Gas-phase reactions of MS + ions (M = Fe, Co, Ni) with alkanes. An FTMS study

Abstract

The gas-phase reactions of MS + ions (M = Fe, Co, Ni) with small alkanes are reported. MS + reacts with hydrocarbons primarily by H 2S loss from the collision complex. This complex can further dissociate by dehydrogenation, creating a metal-polyolefin complex, or by loss of small alkenes. These latter dissociations are similar to the collision-induced dissociation decomposition pathways for the metal-olefin complex and suggest that H 2S loss leaves an internally excited metal-olefin complex. As has been observed for a variety of mono-ligated metal species, MS + shows a preference for CH bond insertion, leading to dehydrogenation, compared with the bare metal ions which predominantly attack CC bonds. The sulfur ligand does not activate reactions as much as an oxygen ligand, which may be attributed to the fact that H 2S loss is less exothermic than H 2O loss. Photodissociation threshold measurements yield D° (FE + −S) = 65 ± 5 kcal mol −1, D°(Co + −S) = 62 ± 5 kcal mol −1, and D°(Ni + −S) = 60 ± 5 kcal mol −1, from which additional thermochemical information is derived.