Ortho -Cycloalkyl substituted N, N ′-diaryliminoacenaphthene-Ni(II) catalysts for polyethylene elastomers; Exploring ring size and temperature effects

Article abstract of DOI:10.1039/c7dt03362a

A family of six unsymmetrical N,N′-diiminoacenaphthene-nickel(ii) bromide complexes, [1-{2,6-(Ph₂CH)₂-4-MeC₆H₂N}-2-(ArN)C₂C₁₀H₆]NiBr₂ (Ar = 2-(C₆H₁₁

Full text of DOI:10.1039/c7dt03362a

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ortho-Cycloalkyl substituted N,N’-
diaryliminoacenaphthene-Ni(II) catalysts for
polyethylene elastomers; exploring ring size and
temperature effects†
Cite this: DOI: 10.1039/c7dt03362a
a,b
c
a,b
c
Hongyi Suo,
Gregory A. Solan, a,b* Yanping Ma,
Wen-Hua Sun
Irina V. Oleynik, Chuanbing Huang, Ivan I. Oleynik,*
a,d
a
a
Tongling Liang
and
*
2 2
A family of six unsymmetrical N,N’-diiminoacenaphthene-nickel(II) bromide complexes, [1-{2,6-(Ph CH) -
4
-MeC
6
6
H
2
2
N}-2-(ArN)C
2
C
10
H
6
]NiBr
2
(Ar = 2-(C
6
H
11)-6-MeC
6
H
2
Ni1, 2-(C
5
H
9
)-6-MeC
6 2 8
H Ni2, 2-(C H15)-
6
-MeC
H
Ni3, 2-(C
6
H
11)-4,6-Me
2
C
6
H
2
Ni4, 2-(C
5
H
9
)-4,6-Me
2
C
6
H
2
Ni5, 2-(C
8
H15)-4,6-Me C H Ni6),
2 6 2
each bearing one ring-size variable 4-R-2-methyl-6-cycloalkyl-substituted N-aryl group and one N’-4-
methyl-2,6-dibenzhydrylphenyl group, have been prepared and fully characterized. The molecular struc-
tures of Ni1, Ni2, Ni3 and Ni5 reveal distorted tetrahedral geometries with different degrees of steric pro-
tection imparted by the two inequivalent N-aryl groups. On activation with either EASC or MMAO, all the
precatalysts are highly active (up to 17.45 × 10 g PE mol−1 (Ni) h−1) for ethylene polymerization at
6
2
0–50 °C with their activities correlating with the type of cycloalkyl ortho-substituent: cyclooctyl (Ni6,
Ni3) > the cyclopentyl (Ni5, Ni2) > cyclohexyl (Ni4, Ni1) for either R = H or Me. Moderately branched to
hyperbranched polyethylenes (T ’s as low as 44.2 °C) can be obtained with molecular weights in the
m
5
−1
Received 10th September 2017,
Accepted 16th October 2017
range 2.14–6.68 × 10 g mol with the branching content enhanced by the temperature of the polymer-
ization. Dynamic mechanical analysis (DMA) and monotonic tensile stress–strain tests have been
employed on the polyethylene samples and reveal the more branched materials to show good elastic
recovery properties (up to 75.5%).
DOI: 10.1039/c7dt03362a
rsc.li/dalton
has facilitated the formation of linear to branched polyethyl-
enes (see A, Chart 1).
Introduction
Since the first reports of α-diimine-M (M = Ni, Pd) catalysts for
the polymerization of ethylene in the mid-1990s, the impor- more sterically demanding α-diimine derivatives have been
With the advances in ortho-substituted aniline synthesis,
1
tant role played by steric properties in the suppression of reported which in-turn have allowed for catalysts that are not
2
chain termination processes has been recognized. In particu- only more active, but are also more thermally robust and yield
lar, the strategic positioning of alkyl substituents (e.g., methyl, polymers with a range of molecular weights and branching
3
,4
isopropyl etc.) at the ortho-positions of the N-aryl groups of the contents.
For example, the incorporation of benzhydryl
5
catalyst and the resulting axial protection of the active species groups as the ortho-substituents (B, Chart 1), has led to
a
Key Laboratory of Engineering Plastics and Beijing National Laboratory for
Molecular Sciences, Institute of Chemistry, Chinese Academy of Sciences,
Beijing 100190, China. E-mail: whsun@iccas.ac.cn
b
CAS Research/Education Center for Excellence in Molecular Sciences,
University of Chinese Academy of Sciences, Beijing 100049, China
c
N.N. Vorozhtsov Novosibirsk Institute of Organic Chemistry, Pr. Lavrentjeva 9,
Novosibirsk 630090, Russia. E-mail: oleynik@nioch.nsc.ru
d
Department of Chemistry, University of Leicester, University Road,
Leicester LE1 7RH, UK. E-mail: gas8@leicester.ac.uk
†
Electronic supplementary information (ESI) available. CCDC 1573415–1573418
for Ni1, Ni2, Ni3 and Ni5. For ESI and crystallographic data in CIF or other elec-
tronic format see DOI: 10.1039/c7dt03362a
Chart 1 Development of α-diiminonickel(II) halide precatalysts.
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reports of catalysts that display high productivity and operate mixture of dichloromethane and ethanol at ambient tempera-
with remarkable thermostability (90 °C or higher), a feature ture (Scheme 1). The ligands are novel and can be synthesized
that has been attributed to the slowing down of chain transfer in a two step procedure involving firstly condensation of ace-
3
a,4c, f,6
processes as well as inhibition of deactivation pathways.
naphthylene-1,2-dione with one equivalent of 2,6-benzhydryl-
7
a,c
More recently, nickel catalysts bearing unsymmetrical 4-methylaniline
to form imine-ketone, 2-(2,6-dibenzhydryl-
α-diimines have been disclosed which benefit from the steric 4-methylphenylimino)acenaphthylenone, which can then be
properties of a N-4-R-2,6-dibenzhydrylphenyl group and the further condensed with the corresponding aniline hydrochlori-
7
8g
tunability of a less sterically bulky N-aryl group (C, Chart 1).
de to form L1–L6 in modest yields. All the ligands have been
1
13
Interestingly, these types of catalysts also combine highly characterized by FT-IR, H/ C NMR spectroscopy and elemen-
activity with high thermally stability and what is more allow tal analysis. The complexes have been similarly characterized
access to highly branched polyethylenes. Elsewhere, cycloalkyl and in addition for Ni1, Ni2, Ni3 and Ni5 by single crystal
groups have started to emerge as compatible ortho-substitu- X-ray diffraction.
ents with nickel-based polymerization precatalysts such as D
Single crystals of Ni1, Ni2, Ni3 and Ni5 suitable for the
reported (Chart 1). Notably, this class of nickel catalyst X-ray determinations were grown by slow diffusion of hexane
display high activity and produce polyethylenes with unusual into dichloromethane solution of the corresponding
branching architectures that exhibit low molecular weights complex. Perspective views of Ni1, Ni2, Ni3 and Ni5 are shown
and narrow polydispersity. in Fig. 1–4; selected bond lengths and angles are listed in
8
a
In recent years our group has been interested in designing Table 1. The structures are closely related and will be dis-
new α-diimine-nickel catalysts that are capable of mediating cussed together. Ni1, Ni2, Ni3 and Ni5 all consist of a single
the formation of hyperbranched polyethylenes that could nickel center surrounded by two nitrogen atoms belonging to
potentially be used as thermoplastic elastomers (TPEs). Such a bidentate N,N′-diiminoacenaphthene and two bromide
materials are attracting widespread interest in academia and ligands to complete a geometry best described a distorted
industry owing to their growing demand in applications such tetrahedral; similar structural features have been reported for a
as the automotive, gaskets, footware, industrial hose and cloth- variety of unsymmetrical 1,2-diiminoacenaphthene derivati-
9
7a
ing industries. However, due to the complexity of some of the ves. The key difference between the structures in this study
1
0,11
current synthetic approaches,
we have been drawn to the relates to the nature of aryl group linked to imine-N2; in Ni1 it
simplicity of a homo-polymerization of ethylene as a more is a 2-cyclohexyl-6-methylphenyl, in Ni2 2-cyclopentyl-6-methyl-
straightforward approach to TPEs and indeed have had some phenyl, in Ni3 2-cyclooctyl-4,6-dimethylphenyl and Ni5 2-cyclo-
success in this endeavour using precatalysts of type C pentyl-4,6-dimethylphenyl. With regard to the cycloalkyl ortho-
1
2
(
Chart 1).
Herein we target a new family of unsymmetrical N,N′-diimino- cyclooctyl ring (Ni3), a chair conformation for cyclohexyl (Ni1)
acenaphthene-nickel(II) bromide complexes (E, Chart 1), and an envelope conformation for the cyclopentyl unit (Ni5,
substituent, a boat–chair conformation is adopted by the
1
3
incorporating one sterically demanding 4-methyl-2,6-dibenz- Ni2). For all four structures the second imine-nitrogen (N1)
hydrylphenyl N-aryl group while the other, 4-R-2-methyl-6- is linked to the same sterically bulky 4-methyl-2,6-dibenz-
cycloalkylphenyl, contains a cycloalkyl ortho-substituent that
can be systematically modified in terms of ring size (viz., cyclo-
pentyl vs. cyclohexyl vs. cyclooctyl). In addition, the 4-R group
presents a further site that will be probed with a view to explor-
ing possible inductive effects. An in-depth study will then be
initiated to optimize catalytic performance and to examine
how these structural features impact on catalytic activity and
the branching content of the resulting polyethylenes. A study
of the mechanical properties of selected polymer samples will
then be conducted to assess their elastomeric properties.
