Enhancing the Activity and Thermal Stability of Nickel Complex

Jan 16, 2015 - Tongling Liang,. † and Wen-Hua Sun*. ,†,∥. †. Key Laboratory of Engineering Plastics and Beijing National Laboratory for Molecu...
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Enhancing the Activity and Thermal Stability of Nickel Complex Precatalysts Using 1‑[2,6-Bis(bis(4-fluorophenyl)methyl)-4-methyl phenylimino]-2-aryliminoacenaphthylene Derivatives Shizhen Du,† Shaoliang Kong,†,‡ Qisong Shi,†,§ Jing Mao,⊥ Cunyue Guo,‡ Jianjun Yi,⊥ Tongling Liang,† and Wen-Hua Sun*,†,∥ †

Key Laboratory of Engineering Plastics and Beijing National Laboratory for Molecular Sciences, Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190, China ‡ School of Chemistry and Chemical Engineering, University of Chinese Academy of Sciences, Beijing 100049, China § College of Materials Science and Engineering, Beijing Institute of Petrochemical Technology, Beijing 102617, China ⊥ Laboratory for Synthetic Resin Research, Institution of Petrochemical Technology, China National Petroleum Corporation, Beijing 100083, China ∥ State Key Laboratory for Oxo Synthesis and Selective Oxidation, Lanzhou Institute of Chemical Physics, Chinese Academy of Sciences, Lanzhou 730000, China S Supporting Information *

ABSTRACT: The series of acenaphthylene-1-[2,6-bis(bis(4-fluorophenyl)methyl)-4methylphenylimino]-2-arylimine derivatives and their dichloronickel complexes were synthesized and fully characterized as well as the single-crystal X-ray diffraction of representative nickel complexes, revealing a distorted tetrahedral geometry. Upon activation with either MAO or Et2AlCl, all nickel complexes showed high activities in ethylene polymerization; moreover, their catalytic systems showed better thermal stabilities on being manipulated at 80 °C as the industrial operating temperature.

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the copolymerization of ethylene with α-olefin(s); interestingly, the branching polyethylenes produced by nickel catalytic systems merit simplified industrial processes. The finely tuned nickel complex precatalysts provide well-controllable polyethylenes regarding the branches and molecular weights.3 Regarding typical nickel precatalysts bearing 1,2-bis(arylimino)acenaphthylenes,10 modified analogues have been observed with higher activities and better thermal stabilities6 as well as producing elastomeric materials,6e which brings a new dawn, due to the fine tuning of ligands, which enhances the catalytic activities and thermal stability of their nickel complex precatalysts. Regarding the 1,2-bis(arylimino)acenaphthylyl nickel precatalysts,6 using 2,6-dibenzhydryl-4-methylbenzenamine significantly enhanced the catalytic properties of the corresponding nickel precatalysts;6a meanwhile its analogue 2,6dibenzhydryl-4-chlorobenzenamine further improved the catalytic activities of the corresponding nickel complexes;6c these observations are consistent with computational conclusions regarding the catalytic activities positively correlated with the

INTRODUCTION Late transition metal complex precatalysts in ethylene polymerization have remained a hot topic in both academic and industrial fields.1−3 Regarding different properties and applications of resultant polyethylenes, these complex precatalysts have been divided into two classes, producing either linear2 or branched polyethylenes.3 Although several pilot processes were conducted, there is no process industrially scaled up yet due to the general and critical problem of the lower thermal stability of the catalytic system. Inspired by temperature-switched 2-benzoxazolyl-6-(1-(arylimino)ethyl)pyridylcobalt complex precatalysts favorable for ethylene polymerization at elevated temperature,4 the bis(imino)pyridyliron or -cobalt precatalysts have been revisited, obtaining thermally stable systems through using benzhydryl-derived ligands.5 Subsequently this methodology of using benzhydrylmodified ligands has been successful in enhancing the catalytic behaviors of nickel complexes incorporating 1,2-bis(arylimino)acenaphthylenes,6 2-(aryliminomethyl)pyridines,7 and 2,3-bis(arylimino)butane derivatives8 as well as the previous efforts with other bulky substituents.9 The massively used linear lowdensity polyethylenes have commonly been produced through © XXXX American Chemical Society

Received: September 13, 2014

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Organometallics core-metal charges. 11 In this work, the 2,6-bis(bis(4fluorophenyl)methyl)-4-methylbenzenamine is sophisticatedly prepared and used to synthesize acenaphthylene-1-[2,6-bis(bis(4-fluorophenyl)methyl)-4-methylphenylimine]-2-arylimine derivatives and their nickel complexes. All organic compounds and the nickel complexes were fully characterized; moreover, all title nickel complexes showed high activities and good thermal stabilities in ethylene polymerization. Herein the detailed syntheses and characterizations of all new compounds are reported as well the catalytic investigation of the title complexes.

