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N-HETEROCYCLIC Carbene Complexes

Iogann Tolbatov, Cecilia Coletti, Alessandro Marrone, Nazzareno Re
Neutral N⁻heterocyclic carbene gold(I) compounds such as IMeAuCl are widely used both in homogeneous catalysis and, more recently, in medicinal chemistry as promising antitumor agents. In order to shed light on their reactivity with protein side chains, we have carried out density functional theory (DFT) calculations on the thermodynamics and kinetics of their reactions with water and various nucleophiles as a model of plausible protein binding sites such as arginine, aspartic acid, asparagine, cysteine, glutamic acid, glutamine, histidine, lysine, methionine, selenocysteine, and the N-terminal group...
February 14, 2019: International Journal of Molecular Sciences
Shuyang Shi, Moon Chul Jung, Caleb Coburn, Abegail Tadle, Daniel Sylvinson M R, Peter I Djurovich, Stephen R Forrest, Mark E Thompson
A series of six luminescent two-coordinate Cu(I) complexes were investigated bearing nonconventional N-heterocyclic carbene ligands, monoamido-aminocarbene (MAC*) and diamidocarbene (DAC*), along with carbazolyl (Cz) as well as mono- and dicyano-substituted Cz derivatives. The emission color can be systematically varied over 270 nm, from violet to red, through proper choice of the acceptor (carbene) and donor (carbazolyl) groups. The compounds exhibit photoluminescent quantum efficiencies up to 100% in fluid solution and polystyrene films with short decay lifetimes (τ ≈ 1 μs)...
February 15, 2019: Journal of the American Chemical Society
Jennifer L Minnick, Doaa Domyati, Rachel Ammons, Laleh Tahsini
Over the last two decades, N-heterocyclic carbene (NHC)-copper catalysts have received considerable attention in organic synthesis. Despite the popularity of copper complexes containing monodentate NHC ligands and recent development of poly(NHC) platforms, their application in C-C and C-heteroatom cross-coupling reactions has been limited. Recently, we reported an air-assisted Sonogashira-type cross-coupling catalyzed by well-defined cationic copper-pincer bis(NHC) complexes. Herein, we report the application of these complexes in Ullmann-type C-X (X = N, O) coupling of azoles and phenols with aryl halides in a relatively short reaction time...
2019: Frontiers in Chemistry
Tsz-Lung Lam, Ka-Chung Tong, Chen Yang, Wai-Lun Kwong, Xiangguo Guan, Ming-De Li, Vanessa Kar-Yan Lo, Sharon Lai-Fung Chan, David Lee Phillips, Chun-Nam Lok, Chi-Ming Che
A panel of iridium(iii) porphyrin complexes containing axial N-heterocyclic carbene (NHC) ligand(s) were synthesized and characterized. X-ray crystal structures of the bis-NHC complexes [IrIII (ttp)(IMe)2 ]+ ( 2a ), [IrIII (oep)(BIMe)2 ]+ ( 2d ), [IrIII (oep)(I i Pr)2 ]+ ( 2e ) and [IrIII (F20 tpp)(IMe)2 ]+ ( 2f ) display ruffled porphyrin rings with mesocarbon displacements of 0.483-0.594 Å and long Ir-CNHC bonds of 2.100-2.152 Å. Variable-temperature 1 H NMR analysis of 2a reveals that the macrocycle porphyrin ring inversion takes place in solution with an activation barrier of 40 ± 1 kJ mol-1 ...
