The Gilded Edge in Acetylenic Scaffolding II: A Computational Study of the Transmetalation Processes Involved in Palladium-Catalyzed Cross-Couplings of Gold(I) Acetylides

Abstract

The palladium-catalyzed cross-coupling reaction between phosphine-gold(I) acetylides and aryl iodides has recently proven as a convenient alternative to the standard Sonogashira reaction, which instead employs terminal alkynes as substrates. This alternative reaction does not require the presence of an amine base, but still, however, requires a copper cocatalyst (CuI). In this theoretical work we have investigated the possible roles that this copper catalyst may play. Three transmetalation pathways can be imagined, proceeding by either (i) transferring the acetylide from gold to copper and thereafter to palladium, (ii) directly transferring the acetylide from gold to palladium, or (iii) directly transferring the acetylide from gold to palladium but aided by a copper coordination to the triple bond. Calculations reveal that the first of these is the most viable reaction pathway, as it involves the initial formation of a very favorable copper/gold acetylide complex. The transmetalations along this pathway r...