Arylation of gold nanoclusters and insights into structure-related CO₂ reduction reaction performances

Abstract

Research on arylgold complexes and ligand-protected gold nanoclusters has proceeded independently thus far due to the difficulty in controllably introducing aryl groups to synthesize arylgold nanoclusters. Herein we synthesized an arylgold Au₁₅ nanocluster, Au₁₅(DPPOE)₃(S-Ph^pMe)₄(Ph)₂, thereby bridging the two independent research fields. Tetraarylborates were exploited as arylating agents to transfer aryl groups onto the nanocluster kernel, triggering the arylation of the Au₁₅ cluster while maintaining the molecular framework. Furthermore, two other arylgold Au₁₅ nanoclusters with halogenated surfaces were controllably synthesized by substituting the arylating agent NaBPh₄ with its benzene ring-halide derivatives. In addition, the change in the electronic structure from Au-SR to Au-aryl and the energetics of the arylation process from Au₁₅-SR to Au₁₅-Ph were elucidated computationally. Furthermore, the catalytic capability of the two Au₁₅ nanoclusters with nuanced ligand differences was investigated in the electrochemical reduction of CO₂, and the comparable reactivity of the two cluster-based nanocatalysts was theoretically rationalized. Our findings have cross-fertilized the fields of arylgold complexes and gold nanoclusters, pointing toward a new avenue of exploration for novel arylgold nanoclusters.

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1 Introduction

Gold nanoclusters have received extensive attention due to their consistently monodisperse sizes and accurately characterized structures.^1–6 These ultrasmall gold nanoparticles exhibit strong quantum-confinement effects and discrete electronic energy levels, which are manifested in their structure-dependent physicochemical properties.^7–16 Structurally, gold nanoclusters consist of metallic kernels containing “free electrons” that are protected by motif surfaces that include “peripheral ligands”.^17–20 Among them, the peripheral ligands play a significant role in directing the surface chemistry of metal nanoclusters, which further determines their intracluster structures, intercluster interactions, and physicochemical properties.^21–25 To date, several types of peripheral ligands have been employed to stabilize gold nanoclusters, including thiolate,^26–28 phosphine,^29–31 halogens,^32–34 alkynyl,^35–37 carbene,^38–40 and pyridine.^41,42 Due to the diverse binding capacities and coordination modes between different peripheral ligands and gold atoms, ligand engineering, as well as ligand exchange, has served as a versatile approach for regulating the electronic/geometric structures of gold nanoclusters.^43,44

The construction of gold nanoclusters is always associated with the reduction of their Au^I complexes; for example, the relationships between Au^I-PPh₃ complexes and phosphine-stabilized clusters,^45,46 Au_x^I(SR)_y complexes and thiolate-stabilized clusters,^47,48 Au_x^I(C≡R)_y complexes and alkynyl-stabilized clusters,⁴⁹ etc. The chemistry of arylgold has been developed for more than half a century to anchor arene groups onto gold atoms, giving rise to arylgold complexes with widespread applications in catalysis and emitting devices.^50–54 However, little has been achieved in constructing arylgold complex-related arylgold nanoclusters that contain Au⁰ kernels and free electrons. To our knowledge, there is only one case of arylgold nanoclusters being achieved through ligand exchange with a maintained template—the neutral Au₁₀(C₆F₅)₄(PPh₃)₅, prepared by reacting Au₉(PPh₃)₈ with arylgold Au(C₆F₅)₂ complexes, and the phenyl-stabilized Au₄₄ was synthesized directly via a one-pot reducing procedure.^55,56 The attainment of arylated gold nanoclusters with atomic precision is highly desirable to expand their research scope and allow the fabrication of new cluster members with novel structures, compositions and performances. One idea is to leverage the knowledge and chemistry of arylgold complexes. Indeed, tetraarylborates or their derivatives have been extensively exploited for the construction of arylgold complexes (or other arylmetal complexes) via C–B bond cleavage followed by aryl-gold bond formation;^57–59 however, whether such an arylation strategy works for arylgold nanoclusters remains unexplored.

