New bi-nuclear and multi-nuclear α-diimine/nickel catalysts for ethylene polymerization

Article abstract of DOI:10.1016/j.molcata.2004.10.013

Bi-nickel-centre catalysts {[2,6-diisopropyl-C₆H ₃NC(CH₃)(CH₃)CN3,5-di-RC₆H ₂CH₂3′,5′-di-RC₆H ₂NC(CH₃)(CH₃)CN2,6-diisopropyl-C _6<

Full text of DOI:10.1016/j.molcata.2004.10.013

Journal of Molecular Catalysis A: Chemical 227 (2005) 153–161
New bi-nuclear and multi-nuclear ␣-diimine/nickel catalysts
for ethylene polymerization
He-Kuan Luo∗, Herbert Schumann∗∗
Institut fu¨r Chemie, Technischen Universuta¨t Berlin (TU-Berlin), Straße des 17, Juni 135, D-10623 Berlin, Germany
Received 9 July 2004; received in revised form 22 August 2004; accepted 7 October 2004
Available online 10 December 2004
Abstract
Bi-nickel-centre catalysts {[2,6-diisopropyl-C6 H3 N=C(CH3) (CH3)C=N 3,5-di-R C6H2 CH2 3ꢀ,5ꢀ-di-R C6H2 N=C(CH3)
(CH3)C=N 2,6-diisopropyl-C6H3][NiCl2]2; R, CH(CH3)2, CH2CH3, CH3} were prepared by Schiff-base condensation of 2,3-
butanedione with 2,6-diisopropylaniline and substituted bis-aniline, and subsequent metathesis reaction with (DME)NiCl2. Multi-nickel-
centrecatalysts { [( N=C(CH3) (CH3)C=N 3,5-di-R C6H2 CH2 3ꢀ,5ꢀ-di-R C6H2 ) NiCl2]n ;R, CH(CH3)2, n = 4.0;R, CH2CH3,
n = 4.0; R, CH3, n = 2.5} were prepared by Schiff-base condensation of 2,3-butanedione with substituted bis-aniline, and subsequent metathe-
sis reaction with (DME)NiCl2. Comparing with mono-nickel-centre catalysts, the new catalysts have much bigger molecules, particularly
the distance between every two active centres was controlled for bi-nickel-centre catalysts, and the distances among several active centres
were controlled for multi-nickel-centre catalysts, resulting in the micro chemical environment of nickel centre being regulated. The catalytic
evaluation clearly showed that this structural regulation had significant influence on catalytic activity. When the substitute was isopropyl
or ethyl, the new catalysts demonstrated much higher catalytic activity than the corresponding mono-nickel-centre catalysts; but when the
substitute was methyl, the new catalysts demonstrated lower catalytic activity than the corresponding mono-nickel-centre catalysts. The most
efficient new catalyst was multi-nickel-centre catalyst with ethyl as substitute, which catalytic activity was high up to 3220 gPE/(gNi h) at
25 ◦C with Al(MAO)/Ni ratio at 500.
© 2004 Elsevier B.V. All rights reserved.
Keywords: ␣-Diimine; Nickel; Catalyst; Ethylene; Polyethylene
1. Introduction
have been developed very quickly in the past two decades
because of their more excellent capability to control the mi-
crostructures of polyolefins by regulating the microstructures
of well-defined transition metal complexes used as precata-
lysts [1–6].
Among well-defined catalysts, most attention has ever
been focused on early transition metal do and lanthanide dofn
systems [7–10]. But in the past several years, there has rapidly
growing interest in the area of late-transition metal catalysts
for ethylene and ␣-olefins polymerization. Recent develop-
mentshaveresultedinhighlyactivelate-transitionmetalcata-
lysts [4–6]. In this field, the key milestones have been the dis-
coveries of the ␣-diimine/Ni(II) and Pd(II) catalysts [11–19],
and the 2,6-bis(imino)pyridine/Fe(II) and Co(II) catalysts
[20–29], both of which are highly active catalysts for ethy-
lene polymerization upon activation with methyl aluminox-
ane (MAO). Comparing with early transition metal catalysts,
Driven by industrial desire to obtain ever greater control
over the properties of polyolefins to satisfy the increasing de-
mands of human beings and market, the search for new highly
active and selective catalysts for ethylene and ␣-olefins poly-
merization has always been an active research field in the past
half century. Following the discovery and industrial applica-
tion of multi-site Ziegler–Natta type catalysts, well-defined
single-site catalysts have attracted extensive attention and
∗
Corresponding author. Present address: School of Chemistry, The
Queen’s University of Belfast, David Keir Building, Stranmillis Road,
Belfast BT9 5AG, UK.
∗∗
Co-corresponding author.
E-mail addresses: hkluo@yahoo.com (H.-K. Luo),
schumann@chem.tu-berlin.de (H. Schumann).
1381-1169/$ – see front matter © 2004 Elsevier B.V. All rights reserved.
doi:10.1016/j.molcata.2004.10.013

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H.-K. Luo, H. Schumann / Journal of Molecular Catalysis A: Chemical 227 (2005) 153–161
such as titanium, zirconium or chromium based catalysts with
high oxophilicity including metallocene type and ligand in-
corporated complex type which are easily being poisoned
by most functionalized olefins, late-transition metal catalysts
have lower oxophilicity, and therefore, have greater func-
tional group tolerance to polar monomers. Actually the ␣-
diimine/Pd(II) catalysts could catalyze the copolymerization
of ethylene with functionized olefins [30–33].
found that substituted bis-aniline could be used to prepared
bi-nuclear and multi-nuclear diimine/Ni(II) catalysts, which
have been proved to be highly active catalysts for ethylene
polymerization. Here, we report the synthesis of these new
ligands, the preparation of bi- and multi-nuclear Ni(II) based
catalysts, and the catalytic studies for ethylene polymeriza-
tion under the activation of methyl aluminoxane.
