Chiral recognition of amino esters by a ruthenium porphyrin complex: kinetics of the exchange process determined by 1H NMR

Abstract The synthesis of a (carbonyl) (valine methyl ester) ruthenium(II) picket-fence complex bearing optically active α-methoxy-α(trifluoromethyl)phenylacetyl residues on both sides of the porphyrin plane (α,β,α,β-isomer) is described. For various amino esters, chiral recognition was observed for the complexation of the ligand with up to 52% enantiomeric excess for tert -leucine methyl ester. The dissociation rate constants of the two enantiomers of valine methyl ester were determined by 1 H NMR using magnetization transfer experiments, showing that the origin of the enantioselectivity in favour of the ( l )-valine (ca. 2.6:1) resides in the difference between the kinetics of the axial ligand dissociation of the two enantiomers.