Article pubs.acs.org/Macromolecules
Ru-Catalyzed Polycondensation of Dialkyl 1,4Phenylenebis(diazoacetate) with Dianiline: Synthesis of Well-Defined Aromatic Polyamines Bearing an Alkoxycarbonyl Group at the Adjacent Carbon of Each Nitrogen in the Main Chain Framework Hiroaki Shimomoto, Hiroto Mukai, Hideaki Bekku, Tomomichi Itoh, and Eiji Ihara* Department of Materials Science and Biotechnology, Graduate School of Science and Engineering, Ehime University, 3 Bunkyo-cho, Matsuyama 790-8577, Japan S Supporting Information *
ABSTRACT: Transition-metal-catalyzed N−H insertion of a diazocarbonyl compound is applied for polycondensation for the first time to give a new type of aromatic polyamine. The well-defined polyamines were obtained by [RuCl2(p-cymene)]2-catalyzed reaction of diethyl 1,4-phenylenebis(diazoacetate) with dianilines bearing a variety of linkers between two aniline units. The polycondensation proceeded at 30 °C in CH2Cl2 with 5.0 mol % of the Ru metal to [NH2 or N2C] to afford the products with Mn = 6400−28 300 in moderate to high yield. Ethoxycarbonyl groups located at an adjacent position to NH imparted solubility to the polyamines, and their glass transition temperatures can be varied depending on the linker structure in a range of 88−173 °C.
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INTRODUCTION For a few decades, diazocarbonyl compounds have been gaining importance in organic syntheses because their unique reactivities can realize a variety of useful organic transformations with some transition-metal catalysts.1−3 In addition, diazocarbonyl compounds have been utilized as a monomer for polymer synthesis, where their reactivities enable polymerization affording polymers with unprecedented chemical structures. For example, a variety of alkyl or aryl diazoacetates have been shown to be polymerized to produce C−C main chain polymers with an alkoxy- or aryloxycarbonyl group at each main chain carbon atom,4−6 and the polymerization has extended the field of C1 polymerization or poly(substituted methylene) synthesis intensively, complementing the conventional vinyl polymerization for the synthesis of C−C main chain polymers. Meanwhile, the reactivity of diazocarbonyl compounds has been utilized in polycondensation,7−11 where one of two bifunctional monomers is bis(diazocarbonyl) compounds, whose N2 moiety is eliminated during propagation. For example, we have reported polycondensation of bis(diazoketone) with bisphenol or dicarboxylic acid to afford poly(ether ketone) or poly(ester ether ketone), respectively, with the catalytic action of a Rh complex (Scheme 1A,B).8,9 Noteworthy in the polymerization is that THF molecules used as solvent were ring-opened and inserted into the polymer main-chain framework in an unprecedented manner along with insertion of a diazo-bearing carbon atom into an OH group, providing a rare example of three-component polycondensa© 2017 American Chemical Society
tion. Furthermore, Liu and our group, independently, have reported polycondensation of bis(diazoacetate)s with CC bond formation as propagation to afford unsaturated polyesters (Scheme 1C).10,11 In the course of our attempt to extend the applicability of polycondensation using bis(diazocarbonyl) compounds, it occurred to us that N−H insertion reaction of the diazo bearing carbon atom is of worth trying to be employed because the general scheme shown below suggests that a unique aromatic polyamine framework can be obtained by C−N bond formation12−16 (Scheme 2). While there have been many