Anthony KERMAGORET - THESES ET MEMOIRES DE L'UDS

Ph
O
3
toluene
PPh3 + Ni(COD) 2 + PPh3 room temp.
Ph
Ph 2
P
O
Ni
2
Ph
PPh 3
(1)
Chapitre VI
The stabilizing donor ligand plays a crucial role in the catalyst behaviour 34 and the use of
more weakly bound ligands, such as pyridine, or of a catalyst promoter in excess, such as
[Ni(COD)2] or [Rh(acac)(C2H4)2], which can scavenge the donor ligand, turns these nickel
complexes from oligomerization into polymerization catalysts. 35 In the absence of a coligand,
a dinuclear complex 4 forms as a result of the stabilization by coordination of the oxygen
atom to another metal centre. 35,36
Ph
Ph 2
P
O
Ph
Ni
Ni
4
Various substituents have been incorporated into the P,O chelate to modify its stereo-
electronic properties and the electrophilicity of the metal centre and examine their impact on
Ph
O
P
Ph 2
the catalyst properties and the nature of the products formed. 37-42
Neutral phosphino-phenolate nickel complexes are known to form ethylene
oligomerization and polymerization catalysts (Scheme 1). 43-48 Heinicke, Keim et al. have
observed that an increase of the basicity of the phosphorus donor atom improves the catalytic
activity, modifies the mass distribution of the products and favors the formation of long chain
polyethylenes. 44-47
Ph 2
P
O
Ni
Ph
R = Ph, Me, Cy
PR 3
R 2
P
O
Ni
Me
R=Ph,Cy, i-Pr, t-Bu
Ph
Ph R
P
O
Ni
R=Ph,Me,i-Pr, t-Bu
Scheme 1 Phosphino-phenolate nickel catalysts
Cationic nickel complexes derived from this ligand family have also been studied
(Scheme 2) and it was found that the effect of an increased P-basicity on the molecular weight
of the oligomers was much lower than in the case of the neutral, phosphino-phenolate
systems. 49 Furthermore, cationic Ni(II) or Pd(II) complexes 5 with phenacyldi-tert-
buytlphosphine or phenacyldiarylphosphine ligands catalyze ethylene polymerization and
4