2-(: N, N -Diethylaminomethyl)-6,7-trihydroquinolinyl-8-ylideneamine-Ni(ii) chlorides: Application in ethylene dimerization and trimerization

Article abstract of DOI:10.1039/d0nj04003g

A series of Ni(ii) complexes with the general formula [2-((NEt2)Me)-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 prepared using a one-pot reaction of 2-(N,N-diethylaminomethyl)-6,7-dihydroquinolin-8(5H)-one with the corresponding aniline and nickel dichloride hexahydrate. The resultant complexes were characterized using elemental analysis and FT-IR spectroscopy, while the mononuclear Ni1 and Ni3 were also the subject of single-crystal X-ray diffraction study. On activation with MMAO, the complexes Ni1-Ni6 displayed good activity in ethylene oligomerization, forming hexenes (ca. 48% 1-hexene) as the major products and exhibiting thermal stability up to 50 °C under 10 atm C2H4. When MAO was applied as the cocatalyst, lower activity was observed, but the catalyst showed higher selectivity toward ethylene dimerization. It is also worth noticing that an induction period was observed as the Ni/MAO catalysts reached their peak activity after 30 min. This journal is

Full text of DOI:10.1039/d0nj04003g

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2‐(N,N‐Diethylaminomethyl)‐6,7‐trihydroquinolinyl‐8‐
ylideneamine‐Ni(II) chlorides: application in ethylene dimerization
and trimerization
Received 00th January 20xx,
Accepted 00th January 20xx
Jiaxin Li,a,b Yanping Ma,b Xinquan Hu,a,* Zygmunt Flisak,c,* Tongling Liang, bWen‐Hua Sunb,d,
*
DOI: 10.1039/x0xx00000x
A series of Ni(II) complexes of the general formula [2‐((NEt2)Me)‐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, has been
prepared by a one‐pot reaction of 2‐(N,N‐diethylaminomethyl)‐6,7‐dihydroquinolin‐8(5H)‐one with the corresponding
aniline and nickel dichloride hexahydrate. The resultant complexes were characterized by elemental analysis and FT‐IR
spectroscopy, while the mononuclear Ni1 and Ni3 were also the subject of the single‐crystal X‐ray diffraction study. On
activation with MMAO, the complexes Ni1–Ni6 displayed good activity in ethylene oligomerization, forming hexenes (ca.
48% 1‐hexene) as the major products and revealing thermal stability up to 50 ºC under 10 atm C2H4. When MAO was
applied as a cocatalyst, lower activity was observed, but the catalyst showed higher selectivity toward ethylene
dimerization. It is also worth noticing that the induction period was observed as the Ni/MAO catalysts reached their peak
activity after 30 min.
transition‐metal complexes in catalysis, researchers turned
their attention toward the tridentate ligands, including
N,P,N[13], N,N,O[14] and N,N,N species.[15,16]
Introduction
In the recent years, a significant progress has been observed
both in the academic and industrial research on the
application of the late‐transition‐metal complexes as the
precatalysts for the ethylene polymerization.[1,2] The Shell
Higher Olefin Process (SHOP) employing the nickel catalyst was
commercialized[3] and the high activity of diimine nickel
complexes in ethylene polymerization was observed by
Brookhart group; these events initiated further comprehensive
study.[4] Exceptional activity in ethylene polymerization and
the selectivity toward α‐olefins demonstrated by the nickel
catalysts developed recently are documented in several
reviews.[5] In such systems, the predominant ligand patterns
Chart 1. Structural modifications of the 2‐iminopyridine‐
nickel(II) halide (
A)
Among the Ni(II) complexes with the nitrogen multidentate
ligands employed in ethylene oligomerization, the systems
[9]
[10]
explored include the N,N [6,7], N,O [8],P,O[8f], P,N and N,S
arrangements. In the wake of Brookhart's[11] and Gibson's[12]
discovery reporting the relevance of the five‐coordinated late‐
based on 6‐benzoxazolylpyridine derivatives (A, Chart 1) show
satisfactory activity with Et2AlCl as the cocatalyst;[17a] we have
also reported the Ni precatalysts bearing carbocyclic‐fused 2‐
iminopyridine ligands[17b]
(B, Chart 1). In the follow‐up study,
we hereby report the synthesis and characterization of the
nickel(II) complexes with the N,N,N tridentate ligand, namely
2‐(N,N‐diethylaminomethyl)‐6,7‐trihydroquinolinyl‐8‐
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.
ylideneamine (C, Chart 1). Upon activation with MAO and
c. Faculty of Chemistry, University of Opole, Oleska 48, 45‐052 Opole, Poland.
d. Key Laboratory of High‐Performance Synthetic Rubber and its Composite
Materials, Changchun Institute of Applied Chemistry, Chinese Academy of
Sciences, Changchun 130022, China
† CCDC 2005997 and 2005998 contains the supplementary crystallographic data
for complexes Ni1 and Ni3, respectively. These data can be obtained free of charge
via www.ccdc.cam.ac.uk/data_request/cif, The Cambridge Crystallographic Data
Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: +44 1223 336033.
