Ion Pairs of Weakly Coordinating Cations and Anions: Synthesis and Application for Sulfide to Sulfoxide Oxidations

A series of salts containing the weakly coordinating cations (WCC) 1-butyl-3-methylimidazolium ([Bmim](+)), 1-butyl-2,3-dimethylimidazolium ([B dmim](+)), 1-dodecyl-3-methylimidazolium ([C(12)mim](+)), tetrabutylphosphonium ([PBu4](+)), tributyltetradecylphosphonium ([P4,4,4,14](+)), tetrabutylanunonium ([NBu4](+)), and 1,1,3,3-tetramethylguanidium ([TMG](+)) and fluorinated tetraarylborate anions of the type [B(Ar-F)(4)] (Ar-F = C6F5, C6H3-3,5-(CF3)(2)) were synthesized and characterized. The influence of cations and anions on the physical properties of the obtained compounds was examined. In case of the compound [TMG][B(C6F5)(4)] hydrogen-fluorine contacts between cation and anion are present in the solid state. Owing to H center dot center dot center dot F contacts between hydrogen peroxide and the fluorine substituents of the anion and the resulting activation of H2O2 in solution, the compound [P4,4,4,14][B(C6H3-3,5-(CF3)(2))(4)] is applicable as an efficient mediator for the oxidation of sulfides to sulfoxides.