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Journal articles on the topic 'NHC carbene'

Author: Grafiati

Published: 6 September 2023

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1

Mokfi, Moloud, Jörg Rust, Christian W. Lehmann, and Fabian Mohr. "Facile N9-Alkylation of Xanthine Derivatives and Their Use as Precursors for N-Heterocyclic Carbene Complexes." Molecules 26, no. 12 (June 17, 2021): 3705. http://dx.doi.org/10.3390/molecules26123705.

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The xanthine-derivatives 1,3,7-trimethylxanthine, 1,3-dimethyl-7-benzylxanthine and 1,3-dimethyl-7-(4-chlorobenzyl)xanthine are readily ethylated at N9 using the cheap alkylating agents ethyl tosylate or diethyl sulfate. The resulting xanthinium tosylate or ethyl sulfate salts can be converted into the corresponding PF6- and chloride salts. The reaction of these xanthinium salts with silver(I) oxide results in the formation of different silver(I) carbene-complexes. In the presence of ammonia, ammine complexes [Ag(NHC)(NH3)]PF6 are formed, whilst with Et2NH, the bis(carbene) salts [Ag(NHC)2]PF6 were isolated. Using the xanthinium chloride salts neutral silver(I) carbenes [Ag(NHC)Cl] were prepared. These silver complexes were used in a variety of transmetallation reactions to give the corresponding gold(I), ruthenium(II) as well as rhodium(I) and rhodium(III) complexes. The compounds were characterized by various spectroscopic methods as well as X-ray diffraction.

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2

Jutand, Anny, Julien Pytkowicz, Sylvain Roland, and Pierre Mangeney. "Mechanism of the oxidative addition of aryl halides to bis-carbene palladium(0) complexes." Pure and Applied Chemistry 82, no. 7 (May 4, 2010): 1393–402. http://dx.doi.org/10.1351/pac-con-09-09-22.

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Bis-N-heterocyclic carbenes Pd0 complexes, Pd0(NHC)2, are efficient catalysts in Heck reactions performed with aryl bromides or chlorides. The Pd0(NHC)2 that are not stable are generated in situ from PdII precursors PdY2(NHC)2 (Y = halides) after a chemical reduction. The latter procedure can be mimicked by an electrochemical reduction. The transient Pd0(NHCBn)2 is generated by electrochemical reduction of PdY2(NHCBn)2, and its reactivity in oxidative addition to aryl bromides and chlorides is characterized by the same electrochemical technique with the determination of the rate constants. Pd0(NHCBn)2 is found to be more reactive than the mixed complex Pd0(NHCBn)(PPh3). Both are the reactive species in an associative mechanism. Comparison with the isolated Pd0(NHCtBu)2 reveals that Pd0(NHCBn)2 is more reactive than Pd0(NHCtBu)2 even if the latter reacts via the mono-carbene Pd0(NHCtBu) in a dissociative mechanism. This suggests that the formation of mono-carbene Pd0(NHC) is not a guarantee for a fast oxidative addition because it is always generated at low concentration in its equilibrium with the related nonreactive bis-carbene Pd0(NHC)2.

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3

Nonnenmacher, Michael, Dominik M. Buck, and Doris Kunz. "Experimental and theoretical investigations on the high-electron donor character of pyrido-annelated N-heterocyclic carbenes." Beilstein Journal of Organic Chemistry 12 (August 23, 2016): 1884–96. http://dx.doi.org/10.3762/bjoc.12.178.

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Rh(CO)2Cl(NHC) complexes of dipyrido-annelated N-heterocyclic carbenes were prepared. From the C–H coupling constant of the respective imidazolium salts and the N–C–N angle of the N-heterocyclic carbene (NHC), a weaker σ-donor character than that of typical unsaturated NHCs is expected. However, the IR stretching frequencies of their Rh(CO)2Cl complexes suggest an electron-donor character even stronger than that of saturated NHCs. We ascribe this to the extremely weak π-acceptor character of the dipyrido-annelated NHCs caused by the conjugated 14 πe− system that thus allows for an enhanced Rh–CO backbonding. This extremely low π-acceptor ability is also corroborated by the 77Se NMR chemical shift of −55.8 ppm for the respective selenourea, the lowest value ever measured for imidazole derived selenoureas. DFT-calculations of the free carbene confirm the low σ-donor character by the fact that the σ-orbital of the carbene is the HOMO−1 that lies 0.58 eV below the HOMO which is located at the π-system. Natural population analysis reveals the lowest occupation of the pπ-orbital for the saturated carbene carbon atom and the highest for the pyrido-annelated carbene. Going from the free carbene to the Rh(CO)2Cl(NHC) complexes, the increase in occupancy of the complete π-system of the carbene ligand upon coordination is lowest for the pyrido-annelated carbene and highest for the saturated carbene.

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4

Liu, Ming, Jan C. Namyslo, Martin Nieger, Mika Polamo, and Andreas Schmidt. "From betaines to anionic N-heterocyclic carbenes. Borane, gold, rhodium, and nickel complexes starting from an imidazoliumphenolate and its carbene tautomer." Beilstein Journal of Organic Chemistry 12 (December 8, 2016): 2673–81. http://dx.doi.org/10.3762/bjoc.12.264.

