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Journal articles on the topic 'NHC ligands'

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Author: Grafiati

Published: 4 June 2021

Last updated: 11 February 2022

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1

Rais, Eduard, Ulrich Flörke, and René Wilhelm. "Crystal structures of diiodidobis[(1S,5S)-4-mesityl-1,2,8,8-tetramethyl-2,4-diazabicyclo[3.2.1]octan-3-ylidene-κC3]palladium(IV) and dichlorido[(1S,5S)-4-mesityl-1,2,8,8-tetramethyl-2,4-diazabicyclo[3.2.1]octan-3-ylidene-κC3](triphenylphosphane-κP)palladium(IV)." Acta Crystallographica Section E Crystallographic Communications 71, no. 8 (July 11, 2015): 919–22. http://dx.doi.org/10.1107/s2056989015013055.

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The molecular structures of the chiral title compounds, [Pd(C19H28N2)2I2], (I), and [Pd(C19H28N2)Cl2(C18H15P)], (II), show a distorted square-planar coordination around the PdIIatoms with two halogenide (Hal) ligands each and two N-heterocyclic carbene (NHC) ligands in (I) or one NHC and one triphenylphosphane ligand in (II). The deviations of the PdIIatoms from theL2Hal2best plane (L= NHC or triphenylphosphane ligand) are 0.206 (1) Å for (I) and 0.052 (1) Å for (II). The crystal packings exhibit intermolecular C—H...Hal hydrogen bonds.

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2

Suresh, Lakshmi, Ralte Lalrempuia, Jonas B. Ekeli, Francis Gillis-D’Hamers, Karl W. Törnroos, Vidar R. Jensen, and Erwan Le Roux. "Unsaturated and Benzannulated N-Heterocyclic Carbene Complexes of Titanium and Hafnium: Impact on Catalysts Structure and Performance in Copolymerization of Cyclohexene Oxide with CO2." Molecules 25, no. 19 (September 23, 2020): 4364. http://dx.doi.org/10.3390/molecules25194364.

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Tridentate, bis-phenolate N-heterocyclic carbenes (NHCs) are among the ligands giving the most selective and active group 4-based catalysts for the copolymerization of cyclohexene oxide (CHO) with CO2. In particular, ligands based on imidazolidin-2-ylidene (saturated NHC) moieties have given catalysts which exclusively form polycarbonate in moderate-to-high yields even under low CO2 pressure and at low copolymerization temperatures. Here, to evaluate the influence of the NHC moiety on the molecular structure of the catalyst and its performance in copolymerization, we extend this chemistry by synthesizing and characterizing titanium complexes bearing tridentate bis-phenolate imidazol-2-ylidene (unsaturated NHC) and benzimidazol-2-ylidene (benzannulated NHC) ligands. The electronic properties of the ligands and the nature of their bonds to titanium are studied using density functional theory (DFT) and natural bond orbital (NBO) analysis. The metal–NHC bond distances and bond strengths are governed by ligand-to-metal σ- and π-donation, whereas back-donation directly from the metal to the NHC ligand seems to be less important. The NHC π-acceptor orbitals are still involved in bonding, as they interact with THF and isopropoxide oxygen lone-pair donor orbitals. The new complexes are, when combined with [PPN]Cl co-catalyst, selective in polycarbonate formation. The highest activity, albeit lower than that of the previously reported Ti catalysts based on saturated NHC, was obtained with the benzannulated NHC-Ti catalyst. Attempts to synthesize unsaturated and benzannulated NHC analogues based on Hf invariably led, as in earlier work with Zr, to a mixture of products that include zwitterionic and homoleptic complexes. However, the benzannulated NHC-Hf complexes were obtained as the major products, allowing for isolation. Although these complexes selectively form polycarbonate, their catalytic performance is inferior to that of analogues based on saturated NHC.

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3

Chan, Chung Ying, and Peter J. Barnard. "Rhenium complexes of bidentate, bis-bidentate and tridentate N-heterocyclic carbene ligands." Dalton Transactions 44, no. 44 (2015): 19126–40. http://dx.doi.org/10.1039/c5dt03295d.

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Rhenium(i) tricarbonyl complexes of a range of bidentate, bis-bidentate and tridentate NHC ligands have been prepared. These NHC ligands are of interest for possible applications in the development of Tc-99m or Re-186/188 radiopharmaceuticals and the stability of two complexes were evaluated in ligand challenge experiments using the metal binding amino acids l-histidine or l-cysteine.

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4

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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5

Diesel, Johannes, and Nicolai Cramer. "Modular Chiral N-Heterocyclic Carbene Ligands for the Nickel-Catalyzed Enantioselective C–H Functionalization of Heterocycles." CHIMIA International Journal for Chemistry 74, no. 4 (April 29, 2020): 278–84. http://dx.doi.org/10.2533/chimia.2020.278.

