Due to favorable Coulombic effects, cationic main group Lewis acids should be
more Lewis acidic than their neutral counterparts. To investigate this idea, this
dissertation has been dedicated to the synthesis, characterization and anion binding
properties of new cationic Lewis acids for selective anion complexation. The cationic
borane [p-(Mes2B)C6H4(PPh3)] displays an enhanced anion affinity towards fluoride
due to a combination of Coulombic and hydrophobic effects, and can be used to detect
fluoride at levels below 4 ppm in water. A related phosphonium borane featuring a
chromophoric dansyl amide moiety has been synthesized and used for the fluorescence
turn on sensing of CN−. This borane is very sensitive and can be used to measure
cyanide concentration in the 20-30 ppb range in water.
The bidentate borane [o-(Mes2B)C6H4(PPh2Me)] is selective for N3
− over F− in
water/chloroform biphasic mixtures because of the lipophilic character of the azide
anion, as well as its ability to interact with both the boron and phosphorus Lewis acidic
sites of the receptor via chelation (lp(N)s*(P-C)). Sulfonium borane [o(Mes2B)C6H4(SMe2)] can detect up to 50 ppb of cyanide in water at pH 7 due to
favorable Coulombic effects. The sulfonium moiety interacts with the cyanide anion
through both bonding and back-bonding interactions, thus enhancing the unusual affinity
of [o-(Mes2B)C6H4(SMe2)] towards cyanide.
This approach can be extended to Lewis acids containing fluorosilanes such as
[1-Ant2FSi-2-Me2S-(C6H4)] whose fluoride affinity exceeds that of neutral fluorosilanes
by several orders of magnitude.
| Identifer | oai:union.ndltd.org:tamu.edu/oai:repository.tamu.edu:1969.1/ETD-TAMU-2010-08-8430 |
| Date | 2010 August 1900 |
| Creators | Kim, Youngmin |
| Contributors | Gabbaï, François P. |
| Source Sets | Texas A and M University |
| Language | en_US |
| Detected Language | English |
| Type | thesis, text |
| Format | application/pdf |
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