Synthesis, Characterization, and Solid-State Structure of [8]Cycloparaphenylenes with Inherent Chirality

We report here the synthesis of two [8]cycloparaphenylenes ([8]CPP) derivatives, 1 and 2, bearing a monosubstituted benzene moiety. The presence of the substituent implies a planar chirality for the monosubstituted [8]CPP 1 and 2, whose configuration is here described by applying the chirality descriptors pR and pS. Experimental evidence of this planar chirality has been obtained through ¹H VT NMR studies and by addition of Pirkle's reagent. This was confirmed by the X-ray crystal structure of 2, which represents an interesting example of solid-state structure of a monosubstituted [8]CPP derivative. Derivative 2 crystallizes in two monoclinic crystal forms (α and β), which show a herringbone motif. The [8]CPP ring of the α form encapsulates two dichloromethane molecules, held through C-H···π interactions, while in the β form, open channels are partially filled by highly disordered solvent molecules.