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N-HETEROCYCLIC Carbene Complexes

Claudia Schmidt, Lucia Albrecht, Shantheya Balasupramaniam, Rainer Misgeld, Bianka Karge, Mark Brönstrup, Aram Prokop, Knut Baumann, Stephan Reichl, Ingo Ott
Gold complexes with N-heterocyclic carbene (NHC) ligands have been attracting major attention in medicinal inorganic chemistry based on their favorable antiproliferative effects and the structural versatility of the coordinated NHC ligands. Here we present a novel complex of the type (NHC)2Au+, which represents a substantially improved and selective TrxR inhibitor compared to close structural analogues. The complex is highly stable in various solutions over 96 hours, however, comparative cellular uptake studies indicate metabolic transformations inside cells over time...
December 5, 2018: Metallomics: Integrated Biometal Science
Zeming Huang, Shaowu Wang, Xiancui Zhu, Qingbing Yuan, Yun Wei, Shuangliu Zhou, Xiaolong Mu
Four amidate-functionalized N-heterocyclic carbene (NHC) rare-earth metal amido complexes [(κ2 -N,O-κ1 -L)2 REN(SiMe3 )2 ] (L = 1-(C6 H5 C═ONCH2 CH2 )-3-(CH3 )3 C6 H2 (N(CH)2 NC)) [RE = Er (1), Y (2), Dy (3), Gd (4)] were synthesized by one-pot reactions of 2 equiv of (1-(C6 H5 C═ONHCH2 CH2 )-3-(CH3 )3 C6 H2 -(N(CH)2 NCH))Br (H2 LBr) with 5 equiv of KN(SiMe3 )3 followed by treatment with 1 equiv of RECl3 in tetrahydrofuran at -40 °C. These complexes were fully characterized, and their catalytic activities toward hydroboration of unactivated imines and nitriles were investigated, and it was found that these complexes displayed excellent activities as well as remarkable functional group compatibility for imine and nitrile substrates such as halo-, alkyl-, hydroxyl-, N, N-dimethylamino-, and nitro- substituents...
December 3, 2018: Inorganic Chemistry
Dongyang Wang, Qi Chen, Xuebing Leng, Liang Deng
Aiming to get knowledge on the reactivity of low-coordinate cobalt(0) species toward primary phosphines, the reactions of [(IPr)Co(vtms)2 ] and [(ICy)2 Co(vtms)] (IPr = 1,3-bis(2',6'-diisopropylphenyl)imidazol-2-ylidene, ICy = 1,3-dicyclohexylimidazol-2-ylidene, and vtms = vinyltrimethylsilane) with several primary aryl phosphines have been examined. The reactions of [(IPr)Co(vtms)2 ] and [(ICy)2 Co(vtms)] with H2 PDmp (Dmp = 2,6-dimesitylphenyl) at 80 °C furnish the diamagnetic cobalt(I) phosphido complexes [(NHC)Co(PHDmp)] (NHC = IPr, 1; ICy, 2) that feature the Co-(η6 -mesityl) interaction...
December 3, 2018: Inorganic Chemistry
Yang Wang, Ling-Bo Qu, Donghui Wei
The novel base-controlled mechanisms for N-heterocyclic carbene (NHC)-catalyzed divergent [3 + 3] and [3 + 2] annulation reactions were examined by using DFT method. The reaction initiates with the complexation of NHC and enal to give the Breslow intermediate, which diverges afterward. Then, the azomethine imine can either react with Breslow intermediate to give six-membered ring product, or the β-carbon protonation happens for forming the enolate intermediate controlled by different bases. The formed enolate intermediate reacts with azomethine imine to afford five-membered ring product...
November 29, 2018: Chemistry, An Asian Journal
Magdalena Quezada-Miriel, J Rubén Ochoa-Sanfelice, Sebastian Mendoza-Tellez, Diego Martinez-Otero, Matthew Asay
Saturated N-heterocyclic carbenes have unique ligand properties that differ even from their unsaturated analogs. While the unsaturated version has been extensively used in multidentate ligand scaffolds, the incorporation of the saturated version is less common. Here we report the straightforward synthesis of a new bis-saturated N-heterocyclic carbene ligand wherein the carbene moieties are linked by a flexible meta-xylyl unit. Carbene metal complexes of the proligand can be generated by direct metalation, transmetallation or base assisted metalation all of which lead to monodentate coordination modes of silver or iridium...
