Gas-phase studies of group-11 cation (Cu⁺, Ag⁺, and Au⁺) reactions with 2-propanol in a supersonic beam-expansion source

The gas-phase reactions of group-11 ions (Cu⁺,Ag⁺, and Au⁺) with 2-propanol were investigated using laser vaporization combined with supersonic beam expansion in a time-of-flight mass spectrometer. A number of reaction pathways, including assoication, dehydrogenation, and dehydration, were observed. Among these metal ions, Au⁺ is highly reactive toward 2-propanol. The experimental results are parallel to studies by Wilkins et al. using an FT-ICR mass spectrometer (J. Am. Chem. Soc., 107, 7316 (1985)). The geometries and binding energies of all complexes M⁺-L, where M⁺ = Cu⁺, Ag⁺, and Au⁺, L = 2-propanol, acetone, propene, and H₂O, were estimated using Møller-Plesset perturbation (MP2) and density functional theory (BLYP). The bond strengths of the complex ions involving gold revealed the strongest bonding, due to a relativistic effect. The energetic relationship between the reactants and the products facilitated an interpretation of the observed exit channels. Because of the supersonic beam source employed, larger clusters containing metal ions were generated as well. Because the cluster sizes with solvent molecules were ≥ 2, the reactivities were apparently limited to Cu⁺ and Ag⁺ clusters, while the reactive nature changed in Au⁺ along with the formation of acetone, lacking in the bare Au⁺ reactions. For larger clusters, calculations on Ag⁺ - (2-propanol)₂ and Ag⁺ - (2-propanol)(acetone) complexes using BLYP were performed to obtain their energetics.