Noncovalent interactions in metal complexes. 16. Stereoselectivity of 1:3 complexes of Sc, Y, La, Al, Ga, and In ions with 4-(1-menthyloxy)-1-phenyl-1,3-butanedione and 4-(1-Menthyloxy)-1-p-tolyl-1,3-butanedione

1:3 complexes of Sc3+, Y3+, La3+, Al3+, Ga3+, and In3+ with 4-(l-menthyloxy)-1-phenyl-1,3-butanedione (H(l-moBa)) and 4-(l-menthyloxy)-1-p-tolyl-1,3-butanedione (H(l-moba-Me)) have been prepared, and their stereoselectivities have been examined in view of a noncovalent interligand interactions. The distributions of the diastereomers for the relatively inert Al and Ga complexes are determined by 1H NMR spectroscopy, and the results demonstrate that the fac/mer ((fac-Δ + fac-Λ)/(mer-Δ + mer-Λ)) ratio is larger than the statistical value (1/3) for all of these cases. On the basis of circular dichroism induced at the ligand π-π* transition, the configuration of the preferred diastereomer in solution is determined as fac-Λ for all of the complexes. The stereoselectivity that produces the fac-Λ isomer is enhanced when the size of the central ion becomes larger. On the basis of these facts, the stereoselectivity of the complexes is attributed to the operation of a noncovalent interaction in the form of a left-handed three-bladed propeller, comprising three interligand I-menthyl-aryl contacts. 29 refs., 7 figs., 3 tabs