Tetraphenylborate, perfluorinated

The cationic rhodium catalyst in Scheme 8.8 is rendered soluble in SCCO2 by the anion, BArF, a perfluorinated tetraphenylborate counter-anion (Figure 8.9). 

The same silyl ion also was examined in condensed phases by Lambert with his perfluorinated tetraphenylborate counterion [41]. While the solid state structure of this complex is not known, its Si shift is 107.6 ppm, close to the Reed s value. As the silicon atom might be coordinated to one or to two fluorine atoms [42], we calculated model complexes of SiMe3 with methyl fluoride and with cis-difluorethene. The smaller fluorine atoms are able to approach closer to silicon than bromine (Fig. 16), but the shift in electron density towards the cationic moiety is negligible. 

Perfluorinated triphenyl boron and perfluorinated tetraphenylborate species have stoichiometric advantages compared to MAO, but they have specific drawbacks including higher cost... 

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