reports on the N−H insertion of diazocarbonyl compounds including inter- and intramolecular reaction using a variety of substrates, most promising results with respect to our objective are found in the literature by Xu, Che, and co-workers published in 2008.17 In the paper, they reported that [RuCl2(pcymene)]2 efficiently catalyzed N−H insertion of ethyl phenyldiazoacetate (1) with aniline to afford ethyl 2-(phenylamino)-2-phenylacetate almost quantitatively in CH2Cl2 at room temperature. On the basis of the results, we can expect that if bifunctional diazoacetate, such as diethyl 1,4phenylenebis(diazoacetate) (2), is available, we can prepare aromatic polyamine of a general structure 4, where the alkoxycarbonylmethylene unit is located at an adjacent carbon to NH and two aniline units derived from 3 are connected with Received: September 14, 2017 Revised: October 31, 2017 Published: November 17, 2017 9233
DOI: 10.1021/acs.macromol.7b01994 Macromolecules 2017, 50, 9233−9238
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Scheme 1. Polycondensation Using Bis(diazocarbonyl) Compounds
Article
EXPERIMENTAL SECTION
Materials. Dichloro(p-cymene)ruthenium(II) dimer ([RuCl2(pcymene)]2; Sigma-Aldrich), 5,10,15,20-tetraphenyl-21H,23H-porphine iron(III) chloride (FeTPPCl; Sigma-Aldrich, >94%), diethyl 1,4phenylenediacetate (Tokyo Chemical Industry, >98.0%), 4,4′diaminodiphenylmethane (3a; Tokyo Chemical Industry, >98.0%), 4,4′-diaminodiphenyl ether (3b; Tokyo Chemical Industry, >98.0%), 4,4′-(1,4-phenylenediisopropylidene)bisaniline (3c; Sigma-Aldrich, >99%), 2,2-bis(4-isocyanatophenyl)hexafluoropropane (3d; Tokyo Chemical Industry, >98.0%), bis(4-aminophenyl) sulfone (3e; Tokyo Chemical Industry, >98.0%), N,N′-diethyl-1,6-diaminohexane (Tokyo Chemical Industry, >97.0%), 1,8-diazabicyclo[5.4.0]-7-undecene (DBU; Tokyo Chemical Industry, >98.0%), CaH2 (Nacalai Tesque, >99.0%), Na2SO4 (Nacalai Tesque, >98.5%), and MgSO4 (Wako Pure Chemical Industries, >98.0%) were used as received. Acetonitrile (Wako Pure Chemical Industries, >99.5%) and CH2Cl2 (Junsei Chemical, >99%) were dried over CaH2 and used without further purification. p-Toluenesulfonyl azide was prepared according to the literature.18 Monomer Synthesis. Under a N2 atmosphere, an acetonitrile (70 mL) solution of diethyl 1,4-phenylenediacetate (2.00 g, 7.99 mmol) and p-toluenesulfonyl azide (3.48 g, 17.6 mmol) was placed in a round-bottomed flask. An acetonitrile (30 mL) solution of DBU (3.00 mL, 20.0 mmol) was added to the flask at room temperature, and the mixture was stirred overnight at the temperature. After the addition of water (100 mL), the mixture was filtrated, and the residue was purified with preparative size-exclusion chromatography (SEC) to give 2 as an orange solid (yield: 52%). 1H NMR (500 MHz, CDCl3, δ): 7.50 (s, 4H, −Ph[−H]−), 4.33 (q, J = 7.0 Hz, 4H, −CO2CH2CH3), 1.34 (t, J = 7.0 Hz, 6H, −CO2CH2CH3). 13C NMR (126 MHz, CDCl3, δ): 165.3 (−CO2Et), 124.4 (−Ph[−C]−), 123.0 (−Ph[−C]−), 63.5 (N2C−), 61.2 (−CO2CH2CH3), 14.6 (−CO2CH2CH3). Anal. Calcd for C14H14N4O4: C, 55.63; H, 4.67; N, 18.53. Found: C, 55.67; H, 5.13; N, 17.62. Polymerization Procedure. As a typical procedure, polycondensation of 2 with 3d (run 7 in Table 1) was described as follows. Under
Scheme 2. N−H Insertion of Ethyl Phenyldiazoacetate (1) with Aniline and Its Application to Polycondensation Affording Polyamines
Table 1. Polycondensation of 2 with 3a−3aa run dianiline 1 2 3 4 5 6 7 8
3a 3a 3a 3a 3b 3c 3d 3e
[catalyst] (mol %)b
temp (°C)
time
yield (%)c
Mnd
Mw/Mnd
