Self-immobilized catalysts for ethylene polymerization: Neutral, single-component salicylaldiminato phenyl nickel(II) complexes bearing allyl substituents

Article abstract of DOI:10.1039/b110258n

A new family of self-immobilized ethylene polymerization catalysts, derived from neutral, single-component salicylaldiminato phenyl nickel complexes, is described.

Full text of DOI:10.1039/b110258n

Self-immobilized catalysts for ethylene polymerization: neutral,
single-component salicylaldiminato phenyl nickel(II) complexes bearing
allyl substituents†
Dao Zhang, Guo-Xin Jin* and Ninghai Hu
State Key Laboratory of Polymer Physics and Chemistry, Changchun Institute of Applied Chemistry,
Chinese Academy of Sciences, Changchun 130 022, P. R. China. E-mail: gxjin@ciac.jl.cn
Institute of Chemistry and Environmental Sciences, Nanjing Normal University, Nanjing 210 097, P. R.
China
Received (in Cambridge, UK) 9th November 2001, Accepted 13th January 2002
First published as an Advance Article on the web 28th February 2002
A new family of self-immobilized ethylene polymerization
catalysts, derived from neutral, single-component salicyl-
aldiminato phenyl nickel complexes, is described.
An X-ray crystallographic structure analysis was carried out
for complex 5.§ As depicted in Fig. 1, complex 5 contains a
chelating salicylaldiminato ligand, a triphenylphosphine group
and a phenyl group. The Ni atom with four atoms of ligands (P,
O, N, C(1)) are arranged almost exactly planar. The plane of the
C (1) and C(7) phenyl rings are oriented almost orthogonally
(82.6 and 86.1°, respectively) to this plane. However, the
dihedral angle defined by C(24) phenyl ring and the nickel
coordination plane is only 13.0°. The cis angles at nickel are in
the range 85.61–93.56°. The Ni–O, Ni–N and Ni–C(1) bond
distances are similar to those in known nickel complexes.8,9 The
Ni–P bond of 5 (2.1838(12) Å) is more than 0.01 Å longer than
those of other complexes with the N–O bidentate ligand
(2.163(2) Å,9b 2.172(2) Å8).
Table 1 summarizes the catalytic performance of the self-
immobilized salicylaldiminato nickel(II) catalysts. In general,
high molecular weight and high activity are accomplished by
changing the ligand structure (introducing substituents at the
R1, R2 and R3 positions) and polymerization conditions
(including temperature, pressure of ethylene, and catalyst
loading) without any co-catalysts. 13C NMR analyses of the
polymers generated by these self-immobilized catalysts reveal
that there are only methyl branches in linear polyethylene. The
bulk density of PE produced by these catalysts are in the range
of 0.148–0.278 g cm23. In order to improve the morphology of
polymer products, catalysts 2–5 were co-polymerized with
styrene to generate polymerized Ni catalysts and SiO2-
supported core–shell catalysts. Further investigations of these
aspects are in progress.
Nickel catalysts have provided some of the most significant
advances in late transition metal olefin polymerization catalysis
and have given some of the most promising results.1 More
recently, Younkin et al. reported a new family of neutral, single-
component, salicylaldiminato nickel(II) catalysts that were
highly active systems for olefin polymerization.2
A great deal of interest has been focused on the heterogeniza-
tion of catalysts for olefin polymerization.3 Alt et al. developed
self-immobilized metallocene catalysts, involving the synthesis
of metallocene catalysts with an olefin or alkyne function that
can be used as a comonomer in the polymerization process.4
Here we synthesized a series of neutral, single-component
salicylaldiminato nickel complexes bearing allyl substituents as
self-immobilized catalysts that produce, without any cocata-
lysts, linear polymers with new microstructure.
The self-immobilized catalysts 1–5 (Scheme 1) were synthe-
sized via a modified literature procedure. 4-Allyl-2,6-dialkyl-
aniline was obtained from allyl chloride and 2,6-dialkylaniline
by rearranging with zinc chloride in refluxing xylene.5 Treat-
ment of an o-substituted phenol derivative with paraformalde-
hyde in the presence of SnCl4 produced a salicylaldehyde
derivative.6 3,5-Dinitrosalicylaldehyde was synthesized by
nitrating salicylaldehyde twice.7 This salicylaldehyde deriva-
tive reacted with allyl-substituted aniline, via Schiff base
condensation, to afford a salicyldimine ligand. The correspond-
ing nickel complex was obtained by the reaction of trans-
[Ni(Ph)Cl(PPh3)2] with 1 equiv. of the sodium salt of the
ligand.‡ 8
Changing the bulky substituents at the R1 or R3 position
influenced polymerization activity because they could shield
the axial faces and retard chain termination. For example,
complex 4 (R1 = Ph) displayed an activity of 1.8 3 105 g PE
