New octahedral bis-α-diimine nickel(II) complexes containing chloro-substituted aryl groups: Synthesis, characterization and testing as ethylene polymerisation catalysts

Article abstract of DOI:10.1016/j.jorganchem.2011.07.009

Three new 20-electron bis-α-diimine nickel (II) complexes containing chloro-substituted ligands, bis{bis[N,N′-(3-chloro-2-methylphenyl)imino]- 1,2-dimethylethane}dibromonickel 2a, bis{bis[N,N′-(3-chloro-2,6- dimethylphenyl)imino]-1,2-dimethylethane}dibromonickel 2b and bis{bis[N,N′-(4-chloro-2,6-dimethyl-phenyl)imino]-1,2-dimethylethane} dibromonickel 2c, were synthesized and characterized. The molecular structure of complex 2a was determined by X-ray crystallography. In the solid state, complex 2a has a pseudo-octahedral geometry about the nickel center, containing two α-diimine ligands in the pseudo-equatorial plane and two trans bromide ligands occupying the axial positions. These complexes, activated by diethylaluminum chloride (DEAC) were tested in the polymerization of ethylene under mild conditions. NMR analysis shows that highly branched polyethylenes are obtained using these bis-α-diimine nickel(II) complexes containing electron-withdrawing Cl groups in the aryl groups (e.g. 84 branches/1000 C, at 20 °C). The catalytic activity, polymer molecular weight and polymer degree of branching were significantly affected by the number of methyl substituents in the ortho-aryl position and the chlorine substituent position in the aryl rings of the coordinated α-diimine ligands.

Full text of DOI:10.1016/j.jorganchem.2011.07.009

Journal of Organometallic Chemistry 696 (2011) 3251e3256
Contents lists available at ScienceDirect
Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
New octahedral bis-a-diimine nickel(II) complexes containing chloro-substituted
aryl groups: Synthesis, characterization and testing as ethylene polymerisation
catalysts
,
a
b
b
a
a
Jianchao Yuan a , Tongjian Mei , Pedro T. Gomes , Maria M. Marques , Xuehu Wang , Yufeng Liu ,
*
Chengping Miao a, Xiaoli Xie a
a Key Laboratory of Eco-Environment-Related Polymer Materials of Ministry of Education, Key Laboratory of Polymer Materials of Gansu Province,
College of Chemistry & Chemical Engineering, Northwest Normal University, Lanzhou 730070, China
b Centro de Química Estrutural, Departamento de Engenharia Química e Biológica, Instituto Superior Técnico, Av. Rovisco Pais 1, 1049-001 Lisboa, Portugal
a r t i c l e i n f o
a b s t r a c t
Article history:
Three new 20-electron bis-a-diimine nickel (II) complexes containing chloro-substituted ligands, bis{bis
[N,N0-(3-chloro-2-methylphenyl)imino]-1,2-dimethylethane}dibromonickel 2a, bis{bis[N,N0-(3-chloro-2,6-
dimethylphenyl)imino]-1,2-dimethylethane}dibromonickel 2b and bis{bis[N,N0-(4-chloro-2,6-dimethyl-
phenyl)imino]-1,2-dimethylethane}dibromonickel 2c, were synthesized and characterized. The molecular
structure of complex 2awasdetermined by X-raycrystallography. In the solid state, complex 2ahasa pseudo-
Received 6 June 2011
Received in revised form
7 July 2011
Accepted 7 July 2011
octahedral geometry about the nickel center, containing two a-diimine ligands in the pseudo-equatorial
plane and two trans bromide ligands occupying the axial positions. These complexes, activated by dieth-
ylaluminum chloride (DEAC) were tested in the polymerization of ethylene under mild conditions. NMR
Keywords:
a
-Diimine
Branched polyethylene
Crystal structure
Ethylene
Nickel complex
Polymerization
analysis shows that highly branched polyethylenes are obtained using these bis-a-diimine nickel(II)
complexes containing electron-withdrawing Cl groups in the aryl groups (e.g. 84 branches/1000 C, at 20 ꢀC).
The catalytic activity, polymer molecular weight and polymer degree of branching were significantly affected
by the number of methyl substituents in the ortho-aryl position and the chlorine substituent position in the
aryl rings of the coordinated a-diimine ligands.
Ó 2011 Elsevier B.V. All rights reserved.
1. Introduction
recent development of late transition metal olefin polymerization
catalysts. A variety of -diimine ligands containing substituted
a
The discovery of Ni(II) and Pd(II)
a
-olefin polymerisation cata-
N-aryl rings, including those with steric bulk and ortho and para
substituted position modifications in the aryl rings [18e24], back-
lysts containing
a bulky a-diimine ligand, [MX2(a-diimine)]
(M ¼ Ni, Pd; X ¼ halide), by Brookhart and co-workers [1e8], has
bone effects on the
-diimine ligand systems [30,31], teraryl substituted-
ligands [32e35], cyclophane-based -diimine ligands [36e39],
were employed to study their influence on the catalytic activity of
the 16-electron Ni(II) and Pd(II) [MX2( -diimine)] precatalysts.
However, the effect of electron-withdrawing N-aryl rings substit-
uents, especially of Cl atoms, on the catalytic behavior of -diimine-
a
-diimine ligand structure [25e29], chiral
stimulated renewed interest in the chemistry of 1,4-diazadiene
a
a-diimine
ligands and their complexes. The coordination chemistry of
a
-dii-
a
mine ligands of the type N,N0-diaryl-1,4-diaza-1,3-butadiene (Ar-
DAB) or bis(arylimino)acenaphthene (Ar-BIAN) to late transition
metals has attracted much interest due to their unusual electron
donor and acceptor properties [9,10]. Organometallic compounds
containing Ar-DAB or Ar-BIAN ligands have been extensively
studied in recent years as catalysts for the oligomerisation and
a
a
Ni(II) complexes and the properties of the resulting polymers has
only been reported in limited cases.
polymerisation of
The ligand structure has a dramatic effect on the reactivity of
organometallic complexes. This has been especially evident in the
a
-olefins [11e17].
