The ion–molecule reactions of the rhenium oxide anions, [ReO _x]⁻ ( x = 2–4) with the organic substrates methane, ethene, methanol, and acetic acid have been examined in a linear ion trap mass spectrometer. The only reactivity observed was between [ReO₂]⁻ and acetic acid. Isotope-labelled experiments and high-resolution mass spectrometry measurements were used to assign the formulas of the ionic products. Collision-induced dissociation and ion–molecule reactions with acetic acid were used to probe the structures of the mass-selected primary product ions. Density functional theory calculations [PBE0/LanL2DZ6-311+G(d)] were used to suggest possible structures. The three primary product channels observed are likely to arise from the formation of the metallalactone [ReO₂(CH₂CO₂)]⁻ ( m/z 277) and H₂, [CH₃ReO₂(OH)]⁻ ( m/z 251) and CO, and [ReO₃]⁻ ( m/z 235), H₂ and CH₂CO.