Results and discussion
Synthesis and characterization
The N,N′-diiminoacenaphthene-nickel(II) bromides, [1-{2,6-
(
Ph
MeC
Ni3, 2-(C H )-4,6-Me C H Ni4, 2-(C H )-4,6-Me C H Ni5,
2
CH)
2
-4-MeC
Ni1, 2-(C
6
H
2
N}-2-(ArN)C
2
C
10
H
6
]NiBr
2
(Ar = 2-(C
6
H11)-6-
6
H
2
5
H
9
)-6-MeC
6
H
2
Ni2, 2-(C
8
H
15)-6-MeC
6 2
H
6
11
2
6
2
5
9
2
6
2
2
8 2 6 2
-(C H15)-4,6-Me C H Ni6), can be readily prepared in reason-
able to good yield by treatment of the corresponding ligand,
L1–L6, with NiBr (DME) (DME = 1,2-dimethoxyethane) in a Scheme 1 Synthesis of L1–L6 and Ni1–Ni6.
2
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Fig. 4 OLEX2 representation of Ni4 with the thermal ellipsoids shown
at the 30% probability level; all hydrogen atoms have been omitted for
clarity.
Fig. 1 OLEX2 representation of Ni1 with the thermal ellipsoids shown
at the 30% probability level; all hydrogen atoms have been omitted for
clarity.
Table 1 Selected bond lengths (Å) and angles (°) for Ni1, Ni2, Ni3 and
Ni5
Ni1
Ni2
Ni3
Ni5
Bond lengths (Å)
Ni(1)–Br(1)
Ni(1)–Br(2)
Ni(1)–N(1)
Ni(1)–N(2)
N(1)–C(1)
N(1)–C(25)
N(2)–C(12)
N(2)–C(23)
2.3378(6)
2.3277(6)
2.035(2)
2.024(2)
1.289(3)
1.449(3)
1.284(3)
1.449(3)
2.3294(9)
2.3436(8)
2.040(3)
2.020(3)
1.289(5)
1.448(5)
1.288(5)
1.445(5)
2.3481(8)
2.3333(7)
2.036(2)
2.023(2)
1.283(3)
1.452(3)
1.283(3)
1.443(3)
2.3274(6)
2.3428(7)
2.029(2)
2.036(3)
1.292(4)
1.446(4)
1.281(4)
1.449(4)
Bond angles (°)
N(1)–Ni(1)–N(2)
Br(1)–Ni(1)–Br(2)
N(1)–Ni(1)–Br(1)
N(2)–Ni(1)–Br(1)
N(1)–Ni(1)–Br(2)
N(2)–Ni(1)–Br(2)
82.87(8)
82.86(14)
125.31(3)
109.33(10)
110.76(10)
112.34(10)
108.11(10)
82.61(8)
83.26(10)
124.39(3)
110.47(7)
119.14(8)
109.11(7)
102.79(8)
122.84(2)
111.17(6)
110.10(6)
112.14(6)
110.62(6)
122.28(2)
114.50(6)
106.52(6)
111.89(6)
111.75(6)
Fig. 2 OLEX2 representation of Ni2 with the thermal ellipsoids shown
at the 30% probability level; all hydrogen atoms have been omitted for
clarity.
hydrylphenyl group. The bite angles for the bidentate ligands are
similar [N1–Ni1–N2: 82.78(8) (Ni1), 82.86(14) (Ni2), 82.61(8)
(
Ni3), 83.26(10)° (Ni5)], while the Br1–Ni–Br2 angles show
some modest variation (range: 122.28(2)–125.31(3)°). Despite
the inequivalent steric and electronic properties of the
cycloalkyl-substituted N-aryl groups, there are only minor
differences in the corresponding Ni1–N2 bond distances
(
range: 2.020(3)–2.036(3) Å). The N1–C1 [1.289(3) Å (Ni1), 1.289(5)
Å (Ni2), 1.283(3) Å (Ni3), 1.292(4) Å (Ni5)] and N2–C12
1.284(3) Å (Ni1), 1.288(5) Å (Ni2), 1.283(3) Å (Ni3), 1.281(4) Å
Ni5)] bond lengths are consistent with CvN double bond
[
(
character, while the imine vectors are essentially co-planar
with the neighboring acenaphthene unit. In all cases the
4
-methyl-2,6-dibenzhydryl phenyl group adopts an orientation
almost perpendicular to the corresponding N1, N2, Ni1 plane
range: 85.11–88.38°). By contrast, the cycloalkyl-substituted
N-aryl group shows some variation in the degree of inclination
88.47° (Ni1), 87.46° (Ni2), 76.73° (Ni3), 72.61° (Ni5)]. The
(
[
Fig. 3 OLEX2 representation of Ni3 with the thermal ellipsoids shown
at the 30% probability level; all hydrogen atoms have been omitted for
clarity.
bulky cyclooctyl group in Ni3 is likely responsible for the
observed tilting of the aryl group away from perpendicular,
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however, it is unclear why the ortho-cyclopentyl groups in Ni2 polymerization were observed with the order, in terms of co-
in Ni5 show such a difference in inclination. catalyst, following: EASC > Et AlCl > MMAO > MAO. While it is
Both the ligands, L1–L6, and complexes, Ni1–Ni6, exhibit clear that all the co-catalysts employed are effective at activat-
2
1
4
two imine absorption bands in their IR spectra with the pair ing Ni6, it is unclear why the chloroaluminum-type co-cata-
for the complexes shifted to lower wavenumber by ca. 20 cm−
an observation that is consistent with effective coordination
between the metal and the two imine nitrogen atoms. All the g PE mol (Ni) h ]. Nevertheless, similar observations have
1
,
lysts deliver higher activities [13.79–16.23 × 10 g PE mol (Ni)
6
−1
−
1
6
h
] than their aluminoxane counterparts [10.84–10.93 × 10
−
1
−1
3
b,15
complexes display microanalytical data that is in accord with been noted elsewhere for related nickel precatalysts.
Based
their elemental composition.
on catalytic activity, EASC and MMAO were selected as repre-
sentative members of each type of activator for subsequent
evaluations.
Optimization and evaluation of Ni1–Ni6/EASC. With a view
to optimizing the reaction conditions and exploring the effect
of these conditions on the polymer structure, Ni6 was again
used as the test precatalyst, this time using solely EASC as the
co-catalyst. In particular, a study was conducted to determine
the optimal molar ratio of Al to Ni, temperature and run time;
the results are collected in Table 3.
Catalyst evaluation for ethylene polymerization
Co-catalyst screen. With the aim to identify the most suit-
able co-catalyst for the polymerization, Ni6 was chosen as the
test precatalyst and the type of aluminum alkyl co-catalyst
varied with the pressure of ethylene maintained at 10 atmos-
pheres and the run temperature at 30 °C (Table 2). In particu-
lar, four co-catalysts were evaluated namely methyl-
aluminoxane (MAO), modified methylaluminoxane (MMAO),
ethylaluminum sesquichoride (EASC) and diethylaluminum
Firstly, on increasing the molar ratio of Al/Ni from 400 to
900, with the temperature kept at 30 °C and the duration of the
2
chloride (Et AlCl). In each case very high activities for ethylene
run at 30 minutes, the activity increased to a very high level of
6
−1
−1
1
7.45 × 10 g PE mol (Ni) h with an Al/Ni ratio of 700
(
entries 1–6, Table 3), which is much higher than that
Table 2 Ethylene polymerization using Ni6 with four different co-
catalysts
observed with precatalysts of similar structure reported else-
where. Notably as the number of molar equivalents of EASC
a
7a
b
c
c
d
is increased from 400 to 900 the molecular weight steadily
Entry Co-cat. Al/Ni Yield (g) Activity
M
w
M
w
/M
n
m
T (°C)
drops. This observation is consistent with previous fin-
1
2
3
4
MAO
2000 10.84
10.84
10.93
16.23
13.78
4.27 2.62
4.45 2.48
3.89 2.25
3.94 2.29
57.5
66.5
44.4
49.1
7c,16
dings,
and can be attributed to increased chain transfer
MMAO 2000 10.93
from the active nickel species to aluminum yielding polyethyl-
enes with lower molecular weight and narrower molecular
weight distribution (see Fig. 5a).
Secondly, to understand the influence of reaction tempera-
ture, the polymerization was studied at temperatures between
EASC
Et AlCl
500 16.23
500 13.78
2
a
Conditions: 2.0 μmol of Ni6; 10 atm of ethylene; total volume
b
6
−1
−1
c
5
1
w
00 mL; 30 min; 30 °C. Activity: 10 g PE mol (Ni) h . M : 10
−1 d
g mol ; M
w
and M
w
/M
n
determined by GPC. Determined by DSC.
a
Table 3 Ethylene polymerization using Ni1–Ni6/EASC
b
c
c
d
Entry
Pre-cat.
Al/Ni
T (°C)
t (min)
Yield (g)
Activity
M
w
M
w
/M
n
m
T (°C)
1
2
3
4
5
6
7
8
9
Ni6
Ni6
Ni6
Ni6
Ni6
Ni6
Ni6
Ni6
Ni6
Ni6
Ni6
Ni6
Ni6
Ni1
Ni2
Ni3
Ni4
Ni5
Ni6
Ni6
400
500
600
700
800
900
700
700
700
700
700
700
700
700
700
700
700
700
700
700
30
30
30
30
30
30
20
40
50
30
30
30
30
30
30
30
30
30
30
30
30
30
30
30
30
30
30
30
30
5
15
45
60
30
30
30
30
30
30
30
14.22
16.23
15.33
17.45
15.14
12.60
2.11
7.72
3.88
2.17
6.76
20.10
22.01
6.64
7.96
11.06
9.05
12.20
5.13
1.15
14.22
16.23
15.33
17.45
15.14
12.60
2.11
7.72
3.88
13.04
13.52
13.40
11.01
6.64
7.96
11.06
9.05
12.20
5.13
1.15
4.29
3.89
3.74
3.68
3.37
3.07
4.43
2.89
2.69
2.99
3.40
4.15
4.56
4.51
3.91
3.85
4.34
4.24
2.40
4.52
2.47
2.25
2.29
2.38
2.16
2.22
2.39
1.97
2.34
2.14
2.10
2.38
2.05
2.25
2.14
2.20
2.15
1.87
1.59
1.99
53.1
44.4
49.1
50.9
63.3
91.1
103.6
51.3
44.2
79.4
64.0
56.7
55.1
78.7
57.8
56.4
53.5
41.5
23.1
60.6
10
11
12
13
14
15
16
17
18
19
20
e
f
a
Conditions: 2.0 μmol of Ni6; 10 atm of ethylene; total volume 100 mL. Activity: 10 g PE mol (Ni) h−1
b
6
−1
c
w w w n
. M and M /M deter-
: 10 g mol−1; M
5
d
e
f
mined by GPC. Determined by DSC. 5 atm. 1 atm.
