The precise editing of surface sites on a molecular-like gold catalyst for modulating regioselectivity

Dual Catalysis of Gold Nanoclusters: Photocatalytic Cross-Dehydrogenative Coupling by Cooperation of Superatomic Core and Molecularly Modified Staples

Thiolate-protected gold nanoclusters (AuNCs) have attracted significant attention as nano-catalysts, revealing a superatomic core and gold-thiolate staples as distinct structural units. Here, we demonstrate the unprecedented dual catalytic activity of thiolate-protected [Au25 (SR)18 ]- nanoclusters, involving both photosensitized 1 O2 generation by the Au13 superatomic core and catalytic carbon-carbon bond formation facilitated by Au2 (SR)3 staples. This synergistic combination of two different catalytic units enables efficient cross-dehydrogenative coupling of terminal alkynes and tertiary aliphatic amines to afford propargylamines in high yields of up to 93 %. Mixed-ligand AuNCs bearing both thiolate and alkynyl ligands revealed the intermediacy of the alkynyl-exchanged AuNCs toward both photosensitization and C-C bond-forming catalytic cycles. Density functional theory calculations also supported the intermediacy of the alkynyl-exchanged AuNCs. Thus, the use of ligand-protected metal nanoclusters has enabled the development of an exceptional multifunctional catalyst, wherein distinct nanocluster components facilitate cooperative photo- and chemo-catalysis.

Recent Advances in Ligand Engineering for Gold Nanocluster Catalysis: Ligand Library, Ligand Effects and Strategies

Advances in new ligands in the last decade facilitated in-depth studies on the property-relationship of gold nanoclusters and promoted the rational synthesis and related applications of such materials. Currently, more and more new ligands are being explored; thus, the ligand library of AuNCs is being expanded fast, which also enables investigation of ligand effects of AuNCs via direct comparison of different ligating shell with the identical gold core. It is now widely accepted that ligands influence the properties of AuNCs enormously including stability, catalysis, photoluminescence among others. These studies inspired ligand engineering of AuNCs. One of the goals for ligand engineering is to develop ligated AuNC catalysts in which the ligands are able to exert big-enough influence on electronic and steric control over catalysis as in a transition-metal or an enzyme system. Although increasing attention is paid to the further expansion of ligand library, the investigation of design principles and strategies regarding ligands are still in their infant stage. This review summarizes the ligands for AuNC synthesis, the ligand effects on stability and catalysis, and recently developed strategies in promoting AuNC catalytic performance via ligand manipulation.

Size Effects of Atomically Precise Gold Nanoclusters in Catalysis

The emergence of ligand-protected, atomically precise gold nanoclusters (NCs) in recent years has attracted broad interest in catalysis due to their well-defined atomic structures and intriguing properties. Especially, the precise formulas of NCs provide an opportunity to study the size effects at the atomic level without complications by the polydispersity in conventional nanoparticles that obscures the relationship between the size/structure and properties. Herein, we summarize the catalytic size effects of atomically precise, thioate-protected gold NCs in the range of tens to hundreds of metal atoms. The catalytic reactions include electrochemical catalysis, photocatalysis, and thermocatalysis. With the precise sizes and structures, the fundamentals underlying the size effects are analyzed, such as the surface area, electronic properties, and active sites. In the catalytic reactions, one or more factors may exert catalytic effects simultaneously, hence leading to different catalytic-activity trends with the size change of NCs. The summary of literature work disentangles the underlying fundamental mechanisms and provides insights into the size effects. Future studies will lead to further understanding of the size effects and shed light on the catalytic active sites and ultimately promote catalyst design at the atomic level.

Effects of ligand tuning and core doping of atomically precise copper nanoclusters on CO2 electroreduction selectivity

Atomically precise nanoclusters (NCs) provide opportunities for correlating the structure and electrocatalytic properties at atomic level. Herein, we report the single-atom doping effect and ligand effect on CO₂ electroreduction (eCO₂RR) by comparing monogold-doped Au₁Cu₂₄ and homocopper Cu₂₅ NCs protected by triphenylphosphine or/and tris(4-fluorophenyl)phosphine. Catalytic results revealed that the electronic distribution of Cu₂₅ NCs is enormously contracted by doping Au atoms, entitling it to exhibit the unique inhibition of hydrogen evolution reaction. And the inductive effect of ligand strongly favors the formation of formate in eCO₂RR. Overall, this work will provide guidance for the rational design of the copper-based catalysts in the eCO₂RR.

