Active-metal template clipping synthesis of novel [2]rotaxanes

• Cătălin C. Anghel,
• Teodor A. Cucuiet,
• Niculina D. Hădade and
• Ion Grosu

Beilstein J. Org. Chem. 2023, 19, 1776–1784, doi:10.3762/bjoc.19.130

• obtained by CuAAC in the presence of CuCl(SIMes)(4,7-diclorophenantroline) as catalyst, with very good yields. Next, we set to study the ability of compound 6 to form copper(I) complexes able to act as active-metal templates for [2]rotaxane synthesis. Therefore, complexation studies of 6 with CuCl(SIMes

• ) were performed and analyzed by HRMS, demonstrating formation of the complex (see Supporting Information File 1, Figure S15). The HRESI(+)-MS spectrum showed the base peak at m/z = 2029.1594 corresponding to [Cu(6)(SIMes)]+. With this complex in our hands we set to investigate the synthesis of [2

• . Our results proved that the CuAAC reaction catalyzed by copper(I) N-heterocyclic carbenes can be successfully used in the synthesis of [2]rotaxanes. This, combined with the fast and simple assembly of [CuCl(SIMes)] [45][46] could lead to the development of a Cu(I) NHC click chemistry in the field of

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

• , mixtures of mono- and bisNHC complexes were systematically obtained from [(IMes)AgCl], [(SIMes)AgCl], and [(ICy)AgCl] [15]. Kolychev obtained NHC–Cu(I) complexes 71 in high yields through transmetallation by reacting an equimolar amount of [(6-Dipp)AgBr] (70, n = 1) or [(7-Dipp)AgBr] (70, n = 2) with

• the 1,3-dipole enhancing its nucleophilicy. The latter subsequently reacts with the 1,3-dipolarophile to afford the cycloadduct. In 2010, Diez-González et al. utilized NHC–Cu(I) complexes, [(IAd)CuI] and [(SIMes)CuBr] (see Scheme 6 for abbreviations) for catalyzing the [3 + 2] cycloaddition of azides

CuAAC-inspired synthesis of 1,2,3-triazole-bridged porphyrin conjugates: an overview

• Dileep Kumar Singh

Beilstein J. Org. Chem. 2023, 19, 349–379, doi:10.3762/bjoc.19.29

• triazoloporphyrins 32a–c and triazole-bridged bisporphyrins 34 in good yields. The “click reaction” of azidoporphyrin 30 with the terminal alkynes 31a–c and 33 in a THF/water (3:1) mixture was investigated by using different catalytic systems. Among these, copper carbene (SIMes)CuBr proved to be a better catalyst

• (I)-catalysts such as CuI, (SIMes)CuBr, Cu(MeCN)4PF6, and CuBr(PPh3)3 have been also used in some reactions. Furthermore, a few reports describe the use of ligands like DIPEA, TBTA, NMP, Et3N, etc. along with copper catalysts to stabilize the Cu(I)-oxidation state and speed up the click reaction. It

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

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

• the synthesis of a family of corresponding ortho-substituted N-fluorophenyl, N’-aryl NHC Ru complexes (Figure 4) [13][14]. The behavior of this catalyst family was tested in the RCM of diethyl diallylmalonate (7, Scheme 1) and compared with that of GII-SIMes and HGII-SIMes. Interestingly, catalysts 3a

• and 4a clearly outperformed GII-SIMes, with catalyst 4a emerging as the most efficient of all (>97% conversion in 9 min). Complex 5a showed a higher initiation rate with respect to GII-SIMes, but eventually was found to be less efficient due to a decrease in its catalytic activity related to

• concomitant decomposition. As for Hoveyda-type catalysts 3b, 4b and 5b, they all disclosed lower activity than the parent complex HGII-SIMes, with catalyst 5b being the least efficient of all in this series (>97% conversion in 100 min). Finally, 6a as well as the phosphine-free 6b showed to be very poor

