Ligand effects, solvent cooperation, and large kinetic solvent deuterium isotope effects in gold(I)-catalyzed intramolecular alkene hydroamination

• Ruichen Lan,
• Brock Yager,
• Yoonsun Jee,
• Cynthia S. Day and
• Amanda C. Jones

Beilstein J. Org. Chem. 2024, 20, 479–496, doi:10.3762/bjoc.20.43

• opposite effect is observed [60]. Ligand effects. Early studies identified two key strategies for improving alkene hydroamination, switching from an electron-withdrawing catalyst (Ph3PAuCl/AgOTf) to an electron-donating catalyst (IPrAuCl/AgOTf (IPr = 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene), or by

Aldiminium and 1,2,3-triazolium dithiocarboxylate zwitterions derived from cyclic (alkyl)(amino) and mesoionic carbenes

• Nedra Touj,
• François Mazars,
• Guillermo Zaragoza and
• Lionel Delaude

Beilstein J. Org. Chem. 2023, 19, 1947–1956, doi:10.3762/bjoc.19.145

• heterocycles; zwitterions; Introduction Following the seminal discovery from the group of Arduengo, who isolated and fully characterized 1,3-di(1-adamantyl)imidazol-2-ylidene in 1991 [1], stable divalent carbon species have evolved from fleeting intermediates to ubiquitous catalysts, ligands, and reagents in

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

• heteroleptic Cu(I) complexes combining the malonic acid-derived anionic NHC and a neutral imidazol-2-ylidene were also obtained in a very selective manner (Scheme 12). As discussed later, many of these complexes were employed as catalysts. In 2015, Collins et al. [27] compared the stability and reactivity of

• used 1,3-diisopropylbenzimidazol-2-ylidene (iPr2-bimy) and 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene (IPr) (Scheme 28) [40]. The structures of all the synthesized complexes were confirmed by X-ray crystallography. A similar strategy was followed for stabilizing copper- and silver tert

• derivatives with CO2 using 1,2,3-triazol-5-ylidene copper(I) complexes (tzNHC–Cu) as the catalyst followed by treatment with alkyl iodide to obtain the corresponding esters in moderate to very good yields. The catalytic activity of (tzNHC–Cu) was found to be better than the imidazol-2-ylidene copper(I

Formal total synthesis of macarpine via a Au(I)-catalyzed 6-endo-dig cycloisomerization strategy

• Jiayue Fu,
• Bingbing Li,
• Zefang Zhou,
• Maosheng Cheng,
• Lu Yang and
• Yongxiang Liu

Beilstein J. Org. Chem. 2022, 18, 1589–1595, doi:10.3762/bjoc.18.169

• ) and tert-butyldimethylsilyl chloride (TBSCl) (Scheme 5). To find the best cycloisomerization conditions, the 1,5-enyne substrate 10 was subjected to different reaction conditions as listed in Table 1. It was observed that [1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene]gold(I) chloride (IPrAuCl

• , including triphenylphosphane (Ph3P), [1,1'-biphenyl]-2-yl-di-tert-butylphosphane (JohnPhos) dicyclohexyl(2',4'-diisopropyl-3,6-dimethoxy-[1,1'-biphenyl]-2-yl)phosphane (BrettPhos) (Table 1, entries 4–6) revealed that 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene (IPr) was still the best one (Table 1

• ). The Au(I)-catalyzed cycloisomerization reaction of substrate 10 occurred under the catalysis of 5 mol % [1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene]gold(I) chloride (IPrAuCl) and 5 mol % silver hexafluoroantimonate (AgSbF6) [25][26] in anhydrous DCM at room temperature for 2 h forming a benzene

Electron-rich triarylphosphines as nucleophilic catalysts for oxa-Michael reactions

• Susanne M. Fischer,
• Simon Renner,
• A. Daniel Boese and
• Christian Slugovc

Beilstein J. Org. Chem. 2021, 17, 1689–1697, doi:10.3762/bjoc.17.117

• prepared with nucleophilic catalysis using 10 mol % N-heterocyclic carbenes such as 1,3,4-triphenyl-4,5-dihydro-1H-1,2,4-triazol-5-ylidene or 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene. The polymerization was carried out at room temperature for 24 h and no solvent was used. The resulting reaction

Aerobic synthesis of N-sulfonylamidines mediated by N-heterocyclic carbene copper(I) catalysts

• Faïma Lazreg,
• Marie Vasseur,
• Alexandra M. Z. Slawin and
• Catherine S. J. Cazin

