Nickel(II) complexes chelated by 2,6-pyridinedicarboxamide: Syntheses, characterization, and ethylene oligomerization

Article abstract of DOI:10.1039/c6nj00559d

N,N′-Bis(2,6-R-phenyl)-2,6-pyridinedicarboxamides (L: R = Cl, L1; R = F, L2; R = H, L3; R = Me, L4; R = Et, L5; R = ⁱPr, L6) were designed as neutral ligands, and the corresponding nickel complexes LNiBr₂ (Ni1-Ni6) were synthesized a

Full text of DOI:10.1039/c6nj00559d

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DOI: 10.1039/C6NJ00559D
Journal Name
ARTICLE
Nickel(II) Complexes Chelated by 2,6-Pyridinedicarboxamide:
Syntheses, Characterization, and Ethylene Oligomerization
Jie Zhang,a Shaofeng Liu,b,* Antai Li,a Hongqi Ye,a,* Zhibo Lib
Received 00th January 20xx,
Accepted 00th January 20xx
ABSTRACT：N,N′-Bis(2,6-R-phenyl)-2,6-pyridinedicarboxamide (L: R = Cl, L1; R = F, L2; R = H, L3; R = Me, L4; R = Et, L5; R =
iPr, L6) were designed as neutral ligands, and the corresponding nickel complexes LNiBr2 (Ni1-Ni6) were synthesized as
precatalysts for ethylene oligomerization. All new ligands were fully characterized by NMR, FT-IR spectra, and elemental
analysis, while the nickel complexes were examined by FT-IR spectra and elemental analysis. The coordination mode of
ligand with nickel in complexes Ni5 and Ni6 was tridentate by O^N^O as established by single crystal X-ray diffractions. All
the nickel complexes Ni1-Ni6 were tested for ethylene oligomerization with different alkylaluminums as cocatalysts, and
diethylaluminum chloride (Et2AlCl) was proved to be the most effective. Upon activation with Et2AlCl, all nickel complexes
showed high catalytic activity (up to 7.55 × 105 g·mol-1(Ni)·h-1·atm-1) with good selectivity for α-C4.
DOI: 10.1039/x0xx00000x
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essential to sustain life, forming the peptide bonds in proteins
such as enzymes and being found in numerous natural
products as well as synthetic pharmaceutical molecules. The
1. Introduction
Ethylene oligomerization represents a topic of considerable
interest in both academia and industry since the productions
of linear α-olefins (LAO) are extensively used in the
preparation of detergents, lubricants, as well as comonomers
for the synthesis of linear low density polyethylene (LLDPE).1
Late transition metals are promising candidates for the
development of oligomerization catalysts due to their favoring
chain transfer over propagation during the catalytic cycles.2
Among them, nickel has been proved the preference for
ethylene oligomerization,3 and many systems based on this
metal have provided very intriguing catalytic results.4 The
remarkable catalytic systems include the Shell Higher Olefin
Process (SHOP)5 employing the neutral nickel complex
Ni(P,O)(PR3)R’ and Brookhart’s cationic Ni(II)-based catalysts of
amide linkages have the advantage of convenient synthesis
and high stability, and could act as chelating sites for transition
metals with various coordination modes, which makes it to be
a promising ligand and attracts much attention in coordination
chemistry.11 In the earlier work (Chart 1), we studied titanium
complexes for ethylene polymerization based on N-(2-
methylquinolin-8-yl)benzamide
benzimidazolylpyridine-2-carboxylimidate
benzimidazolylquinolin-8-yl)benzamide
(
A
),12
)
6-
13
(
B
and N-(2-
(
C
),14 in which the
amide carbonyl groups acted as anionic ligands and exhibit
bidentate O^N, monodentate O and N-coordination mode,
respectively. We also investigated titanium (
) complexes bearing the same ligand, 2-benzimidazolyl-N-
phenylquinoline-8-carboxamide.15
The amide group
D) and chromium
(
E
+ 6
the type [ArN=C(R)C(R)=NAr]MCH3 . Inspired by the
coordinated with the titanium and chromium center by anionic
oxygen and neutral oxygen, respectively. Moreover, the amide
group exhibits excellent ability to tune the electronic effect of
the catalysts due to the resonance and tautomerization (Chart
2),16 which promises it to be a suitable candidate as the ligand
pioneering research, considerable attention has been paid on
the development of new nickel complexes bearing bidentate7
and tridentate ligands8 for ethylene oligomerization and
polymerization. The key part of the development has recently
been focused on well-design of suitable ligands in order to
improve catalytic performances, and the relationships
between catalyst structure and catalytic properties were well
summarized in recent review.9
for the synthesis of metal complex catalysts. In this context,
R
R
N
R
N
N
N
N
N
N
N
O
R
N
N
Cl
Cl
Ti
Ti
Ti
O
O
The amide bond is one of the most important functional
Cp
Cl
Cp
Cl
Cp
groups in contemporary chemistry and in nature.10 It is
B
C
A
R
R
R
H
N
H
N
R
HN
N
N
N
a. Department of Chemistry and Engineering, Central South University, Changsha
410083, P. R. China. E-mail: yeslab@csu.edu.cn
N
N
N
N
N
O
O
O
O
Cr
Cl
Ti
H
Ni
R
R
Cl
Cl
b. School of Polymer Science and Engineering, Qingdao University of Science and
Technology, Qingdao 266042, P. R. China. E-mail: shaofengliu@qust.edu.cn
R
R
Cp Cl
Br
Br
This Work
E
D
†
Electronic Supplementary Information (ESI) available: CCDC 1445082 and
Chart 1. Ethylene Polymerization and Oligomerization
1445083. For crystallographic data in CIF or other electronic format see
DOI: 10.1039/x0xx00000x
Catalysts Supported by Amide Ligands.
