Application of N-heterocyclic carbene–Cu(I) complexes as catalysts in organic synthesis: a review

• Nosheen Beig,
• Varsha Goyal and
• Raj K. Bansal

Beilstein J. Org. Chem. 2023, 19, 1408–1442, doi:10.3762/bjoc.19.102

• catalysts for hydrosilylation and [3 + 2] cycloaddition discussed later [39]. 1.4 By ligand displacement Corrigan and co-worker stabilized homoleptic copper- and silver bis(trimethylsilyl)phosphido compounds [M6{P(SiMe3)2}6] (M = Cu, Ag) through their coordination with NHC ligands. For this purpose, they

• -Ph) in this manner (Scheme 29) [42]. The X-ray studies revealed two major structure types of the compounds [(NHC)Cu-ER3] in the solid state. In the case of bulky NHC ligands, such as IDipp, IMes, and It-Bu, the CuI complexes with ER3 = SiMe2Ph, SiPh3, SnMe3 as well as for Ph and CC-Ph, have monomeric

• -naphthol moiety 193 afforded the highest yield and enantioselectivity. On protecting the hydroxy group in the ligand as methyl ether, the reaction efficiency decreased remarkably. However, on using NHC ligands without oxygen atom, such as analogues of 193, IMes, and SIMes, no conversion occurred. 2.8 C(sp2

Pyridine C(sp²)–H bond functionalization under transition-metal and rare earth metal catalysis

• Haritha Sindhe,
• Malladi Mounika Reddy,
• Karthikeyan Rajkumar,
• Akshay Kamble,
• Amardeep Singh,
• Anand Kumar and
• Satyasheel Sharma

Beilstein J. Org. Chem. 2023, 19, 820–863, doi:10.3762/bjoc.19.62

• . Also, metal–NHC complexes have wide application in catalysis and various organic transformations and a range of metal–NHCs served as catalysts. In 2010, using NHC ligands, Yap and co-workers [90] developed a method for the direct para and meta-C–H alkenylation of pyridines with 4-octyne (107) using a

• oxidized by Cu(II) to complete the catalytic cycle. Next, considering the role of N-heterocyclic carbene (NHC) ligands acting as directing group as well as functionalizing unit in arene C–H functionalization reactions with alkynes, Choudhury and group [106] in 2015 developed a protocol for the

• regeneration of 189 (Scheme 36b). In 2019, using NHC ligands, a protocol for the regio- and enantioselective C–H cyclization of pyridines was reported by Shi and co-workers [107] toward the direct asymmetric pyridine C–H alkylation (Scheme 37). The authors found that alkene-tethered C2 pyridine 193, C3

Recent advances in palladium-catalysed asymmetric 1,4–additions of arylboronic acids to conjugated enones and chromones

• Jan Bartáček,
• Jan Svoboda,
• Martin Kocúrik,
• Jaroslav Pochobradský,
• Alexander Čegan,
• Miloš Sedlák and
• Jiří Váňa

Beilstein J. Org. Chem. 2021, 17, 1048–1085, doi:10.3762/bjoc.17.84

• oxidative Heck-type product. The authors stated that as a result of the coordination with PPh3, there is a steric hindrance disfavouring the β-hydride elimination [43]. Catalytic systems based on NHC ligands Historically, the second type of ligands used were N-heterocyclic carbenes (NHC). The first use was

Using multiple self-sorting for switching functions in discrete multicomponent systems

• Amit Ghosh and
• Michael Schmittel

Beilstein J. Org. Chem. 2020, 16, 2831–2853, doi:10.3762/bjoc.16.233

• BPh4− at the cage [Co6(10')4]12+ (SelfSORT-I). Double self-sorting (only structural) Hahn et al. demonstrated for the first time that poly-NHC ligands furnish metallosupramolecular assemblies through narcissistic self-sorting [53]. The one-pot reaction of the tris-NHC ligands 13–15 with different

Efficient [(NHC)Au(NTf₂)]-catalyzed hydrohydrazidation of terminal and internal alkynes