Scheme 1. Synthetic Procedures for L1−L5 and C1−C5

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RESULTS AND DISCUSSIONS Synthesis and Characterization of the Organic Compounds and Their Nickel Complexes. The stoichiometric condensation reaction of acenaphthylene-1,2-dione and 2,6-bis(bis(4-fluorophenyl)methyl)-4-methylbenzenamine was conducted in the presence of a catalytic amount of ptoluenesulfonic acid in the mixture solvent of dichloromethane and ethanol at room temperature, and its product, 2-[2,6bis(bis(4-fluorophenyl)methyl)-4-methylphenylimino]acenaphthylenone, was isolated and purified on column chromatography in a moderate yield. Further condensation reactions of 2-[2,6-bis (bis(4-fluorophenyl)methyl)-4methylphenylimino]acenaphthylen-1-one and various anilines were individually conducted to form the acenaphthylene-1-[2,6bis(bis(4-fluorophenyl)methyl)-4-methylphenylimino]-2-arylimine derivatives (L1−L5) in acceptable yields. All the organic compounds were fully characterized by FT-IR spectra, NMR measurements, and their elemental analyses. The unsymmetrical 1,2-diiminoacenaphthylenes (L1−L5) individually reacted with (DME)NiCl2 in dichloromethane to form the αdiiminonickel(II) dichloride complexes (C1−C5) in good yields, respectively. The synthetic procedures for the organic compounds and the nickel complexes are shown in Scheme 1. The FT-IR spectra of these nickel complexes (C1−C5) indicated the clear shift of ν(CN) stretching vibrations into a lower field around 1650 and 1620 cm−1 in comparison to their free organic compounds (L1−L5) around 1660 and 1630 cm−1, illustrating the effective coordination between the nickel ion and Nimino atom. Moreover, their elemental analyses are consistent with the formulas of C1−C5. To confirm the absolute structures of nickel complexes in the solid state, the single crystals of representative complexes were obtained and submitted for an X-ray crystallographic study. X-ray Crystallographic Study. Crystals of complexes C4 and C5 suitable for single-crystal X-ray diffraction analysis were obtained by layering diethyl ether onto their dichloromethane solutions, respectively. In the solid state, the complex C4 is mononuclear; however, the complex C5 is a centrosymmetric dimer. Their molecular structures are shown in Figures 1 and 2, and their selected bond lengths and angles are tabulated in Table 1. As shown in Figure 1, complex C4 showed a distorted tetrahedral geometry with the basal plane of N1, N2, and Cl1 atoms and the apical atom of Cl2; these four atoms coordinated around the nickel center, which was located outside with a deviation of 0.935 Å of the basal plane along with the N1− Ni1−N2 angle of 83.14 (13)° and bond lengths of Ni1−N1 2.021(4) Å and Ni1−N2 2.035(3) Å. The bonds N1−C12 (1.269(5) Å) and N2−C11 (1.289(5) Å) are of typical CN double-bond character and shorter than the bonds N1−C13 (1.462(5) Å) and N2−C22 (1.448(5) Å). The dihedral angle of

Figure 1. ORTEP drawing of complex C4. Thermal ellipsoids are shown at the 30% probability level, and H atoms are omitted for clarity.

Figure 2. ORTEP drawing of C5. Thermal ellipsoids are shown at the 30% probability level. Hydrogen atoms have been omitted for clarity.

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Organometallics Table 1. Selected Bond Lengths and Angles for C4 and C5 C4 Ni(1)−N(1) Ni(1)−N(2) Ni(1)−Cl(1) Ni(1)−Cl(2) N(1)−C(12) N(2)−C(11) N(1)−C(13) N(2)−C(22) N(2)−C(24) N(1)−Ni(1)−N(2) N(1)−Ni(1)−Cl(2) N(2)−Ni(1)−Cl(2) N(1)−Ni(1)−Cl(1) N(2)−Ni(1)−Cl(1) Cl(1)−Ni(1)−Cl(2)

Bond Lengths (Å) 2.021(4) 2.035(3) 2.2046(14) 2.2018(14) 1.269(5) 1.289(5) 1.462(5) 1.448(5)

Table 2. Ethylene Polymerization by Complex C4 with Various Cocatalystsa

C5 2.133(3) 2.103(3) 2.2564(11) 2.3779(10) 1.290(4) 1.288(4) 1.438(4)

cocat.

Al/Ni

actb

Mwc

Mw/Mnc

Tmd/°C

1 2 3 4

MAO MMAO Et2AlCl Me2AlCl

1000 1000 200 200

9.28 4.72 7.01 trace

5.64 8.08 3.81

1.79 2.91 3.13

63.4 94.4 57.2

a General conditions: 2.0 μmol of Ni, 100 mL of toluene, 10 atm of ethylene, 30 min, 30 °C. b106 g of PE (mol of Ni)−1 h−1. cDetermined by GPC, and Mw: 105 g mol−1. dDetermined by DSC.

1.448(4) Bond Angles (deg) 83.14(13) 107.48(11) 110.83(9) 110.79(11) 108.70(9) 127.15(6)

entry

identify the true reason. Herein, to target the catalytic systems with higher activity as well as minimize routine work, the catalytic systems with either MAO or Et2AlCl cocatalysts are further investigated. Ethylene Polymerization in the Presence of MAO. Regarding the catalytic system with MAO, the complex C4 was extensively investigated to optimize the polymerization parameters such as the molar ratio of Al/Ni, time, and temperature, and the obtained results are tabulated in Table 3. On increasing the Al/Ni ratios from 500 to 4000 (entries 1−7, Table 3) at 30 °C within 30 min, the optimum performance reached 1.10 × 107 g of PE (mol of Ni)−1 h−1 at the Al/Ni ratio of 2000 (entry 4, Table 3). In comparison with its analogues bearing benzhydryl-modified α-diimine ligands,6 the current complex C4 showed the highest activity,6b moreover, with another advantage of consuming less MAO. To understand the influence of the reaction temperature, the catalytic system was studied by varying the temperature from 20 to 80 °C (entries 4 and 8−12, Table 3) at an Al/Ni ratio of 2000 for 30 min, with the optimum temperature observed as 30 °C (entry 4, Table 3). The observed activities decreased as the reaction temperature increased from 40 to 80 °C (entries 9−12, Table 3); it is worth mentioning, however, that the polymerization at 80 °C still maintained good activity, at 1.87 × 106 106 g of PE (mol of Ni)−1 h−1. The observation of lower activities at higher temperatures appears because of the partial deactivation of the active species and the linear gradient of lower solubility of ethylene in toluene at elevated temperatures;12 therefore, adjusted activities were obtained through calculating the ethylene concentrations at different temperatures (Cethylene, mol L−1 atm−1, Table 3). According to the adjusted activities in the range of temperatures from 20 to 80 °C (entries 4 and 8− 12, Table 3), two temperatures appeared as the optimum (entries 4 and 11, Table 3), indicating two possible active species. Regarding the lifetime of active species, the catalytic system was terminated at different times (entries 4, 13−15, Table 3); the highest activity was observed within 15 min (entry 13, Table 3), probably reflecting that the active species were quickly formed with adding MAO. The active species were gradually deactivated as the the reaction time was prolonged (entries 13−15, Table 3). On the basis of the above observed activities as the highest, the optimum condition is assigned as the Al/Ni ratio 2000 at 30 °C within 30 min; therefore other analogues were investigated for their behaviors toward ethylene polymerization (entries 16−19, Table 3), illustrating high activities in all cases. According to the observed activities (entries 4 and 16−19, Table 3), the activity decreased in the order C4 [2,4,6-tri(Me)] > C5 [2,6-di(Et)-4-Me], C3 [2,6-di(i-Pr)] > C1 [2,6-di(Me)] > C2 [2,6-di(Et)]. The catalytic performances could not be explained with the sole factor of either steric or electronic

