Exo- and endocyclic oxazolinyl-phosphane palladium complexes:: Catalytic behavior in allylic alkylation processes

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 C=N oxazoline bond and metal ring position. Ionic palladium(II) complexes containing N,P-bidentate ligands and allyl groups (eta(3)-C3H5 for 16-22 and eta(3)-1,3-Ph-2-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 (1) 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 1. 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).