(mol Ni)21 h21, while complex 1 (R1 = H) and complex 3 (R1
=
tBu) exhibited no activity for ethylene polymerization.
Scheme 1
Fig. 1 The molecular structure of 5. Selected bond lengths (Å) and angles
(°): Ni–O 1.903(2), Ni–P 2.1838(12),Ni–N 1.932(3), C(24)–O 1.302(3),
C(18)–N 1.293(4), C(7)–N 1.451(4), C(24)–C1(9) 1.438(4), C(18)–C(19)
1.411(4); C(1)–Ni–N 93.56(13), C(1)–Ni–P 85.61(11), N–Ni–O 93.08(11),
C(1)–Ni–O 165.7(2), N–Ni–P 171.01(10), O–Ni–P 89.75.
† Electronic supplementary information (ESI) available. Synthesis and
spectroscopic data for 5, spectroscopic data for 1–4. See http://www.rsc.org/
suppdata/cc/b1/b110258n/
574
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Fig. 2 Proposed mechanism for the ‘self-immobilization’ of a homogeneous neutral nickel(II) complex.
Table 1 Ethylene polymerization results of self-immobilized catalystsa
State Basic Research Projects (G 1999064800) is gratefully
acknowledged.
Catalyst/
Run mmol
c
c
T/°C 1025P/Pa Activityb Mw
Mw/Mn
Notes and references
1
2
3
4
5
6
7
8
9
10
11f
12
13
1 (65)
2 (65)
3 (65)
4 (65)
5 (65)
8d (65)
4e (65)
4 (65)
4 (33)
4 (15)
4 (33)
4 (33)
4 (33)
27
27
27
27
27
27
27
27
27
27
27
37
57
4.0
4.0
4.0
4.0
4.0
4.0
4.0
2.0
4.0
4.0
4.0
3.0
3.0
0
2.9
0
—
—
32.0
—
‡ For example, synthesis of 5: a solution of 1.0 g (1.44 mmol) chloro(trans-
di(triphenylphosphine))phenylnickel(II) and 0.545 g (1.5 mmol) of the
sodium salt of 3-phenyl-2-hydroxybenzaldehyde (2,6-dimethylanil) in
benzene (30 ml) was stirred at room temperature. After 24 h, the reaction
mixture was separated by centrifugation and the upper clear solution was
concentrated in vacuo. Hexane was added to the reaction mixture and a red
crystalline solid was obtained on separation by centrifugation and dried in
vacuo. Yield, 0.95 g (86%). An analogous method was used for preparation
of complexes 1–4. 1: Yield, 0.81 g (78%). 2: Yield, 1.05 g (90%). 3: Yield,
0.92 g (81%). 4: Yield, 0.95 g (83%).
§ Crystal data for 5: C48H42NNiOP, M = 738.51, triclinic, space group P1,
a = 9.481(4), b = 9.610(2), c = 22.451(10) Å, a = 101.01(3), ß =
100.84(3), g = 92.93(3)°, V = 1964.0(13) Å3, Z = 2, Dc = 1.249 g cm23
m(Mo-Ka) = 0.71073 Å, T = 293 K, red flat-crystal, 8568 independent
measured reflections, F2 refinement, R1 = 0.0437, wR2 = 0.0665, 6927
independent observed reflections (I > 2s(I), 3.78 5 2q 5 50.06), 471
parameters. CCDC reference number 154062. See http://www.rsc.org/
suppdata/cc/b1/b110258n/
192.4
—
66.4
121.8
207.0d
—
109.5
92.7
233.3
121.6
165.9
10.6
1.8
0.9
0.1
1.3
0.9
3.1
2.4
3.7
1.8
2.2
12.8
4.6
2.2d
—
7.5
9.9
3.1
3.0
4.3
2.3
¯
,
Conditions:a toluene; 120 ml, polymerization reaction; 1 h. b 105 g PE (mol
Ni)21 h21 c Mw (310 23) and Mw/Mn values were determined by GPC
.
measurement. d See ref. 2a. e Polymerization in the presence of 3 ml
methacrylate (MA). f Reaction time was 36 min.
1 For example: (a) L. K. Johnson, C. M. Killian and M. Brookhart, J. Am.
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Attachment of a methyl group, which was sterically smaller
than isopropyl group, at the R3 position, dramatically decreased
activity. Moreover, complex 4 showed a slight drop in activity
when 3 ml of methylacrylate (MA) was added to the
polymerization system, which indicated that the self-im-
mobilized neutral nickel catalysts are also tolerant of polar
monomers. The methylacrylate as functional olefin was not
incorporated into the polymer chain, which suggested that
addition of MA did not destroy the catalytic activity. Results
with complex 2 showed electron-withdrawing groups such as
nitro groups enhanced catalytic activity.
Most notable is the dramatic increase in polymerization
activity and clean behaviour because of the self-immobilizing
effect of the neutral nickel catalysts. Catalyst 4 is much more
active than the corresponding allyl-free analogues (runs 4, 6).
The mechanism of the self-immobilization is still not quite
clear. However, the proposed mechanism for the ‘self-im-
mobilization’ of the neutral nickel catalysts is that as soon as
ethylene is applied to the solution of the self-immobilized
catalysts, the ethylene is polymerized and simultaneously
catalyst molecules are incorporated into the growing polymer
due to their allyl functions. As a consequence the homogenous
catalyst is transferred to a heterogeneous system without
requiring any support. Active centers distributed on the polymer
chain are situated to make the best use of their catalytic
activities (Fig. 2).
3 G. G. Hlatky, Chem. Rev., 2000, 100, 1347.
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Financial support by the National Nature Science Foundation
of China (29974029, 29925101) and by Special Funds for Major
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