Article Cite This: Organometallics XXXX, XXX, XXX-XXX
pubs.acs.org/Organometallics
Ethylene Polymerization by Dinuclear Xanthene-Bridged Imino- and Aminopyridyl Nickel Complexes Chunyong Rong,† Fuzhou Wang,*,†,‡ Weimin Li,† and Min Chen*,† †
Advanced Catalysis and Green Manufacturing Collaborative Innovation Center, School of Pertrochemical Engineering, Changzhou University, Changzhou 213164, China ‡ Graduate School of Engineering, Hiroshima University, Higashi-Hiroshima 739-8527, Japan S Supporting Information *
ABSTRACT: A series of xanthene-bridged dinucleating ligands bearing imino- and aminopyridyl moieties and their nickel complexes were synthesized and characterized. The properties of these dinuclear complexes in ethylene polymerization were studied in comparison with the corresponding mononuclear nickel complexes. The iminopyridyl dinuclear nickel complexes activated by methylaluminoxane (MAO) showed higher catalytic activities (up to 2.2 × 106 g of PE (mol Ni)−1 h−1), higher molecular weights, and produced polyethylene with much lower branching density (27/1000C) than their mononuclear analogues. Similar trends were observed for the aminopyridyl dinuclear complexes. A metal−metal cooperativity effect was proposed to be able to slow down the β-hydride elimination and the corresponding chain-walking process. These results clearly demonstrated the great potentials of dinuclear nickel catalysts with the xanthene-bridged coordination modes in controlling the ethylene polymerization process as well as the microstructures of the resulting polyethylene products.
■
INTRODUCTION Over the past two decades, nickel and palladium catalysts1 for ethylene and α-olefin polymerizations have drawn much attention because of their unique chain-walking polymerization mechanism.2 There are many papers for olefin polymerization using mononuclear nickel and palladium catalysts ligated by αdiimine,3,4 iminopyridine,5 salicylaldimine,6 phosphinesulfonate,7 and many others. However, only a limited number of dinuclear nickel catalysts have been reported for olefin polymerization,8 and there have been no examples of xanthene-bridged dinuclear nickel complexes bearing iminoor aminopyridyl moieties. In addition to the early diimine-based catalysts,9 some other catalysts incorporating a single ortho-substituted iminopyridyl structure have been reported.10−13 For example, a series of dimeric iminopyridyl nickel catalysts (I, Scheme 1) have been shown to be active in ethylene polymerization, generating polyethylene with molecular weight of less than 3500 at temperatures higher than 20 °C.10 Sun et al. reported that a series of dibenzhydryl-substituted 2-iminopyridyl nickel catalysts (II, Scheme 1) showed high catalytic activities in ethylene polymerization of up to 107 g of PE (mol Ni) −1 h−1,11 but only produced branched polyethylene with low molecular weight (Mn < 1000 g mol−1). Brookhart et al. reported that 8arylnaphthyl-substituted iminopyridine nickel catalysts (III, Scheme 1) were effective in retarding chain transfer.12 These © XXXX American Chemical Society
catalysts produced branched polyethylenes (ca. 30−90 branches per 1000 carbons) with molecular weight of up to 2.6 × 104 g mol−1. Recently, Chen et al. reported a series of iminopyridyl nickel catalysts (IV, Scheme 1) containing both the dibenzhydryl and the naphthyl moieties, which can polymerize ethylene with high activity and high thermal stability13 and generate polyethylene with molecular weight of up to one million. Dinuclear metal complexes8,14 have been explored in catalysis with the potential of cooperative effects between two proximate active metal centers, including the applications in ethylene polymerization. For example, Fu et al. reported the synthesis of a series of dinuclear nickel catalysts (V, Scheme 1) with conjugated α-diimine ligands.15 The activities of these catalysts were higher than those of the corresponding mononuclear catalyst under the same conditions. Sun et al. designed some methylene-bridged dinuclear nickel catalysts with bisiminopyridine ligands (VI, Scheme 1).16 These catalysts showed good activities for ethylene oligomerization and polymerization in the presence of MAO and produced mixtures of oligomers and polyethylenes. Solan et al. reported bimetallic nickel complexes (VII, Scheme 1) bearing 2,3,5,6-tetramethylbenzene-linked iminopyridines capable of generating mixtures of waxes and Received: September 12, 2017
A
DOI: 10.1021/acs.organomet.7b00698 Organometallics XXXX, XXX, XXX−XXX
Article
Organometallics Scheme 1. Selected Examples of Previously Reported Iminopyridyl and Dinuclear Nickel Catalysts
Scheme 2. Synthesis of the Dinucleating Ligands and the Corresponding Nickel Complexes
low molecular weight solid polyethylene.17 Takeuchi et al. designed a dinuclear nickel complex (IX, Scheme 1) with a double-decker structure.18a This catalyst enabled selective copolymerization of ethylene with other various bifunctional comonomers. Recently, they also reported ethylene polymerization studies of a double-decker dinickel complex (X, Scheme 1) containing two salicylaldimine groups with a xanthene moiety as the bridge.18b Agapie et al. reported the binuclear nickel complexes linked by a rigid phenyl moiety and realized copolymerization of ethylene with tertiary aminoolefins.19 The Ni−Ni cooperativity effect may be responsible for the unique properties of these dinuclear catalysts. Recently, Chen et al. designed some dinuclear α-diimine nickel complexes20 bearing xanthene, biphenylene, and
