Fluorinated Nickel(II) Phenoxyiminato Catalysts: Exploring the Role of

Article pubs.acs.org/Macromolecules

Fluorinated Nickel(II) Phenoxyiminato Catalysts: Exploring the Role of Fluorine Atoms in Controlling Polyethylene Productivities and Microstructures Jianchun Wang, Erdong Yao, Zhongtao Chen, and Yuguo Ma* Beijing National Laboratory for Molecular Sciences (BNLMS), Center for Soft Matter Science and Engineering, Key Lab of Polymer Chemistry & Physics of Ministry of Education, College of Chemistry, Peking University, Beijing 100871, China S Supporting Information *

ABSTRACT: A series of neutrally charged Ni(II) phenoxyiminato catalysts with fluorine atoms at different positions on the N-terphenyl motif are synthesized, and their abilities to polymerize ethylene are compared. At 25 °C, the orthofluorinated Ni-5F, Ni-3F′, and Ni-2F achieve significantly higher polymerization activities than Ni-3F and Ni-0F. In addition, branch density and molecular weight of the obtained polyethylenes vary gradually in the order of Ni-5F, Ni-3F, Ni-3F′, Ni-2F, and Ni-0F. Based on the X-ray crystal structure and 19F NMR spectra, the ortho fluorine atoms are found to make terphenyl groups more rigid and bulky. Theoretical calculations suggest that the increased steric bulk of terphenyl motif leads to an increase in the ground state energy of the resting state species relative to the migratory insertion transition state, and consequently, lowered migratory insertion barriers are expected in Ni-5F, Ni-3F′, and Ni-2F. On the other hand, the weak hydrogen bonding between the ortho fluorine atoms and coordinated ethylene in insertion transition state is also proposed in favor of insertion. Similar to previous reports, polyethylene microstructure was mainly related to electronic effects of fluorine atoms.

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INTRODUCTION Since the pioneering discovery of cationic Ni(II)- and Pd(II)based α-diimine catalysts by Brookhart1 and neutral Ni(II) phenoxyiminato catalysts by Grubbs,2 catalytic polymerization of olefins by late transition metal complexes3 has attracted much attention due to their lower oxophilicity in comparison with early transition metal catalysts. Under ethylene homopolymerization conditions, these catalysts yield polyethylene that range from linear to highly branched, through a process termed as “chain walking”.4 Of various cationic and neutral catalyst systems, the nickel phenoxyiminato system stands out in their tolerance toward polar additives2b and even can be carried out in aqueous emulsion.5 Catalytic properties are commonly modified by adjusting two specific properties: steric and electronic effects of the ligands. One major breakthrough in designing Ni(II) and Pd(II) catalysts was the discovery of the role of bulky groups in ligands.1 These bulky groups are crucial for blockage of the axial coordination sites and reduction of chain transfer.3b Ligand electronic structures of both Grubbs-type and Brookhart-type catalysts were also found to have a significant effect on microstructure of the polyethylene: depending on the substituent electronics, high molecular weight linear polyethylene or low molecular weight branched polyethylene are formed.2a,b,6 Mecking reported a series of single-component terphenyl phenoxyiminato Ni(II) ethylene polymerization catalysts bearing remote electron-withdrawing or electrondonating groups.7 It was suggested that polymer branching and © XXXX American Chemical Society

molecular weight are mainly controlled by electronics of these substituents, despite their remoteness from the nickel center. On the other hand, weak attractive interactions were also employed in modulating catalytic properties. In fields of fluorinated group IV catalysts, weak interactions have been well-accepted as explanations for the living character of polymerization.8 Chan and co-workers also have provided considerable experimental evidence for the existence of these interactions.9 As for late transition metals, introducing fluorine substituents into the α-diimine ligand was reported to increase the molecular weight of polyethylene (Chart 1A), albeit at the expense of activity.10 It has been suggested that a M···F interaction stabilizes the reactive 14-e− agostic species, which is the key intermediate that precedes chain walking and chain transfer. Similarly, the Grubbs-type catalyst bearing CF3 group (Chart 1B) was also suggested to be unique in the formation of linear high molecular weight polyethylene due to an H···F interaction with the growing chain.11 But recently, a nonfluorinated NO2-substituted catalyst was found to produce linear high molecular weight polyethylene, demonstrating that CF3-substituted catalyst is not unique.7d Still, the possibility that the oxygen atoms in NO2 group involve in similar weak interactions as fluorine atoms cannot be precluded. Received: May 20, 2015 Revised: July 21, 2015

