Synthesis and characterization of 2-(2-benzhydrylnaphthyliminomethyl) pyridylnickel halides: Formation of branched polyethylene

Article abstract of DOI:10.1039/c3dt53205d

A series of 2-(2-benzhydrylnaphthyliminomethyl)pyridine derivatives (L1-L3) was prepared and used to synthesize the corresponding bis-ligated nickel(ii) halide complexes (Ni1-Ni6) in good yield. The molecular structures of representative complexes, namely the bromide Ni3 and the chloride complex Ni6, were confirmed by single crystal X-ray diffraction, and revealed a distorted octahedral geometry at nickel. Upon activation with either methylaluminoxane (MAO) or modified methylaluminoxane (MMAO), all nickel complex pre-catalysts exhibited high activities (up to 2.02 × 10⁷ g(PE) mol ^-1(Ni) h^-1) towards ethylene polymerization, producing branched polyethylene of low molecular weight and narrow polydispersity. The influence of the reaction parameters and the nature of the ligands on the catalytic behavior of the title nickel complexes were investigated.

Full text of DOI:10.1039/c3dt53205d

Dalton
Transactions
View Article Online
View Journal | View Issue
PAPER
Synthesis and characterization of 2-(2-
benzhydrylnaphthyliminomethyl)pyridylnickel
halides: formation of branched polyethylene†
Cite this: Dalton Trans., 2014, 43,
3339
Erlin Yue,a,b Qifeng Xing,b Liping Zhang,b Qisong Shi,b Xiao-Ping Cao,*a Lin Wang,b
Carl Redshaw*c and Wen-Hua Sun*a,b
A series of 2-(2-benzhydrylnaphthyliminomethyl)pyridine derivatives (L1–L3) was prepared and used to
synthesize the corresponding bis-ligated nickel(II) halide complexes (Ni1–Ni6) in good yield. The mole-
cular structures of representative complexes, namely the bromide Ni3 and the chloride complex Ni6,
were confirmed by single crystal X-ray diffraction, and revealed a distorted octahedral geometry at nickel.
Upon activation with either methylaluminoxane (MAO) or modified methylaluminoxane (MMAO), all nickel
complex pre-catalysts exhibited high activities (up to 2.02 × 107 g(PE) mol−1(Ni) h−1) towards ethylene
polymerization, producing branched polyethylene of low molecular weight and narrow polydispersity.
The influence of the reaction parameters and the nature of the ligands on the catalytic behavior of the
title nickel complexes were investigated.
Received 13th November 2013,
Accepted 4th December 2013
DOI: 10.1039/c3dt53205d
www.rsc.org/dalton
accessing branched polyethylenes mostly rely on the copoly-
merization of ethylene with α-olefins. Nickel pre-catalysts are
Introduction
Polyolefin materials are extensively used in our daily life and providing new approaches to highly branched polyethylene,
the annual consumption amounts to over 130 million tonnes. and the resulting new polymers can potentially exhibit new
In order to produce advanced polyolefins using new catalytic properties and may yield a new family of advanced polyethyl-
systems, attention has switched to late-transition metal enes.2b Therefore, the syntheses of nickel complexes have
complex pre-catalysts in both the industrial and academic extensively been conducted through designing new ligands
arenas.1,2 Since the discovery of the α-diiminometal (Ni or Pd) with modification via the use of different substituents.6
complexes3 and bis(imino)pyridylmetal (Fe or Co) complexes,4 As an example, 2-iminopyridylnickel complex pre-catalysts (A,
the characteristic features of the polyethylene obtained have Scheme 1) exhibited high activities towards ethylene polymer-
been shown to rely on the metal employed: highly linear poly- ization or oligomerization,7 whilst the methyl-bridged binuc-
ethylene was generally produced from either iron or cobalt lear complex pre-catalysts (B, Scheme 1) performed ethylene
complex pre-catalysts,1,2a whereas branched polyethylene was oligomerization and polymerization.8,9 Recently, progress has
commonly observed from catalytic systems based on nickel been made through the use of benzhydryl-substituted
complex pre-catalysts.1,2b The polymerization mechanism anilines,10–12 and the 2-iminopyridylnickel complex model
operating within nickel systems is an illustration of how (C, Scheme 1) was revisited to reveal high activities solely for
hydrogen-elimination facilitates chain-transfer to produce ethylene polymerization.13
branched polymers.5 Currently, industrial processes for
Subsequently, new benzhydryl-substituted naphthylamines
were designed and were used to prepare 2-(1-(2-benzhydryl-
naphthylimino)ethyl)pyridylnickel complexes (D, Scheme 1),
which revealed high activities of up to 1.22 × 107 g(PE)
mol−1(Ni) h−1 towards ethylene polymerization.14 Given this,
the 2-(2-benzhydrylnaphthyliminomethyl)pyridine derivatives
are also of interest, particularly in terms of their nickel com-
plexes and the polymerization catalysis thereof. Interest-
ingly, such 2-(2-benzhydrylnaphthyliminomethyl)pyridylnickel
halide complexes are bis-ligated complexes (E, Scheme 1),
which according to the literature would be expected to be inac-
tive in catalysis polymerization.15 However, the title nickel
aState Key Laboratory of Applied Organic Chemistry, College of Chemistry and
Chemical Engineering, Lanzhou University, Lanzhou 730000, China.
E-mail: caoxplzu@163.com; Fax: +0931-8912582; Tel: +0931-3911268
bKey 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; Fax: +86 10 6261 8239;
Tel: +86 10 6255 7955
cDepartment of Chemistry, University of Hull, Hull, HU6 7RX, UK.
E-mail: c.redshaw@hull.ac.uk; Fax: +44 (0)1482 466410; Tel: +44 (0)1482 465219
†CCDC 971667 for Ni3 and 971668 for Ni6. For crystallographic data in CIF or
other electronic format see DOI: 10.1039/c3dt53205d
This journal is © The Royal Society of Chemistry 2014
Dalton Trans., 2014, 43, 3339–3346 | 3339

View Article Online
Paper
Dalton Transactions
1
characterized by FT-IR, H and 13C NMR spectroscopy as well
as by elemental analysis.