Conversely, the report of 20-electron complexes of NiX2 bearing
four coordinated nitrogen atoms that exhibit catalytic activity in
the oligomerization or polymerization of olefins has also been
scarce, being limited to the cases where the NiX2 fragment is
coordinated to two
([NiBr2(Ar-BIAN)2]) [21] or to a tetradentate N,N,N,N-chelating
-diimine ligand ([NiBr2(N,N,N,N- -diimine)]) [40,41].
a-diimine ligands of the aryl-BIAN type
* Corresponding author. Tel.: þ86 931 797 1539; fax: þ86 931 7971261.
E-mail address: jianchaoyuan@nwnu.edu.cn (J. Yuan).
a
a
0022-328X/$ e see front matter Ó 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2011.07.009

3252
J. Yuan et al. / Journal of Organometallic Chemistry 696 (2011) 3251e3256
In this paper, we report the synthesis and characterization of
three new 20-electron octahedral bis- -diimine Ni(II) complexes of
acenaphthene]dibromonickel [21], which contains two
ligands of the aryl-BIAN type. In fact, the NieN bond distances in
a-diimine
a
the type [NiBr2(Ar-DAB)2] bearing electron-withdrawing substitu-
ents Cl in the para- or meta-aryl positions of the Ar-DAB ligand and
their catalytic behaviors in the polymerization of ethylene when
activated by diethylaluminum chloride (DEAC).
complex 2a (2.112e2.116 Å) are similar to that determined for that
compound (2.144 Å), as well as the NieBr bond distances
(2.5797e2.6128 Å for complex 2a vs. 2.5354 Å) and the two
bromine atoms are situated in the trans-position (BreNieBr angle,
179ꢀ for complex 2a vs. 180ꢀ), whereas the halide ligands display
a cis geometry in the majority of the other nickel complexes con-
taining two DAB-type ligands with non-aryl and non-bulky
N-imine substituents [42e46]. The two imino C]N bonds have
typical double bond character with C]N bond lengths of 1.272 Å.
2. Results and discussion
2.1. Synthesis and characterization of ligands 1aec and complexes
2aec
The aryl rings of each of the a-diimines lie nearly perpendicular to
the plane formed by the nickel and coordinated nitrogen atoms,
and face each others in a staggered conformation.
The general synthetic route to three nickel(II) complexes 2aec is
shown in Scheme 1. The free Ar-DAB ligands 1aec were prepared
by the condensation of two equivalents of the appropriate aniline
with one equivalent of 2,3-butanedione, usually in the presence of
an acid catalyst. The compounds (1aec) were characterized by 1H
NMR and 13C NMR and were found elementally pure.
The reaction of 1 equivalent of [NiBr2(DME)] and 2 equivalents
of the a-diimine ligands 1aec, in CH2Cl2, led to the displacement of
1,2-dimethoxyethane and afforded the catalyst precursors 2aec as
moderately air-stable light red microcrystalline solids in good
2.2. Polymerization of ethylene with nickel complexes 2aec
The three complexes 2a, 2b and 2c, activated by dieth-
ylaluminum chloride (DEAC), were tested as catalyst precursors for
the polymerization of ethylene, under the same reaction condi-
tions. The results of the polymerization experiments are shown in
Table 2. Noteworthy is the fact that blank experiments carried out
with DEAC alone, under similar conditions, showed its inability to
polymerize ethylene on its own.
yields. Due to the geometry around the nickel atom, these bis-a-
diimine Ni(II) complexes are paramagnetic and their 1H NMR is not
For a ratio [Al]/[Ni] ¼ 600, an increase in the reaction temper-
ature in the range 0e40 ꢀC increases the activity of precatalysts 2b
and 2c (containing two methyl substituents in both ortho aryl
positions) activated by DEAC, (2b: entries 6e8; 2c: entries 11e13),
while precatalyst 2a (containing a single methyl substituent in one
of the ortho aryl positions) revealed to be inactive (entries 1e3). An
increase of the [Al]/[Ni] ratio in the range 600e1500 increases the
activity of all the precatalysts, at 20 ꢀC, which seem to go through
a maximum around [Al]/[Ni] ¼ 1000 (2a: entries 2, 4 and 5; 2b:
entries 7, 9 and 10; 2c: entries 12, 14 and 15). The molecular weight
of the polyethylenes (PE) produced under these conditions were
found to slightly increase, in the case of 2b, or decrease, in the cases
of 2a and 2c, with an increasing [Al]/[Ni] ratio.
assignable. The elemental analyses of complexes 2aec fit the stoi-
chiometry Ni:a-diimine of 1:2 ([NiBr2(Ar-DAB)2]), which is further
corroborated by the molecular structure obtained by X-ray struc-
tural studies. In fact, suitable crystals of 2a for X-ray diffraction
were obtained by double layering a solution of the complex in
CH2Cl2 with n-hexane. The molecular structure of complex 2a was
determined and the corresponding ORTEP diagram is shown in
Fig. 1, while selected bond distances and angles are summarized in
Table 1.
