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

• may be mentioned here that the complexes [(SIPr)CuX] (X = Cl, Br, I) were also prepared through transmetalation, a method that will be discussed later. In contrast to the aforementioned complexes, [(IMes)CuX] and [(SIMes)CuX] (X = Cl, Br) were best prepared from the corresponding NHC·HCl precursors

• , K2CO3, or Cs2CO3) in the presence of copper chlorides (Scheme 11). However, this protocol required environmental unfriendly solvents such as 3-chloropyridine and high temperatures. In general, CuCl gave higher yields than CuCl2·2H2O typically ranging from 70 to 99% [24]. Furthermore, an IMes–CuCl

• anionic hybrid NHC, “IMes-acac” consisting of fused diaminocarbene and acetylacetonato units. The latter afforded a series of representative Cu(I) complexes through bidentate coordination (Scheme 16) [30]. 1.2 Deprotonation of NHC-precursors with Cu2O Another important and facile method involves heating

Recent advances in Cu-catalyzed C(sp³)–Si and C(sp³)–B bond formation

• Balaram S. Takale,
• Ruchita R. Thakore,
• Elham Etemadi-Davan and
• Bruce H. Lipshutz

Beilstein J. Org. Chem. 2020, 16, 691–737, doi:10.3762/bjoc.16.67

• (307) was established using CuBr/JohnPhos/LiO-t-Bu and CuCl/IMes/NaO-t-Bu, respectively, in the presence of I-CH2F (361) as the methylfluorinating agent, affording products reflecting excellent control of regioselectivity. This transformation is useful for the synthesis, e.g., of monofluorinated

Copper-catalyzed enantioselective conjugate addition of organometallic reagents to challenging Michael acceptors

• Delphine Pichon,
• Jennifer Morvan,
• Christophe Crévisy and
• Marc Mauduit

Beilstein J. Org. Chem. 2020, 16, 212–232, doi:10.3762/bjoc.16.24

• -catalyzed conjugate addition of alkyl boranes to α,β-unsaturated 2-acyl-1-methylbenzimidazoles 33 [36]. Based on a previous study dealing with the CuCl/IMes-catalyzed addition of various alkylated 9BBN derivatives [37], the authors screened a set of various chiral NHC precursors. The imidazolium compound

Allylic cross-coupling using aromatic aldehydes as α-alkoxyalkyl anions

• Akihiro Yuasa,
• Kazunori Nagao and
• Hirohisa Ohmiya

Beilstein J. Org. Chem. 2020, 16, 185–189, doi:10.3762/bjoc.16.21

• silyl ether, which are derived from the Pd-catalyzed allylic silylation of 2a and the Cu-catalyzed silylation of 1a and the subsequent [1,2]-Brook rearrangement, respectively. In this coupling reaction, (SIPr)CuCl was a slightly better copper complex than (IPr)CuCl (62%), (SIMes)CuCl (60%) and (IMes

Recent advances on the transition-metal-catalyzed synthesis of imidazopyridines: an updated coverage

• Gagandeep Kour Reen,
• Ashok Kumar and
• Pratibha Sharma

Beilstein J. Org. Chem. 2019, 15, 1612–1704, doi:10.3762/bjoc.15.165

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

• substituent (Figure 15) at the nitrogen atoms were investigated by Copéret and Thieuleux et al. in the tandem ring-opening–ring-closing alkene metathesis (RO–RCM) of cis-cyclooctene (47) and their performance were compared to those of the classical GII-SIMes and GII-IMes [29]. The dissymmetry of the NHC

• ligand in 59 and 60 allowed for the selective formation of cyclic dimeric and trimeric products in place of polymers from cyclooctene, while the symmetrical analogues GII-SIMes and GII-IMes led mainly to polymers (Figure 15). Following a study on degenerate metathesis reactions that had highlighted a

• sterically demanding diethyl allylmethallylmalonate (9) under standard conditions (Scheme 2) and compared to their unsymmetrical saturated NHC–Ru complexes 90–92 (Figure 18) as well as a set of commercially available catalysts having symmetrical IMes or SIMes NHC ligands. The unsaturated indenylidene

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

• significant role. Keywords: activation; IMes; indenylidene; olefin metathesis; SIMes; Introduction Olefin metathesis has been an intensely studied reaction due to its wide use [1], in industrial applications, especially in petrochemistry [2], i.e., the Phillips Triolefin (PTP) process or the Shell Higher