Among late-transition metal catalysts, the ␣-diimine/
Ni(II) and Pd(II) catalysts [11–19] formed a new kind of
highly active catalysts to convert ethylene to high molecu-
lar mass polyethylene. Regarding previous studies and ap-
plication of nickel catalysts in industry, mostly producing ␣-
olefins by oligomerization which is the basis of the SHELL
higher olefin process (SHOP), this new ␣-diimine/Ni(II) and
Pd(II) catalysts opened a new idea and understanding to
search for new catalysts. The key is to use bulky substitute to
reduce the competing ␤-hydrogen elimination. In particular,
this new nickel(II) and palladium(II) based catalysts could
convert ethylene directly to highly branched polyethylene
without the addition of expensive ␣-olefins, such as 1-hexene
and 1-octene [14].
2. Experimental
2.1. General considerations
All manipulations involving air-sentive materials were
carried out by using standard Schlenk techniques under an
atmosphere of nitrogen. Dichloromethane was distilled from
calcium hydride, toluene and hexane were distilled from
sodium. Methyl aluminoxane solution (10%) in toluene was
purchased from Aldrich to be used directly without any treat-
1
ment. H NMR and 13C NMR were recorded on ARX200
spectrometer. (DME)NiCl2 was prepared according to a re-
ported method [43].
After the ␣-diimine/Ni(II) and Pd(II) catalysts were firstly
published in 1995 by Brookhart and co-workers [11], see (1)
and (2) in Scheme 1, extensive interests have been aroused
on these unque catalysts, up to now, some closely related
catalyst systems have been reported in order to understand
the mechanism more deeply and to develop new catalysts
by Brookhart and some other groups. Brookhart and his co-
workers subsequently developed a new kind of neutral nickel
catalysts derived from bulky anilinotropone ligands [34–37],
see (3) in Scheme 1, which also showed high activity for
ethylene polymerization. Gibson and his co-workers devel-
oped some Ni(II) and Pd(II) catalysts containing iminopyri-
dine ligands [38,39], see (4) in Scheme 1, which generally
demonstrated greatly reduced ethylene polymerization activ-
ity because of lack of steric protection on one side of the axial
position in the square-plannar active species. Besides these,
some nickel catalysts containing diphosphine ligands [40],
and [PO] ligands [41,42], are also active catalysts for ethylene
polymerization. In our effort to search for new highly active
␣-diimine/Ni(II) catalysts for ethylene polymerization, we
2.2. General procedure for ethylene polymerization
The polymerization of ethylene was carried out in a 1 l
glass autoclave equipped with a mechanical stirrer which
stirring rate is adjustable. The autoclave was heated by re-
cycling hot water. Before reaction, the autoclave was dried
by heating at 80 ◦C under vacuum for 2 h, during which pe-
riod the autoclave was swept with dry N2 at least three times.
After the autoclave was dried completely and cooled down
to room temperature, toluene, MAO and catalyst solution in
dichloromethane were introduced in turn with syringes. The
mixture was stirred for several minutes; then, the autoclave
was vacuumed and ethylene was pressed in quickly, imme-
diately the polymerization was initiated and was observed
soon. The reaction pressure, the maxium flow rate of ethy-
lene and the stirring rate were set up at 5.0 bar, 280 mg/min
and 450 rpm, respectively. The catalytic polymerization was
run for 30 min under 25 ◦C. After which time the pressure
was vented and the polymerization was quenched with excess
Scheme 1. Some reported nickel based catalysts for ethylene polymerization.

H.-K. Luo, H. Schumann / Journal of Molecular Catalysis A: Chemical 227 (2005) 153–161
155
ethanol. The produced polymer was taken out by opening the
autoclave, washed with diluted hydrochloric acid and then
ethanol, and then dried in oven at 80 ◦C overnight. Finally,
the polymer was weighed and the reaction rate was calculated
in unit of g PE/(g Ni h).
charged with 3.29 g (18.59 mmol) 2,6-diisopropylaniline,
1.60 g (18.59 mmol) 2,3-butanedione, 30 ml ethanol and
0.4 ml glacial acetic acid, the pale yellow solution was stirred
for one day at room temperature. Then, 3.41 g (9.30 mmol)
4,4ꢀ-methylbis(2,6-diisopropylaniline) and more 30 ml
ethanolwasadded. Thefinalsolutionwasstirredforoneweek
at room temperature while yellow precipitate was produced.
The yellow precipitate was isolated by filtration, washed with
2 × 10 ml ethanol, and dried in vacuum; 4.8 g yellow powder
was obtained; yield, 63%. Anal. calculated for C57H80N4
(%): C, 83.36; H, 9.82; N, 6.82. Found (%): C, 82.46;
2.3. Preparation of ligands and complexes
2.3.1. Preparation of ligand-A1
2, 6-Diisopropyl-C6H3 N C(CH3) (CH3)C N 3,5-di-
R C6H2 CH2 3ꢀ,5ꢀ-di-R C6H2 N C(CH3) (CH3)C N
2,6-diisopropyl-C6H3; R, CH(CH3)2 (for the molecular
structure, see Scheme 2). A 100 ml Schlenk flask was
1
H, 10.10; N, 6.59. H NMR (CDCl3, δ): 1.23, 1.24, 1.26,
1.29 ( CH(CH3)2), 2.15, 2.17 ( N C(CH3) C(CH3) N ),
Scheme 2. The route for the preparation of ligand-A1–A3 and complex-A1–A3.