Trials of the reaction of the 2-(2-benzhydrylnaphthyl-imino-
methyl)pyridine in dichloromethane solution with different
molar ratios of NiCl2 6H2O or (DME)NiBr2 in ethanol were con-
ducted, and the bis-ligated nickel halide (chloride or bromide)
complexes (Ni1–Ni6) were best isolated when using two equi-
valents of organic compound to nickel halide (Scheme 2).
According to the FT-IR spectra, the CvN stretching vibrations
in complexes Ni1–Ni6 were shifted to lower frequencies in the
region 1622–1634 cm−1 with weaker intensity compared to the
peaks at 1642–1643 cm−1 for the free organic compounds,
indicating the effective coordination between the imino-group
and the cationic nickel center. Elemental analysis data were
consistent with these nickel complexes having the formula
L2NiX2 (X = Br, Cl). Crystal structures of a representative
bromide (Ni3) and chloride (Ni6) complexes were determined.
Scheme 1 Models of N,N-bidentate mono- and bi-metallic nickel
complexes.
Single-crystal X-ray diffraction studies
complexes were found to exhibit even higher activities toward
Single crystals of Ni3 and Ni6 suitable for X-ray diffraction ana-
ethylene polymerization than did their 2-(1-(2-benzhydryl- lysis were obtained by layering diethyl ether onto their dichloro-
naphthylimino)ethyl)pyridylnickel analogues.14 Herein, the
methane solutions at room temperature. Both complexes Ni3
synthesis and characterization of the 2-(2-benzhydrylnaphthyl-
and Ni6 are bis-ligated mononickel(II) complexes possessing a
iminomethyl)pyridine derivatives and their nickel complexes distorted octahedral geometry at the nickel center. The mole-
are reported, and the catalytic performances of these nickel
complexes, as well as the properties of the resulting polyethyl-
ene, are investigated.
cular structures of Ni3 and Ni6 are shown in Fig. 1 and 2,
respectively, and their selected bond lengths and angles are
tabulated in Table 1.
As shown in Fig. 1, the nickel center is coordinated by four
nitrogens (N1, N2, N1i and N2i) of the two chelate ligands and
two bromides (Br1 and Br1i), which is similar to the aniline-
based bis(iminopyridyl)nickel dibromide.13,16 There is a five-
membered hetero-nickel plane with N1, Ni1, N2, C1 and C6
atoms, and the bond length of Ni1–N1pyridine 2.068(3) Å is
shorter than that of Ni1–N2imino 2.257(3) Å, reflecting the
stronger bonding between the Nimino and cationic nickel
center. The dihedral angle between the pyridyl and imino-
naphthyl planes is 59.87°, which is similar to that within
the nickel analogues bearing (1-aryliminoethyl)pyridines.13
Results and discussion
Synthesis and characterization
The series of 2-(2-benzhydrylnaphthyliminomethyl)pyridine
derivatives (L1–L3, Scheme 2) was readily synthesized by the
condensation reaction of picolinaldehyde with benzhydryl-
substituted naphthylamines in moderate yields following the
reported procedure.14 All organic compounds were
Fig. 1 ORTEP drawing of Ni3. Thermal ellipsoids are shown at the 30%
Scheme 2 Synthetic procedure for the organic and nickel complexes.
3340 | Dalton Trans., 2014, 43, 3339–3346
probability level. Hydrogen atoms have been omitted for clarity.
This journal is © The Royal Society of Chemistry 2014

View Article Online
Dalton Transactions
Paper
Ethylene polymerization in the presence of MAO
In the presence of the co-catalyst MAO, complex Ni2 was evalu-
ated to optimize the polymerization conditions including the
molar ratio of Al/Ni and the reaction temperature, and the
results are collected in Table 3, which also includes some of
the properties of the obtained polyethylene.
At 30 °C and 10 atm of ethylene, the Al/Ni ratio was
changed from 750 to 2250 (runs 1–7, Table 3), and the highest
activity was observed with the Al/Ni ratio 1500 (run 4, Table 3)
at 1.45 × 107 g(PE) mol−1(Ni) h−1. In general, the molecular
weights of the resultant polyethylene slightly decreased on
increasing the Al/Ni ratio (runs 1–5, Table 3), which was
ascribed to faster chain transfer on increasing the Al concen-
tration.12b However, the catalytic system with the Al/Ni ratio of
2000 (run 6, Table 3) revealed a higher activity than did the
system with the Al/Ni ratio of 1750 (run 5, Table 3). Therefore
there are two maximum activities for such catalytic systems at
different Al/Ni ratios of 1500 and 2000. As seen in the GPC
curve (Fig. 3), all catalytic systems generally exhibited single-
site catalysis with narrow polydispersity for all the obtained
polyethylene.
On fixing the Al/Ni molar ratio at 1500, the reaction temp-
erature was changed from 20 to 60 °C (runs 4, and 8–11,
Table 3); the highest activity observed, namely 1.45 × 107 g (PE)
mol−1(Ni) h−1, was at 30 °C (run 4 in Table 3). The GPC data
indicated that higher molecular weight polyethylene was
obtained at lower temperatures, and the GPC curves are shown
in Fig. 4. These phenomena were consistent with previous
observations for 2-iminopyridylnickel pre-catalysts,6,10,13,14 and
are ascribed to increased chain-transfer and termination at
higher temperature. As well as the GPC measurements, the
melting points of resultant polyethylenes were measured by
differential scanning calorimetry (DSC). The Tm values of the
polyethylene dramatically decreased on elevating the reaction
temperature (runs 4, and 8–11, Table 3), and are slightly
higher than those of their analogs bearing 2-(1-(2-benzhydryl-
naphthylimino)ethyl)pyridines, probably reflecting less
branches in the current systems.
Fig. 2 ORTEP drawing of Ni6. Thermal ellipsoids are shown at the 30%
probability level. Hydrogen atoms have been omitted for clarity.
