Studies of the Reactions of Ortho-,Meta- and Para -Methylanisoles with Transition Metal Ions M + (M = Cr,Fe,Co,Ni,Cu) in the Gas Phase

Gas-phase ion/molecule reactions between transition metal ions (Cr⁺, Fe⁺, Co⁺, Ni⁺ and Cu⁺) and the three isomers of methylanisole were investigated. Ion/molecule adducts were prepared in a modified fast atom bombardment source and their unimolecular fragmentations were studied by metastable ion kinetic energy spectroscopy. Labelled derivatives were used to explain the fragmentation mechanisms. From the experimental results it follows that the chemistry of the three isomers of methylanisole is dominated by the three major reactions: CH₂O loss, dehydrogenation and CH₃^• elimination. This latter reaction competes with demethanation for the ortho isomer of methylanisole. The reactivity of these complexes can be classified in three groups: (i) the reactions of Fe⁺, Co⁺ and Ni⁺ with methylanisoles are similar; the ortho isomer complexes are characterized by the losses of methane and formaldehyde, whereas both the meta and the para isomer eliminate a hydrogen molecule and formaldehyde; (ii) the Cr⁺ complexes of methylanisole exhibit distinct reactivity; in this case an ortho effect is revealed by an intense dehydrogenation; (iii) the Cu⁺ complexes do not display any ortho effect, the loss of CH₃^• together with the formation of CuH are observed for the three isomers of methylanisoles.