Redox Reactions in Palladium Catalysis: On the Accelerating and/or Inhibiting Effects of Copper and Silver Salt Additives in Cross-Coupling Chemistry Involving Electron-rich Phosphine Ligands

摘要

Palladium-catalyzed cross-coupling reactions are widely used to construct carbon-carbon or carbon-heteroatom bonds. These transformations are frequently assisted by more than one metal, and Cu/Pd is probably one of the most frequently applied combinations, for example, in the Sonogashira and Stille reactions. The precise effects of Cu salts in these transformations are not fully understood, but Cu~I is thought to play a catalytic, accelerating role in the transfer of an alkynyl group to Pd in the Sonogashira coupling (through formation of an organocopper species, [Cu(C≡CR)], which in turn is more readily transferred to Pd", Scheme 1).