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The mesomeric betaine imidazolium-1-ylphenolate forms a borane adduct with tris(pentafluorophenyl)borane by coordination with the phenolate oxygen, whereas its NHC tautomer 1-(2-phenol)imidazol-2-ylidene reacts with (triphenylphosphine)gold(I) chloride to give the cationic NHC complex [Au(NHC)2][Cl] by coordination with the carbene carbon atom. The anionic N-heterocyclic carbene 1-(2-phenolate)imidazol-2-ylidene gives the complexes [K][Au(NHC−)2], [Rh(NHC−)3] and [Ni(NHC−)2], respectively. Results of four single crystal analyses are presented.

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5

Sun, Hongsui, Xiao-Yan Yu, Paolo Marcazzan, Brian O. Patrick, and Brian R. James. "Rhodium(I)–(N-heterocyclic carbene)–diphosphine complexes." Canadian Journal of Chemistry 87, no. 9 (September 2009): 1248–54. http://dx.doi.org/10.1139/v09-118.

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Reactions of [RhCl(COE)(IPr)]2 (1) and [RhCl(COE)(IMes)]2 (2) (COE = cyclooctene; IPr = N,N′-bis(2,6-diisopropylphenyl)imidazolin-2-ylidene; IMes = N,N′-bis(2,4,6-trimethylphenyl)imidazolin-2-ylidene) with the diphosphines Ph2P(CH2)nPPh2 and 1,2-bis(diphenylphosphino)benzene (dppbz) give the N-heterocyclic carbene (NHC) – diphosphine – rhodium(I) complexes: RhCl(NHC)[Ph2P(CH2)nPPh2] [NHC = IPr, n = 1 (3); NHC = IMes, n = 1 (4); NHC = IPr, n = 2 (5); NHC = IMes, n = 2 (6); NHC = IPr, n = 4 (7); NHC = IMes, n = 4 (8)] and RhCl(NHC)(dppbz) [NHC = IPr (9); NHC = IMes (10)]. All the complexes are characterized by 1H, 31P{1H}, and 13C{1H} NMR spectroscopy, elemental analysis, and mass spectrometry. Complexes 3, 7, and 9 are also characterized crystallographically. In benzene solution, the complexes decompose in the presence of O2 with formation of the diphosphine dioxide, whereas reaction with CO leads to replacement of the NHC ligand to give known carbonyl–diphosphine complexes.

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6

Longevial, Jean-François, Mamadou Lo, Aurélien Lebrun, Danielle Laurencin, Sébastien Clément, and Sébastien Richeter. "Molecular complexes and main-chain organometallic polymers based on Janus bis(carbenes) fused to metalloporphyrins." Dalton Transactions 49, no. 21 (2020): 7005–14. http://dx.doi.org/10.1039/d0dt00594k.

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Janus bis(N-heterocyclic carbenes) composed of a porphyrin core with two N-heterocyclic carbene (NHC) heads fused to opposite pyrroles were used as bridging ligands for the preparation of metal complexes.

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7

Rupar, Paul A., Michael C. Jennings, and Kim M. Baines. "The reactivity of an anionic gallium N-heterocyclic carbene analogue with a solution stable digermene." Canadian Journal of Chemistry 85, no. 2 (February 1, 2007): 141–47. http://dx.doi.org/10.1139/v07-002.

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The reaction of the anionic gallium(I) N-heterocyclic carbene (NHC) analogue 3 with the solution stable digermene 5 results in the formation of the gallium NHC – germylene complex 8. The gallium NHC – germylene complex 8 was derivatized with CH3I and (CH3)3SiCl.Key words: digermene, carbene analogue, germylene, gallium(I).

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8

Hock, Andreas, Luis Werner, Christian Luz, and Udo Radius. "N-Heterocyclic carbene and cyclic (alkyl)(amino)carbene adducts of gallium hydrides, gallium chlorides and gallium hydrochlorides." Dalton Transactions 49, no. 32 (2020): 11108–19. http://dx.doi.org/10.1039/d0dt02070b.

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A detailed study on the synthesis and characterization of NHC gallane adducts (NHC)·GaH₃, (NHC)·GaH₂Cl, and (NHC)·GaHCl₂ and the reactivity of these adducts with the cyclic (alkyl)(amino)carbene cAAC^Me is presented.

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9

Ojha, Minita, Shweta Choudhary, and Raj K. Bansal. "3-Benzylbenzothiazolylidene Carbene Catalyzed Isomerization of Dimethyl Maleate to Dimethyl Fumarate: Experimental and Theoretical Results." Current Organocatalysis 7, no. 2 (July 2, 2020): 108–17. http://dx.doi.org/10.2174/2213337206666191018111354.

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Background: N-Heterocyclic Carbenes (NHCs) have emerged as ubiquitous species having applications in a broad range of fields, including organocatalysis and organometallic chemistry. Since Arduengo and co-workers first isolated a bottlable NHC, namely imidazol-2-ylidene derivative, these nucleophilic species have attained a prominent place in synthetic organic chemistry. The NHC-induced non-asymmetric catalysis has turned out to be a really fruitful area of research in recent years. Methods and Results: The quantitative aspects of the experimental and theoretical investigation of isomerization of dimethyl maleate to dimethyl fumarate catalyzed by an N-heterocyclic carbene (NHC), namely 3-benzylbenzothiazolylidene are being reported for the first time. Dimethyl maleate on treating with 3-benzylbenzothiazolylidene carbene (10 mol%), generated in situ from the reaction of 3- benzylbenzothiazolium bromide with triethylamine in diethyl ether at room temperature under nitrogen atmosphere isomerizes quantitatively to dimethyl fumarate. Theoretical investigation of a model reaction scheme at the wB97XD/6-31+G(d) level reveals that initial attack of the carbene, which is the ratedetermining step, is followed by rotation about the C-C bond in preference to a higher activation free energy path involving proton abstraction. The species so formed splits off the carbene to yield dimethyl fumarate. Eyring equation has been used to rationalize the effect of temperature on the isomerization rate. Conclusions and Perspective: 3-Benzylbenzothiazolylidene carbene catalyzes the isomerization of dimethyl maleate to its trans-isomer. This carbene can be used in other catalytic reactions, such as acyloin condensation and Stetter reaction.