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DOI: 10.1039/C6NJ00559D
Chart 2. (a) Amide Resonance and (b) Amide Tautomerization.
we report the convenient synthesis and characterization of a
series of nickel complexes bearing tridentate neutral N,N′-
bis(2,6-R-phenyl)-2,6-pyridinedicarboxamide ligands. The two
amide groups coordinated with Ni by neutral oxygens
confirmed by X-ray diffractions. The catalytic performances for
ethylene oligomerization under various reaction conditions
were investigated. Upon treatment with aluminum activators,
in particular with Et2AlCl, these nickel (II) complexes showed
high catalytic activities up to 7.55 × 105 g·mol-1(Ni)·h-1·atm-1
with good selectivity, which is one of the most active nickel
catalysts for ethylene dimerization. The effects of reaction
parameters and the substituents of ligands on catalytic activity
and selectivity were fully studied.
Scheme 1. Synthesis of Ligands (L1
-
L6) and Nickel complexes
(
Ni1 Ni6).
-
LNiBr2 and color is yellowish. This was confirmed by 1H NMR of
Ni5 in CD3OD (Figure S1 in ESI), in which there were no
resonances at 3.60 and 1.19 ppm for coordinated ethanol. This
was also confirmed by FT-IR experiments based on yellowish
powder sample and green crystal sample (Figure S2 and S3,
respectively, in ESI). In the spectrum of green crystal sample,
there is a strong signal over 3300 cm-1, which is corresponding
to the OH groups (from CH3OH and H2O). In contrast, this
signal was absent in the spectrum of yellowish powder sample.
In terms of FT-IR spectra of Ni complexes and ligands, the C=O
stretching frequencies in Ni complexes shifted to lower values
between 1635 and 1624 cm-1 with somewhat weaker intensity
compared with those of the corresponding free ligands (see
Experimental section). Such features were consistent with the
existence of coordination between the amide oxygen atom
and the nickel center.17
2. Results and discussion
2.1. Synthesis and Characterization of the Ligands and Complexes
With the modification of reported procedure,11c the ligands
2,6-pyridinedicarboxamide derivatives were synthesized in
high yields (Scheme 1). 2,6-Pyridinedicarboxylic acid was
quantitatively transformed to 2,6-pyridine carbonyl dichloride
in the presence of excess of thionyl chloride, which directly
reacted with 2,6-disubstituted aniline to form the
corresponding ligands. All ligands were confirmed by FT-IR and
1H and 13C NMR spectroscopy as well as by elemental analysis.
2.2. Crystal Structures
Single crystals of Ni5 and Ni6 were grown by diffusing diethyl
ether into their methanol solution and ethanol solution,
respectively. Ni5·CH3OH·2H2O and Ni6·3C2H5OH possessed
distorted octahedral coordination geometry around the Ni
center, as shown in Figure 1 and 2 with the selected bond
lengths and angles. The octahedral geometry around the Ni
center was formed by one N atom of pyridine, two O atoms of
amide groups, two O atoms of coordinated solvent molecular
(methanol and water in Ni5·CH3OH·2H2O and two ethanol in
Ni6·3C2H5OH), and one Br atom. The other Br atom was
displaced from its coordinated site and acted as a counterion,
which was also found for the previous reported Ni and Cr
complexes.8e, 17 In Ni5·CH3OH·2H2O the tridentate ligand was
situated around the Ni center in a meridional manner (O^N^O)
and the two chelating rings (Ni1-O1-C11-C12-N2, Ni1-O2-C17-
C16-N2) were coplanar. The nickel atom (Ni1) and the mutually
trans-disposed bromide (Br1) and oxygen (O3) of coordinated
methanol were almost in one line [Br1-Ni1-O3 = 178.34(14)°]
with N2, O1, O2, and O4 atoms located in the equatorial plane.
