Telechelic Helical Poly(quinoxaline-2,3-diyl)s Containing a

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Letter Cite This: ACS Macro Lett. 2019, 8, 479−485

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Telechelic Helical Poly(quinoxaline-2,3-diyl)s Containing a Structurally Defined, Circularly Polarized Luminescent Terquinoxaline Core: Synthesis by Core-Initiated Bidirectional Living Polymerization Shogo Kuriyama,† Yuuya Nagata, and Michinori Suginome*

ACS Macro Lett. Downloaded from pubs.acs.org by UNIV OF VICTORIA on 04/07/19. For personal use only.

Department of Synthetic Chemistry and Biological Chemistry, Graduate School of Engineering, Kyoto University, Kyoto 606-8501, Japan S Supporting Information *

ABSTRACT: We have designed and synthesized divalent initiators that contain a fluorescent terquinoxaline unit with two palladium groups for the living polymerization of 1,2diisocyanobenzenes. Using these divalent initiators, the bidirectional living polymerization of a monomer bearing (S)-butoxymethyl side chains afforded telechelic helical poly(quinoxaline-2,3-diyl)s (PQXs), which consist of a terquinoxaline unit at the center of the polymer chain and chiral oligomeric blocks on both sides. The location of the core unit was confirmed by NMR spectroscopy and photoluminescence measurements. Upon changing the solvent from CHCl3 to 1,1,2-trichloroethane, these PQXs exhibit both left- and right-handed circularly polarized luminescence with dissymmetry factors of approximately 1.0 × 10−3.

I

polymerization of 1,2-diisocyanobenzenes using organopalladium or -nickel complexes as initiators.7 PQXs adopt helical conformation owing to the steric repulsion of the two substituents at the 5- and 8-positions on the quinoxaline ring, and their helical structures are effectively controlled by incorporation of chiral monomer units bearing chiral side chains. It should be noted that every main chain of the PQX adopts purely right- (P) or left-handed (M) backbones, and the ratio of the P- and M-helical chains of the PQX can be perfectly switched by changing the organic solvent (solventdependent helix inversion).8 We have previously established that the random incorporation of small fragments of achiral ligand units and nucleophilic units in the helical backbone renders PQXs highly enantioselective chiral catalysts for asymmetric catalysis.9,10 Moreover, the random incorporation of achiral fluorescent monomer units endows PQXs with circularly polarized luminescence (CPL) properties, where the chirality is also switchable by changing the organic solvent as a result of the solvent-dependent helix inversion of the polymer backbone.11 These examples demonstrate that the backbone of PQXs allows transmission of its helical chirality to the achiral functional units, i.e., catalytically active sites or luminophores, leading to new chiral functions. Our research group is particularly interested in creating fine-tuned chiral environments around functional monomers through the incorporation

ncreasing attention has been focused on the utility of helical macromolecules in a variety of chirality-oriented applications,1 including asymmetric catalysis,2 chiral separations,3 and the generation of circularly polarized light.4 To realize such chiral functionality, monomer units that bear intrinsically achiral groups (the ones responsible for those functions) are incorporated into nonracemic helical macromolecular scaffolds.2b−d,m,4d−h This molecular design allows the induction of chirality around the achiral functional unit through chirality transfer from the chiral macromolecular scaffold(s). With this strategy based upon random copolymerization, however, creation and optimization of functions rely solely on the structural modification of a single achiral functional unit. Since chiral functions often strongly depend on adjacent units, the precise design of the structure of oligomeric units containing both functional and neighboring units is highly desirable. In this context, it is of particular importance that the precisely designed functional core is not located at the terminus but in the middle of the polymer chain to acquire the rigid chiral conformation that is transferred from the macromolecular helical backbone. In principle, this type of macromolecule can be obtained by “core-initiated bidirectional living polymerizations”,5 in which precisely designed oligomeric divalent initiators are used. Although divalent initiators have been employed in living polymerizations to prepare center-functionalized polymers,6 there is no precedence for their use in helical polymer synthesis to create new chiral functionality. Poly(quinoxaline-2,3-diyl)s (PQXs hereafter) form a unique class of helical polymers that are synthesized by living © XXXX American Chemical Society

Received: March 6, 2019 Accepted: April 4, 2019

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DOI: 10.1021/acsmacrolett.9b00165 ACS Macro Lett. 2019, 8, 479−485