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10

Kelemen, Z., R. Streubel, and L. Nyulászi. "Zwitterionic carbene adducts and their carbene isomers." RSC Advances 5, no. 52 (2015): 41795–802. http://dx.doi.org/10.1039/c5ra07039b.

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11

Zhu, Tingshun, Ke Xu, and Ziyuan Wang. "N-Heterocyclic Carbene-Organocatalyzed Arene Formation: Application in Atroposelective Synthesis of Polysubstituted Benzenes." Synlett 31, no. 10 (February 3, 2020): 925–32. http://dx.doi.org/10.1055/s-0039-1690814.

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In recent decades, organocatalysis by N-heterocyclic carbenes (NHCs) has emerged as a versatile and powerful method in organic synthesis. As a result of the power of NHC organocatalysis to produce cyclic compounds, polysubstituted benzenes, which are among the most important cyclic compounds in organic chemistry, can be synthesized efficiently and selectively. This article briefly summarizes the history of NHC organocatalysis, including recent developments in benzene-formation methods, and highlights our recent work in atroposelective arene formation by carbene-catalyzed formal [4+2] cycloadditions. We expect that more NHC-catalyzed methods for the synthesis of asymmetric arenes will be developed in the near future, providing shortcuts to syntheses of sophisticated chiral functional molecules with polysubstituted benzene nuclei.

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12

Jacobsen, Heiko, Andrea Correa, Albert Poater, Chiara Costabile, and Luigi Cavallo. "Understanding the M(NHC) (NHC=N-heterocyclic carbene) bond." Coordination Chemistry Reviews 253, no. 5-6 (March 2009): 687–703. http://dx.doi.org/10.1016/j.ccr.2008.06.006.

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13

Zhang, Dongxiang, Jie Li, Xiao Dong, Xing Zhou, Zhi Yang, and Herbert W. Roesky. "N-Heterocyclic Carbene-facilated Condensation of 3-Methylphenylboronic Acid to the Boroxine." Zeitschrift für Naturforschung B 68, no. 5-6 (June 1, 2013): 453–57. http://dx.doi.org/10.5560/znb.2013-2342.

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The adduct of (3-MeC6H4)3B3O3 with an N-heterocyclic carbene (NHC=1,3-diethyl-4,5- dimethylimidazol-2-ylidene) was prepared by reacting 2.5 equiv. of 3-methylphenylboronic acid with 1 equiv. of the NHC. This reaction shows a novel carbene-facilitated condensation of substituted phenylboronic acid monomers. The structure of the compound (3-MeC6H4)3B3O3(NHC) (1) has been characterized by 1H NMR spectroscopy, elemental analysis, and single-crystal X-ray diffraction studies

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14

Jahnke, Mareike C., Tania Pape, and F. Ekkehardt Hahn. "Ligand Exchange at a Gold(I) Carbene Complex." Zeitschrift für Naturforschung B 68, no. 5-6 (June 1, 2013): 467–73. http://dx.doi.org/10.5560/znb.2013-3076.

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Gold complex [AuCl(NHC)] (NHC=N,N0-dipropylbenzimidazolin-2-ylidene) 1 undergoes facile substitution reactions at the gold(I) center. Treatment of 1 with anionic phenylacetylide or thiophenolate led to the neutral gold complexes 2 and 3, respectively. The cationic gold complexes [Au(NHC)(pyridine)](BF4) [4]BF4 and [Au2(NHC)2(4,4'-bipyridine)](BF4)2 [5](BF4)2 were obtained via abstraction of the chloro ligand from 1 and reaction with the appropriate amine. Reaction of 1 with AgBF4 in the presence of PPh3 instead of an amine led to an inseparable product mixture of the mixed NHC=PPh3 complex [6]BF4, the dicarbene complex [Au(NHC)2]BF4, [7]BF4, and [Au(PPh3)2]BF4, [8]BF4. Crystals of 2 and [6]BF4 were obtained, and X-ray diffraction structure analyses revealed that the gold(I) atoms are coordinated in a linear fashion by the NHC and the co-ligand

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15

Azpíroz, Ramón, Mert Olgun Karataş, Vincenzo Passarelli, Ismail Özdemir, Jesús J. Pérez-Torrente, and Ricardo Castarlenas. "Preparation of Mixed Bis-N-Heterocyclic Carbene Rhodium(I) Complexes." Molecules 27, no. 20 (October 18, 2022): 7002. http://dx.doi.org/10.3390/molecules27207002.

