Comparison of the catalytic activity for the Suzuki–Miyaura reaction of (η⁵-Cp)Pd(IPr)Cl with (η³-cinnamyl)Pd(IPr)(Cl) and (η³-1-t-Bu-indenyl)Pd(IPr)(Cl)

• Patrick R. Melvin,
• Nilay Hazari,
• Hannah M. C. Lant,
• Ian L. Peczak and
• Hemali P. Shah

Beilstein J. Org. Chem. 2015, 11, 2476–2486, doi:10.3762/bjoc.11.269

• and feature strongly electron-donating and sterically bulky phosphine or N-heterocyclic carbene (NHC) ancillary ligands [6][7]. In particular, precatalysts of the type (η3-allyl)Pd(NHC)(Cl) have shown excellent activity for the Suzuki–Miyaura reaction, with systems incorporating an η3-cinnamyl moiety

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

• derivatives, whereas the use of triethyl orthoformate under microwave irradiation was most appropriate for the fast and efficient synthesis of imidazolinium salts. This strategy was applied to the synthesis of six common N-heterocyclic carbene precursors, namely, 1,3-dimesitylimidazolium chloride (IMes·HCl

• scattered in the literature, often relegated to supporting information, and comparison of their respective merits has become more and more challenging. In this report, we aimed at collecting a series of efficient synthetic protocols for the preparation of eight common N-heterocyclic carbene precursors

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

• heteroleptic complexes, bearing one N-heterocyclic carbene (NHC) (16–19, Figure 1) and one phosphine as ligands, represented the second crucial turning point in this chemistry. Following Herrmann’s report on bis-NHC ruthenium complexes (10–15) and their low activity [39], independently and simultaneously the

Hexacoordinate Ru-based olefin metathesis catalysts with pH-responsive N-heterocyclic carbene (NHC) and N-donor ligands for ROMP reactions in non-aqueous, aqueous and emulsion conditions

• Shawna L. Balof,
• K. Owen Nix,
• Matthew S. Olliff,
• Sarah E. Roessler,
• Arpita Saha,
• Kevin B. Müller,
• Ulrich Behrens,
• Edward J. Valente and
• Hans-Jörg Schanz

Beilstein J. Org. Chem. 2015, 11, 1960–1972, doi:10.3762/bjoc.11.212

Influence of bulky yet flexible N-heterocyclic carbene ligands in gold catalysis

• Alba Collado,
• Scott R. Patrick,
• Danila Gasperini,
• Sebastien Meiries and
• Steven P. Nolan

Beilstein J. Org. Chem. 2015, 11, 1809–1814, doi:10.3762/bjoc.11.196

• ) 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

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

• corresponding nickel–NHC complexes with [Ru(p-cymene)2Cl2]2 in refluxing acetonitrile solution. The crystal structures of three complexes determined by X-ray analyses show that the central Ru(II) atoms are coordinated by pyrimidine- or pyridine-functionalized N-heterocyclic carbene and acetonitrile ligands

• molecular structures of the complexes 4 and 5 were also studied by X-ray diffraction analysis. These ruthenium complexes have proven to be efficient catalysts for transfer hydrogenation of various ketones. Keywords: N-heterocyclic carbene; ruthenium; transfer hydrogenation; Introduction N-Heterocyclic

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

• species is also discussed, with either pyridine or phosphine ligands to dissociate. Keywords: cis; density functional theory (DFT); N-heterocyclic carbene; olefin metathesis; ruthenium; Introduction Organic synthesis is based on reactions that drive the formation of carbon–carbon bonds [1]. Olefin

• under mild conditions. The next step was the substitution of one phosphine group by an N-heterocyclic carbene, NHC, which strongly increases the activity [11][12][13][14][15]. And, furthermore, a detailed comprehensive analysis of the chemical mechanics of these Grubbs catalysts was required. Once a

Grubbs–Hoveyda type catalysts bearing a dicationic N-heterocyclic carbene for biphasic olefin metathesis reactions in ionic liquids

• Maximilian Koy,
• Hagen J. Altmann,
• Benjamin Autenrieth,
• Wolfgang Frey and
• Michael R. Buchmeiser

