Highly Robust Nickel Catalysts Containing Anilinonaphthoquinone

Nov 17, 2017 - Graduate School of Engineering, Hiroshima University, Higashi-Hiroshima 739-8527, Japan. Macromolecules , 2017, 50 (23), pp 9216–9221...
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Highly Robust Nickel Catalysts Containing Anilinonaphthoquinone Ligand for Copolymerization of Ethylene and Polar Monomers Xia Fu,† Lingjun Zhang,† Ryo Tanaka,‡ Takeshi Shiono,*,‡ and Zhengguo Cai*,† †

State Key Laboratory for Modification of Chemical Fibers and Polymer Materials, College of Materials Science and Engineering, Donghua University, Shanghai 201620, P. R. China ‡ Graduate School of Engineering, Hiroshima University, Higashi-Hiroshima 739-8527, Japan S Supporting Information *

ABSTRACT: Copolymerizations of ethylene with polar monomers such as 5-hexene-1-yl acetate and allyl acetate are explored using nickel complexes bearing a class of anilinonaphthoquinone ligands. High tolerability of this complex toward polar comonomer is achieved by the installation of sterically bulky substituent on the aniline ligand. Moreover, the heterogenization of the nickel complexes using silica-supported modified methylaluminoxane enhances the copolymerization performances. The catalyst is highly active and thermally stabile to give semicrystalline ester-functionalized high molecular weight polyethylenes.

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INTRODUCTION Late transition metal complexes have attracted significant attention as olefin (co)polymerization catalysts with polar monomers to produce functionalized polyolefins.1−6 In contrast to the burgeoning palladium-based catalysts, earth-abundant and low-cost nickel-based catalysts generally display poor performance in these copolymerizations owing to their intrinsically low thermal stability and high oxophilicity.7,8 Recent advances have been made for enhancing the performance of nickel catalysts by tuning steric and electronic properties of metal center through rational ligand design as well as the use of bimetallic catalysts.9−15 Despite these achievements, most of the catalysts showed much lower activity in the copolymerization than in the ethylene homopolymerization to produce low molecular weight copolymers, and the scope of polar monomers copolymerized was narrower than that with palladium catalysts. Shimizu et al. recently reported an exciting class of highly active nickel catalysts bearing phosphinophenolate ligand, which copolymerize ethylene and alkyl acrylates to give highly linear and high molecular weight copolymers.16 The heterogenization of single-site catalysts is essential in slurry- and gas-phase polymerization processes to control the morphology of resulting polymer and to avoid reactor fouling.17,18 In general, two methods have been applied for the heterogenization of nickel catalysts for olefin polymerization. One is using a solid cocatalyst, and the other is tethering a nickel complex. However, the significantly low activity of the former19−22 and the more complicated synthetic route of the latter23−27 limited their application. Recently, Conley et al. reported the copolymerization of ethylene and methyl 10-undecenoate using α-diimine nickel catalyst supported on sulfated zirconia with low activity and 0.4 mol % incorporation of the polar monomer.28 © XXXX American Chemical Society

Nickel and palladium catalysts composed of zwitterionic complexes are more reactive in ethylene oligomerization and (co)polymerization due to decrease in the electron density of the metal center and/or the remotely coordinated counterion.29−34 In this regard, we have reported the anilinonaphthoquinone-ligated nickel complex (3) for homo- and copolymerization ethylene with 1-hexene.35−37 Here we report that steric bulk at axial position in anilinonaphthoquinone nickel complex (1) is efficient for the copolymerization of ethylene with polar monomers. Moreover, we present that the heterogenization of the nickel complexes using silica-supported modified methylaluminoxane (MMAO/SiO2) (Scheme 1) enhances the copolymerization performance.

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RESULTS AND DISCUSSION The anilinonaphthoquinone-based nickel complexes were prepared by the reaction of each ligand with 1 equiv of NaH followed by the complexation with 1 equiv of trans[Ni(PPh3)2PhCl] in good yield (∼66%).35 X-ray structure Scheme 1. A Plausible Heterogenization of Ni Complexes on Silica-Supported MMAO

Received: September 8, 2017 Revised: October 31, 2017

A

DOI: 10.1021/acs.macromol.7b01947 Macromolecules XXXX, XXX, XXX−XXX

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Macromolecules analysis confirmed the identical and molecular structure of complexes 1 and 2. Both nickel complexes exhibited a distorted square-planar coordination geometry around the nickel center, and the aniline plane sits at nearly perpendicular to the naphthoquinone plane. The effective blockage of the axial position of the nickel center in 1 was observed.

