The Lewis superacid Al[N(C6F5)2]3 and its higher homolog Ga[N(C6F5)2]3 – structural features, theoretical investigation and reactions of a metal amide with higher fluoride ion affinity than SbF5. Issue 1 (2nd November 2017)

• Record Type: Journal Article
• Authors: Kögel, J. F.; Sorokin, D. A.; Khvorost, A.; Scott, M.; Harms, K.; Himmel, D.; Krossing, I.; Sundermeyer, J.
• Is Part Of: Chemical science. Volume 9:Issue 1(2018)
• Page Start: 245
• Page End: 253
• Publication Date: 2017-11-02
• Subjects: Chemistry -- Periodicals; 540.5
• DOI: 10.1039/c7sc03988c
• Languages: English
• ISSNs: 2041-6520

Abstract

Abstract : Lewis superacid with higher fluoride ion affinity than SbF5 . Abstract : Herein we present the synthesis of the two Lewis acids Al[N(C6 F5 )2 ]3 (ALTA) and Ga[N(C6 F5 )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(C6 F5 )2 ]3 and Ga[N(C6 F5 )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(C6 F5 )2 )3 ] − and [AsPh4 ] + [ClGa(N(C6 F5 )2 )3 ] − contain interesting weakly coordinating anions. The reaction of Al[N(C6 F5 )2 ]3 with trityl fluoride yielded [CPh3 ] + [FAl(N(C6 F5 )2 )3 ] − which could find application in the activation of metallocene polymerization catalysts. The qualitative Lewis acidity of Al[N(C6 F5 )2 ]3 and Ga[N(C6 F5 )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(C6 F5 )2 ]3 and 472 kJ mol −1 for Ga[N(C6 F5 )2 ]3 . Thus, Al[N(C6 F5 )2 ]3 can be considered a Lewis superacid with a fluoride affinity higher than SbF5 (493 kJ mol −1 ) whereas the FIA of the corresponding gallium complex is slightly below the threshold to Lewis superacidity.