Homoleptic Gold Acetonitrile Complexes with Medium to Very Weakly Coordinating Counterions: Effect on Aurophilicity?. Issue 42 (4th September 2016)

• Record Type: Journal Article
• Authors: Engesser, Tobias A.; Friedmann, Christian; Martens, Arthur; Kratzert, Daniel; Malinowski, Przemysław J.; Krossing, Ingo
• Is Part Of: Chemistry. Volume 22:Issue 42(2016)
• Page Start: 15085
• Page End: 15094
• Publication Date: 2016-09-04
• Subjects: anions -- auroborates -- aurophilicity -- gold -- nitrosyl salts; Chemistry -- Periodicals; 540
• DOI: 10.1002/chem.201602797
• Languages: English
• ISSNs: 0947-6539

Abstract

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(OR F )4 ] − ; R F = 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 CH2 Cl2, led to decomposition of the [Al(OR F )4 ] − anion and formation of [NO(CH2 Cl2 )2 ] + [F(Al(OR F )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 )3 CN] − 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(OR F )4 ] −, is facile and, for example, [Au(PPh3 )(NCMe)] + [Al(OR F )4 ] − can be selectively generated. This reactivity opens the possibility to generate various [AuL 1 L 2 ] + [Al(OR F )4 ] − salts through consecutive ligand‐exchange reactions that offer access to a huge variety of Au I complexes for gold catalysis. Abstract : Gold(I) variations : Oxidation of gold by [NO] + [WCA] − in acetonitrile led to structurally diverse [Au(NCMe)2 ] + [WCA] − salts ([WCA] − =weakly coordinating anion; [BF4 ] −, [GaCl4 ] −, [B(CF3 )4 ] −, or [Al(OC(CF3 )3 )4 ] − ). Monomers, dimers, and chains of [Au(NCMe)2 ] + cations form depending on the WCA. [Au(NCMe)2 ] + [Al(OC(CF3 )3 )4 ] − is the only salt to be stable at room temperature; it is a versatile reagent for further chemistry, and reacts directly to give the [Au(PPh3 )(NCMe)] + complex.