Alkynes are a class of organic compounds and are a type of unsaturated aliphatic hydrocarbons. The molecular formula of straight-chain mono alkyne is CnH2n-2. Carbon nanotubes (CNTs), a kind of nanomaterials with special electrons structure, good physical and chemical properties, are widely used in the fields of physics, chemistry and materials. In fact, the optical and electronic properties of carbon nanostructures are related to their precise three-dimensional arrangement of carbon atoms. In recent years, bottom-up organic synthesis strategies have enabled the preparation of carbon nanostructures (such as substructures of CNTs, also known as carbon nanorings and carbon nanobelts), and size, connectivity, and even heteroatom doping can be controlled with atomic precision. It may be more attractive to use organic synthesis strategies to prepare carbon nanomaterials with unique topological structures, especially mechanical interlocking structures.
Recently, researchers have developed a multifunctional active template method to realize the alkyne-alkyne cross-coupling reaction catalyzed by metal ions in the central cavity of the macrocycle; the resulting interlocked products can then be transformed into fully π-conjugated structures in subsequent synthetic steps.
In order to evaluate the feasibility of this method, the researchers synthesized pyridine-containing macrocyclic compounds in high yield and gram/half gram scale, which can efficiently perform AT-CC reaction with excess coupling reagents to give rotaxanes. Next, the rotaxanes were converted to the corresponding bis-boronate esters by Miyaura borylation, followed by the corresponding catenanes under dilute Suzuki-Miyaura cross-coupling conditions. To obtain higher-order interlocking molecules, the researchers used Suzuki-Miyaura cross-coupling to obtain catenanes, but this reaction only produced a complex mixture of oligomeric products. To avoid these problems, the researchers prepared similar rotaxane synthons using template macrocycles, which were reacted under macrocyclization conditions to give catanes in moderate yields, finally, the catenane composed entirely of π-conjugated units consisting of [12+4]CPP and linking two diaza-CPPs can be obtained in 6% yield after aromatization.
The researchers confirmed the catenane structure through X-ray diffraction analysis. Next, the researchers attempted to synthesize higher-order [n]rotaxanes (n>2) with complete conjugation. To this end, they prepared rotaxanes in which a tBu-substituted triphenyl group was mounted at one end of the molecule. This bulky substituent acts as a permanent terminator that remains at the end of the molecule after removal of the silyl group.
Finally, the researchers wanted to study the interaction of macrocyclic ligands with Cu catalysts. The researchers synthesized a macrocyclic compound with only one pyridine ring, but no interlocked products were observed in the AT-CC reaction it participated in. This result indicates that the co-existence of two pyridine rings can coordinate well with copper ions inside the macrocyclic cavity. In addition, the researchers investigated whether the geometry of the alternative ligands was suitable for AT chemistry.
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Reference
- Active template strategy for the preparation of π-conjugated interlocked nanocarbons
Nat. Chem., 2023, 15, 170-176
