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

• ; homogeneous catalysis; NHC ligands; palladium; Suzuki–Miyaura reaction; Introduction The Suzuki–Miyaura reaction is a powerful synthetic method for forming C–C bonds between aryl halides or pseudo halides and organoborane containing species [1][2][3][4][5]. The most active catalysts are generally based on Pd

• -systems [40]. Strong evidence for a Pd–Pd single bond is provided by the Pd–Pd distance of 2.5669(4) Å [41]. Presumably for steric reasons the NHC ligands are bent away from the bridging Cp ligand and the C–Pd–Pd (C of IPr) bond angles are significantly less than 180° (Pd(1)–Pd(2)–C(7) 164.9(1) and Pd(2

• was calculated by using relative integrations of the Cp protons from Cp and CpDim to yield a K of 1.1. General depictions of allyl and related precatalysts that are highly active for the Suzuki–Miyaura reaction with NHC ligands. Comparison of catalytic performance of Cin, Cp and tBuInd for a series of

Copper-catalyzed asymmetric conjugate addition of organometallic reagents to extended Michael acceptors

• Thibault E. Schmid,
• Sammy Drissi-Amraoui,
• Christophe Crévisy,
• Olivier Baslé and
• Marc Mauduit

Beilstein J. Org. Chem. 2015, 11, 2418–2434, doi:10.3762/bjoc.11.263

• catalytic applications [22][23]. Amongst the myriad of available NHC ligands, chiral unsymmetrical NHC ligands appeared as particularly potent in asymmetric catalysis, and were investigated in copper-catalyzed conjugate additions [24]. Recently, a multicomponent synthesis enabled the facile access to a wide

• performance in terms of enantioselectivity, and was used in combination with Cu(OTf)2 in the 1,6-ACA of cyclic dienones of the type 30 (Scheme 6). NHC ligands also enabled a total regioselectivity and ees ranging from 58 to 91%. Given the efficiency of (R)-Binap L4 in Cu-catalyzed 1,4-ACA on α,β-unsaturated

• diethylzinc. Efficiency of DiPPAM ligand in 1,6-ACA of dialkylzinc to cyclic dienones. Sequential 1,6/1,4-ACA reactions involving linear aryldienones. Unsymmetrical hydroxyalkyl NHC ligands in 1,6-ACA of cyclic dienones. Performance of atropoisomeric diphosphines in 1,6-ACA of Et2Zn on cyclic dienones

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

• just a single example, NHC ligands played a crucial role in the development of highly efficient ruthenium initiators for olefin metathesis and related reactions [18][19][20][21]. Lately, these divalent carbon species have also emerged as powerful nucleophilic organocatalysts for polymer chemistry [22

• imidazolylidene backbone in 1999 while searching for bulky NHC ligands to coordinate onto palladium catalysts for Kumada cross-coupling reactions [57]. The resulting carbene was nicknamed IPr and this designation still persists in the literature, although IDip is a more fitting acronym to avoid any confusion with

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

• carbenes (NHCs) [2] are an interesting class of catalysts [3][4], due to the fascinating characteristics of NHC ligands, which can be designed to have a wide range of steric and electronic properties [5][6][7]. Nickel catalysts of the form [Ni(Cp)X(NHC)] have been shown to be versatile and relatively easy

Ru complexes of Hoveyda–Grubbs type immobilized on lamellar zeolites: activity in olefin metathesis reactions

• Hynek Balcar,
• Naděžda Žilková,
• Martin Kubů,
• Michal Mazur,
• Zdeněk Bastl and
• Jiří Čejka

Beilstein J. Org. Chem. 2015, 11, 2087–2096, doi:10.3762/bjoc.11.225

• cationic tags on NHC ligands were linker-free immobilized on the surface of lamellar zeolitic supports (MCM-22, MCM-56, MCM-36) and on mesoporous molecular sieves SBA-15. The activity of prepared hybrid catalysts was tested in olefin metathesis reactions: the activity in ring-closing metathesis of