1.0 5.0 5.0 5.0 5.0 5.0 5.0 5.0
30 30 30 −20 30 30 30 30
24 24 72 24 24 24 24 24
47 70 64 trace 84 92 40 45
8100 13100 14600 n.d. 11400 20900 28300 6400
1.6 1.9 2.0 n.d. 1.9 2.0 1.9 1.7
a
In CH2Cl2, [RuCl2(p-cymene)]2 = 2.0 mM. bPercentage of the Ru metal to [NH2 or N2C]. cDetermined by gravimetry after purification with preparative SEC. dDetermined by SEC. a N2 atmosphere, a CH2Cl2 (3.0 mL) solution of 2 (60.5 mg, 0.20 mmol) and 3d (66.9 mg, 0.20 mmol) was placed in a Schlenk tube. A CH2Cl2 (2.0 mL) solution of [RuCl2(p-cymene)]2 (6.12 mg, 1.0 × 10−2 mmol) was added, and the mixture was stirred at 30 °C for 24 h. After CH2Cl2 was added, the mixture was transferred to a separatory funnel, washed with water, and dried over MgSO4. After volatiles were removed under reduced pressure, the residue was subjected to purification by preparative SEC to give a polymer as a pale purple solid (47.5 mg, 40%). Measurements. The polymer’s molecular weight distributions were measured by means of SEC in CHCl3 at 40 °C on polystyrene gel columns connected to a pump (Shimadzu, LC-6AD), a column oven (Jasco, CO-2065 Plus), an ultraviolet detector (Shimadzu, SPD-20A), and a refractive index detector (Shimadzu, RID-20A). The columns used for the SEC analyses was a combination of TSKgel G4000Hxl
a variety of linkers (X) between them. In this general structure, there are two important advantages compared to conventional aromatic polyamines: (1) the alkoxycarbonyl group can impart solubility to the resulting polymers; (2) the choice of the linker X enables us to adjust physical properties such as glass transition temperature (Tg) by controlling the mobility or flexibility of the polymer main chain. Accordingly, in this paper, we are trying to realize polycondensation of bis(diazoacetate) with dianiline for the first time to establish a new strategy for the synthesis of unique aromatic polyamines. 9234
DOI: 10.1021/acs.macromol.7b01994 Macromolecules 2017, 50, 9233−9238
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Macromolecules (Tosoh, exclusion limit molecular weight = 4 × 105, column size = 300 mm × 7.8 mm i.d., average particle size = 5 μm) and Shodex K-802.5 (Shodex, exclusion limit molecular weight = 2 × 104, column size = 300 mm × 8.0 mm i.d.). The number-average molecular weight (Mn) and polydispersity ratio [weight-average molecular weight/numberaverage molecular weight (Mw/Mn)] were calculated from the chromatographs based on eight polystyrene standards (Mp = 2.50 − 321 × 103) and 1,3-diphenylpropane (molecular weight = 196.3). Purification by preparative SEC was performed on a JAI LC-918R equipped with a combination of columns of a JAIGEL-3H and a JAIGEL-2H (Japan Analytical Industry, exclusion limit molecular weight = 70K and 5K for polystyrene, respectively; column size = 600 mm × 20 mm i.d.) using CHCl3 as eluent at a flow rate of 3.8 mL/min at room temperature. NMR spectra were recorded on a Bruker Avance 400 (400 MHz for 1H and 100 MHz for 13C) or an Avance 500 (500 MHz for 1H and 126 MHz for 13C) spectrometer at room temperature (monomers) or at 50 °C (polymers). The glass transition temperature (Tg) of polymers was determined by differential scanning calorimetry (DSC; Seiko Instruments Inc., EXSTAR DSC6000) in the range from −100 to 200 °C for product polymers. The heating and cooling rates were 10 °C/min. The Tg of the polymers was defined as the temperature of the midpoint of a heat capacity change on the second heating scan. Elemental analyses were performed on a YANAKO CHN Corder MT-5.
