Molecular and Supramolecular Synthesis with Dibenzofuran-Containing Systems

The 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 (BPP 34 C 10), 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 pi-pi stacks. The dibenzofuran-containing catenanes also form two-dimensional supramolecular arrays in the solid state on account of extended pi-pi 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 horseshoe-like fashion by the 2.8-disubstituted dibenzofuran unit, However, this superstructure is not retained in the 1:1 complex of the tecton with BPP 34 C 10: cocrystallization of the tecton with this crown ether opens the macrocyclic two-component supermolecule to afford a hydrogen-bonded pseudopolyrotaxane.