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N-Heterocyclic carbenes (NHCs) are the ligands of choice in a large variety of transformations entailing different transition metals. However, the number and variety of chiral NHCs suitable as stereo-controlling ligands in asymmetric catalysis remains limited. Herein we highlight the introduction of a modular NHC ligand family, consisting of a chiral version of the widely used IPr ligand. These chiral NHC ligands were applied in the nickel-catalyzed enantioselective C–H functionalization of N-heterocycles. Nickel-NHC catalysis unlocked the stereoselective C–H annulation of 2- and 4-pyridones, delivering fused bicyclic compounds found in many biologically active compounds. Applying a bulky, yet flexible ligand scaffold enabled the highly enantioselective C–H functionalization of pyridones under mild conditions. The introduction of a bulky chiral SIPr analogue enabled the nickel-catalyzed enantioselective C–H functionalization of indoles, yielding valuable tetrahydropyridoindoles. Additionally, pyrrolopyridines, pyrrolopyrimidines and pyrroles were efficiently functionalized, delivering chiral annulated azoles.

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6

Diaz-Rodriguez, Roberto M., Katherine N. Robertson, and Alison Thompson. "Classifying donor strengths of dipyrrinato/aza-dipyrrinato ligands." Dalton Transactions 48, no. 22 (2019): 7546–50. http://dx.doi.org/10.1039/c9dt01148j.

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7

Bouché, Mathilde, Bruno Vincent, Thierry Achard, and Stéphane Bellemin-Laponnaz. "N-Heterocyclic Carbene Platinum(IV) as Metallodrug Candidates: Synthesis and 195Pt NMR Chemical Shift Trend." Molecules 25, no. 14 (July 9, 2020): 3148. http://dx.doi.org/10.3390/molecules25143148.

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A series of octahedral platinum(IV) complexes functionalized with both N-heterocyclic carbene (NHC) ligands were synthesized according to a straightforward procedure and characterized. The coordination sphere around the metal was varied, investigating the influence of the substituted NHC and the amine ligand in trans position to the NHC. The influence of those structural variations on the chemical shift of the platinum center were evaluated by 195Pt NMR. This spectroscopy provided more insights on the impact of the structural changes on the electronic density at the platinum center. Investigation of the in vitro cytotoxicities of representative complexes were carried on three cancer cell lines and showed IC50 values down to the low micromolar range that compare favorably with the benchmark cisplatin or their platinum(II) counterparts bearing NHC ligands.

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8

Bertini, Simone, and Martin Albrecht. "O-Functionalised NHC Ligands for Efficient Nickel-catalysed C–O Hydrosilylation." CHIMIA International Journal for Chemistry 74, no. 6 (June 24, 2020): 483–88. http://dx.doi.org/10.2533/chimia.2020.483.

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A series of C,O-bidentate chelating mesoionic carbene nickel(ii) complexes [Ni(NHC^PhO)2] (NHC = imidazolylidene or triazolylidene) were applied for hydrosilylation of carbonyl groups. The catalytic system is selective towards aldehyde reduction and tolerant to electron-donating and -withdrawing group substituents. Stoichiometric experiments in the presence of different silanes lends support to a metal–ligand cooperative activation of the Si–H bond. Catalytic performance of the nickel complexes is dependent on the triazolylidene substituents. Butyl-substituted triazolylidene ligands impart turnover numbers up to 7,400 and turnover frequencies of almost 30,000 h-1, identifying this complex as one of the best-performing nickel catalysts for hydrosilylation and demonstrating the outstanding potential of O-functionalised NHC ligands in combination with first-row transition metals.

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9

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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10

Yabune, Natsuki, Hiroshi Nakajima, and Takanori Nishioka. "Electronic and steric impact of bis-NHC ligands on reactions of Pt3S2 cores in trinuclear complexes bearing bis-NHC ligands with various lengths of alkylene bridges." Dalton Transactions 50, no. 35 (2021): 12079–82. http://dx.doi.org/10.1039/d1dt02747f.

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A silver(i) ion attacks the sulfide ligand of a triplatinum complex bearing ethylene-bridged bis-NHC ligands to afford a heptanuclear complex with two Ag–S bonds due to the steric hindrance of the ligands covering the Pt–Pt bonds.

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11

Tresin, Federica, Valentina Stoppa, Marco Baron, Andrea Biffis, Alfonso Annunziata, Luigi D’Elia, Daria Maria Monti, et al. "Synthesis and Biological Studies on Dinuclear Gold(I) Complexes with Di-(N-Heterocyclic Carbene) Ligands Functionalized with Carbohydrates." Molecules 25, no. 17 (August 24, 2020): 3850. http://dx.doi.org/10.3390/molecules25173850.

