Mixed-Ligand Approach to Palladium-Catalyzed Direct Arylation

Apr 16, 2015 - ABSTRACT: This paper reports the synthesis of an alternating copolymer consisting of dithienosilole (DTS) and thienopyrroledione. (TPD)...
0 downloads 0 Views 458KB Size
Download PDF
Article pubs.acs.org/Macromolecules

Mixed-Ligand Approach to Palladium-Catalyzed Direct Arylation Polymerization: Synthesis of Donor−Acceptor Polymers with Dithienosilole (DTS) and Thienopyrroledione (TPD) Units Eisuke Iizuka,† Masayuki Wakioka,† and Fumiyuki Ozawa*,†,‡ †

International Research Center for Elements Science (IRCELS), Institute for Chemical Research, Kyoto University, Uji, Kyoto 611-0011, Japan ‡ ACT-C, Japan Science and Technology Agency, Uji, Kyoto 611-0011, Japan S Supporting Information *

ABSTRACT: This paper reports the synthesis of an alternating copolymer consisting of dithienosilole (DTS) and thienopyrroledione (TPD) units via palladium-catalyzed direct arylation polymerization (DArP). Although DArP has recently attracted much attention as an easy synthetic method of π-conjugated polymers without the need for prepreparation of organometallic monomers, there are two major problems that must be eliminated. One is homocoupling producing structural defects in the polymer chain, and the other is byproduction of insoluble materials. In this study, we have found that the combined use of P(2-MeOC6H4)3 and P(2-Me2NC6H4)3 ligands effectively prevents these side reactions, resulting in poly(DTS-alt-TPD) (MnGPC = 15000, Mw/Mn = 2.57) with good solubility in high yield (84%).

■

INTRODUCTION π-Conjugated polymers have found wide application in optoelectronic devices. 1,2 Alternating copolymers with donor−acceptor combinations of repeating units (DA polymers) have proven to be a particularly useful component of solar cells, owing to their extremely narrow HOMO−LUMO gaps.2 At present, many of them are prepared by catalytic polycondensation using Migita−Stille cross-coupling.3 However, this method requires prepreparation of aryltin monomers, which are laborious in purification; monomer purity is a crucial factor in polycondensation. Moreover, this polymerization reaction produces a highly toxic byproduct such as Me3SnBr. In this context, a novel polycondensation process utilizing palladium-catalyzed direct arylation (direct arylation polymerization: DArP) has recently emerged as a viable alternative.4 Direct arylation is a simple cross-coupling process between aryl halides and heteroarenes, which does not need organometallic reagents.5 This catalysis proceeds via C−H bond activation of heteroarenes, instead of transmetalation with organometallic reagents.6 It has been recognized that direct arylation is advantageous over conventional cross-coupling reactions in terms of fewer reaction steps and reduced waste generation. Moreover, direct arylation has excellent functional group tolerance. Accordingly, an increasing number of reports have been published,4,7−10 since the first successful example in 2010.7a However, DArP still has two major problems that must be eliminated. One is homocoupling producing structural defects in the polymer chain.10k,l It has been documented that the © XXXX American Chemical Society

structural defects arising from homocoupling causes a notable decrease in the power conversion efficiency of polymer solar cells.11 The other is direct arylation at undesirable C−H positions giving branched and cross-linked polymers, which eventually change to insoluble materials.8e,9b Monomers with less substituted heteroarene units tend to undergo these side reactions. This paper reports the synthesis of DA polymer 3 consisting of dithienosilole (DTS) and thienopyrroledione (TPD) units via DArP (Scheme 1). This polymer has been prepared by Migita−Stille cross-coupling, and shown to exhibit good performance in solar cells.12 On the other hand, while the Scheme 1. Direct Arylation Polymerization of 1 and 2

Received: March 12, 2015 Revised: April 7, 2015

A

DOI: 10.1021/acs.macromol.5b00526 Macromolecules XXXX, XXX, XXX−XXX

Article

Macromolecules Table 1. Ligand Effects on Direct Arylation Polymerization of 1 and 2 (Scheme 1)a run