In the solid state, the structure of complex 2a shows two Ar-DAB
and two bromide ligands featuring a six-coordinate distorted
octahedral geometry around the nickel center, having a C2 molec-
ular symmetry. The nickel atom occupies a crystallographic inver-
The performances of the nickel precatalysts are significantly
affected by the position of the chlorine substituent on the aryl rings
sion centre and only
a half of the molecule is symmetry
independent. The two -diimine ligands coordinate the nickel atom
a
of the the bis-a-diimine Ni(II) complexes 2aec (Table 2). Complex
in the equatorial plane, their corresponding DAB planes making
a dihedral angle of 11.25ꢀ, whereas the two bromide ligands lie in
the axial positions, their bonds to the nickel atom being perpen-
dicular (89.98ꢀ) to the average plane defined by the nitrogens and
the nickel atoms. Its structure is quite similar to that reported in the
2b, bearing a Cl substituent in the meta-aryl position of the ligand
(two methyl groups in the ortho-aryl positions), displays the
highest catalytic activity, of 7.08 ꢁ 105 g PE/(mol Ni$h$bar), and
produces one of the highest molecular weights (Mn ¼ 53600, entry
9, 20 ꢀC, [Al]/[Ni] ¼ 1000) among our three complexes. Complex 2c,
bearing a Cl substituent in the para-aryl position of the ligand (also
with two methyl groups in the ortho-aryl positions), exhibits
a slightly lower catalytic activity of 6.81 ꢁ 105 g PE/(mol Ni$h$bar)
and yields polyethylene with substantially lower molecular weight
(Mn ¼ 39 800, entry 14, 20 ꢀC, [Al]/[Ni] ¼ 1000). This shows that a Cl
substituent in the meta-aryl position (2b) increases the rate of chain
propagation (migratory insertion of coordinated ethylene into the
literature for the other [NiX2(N,N0-diaryl-
characterized by X-ray, the bis[bis(N,N’-2,3-dichlorophenylimino)
a-diimine)2] compound
Ni-chain alkyl bond) and decreases the rate of chain transfer (b-
hydrogen transfer to the metal or to the monomer) in comparison
with that in the para-aryl position (2c). For the same ratio [Al]/
[Ni] ¼ 1000, complex 2a, bearing Cl substituent in the meta-aryl
position in the ligand (only one methyl group in the ortho-aryl
position), shows the lowest catalytic activity (1.90 ꢁ 105 g PE/(mol
Ni$h$bar)) and produces the lowest molecular weight
(Mn ¼ 15 200, Entry 4, 20 ꢀC) of the three precatalysts. These results
indicate that the rate of chain propagation is greatly promoted by
the bulkiness of the ligand’s aryl rings. As a result, the following
activity trend can be summarized for our Cl substituted precatalysts
under low ethylene pressure (1.2 bar), in the range 0e40 ꢀC:
2b > 2c > 2a.
Scheme 1. Syntheses of
mine nickel(II) dibromide complexes 2ae2c.
a-diimine ligands 1ae1c and their corresponding bis-a-dii-

J. Yuan et al. / Journal of Organometallic Chemistry 696 (2011) 3251e3256
3253
Fig. 1. ORTEP drawing of complex 2a with 30% probability displacement ellipsoid. The hydrogen atoms are omitted for clarity.
In general, all the three catalysts exhibited high activities toward
ethylene polymerization (106 105
activities PE/(mol
could give rise to the corresponding cationic alkyl unsaturated
active species (Scheme 2, route b).
ꢂ
ꢂ
g
Ni$h$bar)) under low ethylene pressure, which are comparable to
those of metallocene catalysts [47]. The polymerization activities
obtained in this work (2b: 7.08 ꢁ 105 g PE/(mol Ni$h$bar); 2c:
6.81 ꢁ105 g PE/(mol Ni$h$bar), when activated by DEAC) showed to
be of the same order of magnitude of those observed for 16-
electron [NiBr2(Ar-DAB)] catalyst precursors such as the {bis[N,N0-
(2,6-dimethylphenyl)imino]-1,2-dimethylethane}dibromonickel,
which activity reported by Brookhart et al. is ca. 9.00 ꢁ 105 g PE/
(mol Ni$h$bar) [1], although the experimental conditions (reaction
time, 10 min; temperature, 0 ꢀC; pressure, 2 bar; co-catalyst, MAO;
[Al]/[Ni] ¼ 1000) are not exactly the same as those used in the
present work. These high activities may indicate that the active
species operating in the case of our 20-electron precatalysts 2aec
([NiBr2(Ar-DAB)2]) is the same as that admitted for the corre-
sponding 16-electron species [NiBr2(Ar-DAB)] [4]. In fact, similar to
The type and amount of branches formed in the polymerization
of ethylene promoted by typical
a-diimine nickel precatalysts
depends on reaction parameters such as the reaction temperature,
ethylene pressure and ligand bulkiness/structure [4]. As shown in
Table 3, the catalyst systems 2b/DEAC and 2c/DEAC, containing an
electron-withdrawing Cl group, generated polyethylene with high