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H.-K. Luo, H. Schumann / Journal of Molecular Catalysis A: Chemical 227 (2005) 153–161
2.73, 2.77, 2.80, 2.83, 2.87 ( CH(CH3)2), 4.11 ( C N 3,5-
di-R C6H2 CH2 3ꢀ,5ꢀ-di-R C6H2 N C ), 7.09 ( C
N 3,5-di-R C6H2 CH2 3ꢀ,5ꢀ-di-R C6H2 N C ), 7.15–
7.26 (2,6-diisopropyl C6H3 N C ). 13C NMR (CDCl3,
δ): 16.53, 16.57 ( N C(CH3) C(CH3) N ), 22.67, 22.79,
22.98, 23.06 ( CH(CH3)2), 28.48 ( CH(CH3)2), 41.42
( C N 3,5-di-R C6H2 CH2 3ꢀ,5ꢀ-di-R C6H2 N C ),
122.97, 123.16, 135.02, 146.18 (2,6-diisopropyl-
C6H3 N C ), 123.66, 134.97, 136.42, 144.02 ( C N
3,5-di-R C6H2 CH2 3ꢀ,5ꢀ-di-R C6H2 N C ), 168.21,
168.45 ( N C(CH3) C(CH3) N ).
15.91, 16.45 ( N C(CH3) C(CH3) N ), 17.79 ( C N
3, 5-di-(CH3) C6H2 CH2 3ꢀ, 5ꢀ -di-(CH3) C6H2 N C ),
22.67, 23.00 ( CH(CH3)2), 28.42 ( CH(CH3)2), 40.73
( C N 3, 5 -di-R C6H2 CH2 3ꢀ, 5ꢀ -di-R C6H2 N C ),
122.95, 123.72, 135.00, 146.27 (2,6-diisopropyl-C6H3
N C ), 124.59, 128.50, 136.32, 146.13 ( C N 3,5-di-
R C6H2 CH2 3ꢀ,5ꢀ-di-R C6H2 N C ), 168.00, 168.23
( N C(CH3) C(CH3) N ).
2.3.4. Preparation of ligand-B1
[ N C(CH3) (CH3)C N 3,5-di-
R C6H2 CH2 3ꢀ,5ꢀ-di-R C6H2-]n ; R, CH(CH3)2 (for
the molecular structure, see Scheme 3). A 100 ml Schlenk
flask was charged with 1.12 g (13.01 mmol) 2,3-butanedione,
5.25 g (14.32 mmol) 4,4ꢀ-methylbis(2,6-diisopropylaniline),
50 ml ethanol and 0.4 ml glacial acetic acid. The final
mixture was stirred for one week at room temperature while
yellow precipitate was produced. The yellow precipitate
was isolated by filtration, washed with 3× 10 ml ethanol,
and dried in vacuum; 5.29 g yellow powder was obtained;
yield, 98%. Anal. calculated for repeating unit C29H40N2
(%): C, 83.60; H, 9.68; N, 6.72. Found (%): C, 83.34; H,
2.3.2. Preparation of ligand-A2
2, 6-diisopropyl-C6H3 N C(CH3) (CH3)C N 3, 5-di-
R C6H2 CH2 3ꢀ,5ꢀ-di-R C6H2 N C(CH3) (CH3)C N
2,6-diisopropyl-C6H3; R, CH2CH3 (for the molecular
structure, see Scheme2). Thetitlecompoundwaspreparedby
using the same procedure for the preparation of ligand-A1 by
using 2.89 g (9.30 mmol) 4,4ꢀ-methylbis(2,6-diethylaniline)
instead of 3.41 g 4,4ꢀ-methylbis(2,6-diisopropylaniline);
4.3 g yellow powder was obtained; yield, 61%. Anal.
calculated for C53H72N4 (%): C, 83.19; H, 9.48; N, 7.32.
1
1
Found (%): C, 82.89; H,9.90; N, 7.30. H NMR (CDCl3,
10.78; N, 6.99. H NMR (CDCl3, δ): repeating unite: 1.18,
δ): 1.243, 1.256, 1.271 ( CH2CH3), 1.28, 1.29, 1.31, 1.33
( CH(CH3)2), 2.17, 2.19 ( N C(CH3) C(CH3) N ),
2.41, 2.45, 2.49, 2.52 ( CH2CH3), 2.74, 2.78,
2.82, 2.85, 2.89 ( CH(CH3)2), 4.01 ( C N 3,5-di-
R C6H2 CH2 3ꢀ,5ꢀ-di-R C6H2 N C ), 7.07 ( C N
3,5-di-R C6H2 CH2 3ꢀ,5ꢀ-di-R C6H2 N C ), 7.15–7.24
(2,6-diisopropyl-C6H3 N C ). 13C NMR (CDCl3, δ): 13.73
( CH2CH3), 16.24, 16.52 ( N C(CH3) C(CH3) N ),
22.67, 22.98 ( CH(CH3)2), 24.76 ( CH2CH3), 28.45
( CH(CH3)2), 41.08 ( C N 3,5-di-R C6H2 CH2 3ꢀ,5ꢀ-
di-R C6H2 N C ), 122.94, 123.72, 134.99, 146.14 (2,6-
diisopropyl-C6H3 N C ), 126.79, 130.46, 136.49, 145.30
( C N 3, 5-di-R C6H2 CH2 3ꢀ, 5ꢀ -di-R C6H2 N C ),
168.11, 168.16 ( N C(CH3) C(CH3) N ).
