Homochiral [2.2]Paracyclophane Self‐Assembly Promoted by Transannular Hydrogen Bonding

Abstract

[2.2]paracyclophane (pCp), unlike many π-building blocks, has been virtually unexplored in supramolecular constructs. Reported here is the synthesis and characterization of the first pCp derivatives capable of programmed self-assembly into extended cofacial π-stacks in solution and the solid state. The design employs transannular (intramolecular) hydrogen bonds (H-bonds), hitherto unstudied in pCps, between pseudo-ortho-positioned amides of a pCp-4,7,12,15-tetracarboxamide (pCpTA) to preorganize the molecules for intermolecular H-bonding with π-stacked neighbors. X-ray crystallography confirms the formation of homochiral, one-dimensional pCpTA stacks helically laced with two H-bond strands. The chiral sense is dictated by the planar chirality (Rp or Sp ) of the pCpTA monomers. A combination of NMR, IR, and UV/Vis studies confirms the formation of the first supramolecular pCp polymers in solution.

Beyond Simple Substitution Patterns – Symmetrically Tetrasubstituted [2.2]Paracyclophanes as 3D Functional Materials

“…A fascinating approach to incorporate racemic homo tetrasubstituted PC into chiral functional materials was presented by Castellano and co‐workers in 2016 . They synthesized bis(ps‐ meta )‐ para substituted tetraamide 45 in which the amides allow for efficient intra‐ and intermolecular hydrogen bonding.…”

“…a) Unit cell containing each enantiomorphic asymmetric unit, b) side view of extended PC stacks, c) packing diagram showing different stacks from a top down view. Reproduced with permission from ref …”

“…[30,31] A fascinating approach to incorporate racemic homo tetrasubstituted PC into chiral functional materials was presented by Castellano and co-workers in 2016. [32] They synthesized bis-(ps-meta)-para substituted tetraamide 45 in which the amides allow for efficient intra-and intermolecular hydrogen bonding. The molecules form well-defined 1D columns, in which the racemic molecules are separated such that the monomers in a particular column have the same chirality (Scheme 13).…”

Molecular modelling of supramolecular one dimensional polymers

“…46,47 The orientation of functional groups, primarily in the linker moiety, can give rise to several low-lying geometries of the monomer, the existence of which can be obtained from crystallographic studies. [48][49][50] Superstructures formed by 1-d supramolecular polymers are to a large extent, bers. These bers show dynamic selfassembly and dis-assembly in response to change in environment, which are the advantages of supramolecular polymers over the traditional ones.…”

“…These bers show dynamic selfassembly and dis-assembly in response to change in environment, which are the advantages of supramolecular polymers over the traditional ones. Thus, in this review, we focus on modelling studies of one dimensional polymers, 48,[51][52][53][54][55] a topic which has been reviewed recently by Bochicchio and Pavan recently. 55 The experimental interest in these materials is from optoelectronic applications point of view.…”