Thermal Chemistry of C3 Allyl Groups on Pt(111)

Abstract

The thermal chemistry of allyl iodide and of allyl bromide adsorbed on Pt(111) was investigated by temperature-programmed desorption (TPD) and reflection−absorption infrared (RAIRS) spectroscopies. On the clean Pt(111) surface, both allyls were found to bond to the surface via the halogen atom in a gauche conformation and with the C−C−C plane close to parallel to the surface. In the presence of surface hydrogen, allyl iodide was found to tilt backward such that the C−C−C plane adopts a more vertical orientation on the surface; in this more upright geometry, both cis and gauche isomers were identified. With both molecules the facile thermally activated cleavage of the carbon−halogen bond results in the formation of C3 allylic species on the surface. A η1 allylic moiety was identified by RAIRS in the high-exposure regime of allyl iodide after annealing to 200 K, and the formation of a second η3 allylic intermediate was inferred from TPD experiments with coadsorbed hydrogen and deuterium. At low surface conc...