Anthony KERMAGORET - THESES ET MEMOIRES DE L'UDS

Chapitre IV
been used previously in ethylene oligomerization and we shall now examine the catalytic
properties of complexes 17, 18 and 20-22 in this reaction.
O
O N
PPh 2
Ni
Cl
Cl
R
N
Cl
O
Ni
Cl
PPh 2
26 27 R = H
28 R = Me
Figure 3. ORTEP view of the molecular structure of 22 (ellipsoids enclose of 50% electronic
density, H atoms are omitted for clarity).
This structural study emphasizes the influence of sometimes seemingly minor
variations in the stereoelectronic properties of the ligands on the structure of their
corresponding Ni(II) complexes. With related phosphino-oxazoline and –thiazoline ligands,
it was recently found that tetranuclear Ni(II) complexes are formed and a dramatic effect of
pressure was evidenced which results in its breaking into four mononuclear complexes. 67
3. Catalytic oligomerization of ethylene
Complexes 17, 18 and 20-22 have been tested as precatalysts in the oligomerization
of ethylene with variable amounts of AlEtCl2 or MAO as cocatalyst. In previous studies,
[NiCl2(PCy3)2], which is a typical α-olefin dimerization catalyst, 68 was used to compare the
catalytic results but considering the sensitivity of this complex, we choose another reference
compound, [NiCl2{P(n-Bu3)}2] which is diamagnetic and thus readily amenable to purity
check by NMR spectroscopy and is also highly active in oligomerization with AlEtCl2. 69
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