degrees of branching at 20 ꢀC. The total branching degrees of the
polymer samples prepared with 2b/DEAC (entries 9 and 10: 84 and
76 branches/1000 C, respectively) and 2c/DEAC (entries 14 and 15:
82 and 84 branches/1000 C, respectively) are much higher than
those observed for similar non-chlorinated precatalyst/DEAC
systems such as {bis[N,N0-(4-tert-butyl-diphenylsilyl-2,6-diiso-
propylphenyl)imino]acenaphthene}dibromonickel (45 branches/
1000 C, at 20 ꢀC) [1,4] or precatalyst/MAO systems such as {bis[N,N0-
(2,6-dimethylphenyl)imino]-1,2-dimethylethane}dibromonickel (20
branches/1000 C, at 0 ꢀC) [4], {bis[N,N0-(2,6-diisopropylphenyl)
imino]-1,2-dimethylethane}dibromonickel (48, 30, 67, 80 and 90
branches/1000 C, at 0, 25, 50, 65 and 80 ꢀC, respectively) [4], {bis
[N,N0-(2,6-diisopropylphenyl)imino]acenaphthene}dibromonickel
(65 branches/1000 C, at 25 ꢀC) [4], although the reaction conditions
are not exactly the same as in the present work. Therefore, the
precatalysts containing ortho-dialkyl substituted aryl rings and an
what was proposed by other authors [21], the bis-a-diimine nick-
el(II) used in the present work may be involved in an equilibrium
where one of the Ar-DAB ligands dissociates, giving rise to a 16-
electron complex [NiBr2(Ar-DAB)], which can also be originated
by the coordination/abstraction from the precatalysts of one of such
donor chelating ligands to the Lewis acidic co-catalyst (AlEt2Cl)
(Scheme 2, route a). The 16-electron [NiBr2(Ar-DAB)] precatalyst
can then follow the classical polymerization mechanism put
forward by Brookhart and co-workers [4]. Alternatively, the hem-
Table 2
ilabile
electron complexes containing unidentate
proposed for the recently reported tetradentate N,N,N,N-chelated
-diimine nickel complexes [41], which, upon reaction with AlEt2Cl,
a-diimine ligands may partially dissociate giving rise to 16-
Ethylene polymerizations using nickel precatalysts 2a, 2b and 2c activated by DEAC.a
a-diimine ligands, as
Entry Precatalyst [Al]/[Ni] Tp Yield Activity ꢁ 10ꢃ5
Mn ꢁ 10ꢃ4
M
w/Mn
b
b
(ꢀC) (g)
(g PE/(mol Ni$h$bar)) (g/mol)
a
1
2
3
4
5
6
7
8
2a
2a
2a
2a
2a
2b
2b
2b
2b
2b
2c
2c
2c
2c
2c
600
600
600
1000
1500
600
600
600
1000
1500
600
0
Traces e
e
e
e
e
20 Traces e
40 Traces e
20 0.41 1.90
20 0.40 1.85
e
Table 1
Selected bond lengths (Å) and angles (ꢀ) for complex 2a.
e
1.52
1.45
2.93
2.55
3.31
5.36
5.39
4.94
4.53
3.47
3.98
3.41
1.85
1.79
1.61
1.75
1.82
1.76
1.73
1.56
1.59
1.68
1.60
1.61
Bond lengths
(Å)
2.112(4)
Bond angles
(ꢀ)
77.37(16)
103.20(17)
174.66(13)
173.65(14)
102.40(16)
77.63(16)
122.2(5)
0
0.32 1.48
Ni(1)eN(3)
Ni(1)eN(4)
Ni(1)eN(2)
Ni(1)eN(1)
Ni(1)eBr(2)
Ni(1)eBr(1)
C(1)eC(6)
C(1)eN(1)
C(2)eC(3)
C(2)eC(7)
C(3)eC(4)
C(3)eCl(1)
C(4)eC(5)
C(5)eC(6)
N(3)eNi(1)eN(4)
N(3)eNi(1)eN(2)
N(4)eNi(1)eN(2)
N(3)eNi(1)eN(1)
N(4)-Ni(1)eN(1)
N(2)eNi(1)eN(1)
C(6)eC(1)eC(2)
C(2)eC(1)eN(1)
C(1)-C(2)eC(7)
N(3)eNi(1)-Br(1)
N(4)eNi(1)eBr(1)
N(2)eNi(1)eBr(1)
N(1)-Ni(1)-Br(1)
Br(2)eNi(1)eBr(1)
20 0.39 1.81
40 0.84 3.89
20 1.53 7.08
20 1.45 6.71
2.112(4)
2.113(4)
2.116(4)
2.5797(18)
2.6128(18)
1.383(7)
1.433(6)
1.405(7)
1.484(7)
1.346(8)
1.743(6)
1.351(8)
1.402(8)
9
10
11
12
13
14
15
0
0.25 1.16
600
600
1000
1500
20 0.33 1.53
40 0.82 3.80
20 1.47 6.81
20 1.43 6.62
120.4(4)
122.0(5)
86.62(10)
92.45(9)
92.89(10)
87.05(10)
179.00(3)
a
Polymerization conditions: n(Ni) ¼ 3.6
m
mol; pressure of C2H4 ¼ 1.2 bar
(absolute); Polymerization time tp
¼
0.5 h; solvent toluene (50 ml);
¼
Tp ¼ polymerization temperature.
b
Determined by GPC/SEC.

3254
J. Yuan et al. / Journal of Organometallic Chemistry 696 (2011) 3251e3256
Scheme 2. Possible dissociative equilibria involving 2ae2c and initiation of the polymerization of ethylene.
additional electron-withdrawing Cl substituent favor the Chain-
Walking mechanism [4].
activities. Complex 2a, containing only one methyl substituent in
the ortho positions and a meta-aryl Cl substituent, shows consid-
erably lower activities, branching degrees and molecular weights in
relation to those of 2b and 2c.
The total branching degree of the polymer sample obtained with
2a (entry 4: 31 branches/1000 C) is much lower than those of 2b
and 2c. This difference is a consequence of the fact that 2a has less
bulky aryl groups (only one methyl substituent in the ortho posi-
tions) than 2b and 2c (two methyl substituents in the ortho posi-
tions). As can be seen in Table 3, precatalysts 2b and 2c give rise to
polyethylenes with lower crystallinities, and thus lower melting
points, than that produced by 2a, which supports their higher
degree of branching.
