Gas-Phase Reactions of Homo- and Heteronuclear Clusters MM′⁺ (M, M′=Fe, Co, Ni) with Linear Alkanenitriles

Fourier-transform ion-cyclotron-resonance mass spectrometry is used to investigate the reactions of mass-selected homo- and heteronuclear clusters MM′⁺ (M, M′=Fe, Co, Ni) with linear alkanenitriles. The reactions with pentanenitrile are examined in detail by means of deuterium-labeling studies. In comparison to the previously studied atomic cations Fe⁺, Co⁺, and Ni⁺, the diatomic cluster cations react more specifically and only insert in CH bonds in the initial step, whereas the bare ions M⁺ activate both CH and CC bonds. Like for the atomic cations, dehydrogenation proceeds via remote functionalization of the terminal positions of the substrate, although H-scrambling processes, preceding dehydrogenation, are more pronounced for the dinuclear cluster cations. The Ni-containing cluster cations CoNi⁺ and Ni are unique in that they bring about double dehydrogenation as well as activation of CC bonds subsequently to the first dehydrogenation. The latter kind of reaction is also partly observed for the [RCN−H₂]-complexes of FeCo⁺, Co, and FeNi⁺ in their secondary reactions with pentanenitrile. The behavior of the Fe-containing cluster cations Fe and FeCo⁺ is more subtle compared to that of the Ni-containing clusters Ni and CoNi⁺ as well as that of homonuclear Co. Based on extensive labeling experiments, dehydrogenation of pentanenitrile by these cluster cations follows a 1,2-elimination mode, whereas loss of H₂ from the Fe and FeCo⁺ complexes of the substrate proceeds to some extent via a 1,1-elimination involving the unactivated Me group of the substrate. A more quantitative description of the labeling distribution has been achieved by extensive modeling.