Table 1. Ethylene Polymerization with Complexes 1, 2, and 3 Activated by DMMAOa entry cat. 1f 2 3 4 5 6 7

1 1 1 2 2 3 3

T (°C)

yield (g)

activityb

Mnc (104)

Mw/Mnc

Bd

Tme (°C)

40 40 80 40 80 40 80

0.75 0.84 0.84 0.76 0.22 1.26 0.79

430 2000 2000 1800 530 3000 1900

22.1 11.4 1.68 0.07 0.09 9.10 4.16

2.13 2.36 2.13 2.23 5.72 3.91 1.48

1 6 12 −g −g 6 10

130 128 116 −g −g 129 125

Polymerization conditions: Ni = 5 μmol, dMMAO = 0.5 mmol, ethylene = 1.0 MPa, solvent = toluene, total volume = 30 mL, time = 5 min. bActivity in kg-polymer mol-Ni−1 h−1. cDetermined by GPC using polystyrene standards. dB = number of branches per 1000 C atoms, determined by 1H NMR. eDetermined by DSC. fWithout cocatalyst (dMMAO). gNot determined. a

density of PE was increased by raising the polymerization temperature accompanied by the decrease in the molecular weight of PE. Second, ethylene copolymerization with polar monomers using complexes 1 and 3 was investigated (Table 2). To our surprise, 1 showed very high activity of ∼3000 kg mol−1 h−1 for the copolymerization of ethylene with 5-hexene-1-yl acetate, of which value was higher than that of homopolymerization. In contrast, 3 showed much lower copolymerization activity than 1 and afforded lower molecular weight polymer. The enhanced tolerance of nickel complex 1 toward the polar monomer is in good accordance with that of earlier observation using late transition metal catalysts that the steric hindrance at axial position on the metal plays an important role.38−41 However, high polymerization temperature shut down the copolymerization activity (48 kg mol−1 h−1 at 80 °C). The comonomer incorporation increased (0.76−1.60 mol %) with rising the concentration of the polar monomer in the feed. However, the molecular weight of the copolymers decreased significantly (4800−7700). Complex 1 conducted copolymerization of ethylene with allyl acetate in moderate activities (10−50 kg mol−1 h−1) to produce the copolymers with molecular weight of 1700−8100 g mol−1 and polar monomer incorporation of 0.14−0.49 mol %. The presence of the polar comonomer in the main chain of copolymer was confirmed according to the spectroscopic data of the literature. To the best of our knowledge, only one kind of nickel catalysts bearing aryloxycarbene (IzQO) ligand was reported to produce ethylene/allyl acetate copolymers (Mn up to 8500 g mol−1, incorporation up to 0.83 mol %) with low activity (0.50 kg mol−1 h−1).14 Third, the nickel complexes 1 and 3 were heterogenized by using MMAO/SiO2. The MMAO/SiO2 was formed efficiently from the MMAO in the presence of SiO2. In contrast to the homogeneous system (Figure 3a), MMAO/SiO2 stained in blue and precipitated from colorless supernatant in the presence of the polar monomers (Figure 3b). The ICP spectroscopy measurement indicated that the supernatant did not contain free alkylaluminums and unreacted MMAO. These results testified efficient formation of the heterogeneous nickel catalyst. The results of homo- and copolymerization of ethylene with the polar monomers are shown in Table 3. Contrary to our expectation, the heterogeneous catalysts showed approximately 2 times higher activity (up to 5200 kg mol−1 h−1), affording

Figure 1. Molecular structure of complex 1. H atoms are omitted for clarity. Selected bond lengths (Å) and angles (deg): Ni1−N1 = 1.929(4), Ni1−C1 = 1.871(5), Ni1−O1 = 1.955(3), Ni1−P1 = 2.1624(14), N1−Ni1−O1 = 83.14(14), and C1−Ni1−P1 = 88.86(14).

Figure 2. Molecular structure of complex 2. H atoms are omitted for clarity. Selected bond lengths (Å) and angles (deg): Ni1−N1 = 1.9059(18), Ni1−C19 = 1.877(2), Ni1−O1 = 1.9431(15), Ni1−P1 = 2.1521(6), N1−Ni1−O1 = 82.377, and C19−Ni1−P1 = 90.68(7).

First, the complexes were employed in homopolymerization of ethylene (Table 1). Complex 1 ligated by the bulkier 2,6dibezhydrylaniline alone can initiate ethylene polymerization with activity of 430 kg mol−1 h−1 at 40 °C. Addition of 100 equiv of trialkylaluminum-free dried MMAO (dMMAO) resulted in approximately 5-fold increase in the activity (up to 2000 kg mol−1 h−1) and maintained high activity even at 80 °C, indicating high thermal stability of nickel catalyst 1. Although previously reported 3 ligated by 2,6-diisopropylaniline showed higher activity than 1 at 40 °C, the activity decreased to two-thirds at 80 °C. On the other hand, 2 bearing electron-donating methoxy groups on the aniline ligand showed less thermal stability and afforded much lower molecular weight polymers. At 40 °C, complexes 1 and 3 produced semicrystalline high molecular weight polyethylenes (PE) with high melting point and low density of short chain branches, as can be determined from the 13C NMR spectra. The branching B

DOI: 10.1021/acs.macromol.7b01947 Macromolecules XXXX, XXX, XXX−XXX

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Macromolecules Table 2. Copolymerization of Ethylene with Polar Monomers with Complexes 1 and 3 Activated by DMMAOa entry cat. 1 2 3 4 5 6 7 8

ethylene (MPa)

comonomerb (mmol)

temp (°C)

time (min)

yield (g)

activity (kg mol−1 h−1)