MMAO, they show acceptable catalytic activity toward
ethylene dimerization and trimerization with high selectivity
for α‐C4. The influence of the reaction parameters on the
catalytic performance has been investigated in detail.
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Results and discussion
Synthesis and characterization
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DOI: 10.1039/D0NJ04003G
One‐pot template reaction of 2‐(N,N‐diethylaminomethyl)‐6,7‐
dihydroquinolin‐8(5H)‐one (
1
), the corresponding aniline and
NiCl2 6H2O, with o‐xylene as solvent (Scheme 1) was used to
sythesise the 2‐(N,N‐diethylaminomethyl)‐5,6,7‐
.
trihydroquinolinyl‐8‐ylideneamine‐Ni(II) chlorides of the
general formula [2‐(NEt2)Me)‐8‐{N(Ar)}C9H8N]NiCl2, where Ar =
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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. All six complexes were characterized by FT‐IR
spectroscopy and elemental analysis. In addition, crystals of
Ni1 and Ni3 were the subject of the single‐crystal X‐ray
diffraction study.
Fig. 1. ORTEP representation of Ni1 with the thermal ellipsoids
set at the 30% probability level; hydrogen atoms have been
omitted for clarity.
Scheme 1. One‐pot template synthesis of Ni1–Ni6 from 1
Crystallographic study
Single crystals of the nickel complexes Ni1 and Ni3 suitable for
the X‐ray diffraction study were obtained by a slow diffusion of
n‐hexane into the corresponding dichloromethane solutions.
The ORTEP diagrams of the molecular structures are shown in
Figs. 1–3. The selected bond lengths and angles are listed in
Table S2. The geometry of both five‐coordinated complexes
Ni1 and Ni3 is best described as a distorted trigonal bipyramid
with the nickel center surrounded by three nitrogen atoms of
the ligand and two chlorine atoms. In Ni1, the two nitrogen
atoms N(1) and N(3) occupy the axial positions and form an
angle of 101.32(5)° with the nickel atom. The N(3)–C(9) bond
length is equal 1.283(3)Å and it is smaller than the N(3)–C(11)
at 1.437(3) Å, which clearly indicates a C=N double bond. In
Ni1, the C(9)–N(3)–C(11) bond angle of 118.99(13)° is smaller
than this in Ni3 equal 122.42(18)°, which reflects the amount
of steric hindrance exerted by the aryl substituent at the imine
nitrogen atom. The Ni–N bond lengths follow the trend similar
to this observed previously for the nickel(II) and chromium(III)
complexes with bis(imino)pyridine ligands:[16] Ni(1)–N(1) >
Ni(1)–N(3) > Ni(1)–N(2). The two Ni–Cl bonds are significantly
different from each other in both complexes. The
corresponding values are equal 2.3234(6)° and 2.2445(6)° in
Ni1; 2.2893(5)° and 2.2434(4)° in Ni3, respectively. In the FT‐IR
Fig. 2. ORTEP representation of Ni3 with the thermal ellipsoids
set at the the 30% probability level. Hydrogen atoms have
been omitted for clarity.
Ethylene oligomerization
To explore the performance of 2‐(N,N‐diethylaminomethyl)‐
6,7‐trihydroquinolinyl‐8‐ylideneamine‐Ni(II)
chlorides
in
ethylene oligomerization, Ni4 was chosen as the initial
precatalyst. It was activated by four different cocatalysts,
including
modified
methylaluminoxane
(MMAO),
methylaluminoxane (MAO), ethylaluminium sesquichloride
(Et3Al2Cl3, EASC) and methylaluminium sesquichloride
(Me3Al2Cl3, MASC) in order to select the best combination. The
experiments were carried out at 30 ºC and 10 atm ethylene
pressure (Table 1), indicating that the O‐donors of
aluminoxanes are necessary to activate the nickel species.[18]
On the basis of these results, the Ni4/MMAO system was
identified as the preferred catalyst reaching the activity of 2.7
× 105 g∙mol‐1 (Ni) h‐1 and generating mainly the C6 oligomers
(95.6%). The remaining part of the product was composed of
exclusively α‐C4. The Ni4/MAO system displayed low activity of
0.8 × 105 g∙mol‐1 (Ni) h‐1 but C4 was found as the only product.