Manipulating the organic-inorganic interface of atomically precise Au36(SR)24 catalysts for CO oxidation

Here, we report a series of atomically precise Au₃₆ nanoclusters protected by thiol ligands to explore the influence of organic-inorganic interfaces, that is, the local environment around heterogeneous catalysts, on catalytic oxidation of CO. Our studies give molecular-level insights into the relationship between the catalytic reactivity and the metal-ligand surface bonding, which tunes access to the active sites, thereby precisely tailoring the activity of the Au₃₆ catalysts for CO oxidation.

The ligand effect of atomically precise gold nanoclusters in tailoring catalytic properties

It is well known that surface ligands are vital layers for ligand-protected Au_n nanoclusters. Improving the knowledge of the relationship between ligands and catalytic properties is a forefront research topic for Au_n nanoclusters. Enormous effort has been devoted to realizing the ligand effect in synthesis, including well-controlled sizes and shapes as well as structural transformation. However, the crucial function of surface ligands has not been addressed yet in catalytic reactions. Here, this review mainly aims to summarize the recent progress concerning the influence of surface ligand layers on catalytic activity and selectivity, based on the various types of ligand protected Au_n nanoclusters. Besides, the potential challenges and opportunities of Au_n nanoclusters are indicated, mainly in terms of surface ligands to guide the improvement of catalytic performances.

On the photocatalysis evolution of heteroatom-doped Ag4M2 nanoclusters

Atomically precise metal nanoclusters doped with one or more heteroatom of other metals have exhibited extraordinary catalytic properties. Here we report a series of thiolate-protected Ag4M2 (M is dopant Ni, Pd and Pt) nanoclusters that adopt a similar structural framework like a distorted hexahedron, in which four Ag atoms are located at the midpoints of four side edges and two metal heteroatoms reside on the centres of the top and the bottom planes. The opposite orders of the catalytic performances of the three catalysts for the photocatalytic degradation of the methyl orange and rhodamine B dyes are found, which is attributed to two different types of inter-molecular recombination mechanisms. In both photocatalytic systems, both the catalyst and the dye are visible-light active, and the inter-molecular recombination of the photo-excited hole in the catalyst and the photo-excited electron in the dye leads to charge separation across the system comprising the catalyst and the dye. The study represents an important step towards developing the precise tailoring of the composition and structure to control the physicochemical properties of metal nanoclusters.

Distinct structure assembly driven by metal-ligand binding in Au23 nanoclusters and its relation to photocatalysis

Here, we introduce two Au₂₃ nanoclusters to unveil the significance of metal-ligand binding-induced assembly. The Au₂₃ cluster protected by the thiolate ligand is packed in the shell-by-shell arrangement, while the Au₂₃ cluster capped by dual ligands of thiolate and PPh₃ is constructed from the assembly of Au₄ tetrahedra. Furthermore Au₂₃ from Au₄ tetrahedron-based assembly is capable of converting absorbed visible light into more excitons, compared to Au₂₃ from shell-by-shell assembly, thus exhibiting more efficient photocatalysis.

Cd-driven surface reconstruction and photodynamics in gold nanoclusters

With atomically precise gold nanoclusters acting as a starting unit, substituting one or more gold atoms of the nanocluster with other metals has become an effective strategy to create metal synergy for improving catalytic performances and other properties. However, so far detailed insight into how to design the gold-based nanoclusters to optimize the synergy is still lacking, as atomic-level exchange between the surface-gold (or core-gold) and the incoming heteroatoms is quite challenging without changing other parts. Here we report a Cd-driven reconstruction of Au44(DMBT)28 (DMBT = 3,5-dimethylbenzenethiol), in which four Au2(DMBT)3 staples are precisely replaced by two Au5Cd2(DMBT)12 staples to form Au38Cd4(DMBT)30 with the face-centered cubic inner core retained. With the dual modifications of the surface and electronic structure, the Au38Cd4(DMBT)30 nanocluster exhibits distinct excitonic behaviors and superior photocatalytic performances compared to the parent Au44(DMBT)28 nanocluster.