January 7, 2019: Chemical Science
Lorenz J Schiegerl, Mohand Melaimi, Daniel R Tolentino, Wilhelm Klein, Guy Bertrand, Thomas F Fässler
The coordination of Ge9 Zintl clusters at (carbene)CuI moieties is explored, and the complexes [(CAAC)Cu]2 [η3 -Ge9 {Si(TMS)3 }2 ] (1), (CAAC)Cu[η3 -Ge9 {Si(TMS)3 }3 ] (2), and (MIC)Cu[η3 -Ge9 {Si(TMS)3 }3 ] (3) are compared with their known N-heterocyclic carbene (NHC) derivatives (A and B), where CAAC = cyclic (alkyl)amino carbene, MIC = mesoionic carbene, and TMS = trimethylsilane. In analogy to the NHC derivatives, the synthesis of 1-3 proceeds by single-step reactions of (CAAC)CuCl or (MIC)CuCl with the [Ge9 R2 ]2- and [Ge9 R3 ]- [R = Si(TMS)3 ] cluster ligands, respectively, and yields complexes of (carbene)CuI (carbene = CAAC, MIC) moieties exhibiting η3 -coordination modes of the Ge9 deltahedron to the Cu atom...
February 11, 2019: Inorganic Chemistry
Toshiki Nishiura, Asako Takabatake, Mariko Okutsu, Jun Nakazawa, Shiro Hikichi
Exposure of O2 to a reaction mixture containing bis(acac)cobalt(ii), a facially capping tris(N-heterocyclic carbene)borate ligand and 1-methylimidazole yields a heteroleptic cobalt(iii) complex with acac, 1-methylimidazole and tris(NHC)borate ligands. meta-Chloroperbenzoic acid is efficiently activated by this heteroleptic complex to catalytically oxidize cyclohexane at ambient temperature.
February 5, 2019: Dalton Transactions: An International Journal of Inorganic Chemistry
Birte M Zimmermann, Sarah C K Kobosil, Johannes F Teichert
A simple and air-stable copper(i)/N-heterocyclic carbene complex enables the catalytic hydrogenation of enoates and enamides, hitherto unreactive substrates employing homogeneous copper catalysis and H2 as a terminal reducing agent. This atom economic transformation replaces commonly employed hydrosilanes and can also be carried out in an asymmetric fashion.
February 4, 2019: Chemical Communications: Chem Comm
Patrycja Żak, Małgorzata Bołt, Beata Dudziec, Maciej Kubicki
A new platinum complex bearing bulky N-heterocyclic carbene ligand of the general formula [Pt(IPr*Ph)(dvtms)] (where IPr*Ph = 1,3-bis{2,4,6-tris(diphenylmethyl)phenyl}imidazol-2-ylidene, dvtms = divinyltetramethyldisiloxane) exhibits a high catalytic activity towards E-selective dimerization of ethynyl substituted siloxysilsesquioxanes. This process leads to a novel class of functionalized silsesquioxane derivatives, resembling their dumbbell-shaped silsesquioxane analogues.
January 31, 2019: Dalton Transactions: An International Journal of Inorganic Chemistry
Ya-Wen Zhang, Rajorshi Das, Yang Li, Yao-Yu Wang, Ying-Feng Han
The metal-controlled self-assembly of organometallic molecular cylinders from a series of imidazo[1,5-a]pyridine-based tris-NHC ligands has been described. The imidazo[1,5-a]pyridinium salts H3-L(PF6)3 (L = 4a-4c) react with 1.5 equiv of Ag2O to yield the trinuclear AgI hexacarbene cages [Ag3(L)2](PF6)3 (L = 4a-4c), where three AgI ions are sandwiched between the two tricarbene ligands. The silver(I) complexes [Ag3(L)2](PF6)3 (L = 4a-4c) undergo facile transmetalation reaction in presence of 3 equiv of AuCl(THT) leading to the formation of trinuclear AuI cylinder-like cages [Ag3(L)2](PF6)3 (L = 4a-4c) without destruction of the metallosupramolecular structure...
January 29, 2019: Chemistry: a European Journal
Wen Dai, Dennis P Curran, John C Walton
Radical H-atom abstraction from a set of N-heterocyclic carbene (NHC) complexes of alkenylboranes bearing two tert-butyl ester substituents was studied by EPR spectroscopy. The initial boraallyl radical intermediates rapidly ring closed onto the O-atoms of their distal ester groups in 5-endo mode to yield 1,2-oxaborole radicals. Unexpectedly, two structural varieties of these radicals were identified from their EPR spectra. These proved to be two stable rotamers in which the carbonyl group of the tert-butyl ester was oriented towards and away from the NHC ring...
