2,2′-Bipyridyl-Embedded Cycloparaphenylenes as a General Strategy To Investigate Nanohoop-Based Coordination Complexes

Because
of their unique cyclic architectures, tunable electronic
properties, and supramolecular chemistries, cycloparaphenylenes (CPPs)
have the potential to act as a new class of ligands for coordination
cages, metal–organic frameworks, and small-molecule transition-metal
complexes. However, currently there is no general strategy to coordinate
the cyclic framework to a variety of metal centers. We report here
a general and scalable synthetic strategy to embed 2,2′-bipyridine
units into the backbone of CPPs. We use this approach to synthesize
a 2,2′-bipyridine-embedded [8]­CPP, which we show can successfully
coordinate to both Pd­(II) and Ru­(II) metal centers. The resulting
coordination complexes, a Pd­(II)–nanohoop dimer and a bis­(bipyridyl)­ruthenium­(II)-functionalized
nanohoop, show unique solid-state and photophysical properties. This
work provides a proof of concept for a general strategy to use nanohoops
and their derivatives as a new class of ligands.