In this work, we report the arylation of gold nanoclusters (Scheme 1). The starting [Au₁₅(DPPOE)₃(S-Ph^pMe)₆]⁺ nanocluster [Au₁₅-SR for short; DPPOE = bis(2-diphenylphosphinophenyl)ether] has two weak surface Au-SPh^pMe bonds. The introduction of NaBPh₄ into the solution of Au₁₅-SR results in the cleavage of C–B bonds of [BPh₄]⁻, triggered by cluster catalysis. The dissociated phenyl groups attack the two weak Au–S bonds on Au₁₅-SR and displace the corresponding two S-Ph^pMe groups from the cluster surface, leading to the generation of an arylgold [Au₁₅(DPPOE)₃(S-Ph^pMe)₄(Ph)₂]⁺ nanocluster (Au₁₅-Ph for short). We further show that this approach can also be used to synthesize arylgold cluster derivatives, [Au₁₅(DPPOE)₃(S-Ph^pMe)₄(Ph-F)₂]⁺ and [Au₁₅(DPPOE)₃(S-Ph^pMe)₄(Ph-Cl)₂]⁺ (Au₁₅-Ph-F and Au₁₅-Ph-Cl for shorts, respectively). In addition, we employ computational chemistry to understand the driving force behind the ligand displacement reaction on the cluster surface from Au-SR to Au-aryl. Besides, the catalytic performances of the two Au₁₅ cluster-based nanocatalysts in the CO₂ reduction reaction were investigated experimentally and theoretically. Overall, the findings of this work provide impetus for future experimental and theoretical developments in arylgold nanoclusters.

Scheme 1 Illustration of the arylation of gold nanoclusters. The Au₁₅(DPPOE)₃(SR)₆ cluster precursor undergoes arylation to produce the arylgold Au₁₅(DPPOE)₃(SR)₄(Ph)₂ nanocluster in the presence of [BPh₄]⁻.

2 Results and discussion

The Au₁₅-SR nanocluster was prepared by a one-pot synthetic procedure via reducing the Au-SR-DPPOE complexes with NaBH₄ (see the ESI for more details; Fig. S1†). Despite several attempts, the crystallization and structural determination of the Au₁₅-SR nanocluster were unsuccessful due to its instability, which was evaluated by monitoring its optical absorption as a function of time at room temperature. As shown in Fig. S2,† the characteristic UV-vis absorptions of Au₁₅-SR gradually decreased in intensity after three hours and completely disappeared within 24 hours, indicating degradation. With the help of electrospray ionization-mass spectrometry (ESI-MS) and thermogravimetric analysis (TGA), we determined the chemical formula of the nanocluster to be [Au₁₅(DPPOE)₃(S-Ph^pMe)₆]⁺ (Fig. S3 and S4†). To further confirm the valence state of Au₁₅-SR, we performed ESI-MS with the addition of Cs⁺ cations. The mass results were consistent with those obtained without Cs⁺, further confirming the chemical formula of the Au₁₅-SR nanocluster as [Au₁₅(DPPOE)₃(S-Ph^pMe)₆]⁺ (Fig. S5†).

Inspired by the arylation of tetraarylborates in constructing arylgold complexes, we attempted to anchor the aryl groups onto the Au₁₅-SR surface to substitute them for the two detachable thiolate ligands. As shown in Fig. 1A, NaBPh₄ was used as the arylating agent to stabilize the Au₁₅ cluster framework (see more synthetic details in the ESI†). The ESI-MS results suggested the transformation of the nanocluster from Au₁₅-SR to Au₁₅-Ph as well as the substitution of the two detachable thiolate ligands with phenyl groups on the nanocluster surface (Fig. 1B and S6†), demonstrating the successful arylation of the Au₁₅ nanocluster. Of note, in the only one reported case of the arylgold nanocluster, Au₁₀(C₆F₅)₄(PPh₃)₅, the arylation was achieved by introducing arylgold complexes into the nanocluster precursor, which altered the cluster framework. By comparison, we herein accomplished the template-maintained arylation of gold nanoclusters through a simple ligand-exchange-triggered arylation approach.

