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Mechanochemical halogenation of unsymmetrically substituted azobenzenes.

ABSTRACT: The direct and selective mechanochemical halogenation of C-H bonds in unsymmetrically substituted azobenzenes using N-halosuccinimides as the halogen source under neat grinding or liquid-assisted grinding conditions in a ball mill has been described. Depending on the azobenzene substrate used, halogenation of the C-H bonds occurs in the absence or only in the presence of Pd^II catalysts. Insight into the reaction dynamics and characterization of the products was achieved by in situ Raman and ex situ NMR spectroscopy and PXRD analysis. A strong influence of the different 4,4'-substituents of azobenzene on the halogenation time and mechanism was found.

SUBMITTER: Barisic D

PROVIDER: S-EPMC9235908 | biostudies-literature | 2022

REPOSITORIES: biostudies-literature

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Mechanochemical halogenation of unsymmetrically substituted azobenzenes.

Barišić Dajana D Pajić Mario M Halasz Ivan I Babić Darko D Ćurić Manda M

Beilstein journal of organic chemistry 20220615

The direct and selective mechanochemical halogenation of C-H bonds in unsymmetrically substituted azobenzenes using <i>N</i>-halosuccinimides as the halogen source under neat grinding or liquid-assisted grinding conditions in a ball mill has been described. Depending on the azobenzene substrate used, halogenation of the C-H bonds occurs in the absence or only in the presence of Pd<sup>II</sup> catalysts. Insight into the reaction dynamics and characterization of the products was achieved by in s ...[more]

PMID: 35821698

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Project description:A series of heteroleptic three-coordinate Cu(i) complexes bearing monodentate N-heterocyclic carbene (NHC) ligands of the type 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene (IPr) and 1,3-bis(2,6-diisopropylphenyl)imidazolidin-2-ylidene (SIPr), and bidentate N-donor ligands of the type unsymmetrically-substituted dimethyl dipyridylamine (Me2Hdpa) and bis(mesityl)biazanaphthenequinone (mesBIAN) have been synthesized. The complexes [Cu(IPr)(3,4'-Me2Hdpa)]PF6, 1; [Cu(IPr)(3,5'-Me2Hdpa)]PF6, 2; [Cu(IPr)(3,6'-Me2Hdpa)]PF6, 3; [Cu(IPr)(mesBIAN)]PF6, 6; [Cu(SIPr)(3,4'-Me2Hdpa)]PF6, 7; [Cu(SIPr)(3,5'-Me2Hdpa)]PF6, 8; and [Cu(SIPr)(3,3'-Me2Hdpa)]PF6, 11 have been characterized by 1H and 13C NMR spectroscopies, elemental analysis, cyclic voltammetry, and photophysical studies in solid and solution phase. Single crystal X-ray structures were obtained for all complexes except 11. The crystallographic data reveal a mononuclear structure for all complexes with the copper atom ligated by one C and two N atoms. The UV-Vis absorption spectra of all dipyridylamine complexes in CH2Cl2 show a strong ligand-centered absorption band around 250 nm and a strong metal-to-ligand charge transfer (MLCT) band around 300 nm. When irradiated with UV light, the complexes exhibit strong emission maxima at 453-482 nm with photoluminescence quantum yields (PLQY) ranging from 0.21 to 0.87 in solid state. While the PLQY values are comparable to those of the symmetrical [Cu(IPr)(Me2Hdpa)]PF6 complexes, a stabilizing CH-π interaction has been reduced in the current systems. In particular, complex 3 lacks any strong CH-π interaction, but emits more efficiently than 1 and 2 wherein the interactions exist. Structural data analysis was performed to clarify the role of ligands' plane angle and the NH/CH⋯F interactions to the observed light interaction of unsymmetrical [Cu(NHC)(Me2Hdpa)]PF6 complexes. DFT calculations were performed to assist in the assignment of the electronic structure and excited state behavior of the complexes.

Dataset Information

Mechanochemical halogenation of unsymmetrically substituted azobenzenes.

Publications

Mechanochemical halogenation of unsymmetrically substituted azobenzenes.

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