| Abstract
| - The chemisorptive enantioselectivity of propylene oxide is examined on Pd(111) surfaces templated by chiral2-methylbutanoate and 2-aminobutanoate species. It has been found previously that chiral propylene oxide ischemisorbed enantiospecifically onto Pd(111) surfaces modified by either (R)- or (S)-2-butoxide. Theenantiomeric excess (ee) varied with template coverage, reaching a maximum of ∼31%. Templating thesurface using 2-methylbutanoate, where the chiral center is identical to that in the 2-butoxide species, but isnow anchored to the surface by a carboxylate rather than an alkoxide linkage, shows no enantiospecificity.The enantioselectivity is restored when the methyl group is replaced by an amine group, where a maximumee value of ∼27% is found. DFT calculations and infrared measurements suggest that the structures of thebutyl group on the surface are similar for both 2-butoxide and 2-methylbutanoate species, implying that grossconformational changes are not responsible for differences in chemisorptive enantioselectivity. There is noclear correlation between the location of the chiral center and enantioselectivity, suggesting that differencesin the template adsorption site are also not responsible for the lack of enantioselectivity. It is proposed thatthe 2-butyl group in 2-methylbutanoate species is less rigidly bonded to the surface than that in 2-butoxides,allowing the chiral center to rotate azimuthally. It is postulated that the role of the amino group in2-aminobutanoate species is to anchor the chiral group to the surface to inhibit azimuthal rotation.
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