Toward Perfect Regiocontrol for β-Selective Cyclopolymerization

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

Toward Perfect Regiocontrol for β‑Selective Cyclopolymerization Using a Ru-Based Olefin Metathesis Catalyst Kijung Jung,† Kunsoon Kim,† Jong-Chan Sung,† Tonia S. Ahmed,‡ Soon Hyeok Hong,† Robert H. Grubbs,‡ and Tae-Lim Choi*,† †

Department of Chemistry, Seoul National University, Seoul 08826, Republic of Korea The Arnold and Mabel Beckman Laboratory of Chemical Synthesis, Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, California 91125, United States

‡

S Supporting Information *

ABSTRACT: Ru-based metathesis catalysts employed in cyclopolymerization (CP) of 1,6-heptadiyne derivatives have promoted regioselective α-addition to alkynes, forming various conjugated polyenes containing exclusively five-membered repeat units. Recently, we discovered that a new chelated Ru catalyst could promote regioselective β-addition to produce analogous polyenes containing six-membered rings with moderate to good β-selectivity. Since then, we have focused our research on pursuing more active and β-selective regiocontrol to produce conjugated polymers with excellent βselectivity, with a much broader range of monomers. Herein, we demonstrate highly β-selective CP by combining a new dithiolate-chelated Ru-based catalyst with weakly coordinating pyridine additives, which significantly enhance the conversion and β-selectivity. An in-depth mechanistic investigation by 1H NMR revealed a prominent role for the additives, which improve the stability of the propagating carbene.

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INTRODUCTION Cyclopolymerization (CP) of terminal diynes via an olefin metathesis is one of the most efficient and powerful tools for the synthesis of conjugated polymers.1 Although the promises of CP were introduced to the polymer science community with extensive studies using ill-defined catalysts, such as Ziegler-type catalysts,2,3 MoCl5, and WCl6,4−8 the first breakthrough came with the development of well-defined catalysts by the Schrock group, who provided a mechanistic understanding of CP and structural analyses of the resulting conjugated polyenes.9,10 Recently, this field was revisited by polymer chemists because modified Grubbs catalysts11−16 developed by the Buchmeiser group, and even user-friendly Grubbs catalysts17−20 based on Ru promoted excellent CP with outstanding reactivity and tolerance toward air, moisture, and many functional groups.21−25 Therefore, various macromolecules with interesting architectures have been prepared, thereby extending the scope of CP.26−31 One of the most important issues for CP is controlling regioselectivity, which is determined by the orientation of the approaching metal carbenes toward the terminal alkynes.32 For example, 1,6-heptadiyne derivatives undergo CP to produce five-membered rings by α-addition, where the metal approaches the side chains (Scheme 1a, pathway I). Orientation of the metal away from the side chain for β-addition allows for CP to give six-membered rings (pathway II). Initially, classical illdefined catalysts and several Mo-based Schrock catalysts did not provide sufficient regiocontrol.1 Thus, much effort was put © XXXX American Chemical Society

into developing strategies for highly regioselective CP to produce well-defined conjugated polyenes. Finally, after the pioneering work of the Schrock and Buchmeiser groups, conjugated polyenes containing either six-33,34 or fivemembered rings35−38 were successfully prepared by modifying Mo catalysts. Another breakthrough came when the Buchmeiser group reported the first CP employing user-friendly Rubased catalysts to give five-membered-ring polyenes via complete α-addition.11−15,39,40 Our group also reported living/controlled CP using a fast-initiating, third-generation Grubbs catalyst (Scheme 1b, Ru1).17−19,28,29 Nonetheless, for a long time, even after screening various catalysts, Ru-catalyzed βselective CP seemed nearly impossible, as if α-addition was the intrinsic selectivity of Ru carbenes. Only one example of βselective CP had been reported, from just one monomer.33,34 However, a new class of Ru-based catalysts containing a chelating adamantyl group on the N-heterocyclic carbene (NHC) ligand (Ru2),41 known as Grubbs Z-selective catalysts, have been recently developed and produce Z-olefins in a variety of olefin metathesis reactions.42 Using this unique catalyst which shows unconventional selectivity, we recently reported a ring-closing enyne metathesis via exclusive β-selectivity and CP to produce conjugated polyenes with good to high β-selectivity (67−95%).43 After extensive optimization of the monomer Received: May 6, 2018 Revised: May 28, 2018