November 27, 2018: Dalton Transactions: An International Journal of Inorganic Chemistry
Greco González Miera, Aitor Bermejo López, Elisa Martínez-Castro, Per-Ola Norrby, Belén Martín-Matute
1,4- and 1,5-Diols undergo cyclodehydration upon treatment with cationic N-heterocyclic carbene (NHC) Ir(III) complexes to give tetrahydrofurans and tetrahydropyrans, respectively. The mechanism was investigated, and a metal-hydride-driven pathway is proposed for all substrates, with the exception of very electron rich ones, which contrasts with the well-established classical pathways involving nucleophilic substitutions.
November 26, 2018: Chemistry: a European Journal
Malka Mora, M Concepción Gimeno, Renso Visbal
This tutorial review covers the recent advances made in the study of gold complexes containing N-heterocyclic carbene ligands with biological properties. The great stability, ease of modulation of the electronic properties and excellent σ-donating capacity displayed by NHCs allow gold-NHC derivatives to reach high stability in biological media and relatively good internalization into cells and for that they have emerged as excellent potential chemotherapeutics. The new gold-NHC derivatives show superior anticancer activity compared to other standards such as Cisplatin or Auranofin...
November 26, 2018: Chemical Society Reviews
Franck Ulm, Amalia I Poblador-Bahamonde, Sabine Choppin, Stéphane Bellemin-Laponnaz, Michael J Chetcuti, Thierry Achard, Vincent Ritleng
Neutral nickel-N-heterocyclic carbene complexes, (κ1-C)-[NiCpBr{R-NHC-(CH2)2SR'}] [Cp = η5-C5H5; R-NHC-(CH2)2SR' = 1-mesityl-3-[2-(tert-butylthio)ethyl]- (1a), 1-mesityl-3-[2-(phenylthio)ethyl]- (1b), 1-benzyl-3-[2-(tert-butylthio)ethyl]- (1c), 1-benzyl-3-[2-(phenylthio)ethyl]-imidazol-2-ylidene (1d)], which bear a N-bound thioether side arm, were prepared by the reaction of nickelocene with the corresponding imidazolium bromides [R-NHC-(CH2)2SR'·HBr] (a-d), via conventional or microwave heating. The 1H NMR spectra of the benzyl-substituted species 1c and 1d showed signals for diastereotopic NCH2CH2S protons at room temperature...
November 23, 2018: Dalton Transactions: An International Journal of Inorganic Chemistry
Salvador B Muñoz, Valerie E Fleischauer, William W Brennessel, Michael L Neidig
Iron and N -heterocyclic carbenes (NHCs) have proven to be a successful pair in catalysis, with reactivity and selectivity being highly dependent on the nature of the NHC ligand backbone saturation and N -substituents. Four (NHC)Fe(1,3-dioxan-2-ylethyl)2 complexes have been isolated and spectroscopically characterized to correlate their reactivity to steric effects of the NHC from both the backbone saturation and N -substituents. Only in the extreme case of SIPr where NHC backbone and N -substituent steric effects are the largest is there a major structural perturbation observed crystallographically...
September 24, 2018: Organometallics
Lorenz Pardatscher, Mario J Bitzer, Christian Jandl, Jens W Kück, Robert M Reich, Fritz E Kühn, Walter Baratta
The cationic abnormal N-heterocyclic carbene complex [Ru(OAc)(dppe)(PC)]Br (2b) (PC = bidentate phosphine-carbene ligand) has been obtained by treatment of the neutral derivative RuBr(OAc)(PPh3)(PC) (2a) with dppe in THF. Reaction of 2b with Ag2O afforded the heterobimetallic complex Ru(OAc)(dppe)(PC)AgBr (2c) which can be easily transmetallated with [Ir(cod)Cl]2 giving Ru(OAc)(dppe)(PC)IrCl(cod) (2d). Similarly, [{Ru(OAc)(PC)(PC')}2Ag][AgBr2] (1b) reacts with [Ir(cod)Cl]2 with formation of Ru(OAc)(PC)(PC')IrCl(cod) (1e)...
