[Sb(C6F5)4][B(C6F5)4]: An Air Stable, Lewis Acidic Stibonium Salt That Activates Strong Element-Fluorine Bonds

As part of our ongoing interest in main group Lewis acids for fluoride anion complexation and element-fluorine bond activation, we have synthesized the stibonium borate salt [Sb­(C6F5)4]­[B­(C6F5)4] (3). The perfluorinated stibonium cation [Sb­(C6F5)4]+ present in this salt is a potent Lewis acid which abstracts a fluoride anion from [SbF6]− and [BF­(C6F5)3]− indicating that it is a stronger Lewis acid than SbF5 and B­(C6F5)3. The unusual Lewis acidic properties of 3 are further reflected by its ability to polymerize THF or to promote the hydrodefluorination of fluoroalkanes in the presence of Et3SiH. While highly reactive in solution, 3 is a perfectly air stable salt, making it a convenient Lewis acidic reagent.