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

• methoxyethene as a substrate (Scheme 2). This substrate was selected in order to facilitate our analysis [39]. Computationally no significant differences exist by using ethene or methoxyethene [40][41]. The saturation of the backbone of the NHC has also been taken into account, thus considering either the SIMes

• 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

Comparative profiling of well-defined copper reagents and precursors for the trifluoromethylation of aryl iodides

• Peter T. Kaplan,
• Jessica A. Lloyd,
• Mason T. Chin and
• David A. Vicic

Beilstein J. Org. Chem. 2017, 13, 2297–2303, doi:10.3762/bjoc.13.225

• [10][11]. [(SIMes)CuCF3] (1, SIMes = 1,3-bis(2,4,6-trimethylphenyl)-4,5-dihydroimidazol-2-ylidene), which is in equilibrium with [(SIMes)2Cu][Cu(CF3)2] (2), can either be used directly or prepared in situ through the reaction of [(SIMes)Cu(O-t-Bu)] (3) with Me3SiCF3 (Scheme 2) [10]. Phenanthroline

• relative to [(phen)CuCF3] and gave product yields less than 10% (Figure 1). We then compared B2, the highest performing [(phen)CuCF3] system in DMF, to the performance of isolated A1 and in situ generated (A2) [(SIMes)CuCF3] as well as to the [(PPh3)3CuCF3 + dtbpy] combination (C1) under their reported

• performance improvement may be possible. System A1, on the other hand, displays sluggish reactivity at early reaction times, but steadily produces 4-(trifluoromethyl)-1,1’-biphenyl in yields that are slightly higher than C1 after 30 hours. [(SIMes)Cu(CF3)], generated in situ from [(SIMes)Cu(O-t-Bu)] and

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

• as the original starting complex M32 does. Trapping the active species of the SIMes analogues failed. To shed light about the different behavior of complexes 2a and 2b we envisaged DFT calculations. The optimized geometry of 2b is in perfect agreement with the X-ray structure [48] (rmsd = 0.032 Å and

• chloride trans to the alkylidene group. The next step corresponds to a rotation of the chloride ligand from the coordination position trans to alkylidene ligand to a coordination position cis to both the alkylidene and the SIMes ligands. This rearrangement requires dissociation of the quinolinolate N atom

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

• -dimesitylimidazolin-2-ylidene (SIMes), was first isolated in 1995 by Arduengo et al. [61] who later disclosed the experimental details of the synthetic path leading to this stable NHC and its immediate precursor, 1,3-dimesitylimidazolinium chloride (SIMes·HCl) [43]. The latter salt was obtained in three steps

Olefin metathesis in air

• Lorenzo Piola,
• Fady Nahra and
• Steven P. Nolan

Beilstein J. Org. Chem. 2015, 11, 2038–2056, doi:10.3762/bjoc.11.221

• provides steric protection to the metal center and its σ-donating ability stabilizes both the pre-catalyst and the catalytically operating intermediate [49]. The most active being complex 15, bearing SIMes (1,3-bis(2,4,6-trimethylphenyl)-4,5-dihydroimidazol-2-ylidene, 17) as ligand, is known nowadays as

• 2000, the Hoveyda–Grubbs 2nd generation catalyst was reported (33), simultaneously, by Hoveyda (Scheme 6, entry 1) [54] and Blechert (Scheme 6, entry 2) [55] bearing a SIMes ligand instead of the phosphine. Complex 33 was able to perform RCM of trisubstitued olefins and CM in high efficiency, and

• . Also reported was the cyclization of N-allyl-N-(methallyl)tosylamide (79) in nondegassed and undistilled ethyl acetate (ACS grade), catalyzed by 87 (0.25 mol %), at 70 °C in 1 h with a conversion of 98%. In 2014, Grela and co-workers reported the synthesis N,N-unsymmetrically substituted SIMes-bearing

Nitro-Grela-type complexes containing iodides – robust and selective catalysts for olefin metathesis under challenging conditions

• Andrzej Tracz,
• Mateusz Matczak,
• Katarzyna Urbaniak and
• Krzysztof Skowerski

