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Benhassine A, Chouiter MI, Kara Ali M, Kacem-Chaouche N, Merazig H, Bencharif M, Belfaitah A. New Cd(II) complex derived from (1-methylimidazol-2-yl) methanol: Synthesis, crystal structure, spectroscopic study, DFT and TD-DFT calculations, antimicrobial activity and free-radical scavenging capacity. J Mol Struct 2022. [DOI: 10.1016/j.molstruc.2022.132583] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
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2
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Melancon KM, Cundari TR. Computational investigations of NHC-backbone configurations for applications in organocatalytic umpolung reactions. Org Biomol Chem 2020; 18:7437-7447. [PMID: 32940280 DOI: 10.1039/d0ob01267j] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023]
Abstract
Density functional theory (DFT) and multiconfigurational self-consistent field theory (MCSCF) methods are employed to investigate variation of the electronic properties of various N-heterocyclic carbenes. Alterations to the backbone by increased or decreased conjugation, heteroatom substitution in the NHC ring, and electron-donating or -withdrawing backbone substituents are modeled. The MCSCF calculations show extensive delocalization of both the highest occupied and lowest unoccupied molecular orbitals for NHCs with polymerizable backbone substituents. The free energies of the intermediates and transition structures for benzoin condensation are also shown to be sensitive to substitution of the NHC backbone. Taken together, these results imply great sensitivity of the reactivity of poly(NHC) catalysts to backbone modification at this moiety. Implications with respect to enhancement of poly(NHC)s employed in umpolung catalysis are discussed.
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Affiliation(s)
- Kortney M Melancon
- University of North Texas, Department of Chemistry, Denton, Texas 76201, USA.
| | - Thomas R Cundari
- University of North Texas, Department of Chemistry, Denton, Texas 76201, USA.
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Preparation and Application of Silica Films Supported Imidazolium-Based Ionic Liquid as Efficient and Recyclable Catalysts for Benzoin Condensations. Catal Letters 2019. [DOI: 10.1007/s10562-019-03030-z] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
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4
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Zhao Y, Xu H, Lu K, Qu Y, Zhu L, Wang S. Experimental and Kinetic Study of Arabinose Conversion to Furfural in Renewable Butanone–Water Solvent Mixture Catalyzed by Lewis Acidic Ionic Liquid Catalyst. Ind Eng Chem Res 2019. [DOI: 10.1021/acs.iecr.9b03420] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Yuan Zhao
- State Key Laboratory of Clean Energy Utilization, Zhejiang University, Zheda Road 38, Hangzhou 310027, China
| | - Hao Xu
- State Key Laboratory of Clean Energy Utilization, Zhejiang University, Zheda Road 38, Hangzhou 310027, China
| | - Kaifeng Lu
- State Key Laboratory of Clean Energy Utilization, Zhejiang University, Zheda Road 38, Hangzhou 310027, China
| | - Yang Qu
- State Key Laboratory of Clean Energy Utilization, Zhejiang University, Zheda Road 38, Hangzhou 310027, China
| | - Lingjun Zhu
- State Key Laboratory of Clean Energy Utilization, Zhejiang University, Zheda Road 38, Hangzhou 310027, China
| | - Shurong Wang
- State Key Laboratory of Clean Energy Utilization, Zhejiang University, Zheda Road 38, Hangzhou 310027, China
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Miao H, Schmidt J, Heil T, Antonietti M, Willinger M, Guterman R. Formation and Properties of Poly(Ionic Liquid)-Carbene Nanogels Containing Individually Stabilized Silver Species. Chemistry 2018; 24:5754-5759. [PMID: 29508930 DOI: 10.1002/chem.201800448] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/29/2018] [Indexed: 01/02/2023]
Abstract
Imidazolium-based ionic liquids have the ability to undergo a variety of chemical reactions through an N-heterocyclic carbene (NHC) intermediate, which has expanded the chemical toolbox for new applications. Despite their uses and exploration, the carbene-forming properties and applications of their polymeric congeners, poly(ionic liquid)s (PILs), is still underdeveloped. Herein, we explore the NHC-forming properties of a theophylline-derived PIL for nanogel synthesis. Using silver oxide as both the carbene-forming reagent and cross-linker, nanogels containing individually stabilized ions can be created with different sizes and morphology, including large "galaxy-like" superstructures. Using high-resolution TEM techniques, we directly observed the sub-nanometer structure of these constructs. These features combined exemplify the unique chemistry of poly-NHCs for single-metal-ion-stabilization nanogel design.
