for Au(CO)Cl and Au(CF(3))CO suggest that the experimentally observed blue shift in ?(CO) of these compounds may at least partly be caused by intermolecular forces. PMID:23273108

Celik, Mehmet Ali; Dash, Chandrakanta; Adiraju, Venkata A K; Das, Animesh; Yousufuddin, Muhammed; Frenking, Gernot; Dias, H V Rasika

2013-01-18

102

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

Science.gov (United States)

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

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

2015-02-01

103

Oxyanion steering and CH-? interactions as key elements in an N-heterocyclic carbene-catalyzed [4 + 2] cycloaddition.  

Science.gov (United States)

The N-heterocyclic carbene catalyzed [4 + 2] cycloaddition has been shown to give ?,?-unsaturated ?-lactones in excellent enantio- and diastereoselectivity. However, preliminary computational studies of the geometry of the intermediate enolate rendered ambiguous both the origins of selectivity and the reaction pathway. Here, we show that a concerted, but highly asynchronous, Diels-Alder reaction occurs rather than the stepwise Michael-type or Claisen-type pathways. In addition, two crucial interactions are identified that enable high selectivity: an oxyanion-steering mechanism and a CH-? interaction. The calculations accurately predict the enantioselectivity of a number of N-heterocyclic carbene catalysts in the hetero-Diels-Alder reaction. PMID:22765294

Allen, Scott E; Mahatthananchai, Jessada; Bode, Jeffrey W; Kozlowski, Marisa C

2012-07-25

104

A spiroborate-based anionic bis-N-heterocyclic carbene.  

Science.gov (United States)

A twisted mono-cationic bis-benzimidazolium salt was serendipitously isolated from the dehydrative condensation of 5,6-dihydroxyl-1,3-dimesityl-benzimidazolium and 1,4-benzenediboronic acid. Subsequent deprotonation of the benzimidazolium salt led to the formation of a spiroborate-linked free bis-NHC, which was further transformed into the corresponding diborane adduct and the di-Rh complex. PMID:24395106

Su, Jia-Hong; Lee, Gene-Hsiang; Peng, Shie-Ming; Chiu, Ching-Wen

2014-02-28

105

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

Directory of Open Access Journals (Sweden)

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

Min Shi

2011-05-01

106

Direct C-H bond arylation of (benzo)oxazoles with aryl chlorides catalyzed by N-heterocyclic carbene-palladium(II)-1-methylimidazole complex.  

Science.gov (United States)

The direct C-H bond arylation of (benzo)oxazoles with aryl chlorides was achieved catalyzed by a well-defined NHC-Pd(II)-Im complex. Under the optimal conditions, various aryl chlorides were successfully applied as the arylating reagents to achieve the 2-aryl (benzo)oxazoles in acceptable to high yields, providing a convenient and alternative method for the direct C-H bond arylation of (benzo)oxazoles and enriching the chemistry of the NHC-Pd(II) complex in organic synthesis. PMID:24670076

Shen, Xiao-Bao; Zhang, Yun; Chen, Wen-Xin; Xiao, Zheng-Kang; Hu, Ting-Ting; Shao, Li-Xiong

2014-04-01

107

N-heterocyclic carbene-palladium(II)-1-methylimidazole complex-catalyzed Suzuki-Miyaura coupling of aryl sulfonates with arylboronic acids.  

Science.gov (United States)

A well-defined NHC-Pd(II)-Im complex 1 was found to be an effective catalyst for the Suzuki-Miyaura coupling of aryl sulfonates including tosylates and phenylsulfonates with arylboronic acids, giving the desired coupling products in good to high yields. Acceptable yields can also be achieved even by using the less reactive mesylates as the substrates. It is worthy of noting here that this is the first example of NHC-Pd(II) complex-catalyzed Suzuki-Miyaura coupling of aryl sulfonates with arylboronic acids, enriching an inexpensive, convenient, and alternative method for the synthesis of biaryl compounds. PMID:22804630

Wang, Zhan-Yong; Chen, Gao-Qi; Shao, Li-Xiong

2012-08-01

108

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

109

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

Science.gov (United States)

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

110

N-heterocyclic carbene-palladium(II)-1-methylimidazole complex-catalyzed direct C-H bond arylation of (benz)imidazoles with aryl chlorides.  

Science.gov (United States)

(Benz)imidazoles can be efficiently functionalized by (hetero)aryl chlorides via direct C-H bond arylation in the presence of a well-defined NHC-Pd(II)-Im complex. Under the optimal conditions, various activated, unactivated, and deactivated (hetero)aryl chlorides were successfully applied as the arylating reagents to achieve the 2-(hetero)aryl (benz)imidazoles in acceptable to high yields, giving a facile and alternative methodology for the direct C-H bond arylation of (benz)imidazoles. PMID:24869774

Gu, Zheng-Song; Chen, Wen-Xin; Shao, Li-Xiong

2014-06-20

111

N-heterocyclic carbene formation induced fluorescent and colorimetric sensing of fluoride using perimidinium derivatives.  

Science.gov (United States)

In this study, two perimidinium derivatives (1 and 2) were designed, synthesized, and developed as efficient fluorescent and colorimetric chemodosisensors for F(-) in DMSO or more competitive media (DMSO containing 10?% water). In the presence of F(-) , the yellow and non-fluorescent solution of 1/2 became colourless and exhibited strong blue fluorescence. This unique spectroscopic behaviour of 1/2 towards F(-) was attributed to the formation of N-heterocyclic carbene deprotonated by F(-) , which immediately reacted with water to give a colourless and fluorescent carbinol. Interestingly, it was found that this carbinol intermediate was unstable and further underwent a redox disproportionation to generate two other optically changed compounds. All the proposed mechanisms for the sensing process have been carefully confirmed by experiments. PMID:25346203

Zhang, Dawei; Yang, Haiqiang; Martinez, Alexandre; Jamieson, Kelsey; Dutasta, Jean-Pierre; Gao, Guohua

2014-12-15

112

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

Science.gov (United States)

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

113

Intramolecular cyclotrimerization of triynes catalyzed by N-heterocyclic carbene-CoCl2/Zn or -FeCl3/Zn.  

Science.gov (United States)

[reaction: see text] Triynes 1 could effectively be cyclotrimerized to annulated benzenes 2 by treatment with a catalytic amount of zinc powder, N-heterocyclic carbene, and CoCl(2) or FeCl(3). PMID:15987206

Saino, Naoko; Kogure, Daisuke; Okamoto, Sentaro

2005-07-01

114

N-heterocyclic carbene-catalyzed [4 + 2] cycloaddition of ketenes and 3-aroylcoumarins: highly enantioselective synthesis of dihydrocoumarin-fused dihydropyranones.  

Science.gov (United States)

The N-heterocyclic carbene-catalyzed [4 + 2] cyclization of ketenes and 3-aroylcoumarins has been developed to give the corresponding dihydrocoumarin-fused multisubstituted dihydropyranones in high yield with good diastereoselectivity and high enantioselectivity. PMID:23117299

Jian, Teng-Yue; Chen, Xiang-Yu; Sun, Li-Hui; Ye, Song

2013-01-01

115

Synthesis of New Chiral N-Heterocyclic Carbenes and Abnormal Carbenes  

OpenAIRE

Chapter 1 Carbenes have fascinated organic chemists ever since the first evidence of their existence. The isolation and first crystallographic analysis of a stable NHC by Arduengo, in 1991, has had a major impact on the application of NHCs in chemistry. NHCs are widely used as ligands for transition metals, but also as catalysts in their own right. The aim of this project is to synthesise novel monodentate chiral NHCs 1 in order to induce a high level of stereocontrol in a s...

Levy, Jean-noel

2011-01-01

116

Enantioselective sulfonation of enones with sulfonyl imines by cooperative N-heterocyclic-carbene/thiourea/tertiary-amine multicatalysis.  

Science.gov (United States)

Many hands make light work: In an organocatalytic asymmetric sulfonation of enones, the activation of a sulfonyl imine by an N-heterocyclic carbene (NHC) catalyst led to the release of a sulfinic anion, which underwent nucleophilic addition to the enone. The enantioselectivity of the process was controlled by a chiral thiourea/amine co-catalyst through anion recognition and hydrogen-bonding interactions. Tol=p-tolyl. PMID:24115649

Jin, Zhichao; Xu, Jianfeng; Yang, Song; Song, Bao-An; Chi, Yonggui Robin

2013-11-18

117

[3+2] Fragmentation of an [RP(5)Cl](+) cage cation induced by an N-heterocyclic carbene.  

Science.gov (United States)

The cage compound [DippP5 Cl][GaCl4 ] (Dipp=2,6-diisopropylphenyl) reacts with an NHC (N-heterocyclic carbene) by an unprecedented [3+2] fragmentation of the P5 (+) core. This yields an imidazoliumyl-substituted P3 species featuring a triphosphaallyl anion motif and a neutral P2 compound. The mechanism of the fragmentation reaction was elucidated by means of experimental and quantum chemical methods. PMID:24038818

Holthausen, Michael H; Surmiak, Sabrina K; Jerabek, Paul; Frenking, Gernot; Weigand, Jan J

2013-10-11

118

N-Heterocyclic Carbene Catalyzed Enantioselective ?-Fluorination of Aliphatic Aldehydes and ?-Chloro Aldehydes: Synthesis of ?-Fluoro Esters, Amides, and Thioesters.  

Science.gov (United States)

The asymmetric fluorination of azolium enolates that are generated from readily available simple aliphatic aldehydes or ?-chloro aldehydes and N-heterocyclic carbenes (NHCs) is described. The process significantly expands the synthetic utility of NHC-catalyzed fluorination and provides facile access to a wide range of ?-fluoro esters, amides, and thioesters with excellent enantioselectivity. Pyrazole was identified as an excellent acyl transfer reagent for catalytic amide formation. PMID:25394812

Dong, Xiuqin; Yang, Wen; Hu, Weimin; Sun, Jianwei

2015-01-01

119

[bmim][Br] as a solvent and activator for the Ga-mediated Barbier allylation: direct formation of an N-heterocyclic carbene from Ga metal.  

Science.gov (United States)

The room-temperature ionic liquid (RTIL) [bmim][Br] has been found to be an excellent green and inexpensive medium for the Ga-mediated allylation of aromatic and aliphatic aldehydes and ketones. The RTIL activated the metal via formation of a Ga-N-heterocyclic carbene complex that assisted in the completion of the reaction at ambient temperature with only 0.5 equiv of Ga and 1.2 equiv of allyl bromide with respect to the carbonyl substrates. The present protocol required a much shorter time than those reported in the literature using other metals and solvents and proceeded with good yields and excellent selectivity. PMID:23198818

Goswami, Dibakar; Chattopadhyay, Angshuman; Sharma, Anubha; Chattopadhyay, Subrata

2012-12-21

120

Dehydrogenation of saturated CC and BN bonds at cationic N-heterocyclic carbene stabilized M(III) centers (M = Rh, Ir).  

OpenAIRE

Chloride abstraction from the group 9 metal bis(N-heterocyclic carbene) complexes M(NHC)(2)(H)(2)Cl [M = Rh, Ir; NHC = IPr = N,N'-bis(2,6-diisopropylphenyl)imidazol-2-ylidene or IMes = N,N'-bis(2,4,6-trimethylphenyl)imidazol-2-ylidene] leads to the formation of highly reactive cationic species capable of the dehydrogenation of saturated CC and BN linkages. Thus, the reaction of Ir(IPr)(2)(H)(2)Cl (1) with Na[BAr(f)(4)] in fluorobenzene generates [Ir(IPr)(2)(H)(2)](+)[BAr(f)(4)](-) (4) in whic...

Tang, Cy; Thompson, Al; Aldridge, S.

2010-01-01

121

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

DEFF Research Database (Denmark)

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

Makarov, Ilya; Fristrup, Peter

2012-01-01

122

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

Directory of Open Access Journals (Sweden)

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

Marta Feroci

2011-12-01

123

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

Science.gov (United States)

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

124

Expanded-ring N-heterocyclic carbenes efficiently stabilize gold(I) cations, leading to high activity in ?-acid-catalyzed cyclizations.  

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A series of six- and seven-membered expanded-ring N-heterocyclic carbene (er-NHC) gold(I) complexes has been synthesized using different synthetic approaches. Complexes with weakly coordinating anions [(er-NHC)AuX] (X(-) = BF4(-), NTf2(-), OTf(-)) were generated in solution. According to their (13)C?NMR spectra, the ionic character of the complexes increases in the order X(-) = Cl(-) < NTf2(-) < OTf(-) < BF4(-). Additional factors for stabilization of the cationic complexes are expansion of the NHC ring and the attachment of bulky substituents at the nitrogen atoms. These er-NHCs are bulkier ligands and stronger electron donors than conventional NHCs as well as phosphines and sulfides and provide more stabilization of [(L)Au(+)] cations. A comparative study has been carried out of the catalytic activities of five-, six-, and seven-membered carbene complexes [(NHC)AuX], [(Ph3 P)AuX], [(Me2S)AuX], and inorganic compounds of gold in model reactions of indole and benzofuran synthesis. It was found that increased ionic character of the complexes was correlated with increased catalytic activity in the cyclization reactions. As a result, we developed an unprecedentedly active monoligand cationic [(THD-Dipp)Au]BF4 (1,3-bis(2,6-diisopropylphenyl)-3,4,5,6-tetrahydrodiazepin-2-ylidene gold(I) tetrafluoroborate) catalyst bearing seven-membered-ring carbene and bulky Dipp substituents. Quantitative yields of cyclized products were attained in several minutes at room temperature at 1?mol?% catalyst loadings. The experimental observations were rationalized and fully supported by DFT calculations. PMID:24682976

Morozov, Oleg S; Lunchev, Andrey V; Bush, Alexander A; Tukov, Aleksandr A; Asachenko, Andrey F; Khrustalev, Victor N; Zalesskiy, Sergey S; Ananikov, Valentine P; Nechaev, Mikhail S

2014-05-12

125

Theoretical investigations of the reactivities of four-membered N-heterocyclic carbene analogues of the group 13 elements.  

Science.gov (United States)

The potential energy surfaces for the chemical reactions of four-membered N-heterocyclic group 13 heavy carbeneoid species have been studied using density functional theory (Becke, 3-parameter, Lee-Yang-Parr (B3LYP)/Los Alamos National Laboratory 2-Double-Zeta (LANL2DZ)). Five four-membered group 13 heavy carbeneoid species, iPr2NC(NAr)2E:, where E ¼ B, Al, Ga, In, and Tl, have been chosen as model reactants in this work. Also, three kinds of chemical reactions, CAH bond insertion, alkene cycloaddition, and dimerization, have been used to study the chemical reactivities of these group 13 fourmembered N-heterocyclic carbeneoid species. In principle, our present theoretical work predicts that the larger the ffNEN bond angle of the four-membered group 13 iPr2NC(NAr)2E: species, the smaller the singlet–triplet splitting, the lower the activation barrier, and, in turn, the more rapid its chemical reactions to various chemical species. Moreover, our theoretical investigations suggest that the relative carbenic reactivity decreases in the following order: B > Al > Ga > In > Tl. That is, the heavier the group 13 atom (E), the more stable its fourmembered carbeneoid toward chemical reactions is. As a result, our computations predict that the four-membered heavy group 13 iPr2NC(NAr)2E: species (E ¼ Al, Ga, In, and Tl) should be both kinetically and thermodynamically stable, and can be readily synthesized and isolated at room temperature. Furthermore, the singlet–triplet energy splitting of the four-membered group 13 iPr2NC(NAr)2E: species, as described in the configuration mixing model attributed to the work of Pross and Shaik, can be used as a diagnostic tool to predict their reactivities. The results obtained allow a number of predictions to be made. PMID:22167870

Wu, Chi-Shiun; Su, Ming-Der

2012-01-01

126

N-heterocyclic carbene catalyzed annulation of benzofuran-2,3-diones and enals: a concise synthesis of spiro-bis-lactone.  

Science.gov (United States)

The N-heterocyclic carbene catalyzed annulation of benzofuran-2,3-diones and enals via homoenolate intermediates is described. The reaction provided a direct and efficient method for the synthesis of spiro-bis-lactones. The ketone-carbonyl group annulated products and the ester-carbonyl group annulated products can be obtained as major products with good yields by convenient catalyst regulation. Furthermore, commercially available thiazolium salt can also catalyze this reaction with modest yield. PMID:23868545

Wang, Ze-Dong; Wang, Feng; Li, Xin; Cheng, Jin-Pei

2013-09-14

127

DFT investigation on mechanisms and stereoselectivities of [2 + 2 + 2] multimolecular cycloaddition of ketenes and carbon disulfide catalyzed by N-heterocyclic carbenes.  

Science.gov (United States)

The first theoretical investigation using density functional theory (DFT) methods to study the detailed reaction mechanisms of stereoselective [2 + 2 + 2] multimolecular cycloaddition of ketene (two molecules) and carbon disulfide (CS2, one molecule) which is catalyzed by N-heterocyclic carbene (NHC) is presented in this paper. The calculated results indicate that this reaction occurs through four steps: the complexation of NHC with ketene (channel 1a) rather than with CS2 (channel 1b), addition of CS2 (channel 2b) but not dimerization of ketene (channel 2a), formal [4 + 2] cycloaddition with a second molecule of ketene (channel 3a) rather than intramolecular [2 + 2] cycloaddition (channel 3b), and finally regeneration of NHC. The second step is revealed to be the rate-determining step. Moreover, the stereoselectivities associated with the chiral carbon center and the carbon double bond are predicted to be respectively determined in the second and third steps and respectively R and E configurations dominated, which are in good agreement with the experimental results. Furthermore, the possible mechanisms of the identical [2 + 2 + 2] cycloaddition catalyzed by N,N-dimethylpyridin-4-amine (DMAP) have also been investigated to help understand the ring closure mechanism proceeding in the third step. PMID:24188481

Zhang, Wen-Jing; Wei, Dong-Hui; Tang, Ming-Sheng

2013-12-01

128

Synthesis and Characterization of Di- and Tetracarbene Iron(II) Complexes with Chelating N-Heterocyclic Carbene Ligands and Their Application in Aryl Grignard–Alkyl Halide Cross-Coupling  

OpenAIRE

A series of new and known bis(imidazolium) chloride and bromide salts bridged by either a methylene group (1?8, 10a,b) or an ethylene group (9a,b) and bearing different N substituents (Me, Et, Bn, tBu, Mes) have been reacted with [Fe{N(SiMe3)2}2]2 to yield the four-coordinate iron(II) complexes [LFeX2] (11?20; X = Cl, Br; L = chelating bis(imidazolylidene) ligand). Molecular structures of six of these complexes have been characterized by X-ray crystallography, and ...

Meyer, Steffen; Orben, Claudia Manuela; Demeshko, Serhiy; Dechert, Sebastian; Meyer, Franc

2011-01-01

129

Two-component, three-molecule reactions between 2,3-dihydroinden-1-ones and aryl chlorides catalyzed by an N-heterocyclic carbene-palladium(II)-1-methylimidazole complex.  

Science.gov (United States)

The two-component, three-molecule reactions between 2,3-dihydroinden-1-ones and aryl chlorides were achieved in the presence of an NHC-Pd(II)-Im complex. Under the optimal conditions, all reactions performed well to give the corresponding products in moderate to high yields. PMID:24228996

Yin, Hui-Ying; Liu, Meng-Yuan; Shao, Li-Xiong

2013-12-01

130

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

Science.gov (United States)

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

Yuan, Dan; Huynh, Han Vinh

2013-06-01

131

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

132

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

133

N-heterocyclic carbene-palladium(II)-1-methylimidazole complex catalyzed ?-arylation of oxindoles with aryl chlorides and aerobic oxidation of the products in a one-pot procedure.  

Science.gov (United States)

NHC-Pd(II)-Im complex 1 was found to be an effective catalyst for the ?-arylation of unprotected oxindoles with aryl chlorides to give products 4 in 44-98% yields under a N2 atmosphere. Furthermore, if the reactions were first performed under conditions identical to those for the ?-arylation reaction for 12 h and then exposed to air for another 3 h, 3-aryl-3-hydroxy-2-oxindoles 5 can be obtained in 49-84% yields in a one-pot procedure. PMID:23451859

Xiao, Zheng-Kang; Yin, Hui-Ying; Shao, Li-Xiong

2013-03-15

134

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

135

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

OpenAIRE

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

136

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

Directory of Open Access Journals (Sweden)

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

137

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

OpenAIRE

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

138

Catalytic Hydrodechlorination of Benzyl Chloride Promoted by Rh-N-heterocyclic Carbene Catalysts.  

Science.gov (United States)

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

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

2015-02-01

139

Iron(II) complexes of ditopic carbanionic carbenes.  

OpenAIRE

Reaction of dimesityliron(II) (Fe2(mes)4) with the N-heterocyclic carbenes 1,3-bis(2,6-diisopropylphenyl)-imidazol-2-ylidene (IPr) and 1,3-bis(2,6-dimethylphenyl)hexahydropyrimidin-2-ylidene (6-Xyl) afforded the novel trigonal planar complexes [Fe(IPr)(mes)2] (1) and [Fe(6-Xyl)(mes)2] (2), respectively. Both species were structurally characterized by single crystal X-ray diffraction and display structures and magnetic responses consistent with a quintet ground state (S = 2). Reaction of 1 wit...

Musgrave, Ra; Turbervill, Rs; Irwin, M.; Herchel, R.; Goicoechea, Jm

2014-01-01

140

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

Science.gov (United States)

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

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

2012-08-01

141

Reaction of an N-Heterocyclic Carbene-Stabilized Silicon(II) Monohydride with Alkynes: [2+2+1] Cycloaddition versus Hydrogen Abstraction.  

Science.gov (United States)

An in depth study of the reactivity of an N-heterocyclic carbene (NHC)-stabilized silylene monohydride with alkynes is reported. The reaction of silylene monohydride 1, tBu3 Si(H)Si?NHC, with diphenylacetylene afforded silole 2, tBu3 Si(H)Si(C4 Ph4 ). The density functional theory (DFT) calculations for the reaction mechanism of the [2+2+1] cycloaddition revealed that the NHC played a major part stabilizing zwitterionic transition states and intermediates to assist the cyclization pathway. A significantly different outcome was observed, when silylene monohydride 1 was treated with phenylacetylene, which gave rise to supersilyl substituted 1-alkenyl-1-alkynylsilane 3, tBu3 Si(H)Si(CH?CHPh)(C?CPh). Mechanistic investigations using an isotope labelling technique and DFT calculations suggest that this reaction occurs through a similar zwitterionic intermediate and subsequent hydrogen abstraction from a second molecule of phenylacetylene. PMID:25413306

Eisenhut, Carsten; Szilvási, Tibor; Breit, Nora C; Inoue, Shigeyoshi

2014-11-20

142

Palladium-N-heterocyclic carbene (NHC)-catalyzed asymmetric synthesis of indolines through regiodivergent C(sp3)-H activation: scope and DFT study.  

Science.gov (United States)

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

143

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

OpenAIRE

A series of imidazolidinium ligand precursors are metallated with Ag2O to give silver(I) N-heterocyclic carbene complexes. All compounds were fully characterized by elemental analyses, 1H-NMR, 13C-NMR and IR spectroscopy techniques. All compounds studied in this work were screened for their in vitro antimicrobial activities against the standard strains: Enterococcus faecalis (ATCC 29212), Staphylococcus aureus (ATCC 29213), Escherichia coli (ATCC 25922), Pseudomonas aeruginosa (ATCC 27853) an...

?lknur Özdemir; Emine Özge Özcan; Selami Günal; Nevin Gürbüz

2010-01-01

144

Unprecedented silicon(II)?calcium complexes with N-heterocyclic silylenes.  

Science.gov (United States)

The first N-heterocyclic silylene (NHSi) complexes of any s-block element to date are reported for calcium: [(?(5)-C5Me5)2Ca?:Si(O-C6H4-2-(t)Bu){(N(t)Bu)2CPh}] (6) and [(?(5)-C5Me5)2Ca?:Si(N(t)BuCH)2] (7). Complexes 6 and 7 are isolable in a facile way upon reaction of the corresponding free N-heterocyclic silylenes (NHSis) with [(?(5)-C5Me5)2Ca] (2). Complexes 6 and 7 were fully characterised by spectroscopic means and the single crystal X-ray diffraction analysis of 6 is also reported. Analysis of the bonding situation by DFT methods including a Bader Atoms in molecules (AIM) analysis is also reported. The bonding interaction between the Si and Ca centres in complexes 6 and 7 can best be viewed as ?-donor-acceptor interactions, with a considerable ionic contribution in the bond. The reactivity towards the oxygen containing substrates THF and benzophenone is also discussed. PMID:25382093

Blom, Burgert; Klatt, Günter; Gallego, Daniel; Tan, Gengwen; Driess, Matthias

2015-01-14

145

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

146

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)

147

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

Directory of Open Access Journals (Sweden)

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

?lknur Özdemir

2010-04-01

148

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

Science.gov (United States)

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

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

2009-05-21

149

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

150

Iron(II) complexes of ditopic carbanionic carbenes.  

Science.gov (United States)

Reaction of dimesityliron(II) (Fe2(mes)4) with the N-heterocyclic carbenes 1,3-bis(2,6-diisopropylphenyl)-imidazol-2-ylidene (IPr) and 1,3-bis(2,6-dimethylphenyl)hexahydropyrimidin-2-ylidene (6-Xyl) afforded the novel trigonal planar complexes [Fe(IPr)(mes)2] (1) and [Fe(6-Xyl)(mes)2] (2), respectively. Both species were structurally characterized by single crystal X-ray diffraction and display structures and magnetic responses consistent with a quintet ground state (S = 2). Reaction of 1 with KC8 in THF afforded K(+) salts of the anionic complex [{:C[N(2,6-(i)Pr2C6H3)]2(CH)C}2Fe(mes)](-) (3) and the homoleptic organometallic anion [Fe(mes)3](-) (4). By contrast, reduction of 2 resulted in extensive decomposition and intractable product mixtures. Complex 3 is coordinated by two ditopic carbanionic carbenes via the C4/C5 position while the C2 position retains unquenched carbenic character and remains vacant for further coordination. This was corroborated by reacting solutions of 3 with one and two equivalents of triethylaluminium (AlEt3) which resulted in the formation of [{Et3Al:C[N(2,6-(i)Pr2C6H3)]2(CH)C}{:C[N(2,6-(i)Pr2C6H3)]2(CH)C}Fe(mes)](-) (5) and [{Et3Al:C[N(2,6-(i)Pr2C6H3)]2(CH)C}2Fe(mes)](-) (6), respectively. Both of these species were structurally characterized as [K(2,2,2-crypt)](+) salts. PMID:24185197

Musgrave, Rebecca A; Turbervill, Robert S P; Irwin, Mark; Herchel, Radovan; Goicoechea, Jose M

2014-03-21

151

Pyrene-based bisazolium salts: from luminescence properties to janus-type bis-N-heterocyclic carbenes.  

Science.gov (United States)

A series of pyrene-based bisazolium salts have been obtained starting from 4,5,9,10-tetrabromo-2,7-di-tert-butylpyrene. The synthetic procedure to the pyrene-bisazoliums (PBIs) reveals an unexpected behavior, as a consequence of the presence of the alkyl groups (alkyl=Me, Et, n-Pr, and n-Bu) coming from the trisalkoxyformate in the final products, instead of the expected tBu of tAmyl groups from the starting tetra-aminated pyrenes. All bisazoliums show fluorescence properties, with emissions in the range of 370-420?nm, and quantum yields ranging from 0.29 to 0.41. The PBIs were used as bis-NHC precursors in the preparation of a series of dirhodium and diiridium complexes, which have been fully characterized. The electrochemical studies on selected dimetallic complexes reveal that the electronic communication between the metals through the polyaromatic linker is negligible. PMID:24753109

Gonell, Sergio; Poyatos, Macarena; Peris, Eduardo

2014-07-28

152

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

Science.gov (United States)

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

153

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

Science.gov (United States)

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

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

2015-02-16

154

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

OpenAIRE

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; Ai-Ping Jin; Li-Xiong Shao

2012-01-01

155

Syntheses, structural, computational, and thermal analysis of acid-base complexes of picric acid with N-heterocyclic bases.  

Science.gov (United States)

Four new acid-base complexes using picric acid [(OH)(NO2)3C6H2] (PA) and N-heterocyclic bases (1,10-phenanthroline (phen)/2,2';6',2"-terpyridine (terpy)/hexamethylenetetramine (hmta)/2,4,6-tri(2-pyridyl)-1,3,5-triazine (tptz)) were prepared and characterized by elemental analysis, IR, NMR and X-ray crystallography. Crystal structures provide detailed information of the noncovalent interactions present in different complexes. The optimized structures of the complexes were calculated in terms of the density functional theory. The thermolysis of these complexes was investigated by TG-DSC and ignition delay measurements. The model-free isoconversional and model-fitting kinetic approaches have been applied to isothermal TG data for kinetics investigation of thermal decomposition of these complexes. PMID:24011225

Goel, Nidhi; Singh, Udai P

2013-10-10

156

Easy access to uranium nucleophilic carbene complexes  

International Nuclear Information System (INIS)

Metathesis reactions of UCl4 with Li2C(Ph2PS)2 in Et2O only afforded the tris-carbene complex [{Li(OEt2)}2-U{=C(Ph2PS)2}3](1), while the bis- and mono-carbene compounds [U{=C(Ph2PS)2}2(THF)2] (2) and [{Li(THF)2}2U{=C(Ph2PS)2}Cl4] (3) were obtained by treatment of UCl4 with Li2C(Ph2PS)2 in a mixture of THF and toluene. The bis- carbene complex 2 was also obtained either from the comproportionation reaction of 1 and UCl4 or protonolysis reaction of U(NEt2)4 with H2C(Ph2PS)2 and was transformed into the mono- carbene complex [U{=C(Ph2PS)2}Cl2(THF)2] (4) by further reaction with UCl4. The utility of these complexes as precursors is illustrated by the synthesis of the bis-cyclopentadienyl derivative [Cp2U{=C(Ph2PS)2}] (5) by treatment of 3 with TlCp. The crystal structures of [U{=C(Ph2PS)2}2(py)2]center dot 1.5py.0.5THF and 5.toluene are reported. (authors)

157

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

Science.gov (United States)

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

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

2015-02-01

158

A user-friendly, all-purpose Pd-NHC (NHC=N-heterocyclic carbene) precatalyst for the negishi reaction: a step towards a universal cross-coupling catalyst.  

Science.gov (United States)

We have developed the first user-friendly Negishi protocol capable of routinely cross-coupling all combinations of alkyl and aryl centers. The use of an easily synthesized, air stable, highly active, well-defined precatalyst PEPPSI-IPr (1; PEPPSI=pyridine-enhanced precatalyst preparation, stabilization and initiation; IPr=diisopropylphenylimidazolium derivative) substantially increases the scope, reliability, and ease-of-use of the Negishi reaction. All organohalides and routinely used pseudohalides were excellent coupling partners, with the use of chlorides, bromides, iodides, triflates, tosylates, and mesylates resulting in high yield of the coupled product. Furthermore, all reactions were performed by using general laboratory techniques, with no glove-box necessary as the precatalyst was weighed and stored in air. Utilization of this methodology allowed for the easy synthesis of an assortment of sterically encumbered biaryls and druglike heteroaromatics, demonstrating the value of the PEPPSI-IPr system. Furthermore, this is also the first time Pd-NHC (NHC=N-heterocyclic carbene) methodology has surpassed the related phosphine-ligated Negishi processes both in activity and use. PMID:16568493

Organ, Michael G; Avola, Stephanie; Dubovyk, Igor; Hadei, Niloufar; Kantchev, Eric Assen B; O'Brien, Christopher J; Valente, Cory

2006-06-14

159

Easy access to uranium nucleophilic carbene complexes  

Energy Technology Data Exchange (ETDEWEB)

Metathesis reactions of UCl{sub 4} with Li{sub 2}C(Ph{sub 2}PS){sub 2} in Et{sub 2}O only afforded the tris-carbene complex [{l_brace}Li(OEt{sub 2}){r_brace}{sub 2}-U{l_brace}=C(Ph{sub 2}PS){sub 2{r_brace}3}](1), while the bis- and mono-carbene compounds [U{l_brace}=C(Ph{sub 2}PS){sub 2{r_brace}2}(THF){sub 2}] (2) and [{l_brace}Li(THF){sub 2{r_brace}2}U{l_brace}=C(Ph{sub 2}PS){sub 2}{r_brace}Cl{sub 4}] (3) were obtained by treatment of UCl{sub 4} with Li{sub 2}C(Ph{sub 2}PS){sub 2} in a mixture of THF and toluene. The bis- carbene complex 2 was also obtained either from the comproportionation reaction of 1 and UCl{sub 4} or protonolysis reaction of U(NEt{sub 2}){sub 4} with H{sub 2}C(Ph{sub 2}PS){sub 2} and was transformed into the mono- carbene complex [U{l_brace}=C(Ph{sub 2}PS){sub 2}{r_brace}Cl{sub 2}(THF){sub 2}] (4) by further reaction with UCl{sub 4}. The utility of these complexes as precursors is illustrated by the synthesis of the bis-cyclopentadienyl derivative [Cp{sub 2}U{l_brace}=C(Ph{sub 2}PS){sub 2}{r_brace}] (5) by treatment of 3 with TlCp. The crystal structures of [U{l_brace}=C(Ph{sub 2}PS){sub 2}{r_brace}2(py){sub 2}]center dot 1.5py.0.5THF and 5.toluene are reported. (authors)

Tourneux, Jean-Christophe; Berthet, Jean-Claude; Thuery, Pierre; Ephritikhine, Michel [CEA, IRAMIS, SIS2M, CNRSUMR3299, 91191, Gif-sur-Yvette (France); Mezailles, Nicolas; Le Floch, Pascal [Laboratoire ' Heteroelements et Coordination' , Ecole Polytechnique, CNRS, 91128, Palaiseau Cedex (France)

2010-07-01

160

Speciation of cobalt, nickel and zinc-ethylenediaminediacetate complexes with N-heterocycle ligand - Synthesis, spectroscopic and structural studies  

Science.gov (United States)

Cobalt, nickel and zinc N-heterocycle chelated ethylenediaminediacetates [Co(edda)(phen)]·(NH 4Cl)·1/3H 2O ( 1), [Ni(edda)(phen)]·3H 2O ( 2), [Co(edda)(bpy)]·(NH 4Cl)·2H 2O ( 3), [Ni(edda)(bpy)]·4H 2O ( 4), [Zn(edda)(bpy)]·4H 2O ( 5) (H 2edda = ethylenediaminediacetic acid, phen = 1,10-phenanthroline, bpy = 2,2'-bipyridine) were isolated in pure forms and characterized spectroscopically. The X-ray structural analyses reveal that neutral mononuclear complexes contain both edda and phen/bpy ligands. Divalent metal ions are octahedrally bound by a bidentate phen or bpy ligand, and a tetradentately edda through carboxyl and amine groups. The co-existences of phen/bpy and edda in the complexes show no decomposition between phen/bpy and edda ligands. This is supported by the trace of 13C NMR spectra with less-bound zinc complex. Further comparisons of the bond distances between Co 2+/Ni 2+/Zn 2+ ions with edda indicate that cobalt and nickel interact much stronger than those of zinc complexes.