A

DOI: 10.1021/acs.macromol.5b01090 Macromolecules XXXX, XXX, XXX−XXX

Macromolecules

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Chart 1. Fluorinated Late Transition Metal Catalysts and the Proposed Roles of Fluorine Atoms

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EXPERIMENTAL SECTION

Materials and Methods. All manipulations with air- and moisture-sensitive compounds were carried out under dry nitrogen using standard Schlenk line techniques or a mBraun glovebox with a high capacity recirculator ( Ni3F > Ni-3F′ > Ni-2F, which might shed some light on the relative electron-withdrawing ability of corresponding ligands (Figure S3). However, in the case of Ni-0F, the 31P NMR peak is unexpectedly shifted downfield. X-ray Crystallographic Study. Crystals of complexes Ni5F and Ni-3F suitable for single-crystal X-ray diffraction analysis were obtained by gradually evaporating their dichloromethane solutions. The structures are shown in Figures 1 and 2, respectively. The coordination geometry with the naphthyl group trans to the phenoxy group agrees with other reported salicylaldiminato complexes.2b By close comparison, we can see that the biggest difference between the molecular geometries of Ni-5F and Ni-3F is the average dihedral angles between the

Figure 1. Crystal structure of complex Ni-5F. Thermal ellipsoids are drawn at the 50% probability level.

Figure 2. Crystal structure of complex Ni-3F. Thermal ellipsoids are drawn at the 50% probability level.

central arene ring and the side arene ring on the N-terphenyl motif, which are 71.7° and 59.4°, respectively (Table S11). This conformational strain is caused by the steric hindrance of the ortho fluorine, and such a similar ortho fluorine effect has also been observed in previous reports.22 As a collaborative evidence, the 19F NMR spectra of Ni-5F, Ni-3F′, and Ni-2F also indicate that rotation of the fluorinated phenyl groups is sterically hindered at room temperature, which rendered all the fluorines inequivalent (Figure S4). As a comparison, the 3,4,5trifluorophenyl groups in Ni-3F are free to rotate around the aryl C−C bonds in the NMR time scale. These results imply that the introduction of fluorine atoms at ortho position might impose steric hindrance, which is believed to favor olefin polymerization.3b No evidence of significant Ni···F interaction is observed in the precatalyst Ni-5F and Ni-3F: the closest Ni··· F distances are 4.03 and 5.53 Å, while the sum of the Ni and F van der Waals radii is 3.31 Å.21 But these data could not preclude the Ni···F interactions in the 14-e− active species of Ni-5F and Ni-3F. Ethylene Polymerizations. Ethylene homopolymerizations were performed using B(C6F5)3 as a phosphine scavenger in toluene at a constant 95 psig ethylene pressure (Table 1). Precatalyst Ni-5F produces linear high molecular weight polyethylene with high activity. In comparison with nonfluorinated precatalyst Ni-0F, the resulting polyethylene by Ni5F displays higher productivity (2.93 g vs 0.10 g), much greater C

DOI: 10.1021/acs.macromol.5b01090 Macromolecules XXXX, XXX, XXX−XXX

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Macromolecules Table 1. Ethylene Polymerization Resultsa entry

precat.