1

L1 (per Pd)

L2 (per Pd)

time (h)

insoluble materialsb

yieldc (%)

Mnd

Mw/Mnd

1 2 3 4 5 6 7 8

1a 1b 1b 1b 1b 1b 1b 1b

2 2 0 2 2 2 2 2

0 0 2 1 1.5 1.5 2 2

24 24 48 24 24 48 48 96

yes yes no yes no yes no no

73 18 0 28 29 50 84 80

14800 14900 − 14600 11300 16300 15000 15100

28.2 2.19 − 2.27 1.79 2.64 2.57 2.41

Reactions were performed in toluene (1 mL) at 100 °C, except for run 1 (120 °C), using 1 (0.5 mmol), 2 (0.5 mmol), PivOH (0.50 mmol), Cs2CO3 (1.5 mmol), Pd2(dba)3·CHCl3 (2.5 μmol), and ligand(s). bInsolubilization: occurred (yes) or not occurred (no). cYield of CHCl3 extract after Soxhlet extraction with acetone, hexane, and CHCl3. dEstimated by GPC calibration based on polystyrene standards (o-Cl2C6H4, 140 °C).

a

same polymer was prepared by DArP, it was reported that the polymerization involved byproduction of insoluble materials and the synthetic results were difficult to reproduce.8d In this study, we attempted to find an effective solution for this problem, using a novel catalytic direct arylation system that we have developed.7 Unlike common catalytic systems, our system is sufficiently reactive even in toluene as a nonpolar solvent. This unique catalytic property is provided by P(2-MeOC6H4)3 (L1) or P(2-Me2NC6H4)3 (L2) having ortho-substituents with coordination ability (Scheme 1).13 Herein, we disclose that the combined use of L1 and L2 effectively reduces side reactions including homocoupling and enables the synthesis of 3 with good solubility in high yield.

■

RESULTS AND DISCUSSION Table 1 lists the results of polymerization under several catalytic conditions. First of all, DTS dibromide 1a (0.50 mmol) was reacted with TPDH2 (2, 0.50 mmol), under our standard catalytic conditions,7c using Pd2(dba)3·CHCl3 (0.5 mol % = 1.0 mol % Pd) and L1 (2.0 mol %) as catalyst precursors, toluene (1 mL) as a solvent, and PivOH (0.50 mmol) and Cs2CO3 (1.5 mmol) as additives. The reaction did not occur at 100 °C, but proceeded at 120 °C (run 1). However, the resulting polymer contained insoluble materials, which remained in the Soxhlet thimble after extraction with hot CHCl3. Moreover, the extract exhibited a significantly broad molecular weight distribution arising from a fronting peak. Thus, next we examined the reaction at lower temperature using diiodide 1b instead of dibromide 1a (run 2). In this case, the reaction proceeded at 100 °C; however, a major part of the product was still insoluble in hot CHCl3, and a polymeric compound with MnGPC = 14900 (Mw/Mn = 2.19) was obtained in low yield from the CHCl3 extract. To investigate the cause of the formation of insoluble materials, the structures of oligomeric products formed at an early stage of polymerization were examined by NMR spectroscopy in detail (Figure 1). In entry 1, the reaction of 1b and 2 was conducted for 20 min under the catalytic conditions of run 2 in Table 1, and an oligomeric compound with MnGPC = 3000 (Mw/Mn = 1.72) was isolated in 68% yield from the reaction mixture by precipitation in MeOH. Figure 1a shows the aromatic region of the 1H NMR spectrum: see the Supporting Information for a detailed description of the peak assignments using model compounds.14−16 Signals A and B are attributed to DTS units in DTS−TPD−TPD−DTS and DTS− TPD−DTS linkages in the main chain, respectively.14 On the other hand, signals a−e are assigned to the ring protons of DTS-I, DTS-H, and TPD-H groups at the chain ends.15 Signal

