Fragmentation of ion–molecule adducts of transition metal ions with aromatic ring-containing nitriles in the gas phase

Gas-phase ion–molecule reactions of transition metal ions, M⁺ (M⁺ = Ni⁺, Co⁺, Fe⁺ and Mn⁺), with six aromatic ring-containing nitriles were investigated in a modified fast atom bombardment (FAB) source. It is shown that the monoadduct, (Ph(CH₂)_nCN)–M⁺, is one of the most abundant ion–molecule reaction products. The main fragments in the FAB source are the C₇H₇]⁺ and C₈H₉]⁺ ions, and their formation is shown to involve metal ion insertion into the nitriles rather than direct bond cleavage from the ‘free’ or complexed nitriles after FAB ionization. An intramolecular oxidation–reduction reaction, giving C₇H₇]⁺, is found in the metastable and collisionally induced dissociations of benzyl nitrile adducts accompanied by neutral MCN formation, but not seen for longer chain samples. An ortho effect is observed in the elimination of HCN from the 2-methylbenzyl nitrile adduct ions. This reaction dominates the metastable ion spectrum of the adduct of Mn⁺, whereas metal detachment is nearly the major process for the other complexes of Mn⁺. The different bond-insertion selectivities of the metal ions are also shown.