T (°C)

yield (g)

TOFb

branchesc

Mnd

Mw/Mnd

1 2 3 4 5 6

Ni-5F Ni-3F Ni-3F′ Ni-2F Ni-0F Ni-5F

25 25 25 25 25 50

2.93 0.96 5.95 3.32 0.10 5.64

7848 2569 15957 8904 268 15102

14 19 20 21 51 55e

61.7 24.3 13.8 11.4 3.7 6.4

2.57 2.67 2.06 2.36 3.25 2.16

First, we come to examine whether fluorine atoms would stabilize 14-e− active species by Ni···F or H···F weak interaction in our catalytic system; that is, we need to examine the relative strength of the agostic interaction and Ni···F or H···F weak interactions. In Figure 3, the top structure (agostic complex)

a Polymerization conditions: 20 μmol of precatalyst, 40 μmol of B(C6F5)3, 25 mL of toluene, 95 psig of C2H4, 25 °C, 40 min. Polymerizations were performed in duplicate. bIn 103 mol [C2H4] mol−1 [Ni] h−1. cDetermined from 13C NMR and is reported as the number of branchs per 1000 carbons. dIn 103 g mol−1; obtained by GPC versus polystyrene standards. eDetermined from 1H NMR and is reported as the number of branches per 1000 carbons.

Mn (61.7 vs 3.7 kDa), and far lower branch density (14 vs 51 branches/1000C). As expected, degrees of branching increase with temperature, while molecular weights decrease, due to increased β-hydrogen elimination at higher temperature (entry 1 vs 6). The gel permeation chromatography (GPC) curves of obtained polymers give relatively narrow polydispersities (Figure S37 and Table 1) and support that these precatalysts give rise to single site catalysts. This result resembles the catalytic properties of those previously reported fluorinated nickel catalysts, and the polyethylene structure is similar to the previous reports according to the 13 C NMR (Figure S28).7a,d,e,11 Comparison of polymerization results with precatalysts Ni2F, Ni-3F′, and Ni-3F would give us more insight into the role of fluorine atoms. Here, three trends are observed: first, the polymerization activities of Ni-5F, Ni-3F′, and Ni-2F with ortho fluorine atoms are significantly higher than those of Ni-3F and Ni-0F; second, the branch density of the resulting polyethylenes increases gradually in the order of Ni-5F, Ni3F, Ni-3F′, Ni-2F, and Ni-0F; third, the molecular weights of obtained polyethylene decrease gradually in the same trend. It is particularly interesting to compare the data of Ni-3F with Ni3F′. With similar electron-withdrawing ability, Ni-3F and Ni3F′ produce polyethylene with similar Mn and branch densities; however, Ni-3F′ is much more productive because of the ortho fluorine atoms it possesses. As we know, rapid olefin insertion would lead to enhanced activities. It is reasonable to speculate that ortho fluorine atoms may be the key factor to accelerate ethylene insertion. On the other hand, polymer branching is caused by chain walking, which is dependent on the competition between olefin insertion and β-H elimination. Thus, the formation of highly linear polyethylene is due to facilitated ethylene insertion relative to β-H elimination. Similarly, increased Mn is associated with retarded chain transfer relative to ethylene insertion. Therefore, we speculate that the electron-withdrawing ability of fluorinated arene group is decisive in controlling the polymer microstructure by tuning the relative rates of these elementary steps. Theoretical Calculations. In order to obtain better insight into the polymerization mechanism, DFT calculations were performed to examine the role of fluorine atoms. In this theoretical study, PBE-D is employed, which was reported to give the best agreement with the experimental data for neutral nickel polymerization catalysts.20,23 We have thus chosen an approach in which, unless explicitly noted, the energies reported are those obtained by using the PBE-D functional.