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Affiliation(s)
- Han Miao
- Department of Colloid Chemistry, Max Planck Institute for Colloids and Interfaces, MPI Research Campus Golm, Am Mühlenberg 1, 14476, Potsdam, Germany
| | - Johannes Schmidt
- Department of Functional Materials, Technical University Berlin, Hardenbergstrasse 40, 10623, Berlin, Germany
| | - Tobias Heil
- Department of Colloid Chemistry, Max Planck Institute for Colloids and Interfaces, MPI Research Campus Golm, Am Mühlenberg 1, 14476, Potsdam, Germany
| | - Markus Antonietti
- Department of Colloid Chemistry, Max Planck Institute for Colloids and Interfaces, MPI Research Campus Golm, Am Mühlenberg 1, 14476, Potsdam, Germany
| | - Marc Willinger
- Department of Colloid Chemistry, Max Planck Institute for Colloids and Interfaces, MPI Research Campus Golm, Am Mühlenberg 1, 14476, Potsdam, Germany
| | - Ryan Guterman
- Department of Colloid Chemistry, Max Planck Institute for Colloids and Interfaces, MPI Research Campus Golm, Am Mühlenberg 1, 14476, Potsdam, Germany
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Ragno D, Di Carmine G, Brandolese A, Bortolini O, Giovannini PP, Massi A. Immobilization of Privileged Triazolium Carbene Catalyst for Batch and Flow Stereoselective Umpolung Processes. ACS Catal 2017. [DOI: 10.1021/acscatal.7b02164] [Citation(s) in RCA: 41] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022]
Affiliation(s)
- Daniele Ragno
- Dipartimento di Scienze Chimiche e Farmaceutiche, Università di Ferrara, Via Luigi Borsari, 46, I-44121 Ferrara, Italy
| | - Graziano Di Carmine
- Dipartimento di Scienze Chimiche e Farmaceutiche, Università di Ferrara, Via Luigi Borsari, 46, I-44121 Ferrara, Italy
| | - Arianna Brandolese
- Dipartimento di Scienze Chimiche e Farmaceutiche, Università di Ferrara, Via Luigi Borsari, 46, I-44121 Ferrara, Italy
| | - Olga Bortolini
- Dipartimento di Scienze Chimiche e Farmaceutiche, Università di Ferrara, Via Luigi Borsari, 46, I-44121 Ferrara, Italy
| | - Pier Paolo Giovannini
- Dipartimento di Scienze Chimiche e Farmaceutiche, Università di Ferrara, Via Luigi Borsari, 46, I-44121 Ferrara, Italy
| | - Alessandro Massi
- Dipartimento di Scienze Chimiche e Farmaceutiche, Università di Ferrara, Via Luigi Borsari, 46, I-44121 Ferrara, Italy
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8
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Khalafi-Nezhad A, Shekouhy M, Sharghi H, Aboonajmi J, Zare A. A new more atom-efficient multi-component approach to tetrasubstituted imidazoles: one-pot condensation of nitriles, amines and benzoin. RSC Adv 2016. [DOI: 10.1039/c6ra11171h] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
A new more atom-efficient multi-component approach for the synthesis of tetrasubstituted imidazoles via the one-pot condensation of nitriles, primary amines and benzoin has been described.
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Affiliation(s)
- Ali Khalafi-Nezhad
- Department of Chemistry
- College of Sciences
- Shiraz University
- Shiraz 71454
- Iran
| | - Mohsen Shekouhy
- Department of Chemistry
- College of Sciences
- Shiraz University
- Shiraz 71454
- Iran
| | - Hashem Sharghi
- Department of Chemistry
- College of Sciences
- Shiraz University
- Shiraz 71454
- Iran
| | - Jasem Aboonajmi
- Department of Chemistry
- College of Sciences
- Shiraz University
- Shiraz 71454
- Iran
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9
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Yan B, Zang H, Jiang Y, Yu S, Chen EYX. Recyclable montmorillonite-supported thiazolium ionic liquids for high-yielding and solvent-free upgrading of furfural and 5-hydroxymethylfurfural to C10 and C12 furoins. RSC Adv 2016. [DOI: 10.1039/c6ra14594a] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
Six Na+/montmorillonite (MMT) – supported thiazolium (TM) ionic liquids (ILs) have been synthesized and employed to catalyze the highly selective condensation of furfural (FF) and 5-hydroxymethylfurfural (HMF) into C10 and C12 furoins, respectively.
