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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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2
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Yan P, Xi S, Peng H, Mitchell DRG, Harvey L, Drewery M, Kennedy EM, Zhu Z, Sankar G, Stockenhuber M. Facile and Eco-Friendly Approach To Produce Confined Metal Cluster Catalysts. J Am Chem Soc 2023; 145:9718-9728. [PMID: 37084330 DOI: 10.1021/jacs.3c01304] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 04/23/2023]
Abstract
Zeolite-supported metal nanocluster catalysts have attracted significant attention due to their broad application in heterogeneously catalyzed reactions. The preparation of highly dispersed metal catalysts commonly involves the use of organic compounds and requires the implementation of complicated procedures, which are neither green nor deployable at the large scale. Herein, we present a novel facile method (vacuum-heating) which employs a specific thermal vacuum processing protocol of catalysts to promote the decomposition of metal precursors. The removal of coordinated H2O via vacuum-heating restricts the formation of intermediates (metal-bound OH species), resulting in catalysts with a uniform, metal nanocluster distribution. The structure of the intermediate was determined by in situ Fourier transform infrared, temperature-programmed decomposition, and X-ray absorption spectroscopy (XAS) measurements. This alternative synthesis method is eco-friendly and cost-effective as the procedure occurs in the absence of organic compounds. It can be widely used for the preparation of catalysts from different metal species (Ni, Fe, Cu, Co, Zn) and precursors and is readily scaled-up.
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Affiliation(s)
- Penghui Yan
- Chemical Engineering, School of Engineering, University of Newcastle, Callaghan, NSW 2308, Australia
- School of Chemical Engineering, University of Queensland, St Lucia, QLD 4072, Australia
| | - Shibo Xi
- Institute of Sustainability for Chemicals, Energy and Environment (ISCE2), Agency for Science, Technology and Research (A*STAR), 1 Pesek Road, Jurong Island 627833, Singapore
| | - Hong Peng
- School of Chemical Engineering, University of Queensland, St Lucia, QLD 4072, Australia
| | - David R G Mitchell
- Electron Microscopy Centre, AIIM Building, Innovation Campus, University of Wollongong, Fairy Meadow, NSW 2519, Australia
| | - Luke Harvey
- Chemical Engineering, School of Engineering, University of Newcastle, Callaghan, NSW 2308, Australia
| | - Matthew Drewery
- Chemical Engineering, School of Engineering, University of Newcastle, Callaghan, NSW 2308, Australia
| | - Eric M Kennedy
- Chemical Engineering, School of Engineering, University of Newcastle, Callaghan, NSW 2308, Australia
| | - Zhonghua Zhu
- School of Chemical Engineering, University of Queensland, St Lucia, QLD 4072, Australia
| | - Gopinathan Sankar
- Department of Chemistry, University College London, 20 Gordon Street, London WC1H 0AJ, U.K
| | - Michael Stockenhuber
- Chemical Engineering, School of Engineering, University of Newcastle, Callaghan, NSW 2308, Australia
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5,8-Di-tert-butyl-2-hydroxy-1H-benzo[de]isoquinoline-1,3(2H)-dione—A New Lipophilic N-oxyl Radical Precursor. MOLBANK 2023. [DOI: 10.3390/m1543] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/12/2023] Open
Abstract
N-hydroxyimides are widely known as organocatalysts for aerobic oxidation and oxidative coupling reactions, in which corresponding imide-N-oxyl radicals play the role of catalytically active hydrogen atom abstracting species. The drawbacks of many N-hydroxyimides are poor solubility in low polarity solvents and limited activity in the cleavage of unactivated C–H bonds. To overcome these shortcomings, we have synthesized a new lipophilic N-hydroxyimide, 5,8-di-tert-butyl-2-hydroxy-1H-benzo[de]isoquinoline-1,3(2H)-dione, with high solubility in low-polarity solvents such as DCM. According to the EPR study, the stability of the corresponding imide-N-oxyl radical is comparable to that of the non-tert-butylated analogue, naphthalimide-N-oxyl radical. DFT calculations showed that the NO–H bond dissociation enthalpy (BDE) in the synthesized tert-butylated-N-hydroxynaphthalimide is one of the highest in N-hydroxyimide series, which corresponds to high hydrogen atom abstracting reactivity and may be useful in catalysis of strong C–H bond oxidative cleavage. The synthesized compound can be considered as catalyst for liquid-phase free-radical oxidation and oxidative coupling reactions in non-polar media where solubility was previously the limiting factor.
