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.
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