Ion pairs of weakly coordinating cations and anions: Synthesis and application for sulfide to sulfoxide oxidations

Abstract

A series of salts containing the weakly coordinating cations (WCC) 1-butyl-3-methylimidazolium ([Bmim]+), 1-butyl-2,3-dimethylimidazolium ([Bdmim]+), 1-dodecyl-3-methylimidazolium ([C12mim]+), tetrabutylphosphonium ([PBu4]+), tributyltetradecylphosphonium ([P4,4,4,14]+), tetrabutylammonium ([NBu4]+), and 1,1,3,3-tetramethylguanidium ([TMG]+) and fluorinated tetraarylborate anions of the type [B(ArF)4] (ArF = 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⋯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.