4. Experimental
4.1. General considerations
All manipulations involving air and/or water sensitive
compounds were carried out with standard Schlenk techniques
under nitrogen. Methylene chloride and o-dichlorobenzene were
pre-dried with 4 Å molecular sieves and distilled from CaH2 under
dry nitrogen. Toluene, diethyl ether, and 1, 2-dimethoxyethane
(DME) were distilled from sodium/benzophenone under N2 atmo-
sphere. Anhydrous NiBr2 (99%), Diethylaluminum chloride (DEAC,
3. Conclusions
Three new 20-electron octahedral bis-a-diimine dibromonick-
el(II) complexes containing different chloro-substituted aryl groups
(2aec) have been prepared and characterized. These compounds
show a pseudo-octahedral geometry around the nickel atom.
Complexes 2aec, when activated by diethylaluminum (DEAC),
behave as catalysts for the polymerization of ethylene, showing
high activities of the order of those presented by classical 16-
0.9
M solution in toluene) were obtained from Acros. 2,3-
Butanedione (98%), 3-chloro-2-methylaniline (98%), 3-chloro-2,6-
dimethylaniline (98%) and 4-chloro-2,6-dimethylaniline (98%),
were purchased from Alfa Aesar, and used without further purifi-
cation. [NiBr2(DME)] was synthesized according to the literature
[49].
electron Brookhart’s
a-diimine nickel(II) catalysts. The influence
NMR spectra were recorded at 400 (13C) and 100 (1H) MHz,
respectively, on a Varian Mercury plus-400 instrument, using TMS
as internal standard. FTIR spectra were recorded on a Digilab Merlin
FTS 3000 FTIR spectrophotometer on KBr pellets. Differential
Scanning Calorimetry (DSC) analyses of the polymers were per-
formed on a PerkineElmer 7 Series thermal analysis system in the
range of 25e250 ꢀC, at a heating rate of 10 ꢀC/min. The molecular
weights and molecular weight distributions (MWD) of the poly-
mers were determined by Gel Permeation Chromatography/Size-
of a chlorine substitution in the ligand’s aryl rings meta and para
positions was studied, being the higher branching degrees of the
polyethylenes synthesized the most important difference in rela-
tion to non-chlorinated a-diimine nickel precatalysts. Additionally,
the precatalyst 2b, bearing a Cl substituent in the meta position of
the ligand’s 2,6-dimethylarylimine rings, showed the highest
catalytic activity and produced the higher molecular weight poly-
ethylenes, whereas 2c, bearing a Cl substituents in the para posi-
tion, produces lower molecular weights with similar catalyst
Exclusion Chromatography (GPC/SEC) via
a Waters Alliance
Table 3
GPCV2000 chromatograph, using 1, 2, 4-trichlorobenzene as the
eluent, at a flow rate of 1.0 ml/min and operated at 140 ꢀC.
Thermal analysis and branching degrees of selected polyethylene samples.
a
a
a
Entry
Precatalyst
Tp (ꢀC)
Tm
Td
cc
Branches
/1000Cb
(ꢀC)
(ꢀC)
(%)
4.2. X-ray structure determinations
4
9
10
14
15
2a
2b
2b
2c
2c
20
20
20
20
20
113
89
94
76
78
383
381
380
382
381
50.7
24.3
23.1
16.6
31
84
76
82
84
Single crystals of complex 2a suitable for X-ray analysis were
obtained at ꢃ30 ꢀC by dissolving the nickel complex in CH2Cl2,
following by slow layering of the subsequent solution with
n-hexane. Data collections were performed at 296(2) K on a Bruker
SMART APEX diffractometer with a CCD area detector, using
0.12
a
Determined by DSC. Tp ¼ polymerization temperature; Tm ¼ melting temper-
ature; Td ¼ decomposition temperature; cc ¼ crystallinity [48].
b
Estimated by 1H NMR [7].
graphite monochromated MoK
a
radiation (
l
¼ 0.71073 Å). The

J. Yuan et al. / Journal of Organometallic Chemistry 696 (2011) 3251e3256
3255
determination of crystal class and unit cell parameters was carried
out by the SMART program package. The raw frame data were
processed using SAINT and SADABS to yield the reflection data file.
The structures were solved by using the SHELXTL program.
Refinement was performed on F2 anisotropically for all non-
hydrogen atoms by the full-matrix least-squares method. The
hydrogen atoms were placed at the calculated positions and were
included in the structure calculation without further refinement of
the parameters. Crystal data, data collection, and refinement
parameters are listed in Table 4.
with cold ethanol and dried under vacuum. Yield: 0.94 g (88.5%). 1H
NMR (400 MHz, CDCl3, , ppm): 1.93 (d, 6H, AreoeCH3), 1.96 (s, 6H,
CeCH3), 2.01 (d, 6H, AreoeCH3) 6.93e7.19 (m, 4H, Ar-H). 13C NMR
(100 MHz, CDCl3, , ppm): 14.73 (CeCH3), 16.01 (AreoeCH3 near
Cl), 17.65 (AreoeCH3), 122.78 (AreCeoeCH3 near Cl), 123.32
(AreCeoeCH3), 123.87 (ArepeC), 128.44 (AremeC), 132.44
(AreCeCl), 149.27 (AreCeN), 168.63 (C]N). FTIR (KBr, cmꢃ1): 1642
(vC¼N). Anal. Calcd. For C20H22N2Cl2: C, 66.48; H, 6.14; N, 7.75.
