Ethylene oligomerization with 2-hydroxymethyl-5,6,7-trihydroquinolinyl-8-ylideneamine-Ni(II) chlorides

Article abstract of DOI:10.1016/j.jorganchem.2021.121720

A series of Ni complexes of the general formula [2-(MeOH)-8-{N(Ar)}C₉H₈N]NiCl₂, where Ar = 2,6-Me₂C₆H₃ in Ni1; 2,6-Et₂C₆H₃ in Ni2; 2,6-i-Pr₂C₆H₃ in Ni3; 2,4,6-Me₃C₆H₂ in Ni4; 2,6-Et₂-4-MeC₆H₂ in Ni5 and 2,4,6-t-Bu₃C₆H₂ in Ni6 has been synthesized and characterized by elemental analysis and IR spectroscopy. On activation with MMAO or Et₂AlCl, these complexes showed high activity in ethylene oligomerization, reaching 2.23 × 10⁶ g·mol^–1 (Ni) h^–1 at 30 °C with the Al/Ni ratio of 5500 and 9.11 × 10⁵ g·mol^–1 (Ni) h^–1 with the Al/Ni of 800, respectively. Moreover, the content of α-C₄ indicated high selectivity exceeding 99% in the Ni/Et₂AlCl system. Comparing with the previous report by our group, this work discloses higher activity, presumably due to the substituent at the 2-position within the ligand influencing the steric hindrance around the metal atom. Furthermore, it is worth noting that the branched alkenes have been observed (iso-C₆: 35.3 – 57.2%) in the oligomerization products.

Full text of DOI:10.1016/j.jorganchem.2021.121720

Journal of Organometallic Chemistry 937 (2021) 121720
Contents lists available at ScienceDirect
Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
Ethylene oligomerization with 2-hydroxymethyl-5,6,7-
trihydroquinolinyl-8-ylideneamine-Ni(II) chlorides
Lei Xua,b,1, Jiaxin Lia,b,1, Wenhua Linb, Yanping Mab, Xinquan Hua,∗, Zygmunt Flisakb,c,∗
Wen-Hua Sunb,∗
,
a College of Chemical Engineering, Zhejiang University of Technology, Hangzhou 310014, China
b Key Laboratory of Engineering Plastics and Beijing National Laboratory for Molecular Sciences, Institute of Chemistry, Chinese Academy of Sciences, Beijing
100190, China
c Faculty of Chemistry, University of Opole, Oleska 48, 45-052 Opole, Poland
a r t i c l e i n f o
a b s t r a c t
Article history:
A series of Ni complexes of the general formula [2-(MeOH)-8-{N(Ar)}C9H8N]NiCl2, where Ar = 2,6-
Me2C6H3 in Ni1; 2,6-Et2C6H3 in Ni2; 2,6-i-Pr2C6H3 in Ni3; 2,4,6-Me3C6H2 in Ni4; 2,6-Et2-4-MeC6H2 in
Ni5 and 2,4,6-t-Bu3C6H2 in Ni6 has been synthesized and characterized by elemental analysis and IR
spectroscopy. On activation with MMAO or Et2AlCl, these complexes showed high activity in ethylene
oligomerization, reaching 2.23 × 106 g·mol–1 (Ni) h–1 at 30 °C with the Al/Ni ratio of 5500 and 9.11 × 105
g·mol–1 (Ni) h–1 with the Al/Ni of 800, respectively. Moreover, the content of α-C4 indicated high selec-
tivity exceeding 99% in the Ni/Et2AlCl system. Comparing with the previous report by our group, this
work discloses higher activity, presumably due to the substituent at the 2-position within the ligand in-
fluencing the steric hindrance around the metal atom. Furthermore, it is worth noting that the branched
alkenes have been observed (iso-C6: 35.3 – 57.2%) in the oligomerization products.
Received 28 December 2020
Revised 22 January 2021
Accepted 26 January 2021
Available online 29 January 2021
Keywords:
Ethylene oligomerization
Nickel complexes
Co-catalyst
Substituent effect
Selectivity
© 2021 Elsevier B.V. All rights reserved.
Activity
Introduction
fused iminopyridine ligands (A, Chart 1) [12], which displayed fa-
vorable activity in ethylene polymerization. Interestingly, modifica-
Since the discovery of the aryl-substituted α-diimine nickel cat-
alysts for olefin polymerization [1], the late-transition-metal-based
systems have been a hot topic of significant interest in both the
industry and academia [2]. Whereas the structural properties of
the catalysts play a key role in determining the polymer proper-
ties, it is also demonstrated that the effects of temperature and
pressure are equally important [3]. In the past decades, the papers
on ethylene polymerization and oligomerization catalysts mush-
roomed, reporting extensive results on the nickel complexes sup-
ported by the bidentate N^N [4,5], N^P [6], N^O [7] and P^O [8],
as well as the tridentate N^N^N [9] and N^N^O [10] motifs. Among
these species, the Ni(II) complexes bearing the N^N ligands are the
most attractive due to easy synthesis and superior catalytic perfor-
mance.
tions of the substituent at the 2-position of the pyridine moiety in
A also led to the active polymerization catalyst (B, Chart 1) [13].
Recently, we have reported a series of 2-acetyloxymethyl-quinoline
nickel complexes [14], which exhibit high activity and selectivity
toward α-C4 in ethylene oligomerization (C, Chart 1). To explore
other substitution patterns, we synthesized and characterized cer-
tain new nickel complexes (D, Chart 1). An in-depth study was
conducted to determine the effects of the precatalyst structure, the
type and amount of a co-catalyst, temperature, and reaction time
on the activity and selectivity in ethylene oligomerization.
Results and discussion
Synthesis and characterization
Our group focused on the design and synthesis of the new
late-transition-metal complexes for ethylene polymerization and
oligomerization [11], such as the Ni complexes bearing carbocyclic-
Initially, a two-step route was attempted in order to obtain the
nickel complex. In the first step, the imine ligands were synthe-
sized from 2-hydroxymethyl-5,6,7-trihydroquinolin-8-one (1), the
corresponding aniline, the catalytic amount of p-TsOH, and o-
xylene as the solvent. Then we intended to carry out the reac-
tions of the resultant ligands with nickel chloride. Unfortunately,
we were unable to purify the target Schiff-base ligands by the col-
∗
Corresponding authors.