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When the pressure of ethylene was lowered from 10 to 1 atmos-
pheres, the activity also dropped which can be attributed to
mass transport limitations of the monomer at this low ethyl-
4
d
ene concentration.
Based on the above results using Ni6/EASC, the optimum
conditions were identified as: Al/Ni molar ratio of 700, 30 °C
reaction temperature and a run time of 30 minutes. To estab-
lish the relationship between structural variations in the pre-
catalyst and catalytic performance in ethylene polymerization,
the remaining complexes (Ni1–Ni5) were also investigated using
these conditions (entries 14–18, Table 3). All the complexes
6
exhibited good activities in the range 6.64–17.45 × 10 g PE
−
1
−1
mol (Ni) h with the overall order being Ni6 (2-cyclooctyl-
4,6-methyl) > Ni5 (2-cyclopentyl-4,6-methyl) > Ni3 (2-cyclooctyl-
6-methyl) > Ni4 (2-cyclohexyl-4,6-methyl) > Ni2 (2-cyclopentyl-
6-methyl) > Ni1 (2-cyclohexyl-6-methyl). In terms of the par-
ticular 4-R group, Ni3 (2-cyclooctyl-6-methyl) > Ni2 (2-cyclo-
pentyl-6-methyl) > Ni1 (2-cyclohexyl-6-methyl) for R = H while for
R = Me, Ni6 (2-cyclooctyl-4,6-methyl) > Ni5 (2-cyclopentyl-4,6-
methyl) > Ni4 (2-cyclohexyl-4,6-methyl). Several points emerge
from examination of these findings. Firstly, the type of
w
Fig. 5 Molecular weight (M ) and PDI versus (a) molar ratio of Al/Ni (b)
reaction temperature and (c) reaction time using Ni6/EASC.
2
7
0 and 50 °C (entries 4–9, Table 3) with the Al/Ni ratio fixed at cycloalkyl group positioned at the ortho-position of the N-aryl
00 and the reaction time at 30 minutes. Inspection of the group affects catalytic activity with the largest ring system,
data reveals the optimum temperature in terms of catalytic cyclooctyl giving the highest activities (Ni6, Ni3). Somewhat
activity to be 30 °C (entry 4, Table 2). As the temperature is surprisingly the smaller cyclopentyl-systems (Ni5, Ni2) are
increased above 30 °C the activity steadily decreases, an obser- more active than their cyclohexyl counterparts (Ni4, Ni1).
vation that can be accredited to the partial deactivation of the Secondly, the nature of the 4-R group is also influential on
active species; similar results have been seen with related pre- catalytic activity with 4-Me derivatives more active than their
7
a,12a,16c
catalysts.
Indeed, the capacity of the N-aryl moieties to 4-H analogues. To explain the superior performance of the
freely rotate at elevated temperature, resulting in increased cyclooctyl systems it would seem plausible that the flexible
associative displacement and/or C–H activation, has been conformation of the cyclooctyl ring can protect the metal
suggested as a reason behind this lowering in activity noted in center in the active catalyst but not impede the approach of
4
d
previously reported α-diimine-nickel catalyts. With regard to the ethylene monomer. By contrast, the protection of active
the molecular weight of the polyethylene, this was found to species with the cyclohexyl and cyclopentyl would appear less
decrease as the reaction temperature was raised from 20 to effective. The positive effect on catalytic activity imposed by
5
0 °C, in accordance with more facile chain transfer and ter- the presence of a para-methyl group (Ni4, Ni5 and Ni6) has
mination (see Fig. 5b). Notably, the lowest temperature run at some precedent and is likely due to its the electron donating
3
a,17
2
0 °C afforded polymer displaying the highest melting temp- properties and influence on the active species.
erature (T
m
) of 103.6 °C consistent with more linear properties
Optimization and evaluation of Ni1–Ni6/MMAO. In a
of this sample.
manner similar to that described with EASC, this time using
Thirdly, the lifetime of the catalyst was examined by deter- MMAO as the co-catalyst and Ni6 as the precatalyst, we set about
mining the catalytic activity at 5, 15, 30, 45 and 60 minutes. again optimizing the reaction conditions and exploring the effects
Examination of the data reveals the maximum activity to occur on the polymer properties; the data are collected in Table 3. In
6
−1
−1
after 30 minutes (17.45 × 10 g PE mol (Ni) h ) and then general, catalysts based on Ni6/MMAO when compared with Ni6/
steadily decrease over the second 30 minutes (entries 4 and 10–13, EASC, exhibit similarly high activity but display higher molecular
Table 3). The lower activities observed in the 5–15 minutes weights as well as broader PDIs and higher Tm values.
timeframe can be ascribed to the induction period required to
On varying the molar ratio of Al/Ni from 1000 to 3000, the
6
−1
−1
fully generate the active species. Beyond 30 minutes, the activity increased to a peak of 10.93 × 10 g PE mol (Ni) h
6
activity drops from its maximum to a level of 11.01 × 10 g PE with the ratio at 2000 and then decreased (entries 1–7,
−
1
−1
mol (Ni) h after 60 minutes with the onset of catalyst de- Table 4). In addition, the polyethylenes obtained with different
activation. Nevertheless, despite this apparent catalyst decay molar equivalents of MMAO showed a slight variation in poly-
this still represents good activity and highlights the stability of dispersity, while the molecular weight generally lowered on
this catalyst. With regard to the molecular weight this raising the molar ratio (Fig. 6a).
increases over the duration of the test (see Fig. 5c) with the
With respect to the effect of temperature, we carried out the
resultant polyethylenes showing narrow polydispersity (PDI polymerization at 20, 30, 40 and 50 °C (entries 4 and 8–10,
range: 1.97–2.38) in accord with a single site active species. Table 4). Once again 30 °C was found to be the optimum temp-
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a
Table 4 Ethylene polymerization using Ni1–Ni6/MMAO
b
c
c
d
Entry
Pre-cat.
Al/Ni
T (°C)
t (min)
Yield (g)
Activity
M
w
M
w
/M
n
m
T (°C)
1
2
3
4
5
6
7
8
9
Ni6
Ni6
Ni6
Ni6
Ni6
Ni6
Ni6
Ni6
Ni6
Ni6
Ni6
Ni6
Ni6
Ni6
Ni1
Ni2
Ni3
Ni4
Ni5
Ni6
Ni6
1000
1500
1750
2000
2250
2500
3000
2000
2000
2000
2000
2000
2000
2000
2000
2000
2000
2000
2000
2000
2000
30
30
30
30
30
30
30
20
40
50
30
30
30
30
30
30
30
30
30
30
30
30
30
30
30
30
30
30
30
30
30
5
15
45
60
30
30
30
30
30
30
30
6.22
6.72
7.10
10.93
9.12
6.11
5.83
6.57
5.32
3.91
2.21
5.32
14.67
16.71
3.92
4.21
4.92
5.07
8.20
4.21
0.56
6.22
6.72
7.10
10.93
9.12
6.11
5.83
6.57
5.32
3.91
13.24
10.64
9.77
8.35
3.92
4.21
4.92
5.07
8.20
4.21
0.56
5.99
5.73
5.52
4.91
4.82
4.67
4.58
6.68
4.76
3.47
3.90
4.93
4.52
2.14
4.16
3.95
5.79
4.82
3.96
2.67
4.81
2.61
2.40
2.58
2.22
2.63
2.66
2.89
3.08
2.60
2.19
2.50
2.85
2.41
2.01
2.28
2.09
2.39
2.10
2.41
1.89
2.51
80.0
78.1
72.8
66.5
73.1
73.0
74.2
99.1
64.6
45.6
70.7
69.8
64.2
75.9
56.6
70.9
69.5
66.6
61.6
30.7
70.3
10
11
12
13
14
15
16
17
18
19
20
21
e
f
a
Conditions: 2.0 μmol of Ni6; 10 atm of ethylene; total volume 100 mL. Activity: ×10 g PE mol (Ni) h−1
b
6
−1
c
: ×10 g mol−1; M
5
.
M
w
w
and M
w
/M
n
d
e
f
determined by GPC. Determined by DSC. 5 atm. 1 atm.
3.24 × 10 g PE mol (Ni) h−1 (entries 4 and 11–14, Table 4)
6
−1
1
highlighting the fast induction period of this particular cata-
lyst. Beyond 5 minutes the activity gradually decreases reach-
6
−1
−1
ing its lowest value of 8.35 × 10 g PE mol (Ni) h (entry 14,
Table 4) after 60 minutes representing a 37% decrease. In
terms of the PDI, a slightly wider variation with time (range:
2.01–2.85) was displayed when compared to that observed with
EASC, while the molecular weights increased to a maximum
between 15 and 30 minutes and then gradually decreased
(
Fig. 6c).