Fig. 1 Arylation of the gold nanocluster. (A) Scheme illustrating the arylation of the Au₁₅-SR precursor to produce the arylgold Au₁₅-Ph nanocluster in the presence of [BPh₄]⁻. Accompanying the cluster arylation, two thiolate ligands of Au₁₅-SR were detached, and two aryl ligands were anchored onto the cluster surface. Color labels: orange/green = Au; yellow/red = S; magenta = P; green = O; grey = C; pink = C of the detachable thiolate ligands; cerulean = C of the aryl ligands. Some C and H atoms are omitted for clarity. (B) ESI-MS results of the Au₁₅-SR precursor and the arylgold Au₁₅-Ph nanocluster in the presence of NaBPh₄. The stray mass signals at ∼3000 Da stemmed from the introduction of [BPh₄]⁻, which were absent in the mass spectrum of the Au₁₅-Ph cluster (Fig. S6†). (C) Time-dependent optical absorption spectra of the transformation from Au₁₅-SR to Au₁₅-Ph.

The optical absorptions of the Au₁₅-SR and Au₁₅-Ph nanoclusters were compared. An intense optical absorption peak for Au₁₅-SR was detected at 355 nm (Fig. 1C). Following the cluster arylation, the 355 nm signal remained unchanged, and a characteristic band appeared at 410 nm. Optical absorption was also observed for the crystal of Au₁₅-Ph with a similar peak intensity, demonstrating the high conversion efficiency of the cluster arylation. More importantly, the arylgold Au₁₅-Ph displayed a robust cluster template that enabled crystallization (Fig. S7†), and the atomically precise structure of this arylgold nanocluster could be determined. Additionally, the stability of Au₁₅-Ph in O₂, at various temperatures, and in different solvents was tested. The nanocluster exhibited good stability in the presence of oxygen and in different solvents. However, the nanocluster decomposed gradually when the temperature exceeded 70 °C (Fig. S8†). Besides, the cyclic voltammetry tests of Au₁₅-SR and Au₁₅-Ph nanoclusters demonstrated that the energy gap between the first oxidation peak and the first reduction peak increased upon arylation of the gold nanocluster (Fig. S9†), which was consistent with the trend observed for the calculated HOMO–LUMO gap of the two nanoclusters (discussed below).

Structurally, the Au₁₅-Ph nanocluster contained an icosahedral Au₁₃ kernel (Fig. 2A), which was enwrapped by three bidentate DPPOE ligands and two dimeric Au₁(SR)₂ motif structures via Au–P and Au–S interactions, respectively, giving rise to an Au₁₅(DPPOE)₃(SR)₄ structure (Fig. 2B–D). In this context, of the 12 surface Au atoms on this Au₁₃ kernel, six Au atoms and four Au atoms were capped by phosphine and thiol ligands, respectively, while two Au atoms remained bare on Au₁₅(DPPOE)₃(SR)₄ (Fig. 2D). Two aryl ligands, originating from the arylating agent NaBPh₄, further stabilized the remaining two bare Au atoms, completing the overall structure of the arylgold Au₁₅-Ph nanocluster (Fig. 2E–G). Considering their similar optical absorptions, we propose that the Au₁₅-SR and Au₁₅-Ph nanoclusters exhibited the same cluster framework; accordingly, the two detachable thiolate ligands of Au₁₅-SR should also anchor onto its Au₁₃ kernel independently, and their dissociation would expose the cluster kernel directly to the external environment, leading to the instability of the nanocluster. In contrast, the aryl ligands adhered onto the Au₁₅-Ph cluster surface firmly with the assistance of several intracluster C–H⋯π interactions (Fig. 2H). Specifically, three types of C–H⋯π interactions were detected, including (i) the type I interaction between C–H from aryl ligands and π from phosphine ligands (Fig. 2I), (ii) the type II interaction between C–H from thiol ligands and π from aryl ligands, and (iii) the type III interaction between C–H from aryl ligands and π from thiol ligands (Fig. 2J). Collectively, each aryl ligand was locked by a combination of adjacent DPPOE and Au₁(SR)₂ ligands via multiple C–H⋯π interactions, realizing the high robustness of the Au₁₅-Ph framework. In addition, we compared the bond lengths of the standard Au₁₃ nanocluster with those of Au₁₅-Ph and found that the Au₁₃ kernel was more tightly arranged than that of Au₁₅-Ph (Table S4†).