A

DOI: 10.1021/acs.macromol.8b00969 Macromolecules XXXX, XXX, XXX−XXX

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Scheme 1. (a) Two Possible Pathways for CP of 1,6-Heptadiynes, (b) Various Ru-Based Catalysts, and (c) Proposed Model for the Preference of β-Addition in Ru3-Catalyzed CP

structures and reaction conditions, a dialkyne monomer derived from di-tert-butyl malonate underwent CP with up to 93% of six-membered rings or β-selectivity. We proposed that this new regioselectivity originated from a side-bound pathway of alkynes toward the Ru center,44−46 which was contrary to the well-known, bottom-bound pathway for conventional Grubbs catalysts.47,48 Although this was a meaningful achievement as the first example for Ru catalysts to undergo β-selective CP, there still remained some drawbacks: only malonate monomers bearing sterically bulky groups showed good β-selectivity at a low temperature (e.g., −40 °C), and long reaction times (over 36 h) were therefore required. We thus explored the possibility of developing significantly improved β-selective CP, and anticipated Ru catalysts containing catechothiolate ligands developed by the Hoveyda group (Ru3)49 would operate by a similar mechanism49−53 and show β-selective CP, as depicted in Scheme 1c. Indeed, we recently reported preliminary data for β-selective CP by Ru3 and the origin of the α- and β-selectivity of CP based on electronic and steric factors of various Ru catalysts via density functional theory (DFT) calculations.54 The calculations indicated the carbene on Ru3 would become less electrophilic due to stronger π-back-donation from Ru, which increased the barrier for α-addition, thereby favoring β-addition even more so than Ru2. With this preliminary data, we decided to investigate the breadth of the monomer scope and the versatility of CP in detail by understanding the factors that contribute to the activity and β-selectivity of CP. Here, we report superior β-selective CP by Ru3 at room temperature and disclose our full account of the complete screening of additives and numerous monomers. Further, detailed kinetic studies reveal mechanistic insights leading to plausible models for improved β-selective CP.

Scheme 2. Cyclopolymerization of M1 Using Ru3 with Various Pyridine Additivesa

a

Conversion and regioselectivity were determined by 1H NMR spectra.

noncoordinating dichloromethane (DCM). This was rather surprising because DCM is a poor reaction solvent for conventional CP.17 Notably, the six-membered-ring selectivity as a result of β-addition was quite high, 5.9:1, as determined by 1 H NMR,55 compared to the previous moderate selectivity of 3.4:1 obtained by Ru2 at room temperature.43 In order to further increase the β-selectivity, CP was conducted at a low temperature by adopting the strategy used in our previous study using Ru2.43 However, the result was not satisfactory, providing only 10% conversion of the monomer at 0 °C. Instead, we screened some pyridine derivatives as an additive (Scheme 2) because our previous results for CP using Ru1 indicated that weakly coordinating ligands such as 3,5dichloropyridine enhanced polymerization efficiency and controllability.19 Unfortunately, addition of 10 equiv of pyridine to the initiator Ru3 resulted in an insignificant improvement in monomer conversion and selectivity (83% and 6.1:1), while various 3-halogen-substituted pyridines, such as 3-ClPy, 3BrPy, and 3-IPy, led to significantly higher β-selectivity (8.8−

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RESULTS AND DISCUSSION As an initial attempt, we tested diethyl dipropargylmalonate (DEDPM, M1, Scheme 2), one of the most commonly studied monomers for CP, with a monomer to initiator (Ru3) ratio (M/I) of 30:1 at room temperature. While the monomer conversion in tetrahydrofuran (THF) was low as 34%, it dramatically increased to 76% by changing the solvent to B

DOI: 10.1021/acs.macromol.8b00969 Macromolecules XXXX, XXX, XXX−XXX

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Macromolecules Table 1. Cyclopolymerization of 1,6-Heptadiynes Containing Various Substituents Using Ru3

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

monomer

M/I/Add

time (h)

conva (%)

yieldb (%)

Mnc (Da)

PDIc

6:5d

M1 M1 M2 M2 M3 M3 M4 M4 M5 M5 M6 M6 M7 M7 M8 M8 M9 M9 M10 M10 M11 M11

30/1/− 30/1/10 30/1/− 30/1/10 30/1/− 30/1/10 30/1/− 30/1/10 30/1/− 30/1/10 30/1/− 30/1/10 30/1/− 30/1/10 30/1/− 30/1/10 30/1/− 30/1/10 30/1/− 30/1/10 30/1/− 30/1/10

1 3 1 3 1 3 1 3 1 3 1 3 1 3 1 3 1 3 1 3 1 3

76 91 93 >99 95 >99 >99 >99 84 >99 51 60 >99 >99 27 95 32 88 76 >99 >99 >99

56 89 81 >99 93 77 76 98 53 75 47 33 89 64 nd 60 nd 64 70 68 70 80

4.7K 8.7K 12.9K 13.5K 16.1K 18.8K 9.6K 12.5K 15.3K 17.6K 6.7K 6.8K 19.6K 8.5K nd 15.0K nd 9.6K 8.6K 7.9K 25.8K 14.2K

1.50 1.75 1.77 1.58 1.71 1.46 1.52 1.41 1.61 1.34 1.51 1.50 1.79 1.41 nd 1.30 nd 1.66 1.60 1.81 1.92 1.45

5.8:1 11.0:1 6.8:1 14.7:1 16.6:1 26.8:1 8.2:1 6.2:1 11.8:1 8.6:1 6-only 6-only 6-only 6-only nd 6-only nd 6-only 8.0:1 12.0:1 6-only 6-only

Determined by 1H NMR. bPrecipitated in hexane at −78 °C. cDetermined by THF SEC calibrated using polystyrene standards. dDetermined by C NMR. ePrecipitated in methanol at −78 °C.