With the optimal conditions established for Ni6/MMAO,
with the Al/Ni molar ratio set at 2000, the temperature at 30 °C
and a run time of 30 minutes, Ni1–Ni5 were screened using
these conditions (entries 4 and 15–19, Table 4). As with the
EASC study, Ni6/MMAO showed the highest activity; albeit less
than with Ni6/EASC. Likewise, the correlation between the
activities of all the complexes showed a similar trend, Ni6
(
(
(
2-cyclooctyl-4,6-methyl) > Ni5 (2-cyclopentyl-4,6-methyl) > Ni4
2-cyclohexyl-4,6-methyl) > Ni3 (2-cyclooctyl-6-methyl) > Ni2
2-cyclopentyl-6-methyl) > Ni1 (2-cyclohexyl-6-methyl) with the
Fig. 6 Molecular weight (M
run temperature and (c) reaction time using Ni6/MMAO.
w
) and PDI versus (a) molar ratio of Al/Ni (b)
exception that Ni4 and Ni3 exchange places. On the basis of
the R group, however, the trend was identical to that seen for
EASC. Hence for R = H, Ni3 (2-cyclooctyl-6-methyl) > Ni2
erature in line with that observed with EASC. Over the tempera- (2-cyclopentyl-6-methyl) > Ni1 (2-cyclohexyl-6-methyl), while
ture range the molecular weight of the polyethylene was found with R = Me the order is Ni6 (2-cyclooctyl-4,6-methyl) > Ni5
to decrease as the reaction temperature was increased in agree- (2-cyclopentyl-4,6-methyl)
ment with more facile chain transfer and termination Once again this study highlights the important role played by
Fig. 6b). The lowest temperature run at 20 °C afforded poly- the cyclooctyl group in affecting catalytic activity which is sup-
mers displaying the highest Tm values characteristic of more plemented by the presence of a para-methyl group.
linear properties of the polymer. Polyethylene microstructures. Inspection of the two sets of
Unlike with EASC, the MMAO-promoted polymerization dis- polymerization data (Tables 3 and 4), reveals the T values of
played the highest activity after 5 minutes which was up to the polymers obtained in the runs performed at 30 °C or above
>
Ni4 (2-cyclohexyl-4,6-methyl).
(
m
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1
2a,16c,18
to be under 80 °C suggesting a high branching content.
1
3
To verify this, high temperature C NMR spectroscopy was
performed on the sample obtained using the more active
catalysts Ni6/EASC (entry 4, Table 3) and Ni6/MMAO at 30 °C
(
5
entry 4, Table 4) and compared with the data obtained at
0 °C (entry 9, Table 3 and entry 10, Table 4). The NMR signals
were assigned on the basis of previously reported characteriz-
1
8b
ation data.
0 °C (Fig. 7) contains 113 branches/1000 carbons, with the
predominant types being methyl (64%), ethyl (5.5%), propyl
7.5%), butyl (2.0%) and longer chains (21%). Comparatively,
The polyethylene generated using Ni6/EASC at
3
(
the polymer obtained using Ni6/MMAO at 30 °C (Fig. 8) dis-
plays 89 branches/1000 carbons, with the main types of
branches being only methyl (72%) and longer chain branches
(
28%). The higher degree of branching with Ni6/EASC over
1
3
Fig. 8
C NMR spectrum of the polyethylene sample obtained using
Ni6/MMAO at this run temperature is also consistent with the
lower observed Tm values (50.9 vs. 66.5 °C, respectively).
By contrast, the polymer obtained at 50 °C for Ni6/EASC
Ni6/MMAO at 30 °C (entry 4, Table 4).
(Fig. 9) shows a higher branching content at 134 branches/
1
000 carbons. In comparison with that at obtained at 30 °C
the content of methyl-type branches increases from 64 to 67%,
while the percentage of longer chain branches decreases from
21 to 12%. For the polymer obtained using Ni6/MMAO at
50 °C (Fig. 10), the total branching content is also higher at
122 branches/1000 carbons. However, the resulting polymers
display a different distribution of branches over the tempera-
ture range. At 50 °C, the content of methyl-type branches
using Ni6/MMAO decreases from 72 to 67% and the longer
chain branches lowers from 28 to 10%, while the short chain
branches, including ethyl, propyl, butyl and amyl branches,
increase from zero to 9.5%, 8.5%, 4.0%, 1.0%, respectively.
Overall, raising the temperature of the polymerization run
leads to an increase in the branching content with the result
that the polymer becomes less crystalline and more
amorphous.
13
Fig. 9
C NMR spectrum of the polyethylene sample obtained using
Mechanical properties of the polyethylenes. Given the Ni6/EASC at 50 °C (entry 9, Table 3).
observed branching content of the polyethylenes, a selection
1
3
13
Fig. 7
C NMR spectrum of the polyethylene sample obtained using
Fig. 10
C NMR spectrum of the polyethylene sample obtained using
Ni6/EASC at 30 °C (entry 4, Table 3).
Ni6/MMAO at 50 °C (entry 10, Table 4).
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of samples was used to assess their mechanical properties and
in turn their elastomeric properties. A total of eight samples
were selected, four derived from Ni6/EASC and four from Ni6/
MMAO each obtained at four different temperatures (20, 30,
4
0, 50 °C). The samples, designated, EASC-20, EASC-30,
EASC-40, EASC-50 (entries 7, 4, 8 and 9, Table 3), MMAO-20,
MMAO-30, MMAO-40 and MMAO-50 (entries 8, 4, 9 and 10,
Table 4) were then subjected to stress–strain testing and
1
9
dynamic mechanical analysis (DMA) (Table 5).
Firstly, the monotonic tensile stress–strain data were
recorded on all samples. Each mechanical test was performed
with an average of five specimens at 30 °C with 70% air
humidity. For the EASC samples, the lowest ultimate tensile
strength (1.75 MPa) and strain at break (252.2%) was observed
by EASC-50, which can be ascribed to it being almost amor-
Fig. 11 Stress–strain curves for EASC-20, EASC-30, EASC-40 and
EASC-50; the end points of the curves correspond to tensile failure of
the samples.
phous (Fig. 11). Indeed, this sample shows the lowest X
c
at
0
.1%, the lowest T at 44.2 °C and the lowest melting enthalpy
m
) of the series at 0.3 J g− (cf. 88 J g for EASC-20). On
1
−1
20
(
ΔH
increasing the crystallinity from 0.12% (EASC-50) to 9.70%
EASC-30), the ultimate tensile stress and elongation at break
m
(
also increase from 0.12 to 9.70 MPa and 252.2 to 590.0%,
respectively. Conversely, the most crystalline sample EASC-20
(
Xc = 35.5%, Tm = 106.6 °C) displays the opposite trend, with
the ultimate tensile stress increasing but the elongation at
break sharply decreasing. With regard to the samples obtained
using MMAO, similar features are evident but in general
exhibit comparatively higher crystallinity [X
c
=
6.56%
MMAO-50, 16.7% MMAO-40, 22.9% MMAO-30] with the effect
that the ultimate tensile stress data is also relatively higher. As
evidenced by these stress–strain tests, the polymers obtained
at higher temperature show better elastomeric properties
2
1
which can be attributed to their higher branching content.
In general, the degree of stretching relates to the crystallinity
) and to some degree the molecular weight with the upshot
that elasticity is mainly caused by low crystallinity. The
environmental scanning electron micrographs (ESEM) of
EASC-30 and EASC-50 shown in Fig. 12 further highlight the
Fig. 12 ESEM of EASC-30 (top) and EASC-50 (bottom) at different mag-
nifications: (a) 100, (b) 500, (c) 300 and (d) 500.
(X
c
2
2
effects of temperature on the crystallinity, in this case by the tallinity while the fracture becomes rougher in EASC-50 with
assessment of the fracture appearance. Sample EASC-30 shows additional deformation evident on account of its decreased
a smoother fracture surface owing to its relatively higher crys- crystallinity.
Secondly, the stress–strain recovery tests were also per-
formed on the polymer samples. Specifically, the data were col-
Table 5 Selected properties of EASC-20 to EASC-50 and MMAO-20 to lected at −10 °C and 30 °C using all eight samples by dynamic
MMAO-50
mechanical analysis (DMA) (Fig. 13). Each recovery test
involves 10 cycles to allow testing for elastic extenuation.
Samples EASC-20 and MMAO-20 were found too stiff to
stretch, with the result that they went beyond the stretch limit
of the instrument. Nonetheless, these findings further support
that these particular polymers are more linear hence display a
c
c
Stress
Strain
(%)
a
b
a
Sample
T (°C)
T
m
(°C)
M
w
X
c
(%) (MPa)
EASC-20
EASC-30
EASC-40
EASC-50
MMAO-20 20
MMAO-30 30
MMAO-40 40
MMAO-50 50
20
30
40
50
103.6
50.9
51.3
44.2
99.1
66.5
64.6
45.6
4.43 35.5
3.60 9.70
2.89 4.53
3.26 0.12
6.68 29.5
4.91 22.9
4.76 16.7
3.47 6.56
12 ± 0.7 498 ± 8
4.8 ± 0.9 590 ± 72
2.1 ± 0.7 552 ± 43
1.8 ± 0.3 252 ± 64 higher crystalline content. On the other hand, the other
8.0 ± 0.5 131 ± 54
5.7 ± 0.2 481 ± 13
3.9 ± 0.4 469 ± 58
samples behaved satisfactorily in the test and showed that the
elastic recovery decreased relatively little whilst maintaining
2.5 ± 0.4 402 ± 46 good elasticity even after 10 cycles. For EASC-30, EASC-40, and
EASC-50, as the temperature was increased from −10 to 30 °C,
the elastic recovery increased from 40.7 to 66.6%, 41.7 to
70.4%, 43.5 to 75.5%, respectively. Conversely, the Young’s
a
°
°
°
°
ꢀ1 20
Determined by DSC; Xc ¼ ΔHf ðTmÞ=ΔH ðT Þ; ΔH ðT Þ ¼ 248:3 J g
.
f
m
f
m
b
5
−1
c
w
M : ×10 g mol ; determined by GPC. Determined using a universal
tester.
