Iodo-Bridged Transition States; New Mechanistic Pathways for Base-Catalyzed Halogen Dance
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ORIGINAL ARTICLE
Iodo‑Bridged Transition States; New Mechanistic Pathways for Base‑Catalyzed Halogen Dance Nader Sakhaee1 · Sahar Sakhaee2 · Esmail Doustkhah3 · Akbar mobaraki4 · Ahmad Takallou5 · Mohammad Hossein Sakhaee6 Received: 23 April 2020 / Accepted: 19 October 2020 © The Tunisian Chemical Society and Springer Nature Switzerland AG 2020
Abstract First reported by Joseph Bunnet et al., base-catalyzed halogen dance reaction has puzzled chemists for decades, to come up with new ideas regarding the mechanism of this chemical reaction. A series of deprotonation followed by fast metal-halogen exchanges are among the most recent mechanisms reported so far. Using density functional theory, DFT, computations and focused on the Bunnet type isomerization halogen dance reactions of iodobenzene derivatives, iodo-bridged transition state, TS, are proposed. The new TS is then used to lay out 8 possible isomerization and 18 possible disproportionation paths. The possible mechanistic pathways are then carefully analyzed based on TS’s energy and protonation/deprotonation steps to find the most suitable pathways. These mechanistic pathways, sketch a comprehensive pattern for base-catalyzed halogen dance. There is still a lot to study in the chemistry of poly halogenated aryls. Keywords Nonaqueous strongly basic medium · Mechanistic pathways · Disproportionation paths · Iodo-bridged transition state · Dynamic domino mechanisms · Base-catalyzed halogen dance
1 Introduction Reactions of aryl halides with strong bases like potassium amides has long been studied by chemists like Chichibain and Bunnet. However, the role of strong basic media in these reactions has gained little notice. In fact strong non-aqueous basic media [1, 2] is a vast realm, the niches of which are yet Electronic supplementary material The online version of this article (https://doi.org/10.1007/s42250-020-00197-6) contains supplementary material, which is available to authorized users. * Nader Sakhaee [email protected] 1
Department of Chemistry, University of Illinois UrbanaChampaign, Urbana, IL 61820, USA
2
Islamic Azad University, Mashhad Branch, Mashhad, Iran
3
International Center for Materials Nanoarchitechtonics (MANA), National Institute for Materials Science (NIMS), 1‑1 Namiki, Tsukuba, Ibaraki 305‑0044, Japan
4
Department of Chemistry, Tarbiat Modarres University, P.O. Box, 14115‑175 Tehran, Iran
5
Department of Chemistry, Kharazmi University, Tehran, Iran
6
Mashhad University of Medical Sciences, Mashhad, Iran
to be fully understood. Aryl halide reactions in basic media has appeared in literature with different names like halogen scrambling, halogen migration [3], halogen isomerization, halogen dance, or base catalyzed halogen dance [4–7], which implies the lack of a consensus for the underpinning mechanism. Bunnet et al., published a paper [4] on the so called base catalyzed Halogen dance, HD, reaction [8, 9]. The report revolutionized our understanding of the reaction, ruled out then accepted benzyne mechanism
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