Механізм реакції ненасичених сполук з солями арендіазонію. Йон-радикальне приєднання до кратного зв’язку

Abstract

Узагальнено результати досліджень реакції Меєрвейна. Проаналізовано роль купрокаталізу в процесі, кінетичні дані, роль комплексних інтермедіатів, некупрокаталітичні методи ініціювання, стереохімічні аспекти реакції. Запропоновано йонрадикальний механізм для взаємодії ненасичених сполук з солями арендіазонію. Ключові слова: реакція Меєрвейна, солі арендіазонію, купрокаталіз, йон-радикали.

Results of Meerwein reaction study have been reviewed. Current article analyzes available data on catalyst role in the reaction process, as well as kinetic study of reaction, role of complex intermediates, noncuprocatalytic methods of initiations and stereochemistry of reaction. Analysis of literature data suggests that the main model for the course of reaction of arenediazonium salts with olefins is ion-radical reaction. The novel ion-radical mechanism for interaction of unsaturated compounds with arenediazonium salts is proposed. The reaction take place of the catalyst surface. The catalyst is not the ion of Cu(I) or Cu(II), but a catalytic system Cu+ D Cu2+ , enabling electron transfer from olefine to diazonium ion and cation-radical of alkene was formed. Huge experimental material related to this reaction undoubtfuly indicates that the important factor needed for explanation of the mechanism is the nature of alkene. Cis-trans-isomerisation of alkenes in this reaction, numerous rearrangements, and influence of substitutes could be explained only in frames of ion-radical mechanism. The criteria of reaction course through the formation of ion-radicals can serve cistrans-isomerisation of unreacted substrates as a result of loosening of double bond in ion-radical state. By UVspectroscopy the radical cations in the system (>C=C< + Cu2+) were detected. Catalysis by Cu(I) and Cu(II) salts in Meerwein reaction is explained by two catalytic cycles Cu+ D Cu2+ and formation of heteroligandous complex ion. In the process of single electron transfer both forms catalyst take place: Cu(II) is oxidizing substrate molecule, while Cu(I) is reducing diazonium ion. The presence of two catalytic cycles is suggested by formation of both ion-radicals and radicals. The formed aryl radical without exiting an activated complex of [arenediazonium tetrachlorocuprate(II) – olefin or arenediazonium salt– catalyst–olefin] reacts with double bond and forms aryl-substituted alkyl radical, the later was detected by ESR. This radical transfers electron through copper(II) to cation-radical of alkene with the formation of reaction product. The needed reaction component is water, whose role is, probably, in the formation of hexaaqua ions [Cu(H2O)6] 2+ , in which water molecules are easily replaced by other ligands. Substituted usually are not more than four water molecules (inner-sphere coordination). Ligand exchange and reaction between them play important role in anionarylation reaction. During the formation of active intermediate complexes, containing ligands of different nature, the reaction between them is possible, especially in the case of labile complexes. This can explain the formation of isomerization products during the use of arylalkens, when formation of intermediate cyclic pheniletenylic carbocation is possible. The detailed study of possibility of ion-radical mechanism for more complex multicomponent reaction – cuprocatalytic reaction of arenediazonium salts, styrene and sulphur(IV) oxide – also confirms the occurrence of single-electron transfer by participation of Cu+ D Cu2+ system. Analysis of literature data and obtained results suggests that interaction of unsaturated compounds with arenediazonium salts, which can be realized as anionarylation or as arylation, is an ionradical process. Reaction mechanism can be interpreted as ion-radical addition to double bond АRN. Key words: Meerwein reaction, arenediazonium salts, cuprous catalysis, ion-radicals.

Обобщены результаты исследований реакции Меервейна. Проанализировано роль купрокатализа в процессе, кинетические данные, роль комплексных интермедиатов, некупрокаталитические методы инициирования и стереохимические аспекты реакции. Предложен новый ионрадикальный механизм для взаимодействия непредельных соединений с солями арендиазония. Ключевые слова: реакция Меервейна, соли арендиазония, купрокатализ, ионрадикалы.