Found: C, 66.46; H, 6.15; N, 7.76.
d
d
4.3.3. Synthesis of bis[N,N0-(4-chloro-2,6-dimethylphenyl)imino]-
1,2-dimethylethane (1c)
4.3. Syntheses and characterizations of ligands and complexes
Formic acid (0.5 ml) was added to a stirred solution of 2,3-
butanedione (0.260 g, 3 mmol) and 4-chloro-2,6-dimethylaniline
(0.934 g, 6 mmol) in methanol (20 ml). The mixture was refluxed
for 24 h, then cooled and the precipitate was separated by filtration.
The solid was recrystallized from EtOH/CH2Cl2 (v/v ¼ 10:1), washed
with cold ethanol and dried under vacuum. Yield: 1.00 g (92%). 1H
The syntheses of ligands 1aec and the corresponding complexes
2aec were adapted from the literature [50,51].
4.3.1. Synthesis of bis[N,N0-(3-chloro-2-methylphenyl)imino]-1,2-
dimethylethane (1a)
NMR (400 MHz, CDCl3,
d
, ppm): 2.00 (s, 12H, AreoeCH3), 2.01 (s,
Formic acid (0.5 ml) was added to a stirred solution of 2,3-
butanedione (0.260 g, 3 mmol) and 3-chloro-2-methylaniline
(0.850 g, 6 mmol) in methanol (20 ml). The mixture was refluxed
for 24 h, then cooled and the precipitate was separated by filtration.
The solid was recrystallized from EtOH/CH2Cl2 (v/v ¼ 8:1), washed
with cold ethanol and dried under vacuum. Yield: 0.91 g (91%). 1H
6H, CeCH3), 7.07 (s, 4H, AreH). 13C NMR (100 MHz, CDCl3,
d
, ppm):
15.90 (CeCH3), 17.69 (AreCH3), 126.49(ArepeC), 127.68
(AreCeoeCH3), 128.06 (AreCeCl),146.71 (AreCeN),168.63 (C]N).
FTIR (KBr, cmꢃ1): 1640 (vC¼N). Anal. Calcd. For C20H22N2Cl2: C,
66.48; H, 6.14; N, 7.75. Found: C, 66.46; H, 6.15; N, 7.76.
NMR (400 MHz, CDCl3,
CeCH3), 6.57 (d, 2H, AreH, J ¼ 7.2 Hz), 7.14 (t, 4H, AreH, J ¼ 7.6 Hz).
13C NMR (100 MHz, CDCl3,
, ppm): 14.71 (CeCH3) 15.71 (AreCH3),
116.16 (Areo-C), 124.63 (AreCeCH3), 125.08 (Arep-C), 126.86
(AremeC), 135.26 (AreCeCl), 150.56 (AreCeN),168.25 (C]N). FTIR
(KBr, cmꢃ1): 1644 (vC¼N). Anal. Calcd. For C18H18N2Cl2: C, 64.87; H,
5.44; N, 8.41. Found: C, 64.88; H, 5.44; N, 8.40.
d, ppm): 2.11 (s, 6H, AreoeCH3), 2.16 (s, 6H,
4.3.4. Synthesis of bis{bis[N,N0-(3-chloro-2-methylphenyl)imino]-
1,2-dimethylethane}dibromonickel (2a)
d
[NiBr2(DME)] (0.310 g, 1.0 mmol), ligand 1a (0.733 g, 2.2 mmol)
and dichloromethane (40 ml) were mixed in a Schlenk flask and
stirred at room temperature for 16 h. The resulting suspension was
filtered. The solvent was removed under vacuum and the residue
was washed with diethyl ether (3 ꢁ 16 ml), and then dried under
vacuum at room temperature to give catalyst 2a (0.73 g, 82% yield).
FTIR (KBr, cmꢃ1): 1635 (vC¼N). Anal. Calcd. For C36H36 N4Cl4NiBr2: C,
48.86; H, 4.10; N, 6.33. Found: C, 48.80; H, 4.12; N, 6.34.
4.3.2. Synthesis of bis[N,N0-(3-chloro-2,6-dimethylphenyl)imino]-
1,2-dimethylethane (1b)
Formic acid (0.5 ml) was added to a stirred solution of 2,3-
butanedione (0.260 g, 3 mmol) and 3-chloro-2,6-dimethylaniline
(0.934 g, 6 mmol) in methanol (20 ml). The mixture was refluxed
for 24 h, then cooled and the precipitate was separated by filtration.
The solid was recrystallized from EtOH/CH2Cl2 (v/v ¼ 10:1), washed
4.3.5. Synthesis of bis{bis[N,N0-(3-chloro-2,6-dimethylphenyl)
imino]-1,2-dimethylethane}dibromonickel (2b)
[NiBr2(DME)] (0.310 g, 1.0 mmol), ligand 1b (0.795 g, 2.2 mmol)
and dichloromethane (40 ml) were mixed in a Schlenk flask and
stirred at room temperature for 16 h. The resulting suspension was
filtered. The solvent was removed under vacuum and the residue
was washed with diethyl ether (3 ꢁ 16 ml), and then dried under
vacuum at room temperature to give catalyst 2b (0.75 g, 79.6%
yield). FTIR (KBr, cmꢃ1): 1627 (vC¼N). Anal. Calcd. For
C40H44N4Cl4NiBr2: C, 51.05; H, 4.71; N, 5.95. Found: C, 51.02; H,
4.77; N, 5.91.
Table 4
Crystal data and structure refinements of complex 2a.
