- Synthesis of 1,3-dialkylimidazolium and 1,3-dialkylbenzimidazolium salts
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A number of N-alkylimidazoles and N-alkylbenzimidazoles were synthesized by reactions of imidazole and benzimidazole with alkyl halides. The reaction rate increases by a factor of 2 to 3 under conditions of microwave activation. Subsequent treatment of the resulting N-alkylazoles with alkyl halides afforded the corresponding 1,3-dialkylimidazolium and 1,3-dialkylbenzimidazolium halides.
- Starikova,Dolgushin,Larina,Ushakov,Komarova,Lopyrev
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- Cyclometallated Platinum(II) Complexes with a Phenylpropene-Derived π/σ-Chelator and N-Heterocyclic Carbenes
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A series of heteroleptic platinum(II) complexes of the general formula [PtX(iPrEug)(NHC)] (2–7) bearing the organometallic π/σ-chelator iPrEug (isopropyl eugenoxyacetate), with varying X (halido) and NHC (N-heterocyclic carbene) ligands derived from imidazole, benzimidazole, and triazole, were prepared and fully characterized by elemental analyses, ESI mass spectrometry, and IR and NMR spectroscopy. Complexes 3 and 5–7 were also characterized by single-crystal X-ray diffraction. These air-stable complexes are rare examples of platinum(II) compounds containing three different types of carbon donors, that is, aryl, carbene, and olefin. Unsymmetrical NHCs led to rotameric pairs of 4 and 5 exhibiting different NMR spectroscopic features. Spectroscopic studies also revealed that the introduction of a NHC leads to a weakening of the metal–olefin bond and strengthening of the metal–aryl bond. On the other hand, backbone and thus electronic variations among the NHCs show little influence on the bonding of the iPrEug chelator.
- Huynh, Han Vinh,Pham, Van Thong,Chi, Nguyen Thi Thanh
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- Synthesis, crystal structure, and catalytic activity of bridged-bis(N-heterocyclic carbene) palladium(II) complexes in selective Mizoroki-Heck cross-coupling reactions
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A series of three 1,3-propanediyl bridged bis(N-heterocyclic carbene)palladium(II) complexes (Pd-BNH1, Pd-BNH2, and Pd-BNH3), with + I effect order of the N-substituents of the ligand (isopropyl > benzyl > methoxyphenyl), was the subject of a spectroscopic, structural, computational and catalytic investigation. The bis(NHC)PdBr2 complexes were evaluated in Mizoroki-Heck coupling reactions of aryl bromides with styrene or acrylate derivatives and showed high catalytic efficiency to produce diarylethenes and cinnamic acid derivatives. The X-ray structure of the most active palladium complex Pd-BNH3 shows that the Pd(II) center is bonded to the two carbon atoms of the bis(N-heterocyclic carbene) and two bromide ligands in cis position, resulting in a distorted square planar geometry. The NMR data of Pd-BNH3 are consistent with a single chair-boat rigid conformer in solution with no dynamic behavior of the 8-membered ring palladacycle in the temperature range 25–120 °C. The catalytic activities of three Pd-bridged bis(NHC) complexes in the Mizoroki-Heck cross-coupling reactions were not found to have a direct correlation with +I effect order of the N-substituents of the ligand. However, a direct correlation was found between the DFT calculated absolute softness of the three complexes with their respective catalytic activity. The highest calculated softness, in the case of Pd-BNH3, is expected to favor the coordination steps of both the soft aryl bromides and alkenes in the Heck catalytic cycle.
