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Stable Organic Radicals
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Stable Organic Radicals

A special issue of Molecules (ISSN 1420-3049). This special issue belongs to the section "Organic Chemistry".

Deadline for manuscript submissions: closed (30 June 2021) | Viewed by 21267

Special Issue Editor

Prof. Dr. Evgeny Tretyakov

E-Mail Website
Guest Editor
N.N. Vorozhtsov Novosibirsk Institute of Organic Chemistry, Siberian Branch of the Russian Academy of Sciences, Novosibirsk, Russia
Interests: organic radicals; diradicals and high spin polyradicals; molecule-based magnets including metal-radical magnets; self-assembly and supramolecular interactions; magneto-structural correlations; magnetic sensors and probes; applications in chemistry, biology, and medicine
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

The versatility and wide potential of stable organic radicals have continued to allow the discovery of unique and sometimes unexpected properties and functions that are being utilized in functional devices. Cutting-edge research in the field of chemistry and the application of stable radicals have been performed based on clearly defined strategic objectives as well as an emergent approach that comes from unpredicted discoveries. Only a decade or so has passed since stable high-spin molecules with parallel spin alignment (triplet diradicals) were developed. Also recently, there have been widespread efforts aimed at developing new materials with technologically relevant properties (magnetism, conductivity, recharging battaries) for which stable radicals are excellent functioanal blocks due to the presence of unpaired electrons. Polymer chemistry received a significant boost after the development of stable-radical-mediated living radical polymerization processes. Nowadays, stable radicals play an important role as spin probes for the investigation and real-time monitoring of microstructure and membrane dynamics, metabolism and oxygenation, and the pH and redox status in cellular systems for studying the dynamics in biological systems.

This Special Issue aims to attract contributions on all aspects of the chemistry and application of stable organic radicals to stimulate inter-science exchange with ideas and opinions, providing mutual benefits and further progress in the synthesis, study, and new applications of stable organic radicals and their derivatives.

Prof. Dr. Evgeny Tretyakov
Guest Editor

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Keywords

  • organic radicals
  • diradicals and high spin polyradicals
  • molecule-based magnets including metal-radical magnets
  • self-assembly and supramolecular interactions
  • magneto-structural correlations
  • magnetic sensors and probes
  • applications in chemistry, biology, and medicine

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Published Papers (6 papers)