naphthalene groups as the bridge. Interestingly, these nickel complexes led to the formation of semicrystalline polyethylene with much lower branching density compared with the mononuclear analogue in ethylene polymerization. The Ni− Ni cooperativity effect invoked by xanthene-bridged dinucleating ligands was proposed to be able to slow down the β-hydride elimination process and correspondingly slow down the chainwalking process. In this work, the synthesis and characterization of some xanthene-bridged dinuclear nickel complexes bearing imino- and aminopyridyl moieties and their properties in ethylene polymerization were reported. The corresponding mononuclear complexes were studied for comparison. The effects of catalyst structures and polymerization conditions on B
DOI: 10.1021/acs.organomet.7b00698 Organometallics XXXX, XXX, XXX−XXX
Article
Organometallics
X-ray Crystallographic Studies. Suitable crystals of complex Ni2-C′ for X-ray diffraction were obtained at room temperature by double layering a CH2Cl2 solution of the complex Ni2-C with n-hexane in air. The molecular structure of Ni2-C′ was confirmed by single-crystal X-ray diffraction, and the corresponding ORTEP diagram is shown in Figure 1. Crystal data, data collection, and refinement parameters are listed in Table S1 (see the Supporting Information). In the solid state, complex Ni2-C′ clearly shows the xanthene-bridged 2-pyridinemethanamine dimeric structure with two Ni centers connected by two bromide bridges. In each unit, the two aminopyridyl N atoms, three Br atoms, and a H2O molecule from the moisture coordinated to a Ni atom in a six-coordinated distorted octahedral geometry. The two Br bridges and the two amine groups bonded to the Ni center in cis configuration, and the isolated Br ions linked to the same Ni atom in trans configuration. Interestingly, in the molecular structure of Ni2-C′ (Figure 1), two Br bridges were observed, leading to a very short Ni−Ni distance (3.6452 Å). This strongly suggested that the two Ni center can get close to each other, which may induce a metal−metal cooperativity21 effect in olefin polymerization.20b However, upon activation during polymerization, the electrostatic repulsion between the two Ni centers may lead to a longer Ni−Ni distance. Ethylene Polymerization Studies. All the dibromonickel complexes were applied to ethylene polymerization activated by MAO at the [Al]/[Ni] molar ratio of 500 for 30 min under 9 atm of ethylene, and the results are listed in Table 1. All the nickel complexes displayed high activities in ethylene polymerization on the level of 105 g of PE (mol Ni)−1 h−1 at low temperatures, and the catalytic activities were decreased with increasing temperatures from 20 to 60 °C, except Ni2-C (the highest activity was observed at 40 °C, entry 8, Table 1). For polymerizations at 60 °C, the dinuclear complexes showed higher activities than the corresponding mononuclear analogues (entries 3, 6, 9, 12, 18, 21, and 24, Table 1). This can be rationalized by the metal−metal cooperativity effects of the dinuclear complexes that leads to enhance thermal stability of the active species. The polymer molecular weights were also decreased with polymerization temperature from 20 to 60 °C. This indicates that fast chain transfer takes place at higher temperatures. The effect of catalyst structures was investigated by comparing the corresponding dinuclear complexes and mononuclear analogues. At 20 °C, the polymerization activity decreased in the following order, Ni2-A ≥ Ni-B ≥ Ni2-C ≥ Ni2B ≥ Ni-A ≥ Ni-D ≥ Ni-C ≥ Ni2-D. This could originate from ligand steric effects or the metal−metal cooperativity effect. For example, complex Ni2-A showed activity higher than that of the corresponding mononuclear analogue Ni-A and produced polymers with higher molecular weight (entries 1−3 and 13− 15, Table 1). At 20 and 40 °C, complex Ni2-B showed activity lower than that of the corresponding mononuclear analogue Ni-B but produced polymers with higher molecular weight (entries 4, 5, 16, and 17, Table 1). The complexes with isopropyl groups (Ni2-A and Ni2-C) showed activity higher than that with the corresponding methyl groups (Ni2-B and Ni2-D). The higher molecular weight of the polymers obtained by Ni2-A and Ni2-C suggest that the ortho-isopropyl could efficiently suppress chain-transfer reactions. In general, the dinuclear complexes showed good thermal stability and catalytic activity, generating polyethylene with high molecular weight compared to mononuclear analogues. These improve-
productivity, molecular weights, and branching density were investigated in detail.
■
RESULTS AND DISCUSSION Synthesis and Characterization of the XantheneBridged Dinuclear Nickel Complexes. The Suzuki coupling reactions of xanthene diboronic acid with 2 equiv of bromosubstituted aniline derivatives afforded the desired xanthenebridged dianiline derivatives20 in high yields without using column chromatography. The iminopyridyl dinucleating ligands L-A and L-B were prepared by the condensation reaction of 1 equiv of xanthene-bridged dianiline with 2 equiv of 2pyridinecarboxaldehyde, in the presence of a catalytic amount of p-toluenesulfonic acid (Scheme 2). These pure ligands were obtained by methanol wash in 90 and 85% yields. The corresponding 2-pyridinemethanamine ligands L-C and L-D were obtained from the nucleophilic addition reaction of ligands L-A and L-B by trimethylaluminum (Al(CH3)3). The pure ligands were obtained by recrystallization from hexanes in 89 and 84% yields. These dinucleating ligands were characterized by 1H NMR, 13C NMR, and HRMS spectroscopy. The reactions of two equimolar amounts of (DME)NiBr2 (DME = 1,2-dimethoxyethane) and the corresponding ligands L-A−L-D in CH2Cl2 led to the formation of the dinuclear nickel complexes Ni2-A−Ni2-D as brown solids in 67−80% yields, respectively. These complexes were characterized by mass spectrometry and elemental analysis. The dinuclear nickel complexes with bromine-bridged structure (Figure 1) were obtained based on X-ray analysis. Therefore, the brominebridged structures4b,20 of dinuclear nickel complexes are described in Scheme 2. For comparison, the mononuclear analogues (Ni-A−Ni-D) 10 were prepared according to literature procedures.