- El Ali, Bassam,Fettouhi, Mohammed,Iali, Wissam,Mansour, Waseem,Suleiman, Rami
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- Novel and efficient bridged bis(N-heterocyclic carbene)palladium(II) catalysts for selective carbonylative Suzuki–Miyaura coupling reactions to biaryl ketones and biaryl diketones
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Bridged N,N′-substituted bisbenzimidazolium bromide salts (L1, L2, and L3) were synthesized and fully characterized. Reactions of palladium acetate with L1, L2, and L3 afforded corresponding new bridged bis(N-heterocyclic carbene)palladium(II) complexes (C1, C2, and C3) in high yields. The X-ray structure of complex C1 showed that the Pd(II) ion is bonded to the two carbon atoms of the bis(N-heterocyclic carbene) and two bromido ligands are in the cis position, resulting in a distorted square planar geometry. The three Pd(NHC)2Br2 complexes C1, C2, and C3 were evaluated in carbonylative Suzuki–Miyaura coupling reactions of aryl boronic acids with aryl halides and displayed high catalytic activity with low catalyst loading. The coupling reactions of aryl bromides were selective towards the carbonylation product at higher carbon monoxide pressure.
- El Ali, Bassam,Fettouhi, Mohammed,Mansour, Waseem
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- Visible-light-induced aerobic oxidative desulfurization of 2-mercaptobenzimidazolesviaa sulfinyl radical
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A mild transition-metal-free non-toxic aerobic photoredox system was found to enable highly efficient desulfurization of 2-mercaptobenzimidazoles. This viable catalytic system includes Rose Bengal in a low catalyst loading as a photosensitizer and cheap, non-toxic NaCl in a catalytic amount as an additive, combined with an oxygen atmosphere. This protocol provides an important alternative access to a broad range of benzimidazole and deuterated benzimidazole products in generally high yields with good tolerance of various synthetically and pharmaceutically useful functionalities. The mechanistic studies reveal that both single electron transfer and energy transfer probably occur in the initial step and a sulfinyl radical intermediate is involved in the key desulfurization process.
- Deng, Guo-Jun,Fu, Mei,Huang, Huawen,Ji, Xiaochen,Li, Yongtong
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supporting information
p. 5594 - 5598
(2020/09/21)
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- Methods of Forming Carbene-Functionalized Composite Materials
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Deposition of carbene monolayers that excluded starting anions, such as iodide ions, has been achieved. Anions such as iodide are a typical contaminant in carbene hydrogen carbonate salts when synthesized using the state-of-the-art method. A method is described for eliminating substantially all starting anion (e.g., iodide) contamination from the monolayer. Air stable, purified carbenes precursors were used to deposit an intact monolayer on the surface of some industrially relevant metals. The monolayer's ability to protect these metals against, for example, oxidation has been demonstrated.
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Paragraph 0498; 0499
(2019/06/14)
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- Bis-benzimidazolium-palladium system catalyzed Suzuki-Miyaura coupling reaction of aryl bromides under mild conditions
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Bis-benzimidazolium salts were prepared successfully from commercially available and inexpensive o-phenylenediamine through a series of simple reactions. The bis-NHC-Pd complexes prepared in situ can catalyze Suzuki-Miyaura cross-coupling reaction under very mild conditions in aqueous media with excellent yields. The efficiency of this reaction is demonstrated by its compatibility with a range of functional groups. Di-ortho-substituted biaryls could be accomplished in 89–99% yields. Moreover, the rigorous exclusion of air or moisture is not required in these transformations.
- Lin, Yi-Rang,Chiu, Chien-Cheng,Chiu, Huai-Tsu,Lee, Dong-Sheng,Lu, Ta-Jung
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- N-Heterocyclic Carbenes as a Robust Platform for Surface-Enhanced Raman Spectroscopy
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Surface-enhanced Raman spectroscopy (SERS) underpins a wide range of commercial and fundamental applications. SERS often relies on ligands, usually thiols, bound to a noble metal surface. The difficulty of straightforward thiol synthesis combined with their instability on surfaces highlights the need for alternative ligand design. We present the first example of SERS utilizing N-heterocyclic carbene ligands. A general three step synthesis is presented for functionalized NHC-CO2 adducts. These ligands are deposited on SERS-active gold film-over-nanosphere substrates (AuFONs) in solvent-free and base-free conditions, which prevents fouling. The resulting films are found to be robust and capable of postsynthetic modifications.
- Dejesus, Joseph F.,Trujillo, Michael J.,Camden, Jon P.,Jenkins, David M.