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Affiliation(s)
- Bing Yan
- State Key Laboratory of Hollow Fiber Membrane Materials and Processes
- Department of Environmental and Chemistry Engineering
- Tianjin Polytechnic University
- 300387 Tianjin
- China
| | - Hongjun Zang
- State Key Laboratory of Hollow Fiber Membrane Materials and Processes
- Department of Environmental and Chemistry Engineering
- Tianjin Polytechnic University
- 300387 Tianjin
- China
| | - Yi Jiang
- State Key Laboratory of Hollow Fiber Membrane Materials and Processes
- Department of Environmental and Chemistry Engineering
- Tianjin Polytechnic University
- 300387 Tianjin
- China
| | - Songbai Yu
- State Key Laboratory of Hollow Fiber Membrane Materials and Processes
- Department of Environmental and Chemistry Engineering
- Tianjin Polytechnic University
- 300387 Tianjin
- China
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10
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Chung J, Seo UR, Chun S, Chung YK. Poly(3,4-dimethyl-5-vinylthiazolium)/DBU-Catalyzed Thioesterification of Aldehydes with Thiols. ChemCatChem 2015. [DOI: 10.1002/cctc.201501140] [Citation(s) in RCA: 29] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023]
Affiliation(s)
- Junyong Chung
- Department of Chemistry; Seoul National University; Seoul 151-747 Korea
| | - Ue Ryung Seo
- Department of Chemistry; Seoul National University; Seoul 151-747 Korea
| | - Supill Chun
- Department of Chemistry; Seoul National University; Seoul 151-747 Korea
| | - Young Keun Chung
- Department of Chemistry; Seoul National University; Seoul 151-747 Korea
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11
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An investigation of the catalytic potential of potassium cyanide and imidazolium salts for ultrasound-assisted synthesis of benzoin derivatives. JOURNAL OF SAUDI CHEMICAL SOCIETY 2015. [DOI: 10.1016/j.jscs.2012.05.005] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
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12
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Wang L, Chen EYX. Recyclable Supported Carbene Catalysts for High-Yielding Self-Condensation of Furaldehydes into C10 and C12 Furoins. ACS Catal 2015. [DOI: 10.1021/acscatal.5b01410] [Citation(s) in RCA: 45] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Lu Wang
- Department of Chemistry, Colorado State University, Fort Collins, Colorado 80523-1872, United States
| | - Eugene Y.-X. Chen
- Department of Chemistry, Colorado State University, Fort Collins, Colorado 80523-1872, United States
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Molina de la Torre JA, Albéniz AC. N-Heterocyclic Carbenes Supported on Vinylic Addition Polynorbornene: A Recyclable and Recoverable Organocatalyst. ChemCatChem 2014. [DOI: 10.1002/cctc.201402767] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
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14
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Seo UR, Chung YK. Poly(4-vinylimidazolium) iodides: a highly recyclable organocatalyst precursor for benzoin condensation reaction. RSC Adv 2014. [DOI: 10.1039/c4ra05073h] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
The development of highly efficient, recyclable poly(4-vinylimidazolium) iodides (2) for the benzoin condensation reaction under mild reaction conditions is discussed: poly(4-vinylN-heterocyclic carbene)s (3) obtained from2showed a higher catalytic activity and could be successfully recovered and reused over seven times without loss of performance.
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Affiliation(s)
- Ue Ryung Seo
- Department of Chemistry
- College of Natural Sciences
- Seoul National University
- Seoul 151-747, Korea
| | - Young Keun Chung
- Department of Chemistry
- College of Natural Sciences
- Seoul National University
- Seoul 151-747, Korea
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15
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Clay supported titanium catalyst for the solvent free synthesis of tetrasubstituted imidazoles and benzimidazoles. ACTA ACUST UNITED AC 2013. [DOI: 10.1016/j.molcata.2013.04.004] [Citation(s) in RCA: 35] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
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16
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Fèvre M, Pinaud J, Gnanou Y, Vignolle J, Taton D. N-Heterocyclic carbenes (NHCs) as organocatalysts and structural components in metal-free polymer synthesis. Chem Soc Rev 2013; 42:2142-72. [PMID: 23288304 DOI: 10.1039/c2cs35383k] [Citation(s) in RCA: 399] [Impact Index Per Article: 36.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
Abstract
The chemistry of N-heterocyclic carbenes (NHCs) has witnessed tremendous development in the past two decades: NHCs have not only become versatile ligands for transition metals, but have also emerged as powerful organic catalysts in molecular chemistry and, more recently, in metal-free polymer synthesis. To understand the success of NHCs, this review first presents the electronic properties of NHCs, their main synthetic methods, their handling, and their reactivity. Their ability to activate key functional groups (e.g. aldehydes, esters, heterocycles, silyl ketene acetals, alcohols) is then discussed in the context of molecular chemistry. Focus has been placed on the activation of substrates finding analogies with monomers (e.g. bis-aldehydes, multi-isocyanates, cyclic esters, epoxides, N-carboxyanhydrides, etc.) and/or initiators (e.g. hydroxy- or trimethylsilyl-containing reagents) employed in such "organopolymerisation" reactions utilizing NHCs. A variety of metal-free polymers, including aliphatic polyesters and polyethers, poly(α-peptoid)s, poly(meth)acrylates, polyurethanes, or polysiloxanes can be obtained in this way. The last section covers the use of NHCs as structural components of the polymer chain. Indeed, NHC-based photoinitiators, chain transfer agents or functionalizing agents, as well as bifunctional NHC monomer substrates, can also serve for metal-free polymer synthesis.