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ACS Macro Letters

I2. The resulting diketone 3 readily reacted with substituted ophenylenediamines 4a−c to give terquinoxalines 2a−c, which bear different central units, in high yield. The reaction of 2a−c with bis(dibenzylideneacetone)palladium (Pd(dba)2) and PMe2Ph for 48 h in THF at 80 °C furnished dipalladium complexes 1a−c after recrystallization. The solid-state structure of 1c was determined by single-crystal X-ray diffraction analysis. The terquinoxaline core forms a helical structure with the palladium units on both termini, and two PMe2Ph ligands are bound to each palladium center in a trans fashion. The monopalladium, i.e., monovalent, initiator 6a was obtained from the reaction of 1 equiv of Pd(dba)2 and PMe2Ph with 2a at 50 °C (44% yield after recrystallization). The polymerization of 40, 60, 80, and 100 equiv of chiral diisocyanobenzene M1 was carried out with the thus obtained divalent initiator 1a in toluene at 60 °C. After complete consumption of M1 (72 h), the reaction mixture was quenched with NaBH4 and purified by preparative gel permeation chromatography (GPC) to give P1a(40), P1a(60), P1a(80), and P1a(100) (Table 1). The values of Mn increased linearly

of precisely synthesized oligomeric core units. Herein, we demonstrate new bidirectional living polymerizations using telechelic terquinoxalines as divalent initiators, which were prepared separately by nonpolymerization-based synthesis. The emission of CPL from the thus obtained PQXs was confirmed, indicating that the location of the core units and the structure of the neighboring units have a significant impact on the properties of the PQXs. Terquinoxaline-based divalent initiators 1a−c were prepared from the corresponding dichloroterquinoxalines 2a−c by oxidative addition to a palladium(0) complex (Scheme 1). It Scheme 1. Synthesis of Terquinoxalines and Palladium Initiatorsa

Table 1. Polymerization of M1 Using Palladium Initiators

a

Reagents and conditions: (i) NaCN (20 mol %), EtOH/H2O, reflux, 4 h, (87%). (ii) I2 (1 equiv), NaOAc (2 equiv), CH2Cl2/EtOH, reflux, 13 h, (84%). (iii) 4 (1 equiv), AcOH or TsOH (30 mol %), toluene, reflux, 13 h (2a: 90%; 2b: 80%; 2c: 91%). (iv) Pd(dba)2 (3 equiv), PMe2Ph (9 equiv), THF, 80 °C, 48 h (1a: 49%; 1b: 63%; 1c: 61%; all yields after recrystallization). (v) Pd(dba)2 (2 equiv), PMe2Ph (6 equiv), THF, 50 °C, 24 h (6a: 44% after recrystallization). bThe substituents on the phosphorus atoms and hydrogens are omitted for clarity.

PQX

initiator

n

yield (%)

Mn (/104)a

Mw/Mn (PDI)a

P1a(40) P1a(60) P1a(80) P1a(100) P1b(60) P1c(60) P2a(40)

1a 1a 1a 1a 1b 1c 6a

40 60 80 100 60 60 40

69 72 81 70 73 65 81

0.86 1.38 1.72 2.18 1.20 1.22 0.90

1.19 1.21 1.25 1.26 1.19 1.24 1.21

a

Molecular weights were determined by GPC using polystyrene standards.

is important to note that 2a−c were prepared from the common α-diketone 3 via the formation of a central quinoxaline ring by treatment with differently substituted ophenylenediamines 4a−c. This strategy allowed the facile preparation of various divalent initiators bearing different central quinoxaline units. The common intermediate 3 can be prepared from aldehyde 5. According to this synthetic strategy, diketone 3 was synthesized from 5 in 73% yield via a cyanidecatalyzed benzoin condensation, followed by an oxidation with

with the monomer ratio, while the polydispersity indexes (PDIs) remained almost constant (Figure 1a). These results suggest that such polymerizations proceed in a living fashion. The thus obtained polymers were characterized by matrix laser-assisted desorption/ionization time-of-flight mass (MALDI-TOF-MS) spectroscopy (see the SI for details). In the MALDI-TOF-MS spectrum of P1a(40), ion signals were observed at intervals of 328.3, which corresponds to the m/z value of the chiral unit (328.2). An analysis of the peaks by a 480

DOI: 10.1021/acsmacrolett.9b00165 ACS Macro Lett. 2019, 8, 479−485

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ACS Macro Letters

Figure 1. (a) Plot of Mn and Mw/Mn for P1a(n) as a function of the monomer ratio (n). 1H NMR spectra (CDCl3) from 11.0 to 9.0 ppm for (b) P1a(40) and (c) P2a(40).

Figure 2. (a) CD spectra of P1a(n) in CHCl3 and 1,1,2-TCE; a mixed 1,1,2-TCE/THF (8:2, v/v) solvent was used for P1a(100) due to its low solubility in neat 1,1,2-TCE. (b) CD spectra of P1a(60)−P1c(60) in CHCl3 and 1,1,2-TCE (2.60−3.23 × 10−2 g/L).