Figure 1. 1H NMR spectra of DArP products at an early stage of polymerization (C2D2Cl4, 130 °C, 400 MHz). (∗) Free TPDH2.

a is due to the inside protons of DTS-I and DTS-H groups, whereas sharp singlets b and d are due to the outside protons of TPD-H and DTS-I groups, respectively. Moreover, two sets of doublets c and e with the same intensity are ascribed to the DTS-H group. On the basis of the relative intensity of these signals and of NCH2 signals of TPD units around δ 3.7, the average number of DTS and TPD units incorporated in the whole molecule and in the terminal positions was evaluated as summarized in entry 1 in Table 2. The NMR molecular weight was estimated to be MnNMR = 3900, the value of which was consistent with the GPC value (MnGPC = 3000). Thus, we could find two types of side reactions in the catalytic polymerization using L1. One is homocoupling of TPD-H groups to afford TPD−TPD bonds, and the other is the reduction of DTS-I to DTS-H terminus. On the other hand, to our surprised, DTS−DTS bonds that are expected to be formed as a counterpart of TPD−TPD bonds in homocoupling B

DOI: 10.1021/acs.macromol.5b00526 Macromolecules XXXX, XXX, XXX−XXX

Article

Macromolecules Table 2. Analytical Data for Figure 1a averaged unit number in each molecule entry

DTS/TPD [cross/homo]b

DTS-I/DTS-H/TPD-H

MnNMR

MnGPC

Mw/Mn

1 2

5.42/5.76 [9.73/0.26] 4.68/4.80 [8.36/0.12]

0.86/0.26/0.88 0.88/0.12/1.00

3900 3300

3000 2500

1.72 1.67

a

Isolated yields after MeOH precipitation (twice) are as follows: 68% (run 1), 61% (run 2). bThe number of DTS−TPD (cross) and TPD−TPD (homo) bonds in each molecule.

could not be detected to any extent.16 In this case, the reduction of DTS-I to DTS-H is very likely to keep the redox balance with the oxidative coupling of TPD-H groups (eq 1). Actually, the number of DTS-H groups was identical to that of TPD−TPD bonds (0.26). The ratio of TPD−TPD (homo) to DTS−TPD (cross) bonds was estimated to be 3:97.

Figure 2 compares the 1H NMR spectra of the polymers derived from run 2 (3I) and run 7 (3II) in Table 1. The signal

Pd‐catalyst

DTS‐I + 2TPD‐H ⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯→ DTS‐H + TPD−TPD + HI (1)

In relation to the homocoupling process in DArP, we have demonstrated that L2 causes highly regioregular polymerization of 2-bromo-3-hexylthiophene to give poly(3-hexylthiophene) in 99% regularity,7a,b whereas the regioregularity gained with L1 is up to 96%.7b Since the drop in regioregularity is due to the occurrence of homocoupling, we may anticipate that L2 prevents the homocoupling in the present polymerization system as well. Thus, we introduced L2 together with L1 (entry 2 in Figure 1). As a result, the side reactions in eq 1 were reduced to a considerable extent. Figure 1b shows the 1H NMR spectrum of the product of entry 2, which was isolated in 61% yield by precipitation in MeOH (MnGPC = 2500, Mw/Mn = 1.67). It is seen that signal A arising from the DTS−TPD−TPD−DTS linkage is significantly weakened, compared with entry 1. The ratio of TPD− TPD (homo) to DTS−TPD (cross) bonds was reduced to 1:99. This change was associated with weakening of the signals of DTS-H terminus (c and e). In fact, the same number of DTS-H groups as TPD−TPD bonds were detected (0.12). Another important finding in entry 2 is the presence of the same number of DTS (DTS-I + DTS-H) and TPD (TPD-H) units at the chain ends.17 Accordingly, we concluded that the DArP process was significantly improved with the aid of L2. Thus, we attempted the synthesis of desired polymer 3 in the presence of L2. To our delight, the addition of L2 not only prevented the homocoupling in eq 1, but also suppressed the formation of insoluble materials. The results are listed in runs 3−8 in Table 1. No polymer formation was observed only with L2, in the absence of L1 (run 3). On the other hand, polymerization proceeded in mixed ligand systems containing L1 (2 equiv/Pd) and L2 (variable). Insoluble materials kept forming in the presence of 1 equiv/Pd of L2 (run 4). The addition of 1.5 equiv/Pd of L2 suppressed the insolubilization; however, the polymerization became notably slow, and an oligomeric compound soluble in hot hexane was obtained as the major product (run 5). The molecular weight increased with a prolonged reaction time, but insoluble materials were generated again (run 6). Finally, we could prepare polymer 3 with good solubility in 84% yield in the presence of 2 equiv/Pd of L2 (run 7). The molecular weight attained MnGPC = 15000 (Mw/Mn = 2.57) after 48 h (run 7), and remained unchanged after 96 h (run 8), where insoluble materials could not be detected upon Soxhlet extraction with hot CHCl3.

