Gas-Phase Reactions of Homo- and ... - Institut für Chemie

Helvetica Chimica Acta ± Vol. 88 (2005) 1419
the disintegration of the NiM ‡ (Mˆ Fe, Co) clusters, the charged Ni ‡ -atom sticks to the
nitrile, while atomic Fe and Co are eliminated in their neutral states (Eqns. 19, 22, 57,
59, 62, and 64). We note in passing that an interdependence of the bond energy
D 0(M ‡ M') between two different metal atoms in cluster cations and their reactivity
has been reported previously. For example, FeV ‡ with a large dissociation energy of
D 0(V ‡ Fe) ˆ 314 21 kJ mol 1 [31] 3 ) reacts neither with alkanes nor with linear
alkenes, but only with strained cyclic alkenes; CoFe ‡ , CuFe ‡ , and FeSc ‡ with
dissociation energies of D 0(Co ‡ Fe) ˆ 276 29 kJ mol 1 [29], D 0(Cu ‡ Fe) ˆ
222 29 kJ mol 1 [32] 4 ), and D 0(Fe ‡ Sc) ˆ 201 21 kJ mol 1 [33] also show no
reactivity toward alkanes and only activate C H bonds of higher alkenes starting with
butene; in contrast, FeMg ‡ with a dissociation energy of only D 0(Fe ‡ Mg) ˆ 142
21 kJ mol 1 dehydrogenates even alkanes, starting from pentane [34].
Conclusions. ± The reactions of the homo- and heteronuclear clusters MM' ‡ (M,
M' ˆ Fe, Co, Ni) with some linear nitriles show, at least superficially, many similarities.
However, the behavior of these dinuclear clusters is very distinct from that of the
corresponding atomic cations Fe ‡ ,Co ‡ , and Ni ‡ . Whereas Fe ‡ ,Co ‡ , and Ni ‡ activate
both C H and C C bonds of nitriles, and, in addition, follow some intriguing metalspecific
mechanisms, the diatomic cluster cations only insert in C H bonds in the initial
activation step. From the more reactive Ni-containing cluster cations FeNi ‡ , CoNi ‡ ,
and Ni ‡ 2 ± in comparison to dinuclear Ni-free clusters ± the two latter ones activate
C C bonds after initial C H bond activation. Further, for both the dinuclear as well as
the atomic cations, the regioselectivity of C H bond activation mainly follows the
concept of remote functionalization. Quite likely, this is a consequence of a linear endon
arrangement of the atomic or dinuclear cluster cations to the nitriles investigated.
However, subtle mechanistic variations which are supported by detailed modeling of
the isotope distributions seem to be operative, and electronic structure calculations [35]
are suggested to uncover the origin of these effects.
We are grateful to the Deutsche Forschungsgemeinschaft (DFG) and the Fonds der Chemischen Industrie
for financial support.
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3 ) D0(Fe ‡ V) ˆ 444 21 kJ mol 1 [31].
4 ) D0(Fe ‡ Cu) ˆ 234 29 kJ mol 1 [32].