Mnc (103)

Mw/Mnc

incorpd (mol %)

T me (°C)

1.0 1.0 1.0 1.0 0.5 1.0 1.0 0.5

HAc (40) HAc (40) HAc (40) HAc (60) HAc (40) HAc (40) AAc (40) AAc (40)

40 40 40 40 40 80 40 40

5.0 15 15 15 15 30 60 60

1.28 3.78 0.14 0.92 0.54 0.12 0.23 0.04

3060 3020 110 740 420 48 50 10

7.66 6.28 0.83 7.63 4.84 −f 8.15 1.76

9.77 3.26 2.06 10.5 3.83 −f 2.98 3.00

0.76 −f −f 1.31 1.60 −f 0.14 0.49

120 −f −f 115 113 −f 125 118

1 1 3 1 1 1 1 1

Polymerization conditions: Ni = 5 μmol, dMMAO = 0.5 mmol, solvent = toluene, total volume = 30 mL. bHAc = 5-hexenyl acetate, AAc = ally acetate. cMeasured by GPC using polystyrene standards. dComonomer incorporation was determined by 1H NMR analysis. eDetermined by DSC. f Not determined a

copolymers with 1 order of magnitude higher molecular weight. Ethylene/5-hexene-1-yl acetate copolymerization showed the highest activity of 4700 kg mol−1 h−1 to produce the highest molecular weight copolymer (Mn up to 180 000) among the copolymerizations conducted. Interestingly, the heterogeneous system exhibited higher tolerance toward the polar monomers, where complex 3 can promote ethylene/5hexene-1-yl acetate copolymerization at 40 °C (entry 7, Table 3), and complex 1 exhibited high activity even at 80 °C (entry 8, Table 3). Although slightly lower incorporation of the polar monomers was observed in the heterogeneous system under the same copolymerization conditions, the heterogeneous system can also promote the copolymerizations of ethylene and allyl acetate. The ability of this nickel catalyst demonstrates a big advantage for the development of the late transition metal catalysts in the copolymerization of ethylene with polar monomers.

Figure 3. Photographs of the catalytic system: (a) homogeneous Ni− MMAO; (b) heterogeneous Ni−MMAO/SiO2.

higher molecular weight PE (Mn up to 273 000) as compared to the results of homopolymerization with the homogeneous system at 40 °C. In general, the use of solid-supported cocatalyst always results in significant decrease in activity due to the steric hindrance around the active species because the counteranion locates on the bulky solid surface.19−22 The opposite trend in this catalyst can be attributed to the absence of the counterion by the formation of zwitterionic nickel catalyst upon remotely coordinated MMAO/SiO2 (Scheme 1). Slightly increased activity (5900 kg mol−1 h−1) at 80 °C indicated higher thermal stability of the heterogeneous catalyst. Narrow molecular weight distribution (∼2.50) of resulting polymers with unimodal GPC curve testified to the formation of the uniform active species in this heterogeneous nickel catalyst. Complex 1 activated by MMAO/SiO2 promoted the copolymerization with higher activity to produce the

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CONCLUSIONS In conclusion, we developed a class of anilinonaphthoquinonebased nickel complexes for the copolymerization of ethylene with polar monomers. Nickel complex 1 containing bulky dibezhydrylaniline ligand exhibited unique abilities for ethylene/5-hexene-1-yl acetate copolymerization with activities of up to 3060 kg mol−1 h−1 to give highly linear copolymers possessing in-chain polar monomer units. The complex was also able to promote copolymerization of ethylene with allyl acetate with moderate activity and Mn value. The heterogenization of the nickel complexes exhibited enhanced copolymerization performances in terms of high copolymerization activity

Table 3. Homo- and Copolymerization of Ethylene with Polar Monomers by Heterogeneous Nickel Catalystsa entry 1 2 3 4 5 6 7 8 9 10

cat. (μmol) 1 3 1 3 1 1 3 1 3 1

(5.0) (5.0) (2.0) (2.0) (5.0) (5.0) (5.0) (5.0) (5.0) (5.0)

comonomerb (mmol)

HAc (30) HAc (60) HAc (30) HAc (20) HAc (20) AAc (30)

temp (°C) 40 40 80 80 40 40 40 80 80 40

time (min) 5.0 5.0 5.0 5.0 5.0 7.0 5.0 5.0 5.0 60

yield (g) 2.17 2.19 0.98 0.85 1.96 1.80 1.57 0.49 0.04 0.13

activity (kg mol−1 h−1) 5200 5300 5900 5100 4700 3100 3800 1200 96 26

Mnc (104) 27.3 8.11 4.37 2.10 10.8 18.0 14.3 3.11 8.78 1.24

Mw/Mnc

incorpd (mol %)

Tme (°C)

2.55 2.68 2.17 2.40 3.76 2.68 3.27 3.48 3.09 5.18

− −f −f −f 0.56 0.66 0.60 0.94 −f 0.19

128 130 111 124 123 123 128 114 −f 124

f

a

Polymerization conditions: Al/Ni = 100, solvent = toluene, total volume = 30 mL of ethylene = 1.0 MPa. bHAc = 5-hexenyl acetate, AAc = ally acetate. cDetermined by GPC using polystyrene standards. dComonomer incorporation was determined by 1H NMR analysis. eDetermined by DSC. f Not determined. C

DOI: 10.1021/acs.macromol.7b01947 Macromolecules XXXX, XXX, XXX−XXX

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Macromolecules (up to 4700 kg mol−1 h−1), high molecular weight of copolymer (Mn up to 180 000), and good tolerance toward the polar monomers.