1.22 ( CH(CH3)2), 2.13 ( N C(CH3) (CH3)C N ), 2.69,
2.72, 2.75, 2.79, 2.82 ( CH(CH3)2), 4.07 ( C N 3,5-di-
R C6H2 CH2 3ꢀ,5ꢀ-di-R C6H2 ), 7.05 ( C N 3,5-di-
R C6H2 CH2 3ꢀ,5ꢀ-di-R C6H2 ). End group: 1.30, 1.35
( C N 3,5-di-((CH3)2CH) C6H2 CH2 3ꢀ,5ꢀ-di-((CH3)2
CH) C6H2 NH2), 2.90, 2.94, 2.98, 3.01, 3.04 ( C
N 3,5-di-((CH3)2CH) C6H2 CH2 3ꢀ,5ꢀ-di-((CH3)2CH)
C6H2 NH2), 3.98 ( C N 3,5-di-((CH3)2CH) C6H2
CH2 3ꢀ,5ꢀ-di-((CH3)2CH) C6H2 NH2), 6.92 ( C N 3,5-
di-((CH3)2CH) C6H2 CH2 3ꢀ, 5ꢀ -di-((CH3)2CH) C6H2
NH2). 13C NMR (CDCl3, ␦): repeating unite: 16.55
( N C(CH3) C(CH3) N ), 22.78, 23.04 ( CH(CH3)2),
27.93 ( CH(CH3)2), 41.40 ( C N 3,5-di-R C6H2
CH2 3ꢀ,5ꢀ-di-R C6H2 ), 123.64, 134.97, 136.37, 144.03
( C N 3,5-di-R C6H2 CH2 3ꢀ,5ꢀ-di-R C6H2 ), 168.50
( N C(CH3) C(CH3) N ). End group: 22.51 ( C N
3,5-di-((CH3)2CH) C6H2 CH2 3ꢀ,5ꢀ-di-((CH3)2CH) C6
H2 NH2), 27.84 ( C N 3,5-di-((CH3)2CH) C6H2 CH2
3ꢀ,5ꢀ-di-((CH3)2CH) C6H2 NH2), 41.27 ( C N 3,5-
di-((CH3)2CH) C6H2 CH2 3ꢀ,5ꢀ-di-((CH3)2CH) C6H2
NH2), 123.16, 131.31, 132.52, 137.97 ( C N 3,5-di-
((CH3)2CH) C6H2 CH2 3ꢀ, 5ꢀ -di-((CH3)2CH) C6H2
NH2).
2.3.3. Preparation of ligand-A3
2, 6-Diisopropyl-C6H3 N C(CH3) (CH3)C N 3, 5-di-
R C6H2 CH2 3ꢀ,5ꢀ-di-R C6H2 N C(CH3) (CH3)C N
2,6-diisopropyl-C6H3; R, CH3 (for the molecular structure,
see Scheme 2). The title compound was prepared by using
the same procedure for the preparation of ligand-A1 by us-
ing 2.37 g (9.30 mmol) 4,4ꢀ-methylbis(2,6-dimethylaniline)
instead of 3.41 g 4,4ꢀ-methylbis(2,6-diisopropylaniline);
2.24 g yellow powder was obtained; yield, 34%. Anal.
calculated for C49H64N4 (%): C, 83.00; H, 9.10; N,
7.90. Found (%): C, 82.52; H,9.44; N, 7.89. 1H NMR
(CDCl3, δ): 1.22, 1.24, 1.26, 1.27 ( CH(CH3)2), 2.09
( C N 3,5-di-(CH3) C6H2 CH2 3ꢀ,5ꢀ-di-(CH3) C6H2
N C ), 2.13 ( N C(CH3) C(CH3) N ), 2.74, 2.77,
2.79, 2.81, 2.84 ( CH(CH3)2), 3.93 ( C N 3,5-di-
R C6H2 CH2 3ꢀ,5ꢀ-di-R C6H2 N C ), 6.99 ( C N
3,5-di-R C6H2 CH2 3ꢀ,5ꢀ-di-R C6H2 N C ), 7.11–7.24
(2,6-diisopropyl-C6H3 N C ). 13C NMR (CDCl3, δ):
2.3.5. Preparation of ligand-B2
[ N C(CH3) (CH3)C N 3,5-di-R C6H2 CH2 3ꢀ,5ꢀ
-di-R C6H2-]n ; R, CH2CH3 (for the molecular structure,
see Scheme 3). The title compound was prepared by using
the same procedure for the preparation of ligand-B1 by
using 1.07 g (12.43 mmol) 2,3-butanedione and 4.25 g
(13.69 mmol) 4,4ꢀ-methylbis(2,6-diethylaniline); 3.57 g
yellow powder was obtained; yield, 80%. Anal. calculated
for repeating unit C25H32N2(%): C, 83.29; H, 8.95; N, 7.77.

H.-K. Luo, H. Schumann / Journal of Molecular Catalysis A: Chemical 227 (2005) 153–161
157
Scheme 3. The route for the preparation of ligand-B1–B3 and complex-B1–B3.
1
H2 CH2 3ꢀ,5ꢀ-di-(CH3CH2) C6H2 NH2), 126.50, 127.71,
129.88, 139.38 ( C N 3,5-di-(CH3CH2) C6H2 CH2
3ꢀ,5ꢀ-di-(CH3CH2) C6H2 NH2).
