Enhancement on Alternating Copolymerization of Carbon Monoxide

Article Cite This: Macromolecules XXXX, XXX, XXX−XXX

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Enhancement on Alternating Copolymerization of Carbon Monoxide and Styrene by Dibenzobarrelene-Based α‑Diimine Palladium Catalysts Zefan Xiao, Handou Zheng, Cheng Du, Liu Zhong, Heng Liao, Jie Gao, Haiyang Gao,* and Qing Wu School of Materials Science and Engineering, PCFM Lab, GD HPPC Lab, Sun Yat-sen University, Guangzhou 510275, China

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S Supporting Information *

ABSTRACT: CO/styrene copolymerization by α-diimine palladium catalysts is a promising method for direct synthesis of polyketones. The effect of the catalyst backbone structure on CO/styrene copolymerization has been studied with the aim of developing robust α-diimine palladium catalysts able to improve the polymerization productivity and controllability. Dibenzobarrelene derived α-diimine palladium catalysts without o-aryl substituents were designed and synthesized for CO/styrene alternating copolymerization. Introduction of the rigid and bulky dibenzobarrelene backbone enhanced the thermal stability and the productivity of palladium catalyst. The dibenzobarrelene ligand backbone also improved the polymerization controllability, and living CO/styrene copolymerizations were achieved at 15 °C using α-diimine palladium catalysts in CH2Cl2. The steric hindrance of backbone and the π−π stacking between the dibenzobarrelene backbone and the aniline played crucial roles in stereocontrol and productivity.

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INTRODUCTION Polyketones generated by olefin/carbon monoxide (CO) alternating copolymerization have been of great interest over the past decades due to their unusual properties, the wide range of application as engineering material, and the cheap and available stocks.1,2 Moreover, the postfunctionalization of the polyketone macromolecules is possible with no degradation of the polymeric chain yielding new polymeric materials because of the presence of the carbonyl group.3−7 The late transition metal catalysts, especially palladium-based catalysts, are capable for catalyzing olefin/CO copolymerization efficiently.8−10 The diphosphine palladium catalysts are highly efficient for alkene/CO copolymerization,8 and a CO/ ethylene/propylene terpolymer called “Carilon” has been successfully commercialized by Shell Company.11 However, diphosphine palladium catalysts are not suited for vinyl arene/ CO copolymerization.12 Instead, palladium catalysts bearing bidentate nitrogen ligands can efficiently catalyze styrene/CO copolymerization.12−33 Two noteworthy examples are the 2,2′bipyridine palladium catalysts and the 1,10-phenanthroline palladium catalysts, which are excellent catalysts for the copolymerizations of styrene or 4-tert-butylstyrene with CO, yielding the perfectly alternating polyketones.12−20 α-Diimine palladium catalysts for vinyl arene/CO copolymerization have recently attracted considerable interest because of easy modifications on steric and electronic effects.34,35 Previous documents have mainly addressed the steric effect of o-aryl substituents on the productivity and the stereocontrol on vinyl arene/CO copolymerization.36−40 Additionally, mechanistic studies have demonstrated that the © XXXX American Chemical Society

resting state is the palladium−acyl−carbonyl species, and the rate-limiting step is the coordination of vinyl arene monomer.19,41 Therefore, bulky o-aryl substituents of αdiimine ligand usually lead to a decrease in productivity and molecular weight of polyketone because of the steric repulsion between vinyl arene monomer and o-aryl substituents of the ligand,37−39 which is contrast to the steric effect on olefin polymerization using α-diimine nickel and palladium catalyst.42−48 On the other hand, less bulky o-aryl substituents generally lead to a short lifetime of palladium catalysts because of their poor stability although introduction of electrondonating groups on the meta-/para-position of the aniline moieties can improve the stability of palladium catalysts.35,43 Less bulky o-aryl substituents also hardly suppress the chain transfer reaction (β-hydrogen elimination or monomer-assisted β-hydrogen abstraction) and the access of counterion to metal center,19,37 thereby lowing molecular weight and broadening polydispersity of copolymer.39,49 The design of the α-diimine palladium catalyst with the subtle steric bulk of o-aryl for CO/ vinyl arene copolymerizations thus remains a great challenge. In comparison with modification on the aniline moiety, a few modifications of backbone in the α-diimine palladium catalyst for CO/styrene copolymerization were studied. Although the hydrogen derived α-diimine palladium catalyst (ArNC(R)−(R)CNAr, R = H) was more highly active than the methyl- and acenaphthene-based α-diimine palladium Received: August 18, 2018 Revised: October 23, 2018

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DOI: 10.1021/acs.macromol.8b01786 Macromolecules XXXX, XXX, XXX−XXX

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Macromolecules Scheme 1. Synthetic Route of α-Diimine Palladium Complexes

catalysts (R = Me, acenaphthene),37 the steric effect of the backbone substituent should be ruled out because of the square-planar conformation of palladium complexes. Herein, we proposed a promising approach to enhancement on palladium-catalyzed CO/styrene copolymerization by increasing the steric bulk of the α-diimine ligand backbone while this approach is highly efficient for enhancing stability and living fashion of α-diimine nickel and palladium catalysts for (co)polymerization of ethylene and polar monomer.43−45,50,51 A series of dibenzobarrelene-based α-diimine palladium catalysts without o-aryl substituents have been synthesized for living alternating CO/styrene copolymerization by moving steric bulk from the o-aryl to the ligand backbone. We envisioned that the bulk of the rigid dibenzobarrelene backbone showed a steric effect on the palladium center and expectedly inhibited the chain transfer reaction as well as the access of counterion to metal center, and no substituents on the ortho-position of aryl provided an open space for coordination of styrene monomer. The unprecedented influence of π−π stacking between the dibenzobarrelene backbone and the aniline on the productivity and the stereocontrol in CO/styrene copolymerization was also discovered.

CH2Cl2. Normally, the chloromethylpalladium complexes N1−N4 displayed a distorted square-planar coordination around the palladium center (Figures 1−4). The bulky and

Figure 1. Crystal structure of α-diimine palladium complex N1 (front and side views). The hydrogen atoms and two CH2Cl2 molecules are omitted for clarity.

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RESULTS AND DISCUSSION Synthesis and Characterization of Palladium Complexes. Dibenzobarrelene derived α-diimine palladium complexes with m-/p-methoxy groups but without o-aryl substituents were designed based on previously reported steric and electronic effects of the aniline moiety. 34,52 The chloromethylpalladium complexes (N1−N3) were prepared according to similar synthetic route (Scheme 1).50,53 These neutral palladium complexes were further treated with sodium tetrakis(3,5-bis(trifluoromethyl)phenyl)borate (NaBArF) and acetonitrile to yield the cationic palladium complexes [(αdiimine)Pd(CH3CN)Me] +BArF− (1−3).42,50 All of the reported α-diimine palladium complexes were fully characterized by 1H and 13C NMR and elemental analysis. Acenaphthene (N4 and 4) and methyl (N5 and 5) derived α-diimine palladium complexes were also prepared and used for copolymerization comparison (Scheme 1). Single crystals of neutral palladium complexes N1−N4 suitable for X-ray diffraction analysis were obtained by slow diffusion of hexane into the palladium complex solution in

Figure 2. Crystal structure of α-diimine palladium complex N2 (front and side views). The hydrogen atoms are omitted for clarity.

