Enantioselective Reactions on a Au/Pd(111) Surface Alloy with Coadsorbed Chiral 2-Butanol and Propylene Oxide

The coadsorption of R - and S -propylene oxide with R -2-butanol was studied on a dilute Au/Pd(111) alloy containing ∼8% gold using temperature-programmed desorption and reflection absorption infrared spectroscopy. Alloy formation strongly affects the surface chemistry of these molecules as compared to clean Pd(111). A portion of the propylene oxide decomposes to form CO and ethylidyne species on the alloy, while on clean Pd(111), it adsorbs reversibly. 2-Butanol reacts to form a 2-butoxide species on the alloy that either rehydrogenates to form 2-butanol or undergoes a β-hydride elimination reaction to yield 2-butanone. Coadsorption of R -2-butanol with either R - or S -propylene oxide led to a larger 2-butanone yield in the presence of S -propylene oxide with an enantiomeric excess (ee) of ∼14%. This led to an enantioselective depletion of the 2-butoxide species such that the subsequent 2-butanol formation is highly enantioselective, with 100% ee.