Facile and systematic access to the least-coordinating WCA [(R(F)O)(3)Al–F–Al(OR(F))(3)](–) and its more Lewis-basic brother [F–Al(OR(F))(3)](–) (R(F) = C(CF(3))(3))

By reaction of the Lewis acid Me(3)Si–F–Al(OR(F))(3) with a series of [PF(6)](–) salts, gaseous PF(5) and Me(3)Si–F are liberated and salts of the anion [F–Al(OR(F))(3)](–) ([f–al](–); R(F) = C(CF(3))(3)) can be obtained. By addition of another equivalent of Me(3)Si–F–Al(OR(F))(3) to [f–al](–), gaseous Me(3)Si–F is released and salts of the least coordinating anion [(R(F)O)(3)Al–F–Al(OR(F))(3)](–) ([al–f–al](–)) are formed. Both procedures work for a series of synthetically useful cations including Ag(+), [NO](+), [Ph(3)C](+) and in very clean reactions with 5 g batch sizes giving excellent yields typically exceeding 90%. In addition, the synthesis of Me(3)Si–F–Al(OR(F))(3) has been optimized and scaled up to 85 g batches in an one-pot procedure. These anions could previously only be obtained by difficult to control decomposition reactions of [Al(OR(F))(4)](–) or by halide abstraction reactions with Me(3)Si–F–Al(OR(F))(3), generating relatively large countercations that are unsuited for further use as universal starting materials. Especially [al–f–al](–) is of interest for the stabilization of reactive cations, since it is even weaker coordinating than [Al(OR(F))(4)](–) and more stable against strong electrophiles. This bridged anion can be seen as an adduct of [f–al](–) and Al(OR(F))(3). Thus, it is similarly Lewis acidic as BF(3) and eventually reacts with nucleophiles (Nu) from the reaction environment to yield Nu–Al(OR(F))(3) and [f–al](–). This prevents working with [al–f–al](–) salts in ethereal or other donor solvents. By contrast, the [f–al](–) anion is no longer Lewis acidic and may therefore be used for reactions involving stronger nucleophiles than the [al–f–al](–) anion can withstand. Subsequently it may be transformed into the [al–f–al](–) salt by simple addition of one equivalent of Me(3)Si–F–Al(OR(F))(3).