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naphthoquinone (1.74 g, 10 mmol, 1.0 equiv) in m-cresol (35 mL), and trifluoroacetic acid (0.23 mL, 3.1 mmol, 0.32 equiv) was added into the flask as the reaction catalyst. 2,6- Dimethoxyaniline (1.53 g, 10 mmol, 1.0 equiv) was added dropwise into the flask. The mixture was heated with stirring at 100 °C for 4 h. Then the mixture was poured into 900 mL of 5 wt % aqueous sodium hydroxide, and the product was formed in the aqueous sodium hydroxide. Finally, the precipitate was filtered, washed by water, and dried under vacuum at 70 °C for 12 h. The residual solution was purified by recrystallization using acetic acid. The pure desired ligand L2 was obtained as dark red powder at 77% yield (2.37 g, 7.68 mmol). 1H NMR (CDCl3): δ (ppm) = 8.12− 8.11 (d, 1H), 8.09−8.08 (d, 1H), 7.73−7.71 (t, 1H), 7.65−7.63 (t, 1H), 7.25−7.22 (t, 1H), 7.21 (s, 1H), 6.64−6.63 (d, 2H), 5.56 (s, 1H), 3.85 (s, 6H). 13C NMR (CDCl3): δ (ppm) = 183.9, 182.4, 154.8, 145.8, 134.6, 133.7, 132.2, 130.9, 128.1, 126.4, 126.2, 114.4, 105.5, 104.4, 56.0. Anal. Calcd for C18H15NO4: C, 69.89; H, 4.89; N, 4.53. Found: C, 69.78; H, 4.85; N, 4.51. Synthesis of Nickel Complex 1. The complex 1 was synthesized by applying the literature procedure.1 A Schlenk flask was charged with ligand L1 (0.5953 g, 1 mmol, 1.0 equiv), KH (0.044 g, 1.1 mmol, 1.1 equiv), and THF (50 mL), and then the mixture was stirred for 6 h at room temperature to afford potassium salt of L1. The THF solution of potassium salt was added slowly into the THF (30 mL) solution of trans-[Ni(PPh3)2PhCl] (0.6941 g, 1 mmol, 1.0 equiv), which was prepared according to the literature,3 and the solution was stirred for 12 h at room temperature. The reaction solution was filtered off under a nitrogen atmosphere. Then the filtrate was evaporated to dryness under vacuum and washed by n-hexane (3 × 80 mL). The solid thus obtained was purified by recrystallization with a mixture of THF/nhexane to afford dark blue X-ray quality single crystals at 55% yield (0.5448 g, 0.55 mmol). The crystals contained 0.5 equiv of THF. 1H NMR (C6D6): δ (ppm) = 8.01−8.00 (d, 1H), 7.54−7.49 (m, 11H), 7.21−7.20 (d, 5H), 7.14−7.13 (d, 5H), 7.05−7.05 (t, 9H), 6.99−6.98 (d, 5H), 6.92 (s, 2H), 6.83−6.81 (t, 2H), 6.77−6.70 (m, 3H), 6.56− 6.54 (t, 1H), 6.49 (s, 2H), 6.43−6.41 (t, 2H), 4.57 (s,1H), 1.81 (s, 3H). 13C NMR (C6D6): δ (ppm) = 178.7, 160.7, 144.7, 143.8, 140.9, 138.3, 134.4, 134.3, 134.2, 134.0, 132.4, 130.9, 130.6, 130.4, 130.0, 129.8, 129.5, 128.8, 128.7, 128.6, 128.5, 126.9, 126.4, 126.3, 122.5, 106.7, 53.1, 21.4. 31P NMR (C6D6): δ (ppm) = 28.66. Anal. Calcd for two complexes 2(C67H52NNiO2P) and one THF (C4H8O): C, 80.55; H, 5.49; N, 1.36. Found: C, 80.44; H, 5.31; N, 1.31. Synthesis of Nickel Complex 2. A Schlenk flask was charged with ligand L2 (0.3091 g, 1 mmol, 1.0 equiv), NaH (0.0264 g, 1.1 mmol, 1.1 equiv), and THF (50 mL), and then the mixture was stirred for 3 h at room temperature to afford sodium salt of L2. The THF solution of sodium salt was added slowly into the THF (30 mL) solution of trans-[Ni(PPh3)2PhCl] (0.6941 g, 1 mmol, 1.0 equiv), and the solution was stirred for 12 h at room temperature. The reaction solution was filtered off under a nitrogen atmosphere. Then the filtrate was evaporated to dryness under vacuum and washed by n-hexane (3 × 80 mL). The solid thus obtained was purified by recrystallization with a mixture of THF/n-hexane to afford dark blue X-ray quality single crystal at 58% yield (0.4093 g, 0.58 mmol). 1H NMR (C6D6): δ (ppm) = 8.24 (s, 1H), 7.51−7.48 (t, 6H), 7.12−7.11 (d, 1H), 7.04− 6.99 (dd, 11H), 6.83−6.77 (m, 2H), 6.68 (s, 1H), 6.49−6.47 (t, 1H), 6.42−6.40 (t, 2H), 6.19−6.11 (m, 2H), 5.92−5.87 (m, 1H), 3.40 (s, 6H). 31P NMR (C6D6): δ (ppm) = 28.71. Anal. Calcd for C42H34NNiO4P: C, 71.41; H, 4.85; N, 1.98. Found: C, 71.21; H, 4.89; N, 1.92. Preparation of DMMAO and Silica-Supported MMAO (MMAO/SiO2). The 150 mL toluene solution of MMAO (2.43 mol/L) was evaporated under vacuum and washed five times with 80− 100 mL of n-hexane to remove trialkylaluminum, and then dMMAO was obtained as the white powder (24.1 g). The silica gel was calcined at 600 °C for 4 h, and then the silica (10.0 g) and dMMAO (10.0 g) were added into toluene (80−100 mL) at 0 °C under a nitrogen atmosphere. The mixture was stirred for 5 h at room temperature, and supernatant liquid was moved. The precipitate was washed five times with 80−100 mL of n-hexane and dried under vacuum. The white powder of MMAO/SiO2 was obtained

