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Abstract
Nitroxides, also known as nitroxyl radicals, are long-lived or stable radicals with the general structure R1R2N-O•. The spin distribution over the nitroxide N and O atoms contributes to the thermodynamic stability of these radicals. The presence of bulky N-substituents R1 and R2 prevents nitroxide radical dimerization, ensuring their kinetic stability. Despite their reactivity toward various transient C radicals, some nitroxides can be easily stored under air at room temperature. Furthermore, nitroxides can be oxidized to oxoammonium salts (R1R2N═O+) or reduced to anions (R1R2N-O-), enabling them to act as valuable oxidants or reductants depending on their oxidation state. Therefore, they exhibit interesting reactivity across all three oxidation states. Due to these fascinating properties, nitroxides find extensive applications in diverse fields such as biochemistry, medicinal chemistry, materials science, and organic synthesis. This review focuses on the versatile applications of nitroxides in organic synthesis. For their use in other important fields, we will refer to several review articles. The introductory part provides a brief overview of the history of nitroxide chemistry. Subsequently, the key methods for preparing nitroxides are discussed, followed by an examination of their structural diversity and physical properties. The main portion of this review is dedicated to oxidation reactions, wherein parent nitroxides or their corresponding oxoammonium salts serve as active species. It will be demonstrated that various functional groups (such as alcohols, amines, enolates, and alkanes among others) can be efficiently oxidized. These oxidations can be carried out using nitroxides as catalysts in combination with various stoichiometric terminal oxidants. By reducing nitroxides to their corresponding anions, they become effective reducing reagents with intriguing applications in organic synthesis. Nitroxides possess the ability to selectively react with transient radicals, making them useful for terminating radical cascade reactions by forming alkoxyamines. Depending on their structure, alkoxyamines exhibit weak C-O bonds, allowing for the thermal generation of C radicals through reversible C-O bond cleavage. Such thermally generated C radicals can participate in various radical transformations, as discussed toward the end of this review. Furthermore, the application of this strategy in natural product synthesis will be presented.
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Affiliation(s)
- Dirk Leifert
- Organisch-Chemisches Institut, Westfälische Wilhelms-Universität, Corrensstrasse 40, 48149 Münster, Germany
| | - Armido Studer
- Organisch-Chemisches Institut, Westfälische Wilhelms-Universität, Corrensstrasse 40, 48149 Münster, Germany
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Unsymmetric bi-functional Mn-salen complex bearing TEMPO and Mn-complex for the synthesis of magnetic Mn/TEMPO-doped Fe3O4 NPs: a simple catalyst (magnetic oxidant) for selective oxidation of alcohols. RESEARCH ON CHEMICAL INTERMEDIATES 2022. [DOI: 10.1007/s11164-022-04873-9] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/07/2022]
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Khalaf E, Alameri AA, Malviya J, Kumar TCHA, Altalbawy FMA, Alfilh RHC, Kazemnejadi M. Synthesis of Highly Porous Mn2O3-Doped Fe3O4 NPs with a Dual Catalytic Function Using Asymmetric Water Soluble Mn-Salen Complex as a Reducing Agent and Template: Catalytic Activity over One-Pot Strecker Synthesis from Alcohols in Recyclable TAIm[CN] Ionic Liquid. Catal Letters 2022. [DOI: 10.1007/s10562-022-04210-0] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
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Surfactant free stable cobalt oxide nanocolloid in water by pulsed laser fragmentation and its thin films for visible light photocatalysis. Colloids Surf A Physicochem Eng Asp 2020. [DOI: 10.1016/j.colsurfa.2020.124657] [Citation(s) in RCA: 14] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
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Dai Q, Tang J. The optical and magnetic properties of CoO and Co nanocrystals prepared by a facile technique. NANOSCALE 2013; 5:7512-7519. [PMID: 23832010 DOI: 10.1039/c3nr01971c] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/02/2023]
Abstract
CoO and Co nanocrystals with cubic crystal structures were prepared by thermal decomposition of cobalt(II) acetate tetrahydrate in a mixture of oleylamine and oleic acid under the protection of nitrogen gas at 300 °C for 2 h. The products of CoO or Co nanocrystals are determined by the relative amount of oleylamine due to its reducibility. The sizes and shapes of CoO or Co can be controlled by the ratio of cobalt : oleylamine : oleic acid due to different binding capabilities of the two capping ligands (oleylamine and oleic acid). A modification of the surface state by surface passivation arising from the capping ligands for CoO nanocrystals leads to the blue shift of the ligand-metal charge transfer (LMCT) absorption. Room temperature ferromagnetism originating from uncompensated surface spins, as well as magnetic moments weakly exchange coupled to the CoO lattice due to defects inside CoO nanoparticles, are observed. The magnetic behaviors of CoO and Co nanoparticles also shed light on the synthesis and the magnetic properties of the antiferromagnetic and ferromagnetic nanomaterials.