Furthermore, no oligomers were detected by the GC for the
other cocatalysts. Based on the above, MMAO and MAO were
chosen for further investigation.
spectra of Ni1–Ni6, absorption bands are seen in the range of
1590–1601 cm‐1; these are typical for the imines bound to
Ni(II).[7,15,16] The microanalytical data for the Ni1
–Ni6
complexes correspond to the LNiCl2 formula.
2 | J. Name., 2012, 00, 1‐3
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Table 1 Cocatalyst screening with Ni4 as the precatalyst[a]
Oligomer Distribution[c] (%)
Entry
Cocatalyst
Al/Ni
Activity[b]
C4/∑C
α‐C4
C6/∑C
α‐C6
8
9
1
2
3
4
MMAO
MAO
2000
2000
500
2.7
0.8
‐
4.4
100
‐
>99
95.6
41.0
>99
‐
‐
‐
‐
‐
‐
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
EASC
‐
MASC
500
‐
‐
‐
[a] General conditions: 3 μmol of Ni4, 10 atm of C2H4, 100 mL of toluene; reaction time 30 min; [b] 105 g∙mol–1 (Ni) h–1;
[c] Determined by GC and ∑C signifies the total amount of oligomers.
Table 2 Ethylene oligomerization using MMAO as a cocatalyst [a]
Oligomer Distribution[c] (%)
Entry
1
Precatalyst T, °C Al/Ni t, min Activity[b] C4/∑C α-C4 C6/∑C α-C6
Ni4
Ni4
Ni4
Ni4
Ni4
Ni4
Ni4
Ni4
Ni4
Ni4
Ni4
Ni4
Ni4
Ni4
Ni4
Ni1
Ni2
Ni3
Ni5
Ni6
30
30
30
30
30
30
20
40
50
60
40
40
40
40
40
40
40
40
40
40
1500 30
2000 30
2250 30
2500 30
2750 30
3000 30
2500 30
2500 30
2500 30
2500 30
2.2
2.7
4.2
5.5
5.0
4.6
4.2
7.7
7.7
4.5
48.0
12.6
2.5
1.3
2.8
8.0
6.2
2.2
1.7
2.1
5.0
>99 95.0
>99 95.6
>99 88.6
>99 89.7
>99 97.5
>99 96.8
>99 89.9
>99 91.5
47.8
46.0
47.1
47.0
48.2
48.5
46.0
43.9
46.9
43.8
46.9
46.4
46.4
45.0
46.9
46.5
46.8
46.3
44.0
44.5
2
4.4
3
11.4
10.3
2.5
4
5
6
3.2
7
10.1
8.5
8
9
8.1
>99
>99 92.5
>99 87.7
91.9
10
11
12
13
14
15[d]
16
17
18
19
20
7.5
2500
5
12.3
11.7
6.0
2500 15
2500 45
2500 60
2500 30
2500 30
2500 30
2500 30
2500 30
2500 30
>99 88.3
>99 94.0
>99 94.2
>99 95.5
5.8
5.0
10.6
11.7
7.3
>99
>99
89.4
88.3
>99 92.7
>99 91.3
>99 95.6
8.7
4.4
[a] General conditions: 3 μmol of precatalyst, 10 atm of C2H4, 100 mL of toluene; reaction time 30 min; [b] 105 g·mol–1 (Ni)·h–1;
[c] Determined by GC and ∑C signifies the total amount of oligomers; [d] 5 atm of C2H4.
g∙mol‐1 (Ni) h‐1 was found at at the value of 2500. Beyong this
Catalytic evaluation using MMAO
point, the activity gradually decreases (entries 1–6, Table 2).
The selectivity toward C4 displays a wide range from 2.5% to
11.4%, while the composition of α‐C4 and α‐C6 is stable with
more than 99% and less than 50%, respectively.Secondly, the
influence of temperature on oligomerization was explored
with the Al/Ni molar ratio established at 2500. The activity of
To establish the optimum reaction conditions for the
Ni/MMAO systems, the precatalyst, the Al/Ni ratio, the
reaction temperature and the oligomerization time were
varied. The results of our screening are summarized in Table 2.
Firstly, the Al/Ni ratio was varied from 1000 to 3000 with the
temperature kept at 30 °C. The highest activity of 5.5 × 105
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