Beilstein J. Org. Chem. 2015, 11, 1823–1832, doi:10.3762/bjoc.11.198

• properties. Great improvement of catalyst efficiency in the transformation of sterically non-demanding alkenes have been achieved by the replacement of the classical SIMes ligand with the bulkier SIPr ligand (Scheme 1) [8][9]. Metathesis catalysts with even larger NHC ligands have also been reported, but

• products with 80–88% yields (0.25 mol % of catalyst, 40 or 70 °C). The catalysts containing a less sterically crowded SIMEs ligand delivered 2 with poor yield, usually accompanied by significant amounts of byproducts 21 and 22. This demonstrates that large substituents in N-heterocyclic ligands (NHC) not

A comprehensive study of olefin metathesis catalyzed by Ru-based catalysts

• Albert Poater and
• Luigi Cavallo

Beilstein J. Org. Chem. 2015, 11, 1767–1780, doi:10.3762/bjoc.11.192

• ligands (less than SIMes) and/or substrates [50][51], favored the side-bound structures over the bottom-bound ones as suggested by Goddard and Grubbs, respectively [16][17][18]. This is a possible explanation of why there is experimental evidence for some structures with side confirmation. On the other

• HOMO of the NHC. When 1st and 2nd generation catalysts are compared, system 1, with the PCy3 ligand, behaves rather similary to the 2nd generation catalyst 7, with a SIMes NHC ligand. Substitution of the Cl ligands of 7 with the far bulkier O(C6F5) ligands, such as in 9, increases the preference for

• the Cl atom cis to the SIMes ligand. Moving to the pseudo-halide systems with a chelating ligand, the most striking difference is in the absolute C2H4 coordination energy, roughly 30 kcal/mol, which is about 15 kcal/mol better than in the non-chelating ligands. The chelating ligand has a minor effect

Latent ruthenium–indenylidene catalysts bearing a N-heterocyclic carbene and a bidentate picolinate ligand

• Thibault E. Schmid,
• Florian Modicom,
• Adrien Dumas,
• Etienne Borré,
• Loic Toupet,
• Olivier Baslé and
• Marc Mauduit

Beilstein J. Org. Chem. 2015, 11, 1541–1546, doi:10.3762/bjoc.11.169

• established [26]. Therefore, using only CuCl as a phosphine scavenger, we investigated the picolinic acid addition using the commercially available M2 complex 1 [27], featuring the NHC SIMes (SIMes = 1,3-bis(2,4,6-trimethylphenyl)-4,5-dihydroimidazol-2-ylidene) as a precursor. To our delight, using only 1.1

• , the SIMes-based complex 2 and the 4-bromo-substituted complex 4b were evaluated and compared with complex 4a under these optimized reaction conditions (Figure 3). While in the absence of acid, 2 displayed no catalytic activity after 30 min, the complex 4b bearing a more electron-deficient picolinate

• ligand demonstrated modest latency potential with 5% conversion after this period. In both cases, activation of the catalysts with 150 equiv of TFA did not provide full conversion of the benchmark substrate. Notably, despite a faster initiation rate, the SIMes-based catalyst 2 afforded a lower conversion

Ruthenium indenylidene “1^st generation” olefin metathesis catalysts containing triisopropyl phosphite

• Stefano Guidone,
• Fady Nahra,
• Alexandra M. Z. Slawin and
• Catherine S. J. Cazin

Beilstein J. Org. Chem. 2015, 11, 1520–1527, doi:10.3762/bjoc.11.166

• [10][11][12][13][24]. In order to reduce the cost of the Ru-based pre-catalyst, our group has investigated the use of phosphites as an economical alternative to phosphines. The reaction of triisopropyl phosphite with the pyridine-containing indenylidene complex [RuCl2(Ind)(SIMes)(py)] (SIMes = N,N

Advancements in the mechanistic understanding of the copper-catalyzed azide–alkyne cycloaddition