CHCl3 and +1.71 × 10−3 in 1,1,2-TCE). Because the homo40-mer derived solely from (S)-M1 adopts a pure helical conformation in both solvents,8b the 40 chiral units in P1a(40) should be enough to induce a purely single-handed backbone. However, the CD intensities indicated that P1a(40) did not adopt the purely single-handed backbone. These results suggest that the inclusion of the terquinoxaline core in the polymer main chain reduces the efficiency of helix induction. We believe that this finding is related to our recent study on the “abnormal” sergeants-and-soldiers effect, where the structure of the achiral unit strongly affects the efficiency and even direction of helix induction.8e,f,11b In fact, P2a(40), in which the terquinoxaline core is located at the terminus of the main chain, shows stronger CD intensity than P1a(40) because the abnormal sergeants-and-soldiers effect depends on the number of the boundary between chiral and achiral blocks (Figure S4 in SI). Moreover, a comparison of the CD spectra of P1a(60), P1b(60), and P1c(60) revealed that the central unit of the terquinoxaline core does not affect the induction of helicity (Figure 2b). Subsequently, we recorded the photoluminescence (PL) spectra of P1a(60), P1b(60), and P1c(60). P1a(60) exhibits blue emission (476 nm), while P1b(60) and P1c(60) show yellow (515 nm) to orange (570 nm) emission under UV irradiation at 365 nm (Figure 3a,b). It should be noted that, although the neighboring units are different, the emission wavelengths of P1a(60), P1b(60), and P1c(60) are very similar to those of the corresponding random copolymers P3a−c, which contain five luminophore units and 95 chiral

least-squares method revealed that the m/z values of the observed ion signals could be expressed by the equation 328.3n + 924.8 (terquinoxaline unit) + (1.0 × 2) (terminal H atoms) + 23.0 (Na). The obtained formula was thus in good agreement with the expected one (328.2n + 924.4 + (1.0 × 2) + 23.0). The structure of the polymers was also characterized by 1H NMR spectroscopy. The terminal analysis revealed that P1a(40) presents only the terminal proton on the chiral units (Ha in Figure 1b). In contrast, the spectrum of P2a(40), which was obtained from the reaction of monovalent M1 and 6a, shows two distinctive protons assignable to the terquinoxaline unit (Hb) and the chiral unit (Ha) (Figure 1c). This comparison clearly indicates that chain growth proceeded on both sides of the divalent palladium initiator, leading to the terquinoxaline core being located at the center of the polymer chain. We then measured the circular dichroism (CD) and UV−vis absorption spectra of the synthesized polymers P1 and P2 in CHCl3 and 1,1,2-trichloroethane (1,1,2-TCE) to determine the sense and degree of the helix induction. As observed in our previous studies, all PQXs bearing chiral units derived from (S)-M1 adopt an M-helical conformation in CHCl3 and a Phelical conformation in 1,1,2-TCE (Figure 2a).8a,b Among the series of P1a polymers with different polymerization degrees, the 60mer to 100mer (P1a(60−100)) exhibit almost the same CD intensity in CHCl3 (−2.34 to −2.40 × 10−3) and 1,1,2TCE (+2.81 to +2.90 × 10−3), while the CD intensity of the 40mer (P1a(40)) was significantly lower (−1.98 × 10−3 in 481

DOI: 10.1021/acsmacrolett.9b00165 ACS Macro Lett. 2019, 8, 479−485

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ACS Macro Letters

Figure 3. (a) PL spectra of P1a(60)−P1c(60) in CHCl3. (b) Photograph of P1a(60)−P1c(60) in CHCl3 under irradiation with UV light (365 nm). (c) Structure of random copolymers P3a−c. (d) PL spectra of P1a(60), P2a(60), and 2a in CHCl3 (2.80−3.23 × 10−2 g/L for P1a(60)− P1c(60), 1.75 × 10−3 g/L for P2a(40), 1.99 × 1 0−3 g/L for 2a).