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st
th
Fig. 14 Stress–strain recovery tests for the 1 and 10 cycle for
MMAO-30 at −10 °C and 30 °C.
st
found to be 43.5% which compares with 61.2% at the 1 cycle.
st
Similarly at 30 °C, the value lowered from 64.8% (1 cycle) to
th
5
1.8% (10 cycle) highlighting the gradual loss in elasticity
after being stretched multiple times. All the data show a temp-
erature dependence, which indicates that the elastic properties
in this case are more likely influenced by crystallinity than by
23
molecular weight or molecular weight distribution. In com-
parison with our previous findings the specimens generated in
1
2a
this study, with one exception,
exhibit higher elastic recov-
ery as well as larger Young’s moduli. The improvement in
Young’s modulus makes the elastomers stronger and more
resistant to external damage which broadens the application of
these materials. Once again this reinforcement can be attribu-
2
4
ted to the increased degree of crystallinity.
Conclusions
A range of distinct 4-R-2-methyl-6-cycloalkyl-substituted aryl
groups (cycloalkyl = cyclopentyl, cyclohexyl or cyclooctyl and
R = Me or H) have been successfully integrated into an unsym-
metrical diaryliminoacenaphthene ligand frame allowing
access to the nickel(II) bromide complexes, Ni1–Ni6. All com-
plexes and ligands have been characterized by a combination
of NMR and FTIR spectroscopy as well as by elemental ana-
lysis; single crystal X-ray diffraction studies have been per-
formed on Ni1, Ni2, Ni3 and Ni5. On activation with EASC and
MMAO, all the complexes displayed high activities towards
ethylene polymerization between 20–50 °C with the ortho-sub-
Fig. 13 Stress–strain recovery tests for EASC-30, EASC-40, EASC-50,
MMAO-30, MMAO-40 and MMAO-50 at −10 °C and 30 °C.
moduli for the corresponding samples decreased sharply from stituted cyclooctyl systems (Ni6, Ni3) proving more active than
1
2
2.4 MPa to 5.96 MPa, 12.3 MPa to 5.32 MPa and 6.85 MPa to the cyclopentyl (Ni5, Ni2) and cyclohexyl (Ni4, Ni1) counter-
.93 MPa. In the same way, the MMAO samples, MMAO-30, parts for a given R group. Moreover, the branching content of
MMAO-40 and MMAO-50, exhibited similar trends and com- the polymers could be influenced by the temperature of the
parable elastic recovery with the elastic recovery increasing polymerization run with hyperbranched materials accessible at
from 47.0 to 51.8%, 47.6 to 56.0% and 48.8 to 70.4%, respect- the higher temperatures. The mechanical and elasticity pro-
ively, while the Young’s moduli dropped from 23.4 MPa to 11.3 perties of these materials have been thoroughly investigated
MPa, 21.8 MPa to 10.5 MPa and 9.28 MPa to 4.53 MPa.
and reveal features comparable with thermoplastic elastomers.
7
a
With specific regard to MMAO-30, the elastic recovery for Compared with previously work conducted by the Sun and
st
8d
the 1 cycle obtained at either −10 °C or 30 °C resembles Ivanchev groups, this work has some advantages in terms of
th
that observed at the 10 cycle at the same two temperatures higher catalytic activities and lower Tm values for the
th
(
Fig. 14). At −10 °C, the elastic recovery at the 10 cycle was polymers.
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removal and drying under reduced pressure, the product was
isolated as an orange solid (8.68 g, 72%). H NMR (400 MHz,
CDCl , TMS): δ 8.04 (t, J = 7.8 Hz, 2H), 7.76 (m, 2H), 7.27 (s,
3
Experimental
General considerations
1
All manipulations of air- and/or moisture-sensitive compounds 1H), 7.24 (s, 2H), 7.19 (d, J = 7.1 Hz, 2H), 7.08 (d, J = 7.2 Hz,
were carried out under a nitrogen atmosphere using standard 5H), 6.88 (d, J = 7.3 Hz, 4H), 6.81 (s, 3H), 6.61 (t, J = 7.5 Hz,
Schlenk techniques. Toluene was refluxed over sodium benzo- 4H), 6.44 (t, J = 7.3 Hz, 2H), 6.15 (d, J = 7.1 Hz, 1H), 5.45 (s,
1
3
3
phenone and distilled under nitrogen prior to use. 2H), 2.28 (s, 3H). C NMR (101 MHz, CDCl , TMS): δ 189.91,
Methylaluminoxane (MAO, 1.46 M solution in toluene) and 162.50, 146.08, 143.11, 142.61, 141.91, 133.36, 131.94, 131.89,
modified methylaluminoxane (MMAO, 2.0 M in heptane, 3A) 129.83, 129.59, 128.84, 128.54, 128.29, 127.93, 127.13, 126.33,
were purchased from Akzo Nobel Corp. Diethylaluminum 125.64, 124.06, 121.67, 52.29, 21.67. IR (KBr; cm− ): 3026 (w),
1
chloride (Et AlCl, 1.17 M in toluene) and ethylaluminum ses- 1722 (νCvO, s), 1650 (νCvN, m), 1596 (s), 1489 (s), 1446 (s),
2
quichloride (Et
chased from Acros Chemicals. High-purity ethylene was pur- Anal. calcd for C45
chased from Beijing Yansan Petrochemical Co. and used as Found: C, 89.22; H, 5.67; N, 2.29.
3
Al
2
Cl
3
, EASC, 0.87 M in toluene) were pur- 1269 (m), 1268 (w), 1026 (s), 908 (m), 827 (m), 774 (s), 745 (s).
H
33NO (603.77): C, 89.52; H, 5.51; N, 2.32.
received. Other reagents were purchased from Aldrich, Acros
or local suppliers. NMR spectra were recorded on a Bruker
Synthesis of L1–L6
6 2 6 6 3 2 10 6
1-{2,6-(Ph CH) -4-MeC H N}-2-{2-(C H11)-6-MeC H N}C C H
2
2
DMX 400 MHz instrument at ambient temperature using TMS (L1). A solution of 2-(2,6-dibenzhydryl-4-methylphenylimino)
as an internal standard; δ values are given in ppm and J values acenaphthylenone (1.206 g, 2.0 mmol), 2-cyclohexyl-6-methyl-
in Hz. IR spectra were recorded on a PerkinElmer System 2000 phenylamine hydrochloride (0.450 g, 2.0 mmol) and a catalytic
FT-IR spectrometer. Elemental analysis was carried out using a amount of p-toluenesulfonic acid in toluene (50 mL) were
Flash EA 1112 microanalyzer. Molecular weights and mole- stirred and heated to reflux for 16 h. After removal of the vola-
cular weight distributions (MWD) of the polyethylene were tiles under reduced pressure, the residue was purified by
determined using a PL-GPC220 instrument at 150 °C, with alumina column chromatography with petroleum ether/di-
1
,2,4-trichlorobenzene as the solvent. Melting points of the chloromethane (1/1 v/v) as the eluent to afford L1 as a yellow
1
polyethylenes were measured from the second scanning run solid (0.29 g, 19%). H NMR (400 MHz, CDCl
on a PerkinElmer DSC-7 differential scanning calorimeter J = 8.2 Hz, 1H), 7.50 (d, J = 8.2 Hz, 1H), 7.29 (m, 2H), 7.24 (s,
DSC) under a nitrogen atmosphere; in the procedure, a 2H), 7.22 (s, 1H), 7.19 (d, J = 7.2 Hz, 4H), 7.15 (t, J = 4.7 Hz,
sample of about 5.0 mg was heated to 150 °C at a rate of 10 °C 1H), 7.09 (d, J = 7.9 Hz, 2H), 7.00 (d, J = 7.2 Hz, 2H), 6.91 (d, J =
3
, TMS): δ 7.70 (d,
(
−
1
min and kept for 5 min at 150 °C to remove the thermal 7.3 Hz, 2H), 6.86 (m, 2H), 6.81 (s, 1H), 6.55 (t, J = 7.8 Hz, 4H),
history and then cooled at a rate of 10 °C min to −20 °C.