Figure 2. 1H NMR spectra of DArP products in run 2 (3I) and run 7 (3II) in Table 1 (C2D2Cl4, 130 °C, 400 MHz). (∗) Unknown signals (see text).

assignment follows that in Figure 1. The most remarkable feature of 3I (a) is the absent of DTS-I (d) and TPD-H (b) groups at the chain ends; i.e., both termini are substituted with DTS-H (c and e) formed by the reduction of DTS-I. Moreover, broad signals arising from the DTS units in structural defects are observed at δ 7.43, 7.37, and 7.21; the signal at δ 7.21 is assignable to the inside protons of DTS−DTS homocoupling units,16 whereas the signals at δ 7.43 and 7.37 are possibly due to the DTS units in branched structures. On the other hand, polymer 3II prepared using L1 and L2 exhibited the 1H NMR spectrum in Figure 2b, comparable to that of the oligomeric analogue in Figure 1b. The signals of three kinds of terminal groups (DTS-I/DTS-H/TPD-H) were detected in a 0.61/0.36/1.03 ratio. The ratio of TPD−TPD (homo) to DTS−TPD (cross) bonds was estimated to be 2:98, the value of which is slightly larger than that of the oligomer, but is still on a well-controlled level. Figure 3 compares UV−vis spectra of polymers 3I and 3II. Also included is the spectrum of 3III with an enhanced molecular weight (MnGPC = 25800, Mw/Mn = 2.02), which was prepared by Soxhlet extraction of 3II with CH2Cl2 and CHCl3 (29% recovery). Two strong absorptions are observed around 614 and 670 nm. The intensity at 670 nm is enhanced in the order 3I < 3II < 3III, whereas the absorption around 560 nm, which is ascribable to the DTS−TPD−TPD−DTS linkage,18 reduces its intensity in the reverse order. Thus, it is reasonable that the absorption change from 3I to 3III reflects the elongation of the donor−acceptor type repeating chain and the decrease in the structural defects. We also confirmed that the absorption spectrum of 3III (MnGPC = 25800) is in good agreement with that of the copolymer (MnGPC = 28000) prepared by Migita−Stille cross-coupling polymerization12a (Figure S9). C

