Gas-phase reactions of homo- and heteronuclear clusters MM '(+) (M, M ' = Fe, Co, Ni) with linear alkanenitriles

Fourier-transform ion-eyelotron-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 - H-2]-complexes of FeCo+, Co-2(+), 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-+(2) and CoNi+ as well as that of homonuclear Co-2(+). Based on extensive labeling experiments, dehydrogenation of pentanenitrile by these cluster cations follows a 1,2-elimination mode, whereas loss of H-2 from the Fe-2(+) 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.