The plane of amide groups was almost coplanar with the
pyridine ring (2.68°), while the phenyl ring on the nitrogen was
perpendicular to this pyridine ring (88.79°) and the
coordination plane (89.40°), which was similar to that
observed in nickel dibromide complexes ligated by α-dimine
and bis(arylimino)pyridyl.6, 18 The C-O bond (C11-O1 = 1.252(7)
Å) was slightly longer than the characteristic C=O bond (1.19-
The nickel complexes Ni1-Ni6 were prepared by mixing
NiBr2·6H2O with 1 equiv. of the corresponding ligands in
ethanol at room temperature (Scheme 1). The yellowish nickel
complexes were precipitated from the solutions by adding
diethyl ether and were collected by filtration, washed with
diethyl ether, and dried under vacuum overnight. All nickel
complexes were isolated as air-stable yellowish powders in
high yields and characterized by FT-IR spectra, elemental
analysis and NMR (see experimental section and ESI), which
were in agreement with the formula LNiBr2. Note that the
nickel complexes prepared by this method and also used in the
catalytic test (yellowish powder) contained no coordinated
solvents as indicated by elemental analysis, although
coordinated solvent molecules were found in the crystal
structures of Ni5 and Ni6 (see Crystal Structures section). The
Ni complexes in MeOH or EtOH solutions are probably cationic
complexes, similar as ones in solid state as shown by X-ray
diffractions, due to solvent molecules coordinated. Howerver,
the coordinated solvent molecules were ready to lose under
vacuum to give the neutral compounds, of which formula is
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Table 1. Effect of cocatalysts on ethylene reactivity with Ni5a
.
View Article Online
DOI: 10.1039/C6NJ00559D
oligomers
distribution (%)d
entry
cocat.
MAO
Al/Ni activityb
TONc
C4/ΣC α-C4 C6/ΣC
1
2
3
4
1500
4.42
4.15
70.3
14.7
7900
7400
98.9
98.2
98.9
97.1
90.1
92.0
72.0
75.0
1.1
1.8
1.1
2.9
MMAO 1500
Et2AlCl
EtAlCl2
200
200
125000
26200
aConditions: 5 μmol Ni5; 10 atm of ethylene; 20
°
C, 30 min,
toluene (total volume 100 mL). b104 g·mol-1(Ni)·h-1·atm-1.
cTurnover number = mol of ethylene consumed/mol of Ni
catalyst. dDetermined by GC.
complex catalysts. The coordination geometry around Ni in
Ni6·3C2H5OH was similar as that in Ni5·CH3OH·2H2O and the
only difference was that the coordinated solvent molecular
were two ethanol.
Figure 1. ORTEP of the molecular structure of Ni5·CH3OH·2H2O.
Ellipsoids at 50% probability level. Hydrogen atoms and one
H2O molecular uncoordinated were omitted for clarity.
Selected distances (Å) and angles (deg): Ni1-Br1 2.5132(10),
Ni1-O1 2.110(4), Ni1-O2 2.138(4), Ni1-O3 2.097(4), Ni1-O4
2.3. Ethylene Oligomerization
2.019(4), Ni1-N2 1.992(5), C11-O1 1.252(7), C17-O2 1.253(7), Activated by methylaluminoxane (MAO) or MMAO, Ni5
C11-N1 1.322(7), C17-N3 1.323(7); O1-Ni1-N2 78.53(17), O2- showed moderate activities for ethylene oligomerization
Ni1-N2 77.26(16), O1-Ni1-O4 97.17(18), O2-Ni1-O4 106.86(18), (entrie 1 and 2, Table 1). However, when diethylaluminum
O1-Ni1-O2 155.53(15), N3-Ni1-O4 175.11(19), Br1-Ni1-O3 chloride (Et2AlCl) or ethylaluminum dichloride (EtAlCl2) were
178.34(14).
used as the activators, the catalytic activities were an order of
magnitude higher (Table 1) with relatively lower selectivity for
α-olefins, which was also observed for other tridentate nickel
systems.19 In particular, Ni5/Et2AlCl system showed the highest
activity (7.03 × 105 g·mol-1(Ni)·h-1·atm-1), which was 16× higher
as compared to that of Ni5/MAO system (entry 1 vs entry 3,
Table 1). Based on the results observed for complex Ni5
Et2AlCl was selected as the cocatalyst for further investigation.
