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N-HETEROCYCLIC Carbene Complexes

Michael R Buchmeiser
The concepts of functional precision polymers and the latest accomplishments in their synthesis are summarized. Synthetic concepts based on chain growth polymerization are compared to iterative synthetic approaches. Here, the term "functional precision polymers" refers to polymers that are not solely hydrocarbon-based but contain functional groups and are characterized by a highly ordered primary structure. If insertion polymerization is used for their synthesis, olefin metathesis-based polymerization techniques, that is, ring-opening metathesis polymerization (ROMP), acyclic diene metathesis (ADMET) polymerization, and the regio- and stereoselective cyclopolymerization of α,ω-diynes are almost exclusively applied...
August 17, 2018: Macromolecular Rapid Communications
Yuna Kim, Hanseul Lee, Sunga Park, Yunmi Lee
A mild and efficient method for the synthesis of allenes through selective copper-catalyzed hydride addition to propargylic chlorides using commercially available diisobutylaluminum hydride has been developed. This transformation, which is promoted by a readily accessible N-heterocyclic carbene-copper complex, provides a wide range of new and versatile functionalized allenes in good to excellent yields with high regio- and stereoselectivities.
August 16, 2018: Organic Letters
Vaishnavi Somasundaram, Praveen N Gunawardene, Alexander M Polgar, Mark S Workentin, John F Corrigan
The reaction of N-heterocyclic carbene (NHC) Group 11 metal complexes, [(NHC)M-X] (X = chloride, acetate), with the new azide-modified arylthiol 1-HSCH2 -2,5-Me2 -4-N3 CH2 -C6 H2 , 1 (for M = Au; X = Cl), or 1-Me3 SiSCH2 -2,5-Me2 -4-N3 CH2 -C6 H2 , 2 (for M = Cu, X = Cl; M = Ag, X = OAc), affords the "clickable" NHC-metal thiolates [( i Pr2 -bimy)Au-(1-SCH2 -2,5-Me2 -4-N3 CH2 -C6 H2 )], 5; [(IPr)Au-(1-SCH2 -2,5-Me2 -4-N3 CH2 -C6 H2 )], 6; [(IPr)Ag-(1-SCH2 -2,5-Me2 -4-N3 CH2 -C6 H2 )], 7; and [(IPr)Cu-(1-SCH2 -2,5-Me2 -4-N3 CH2 -C6 H2 )], 8 ( i Pr2 -bimy = 1,3-di-isopropylbenzimidazol-2-ylidene, IPr = 1,3-bis(2,6-di-iso-propylphenyl)imidazol-2-ylidene)...
August 16, 2018: Inorganic Chemistry
Danielle Curran, Oyinlola Dada, Helge Müller-Bunz, Matthias Rothemund, Goar Sánchez-Sanz, Rainer Schobert, Xiangming Zhu, Matthias Tacke
Ten novel N -heterocyclic carbene gold(I) complexes derived from lepidiline A (1,3-dibenzyl-4,5-dimethylimidazolium chloride) are reported here with full characterisation and biological testing. (1,3-Dibenzyl-4,5-diphenylimidazol-2-ylidene)gold(I) chloride (NHC*-AuCl) ( 1 ) was modified by substituting the chloride for the following: cyanide ( 2 ), dithiocarbamates ( 3 ⁻ 5 ), p -mercaptobenzoate derivatives ( 12 ⁻ 14 ) and N -acetyl-l-cysteine derivatives ( 15 ⁻ 17 ). All complexes were synthesised in good yields of 57⁻78%...
August 14, 2018: Molecules: a Journal of Synthetic Chemistry and Natural Product Chemistry
Ying-Chun Chen, Ben-Xian Xiao, Xin-Yue Gao, Wei Du
Numerous protocols have been developed for the functionalizations of aromatic substances. Among them, the strategy in which aromatic substrates are activated by in situ generating dearomatizative intermediates represents a highly efficient but challenging one, especially in the field of asymmetric catalysis. In this Concept, the application of some well-established chiral Lewis base catalysis, including primary/ secondary amines and N-heterocyclic carbenes, which can covalently form catalyst-tethered dearomatizative ortho/para-quinodimethane species with diverse heteroaryl or aryl carbonyl substrates, is summarized in a number of asymmetric cycloaddition or addition reactions with diverse reagents generally having electrophilic properties...