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Research

10 pages, 1349 KiB  
Article
Syntheses and Study of a Pyrroline Nitroxide Condensed Phospholene Oxide and a Pyrroline Nitroxide Attached Diphenylphosphine
by Mostafa Isbera, Balázs Bognár, Ferenc Gallyas, Attila Bényei, József Jekő and Tamás Kálai
Molecules 2021, 26(14), 4366; https://doi.org/10.3390/molecules26144366 - 19 Jul 2021
Cited by 5 | Viewed by 2839
Abstract
The reaction of a diene nitroxide precursor with dichlorophenylphosphine in a McCormac procedure afforded 1,1,3,3-tetramethyl-5-phenyl-1,2,3,4,5,6-hexahydrophospholo[3,4-c]pyrrole-5-oxide-2-oxyl. Lithiation of the protected 3-iodo-pyrroline nitroxide followed by treatment with chlorodiphenylphosphine after deprotection afforded (1-oxyl-2,2,5,5-tetramethyl-2,5-dihydro-1H-pyrrol-3-yl)diphenylphosphine oxide, and after reduction, (1-oxyl-2,2,5,5-tetramethyl-2,5-dihydro-1H-pyrrol-3-yl)diphenylphosphine was realized, which was [...] Read more.
The reaction of a diene nitroxide precursor with dichlorophenylphosphine in a McCormac procedure afforded 1,1,3,3-tetramethyl-5-phenyl-1,2,3,4,5,6-hexahydrophospholo[3,4-c]pyrrole-5-oxide-2-oxyl. Lithiation of the protected 3-iodo-pyrroline nitroxide followed by treatment with chlorodiphenylphosphine after deprotection afforded (1-oxyl-2,2,5,5-tetramethyl-2,5-dihydro-1H-pyrrol-3-yl)diphenylphosphine oxide, and after reduction, (1-oxyl-2,2,5,5-tetramethyl-2,5-dihydro-1H-pyrrol-3-yl)diphenylphosphine was realized, which was also supported by X-ray single crystal diffraction measurements. This pyrroline diphenylphosphine derivative was converted to hexadecylphosphonium salt, which is an analogue of antineoplastic agent, MITO-CP. Full article
(This article belongs to the Special Issue Stable Organic Radicals)
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12 pages, 2489 KiB  
Article
Fluorinated Organic Paramagnetic Building Blocks for Cross-Coupling Reactions
by Larisa V. Politanskaya, Pavel A. Fedyushin, Tatyana V. Rybalova, Artem S. Bogomyakov, Nargiz B. Asanbaeva and Evgeny V. Tretyakov
Molecules 2020, 25(22), 5427; https://doi.org/10.3390/molecules25225427 - 19 Nov 2020
Cited by 10 | Viewed by 2270
Abstract
New stable polyfluorinated nitroxide radicals for use in cross-coupling reactions, namely, N-tert-butyl-N-oxyamino-2,3,5,6-tetrafluoro-4-iodobenzene and N-tert-butyl-N-oxyamino-2,3,5,6-tetrafluoro-4-ethynylbenzene, were prepared from perfluoroiodobenzene. The reaction of the polyfluoro derivative with tert-butylamine under autoclaving conditions leading to the [...] Read more.
New stable polyfluorinated nitroxide radicals for use in cross-coupling reactions, namely, N-tert-butyl-N-oxyamino-2,3,5,6-tetrafluoro-4-iodobenzene and N-tert-butyl-N-oxyamino-2,3,5,6-tetrafluoro-4-ethynylbenzene, were prepared from perfluoroiodobenzene. The reaction of the polyfluoro derivative with tert-butylamine under autoclaving conditions leading to the formation of N-tert-butyl-2,3,5,6-tetrafluoro-4-iodoaniline proved to be the key stage of the whole process. The fluorinated tert-butyl iodophenyl nitroxide was found to form in a solid state via N–O···I halogen bonds, a one-dimensional assembly of the radicals. The acceptor role of the nitroxide group in the halogen bonding changes to a donor role when the nitroxide reacts with Cu(hfac)2. In the last case, zero-dimensional assembly prevails, giving a three-spin complex with axial coordinated nitroxide groups and, as a consequence, causing ferromagnetic intramolecular exchange interactions between Cu(II) and radical spins. Full article
(This article belongs to the Special Issue Stable Organic Radicals)
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9 pages, 1357 KiB  
Article
Synthesis of Nitroxide Diradical Using a New Approach
by Pavel Fedyushin, Tatyana Rybalova, Nargiz Asanbaeva, Elena Bagryanskaya, Alexey Dmitriev, Nina Gritsan, Maxim Kazantsev and Evgeny Tretyakov
Molecules 2020, 25(11), 2701; https://doi.org/10.3390/molecules25112701 - 11 Jun 2020
Cited by 11 | Viewed by 3592
Abstract
A new synthetic pathway to diradical organic systems is proposed. The effectiveness of this approach was exemplified by the synthesis of a new nitroxide diradical. An interaction of perfluorobiphenyl with lithium tert-butylamide, followed by oxidation of the thusly formed N4,N [...] Read more.
A new synthetic pathway to diradical organic systems is proposed. The effectiveness of this approach was exemplified by the synthesis of a new nitroxide diradical. An interaction of perfluorobiphenyl with lithium tert-butylamide, followed by oxidation of the thusly formed N4,N4′-di-tert-butyl-2,2′,3,3′,5,5′,6,6′-octafluorobiphenyl-4,4′-diamine with meta-chloroperoxybenzoic acid, led to the polyfluorinated nitroxide diradical, N,N′-(perfluorobiphenyl-4,4′-diyl)bis(N-tert-butyl(oxyl)amine), with a good total yield. The polyfluorinated diradical is stable and can be isolated in free form and completely characterized. The structure of the nitroxide diradical was proved by single-crystal X-ray diffraction analysis. According to the X-ray diffraction data, the diradical is considerably twisted: dihedral angles between the planes of the nitroxide groups and aromatic cycles are 65.1° and 69.5°, and between aromatic cycles 52.6°. Quantum chemical calculations predict well-balanced size of both intramolecular and intermolecular exchange interactions with J from −2.65 to −1.14 cm−1. Full article
(This article belongs to the Special Issue Stable Organic Radicals)
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16 pages, 2891 KiB  
Article
Syntheses and Reactions of Pyrroline, Piperidine Nitroxide Phosphonates
by Mostafa Isbera, Balázs Bognár, József Jekő, Cecilia Sár, Kálmán Hideg and Tamás Kálai
Molecules 2020, 25(10), 2430; https://doi.org/10.3390/molecules25102430 - 22 May 2020
