Tuning the Magic Sizes and Optical Properties of Atomically Precise Bidentate N‐Heterocyclic Carbene‐Protected Gold Nanoclusters via Subtle Change of N‐Substituents

Abstract

Owing to the atomically precise structures, metal nanoclusters (NCs) have always served as model molecular tools to analyze NC surface chemistry and to investigate structure−property correlations. Herein, a series of bis‐N‐heterocyclic carbene (NHC)‐protected NCs of type [Au11(bis‐NHC)5]3+ and [Au13(bis‐NHC)5Br2]3+ obtained from direct reduction of Au−bis‐NHC complexes are described. The NCs type obtained depends on the N‐wingtip substituents of the Au−bis‐NHC complexes. Subtle changes in the lengths of the N‐wingtip substituents enable the fine‐tuning of the kernel with either Au11 or Au13 clusters. Among them, [Au11(bis‐NHC)5]3+ cluster is the first homoleptic NHC‐stabilized Au NC. The composition and structures of these NCs are unequivocally determined by single crystal X‐ray crystallography and electrospray ionization mass spectrometry. Contrary to the non‐emissive Au11 cluster, the Au13 NC exhibits high emission in solution and the luminescence properties are severely dependent onto the substituent effects. Additionally, peculiar Au⋯HC interactions are present in NHC‐protected clusters.

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

“…Ligand-protected metal nanoclusters have emerged as an important class of nanomaterials with applications in bioimaging, optoelectronics, , and electrocatalysis. , Their atomically precise nature provides detailed insight into size–property relationships and an in-depth description of the bonding interaction between ligands and their metal core. , While thiol, , phosphine, and alkynyl-protected clusters have been widely explored, N-heterocyclic carbenes (NHCs) have been much less explored. , NHC-protected nanoclusters with metal core sizes Au 6 , Au 11 , Au 13 , and Au 25 have been reported, − and larger clusters were isolated by employing NHCs in combination with alkynyl (Au 23 ) and thiolate (Au 44 ) ligands. , NHC-protected clusters have been prepared with high stability and the ability to reduce CO 2 electrocatalytically …”

Synthesis and Characterization of Enantiopure Chiral Bis NHC-Stabilized Edge-Shared Au10 Nanocluster with Unique Prolate Shape

“…11 In 2019, our group reported the use of NHCs to protect gold nanoclusters, resulting in the first NHCstabilized Au 11 12 and Au 13 13 nanoclusters. Later, the groups of Han, Zang, Mak, Tsukuda, and Zheng described successful syntheses of NHC-protected Au 11 , 14 Au 13 , 15 Au 23 , 16 Au 25 , 17 and Au 44 18 nanoclusters, illustrating the potential of NHCs as stabilizing ligands for gold nanoclusters.…”

N-Heterocyclic Carbene-Stabilized Gold Nanoclusters with Organometallic Motifs for Promoting Catalysis

“…Together with the well-defined structures that can be determined by X-ray crystallography, the presence of both organic ligands and metal–metal bonds makes ligand-protected atomically precise metal nanoclusters (NCs) an ideal model catalyst system to bridge the gap between organometallic catalysts and metal nanocatalysts. − For example, the surface coordination structures of ligands, e.g., phosphine, thiolate, alkynyl, and N-heterocyclic carbene (NHC), on metal NCs have now been well demonstrated. ,, Moreover, the molecular understanding of their catalytic mechanism is expected to provide insights on how surface ligands and metal–metal interactions interplay together to determine the catalytic performance of metal catalysts. − Among them, the recently emerging Au NCs protected by NHCs are expected to serve as an ideal candidate for catalytic mechanism investigations due to their outstanding stability but possible presence of exposure metal sites. − On the other hand, homogeneous gold catalysts with NHC-Au-X structures have been widely applied in chemical transformations, including, but not limited to, the activation and transformation of alkynes, alkenes, and allenes . While the NHC ligands prevent the complex decomposition, and control electronic and steric effects for modulating catalysis, the anionic (X) ligands help balance the charge and often get involved in catalytic cycles by ligand exchange with substrates .…”