Enantioselective chemisorption of propylene oxide on a 2-butanol modified Pd(111) surface: the role of hydrogen-bonding interactions.

The enantioselective chemisorption of R- and S-propylene oxide has been measured either on clean Pd(111) that has been exposed to S-2-butanol at various temperatures to vary the proportion of 2-butanol and 2-butoxide species or by adsorbing S-2-butanol on oxygen-covered Pd(111) to form exclusively 2-butoxide. The results reveal that enantioselective chemisorption is only found when 2-butanol is present on the surface. This is ascribed to enantiospecific hydrogen-bonding interactions between 2-butanol and propylene oxide. Measurements of the variation in enantiospecificity with 2-butanol exposure suggest that propylene oxide can interact either with a single adsorbed 2-butanol molecule or, at higher coverages, with two adsorbed 2-butanol species to form enantioselective sites.