−1
13
C
6.46 (d, J = 7.2 Hz, 1H), 6.39 (t, J = 7.7 Hz, 2H), 5.89 (d, J = 7.2
NMR spectra of the polyethylenes were recorded on a Bruker Hz, 1H), 5.68 (s, 1H), 5.64 (s, 1H), 2.86 (m, 1H), 2.32 (s, 3H),
DMX-300 MHz instrument at 135 °C in deuterated 1,1,2,2-tet- 2.17 (s, 3H), 2.03 (d, J = 14.5 Hz, 1H), 1.73 (d, J = 12.1 Hz, 1H),
rachloroethane with TMS as an internal standard. The stress– 1.57 (m, 2H), 1.52–1.45 (m, 2H), 1.40–1.24 (m, 2H), 1.15 (m,
1
3
strain curves were obtained using a universal tester (Instron 2H). C NMR (101 MHz, CDCl
122, UK), while the ESEM measurements was undertaken 148.39, 146.72, 143.75, 141.78, 139.97, 136.98, 135.67, 133.58,
using an environmental scanning electron microscope 132.80, 132.40, 129.86, 129.76, 129.62, 129.10, 128.75, 128.31,
QUanta feg200) at 20 kV. The stress–strain recovery tests at 128.12, 127.81, 127.74, 127.26, 126.99, 126.07, 125.59, 124.69,
3
, TMS): δ 162.32, 155.27,
1
(
different temperatures were carried out using a dynamic mech- 124.43, 124.13, 122.28, 52.15, 38.94, 34.87, 33.58, 27.01, 26.80,
anical analyzer (DMA 800, TA) under controlled force mode. 26.16, 21.64, 18.85. IR (KBr; cm− ): 3025 (w), 2923 (w), 1663
1
2
,6-Dibenzhydryl-4-methylaniline, 2-cyclohexyl-6-methylaniline (νCvN, m), 1643 (νCvN, m), 1594 (m), 1494 (m), 1445 (s), 1235
hydrochloride, 2-cyclopentyl-6-methylaniline hydrochloride, (w), 1078 (m), 1034 (m), 923 (m), 857 (w), 828 (m), 765 (s), 741
-cyclooctyl-6-methylaniline hydrochloride, 2-cyclohexyl-4,6-di- (s). Anal. calcd for C58 (775.05): C, 89.88; H, 6.51; N,
methylaniline hydrochloride, 2-cyclopentyl-4,6-dimethylaniline 3.61. Found: C, 89.90; H, 6.53; N, 3.57.
hydrochloride, 2-cyclooctyl-4,6-dimethylaniline hydrochloride, 1-{2,6-(Ph CH) -4-MeC H N}-2-{2-(C H )-6-MeC H N}C C H
2
50 2
H N
2
2
6
2
5
9
6
3
2 10 6
8
g
have been prepared using literature methods.
(L2). Using a similar procedure and molar ratios to that
described for L1 but with 2-cyclopentyl-6-methylphenylamine
Synthesis and characterization
hydrochloride as the amine, L2 was obtained as a yellow
1
2
-(2,6-Dibenzhydryl-4-methylphenylimino)acenaphthylenone. powder (0.15 g, 10%). H NMR (400 MHz, CDCl
3
, TMS): δ 7.70
A mixture of 2,6-dibenzhydryl-4-methylphenylamine (8.78 g, (d, J = 8.2 Hz, 1H), 7.53 (d, J = 8.3 Hz, 1H), 7.29 (m, 2H), 7.23
0.0 mmol) and acenaphthylene-1,2-dione (3.64 g, 20.0 mmol) (s, 2H), 7.21 (d, J = 4.8 Hz, 2H), 7.18 (s, 1H), 7.16 (d, J = 3.2 Hz,
2
was dissolved in dichloromethane (200 mL) and a catalytic 1H), 7.14 (s, 3H), 7.11 (d, J = 5.0 Hz, 2H), 7.08 (s, 1H),
amount of p-toluenesulfonic acid in ethanol (10 mL) added. 6.97–6.86 (m, 5H), 6.80 (d, J = 10.0 Hz, 2H), 6.62 (t, J = 7.6 Hz,
After stirring overnight in room temperature, the solvent was 2H), 6.56 (t, J = 7.6 Hz, 2H), 6.46 (t, J = 6.9 Hz, 2H), 6.40 (dd, J
removed under reduced pressure and the residue purified by = 14.2, 6.8 Hz, 1H), 6.01 (d, J = 7.1 Hz, 1H), 5.62 (s, 2H), 3.25
column chromatography on alumina with petroleum ether/di- (m, 1H), 2.28 (s, 3H), 2.20 (s, 3H), 2.16–2.08 (m, 1H), 1.82–1.42
1
3
chloromethane (1/1 v/v) as the eluent. Following solvent (m, 7H). C NMR (101 MHz, CDCl , TMS): δ 163.57, 161.84,
3
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1
1
1
1
4
48.94, 146.75, 143.50, 141.91, 141.81, 139.95, 134.22, 132.59, calcd for C59
H
52
N
2
(789.08): C, 89.81; H, 6.64; N, 3.55. Found:
32.29, 132.17, 129.81, 129.74, 129.55, 128.95, 128.85, 128.74, C, 89.95; H, 6.56; N, 3.49.
6 2 5 9 2 6 2 2 10 6
28.57, 128.07, 127.83, 127.78, 127.66, 127.20, 126.87, 126.05, 1-{2,6-(Ph CH) -4-MeC H N}-2-{2-(C H )-4,6-Me C H N} C C H
2
2
25.54, 125.41, 124.48, 124.20, 124.02, 122.21, 52.17, 52.12, (L5). Using a similar procedure and molar ratios to that
0.33, 35.91, 33.76, 26.05, 21.53, 18.54. IR (KBr; cm−1): 3235 described for L1 but with 2-cyclopentyl-4,6-dimethyl-phenyl-
(
(
w), 2947 (w), 1660 (νCvN, m), 1640 (νCvN, m), 1594 (m), 1493 amine hydrochloride as the amine, L5 was obtained as a
1
m), 1445 (m), 1257 (m), 1079 (m), 1033 (w), 921 (m), 853 (m), yellow powder (0.19 g, 16%). H NMR (400 MHz, CDCl
3
, TMS):
8
8
28 (m), 766 (s), 740 (s). Anal. calcd for C H N (761.03): C, δ 7.73 (d, J = 8.2 Hz, 1H), 7.63 (d, J = 8.2 Hz, 1H), 7.31 (m, 2H),
5
7
48 2
9.96; H, 6.36; N, 3.68. Found: C, 89.98; H, 6.50; N, 3.52.
2 10 6
-{2,6-(Ph CH) -4-MeC N}-2-{2-(C 15)-6-MeC N}C C H
7.23 (s, 2H), 7.21 (d, J = 4.8 Hz, 2H), 7.18 (s, 1H), 7.16 (d, J =
3.2 Hz, 1H), 7.14 (s, 3H), 7.11 (d, J = 5.0 Hz, 2H), 7.08 (s, 1H),
1
2
2
6
H
2
8
H
6
H
3
(L3). Using a similar procedure and molar ratios to that 6.97–6.86 (m, 5H), 6.80 (d, J = 10.0 Hz, 2H), 6.62 (t, J = 7.6 Hz,
described for L1 but with 2-cyclooctyl-6-methylphenylamine 2H), 6.56 (t, J = 7.6 Hz, 2H), 6.01 (d, J = 7.1 Hz, 1H), 5.71 (s,
hydrochloride as the amine, L3 was obtained as a yellow 1H), 5.67 (s, 1H), 3.33–3.14 (m, 1H), 2.42 (s, 3H), 2.28 (s, 3H),
1
13
powder (0.24 g, 15%). H NMR (400 MHz, CDCl , TMS): δ 7.73 2.21 (s, 3H), 1.83–1.20 (m, 8H). C NMR (101 MHz, CDCl3,
3
(d, J = 8.2 Hz, 1H), 7.52 (d, J = 8.3 Hz, 1H), 7.34–7.27 (m, 2H), TMS): δ 163.64, 162.02, 146.83, 146.48, 143.56, 143.53, 141.95,
7
2
.24 (s, 2H), 7.22 (s, 1H), 7.21–7.14 (m, 5H), 7.11 (d, J = 7.4 Hz, 141.84, 139.95, 133.97, 133.12, 132.55, 132.32, 132.21, 129.83,
H), 6.97 (d, J = 7.3 Hz, 2H), 6.91 (t, J = 10.7 Hz, 3H), 6.85 (d, 129.75, 129.58, 128.96, 128.90, 128.73, 128.65, 128.45, 128.07,
J = 7.6 Hz, 1H), 6.81 (s, 1H), 6.60 (t, J = 7.5 Hz, 2H), 6.56–6.42 127.81, 127.78, 127.66, 127.19, 126.84, 126.04, 125.54, 125.41,
(
1
2
m, 4H), 6.34 (t, J = 7.3 Hz, 1H), 5.89 (d, J = 7.1 Hz, 1H), 5.70 (s, 124.77, 124.20, 124.18, 122.24, 53.41, 52.18, 52.13, 40.33,
H), 5.64 (d, J = 11.6 Hz, 1H), 3.24–2.91 (m, 1H), 2.29 (s, 3H), 35.88, 33.73, 26.06, 21.53, 21.26, 18.45. IR (KBr; cm ): 3654
.21 (d, J = 13.9 Hz, 3H), 2.11–1.92 (m, 1H), 1.85 (m, 1H), 1.70 (w), 2946 (s), 1660 (νCvN, m), 1638 (νCvN, m), 1594 (m), 1491
−
1
(
s, 1H), 1.68–1.58 (m, 2H), 1.57–1.47 (m, 4H), 1.37–1.15 (m, (s), 1438 (s), 1256 (m), 1081 (w), 1033 (w), 921 (m), 853 (m),
1
3
5
1
1
1
1
1
7
2
H). C NMR (101 MHz, CDCl , TMS): δ 166.44, 162.21, 830 (m), 766 (s), 741 (s). Anal. calcd for C H N (775.05): C,
3
5
8
5
0
2
48.45, 146.79, 143.75, 143.64, 141.86, 141.76, 139.90, 135.55, 89.88; H, 6.50; N, 3.61. Found: C, 89.91; H, 6.47; N, 3.62.