August 15, 2018: Chemistry: a European Journal
Yuliang Yang, Guo Lihua, Zhenzhen Tian, Xicheng Liu, Yuteng Gong, Hongmei Zheng, Xingxing Ge, Zhe Liu
A family of novel imine-N-heterocyclic carbene ruthenium(II) complexes of the general formula [(η6-p-cymene)Ru(C^N)Cl]PF6- (where C^N is imine-N-heterocyclic carbene chelating ligand with varying substituents) have been prepared and characterized. In this imine-N-heterocyclic carbene chelating ligand framework, there are three potential sites that can be modified, which distinguishes this class of ligand and provides a body of flexibilities and opportunities to tune the cytotoxicity of these ruthenium(II) complexes...
August 12, 2018: Chemistry, An Asian Journal
Chen Zhang, Marie-Lise Maddelein, Raymond Wai-Yin Sun, Heinz Gornitzka, Olivier Cuvillier, Catherine Hemmert
A series of four new mononuclear cationic gold(I) complexes containing nitrogen functionalized N-heterocyclic carbenes (NHCs) was synthesized and fully characterized by spectroscopic methods. The X-ray structures of three complexes are presented. These lipophilic gold(I) complexes originate from a pharmacomodulation of previously described gold(I)-NHC complexes, by replacing an aliphatic spacer with an aromatic one. The Log P values of the resulting complexes increased by 0.7-1.5, depending on the substituents in comparison to the aliphatic-linker systems...
August 2, 2018: European Journal of Medicinal Chemistry
Hsueh-Ju Liu, Micah S Ziegler, T Don Tilley
An unusual cyclometalation reaction results from a C-C bond activation in Cp*(IPr)RuCl to give Cp*(IPr')Ru(L) featuring a NHC-C(sp2) chelating ligand (5-L; L = propene, N2; IPr = 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene; IPr' = 1-(6-isopropylphenyl)-3-(2,6-diisopropylphenyl)imidazol-2-ylidene). DFT calculations were employed to elucidate the C-C bond activation pathway. Reactions of cyclometalated ruthenium complexes bearing NHC-C(sp2) and NHC-C(sp3) ligands (5-L and Cp*(IXy-H)Ru(N2), 1a, respectively where IXy = 1,3-bis(2,6-dimethylphenyl)-imidazol-2-ylidene; IXy-H is the deprotonated form of (IXy)) are reported...
August 7, 2018: Dalton Transactions: An International Journal of Inorganic Chemistry
Mathilde Bouché, Antoine Bonnefont, Thierry Achard, Stéphane Bellemin-Laponnaz
Platinum(iv) complexes stabilized by N-heterocyclic carbene ligands of the type [(NHC)PtX4L], where L is a neutral nitrogen-based ligand and X is a halide anion (Br, Cl), were prepared by using straightforward and high-yielding synthetic routes and the scope was extended to amphiphilic derivatives. The complexes were fully characterized and the molecular structure of the three derivatives was determined by single-crystal X-ray analyses. The complexes demonstrated in vitro antiproliferative activities against several cancer cell lines...
August 3, 2018: Dalton Transactions: An International Journal of Inorganic Chemistry
Dnyaneshwar Rasale, Kiran Patil, Basilius Sauter, Stefanie Geigle, Saule Zhanybekova, Dennis Gillingham
We show here that copper carbenes generated from diazo acetamides alkylate single RNAs, mRNAs, or pools of total transcriptome RNA, delivering exclusively alkylation at the O6 position in guanine (O6G). Although the reaction is effective with free copper some RNA fragmentation occurs, a problem we resolve by developing a novel water-stable copper N-heterocyclic carbene complex. Carboxymethyl adducts at O6G are known mutagenic lesions in DNA but their relevance in RNA biochemistry is unknown. As a case-in-point we re-examine an old controversy regarding whether O6G damage in RNA is susceptible to direct RNA repair...