80.59(11) 160.96(8) 90.94(8) 101.57(8) 104.22(8) 97.02(5)

the N1, N2, and Ni1 and N1, N2, and Cl1 planes is 38.05°; however, the N1, N2, and Ni1 plane is almost perpendicular to the aryl rings with dihedral angles of 89.63° to aryl linked to N1 and 87.60° to aryl linked to N2, respectively. Different from its analogue C4, complex C5 is a centrosymmetric dichloro-bridged dinickel compound with a distorted square-based pyramidal geometry around the nickel atoms,7e in which the N1, N2, Cl2, and Cl2i atoms formed the basal plane with an apical atom of Cl1 and the nickel atom located inside with a deviation of 0.465 Å from the basal plane with the angle N1−Ni1−N2 of 80.59(11)°. The bond lengths Ni1−N1 (2.133(3) Å) and Ni1−N2 (2.103(3) Å) resemble the observed data in C4. The bonds N1−C12 (1.290(4) Å) and N2−C11 (1.288(4) Å) are also consistent with typical CN double-bond character and shorter than the single-bond N1− C13 (1.438(4) Å) and N2−C24 (1.448(4) Å). The N1, N2, and Ni1 plane formed dihedral angles of 87.35° to the aryl ring on N1 and 84.00° to the aryl linked on N2, respectively. Although complexes C4 and C5 showed different coordination geometries around the nickel atoms, there is no clear cause regarding the aggregation as either monomer or dimer in the solid state, but the mononuclear form is more favorable in most cases.6a−c The different ortho-substituents (R1 = Me for C4 vs R1 = Et for C5) could not be the reliable reason because the different forms as monomer and dimer were observed within the pair of analogous nickel complexes regarding ligand compounds bearing para-methyl or not.6d In addition, the monometallic form is assumed in the solution and catalytic system. Ethylene Polymerization. Complex C4 was explored with various alkylaluminium reagents at ambient temperature under 10 atm of ethylene in order to find suitable cocatalysts (see Table 2). Besides Me2AlCl, the promising cocatalysts including MAO, MMAO, and Et2AlCl efficiently activated the nickel precatalyst with high activities. The obtained polyethylenes possessed molecular weights in the range of 105 g mol−1 and narrow polydispersity as well as low Tm values. Commonly the cocatalyst is assumed to activate a metal complex through alkylation in order to form an active species. The significant difference between Et2AlCl and MAO or MMAO would be caused by the involvement of alkyloxy substituents within MAO and MMAO; however, there is less information to theoretically C

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Organometallics Table 3. Catalytic Behavior of Complexes C1−C5/ MAOa entry

precat

T/°C

t/min

Al/Ni

actb

adjusted actc

Mwd

Mw/Mnd

Tme/°C

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19

C4 C4 C4 C4 C4 C4 C4 C4 C4 C4 C4 C4 C4 C4 C4 C1 C2 C3 C5

30 30 30 30 30 30 30 20 40 50 60 80 30 30 30 30 30 30 30

30 30 30 30 30 30 30 30 30 30 30 30 15 45 60 30 30 30 30

500 1000 1500 2000 2500 3000 4000 2000 2000 2000 2000 2000 2000 2000 2000 2000 2000 2000 2000

1.02 9.28 9.37 10.98 8.39 7.02 4.51 6.59 4.87 4.71 4.28 1.87 12.14 7.43 5.81 7.92 7.32 9.73 10.30

0.81 7.38 7.45 8.73 6.67 5.58 3.59 4.53 4.44 4.88 4.99 2.72 9.65 5.91 4.62 6.30 5.82 7.73 8.19

8.36 5.64 5.11 4.33 3.97 3.56 3.11 7.03 4.00 2.88 2.32 1.66 2.86 4.42 4.86 4.86 6.24 4.92 5.34

2.12 1.79 2.53 1.80 2.96 3.30 2.51 3.71 2.68 2.36 2.38 2.78 2.56 2.59 2.42 2.62 3.30 3.18 3.19

111.2 63.4 53.4 55.3 58.9 62.9 92.0 98.9 47.2 45.4 43.7 40.5 54.3 57.7 59.0 85.5 89.3 73.9 56.8

General conditions: 2.0 μmol of Ni; 100 mL of toluene for 10 atm of ethylene. b106 g of PE (mol of Ni)−1 h−1. c106 g of PE (mol of Ni)−1 h−1 Cethylene−1. dMw: 105 g mol−1; Mw and Mw/Mn determined by GPC. eDetermined by DSC. a

resultant polyethylenes at different temperature are shown in Figure 4, indicating that polyethylenes with lower molecular

influences, but likely were caused by a combination of both steric and electronic effects. In addition to the catalytic performances considered, the properties of obtained polyethylenes are also of important consideration. Due to the changing Al/Ni molar ratios in the C4/MAO system, the GPC curves of the resultant polyethylenes showed a clear tendency (Figure 3): the higher the

Figure 4. GPC curves for the polyethylenes obtained by the C4/MAO system at different temperatures (entries 4 and 8−12 in Table 3).

weights were produced at higher polymerization temperature. This is also consistent with the literature observation.6b,c,9a,13 However, with careful observation of the GPC curves shown in Figure 4, the resultant polyethylenes produced at 30 °C (entry 4, Table 3) and 50 or 60 °C (entries 10 and 11, Table 3) possessed narrower polydispersities, indicating the species as a single-site catalyst, which is consistent with the observation of the above adjusted activities with two optimum temperatures. Meanwhile the molecular weights of resultant polyethylenes also changed due to different active species. Regarding the lifetime of active species within the C4/MAO system, the highest activity was observed as 1.21 × 107 g of PE (mol of Ni)−1 h−1 within 15 min (entry 13, Table 3); on extending the reaction time (entries 4, 13−15, Table 3), the activities gradually decreased. The active species were quickly formed when adding the cocatalyst, but were gradually deactivated in the polymerization system; meanwhile the

Figure 3. GPC curves for the polyethylenes by the C4/MAO system with various Al/Ni ratios (entries 1−7 in Table 3).