Empirical Formula
Formula mass
Temperature (K)
Wavelength (Å)
Crystal size (mm3)
Crystal system
Space group
a (Å)
C36H36Br2Cl4N4Ni
885.02
296(2) K
0.71073
0.38 ꢁ 0.36 ꢁ 0.35
Monoclinic
P21/c
15.260(10)
4.3.6. Synthesis of bis{bis[N,N0-(4-chloro-2,6-dimethylphenyl)
imino]-1,2-dimethylethane}dibromonickel (2c)
b (Å)
12.417(8)
c (Å)
23.979(15)
4364(5)
[NiBr2(DME)] (0.310 g, 1.0 mmol), ligand 1c (0.795 g, 2.2 mmol)
and dichloromethane (40 ml) were mixed in a Schlenk flask and
stirred at room temperature for 16 h. The resulting suspension was
filtered. The solvent was removed under vacuum and the residue
was washed with diethyl ether (3 ꢁ 16 ml), and then dried under
vacuum at room temperature to give catalyst 2c (0.84 g, 89.3%
yield). FTIR (KBr, cmꢃ1): 1629 (vC¼N). Anal. Calcd. For
C40H44N4Cl4NiBr2: C, 51.05; H, 4.71; N, 5.95. Found: C, 51.01; H,
4.79; N, 5.93.
V (Å3)
Z
4
Density (calcd.) (mg/cm3)
Absorption coefficient (mmꢃ1
F(000)
1.347
2.548
1784
2.15 to 25.20
)
Theta range for data collec. (ꢀ)
Limiting indices
Reflections collected
Independent reflections
Rint
ꢃ16 ꢄ h ꢄ 18, ꢃ14 ꢄ k ꢄ 14, ꢃ28 ꢄ l ꢄ 28
28 326
7829
0.0514
99.6%
Completeness to
q
¼ 25.20ꢀ
Final R indices [I > 2
R indices (all data)
Refinement method
s
(I)]
R1 ¼ 0.0549, wR2 ¼ 0.1229
R1 ¼ 0.1026, wR2 ¼ 0.1354
Full-matrix least-squares on F2
1.011
4.4. Procedure for the polymerization of ethylene
Goodness-of-fit on F2
The polymerization of ethylene was carried out in a flame dried
250 ml crown capped pressure bottle sealed with neoprene septa.
After drying the polymerization bottle under N2 atmosphere, 50 ml
Max. and min. transmission
0.4692 and 0.4444
0.787 and ꢃ0.614
Largest diff. peak and hole (e.Åꢃ3
)

3256
J. Yuan et al. / Journal of Organometallic Chemistry 696 (2011) 3251e3256
[13] D. Takeuchi, Y. Fukuda, S. Park, K. Osakada, Macromolecules 42 (2009)
5909e5912.
of dry toluene was added to the polymerization bottle. The
resulting solvent was then saturated with a prescribed ethylene
pressure. The co-catalyst (MAO) was then added in Al/Ni molar
ratios in the range of 600e1500 to the polymerization bottle via
a syringe. At this time, the solutions were thermostated to the
desired temperature and allowed to equilibrate for 15 min.
Subsequently, an o-dichlorobenzene solution of Ni catalyst was
added to the polymerization reactor. The polymerization, con-
ducted under a dynamic pressure of ethylene (absolute pressur-
e ¼ 1.2 bar), was terminated by quenching the reaction mixtures
with 100 ml of a 2% HCleMeOH solution. The precipitated polymer
was filtered, washed with methanol and dried under vacuum at
60 ꢀC to a constant weight.
[14] M.M. Wegner, A.K. Ott, B. Rieger, Macromolecules 43 (2010) 3624e3633.
[15] Y. Choi, J.B.P. Soares, Polymer 51 (2010) 2271e2276.
[16] D.H. Camachoa, Z. Guan, Chem. Commun. 46 (2010) 7879e7893.
ꢀ
ꢀ
[17] J. Peleska, Z. Hostálek, D. Hasalíková, J. Merna, Polymer 52 (2011) 275e281.
[18] M. Helldörfer, W. Milius, H.G. Alt, J. Mol, Catal. A: Chem. 197 (2003) 1e13.
[19] C. Popeney, Z. Guan, Organometallics 24 (2005) 1145e1155.
[20] H.R. Liu, P.T. Gomes, S.I. Costa, M.T. Duarte, R. Branquinho, A.C. Fernandes,
J.C.W. Chien, R.P. Singh, M.M. Marques, J. Organomet. Chem. 690 (2005)
1314e1323.
[21] C.L. Song, L.M. Tang, Y.G. Li, X.F. Li, J. Chen, Y.S. Li, J. Polym. Sci. Part A: Polym.
Chem. 44 (2006) 1964e1974.
[22] G.W. Son, K.B. Bijal, D.W. Park, C.S. Ha, I. Kim, Catal. Today 111 (2006) 412e416.
[23] J.Y. Liu, Y.G. Li, Y.S. Li, N.H. Hu, J. Appl. Polym. Sci. 109 (2008) 700e707.
[24] B.K. Bahuleyan, G.W. Son, D.W. Park, C.S. Ha, I. Kim, J. Polym. Sci. Part A:
Polym. Chem. 46 (2008) 1066e1082.
[25] T. Schleis, T.P. Spaniol, J. Okuda, J. Heinemann, R. Mülhaupt, J. Organomet.
Chem. 569 (1998) 159e167.
[26] M. Helldörfer, J. Backhaus, H.G. Alt, Inorg. Chimi. Acta 351 (2003) 34e42.
[27] M. Helldörfer, J. Backhaus, W. Milius, H.G. Alt, J. Mol. Catal. A: Chem. 193
(2003) 59e70.
[28] F. Alobaidia, Z. Ye, S. Zhu, Polymer 45 (2004) 6823e6829.
[29] F.S. Liu, H.B. Hu, Y. Xu, L.H. Guo, S.B. Zai, K.M. Song, H.Y. Gao, L. Zhang,
F.M. Zhu, Q. Wu, Macromolecules 42 (2009) 7789e7796.