2 10 6
32.65, 132.26, 132.14, 129.83, 129.80, 129.74, 129.69, 129.57, 1-{2,6-(Ph CH) -4-MeC N}-2-{2-(C 15)-4,6-Me N} C C H
2
2
6 2
H
8
H
2
C
6
H
2
29.53, 129.44, 129.05, 128.78, 128.70, 128.59, 128.22, 128.13, (L6). Using a similar procedure and molar ratios to that
28.03, 127.72, 127.65, 127.16, 126.90, 126.02, 125.98, 125.52, described L1 but with 2-cyclooctyl-4,6-dimethyl-phenylamine
25.44, 124.59, 124.51, 124.32, 124.00, 122.17, 77.34, 77.02, hydrochloride as the amine, L6 was obtained as a yellow
1
6.70, 52.11, 52.01, 38.89, 34.76, 33.50, 26.98, 26.93, 26.73, powder (0.20 g, 12%). H NMR (400 MHz, CDCl , TMS): δ 7.68
3
−
1
6.09, 21.53, 18.72. IR (KBr; cm ): 3025 (w), 2917 (m), 2851 (d, J = 8.2 Hz, 1H), 7.49 (t, J = 8.5 Hz, 1H), 7.27 (s, 1H), 7.21 (d,
(
(
(
w), 1664 (νCvN, m), 1643 (νCvN, m), 1594 (m), 1494 (m), 1446 J = 8.1 Hz, 3H), 7.16 (dd, J = 13.1, 7.3 Hz, 4H), 7.09 (d, J = 7.5
s), 1252 (w), 1077 (m), 1034 (m), 923 (m), 857 (w), 828 (m), 765 Hz, 3H), 6.96 (d, J = 8.0 Hz, 3H), 6.90 (d, J = 6.8 Hz, 3H),
s), 741 (s). Anal. calcd for C60H N (803.11): C, 89.73; H, 6.78; 6.86–6.77 (m, 2H), 6.59 (dd, J = 15.9, 7.6 Hz, 3H), 6.54–6.44 (m,
54 2
N, 3.49. Found: C, 89.68; H, 6.85; N, 3.47.
-{2,6-(Ph CH) -4-MeC H N}-2-{2-(C H )-4,6-Me C H N} C C H
2 10 6
3H), 6.33 (t, J = 7.4 Hz, 1H), 5.88 (d, J = 7.1 Hz, 1H), 5.64 (d, J =
6.2 Hz, 2H), 3.01 (m, 1H), 2.41 (s, 3H), 2.28 (s, 3H), 2.17 (s,
1
2
2
6
2
6
11
2
6
2
(L4). Using a similar procedure and molar ratios to that 3H), 2.02–1.91 (m, 1H), 1.82 (dd, J = 18.8, 11.2 Hz, 1H), 1.68 (s,
described for L1 but with 2-cyclohexyl-4,6-dimethyl- 1H), 1.62–1.55 (m, 2H), 1.53–1.46 (m, 3H), 1.46–1.28 (m, 6H).
1
3
phenylamine hydrochloride as the amine, L4 was obtained as
C NMR (101 MHz, CDCl , TMS): δ 162.15, 146.84, 145.35,
3
1
a yellow powder (0.24 g, 15%). H NMR (400 MHz, CDCl
3
,
143.91, 143.73, 141.97, 141.68, 139.85, 136.83, 132.96, 132.58,
TMS): δ 7.70 (d, J = 8.2 Hz, 1H), 7.50 (d, J = 8.3 Hz, 1H), 7.29 (d, 132.29, 132.14, 129.83, 129.71, 129.61, 129.48, 129.03, 128.78,
J = 7.8 Hz, 2H), 7.24 (s, 1H), 7.23–7.16 (m, 4H), 7.11 (d, J = 6.5 128.67, 128.47, 127.99, 127.73, 127.60, 127.16, 126.87, 125.98,
Hz, 3H), 7.02 (d, J = 6.8 Hz, 2H), 6.96 (s, 1H), 6.92 (d, J = 7.5 125.93, 125.71, 125.56, 125.35, 124.32, 124.22, 122.04, 52.16,
Hz, 2H), 6.88 (s, 1H), 6.87–6.80 (m, 2H), 6.55 (m, 5H), 6.40 (t, 51.77, 39.35, 33.06, 32.43, 27.70, 27.61, 25.87, 25.42, 25.30,
J = 7.3 Hz, 2H), 5.90 (d, J = 7.0 Hz, 1H), 5.69 (s, 1H), 5.64 (s, 21.53, 21.28, 18.68. IR (KBr; cm− ): 3022 (w), 2923 (m), 2853
1
1
H), 2.85 (m, 1H), 2.42 (s, 3H), 2.29 (s, 3H), 2.16 (s, 3H), 2.02 (m), 1656 (νCvN, m), 1639 (νCvN, m), 1597 (m), 1468 (m), 1442
(
d, J = 12.5 Hz, 1H), 1.72 (t, J = 15.4 Hz, 1H), 1.45 (m, 5H), 1.18 (s), 1275 (m), 1036 (m), 926 (m), 859 (s), 828 (s), 779 (s), 742
1
3
(m, 1H). C NMR (101 MHz, CDCl , TMS): δ 163.88, 162.35, (s). Anal. calcd for C H N (817.13): C, 89.66; H, 6.91; N,
3 61 56 2
1
1
1
1
1
2
46.89, 145.96, 143.79, 143.68, 141.91, 141.81, 139.89, 135.38, 3.43. Found: C, 89.61; H, 6.89; N, 3.50.
33.09, 132.59, 132.27, 132.18, 129.84, 129.81, 129.76, 129.58,
29.54, 129.07, 128.92, 128.70, 128.45, 128.01, 127.71, 127.63,
Synthesis of Ni1–Ni6
[1-{2,6-(Ph CH) -4-MeC H N}-2-{2-(C H )-6-MeC H N}C C H ]
2
2
6
2
6
11
6
2
2 10 6
2 2
27.14, 126.86, 126.00, 125.96, 125.50, 125.42, 125.21, 124.28, NiBr (Ni1). L1 (0.162 g, 0.21 mmol) and NiBr (DME) (0.062 g,
24.21, 122.18, 53.37, 52.13, 52.02, 38.88, 34.80, 33.51, 31.58, 0.20 mmol) were added to a Schlenk tube together with
7.03, 26.77, 26.15, 22.64, 21.51, 21.21, 18.60, 14.08. IR (KBr; ethanol (2 mL) and dichloromethane (10 mL). The reaction
−
1
cm ): 3024 (w), 2922 (s), 2851 (m), 1655 (νCvN, m), 1632 mixture was stirred at room temperature overnight after which
(
νCvN, m), 1595 (m), 1493 (m), 1443 (s), 1232 (m), 1075 (m), time diethyl ether (30 mL) was added to precipitate the
1
034 (m), 924 (m), 857 (m), 829 (m), 779 (s), 743 (s). Anal. complex. The precipitate was filtered, washed with diethyl
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ether (3 × 15 mL) and dried under reduced pressure to give Ni1 3021 (w), 2927 (m), 2361 (w), 1645 (νCvN, m), 1619 (νCvN, m),
−
1
as a red powder (0.10 g, 49%). IR (KBr; cm ): 3028 (w), 1593 (s), 1578 (m), 1480 (s), 1437 (vs), 1291 (m), 1026 (m), 863
2
1
7
922 (m), 2852 (m), 1645 (νCvN, m), 1620 (νCvN, m), 1582 (s), (w), 760 (vs), 717 (vs). Anal. calcd for C59
494 (m), 1448 (s), 1294 (m), 1032 (m), 827 (m), 772 (w), C, 70.33; H, 5.20; N, 2.78. Found: C, 70.28; H, 5.22; N, 2.81.
48 (w). Anal. calcd for C H Br N Ni (993.55): C, 70.12; [1-{2,6-(Ph CH) -4-MeC H N}-2-{2-(C H )-4,6-Me C H N}C C H ]
2 2
H52Br N Ni (1007.58):
5
8
50
2
2
2
2
6
2
5
9
2
6
2
2 10 6
H, 5.07; N, 2.82. Found: C, 70.20; H, 4.88; N, 2.90.
2
NiBr (Ni5). Using a similar procedure and molar ratios to that
[
1-{2,6-(Ph
2
CH)
2
-4-MeC
6
H
2
N}-2-{2-(C
5
H
9
)-6-MeC
6
H
2
N}C
2
C
10
H
6
]
described for Ni1 but with L5 as the ligand, Ni5 was obtained
NiBr (Ni2). Using a similar procedure and molar ratios to that as a red powder (0.04 g, 20%). IR (KBr; cm− ): 3012 (w), 2917
1
2
described for Ni1 but with L2 as the ligand, Ni2 was obtained (m), 2351 (m), 1646 (νCvN, m), 1620 (νCvN, m), 1593 (s), 1579
−
1
as a red powder (0.13 g, 66%). IR (KBr; cm ): 3020 (w), 2960 (s), 1484 (s), 1442 (vs), 1287 (m), 1021 (m), 850 (w), 764 (s), 704
(w), 2359 (w), 1646 (νCvN, m), 1620 (νCvN, m), 1590 (s), 1579 (vs). Anal. calcd for C H Br N Ni (993.55): C, 70.12; H, 5.07;
58 50 2 2
(m), 1485 (s), 1433 (s), 1287 (m), 1021 (m), 815 (w), 764 (m), N, 2.82. Found: C, 70.21; H, 5.21; N, 2.75.
7
4
29 (m). Anal. calcd for C57
.94; N, 2.86. Found: C, 69.99; H, 4.85; N, 2.79.
1-{2,6-(Ph CH) -4-MeC N}-2-{2-(C 15)-6-MeC
NiBr (Ni3). Using a similar procedure and molar ratios to that was obtained as a red powder (0.16 g, 80%). IR (KBr; cm ):
described for Ni1 but with L3 as the ligand, Ni3 was obtained 3025 (w), 2917 (m), 2852 (w), 1647 (νCvN, m), 1623 (νCvN, m),
H
48Br
2
N
2
Ni (979.53): C, 69.89; H,
[1-{2,6-(Ph
2 2 6 2 8 2 6 2
CH) -4-MeC H N}-2-{2-(C H15)-4,6-Me C H N}
C C H ]NiBr (Ni6). Using a similar procedure and molar
2
10
6
2
[
2
2
H
6 2
8
H
6 3 2 10 6
H N}C C H ]
ratios to that described for Ni1 but with L6 as the ligand, Ni6
−
1
2
−
1
as a red powder (0.18 g, 98%). IR (KBr; cm ): 3030 (w), 2910 1579 (s), 1497 (s), 1443 (vs), 1288 (m), 1036 (m), 861 (w), 828
(
(
(
m), 2353 (w), 1645 (νCvN, m), 1619 (νCvN, m), 1599 (s), 1578 (w), 770 (s), 743 (vs). Anal. calcd for C61
m), 1488 (s), 1445 (s), 1291 (m), 1034 (m), 820 (w), 769 (s), 743 C, 70.75; H, 5.45; N, 2.71. Found: C, 70.82; H, 5.39; N, 2.65.
vs). Anal. calcd for C60 Ni (1036.64): C, 70.54; H, 5.33;
2 2
H56Br N Ni (1035.63):
H
2 2
54Br N
X-ray crystallographic studies
N, 2.74. Found: C, 70.61; H, 5.32; N, 2.72.