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Liu XH, Yu HY, Huang JY, Su JH, Xue C, Zhou XT, He YR, He Q, Xu DJ, Xiong C, Ji HB. Biomimetic catalytic aerobic oxidation of C-sp(3)-H bonds under mild conditions using galactose oxidase model compound Cu IIL. Chem Sci 2022; 13:9560-9568. [PMID: 36091900 PMCID: PMC9400635 DOI: 10.1039/d2sc02606f] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/10/2022] [Accepted: 07/28/2022] [Indexed: 11/21/2022] Open
Abstract
Developing highly efficient catalytic protocols for C-sp(3)-H bond aerobic oxidation under mild conditions is a long-desired goal of chemists. Inspired by nature, a biomimetic approach for the aerobic oxidation of C-sp(3)-H by galactose oxidase model compound CuIIL and NHPI (N-hydroxyphthalimide) was developed. The CuIIL-NHPI system exhibited excellent performance in the oxidation of C-sp(3)-H bonds to ketones, especially for light alkanes. The biomimetic catalytic protocol had a broad substrate scope. Mechanistic studies revealed that the CuI-radical intermediate species generated from the intramolecular redox process of CuIILH2 was critical for O2 activation. Kinetic experiments showed that the activation of NHPI was the rate-determining step. Furthermore, activation of NHPI in the CuIIL-NHPI system was demonstrated by time-resolved EPR results. The persistent PINO (phthalimide-N-oxyl) radical mechanism for the aerobic oxidation of C-sp(3)-H bond was demonstrated.
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Affiliation(s)
- Xiao-Hui Liu
- Fine Chemical Industry Research Institute, School of Chemical Engineering and Technology, Sun Yat-sen University Zhuhai 519082 China
| | - Hai-Yang Yu
- Fine Chemical Industry Research Institute, School of Chemical Engineering and Technology, Sun Yat-sen University Zhuhai 519082 China
| | - Jia-Ying Huang
- Fine Chemical Industry Research Institute, School of Chemical Engineering and Technology, Sun Yat-sen University Zhuhai 519082 China
| | - Ji-Hu Su
- CAS Key Laboratory of Microscale Magnetic Resonance, University of Science and Technology of China Hefei 230026 China
| | - Can Xue
- Fine Chemical Industry Research Institute, School of Chemical Engineering and Technology, Sun Yat-sen University Zhuhai 519082 China
| | - Xian-Tai Zhou
- Fine Chemical Industry Research Institute, School of Chemical Engineering and Technology, Sun Yat-sen University Zhuhai 519082 China
| | - Yao-Rong He
- Fine Chemical Industry Research Institute, School of Chemistry, Sun Yat-sen University Guangzhou 510275 China
| | - Qian He
- Fine Chemical Industry Research Institute, School of Chemistry, Sun Yat-sen University Guangzhou 510275 China
| | - De-Jing Xu
- Fine Chemical Industry Research Institute, School of Chemical Engineering and Technology, Sun Yat-sen University Zhuhai 519082 China
| | - Chao Xiong
- Fine Chemical Industry Research Institute, School of Chemistry, Sun Yat-sen University Guangzhou 510275 China
| | - Hong-Bing Ji
- Fine Chemical Industry Research Institute, School of Chemistry, Sun Yat-sen University Guangzhou 510275 China
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Abstract
