Squeezing Fluoride out of Water with a Neutral Bidentate Antimony(V) Lewis Acid

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Abstract
Because of hydration, fluoride ions in water typically elude complexation by neutral Lewis acids. Here, we show how this limitation can be overcome with a bidentate Lewis acid containing two antimony(V) centers. This derivative (2) is obtained by the simple reaction of 4,5‐bis(diphenylstibino)‐9,9‐dimethylxanthene (1) with two equivalents of 3,4,5,6‐tetrachlorobenzoquinone (o‐chloranil). It features two square‐pyramidal stiborane units oriented in a face‐to‐face fashion. Titration experiments show that this new bidentate Lewis acid binds fluoride in aqueous solutions containing 95 % water with a binding constant (K) of 700±30 M−1. The structure of the fluoride adduct confirms fluoride anion chelation between the two antimony centers.

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