501432-99-1Relevant articles and documents
Influence of fluorination and boronic group synergy on the acidity and structural behavior of o-phenylenediboronic acids
Durka, Krzysztof,Lulinski, Sergiusz,Serwatowski, Janusz,Wozniak, Krzysztof
, p. 1608 - 1616 (2014/05/06)
The solid-state and solution structural properties and acidity of a series of fluorinated 1,2-phenylenediboronic acids were investigated. Solution NMR studies indicate that these compounds equilibrate with their dehydrated forms, in the simplest case presumably possessing the cyclic benzoxadiborole structure. Ab initio calculations showed that the stability of such cyclic semianhydrides is improved by fluorination of the aromatic ring and complexation of one of the boron centers with water. This was demonstrated by the crystal structure determination of tetrafluoro-1,2-phenylenediboronic acid. The coordinated water molecule participates in very strong intermolecular hydrogen bonding with the OH group bonded to the four-coordinate boron center (dO...O = 2.423(2) A, Eint = -87 kJ mol-1). This indicates that in fact this compound is an oxonium, i.e., Bronsted acid, which is exceptional for boronic acids. Under different crystallization conditions, tetrafluoro-1,2-phenylenediboronic acid dimerizes by aggregation of boronic groups, which leads to the formation of an uncommon eight-membered B 4O4 ring. Such a coordination dimer exists as the boat conformer, featuring π-π interactions of fluorinated aromatic rings. The enhanced acidity of 1,2-phenylenediboronic acids can be rationalized in terms of a synergic effect of two adjacent boronic groups and is manifested by relatively low pKa values ranging from 6.0 (1,2-phenylenediboronic acid) to only 3.0 for the perfluorinated derivative.
The basicity gradient-driven migration of iodine: Conferring regioflexibility on the substitution of fluoroarenes
Rausis, Thierry,Schlosser, Manfred
, p. 3351 - 3358 (2007/10/03)
Six different fluoroarenes were submitted to the same transformations. Direct deprotonation with alkyllithium or lithium dialkylamide as reagents and subsequent carboxylation afforded the acids 1, 6, 11, 16, 18, and 23. If the aryllithium intermediate was trapped with iodine rather than with dry ice, an iodofluoroarene (2, 7, 12, 17, 19, and 24) was formed. This, upon treatment with lithium diisopropylamide, underwent deprotonation and iodine migration. The resulting new aryllithium species was intercepted either by carboxylation, to give the acids 3, 8, 13, 20, and 25, or by neutralization, to produce the iodofluoroarenes 4, 9, 14, 21, and 26. The latter family of compounds was converted into another set of acids 5, 10, 15, 22, and 27 by subsequent treatment with butyllithium or isopropylmagnesium chloride and carbon dioxide. ( Wiley-VCH Verlag GmbH, 69451 Weinheim, Germany, 2002).