Fig. 2 Structural anatomy of the arylgold Au₁₅-Ph nanocluster. (A) The innermost icosahedral Au₁₃ kernel. (B) The bidentate DPPOE cap. (C) The dimeric Au₁(SR)₂ motif. (D) The Au₁₅(DPPOE)₃(SR)₄ structure. (E) The aryl ligand. (F and G) The overall structure of the Au₁₅-Ph nanocluster. (H–J) The intracluster C–H⋯π interactions stabilizing the aryl ligands on the nanocluster surface. The interactions are highlighted in colors corresponding to the π-donating groups. Color labels: orange/green = Au; yellow = S; magenta = P; green = O; grey = C; cerulean = C of the aryl ligands; pale magenta = C of the phosphine ligands; pale yellow = C of the thiol ligands; white = H. Some C and H atoms are omitted for clarity.

We further expanded the cluster system of arylgold Au₁₅ by substituting the arylating agent [BPh₄]⁻ with its benzene ring-halide derivatives—[B(Ph-F)₄]⁻ and [B(Ph-Cl)₄]⁻. As shown in Fig. S10 and S11,† the ESI-MS and UV-vis results demonstrated the successful arylation of Au₁₅-SR and the generation of [Au₁₅(DPPOE)₃(S-Ph^pMe)₄(Ph-F)₂]⁺ and [Au₁₅(DPPOE)₃(S-Ph^pMe)₄(Ph-Cl)₂]⁺ (Au₁₅-Ph-F and Au₁₅-Ph-Cl for short, respectively). All three arylgold Au₁₅ nanoclusters exhibited the same molecular composition, [Au₁₅(DPPOE)₃(S-Ph^pMe)₄(Ph-X)₂]⁺ (X = H, F, or Cl), suggesting their closed-shell electronic structures with a nominal electron count of eight (i.e., 15 (Au) − 4 (SR) − 2 (Ph-X) − 1 (charge) = 8), tallying with the icosahedral unit in the cluster framework. Besides, the X-ray photoelectron spectroscopy (XPS) results showed that the binding energies of Au_4f in the three arylgold nanoclusters showed remarkable blue-shifts relative to Au₁₅-SR. (Fig. S12†). The stability of these Au₁₅ nanoclusters bearing different aryl groups was analyzed, and both Au₁₅-Ph-F and Au₁₅-Ph-Cl exhibited excellent stability over 24 hours (Fig. S13†). Structurally, the Au₁₅-Ph-F and Au₁₅-Ph-Cl clusters displayed analogous geometric structures and intramolecular interactions to their initial arylgold Au₁₅-Ph nanocluster (Fig. S14 and S15†); however, due to the substituent effects on the aryl ligands, the three clusters expressed slight differences in terms of their atomic packing and bond lengths. Specifically, the icosahedral Au₁₃ kernels of the three nanoclusters were similar, considering their analogous average lengths of Au(icosahedral core)–Au(icosahedral core) and Au(icosahedral core)–Au(icosahedral surface) bonds (Fig. S16†). However, for the kernel–shell interactions of the cluster framework, a closer interaction was detected for both Au₁₅-Ph-F and Au₁₅-Ph-Cl relative to the Au₁₅-Ph nanocluster due to the shortened bond lengths between Au atoms on the icosahedral surface and S/P/C atoms from peripheral ligands (Fig. S17 and S18†). In this context, the substituent group (i.e., F or Cl) increased the electron-withdrawing capability of the aryl ligand and strengthened the interactions between gold kernels of nanoclusters and peripheral ligands. Besides, the substituent effects also influenced the crystalline packing of these arylgold nanoclusters (Fig. S19†)—although all three cluster entities were crystallized in a triclinic crystal system with a P1̄ space group, they exhibited different crystalline parameters, including cell lengths, cell angles, crystal densities, etc.