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A series of mixed bis-NHC rhodium(I) complexes of type RhCl(η2-olefin)(NHC)(NHC’) have been synthesized by a stepwise reaction of [Rh(μ-Cl)(η2-olefin)2]2 with two different NHCs (NHC = N-heterocyclic carbene), in which the steric hindrance of both NHC ligands and the η2-olefin is critical. Similarly, new mixed coumarin-functionalized bis-NHC rhodium complexes have been prepared by a reaction of mono NHC complexes of type RhCl(NHC-coumarin)(η2,η2-cod) with the corresponding azolium salt in the presence of an external base. Both synthetic procedures proceed selectively and allow the preparation of mixed bis-NHC rhodium complexes in good yields.

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16

Rey, Yannick P., and Ryan Gilmour. "Modulating NHC catalysis with fluorine." Beilstein Journal of Organic Chemistry 9 (December 6, 2013): 2812–20. http://dx.doi.org/10.3762/bjoc.9.316.

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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 β-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).

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17

Haslinger, S., A. C. Lindhorst, J. W. Kück, M. Cokoja, A. Pöthig, and F. E. Kühn. "Isocyanide substitution reactions at the trans labile sites of an iron(ii) N-heterocyclic carbene complex." RSC Advances 5, no. 104 (2015): 85486–93. http://dx.doi.org/10.1039/c5ra18270k.

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A variety of isocyanide-substituted Fe(ii) N-heterocyclic carbene (NHC) complexes has been synthesized, starting from an Fe(ii) NHC complex with an equatorial, tetradentate bis(pyridyl-NHC) ligand (NCCN).

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18

Li, Jie, Jiaqi Yao, Weiping He, Fan Yang, and Xiaoming Liu. "Modular Synthesis of New Bicyclic Carbene Precursors." Letters in Organic Chemistry 16, no. 12 (October 9, 2019): 951–54. http://dx.doi.org/10.2174/1570178616666190212125426.

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: A series of new N-heterocyclic carbene (NHC) precursors, containing bicyclic pyrrolo[1,2- c]imidazole framework, were prepared from N-(tert-butoxycarbonyl)-L-proline (1-Boc-L-proline). The sequential attachment of nitrogen nucleophiles and subsequent ring closure gave the desired bicyclic NHC precursors in good yields. The structures of these new NHC precursors were determined on the basis of spectroscopic techniques, including NMR and MS.

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19

Wang, Yu-Ting, Bin-Bin Gao, Fan Wang, Shi-Yuan Liu, Hong Yu, Wen-Hua Zhang, and Jian-Ping Lang. "Palladium(ii) and palladium(ii)–silver(i) complexes with N-heterocyclic carbene and zwitterionic thiolate mixed ligands: synthesis, structural characterization and catalytic properties." Dalton Transactions 46, no. 6 (2017): 1832–39. http://dx.doi.org/10.1039/c6dt04599e.

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20

Buchspies, Jonathan, Md Mahbubur Rahman, and Michal Szostak. "Suzuki–Miyaura Cross-Coupling of Amides Using Well-Defined, Air- and Moisture-Stable Nickel/NHC (NHC = N-Heterocyclic Carbene) Complexes." Catalysts 10, no. 4 (March 31, 2020): 372. http://dx.doi.org/10.3390/catal10040372.

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In this Special Issue on N-Heterocyclic Carbenes and Their Complexes in Catalysis, we report the first example of Suzuki–Miyaura cross-coupling of amides catalyzed by well-defined, air- and moisture-stable nickel/NHC (NHC = N-heterocyclic carbene) complexes. The selective amide bond N–C(O) activation is achieved by half-sandwich, cyclopentadienyl [CpNi(NHC)Cl] complexes. The following order of reactivity of NHC ligands has been found: IPr > IMes > IPaul ≈ IPr*. Both the neutral and the cationic complexes are efficient catalysts for the Suzuki–Miyaura cross-coupling of amides. Kinetic studies demonstrate that the reactions are complete in < 1 h at 80 °C. Complete selectivity for the cleavage of exocyclic N-acyl bond has been observed under the experimental conditions. Given the utility of nickel catalysis in activating unreactive bonds, we believe that well-defined and bench-stable [CpNi(NHC)Cl] complexes will find broad application in amide bond and related cross-couplings of bench-stable acyl-electrophiles.

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21

Zhang, Guowen, Man Chao, Shuting Wang, Mengxia Zhu, Dou Wang, Guangsheng Pang, and Yanhui Shi. "Synthesis and Catalytic Activity of Chiral Dicarbene Dipalladium Complexes Incorporating the S-binaphthol Unit." Journal of Chemical Research 42, no. 1 (January 2018): 54–56. http://dx.doi.org/10.3184/174751918x15168768395864.

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A series of chiral di-N-heterocyclic carbene (NHC) dipalladium complexes, [{PdPyCl2}2(di-NHC)], in which di-NHC represents a di-imidazolylidene, featuring an (S)-3,3′-dimethyl-2,2′-dimethoxy-1,1′-binaphthalene spacer between the carbene units, have been prepared. The influence of ligand size on the catalytic activity of these complexes in the Suzuki reaction of phenylboronic acid with p-bromotoluene has been investigated. The most sterically hindered complex, bearing the di-isopropylphenyl group, showed the greatest catalytic activity, and it is active for various aryl halides with different electronic and steric properties.

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22

Duan, Yulian, Tao Wang, Qingxiao Xie, Xiaobo Yu, Weijie Guo, Jianhui Wang, and Guiyan Liu. "Highly efficient nitrogen chelated ruthenium carbene metathesis catalysts." Dalton Transactions 45, no. 48 (2016): 19441–48. http://dx.doi.org/10.1039/c6dt03899a.

