π, π-allyl, and trimethylenemethane complexes derived from isobutylene adsorption on oxygen-activated Ag(110)

Abstract

In this work the use of atomic oxygen on Ag(110) to synthesize two unusual intermediates, π-2-methylallyl CH 3C(CH 2) 2(a) and trimethylenemethane C(CH 2) 3(a), was investigated. Isobutylene (2-methylpropene) (CH 3) 2CCH 2 adsorbs weakly, without reaction on clean Ag(110) held at 115 K, desorbing from two overlapping states with binding energies of 9.0 kcal mol −1 (37.9 kJ mol −1) and 11.5 kcal mol −1 (48.1 kJ mol −1), respectively. No multilayer formation is observed at surface temperatures of ⩾ 115 K. Co-adsorption of isobutylene and atomic oxygen on Ag(110) results in C-H bond activation via an acid-base mechanism, a reaction pathway which has been observed previously for acidic alkenes. Surface hydroxyl groups are formed at temperatures as low as 115 K. Although the major products are CO 2(g) and h 2o (g), a small amount of (CH 3) 2CCH 2(g) evolves near 310 K. Eviden for the formation of co-adsorbed π-2-methylallyl (CH 3)C(CH 2) 2(a) and trimethylenemethane C(CH 2) 3(a) was obtained by the combined use of temperature-programmed reaction spectroscopy (TPRS) and electron energy loss spectroscopy (EELS).