Figure 1. Molecular structures of Ni2-C′ with 30% probability level, and H atoms have been omitted for clarity. Selected bond lengths (Å) and angles (deg): Br1−Ni1 = 2.6319(15), Br2−Ni1 = 2.5222(15), N1−Ni1 = 2.195(9), N2−Ni1 = 2.041(8), Br3−Ni1 = 2.5780(16), O2−Ni1 = 2.087(8), Br4−Ni2 = 2.4643(17), N3−Ni2 = 2.105(14), N4−Ni2 = 2.062(8); Ni1−Br1−Ni2 = 90.40(5), N1−Ni1−N2 = 80.4(3), Br1−Ni1−Br2 = 82.97(5), N3−Ni2−N4 = 81.8(3), Br1− Ni2−Br2 = 86.35(5). C
DOI: 10.1021/acs.organomet.7b00698 Organometallics XXXX, XXX, XXX−XXX
Article
Organometallics Table 1. Effect of Catalyst and Temperature on Ethylene Polymerizationa entry
precat.
T (°C)
yield (g)
activityb
Mnc
Mw/Mnc
Bd
Tme (°C)
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24
Ni2-A Ni2-A Ni2-A Ni2-B Ni2-B Ni2-B Ni2-C Ni2-C Ni2-C Ni2-D Ni2-D Ni2-D Ni-A Ni-A Ni-A Ni-B Ni-B Ni-B Ni-C Ni-C Ni-C Ni-D Ni-D Ni-D
20 40 60 20 40 60 20 40 60 20 40 60 20 40 60 20 40 60 20 40 60 20 40 60
5.51 2.75 1.40 4.22 1.58 1.15 1.17 2.01 0.46 0.79 0.55 0.28 2.33 2.21 0.53 5.11 1.86 1.12 1.44 1.30 0.21 2.26 0.81 0.13
22.04 11.00 5.60 16.88 6.32 4.60 4.68 8.04 1.84 3.16 2.20 1.12 9.32 8.84 2.12 20.44 7.44 4.48 5.76 5.20 0.84 9.04 3.24 0.52
3800 2500 1500 2400 1100 600 4700 1700 1100 3100 1800 1000 2500 1000 900 1300 600 600 2300 1700 700 2500 2000 500
2.7 2.4 3.7 2.8 3.8 4.1 3.3 3.4 3.4 3.6 4.5 3.2 2.3 2.1 2.4 2.1 3.1 2.5 5.2 4.7 2.5 4.4 3.7 2.4
40 46 52 27 32 39 61 68 72 58 69 76 66 72 79 60 69 76 65 72 80 76 82 88
107.2; 119.5
111.8; 120.0 76.3 117.8
117.9 115.7 101.1 111.4 104.5
56.3
a Polymerization conditions: Ni = 5 μmol; cocatalyst MAO, Al/Ni = 500; CH2Cl2 = 2 mL, toluene = 20 mL; 9 atm of ethylene; time = 30 min. b105 g of PE (mol Ni)−1 h−1. cMn in g mol−1; Mn and Mw/Mn determined by GPC. dBranching numbers per 1000C were determined by 1H NMR. eMelting temperature determined by differential scanning calorimetry.
effects to slow down the β-hydride elimination and, correspondingly, the chain-walking process.20 For example, the branching number of polyethylene obtained by Ni-B (63/ 1000C at 20 °C) was much higher than by Ni2-B (27/1000C). A similar difference was observed for Ni-A (67/1000C) versus Ni2-A (40/1000C). While the branching number of polyethylene obtained by Ni-C (66/1000C) and Ni-D (74/1000C) at 20 °C was slightly higher than that by Ni2-C (61/1000C) and Ni2-D (59/1000C), respectively. In addition, the branching density was also affected by ligand steric effects on the aniline rings. For example, the branching number of polyethylenes obtained by iminopyridyl complexes Ni2-A (40−52/1000C) and Ni-A (67−79/1000C) with isopropyl groups was higher than those with the corresponding complexes Ni2-B (27−39/1000C) and Ni-B (63−76/1000C) with methyl groups, respectively. The branching densities of the polyethylenes obtained by aminopyridyl complexes [Ni2-C (iPr, 61−72/1000C) versus Ni2-D (Me, 59−76/1000C); Ni−C (iPr, 66−80/1000C) versus Ni-D (Me, 74−88/1000C)] showed almost the opposite trend. Generally, the iminopyridyl dinuclear complex Ni2-A showed high catalytic activity of up to 2.2 × 106 g of PE (mol Ni)−1 h−1, and Ni2-B produced semicrystalline polyethylene with low branching density (27/1000C) and high melting temperature (up to 120.0 °C), while the aminopyridyl dinuclear complex Ni2-C produced polyethylene with high molecular weight (4700 g mol−1). Both the metal−metal cooperativity effect and ligand steric effect may play key roles in determining the properties of these metal complexes.