For the preparation of arylgold complexes (or other arylmetal complexes), tetraarylborates were extensively exploited as arylating agents to deliver aromatic groups via C–B bond cleavage. For the arylation process from Au₁₅-SR to Au₁₅-Ph, the initiation reaction should be the C–B bond cleavage of [BPh₄]⁻ catalyzed by the nanocluster, the same as the reaction between gold complexes and borate species (Fig. S20†).^60,61 Indeed, the nuclear magnetic resonance (NMR) and gas chromatography mass spectrometry (GC-MS) results identified BPh₃ and biphenyl as by-products of the nanocluster arylation, which were considered as fragment products from the C–B bond cleavage of [BPh₄]⁻ (Fig. S21–S24†). Besides, the GC results also identified the presence of benzene in the by-product (Fig. S25†). Interestingly, the Au₁₅-SR nanocluster could catalyze the C–B bond cleavage of tetraarylborates, which further contributed to the nanocluster arylation. However, for the reported nanoclusters with similar thiol and DPPOE ligands, no C–B bond cleavage of the introduced [BPh₄]⁻ was observed (Fig. S26†).⁶² Indeed, the introduction of [BPh₄]⁻ in previous cluster research aimed at substituting small-sized counterions (e.g., Cl⁻) in positively charged nanoclusters for facilitating their crystallization. In this work, the two detachable thiolate ligands on Au₁₅-SR led to its instability, while, the partially exposed gold kernel might endow the cluster molecule with high catalytic capacity towards the C–B bond cleavage of tetraarylborates. In addition, the dissociated aryl group from [BPh₄]⁻ further activated the Au₁₅-SR molecule, triggering the complete dissociation of the two detachable thiolate ligands on the cluster surface by anchoring onto these two positions via Au–aryl interactions, giving rise to the final arylgold Au₁₅-Ph nanocluster (Fig. S20†). In this context, the arylation of this Au₁₅ cluster template could be accomplished. Of note, the Au–aryl interactions in Au₁₅-Ph were much more robust than the Au–S interactions at the two ligand-exchanging sites, and the anti-arylation from Au₁₅-Ph to Au₁₅-SR was not successful (Fig. S27†).

To understand the thermodynamic driving force of the arylation process from Au₁₅-SR to Au₁₅-Ph, we employed density functional theory (DFT) calculations to calculate the reaction energy of the arylation process (see the ESI† for more details). Modelling the complete arylation process required determining the speciation of the side products involving SR, which was challenging due to the high complexity of the reaction system. To simplify the process, we used the phenyl group and the thiolate group in their radical states; in other words, the reaction was a measure of the relative binding energy of Au₁₅-Ph versus Au₁₅-SR. The structure of the Au₁₅-Ph was taken from its crystal structure and the Au₁₅-SR cluster was built by substituting -SR for the two -Ph groups. Geometry optimizations were performed before calculating the reaction energy. For Au₁₅-Ph, the DFT optimized structure shows a small deviation (RMSD = 0.4 Å) compared to the crystal structure. The calculated reaction energy for the arylation process from Au₁₅-SR to Au₁₅-Ph was determined to be −33.85 kcal mol⁻¹, suggesting that the reaction [Au₁₅(DPPOE)₃(SR)₆]⁺ + 2Ph* → [Au₁₅(DPPOE)₃(SR)₄Ph₂]⁺ + 2SR* is very favorable; in other words, each Au-Ph bond was about 17 kcal mol⁻¹ more stable than the corresponding Au-SR bond. This finding corroborated our experimental strategy of using phenyl groups to displace the weekly bonded -SR groups on Au₁₅-SR. To understand the origin of the higher stability of Au₁₅-Ph vs. Au₁₅-SR, we analyzed the frontier orbitals of the two clusters. As can be seen from Fig. 3, the Au₁₅-Ph cluster has a slighter larger band gap and a lower HOMO level, indicating its higher stability. More importantly, although both clusters are eight-electron systems according to the superatomic complex model, their HOMO orbitals exhibit very different characteristics: the HOMO of Au₁₅-SR is dominated by the two weakly bound SR groups, while that of Au₁₅-Ph features a combination of the P-type superatomic orbital of the metal core and the -Ph ligands. In other words, the more covalent or conjugated interactions between Au₁₅ and the two -Ph ligands via the Au–C bonds stabilized the cluster, while the two -SR groups had weaker interactions with the valence electrons of the cluster core. The charge density difference plot of the Au₁₅-Ph cluster confirmed the strong charge accumulation between the Au and C atom centers due to the formation of the covalent Au–C bond (Fig. S28†).