Ji, Jin-Long; Huang, Li-Qing; Cai, Yan; Yu, La-Jia; Zhou, Zhao-Hui

2011-05-01

161

Electronic spectra of N-heterocyclic pentacyanoferrate(II) complexes in different solvents, studied by multiconfigurational perturbation theory.  

Science.gov (United States)

Ligand-field and charge-transfer spectra of N-heterocyclic pentacyanoferrate(II) complexes [Fe(CN)5L]n? were investigated using multiconfigurational perturbation theory. The spectrum of [Fe(CN)5(py)]3– was studied in detail under vacuum and in the following polarizable continuum model (PCM) simulated solvents: acetone, acetonitrile, dimethylsulfoxide (DMSO), ethanol, methanol, and water. The ligand-field states proved to be rather insensitive to the solvent environment, whereas much stronger solvent effects were observed for the charge-transfer (CT) transitions. The nature of the intense band was confirmed as a metal-to-ligand charge transfer originating from a 3d(xz)????(b1)* (L)-orbital transition. The difference between the calculated and experimental transition energy of this CT transition is minimal for aprotic solvents, but increases strongly with the solvent proton donor ability in the protic solvents. In an attempt to improve the description of this CT state, up to 14 solvent molecules were explicitly included in the quantum model. In DMSO, the spectra of complexes with ligands L (where L is pyridine, 4-picoline, 4-acetylpyridine, 4-cyanopyridine, pyrazine, and N-methylpyrazinium) correlate very well with the experiment. PMID:23992205

Formiga, André Luiz Barboza; Vancoillie, Steven; Pierloot, Kristine

2013-09-16

162

Chemistry of transition metal carbene complexes: nucleophilic substitution reactions of cyanamide anion to Fischer carbene complexes.  

Science.gov (United States)

Rate constants for the reactions of cyanamide anion N?C-NH(-) with Fischer carbene complexes of the type (CO)(5)M=C(XR)C(6)H(4)Z with M = Cr and W, XR = SMe and OMe, Z = NMe(2), OMe, Me, H, F, Cl and CF(3) in 50% MeCN-50% water (v/v) at 25 °C are reported. N?C-NH(-) shows a much higher reactivity towards these carbene complexes than OH(-), primary aliphatic amines (e.g. n-butylamine) or secondary alicyclic amines (e.g. piperidine) but is slightly less reactive than thiolate ions (e.g. HOCH(2)CH(2)S(-)). The alkoxy carbene complexes were found to react faster than the thiomethyl derivatives, consistent with previous findings for alkoxide ion, CH(CN)(2)(-), OH(-), amine and thiolate ion nucleophiles. Hammett ? values are 3.00 ± 0.08 (k(1)) and 2.98 ± 0.08 (k(2)) for Cr-OMe-Z-N?C-NH(-) reactions and 0.94 ± 0.05 (k(1)) for Cr-SMe-Z-N?C-NH(-) reactions. The ? values for the reaction of Cr-OMe-Z and Cr-SMe-Z with CH(CN)(2)(-) and DABCO (1,4-diazabicyclo[2.2.2]octane) (in 50% MeCN-50% H(2)O (v/v) are comparable to the present reactions. The much higher reactivity and hence much higher ? value for methoxy carbene complexes over the corresponding thiomethyl derivatives is best explained by considering the substituent effects not only on the transition state (TS) but also on the reactant, and consistent with the previously observed pattern. Higher k(1)(W)/k(1)(Cr) ratios for (thiomethyl)carbene complexes as well as methoxy and ethoxycarbene complexes are related to the intrinsic rate constant which is higher for tungsten-carbene complexes than the corresponding Cr ones resulting in an enhanced ratio. This can also be explained by considering the electronegativity of Cr and W, which is higher for the latter; as a result the negative charge on the central metal atom is more localized in case of W causing destabilization of the TS and hence higher reactivity. PMID:23076623

Gangopadhyay, Sumana; Mistri, Tarun; Dolai, Malay; Alam, Rabiul; Ali, Mahammad

2013-01-14

163

Chelating C4-bound imidazolylidene complexes through oxidative addition of imidazolium salts to palladium(0)  

OpenAIRE

Oxidative addition of donor-functionalised 4-iodoimidazolium salts to palladium(0) provides a selective route for the preparation of abnormal chelating N-heterocyclic carbene complexes and enables the introduction of a variety of donor groups. The activation of the C4 position does not necessitate protection of the imidazolium C2 position, thereby leaving this site available for further modification. While metallation of the unsubstituted C2 position of the N-heterocyclic carbene ligand was u...

Kru?ger, Anneke; Kluser, Evelyne; Mu?ller-bunz, Helge; Neels, Antonia; Albrecht, Martin

2011-01-01

164

Pyrido[1,2-a][1,2,4]triazol-3-ylidenes as a new family of stable annulated N-heterocyclic carbenes: synthesis, reactivity, and their application in coordination chemistry and organocatalysis.  

Science.gov (United States)

General synthetic avenues to the pyrido-annulated triazolium salts with different steric and electronic properties have been developed. This architecture can be readily altered with different N-alkyl or aryl substituents at the N2 position of the triazole ring and modifications to the pyridine backbone. Deprotonation of the triazolium salts 12 with NaH led to formation of stable carbenes 11 at room temperature as clearly demonstrated through ESI mass spectra and by observation of the characteristic (13)C NMR resonance for the carbene carbon at delta = 202-208 ppm. In sharp contrast, treatment of these triazolium salts with K2CO3 led to dimerization of free carbenes 11. The dimeric enetetramine (11b)2 could react with elemental sulfur to deliver the corresponding thiourea 16 in toluene at 80 degrees C in good yield. A silver complex with the pyrido[1,2-a][1,2,4]triazol-3-ylidene is described, and the molecular structure of complex 17 was established by X-ray crystallography. The triazolium salts 12 turned out to be powerful catalysts in catalytic benzoin condensations and transesterifications at 25 degrees C. The catalytic activity was largely dependent on the steric and electronic nature of the R(1) and R(2) substituents of the triazolium salt. We rationalized that this type of triazolium-catalyzed benzoin condensations should undergo the "traditional" Breslow mechanism rather than the pathway of the dimer (11)2 as the real catalytic species. PMID:18844416

Ma, Yajun; Wei, Siping; Lan, Jingbo; Wang, Jingzhi; Xie, Rugang; You, Jingsong

2008-11-01

165

Nitrosyl and carbene iron complexes bearing a ?(3)-SNS thioamide pincer type ligand.  

Science.gov (United States)

The previously reported monochelate iron complex with ?(3) SNS thioamide pincer ligand, 2,6-bis(N-2,6-bis(diphenylmethyl)-4-isopropylphenyliminothiolate)pyridine (L(DPM)), [Fe(THF)2(?(3)-L(DPM))], gave novel complexes, [Fe(NHC)(?(3)-L(DPM))] and [Fe(NO)2(?(3)-L(DPM))], by substitution reactions with N-heterocyclic carbene (NHC) and NO molecules, respectively. The X-ray crystal structure of the [Fe(NHC)(?(3)-L(DPM))] complex revealed a unique square planar iron(ii) complex, which was determined to be in an intermediate spin state (S = 1) in benzene from the Evans method. The [Fe(NO)2(?(3)-L(DPM))] complex was determined to have a trigonal bipyramidal geometry from X-ray analysis and was indicated to be diamagnetic from the (1)H NMR spectrum. The ?(NO) stretching vibration of this complex showed two peaks at 1840 cm(-1) and 1790 cm(-1), and also the Fe-N-O bond angles were 168.9(2)° and 168.03(19)°. These findings suggest that the two coordinated NO molecules have neutral radical character, and they are antiferromagnetically coupled with the high-spin iron center. PMID:25407757

Suzuki, Tatsuya; Matsumoto, Jun; Kajita, Yuji; Inomata, Tomohiko; Ozawa, Tomohiro; Masuda, Hideki

2015-01-21

166

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

Directory of Open Access Journals (Sweden)

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

Murat Yi?it

2009-06-01

167

Syntheses and structural characterizations of 24-membered dimetal (Mn, Ni, Fe) macrocyclic complexes and the C-S bond formation between acetylacetone and a mercapto N-heterocycle.  

Science.gov (United States)

An organic ligand 2,5-di(3-pentanedionylthio)-1,3,4-thiadiazole (H2L) reacts with metal (Mn, Ni, Fe) salts, resulting in 24-membered dimetal macrocyclic complexes [MnL(H2O)(dmso)](2).2dmso, [NiL(H2O)(dmf)](2).2dmf, [MnL(dmf)2]2 and [Fe2L2(solvent)2(SO4)] (solvent=dmso; H2O ; dmf). Di-manganese macrocyclic complexes [MnL(dmf)(dmso)]2 and [MnL(H2O)2](2).6H2O can also be obtained directly by aerobic assembly reaction of MnCl2, dipotassium 1,3,4-thiadiazole-2,5-dithiolate (K2tdadt) and acetylacetone (H2acac) in various solvents, accompanying a C-S bond formation between acetylacetone and the mercapto N-heterocycle. Disulfide has been considered as the intermediate in the assembly reaction. Meanwhile an assembly reaction including MnCl2, 2-mercaptobenzimidazole and H2acac has produced an organic compound 2-(3-pentanedionylthio)benzimidazole with a new C-S bond. These dimetal complexes have similar macrocyclic structures, in which solvent molecules and sulfate coordinate to the octahedral metal in trans-configuration, whereas a pair of water molecules are located in octahedral cis-positions for owing to a small steric effect. A host cavity of sufficiently large size exists in the macrocyclic structure to trap the solvent molecules and the sulfate anion. The IR spectra have been used to assign the solvent molecules trapped and the sulfate anion which is shown as a bridged bidentate ligand. Thermal analyses show the stability of the macrocyclic backbone below 200 degrees C and gradual release processes of the trapped solvent molecules. Decomposition and oxidation of the dimetal macrocycle backbone occur at 300-500 degrees C, resulting in a metal sulfate. Further decomposition led to metal oxide at 500-600 degrees C. PMID:17028714

Zhang, Xiaofeng; Chen, Hui; Ma, Chengbing; Chen, Changneng; Liu, Qiutian

2006-09-01

168

Carbene-stabilized beryllium borohydride.  

Science.gov (United States)

The reaction of N-heterocyclic carbene, L:, with BeCl(2) quantitatively yields L:BeCl(2)1 (L: = :C{N(2,6-Pr(i)(2)C(6)H(3))CH}(2)). The carbene-stabilized beryllium borohydride monomer L:Be(BH(4))(2)2 is prepared by the reaction of 1 with LiBH(4). Compound 3, prepared by the reaction of 2 with Na(2)[Fe(CO)(4)]·dioxane, represents an unusual "dual reduction" of the imidazole ring (i.e., hydroboration of the C?C backbone and hydrogenation of the C2 carbene center). PMID:22670857

Gilliard, Robert J; Abraham, Mariham Y; Wang, Yuzhong; Wei, Pingrong; Xie, Yaoming; Quillian, Brandon; Schaefer, Henry F; Schleyer, Paul V R; Robinson, Gregory H

2012-06-20

169

Chelating C4-bound imidazolylidene complexes via oxidative addition of imidazolium salts to palladium(0)  

OpenAIRE

Oxidative addition of donor-functionalised 4-iodoimidazolium salts to palladium(0) provides a selective route for the preparation of chelating abnormal N-heterocylic carbene complexes and enables the introduction of a variety of donor groups. The activation of the C4 position does not necessitate the imidazolium C2 position to be protected, leaving this site available for further modification. While metallation of the unsubstituted C2 position of the N-heterocyclic carbene ligand was unsucces...

Kru?ger, Anneke; Kluser, Evelyne; Mu?ller-bunz, Helge; Neels, Antonia; Albrecht, Martin

2012-01-01

170

Intramolecular C-H/O-H bond cleavage with water and alcohol using a phosphine-free ruthenium carbene NCN pincer complex.  

Science.gov (United States)

Transition metal complexes that exhibit metal-ligand cooperative reactivity could be suitable candidates for applications in water splitting. Ideally, the ligands around the metal should not contain oxidizable donor atoms, such as phosphines. With this goal in mind, we report new phosphine-free ruthenium NCN pincer complexes with a central N-heterocyclic carbene donor and methylpyridyl N-donors. Reaction with base generates a neutral, dearomatized alkoxo-amido complex, which has been structurally and spectroscopically characterized. The tert-butoxide ligand facilitates regioselective, intramolecular proton transfer through a C?H/O?H bond cleavage process occurring at room temperature. Kinetic and thermodynamic data have been obtained by VT NMR experiments; DFT calculations support the observed behavior. Isolation and structural characterization of a doubly dearomatized phosphine complex also strongly supports our mechanistic proposal. The alkoxo-amido complex reacts with water to form a dearomatized ruthenium hydroxide complex, a first step towards phosphine-free metal-ligand cooperative water splitting. PMID:25266279

Prokopchuk, Demyan E; Tsui, Brian T H; Lough, Alan J; Morris, Robert H

2014-12-15

171

Methylation of secondary amines with dialkyl carbonates and hydrosilanes catalysed by iron complexes.  

Science.gov (United States)

Methylation of secondary amines was achieved using dimethyl carbonate or diethyl carbonate as the C1 source under the catalysis of well-defined half-sandwich iron complexes bearing an N-heterocyclic carbene ligand. The reaction proceeded under mild conditions in the presence of hydrosilanes as the reductants, and the amines were obtained with good to excellent isolated yields. PMID:25285339

Zheng, Jianxia; Darcel, Christophe; Sortais, Jean-Baptiste

2014-11-25

172

Cyclic (Amino)[bis(ylide)]carbene as an Anionic Bidentate Ligand for Transition Metal Complexes  

OpenAIRE

The 3-triphenylphosphonio-N-(2,6-diisopropylphenyl)-pyrole reacts with two equivalents of methyl lithium to afford a lithium adduct in which a cyclic (amino)[bis(ylide)]carbene, a novel type of NHC, acts as a 1,4-bidentate ligand via the carbene center and the exocyclic ylidic carbon. This species readily undergoes transmetallation reactions, which allows for the synthesis of a variety of transition metal complexes.

Asay, Matthew; Donnadieu, Bruno; Baceiredo, Antoine; Soleilhavoup, Michele; Bertrand, Guy

2008-01-01

173

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

Science.gov (United States)

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

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

2014-08-18

174

The Regio- and Stereospecific Intermolecular Dehydrative Alkoxylation of Allylic Alcohols Catalyzed by a Gold(I) N-Heterocyclic Carbene Complex  

OpenAIRE

A 1:1 mixture of (IPr)AuCl [IPr = 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidine] and AgClO4 catalyzes the intermolecular dehydrative alkoxylation of primary and secondary allylic alcohols with aliphatic primary and secondary alcohols to form allylic ethers. These transformations are regio- and stereospecific with preferential addition of the alcohol nucleophile at the ?-position of the allylic alcohol syn to the departing hydroxyl group and with predominant formation of the E stereoisomer...

Mukherjee, Paramita; Widenhoefer, Ross A.

2013-01-01

175

The regio- and stereospecific intermolecular dehydrative alkoxylation of allylic alcohols catalyzed by a gold(I) N-heterocyclic carbene complex.  

Science.gov (United States)

A 1:1 mixture of [AuCl(IPr)] (IPr = 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidine) and AgClO(4) catalyzes the intermolecular dehydrative alkoxylation of primary and secondary allylic alcohols with aliphatic primary and secondary alcohols to form allylic ethers. These transformations are regio- and stereospecific with preferential addition of the alcohol nucleophile at the ?-position of the allylic alcohol syn to the departing hydroxyl group and with predominant formation of the E stereoisomer. The minor ? regioisomer is formed predominantly through a secondary reaction manifold involving regioselective ?-alkoxylation of the initially formed allylic ether rather than by the direct ?-alkoxylation of the allylic alcohol. PMID:23348826

Mukherjee, Paramita; Widenhoefer, Ross A

2013-03-01

176

Hydrolysis of Fischer carbene complexes. Steric effects of the pi-donor group.  

Science.gov (United States)

Rate constants for the hydrolysis of Fischer carbenes (CO)5Cr=C(OR)Ph (R = n-propyl, neopentyl, isopropyl, and menthyl) in 50% MeCN-50% water (v/v) at 25 degrees C are reported. The rate constants for the addition of -OH to the carbene carbon are 5.3, 3.7, 0.84, and 0.01 M(-1) s(-1), respectively. These rate constants give linear correlations with the corresponding rate constants for the hydrolysis of esters such as acetate, benzoate, and formiate. The slopes of the plots of the observed rate constants for the carbenes vs the rate constants for the esters are 1.4 and 1.2 for acetate and benzoate, respectively, indicating that the factors that decrease the reactivity of the two types of compounds are similar, but the carbenes show higher sensitivity. The rate constants are well correlated with several steric parameters giving a value of -3.84 for the Charton's psi parameter. The results show that the steric bulkiness of the R group is the main factor determining the reactivity differences for these carbene complexes. PMID:16526789

Zoloff Michoff, Martin E; de Rossi, Rita H; Granados, Alejandro M

2006-03-17

177

Reactivity of Tp(Me2) -supported yttrium alkyl complexes toward aromatic N-heterocycles: ring-opening or C-C bond formation directed by C-H activation.  

Science.gov (United States)

Unusual chemical transformations such as three-component combination and ring-opening of N-heterocycles or formation of a carbon-carbon double bond through multiple C-H activation were observed in the reactions of Tp(Me2) -supported yttrium alkyl complexes with aromatic N-heterocycles. The scorpionate-anchored yttrium dialkyl complex [Tp(Me2) Y(CH2 Ph)2 (THF)] reacted with 1-methylimidazole in 1:2 molar ratio to give a rare hexanuclear 24-membered rare-earth metallomacrocyclic compound [Tp(Me2) Y(?-N,C-Im)(?(2) -N,C-Im)]6 (1; Im=1-methylimidazolyl) through two kinds of C-H activations at the C2- and C5-positions of the imidazole ring. However, [Tp(Me2) Y(CH2 Ph)2 (THF)] reacted with two equivalents of 1-methylbenzimidazole to afford a C-C coupling/ring-opening/C-C coupling product [Tp(Me2) Y{?(3) -(N,N,N)-N(CH3 )C6 H4 NHCH?C(Ph)CN(CH3 )C6 H4 NH}] (2). Further investigations indicated that [Tp(Me2) Y(CH2 Ph)2 (THF)] reacted with benzothiazole in 1:1 or 1:2 molar ratio to produce a C-C coupling/ring-opening product {(Tp(Me2) )Y[?-?(2) :?(1) -SC6 H4 N(CH?CHPh)](THF)}2 (3). Moreover, the mixed Tp(Me2) /Cp yttrium monoalkyl complex [(Tp(Me2) )CpYCH2 Ph(THF)] reacted with two equivalents of 1-methylimidazole in THF at room temperature to afford a trinuclear yttrium complex [Tp(Me2) CpY(?-N,C-Im)]3 (5), whereas when the above reaction was carried out at 55?°C for two days, two structurally characterized metal complexes [Tp(Me2) Y(Im-Tp(Me2) )] (7; Im-Tp(Me2) =1-methyl-imidazolyl-Tp(Me2) ) and [Cp3 Y(HIm)] (8; HIm=1-methylimidazole) were obtained in 26 and 17?% isolated yields, respectively, accompanied by some unidentified materials. The formation of 7 reveals an uncommon example of construction of a C?C bond through multiple C-H activations. PMID:24339020

Yi, Weiyin; Zhang, Jie; Huang, Shujian; Weng, Linhong; Zhou, Xigeng

2014-01-13

178

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

179

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

OpenAIRE

A flexible, efficient and straightforward methodology for the synthesis of N-heterocyclic carbene gold(I)–amide complexes is reported. Reaction of the versatile building block [Au(OH)(IPr)] (1) (IPr = 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene) with a series of commercially available (hetero)aromatic amines leads to the synthesis of several [Au(NRR’)(IPr)] complexes in good yields and with water as the sole byproduct. Interestingly, these complexes present luminescence properties. U...

Go?mez-sua?rez, Adria?n; Nelson, David J.; Thompson, David G.; Cordes, David B.; Graham, Duncan; Slawin, Alexandra M. Z.; Nolan, Steven P.

2013-01-01

180

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

Science.gov (United States)

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

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

2014-12-15

181

Multi-component reactions involving group 6 Fischer carbene complexes: a source of inspiration for future catalytic transformations.  

Science.gov (United States)

The ability of heteroatom stabilized Fischer carbene complexes (FCCs) to participate in multicomponent reactions (MCRs) has become a characteristic of such organometallics, particularly of chromium carbenes. This feature article updates the main results in this field during the last lustrum, highlighting the ability of FCCs for the construction of densely functionalized frameworks, mainly through the successive incorporation of unsaturated moieties (alkynes, CO ligands,…) in a sequential manner. Examples where up to seven components are coupled will be presented. PMID:20835424

Fernández-Rodríguez, Manuel Ángel; García-García, Patricia; Aguilar, Enrique

2010-11-01

182

Metathesis of alkenes using ruthenium carbene complexes / K.N.G. Mtshatsheni  

OpenAIRE

In this study different ruthenium carbene complexes, Grubbs 1 and 2 were investigated for the reactions of 1-, 2-, 3-octene and 1-tetradecene. All reactions were conducted in glass mini reactors equipped with Mininert® valves under a dry nitrogen atmosphere. A heating block was used to heat the reactors. Gas chromatography was used to determine the product composition of reaction mixtures. The influence of reaction temperature, solvents and catalyst concentration on the rea...

Mtshatsheni, Kgomotso Ntombizodwa Gina

2005-01-01

183

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

OpenAIRE

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

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

2005-01-01

184

Fluoride, bifluoride and trifluoromethyl complexes of iridium(i) and rhodium(i).  

Science.gov (United States)

Herein we report robust methods for the preparation and full characterisation of a range of Ir(i) and Rh(i) fluoride and bifluoride complexes using N-heterocyclic carbenes (NHCs) as ancillary ligands. The processes that link the fluoride and the bifluoride species are investigated and reports of the first Ir-bifluoride and Ir(i)-NHC and Rh(i)-NHC trifluoromethyl complexes are revealed. PMID:25358404

Truscott, Byron J; Nahra, Fady; Slawin, Alexandra M Z; Cordes, David B; Nolan, Steven P

2015-01-01

185

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

186

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

International Nuclear Information System (INIS)

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

187

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

OpenAIRE

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

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

2010-01-01

188

A persistent P,N-heterocyclic carbenew  

OpenAIRE

Conjugate acids of cyclic (amino)(phosphino)carbenes (P-NHCs) have been prepared, and several di erent processes have been observed during their deprotonation, which include the formation of a metastable P-NHC, an azomethine ylide, and a bicyclic phosphirane.

Frey, Guido D.; Song, Maoying; Bourg, Jean-baptiste; Donnadieu, Bruno; Soleilhavoup, Michele; Bertrand, Guy

2008-01-01

189

Electrochemical illumination of thienyl and ferrocenyl chromium(0) Fischer carbene complexes  

OpenAIRE

A series of ferrocenyl and thienyl mono- and biscarbene chromium(0) complexes 1–6 were synthesised. The complexes were characterised both spectroscopically and electrochemically, and the single crystal X-ray structure of 3 was determined. Electrochemical measurements in CH2Cl2 revealed that the carbene double bond of 1–6 is reduced to an anion radical, ?Cr–C? at formal reduction potentials

Westhuizen, Belinda; Swarts, Pieter J.; Strydom, Ian; Liles, David C.; Fernandez, Israel; Swarts, Jannie C.; Bezuidenhout, Daniela Ina

2013-01-01

190

Synthesis and reactivity of metal carbene complexes with heterobiaryl spacer substituents  

OpenAIRE

Mono- and binuclear Fischer carbene complexes, [M(CO)5{C(OR)Ar-ArX}], X = H, {C(OR)M(CO)5}; M, M = W or Cr; R = Me, Et or (CH2)4OMe; Ar = thiophene, N-methylpyrrole or furan units 1–20, were synthesized. For this purpose, mono-, bi- or stepwise lithiated bithiophene, N,N-dimethylbipyrrole, thienylfuran and N-methyl(thienyl)pyrrole were reacted with chromium and tungsten hexacarbonyl precursors. Dilithiation in the 2- and 9-positions of N-methyl(thienyl)pyrrole could not be achieved. Alkylat...

Lotz, Simon; Crause, Chantelle; Olivier, Andrew John; Liles, David C.; Go?rls, Helmar; Landman, Marile; Bezuidenhout, Daniela Ina

2008-01-01

191

Oxygenation of ruthenium carbene complexes containing naphthothiophene or naphthofuran: spectroscopic and DFT studies.  

Science.gov (United States)

The aryl propargylic alcohol 1-[2-(thiophen-3-yl)phenyl]prop-2-yn-1-ol (1a) is readily prepared from 2-(thiophen-3-yl)benzaldehyde. In the presence of visible light, treatment of 1a with one-half mole equivalent of [Ru]Cl ([Ru]=Cp(dppe)Ru) (dppe=1,2-bis(diphenylphosphino)ethane) and NH4PF6 in O2 affords the naphtha[2,1-b]thiophene-4-carbaldehyde (4a) in high yields. The cyclization reaction of 1a proceeds through the formation of the carbene complex 2a that contains the naphtha[2,1-b]thiophene ring, which is isolated in a 1:1 stoichiometric reaction. The C-C bond formation between the inner carbon of the terminal triple bond and the heterocyclic ring is confirmed by structure determination of 2a using single-crystal X-ray diffraction analysis. Facile oxygenation of 2a by O2 yields the aldehyde product 4a accompanied by the formation of phosphine oxide of dppe. Oxygen is most likely activated by coordination to the ruthenium center when one PPh2 unit of the dppe ligand dissociates. This dissociated PPh2 unit then reacts with the coordinated oxygen nearby to generate half-oxidized dppe ligand and an unobserved oxo-carbene intermediate. Coupling of the oxo/carbene ligands followed by demetalation then yields 4a. Presumably the resulting complex with the half-oxidized dppe ligand continuously promotes cyclization/oxygenation of 1a to yield the second aldehyde molecule. In alcohol such as MeOH or EtOH, the oxygenation reaction affords a mixture of 4a and the corresponding esters 5a or 5a'. Four other aryl propargylic alcohols 1b-e, which contain thiophen-2-yl, isopropenyl, fur-3-yl, and fur-2-yl, respectively, on the aryl ring are also prepared. Analogous aldehydes 4b-e are similarly prepared from 1b-e, respectively. For oxygenations of 1b, 1d, and 1e in alcohol, mixtures of aldehyde 4, ester 5, and acetal 8 are obtained. The carbene complex 2b obtained from 1b was also characterized by single-crystal X-ray diffraction analysis. The UV/Vis spectra of 2a and 2b consist of absorption bands with a high extinction coefficient. From DFT calculations on 2a and 2b, the visible light is found to populate the LUMO antibonding orbital of mainly Ru=C bonds, thereby weakening the Ru=C bond and promoting the oxygenation/demetalation reactions of 2. PMID:23929767

Tsai, Fu-Yuan; Lo, Ji-Xian; Hsu, Hsin-Tzu; Lin, Ying-Chih; Huang, Shou-Ling; Wang, Ju-Chun; Liu, Yi-Hong

2013-11-01

192

A 4,5-diphosphino-substituted imidazolium salt: a building block for the modular synthesis of mixed diphosphine-NHC heterometallic complexes.  

Science.gov (United States)

Fused in the same molecule! An N-heterocyclic carbene and a diphosphine are generated and used in the modular synthesis of a variety of target heterometallic complexes. The experimental approach involves formation of a unique 4,5-bis(diphenylphosphino)-1,3-dimethyl-imidazolium salt, simply by starting from 1-methylimidazole (see scheme; M(1) = Cr, Mn; M(2) = Au, Rh, Pd; LiHMDS = LiN(SiMe(3))(2)). PMID:22407582

Ruiz, Javier; Mesa, Alejandro F

2012-04-10

193

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

Science.gov (United States)

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

Dahcheh, Fatme; Stephan, Douglas W

2014-12-23

194

A bonding model for gold(I) carbene complexes  

OpenAIRE

The last decade has witnessed dramatic growth in the number of reactions catalyzed by electrophilic gold complexes. While proposed mechanisms often invoke the intermediacy of gold-stabilized cationic species, the nature of bonding in these intermediates remains unclear. Herein, we propose that the carbon-gold bond in these intermediates is comprised of varying degrees of both ? and ?-bonding; however, the overall bond order is generally less than or equal to unity. The bonding in a given go...

Benitez, Diego; Shapiro, Nathan D.; Tkatchouk, Ekaterina; Wang, Yiming; Goddard, William A.; Toste, F. Dean

2009-01-01

195

Generation of carbene complexes in decomposition of organometallic compounds of transition metals  

International Nuclear Information System (INIS)

A method of forming carbine complexes initiating polymerization of cycloolephines with use being made of a redox system is considered herein. It has been established that one of such systems may involve decomposition of compounds of the general formula Rsub(3)ZCHsub(2)WXsub(n). There is described the decomposition of an organo-metallic compound, accompanied by formation of radicals (CH3)SicH2WCL5 initiating polymerization of cycloolephines at temperatures down to -78 deg C. The decomposition products are identified by gas-liquid chromatography, paramagnetic resonance and mass-spectrometry techniques. The composition of the decomposition products is given. It is concluded that some organo-metallic compounds of transition metals may serve as sources of carbenes in solutions at low temperatures

196

Rhodium carbene complexes as versatile catalyst precursors for Si-H bond activation.  

Science.gov (United States)

Rhodium(III) complexes comprising monoanionic C,C,C-tridentate dicarbene ligands activate Si-H bonds and catalyse the hydrolysis of hydrosilanes to form silanols and siloxanes with concomitant release of H(2). In dry MeNO(2), selective formation of siloxanes takes place, while changing conditions to wet THF produces silanols exclusively. Silyl ethers are formed when ROH is used as substrate, thus providing a mild route towards the protection of alcohols with H(2) as the only by-product. With alkynes, comparably fast hydrosilylation takes place, while carbonyl groups are unaffected. Further expansion of the Si-H bond activation to dihydrosilanes afforded silicones and polysilyl ethers. Mechanistic investigations using deuterated silane revealed deuterium incorporation into the abnormal carbene ligand and thus suggests a ligand-assisted mechanism involving heterolytic Si-H bond cleavage. PMID:22162081

Krüger, Anneke; Albrecht, Martin

2012-01-01

197

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

198

Role of gold(I) ?-oxo carbenes in the oxidation reactions of alkynes catalyzed by gold(I) complexes.  

Science.gov (United States)

The gas phase structures of gold(I) complexes formed by intermolecular oxidation of selected terminal (phenylacetylene) and internal alkynes (2-butyne, 1-phenylpropyne, diphenylacetylene) were investigated using tandem mass spectrometry and ion spectroscopy in conjunction with quantum-chemical calculations. The experiments demonstrated that the primarily formed ?-gold(I) vinyloxypyridinium complexes readily undergo rearrangement, dependent on their substituents, to either gold(I) ?-oxo carbenenoids (a synthetic surrogate of the ?-oxo carbenes) or pyridine adducts of gold(I) enone complexes in the condensed phase and that the existence of naked ?-oxo carbenes is highly improbable. Isotopic labeling experiments performed with the reaction mixtures clearly linked the species that exist in solution to the ions transferred to the gas phase. The ions were then fully characterized by CID experiments and IRMPD spectroscopy. The conclusions based on the experimental observations perfectly correspond with the results from quantum-chemical calculations. PMID:25068382

Schulz, Ji?í; Jašíková, Lucie; Skríba, Anton; Roithová, Jana

2014-08-13

199

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

200

Electrochemical illumination of thienyl and ferrocenyl chromium(0) Fischer carbene complexes.  

Science.gov (United States)

A series of ferrocenyl and thienyl mono- and biscarbene chromium(0) complexes 1-6 were synthesised. The complexes were characterised both spectroscopically and electrochemically, and the single crystal X-ray structure of 3 was determined. Electrochemical measurements in CH2Cl2 revealed that the carbene double bond of 1-6 is reduced to an anion radical, (-)Cr-C? at formal reduction potentials 0.95 V. The reactivity towards follow-up chemical reactions of the anodically produced Cr(II) species is much higher than the reactivity of the cathodically produced radical anions as the latter was still observably reoxidised to the parent Cr=C species at fast scan rates. The ferrocenyl group is oxidised electrochemically reversibly to ferrocenium at larger potentials than the electrochemically reversible oxidation of the Cr(0) centre to Cr(I). That all redox centres in 1-6 are involved in one-electron transfer steps was confirmed by comparing the ferrocenyl voltammetric wave with those of the other redox centres in linear sweep voltammetric experiments. The ferrocenyl group was electrochemically shown to stabilise the Cr=C centre almost as much as the NHBu, and much more than the ethoxy and thienyl groups. PMID:23417243

van der Westhuizen, Belinda; Swarts, Pieter J; Strydom, Ian; Liles, David C; Fernández, Israel; Swarts, Jannie C; Bezuidenhout, Daniela I

2013-04-21

201

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

202

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

Science.gov (United States)

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

Wang, Fen; Meng, Qingxi; Li, Ming

203

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

OpenAIRE

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 spectr...

Monot, Julien; Fensterbank, Louis; Malacria, Max; Laco?te, Emmanuel; Geib, Steven J.; Curran, Dennis P.

2010-01-01

204

Spectral, structural, and electrochemical properties of ruthenium porphyrin diaryl and aryl(alkoxycarbonyl) carbene complexes: influence of carbene substituents, porphyrin substituents, and trans-axial ligands.  

Science.gov (United States)

A wide variety of ruthenium porphyrin carbene complexes, including [Ru(tpfpp)(CR(1)R(2))] (CR(1)R(2) = C(p-C(6)H(4)Cl)(2) 1 b, C(p-C(6)H(4)Me)(2) 1 c, C(p-C(6)H(4)OMe)(2) 1 d, C(CO(2)Me)(2) 1 e, C(p-C(6)H(4)NO(2))CO(2)Me 1 f, C(p-C(6)H(4)OMe)CO(2)Me 1 g, C(CH==CHPh)CO(2)CH(2)(CH==CH)(2)CH(3) 1 h), [Ru(por)(CPh(2))] (por=tdcpp 2 a, 4-Br-tpp 2 b, 4-Cl-tpp 2 c, 4-F-tpp 2 d, tpp 2 e, ttp 2 f, 4-MeO-tpp 2 g, tmp 2 h, 3,4,5-MeO-tpp 2 i), [Ru(por)[C(Ph)CO(2)Et

Li, Yan; Huang, Jie-Sheng; Xu, Guo-Bao; Zhu, Nianyong; Zhou, Zhong-Yuan; Che, Chi-Ming; Wong, Kwok-Yin

2004-07-19

205

Oxidation-promoted activation of a ferrocene C-H bond by a rhodium complex.  