[30] A.E. Cherian, E.B. Lobkovsky, G.W. Coates, Chem. Commun. 20 (2003)
2566e2567.
[31] A.E. Cherian, J.W. Rose, E.B. Lobkovsky, G.W. Coates, J. Am. Chem. Soc. 127
(2005) 13770e13771.
[32] A.S. Ionkin, W.J. Marshall, Organometallics 23 (2004) 3276e3283.
[33] A.S. Ionkin, W.J. Marshall, J. Organomet. Chem. 689 (2004) 1057e1063.
[34] D. Meinhard, M. Wegner, G. Kipiani, A. Hearley, P. Reuter, S. Fischer, O. Marti,
B. Rieger, J. Am. Chem. Soc. 129 (2007) 9182e9191.
Acknowledgments
We thank the National Natural Science Foundation of China
(20964003) for funding. We also thank Key Laboratory of Eco-
Environment-Related Polymer Materials of Ministry of Education,
Key Laboratory of Polymer Materials of Gansu Province (Northwest
Normal University), for financial support. P.T.G. and M.M.M. thank
the Fundação para Ciência e Tecnologia for financial support
(Project PTDC/EQU-EQU/110313/2009, co-financed by FEDER).
Appendix A. Supplementary material
[35] M. Schmid, R. Eberhardt, M. Klinga, M. Leskela, B. Rieger, Organometallics 20
(2001) 2321e2330.
CCDC 809390 contains the supplementary crystallographic data
for complex 2a. These data can be obtained free of charge from The
Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/
data_request/cif.
[36] C.S. Popeney, D.H. Camacho, Z. Guan, J. Am. Chem. Soc. 129 (2007)
10062e10063.
[37] D.H. Leung, J.W. Ziller, Z. Guan, J. Am. Chem. Soc. 130 (2008) 7538e7539.
[38] C.S. Popeney, Z. Guan, J. Am. Chem. Soc. 131 (2009) 12384e12393.
[39] C.S. Popeney, A.L. Rheingold, Z. Guan, Organometallics 28 (2009)
4452e4463.
[40] L. Li, C.S.B. Gomes, P.T. Gomes, M.T. Duarte, Z. Fan, Dalton Trans. 40 (2011)
3365e3380.
References
[41] L. Li, P.T. Gomes, M.A.N.D.A. Lemos, F. Lemos, Z. Fan, Macromol. Chem. Phys.
212 (2011) 367e374.
[42] F. Abraham, J.P. Capon, G. Nowogrocki, S. Sueur, C. Bremard, Cryst. Struct.
Commun. 11 (1982) 971e974.
[43] H. Endres, Z. Anorg, Allg. Chem. 513 (1984) 78e88.
[44] H. Endres, Acta Crystallogr. Sect. C: Cryst. Struct. Commun. 41 (1985)
1423e1426.
[1] L.K. Johnson, C.M. Killian, M. Brookhart, J. Am. Chem. Soc. 117 (1995)
6414e6415.
[2] C.M. Killian, D.J. Tempel, L.K. Johnson, M. Brookhart, J. Am. Chem. Soc. 118
(1996) 11664e11665.
[3] C.M. Killian, L.K. Johnson, M. Brookhart, Organometallics 16 (1997)
2005e2007.
[45] E. Zangrando, M. Trani, E. Stabon, C. Carfagna, B. Milani, G. Mestroni, Eur. J.
Inorg. Chem. 14 (2003) 2683e2692.
[46] T. Yoshioka, K. Matsushima, G. Hihara, H. Miyamae, Anal. Sci. X-Ray Struct.
Anal. Online 22 (2006) x205ex206.
[4] S.D. Ittel, L.K. Johnson, M. Brookhart, Chem. Rev. 100 (2000) 1169e1203.
[5] L.K. Johnson, S. Mecking, M. Brookhart, J. Am. Chem. Soc. 118 (1996) 267e268.
[6] S. Mecking, L.K. Johnson, L. Wang, M. Brookhart, J. Am. Chem. Soc. 120 (1998)
888e899.
[47] W. Kaminsky, Macromol. Chem. Phys. 197 (1996) 3907e3945.
[48] B. Wunderlich, C.M. Cormier, J. Polym. Sci. Part A-2: Polym. Phys. 5 (1967)
987e988.
[7] A.C. Gottfried, M. Brookhart, Macromolecules 36 (2003) 3085e3100.
[8] H.S. Schrekker, V. Kotov, P. Preishuber-Pflugl, P. White, M. Brookhart,
Macromolecules 39 (2006) 6341e6354.
[49] L.G.L. Ward, J.R. Pipal, Inorg. Synth. 13 (1972) 162e163.
[50] R.J. Maldanis, J.S. Wood, A. Chandrasekaran, M.D. Rausch, J.C.W. Chien,
J. Organomet. Chem. 645 (2002) 158e167.
[9] R.A. Klein, F. Hartl, C.J. Elsevier, Organometallics 16 (1997) 1284e1291.
[10] R. van Asselt, C.J. Elsevier, C. Amatore, A. Jutand, Organometallics 16 (1997)
317e328.
[51] J.C. Yuan, L.C. Silva, P.T. Gomes, P. Valerga, J.M. Campos, M.R. Ribeiro,
J.C.W. Chien, M.M. Marques, Polymer 46 (2005) 2122e2132.
[11] Z. Guan, C.S. Popeney, Top. Organomet. Chem. 26 (2009) 179e220.
[12] L. Li, M. Jeon, S.Y. Kim, J. Mol, Catal. A: Chem. 303 (2009) 110e116.