Enantioselective decomposition of chiral alkyl bromides on Cu(643): Effects of moving the chiral center

The enantioselective surface chemistry of two chiral alkyl halides, S-1-bromo-2-methylbutane and R-2-bromobutane, have been compared on the naturally chiral Cu(643) surfaces. Temperature programmed reaction spectroscopy was used to quantify the yields of the various decomposition products during heating. A fraction of the adsorbed alkyl bromides desorb intact while the remainder decomposes by debromination to form either S-2-methyl-1-butyl or R-2-butyl groups on the surfaces. The S-2-methyl-1-butyl group then reacts by b-hydride elimination to form 2-methyl-1-butene or by hydrogenation to form 2-methylbutane. The R-2-butyl group reacts by bhydride elimination to form butene or by hydrogenation to form butane. This surface chemistry on Cu(643) is not enantioselective at low coverages but is enantioselective at high coverages. In R-2-bromobutane the chiral carbon atom coincides with the debromination reaction center while the b-hydride elimination centers are achiral. In S-1-bromo-2-methylbutane the chiral carbon atom coincides with the b-hydride elimination reaction center while the center for debromination is achiral. Results show that the enantioselectivities are influenced by the surface structure to a greater extent than they are by the adsorbate structure. 2006 Elsevier B.V. All rights reserved.