- Email: [email protected]
Nickel complexes incorporating pyrazole-based ligands for ethylene dimerization to 1-butylene
Accepted Manuscript Nickel Complexes Incorporating Pyrazole-Based Ligands for Ethylene Dimerization to 1-Butylene Tao Wang, Bo Dong, Yan-Hui Chen, Guo-Liang Mao, Tao Jiang PII:
S0022-328X(15)00253-3
DOI:
10.1016/j.jorganchem.2015.04.041
Reference:
JOM 19027
To appear in:
Journal of Organometallic Chemistry
Received Date: 30 December 2014 Revised Date:
25 February 2015
Accepted Date: 6 April 2015
Please cite this article as: T. Wang, B. Dong, Y.-H. Chen, G.-L. Mao, T. Jiang Nickel Complexes Incorporating Pyrazole-Based Ligands for Ethylene Dimerization to 1-Butylene, Journal of Organometallic Chemistry (2015), doi: 10.1016/j.jorganchem.2015.04.041. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
ACCEPTED MANUSCRIPT
Graphical Abstract
Nickel Complexes Incorporating Pyrazole-Based Ligands for Ethylene Dimerization to 1-Butylene
RI PT
Tao Wang a, Bo Dong a, Yan-Hui Chen a, Guo-Liang Mao b, Tao Jiang a, b,∗
AC C
EP
TE D
M AN U
SC
The nickel complexes with MAO, EADC or DEAC showed moderate activity for ethylene dimerization toward 1-C4. The catalysts showed higher catalytic activity with DEAC than other cocatalysts. The catalysts give the highest selectivity when MAO use as cocatlyst.
ACCEPTED MANUSCRIPT
Graphical Abstract
Nickel Complexes Incorporating Pyrazole-Based Ligands for Ethylene Dimerization to 1-Butylene
RI PT
Tao Wang a, Bo Dong a, Yan-Hui Chen a, Guo-Liang Mao b, Tao Jiang a, b,∗
AC C
EP
TE D
M AN U
SC
Ni complexes incorporating pyrazole-based ligands with different co-catalyst for ethylene dimerization.
ACCEPTED MANUSCRIPT
Nickel Complexes Incorporating Pyrazole-Based Ligands for Ethylene Dimerization to 1-Butylene Tao Wang a, Bo Dong a, Yan-Hui Chen a, Guo-Liang Mao b, Tao Jiang a, b, ∗1 a
College of Material Science and Chemical Engineering, Tianjin University of Science & Technology, Tianjin
RI PT
300457, China b
College of Chemistry and Chemical Engineering, Northeast Petroleum University, Daqing 163318, China
SC
Abstract
In this study we synthesized and characterized bis(3,5-dimethylpyrazolyl)dimethylsilane (L1) and by
reacting
L1
or
L2
with
M AN U
bis(3,5-dimethylpyrazolyl)phenylphosphine (L2) and then prepared bidentate (N^N) nickel complexes NiBr2(DME).
In
combination
with
methylaluminoxane,
diethylchloroaluminum or ethyldichloroaluminum (EADC) as co-catalyst, L1/Ni and L2/Ni complexes exhibited moderate catalytic activities (240-1310 kg/molNi·h) and high selectivities (up to 93.2%) for ethylene dimerization toward 1-butylene. The catalytic performance was substantially affected by the co-catalyst type and ligand environment, especially the bridge atom.
AC C
EP
TE D
Keywords: Ethylene oligomerization; 1-Butylene; Pyrazole; Nickel complexes
Corresponding author. E-mail address: [email protected]. Fax: +86-22-60602936; Tel: +86-22-60601230.
1
ACCEPTED MANUSCRIPT 1. Introduction Linear α-olefins are normally used for the preparation of branched polyethylene and other chemicals, such as detergents, synthetic lubricants and plasticizer alcohols. Oligomerization of ethylene to linear α-olefin have played an important role in the industrial process. Ethylene dimerization and oligomerization reactions were typically carried out using homogeneous late-transition-metal catalysts, particularly nickel-based catalysts [1-6]. A number of selective ethylene dimerization catalysts based on
RI PT
nickel complexes have been extensively studied and developed [7-9]. Nickel complexes that based on various chelating-ligand topologies were studied most frequently [10-14]. Besides the choice of the metal center, the desired catalytic selectivity can be tuned by designing ancillary ligands with the desired structural and electronic properties to assist the generation and stabilization of active species for selective ethylene oligomerization [15-18]. Usually, pyrazole-based ligands are used as either terminal or bridging ligands with bidentate chelation at each metal center. Currently, pyrazole ligands
SC
research mainly focus on bridging pyrazole atoms (such as carbon, silicon and boron on bridging the bridge bidentate or tridentate ligands) or changing the substituents of the ligands. It will change the space structure of ligand, coordination ability and influence the metal central atoms, changing the
M AN U
catalytic performance [19-21]. Oliveira and his coworkers have reported that the tridentate catalyst which was formed with pyrazol ligand (NNN or NSN) and Ni gave high activity and selectivity for ethylene dimerization to 1-butene. They also found that changing the substituent of pyrazole would change the catalyst performance effectively, increasing the electronic properties of substituents could effectively increase the activity of the catalyst [22]. Ainooson and his coworkers reported that catalysts that consisted of 3,5-dimethyl pyrazole bidentate ligands with iron, cobalt, nickel or palladium in the ethylene oligomerization showed different catalytic activities. The nickel complexes with
TE D
ethyldichloroaluminum (EADC) possessed the highest catalytic activity and selectivity for the ethylene oligomerization to butenes and hexenes [23]. We are interested in the design of new pyrazole ligands used in Ni-based catalysts for ethylene dimerization to 1-butylene with high catalytic activity, selectivity and long lifetime. Like S, C and B atom, phosphine or silicon were often used in the design of novel ligands as connecting heteroatoms[24]. However, corresponding bidentate pyrazole ligands
EP
featuring Si and P bridging atoms have never been explored previously in conjunction with transition metals for preparing catalysts used for ethylene oligomerization. Herein, we report the synthesis and characterization of nickel complexes with bidentate
AC C
bis(3,5-dimethylpyrazolyl)dimethylsilane (L1) or bis(3,5-dimethylpyrazolyl)phenylphosphine (L2) ligands, as well as their catalytic behavior for ethylene dimerization toward 1-butene. We also discuss the effects of the reaction temperature, the Al-to-Ni molar ratio and the co-catalysts types on the catalytic activity and selectivity of these complexes.
2. Experimental 2.1 Materials
3,5-Dimethylpyrazole, dichlorodimethylsilane, dichlorophenylphosphine, n-butyllithium (2.4 mol/L in hexanes), and NiBr2(DME) were purchased from Aldrich and used as received. Polymerization-grade ethylene was obtained from Tianjin Summit Specialty Gases (China). Methylaluminoxane (MAO, 1.4 mol/L in toluene), diethylchloroaluminum (DEAC, 1.4 mol/L in toluene), EADC (1.4 mol/L in toluene), triethylaluminum (TEAL, 1.4 mol/L in toluene), trimethylaluminium (TMAL, 1.4 mol/L in toluene), triisobutylaluminium (TIBA, 1.4 mol/L in toluene) were purchased from Albemarle (USA). Toluene, tetrahydrofuran (THF), dichloromethane and 2
ACCEPTED MANUSCRIPT n-hexane were dried and degassed prior to use. 2.2 Synthesis of ligands All air- and/or water-sensitive reactions were conducted under a dry N2 atmosphere in oven-dried flasks using standard Schlenk techniques or in a glove box. 2.2.1 Bis(3,5-dimethylpyrazolyl)dimethylsilane (L1) 2.4 M n-BuLi solution in hexanes (0.44 mL, 1.05 mmol) was added dropwise to a solution of
RI PT
3,5-dimethylpyrazole (96.1 mg, 1.0 mmol) in n-hexane (50 mL) at –78 °C. The mixture was stirred for 4 h, resulting in a light-yellow cloudy solution. Dichlorodimethylsilane (60.28 µL, 0.5 mmol) was added to the above solution, and then the mixture was stirred for 24 h. The precipitated LiCl salt was filtered off and the filtrate was concentrated to give a white residue. Recrystallization (benzene/n-hexane) provided L1 in 90% yield. 1H NMR (δ, ppm, CDCl3, TMS): 0.939 (s, 6H, CH3Si), 1.890 (s, 6H, (CH3)2pz), 2.250 (s, 6H, (CH3)2pz), 5.869 (s, 2H, H-4 in (CH3)2pz). 13C NMR (δ, ppm, 2.2.2 Bis(3,5-dimethylpyrazolyl)phenylphosphine (L2)
SC
CDCl3): 1.65, 16.11, 17.88, 27.52, 28.55, 108.58, 109.88, 136.62, 137.49, 145.81, 147.07.