Figure 3. Crystal structure of α-diimine palladium complex N3 (front and side views). The hydrogen atoms and a CH2Cl2 molecule are omitted for clarity. B


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exist in both the solution and the solid.60,61 Therefore, the unique dibenzobarrelene backbone provides the steric effect and the π−π stacking interaction, which is anticipated to have a great influence on CO/styrene copolymerization. CO/Styrene Copolymerization. Cationic palladium complexes were active for CO/styrene copolymerization. In the reported literature, 1,4-benzoquinone (BQ) was added into catalytic systems as an oxidant promoter to inhibit the decomposition of the active species (Pd2+) to inactive palladium metal (Pd0) and improve the lifetime of palladium catalyst and as a radical scavenger to prohibit the radical polymerization of styrene.1 Herein, effects of solvent and of 1,4-benzoquinone were first studied using catalyst 3. Polymerization results in Table 2 showed that catalyst 3 exhibited a higher productivity and produced a lower molecular weight copolymer in 2,2,2-trifluoroethanol (CF3CH2OH) than that in dichloromethane. In 2,2,2-trifluoroethanol, the presence of 1,4benzoquinone led to a drop in molecular weight of the copolymer because of rapid chain transfer. These observations were in agreement with previous reports.14,62,63 However, the addition of 1,4-benzoquinone led to an increase in molecular weight of the copolymer with decreased polydispersity index (PDI) in CH2Cl2. These results strongly indicated that 1,4benzoquinone remarkably promoted copolymerization in CH2Cl2 and could not play a role of chain transfer agent in the absence of alcoholic environment. CO/styrene copolymerizations were further studied using cationic palladium catalysts 1−3 under various temperatures (Table 3) in the presence of 1,4-benzoquinone in CH2Cl2. Generally, palladium catalysts were highly sensitive to reaction temperature toward CO/styrene copolymerizations. A slight temperature variation of 5 °C led to a significant change in productivity and copolymer molecular weight. When the reaction temperature was increased from 10 to 25 °C, the productivity of three palladium catalysts 1−3 greatly increased. When the temperature was further increased to 30 °C, catalysts 1 and 2 showed decreased productivity while catalyst 3 exhibited increased productivity. Palladium catalyst 3 showed the highest productivity under same conditions, which was consistent with previously reported electron-donating effect on CO/styrene copolymerizations.34,35,37 Besides, the molecular weight of copolymers increased and then decreased while the polydispersity index (PDI) became broad consistently with increased reaction temperature. The highest molecular weight and narrow PDI values (PDI < 1.20) were observed at 15 °C. On the basis of narrow polydispersity, the theoretical molecular weights of the obtained copolymers could be calculated by the ratios of the weight of the produced polymer to the amount of palladium catalyst used. The theoretical values were larger than the actual measured values at 20 °C (entries 8 and 13 in Table 3), indicating that occurrence of chain transfer reaction. The calculation results in Table 3 and

Figure 4. Crystal structure of α-diimine palladium complex N4 (front and side views). The hydrogen atoms and a CH2Cl2 molecule are omitted for clarity.

rigid dibenzobarrelene backbone of palladium complexes can effectively shield the back space of palladium metal and show moderate axial steric effect. For the dibenzobarrelene derived α-diimine palladium complex with bulky o-diisopropyl groups for ethylene polymerization, it has been reported that aniline moieties are nearly perpendicular to the five-membered Pd− diimine ring plane.50 However, it is noteworthy that aniline moieties of palladium complexes N1−N3 without o-aryl substituents are nearly parallel to the aryl rings of the dibenzobarrelene backbone. Crystal parameters in Table 1 Table 1. Crystal Parameters with Regard to the π−π Stacking Effect of Complexes N1−N4 Pd dihedral angles between dibenzobarrelene complex and aniline (deg)

vertical distance of two aryl (Å)

6.4241, 15.687 2.943, 5.857 14.154, 23.978 66.229, 88.778

N1 N2 N3 N4

2.5435, 2.6093 2.1735, 2.2580 2.3502, 2.8922

show that dihedral angles between the aniline moieties and the aryl ring of dibenzobarrelene are below 20° and vertical distances of two aryl rings are within 3 Å for palladium complexes N1 and N2. These crystal data strongly indicate the existence of the offset or slipped π−π stacking interaction, which has different conformations to face-to-face and edge-toface stacking interactions.54−57 According to the definitions of the pitch and roll angles presented by Curtis for the paralleldisplaced description of the offset π−π stacking, palladium complexes N1 and N2 have a “roll” π−π stacking.58 The reducing π−π stacking effect is observed for palladium complex N3 with increased methoxy groups. The unconcerned π−π stacking interactions are also present on a dibenzobarrelenebased α-diimine nickel complex with 2-substituents and a palladium complex with 4-substituents.53,59 For acenaphthyl αdiimine palladium analogue N4, no π−π stacking interaction is observed although the acenaphthene ring is aromatic (Figure 4). Besides, the π−π stacking interaction has been proved to

Table 2. Effects of BQ and of Solvent on CO/Styrene Copolymerization Using 3a entry

[BQ]/[Pd]

solvent

yield (g)

productivity (g CP/g Pd)

Mnb (kg/mol)

PDIb

1 2 3 4

5 0 5 0

CH2Cl2 CH2Cl2 CF3CH2OH CF3CH2OH

1.7812 0.3320 2.4212 1.3423

1318 250 1790 990

63.1 29.7 3.7 5.2

1.27 1.39 1.27 1.31

Polymerization conditions: 12.7 μmol of Pd catalyst, [styrene]/[Pd] = 6800, 1.0 atm of CO (absolute pressure), T = 30 °C, t = 24 h, 20 mL of solvent. bMolecular weight and PDI were determined by GPC using tetrahydrofuran as eluent.

a

C


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Macromolecules Table 3. CO/Styrene Copolymerization Results by Palladium Catalysts 1−5a entry

catalyst

temp (°C)

yield (g)


Mn‑GPCb (kg/mol)

PDI

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25

1 1 1 1 1 2 2 2 2 2 3 3 3 3 3 4 4 4 4 4 5 5 5 5 5

30 25 20 15 10 30 25 20 15 10 30 25 20 15 10 30 25 20 15 10 30 25 20 15 10

0.9682 1.1909 0.7940 0.7122 0.4385 1.4111 1.4913 1.3939 1.0007 0.6510 1.7812 1.6378 1.5330 1.1852 0.6762 1.3284 1.4994 1.3458 1.0067 0.6565 0.1741 0.2239 0.2257 0.2147 0.1951

716 881 587 527 324 1044 1103 1031 740 482 1318 1212 1134 877 500 983 1109 996 745 486 129 166 167 159 144

40.4 76.8 80.1 85.6 55.6 53.1 57.8 87.3 91.4 67.0 63.1 65.4 86.9 96.0 63.4 5.8 9.4 16.3 27.2 30.9 4.2 5.9 8.2 11.2 16.1

1.49 1.27 1.19 1.04 1.02 1.50 1.34 1.19 1.12 1.04 1.27 1.26 1.23 1.18 1.10 1.69 1.68 1.62 1.39 1.34 1.38 1.47 1.49 1.49 1.38

Mn‑theorc (kg/mol)

62.5 56.1 34.5

109.8 78.8 51.2

120.7 93.3 53.2

a Polymerization conditions: 12.7 μmol of Pd catalyst, [styrene]/[Pd] = 6800, [1,4-benzoquinone]/[Pd] = 5, 1.0 atm of CO (absolute pressure), t = 24 h, 20 mL of CH2Cl2. bMolecular weight and PDI were determined by GPC using chloroform (entries 1−5) or tetrahydrofuran (entries 6−25) as eluent. cTheoretical molecular weights were calculated by the ratios of the weight of the produced polymer to the amount of palladium catalyst used.

