Homoleptic Gold Acetonitrile Complexes with Medium to Very Weakly Coordinating Counterions: Effect on Aurophilicity?

A series of gold acetonitrile complexes [Au(NCMe) ] [WCA] with weakly coordinating counterions (WCAs) was synthesized by the reaction of elemental gold and nitrosyl salts [NO] [WCA] in acetonitrile ([WCA] =[GaCl ] , [B(CF ) ] , [Al(OR ) ] ; R =C(CF ) ). In the crystal structures, the [Au(NCMe) ] 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) ] units). An attempt to prepare [Au(L) ] units, even with less weakly basic solvents like CH Cl , led to decomposition of the [Al(OR ) ] anion and formation of [NO(CH Cl ) ] [F(Al(OR ) ) ] . 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(CF ) CN] was prepared. Its reaction with gold unexpectedly produced [Au(NCMe) ] [Au(NCB(CF ) ) ] , in which the cyanoborate counterion acts as an anionic ligand itself. Interestingly, the auroborate anion [Au(NCB(CF ) ) ] behaves as a weakly coordinating counterion, which becomes evident from the crystallographic data and the vibrational spectral characteristics of the [Au(NCMe) ] cation in this complex. Ligand exchange in the only room temperature stable salt of this series, [Au(NCMe) ] [Al(OR ) ] , is facile and, for example, [Au(PPh )(NCMe)] [Al(OR ) ] can be selectively generated. This reactivity opens the possibility to generate various [AuL L ] [Al(OR ) ] salts through consecutive ligand-exchange reactions that offer access to a huge variety of Au complexes for gold catalysis.