Table 1 Selected bond lengths (Å) and angles (°) for Ni3 and Ni6
Ni3
Ni6
Bond lengths (Å)
Ni(1)–N(1)
2.068(3)
2.257(3)
2.068(3)
2.257(3)
2.5415(6)
Ni(1)–N(1)
Ni(1)–N(2)
Ni(1)–N(1i)
Ni(1)–N(2i)
Ni(1)–Cl(1)
2.086(3)
2.234(3)
2.086(3)
2.234(3)
2.4024(9)
Ni(1)–N(2)
Ni(1)–N(1i)
Ni(1)–N(2i)
Ni(1)–Br(1)
Bond angles (°)
N(1)–Ni(1)–N(2)
N(1)–Ni(1)–N(1i)
N(1i)–Ni(1)–N(2)
N(1)–Ni(1)–N(2i)
N(1i)–Ni(1)–N(2i)
N(2)–Ni(1)–N(2i)
N(1)–Ni(1)–Br(1)
N(1i)–Ni(1)–Br(1)
N(2)–Ni(1)–Br(1)
N(2i)–Ni(1)–Br(1)
78.08(10)
180.00(17)
101.92(15)
101.92(15)
78.08(10)
180.0(3)
87.98(8)
92.02(8)
96.26(7)
83.74(7)
N(1)–Ni(1)–N(2)
N(1)–Ni(1)–N(1i)
N(1i)–Ni(1)–N(2)
N(1)–Ni(1)–N(2i)
N(1i)–Ni(1)–N(2i)
N(2)–Ni(1)–N(2i)
N(1)–Ni(1)–Cl(1)
N(1i)–Ni(1)–Cl (1)
N(2)–Ni(1)–Cl (1)
N(2i)–Ni(1)–Cl (1)
78.13(10)
180.00(18)
101.87(10)
101.87(10)
78.13(10)
180.00(13)
91.33(8)
88.67(8)
83.32(7)
96.68(7)
A closely similar structure was observed for the chloride ana-
logue Ni6 (Fig. 2 and Table 1).
Catalytic behavior toward ethylene polymerization
On the basis of above results, the optimum conditions with
Various co-catalysts such as MAO, MMAO and Et2AlCl were an Al/Ni ratio of 1500 at 30 °C were utilized to explore the cata-
used to activate the nickel pre-catalyst Ni2 for ethylene lytic behavior of all the other nickel pre-catalysts Ni1 and
polymerization (runs 1–3 in Table 2), which indicated that Ni3–Ni6 (runs 12–16, Table 3). All nickel pre-catalysts exhibited
higher catalytic activities in ethylene polymerization were high activities towards ethylene polymerization, which
achievable when employing either MAO or MMAO.
differs from reported bis-ligated nickel pre-catalysts which
usually possess low catalytic activities.15 In addition, the two
halides are located in trans positions, which is not favorable
for coordination insertion; the transformation of these bis-
ligated nickel species into mono-ligated active species is
assumed to occur during the ethylene polymerization.17 It is
noteworthy that the nickel pre-catalysts (Ni3 and Ni6) bearing
more benzhydryl substituents exhibited relatively higher acti-
vities than did their analogues, which is different from the
catalytic performances by the analogues ligated by 2-(1-(2-
benzhydrylnaphthylimino)ethyl)pyridines in the presence of
Et2AlCl.14
Table 2 Ethylene polymerization by Ni2 using various co-catalystsa
Co-
Mw/g
−1 c
Run catalyst Al/Ni Yield/g Activityb mol
Mw/Mn
Tm/°Cd
c
1
2
3
MAO
MMAO 1000
Et2AlCl 300
1000 11.3
11.3
4.88
3.14
2817
2251
1425
2.45
2.24
1.88
109.3
111.7
101.2
4.88
3.14
a General conditions: 2 μmol of Ni; 30 min; 30 °C; 100 mL of toluene
for 10 atm of ethylene. b 106 g(PE) mol−1(Ni) h−1
.
c Determined by GPC.
d Determined by DSC.
This journal is © The Royal Society of Chemistry 2014
Dalton Trans., 2014, 43, 3339–3346 | 3341

View Article Online
Paper
Dalton Transactions
Table 3 Ethylene polymerization by Ni1–Ni6/MAOa
Activityb
Mw c/g mol−1
Mw/Mn
Tmd/°C
c
Run
Pre-cat.
Al/Ni
T/°C
Yield/g
1
2
3
4
5
6
7
8
Ni2
Ni2
Ni2
Ni2
Ni2
Ni2
Ni2
Ni2
Ni2
Ni2
Ni2
Ni1
Ni3
Ni4
Ni5
Ni6
750
1000
1250
1500
1750
2000
2250
1500
1500
1500
1500
1500
1500
1500
1500
1500
30
30
30
30
30
30
30
20
40
50
60
30
30
30
30
30
1.10
11.3
11.5
14.5
10.5
13.4
11.5
5.26
10.5
6.27
4.14
17.5
20.2
9.13
10.7
12.0
1.10
11.3
11.5
14.5
10.5
13.4
11.5
5.26
10.5
6.27
4.14
17.5
20.2
9.13
10.7
12.0
3093
2817
2434
1718
1700
1722
1850
5939
1642
942
716
1300
618
2701
2566
1112
2.54
2.45
2.34
2.23
2.06
2.12
2.16
2.82
1.95
1.71
1.68
2.06
2.03
2.17
2.25
1.89
122.4
109.3
107.5
103.4
87.0
104.4
105.8
124.1
101.5
67.3
58.5
77.9
65.9
118.7
84.9
9
10
11
12
13
14
15
16
84.8
a General conditions: 2 μmol of Ni; 30 min; 100 mL of toluene. b 106 g(PE) mol−1(Ni) h−1 c Determined by GPC. d Determined by DSC.
.
Fig. 5 13C NMR spectrum of the polyethylene by Ni2/MAO at 60 °C
(run 11 in Table 3).
Table 4 Percentage of branches for the polyethylene (run 11 in
Table 3)18
Fig. 3 GPC traces for the polyethylene by Ni2/MAO system with
various Al/Ni ratios (runs 1–7 in Table 3).
Chem.
shifts/
ppm
Peak
no.
Integral
exp.