Table S1 showed that the theoretical molecular weights of copolymers produced by palladium catalyst 3 with 3,4,5trimethoxyanilines were well consistent with the determined molecular weight by GPC, while the determined molecular weights of copolymers produced by palladium catalysts 1 and 2 were larger than the theoretical molecular weights by factors of ∼1.5 and ∼1.1, respectively. This could be attributed to different initiation efficiencies of living palladium catalysts, and introduction of methoxy groups enhanced the initiation efficiency of palladium catalysts for CO/styrene copolymerization. Encouraged by the enhancement of 3,4,5-trimethoxyanilines, we further synthesized acenaphthene (4) and methyl (5) derived α-diimine palladium catalysts with 3,4,5-trimethoxyanilines and investigated backbone effect of palladium catalysts on CO/styrene copolymerization. Comparisons of copolymerization results using catalysts 3 versus 4 versus 5 at same reaction conditions (entries 11−25 in Table 3) clearly demonstrated ligand backbone effects. As initially envisioned, the introduction of the bulky backbone remarkably enhanced the thermal stability of the α-diimine palladium catalysts and polymerization controllability. The methyl-based α-diimine palladium catalyst 5 showed the lowest productivity and produced the lowest molecular weight copolymer. When acenaphthene was used instead of methyl on the backbone, enhanced productivity and increased molecular weight were observed. At elevated temperature of 30 °C, acenaphthene derived α-diimine palladium catalyst 4 also showed reduced productivity, but dibenzobarrelene derived palladium catalyst 3 showed the highest productivity. More notably, molecular

weight distributions of copolymers became narrow when the dibenzobarrelene was installed on the backbone, and narrowly dispersed copolymers (PDI < 1.20) were produced in a living fashion below 15 °C. To reliably calculate productivity and probe the thermal stability of catalyst 3, CO/styrene copolymerizations using catalyst 3 were performed above 30 °C using chlorobenzene as reaction solvent instead of low-boiling-point CH2Cl2 (Table 4). Catalyst 3 was slightly less active in chlorobenzene than the system in CH2Cl2 at the same conditions (30 °C) and produced lower molecular weight polymers with broad distributions (entry 11 in Table 3 versus entry 8 in Table 4) Table 4. CO/Styrene Copolymerization Results Using 3 at High Temperaturesa entry

temp (°C)

time (h)

yield (g)


Mnb (kg/mol)

PDIb

1 2 3 4 5 6 7 8

60 50 40 40 40 40 35 30

24 24 8 16 24 32 24 24

0.9287 1.6700 0.6579 1.3357 1.9367 2.6012 1.7364 1.5070

687 1236 487 988 1433 1925 1285 1115

4.1 6.7 20.4 21.2 22.4 23.5 43.1 56.9

1.34 1.56 1.68 1.81 1.88 1.89 1.69 1.63

a Polymerization conditions: 12.7 μmol of Pd catalyst, [styrene]/[Pd] = 6800, [1,4-benzoquinone]/[Pd] = 5, 1.0 atm of CO (absolute pressure), 20 mL of chlorobenzene. bMolecular weight and polydispersity index were determined by GPC using THF as eluent.

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Macromolecules because of the difference in solvent polarity. With increased temperature from 30 to 60 °C in chlorobenzene, the productivity of catalyst 3 increased and then decreased, and the highest productivity was achieved at 40 °C. Slightly reduced productivity and drop in polymer molecular weight were observed at 50 °C, suggesting that catalyst 3 was stable whereas chain transfer reaction greatly accelerated. The activity of catalyst 3 (productivity/h) at different time periods ranging from 8 to 32 h was used to test the catalyst lifetime at 40 °C in chlorobenzene. Figure 5 clearly shows that activity values

Scheme 2. Palladium-Catalyzed CO/Styrene Copolymerization and the π−π Stacking Assisted Coordination of Styrene for the Dibenzobarrelene-Based αDiimine Palladium

anthracene ring of aromatic aniline and styrene monomer was presumed.39 The living feature of copolymerization was further investigated using 1−3 at 15 °C (Table S1). Figure 6 shows

Figure 5. Plots of activity versus reaction time in CO/styrene copolymerization using 3 at 40 °C in chlorobenzene and the image of system solutions of 3 and 5.

remained relatively constant while polymer molecular weight slightly increased with prolonging time (Table 4). The palladium black generated from the decomposition of the catalyst in the polymerizing mixture was not observed for catalyst 3, whereas it appeared for the palladium catalyst 5 with dimethyl backbone at 30 °C (Figure 5). These results strongly indicated that bulky dibenzobarrelene backbone enhanced the thermal stability, the productivity of α-diimine palladium catalysts, and the polymerization controllability. The enhancement of the dibenzobarrelene backbone on CO/styrene copolymerization can be attributed to the unique nature of the bulky dibenzobarrelene backbone. The rigid dibenzobarrelene backbone kinetically improve the stability of palladium complexes because of a similar well-known Thorpe− Ingold effect between nitrogen donor atoms. The steric demand of the dibenzobarrelene backbone not only is expected to suppress the chain transfer reaction and enhance the controllability but also shields the back space of palladium center,50 thereby prohibiting the access of counterion to metal center and improving productivity.37 On the other hand, the resting state is the palladium−acyl−carbonyl species and the rate-limiting step is the coordination of styrene monomer for palladium-catalyzed CO/styrene copolymerization.19,41 The offset π−π stacking between the aniline and the dibenzobarrelene backbone may affect the enantioselective coordination of the styrene monomer.39 The formation of the offset π−π stacking among three aryl rings promotes the coordination of styrene monomer, thus improving the productivity (Scheme 2). Carfagna previously proposed a hypothesis on π−π stacking to explain enhanced productivity in aryl α-diimine palladium-catalyzed CO/styrene copolymerization, whereas no any evidence on π−π stacking was provided. A stabilizing effect deriving from a π−π stacking interaction between the

Figure 6. Plots of Mn (●, ◆, ▲) and PDI (○, ◇, △) as a function of styrene conversion using catalysts 1−3 at 15 °C and GPC curves of copolymers obtained by catalyst 3.

symmetric GPC traces of the copolymers obtained by 3 at different conversions of styrene monomer without tail peaks, which shift to the higher molecular weight region with the increased monomer conversion. Plots of number-average molecular weights (Mn) as a function of styrene conversion also illustrate that Mn grows linearly with the styrene conversion, and PDI (Mw/Mn) values are below 1.20 within 30 h, proving living copolymerizations with long lifetime using three catalysts 1−3. The copolymer with high molecular weight (Mn = 1.1 × 105 g mol−1) was formed after 30 h using 3, and its PDI was still precisely controlled (PDI = 1.18). To the best of our knowledge, this represents one of few samples on living copolymerization of CO and styrene using palladium catalysts.14 Alternating CO/styrene copolymerization mechanism has been previously investigated, and the end groups of polyketone chain have been also analyzed by MALDI-TOF-MS to elucidate the polymerization reaction cycles involving the initiation and chain transfer/termination.14,62 Herein, we characterized the chain end groups of low-molecular-weight polyketones by NMR analysis. Figure 7 shows 1H NMR of the polyketone produced in the trifluoroethanol CF3CH2OH (Mn = 3700, entry 3 in Table 2). The characteristic signals of CC double bond were observed at 5.75 and 5.23 ppm, indicating the form of chain terminal b (−CHCHPh) by β-hydrogen E