E-mail addresses: xinquan@zjut.edu.cn (X. Hu), zgf@uni.opole.pl (Z. Flisak),
whsun@iccas.ac.cn (W.-H. Sun).
1
Lei Xu and Jiaxin Li made equal contributions in this work.
https://doi.org/10.1016/j.jorganchem.2021.121720
0022-328X/© 2021 Elsevier B.V. All rights reserved.

L. Xu, J. Li, W. Lin et al.
Journal of Organometallic Chemistry 937 (2021) 121720
Chart 1. Structural development of the carbocyclic-fused iminopyridine-nickel(II) halide (A).
Scheme 1. One-pot template assembly of Ni1 – Ni6 from 1.
umn chromatography due to their instability. Therefore, the cor-
responding N-(2-hydroxymethyl-5,6,7-trihydro-quinolin-8-ylidene)
arylamino-nickel dichlorides of the general formula [2-MeOH-8-
{N(Ar)}C9H8N]NiCl2, where Ar = 2,6-Me2C6H3 in Ni1; 2,6-Et2C6H3
in Ni2; 2,6-i-Pr2C6H3 in Ni3; 2,4,6-Me3C6H2 in Ni4; 2,6-Et2-4-
MeC6H2 in Ni5; 2,4,6-t-Bu3C6H2 in Ni6] were prepared by a one-
pot reaction of 2-hydroxymethyl-5,6,7-trihydroquinolin-8-one (1),
the corresponding aniline and NiCl2·6H2O with o-xylene as sol-
vent (Scheme 1). All six complexes were characterized by FT-
IR spectroscopy and elemental analysis. The results of elemental
analysis are in accordance with the formula corresponding to the
structure described in Scheme 1. FT-IR spectroscopy suggests that
the strong peak (1693 cm−1, νC=O) originally present in the 2-
(hydroxymethyl)-6,7-dihydroquinolin-8(5H)-one, disappears in the
nickel complexes, which means that the C=O band is replaced with
The oligomerization results shown in Table 1 indicate that the
system employing MMAO as a co-catalyst attained the highest ac-
tivity reaching 0.72 × 106 g·mol–1 (Ni) h–1 with C6 as the major
product (88.8%) and 1-butene as the minor one (11.2%). The Et2AlCl
co-catalyst took the second place with the activity of 0.35 × 106
g·mol–1 (Ni) h–1 and the iso-C6 was generated (35.2%). The dif-
ferent products should be attributed to the β-H elimination and
the chain walking effect; the plausible mechanism is illustrated in
Scheme 2 [15]. The other two co-catalysts, MAO and EASC, showed
nearly no activity in ethylene oligomerization. This situation is not
unique and can be seen in the previous literature reports [15c].
Certain co-catalyst may show no activity in ethylene polymeriza-
tion and oligomerization because the reaction of nickel complexes
with the co-catalyst leads to rapid ligand scrambling and the lat-
ter process is accompanied by the Ni reduction to the zerovalent
state [15c]. We assume that this effect occurs when MAO and EASC
are used as co-catalyst to react with Ni6. Based on these results,
MMAO and Et2AlCl were selected as the co-catalysts for further
study.
the C=N. Nickel complexes show a strong peak around 1610 cm−1
,
at a lower wavenumber comparing with the C=N of free imine
(1640 cm−1). This finding implies that the nitrogen atom of the
imine group is coordinated with the nickel atom. Furthermore, the
characteristic peak of the OH group can still be seen in the IR spec-
trum of nickel complexes. Hence, we are convinced that the nickel
center is coordinated with the bidentate ligand (N, N), rather than
the tridentate one (N, N, O).
2.2.1. Catalytic evaluation with MMAO
The catalytic properties of the nickel complexes in ethylene
oligomerization were investigated in detail for several parameters,
such as the Al/Ni molar ratio, reaction temperature and polymer-
ization time. Ni6 was again used as the test precatalyst; then the
remaining compounds were also examined. The results are sum-
marized in Table 2.
2.2. Ethylene oligomerization
Initially, the Ni6 was selected as the precatalyst for ethylene
oligomerization and both the activity and the oligomer distribu-
tions were measured with four types of co-catalysts, including
modified methylaluminoxane (MMAO), methylaluminoxane (MAO),
ethylaluminium sesquichloride (Et3Al2Cl3, EASC), and diethylalu-
minium chloride (Et2AlCl). The temperature of 30 °C and 10 atm
of ethylene were used as the initial conditions (Table 1).
On the variation of the Al/Ni molar ratio from 2000 to 6000
(entries 1 – 7 in Table 2), the Ni precatalyst shows the highest ac-
tivity of 2.14 × 106 g·mol–1 (Ni) h–1 at the relatively high Al/Ni
ratio of 5500 (entry 6, Table 2). From the perspective of oligomeric
products, the content of C6 is higher for low concentrations of the
co-catalyst, with a maximum of 91.1% at the Al/Ni ratio of 2000
2

L. Xu, J. Li, W. Lin et al.
Journal of Organometallic Chemistry 937 (2021) 121720
Table 1
Co-catalyst screening with Ni6 as the precatalyst[a]
.
Oligomer Distribution[c] (%)
Entry
Co-catalyst
Al/Ni
Activity[b]
C4/ꢀC
α-C4/C4
C6/ꢀC
α-C6/C6
iso-C6/C6
1
MMAO
2000
0.72
11.2
88.8
88.8
47.9
–
234
MAOEASCEt2AlCl
2000400400
0.01–0.35
100–85.4
100–97.3
––14.6
––41.4
––35.2
[a] General conditions: 2 μmol of Ni6, 10 atm of C2H4, 100 mL of toluene, 30 °C, 30 min;
[b] 106 g·mol–1 (Ni) h–1
.
