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Dalton Transactions

The international journal for inorganic, organometallic and bioinorganic chemistry



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Dalton Trans., 2009, 9169 - 9175, DOI: 10.1039/b913030f

Colorimetric turn-on sensing of fluoride ions in H2O/CHCl3 mixtures by pyridinium boranes

Casey R. Wade and François P. Gabbaï

As part of our interest in chemistry of cationic boron compounds as anion receptors, we have synthesized 2-(4-dimestylborylphenyl)-N-methyl-pyridinium triflate ([ 3]OTf) and 2-(5-dimesitylborylthiophen-2-yl)-N-methyl-pyridinium triflate ([ 4]OTf) by reaction of the corresponding pyridyl derivatives with MeOTf. Both [ 3]OTf and [ 4]OTf extract fluoride ions biphasically (H2O/CHCl3) to form the zwitterionic fluoroborates 3-F and 4-F, which have been structurally characterized. Remarkably, fluoride binding induces a red-shift of the low energy absorption band of these boranes (from 319 nm to 368 nm for 3/ 3-F and from 355 nm to 430 nm for 4/ 4-F) leading to the appearance of a yellow color. The origin of this turn-on colorimetric response is attributed to an intramolecular charge transfer process involving the triorganofluoroborate moiety as the donor and the pyridinium moiety as the acceptor.

Graphical abstract image for this article (ID: b913030f)