EXPERIMENTAL SECTION

Materials. All solvents were distilled or purified by the PS-MD-5 (Innovative Technology) solvent purification system. Research grade ethylene was purified by dehydration column of ZHD-20 and deoxidation column of ZHD-20A. Allyl acetate (AAc) and 5-hexenyl acetate (HAc) were dried by calcium hydride and distilled before use. MMAO was donated by Tosoh-Finechem Co., Ltd. 955 SiO2 was purchased from Grace Davison Co., Ltd. All the other reagents were purchased and used as received. General Methods. All manipulations were carried out using standard Schlenk techniques or glovebox under a nitrogen atmosphere. NMR spectra were recorded on a Bruker-600 spectrometer at ambient temperature unless otherwise indicated. NMR analyses of polymers were performed in 1,1,2,2-tetrachloroethane-d2 at 110 °C. The chemical shifts of the 1H NMR spectra are referenced to the residual proton resonance of chloroform-d (δ: 7.26), DMSO-d6 (δ: 2.50), and 1,1,2,2-tetrachloroethane-d2 (δ: 5.91). The chemical shifts of the 13C HMR spectra are referenced to the carbon resonance of chloroform-d (δ: 77.16) and 1,1,2,2-tetrachloroethane-d2 (δ: 74.47). Molecular weight and molecular weight distribution of the polymers were determined by a polymer laboratory PL GPC-220 with one guard column (PL# 1110-1120), two 30 cm columns (PLgel 10 μm MIXED-B 7.5 × 300 mm), and a refractive index (RI) detector. Polymer characterization was carried out at 145 °C using 1,2,4trichlorobenzene as eluent and calibrated by polystyrene standards and are corrected by universal calibration using the Mark−Houwink parameters of Pudin: K = 1.75 × 10−2 cm3/g and α = 0.67 for polystyrene and K = 5.90 × 10−2 cm3/g and α = 0.69 for polyethylene. The single crystals were mounted under a nitrogen atmosphere at low temperature, and data collection was made on a Bruker APEX2 diffractometer using graphite monochromated with Mo Kα radiation (λ = 0.710 73 Å). Differential scanning calorimetry (DSC) analyses were performed on a TA differential scanning calorimeter Q2000, and the DSC curves of the samples were recorded under a nitrogen atmosphere at a heating rate of 10 °C/min from 40 to 180 °C. Elemental analyses were performed with the Vario ELIII elemental analyzers manufactured by Elementar Analysensysteme GmbH. Inductive coupled plasma (ICP) emission spectrometer analyses (Prodigy ICP, Leeman Laboratories, USA) were carried out with wavelength range of 165−800 nm and resolution ≤0.005 nm. Synthesis of 2-(4-Methyl-2,6-bis(diphenylmethyl)anilino)1,4-naphthoquinone Ligand L1. Ligand L1 was synthesized by literature procedures.1 Toluene was chosen as the reactive solvent. A 250 mL flask was charged with 4-methyl-2,6-bis(diphenylmethyl)aniline 2 (4.39 g, 10 mmol, 1.0 equiv) and 2-hydroxy-1,4naphthoquinone (1.74 g, 10 mmol, 1.0 equiv), and 75 mL of toluene was added into the flask to dissolve the mixture. Then, trifluoroacetic acid (0.23 mL, 3.1 mmol, 0.32 equiv) was added into the flask as the reaction catalyst. The solution was heated with stirring at 110 °C under refluxing for 24 h, cooled down, and crystallized out ligand crystal. Finally, the crystal was filtered, washed by a small amount of water, and dried under vacuum at 70 °C for 12 h. The residual solution was purified by recrystallization using acetic acid. The pure desired ligand L1 was obtained as an orange-red crystalline solid at 74% yield (4.39 g, 7.38 mmol). 1H NMR ((CD3)2SO): δ (ppm) = 8.72 (s, 1H), 7.98−7.96 (d, 1H), 7.80−7.69 (m, 3H), 7.30−7.27 (t, 4H), 7.22−7.18 (t, 2H), 7.09−7.05 (t, 8H), 6.98−6.92 (q, 6H), 6.70 (s, 2H), 5.71 (s, 2H), 4.62 (s, 1H), 2.16 (s, 3H). 13C NMR (CDCl3): δ (ppm) = 183.2, 181.4, 147.1, 143.2, 142.6, 142.3, 138.28, 134.8, 133.5, 132.2, 131.1, 130.6, 129.9, 129.7, 129.1, 128.6, 128.6, 126.7, 126.7, 126.4, 126.2, 103.0, 52.6, 21.8. Anal. Calcd for C43H33NO2: C, 86.69; H, 5.58; N, 2.35. Found: C, 86.95; H, 5.62; N, 2.31. Synthesis of 2-(2,6-Dimethoxyanilino)-1,4-naphthoquinone Ligand L2. The ligand L2 was synthesized by applying the literature procedure.1 A 250 mL flask was charged with 2-hydroxy-1,4D

