Molecular and Supramolecular Synthesis with Dibenzofuran‐Containing Systems

Abstract

AbstractThe template‐directed syntheses of two new tetracationic cyclophanes, cyclobis(paraquat‐2,8‐dibenzofuran) and cyclobis(paraquat‐3,7‐dibenzofuran), incorporating dibenzofuran subunits has been accomplished. Initially, the cyclophanes were self‐assembled around a macrocyclic polyether template, bis‐p‐phenylene[34]crown‐10 (BPP34C10), to form catenanes: the mechanical bond order of the catenane formed determined the requisite “amacrocyclic” templates for synthesis of the free cyclophane. X‐ray crystallography shows that both of the cyclophanes possess rectangular covalent frameworks. Furthermore, these cyclophanes form self‐assembled tapes in the solid state, since the dibenzofuran moieties have a tendency to associate with each other through crossed ∞–∞ stacks. The dibenzofuran‐containing catenanes also form two‐dimensional supramolecular arrays in the solid state on account of extended ∞–∞ stacking interactions. In addition, the serendipitous discovery of a plerotopic tecton (consisting of a dibenzofuran nucleus covalently linked from the 2‐ and 8‐positions by methylene groups to 4,4′‐pyridylpyridinium (hydrogen bond acceptor) and protonated bipyridinium (hydrogen bond donor) units) has been made. The tecton dimerizes in the solid state to form a supramolecular macrocycle, since its complementary hydrogen bonding sites are oriented in a horseshoelike fashion by the 2,8‐disubstituted dibenzofuran unit. However, this superstructure is not retained in the 1:1 complex of the tecton with BPP34C10: cocrystallization of the tecton with this crown ether opens the macrocyclic two‐component supermolecule to afford a hydrogen‐bonded pseudopolyrotaxane.