• (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

• or isopropyl groups at the ortho positions of the phenyl substituent, compared to the unsubstituted 1 and 2. Comparing IMes vs SIMes, the activation is about 1 kcal/mol more favoured for the unsaturated system [42][43]. The absolute difference of 1 kcal/mol is maintained throughout the mechanism

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

• Grubbs complexes featuring either SIMes (1,3-bis(2,4,6-trimethylphenyl)-4,5-dihydroimidazol-2-ylidene) or IMes (1,3-bis(2,4,6-trimethylphenyl)imidazol-2-ylidene) ligands are another class of important ruthenium-based metathesis catalysts, where the initiation relies on phosphine dissociation. The

• experimental values for PCy3 dissociation for these catalysts are 23.0 ± 0.4 and 24 ± 1 kcal/mol for SIMes-containing and IMes-containing systems, respectively [57]. Recently Grubbs synthesized and described also a novel metathesis catalyst featuring a labile carbodicarbene ligand replacing PCy3 [48]. Inspired

• by these results we decided to design similar systems with either SIMes or IMes and cationic carbenes. For all systems 1–3-GrII and 1–3-GrII_IMes the energy barriers of initiation are relatively high (30–40 kcal/mol, Scheme 4), indicating that these complexes are completely unsuitable for olefin

Hydroarylations by cobalt-catalyzed C–H activation

• Rajagopal Santhoshkumar and
• Chien-Hong Cheng

Beilstein J. Org. Chem. 2018, 14, 2266–2288, doi:10.3762/bjoc.14.202

• DMPU provided C–H alkylated products 24 in good yields with high linear selectivity (Scheme 16). Later, Yoshikai’s group reported a ligand-controlled hydroarylation of styrenes with 2-phenylpyridines 3 in the presence of CoBr2-IMes and CoBr2-PCy3 catalysts to synthesize linear and branched selective

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

• wave at a half-wave potential of E1/2 = 0.64 mV, which is significantly lower than the half-wave potential (E1/2 = 0.72 mV) exhibited by the monometallic NHC-based complex [NiCpCl(IMes)] [50] (IMes = 1,3-mesitylimidazolylidene). This is in agreement with the stronger electron-donating character for the

• ligand in 4 compared to IMes. From the differential pulse voltammetry (DPV) analysis generated for 4 it can be seen that there is only one redox event taking place, thus evidencing that the trimetallic complex 4 contains three nickel fragments that are essentially decoupled. Since we previously evaluated

N-Heterocyclic carbenes

• Steven P. Nolan

Beilstein J. Org. Chem. 2015, 11, 2474–2475, doi:10.3762/bjoc.11.268

• seminal work of Bertrand [1] and Arduengo [2] (and mostly post-1994–1995) the field has underwent fantastic advances. Carbenes such as 1,3-dimesityl-1,3-dihydro-2H-imidazol-2-ylidene (IMes) and the 2,6-diisopropylphenyl analogue (IPr) have become commonplace, replacing tertiary phosphanes as modifying

Copper-catalyzed stereoselective conjugate addition of alkylboranes to alkynoates

• Takamichi Wakamatsu,
• Kazunori Nagao,
• Hirohisa Ohmiya and
• Masaya Sawamura

Beilstein J. Org. Chem. 2015, 11, 2444–2450, doi:10.3762/bjoc.11.265

• as PPh3 and PCy3 or the DPPE bisphopshine was also effective in promotion of the reaction, but resulted in a reduced stereoselectivity (Table 1, entries 2–4). No reaction occurred with N-heterocyclic carbenes (NHC) such as IMes or IPr (Table 1, entries 5 and 6). The reaction with (IMes)CuCl or (IPr

Efficient synthetic protocols for the preparation of common N-heterocyclic carbene precursors

• Morgan Hans,
• Jan Lorkowski,
• Albert Demonceau and
• Lionel Delaude

Beilstein J. Org. Chem. 2015, 11, 2318–2325, doi:10.3762/bjoc.11.252

• tetrafluoroborate without any apparent complication [59]. We have further optimized this procedure on the occasion of a mechanistic study of the Staudinger reaction catalyzed by NHC·ketene zwitterions (Scheme 5) [60]. Synthesis of 1,3-dimesitylimidazolinium chloride The “saturated” analogue of the IMes carbene, 1,3