Percentage over
total branching
Branch content
1
1
2
4
6
7
11
12
13
14
15
16
17
20
11.16
11.39
14.09
19.97
20.29
22.87
27.26
27.44
27.81
29.32
29.6
0.68
0.73
6.41
5.86
0.55
5.18
3.93
10.24
1
1.16
11.13
125.91
11.8
4.74
Nm
3.12
0
0
0.5
0.147
1.71
0.965
2.29
4.74
0
121.17
60.585
13.472
1
1
2
4
6
7
11
12
13
14
15
16
17
Nm(1,4)
Nm(1,5)
Nm(1,6)
Ne
Np
Nb
Na
Nl
Nl(1,4)
δδCH2
[E]
30
30.37
32.2
[R]
Fig. 4 GPC curves for the polyethylene obtained using the Ni2/MAO
system at different temperatures (runs 4, 8–11 in Table 3).
Total branching =
182 Branches/
1000 C
21
22
25
26
26
28
29
33
32.79
33.2
2.29
4.12
1.93
1.78
1.55
1.71
8.12
0.44
The 13C NMR spectrum for the polyethylene obtained from
the Ni2/MAO at 60 °C (run 11 in Table 3) is shown in Fig. 5.
Interpreted according to the literature,18 there are 182
branches per 1000 carbons, and the signals are presented in
Table 4, which indicates that the main branches include
33.96
34.48
34.81
37.03
37.52
39.61
Methyl branches
Ethyl branches
Propyl branches
Butyl branches
Amyl branches
Long branches
26.88%
1.09%
12.69%
7.16%
17.00%
35.18%
3342 | Dalton Trans., 2014, 43, 3339–3346
This journal is © The Royal Society of Chemistry 2014

View Article Online
Dalton Transactions
Paper
Table 5 Ethylene polymerization by Ni1–Ni6/MMAOa
Act.b
Mw c/g mol−1
Mw/Mn
Tm d/°C
c
Run
Pre-cat.
Al/Ni
T/°C
t/min
Yield/g
1
2
3
4
5
6
7
8
Ni2
Ni2
Ni2
Ni2
Ni2
Ni2
Ni2
Ni2
Ni2
Ni2
Ni2
Ni2
Ni1
Ni3
Ni4
Ni5
Ni6
1000
1250
1500
1750
2000
1750
1750
1750
1750
1750
1750
1750
1750
1750
1750
1750
1750
30
30
30
30
30
20
40
50
60
30
30
30
30
30
30
30
30
30
30
30
30
30
30
30
30
30
10
20
40
30
30
30
30
30
4.88
6.71
7.30
8.99
5.71
4.68
6.49
2.05
0.83
4.00
6.26
9.57
10.2
10.9
6.32
7.36
7.84
4.88
6.71
7.30
8.99
5.71
4.68
6.49
2.05
0.83
12.0
9.39
7.18
10.2
10.9
6.32
7.36
7.84
2251
2054
1797
1659
1487
3867
1234
1157
1075
1017
1413
1984
1623
959
2.24
2.19
2.16
2.12
2.08
2.73
1.80
2.19
1.78
1.92
1.96
2.17
2.19
1.91
2.27
2.16
1.84
111.7
110.6
108.1
106.8
105.0
118.1
100.6
77.2
9
66.0
10
11
12
13
14
15
16
17
113.1
113.9
114.1
105.3
83.9
109.5
111.3
88.6
2144
2099
1073
a General conditions: 2 μmol of Ni; 100 mL of toluene for 10 atm of ethylene. b 106 g(PE) mol−1(Ni) h−1 c Determined by GPC. d Determined by
.
DSC.
methyl (26.88%), some long chains (35.18%) and amyl chains
(17.00%), which is consistent with the observations for the
analogue system comprising the 2-(1-(2-benzhydrylnaphthyl-
imino)ethyl)pyridylnickel halide complexes.14
Ethylene polymerization in the presence of MMAO
In a similar manner, the pre-catalyst Ni2 in the presence of
MMAO was explored (runs 1–9, Table 5), and the highest
activity of 8.99 × 106 g(PE) mol−1(Ni) h−1 was obtained with the
Al/Ni ratio of 1750 at 30 °C (run 4 in Table 5). On comparison
Fig. 6 GPC curves of polyethylene obtained using the Ni2/MMAO
system over different times (runs 4, 10–12 in Table 5).
with the system using MAO, the system with MMAO is less
thermally stable, whilst the resultant polyethylene exhibited
relatively lower molecular weights and narrower PDIs, but
slightly higher melting points suggestive of less branching.
Regarding the lifetime of the active species, the polymeriz-
ation was conducted over different periods from 10 to 40 min
(runs 4, and 10–12, Table 5). On prolonging the reaction time,
the catalytic activities slightly decreased, whilst the obtained
polyethylene revealed higher molecular weight and wider
polydispersity (Fig. 6). These results are consistent with
the observations for the reported nickel analogues bearing the
2-iminopyridine ligand system.10,13,14
All the other nickel pre-catalysts were investigated in the
presence of MMAO, and were found to perform with good
activities in ethylene polymerization under the optimum con-
ditions of Al/Ni molar ratio 1750 at 30 °C (runs 13–17,
Table 5). Regarding the influences of reaction parameters and
the nature of ligands, the tendency of catalytic performance of
the Ni/MMAO systems is highly similar to the observation
of the Ni/MAO; however, the system with MMAO exhibited
slightly lower activity and produced lower molecular weight
polyethylene than did the system using MAO.
Conclusion
The series of 2-(2-benzhydrylnaphthyliminomethyl)pyridine
derivatives and their nickel halide complexes were synthesized
and fully characterized, and single crystal X-ray diffraction
revealed the complexes Ni3 and Ni6 to contain bis-ligated
mononickel with a distorted octahedral geometry at the metal.
All the nickel complex pre-catalysts, activated by either MAO
or MMAO, exhibited high activities (up to 2.02 × 107 g(PE)
mol−1(Ni) h−1) towards ethylene polymerization, and produced
polyethylene of lower molecular weight and narrow molecular
polydispersity. This is a rare example of bis-ligated nickel
halides performing with high activities towards ethylene
polymerization, especially given that the two halides are trans.