[
1-{2,6-(Ph CH) -4-MeC H N}-2-{2-(C H )-4,6-Me C H N} Single crystals of Ni1, Ni2, Ni3 and Ni5 suitable for the X-ray
2
2
6
2
6
11
2
6
2
C
2
C
10
H
6
]NiBr
2
(Ni4). Using a similar procedure and molar diffraction analysis were obtained by laying diethyl ether on a
ratios to that described for Ni1 but with L4 as the ligand, Ni4 dichloromethane solution of the corresponding complex at
was obtained as a red powder (0.04 g, 20%). IR (KBr; cm− ): room temperature. With graphite monochromated Mo-Kα radi-
1
Table 6 Crystal data and structure refinements for Ni1, Ni2, Ni3 and Ni5
Ni1
Ni2
Ni3
Ni5
Empirical formula
Formula weight
Temperature/K
Wavelength/Å
Crystal system
Space group
a/Å
b/Å
c/Å
Alpha/°
Beta/°
C
58
H
50Br
2
2
N Ni
C
61
H
58Br
2
2
N NiO
C
60
H
54Br
2 2
N Ni
62 2 2
C H60Br N NiO
1067.61
293(2)
993.53
173.15
0.71073
Monoclinic
P2 /n
10.658(2)
18.896(4)
25.117(5)
90.00
95.19(3)
90.00
1053.58
173.15
0.71073
Monoclinic
P2 /n
10.612(2)
18.490(4)
25.591(5)
90.00
95.00(3)
90.00
5002.4(17)
4
1.399
2.029
1036.64
293(2)
0.71073
Triclinic
Pˉ1
10.987(2)
12.500(3)
19.151(4)
102.42(3)
93.70(3)
93.95(3)
2553.9(9)
2
0.71073
Monoclinic
P2 /c
1
1
1
10.526(2)
17.767(4)
27.812(6)
90.00
94.73(3)
90.00
5183.5(18)
4
1.368
Gamma/°
Volume/Å
3
5037.8(17)
4
1.310
Z
D
μ/mm
−3
calcd/(g cm
)
1.439
2.091
−
1
2.009
1.959
F(000)
Crystal size/mm
θ range/°
Limiting indices
2040.0
0.20 × 0.20 × 0.20
2.70–54.94
2176.0
1136.0
2208.0
3
0.14 × 0.10 × 0.09
3.196–54.97
−13 ≤ h ≤ 13
−24 ≤ k ≤ 24
−33 ≤ l ≤ 33
68 422
11 424
0.0415
608
99.7%
0.32 × 0.31 × 0.12
2.18–55.00
−14 ≤ h ≤ 14
−16 ≤ k ≤ 16
−24 ≤ l ≤ 24
28 595
11 649
0.0395
643
99.1%
0.43 × 0.20 × 0.05
2.72–54.98
−13 ≤ h ≤ 13
−23 ≤ k ≤ 23
−36 ≤ l ≤ 36
70 411
11 865
0.0536
618
99.8%
−13 ≤ h ≤ 13
−
24 ≤ k ≤ 24
32 ≤ l ≤ 32
−
No. of rflns collected
No. unique rflns
R(int)
No. of params
Completeness to θ
56 893
11 483
0.0483
570
99.6%
1.130
2
Goodness of fit on F
1.107
1.070
1.221
Final R indices [I ≥ 2σ(I)]
R
1
= 0.0492
wR = 0.1079
= 0.0545
wR = 0.1108
0.38 and −0.55
R
1
= 0.0486
wR = 0.1225
= 0.0518
wR = 0.1249
0.99 and −1.04
R
1
= 0.0439
wR = 0.1044
= 0.0488
wR = 0.1077
0.72 and −0.65
R
1
= 0.0557
wR = 0.1257
= 0.0597
wR = 0.1312
0.39 and −0.71
2
2
2
2
R indices (all data)
R
1
R
1
R
1
R
1
2
2
2
2
Largest diff. peak and hole/(e Å−
3
)
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ation (λ = 0.71073 Å) at 173(2) K, cell parameters were obtained
by global refinement of the positions of all collected reflec-
tions. Intensities were corrected for Lorentz and polarization
effects and empirical absorption. The structures were solved
by direct methods and refined by full-matrix least squares on
2 (a) G. J. P. Britovsek, V. C. Gibson, S. J. McTavish,
G. A. Solan, A. J. P. White, B. S. Kimberley, P. J. Maddox
and D. J. Williams, Chem. Commun., 1998, 849;
(b) G. J. P. Britovsek, M. Bruce, V. C. Gibson,
B. S. Kimberley, P. J. Maddox, S. Mastroianni,
S. J. McTavish, C. Redshaw, G. A. Solan, S. Strömberg,
A. J. P. White and D. J. Williams, J. Am. Chem. Soc., 1999,
121, 8728.
3 (a) L. Zhong, G. Li, G. Liang, H. Gao and Q. Wu,
Macromolecules, 2017, 50, 2675; (b) Z. Wang, Q. Liu,
G. A. Solan and W.-H. Sun, Coord. Chem. Rev., 2017, DOI:
10.1016/j.ccr.2017.06.003; (c) Z. Wang, Y. Zhang, Y. Ma,
X. Hu, G. A. Solan, Y. Sun and W.-H. Sun, J. Polym. Sci., Part
A: Polym. Chem., 2017, 55, 3494–3505.
2
F . All hydrogen atoms were placed in calculated positions.
Structure solution and refinement were performed by using
2
5
the Olex2 1.2 package. Details of the X-ray structure determi-
nations and refinements are provided in Table 6.
Polymerization studies
Ethylene polymerization at 1 atm ethylene pressure. The
polymerization at 1 atm ethylene pressure was carried out in a
Schlenk tube. Complex Ni6 was added followed by toluene
(
30 mL) and then the required amount of co-catalyst (EASC,
MMAO) introduced by syringe. The solution was then stirred at
0 °C under 1 atm of ethylene pressure. After 30 min, the solu-
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3
tion was quenched with 10% hydrochloric acid in ethanol. The
polymer was washed with ethanol, dried under reduced
pressure at 40 °C and then weighed.
Ethylene polymerization at 5/10 atm ethylene pressure. The
polymerization at high ethylene pressure was carried out in a
stainless-steel autoclave (0.25 L) equipped with an ethylene
pressure control system, a mechanical stirrer and a tempera-
ture controller. At the required reaction temperature, the pre-
catalyst (2.0 μmol) dissolved in toluene (50 mL) was injected
into the autoclave, followed by freshly distilled toluene
(
25 mL). The required amount of co-catalyst (MAO, MMAO,
Et AlCl, EASC) and more toluene (25 mL) were then injected
2
successively to complete the addition. The autoclave was
immediately pressurized to high ethylene pressure and the
stirring commenced. After the required reaction time, the
ethylene pressure was vented and the reaction quenched with
1
0% hydrochloric acid in ethanol. The polymer was collected
and washed with ethanol and dried under reduced pressure at
0 °C and weighed.
5 (a) J. L. Rhinehart, N. E. Mitchell and B. K. Long, ACS
Catal., 2014, 4, 2501; (b) J. L. Rhinehart, L. A. Brown and
B. K. Long, J. Am. Chem. Soc., 2013, 135, 16316.
5
6
D. Zhang, E. T. Nadres, M. Brookhart and O. Daugulis,
Organometallics, 2013, 32, 5136.
Conflicts of interest
7
(a) H. Liu, W. Zhao, X. Hao, C. Redshaw, W. Huang and
W.-H. Sun, Organometallics, 2011, 30, 2418; (b) S. Kong,
C. Guo, W. Yang, L. Wang, W.-H. Sun and R. Glaser,
J. Organomet. Chem., 2013, 725, 37; (c) L. Fan, S. Du,
C. Guo, X. Hao and W.-H. Sun, J. Polym. Sci., Part A: Polym.
Chem., 2015, 53, 1369; (d) W. Zhao, E. Yue, X. Wang,
W. Yang, Y. Chen, X. Hao, X. Cao and W.-H. Sun, J. Polym.
Sci., Part A: Polym. Chem., 2017, 55, 988.
There are no conflicts to declare.
Acknowledgements
This work was supported by the National Natural Science
Foundation of China (No. 21374123 and U1362204) and the
National Key Research and Development Program of China
8
(a) Z. Sun, E. Yue, M. Qu, I. V. Oleynik, I. I. Oleynik, K. Li,
T. Liang, W. Zhang and W.-H. Sun, Inorg. Chem. Front.,
(2016YFB1100800). GAS thanks the Chinese Academy of
Sciences for a Visiting Professorship.
2015, 2, 223; (b) Z. Sun, F. Huang, M. Qu, E. Yue,
I. V. Oleynik, I. I. Oleynik, Y. Zeng, T. Liang, K. Li,
W. Zhang and W.-H. Sun, RSC Adv., 2015, 5, 77913;
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