Abstract
Neutral and cationic half-sandwich (η6 -p -cymene)ruthenium complexes 9 -12 with
chiral Schiff base ligands derived from binaphthylamino derivatives
and salicylaldehyde, diphenyl(2-formylphenyl)phosphane, and 2-pyridinealdehyde
form two diastereomers which only differ in the metal
configuration. From the diastereomeric mixtures of compounds 10 and 12 the
major diastereomers crystallize, whereas for compound 9 both diastereomers co-crystallize in
a 1:1 ratio in the same single crystal. In compounds 13 and 14 containing the reduced Schiff base ligands,
the nitrogen atom of the secondary amine functionality becomes another
chiral center. In solution at room temperature the various diastereomers interconvert
rapidly. The new compounds were used as catalysts in the enantioselective
transfer hydrogenation of acetophenone with 2-propanol and in the
Diels-Alder reaction of cyclopentadiene with methacrolein.
Key words
enantioselectivity - catalysis - ruthenium
half-sandwich complexes - 1,1′-binaphthyl ligands - chiral imines
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