The nickel complexes bearing 2-(aryliminomethyl)pyridines
showed slightly higher activity than their analogues bearing
2-(1-(arylimino)ethyl)pyridine derivatives.14
This journal is © The Royal Society of Chemistry 2014
Dalton Trans., 2014, 43, 3339–3346 | 3343

View Article Online
Paper
Dalton Transactions
NMR (400 MHz, CDCl3, TMS): δ 8.70 (d, 1H, J = 4.8 Hz, Py-H),
8.20 (d, 1H, J = 8.0 Hz, Py-H), 8.09 (s, 1H, –CHvN), 7.96 (d,
1H, J = 8.4 Hz, Py-H), 7.86–7.79 (m, 2H, Py-H and Ar-H),
Experimental section
General consideration
All manipulations involving air- and moisture-sensitive com- 7.42–6.90 (m, 23H, Ar-H), 6.68 (s, 1H, Ar-H), 6.17 (s, 1H,
pounds were carried out under a nitrogen atmosphere using –CHPh2), 5.71 (s, 1H, –CHPh2). 13C NMR (100 MHz, CDCl3,
standard Schlenk techniques. Toluene was refluxed over TMS): 165.6, 154.2 (–CHvN), 149.9, 145.7, 143.8, 143.7, 136.8,
sodium and distilled under nitrogen prior to use. Methyl- 135.7, 131.2, 130.3, 129.6, 129.5, 129.4, 128.6, 128.4, 128.2,
aluminoxane (MAO, 1.46 M solution in toluene) and modified 127.5, 126.3, 126.2, 126.1, 125.5, 124.3, 124.2, 121.9, 53.0
methylaluminoxane (MMAO, 1.93 M in heptane) were pur- (–CHPh2), 51.7 (–CHPh2). FT-IR (KBr, disk, cm−1): 3053, 3024,
chased from Akzo Nobel Corp. Diethylaluminium chloride 1643 (νCvN), 1578, 1491, 1440, 1384, 1342, 1252, 1155, 1075,
(Et2AlCl, 0.5 M in toluene) was purchased from Acros Chemi- 1030, 991, 948, 915, 753, 736, 698. Anal. Calcd for C42H32N2
cals. High-purity ethylene was purchased from Beijing Yansan (564.26) C, 89.33; H, 5.71; N, 4.96%; Found: C, 89.09; H, 5.74;
Petrochemical Co. and used as received. Other reagents were N, 4.90%.
purchased from Aldrich, Acros, or local suppliers. NMR
2-(2,4,7-Tribenzhydrylnaphthyliminomethyl)pyridine
(L3).
spectra were recorded on a Bruker DMX 400 MHz instrument Using the same procedure as for the synthesis of L1, L3 was
at ambient temperature using TMS as an internal standard; IR prepared as a yellow solid in 64% yield. Mp: 110–111 °C. 1H
spectra were recorded on a Perkin-Elmer System 2000 FT-IR NMR (400 MHz, CDCl3, TMS): δ 8.68 (d, 1H, J = 4.4 Hz, Py-H),
spectrometer. Elemental analysis was carried out using a Flash 8.00 (d, 1H, J = 7.6 Hz, Py-H), 7.95 (s, 1H, –CHvN), 7.87 (d,
EA 1112 micro-analyzer. Molecular weights and molecular 1H, J = 8.8 Hz, Py-H), 7.78 (t, 1H, J = 7.6 Hz, Py-H), 7.40–6.88
weight distribution (MWD) of polyethylene were determined (m, 33H, Ar-H), 6.64 (s, 1H, Ar-H), 6.12 (s, 1H, –CHPh2), 5.65
by PL-GPC220 at 150 °C, with 1,2,4-trichlorobenzene as the (s, 1H, –CHPh2), 5.57 (s, 1H, –CHPh2). 13C NMR (100 MHz,
solvent. The melting points of polyethylene were measured CDCl3, TMS): 165.6, 154.1 (–CHvN), 149.7, 145.6, 143.9, 143.8,
from the second scanning run on a Perkin-Elmer TA-Q2000 143.7, 140.9, 136.8, 136.6, 135.6, 130.2, 130.0, 129.6, 129.5,
differential scanning calorimetry (DSC) analyzer under a nitro- 129.4, 128.6, 128.4, 128.3, 128.2, 128.1, 127.7, 126.3, 126.2,
gen atmosphere. In the procedure, a sample of about 4.0 mg 125.4, 124.5, 124.3, 121.9, 56.9 (–CHPh2), 53.0 (–CHPh2), 51.7
was heated to 140 °C at a rate of 20 °C min−1 and kept for (–CHPh2). FT-IR (KBr, disk, cm−1): 3056, 3024, 1642 (νCvN),
2 min at 140 °C to remove the thermal history and then cooled 1597, 1493, 1446, 1375, 1336, 1182, 1074, 1032, 920, 779, 746,
at a rate of 20 °C min−1 to −40 °C. 13C NMR spectra of the 700. Anal. Calcd for C55H42N2 (730.33) C, 90.38; H, 5.79; N,
polyethylenes were recorded on a Bruker DMX 300 MHz instru- 3.83%; Found: C, 89.90; H, 5.89; N, 3.70%.
ment at 135 °C in deuterated 1,2-dichlorobenzene with TMS as
an internal standard.
Synthesis of nickel complexes
General procedure. NiCl2·6H2O (0.25 mmol) or (DME)NiBr2
(0.25 mmol) was dissolved in 5 mL ethanol and added to the
Synthesis of ligands
2-(2-Benzhydrylnaphthyliminomethyl)pyridine (L1). A solu- solution of the ligand (0.5 mmol) in 5 mL CH2Cl2. The mixture
tion of picolinaldehyde (0.221 g, 2.06 mmol), 2-benzhydryl- was stirred for 12 h, and then diethyl ether was poured into
naphylamine (0.670 g, 2.17 mmol) and a catalytic amount of the mixture to precipitate the complex. The precipitant was
p-toluenesulfonic acid (0.079 g, 0.41 mmol) in toluene (80 mL) collected by filtration, washed with diethyl ether (3 × 5 mL),
was refluxed for 8 h. The solvent was evaporated under and dried under vacuum at 60 °C.
reduced pressure, and then the residue was purified by
Bis(2-(2-benzhydrylnaphthyliminomethyl)pyridyl)nickel
column chromatography on basic alumina with the eluent of bromide (Ni1, yellow, 92% yield): FT-IR (KBr, disk, cm−1):
petroleum ether–ethyl acetate (v : v = 20 : 1) to afford a yellow 3060, 3024, 1622 (νCvN), 1596, 1493, 1446, 1375, 1322, 1261,
solid in 76% isolated yield. Mp: 108–109 °C. 1H NMR 1076, 1027, 782, 741, 700. Anal. Calcd for C58H44Br2N4Ni
(400 MHz, CDCl3, TMS): δ 8.71 (d, 1H, J = 4.8 Hz, Py-H), 8.19 (1012.13): C, 68.60; H, 4.37; N, 5.52%. Found: C, 68.36;
(d, 1H, J = 8.0 Hz, Py-H), 8.05 (s, 1H, –CHvN), 7.87–7.82 (m, H, 4.48; N, 5.46%.
