Chiral Ruthenium−Bis(oxazolinyl)pyridine Complexes of α,β-Unsaturated Carbonyl Compounds: Enantioface-Selective Coordination of Olefins

The reaction of [(p-cymene)RuCl2]2 and 2,6-bis(oxazolinyl)pyridines (Pybox; 1) in the
presence of α,β-unsaturated carbonyl compounds as prochiral olefins gave η2-olefin complexes.
On the basis of NOE measurements and X-ray structural studies of (Ph-Pybox)RuCl2(methyl
acrylate) (8a) and (Me-Pybox)RuCl2(acrolein) (10b) complexes, we revealed that the chiral
(S,S)-(Pybox)RuCl2 fragments are differentiated with regard to the one enantioface (si face)
of the olefins, fixing the carbonyl moieties in an s-trans conformation. X-ray diffraction of
the nonsubstituted (dH-Pybox)RuCl2(acrolein) (10d) indicated that the preferential s-trans
arrangements of α,β-unsaturated carbonyl compounds bound to the (Pybox)RuCl2 fragments
are not due to the substituents on the Pybox ligands but to the octahedral structures of the
(Pybox)RuCl2(olefin) complexes, especially affected by the chlorine atoms at the apical
positions on the ruthenium atom. We also found that the (Pybox)RuCl2 fragments act as
efficient chiral assemblies for the asymmetric alkylation of the coordinated acrolein with
phenyllithium, resulting in 87% ee of the corresponding alcohol 11.