Beilstein J. Org. Chem. 2020, 16, 482–491, doi:10.3762/bjoc.16.43

• copper(I) complexes were found highly efficient under solvent-free and aerobic conditions. Stoichiometric reactions support the release of one NHC and the formation of a copper(I) acetylide as key elements in the catalytic cycle. Experimental N,N’-Bis{2,6-(diisopropyl)phenyl}imidazol-2-ylidene(pyridine

• , 58.39; H, 6.16; N, 6.08. 1-{2,6-(Diisopropyl)phenyl}-3-methyl-4-(4-tert-butylphenyl)-1,2,3-triazol-5-ylidene-(N,N’-bis{2,6-(diisopropyl)phenyl}imidazol-2-ylidene)copper(I) tetrafluoroborate, [Cu(IPr)(Triaz)]BF4 (5). In a glovebox, a microwave vial was charged with [Cu(Cl)(IPr)] (200.0 mg, 0.41 mmol

Synthesis and selected transformations of 2-unsubstituted 1-(adamantyloxy)imidazole 3-oxides: straightforward access to non-symmetric 1,3-dialkoxyimidazolium salts

• Grzegorz Mlostoń,
• Małgorzata Celeda,
• Katarzyna Urbaniak,
• Marcin Jasiński,
• Vladyslav Bakhonsky,
• Peter R. Schreiner and
• Heinz Heimgartner

Beilstein J. Org. Chem. 2019, 15, 497–505, doi:10.3762/bjoc.15.43

• . Deprotonation of the latter with triethylamine in the presence of elemental sulfur allows the in situ generation of the corresponding imidazol-2-ylidene, which traps elemental sulfur yielding a 1,3-dihydro-2H-imidazole-2-thione as the final product. Keywords: alkoxyamines; imidazole N-oxides; imidazolium salts

• -tetramethylcyclobutane-1,3-dione. Imidazolium salts are of special importance as they are widely used as ionic liquids or precursors of imidazole-based nucleophilic carbenes (imidazol-2-ylidenes). For example, deprotonation of 1,3-diadamantylimidazolium chloride led to the first stable imidazol-2-ylidene (the so-called

• (5) atoms appeared at 6.69 ppm, and in the 13C NMR spectrum, the C(4) and C(5) atoms gave only one signal localized at 114.6 ppm. Apparently, deprotonation of the imidazolium cation results in the formation of the nucleophilic imidazol-2-ylidene 16, which in situ reacts with elemental sulfur

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

• (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

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

From betaines to anionic N-heterocyclic carbenes. Borane, gold, rhodium, and nickel complexes starting from an imidazoliumphenolate and its carbene tautomer

• Ming Liu,
• Jan C. Namyslo,
• Martin Nieger,
• Mika Polamo and
• Andreas Schmidt

Beilstein J. Org. Chem. 2016, 12, 2673–2681, doi:10.3762/bjoc.12.264

• .12.264 Abstract The mesomeric betaine imidazolium-1-ylphenolate forms a borane adduct with tris(pentafluorophenyl)borane by coordination with the phenolate oxygen, whereas its NHC tautomer 1-(2-phenol)imidazol-2-ylidene reacts with (triphenylphosphine)gold(I) chloride to give the cationic NHC complex [Au

• (NHC)2][Cl] by coordination with the carbene carbon atom. The anionic N-heterocyclic carbene 1-(2-phenolate)imidazol-2-ylidene gives the complexes [K][Au(NHC−)2], [Rh(NHC−)3] and [Ni(NHC−)2], respectively. Results of four single crystal analyses are presented. Keywords: anionic ligand; carbene

• tautomer; imidazol-2-ylidene; mesoionic compound; mesomeric betaine; Introduction Since the first isolation of a stable N-heterocyclic carbene (NHC) [1] in 1991 this compound class has provided numerous highly efficient ligands of NHC-metal catalysts for cross-coupling reactions [2][3][4][5][6][7

Reactivity studies of pincer bis-protic N-heterocyclic carbene complexes of platinum and palladium under basic conditions

• David C. Marelius,
• Curtis E. Moore,
• Arnold L. Rheingold and
• Douglas B. Grotjahn

Beilstein J. Org. Chem. 2016, 12, 1334–1339, doi:10.3762/bjoc.12.126

• even longer. In 1968, Wanzlick and Öfele separately synthesized mercury(II) and chromium(0) imidazol-2-ylidene complexes [3]. Nearly 50 years of NHC ligand research have demonstrated the importance of the electronic and steric effects that can be modified by altering the alkyl or aryl groups on each