2H, Py-H), 7.76 (d, 1H, J = 8.4 Hz, Ar-H), 7.59 (d, 1H, J = 8.4 Hz,
Bis(2-(2,4-dibenzhydrylnaphthyliminomethyl)pyridyl)nickel
Ar-H), 7.48–7.37 (m, 3H, Ar-H), 7.24–7.09 (m, 11H, Ar-H), 5.84 bromide (Ni2, yellow, 95% yield): FT-IR (KBr, disk, cm−1):
(s, 1H, –CHPh2). 13C NMR (100 MHz, CDCl3, TMS): 165.7, 3059, 3024, 1633 (νCvN), 1597, 1571, 1493, 1446, 1355, 1307,
154.2 (–CHvN), 149.9, 146.9, 143.9, 136.8, 133.1, 129.8, 128.7, 1224, 1156, 1107, 1072, 1029, 945, 764, 742, 700. Anal. Calcd
128.4, 128.0, 127.6, 126.4, 126.1, 125.9, 125.7, 125.6, 124.1, for C84H64Br2N4Ni (1344.29): C, 74.85; H, 4.79; N, 4.16%.
123.5, 122.0, 51.8 (–CHPh2). FT-IR (KBr, disk, cm−1): 3052, Found: C, 74.59; H, 4.96; N, 4.02%.
3024, 1642 (νCvN), 1576, 1466, 1302, 1275, 1098, 810, 748, 736,
Bis(2-(2,4,7-tribenzhydrylnaphthyliminomethyl)pyridyl)nickel
698. Anal. Calcd for C29H22N2 (398.18): C, 87.41; H, 5.56; N, bromide (Ni3, yellow, 84% yield): FT-IR (KBr, disk, cm−1):
7.03%; Found: C, 87.26; H, 5.79; N, 6.93%.
3060, 3025, 1628 (νCvN), 1597, 1493, 1447, 1376, 1325, 1264,
2-(2,4-Dibenzhydrylnaphthyliminomethyl)pyridine
(L2). 1076, 1028, 782, 748, 698. Anal. Calcd for C110H84Br2N4Ni
Using the same procedure as for the synthesis of L1, L2 was (1676.44): C, 78.62; H, 5.04; N, 3.33%. Found: C, 78.36; H,
prepared as a yellow solid in 72% yield. Mp: 147–148 °C. 1H 5.28; N, 3.26%.
3344 | Dalton Trans., 2014, 43, 3339–3346
This journal is © The Royal Society of Chemistry 2014

View Article Online
Dalton Transactions
Paper
Bis(2-(2-benzhydrylnaphthyliminomethyl)pyridyl)nickel
chloride (Ni4, yellow, 91% yield): FT-IR (KBr, disk, cm−1):
3061, 2973, 1633 (νCvN), 1596, 1573, 1504, 1382, 1304, 1227,
1155, 1108, 1067, 1043, 810, 780, 751, 705. Anal. Calcd for
C58H44Cl2N4Ni (924.23): C, 75.18; H, 4.79; N, 6.05%. Found: C,
75.02; H, 4.86; N, 5.98%.
Bis(2-(2,4-dibenzhydrylnaphthyliminomethyl)pyridyl)nickel
chloride (Ni5, yellow, 83% yield): FT-IR (KBr, disk, cm−1):
3060, 3023, 1634 (νCvN), 1598, 1573, 1491, 1447, 1377, 1308,
1224, 1157, 1108, 1074, 948, 765, 743, 700. Anal. Calcd for
C84H64Cl2N4Ni (1256.39): C, 80.13; H, 5.12; N, 4.45%. Found:
C, 79.98; H,5.26; N, 4.38%.
Table 6 Crystal data and structure refinement for Ni3 and Ni6
Identification code
Ni3
Ni6
Crystal color
Empirical formula
Formula weight
Temperature/K
Wavelength/Å
Crystal system
Space group
a/Å
Red
Red
C110H84Br2N4Ni
C110H84Cl2N4Ni
1591.42
100(2)
0.71073
Monoclinic
P2(1)/n
17.393(4)
15.219(3)
18.207(4)
90
1680.34
173(2)
0.71073
Monoclinic
P2(1)/c
17.508(3)
15.393(3)
24.027(8)
90
b/Å
c/Å
Alpha/°
Beta/°
130.853(18)
90
4898(2)
2
1.139
1.060
95.81(3)
90
4794.6(17)
2
1.102
0.305
Bis(2-(2,4,7-tribenzhydrylnaphthyliminomethyl)pyridyl)nickel
chloride (Ni6, yellow, 84% yield): FT-IR (KBr, disk, cm−1):
3058, 3025, 1629 (νCvN), 1597, 1492, 1448, 1353, 1306, 1156,
1111, 1076, 1028, 894, 742, 701. Anal. Calcd for
Gamma/°
Volume/Å3
Z
Dcalcd/(g cm−3
μ/mm−1
)
F(000)
Crystal size/mm
1740
0.81 × 0.61 ×
0.27
1668
0.33 × 0.26 ×
0.14
C
110H84Cl2N4Ni (1588.54): C, 83.02; H, 5.32; N, 3.52%. Found:
C, 82.98; H, 5.48; N, 3.46%.