[c] Determined by GC; C4, α-C4, C6, α-C6, and iso-C6 stand for total amount of butene, 1-butene, hexene, 1-hexene, and
iso-hexene, respectively; ꢀC signifies the total amount of oligomers.
Scheme 2. Plausible mechanism of ethylene oligomerization catalyzed by Ni1/MMAO and Ni1/Et2AlCl.
(entry 1, Table 2). The selectivity toward α-C6 remains nearly con-
stant at around 49% throughout the oligomerization tests described
above.
presumably the result of the inhibiting effect of β-H elimination.
With the ethylene pressure reduced to 5 atm, the activity drops to
1.12 × 106 g·mol–1 (Ni) h–1, while more 1-butene is produced com-
paring with the original ethylene pressure of 10 atm: 94.6% and
74.3%, respectively. In brief, these results highlight the importance
of the reaction temperature, Al/Ni ratio, and reaction time for both
the catalytic activity and selectivity toward 1-butene.
Then, with the Al/Ni ratio fixed at 5500, the reaction temper-
ature was raised from 20°C to 50°C and the highest activity of
2.14 × 106 g·mol–1 (Ni) h–1 was found at 30°C (entry 6 vs. entries
8 – 10, Table 2). In addition, the content of C4 displays a downward
trend (from 19.5% to 12.5%) as the temperature is increased, which
was also observed in previous reports [16]. On the contrary, the
content of α-C4 shows an opposite trend arriving at a peak value
of 95.7% at 50°C, while the 1-hexene maintains a stable value of
approximately 49%.
Finally, the optimal conditions established in the experiments
described above, i.e. Al/Ni = 5500, PC2H4 = 10 atm, T = 30°C and
t = 30 min were used to test the catalytic performance of the
remaining Ni complexes (Ni1 – Ni5) and the results are listed in
Table 2 (entries 16 – 20, Table 2). Comparing with the precatalyst
of a similar structure published previously (entry 21, Table 2), Ni1
– Ni6 show higher activities. As for the C4 products, the selectiv-
ity of the Ni3 complex reaches 93.4% (entry 18, Table 2). Moreover,
little influence of the catalyst structure on the selectivity toward
α-C6 was observed.
On prolonging the reaction time, the activity promptly de-
creases from 11.6 × 106 g·mol–1 (Ni) h–1 to 0.23 × 106 g·mol–1
(Ni) h–1 at 5 min and 60 min, respectively; meanwhile the 1-
butene content is reduced consequently. On the other hand, the
total C4 product content remains constant at around 16%, which is
3

L. Xu, J. Li, W. Lin et al.
Journal of Organometallic Chemistry 937 (2021) 121720
Table 2
Ethylene oligomerization with MMAO as the co-catalyst[a]
.
Oligomer Distribution[c] (%)
Entry
Precatalyst
T,°C
Al/Ni
t, min
Activity[b]
C4/ꢀC
α-C4/C4
C6/ꢀC
α-C6/C6
1
Ni6
Ni6
Ni6
Ni6
Ni6
Ni6
Ni6
Ni6
Ni6
Ni6
Ni6
Ni6
Ni6
Ni6
Ni6
Ni1
Ni2
Ni3
Ni4
Ni5
C
30
30
30
30
30
30
30
20
40
50
30
30
30
30
30
30
30
30
30
30
30
2000
3000
4000
4500
5000
5500
6000
5500
5500
5500
5500
5500
5500
5500
5500
5500
5500
5500
5500
5500
300
30
30
30
30
30
30
30
30
30
30
5
0.71
0.80
1.52
1.68
1.83
2.14
1.74
1.93
2.02
1.78
11.6
4.16
0.55
0.23
1.12
2.15
2.08
2.11
2.23
2.08
0.36
8.8
14.2
60.9
47.4
60.8
53.6
79.3
60.8
54.3
86.6
95.7
86.1
70.3
60.7
53.6
94.6
88.5
80.4
93.4
75.9
67.3
74.1
91.1
80.6
78.4
80.5
80.0
83.6
81.9
80.5
85.4
87.5
83.9
83.6
83.7
76.5
85.6
86.1
86.4
87.1
84.4
81.9
85.6
49.9
49.9
48.8
49.6
48.9
49.6
48.7
47.3
49.3
49.3
49.5
47.6
49.5
49.9
51.0
49.6
48.9
49.1
49.0
48.8
47.5
2
19.4
21.6
19.5
20.0
16.4
18.1
19.5
14.6
12.5
16.1
16.4
16.3
23.5
14.4
13.9
13.6
12.9
15.5
18.1
14.4
3
4
5
6
7
8
9
10
11
12
13
14
15
45
60
30
30
30
30
30
30
30
[d]
15
16
17
18
19
20
21e
[a] General conditions: 2 μmol of precatalyst, 10 atm of C2H4, 100 mL of toluene;
[b] 106 g·mol–1 (Ni)·h–1
;
[c] Determined by GC; C4, α-C4, C6, and α-C6 stand for total amount of butene, 1-butene, hexene and 1-
hexene, respectively; ꢀC signifies the total amount of oligomers.
[d] 5 atm of C2H4.
[e] Catalyzed by 4 μmol of complex C (Chart 1).
Table 3
Ethylene oligomerization with Et2AlCl as the co-catalyst[a]
.