2.3.1. Effects of the Ratio of Et2AlCl, Reaction Temperature
and Time on Catalytic Behavior
,
The effects of the reaction parameters (Al/Ni, reaction
temperature and time) on the catalytic activities were
investigated with complex Ni5 and the results were
summarized in Table 2. Both Al/Ni and temperature
significantly affected the catalytic performance (activity and
distribution of oligomers). Initial experiments tested the Al/Ni
molar ratio (100 to 300) at 20 °C for 30 min. The catalytic
activities reached the optimum value of 7.03 × 105 g·mol-
1(Ni)·h-1·atm-1 with the Al/Ni ratio of 200 (entry 3 in Table 2),
which is much higher than well known bidentate α-diimine Ni
catalysts (1.36 × 105 g·mol-1(Ni)·h-1·atm-1; 35 oC, 28 atm and 60
min),20 trihydroquinolin-amino Ni catalysts (4.54 × 105 g·mol-
1(Ni)·h-1·atm-1; 20 oC, 10 atm and 30 min)21 and tridentate
pyridyl-quinolin-amine Ni catalysts (0.66 × 105 g·mol-1(Ni)·h-
Figure 2. ORTEP of the molecular structure of Ni6·3C2H5OH.
Ellipsoids at 50% probability level. Hydrogen atoms and one
free C2H5OH molecular uncoordinated were omitted for clarity.
Selected distances (Å) and angles (deg): Ni1-Br1 2.5144(10),
Ni1-O1 2.093(4), Ni1-O2 2.125(4), Ni1-O3 2.123(4), Ni1-O4
2.018(4), Ni1-N2 1.976(4), C1-O1 1.246(6), C7-O2 1.246(6), C1-
N1 1.341(7), C7-N3 1.332(6); O1-Ni1-N2 78.58(16), O2-Ni1-N2
77.75(16), O1-Ni1-O4 100.63(16), O2-Ni1-O4 102.34(16), O1-
Ni1-O2 154.91(15), N2-Ni1-O4 175.65(18), Br1-Ni1-O3
175.70(12).
1.23 Å), indicating partial electron donation by oxygen to the
central metal, but this was shorter than the C-O single bond
(1.42-1.46 Å). Similar phenomena were also observed in our
other reported chromium systems containing the amide group
as a neutral ligand.17 Moreover, The C11-N1 bond length
(1.322(7) Å) was shorter than a typical C-N single bond (1.33-
1.36 Å) in free amide linkages but longer than a C=N double
bond (1.26-1.29 Å), indicating the resonance and
tautomerization features of the amide group due to
coordination with metal center.16 These features endue the
amide group with the advantage of tuning electronic effect
and make it to be a suitable candidate as the ligand for metal
o
1·atm-1; 20 C, 10 atm and 20 min).8e This catalyst exhibited
high activity and represented a unique characteristic for
ethylene oligomerization, in particular, considering its
convenient synthesis. Upon further increasing the Al/Ni ratio, a
slight decrease of the catalytic activity and the selectivity for α-
C4 was observed. Besides the Al/Ni ratio, the reaction
temperature also affected the catalytic activity and selectivity.
Generally, increasing the reaction temperature could lead to a
significant decrease in activity for nickel catalysts,8e, 22 owing to
the decomposition of the active species and lower ethylene
solubility at higher temperature. In the case of current
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Table 2. Ethylene Oligomerization of the Ni5/Et2AlCl Systema.
Table 3. Ethylene Oligomerization of the NiV1ie-wNAi6rt/icEletO2AnlliCnel
Systema.
DOI: 10.1039/C6NJ00559D
oligomers
T
t
distribution (%)c
Oligomers distribution (%)c
entry Al/Ni
activityb
(°C) (min)
entry Cat.
