| Abstract
| - A wide range of NCN pincer palladium complexes, [4-tert-butyl-2,6-bis(N-alkylimino)phenyl]chloropalladium (alkyl = n-butyl, benzyl, cyclohexyl, tert-butyl, adamantyl, phenyl, 4-methoxyphenyl), werereadily prepared from trans-(4-tert-butyl-2,6-diformylphenyl)chlorobis(triphenylphosphine)palladium viadehydrative introduction of the corresponding alkylimino ligand groups (ligand introduction route) in excellentyields (71−98%). NMR studies on this route for forming pincer complexes revealed the intermediacy of[4-tert-butyl-2,6-bis(N-alkylimino)phenyl]chlorobis(triphenylphosphine)palladium which is in equilibrium withthe corresponding NCN pincer complexes via coordination/dissociation of the intramolecular imino groupsand triphenylphosphine ligands. A series of chiral NCN pincer complexes bearing pyrroloimidazolone unitsas the trans-chelating donor groups, [4-tert-butyl-2,6-bis{(3R,7aS)-2-phenylhexahydro-1H-pyrrolo[1,2-c]imidazol-1-on-3-yl}phenyl]chloropalladium, were also prepared from the same precursor via condensationwith proline anilides in high yields. The catalytic properties of the NCN imino and the NCN pyrroloimidazolonepincer palladium complexes were examined in the Heck reaction and the asymmetric Michael reaction todemonstrate their high catalytic activity and high enantioselectivity.
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