Oligomer Distribution[c] (%)
Entry
Precatalyst
T,°C
Al/Ni
t, min
Activity[b]
C4/ꢀC
α-C4/C4
C6/ꢀC
α-C6/C6
iso-C6/C6
1
Ni6
Ni6
Ni6
Ni6
Ni6
Ni6
Ni6
Ni6
Ni6
Ni6
Ni6
Ni6
Ni6
Ni1
Ni2
Ni3
Ni4
Ni5
30
30
30
30
30
30
20
40
30
30
30
30
30
30
30
30
30
30
400
600
700
800
900
1000
800
800
800
800
800
800
800
800
800
800
800
800
30
30
30
30
30
30
30
30
5
3.82
6.91
8.12
9.11
6.70
6.40
4.31
4.47
98.2
28.5
5.77
3.23
2.00
6.02
6.63
8.24
6.04
9.13
79.1
56.1
64.9
68.5
57.4
54.8
81.0
81.7
76.5
72.6
51.4
27.9
52.6
18.9
26.6
32.9
4.10
46.6
97.3
98.6
97.6
95.2
98.1
97.7
98.1
97.3
96.8
96.8
98.2
>99
94.3
>99
>99
>99
>99
96.1
20.9
43.9
35.1
31.5
42.6
45.2
19.0
18.3
23.5
27.4
48.6
72.0
47.4
81.0
73.4
67.1
95.9
53.4
41.4
38.6
32.8
38.7
38.7
38.9
40.1
40.7
33.3
33.2
33.0
33.4
33.2
32.5
33.2
27.3
27.9
27.7
35.3
38.8
48.1
39.1
38.4
38.4
36.3
36.4
46.9
47.4
47.0
47.1
47.6
47.3
47.4
57.2
56.4
68.1
2
3
4
5
6
7
8
9
10
11
12
13[d]
14
15
16
17
18
15
45
60
30
30
30
30
30
30
[a] General conditions: 2 μmol of precatalyst, 10 atm of C2H4, 100 mL of toluene;
[b] 105 g·mol–1 (Ni)·h–1
;
[c] Determined by GC; C4, α-C4, C6, α-C6, and iso-C6 stand for total amount of butene, 1-butene, hexene, 1-hexene, and
iso-hexene, respectively; ꢀC signifies the total amount of oligomers.
[d] 5 atm of C2H4.
2.2.2. Catalytic evaluation with Et2AlCl
the values of 1-hexene content were stable and above 38%. It is
worth noting that the content of iso-C6 determined by GC is com-
parable to that of α-C6, which could have been caused by the β-H
transfer.
A screening strategy similar to that employed for the Ni/MMAO
systems was adopted; the Ni6 was selected as a test precatalyst
and Et2AlCl as a co-catalyst. The results are summarized in Table 3.
The effect of the Al/Ni ratio was first explored with the tem-
perature fixed at 30°C (entries 1 – 6, Table 3). On increasing the
ratio from 400 to 1000, the highest activity of 9.11 × 105 g·mol–1
(Ni) h–1 was observed at the value of 800. Comparing with the
Ni/MMAO systems, significantly higher selectivity toward α-C4, ex-
ceeding 94%, was attained at the expense of activity. Meanwhile,
With the Al/Ni ratio set at 800, the polymerization temperature
was varied from 20°C to 40°C. The highest activity of 9.11 × 105
g·mol–1 (Ni) h–1 was identified at 30°C. Indeed, the temperature of
30°C is usually found optimal for the oligomerization with the Ni
complexes [17]; however, we found the lowest 1-butene content at
this temperature (entry 4 vs entries 7 – 8, Table 3).
4

L. Xu, J. Li, W. Lin et al.
Journal of Organometallic Chemistry 937 (2021) 121720
With regard to reaction time, the activity of the Ni/Et2AlCl sys-
tems shows a similar trend to that with MMAO (entries 9 – 12,
Table 3). Indeed, the highest activity of 9.82 × 106 g mol–1 (Ni)
h–1 is seen after 5 minutes, with the comparable result for MMAO
as a co-catalyst and after the same reaction time. Moreover, the
content of C4 decreases gradually with time, while the content of
1-butene is practically constant at nearly 100%. The amounts of 1-
hexene and iso-C6 are also constant, albeit at only 33% and 47%,
respectively. These results indicate that the reaction time has little
influence on the distribution of ethylene oligomers. Lowering the
pressure from 10 to 5 atm C2H4, under otherwise identical condi-
tions, brings about the activity drop from 9.11 to 2.0 × 105 g mol–1
(Ni) h–1 with an increased preference for C6 products (entries 4
and 13, Table 3).
toluene) and ethylaluminium sesquichloride (EASC, 0.87 M in n-
heptane) were supplied from Acros Chemical. Other reagents were
purchased from Aldrich, Acros, or local suppliers. IR spectra were
recorded on a Perkin-Elmer System 2000 FT-IR spectrometer. Ele-
mental analyses (C, H, and N) were performed on a Flash EA 1112
microanalyzer. Gas chromatographic (GC) analysis was performed
with a VARIAN CP-3800 gas chromatograph equipped with a flame
ionization detector and a 30 m (0.2 mm i.d., 0.25 mm film thick-
ness). The mixture of the product can be separated by tempera-
ture programming and the individual products show different re-
tention time. The details of the calculation process can be seen
in the SI. The compound 2-(hydroxymethyl)-6,7-dihydroquinolin-
8(5H)-one (1) was prepared using the literature procedure [18]; all
anilines were obtained from commercial suppliers.
Using the optimal conditions established with Ni6/Et2AlCl
(Al/Ni = 800, PC2H4 = 10 atm, T = 30°C and t = 30 min), Ni1 –
Ni6 were screened accordingly, and the results are summarized in
Table 3 (entries 14 – 18). Inspection of the data reveals the activ-
Synthesis of [2-(MeOH)-8-{N(Ar)}C9H8N]NiCl2 (Ni1 – Ni6)