units derived from (S)-M1 (Figure 3c).11a A comparison of the PL spectra of trimer 2a, P1a(60), and P2a(40) allowed us to elucidate the conformation of the terquinoxaline units located at the center of the helical main chain (Figure 3d). Thus, P2a(40), in which the terquinoxaline core is located at the terminus, presents a PL spectrum quite similar to that of 2a. In contrast, the PL spectrum of P1a(60) was blue-shifted by 40 nm. These results suggest that the terquinoxaline core located at the center of the helical main chain is more constrained than that located at the terminus of the helix, leading to a shift of the emission wavelength. Then, we measured the CPL spectra of dilute CHCl3 and 1,1,2-TCE solutions of P1a(60), P1b(60), and P1c(60). P1a(60)−P1c(60) showed negative CPL signals in CHCl3 with gCPL values at the maximum PL wavelength from −1.19 to −1.50 × 10−3 (Figure 4a−c) due to their M-helical main chains. After helical inversion in 1,1,2-TCE, the spectra of P1a(60)−P1c(60) show positive peaks derived from the Phelical conformation (g CPL = 0.94 to 1.26 × 10 −3 ). Interestingly, the |gCPL| values are higher than those of the random copolymers P3a−c (gCPL = −0.51 to −1.10 × 10−3 in CHCl3; 0.12 to 0.76 × 10−3 in 1,1,2-TCE).11a Interestingly, P1c(60) in 1,1,2-TCE exhibits a gCPL value of 0.94 × 10−3, which is approximately eight times that of P3c (gCPL = 0.12 × 10−3).11a Although the exact details underpinning this behavior

are not entirely clear at this point, the present results suggest that the structure and location of the luminophore core can enhance the CPL properties of PQXs. It is also worth noting that the CPL handedness of P2a is opposite to that of P1a(60) in both CHCl3 and 1,1,2-TCE, even if the same screw sense was induced on the PQX main chain (Figure 4d). This result corroborates the notion that the chiral structure of the luminophore varies with its location within the polymer main chain. In summary, we have developed a method for the bidirectional living polymerization of 1,2-diisocyanobenzenes using divalent organopalladium initiators that bear a terquinoxaline core. On the basis of 1H NMR, CD, PL, and CPL spectra, we confirmed that the terquinoxaline core is located at the center of the PQX main chain rather than at its terminus. To the best of our knowledge, this is the first example for the synthesis of dynamic helical polymers containing a specific oligomer sequence in the middle of the polymer main chain. At this central position, the terquinoxaline unit adopts a more constrained chiral conformation on account of the chirality transfer from the PQX backbone compared to the case of PQXs bearing the terquinoxaline core at the terminus. The resulting structural differences in the core units lead to a blue-shift of the PL and enhanced CPL emission in terms of glum values, as well as an inversion of the CPL 482

DOI: 10.1021/acsmacrolett.9b00165 ACS Macro Lett. 2019, 8, 479−485

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Figure 4. CPL spectra of (a) P1a(60), (b) P1b(60), (c) P1c(60), and (d) P2a(40) in CHCl3 and 1,1,2-TCE (2.80−3.23 × 10−2 g/L for P1a(60)−P1c(60); 1.75 × 10−2 g/L for P2a(40)).

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ACKNOWLEDGMENTS The authors are grateful to Prof. Yoshiki Chujo and Dr. Masayuki Gon (Department of Polymer Chemistry, Graduate School of Engineering, Kyoto University) for carrying out the CPL measurements. The synchrotron X-ray diffraction measurements of 2a and 2b were performed at the BL40XU beamline of SPring-8 with the approval of JASRI (proposals 2017A1132, 2018A1114, and 2018B1125) by Prof. Takuji Hatakeyama (Kwansei Gakuin University) and Dr. Nobuhiro Yasuda (JASRI). Financial support for this research was provided by JSPS KAKENHI grants 16J07304 (to S.K.) and JP15H05811 in the context of the project “Precisely Designed Catalysts with Customized Scaffolding” (to M.S.), as well as by a Japan Science and Technology Corporation (CREST) grant “Establishment of Molecular Technology towards the Creation of New Function” (to M.S.).

handedness. We are convinced that this new synthetic approach will allow the development of new chiral functionality in PQXs.

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ASSOCIATED CONTENT

S Supporting Information *

These materials are available free of charge via the Internet at The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acsmacrolett.9b00165. Experimental procedures and spectral data for all new compounds (PDF) X-ray crystallographic data for 1c·2C4H10O, 2a, 2b, 6a· C4H8O, 7a·C6H14·0.5C6H6, and S3 (ZIP)

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected].