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an Mn up to 14 kDa with a greater incorporation of sixmembered rings, either without or with the additive (6.8:1 and 14.7:1, respectively, entries 3 and 4). We then tested M3 derived from di-tert-butyl malonate, which showed the highest polymerization efficiency and selectivity in the previous study using Ru2,43 and the selectivity dramatically improved, generating the corresponding P3 with an Mn up to 19 kDa and higher β-selectivity of 16.6:1 and 26.8:1 (entries 5 and 6). Additionally, amide-containing M4 and another ester-containing M5 were tested for CP to give P4 and P5 with good to excellent conversion and high selectivity (8.2:1 in entry 7 and 11.8:1 in entry 9), while the 3,5-Cl2Py additive seemed to negatively affect the β-selectivity (entries 8 and 10). To expand the monomer range in CP, we then examined CP of various ether-containing 1,6-heptadiyne derivatives (M6− M10). First, M6 containing a monosubstituted TBS-protected ether group at the C4 position was polymerized under standard conditions to give a low conversion of 51%, but to our surprise, P6 contained only six-membered rings via exclusive β-addition, as determined by 13C NMR analysis (Table 1, entry 11). Again,

12.8:1) with low to good conversions. To our delight, 3,5dichloropyridine (3,5-Cl2Py) significantly enhanced both polymerization efficiency and regioselectivity (91% conversion, 11.6:1), while analogous 3,5-dibromopyridine and 3,5-lutidine gave even lower conversion and selectivity than in the case without additives. A series of 4-substituted pyridines were also examined, but other than 4-iodopyridine, which gave a good result (74% conversion, 14.3:1), both electron-donating (Me or OMe) and electron-withdrawing (CF3) groups led to poor results. Among the various pyridine derivatives tested, 3,5dichloropyridine was selected as the optimal additive that gave the best conversion and selectivity. With this optimized condition, we investigated the CP of various ester-containing monomers (M1−M5) that showed good efficiency and selectivity with the previous Ru2 catalyst.43 As depicted in Scheme 1, M1 was successfully polymerized to give the corresponding polymer P1, and its regioselectivity calculated from 1H NMR spectra matched well with that from the 13C NMR spectra (Table 1, entries 1 and 2). Compared to M1, M2 containing a bulkier isopropyl group afforded P2 with C

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the six-membered rings prepared using Ru3 appeared at 174.2 and 60.4 ppm, respectively (Figure 1b). Interestingly, the same polymer P11 prepared using Ru2 showed a mixture of two signals corresponding to the two possible regiochemistries in both the 1H and 13C NMR spectra (Figure 1a,b), and the ratio between six- and five-membered rings was determined to be 1.4:1 by NMR integration. Overall, the reactivity of Ru2 and Ru3 toward various monomers appeared to be similar, but the β-selectivity at room temperature to give six-membered-ring repeat units on the polymer backbone was far higher in the Ru3 case (summarized in Scheme 3). For M1−M4 derived from malonates, moderate to good β-selectivity (3.4:1−6.5:1) was observed with Ru2, but β-selectivity significantly increased to 8.2:1−26.8:1 with Ru3 (Scheme 3). Surprisingly, for other monomers, Ru2 afforded the corresponding polymers with poor regioselectivity (nearly 1:1 mixtures of five- and sixmembered rings), whereas Ru3 promoted excellent β-selective CP to produce polymers containing exclusively six-memberedrings (M6, M7, M9, and M11) or as a major portion (M5 and M10, ∼12:1) (Scheme 3). To gain better insight into why the additive to Ru3 enhances activity, a series of in situ kinetic experiments were conducted by monitoring the polymerization of a model compound M1 by 1 H NMR ([M]:[I] = 20:1 in 0.1 M DCM-d2, Figure 2). The initial benzylidene in Ru3 at 14.27 ppm shifted to 12.24 ppm, corresponding to a new propagating carbene. Meanwhile, adding the additive 3-ClPy57 resulted in another chemical shift for the propagating carbene to 15.28 ppm (Figure 2a). By monitoring the conversion, CP without pyridine additives proceeded about 4 times faster than with 7 equiv of additives (Figure 2b, kp = 0.126 vs 0.458, see Supporting Information). However, the population of propagating carbene increased up to 56% with the additive compared to a maximum of 31% in the case of no additive (Figure 2c). Further, decrease in the propagating carbene or catalyst decomposition was significantly slower with the additive. This result indicates that the additive indeed coordinates to the Ru metal, thereby enhancing the stability of the propagating carbenes.19 Therefore, although polymerization is slower owing to competitive coordination of the additive, a higher conversion is obtained because of a longer lifetime of the propagating carbenes (Figure 2c). More significantly, the β-selectivity could be monitored by integrating the allylic signal from the five-membered-ring repeating unit, and as a result, lower α-selectivity (4.4% vs 7.4%) or higher βselectivity (21.7:1 vs 12.5:1) was observed with the additive in the NMR tube reaction (Figure 2d). Although it is not clear how the additive enhances βselectivity, we suggest a plausible model for the additive’s effect on CP when using Ru3 (Figure 3).58 Initiation of Ru3 generates an unstable 14 e− active species, which readily decomposes to give low conversion in CP. However, the right pyridine additives can enhance the stability of the propagating species by weak coordination to the metal, which lowers the termination rate. These features allow for more efficient polymerization, which somehow produces higher β-selectivity as well. We characterized the optical, electronic, and physical properties of the new conjugated polyenes prepared via βaddition, which are summarized in Table S2. From the UV−vis absorption spectra, λmax of the conjugated polyenes with sixmembered rings appears between 519 and 539 nm, which is significantly lower than that of five-membered-ring polymers (around 590 nm), and no vibronic peak derived from 0−0, 0−1

