Polynorbornene-Based Double-Stranded ... - ACS Publications

Mar 13, 2012 - Kyle F. Biegasiewicz , Justin R. Griffiths , G. Paul Savage , John Tsanaktsidis , and Ronny Priefer. Chemical Reviews 2015 115 (14), 67...
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Polynorbornene-Based Double-Stranded Ladderphanes with Cubane, Cuneane, Tricyclooctadiene, and Cyclooctatetraene Linkers Nai-Hua Yeh, Chih-Wei Chen, Shern-Long Lee, Hung-Jen Wu, Chun-hsien Chen,* and Tien-Yau Luh* Department of Chemistry, National Taiwan University, Taipei, Taiwan 106 S Supporting Information *

ABSTRACT: Double-stranded ladderphanes 2, 3, and 5 having cubane, cuneane, and cyclooctatetraene linkers are synthesized by ring-opening metathesis polymerization (ROMP) of the corresponding bisnorbornene monomers 10, 11, and 13, respectively. Attempts to polymerize the corresponding tricyclooctadiene-linked bisnorbornene 12 are not successful, starting monomer being recovered. Polymer with this tricyclic diene linker 4 is obtained from the rhodium-catalyzed isomerization of 2. The scanning tunneling microscopic (STM) image of 2 shows an ordered pattern on the graphite surface by self-assembly.

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INTRODUCTION Cubane represents one of the most fascinating molecules not only for its unique structural feature but also for other potential applications.1 Cubane skeleton, although highly strained, exhibits extraordinary stability under various conditions. Incorporation of cubane moiety into oligomers and polymers has been sporadically explored.2−6 Thus, [n]cubylcubanes and oligocubyl rods are synthesized from the treatment of diiodocubane or diiodooligocubyl with tert-butyllithium.1b,2 Polymerization of bishomoallylcubane by cross-metathesis gives the corresponding oligomers with six to seven repeat units.3 In addition to polyamides4 and polyacrylates,5 cubane-containing polynorbornenes are obtained by the ring-opening metathesis polymerization (ROMP) of the corresponding diastereomeric mixture of exo- and endo-norbornene esters.6 Incorporation of valence isomers of cubane (such as substituted cuneane or tricycle[4.2.0.02,5]octadiene) other than a cyclooctatetraene derivative5 into a polymer has not been explored. We recently reported a series of symmetrical7 and unsymmetrical8 double-stranded polynorbornene-based ladderphanes 1 having a range of different rigid aromatic or organometallic linkers.9 Related disulfide-based ladderphanes have recently been disclosed.10 Like a DNA molecule, the aromatic linkers in these ladderphanes are cofacially aligned, and the corresponding single-stranded polynorbornenes can undergo replication generating a daughter polymer.7−9 Each of the monomeric unit in 1 spans about 5−6 Å.7−9,11 The smallest possible dimensions of cylindrical 1,4-disubstituted cubane derivatives and related substituted C8H6-valence isomers such as cuneane, syntricycle[4.2.0.02,5]octadiene, or cyclooctatetraene are no more than 3.8 Å.12 It is envisaged that a cubane derivative and related valence isomers can fit into this space and, therefore, could be used as linkers for double-stranded ladderphanes. In this paper, we wish to report the synthesis and characterization of a range of double-stranded polybisnorbornenes 2−5 using cubane and its valence isomers as linkers. © 2012 American Chemical Society

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RESULTS AND DISCUSSION Cubanedicarbinol 6 was synthesized according to literature procedures.13 Reduction of dimethyl 2,6-cuneanedicarboxylate 712c,14 by LAH gave 75% yield of 8. Diol 6 was allowed to react with acid chloride 9b in the presence of Et3N to afford the corresponding monomer 10 in 73% yield (Scheme 1). In a similar manner, monomer 11 was prepared. Treatment of 10 with 5 mol % [Rh(NBD)Cl]2 in CHCl3−toluene at rt gave the corresponding tricyclooctadiene derivative 12 in 75% yield.15 When the reaction was carried at refluxing temperature, cyclooctatetraene-linked bisnorbornene 13 was obtained in 70% yield (Scheme 1).5,15b ROMP of 10 with 20 mol % of the first generation of the Grubbs catalyst (G-I) gave the corresponding polymer 2 in Received: January 4, 2012 Revised: March 2, 2012 Published: March 13, 2012 2662

