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

• copper(I) bromide in CH2Cl2 (Scheme 24) [31]. Nakamura et al. synthesized for the first time a copper complex with a 1,2,3-triazole carbene ligand in 2011. Complexes of copper with 1,4-diphenyl-, 1,4-dimesityl-, and 1-(2,6-diisopropylphenyl)-4-(3,5-xylyl)-1,2,3-triazol-5-ylidene were prepared through

• heterocyclic compounds with CO2 resulting in higher yields than those obtained with the imidazolylidene carbene ligand, IPr (Scheme 70). 2.7 C(sp2)–H Alkenylation and allylation In 2016, Chang and co-worker [93] achieved an NHCs–Cu-catalyzed efficient C(sp2)–H allylation of polyfluoroarenes 183 and

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

• with a bulky N-heterocyclic carbene ligand and (2,6-t-Bu2-4-Me-C6H2O)2AlMe (MAD) as the Lewis acid which allowed the direct C-4 alkylation of pyridines 1 (Scheme 12a). With the optimized reaction conditions in hand the group also screened the alkene and pyridine substrate scope which resulted C4

• intermolecular C–H annulation of NHC-substituted pyridines with a variety of internal alkynes 187 under rhodium catalysis for the synthesis of annulated and highly decorated pyridines 188 (Scheme 36). The authors used the N-heterocyclic carbene ligand as directing group to prepare imidazo[1,2-a][1,6

Enolates ambushed – asymmetric tandem conjugate addition and subsequent enolate trapping with conventional and less traditional electrophiles

• Péter Kisszékelyi and
• Radovan Šebesta

Beilstein J. Org. Chem. 2023, 19, 593–634, doi:10.3762/bjoc.19.44

• , which begins with a Cu-catalyzed enantioselective conjugate addition/enolate alkylation tandem reaction sequence utilizing the N-heterocyclic carbene ligand L40 [112]. Ketone 232 was isolated in 61% yield and 81% ee. Hereafter, the authors were able to synthesize the complex tetracyclic structure within

Application of olefin metathesis in the synthesis of functionalized polyhedral oligomeric silsesquioxanes (POSS) and POSS-containing polymeric materials

• Patrycja Żak and
• Cezary Pietraszuk

Beilstein J. Org. Chem. 2019, 15, 310–332, doi:10.3762/bjoc.15.28

• undergoes fast decomposition as a result of β-transfer of the silyl group in the appropriate β-(silyl)rutenacyclobutane complex to ruthenium followed by reductive elimination of the corresponding propene derivative (Scheme 1c). The transformation resulted in complexes that do not contain a carbene ligand

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

• NHC ligand. This result suggests that a fast propagation ensured by a smaller carbene ligand rather than robustness ascribed to larger catalysts is a prerequisite for the efficient metathesis in homogeneous aqueous conditions. Except in the case of catalyst 3a, exhibiting the lowest activity under

Water-soluble SNS cationic palladium(II) complexes and their Suzuki–Miyaura cross-coupling reactions in aqueous medium

• Alphonse Fiebor,
• Richard Tia,
• Banothile C. E. Makhubela and
• Henok H. Kinfe

Beilstein J. Org. Chem. 2018, 14, 1859–1870, doi:10.3762/bjoc.14.160

• catalyst for subsequent reactions after simple phase separation [31]. However, the commonly employed phosphorous and carbene ligand-based palladium(II) complexes are found to be in most cases sensitive to moisture and air limiting the scope of their catalytic application in aqueous reactions [32][33]. This

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

• 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. Keywords: carbonyl complexes

• occupation for the carbene dipiy (0.738) at C3, which decreases in the order 6 πe− carbene III (0.687), 4 πe− carbene II (0.592) and the acyclic 4πe− carbene I (0.618) (Table 3). For the rhodium complexes these values are higher, so that an overall π-electron-withdrawing character of the carbene ligand can

• metal π-donor bond are revealed. One is found for the II-Rh complex between the HOMO−2 of the ligand and the dxy orbital of Rh (plus contributions of the chlorido and the antibonding π-orbital of the cis-CO ligand) at −9.07 eV (HOMO−9) (Figure 5). The other is found between the HOMO−1 of the carbene