we tested the polymerization with the 3,5-Cl2Py additive, and P6 again gave exclusive six-membered-ring selectivity, with a higher conversion of 60% (entry 12). CP of M7 with bulkier bis-substituted TBS afforded complete conversion and exclusive β-selectivity under both without or with the additive (entries 13 and 14). Monomers containing bulky substituents, such as M8 and M9, showed lower reactivity and unsatisfactory conversions at room temperature (27% and 32%, respectively, entries 15 and 17), but with the help of the additive, both polymerized well to give P8 and P9 with excellent β-selectivity (94% and 88%, respectively, entries 16 and 18). M10, having an ethyl ether side chain, exhibited good polymerization efficiency (76%), but decreased β-selectivity compared to M9 was observed, owing to smaller side chains (8.0:1, entry 19). Fortunately, both conversion and selectivity improved to 99% and 12:1, respectively, with the help of the additive (entry 20). On the basis of the critical influence of steric factors on βselectivity, we designed a new monomer M11 that contains both ester and bulky ether moieties,56 which produced P11 with excellent conversion, β-regioselectivity (>99:1), and high Mn (up to 25 kDa) under both polymerization conditions (entries 21 and 22). Unfortunately, polydispersity indices (PDIs) of all polymers were relatively broad, unlike the living CP via α-addition using fast-initiating catalyst.17−19,28,29 We attribute this to slow initiation of Ru3 (see Supporting Information), and it seems that achieving living CP via βaddition would be still quite challenging since the initiation is an intrinsic property of the catalyst. In short, we successfully promoted CP of various monomers via selective β-addition, thereby significantly expanding the monomer scope range compared to previous reports.43 To highlight the superior β-selectivity of Ru3 over the previous Ru2, we compared the 1H and 13C NMR spectra of P11 prepared using Ru1, Ru2, and Ru3 as a representative example (Figure 1). P11 produced using Ru1 via exclusive α-

Figure 1. Comparison of (a) 1H NMR and (b) 13C NMR spectra of P11 synthesized using various Ru catalysts.

addition showed a single peak at 6.7 ppm (olefin proton by 1H NMR) while the same P11 produced via exclusive β-addition showed the olefin proton at a completely different region (5.7− 6.2 ppm, Figure 1a). The backbone selectivity of these conjugated polyenes was also analyzed using 13C NMR; P11 synthesized using Ru1 showed distinctive signals corresponding to the carbonyl and quaternary carbon in the five-membered rings at 176.3 and 60.9 ppm, whereas the analogous carbons on D

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Macromolecules Scheme 3. Comparison of the Polymerization Efficiency and Selectivity Using Ru2 and Ru3

a

See ref 43. bM/I = 50/1.

Figure 2. (a) 1H NMR spectra of the initial carbene of Ru3 (i) and propagating carbene of Ru3 without and with additive (ii, iii). Plots of (b) monomer conversion, (c) propagating carbene, and (d) five-membered ring composition vs time for the CP of M1 with [M]:[I] = 20:1.

substituents, from 219 to 370 °C, while their glass transition

transition is observed. On the other hand, their optical band gaps obtained from the onset point from the UV−vis spectra were consistently lower by approximately 0.1 eV (1.9 vs 2.0 eV). For thermal properties, we found that the decomposition temperature (Td) appears to increase with increasing size of the

temperatures (Tg) are not much different (71 to 133 °C). E

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ACKNOWLEDGMENTS The financial support from Creative Research Initiative Program and the Nano-Material Technology Development Program through NRF is acknowledged. K.K. is supported by NRF-Global Ph.D. Fellowship program (Grant NRF2015H1A2A1033766). We thank NCIRF and NICEM at SNU for supporting 13C NMR experiments and LINC at Sogang University for supporting HR-MS experiments.

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Figure 3. Proposed scheme showing the effects of pyridine additive.