M AN U
Triethylamine (3.05 mL, 22 mmol) was added to a solution of 3,5-dimethylpyrazole (1.9226 g, 20 mmol) in THF (100 mL). Then dichlorophenylphosphine (1.4 mL, 10 mmol) was added dropwise to the solution at 0 °C. The mixture was stirred for 12 h, resulting in a white cloudy solution, and then the mixture was stirred for 12 h at 50 °C. The precipitate was filtered off and the filtrate was concentrated to give white oil. The resulting oil was redissolved in petroleum ether and filtered. The solvent was removed in vacuo giving the resulting product as an oil which provided L2 in 94% yield. 1H NMR (δ, ppm, CDCl3, TMS): 2.216 (s, 6H, CH3), 2.387 (s, 6H, CH3), 5.898 (s, 2H, CH), 7.208–7.355 (m, 5H, Ph). 13C NMR (δ, ppm, CDCl3): 12.99, 13.98, 108.75, 128.44, 128.49, 129.53, 129.54, 130.69, 130.89,
TE D
135.38, 148.60, 148.76, 153.45, 153.52. 31P NMR (δ, ppm, CDCl3, H3PO4): 59.74. 2.3 Synthesis of metal complexes
Nickel complexes were prepared by mixing equimolar amounts of the metal halide and the ligands in THF; they were isolated as diamagnetic solids in yields of 76.9% and 72.0%. These complexes are insoluble in nonpolar solvents (e.g., n-hexane, cyclohexane), but can be dissolved in polar solvents
EP
(e.g., toluene, THF).
2.3.1 L1/NiBr2 complex
AC C
A freshly prepared solution of L1 (273.2 mg, 1.1 mmol) in toluene was added to a solution of NiBr2(DME) (308.6 mg, 1.0 mmol) in THF (10 mL). After the resulting dark blue solution had been stirred for 24 h, the solvent was evaporated using a cold trap and vacuum pump and then the solid residue was washed three times with n-hexane. Drying in vacuo provided a dark blue powder. Yield: 428.8 mg, 0.77 mmol, 76.9%. EI-MS: m/z 465 [M+]. C12H20Br2N4NiSi: Calcd. C 30.87, H 4.32, N 12.00; Found: C 30.59, H 4.44, N 12.25. 2.3.2 L2/ NiBr2 complex A freshly prepared solution of L2 (328.2 mg, 1.1 mmol) in THF was added to a solution of NiBr2(DME) (308.6 mg, 1.0 mmol) in THF (10 mL). After the resulting purple solution had been stirred for 24 h, the solvent was evaporated using a cold trap and vacuum pump and then the solid residue was washed three times with n-hexane. Drying in vacuo provided a dark blue powder. Yield: 437.0 mg, 0.72 mmol, 72.0%. EI-MS: m/z 515[M+]. C16H19Br2N4PNi: Calcd. C 37.18, H 3.71, N 10.84; Found: C 37.35, H 3.66, N 10.69. 3
ACCEPTED MANUSCRIPT
Scheme 1. Structures of complex L1/Ni and L2/Ni
RI PT
2.4 General oligomerization procedure
Ethylene oligomerization runs were performed in the Lab of Grest transparent glass reactor. Reactor heated in an oil bath，which was equipped with a magnetic stirrer bar, a thermocouple, a pressure meter, and needle valves for injections. The glass reaction vessel was dried in an oven at 105 °C for 2 h prior to each run, purged under vacuum to remove air, and then brought back to
SC
atmospheric pressure using high-purity N2 and ethylene; this cycle was repeated three times. The reactor was then charged with solvent and stirred magnetically under an atmosphere of ambient ethylene. After the desired reaction temperature had been established, the co-catalyst and metal
M AN U
complexes were injected into the reactor. With stirring, the reactor was brought to the working pressure and fed continuously with ethylene until the end of each reaction was reached (generally after 30 min). The reactor was cooled to 0 °C and the excess ethylene was bled off. The samples of the organic layer were taken and analyzed through Agilent gas chromatography (GC) with flame-ionization detection (FID). The polymer was isolated by filtration, washed with ethanol and then dried at 50°C in a vacuum oven.
3. Results and discussion
TE D
3.1 Effect of reaction temperature on catalytic properties for the oligomerization of ethylene From the Table 1 we can see that the catalytic activity of the both of the catalysts initially increased upon increasing the reaction temperature, reached maximum near 30 °C and then decreased significantly as the temperature increasing. It indicates that the reaction temperature has an obvious influence on the catalytic activity for the ethylene oligomerization. Higher oligomerization temperature
EP
will resulted in lower activities for both homogeneous and supported complexes due to decreasing ethylene solubility in toluene and increasing deactivation rate of active sites at high temperature [25]. The selectivity of the complex in ethylene oligomerization is substantially affected by the ligand
AC C
environment. In most cases, the selectivity toward butene of the L2/NiBr2 complex was higher than that of the L1/NiBr2 complex. The introduction of Phenyl substituent as compared to methyl groups on the pyrazolyl groups led to noticeable decrease in catalytic activity but higher C4 selectivity. This observation suggests that the chelating ring size of the bidentate bis(pyrazolyl) ligand determines the formation of an active catalyst. For the two nickel complexes activated with MAO, the selectivity to C4 is high, attaining
24.8-92.7% of the total amount of olefins formed in the oligomerization reactions. At the 30 °C, the L2/NiBr2 complex gives the highest selectivity (92.7%) to C4 with no polymer was detected.
4
ACCEPTED MANUSCRIPT Table 1 The Effect of Reaction Temperature on Catalytic Properties of Ni complexes
Selectivity (wt%)
Activity
T (°C)
(kg/molNi·h)
C4 =
α-C4
cis-C4
trans-C4
C6 =
C8 =
PE
20
270
74.6
64.3
6.3
4.0
23.1
2.3
n.d.
30
340
90.4
83.8
4.3
2.3
8.5
1.2
n.d.
40
252
87.1
75.5
6.7
4.9
11.1
1.8
n.d.
50
151
86.9
72.3
8.0
6.7
11.8
1.7
n.d.
60
127
68.7
48.2
11.6
8.9
19.7
3.1
8.6
70
84
39.8
16.9
12.3
10.6
10.3
3.3
46.7
20
203
77.6
66.5
6.2
4.9
20.4
2.0
n.d.
30
240
92.7
84.4
5.6
2.7
6.1
1.3
n.d.
40
185
90.2
81.2
5.5
3.5
8.7
1.0
n.d.
50
125
89.4
74.6
8.7
6.2
9.4
1.2
n.d.
60
116
81.6
62.4
10.5
8.7
8.3
1.5
8.5
70
70
24.8
M AN U
Catalyst
2.6
63.8
SC
L2/Ni
8.7
7.5
RI PT
L1/Ni
8.6
8.8
Reaction Conditions: c(Cat)=0.384 mmol/L, n(Al)/n(Ni)=800, P=0.8 MPa, t=30 min, solvent=20 mL (toluene); MAO used as co-catalyst.