ments in the catalytic performances of dinuclear complexes may also originate from metal−metal cooperative effect. The branching densities of the obtained polyethylenes were determined by 1H NMR spectroscopy,9a and the results are shown in Table 1. The branching densities (27−88/1000C) were increased with polymerization temperatures from 20 to 60 °C. As shown in Figure 2, the dinuclear complexes led to polyethylene with branching density significantly lower than that of the mononuclear analogues at room temperature. In addition, lower branching density was observed for the iminopyridyl dinuclear complexes compared with that for the corresponding aminopyridyl dinuclear complexes. It is attributed to the ability of the metal−metal cooperativity
Figure 2. Comparison of branching density of the polyethylene generated at 20 °C. D
DOI: 10.1021/acs.organomet.7b00698 Organometallics XXXX, XXX, XXX−XXX
Article
Organometallics
■
for L-A, L-B was obtained as a yellow solid (1.18 g, 85%): 1H NMR (500 MHz, CDCl3, ppm) δ 8.66 (m, 2H, NCH), 8.42 (s, 2H, pydineH), 8.28 (dt, J = 7.8, 1.1 Hz, 2H, pydine-H), 7.67 (td, J = 7.7, 1.7 Hz, 2H, pydine-H), 7.39 (m, 4H, pydine-H, aryl-H), 7.23 (dd, J = 7.5, 1.7 Hz, 2H, aryl-H), 7.13 (m, 2H, aryl-H), 7.08 (s, 4H, aryl-H), 1.98 (s, 12H, aryl-CH3), 1.75 (s, 6H, xanthene-CH3); 13C{1H} NMR (125 MHz, CDCl3, ppm) δ 162.9, 155.0, 149.5, 148.8, 147.5, 136.5, 133.6, 130.5, 130.0, 129.5, 129.0, 126.5, 125.0, 124.9, 123.0, 121.3, 34.6 (C(CH3)2), 32.7 (C(CH3)2), 18.3 (CH3); HRMS (m/z) calcd for C43H39N4O 627.3124; found 627.3257 [M + H]+. 4,4′-(9,9-Dimethylxanthene-4,5-diyl)-N,N′-(2-pyridinemethanamine)-bis(2,6-diisopropylanil) (L-C). Trimethylaluminum (12 mmol) was added slowly into a solution of L-A (1.47 g, 2 mmol) in 25 mL of toluene. The mixture was refluxed under N2 for 5 h. The mixture was quenched with 1 N NaOH solution in an ice bath. The organic layer was washed twice with brine, dried, filtered, and removed of solvent under reduced pressure. Recrystallization from hexane afforded L-C as a white crystal (1.36 g, 89%): 1H NMR (500 MHz, CDCl3, ppm) δ 8.60 (m, 2H, pydine-H), 7.52 (m, 2H, pydine-H), 7.39 (dd, J = 7.5, 2.0 Hz, 2H, pydine-H), 7.10−7.17 (m, 10H, pydine-H, aryl-H), 7.04 (m, 2H, aryl-H), 4.11 (dd, J = 8.6, 4.8 Hz, 2H, CHCH3), 3.94 (s, 2H, NH), 3.03 (m, 4H, CH(CH3)2), 1.76 (s, 6H, xantheneCH3), 1.44 (m, 6H, CHCH3), 0.95 (d, J = 6.7 Hz, 12H, CH(CH3)2), 0.77 (d, J = 6.8 Hz, 12H, CH(CH3)2); 13C{1H} NMR (125 MHz, CDCl3, ppm) δ 163.6, 149.3, 146.9, 141.2, 141.0, 136.2, 132.7, 130.7, 130.4, 130.1, 124.8, 124.6, 122.7, 121.9, 121.7, 60.6 (CHCH3), 34.1 (CHCH3), 33.9 (C(CH3)2), 33.7 (C(CH3)2), 27.5 (CH(CH3)2), 24.2 (CH(CH3)2), 24.1 (CH(CH3)2), 22.4 (CH(CH3)2); HRMS (m/z) calcd for C53H63N4O 771.5002; found 771.4367 [M + H]+. 4,4′-(9,9-Dimethylxanthene-4,5-diyl)-N,N′-(2-pyridinemethanamine)-bis(2,6-dimethylanil) (L-D). Using the same synthetic procedure for L-C, L-D was obtained as a white crystal (1.12 g, 84%): 1H NMR (500 MHz, CDCl3, ppm) δ 8.44 (m, 2H, pydine-H), 7.33 (m, 2H, pydine-H), 7.19 (d, J = 7.4 Hz, 2H, pydine-H), 7.01 (d, J = 8.0 Hz, 4H, pydine-H, aryl-H), 6.9 (m, 4H, aryl-H), 6.80 (s, 4H, arylH), 4.31 (m, 2H, CHCH3), 3.94 (s, 2H, NH), 1.86 (s, 12H, aryl-CH3), 1.53 (m, 6H, xanthene-CH3), 1.36 (m, 6H, CHCH3); 13C{1H} NMR (125 MHz, CDCl3, ppm) δ 164.2, 149.2, 147.5, 143.9, 136.2, 130.4, 130.2, 130.0, 128.8, 128.4, 124.2, 122.7, 121.9, 121.3, 57.8 (CHCH3), 34.4 (C(CH3)2), 32.3 (C(CH3)2), 23.1 (CHCH3), 18.8 (aryl-CH3); HRMS (m/z) calcd for C45H47N4O 659.3750; found 659.4578 [M + H]+. Synthesis of the Nickel Complexes. All complexes were prepared in a similar manner by the reaction of (DME)NiBr2 with the corresponding ligands in dichloromethane. A typical synthetic procedure of Ni2-A is as follows: [(DME)NiBr2] (0.17 g, 0.54 mmol) and L-A20a (0.20 g, 0.27 mmol) were combined in a Schlenk flask under a N2 atmosphere. CH2Cl2 (20 mL) was added, and the reaction mixture was stirred at room temperature for 12 h. The resulting suspension was filtered. The solvent was removed under vacuum, and the brown solid powder was washed with diethyl ether (2 × 10 mL) and then dried under vacuum at room temperature to obtain Ni2-A (0.25 g, 79%); MALDI-TOF-MS (m/z) calcd for C51H54Br3N4Ni2O 1092.0412; found 1092.0499 [M − Br] + . Anal. Calcd for C51H54Br4N4Ni2O: C, 52.09; H, 4.63; N, 4.76. Found: C, 52.38; H, 4.69; N, 4.57. Ni2-B was obtained as a brown solid (0.27 g, 80%): MALDI-TOFMS (m/z) calcd for C43H38Br3N4Ni2O 979.9160; found 980.0365 [M − Br]+. Anal. Calcd for C43H38Br4N4Ni2O: C, 48.55; H, 3.60; N, 5.27. Found: C, 48.38; H, 3.69; N, 5.57. Ni2-C was obtained as a brown solid (0.21 g, 67%): MALDI-TOFMS (m/z) calcd for C53H62Br3N4Ni2O 1124.0882; found 1124.0365 [M − Br]+. Anal. Calcd for C53H62Br4N4Ni2O: C, 52.78; H, 5.01; N, 4.65. Found: C, 52.38; H, 4.69; N, 4.57. Ni2-D was obtained as a brown solid (0.23 g, 70%): MALDI-TOFMS (m/z) calcd for C45H46Br3N4Ni2O 1011.9610; found 1012.0365 [M − Br]+. Anal. Calcd for C45H46Br4N4Ni2O: C, 49.32; H, 4.23; N, 5.11. Found: C, 49.38; H, 3.69; N, 5.47. Procedure for Ethylene Polymerization. In a typical experiment, ethylene polymerization was performed in a 350 mL thick-
CONCLUSIONS In summary, four new xanthene-bridged dinucleating ligands bearing imino- and aminopyridyl moieties and their dinuclear nickel complexes were synthesized and characterized. These dinucleating ligands were designed in an attempt to modulate the coordination environment, steric and metal−metal cooperativity effects, and the electronic density of the metal center, which may eventually translate into the modulation of catalyst properties as well polymer microstructures. In addition, the properties of these dinuclear complexes in ethylene polymerization were compared with the corresponding mononuclear nickel complexes. These iminopyridyl dinickel complexes showed higher catalytic activities, and produced polyethylene with much lower branching density (27/1000C) than their mononuclear analogues. These results demonstrated the potential applications of metal−metal cooperativity effect in controlling the ethylene polymerization process, especially the capability of slowing down β-hydride elimination and the corresponding chain-walking process.
