Enantioselective Surface Chemistry of R-2-bromobutane on Cu(643)~(R&S)and Cu(531)~(R&S)

摘要

The enantioselective surface chemistry of chiral R-2-bromobutane was studied on the naturally chiral Cu-(643)~(R&S)and Cu(531)~(R&S)surfaces by comparing relative product yields during temperature-programmed reaction spectroscopy.Molecularly adsorbed R-2-bromobutane can desorb molecularly or debrominate to form R-2-butyl groups on the surfaces.The R-2-butyl groups react further by beta-hydride elimination to form 1- or 2-butene or by hydrogenation to form butane.Temperature-programmed reaction spectroscopy was used to quantify the relative yields of the various reaction products.At low coverages of R-2-bromobutane on Cu-(643)~(R&S)and Cu(531)~(R&S),the surface chemistry is not enantioselective.At monolayer coverage,however,the product yields indicate that the R-2-bromobutane decomposition reaction rates are sensitive to the handedness of the two chiral surfaces.The impact of surface structure on enantioselectivity was examined by studying the chemistry of R-2-bromobutane on both Cu(643)~(R&S)and Cu(531)~(R&S).The selectivity of R-2-bromobutane desorption versus debromination is enantiospecific and differs significantly from Cu(643)to Cu(531).The selectivity of the R-2-butyl reaction by beta-hydride elimination versus hydrogenation is only weakly enantiospecific and is similar on both the Cu(643)and Cu(531)surfaces.These results represent the first quantitative observations of enantioselectivity in reactions with well-known mechanisms probed using a simple adsorbate on naturally chiral metal surfaces.