3.2 Effect of Al/Ni molar ratio on catalytic properties
Table 2 displays the influence of Al/Ni molar ratio on the catalytic activity and selectivity of the catalysts. Upon increasing the Al/Ni molar ratio from 200 to 800, all of the catalytic activity and
TE D
selectivity toward butene increased significantly. This trend could be attributed to increased chain transfer to the co-catalyst or greater chain termination due to increased catalytic activities [26]. When the Al/Ni molar ratio increased from 800 to 1000, the activity and the selectivity to C4 decreased. The decrease of activity and selectivity could be expected because the excessive MAO may have interfered with the formation of active metal species and/or caused their over-reduction [27].
L1/Ni
L2/Ni
Selectivity (wt%)
Al/Ni
Activity
(mol/mol)
(kg/molNi·h)
C4 =
α-C4
cis-C4
trans-C4
C6 =
C8 =
PE
200
87
76.3
58.3
10.6
7.3
16.9
2.8
n.d.
400
264
78.3
63.5
7.4
7.4
19.0
2.7
n.d.
600
304
86.2
69.3
9.4
7.6
11.8
2.0
n.d.
800
340
90.4
83.8
4.3
2.3
8.5
1.2
n.d.
1000
373
83.9
73.5
6.7
3.7
11.5
1.4
3.2
200
116
87.0
72.4
8.8
5.8
11.4
1.6
n.d.
400
140
87.2
75.1
7.7
4.4
9.2
1.6
n.d.
600
203
88.8
79.5
6.3
3.0
10.2
1.0
n.d.
800
240
92.7
84.4
5.6
2.7
6.1
1.3
n.d.
1000
247
84.5
71.4
9.6
3.5
8.9
1.3
5.3
AC C
Catalyst
EP
Table 2 The Effect of Al/Ni Molar Ratios on Catalytic Properties of Ni complexes
o
Conditions: c(Cat)=0.384 mmol/L, T=30 C, P=0.8 MPa, t=30 min, solvent=20 mL (toluene); MAO used as co-catalyst.
3.3 Effect of the reaction time on catalytic properties 5
ACCEPTED MANUSCRIPT Table 3 reveals that the reaction time has a slight effect on the activity of the catalysts. The catalytic activity increased a little upon increasing the reaction time. The reaction time significantly affected the selectivity to 1-butene. The selectivity to C4 olefins is high and stable (87.0-93.2%). However, by varying the reaction time from 15 to 60 min, chain isomerization transfer happened which was always relative to chain propagation. Based on these results, it was found that increasing the reaction time resulted in higher quantity of trans-C4 and cis-C4 owing to the isomerization process
Table 3 The Effect of Reaction Time on Catalytic Properties of Ni complexes
L2/Ni
Selectivity (wt%)
Activity (kg/molNi·h)
C4
=
α-C4
cis-C4
trans-C4
C6 =
C8 =
C10=
15
281
87.0
83.2
2.5
1.3
11.2
1.8
n.d.
30
340
90.4
83.8
4.3
2.3
8.5
1.2
n.d.
45
363
89.8
76.6
8.3
4.9
13.3
1.6
n.d.
60
387
89.8
72.6
7.3
10.1
13.0
1.2
n.d.
15
217
88.2
86.2
1.3
0.7
10.4
1.4
n.d.
30
240
92.7
84.4
5.6
2.7
6.1
1.3
n.d.
45
253
92.8
77.3
8.6
6.9
6.1
1.1
n.d.
60
260
93.2
72.8
11.1
9.4
5.6
1.2
n.d.
SC
L1/Ni
t(min)
M AN U
Catalyst
RI PT
involving α-C4.
Reaction Conditions: c(Cat)=0.384 mmol/L, T=30 °C, n(Al)/n(M)=800, P=0.8 MPa, solvent=20 mL (toluene), MAO was used as co-catalyst.
3.4 Effect of Co-catalysts on Catalytic Properties
Compared with the MAO system, DEAC system and EADC system performed a better activity.
TE D
The selectivity toward 1-butene with EADC as activator was larger than that of DEAC, but the catalytic activity was opposite. The obvious reason for performance of two types of co-catalysts probably lies in the composition of the chlorine in the co-catalysts [22]. For the TEAL, TMAL and TIBA system, the activities was obviously different with the corresponding MAO system. It was possibly because the difference of the alkyl-metal bond formed by alkylation might result in the
EP
different dimerization activity of Ni(II) catalyst. On the other hand, the different three-dimensional structure of co-catalysts might also be the reason of their unique performance, the influence of space steric hindrance of aluminum was very obvious. The selectivities of 1-butene synthesized by ethylene
AC C
dimerization catalyzed by DEAC, EADC, TEAL, TMAL or TIBA systems were lower than that by MAO
system.
The
catalytic
selectivity
to
1-butene
were
in
order
of
MAO>EADC>TEAL>TIBA>TMAL>DEAC. From the Table 4, it was found that 1-octene was obtained in the MAO system, but not in the other co-catalyst systems. It indicated that the co-catalyst has an important effect in catalytic systems. The relationship between activator structure and its performance needs to be researched further.
6
ACCEPTED MANUSCRIPT Table 4 The Effect of Co-catalysts on Catalytic Properties of Ni complexes
L2/Ni
Selectivity (wt%)
Activity (kg/molNi·h)
C4 =
α-C4
cis-C4
trans-C4
C6 =
C8 =
MAO
340
90.4
83.8
4.3
2.3
8.5
1.2
DEAC
961
61.4
53.6
5.1
2.6
38.6
n.d.
EADC
575
88.4
82.7
3.1
2.5
11.6
n.d.
TEAl
29
82.7
76.3
4.6
1.7
17.3
n.d.
TMAl
6
76.4
63.6
7.5
5.3
23.6
n.d.
TIBA
26
77.8
55.5
11.7
8.6
22.2
n.d.
MAO
240
92.7
84.4
5.6
2.7
6.1
1.3
DEAC
1310
60.5
54.4
3.7
2.3
39.5
n.d.
EADC
554
83.4
77.9
3.4
2.2
16.6
n.d.
TEAl
57
80.1
75.2
3.0
2.0
19.9
n.d.
TMAl
7
76.3
65.5
5.9
TIBA
49
78.3
61.5
9.7
o
RI PT
L1/Ni
Co-catalyst
SC
Catalyst
4.9
23.7
n.d.
7.1
21.7
n.d.
M AN U
Reaction Conditions: c(Cat)=0.384 mmol/L, T=30 C, n(Al)/n(Ni)=800, P=0.8 MPa, t=30 min, solvent=20 mL (toluene).
Oligomerization using EADC instead of MAO as co-catalyst was systematically studied. By comparing the results with those using MAO as co-catalyst, it produced in general much more active systems (164-605 Kg/molNi·h), along with lower selectivity for butene (74.2-89.0%) (seen in Table 5). By comparing the catalytic performance of L1/NiBr2 complexes and L2/NiBr2 complexes, it can be concluded that the structure of the ligand has important impact on the activity and selectivity of the catalyst. Firstly, electron donating methyl substituents could be more expected to stabilize the active
TE D
cationic species or facilitate its formation than the phenyl substituents. It is possible to enlarge the number of active sites or even to make the coordination of the counterion less tight, thus enhancing the overall activity [28]. Secondly, the atomic radius of Si is longer than that of P atom, but the electronegativity of Si is lower than that of P. These differences in the physical properties of the bridging atoms resulted in different bite angles of the ligands. Bite angle effects are usually rationalized
EP
as a combination of steric effects (related to ligand-ligand and ligand-substrate repulsion) and electronic effects (related to the bite angle of the donor orbitals to the metal center); which affected the
AC C
strength of metal hybridization and, consequently, the metal orbital energies and catalytic reactivities.