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Affiliation(s)
- Maréva Fèvre
- Centre National de la Recherche Scientifique, Laboratoire de Chimie des Polymères Organiques, 16 avenue Pey-Berland, F-33607 Pessac cedex, France
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Adam F, Hassan HE, Hello KM. The synthesis of N-heterocyclic carbene–silica nano-particles and its catalytic activity in the cyclization of glycerol. J Taiwan Inst Chem Eng 2012. [DOI: 10.1016/j.jtice.2012.01.013] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/28/2022]
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18
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Jorapur YR, Chi DY. Intramolecular Cycloalkylation of Pyrrole in Ionic Liquids and Immobilized Ionic Liquids. B KOREAN CHEM SOC 2011. [DOI: 10.5012/bkcs.2011.32.8.3130] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
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19
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Powell AB, Suzuki Y, Ueda M, Bielawski CW, Cowley AH. A Recyclable, Self-Supported Organocatalyst Based on a Poly(N-Heterocyclic Carbene). J Am Chem Soc 2011; 133:5218-20. [DOI: 10.1021/ja200602e] [Citation(s) in RCA: 54] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Adam B. Powell
- Department of Chemistry and Biochemistry, The University of Texas at Austin, Austin, Texas 78712-0165, United States
| | - Yasuo Suzuki
- Department of Organic and Polymeric Materials, Tokyo Institute of Technology, Tokyo 152-8552, Japan
| | - Mitsuru Ueda
- Department of Organic and Polymeric Materials, Tokyo Institute of Technology, Tokyo 152-8552, Japan
| | - Christopher W. Bielawski
- Department of Chemistry and Biochemistry, The University of Texas at Austin, Austin, Texas 78712-0165, United States
| | - Alan H. Cowley
- Department of Chemistry and Biochemistry, The University of Texas at Austin, Austin, Texas 78712-0165, United States
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Mavis ME, Yolacan C, Aydogan F. An investigation of the catalytic potential of mono- and dicationic imidazolium N-heterocyclic carbenes in the benzoin condensation. Tetrahedron Lett 2010. [DOI: 10.1016/j.tetlet.2010.06.099] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/19/2022]
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21
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Aupoix A, Pégot B, Vo-Thanh G. Synthesis of imidazolium and pyridinium-based ionic liquids and application of 1-alkyl-3-methylimidazolium salts as pre-catalysts for the benzoin condensation using solvent-free and microwave activation. Tetrahedron 2010. [DOI: 10.1016/j.tet.2009.11.110] [Citation(s) in RCA: 62] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/20/2022]
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22
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Supported heteropoly acids offering strong option for efficient and cleaner processing for the synthesis of imidazole derivatives under solvent-free condition. Mol Divers 2010; 15:125-34. [DOI: 10.1007/s11030-009-9213-1] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/21/2009] [Accepted: 11/18/2009] [Indexed: 10/19/2022]
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Mohanazadeh F, Aghvami M. Thiazolium Salt Immobilized on Ionic Liquid: An Efficient Catalyst and Solvent for Preparation of α-Hydroxyketones. PHOSPHORUS SULFUR 2007. [DOI: 10.1080/10426500701501565] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022]
Affiliation(s)
- Farajollah Mohanazadeh
- a Institute of Industrial Chemistry, Iranian Research Organization for Science and Technologies , Tehran , Iran
| | - Majid Aghvami
- b Department of Chemistry , Tarbiat Moallem University , Tehran , Iran
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Bellina F, Cauteruccio S, Rossi R. Synthesis and biological activity of vicinal diaryl-substituted 1H-imidazoles. Tetrahedron 2007. [DOI: 10.1016/j.tet.2007.02.075] [Citation(s) in RCA: 164] [Impact Index Per Article: 9.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/08/2023]