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23

Boubakri, L., S. Yasar, V. Dorcet, T. Roisnel, C. Bruneau, N. Hamdi, and I. Ozdemir. "Synthesis and catalytic applications of palladium N-heterocyclic carbene complexes as efficient pre-catalysts for Suzuki–Miyaura and Sonogashira coupling reactions." New Journal of Chemistry 41, no. 12 (2017): 5105–13. http://dx.doi.org/10.1039/c7nj00488e.

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A new palladium complex series with N-heterocyclic carbene (NHC), pyridine and phosphine ligands, PdCl₂(L)NHC (2a–c)(L = NHC), PdCl₂(L¹)NHC(3a–c)(L¹ = pyridine), PdCl₂(L²)NHC(4a–c)(L² = triphenylphosphine) was synthesised and fully characterized.

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24

Köppe, R., and H. Schnöckel. "The boron–boron triple bond? A thermodynamic and force field based interpretation of the N-heterocyclic carbene (NHC) stabilization procedure." Chemical Science 6, no. 2 (2015): 1199–205. http://dx.doi.org/10.1039/c4sc02997f.

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From thermodynamic and force constant discussion a new description of bonding of B₂(NHC)₂ (NHC = N-heterocyclic carbene C₃N₂H₂(C₆H₃Prⁱ₂-2,6)₂) as NHCBBNHC rather than NHC→BB←NHC is given.

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25

Roy, Matthew M. D., Michael J. Ferguson, Robert McDonald, and Eric Rivard. "Approaching monocoordination at a silver(i) cation." Chemical Communications 54, no. 5 (2018): 483–86. http://dx.doi.org/10.1039/c7cc08418h.

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26

Dhara, Debabrata, Pankaj Kalita, Subhadip Mondal, Ramakirushnan Suriya Narayanan, Kaustubh R. Mote, Volker Huch, Michael Zimmer, et al. "Reactivity enhancement of a diphosphene by reversible N-heterocyclic carbene coordination." Chemical Science 9, no. 18 (2018): 4235–43. http://dx.doi.org/10.1039/c8sc00348c.

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27

Lewis-Alleyne, Lesley C., Bassem S. Bassil, Tobias Böttcher, and Gerd-Volker Röschenthaler. "Selective synthesis of cis- and trans-[(NHCMe)2PtCl2] and [NHCMePt(cod)Cl][NHCMePtCl3] using NHCMeSiCl4." Dalton Trans. 43, no. 42 (2014): 15700–15703. http://dx.doi.org/10.1039/c4dt02214a.

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NHC^MeSiCl₄ was used to selectively synthesise cis and trans-[(NHC^Me)₂PtCl₂], as well as [NHC^MePt(cod)Cl][NHC^MePtCl₃], which revealed the first ever N-heterocyclic carbene analogue of the Cossa's salt anion.

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28

Yang, Longhua, Yanli Yuan, Hongming Wang, Ning Zhang, and Sanguo Hong. "Theoretical insights into copper(i)–NHC-catalyzed C–H carboxylation of terminal alkynes with CO2: the reaction mechanisms and the roles of NHC." RSC Adv. 4, no. 61 (2014): 32457–66. http://dx.doi.org/10.1039/c4ra00254g.

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29

Prencipe, Filippo, Anna Zanfardino, Michela Di Napoli, Filomena Rossi, Stefano D’Errico, Gennaro Piccialli, Giuseppe Felice Mangiatordi, et al. "Silver (I) N-Heterocyclic Carbene Complexes: A Winning and Broad Spectrum of Antimicrobial Properties." International Journal of Molecular Sciences 22, no. 5 (March 2, 2021): 2497. http://dx.doi.org/10.3390/ijms22052497.

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The evolution of antibacterial resistance has arisen as the main downside in fighting bacterial infections pushing researchers to develop novel, more potent and multimodal alternative drugs.Silver and its complexes have long been used as antimicrobial agents in medicine due to the lack of silver resistance and the effectiveness at low concentration as well as to their low toxicities compared to the most commonly used antibiotics. N-Heterocyclic Carbenes (NHCs) have been extensively employed to coordinate transition metals mainly for catalytic chemistry. However, more recently, NHC ligands have been applied as carrier molecules for metals in anticancer applications. In the present study we selected from literature two NHC-carbene based on acridinescaffoldand detailed nonclassicalpyrazole derived mono NHC-Ag neutral and bis NHC-Ag cationic complexes. Their inhibitor effect on bacterial strains Gram-negative and positivewas evaluated. Imidazolium NHC silver complex containing the acridine chromophore showed effectiveness at extremely low MIC values. Although pyrazole NHC silver complexes are less active than the acridine NHC-silver, they represent the first example of this class of compounds with antimicrobial properties. Moreover all complexesare not toxic and they show not significant activity againstmammalian cells (Hek lines) after 4 and 24 h. Based on our experimental evidence, we are confident that this promising class of complexes could represent a valuable starting point for developing candidates for the treatment of bacterial infections, delivering great effectiveness and avoiding the development of resistance mechanisms.