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realized perfectly alternating CO/styrene copolymerization.34,64,65 The stereochemistry of the CO/styrene copolymers was further characterized by 13C NMR spectroscopy recording the spectra in a mixture solution of 1,1,1,3,3,3-hexafluoroisopropanol (HFIP) and CDCl3. Figure 9 showed the ipso-

Figure 7. 1H NMR spectrum of the copolymer obtained by 3 in CF3CH2OH.

elimination. 19F NMR of the polyketone produced in the trifluoroethanol further showed two resonances at −62.44 and −73.57 ppm (Figure 8), which were assigned to the chain

Figure 9. The ipso-carbon atom region on 13C NMR spectra of CO/ styrene copolymers by catalysts 1−5.

carbon region (137−135 ppm) on 13C NMR spectra of the CO/styrene copolymers, and the microtacticity was determined by integration of the signals assigned to the ipso-carbon atom. The calculated triads in Table 5 showed that Table 5. Stereoregularity of CO/Styrene Copolymers Produced by Catalysts 1−5 stereoregularity (triads %)b

Figure 8. 19F NMR spectrum of the copolymer obtained by 3 in CF3CH2OH.

entry 1 3 5 6 11 16 21

beginning groups CF3CH2OOC− (g) and the chain terminal CF3CH2OCH(Ph)− (h), respectively. The chain beginning group CF3CH2OOC− (g) was derived from the oxidation of the Pd−H intermediate by the 1,4-benzoquinone, while the terminal CF3CH2OCH(Ph)− (d) was originated from chain transfer to trifluoroethanol (Scheme S4 in the Supporting Information). The integral of 1H NMR further showed that chain transfer by β-hydrogen or monomer-assisted β-hydrogen abstraction (red route in Scheme S4) was predominant, and a small amount of chain transfer to trifluoroethanol was also proved by 19F NMR.19 However, the polyketone produced in CH2Cl2 in a living fashion did not show CC double bond resonances in the 1H NMR spectrum (Figure S36), indicating no occurrence of chain transfer/termination (Scheme S4). In chlorobenzene, the low-molecular-weight polyketone produced at 60 °C showed CC double bond signals (entry 1 in Table 4), and the beginning methyl a was also observed (Figure S37). The molecular weight of the copolymer calculated by 1H NMR (Mn = 4200) was consistent with the value determined by GPC (Mn = 4100). Therefore, the chain transfer took place by βhydrogen elimination or monomer-assisted β-hydrogen abstraction,19 and 1,4-benzoquinone did not play a role of chain transfer agent in the absence of alcoholic environment, which was well consistent with experimental results in Table 2. The copolymerization products are real polyketone polymers without homopolystyrene. 1H NMR spectroscopies (Figure 7 and Figure S38) of copolymerization products showed that no characteristic signals of the methylene on consecutive styrene unit were observed at 1.8−1.2 ppm, indicating that all these α-diimine palladium catalysts 1−5

a

catalyst

T (°C)

ll

lu + ul

uu

Tg (°C)

1 1 1 2 3 4 5

30 20 10 30 30 30 30

1 1 1 3 5 29 25

29 26 26 35 51 57 61

70 73 73 62 44 14 14

111 113 112 112 111 103 100

a

All entries are in Table 3. bCalculated from the intensities of the 13C NMR ipso-carbon atom resonances.

polymerization temperature had almost no influence on the stereoregularity, but the dibenzobarrelene backbone significantly affected the stereoregularity of the CO/styrene copolymers. Methyl and acenaphthene derived α-diimine palladium catalysts 4 and 5 afforded random copolymers with nearly same triads (ll = 25−29%, uu = 14%). However, catalysts 1−3 with dibenzobarrelene backbone produced syndiotacticity-rich copolymers with uu triads of 44−70% and the almost absence of ll triads. Previously, Carfagna reported that the steric effect of o-aryl substituents on the stereoregularity of the CO/styrene copolymers and presented a ligand-assisted chain-end stereocontrol mechanism.38 Herein, the influence of dibenzobarrelene backbone on stereocontrol was also reasonably interpreted by a π−π stacking-assisted chain-end stereocontrol mechanism. Besides, the π−π stacking between aniline and the dibenzobarrelene backbone might affect the enantioselective coordination of the styrene monomer to forming the π−π stacking among three aryl rings (Scheme 2),38 which might be responsible for syndioselectivity. This speculation was further supported by the effect of the methoxy on syndioselectivity. The syndiotacticity (uu trials) of CO/styrene copolymers was F


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Future work is focused on copolymerizations of CO with various vinyl arene monomers and stereocontrol.

decreased by increasing numbers of methoxy group on the meta-position of aniline. As shown in crystal parameters with regard to the π−π stacking effect of palladium complexes in Table 1, catalysts 1 and 2 have stronger π−π stacking between the dibenzobarrelene backbone and aniline moieties than catalyst 3 with three methoxy groups, thereby having a higher syndioselectivity. In addition to previously reported steric and electronic effects on stereocontrol in palladium-catalyzed CO/ styrene copolymerization,32,36,39 the π−π stacking that we describe here provides a new access to tuning the stereoregularity of the CO/styrene copolymers. With increased the syndiotacticity of CO/styrene copolymers, the solubility of the copolymer became poor. The products obtained by catalysts 2−5 were easily dissolved tetrahydrofuran (THF) and CHCl3, while the polymers obtained by catalyst 1 have poor solubility in THF. Differential scanning calorimetry (DSC) in Figure 10 showed that only one

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EXPERIMENTAL SECTION

General Procedures. All manipulations involving air- and moisture-sensitive compounds were performed under an atmosphere of dried and purified nitrogen using standard vacuum-line, Schlenk, or glovebox techniques. Materials. Anhydrous dichloromethane, chlorobenzene, diethyl ether, and hexane were dried and purified by standard methods and freshly distilled under nitrogen. ZnCl2 was stored in the oven at 110 °C overnight prior to use. Anthracene, vinylene carbonate, and trifluoroacetic acid were purchased from Energy Chemical and used as received. Substituted anilines were purchased from Tokyo Chemical Industry and used as received. Carbon monoxide (CP grade 99.99%) was supplied by Air Liquid. Styrene monomer was also purchased from Energy Chemical, dried over CaH2, and then freshly distilled under vacuum prior to use in polymerization. Other commercially available reagents were purchased and used without purification. Measurements. Elemental analyses (C, H, and N) were performed on a Vario EL microanalyzer. NMR spectra of ligands, palladium complexes, and polymers were performed on Bruker 400 MHz instruments in CDCl3 or CD3OD using TMS as a reference. 13C NMR spectra of polyketones were recorded in 1,1,1,3,3,3-hexafluoroisopropanol with addition of CDCl3 for locking purposes. GPC analyses of the molecular weights and molecular weight distributions (PDI = Mw/Mn) of the polymers were performed on a Waters Breeze 2 GPC chromatograph equipped with a differential refractive-index detector. Tetrahydrofuran (THF) or chloroform was used as the eluent at a flow rate of 1.0 mL/min. DSC analyses were conducted with a PerkinElmer DSC-4000 system. The DSC curves were recorded as second heating curves from 30 to 300 °C at a heating rate of 10 °C/min and a cooling rate of 10 °C/min. Crystal Structure Determination. The crystals of palladium complexes were mounted on a glass fiber and transferred to a Bruker CCD platform diffractometer. Data obtained with the ω−2θ scan mode were collected on a Bruker SMART 1000 CCD diffractometer with graphite-monochromated Cu Kα radiation (λ = 1.54184 Å) or Mo Kα radiation (λ = 0.71073 Å). The structures were solved using direct methods, while further refinement with full-matrix least-squares on F2 was obtained with the SHELXTL program package. All nonhydrogen atoms were refined anisotropically. Hydrogen atoms were introduced in calculated positions with the displacement factors of the host carbon atoms. Copolymerization of CO/Styrene. In a typical copolymerization, a round-bottom Schlenk flask with a stirring bar was heated for 3 h at 150 °C under vacuum and then cooled to room temperature. The solution of palladium catalyst (1.27 × 10−5 mol) and 1,4benzoquinone ([BQ]/[Pd] = 5) in dichloromethane were added into the glass reactor equipped with a CO gas line. After establishment of the reaction temperature, the system was continuously stirred for 5 min, and then 10 mL of styrene was added by syringe to the well-stirred solution. The reaction temperatures were controlled with an external water bath or a cooler in polymerization experiments. The solution was allowed to react for the desired time at 1 atm CO (absolute pressure). Polymerization was terminated by pouring the reaction mixture into 100 mL of acidic methanol (95:5 methanol/HCl) and stirred for 0.5 h at room temperature. To remove metallic palladium, the polymer was dissolved in CHCl3, filtered through Celite, and precipitated with methanol. The solid was washed thoroughly with methanol and dried under vacuum to constant weight. Synthesis of α-Diimine Ligands. 9,10-Dihydro-9,10-ethanoanthracene-11,12-dione compounds were prepared according to the literature.66,67 The condensation reaction of the α-dione compound with the corresponding aniline facilely produced the α-diimine ligands L1 and L5 in high purity,52,68 and L2−L4 were prepared by a transamination reaction (Schemes S1−S3).34