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Scheme 1. Synthesis of Monomers 10−13a

cyclobutene derivatives are known to undergo ROMP upon treatment with a variety of metal−carbene catalysts.17 Indeed, tricyclooctadiene has been used as a cross-linking agent for olefin metathesis polymerization.18 It seems likely that the ruthenium catalyst may interact preferentially with the double bonds in tricyclooctadiene moiety in 12. A DCM solution of 18, prepared from 17, was allowed to react with 1 equiv of G-I catalyst at rt for 1 h (Scheme 2). α,α′-Diacetoxyl-p-xylene 19 Scheme 2. Reaction of 18 with G-I Catalysta

Reagents and conditions: (a) [Rh(NBD)Cl]2, CHCl3−toluene, rt, %; (b) G-I catalyst (1 equiv), CDCl3, %.

a

was obtained in 58% yield. An extrusion of a C2H2 moiety from tricyclooctadiene scaffold may take place. The discrepancy between this work and literature results with parent tricyclooctadiene18 is striking. Presumably, the presence of substituents in 18 may lead to different selectivity, although the actual mode of the reaction remains unclear at this stage. It is worthy to note that a stoichiometric amount of G-I catalyst was required for this transformation. Accordingly, 80% recovery of 12 from the reaction with 20 mol % of G-I described above is understandable. Since tricyclooctadiene linker is obtained by rhodiumcatalyzed ring-opening reaction,15 it is envisaged that polymer 2 might also undergo similar ring-opening reaction. Thus, treatment of 2 with 5 mol % [Rh(NBD)Cl]2 in CHCl3− toluene at rt gave 4 in 85% yield (Mn = 6100, PDI = 1.3, DP = 9). The three olefinic protons in the tricyclooctadiene linker in 4 appears at δ 6.1 ppm as a broad peak in the 1H NMR spectrum. The corresponding carbon signals in the 13C NMR spectrum emerge at 128.6, 135.3 (two types of carbon), and 144.6 ppm. Ethanolysis of 4 under the same conditions as described above gave diol 15 and 14c (Mn = 2700, PDI = 1.2, DP = 9) in 48% and 60%, respectively. As described above, monomer 13 was obtained from the thermolysis of 10 in the presence of the rhodium catalyst. Similar thermal treatment of 4 in the presence of [Rh(NBD)Cl]2 in refluxing toluene−CHCl3 mixed solvent,5,15b however, resulted in the recovery of 4 in essentially quantitative yield.19 Polymer 5 (Mn = 6500, PDI = 1.3, DP = 10) was obtained in 87% yield from the ROMP of 13 with G-I catalyst. The 1H NMR of 5 shows broad peaks at δ 5.8−6.1 ppm attributed to the olefinic protons of the cyclooctatetraene linkers. Ethanolysis of 5 under the same conditions as described above gave diol 16 and 14d (Mn = 3200, PDI = 1.3, DP = 11) in 50% and 68%, respectively. It is worthy to note that cyclooctatetraene moiety in 13 were stable under these conditions.20 Thermal Gravimetric Analyses (TGA) of 2−5. Relatively speaking, polymers 2−5 were quite thermally stable. The temperatures with 5% weight loss for 2, 3, 4, and 5 were 244, 299, 276, and 304 °C, respectively, as revealed by TGA measurements. The DSC studies, however, indicate that none of these ladderphanes exhibit glass transition temperatures.21 Scanning Tunneling Microscopic Images. The scanning tunneling microscopy (STM) image of 2 shows a well-aligned

a Reagents and conditions: (a) (COCl)2, (b) 6, Et3N, 73%; (c) 8, pyridine, 67%; (d) [Rh(NBD)Cl]2, CHCl3−toluene, rt, 75%; (e) [Rh(NBD)Cl]2, CHCl3−toluene, reflux, 70%.

90% yield (Mn = 6000, PDI = 1.3, degree of polymerization [DP] = 9). The absorption for the protons on cubane linker in 2 in the 1H NMR spectrum appears as a broad peak centered at δ 3.86 ppm. The corresponding carbon signal in the 13C NMR spectrum of 2 exhibits at δ 44.5 ppm, in addition to the quarternary carbons at δ 57.0 ppm. Ethanolysis of 2 with NaOEt in EtOH and DCM gave 6 in 54% yield in addition to single-stranded polynorbornene 14a11b in 65% yield (Mn = 2900, PDI = 1.2, DP = 10). A similar degree of polymerization between 2 and 14 indicates that 2 would be a double-stranded ladderphane.