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Affiliation(s)
- Qilin Dai
- Department of Physics & Astronomy, University of Wyoming, Laramie, WY 82071, USA
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Lomont JP, Nguyen SC, Harris CB. Reactivity of TEMPO toward 16- and 17-electron organometallic reaction intermediates: a time-resolved IR study. J Am Chem Soc 2013; 135:11266-73. [PMID: 23819559 DOI: 10.1021/ja404476m] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
The (2,2,6,6-tetramethylpiperidin-1-yl)oxyl radical (TEMPO) has been employed for an extensive range of chemical applications, ranging from organometallic catalysis to serving as a structural probe in biological systems. As a ligand in an organometallic complex, TEMPO can exhibit several distinct coordination modes. Here we use ultrafast time-resolved infrared spectroscopy to study the reactivity of TEMPO toward coordinatively unsaturated 16- and 17-electron organometallic reaction intermediates. TEMPO coordinates to the metal centers of the 16-electron species CpCo(CO) and Fe(CO)4, and to the 17-electron species CpFe(CO)2 and Mn(CO)5, via an associative mechanism with concomitant oxidation of the metal center. In these adducts, TEMPO thus behaves as an anionic ligand, characterized by a pyramidal geometry about the nitrogen center. Density functional theory calculations are used to facilitate interpretation of the spectra and to further explore the structures of the TEMPO adducts. To our knowledge, this study represents the first direct characterization of the mechanism of the reaction of TEMPO with coordinatively unsaturated organometallic complexes, providing valuable insight into its reactions with commonly encountered reaction intermediates. The similar reactivity of TEMPO toward each of the species studied suggests that these results can be considered representative of TEMPO's reactivity toward all low-valent transition metal complexes.
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Affiliation(s)
- Justin P Lomont
- Department of Chemistry, University of California, Berkeley, Berkeley 94720, California, USA
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Tebben L, Studer A. Nitroxides: applications in synthesis and in polymer chemistry. Angew Chem Int Ed Engl 2011; 50:5034-68. [PMID: 21538729 DOI: 10.1002/anie.201002547] [Citation(s) in RCA: 505] [Impact Index Per Article: 38.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/28/2010] [Indexed: 01/23/2023]
Abstract
This Review describes the application of nitroxides to synthesis and polymer chemistry. The synthesis and physical properties of nitroxides are discussed first. The largest section focuses on their application as stoichiometric and catalytic oxidants in organic synthesis. The oxidation of alcohols and carbanions, as well as oxidative C-C bond-forming reactions are presented along with other typical oxidative transformations. A section is also dedicated to the extensive use of nitroxides as trapping reagents for C-centered radicals in radical chemistry. Alkoxyamines derived from nitroxides are shown to be highly useful precursors of C-centered radicals in synthesis and also in polymer chemistry. The last section discusses the basics of nitroxide-mediated radical polymerization (NMP) and also highlights new developments in the synthesis of complex polymer architectures.
