om020475u_si_002.pdf (48.13 kB)
Backbone Effect of MAP Ligands on Their Coordination Patterns with Palladium(II)
journal contribution
posted on 2003-03-27, 00:00 authored by Yi Wang, Xin Li, Jie Sun, Kuiling DingThe 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, Cσ) 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 (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.
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chiral ligandschelating modenucleophilic attackcoordination patternsNMR studiesMAP Ligandschiral Pregiochemical memory effectC σdimethyl malonateN vs PCoordination Patternssolution behaviorsallylic substitutionchelating modesBackbone EffectN auxiliarieschiral inducerallylpalladium complexesbinaphthyl backbone
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