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CONCLUSION In summary, we successfully synthesized various conjugated polyenes containing six-membered-ring repeat units via highly selective β-addition in the CP of 1,6-heptadiynes using a new Ru-based catalyst (Ru3). On the basis of our recent findings on the geometry and electronic character of Ru3, and with the help of pyridine additives, we developed efficient and regioselective CP, which afforded far greater β-selectivity than the previously reported CP using another chelated catalyst (Ru2). In particular, while Ru2 promoted satisfactory βselective CP only with malonate-type monomers, and very poor selectivity for various other monomers, Ru3 exhibited high to exclusive β-selectivity for all monomers, demonstrating its superior monomer scope. Through in-depth mechanistic investigation using 1H NMR spectroscopy, we found that pyridine additives play an important role in enhancing not only the stability of the propagating carbenes but also the β-addition regioselectivity. Finally, the optoelectronic and thermal properties of the resulting conjugated polymers were compared with those of previously reported polyenes containing fivemembered rings. These extensive studies on CP using a Ru catalyst bearing catechothiolate ligands and the effect of exogenous pyridine additives should expand the understanding and applicability of Ru-catalyzed olefin metathesis polymerization.

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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.8b00969. Experimental procedures, characterizations, NMR spectra for new compounds and polymers, SEC traces, and other supporting experiments (PDF)

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REFERENCES

(1) Choi, S. K.; Gal, Y. S.; Jin, S. H.; Kim, H. K. Poly(1,6heptadiyne)-Based Materials by Metathesis Polymerization. Chem. Rev. 2000, 100, 1645−1682. (2) Stille, J. K.; Frey, D. A. Polymerization of Non-conjugated Diynes by Complex Metal Catalysts. J. Am. Chem. Soc. 1961, 83, 1697−1701. (3) Gibson, H. W.; Bailey, F. C.; Epstein, A. J.; Rommelmann, H.; Kaplan, S.; Harbour, J.; Yang, X. Q.; Tanner, D. B.; Pochan, J. M. Poly(1,6-heptadiyne), a Free-Standing Polymer Film Dopable to High Electrical Conductivity. J. Am. Chem. Soc. 1983, 105, 4417−4431. (4) Kim, Y. H.; Gal, Y. S.; Kim, U. Y.; Choi, S. K. Cyclopolymerization of Dipropargylsilanes by Transition-Metal Catalysts. Macromolecules 1988, 21, 1991−1995. (5) Ryoo, M. S.; Lee, W. C.; Choi, S. K. Cyclopolymerization of Diethyl Dipropargylmalonate by Transition Metal Catalysts. Macromolecules 1990, 23, 3029−3031. (6) Jang, M. S.; Kwon, S. K.; Choi, S. K. Cyclopolymerization of Diphenyldipropargylmethane by Transition Metal Catalysts. Macromolecules 1990, 23, 4135−4140. (7) Kang, K. L.; Kim, S. H.; Cho, H. N.; Choi, K. Y.; Choi, S. K. A New Class of Conjugated Ionic Polyacetylene. Cyclopolymerization of Dihexyldipropargylammonium Salts by Metathesis Catalysts. Macromolecules 1993, 26, 4539−4543. (8) Gal, Y. S.; Jin, S. H.; Park, J. W.; Lee, W. C.; Lee, H. S.; Kim, S. Y. Cyclopolymerization of Dipropargylfluorene by Transition-Metal Catalysts. J. Polym. Sci., Part A: Polym. Chem. 2001, 39, 4101−4109. (9) Fox, H. H.; Schrock, R. R. Living Cyclopolymerization of Diethyl Dipropargylmalonate by Mo(CH-t-Bu)(NAr)[OCMe(CF3)2]2 in Dimethoxyethane. Organometallics 1992, 11, 2763−2765. (10) Fox, H. H.; Wolf, M. O.; O’Dell, R.; Lin, B. L.; Schrock, R. R.; Wrighton, M. S. Living Cyclopolymerization of 1,6-Heptadiyne Derivatives Using Well-Defined Alkylidene Complexes: Polymerization Mechanism, Polymer Structure, and Polymer Properties. J. Am. Chem. Soc. 1994, 116, 2827−2843. (11) Krause, J. O.; Zarka, M. T.; Anders, U.; Weberskirch, R.; Nuyken, O.; Buchmeiser, M. R. Simple Synthesis of Poly(acetylene) Latex Particles in Aqueous Media. Angew. Chem., Int. Ed. 2003, 42, 5965−5969. (12) Krause, J. O.; Nuyken, O.; Buchmeiser, M. R. Factors Relevant for the Ruthenium−Benzylidene-Catalyzed Cyclopolymerization of 1,6-Heptadyines. Chem. - Eur. J. 2004, 10, 2029−2035. (13) Halbach, T. S.; Krause, J. O.; Nuyken, O.; Buchmeiser, M. R. Stereoselective Cyclopolymerization of Polar 1,6-Heptadiynes by Novel, Tailor-Made Ruthenium-Based Metathesis Catalysts. Macromol. Rapid Commun. 2005, 26, 784−790. (14) Mayershofer, M. G.; Nuyken, O.; Buchmeiser, M. R. Bi- and Trinuclear Ruthenium Alkylidene Triggered Cyclopolymerization of 1,6-Heptadiynes: Access to An−X−An Block and (An)3X Tristar Copolymers. Macromolecules 2006, 39, 3484−3493. (15) Kumar, P. S.; Wurst, K.; Buchmeiser, M. R. Factors Relevant for the Regioselective Cyclopolymerization of 1,6-Heptadiynes, N,NDipropargylamines, N,N-Dipropargylammonium Salts, and Dipropargyl Ethers by RuIV−Alkylidene-Based Metathesis Initiators. J. Am. Chem. Soc. 2009, 131, 387−395. (16) Sudheendran, M.; Horecha, M.; Kiriy, A.; Gevorgyan, S. A.; Krebs, F. C.; Buchmeiser, M. R. Cyclopolymerization-Derived BlockCopolymers of 4,4-Bis(octyloxymethyl)-1,6-Heptadiyne with 4,4Dipropargyl malonodinitrile for Use in Photovoltaics. Polym. Chem. 2013, 4, 1590−1599.

AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected] (T.-L.C.). ORCID

Soon Hyeok Hong: 0000-0003-0605-9735 Robert H. Grubbs: 0000-0002-0057-7817 Tae-Lim Choi: 0000-0001-9521-6450 Notes

The authors declare no competing financial interest. F

DOI: 10.1021/acs.macromol.8b00969 Macromolecules XXXX, XXX, XXX−XXX

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Macromolecules

Acetylene and Diethyl Dipropargylmalonate. Macromolecules 1996, 29, 8990−8991. (35) Anders, U.; Nuyken, O.; Buchmeiser, M. R.; Wurst, K. Stereoselective Cyclopolymerization of 1,6-Heptadiynes: Access to Alternating cis-trans-1,2-(Cyclopent-1-enylene)vinylenes by Fine-Tuning of Molybdenum Imidoalkylidenes. Angew. Chem., Int. Ed. 2002, 41, 4044−4047. (36) Anders, U.; Wagner, M.; Nuyken, O.; Buchmeiser, M. R. First Controlled Cyclopolymerization of Diethyl Dipropargylmalonate by MoCl5−n-Bu4Sn−EtOH−Quinuclidine and MoOCl 4−n-Bu4Sn− EtOH−Quinuclidine To Give Highly Regular Polyenes Consisting Exclusively of 1,2-(Cyclopent-1-enylene)−Vinylene Units. Macromolecules 2003, 36, 2668−2673. (37) Buchmeiser, M. R.; Sen, S.; Unold, J.; Frey, W. N-Heterocyclic Carbene, High Oxidation State Molybdenum Alkylidene Complexes: Functional-Group-Tolerant Cationic Metathesis Catalysts. Angew. Chem., Int. Ed. 2014, 53, 9384−9388. (38) Herz, K.; Unold, J.; Hänle, J.; Schowner, R.; Frey, W.; Buchmeiser, M. R.; Sen, S. Mechanism of the Regio- and Stereoselective Cyclopolymerization of 1,6-Hepta- and 1,7-Octadiynes by High Oxidation State Molybdenum−Imidoalkylidene N-Heterocyclic Carbene Initiators. Macromolecules 2015, 48, 4768−4778. (39) Vygodskii, Y. S.; Shaplov, A. S.; Lozinskaya, E. I.; Vlasov, P. S.; Malyshkina, I. A.; Gavrilova, N. D.; Kumar, P. S.; Buchmeiser, M. R. Cyclopolymerization of N,N-Dipropargylamines and N,N-Dipropargyl Ammonium Salts. Macromolecules 2008, 41, 1919−1928. (40) Autenrieth, B.; Anderson, E. B.; Wang, D.; Buchmeiser, M. R. Reactivity of the Dicationic Ruthenium, D.; Buchmeiser, M. R.,., 2+ 4− 3(IMesH2)(=CHHvity of the6H4)], (BF )2] in Ring-Opening Metathesis and Cyclopolymerization. Macromol. Chem. Phys. 2013, 214, 33−40. (41) Keitz, B. K.; Endo, K.; Patel, P. R.; Herbert, M. B.; Grubbs, R. H. Improved Ruthenium Catalysts for Z-Selective Olefin Metathesis. J. Am. Chem. Soc. 2012, 134, 693−699. (42) Herbert, M. B.; Grubbs, R. H. Z-Selective Cross Metathesis with Ruthenium Catalysts: Synthetic Applications and Mechanistic Implications. Angew. Chem., Int. Ed. 2015, 54, 5018−5024. (43) Jung, K.; Kang, E. H.; Sohn, J. H.; Choi, T. L. Highly β-Selective Cyclopolymerization of 1,6-Heptadiynes and Ring-Closing Enyne Metathesis Reaction Using Grubbs Z-Selective Catalyst: Unprecedented Regioselectivity for Ru-Based Catalysts. J. Am. Chem. Soc. 2016, 138, 11227−11233. (44) Liu, P.; Xu, X.; Dong, X.; Keitz, B. K.; Herbert, M. B.; Grubbs, R. H.; Houk, K. N. Z-Selectivity in Olefin Metathesis with Chelated Ru Catalysts: Computational Studies of Mechanism and Selectivity. J. Am. Chem. Soc. 2012, 134, 1464−1467. (45) Dang, Y.; Wang, Z. X.; Wang, X. A Thorough DFT Study of the Mechanism of Homodimerization of Terminal Olefins through Metathesis with a Chelated Ruthenium Catalyst: From Initiation to Z Selectivity to Regeneration. Organometallics 2012, 31, 7222−7234. (46) Dang, Y.; Wang, Z. X.; Wang, X. Does the Ruthenium Nitrato Catalyst Work Differently in Z-Selective Olefin Metathesis? A DFT Study. Organometallics 2012, 31, 8654−8657. (47) Romero, P. E.; Piers, W. E. Direct Observation of a 14-Electron Ruthenacyclobutane Relevant to Olefin Metathesis. J. Am. Chem. Soc. 2005, 127, 5032−5033. (48) Wenzel, A. G.; Grubbs, R. H. Ruthenium Metallacycles Derived from 14-Electron Complexes. New Insights into Olefin Metathesis Intermediates. J. Am. Chem. Soc. 2006, 128, 16048−16049. (49) Koh, M. J.; Khan, R. K.; Torker, S.; Yu, M.; Mikus, M. S.; Hoveyda, A. H. High-Value Alcohols and Higher-Oxidation-State Compounds by Catalytic Z-Selective Cross-Metathesis. Nature 2015, 517, 181−186. (50) Khan, R. K.; Torker, S.; Hoveyda, A. H. Readily Accessible and Easily Modifiable Ru-Based Catalysts for Efficient and Z-Selective Ring-Opening Metathesis Polymerization and Ring-Opening/CrossMetathesis. J. Am. Chem. Soc. 2013, 135, 10258−10261. (51) Koh, M. J.; Khan, R. K.; Torker, S.; Hoveyda, A. H. Broadly Applicable Z- and Diastereoselective Ring-Opening/Cross-Metathesis