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p. 1247 - 1250
(2018/02/09)
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- Non-symmetrically p-nitrobenzyl- and p-cyanobenzyl-substituted N-heterocyclic carbene-silver(I) complexes: synthesis, characterization and antibacterial studies
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Various nitro/nitrile-functionalized benzimidazol-2-ylidene carbene complexes of silver(I) (7a–d and 11a–d) were synthesized by combination of 1-allyl/1-isopropyl/1-sec-butyl/1-isopentyl-3-(nitro/cyano-benzyl)-3H-benzimidazol-1-ium hexafluorophosphate (6a
- Subramanya Prasad,Shahini,Patil, Shivaputra A.,Huang, Xiaojun,Bugarin, Alejandro,Patil, Siddappa A.
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p. 600 - 614
(2017/02/05)
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- CO2 as a C1 Source: B(C6F5)3-Catalyzed Cyclization of o-Phenylene-diamines To Construct Benzimidazoles in the Presence of Hydrosilane
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The catalytic construction of benzimidazoles using CO2 as a carbon source represents a facile and sustainable approach to obtaining these valuable compounds. Herein, we describe the B(C6F5)3-catalyzed synthesis of benzimidazoles via cyclization of o-phenylenediamines with CO2 and PhSiH3. This metal-free catalytic route achieves the desired products in high yield under convenient reaction conditions and is applicable to a broad substrate scope. A plausible mechanism for the reaction involving a frustrated Lewis pair pathway is proposed based on spectroscopic characterization (e.g., 13C NMR) of the reaction intermediates.
- Zhang, Zhenbei,Sun, Qiangsheng,Xia, Chungu,Sun, Wei
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supporting information
p. 6316 - 6319
(2016/12/23)
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- N-heterocyclic carbenes: VIII. Benzimidazolium diterpene salts with an oxo group in substituent
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Benzimidazolium salts with an oxo group in the substituent are synthesized from a diterpene ketone.
- Denisov,Usatykh,Gorbunov,Maiorova,Glushkov
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p. 705 - 710
(2014/07/08)
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- N-heterocyclic carbene-catalyzed α-alkylation of ketones with primary alcohols
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Several N-heterocyclic carbene precursors are synthesized and used in the α-alkylations of ketones with primary alcohols. With the assistance of a base, these N-heterocyclic carbenes can catalyze the reaction smoothly to furnish dialkylated ketones in good-to-excellent yields.
- Zhu, Yanfang,Cai, Chun,Lu, Guoping
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p. 1666 - 1671
(2015/01/09)
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- Synthesis and characterization of ortho-Xylyl linked bis-benzimidazolium salts
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A number of N-alkylbenzimidazoles were synthesized by reactions of benzimidazole with alkyl halides (i-prBr, BuCl, BzCl, HeptBr, EtBr, PrBr). The subsequent treatment of the resulting N-alkylzoles with 1,2-bis(bromomethylene) benzene afforded corresponding bisbenzimidazolium salts. All the compounds were characterized by spectroscopic techniques (NMR and FT-IR) and microanalysis.
- Haque, Rosenani A.,Iqbal, Muhammad Adnan
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scheme or table
p. 2625 - 2628
(2012/08/27)
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- Facile synthesis of benzimidazolin-2-chalcogenones: Nature of the carbon-chalcogen bond
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A new method using chalcogen nucleophiles E2-/E2 2- (E = S, Se, Te) for the convenient and high yield synthesis of benzimidazolin-2-chalcogenones has been developed. The reaction of strong nucleophiles E2-/E22- with various benzimidazolium salts under mild conditions afforded benzimidazolin-2- chalcogenones (10a-10g) in better yield compared to the other methods involving E0 powder. Benzimidazolin-2-tellurones were found to be unstable when pyridyl/phenyl groups were bonded to one of the nitrogens of the benzimidazolium salts and the reaction led to the isolation of the corresponding diamines (12a and 12b). The selenones/tellurones could be easily oxidized to the corresponding dihaloderivatives (16a-16e) by the reaction of the chalcogenones with bromine/iodine. The nature of the carbon-chalcogen double bond has been investigated with the help of single crystal X-ray, NMR spectroscopy and Density Functional Theory (DFT) calculations.
