Abstract
A series of arylimino-phenanthroline-cobalt(II) chloride complexes have been synthesised in which the 4-position of the 2,6-diisopropyl-substituted aryl group has been systematically modified to include electron donating and electron withdrawing substituents; the performance of the complexes as precatalysts for ethylene oligomerisation has been probed.
The 2-imino-1,10-phenanthroline ligands, 1,10-C
12H
7N
2-2-CR
N(2,6-
i-Pr
2-4-R
1-C
6H
2) [R
=
R
1
=
H (
L1); R
=
H, R
1
=
Br (
L2); R
=
H, R
1
=
CN (
L3); R
=
H, R
1
=
i-Pr (
L4); R
=
Me, R
1
=
H (
L5); R
=
Me, R
1
=
i-Pr (
L6)], have been prepared in high yield from the condensation reaction of 1,10-C
12H
7N
2-2-CR
O (R
=
H, Me) with one equivalent of the corresponding 4-substituted 2,6-diisopropylaniline. The molecular structures of
L2,
L5 and
L6 reveal the imino nitrogen atoms to adopt a transoid configuration with respect to the phenanthrolinyl nitrogen atoms. Treatment of
Lx with one equivalent of CoCl
2 in
n-BuOH at 90
°C gives the high spin complexes, (
Lx)CoCl
2 [
Lx
=
L1 (
1a),
L2 (
1b),
L3 (
1c),
L4 (
1d),
L5 (
1e),
L6 (
1f)], in which the metal centres exhibit distorted square pyramidal geometries. Activation of
1a–1f with excess methylaluminoxane (MAO) gives catalysts that are modestly active for the oligomerisation of ethylene affording mainly linear α-olefins along with some degree of internal olefins. While the donor capability of the 4-position of the
N-aryl group does not appear to affect the activity of the catalyst, it does have an influence on the ratio of α-olefins to internal olefins. Single crystal X-ray diffraction studies have been performed on
L2,
L5,
L6,
1a,
1c and
1f.