both polymer yield and Mn, 70% and 13 100, respectively (run 2). Further elongation of reaction period to 72 h did not improve the polymerization results (run 3). The polymerization at lower temperature of −20 °C did not afford a polymeric product (run 4). Figure 1 shows the 1H NMR spectra of a polymeric product obtained in run 3 along with its monomers. In the spectrum of the polymer, the signals at 5.0 and 4.7 ppm can be assignable to methine and NH protons, respectively, associated with the newly formed C−N bond after polycondensation via N−H insertion. The assignment of the latter was confirmed by the hydrogen/deuterium exchange, and the 1H NMR spectrum is shown in the Supporting Information. All other signals corresponding to the repeating unit of the polymer are slightly shifted to the upfield compared to those of its monomers. Noteworthy is that sharp signals are observed for all the protons derived from the expected repeating unit structure obtained by the N−H insertion; no additional signal is observed except for those come from H2O in the CDCl3 at 1.5 ppm and silicone grease at 0.07 ppm. The signal appearance strongly supports the exclusive progress of the N−H insertion and the formation of a well-defined polyamine. Likewise, the 13 C NMR spectrum of the polymer in Figure 2 has similar characteristics; all the expected signals appear as relatively sharp ones, and no other signal is observed at all. Because the carbon atoms bearing an ethoxycarbonyl group are chiral, a pair of diastereomeric combinations of isomeric structures should exist in the sequence of the −C*H(CO2Et)PhC*H(CO2Et)− unit. Indeed, reflecting the presence of a pair of the diastereomers, two signals with an equal intensity are observed for the carbonyl carbons located at adjacent positions to the chiral carbons (inset in Figure 2A). If we can conduct the N−H insertion enantioselectively, the structural characteristic would be utilized to induce chiral secondary structures to the resulting polymers. In accord with the well-defined structure confirmed by these spectra, elemental analysis of the polyamine sample gave satisfactory results (Supporting Information). The product has enough solubility toward CHCl3 and THF, demonstrating the solubilizing effect of the ethoxycarbonyl substituents in each repeating unit. A series of linker structures were employed for the dianiline monomers, and the polymerization results under the standard condition are listed in Table 1. When ether (−O−) and α,α,α′,α′-tetramethylxylylene units (3b and 3c) were employed, products with Mn of 11 400 and 20 900, respectively, were obtained in high yield (runs 5 and 6). A dianiline with a bis(trifluoromethyl)methylene linker 3d afforded a high Mn (28 300) product, despite the yield became much lower to 40% (run 7). A sulfone-linked dianiline 3e gave a product with lower Mn and yield (Mn = 6400 and 45% yield). Most importantly, all the polyamines obtained from 3b−3e are soluble in CHCl3 and THF and have well-defined structures confirmed by 1H and 13C NMR and elemental analyses as well as in the above-described case of 3a. As a representative example, 1H and 13C NMR spectra of 4b and 4c are shown in Figure 3, where all the required signals appear without ones from any contaminated species. Other NMR spectra and elemental analyses data for these products are described in the Supporting Information. Even though N−H insertion of aliphatic amine instead of aniline proceeded in an analogous efficient manner with [RuCl2(p-cymene)]2 in the literature,17 an ill-defined polymeric product was obtained when aliphatic diamine was used instead of dianiline as a monomer for the polycondensation under the
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RESULTS AND DISCUSSION Monomer Synthesis. Although ethyl phenyldiazoacetate (1), monofunctional counterpart of diethyl 1,4-phenylenebis(diazoacetate) (2), has been frequently used in organic reaction as an activated donor−acceptor type diazocarbonyl compound,3 2 has not appeared in the literature so far. However, applying the same procedure for the synthesis of 117 successfully afforded 2 as shown in Scheme 3. The compound Scheme 3. Synthesis of 2
