A novel chiral phosphino-phosphaferrocene: Its coordination behavior and application to palladium-catalyzed asymmetric allylic alkylation

The synthesis of a novel chiral phosphino-phosphaferrocene ligand is described. The ligand possesses two electronically distinctive donor moieties and behaves either as a monodentate (with a free phosphaferrocene) or a bidentate ligand depending on stoichiometry with a coordinating transition-metal center. In the palladium-catalyzed asymmetric allylic alkylation of 1,3-diphenyl-2-propenyl acetate, a clear correlation was observed between the enantioselectivity of the reaction and a Pd/phosphino-phosphaferrocene molar ratio. With a deficient amount (to the Pd) of the chiral ligand, the highest enantioselectivity (99% ee) was achieved.