Science.gov (United States)

The oxidation of a rhodium(I) complex containing a ferrocene-based heterodifunctional phosphine N-heterocyclic carbene (NHC) ligand produces a stable, planar chiral rhodium(III) complex with an unexpected C-H activation on ferrocene. The oxidation of rhodium(I) to rhodium(III) may be accomplished by initial oxidation of ferrocene to ferrocenium and subsequent electron transfer from rhodium to ferrocenium. Preliminary catalytic tests showed that the rhodium(III) complex is active for the Grignard-type arylation of 4-nitrobenzaldehyde via C-H activation of 2-phenylpyridine. PMID:23467475

Labande, Agnès; Debono, Nathalie; Sournia-Saquet, Alix; Daran, Jean-Claude; Poli, Rinaldo

2013-05-14

206

Carbene-, Vinylidene and Allenylidene-Complexes of Ruthenium with Heteroscorpionate Ligands  

OpenAIRE

Im Rahmen der vorliegenden Dissertation wurden neutrale Carben-, Vinyliden- und Allenyliden-Komplexe mit Bispyrazolylacetato-Liganden synthetisiert und charakterisiert. Die erhaltenen Komplexe wiesen fast durchgängig eine für Organometallverbindungen sehr hohe Stabilität gegenüber Sauerstoff und Wasser auf. Für die Benzyliden-Komplexe wurde Aktivität als Katalysatoren in der Ringschlussmetathese gefunden. Fragen zur strukturellen Isomerie wurden mittels zweidimensionaler NMR-Experimente...

Kopf, Henning

2008-01-01

207

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

International Nuclear Information System (INIS)

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

208

On the mechanism of the palladium bis(NHC) complex catalyzed CH functionalization of propane: experiment and DFT calculations.  

Science.gov (United States)

We report a detailed mechanistic study on the CH functionalization of alkanes by palladium complexes with chelating bis(N-heterocyclic carbene) (NHC) complexes. The experimental results are complemented by detailed DFT calculations, which allow us to rationalize the regioselectivity and the catalytic activity. The study includes a library of catalysts with different electronic and steric properties, kinetic data, and isotope effects. The combined experimental and computational results favor a mechanism involving organometallic palladium(IV) intermediates. Furthermore, it is shown that at high halide loadings a different mechanism is operative. PMID:25251747

Munz, Dominik; Strassner, Thomas

2014-11-01

209

Controlled CO release using photochemical, thermal and electrochemical approaches from the amino carbene complex [(CO)?CrC(NC?H?)CH?].  

Science.gov (United States)

Multimodal photo, thermal and electrochemical approaches toward CO release from the amino carbene complex [(CO)5CrC(NC4H8)CH3] is reported. Picosecond time resolved infrared spectroscopy was used to probe the photo-induced early state dynamics leading to CO release, and DFT calculations confirmed that CO release occurs from a singlet excited state. PMID:25188765

McMahon, Suzanne; Rochford, Jonathan; Halpin, Yvonne; Manton, Jennifer C; Harvey, Emma C; Greetham, Gregory M; Clark, Ian P; Rooney, A Denise; Long, Conor; Pryce, Mary T

2014-10-21

210

Competitive pathways in the reaction of lithium oxy-ortho-quinodimethanes and Fischer alkoxy alkynyl carbene complexes: synthesis of highly functionalised seven-membered benzocarbocycles.  

Science.gov (United States)

Up to four different outcomes have been found for the reaction between 1-oxy-ortho-quinodimethanes (oQDMs) and alkoxy alkynyl Fischer carbene complexes (FCCs). The product formed depends on the structure of both reagents and on the reaction solvent. The pathways can be topologically classified as a [4C+2C], a [3(2C+O)+3C], and two different [4C+3C] processes and, in all these sequences, 1-oxy-oQDMs behave as enolates or as vinylogous enolates. The reaction of Choy and Yang's unsubstituted oQDM 1 with tungsten alkynyl FCCs is solvent controlled; thus, selective formation of benzocycloheptenones can be achieved in THF, whereas exclusive synthesis of benzocycloheptene ketals is reached in diethyl ether. On the other hand, THF is the solvent of choice to form benzocycloheptene ketals when an alkyl or aryl group is placed at position?1 of the oQDM in its reaction with tungsten carbene complexes; however, a pyranylidene carbene complex is formed when a chromium carbene complex is used. Alternatively, the presence of bulky alkoxy groups in the FCC component favours a Diels-Alder aromatisation sequence, which leads to 1-naphthyl FCCs. Furthermore, the isolation and the characterisation of several deuterated compounds by labelling experiments have provided some insight into the reaction pathways, and mechanisms consistent with those findings have been established and several reaction intermediates have been identified. PMID:21207574

García-García, Patricia; Novillo, Carlos; Fernández-Rodríguez, Manuel A; Aguilar, Enrique

2011-01-10

211

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

212

Cleavage of Ni-(?2-S)-Ni Bridges in Dinuclear Nickel(II) Dithiolate Pincer Complexes and Related Reactions  

OpenAIRE

Pyridine-2,6-dimethanethiolate and pyridine-2,6-dithiocarboxylate form sparingly soluble NiII pincer complexes formulated as [Ni(pdmt)]2 and [Ni(pdtc)]2, respectively, with two Ni-(?2-S)-Ni bridges. In acetonitrile reaction systems, the latter undergoes the facile bridge cleavage reactions [Ni(pdtc)]2 + 2L0,? ? 2[Ni(pdtc)L]0,? with an extensive set of nucleophiles to afford planar mononuclear products with L? = halide, CN, Me3SiO?, RS? and L0 = Et3P and a N-heterocyclic carbene. ...

Huang, Deguang; Deng, Liang; Sun, Jibin; Holm, R. H.

2009-01-01

213

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

214

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

215

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

Science.gov (United States)

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

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

2014-10-01

216

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

Energy Technology Data Exchange (ETDEWEB)

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

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

2010-07-01

217

Cyclic Alkyl Amino Carbene (CAAC) Ruthenium Complexes as Remarkably Active Catalysts for Ethenolysis.  

Science.gov (United States)

An expanded family of ruthenium-based metathesis catalysts bearing cyclic alkyl amino carbene (CAAC) ligands was prepared. These catalysts exhibited exceptional activity in the ethenolysis of the seed-oil derivative methyl oleate. In many cases, catalyst turnover numbers (TONs) of more than 100?000 were achieved, at a catalyst loading of only 3?ppm. Remarkably, the most active catalyst system was able to achieve a TON of 340?000, at a catalyst loading of only 1?ppm. This is the first time a series of metathesis catalysts has exhibited such high performance in cross-metathesis reactions employing ethylene gas, with activities sufficient to render ethenolysis applicable to the industrial-scale production of linear ?-olefins (LAOs) and other terminal-olefin products. PMID:25522160

Marx, Vanessa M; Sullivan, Alexandra H; Melaimi, Mohand; Virgil, Scott C; Keitz, Benjamin K; Weinberger, David S; Bertrand, Guy; Grubbs, Robert H

2015-02-01

218

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

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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

219

Expanded ring diaminocarbene palladium complexes: synthesis, structure, and Suzuki-Miyaura cross-coupling of heteroaryl chlorides in water.  

Science.gov (United States)

A series of new 6- and 7-membered N-heterocyclic carbene (NHC) complexes of palladium (NHC)Pd(cinn)Cl (cinn = cinnamyl = 3-phenylallyl) were synthesized and characterized structurally in the solid state. The influence of ring size (5, 6 or 7) and bulkiness of N-aryl substituents (Mes = 2,4,6-trimethylphenyl, or Dipp = 2,6-diisopropylphenyl) in carbenes on palladium catalysed Suzuki-Miyaura cross-coupling was revealed. Due to the unique stereoelectronic properties of expanded ring NHCs, a versatile, highly efficient green protocol of coupling of heteroaromatic chlorides and bromides with boronic acids has been developed. High quantitative yields of biaryls were achieved with water as solvent, under air, using low catalyst and phase transfer agent loadings, and with mild and environmentally benign base NaHCO3. PMID:23493919

Kolychev, Eugene L; Asachenko, Andrey F; Dzhevakov, Pavel B; Bush, Alexander A; Shuntikov, Viacheslav V; Khrustalev, Victor N; Nechaev, Mikhail S

2013-05-21

220

Tantalum catalyzed hydroaminoalkylation for the synthesis of ?- and ?-substituted N-heterocycles.  

Science.gov (United States)

Unprotected secondary amines are directly alkylated by C-H functionalization adjacent to nitrogen, thereby opening new routes toward the synthesis of ?- and ?-alkylated N-heterocycles. ?-Alkylated piperidine, piperazine, and azepane products are prepared from heterocycles and alkenes in an atom-economic reaction with excellent regio- and diastereoselectivity. ?-Alkylated N-heterocycles are synthesized via a scalable one-pot alkylation/cyclization procedure generating 3-methylated azetidines, pyrrolidines, and piperidines. PMID:23600625

Payne, Philippa R; Garcia, Pierre; Eisenberger, Patrick; Yim, Jacky C-H; Schafer, Laurel L

2013-05-01

221

Fischer-type gold(I) carbene complexes stabilized by aurophilic interactions  

OpenAIRE

The synthesis and structure of rare acyclic alkoxy- and aminocarbene complexes of gold(I) are reported, including a novel ferrocenophane dinuclear biscarbene complex. X-Ray diffraction analyses and DFT calculations reveal that these complexes are stabilized by genuine aurophilic interactions.

Bezuidenhout, Daniela Ina; Westhuizen, Belinda; Rosenthal, Amos J.; Wo?rle, Michael; Liles, David C.; Fernandez, Israel

2014-01-01

222

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

223

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

224

Lanthanide tri-benzyl complexes: structural variations and useful precursors to phosphorus-stabilised lanthanide carbenes.  

Science.gov (United States)

Reaction of [Ln(I)3(THF)4] (Ln = Ce, Pr) or [Ln(I)3(THF)3.5] (Ln = Nd, Sm, Gd, Dy, Er) with three equivalents of [KBz] (Bz = CH2C6H5) at 0 degrees C afforded the corresponding lanthanide tri-benzyl complexes [Ln(Bz)3(THF)3] [Ln = Ce (2), Pr (3), Nd (4), Sm (5), Gd (6), Dy (7), Er (8) La (11)] in 48-75% crystalline yields, with the exception of the redox active samarium complex, which was isolated in poor (20%) yield. Complexes 2-8 were found to adopt distorted octahedral geometries, where the Bz and THF groups are bound in a mutually fac manner in the solid state. Although the series is structurally similar, classification of three structural types can be made on the basis of the lanthanide contraction: (i) complexes which exhibit three eta(2) Ln...C(ipso) contacts (1-4, 11); (ii) complexes which show one eta(2) Ln...C(ipso) contact (5); (iii) complexes with no multi-hapto interactions (6-8). For ytterbium, the mixed valence, Yb(II)/Yb(III) complex [Yb(II)(Bz)(THF)5]+[Yb(III)(Bz)4(THF)2]- (9) was reproducibly formed at 0 degrees C and -78 degrees C as a result of partial (50%) Yb(III) --> Yb(II) reduction with concomitant formation of half an equivalent of 1,2-diphenylethane by oxidative coupling. Tri-valent [Yb(Bz)3(THF)3] (10) was apparently not formed. The synthetic utility of tri-benzyl lanthanide complexes 2-8 and 11 were tested in reactions with the bis-(iminophosphorano)methane H2C(PPh2NSiMe3)2 (H2-BIPM), which afforded [Ln(BIPM)(H-BIPM)] [Ln = La (12), Ce (13), Pr (14), Nd (15), Sm (16), Gd (17)] and [Ln(BIPM)(Bz)(THF)] [Ln = Dy (18), Er (19)]. Compounds 2-9 and 12-19 have been variously characterised by X-ray crystallography, multi-nuclear NMR spectroscopy, FTIR spectroscopy, room temperature Evans method solution magnetic moments and CHN micro-analyses. PMID:20023987

Wooles, Ashley J; Mills, David P; Lewis, William; Blake, Alexander J; Liddle, Stephen T

2010-01-14

225

Rhodium carbene complexes as versatile catalyst precursors for Si–H bond activation  

OpenAIRE

Rhodium(III) complexes comprising monoanionic C,C,C-tridentate dicarbene ligands activate Si–H bonds and catalyse the hydrolysis of hydrosilanes to form silanols and siloxanes with concomitant release of H2. In dry MeNO2, selective formation of siloxanes takes place, while changing conditions to wet THF produces silanols exclusively. Silylethers are formed when ROH is used as substrate, thus providing a mild route towards the protection of alcohols with H2 as the only by-product. With alkyn...

Kru?ger, Anneke; Albrecht, Martin

2012-01-01

226

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

227

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

Science.gov (United States)

Summary A flexible, efficient and straightforward methodology for the synthesis of N-heterocyclic carbene gold(I)–amide complexes is reported. Reaction of the versatile building block [Au(OH)(IPr)] (1) (IPr = 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene) with a series of commercially available (hetero)aromatic amines leads to the synthesis of several [Au(NRR’)(IPr)] complexes in good yields and with water as the sole byproduct. Interestingly, these complexes present luminescence properties. UV–vis and fluorescence measurements have allowed the identification of their excitation and emission wavelengths (?max). These studies revealed that by selecting the appropriate amine ligand the emission can be easily tuned to achieve a variety of colors, from violet to green. PMID:24204434

Gómez-Suárez, Adrián; Nelson, David J; Thompson, David G; Cordes, David B; Graham, Duncan; Slawin, Alexandra M Z

2013-01-01

228

Concise formal synthesis of (-)-7-deoxyloganin via N-heterocyclic carbene catalysed rearrangement of ?,?-unsaturated enol esters.  

Science.gov (United States)

NHC catalysed rearrangement of ?,?-unsaturated enol esters derived from formyl acetates and cyclopentyl annulated ?,?-unsaturated acids provides the cyclopentapyranone core of (-)-7-deoxyloganin (1) with diastereo- and chemoselectivity in 6 steps starting from (-)-citronellal. The elaboration to the natural product has been investigated using two new approaches. The most successful intercepts our previous work on (-)-7-deoxyloganin (1) allowing completion of a formal total synthesis in 10-steps. PMID:22024770

Candish, Lisa; Lupton, David W

2011-12-01

229

N-heterocyclic carbene/Lewis acid strategy for the stereoselective synthesis of spirocyclic oxindole-dihydropyranones.  

Science.gov (United States)

Under the cooperative catalysis of NHC/Lewis acid, the mild, straightforward [4 + 2] annulation of ?-bromo-?,?-unsaturated aldehydes bearing ?-H with isatin derivatives gave spirocyclic oxindole-dihydropyranones stereoselectively. This approach is particularly attractive due to the concise construction, avoidance of external oxidants, and the potential utilization value of final products in molecular biology and pharmacy. PMID:24987936

Xiao, Zhaoxin; Yu, Chenxia; Li, Tuanjie; Wang, Xiang-Shan; Yao, Changsheng

2014-07-18

230

Quantum-chemical investigation of the nature of metal-carbene and metal-olefin bonds in complexes [ClnM(C2H4)]- (M=Mo,Pd)  

International Nuclear Information System (INIS)

On the basis of electron structure calculation using Huckel method comparative investigation of the nature of metal-ethylidene and metal-ethylene bonds in complexes [Cl5Mo(C2H4)]- and [Cl3Pd(C2H4)]-, and also carbene complex stability regarding olefine izomerization is carried out. It is shown that metal-ethylidene bond in the above complexes is stronger than metal-ethylene one, and Mo(4)-ethylidene bond is stronger than Pd(2)-ethylidene one. It is supposed that relative stability of alkylidene structures may be one of the reasons of catalytic activity of Mo(4) compounds in olefine metathesis and oligomerization reactions in which carbene complex is considered as an intermediate

231

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

232

More sustainable formation of C-N and C-C bonds for the synthesis of N-heterocycles.  

Science.gov (United States)

Heterocycles made green: New methodologies for the synthesis of pyrroles were recently developed based on domino Ir- and Ru-catalyzed amination and alkylations of alcohols. The concept provides a greener approach to interesting N-heterocyclic compounds. PMID:23775609

Schranck, Johannes; Tlili, Anis; Beller, Matthias

2013-07-22

233

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

234

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

Directory of Open Access Journals (Sweden)

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

Koichiro Oshima

2009-08-01

235

Cationic Rh and Ir complexes containing bidentate imidazolylidene-1,2,3-triazole donor ligands: synthesis and preliminary catalytic studies.  

Science.gov (United States)

A series of new cationic Rh(I), Rh(III) and Ir(III) complexes containing hybrid bidentate N-heterocyclic carbene–1,2,3-triazolyl donor of general formulae [Rh(CaT)(COD)]BPh4 (2a–d), [Rh(CaT)(CO)2]BPh4 (3a–d) and [M(CaT)(Cp*)Cl]BPh4 (M = Rh, 4a–d; M = Ir, 5a–c), where CaT = bidentate N-heterocyclic carbene–triazolyl ligands, COD = 1,5-cyclooctadiene and Cp* = 1,2,3,4,5-pentamethylcyclopentadienyl, were synthesised. The imidazolium–1,2,3-triazolyl pre-ligands (1a–c and 1e–i) were readily prepared using the Cu(I) catalysed ‘click reaction’ between phenyl azide or benzyl azides with propargyl functionalised imidazolium salts. The single crystal solid state structures of complexes 2a–d; 3a–b; 4a–d and 5a–b confirm the bidentate coordination of the NHC–1,2,3-triazolyl ligand with the NHC coordinating via the ‘normal’ C2-carbon and the 1,2,3-triazolyl donor coordinating via the N3? atom to form six membered metallocycles. These complexes are the first examples of Rh and Ir complexes containing the hybrid NHC–1,2,3-triazolyl ligands which exhibit a bidentate coordination mode. A number of these complexes showed limited efficiency as catalysts for the intramolecular hydroamination of 4-pentyn-1-amine to 2-methylpyrroline. PMID:23959044

Vuong, Khuong Q; Timerbulatova, Marina G; Peterson, Matthew B; Bhadbhade, Mohan; Messerle, Barbara A

2013-10-21

236

Metal–metal interaction in Fischer carbene complexes : a study of ferrocenyl and biferrocenyl tungsten alkylidene complexes  

OpenAIRE

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 trifluoromethane...

Westhuizen, Belinda; Speck, J. Matthaus; Korb, Marcus; Friedrich, Joachim; Bezuidenhout, Daniela Ina; Lang, Heinrich

2013-01-01

237

From bis(N-Alkylimidazole) to bis(NH–NHC) in rhenium carbonyl complexes  

OpenAIRE

Two birds, one stone: A deprotonation–protonation sequence using only one molar equivalent of base and acid transforms two N-alkylimidazole molecules into N-heterocyclic carbene ligands (see scheme; black?C, gray?H, green?F, blue?N, red?O, cyan?Re, yellow?S).

Huertos, Miguel A.; Pe?rez, Julio; Riera, Luci?a

2010-01-01

238

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

Science.gov (United States)

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

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

2014-12-01

239

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

International Nuclear Information System (INIS)

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

240

[Au(dien)(N-heterocycle)](3+): Reactivity with Biomolecules and Zinc Finger Peptides.  

Science.gov (United States)

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

Spell, Sarah R; Farrell, Nicholas P

2015-01-01

241

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

Science.gov (United States)

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

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

2013-01-01

242

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

Science.gov (United States)

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

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

1995-11-01

243

The first bismuth-NHC complexes.  

Science.gov (United States)

The synthesis, isolation and crystallographic characterization of the first N-heterocyclic carbene adducts of bismuth is reported, by direct reaction of the Dipp2NHC (Dipp = 2,6-diisopropylphenyl) or (i)Pr2(Me2)NHC with BiCl3. This represents the last non-radioactive element from groups 13-17 for which an NHC-element fragment remained unreported. PMID:24150033

Aprile, Antonino; Corbo, Robert; Vin Tan, Kel; Wilson, David J D; Dutton, Jason L

2014-01-14

244

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

Science.gov (United States)

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

Soleilhavoup, Michèle; Bertrand, Guy

2015-02-17

245

6?-N-Heterocyclic Substituted Naltrexamine Derivative NAP as a Potential Lead to Develop Peripheral Mu Opioid Receptor Selective Antagonists  

OpenAIRE

A 6?-N-heterocyclic substituted naltrexamine derivative, NAP, was proposed as a peripheral mu opioid receptor (MOR) selective antagonist based on the in vitro and in vivo pharmacological and pharmacokinetic studies. To further validate this notion, several functional assays were carried out to fully characterize this compound. In the charcoal gavage and intestinal motility assay in morphine-pelleted mice, when administered 0.3 mg/kg or higher doses up to 3 mg/kg subcutaneously, NAP significa...

Yuan, Yunyun; Stevens, David L.; Braithwaite, Amanda; Scoggins, Krista L.; Bilsky, Edward J.; Akbarali, Hamid I.; Dewey, William L.; Zhang, Yan

2012-01-01

246

Study of the factors supporting the selective complexation of the trivalent lanthanide and actinide ions; Etude des facteurs favorisant la complexation selective des ions lanthanides et actinides trivalents  

Energy Technology Data Exchange (ETDEWEB)

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

Mehdoui, T

2005-09-15

247

N-heterocyclic carbene (NHC) ligands annulated to free-base porphyrins: modulation of the electronic properties of the NHC upon protonation or metallation of the porphyrin.  

Science.gov (United States)

NHC ligands annulated to free-base porphyrins can be reversibly switched between electron-poor and electron-rich states upon protonation and deprotonation of the inner nitrogen atoms of the porphyrin. Metallation of the macrocycle with nickel(II) locks the peripheral NHC ligand in its electron-rich state. PMID:21249236

Lefebvre, Jean-François; Lo, Mamadou; Leclercq, Dominique; Richeter, Sébastien

2011-03-14

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

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

250

Umpolung reactions in an ionic liquid catalyzed by electrogenerated N-heterocyclic carbenes. Synthesis of saturated esters from activated ?,?-unsaturated aldehydes.  

Science.gov (United States)

The umpolung reaction of ?,?-unsaturated aldehydes to saturated esters has been carried out in an ionic liquid by organocatalysis of electrogenerated NHC. The roles of solvent, precatalyst and proton donor of the ionic liquid have been verified and good to high yields of esters have been obtained using a "green" and mild methodology. PMID:22517053

Feroci, Marta; Chiarotto, Isabella; Orsini, Monica; Pelagalli, Romina; Inesi, Achille

2012-05-28

251

Computational and experimental investigations of CO2 and N2O fixation by sterically demanding N-heterocyclic carbenes (NHC) and NHC/borane FLP systems.  

Science.gov (United States)

The sterically demanding NHCs 1,3-di-tert-butylimidazolin-2-ylidene (1a), 1,3-di-tert-butyl-4,5-dimethylimidazolin-2-yildene (1b), and also the corresponding frustrated Lewis pair combinations 1a,b/B(C6F5)3 react readily with CO2 to form the NHC·CO2 (5a,b) and the NHC·CO2·B(C6F5)3 (9a,b) adducts, respectively. However, N2O activation and isolation of the NHC·N2O adduct (6) was only possible for NHC 1a. On heating, the NHC·N2O adduct 6 degrades to 1a, N2O, N2 and the urea derivative 7. Nevertheless, an NHC·N2O adduct of 1b was obtained with the FLP system 1b/B(C6F5)3. In contrast, for the FLP combination 1a/B(C6F5)3, N2O coordination appears to be slower than the self-deactivation. Hence, only the self-deactivation product 3 was observed under an N2O atmosphere. DFT calculations give insights into the CO2 and N2O activation process with 1a,b and 1a,b/B(C6F5)3. PMID:24217215

Theuergarten, Eileen; Bannenberg, Thomas; Walter, Marc D; Holschumacher, Dirk; Freytag, Matthias; Daniliuc, Constantin G; Jones, Peter G; Tamm, Matthias

2014-01-28

252

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

Science.gov (United States)

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

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

2014-10-27

253

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

International Nuclear Information System (INIS)

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

254

Orientation and stereodynamic paths of planar monodentate ligands in square planar nickel N2S complexes.  

Science.gov (United States)

The well-established presence of histidine donors in binding sites of Ni-containing biomolecules prompts the study of orientational preference and stereodynamic nature of flat monodentate ligands (L = imidazoles, pyridine and an N-heterocyclic carbene) bound to planar N(2)SNi moieties. Square planar [N(2)SNiL](n+) complexes are accessed through bridge-splitting reactions of dimeric, thiolate-S bridged [N(2)SNi](2) complexes. The solid state molecular structures of three mononuclear products, and three monothiolate bridged dinickel complexes, reveal that the plane of the added monodentate ligand orients largely orthogonal to the N(2)SNiL square plane. Variable temperature (1)H NMR characterization of dynamic processes and ground state isomer ratios of imidazole complexes in their stopped exchange limiting spectra, readily correlate with density functional theory (DFT)-guided interpretation of Ni-L rotational activation barriers. Full DFT characterization finds Ni-L bond lengthening as well as a tetrahedral twist distortion in the transition state, reaching a maximum in the NHC complex, and relating mainly to the steric hindrance derived both from the ligand and the binding pocket. In the case of the imidazole ligands a minor electronic contribution derives from intramolecular electrostatic interactions (imidazole C-2 C-H(delta+)- - S(delta-) interaction). Computational studies find this donor-acceptor interaction is magnified in O-analogues, predicting coplanar arrangements in the ground state of N(2)ON(imid)Ni complexes. PMID:20507173

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

2010-06-21

255

TOF-SIMS analysis of N-heterocyclic compounds-implications for the Rosetta/COSIMA Mission  

Science.gov (United States)

The European Rosetta spacecraft launched on March 2004 will reach the comet 67/P-Churyumov-Gerasimenko in 2014 to perform the most exhaustive study ever achieved on comets (Glassmeier et al. 2007). The COmetary Secondary Ion Mass Analyser (COSIMA) carried on board will focus on chemical analysis of cometary dust grains collected in situ on a variety of metallic targets. COSIMA's goals are the in-situ characterisation of the atomic, molecular and isotopic composition of cometary dust grains. These analyses will provide inorganic and organic data about pristine solar system material (Kissel et al. 2007). COSIMA is a time-of-flight secondary ion mass spectrometer (TOF-SIMS) using an indium liquid metal ion source. Spectra inter-pretation of complex unknown samples with COSIMA instrument will be difficult due to the limited mass resolution (M/M of 2000 at m=100 amu) which excludes unambiguous compounds identification and requires preliminary work with reference samples. To help the interpretation of COSIMA spectra calibration laboratory work is in progress using the twin of the COSIMA flight instrument located at Katlenburg-Lindau (Germany) and the prototype of COSIMA in Orléans (France). Here we report the analysis of 100-400m deposits of organics performed with the COSIMA prototype based in Orléans. The organics are expected to be minor peaks, making their identification not simple. Nucleobase molecules, especially the purine bases, are among the building of the replicating molecules of life (DNA and RNA). Scour the universe in an attempt to find such a natural source of nucleobases is of fundamental significance in considerations of the origin of life (Lazcano Miller 1996) Therefore we focused our work on N-heterocyclic compounds which are believed to be present in comets or which belong to the chemical family of such molecules (Krueger Kissel 2006). Experiments have been performed on nine compounds: adenine, guanine, imidazole, 2-aminopyrimidine, cytosine, isocytosine, thymine, 4-aminopyrimidine and uracil. The first step was to characterize all these pure ni-trogenous organic molecules by their high statistics of positive and negative spectra. Deep examination has then been performed to look for peculiarity: we tried to differentiate i) the fragmentation peaks of a complex molecule from the quasi-molecular peak of pure compounds at the same mass and ii) characteristic features between isomers. For almost all compounds, highly intensive parent-like secondary ions of the general composition [M+H]+ or [M-H]-and characteristically large fragment ions correlated with functional groups were emitted. None possible ambiguities were revealed between the peaks from the actual molecule and the same one in a substructure form: they have two different spectral features. The two molecules were even distinguishable in binary mixture experiments. References: Glassmeier KH et al. (2007) Space Sci. Rev. 128, 1-21. Kissel J et al. (2007) Space Sci. Rev. 128, 823-867 Lazcano A Miller S.L. (1996) Cell 85, 793-798 Krueger F.R. Kissel J. (2006) Eds Springer, p 325-339

Le Roy, Léna; Briois, Christelle; Thirkell, Laurent; Cottin, Hervé; Fray, Nicolas; Poulet, Gilles; Hilchenbach, Martin

256

?-Hydroxy coordination of mononuclear vanadyl citrate, malate and S-citramalate with N-heterocycle ligand, implying a new protonation pathway of iron-vanadium cofactor in nitrogenase.  

Science.gov (United States)

Unlike the most of ?-alkoxy coordination in ?-hydroxycarboxylates to vanadium, novel ?-hydroxy coordination to vanadium(IV) has been observed for a series of chiral and achiral monomeric ?-hydroxycarboxylato vanadyl complexes [VO(H2cit)(bpy)]·2H2O (1), [VO(Hmal)(bpy)]·H2O (2), [VO(H2cit)(phen)]·1.5H2O (3), [VO(Hmal)(phen)]·H2O (4), and [(?)VO(S-Hcitmal)(bpy)]·2H2O (5), [VO(H2cit)(phen)]2·6.5H2O (6), which were isolated from the reactions of vanadyl sulfate with ?-hydroxycarboxylates and N-heterocycle ligands in acidic solution. The complexes feature a tridentate citrate, malate or citramalate that chelates to vanadium atom through their ?-hydroxy, ?-carboxy and ?-carboxy groups; while the other ?-carboxylic acidic group of citrate is free to participate strong hydrogen bonds with lattice water molecule. The neutral ?-hydroxy group also forms strong intermolecular hydrogen bonds with water molecule and the negatively-charged ?-carboxy group in the environment. The inclusion of a hydrogen ion in ?-alkoxy group results in the formation of a series of neutral complexes with one less positive charge. There are two different configurations of citrate with respect to the trans-position of axial oxo group, where the complex with trans-hydroxy configuration seems more stable with less hindrance. The average bond distances of VOhydroxy and VO?-carboxy are 2.196 and 2.003Å respectively, which are comparable to the VO distance (2.15Å) of homocitrate in FeV-cofactor of V-nitrogenase. A new structural model is suggested for R-homocitrato iron vanadium cofactor as VFe7S9C(R-Hhomocit) (H4homocit=homocitric acid) with one more proton in homocitrate ligand. PMID:25240212

Chen, Can-Yu; Chen, Mao-Long; Chen, Hong-Bin; Wang, Hongxin; Cramer, Stephen P; Zhou, Zhao-Hui

2014-12-01

257

Gold(I) biscarbene complexes derived from vascular-disrupting combretastatin A-4 address different targets and show antimetastatic potential.  

Science.gov (United States)

Gold N-heterocyclic carbene (NHC) complexes are an emerging class of anticancer drugs. We present a series of gold(I) biscarbene complexes with NHC ligands derived from the plant metabolite combretastatin A-4 (CA-4) that retain its vascular-disrupting effect, yet address different cellular and protein targets. Unlike CA-4, these complexes did not interfere with tubulin, but with the actin cytoskeleton of endothelial and cancer cells. For the highly metastatic 518A2 melanoma cell line this effect was accompanied by a marked accumulation of cells in the G1 phase of the cell cycle and a suppression of active prometastatic matrix metalloproteinase-2. Despite these mechanistic differences the complexes were as strongly antivascular as CA-4 both in vitro in tube formation assays with human umbilical vein endothelial cells, and in vivo as to blood vessel disruption in the chorioallantoic membrane of chicken eggs. The antiproliferative effect of the new gold biscarbene complexes in a panel of six human cancer cell lines was impressive, with low sub-micromolar IC50 values (72 h) even against CA-4-refractory HT-29 colon and multidrug-resistant MCF-7 breast carcinoma cells. In preliminary studies with a mouse melanoma xenograft model the complexes led to significant decreases in tumor volume while being very well tolerated. PMID:24648184

Muenzner, Julienne K; Biersack, Bernhard; Kalie, Hussein; Andronache, Ion C; Kaps, Leonard; Schuppan, Detlef; Sasse, Florenz; Schobert, Rainer

2014-06-01

258

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

Science.gov (United States)

The well-established presence of histidine donors in binding sites of Ni-containing biomolecules prompts the study of orientational preference and stereodynamic nature of flat monodentate ligands (L = imidazoles, pyridine and an N-heterocyclic carbene) bound to planar N2SNi moieties. Square planar [N2SNiL]n+ complexes are accessed through bridge-splitting reactions of dimeric, thiolate-S bridged [N2SNi]2 complexes. The solid state molecular structures of three mononuclear products, and three monothiolate bridged dinickel complexes, reveal that the plane of the added monodentate ligand orients largely orthogonal to the N2SNiL square plane. Variable temperature 1H NMR characterization of dynamic processes and ground state isomer ratios of imidazole complexes in their stopped exchange limiting spectra, readily correlate with DFT-guided interpretation of Ni-L rotational activation barriers. Full DFT characterization find Ni-L bond lengthening as well as a tetrahedral twist distortion in the transition state, reaching a maximum in the NHC complex, and relating mainly to the steric hindrance derived both from the ligand and the binding pocket. In the case of the imidazole ligands a minor electronic contribution derives from intramolecular electrostatic interactions (imidazole C-2 C-H?+- - S?? interaction). Computational studies find this donor-acceptor interaction is magnified in O-analogues, predicting coplanar arrangements in the ground state of N2ONimidNi complexes. PMID:20507173

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

2010-01-01

259

Computational Chemistry Studies on the Carbene Hydroxymethylene  

Science.gov (United States)

A density functional theory computational chemistry exercise on the structure and vibrational spectrum of the carbene hydroxymethylene is presented. The potential energy curve for the decomposition reaction of the carbene to formaldehyde and the geometry of the transition state are explored. The results are in good agreement with recent…

Marzzacco, Charles J.; Baum, J. Clayton

2011-01-01

260

Chemical and thermal stability of N-heterocyclic ionic liquids in catalytic C-H activation reactions.  

Science.gov (United States)

(1)H-NMR spectrum analyses are applied to study the chemical and thermal stability of selected N-heterocyclic ionic liquids within the reaction system that can highly efficiently activate a C-H bond of methane and convert it into the C-O bond in methanol. Our results indicate that under such reaction conditions involving using a powerful Pt-based catalyst and strong acidic solvent, the aromatic ring of an imidazolium cation becomes unstable generating an ammonium ion (NH(4)(+)). Our results also suggest that the instability of the imidazolium ring is more chemically (participation in reactions) than thermally based. Modifications of the aromatic ring structure such as pyrazolium and triazolium cations can increase the chemical/thermal stability of ionic liquids under these reaction conditions. PMID:24942984

Chen, Guanyi; Kang, Shujuan; Ma, Qisheng; Chen, Weiqun; Tang, Yongchun

2014-11-01

261

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

Science.gov (United States)

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

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

2015-02-23

262

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

Science.gov (United States)

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

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

2014-12-10

263

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

264

Conformationally constrained N-heterocyclic phosphine-diimine with dual functionality.  

