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N-0 Chelated Nickel(II) Complexes as Catalysts for Ethene Oligomerisation, Polymerisation and Ethene/Carbon Monoxide Co-Polymerisation

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Desjardins, Sylvie Yolande (1997) N-0 Chelated Nickel(II) Complexes as Catalysts for Ethene Oligomerisation, Polymerisation and Ethene/Carbon Monoxide Co-Polymerisation. Unspecified thesis, University of Tasmania.

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Abstract

This thesis reports on the use of square planar nickel(II) complexes
containing N-0 chelates as homogeneous catalyst precursors for carbon-carbon
bond formation reactions. A series of new arylnickel phosphine complexes have
been prepared. Complexes are of the type [NiR(N-0)L] [R = o-tolyl, N-0 = 2-
pyridinecarboxylate pyca, L = PPh3 (la); R = o-tolyl, N-0 = p y c a, L =
P(CH2Ph)3 (lb); R = o-tolyl, N-0 = pyca, L = PMePh2 (lc); R = o-tolyl, N-0 =
PYca, L = PMe2Ph (1d); R = o-tolyl, N-0 = pyca, L = PCy3 (le); R = mesityl, NO
= pyca, L = PMePh2 (10; R = phenyl, N-0 = pyca, L = PPh3 (lg); R = p-tolyl,
N-0 = pyca, L = PPh3 (lh); R = mesityl, N-0 = 2-pyridineacetate pyac, L =
PMePh2 (2a); R = o-tolyl, N-0 = 2-pyrazinecarboxylate pyzca, L = PPh3 (3a); R
= o-tolyl, N-0 = pyzca, L = P(CH2Ph)3 (3b); R = o-tolyl, N-0 = 4-nitro-2-
pyridinecarboxylate 4-NO 2-pyca, L = PPh3 (4a); R = o-tolyl, N-0 = 4-methoxy-
2-pyridinecarboxylate 4-Me0-pyca, L = PPh3 (5a)]. The complexes differ in the
steric and electronic nature of the monodentate phosphine ligand, the size of the
metallacycle (5-membered or 6-membered (2a)) and in the basicity of the N-0
-chelate. Crystal structure for the complexes [Ni(o-tolyl)pycaPPh3], [Ni(o-toly1)4-
NO2
-pycaPPh3], [Ni(mesityl)pycaPMePh2] and [Ni(mesityl)p y a cPMePh2]
indicate that the complexes have a square planar coordination with the phosphine
ligand trans to the nitrogen atom.
Upon warming, the complexes form moderately active single component
catalysts for the oligomerisation of ethene. Products are 95-98% linear containing
60-80% a-olefins and show a geometric distribution of chain lengths. The effects
of phosphine ligands, chelate ring size and chelate basicitS, on the catalytic
performance have been studied. Catalyst activities and product distributions are
highly dependant on the phosphine ligand present. Highest activities are obtained
with complexes [Ni(o-tolyl)pycaPPh3 ] and [Ni(o-tolyl)pycaP(CH2Ph)31 and the
highest percentage of linear a-olefins in the product is generated by [Ni(otolyl)pycaPMe2Ph].
Addition of excess PPh3 to the catalysts derived from [Ni(otolyl)pycaPPh3]
provides mechanistic information on the oligomerisation
process. The results are interpreted in terms of an associative insertion
mechanism for the oligomerisation catalysts.

The catalytic behaviour of the complexes vary greatly when the bidentate
ligand is substituted in the 4-position of the pyridyl ring. It was found that
complexes [Ni(o-toly1)4-NO2-pycaPPh3 ], [Ni(o-tolyl)pyzcaPPh 3 ] and [Ni(otoly1)4-Me0-pycaPPh
3 ] act as polymerisation catalysts and produce high molecular weight polyethylene. The possibility of two different insertion
pathways being followed for the oligomerisation catalysts and the polymerisation
catalysts may explain the different products obtained. Remarkably, the
polymerisation catalysts are active for the copolymerisation of ethene with carbon
monoxide and produce high molecular weight perfectly alternating polyketone.
The complexes also form a moderately active catalytic system for the
dimerisation of propene in the presence of alkyl aluminium co-catalysts such as
A1Et2
C1 ' A1EtC1 2 and methylaluminoxane (MAO). The reaction has been
examined as a function of catalyst, co-catalyst, and solvent. The activity and
isomer distribution are shown to depend on the phosphine and bidentate ligands.
The nature of the co-catalyst greatly affects the catalytic performance. The results
are consistent with a bimetallic Ni-Al catalytic intermediate in equilibrium with
excess co-catalyst.

Item Type: Thesis (Unspecified)
Copyright Holders: The Author
Additional Information:

Includes bibliography

Date Deposited: 09 Dec 2014 00:16
Last Modified: 11 Mar 2016 05:55
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