Half-sandwich nickel(II) complexes bearing 1,3-di(cycloalkyl)imidazol-2-ylidene ligands

• Johnathon Yau,
• Kaarel E. Hunt,
• Laura McDougall,
• Alan R. Kennedy and
• David J. Nelson

Beilstein J. Org. Chem. 2015, 11, 2171–2178, doi:10.3762/bjoc.11.235

• prepared [Ni(η1-Cp)(η5-Cp)(IMes)] (1) from the reaction of the free carbene with nickelocene (IMes = 1,3-bis(2,4,6-trimethylphenyl)imidazol-2-ylidene) (Scheme 1a) [9]. Complexes of the form [NiCl(Cp)(NHC)], such as complex 2, are typically prepared by simply heating nickelocene with the corresponding

• their lower TEP compared to IPr, IMes, and IPr*, for example [7][26][27]. The crystal structure data for [NiCl(Cp)(ICy)] (3) reveal five different Ni–C distances between the nickel centre and the cyclopentadienyl ligand, spanning a range of ca. 0.14 Å. These bond lengths are indicative of distortion

• versus sealed tubes. Molecular structures of complexes [NiCl(Cp)(ICy)] (3) (left) and [NiCl(Cp)(IDD)] (4) (right) as determined by single crystal X-ray diffraction. Displacement ellipsoids are drawn at 50% probability. Most H atoms are excluded for clarity. Synthesis of [Ni(η1-Cp)(η5-Cp)(IMes)] (1) and

A facile synthetic route to benzimidazolium salts bearing bulky aromatic N-substituents

• Gabriele Grieco,
• Olivier Blacque and
• Heinz Berke

Beilstein J. Org. Chem. 2015, 11, 1656–1666, doi:10.3762/bjoc.11.182

• ][45][48][53][54] of either 6 and 7 failed. For instance, the method of Hintermann [23] that uses the combination of paraformaldehyde and trimethylsilyl chloride (TMSCl) gave satisfying results in the preparation of the known IMes and IPr derivatives, but failed for the synthesis of both 1-Cl and 2-Cl

Acid, silver, and solvent-free gold-catalyzed hydrophenoxylation of internal alkynes

• Marcia E. Richard,
• Daniel V. Fraccica,
• Kevin J. Garcia,
• Erica J. Miller,
• Rosa M. Ciccarelli,
• Erin C. Holahan,
• Victoria L. Resh,
• Aakash Shah,
• Peter M. Findeis and
• Robert A. Stockland Jr.

Beilstein J. Org. Chem. 2013, 9, 2002–2008, doi:10.3762/bjoc.9.235

• , we extend the chemistry to the synthesis of arylgold compounds containing carbene ligands. Results and Discussion The synthesis of the carbene-ligated arylgold compounds was accomplished using (NHC)AuCl (NHC = IMes, SIMes, IPr, SIPr) precursors. For the initial screening runs, (IMes)AuCl and 4-tert

• -butylphenylboronic acid were chosen as representative substrates. The same protocol that was successful for the synthesis of arylgold compounds from (JohnPhos)AuCl or (t-BuXPhos)AuCl afforded incomplete conversion and the formation of an intractable mixture of gold compounds when (IMes)AuCl was used. After some

• experimentation with the reaction conditions and different mineral bases, the key issue appeared to be the use of THF as the solvent. Changing from THF to iPrOH afforded high yields of (IMes)Au(C6H4t-Bu) after heating at 50 °C for 20 minutes. Once a successful protocol was determined for the model system, the

True and masked three-coordinate T-shaped platinum(II) intermediates

• Manuel A. Ortuño,
• Salvador Conejero and
• Agustí Lledós

Beilstein J. Org. Chem. 2013, 9, 1352–1382, doi:10.3762/bjoc.9.153

• -heterocyclic carbene (NHC) ligands (Figure 6), which have been proven to be useful stabilizing electron-deficient transition-metal species [25][26][27]. In this regard, recent studies state that the use of IMes* (4,5-dimethyl-1,3-bis(2,4,6-trimethylphenyl)imidazol-2-ylidene) and IMes (1,3-bis(2,4,6