On the mechanism of imine elimination from Fischer tungsten carbene complexes

• Philipp Veit,
• Christoph Förster and
• Katja Heinze

Beilstein J. Org. Chem. 2016, 12, 1322–1333, doi:10.3762/bjoc.12.125

• related pentacarbonyl complexes of bis[di(isopropyl)amino]carbene 10 [49] M(CO)5(10) (M = Cr, Mo, W) readily decarbonylate at room temperature to give the tetracarbonyl complexes M(CO)4(κC,κN-10) with a side-on coordinated carbene ligand (Scheme 1e) [50][51][52]. Under CO atmosphere, the molybdenum and

• resonances are found in a similar region as for other (pentacarbonyl)tungsten complexes W(CO)5(E-14R) with the α-ferrocenyl NH carbene ligand :C(NHR)Fc E-14R (R = Me, Et, n-Pr [23], n-Bu [25], n-Pent [21]). Due to additional ring-current effects and non-classical NH···Fe hydrogen bonding [54][55][56][57][58

• states. The Gibbs free energies are reported at 298 K. The first pathway comprises the migration–elimination mechanism involving a 1,2-H shift at the coordinated carbene ligand E-2 or Z-2 in W(CO)5(E-2) or W(CO)5(Z-2) followed by dissociation of the respective imine E-3 (pathway 1a, Scheme 3) or Z-3

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

• ppm in 3) when the N-heterocyclic carbene ligand is situated trans to the N-atom of the quinolinolate. The corresponding proton of the second quinolinolate ligand (with the N-atom situated cis to the NHC) is high-field shifted and resonates at 5.48 (in 1b), 5.32 (in 2b) and 5.9 (in 4). The OC-6-14

New metathesis catalyst bearing chromanyl moieties at the N-heterocyclic carbene ligand

• Agnieszka Hryniewicka,
• Szymon Suchodolski,
• Agnieszka Wojtkielewicz,
• Jacek W. Morzycki and
• Stanisław Witkowski

Beilstein J. Org. Chem. 2015, 11, 2795–2804, doi:10.3762/bjoc.11.300

Pyridylidene ligand facilitates gold-catalyzed oxidative C–H arylation of heterocycles

• Kazuhiro Hata,
• Hideto Ito,
• Yasutomo Segawa and
• Kenichiro Itami

Beilstein J. Org. Chem. 2015, 11, 2737–2746, doi:10.3762/bjoc.11.295

• as a DFT study, indicated unusual stability of gold(III) species stabilized by strong electron donation from the 2-pyridylidene ligand. Thus, the gold(I)-to-gold(III) oxidation process is thought to be facilitated by the highly electron-donating 2-pyridylidene ligand. Keywords: carbene ligand; C–H

Rhodium, iridium and nickel complexes with a 1,3,5-triphenylbenzene tris-MIC ligand. Study of the electronic properties and catalytic activities

• Carmen Mejuto,
• Beatriz Royo,
• Gregorio Guisado-Barrios and
• Eduardo Peris

Beilstein J. Org. Chem. 2015, 11, 2584–2590, doi:10.3762/bjoc.11.278

• , Portugal 10.3762/bjoc.11.278 Abstract 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

• nature of the carbene ligand while maintaining a similar structural environment on the catalyst. The catalytic addition of arylboronic acids to α,β-unsaturated ketones [58][59][60][61][62] is a process for which several Rh(I)-NHC complexes have afforded excellent activities and chemoselectivities [58][63

• obtaining a series of Rh(I), Ir(I) and Ni(II) complexes. Interestingly, the tris-MIC complex of Ni is the first trimetallic Ni complex with a tris-carbene ligand. The electron-donating properties of the ligand were assessed by cyclic voltammetry and by IR spectroscopy of the corresponding carbonylated tris

Synthesis and structures of ruthenium–NHC complexes and their catalysis in hydrogen transfer reaction

• Chao Chen,
• Chunxin Lu,
• Qing Zheng,
• Shengliang Ni,
• Min Zhang and
• Wanzhi Chen

