Influence of Amide Connectivity on the Hydrogen‐Bond‐Directed Self‐Assembly of [n.n]Paracyclophanes.

Reported here is the synthesis and self‐assembly characterization of [n.n]paracyclophanes ([n.n]pCps, n=2, 3) equipped with anilide hydrogen bonding units. These molecules differ from previous self‐assembling [n.n]paracyclophanes ([n.n]pCps) in the connectivity of their amide hydrogen bonding units (C‐centered/carboxamide vs. N‐centered/anilide). This subtle change results in a ≈30‐fold increase in the elongation constant for the [2.2]pCp‐4,7,12,15‐tetraanilide ([2.2]pCpNTA) compared to previously reported [2.2]pCp‐4,7,12,15‐tetracarboxamide ([2.2]pCpTA), and a ≈300‐fold increase in the elongation constant for the [3.3]pCp‐5,8,14,17‐tetraanilide ([3.3]pCpNTA) compared to previously reported [3.3]pCp‐5,8,14,17‐tetracarboxamide ([3.3]pCpTA). The [n.n]pCpNTA monomers also represent the reversal of a previously reported trend in solution‐phase assembly strength when comparing [2.2]pCpTA and [3.3]pCpTA monomers. The origins of the assembly differences are geometric changes in the association between [n.n]pCpNTA monomers—revealed by computations and X‐ray crystallography—resulting in a more favorable slipped stacking of the intermolecular π‐surfaces ([n.n]pCpNTA vs. [n.n]pCpTA), and a more complementary H‐bonding geometry ([3.3]pCpNTA vs. [2.2]pCpNTA). [ABSTRACT FROM AUTHOR]