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A 'passivated precursor' approach is developed for the efficient synthesis and isolation of all‐alkynyl‐protected gold nanoclusters. Direct reduction of dpa‐passivated precursor Au‐dpa (Hdpa=2,2'‐dipyridylamine) in one‐pot under ambient conditions gives a series of clusters including Au22(C≡CR)18 (R=−C6H4−2−F), Au36(C≡CR)24, Au44(C≡CR)28, Au130(C≡CR)50, and Au144(C≡CR)60. These clusters can be well separated via column chromatography. The overall isolation yield of this series of clusters is 40 % (based on gold), which is much improved in comparison with previous approaches. It is notable that the molecular structure of the giant cluster Au130(C≡CR)50 is revealed, which presents important information for understanding the structure of the mysterious Au130 nanoclusters. Theoretical calculations indicated Au130(C≡CR)50 has a smaller HOMO‐LUMO gap than Au130(S−C6H4−4−CH3)50. This facile and reliable synthetic approach will greatly accelerate further studies on all‐alkynyl‐protected gold nanoclusters. [ABSTRACT FROM AUTHOR]

Atomically precise gold nanoclusters provide great opportunities to explore the relationship between the structure and properties of nanogold catalysts. A nanocluster consists of a metal core and a surface ligand shell, and both the core and shell have significant effects on the catalytic properties. Thanks to their precise structures, the active metal site of the clusters can be readily identified and the effects of ligands on catalysis can be disclosed. In this Minireview, we summarize recent advances in catalytic research of gold nanoclusters, emphasizing four strategies for constructing open metal sites, including by post‐treatment, the bulky ligands strategy, the surface geometric mismatch method, and heteroatom doping procedures. We also discuss the effects of ligands on the catalytic activity, selectivity, and stability of gold cluster catalysts. Finally, we present future challenges relating to gold cluster catalysis. [ABSTRACT FROM AUTHOR]

Copper hydrides are important hydrogenation catalysts, but their poor stability hinders the practical applications. Ligand engineering is an effective strategy to tackle this issue. An amidinate ligand, N,N′-Di(5-trifluoromethyl-2-pyridyl)formamidinate (Tf-dpf) with four N-donors has been applied as a protecting agent in the synthesis of stable copper hydride clusters: Cu11H3(Tf-dpf)6(OAc)2 (Cu11) with three interfacial μ5-H and [Cu12H3(Tf-dpf)6(OAc)2]·OAc (Cu12) with three interstitial μ6-H. A solvent-triggered reversible interconversion between Cu11 and Cu12 has been observed thanks to the flexibility of Tf-dpf. Cu11 shows high activity in the reduction of 4-nitrophenol to 4-aminophenol, while Cu12 displays very low activity. Deuteration experiments prove that the type of hydride is the key in dictating the catalytic activity, for the interfacial μ5-H species in Cu11 are involved in the catalytic cycle whereas the interstitial μ6-H species in Cu12 are not. This work highlights the role of hydrides with regard to catalytic hydrogenation activity. Copper hydrides have been studied for their exciting structural chemistry and applications in hydrogenation catalysis. Here, the authors uncover the role of the amidinate ligand in yielding two closely related copper hydride clusters with quite different catalytic hydrogenation activity. [ABSTRACT FROM AUTHOR]

A 'passivated precursor' approach is developed for the efficient synthesis and isolation of all‐alkynyl‐protected gold nanoclusters. Direct reduction of dpa‐passivated precursor Au‐dpa (Hdpa=2,2'‐dipyridylamine) in one‐pot under ambient conditions gives a series of clusters including Au22(C≡CR)18 (R=−C6H4−2−F), Au36(C≡CR)24, Au44(C≡CR)28, Au130(C≡CR)50, and Au144(C≡CR)60. These clusters can be well separated via column chromatography. The overall isolation yield of this series of clusters is 40 % (based on gold), which is much improved in comparison with previous approaches. It is notable that the molecular structure of the giant cluster Au130(C≡CR)50 is revealed, which presents important information for understanding the structure of the mysterious Au130 nanoclusters. Theoretical calculations indicated Au130(C≡CR)50 has a smaller HOMO‐LUMO gap than Au130(S−C6H4−4−CH3)50. This facile and reliable synthetic approach will greatly accelerate further studies on all‐alkynyl‐protected gold nanoclusters. [ABSTRACT FROM AUTHOR]