Science.gov (United States)

Condensation of octahydro-2,2'-bipyrimidine with P(NMe2)3 gave a 1,3,2-diazaphospholidine-4,5-diimine 4a in which the "open" (exo/exo) conformation of the diimine unit was enforced by incorporation into a tricyclic molecular backbone. The coordination behavior of this potentially ambident ligand was sampled in reactions with ([(nbd)W(CO)4] and [CpCo(CO)2]) and pnictogen halides ECl3 (E = P, As, Sb). While PCl3 reacted under ring metathesis, all other reactions gave isolable complexes of composition (4a)MLn (MLn = W(CO)5, CpCo(CO), AsCl3, SbCl3); attempted recrystallization of the As-adduct yielded a complex (4a)(AsCl3)2 which was also accessible from reaction of 4a with 2 equiv of AsCl3. Single-crystal X-ray diffraction studies revealed that the ligand in [(4a)W(CO)5] and [(4a)CpCo(CO)] binds through its phosphorus lone-pair; [(4a)SbCl3] and [(4a)(AsCl3)2] contain a T-shaped ECl3 unit which binds to the chelating diimine moiety, and associate further via chloride bridges to give centrosymmetric dimers. Reactions of 4a with excess metal substrates gave no evidence that formation of bimetallic complexes with ?-bridging 1?(2)(N,N')-2?P-coordination is feasible; the extra AsCl3 moiety in [(4a)(AsCl3)2] avoids this coordination mode by interacting with the peripheral chlorides of the central core. The observed selectivity suggests that ligand 4a specifically addresses transition metal centers with low positive charge and some back-bonding capacity through the phosphorus lone-pair, and electrophiles that behave essentially as "pure" Lewis acids through the diimine unit. This assumption was confirmed by DFT studies which disclosed further that binding of the first metal center deactivates the opposite binding site and thus strongly inhibits the formation of dinuclear complexes. PMID:23514329

Mourgas, Georgios; Nieger, Martin; Förster, Daniela; Gudat, Dietrich

2013-04-01

265

Preparation of phenalenes and hydronaphthacenes through tandem alkyne Fischer-carbene complex coupling and inter- or intramolecular Diels-Alder reactions  

OpenAIRE

The rapid construction of phenalenes through the reaction of 8-alkynyltetralones with Fischer carbine complexes followed by either inter- or an intramolecular Diels-Alder reaction is presented. As a showcase of the synthetic utility of this process, the rapid construction of polycyclic ring systems containing the tetracycline core has been demonstrated through an iterative application of this reaction sequence.

Patti, Rajesh Kumar; Duan, Shaofeng; Wang, Zhipeng; Herndon, James W.

2011-01-01

266

Reactivity of a frustrated lewis pair and small-molecule activation by an isolable Arduengo carbene-B{3,5-(CF3)2C6H3}3 complex.  

Science.gov (United States)

Tris[3,5-bis(trifluoromethyl)phenyl]borane reacts with the sterically demanding Arduengo carbenes 1,3-di-tert-butylimidazolin-2-ylidene and 1,3-bis(2,6-diisopropylphenyl)imidazolin-2-ylidene to form isolable normal adducts. In the case of 1,3-di-tert-butylimidazolin-2-ylidene, the adduct exhibits dynamic behaviour in solution and frustrated-Lewis-pair (FLP) reactivity. Fast cleavage of dihydrogen and THF, the C-H activation of phenylacetylene, and carbon dioxide fixation were achieved by using solutions of this adduct in benzene. This adduct is stable at room temperature in the absence of suitable substrates; however, thermal rearrangement into an abnormal carbene-borane adduct can be observed. In contrast, the 1,3-bis(2,6-diisopropylphenyl)imidazolin-2-ylidene adduct exhibits no evidence of FLP reactivity or of dissociation in solution. DFT calculations confirmed the experimental behaviour and stability of these carbene-borane adducts. PMID:23150467

Kolychev, Eugene L; Bannenberg, Thomas; Freytag, Matthias; Daniliuc, Constantin G; Jones, Peter G; Tamm, Matthias

2012-12-21

267

Steriese en elektroniese effek van metaalbevattende substituente op Fischer-karbeenmetaalbondelverbindings The steric and electronic effects of metal-containing substituents on Fischer carbene metal clusters  

Directory of Open Access Journals (Sweden)

Full Text Available Die insluiting van verskillende oorgangsmetaalfragmente by komplekse word reeds die afgelope aantal jare wyd bestudeer om die effek van die verskillende metaalfragmente op die reaktiwiteit van die ligande en die chemie van die komplekse te ondersoek.Novel Group VI transition metal Fischer carbene complexes containing three different transition metal substituents, all in electronic contact with the carbene carbon atom, were synthesised.

Editorial Office

2009-09-01

268

A fullerene-carbene adduct as a crystalline molecular rotor: remarkable behavior of a spherically-shaped rotator.  

Science.gov (United States)

A new fullerene structure was recently obtained from the reaction of a Lewis basic N-heterocyclic carbene (NHC) and the Lewis acidic C60. The molecular features of the zwitterionic adduct can be described as a molecular rotor with the fullerene cage acting as the rotator that spins about one distinct axis given by its C-C single bond linkage with the imidazolium heterocycle stator. A detailed structural analysis of the compound by means of single-crystal X-ray diffraction (XRD) revealed significant differences in the packing motifs of solvent-free and solvent-containing crystals. Variable temperature single-crystal XRD experiments (80 K ? T ? 480 K) carried out to investigate the rotational dynamics of the fullerene group in the higher quality solvent-free structure revealed atomic displacement parameters consistent with fast rotation of the highly symmetric fullerene in the solid state, whereas the imidazolium unit remains in a fixed position and therefore represents the stator. DFT and semiempirical calculations were applied to get insight into the profile of the rotational potential of the fullerene unit, particularly considering interactions with the neighboring molecules in the crystal lattice. The results indicate that the crystal environment leads to the presence of one lowest energy minimum that is connected to seven others that are slightly higher in energy through rotational barriers of approximately 1.5-2.5 kcal mol(-1). PMID:24852314

Lorbach, Andreas; Maverick, Emily; Carreras, Abel; Alemany, Pere; Wu, Guang; Garcia-Garibay, Miguel A; Bazan, Guillermo C

2014-07-01

269

Ionic origins of carbenes in space  

International Nuclear Information System (INIS)

The author reports experiments which suggest that a much higher proportion of the ion chemistry in partially ionized regions in space is directed towards the formation of carbene molecules than has previously been recognized. Plausible reaction paths are identified, which lead to both known and previously unknown carbenes, such as the cyclopropenylidene ring and long carbon-chain molecules. The cyclopropenylidene ring has recently been reported to be ubiquitous in the Galaxy, whereas long carbon-chain molecules have been implicated in the origin of diffuse interstellar lines. (author)

270

How to make the ?0?2 singlet the ground state of carbenes.  

Science.gov (United States)

Successful strategies have previously been developed to stabilize the ?(2)?(0) singlet states of carbenes, relative to ?(1)?(1) triplet states. However, little or no attention has been paid to the stabilization of the ?(0)?(2) singlet states. We present two simple strategies to stabilize the ?(0)?(2) singlet states of carbenes, relative to both the ?(2)?(0) singlet and ?(1)?(1) triplet states. These strategies consist of destabilization of the carbene ? orbital by two, adjacent, sp(2) nitrogen lone pairs of electrons and stabilization of the carbene 2p-? orbital by incorporating it into a five-membered ring, containing two double bonds, or into a six-membered ring, containing two double bonds and a sixth atom that has a low-lying empty ? orbital. B3LYP, CASPT2, and CCSD(T) calculations have been performed in order to assess the success of these strategies in creating derivatives of cyclopenta-2,4-dienylidene and cyclohexa-2,5-dienylidene with ?(0)?(6) singlet ground states. Differences between the calculated geometries and binding energies of the Xe complexes of the ?(0)?(6) singlet ground state of 2,5-diazacyclopentadienylidene (5) and the ?(2)?(0) singlet states of CH2 and CF2 are discussed. PMID:24007553

Chen, Bo; Rogachev, Andrey Yu; Hrovat, David A; Hoffmann, Roald; Borden, Weston Thatcher

2013-09-18

271

An intermediate cobalt(IV) nitrido complex and its N-migratory insertion product.  

Science.gov (United States)

Low-temperature photolysis experiments (T = 10 K) on the tripodal azido complex [(BIMPN(Mes,Ad,Me))Co(II)(N3)] (1) were monitored by EPR spectroscopy and support the formation of an exceedingly reactive, high-valent Co nitrido species [(BIMPN(Mes,Ad,Me))Co(IV)(N)] (2). Density functional theory calculations suggest a low-spin d(5), S = 1/2, electronic configuration of the central cobalt ion in 2 and, thus, are in line with the formulation of complex 2 as a genuine, low-spin Co(IV) nitride species. Although the reactivity of this species precludes handling above 50 K or isolation in the solid state, the N-migratory insertion product [(NH-BIMPN(Mes,Ad,Me))Co(II)](BPh4) (3) is isolable and was reproducibly synthesized as well as fully characterized, including CHN elemental analysis, paramagnetic (1)H NMR, IR, UV-vis, and EPR spectroscopy as well as SQUID magnetization and single-crystal X-ray crystallography studies. A computational analysis of the reaction pathway 2 ? 3 indicates that the reaction readily occurs via N-migratory insertion into the Co-C bond (activation barrier of 2.2 kcal mol(-1)). In addition to the unusual reactivity of the nitride 2, the resulting divalent cobalt complex 3 is a rare example of a trigonal pyramidal complex with four different donor ligands of a tetradentate chelate-an N-heterocyclic carbene, a phenolate, an imine, and an amine-binding to a high-spin Co(II) ion. This renders complex 3 chiral-at-metal. PMID:25243488

Zolnhofer, Eva M; Käß, Martina; Khusniyarov, Marat M; Heinemann, Frank W; Maron, Laurent; van Gastel, Maurice; Bill, Eckhard; Meyer, Karsten

2014-10-22

272

NHC?SiCl4 : An Ambivalent Carbene-Transfer Reagent.  

Science.gov (United States)

The addition of BCl3 to the carbene-transfer reagent NHC?SiCl4 (NHC=1,3-dimethylimidazolidin-2-ylidene) gave the tetra- and pentacoordinate trichlorosilicon(IV) cations [(NHC)SiCl3 ](+) and [(NHC)2 SiCl3 ](+) with tetrachloroborate as counterion. This is in contrast to previous reactions, in which NHC?SiCl4 served as a transfer reagent for the NHC ligand. The addition of BF3 ?OEt2 , on the other hand, gave NHC?BF3 as the product of NHC transfer. In addition, the highly Lewis acidic bis(pentafluoroethyl)silane (C2 F5 )2 SiCl2 was treated with NHC?SiCl4 . In acetonitrile, the cationic silicon(IV) complexes [(NHC)SiCl3 ](+) and [(NHC)2 SiCl3 ](+) were detected with [(C2 F5 )SiCl3 ](-) as counterion. A similar result was already reported for the reaction of NHC?SiCl4 with (C2 F5 )2 SiH2 , which gave [(NHC)2 SiCl2 H][(C2 F5 )SiCl3 ]. If the reaction medium was changed to dichloromethane, the products of carbene transfer, NHC?Si(C2 F5 )2 Cl2 and NHC?Si(C2 F5 )2 ClH, respectively, were obtained instead. The formation of the latter species is a result of chloride/hydride metathesis. These compounds may serve as valuable precursors for electron-poor silylenes. Furthermore, the reactivity of NHC?SiCl4 towards phosphines is discussed. The carbene complex NHC?PCl3 shows similar reactivity to NHC?SiCl4 , and may even serve as a carbene-transfer reagent as well. PMID:25363673

Böttcher, Tobias; Steinhauer, Simon; Lewis-Alleyne, Lesley C; Neumann, Beate; Stammler, Hans-Georg; Bassil, Bassem S; Röschenthaler, Gerd-Volker; Hoge, Berthold

2015-01-01

273

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 (1), [Ln2(Hdppd)2(H2O)4·(H2O)3]n [Ln = Sm (2), Eu (3)] and [Ln(Hdppd)(H2O)3·H2O]n [Ln = Gd (4), Tb (5), Dy (6), Ho (7), Er (8)] [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 3 and 5 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 2-8 were measured and discussed. Compound 6 exhibits frequency dependent out-of-phase signals, and ferromagnetic coupling exists in 8. 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

2014-12-14

274

Reactivity of the uranium(IV) carbene complex [U(BIPM(TMS))(Cl)(?-Cl)?Li(THF)?] (BIPM(TMS) = {C(PPh?NSiMe?)?}) towards carbonyl and heteroallene substrates: metallo-Wittig, adduct formation, C-F bond activation, and [2 + 2]-cycloaddition reactions.  

Science.gov (United States)

The reactivity of the uranium(IV) carbene complex [U(BIPM(TMS))(Cl)(?-Cl)2Li(THF)2] (1, BIPM(TMS) = {C(PPh2NSiMe3)2}) towards carbonyl and heteroallene substrates is reported. Reaction of 1 with benzophenone proceeds to give the metallo-Wittig terminal alkene product Ph2C=C(PPh2NSiMe3)2 (2); the likely "UOCl2" byproduct could not be isolated. Addition of the bulky ketone PhCOBu(t) to 1 resulted in loss of LiCl, coordination of the ketone, and dimerisation to give [U(BIPM(TMS))(Cl)(?-Cl){OC(Ph)(Bu(t))}]2 (3). The reaction of 1 with coumarin resulted in ring opening of the cyclic ester and a metallo-Wittig-type reaction to afford [U{BIPM(TMS)[C(O)(CHCHC6H4O-2)]-?(3)-N,O,O'}(Cl)2(THF)] (4) where the enolate product remains coordinated to uranium. The reaction of PhCOF with 1 resulted in C-F bond activation and oxidation resulting in isolation of [U(O)2(Cl)2(?-Cl)2{(?-LiDME)OC(Ph)=C(PPh2NSiMe3)(PPh2NHSiMe3)}2] (5) along with [U(Cl)2(F)2(py)4] (6). The reactions of 1 with tert-butylisocyanate or dicyclohexylcarbodiimide resulted in the isolation of the [2 + 2]-cycloaddition products [U{BIPM(TMS)[C(NBu(t)){OLi(THF)2(?-Cl)Li(THF)3}]-?(4)-C,N,N',N''}(Cl)3] (7) and [U{BIPM(TMS)[C(NCy)2]-?(4)-C,N,N',N''}(Cl)(?-Cl)2Li(THF)2] (8). Complexes 2-8 have been variously characterised by single crystal X-ray diffraction, multi-nuclear NMR and FTIR spectroscopies, Evans method solution magnetic moments, variable temperature SQUID magnetometry, and elemental analyses. PMID:24798878

Cooper, Oliver J; Mills, David P; Lewis, William; Blake, Alexander J; Liddle, Stephen T

2014-10-14

275

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

276

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)

277

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

Science.gov (United States)

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

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

2009-03-01

278

Propane activation by palladium complexes with chelating bis(NHC) ligands and aerobic cooxidation.  

Science.gov (United States)

The development of efficient aerobic oxidation methods remains a challenge for the selective functionalization of C-H bonds in alkanes. Herein we report the development of a C-H functionalization procedure for propane by using a palladium catalyst with chelating bis(N-heterocyclic carbene) ligands in trifluoroacetic acid together with a vanadium co-catalyst. Halides play a decisive role in the reaction. The experimental results are presented together with supporting kinetic data and an isotope effect. The reaction can be run with dioxygen as the oxidant if vanadium salts and halides are present in the reaction mixture. Experimental as well as computational results favor a mechanism involving C-H activation by palladium(II), followed by oxidation to palladium(IV) by bromine. PMID:24482080

Munz, Dominik; Strassner, Thomas

2014-02-24

279

Phosphaalkene vs. phosphinidene: the nature of the P-C bond in carbonyl-decorated carbene ? PPh adducts.  

Science.gov (United States)

Treatment of dichlorophenylphosphine with two equivalents of carbonyl-decorated carbenes results in a two-electron reduction of the phosphorus centre concomitant with carbene oxidation to afford novel phosphaalkenes as confirmed via crystallographic, spectroscopic, and DFT analyses. PMID:23925541

Rodrigues, Roberta R; Dorsey, Christopher L; Arceneaux, Chelsee A; Hudnall, Todd W

2014-01-01

280

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

281

Synthesis and characterization of distonic radical, biradical and carbene ions  

OpenAIRE

The synthesis and characterization of distonic radical, biradical and carbene anions were studied with the use of a flowing afterglow-triple quadrupole instrument. A new synthetic strategy for gas-phase synthesis of negative ions with multiple open valence sites was developed. This method, which is based on the reaction of organic anions with molecular fluorine, allowed effective synthesis of a series of negative ions of biradicals and triradicals that are of great theoretical importance. The...

Hu, Jun

1997-01-01

282

Deprotonation of a borohydride: synthesis of a carbene-stabilized boryl anion.  

Science.gov (United States)

An acidic hydride! Thanks to the presence of a ?-acceptor cyclic alkyl amino carbene and of two electron-withdrawing nitrile groups, a borohydride reacts with a base to give a carbene-stabilized boryl anion, which reacts with carbon and metal electrophiles at the boron center. Dipp = 2,6-diisopropylphenyl, KHMDS = potassium bis(trimethylsilyl)amide. PMID:23765789

Ruiz, David A; Ung, Gaël; Melaimi, Mohand; Bertrand, Guy

2013-07-15

283

On the stability of perfluoroalkyl-substituted singlet carbenes: a coupled-cluster quantum chemical study.  

Science.gov (United States)

A series of trifluoromethyl-substituted carbenes R-C(:)-CF3 (R = NMe2, OMe, F, PMe2, P(NMe2)2, P(N(Pr-i)2)2, SMe, Cl); (dimethylamino)(perfluoroalkyl)carbenes Me2N-C(:)-R (R = CF3, C2F5, n-C3F7, i-C3F7, and t-C4F9) and symmetrically substituted carbenes R-C(:)-R (R = NMe2, OMe, F, PMe2, SMe, Cl) have been investigated by means of quantum chemistry methods. Different levels of approximation were used, including the CCSD(T) approach also known in quantum chemistry as the "golden standard", in combination with three different basis sets (TZVP, cc-pVDZ, cc-pVTZ). Relative stabilities of carbenes have been estimated using the differences between the singlet and triplet ground state energies (?EST) and energies of the hydrogenation reaction for the singlet and triplet ground states of the carbenes. The latter seem to correlate better with stability of carbenes than the ?EST values. The (13)C NMR chemical shifts of the methylidene carbon indicate the more high-field chemical shift values in the known, isolable carbenes compared to the unstable ones. This is the first report on the expected chemical shifts in the highly unstable singlet carbenes. Using these criteria, some carbene structures from the studied series (as, for instance, Me2N-C(:)-CF3, Me2N-C(:)-C3F7-i) are proposed as good candidates for the experimental preparation. PMID:24471524

Rozhenko, Alexander B; Schoeller, Wolfgang W; Leszczynski, Jerzy

2014-02-27

284

Alkenyl-functionalized NHC iridium-based catalysts for hydrosilylation  

OpenAIRE

A family of alkenyl-functionalized N-heterocyclic-carbene–iridium(I) complexes has been synthesized, providing a series of mono-coordinated, bis-chelate and pincer alkenyl-NHC species. Olefin coordination is highly influenced by the nature of the substituents on the NHC ring, and on the length of the alkenyl branch. A fluxional process involving coordination/decoordination of the olefin in bis-allyl-NHC complexes has been studied, and the activation parameters have been deter...

Zanardi, Alessandro; Peris Fajarne?s, Eduardo; Mata Marti?nez, Jose? Antonio

2008-01-01

285

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

DEFF Research Database (Denmark)

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

HØj, Martin; Kvaskoff, David

2014-01-01

286

Selectivity control in alkylidene carbene-mediated C-H insertion and allene formation.  

Science.gov (United States)

Regioselectivity of alkylidene carbene-mediated C-H insertion was explored utilizing electronic, conformational, steric, and stereoelectronic effects. Relying on these factors, highly regio- and chemoselective carbene insertion reaction of C-H bonds in different environments could be obtained. The observed selectivity clearly indicates that an electronic effect plays a more important role than steric effect. In general, C-H bonds in conformationally rigid cyclic environments are less reactive than those in acyclic systems toward carbene insertion, and in this situation, a competing intermolecular reaction between alkylidene carbene and trimethylsilyldiazomethane led to the formation of allenylsilanes. The formation of allenylsilane becomes more favorable as the concentration of reaction becomes higher, as well as the C-H bonds undergoing insertion becomes electronically and conformationally deactivated. PMID:21244086

Zheng, Jun-Cheng; Yun, Sang Young; Sun, Chunrui; Lee, Nam-Kyu; Lee, Daesung

2011-02-18

287

Oxidative Addition at a Carbene Center: Synthesis of an Iminoboryl-CAAC Adduct.  

Science.gov (United States)

The reaction of a cyclic (alkyl)(amino)carbene (CAAC) with dichloro- and dibromobis(trimethylsilyl)aminoborane results in the formation of haloiminoborane-CAAC adducts. When the iodo analogue is used, an oxidative addition at the carbene center affords a cationic iminoboryl-CAAC adduct, featuring a boron-nitrogen triple bond. Similar salts are also obtained by halide abstraction from the chloro- and bromoiminoborane-CAAC adducts. The reactivity of all of these compounds towards CO2 is discussed. PMID:25414006

Dahcheh, Fatme; Stephan, Douglas W; Bertrand, Guy

2015-01-01

288

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

Science.gov (United States)

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

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

2015-01-12

289

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

OpenAIRE

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

Michel Chiarucci; Mirko Locritani; Gianpiero Cera; Marco Bandini

2011-01-01

290

1,3-Bis(2,4,6-trimethylphenyl-3H-imidazol-1-ium tetraoxidorhenate(VII  

Directory of Open Access Journals (Sweden)

Full Text Available The title compound, (C21H25N2[ReO4], was formed as the unexpected product in an attempted synthesis of a rhenium(I–N-heterocyclic carbene (NHC complex. The compound has crystallographic mirror symmetry with both the cation and the tetrahedral anion located across a mirror plane. The cation and anion are linked by a C—H...O hydrogen bond.

Marilé Landman

2011-12-01

291

CASSCF and CASPT2 calculations of hole-doped amines with triplet carbene groups. Possibilities of high- Tc organic ferrimagnets  

Science.gov (United States)

Ab initio CASSCF and CASPT2 calculations were carried out for hole-doped amines with triplet carbene groups such as monocations of bis(methylene) and tris(methylene) amines in order to confirm previous spin polarization (SP) and delocalization (SD) rules for ion-radicals. The ground states for the hole-doped bis(methylene) and tris(methylene) amines were calculated to be quartet and sextet, respectively. The low (LS)- and high (HS)-spin crossover occurred upon hole doping, being consistent with the SD rules. Implications of the calculated results are discussed in relation to possibilities of organic ferri- and ferro-magnets composed of CT complexes with radical substituents.

Yamanaka, S.; Okumura, M.; Nagao, H.; Yamaguchi, K.

1995-02-01

292

Relativistic effects in the cationic platinum carbene PtCH + 2  

Science.gov (United States)

Fully relativistic four-component Dirac-Fock Coulomb calculations in conjunction with a second-order perturbational estimate for the correlation energy have been performed in benchmark calculations on geometric and electronic structures as well as the binding energy of the cationic platinum carbene complex PtCH+2. The relativistic stabilization of this species amounts to as much as 50 kcal/mol and the combination of relativistic and correlation effects shorten the Pt-C bond length by nearly 1 bohr, changing the bond order from one to two. The relative importance of spin-free and spin-dependent relativistic effects on the geometry, the electronic structure, and the binding energy is evaluated by comparison to the Douglas-Kroll method. Relativistic effective core potentials are shown to describe the spin-free effects reliably. The best theoretical estimate for the bond dissociation energy underestimates the experimental value by 13% due to truncation errors in the one- and n-particle space treatments. The mixed Hartree-Fock/density-functional method Becke3-Lee-Yang-Parr performs surprisingly well with respect to the structure and binding energy of the target molecule.

Heinemann, Christoph; Schwarz, Helmut; Koch, Wolfram; Dyall, Kenneth G.

1996-03-01

293

Rotational spectrum and theoretical structure of the carbene HC4N  

Science.gov (United States)

Following a high-level coupled cluster calculation, the rotational spectrum of the bent HC4N singlet carbene was detected in a supersonic molecular beam by Fourier transform microwave spectroscopy. The three rotational constants, the leading centrifugal distortion constants, and two nitrogen hyperfine coupling constants were determined to high accuracy. The rotational constants agree with those calculated ab initio to better than 0.5%. Like the isoelectronic C5H2 carbene of similar structure, HC4N was found to have fairly large centrifugal distortion and a large inertial defect. The calculated dipole moment of HC4N is 2.95 D.

McCarthy, M. C.; Apponi, A. J.; Gordon, V. D.; Gottlieb, C. A.; Thaddeus, P.; Daniel Crawford, T.; Stanton, John F.

1999-10-01

294

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)

295

Phosphines with N-heterocyclic boranyl substituents.  

Science.gov (United States)

A lithio-diazaborole reacted with diamino-chlorophosphines via metathesis to yield previously unavailable phosphinoboranes bearing amino substituents at both the phosphorus and boron atoms, and with Ph2PCl and Mes*PCl2via chloride transfer and reductive PP coupling to give a chloro-diazaborole and the corresponding diphosphine or diphosphene, respectively. Diazaboroles with phenylphosphino- and PH2-substituents were nonetheless accessible via inverse metathesis upon treatment of a bromoborane precursor with phosphides PhnPH2-nM (n = 0-2, M = Li, K). The products were characterised by spectroscopic data and in most cases by single-crystal X-ray diffraction studies which show the molecules to exhibit strongly pyramidal coordination at the phosphorus atom and long BP bonds of 1.93-1.95 Å. The insensitivity of the BP distance towards substituent effects and the tolerance of large sterically induced torsional twists along the BP bond axis suggest the presence of pure single bonds without any contribution from P?B dative ?-interactions. This view was confirmed by DFT studies which indicate further that the molecules lack a significant electrophilic character at boron but may act as potential ?-donor/?-acceptor ligands through the phosphorus atom. PMID:24142130

Kaaz, M; Bender, J; Förster, D; Frey, W; Nieger, M; Gudat, D

2014-01-14

296

Low-lying electronic states of unsaturated carbenes. Comparison with methylene  

International Nuclear Information System (INIS)

The lowest singlet and triplet electronic states of methylene, H2C:, vinylidene, H2CC:, and vinylidenecarbene, H2CCC:, are studied theoretically at the spin-unrestricted Hartree--Fock (HF) and spin-unrestricted many-body perturbation theory (MBPT) levels of approximation. Calculations at both levels predict a triplet ground state for methylene and singlet ground states for vinylidene and vinylidenecarbene. MBPT singlet--triplet energy splittings are found to be -13.1 kcal/mol for methylene, 51.1 kcal/mol for vinylidene, and 48.7 kcal/mol for vinylidenecarbene. A comparison of the effects of correlation on electronic structure is made between the parent carbene, methylene, and each of these unsaturated carbenes. From electronic structure trends observed in H2C:, H2CC:, and H2CCC:, singlet ground states are predicted for the extended unsaturated carbenes H2CCC:, and H2CCCC:, the next members of the series. The importance of d-type carbon polarization functions in basis sets used for the calculation of electronic structure properties in unsaturated carbenes is demonstrated by comparison with results in which d functions are not included in the basis. 4 tables, 54 references

297

Selenophene transition metal complexes  

Energy Technology Data Exchange (ETDEWEB)

This research shows that selenophene transition metal complexes have a chemistry that is similar to their thiophene analogs. Selenophene coordination has been demonstrated and confirmed by molecular structure in both the {eta}{sup 5}- and the {eta}{sup 1}(Se)-coordination modes. The reaction chemistry of selenophene complexes closely resembles that of the analogous thiophene complexes. One major difference, however, is that selenophene is a better donor ligand than thiophene making the selenophene complexes more stable than the corresponding thiophene complexes. The {sup 77}Se NMR chemical shift values for selenophene complexes fall within distinct regions primarily depending on the coordination mode of the selenophene ligand. In the final paper, the C-H bond activation of {eta}{sup 1}(S)-bound thiophenes, {eta}{sup 1}(S)-benzothiophene and {eta}{sup 1}(Se)-bound selenophenes has been demonstrated. The deprotonation and rearrangement of the {eta}{sup 1}(E)-bound ligand to the carbon bound L-yl complex readily occurs in the presence of base. Reprotonation with a strong acid gives a carbene complex that is unreactive towards nucleophilic attack at the carbene carbon and is stable towards exposure to air. The molecular structure of [Cp(NO)(PPh{sub 3})Re(2-benzothioenylcarbene)]O{sub 3}SCF{sub 3} was determined and contains a Re-C bond with substantial double bond character. Methyl substitution for the thienylcarbene or selenylcarbene gives a carbene that rearranges thermally to give back the {eta}{sup 1}(E)-bound complex. Based on these model reactions, a new mechanism for the H/D exchange of thiophene over the hydrodesulfurization catalyst has been proposed.

White, C.J.

1994-07-27

298

Synthesis of Transient and Stable C-Amino Phosphorus Ylides and Their Fragmentation into Transient and Stable Carbenes  

OpenAIRE

Only basic phosphines, such as tris(dimethylamino)phosphine, allow for the synthesis of a stable acyclic ?-amino phosphonium salt 1c, which upon deprotonation with butyllithium affords the corresponding stable C-amino phosphorus ylide 2c. In contrast, cyclic ?-amino phosphonium salts 5a and 5b are stable despite the presence of weakly basic triarylphosphine fragments. They are prepared by intramolecular insertion of the carbene center of (amino)(phosphonio)carbenes into the CH bond of a pho...

Canac, Yves; Conejero, Salvador; Soleilhavoup, Miche?le; Donnadieu, Bruno; Bertrand, Guy

2006-01-01

299

Engineering carbene rearrangements in crystals: from molecular information to solid-state reactivity.  

Science.gov (United States)

Although severely restricted, reactions in crystals have delivered some of the most impressive examples of chemical control and provided an ideal medium for detailed mechanistic studies. However, to take full advantage of their potential and avoid their shortcomings, a systematic approach for the reliable design of reaction in crystals is required. To that end, strategies based on structural and energetic information contained at the molecular level have been explored with reactions involving carbene rearrangements. PMID:12859210

Garcia-Garibay, Miguel A

2003-07-01

300

Formation of carbene and carbine particles during decomposition of molybdenum benzyl derivatives  

International Nuclear Information System (INIS)

A qualitative composition of hydrocarbon products of interaction of benzyl magnesium chlorides and MoCl5 in diethylene and dibutyl ethers has been studied. Hydrocarbon reaction products mainly consist of toluene and dibenzyl and small quantities of totan and stilbene. Total residue after the reaction contains some quantity of ''benzyl'' groups bound with Mo or Mg. Carbene and carbine particles disappear at the expense of secondary reactions with organo-metallic compounds of Mo or Mg

301

Steady state and laser flash photolysis studies of ferrocenyl group VI fischer-carbenes and metalloporphyrins  

OpenAIRE

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

302

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

Directory of Open Access Journals (Sweden)

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

XIAOJUN TAN

2010-05-01

303

Explicit role of dynamical and nondynamical electron correlation on singlet-triplet splitting in carbenes  

Energy Technology Data Exchange (ETDEWEB)

Density functional theoretical studies have been performed on carbene systems to determine the singlet-triplet splitting and also to explore the role of electron correlation. Using an approximate method of separation of dynamical and nondynamical correlation, it is found that dynamical and nondynamical electron correlation stabilizes the singlet state relative to the triplet for halo carbenes in both BLYP and B3LYP methods. Calculations performed on higher homologues of methylene suggest that beyond CH(CH{sub 3}), both the electron correlations have leveling effect in stabilizing the singlet state relative to the triplet. It has also been observed while dynamical electron correlation fails to provide any substantial degree of stabilization to the singlet states of higher homologues of methylene in B3LYP method, an opposite trend is observed for nondynamical counterpart. Among the larger systems studied (9-triptycyl)({alpha}-naphthyl)-carbene has the highest stability of the triplet state whereas bis-imidazol-2-ylidenes has the most stable singlet state. Interestingly, the values of the dynamical electron correlation for each state of each system studied are different for the two methods used. The reason behind this apparent discrepancy lies in the fact that the coefficients of the LYP part in B3LYP and BLYP functionals are different.

Seal, Prasenjit [Department of Chemistry, University of Calcutta, 92, A.P.C. Ray Road, Kolkata - 700 009 (India); Chakrabarti, Swapan [Department of Chemistry, University of Calcutta, 92, A.P.C. Ray Road, Kolkata - 700 009 (India)], E-mail: swapanchem@yahoo.co.in

2007-02-14

304

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

305

DFT STUDY ON THE MECHANISM OF THE ADDITION REACTION BETWEEN CARBENE AND GLYCINE  

Scientific Electronic Library Online (English)

Full Text Available SciELO Chile | Language: English Abstract in english The mechanism of addition reaction between the singlet carbene and glycine has been investigated at the B3LYP/6-311+G* level of theory, including geometry optimization and vibrational analysis for the involved stationary points on the potential energy surface. Computational results suggest that ther [...] e are two reaction pathways (1) and (2) during the addition process. In the pathway (1), carbene attacks the C=O bond from the H¹C¹C² side of glycine to form an intermediate (IM1), which is a barrier-free exothermic reaction. Then, IM1 isomerizes to a product (Pro1) via a transition state (TS1) with a potential barrier of 25.7 kJ/mol. Similarly, in the pathway (2), carbene attacks the C=O bond from the H²C¹C² side of glycine to form an intermediate IM2. Subsequently, IM2 isomerizes to Pro2 via TS2, where the Pro2 and Pro1 are enantiomers actually. The calculated potential barrier of 51.3 kJ/mol is higher than that of the pathway (1). Correspondingly, the reaction energy for the both pathways is -258.5 kJ/mol. Additionally, the atoms in molecules (AIM) theory has also been performed to characterize the bonding interaction and structural features for the addition reaction.

XIAOJUN, TAN; WEIHUA, WANG; PING, LI; JINSONG, GU; GUORONG, WANG; DANGSHENG, WANG; TAO, LI.

306

Ruthenium-catalyzed synthesis of functional conjugated dienes via addition of two carbene units to alkynes.  

Science.gov (United States)

The reaction of a variety of alkynes with N(2)CHSiMe(3), in the presence of Cp*RuCl(cod) as the catalyst precursor, leads to the general formation of functional conjugated dienes. This selective formation results from the ruthenium-catalyzed creation of two carbon-carbon double bonds in a single step under mild conditions. Terminal alkynes produce 1,4-bistrimethylsilylbuta-1,3-dienes with Z stereoselectivity for the less hindered double bond whereas disubstituted alkynes favor E-configuration for the same double bond. Diynes react also as monoalkynes, and only one triple bond is transformed to give disilylated dienynes. The reaction can be applied to the in situ desilylation in methanol and formation of monosilylated dienes. The catalytic formation of 1,4-bisfunctional buta-1,3-dienes can also take place with N(2)CHCO(2)Et and N(2)CHPh. The reaction can be understood by addition of two carbene units to triple bonds. An initial [2 + 2] addition of the Ru=CHSiMe(3) bond with the alkyne triple bond leads to an alkenyl ruthenium-carbene species capable of coordinating a second carbene unit to produce conjugated dienes. PMID:20459106

Le Paih, Jacques; Vovard-Le Bray, Chloé; Dérien, Sylvie; Dixneuf, Pierre H

2010-06-01

307

Enantioselective synthesis of beta-trifluoromethyl-beta-lactones via NHC-catalyzed ketene-ketone cycloaddition reactions.  

