<i>ortho</i>-Functionalization of azobenzenes<i>via</i>hypervalent iodine reagents

Tommaso, Ester Maria Di; Walther, Melanie; Staubitz, Anne; Olofsson, Berit

doi:10.1039/d3cc01060k

Cited by 3 publications

(3 citation statements)

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“…Numerous stimuli-responsive devices are based on the photoinduced reversible cis – trans isomerization of azobenzenes used as switchable components. − Recently, azobenzenes tetra-substituted in their ortho -positions attracted attention due to their unusual spectral, structural, and acid–base properties. − This stimulated the development of new synthetic approaches to ortho -functionalization of azobenzenes , as well as in-depth investigation of structural and physicochemical properties of these compounds. − In the course of our study with model tetra- ortho -substituted compounds 1 and 2 , we observed an unusual solvent effect on the kinetics of the thermal cis -to- trans isomerization of 1 : the reaction rate strongly decreased in a series of solvents of increased polarity from hexane to dimethyl sulfoxide (DMSO) but then sharply increased in even more polar protic solvents . Since solvent effects are often used as important criteria for interpretation of isomerization mechanisms, we undertook a more detailed study of the kinetics of cis -to- trans isomerization of 1 and 2 , the results of which are presented in this paper.…”

Section: Introductionmentioning

confidence: 77%

“…1−6 Recently, azobenzenes tetra-substituted in their ortho-positions attracted attention due to their unusual spectral, structural, and acid− base properties. 7−9 This stimulated the development of new synthetic approaches to ortho-functionalization of azobenzenes 10,11 as well as in-depth investigation of structural and physicochemical properties of these compounds. 12−15 In the course of our study with model tetra-ortho-substituted compounds 1 and 2, we observed an unusual solvent effect on the kinetics of the thermal cis-to-trans isomerization of 1: the reaction rate strongly decreased in a series of solvents of increased polarity from hexane to dimethyl sulfoxide (DMSO) but then sharply increased in even more polar protic solvents.…”

Section: ■ Introductionmentioning

confidence: 99%

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Solvent and Temperature Dependencies of the Rates of Thermal Cis-to-Trans Isomerization of Tetra-(ortho)substituted 4-Aminoazobenzenes Containing 2,6-Dimethoxy Groups

Ramírez-Rave,

Ortega-Valdovinos,

González-Castro

et al. 2024

J. Phys. Chem. B

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The kinetics of thermal cis-to-trans isomerization of two tetra-(ortho)substituted 4-aminoazobenzene derivatives containing 2,6dimethoxy groups in the 4-aminobenzene ring and either 2′,6′dimethyl (1) or 2′,6′-dichloro groups in another ring was studied in 16 and 9 solvents, respectively, at room temperature. In addition, the kinetics of isomerization of 1 was studied at variable temperatures in 6 solvents. The solvent effects were analyzed in terms of multiparameter correlations using the Kamlet-Taft, Catalan, and Laurence scales. The temperature dependencies were analyzed in terms of the isokinetic relationship by using Exner's method. The correlation analysis was also extended to several previously reported systems, including isomerization of unsubstituted 4-aminoazobenzene and push−pull 4-NR 2 -4′-NO 2 azobenzenes. It was established that for all 4-aminoazobenzenes in contrast to push−pull azobenzenes, the increase in solvent dipolarity does not affect or even inhibit isomerization rates; however, the increase in solvent acidity induces large rate accelerations. The isokinetic relationship holds only in aprotic solvents, while in alcohols and water, the temperature dependencies do not pass through the common point at T = T iso , indicating different mechanisms operating in protic and aprotic solvents. The acceleration effect by protic solvents does not represent a type of general acid catalysis as follows from the small solvent isotope effect k H /k D = 1.26 in water. It is suggested that protic solvents induce a change in the reaction mechanism supposedly from inversion to rotation by hydrogen bonding stabilization of the negative charge developed on the azo group in a resonance structure involving a 4-amino group.