(17) Kang, E. H.; Lee, I. S.; Choi, T. L. Ultrafast Cyclopolymerization for Polyene Synthesis: Living Polymerization to Dendronized Polymers. J. Am. Chem. Soc. 2011, 133, 11904−11907. (18) Lee, I. S.; Kang, E. H.; Park, H.; Choi, T. L. Controlled Cyclopolymerisation of 1,7-Octadiyne Derivatives Using Grubbs Catalyst. Chem. Sci. 2012, 3, 761−765. (19) Kang, E. H.; Yu, S. Y.; Lee, I. S.; Park, S. E.; Choi, T. L. Strategies to Enhance Cyclopolymerization using Third-Generation Grubbs Catalyst. J. Am. Chem. Soc. 2014, 136, 10508−10514. (20) Kang, C.; Kang, E. H.; Choi, T. L. Successful Cyclopolymerization of 1,6-Heptadiynes Using First-Generation Grubbs Catalyst Twenty Years after Its Invention: Revealing a Comprehensive Picture of Cyclopolymerization Using Grubbs Catalysts. Macromolecules 2017, 50, 3153−3163. (21) Guo, M.; Sun, R.; Han, H.; Wu, J.; Xie, M.; Liao, X. Metathesis Cyclopolymerization of 1,6-Heptadiyne Derivative toward Triphenylamine-Functionalized Polyacetylene with Excellent Optoelectronic Properties and Nanocylinder Morphology. Macromolecules 2015, 48, 2378−2387. (22) Wang, J.; Li, H.; Liao, X.; Xie, M.; Sun, R. Synthesis of TriazoleDendronized Polyacetylenes by Metathesis Cyclopolymerization and Their Conductivity. Polym. Chem. 2016, 7, 4912−4923. (23) Wu, J.; Wang, C.; Zhou, D.; Liao, X.; Xie, M.; Sun, R. Branched 1,2,3-Triazolium-Functionalized Polyacetylene with Enhanced Conductivity. Macromol. Rapid Commun. 2016, 37, 2017−2022. (24) Wu, J.; Li, H.; Zhou, D.; Liao, X.; Xie, M.; Sun, R. Metathesis Cyclopolymerization of Substituted 1,6-Heptadiyne and Dual Conductivity of Doped Polyacetylene Bearing Branched Triazole Pendants. J. Polym. Sci., Part A: Polym. Chem. 2017, 55, 485−494. (25) Li, H.; Wang, J.; Han, H.; Wu, J.; Xie, M. Dual Conductivity of Ionic Polyacetylene by the Metathesis Cyclopolymerization of Dendronized Triazolium-Functionalized 1,6-Heptadiyne. React. Funct. Polym. 2018, 127, 20−28. (26) Kim, J.; Kang, E. H.; Choi, T. L. Cyclopolymerization To Synthesize Conjugated Polymers Containing Meldrum’s Acid as a Precursor for Ketene Functionality. ACS Macro Lett. 2012, 1, 1090− 1093. (27) Kang, E. H.; Choi, T. L. Coil-to-Rod Transition of Conjugated Polymers Prepared by Cyclopolymerization of 1,6-Heptadiynes. ACS Macro Lett. 2013, 2, 780−784. (28) Song, J. A.; Park, S. E.; Kim, T. S.; Choi, T. L. N-Containing 1,7Octadiyne Derivatives for Living Cyclopolymerization Using Grubbs Catalysts. ACS Macro Lett. 2014, 3, 795−798. (29) Song, J. A.; Choi, T. L. Seven-Membered Ring-Forming Cyclopolymerization of 1,8-Nonadiyne Derivatives Using Grubbs Catalysts: Rational Design of Monomers and Insights into the Mechanism for Olefin Metathesis Polymerizations. Macromolecules 2017, 50, 2724−2735. (30) Yang, S.; Shin, S.; Choi, I.; Lee, J.; Choi, T.-L. Direct Formation of Large-Area 2D Nanosheets from Fluorescent Semiconducting Homopolymer with Orthorhombic Crystalline Orientation. J. Am. Chem. Soc. 2017, 139, 3082−3088. (31) Shin, S.; Gu, M. L.; Yu, C. Y.; Jeon, J.; Lee, E.; Choi, T. L. Polymer Self-Assembly into Unique Fractal Nanostructures in Solution by a One-Shot Synthetic Procedure. J. Am. Chem. Soc. 2018, 140, 475−482. (32) Fox, H. H.; Wolf, M. O.; O’Dell, R.; Lin, B. L.; Schrock, R. R.; Wrighton, M. S. Living Cyclopolymerization of 1,6-Heptadiyne Derivatives Using Well-Defined Alkylidene Complexes: Polymerization Mechanism, Polymer Structure, and Polymer Properties. J. Am. Chem. Soc. 1994, 116, 2827. (33) Schattenmann, F. J.; Schrock, R. R.; Davis, W. M. Preparation of Biscarboxylato Imido Alkylidene Complexes of Molybdenum and Cyclopolymerization of Diethyldipropargylmalonate To Give a Polyene Containing Only Six-Membered Rings. J. Am. Chem. Soc. 1996, 118, 3295−3296. (34) Schattenmann, F. J.; Schrock, R. R. Soluble, Highly Conjugated Polyenes via the Molybdenum-Catalyzed Copolymerization of G