7
ACCEPTED MANUSCRIPT Table 5 The Effect of EADC on the Catalytic Properties of Ni complexes
L2/Ni
T
Activity
(mol/mol)
(oC)
(kg/molNi·h)
C4 =
α-C4
cis-C4
trans-C4
C6 =
C8 =
EADC
200
30
164
79.1
63.3
9.2
6.6
20.9
n.d.
EADC
400
30
297
84.4
71.6
7.7
5.0
15.6
n.d.
EADC
600
30
418
87.0
76.8
6.2
4.0
13.0
n.d.
EADC
800
30
575
88.4
82.7
3.1
2.5
11.6
n.d.
EADC
1000
30
605
89.0
81.2
4.3
3.6
11.0
n.d.
EADC
200
30
201
74.2
58.6
8.4
7.2
25.8
n.d.
EADC
400
30
298
77.4
64.4
7.3
5.8
22.6
n.d.
EADC
600
30
415
79.8
71.0
5.5
3.3
20.2
n.d.
EADC
800
30
554
83.4
77.9
3.4
2.2
16.6
n.d.
EADC
1000
30
589
84.3
78.5
3.1
2.7
15.8
n.d.
RI PT
L1/Ni
Selectivity (wt%)
Al/Ni
Co-catalyst
SC
Catalyst
Reaction Conditions: c(Cat)=0.384 mmol/L, P=0.8 MPa, t=30 min, solvent=20 mL (toluene).
4. Conclusion
M AN U
Two new nickel complexes based on bidentate ligands featuring Si and P bridging atoms (L1 and L2, respectively) have been prepared and evaluated for ethylene oligomerization under MAO, DEAC, EADC, TEAL, TMAL and TIBA activation. With the increase of temperature, catalyst activity and selectivity decreased, becausing of the decreased ethylene solubility in toluene and increased deactivation rate of active sites. The excessive co-catalysts may have interfered with the formation of active metal species and/or caused their over-reduction, which will decrease the catalyst activity and selectivity. Increasing the reaction time has a little influence on the activity of the catalysts. But the
TE D
isomerization process involving α-C4 made the higher quantity of trans-C4 and cis-C4, thus the selectivity of the α-C4 decreased. From the research, we get the best reaction conditions (30 oC, n(Al)/n(Ni)=800, 30 min) for the catalysts. The DEAC-activating systems and EADC-activating systems give higher activity for the ethylene oligomerization, but the selectivity of DEAC is the lowest. The catalytic selectivity to 1-butene are in order of MAO>EADC>TEAL>TIBA>TMAL>DEAC.
EP
Acknowledgments
This study was supported by the National Natural Science Foundation of China (U1162114),
AC C
Program for New Century Excellent Talents in University (NCET-07-0142) and the Provincial Key Laboratory of Oil & Gas Chemical Technology (HXHG2012-04). Open Access
This article is distributed under the terms of the Creative Commons Attribution License which
permits any use, distribution, and reproduction in any medium, provided the original author(s) and the source are credited.
References [1] D. Chandran, K.M. Lee, H.C. Chang, G.Y. Song, J.E. Lee, H. Suh, I. Kim, J. Organomet. Chem. 718 (2012) 8-13. [2] M.K. Ainooson, S.O. Ojwach, I.A. Guzei, L.C. Spencer, J. Darkwa, J. Organomet. Chem. 696 (2011) 1528-1535. [3] S.V. Kulangara, A. Jabri, I. Korobkov, S. Gambarotta, R. Duchateau, Organometallics. 31 (2012) 8
ACCEPTED MANUSCRIPT 6085-6094. [4] A.H.D.P.S. Ulbrich, R.R. Campedelli, J.L.S. Milani, J.H.Z. dos Santos, O. de L. Casagrande Jr., Appl. Catal. A: Gen. 453 (2013) 280-286. [5] S.M. Nelana, J. Darkwa, I.A. Guzei, S.F. Mapolie, J. Organomet. Chem. 689 (2004) 1835-1842. [6] S.A. Svejda, L.K. Johnson, M. Brookhart, J. Am. Chem. Soc. 121 (1999) 10634-10635. [7] Y.F. Chen, G. Wu, G.C. Bazan, Angew. Chem. Int. Ed. 44 (2005) 1108-1112. (2013) 1806-1868.
RI PT
[8] A. Otero, J. Fernández-Baeza, A. Lara-Sánchez, L.F. Sánchez-Barba, Coordin. Chem. Rev. 257 [9] M.K. Ainooson, I.A. Guzei, L.C. Spencer, J. Darkwa, Polyhedron 53 (2013) 295-303.
[10] C.M. Killian, D.J. Tempel, L.K. Johnson, M. Brookhart, J. Am. Chem. Soc. 118 (1996) 11664-11665. [11] V.C. Gibson, S.K. Spitzmesser, Chem. Rev. 103 (2003) 283-316.
SC
[12] R. Mukherjee, Coord. Chem. Rev. 203 (2000) 151-218.
[13] V.C. Gibson, C. Redshaw, G.A. Solan, Chem. Rev. 107 (2007) 1745-1776.
[14] L.F. Groux, D. Zargarian, L.C. Simon, J.B.P. Sares, J. Mol. Catal. A: Chem. 193 (2003) 51-58. [15] D.W. Stephan, F. Guérin, R.E.V.H. Spence, L. Koch, X. Gao, S.J. Brown, J.W. Swabey, Q. Wang,
M AN U
W. Xu, P. Zoricak, D.G. Harrison, Organometallics. 18 (1999) 2046-2048.
[16] A.H.D.P.S. Ulbrich, A.L. Bergamo, O.L. Casagrande, Catal. Commun. 16 (2011) 245-249. [17] K.N. Tayade, M.V. Mane, S. Sen, C.N. Murthy, G.L. Tembe, S.M. Pillai, K. Vanka, S. Mukherjee, J. Mol. Catal. A: Chem. 366 (2013) 238-246.
[18] P.J.W. Deckers, B. Hessen, J.H. Teuben, Angew. Chem. Int. Ed. 40 (2001) 2516-2519. [19] W.P. Kretschmer, C. Dijkhuis, A. Meetsma, B. Hessen, J.H. Teuben, Chem. Commun. (2002) 608-609.
TE D
[20] Y. Yang, Z. Liu, B.P. Liu, R. Duchateau, ACS Catal. 3 (2013) 2353-2361. [21] M.E. Bluhm, C. Folli, M. Döring, J. Mol. Catal. A: Chem. 212 (2004) 13-18. [22] L.L. de Oliveira, R.R. Campedelli, Maria C.A. Kuhna, J F Carpentier, O L. Casagrande Jr. J. Mol. Catal. A: Chem. 288 (2008) 58-62.
[23] M. K. Ainooson, I. A. Guzei, L. C. Spencer, J. Darkwa, Polyhedron, 53 (2013) 295-303.
EP
[24] S. D. Ittel, L. K. Johnson, M. Brookhart, Chem. Rev. 100 (2000) 1169-1204. [25] C.Y. Guo, H. Xu, M.G. Zhang, X.H. Zhang, F.W. Yan, G.Q. Yuan, Catal. Commun. 10 (2009) 1467-1471.
AC C
[26] E.Y. Chen, T.J. Marks, Chem. Rev. 100 (2000) 1391-1434. [27] H.S. Abbo, S.J. Titinchi, Molecules. 18 (2013) 4728-4738.
[28] W. Spaleck, F. Kueber, A. Winter, J. Rohrmann, B. Bachmann, M. Antberg, Organometallics 13 (1994) 954-963.
9
ACCEPTED MANUSCRIPT Highlights Bidentate nickel complexes were evaluated as ethylene dimerization catalysts.
Pre-catalysts activated with MAO, Et2AlCl and EtAlCl2 co-catalysts.