• Regina Berg and
• Bernd F. Straub

Beilstein J. Org. Chem. 2013, 9, 2715–2750, doi:10.3762/bjoc.9.308

• , the azide substrates could be prepared in situ by reaction of the corresponding bromide with sodium azide. For example, the reaction of benzyl bromide with sodium azide and phenylacetylene in the presence of 2 mol % [(SIMes)CuBr] in water gave 86% 1-benzyl-4-phenyl-1H-1,2,3-triazole within 18 hours at

• that CuAAC catalysis with [(SIMes)CuCl] can be notably improved by addition of aromatic nitrogen donor ligands [149]. For example, fast homogeneous catalysis in water/alcohol solvent mixtures is possible with [(SIMes)CuCl] in the presence of 4-DMAP or 1,10-phenanthroline (Scheme 11). The catalyst

• complex [(SIMes)CuCl(phen)] could be isolated as red crystals and a single crystal X-ray structure shows a distorted tetrahedral coordination geometry at the metal centre. Peak broadening indicative of ligand exchange was observed on the NMR time scale and the association constant of phenanthroline was

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

• substituents. In general, the use of 4-tert-butylphenylboronic acid gave higher yields of the arylgold compounds than 4-methoxyphenylboronic acid. Once isolated by column chromatography (basic alumina), the arylgold compounds were relatively stable white solids. The IMes and SIMes examples (4–6) were the least

• of carbene-ligated gold compounds on the addition reaction, catalysts 4–9 were screened (Table 1). When IMes or SIMes based catalysts 4, 5, or 6 were used, lower yields of the vinyl ethers were observed. Examining the reaction vessels when 4, 5, and 6 were used revealed the formation of a significant

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

• transition state is favored. The fact that the cis transition state is of lower or similar energy to the trans transition state, despite of the higher stability of the forming trans C=C skeleton, indicates that the SIMes ligand is more suitable to host a cis forming C=C bond rather than a trans C=C bond

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

• /z (%) = 340 (1) [M+], 308 (7), 290 (3), 276 (16), 265 (1), 207 (1), 165 (7), 151 (11), 133 (12), 121 (13), 109 (18), 95 (38), 81 (59), 74 (44), 67 (58), 55 (100). The ruthenium metathesis catalysts used. (SIMes: 1,3-bis-(2,4,6-trimethylphenyl)-4,5-dihydroimidazol-2-ylidene). Cross-metathesis of

Tandem catalysis of ring-closing metathesis/atom transfer radical reactions with homobimetallic ruthenium–arene complexes

• Yannick Borguet,
• Xavier Sauvage,
• Guillermo Zaragoza,
• Albert Demonceau and
• Lionel Delaude

Beilstein J. Org. Chem. 2010, 6, 1167–1173, doi:10.3762/bjoc.6.133

• complex [RuCl2(=CHPh)(SIMes)(PCy3)], CuCl, and dHbipy (SIMes is 1,3-dimesitylimidazolin-2-ylidene, dHbipy is 4,4'-di-n-heptyl-2,2'-bipyridine) was able to promote the ATRA of trichloroacetic acid onto cyclopentadiene followed by a lactonization into 3,3-dichloro-3,3a,4,6a-tetrahydro-2H-cyclopenta[b]furan

New library of aminosulfonyl-tagged Hoveyda–Grubbs type complexes: Synthesis, kinetic studies and activity in olefin metathesis transformations

• Etienne Borré,
• Frederic Caijo,
• Christophe Crévisy and
• Marc Mauduit

Beilstein J. Org. Chem. 2010, 6, 1159–1166, doi:10.3762/bjoc.6.132

• Hoveyda-like complexes. Complexes 4a, 4b and 4f can be considered to be activated catalysts, while catalyst 4g bearing a more sterically demanding NHC (SIPr) ligand shows a faster initiation compared to its SIMes analogue catalyst 4b. Additionally, 4g gave the best conversion over a reaction time of one

• hour. In order to investigate potential substrate dependency, the activity of the five SIMes-catalysts 4a–e was evaluated in three different cross-metathesis (CM) reactions involving methyl acrylate, methyl vinyl ketone (MVK) and acrylonitrile as electro-deficient alkenes and the two electron-rich