A General Approach for the Synthesis of Arylxenonium(II) Tetrafluoroborates

Arylxenonium(II) salts are the most numerous group of organoxenon compounds, i.e., those containing Xe-C bonds, and must be prepared by different routes that lack universality. Here, we present a general synthetic approach to arylxenonium(II) tetrafluoroborates [RXe][BF₄] containing different degrees of fluorination at the aryl group R via processes that do not require the use of reactive gases or special equipment. The new synthetic access relies on the generation of aryldifluoroboranes RBF₂ in dichloromethane solution by means of the reaction of K[RBF₃] and BF₃·OEt₂, which are then transformed in a subsequent step to [RXe][BF₄] salts. This route is not only more accessible than previously existing methods but also yields arylxenonium(II) tetrafluoroborates in higher yield and purity. Nevertheless, for highly acidic aryldifluoroborane species, namely those with R = C₆F₅, C₆HF₄, coordination of diethyl ether to the boron center prevents the transfer of the R group to the xenon atom. In these cases, a one-pot procedure starting from BR₃, XeF₂ and BF₃·OEt₂ enables their easy synthesis, including that of the novel compound [(2,3,5,6-C₆HF₄)Xe][BF₄]. By means of the analysis of ¹¹B NMR spectra of the aryldifluoroborane mixtures and theoretical calculations, the design of new organoxenonium(II) tetrafluoroborates through one route or the other can be tackled.