In a similar manner, ROMP of 11 under similar conditions using 12 mol % of the G-I catalyst gave 3 in 83% yield (Mn = 10 200, PDI = 1.8, DP = 16). Four of the six cuneane protons in 2 appear at δ 2.20−2.55 ppm. Ethanolysis of 3 gave 14 in 74% yield (Mn = 4300, PDI = 1.3, DP = 17) and diol 8 (85%). These results suggest that cuneane skeleton is also stable under the ROMP conditions. A similar degree of polymerization between 3 and 14b supports the double-stranded nature of 3. Attempts to polymerize 12 with G-I catalyst were unsuccessful. Upon mixing of 12 and 20 mol % of the G-I catalyst, the DCM solution turned red immediately. After stirring for 1 h, starting 12 was recovered in 80% yield. Cyclobutene is more strained than 2-norbornene,16 and 2663

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motif on highly ordered pyrolytic graphite (HOPG) surface.22 The brighter and darker parts of the lamellae can be ascribed to the aromatic cores and cubane parts of 2, respectvely, due to the magnitude of conductance. The apparent width of each stripe (from the bright spot of one stripe to the bright spot of the adjacent stripe) shown in Figure 1 is about 2.9 nm, which is

Biosystem, Foster City) using the MALDI method equipped with an Nd/YAG laser (335 nm) operating at a repetition rate of 200 Hz, or a Waters LCT Premier XE (Waters Corp., Manchester, UK) using the ESI method withdual ionization ESCi (ESI/APCi) source options. GPC was performed on a Waters GPC instrument equipped with Waters 1515 HPLC pump using Waters 2487 absorbance detector. Polymer (∼0.5 mg) in THF (0.1 mL) was filtered through a 0.5 μm filter, and 20 μL of the sample was injected into Shodex KF-G, Styragel HR2, Styragel HR3, and Styragel HR4 columns (7.8 × 300 mm) were with oven temperature at 40 °C using standard polystyrene samples (1.84 × 105−996 Da) for calibration. THF was used as the eluent (flow rate = 1.0 mL min−1). Waters Empower HPLC/GPC network software was used for data analyses. Thermogravimetry analysis (TGA) measurements were performed on a Dynamic Q500 thermogravimetric analyzer in conjunction with TA Instruments 5100 system at a scan rate of 10 °C/min under a nitrogen atmosphere. Differential scanning calorimetry (DSC) measurements were performed on a LT-Modulate DSC 2920 instrument in conjunction with the TA Instruments 5100 system at a scan rate of 10 °C/min under a nitrogen atmosphere. 2,6-Bis(hydroxymethyl)cuneane (8). Under N2, to a suspension of LAH (250 mg, 6.59 mmol) in THF (20 mL) at 0 °C was added dropwise a solution of dimethyl 2,6-cuneanedicarboxylate 712c,14 (250 mg, 1.14 mmol) in THF (20 mL), and the mixture was stirred for 12 h. The reaction was quenched by 10% NaOH (1.0 mL). The mixture was filtered and evaporated in vacuo to afford the residue, which was purified by flash column chromatography (silica gel, EA) to afford 8 as a white solid (140 mg, 75%): mp 83−84 °C. 1H NMR (400 MHz, CDCl3): δ 1.15−1.22 (br, 2 H), 2.25−2.28 (m, 2 H), 2.35−2.40 (m, 2 H), 2.74−2.77(m, 2 H), 3.60 (d, J = 12.0 Hz, 2 H), 3.69 (d, J = 12.0 Hz, 2 H); 13C NMR (100 MHz, CDCl3) δ 34.3, 35.1, 39.4, 48.3, 62.5. IR (KBr): ν 3419, 1635, 1011 cm−1. HRMS (FAB) (M+): calcd for C10H12O2 164.0837; found 164.0834. Monomer 10. Under N2, to a solution of 1,4-bis(hydoxymethyl)cubane13 