Abstract
Near-edge X-ray absorption fine structure (NEXAFS) and X-ray photoelectron spectroscopy have been used to characterise the adsorption and reactivity of methyl pyruvate and (S)-(−)-1-(1-napthyl) ethylamine ((S)-NEA) on Pt{111}. Methyl pyruvate polymerises at room temperature yielding chains that contain CO bonds and no CC bonds; the CO bonds are inclined at 64±5° with respect to the metal surface. Polymerisation probably occurs by an aldol condensation that involves elimination of methanol. This mechanism is in excellent accord with the intramolecular bonding deduced from the NEXAFS results. These findings suggest that irreversible deactivation during start-up or steady state operation of Pt catalysts during enantioselective hydrogenation of alkyl pyruvates can be due to hydrogen starvation, which results in polymerisation of the prochiral reactant. For (S)-NEA, the naphthalene ring is inclined at 46±5° with respect to the metal surface. It is proposed that (S)-NEA binds to the surface via contributions from both the aromatic π-system and the lone pair of electrons on the amine nitrogen atom.
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