• Maximillian Heidrich and
• Herbert Plenio

Beilstein J. Org. Chem. 2020, 16, 2080–2086, doi:10.3762/bjoc.16.175

• catalysts with such ligands also display high activities in other gold-catalyzed reactions. Results and Discussion Catalyst screening: Five different [(NHC)Au(NTf2)] complexes 1, 2, 3, 4, and 5 with bulky NHC ligands were tested in the hydrohydrazidation of phenylacetylene with benzohydrazide (Scheme 2; T

• . In this group of gold complexes with sterically demanding NHC ligands, the NHC ligands with intermediate bulk provided the best catalytic performance. The use of the bulkiest complex 2 [46], resulted only in modest substrate conversion. Nonetheless, all of the tested complexes performed much better

A systematic review on silica-, carbon-, and magnetic materials-supported copper species as efficient heterogeneous nanocatalysts in “click” reactions

• Pezhman Shiri and
• Jasem Aboonajmi

Beilstein J. Org. Chem. 2020, 16, 551–586, doi:10.3762/bjoc.16.52

• 1,2-dichloroethane by ultrasonication. After adding N,N-diisopropylethylamine, the mixture was heated at reflux for 20 h. The nanoparticles 107 were magnetically separated and finally, the corresponding complexes of copper(I) and copper(II) with the NHC ligands, 108–111, were prepared as shown in

Copper-catalyzed enantioselective conjugate reduction of α,β-unsaturated esters with chiral phenol–carbene ligands

• Shohei Mimura,
• Sho Mizushima,
• Yohei Shimizu and
• Masaya Sawamura

Beilstein J. Org. Chem. 2020, 16, 537–543, doi:10.3762/bjoc.16.50

• enantioselectivity. Conclusion A chiral phenol–NHC ligand efficiently promoted the enantioselective conjugate reduction of α,β-unsaturated esters with a hydrosilane. To the best of our knowledge, this is the first demonstration of the applicability of chiral NHC ligands in Cu-catalyzed enantioselective conjugate

Progress in metathesis chemistry

• Karol Grela and
• Anna Kajetanowicz

Beilstein J. Org. Chem. 2019, 15, 2765–2766, doi:10.3762/bjoc.15.267

• by Kotha et al. [4], on artificial metalloproteins by Okuda et al. [5], on stereoretentive ruthenium dithiolate catalysts by Mauduit et al. [6], on unsymmetrical NHC ligands by Grisi et al. [7], on polymers by Kudryavtsev [8] and on polyhedral oligomeric silsesquioxanes by Pietraszuk et al. [9

Aqueous olefin metathesis: recent developments and applications

• Valerio Sabatino and
• Thomas R. Ward

Beilstein J. Org. Chem. 2019, 15, 445–468, doi:10.3762/bjoc.15.39

• . Water can lead to the formation of catalytically inactive Ru hydride species. Fürstner et al. isolated these complexes as byproducts during the synthesis of Grubbs second generation-type catalysts with saturated NHC ligands [29]. In this specific case, the formation of the metal hydride complex is

Ammonium-tagged ruthenium-based catalysts for olefin metathesis in aqueous media under ultrasound and microwave irradiation

• Łukasz Gułajski,
• Andrzej Tracz,
• Katarzyna Urbaniak,
• Stefan J. Czarnocki,
• Michał Bieniek and
• Tomasz K. Olszewski

Beilstein J. Org. Chem. 2019, 15, 160–166, doi:10.3762/bjoc.15.16

• –d) and also included catalysts having differently sized NHC ligands (2a,c). For testing the catalysts performances, we selected the RCM of the water-soluble substrate 12 (Table 2). Under the reaction conditions the classical catalyst 5 (0.25 mol %) was not soluble resulting in poor yields and

Ruthenium-based olefin metathesis catalysts with monodentate unsymmetrical NHC ligands

• Veronica Paradiso,
• Chiara Costabile and
• Fabia Grisi

Beilstein J. Org. Chem. 2018, 14, 3122–3149, doi:10.3762/bjoc.14.292

• , ruthenium olefin metathesis complexes bearing N-heterocyclic carbene (NHC) ligands, known as second generation catalysts (Figure 1), have shown improved catalytic efficiency over other metathesis catalysts [3][4]. Moreover, their catalytic properties can be finely modulated through variation of the steric