Found (%): C, 82.51; H, 9.51; N, 7.67. H NMR (CDCl3,
δ): repeating unite: 1.21, 1.25, 1.28 ( CH2CH3), 2.19
( N C(CH3) (CH3)C N ), 2.35, 2.45, 2.48, 2.56
( CH2CH3), 4.05 ( C N 3,5-di-R C6H2 CH2 3ꢀ,5ꢀ-
di-R C6H2 ), 7.07 ( C N 3,5-di-R C6H2 CH2 3ꢀ,5ꢀ-
di-R C6H2 ). End group: 1.34, 1.38 ( C N 3,5-di-
(CH3CH2) C6H2 CH2 3ꢀ,5ꢀ-di-(CH3CH2) C6H2 NH2),
2.60, 2.63 ( C N 3,5-di-(CH3CH2) C6H2 CH2 3ꢀ,5ꢀ-
di-(CH3CH2) C6H2 NH2), 3.97 ( C N 3,5-di-(CH3
CH2) C6H2 CH2 3ꢀ,5ꢀ-di-(CH3CH2) C6H2 NH2), 6.93
( C N 3,5-di-(CH3CH2) C6H2 CH2 3ꢀ,5ꢀ-di-(CH3CH2)
C6H2 NH2). 13C NMR (CDCl3, δ): repeating unite: 13.71
( CH2CH3), 16.13 ( N C(CH3) C(CH3) N ), 24.72
( CH2(CH3)), 41.03 ( C N 3,5-di-R C6H2 CH2 3ꢀ,5ꢀ-
di-R C6H2 ), 126.71, 130.41, 136.43, 145.28 ( C N
3,5-di-R C6H2 CH2 3ꢀ,5ꢀ-di-R C6H2 ), 168.14 ( N
C(CH3) C(CH3) N ). End group: 13.11 ( C N 3,5-di-
(CH3CH2) C6H2 CH2 3ꢀ,5ꢀ-di-(CH3CH2) C6H2 NH2),
24.32( C N 3,5-di-(CH3CH2) C6H2 CH2 3ꢀ,5ꢀ-di-(CH3
CH2) C6H2 NH2), 40.87 ( C N 3,5-di-(CH3CH2) C6
2.3.6. Preparation of ligand-B3
[ N C(CH3) (CH3)C N 3,5-di-R C6H2 CH2 3ꢀ,5ꢀ
-di-R C6H2-]n ; R, CH3 (for the molecular structure,
see Scheme 3). The title compound was prepared by using
the same procedure for the preparation of ligand-B1 by
using 1.16 g (13.47 mmol) 2,3-butanedione and 3.77 g
(14.82 mmol) 4,4ꢀ-methylbis(2,6-dimethylaniline); 3.60 g
yellow powder was obtained; yield, 88%. Anal. calculated
for repeating unit C21H24N2 (%): C, 82.85; H, 7.95; N,
9.20. Found (%): C, 80.78; H, 7.46; N, 9.31. 1H NMR
(CDCl3, δ): repeating unite: 2.13 ( C N 3,5-di-(CH3) C6
H2 CH2 3ꢀ,5ꢀ-di-(CH3) C6H2 ), 2.24 ( N C(CH3)
(CH3) C N ), 3.96 ( C N 3,5-di-R C6H2 CH2 3ꢀ,5ꢀ-
di-R C6H2 ), 7.03 ( C N 3,5-di-R C6H2 CH2 3ꢀ,5ꢀ-di-
R C6H2 ). End group: 2.17 ( C N 3,5-di-(CH3) C6H2
CH2 3ꢀ,5ꢀ-di-(CH3) C6H2 NH2), 3.88 ( C N 3,5-di-

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Scheme 4. The route for the preparation of ligand-C1–C3 and complex-C1–C3.
(CH3) C6H2 CH2 3ꢀ,5ꢀ-di-(CH3) C6H2 NH2),
6.90
2.3.8. Preparation of complex-A2
( C N 3,5-di-(CH3) C6H2 CH2 3ꢀ,5ꢀ-di-(CH3) C6H2
{[2,6-Diisopropyl-C6H3 N C(CH3) (CH3)C N 3,5-
di-R C6H2 CH2 3ꢀ, 5ꢀ -di-R C6H2 N C(CH3) (CH3)-
C N 2,6-diisopropyl-C6H3][NiCl2]2; R, CH2CH3} (for
the molecular structure, see Scheme 2). The title compound
was prepared with the same procedure for the preparation
of complex-A1 by using 1.13 g (5.14 mmol) (DME)NiCl2
and 1.98 g (2.59 mmol) ligand-A2; 2.06 g red/brown solid
product was obtained; yield, 78%. Anal. calculated for
C53H72N4 Ni2Cl4 (%): C, 62.14; H, 7.08; N, 5.47. Found
(%): C, 60.38; H, 7.51; N, 5.46.
NH2). 13C NMR (CDCl3, δ): repeating unite: 15.76 ( N
C(CH3) C(CH3) N ),
C6H2 CH2 3ꢀ,5ꢀ-di-(CH3) C6H2 ), 40.61 ( C N 3,5-
di-(CH3) C6H2 CH2 3ꢀ,5ꢀ-di-(CH3) C6H2 ),
124.52,
17.73
( C N 3,5-di-(CH3)
128.39, 136.22, 146.24 ( C N 3,5-di-(CH3) C6H2
CH2 3ꢀ,5ꢀ-di-(CH3) C6H2 ), 168.09 ( N C(CH3) C
(CH3) N ). End group: 17.51 ( C N 3,5-di-(CH3)
C6H2 CH2 3ꢀ,5ꢀ-di-(CH3) C6H2 NH2), 40.32 ( C N
3, 5-di-(CH3) C6H2 CH2 3ꢀ, 5ꢀ -di-(CH3) C6H2 NH2),
121.63, 128.58, 130.97, 140.55 ( C N 3,5-di-(CH3)
C6H2 CH2 3ꢀ,5ꢀ-di-(CH3) C6H2 NH2).
2.3.9. Preparation of complex-A3
Ligand-C1–C3 were prepared accoding to literature [44],
see Scheme 4.
