A Stable Open-Shelled Au26 Nanocluster with Remarkable Performance in Selective Oxidation of Benzyl Alcohol

Open metal sites are crucial in catalysis. We have used a “loose coordination strategy” (LCS) to preorganize open metal sites in gold cluster catalysts. A gold nanocluster with composition of [Au₂₆(3,4-Me₂-Ph-form)₉(ⁱPr₂-imy)₃(Me₂S)](BF₄)₂ (ⁱPr₂-imy=1,3-Diisopropylimidazolium tetrafluoroborate, 3,4-Me₂-Ph-form=N,N′-Di(3,4-dimethyl-phenyl)formamidine) (Au₂₆) has been obtained by one pot synthesis, i.e. the direct reduction of Me₂SAuCl in the presence of N-heterocyclic carbenes and amidinate ligands. ESI-TOF-MS reveals that the Me₂S ligand is detached from the cluster to form open sites. The accessibility of the exposed Au atoms has been confirmed quantitatively by luminescent titration with 2-naphthalenethiol. Surprisingly, Au₂₆ has 15 valence electrons, and the presence of an unpaired electron is confirmed by superconducting quantum interference device (SQUID) and electron paramagnetic resonance (EPR). This open-shelled Au₂₆ not only shows unexpected high stability but also exhibits excellent catalytic performance toward the selective oxidation of benzyl alcohol to benzaldehyde, achieving a remarkable turnover number up to 100670.