■
EXPERIMENTAL SECTION
General Considerations. All experiments were carried out under a dry nitrogen atmosphere by using standard Schlenk techniques or a glovebox. Deuterated solvents for NMR spectroscopy were dried and distilled prior to use. 1H and 13C NMR spectra were recorded with a Bruker Ascend 400 spectrometer at ambient temperature unless otherwise stated. The chemical shifts of the 1H and 13C NMR spectra were referenced to tetramethylsilane (TMS). Coupling constants are in hertz. Elemental analysis was performed by the Analytical Center of the University of Science and Technology of China. Mass spectra were recorded on a P-SIMS-Gly from Bruker Daltonics Inc. (EI+). X-ray diffraction data were collected at 298(2) K on a Bruker Smart CCD area detector with graphite-monochromated Mo Kα radiation (λ = 0.71073 Å). Gel permeation chromatography (GPC) was carried out at 150 °C by using a PL-GPC 220 high-temperature GPC system. 1,2,4-Trichlorobenzene was used as the solvent at a flow rate of 1.0 mL min−1, and the system was calibrated by using a polystyrene standard and was corrected for linear polyethylene by universal calibration by using the Mark−Houwink parameters of Rudin: K = 1.75 × 10−2 cm3 g−1 and R = 0.67 for polystyrene and K = 5.90 × 10−2 cm3 g−1 and R = 0.69 for polyethylene. Dichloromethane, toluene, tetrahydrofuran, and hexanes were purified by solvent purification systems. 4,4′-(9,9Dimethylxanthene-4,5-diyl)-bis(2,6-diisopropylaniline), 4,4′-(9,9-dimethylxanthene-4,5-diyl)-bis(2,6-dimethylaniline), Ni-A, Ni-B, Ni-C, and Ni-D were prepared according to reported procedures.10,20 All other reagents were purchased from commercial sources and used without purification. Synthesis of the Dinucleating Ligands. 4,4′-(9,9-Dimethylxanthene-4,5-diyl)-N,N′-(2-pyridinylmethylene)-bis(2,6-diisopropylanil) (L-A). A 50 mL round-bottom flask was charged with 4,4′-(9,9dimethylxanthene-4,5-diyl)-bis(2,6-diisopropylaniline) (1.00 g, 1.79 mmol), 2-pyridinecarboxaldehyde (1.30 g, 12.1 mmol), toluene (30 mL), and a catalytic amount of p-toluenesulfonic acid. After being refluxed for 24 h, the mixture was concentrated to about 10 mL. When a layer of 20 mL of methanol was added, the mixture was recrystallized at −20 °C to afford L-A as a yellow solid (1.21 g, 90%): 1H NMR (500 MHz, CDCl3, ppm) δ 8.58 (d, J = 4.9 Hz, 2H, NCH), 8.22 (m, 4H, pydine-H), 7.74 (t, J = 7.7 Hz, 2H, pydine-H), 7.32 (m, 4H, aryl-H), 7.19 (m, 6H, pydine-H, aryl-H), 7.07 (t, J = 7.7 Hz, 2H, aryl-H), 2.76 (m, 4H, CH(CH3)2), 1.72 (s, 6H, xanthene-CH3), 0.88 (d, J = 7.0 Hz, 24H, CH(CH3)2); 13C{1H} NMR (125 MHz, CDCl3, ppm) δ 162.5, 154.8, 149.6, 147.7, 147.1, 136.7, 136.6, 134.4, 130.8, 130.5, 130.2, 125.4, 125.2, 124.4, 122.9, 121.7, 34.3 (C(CH3)2), 34.1 (C(CH3)2), 28.1 (CH(CH3)2), 23.4 (CH(CH3)2); HRMS (m/z) calcd for C51H55N4O 739.4376; found 739.4358 [M + H]+. 4,4′-(9,9-Dimethylxanthene-4,5-diyl)-N,N′-(2-pyridinylmethylene)-bis(2,6-dimethylanil) (L-B). Using the same synthetic procedure E
DOI: 10.1021/acs.organomet.7b00698 Organometallics XXXX, XXX, XXX−XXX
Article
Organometallics
G. W. J. Am. Chem. Soc. 2014, 136, 7213−7216. (f) Guo, L. H.; Chen, C. L. Sci. China: Chem. 2015, 58, 1663−1673. (g) Guo, L. H.; Dai, S. Y.; Sui, X. L.; Chen, C. L. ACS Catal. 