The structure and reactivity of norbornadiene (NBD) adsorbed on Pt(111) has been studied by several physical techniques. At 130 K, NBD is bound to the surface in an unusual way: through only one C-C double bond and through an agostic interaction involving one of the C-H bonds of the bridging CH2 group. The latter interaction is characterized by an intense, broad band centered at 2670 cm-1 (fwhm nearly equals 50 cm-1) in the RAIR spectra. The data strongly suggest that the other C-C double bond of NBD does not interact with the surface. This unusual binding mode, which may be adopted because steric factors favor it over the alternative η2:η2 geometry, persists to 220-260 K, whereupon the agostic C-H bond is cleaved to give a norbornadienyl intermediate that is stable to 400-450 K. In this latter temperature range the norbornadienyl intermediate decomposes, probably via a retro cyclization reaction, to give benzene and dihydrogen (which desorb) and a fractional monolayer of carbon (which remains on the surface). Comparisons of the low-frequency C-H stretching mode seen for NBD with those seen for other adsorbed hydrocarbons suggest that the line width of these modes is largely due to inhomogeneous broadening, not to dispersion or lifetime effects.
ASJC Scopus subject areas
- Physical and Theoretical Chemistry
- Organic Chemistry
- Inorganic Chemistry