• ruthenium complexes with monodentate NHC ligands bearing unsymmetrical N-aryl, N’-aryl groups were reported by Blechert [12], who synthesized Grubbs and Hoveyda-type complexes with N-phenyl, N’-mesityl NHC substituents (1a,b in Figure 2). Both complexes were air stable, but in CH2Cl2 solution complex 1b

• , involves a pericyclic reaction followed by an irreversible oxidation step, and, finally, a rearomatization. To avoid the C–H activation of aryl-substituted NHC ligands the corresponding ortho positions have to be substituted by different groups. Indeed, almost contemporaneously, Grubbs et al. reported on

A tutorial review of stereoretentive olefin metathesis based on ruthenium dithiolate catalysts

• Daniel S. Müller,
• Olivier Baslé and
• Marc Mauduit

Beilstein J. Org. Chem. 2018, 14, 2999–3010, doi:10.3762/bjoc.14.279

• NHC ligand. To avoid steric repulsions, the substituents at the α-positions of the metallacycle point away from the N-aryl groups of the NHC-ligands. In contrast, the substituents at the β-position can point up or down. For the reaction with Z-alkenes (Figure 3a), the substituent at the β-position has

The activity of indenylidene derivatives in olefin metathesis catalysts

• Maria Voccia,
• Steven P. Nolan,
• Luigi Cavallo and
• Albert Poater

Beilstein J. Org. Chem. 2018, 14, 2956–2963, doi:10.3762/bjoc.14.275

• (1,3-bis(2,4,6-trimethylphenyl)-4,5-dihydroimidazol-2-ylidene) and the IMes (1,3-bis(2,4,6-trimethylphenyl)imidazol-2-ylidene) NHC ligands. The group trans to the NHC ligand is triphenylphosphine for all catalysts. Table 1 includes the energy profiles for the substituted indenylidenes, bearing methyl

• substitution, being 4.2 and 3.4 kcal/mol relatively more stable for systems 3 and 5, respectively, with respect to 1. This effect of reducing steric hindrance between the ylidene and the NHC ligands was examined previously, with the exchange of benzylidene by indenylidene [51]; and with larger NHC ligands [52

• (GIAO), at the BP86/SVP level. The magnetic shielding tensor was calculated for ghost atoms located at the centre of the rings determined by the nonweighted mean of the heavy atom coordinates. Topographic steric maps (plane xy) of the NHC ligands of species I for the studied SIMes–Ru complexes 1, 3 and

The influence of the cationic carbenes on the initiation kinetics of ruthenium-based metathesis catalysts; a DFT study

• Magdalena Jawiczuk,
• Angelika Janaszkiewicz and
• Bartosz Trzaskowski

Beilstein J. Org. Chem. 2018, 14, 2872–2880, doi:10.3762/bjoc.14.266

• of metathesis results from the high stabilities and efficiencies of Ruthenium catalysts stabilised by NHC moieties. In this class of compounds NHC ligands, with the poor π-acceptor and strong σ-donor properties, stabilize the 14-electron ruthenium active species during the catalytic cycle [11][12

• Schanz and co-workers synthesized also Hoveyda-like complexes with ammonium groups introduced into the aryl rings of the NHC ligands [25]. Most of these complexes showed good efficiency in selected metathesis reactions. Interestingly in all reported cases of ammonium tagged Ru–alkylidene metathesis

• metathesis. Precatalysts with unsaturated NHC ligands are estimated to have slightly lower Gibbs free energy barriers than saturated ones by ca. 3–5 kcal/mol (Table 3). Interestingly, the free energies in water are 3–12 kcal/mol lower indicating that 1-GrII and 2-GrII may act as very slow metathesis

Recent advances in phosphorescent platinum complexes for organic light-emitting diodes