August 14, 2018: Chemical Communications: Chem Comm
Victor M Chernyshev, Oleg V Khazipov, Maxim A Shevchenko, Andrey Yu Chernenko, Alexander V Astakhov, Dmitry B Eremin, Dmitry V Pasyukov, Alexey S Kashin, Valentine P Ananikov
Numerous reactions are catalyzed by complexes of metals (M) with N-heterocyclic carbene (NHC) ligands, typically in the presence of oxygen bases, which significantly shape the performance. It is generally accepted that bases are required for either substrate activation (exemplified by transmetallation in the Suzuki cross-coupling), or HX capture ( e.g. in a variety of C-C and C-heteroatom couplings, the Heck reaction, C-H functionalization, heterocyclizations, etc. ). This study gives insights into the behavior of M(ii)/NHC (M = Pd, Pt, Ni) complexes in solution under the action of bases conventionally engaged in catalysis (KOH, NaOH, t -BuOK, Cs2 CO3 , K2 CO3 , etc...
July 7, 2018: Chemical Science
Conor Pranckevicius, J Oscar C Jimenéz-Halla, Marius Kirsch, Ivo Krummenacher, Holger Braunschweig
The coordination chemistry and stability of aminoborylene ligands bearing different N-heterocyclic carbene (NHC) stabilizing groups has been investigated with Group VI and VIII metals. NHC-aminoborylene complexes have been accessed via reduction of NHC-dihaloaminoborane adducts with Na2 [M(CO) x ] species (M = Fe, Ru, Cr, W). Imidazol-2-ylidene-stabilized aminoborylene ligands were found to afford thermally robust metal-borylene complexes, which are inert to oxidation, hydrolysis, and insertion of unsaturated substrates...
August 10, 2018: Journal of the American Chemical Society
Yu Pan, Aijing Zhao, Yang Li, Wenqiang Li, Yat-Ming So, Xiaoming Yan, Gaohong He
Bis(oxazoline)-derived N-heterocyclic carbene (IBiox) supported rare-earth (Sc, Y, Lu) trialkyl complexes have been synthesized and structurally characterized, and their catalytic activity in the (co)polymerization of α-olefins has been studied. The treatment of Ln(CH2SiMe3)3(THF)2 with one equivalent of freshly prepared IBiox afforded the rare-earth metal complexes (IBiox)Ln(CH2SiMe3)3THFn (Ln = Sc (1), n = 0; Y (2), n = 1; and Lu (3), n = 1) in good yields. Single crystal X-ray diffraction study showed that 1 is pseudo tetrahedral, while 2 and 3 are distorted trigonal bipyramidal with coordinated THF...
July 20, 2018: Dalton Transactions: An International Journal of Inorganic Chemistry
Anuj Kumar, Afsana Naaz, A P Prakasham, Manoj Kumar Gangwar, Raymond J Butcher, Dulal Panda, Prasenjit Ghosh
Five enantiomeric pairs of palladium complexes of 1,2,4-triazole-derived chiral N-heterocyclic carbene ligands were investigated to probe the influence of chirality on the compound's anticancer activity. Although no chirality-related influence was observed for any of the enantiomeric pair, strong anticancer activity was seen for a particular pair, (1 S ,2 S ,5 R )- 1c and (1 R ,2 R ,5 S )- 1c , which was significantly more active than the benchmark drug cisplatin for human breast cancer cells, MCF-7 (ca. 24-27-fold), and human cervical cancer cells, HeLa (ca...
August 31, 2017: ACS Omega
Michael Trose, Stuart Burnett, Simon J Bonyhady, Cameron Jones, David B Cordes, Alexandra M Z Slawin, Andreas Stasch
The mixed N-heterocyclic carbene (NHC) complexes NHCAlHxI3-x, where NHC is IDip or IMes ((HCNAr)2C:, Ar = 2,6-iPr2C6H3 = Dip (IDip); or 2,4,6-Me3C6H2 = Mes (IMes)), x = 1 or 2, were either prepared from NHCAlH3 and NHCAlI3 or by halogenation of NHCAlH3 with MeI. Reaction of [(IDip)AlHxI3-x], with x = 0-3, with another equivalent of IDip afforded either fluxional equilibria in benzene solution for x = 0, no reaction for x = 3, or the new mixed normal-abnormal NHC-coordinated ionic complexes [(IDip)AlH2(aIDip)]I (9) and [(IDip)AlHI(aIDip)]I (10), where aIDip is the abnormal IDip carbene tautomer bonded through its 4-position...
