Anthony KERMAGORET - THESES ET MEMOIRES DE L'UDS

Chapitre IV
The analysis of the different C6 oligomers was performed in order to differentiate between a
chain growth mechanism and the reinsertion of butenes. The formation of 2-hexene, 3-
hexene and 2-ethyl-1-butene by reinsertion of 1-butene and the formation of 3-methyl-2-
pentene and 3-methyl-1-pentene by reinsertion of 2-butene depending on the insertion mode
(2,1- or 1,2-insertion) has been discussed previously. 27 Isomerization of 1-hexene leads to the
formation of 2-hexene and 3-hexene.
3.1 Use of AlEtCl2 as cocatalyst.
Complexes 17, 18 and 20-22 have been tested in the presence of 2, 4 or 6 equivalents
of AlEtCl2 (Al/Ni ratios of 2, 4 or 6, respectively) and the catalytic results are presented in
Table 3 and shown in Figures 4-6.
The highest activities were obtained for complex 18 with turnover frequencies (TOF) of
78200 and 91200 mol C2H4/(mol Ni·h), either with 4 or 6 equivalents of AlEtCl2,
respectively. Complexes 17, 20, 21 and 22 had similar activities (Figure 4), which increased
with the amount of cocatalyst, between 17000 and 20400 mol C2H4/(mol Ni·h) with 2
equivalents of AlEtCl2, 43500 and 46700 mol C2H4/(mol Ni·h) with 4 equivalents and 56600
and 63600 with 6 equivalents However, 20 showed very low activity with 2 equivalents of
AlEtCl2 (1100 mol C2H4/(mol Ni·h)).
The selectivity for 1-butene was modest and less than 17% for all the complexes
except for 20 with 2 equivalents of AlEtCl2 (72%, Figure 6). The high concentration of 2-
butene indicates that isomerization of 1-butene is largely favored. The exothermicity of the
catalytic reaction (temperature up to 115 °C) with very active systems is most likely
responsible for the lower selectivity in 1-butene. 70 The selectivities for C4 olefins were
between 97% and 50% for complexes 17, 18 and 20-22 (Figure 5) and this showed that
dimerization is much favored over chain growth. The second largest is constituted by the
hexenes (Table 3) with the reinsertion of 1-butene and 2-butene being very significant on the
basis of the branched olefins formed (Table 4).
Increasing the amount of AlEtCl2 had a significant influence on the catalytic results
by forming a more active but less selective system. Higher activities were associated with an
increasing isomerization of 1-butene to 2-butene. With 18, for example, the fraction of 1-
butene decreased from 13% to 2%. The higher concentration of 2-butene favored its
reinsertion to give C6 oligomers (Table 4).
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