Fluorinated antimony(v) derivatives: strong Lewis acidic properties and application to the complexation of formaldehyde in aqueous solutions

Abstract

As part of our ongoing studies of water tolerant Lewis acids, we have synthesized and investigated the properties of Sb(C₆F₅)₃(O₂C₆Cl₄), a fluorinated stiborane whose Lewis acidity approaches that of B(C₆F₅)₃. While chloroform solutions of this Lewis acid can be kept open to air or exposed to water for extended periods of time, this new Lewis acid reacts with P^tBu₃ and paraformaldehyde to form the corresponding formaldehyde adduct ^tBu₃P–CH₂–O–Sb(C₆F₅)₃(O₂C₆Cl₄). To test if this reactivity can also be observed with systems that combine the phosphine and the stiborane within the same molecule, we have also prepared o-C₆H₄(PPh₂)(SbAr₂(O₂C₆Cl₄)) (Ar = Ph, C₆F₅). These yellow compounds, which possess an intramolecular P→Sb interaction, are remarkably inert to water but do, nonetheless, react with and accomodate formaldehyde into the P/Sb pocket. In the case of the fluorinated derivative o-C₆H₄(PPh₂)(Sb(C₆F₅)₂(O₂C₆Cl₄)), formaldehyde complexation, which occurs in water/dichloromethane biphasic mixtures, is accompanied by a colourimetric turn-off response thus highlighting the potential that this chemistry holds in the domain of molecular sensing.