Beilstein J. Org. Chem. 2015, 11, 1786–1795, doi:10.3762/bjoc.11.194

• ][17][18] and in complex 1. The bond distance of Ru–Nacetonitrile (2.113 Å) at the trans-position of the carbene ligand is longer than the other three Ru–Nacetonitrile bonds (2.023–2.033 Å) and the Ru–Npyrimidine (2.064 Å). Similarly, the reaction of the in situ generated nickel–NHC complex from

• –N angles of the three acetonitrile ligands and the Ru(II) ion are 86.03, 89.12 and 174.99°, respectively. Similar to complex 2, the bond distance of Ru–Nacetonitrile (2.130 Å) at the trans-position of the carbene ligand is slightly longer than the other bond distances of Ru–Nacetonitrile (2.030 and

• 2 and 3 are a bit better than 1 for this transformation. The trans-effect of carbene ligand may promote the substitution of trans-positioned acetonitrile ligand by other substrates in the catalytic reaction. Since complexes 2 and 3 are found to be the efficient catalysts for transfer hydrogenation

Consequences of the electronic tuning of latent ruthenium-based olefin metathesis catalysts on their reactivity

• Karolina Żukowska,
• Eva Pump,
• Aleksandra E. Pazio,
• Krzysztof Woźniak,
• Luigi Cavallo and
• Christian Slugovc

Beilstein J. Org. Chem. 2015, 11, 1458–1468, doi:10.3762/bjoc.11.158

• coordination site (trans to the carbene ligand) can activate the (pre-)catalyst by lowering the energy barrier TS1trans to reach the active 14-electron species [14][56][57]. As both substituents, the CHO and the CN group, sterically shield the vacant coordination site, it is easily conceivable that such

Highly selective palladium–benzothiazole carbene-catalyzed allylation of active methylene compounds under neutral conditions

• Antonio Monopoli,
• Pietro Cotugno,
• Carlo G. Zambonin,
• Francesco Ciminale and
• Angelo Nacci

Beilstein J. Org. Chem. 2015, 11, 994–999, doi:10.3762/bjoc.11.111

• from Pd2dba3 and 3-methylbenzothiazolium salt V as precursors. A comparison of the performance of benzothiazole carbene with phosphanes and an analogous imidazolium carbene ligand is also proposed. Keywords: active methylene compounds; allylic carbonates; Pd–benzothiazol-2-ylidene complex; Tsuji–Trost

• -allylated product 1 (Table 1, entry 12). Interestingly, the same result was achieved using the Pd–carbene complex prepared in situ from Pd2dba3 and 3-methylbenzothiazolium iodide (V) as a carbene precursor (Table 1, entry 14). In this case, to generate the carbene ligand, the addition of the base NaH was

• induction period was observed, thus indicating the need for the reduction of the Pd(II) precatalyst to the Pd(0) active species (Table 1, entry 15). Finally, we also compared the performance of our 3-methylbenzothiazol-2-ylidene carbene ligand with that of the analogous 1,3-dimethylimidazol-2-ylidene by

Gold(I)-catalyzed hydroarylation reaction of aryl (3-iodoprop-2-yn-1-yl) ethers: synthesis of 3-iodo-2H-chromene derivatives

• Pablo Morán-Poladura,
• Eduardo Rubio and
• José M. González

Beilstein J. Org. Chem. 2013, 9, 2120–2128, doi:10.3762/bjoc.9.249

• , the influence of the ancillary ligand and the arene over the cyclization products was recognized [43]. The catalyst based on the N-heterocyclic carbene ligand IPr [49] (IPr: 1,3-bis(2,6-diisopropyl)phenylimidazol-2-ylidene), was identified as suitable controller to favor the formation of the product

N-Heterocyclic carbene–palladium catalysts for the direct arylation of pyrrole derivatives with aryl chlorides

• Ismail Özdemir,
• Nevin Gürbüz,
• Nazan Kaloğlu,
• Öznur Doğan,
• Murat Kaloğlu,
• Christian Bruneau and
• Henri Doucet