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Macromolecules (19.2 g, 5.29 mmol-Al/g, measured by ICP). Al was not detected in the solution of MMAO/SiO2−toluene (under the polymerization conditions), indicating MMAO/SiO2 did not contain unreacted MMAO. General Polymerization and Copolymerization Procedure. All (co)polymerization reactions were performed in a 200 mL Quickopen Micro Autoclaves/Pressure Vessels purchased from Anhui Kemi Machinery Technology Co., Ltd. Before polymerization, the reactor should be cleaned and evacuated at 110 °C for an hour. The certain amounts of the dMMAO or MMAO/SiO2, toluene, and the comonomer were added into the reactor under a nitrogen atmosphere, and the mixture was stirred continuously. When the temperature was established, the catalyst solution of toluene was added into the reactor. The reactor was then pressurized with ethylene. The polymerization was conducted for the certain time and terminated with acidic alcohol. The polymers obtained were washed by alcohol to remove MMAO and ligand residue and dried under vacuum at 80 °C for 6 h until a constant weight was reached.

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(3) Chen, E. Y. X. Coordination Polymerization of Polar Vinyl Monomers by Single-Site Metal Catalysts. Chem. Rev. 2009, 109, 5157−5214. (4) Nakamura, A.; Ito, S.; Nozaki, K. Coordination-Insertion Copolymerization of Fundamental Polar Monomers. Chem. Rev. 2009, 109, 5215−5244. (5) Nakamura, A.; Anselment, T. M. J.; Claverie, J.; Goodall, B.; Jordan, R. F.; Mecking, S.; Rieger, B.; Sen, A.; van Leeuwen, P. W. N. M.; Nozaki, K. Ortho-Phosphinobenzenesulfonate: A Superb Ligand for Palladium-Catalyzed Coordination-Insertion Copolymerization of Polar Vinyl Monomers. Acc. Chem. Res. 2013, 46, 1438−1449. (6) Carrow, B. P.; Nozaki, K. Transition-Metal-Catalyzed Functional Polyolefin Synthesis: Effecting Control through Chelating Ancillary Ligand Design and Mechanistic Insights. Macromolecules 2014, 47, 2541−2555. (7) Johnson, L. K.; Mecking, S.; Brookhart, M. Copolymerization of Ethylene and Propylene with Functionalized Vinyl Monomers by Palladium(II) Catalysts. J. Am. Chem. Soc. 1996, 118, 267−268. (8) Mecking, S.; Johnson, L. K.; Wang, L.; Brookhart, M. Mechanistic Studies of the Palladium-Catalyzed Copolymerization of Ethylene and α-Olefins with Methyl Acrylate. J. Am. Chem. Soc. 1998, 120, 888−899. (9) Younkin, T. R.; Connor, E. F.; Henderson, J. I.; Friedrich, S. K.; Grubbs, R. H.; Bansleben, D. A. Neutral, Single-Component Nickel(II) Polyolefin Catalysts That Tolerate Heteroatoms. Science 2000, 287, 460−462. (10) Connor, E. F.; Younkin, T. R.; Henderson, J. I.; Hwang, S.; Grubbs, R. H.; Roberts, W. P.; Litzau, J. J. Linear Functionalized Polyethylene Prepared with Highly Active Neutral Ni(II) Complexes. J. Polym. Sci., Part A: Polym. Chem. 2002, 40, 2842−2854. (11) Radlauer, M. R.; Buckley, A. K.; Henling, L. M.; Agapie, T. Bimetallic Coordination Insertion Polymerization of Unprotected Polar Monomers: Copolymerization of Amino Olefins and Ethylene by Dinickel Bisphenoxyiminato Catalysts. J. Am. Chem. Soc. 2013, 135, 3784−3787. (12) Takeuchi, D.; Chiba, Y.; Takano, S.; Osakada, K. DoubleDecker-Type Dinuclear Nickel Catalyst for Olefin Polymerization: Efficient Incorporation of Functional Co-monomers. Angew. Chem., Int. Ed. 2013, 52, 12536−12540. (13) Long, B. K.; Eagan, J. M.; Mulzer, M.; Coates, G. W. SemiCrystalline Polar Polyethylene: Ester-Functionalized Linear Polyolefins Enabled by a Functional-Group-Tolerant, Cationic Nickel Catalyst. Angew. Chem., Int. Ed. 2016, 55, 7106−7110. (14) Tao, W.; Nakano, R.; Ito, S.; Nozaki, K. Copolymerization of Ethylene and Polar Monomers by Using Ni/IzQO Catalysts. Angew. Chem., Int. Ed. 2016, 55, 2835−2839. (15) Chen, M.; Chen, C. L. Rational Design of High-Performance Phosphine Sulfonate Nickel Catalysts for Ethylene Polymerization and Copolymerization with Polar Monomers. ACS Catal. 