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The design of novel metal complexes with N-heterocyclic carbene (NHC) ligands that display biological activity is an active research field in organometallic chemistry. One of the possible approaches consists of the use of NHC ligands functionalized with a carbohydrate moiety. Two novel Au(I)–Au(I) dinuclear complexes were synthesized; they present a neutral structure with one bridging diNHC ligand, having one or both heterocyclic rings decorated with a carbohydrate functionality. With the symmetric diNHC ligand, the dicationic dinuclear complex bearing two bridging diNHC ligands was also synthesized. The study was completed by analyzing the antiproliferative properties of these complexes, which were compared to the activity displayed by similar mononuclear Au(I) complexes and by the analogous bimetallic Au(I)–Au(I) complex not functionalized with carbohydrates.

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12

Jamil, Mohamad Shazwan Shah, and Nor Azam Endot. "Influence of Fluorine Substituents on the Electronic Properties of Selenium-N-Heterocyclic Carbene Compounds." Molecules 25, no. 21 (November 6, 2020): 5161. http://dx.doi.org/10.3390/molecules25215161.

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N-heterocyclic carbenes (NHCs) are common ancillary ligands in organometallic compounds that are used to alter the electronic and steric properties of a metal centre. To date, various NHCs have been synthesised with different electronic properties, which can be done by modifying the backbone or changing the nitrogen substituents group. This study describes a systematic modification of NHCs by the inclusion of fluorine substituents and examines the use of selenium-NHC compounds to measure the π-accepting ability of these fluorinated NHC ligands. Evaluation of the 77Se NMR chemical shifts of the selenium adducts reveals that fluorinated NHCs have higher chemical shifts than the non-fluorinated counterparts, IMes and IPh. Higher 77Se NMR chemical shifts values indicate a stronger π-accepting ability of the NHC ligands. The findings of this study suggest that the presence of fluorine atoms has increased the π-accepting ability of the corresponding NHC ligands. This work supports the advantage of the 77Se NMR chemical shifts of selenium-NHC compounds for assessing the influence of fluorine substituents on NHC ligands.

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13

Czarnocki, Stefan, Louis Monsigny, Michał Sienkiewicz, Anna Kajetanowicz, and Karol Grela. "Ruthenium Olefin Metathesis Catalysts Featuring N-Heterocyclic Carbene Ligands Tagged with Isonicotinic and 4-(Dimethylamino)benzoic Acid Rests: Evaluation of a Modular Synthetic Strategy." Molecules 26, no. 17 (August 28, 2021): 5220. http://dx.doi.org/10.3390/molecules26175220.

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A modular and flexible strategy towards the synthesis of N-heterocyclic carbene (NHC) ligands bearing Brønsted base tags has been proposed and then adopted in the preparation of two tagged NHC ligands bearing rests of isonicotinic and 4-(dimethylamino)benzoic acids. Such tagged NHC ligands represent an attractive starting point for the synthesis of olefin metathesis ruthenium catalysts tagged in non-dissociating ligands. The influence of the Brønsted basic tags on the activity of such obtained olefin metathesis catalysts has been studied.

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14

Tacke, Matthias, Oyinlola Dada, Cillian O'Beirne, Xiangming Zhu, and Helge Müller-Bunz. "The non-isomorphous crystal structures of NHC—Au—Cl and NHC—Au—Br (NHC is 1,3-dibenzyl-4,5-diphenylimidazol-2-ylidene)." Acta Crystallographica Section C Structural Chemistry 72, no. 11 (October 5, 2016): 857–60. http://dx.doi.org/10.1107/s2053229616015205.

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Gold monochloride and monobromide can be transformed into monomeric complexes by ligands such as CO, PPh3or Me2S, and such ligand-stabilized gold monochloride compounds have been investigated as catalysts, luminescent materials and anticancer drugs, especially when coordinated to a lipophilic benzyl-substituted N-heterocyclic carbene (NHC) ligand. The triclinic structures of NHC–Au–Cl {chlorido(1,3-dibenzyl-4,5-diphenylimidazol-2-ylidene)gold, [AuCl(C29H24N2)]} and NHC—Au—Br {bromido(1,3-dibenzyl-4,5-diphenylimidazol-2-ylidene)gold, [AuBr(C29H24N2)]}, determined by X-ray crystallography at 100 K, have one and four molecules, respectively, in their asymmetric units. The chloride compound shows an almost linear C—Au—Cl fragment [179.76 (8)°], with an Au—C distance of 1.976 (3) Å and an Au—Cl distance of 2.3013 (6) Å, while the bromide compound shows surprisingly large geometry deviations, from 1.969 (12) to 2.016 (10) Å for the Au—C distance and from 2.4279 (14) to 2.4796 (12) Å for the Au—Br distance, in the four independent molecules.