Science.gov (United States)

The highly diastereo- and enantioselective synthesis of beta-trifluoromethyl-beta-lactones bearing two contiguous stereocenters was realized by chiral N-heterocyclic carbene-catalyzed formal cycloaddition reaction of alkyl(aryl)ketenes and trifluoromethyl ketones. PMID:19681591

Wang, Xiao-Na; Shao, Pan-Lin; Lv, Hui; Ye, Song

2009-09-17

308

Palladation of diimidazolium salts at the C4 position: access to remarkably electron-rich palladium(II) centers  

OpenAIRE

Palladation of C2-protected diimidazolium salts with Pd(OAc)? afforded complexes comprising C4-bound N-heterocyclic dicarbene ligands. The reactivity of these complexes towards Lewis acids (AgBF?, AgOAc) and Brønsted acids (H?SO?, H?PO?, HOAc) revealed that abnormal C4 bonding of the carbenes markedly increases the nucleophilicity of the coordinated palladium center as compared to C2 bonding. Despite its formal +2 charge, the palladium center in these complexes is best described ...

Heckenroth, Marion; Kluser, Evelyne; Neels, Antonia; Albrecht, Martin

2008-01-01

309

Imidazole to NHC rearrangements at molybdenum centers. An experimental and theoretical study  

OpenAIRE

Both manganese and rhenium complexes of the type [M(bipy)(CO)3(N-RIm)]+ (bipy=2,2’-bipyridine) undergo deprotonation of the central CH group of the N-alkylimidazole (N-RIm) ligand when treated with a strong base. However, the outcome of the reaction is very different for either metal. For Mn, the addition of the equimolar amount of an acid to the product of the deprotonation affords an N-heterocyclic carbene (NHC) complex, whereas for Re, once the deprotonation of the central imidazole CH g...

Brill, Marcel; Huertos, Miguel A.; Pe?rez, Julio; Riera, Luci?a

2011-01-01

310

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.

311

Gold-catalyzed tandem cycloisomerization/functionalization of in situ generated ?-oxo gold carbenes in water.  

Science.gov (United States)

A gold-catalyzed tandem cycloisomerization/functionalization of in situ generated ?-oxo gold carbenes in water has been developed, which provides ready access to highly functionalized indole derivatives from o-alkynyl anilines and ynamides. Importantly, gold serves dual catalytic roles to mediate both the cycloisomerization of o-alkynyl anilines and the intermolecular oxidation of ynamides at the same time, thus providing a new type of concurrent tandem catalysis. The use of readily available starting materials, a simple procedure, and mild reaction conditions are other notable features of this method. PMID:25229883

Shen, Cang-Hai; Li, Long; Zhang, Wei; Liu, Shuang; Shu, Chao; Xie, Yun-Er; Yu, Yong-Fei; Ye, Long-Wu

2014-10-01

312

Palladation of diimidazolium salts at the C4 position: access to remarkably electron-rich palladium(II) centers.  

Science.gov (United States)

Palladation of C2-protected diimidazolium salts with Pd(OAc)2 afforded complexes comprising C4-bound N-heterocyclic dicarbene ligands. The reactivity of these complexes towards Lewis acids (AgBF4, AgOAc) and Brønsted acids (H2SO4, H3PO4, HOAc) revealed that abnormal C4 bonding of the carbenes markedly increases the nucleophilicity of the coordinated palladium center as compared to C2 bonding. Despite its formal +2 charge, the palladium center in these complexes is best described as a Lewis base. The abnormal carbene bonding mode induces new reaction patterns such as the formation of a Pd-Ag adduct. Based on metallation studies including the palladation of a dissymmetric diimidazolium salt, a rationale for the selective activation of the C4-H bond in the diimidazolium precursor salts is proposed. PMID:18985257

Heckenroth, Marion; Kluser, Evelyne; Neels, Antonia; Albrecht, Martin

2008-11-28

313

Crystal structure of {3-[3,5-bis(2,6-dimethylphenyl-1,2-phenylene]-1-(2,6,2??,6??-tetramethyl-1,1?:3?,1??-terphenyl-5?-ylimidazol-2-ylidene}chlorido(?6-p-cymeneruthenium(II benzene disolvate  

Directory of Open Access Journals (Sweden)

Full Text Available The title compound, [Ru(C47H43N2Cl(C10H14]·2C6H6, crystallized with two independent molecules of benzene. One of the N-aryl moieties of the N-heterocyclic carbene (NHC ligand underwent cyclometallation to form a five-membered ruthenacycle. The complex has a three-legged piano-stool structure with two C atoms incorporated in the five-membered ruthenacycle and a Cl atom as legs. The ruthenacycle is essentially coplanar with the imidazole ring of the NHC ligand, making a dihedral angle of 0.85?(8°.

Shohei Sase

2014-12-01

314

Crystal structure of {3-[3,5-bis­(2,6-di­methyl­phen­yl)-1,2-phenyl­ene]-1-(2,6,2??,6??-tetra­methyl-1,1?:3?,1??-ter­phen­yl-5?-yl)imidazol-2-yl­idene}chlorido­(?6-p-cymene)ruthenium(II) benzene disolvate  

Science.gov (United States)

The title compound, [Ru(C47H43N2)Cl(C10H14)]·2C6H6, crystallized with two independent mol­ecules of benzene. One of the N-aryl moieties of the N-heterocyclic carbene (NHC) ligand underwent cyclo­metallation to form a five-membered ruthenacycle. The complex has a three-legged piano-stool structure with two C atoms incorporated in the five-membered ruthenacycle and a Cl atom as legs. The ruthenacycle is essentially coplanar with the imidazole ring of the NHC ligand, making a dihedral angle of 0.85?(8)°. PMID:25553006

Sase, Shohei; Ikehara, Yuriko; Goto, Kei

2014-01-01

315

Crystal structure of {3-[3,5-bis-(2,6-di-methyl-phen-yl)-1,2-phenyl-ene]-1-(2,6,2'',6''-tetra-methyl-1,1':3',1''-ter-phen-yl-5'-yl)imidazol-2-yl-idene}chlorido-(?(6)-p-cymene)ruthenium(II) benzene disolvate.  

Science.gov (United States)

The title compound, [Ru(C47H43N2)Cl(C10H14)]·2C6H6, crystallized with two independent mol-ecules of benzene. One of the N-aryl moieties of the N-heterocyclic carbene (NHC) ligand underwent cyclo-metallation to form a five-membered ruthenacycle. The complex has a three-legged piano-stool structure with two C atoms incorporated in the five-membered ruthenacycle and a Cl atom as legs. The ruthenacycle is essentially coplanar with the imidazole ring of the NHC ligand, making a dihedral angle of 0.85?(8)°. PMID:25553006

Sase, Shohei; Ikehara, Yuriko; Goto, Kei

2014-12-01

316

NHC–Cu-Catalyzed Silyl Conjugate Additions to Acyclic and Cyclic Dienones and Dienoates. Efficient Site-, Diastereo- and Enantioselective Synthesis of Carbonyl-Containing Allylsilanes  

OpenAIRE

Efficient and highly diastereo- and enantioselective conjugate additions of phenyldimethylsilyl units to acyclic and cyclic dienones and dienoates are disclosed. The C–Si bond forming reactions are catalyzed by 2.0–2.5 mol % of a copper complex of a chiral monodentate N-heterocyclic carbene; the requisite reagent, PhMe2Si–B(pin), is commercially available or can be easily prepared. Transformations generate allylsilanes in up to 98% yield and >99:1 enantiomeric ratio, and proceed with co...

Lee, Kang-sang; Wu, Hao; Haeffner, Fredrik; Hoveyda, Amir H.

2012-01-01

317

Gold(I)-Catalyzed Intramolecular Dihydroamination of Allenes with N,N?-Disubstituted Ureas to Form Bicyclic Imidazolidin-2-ones  

OpenAIRE

Reaction of N-?-allenyl urea 1 with a catalytic 1:1 mixture of gold(I) N-heterocyclic carbene complex (5)AuCl [5 = 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidine] and AgPF6 at room temperature for 2 h led to isolation of bicyclic imidazolidin-2-one 4 in 93% yield as a single diastereomer. Gold-catalyzed dihydroamination was effective for a number of N-?- and N-?-allenyl ureas to form the corresponding bicyclic imidazolidin-2-ones in good yield with high diastereoselectivity.

Li, Hao; Widenhoefer, Ross A.

2009-01-01

318

Synthesis of unprotected and borane-protected cyclic phosphines using Ru- and Mo- based olefin metathesis catalysts.  

OpenAIRE

Ru- and Mo-based catalysts can be used in ring closing metathesis (RCM) reactions to synthesise cyclic phosphines protected as their borane complexes. The compatibility of the Schrock Mo-catalyst and the N-heterocyclic carbene Ru-catalysts with this class of substrates is particularly noteworthy as asymmetric RCM (ARCM) is now emerging as a new tool for the preparation of homochiral phosphines. One of the key results is that the Mo-catalyst allows the ring closure of the unprotected diallylph...

Slinn, Ca; Redgrave, Aj; Hind, Sl; Edlin, C.; Nolan, Sp; Gouverneur, V.

2003-01-01

319

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

320

Evidence for the cyclic CN2 carbene in the gas phase.  

Science.gov (United States)

3-Halodiazirine-3-carboxylic acids (c-CN2XCOOH, X = Cl or Br) were prepared from their esters and converted to the corresponding sodium salts. Collision-induced dissociation (CID) of the carboxylate ions led exclusively to the loss of CO2 and the resulting c-CN2X(-) ions dissociated to c-CN2 carbene at low energies. The bond dissociation energy (BDE) for c-CN2Br(-) was found to be less than 8 kcal/mol using CID of the anion generated by electrospray ionization of the carboxylate. The analogous difluoro system (CF2XCOOH/CF2X(-)/CF2) exhibits similar dissociative behavior. All experimental BDEs are in very good agreement with MP4/aug-cc-pVTZ calculations. PMID:25296289

Hanzlová, Eva; Vá?a, Ji?í; Shaffer, Christopher J; Roithová, Jana; Martin?, Tomáš

2014-10-17

321

C1 polymerisation and related C-C bond forming 'carbene insertion' reactions.  

Science.gov (United States)

In this critical review we summarise the currently available 'C1 polymerisation' techniques as valuable alternatives for 'C2 polymerisation' in the preparation of saturated main-chain carbon-based polymers. C1 polymerisation involves the growth of polymers from monomers delivering only one functionalised carbon unit (C1 monomers; typically 'carbene precursors') in each chain-growth step, which contrasts with common polymerisation of C=C bond containing substrates (C2 monomers). In the general introduction (section 1) we comment on the availability of C1 monomers and the most important differences between C1 and C2 polymerisation techniques, highlighting the opportunities provided by C1 polymerisation to prepare new polymer structures. In section 2 we describe several Lewis acid mediated C1 polymerisation reactions based on diazocompounds and sulfur ylides as C1 monomers. Some of these are 'living polymerisation' reactions which allow the synthesis of functional telechelic block-copolymers and polymethylenic homo-polymers with a wide variety of different functional end-groups at both polymer chain-ends in a controlled fashion. Miscellaneous related reactions of other C1 monomers are described in section 3. Transition metal mediated C1 polymerisation methods in section 4 allow the polymerisation of polar functionalised C1 monomers. Several homogeneous and heterogeneous catalysts are capable of producing polymers from a variety of diazo compounds, some of which even allow the formation of stereoregular polar functionalised polymers (which is a major challenge in traditional olefin polymerisation). An overview of the current state-of-the art, challenges and opportunities, as well as an overview of the available mechanistic information (sections 4 and 5) is provided. Some related C-C bond forming reactions proceeding via (migratory) carbene insertion (section 6) are also discussed (106 references). PMID:20419216

Jellema, Erica; Jongerius, Anna L; Reek, Joost N H; de Bruin, Bas

2010-05-01

322

Photolysis of 4-chlororesorcinol in water: competitive formation of a singlet ketene and a triplet carbene.  

Science.gov (United States)

Research on photoinduced reactions of halogenated phenols is of interest for environmental photochemistry and for synthetic organic chemistry. Previous studies have uncovered interesting mechanistic features, including ring contraction from benzene to cyclopentadiene from ortho derivatives and two-electron processes forming carbocations and carbenes from para derivatives. In the present work, we studied the aqueous photochemistry of 4-chlororesorcinol (1), which combines the conformational properties of both types of derivatives, using nanosecond transient absorption spectroscopy and photoproduct analysis. The absorption spectra obtained upon pulsed laser excitation of 1 showed the occurrence of both o-Cl and p-Cl elimination, the first observed transients being the ketene 3-hydroxy-6-fulvenone (2, ?(max) = 255 nm) and the carbene 2-hydroxy-4-oxo-2,5-cyclohexadienylidene (3, ?(max) = 405 and 395 nm). The reactivities of 2 and 3, the spectra of the secondary transients and the analysis of the final products showed that the two HCl elimination pathways take place concurrently. Most probably, the bifurcation step is the competition between intersystem crossing on the molecular level and o-Cl elimination on the singlet surface; p-Cl elimination proceeds on the triplet surface. Remarkably, the quantum yield of p-Cl elimination from 1 is lower by one order of magnitude compared to that found in para-halogenated phenols, while that of o-Cl elimination from 1 is comparable to ortho-halogenated phenol. To explain this result, we propose that o-Cl elimination is the major deactivation step, forming an intermediate singlet cation which is able to recombine to ground state 1, thereby limiting the observed photochemical quantum yields. PMID:20859579

Richard, Claire; Krajnik, Paul; Grabner, Gottfried

2010-11-14

323

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

Science.gov (United States)

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 carbene (NHC) complexes [Ag2LBr2/Au2LBr2; 2a/3a], [(Ag2L2)(PF6)2/(Au2L2)(PF6)2; 2b/3b] were developed from their corresponding ligands. All compounds were screened for their antimicrobial activities against multiple keratitis-associated human eye pathogens, including bacteria and fungi. Complexes 2a and 3a showed highest activity, and the effectiveness of 3a was also studied, focusing eradication of pathogen biofilm. Furthermore, the structures of 1a, 2a and 3b were determined using single crystal X-ray analysis, 2b and 3a were optimized theoretically. The mechanism of action of 3a was evaluated by scanning electron microscopy and docking experiments, suggesting that its target is the cell membrane. In summary, 3a may be helpful in developing antimicrobial therapies in patients suffering from keratitis-associated eye infections caused by multidrug-resistant pathogens. PMID:23554886

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

2013-01-01

324

A spectroscopic study of the reaction of the carbene, tetrabromocyclopentadienylidene, with O 2 in low temperature matrices  

Science.gov (United States)

The photolysis of tetrabromodiazocyclopentadiene ( 2) in low temperature Ar and N 2 matrices generates the carbene, tetrabromocyclopentadienylidene ( 3). In O 2-doped matrices, ( 3) reacts with oxygen yielding first tetrabromocyclopentadienone O-oxide ( 4), identification of which was aided by experiments with isotopically labelled oxygen, and then tetrabromocyclopentadienone ( 5) and tetrabromo-?-pyrone ( 6). The matrix uv-visible and infrared absorption spectra of tetrabromocyclopentadienone O-oxide ( 4) are reported.

Dunkin, Ian R.; McCluskey, Adam

1994-01-01

325

Synthesis and characterization of reactive intermediates: The study of biradical, carbene, nitrene and carbyne negative ions in the gas phase  

OpenAIRE

The synthesis and characterization of carbene, nitrene, carbyne and biradical negative ions were studied using the flowing afterglow-triple quadrupole apparatus. These include the negative ions of phenylcarbene, 3-ethoxyphenylnitrene, phenylcarbyne and 2,4-dimethylenecyclobutane-1,3-diyl, respectively. Various experimental gas-phase acidities, electron affinities and halide dissociation energies were combined in thermochemical cycles to derive the heats of formation of phenylcarbene, phenylca...

Hill, Brian Trenton

2000-01-01

326

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

327

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

Directory of Open Access Journals (Sweden)

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

Nuno R. Candeias

2007-01-01

328

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

Scientific Electronic Library Online (English)

Full Text Available SciELO Brazil | Language: Portuguese Abstract in portuguese [...] Abstract in english A five-session laboratory experiment is described for the synthesis of a beta-lactam via Rh(II) catalysed intramolecular C-H insertion of a alpha-diazo-alpha-ethoxycarbonylacetamide. The metallo-carbene, responsible for the C-H bond activation, was generated from the diazo substrate and the catalyst [...] Rh2(OAc)4. The high stability and solubility of the catalyst and the exclusive C-H insertion of the Rh-carbene allows the synthesis of this important heterocycle in water and the catalyst reutilization.

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

1768-17-01

329

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

Energy Technology Data Exchange (ETDEWEB)

A five-session laboratory experiment is described for the synthesis of a beta-lactam via Rh(II) catalysed intramolecular C-H insertion of a alpha-diazo-alpha-ethoxycarbonyl acetamide. The metallo-carbene, responsible for the C-H bond activation, was generated from the diazo substrate and the catalyst Rh{sub 2}(OAc){sub 4}. The high stability and solubility of the catalyst and the exclusive C-H insertion of the Rh-carbene allows the synthesis of this important heterocycle in water and the catalyst reutilization. (author)

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

2007-07-01

330

Cyclopentadienylidene: aromaticity and antiaromaticity of the ?- and ?-cyclic conjugation systems in cyclic conjugated carbenes  

International Nuclear Information System (INIS)

The feasibility was discussed for the prediction of electronic structural characteristics of cyclic conjugated carbenes on the basis not only of the ?-cyclic conjugation system but also of the ?-cyclic conjugation system. The features found are in accord both with the results of quantum chemical calculations and the available experimental data. As an example, a detailed examination was carried out on cyclopentadienylidene. MINDO/3, MNDO and ab initio calculations with the STO-3G and 4-31G bases showed that the ground state of cyclopentadienylidene is a triplet (3B1, planar C/sub 2v/ structure). The reasons were discussed for the lability of the planar 6? and 4? electron C/sub 2v/ geometric configurations of the singlet 1A1 state which do not correspond to minima on the potential energy surfaces of C5H4. The scheme for the isomerization of acoplanar C/sub s/ structures of the singlet state of cyclopentadienylidene was shown to be the inverted scheme for the interconversion of 6? and 4? electron forms. The bifurcation of the completely symmetrical pathway of this interconversion leads to C/sub s/ structures

331

Synthesis and characterisation of the aminocarbene complexes [(eta(5)-C5H5)Fe(CO)(PPh3){=C(NHR2)(CH2R1)}]+BF4- [R-1 = H, Me or Pr; R-2 = H, Me, Et, CHMe2, CH2Ph, CH(Me)Ph, CH2CH=CH2 or CH2CH2OH  

OpenAIRE

A number of secondary aminocarbenes of the type (RS)-[(?5-C5H5)Fe(CO)(PPh 3){=C(CH2R1)(NHR2)}] +BF4- were synthesised in very good yield [66-99%, R1 = H, Me or Pr; R2 = H, Me, Et, CHMe2, CH2Ph, CH(Me)Ph, CH2CH=CH2 or CH2CH2OH]. The absolute configuration of one of the carbenes was established by a single-crystal X-ray diffraction experiment. The chemistry of the carbene complexes was investigated.

Davies, Sg; Edwards, Aj; Jones, S.; Metzler, MR; Yanada, K.; Yanada, R.

1998-01-01

332

Pull-push mechanism for the 1,2-hydrogen rearrangement of carbenes. Substituent and deuterium isotope effects for thermal decomposition of 1-phenyl-2-diazopropanes  

International Nuclear Information System (INIS)

Intramolecular and intermolecular deuterium isotope effects have been measured for the thermal carbene H rearrangements of three substituted 1-phenyl-2-diazopropanes-1-d in hexane at 250C. The isotope effects, k/sub H//k/sub D/, vary from ca. 1.2 to 1.5, increasing with electron-withdrawing substituents, for the formation of both cis- and trans-?-methylstyrenes. Product ratios were determined for these compounds as well as the corresponding undeuterated ones, permitting calculation of intermolecular primary and secondary isotope effects. In addition, the competition among the cis and trans products and the product of H migration from the terminal methyl group permitted determination of Hammett rho values of ca. -1 for the competition between benzylic and terminal migration. The results strongly indicate a ''pull-push'' mechanism, which can be pictured roughly as electrophilic attack on the C--H bond by the phantom p orbital of the carbene along with backside nucleophilic attack by the carbene unshared electron pair to push the H away and form the ? bond. The data are believed to be consistent only with a nonzero barrier for the carbene hydrogen rearrangement

333

Domino Michael addition-carbene rearrangement-cyclization reaction of 1-alkynyl(aryl)-lambda3-bromanes with 2-mercapto-1,3-benzazoles.  

Science.gov (United States)

Exposure of 1-alkynyl[p-(trifluoromethyl)phenyl](tetrafluoroborato)-lambda3-bromanes to 2-mercaptobenzimidazole or benzothiazole in dichloromethane at 0 degrees C under argon resulted in a domino Michael addition-carbene rearrangement-cyclization reaction to produce directly tricyclic heterocycles in high yields, whereas the reaction with 2-mercaptobenzoxazole afforded 1-alkynyl sulfides. PMID:16220178

Ochiai, Masahito; Tada, Norihiro

2005-10-28

334

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

335

Mechanism of host-guest complex formation and identification of intermediates through NMR titration and diffusion NMR spectroscopy.  

Science.gov (United States)

The formation of host-guest (H-G) complexes between 1,8-bis[(diethylgallanyl)ethynyl]anthracene (H) and the N-heterocycles pyridine and pyrimidine (G) was studied in solution using a combination of NMR titration and diffusion NMR experiments. For the latter, diffusion coefficients of potential host-guest structures in solution were compared with those of tailor-made reference compounds of similar shape (synthesized and characterized by NMR, HRMS, and in part XRD). Highly dynamic behavior was observed in both cases, but with different host-guest species and equilibria. With increasing concentrations of the pyridine guest, the equilibrium H2?H2?(1)-G1?HG2 is observed (in the second step a host dimer coordinates one guest molecule); for pyrimidine the equilibrium H2?H1?(2)-G1?HG2 is observed (the formation of a 1:1 aggregate is the second step). PMID:24925835

Lamm, Jan-Hendrik; Niermeier, Philipp; Mix, Andreas; Chmiel, Jasmin; Neumann, Beate; Stammler, Hans-Georg; Mitzel, Norbert W

2014-07-21

336

Photochemical generation, intramolecular reactions, and spectroscopic detection of oxonium ylide and carbene intermediates in a crystalline ortho-(1,3-dioxolan-2-yl)-diaryldiazomethane.  

Science.gov (United States)

Photochemical excitation of a diaryldiazomethane with an ortho-acetal both in solution and in crystals led to products that originate from the expected diarylcarbene and form an intramolecular oxonium ylide. While crystals strongly favored the formation of a benzocyclobutane by intramolecular hydrogen abstraction in the triplet carbene, reactions in benzene led exclusively to products that derive from the oxonium ylide. Studies in methyl cyclohexane glasses and in mixed crystals at 77 K led to the spectroscopic detection of triplet carbene (3)C, which partially transformed into a new species that we assign as the sought-after oxonium ylide Y. The formation of a formally ionic intermediate suggests that the scope of reactions by reactive intermediates in crystalline solids may be broader than it is generally assumed. PMID:19262929

Garcia-Garibay, Miguel A; Dang, Hung

2009-03-21

337

Oxorhenium complexes as aldehyde-olefination catalysts.  

Science.gov (United States)

Several oxorhenium compounds in the formal oxidation states V and VII are examined as catalysts for the aldehyde-olefination starting from diazo compounds, phosphines, and aldehydes. Of these, [ReMeO2(eta2-alkyne)] complexes provide the simplest catalysts to study, although [ReOCl3(PPh3)2] still remains the most efficient rhenium catalyst for aldehyde-olefination described to date. Prior to the reaction with the Re catalysts the phosphine and the diazo compound react to form a phosphazine. No catalytic reaction occurs in cases where no phosphazine formation is observed. The first step of the catalytic cycle involves the formation of a carbene intermediate by the reaction of phosphazine and catalyst under extrusion of phosphine oxide and dinitrogen. In a second step the carbene reacts with aldehyde under olefin formation and catalyst regeneration. Excess of alkyne as well as the presence of ketones slows down the catalytic reaction. The olefination of 4-nitrobenzaldehyde with diazomalonate is possible with these Re catalysts. In contrast, this reaction does not take place either in the classical Wittig fashion from Ph3P=C(CO2Et)2 and aldehyde or by use of all other catalysts for aldehyde olefination reactions reported to date. Catalytic ylide formation from diazo compounds seems therefore not to be the only pathway through which catalytic aldehyde-olefination reactions can proceed. PMID:15526317

Santos, Ana M; Pedro, Filipe M; Yogalekar, Ameya A; Lucas, Isabel S; Romão, Carlos C; Kühn, Fritz E

2004-12-01

338

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

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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

339

In Vitro and Murine Efficacy and Toxicity Studies of Nebulized SCC1, a Methylated Caffeine-Silver(I) Complex, for Treatment of Pulmonary Infections ?  

OpenAIRE

The expanding clinical challenge of respiratory tract infections due to resistant bacteria necessitates the development of new forms of therapy. The development of a compound composed of silver coupled to a methylated caffeine carrier (silver carbene complex 1 [SCC1]) that demonstrated in vitro efficacy against bacteria, including drug-resistant organisms, isolated from patients with respiratory tract infections was described previously. The findings of current in vitro studies now suggest th...

Cannon, Carolyn L.; Hogue, Lisa A.; Vajravelu, Ravy K.; Capps, George H.; Ibricevic, Aida; Hindi, Khadijah M.; Kascatan-nebioglu, Aysegul; Walter, Michael J.; Brody, Steven L.; Youngs, Wiley J.

2009-01-01

340

Synthesis, structure and electrochemistry of Fischer alkoxy- and aminocarbene complexes of tungsten : the use of DFT to predict and understand oxidation and reduction potentials  

OpenAIRE

Reactions of Fischer alkoxycarbene complexes [W(CO)5{C(OEt)Ar}], Ar = thienyl (1) or furyl (2), with ethylene diamine lead to the formation of two different reaction products: an aminolysis product (5 or 6) where the ethoxy substituent of the carbene ligand is replaced by the ethylene diamine moiety, as well as a chelated product where aminolysis and substitution of one carbonyl ligand had taken place, yielding 7 or 8. Aminolysis of 1 and 2 with cyclohexyl amine (CHA) pro...

Landman, Marile?; Pretorius, Rene?; Buitendach, Blenerhassitt E.; Rooyen, Petrus H.; Conradie, Jeanet

2013-01-01

341

Gold(I)-NHC complexes of antitumoral diarylimidazoles: structures, cellular uptake routes and anticancer activities.  

Science.gov (United States)

Five new heterocyclic gold carbene complexes were prepared, four chlorido-[1,3-dimethyl-4,5-diarylimidazol-2-ylidene]gold complexes 6a-d and a chlorido-[1,3-dibenzylimidazol-2-ylidene]gold complex 11, and three of them were characterised by X-ray single crystal analyses. They were tested for cytotoxicity against a panel of four human cancer cell lines and non-malignant fibroblasts, for tubulin interaction, and for the pathways of their uptake into 518A2 melanoma cells. All complexes showed cytotoxic activity in the micromolar IC(50) range with distinct selectivities for certain cell lines. In stark contrast to related metal-free 1-methyl-4,5-diarylimidazoles, the complexes 6 and 11 did not noticeably inhibit the polymerisation of tubulin to give microtubules. The cellular uptake of complexes 6 occurred mainly via the copper transporter (Ctr1) and the organic cation transporters (OCT-1/2). Complex 11 was accumulated preferentially via the organic cation transporters and by Na(+)/K(+)-dependent endocytosis. The new gold carbene complexes seem to operate by a mechanism different from that of the parent 1-methylimidazolium ligands. PMID:22112840

Kaps, Leonard; Biersack, Bernhard; Müller-Bunz, Helge; Mahal, Katharina; Münzner, Julienne; Tacke, Matthias; Mueller, Thomas; Schobert, Rainer

2012-01-01

342

Metallacumulenes and carbide complexes. Final performance report  

Energy Technology Data Exchange (ETDEWEB)

We investigated many aspects of transition metal complexes of carbon-rich ligands, including cumulated transition metal carbene complexes of the types vinylidene (M=C=CR{sub 2})(M = Fe, Ru, Os, Mo, W), allenylidene (M=C=C=CR{sub 2}), and butatrienylidene (M=C=C=CR{sub 2}), as well as ``naked`` carbon ligands C{sub 1}, C{sub 2}, and C{sub 3}. In the last 3 years, we began to put some effort into studying the fullerenes. Finally, we investigated initial aspects of the coordination chemistry of thiophenes, from the perspectives of (1) modeling the transition- metal-catalyzed hydrodesulfurization of fossil fuels and (2) development of metal-doped, polythiophene-based polymers.

Selegue, J.P.

1992-12-31

343

(Eta2-alkyne)methyl(dioxo)rhenium complexes as aldehyde-olefination catalysts.  

Science.gov (United States)

Complexes CH3ReO2L (L = 2-butyne, 3-hexyne, diphenylacetylene) are catalysts for the olefination of aldehydes, using 4-nitrobenzaldehyde (4-nba) as the standard aldehyde and ethyldiazoacetate (eda) as the diazo compound. Spectroscopic studies including in situ 31P, 17O, 13C, and 1H NMR spectroscopy are used to elucidate the mechanism and the nature of the active species. One of the key steps of the mechanism is the rapid formation of phosphazine at the beginning of the cycle and its subsequent reaction with the metal dioxide complex to form the catalytically active carbene species. PMID:12603128

Santos, Ana M; Romão, Carlos C; Kühn, Fritz E

2003-03-01

344

One-pot asymmetric synthesis of quaternary pyrroloindolones through a multicatalytic N-allylation/hydroacylation sequence.  

Science.gov (United States)

An intramolecular, quaternary carbon center forming hydroacylation of ?-substituted acrylates has been discovered. This interesting transformation can be readily incorporated into a multicatalytic tandem process enabled by a combination of nucleophilic tertiary amine and N-heterocyclic carbene catalysis. With no additional stoichiometric base required, this transformation affords the quaternary pyrroloindolones with high levels of enantioselectivity. PMID:25079294

Lu, Hong; Lin, Jun-Bing; Liu, Jin-Yu; Xu, Peng-Fei

2014-09-01

345

Nickel-catalysed carboxylation of organoboronates.  

Science.gov (United States)

A nickel/N-heterocyclic carbene (NHC) catalysed carboxylation of aryl-, heteroaryl- and alkenylboronates, affording the corresponding carboxylic acids, has been developed. This transformation proceeds under one atmosphere of CO2 with a broad range of substrates and exhibits good functional group compatibility. PMID:24915842

Makida, Yusuke; Marelli, Enrico; Slawin, Alexandra M Z; Nolan, Steven P

2014-07-28

346

Photoswitchable NHC-promoted ring-opening polymerizations.  

Science.gov (United States)

The UV-induced photocyclization of a dithienylethene-annulated N-heterocyclic carbene precatalyst enabled photoswitchable ring-opening polymerizations of ?-caprolactone and ?-valerolactone. The polymerizations proceeded efficiently in ambient light, however UV irradiation attenuated the reaction rate (k(amb)/k(UV) = 59). Subsequent visible light exposure reversed the photocyclization and restored catalytic activity. PMID:23665923

Neilson, Bethany M; Bielawski, Christopher W

2013-06-18

347

NHC-catalysed highly selective aerobic oxidation of nonactivated aldehydes  

Directory of Open Access Journals (Sweden)

Full Text Available This publication describes a highly selective oxidation of aldehydes to the corresponding acids or esters. The reaction proceeds under metal-free conditions by using N-heterocyclic carbenes as organocatalysts in combination with environmentally friendly oxygen as the terminal oxidation agent.

Lennart Möhlmann

2013-03-01

348

NHC-catalyzed oxidative ?-addition of ?,?-unsaturated aldehydes to isatins: a high-efficiency synthesis of spirocyclic oxindole-dihydropyranones.  

Science.gov (United States)

This manuscript discloses an efficient construction of the spirocyclic oxindole-dihydropyranone scaffold via the N-heterocyclic carbene (NHC)-catalyzed oxidative ?-functionalization of ?,?-unsaturated aldehydes bearing ?-H with isatin derivatives. The ready availability of the starting materials, easy work-up, mild reaction conditions and the potential utilization value of the products make this strategy attractive. PMID:24518966

Liu, Rui; Yu, Chenxia; Xiao, Zhaoxin; Li, Tuanjie; Wang, Xiangshan; Xie, Yuanwei; Yao, Changsheng

2014-03-28

349

NHC-catalysed highly selective aerobic oxidation of nonactivated aldehydes  

OpenAIRE

This publication describes a highly selective oxidation of aldehydes to the corresponding acids or esters. The reaction proceeds under metal-free conditions by using N-heterocyclic carbenes as organocatalysts in combination with environmentally friendly oxygen as the terminal oxidation agent.

Hlmann, Lennart M.; Stefan Ludwig; Siegfried Blechert

2013-01-01

350

PHOTOFRAGMENTATION VOLTAMMETRY STUDIES OF THE AMINOCARBENE COMPLEXES [(ETA(5)-C5H5)FE(CO)(L)(=C(NHR(1))(R(2))]BF4 [L = PPH3, P(P-TOL)3, R(1) = ME, CH2PH, R(2) = ME, BU  

OpenAIRE

The synthesis of the complexes [(?5-C5H5)Fe(CO)(L){=C(NHR 1)(R2)}]BF4 [L = PPh3, P(p-Tol)3; R1 = Me, CH2Ph; R2 = Me, Bu] is described. Photofragmentation voltammetry is used to demonstrate that the primary photoprocess is loss of the phosphine ligand in all four carbene complexes. A common intermediate is observed when the analogous aminocarbenes are studied.

Davies, S.; Metzler, M.; Watkins, W.; Compton, R.; Booth, J.; Eklund, J.

1993-01-01

351

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

Science.gov (United States)

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

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

2014-10-21

352

Cobalt carbene ion: reactions of Co+ with C2H4, cyclo-C3H6, and cyclo-C2H4O  

International Nuclear Information System (INIS)

An ion beam apparatus is employed to study the formation of the cobalt carbene ion, CoCH2+. This ion is produced in the endothermic reaction of cobalt ions with ethene and cyclopropane and in an exothermic reaction with ethylene oxide. A model is proposed to account for the dependence of experimental cross sections on relative kinetic energy for the endothermic reactions. Using this model to interpret the experimental results, a bond dissociation energy D 0(Co+-CH2) = 3.7 +- 0.3 eV is derived

353

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)

354

Synthesis and structure of new thio, seleno, thiocarbene and selenocarbene complexes of tungsten pentacarbonyl  

International Nuclear Information System (INIS)

The insertion of the anionic species PhCCS- and PhCCSe- into the W-carbene bond in (CO)5W=C(OEt)Ph was investigated. The anionic adduct resulting from the addition of PhCCX- (X = S or Se) to the carbene complex proved to be a versatile synthetic reagent, in all cases leading to products in which the acetylenic unit is inserted into the W=C bond. The incorporation of a vinyl fragment into all products seems to be the inevitable result of the presence of the acetylenic unit in the reagent. The synthetic versatility of the system is centered around the apparent ability of the anionic adduct to offer either the X or the C atom in the C-X fragment as a nucleophilic centre. It was possible, by reaction of the anionic complex with HCl, to isolate complexes of the ?,?- unsaturated thio- and selenoaldehydes (CO)5W-X=C(H)-C(Ph)=C(Ph)OEt (X = S or Se) with the phenyl groups in the cis configuration. The ambident character of the anionic complex was evident in the isolation of a series of complexes with cyclic ligands of the types =C-C(Ph)=C(Ph)XY (X = S or Se; Y = S or Se) and -X=C-C(Ph)=C(Ph)YZ(X=Y=Z = S ; X = Se, Y=Z = S or Se) when elemental sulphur (or selenium) was used as the electrophilic reagent. In a series of similar reactions ring closure could be prevented and ?,?-unsaturated thio- and seleno carbenes were obtained by the use of good alkylating agents. These results led to the synthesis of the interesting bino the synthesis of the interesting binuclear complex (CO)5W=C-{S-Fe(CO)2Cp}-C(Ph)=C(OEt)Ph. The nucleophylic character of the carbon atom could also be used to prepare a novel series of ?,?-unsaturated dithio diseleno and mixed thio-seleno ester ligands. The crystal structures of eight key compounds were determined by X-ray diffraction methods. 18 tabs., 42 figs., 88 refs

355

Selective synthesis of carbonylated N-heterocycles by homogeneous and heterogeneous multi-catalysis  

OpenAIRE

The one-pot selective synthesis of 4-quinolones and indoxyls was achieved through a carbonylative Sonogashira coupling followed by cyclization. A study in homogeneous catalysis revealed that the nature of catalysts in presence controlled the selectivity toward each compounds. Whereas the first coupling step is palladium catalyzed, the cyclizations require organic nucleophilic species. Thus, 4-quinolones were obtained by one-pot multi-catalysis {[Pd]+amine} and indoxyls by one-pot tandem catal...