(a) Ar
=
2,6-Me2C6H3 (Ni1). To
a
solution of 2-
(hydroxymethyl)-6,7-dihydroquinolin-8(5H)-one (1) (354 mg,
2
mmol), 2,6-dimethylaniline (363 mg, 3 mmol) and NiCl2·6H2O
(451 mg, 1.9 mmol) in toluene (100 mL) a catalytic amount of
p-toluenesulfonic acid (76 mg, 20 mol%) was added. The reaction
mixture was stirred and refluxed for 8 h. After cooling to room
temperature, the mixture was filtered and all volatiles removed by
rotary evaporator. Finally, the complex was washed with diethyl
ether, filtered, dried and collected as a pale-yellow solid (419
mg, 50%). FT-IR (cm−1): 3501 (m), 3381 (s), 3304 (s), 2847 (w),
1605 (m), 1512 (m), 1474 (m), 1441 (m), 1375 (w), 1273 (w), 1196
(w), 1091 (w), 1031 (w), 990 (w), 764 (m), 563(s). Anal. Calc. for
C18 H20Cl2N2NiO (409.96): C, 52.73; H, 4.92; N, 6.83. Found: C,
52.42 H, 5.13; N, 7.00%.
ities in the range between 6.02 and 9.11 × 105 g mol–1 (Ni) h–1
,
with the following decreasing order: Ni6 > Ni5 > Ni3 > Ni2 > Ni4
> Ni1. Moreover, the content of C4 shows an upward trend with
the growing bulkiness of the substituent, except for Ni4. Compar-
ing with the MMAO runs, there are some differences in the activity
order, i.e. the bulkiest precatalyst (Ni6) now gives the most active
catalyst, rather than Ni1 or Ni4.
When further comparing the Ni/MMAO and the Ni/Et2AlCl sys-
tems, the activity of the former is much higher, while the latter
produces higher content of α-C4 with a stable value exceeding 94%
throughout the entire set of reactions. Furthermore, there is no GC
evidence of branched products with MMAO as the co-catalyst.
Comparing with the previous reports on similar oligomeriza-
tion catalysts published by our group (see e.g. C, Chart 1) [14], the
current systems attain much higher catalytic activity. Besides, the
content of C4 is higher than that obtained with the other Ni com-
plexes; however, the 1-butene content is lower, which could be at-
tributed to the steric hindrance of the substituent at the 2-position
in the precatalyst.
(b) Ar = 2,6-Et2C6H3 (Ni2). By using a similar procedure as de-
scribed for Ni1, but with 2,6-diethylaniline as the amine, Ni2 was
obtained as a yellow powder (612 mg, 68%). FT-IR (cm−1): 3492
(m), 3393 (m), 2962 (w), 2874 (w), 1614 (m), 1515 (m), 1454 (m),
1382 (w), 1347 (w), 1262 (w), 1188 (w), 1115 (w), 802 (m), 724 (s),
575 (s). Anal. Calc. for C20H24Cl2N2NiO (438.02): C, 54.84; H, 5.52;
N, 6.40; Found: C, 54.61 H, 5.33; N, 6.18%.
(c) Ar = 2,6-i-Pr2C6H3 (Ni3). By using a similar procedure as
described for Ni1, but with 2,6-diisopropylaniline as the amine,
Ni3 was obtained as a yellow powder (500 mg, 52%). FT-IR (cm−1):
3500 (m), 3392 (m), 2960 (m), 2929 (w), 1615 (m), 1515 (w), 1460
(m), 1383 (w), 1361 (w), 1357 (w), 1271 (w), 1215 (w), 1184 (w),
1143 (w), 930 (w), 802 (m), 777 (m), 726 (m), 570 (s). Anal. Calc.
for C22H28Cl2N2NiO (466.07): C, 56.69; H, 6.06; N, 6.01; Found: C,
56.77; H, 6.23; N, 6.10%.
Conclusions
A
series
of
2-hydroxymethyl-substituted
5,6,7-
trihydroquinolinyl-8-ylideneamine-Ni(II) chloride complexes (Ni1
– Ni6) was synthesized and characterized. With MMAO as the
co-catalyst, the Ni complexes displayed high activities at a range of
2.00 – 2.23 × 106 g mol–1 (Ni) h–1, performing both dimerization
and trimerization. When Et2AlCl was employed, distinctly lower
activity, ranging from 6.02 to 9.11 × 105 g mol–1(Ni) h–1 was
attained, but the catalyst offered an excellent selectivity toward
α-C4, up to 99%. Also, iso-C6 was observed, probably due to the
chain walking effect. It could be speculated that a further increase
in the steric hindrance of the substituent at the 2-position in the
precatalyst may improve the activity.
(d) Ar = 2,4,6-Me3C6H2 (Ni4). By using a similar procedure as
described for Ni1, but with 2,4,6-trimethylaniline as the amine, Ni4
was obtained as a yellow powder (516 mg, 59%). FT-IR (cm−1):
3305 (m), 2960 (w), 2915 (w), 1623 (m), 1593 (m), 1509 (w),
1479 (m), 1446 (m), 1377 (w), 1272 (w), 1208 (m), 1148 (w), 1086
(w), 1037 (w), 851 (m), 501 (s). Anal. Calc. for C19 H22Cl2N2NiO
(423.99): C, 53.82; H, 5.23; N, 6.61; Found: C, 53.59; H, 5.55;
N, 6.74%.
(e) Ar = 2,6-Et2-4-MeC6H2 (Ni5). By using a similar procedure
as described for Ni1, but with 2,6-diethyl-4-methylaniline as the
amine, Ni5 was obtained as a yellow powder (713 mg, 78%). FT-
IR (cm−1): 3508 (m), 3394 (m), 3194 (m), 2967 (m), 2913 (m),
1613 (m), 1515 (w), 1454 (m), 1407 (w), 1377 (w), 1263 (w), 1056
(m), 858 (m), 799 (m), 576 (s). Anal. Calc. for C21H26Cl2N2NiO
(452.04): C, 55.80; H, 5.80; N, 6.20; Found: C, 56.01; H, 5.74;
N, 6.33%.