• nitrogen atom. Less common are protic imidazol-2-ylidene (PNHC) ligands with a hydrogen atom on one or both of the stabilizing nitrogens. The synthesis of PNHC complexes has proven to be a challenge, which has limited studies of their reactivity [4][5][6][7][8]. Protic imidazol-2-ylidene ligands (e.g., 1

Scope and limitations of the dual-gold-catalysed hydrophenoxylation of alkynes

• Adrián Gómez-Suárez,
• Yoshihiro Oonishi,
• Anthony R. Martin and
• Steven P. Nolan

Beilstein J. Org. Chem. 2016, 12, 172–178, doi:10.3762/bjoc.12.19

• methodology (Scheme 2). With that aim we reacted diphenylacetylene (1a) with several phenols, 2a–o, in toluene, using 0.5 mol % of [{Au(IPr)}2(µ-OH)][BF4] (IPr = 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene) as the catalyst. Functional groups such as nitriles (3aa), ketones (3ab), esters (3ac), aldehydes

Direct estimate of the internal π-donation to the carbene centre within N-heterocyclic carbenes and related molecules

• Diego M. Andrada,
• Nicole Holzmann,
• Thomas Hamadi and
• Gernot Frenking

Beilstein J. Org. Chem. 2015, 11, 2727–2736, doi:10.3762/bjoc.11.294

• weakest X→p(π) π-donation while mesoionic carbenes possess the strongest π-donation. Keywords: bonding analysis; N-heterocyclic carbenes; π-donation; Introduction Since the isolation and unambiguous characterization of imidazol-2-ylidene by Arduengo in 1991 [1], the chemistry of stable singlet carbenes

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

• activity of (η5-Cp)Pd(IPr)(Cl) (IPr = 1,3-bis(2,6-diisopropylphenyl)-1,3-dihydro-2H-imidazol-2-ylidene, Cp) with two commercially available catalysts (η3-cinnamyl)Pd(IPr)(Cl) (Cin) and (η3-1-t-Bu-indenyl)Pd(IPr)(Cl) (tBuInd). We show that Cp gives slightly better catalytic activity than Cin, but

• ) (IPr = 1,3-bis(2,6-diisopropylphenyl)-1,3-dihydro-2H-imidazol-2-ylidene, Cp) to the analogous (η3-cinnamyl)Pd(IPr)(Cl) (Cin) and (η3-1-t-Bu-indenyl)Pd(IPr)(Cl) (tBuInd) precatalysts [20]. We show that the performance of Cp fits into our model of precatalyst performance based on the speed at which a

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

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

• -methylphenyl)imidazolium chloride (IDip*·HCl or IPr*·HCl). Keywords: cyclization; experimental procedure; imidazolinium salt; imidazolium salt; microwave heating; Introduction Since Arduengo and co-workers successfully isolated and characterized the first imidazol-2-ylidene derivative in 1991 [1][2], stable

• ][23] and organic synthesis [24][25][26]. In particular, they were successfully employed for the umpolung of carbonyl compounds, sometimes in an asymmetric fashion [27][28][29]. Currently, the NHCs most frequently encountered are based on the imidazol-2-ylidene and imidazolin-2-ylidene scaffolds, which

• 1,3-di(isopropyl)imidazol-2-ylidene. Thus, 1,3-bis(2,6-diisopropylphenyl)imidazolium chloride (IDip·HCl) was obtained following a two-step procedure that first involved the condensation of glyoxal and two equivalents of 2,6-diisopropylaniline into the corresponding diazabutadiene. This intermediate

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

• singlet for the cyclopentadienyl ligand in each complex suggests that this ligand rotates faster than the NMR timescale, while a sharp singlet was also observed for the imidazol-2- ylidene backbone protons. The cycloalkyl nature of the N-substituents results in most of the proton signals for these species

• appearing as broad multiplets, even at high fields. The methine signal for the cycloalkyl substituents is discrete, appearing at δH = 6.01 ppm for ICy and δH = 6.28 ppm for IDD as a triplet of triplets and an apparent quintet, respectively. In the carbon NMR spectra, the imidazol-2-ylidene C2 signals

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

• '-dimethyl-3,3'-methylene-diimidazol-2,2'-diylidene) [40]. Ruthenium picolyl–NHC complex [(η5-C5Me5)-Ru(L)(CH3CN)][PF6] (L = 3-methyl-1-(2-picolyl)imidazol-2-ylidene) is so far one of the most efficient catalyst for transfer hydrogenation of acetophenone which gave 1-phenylethanol in a conversion of 93% with