Cited by 8 | Viewed by 3762
Abstract
Organophosphorus compounds occupy a significant position among the plethora of organic compounds, but a limited number of paramagnetic phosphorus compounds have been reported, including paramagnetic phosphonates. This paper describes the syntheses and further transformations of pyrroline and piperidine nitroxide phosphonates by well-established methods, [...] Read more.
Organophosphorus compounds occupy a significant position among the plethora of organic compounds, but a limited number of paramagnetic phosphorus compounds have been reported, including paramagnetic phosphonates. This paper describes the syntheses and further transformations of pyrroline and piperidine nitroxide phosphonates by well-established methods, such as the Pudovik, Arbuzov and Horner-Wadsworth-Emmons (HWE) reactions. The reaction of paramagnetic α-bromoketone produced a vinylphosphonate in the Perkow reaction. Paramagnetic α-hydroxyphosphonates could be subjected to oxidation, elimination and substitution reactions to produce various paramagnetic phosphonates. The synthesized paramagnetic phosphonates proved to be useful synthetic building blocks for carbon-carbon bond-forming reactions in the Horner-Wadsworth-Emmons olefination reactions. The unsaturated compounds achieved could be transformed into various substituted pyrroline nitroxides, proxyl nitroxides and paramagnetic polyaromatics. The Trolox® equivalent antioxidant capacity (TEAC) of new phosphonates was also screened, and tertiary α-hydroxyphosphonatate nitroxides exhibited remarkable antioxidant activity. Full article
(This article belongs to the Special Issue Stable Organic Radicals)
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13 pages, 5258 KiB  
Article
(Pyrrole-2,5-Diyl)-Bis(Nitronyl Nitroxide) and-Bis(Iminonitroxide): Specific Features of the Synthesis, Structure, and Magnetic Properties
by Evgeny Tretyakov, Anastasia Tkacheva, Galina Romanenko, Artem Bogomyakov, Dmitri Stass, Alexander Maryasov, Ekaterina Zueva, Boris Trofimov and Victor Ovcharenko
Molecules 2020, 25(7), 1503; https://doi.org/10.3390/molecules25071503 - 26 Mar 2020
Cited by 9 | Viewed by 3265
Abstract
In contrast to diradicals connected by alternant hydrocarbons, only a few studies have addressed diradicals connected by nonalternant hydrocarbons and their heteroatom derivatives. Here, the synthesis, structure, and magnetic properties of pyrrole-2,5-diyl–linked bis(nitronyl nitroxide) and bis(iminonitroxide) diradicals are described. The diradicals show characteristic [...] Read more.
In contrast to diradicals connected by alternant hydrocarbons, only a few studies have addressed diradicals connected by nonalternant hydrocarbons and their heteroatom derivatives. Here, the synthesis, structure, and magnetic properties of pyrrole-2,5-diyl–linked bis(nitronyl nitroxide) and bis(iminonitroxide) diradicals are described. The diradicals show characteristic electron spin resonance spectra in dilute glassy solutions, from which conclusions about the presence of distinct conformations, their symmetry, and interspin distance were made. X-ray diffraction analysis of the diradicals revealed that paramagnetic moieties lie in the plane of the pyrrole ring, because of the formation of an intramolecular hydrogen bond, ONO…H−N, with O…H distances of 2.15–2.23 Å. The N–O groups participating in the formation of H-bonds have greater bond lengths (~1.29 Å) as compared with nonparticipating groups (~1.27 Å). The nitronyl nitroxide and iminonitroxide diradicals showed an intramolecular antiferromagnetic interaction, with J = −77.3 and −22.2 cm−1, respectively (H = −2JS1⋅S2). Full article
(This article belongs to the Special Issue Stable Organic Radicals)
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14 pages, 2060 KiB  
Article
Aromatic SNF-Approach to Fluorinated Phenyl tert-Butyl Nitroxides
by Evgeny Tretyakov, Pavel Fedyushin, Elena Panteleeva, Larisa Gurskaya, Tatyana Rybalova, Artem Bogomyakov, Elena Zaytseva, Maxim Kazantsev, Inna Shundrina and Victor Ovcharenko
Molecules 2019, 24(24), 4493; https://doi.org/10.3390/molecules24244493 - 8 Dec 2019
Cited by 13 | Viewed by 3708
Abstract
The interaction of octafluorotoluene (1a), as well as pentafluorobenzonitrile (1b) with tert-butylamine, followed by the oxidation of thus formed tert-butylanilines (2a,b) with meta-chloroperoxybenzoic acid led to functionalized perfluorinated phenyl tert-butyl nitroxides [...] Read more.
The interaction of octafluorotoluene (1a), as well as pentafluorobenzonitrile (1b) with tert-butylamine, followed by the oxidation of thus formed tert-butylanilines (2a,b) with meta-chloroperoxybenzoic acid led to functionalized perfluorinated phenyl tert-butyl nitroxides [namely, 4-(N-tert-butyl(oxyl)amino)heptafluorotoluene (3a) and 4-(N-tert-butyl(oxyl)amino)tetrafluorobenzonitrile (3b)] with nearly quantitative total yields. The molecular and crystal structures of nitroxide 3a were proved by single crystal X-ray diffraction analysis. The radical nature of both nitroxides was confirmed by ESR data. The interaction of Cu(hfac)2 with the obtained nitroxides 3a,b gave corresponding trans-bis(1,1,1,5,5,5-hexafluoropentane-2,4-dionato-κ2O,O′)bis{4-(N-tert-butyl(oxyl)amino)perfluoroarene-κO}copper (II) complexes ([Cu(hfac)2(3a)2] and [Cu(hfac)2(3b)2]). X-ray crystal structure analysis showed square bipyramid coordination of a centrally symmetric Cu polyhedron with the axial positions occupied by oxygen atoms of the nitroxide groups. Magnetic measurements revealed intramolecular ferromagnetic exchange interactions between unpaired electrons of Cu(II) ions and paramagnetic ligands, with exchange interaction parameters JCu–R reaching 53 cm−1. Full article
(This article belongs to the Special Issue Stable Organic Radicals)
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