REFERENCES

(1) Yashima, E.; Ousaka, N.; Taura, D.; Shimomura, K.; Ikai, T.; Maeda, K. Supramolecular Helical Systems: Helical Assemblies of Small Molecules, Foldamers, and Polymers with Chiral Amplification and Their Functions. Chem. Rev. 2016, 116, 13752−13990. (2) (a) Yashima, E.; Maeda, Y.; Okamoto, Y. Synthesis of poly N-(4ethynylbenzyl)ephedrine and its use as a polymeric catalyst for enantioselective addition of dialkylzincs to benzaldehyde. Polym. J. (Tokyo, Jpn.) 1999, 31, 1033−1036. (b) Reggelin, M.; Schultz, M.; Holbach, M. Helical chiral polymers without additional stereogenic units: A new class of ligands in asymmetric catalysis. Angew. Chem., Int. Ed. 2002, 41, 1614−1617. (c) Reggelin, M.; Doerr, S.; Klussmann, M.; Schultz, M.; Holbach, M. Helically chiral polymers: A class of ligands for asymmetric catalysis. Proc. Natl. Acad. Sci. U. S. A. 2004, 101, 5461−5466. (d) Miyabe, T.; Hase, Y.; Iida, H.; Maeda, K.; Yashima, E. Synthesis of Functional Poly(phenyl isocyanide)s with Macromolecular Helicity Memory and Their Use as Asymmetric Organocatalysts. Chirality 2009, 21, 44−50. (e) Terada, K.; Masuda, T.; Sanda, F. Asymmetric Reduction of Aromatic Ketimines in the

ORCID

Yuuya Nagata: 0000-0001-5926-5845 Michinori Suginome: 0000-0003-3023-2219 Present Address

† Department of Systems Innovation, School of Engineering, The University of Tokyo, 7−3−1 Hongo, Bunkyo-ku, Tokyo 113−8656, Japan.

Author Contributions

The initial experimental design was proposed by M.S. in association with Y.N. All experimental work was performed by S.K. The manuscript has been written through contributions of all authors. All authors have given approval to the final version of the manuscript. Notes

The authors declare no competing financial interest. 483

DOI: 10.1021/acsmacrolett.9b00165 ACS Macro Lett. 2019, 8, 479−485

Letter

ACS Macro Letters Presence of Helical Polymer as Catalyst. J. Polym. Sci., Part A: Polym. Chem. 2009, 47, 4971−4981. (f) Megens, R. P.; Roelfes, G. Asymmetric Catalysis with Helical Polymers. Chem. - Eur. J. 2011, 17, 8514−8523. (g) Ikeda, A.; Terada, K.; Shiotsuki, M.; Sanda, F. Synthesis of Polymers Bearing Proline Moieties in the Side Chains and Their Application as Catalysts for Asymmetric Induction. J. Polym. Sci., Part A: Polym. Chem. 2011, 49, 3783−3796. (h) Itsuno, S. Polymeric Chiral Catalyst Design and Chiral Polymer Synthesis; John Wiley & Sons: Hoboken, NJ, 2011; pp 223−266. (i) Miyake, G. M.; Iida, H.; Hu, H.-Y.; Tang, Z. L.; Chen, E. Y.-X.; Yashima, E. Synthesis of Helical Poly(phenylacetylene)s Bearing Cinchona Alkaloid Pendants and Their Application to Asymmetric Organocatalysis. J. Polym. Sci., Part A: Polym. Chem. 2011, 49, 5192−5198. (j) Tang, Z. L.; Iida, H.; Hu, H.-Y.; Yashima, E. Remarkable Enhancement of the Enantioselectivity of an Organocatalyzed Asymmetric Henry Reaction Assisted by Helical Poly(phenylacetylene)s Bearing Cinchona Alkaloid Pendants via an Amide Linkage. ACS Macro Lett. 2012, 1, 261−265. (k) Zhang, D. Y.; Ren, C.; Yang, W.; Deng, J. Helical Polymer as Mimetic Enzyme Catalyzing Asymmetric Aldol Reaction. Macromol. Rapid Commun. 