Cyclobis(paraquat-p-phenylene)

Cyclobis(paraquat-p-phenylene)
Identifiers
CAS Number	117271-76-8 (Tetracation); 117271-78-0 (Tetrachloride);
3D model ( JSmol)	Interactive image;
ChemSpider	3655997;
PubChem CID	4457151;
	InChI InChI=1S/C36H32N4/c1-2-30-4-3-29(1)25-37-17-9-33(10-18-37)35-13-21-39(22-14-35)27-31-5-7-32(8-6-31)28-40-23-15-36(16-24-40)34-11-19-38(26-30)20-12-34/h1-24H,25-28H2/q+4 Key: URORLZXVTFVIPS-UHFFFAOYSA-N; InChI=1/C36H32N4/c1-2-30-4-3-29(1)25-37-17-9-33(10-18-37)35-13-21-39(22-14-35)27-31-5-7-32(8-6-31)28-40-23-15-36(16-24-40)34-11-19-38(26-30)20-12-34/h1-24H,25-28H2/q+4 Key: URORLZXVTFVIPS-UHFFFAOYAV;
	SMILES c1cc2ccc1C[n+]3ccc(cc3)-c4cc[n+](cc4)Cc5ccc(cc5)C[n+]6ccc(cc6)-c7cc[n+](cc7)C2;
Properties
Chemical formula	C36H32N4
Molar mass	520.663 g·mol−1
Appearance	white solid
	Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). Infobox references

Cyclobis(paraquat-p-phenylene) (formally a derivative of

aromatic units connected by methylene bridges. It is able to incorporate small guest molecule and has played an important role in host–guest chemistry and supramolecular chemistry.^[2]

The cyclophane is also referred to as Stoddart's blue box because its inventor,

J. Fraser Stoddart, illustrates the electron-poor areas of molecules in a blue shade.^[3]

Synthesis

For synthesis of cyclobis(paraquat-p-phenylene), 4,4'-bipyridine is reacted with 1,4-bis(bromomethyl)benzene to 1,1′-[1,4-phenylenebis-(methylene)]bis(4,4′-bipyridine), which is reacted in a template synthesis again with 4,4′-bipyridine to the final product. A common template for this synthesis is 1,5-bis[2-(2-methoxyethoxy)ethoxy]naphthalene.^[1]

Host guest chemistry

Cyclobis(paraquat-p-phenylene) is able to incorporate small guest molecules forming a

π-electron density. Also an enlargement of the π-system enhances the binding. The kinetics of complex formation and dissociation depends on the bulkiness of the guest.^[4]

One molecule which is able to form stable complexes with cyclobis(paraquat-p-phenylene) is tetrathiafulvalene (TTF). Numerous derivatives are based on the chelating ability of tetrathiafulvalene. The modifications include mechanically entrapped compounds such as catenanes and rotaxanes, molecular switches and larger supramolecular structures.^[4]

The charge-transfer interactions, present in complexes of cyclobis(paraquat-p-phenylene), can be compared as structural motif with the more commonly used

association constant. Due to the lower association constant many fewer charge transfer complexes are known. Other non-covalent bonds such as solvophobic forces, metal-ligand interaction can be used to increase the association constant; numerous structures based on this strategy are known in literature.^[5]

It was shown that the choice of the counterion of cyclobis(paraquat-p-phenylene) has a large influence on the association constant of the corresponding host–guest complex.^[6] It is often used as hexafluorophosphate salt because in this form it is soluble in organic solvents.

Utilization

To create

coulomb repulsion around itself until the cyclobis(paraquat-p-phenylene) encloses the DNP unit. A reverse movement occurs when the TTF unit is reduced again. This first example that proved the general feasibility, many more have followed.^[8]

Derivates

Numerous

foldamers and liquid crystalline phases. In analogy to biological systems, which are assembled by hydrogen bonds to form supramolecular structures, the charge-transfer complexation is here an alternative.^[5]