{[2,6-Diisopropyl-C6H3 N C(CH3) (CH3)C N 3,5-
di-R C6H2 CH2 3ꢀ,5ꢀ-di-R C6H2 N C(CH3) (CH3)-
C N 2,6-diisopropyl-C6H3][NiCl2]2; R, CH3} (for the
molecular structure, see Scheme 2). The title compound
was prepared with the same procedure for the preparation
of complex-A1 by using 0.85 g (3.87 mmol) (DME)NiCl2
and 1.38 g (1.95 mmol) ligand-A3; 1.26 g red/brown solid
product was obtained; yield, 67%. Anal. calculated for
C49H64N4Ni2Cl4 (%): C, 60.78; H, 6.66; N, 5.79. Found
(%): C, 59.73; H, 7.09; N, 5.39.
2.3.7. Preparation of complex-A1
{[2,6-Diisopropyl-C6H3 N C(CH3) (CH3)C N 3,5-
di-R C6H2 CH2 3ꢀ, 5ꢀ -di-R C6H2 N C(CH3) (CH3)-
C N 2,6-diisopropyl-C6H3][NiCl2]2; R, CH(CH3)2} (for
the molecular structure, see Scheme 2). A 50 ml Schlenk
flask was charged with 0.55 g (2.50 mmol) (DME)NiCl2, to
which a solution of 1.07 g (1.30 mmol) ligand-A1 in 30 ml
dichloromethane was added under stirring. The resulting
red/brown mixture was stirred under room temperature over
night. After which time the mixture was filtrated to give
a clear red/brown solution which gave a red/brown solid
by removing the solvent dichloromethane under reduced
pressure. The red/brown solid product was washed with 3×
10 ml hexane, then dried in vacuum; 1.30 g product was
obtained; yield, 92%. Anal. calculated for C57H80N4Ni2Cl4
(%): C, 63.36; H, 7.46; N, 5.19. Found (%): C, 61.78; H,
7.47; N, 5.04.
2.3.10. Preparation of complex-B1
{ [( N C(CH3) (CH3)C N 3, 5 -di-R C6H2 CH2
3ꢀ,5ꢀ-di-R C6H2 )NiCl2]n ; R, CH(CH3)2} (for the
molecular structure, see Scheme 3). The title compound
was prepared with the same procedure for the preparation
of complex-A1 by using 0.62 g (2.82 mmol) (DME)NiCl2
and 1.19 g (2.86 mmol repeating unit) ligand-B1; 1.04 g
red/brown solid product was obtained; yield, 66%. Anal.
calculated for repeating unit C29H40N2NiCl2 (%): C,

H.-K. Luo, H. Schumann / Journal of Molecular Catalysis A: Chemical 227 (2005) 153–161
159
63.76; H, 7.38; N, 5.13. Found (%): C, 62.76; H, 8.21;
N, 5.03.
New ligands were synthesized by Schiff-base condensa-
tion using a little glacial acetic acid as promoter in ethanol.
Ligands A1–A3 were synthesized by first condensation of
2,3-butanedione with one equivalent 2,6-diisopropylaniline
to give an intermediate 3-(2,6-diisopropylphenylimino)-
2-butanone [45], without isolation which were then
condensed with 0.5 equivalent of substituted bis-aniline
4,4ꢀ-methylbis(2,6-diisopropylaniline), 4,4ꢀ-methylbis(2,6-
diethylaniline) or 4,4ꢀ-methylbis(2,6-dimethylaniline),
respectively, see Scheme 2; ligands B1–B3 were synthesized
straightforward by condensation of 2,3-butanedione with
one equivalent substituted bis-aniline 4,4ꢀ-methylbis(2,6-
2.3.11. Preparation of complex-B2
{ [( N C(CH3) (CH3)C N 3, 5 -di-R C6H2 CH2
3ꢀ,5ꢀ-di-R C6H2 )NiCl2]n ; R, CH2CH3} (for the molec-
ular structure, see Scheme 3). The title compound was
prepared with the same procedure for the preparation of
complex-A1 by using 0.87 g (3.96 mmol) (DME)NiCl2
and 1.44 g (3.99 mmol repeating unit) ligand-B2; 0.91g
red/brown solid product was obtained; yield, 46%. Anal.
calculated for repeating unit C25H32N2NiCl2 (%): C, 61.26;
H, 6.58; N, 5.72. Found (%): C, 60.21; H, 7.18; N, 5.81.
diisopropylaniline),
4,4ꢀ-methylbis(2,6-diethylaniline)
or 4,4ꢀ-methylbis(2,6-dimethylaniline), respectively, see
Scheme 3. Once the ligands were obtained, the correspond-
ing complexes can be prepared conveniently according to a
literature method [11].
2.3.12. Preparation of complex-B3
{ [( N C(CH3) (CH3)C N 3, 5 -di-R C6H2 CH2
3ꢀ,5ꢀ-di-R C6H2 )NiCl2]n ; R, CH3} (for the molecular
structure, see Scheme 3). The title compound was prepared
with the same procedure for the preparation of complex-A1
by using 1.23 g (5.60 mmol) (DME)NiCl2 and 1.73 g
(5.68 mmol repeating unit) ligand-B3; 0.35 g red/brown
solid product was obtained; yield, 14%. Anal. calculated for
repeating unit C21H24N2NiCl2 (%): C, 58.11; H, 5.57; N,
6.45. Found (%): C, 54.73; H, 5.54; N, 6.07.
In the preparation of ligands B1–B3, a little excess
(10%) of substituted bis-anilines were used to make the
main end groups of the obtained ligand to be aniline-
type end group (see Scheme 3). 13C NMR showed that,
when the substituted bis-aniline was 4,4ꢀ-methylbis(2,6-
diethylaniline), only aniline-type end groups were found;
but when the substituted bis-aniline was 4,4ꢀ-methylbis(2,6-
diisopropylaniline) or 4,4ꢀ-methylbis(2,6-dimethylaniline),
besides aniline-type end groups, a little amount of ketone-
type end groups were found (see Scheme 5). The number of
the repeating unit can be calculated from 1H NMR integra-
tion of CH2 group in C N 3,5-di-R C6H2 CH2 3ꢀ,5ꢀ-
di-R C6H2 . In ligands B1–B3, n is 4.0, 4.0 and 2.5, res-
pectively.
