Homoleptic Gold Acetonitrile Complexes with Medium to Very Weakly Coordinating Counterions: Effect on Aurophilicity?
A series of gold acetonitrile complexes [Au(NCMe)2]+[WCA]-with weakly coordinating counterions (WCAs) was synthesized by the reaction of elemental gold and nitrosyl salts [NO]+[WCA]-in acetonitrile ([WCA]-=[GaCl4]-, [B(CF3)4]-, [Al(ORF)4]-; RF=C(CF3)3). In the crystal structures, the [Au(NCMe)2]+units appeared as monomers, dimers, or chains. A clear correlation between the aurophilicity and the coordinating ability of counterions was observed, with more strongly coordinating WCAs leading to stronger aurophilic contacts (distances, C-N stretching frequencies of [Au(NCMe)2]+units). An attempt to prepare [Au(L)2]+units, even with less weakly basic solvents like CH2Cl2, led to decomposition of the [Al(ORF)4]-anion and formation of [NO(CH2Cl2)2]+[F(Al(ORF)3)2]-. All nitrosyl reagents [NO]+[WCA]-were generated according to an optimized procedure and were thoroughly characterized by Raman and NMR spectroscopy. Moreover, the to date unknown species [NO]+[B(CF3)3CN]-was prepared. Its reaction with gold unexpectedly produced [Au(NCMe)2]+[Au(NCB(CF3)3)2]-, in which the cyanoborate counterion acts as an anionic ligand itself. Interestingly, the auroborate anion [Au(NCB(CF3)3)2]-behaves as a weakly coordinating counterion, which becomes evident from the crystallographic data and the vibrational spectral characteristics of the [Au(NCMe)2]+cation in this complex. Ligand exchange in the only room temperature stable salt of this series, [Au(NCMe)2]+[Al(ORF)4]-, is facile and, for example, [Au(PPh3)(NCMe)]+[Al(ORF)4]-can be selectively generated. This reactivity opens the possibility to generate various [AuL1L2]+[Al(ORF)4]-salts through consecutive ligand-exchange reactions that offer access to a huge variety of AuIcomplexes for gold catalysis.
Institut für Anorganische und Analytische Chemie und Freiburger Materialforschungszentrum (FMF), Universität Freiburg, Albertstr. 21, 79104, Freiburg, Germany.
Tobias A
TA
Engesser
Institut für Anorganische und Analytische Chemie und Freiburger Materialforschungszentrum (FMF), Universität Freiburg, Albertstr. 21, 79104, Freiburg, Germany.
Christian
C
Friedmann
Institut für Anorganische und Analytische Chemie und Freiburger Materialforschungszentrum (FMF), Universität Freiburg, Albertstr. 21, 79104, Freiburg, Germany.
Arthur
A
Martens
Institut für Anorganische und Analytische Chemie und Freiburger Materialforschungszentrum (FMF), Universität Freiburg, Albertstr. 21, 79104, Freiburg, Germany.
Daniel
D
Kratzert
Institut für Anorganische und Analytische Chemie und Freiburger Materialforschungszentrum (FMF), Universität Freiburg, Albertstr. 21, 79104, Freiburg, Germany.
Przemysław J
PJ
Malinowski
Institut für Anorganische und Analytische Chemie und Freiburger Materialforschungszentrum (FMF), Universität Freiburg, Albertstr. 21, 79104, Freiburg, Germany. krossing@uni-freiburg.de.
Ingo
I
Krossing
anions; auroborates; aurophilicity; gold; nitrosyl salts