January 21, 2019: Journal of Organic Chemistry
Mitsutaka Takeda, Atsuhisa Mitsui, Kazunori Nagao, Hirohisa Ohmiya
The copper-catalyzed reductive coupling of two different carbonyl compounds has been achieved. The reaction of aromatic aldehydes and arylketones with a silylboronate in the presence of a catalytic amount of CuCl-N-heterocyclic carbene (NHC) complex and a stoichiometric amount of alkoxide base yielded cross-coupled 1,2-diol derivatives. A reaction pathway is proposed that involves the catalytic formation of a nucleophilic a-silyloxybenzylcopper(I) species from the aromatic aldehyde and its subsequent coupling with the arylketone...
January 17, 2019: Journal of the American Chemical Society
Katharine R Sampford, Jamie L Carden, Edward B Kidner, Abigail Berry, Kingsley J Cavell, Damien M Murphy, Benson M Kariuki, Paul D Newman
A series of diaryl, mono-aryl/alkyl and dialkyl mono- and bicyclic expanded-ring N-heterocyclic carbenes (ER-NHCs) have been prepared and their complexation to Au(i) investigated through the structural analysis of fifteen Au(NHC)X and/or [Au(NHC)2]X complexes. The substituted diaryl 7-NHCs are the most sterically encumbered with large buried volume (%VB) values of 40-50% with the less flexible six-membered analogues having %VB values at least 5% smaller. Although the bicyclic systems containing fused 6- and 7-membered rings (6,7-NHCs) are constrained with relatively acute NCN bond angles, they have the largest %VB values of the dialkyl derivatives reported here, a feature related to the fixed conformation of the heterocyclic rings and the compressional effect of a pre-set methyl substituent...
January 17, 2019: Dalton Transactions: An International Journal of Inorganic Chemistry
Alexander Hofmann, Conor Pranckevicius, Tobias Tröster, Holger Braunschweig
Reactions between BIII species and the novel nucleophilic cyclopentadienyl-stabilized AlI reagent (1) result in a diversity of complexes bearing different Al/B oxidation states and coordination geometries. With the triarylborane B(C6F5)3, a simple AlI→BIII adduct is formed. In contrast, a bulky aryldihaloborane leads to oxidative addition and the formation of a covalent bora-alane species. With an N-heterocyclic carbene-stabilized amino(bromo)borenium ion a redox reaction was observed, where the product is a borylene-alane BI→AlIII complex...
January 15, 2019: Angewandte Chemie
Andrew C Marr, Patrick J Morgan, Graham C Saunders, Hayden P Thomas
The reaction between haloform, the complexes [Cp*IrCl2(κC-MeNC3H2NCH2Ar)] (Ar = C6H3F2-2,6, C6H3F-2-Cl-6, C6H3Me2-2,6) and silver(i) oxide proceeded by carbon-halogen bond fission to yield the carbonate complexes [Cp*Ir(κ2O-CO3)(κC-MeNC3H2NCH2Ar)].
January 14, 2019: Dalton Transactions: An International Journal of Inorganic Chemistry
Lubomír Rulíšek, Michal Straka, Erik Andris, Jan Vícha, Aleš Růžička, Jana Roithová
Despite substantial evidence of short Au···H-X contacts derived from a number of X-ray structures of Au(I) compounds, the nature of Au(I)···H bonding has not been clearly understood. Herein, we present the first spectroscopic evidence for intramolecular Au(I)···H+-N hydrogen bond in a [Cl Au L]+ complex, where L is protonated N-heterocyclic carbene. The complex was isolated in the gas phase and characterized by helium-tagging infrared photodissociation spectra (IRPD), which feature H+-N mode derived bands evidencing the intramolecular Au(I)···H+-N bond...