DOI: 10.1021/acs.macromol.5b00526 Macromolecules XXXX, XXX, XXX−XXX

Article

Macromolecules

according to the literature. The other chemicals were obtained from commercial sources and used without purification. Preparation of Oligomeric Compounds in Figure 1. A typical procedure is reported for entry 2. A mixture of 1b (0.50 mmol, 0.538 M in toluene), 2 (133 mg, 0.50 mmol), Pd2(dba)3·CHCl3 (2.60 mg, 2.5 μmol), L1 (3.52 mg, 10 μmol), L2 (3.92 mg, 10 μmol), Cs2CO3 (489 mg, 1.5 mmol), and PivOH (51.1 mg, 0.50 mmol) in toluene (1.0 mL in total) was heated at 100 °C for 6 h. The mixture was cooled to room temperature, diluted with CHCl3 (40 mL), and washed with water (3 × 5 mL) and then with a 5N aqueous HCl solution (5 mL). The organic phase was poured into vigorously stirred MeOH (150 mL) to afford a dark purple precipitate, which was dissolved in CHCl3 (40 mL) and poured into vigorously stirred MeOH (150 mL) again. The resulting precipitate was collected by filtration using a membrane filter (0.5 mm), washed with MeOH, and dried under vacuum at room temperature overnight (61%, MnGPC = 2500, Mw/Mn = 1.67). The reaction using L1 (entry 1) was similarly conducted, and an oligomeric compound with MnGPC = 3000 (Mw/Mn = 1.72) was obtained (68%). The 1H NMR spectra of these oligomers are given in Figure S2, Supporting Information. Preparation of Poly(DTS-alt-TPD) via Direct Arylation Polymerization. A mixture of 1b (0.50 mmol, 0.538 M in toluene), 2 (133 mg, 0.50 mmol), Pd2(dba)3·CHCl3 (2.60 mg, 2.5 μmol), L1 (3.52 mg, 10 μmol), L2 (3.92 mg, 10 μmol), Cs2CO3 (489 mg, 1.5 mmol), and PivOH (51.1 mg, 0.50 mmol) in toluene (1.0 mL in total) was stirred at room temperature for 0.5 h, and then at 100 °C for 48 h. The mixture was cooled to room temperature, diluted with CHCl3 (100 mL), and washed with water (3 × 10 mL) and then with a 5 N HCl solution (10 mL). The organic phase was poured into vigorously stirred MeOH (300 mL), and a dark purple precipitate was collected by filtration, washed with MeOH, and dried under vacuum overnight. The product was purified by Soxhlet extraction with acetone, hexane, and CHCl3. No colored material remained in the extraction thimble after Soxhlet extraction. The CHCl3 extract was concentrated (ca. 30 mL) and poured into vigorously stirred MeOH (300 mL), giving polymer 3II in 84% yield (286 mg, Mn = 15,000, Mw/Mn = 2.57). A part of the product (124 mg) was subjected to Soxhlet extraction with CH2Cl2 and CHCl3, and polymer 3III with enhanced molecular weight (MnGPC = 25800, Mw/Mn = 2.02) was obtained (35.6 mg). The 1H NMR spectra of polymer 3I and 3II are reported in Figure S3.

Figure 3. UV−vis spectra of (a) 3I, (b) 3II, and (c) 3III (o-Cl2C6H4). Wavenumbers of two maximum absorptions (nm) are as follows: (a) 613, 667; (b) 615, 670; (c) 614, 671.

■

CONCLUSION We have reported the synthesis of an alternating copolymer with dithienosilole (DTS) and thienopyrroledione (TPD) units via palladium-catalyzed direct arylation polymerization (DArP). While the DArP between DTSX2 (1) and TPDH2 (2) has a strong tendency to form insoluble materials, the combined use of P(2-MeOC6H4)3 (L1) and P(2-Me2NC6H4)3 (L2) enables the synthesis of desired polymer 3 with good solubility. Moreover, NMR investigations into the early stage of polymerization reveal two types of side reactions affording structural defects, the oxidative coupling (homocoupling) of TPD-H groups and the reduction of DTS-I to DTS-H (eq 1). The combined use of L1 and L2 is also effective in preventing these side reactions. Thus, we have succeeded in wellcontrolled synthesis of poly(DTS-alt-TPD) in high yield, without the formation of insoluble materials. It is noteworthy that the catalytic system giving higher content of structural defects has a higher tendency to form insoluble materials in the later stage of polymerization. The 1H NMR spectrum of 3I, which is the remaining part of insoluble materials (run 2 in Table 1), exhibits undesirable signals assignable to the DTS units in DTS−DTS homocoupling and branched structures (Figure 2a). In contrast, polymer 3II prepared using L1 and L2 (run 7 in Table 1) does not show such signals (Figure 2b). Because these structural defects based on DTS units are produced when a relatively large quantity of DTS-H group is generated, there is a possibility that the DTSH group arising from the reduction of DTS-I terminus leads to the DTS−DTS homocoupling and branching, and finally to the formation of insoluble materials via cross-linking. If this is the case, we may consider that L2 prevents the reduction of DTS-I terminus, whereas L1 promotes the polymerization. A detailed study on the role of L2 is now underway in this research group.