• Cristina Cebrián and
• Matteo Mauro

Beilstein J. Org. Chem. 2018, 14, 1459–1481, doi:10.3762/bjoc.14.124

• components (sky-blue-orange); ii) using a phosphorescent material to partially down-convert UV or blue light from a LED source; the latter seems a promising option to date. The group of Sicilia has recently applied some cyclometallated platinum(II) complexes bearing NHC ligands to develop WOLEDs, whose

Cobalt-catalyzed directed C–H alkenylation of pivalophenone N–H imine with alkenyl phosphates

• Wengang Xu and
• Naohiko Yoshikai

Beilstein J. Org. Chem. 2018, 14, 709–715, doi:10.3762/bjoc.14.60

• Grignard reagent would furnish the alkenylation product 3·MgX and regenerate the species A. While the relationship between the ligand and the catalytic activity remains unclear, we speculate that a strong σ-donating ability of NHC ligands would facilitate the SET step among others. Conclusion In summary

• architecture proved to have a significant impact on the efficiency of the present C–H/electrophile coupling. We anticipate that the elaboration of NHC ligands would also be instrumental to the improvement of other C–H activation and related transformations promoted by low-valent cobalt complexes [32][33][34

An efficient Pd–NHC catalyst system in situ generated from Na₂PdCl₄ and PEG-functionalized imidazolium salts for Mizoroki–Heck reactions in water

• Nan Sun,
• Meng Chen,
• Liqun Jin,
• Wei Zhao,
• Baoxiang Hu,
• Zhenlu Shen and
• Xinquan Hu

Beilstein J. Org. Chem. 2017, 13, 1735–1744, doi:10.3762/bjoc.13.168

• functionalization of the N atom of the NHC ring allows for the possible incorporation of water soluble moieties, thus providing more opportunities for water soluble catalyst design [37][38][39]. Since the pioneering report of a sulfonate-functionalized NHC ligand by Shaughnessy [40], a number of water-soluble NHC

• ligands, functionalized with sulfonate- [41][42][43][44][45][46], carboxylate- [47][48][49][50][51][52], polyether- [53][54][55][56][57][58][59] and other hydrophilic groups [60][61][62][63], have been developed and used in the aqueous Pd-catalyzed cross-coupling reactions. Among them, most of them were

Experimental and theoretical investigations on the high-electron donor character of pyrido-annelated N-heterocyclic carbenes

• Michael Nonnenmacher,
• Dominik M. Buck and
• Doris Kunz

Beilstein J. Org. Chem. 2016, 12, 1884–1896, doi:10.3762/bjoc.12.178

• most common types of NHC ligands L. A graphical illustration of these values is depicted in Figure 3. It shows that the dipyrido-annelated carbenes have an overall donor capacity that lies in between that of acyclic (Ia) or ferrocene bridged (Ib) diaminocarbenes and saturated imidazolidin-2-ylidenes

Methylpalladium complexes with pyrimidine-functionalized N-heterocyclic carbene ligands

• Dirk Meyer and
• Thomas Strassner

Beilstein J. Org. Chem. 2016, 12, 1557–1565, doi:10.3762/bjoc.12.150

• Dirk Meyer Thomas Strassner Physikalische Organische Chemie, TU Dresden, Bergstraße 66, 01062 Dresden, Germany 10.3762/bjoc.12.150 Abstract A series of methylpalladium(II) complexes with pyrimidine-NHC ligands carrying different aryl- and alkyl substituents R ([((pym)^(NHC-R))PdII(CH3)X] with X

• byproduct of the methanol synthesis. Sen reported the activity of palladium(II) catalysts for the oxidation of methane [21] and several groups contributed to the progress in the field which is summarized in recent reviews [22][23]. The system based on N-heterocyclic carbene (NHC) ligands developed in our

Bi- and trinuclear copper(I) complexes of 1,2,3-triazole-tethered NHC ligands: synthesis, structure, and catalytic properties

• Shaojin Gu,
• Jiehao Du,
• Jingjing Huang,
• Huan Xia,
• Ling Yang,
• Weilin Xu and
• Chunxin Lu