Al/Ni molar ratio catalytic system used, the lower molecular weight polyethylenes obtained (entries 1−7, Table 3). Such a phenomenon has been commonly observed with its αdiiminonickel analogue systems,6b,c,9a,13 being interpreted that the higher molar ratios of Al/Ni enhance the possibility of chain transfers from the active nickel species onto the aluminum species, easily terminating the polymeric chains. According to the literature observations,6b,c,9a,13 the fast terminations of polymeric chains generally occurred along with temperature elevation in ethylene polymerization; that could explain the observed activities within the C4/MAO system (entries 4, 8−12, Table 3). Moreover, the GPC curves of the D

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Organometallics molecular weights of the obtained polyethylenes slightly increased with longer reaction time (Figure 5).

Figure 7. 13C NMR spectrum of the polyethylenes obtained with C4/ MAO at 50 °C (entry 10 in Table 3).

the optimum polymerization parameters through varying the Al/Ni molar ratio, reaction time, and temperature. The results are tabulated in Table 4, illustrating a plausibly economic system because of less cocatalyst Et2AlCl consumption. Employing different molar ratios of Al/Ni, higher activities were gradually observed along with increasing the Al/Ni molar ratio from 200 to 400 (entries 1−3, Table 4), and the system with 400 Al/Ni showed the best activity up to 1.21 × 107 g of PE (mol of Ni)−1 h−1; however, on further increasing the Al/Ni molar ratios to 500 and 600 (entries 4 and 5, Table 4), the catalytic activities were only slightly decreased. Interestingly, regarding the obtained polyethylenes, the higher Al/Ni molar ratios resulted in lower molecular weights with slight changes in polydispersity (entries 1−5, Table 4), and their GPC curves are shown in Figure 8. Having considered the thermal stability of the catalytic system, although the optimum temperature of 30 and 40 °C was indicated with a negligible difference of their activities, 1.21 × 107 g of PE (mol of Ni)−1 h−1 at 30 °C (entry 3, Table 4) and 1.16 × 107 g of PE (mol of Ni)−1 h−1 at 40 °C (entry 7, Table 4), the catalytic system was still maintained at 4.87 × 106 g of PE (mol of Ni)−1 h−1 at the common industrial operating temperature of 80 °C (entry 10, Table 4). Regarding the influence of ethylene concentration in toluene, the catalytic performance showed the optimum temperature as 50 °C (entry 8, Table 4). Moreover, the catalytic activities were well maintained at elevated temperatures of 50−80 °C (entries 8− 10, Table 4), indicating better thermal stability of the system with Et2AlCl than with MAO. Although molecular weights of obtained polyethylenes gradually decreased with increasing polymerization temperature, consistent with most systems of late-transition-metal complex precatalysts,1,2 the polydispersity was generally narrow, around 2.5, indicating single-site catalysis. Their GPC curves are illustrated in Figure 9. The low melting points (Tm values, most of them around 50 °C) of the obtained polyethylenes presupposed polyethylenes with high branching content. To identify the presence of branches, the polyethylene samples obtained at 30 °C (entry 3, Table 4) and at 50 °C (entry 8, in Table 4) were examined by 13 C NMR spectroscopy, and their charts are shown in Figures 10 and 11. As shown in Figure 10, the polyethylene obtained at 30 °C contained 95 branches per 1000 carbons including methyl (63.8%), ethyl (9.1%), propyl (8.9%), and longer chains (18.2%), while the polyethylenes obtained at 50 °C (see Figure 11) possessed 150 branches per 1000 carbons with 33.5% methyl, 7.1% ethyl, and 59.4% other long chains. The polyethylenes with molecular weights in the range of 105 g mol−1 and 10% branches suggest their high potential in

Figure 5. GPC curves for the polyethylenes obtained by the C4/MAO system at different times (entries 4 and 13−15 in Table 3).

According to the GPC measurement, all obtained polyethylenes generally showed a narrow polydispersity; however, their melting points (Tm) were observed at relatively lower values. Such phenomena illustrated the potential of the polyethylenes containing more branches, which commonly occurred with polyethylenes produced by nickel systems3,5,6 due to chain migration.14 The representative polyethylenes obtained by the C4/MAO system at 30 and 50 °C (entries 4 and 10, Table 3) were characterized by 13C NMR measurement. As shown in Figure 6, being interpreted according to the

Figure 6. 13C NMR spectrum of the polyethylenes obtained with C4/ MAO at 30 °C (entry 4 in Table 3).

literature,15 the polyethylene produced at 30 °C possessed 113 branches per 1000 carbons including methyl (61.8%), ethyl (5.8%), propyl (3.1%), and longer chains (29.3%), while the polyethylene obtained at 50 °C (see Figure 7) had 140 branches per 1000 carbons, containing 62.3% methyl, 15.8% ethyl, and 21.9% longer chains. The observation confirmed that higher branching was achieved as the polymerization temperature was increased, and the current system produced polyethylenes with higher branching than those by its analogues.6c In general, the catalytic activities have been well maintained within a range of reaction temperature, which is an advantage to be potentially modified for industrial application. Targeting the potentially industrial applications, more explorations would still be necessary to finely optimize the polymerization parameters for the experimental catalytic systems as well as the characteristic properties of obtained polyethylenes. Ethylene Polymerization in the Presence of AlEt2Cl. Using Et2AlCl as cocatalyst, the precatalyst C4 was again explored for E

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Organometallics Table 4. Catalytic Behavior of Complexes C1−C5/AlEt2Cla entry

precat

T/°C

t/min

Al/Ni

activityb

adjusted actc

Mwd

Mw/Mnd

Tme/°C

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17

C4 C4 C4 C4 C4 C4 C4 C4 C4 C4 C4 C4 C4 C1 C2 C3 C5

30 30 30 30 30 20 40 50 60 80 30 30 30 30 30 30 30

30 30 30 30 30 30 30 30 30 30 15 45 60 30 30 30 30

200 300 400 500 600 400 400 400 400 400 400 400 400 400 400 400 400

7.01 12.01 12.13 11.26 11.00 4.42 11.61 10.75 5.91 4.87 12.54 10.03 7.65 12.05 10.18 12.72 12.75

