Postclustering Dynamic Covalent Modification for Chirality Control and Chiral Sensing

Cluster-based functional materials are appealing, because clusters are well-defined building units that can be rationally incorporated for the tuning of structures and properties. Postclustering modification (PCM) allows for tailoring properties through the structural modification of a cluster with preorganized funtional groups. By introducing aldehydes into a robust gold–silver cluster via a protection–deprotection process, we manage to synthesize a new cluster bearing six reactive sites, which are available for PCM through dynamic covalent imine bonds formation with chiral monoamines. Chirality is transferred from the amine to the gold–silver cluster. The homochirality of the resulted cluster has been confirmed by X-ray structural determination and CD spetroscopy. Intense CD signals make it practical for chiral recognition and <i>ee</i> value determination of chiral monoamines. The strategy of prefunctionalizing of cluster and the concept of PCM open a broader prospect for cluster design and applications

Postclustering Dynamic Covalent Modification for Chirality Control and Chiral Sensing

Cluster-based functional materials are appealing, because clusters are well-defined building units that can be rationally incorporated for the tuning of structures and properties. Postclustering modification (PCM) allows for tailoring properties through the structural modification of a cluster with preorganized funtional groups. By introducing aldehydes into a robust gold–silver cluster via a protection–deprotection process, we manage to synthesize a new cluster bearing six reactive sites, which are available for PCM through dynamic covalent imine bonds formation with chiral monoamines. Chirality is transferred from the amine to the gold–silver cluster. The homochirality of the resulted cluster has been confirmed by X-ray structural determination and CD spetroscopy. Intense CD signals make it practical for chiral recognition and <i>ee</i> value determination of chiral monoamines. The strategy of prefunctionalizing of cluster and the concept of PCM open a broader prospect for cluster design and applications

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) (<b>1</b>), 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 (<b>2</b>). 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 <b>2</b> emits bright green light in the solid state at room temperature upon UV irradiation

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) (<b>1</b>), 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 (<b>2</b>). 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 <b>2</b> emits bright green light in the solid state at room temperature upon UV irradiation

Highly Active Gold(I)–Silver(I) Oxo Cluster Activating sp³ C–H Bonds of Methyl Ketones under Mild Conditions

The activation of C­(sp³)–H bonds is challenging, due to their high bond dissociation energy, low proton acidity, and highly nonpolar character. Herein we report a unique gold­(I)–silver­(I) oxo cluster protected by hemilabile phosphine ligands [OAu₃Ag₃(PPhpy₂)₃]­(BF₄)₄ (<b>1</b>), which can activate C­(sp³)–H bonds under mild conditions for a broad scope of methyl ketones (RCOCH₃, R = methyl, phenyl, 2-methylphenyl, 2-aminophenyl, 2-hydroxylphenyl, 2-pyridyl, 2-thiazolyl, <i>tert</i>-butyl, ethyl, isopropyl). Activation happens via triple deprotonation of the methyl group, leading to formation of heterometallic Au­(I)–Ag­(I) clusters with formula RCOCAu₄Ag₄(PPhpy₂)₄(BF₄)₅ (PPhpy₂ = bis­(2-pyridyl)­phenylphosphine). Cluster <b>1</b> can be generated <i>in situ</i> via the reaction of [OAu₃Ag­(PPhpy₂)₃]­(BF₄)₂ with 2 equiv of AgBF₄. The oxo ion and the metal centers are found to be essential in the cleavage of sp³ C–H bonds of methyl ketones. Interestingly, cluster <b>1</b> selectively activates the C–H bonds in −CH₃ rather than the N–H bonds in −NH₂ or the O–H bond in −OH which is traditionally thought to be more reactive than C–H bonds. Control experiments with butanone, 3-methylbutanone, and cyclopentanone as substrates show that the auration of the C–H bond of the terminal methyl group is preferred over secondary or tertiary sp³ C–H bonds; in other words, the C–H bond activation is influenced by steric effect. This work highlights the powerful reactivity of metal clusters toward C–H activation and sheds new light on gold­(I)-mediated catalysis