Experimental section
General considerations
All manipulations of air- and moisture-sensitive compounds
were performed under
a nitrogen atmosphere using standard
(f) Ar = 2,4,6-t-Bu3C6H2 (Ni6). By using a similar procedure as
described for Ni1, but with 2,4,6-tri-tert-butylaniline as the amine,
Ni6 was obtained as a yellow powder (156 mg, 14%). FT-IR (cm−1):
3378 (m), 2952 (s), 1670 (s), 1641 (m), 1595 (s), 1474 (s), 1431 (m),
1392 (m), 1360 (m), 1334 (w), 1285 (w), 1270 (w), 1208 (m), 1118
(m), 1106 (m), 1065 (w), 1040 (w), 920 (w), 889 (w), 841 (m), 824
Schlenk techniques. Solvents were distilled for 8h under nitro-
gen with the appropriate drying agents prior to use. The co-
catalysts, MAO (1.46 M in toluene) and MMAO (1.93 M in hep-
tane), were provided by Albemarle Corporation. High-purity ethy-
lene was purchased from Beijing Yanshan Petrochemical Company
and used as received. Diethylaluminum chloride (Et2AlCl, 1.17 M in
5

L. Xu, J. Li, W. Lin et al.
Journal of Organometallic Chemistry 937 (2021) 121720
(w), 755 (w), 712 (w). Anal. Calc. for C28H40Cl2N2NiO (550.23): C,
61.12; H, 7.33; N, 5.09; Found: C, 61.34; H, 7.45; N, 5.36%.
[4] (a) P. Hao, S. Zhang, W.-H. Sun, Q. Shi, S. Adewuyi, X. Lu, P. Li, Organometallics
26 (2007) 2439–2446, doi:10.1021/om070049e; (b) S. Song, T. Xiao, T. Liang,
F. Wang, C. Redshaw, W.-H. Sun, Catal. Sci. Technol. 1 (2011) 69–75, doi:10.
1039/C0CY00002G; (c) Y. Chen, S. Du, C. Huang, G.A. Solan, X. Hao, W.-
H. Sun, J. Polym. Sci., Part A: Polym. Chem. 55 (2017) 1971–1983, doi:10.
1002/pola.28562; (d) Y. Zeng, Q. Mahmood, X. Hao, W.-H. Sun, J. Polym.
Sci., Part A: Polym. Chem. 55 (2017) 1910–1919, doi:10.1002/pola.28563; (e)
Q.Zhang A.Vignesh, Y. Ma, T. Liang, W.-H. Sun, Polymer 187 (2020) 122089,
doi:10.1016/j.polymer.2019.122089; (f) S. Yuan, Z. Fan, Q. Zhang, Z. Flisak,
Y. Ma, Y. Sun, W.-H. Sun, Appl. Organomet. Chem. 34 (2020) 5638, doi:10.1002/
aoc.5638.
Oligomerization of ethylene
The ethylene oligomerization at 5 or 10 atm ethylene was car-
ried out in a 250 mL stainless steel autoclave equipped with an
ethylene pressure control system, a mechanical stirrer, and a tem-
perature controller. After the air was removed under reduced pres-
sure and the reactor was backfilled with nitrogen two times and
ethylene one time, the solution of the appropriate Ni complex (Ni1
– Ni6, 2 μmol) in toluene (25 mL), was injected into the auto-
clave and more toluene (25 mL) was then added to completely
wash any residual precatalyst into the autoclave. Then the required
amount of co-catalyst was added promptly, followed by remain-
ing toluene (50 mL). Instantaneously, the pressure was increased to
10 atm C2H4 and stirring initiated. After the designated time with
the selected values of temperature and pressure, the autoclave was
cooled with an ice bath, and the pressure was slowly released. A
small amount of cooled reaction solution (about 1 mL) was col-
lected and quenched with 5% HCl (0.2 mL) and the residuum was
quenched by ethyl alcohol with the hydrochloric acid (2 mL). A
sample of the resultant liquid (0.02 μL) was then immediately in-
jected into the GC instrument to determine the distribution of the
oligomers. The mass of C4 and C6 was calculated based on the ra-
tio of the corresponding peaks to the toluene peak in the gas chro-
matogram.
[5] (a) P. Yang, Y. Yang, C. Zhang, X.-J. Yang, H.-M. Hu, Y. Gao, B. Wu, In-
org. Chim. Acta 362 (2009) 89–96, doi:10.1016/j.ica.2008.03.018; (b) L. Wang,
C. Zhang, Z.-X. Wang, Eur. J. Inorg. Chem. 17 (2007) 2477–2487, doi:10.1002/
ejic.200700020; (c) E. Yue, L. Zhang, Q. Xing, X. Cao, X. Hao, C. Redshaw, W.-
H. Sun, Dalton Trans 43 (2014) 423–431, doi:10.1039/C3DT52234B; (d) L. Fan,
S. Du, C.-Y. Guo, X. Hao, W.-H. Sun, J. Polym. Sci., Part A: Polym. Chem. 53
(2015) 1369–1378, doi:10.1002/pola.27572; (e) M. Zada, A. Vignesh, L. Guo,
R. Zhang, W. Zhang, Y. Ma, Y. Sun, W.-H Sun, ACS Omega 5 (2020) 10610–
10625, doi:10.1021/acsomega.0c01208.
[6] (a) W.-H. Sun, Z. Li, H. Hu, B. Wu, H. Yang, N. Zhu, X. Leng, H. Wang, New J.
Chem. 26 (2002) 1474–1478, doi:10.1039/B203738F; (b) H.-Y. Wang, G.-X. Jin,
Eur. J. Inorg. Chem. 9 (2005) 1665–1670, doi:10.1002/ejic.200400856; (c) L.-
P. Song, W. Zhao, J.-L. Huang, S.-Z. Zhu, Chin. J. Chem. 23 (2005) 669–672,
doi:10.1002/cjoc.200590669; (d) Z. Weng, S. Teo, T.S.A. Hor, Organometallics
25 (2006) 4878–4882, doi:10.1021/om060607; (e) D.-P. Song, W.-P. Ye, Y.-
X. Wang, J.-Y. Liu, Y.-S. Li, Organometallics 28 (2009) 5697–5704, doi:10.1021/
om900477k; (f) M. Höhne, N. Peulecke, K. Konieczny, B.H. Meller, U, Rosen-
thal, ChemCatChem.
9 (2017) 2467–2472, doi:10.1002/cctc.201700448; (g)
G. Si, Y. Na, C. Chen, ChemCatChem 10 (2018) 5135–5140, doi:10.1002/cctc.
201800957.