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30

Raed, Anas Abo, Vasudevan Dhayalan, Shahar Barkai, and Anat Milo. "N-Heterocyclic Carbene Triazolium Salts Containing Brominated Aromatic Motifs: Features and Synthetic Protocol." CHIMIA International Journal for Chemistry 74, no. 11 (November 25, 2020): 878–82. http://dx.doi.org/10.2533/chimia.2020.878.

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In this work, we provide a brief overview of the role of N-aryl substituents on triazolium N-heterocyclic carbene (NHC) catalysis. This synopsis provides context for the disclosed synthetic protocol for new chiral N-heterocyclic carbene (NHC) triazolium salts with brominated aromatic motifs. Incorporating brominated aryl rings into NHC structures is challenging, probably due to the substantial steric and electronic influence these substituents exert throughout the synthetic protocol. However, these exact characteristics make it an interesting N-aryl substituent, because the electronic and steric diversity it offers could find broad use in organometallic- and organo-catalysis. Following the synthetic reaction by NMR guided the extensive modification of a known protocol to enable the preparation of these challenging NHC pre-catalysts.

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31

Beil, Andreas, Robert J. Gilliard, and Hansjörg Grützmacher. "From the parent phosphinidene–carbene adduct NHCPH to cationic P4-rings and P2-cycloaddition products." Dalton Transactions 45, no. 5 (2016): 2044–52. http://dx.doi.org/10.1039/c5dt03014e.

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The parent phosphinidene–carbene adduct NHCPH reacts with chlorophosphanes yielding NHC-supported chlorodiphosphanes, which can be transformed to novel P₄-rings and reactive 1,2-diphosphenes.

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32

Zhang, Bo, Yu’ai Duan, Xin Zhang, and Shuai Guo. "Uncommon carbene-to-azole ligand rearrangement of N-heterocyclic carbenes in a ruthenium system." Chemical Communications 57, no. 56 (2021): 6879–82. http://dx.doi.org/10.1039/d1cc01871j.

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33

Cingolani, Andrea, Cristiana Cesari, Stefano Zacchini, Valerio Zanotti, Maria Cristina Cassani, and Rita Mazzoni. "Straightforward synthesis of iron cyclopentadienone N-heterocyclic carbene complexes." Dalton Transactions 44, no. 44 (2015): 19063–67. http://dx.doi.org/10.1039/c5dt03071d.

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34

Furst, Marc R. L., and Catherine S. J. Cazin. "Copper N-heterocyclic carbene (NHC) complexes as carbene transfer reagents." Chemical Communications 46, no. 37 (2010): 6924. http://dx.doi.org/10.1039/c0cc02308f.

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35

Cesari, C., S. Conti, S. Zacchini, V. Zanotti, M. C. Cassani, and R. Mazzoni. "Sterically driven synthesis of ruthenium and ruthenium–silver N-heterocyclic carbene complexes." Dalton Trans. 43, no. 46 (2014): 17240–43. http://dx.doi.org/10.1039/c4dt02747g.

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36

Bélanger-Bouliga, Marilyne, Raja Mahious, Poulomsongo Iman Pitroipa, and Ali Nazemi. "Perylene diimide-tagged N-heterocyclic carbene-stabilized gold nanoparticles: How much ligand desorbs from surface in presence of thiols?" Dalton Transactions 50, no. 16 (2021): 5598–606. http://dx.doi.org/10.1039/d1dt00064k.

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Fluorescence restoration in perylene diimide–gold nanoparticle hybrids, stabilized by N-heterocyclic carbene (NHC) ligands, in presence of thiols is used to quantify the extent of NHC displacement from gold surface.

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37

Babaee, Saeed, Mahmoud Zarei, and Mohammad Ali Zolfigol. "MOF-Zn-NHC as an efficient N-heterocyclic carbene catalyst for aerobic oxidation of aldehydes to their corresponding carboxylic acids via a cooperative geminal anomeric based oxidation." RSC Advances 11, no. 57 (2021): 36230–36. http://dx.doi.org/10.1039/d1ra05494e.

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As an efficient heterogenous N-heterocyclic carbene (NHC) catalyst, MOF-Zn-NHC was used in the aerobic oxidation of aryl aldehydes to their corresponding carbocyclic acids via an anomeric based oxidation.

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38

Tegeder, Patricia, Marcello Marelli, Matthias Freitag, Laura Polito, Sebastian Lamping, Rinaldo Psaro, Frank Glorius, Bart Jan Ravoo, and Claudio Evangelisti. "Metal vapor synthesis of ultrasmall Pd nanoparticles functionalized with N-heterocyclic carbenes." Dalton Transactions 47, no. 36 (2018): 12647–51. http://dx.doi.org/10.1039/c8dt02535e.

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The synthesis of N-heterocyclic carbene (NHC)-stabilized palladium nanoparticles (PdNPs) by an entirely new strategy comprising the NHC functionalization of ligand-free PdNPs obtained by metal vapor synthesis is described.

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39

Majhi, Paresh Kumar, Keith C. F. Chow, Tom H. H. Hsieh, Eric G. Bowes, Gregor Schnakenburg, Pierre Kennepohl, Rainer Streubel, and Derek P. Gates. "Even the normal is abnormal: N-heterocyclic carbene C2 binding to a phosphaalkene without breaking the PC π-bond." Chemical Communications 52, no. 5 (2016): 998–1001. http://dx.doi.org/10.1039/c5cc08181e.

