Masked alkynes for synthesis of threaded carbon chains

Area of Science:

• Materials Science
• Supramolecular Chemistry
• Carbon Allotropes

Background:

• Polyynes are unstable 1D carbon chains that evolve towards carbyne with increasing length.
• Supramolecular encapsulation was proposed to stabilize long polyynes via polyrotaxanes.
• Synthesizing polyrotaxanes with numerous macrocycles has been a significant challenge.

Purpose of the Study:

• To develop a method for synthesizing polyrotaxanes with long polyynes.
• To achieve stabilization of polyynes in the length regime approaching carbyne.
• To explore new routes to cyclocarbons and catenanes.

Main Methods:

• Utilized cobalt-masked alkynes to temporarily coordinate and protect the C≡C triple bonds.
• Employed these masked alkynes in supramolecular synthesis to thread macrocycles.
• Synthesized polyrotaxanes and related carbon structures like catenanes.

Main Results:

• Successfully synthesized polyrotaxanes with up to 34 contiguous triple bonds (C68), featuring four threaded macrocycles.
• Achieved polyyne structures in a length regime where electronic properties converge towards carbyne.
• Demonstrated the synthesis of [3]catenanes and [5]catenanes using cobalt complexes of cyclo[40]carbon and cyclo[80]carbon.

Conclusions:

• Cobalt-masked alkynes provide an effective strategy for synthesizing complex polyyne polyrotaxanes.
• This method overcomes previous synthetic limitations, enabling access to long polyynes and carbyne-like materials.
• The approach also offers new pathways for constructing cyclocarbons and catenanes.