November 20, 2018: Dalton Transactions: An International Journal of Inorganic Chemistry
Yuliang Yang, Lihua Guo, Xingxing Ge, Shaopeng Shi, Yuteng Gong, Zhishan Xu, Xiaofeng Zheng, Zhe Liu
We herein report the synthesis, characterization, catalytic ability in converting coenzyme NADH to NAD+ and anticancer activity of half-sandwich iridium(III) complexes, [(η5 -Cpxbiph )Ir(C^N)Cl]PF6 - , where Cpxbiph  = tetramethyl(biphenyl)cyclopentadienyl, C^N = varying imine-N-heterocyclic carbene ligands. The molecular structure of [(η5 -Cpxbiph )Ir(L6)Cl]PF6 (complex Ir6), exhibiting the familiar "piano-stool" geometry, has been authenticated by X-ray crystallography. The anticancer activities of these complexes can be governed via substituent effects of three tunable domains and the ligand substituted variants offer an effective chelate ligand set that distinguishes anticancer activity and catalytic ability...
November 10, 2018: Journal of Inorganic Biochemistry
Maria Giulia Fabbrini, Damiano Cirri, Alessandro Pratesi, Lorenzo Ciofi, Tiziano Marzo, Annalisa Guerri, Silvia Nistri, Alfonso Dell'Accio, Tania Gamberi, Mirko Severi, Andrea Bencini, Luigi Messori
The silver(I) NHC (N-heterocyclic carbene) complex bis(1-(anthracen-9-ylmethyl)-3-ethylimidazol-2-ylidene) silver chloride, ([Ag(EIA)2]Cl) hereafter, bearing two anthracenyl fluorescent probes has been synthesized and characterised. [Ag(EIA)2]Cl is stable in organic solvents and under physiological-like conditions, and shows potent cytotoxic effects in vitro toward human SH-SY5Y neuroblastoma cells. The interactions of [Ag(EIA)2]Cl with a few model biological targets have been studied here as well as its ability to be internalized in cells...
November 16, 2018: ChemMedChem
Yuebiao Zhou, Ying Shi, Sebastian Torker, Amir H Hoveyda
The first broadly applicable strategy for SN 2″-selective and enantioselective catalytic substitution is disclosed. Transformations are promoted by 5.0 mol% of a sulfonate-containing NHC-Cu complex (NHC = N-heterocyclic carbene), and are carried out in the presence of commercially available allenyl-B(pin) (pin = pinacolato) or a readily accessible silyl-protected propargyl-B(pin). Acyclic, or aryl-, heteroaryl-, and alkyl-substituted penta-2,4-dienyl phosphates, as well as those bearing either only 1,2-disubstituted olefins or a 1,2-disubstituted and a trisubstituted alkene were found to be suitable starting materials...
November 16, 2018: Journal of the American Chemical Society
Xiang-Yu Chen, Sun Li, Fabrizio Vetica, Mukesh Kumar, Dieter Enders
Organocatalytic domino processes have become a rapidly growing area of research. N-heterocyclic carbenes (NHCs) have emerged as powerful organocatalysts for various transformations and continue to have widespread application. In the last decade, domino reactions catalyzed by NHCs have seen significant progress since the different activation modes could be successfully combined in one process. The most attractive features of these domino sequences include the readily available catalysts and substrates, the simple operational procedures, and the rapid assembly of complex molecular scaffolds with excellent levels of stereocontrol under mild reaction conditions...
