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 (CCN(3-)) 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-CCN(3-) 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.