• cis-3-hexenyl acetate, the created catalytically active centers were able to ensure rapid propagation regardless the kind of substrate molecules. Conclusion Hoveyda–Grubbs type metathesis catalysts with quaternary ammonium tags on NHC ligands HGIIN+Cl− and HGIIN+PF6− were immobilized on lamellar

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

• hydrophilic phosphine ligands [22][23][24][25], NHC ligands [26][27][28][29], N-donor ligands [30], alkylidene moieties [31][32][33] or combinations of these structural features [34][35][36][37]. Another recent development in homogeneous catalysis, and olefin metathesis in particular, have become switchable

Stereochemistry of ring-opening/cross metathesis reactions of exo- and endo-7-oxabicyclo[2.2.1]hept-5-ene-2-carbonitriles with allyl alcohol and allyl acetate

• Piotr Wałejko,
• Michał Dąbrowski,
• Lech Szczepaniak,
• Jacek W. Morzycki and
• Stanisław Witkowski

Beilstein J. Org. Chem. 2015, 11, 1893–1901, doi:10.3762/bjoc.11.204

• , while the 1-2 vs 1-3 ratio was almost the same as those in other experiments. It should be noted that less sterically demanding o-tolyl-N-substituents in NHC-ligands provide more space around the ruthenium center. In general, ROCM reactions are most successful when highly strained substrates are used

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

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

• spectroscopies and elemental analysis. The 13C{1H} NMR spectra of all the complexes showed a singlet in the low field region of the spectra corresponding to the carbenic carbon atom of the molecule. These signals appear at 167.5–167.8 ppm, in agreement with other [Au(NHC)(NTf2)] complexes bearing unsaturated NHC

• ligands [46][50]. Each 19F{1H} NMR spectrum contains a singlet at ca. −76 ppm, in agreement with the presence of an inner-sphere NTf2 ligand [50]. Catalytic transformations Once fully characterised, the catalytic activity of the new complexes was investigated. To this end, three model reactions were

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

• ]. Among NHCs, functionalized NHC ligands have been extensively studied in recent years because of their intriguing structural diversities and potential applications in coordination chemistry and homogenous catalysis. NHC ligands containing additional phosphine, nitrogen, oxygen, and sulfur donating groups

• ligands and two acetonitrile ligands in an octahedral geometry. One NHC ligand, one acetonitrile ligand and one carbon atom of the other NHC ligand occupy the equatorial plane in which two carbon atoms of two NHC ligands are mutually trans-arranged. The remaining acetonitrile ligand and one nitrogen atom

• 176.42°. The rest coordination nitrogen atoms of acetonitrile and phenanthroline lie on the axial positions with the N(7)–Ru(1)–N(5) angle of 173.74°. Conclusion In summary, Ru–NHC complexes bearing pyrimidine- and pyridine-functionalized NHC ligands have been prepared through a carbene transfer reaction

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

• systems. Also for those that present rather stable cis geometry at the level of the coordination intermediate, such as system 15. As already indicated, this is due to the steric pressure of the PCy3 or NHC ligands on the bulkier substrate. Interestingly, in all the systems considered the energy barrier

• differentiation between the power of the three effects, steric, electronic and solvent, has turned out be a hazard to make predictions difficult. However the CF3 groups have become key to explain the electronic effects, as well as the t-Bu for steric effects. Steric effects owing to interaction between bulky NHC

• ligands [16] and bulky substrates make the bottom reaction pathway more likely surpassing the other effects. Finally the solvent effect helps the stabilization of the side-bound isomer, but at a higher degree for the high sterically demanding complexes. As already stated by Goddard, polar solvents favor

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

• We were attracted by NHC ligands containing a diamino function at the aromatic ring as realized in 1 [20][21][22] since such ligands can be permanently quaternized to the corresponding dicationic species via double alkylation. Additionally, they remain structurally closely related to mesitylene-based

• NHC ligands. Attempts to synthesize ionic Ru-based olefin metathesis catalysts using imidazolinium salts bearing two quaternary ammonium groups turned out to be unsuccessful, probably due to their insolubility in common organic solvents. However, quaternization of RuCl2(H2ITap)(=CH–(2-(2-PrO-C6H4

