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.