A High‐Yielding Active Template Click Reaction (AT−CuAAC) for the Synthesis of Mechanically Interlocked Nanohoops

A precursor to a 2,2′-bipyridine embedded [9]cycloparaphenylene (bipy[9]CPP) has been used to generate mechanically interlocked [2]rotaxane molecules in high yield through an active template azide-alkyne cycloaddition (AT−CuAAC) reaction. These [2]rotaxanes then serve as key intermediates to nanohoop[2]catenane structures.

Abstract

Mechanically interlocked molecules (MIMs) represent an exciting yet underexplored area of research in the context of carbon nanoscience. Recently, work from our group and others has shown that small carbon nanotube fragments—[n]cycloparaphenylenes ([n]CPPs) and related nanohoop macrocycles—may be integrated into mechanically interlocked architectures by leveraging supramolecular interactions, covalent tethers, or metal-ion templates. Still, available synthetic methods are typically difficult and low yielding, and general methods that allow for the creation of a wide variety of these structures are limited. Here we report an efficient route to interlocked nanohoop structures via the active template Cu-catalyzed azide-alkyne cycloaddition (AT−CuAAC) reaction. With the appropriate choice of substituents, a macrocyclic precursor to 2,2′-bipyridyl embedded [9]CPP (bipy[9]CPP) participates in the AT−CuAAC reaction to provide [2]rotaxanes in near-quantitative yield, which can then be converted into the fully π-conjugated catenane structures. Through this approach, two nanohoop[2]catenanes are synthesized which consist of a bipy[9]CPP catenated with either Tz[10]CPP or Tz[12]CPP (where Tz denotes a 1,2,3-triazole moiety replacing one phenylene ring in the [n]CPP backbone).

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