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Affiliation(s)
- Ludger Tebben
- Organisch-Chemisches Institut, Westfälische Wilhelms-Universität, Corrensstrasse 40, 48149 Münster, Germany
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Yang H, Zhou H, Zhang C, Li X, Hu H, Wu H, Yang S. Water-soluble magnetic CoO nanocrystals functionalized with surfactants as T2-weighed MRI contrast agents in vitro. Dalton Trans 2011; 40:3616-21. [DOI: 10.1039/c1dt10107b] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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Liu S, Ding N, Ye E, Zong Y, Wang D, Knoll W, Han MY. Oxidation-induced constituent separation of magnetic exchange biased Fe/CoO nanocrystals. Chem Commun (Camb) 2009:6255-7. [DOI: 10.1039/b912976f] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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Tüysüz H, Liu Y, Weidenthaler C, Schüth F. Pseudomorphic Transformation of Highly Ordered Mesoporous Co3O4 to CoO via Reduction with Glycerol. J Am Chem Soc 2008; 130:14108-10. [DOI: 10.1021/ja806202v] [Citation(s) in RCA: 118] [Impact Index Per Article: 7.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Harun Tüysüz
- Max-Planck Institut für Kohlenforschung, Kaiser-Wilhelm-Platz 1, D-45470 Mülheim an der Ruhr, Germany
| | - Yong Liu
- Max-Planck Institut für Kohlenforschung, Kaiser-Wilhelm-Platz 1, D-45470 Mülheim an der Ruhr, Germany
| | - Claudia Weidenthaler
- Max-Planck Institut für Kohlenforschung, Kaiser-Wilhelm-Platz 1, D-45470 Mülheim an der Ruhr, Germany
| | - Ferdi Schüth
- Max-Planck Institut für Kohlenforschung, Kaiser-Wilhelm-Platz 1, D-45470 Mülheim an der Ruhr, Germany
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Zhang H, Du N, Wu P, Chen B, Yang D. Functionalization of carbon nanotubes with magnetic nanoparticles: general nonaqueous synthesis and magnetic properties. NANOTECHNOLOGY 2008; 19:315604. [PMID: 21828791 DOI: 10.1088/0957-4484/19/31/315604] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/31/2023]
Abstract
A novel approach has been developed to synthesize magnetic nanoparticle and carbon nanotube (CNT) core-shell nanostructures, such as CoO/CNTs and Mn(3)O(4)/CNTs, by the nonaqueous solvothermal treatment of metal carbonyl on CNT templates using hexane as the solvent. The morphological and structural characterizations indicate that numerous cubic CoO or tetragonal Mn(3)O(4) nanoparticles are deposited on the surfaces of the CNTs to form CNT-based core-shell nanostructures. It is revealed that the hydrophobic interaction between nanoparticles and CNTs in hexane plays the critical role for the formation of CNT-based core-shell nanostructures. A physical property measurement system (PPMS-9, Quantum Design) analysis indicates that the CoO/CNT core-shell nanostructures show weak ferromagnetic performance at 300 K due to the ferromagnetic Co clusters and the uncompensated surface spin states, while the Mn(3)O(4)/CNT core-shell nanostructures display ferromagnetic behavior at low temperature (34.5 K), which transforms into paramagnetic behavior with increasing temperature.