The oxidation of hydrocarbons of different structures under the same conditions is an important stage in the study of the chemical properties of both the hydrocarbons themselves and the oxidation catalysts. In a 50% H2O2/Cu2Cl4·2DMG/CH3CN system, where DMG is dimethylglyoxime (Butane-2,3-dione dioxime), at 50 °C under the same or similar conditions, we oxidized eleven RH hydrocarbons of different structures: mono-, bi- and tri-cyclic, framework and aromatic. To compare the composition of the oxidation products of these hydrocarbons, we introduced a new quantitative characteristic, “distributive oxidation depth D(O), %” and showed the effectiveness of its application. The adiabatic ionization potentials (AIP) and the vertical ionization potentials (VIP) of the molecules of eleven oxidized and related hydrocarbons were calculated using the DFT method in the B3LYP/TZVPP level of theory for comparison with experimental values and correlation with D(O). The same calculations of AIP were made for the molecules of the oxidant, solvent, DMG, related compounds and products. It is shown that component X, which determines the mechanism of oxidation of hydrocarbons RH with AIP(Exp) ≥ AIP(X) = 8.55 ± 0.03 eV, is a trans-DMG molecule. Firstly theoretically estimated experimental values of AIP(trans-DMG) = 8.53 eV and AIP(cis-DMG) = 8.27 eV.
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Andrade MA, Martins LMDRS. Organocatalysis Meets Hydrocarbon Oxyfunctionalization: the Role of
N
‐Hydroxyimides. European J Org Chem 2021. [DOI: 10.1002/ejoc.202100479] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Affiliation(s)
- Marta A. Andrade
- Centro de Química Estrutural and Departamento de Engenharia Química, Instituto Superior Técnico Universidade de Lisboa 1049-001 Lisboa Portugal
| | - Luísa M. D. R. S. Martins
- Centro de Química Estrutural and Departamento de Engenharia Química, Instituto Superior Técnico Universidade de Lisboa 1049-001 Lisboa Portugal
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Abstract
Tertiary tetraols of adamantane (C10H16, Tricyclo[3.3.1.1(3,7)]decan) have been widely used for the synthesis of highly symmetric compounds with unique physical and chemical properties. The methods for one-stage simultaneously selective, deep, and cheap oxidation of adamantane to tetraols of different structures have not yet been developed. In this research, chemically simple, cheap, and environmentally friendly reagents are used and that is the first step in this direction. The conditions, under which the impact of a hydrogen peroxide water solution on adamantane dissolved in acetonitrile results in full conversion of adamantane and formation of a total 72% mixture of its tri-, tetra-, and penta-oxygenated products, predominantly poliols, have been found. Conversion and adamantane oxidation depth are shown to depend on the ratio of components of the water-acetonitrile solution and the method of oxidizer solution introduction when using the dimer form of 1:1 dimethylglyoxime and copper dichloride complex as a catalyst. Under the conditions of mass-spectrometry ionization by electrons (70 eV), fragmentation across three C–C bonds of the molecular ions framework of adamantane tertiary alcohols Ad(OH)n in the range n = 0–4 increases linearly with the rise of n.
