Diyne formation from alkynes in the presence of palladium pincer complexes

1,3-Diynes are valuable building blocks for biologically active molecules and precursors of polymers, macrocycles and supramolecular structures. The combination of metal catalysts and molecular oxygen is considered a suitable protocol for the direct homocoupling of alkynes leading to diynes. Regarding the catalyst, palladium species have proved to be efficient and selective, but copper salts as co-catalysts and/or stoichiometric amounts of reoxidants are often needed. Palladium pincer complexes are presented as alternative palladium sources for the homocoupling of alkynes in an environmentally friendly solvent as polyethylene glycol, in the absence of any other co-catalyst and under aerobic conditions