Geminal Tetraauration of Acetonitrile: Hemilabile-Phosphine-Stabilized
Au<sub>8</sub>Ag<sub>4</sub> Cluster Compounds
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Abstract
Unprecedented
geminal tetraauration of acetonitrile has been realized
through C–H activation by Au(I)–Ag(I) clusters under
mild conditions. The reaction of [OAu<sub>3</sub>Ag(dppy)<sub>3</sub>](BF<sub>4</sub>)<sub>2</sub> (dppy = diphenylphosphino-2-pyridine)
(<b>1</b>), AgBF<sub>4</sub>, and acetonitrile in the presence
of methanol at room temperature resulted in the isolation of the novel
cluster [(CCN)<sub>2</sub>Au<sub>8</sub>Ag<sub>4</sub>(dppy)<sub>8</sub>(CH<sub>3</sub>CN)<sub>2</sub>](BF<sub>4</sub>)<sub>6</sub> (<b>2</b>). The centrosymmetric structure consists of two Au<sub>4</sub>Ag<sub>2</sub> motifs stabilized by hemilabile phosphines. Triply
deprotonated acetonitrile (CCN<sup>3–</sup>) is found in a
Au<sub>4</sub>Ag 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 μ<sub>5</sub>-CCN<sup>3–</sup> 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 <b>2</b> emits bright green light in the solid state at room temperature
upon UV irradiation
