Asymmetric Twisting of C-Centered Octahedral Gold(I) Clusters by Chiral N-Heterocyclic Carbene Ligation

Abstract

Asymmetric induction of metal clusters by ligation of chiral ligands is intriguing in terms of the mechanism of chirality transfer and the stability of the resulting chiral structure. Here we report the asymmetric induction of C-centered hexagold(I) CAu I 6 clusters into an asymmetrically twisted structure through monodentate, chiral benzimidazolylidene-based N-heterocyclic carbene (NHC) ligands. X-ray diffraction analysis revealed that the NHC-ligated CAu I 6 cluster was diastereoselectively twisted with directionally selective, bond length expansion, and contraction of the Au•••Au contacts and that the original cluster with high symmetry was transformed into an optically pure, asymmetric CAu I 6 cluster with C 1 symmetry. Moreover, the circular dichroism spectroscopy and the time-dependent density functional theory calculation confirmed that the asymmetrically twisted CAu I 6 structure was maintained even in solution. Such asymmetric induction of configurationally stable metal clusters would greatly expand the molecular design possibilities of asymmetric catalysts and chiroptical materials by utilizing library chiral NHC ligands.

Achiral-Core-Metal Change in Isomorphic Enantiomeric Ag12Ag32 and Au12Ag32 Clusters Triggers Circularly Polarized Phosphorescence

“…SCXRD analysis demonstrates that R / S -Ag 12 Ag 32 and R / S -Au 12 Ag 32 crystallize in the chiral cubic space group P 432 (Tables S2 and S3), which is rarely observed among crystallized chiral clusters. − S -type S -Ag 12 Ag 32 and S -Au 12 Ag 32 as representatives are described in the following structural analysis. The inorganic framework of the S -Ag 12 Ag 32 cluster can be described as a concentric three-layer core-shell structure S 2– @Ag 12 @S 8 @Ag 32 with S 2– as the anion template, similar to a Russian nesting doll (Figure a).…”

“…So far, the enantiopure clusters all protected by homochiral thiolate ligands have been scarce. At present, chiral P-based, CC-based, and NHC-stabilized ligands have been successfully used for preparing enantiopure metal clusters characterized by SCXRD. − However, because of the difficulty in synthesis, there are few chiral sulfur-based ligands for the synthesis of atomically precise metal clusters, although chiral sulfur ligands (GSH) are first used to prepare gold clusters …”

Synthesis of Pincer type carbene and their Ag(I)-NHC complexes, and their Antimicrobial activities

“…The XRD peaks at 2θ= 12.18, 12.84, 14.61 and 45.64 o can be observed in Figure 8b. This can also be due to the structured formation of NHCs [49].…”

Ligand-Induced Cuboctahedral versus Icosahedral Core Isomerism within Eight-Electron Heterocyclic-Carbene-Protected Gold Nanoclusters

“…It turns out that, within the framework of our general investigations on the stabilization of AuNCs by N-heterocyclic carbenes (NHCs), − we found that some NHCs can, in certain circumstances, stabilize cuboctahedral cluster cores, suggesting rational control of the core structure with respect to the nature of the ligand shell. NHCs have been recently introduced in AuNC chemistry as alternative neutral two-electron ligands of phosphines and appear to favor promising photoemissive properties. − This is why we recently investigated, by means of density functional theory (DFT) calculations (see the Supporting Information for Computational Details), hypothetical NHC analogues of the eight-electron phosphine/halogenide heteroleptic clusters [Au 13 (PR 3 ) n X 12– n ] ( n −7)+ (X = halogen). ,− Interestingly, our calculations show that, at least in the tetrabromide case, the cuboctahedral [Au 13 (NHC) 8 Br 4 ] + species can be stabilized, as described below.…”

“…Finally, because of the relevant photoluminescent properties reported for the experimentally characterized NHC-protected AuNC series − ascribed to a phosphorescent emission originating from the T 1 → S 0 decay, it is also interesting to see the difference in the phosphorescent emissions induced by core isomerization in the investigated [Au 13 ( i PrIm) 8 Br 4 ] + isomers. As for most of the known eight-electron superatoms , the T 1 states of both isomers can be viewed as the result of a HOMO (1P) → LUMO (1D) excitation (Figures S5 and S6).…”