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Focus on Chemistry of the 10-Dioxane-nido-7,8-dicarba-undecahydrido Undecaborate Zwitterion; Exceptionally Easy Abstraction of Hydrogen Bridge and Double-Action Pathways Observed in Ring Cleavage Reactions with OH as Nucleophile

1
Institute of Inorganic Chemistry of Czech Academy of Sciences, 25068 Řež, Czech Republic
2
Department of General and Inorganic Chemistry, Faculty of Chemical Technology, University of Pardubice, Studentská 95, 53210 Pardubice, Czech Republic
*
Author to whom correspondence should be addressed.
These authors contributed equally to this article.
This article is dedicated to the memory of the Bohumil Štíbr, our mentor, colleague and friend, who unfortunately passed away soon before he could reach the age of 80 and in recognition of his outstanding contributions to carborane and heteroborane chemistries.
Academic Editors: Igor B. Sivaev, Narayan S. Hosmane and Bohumír Grűner
Molecules 2020, 25(4), 814; https://doi.org/10.3390/molecules25040814
Received: 20 January 2020 / Revised: 8 February 2020 / Accepted: 11 February 2020 / Published: 13 February 2020
Ring cleavage of cyclic ether substituents attached to a boron cage via an oxonium oxygen atom are amongst the most versatile methods for conjoining boron closo-cages with organic functional groups. Here we focus on much less tackled chemistry of the 11-vertex zwitterionic compound [10-(O-(CH2-CH2)2O)-nido-7,8-C2B9H11] (1), which is the only known representative of cyclic ether substitution at nido-cages, and explore the scope for the use of this zwitterion 1 in reactions with various types of nucleophiles including bifunctional ones. Most of the nitrogen, oxygen, halogen, and sulphur nucleophiles studied react via nucleophilic substitution at the C1 atom of the dioxane ring, followed by its cleavage that produces six atom chain between the cage and the respective organic moiety. We also report the differences in reactivity of this nido-cage system with the simplest oxygen nucleophile, i.e., OH. With compound 1, reaction proceeds in two possible directions, either via typical ring cleavage, or by replacement of the whole dioxane ring with -OH at higher temperatures. Furthermore, an easy deprotonation of the hydrogen bridge in 1 was observed that proceeds even in diluted aqueous KOH. We believe this knowledge can be further applied in the design of functional molecules, materials, and drugs. View Full-Text
Keywords: borane; carborane; dicarbollide ion; oxonium atom; nucleophilic substitution borane; carborane; dicarbollide ion; oxonium atom; nucleophilic substitution
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Bakardjiev, M.; El Anwar, S.; Bavol, D.; Růžičková, Z.; Grűner, B. Focus on Chemistry of the 10-Dioxane-nido-7,8-dicarba-undecahydrido Undecaborate Zwitterion; Exceptionally Easy Abstraction of Hydrogen Bridge and Double-Action Pathways Observed in Ring Cleavage Reactions with OH as Nucleophile . Molecules 2020, 25, 814.

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