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Section: Introductionmentioning

confidence: 77%

Section: ■ Introductionmentioning

confidence: 99%

Solvent and Temperature Dependencies of the Rates of Thermal Cis-to-Trans Isomerization of Tetra-(ortho)substituted 4-Aminoazobenzenes Containing 2,6-Dimethoxy Groups

Ramírez-Rave,

Ortega-Valdovinos,

González-Castro

et al. 2024

J. Phys. Chem. B

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“…Triblock polymer brushes in which one block contains azobenzene units have been used for the fabrication of smart nonwoven fabric showing great potential in treating compilated polluted water from most industrial fields 11 . Thus, there is still a need for designing and preparation of novel azo materials with enhanced functionalities via the synthesis of new azobenzene derivatives or their incorporation into polymers or other materials, which enable isomerization in the solid state giving the opportunity for the construction of innovative materials 12 – 14 . Various types of azo polymers have been developed.…”

Section: Introductionmentioning

confidence: 99%

Photoresponse of new azo pyridine functionalized poly(2-hydroxyethyl methacrylate-co-methyl methacrylate)

Konieczkowska,

Neugebauer,

Kozanecka-Szmigiel

et al. 2024

Sci Rep

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A new azo polymer containing photoisomerizable azo pyridine functionalities was synthesized via Mitsunobu reaction of 4-(4-hydroxyphenylazo)pyridine with poly(2-hydroxyethyl methacrylate-co-methyl methacrylate) (p(HEMA-co-MMA)) for creating new photochromic materials. The resulting polymer with azo pyridine side groups was characterized for structural, thermal, and optical properties. UV–vis, 1H NMR and IR spectroscopies confirmed that all hydroxyl groups in p(HEMA-co-MMA) were substituted with azo dye. The obtained azo copolymer exhibited high thermal stability (around 240 °C) and a glass transition temperature (113 °C), promising for applications. The trans-to-cis isomerization upon UV irradiation and the thermal back reaction of the azo chromophore in the copolymer in the solid state was studied. A photostationary state with 50% content of cis-isomers upon 6 min of UV irradiation was reached, and during 48 h dark relaxation at ambient temperature, all cis-isomers converted to the trans form. Additionally, the possibility of efficient photogeneration of surface relief gratings with high amplitude of azo copolymer surface modulation was demonstrated.

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Recent Progress in Synthetic Applications of Hypervalent Iodine(III) Reagents

Yoshimura,

Zhdankin

2024

Chem. Rev.

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Hypervalent iodine(III) compounds have found wide application in modern organic chemistry as environmentally friendly reagents and catalysts. Hypervalent iodine reagents are commonly used in synthetically important halogenations, oxidations, aminations, heterocyclizations, and various oxidative functionalizations of organic substrates. Iodonium salts are important arylating reagents, while iodonium ylides and imides are excellent carbene and nitrene precursors. Various derivatives of benziodoxoles, such as azidobenziodoxoles, trifluoromethylbenziodoxoles, alkynylbenziodoxoles, and alkenylbenziodoxoles have found wide application as group transfer reagents in the presence of transition metal catalysts, under metal-free conditions, or using photocatalysts under photoirradiation conditions. Development of hypervalent iodine catalytic systems and discovery of highly enantioselective reactions using chiral hypervalent iodine compounds represent a particularly important recent achievement in the field of hypervalent iodine chemistry. Chemical transformations promoted by hypervalent iodine in many cases are unique and cannot be performed by using any other common, non-iodine-based reagent. This review covers literature published mainly in the last 7−8 years, between 2016 and 2024.

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ortho-Functionalization of azobenzenesviahypervalent iodine reagents

Abstract: Ortho-functionalized azobenzenes are much sought after molecular switches, as they may be turned to absorb in the visible range of light and the (Z)-isomers can have high thermal half-lives. To...

Cited by 3 publications

References 58 publications

Solvent and Temperature Dependencies of the Rates of Thermal Cis-to-Trans Isomerization of Tetra-(ortho)substituted 4-Aminoazobenzenes Containing 2,6-Dimethoxy Groups

Solvent and Temperature Dependencies of the Rates of Thermal Cis-to-Trans Isomerization of Tetra-(ortho)substituted 4-Aminoazobenzenes Containing 2,6-Dimethoxy Groups

Photoresponse of new azo pyridine functionalized poly(2-hydroxyethyl methacrylate-co-methyl methacrylate)

Recent Progress in Synthetic Applications of Hypervalent Iodine(III) Reagents

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