Advances in verdazyl chemistry
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Reviews Advances in verdazyl chemistry G. N. Lipunova,a,b T. G. Fedorchenko,a A. N. Tsmokalyuk,b and O. N. Chupakhina,b aI.
Ya. Postovsky Institute of Organic Synthesis, Ural Branch of the Russian Academy of Sciences, 22/20 ul. S. Kovalevskoy, 620990 Yekaterinburg, Russian Federation. E-mail: [email protected]; fl[email protected] bUral Federal University named after the First President of Russia B. N. Yeltsin, 19 ul. Mira, 620002 Yekaterinburg, Russian Federation The main advances in the synthesis and studies of the properties of new stable heterocyclic verdazyl radicals and verdazyl radical coordination chemistry are reviewed. The promising applications of these radicals are also discussed. Key words: verdazyl, oxoverdazyl, biradical, ESR spectra, metal complexes, magnetic properties.
Introduction Spin delocalized stable π radicals that exhibit paramagnetic behaviors are important building blocks for manufacturing high-tech materials for technological and biological applications.1—3 An example of the stable radicals is heterocyclic verdazyl radicals that can be divided into two groups according to the nature of the 6-position substituent: (1) the Kuhn verdazyls with the sp3 hybridized carbon atom and (2) oxoverdazyls with the carbonyl function. High chemical stability, synthetic versatility, and complexation ability towards metal ions render verdazyls one of the largest and most interesting families of stable organic radicals. The metal—verdazyl complexes attract close attention of the researchers since they can be used for designing new hybrid materials. Coordination chemistry of verdazyl radicals was recently reviewed.4 Another field that maintains an increased interest to verdazyls is
their application in the synthesis of photoswitchable spin systems and organic materials with conducting properties.5,6
Previously,7 we have reviewed the synthetic strategies, structures, general properties, and reactivity of verdazyl radicals and their metal complexes and gave a survey of their applications. However, during the last five-six years numerous works describing new approaches to functionalized verdazyl derivatives, coordination complexes of verdazyls, and their novel promising applications have
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 7, pp. 1203—1222, July, 2020. 1066-5285/20/6907-1203 © 2020 Springer Science+Business Media LLC
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Lipunova et al.
Russ. Chem. Bull., Int. Ed., Vol. 69, No. 7, July, 2020
been published. This review provides an up-to-date survey to these new achievements in chemistry of verdazyl radicals and metal—verdazyl complexes. Synthesis and properties of new verdazyls Synthetic approaches to the Kuhn verdazyls and oxoverdazyls are well developed and described in the literature,1,8—11 including a paper12 devoted to the preparative chemistry of common stable paramagnets. New derivatives are most often synthesized by modification of the functional groups present in the structure of verdazyls as well as by introduction of new substituents at the position 3 o
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