Genelot, Marie

2011-01-01

356

Coupling Reactions of ?-Bromocarboxylate with Non-Aromatic N-Heterocycles  

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Full Text Available The conditions for the C-N bond forming reaction (C-N coupling reaction between ?-bromocarboxylate and nitrogen-containing non-aromatic heterocyclic rings under heterogeneous copper(I oxide catalysis are investigated in this paper. All the generated compounds were fully characterized by IR, NMR and MS spectroscopy. Ab initio/DFT calculations of partial charges on nitrogen atoms in all the discussed heterocycles and on C(2 of carboxylate under applied conditions were predicted. These in silico results correlate relatively with the experimental observations.

Jozef Csollei

2009-08-01

357

Synthesis, characterization, and crystal structure of two ?,?-unsaturated ketones with N-heterocycle  

Science.gov (United States)

Two ?,?-unsaturated ketones: C22H16N2O ( 1), ( E)-3-(4-(1 H-benzo[d]imidazol-1-yl)phenyl)-1-phenylprop-2-en-1-one and C19H16N2O2 ( 2), ( E)-3-(4-(1 H-pyrazol-1-yl)phenyl)-1-(4-methoxyphenyl)prop-2-en-1-one were synthesized and characterized by X-ray diffraction analyses, EA, 1H NMR-, and IR-spectra. In the crystal structure of 1, molecules are linked through intermolecular hydrogen bonds, C-H⋯? and ?⋯? interactions forming a 3-D network, while in the crystal structures of 2, molecules are assembled by the C-H⋯O, C-H⋯N hydrogen bonds and C-H⋯? interactions into an infinite 3-D supramolecular structure. A particularly interesting feature of the packing in the structure of 2, is the extensive contribution of C-H⋯? interactions, involving two hydrogen atoms from each of the methyl groups of the methoxy substituents.

Wang, G.-F.; Sun, S.-W.; Gong, Q.-J.; Sun, H.

2014-12-01

358

Transient negative ions in benzene. Some N-heterocyclic and mono-substituted derivatives  

International Nuclear Information System (INIS)

Electron transmission spectroscopy is used to study transient negative ions or shape resonances in various benzene derivatives. Because of the long lifetime of these ions (? > 10-14 S) the vibrational structure of their first two electronic states is observed superposed on the total electron cross section curves in the energy range 0-6 eV and the corresponding adiabatic electron affinities are determined. The comparison of the first electron affinity with the first ionization potential and the energy on the first excited state of each of the derivatives is used to characterize the 'donor' substituents on the benzene ring. As a complementary study, these derivatives are studied in the liquid phase using polarography (cyclic voltametry). The linear correlation established between polarographic potentials measured in dimethyl formamide and the electron affinities was used to deduce electron affinities for several molecules which are difficult to measure in the gas phase. (author)

359

A functional triazine framework based on N-heterocyclic building blocks  

OpenAIRE

Covalent organic frameworks constitute a subclass of polymeric materials offering enhanced porosity, functionality and stability. In this work a covalent triazine framework based on bipyridine building blocks is presented, along with a comprehensive elucidation of its local structure, porosity, and capacity for metal uptake. A typical synthesis was carried out under ionothermal conditions at 400-700 degrees C using ZnCl2 as a Lewis acidic trimerization catalyst. A high degree of local order a...

Hug, Stephan; Tauchert, Michael E.; Li, Shen; Pachmayr, Ursula E.; Lotsch, Bettina V.

2012-01-01

360

New iodocuprates(I) with N-heterocyclic molecules as the cations  

Energy Technology Data Exchange (ETDEWEB)

Under the hydrothermal conditions, the reactions between CuI, KI and bp/bpp (bp=4,4?-bipiperidine, bpp=1,3-bis(4-piperidyl)propane) in an acidic alcohol solution produced three new organically templated iodocuprates(I) as [H{sub 2}bp]{sub 2}[Cu{sub 2}I{sub 6}] 1, [tmbp][Cu{sub 2}I{sub 4}] 2 and [tmbpp] 2 [Cu{sub 4}I{sub 8}]·2H{sub 2}O 3 (tmbp{sup 2+}=N,N,N?,N?-tetramethyl-4,4?-bipiperidinium; tmbpp{sup 2+}=N,N,N?,N?-tetramethyl-1,3-bis(4-piperidyl)propane dication). X-ray analysis revealed that (i) tmbp{sup 2+} and tmbpp{sup 2+} in compounds 2 and 3 originated from the complete N-alklation of bp/bpp with CH{sub 3}OH; (ii) templated by H{sub 2}bp{sup 2+}, the inorganic anion [Cu{sub 2}I{sub 6}]{sup 2?} of 1 possesses a dinuclear structure, whereas templated by tmbp{sup 2+}, the inorganic anion [Cu{sub 2}I{sub 4}]{sup 2?} of 2 exhibits a one-dimensional (1D) chain structure; (iii) templated by tmbpp{sup 2+}, the inorganic anion [Cu{sub 4}I{sub 8}]{sup 4?} of 3 shows a cubane-like structure modified by four terminal I{sup ?} ions. The photoluminescence analysis indicates that compounds 1 and 2 emit blue light, while compound 3 emits green light. - Graphical abstract: By employing hydrothermal in situ N-alkylation of bp/bpp with CH{sub 3}OH, three new organically templated iodocuprates(I) were obtained. Display Omitted - Highlights: • Three new organically templated iodocuprates(I) were reported. • Cations tmbp{sup 2+} and tmbpp{sup 2+} originated from in situ alkylation of bp/bpp with CH{sub 3}OH. • H{sup +} and I{sup ?} play a key role in alkylation of bp/bpp with CH{sub 3}OH. • Photoluminescence emission for iodocuprates(I) is related to Cu···Cu interaction.

Zhao, Jin-Jing [College of Chemistry and State Key Laboratory of Inorganic Synthesis and Preparative Chemistry, Jilin University, Changchun, Jilin 130023 (China); Zhang, Xiao [State Key Lab of Urban Water Resource and Environment (SKLUWRE) and Academy of Fundamental and Interdisciplinary Science, Harbin Institute of Technology, Harbin, Heilongjiang 150080 (China); Wang, Yan-Ning; Jia, Hong-Li [College of Chemistry and State Key Laboratory of Inorganic Synthesis and Preparative Chemistry, Jilin University, Changchun, Jilin 130023 (China); Yu, Jie-Hui, E-mail: jhyu@jlu.edu.cn [College of Chemistry and State Key Laboratory of Inorganic Synthesis and Preparative Chemistry, Jilin University, Changchun, Jilin 130023 (China); Xu, Ji-Qing, E-mail: xjq@mail.jlu.edu.cn [College of Chemistry and State Key Laboratory of Inorganic Synthesis and Preparative Chemistry, Jilin University, Changchun, Jilin 130023 (China)

2013-11-15

361

New iodocuprates(I) with N-heterocyclic molecules as the cations  

International Nuclear Information System (INIS)

Under the hydrothermal conditions, the reactions between CuI, KI and bp/bpp (bp=4,4?-bipiperidine, bpp=1,3-bis(4-piperidyl)propane) in an acidic alcohol solution produced three new organically templated iodocuprates(I) as [H2bp]2[Cu2I6] 1, [tmbp][Cu2I4] 2 and [tmbpp] 2 [Cu4I8]·2H2O 3 (tmbp2+=N,N,N?,N?-tetramethyl-4,4?-bipiperidinium; tmbpp2+=N,N,N?,N?-tetramethyl-1,3-bis(4-piperidyl)propane dication). X-ray analysis revealed that (i) tmbp2+ and tmbpp2+ in compounds 2 and 3 originated from the complete N-alklation of bp/bpp with CH3OH; (ii) templated by H2bp2+, the inorganic anion [Cu2I6]2? of 1 possesses a dinuclear structure, whereas templated by tmbp2+, the inorganic anion [Cu2I4]2? of 2 exhibits a one-dimensional (1D) chain structure; (iii) templated by tmbpp2+, the inorganic anion [Cu4I8]4? of 3 shows a cubane-like structure modified by four terminal I? ions. The photoluminescence analysis indicates that compounds 1 and 2 emit blue light, while compound 3 emits green light. - Graphical abstract: By employing hydrothermal in situ N-alkylation of bp/bpp with CH3OH, three new organically templated iodocuprates(I) were obtained. Display Omitted - Highlights: • Three new organically templated iodocuprates(I) were reported. • Cations tmbp2+ and tmbpp2+ originated from in situ alkylation of bp/bpp with CH3OH. • H+ and I? play a key role in alkylation of bp/bpp with CH3OH. • Photoluminescence emission for iodocuprates(I) is related to Cu···Cu interaction

362

An electronic structure theory investigation of the physical chemistry of the intermolecular complexes of cyclopropenylidene with hydrogen halides.  

Science.gov (United States)

The proton accepting and donating abilities of cyclopropenylidene (c-C(3)H(2)) on its complexation with hydrogen halides H-X (X = F, Cl, Br) are analyzed using density-functional theory with three functionals (PBE0, B3LYP, and B3LYP-D) and benchmarked against second-order Møller-Plesset (MP2) theory. Standard signatures including, inter alia, dipole moment enhancement, charge transfer from the carbenic lone pair to the antibonding ?*(H-X) orbital, and H-X bond elongation are examined to ascertain the presence of hydrogen bonding in these complexes. The latter property is found to be accompanied with a pronounced red shift in the bond stretching frequency and with a substantial increase in the infrared intensity of the band on complex formation. The MP2/aug-cc-pVTZ c-C(3)H(2)···H-F complex potential energy surface turns out to be an asymmetric deep single well, while asymmetric double wells are found for the c-C(3)H(2)···H-Cl and c-C(3)H(2)···H-Br complexes, with an energy barrier of 4.1 kcal mol(-1) for proton transfer along the hydrogen bond in the latter complex. Hydrogen-bond energy decomposition, with the reduced variational space self-consistent field approach, indicates that there are large polarization and charge-transfer interactions between the interacting partners in c-C(3)H(2)···H-Br compared to the other two complexes. The C···H bonds are found to be predominantly ionic with partial covalent character, unveiled by the quantum theory of atoms in molecules. The present results reveal that the c-C(3)H(2) carbene divalent carbon can act as a proton acceptor and is responsible for the formation of hydrogen bonds in the complexes investigated. PMID:22696309

Varadwaj, Pradeep R; Varadwaj, Arpita; Peslherbe, Gilles H

2012-10-01

363

Modulating NHC catalysis with fluorine  

Science.gov (United States)

Summary Fluorination often confers a range of advantages in modulating the conformation and reactivity of small molecule organocatalysts. By strategically introducing fluorine substituents, as part of a ?-fluoroamine motif, in a triazolium pre-catalyst, it was possible to modulate the behaviour of the corresponding N-heterocyclic carbene (NHC) with minimal steric alterations to the catalyst core. In this study, the effect of hydrogen to fluorine substitution was evaluated as part of a molecular editing study. X-ray crystallographic analyses of a number of derivatives are presented and the conformations are discussed. Upon deprotonation, the fluorinated triazolium salts generate catalytically active N-heterocyclic carbenes, which can then participate in the enantioselective Steglich rearrangement of oxazolyl carbonates to C-carboxyazlactones (e.r. up to 87.0:13.0). PMID:24367445

Rey, Yannick P

2013-01-01

364

3,3?-Dimethyl-1,1?-(methylenedi-p-phenylenediimidazolium bis(hexafluorophosphate  

Directory of Open Access Journals (Sweden)

Full Text Available The title N-heterocyclic carbene compound, C21H22N42+·2PF6?, crystallizes as an inversion twin. There are two independent N-heterocyclic carbene dications (A and B and four independent hexafluorophosphate anions in the asymmetric unit. The cations are L-shaped with the benzene rings being inclined to one another by 88.82?(16° in cation A and 87.03?(16° in cation B. The imidazole rings make dihedral angles of 35.7?(2 and 32.83?(18° with the attached benzene rings in cation A, and 30.14?(19 and 31.96?(18° in cation B. In the crystal, the cations are linked via C—H...F hydrogen bonds, forming a three-dimensional network. ?–? interactions involving the benzene and imidazole rings [centroid–centroid distances = 3.602?(2 and 3.723?(2?Å] and C—H...? interactions are also present.

Kun Huang

2010-09-01

365

Intramolecularly Stabilised Group?10 Metal Stannyl and Stannylene Complexes: Multi-pathway Synthesis and Observation of Platinum-to-Tin Alkyl Transfer.  

Science.gov (United States)

Reaction of [PdClMe(P^N)2 ] with SnCl2 followed by Cl-abstraction leads to apparent Pd?C bond activation, resulting in methylstannylene species trans-[PdCl{(P^N)2 SnClMe}][BF4 ] (P^N=diaryl phosphino-N-heterocycle). In contrast, reaction of Pt analogues with SnCl2 leads to Pt?Cl bond activation, resulting in methylplatinum species trans-[PtMe{(P^N)2 SnCl2 }][BF4 ]. Over time, they isomerise to methylstannylene species, indicating that both kinetic and thermodynamic products can be isolated for Pt, whereas for Pd only methylstannylene complexes are isolated. Oxidative addition of RSnCl3 (R=Me, Bu, Ph) to M(0) precursors (M=Pd or Pt) in the presence of P^N ligands results in diphosphinostannylene pincer complexes trans-[MCl{(P^N)2 SnCl(R)}][SnCl4 R], which are structurally similar to the products from SnCl2 insertion. This showed that addition of RSnCl3 to M(0) results in formal Sn?Cl bond oxidative addition. A probable pathway of activation of the tin reagents and formation of different products is proposed and the relevancy of the findings for Pd and Pt catalysed processes that use SnCl2 as a co-catalyst is discussed. PMID:25424321

Warsink, Stefan; Derrah, Eric J; Boon, Cornelis A; Cabon, Yves; de Pater, Jeroen J M; Lutz, Martin; Klein Gebbink, Robertus J M; Deelman, Berth-Jan

2014-11-25

366

Experimental and theoretical study of the kinetics of dissociation in cis-[RuCl2(P-P)(N-N)] type complexes  

International Nuclear Information System (INIS)

The substitution reactions [RuCl2(P-P)(N-N)] + L ? [RuCl(L)(P-P)(N-N)]+ + Cl-, where P.P = 1,4-bis(diphenylphosphino)butane and N-N = 2,2' -bipyridine, 4,4' L-dimethoxy-2,2' L- bipyridine, 4,4' L-dimethylpyridine-2,2' L-bipyridine and 4,4' L-dichloro-2,2' L-bipyridine, L = pyridine (py) or 4-methylpyridine (4-pic), were studied under pseudo-first order conditions. The reactions proceeded by means of a dissociative mechanism. The rate constants of the substitution reactions increased as the pKa of the N-heterocyclic ligands increased and as the oxidation potential of the metal center decreased. The greater the participation of the atomic d orbitals of the metal in the HOMO, according to DFT calculations, the easier is the dissociation of the chloride from the coordination sphere of the complex. In the 31P{1H} NMR spectra of the series of complexes of general formula [RuCl(L)(P-P)(N-N)]PF6, there are two doublets with ?? < 1. This is consistent with products formed by dissociation of the chloride trans to one of the phosphorus atoms in the precursors. (author)

367

Experimental and theoretical study of the kinetics of dissociation in cis-[RuCl{sub 2}(P-P)(N-N)] type complexes  

Energy Technology Data Exchange (ETDEWEB)

The substitution reactions [RuCl{sub 2}(P-P)(N-N)] + L {yields} [RuCl(L)(P-P)(N-N)]{sup +} + Cl{sup -}, where P.P = 1,4-bis(diphenylphosphino)butane and N-N = 2,2' -bipyridine, 4,4' L-dimethoxy-2,2' L- bipyridine, 4,4' L-dimethylpyridine-2,2' L-bipyridine and 4,4' L-dichloro-2,2' L-bipyridine, L = pyridine (py) or 4-methylpyridine (4-pic), were studied under pseudo-first order conditions. The reactions proceeded by means of a dissociative mechanism. The rate constants of the substitution reactions increased as the pK{sub a} of the N-heterocyclic ligands increased and as the oxidation potential of the metal center decreased. The greater the participation of the atomic d orbitals of the metal in the HOMO, according to DFT calculations, the easier is the dissociation of the chloride from the coordination sphere of the complex. In the {sup 31}P{l_brace}{sup 1}H{r_brace} NMR spectra of the series of complexes of general formula [RuCl(L)(P-P)(N-N)]PF{sub 6}, there are two doublets with {Delta}{sigma} < 1. This is consistent with products formed by dissociation of the chloride trans to one of the phosphorus atoms in the precursors. (author)

Monteiro, Marcos C.R.; Machado, Sergio de Paula, E-mail: sergiopm@iq.ufrj.b [Universidade Federal do Rio de Janeiro (UFRJ), RJ (Brazil). Inst. de Quimica; Nascimento, Fabio B.; Valle, Eliana M.A.; Batista, Alzir A. [Universidade Federal de Sao Carlos (UFSCAR), Sao Carlos, SP (Brazil). Dept. de Quimica; Ellena, Javier; Castellano, Eduardo E. [Universidade de Sao Paulo (IFSC/USP), Sao Carlos, SP (Brazil). Inst. de Fisica

2010-07-01

368

THEORETICAL STUDY OF THE MECHANISM OF CYCLOADDITION REACTION BETWEEN DICHLORO-SILYLENE CARBENE(CL2SI=C:) AND ACETONE  

Scientific Electronic Library Online (English)

Full Text Available SciELO Chile | Language: English Abstract in english The mechanism of the cycloaddition reaction between singlet dichloro-silylene carbene and acetone has been investigated with DFT, including geometry optimization and vibrational analysis for the involved stationary points on the potential energy surface. The energies of the different conformations a [...] re calculated by CCSD(T)//B3LYP/6-31G* method. From the potential energy profile, it can be predicted that the reaction has two competitive dominant reaction pathways. The channel (I) consists of two steps: (1) the two reactants firstly form a four-membered ring intermediate through a barrier-free exothermic reaction of 307.1 kJ/mol; (2) four-membered ring intermediate then isomerizes to a CH3-transfer product via a transition state with energy barrier of 11.3 kJ/mol. The process of channel (II) is as following: on the basis of four-membered ring intermediate created between the two reactants, four-membered ring intermediate further reacts with acetone to form the intermediate through a barrier-free exothermic reaction of 165.8 kJ/mol; Then, intermediate isomerizes to a silicic bis-heterocyclic product via a transition state, for which the barrier is 57.6 kJ/mol.

XIUHUI, LU; PINGPING, XIANG; LEYI, SHI; JUNFENG, HAN; ZHENXIA, LIAN.

369

A benzobisimidazolium-based fluorescent and colorimetric chemosensor for CO2.  

Science.gov (United States)

A new sensor for the fluorescent and colorimetric detection of CO(2) is described. The system utilizes fluoride to activate a tetrapropyl benzobisimidazolium salt and operates in the absence of an exogenous base. On the basis of spectroscopic and theoretical analyses, the mode of action of the present system is ascribed to the fluoride-induced formation of an N-heterocyclic carbene intermediate that reacts with CO(2) to form an imidazolium carboxylate. PMID:22931227

Guo, Zhiqian; Song, Na Ri; Moon, Jong Hun; Kim, Myounwoo; Jun, Eun Jin; Choi, Jiyoung; Lee, Jin Yong; Bielawski, Christopher W; Sessler, Jonathan L; Yoon, Juyoung

2012-10-31

370

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

371

1-(1H-Benzimidazol-1-ylmeth­yl)-3-[2-(di­isopropyl­amino)eth­yl]-1H-benzimid­azolium bromide 0.25-hydrate  

OpenAIRE

The title N-heterocyclic carbene derivative, C23H30N5+·Br?·0.25H2O, was synthesized using microwave heating and was characterized by 1H and 13C NMR spectroscopy and a single-crystal X-ray diffraction study. The structure of the title compound are stabilized by a network of intra- and intermolecular C—H...Br hydrogen-bonding interactions. The crystal structure is further stabilized by ?–? stacking interactions between benzene an...

Hakan Arslan; Don VanDerveer; Serpil Demir; smail Özdemir; Bekir Çetinkaya

2009-01-01

372

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

373

Synthesis of azoimidazolium dyes with nitrous oxide.  

Science.gov (United States)

A new method for the synthesis of industrially important azoimidazolium dyes is presented. The procedure is based on a reagent which is rarely used in the context of synthetic organic chemistry: nitrous oxide ("laughing gas"). N2 O is first coupled to N-heterocyclic carbenes. Subsequent reaction with aromatic compounds through an AlCl3 -induced C?H activation process provides azoimidazolium dyes in good yields. PMID:25420599

Tskhovrebov, Alexander G; Naested, Lara C E; Solari, Euro; Scopelliti, Rosario; Severin, Kay

2015-01-19

374

A Facile Route to C2-Substituted Imidazolium Ionic Liquids  

OpenAIRE

A convenient route for the preparation of C2-substituted imidazolium ionic liquids is reported. This method involves the alkylation of N-heterocyclic carbenes, which are readily generated from the C2-unsubstituted imidazolium ionic liquids. It works well for non-functionalized alkyl chlorides, and less well for alkyl bromides and iodides, likely due to competing elimination reactions. The resulting C2-substituted salts can be transformed into ionic liquids via standard anion metathesis reacti...

Handy, Scott T.; Elliot Ennis

2009-01-01

375

Formation and properties of a bicyclic silylated digermene.  

Science.gov (United States)

In the presence of PMe3 or N-heterocyclic carbenes, the reaction of oligosilanylene dianions with GeCl2?dioxane gives germylene-base adducts. After base abstraction, the free germylenes can dimerize by formation of a digermene. An electrochemical and theoretical study of a bicyclic tetrasilylated digermene revealed formation of a comparably stable radical anion and a more reactive radical cation, which were characterized further by UV/Vis and ESR spectroscopy. PMID:24981992

Hlina, Johann; Baumgartner, Judith; Marschner, Christoph; Albers, Lena; Müller, Thomas; Jouikov, Viatcheslav V

2014-07-21

376

Asymmetric NHC-catalyzed aza-Diels-Alder reactions: highly enantioselective route to ?-amino acid derivatives and DFT calculations.  

Science.gov (United States)

A facile N-heterocyclic carbene catalytic enantioselective aza-Diels-Alder reaction of oxodiazenes with ?-chloroaldehydes as dienophile precursors is reported, with excellent enantioselectivity (ee > 99%) and excellent yield (up to 93%). DFT study showed that cis-TSa, formed from a top face approach of oxodiazene to cis-IIa, is the most favorable transition state and is consistent with the experimental observations. PMID:24987938

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

2014-08-01

377

1,3-Bis(pyren-1-yl)imidazolium chloride (IPyr·HCl)  

OpenAIRE

A novel UV-A-light absorbing N-heterocyclic carbene precursor imidazolium salt 2 was synthesized by reaction of 1,4-bis(pyren-1-yl)-1,4-diazadiene 1 with paraformaldehyde in the presence of chlorotrimethylsilane. The title compound was characterized by 1H-NMR, 13C-NMR, 2D-NMR, mass spectrometry, IR and UV/VIS spectroscopy.

Peter Schroll; Burkhard König

2011-01-01

378

The fluorine-NHC gauche effect: a structural and computational study  

OpenAIRE

Herein, we report the synthesis and X-ray structural analysis of a collection of fluorinated metal N-heterocyclic carbenes (Ag, Au, Pd, Rh, Ir) and their precursor salts. The common structural feature of these species is a flanking fluoroethyl group which is either freely rotating or embedded within a bicyclic framework. Solid state analysis confirmed a gauche conformational preference in all cases with the fluorine adopting a syn clinal arrangement (?[NCCF] ~ 60°) with respe...

Paul, S.; Schweizer, W. B.; Rugg, G.; Senn, H. M.; Gilmour, R.

2013-01-01

379

Gold-catalyzed Intermolecular [4C + 3C] Cycloaddition Reactions  

OpenAIRE

In the presence of the N-heterocyclic carbene gold catalyst (NHC-AuIPr, 7), propargyl esters 1a–f and 13 undergo a [4C + 3C] cycloaddition reaction with cyclopentadiene and furan under mild conditions. The evidence suggests the formation of the seven-membered ring occurs by a direct cycloaddition process, rather than a stepwise cyclopropanation/Cope rearrangement sequence.

Gung, Benjamin W.; Bailey, Lauren N.; Wonser, Josh

2010-01-01

380

Ruthenium complexes with chiral tetradentate PNNP ligands: asymmetric catalysis from the viewpoint of inorganic chemistry.  

Science.gov (United States)

This is a personal account of the application of ruthenium complexes containing chiral tetradentate ligands with a P(2)N(2) ligand set (PNNP) as catalyst precursors for enantioselective "atom transfer" reactions. Therewith are meant reactions that involve bond formation between a metal-coordinated molecule and a free reagent. The reactive fragment (e.g. carbene) is transferred either from the metal to the non-coordinated substrate (e.g. olefin) or from the free reagent (e.g. F(+)) to the metal-bound substrate (e.g.beta-ketoester), depending on the class of catalyst (monocationic, Class A; or dicationic, Class B). The monocationic five-coordinate species [RuCl(PNNP)](+) and the six-coordinate complexes [RuCl(L)(PNNP)](+) (L = Et(2)O, H(2)O) of Class A catalyse asymmetric epoxidation, cyclopropanation (carbene transfer from the metal to the free olefin), and imine aziridination. Alternatively, the dicationic complexes [Ru(L-L)(PNNP)](2+) (Class B), which contain substrates that act as neutral bidentate ligands L-L (e.g., beta-ketoesters), catalyse Michael addition, electrophilic fluorination, and hydroxylation reactions. Additionally, unsaturated beta-ketoesters form dicationic complexes of Class B that catalyse Diels-Alder reactions with acyclic dienes to produce tetrahydro-1-indanones and estrone derivatives. Excellent enantioselectivity has been achieved in several of the catalytic reactions mentioned above. The study of key reaction intermediates (both in the solid state and in solution) has revealed significant mechanistic aspects of the catalytic reactions. PMID:20676450

Mezzetti, Antonio

2010-09-14

381

Activation et transfert de l'oxygène moléculaire catalysés par les complexes des métaux de transition Activation and Tranfer of Molecular Oxygen Catalyzed by Transition Metal Complexes  

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Full Text Available Cet article tente de rationaliser les différents processus par lesquels les complexes des métaux de transition permettent d'activer l'oxygène moléculaire et de le transférer sélectivement sur des substrats définis. Après un bref rappel des propriétés de l'oxygène moléculaire et de ses associations possibles avec les métaux, nous distinguons trois voies essentielles par les-quelles l'oxygène peut être activé a Les oxydations catalysées par les complexes de type peroxo dans lesquelles substrat et oxygène sont coordinés ensemble sur le même métal formant intermédiairement un peroxométallocycle. b Les oxydations catalysées par les complexes superoxo dans lesquelles l'attaque du substrat s'effectue sur l'oxygène coordiné au métal. c Les oxydations catalysées par les complexes oxo dans lesquelles ces derniers ont un comportement carbénique. This article attempts to make a rational explanation of the different processes by which transition metal complexes can be used to activate molecular oxygen and selectively transfer it on specific substrates. After a brief review of the properties of molecular oxygen and of its possible associations with metals, a distinction is made between three basic ways of activating oxygen: a Oxidations catalyzed by peroxo-type complexes in which substrate and oxygen are both coordinated on the saure metal forming transiently a peroxometallocycle. b Oxidations catalyzed by superoxo complexes in which the substrate attacks the coordinated oxygen. c Oxidations catalyzed by oxo complexes in which these oxo complexes have a carbenic behavior.

Nimoun H.

2006-11-01

382

Selectively Measuring ??Back-Donation in Gold(I) Complexes by NMR Spectroscopy.  

Science.gov (United States)

Even though the Dewar-Chatt-Duncanson model has been successfully used by chemists since the 1950s, no experimental methodology is yet known to unambiguously estimate the constituents (donation and back-donation) of a metal-ligand interaction. It is demonstrated here that one of these components, the metal-to-ligand ??back-donation, can be effectively probed by NMR measurements aimed at determining the rotational barrier of a C?N bond (?Hr (?) ) of a nitrogen acyclic carbene ligand. A large series of gold(I) complexes have been synthesized and analyzed, and it was found that the above experimental observables show an accurate correlation with back-donation, as defined theoretically by the appropriate charge displacement originated upon bond formation. The proposed method is potentially of wide applicability for analyzing the ligand effect in metal catalysts and guiding their design. PMID:25504684

Ciancaleoni, Gianluca; Biasiolo, Luca; Bistoni, Giovanni; Macchioni, Alceo; Tarantelli, Francesco; Zuccaccia, Daniele; Belpassi, Leonardo

2015-02-01

383

Palladium-Catalyzed Heck Coupling Reaction of Aryl Bromides in Aqueous Media Using Tetrahydropyrimidinium Salts as Carbene Ligands  

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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

384

Complexation of lanthanides, actinides and transition metal cations with a 6-(1,2,4-triazin-3-yl)-2,2':6',2''-terpyridine ligand: implications for actinide(III)/lanthanide(III) partitioning.  

Science.gov (United States)

The quadridentate N-heterocyclic ligand 6-(5,5,8,8-tetramethyl-5,6,7,8-tetrahydro-1,2,4-benzotriazin-3-yl)-2,2'?:?6',2''-terpyridine (CyMe(4)-hemi-BTBP) has been synthesized and its interactions with Am(III), U(VI), Ln(III) and some transition metal cations have been evaluated by X-ray crystallographic analysis, Am(III)/Eu(III) solvent extraction experiments, UV absorption spectrophotometry, NMR studies and ESI-MS. Structures of 1:1 complexes with Eu(III), Ce(III) and the linear uranyl (UO(2)(2+)) ion were obtained by X-ray crystallographic analysis, and they showed similar coordination behavior to related BTBP complexes. In methanol, the stability constants of the Ln(III) complexes are slightly lower than those of the analogous quadridentate bis-triazine BTBP ligands, while the stability constant for the Yb(III) complex is higher. (1)H NMR titrations and ESI-MS with lanthanide nitrates showed that the ligand forms only 1:1 complexes with Eu(III), Ce(III) and Yb(III), while both 1:1 and 1:2 complexes were formed with La(III) and Y(III) in acetonitrile. A mixture of isomeric chiral 2:2 helical complexes was formed with Cu(I), with a slight preference (1.4:1) for a single directional isomer. In contrast, a 1:1 complex was observed with the larger Ag(I) ion. The ligand was unable to extract Am(III) or Eu(III) from nitric acid solutions into 1-octanol, except in the presence of a synergist at low acidity. The results show that the presence of two outer 1,2,4-triazine rings is required for the efficient extraction and separation of An(III) from Ln(III) by quadridentate N-donor ligands. PMID:22729349

Lewis, Frank W; Harwood, Laurence M; Hudson, Michael J; Drew, Michael G B; Sypula, Michal; Modolo, Giuseppe; Whittaker, Daniel; Sharrad, Clint A; Videva, Vladimira; Hubscher-Bruder, Véronique; Arnaud-Neu, Françoise

2012-08-14

385

Synthesis of a stable adduct of dialane(4) (Al2H4) via hydrogenation of a magnesium(I) dimer.  

Science.gov (United States)

The desorption of dihydrogen from magnesium(II) hydride, MgH2 (containing 7.6 wt% H), is reversible. MgH2 therefore holds promise as a hydrogen storage material in devices powered by fuel cells. We believed that dimeric magnesium(I) dimers (LMgMgL, L=?-diketiminate) could find use as soluble models to aid the study of the mechanisms and/or kinetics of the hydrogenation of magnesium and its alloys. Here, we show that LMgMgL can be readily hydrogenated to yield LMg(µ-H)2MgL by treatment with aluminium(III) hydride complexes. In one case, hydrogenation was reversed by treating LMg(µ-H)2MgL with potassium metal. The hydrogenation by-products are the first thermally stable, neutral aluminium(II) hydride complexes to be produced, one of which, [{(IPr)(H)2Al}2] (IPr=:C[{(C6H3-i-Pr(2)-2,6)NCH}2]), is an N-heterocyclic carbene adduct of the elusive parent dialane4 (Al2H4). A computational analysis of this compound is presented. PMID:20861903

Bonyhady, Simon J; Collis, David; Frenking, Gernot; Holzmann, Nicole; Jones, Cameron; Stasch, Andreas

2010-10-01

386

Electronic excitations in Fischer-type Cr and W aminocarbene complexes: a combined ab initio and experimental study.  

Science.gov (United States)

The influence of the substitution on the carbene ligand in the series of Fischer-type Cr and W aminocarbene complexes was studied experimentally by UV-vis spectroscopy and theoretically by comparative ab initio SA-CASSCF/MS-CASPT2 and TD-DFT methods. Both calculations interpreted the experimental UV-vis spectra and their variations caused by substitution effects well. TD-DFT analysis of individual transitions using electron density redistributions indicated that the variation of the absorption spectra due to substitution is accompanied by a change in the character of the low-lying excited states participating in the visible bands. Correlated MS-CASPT2 calculations confirmed the TD-DFT assignments of the lowest-lying transitions in the visible region almost quantitatively. PMID:24117112

Kvapilová, Hana; Hoskovcová, Irena; Kayanuma, Megumi; Daniel, Chantal; Záliš, Stanislav

2013-11-14

387

A New Synthetic Method for the Preparation of Protonated-NHCs and Related Compounds.  