Figure 10. DSC curves of CO/styrene copolymers obtained by catalysts 1−5 at 30 °C.

glass transition was observed for all of samples, and no melting peak appeared on the secondary heating curves of DSC analysis. Dibenzobarrelene-based palladium catalysts 1−3 afforded CO/styrene copolymers with higher glass-transition temperature (Tg) than 4 and 5, which was attributed to the increased syndiotacticity of the copolymer.

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CONCLUSIONS In summary, we have reported α-diimine palladium catalysts with the dibenzobarrelene backbone that catalyze living alternating CO/styrene copolymerization. Introduction of the rigid and bulky dibenzobarrelene backbone and electrondonating m-/p-methoxy groups on aniline moieties enhanced the thermostability and productivity of the α-diimine palladium catalyst. The dibenzobarrelene ligand backbone also improved the controllability in molecular weight and stereoselectivity of CO/styrene copolymer, and living CO/ styrene copolymerizations were successfully achieved using three α-diimine palladium catalysts 1−3. The obtained CO/ styrene products obtained by catalysts 1−3 were syndiotacticity-rich alternating copolymers with glass-transition temperatures of ∼112 °C. The π−π stacking among three aromatic rings of the aniline, the dibenzobarrelene, and the styrene played crucial roles in productivity and stereocontrol. In addition to previously reported steric and electronic effect of the aryl substituents, a novel approach was provided for enhancement on alternating CO/styrene copolymerization by the steric effect and the π−π stacking of the ligand backbone. G


Article

Macromolecules

5.50 (s, 2H, CH), 3.93 (s, 6H, p-OCH3), 3.87 (s, 12H, m-OCH3). 13C NMR (100 MHz, CDCl3), δ (ppm): 161.12 (CN), 153.68 (Ar− C−m-OCH3), 146.16 (Ar−C in backbone), 138.75 (Ar−C−N), 134.55 (Ar−C−p-OCH3), 127.93, 124.86 (Ar−C in backbone), 97.18 (Ar−C), 61.10 (p-OCH3), 56.15 (m-OCH3), 50.31 (CH). Anal. Calcd for C34H32N2O6: C, 72.32; H, 5.71; N, 4.96. Found: C, 72.29; H, 5.71; N, 4.93.

L1 (Ar−NC(An)−(An)CN−Ar) (An = dibenzobarrelene, Ar = 4-methoxyaniline): 9,10-Dihydro-9,10-ethanoanthracene-11,12dione (2.34 g, 10.0 mmol), dry zinc chloride (4.09 g, 30.0 mmol), and 4-methoxyaniline (2.71 g, 22.0 mmol) were suspended in acetic acid (10 mL) under a nitrogen atmosphere. The mixture was reflux heated for 45 min and then filtered. The solid was washed with diethyl ether (3 × 2 mL) and dried. In a separating funnel, the obtained solid was dissolved in dichloromethane, and a saturated solution of potassium oxalate was added. After shaking for 5 min, the organic layer was separated, washed with water (3 × 50 mL), dried with sodium sulfate, filtered, and evaporated to dryness. The residual solids were further purified by recrystallization from ethanol to give L1 as yellow crystals in 90% yield. 1H NMR (400 MHz, CD3OD), δ (ppm): 7.36−7.21 (m, 8H, Ar−H), 7.03 (s, 4H, Ar−H), 6.91 (d, 4H, Ar−H), 5.52 (s, 2H, CH), 3.91 (s, 6H, p−OCH3). 13C NMR (100 MHz, CDCl3), δ (ppm): 160.91 (CN), 156.75 (Ar−C−p-OCH3), 143.18 (Ar−C−N), 138.67 (Ar−C in backbone), 127.78 (Ar−C in backbone), 124.58 (Ar−C in backbone), 121.51 (Ar−C), 114.42 (Ar−C), 55.19 (p-OCH3), 50.01 (CH). Anal. Calcd for C30H24N2O2: C, 81.06; H, 5.44; N, 6.30. Found: C, 81.01; H, 5.46; N, 6.27.

L4, Ar−NC(An)−(An)CN−Ar (An = acenaphthene, Ar = 3,4,5-trimethoxyphenyl). L4 was synthesized similarly to L2 using acenaphthequinone and 3,4,5-trimethoxyaniline. L4 was collected as orange crystals in 92% yield. 1H NMR (400 MHz, CDCl3), δ (ppm): 7.94 (d, 2H, Ar−H), 7.45 (t, 2H, Ar−H), 7.09 (d, 2H, Ar−H), 6.38 (s, 4H, Ar−H), 5.50 (s, 2H, CH), 3.95 (s, 6H, p-OCH3), 3.83 (s, 12H, m-OCH3). 13C NMR (400 MHz, CDCl3), δ (ppm): 161.70 (CN), 154.18 (Ar−C−m-OCH3), 147.85 (Ar−C−N), 141.75 (Ar−C in backbone), 134.68 (Ar−C−p-OCH3), 131.29, 129.20, 128.16, 127.79, 124.19 (Ar−C in backbone), 95.38 (Ar−C), 61.20 (pOCH3), 56.11 (m-OCH3). Anal. Calcd for C30H28N2O6: C, 70.30; H, 5.51; N, 5.47. Found: C, 70.32; H, 5.51; N, 5.46.