Activity and selectivity were temperature, Al/Ni ratio and co-catalysts dependent.
Ligand substituents and bridging atoms had a great influence on the activity.
AC C
EP
TE D
M AN U
SC
RI PT
S0022-328X(15)00253-3
DOI:
10.1016/j.jorganchem.2015.04.041
Reference:
JOM 19027
To appear in:
Journal of Organometallic Chemistry
Received Date: 30 December 2014 Revised Date:
25 February 2015
Accepted Date: 6 April 2015
Please cite this article as: T. Wang, B. Dong, Y.-H. Chen, G.-L. Mao, T. Jiang Nickel Complexes Incorporating Pyrazole-Based Ligands for Ethylene Dimerization to 1-Butylene, Journal of Organometallic Chemistry (2015), doi: 10.1016/j.jorganchem.2015.04.041. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
ACCEPTED MANUSCRIPT
Graphical Abstract
Nickel Complexes Incorporating Pyrazole-Based Ligands for Ethylene Dimerization to 1-Butylene
RI PT
Tao Wang a, Bo Dong a, Yan-Hui Chen a, Guo-Liang Mao b, Tao Jiang a, b,∗
AC C
EP
TE D
M AN U
SC
The nickel complexes with MAO, EADC or DEAC showed moderate activity for ethylene dimerization toward 1-C4. The catalysts showed higher catalytic activity with DEAC than other cocatalysts. The catalysts give the highest selectivity when MAO use as cocatlyst.
ACCEPTED MANUSCRIPT
Graphical Abstract
Nickel Complexes Incorporating Pyrazole-Based Ligands for Ethylene Dimerization to 1-Butylene
RI PT
Tao Wang a, Bo Dong a, Yan-Hui Chen a, Guo-Liang Mao b, Tao Jiang a, b,∗
AC C
EP
TE D
M AN U
SC
Ni complexes incorporating pyrazole-based ligands with different co-catalyst for ethylene dimerization.
ACCEPTED MANUSCRIPT
Nickel Complexes Incorporating Pyrazole-Based Ligands for Ethylene Dimerization to 1-Butylene Tao Wang a, Bo Dong a, Yan-Hui Chen a, Guo-Liang Mao b, Tao Jiang a, b, ∗1 a
College of Material Science and Chemical Engineering, Tianjin University of Science & Technology, Tianjin
RI PT
300457, China b
College of Chemistry and Chemical Engineering, Northeast Petroleum University, Daqing 163318, China
SC
Abstract
In this study we synthesized and characterized bis(3,5-dimethylpyrazolyl)dimethylsilane (L1) and by
reacting
L1
or
L2
with
M AN U
bis(3,5-dimethylpyrazolyl)phenylphosphine (L2) and then prepared bidentate (N^N) nickel complexes NiBr2(DME).
In
combination
with
methylaluminoxane,
diethylchloroaluminum or ethyldichloroaluminum (EADC) as co-catalyst, L1/Ni and L2/Ni complexes exhibited moderate catalytic activities (240-1310 kg/molNi·h) and high selectivities (up to 93.2%) for ethylene dimerization toward 1-butylene. The catalytic performance was substantially affected by the co-catalyst type and ligand environment, especially the bridge atom.
AC C
EP
TE D
Keywords: Ethylene oligomerization; 1-Butylene; Pyrazole; Nickel complexes
Corresponding author. E-mail address: [email protected]. Fax: +86-22-60602936; Tel: +86-22-60601230.
1
ACCEPTED MANUSCRIPT 1. Introduction Linear α-olefins are normally used for the preparation of branched polyethylene and other chemicals, such as detergents, synthetic lubricants and plasticizer alcohols. Oligomerization of ethylene to linear α-olefin have played an important role in the industrial process. Ethylene dimerization and oligomerization reactions were typically carried out using homogeneous late-transition-metal catalysts, particularly nickel-based catalysts [1-6]. A number of selective ethylene dimerization catalysts based on
RI PT
nickel complexes have been extensively studied and developed [7-9]. Nickel complexes that based on various chelating-ligand topologies were studied most frequently [10-14]. Besides the choice of the metal center, the desired catalytic selectivity can be tuned by designing ancillary ligands with the desired structural and electronic properties to assist the generation and stabilization of active species for selective ethylene oligomerization [15-18]. Usually, pyrazole-based ligands are used as either terminal or bridging ligands with bidentate chelation at each metal center. Currently, pyrazole ligands
SC
research mainly focus on bridging pyrazole atoms (such as carbon, silicon and boron on bridging the bridge bidentate or tridentate ligands) or changing the substituents of the ligands. It will change the space structure of ligand, coordination ability and influence the metal central atoms, changing the
M AN U
catalytic performance [19-21]. Oliveira and his coworkers have reported that the tridentate catalyst which was formed with pyrazol ligand (NNN or NSN) and Ni gave high activity and selectivity for ethylene dimerization to 1-butene. They also found that changing the substituent of pyrazole would change the catalyst performance effectively, increasing the electronic properties of substituents could effectively increase the activity of the catalyst [22]. Ainooson and his coworkers reported that catalysts that consisted of 3,5-dimethyl pyrazole bidentate ligands with iron, cobalt, nickel or palladium in the ethylene oligomerization showed different catalytic activities. The nickel complexes with
TE D
ethyldichloroaluminum (EADC) possessed the highest catalytic activity and selectivity for the ethylene oligomerization to butenes and hexenes [23]. We are interested in the design of new pyrazole ligands used in Ni-based catalysts for ethylene dimerization to 1-butylene with high catalytic activity, selectivity and long lifetime. Like S, C and B atom, phosphine or silicon were often used in the design of novel ligands as connecting heteroatoms[24]. However, corresponding bidentate pyrazole ligands
EP
featuring Si and P bridging atoms have never been explored previously in conjunction with transition metals for preparing catalysts used for ethylene oligomerization. Herein, we report the synthesis and characterization of nickel complexes with bidentate
AC C
bis(3,5-dimethylpyrazolyl)dimethylsilane (L1) or bis(3,5-dimethylpyrazolyl)phenylphosphine (L2) ligands, as well as their catalytic behavior for ethylene dimerization toward 1-butene. We also discuss the effects of the reaction temperature, the Al-to-Ni molar ratio and the co-catalysts types on the catalytic activity and selectivity of these complexes.
2. Experimental 2.1 Materials
3,5-Dimethylpyrazole, dichlorodimethylsilane, dichlorophenylphosphine, n-butyllithium (2.4 mol/L in hexanes), and NiBr2(DME) were purchased from Aldrich and used as received. Polymerization-grade ethylene was obtained from Tianjin Summit Specialty Gases (China). Methylaluminoxane (MAO, 1.4 mol/L in toluene), diethylchloroaluminum (DEAC, 1.4 mol/L in toluene), EADC (1.4 mol/L in toluene), triethylaluminum (TEAL, 1.4 mol/L in toluene), trimethylaluminium (TMAL, 1.4 mol/L in toluene), triisobutylaluminium (TIBA, 1.4 mol/L in toluene) were purchased from Albemarle (USA). Toluene, tetrahydrofuran (THF), dichloromethane and 2
ACCEPTED MANUSCRIPT n-hexane were dried and degassed prior to use. 2.2 Synthesis of ligands All air- and/or water-sensitive reactions were conducted under a dry N2 atmosphere in oven-dried flasks using standard Schlenk techniques or in a glove box. 2.2.1 Bis(3,5-dimethylpyrazolyl)dimethylsilane (L1) 2.4 M n-BuLi solution in hexanes (0.44 mL, 1.05 mmol) was added dropwise to a solution of
RI PT
3,5-dimethylpyrazole (96.1 mg, 1.0 mmol) in n-hexane (50 mL) at –78 °C. The mixture was stirred for 4 h, resulting in a light-yellow cloudy solution. Dichlorodimethylsilane (60.28 µL, 0.5 mmol) was added to the above solution, and then the mixture was stirred for 24 h. The precipitated LiCl salt was filtered off and the filtrate was concentrated to give a white residue. Recrystallization (benzene/n-hexane) provided L1 in 90% yield. 1H NMR (δ, ppm, CDCl3, TMS): 0.939 (s, 6H, CH3Si), 1.890 (s, 6H, (CH3)2pz), 2.250 (s, 6H, (CH3)2pz), 5.869 (s, 2H, H-4 in (CH3)2pz). 13C NMR (δ, ppm, 2.2.2 Bis(3,5-dimethylpyrazolyl)phenylphosphine (L2)
SC
CDCl3): 1.65, 16.11, 17.88, 27.52, 28.55, 108.58, 109.88, 136.62, 137.49, 145.81, 147.07.
