The thermal chemistry of 1-methyl-1-cyclopentene (1MCp) and methylene cyclopentane (MeCp) was
investigated on clean and hydrogen- and deuterium-predosed Pt(111) single-crystal surfaces by temperature-programmed desorption and reflection−absorption infrared spectroscopy. It was found that MeCp isomerizes
easily to 1MCp but that the reverse reaction does not occur, at least under our experimental conditions. The
MeCp to 1MCp isomerization is aided by the presence of coadsorbed hydrogen, and occurs through the
formation of a common 1-methyl-1-cyclopentyl (1MCp−Pt) surface intermediate; that intermediate then
undergoes β-hydride elimination selectively at the ring position to form the 1MCp product. In addition to
this isomerization, both 1MCp and MeCp also dehydrogenate on the Pt(111) surface to form a
methylcyclopentadiene species, at 325 and 350 K, respectively. A small amount of benzene desorption is
detected above 500 K with both reactants, indicative of a ring enlargement reaction. No evidence for the
activation of any of the allylic hydrogens was obtained in either molecule.