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40

Kearney, Lauren, Michael P. Brandon, Andrew Coleman, Ann M. Chippindale, František Hartl, Ralte Lalrempuia, Martin Pižl, and Mary T. Pryce. "Ligand−Structure Effects on N−Heterocyclic Carbene Rhenium Photo− and Electrocatalysts of CO2 Reduction." Molecules 28, no. 10 (May 17, 2023): 4149. http://dx.doi.org/10.3390/molecules28104149.

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Three novel rhenium N−heterocyclic carbene complexes, [Re]−NHC−1−3 ([Re] = fac−Re(CO)3Br), were synthesized and characterized using a range of spectroscopic techniques. Photophysical, electrochemical and spectroelectrochemical studies were carried out to probe the properties of these organometallic compounds. Re−NHC−1 and Re−NHC−2 bear a phenanthrene backbone on an imidazole (NHC) ring, coordinating to Re by both the carbene C and a pyridyl group attached to one of the imidazole nitrogen atoms. Re−NHC−2 differs from Re−NHC−1 by replacing N−H with an N−benzyl group as the second substituent on imidazole. The replacement of the phenanthrene backbone in Re−NHC−2 with the larger pyrene gives Re−NHC−3. The two−electron electrochemical reductions of Re−NHC−2 and Re−NHC−3 result in the formation of the five−coordinate anions that are capable of electrocatalytic CO2 reduction. These catalysts are formed first at the initial cathodic wave R1, and then, ultimately, via the reduction of Re−Re bound dimer intermediates at the second cathodic wave R2. All three Re−NHC−1−3 complexes are active photocatalysts for the transformation of CO2 to CO, with the most photostable complex, Re−NHC−3, being the most effective for this conversion. Re−NHC−1 and Re−NHC−2 afforded modest CO turnover numbers (TONs), following irradiation at 355 nm, but were inactive at the longer irradiation wavelength of 470 nm. In contrast, Re−NHC−3, when photoexcited at 470 nm, yielded the highest TON in this study, but remained inactive at 355 nm. The luminescence spectrum of Re−NHC−3 is red−shifted compared to those of Re−NHC−1 and Re−NHC−2, and previously reported similar [Re]−NHC complexes. This observation, together with TD−DFT calculations, suggests that the nature of the lowest−energy optical excitation for Re−NHC−3 has π→π*(NHC−pyrene) and dπ(Re)→π*(pyridine) (IL/MLCT) character. The stability and superior photocatalytic performance of Re−NHC−3 are attributed to the extended conjugation of the π−electron system, leading to the beneficial modulation of the strongly electron−donating tendency of the NHC group.

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41

Cicač-Hudi, M., S. H. Schlindwein, C. M. Feil, M. Nieger, and D. Gudat. "Isolable N-heterocyclic carbene adducts of the elusive diiodophosphine." Chemical Communications 54, no. 55 (2018): 7645–48. http://dx.doi.org/10.1039/c8cc03972k.

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42

Gómez-Suárez, Adrián, Rubén S. Ramón, Alexandra M. Z. Slawin, and Steven P. Nolan. "Synthetic routes to [Au(NHC)(OH)] (NHC = N-heterocyclic carbene) complexes." Dalton Transactions 41, no. 18 (2012): 5461. http://dx.doi.org/10.1039/c2dt30294b.

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43

Beig, Nosheen, Varsha Goyal, Raakhi Gupta, and Raj K. Bansal. "N-Heterocyclic Carbenes–CuI Complexes as Catalysts: A Theoretical Insight." Australian Journal of Chemistry 74, no. 7 (2021): 503. http://dx.doi.org/10.1071/ch20332.

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The electronic structures of N-heterocyclic carbenes (NHC) imidazolinylidene, thiazolinylidene, imidazolylidene, thiazolylidene, and 1,2,4-triazolylidene and their complexes with cuprous halides (CuX, X=Cl, Br, I) were investigated theoretically at the B3LYP/def2-SVP level. In contrast to other NHCs, imidazolylidene and 1,2,4-triazolylidene do not dimerize owing to the negligible coefficient of the vacant p-orbital at the carbene centre in their respective LUMOs. This is further supported by their greater thermodynamic and kinetic stabilities revealed by greater activation free energies and smaller standard free energies for their dimerization. Second-order perturbation interactions in the natural bond orbital (NBO) analysis of the NHCs indicate that six π electrons are delocalized in imidazolylidene, thiazolylidene, and 1,2,4-triazolylidene, conferring aromatic character and thereby enhancing their thermodynamic stability. NBO analysis reveals the existence of effective back bonding from a d orbital of Cu to the NHC, increasing the Wiberg bond index of the C–Cu bond to ~1.5. Owing to the large electronic chemical potential (μ) and high nucleophilicity indices, NHCs are able to transfer their electron density effectively to the cuprous halides having low μ values and high electrophilicity indices to yield stable NHC–CuI complexes. Large values of the Fukui function f(r) at the carbene centre of the NHCs and Cu atom of the NHC–CuI complexes indicate their softness. Imidazolylidene was found to be the softest, rationalizing wide use of this class of NHCs as ligands. The coordination of the NHCs to cuprous halides is either barrierless or has a very low activation free energy barrier. In the A3 reaction wherein NHC–Cu(I) complexes are used as catalyst, the reaction of NHC–CuI with phenylacetylene changes the latter into acetylide accompanied by raising the energy level of its HOMO considerably compared with the level of the uncomplexed alkyne, making its reaction with benzaldehyde barrierless.