R
activityb
C4/ΣC α-C4 C6/ΣC
C4/ΣC
98.3
96.8
98.8
98.9
98.9
99.0
α-C4
82.4
76.0
67.2
67.4
72.0
77.2
C6/ΣC
1.7
3.2
1.2
1.1
1
2
3
4
5
6
7
8
9
100
150
200
250
300
200
200
200
200
20
20
20
20
20
50
80
20
20
30
30
30
30
30
30
30
15
60
4.73
5.93
7.03
6.38
5.84
4.24
1.65
7.70
5.93
100
84.9
-
1
2
3
4
5
6
Ni1 Cl
Ni2
Ni3
1.27
1.08
2.18
98.5
98.9
98.7
98.7
99.3
96.8
99.0
98.5
79.2 1.5
72.0 1.1
60.7 1.3
61.0 1.3
68.9 0.7
68.4 3.2
72.4 1.0
67.2 1.5
F
H
Ni4 Me 5.76
Ni5 Et 7.03
1.1
1.0
Ni6 iPr 7.55
aConditions: 5 μmol metal complex; 10 atm of ethylene; 20
°
C,
30 min, toluene (total volume 100 mL). In units of 105 g·mol-
b
1(Ni)·h-1·atm-1. cDetermined by GC.
aConditions: 5 μmol Ni5; 10 atm of ethylene; toluene (total
volume 100 mL). bIn units of 105 g·mol-1(Ni)·h-1·atm-1.
cDetermined by GC.
catalytic system, although the similar tendency was observed
for complex Ni5, the activities at high temperature still
remained excellent. Note that even at 80 °C the activity was as
high as 1.65 × 105 g·mol-1(Ni)·h-1·atm-1 (entry 7 in Table 2),
indicating the title nickel complexes had relatively good
thermal stability. Moreover, the selectivity for α-C4 decreased
slightly at elevated temperature, indicating that isomerization
was favorable at higher temperature. The stability of catalytic
system with time was investigated at 15 min, 30 min and 60
min. Note that from 15 min to 30 min the catalytic system
exhibited excellent stability in the terms of activity and
selectivity for α-C4 (entry 8 vs entry 3 in Table 2). With the
reaction time extending to 60 min, the activities decreased
from 7.70 × 105 g·mol-1(Ni)·h-1·atm-1 (entry 8 in Table 2) to 5.93
× 105 g·mol-1(Ni)·h-1·atm-1 (entry 9 in Table 2), meantime the
selectivity also decreased slightly.
Figure 3. Effect of the nature of the complexes on ethylene
reactivity (Table 3).
deactivation. In addition, the bulkier substituents enhanced
the solubility of the complexes. As far as the selectivity for α-C4
of the product, both of electon-withdrawing effect and bulky
steric effect leaded to higher selectivity due to the depression
of isomerization (Figure 3, red).
2.3.2. Effect of the Nature of the Complexes on Their Catalytic
Activities
3. Conclusions
A series of stable and conveniently synthetic (O^N^O) ligands,
N,N′-bis(2,6-R-phenyl)-2,6-pyridinedicarboxamide derivatives
Employing the optimum reaction conditions selected by using
complex Ni5 (molar ratio of Et2AlCl/Ni = 200, temperature =
20 °C, 30 min and 10 atm ethylene), Ni1-Ni6 displayed high
(
L1
-
L6), were prepared, and used as neutral ligands to form the
Ni1 Ni6). All Ni(II) complexes were
nickel complexes
(
-
catalytic activities and the results were summarized in Table 3.
The substituents had remarkable influence on both of the
activity and selectivity for α-C4, which was also observed for
other tridentate catalytic nickel systems.19, 22-23 In Table 3 and
Figure 3, the complexes Ni1 and Ni2 bearing R as halides (Cl
and F) showed much lower activity (blue) but higher selectivity
for α-C4 (red) of the product as compared to Ni5, suggesting
that electron withdrawing substituent R was not favorable for
better catalytic activities but could depress the isomerization.
The highest activity was obtained for complex Ni6 (R = iPr) with
7.55 × 105 g·mol-1(Ni)·h-1·atm-1 (entry 6 in Table 3 and Figure 3),
then followed by complex Ni5 (R = Et), Ni4 (R = Me) and Ni3 (R
= H), suggesting the bulkier substituents would lead to
increase in the catalytic activity of the nickel complexes. This is
also consistent with the phenomenon observed for Ni1 (R = Cl)
and Ni2 (R = F). It was believed that the active species with less
bulky substituents were exposed to not only ethylene but also
other reactants (impurities), and this resulted in the
characterized by elemental and spectroscopic analysis along
with X-ray crystallographic analysis for the representative
complex Ni5 and Ni6. Upon treatment with Et2AlCl, these
nickel (II) complexes showed high catalytic activities of up to
7.55 × 105 g·mol-1(Ni)·h-1·atm-1. Both of the electron-donating
and bulky R-substituents on the N-aryl ring significantly
exerted positive effects on the catalytic activities. Thus, their
catalytic activities varied in the order of Ni1 (with iPr
substituents)
＞
Ni2 (with Et)
＞Ni3 (with Me) ＞Ni4 (with H)
＞
Ni6 (with Cl)
＞Ni5 (with F).