5.57 9.55 9.64 8.95 8.74 3.04 10.57 11.13 6.90 7.08 9.97 7.97 6.08 9.58 8.09 10.11 10.14

3.91 3.81 3.66 3.58 2.45 6.38 3.62 3.28 2.46 2.01 2.93 4.36 5.85 4.13 5.83 6.70 4.75

3.13 2.90 2.70 2.52 2.41 2.66 2.74 2.25 2.45 2.57 2.37 2.05 2.13 3.00 2.62 3.29 2.73

57.2 49.6 51.4 51.7 47.7 90.8 48.2 43.5 41.7 40.4 44.8 52.0 54.4 49.2 51.4 41.2 48.3

General conditions: 2.0 μmol of Ni; 100 mL of toluene for 10 atm of ethylene. b106 g of PE (mol of Ni)−1 h−1. c106 g of PE (mol of Ni)−1 h−1 Cethylene−1. dMw: 105 g mol−1; Mw and Mw/Mn determined by GPC. eDetermined by DSC. a

Figure 10. 13C NMR spectrum of the polyethylenes obtained with the C4/Et2AlCl system at 30 °C (entry 3 in Table 4).

Figure 8. GPC curves for polyethylenes obtained with the C4/Et2AlCl system with various Al/Ni ratios (entries 1−5 in Table 4).

Figure 11. 13C NMR spectrum of the polyethylenes obtained with C4/Et2AlCl at 50 °C (entry 8 in Table 4).

Moreover, by prolonging the reaction time (entries 3, 11−13, in Table 4), the system was observed with gradually decreased activities. Meanwhile the molecular weights of obtained polyethylenes increased slightly with longer reaction periods, and their GPC measurements are shown in Figure 12. With the optimum conditions of the Al/Ni molar ratio of 400 at 30 °C, all the other complexes were investigated (entries 14−17, Table 4). Their activities showed the order C4 [2,4,6tri(Me)] > C5 [2,6-di(Et)-4-Me], C3 [2,6-di(i-Pr)] > C1 [2,6di(Me)] > C2 [2,6-di(Et)] (entries 3, 14−17, Table 4), which was consistent with the observation of the catalytic system with MAO of complexes C1−C5. In general, the C1−C5/Et2AlCl systems have better catalytic activities than those of the C1− C5/MAO systems, also producing polyethylenes containing a

Figure 9. GPC curves for the polyethylenes obtained using the C4/ Et2AlCl system at different temperatures (entries 3 and 6−10 in Table 4).

applications such as adducts of lubricants and pour-point depressants, which have been highly demanded in industry and commonly produced by copolymerization. The current system produces polyethylene solely by the cheaper nickel complex and easily available Et2AlCl; therefore it is worth industrial consideration. F