■

■

ASSOCIATED CONTENT

S Supporting Information *

Additional experimental procedures and spectroscopic data. This material is available free of charge via the Internet at http://pubs.acs.org.

■

AUTHOR INFORMATION

Corresponding Author

*(F.O.) E-mail: [email protected]. Notes

The authors declare no competing financial interest.

■

ACKNOWLEDGMENTS This work was supported by KAKENHI (23350042, 24750088) from the Japan Society for the Promotion of Science and the ACT-C program of Japan Science and Technology Agency. We are grateful to Profs. Y. Murata and A. Wakamiya (ICR, Kyoto University) for analytical GPC assistance.

EXPERIMENTAL SECTION

■

General Considerations. All manipulations were performed under a nitrogen atmosphere using Schlenk techniques or a glovebox. Toluene was dried over Na/Ph2CO, distilled, and stored over activated MS4A. Cs2CO3 was dried overnight at 120 °C under vacuum and handled in a glovebox. PivOH was distilled and handled in a glovebox. Monomer 1a was obtained from a commercial source. Monomer 1b was prepared as reported in the Supporting Information. Monomer 2,19 Pd2(dba)3·CHCl3,20 and P(2-Me2NC6H4)3 (L2)21 were prepared

REFERENCES

(1) (a) Yamamoto, T. Bull. Chem. Soc. Jpn. 2010, 83, 431. (b) Leclerc, M., Morin, J.-F., Eds. Design and Synthesis of Conjugated Polymers; Wiley-VCH: Weinheim, Germany, 2010. (2) (a) Boudreault, P. L. T.; Najari, A.; Leclerc, M. Chem. Mater. 2011, 23, 456. (b) Beaujuge, P. M.; Frechet, J. M. J. J. Am. Chem. Soc. D