θ Range (°C)
Limiting indices
1.54–24.99
−15 ≤ h ≤ 20
−18 ≤ k ≤ 18
−28 ≤ l ≤ 22
30 479
8618
0.0544
529
99.9%
1.072
R1 = 0.0563
wR2 = 0.1724
R1 = 0.0641
wR2 = 0.1822
0.564 and
−0.690
1.54–27.46
−22 ≤ h ≤ 22
−19 ≤ k ≤ 19
−23 ≤ l ≤ 23
36 390
10 927
0.1017
530
99.6%
1.061
R1 = 0.0810
wR2 = 0.2164
R1 = 0.1051
wR2 = 0.2300
0.512 and
−0.878
X-ray crystallographic studies
Single crystals of Ni3 and Ni6 suitable for X-ray diffraction ana-
lyses were obtained by slow diffusion of diethyl ether onto the
respective dichloromethane solution at room temperature.
X-ray studies were carried out on a Rigaku Saturn 724+ CCD
with graphite-monochromatic Mo-Kα radiation (λ = 0.71073 Å)
at 173(2) K (Ni3) and 100(2) K (Ni6), cell parameters were
obtained by global refinement of the positions of all collected
reflections. Intensities were corrected for Lorentz and polariz-
ation effects and empirical absorption. The structures were
solved by direct methods and refined by full-matrix least
squares on F2. All hydrogen atoms were placed in calculated
positions. Structure solution and refinement were performed
by using the SHELXL-97 package.19 Within the structure
refinement of Ni3 and Ni6, there were free solvent molecules
which have no influence on the geometry of the main com-
pounds. Therefore, the SQUEEZE option of the crystallo-
graphic program PLATON20 was used to remove these free
solvents from the structure. Details of the X-ray structure deter-
minations and refinements are provided in Table 6.
No. of rflns collected
No. unique rflns
R(int)
No. of params
Completeness to θ
Goodness of fit on F2
Final R indices [I > 2∑(I)]
R indices (all data)
Largest diff. peak, and hole/
(e Å−3
)
Acknowledgements
This work is supported by NSFC no. 21374123, 21272098 and
U1362204. The EPSRC is thanked for the award of a travel
grant (to CR).
Notes and references
General procedure for ethylene polymerization
A 250 mL stainless steel autoclave equipped with a mechanical
stirrer and a temperature controller was used to perform ethyl-
ene polymerization. The autoclave was evacuated by a vacuum
pump and back-filled twice with N2 and once with ethylene.
When the desired reaction temperature was reached, 30 mL
toluene was added under ethylene atmosphere, and the nickel
pre-catalyst in 20 mL toluene was injected. The required
amount of co-catalysts (MAO, MMAO or Et2AlCl) and
additional toluene (maintaining the total volume as 100 mL in
the reactor) were added by a syringe. The reaction mixture was
intensively stirred for the desired time under 10 atm of ethyl-
ene and maintained at this level by constant feeding of ethyl-
ene. The reaction was quenched by addition of acidic ethanol.
The precipitated polymer was washed with ethanol several
times and dried in vacuo.
1 (a) S. D. Ittel, L. K. Johnson and M. Brookhart, Chem. Rev.,
2000, 100, 1169–1203; (b) V. C. Gibson and
S. K. Spitzmesser, Chem. Rev., 2003, 103, 283–315;
(c) C. Bianchini, G. Giambastiani, I. G. Rios, G. Mantovani,
A. Meli and A. M. Segarra, Coord. Chem. Rev., 2006, 250,
1391–1418; (d) V. C. Gibson, C. Redshaw and G. A. Solan,
Chem. Rev., 2007, 107, 1745–1776; (e) C. Bianchini,
G. Giambastiani, L. Luconi and A. Meli, Coord. Chem. Rev.,
2010, 254, 431–455; (f) F. Speiser, P. Braunstein and
L. Saussine, Acc. Chem. Res., 2005, 38, 784–793.
2 (a) W. Zhang, W.-H. Sun and C. Redshaw, Dalton Trans.,
2013, 42, 8988–8997; (b) R. Gao, W.-H. Sun and
C. Redshaw, Catal. Sci. Technol., 2013, 3, 1172–1179.
3 (a) L. K. Johnson, C. M. Killian and M. Brookhart, J. Am.
Chem. Soc., 1995, 117, 6414–6415; (b) C. M. Killian,
This journal is © The Royal Society of Chemistry 2014
Dalton Trans., 2014, 43, 3339–3346 | 3345

View Article Online
Paper
Dalton Transactions
D. J. Tempel, L. K. Johnson and M. Brookhart, J. Am. Chem.
Soc., 1996, 118, 11664–11665.
4 (a) B. L. Small, M. Brookhart and A. M. A. Bennett, J. Am.
Chem. Soc., 1998, 120, 4049–4050; (b) G. J. P. Britovsek,
V. C. Gibson, B. S. Kimberley, P. J. Maddox, S. J. McTavish,
8 S. Jie, D. Zhang, T. Zhang, W.-H. Sun, J. Chen, Q. Ren,
D. Liu, G. Zheng and W. Chen, J. Organomet. Chem., 2005,
690, 1739–1749.
9 B. K. Bahuleyan, U. Lee, C. Ha and I. Kim, Appl. Catal., A,
2008, 351, 36–44.
G. A. Solan, A. J. P. White and D. J. Williams, Chem. 10 (a) J. Yu, H. Liu, W. Zhang, X. Hao and W.-H. Sun, Chem.
Commun., 1998, 849–850.
Commun., 2011, 47, 3257–3259; (b) J. Yu, W. Huang,
L. Wang, C. Redshaw and W.-H. Sun, Dalton Trans., 2011,
40, 10209–10214; (c) W. Zhao, J. Yu, S. Song, W. Yang,
H. Liu, X. Hao, C. Redshaw and W.-H. Sun, Polymer, 2012,
53, 130–137; (d) J. Lai, X. Hou, Y. Liu, C. Redshaw and
W.-H. Sun, J. Organomet. Chem., 2012, 702, 52–58;
(e) X. Cao, F. He, W. Zhao, Z. Cai, X. Hao, T. Shiono,
C. Redshaw and W.-H. Sun, Polymer, 2012, 53, 1870–1880;
(f) F. He, W. Zhao, X.-P. Cao, T. Liang, C. Redshaw and
W.-H. Sun, J. Organomet. Chem., 2012, 713, 209–216.