Complex-C1–C3 were prepared accoding to literature
[11], see Scheme 4.
3. Results and discussions
3.1. Synthesis of new ligands and complexes
The aim of this paper is to develop a convenient and prac-
tical method to prepare new highly active ␣-diimine/nickel
catalysts to regulate the catalytic performances for ethylene
polymerization. The basic idea is to utilize substituted bis-
anline instead of half or all the substituted anline to prepare
new ligands and corresponding complexes. By this way, the
molecular structures of the new catalysts were modified, in
particular, the distance between every two active centres was
controlled for bi-nickel-centre catalysts, in a similar way, the
distances among several active centres were controlled for
multi-nickel-centre catalysts, resulting in the micro chemical
environment of nickel centre being regulated. This structural
regulation may strongly influence the catalytic performances,
such as catalytic activity. Under the guide of this basic idea,
two kinds of new catalysts including bi-nickel-centre cata-
lysts {[2,6-diisopropyl-C6H3 N C(CH3) (CH3)C N 3,5
-di-R C6H2 CH2 3ꢀ,5ꢀ-di-R C6H2 N C(CH3) (CH3)C
N 2,6-diisopropyl-C6H3][NiCl2]2; R, CH(CH3)2, CH2
CH3, CH3} and multi-nickel-centre catalysts { [( N
C(CH3) (CH3)C N 3,5-di-R C6H2 CH2 3ꢀ,5ꢀ-di-R C6
H2 )NiCl2]n ; R, CH(CH3)2, n = 4.0; R, CH2CH3,
n = 4.0; R, CH3, n = 2.5}, were prepared and studied for
catalytic ethylene polymerization in toluene using MAO as
cocatalyst.
3.2. Catalytic studies for ethylene polymerization
The catalytic evaluation of new catalysts was carried out
in toluene using MAO as cocatalyst. Comparative studies
were also performed with mono-nickel-centre catalysts. The
results were shown in Table 1.
The results showed that the catalytic activity varied sig-
nificantly for catalysts of different kinds and for the same
Scheme 5. Ketone-type end groups in ligand-B1 (the first) and ligand-B3
(the second). (*) 13C NMR data.

160
H.-K. Luo, H. Schumann / Journal of Molecular Catalysis A: Chemical 227 (2005) 153–161
Table 1
Catalytic results of new catalysts for ethylene polymerization
Entry
Complex
Yield (g)
Activity (g/gNi h)
Colour
1
Polymerization status
2
3
1
2
3
4
5
6
7
8
9
A1
A2
A3
B1
B2
B3
C1
C2
C3
9.2
8.3
13.1
6.7
16.1
12.4
3.5
1840
Orange
Orange
Orange
Orange
Orange
Orange
Yellow
Yellow
Yellow
Green
Green
Green
Pale green
Pale green
Pale green
Green
Green
Pale yellow
Green
Green
Green
Pale green
Pale green
Pale green
From green to pale white
Green
From pale yellow to orange
Gooey
Gooey
Slurry
Gooey
Slurry
1660
2620
1340
3220
2480
700
Slurry
Gooey
Solutiona
Solutiona
7.1
16.7
1420
3320
Reaction conditions: 1 l glass autoclave, 150 ml toluene as solvent, 0.01 mmol Ni in 5 ml dichloromethane, 3.3 ml MAO as co-catalyst; stirring rate, 400/min;
25 ◦C; set point of ethylene pressure, 5.0 bar; maximum flow of ethylene, 280 mg/min; polymerization for 30 min. (1) Solution of precatalyst in dichloromethane
(0.002 mmol Ni/ml); (2) after combination with MAO; (3) during polymerization.
a
Polyethylene precipitated out after the polymerization was quenched with excess ethanol. But for A1–A3 and B1–B3 complexes, polyethylene precipitated
out quickly during the polymerization.
kind catalyst with different substitutes. Among bi-nickel-
centre catalysts, the highest activity was achieved when the
substitute is methyl. Amongst multi-nickel-centre catalysts,
the highest activity was achieved when the substitute is
ethyl; Among mono-nickel-centre catalysts, the highest ac-
tivity was achieved when the substitute is methyl. Compar-
ing the new catalysts, including bi-nickel-centre catalysts and
multi-nickel-centre catalysts, with mono-nickel-centre cata-
lysts, it could be found that both bi-nickel-centre catalysts
and multi-nickel-centre catalysts demonstrated much higher
catalytic activity for ethylene polymerization when the sub-
stitute was isopropyl or ethyl; but when the substitute was
methyl, the new catalysts demonstrated lower catalytic ac-
tivity than mono-nickel catalysts. The most active new cata-
lyst was multi-nickel-centre catalyst with ethyl as substitute
with the catalytic activity high up to 3220 gPE/(gNi h) (run
no. 5), which is comparable with the highest catalytic activ-
ity 3320 g/(gNi h) (run no. 9) of mono-nickel-centre catalyst
with methyl as substitute under the same reaction conditions.
