Studies on the 1,2-Migrations in Pd-Catalyzed Negishi Couplings with JosiPhos Ligands

We report an initial investigation with the goal of determining the factors that control the 1,2-migration in the Negishi cross-coupling, which is promoted by palladium catalyst systems generated with JosiPhos ligands. Several of the factors that were demonstrated to be important for the 1,2-migration include (1) the nucleophilicity of the organometallic reagent, which possibly influences the transmetalation step in direct competition with the intermediate beta-hydride elimination of the alkenyl Pd(II) species; (2) the structural features of the vinyl tosylates and phosphates, in which substrates possessing a bulky Cl substituent displayed highest propensity for undergoing the 1,2-migration under the coupling reaction conditions: and (3) the structure of the JosiPhos ligand, where both the sterical bulk and choice of substituents on the ferrocenyl phosphino group greatly influence the catalytic activity of the palladium complex and its capacity to facilitate the 1,2-migration.