6 (328 mg, 2 mmol) and Et3N (600 mg, 6 mmol) in DCM (60 mL) at 0 °C was added a solution of 9b freshly prepared from the corresponding carboxyl acid7 (1.1 g, 4.1 mmol) in DCM (50 mL). The mixture was gradually warmed to rt and stirred for 10 h, poured into water (100 mL), and extracted with DCM (100 mL × 2). The organic layer was washed with brine (100 mL × 2), dried (MgSO4), filtered, and evaporated in vacuo. The residue was chromatographed on silica gel (DCM) to afford 10 (932 mg, 73%); mp 246−248 °C. 1H NMR (400 MHz, CDCl3): δ 1.53 (d, J = 8.4 Hz, 2 H), 1.63 (d, J = 8.4 Hz, 2 H), 2.96−3.00 (m, 8 H), 3.09−3.11 (m, 4 H), 3.28−3.33 (m, 4 H), 3.87 (s, 6 H), 4.42 (s, 4 H), 6.17 (s, 4 H), 6.39 (d, J = 8.8 Hz, 4 H), 7.86 (d, J = 8.8 Hz, 4 H). 13C NMR (100 MHz, CDCl3): δ 44.5, 45.4, 46.6, 50.5, 52.1, 57.1, 64.5, 110.9, 0.6, 131.1, 135.8, 150.4, 167.3. IR (KBr): ν 3058, 2965, 2848, 1698, 1605, 1524, 1473, 1378, 1271, 1177, 1104, 970, 828, 768 cm−1. HRMS (MALDI) (M + H+): calcd for C42H43N2O4 639.3223; found 639.3240. Monomer 11. To a solution of acyl chloride 9b which was fresh prepared from corresponding carboxyl acid7 (300 mg, 1.18 mmol) in pyridine (20 mL) was added a solution of 8 (100 mg, 0.61 mmol) in pyridine (20 mL), and the mixture was refluxed for 12 h. Water (250 mL) and DCM (250 mL) were added. The organic layer was washed with brine (100 mL), dried (MgSO4), filtered, and evaporated in vacuo to afford the residue which was chromatographed on silica gel (DCM/ EA = 30/1) to afford 11 as a white solid (261 mg, 67%); mp 190 °C (dec.). 1H NMR (400 MHz, CDCl3): δ 1.52 (d, J = 8.2 Hz, 2 H), 1.62 (t, J = 8.2 Hz, 2 H), 2.33−2.36 (m, 2 H), 2.40−2.42 (m, 2 H), 2.69− 2.71 (m, 2 H), 2.94−3.05 (m, 8 H), 3.05−3.10 (m, 4 H), 3.25− 3.32(m, 4 H), 4.23 (d, J = 12.0 Hz, 2 H), 4.33 (t, J = 12.0 Hz, 2 H), 6.16 (s, 4 H), 6.38 (d, J = 8.4 Hz, 4 H), 7.85 (t, J = 8.4 Hz, 4 H). 13C NMR (100 MHz, CDCl3): δ 34.7, 36.1, 40.3, 45.0, 45.5, 46.7, 50.5, 52.1, 63.8, 110.7, 116.5, 131.1, 135.6, 150.1, 166.9. IR (KBr): ν 3050, 2964, 2933, 2847, 1697, 1605, 1523, 1474, 1379, 1273, 1178, 1098, 969, 830, 769, 725 cm−1. HRMS (FAB) (M + H+): calcd for C42H43N2O4 639.3223; found 639.3219. Monomer 12. A solution of 10 (300 mg, 0.47 mmol) and [Rh(NBD)Cl]2 (10.8 mg, 0.023 mmol)5,15 in anhydrous toluene and

Figure 1. STM images of 2 on H. Imaging conditions of Ebias, itunneling, and image size: 0.68 V, 174 pA, and 22 × 22 nm.

consistent with the estimated width for 2 (ca. 2.6 nm23) plus van der Waals spacing. In addition, the two adjacent monomeric units in 2 are separated by ∼0.6 nm, which would match nicely to the span for each of the monomric unit in polynorbornene-based ladderphanes.7−10 As shown in Figure 1, a dark line is present in the center along the longitudinal axis of the polymer separating each stripe into two symmetrical parts. Presumably, the cubane moiety, which is nonconductive, would occupy at the center aligned coherently along the polymeric axis. Like those of double-stranded ladderphanes,7−9,24a the present result indicates that the assembly of the polymeric molecules 2 may also exhibit π−π attractions between end groups (vinyl and styryl) along longitudinal axis of the polymers and van der Waals interactions between the neighboring polymeric backbones.