Fig. 3 Frontier orbital analyses of nanoclusters. Orbital diagram and HOMO/LUMO orbitals of [Au₁₅(DPPOE)₃(SR)₆]⁺ (left) and [Au₁₅(DPPOE)₃(SR)₄(Ph)₂]⁺ nanoclusters (right).

Considering the nuanced differences in ligands between Au₁₅-SR and Au₁₅-Ph nanoclusters, we investigated their capability in electrochemically reducing CO₂ to CO (CO₂RR). The electrocatalytic CO₂RR was selected as the model reaction due to the outstanding efficiency of gold in this process and the promising prospects it offers for both fundamental and practical investigations.⁶³ The linear sweep voltammetry (LSV) results revealed that Au₁₅-SR displayed a higher current density and a lower onset potential than Au₁₅-Ph in CO₂-saturated aqueous 0.5 M KHCO₃ solution, indicating that the Au₁₅-Ph cluster-based catalyst showed lower CO₂RR efficiency relative to Au₁₅-SR (Fig. 4A). Then, we gathered the gas products produced by the CO₂RR process and analyzed them by gas chromatography (GC). Gas chromatography detected only H₂ and CO in gas products, demonstrating a total faradaic efficiency (FE) of approximately 100% for CO and H₂. As depicted in Fig. 4B, the potential-dependent FE for CO formation was analyzed for two Au₁₅ nanoclusters. Au₁₅-SR revealed a slightly higher selectivity for CO production, achieving the highest remarkable FE_CO over 96.2% at −0.7 V, compared to 92.9% for Au₁₅-Ph. In other words, Au₁₅-SR and Au₁₅-Ph nanoclusters generated CO across all potentials, but Au₁₅-SR exhibited slightly higher CO production than Au₁₅-Ph (Fig. 4B). In addition, the CO partial current density activity for both Au₁₅-SR and Au₁₅-Ph nanoclusters increased with growing overpotentials (Fig. 4C). Notably, Au₁₅-SR exhibited approximately a two-fold enhancement over Au₁₅-Ph at −0.8 or 0.7 V. The CO production efficiency of Au₁₅-SR was much higher than that of Au₁₅-Ph, showing a comparable turnover frequency (TOF) of the two nanoclusters (Fig. S29†). Additionally, electrochemical impedance spectroscopy (EIS) was performed on Au₁₅-SR and Au₁₅-Ph to access charge-transfer resistance, and the Au₁₅-SR nanocluster exhibited a remarkably smaller semi-circular arc, suggesting its faster electrode kinetics (Fig. 4D). We proposed that the homogeneity of the Au₁₅-SR cluster molecule resulted in smaller charge transfer resistance of the electrolyte and the catalyst, thereby making it easier for electrons to penetrate the catalyst. Furthermore, the electrocatalytic stability of Au₁₅-SR and Au₁₅-Ph was tested at −0.7 V, both showing high robustness over 8 hours (Fig. S30†), further evidenced by their maintained UV-vis, XPS, and transmission electron microscopy results (Fig. S31–S33†).

Fig. 4 Electrochemical performance of Au₁₅-SR and Au₁₅-Ph nanoclusters. (A) The LSV of Au₁₅-SR and Au₁₅-Ph nanoclusters. (B) The CO faradaic efficiency within the range of −1 to −0.6 V vs. the reversible hydrogen electrode (RHE). (C) The CO partial current density (j_co). (D) The EIS of Au₁₅-SR and Au₁₅-Ph nanoclusters.