is obtained as an orange solid in 52% yield and is satisfactorily stable upon handling and storage under atmospheric conditions. The successful synthesis of 2 suggests that we can prepare longer alkyl ester analogues than ethyl in 2 starting from a commercially available 1,4-phenylenediacetic acid, in case a higher solubilizing effect by the ester substituent is required depending on the dianiline structures. Polycondensation. Among the transition-metal catalysts reported for the N−H insertion of 1 with aniline, we chose [RuCl2(p-cymene)]2, which is commercially available and gave a quite satisfactory result for the reaction (in CH2Cl2, 2 mol % of the Ru metal to [NH2 or N2C], 10 min, 98% yield) in the literature.17 Accordingly, we simply applied the reported conditions to the polycondensation of 2 with dianiline 3a bearing a CH2 linker (Scheme 2 and Table 1). When the reaction was conducted with a feed ratio of ([2] = [3a])/[Ru] = 50 (1.0 mol % of the Ru metal to [NH2 or N2C]) in CH2Cl2 for 24 h, a polymeric product was obtained in 47% yield after purification with preparative recycling SEC with CHCl3 (Table 1, run 1). According to SEC analysis of the product, the number-average molecular weight (Mn) based on polystyrene standards was estimated to be 8100. The increase of the amount of Ru metal to 5.0 mol % to the monomer functional groups resulted in the improvement with respect to 9235
DOI: 10.1021/acs.macromol.7b01994 Macromolecules 2017, 50, 9233−9238
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Macromolecules
Figure 1. 1H NMR spectra of (A) 4a (Table 1, run 3), (B) 2, and (C) 3a (∗: solvent, water, or grease).
Figure 2. 13C NMR spectra of (A) 4a (Table 1, run 3), (B) 2, and (C) 3a (∗: solvent, water, or grease).
same conditions. Likewise, with the Fe(III) tetraphenylporphyrin chloride (FeTPPCl) complex,19 which was reported to be as effective for the N−H insertion of 1 with aniline as the Ru complex, ill-defined polymeric product was obtained (Supporting Information). Tg Measurement. Figure 4 illustrates the results of Tg measurement of polymers 4a−4e by DSC analyses. As clearly seen from the charts, Tgs of these polymers are highly
dependent on the linker structure because the polymer structures differ only in the linker moiety. Whereas Tgs of 4a−4c are in the range of 88−107 °C, the introduction of (CF3)2C and S(=O)2 linkers are effective in increasing the Tg to a much higher range of 151−173 °C. These results indicate that we can control physical properties of polyamines obtained by this polycondensation by a choice of the linker structure. Along with the option of ester substituent in the bis(diazoacetate)s, 9236
DOI: 10.1021/acs.macromol.7b01994 Macromolecules 2017, 50, 9233−9238
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Macromolecules
Figure 3. (A) 1H and (B) 13C NMR spectra of 4b (Table 1, run 5) and (C) 1H and (D) 13C NMR spectra of 4c (Table 1, run 6) (∗: solvent, water, or grease).
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CONCLUSIONS We have demonstrated that N−H insertion of bis(diazocetate) with dianiline can be effectively applied to polycondensation to afford well-defined aromatic polyamines. The polyamines have characteristic structures in terms of the presence of an alkoxycarbonyl group on the adjacent carbon atom to NH in the polymer main chain, and the alkoxycarbonyl group can impart solubility to the resulting polyamines. Such a structure of polyamines cannot be prepared by other synthetic strategy. Furthermore, the controllability of Tg of the resulting polyamines by the choice of a dianiline linker was demonstrated clearly, which could be another important advantage with respect to application to polymeric materials synthesis. We believe that these results broaden the applicability and generality of diazocarbonyl compounds as a monomer for polymer synthesis.
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Figure 4. DSC thermograms of 4a (Table 1, run 3), 4b (Table 1, run 5), 4c (Table 1, run 6), 4d (Table 1, run 7), and 4e (Table 1, run 8).
