| 研究実績の概要 |
N-heterocyclic carbenes (NHCs) have recently emerged as valuable alternatives to thiols or phosphines for the stabilization of metal surfaces, nanoparticles, and clusters. The neutral, electron-rich NHCs form a strong covalent bond with the metal, which is important in providing stability to metal nanoclusters.
Thus far we have been able to synthesize a series of chiral Au13 nanoclusters via the direct reduction of achiral dinuclear Au(I) halide complexes ligated by ortho-xylyl-linked bis-N-heterocyclic carbene (bisNHC) ligands. A broad range of functional groups are tolerated as wingtip substituents, allowing for the synthesis of a variety of functionalized chiral Au13 nanoclusters. We have used single-crystal X-ray crystallography to confirm the molecular formula to be [Au13(bisNHC)5Cl2]Cl3, with a chiral helical arrangement of the five bidentate NHC ligands around the icosahedral Au13 core. This Au13 nanocluster is highly luminescent, with a quantum yield of 23%. The two enantiomers of the Au13 clusters can be separated by chiral HPLC, and the isolated enantiomers characterized by circular dichroism spectroscopy. The clusters synthesized by us show remarkable stability, including configurational stability, opening the door to further investigation of the effect of chirality on these clusters. Our preliminary results showed that this bisNHC Au13 nanocluster is friendly to cells and can be used for the cell imaging.
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| 今後の研究の推進方策 |
In the next FY, we will use the above Au13 nanoclusters protected by bisNHC carbine to test their catalytic activity in the direct C-H functionalization of alkylamines under visible light conditions. Both TON and TOF will be used to compare the catalytic reactivity of synthesized Au clusters. Under the photocatalytic system, highly reactive oxygen species may be formed by the interaction between NHC modified Au nanoclusters and O2, which can be also used for the oxidative radical coupling of Csp3C-H compounds in the photocatalytic system. Besides, we will also use this type of bisNHC-modified chiral Au clusters in asymmetric catalysis. The direct reduction of ketones and kinetic resolution of alcohols will be chosen as the reactions. Due to the high quantum yield of [Au13(bisNHC)5Cl2]Cl3, we will apply this type of bis-NHC Au13 nanocluster in cell imaging, which will be of great importance in biology.
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