Backbone effect of MAP ligands on their coordination patterns with palladium(II)

The allylpalladium complexes (R)-4 and (R)-5 of chiral P, N auxiliaries (R)-1 and (R)-3 have been prepared. The X-ray structures of the complexes have been determined, and the results clearly show that two different chelating modes (P, N vs P, C,) are involved. The coordination patterns of donating atoms were dependent on the binaphthyl backbone of the chiral ligands. The isodesymmetrization revealed that the reaction occurs without regio-chemical memory effect, which demonstrates a full dynamic equilibrium has been attained before nucleophilic attack. These results, combined with the solution behaviors of the complexes revealed by NMR studies, provided a further understanding of their asymmetric induction in allylic substitution of 1,3-diphenylprop-2-en-1-yl acetate with dimethyl malonate. The dramatic enhancement of enantioselectivity with (R)-3 as a chiral inducer can be related to the different chelating mode of catalyst (R)-5 from that of (R)-4. The change of bite angles of the two donors with palladium in the complexes (R)-4 and (R)-5 was considered as a direct reason for their dramatically different enanatioselectivities in the catalysis.