2016, 6, 428−441. (3) (a) Johnson, L. K.; Mecking, S.; Brookhart, M. J. Am. Chem. Soc. 1996, 118, 267−268. (b) Guan, Z.; Cotts, P. M.; McCord, E. F.; McLain, S. J. Science 1999, 283, 2059−2062. (c) Wang, F. Z.; Tanaka, R.; Li, Q. S.; Yuan, J. C.; Nakayama, Y.; Shiono, T. J. Mol. Catal. A: Chem. 2015, 398, 231−240. (d) Dai, S. Y.; Sui, X. L.; Chen, C. L. Angew. Chem., Int. Ed. 2015, 54, 9948−9953. (e) Guo, L. H.; Dai, S. Y.; Chen, C. L. Polymers 2016, 8, 37. (f) Dai, S. Y.; Chen, C. L. Angew. Chem., Int. Ed. 2016, 55, 13281−13285. (g) Dai, S. Y.; Zhou, S. X.; Zhang, W.; Chen, C. L. Macromolecules 2016, 49, 8855−8862. (h) Sui, X. L.; Hong, C. W.; Pang, W. M.; Chen, C. L. Mater. Chem. Front 2017, 1, 967−972. (i) Na, Y. N.; Zhang, D.; Chen, C. L. Polym. Chem. 2017, 8, 2405−2409. (j) Li, M.; Wang, X. B.; Luo, Y.; Chen, C. L. Angew. Chem., Int. Ed. 2017, 56, 11604−11609. (k) Lian, K.; Zhu, Y.; Li, W.; Dai, S. Y.; Chen, C. L. Macromolecules 2017, 50, 6074−6080. (l) Chen, Z.; Liu, W.; Daugulis, O.; Brookhart, M. J. Am. Chem. Soc. 2016, 138, 16120−16129. (m) Zhao, M. H.; Chen, C. L. ACS Catal. 2017, 7, 7490−7494. (4) (a) Zhang, D.; Nadres, E. T.; Brookhart, M.; Daugulis, O. Organometallics 2013, 32, 5136−5413. (b) Wang, F. Z.; Yuan, J. C.; Song, F. Y.; Li, J.; Jia, Z.; Yuan, B. N. Appl. Organomet. Chem. 2013, 27, 319−327. (c) Yuan, J. C.; Wang, F. Z.; Xu, W. B.; Mei, T. J.; Li, J.; Yuan, B. N.; Song, F. Y.; Jia, Z. Organometallics 2013, 32, 3960−3968. (d) Yuan, J. C.; Wang, F. Z.; Yuan, B. N.; Jia, Z.; Song, F. Y.; Li, J. J. Mol. Catal. A: Chem. 2013, 370, 132−139. (e) Tao, W. J.; Li, J. F.; Peng, A. Q.; Sun, X. L.; Yang, X. H.; Tang, Y. Chem. - Eur. J. 2013, 19, 13956−13961. (f) Liu, J.; Chen, D. R.; Wu, H.; Xiao, Z. F.; Gao, H. Y.; Zhu, F. M.; Wu, Q. Macromolecules 2014, 47, 3325−3331. (g) Wang, F. Z.; Tanaka, R.; Cai, Z. G.; Nakayama, Y.; Shiono, T. Polymers 2016, 8, 160. (h) Wang, R. K.; Zhao, M. H.; Chen, C. L. Polym. Chem. 2016, 7, 3933−3938. (i) Zou, W. P.; Chen, C. L. Organometallics 2016, 35, 1794−1801. (k) Long, B. K.; Eagan, J. M.; Mulzer, M.; Coates, G. W. Angew. Chem. 2016, 128, 7222−7226. (5) (a) Bianchini, C.; Giambastiani, G.; Luconi, L.; Meli, A. Coord. Chem. Rev. 2010, 254, 431−455. (b) Yu, J.; Zeng, Y.; Huang, W.; Hao, X.; Sun, W. H. Dalton Trans. 2011, 40, 8436−8443. (c) Zhang, L.; Hao, X.; Sun, W. H.; Redshaw, C. ACS Catal. 2011, 1, 1213−1220. (d) Song, S.; Xiao, T.; Wang, L.; Redshaw, C.; Wang, F.; Sun, W. H. J. Organomet. Chem. 2012, 699, 18−25. (e) Huang, F.; Sun, Z. L.; Du, S. Z.; Yue, E. L.; Ba, J. J.; Hu, X. Q.; Liang, T. L.; Galland, G. B.; Sun, W. H. Dalton Trans. 2015, 44, 14281−14292. (6) (a) Younkin, T. R.; Connor, E. F.; Henderson, J. I.; Friedrich, S. K.; Grubbs, R. H.; Bansleben, D. A. Science 2000, 287, 460−462. (b) Weberski, M. P.; Chen, C.; Delferro, M.; Zuccaccia, C.; Macchioni, A.; Marks, T. J. Organometallics 2012, 31, 3773−3789. (c) Weberski, M. P.; Chen, C.; Delferro, M.; Marks, T. J. Chem. - Eur. J. 2012, 18, 10715−10732. (d) Stephenson, C. J.; McInnis, J. P.; Chen, C.; Weberski, M. P.; Motta, A.; Delferro, M.; Marks, T. J. ACS Catal. 2014, 4, 999−1003. (e) Wiedemann, T.; Voit, G.; Tchernook, A.; Roesle, P.; Göttkerschnetmann, I.; Mecking, S. J. Am. Chem. Soc. 2014, 136, 2078−2085. (f) Ö lscher, F.; Göttkerschnetmann, I.; Monteil, V.; Mecking, S. J. Am. Chem. Soc. 2015, 137, 14819−14828. (g) Hu, X. H.; Dai, S. Y.; Chen, C. L. Dalton Trans. 2016, 45, 1496−1503. (7) (a) 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. Acc. Chem. Res. 2013, 46, 1438−1449. (b) Carrow, B. P.; Nozaki, K. Macromolecules 2014, 47, 2541−2555. (c) Liang, T.; Chen, C. L. Organometallics 2017, 36, 2338−2341. (d) Chen, M.; Yang, B. P.; Chen, C. L. Angew. Chem., Int. Ed. 2015, 54, 15520− 15524. (e) Chen, M.; Zou, W. P.; Cai, Z. G.; Chen, C. L. Polym. Chem. 2015, 6, 2669−2676. (f) Sui, X. L.; Dai, S. Y.; Chen, C. L. ACS Catal. 2015, 5, 5932−5937. (g) Nakano, R.; Nozaki, K. J. Am. Chem. Soc. 2015, 137, 10934−10937. (h) Ota, Y.; Ito, S.; Kobayashi, M.; Kitade, S.; Sakata, K.; Tayano, T.; Nozaki, K. Angew. Chem., Int. Ed. 2016, 55, 7505−7509. (i) Jian, Z.; Falivene, L.; Boffa, G.; Ortega Sánchez, S.; Caporaso, L.; Grassi, A.; Mecking, S. Angew. Chem., Int. Ed. 2016, 55, 14378−14383. (j) Chen, M.; Chen, C. L. ACS Catal. 2017, 7, 1308−