Science.gov (United States)

Protonated versions of N-heterocyclic carbenes (NHC,H(+)) are classically prepared by closing the ring through the introduction of the CH+ fragment. He we report a totally different synthetic approach, which can be viewed as the addition of a 1,3-diazaallyl anion to a compound featuring two leaving groups (hereafter named "di-electrophile"). Using 1,3- and 1,4-dibromides, six and seven membered NHC,H(+)s have been prepared in good yields. Similarly, with 1,3,2-dioxathiolane-2,2-dioxide as a di-electrophile, imidazolidinium salts were obtained. To illustrate its broad scope of application, this synthetic route has been expanded to the preparation of protonated cyclic amino alkyl carbenes (CAACs) and amino thio carbenes, using 1-aza-allyl and 1,3-azathio-allyl anions, respectively. PMID:19543436

Jazzar, Rodolphe; Liang, Hongze; Donnadieu, Bruno; Bertrand, Guy

2006-01-01

388

Carney Complex  

Science.gov (United States)

... Carney Complex Request Permissions Print to PDF Carney Complex This section has been reviewed and approved by ... Net Editorial Board , 10/2014 What is Carney complex? Carney complex is a hereditary condition associated with: ...

389

O uso de cálculos teóricos como ferramenta para a detecção de moléculas no meio interestelar: o caso dos carbenos CnNH (n=1, 3 e 5 Use of theoretical calculations as a tool for the detection of molecules in the interestellar medium: the case of the c n nh (n= 1, 3 and 5 carbenes  

Directory of Open Access Journals (Sweden)

Full Text Available This work reviews some applications of ab initio molecular orbital calculations to the elucidation of structures of interstellar molecules. The case of the CnNH (n=1, 3 and 5 carbenes is extensively analyzed and discussed. Theoretical conformational analysis and predicted values for the rotational constants and dipole moments of the singlet state of C5NH are reported for the first time and a comparison is performed with results previously obtained for C3NH and CNH.

João Bosco P. da Silva

1997-10-01

390

Smaller than a nanoparticle with the design of discrete polynuclear molecular complexes displaying near-infrared to visible upconversion.  

Science.gov (United States)

This work shows that the operation of near-infrared to visible light-upconversion in a discrete molecule is not limited to non-linear optical processes, but may result from superexcitation processes using linear optics. The design of nine-coordinate metallic sites made up of neutral N-heterocyclic donor atoms in kinetically inert dinuclear [GaEr(L1)3](6+) and trinuclear [GaErGa(L2)3](9+) helicates leads to [ErN9] chromophores displaying unprecedented dual visible nanosecond Er((4)S3/2?(4)I15/2) and near-infrared microsecond Er((4)I13/2?(4)I15/2) emissive components. Attempts to induce one ion excited-state absorption (ESA) upconversion upon near-infrared excitation of these complexes failed because of the too-faint Er-centred absorption cross sections. The replacement of the trivalent gallium cation with a photophysically-tailored pseudo-octahedral [CrN6] chromophore working as a sensitizer for trivalent erbium in [CrEr(L1)3](6+) improves the near-infrared excitation efficiency, leading to the observation of a weak energy transfer upconversion (ETU). The connection of a second sensitizer in [CrErCr(L2)3](9+) generates a novel mechanism for upconversion, in which the superexcitation process is based on the Cr(III)-sensitizers. Two successive Cr?Er energy transfer processes (concerted-ETU) compete with a standard Er-centred ETU, and a gain in upconverted luminescence by a factor larger than statistical values is predicted and observed. PMID:25357092

Zare, Davood; Suffren, Yan; Guénée, Laure; Eliseeva, Svetlana V; Nozary, Homayoun; Aboshyan-Sorgho, Lilit; Petoud, Stéphane; Hauser, Andreas; Piguet, Claude

2014-10-30

391

Highly nucleophilic acetylide, vinyl, and vinylidene complexes. Final progress report, 1 January 1991--31 March 1994  

Energy Technology Data Exchange (ETDEWEB)

In the course of this research the authors found that the anionic alkynyl complex [Cp{prime}(CO)(PPh{sub 3})Mn-C{triple_bond}C-CH{sub 3}]{sup {minus}} can be generated in situ by the addition of two equivalents of n-BuLi to a solution of the carbene complex Cp{prime}(CO)(PPh{sub 3})Mn{double_bond}C(OMe)CH{sub 2}CH{sub 3}. It was also found that the highly nucleophilic propynyl complex [Cp(CO)(PPh{sub 3})Mn-C{triple_bond}C-Me]{sup {minus}} reacts with a variety of aldehydes and ketones in the presence of BF{sub 3}{center_dot}Et{sub 2}O to give, after quenching with MeOH, a series of cationic vinylcarbyne complexes of the general form [Cp(CO)(PPh{sub 3})Mn{triple_bond}C-C(Me){double_bond}C(R)(R{prime})]BF{sub 4}. The cationic alkylidyne complexes [Cp(CO){sub 2}M{triple_bond}C-CH{sub 2}R]{sup +} [M = Re, R = H, M = Mn, R = H, Me, Ph] have been found to undergo facile deprotonation to give the corresponding neutral vinylidene complexes Cp(CO){sub 2}M{double_bond}C{double_bond}C(H)R. The authors have also investigated reactions relevant to the halide promoted Fe and Ru catalyzed carbonylation of nitroaromatics. The final part of this work has involved investigations of metal-oxo complexes.

Geoffroy, G.L.

1994-10-04

392

Synthesis of 3,3-Disubstituted Oxindoles by Palladium-Catalyzed Asymmetric Intramolecular ?-Arylation of Amides: Reaction Development and Mechanistic Studies.  

Science.gov (United States)

Palladium complexes incorporating chiral N-heterocyclic carbene (NHC) ligands catalyze the asymmetric intramolecular ?-arylation of amides producing 3,3-disubstituted oxindoles. Comprehensive DFT studies have been performed to gain insight into the mechanism of this transformation. Oxidative addition is shown to be rate-determining and reductive elimination to be enantioselectivity-determining. The synthesis of seven new NHC ligands is detailed and their performance is compared. One of them, L8, containing a tBu and a 1-naphthyl group at the stereogenic centre, proved superior and was very efficient in the asymmetric synthesis of fifteen new spiro-oxindoles and three azaspiro-oxindoles often in high yields (up to 99?%) and enantioselectivities (up to 97?%?ee; ee=enantiomeric excess). Three palladacycle intermediates resulting from the oxidative addition of [Pd(NHC)] into the aryl halide bond were isolated and structurally characterized (X-ray). Using these intermediates as catalysts showed alkene additives to play an important role in increasing turnover number and frequency. PMID:23893893

Katayev, Dmitry; Jia, Yi-Xia; Sharma, Akhilesh K; Banerjee, Dipshikha; Besnard, Céline; Sunoj, Raghavan B; Kündig, E Peter

2013-07-25

393

Detection and Evolution of Complex Hydrocarbons in TMC  

Science.gov (United States)

The cold, dark cloud cores are the important sites to probe the interstellar chemistry prevailing prior to the onset of collapse. TMC1 is an ideal object to study the chemistry in dark clouds under quiescent conditions. It shows a carbon rich chemistry with chemical gradients across its densest ridge extending over 0.2 pc x 0.6 pc. We present the results of the DSN 70m observations of complex carbon chain mol ecules (cumelene carbenes H_2C_n, radicals C_nH, cyanopolyynes HC_{2n+1}N, cumulene rings C_nH_2) at a few locations (CCS, cyanopolyyne, ammonia and SO peaks) along TMC1 ridge. We report the first detection of C_8H in TMC. Large differences are seen in t he intensity ratios among these molecules at different velocities as well as po sitions. Our results indicate differences in the chemical evolutionary statu s among the clumps in the TMC1 ridge. This can be interpreted in terms of a de nsity and time dependent chemical models for the formation and evolution of co mplex molecules. This research was conducted at the Jet Propulsion Laboratory, California Institute of Technology under support from the National Aeronautics and Space Administration.

Velusamy, T.; Langer, W. D.

1998-12-01

394

Trianionic pincer and pincer-type metal complexes and catalysts.  

Science.gov (United States)

Trianionic pincer and pincer-type ligands are the focus of this review. Metal ions from across the periodic table, from main group elements, transition metals, and the rare earths, are combined with trianionic pincer ligands to produce some of the most interesting complexes to appear in the literature over the past decade. This review provides a comprehensive examination of the synthesis, characterization, properties, and catalytic applications of trianionic pincer metal complexes. Some of the interesting applications employing trianionic pincer and pincer-type complexes include: (1) catalyzed aerobic oxidation, (2) alkene isomerization, (3) alkene and alkyne polymerization, (4) nitrene and carbene group transfer, (5) fundamental transformations such as oxygen-atom transfer, (6) nitrogen-atom transfer, (7) O2 activation, (8) C-H bond activation, (9) disulfide reduction, and (10) ligand centered storage of redox equivalents (i.e. redox active ligands). Expansion of the architecture, type of donor atoms, chelate ring size, and steric and electronic properties of trianionic pincer ligands has occurred rapidly over the past ten years. This review is structured according to the type of pincer donor atoms that bind to the metal ion. The type of donor atoms within trianionic pincer and pincer-type ligands to be discussed include: NCN(3-), OCO(3-), CCC(3-), redox active NNN(3-), NNN(3-), redox active ONO(3-), ONO(3-), and SNS(3-). Since this is the first review of trianionic pincer and pincer-type ligands, an emphasis is placed on providing the reader with in-depth discussion of synthetic methods, characterization data, and highlights of these complexes as catalysts. PMID:24927219

O'Reilly, Matthew E; Veige, Adam S

2014-09-01

395

Complex chemistry  

International Nuclear Information System (INIS)

This book introduces complex chemistry with ten chapters, which include development of complex chemistry on history coordination theory and Warner's coordination theory and new development of complex chemistry, nomenclature on complex with conception and define, chemical formula on coordination compound, symbol of stereochemistry, stereo structure and isomerism, electron structure and bond theory on complex, structure of complex like NMR and XAFS, balance and reaction on solution, an organo-metallic chemistry, biology inorganic chemistry, material chemistry of complex, design of complex and calculation chemistry.

396

Alkane Metathesis with the Tantalum Methylidene [(?SiO)Ta(?CH2)Me2]/[(?SiO)2Ta(?CH2)Me] Generated from Well-Defined Surface Organometallic Complex [(?SiO)Ta(V)Me4].  

Science.gov (United States)

By grafting TaMe5 on Aerosil700, a stable, well-defined, silica-supported tetramethyl tantalum(V) complex, [(?SiO)TaMe4], is obtained on the silica surface. After thermal treatment at 150 °C, the complex is transformed into two surface tantalum methylidenes, [(?SiO)2Ta(?CH2)Me] and [(?SiO)Ta(?CH2)Me2], which are active in alkane metathesis and comparable to the previously reported [(?SiO)2TaHx]. Here we present the first experimental study to isolate and identify a surface tantalum carbene as the intermediate in alkane metathesis. A systematic experimental study reveals a new reasonable pathway for this reaction. PMID:25557135

Chen, Yin; Abou-Hamad, Edy; Hamieh, Ali; Hamzaoui, Bilel; Emsley, Lyndon; Basset, Jean-Marie

2015-01-21

397

Preparation of Second Generation Ionic Liquids by Efficient Solvent-Free Alkylation of N-Heterocycles with Chloroalkanes  

Directory of Open Access Journals (Sweden)

Full Text Available Non-conventional techniques, such as microwave (MW and power ultrasound(US as well as combined MW/US irradiation, have been used to promote one-potsynthesis of second-generation ionic liquids (ILs, cutting down reaction times andimproving yields. However, the use of chloroalkanes in the alkylation of N-heterocyclesrequires more drastic conditions if results are to match those obtained with more reactivealkyl halides. The present paper describes a series of MW- or MW/US-promoted ILpreparations starting from chloroalkanes and classic heterocycles (1-methylimidazole,pyridine and 1-methylpyrrolidine. When reactions were carried out under conventionalheating in an oil bath they required longer reaction times and gave poorer yields. 1H-NMRanalysis and ion-exchange chromatography showed that the present solventless procedureafforded ILs of satisfactory purity. The observed high yields (usually 70-98% isolated,and short reaction times showed that a straightforward access to ILs can be also achievedwith the use of alkyl chlorides, resulting in a considerable reduction of costs.

Werner Bonrath

2008-01-01

398

Preparation of Second Generation Ionic Liquids by Efficient Solvent-Free Alkylation of N-Heterocycles with Chloroalkanes  

OpenAIRE

Non-conventional techniques, such as microwave (MW) and power ultrasound(US) as well as combined MW/US irradiation, have been used to promote one-potsynthesis of second-generation ionic liquids (ILs), cutting down reaction times andimproving yields. However, the use of chloroalkanes in the alkylation of N-heterocyclesrequires more drastic conditions if results are to match those obtained with more reactivealkyl halides. The present paper describes a series of MW- or MW/US-promoted ILpreparati...

Werner Bonrath; Julien Estager; Jean-Marc Lévêque; Luisa Boffa; Emanuela Calcio Gaudino; Giancarlo Cravotto

2008-01-01

399

AN EFFICIENT AQUEOUS N-HETEROCYCLIZATION OF ANILINE DERIVATIVES: MICROWAVE-ASSISTED SYNTHESIS OF N-ARYL AZACYCLOALKANES  

Science.gov (United States)

N-aryl azacycloalkanes, an important class of building blocks in natural product and pharmaceuticals, are synthesized via an efficient and simple eco-friendly protocol that involves double N-alkylation of aniline derivatives. The reaction is accelerated by exposure to microwaves ...

400

AN EFFICIENT AND SIMPLE AQUEOUS N-HETEROCYCLIZATION OF ANILINE DERIVATIVES: MICROWAVE-ASSISTED SYNTHESIS OF N-ARYL AZACYCLOALKANES  

Science.gov (United States)

An efficient and clean synthesis of N-aryl azacycloalkanes from alkyl dihalides and aniline derivatives has been achieved using microwave irradiation in an aqueous potassium carbonate medium. The phase separation can simplify the product isolation and reduce usage of vol...

401

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

International Nuclear Information System (INIS)

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 pKHB values for the three ligands. Curve fitting of the isotherm for pyridine binding to this polymer to the Langmuir model gave an approximate Kd of 1.1±0.1 mM and a binding site concentration of 57±2 mmol g-1. Acridine binding did not show saturation behaviour and was non-specific and cooperative in nature

402

Bucolic Complexes  

CERN Document Server

In this article, we introduce and investigate bucolic complexes, a common generalization of systolic complexes and of CAT(0) cubical complexes. This class of complexes is closed under Cartesian products and amalgamations over some convex subcomplexes. We study various approaches to bucolic complexes: from graph-theoretic and topological viewpoints, as well as from the point of view of geometric group theory. Bucolic complexes can be defined as locally-finite simply connected prism complexes satisfying some local combinatorial conditions. We show that bucolic complexes are contractible, and satisfy some nonpositive-curvature-like properties. In particular, we prove a version of the Cartan-Hadamard theorem, the fixed point theorem for finite group actions, and establish some results on groups acting geometrically on such complexes. We also characterize the 1-skeletons (which we call bucolic graphs) and the 2-skeletons of bucolic complexes. In particular, we prove that bucolic graphs are precisely retracts of Ca...

Brešar, Bostjan; Chepoi, Victor; Gologranc, Tanja; Osajda, Damian

2012-01-01

403

Complex Numbers  

Science.gov (United States)

This is a short study guide from the University of Maryland's Physics Education Research Group on introducing, interpreting, and using complex numbers. Mathematical equations are included to help students understand the nature of complex numbers.

2010-04-01

404

Ternary complexes  

International Nuclear Information System (INIS)

The stability constants of mixed pyridine dicarboxylic-dicarboxylic acid complexes of uranyl ion have been determined at 300C and ionic strength ? = 0.1 M(NaCLO4). The pyridine dicarboxylic used is quinolinic and the dicarboxylic acids are malonic, succinic, itaconic, glutaric and adipic acid. In all these systems the ternary complexes were more stable than the corresponding binary complexes. The stabilities of the ternary complexes depend on the nature of the donor atoms, size of the chelate ring and steric hindrance in one of the binary complexes. (author)

405

O uso de cálculos teóricos como ferramenta para a detecção de moléculas no meio interestelar: o caso dos carbenos CnNH (n=1, 3 e 5) / Use of theoretical calculations as a tool for the detection of molecules in the interestellar medium: the case of the c n nh (n= 1, 3 and 5) carbenes  

Scientific Electronic Library Online (English)

Full Text Available SciELO Brazil | Language: Portuguese Abstract in portuguese [...] Abstract in english This work reviews some applications of ab initio molecular orbital calculations to the elucidation of structures of interstellar molecules. The case of the CnNH (n=1, 3 and 5 ) carbenes is extensively analyzed and discussed. Theoretical conformational analysis and predicted values for the rotational [...] constants and dipole moments of the singlet state of C5NH are reported for the first time and a comparison is performed with results previously obtained for C3NH and CNH.

João Bosco P. da, Silva; Benício B., Neto; Mozart N., Ramos.

1997-10-01

406

Ionic liquids as precatalysts in the highly stereoselective conjugate addition of ?,?-unsaturated aldehydes to chalcones.  

Science.gov (United States)

Imidazolium-based ionic liquids (ILs) serve both as recyclable reaction media and as precatalysts for the N-heterocyclic carbene-catalyzed conjugate addition of ?,?-unsaturated aldehydes to chalcones. The reaction produces a broad scope of 1,6-ketoesters incorporating an anti-diphenyl moiety in high yields and with high stereoselectivity. In recycling experiments, the IL can be reused up to five times with retained reactivity and selectivity. Moreover, the 1,6-ketoesters form self-assembled organogels in aliphatic hydrocarbons. The reaction protocol is robust, easily operated, scalable and highly functionalized compounds can be obtained from inexpensive and readily accessible starting materials. PMID:25201607

Ta, Linda; Axelsson, Anton; Bijl, Joachim; Haukka, Matti; Sundén, Henrik

2014-10-20

407

A New Synthetic Method for the Preparation of Protonated-NHCs and Related Compounds  

OpenAIRE

Protonated versions of N-heterocyclic carbenes (NHC,H+) are classically prepared by closing the ring through the introduction of the CH+ fragment. He we report a totally different synthetic approach, which can be viewed as the addition of a 1,3-diazaallyl anion to a compound featuring two leaving groups (hereafter named “di-electrophile”). Using 1,3- and 1,4-dibromides, six and seven membered NHC,H+s have been prepared in good yields. Similarly, with 1,3,2-dioxathiolane-2,2-dioxide as a d...

Jazzar, Rodolphe; Liang, Hongze; Donnadieu, Bruno; Bertrand, Guy

2006-01-01

408

Palladium-Catalyzed ?-Arylation of Arylketones at Low Catalyst Loadings.  

Science.gov (United States)

A general catalytic protocol for the ?-arylation of aryl ketones has been developed. It involves the use of a preformed, bench-stable Pd-N-heterocyclic carbene pre-catalyst bearing IHept as an ancillary ligand, and allows the coupling of various functionalized coupling partners at very low catalyst loading. Careful choice of the solvent/base system was crucial to obtain optimum catalyst performance. The pre-catalyst was also successfully tested in the synthesis of an industrially relevant compound. PMID:25414140

Marelli, Enrico; Corpet, Martin; Davies, Sian R; Nolan, Steven P

2014-12-22

409

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

410

Iron-catalyzed directed c2-alkylation and alkenylation of indole with vinylarenes and alkynes.  

Science.gov (United States)

An iron-N-heterocyclic carbene catalyst generated from an iron(III) salt, an imidazolinium salt, and a Grignard reagent promotes alkylation and alkenylation reactions at the indole C2-position with vinylarenes and internal alkynes, respectively, via imine-directed C-H activation. The former reaction affords 1,1-diarylalkane derivatives with exclusive regioselectivity. Deuterium-labeling experiments suggest that these reactions involve oxidative addition of the C-H bond to the iron center, insertion of the unsaturated bond into the Fe-H bond, and C-C reductive elimination. PMID:25575183

Wong, Mun Yee; Yamakawa, Takeshi; Yoshikai, Naohiko

2015-02-01

411

1-(2-Phenylbenzyl)-3-(2,4,6-trimethylbenzyl)imidazolidinium bromide  

OpenAIRE

In the title salt, C26H29N2+·Br?, which may serve as a precursor for N-heterocyclic carbenes, the imidazolidine ring adopts a twist conformation with a pseudo-twofold axis passing through the N—C—N carbon and the opposite C—C bond. The N—C—N bond angle [113.0?(4)°] and C—N bond lengths [1.313?(6) and 1.305?(6)?Å] confirm the existence of strong resonance in this part of the molecule. In the crystal, a C—H.....

Hakan Arslan; Don VanDerveer; Sedat Ya?ar; smail Özdemir; Bekir Çetinkaya

2009-01-01

412

Silver-Free Activation of Ligated Gold(I) Chlorides: The Use of [Me3 NB12 Cl11 ](-) as a Weakly Coordinating Anion in Homogeneous Gold Catalysis.  

Science.gov (United States)

Phosphane and N-heterocyclic carbene ligated gold(I) chlorides can be effectively activated by Na[Me3 NB12 Cl11 ] (1) under silver-free conditions. This activation method with a weakly coordinating closo-dodecaborate anion was shown to be suitable for a large variety of reactions known to be catalyzed by homogeneous gold species, ranging from carbocyclizations to heterocyclizations. Additionally, the capability of 1 in a previously unknown conversion of 5-silyloxy-1,6-allenynes was demonstrated. PMID:25394284

Wegener, Michael; Huber, Florian; Bolli, Christoph; Jenne, Carsten; Kirsch, Stefan F

2015-01-12

413

An electrochemical alternative strategy to the synthesis of ?-lactams  

International Nuclear Information System (INIS)

Electrochemically induced cyclization of bromoamides to ?-lactams has been achieved in room-temperature ionic liquids (RTILs). The use of volatile, organic solvents (VOCs) and of supporting electrolytes may be avoided. Proton exchange reaction between amide substrates and suitable electrogenerated bases gives rise to a C4 carbanion which undergoes cyclization to ?-lactam via intramolecular nucleophilic substitution (C3-C4 bond formation). ?-Lactams have been isolated in good to elevated yields. The 'non innocent' nature of the RTILs (imidazolium-based salts) is considered. Proton exchange reaction between N-dialkylimidazolium cation and EGB yielding N-heterocyclic carbene is discussed

414

Synthesis and reactivity of electron poor allenes: formation of completely organic frustrated Lewis pairs.  

Science.gov (United States)

The synthesis of several electron poor allenes bearing electron withdrawing substituents is described and their use as Lewis acids in the field of frustrated Lewis pair (FLP) chemistry reported. At room temperature the combination of N-heterocyclic carbenes (NHC) with the allenes under study invariably afforded the corresponding Lewis adducts; however, at -78 °C this reaction is in most of the cases inhibited and kinetically induced organic FLPs are formed. Under these conditions the activation of S-S bonds in disulfides has been achieved in excellent yields. PMID:22526755

Palomas, David; Holle, Sigrid; Inés, Blanca; Bruns, Hans; Goddard, Richard; Alcarazo, Manuel

2012-08-14

415

A Pt/sup II/-alkane complex with pentacoordinated carbon as the first intermediate of reactions of oxidation and multiple H/D exchange of alkanes in aqueous solutions of Pt/sup II/-Pt/sup IV/ chlorides  

International Nuclear Information System (INIS)

The activation of alkanes and cycloalkanes (RH = C/sub n/H/sub n/) in the system Pt/sup II/-Pt/sup IV/-Cl--D+-D2O leads to products of oxidation and multiple H/D exchange (C/sub n/H/sub m-i/D/sub i/). We found that under conditions of competition of exchange and oxidation of cyclohexane, the parameter M0 = i (the average number of D atoms in the exchange product at the initial moment) increases with increasing concentration of D+, while the mechanism requires a decrease in M0 with increasing [D+]. This result permits an assured selection in favor of the alkane-alkyl mechanism rather than the alkyl-carbene mechanism, and made it possible to conclude that the first kinetically significant intermediate of the reaction is the Pt/sup II/-alkane complex

416

Complex Numbers  

Science.gov (United States)

The objective of this lesson is to gain a better understanding of complex numbers and their graphs Situation: The Swiss Mathemation, Jean Robert Argand developed a means to graphically represent complex numbers. This led to solving problems related to altenating electrical current, which provides current day luxuries. Could you do the same? Current Knowledge: Use your knowledge of complex number and the coordinate system and with your partner, ...

Pierce, Mrs.

2010-11-16

417

Engaging complexity  

Directory of Open Access Journals (Sweden)

Full Text Available In this article, I discuss studies in complexity and its epistemological implications for systematic and practical theology. I argue that engagement with complexity does not necessarily assurea non-reductionist approach. However, if complexity is engaged transversally, it becomes possible to transcend reductionist approaches. Moreover, systematic and practical the ologians can draw on complexity in developing new ways of understanding and, therefore, new ways of describing the focus, epistemic scope and heuristic structures of systematic and practical theology. Firstly, Edgar Morin draws a distinction between restricted and general complexity based on the epistemology drawn upon in studies in complexity. Moving away from foundationalist approaches to epistemology, Morin argues for a paradigm of systems. Secondly,I discuss Kees van Kooten Niekerk’s distinction between epistemology, methodology andontology in studies in complexity and offer an example of a theological argument that drawson complexity. Thirdly, I argue for the importance of transversality in engaging complexity by drawing on the work of Wentzel van Huyssteen and Paul Cilliers. In conclusion, I argue that theologians have to be conscious of the epistemic foundations of each study in complexity, and these studies illuminate the heart of Reformed theology. Intradisciplinary and/or interdisciplinary implications: Therefore, this article has both intradisciplinary and interdisciplinary implications. When theologians engage studies incomplexity, the epistemological roots of these studies need to be considered seeing thatresearchers in complexity draw on different epistemologies. Drawing on transversality wouldenhance such considerations. Furthermore, Edgar Morin’s and Paul Cilliers’ approach tocomplexity will inform practical and theoretical considerations in church polity and unity.

Gys M. Loubser

2014-08-01

418

SO2- yet another two-faced ligand.  

Science.gov (United States)

Experimentally known adducts of SO2 with transition metal complexes have distinct geometries. In the present paper, we demonstrate by a bonding analysis that this is a direct consequence of sulfur dioxide acting as an acceptor in one set, square-planar complexes of d(8) and linear two-coordinated complexes of d(10) transition metals, and as a donor with other compounds, well-known paddle-wheel [Rh2(O2CCF3)4] and square-pyramidal [M(CO)5] (M = Cr, W) complexes. Bonding energy computations were augmented by the natural bond orbital (NBO) analysis and energy decomposition analysis (EDA). When the SO2 molecule acts as an acceptor, bonding in the bent coordination mode to the axial position of the d(8) or the d(10) metal center, the dominant contributor to the bonding is LAO(S) (Lewis Acidic Orbital, mainly composed of the px-orbital of the S atom) as an acceptor, while a dz(2) orbital centered on the metal is the corresponding donor. In contrast, the distinct collinear (or linear) coordination of the SO2 bound at the axial position of [Rh2(O2CCF3)4] and/or [M(CO)5] is associated with a dominant donation from a lone pair localized on the sulfur atom, ?*(Rh-Rh) and/or empty LAO(M) (mainly composed of the dz(2) orbital of the metal), respectively, acting as an acceptor orbital. The donor/acceptor capabilities of the SO2 molecule were also checked in adducts with organic Lewis acids (BH3, B(CF3)3) and Lewis bases (NH3, N(CH3)3, N-heterocyclic carbene). PMID:25475579

Li, Jingbai; Rogachev, Andrey Yu

2015-01-21

419

Terminal and bridging parent amido 1,5-cyclooctadiene complexes of rhodium and iridium.  

Science.gov (United States)

The ready availability of rare parent amido d(8) complexes of the type [{M(?-NH2)(cod)}2] (M=Rh (1), Ir (2); cod=1,5-cyclooctadiene) through the direct use of gaseous ammonia has allowed the study of their reactivity. Both complexes 1 and 2 exchanged the di-olefines by carbon monoxide to give the dinuclear tetracarbonyl derivatives [{M(?-NH2)(CO)2}2 ] (M=Rh or Ir). The diiridium(I) complex 2 reacted with chloroalkanes such as CH2Cl2 or CHCl3, giving the diiridium(II) products [(Cl)(cod)Ir(?-NH2)2Ir(cod)(R)] (R=CH2Cl or CHCl2) as a result of a two-center oxidative addition and concomitant metal-metal bond formation. However, reaction with ClCH2CH2Cl afforded the symmetrical adduct [{Ir(?-NH2)(Cl)(cod)}2] upon release of ethylene. We found that the rhodium complex 1 exchanged the di-olefines stepwise upon addition of selected phosphanes (PPh3, PMePh2, PMe2Ph) without splitting of the amido bridges, allowing the detection of mixed COD/phosphane dinuclear complexes [(cod)Rh(?-NH2)2Rh(PR3)2], and finally the isolation of the respective tetraphosphanes [{Rh(?-NH2)(PR3)2}2]. On the other hand, the iridium complex 2 reacted with PMe2 Ph by splitting the amido bridges and leading to the very rare terminal amido complex [Ir(cod)(NH2)(PMePh2)2]. This compound was found to be very reactive towards traces of water, giving the more stable terminal hydroxo complex [Ir(cod)(OH)(PMePh2)2]. The heterocyclic carbene IPr (IPr=1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene) also split the amido bridges in complexes 1 and 2, allowing in the case of iridium to characterize in situ the terminal amido complex [Ir(cod)(IPr)(NH2)]. However, when rhodium was involved, the known hydroxo complex [Rh(cod)(IPr)(OH)] was isolated as final product. On the other hand, we tested complexes 1 and 2 as catalysts in the transfer hydrogenation of acetophenone with iPrOH without the use of any base or in the presence of Cs2CO3, finding that the iridium complex 2 is more active than the rhodium analogue 1. PMID:23504929

Mena, Inmaculada; Jaseer, E A; Casado, Miguel A; García-Orduña, Pilar; Lahoz, Fernando J; Oro, Luis A

2013-04-26

420

Lutetium-methanediide-alkyl complexes: synthesis and chemistry.  

Science.gov (United States)

The first four-coordinate methanediide/alkyl lutetium complex (BODDI)Lu2 (CH2 SiMe3 )2 (?2 -CHSiMe3 )(THF)2 (BODDI=ArNC(Me)CHCOCHC(Me)NAr, Ar=2,6-iPr2 C6 H3 ) (1) was synthesized by a thermolysis methodology through ?-H abstraction from a Lu-CH2 SiMe3 group. Complex 1 reacted with equimolar 2,6-iPrC6 H3 NH2 and Ph2 C+O to give the corresponding lutetium bridging imido and oxo complexes (BODDI)Lu2 (CH2 SiMe3 )2 (?2 -N-2,6-iPr2 C6 H3 )(THF)2 (2) and (BODDI)Lu2 (CH2 SiMe3 )2 (?2 -O)(THF)2 (3). Treatment of 3 with Ph2 C=O (4?equiv) caused a rare insertion of Lu-?2 -O bond into theC=O group to afford a diphenylmethyl diolate complex 4. Reaction of 1 with PhN=C=O (2?equiv) led to the migration of SiMe3 to the amido nitrogen atom to give complex (BODDI)Lu2 (CH2 SiMe3 )2 -?-{PhNC(O)CHC(O)NPh(SiMe3 )-?(3) N,O,O}(THF) (5). Reaction of 1 withtBuN=C formed an unprecedented product (BODDI)Lu2 (CH2 SiMe3 ){?2 -[?(2) :?(2) -tBuN=C(=CH2 )SiMe2 CHC=NtBu-?(1) N]}(tBuN=C)2 (6) through a cascade reaction of N=C bond insertion, sequential cyclometalative ?-(sp(3) )-H activation, C=C bond formation, and rearrangement of the newly formed carbene intermediate. The possible mechanistic pathways between 1, PhN=C=O, and tBuN=C were elucidated by DFT calculations. PMID:25284379

Li, Shihui; Wang, Meiyan; Liu, Bo; Li, Lei; Cheng, Jianhua; Wu, Chunji; Liu, Dongtao; Liu, Jingyao; Cui, Dongmei

2014-11-17

421

Bis{1-[2-(diphenylphosphanylethyl]-3-ethylimidazol-2-ylidene}nickel(II diiodide acetonitrile disolvate  

Directory of Open Access Journals (Sweden)

Full Text Available The molecular structure of the title compound, [Ni(C19H21N2P2]I2·2CH3CN, shows two six-membered N-heterocyclic carbene/phosphane chelate rings that form a nearly square-planar coordination geometry around the NiII atom, which lies 0.190?(1?Å above the C2P2 plane. The sum of the bond angles at the NiII atom is 358.68?(6°, with C—Ni—P bite angles of 82.89?(5 and 84.08?(6°. The two carbene rings make a dihedral angle of 52.65?(8°.

Aziza Ahmida

2012-07-01

422

Metal-ligand cooperation on a diruthenium platform: selective imine formation through acceptorless dehydrogenative coupling of alcohols with amines.  

Science.gov (United States)

Metal-metal singly-bonded diruthenium complexes, bridged by naphthyridine-functionalized N-heterocyclic carbene (NHC) ligands featuring a hydroxy appendage on the naphthyridine unit, are obtained in a single-pot reaction of [Ru2(CH3COO)2(CO)4] with 1-benzyl-3-(5,7-dimethyl-1,8-naphthyrid-2-yl)imidazolium bromide (BIN?HBr) or 1-isopropyl-3-(5,7-dimethyl-1,8-naphthyrid-2-yl)imidazolium bromide (PIN?HBr), TlBF4, and substituted benzaldehyde containing an electron-withdrawing group. The modified NHC-naphthyridine-hydroxy ligand spans the diruthenium unit in which the NHC carbon and hydroxy oxygen occupy the axial sites. All the synthesized compounds catalyze acceptorless dehydrogenation of alcohols to the corresponding aldehydes in the presence of a catalytic amount of weak base 1,4-diazabicyclo[2.2.2]octane (DABCO). Further, acceptorless dehydrogenative coupling (ADHC) of the alcohol with amines affords the corresponding imine as the sole product. The substrate scope is examined with 1 (BIN, p-nitrobenzaldehyde). A similar complex [Ru2(CO)4(CH3COO)(3-PhBIN)][Br], that is devoid of a hydroxy arm, is significantly less effective for the same reaction. Neutral complex 1?a, obtained by deprotonation of the hydroxy arm in 1, is found to be active for the ADHC of alcohols and amines under base-free conditions. A combination of control experiments, deuterium labeling, kinetic Hammett studies, and DFT calculations support metal-hydroxyl/hydroxide and metal-metal cooperation for alcohol activation and dehydrogenation. The bridging acetate plays a crucial role in allowing ?-hydride elimination to occur. The ligand architecture on the diruthenium core causes rapid aldehyde extrusion from the metal coordination sphere, which is responsible for exclusive imine formation. PMID:24715433

Saha, Biswajit; Rahaman, S M Wahidur; Daw, Prosenjit; Sengupta, Gargi; Bera, Jitendra K

2014-05-19

423

Complex Covariance  

Directory of Open Access Journals (Sweden)

Full Text Available According to some generalized correspondence principle the classical limit of a non-Hermitian quantum theory describing quantum degrees of freedom is expected to be the well known classical mechanics of classical degrees of freedom in the complex phase space, i.e., some phase space spanned by complex-valued space and momentum coordinates. As special relativity was developed by Einstein merely for real-valued space-time and four-momentum, we will try to understand how special relativity and covariance can be extended to complex-valued space-time and four-momentum. Our considerations will lead us not only to some unconventional derivation of Lorentz transformations for complex-valued velocities, but also to the non-Hermitian Klein-Gordon and Dirac equations, which are to lay the foundations of a non-Hermitian quantum theory.

