Axially-Chiral Catenanes and π-Electron Deficient Receptors

The design of a new class of chiral [2]catenanes is reported. The self-assembly of [2]catenanes comprising one or two 3,3'-bitolyl spacers in the pi-electron-deficient component, and bis-p-phenylene-34-crown-10 (BPP34C10) as the pi-electron-rich component, is described. The X-ray crystal structures, together with solution-state dynamic H-1 NMR spectroscopic studies, show that the degree of order characterizing the molecular structures is substantially different from that of the ''parent'' [2]-catenane, comprising cyclobis(paraquat-p-phenylene) and BPP34C10. When appropriately substituted in their ortho positions, bitolyl compounds can support axial chirality: the self-assembly of axially chiral [2]catenanes, comprising one or two 3,3'-disubstituted-2,2'-dihydroxy-1,1'-binaphthyl spacers, has been achieved in good yields, showing that the introduction of the bulky, axially chiral spacer and the consequent distortion of the cavity of the pi-electron-deficient component still permits good molecular recognition between the components leading to efficient catenane production. X-ray crystallography suggests that this recognition is driven by hydrogen bonding and pi-pi stacking interactions between the complementary subunits. The hydroxyl groups on the chiral spacer were further functionalized as benzoyl esters in a [2]catenane as well as in the tetracationic cyclophanes; that is, chemistry can be done on these catenanes. The chiral tetracationic cyclophanes exhibit good enantiomeric differentiation toward the D- and L-enantiomers of aromatic amino acids in water and their N-acetylated derivatives in organic solvents.