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

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

• 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

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

• (NHC) ligands [8][9][10]. Recently, we have been very active in the synthesis and characterization of new gold(I)–NHC complexes and the study of their reactivity, with a special focus on the development of straightforward methodologies [11][12]. As a result of our investigations, we have recently

• transition. Therefore, the use of different NHC ligands should also allow access to different fluorescence behavior. Conclusion A novel series of NHC-bearing gold(I)–amide complexes have been prepared using a simple, straightforward synthetic route that can be conducted using reagent-grade materials on 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

• studies [43]. This is one of the rare neutral T-shaped Pt(II) complexes. Referring to NHC ligands, Rivada-Wheelaghan et al. isolated the three-coordinate methyl [Pt(Me)(IPr)2]+ (A10) and cyclometalated [Pt(NHC’)NHC]+ complexes (NHC = IPr A11a, It-Bu (1,3-bis(tert-butyl)imidazol-2-ylidene) A11b; NHC

• ][28][39][44]. This procedure has been successfully employed for the generation of complexes stabilized by two phosphine PR3 or two NHC ligands, in which the third coordination site is occupied by alkyl, hydride or boryl ligands. Therefore, high trans-influence ligands are present in all these cases

Alkyne hydroarylation with Au N-heterocyclic carbene catalysts

• Cristina Tubaro,
• Marco Baron,
• Andrea Biffis and
• Marino Basato

Beilstein J. Org. Chem. 2013, 9, 246–253, doi:10.3762/bjoc.9.29

• Cristina Tubaro Marco Baron Andrea Biffis Marino Basato Dipartimento di Scienze Chimiche, Università degli Studi di Padova, via Marzolo 1, 35131 Padova, Italy 10.3762/bjoc.9.29 Abstract Mono- and dinuclear gold complexes with N-heterocyclic carbene (NHC) ligands have been employed as catalysts in

• (II) salts as catalyst [8][9][10]. Palladium complexes with N-heterocyclic carbene (NHC) ligands have since been showcased as highly efficient catalysts for this reaction [11][12][13][14]. Alternative catalytic systems based on salts or complexes of other noble metals, such as platinum [15][16][17

• reaction [12][13][14]. Recently, we have extended our interest in the organometallic chemistry of such ligands to group 11 metals, in particular gold(I) and gold(III) centers [54][55][56]. In the present contribution we would like to assess the catalytic efficiency of such gold complexes with NHC ligands

Extending the utility of [Pd(NHC)(cinnamyl)Cl] precatalysts: Direct arylation of heterocycles

• Anthony R. Martin,
• Anthony Chartoire,
• Alexandra M. Z. Slawin and
• Steven P. Nolan

Beilstein J. Org. Chem. 2012, 8, 1637–1643, doi:10.3762/bjoc.8.187

• with NHC ligands being SIPr (1,3-bis(2,6-diisopropylphenyl)-4,5-dihydroimidazol-2-ylidene), IPr (1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene), IPr* (1,3-bis(2,6-bis(diphenylmethyl)-4-methylphenyl)imidazol-2-ylidene) and IPr*Tol (1,3-bis(2,6-bis(di-p-tolylmethyl)-4-methylphenyl)imidazol-2-ylidene

• difference between 1 and 2 underlines the fact that the difference in the σ-donation properties of the NHC ligands [38][39][40][41] is not likely to play a crucial role in the catalytic activity. In comparison with the previously mentioned methodologies to perform this C–H functionalization [27][28][29][30

Synthesis of axially chiral oxazoline–carbene ligands with an N-naphthyl framework and a study of their coordination with AuCl·SMe₂

• Feijun Wang,
• Shengke Li,
• Mingliang Qu,
• Mei-Xin Zhao,
• Lian-Jun Liu and
• Min Shi

Beilstein J. Org. Chem. 2012, 8, 726–731, doi:10.3762/bjoc.8.81

• reported a type of NHC–Au(I) complexes 2 containing C2-symmetric bis(NHC)-ligands with two imidazolin-2-ylidene moieties on a chiral dioxolane backbone, produced in up to 95% ee by hydrogenation of a prochiral alkene [11]. Recently, Toste and co-workers reported a novel family of axially chiral (acyclic