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15

Ou, Arnold, Linglin Wu, Alvaro Salvador, Gellert Sipos, Guangzhen Zhao, Brian W. Skelton, Alexandre N. Sobolev, and Reto Dorta. "New, potentially chelating NHC ligands; synthesis, complexation studies, and preliminary catalytic evaluation." Dalton Transactions 46, no. 11 (2017): 3631–41. http://dx.doi.org/10.1039/c6dt04534k.

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16

Warsink, Stefan, and Andreas Roodt. "trans-Bis[1-(2-benzamidoethyl)-3-(2,4,6-trimethylphenyl)imidazol-2-ylidene]dichloridopalladium(II)." Acta Crystallographica Section E Structure Reports Online 68, no. 8 (July 18, 2012): m1075—m1076. http://dx.doi.org/10.1107/s1600536812031868.

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In the title compound, [PdCl2(C21H23N3O)2], the PdIIatom is located on an inversion centre and is coordinated in a slightly distorted square-planar environment by the chloride andN-heterocyclic carbene (NHC) ligands in mutualtranspositions. There are several hydrogen-bonding interactions, the most significant of which is a hydrogen bond between the amide moiety of the NHC and the chloride ligand. These hydrogen-bond interactions form a three-dimensional network.

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17

Jahnke, Mareike C., Jennifer Paley, Florian Hupka, Jan J. Weigand, and F. Ekkehardt Hahn. "Silver and Gold Complexes with Benzimidazolin-2-ylidene Ligands." Zeitschrift für Naturforschung B 64, no. 11-12 (December 1, 2009): 1458–62. http://dx.doi.org/10.1515/znb-2009-11-1228.

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The dicarbene silver complexes 1a, b of the type [Ag(NHC)2][AgBr2] (NHC = N,N'-dialkylbenzimidazolin- 2-ylidene) have been prepared from the parent benzimidazolium salts by reaction with silver oxide. The silver complexes have been used for the transfer of the carbene ligand to gold(I) giving the gold complexes [AuCl(NHC)] 2a, b in good yields. Crystals of 2a, b have been obtained from chloroform/pentane solutions, and X-ray diffraction structure analyses revealed gold(I) atoms coordinated in a linear fashion by an NHC carbon atom and a chloro ligand

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18

Parida, Rakesh, Subhra Das, Lucas José Karas, Judy I.-Chia Wu, Gourisankar Roymahapatra, and Santanab Giri. "Superalkali ligands as a building block for aromatic trinuclear Cu(i)–NHC complexes." Inorganic Chemistry Frontiers 6, no. 11 (2019): 3336–44. http://dx.doi.org/10.1039/c9qi00873j.

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Imidazole and benz-imidazole based different NHC ligands have been designed to make tri nuclear aromatic Cu(i)@NHC complex. First principle calculation suggest that all the ligands are superalkali and the complexes are sp² hybridized.

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19

He, Fen, Xin Yang, Zhi-Yue Tian, Han-Guang Wang, and Ying Xue. "Theoretical investigation on the structures and bonding properties of Pd(II), Pt(II) and Ni(II) complexes with tridentate CNC-pincer N-heterocyclic carbene ligands." Journal of Theoretical and Computational Chemistry 15, no. 05 (August 2016): 1650037. http://dx.doi.org/10.1142/s0219633616500371.

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The density functional theory (DFT) has been applied for the analysis of the bond between group 10 metals and N-heterocyclic carbene (NHC) in complexes (MCl(L-X): M [Formula: see text] Pd(II), Pt(II), and Ni(II), L-X[Formula: see text][2-(3-methylimidazolin-4,5-bisX-2-yliden-1-yl)-4-phenyl] amido, X [Formula: see text]H, Cl and CN). Full geometry optimizations have been performed for all the ligands (L-X[Formula: see text] anions), MCl[Formula: see text] cations, and the complexes. In the ligands, the energy levels of the carbon [Formula: see text] lone-pair orbitals suggest the trend L-H[Formula: see text] L-Cl[Formula: see text] L-CN[Formula: see text] for the donor strength. The role of the M–NHC interaction in complexes was investigated by natural bond orbital (NBO) analysis. The results show that the NHC–M bond consists of the components originating from the L[Formula: see text]M donation and the M[Formula: see text]Carbene C back-donation and the metal[Formula: see text]the ring of NHC back-donation. The transition-metal strongly affects the donation and back-donation. The interaction between the metal and the NHC ligand can be influenced by the central metal and the substituent on the ring of NHC.

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20

Cerezo-Navarrete, Christian, Patricia Lara, and Luis M. Martínez-Prieto. "Organometallic Nanoparticles Ligated by NHCs: Synthesis, Surface Chemistry and Ligand Effects." Catalysts 10, no. 10 (October 3, 2020): 1144. http://dx.doi.org/10.3390/catal10101144.