Beilstein J. Org. Chem. 2015, 11, 1632–1638, doi:10.3762/bjoc.11.178

• , H2ITapMe2 = 1,3-bis(2’,6’-dimethyl-4’-trimethylammoniumphenyl)-4,5-dihydroimidazol-2-ylidene, OTf− = CF3SO3−) based on a dicationic N-heterocyclic carbene (NHC) ligand was prepared. The reactivity was tested in ring opening metathesis polymerization (ROMP) under biphasic conditions using a nonpolar organic

• leaching into the product was below the limit of detection, i.e., <2.5 ppm. The results are summarized in Table 3. Conclusion The first dicationic Ru–alkylidene catalyst based on an N-heterocyclic carbene bearing two quaternary ammonium groups, [(RuCl2(H2ITapMe2)(=CH–2-(2-PrO)-C6H4))2+ (OTf−)2] (Ru-2), was

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

• Cedex, France 10.3762/bjoc.11.169 Abstract A silver-free methodology was developed for the synthesis of unprecedented N-heterocyclic carbene ruthenium indenylidene complexes bearing a bidentate picolinate ligand. The highly stable (SIPr)(picolinate)RuCl(indenylidene) complex 4a (SIPr = 1,3-bis(2-6

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

• general, the commonly used Ru(II)-based pre-catalysts have five ligands in the metal coordination sphere and adopt a distorted square pyramidal geometry (Figure 1). The basic components of this structure include two L-type ligands mutually trans (e.g., phosphines and N-heterocyclic carbene) and two

Cathodic hydrodimerization of nitroolefins

• Michael Weßling and
• Hans J. Schäfer

Beilstein J. Org. Chem. 2015, 11, 1163–1174, doi:10.3762/bjoc.11.131

• reported to be converted quantitatively to the hydrodimer 3 with SmI2 [19]. A catalytic reductive β,β-carbon coupling of nitroalkenes catalyzed by a N-heterocyclic carbene has been reported recently. Diastereomers are formed, whose dr (d,l- over meso-ratio) ranges between 66:34 to 90:10. The interesting

Gold-catalyzed formation of pyrrolo- and indolo-oxazin-1-one derivatives: The key structure of some marine natural products

• Sultan Taskaya,
• Nurettin Menges and
• Metin Balci

Beilstein J. Org. Chem. 2015, 11, 897–905, doi:10.3762/bjoc.11.101

• fully recovered. Gold N-heterocyclic carbene complexes, in conjunction with a silver salt, were found to efficiently catalyze different types of reactions [67][68][69]. Therefore, 15 was reacted with [(NHC)AuCl] complex in the presence of AgOTf as the cocatalyst in chloroform. Beside the expected

• to acid 15 (Scheme 3) [56]. The acid 15 was reacted with various metal catalysts in chloroform at different temperatures and for different reaction times. Five different catalysts were tried (Table 1). Surprisingly, no reaction was observed when the reaction was conducted with the N-heterocyclic

• carbene (NHC) complex of Au(I) in chloroform (Table 1, entry 5). Reactions with InCl3 and PtCl2(PPh3)3 as catalysts gave very poor yields of exo-dig cyclization product 7 after 24 h (entries 3 and 4). AgOTf and AuCl3 were also screened and AuCl3 was identified as the optimal choice due to the shorter

Diastereoselective and enantioselective conjugate addition reactions utilizing α,β-unsaturated amides and lactams

• Katherine M. Byrd

Beilstein J. Org. Chem. 2015, 11, 530–562, doi:10.3762/bjoc.11.60

• can be transformed into a number of functional groups [97]. In Procter’s work, they used a Cu(I)–NHC (N-heterocyclic carbene) system to catalyze the asymmetric transfer of silicon from PhMe2SiBpin [98][99] to α,β-unsaturated amides and lactams through activation of the Si–B bond [96] (Scheme 10

Chemoselective O-acylation of hydroxyamino acids and amino alcohols under acidic reaction conditions: History, scope and applications

• Tor E. Kristensen

Beilstein J. Org. Chem. 2015, 11, 446–468, doi:10.3762/bjoc.11.51

Cross-dehydrogenative coupling for the intermolecular C–O bond formation

• Igor B. Krylov,
• Vera A. Vil’ and
• Alexander O. Terent’ev

Beilstein J. Org. Chem. 2015, 11, 92–146, doi:10.3762/bjoc.11.13

• instead of aldehydes (Table 4). It is supposed that under the reaction conditions primary alcohol is initially oxidized to aldehyde without the participation of N-heterocyclic carbene [106][113][123][124]. The oxidative esterification of aldehydes with racemic mixtures of alcohols catalyzed by chiral N

