The cleavage of molecular N₂ is often challenging, as six electrons are needed to reduce and split the N₂ molecule. N₂ cleavage reactions that have been reported to date have been carried out in the absence of olefins or alkynes, which are more easily reduced than gaseous N₂.

Joachim Ballmann and colleagues, University of Heidelberg, Germany, have found that the cleavage of N₂ can be accomplished in the presence of a coordinated alkyne. The team used a molybdenum complex together with a sodium/lead alloy as a reductant. To achieve the desired selectivity, the rotational freedom of the alkyne was restricted by embedding it within the backbone of a PCCP-type pincer ligand that coordinates through two P atoms and the alkyne group. A molybdenum nitrido complex (pictured) was obtained upon N₂ splitting.

No side reactions of the alkyne were observed—not even during further N-functionalization of the molybdenum nitride. The finding that the strong N≡N bond can be cleaved in the presence of a weaker, but spatially constrained C≡C bond shows that alkyne reduction is not necessarily always preferred over N₂ reduction

• Molybdenum‐Mediated N₂‐Splitting and Functionalization in the Presence of a Coordinated Alkyne,
  Hannah K. Wagner, Hubert Wadepohl, Joachim Ballmann,
  Angew. Chem. Int. Ed. 2021.
  https://doi.org/10.1002/anie.202111325