Beilstein J. Org. Chem. 2013, 9, 303–312, doi:10.3762/bjoc.9.35

• imidazolylidene carbene ligands for the Pd-catalyzed direct arylation of pyrroles or indoles using bromobenzene and aryl iodides [42]. They observed that an important steric demand on the carbene ligand led to better results. Recently, the use of palladium(II) acetate complexes bearing both a phosphine and a

• carbene ligand, was reported by Lee and co-workers for the direct arylation of imidazoles with some aryl chlorides [46]. However, to our knowledge, N-heterocyclic carbene ligands have not yet been employed for the palladium-catalyzed direct arylation of pyrroles with aryl chlorides. As carbene ligands

• chlorides can be promoted by N-heterocyclic carbene ligands associated to palladium. So far, the reason for the influence of the nature of the carbene ligand on such couplings remains unclear. However, the presence of bulky N-substituents on the benzimidazole ring, such as 3,5-di-tert-butylbenzyl (1–4) or

Recent developments in gold-catalyzed cycloaddition reactions

• Fernando López and
• José L. Mascareñas

Beilstein J. Org. Chem. 2011, 7, 1075–1094, doi:10.3762/bjoc.7.124

• regenerating the catalyst (PtCl2). In addition, DFT calculations suggested that gold catalysts could be even more active than PtCl2. Accordingly, the use of a cationic Au(I) catalyst containing a σ-donating N-heterocyclic carbene ligand (Au6/AgSbF6, Scheme 26) enabled these reactions at lower temperatures and

Synthesis of chiral mono(N-heterocyclic carbene) palladium and gold complexes with a 1,1'-biphenyl scaffold and their applications in catalysis

• Lian-jun Liu,
• Feijun Wang,
• Wenfeng Wang,
• Mei-xin Zhao and
• Min Shi

Beilstein J. Org. Chem. 2011, 7, 555–564, doi:10.3762/bjoc.7.64

• the presence of t-BuOK at 50 °C to give [(NHC)Pd(allyl)I] complex (S)-7 in 70% yield as a yellow solid after purification by silica gel column chromatography (Scheme 2) [45][46]. Due to the stereochemical orientation of π-allyl group relative to the unsymmetrical carbene ligand, this NHC–Pd complex

The intriguing modeling of cis–trans selectivity in ruthenium-catalyzed olefin metathesis

• Naeimeh Bahri-Laleh,
• Raffaele Credendino and
• Luigi Cavallo

Beilstein J. Org. Chem. 2011, 7, 40–45, doi:10.3762/bjoc.7.7

• SIMes N-heterocyclic carbene ligand, see Scheme 2. Although it is well known that the steric hindrance of the olefin substituent has a remarkable role on both reactivity and products distribution, propene can still be considered as a prototype of terminal olefins, and can provide insights into the

The cross-metathesis of methyl oleate with cis-2-butene-1,4-diyl diacetate and the influence of protecting groups

• Arno Behr and
• Jessica Pérez Gomes

Beilstein J. Org. Chem. 2011, 7, 1–8, doi:10.3762/bjoc.7.1

• and an inexpensive base chemical was prepared. Various metathesis catalysts were investigated, disclosing that the Schiff base ruthenium indenylidene catalyst [Ru]-7 bearing a N-heterocyclic carbene ligand, which is an already industrial implemented metathesis catalyst, led to high conversions and

Halide exchanged Hoveyda-type complexes in olefin metathesis

• Julia Wappel,
• César A. Urbina-Blanco,
• Mudassar Abbas,
• Jörg H. Albering,
• Robert Saf,
• Steven P. Nolan and
• Christian Slugovc

Beilstein J. Org. Chem. 2010, 6, 1091–1098, doi:10.3762/bjoc.6.125

• 16.10 ppm. All other features of the 1H NMR spectrum of 2 are similar to those of 1 indicating slightly hindered rotation of the N-heterocyclic carbene ligand and a trans-disposition of the two halide ligands. In contrast, the rotation of the NHC ligand around the Ru–NHC bond in 3 is hindered as shown