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

BONELLO, J M; SYKES, E C H; LINDSAY, R; WILLIAMS, F J; SANTRA, A K; LAMBERT, R M

SURFACE SCIENCE

ELSEVIER SCIENCE BV

Año: 2001 vol. 482 p. 207 - 214

0039-6028

Near-edge X-ray absorption ®ne 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{1 1 1}. Methyl pyruvate polymerises at room temperature yielding chains that contain CdO bonds and no CdC bonds; the CdO 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 ®ndings 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 p-system and the lone pair of electrons on the amine nitrogen atom. Ó 2001 Elsevier Science B.V. All rights reserved.