Selective and Reversible Fluoride Complexation from Water by a Cyclic Tri(phosphonio)methanide Dication.

Tri(phosphonio)methanide dication 3(2+) , prepared from a trifluoromethylsulfanylphosphonium dication (1(2+) ) via an intramolecular electrophilic aromatic substitution reaction, is an unexpected P-based, water-resistant Lewis acid that is capable to selectively and reversibly bind fluoride ions from organic/aqueous biphasic solution. The formed complex is an unusual fluorophosphorane ([3-F]OTf). The multiple donor-acceptor interactions of 3(2+) that are crucial for the fluoride fixation have been elucidated by quantum chemical calculation. Compound [3-F]OTf can also be used as a convenient anhydrous fluoride ion source and was probed as a suitable catalyst of the silylotrifluoromethylation of various aldehydes.