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

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Helvetica Chimica Acta ± Vol. 88 (2005)
Table 2. Reactions of the Homo- and Heteronuclear Cluster Cations MM' ‡ (M, M' ˆ Fe, Co, Ni) with Pentanenitrile
Fe ‡
2 ‡ n-C4H9CN S k ˆ 1.05 ´ 10 9 cm3 s 1
f ˆ 0.33
[Fe 2C 5H 9N] ‡ 65% (6)
[Fe 2C 5H 7N] ‡ ‡ H 2 35% (7)
Co ‡ 2 ‡ n-C4H9CN [Co2C5H9N] ‡ [Co2C5H7N] 74% (8)
‡ S k ˆ 1.15 ´ 10
‡ H2 26% (9)
9 cm3 s 1
f ˆ 0.37
[Ni2C5H7N] ‡ ‡ H2 5% (10)
[Ni2C5H5N] ‡ ‡ 2H2 62% (11)
Ni ‡ 2 ‡ n-C4H9CN [NiC5H9N] ‡ ‡ Ni 5% (12)
[Ni2C4H6] ‡ ‡ [CH3N] 18% (13)
[Ni2C3H3N] ‡ S k ˆ 2.13´ 10
‡ [C2H6] 10% (14)
9 cm3 s 1
f ˆ 0.68
FeCo ‡ ‡ n-C 4H 9CN
S k ˆ 1.1 ´ 10 9 cm 3 s 1
f ˆ 0.35
[FeCoC 5H 9N] ‡ 68% (15)
[FeCoC 5H 7N] ‡ ‡ H 2 32% (16)
[FeNiC 5H 9N] ‡ 10% (17)
FeNi ‡ ‡ n-C 4H 9CN [FeNiC 5H 7N] ‡ ‡ H 2 80% (18)
[NiC 5H 9N] ‡ ‡ Fe 10% (19)
S k ˆ 1.7 ´ 10 9 cm 3 s 1
f ˆ 0.54
CoNi ‡ ‡ n-C 4H 9CN
S k ˆ 2.5 ´ 10 9 cm 3 s 1
f ˆ 0.80
[CoNiC5H7N] ‡ ‡ H2 40% (20)
[CoNiC5H5N] ‡ ‡ 2H2 25% (21)
[NiC5H9N] ‡ ‡ Co 25% (22)
[CoNiC3H3N] ‡ ‡ [C2H6] 10% (23)
modeling 1 ) for the elimination of molecular H 2 was carried out with the following
boundary conditions taken into account, which were defined by the experimental
results. i) The different modes of dehydrogenation in the case of Fe ‡ 2 and FeCo ‡ were
considered by weight factors f 1,1 and f 1,2 for the 1,1- and 1,2-eliminations, respectively. ii)
Because alkyl H-atoms do not equilibrate completely, the weight factor f scr accounts for
the extent of the H/D scrambling in the backbone; however, f scr does not represent an
additional, free parameter for the modeling but is determined by the parameters f 1,1
and/or f 1,2 (f scr ˆ 1 f 1,1 f 1,2). iii) The equilibration of the H/D atoms does not
necessarily include the complete alkyl chain for every cluster ion examined, but only
part of it; this situation is taken into account by the statistical probabilities p scr(XY) (X,
Yˆ H, D) to eliminate H 2/HD/D 2 only from those positions which are involved in the
equilibration (Table 4).iv) Dehydrogenation is associated with a non-negligible kinetic
isotope effect (KIE). With these conditions, the general algebraic structures of the
1 ) For a description of the technical details of the modeling procedure used, see [21a] and references cited
therein.