Beilstein J. Org. Chem. 2016, 12, 863–873, doi:10.3762/bjoc.12.85

• , reports concerning their preparation and use of 1,4-disubstituted-1,2,3-triazoles bearing NHC ligands are rare [22][23]. Elsevier et al. [23] reported several of palladium(II) complexes containing a heterobidentate N-heterocyclic carbene-triazolyl ligand. These palladium(II) complexes are active

• and platinum complexes containing 1,2,3-triazole-tethered NHC ligands. The obtained palladium complexes displayed high activity in aqueous Suzuki–Miyaura cross-coupling reactions. We are interested in the synthesis and use of functionalized NHC ligands [20][28][29][30][31]. Herein, the synthesis

• copper atoms are bridged by three NpyridineCNtriazole NHC ligands forming a Cu3 ring with three Cu–Cu–Cu angles of 60.0. The geometry of the copper center can be described as distorted trigonal planar. Each copper ion is coordinated by one pyridine, one triazole, and two benzimidazolylidene ligands

Iridium/N-heterocyclic carbene-catalyzed C–H borylation of arenes by diisopropylaminoborane

• Mamoru Tobisu,
• Takuya Igarashi and
• Naoto Chatani

Beilstein J. Org. Chem. 2016, 12, 654–661, doi:10.3762/bjoc.12.65

• C–H borylation [2], the reaction failed to give 2-B under these conditions (Table 1, entry 1). Several mono- and diphosphine ligands were found to be active for the formation of 2-B, but the best yield was only 21% (Table 1, entries 2–6). Our success in C–H borylation using NHC ligands [8][10] led

• us to investigate a series of NHC ligands for this process. Among the NHC ligands examined, 1,3-dicyclohexylimidazol-2-ylidene (ICy) [28][29][30][31][32][33] was found to be most effective, giving 2-B in 33% yield with a 2-/3-borylation ratio of 88:12 (Table 1, entry 9). It should be noted that [Ir

Scope and limitations of the dual-gold-catalysed hydrophenoxylation of alkynes

• Adrián Gómez-Suárez,
• Yoshihiro Oonishi,
• Anthony R. Martin and
• Steven P. Nolan

Beilstein J. Org. Chem. 2016, 12, 172–178, doi:10.3762/bjoc.12.19

• metal and main-group chemistry [10][11][12][13]. We have been interested in exploring the use of NHC ligands in transition metal complexes for the development of highly active and well-defined catalysts. One of our main interests during the last decade has been to study the use of gold–NHC species as

Simple activation by acid of latent Ru-NHC-based metathesis initiators bearing 8-quinolinolate co-ligands

• Julia Wappel,
• Roland C. Fischer,
• Luigi Cavallo,
• Christian Slugovc and
• Albert Poater

Beilstein J. Org. Chem. 2016, 12, 154–165, doi:10.3762/bjoc.12.17

• different NHC ligands. At the example of initiators 2a and 2b it was shown that the arrangement of the ligands around the ruthenium centre can drastically influence the activity of metathesis initiators. Just by changing the positioning of one of the two quinolinolate ligands the catalytic activity is

Versatile deprotonated NHC: C,N-bridged dinuclear iridium and rhodium complexes

• Albert Poater

Beilstein J. Org. Chem. 2016, 12, 117–124, doi:10.3762/bjoc.12.13

• Albert Poater Institut de Química Computacional i Catàlisi, Departament de Química, Universitat de Girona, Campus de Montilivi, E-17071 Girona, Spain 10.3762/bjoc.12.13 Abstract Bearing the versatility of N-heterocyclic carbene (NHC) ligands, here density functional theory (DFT) calculations

Effective immobilisation of a metathesis catalyst bearing an ammonium-tagged NHC ligand on various solid supports

• Krzysztof Skowerski,
• Jacek Białecki,
• Stefan J. Czarnocki,
• Karolina Żukowska and
• Karol Grela

Beilstein J. Org. Chem. 2016, 12, 5–15, doi:10.3762/bjoc.12.2

• ruthenium [19][20][21][22][23][24]. In other contributions originating from the same group, heterogeneous catalysts covalently connected to a monolithic support via NHC ligands were presented [25][26]. These initiators were suitable for continuous metathesis processes and provided products with low residual