Frieder Kleefeld

2013-01-01

424

Complex Systems  

OpenAIRE

The study of Complex Systems is considered by many to be a new scientific field, and is distinguished by being a discipline that has applications within many separate areas of scientific study. The study of Neural Networks, Traffic Patterns, Artificial Intelligence, Social Systems, and many other scientific areas can all be considered to fall within the realm of Complex Systems, and can be studied from this new perspective. The advent of more capable computer systems has all...

Goldberger, Ary L.

2006-01-01

425

Complex Philosophy  

OpenAIRE

We present several philosophical ideas emerging from the studies of complex systems. We make a brief introduction to the basic concepts of complex systems, for then defining "abstraction levels". These are useful for representing regularities in nature. We define absolute being (observer independent, infinite) and relative being (observer dependent, finite), and notice the differences between them. We draw issues on relative causality and absolute causality among abstraction...

Gershenson, Carlos

2001-01-01

426

Statistical Complexity  

CERN Document Server

The understanding of electron density as the carrier of all the information of a multielectronic system is implicit in the theorems of density functional theory. Information theoretical based measures giving a quantitative understanding of statistical complexity of such systems is shaping up as a new area of research in chemical physics. This book is the first monograph of its kind covering the aspects of complexity measure in atoms and molecules.

Sen, Kalidas D

2011-01-01

427

Theoretical investigations on the mechanism of benzoin condensation catalyzed by pyrido[1,2-a]-2-ethyl[1,2,4]triazol-3-ylidene.  

Science.gov (United States)

A new annulated N-heterocyclic carbene (NHC), pyrido[1,2-a]-2-ethyl[1,2,4]triazol-3-ylidene, has been synthesized and its good catalytic activity for benzoin condensation has been experimentally determined by You and co-workers recently [ Ma , Y. J. , Wei , S. P. , Lan , J. B. , Wang , J. Z. , Xie , R. G. , and You , J. S. J. Org. Chem. 2008 , 73 , 8256 ]. In this work, the mechanism of the title reaction has been intensively studied computationally by employing the density functional theory (B3LYP) method in conjunction with 6-31+G(d) and 6-311+G(2d,p) basis sets. Our results indicate that path A (in which a sequence of intermolecular proton transfers between two carbene/benzaldehyde coupling intermediates affords enamine) and path B (in which a t-BuOH assisted hydrogen transfer generates enamine) proposed on the basis of the Breslow mechanism are competitive for their similar barriers. In path A, the first intermolecular proton transfer between two N-heterocyclic carbene/benzaldehyde coupled intermediates to form tertiary alcohol and enolate anion is theoretically the rate-determining step with corresponding barrier (30.93 kcal/mol), while the t-BuOH assisted hydrogen transfer generating Breslow enamine is the rate-determining step with corresponding barrier (28.84 kcal/mol) in path B. The coupling of carbene and benzaldehyde, and the coupling of enamine and another benzaldehyde to form a C-C bond are partially rate-determining for their relatively significant barriers (24.06 and 26.95 kcal/mol, respectively), being the same in both paths A and B. Our results are in nice agreement with the experimental result in a kinetic investigation of thiazolium ion-catalyzed benzoin condensation performed by White and Leeper in 2001. PMID:21306173

He, Yunqing; Xue, Ying

2011-03-01

428

Unusual carbon monoxide activation, reduction, and homologation reactions of 5f-element organometallics: the chemistry of carbene-like dihaptoacyls  

International Nuclear Information System (INIS)

This article reviews recent results on the chemical, spectral and structural properties of bis(pentamethylcyclopentadienyl) thorium and uranium dihaptoacyl complexes produced by migratory insertion of carbon monoxide into actinide-carbon sigma bonds. The high coordinative unsaturation and oxygen affinity of the ligation environment produces a marked perturbation of the bonding and reactivity toward that of a coordinated oxycarbene: M(eta2-OCR). Reactivity patterns observed include hydrogen atom and trimethylsilyl migration to the acyl carbon, as well as coupling with additional carbon monoxide to produce a dimeric complex of the enedionediolate ligand, OC(R)(anti O)C=C(anti O)(R)CO. The dihaptoacyls insert into the Th-H bond of ]Th[(CH3)5C5]2H2]2. For Th[(CH3)5C5]2[eta2-COCH2C(CH3)3]Cl, this results, via ?-hydride elimination, in catalytic isomerization to Th[(CH3)5C5]2-[trans-OC(H)=C(H)C(CH3)3]. In the presence of hydrogen gas, the hydride catalytically hydrogenates the dihaptoacyls to alkoxides (M(eta2-COR)?M-OCH2R). Mechanistic studies include kinetic measurements as well as isotopic labelling and stereochemical analysis. 102 references

429

Tableau complexes  

CERN Document Server

Let X,Y be finite sets and T a set of functions from X -> Y which we will call "tableaux". We define a simplicial complex whose facets, all of the same dimension, correspond to these tableaux. Such_tableau_complexes_ have many nice properties, and are frequently homeomorphic to balls, which we prove using vertex decompositions. In our motivating example, the facets are labeled by semistandard Young tableaux, and the more general interior faces are labeled by Buch's set-valued semistandard tableaux. One vertex decomposition of this "Young tableau complex" parallels Lascoux's transition formula for vexillary double Grothendieck polynomials. Consequently, we obtain formulae (both old and new) for these polynomials. In particular, we present a common generalization of the formulae of Wachs and Buch, each of which imply the classical tableau formula for Schur polynomials.

Knutson, A; Yong, A; Knutson, Allen; Miller, Ezra; Yong, Alexander

2005-01-01

430

Communication Complexity  

OpenAIRE

The first section starts with the basic definitions following mainly the notations of the book written by E. Kushilevitz and N. Nisan. At the end of the first section I examine tree-balancing. In the second section I summarize the well-known lower bound methods and prove the exact complexity of certain functions. In the first part of the third section I introduce the random complexity and prove the basic lemmas about it. In the second part I prove a better lower bound...

Pa?lvo?lgyi, Do?mo?to?r

2010-01-01

431

Complex Analysis  

CERN Document Server

With this second volume, we enter the intriguing world of complex analysis. From the first theorems on, the elegance and sweep of the results is evident. The starting point is the simple idea of extending a function initially given for real values of the argument to one that is defined when the argument is complex. From there, one proceeds to the main properties of holomorphic functions, whose proofs are generally short and quite illuminating: the Cauchy theorems, residues, analytic continuation, the argument principle.With this background, the reader is ready to learn a wealth of additional m

Stein, Elias M

2009-01-01

432

Gold-catalyzed cycloisomerization of 1,7-enyne esters to structurally diverse cis-1,2,3,6-tetrahydropyridin-4-yl ketones.  

Science.gov (United States)

A synthetic method that relies on gold(I)-catalyzed cycloisomerization of 1,7-enyne esters to prepare highly functionalized cis-1,2,3,6-tetrahydropyridin-4-yl ketone derivatives in good to excellent yields and as a single regio-, diastereo-, and enantiomer is described. By taking advantage of the distinctive differences in the electronic and steric properties between an NHC (NHC = N-heterocyclic carbene) and phosphine ligand in the respective gold(I) complexes, a divergence in product selectivity was observed. In the presence of [PhCNAuIPr](+)SbF6(-) (IPr = 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidine) as the catalyst, tandem 1,3-acyloxy migration/6-exo-trig cyclization/1,5-acyl migration of the substrate was found to selectively occur to give the ?-diketone-substituted 1,2,3,6-tetrahydropyridine adduct. In contrast, reactions with the gold(I) phosphine complex [MeCNAu(JohnPhos)](+)SbF6(-) (JohnPhos = (1,1'-biphenyl-2-yl)-di-tert-butylphosphine) as the catalyst was discovered to result in preferential 1,3-acyloxy migration/6-exo-trig cyclization/hydrolysis of the 1,7-enyne ester and formation of the cis-1,2,3,6-tetrahydropyridin-4-yl ketone derivative. The utility of this piperidine forming strategy as a synthetic tool that makes use of 1,7-enyne esters was exemplified by its application to the synthesis of an enantiopure analogue of the bioactive 2,3,4,4a,5,9b-hexahydroindeno[1,2-c]pyridine family of compounds. PMID:23458312

Rao, Weidong; Sally; Koh, Ming Joo; Chan, Philip Wai Hong

2013-04-01

433

Complex Networks  

CERN Document Server

In the last decade we have seen the emergence of a new inter-disciplinary field focusing on the understanding of networks which are dynamic, large, open, and have a structure sometimes called random-biased. The field of Complex Networks is helping us better understand many complex phenomena such as the spread of  deseases, protein interactions, social relationships, to name but a few. Studies in Complex Networks are gaining attention due to some major scientific breakthroughs proposed by network scientists helping us understand and model interactions contained in large datasets. In fact, if we could point to one event leading to the widespread use of complex network analysis is the availability of online databases. Theories of Random Graphs from Erdös and Rényi from the late 1950s led us to believe that most networks had random characteristics. The work on large online datasets told us otherwise. Starting with the work of Barabási and Albert as well as Watts and Strogatz in the late 1990s, we now know th...

Evsukoff, Alexandre; González, Marta

2013-01-01

434

Cellulose synthesis: a complex complex.  

Science.gov (United States)

Cellulose is the world's most abundant biopolymer and a key structural component of the plant cell wall. Cellulose is comprised of hydrogen-bonded beta-1,4-linked glucan chains that are synthesized at the plasma membrane by large cellulose synthase (CESA) complexes. Recent advances in visualization of fluorescently labelled complexes have facilitated exploration of regulatory modes of cellulose production. For example, several herbicides, such as isoxaben and 2,6-dichlorobenzonitrile that inhibit cellulose production appear to affect different aspects of synthesis. Dual-labelling of cytoskeletal components and CESAs has revealed dynamic feedback regulation between cellulose synthesis and microtubule orientation and organization. In addition, fluorescently tagged CESA2 subunits may substitute for another subunit, CESA6, which suggests both plasticity and specificity for one of the components of the CESA complex. PMID:18485800

Mutwil, Marek; Debolt, Seth; Persson, Staffan

2008-06-01

435

Novel bimetallic Ru-Pt and Fe-Pt complexes [M(C5R5)(L)2((?, ?1 : ?2-P4{Pt(PPh3)2})]Y: synthesis, structure, and exchange processes  

International Nuclear Information System (INIS)

Novel bimetallic Ru-Pt and Fe-Pt complexes, [M(C5R5)(L)2(?1-P4)]Y (M = Ru, Fe; R = H, Me; L= PPh3, 1/2Dppf (Ph2P(C5H4)Fe(C5H4)PPh2), 1/2Dppe (Ph2PCH2CH2PPh2); Y = PF6, CF3SO3, BPh4) were synthesized for the first time by the reaction of ?1-tetraphosphorus complexes of ruthenium(II) and iron(II), [M(C5R5)(L)2(?1-P4)]Y with platinum(0) complex [Pt(?2-C2H4)(PPh3)2] in acetone. The structures and compositions of the title complexes were studied by the 31P NMR, correlated 31P-31P NMR COSY, NOESY, 1H NMR spectroscopy, and elemental analysis. The carbene-like fragment Pt(PPh3)2 generated in situ was found to be inserted at the P-P bond of the ?1-coordinated tetraphosphorus and migrate between the phosphorus atoms of the obtained ligand ?, ?1 : ?2-P4. The exchange process in the novel complexes was investigated

436

Experimental and theoretical study of the kinetics of dissociation in cis-[RuCl2(P-P)(N-N)] type complexes  

Scientific Electronic Library Online (English)

Full Text Available SciELO Brazil | Language: English Abstract in portuguese As reações de substituição [RuCl2(P-P)(N-N)] + L ? [RuCl(L)(P-P)(N-N)]+ + Cl-, onde P-P = 1,4-bis(difenilfosfino)butano e N-N = 2,2´-bipiridina, 4,4´-dimetóxi-2,2´-bipiridina, 4,4´-dimetil-2,2´-bipiridina e 4,4´-dicloro-2,2´-bipiridina, L = piridina (py) ou 4-metilpiridina (4-pic), foram estudadas s [...] ob condições de pseudo-primeira ordem. As reações ocorrem por um mecanismo dissociativo e as constantes de velocidade nas reações de substituição aumentam com o aumento do pKa dos ligantes N-heterocíclicos e com a diminuição dos potenciais de oxidação do centro metálico. Quanto mais alta é a porcentagem de participação dos orbitais atômicos d do metal na formação do HOMO, conforme calculado pelo método DFT, mais fácil é a dissociação do cloreto da esfera de coordenação do complexo. Nos espectros de 31P{¹H} RMN da série de complexos de fórmula geral [RuCl(L)(P-P)(N-N)]PF6, há dois dubletos com ?? Abstract in english The substitution reactions [RuCl2(P-P)(N-N)] + L ? [RuCl(L)(P-P)(N-N)]+ + Cl-, where P-P = 1,4-bis(diphenylphosphino)butane and N-N = 2,2´-bipyridine, 4,4´-dimethoxy-2,2´-bipyridine, 4,4´-dimethylpyridine-2,2´-bipyridine and 4,4´-dichloro-2,2´-bipyridine, L = pyridine (py) or 4-methylpyridine (4-pic [...] ), were studied under pseudo-first order conditions. The reactions proceeded by means of a dissociative mechanism. The rate constants of the substitution reactions increased as the pKa of the N-heterocyclic ligands increased and as the oxidation potential of the metal center decreased. The greater the participation of the atomic d orbitals of the metal in the HOMO, according to DFT calculations, the easier is the dissociation of the chloride from the coordination sphere of the complex. In the 31P{¹H} NMR spectra of the series of complexes of general formula [RuCl(L)(P-P)(N-N)]PF6, there are two doublets with ??

Marcos C. R., Monteiro; Fabio B., Nascimento; Eliana M. A., Valle; Javier, Ellena; Eduardo E., Castellano; Alzir A., Batista; Sergio de Paula, Machado.

1992-19-01

437

Managing Complexity  

Energy Technology Data Exchange (ETDEWEB)

Physical analogs have shown considerable promise for understanding the behavior of complex adaptive systems, including macroeconomics, biological systems, social networks, and electric power markets. Many of today’s most challenging technical and policy questions can be reduced to a distributed economic control problem. Indeed, economically-based control of large-scale systems is founded on the conjecture that the price-based regulation (e.g., auctions, markets) results in an optimal allocation of resources and emergent optimal system control. This paper explores the state of the art in the use physical analogs for understanding the behavior of some econophysical systems and to deriving stable and robust control strategies for them. In particular we review and discussion applications of some analytic methods based on the thermodynamic metaphor according to which the interplay between system entropy and conservation laws gives rise to intuitive and governing global properties of complex systems that cannot be otherwise understood.

Chassin, David P.; Posse, Christian; Malard, Joel M.

2004-08-01

438

Managing Complexity  

CERN Document Server

Physical analogs have shown considerable promise for understanding the behavior of complex adaptive systems, including macroeconomics, biological systems, social networks, and electric power markets. Many of today's most challenging technical and policy questions can be reduced to a distributed economic control problem. Indeed, economically-based control of large-scale systems is founded on the conjecture that the price-based regulation (e.g., auctions, markets) results in an optimal allocation of resources and emergent optimal system control. This paper explores the state of the art in the use physical analogs for understanding the behavior of some econophysical systems and deriving stable and robust control strategies for them. In particular we review and discuss applications of some analytic methods based on a thermodynamic metaphor according to which the interplay between system entropy and conservation laws gives rise to intuitive and governing global properties of complex systems that cannot be otherwis...

Chassin, D P; Posse, C; Chassin, David P.; Malard, Joel; Posse, Christian

2004-01-01

439

Complex wounds.  

Science.gov (United States)

Complex wound is the term used more recently to group those well-known difficult wounds, either chronic or acute, that challenge medical and nursing teams. They defy cure using conventional and simple "dressings" therapy and currently have a major socioeconomic impact. The purpose of this review is to bring these wounds to the attention of the health-care community, suggesting that they should be treated by multidisciplinary teams in specialized hospital centers. In most cases, surgical treatment is unavoidable, because the extent of skin and subcutaneous tissue loss requires reconstruction with grafts and flaps. New technologies, such as the negative pressure device, should be introduced. A brief review is provided of the major groups of complex wounds--diabetic wounds, pressure sores, chronic venous ulcers, post-infection soft-tissue gangrenes, and ulcers resulting from vasculitis. PMID:17187095

Ferreira, Marcus Castro; Tuma, Paulo; Carvalho, Viviane Fernandes; Kamamoto, Fábio

2006-12-01

440

PS complex  

CERN Multimedia

A view of the present PS complex taken at the end of 1972. The earth embankment covering the Ring is clearly visible; in the foreground are the North and South Experimental Halls; to the right is the East Hall, and to the left the Booster surface buildings. The West Hall is too far to the left to seen, and also invisible is the SPS being constructed.

1972-01-01

441

Cosmic Complexity  

Science.gov (United States)

What explains the extraordinary complexity of the observed universe, on all scales from quarks to the accelerating universe? My favorite explanation (which I certainty did not invent) ls that the fundamental laws of physics produce natural instability, energy flows, and chaos. Some call the result the Life Force, some note that the Earth is a living system itself (Gaia, a "tough bitch" according to Margulis), and some conclude that the observed complexity requires a supernatural explanation (of which we have many). But my dad was a statistician (of dairy cows) and he told me about cells and genes and evolution and chance when I was very small. So a scientist must look for me explanation of how nature's laws and statistics brought us into conscious existence. And how is that seemll"!gly Improbable events are actually happening a!1 the time? Well, the physicists have countless examples of natural instability, in which energy is released to power change from simplicity to complexity. One of the most common to see is that cooling water vapor below the freezing point produces snowflakes, no two alike, and all complex and beautiful. We see it often so we are not amazed. But physlc!sts have observed so many kinds of these changes from one structure to another (we call them phase transitions) that the Nobel Prize in 1992 could be awarded for understanding the mathematics of their common features. Now for a few examples of how the laws of nature produce the instabilities that lead to our own existence. First, the Big Bang (what an insufficient name!) apparently came from an instability, in which the "false vacuum" eventually decayed into the ordinary vacuum we have today, plus the most fundamental particles we know, the quarks and leptons. So the universe as a whole started with an instability. Then, a great expansion and cooling happened, and the loose quarks, finding themselves unstable too, bound themselves together into today's less elementary particles like protons and neutrons, liberating a little energy and creating complexity. Then, the expanding universe cooled some more, and neutrons and protons, no longer kept apart by immense temperatures, found themselves unstable and formed helium nuclei. Then, a little more cooling, and atomic nuclei and electrons were no longer kept apart, and the universe became transparent. Then a little more cooling, and the next instability began: gravitation pulled matter together across cosmic distances to form stars and galaxies. This instability is described as a "negative heat capadty" in which extracting energy from a gravitating system makes it hotter -- clearly the 2nd law of thermodynamics does not apply here! (This is the physicist's part of the answer to e e cummings' question: what is the wonder that's keeping the stars apart?) Then, the next instability is that hydrogen and helium nuclei can fuse together to release energy and make stars burn for billions of years. And then at the end of the fuel source, stars become unstable and explode and liberate the chemical elements back into space. And because of that, on planets like Earth, sustained energy flows support the development of additional instabilities and all kinds of complex patterns. Gravitational instability pulls the densest materials into the core of the Earth, leaving a thin skin of water and air, and makes the interior churn incessantly as heat flows outwards. And the heat from the sun, received mostly near the equator and flowing towards the poles, supports the complex atmospheric and oceanic circulations. And because or that, the physical Earth is full of natural chemical laboratories, concentrating elements here, mixing them there, raising and lowering temperatures, ceaselessly experimenting with uncountable events where new instabilities can arise. At least one of them was the new experiment called life. Now that we know that there are at least as many planets as there are stars, it is hard to imagine that nature's ceasess experimentation would not be able to produce life elsewhere

Mather, John C.

2012-01-01

442

Electrochemistry of Fischer alkoxycarbene complexes of chromium: The use of density functional theory to predict and understand oxidation and reduction potentials  

International Nuclear Information System (INIS)

Highlights: •Synthesis, crystal structure and electrochemical study of Fischer ethoxycarbenes. •Density functional theory (DFT) calculated energies of Fischer ethoxycarbenes. •DFT understanding of oxidation and reduction centre of Fischer ethoxycarbenes. •Relationship between first oxidation and first reduction potential and DFT calculated energies. -- Abstract: The electrochemical behaviour of a series of Fischer ethoxycarbene complexes of the type [(CO)5Cr=C(OEt)R] with R = 2-thienyl (1), 2-furyl (2), 2-(N-methylpyrrolyl) (3), N-methyl-2-(2?-thienyl)pyrrole) (4) and 2,2?-thienylfuran (5), is investigated by means of cyclic voltammetry. Results show that the first one electron reduction process is sensitive to the energy, shape and distribution of the LUMO orbital, leading to a linear relationship between the formal reduction potential and the LUMO energy: E0?(Ccarbene) = –0.70 ELUMO–3.44 (R2 = 1.00) which is valid over a large potential range. The dimeric heteroarene substituents of 4 and 5 lead to enhanced stabilization of the reduced complexes 4 and 5, making another one electron reduction possible. The formal reduction potential, E0?(Cr) of the first oxidation process of 1–5 lays within a narrow potential range of 0.43–0.50 V vs. Fc/Fc+, is Cr-based and is mainly sensitive to the electrophilic character of the heteroarene ring directly attached to the carbene carb

443

Complex silumins  

Directory of Open Access Journals (Sweden)

Full Text Available Purpose: The study presents the results of investigations carried out on silumins with additions of Mg, Ni, Cu, Cr, Mo and W. The silumins containing Mg, Cu and Ni are well-known and commonly used in construction of machines and equipment.Design/methodology/approach: Additions of Cr, Mo and W have not been thoroughly investigated yet. They are considered a new family of innovative cast aluminium alloys.Findings: In Al-Si systems they form silicides, like Cr3Si, Mo3Si, W3Si and intermetallic phases of Al13Cr4Si4, Al12Mo, Al12W and AlWSi. The silicides crystallise in cubic lattice of parameters similar to aluminium and silicon.Research limitations/implications: Therefore they can act as crystallisation substrates and occur as separate phases. The examinations under the microscope and X-ray microanalysis of the linear and point distribution of elements confirmed the presence of the above mentioned phases. A combination of two elements, e.g. Cr and Mo, or Cr and W, was observed to cause the formation of complex silicide layers of Mo3Si and (Cr, Mo3Si, or Cr3Si as well as (W, Cr3Si.Originality/value: The presence of the silicides has been indicated as a possible source of the refinement of ?(Al and ?(Si phases. The precipitations of these phases and of the intermetallic phases favour a high degree of the silumins hardening. A characteristic feature is the fact that nucleation and crystallisation of the successive phases takes place at the phase boundaries formed between the previously precipitated phase and solid solution ?. The studies carried out so far have indicated that in complex silumins at high temperatures crystallise the silicides and peritectic phases of Al12W, AlWSi, Al12Mo and Al13Cr4Si4. Phases ? or ? are the next ones to crystallise, followed by complex eutectic ? + ? +Al(Si, Cr, Mo, W, Fe. Further crystallise the phases of Mg2Si, Al3Ni and Al2Cu. The silumins presented here are characterised by high mechanical properties: Rp0,2=320-420MPa, Rm =400-520MPa, A5=0.5-5.0% and elevated hardness of 145-210HB. Further investigations will be carried out to optimise the chemical composition of silumins and the precipitation hardening process parameters to produce alloys characterised by optimum combination of strength, ductility and hardness.

S. Pietrowski

2007-09-01

444

Complexes of clusters and complexes of stars  

OpenAIRE

Most star complexes are in fact complexes of stars, clusters and gas clouds; term "star complexes" was introduced as general one disregarding the preferential content of a complex. Generally the high rate of star formation in a complex is accompanied by the high number of bound clusters, including massive ones, what was explained by the high gas pressure in such regions. However, there are also complexes, where clusters seems to be more numerous in relation to stars than in ...

Efremov, Yu N.

2005-01-01

445

Semicarbazonas e tiossemicarbazonas: o amplo perfil farmacológico e usos clínicos Semicarbazones and thiosemicarbazones: their wide pharmacological profile and clinical applications  

OpenAIRE

This article shows that thiosemicarbazones, semicarbazones and their metal complexes can exhibit target selectivity along with a wide pharmacological profile. Complexes of thiosemicarbazones with cytotoxic or antitumoral activity are presented, some of which show activity against cisplatinum-resistant cells. The inhibition mechanism of the enzyme ribonucleoside diphosphate reductase (RDR), involved in DNA syntheses, by alpha(N)-heterocyclic thiosemicarbazones is discu...

Heloisa Beraldo

2004-01-01

446

On the synthesis, characterization and reactivity of N-heteroaryl-boryl radicals, a new radical class based on five-membered ring ligands.  

Science.gov (United States)

The synthesis and physical characterization of a new class of N-heterocycle-boryl radicals is presented, based on five membered ring ligands with a N(sp(2) ) complexation site. These pyrazole-boranes and pyrazaboles exhibit a low bond dissociation energy (BDE; B?H) and accordingly excellent hydrogen transfer properties. Most importantly, a high modulation of the BDE(B?H) by the fine tuning of the N-heterocyclic ligand was obtained in this series and could be correlated with the spin density on the boron atom of the corresponding radical. The reactivity of the latter for small molecule chemistry has been studied through the determination of several reaction rate constants corresponding to addition to alkenes and alkynes, addition to O2 , oxidation by iodonium salts and halogen abstraction from alkyl halides. Two selected applications of N-heterocycle-boryl radicals are also proposed herein, for radical polymerization and for radical dehalogenation reactions. PMID:24623534

Tehfe, Mohamad-Ali; Schweizer, Stéphane; Chany, Anne-Caroline; Ysacco, Cédric; Clément, Jean-Louis; Gigmes, Didier; Morlet-Savary, Fabrice; Fouassier, Jean-Pierre; Neuburger, Markus; Tschamber, Théophile; Blanchard, Nicolas; Lalevée, Jacques

2014-04-22

447

Highly fluorescent complexes with 3-isocyanoperylene and N-(2,5-di-tert-butylphenyl)-9-isocyano-perylene-3,4-dicarboximide.  

Science.gov (United States)

The perylene derivatives 3-isocyanoperylene (Per-N?C) (4a) and N-(2,5-di-tert-butylphenyl)-9-isocyano-perylene-3,4-dicarboximide (PMI-N?C) (4b) were prepared and used to synthesize gold complexes [AuX(CNR)] (X = C6F5 (5a,b), C6F4-O(n)Bu-p (6b)). The reaction of 5b and 6b with HNEt2 led to the carbene complexes [AuX{C(NEt2)(NHR)}] (7b, 8b), respectively. The molecular structure of complexes 7b and 8b have been determined by X-ray diffraction analysis showing intermolecular ?-stacking of the perylene groups and C6F5 rings and no Au···Au interactions. The derivative compounds [M(CO)5(CNR)] (M = Cr (9a,b), Mo (10a,b) or W (11a,b)) and trans-[Pd(CNR)2(C6F3Cl2)2] (12a,b) were also prepared. All complexes exhibit fluorescence associated with the perylene fragment with emission quantum yields, in solution at room temperature, in the range 0.05-0.93 and emission lifetimes ~ 4 ns. DFT calculations were performed of the absorption spectra of the ligands Per-N?C and PMI-N?C and representative complexes [Au(C6F5)(CNR)], [Cr(CO)5(CNR)], showing a perylene-dominated intraligand ?-?* emissive state, from the HOMO and LUMO orbitals of the perylene chromophore, but with significantly different absorption maxima by the influence of the metal fragment, particularly significant in the Per-N?C derivatives. PMID:24901028

Lentijo, S; Expósito, J E; Aullón, G; Miguel, J A; Espinet, P

2014-07-28

448

Di-, tri-, and tetranuclear copper(I) complexes of phenanthroline-linked dicarbene ligands.  

Science.gov (United States)

A family of 2,9-di(3-R-1H-imidazolium-1-yl)-1,10-phenanthroline iodides and hexafluorophosphates (R = allyl, benzyl, mesityl, picolyl) were synthesized from 2,9-diiodophenanthroline and imidazole or N-substituted imidazoles. Simple reactions of these diimidazolium salts with copper powder at room temperature have afforded a series of multinuclear copper(I)-NHC complexes in good yields. The structures vary depending on the N substituents and counterions. [Cu4(L1)2(MeCN)4](PF6)4 (R = allyl) exhibits a zigzag Cu4 chain with two terminal [Cu(NHC)(MeCN)2] and two internal [Cu(phen)(NHC)] moieties. [Cu3(L2)2](PF6)3 (R = benzyl) contains a strictly linear Cu3 framework with two [Cu(NHC)2] units and a [Cu(phen)2] located at the center. Both complexes [Cu3(L4)2](PF6)3 (R = mesityl) and [Cu3(L5)2](PF6)3 (R = picolyl) consist of a triangular Cu3 core in which two copper(I) ions are surrounded by a phen and a NHC group and the third copper(I) is coordinated by two NHC groups. [Cu3(L3)2](PF6)3 derived from 2,9-di(3-benzyl-1H-benzimidazolium-1-yl)-1,10-phenanthroline hexafluorophosphate can undergo transannulation of the benzimidazolylidene ring giving [Cu2(L3')2](PF6)2. The decomposition process might involve solvent-induced rearrangement of the ligand and hydrolysis of carbene moieties. Treatment of 2,9-di(3-mesityl-1H-benzimidazolium-1-yl)-1,10-phenanthroline iodide with copper powder generated dinuclear complex [Cu2(L4)2][Cu2(?-I)2I2] (R = mesityl) possessing a macrocyclic cation and [Cu2(?-I)2I2](2-) anion. Tetranuclear complex [Cu4(L5)2(?-I)2](CuI3) (R = picolyl) has been obtained from its diimidazolium iodide and copper powder. All Cu(I) complexes have been characterized by X-ray single diffraction analysis, elemental analysis, and NMR spectra. Their redox behavior and fluorescent properties have also been studied. PMID:25216090

Liu, Bo; Pan, Shanfei; Liu, Bin; Chen, Wanzhi

2014-10-01

449

Response of Complex Systems to Complex Perturbations: Complexity Matching  

OpenAIRE

We argue that complex systems, defined as non-Poisson renewal process, with complexity index $\\mu$, exchange information through complexity matching. We illustrate this property with detailed theoretical and numerical calculations describing a system with complexity index $\\mu_{S}$ perturbed by a signal with complexity index $\\mu_{P}$. We focus our attention on the case $1.5 \\leq \\mu_S \\leq 2$ and $1 \\leq \\mu_{P} \\leq 2$. We show that for $\\mu_{S} \\geq \\mu_P$, the system S r...

Allegrini, Paolo; Bologna, Mauro; Grigolino, Paolo; Lukovic, Mirko

2006-01-01

450

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

Energy Technology Data Exchange (ETDEWEB)

Nitrogen heterocycles are present in many compounds of enormous practical importance, ranging from pharmaceutical agents and biological probes to electroactive materials. Direct funtionalization of nitrogen heterocycles through C-H bond activation constitutes a powerful means of regioselectively introducing a variety of substituents with diverse functional groups onto the heterocycle scaffold. Working together, our two groups have developed a family of Rh-catalyzed heterocycle alkylation and arylation reactions that are notable for their high level of functional-group compatibility. This Account describes their work in this area, emphasizing the relevant mechanistic insights that enabled synthetic advances and distinguished the resulting transformations from other methods. They initially discovered an intramolecular Rh-catalyzed C-2-alkylation of azoles by alkenyl groups. That reaction provided access to a number of di-, tri-, and tetracyclic azole derivatives. They then developed conditions that exploited microwave heating to expedite these reactions. While investigating the mechanism of this transformation, they discovered that a novel substrate-derived Rh-N-heterocyclic carbene (NHC) complex was involved as an intermediate. They then synthesized analogous Rh-NHC complexes directly by treating precursors to the intermediate [RhCl(PCy{sub 3}){sub 2}] with N-methylbenzimidazole, 3-methyl-3,4-dihydroquinazolein, and 1-methyl-1,4-benzodiazepine-2-one. Extensive kinetic analysis and DFT calculations supported a mechanism for carbene formation in which the catalytically active RhCl(PCy{sub 3}){sub 2} fragment coordinates to the heterocycle before intramolecular activation of the C-H bond occurs. The resulting Rh-H intermediate ultimately tautomerizes to the observed carbene complex. With this mechanistic information and the discovery that acid co-catalysts accelerate the alkylation, they developed conditions that efficiently and intermolecularly alkylate a variety of heterocycles, including azoles, azolines, dihydroquinazolines, pyridines, and quinolines, with a wide range of functionalized olefins. They demonstrated the utility of this methodology in the synthesis of natural products, drug candidates, and other biologically active molecules. In addition, they developed conditions to directly arylate these heterocycles with aryl halides. The initial conditions that used PCy{sub 3} as a ligand were successful only for aryl iodides. However, efforts designed to avoid catalyst decomposition led to the development of ligands based on 9-phosphabicyclo[4.2.1]nonane (Phoban) that also facilitated the coupling of aryl bromides. They then replicated the unique coordination environment, stability, and catalytic activity of this complex using the much simpler tetrahydrophosphepine ligands and developed conditions that coupled aryl bromides bearing diverse functional groups without the use of a glovebox or purified reagents. With further mechanistic inquiry, they anticipate that researchers will better understand the details of the aforementioned Rh-catalyzed C-H bond functionalization reactions, resulting in the design of more efficient and robust catalysts, expanded substrate scope, and new transformations.

Lewis, Jared; Bergman, Robert; Ellman, Jonathan

2008-02-04

451

AQUEOUS N-HETEROCYCLIZATION OF PRIMARY AMINES AND HYDRAZINES WITH DIHALIDES: MICROWAVE-ASSISTED SYNTHESES OF N-AZACYCLOALKANES, ISOINDOLE, PYRAZOLE, PYRAZOLIDINE AND PHTHALAZINE DERIVATIVES  

Science.gov (United States)

The synthesis of nitrogen-containing heterocycles from alkyl dihalides (ditosylates) and primary amines and hydrazines via a simple and efficient cyclocondensation in alkaline aqueous medium that occurs under microwave irradiation is described. This improved greener synthetic met...

452

Metalated N-heterocyclic reagents prepared by the frustrated Lewis pair TMPMgCl·BF3 and their addition to aromatic aldehydes and activated ketones.  

Science.gov (United States)

Treatment of pyridines, quinoline and methylthiopyrazine with the frustrated Lewis pair TMPMgCl·BF(3) (1) leads to organotrifluoro borates which react readily with a variety of aromatic aldehydes in the absence of a transition metal catalyst. PMID:23389398

Manolikakes, Sophia M; Jaric, Milica; Karaghiosoff, Konstantin; Knochel, Paul

2013-03-14

453

From flag complexes to banner complexes  

OpenAIRE

A notion of an $i$-banner simplicial complex is introduced. For various values of $i$, these complexes interpolate between the class of flag complexes and the class of all simplicial complexes. Examples of simplicial spheres of an arbitrary dimension that are $(i+1)$-banner but not $i$-banner are constructed. It is shown that several theorems for flag complexes have appropriate $i$-banner analogues. Among them are (1) the codimension-$(i+j-1)$ skeleton of an $i$-banner homol...

Klee, Steven; Novik, Isabella

2012-01-01