Palladium-Catalyzed Coupling Reactions: Mechanism of Reductive Elimination. Progress Report, October 1, 1980-June 30, 1981

摘要

The mechanisms of the reductive elimination of alkyl partners from palladium, particularly under reaction conditions characteristic of the palladium-catalyzed coupling of organic halides and organometals, can take place either from Pd(II) or Pd(IV). The coupling of alkyl groups from a dialkylpalladium(II) complex requires that the organic partners be cis to one another. The reaction is a first-order intramolecular process that sometimes requires prior dissociation of a ligand, leading to a Y-or T-shaped intermediate. Coupling also can take place by the prior oxidative addition of organohalide to the dialkylpalladium(II) complex to yield a palladium(IV) species from which reductive elimination takes place rapidly. The reductive elimination step takes place with retention of geometry at an sp exp 2 carbon, and retention of configuration at an sp exp 3 carbon. Which catalytic reversible cycle, Pd(O) implies Pd(II) or Pd(II) implies Pd(IV) operates depends on the organic groups, the ligands and the reaction solvent. (ERA citation 06:035275)