The Lewis superacid Al[N(C(6)F(5))(2)](3) and its higher homolog Ga[N(C(6)F(5))(2)](3) – structural features, theoretical investigation and reactions of a metal amide with higher fluoride ion affinity than SbF(5)

Herein we present the synthesis of the two Lewis acids Al[N(C(6)F(5))(2)](3) (ALTA) and Ga[N(C(6)F(5))(2)](3) (GATA) via salt elimination reactions. The metal complexes were characterized by NMR-spectroscopic methods and X-ray diffraction analysis revealing the stabilization of the highly Lewis acidic metal centers by secondary metal–fluorine contacts. The Lewis acidic properties of Al[N(C(6)F(5))(2)](3) and Ga[N(C(6)F(5))(2)](3) are demonstrated by reactions with Lewis bases resulting in the formation of metallates accompanied by crucial structural changes. The two metallates [Cs(Tol)(3)](+)[FAl(N(C(6)F(5))(2))(3)](–) and [AsPh(4)](+)[ClGa(N(C(6)F(5))(2))(3)](–) contain interesting weakly coordinating anions. The reaction of Al[N(C(6)F(5))(2)](3) with trityl fluoride yielded [CPh(3)](+)[FAl(N(C(6)F(5))(2))(3)](–) which could find application in the activation of metallocene polymerization catalysts. The qualitative Lewis acidity of Al[N(C(6)F(5))(2)](3) and Ga[N(C(6)F(5))(2)](3) was investigated by means of competition experiments for chloride ions in solution. DFT calculations yielded fluoride ion affinities in the gas phase (FIA) of 555 kJ mol(–1) for Al[N(C(6)F(5))(2)](3) and 472 kJ mol(–1) for Ga[N(C(6)F(5))(2)](3). Thus, Al[N(C(6)F(5))(2)](3) can be considered a Lewis superacid with a fluoride affinity higher than SbF(5) (493 kJ mol(–1)) whereas the FIA of the corresponding gallium complex is slightly below the threshold to Lewis superacidity.