4. Experimental
4.1. General Considerations
All manipulations of air and/or moisture sensitive compounds
were performed under N2 using standard Schlenk techniques.
Toluene was dried over sodium-benzophenone under N2.
Methylaluminoxane (MAO, a 1.46 M solution in toluene),
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modified methylaluminoxane (MMAO, 1.93 M in heptane), General Procedure: A solution of NiBr2·6H2O inVeietwhAarnticolelOwnlianes
diethylaluminum chloride (Et2AlCl, 1.7 M in toluene) and other added to a solution of the correspondingDlOigIa: 1n0d.10in39e/tCh6aNnJo00l.5T5h9De
reagents were purchased from Akzo Nobel Corp., Acros reaction mixture was stirred at room temperature for 12 h and
Chemicals, Aladdin or Aldrich. FT-IR spectra were performed diethyl ether was added to form a precipitate. The resulted
on a Perkin-Elmer System 2000 spectrometer or Bruker Tensor precipitate was collected, washed with diethyl ether, and dried
27 instrument. H NMR and 13C NMR spectra were performed under vacuum overnight.
on a Bruker DMX 500 instrument. Elemental analysis was Ni1: yellowish powder in 84%. H NMR (500 MHz, CD3OD) δ:
1
1
tested with a Flash EA 1112 microanalyzer. GC analysis was 8.41 (br, 2 H, py), 8.26 (br, 1 H, py), 7.48 (br, 4 H, Ph), 7.32 (br,
recorded on Varian CP-3800 equipped with a flame ionization 2 H, Ph). 13C NMR (125 MHz, CD3OD) δ: 164.32, 158.25, 147.95,
detector and a 30 m CP-Sil 5 CB column.
4.2. Syntheses and Characterization of the Ligands L1-L6
141.03, 129.56, 126.77, 114.30, 112.46. FT-IR (KBr disk, cm-1):
3270 (s), 1630 (s), 1590 (m), 1548 (s), 1496 (m), 1447 (s), 1334
(m), 1242 (m), 1157 (w), 1144 (w), 1079 (m), 999 (m), 782 (s),
755 (s), 737 (m), 722 (s), 749 (m), 688 (w), 507 (m). Anal. Calcd
for C19H11Br2Cl4N3NiO2: C, 33.88; H, 1.65; N, 6.24. Found: C,
33.75; H, 1.78; N, 6.20.
4.2.1. N,N′-Bis(2,6-dichlorophenyl)-2,6-pyridinedicarboxamide (L1)
The ligand was synthesized through
a modification of
publication procedure.11c 2,6-Pyridinedicarboxylic acid (1.67 g,
10 mmol) and thionyl chloride (20 mL) were added to a 100 mL
flask under nitrogen. The reaction mixture was refluxed with
stirring for 24 h. The excess of thionyl chloride was removed in
1
Ni2: yellowish powder in 81%. H NMR (500 MHz, CD3OD) δ:
8.05 (br, 2 H, py), 7.90 (br, 1 H, py), 7.00 (br, 2 H, Ph), 6.71 (br,
4 H, Ph). 13C NMR (125 MHz, CD3OD) δ: 164.01, 158.33, 148.84,
140.62, 129.42, 126.31, 114.32, 112.25. FT-IR (KBr, cm-1): 3387
(s), 3084 (w), 1635 (s), 1598 (m), 1527 (s), 1473 (s), 1292 (w),
1244 (m), 1155 (w), 1076 (w), 1014 (s), 949 (m), 904 (w), 837
(w), 784 (s), 760 (w), 705 (w), 646 (w). Anal. Calcd for
C19H11Br2F4N3NiO2: C, 37.55; H, 1.82; N, 6.91. Found: C, 37.83;
H, 1.95; N, 7.02.