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44

Yamamoto, Carlos D., Zijie Zhang, and Sabine Chantal E. Stieber. "Crystal structure of (η4-cyclooctadiene)(3,3′-dimesityl-1,1′-methylenediimidazoline-2,2′-diylidene)nickel(0) tetrahydrofuran monosolvate." Acta Crystallographica Section E Crystallographic Communications 74, no. 10 (September 7, 2018): 1396–99. http://dx.doi.org/10.1107/s2056989018012252.

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The crystal structure of the title compound, [Ni(C25H28N4)(C8H12)]·C4H8O or (MesNHC2Me)Ni(COD), which contains a bidentate N-heterocyclic carbene (NHC) ligand with mesityl aryl groups is reported. The complex at 100 K has monoclinic (P21/c) symmetry and a distorted tetrahedral geometry around the nickel center, with the cyclooctadiene ligand coordinated in a κ2,η2 fashion. The bidentate NHC ligand is not planar, with a C(carbene)—Ni—C(carbene) angle of 91.51 (12)°, resulting in the mesityl groups being on the same side of the cyclooctadiene (COD) ligand. One molecule of tetrahydrofuran (THF) is co-crystallized with the nickel complex and has positional disorder.

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45

Collado, Alba, Scott R. Patrick, Danila Gasperini, Sebastien Meiries, and Steven P. Nolan. "Influence of bulky yet flexible N-heterocyclic carbene ligands in gold catalysis." Beilstein Journal of Organic Chemistry 11 (October 2, 2015): 1809–14. http://dx.doi.org/10.3762/bjoc.11.196.

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Three new Au(I) complexes of the formula [Au(NHC)(NTf2)] (NHC = N-heterocyclic carbene) bearing bulky and flexible ligands have been synthesised. The ligands studied are IPent, IHept and INon which belong to the ‘ITent’ (‘Tent’ for ‘tentacular’) family of NHC derivatives. The effect of these ligands in gold-promoted transformations has been investigated.

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46

Frisch, Philipp, and Shigeyoshi Inoue. "NHC-stabilized silyl-substituted silyliumylidene ions." Dalton Transactions 48, no. 28 (2019): 10403–6. http://dx.doi.org/10.1039/c9dt02010a.

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47

Tang, Xiang-Ting, Fan Yang, Ting-Ting Zhang, Yi-Fan Liu, Si-Yu Liu, Tong-Fu Su, Dong-Can Lv, and Wen-Bo Shen. "Recent Progress in N-Heterocyclic Carbene Gold-Catalyzed Reactions of Alkynes Involving Oxidation/Amination/Cycloaddition." Catalysts 10, no. 3 (March 20, 2020): 350. http://dx.doi.org/10.3390/catal10030350.

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Recent rapid development in homogeneous gold catalysis affords an alternative and particularly thriving strategy for the generation of gold carbenes through gold-catalyzed oxidation/amination/cycloaddition of alkynes, while it avoids the employment of hazardous and potentially explosive diazo compounds as starting materials for carbene generation. In addition to facile and secure operation, gold carbenes generated in this strategy display good chemoselectivity distinct from other metal carbenes produced from the related diazo approach. N-heterocyclic carbene (NHC) gold is a special metal complex that can be used as ancillary ligands, which provides enhanced stability and can also act as an efficient chiral directing group. In this review, we will present an overview of these recent advances in alkyne oxidation/amination/cycloaddition by highlighting their specificity and applicability, aiming to facilitate progress in this very exciting area of research.

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48

Iannuzzi, Theresa E., Yafei Gao, Tessa M. Baker, Liang Deng, and Michael L. Neidig. "Magnetic circular dichroism and density functional theory studies of electronic structure and bonding in cobalt(ii)–N-heterocyclic carbene complexes." Dalton Transactions 46, no. 39 (2017): 13290–99. http://dx.doi.org/10.1039/c7dt01748k.

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The combination of simple cobalt salts and N-heterocyclic carbene (NHC) ligands has been highly effective in C–H functionalization, hydroarylation and cross-coupling catalysis, though displaying a strong dependence on the identity of the NHC ligand.

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49

Bauer, Elisabeth B., Marco A. Bernd, Max Schütz, Jens Oberkofler, Alexander Pöthig, Robert M. Reich, and Fritz E. Kühn. "Synthesis, characterization, and biological studies of multidentate gold(i) and gold(iii) NHC complexes." Dalton Transactions 48, no. 44 (2019): 16615–25. http://dx.doi.org/10.1039/c9dt03183a.

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The synthesis and characterization of a novel macrocyclic Au(iii) N-heterocyclic carbene (NHC) complex, a novel macrocyclic tetra-NHC benzimidazole ligand, and the corresponding Ag(i) and Au(i) complexes and initial biological studies are presented.

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50

Wang, Weiran, Hongyu Guo, and Richard A. Jones. "Synthesis and electropolymerization of N-heterocyclic carbene complexes of Pd(ii) and Pt(ii) from an emissive imidazolium salt with a terthiophene backbone." Dalton Transactions 48, no. 38 (2019): 14440–49. http://dx.doi.org/10.1039/c9dt03363g.

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The synthesis of an emissive terthiophene-based imidazolium iodide as the corresponding N-heterocyclic carbene (NHC) preligand (4), and its Pd and Pt–NHC complexes (5a, 5b), along with their electropolymerized electrochromic polymers (P1–3) are reported.

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