DOI: 10.1021/acs.macromol.5b00526 Macromolecules XXXX, XXX, XXX−XXX

Article

Macromolecules 2011, 133, 20009. (c) Zhou, H.; Yang, L.; You, W. Macromolecules 2012, 45, 607. (3) Carsten, B.; He, F.; Son, H. J.; Xu, T.; Yu, L. Chem. Rev. 2011, 111, 1493. (4) Reviews on DArP: (a) Facchetti, A.; Vaccaro, L.; Marrocchi, A. Angew., Chem. Int. Ed. 2012, 51, 3520. (b) Mercier, L. G.; Leclerc, M. Acc. Chem. Res. 2013, 46, 1597. (c) Kowalski, S.; Allard, S.; Zilberberg, K.; Riedl, T.; Scherf, U. Prog. Polym. Sci. 2013, 38, 1805. (d) Okamoto, K.; Zhang, J.; Housekeeper, J. B.; Marder, S. R.; Luscombe, C. K. Macromolecules 2013, 46, 8059. (e) Rudenko, A. E.; Thompson, B. C. J. Polym. Sci., Part A: Polym. Chem. 2015, 53, 135. (5) Reviews on catalytic direct arylation: (a) Alberico, D.; Scott, M. E.; Lautens, M. Chem. Rev. 2007, 107, 174. (b) Satoh, T.; Miura, M. Chem. Lett. 2007, 36, 200. (c) Seregin, I. V.; Gevorgyan, V. Chem. Soc. Rev. 2007, 36, 1173. (d) Ackermann, L.; Vicente, R.; Kapdi, A. R. Angew. Chem., Int. Ed. 2009, 48, 9792. (e) Bellina, F.; Rossi, R. Tetrahedron 2009, 65, 10269. (f) Miura, M.; Satoh, T.; Hirano, K. Bull. Chem. Soc. Jpn. 2014, 87, 751. (6) Reviews on direct arylation mechanism: (a) Boutadla, Y.; Davies, D. L.; Macgregor, S. A.; Poblador-Bahamonde, A. I. Dalton Trans. 2009, 5820. (b) Balcells, D.; Clot, E.; Eisenstein, O. Chem. Rev. 2010, 110, 749. (c) Lapointe, D.; Fagnou, K. Chem. Lett. 2010, 39, 1118. (d) Ackermann, L. Chem. Rev. 2011, 111, 1315. (7) (a) Wang, Q.; Takita, R.; Kikuzaki, Y.; Ozawa, F. J. Am. Chem. Soc. 2010, 132, 11420. (b) Wang, Q.; Wakioka, M.; Ozawa, F. Macromol. Rapid Commun. 2012, 33, 1203. (c) Wakioka, M.; Kitano, Y.; Ozawa, F. Macromolecules 2013, 46, 370. (d) Wakioka, M.; Ichihara, N.; Kitano, Y.; Ozawa, F. Macromolecules 2014, 47, 626. (8) (a) Berrouard, P.; Najari, A.; Pron, A.; Gendron, D.; Morin, P.O.; Pouliot, J.-R.; Veilleux, J.; Leclerc, M. Angew. Chem., Int. Ed. 2012, 51, 2068. (b) Allard, N.; Najari, A.; Pouliot, J.-R.; Pron, A.; Grenier, F.; Leclerc, M. Polym. Chem. 2012, 3, 2875. (c) Grenier, F.; Berrouard, P.; Pouliot, J.-R.; Tseng, H.-R.; Heeger, A. J.; Leclerc, M. Polym. Chem. 2013, 4, 1836. (d) Mercier, L. G.; Aïch, B. R.; Najari, A.; Beaupré, S.; Berrouard, P.; Pron, A.; Robitaille, A.; Tao, Y.; Leclerc, M. Polym. Chem. 2013, 4, 5252. (e) Morin, P.-O.; Bura, T.; Sun, B.; Gorelsky, S. I.; Li, Y.; Leclerc, M. ACS Macro Lett. 2015, 4, 21. (9) (a) Lu, W.; Kuwabara, J.; Kanbara, T. Macromolecules 2011, 44, 1252. (b) Fujinami, Y.; Kuwabara, J.; Lu, W.; Hayashi, H.; Kanbara, T. ACS Macro Lett. 2012, 1, 67. (c) Lu, W.; Kuwabara, J.; Kanbara, T. Polym. Chem. 2012, 3, 3217. (d) Yamazaki, K.; Kuwabara, J.; Kanbara, T. Macromol. Rapid Commun. 2013, 34, 69. (e) Kuwabara, J.; Nohara, Y.; Choi, S. J.; Fujinami, Y.; Lu, W.; Yoshimura, K.; Oguma, J.; Suenobu, K.; Kanbara, T. Polym. Chem. 2013, 4, 947. (f) Choi, S. J.; Kuwabara, J.; Kanbara, T. ACS Sustainable Chem. Eng. 2013, 1, 878. (g) Kuramochi, M.; Kuwabara, J.; Lu, W.; Kanbara, T. Macromolecules 2014, 47, 7378. (10) (a) Sévignon, M.; Papillon, J.; Schulz, E.; Lemaire, M. Tetrahedron Lett. 1999, 40, 5873. (b) Kumar, A.; Kumar, A. Polym. Chem. 2010, 1, 286. (c) Kowalski, S.; Allard, S.; Scherf, U. ACS Macro Lett. 2012, 1, 465. (d) Chang, S.-W.; Waters, H.; Kettle, J.; Kuo, Z.-R.; Li, C.-H.; Yu, C.-Y.; Horie, M. Macromol. Rapid Commun. 2012, 33, 1927. (e) Zhao, H.; Liu, C.-Y.; Luo, S.-C.; Zhu, B.; Wang, T.-H.; Hsu, H.-F.; Yu, H.-h. Macromolecules 2012, 45, 7783. (f) Rudenko, A. E.; Wiley, C. A.; Stone, S. M.; Tannaci, J. F.; Thompson, B. C. J. Polym. Sci., Part A: Polym. Chem. 2012, 50, 3691. (g) Guo, Q.; Dong, J.; Wan, D.; Wu, D.; You, J. Macromol. Rapid Commun. 2013, 33, 522. (h) Okamoto, K.; Housekeeper, J. B.; Micheal, F. E.; Luscombe, C. K. Polym. Chem. 2013, 4, 3499. (i) Homyak, P. D.; Tinkham, J.; Lahti, P. M.; Coughlin, E. B. Macromolecules 2013, 46, 8873. (j) Nakabayashi, K.; Mori, H. Chem. Lett. 2013, 42, 717. (k) Lombeck, F.; Komber, H.; Gorelsky, S. I.; Sommer, M. ACS Macro Lett. 2014, 3, 819. (l) Kowalski, S.; Allard, S.; Scherf, U. Macromol. Rapid Commun. 2014, DOI: 10.1002/marc.201400557. (11) Hendriks, K. H.; Li, W.; Heintges, G. H. L.; van Pruissen, G. W. P.; Wienk, M. M.; Janssen, R. A. J. J. Am. Chem. Soc. 2014, 136, 11128. (12) (a) Chu, T.-Y.; Lu, J.; Beaupré, S.; Zhang, Y.; Pauliot, J.-R.; Zhou, J.; Leclerc, M.; Li, Z.; Ding, J.; Tao, Y. J. Am. Chem. Soc. 2011,