DOI: 10.1021/acs.macromol.8b00969 Macromolecules XXXX, XXX, XXX−XXX

Article

Macromolecules Catalyzed by a Dithiolate Ru Complex. Angew. Chem., Int. Ed. 2014, 53, 1968−1972. (52) Mikus, M. S.; Torker, S.; Hoveyda, A. H. Controllable ROMP Tacticity by Harnessing the Fluxionality of Stereogenic-at-Ruthenium Complexes. Angew. Chem., Int. Ed. 2016, 55, 4997−5002. (53) Johns, A. M.; Ahmed, T. S.; Jackson, B. W.; Grubbs, R. H.; Pederson, R. L. High Trans Kinetic Selectivity in Ruthenium-Based Olefin Cross-Metathesis through Stereoretention. Org. Lett. 2016, 18, 772−775. (54) Jung, H.; Jung, K.; Hong, M.; Kwon, S.; Kim, K.; Hong, S. H.; Choi, T. L.; Baik, M. H. Understanding the Origin of the Regioselectivity in Cyclopolymerizations of Diynes and How to Completely Switch It. J. Am. Chem. Soc. 2018, 140, 834−841. (55) Determining the regioselectivity by 1H NMR was possible only for the M1 case (see Figure S37); otherwise, signals were broad and overlapped. (56) Park, H.; Lee, H. K.; Choi, T. L. Faster Cyclopolymerisation of 4,4-Disubstituted 1,7-Octadiynes Through an Enhanced Thorpe− Ingold Effect. Polym. Chem. 2013, 4, 4676−4681. (57) For the NMR experiment, liquid 3-chloropyridine was used instead of solid 3,5-dichloropyridine because it was easier to add to the NMR tube. (58) Walsh, D. J.; Lau, S. H.; Hyatt, M. G.; Guironnet, D. Kinetic Study of Living Ring-Opening Metathesis Polymerization with ThirdGeneration Grubbs Catalysts. J. Am. Chem. Soc. 2017, 139, 13644− 13647.

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DOI: 10.1021/acs.macromol.8b00969 Macromolecules XXXX, XXX, XXX−XXX