2012, 33, 652−657. (l) Itsuno, S.; Hassan, M. M. Polymer-immobilized chiral catalysts. RSC Adv. 2014, 4, 52023−52043. (m) Ousaka, N.; Yamaguchi, T.; Yashima, E. Remarkable Enhancement of Stability and Helix-sense Excess of Oligo(phenylene ethynylene) Foldamers Assisted by Linking with Achiral (Metallo)salen Tethers and Their Application to Asymmetric Catalysis. Chem. Lett. 2014, 43, 512−514. (n) Wang, H.; Li, N.; Zhang, J.; Wan, X. Synthesis and Properties of a Novel Pyridineoxazoline Containing Optically Active Helical Polymer as a Catalyst Ligand for Asymmetric Diels-Alder Reaction. Chirality 2015, 27, 523−531. (o) Zhang, H.; Deng, J. Helical Polymers Showing Inverse Helicity and Synergistic Effect in Chiral Catalysis: Catalytic Functionality Determining Enantioconfiguration and Helical Frameworks Providing Asymmetric Microenvironment. Macromol. Chem. Phys. 2016, 217, 880−888. (p) Zhou, L.; Chu, B.-F.; Xu, X.-Y.; Xu, L.; Liu, N.; Wu, Z. Q. Significant Improvement on Enantioselectivity and Diastereoselectivity of Organocatalyzed Asymmetric Aldol Reaction Using Helical Polyisocyanides Bearing Proline Pendants. ACS Macro Lett. 2017, 6, 824−829. (q) Shen, L.; Xu, L.; Hou, X.-H.; Liu, N.; Wu, Z.-Q. Polymerization Amplified Stereoselectivity (PASS) of Asymmetric Michael Addition Reaction and Aldol Reaction Catalyzed by Helical Poly(phenyl isocyanide) Bearing Secondary Amine Pendants. Macromolecules 2018, 51, 9547−9554. (3) Shen, J.; Okamoto, Y. Efficient Separation of Enantiomers Using Stereoregular Chiral Polymers. Chem. Rev. 2016, 116, 1094−1138. (4) (a) Fukao, S.; Fujiki, M. Circularly Polarized Luminescence and Circular Dichroism from Si-Si-Bonded Network Polymers. Macromolecules 2009, 42, 8062−8067. (b) Lee, D.; Jin, Y.-J.; Kim, H.; Suzuki, N.; Fujiki, M.; Sakaguchi, T.; Kim, S. K.; Lee, W. E.; Kwak, G. Solvent-to-Polymer Chirality Transfer in Intramolecular Stack Structure. Macromolecules 2012, 45, 5379−5386. (c) Takaishi, K.; Yamamoto, T.; Hinoide, S.; Ema, T. Helical Oligonaphthodioxepins Showing Intense Circularly Polarized Luminescence (CPL) in Solution and in the Solid State. Chem. - Eur. J. 2017, 23, 9249− 9252. (d) Ikai, T.; Kojima, Y.; Shinohara, K.-I.; Maeda, K.; Kanoh, S. Cellulose derivatives bearing pyrene-based π-conjugated pendants with circularly polarized luminescence in molecularly dispersed state. Polymer 2017, 117, 220−224. (e) Ikai, T.; Shimizu, S.; Kudo, T.; Maeda, K.; Kanoh, S. Helical Folding of π-Conjugated Polymers Bearing Glucose-Linked Biphenyl Units in the Main Chain: Application to Circularly Polarized Luminescence Materials. Bull. Chem. Soc. Jpn. 2017, 90, 910−918. (f) Ikai, T.; Awata, S.; Shinohara, K. Synthesis of a helical π-conjugated polymer with a dynamic hydrogen-bonded network in the helical cavity and its circularly polarized luminescence properties. Polym. Chem. 2018, 9, 1541−1546. (g) Ikai, T.; Shimizu, S.; Awata, S.; Shinohara, K. Chiral Amplification in π-Conjugated Helical Polymers with Circularly Polarized Luminescence. Macromolecules 2018, 51, 2328−2334. (h) Zhao, B.; Pan, K.; Deng, J. Intense Circularly Polarized Luminescence Contributed by Helical Chirality of Monosubstituted Polyacetylenes.