Figure 3. Optimized structures of 14-e− active species derived from Ni-5F.24a Agostic complex (top) is 10.3 kcal mol−1 lower in Gibbs free energy than nonagostic complex (down) in the gas phase.24b

involves β-agostic interaction of the growing polymer with the Ni center. The closest Ni···F and H···F distances are 3.10 and 2.54 Å, while the sum of Ni and F van der Waals radii is 3.31 Å and the sum of H and F van der Waals radii is 2.57 Å.21 These data imply that very weak Ni···F or H···F interaction is present in this agostic species. For comparison, in the structure shown below (nonagostic complex), the closest Ni···F and H···F distances decrease to 2.22 and 2.41 Å, respectively, significantly shorter than the sum of corresponding van der Waals radii, which demonstrates that both stronger Ni···F and H···F interactions exist in the nonagostic complex. Natural bond orbital (NBO) second-order perturbation energy analysis also reveals stronger interactions are present in nonagostic complex as well. The Ni···F interaction in the nonagostic complex that corresponds to the donation from a fluorine lone pair orbital to a metal unoccupied 4p orbital is significant larger than that of agostic complex (14.4 vs 2.4 kcal mol−1) (Figure S38). Similarly, H···F interactions of the former, which origin from the donation from a fluorine lone pair orbital to antibonding C−H orbitals was slightly stronger than that of the latter (0.6 vs 0.4 kcal mol−1). Nevertheless, despite the presence of both stronger Ni···F and H···F interactions in the nonagostic complex, the calculated results show that the agostic complex is still energetically favored by 10.3 kcal mol−1 in Gibbs free energy.24b From NBO analysis, we know that the agostic interaction in our system is a very strong interaction (27.9 kcal D

DOI: 10.1021/acs.macromol.5b01090 Macromolecules XXXX, XXX, XXX−XXX

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Macromolecules

Figure 4. Comparative Gibbs free energy profiles (kcal mol−1) associated with the propagation, branch formation, and chain transfer pathways for our catalysts.

mol−1), which mainly corresponds to the donation from the C−H σ bond to the nickel unoccupied 4s orbital (Figure S39). This interesting finding argues that these Ni···F and H···F interactions are not sufficient to suppress the formation of agostic complex in our system because they cannot compensate for the energy loss associated with the absence of agostic interaction. Therefore, it seems rather unlikely that 14-e− active species are changed by either Ni···F or H···F interactions. Then, we performed detailed energy calculation to understand the origin of this fluorine effect. For the Ni-5F complex, the geometric and energetic properties of all intermediates and transition states in the propagation, branch formation, and chain transfer were investigated (Scheme S6), and the ratedetermining steps of these pathways were calculated and compared with those of Ni-0F, Ni-2F, Ni-3F′, and Ni-3F (Figure 4 and Table S13). For the sake of simplicity, only the key transition states of Ni-2F, Ni-3F′, and Ni-3F are plotted in Figure 4. For convenience, we labeled the complex with alkyl group or hydride cis to the nitrogen atom as “cis”. First, Gibbs free energy profiles show that the cis alkyl ethylene species 2acis is the resting state with the lowest free energy, which agrees with previous experiment and theoretical reports.25 Second, the “trans” isomer 2a-trans is generally energetically disfavored than “cis” isomer 2a-cis due to the strong trans influence of nitrogen atom. However, the energy difference between cis and trans isomers obviously decreases in Ni-5F and even is reversed in Ni-2F (Figure 4). Increased steric bulk of the N-terphenyl substituent induced by ortho fluorine atoms leads to a strong repulsion with alkyl group on Ni center and thus increases the energy of the resting state. This result is in line with the data from 19F NMR spectra and X-ray diffraction. Consequently, ethylene insertion is more facile with ortho fluorine atoms, with

