Homoleptic Gold Acetonitrile Complexes with Medium to Very Weakly Coordinating Counterions: Effect on Aurophilicity? |
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| Authors: | Dr Tobias A Engesser Christian Friedmann Arthur Martens Dr Daniel Kratzert Dr Przemys?aw J Malinowski Prof?Dr Ingo Krossing |
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| Institution: | Institut für Anorganische und Analytische Chemie und Freiburger Materialforschungszentrum (FMF), Universit?t Freiburg, Freiburg, Germany |
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| Abstract: | 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 AuI complexes for gold catalysis. |
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| Keywords: | anions auroborates aurophilicity gold nitrosyl salts |
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