Macromolecules 2018, 51, 7104−7111. (i) Li, J.; Peng, X.; Huang, C.; Qi, Q.; Lai, W.-Y.; Huang, W. Control of Circularly Polarized Luminescence from a Boron Ketoiminate-based p-conjugated Polymer via Conformational Locks. Polym. Chem. 2018, 9, 5278− 5285. (5) (a) Kennedy, J. P.; Melby, E. G. Block and Graft Copolymers by Selective Cationic Initiation. II. Synthesis and Characterization of Styrene-isobutylene Block Copolymers by Use of Chlorobrominated Alkanes. J. Polym. Sci., Polym. Chem. Ed. 1975, 13, 29−37. (b) Miyamoto, M.; Sawamoto, M.; Higashimura, T. Synthesis of Telechelic Living Polyvinyl Ethers. Macromolecules 1985, 18, 123− 127. (c) Hawker, C. J.; Hedrick, J. L.; Malmström, E. E.; Trollsas, M.; Mecerreyes, D.; Moineau, G.; Dubois, P.; Jérôme, R. Dual living free radical and ring opening polymerizations from a double-headed initiator. Macromolecules 1998, 31, 213−219. (6) (a) Bernard, J.; Lortie, F.; Fenet, B. Design of Heterocomplementary H-Bonding RAFT Agents - Towards the Generation of Supramolecular Star Polymers. Macromol. Rapid Commun. 2009, 30, 83−88. (b) Chen, S. B.; Bertrand, A.; Chang, X. J.; Alcouffe, P.; Ladavière, C.; Gérard, J.-F.; Lortie, F.; Bernard, J. Heterocomplementary H-Bonding RAFT Agents as Tools for the Preparation of Supramolecular Miktoarm Star Copolymers. Macromolecules 2010, 43, 5981−5988. (c) Lee, S.-H.; Ouchi, M.; Sawamoto, M. Supramolecular X-Shaped Homopolymers and Block Polymers by Midsegment Complementary Hydrogen Bonds: Design of Bifunctional Initiators with Interactive Sites for Metal-Catalyzed Living Radical Polymerization. Macromolecules 2012, 45, 3702−3710. (d) Lee, S.-H.; Ouchi, M.; Sawamoto, M. Chain Center-Functionalized Amphiphilic Block Polymers: Complementary Hydrogen Bond Self-Assembly in Aqueous Solution. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 4498−4504. (e) Lee, S.-H.; Ouchi, M.; Sawamoto, M. Functionalization at the Central Position of Vinyl Polymer Chains: Highly Associable Multipoint Hydrogen Bonds for Complementary SelfAssemblies. Macromol. Rapid Commun. 2014, 35, 431−436. (f) Fonteneau, C.; Pensec, S.; Bouteiller, L. Versatile synthesis of reversible comb-shaped supramolecular polymers. Polym. Chem. 2014, 5, 2496−2505. (7) (a) Ito, Y.; Ihara, E.; Murakami, M.; Shiro, M. New Living Polymerization of 1,2-Diisocyanoarenes via (Quinoxalinyl)palladium Complexes - Synthesis of Poly(2,3-quinoxaline). J. Am. Chem. Soc. 1990, 112, 6446−6447. (b) Ito, Y.; Ihara, E.; Murakami, M. Living Polymerization of 1,2-Diisocyanozrenes Promoted by (Quinoxalinyl) nickel Complexes. Polym. J. 1992, 24, 297−299. (c) Ito, Y.; Miyake, T.; Hatano, S.; Shima, R.; Ohara, T.; Suginome, M. Asymmetric synthesis of helical poly(quinoxaline-2,3-diyl)s by palladium-mediated polymerization of 1,2-diisocyanobenzenes: Effective control of the screw-sense by a binaphthyl group at the chain-end. J. Am. Chem. Soc. 1998, 120, 11880−11893. (d) Yamada, T.; Suginome, M. Synthesis of Helical Rod-Coil Multiblock Copolymers by Living Block Copolymerization of Isocyanide and 1,2-Diisocyanobenzene Using Arylnickel Initiators. Macromolecules 2010, 43, 3999−4002. (e) Nagata, Y.; Ke, Y.-Z.; Suginome, M. Facile Preparation of Poly(quinoxaline-2,3-diyl)s via Aromatizing Polymerization of 1,2-Diisocyanobenzenes Using Phosphine Complexes of Nickel(II) Salts. Chem. Lett. 2015, 44, 53− 55. (8) (a) Yamada, T.; Nagata, Y.; Suginome, M. Non-hydrogenbonding-based, solvent-dependent helix inversion between pure Phelix and pure M-helix in poly(quinoxaline-2,3-diyl)s bearing chiral side chains. Chem. Commun. 2010, 46, 4914−4916. (b) Nagata, Y.; Yamada, T.; Adachi, T.; Akai, Y.; Yamamoto, T.; Suginome, M. Solvent-Dependent Switch of Helical Main-Chain Chirality in Sergeants-and-Soldiers-Type Poly(quinoxaline-2,3-diyl)s: Effect of the Position and Structures of the ″Sergeant″ Chiral Units on the Screw-Sense Induction. J. Am. Chem. Soc. 2013, 135, 10104−10113. (c) Nagata, Y.; Kuroda, T.; Takagi, K.; Suginome, M. Ether solventinduced chirality inversion of helical poly(quinoxaline-2,3-diyl)s containing L-lactic acid derived side chains. Chem. Sci. 2014, 5, 4953−4956. (d) Nagata, Y.; Nishikawa, T.; Suginome, M. Poly(quinoxaline-2,3-diyl)s Bearing (S)-3-Octyloxymethyl Side Chains as 484