January 2, 2019: Angewandte Chemie
Michael L Neidig, Stephanie H Carpenter, Daniel J Curran, Joshua C DeMuth, Valerie E Fleischauer, Theresa E Iannuzzi, Peter G N Neate, Jeffrey D Sears, Nikki J Wolford
Since the pioneering work of Kochi in the 1970s, iron has attracted great interest for cross-coupling catalysis due to its low cost and toxicity as well as its potential for novel reactivity compared to analogous reactions with precious metals like palladium. Today there are numerous iron-based cross-coupling methodologies available, including challenging alkyl-alkyl and enantioselective methods. Furthermore, cross-couplings with simple ferric salts and additives like NMP and TMEDA ( N-methylpyrrolidone and tetramethylethylenediamine) continue to attract interest in pharmaceutical applications...
December 28, 2018: Accounts of Chemical Research
Polly L Arnold, Ryan W F Kerr, Catherine Weetman, Scott R Docherty, Julia Rieb, Faye L Cruickshank, Kai Wang, Christian Jandl, Max W McMullon, Alexander Pöthig, Fritz E Kühn, Andrew D Smith
A series of rare earth complexes of the form Ln(LR )3 supported by bidentate ortho -aryloxide-NHC ligands are reported (LR = 2-O-3,5-t Bu2 -C6 H2 (1-C{N(CH)2 N(R)})); R = i Pr, t Bu, Mes; Ln = Ce, Sm, Eu). The cerium complexes cleanly and quantitatively insert carbon dioxide exclusively into all three cerium carbene bonds, forming Ce(LR ·CO2 )3 . The insertion is reversible only for the mesityl-substituted complex Ce(LMes )3 . Analysis of the capacity of Ce(LR )3 to insert a range of heteroallenes that are isoelectronic with CO2 reveals the solvent and ligand size dependence of the selectivity...
November 14, 2018: Chemical Science
Lara M Groves, Catrin F Williams, Anthony J Hayes, Benjamin D Ward, Marc D Isaacs, Nadine O Symonds, David Lloyd, Peter N Horton, Simon J Coles, Simon J A Pope
A series of cationic, dihydroimidazolinium-functionalized 1,8-naphthalimide fluorophores have been isolated as their hexafluorophosphate salts, [HL]PF6. These pro-ligands react with [AuCl(tht)] in the presence of base to form N-heterocyclic carbene (NHC) complexes, [AuCl(L)]. Two X-ray structures represent a pro-ligand and complex pairing: the latter reveals the two-coordinate linear geometry of the NHC-Au(i) species, as well as intermolecular interactions supported by both ligand π-π stacking and a weak aurophilic interaction of 3...
December 19, 2018: Dalton Transactions: An International Journal of Inorganic Chemistry
Maria Inês P S Leitão, Federico Herrera, Ana Petronilho
Palladium(II) and platinum(II) complexes bearing N-heterocyclic carbenes derived from guanosine are synthesized via oxidative addition, followed by protonation in the presence of acid. Cytotoxicity of the compounds is evaluated in several cell lines. Compounds 2a , 2b , and 3a are selective for glioblastoma U251 cells and are nontoxic toward healthy human embryonic kidney (HEK293) cells.
November 30, 2018: ACS Omega
Shweta Bhagat, Minhajul Arfeen, Gourav Das, Neha Patel, Prasad V Bharatam
Carbocyclic carbenes (CCCs) are a class of nucleophilic carbenes which are very similar to N-heterocyclic carbenes (NHCs) in terms of their reactivity, but they do not contain a stabilizing heteroatom in their cyclic ring system. In this study, 17 representative known CCCs and 34 newly designed CCCs are evaluated using quantum chemical methods, and the results are compared in terms of their stability, nucleophilicity, and proton affinity (PA) parameters. The results are divided on the basis of ring size of the known and reported CCCs...
December 14, 2018: Journal of Computational Chemistry
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