[7] (a) D. Zhang, G. Jin, Organometallics 22 (2003) 2851–2854, doi:10.1021/
om030068y; (b) Q. Ban, J. Zhang, T. Liang, C. Redshaw, W.-H. Sun, J. Organomet.
Chem. 713 (2012) 151–156, doi:10.1016/j.jorganchem.2012.05.015; (c) R. Gao,
W.-H. Sun, C. Redshaw, Catal. Sci. Technol. 3 (2013) 1172–1179, doi:10.1039/
C3CY20691B; (d) M. Ngcobo, G.S. Nyamato, S.O. Ojwach, Mol. Catal. 478 (2019)
110590, doi:10.1016/j.mcat.2019.110590.
[8] (a) J. Heinicke, M. Köhler, N. Peulecke, W. Keim, J. Catal. 225 (2004) 16–23,
doi:10.1016/j.jcat.2004.03.029; (b) P. Kuhn, D. Sémeril, D. Matt, M.J. Chetcutib,
P. Lutz, DaltonTrans. 5 (2007) 515–528, doi:10.1039/B615259G; (c) R.J. Long,
V.C. Gibson, A.J.P. White, Organometallics 27 (2008) 235–245, doi:10.1021/
om7008149.
Declaration of Competing Interest
The authors declare that they have no known competing finan-
cial interests or personal relationships that could have influenced
the work reported in this paper.
[9] (a) M. Zhang, S. Zhang, P. Hao, S. Jie, W.-H. Sun, P. Li, X. Lu, Eur. J. Inorg. Chem.
24 (2007) 3816–3826, doi:10.1002/ejic.200700392; (b) Y. Zhang, C. Huang,
X. Wang, Q. Mahmood, X. Hao, X. Hu, C.-Y. Guo, G.A. Solan, W.-H. Sun, Polym.
Chem. 8 (2017) 995–1005, doi:10.1039/C6PY02089E; (c) Z. Wang, G.A. Solan,
Qaiser Mahmood, Q. Liu, Y. Ma, X. Hao, W.-H. Sun, Organometallics 37 (2018)
380–389, doi:10.1021/acs.organomet.7b00809; (d) V.A. Tuskaev, S.V. Zubke-
vich, D. Saracheno, Svetlana Ch. Gagieva, P.V. Dorovatovskii, E.G. Kononova,
V.N. Khrustalev, D.N. Zarubin, B.M. Bulychev, Y.V. Kissin, Mol. Catal. 464
(2019) 29–38, doi:10.1016/j.mcat.2018.12.018; (e) Z. Wang, Y. Ma, J. Guo,
Q. Liu, G.A. Solan, T. Liang, W.-H. Sun, Dalton Trans 48 (2019) 2582–2591,
doi:10.1039/C8DT04892D; (f) C. Huang, V.A. Zakharov, N.V. Semikolenova,
M.A. Matsko, G.A. Solan, W.-H. Sun, J. Catal. 369 (2019) 1–9, doi:10.1016/j.jcat.
2018.10.028; (g) Y. Huang, R. Zhang, T. Liang, X. Hu, G.A. Solan, W.-H Sun,
Organometallics 38 (2019) 1143–1150, doi:10.1021/acs.organomet.8b00924; (h)
J. Guo, W. Zhang, T. Liang, W.-H Sun, Polyhedron 193 (2021) 114865–114873,
doi:10.1016/j.poly.2020.114865.
Acknowledgements
This work was supported by the National Natural Science Foun-
dation of China (No. 21871275 and 21972125). Z.F. thanks the Chi-
nese Academy of Sciences for a President’s International Fellowship
for Visiting Scientists.
Supplementary materials
Supplementary material associated with this article can be
found, in the online version, at doi:10.1016/j.jorganchem.2021.
121720.
[10] (a) B. Su, J. Zhao, Q. Zhang, W. Qin, Polym Int 58 (2009) 1051–1057,
doi:10.1002/pi.2631; (b) J.D. Azoulay, Y. Schneider, G.B. Galland, G.C. Bazan,
Chem. Commun. (2009) 6177–6179, doi:10.1039/B912743G; (c) D. Mandal,
D. Chakraborty, V. Ramkumar, D.K. Chand, RSC Adv
doi:10.1039/C5RA26721H.
6 (2016) 21706–21718,
[11] (a) W. Chai, J. Yu, L. Wang, X. Hu, C. Redshaw, W.-H. Sun, Inorg. Chim. Acta
385 (2012) 21–26, doi:10.1016/j.ica.2011.12.008; (b) X. Hou, T. Liang, W.-H. Sun,
C. Redshaw, X. Chen, J. Organomet. Chem. 708 (2012) 98–105, doi:10.1016/j.
jorganchem.2012.02.031; (c) S. Song, T. Xiao, L. Wang, C. Redshaw, F. Wang,
W.-H. Sun, J. Organomet. Chem. 699 (2012) 18–25, doi:10.1016/j.jorganchem.
2011.11.001; (d) Q.-S. Shi, X. Hao, C. Redshaw, W.-H. Sun, Chin. J. Polym.
Sci. 31 (2013) 769–777, doi:10.1007/s10118-013-1266-z; (e) F. Huang, Z. Sun,
S. Du, E. Yue, J. Ba, X. Hu, T. Liang, G.B. Galland, W.-H. Sun, Dalton Trans 44
(2015) 14281–14292, doi:10.1039/C5DT01831E; (f) Y. Zhang, C. Huang, X. Wang,
Q. Mahmood, X. Hao, X. Hu, C.-Y. Guo, G.A. Solan, W.-H. Sun, Polym. Chem. 8
(2017) 995–1005, doi:10.1039/C6PY02089E.
References
[1] (a) L.K. Johnson, C.M. Killian, M. Brookhart, J. Am. Chem. Soc. 117 (1995)
6414–6415, doi:10.1021/ja00128a054; (b) C.M. Killian, D.J. Tempel, L.K. John-
son, M. Brookhart, J. Am. Chem. Soc. 118 (1996) 11664–11665, doi:10.1021/
ja962516h; (c) B.L. Small, M. Brookhart, A.M.A. Bennett, J. Am. Chem. Soc.