2017, 7, 1308− 1312. (16) Xin, B. S.; Sato, N.; Tanna, A.; Oishi, Y.; Konishi, Y.; Shimizu, F. Nickel Catalyzed Copolymerization of Ethylene and Alkyl Acrylates. J. Am. Chem. Soc. 2017, 139, 3611−3614. (17) Hlatky, G. G. Heterogeneous Single-Site Catalysts for Olefin Polymerization. Chem. Rev. 2000, 100, 1347−1376. (18) Severn, J. R.; Chadwick, J. C.; Duchateau, R.; Friederichs, N. “Bound but Not Gagged” Immobilizing Single-Site α-Olefin Polymerization Catalysts. Chem. Rev. 2005, 105, 4073−4147. (19) Simon, L. C.; Patel, H.; Soares, J. B. P.; De Souza, R. F. Polyethylene Made with In Situ Supported Ni-Diimine/SMAO: Replication Phenomenon and Effect of Polymerization Conditions on Polymer Microstructure and Morphology. Macromol. Chem. Phys. 2001, 202, 3237−3247. (20) AlObaidi, F.; Ye, Z.; Zhu, S. Ethylene Polymerization with SilicaSupported Nickel-Diimine Catalyst: Effect of Support and Polymerization Conditions on Catalyst Activity and Polymer Properties. Macromol. Chem. Phys. 2003, 204, 1653−1659. (21) Ye, Z.; Alsyouri, H.; Zhu, S.; Lin, Y. S. Catalyst Impregnation and Ethylene Polymerization with Mesoporous Particle Supported Nickel-Diimine Catalyst. Polymer 2003, 44, 969−980.

ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.macromol.7b01947. Synthesis and characterization of the ligands and corresponding complexes, polymerization data and polymer characterization, and X-ray crystallography (PDF) X-ray data of complex 1 (CIF) X-ray data of complex 2 (CIF)

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AUTHOR INFORMATION

Corresponding Authors

*E-mail [email protected] (Z.C.). *E-mail [email protected] (T.S.). ORCID

Lingjun Zhang: 0000-0002-6836-3348 Ryo Tanaka: 0000-0002-6085-074X Takeshi Shiono: 0000-0002-1118-9991 Zhengguo Cai: 0000-0001-5784-3920 Author Contributions

X.F. and L.Z. contributed equally to this work. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This work was supported by National Natural Science Foundation of China (21474013), Program for New Century Excellent Talents in University, the Program for Professor of Special Appointment (Eastern Scholar) at Shanghai Institutions of Higher Learning, and “Shu Guang” project supported by Shanghai Municipal Education Commission and Shanghai Education Development Foundation and the Fundamental Research Funds for the Central Universities.

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REFERENCES

(1) Boffa, L. S.; Novak, B. M. Copolymerization of Polar Monomers with Olefins Using Transition-Metal Complexes. Chem. Rev. 2000, 100, 1479−1493. (2) Dong, J.-Y.; Hu, Y. Design and Synthesis of Structurally WellDefined Functional Polyolefins via Transition Metal-Mediated Olefin Polymerization Chemistry. Coord. Chem. Rev. 2006, 250, 47−65. E

DOI: 10.1021/acs.macromol.7b01947 Macromolecules XXXX, XXX, XXX−XXX

Article

Macromolecules

Phosphinoarenesulfonate Complex of Nickel (II). Chem. Commun. 2011, 47, 6948−6950.