ΔG‡ins being 12.8, 12.1, and 12.5 kcal mol−1 (Figure 4, 2a-cis → TS(2a-trans/3a-cis)) in Ni-5F, Ni-3F′, and Ni-2F, respectively. As a comparison, barriers to ethylene insertion are 14.1 and 13.2 kcal mol−1 in Ni-0F and Ni-3F. From the polymerization result, Ni-3F′ is 6.20 times as productive as Ni3F, which matches the calculated 1.1 kcal/mol energy difference. Third, the ortho fluorine atoms might further lower the insertion barrier by forming C−H···F−C hydrogen bonds in the insertion transition state. For instance, the distance between ortho fluorine atoms and ethylene hydrogen in the optimized insertion transition state of Ni-5F are 2.38 and 2.30 Å (Figure S40), which is shorter than the sum of H and F van der Waals radii (2.57 Å).21 NBO analysis shows that this interaction energy is estimated to be 0.9, 1.1, and 1.1 kcal mol−1 in Ni-5F, Ni-3F′, and Ni-2F, respectively. In one word, elevated energies of resting state as well as the hydrogen bonding in insertion transition states might contribute to enhanced insertion rate in complexes with ortho fluorine atoms. From the foregoing discussion, it is evident that facilitated ethylene insertion is an important feature of Ni-5F that differentiates it from Ni-0F. The increased energy of resting state (2a-cis) in Ni-5F lowers the potential surface as a whole (Figure 4) and thus facilitates insertion, β-H elimination, and chain transfer simultaneously. Nevertheless, the branch density is dependent on the relative Gibbs energy difference: ΔΔG‡ of β-H elimination relative to insertion, which are calculated to be 3.0, 2.8, 2.7, 2.6, and 2.6 kcal mol−1 (Figure 4, TS(2a-trans/3acis) → TS(1a-trans/4a-cis)) for Ni-5F, Ni-3F, Ni-3F′, Ni-2F, and Ni-0F (Table S13), respectively. These calculated data indicate that β-H elimination becomes easier from Ni-5F to Ni0F, which accords well with increased branch density of obtained polyethylenes. Similarly, molecular weight is dependE

DOI: 10.1021/acs.macromol.5b01090 Macromolecules XXXX, XXX, XXX−XXX

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Macromolecules ent on the ΔΔG‡ of chain transfer relative to insertion. The corresponding ΔΔG‡ is 8.1, 8.0, 7.8, 7.7, and 6.1 kcal mol−1 (Figure 4, TS(2a-trans/3a-cis) → TS(4a-cis/8a-cis)) for Ni5F, Ni-3F, Ni-3F′, Ni-2F, and Ni-0F, which is also in line with the trend of molecular weights of corresponding polyethylenes. In addition, NBO population analysis reveals that the natural charges on Ni vary gradually in the order of Ni-5F, Ni-3F, Ni2F, and Ni-0F (Table S14). Such an order is also consistent with the observation of the aforementioned 31P NMR spectra. These pieces of collaborative evidence imply that the electronic character of the fluorinated aryl group is decisive for the control of the polymer microstructure, which is consistent with previous experimental and theoretical results.26

National Basic Research Program (2013CB933501) of the Ministry of Science and Technology of China.