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Article

Organometallics

MHz instrument at 135 °C in deuterated 1,2-dichlorobenzene with TMS as an internal standard. Syntheses and Characterization. 2-[2,6-Bis(bis(4-fluorophenyl)methyl)-4-methylphenylimino]acenaphthylen-1-one. A mixture of acenaphthylen-1,2-dione (3.64 g, 20 mmol) and 2,6-bis[bis(4fluorophenyl)methyl]-4-methylbenzenamine (10.23 g, 20 mmol) were dissolved in 10 mL of EtOH and 200 mL of CH2Cl2 containing a catalytic amount of p-toluenesulfonic acid and stirred for 24 h at room temperature. The solvent was evaporated at reduced pressure to give the crude product, which was chromatographed on aluminum oxide eluting with petroleum ether−ethyl acetate (v/v = 50:1). A 5.50 g amount of the product (red powder) was obtained in 40.7% isolated yield. Mp: 204−206 °C. FT-IR (cm−1): 3066 (w), 2972 (w), 1726 (m), 1651 (m) (ν(CN), m), 1600 (m), 1504 (s), 1452 (m), 1273 (w), 1223 (s), 1156 (s), 1095 (w), 1018 (m), 909 (w), 832 (s), 777 (s), 730 (s). Anal. Calcd for C45H29F4NO (675.71): C, 79.99; H, 4.33; N, 2.07. Found: C, 80.10; H, 4.25; N, 2.10. 1H NMR (CDCl3, 400 MHz, ppm): δ 8.03 (t, J = 8.2 Hz, 2H), 7.83 (d, J = 8.0 Hz, 1H), 7.60 (t, J = 8.0 Hz, 1H), 7.09 (t, J = 7.6 Hz, 1H), 6.99−6.91 (m, 8H), 6.81− 6.77 (m, 4H), 6.73 (s, 2H), 6.296 (t, J = 8.4 Hz, 4H), 6.08 (d, J = 7.2 Hz, 1H), 5.37 (s, 2H), 2.27 (s, 3H). 13C NMR(CDCl3, 100 MHz, ppm): δ 189.4, 162.7, 162.6, 161.9, 160.2, 159.5, 145.7, 142.4, 138.3, 137.4, 133.7, 132.3, 131.6, 131.0, 130.8, 130.7, 130.1, 129.8, 129.0, 128.6, 127.9, 126.6, 123.5, 122.0, 115.2, 115.0, 114.9, 114.7, 50.5, 21.5. Acenaphthylene-1-[2,6-bis(bis(4-fluorophenyl)methyl)-4-methylphenylimino]-2-(2,6-dimethylphenylimine) (L1). A mixture of 2-[2,6bis(bis(4-fluorophenyl)methyl)-4-methylphenylimino]acenaphthylen1-one (1.0 g, 1.5 mmol) and 2,6-dimethylbenzenamine (0.3 g, 2.5 mmol) was dissolved in 80 mL of toluene containing a catalytic amount of p-toluenesulfonic acid, which was refluxed for 10 h using a Dean−Stark trap. The solution was evaporated at reduced pressure to give residual solids, which were chromatographed on aluminum oxide eluting with petroleum ether−ethyl acetate (v/v = 100:1). A 0.46 g amount of L1 (yellow powder) was obtained in 39% isolated yield. Mp: 218−220 °C. FT-IR (cm−1): 3043 (w), 2919 (w), 1661 (ν(C N), m), 1632 (ν(CN), m), 1597, 1505 (s), 1441 (m), 1222 (s), 1156 (s), 1094 (m), 1051 (m), 924 (m), 829 (s), 768 (s), 729 (s). Anal. Calcd for C53H38F4N2 (778.88): C, 81.73; H, 4.92; N, 3.60. Found: C, 81.71; H, 5.07; N, 3.68. 1H NMR (CDCl3, 400 MHz, ppm): δ 7.80 (d, J = 8.4 Hz, 1H), 7.71 (d, J = 8.4 Hz, 1H), 7.30 (t, J = 7.6 Hz, 1H), 7.18 (d, J = 7.2 Hz, 2H), 7.11−7.01 (m, 6H), 6.94 (t, J = 8.4 Hz, 4H), 6.88−6.85 (m, 4H), 6.73 (s, 2H), 6.56 (d, J = 7.2 Hz, 1H), 6.30 (t, J = 8.4 Hz, 4H), 6.06 (d, J = 7.2 Hz, 1H), 5.55 (s, 2H), 2.28 (s, 3H), 2.19 (s, 6H). 13C NMR (CDCl3,100 MHz, ppm): δ 163.6, 163.1, 162.3, 161.2, 159.8, 159.0, 149.1, 146.5, 139.8, 138.6, 138.5, 137.6, 137.5, 133.1, 132.0, 131.2, 131.1, 130.9, 130.8, 130.0, 129.2, 128.7, 128.5, 128.4, 128.2, 127.9, 126.7, 124.6, 123.9, 123.8, 122.1, 115.2, 114.9, 114.8, 114.5, 50.7, 21.5, 18.1. Acenaphthylene-1-[2,6-bis(bis(4-fluorophenyl)methyl)-4-methylphenylimino]-2-(2,6-diethylphenylimine) (L2). Using the same procedure as for the synthesis of L1, L2 (0.36 g, 30% yield) was obtained as a yellow powder. Mp: 232−234 °C. FT-IR (cm−1): 2970 (w), 2934 (w), 1658 (ν(CN), m), 1631 (ν(CN), m), 1596 (m), 1504 (s), 1454 (m), 1220 (s), 1155 (s), 1095 (m), 1045 (m), 927 (m), 830 (s), 767 (s), 728 (s). Anal. Calcd for C55H42F4N2 (806.93): C, 81.86; H, 5.25; N, 3.47. Found: C, 81.40; H, 5.29; N, 3.52. 1H NMR (CDCl3, 400 MHz, ppm): δ 7.78 (d, J = 8.4 Hz, H), 7.68 (d, J = 8.4 Hz, 1H), 7.31−7.21 (m, 4H), 7.03 (d, J = 8.4 Hz, 4H), 7.00−6.92 (m, 5H), 6.88−6.85 (m, 4H), 6.74 (s, 2H), 6.50 (d, J = 7.2 Hz, 1H), 6.28 (t, J = 8.4 Hz, 4H), 5.95 (d, J = 7.6 Hz, 1H), 5.57 (s, 2H), 2.70−2.61 (m, 2H), 2.55−2.45 (m, 2H), 2.29 (s, 3H), 1.17−1.14 (t, J = 7.6 Hz, 6H). 13C NMR (CDCl3,100 MHz, ppm): δ 164.7, 163.2, 162.6, 161.5, 159.6, 159.0, 148.1, 146.6, 139.8, 138.8, 137.4, 133.1, 132.0, 131.1, 131.0, 130.8, 130.5, 130.0, 129.1, 128.8, 128.5, 128.1, 127.6, 126.6, 126.3, 124.3, 123.9, 122.7, 115.1, 114.9, 114.8, 114.6, 50.6, 24.5, 21.5, 14.4. Acenaphthylene-1-[2,6-bis(bis(4-fluorophenyl)methyl)-4-methylphenylimino]-2-(2,6-diisopropylphenylimine) (L3). Using the same procedure as for the synthesis of L1, L3 (0.35 g, 28% yield) was obtained as a yellow powder. Mp: 255−257 °C. FT-IR (cm−1): 2960

Figure 12. GPC curves for the polyethylenes obtained using the C4/ Et2AlCl system at different times (entries 3 and 11−13 in Table 4).

higher number of branches. Considering the economic process and usefulness of the obtained polyethylenes, the C1−C5/ Et2AlCl systems would be of interest for further investigation, and the relative joint adventure has just started with the petrochemical industry.

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CONCLUSIONS A series of 1-(arylimino)-2-[2,6-bis(bis(4-fluorophenyl)methyl)-4-methylphenylimino]acenaphthylnickel(II) chloride complexes was synthesized and full characterized. On activation with MAO or Et2AlCl, all title nickel complexes showed high activities in ethylene polymerization with an activity of up to 107 g of PE (mol of Ni)−1 h−1, illustrating the feature of a single-site active species on the basis of observing narrow polydispersities of the resultant polyethylenes. According to 13C NMR measurements, the obtained polyethylenes possessed high contents of branches. Et2AlCl was approved as a more economic and efficient cocatalyst than its analogue MAO; more importantly, the obtained polyethylenes, with molecular weights in the range of 105 g mol−1 as well as more branches and narrow polydispersities, are highly demanded in the market and industry. Therefore, more extensive investigations are still being conducted in our laboratories.

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EXPERIMENTAL SECTION

General Considerations. All manipulations involving air- and moisture-sensitive compounds were carried out under a nitrogen atmosphere using standard Schlenk techniques. Toluene was refluxed over sodium and distilled under nitrogen prior to use. Methylaluminoxane (MAO, 1.46 M solution in toluene) and modified methylaluminoxane (MMAO, 1.93 M in heptane) were purchased from Albemarle Corp. Diethylaluminum chloride (Et2AlCl, 1.17 M in toluene) and dimethylaluminum chloride (Me2AlCl, 1.00 M in toluene) were purchased from Acros Chemicals. High-purity ethylene was purchased from Beijing Yansan Petrochemical Co. NMR measurements of organic compounds were recorded on a Bruker DMX 400 MHz instrument at ambient temperature using TMS as an internal standard; IR spectra were recorded on a PerkinElmer System 2000 FT-IR spectrometer. Elemental analysis was carried out using a Flash EA 1112 microanalyzer. Molecular weights and molecular weight distributions (MWDs) of polyethylenes were determined by PLGPC220 at 150 °C, with 1,2,4-trichlorobenzene as the solvent. The melting points of polyethylenes were measured from the second scanning run on a PerkinElmer TA-Q2000 differential scanning calorimetry (DSC) analyzer under a nitrogen atmosphere. In the procedure, a sample of about 4.0 mg was heated to 140 °C at a rate of 20 °C/min and kept for 2 min at 140 °C to remove the thermal history and then cooled at a rate of 20 °C/min to −40 °C. 13C NMR spectra of the polyethylenes were recorded on a Bruker DMX 300 G