M AN U
Triethylamine (3.05 mL, 22 mmol) was added to a solution of 3,5-dimethylpyrazole (1.9226 g, 20 mmol) in THF (100 mL). Then dichlorophenylphosphine (1.4 mL, 10 mmol) was added dropwise to the solution at 0 °C. The mixture was stirred for 12 h, resulting in a white cloudy solution, and then the mixture was stirred for 12 h at 50 °C. The precipitate was filtered off and the filtrate was concentrated to give white oil. The resulting oil was redissolved in petroleum ether and filtered. The solvent was removed in vacuo giving the resulting product as an oil which provided L2 in 94% yield. 1H NMR (δ, ppm, CDCl3, TMS): 2.216 (s, 6H, CH3), 2.387 (s, 6H, CH3), 5.898 (s, 2H, CH), 7.208–7.355 (m, 5H, Ph). 13C NMR (δ, ppm, CDCl3): 12.99, 13.98, 108.75, 128.44, 128.49, 129.53, 129.54, 130.69, 130.89,
TE D
135.38, 148.60, 148.76, 153.45, 153.52. 31P NMR (δ, ppm, CDCl3, H3PO4): 59.74. 2.3 Synthesis of metal complexes
Nickel complexes were prepared by mixing equimolar amounts of the metal halide and the ligands in THF; they were isolated as diamagnetic solids in yields of 76.9% and 72.0%. These complexes are insoluble in nonpolar solvents (e.g., n-hexane, cyclohexane), but can be dissolved in polar solvents
EP
(e.g., toluene, THF).
2.3.1 L1/NiBr2 complex
AC C
A freshly prepared solution of L1 (273.2 mg, 1.1 mmol) in toluene was added to a solution of NiBr2(DME) (308.6 mg, 1.0 mmol) in THF (10 mL). After the resulting dark blue solution had been stirred for 24 h, the solvent was evaporated using a cold trap and vacuum pump and then the solid residue was washed three times with n-hexane. Drying in vacuo provided a dark blue powder. Yield: 428.8 mg, 0.77 mmol, 76.9%. EI-MS: m/z 465 [M+]. C12H20Br2N4NiSi: Calcd. C 30.87, H 4.32, N 12.00; Found: C 30.59, H 4.44, N 12.25. 2.3.2 L2/ NiBr2 complex A freshly prepared solution of L2 (328.2 mg, 1.1 mmol) in THF was added to a solution of NiBr2(DME) (308.6 mg, 1.0 mmol) in THF (10 mL). After the resulting purple solution had been stirred for 24 h, the solvent was evaporated using a cold trap and vacuum pump and then the solid residue was washed three times with n-hexane. Drying in vacuo provided a dark blue powder. Yield: 437.0 mg, 0.72 mmol, 72.0%. EI-MS: m/z 515[M+]. C16H19Br2N4PNi: Calcd. C 37.18, H 3.71, N 10.84; Found: C 37.35, H 3.66, N 10.69. 3
ACCEPTED MANUSCRIPT
Scheme 1. Structures of complex L1/Ni and L2/Ni
RI PT
2.4 General oligomerization procedure
Ethylene oligomerization runs were performed in the Lab of Grest transparent glass reactor. Reactor heated in an oil bath，which was equipped with a magnetic stirrer bar, a thermocouple, a pressure meter, and needle valves for injections. The glass reaction vessel was dried in an oven at 105 °C for 2 h prior to each run, purged under vacuum to remove air, and then brought back to
SC
atmospheric pressure using high-purity N2 and ethylene; this cycle was repeated three times. The reactor was then charged with solvent and stirred magnetically under an atmosphere of ambient ethylene. After the desired reaction temperature had been established, the co-catalyst and metal
M AN U
complexes were injected into the reactor. With stirring, the reactor was brought to the working pressure and fed continuously with ethylene until the end of each reaction was reached (generally after 30 min). The reactor was cooled to 0 °C and the excess ethylene was bled off. The samples of the organic layer were taken and analyzed through Agilent gas chromatography (GC) with flame-ionization detection (FID). The polymer was isolated by filtration, washed with ethanol and then dried at 50°C in a vacuum oven.
3. Results and discussion
TE D
3.1 Effect of reaction temperature on catalytic properties for the oligomerization of ethylene From the Table 1 we can see that the catalytic activity of the both of the catalysts initially increased upon increasing the reaction temperature, reached maximum near 30 °C and then decreased significantly as the temperature increasing. It indicates that the reaction temperature has an obvious influence on the catalytic activity for the ethylene oligomerization. Higher oligomerization temperature
EP
will resulted in lower activities for both homogeneous and supported complexes due to decreasing ethylene solubility in toluene and increasing deactivation rate of active sites at high temperature [25]. The selectivity of the complex in ethylene oligomerization is substantially affected by the ligand
AC C
environment. In most cases, the selectivity toward butene of the L2/NiBr2 complex was higher than that of the L1/NiBr2 complex. The introduction of Phenyl substituent as compared to methyl groups on the pyrazolyl groups led to noticeable decrease in catalytic activity but higher C4 selectivity. This observation suggests that the chelating ring size of the bidentate bis(pyrazolyl) ligand determines the formation of an active catalyst. For the two nickel complexes activated with MAO, the selectivity to C4 is high, attaining
24.8-92.7% of the total amount of olefins formed in the oligomerization reactions. At the 30 °C, the L2/NiBr2 complex gives the highest selectivity (92.7%) to C4 with no polymer was detected.
4
ACCEPTED MANUSCRIPT Table 1 The Effect of Reaction Temperature on Catalytic Properties of Ni complexes
Selectivity (wt%)
Activity
T (°C)
(kg/molNi·h)
C4 =
α-C4
cis-C4
trans-C4
C6 =
C8 =
PE
20
270
74.6
64.3
6.3
4.0
23.1
2.3
n.d.
30
340
90.4
83.8
4.3
2.3
8.5
1.2
n.d.
40
252
87.1
75.5
6.7
4.9
11.1
1.8
n.d.
50
151
86.9
72.3
8.0
6.7
11.8
1.7
n.d.
60
127
68.7
48.2
11.6
8.9
19.7
3.1
8.6
70
84
39.8
16.9
12.3
10.6
10.3
3.3
46.7
20
203
77.6
66.5
6.2
4.9
20.4
2.0
n.d.
30
240
92.7
84.4
5.6
2.7
6.1
1.3
n.d.
40
185
90.2
81.2
5.5
3.5
8.7
1.0
n.d.
50
125
89.4
74.6
8.7
6.2
9.4
1.2
n.d.
60
116
81.6
62.4
10.5
8.7
8.3
1.5
8.5
70
70
24.8
M AN U
Catalyst
2.6
63.8
SC
L2/Ni
8.7
7.5
RI PT
L1/Ni
8.6
8.8
Reaction Conditions: c(Cat)=0.384 mmol/L, n(Al)/n(Ni)=800, P=0.8 MPa, t=30 min, solvent=20 mL (toluene); MAO used as co-catalyst.