120 (1998) 4049–4050, doi:10.1021/ja9802100; (d) S.D. Ittel, L.K. Johnson,
M. Brookhart, Chem. Rev. 100 (2000) 1169–1203, doi:10.1021/cr9804644;
(e) V.C. Gibson, S.K. Spitzmesser, Chem. Rev. 103 (2003) 283–315, doi:10.
1021/cr980461r; (f) Z. Wang, Q. Liu, G.A. Solan, W.-H. Sun, Coord. Chem.
Rev. 350 (2017) 68–83, doi:10.1016/j.ccr.2017.06.003; (g) G.E. Bekmukhame-
dov, A.V. Sukhov, A.M. Kuchkaev, D.G. Yakhvarov, Catalysts 10 (2020) 498,
doi:10.3390/catal10050498; (h) H. Olivier-Bourbigou, P.A.R. Breuil, L. Magna,
T. Michel, M. Fernandez Espada Pastor, D. Delcroix, Chem. Rev. 120 (2020)
7919–7983, doi:10.1021/acs.chemrev.0c00076.
[12] J. Yu, Y. Zeng, W. Huang, X. Hao, W.-H. Sun, DaltonTrans. 40 (2011) 8436–8443,
doi:10.1039/C1DT10541H.
[13] J. Yu, X. Hu, Y. Zeng, L. Zhang, C. Ni, X. Hao, W.-H. Sun, New J. Chem. 35 (2011)
178–183, doi:10.1039/C0NJ00516A.
[14] J. Li, Q. Zhang, X. Hu, Y. Ma, G.A. Solan, Y. Sun, W.-H. Sun, Appl. Organomet.
Chem. 34 (2020) 5254, doi:10.1002/aoc.5254.
[2] (a) X. Tang, W.-H. Sun, T. Gao, J. Hou, J. Chen, W. Chen, J. Organomet. Chem.
690 (2005) 1570–1580, doi:10.1016/j.jorganchem.2004.12.027; (b) D. Zhang,
E.T. Nadres, M. Brookhart, O. Daugulis, Organometallics 32 (2013) 5136–5143,
doi:10.1021/om400704h; (c) O.S. Trofymchuk, D.V. Gutsulyak, C. Quintero,
M. Parvez, C.G. Daniliuc, W.E. Piers, R.S. Rojas, Organometallics 32 (2013) 7323–
7333, doi:10.1021/om400847b.
[15] (a) Z. Guan, P.M. Cotts, E.F. McCord, S.J. McLain, Science 283 (1999) 2059–2062,
doi:10.1126/science.283.5410.2059; (b) A. Xiao, L. Wang, Q. Liu, H. Yu, J. Wang,
J. Huo, Q. Tan, J. Ding, W. Ding, A.M. Amin, Macromolecules 42 (6) (2009)
1834–1837, doi:10.1021/ma802352t; (c) I.E. Soshnikov, N.V. Semikolenova,
K.P Bryliakov. A. A. Antonov, W.-H. Sun, E.P. Talsi, Organometallics 39 (2020)
3034–3040, doi:10.1021/acs.organomet.0c00395; (d) S. Chabbra, D.M. Smith,
[3] D.P. Gates, S.A. Svejda, E. Onate, C.M. Killian, L.K. Johnson, P.S. White,
M. Brookhart, Macromolecules 33 (2000) 2320–2334, doi:10.1021/ma991234.
6

L. Xu, J. Li, W. Lin et al.
Journal of Organometallic Chemistry 937 (2021) 121720
N.L. Bell, A.J.B. Watson, M. Buhl, D.J. Cole-Hamilton, B.E. Bode, Science Ad-
vances 6 (2020) 7057, doi:10.1126/sciadv.abd7057.
Polym. Chem. 56 (2018) 1269–1281, doi:10.1002/pola.29008; (c) Y. Wang, A. Vi-
gnesh, M. Qua, Z. Wang, Y. Sun, W.-H. Sun, Eur. Polym. J. 117 (2019) 254–271,
doi:10.1016/j.eurpolymj.2019.05.015; (d) Q. Zhang, R. Zhang, Y. Ma, G.A. Solana,
T. Liang, W.-H. Sun, Appl. Catal. A:Gen. 573 (2019) 73–86, doi:10.1016/j.apcata.
2019.01.016.
[16] (a) X. Hou, T. Liang, W.-H Sun, C. Redshawc, X. Chen, J. Organomet. Chem.
708 (2012) 98–105, doi:10.1016/j.jorganchem.2012.02.031; (b) X. Hou, Z. Cai,
X. Chen, L. Wang, C. Redshaw, W.-H. Sun, Dalton Trans 41 (2012) 1617–1623,
doi:10.1039/C1DT11766A; (c) S. Wang, S. Du, W. Zhang, S. Asuha, W.-H. Sun,
ChemistryOpen 4 (2015) 1–8, doi:10.1002/open.201402113.
[17] (a) L. Guo, D. Zhu, W. Zhang, M. Zada, G.A. Solan, X. Hao, W.-H. Sun, Eur.
Polym. J. 107 (2018) 315–328, doi:10.1016/j.eurpolymj.2018.09.007; (b) J. Guo,
W. Zhang, Q. Mahmood, R. Zhang, Y Sun, W.-H. Sun, J. Polym. Sci., Part A:
[18] (a) F. Huang, W. Zhang, Y. Sun, X.-Q. Hu, G.A. Solan, W.-H. Sun, New J. Chem. 40
(2016) 8012–8023, doi:10.1039/C6NJ01867J; (b) Z. Zong, Q. Yu, N. Sun, B. Hu,
Z. Shen, X.-Q. Hu, L. Jin, Org. Lett. 21 (2019) 5767–5772, doi:10.1021/acs.orglett.
9b02254.
7