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Iwamoto KI, Hamaya M, Hashimoto N, Kimura H, Suzuki Y, Sato M. Benzoin reaction in water as an aqueous medium catalyzed by benzimidazolium salt. Tetrahedron Lett 2006. [DOI: 10.1016/j.tetlet.2006.07.153] [Citation(s) in RCA: 55] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
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Lloyd-Jones GC, Alder RW, Owen-Smith GJJ. Intermolecular Insertion of an N,N-Heterocyclic Carbene into a Nonacidic CH Bond: Kinetics, Mechanism and Catalysis by (K-HMDS)2 (HMDS=Hexamethyldisilazide). Chemistry 2006; 12:5361-75. [PMID: 16673429 DOI: 10.1002/chem.200600266] [Citation(s) in RCA: 37] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
The reaction of 2-[13C]-1-ethyl-3-isopropyl-3,4,5,6-tetrahydropyrimidin-1-ium hexafluorophosphate ([13C1]-1-PF6) with a slight excess (1.03 equiv) of dimeric potassium hexamethyldisilazide ("(K-HMDS)2") in toluene generates 2-[13C]-3-ethyl-1-isopropyl-3,4,5,6-tetrahydropyrimid-2-ylidene ([13C1]-2). The hindered meta-stable N,N-heterocyclic carbene [13C1]-2 thus generated undergoes a slow but quantitative reaction with toluene (the solvent) to generate the aminal 2-[13C]-2-benzyl-3-ethyl-1-isopropylhexahydropyrimidine ([13C1]-14) through formal C-H insertion of C2 (the "carbene carbon") at the toluene methyl group. Despite a significant pKa mismatch (Delta pKa 1+ and toluene estimated to be ca. 16 in DMSO) the reaction shows all the characteristics of a deprotonation mechanism, the reaction rate being strongly dependent on the toluene para substituent (rho = 4.8(+/-0.3)), and displaying substantial and rate-limiting primary (k(H)/k(D) = 4.2(+/-0.6)) and secondary (k(H)/k(D) = 1.18(+/-0.08)) kinetic isotope effects on the deuteration of the toluene methyl group. The reaction is catalysed by K-HMDS, but proceeds without cross over between toluene methyl protons and does not involve an HMDS anion acting as base to generate a benzyl anion. Detailed analysis of the reaction kinetics/kinetic isotope effects demonstrates that a pseudo-first-order decay in 2 arises from a first-order dependence on 2, a first-order dependence on toluene (in large excess) and, in the catalytic manifold, a complex noninteger dependence on the K-HMDS dimer. The rate is not satisfactorily predicted by equations based on the Brønsted salt-effect catalysis law. However, the rate can be satisfactorily predicted by a mole-fraction-weighted net rate constant: -d[2]/dt = ({x2 k(uncat)} + {(1-x2) k(cat)})[2]1[toluene]1, in which x2 is determined by a standard bimolecular complexation equilibrium term. The association constant (Ka) for rapid equilibrium-complexation of 2 with (K-HMDS)2 to form [2(K-HMDS)2] is extracted by nonlinear regression of the 13C NMR shift of C2 in [13C1]-2 versus [(K-HMDS)2] yielding: Ka = 62(+/-7) M(-1); delta(C(2)) in 2=237.0 ppm; delta(C(2)) in [2(K-HMDS)2] = 226.8 ppm. It is thus concluded that there is discrete, albeit inefficient, molecular catalysis through the 1:1 carbene/(K-HMDS)2 complex [2(K-HMDS)2], which is found to react with toluene more rapidly than free 2 by a factor of 3.4 (=k(cat)/k(uncat)). The greater reactivity of the complex [2(K-HMDS)2] over the free carbene (2) may arise from local Brønsted salt-effect catalysis by the (K-HMDS)2 liberated in the solvent cage upon reaction with toluene.
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Affiliation(s)
- Guy C Lloyd-Jones
- The Bristol Centre for Organometallic Catalysis, School of Chemistry, University of Bristol, Cantock's Close, Bristol BS8 1TS, UK.
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Acke D, Orru R, Stevens C. Continuous Synthesis of Tri- and Tetrasubstituted Imidazolesvia a Multicomponent Reaction under Microreactor Conditions. ACTA ACUST UNITED AC 2006. [DOI: 10.1002/qsar.200540194] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
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