vacuum, and
dichloride was obtained. The residue was dissolved in 20 mL
CH2Cl2, followed by an addition of solution of 2,6-
dichloroaniline (20 mmol, 3.24 g) and triethylamine (3.03 g, 30
mmol) in dichloromethane (20 mL) at 0 C. The resulted
a white residue of 2,6-pyridine carbonyl
a
°
reaction mixture was refluxed overnight. All the volatiles were
removed in vacuum and the residue was washed successively
with water and CH2Cl2 to give a white solid (3.60 g, 7.92 mmol,
79.2% yield). 1H NMR (500 MHz, CDCl3) δ: 9.41 (br, 2 H, N-H),
8.56 (d, J = 7.8 Hz, 2 H, py), 8.20 (t, J = 7.8 Hz, 1 H, py), 7.45 (d,
J = 8.1 Hz, 4 H, Ph), 7.26 (t, J = 8.1 Hz, 2 H, Ph). 13C NMR (125
MHz, CDCl3) δ: 161.15 (s), 148.09 (s), 139.53 (s), 133.38 (s),
131.60 (s), 128.67 (s), 128.54 (s), 126.20 (s). Anal. Calcd for
C19H11Cl4N3O2: C, 50.14; H, 2.44; N, 9.23. Found: C, 50.18; H,
2.27; N, 9.16. FT-IR (KBr, cm-1): 3302 (s), 3084 (w), 1680 (s),
1569 (m), 1506 (s), 1455 (s), 1306 (m), 1274 (w), 1224 (w),
1197 (m), 1130 (m), 1101 (m), 1000 (m), 951 (m), 909 (s), 832
(w), 784 (s), 749 (m), 709 (m), 659 (m).
1
Ni3: yellowish powder in 88%. H NMR (500 MHz, CD3OD) δ:
8.43 (d, J = 7.1 Hz, 2 H, py), 8.22 (t, J = 7.1 Hz, 1 H, py), 7.77 (d,
J = 7.5 Hz, 4 H, Ph), 7.39 (t, J = 7.5 Hz, 4 H, Ph), 7.17 (t, J = 7.5
Hz, 2 H, Ph). 13C NMR (125 MHz, CD3OD) δ: 164.05, 148.99,
140.71, 135.60, 134.75, 128.80, 128.11, 126.12. FT-IR (KBr disk,
cm-1): 3270 (s), 1629 (s), 1590 (m), 1545 (s), 1499 (m), 1448 (s),
1335 (m), 1246 (m), 1134 (m), 1079 (m), 1002 (m), 905 (m),
848 (m), 758 (s), 737 (m), 687 (s), 505 (m). Anal. Calcd for
C19H15Br2N3NiO2: C, 42.59; H, 2.82; N, 7.84. Found: C, 42.88; H,
2.97; N, 7.56.
1
Ni4: yellowish powder in 90%. H NMR (500 MHz, CD3OD) δ:
8.37 (br, 2 H, py), 8.21 (br, 1 H, py), 7.09 (br, 6 H, Ph), 2.22 (s,
12 H, Me). 13C NMR (125 MHz, CD3OD) δ: 164.16, 149.86,
4.2.2. N,N′-Bis(2,6-fluorophenyl)-2,6-pyridinedicarboxamide (L2)
Using the above procedure, N,N′-bis(2,6-fluorophenyl)-2,6- 140.78, 136.67, 134.89, 128.86, 128.30, 126.15, 18.20. FT-IR
pyridinedicarboxamide was prepared in 78.5% yield (3.05 g, (KBr disk, cm-1): 3180 (s), 3054 (m), 1630 (s), 1583 (m), 1536 (s),
1
7.85 mmol). H NMR (500 MHz, CDCl3) δ: 9.29 (br, 2 H, N-H), 1475 (m), 1327 (m), 1284 (w), 1218 (w), 1155 (w), 1034 (m),
8.53 (d, J = 7.8 Hz, 2 H, py), 8.16 (t, J = 7.8 Hz, 1 H, py), 7.32- 952 (m), 874 (w), 836 (w), 780 (m), 756 (w), 709 (w), 622 (w).
7.20 (m, 2 H, Ph), 7.01 (t, J = 8.2 Hz, 4 H, Ph). 13C NMR (125 Anal. Calcd for C23H23Br4N3NiO2: C, 46.67; H, 3.92; N, 7.10.
MHz, CDCl3) δ: 161.25 (s), 158.54 (s), 156.80 (s), 148.06 (s), Found: C, 46.55; H, 3.71; N, 7.03.