DOI: 10.1021/om500943u Organometallics XXXX, XXX, XXX−XXX

Article

Organometallics

(s), 1445 (m), 1294 (m), 1219 (s), 1158 (s), 1114 (m), 1047 (w), 1015 (w), 957 (w), 832 (s), 770 (s), 727 (m). Anal. Calcd for C55H42F4N2NiCl2 (936.53): C, 70.54; H, 4.52; N, 2.99. Found: C, 70.66; H, 4.60; N, 3.01. 1-[2,6-Bis(bis(4-fluorophenyl)methyl)-4-methylphenylimino]-2(2,6-diisopropylphenylimino)acenaphthylylnickel dichloride (C3) (0.138 g, 71.5% yield.) was obtained as a deep red powder. FT-IR (cm−1): 2967(w), 1651 (ν(CN), m), 1624 (ν(CN), m), 1600 (m), 1505 (s), 1447 (m), 1292 (m), 1223 (s), 1184 (s), 1157 (m), 1047 (w), 1017 (w), 942 (w), 831 (s), 770 (s), 728 (m). Anal. Calcd for C57H46F4N2NiCl2 (964.58): C, 70.97; H, 4.81; N, 2.90. Found: C, 80.07; H, 4.83; N, 2.96. 1-[2,6-Bis(bis(4-fluorophenyl)methyl)-4-methylphenylimino]-2(2,4,6-trimethylphenylimino)acenaphthylylnickel dichloride (C4) (0.152 g, 82.3% yield) was obtained as a deep red powder. FT-IR (cm−1): 2971 (w), 1651 (ν(CN), w), 1624 (ν(CN), m), 1601 (m), 1591 (m), 1505 (s), 1455 (m), 1295 (m), 1219 (s), 1159 (s), 1114 (m), 1052 (w), 1017(w), 936 (w), 832 (s), 775 (s), 730 (m). Anal. Calcd for C57H46F4N2NiCl2 (922.50): C, 70.31; H, 4.37; N, 3.04. Found: C, 70.45; H, 4.34; N, 3.11. 1-[2,6-Bis(bis(4-fluorophenyl)methyl)-4-methylphenylimino]-2(2,6-diethyl-4-methylphenylimino)acenaphthylylnickel dichloride (C5) (0.133 g, 70.1% yield) was obtained as a deep red powder. FT-IR (cm−1): 2960 (w), 1649 (υ (CN), w), 1623 (υ (CN), m), 1589 (m), 1504 (s), 1442 (m), 1295 (m), 1218 (s), 1156 (s), 1094 (m), 1042 (w), 1014 (w), 961 (w), 831 (s), 776 (s), 727 (m). Anal. Calcd for C57H46F4N2NiCl2 (950.55): C, 70.76; H, 4.67; N, 2.95. Found: C, 70.95; H, 4.63; N, 2.99. X-ray Structure Determination. Single-crystal X-ray diffraction study for C4 and C5 was conducted on a Rigaku Sealed Tube CCD (Saturn 724+) diffractometer with graphite-monochromated Mo Kα radiation (λ = 0.710 73 Å) at 173(2) K, and cell parameters were obtained by global refinement of the positions of all collected reflections. Intensities were corrected for Lorentz and polarization effects and empirical absorption. The structures were solved by direct methods and refined by full-matrix least-squares on F2. All nonhydrogen atoms were refined anisotropically, and all hydrogen atoms were placed in calculated positions. Using the SHELXL-97 package, structural solution and refinement were performed.16 Within the crystals of complexes C4 and C5, there were free solvent molecules observed; the SQUEEZE option of the crystallographic program PLATON was used to remove free solvents,17 which have no influence on the geometry of the complexes.