5 (a) D. G. Musaev, R. D. J. Froese, M. Svensson and
K. Morokuma, J. Am. Chem. Soc., 1997, 119, 367–374;
(b) L. Deng, T. K. Woo, L. Cavallo, P. M. Margl and
T. Ziegler, J. Am. Chem. Soc., 1997, 119, 6177–6186;
(c) D. G. Musaev, M. Svensson and K. Morokuma, Organo-
metallics, 1997, 16, 1933–1945; (d) R. D. Froese,
D. G. Musaev and K. Morokuma, J. Am. Chem. Soc., 1998,
120, 1581–1587; (e) S. A. Svejda, L. K. Johnson and
M. Brookhart, J. Am. Chem. Soc., 1999, 121, 10634–10635;
(f) D. J. Tempel, L. K. Johnson, R. L. Huff, P. S. White and 11 (a) X. Hou, Z. Cai, X. Chen, L. Wang, C. Redshaw and
M. Brookhart, J. Am. Chem. Soc., 2000, 122, 6686–6700;
(g) L. H. Shultz, D. J. Tempel and M. Brookhart, J. Am.
Chem. Soc., 2001, 123, 11539–11555; (h) M. D. Leatherman,
W.-H. Sun, Dalton Trans., 2012, 41, 1617–1623; (b) X. Hou,
T. Liang, W.-H. Sun, C. Redshaw and X. Chen, J. Organomet.
Chem., 2012, 708–709, 98–105.
S. A. Svejda, L. K. Johnson and M. Brookhart, J. Am. Chem. 12 (a) H. Liu, W. Zhao, X. Hao, C. Redshaw, W. Huang and
Soc., 2003, 125, 3068–3081.
6 (a) D. P. Gates, S. A. Svejda, E. Onate, C. M. Killian,
L. K. Johnson, P. S. White and M. Brookhart, Macro-
W.-H. Sun, Organometallics, 2011, 30, 2418–2424;
(b) H. Liu, W. Zhao, J. Yu, W. Yang, X. Hao, C. Redshaw,
L. Chen and W.-H. Sun, Catal. Sci. Technol., 2012, 2, 415–422.
molecules, 2000, 33, 2320–2334; (b) R. J. Maldanis, 13 W.-H. Sun, S. Song, B. Li, C. Redshaw, X. Hao, Y. Li and
J. S. Wood, A. Chandrasekaran, M. D. Rausch and F. Wang, Dalton Trans., 2012, 41, 11999–12010.
J. C. W. Chien, J. Organomet. Chem., 2002, 645, 158–167; 14 E. Yue, L. Zhang, Q. Xing, X. Cao, X. Hao, C. Redshaw and
(c) M. Helldörfer, J. Backhus, W. Milius and H. G. Alt, W.-H. Sun, Dalton Trans., 2014, 43, 423–431.
J. Mol. Catal. A: Chem., 2003, 193, 59–70; (d) H. Zou, 15 (a) T. R. Younkin, E. F. Connor, J. I. Henderson,
F. M. Zhu, Q. Wu, J. Y. Ai and S. A. Lin, J. Polym. Sci., Part A:
Polym. Chem., 2005, 43, 1325–1330; (e) H.-R. Liu,
P. T. Gomes, S. I. Costa, M. T. Duarte, R. Branquinho,
A. C. Fernandes, J. C. W. Chien, R. P. Singh and
M. M. Marques, J. Organomet. Chem., 2005, 690, 1314–1323;
(f) C.-L. Song, L.-M. Tang, Y.-G. Li, X.-F. Li, J. Chen and
Y.-S. Li, J. Polym. Sci., Part A: Polym. Chem., 2006, 44, 1964–
S. K. Friedrich, R. H. Grubbs and D. A. Bansleben, Science,
2000, 287, 460–462; (b) E. F. Connor, T. R. Younkin,
J. I. Henderson, A. W. Waltman and R. H. Grubbs, Chem.
Commun., 2003, 2272–2273; (c) V. C. Gibson,
C. K. A. Gregson, C. M. Halliwell, N. J. Long, P. J. Oxford,
A. J. P. White and D. J. Williams, J. Organomet. Chem.,
2005, 690, 6271–6283.
1974; (g) B. K. Bahuleyan, G. W. Son, D.-W. Park, C.-S. Ha 16 Z. Huang, K. Song, F. Liu, J. Long, H. Hu, H. Gao and
and I. Kim, J. Polym. Sci., Part A: Polym. Chem., 2008, 46,
1066–1082; (h) M. M. Wegner, A. K. Ott and B. Rieger,
Q. Wu, J. Polym. Sci., Part A: Polym. Chem., 2008, 46, 1618–
1628.
Macromolecules, 2010, 43, 3624–3633; (i) C. S. Popeney and 17 J. M. Benito, E. De Jesús, F. J. de la Mata, J. C. Flores,
Z. Guan, Macromolecules, 2010, 43, 4091–4097.
7 (a) T. V. Laine, U. Piironen, K. Lappalainen, M. Klinga,
R. Gómez and P. Gómez-Sal, Organometallics, 2006, 25,
3876–3887.
E. Aitola and M. Leskelä, J. Organomet. Chem., 2000, 606, 18 G. B. Galland, R. F. de Souza, R. S. Mauler and F. F. Nunes,
112–124; (b) T. V. Laine, K. Lappalainen, J. Liimatta, Macromolecules, 1999, 32, 1620–1625.
E. Aitola, B. Lofgren and M. Leskela, Macromol. Rapid 19 G. M. Sheldrick, SHELXTL-97, Program for the Refinement of
Commun., 1999, 20, 487–491; (c) L. Zhang, E. Yue, B. Liu, Crystal Structures, University of Göttingen, Germany, 1997.
P. Serp, C. Redshaw, W.-H. Sun and J. Durand, Catal. 20 L. Spek, Acta Crystallogr., Sect. D: Biol. Crystallogr., 2009, 65,
Commun., 2014, 43, 227–230.
148–155.
3346 | Dalton Trans., 2014, 43, 3339–3346
This journal is © The Royal Society of Chemistry 2014