ASSOCIATED CONTENT
S Supporting Information *
The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.macromol.7b01994.
polyamines with a variety of properties can be prepared by this polycondensation. 9237
DOI: 10.1021/acs.macromol.7b01994 Macromolecules 2017, 50, 9233−9238
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H and 13C NMR spectra for 3b−3e, 4d, and 4e, hydrogen/deuterium exchange 1H NMR spectrum for 4a, assignments of NMR data and elemental analysis data for 4a−4e, and 1H NMR spectra of products obtained by polycondensation of 2 with an aliphatic diamine and polycondensation of 2 with 3a using an Fe complex (PDF)
(12) Yoshizawa, K.; Ito, A.; Tanaka, K.; Yamabe, T. Synthesis of polyaniline by use of the Ullmann reaction. Synth. Met. 1992, 48, 271− 282. (13) Spetseris, N.; Ward, R. E.; Meyer, T. Y. Linear and Hyperbranched m-Polyaniline: Synthesis of Polymers for the Study of Magnetism in Organic Systems. Macromolecules 1998, 31, 3158− 3161. (14) Goodson, F. E.; Hauck, S. I.; Hartwig, J. Palladium-Catalyzed Synthesis of Pure, Regiodefined Polymeric Triarylamines. J. Am. Chem. Soc. 1999, 121, 7527−7539. (15) Zhang, X.-X.; Sadighi, J. P.; Mackewitz, T. W.; Buchwald, S. L. Efficient Synthesis of Well-Defined, High Molecular Weight, and Processible Polyanilines under Mild Conditions via PalladiumCatalyzed Amination. J. Am. Chem. Soc. 2000, 122, 7606−7607. (16) Jang, Y.-J.; Hwang, S.-H.; Choi, T.-L. Iridium-Catalyzed Direct C−H Amidation Polymerization: Step-Growth Polymerization by C− N Bond Formation via C−H Activation to Give Fluorescent Polysulfonamides. Angew. Chem. 2017, 129, 14666. (17) Deng, Q.-H.; Xu, H.-W.; Yuen, A. W.-H.; Xu, Z.-J.; Che, C.-M. Ruthenium-Catalyzed One-Pot Carbenoid N−H Insertion Reactions and Diastereoselective Synthesis of Prolines. Org. Lett. 2008, 10, 1529−1532. (18) Sastraruji, K.; Sastraruji, T.; Ung, A. T.; Griffith, R.; Jatisatienr, A.; Pyne, S. G. Synthesis of stemofoline analogues as acetylcholinesterase inhibitors. Tetrahedron 2012, 68, 7103−7115. (19) Baumann, L. K.; Mbuvi, H. M.; Du, G.; Woo, L. K. Iron Porphyrin Catalyzed N−H Insertion Reactions with Ethyl Diazoacetate. Organometallics 2007, 26, 3995−4002.
AUTHOR INFORMATION
Corresponding Author
*Phone & Fax: +81-89-927-8547; e-mail:
[email protected] (E.I.). ORCID
Eiji Ihara: 0000-0002-0279-5105 Notes
The authors declare no competing financial interest.
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ACKNOWLEDGMENTS This work was supported by a Grant-in-Aid for Scientific Research on Innovative Areas “New Polymeric Materials Based on Element-Blocks (No. 2401)” (JSPS KAKENHI Grant 15H00755) and “Studying the Function of Soft Molecular Systems by the Concerted Use of Theory and Experiment (No. 2503)” (JSPS KAKENHI Grants 26104525 and 16H00841), a Grant-in-Aid for Scientific Research (C) (JSPS KAKENHI Grant 15K05521), and a Grant-in-Aid for Young Scientists (B) (JSPS KAKENHI Grant 16K17916). The authors thank Applied Protein Research Laboratory in Ehime University for its assistance in NMR and Advanced Research Support Center in Ehime University for its assistance in elemental analysis.
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REFERENCES
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