Chiral Carbon Nanorings: Synthesis, Properties and Hierarchical Self-assembly of Chiral Ternary Complexes Featuring a Narcissistic Chiral Self-Recognition for Chiral Amines

Abstract

We report the synthesis and chiroptical properties of novel chiral carbon nanorings Sp-/Rp-[12]PCPP containing a planar chiral [2.2]PCP unit, and demonstrate that Sp-/Rp-[12]PCPP can not only host crown ether 18-Crown-6 to form ring-in-ring complexes with a binding constant 3.35×103 M−1, but also accommodate the complexes of 18-Crown-6 and S/R-protonated amines to form homochiral S@Sp-/R@Rp- and heterochiral S@Rp-/R@Sp- ternary complexes, displaying significantly larger binding constants of up to 3.31×105 M−1 depending on the chiral guests. Importantly, homochiral S@Sp-/R@Rp- ternary complexes exhibit an enhanced CD signal, while the heterochiral S@Rp-/R@Sp- ones have a constant CD signal compared with the chiral carbon nanorings, respectively, which suggests that homochiral S@Sp-/R@Rp- ternary complexes display a highly narcissistic chiral self-recognition for S/R-protonated chiral amines, respectively. Finally, the chiral ternary complexes can be further applied to determine the ee values of chiral guests. The findings highlight a new application of carbon nanorings in supramolecular sensors, beyond the common recognition of π-conjugated molecules.