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(1) (a) Johnson, L. K.; Killian, C. M.; Brookhart, M. J. Am. Chem. Soc. 1995, 117, 6414−6415. (b) Johnson, L. K.; Mecking, S.; Brookhart, M. J. Am. Chem. Soc. 1996, 118, 267−268. (c) Gates, D. P.; Svejda, S. A.; Onate, E.; Killian, C. M.; Johnson, L. K.; White, P. S.; Brookhart, M. Macromolecules 2000, 33, 2320−2334. (d) Leatherman, M. D.; Brookhart, M. Macromolecules 2001, 34, 2748−2750. (2) (a) Wang, C.; Friedrich, S.; Younkin, T. R.; Li, R. T.; Grubbs, R. H.; Bansleben, D. A.; Day, M. W. Organometallics 1998, 17, 3149− 3151. (b) Younkin, T. R.; Connor, E. F.; Henderson, J. I.; Friedrich, S. K.; Grubbs, R. H.; Bansleben, D. A. Science 2000, 287, 460−462. (c) Connor, E. F.; Younkin, T. R.; Henderson, J. I.; Waltman, A. W.; Grubbs, R. H. Chem. Commun. 2003, 2272−2273. (d) Waltman, A. W.; Younkin, T. R.; Grubbs, R. H. Organometallics 2004, 23, 5121− 5123. (3) (a) Mecking, S. Coord. Chem. Rev. 2000, 203, 325−351. (b) Ittel, S. D.; Johnson, L. K.; Brookhart, M. Chem. Rev. 2000, 100, 1169− 1204. (c) Gibson, V. C.; Spitzmesser, S. K. Chem. Rev. 2003, 103, 283−316. (d) Skupov, K. M.; Piche, L.; Claverie, J. P. Macromolecules 2008, 41, 2309−2310. (e) Nakamura, A.; Ito, S.; Nozaki, K. Chem. Rev. 2009, 109, 5215−5244. (f) Camacho, D. H.; Guan, Z. Chem. Commun. 2010, 46, 7879−7893. (g) Makio, H.; Terao, H.; Iwashita, A.; Fujita, T. Chem. Rev. 2011, 111, 2363−2449. (h) Delferro, M.; Marks, T. J. Chem. Rev. 2011, 111, 2450−2485. (i) Nakamura, A.; Anselment, T. M.; Claverie, J.; Goodall, B.; Jordan, R. F.; Mecking, S.; Rieger, B.; Sen, A.; Van Leeuwen, P. W.; Nozaki, K. Acc. Chem. Res. 2013, 46, 1438− 1449. (4) (a) Guan, Z.; Cotts, P. M.; McCord, E. F.; McLain, S. J. Science 1999, 283, 2059−2062. (b) Cherian, A. E.; Rose, J. M.; Lobkovsky, E. B.; Coates, G. W. J. Am. Chem. Soc. 2005, 127, 13770−13771. (c) 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. (5) (a) Bauers, F. M.; Mecking, S. Angew. Chem., Int. Ed. 2001, 40, 3020−3022. (b) Göttker-Schnetmann, I.; Korthals, B.; Mecking, S. J. Am. Chem. Soc. 2006, 128, 7708−7709. (c) Wehrmann, P.; Mecking, S. Macromolecules 2006, 39, 5963−5964. (d) Wehrmann, P.; Zuideveld, M.; Thomann, R.; Mecking, S. Macromolecules 2006, 39, 5995−6002. (6) (a) Popeney, C.; Guan, Z. Organometallics 2005, 24, 1145−1155. (b) Popeney, C. S.; Guan, Z. Macromolecules 2010, 43, 4091−4097. (7) (a) Zuideveld, M. A.; Wehrmann, P.; Röhr, C.; Mecking, S. Angew. Chem. 2004, 116, 887−891. (b) Bastero, A.; Gö ttkerSchnetmann, I.; Röhr, C.; Mecking, S. Adv. Synth. Catal. 2007, 349, 2307−2316. (c) Göttker-Schnetmann, I.; Wehrmann, P.; Röhr, C.; Mecking, S. Organometallics 2007, 26, 2348−2362. (d) Osichow, A.; Göttker-Schnetmann, I.; Mecking, S. Organometallics 2013, 32, 5239− 5242. (e) Wiedemann, T.; Voit, G.; Tchernook, A.; Roesle, P.; Göttker-Schnetmann, I.; Mecking, S. J. Am. Chem. Soc. 2014, 136, 2078−2085. (8) (a) Mitani, M.; Mohri, J.; Yoshida, Y.; Saito, J.; Ishii, S.; Tsuru, K.; Matsui, S.; Furuyama, R.; Nakano, T.; Tanaka, H. J. Am. Chem. Soc. 2002, 124, 3327−3336. (b) Furuyama, R.; Mitani, M.; Mohri, J.; Mori, R.; Tanaka, H.; Fujita, T. Macromolecules 2005, 38, 1546−1552. (c) Bryliakov, K. P.; Talsi, E. P.; Möller, H. M.; Baier, M. C.; Mecking, S. Organometallics 2010, 29, 4428−4430. (d) Möller, H. M.; Baier, M. C.; Mecking, S.; Talsi, E. P.; Bryliakov, K. P. Chem. - Eur. J. 2012, 18, 848−856. (9) (a) Kui, S. C. F.; Zhu, N.; Chan, M. C. W. Angew. Chem., Int. Ed. 2003, 42, 1628−1632. (b) Chan, M. C. W.; Kui, S. C. F.; Cole, J. M.; McIntyre, G. J.; Matsui, S.; Zhu, N.; Tam, K.-H. Chem. - Eur. J. 2006, 12, 2607−2619. (c) Chan, M. C. W. Chem. - Asian J. 2008, 3, 18−27. (d) So, L.-C.; Liu, C.-C.; Chan, M. C. W.; Lo, J. C. Y.; Sze, K.-H.; Zhu, N. Chem. - Eur. J. 2012, 18, 565−573. (10) Popeney, C. S.; Rheingold, A. L.; Guan, Z. Organometallics 2009, 28, 4452−4463.