3.2 Effect of Al/Ni molar ratio on catalytic properties
Table 2 displays the influence of Al/Ni molar ratio on the catalytic activity and selectivity of the catalysts. Upon increasing the Al/Ni molar ratio from 200 to 800, all of the catalytic activity and
TE D
selectivity toward butene increased significantly. This trend could be attributed to increased chain transfer to the co-catalyst or greater chain termination due to increased catalytic activities [26]. When the Al/Ni molar ratio increased from 800 to 1000, the activity and the selectivity to C4 decreased. The decrease of activity and selectivity could be expected because the excessive MAO may have interfered with the formation of active metal species and/or caused their over-reduction [27].
L1/Ni
L2/Ni
Selectivity (wt%)
Al/Ni
Activity
(mol/mol)
(kg/molNi·h)
C4 =
α-C4
cis-C4
trans-C4
C6 =
C8 =
PE
200
87
76.3
58.3
10.6
7.3
16.9
2.8
n.d.
400
264
78.3
63.5
7.4
7.4
19.0
2.7
n.d.
600
304
86.2
69.3
9.4
7.6
11.8
2.0
n.d.
800
340
90.4
83.8
4.3
2.3
8.5
1.2
n.d.
1000
373
83.9
73.5
6.7
3.7
11.5
1.4
3.2
200
116
87.0
72.4
8.8
5.8
11.4
1.6
n.d.
400
140
87.2
75.1
7.7
4.4
9.2
1.6
n.d.
600
203
88.8
79.5
6.3
3.0
10.2
1.0
n.d.
800
240
92.7
84.4
5.6
2.7
6.1
1.3
n.d.
1000
247
84.5
71.4
9.6
3.5
8.9
1.3
5.3
AC C
Catalyst
EP
Table 2 The Effect of Al/Ni Molar Ratios on Catalytic Properties of Ni complexes
o
Conditions: c(Cat)=0.384 mmol/L, T=30 C, P=0.8 MPa, t=30 min, solvent=20 mL (toluene); MAO used as co-catalyst.
3.3 Effect of the reaction time on catalytic properties 5
ACCEPTED MANUSCRIPT Table 3 reveals that the reaction time has a slight effect on the activity of the catalysts. The catalytic activity increased a little upon increasing the reaction time. The reaction time significantly affected the selectivity to 1-butene. The selectivity to C4 olefins is high and stable (87.0-93.2%). However, by varying the reaction time from 15 to 60 min, chain isomerization transfer happened which was always relative to chain propagation. Based on these results, it was found that increasing the reaction time resulted in higher quantity of trans-C4 and cis-C4 owing to the isomerization process
Table 3 The Effect of Reaction Time on Catalytic Properties of Ni complexes
L2/Ni
Selectivity (wt%)
Activity (kg/molNi·h)
C4
=
α-C4
cis-C4
trans-C4
C6 =
C8 =
C10=
15
281
87.0
83.2
2.5
1.3
11.2
1.8
n.d.
30
340
90.4
83.8
4.3
2.3
8.5
1.2
n.d.
45
363
89.8
76.6
8.3
4.9
13.3
1.6
n.d.
60
387
89.8
72.6
7.3
10.1
13.0
1.2
n.d.
15
217
88.2
86.2
1.3
0.7
10.4
1.4
n.d.
30
240
92.7
84.4
5.6
2.7
6.1
1.3
n.d.
45
253
92.8
77.3
8.6
6.9
6.1
1.1
n.d.
60
260
93.2
72.8
11.1
9.4
5.6
1.2
n.d.
SC
L1/Ni
t(min)
M AN U
Catalyst
RI PT
involving α-C4.
Reaction Conditions: c(Cat)=0.384 mmol/L, T=30 °C, n(Al)/n(M)=800, P=0.8 MPa, solvent=20 mL (toluene), MAO was used as co-catalyst.
3.4 Effect of Co-catalysts on Catalytic Properties
Compared with the MAO system, DEAC system and EADC system performed a better activity.
TE D
The selectivity toward 1-butene with EADC as activator was larger than that of DEAC, but the catalytic activity was opposite. The obvious reason for performance of two types of co-catalysts probably lies in the composition of the chlorine in the co-catalysts [22]. For the TEAL, TMAL and TIBA system, the activities was obviously different with the corresponding MAO system. It was possibly because the difference of the alkyl-metal bond formed by alkylation might result in the
EP
different dimerization activity of Ni(II) catalyst. On the other hand, the different three-dimensional structure of co-catalysts might also be the reason of their unique performance, the influence of space steric hindrance of aluminum was very obvious. The selectivities of 1-butene synthesized by ethylene
AC C
dimerization catalyzed by DEAC, EADC, TEAL, TMAL or TIBA systems were lower than that by MAO
system.
The
catalytic
selectivity
to
1-butene
were
in
order
of
MAO>EADC>TEAL>TIBA>TMAL>DEAC. From the Table 4, it was found that 1-octene was obtained in the MAO system, but not in the other co-catalyst systems. It indicated that the co-catalyst has an important effect in catalytic systems. The relationship between activator structure and its performance needs to be researched further.
6
ACCEPTED MANUSCRIPT Table 4 The Effect of Co-catalysts on Catalytic Properties of Ni complexes
L2/Ni
Selectivity (wt%)
Activity (kg/molNi·h)
C4 =
α-C4
cis-C4
trans-C4
C6 =
C8 =
MAO
340
90.4
83.8
4.3
2.3
8.5
1.2
DEAC
961
61.4
53.6
5.1
2.6
38.6
n.d.
EADC
575
88.4
82.7
3.1
2.5
11.6
n.d.
TEAl
29
82.7
76.3
4.6
1.7
17.3
n.d.
TMAl
6
76.4
63.6
7.5
5.3
23.6
n.d.
TIBA
26
77.8
55.5
11.7
8.6
22.2
n.d.
MAO
240
92.7
84.4
5.6
2.7
6.1
1.3
DEAC
1310
60.5
54.4
3.7
2.3
39.5
n.d.
EADC
554
83.4
77.9
3.4
2.2
16.6
n.d.
TEAl
57
80.1
75.2
3.0
2.0
19.9
n.d.
TMAl
7
76.3
65.5
5.9
TIBA
49
78.3
61.5
9.7
o
RI PT
L1/Ni
Co-catalyst
SC
Catalyst
4.9
23.7
n.d.
7.1
21.7
n.d.
M AN U
Reaction Conditions: c(Cat)=0.384 mmol/L, T=30 C, n(Al)/n(Ni)=800, P=0.8 MPa, t=30 min, solvent=20 mL (toluene).
Oligomerization using EADC instead of MAO as co-catalyst was systematically studied. By comparing the results with those using MAO as co-catalyst, it produced in general much more active systems (164-605 Kg/molNi·h), along with lower selectivity for butene (74.2-89.0%) (seen in Table 5). By comparing the catalytic performance of L1/NiBr2 complexes and L2/NiBr2 complexes, it can be concluded that the structure of the ligand has important impact on the activity and selectivity of the catalyst. Firstly, electron donating methyl substituents could be more expected to stabilize the active
TE D
cationic species or facilitate its formation than the phenyl substituents. It is possible to enlarge the number of active sites or even to make the coordination of the counterion less tight, thus enhancing the overall activity [28]. Secondly, the atomic radius of Si is longer than that of P atom, but the electronegativity of Si is lower than that of P. These differences in the physical properties of the bridging atoms resulted in different bite angles of the ligands. Bite angle effects are usually rationalized
EP
as a combination of steric effects (related to ligand-ligand and ligand-substrate repulsion) and electronic effects (related to the bite angle of the donor orbitals to the metal center); which affected the
AC C
strength of metal hybridization and, consequently, the metal orbital energies and catalytic reactivities.