walled glass pressure vessel with a magnetic stirrer bar in a glovebox. After the reactor was dried under N2 atmosphere, the required amount of MAO and toluene (20 mL) was added to the reactor. The pressure vessel was connected to a high-pressure polymerization line, and the solution was degassed. The vessel was warmed to the desired temperature by using an oil bath and allowed to equilibrate for 5 min. Then the catalyst solution in CH2Cl2 (2 mL) was injected into the vessel with a syringe. With rapid stirring, the reactor was pressurized and maintained at 9.0 atm of ethylene. After the desired amount of polymerization time, the vessel was vented and terminated with 150 mL of a 3% HCl−MeOH solution. The polymers obtained were adequately washed with methanol and dried under vacuum at 50 °C for 24 h. Analysis of the polymer branching by 1H NMR spectroscopy: branching density, branches/1000C = (CH3/3)/[(CH + CH2 + CH3)/2] × 1000.9a CH3(alkyl methyl, alk-CH3, m, 0.77−0.95 ppm), CH2 and CH (alk-CH and alk-CH2, m, ca. 1.0−1.45 ppm) refer to the intensities of the methyl, methylene, and methine resonances in 1H NMR spectra.
■
ASSOCIATED CONTENT
* Supporting Information S
The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.organomet.7b00698. NMR spectra of new ligands L-A−L-D (Figures S1−S7); 1 H NMR and DSC curves of polyethylene samples (Figures S8−S35), and crystallographic data (PDF) Accession Codes
CCDC 1508057 contains the supplementary crystallographic data for this paper. These data can be obtained free of charge via www.ccdc.cam.ac.uk/data_request/cif, or by emailing data_
[email protected], or by contacting The Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: +44 1223 336033.
■
AUTHOR INFORMATION
Corresponding Authors
*E-mail:
[email protected]. *E-mail:
[email protected]. ORCID
Fuzhou Wang: 0000-0003-0470-7110 Notes
The authors declare no competing financial interest.
■
ACKNOWLEDGMENTS This work was supported by the National Natural Science Foundation of China (NSFC, 21704094), the Chinese Postdoctoral Science Foundation (2017M612076), Fundamental Research Funds for the Central Universities (WK2060200025), Advanced Catalysis and Green Manufacturing Collaborative Innovation Center (ACGM2016-06-01), and Yixing Taodu Ying Cai Program.
■
REFERENCES
(1) (a) Ittel, S. D.; Johnson, L. K.; Brookhart, M. Chem. Rev. 2000, 100, 1169−1203. (b) Nakamura, A.; Ito, S.; Nozaki, K. Chem. Rev. 2009, 109, 5215−5244. (c) Chen, E. Y. X. Chem. Rev. 2009, 109, 5157−5214. (2) (a) Chen, G.; Ma, X. S.; Guan, Z. J. Am. Chem. Soc. 2003, 125, 6697−6704. (b) Chen, C.; Luo, S.; Jordan, R. F. J. Am. Chem. Soc. 2008, 130, 12892−12893. (c) Chen, C.; Jordan, R. F. J. Am. Chem. Soc. 2010, 132, 10254−10255. (d) Chen, C.; Luo, S. J.; Jordan, R. F. J. Am. Chem. Soc. 2010, 132, 5273−5284. (e) Vaidya, T.; Klimovica, K.; LaPointe, A. M.; Keresztes, I.; Lobkovsky, E. B.; Daugulis, O.; Coates, F
DOI: 10.1021/acs.organomet.7b00698 Organometallics XXXX, XXX, XXX−XXX
Article