April 27, 2018: iScience
Gregorio Guisado-Barrios, Michèle Soleilhavoup, Guy Bertrand
Classical carbenes are usually described as neutral compounds featuring a divalent carbon with only six electrons in their valence shell. It was only in 1988 that our group prepared the first isolable example, in which the carbene center was stabilized by a push-pull effect, using a phosphino and a silyl substituent. In the last 30 years, a myriad of acyclic and cyclic push-pull and push-push carbenes, bearing different heteroatom substituents, have been isolated. Among them, the so-called N-heterocyclic carbenes (NHCs), which include cyclic (alkyl)(amino)carbenes (CAACs), are arguably the most popular...
November 12, 2018: Accounts of Chemical Research
Felix Pape, Lea Brechmann, Johannes F Teichert
Copper(I)/N-heterocyclic carbene (NHC) complexes enable the catalytic generation of nucleophilic hydrides from dihydrogen (H2) and their subsequent transfer to allylic chlorides. The highly chemoselective catalyst displays no concomitant hydrogenation reactivity, as the terminal double bond formed in the hydride transfer remains intact. Switching to deuterium gas (D2) allows for regioselective monodeuteration with excellent isotope incorporation.
November 8, 2018: Chemistry: a European Journal
Nelson Y S Lam, Dianna Truong, Hilke Burmeister, Maria V Babak, Hannah U Holtkamp, Sanam Movassaghi, Daniel Moscoh Ayine-Tora, Ayesha Zafar, Mario Kubanik, Luciano Oehninger, Tilo Söhnel, Jóhannes Reynisson, Stephen M F Jamieson, Christian Gaiddon, Ingo Ott, Christian G Hartinger
The promise of the metal(arene) structure as an anticancer pharmacophore has prompted intensive exploration of this chemical space. While N-heterocyclic carbene (NHC) ligands are widely used in catalysis, they have only recently been considered in metal complexes for medicinal applications. Surprisingly, a comparatively small number of studies have been reported in which the NHC ligand was coordinated to the RuII (arene) pharmacophore and even less with an OsII (arene) pharmacophore. Here, we present a systematic study in which we compared symmetrically substituted methyl and benzyl derivatives with the nonsymmetric methyl/benzyl analogues...
November 8, 2018: Inorganic Chemistry
May Wantz, Mathilde Bouché, Georges Dahm, Neïla Chekkat, Sylvie Fournel, Stéphane Bellemin-Laponnaz
The high interest in N -Heterocyclic platinum carbene complexes in cancer research stems from their high cytotoxicity to human cancer cells, their stability, as well as their ease of functionalization. However, the development of these new molecules as anticancer agents still faces multiple challenges, in particular solubility in aqueous media. Here, we synthesized platinum-NHC bioconjugates that combine water-solubility and cytotoxicity by using polyethyleneimine as polymer carrier. We showed on 8 different types of cells that the activity of these conjugates is modulated by the size of the polymer and the overall density of metal ions onto polymer chains...
November 5, 2018: International Journal of Molecular Sciences
Qing Tang, Guoxiang Hu, Victor Fung, De-En Jiang
Atomically precise, ligand-protected metal nanoclusters are of great interest for their well-defined structures, intriguing physicochemical properties, and potential applications in catalysis, biology, and nanotechnology. Their structure precision provides many opportunities to correlate their geometries, stability, electronic properties, and catalytic activities by closely integrating theory and experiment. In this Account, we highlight recent theoretical advances from our efforts to understand the metal-ligand interfaces, the energy landscape, the electronic structure and optical absorption, and the catalytic applications of atomically precise metal nanoclusters...
November 6, 2018: Accounts of Chemical Research
Shravankumar Kankala, Niranjan Thota, Fredrik Björkling, Myles K Taylor, Ravinder Vadde, Ramesh Balusu
Hit, Lead & Candidate Discovery Cancer is a major global health problem with large therapeutic challenges. Although substantial progress has been made in cancer therapy, there still remains a need to develop novel and effective treatment strategies to treat several relapsed and refractory cancers. Recently, there has been growing demand for considering organometallics as antineoplastic agents. This review is focused on a group of organometallics, silver N-heterocyclic carbene complexes (SCCs) and their anticancer efficacy in targeting multiple pathways in various in vitro cancer model systems...
November 1, 2018: Drug Development Research
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