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Over the last 20 years, the use of metallic nanoparticles (MNPs) in catalysis has awakened a great interest in the scientific community, mainly due to the many advantages of this kind of nanostructures in catalytic applications. MNPs exhibit the characteristic stability of heterogeneous catalysts, but with a higher active surface area than conventional metallic materials. However, despite their higher activity, MNPs present a wide variety of active sites, which makes it difficult to control their selectivity in catalytic processes. An efficient way to modulate the activity/selectivity of MNPs is the use of coordinating ligands, which transforms the MNP surface, subsequently modifying the nanoparticle catalytic properties. In relation to this, the use of N-heterocyclic carbenes (NHC) as stabilizing ligands has demonstrated to be an effective tool to modify the size, stability, solubility and catalytic reactivity of MNPs. Although NHC-stabilized MNPs can be prepared by different synthetic methods, this review is centered on those prepared by an organometallic approach. Here, an organometallic precursor is decomposed under H2 in the presence of non-stoichiometric amounts of the corresponding NHC-ligand. The resulting organometallic nanoparticles present a clean surface, which makes them perfect candidates for catalytic applications and surface studies. In short, this revision study emphasizes the great versatility of NHC ligands as MNP stabilizers, as well as their influence on catalysis.

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21

Andrew, Rhiann E., Lucero González-Sebastián, and Adrian B. Chaplin. "NHC-based pincer ligands: carbenes with a bite." Dalton Transactions 45, no. 4 (2016): 1299–305. http://dx.doi.org/10.1039/c5dt04429d.

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In this frontier article we overview the emergence and scope of NHC-based CCC and CNC pincer systems, i.e. complexes containing mer-tridentate ligands bearing two NHC donor groups, comment on their effectiveness in applications, and highlight areas for future development and exploitation.

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22

Kündig, E. Peter, Yixia Jia, Dmitry Katayev, and Masafumi Nakanishi. "Asymmetric Pd-NHC*-catalyzed coupling reactions." Pure and Applied Chemistry 84, no. 8 (July 1, 2012): 1741–48. http://dx.doi.org/10.1351/pac-con-12-02-10.

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Very high asymmetric inductions result in the Pd-catalyzed intramolecular arylation of amides to give 3,3-disubstituted oxindoles when new in situ-generated chiral N-heterocyclic carbene (NHC*) ligands are employed. Structural studies show that conformational locking to minimize allylic strain is the key to understanding the function of these ligands. New applications of these ligands in the frontier area of asymmetric coupling reactions involving C(sp3)–H bonds are detailed. Highly enantioenriched fused indolines are accessible using either preformed- or in situ-generated Pd-NHC* catalysts. Remarkably, this occurs at high temperature (140–160 °C) via excellent asymmetric recognition of an enantiotopic C–H bond in an unactivated methylene unit.

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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

Schick, Sabrina, Tania Pape, and F. Ekkehardt Hahn. "Coordination Chemistry of Bidentate Bis(NHC) Ligands with Two Different NHC Donors." Organometallics 33, no. 15 (July 29, 2014): 4035–41. http://dx.doi.org/10.1021/om500554t.

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25

Georgiou, Dayne C., Ismael Mahmood, Mohammad A. Haghighatbin, Conor F. Hogan, and Jason L. Dutton. "The final fate of NHC stabilized dicarbon." Pure and Applied Chemistry 89, no. 6 (June 27, 2017): 791–800. http://dx.doi.org/10.1515/pac-2016-1126.

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AbstractIn this paper we report the outcome of the reduction of NHC stabilized acetylenic dications, [NHC-Cn-NHC]2+ for n=2 and 4. The target compounds were NHC stabilized di- and tetracarbon in the form of NHC-Cn-NHC. However, upon chemical reduction, decomposition ensues with release of the free NHC. This effect is also observed in electrochemical studies. This lends credence to Bestman’s hypothesis that two donor ligands cannot stabilize Cn for n=even numbers.

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26

Gardiner, Michael G., David S. McGuinness, and Catriona R. Vanston. "Chelated bis(NHC) complexes of saturated (imidazolin-2-ylidene) NHC ligands: structural authentication and facile ligand fragmentation." Dalton Transactions 46, no. 9 (2017): 3051–58. http://dx.doi.org/10.1039/c7dt00327g.

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27

McQueen, Caitlin M. A., Anthony F. Hill, Chenxi Ma, and Jas S. Ward. "Ruthenium and osmium complexes of dihydroperimidine-based N-heterocyclic carbene pincer ligands." Dalton Transactions 44, no. 47 (2015): 20376–85. http://dx.doi.org/10.1039/c5dt03728j.

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Double geminal aminal C–H activation processes of the dihydroperimidine based NHC pincer pro-ligands H₂C(NCH₂PR₂)₂C₁₀H₆ are described leading to dihydroperimidinylidene complexes including the first osmium examples.