Organometallics 1312. (k) Wada, S.; Jordan, R. F. Angew. Chem., Int. Ed. 2017, 56, 1820−1824. (l) Zhang, D.; Chen, C. L. Angew. Chem., Int. Ed. 2017, 56, 14672−14676. (m) Yang, B. P.; Xiong, S. Y.; Chen, C. L. Polym. Chem. 2017, 8, 6272−6276. (8) (a) Luo, H. K.; Schumann, H. J. Mol. Catal. A: Chem. 2005, 227, 153−161. (b) Takano, S.; Takeuchi, D.; Osakada, K.; Akamatsu, N.; Shishido, A. Angew. Chem., Int. Ed. 2014, 53, 9246−9250. (c) Takeuchi, D.; Takano, S.; Takeuchi, Y.; Osakada, K. Organometallics 2014, 33, 5316−5323. (d) Takano, S.; Takeuchi, D.; Osakada, K. Chem. - Eur. J. 2015, 21, 16209−16218. (e) Hu, T.; Tang, L. M.; Li, X. F.; Li, Y. S.; Hu, N. H. Organometallics 2005, 24, 2628−2632. (f) Rodriguez, B. A.; Delferro, M.; Marks, T. J. Organometallics 2008, 27, 2166−2168. (g) Chen, Z. T.; Yao, E. D.; Wang, J. C.; Gong, X. Y.; Ma, Y. G. Macromolecules 2016, 49, 8848−8854. (9) (a) Jenkins, J. C.; Brookhart, M. Organometallics 2003, 22, 250− 256. (b) McCord, E. F.; McLain, S. J.; Nelson, L. T. J.; Ittel, S. D.; Tempel, D.; Killian, C. M.; Johnson, L. K.; Brookhart, M. Macromolecules 2007, 40, 410−420. (c) Rosar, V.; Meduri, A.; Montini, T.; Fini, F.; Carfagna, C.; Fornasiero, P.; Balducci, G.; Zangrando, E.; Milani, B. ChemCatChem 2014, 6, 2403−2418. (d) Hu, H.; Zhang, L.; Gao, H.; Zhu, F.; Wu, Q. Chem. - Eur. J. 2014, 20, 3225−3233. (e) Wang, F. Z.; Tanaka, R.; Cai, Z. G.; Nakayama, Y.; Shiono, T. Macromol. Rapid Commun. 2016, 37, 1375−1381. (f) Wang, F. Z.; Tanaka, R.; Cai, Z. G.; Nakayama, Y.; Shiono, T. Polymer 2017, 127, 88−100. (g) Wang, F. Z.; Tian, S. S.; Li, R. P.; Li, W. M.; Chen, C. L. Chin. J. Polym. Sci. 2018, DOI: 10.1007/s10118018-2038-6. (10) (a) Laine, T. V.; Lappalainen, K.; Liimatta, J.; Aitola, E.; Löfgren, B.; Leskelä, M. Macromol. Rapid Commun. 1999, 20, 487− 491. (b) Laine, T. V.; Piironen, U.; Lappalainen, K.; Klinga, M.; Aitola, E.; Leskelä, M. J. Organomet. Chem. 2000, 606, 112−114. (11) (a) Sun, W. H.; Song, S.; Li, B.; Redshaw, C.; Hao, X.; Li, Y. S.; Wang, F. Dalton Trans. 2012, 41, 11999−12010. (b) Song, S.; Xiao, T.; Wang, L.; Redshaw, C.; Wang, F.; Sun, W. H. J. Organomet. Chem. 2012, 699, 18−25. (12) Chen, Z.; Allen, K. E.; White, P. S.; Daugulis, O.; Brookhart, M. Organometallics 2016, 35, 1756−1760. (13) Dai, S. Y.; Sui, X. L.; Chen, C. L. Chem. Commun. 2016, 52, 9113−9116. (14) (a) Sujith, S.; Joe, D. J.; Na, S. J.; Park, Y. W.; Choi, C. H.; Lee, B. Y. Macromolecules 2005, 38, 10027−10033. (b) Lee, H.; Kwon, Y.; Lee, S. Y.; Na, S. J.; Han, S. I.; Yun, H.; Lee, H.; Park, Y. W. J. Am. Chem. Soc. 2005, 127, 3031−3037. (c) Xing, Q. F.; Song, K. F.; Liang, T. L.; Liu, Q. B.; Sun, W. H.; Redshaw, C. Dalton Trans. 2014, 43, 7830−7837. (15) Zhu, L.; Fu, Z. S.; Pan, H. J.; Feng, W.; Chen, C.; Fan, Z. Q. Dalton Trans. 2014, 43, 2900−2906. (16) (a) Jie, S. Y.; Zhang, D. H.; Zhang, T. Z.; Sun, W. H.; Chen, J. T.; Ren, Q.; Liu, D. B.; Zheng, G.; Chen, W. J. Organomet. Chem. 2005, 690, 1739−1749. (b) Kong, S.; Song, K.; Liang, T.; Guo, C. Y.; Sun, W. H.; Redshaw, C. Dalton Trans. 2013, 42, 9176−9187. (17) Pelletier, J. D. A.; Fawcett, J.; Singh, K.; Solan, G. A. J. Organomet. Chem. 2008, 693, 2723−2731. (18) (a) Takeuchi, D.; Chiba, Y.; Takano, S.; Osakada, K. Angew. Chem., Int. Ed. 2013, 52, 12536−12540. (b) Takeuchi, D.; Chiba, Y.; Takano, S.; Kurihara, H.; Kobayashi, M.; Osakada, K. Polym. Chem. 2017, 8, 5112−5119. (19) (a) Radlauer, M. R.; Day, M. W.; Agapie, T. J. Am. Chem. Soc. 2012, 134, 1478−1481. (b) Radlauer, M. R.; Day, M. W.; Agapie, T. Organometallics 2012, 31, 2231−2243. (c) Radlauer, M. R.; Buckley, A. K.; Henling, L. M.; Agapie, T. J. Am. Chem. Soc. 2013, 135, 3784− 3787. (20) (a) Wang, R. K.; Sui, X. L.; Pang, W. M.; Chen, C. L. ChemCatChem 2016, 8, 434−440. (b) Na, Y. N.; Wang, X. B.; Lian, K. B.; Zhu, W.; Li, M.; Luo, Yi.; Chen, C. L. ChemCatChem 2017, 9, 1062−1066. (21) (a) Liu, H. F.; Motta, A.; Delferro, M.; Marks, T. J. J. Am. Chem. Soc. 2013, 135, 14460−14460. (b) Liu, H. F.; Motta, A.; Mouat, A. R.; Delferro, M.; Marks, T. J. J. Am. Chem. Soc. 2014, 136, 10460−10469. G
DOI: 10.1021/acs.organomet.7b00698 Organometallics XXXX, XXX, XXX−XXX