Pyridinoacridine alkaloids of marine origin: NMR and MS spectral data, synthesis, biosynthesis and biological activity

• Louis P. Sandjo,
• Victor Kuete and
• Maique W. Biavatti

Beilstein J. Org. Chem. 2015, 11, 1667–1699, doi:10.3762/bjoc.11.183

• -2-chloro-3-cyanopyridine, which was cross-coupled with 3-methylpyridin-2-ylzinc bromide catalyzed by PEPPSI-iPr (pyridine-enhanced precatalyst preparation stabilization and initiation or 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene](3-chloropyridyl)palladium(II) dichloride) under microwave

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

• = 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene) with a series of commercially available (hetero)aromatic amines leads to the synthesis of several [Au(NRR’)(IPr)] complexes in good yields and with water as the sole byproduct. Interestingly, these complexes present luminescence properties. UV–vis and

• )] (1) (IPr = 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene), using [AuCl(IPr)] and an excess of KOH in THF [14][15]. This complex has proven to be an excellent synthon for the preparation of a wide variety of organogold(I) species [16][17][18][19][20][21][22][23]. Two approaches have been developed

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

• platinum complex [Pt(SiMe2Ph)2(IPr)] (IPr = 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene) shows a unique Y-shaped geometry in which the Si–Pt–Si angle is very acute (80.9°) and far from the ideal values for both trigonal-planar and T-shaped structures (Y1, Figure 3) [15]. Computations on non-sterically

• demanding models [Pt(R)2(Im)] (R = SiMe3, Me; Im = imidazol-2-ylidene) appealed to the trans influence of both NHC and silyl ligands to explain the structure. However, a recent DFT investigation concluded that Y1 is better described as a Pt(0) σ-disilane complex [16] than as a Pt(II) disilyl species

• -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

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

Combination of gold catalysis and Selectfluor for the synthesis of fluorinated nitrogen heterocycles

• Antoine Simonneau,
• Pierre Garcia,
• Jean-Philippe Goddard,
• Virginie Mouriès-Mansuy,
• Max Malacria and
• Louis Fensterbank

Beilstein J. Org. Chem. 2011, 7, 1379–1386, doi:10.3762/bjoc.7.162

• of AuCl3, a lower yield of 3a was observed (14%) with trace amounts of 4a and 5a (2% yield each, Table 1, entry 3). The use of the N,N-bis(2,6-diisopropylphenyl)imidazol-2-ylidene (IPr) gold(I) chloride as catalyst led to the formation of 3a in 65% yield, together with 13% yield of 4a. Under these

The role of silver additives in gold-mediated C–H functionalisation

• Scott R. Patrick,
• Ine I. F. Boogaerts,
• Sylvain Gaillard,
• Alexandra M. Z. Slawin and
• Steven P. Nolan

Beilstein J. Org. Chem. 2011, 7, 892–896, doi:10.3762/bjoc.7.102

• complexes bearing N-heterocyclic carbenes (NHC) [9][10] as supporting ligands has enabled the isolation of a “golden synthon”, [Au(OH)(IPr)] 1 (IPr = 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene), that is able to participate in metalation reactions with aromatic C–H bonds (Scheme 1) [11]. The reactivity

Gold-catalyzed naphthalene functionalization

• Pedro J. Pérez,
• M. Mar Díaz-Requejo and
• Iván Rivilla

Beilstein J. Org. Chem. 2011, 7, 653–657, doi:10.3762/bjoc.7.77

• Abstract The complexes IPrMCl (IPr = 1,3-bis(diisopropylphenyl)imidazol-2-ylidene, M = Cu, 1a; M = Au, 1b), in the presence of one equiv of NaBAr'4 (Ar' = 3,5-bis(trifluoromethyl)phenyl), catalyze the transfer of carbene groups: C(R)CO2Et (R = H, Me) from N2C(R)CO2Et to afford products that depend on the

• found that the gold complex IPrAuCl (1b) (IPr = 1,3-bis(diisopropylphenyl)imidazol-2-ylidene) in the presence of one equiv of NaBAr'4 (Ar' = 3,5-bis(trifluoromethyl)phenyl) induced the functionalization of benzene with ethyl diazoacetate to give a mixture of a cycloheptatriene and ethyl 2-phenylacetate