A Nonalternant Aromatic Belt: Methylene-Bridged [6]Cycloparaphenylene Synthesized from Pillar[6]arene

The
synthesis, structure, and properties of methylene-bridged [6]­cycloparaphenylene
([6]­CPP), a nonalternant aromatic belt, are described. This belt-shaped
methylene-bridged [6]­CPP, in which each phenylene unit is tethered
to its neighbors by methylene bridges, was constructed through 6-fold
intramolecular nickel-mediated aryl–aryl coupling of triflate-functionalized
pillar[6]­arene in 18% isolated yield. As compared to the analogous
[6]­CPP, the methylene bridges coplanarize neighboring paraphenylene
units and enhance the degree of π-conjugation, which results
in a significant decrease in energy gap. Moreover, the incorporation
of small molecules in the defined pocket of methylene-bridged [6]­CPP
makes it an attractive supramolecular architecture. Methylene-bridged
[6]­CPP is characterized by high internal strain energy reaching 110.2
kcal mol–1, attributed to its restricted structure.
This work not only exhibits an efficient strategy to construct a new
family of aromatic belt, but also showcases their properties, which
combine the merits of CPPs and pillararenes.

本描述了甲基桥连的[6]环亚苯基([6]CPP)，一种非交替芳香环带的结构、合成与性质。该环带状的甲基桥连[6]CPP，其中每个苯基单元通过甲基桥与相邻单元相连，通过18%的分离产率，通过六次分子内镍催化的芳基-芳基偶联反应构建于三氟甲磺酸功能化的柱[6]芳烃。与类似的[6]CPP相比，甲基桥使相邻的亚苯基单元共平面，增强了π共轭程度，从而显著降低了能隙。此外，将小分子纳入定义的甲基桥连[6]CPP口袋中，使其成为一种具有吸引力的超分子结构。甲基桥连[6]CPP以其高达110.2 kcal mol–1的高内部应变能为特征，这归因于其受限的结构。本研究不仅展示了一种构建新型芳香环带的有效策略，而且还展示了其性质，这些性质结合了CPPs和柱芳烃的优点。