- Manjare, Sudesh T.,Sharma, Sagar,Singh, Harkesh B.,Butcher, Ray J.
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- Stable N-heterocyclic carbenes: N-alkyl-N'-phosphanylbenzimidazol-2- ylidenes
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Three original approaches to the synthesis of N-alkyl-N'- phosphanylbenzimidazolium salts, which are precursors of the corresponding carbenes, were developed. New stable N-alkyl-N'-phosphanylbenzimidazol-2- ylidenes were prepared in good yields. X-ray analysis of a carbene was made and the chemical properties of the carbenes were studied. The reactions with O-, N-, and C-nucleophiles were found to proceed with or without cleavage of the P-N bond. Thermal rearrangement of the carbenes afforded 2-phosphorylated benzimidazoles.
- Marchenko, Anatoliy P.,Koidan, Heorgiy N.,Hurieva, Anastasiia N.,Pervak, Igor I.,Shishkina, Svitlana V.,Shishkin, Oleg V.,Kostyuk, Aleksandr N.
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p. 4018 - 4033
(2012/09/21)
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- Indole RSK inhibitors. Part 2: Optimization of cell potency and kinase selectivity
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A series of inhibitors for the 90 kDa ribosomal S6 kinase (RSK) based on an 1-oxo-2,3,4,5-tetrahydro-1H-[1,4]diazepino[1,2-a]indole-8-carboxamide scaffold were optimized for cellular potency and kinase selectivity. This led to the identification of compound 24, BIX 02565, an attractive candidate for use in vitro and in vivo to explore the role of RSK as a target for the treatment heart failure.
- Kirrane, Thomas M.,Boyer, Stephen J.,Burke, Jennifer,Guo, Xin,Snow, Roger J.,Soleymanzadeh, Lida,Swinamer, Alan,Zhang, Yunlong,Madwed, Jeffery B.,Kashem, Mohammed,Kugler, Stanley,O'Neill, Margaret M.
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p. 738 - 742
(2012/03/11)
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- A mild, one-pot synthesis of disubstituted benzimidazoles from 2-nitroanilines
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A one-pot synthesis of disubstituted benzimidazoles from 2-nitroanilines is described. Hydrogenation of N-substituted 2-nitroanilines with palladium on carbon as catalyst in the presence of trimethyl orthoformate and catalytic pyridinium p-toluenesulfonate (PPTS) at room temperature provided good to excellent yields of the corresponding disubstituted benzimidazoles.
- Hornberger, Keith R.,Adjabeng, George M.,Dickson, Hamilton D.,Davis-Ward, Ronda G.
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p. 5359 - 5361
(2007/10/03)
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- N-Alkylation of anilines, carboxamides and several nitrogen heterocycles using CsF-Celite/alkyl halides/CH3CN combination
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It has been found that the N-alkylation of aniline, carboxamides and heterocyclic compounds bearing an acidic hydrogen atom attached to nitrogen can be accomplished with alkyl halides in acetonitrile and cesium fluoride-celite employed as a solid base. In this manner, pyrrole, indole, pyrazole, imidazole, benzimidazole, carbazole, phthalimide, indazole, indoline, 2-pyrrolidinone, piperidine and 1,2,4-triazole can be successfully alkylated. The procedure is convenient, efficient and generally gives rise to the N-alkylated product exclusively.
- Hayat, Safdar,Atta-Ur-Rahman,Iqbal Choudhary,Khan, Khalid Mohammed,Schumann, Wilhelm,Bayer, Ernst
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p. 9951 - 9957
(2007/10/03)
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- REGIOSELECTIVE N-ALKYLATION OF BENZIMIDAZOLE VIA AN ORGANOTIN ROUTE
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A simple and efficient method for the exclusive N-alkylation of benzimidazole with functional group compatibility has been achieved.
- Soundararajan, R.,Balasubramanian, T.R.
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p. 5555 - 5558
(2007/10/02)
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