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Chiral–Achiral Ligand Synergy in Enhancing the Chiroptical Activity of Diphosphine-Protected Au13 Clusters

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journal contribution
posted on 19.11.2020, 08:29 by Yasuhiko Sato, Masaki Mitani, Hiroshi Yao
We report chiroptical activity in Au13 clusters protected by binary mixed ligands of chiral and achiral diphosphines. S,S-DIOP is used as the chiral diphosphine, and the achiral diphosphine is Xantphos, Dppe, or Dppbz, where S,S-DIOP, Xantphos, Dppe, and Dppbz stand for (4S,5S)-4,5-bis­(diphenylphosphinomethyl)-2,2-dimethyl-1,3-dioxolane, 4,5-bis­(diphenylphosphino)-9,9-dimethylxanthene, 1,2-bis­(diphenylphosphino)­ethane, and 1,2-bis­(diphenylphosphino)­benzene, respectively. The initial feed molar ratio of chiral/achiral ligands is 1/0, 3/1, or 1/1 in the synthesis. Remarkably, the Au13 cluster synthesized at S,S-DIOP/Xantphos = 3/1 ratio exhibits high chiroptical activity or anisotropy factor than that protected by pure S,S-DIOP in a core-based transition region (≤∼4 eV). To account for this chiral–achiral ligand synergy effect, quantum chemical calculations and geometrical quantifications based on the Hausdorff chirality measure (HCM) are performed for model Au13 clusters, giving strong suggestions that the observed chiroptical enhancement can be due both to the effect of limited isomer configurations and larger HCM values compared to that of the Au13 cluster passivated by pure chiral diphosphine. We believe that the present cluster system with chiral–achiral ligand synergy will be a fascinating model for further understanding the cluster structure–chiroptical activity relationships.