[Os-2(CO)(8)(mu(2)-eta(1),eta(1)-propene)] and related complexes as vibrational models for alkenes chemisorbed on single-crystal metal surfaces

The FTIR spectra of [Os-2(CO)(8)(mu(2)-eta(1),eta(1)-C2H3CH3)] and of its m ethyl-d(3) and d(6) isotopologues have been measured and assigned. Comparis on of these vibrational data with previously published EELS and RAIRS studi es of propene chemisorbed on Pt(lll) and Ni(lll) at low temperatures indica tes that, on these surfaces, the propene species are chemisorbed via a (mu( 2)-eta(1),eta(1)-C2H3CH3) bonding mode. However, differences in the intensi ty patterns between the spectra of the adsorbed species compared with that of the model compound imply additional twisting or tilting with respect to the surface. Assignment of the FTIR spectra of the corresponding l-butene a nd trans-2-butene complexes [Os-2(CO)(8)(mu(2)-eta(1),eta(1)-C2H3C2H5)] and [OS2(CO)(8)(mu(2)-eta(1),eta(1)-CH3C2H2CH3)] indicates similar bonding mod es for chemisorbed 1-butene and trans-2-butene on Pt(111). Infrared data fo r the mononuclear propene complex [Os(CO)(4)(eta(2)-C2H3CH3)], on the other hand, are in good agreement with published EEL data for propene on Ru(0001 ) and Rh(111). indicating that at low temperatures on these surfaces, prope ne is chemisorbed as a methyl-substituted "metallacyclopropane-like" specie s. These bonding modes are analogous to those established for low-temperatu re ethene chemisorption on these surfaces.