Synthesis and Structure of [9]Cycloparaphenylene Catenane: An All-Benzene Catenane Consisting of Small Rings

A catenane consisting of two [9]­cyclo­para­phenyl­enes ([9]­CPPs) has been synthesized. Density functional theory calculations suggested that [n]­CPPs (n = 5, 6) are highly strained upon the formation of catenanes compared with the corresponding uncatenated CPPs, whereas [n]­CPP catenanes (n ≥ 7) are not strained. The synthesis of ([9]­CPP)([9]­CPP)­catenane was accomplished via the following route: (i) a spirosilylation, (ii) a nickel(0)-mediated macrocyclization, (iii) a desilylation, and (iv) reductive aromatization reactions. An X-ray diffraction analysis revealed a catenated structure of ([9]­CPP)([9]­CPP)­catenane.