L5, Ar−NC(Me)−(Me)CN−Ar (Ar = 3,4,5-trimethoxyphenyl). 2,3-Butanedione (0.87 mL, 10.0 mmol) was added to methanol (40 mL), and several drops of formic acid were also added. When the solution was stirring, 3,4,5-trimethoxyaniline (3.84 g, 21.0 mmol) was added. The mixture was stirred at room temperature overnight, cooled, filtered, and washed with cool methanol (3 × 2 mL). The residual solids were further purified by recrystallization from ethanol to give L5 as yellow crystals in 93% yield. 1H NMR (400 MHz, CDCl3), δ (ppm): 6.02 (s, 4H, Ar−H), 3.85 (s, 18H, OCH3), 2.20 (s, 6H, CH3). 13C NMR (400 MHz, CDCl3), δ (ppm): 168.70 (CN), 153.04 (Ar−C−m-OCH3), 147.02 (Ar−C−p-OCH3), 134.44 (Ar− C−N), 96.03 (Ar−C), 61.02 (p-OCH3), 56.08 (m-OCH3), 15.61 (CH3). Anal. Calcd for C22H28N2O6: C, 63.45; H, 6.78; N, 6.73. Found: C, 63.40; H, 6.83; N, 6.69. Synthesis of Neutral α-Diimine Palladium Complexes. All neutral α-diimine palladium complexes were prepared by the reaction of Pd(COD)MeCl with the corresponding α-diimine ligand. A typical synthetic procedure for N1 was described as follows: 1.1 mmol of ligand L1 and 1.0 mmol of (COD)PdMeCl were added to a Schlenk tube together with 20 mL of dichloromethane, and the reaction mixture was then stirred for 24 h at room temperature. The solution was evaporated under vacuum to 3 mL, and then 50 mL hexane was added. After being filtered and washed with hexane (3 × 5 mL), the complex was precipitated as an orange solid.

L2 (Ar−NC(An)−(An)CN−Ar) (An = dibenzobarrelene, Ar = 3,5-dimethoxyaniline). 9,10-Dihydro-9,10-ethanoanthracene-11,12dione (2.34 g, 10.0 mmol) and dry zinc chloride (4.09 g, 30.0 mmol) were suspended in 10 mL of acetic acid under a nitrogen atmosphere. The mixture was heated to 50−60 °C, and 3,5-bis(trifluoromethyl)aniline (3.44 mL, 22.0 mmol) was added. The solution was reflux heated for 45 min and then filtered. The solid was washed with diethyl ether (3 × 2 mL) and dried. The obtained solid and 3,5dimethoxyaniline (4.60 g, 30.0 mmol) were dispersed in methanol (30 mL), and stirred at room temperature overnight. The suspension was filtered, and the solid was washed with n-hexane (3 × 2 mL) and dried. In a separating funnel, the obtained solid was dissolved in dichloromethane, and a saturated solution of potassium oxalate was added. After shaking for 5 min, the organic layer was separated, washed with water (3 × 50 mL), dried with sodium sulfate, filtered, and evaporated to dryness. The residual solids were further purified by recrystallization from ethanol to give L2 as yellow crystals in 88% yield. 1H NMR (400 MHz, CDCl3), δ (ppm): 7.38−7.23 (m, 8H, Ar−H), 6.34 (s, 2H, Ar−H), 6.11 (s, 4H, Ar−H), 5.48 (s, 2H, CH), 3.85 (s, 12H, m-OCH3). 13C NMR (100 MHz, CDCl3), δ (ppm): 161.32 (Ar−C−m-OCH3), 160.96 (CN), 152.13 (Ar−C−N), 138.61 (Ar−C in backbone), 127.93 (Ar−C in backbone), 124.96 (Ar−C in backbone), 98.01 (Ar−C), 96.58 (Ar−C), 55.63 (mOCH3), 50.20 (CH). Anal. Calcd for C32H28N2O4: C, 76.17; H, 5.59; N, 5.55. Found: C, 76.18; H, 5.60; N, 5.51.

N1, [(Ar−NC(An)−(An)CN−Ar)]PdCH3Cl (An = dibenzobarrelene, Ar = 4-methoxyaniline). The palladium complex N1 as an orange powder was obtained in 89% yield. 1H NMR (400 MHz, CDCl3), δ (ppm): 7.40−7.23 (m, 8H, Ar−H), 7.18−7.11 (d, 2H, Ar− H), 7.11−7.00 (m, 4H, Ar−H), 6.94−6.88 (d, 2H, Ar−H), 5.47 (s, H, CH), 5.30 (s, H, CH), 3.92 (s, 3H, p-OCH3) 3.89 (s, 3H, p-OCH3),

L3, (Ar−NC(An)−(An)CN−Ar) (An = dibenzobarrelene, Ar = 3,4,5-trimethoxyaniline). L3 was synthesized similarly to L2 using 3,4,5-trimethoxyaniline instead of 3,5-dimethoxyaniline. L3 was collected as yellow crystals in 86% yield. 1H NMR (400 MHz, CDCl3), δ (ppm): 7.38−7.21 (m, 8H, Ar−H), 6.15 (s, 4H, Ar−H), H


Article

Macromolecules 0.68 (s, 3H, Pd−CH3). 13C NMR (100 MHz, CDCl3), δ (ppm): 173.73, 166.26 (CN), 158.91, 158.52 (Ar−C−p-OCH3), 138.28, 137.58 (Ar−C−N), 137.04, 136.67, 128.95, 125.38, 124.56, 123.07 (Ar−C in backbone), 114.61, 114.08 (Ar−C), 55.50, 53.51 (pOCH3), 51.00, 49.44 (CH), 3.32 (Pd−CH3). Anal. Calcd for C31H27ClN2O2Pd: C, 61.91; H, 4.53; N, 4.66. Found: C, 61.88; H, 4.55; N, 4.62.

N5, [Ar−NC(Me)−(Me)CN−Ar]PdCH3Cl (Ar = 3,4,5trimethoxyphenyl). The palladium complex N5 as an orange powder was obtained in 84% yield. 1H NMR (400 MHz, CDCl3), δ (ppm): 6.28 (s, 2H, Ar−H), 6.14 (s, 2H, Ar−H), 3.98 (d, 6H, p-OCH3), 3.87 (s, 6H, m-OCH3), 3.85 (s, 6H, m-OCH3), 2.26 (s, 3H, CH3), 2.15 (s,3H, CH3), 0.77 (s, 3H, Pd−CH3). 13C NMR (400 MHz, CDCl3), δ (ppm): 175.31, 168.95 (CN), 153.84, 153.12 (Ar−C−m-OCH3), 142.75, 141.10 (Ar−C−N), 136.57, 136.24 (Ar−C−p-OCH3), 99.85, 98.59 (Ar−C), 61.02 (p-OCH3), 56.34 (m-OCH3), 21.01, 19.92 (CH3), 3.55 (Pd−CH3). Anal. Calcd for C23H31ClN2O6Pd: C, 48.18; H, 5.45; N, 4.89. Found: C, 48.22; H, 5.48; N, 4.84. Synthesis of Cationic α-Diimine Palladium Complexes. All cationic α-diimine palladium complexes were prepared by the reaction of NaBArF and acetonitrile with the corresponding neutral α-diimine complex. A typical synthetic procedure for 1 was described as follows: 0.5 mmol of palladium complex N1, 0.55 mmol of NaBArF, and 0.5 mL of acetonitrile were added to a Schlenk tube together with 30 mL of diethyl ether, and the reaction mixture was then stirred for 24 h at room temperature. The solution was filtered by Celite and then evaporated under vacuum to 5 mL, and 50 mL of hexane was added. After being filtered and washed with hexane (3 × 5 mL), the complex was collected as a yellow solid.

