C-H oxidation enhancement on a gold nanoisland by atomic-undercoordination induced polarization.

Abstract

C-H activation is of great significance in the chemical industry while an effective solvent-free catalyst is highly desired. This work shows that a gold nanoisland which was inert in the bulk is effective for C-H activation reactions. We investigated the C-H activation of toluene on an Au nanoisland (58 atoms) using relativistic density functional theory (DFT). We found that (i) the bonds between under-coordinated gold atoms (corner site) shrink spontaneously and become stronger; (ii) the valence charges of corner atoms are polarized to the upper edge of the valence band (near the Fermi level), indicating the electron donation ability in the catalytic process; (iii) during C-H oxidation, the indirect path (O2 dissociation and O-H bonding) and direct path (O2-H bonding) were considered. The Au-O2 complex is active enough to abstract a hydrogen atom directly from toluene, with a barrier that is 6.8 kcal mol-1 lower than that of the indirect path; and (iv) a transfer of up to ∼0.8 electrons from gold to O2 occurs. Moreover, hybridization between delocalized gold orbitals and oxygen p-orbitals leads to the stabilization of the singlet spin state of Au58O. Our results suggest that undercoordination-charge-polarization are key factors for the C-H oxidation catalyzed by an Au nanoisland.