Backbone Effect of MAP Ligands on Their Coordination Patterns with Palladium(II)

2003-03-27T00:00:00Z (GMT) by Yi Wang Xin Li Jie Sun Kuiling Ding
The allylpalladium complexes (<i>R</i>)-<b>4 </b>and (<i>R</i>)-<b>5 </b>of chiral P, N auxiliaries (<i>R</i>)-<b>1 </b>and (<i>R</i>)-<b>3 </b>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<sub>σ</sub>) 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 regiochemical 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 (<i>R</i>)-<b>3</b> as a chiral inducer can be related to the different chelating mode of catalyst (<i>R</i>)-<b>5</b> from that of (<i>R</i>)-<b>4</b>. The change of bite angles of the two donors with palladium in the complexes (<i>R</i>)-<b>4</b> and (<i>R</i>)-<b>5 </b>was considered as a direct reason for their dramatically different enanatioselectivities in the catalysis.