July 31, 2018: Dalton Transactions: An International Journal of Inorganic Chemistry
Xiuwen Zhou, Benjamin J Powell
Devices based on deep-blue emitting iridium(III) complexes with N-heterocyclic carbene (NHC) ligands have recently been shown to give excellent performance as phosphorescent organic light-emitting diodes (PHOLEDs). To facilitate the design of even better deep-blue phosphorescent emitters, we carried out density functional theory (DFT) calculations of the lowest triplet (T1 ) potential-energy surfaces upon lengthening the iridium-ligand (Ir-C) bonds. Relativistic time dependent DFT calculations demonstrate that this changes the nature of T1 from a highly emissive metal-to-ligand charge transfer (3 MLCT) state to a metal centered (3 MC) state where the radiative decay rate is orders of magnitude slower than that of the 3 MLCT state...
August 6, 2018: Inorganic Chemistry
Ángela Vivancos, Candela Segarra, Martin Albrecht
Mesoionic carbenes are a subclass of the family of N-heterocyclic carbenes that generally feature less heteroatom stabilization of the carbenic carbon and hence impart specific donor properties and reactivity schemes when coordinated to a transition metal. Therefore, mesoionic carbenes and their complexes have attracted considerable attention both from a fundamental point of view as well as for application in catalysis and beyond. As a follow-up of an earlier Chemical Reviews overview from 2009, the organometallic chemistry of N-heterocyclic carbenes with reduced heteroatom stabilization is compiled for the 2008-2017 period, including specifically the chemistry of complexes containing 1,2,3-triazolylidenes, 4-imidazolylidenes, and related 5-membered N-heterocyclic carbenes with reduced heteratom stabilization such as (is)oxazolylidenes, pyrrazolylidenes, and thiazolylidenes, as well as pyridylidenes as 6-membered N-heterocyclic carbenes with reduced heteroatom stabilization...
July 17, 2018: Chemical Reviews
Jun Cheng, Lijun Wang, Peng Wang, Liang Deng
High-oxidation-state 3d metal species have found a wide range of applications in modern synthetic chemistry and materials science. They are also implicated as key reactive species in biological reactions. These applications have thus prompted explorations of their formation, structure, and properties. While the traditional wisdom regarding these species was gained mainly from complexes supported by nitrogen- and oxygen-donor ligands, recent studies with N-heterocyclic carbenes (NHCs), which are widely used for the preparation of low-oxidation-state transition metal complexes in organometallic chemistry, have led to the preparation of a large variety of isolable high-oxidation-state 3d metal complexes with NHC ligation...
July 16, 2018: Chemical Reviews
Xiaoyu Ren, Marcel Wesolek, Pierre Braunstein
Tritopic NCNHCN' ligands containing a central N-heterocyclic carbene (NHC) donor flanked by two chemically-different nitrogen donors (Nimine and Namine) are evaluated as potential tridentate pincer-type ligands in NiII complexes. The imidazolium chloride [(ImH){C(Me)=NDipp}(C2NMe2)]Cl (1) and the ammonium-imidazolium dichlorides [(ImH){C(Me)=NDipp}(C2NHMe2)]Cl2 (4) and [(ImH){C(Me)=NDipp}(C3NHMe2)]Cl2 (5), differing by the length (C2 or C3) of the alkyl spacer were used as precursors. Oxidative-addition of 1 to [Ni(cod)2] afforded the dinuclear bis-NHC NiII complex [Ni2Cl2{µ-C(Me)=NDipp-κ2Nimine,C}{μ-Im(C2NMe2)-κ3Namine,CNHC,Nimid}{Im[C(Me)=NDipp](C2NMe2)-κ1CNHC}] (2) resulting from partial ligand rearrangement...
July 14, 2018: Chemistry: a European Journal
Wojciech Streciwilk, Alessio Terenzi, Xinlai Cheng, Laura Hager, Yasamin Dabiri, Pascal Prochnow, Julia Elisabeth Bandow, Stefan Wölfl, Bernhard K Keppler, Ingo Ott
Fluorescent 4-ethylthio-1,8-naphthalimides containing rhodium(I) N-heterocyclic carbene (NHC) and ruthenium (II) NHC fragments were synthesised and evaluated for their antiproliferative effects, cellular uptake and DNA-binding activity. Both types of organometallics triggered ligand dependent efficient cytotoxic effects against tumor cells with the rhodium(I) NHC derivatives causing stronger effects than the ruthenium (II) NHC analogues. Antiproliferative effects could also be observed against several pathogenic Gram-positive bacterial strains, whereas the growth of Gram-negative bacteria was not substantially affected...
June 25, 2018: European Journal of Medicinal Chemistry
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