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Wang L, Zhang Y, Yao J, Li H. Metal-Free Synthesis of Sulfones and Sulfoxides through Aldehyde-Promoted Aerobic Oxidation of Sulfides. Catal Letters 2021. [DOI: 10.1007/s10562-021-03706-5] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
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Xiao Y, Song B, Chen Y, Cheng L, Ren Q. ZIF-67 with precursor concentration-dependence morphology for aerobic oxidation of toluene. J Organomet Chem 2020. [DOI: 10.1016/j.jorganchem.2020.121597] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
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Highly efficient transformation of ethylbenzene into acetophenone catalyzed by NHPI/Co(II) using molecular oxygen in hexafluoropropan-2-ol. MOLECULAR CATALYSIS 2020. [DOI: 10.1016/j.mcat.2020.111244] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
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Shen HM, Wang X, Guo AB, Zhang L, She YB. Catalytic oxidation of cycloalkanes by porphyrin cobalt(II) through efficient utilization of oxidation intermediates. J PORPHYR PHTHALOCYA 2020. [DOI: 10.1142/s1088424620500303] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
Abstract
The catalytic oxidation of cycloalkanes using molecular oxygen employing porphyrin cobalt(II) as catalyst was enhanced through use of cycloalkyl hydroperoxides, which are the primary intermediates in oxidation of cycloalkanes, as additional oxidants to further oxidize cycloalkanes in the presence of porphyrin copper(II), especially for cyclohexane, for which the selectivity was enhanced from 88.6 to 97.2% to the KA oil; at the same time, the conversion of cyclohexane was enhanced from 3.88 to 4.41%. The enhanced efficiency and selectivity were mainly attributed to the avoided autoxidation of cycloalkanes and efficient utilization of oxidation intermediate cycloalkyl hydroperoxides as additional oxidants instead of conventional thermal decomposition. In addition to cyclohexane, the protocol presented in this research is also very applicable in the oxidation of other cycloalkanes such as cyclooctane, cycloheptane and cyclopentane, and can serve as a applicable and efficient strategy to boost the conversion and selectivity simultaneously in oxidation of alkanes. This work also is a very important reference for the extensive application of metalloporphyrins in catalysis chemistry.
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Affiliation(s)
- Hai M. Shen
- College of Chemical Engineering, Zhejiang University of Technology, Hangzhou 310014, China
| | - Xiong Wang
- College of Chemical Engineering, Zhejiang University of Technology, Hangzhou 310014, China
| | - A. Bing Guo
- College of Chemical Engineering, Zhejiang University of Technology, Hangzhou 310014, China
| | - Long Zhang
- College of Chemical Engineering, Zhejiang University of Technology, Hangzhou 310014, China
| | - Yuan B. She
- College of Chemical Engineering, Zhejiang University of Technology, Hangzhou 310014, China
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Li F, Tang S, Tang Z, Ye L, Li H, Niu F, Sun X. Synergistic Catalytic Effect of N-Hydroxyphthalimide/Cobalt Tetraamide Phthalocyanine and Its Application for Aerobic Oxidation of Hydrocarbons and Alcohols. Catal Letters 2020. [DOI: 10.1007/s10562-020-03283-z] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
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Selective Hydrogenation of Phenol to Cyclohexanol over Ni/CNT in the Absence of External Hydrogen. ENERGIES 2020. [DOI: 10.3390/en13040846] [Citation(s) in RCA: 20] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/12/2023]
Abstract
Transfer hydrogenation is a novel and efficient method to realize the hydrogenation in different chemical reactions and exploring a simple heterogeneous catalyst with high activity is crucial. Ni/CNT was synthesized through a traditional impregnation method, and the detailed physicochemical properties were performed by means of XRD, TEM, XPS, BET, and ICP analysis. Through the screening of loading amounts, solvents, reaction temperature, and reaction time, 20% Ni/CNT achieves an almost complete conversion of phenol after 60 min at 220 °C in the absence of external hydrogen. Furthermore, the catalytic system is carried out on a variety of phenol derivatives for the generation of corresponding cyclohexanols with good to excellent results. The mechanism suggests that the hydrogenation of phenol to cyclohexanone is the first step, while the hydrogenation of cyclohexanone for the generation of cyclohexanol takes place in a successive step. Moreover, Ni/CNT catalyst can be magnetically recovered and reused in the next test for succeeding four times.
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Shen HM, Zhang L, Deng JH, Sun J, She YB. Enhanced catalytic performance of porphyrin cobalt(II) in the solvent-free oxidation of cycloalkanes (C5~C8) with molecular oxygen promoted by porphyrin zinc(II). CATAL COMMUN 2019. [DOI: 10.1016/j.catcom.2019.105809] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022] Open
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