Fundamental aspects of enantioselective heterogeneous catalysis: a NEXAFS study of methyl pyruvate and (S)-(-)-1-(1-naphthyl) ethylamine on Pt{111}

Near-edge X-ray absorption fine structure (NEXAFS) and X-ray photoelectron spectroscopy have been used to characterise the adsorption and reactivity o f methyl pyruvate and (S-(-)-1-(1-napthyl) ethylamine ((S)-NEA) on Pt{1 1 1 }. Methyl pyruvate polymerises at room temperature yielding chains that con tain C=O bonds and no C=C bonds; the C=O bonds are inclined at 64 +/- 5 deg rees with respect to the metal surface. Polymerisation probably occurs by a n aldol condensation that involves elimination of methanol. This mechanism is in excellent accord with the intramolecular bonding deduced from the NEX AFS results. These findings suggest that irreversible deactivation during s tart-up or steady state operation of Pt catalysts during enantioselective h ydrogenation of alkyl pyruvates can be due to hydrogen starvation, which re sults in polymerisation of the prochiral reactant. For (S)-NEA, the naphtha lene ring is inclined at 46 +/- 5 degrees with respect to the metal surface . It is proposed that (S)-NEA binds to the surface via contributions from b oth the aromatic pi -system and the lone pair of electrons on the amine nit rogen atom. (C) 2001 Elsevier Science B.V. All rights reserved.