(22) Choi, Y.; Soares, J. B. P. Synthesis of Supported Nickel Diimine Catalysts for Ethylene Slurry Polymerization. Macromol. Chem. Phys. 2009, 210, 1979−1988. (23) Boussie, T. R.; Coutard, C.; Turner, H.; Murphy, V.; Powers, T. S. Solid-Phase Synthesis and Encoding Strategies for Olefin Polymerization Catalyst Libraries. Angew. Chem., Int. Ed. 1998, 37, 3272−3275. (24) Schrekker, H. S.; Kotov, V.; Preishuber-Pflugl, P.; White, P.; Brookhart, M. Efficient Slurry-Phase Homopolymerization of Ethylene to Branched Polyethylenes Using α-Diimine Nickel (II) Catalysts Covalently Linked to Silica Supports. Macromolecules 2006, 39, 6341− 6354. (25) He, F.-A.; Zhang, L.-M.; Jiang, H.-L.; Chen, L.-S.; Wu, Q.; Wang, H.-H. A New Strategy to Prepare Polyethylene NanoComposites by Using a Late-Transition-Metal Catalyst Supported on AlEt 3-Activated Organoclay. Compos. Sci. Technol. 2007, 67, 1727. (26) Hu, T.; Li, Y.-G.; Liu, J.-Y.; Li, Y.-S. Syntheses and Ethylene Polymerization Behavior of Supported Salicylaldimine-Based Neutral Nickel (II) Catalysts. Organometallics 2007, 26, 2609−2615. (27) Wucher, P.; Schwaderer, J. B.; Mecking, S. Solid-Supported Single-Component Pd(II) Catalysts for Polar Monomer Insertion Copolymerization. ACS Catal. 2014, 4, 2672−2679. (28) Tafazolian, H.; Culver, D. B.; Conley, M. P. A Well-Defined Ni(II) α-Diimine Catalyst Supported on Sulfated Zirconia for Polymerization Catalysis. Organometallics 2017, 36, 2385−2388. (29) Komon, Z. J. A.; Bu, X.; Bazan, G. C. Synthesis of ButeneEthylene and Hexene-Butene-Ethylene Copolymers from Ethylene via Tandem Action of Well-Defined Homogeneous Catalysts. J. Am. Chem. Soc. 2000, 122, 1830−1831. (30) Lee, B. Y.; Kim, Y. H.; Shin, H. J.; Lee, C. H. Synthesis, Molecular Structures, and Norbornene Polymerization of Methallyl Nickel(II) Complexes of 2-(Diphenylamino) benzoate. Organometallics 2002, 21, 3481−3484. (31) Azoulay, J. D.; Rojas, R. S.; Serrano, A. V.; Ohtaki, H.; Galland, G. B.; Wu, G.; Bazan, G. C. Nickel α-Keto-β-Diimine Initiators for Olefin Polymerization. Angew. Chem., Int. Ed. 2009, 48, 1089−1092. (32) Boardman, B. M.; Bazan, G. C. α-Iminocarboxamidato Nickel Complexes. Acc. Chem. Res. 2009, 42, 1597−1606. (33) Cai, Z.; Shen, Z.; Zhou, X.; Jordan, R. F. Enhancement of Chain Growth and Chain Transfer Rates in Ethylene Polymerization by (Phosphine-sulfonate)PdMe Catalysts by Binding of B(C6F5)3 to the Sulfonate Group. ACS Catal. 2012, 2, 1187−1195. (34) Chen, M.; Zou, W.; Cai, Z.; Chen, C. Norbornene Homopolymerization and Copolymerization with Ethylene by Phosphine-Sulfonate Nickel Catalysts. Polym. Chem. 2015, 6, 2669− 2676. (35) Okada, M.; Nakayama, Y.; Ikeda, T.; Shiono, T. Synthesis of Uniquely Branched Polyethylene by Anilinonaphthoquinone Ligated Nickel Complex Activated with Tris(pentafluorophenyl)borane. Macromol. Rapid Commun. 2006, 27, 1418−1423. (36) Okada, M.; Nakayama, Y.; Shiono, T. Synthesis of Anilinonaphthoquinone-Based Nickel Complexes and Their Application for Olefin Polymerization. J. Organomet. Chem. 2007, 692, 5183− 5189. (37) Okada, M.; Nakayama, Y.; Shiono, T. Heterogenization of an Anilinonaphthoquinone-Chelated Nickel Complex for Ethylene Polymerization Using Silica-Supported Modified Methylaluminoxane. Macromol. Chem. Phys. 2014, 215, 1792−1796. (38) Ketz, B. E.; Ottenwaelder, X. G.; Waymouth, R. M. Synthesis, Structure, and Olefin Polymerization with Nickel(II) N-Heterocyclic Carbene Enolates. Chem. Commun. 2005, 5693−5695. (39) Benson, S.; Payne, B.; Waymouth, R. M. Synthesis and Reactivity of Allyl Nickel(II) N-Heterocyclic Carbene Enolate Complexes. J. Polym. Sci., Part A: Polym. Chem. 2007, 45, 3637−3647. (40) Guironnet, D.; Roesle, P.; Runzi, T.; Gottker-Schnetmann, I.; Mecking, S. Insertion Polymerization of Acrylate. J. Am. Chem. Soc. 2009, 131, 422−423. (41) Perrotin, P.; McCahill, J. S. J.; Wu, G.; Scott, S. L. Linear, High Molecular Weight Polyethylene from a Discrete, Mononuclear F

DOI: 10.1021/acs.macromol.7b01947 Macromolecules XXXX, XXX, XXX−XXX