N-Heterocyclic Carbene-Stabilized Hydrido Au₂₄ Nanoclusters: Synthesis, Structure, and Electrocatalytic Reduction of CO₂

Abstract

Atomically precise hydrido gold nanoclusters are extremely rare but interesting due to their potential applications in catalysis. By optimization of molecular precursors, we have prepared an unprecedented N-heterocyclic carbene-stabilized hydrido gold nanocluster, [Au 24 (NHC) 14 Cl 2 H 3 ] 3+ . This cluster comprises a dimer of two Au 12 kernels, each adopting an icosahedral shape with one missing vertex. The two kernels are joined through triangular faces, which are capped with a total of three hydrides. The hydrides are detected by electrospray ionization mass spectrometry and nuclear magnetic resonance spectroscopy, with density functional theory calculations supporting their position bridging the six uncoordinated gold sites. The reactivity of this Au 24 H 3 cluster in the electrocatalytic reduction of CO 2 is demonstrated and benchmarked against related catalysts.

Selective Semihydrogenation of Polarized Alkynes by a Gold Hydride Nanocluster

“…Three sets of new peaks were evident in the 1 H and 31 P NMR, which were assigned to the formation of mono- and diborohydride products [Au 11 (BH 4 )­Cl­(dppee) 4 ] + and [Au 11 (BH 4 ) 2 (dppee) 4 ] + , along with the gold hydride cluster, [Au 11 HCl­(dppee) 4 ] + (Figure g,h and Figures S29 and S30). A weak signal for the Au–H hydride was observed at 13.3 ppm in the 1 H NMR (Figure e), which was more upfield (shielded) than the chemical shifts for the previously reported gold hydrides ,− and in agreement with the hydridic nature of H – in [Au 11 HCl­(dppee) 4 ] + . The labile Cl – ligands are critical to the formation of the hydridic hydrogen in the [Au 11 HCl­(dppee) 4 ] + cluster.…”

“…28 The selective electrocatatalytic reduction of CO 2 to CO using an NHC-stabilized hydrido gold nanocluster, [Au 24 (NHC) 14 Cl 2 H 3 ] 3+ , has also been reported very recently. 29 Here, we report the discovery of a new undecagold hydride cluster, which has a hydridic hydrogen and can engage in selective semihydrogenation reactions with alkynes containing electron-withdrawing groups. We have synthesized and crystalized a new [Au 11 Cl 2 (dppee) 4 ] + nanocluster using the bidentate dppee ligand.…”

“…One of the major challenges in catalysis is to identify and control the active sites of the catalysts. − Atomically precise gold nanoclusters with well-defined structures have emerged as a new class of model catalysts that allow the identification of the active sites and help the elucidation of catalytic mechanisms. − However, precise control of the catalytic active sites for specific reactions, which underlies enzyme catalysis, is challenging to achieve synthetically. Especially for hydrogenation reactions catalyzed by gold-based nanomaterials, the identification of the active sites is often not possible because of the difficulties in capturing gold hydride intermediates. − Gold hydrides that feature a hydridic hydrogen (H – ) have been proposed as reactive intermediates in hydrogenation reactions involving gold-based nanomaterials; however, prior clusters have featured metallic hydrogens (H • ), − while the identification of hydridic hydrogen has been limited to mononuclear gold complexes. − …”

“…Further studies led to the isolation of two gold hydride clusters, [Au 22 H 4 (dppo) 6 ] 2+ and [Au 22 H 3 (dppee) 7 ] 3+ (dppee = bis­(2-diphenylphosphino)­ethylether), in which the H atoms are shown to bridge the uc Au sites between two Au 11 units. , Recently, a heteroleptic [Au 22 H 3 ] 3+ gold trihydride nanocluster has been synthesized and found to be an efficient and stable electrocatalyst for selective CO 2 -to-CO conversion . The selective electrocatatalytic reduction of CO 2 to CO using an NHC-stabilized hydrido gold nanocluster, [Au 24 (NHC) 14 Cl 2 H 3 ] 3+ , has also been reported very recently …”

Catalytic Conversion of CO2 over Atomically Precise Gold-Based Cluster Catalysts

“…It should be noted that the origin of the active sites of these Au clusters for CO 2 reduction remains fairly controversial, owing to the identification of the active sites based on the DFT calculations rather than the experimental evidence. Besides, several Au n clusters with novel structures have been also reported to show superior electrochemical activity for CO 2 conversion to the gold nanoparticles with large size. − …”