(w), 2930 (w), 1672 (ν(CN), m), 1650 (ν(CN), m), 1599 (m), 1505 (s), 1437 (m), 1221 (s), 1156 (s), 1095 (m), 1040 (m), 920 (m), 829 (s), 782 (s), 729 (s). Anal. Calcd for C57H46F4N2 (834.98): C, 81.99; H, 5.55; N, 3.35. Found: C, 82.07; H, 5.60; N, 3.49. 1H NMR (CDCl3, 400 MHz, ppm): δ 7.76 (d, J = 8.4 Hz, 1H), 7.64 (d, J = 8.0 Hz, 1H), 7.29−7.25 (m, 4H), 7.05−7.01 (m, 4H), 6.97−6.92 (m, 5H), 6.88−6.84 (m, 4H), 6.76 (s, 2H), 6.46 (d, J = 7.2 Hz, 1H), 6.26 (t, J = 8.4 Hz, 4H), 5.86 (d, J = 7.2 Hz, 1H), 5.58 (s, 2H), 3.14−3.07 (m, 2H), 2.30 (s, 3H), 1.28 (d, J = 6.8 Hz, 6H), 1.00 (d, J = 6.8 Hz, 6H). 13 C NMR (CDCl3,100 MHz, ppm): δ 163.9, 162.6, 162.0, 161.8, 160.2, 159.4, 146.9, 146.7, 139.8, 138.9, 137.4, 135.5, 133.1, 132.1, 131.1, 130.9, 130.8, 129.9, 129.1, 128.8, 128.4, 128.0, 127.2, 126.6, 124.7, 123.9, 123.7, 123.3, 50.6, 28.6, 24.2, 23.7, 21.5. Acenaphthylene-1-[2,6-bis(bis(4-fluorophenyl)methyl)-4-methylphenylimino]-2-(2,4,6-trimethylphenylimine) (L4). Using the same procedure as for the synthesis of L1, L4 (0.40 g, 34% yield) was obtained as a yellow powder. Mp: 228−230 °C. FT-IR (cm−1): 2967 (w), 2930 (w), 1652 (ν(CN), m), 1630 (ν(CN), m), 1597 (m), 1504 (s), 1457 (m), 1222 (s), 1154 (s), 1095 (m), 1044 (m), 926 (m), 830 (s), 775 (s), 728 (s). Anal. Calcd for C54H40F4N2 (792.90): C, 81.80; H, 5.08; N, 3.53. Found: C, 81.90; H, 5.21; N, 3.44. 1H NMR (CDCl3, 400 MHz, ppm): δ 7.80 (d, J = 8.0 Hz, 1H), 7.71 (d, J = 8.0 Hz, 1H), 7.32 (t, J = 7.6 Hz, 1H), 7.04−7.00 (m, 7H), 6.96−6.92 (m, 4H), 6.89−6.86 (m, 4H), 6.74 (s, 2H), 6.65 (d, J = 7.2 Hz, 1H), 6.30 (t, J = 8.4 Hz, 4H), 6.07 (d, J = 6.8 Hz, 1H), 5.56 (s, 2H), 2.39 (s, 3H), 2.29 (s, 3H), 2.16 (s, 6H). 13C NMR (CDCl3,100 MHz, ppm): δ 163.7, 162.7, 161.9, 161.4, 160.2, 159.5, 146.5, 139.8, 138.6, 137.6, 133.2, 133.0, 132.1, 131.2, 131.1, 130.9, 130.8, 130.4, 129.2, 129.0, 128.7, 128.6, 128.3, 127.9, 126.6, 124.4, 123.7, 122.2, 115.1, 114.9, 114.8, 114.6, 50.7, 21.5, 20.9, 18.1. Acenaphthylene-1-[2,6-bis(bis(4-fluorophenyl)methyl)-4-methylphenylimino]-2-(2,6-diethyl-4-methylphenylimine) (L5). Using the same procedure as for the synthesis of L1, L5 (0.38 g, 31% yield) was obtained as a yellow powder. Mp: 220−222 °C. FT-IR (cm−1): 2976 (w), 2913 (w), 1660 (ν(CN), m), 1638 (ν(CN), m), 1599 (m), 1505 (s), 1476 (m), 1221 (s), 1155 (s), 1093 (m), 1015 (m), 921 (m), 831 (s), 785 (s), 737 (m). Anal. Calcd for C56H44F4N2 (820.96): C, 81.93; H, 5.40; N, 3.41. Found: C, 81.99; H, 5.45; N, 3.53. 1H NMR (CDCl3, 400 MHz, ppm): δ 7.77 (d, J = 8.0 Hz, 1H), 7.67 (d, J = 8.4 Hz, 1H), 7.30 (t, J = 8.0 Hz, 1H), 7.04−7.00 (m, 6H), 6.98−6.92 (m, 5H), 6.88−6.85 (m, 4H), 6.74 (s, 2H), 6.62 (d, J = 6.8 Hz, 1H), 6.28 (t, J = 8.4 Hz, 4H), 5.95 (d, J = 7.2 Hz, 1H), 5.57 (s, 2H), 2.66−2.56 (m, 2H), 2.52−2.46 (m, 2H), 2.43 (s, 3H), 2.29 (s, 3H), 1.14 (t, J = 7.6 Hz, 6H). 13C NMR (CDCl3, 100 MHz, ppm): δ 163.8, 162.7, 161.9, 161.7, 160.2, 159.4, 146.6, 145.6, 139.8, 138.8, 137.5, 133.5, 133.0, 132.1, 131.2, 131.1, 130.9, 130.8, 130.3, 130.0, 128.9, 128.7, 128.6, 128.5, 128.2, 127.6, 127.1, 126.6, 123.8, 122.7, 115.1, 114.9, 114.8, 114.6, 50.6, 24.5, 21.5, 21.2, 14.5. Synthesis of the Nickel Complexes C1−C5. All complexes were prepared in a similar manner by the reaction of (DME)NiCl2 with the corresponding ligands in dichloromethane. A typical synthetic procedure of C1 is as follows: Acenaphthylene-1-[2,6-bis(bis(4fluorophenyl)methyl)-4-methylphenylimino]-2-(2,6-dimethylphenylimine) (L1) (0.164 g, 0.21 mmol) and (DME)NiCl2 (0.044 g, 0.20 mmol) were added into a Schlenk tube together with 10 mL of dichloromethane, the mixture was stirred for 10 h at room temperature, and excess diethyl ether was added to precipitate the complex. The complex was collected by filtration, washed with diethyl ether (3 × 5 mL), and then dried under vacuum to obtain a deep red powder of 1-[2,6-bis(bis(4-fluorophenyl)methyl)-4-methylphenylimino]-2-(2,6-dimethylphenylimino)acenaphthylylnickel dichloride (C1) (0.159 g, 87.5%). FT-IR (cm−1): 2960 (w), 1653 (ν(CN), w), 1627 (ν(CN), m), 1599 (m), 1504 (s), 1446 (m), 1297 (m), 1218 (s), 1157 (s), 1095 (m), 1045 (w), 1015 (w), 957 (w), 831 (s), 771 (s), 727 (m). Anal. Calcd for C53H38F4N2NiCl2 (908.48): C, 70.07; H, 4.22; N, 3.08. Found: C, 69.91; H, 4.27; N, 3.13. 1-[2,6-Bis(bis(4-fluorophenyl)methyl)-4-methylphenylimino]-2(2,6-diethylphenylimino)acenaphthylylnickel dichloride (C2) (0.132 g, 70.5% yield) was obtained as a deep red powder. FT-IR (cm−1): 2971 (w), 1651 (ν(CN), w), 1624 (ν(CN), m), 1599 (m), 1505

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ASSOCIATED CONTENT

* Supporting Information S

Crystal CIF files for complexes C4 and C5 are available free of charge via the Internet at http://pubs.acs.org.

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AUTHOR INFORMATION

Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This work is supported by National Natural Science Foundation of China (NSFC Nos. 21374123, 51373176, and U1362204).

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REFERENCES

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DOI: 10.1021/om500943u Organometallics XXXX, XXX, XXX−XXX

Article

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DOI: 10.1021/om500943u Organometallics XXXX, XXX, XXX−XXX