N2, [(Ar−NC(An)-(An)CN−Ar)]PdCH3Cl (An = dibenzobarrelene, Ar = 3,5-dimethoxyaniline). The palladium complex N2 as an orange powder was obtained in 86% yield. 1H NMR (100 MHz, CDCl3), δ (ppm): 7.41−7.27 (m, 8H, Ar−H), 6.48 (t, 1H, Ar−H), 6.46 (t, 1H, Ar−H), 6.30 (d, 2H, Ar−H), 6.13 (d, 2H, Ar−H), 5.49 (s, H, CH), 5.17 (s, H, CH), 3.84 (s, 12H, m-OCH3), 0.78 (s, 3H, Pd−CH3). 13C NMR (100 MHz, CDCl3), δ (ppm): 173.15, 166.87 (CN), 161.58, 160.86 (Ar−C−m-OCH3), 146.94, 145.68 (Ar−C− N), 137.35, 136.49, 129.13, 128.99, 125.51, 125.36 (Ar−C in backbone), 100.95, 100.08 (Ar−C), 99.97, 99.26 (Ar−C), 55.71, 55.65 (m-OCH3), 50.99, 49.54 (CH), 3.24 (Pd−CH3). Anal. Calcd for C33H31ClN2O4Pd: C, 59.92; H, 4.72; N, 4.23. Found: C, 59.89; H, 4.76; N, 4.20.

1, [(Ar−NC(An)−(An)CN−Ar)]Pd(CH3CN)CH3[BArF] (An = dibenzobarrelene, Ar = 4-methoxyaniline). The palladium complex 1 as a yellow powder was obtained in 72% yield. 1H NMR (400 MHz, CDCl3), δ (ppm): 7.70 (s, 8H, Ar−H in BArF−), 7.51 (s, 4H, Ar−H in BArF−), 7.44−7.31 (m, 8H, Ar−H in backbone), 7.09 (d, 2H, Ar−H), 7.07−6.97 (m, 4H, Ar−H), 6.86 (d, 2H, Ar−H), 5.41 (s, H, CH), 5.11 (s, H, CH), 3.91 (s, 3H, p-OCH3), 3.84 (s, 3H, pOCH3), 1.97 (s, 3H, CH3CN), 0.61 (s, 3H, Pd−CH3). 13C NMR (100 MHz, CDCl3), δ (ppm): 177.74, 167.96 (CN), 162.58, 162.08, 161.59, 161.09 (Ar−C−B in BArF−), 159.96, 159.51 (Ar−C− p-OCH3), 136.78 (Ar−C−N), 136.70 (Ar−C in backbone), 136.50 (Ar−C−N), 135.90 ((Ar−C in backbone), 134.95 (Ar−C−CF3 in BArF−), 129.91, 129.81 (Ar−C in backbone), 129.48, 129.17, 128.86, 128.76, 128.54 (CF3 in BArF−), 126.05, 125.74, 125.75 (Ar−C in backbone), 123.34, 123.27 (Ar−C in BArF−), 122.91 (Ar−C), 121.41, 120.63 (Ar−C in BArF−), 117.62 (CH3CN), 115.21, 114.96 (Ar−C), 55.74, 55.68 (p-OCH3), 50.98, 49.29 (CH), 7.54 (CH3CN), 2.74 (Pd−CH3). Anal. Calcd for C65H42N3O2BF24Pd: C, 54.58; H, 2.79; N, 2.77. Found: C, 54.53; H, 2.82; N, 2.75.

N3, [(Ar−NC(An)−(An)CN−Ar)]PdCH3Cl (An = dibenzobarrelene, Ar = 3,4,5-trimethoxyaniline). The palladium complex N3 as an orange powder was obtained in 85% yield. 1H NMR (400 MHz, CDCl3), δ (ppm): 7.42−7.28 (m, 8H, Ar−H), 6.41 (s, 2H, Ar− H), 6.21 (s, 2H, Ar−H), 5.56 (s, H, CH), 5.28 (s, H, CH), 3.97 (s, 3H, p-OCH3), 3.96 (s, 3H, p-OCH3), 3.95 (s, 6H, m-OCH3), 3.90 (s, 6H, m-OCH3), 0.79 (s, 3H, Pd−CH3). 13C NMR (100 MHz, CDCl3), δ (ppm): 173.55, 166.69 (CN), 153.94, 153.27 (Ar−C− m-OCH3), 141.08, 139.59 (Ar−C−N), 137.49, 137.06 (Ar−C−pOCH3), 136.60, (Ar−C in backbone), 129.16, 129.05, 125.35, 125.25 (Ar−C in backbone), 100.65, 99.04 (Ar−C), 61.04 (p-OCH3), 56.41 (m-OCH3), 53.48 (CH2Cl2), 51.03, 49.58 (CH), 3.42 (Pd−CH3). Anal. Calcd for C35H35ClN2O6Pd: C, 58.26; H, 4.89; N, 3.88. Found: C, 58.29; H, 4.86; N, 3.84.

N4, Ar−NC(An)−(An)CN−Ar (An = acenaphthene, Ar = 3,4,5-trimethoxyphenyl). The palladium complex N4 as a red powder was obtained in 90% yield. 1H NMR (400 MHz, CDCl3), δ (ppm): 8.09 (q, 2H, Ar−H), 7.54 (m, 2H, Ar−H), 7.42 (d, 1H, Ar−H), 6.78 (d, 1H, Ar−H), 6.48 (s, 2H, Ar−H), 6.44 (s, 2H, Ar−H), 3.96 (d, 6H, p-OCH3), 3.87 (d, 12H, m-OCH3), 1.03 (s, 3H, Pd−CH3). 13C NMR (400 MHz, CDCl3), δ (ppm): 176.22, 166.45 (CN), 154.42, 153.59 (Ar−C−m-OCH3), 143.34, 142.32 (Ar−C−N), 141.12 (Ar− C in backbone), 137.17, 136.80 (Ar−C−p-OCH3), 134.41, 131.30, 130.85, 128.81, 128.62, 126.59, 125.96, 125.33, 125.12 (Ar−C in backbone), 99.46, 98.40 (Ar−C), 61.51, 6.49 (p-OCH3), 56.34, 56.32 (m-OCH3), 4.12 (Pd−CH3). Anal. Calcd for C31H31ClN2O6Pd: C, 55.62; H, 4.67; N, 4.18. Found: C, 55.64; H, 4.62; N, 4.14.

2, [(Ar−NC(An)−(An)CN−Ar)]Pd(CH3CN)CH3[BArF] (An = dibenzobarrelene, Ar = 3,5-dimethoxyaniline). The palladium complex 2 as a yellow powder was obtained in 75% yield. 1H NMR (400 MHz, CDCl3), δ (ppm): 7.70 (s, 8H, Ar−H in BArF−), 7.52 (s, 4H, Ar−H in BArF−), 7.46−7.25 (m, 8H, Ar−H), 6.53 (s, 1H, Ar− H), 6.48 (s, 1H, Ar−H), 6.14 (d, 1H, Ar−H), 6.06 (d, 3H, Ar−H), 5.42 (s, H, CH), 5.18 (s, H, CH), 3.84 (s, 6H, m-OCH3), 3.80 (s, 6H, m-OCH3), 1.99 (s, 3H, CH3CN), 0.72 (s, 3H, Pd−CH3). 13C NMR I


Article

Macromolecules (100 MHz, CDCl3), δ (ppm): 180.10, 168.59 (CN), 162.57 (Ar− C−B in BArF−), 162.12 (Ar−C−m-OCH3), 162.09 (Ar−C−B in BArF−), 162.06 (Ar−C−m-OCH3), 161.60, 161.10 (Ar−C−B in BArF−), 145.48, 145.24 (Ar−C−N), 136.48, 135.76 (Ar−C in backbone), 134.95 (Ar−C−CF3), 130.05, 129.96 (Ar−C), 129.31, 129.20, 128.91, 128.63, 128.57 (CF3 in BArF−), 126.06, 125.93, 125.81 (Ar−C in backbone), 123.35, 121.57, 120.64 (Ar−C in backbone), 123.35, 121.57, 120.64 (Ar−C in BArF−), 117.63 (CH3CN), 100.04, 99.97, 99.62, 98.96 (Ar−C), 55.79, 55.69 (mOCH3), 51.11, 49.51 (CH), 7.32 (CH3CN), 2.53 (Pd−CH3). Anal. Calcd for C67H46N3O4BF24Pd: C, 52.59; H, 3.03; N, 2.75. Found: C, 52.62; H, 3.04; N, 2.73.

