Highly Active Ethene Polymerization Catalysts with Unusual Imine Ligands - Late Transition Metal Polymerization Catalysis - page 79

3.2.4
Ethanol Imine Ligands and their Nickel Complexes

Thus far we have dealt with variations of ligands with frames of known catalyti-
cally active late transition metal compounds. In general, single site catalysts with
late transition metal compounds carry neutral or monoanionic mono-, bi- or tri-
dentate ligands with P, N and/or O (S) donor atoms [8c, 19]. Active nickel cata-
lysts may be obtained with anionic chelating ligands that contain P,O- and N,O-
frames that build 5- and 6-membered metallacycles. 2-Alkoxyimines constitute a
type of anionic bidentate ligand frame that has not been considered up to now as
a possible alternative to established systems. They combine the anionic alkoxy and
a neutral imine entity, reminiscent of alkoxy and phosphane coordination sites in
the SHOP olefin oligomerization catalysts [8, 29]. The alkoxyimine ligands have
three domains where substituents may be varied easily. These are the phenyl
imine ortho positions and the imine and the hydroxy carbon atom substituents
(Chart 3.8).
They are prepared from readily available starting materials along well-estab-
lished reaction pathways (Scheme 3.5).
The first route uses benzoin derivatives as intermediates. These become avail-
able from 1-trimethylsilyloxyphosphonates, which are prepared from aldehydes in
an one-pot procedure. The phosphonates are then transformed into benzoins

,

Chart 3.8 2-Hydroxyimine ligands 102 - 116 , and complexes 117 - 131 .