139.18 (s), 127.86 (s), 126.09 (s), 111.75 (d). Anal. Calcd for Ni5: yellowish powder in 88%. 1H NMR (500 MHz, CD3OD) δ:
C19H11F4N3O2: C, 58.62; H, 2.85; N, 10.79. Found: C, 58.56; H, 8.41 (d, J = 7.6 Hz, 2 H, py), 8.26 (t, J = 7.5 Hz, 1 H, py), 7.24 (t, J
3.07; N, 10.30. FT-IR (KBr, cm-1): 3262 (s), 3102 (w), 1678 (s), = 7.4 Hz, 2 H, Ph), 7.17 (d, J = 7.4 Hz, 4 H, Ph), 2.63 (q, J = 7.3 Hz,
1623 (w), 1599 (m), 1525 (s), 1470 (s), 1439 (w), 1290 (m), 8 H, CH2), 1.17 (t, J = 7.4 Hz, 12 H, CH3). 13C NMR (125 MHz,
1243 (s), 1138 (m), 1072 (m), 1016 (s), 898 (m), 843 (m), 783 CD3OD) δ: 164.82, 149.73, 142.49, 140.34, 133.47, 129.45,
(s), 760 (m), 706 (m), 677 (w), 646 (w).
N,N′-phenyl-2,6-pyridinedicarboxamide
127.04, 125.78, 25.40, 14.77. FT-IR (KBr disk, cm-1): 3168 (s),
(
L3),24 N,N′-bis(2,6- 3045 (m), 1624 (s), 1580 (m), 1538 (s), 1463 (m), 1376 (w),
dimethylphenyl)-2,6-pyridinedicarboxamide
bis(2,6-diethylphenyl)-2,6-pyridinedicarboxamide
N,N′-bis(2,6-diisopropylphenyl)-2,6-pyridinedicarboxamide
(
L4),25
N,N′- 1321 (m), 1283 (w), 1153 (w), 1037 (m), 953 (m), 841 (w), 809
and (w), 762 (m), 722 (w), 622 (m). Anal. Calcd for C27H31Br2N3NiO2:
26
(
L5)
C, 50.04; H, 4.82; N, 6.48. Found: C, 50.41; H, 4.62; N, 6.19.
27
1
(
L6)
were prepared using the above procedure and Ni6: yellowish powder in 86%. H NMR (500 MHz, CD3OD) δ:
confirmed by NMR in according with the literature reports.
4.3. Synthesis of Nickel Complexes
8.36 (d, J = 6.8 Hz, 2 H, py), 8.21 (t, J = 6.8 Hz, 1 H, py), 7.26 (t, J
= 7.1 Hz, 2 H, Ph), 7.19 (d, J = 7.2 Hz, 4 H, Ph), 3.17-3.05 (m, 4 H,
CH), 1.14 (d, J = 6.1 Hz, 24 H, CH3). 13C NMR (125 MHz, CD3OD)
This journal is © The Royal Society of Chemistry 20xx
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δ: 161.24, 149.96, 147.24, 140.67, 132.09, 129.10, 126.20, and P. Lutz, Dalton Trans., 2007, 515-528; (d) Y. Chen, G. Wu and
View Article Online
124.10, 29.59, 23.71. FT-IR (KBr disk, cm-1): 3191 (s), 3047 (w), G. C. Bazan, Angew. Chem., Int. Ed., 2005,DOI: 10.1039/C6NJ00559D
44, 1108-1112.
2964 (m), 1626 (s), 1581 (m), 1538 (s), 1463 (m), 1324 (m), 5. W. Keim, A. Behr, B. Gruber, B. Hoffmann, F. H. Kowaldt, U.
1285 (w), 1218 (w), 1153 (w), 1037 (m), 955 (m), 838 (w), 799 Kuerschner, B. Limbaecker and F. P. Sistig, Organometallics,
(m), 759 (w), 726 (m), 622 (w). Anal. Calcd for C31H39Br2N3NiO2: 1986, 5, 2356-2359.
C, 52.88; H, 5.58; N, 5.97. Found: C, 53.05; H, 5.29; N, 5.77.
4.4. X-ray Crystallographic Studies
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Ethylene oligomerizations were carried out in a 500 mL
stainless steel autoclave. The nickel complex was loaded in a
Schlenk tube, and 50 mL of toluene and the desired amount of
Et2AlCl were added. This mixture and another 50 mL toluene
were added into the autoclave under ethylene atmosphere.
When the desired temperature was reached, 10 atm of
ethylene was introduced to start the reaction. After the
reaction, a small amount of the reaction solution was collected,
ceased with 5% aqueous hydrogen chloride and analyzed by
GC. The yields of oligomers were calculated by referencing
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Acknowledgements
The acknowledgements come at the end of an article after the
conclusions and before the notes and references. The project
was supported by the Natural Science Foundation of China
(NSFC, Grant No. B040102) and Department of Science and
Technology of Qingdao and Shandong Province No 159181jch
and 2015GGX107015.
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Table of Contents
Ni(II) complexes chelated by a neutral tridentate amide ligand are conveniently
prepared and highly active for ethylene oligomerization.