133, 4250. (b) Amb, C. M.; Chen, S.; Graham, K. R.; Subbiah, J.; Small, C. E.; So, F.; Reynolds, J. R. J. Am. Chem. Soc. 2011, 133, 10062. (13) Wakioka, M.; Nakamura, Y.; Montgomery, M.; Ozawa, F. Organometallics 2015, 34, 198. (14) The assignment of signal A is based on the 1H NMR spectra of model compounds, X−DTS−TPD−TPD−DTS−X (X = TMS, I). (15) The assignment of signals a and c−e is based on the 1H NMR spectra of model compounds, X−DTS−TPD−DTS−X (X = H, I). (16) The inside protons of DTS units of a DTS−DTS homocoupling model, Ar−TPD−DTS−DTS−TPD−Ar, appeared at δ 7.19 at 130 °C in C2D2Cl4. (17) This description never means the site-selective introduction of DTS and TPD units to each terminus, although their ratio is 1:1. Actually, MALDI-TOF-MS analysis revealed random distribution of the two units: see Figure S1. (18) Zhang, G.; Wan, X.; Lu, Y.; Li, Y.; Li, Y.; Li, C.; Wua, H.; Chen, Y. Chem. Commun. 2014, 50, 12497. (19) Guo, X.; Ortiz, R. P.; Zheng, Y.; Kim, M.-G.; Zhang, S.; Hu, Y.; Lu, G.; Facchetti, A.; Marks, T. J. J. Am. Chem. Soc. 2011, 133, 13685. (20) Ukai, T.; Kawazura, H.; Ishii, Y. J. Organomet. Chem. 1974, 65, 253. (21) Fritz, H. P.; Gordon, I. R.; Schwarzhans, K. E.; Venanzi, L. M. J. Chem. Soc. 1965, 5210.

E

DOI: 10.1021/acs.macromol.5b00526 Macromolecules XXXX, XXX, XXX−XXX