7
ACCEPTED MANUSCRIPT Table 5 The Effect of EADC on the Catalytic Properties of Ni complexes
L2/Ni
T
Activity
(mol/mol)
(oC)
(kg/molNi·h)
C4 =
α-C4
cis-C4
trans-C4
C6 =
C8 =
EADC
200
30
164
79.1
63.3
9.2
6.6
20.9
n.d.
EADC
400
30
297
84.4
71.6
7.7
5.0
15.6
n.d.
EADC
600
30
418
87.0
76.8
6.2
4.0
13.0
n.d.
EADC
800
30
575
88.4
82.7
3.1
2.5
11.6
n.d.
EADC
1000
30
605
89.0
81.2
4.3
3.6
11.0
n.d.
EADC
200
30
201
74.2
58.6
8.4
7.2
25.8
n.d.
EADC
400
30
298
77.4
64.4
7.3
5.8
22.6
n.d.
EADC
600
30
415
79.8
71.0
5.5
3.3
20.2
n.d.
EADC
800
30
554
83.4
77.9
3.4
2.2
16.6
n.d.
EADC
1000
30
589
84.3
78.5
3.1
2.7
15.8
n.d.
RI PT
L1/Ni
Selectivity (wt%)
Al/Ni
Co-catalyst
SC
Catalyst
Reaction Conditions: c(Cat)=0.384 mmol/L, P=0.8 MPa, t=30 min, solvent=20 mL (toluene).
4. Conclusion
M AN U
Two new nickel complexes based on bidentate ligands featuring Si and P bridging atoms (L1 and L2, respectively) have been prepared and evaluated for ethylene oligomerization under MAO, DEAC, EADC, TEAL, TMAL and TIBA activation. With the increase of temperature, catalyst activity and selectivity decreased, becausing of the decreased ethylene solubility in toluene and increased deactivation rate of active sites. The excessive co-catalysts may have interfered with the formation of active metal species and/or caused their over-reduction, which will decrease the catalyst activity and selectivity. Increasing the reaction time has a little influence on the activity of the catalysts. But the
TE D
isomerization process involving α-C4 made the higher quantity of trans-C4 and cis-C4, thus the selectivity of the α-C4 decreased. From the research, we get the best reaction conditions (30 oC, n(Al)/n(Ni)=800, 30 min) for the catalysts. The DEAC-activating systems and EADC-activating systems give higher activity for the ethylene oligomerization, but the selectivity of DEAC is the lowest. The catalytic selectivity to 1-butene are in order of MAO>EADC>TEAL>TIBA>TMAL>DEAC.
EP
Acknowledgments
This study was supported by the National Natural Science Foundation of China (U1162114),
AC C
Program for New Century Excellent Talents in University (NCET-07-0142) and the Provincial Key Laboratory of Oil & Gas Chemical Technology (HXHG2012-04). Open Access
This article is distributed under the terms of the Creative Commons Attribution License which
permits any use, distribution, and reproduction in any medium, provided the original author(s) and the source are credited.
References [1] D. Chandran, K.M. Lee, H.C. Chang, G.Y. Song, J.E. Lee, H. Suh, I. Kim, J. Organomet. Chem. 718 (2012) 8-13. [2] M.K. Ainooson, S.O. Ojwach, I.A. Guzei, L.C. Spencer, J. Darkwa, J. Organomet. Chem. 696 (2011) 1528-1535. [3] S.V. Kulangara, A. Jabri, I. Korobkov, S. Gambarotta, R. Duchateau, Organometallics. 31 (2012) 8
ACCEPTED MANUSCRIPT 6085-6094. [4] A.H.D.P.S. Ulbrich, R.R. Campedelli, J.L.S. Milani, J.H.Z. dos Santos, O. de L. Casagrande Jr., Appl. Catal. A: Gen. 453 (2013) 280-286. [5] S.M. Nelana, J. Darkwa, I.A. Guzei, S.F. Mapolie, J. Organomet. Chem. 689 (2004) 1835-1842. [6] S.A. Svejda, L.K. Johnson, M. Brookhart, J. Am. Chem. Soc. 121 (1999) 10634-10635. [7] Y.F. Chen, G. Wu, G.C. Bazan, Angew. Chem. Int. Ed. 44 (2005) 1108-1112. (2013) 1806-1868.
RI PT
[8] A. Otero, J. Fernández-Baeza, A. Lara-Sánchez, L.F. Sánchez-Barba, Coordin. Chem. Rev. 257 [9] M.K. Ainooson, I.A. Guzei, L.C. Spencer, J. Darkwa, Polyhedron 53 (2013) 295-303.
[10] C.M. Killian, D.J. Tempel, L.K. Johnson, M. Brookhart, J. Am. Chem. Soc. 118 (1996) 11664-11665. [11] V.C. Gibson, S.K. Spitzmesser, Chem. Rev. 103 (2003) 283-316.
SC
[12] R. Mukherjee, Coord. Chem. Rev. 203 (2000) 151-218.
[13] V.C. Gibson, C. Redshaw, G.A. Solan, Chem. Rev. 107 (2007) 1745-1776.
[14] L.F. Groux, D. Zargarian, L.C. Simon, J.B.P. Sares, J. Mol. Catal. A: Chem. 193 (2003) 51-58. [15] D.W. Stephan, F. Guérin, R.E.V.H. Spence, L. Koch, X. Gao, S.J. Brown, J.W. Swabey, Q. Wang,
M AN U
W. Xu, P. Zoricak, D.G. Harrison, Organometallics. 18 (1999) 2046-2048.
[16] A.H.D.P.S. Ulbrich, A.L. Bergamo, O.L. Casagrande, Catal. Commun. 16 (2011) 245-249. [17] K.N. Tayade, M.V. Mane, S. Sen, C.N. Murthy, G.L. Tembe, S.M. Pillai, K. Vanka, S. Mukherjee, J. Mol. Catal. A: Chem. 366 (2013) 238-246.
[18] P.J.W. Deckers, B. Hessen, J.H. Teuben, Angew. Chem. Int. Ed. 40 (2001) 2516-2519. [19] W.P. Kretschmer, C. Dijkhuis, A. Meetsma, B. Hessen, J.H. Teuben, Chem. Commun. (2002) 608-609.
TE D
[20] Y. Yang, Z. Liu, B.P. Liu, R. Duchateau, ACS Catal. 3 (2013) 2353-2361. [21] M.E. Bluhm, C. Folli, M. Döring, J. Mol. Catal. A: Chem. 212 (2004) 13-18. [22] L.L. de Oliveira, R.R. Campedelli, Maria C.A. Kuhna, J F Carpentier, O L. Casagrande Jr. J. Mol. Catal. A: Chem. 288 (2008) 58-62.
[23] M. K. Ainooson, I. A. Guzei, L. C. Spencer, J. Darkwa, Polyhedron, 53 (2013) 295-303.
EP
[24] S. D. Ittel, L. K. Johnson, M. Brookhart, Chem. Rev. 100 (2000) 1169-1204. [25] C.Y. Guo, H. Xu, M.G. Zhang, X.H. Zhang, F.W. Yan, G.Q. Yuan, Catal. Commun. 10 (2009) 1467-1471.
AC C
[26] E.Y. Chen, T.J. Marks, Chem. Rev. 100 (2000) 1391-1434. [27] H.S. Abbo, S.J. Titinchi, Molecules. 18 (2013) 4728-4738.
[28] W. Spaleck, F. Kueber, A. Winter, J. Rohrmann, B. Bachmann, M. Antberg, Organometallics 13 (1994) 954-963.
9
ACCEPTED MANUSCRIPT Highlights Bidentate nickel complexes were evaluated as ethylene dimerization catalysts.
Pre-catalysts activated with MAO, Et2AlCl and EtAlCl2 co-catalysts.
Activity and selectivity were temperature, Al/Ni ratio and co-catalysts dependent.
Ligand substituents and bridging atoms had a great influence on the activity.
AC C
EP
TE D
M AN U
SC
RI PT