Issue 1, 2018
From the journal:

Chemical Science

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†

J. F. Kögel,‡a   D. A. Sorokin,a   A. Khvorost,a   M. Scott,a   K. Harms,a   D. Himmel, ORCID logo b   I. Krossingb  and  J. Sundermeyer*a  

* Corresponding authors

a Fachbereich Chemie der Philipps-Universität, Hans-Meerwein Str., 35043 Marburg, Germany
E-mail: jsu@staff.uni-marburg.de

b Institut für Anorganische und Analytische Chemie, Freiburger Materialforschungszentrum (FMF), Freiburg Institute for Advanced Studies (FRIAS), Section Soft Matter Science, Universität Freiburg, Albertstr. 21, 79104 Freiburg, Germany

Abstract

Herein we present the synthesis of the two Lewis acids Al[N(C6F5)2]3 (ALTA) and Ga[N(C6F5)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(C6F5)2]3 and Ga[N(C6F5)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(C6F5)2)3]− and [AsPh4]+[ClGa(N(C6F5)2)3]− contain interesting weakly coordinating anions. The reaction of Al[N(C6F5)2]3 with trityl fluoride yielded [CPh3]+[FAl(N(C6F5)2)3]− which could find application in the activation of metallocene polymerization catalysts. The qualitative Lewis acidity of Al[N(C6F5)2]3 and Ga[N(C6F5)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(C6F5)2]3 and 472 kJ mol−1 for Ga[N(C6F5)2]3. Thus, Al[N(C6F5)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.

Graphical abstract: 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

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Article information

DOI
https://doi.org/10.1039/C7SC03988C
Article type
Edge Article
Submitted
11 sep. 2017
Accepted
20 oct. 2017
First published
23 oct. 2017
This article is Open Access

All publication charges for this article have been paid for by the Royal Society of Chemistry
Creative Commons BY license

Chem. Sci., 2018,9, 245-253

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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

J. F. Kögel, D. A. Sorokin, A. Khvorost, M. Scott, K. Harms, D. Himmel, I. Krossing and J. Sundermeyer, Chem. Sci., 2018, 9, 245 DOI: 10.1039/C7SC03988C

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