5, [Ar−NC(Me)−(Me)CN−Ar]Pd(CH3CN)CH3[BArF] (Ar = 3,4,5-trimethoxyphenyl). The palladium complex 5 as a yellow powder was obtained in 81% yield. 1H NMR (400 MHz, CDCl3), δ (ppm): 7.68 (s, 8H, Ar−H in BArF−), 7.52 (s, 4H, Ar−H in BArF−), 6.13 (s, 2H, Ar−H), 6.03 (s, 2H, Ar−H), 3.88 (d, 6H, p-OCH3), 3.81 (d, 12H, m-OCH3), 2.19 (s, 3H, CH3), 2.17 (s, 3H, CH3), 2.02 (s,3H, CH3CN), 0.67 (s, 3H, Pd−CH3). 13C NMR (100 MHz, CDCl3), δ (ppm): 180.38, 171.52 (CN), 162.55, 162.04, 161.57, 161.08 (Ar− C−B in BArF−), 154.35 (Ar−C−m-OCH3), 141.22, 140.92 (Ar−C− N), 137.36 (Ar−C−p-OCH3), 134.93 (Ar−C−CF3 in BArF−), 129.76, 129.48, 129.19, 128.85 (CF3 in BArF−), 126.02, 123.32, 120.60 (Ar−C in BArF−), 117.62 (CH3CN), 98.09, 97.71 (Ar−C), 61.21 (p-OCH3), 56.41 (m-OCH3), 21.24, 19.42 (CH3), 7.34 (CH3CN), 2.53 (Pd−CH3). Anal. Calcd for C57H46N3O6BF24Pd: C, 47.47; H, 3.22; N, 2.91. Found: C, 47.45; H, 3.23; N, 2.86.

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3, [(Ar−NC(An)−(An)CN−Ar)]Pd(CH3CN)CH3[BArF] (An = dibenzobarrelene, Ar = 3,4,5-trimethoxyaniline). The palladium complex 3 as a yellow powder was obtained in 70% yield. 1H NMR (400 MHz, CDCl3), δ (ppm): 7.68 (s, 8H, Ar−H in BArF−), 7.50 (s, 4H, Ar−H in BArF−), 7.44−7.30 (m, 8H, Ar−H), 6.23 (s, 2H, Ar− H), 6.14 (s, 2H, Ar−H), 5.44 (s, H, CH), 5.18 (s, H, CH), 3.96 (s, 3H, p-OCH3), 3.94 (s, 3H, p-OCH3), 3.85 (s, 12H, m-OCH3), 1.99 (s, 3H, CH3CN), 0.71 (s, 3H, Pd−CH3). 13C NMR (100 MHz, CDCl3), δ (ppm): 177.48, 168.52 (CN), 162.54, 162.04, 161.55, 161.06 (Ar−C−B in BArF−), 154.34, 154.30 (Ar−C−m-OCH3), 139.67, 139.49 (Ar−C−N), 137.96, 137.47 (Ar−C−p-OCH3), 136.51, 135.76 (Ar−C in backbone), 134.90 (Ar−C−CF3 in BArF − ), 130.14, 130.05 (Ar−C in backbone), 129.50, 129.18,128.84, 128.72, 128.56 (CF3 in BArF−), 126.01, 125.76, 125.62 (Ar−C in backbone), 123.30, 121.41, 120.60 (Ar−C in BArF−), 117.60 (CH3CN), 98.83 (Ar−C), 61.34, 61.30 (p-OCH3), 56.54, 56.52 (m-OCH3), 51.16, 49.51 (CH), 7.62 (CH3CN), 2.62 (Pd−CH3). Anal. Calcd for C69H50N3O6BF24Pd: C, 52.11; H, 3.17; N, 2.64. Found: C, 52.12; H, 3.13; N, 2.61.

ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.macromol.8b01786. NMR spectra of ligands and palladium complexes, 1H and 13C NMR of polymers, crystallographic data, CO/ styrene living copolymerization data (DOCX) X-ray crystallographic data of N1 (CIF) X-ray crystallographic data of N2 (CIF) X-ray crystallographic data of N3 (CIF) X-ray crystallographic data of N4 (CIF)

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AUTHOR INFORMATION

Corresponding Author

*(H.G.) Fax +86-20-84114033; Tel +86-20-84113250; e-mail [email protected]. ORCID

Haiyang Gao: 0000-0002-7865-3787 Notes

The authors declare no competing financial interest.

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4, [(Ar−NC(An)−(An)CN−Ar)]Pd(CH3CN)CH3[BArF] (An = acenaphthene, Ar = 3,4,5-trimethoxyaniline). The palladium complex 4 as a red powder was obtained in 90% yield. 1H NMR (400 MHz, CDCl3), δ (ppm): 8.11 (m, 2H, Ar−H in backbone), 7.66 (s, 8H, Ar−H in BArF−), 7.55 (m, 2H, Ar−H in backbone), 7.48 (s, 4H, Ar−H in BArF−), 7.42 (d, 1H, Ar−H in backbone), 6.80 (d, 1H, Ar− H in backbone), 6.51 (s, 2H, Ar−H), 6.47 (s, 2H, Ar−H), 3.98 (s, 3H, p-OCH3), 3.97 (s, 3H, p-OCH3), 3.83 (s, 6H, m-OCH3), 3.82 (s, 6H, m-OCH3), 2.08 (s, 3H, CH3CN), 0.92 (s, 3H, Pd−CH3). 13C NMR (100 MHz, CDCl3), δ (ppm): 176.73, 168.34 (CN), 162.51, 162.01, 161.52, 161.02 (Ar−C−B in BArF−), 154.75, 154.50 (Ar−C− m-OCH3), 146.15 (Ar−C−N), 140.97 (Ar−C in backbone), 137.97, 137.60 (Ar−C−p-OCH3), 134.86 (Ar−C−CF3 in BArF−), 133.26, 132.59, 131.53 (Ar−C in backbone), 129.44, 129.15, 128.99, 128.84, 128.68, 128.53 (CF3 in BArF−), 126.62, 125.98, 125.69, 125.28, 124.53 (Ar−C in backbone), 123.27, 121.44, 120.56 (Ar−C in BArF−), 117.56 (CH3CN), 98.22, 97.88 (Ar−C), 61.46, 61.44 (pOCH3), 56.49, 56.46 (m-OCH3), 8.10 (CH3CN), 2.62 (Pd−CH3). Anal. Calcd for C65H46N3O6BF24Pd: C, 50.75; H, 3.01; N, 2.73. Found: C, 50.71; H, 3.03; N, 2.70.

ACKNOWLEDGMENTS This work was supported by grants from National Natural Science Foundation of China (NSFC) (Project 21674130, 51873234), Natural Science Foundation of Guangdong Province (2017A030310349), the Fundamental Research Funds for the Central Universities (17lgjc02), and PetroChina Innovation Foundation (2017D-5007-0505).

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