Dimerisation, rhodium complex formation and rearrangements of N-heterocyclic carbenes of indazoles

• Zong Guan,
• Jan C. Namyslo,
• Martin H. H. Drafz,
• Martin Nieger and
• Andreas Schmidt

Beilstein J. Org. Chem. 2014, 10, 832–840, doi:10.3762/bjoc.10.79

• organocatalysts [15][16]. The N-heterocyclic carbenes of indazole (and pyrazole [17][18]), however, have a chemistry of their own which set them apart from the NHCs of the aforementioned ring systems. Portions of that field have been covered in recent review articles [18][19]. The N-heterocyclic carbene of

• available by copper-catalyzed aryl couplings or Buchwald–Hartwig reactions [22]. Pyrazol-3-ylidenes rearrange similarly to quinolines [17]. We report here on two unexpected rearrangements of indazol-3-ylidene, and trapping reactions of the N-heterocyclic carbene with rhodium. Results and Discussion On

• trying to deprotonate the indazolium salts 12a–e with potassium 2-methylbutan-2-olate in anhydrous dichloromethane at −80 °C to the N-heterocyclic carbene I in the absence of trapping reagents we unexpectedly obtained a mixture of two compounds which are in equilibrium, when the reaction was allowed to

Silver and gold-catalyzed multicomponent reactions

• Giorgio Abbiati and
• Elisabetta Rossi

Beilstein J. Org. Chem. 2014, 10, 481–513, doi:10.3762/bjoc.10.46

• some years later by the research groups of Zou [14], Navarro [15] and Tang [16] (Figure 1). Zou and co-workers reported structurally well-defined N-heterocyclic carbene silver halides of 1-cyclohexyl-3-arylmethylimidazolylidene to be effective catalysts in a model reaction among 3-phenylpropionaldehyde

• stable and coordinatively unsaturated N-heterocyclic carbene silver halide NHC–AgX rather than a silver cation. Thus, a more detailed mechanism was proposed, in which the π-complex of the catalyst with the alkyne I reacts with an amine to form the silver acetylide II and the amine hydrohalide III. The

• . Concurrently, the released N-heterocyclic carbene would re-enter the catalytic cycle. Nevertheless, the reaction suffers from severe limitation on the nature of the R1 group attached to the triple bond of N′-(2-alkynylbenzylidene)hydrazides 42 and only aryl groups proofed to be effective. Broadening the scope

The Flögel-three-component reaction with dicarboxylic acids – an approach to bis(β-alkoxy-β-ketoenamides) for the synthesis of complex pyridine and pyrimidine derivatives

• Mrinal K. Bera,
• Moisés Domínguez,
• Paul Hommes and
• Hans-Ulrich Reissig

Beilstein J. Org. Chem. 2014, 10, 394–404, doi:10.3762/bjoc.10.37

• catalysis. With ruthenium-based catalysts bearing N-heterocyclic carbene (NHC) ligands, RCM usually delivers macrocyclic olefins as mixtures of E- and Z-isomers, in most cases in favor of the E-isomer [70][71][72][73]. The E/Z-ratio is often under thermodynamic control, reflecting the energy difference

Modulating NHC catalysis with fluorine

• Yannick P. Rey and
• Ryan Gilmour

Beilstein J. Org. Chem. 2013, 9, 2812–2820, doi:10.3762/bjoc.9.316

• possible to modulate the behaviour of the corresponding N-heterocyclic carbene (NHC) with minimal steric alterations to the catalyst core. In this study, the effect of hydrogen to fluorine substitution was evaluated as part of a molecular editing study. X-ray crystallographic analyses of a number of

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

• [PPh2(OPh-2-OMe)]} (Figure 3, second row, left) in water proceeds at room temperature to give >95% conversion after three hours. In organometallic catalysis, N-heterocyclic carbene ligands (NHCs) have superseded phosphine ligands in many fields of application [145]. It was thus only a matter of time