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28

Ko, Soo-Byung, Hee-Jun Park, Shaolong Gong, Xiang Wang, Zheng-Hong Lu, and Suning Wang. "Blue phosphorescent N-heterocyclic carbene chelated Pt(ii) complexes with an α-duryl-β-diketonato ancillary ligand." Dalton Transactions 44, no. 18 (2015): 8433–43. http://dx.doi.org/10.1039/c4dt03085k.

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Blue phosphorescent Pt(ii) complexes that display bright blue emission in the solid state have been obtained employing NHC-based C^∧C*-chelate ligands and an α-duryl-β-diketonato ancillary ligand that provides steric blocking to minimize intermolecular interactions.

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29

Pape, Felix, and Johannes Teichert. "Tethered NHC Ligands for Stereoselective Alkyne Semihydrogenations." Synthesis 49, no. 11 (February 17, 2017): 2470–82. http://dx.doi.org/10.1055/s-0036-1590112.

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A copper(I)-catalyzed semihydrogenation of internal alkynes has been developed. A variety of oxygen- and nitrogen-tethered N-heterocyclic carbene (NHC) complexes have been investigated, leading to a highly Z-selective transformation. The catalyst is generated from inexpensive copper(I) chloride in situ and allows catalytic semihydrogenation down to 10 bar H2.

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30

Masoud, Salekh M., Artur K. Mailyan, Vincent Dorcet, Thierry Roisnel, Pierre H. Dixneuf, Christian Bruneau, and Sergey N. Osipov. "Metathesis Catalysts with Fluorinated Unsymmetrical NHC Ligands." Organometallics 34, no. 11 (January 12, 2015): 2305–13. http://dx.doi.org/10.1021/om501077w.

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31

Brendel, Matthias, Jan Wenz, Igor V. Shishkov, Frank Rominger, and Peter Hofmann. "Lithium Complexes of Neutral Bis-NHC Ligands." Organometallics 34, no. 3 (January 22, 2015): 669–72. http://dx.doi.org/10.1021/om501229b.

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32

Wang, Wan-Qiang, Hua Cheng, Ye Yuan, Yu-Qing He, Hua-Jing Wang, Zhi-Qin Wang, Wei Sang, Cheng Chen, and Francis Verpoort. "Highly Efficient N-Heterocyclic Carbene/Ruthenium Catalytic Systems for the Acceptorless Dehydrogenation of Alcohols to Carboxylic Acids: Effects of Ancillary and Additional Ligands." Catalysts 10, no. 1 (December 19, 2019): 10. http://dx.doi.org/10.3390/catal10010010.

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The transition-metal-catalyzed alcohol dehydrogenation to carboxylic acids has been identified as an atom-economical and attractive process. Among various catalytic systems, Ru-based systems have been the most accessed and investigated ones. With our growing interest in the discovery of new Ru catalysts comprising N-heterocyclic carbene (NHC) ligands for the dehydrogenative reactions of alcohols, we designed and prepared five NHC/Ru complexes ([Ru]-1–[Ru]-5) bearing different ancillary NHC ligands. Moreover, the effects of ancillary and additional ligands on the alcohol dehydrogenation with KOH were thoroughly explored, followed by the screening of other parameters. Accordingly, a highly active catalytic system, which is composed of [Ru]-5 combined with an additional NHC precursor L5, was discovered, affording a variety of acid products in a highly efficient manner. Gratifyingly, an extremely low Ru loading (125 ppm) and the maximum TOF value until now (4800) were obtained.

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33

Jónsson, Helgi Freyr, Andreas Orthaber, and Anne Fiksdahl. "Studies on gold(i) and gold(iii) alcohol functionalised NHC complexes." Dalton Transactions 50, no. 15 (2021): 5128–38. http://dx.doi.org/10.1039/d1dt00387a.

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34

Baczewska, Paulina, Katarzyna Śniady, Wioletta Kośnik, and Michał Michalak. "Acenaphthene-Based N-Heterocyclic Carbene Metal Complexes: Synthesis and Application in Catalysis." Catalysts 11, no. 8 (August 14, 2021): 972. http://dx.doi.org/10.3390/catal11080972.

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N-Heterocyclic carbene (NHC) ligands have become a privileged structural motif in modern homogenous and heterogeneous catalysis. The last two decades have brought a plethora of structurally and electronically diversified carbene ligands, enabling the development of cutting-edge transformations, especially in the area of carbon-carbon bond formation. Although most of these were accomplished with common imidazolylidene and imidazolinylidene ligands, the most challenging ones were only accessible with the acenaphthylene-derived N-heterocyclic carbene ligands bearing a π-extended system. Their superior σ-donor capabilities with simultaneous ease of modification of the rigid backbone enhance the catalytic activity and stability of their transition metal complexes, which makes BIAN-NHC (BIAN—bis(imino)acenaphthene) ligands an attractive tool for the development of challenging reactions. The present review summarizes synthetic efforts towards BIAN-NHC metal complexes bearing acenaphthylene subunits and their applications in modern catalysis, with special emphasis put on recently developed enantioselective processes.

