Gold Doubles Down To Couple Alkynes

A. Stephen K. Hashmi’s group at the University of Heidelberg, in Germany, has been exploring homogeneous gold catalysis for a long time. The researchers were recently trying what they assumed would be the insertion of a benzylic C–H bond of a substituted toluene into an iodoalkyne group on an adjacent carbon in the ring, via a gold vinylidene intermediate. But to the group’s surprise, a completely different reaction unfolded. The researchers found the active catalyst contains two organogold fragments that act on different ends of the alkyne bond to dimerize the iodoalkyne in a head-to-tail fashion (shown) to form conjugated enynes (Chem. Eur. J. 2015, DOI: 10.1002/chem.201406594). In related gold vinylidene chemistry, involving conversion of aryl diynes to indene derivatives, Hashmi and coworkers have further discovered that in the presence of water the gold vinylidene intermediate forms a rare gold acyl complex, which sheds CO as part of the catalytic cycle (Angew. Chem. Int. Ed. 2015, DOI: 10.1002/anie.201409859). Although CO has been a key component in heterogeneous (surface) catalysis, the decarbonylation process was previously unknown in homogeneous (solution) gold catalysis, Hashmi says.