Activation of hydrocarbons by W⁺ in the gas phase

The gas-phase reactivity of W⁺ with hydrocarbons containing up to six carbon atoms has been studied by Fourier-transform ion cyclotron resonance mass spectrometry. W⁺ is found to be one of the most reactive bare metal cations studied to date with all hydrocarbons except acetylene being activated at thermal energies. The observed reactivity is dominated by dehydrogenation, which is often multiple. Thus, reaction with propene leads to loss of two dihydrogen molecules (yielding WC₃H₂⁺) and reaction with n-hexane leads to loss of 4 H₂ (yielding WC₆H₆⁺). In all cases, the product ions are themselves reactive with the same neutral species, leading to reaction sequences of various lengths. Isotope labeling, collision-induced dissociation, and ligand exchange experiments have been extensively carried out in order to try to establish the structure of some of the intermediate and final product ions. It turned out that deriving structures from such experiments is much more difficult than for first-row transition metal ions. This is due to the higher reactivity and metal-ligand binding energies of tungsten.