Gold nanoclusters with surface open sites are crucial for practical applications in catalysis. We have developed a surface geometric mismatch strategy by using mixed ligands of different type of hindrance. When bulky phosphine Ph3P and planar dipyridyl amine (Hdpa) are simultaneously used, steric repulsion between the ligands will reduce the ligand coverage of gold clusters. A well‐defined access granted gold nanocluster [Au23(Ph3P)10(dpa)2Cl](SO3CF3)2 (Au23, dpa=dipyridylamido) has been successfully synthesized. Single crystal structural determination reveals that Au23 has eight uncoordinated gold atoms in the shape of a distorted bicapped triangular prism. The accessibility of the exposed Au atoms has been confirmed quantitatively by luminescent titration with 2‐naphthalenethiol. This cluster has excellent performance toward selective oxidation of benzyl alcohol to benzaldehyde and demonstrates excellent stability due to the protection of negatively charged multidentate ligand dpa. [ABSTRACT FROM AUTHOR]

Two homoleptic alkynyl‐protected gold clusters with compositions of Na[Au25(C≡CAr)18] and (Ph4P)[Au25(C≡CAr)18] (Na⋅1 and Ph4P⋅1, Ar=3,5‐bis(trifluoromethyl)phenyl) were synthesized via a direct reduction method. 1 is a magic cluster analogous to [Au25(SR)18]− in terms of electron counts and metal‐to‐ligand ratio. Single‐crystal structure analysis reveals that 1 has an identical Au13 kernel to [Au25(SR)18]−, but adopts a distinctly different arrangement of the six peripheral dimer staple motifs. The steric hindrance of alkynyl ligands is responsible for the D3 arrangement of Au25. The introduction of alkynyl also significantly changes the optical absorption features of the nanocluster as supported by DFT calculations. This magic cluster confirms that there is a similar but quite different parallel alkynyl‐protected metal cluster universe in comparison to the thiolated one. Magic clusters Na[Au25(C≡CAr)18] and (Ph4P)[Au25(C≡CAr)18] (Ar=3,5‐bis(trifluoromethyl)phenyl) exhibit novel connection between staples and the Au13 core. Steric hindrance caused by rigid ligand coordination preference accounts for the different geometric and electronic structures. [ABSTRACT FROM AUTHOR]

An intensely luminescent gold(I)-silver(I) cluster [(C)(AuPPhpy2)6Ag6(CF3CO2)3](BF4)5 (PPhpy2=bis(2-pyridyl)phenylphosphine) ( 3) is synthesized by the reaction of [(C)(AuPPhpy2)6Ag4](BF4)6 with AgCF3CO2. All eight faces of the octahedral C@Au6 core in 3 are capped, that is, six faces are capped by silver ions and two by tetrafluoroborates. Cluster 3 is intensely luminescent in solution with a quantum yield of 92 %. Ligation of CF3CO2− ions is vital for the construction and emission properties of 3, as confirmed by DFT calculations. BF4− ions are involved in the protecting sphere of the metal core, as evidenced by 19F NMR data. The participation of phosphines, CF3CO2−, and BF4− ions in the protection of the emissive core and the enhancement of the rigidity of the cluster result in the high emission efficiency. This is the first example of organic ligands and inorganic anions forming a rigid protecting sphere for luminescent coinage-metal clusters. [ABSTRACT FROM AUTHOR]

A gold(i)–silver(i) cluster bearing six carboxylate groups has been synthesized through the oxidation of its aldehyde precursor and the Au6 core of this cluster displays an octahedral or a trigonal prismatic configuration depending on the crystallization conditions. The reversible interconversion between these two isomers can be triggered in the solid state by the addition or removal of acetonitrile solvent molecules. Interestingly, luminescence changes were observed as each configuration shows different emission colors, yellow for octahedral type and red for the trigonal prismatic one. [ABSTRACT FROM AUTHOR]