Noncovalent modification of cycloparaphenylene by catenane formation using an active metal template strategy

Active metal template (AMT) strategy is a powerful tool for the formation of mechanically interlocked molecules (MIMs) such as rotaxane and catenane. This strategy allows the synthesis of a variety of MIMs, including π-conjugated and/or multicomponent macrocycles. Cycloparaphenylene (CPP) is an emerging molecule with unique cyclic π-conjugated structures and properties, whose diverse modifications are expected for its wide application. However, most CPP modifications require early-stage functionalization and multi-step protocols causing low yielding and less diversity. Although the direct modification of CPPs offers numerous advantages over the early-stage prefunctionalization method, the methodology is limited. Herein, we report the synthesis of a catenane consisting of [9]CPP and a 2,2´-bipyridine macrocycle as a new CPP analog that contains a reliable synthetic scaffold enabling diverse and concise post-functionalization. In accordance with the AMT strategy, [9]CPP–bipyridine catenane was successfully synthesized from cyclohexadiene-based V-shaped units and 2,2´-bipyridine macrocycle ligand through Ni-mediated aryl–aryl coupling followed by desilylation and reductive aromatization. Catalytic C–H borylation/cross-coupling and metal complexation at bipyridine macrocycle moiety, which are effective post-functionalization methods, were also demonstrated with [9]CPP–bipyridine catenane. The structural and photophysical properties of CPP–bipyridine catenane derivatives were investigated by nuclear magnetic resonance analysis, absorption/fluorescence/phosphorescence measurements, and computational studies, compared with properties of pristine [9]CPP. Single crystal X-ray structural analysis revealed that the [9]CPP–bipyridine catenane forms a tridentated complex with a Ag ion inside the CPP ring, which is attributed to the π–π interaction between the bipyridine unit in macrocycle moiety and benzene rings in [9]CPP moiety. The phosphorescence of the Ag complex of [9]CPP–bipyridine catenane was clearly enhanced by the heavy atom effect, demonstrating a new design of phosphorescence material with CPP.