• NHC ligands is supposed to play an active role in the catalytic cycle. After its dissociation from the precatalyst [(NHC)2Cu]X, the free N-heterocyclic carbene can act as a base in the deprotonation of the alkyne substrate (Scheme 12). This protonation of the free N-heterocyclic carbene by the alkyne

Garner’s aldehyde as a versatile intermediate in the synthesis of enantiopure natural products

• Mikko Passiniemi and
• Ari M.P. Koskinen

Beilstein J. Org. Chem. 2013, 9, 2641–2659, doi:10.3762/bjoc.9.300

• . NaOMe reacts with the ligand precursor 26 and forms an N-heterocyclic carbene. The method was tested also with Garner’s aldehyde and two different boronic acid derived nucleophiles (R = Ph or 1-octenyl). High anti-selectivity was observed. With the in situ formed phenyl nucleophile the selectivity was

• an in situ formed N-heterocyclic carbene. In all cases studied, they found both the anti/syn- and the Z/E-selectivity to be high (>20:1), but the chemical yield was varying. Highest yields (78–80%) were achieved with short alkyl chains (R = Me) or when R = phenyl. When the alkyl chain was lengthened

Gold(I)-catalyzed 6-endo hydroxycyclization of 7-substituted-1,6-enynes

• Ana M. Sanjuán,
• Alberto Martínez,
• Patricia García-García,
• Manuel A. Fernández-Rodríguez and
• Roberto Sanz

Beilstein J. Org. Chem. 2013, 9, 2242–2249, doi:10.3762/bjoc.9.263

• cyclization should be noted and only minor amounts (10–15%) of 3a were also formed. Due to the unexpected 6-endo-favored pathway found for substrate 1a [39], we attempted to further improve this selectivity in the hydroxycyclization process (Table 1). Switching the ligand from Ph3P to XPhos or N-heterocyclic

• carbene (IPr) slightly decreases the selectivity for the 6-endo cyclization (Table 1, entry 1 vs entries 2 and 3). However, when the cationic gold complex (JohnPhos)(NCMe)AuSbF6, developed by Echavarren and co-workers [40], was employed as a catalyst a moderate increase in the ratio of 7a vs 3a was

Synthesis of axially chiral gold complexes and their applications in asymmetric catalyses

• Yin-wei Sun,
• Qin Xu and
• Min Shi

Beilstein J. Org. Chem. 2013, 9, 2224–2232, doi:10.3762/bjoc.9.261

• Chemistry, Shanghai Institute of Organic Chemistry, Chinese Academy of Sciences, 354 Fenglin Road, Shanghai 200032, People’s Republic of China 10.3762/bjoc.9.261 Abstract Several novel chiral N-heterocyclic carbene and phosphine ligands were prepared from (S)-BINOL. Moreover, their ligated Au complexes

• = 1525.9(2) Å3; space group: P2(1); Z = 4; Dcalc = 1.626 g/cm3; F000 = 732; final R indices [I > 2sigma(I)]: R1 = 0.0231; wR2 = 0.0538. Synthesis of compound 9. Synthesis of N-heterocyclic carbene precursor. Synthesis of benzimidazolium salt (S)-14. Synthesis of carbene Au complexes. Rotamers of 1a and 1b

Synthesis, characterization and luminescence studies of gold(I)–NHC amide complexes

• Adrián Gómez-Suárez,
• David J. Nelson,
• David G. Thompson,
• David B. Cordes,
• Duncan Graham,
• Alexandra M. Z. Slawin and
• Steven P. Nolan

Beilstein J. Org. Chem. 2013, 9, 2216–2223, doi:10.3762/bjoc.9.260

• Nanometrology, University of Strathclyde, 295 Cathedral Street, Glasgow, G1 1XL, UK 10.3762/bjoc.9.260 Abstract A flexible, efficient and straightforward methodology for the synthesis of N-heterocyclic carbene gold(I)–amide complexes is reported. Reaction of the versatile building block [Au(OH)(IPr)] (1) (IPr

• catalysts in gold-catalyzed processes [1][2][3][4][5][6][7]. This has led several research groups to investigate general, green and straightforward methodologies for the synthesis of organogold complexes. We have focused on the synthesis and study of transition metal complexes bearing N-heterocyclic carbene

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