Helicene Quinones: Redox-Triggered Chiroptical Switching and Chiral Recognition of the Semiquinone Radical Anion Lithium Salt by Electron Nuclear Double Resonance Spectroscopy

详细信息    查看全文

• 作者：David Schweinfurth ; Michal Zalibera ; Michael Kathan ; Chengshuo Shen ; Marcella Mazzolini ; Nils Trapp ; Jeanne Crassous ; Georg Gescheidt ; Fran莽ois Diederich
• 刊名：Journal of the American Chemical Society
• 出版年：2014
• 出版时间：September 17, 2014
• 年：2014
• 卷：136
• 期：37
• 页码：13045-13052
• 全文大小：479K
• ISSN：1520-5126

文摘

We present the synthesis and characterization of enantiomerically pure [6]helicene o-quinones (P)-(+)-1 and (M)-(鈭?-1 and their application to chiroptical switching and chiral recognition. (P)-(+)-1 and (M)-(鈭?-1 each show a reversible one-electron reduction process in their cyclic voltammogram, which leads to the formation of the semiquinone radical anions (P)-(+)-1^{鈥⑩€?/sup> and (M)-(鈭?-1鈥⑩€?/sup>, respectively. Spectroelectrochemical ECD measurements give evidence of the reversible switching between the two redox states, which is associated with large differences of the Cotton effects [螖(螖蔚)] in the UV and visible regions. The reduction of (卤)-1 by lithium metal provides [Li+{(卤)-1鈥⑩€?/sup>}], which was studied by EPR and ENDOR spectroscopy to reveal substantial delocalization of the spin density over the helicene backbone. DFT calculations demonstrate that the lithium hyperfine coupling A(7Li) in [Li+{(卤)-1鈥⑩€?/sup>}] is very sensitive to the position of the lithium cation. On the basis of this observation, chiral recognition by ENDOR spectroscopy was achieved by complexation of [Li+{(P)-(+)-1鈥⑩€?/sup>}] and [Li+{(M)-(鈭?-1鈥⑩€?/sup>}] with an enantiomerically pure phosphine oxide ligand.}