Geminal Tetraauration of Acetonitrile: Hemilabile-Phosphine-Stabilized Au8Ag4 Cluster Compounds

Unprecedented geminal tetraauration of acetonitrile has been realized through C–H activation by Au­(I)–Ag­(I) clusters under mild conditions. The reaction of [OAu3Ag­(dppy)3]­(BF4)2 (dppy = diphenylphosphino-2-pyridine) (1), AgBF4, and acetonitrile in the presence of methanol at room temperature resulted in the isolation of the novel cluster [(CCN)2Au8Ag4(dppy)8(CH3CN)2]­(BF4)6 (2). The centrosymmetric structure consists of two Au4Ag2 motifs stabilized by hemilabile phosphines. Triply deprotonated acetonitrile (CCN3–) is found in a Au4Ag environment with the terminal carbon bridging four Au­(I) centers and the nitrogen donor linking a Ag­(I) ion, which is the first example of a μ5-CCN3– coordination mode. A concerted metalation/deprotonation process for the C–H activation of acetonitrile that indicates the importance of the oxo ion of the oxonium Au­(I) cluster is proposed. Cluster 2 emits bright green light in the solid state at room temperature upon UV irradiation.