Highly Lewis Acidic Bifunctional Organoboranes

Piers, Warren E.; Irvine, Geoffrey J.; Williams, V. Clifford

doi:10.1002/1099-0682(200010)2000:10<2131::aid-ejic2131>3.0.co;2-h

Cited by 135 publications

(110 citation statements)

References 71 publications

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“…When we initiated this work, the fluoride binding constant of chelating diboranes had never been determined. However, it had been firmly established that bifunctional diboranes with rigid aromatic backbones [39][40][41] Figure 1) rather than the targeted diborane. [45][46][47][48] Because of the strain present in the four-membered ring, this borate is very reactive and undergoes ringopening reactions with electrophiles including boron halide reagents.…”

Section: 8-diborylnaphthalenesmentioning

confidence: 99%

Fluoride Ion Recognition by Chelating and Cationic Boranes

2009

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Because of the ubiquity of fluoride ions and their potential toxicity at high doses, researchers would like to design receptors that selectively detect this anion. Fluoride is found in drinking water, toothpaste, and osteoporosis drugs. In addition, fluoride ions also can be detected as an indicator of uranium enrichment (via hydrolysis of UF(6)) or of the chemical warfare agent sarin, which releases the ion upon hydrolysis. However, because of its high hydration enthalpy, the fluoride anion is one of the most challenging targets for anion recognition. Among the various recognition strategies that are available, researchers have focused a great deal of attention on Lewis acidic boron compounds. These molecules typically interact with fluoride anions to form the corresponding fluoroborate species. In the case of simple triarylboranes, the fluoroborates are formed in organic solvents but not in water. To overcome this limitation, this Account examines various methods we have pursued to increase the fluoride-binding properties of boron-based receptors. We first considered the use of bifunctional boranes, which chelate the fluoride anion, such as 1,8-diborylnaphthalenes or heteronuclear 1-boryl-8-mercurio-naphthalenes. In these molecules, the neighboring Lewis acidic atoms can cooperatively interact with the anionic guest. Although the fluoride binding constants of the bifunctional compounds exceed those of neutral monofunctional boranes by several orders of magnitude, the incompatibility of these systems with aqueous media limits their utility. More recently, we have examined simple triarylboranes whose ligands are decorated by cationic ammonium or phosphonium groups. These cationic groups increase the electrophilic character of these boranes, and unlike their neutral analogs, they are able to complex fluoride in aqueous media. We have also considered cationic boranes, which form chelate complexes with fluoride anions. Our work demonstrates that Coulombic and chelate effects are additive and can be combined to boost the anion affinity of Lewis acidic hosts. The boron compounds that we have investigated present a set of photophysical and electrochemical properties that can serve to signal the fluoride-binding event. We can also apply this approach to cyanide complexation and are continuing our investigations in that area.

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Section: 8-diborylnaphthalenesmentioning

confidence: 99%

Fluoride Ion Recognition by Chelating and Cationic Boranes

2009

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“…Especially, perfluoroaryl compounds show several unique properties such as high electron affinity or a rather sterically demanding and p-electron-accepting nature compared with the corresponding non-fluorinated aryl systems. Several reports showed that strong Lewis acidity of a perfluoroaryl ring is efficient for catalytic reactions: perfluoroarylboranes as co-catalyst for the olefin polymerization with group-4 metallocene alkyls [1], bifunctional perfluoroarylboranes for the activation of basic substrates, and the selective binding of anions [2]. For the purpose of application of asymmetric catalysis, chiral bidentate (perfluoroaryl)phosphane ligands were synthesized [3].…”

mentioning

confidence: 99%

Multiple Pentafluorophenylation of 2,2,3,3,5,6,6-Heptafluoro-3,6-dihydro-2H-1,4-oxazine with an Organosilicon Reagent: NMR and DFT Structural Analysis of Oligo(perfluoroaryl) Compounds

Nishida

Fukaya

Hayakawa

et al. 2006

HCA

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F 5 ) was used for the preparation of a series of perfluorinated, pentafluorophenyl-substituted 3,6-dihydro-2H-1,4-oxazines (2 -8), which, otherwise, would be very difficult to synthesize. Multiple pentafluorophenylation occurred not only on the heterocyclic ring of the starting compound 1 (Scheme), but also in para position of the introduced C 6 F 5 substituent(s) leading to compounds with one to three nonafluorobiphenyl (C 12 F 9 ) substituents. While the tris(pentafluorophenyl)-substituted compound 3 could be isolated as the sole product by stoichiometric control of the reagent, the higher-substituted compounds 5 -8 could only be obtained as mixtures. The structures of the oligo(perfluoroaryl) compounds were confirmed by 19 F-and 13 C-NMR, MS, and/or X-ray crystallography. DFT simulations of the 19 F-and 13 C-NMR chemical shifts were performed at the B3LYP-GIAO/6-31++G(d,p) level for geometries optimized by the B3LYP/6-31G(d) level, a technique that proved to be very useful to accomplish full NMR assignment of these complex products.

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“…These observations indicate the influence of the bulkiness of the substituents toward fluoride ion binding [8]. Further, Lewis acid based bidentate fluoride receptors with B/B and B/Hg as binding sites are also known [27][28][29][30][31]. The fluoride binding constants of bidentate boranes increases 3-4 times than the corresponding monofunctional analogs [9].…”

Section: Introductionmentioning

confidence: 96%