• -trimethylphenyl)imidazol-2-ylidene) ligands in [Pt(Me)(NHC)2]+ T4 and [Pt(NHC’)(NHC)]+ T5 (NHC = IMes*, IMes; NHC’ = cyclometalated ligand) provides pure T-shaped species with no agostic stabilization [28]. Additionally, the resulting [Pt(Ar)(IMes*)2]+ T6 formed after C–H bond activation has also proven to be a

• three-coordinate species with no agostic interactions according to the X-ray structure of the derivative T6d, in which the closest Pt–H contact is located at 3.117 Å. The absence of agostic interactions has been attributed to geometrical constraints, the limited flexibility of the mesityl groups in IMes

1-n-Butyl-3-methylimidazolium-2-carboxylate: a versatile precatalyst for the ring-opening polymerization of ε-caprolactone and rac-lactide under solvent-free conditions

• Astrid Hoppe,
• Faten Sadaka,
• Claire-Hélène Brachais,
• Gilles Boni,
• Jean-Pierre Couvercelle and
• Laurent Plasseraud

Beilstein J. Org. Chem. 2013, 9, 647–654, doi:10.3762/bjoc.9.73

• efficiencies and molecular-weight control [20][27][28][29][30][31][32]. Their selectivity and conversion rate are influenced by the nature of the monomer and the carbene used. Sterically encumbered carbenes, such as 1,3-dimesitylimidazol-2-ylidene (IMes, Figure 1), are known to be highly active for the ROP of

Backbone tuning in indenylidene–ruthenium complexes bearing an unsaturated N-heterocyclic carbene

• César A. Urbina-Blanco,
• Xavier Bantreil,
• Hervé Clavier,
• Alexandra M. Z. Slawin and
• Steven P. Nolan

Beilstein J. Org. Chem. 2010, 6, 1120–1126, doi:10.3762/bjoc.6.128

• 10.3762/bjoc.6.128 Abstract The steric and electronic influence of backbone substitution in IMes-based (IMes = 1,3-bis(2,4,6-trimethylphenyl)imidazol-2-ylidene) N-heterocyclic carbenes (NHC) was probed by synthesizing the [RhCl(CO)2(NHC)] series of complexes to quantify experimentally the Tolman

• reaction conditions are required [13][23][24][25]. Herein, we present the synthesis and characterization of three new ruthenium–indenylidene catalysts and their performance in benchmark metathesis transformations. In order to quantify the Tolman electronic parameter associated with IMes-type (IMes = 1,3

• system, since it is easily synthesised and handled [34]. In this work, a series of [RhCl(CO)2(NHC)] complexes were synthesized in order to evaluate the electronic donor ability of the NHCs. The free carbenes were prepared according to literature procedures. Free IMes (4b) [35] and IMesMe (4a) [36] were

Recent progress on the total synthesis of acetogenins from Annonaceae

• Nianguang Li,
• Zhihao Shi,
• Yuping Tang,
• Jianwei Chen and
• Xiang Li

Beilstein J. Org. Chem. 2008, 4, No. 48, doi:10.3762/bjoc.4.48

• of 67 to 1,3-dimesitylimidazol-2-ylidene ruthenium benzylidene catalyst (RuCl2(=C(H)-Ph)(PCy3)(IMes)) after protection of the free hydroxyl group afforded the RCM product 68. Hydrogenation of the double bond of dihydrofuran 68 and iodination of the primary alcohol gave 69, which was then utilized to

Expedient syntheses of the N-heterocyclic carbene precursor imidazolium salts IPr·HCl, IMes·HCl and IXy·HCl

• Lukas Hintermann

Beilstein J. Org. Chem. 2007, 3, No. 22, doi:10.1186/1860-5397-3-22

• prominent members of the family of N-heterocyclic carbenes (NHC) are the sterically encumbered imidazolylidenes IPr and IMes (Figure 1), which can also be considered as analogues of bulky and electron-rich tertiary phosphanes. In contrast to the latter, their synthesis does not involve air-sensitive or

• full experimental data. The carbenes IPr, IMes, IXy and their imidazolium salt precursors Synthetic routes to and diazadiene precursors for imidazolium salts. The imidazolium salt synthesis as a 1, 5-dipolar electrocyclization. Potential side-reactions in the imidazolium salt synthesis. Optimization of