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CONCLUSIONS In this work, both experimental and theoretical results support that both the positions and electronic effect of fluorine atoms remarkably change catalytic properties of neutrally charged Ni(II) phenoxyiminato catalysts. Ethylene polymerization results suggest that the microstructure of the resulting polyethylene is mainly dependent on the electron-withdrawing abilities of fluorinated aryl group, rather than the positions of fluorine atoms. However, ortho fluorine atoms on the Nterphenyl motif significantly influences the conformation of the catalysts and can also form hydrogen bonds in the insertion transition state. Both these two factors are beneficial to improve polymerization activity of Ni-5F, Ni-3F′ and Ni-2F. DFT calculation of relative Gibbs free energies of 14-e− agostic and nonagostic complexes gives out quantitative evidence that Ni··· F interactions cannot disfavor agostic species in our system. Finally, DFT calculation of rate-determining steps shows that the introduction of electron-withdrawing fluorine atoms facilitates ethylene insertion relative to β-hydrogen elimination and chain transfer, which might be the primary reason for the formation of linear high molecular weight polyethylene in Ni5F. Our study contributes to a clearer understanding of remote substituent effect in controlling polymer microstructure, which could provide a guideline for the future rational design of catalysts.

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ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.macromol.5b01090. Details of ligand and catalyst synthesis and characterization, polymerization experiments, polymer characterization, DFT calculations, and X-ray structures (PDF)

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REFERENCES

AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected] (Y.M.). Author Contributions

J.W. and E.Y. contributed equally. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This research was financially supported by National Natural Science Foundation (No. 21074004 and 91227202) and the F

