Exo- and Endocyclic Oxazolinyl−Phosphane Palladium Complexes: Catalytic Behavior in Allylic Alkylation Processes

Abstract

The new bidentate chiral N,P-donor oxazolinyl−phosphane ligands 7−15 are described. Upon coordination to the palladium metal, ligands 7−12 gave endocyclic oxazolinyl−phosphane complexes having seven-membered rings, while ligands 13−15 afforded exocyclic oxazolinyl−phosphinite complexes with six-membered rings, depending on the relative CN oxazoline bond and metal ring position. Ionic palladium(II) complexes containing N,P-bidentate ligands and allyl groups (η3-C3H5 for 16−22 and η3-1,3-Ph2-C3H3 for 23−26) were prepared and fully characterized. X-ray structures were determined for complexes 18 and 19. Pd catalytic systems containing ligands 7−15 were tested in the asymmetric allylic alkylation of the racemic substrates rac-3-acetoxy-1,3-diphenyl-1-propene (I) and rac-3-acetoxy-1-cyclohexene (III). The endocyclic systems show better activites and selectivites (ee values up to 82%) than the exocyclic ones (ee values up to 72%) for substrate I. In particular, palladium endocyclic oxazoline−phosphinite systems containing the PCy2 group (20, 21) give the highest activities, but the best enantioselectivities were observed for those containing PPh2 (18, 19).