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35

Banach, Ł., P. A. Guńka, and W. Buchowicz. "Half-sandwich nickel complexes with ring-expanded NHC ligands – synthesis, structure and catalytic activity in Kumada–Tamao–Corriu coupling." Dalton Transactions 45, no. 21 (2016): 8688–92. http://dx.doi.org/10.1039/c5dt04663g.

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36

Thongpaen, Jompol, Thibault E. Schmid, Loic Toupet, Vincent Dorcet, Marc Mauduit, and Olivier Baslé. "Directed ortho C–H borylation catalyzed using Cp*Rh(iii)–NHC complexes." Chemical Communications 54, no. 59 (2018): 8202–5. http://dx.doi.org/10.1039/c8cc03144d.

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37

Poater, Albert. "Versatile deprotonated NHC: C,N-bridged dinuclear iridium and rhodium complexes." Beilstein Journal of Organic Chemistry 12 (January 22, 2016): 117–24. http://dx.doi.org/10.3762/bjoc.12.13.

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Bearing the versatility of N-heterocyclic carbene (NHC) ligands, here density functional theory (DFT) calculations unravel the capacity of coordination of a deprotonated NHC ligand (pNHC) to generate a doubly C2,N3-bridged dinuclear complex. Here, in particular the discussion is based on the combination of the deprotonated 1-arylimidazol (aryl = mesityl (Mes)) with [M(cod)(μ-Cl)] (M = Ir, Rh) generated two geometrical isomers of complex [M(cod){µ-C3H2N2(Mes)-κC2,κN3}]2). The latter two isomers display conformations head-to-head (H-H) and head-to-tail (H-T) of C S and C 2 symmetry, respectively. The isomerization from the H-H to the H-T conformation is feasible, whereas next substitutions of the cod ligand by CO first, and PMe3 later confirm the H-T coordination as the thermodynamically preferred. It is envisaged the exchange of the metal, from iridium to rhodium, confirming here the innocence of the nature of the metal for such arrangements of the bridging ligands.

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38

Gonell, S., M. Poyatos, and E. Peris. "Pincer-CNC mononuclear, dinuclear and heterodinuclear Au(iii) and Pt(ii) complexes supported by mono- and poly-N-heterocyclic carbenes: synthesis and photophysical properties." Dalton Transactions 45, no. 13 (2016): 5549–56. http://dx.doi.org/10.1039/c6dt00198j.

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The photophysical properties of a family of cyclometallated Au(iii) and Pt(ii) complexes containing a CNC-pincer ligand supported by pyrene-based mono- or bis-NHC ligands are described, and compared with those shown by related dimetallic complexes of Pt/Au and Ru₂.

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39

Winkel, Russell W., Galyna G. Dubinina, Khalil A. Abboud, and Kirk S. Schanze. "Photophysical properties of trans-platinum acetylide complexes featuring N-heterocyclic carbene ligands." Dalton Transactions 43, no. 47 (2014): 17712–20. http://dx.doi.org/10.1039/c4dt01520g.

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40

Simler, Thomas, Andreas A. Danopoulos, and Pierre Braunstein. "Non-symmetrical, potentially redox non-innocent imino NHC pyridine ‘pincers’ via a zinc ion template-assisted synthesis." Dalton Transactions 46, no. 18 (2017): 5955–64. http://dx.doi.org/10.1039/c7dt01014a.

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A Zn^II-promoted modular synthesis allows access to new non-symmetrical, redox-active imino NHC pyridine pincer ligands. Radical anionic and dianionic redox states of the ligand are involved in its Fe^II complexes obtained from FeBr₂/KC₈.

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41

Dey, Sriloy, and T. Keith Hollis. "Accessing Low-Valent Titanium CCC-NHC Complexes: Toward Nitrogen Fixation." Inorganics 9, no. 2 (February 8, 2021): 15. http://dx.doi.org/10.3390/inorganics9020015.

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The dramatic expansion of the earth’s population can be directly correlated with the Haber–Bosch process for nitrogen fixation becoming widely available after World War II. The ready availability of artificial fertilizer derived thereof dramatically improved food supplies world-wide. Recently, artificial nitrogen fixation surpassed the natural process. The Haber–Bosch process is extremely energy and green-house gas intensive due to its high-temperature and H2 demands. Many low valent Ti(II) complexes of N2 are known. We report herein a preliminary investigation of the low-valent chemistry of Ti with the CCC-NHC ligand architecture. These CCC-NHC pincer Ti(IV) complexes are readily reduced with KC8 or Mg powder. Preliminary results indicate very different reactivity patterns with alkynes and phosphines for this ligand architecture versus prior ligands. Successful reduction to an intact low-valent (CCC-NHC)Ti complex was confirmed by re-oxidation with PhICl2.

