The longest polyynes

• A collaboration between Oxford Chemistry and the Central Laser Facility, Rutherford Appleton Laboratory, has demonstrated a new approach to synthesising long chains of carbon–carbon triple bonds (polyynes and polyyne polyrotaxanes, via masked alkynes).
• The team synthesised a [5]rotaxane: a polyyne with 34 triple bonds (68 sp¹-carbon atoms) encapsulated inside the cavities of four threaded macrocycles.
• The polyrotaxanes were prepared using active metal template synthesis and organometallic masking groups [Co₂(CO)₄dppm, where dppm is bis(diphenylphosphino)methane].

Left: Simplified representation of the longest polyyne with a chain of 68 sp¹-carbon atoms. Right: The polyyne [5]rotaxane is synthesised by unmasking an organometallic precursor. (From Nature Chemistry article.)

This is the first time that a polyyne rotaxane has been reported with more than two threaded macrocycles. Encapsulating the polyyne chain inside these macrocycles increases its thermal stability. This work was made possible by the development of efficient reaction conditions for removing the Co₂(CO)₄dppm masking group using peroxy carboxylic acids. The UV-vis absorption maximum and Raman frequency of the C68 polyyne appear to converge with the properties of an infinite carbon chain: carbyne.

You can read more about this study in Nature Chemistry https://www.nature.com/articles/s41557-023-01374-z