The Sonogashira Coupling on Palladium Milling Balls-A new Reaction Pathway in Mechanochemistry

Utilizing direct mechanocatalytical conditions, the Sonogashira coupling was successfully performed on the surface of milling tools by using pure Pd and Pd coated steel balls. The optimization of co-catalyst forming additives led to a protocol, which generates quantitative yields under aerobic conditions for various substrates within as little as 90 minutes. Using state-of-the-art spectroscopic, diffractive, as well as in situ methods lead to the identification of a previously unknown and highly reactive complex of the co-catalyst copper. This new complex differs substantially from the known complexes in liquid phase Sonogashira couplings, proving that reaction pathways in mechanochemistry may differ from those in established synthetic procedures.