CH BOND ACTIVATION IN CH4 AND TERT-BUO(ADS) BY OXYGEN CHEMISORBED ON AG(110) - MOLECULAR-ORBITAL THEORY

Activation of the CH bond in CH4 and Z-BuO(ads) by H transfer to O adsorbed on the Ag(110) surface has been studied by the atom-superposition and electron-delocalization molecular orbital theory. Both abstractions are found to proceed with a low-energy barrier because of the presence of low-lying empty Ag surface orbitals at the Fermi level. Transfer of an electron to the Fermi level alleviates the initial closed-shell repulsion between the CH σ-bond electron pair and the surface O (which is formally O2-) lone-pair orbital that ultimately forms the OH bond. It is concluded that surface O behaves like a radical anion O- or R3C in its ability to form a single bond. This explains the experimental results of Brainard and Madix who observed the formation of isobutylene and isobutylene oxide from t-BuO(ads). Our calculations also suggest the possibility that surface oxygen atoms might insert into CH bonds to form alcohols, which is a result of their ability to exhibit O atom or carbene (R2C:) bonding properties. © 1990, American Chemical Society. All rights reserved.