N-Heterocyclic carbene/Brønsted acid cooperative catalysis as a powerful tool in organic synthesis

• Rob De Vreese and
• Matthias D’hooghe

Beilstein J. Org. Chem. 2012, 8, 398–402, doi:10.3762/bjoc.8.43

• encouraged many chemists to search intensively for new NHC ligands, and this has led to the establishment of a very fruitful research area in organic chemistry [4][5][6][7][8][9][10]. A particularly interesting application comprises the use of “umpolung” reactions [11] (inversion of polarity) catalyzed by N

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

• ]. In particular, they showed that the π-acceptor properties of NHC ligands such as 59 could be enhanced by introducing a second aromatic layer spanning the imidazopyridine-2-ylidene system, whereas the σ-donating abilities of both ligands remain basically equivalent. As a consequence, the new

• esters. NHC ligands with different π-acceptor properties [106]. AuCl3-catalyzed benzannulations reported by Yamamoto. Synthesis of 9-oxabicyclo[3.3.1]nona-4,7-dienes from 1-oxo-4-oxy-5-ynes [40]. Stereocontrolled oxacyclization/(4 + 2)-cycloaddition cascade of ketone–allene substrates [43]. Gold

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

• catalysts in chiral induction reactions [19][20][21][22][23][24][25]. The axially chiral biaryl framework, widely used in the design of chiral ligands such as BINAP [26][27], BINOL [28][29], and boxax [30], has proved to be very rigid, and was introduced in the development of NHC ligands by the Hoveyda

• showed good catalytic activities in the asymmetric intramolecular hydroamination reaction to give the corresponding product in moderate ee. Keywords: chiral mono(N-heterocyclic carbene) complex; Heck–Mizoroki reaction; hydroamination; Suzuki–Miyaura reaction; Introduction N-heterocyclic carbene (NHC

• ) ligands, which have intrinsic characteristics such as strong σ-donor but poor π-acceptor abilities, easy preparation, air and thermal stability of their metal complexes, and convenient introduction of chiral elements, have been widely used as promising ligands in metal-catalyzed transformations [1][2][3

Synthesis of Ru alkylidene complexes

• Renat Kadyrov and
• Anna Rosiak

Beilstein J. Org. Chem. 2011, 7, 104–110, doi:10.3762/bjoc.7.14

• precursors for the “second generation” catalysts bearing NHC ligands are the alkylidene ruthenium complexes coordinated with two phosphines [1]. For recent reviews see [2][3][4]. There are several routes for accessing five-coordinated ruthenium(II) alkylidene complexes such as diazo-transfer [5] and the

Hoveyda–Grubbs type metathesis catalyst immobilized on mesoporous molecular sieves MCM-41 and SBA-15

• Hynek Balcar,
• Tushar Shinde,
• Naděžda Žilková and
• Zdeněk Bastl

Beilstein J. Org. Chem. 2011, 7, 22–28, doi:10.3762/bjoc.7.4

• supports: (a) by exchanging halide ligands X [7][8][9][10][11], (b) by exchanging phosphine and NHC ligands L [12][13], and (c) through the alkylidene ligand [14][15][16][17][18][19]. For these purposes, special ligand molecules with tags suitable for the reaction with the support surface (linkers) are

The catalytic performance of Ru–NHC alkylidene complexes: PCy₃ versus pyridine as the dissociating ligand

• Stefan Krehl,
• Diana Geißler,
• Sylvia Hauke,
• Oliver Kunz,
• Lucia Staude and
• Bernd Schmidt

Beilstein J. Org. Chem. 2010, 6, 1188–1198, doi:10.3762/bjoc.6.136

• pyridines as placeholders. Originally, complex G was synthesized as a precursor for mixed NHC-phosphine complexes other than D [25][26][27][28] or, very recently, for the synthesis of Ru-alkylidenes with two different NHC ligands [29]. Comparatively little information is available concerning the catalytic