Furthermore, the polymerization status could be observed
clearly because the reactor is transparent glass autoclave. The
results showed that the polymerization status was quite dif-
ferent for different kind of catalyst and for the same kind
catalyst with different substitutes, see Table 1. For run nos. 3,
5, 6, the polymerization system is slurry; for run nos. 1, 2, 4,
7, the polymerization system is gooey; For run nos. 8 and 9,
the polymerization system is solution, polyethylene emerged
after the reaction was quenched with excess ethanol.
imine/nickel catalysts for ethylene polymerization, were de-
veloped successfully.
It has been proved that the scale of the substituted aryl
group is one of the key factors of Ni(II) catalyst by reducing
the competitive ␤-H elimination [11]. Comparing with the
mono-nickel-centre catalysts, in bi-nickel-centre catalysts, it
can be considered that one of the two phenyl rings around
each nickel centre was introduced a bulky group at para posi-
tion; In multi-nickel-centre catalysts, it can be considered that
each of the two phenyl rings around each nickel centre was
introduced a bulky group at para position. Although generally
bulky substitutes at ortho positions of the phenyl rings have
great influence on catalytic activity [11], these bulky substi-
tutes at para positions could also have influence on catalytic
activity by affecting the competitive ␤-H elimination in some
extent. On the other hand, these bulky substitutes at para posi-
tions could also make the phenyl ring more electron-enriched,
and therefore, they could slightly affect the coordination be-
tweenchelatingatom(N)andnickelcentre, andprobablythey
could make the coordination bond a little stronger, through
which the catalytic performances, such as catalytic activity
could be regulated. This might be the reason why the bi-
nickel-centre catalysts, the multi-nickel-centre catalysts and
the mono-nickel-centre catalysts demonstrated different cat-
alytic activity even if the substitutes were the same.
The prime difference between new catalysts and mono-
nickel-centre catalysts is that the new catalysts have much
bigger molecules than the mono-nickel-centre catalysts. Par-
ticularly, the distance between every two nickel centres was
controlled for bi-nickel-centre catalysts, and the distances
among several nickel centres were controlled for multi-
nickel-centre catalysts. The experimental results in Table 1
clearly showed that this structural difference resulted in sig-
nificant influence on catalytic activity for ethylene polymer-
ization. Therefore, highly active bi- and multi-nuclear di-
4. Conclusions
A convenient method was developed to prepare new
␣-diimine/nickel catalysts using substituted bis-aniline.
Thus two kinds of new catalysts, including bi-nickel-centre
catalysts
{[2,6-diisopropyl-C6H3 N C(CH3) (CH3)C
N 3, 5 -di-R C6H2 CH2 3ꢀ, 5ꢀ -di-R C6H2 N C(CH3)
(CH3)C N 2,6-diisopropyl-C6H3][NiCl2]2; R,
CH-
(CH3)2, CH2CH3, CH3} and multi-nickel-centre catalysts
{ [( N C(CH3) (CH3)C N 3,5-di-R C6H2 CH2 3ꢀ,5ꢀ-

H.-K. Luo, H. Schumann / Journal of Molecular Catalysis A: Chemical 227 (2005) 153–161
161
di-R C6H2 )NiCl2]n
;
R,
CH(CH3)2, n = 4.0; R,
[15] L.K. Johnson, C.M. Killian, S.D. Arthur, et al., WO 96/23010
(1996).
[16] M.S. Brookhart, L.K. Johnson, S.D. Arthur, et al., US Patent
5886224 (1999).
[17] M.S. Brookhart, L.K. Johnson, C.M. Killian, et al., US Patent
5866663 (1999).
[18] M. S. Brookhart, L. K. Johnson. C. M. Killian, et al., US Patent
5891963 (1999).
[19] M.S. Brookhart, L.K. Johnson. C.M. Killian, et al., US Patent
5880241 (1999).
[20] B.L. Small, M. Brookhart, A.M.A. Bennett, J. Am. Chem. Soc. 120
(1998) 4049.
[21] A.M.A. Bennett, WO 98/27124 (1998).
[22] G.J.P. Britovsek, V.C. Gibson, B.S. Kimberley, et al., Chem. Com-
mun. (1998) 849.
CH2CH3, n = 4.0; R, CH3, n = 2.5}, were prepared.
The catalytic studies showed the new catalysts had highly
catalytic activity for ethylene polymerization. Comparing
with mono-nickel-centre catalysts, the new catalysts demon-
strated much higher catalytic activity when the substitute
was isopropyl or ethyl; But when the substitute was methyl,
the new catalysts demonstrated lower catalytic activity than
mono-nickel-centre catalysts. The most active new catalyst
was multi-nickel-centre catalyst with ethyl as substitute,
which catalytic activity was high up to 3220 gPE/(gNi h) at
25 ◦C with Al(MAO)/Ni ratio at 500.
[23] G.J.P. Britovsek, B.A. Dorer, V.C. Gibson, et al., WO 99/12981
(1999).
[24] V.C. Gibson, O.D. Hoarau, B.S. Kimberley, et al., WO 01/58966
(2001).
Acknowledgment
[25] G.J.P. Britovsek, V.C. Gibson, O.D. Hoarau, et al., Inorg. Chem. 42
(2003) 3454.
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[28] C. Pellecchia, M. Mazzeo, D. Pappalardo, Macromol. Rapid Com-
mun. 19 (1998) 651.
We thank the Alexander von Humboldt Foundation,
the Fonds der Chemischen Industrie and the Deutsche
Forschungsgemeinschaft (Graduiertenkolleg “Synthetische,
mechanistische und reaktionstechnische Aspekte von Metal-
lkatalysatoren”) for support of this work.
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(1996) 267.
[31] S. Mecking, L.K. Johnson, L. Wang, et al., J. Am. Chem. Soc. 120
(1998) 888.
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