DOI: 10.1021/acs.macromol.5b01090 Macromolecules XXXX, XXX, XXX−XXX

Article

Macromolecules (11) Weberski, M. P., Jr.; Chen, C.; Delferro, M.; Zuccaccia, C.; Macchioni, A.; Marks, T. J. Organometallics 2012, 31, 3773−3789. (12) Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.; Robb, M. A.; Cheeseman, J. R.; Scalmani, G.; Barone, V.; Mennucci, B.; Petersson, G. A.; Nakatsuji, H.; Caricato, M.; Li, X.; Hratchian, H. P.; Izmaylov, A. F.; Bloino, J.; Zheng, G.; Sonnenberg, J. L.; Hada, M.; Ehara, M.; Toyota, K.; Fukuda, R.; Hasegawa, J.; Ishida, M.; Nakajima, T.; Honda, Y.; Kitao, O.; Nakai, H.; Vreven, T.; Montgomery, J. A., Jr.; Peralta, J. E.; Ogliaro, F.; Bearpark, M.; Heyd, J. J.; Brothers, E.; Kudin, K. N.; Staroverov, V. N.; Keith, T.; Kobayashi, R.; Normand, J.; Raghavachari, K.; Rendell, A.; Burant, J. C.; Iyengar, S. S.; Tomasi, J.; Cossi, M.; Rega, N.; Millam, J. M.; Klene, M.; Knox, J. E.; Cross, J. B.; Bakken, V.; Adamo, C.; Jaramillo, J.; Gomperts, R.; Stratmann, R. E.; Yazyev, O.; Austin, A. J.; Cammi, R.; Pomelli, C.; Ochterski, J. W.; Martin, R. L.; Morokuma, K.; Zakrzewski, V. G.; Voth, G. A.; Salvador, J. J.; Dannenberg, S.; Dapprich, A. D.; Daniels, O.; Farkas, J. B.; Foresman, J. V.; Ortiz, J.; Cioslowski, P.; Fox, D. J. Gaussian 09, Revision A.02; Gaussian, Inc.: Wallingford, CT, 2010. (13) Perdew, J. P.; Burke, K.; Ernzerhof, M. Phys. Rev. Lett. 1996, 77, 3865−3868. (14) Hay, P. J.; Wadt, W. R. J. Chem. Phys. 1985, 82, 270−283. (15) Francl, M. M.; Pietro, W. J.; Hehre, W. J.; Binkley, J. S.; Gordon, M. S.; DeFrees, D. J.; Pople, J. A. J. Chem. Phys. 1982, 77, 3654−3665. (16) Grimme, S. J.; Antony, J.; Ehrlich, S.; Krieg, H. J. Chem. Phys. 2010, 132, 154104. (17) Foster, J.; Weinhold, F. J. Am. Chem. Soc. 1980, 102, 7211− 7218. (18) Korenaga, T.; Kosaki, T.; Fukumura, R.; Ema, T.; Sakai, T. Org. Lett. 2005, 7, 4915−4917. (19) Hidai, M.; Kashiwagi, T.; Ikeuchi, T.; Uchida, Y. J. Organomet. Chem. 1971, 30, 279−282. (20) Stephenson, C. J.; McInnis, J. P.; Chen, C.; Weberski, M. P.; Motta, A.; Delferro, M.; Marks, T. J. ACS Catal. 2014, 4, 999−1003. (21) (a) Haynes, W. M. CRC Handbook of Chemistry and Physics; CRC Press: Boca Raton, FL, 2012. (b) Bondi, A. J. Phys. Chem. 1964, 68, 441−451. (c) Rowland, R. S.; Taylor, R. J. Phys. Chem. 1996, 100, 7384−7391. (22) (a) Kirsch, P.; Hahn, A. Eur. J. Org. Chem. 2005, 2005, 3095− 3100. (b) Chen, H.; Yao, E.; Xu, C.; Meng, X.; Ma, Y. Org. Biomol. Chem. 2014, 12, 5102−5107. (23) Heyndrickx, W.; Occhipinti, G.; Minenkov, Y.; Jensen, V. R. Chem. - Eur. J. 2011, 17, 14628−14642. (24) (a) Legault, C. Y. CYLview, 1.0b; Université de Sherbrooke, 2009. (b) Calculations from M06-2X (6.8 kcal mol−1) and ωB97XD (9.7 kcal mol−1) functional arrive at almost the same conclusion. (25) (a) Deng, L.; Woo, T. K.; Cavallo, L.; Margl, P. M.; Ziegler, T. J. Am. Chem. Soc. 1997, 119, 6177−6186. (b) Svejda, S. A.; Johnson, L. K.; Brookhart, M. J. Am. Chem. Soc. 1999, 121, 10634−10635. (26) (a) Chan, M. S. W.; Deng, L. Q.; Ziegler, T. Organometallics 2000, 19, 2741−2750. (b) Malinoski, J. M.; Brookhart, M. Organometallics 2003, 22, 5324−5335. (c) Hanley, P. S.; Hartwig, J. F. J. Am. Chem. Soc. 2011, 133, 15661−15673. (d) Wucher, P.; Goldbach, V.; Mecking, S. Organometallics 2013, 32, 4516−4522.

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DOI: 10.1021/acs.macromol.5b01090 Macromolecules XXXX, XXX, XXX−XXX