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42

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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43

Ángel-Jijón, Carlos, David Rendón-Nava, Jose M. Vazques-Pérez, Alejandro Álvarez-Hernández, Daniel Mendoza-Espinosa, and Verónica Salazar-Pereda. "NHC–Au(i) complexes bearing trispyrazolyl borate (Tp) ligands: efficient platforms for bimetallic species." Dalton Transactions 49, no. 19 (2020): 6199–204. http://dx.doi.org/10.1039/d0dt00908c.

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Treatment of NHC–AuCl (NHC = IPr and IMes) complexes with equimolar amounts of KTp^R2 (R = Me, H) salts in tetrahydrofuran produces in high yields the heteroleptic complexes 3–6 with the general formula NHC–Au–Tp^R2.

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44

Turbervill, Robert S. P., and Jose M. Goicoechea. "‘Classical’ and ‘Abnormal’ Bonding in Tin (II) N-Heterocyclic Carbene Complexes." Australian Journal of Chemistry 66, no. 10 (2013): 1131. http://dx.doi.org/10.1071/ch13115.

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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 also contains an ‘abnormal’ C4/C5-bonded carbene (aIPr). These observations highlight the subtle steric and electronic effects affecting the coordination modes of these ligands. Solution phase NMR experiments on 1 and 2 reveal complex behaviour resulting in the protonation of the IPr ligands to yield the 1,3-bis(2,6-diisopropylphenyl)-imidazolium cation via an unidentified reaction mechanism.

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45

Danopoulos, Andreas A., Alexandre Massard, Gilles Frison, and Pierre Braunstein. "Iron and Cobalt Metallotropism in Remote-Substituted NHC Ligands: Metalation to Abnormal NHC Complexes or NHC Ring Opening." Angewandte Chemie 130, no. 44 (September 19, 2018): 14758–62. http://dx.doi.org/10.1002/ange.201808008.

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46

Danopoulos, Andreas A., Alexandre Massard, Gilles Frison, and Pierre Braunstein. "Iron and Cobalt Metallotropism in Remote-Substituted NHC Ligands: Metalation to Abnormal NHC Complexes or NHC Ring Opening." Angewandte Chemie International Edition 57, no. 44 (September 19, 2018): 14550–54. http://dx.doi.org/10.1002/anie.201808008.

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47

Rehm, Tobias, Matthias Rothemund, Julienne K. Muenzner, Awal Noor, Rhett Kempe, and Rainer Schobert. "Novel cis-[(NHC)1(NHC)2(L)Cl]platinum(ii) complexes – synthesis, structures, and anticancer activities." Dalton Transactions 45, no. 39 (2016): 15390–98. http://dx.doi.org/10.1039/c6dt02350a.

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48

Mejuto, Carmen, Beatriz Royo, Gregorio Guisado-Barrios, and Eduardo Peris. "Rhodium, iridium and nickel complexes with a 1,3,5-triphenylbenzene tris-MIC ligand. Study of the electronic properties and catalytic activities." Beilstein Journal of Organic Chemistry 11 (December 14, 2015): 2584–90. http://dx.doi.org/10.3762/bjoc.11.278.

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The coordination versatility of a 1,3,5-triphenylbenzene-tris-mesoionic carbene ligand is illustrated by the preparation of complexes with three different metals: rhodium, iridium and nickel. The rhodium and iridium complexes contained the [MCl(COD)] fragments, while the nickel compound contained [NiCpCl]. The preparation of the tris-MIC (MIC = mesoionic carbene) complex with three [IrCl(CO)2] fragments, allowed the estimation of the Tolman electronic parameter (TEP) for the ligand, which was compared with the TEP value for a related 1,3,5-triphenylbenzene-tris-NHC ligand. The electronic properties of the tris-MIC ligand were studied by cyclic voltammetry measurements. In all cases, the tris-MIC ligand showed a stronger electron-donating character than the corresponding NHC-based ligands. The catalytic activity of the tri-rhodium complex was tested in the addition reaction of arylboronic acids to α,β-unsaturated ketones.

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49

Simler, Thomas, Pierre Braunstein, and Andreas A. Danopoulos. "Coinage metal complexes with bridging hybrid phosphine–NHC ligands: synthesis of di- and tetra-nuclear complexes." Dalton Transactions 45, no. 12 (2016): 5122–39. http://dx.doi.org/10.1039/c6dt00275g.

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50

Krahfuss, Mirjam J., and Udo Radius. "N-Heterocyclic silylenes as ambiphilic activators and ligands." Dalton Transactions 50, no. 20 (2021): 6752–65. http://dx.doi.org/10.1039/d1dt00617g.

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Recent developments of the use of N-heterocyclic silylenes (NHSis), higher homologues of Arduengo-carbenes, as ambiphilic activators and ligands are highlighted and a comparison of NHSi ligands with NHC and phosphine ligands is provided.

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