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Affiliation(s)
- Hui Zhang
- State Key Lab of Silicon Materials and Department of Materials Science and Engineering, Zhejiang University, Hangzhou 310027, People's Republic of China
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Dutta DP, Sharma G, Manna PK, Tyagi AK, Yusuf SM. Room temperature ferromagnetism in CoO nanoparticles obtained from sonochemically synthesized precursors. NANOTECHNOLOGY 2008; 19:245609. [PMID: 21825821 DOI: 10.1088/0957-4484/19/24/245609] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/31/2023]
Abstract
In this paper we report the magnetic properties of nanosized CoO particles, prepared from sonochemically synthesized precursors and characterized using x-ray diffraction (XRD), conventional transmission electron microscopy (TEM) and scanning tunneling electron microscopy combined with energy dispersive x-ray analysis (STEM-EDX) techniques. The nanoparticles were faceted and the sizes varied between 30 and 60 nm depending on the time of annealing. They were stable even in the absence of any organic coating on them. Magnetic measurements reveal the presence of ferromagnetic interactions at low temperatures in the CoO nanoparticles synthesized after 2 and 4 h of annealing of the sonochemically synthesized precursor under nitrogen. However, after 6 h of annealing, the nanoparticles show hysteresis not only at low temperatures (1.5 K) but also at higher temperatures (100 K and room temperature), indicating the presence of room temperature ferromagnetism.
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Affiliation(s)
- Dimple P Dutta
- Chemistry Division, Bhabha Atomic Research Centre, Mumbai 400 085, India
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Hou Y, Xu Z, Sun S. Controlled synthesis and chemical conversions of FeO nanoparticles. Angew Chem Int Ed Engl 2007; 46:6329-32. [PMID: 17645273 DOI: 10.1002/anie.200701694] [Citation(s) in RCA: 250] [Impact Index Per Article: 14.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
Affiliation(s)
- Yanglong Hou
- Department of Chemistry, Brown University, Providence, RI 02912, USA
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Hou Y, Xu Z, Sun S. Controlled Synthesis and Chemical Conversions of FeO Nanoparticles. Angew Chem Int Ed Engl 2007. [DOI: 10.1002/ange.200701694] [Citation(s) in RCA: 65] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
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Synthesis of mixed cobalt–nickel oxydiacetate compounds: The X-ray characterization of [Co0.4Ni0.6(oda)(H2O)3]·1.5H2O. Polyhedron 2007. [DOI: 10.1016/j.poly.2007.03.020] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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Niederberger M, Garnweitner G. Organic reaction pathways in the nonaqueous synthesis of metal oxide nanoparticles. Chemistry 2007; 12:7282-302. [PMID: 16927442 DOI: 10.1002/chem.200600313] [Citation(s) in RCA: 242] [Impact Index Per Article: 14.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Abstract
Nonaqueous-solution routes to metal oxide nanoparticles are a valuable alternative to the known aqueous sol-gel processes, offering advantages such as high crystallinity at low temperatures, robust synthesis parameters and ability to control the crystal growth without the use of surfactants. In the first part of the review we give a detailed overview of the various solution routes to metal oxides in organic solvents, with a strong focus on surfactant-free processes. In most of these synthesis approaches, the organic solvent plays the role of the reactant that provides the oxygen for the metal oxide, controls the crystal growth, influences particle shape, and, in some cases, also determines the assembly behavior. We have a closer look at the following reaction systems in this order: 1) metal halides in alcohols, 2) metal alkoxides, acetates, and acetylacetonates in alcohols, 3) metal alkoxides in ketones, and 4) metal acetylacetonates in benzylamine. All these systems offer some peculiarities with respect to each other, providing many possibilities to control and tailor the particle size and shape, as well as the surface and assembly properties. In the second part we present general mechanistic principles for aqueous and nonaqueous sol-gel processes, followed by the discussion of reaction pathways relevant for nanoparticle formation in organic solvents. Depending on the system several mechanisms have been postulated: 1) alkyl halide elimination, 2) elimination of organic ethers, 3) ester elimination, 4) C--C bond formation between benzylic alcohols and alkoxides, 5) ketimine and aldol-like condensation reactions, 6) oxidation of metal nanoparticles, and 7) thermal decomposition methods.
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Affiliation(s)
- Markus Niederberger
- Max Planck Institute of Colloids and Interfaces, Colloid Chemistry, Research Campus Golm, 14424 Potsdam, Germany.
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