The decarbonylation of acetaldehyde assisted by Co+, which was selected as a representative system of transition metal ions-assisted decarbonylations of acetaldehyde, has been investigated using density functional theory (B3LYP) in conjunction with the 6-3 1+G** and 6-311+G(2df,2pd) basis sets. The geometries and energies of the reactants, intermediates, products and transition states relevant to the reaction were located on the triplet ground potential energy surfaces of [Co, O, C-2, H-4](+). Our calculations indicate the decarbonylation of acetaldehyde takes place through four steps, that is, encounter complexation, C-C activation, aldehyde H-shift and nonreactive dissociation, while C-H activation by Co+ cannot lead to the decarbonylation of acetaldehyde. (c) 2005 Elsevier B.V. All rights reserved.