DFT calculations were then carried out to understand the CO₂RR mechanism of Au₁₅-SR and Au₁₅-Ph nanoclusters. Following previous studies on the electrocatalysis of gold nanoclusters, the active Au site was created by dethiolating one -SR ligand from nanoclusters.^64,65 For Au₁₅-SR, dethiolating the independently anchored ligand was energetically more favorable by 0.76 eV compared to the staple motif ligands (Fig. S34†), leaving the top Au atom from the Au₁₃ kernel as the active site (Fig. 5A). By comparison, for Au₁₅-Ph, the active site was located on the undercoordinated Au atom from the staple motif after dethiolation (Fig. 5B). The Gibbs free energy profile in Fig. 5C shows that CO₂ reduction with Au₁₅-SR was thermodynamically more favorable due to the weaker adsorption of intermediates and the lower limiting potential of 0.43 eV, while the stronger adsorption of *CO with Au₁₅-Ph led to a higher limiting potential of 0.77 eV for CO desorption. The calculation results suggested that it is more favorable to form CO in Au₁₅-SR than in Au₁₅-Ph, in agreement with the experimental observations.

Fig. 5 DFT-optimized structures and the corresponding energetics of CO₂RR. (A) Optimized structures of *COOH and *CO intermediates for singly dethiolated [Au₁₅(DPPOE)₃(SR)₃(Ph)₂]⁺ and (B) singly dethiolated [Au₁₅(DPPOE)₃(SR)₅]⁺ nanoclusters. (C) Free energy profile of the CO₂RR on dethiolated [Au₁₅(DPPOE)₃(SR)₃(Ph)₂]⁺ (blue color) and [Au₁₅(DPPOE)₃(SR)₅]⁺ (red color) nanoclusters at 0 V vs. RHE.

3 Conclusions

In summary, the arylation of gold nanoclusters has been accomplished. The Au₁₅-SR nanocluster carried two detachable thiolate ligands on its surface, accounting for the instability of the cluster framework. On the positive side, the active surface environment of Au₁₅-SR endowed this nanocluster with high catalytic capacity towards the C–B bond cleavage of tetraarylborates. The subsequently generated dissociative aryl groups would activate the surface structure of Au₁₅-SR by anchoring aryl ligands onto the cluster kernel via Au-aryl interactions, giving rise to an arylgold Au₁₅-Ph nanocluster. Besides, two cluster derivatives of arylgold Au₁₅-Ph were developed by functionalizing the aryl ligands with halide substituents. In addition, DFT calculations confirmed the thermodynamic driving force underlying the arylation process from Au₁₅-SR to Au₁₅-Ph and rationalized the higher stability of the Au₁₅-Ph cluster by comparing its frontier orbitals with those of Au₁₅-SR. Furthermore, both Au₁₅ cluster-based nanocatalysts displayed comparable faradaic efficiency in CO₂RR, while Au₁₅-SR exhibited superior CO generation efficiency over Au₁₅-Ph, as derived from experimental results and rationalized by theoretical calculations. Overall, the findings in this work have significant implications for research in both metal nanoclusters and arylgold complexes, and we hope these observations will provide valuable insights for further studies of arylgold nanoclusters.

Data availability

The data that support the findings of this study are available in the ESI† of this article.

Author contributions

C. Zhu conceived and carried out the experiments. B. Li performed the theoretical simulations. C. Li, L. Lu, H. Li, and X. Yuan assisted in the synthesis and CO₂RR measurements. X. Kang, D.-e. Jiang, and M. Zhu supervised the project. All authors commented on and agreed to the manuscript.

Conflicts of interest

There are no conflicts to declare.

Acknowledgements

We acknowledge the financial support from the NSFC (22371003, 22101001, and 22471001), the Ministry of Education, Natural Science Foundation of Anhui Province (2408085Y006), the University Synergy Innovation Program of Anhui Province (GXXT-2020-053), and the Scientific Research Program of Universities in Anhui Province (2022AH030009). D.-e. Jiang acknowledges Vanderbilt University for support.

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Footnotes

† Electronic supplementary information (ESI) available: Fig. S1–S33 and Tables S1–S5. CCDC 2307548–2307550. For ESI and crystallographic data in CIF or other electronic format see DOI: https://doi.org/10.1039/d5sc01200g

‡ C. Z. and B. L. contributed equally to this work.

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