DOI: 10.1021/acsmacrolett.9b00165 ACS Macro Lett. 2019, 8, 479−485

Letter

ACS Macro Letters an Efficient Amplifier of Alkane Solvent Effect Leading to Switch of Main-Chain Helical Chirality. J. Am. Chem. Soc. 2014, 136, 15901− 15904. (e) Nagata, Y.; Nishikawa, T.; Suginome, M. Exerting Control over the Helical Chirality in the Main Chain of Sergeants-andSoldiers-Type Poly(quinoxaline-2,3-diyl)s by Changing from Random to Block Copolymerization Protocols. J. Am. Chem. Soc. 2015, 137, 4070−4073. (f) (12) Nagata, Y.; Nishikawa, T.; Suginome, M. Solvent Effect on the Sergeants-and-Soldiers Effect Leading to Bidirectional Induction of Single-Handed Helical Sense of Poly(quinoxaline-2,3-diyl)s Copolymers in Aromatic Solvents. ACS Macro Lett. 2016, 5, 519−522. (g) Nagata, Y.; Nishikawa, T.; Suginome, M.; Sato, S.; Sugiyama, M.; Porcar, L.; Martel, A.; Inoue, R.; Sato, N. Elucidating the Solvent Effect on the Switch of the Helicity of Poly(quinoxaline-2,3-diyl)s: A Conformational Analysis by SmallAngle Neutron Scattering. J. Am. Chem. Soc. 2018, 140, 2722−2726. (h) Suginome, M.; Yamamoto, T.; Nagata, Y. Poly(quinoxaline-2,3diyl)s: A Fascinating Helical Macromolecular Scaffold for New Chiral Functions. Yuki Gosei Kagaku Kyokaishi 2015, 73, 1141−1155. (9) (a) Yamamoto, T.; Suginome, M. Helical Poly(quinoxaline-2,3diyl)s Bearing Metal-Binding Sites as Polymer-Based Chiral Ligands for Asymmetric Catalysis. Angew. Chem., Int. Ed. 2009, 48, 539−542. (b) Yamamoto, T.; Yamada, T.; Nagata, Y.; Suginome, M. HighMolecular-Weight Polyquinoxaline-Based Helically Chiral Phosphine (PQXphos) as Chirality-Switchable, Reusable, and Highly Enantioselective Monodentate Ligand in Catalytic Asymmetric Hydrosilylation of Styrenes. J. Am. Chem. Soc. 2010, 132, 7899−7901. (c) Yamamoto, T.; Akai, Y.; Nagata, Y.; Suginome, M. Highly Enantioselective Synthesis of Axially Chiral Biarylphosphonates: Asymmetric Suzuki-Miyaura Coupling Using High-Molecular-Weight, Helically Chiral Polyquinoxaline-Based Phosphines. Angew. Chem., Int. Ed. 2011, 50, 8844−8847. (d) Akai, Y.; Yamamoto, T.; Nagata, Y.; Ohmura, T.; Suginome, M. Enhanced Catalyst Activity and Enantioselectivity with Chirality-Switchable Polymer Ligand PQXphos in Pd-Catalyzed Asymmetric Silaborative Cleavage of meso-Methylenecyclopropanes. J. Am. Chem. Soc. 2012, 134, 11092− 11095. (e) Suginome, M.; Yamamoto, T.; Nagata, Y.; Yamada, T.; Akai, Y. Catalytic asymmetric synthesis using chirality-switchable helical polymer as a chiral ligand. Pure Appl. Chem. 2012, 84, 1759− 1769. (f) Yamamoto, T.; Akai, Y.; Suginome, M. Chiral Palladacycle Catalysts Generated on a Single-Handed Helical Polymer Skeleton for Asymmetric Arylative Ring Opening of 1,4-Epoxy-1,4-dihydronaphthalene. Angew. Chem., Int. Ed. 2014, 53, 12785−12788. (g) Yoshinaga, Y.; Yamamoto, T.; Suginome, M. Chirality-Switchable 2,2’Bipyridine Ligands Attached to Helical Poly(quinoxaline-2,3-diyl)s for Copper-Catalyzed Asymmetric Cyclopropanation of Alkenes. ACS Macro Lett. 2017, 6, 705−710. (10) Yamamoto, T.; Murakami, R.; Suginome, M. Single-Handed Helical Poly(quinoxaline-2,3-diyl)s Bearing Achiral 4-Aminopyrid-3-yl Pendants as Highly Enantioselective, Reusable Chiral Nucleophilic Organocatalysts in the Steglich Reaction. J. Am. Chem. Soc. 2017, 139, 2557−2560. (11) (a) Nishikawa, T.; Nagata, Y.; Suginome, M. Poly(quinoxaline2,3-diyl) as a Multifunctional Chiral Scaffold for Circularly Polarized Luminescent Materials: Color Tuning, Energy Transfer, and Switching of the CPL Handedness. ACS Macro Lett. 2017, 6, 431−435. (b) Nagata, Y.; Nishikawa, T.; Suginome, M. Abnormal sergeantsand-soldiers effects of poly(quinoxaline-2,3-diyl)s enabling discrimination of one-carbon homologous n-alkanes through a highly sensitive solvent-dependent helix inversion. Chem. Commun. 2018, 54, 6867−6870.

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DOI: 10.1021/acsmacrolett.9b00165 ACS Macro Lett. 2019, 8, 479−485