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CONCLUSION In summary, we have demonstrated the first polynorbornenebased double-stranded ladderphanes with nonaromatic linkers. Cubane and three other C8H6 valence isomeric linkers in these polymers 2−5 are stable under the polymerization conditions. The present results suggest that double-stranded ladderphanes can be easily accessible by the G-I-catalyzed ROMP protocol, as long as a rigid linker with a span less than 6 Å11a is used to connect two norbornene moieties fused with endo-Narylpyrrolidine ring. These ladderphanes are coherently aligned on the HOPG surface to form an ordered pattern by selfassembly as depicted in Figure 1. This phenomenon now appears to be a general feature in these polynorbornene-based ladderphanes.

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EXPERIMENTAL SECTION

General. Melting points were measured with Fargo MP-1D melting point apparatus and not calibrated. 1H and 13C NMR spectra were recorded on a Varian 400 Unity Plus or a Bruker Advance-400 MHz FT-NMR spectrometer (400 MHz) using CDCl3 as solvent at ambient temperature. The chemical shift of CDCl3 was calibrated at 7.26 ppm in 1H NMR spectra and 77.0 ppm in 13C NMR. Infrared spectra (IR) were obtained by using Thermo Nicolet Avatar 360 ESP FT-IR spectrometer and configured with EZ OMNIC software. Highresolution mass spectroscopy was obtained by using a Jeol-JMS-700 mass spectrometer using the FAB method with a 3-nitrobenzyl alcohol matrix, an Applied Biosystems 4800 Proteomics Analyzer (Applied 2664

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1384, 1277, 1178, 1094, 1070, 826, 766 cm−1. GPC (THF): Mn = 6100, PDI = 1.3. General Procedure of Ethanolysis of Polymers 2−5. Under N2, to a solution of polymer 2 (0.14−0.15 mmol) in DCM (20 mL) was added NaOEt solution (3 mL) which was freshly prepared from Na (9.0 g, 0.391 mmol) dissolved in (100 mL) was stirred at rt for 48 h. Water (100 mL) and DCM (100 mL) were added. The organic layer was separated and washed with brine and dried with MgSO4. The resulting solution was concentrated, and the resulting DCM solution was added to MeOH and the precipitate was collected by centrifuge to give afford the polymer 14 as a white solid. 1H NMR (400 MHz, CDCl3): δ 1.30−1.37 (br, 4 H), 1.80−1.83 (br, 1 H), 2.62−2.78 (br, 2 H), 2.80−3.10 (br, 2 H), 3.10−3.30 (br, 4 H), 4.20−4.35 (br, 2H), 5.30−5.50 (br, 2 H), 6.42−6.60 (br, 2 H), 7.81−7.88 (br, 2 H). 13C NMR (100 MHz, CDCl3): δ 14.5, 35.6, 36.2, 44.6, 44.7, 44.9, 46.5, 46.7, 46.9, 49.5, 60.1, 111.4, 117.4, 131.2, 131.7, 132.0, 150.8, 167.0. The supernatant was evaporated in vacuo, and the residue was chromatographed on silica gel (EA) to afford the diol linker. 14a (65%, White Solid). Mn = 2900, PDI = 1.2, and 6 (white solid, 54%).13 14b (74%, White Solid). Mn = 4800, PDI = 1.3, and 8 (white solid, 85%). 14c (60%, White Solid). Mn = 2700, PDI = 1.2, and 15 as a colorless liquid (12.3 mg, 48%). 1H NMR (400 MHz, CDCl3): δ 1.50−1.55 (br, 2H), 2.70−2.78 (m, 1 H), 3.01−3.05 (m, 1 H), 3.10− 3.18 (m, 1 H), 3.72 (d, J = 11.2 Hz, 1 H), 3.82 (d, J = 11.2 Hz, 1 H), 4.05 (ABq, J = 14.4 Hz, 2 H), 6.03 (t, J = 2.8 Hz, 2 H), 6.14 (t, J = 2.4 Hz, 1 H). 13C NMR (100 MHz, CDCl3): δ 36.3, 36.4, 40.4, 53.2, 60.6, 64.3, 128.3, 135.8, 136.6, 148.8. IR (KBr): ν 3351, 2958, 2924, 2854, 1463, 1269, 1017 cm−1. HRMS (ESI, M − H+): calcd for C10H11O2 163.0759; found 163.0768. 14d (68%, White Solid). Mn = 3200, PDI = 1.3, and 16 as a colorless liquid (11.6 mg, 50%). 1H NMR (400 MHz, CDCl3): δ 1.30−1.35 (br, 2H), 4.05 (d, J = 6.8 Hz, 4H), 5.81−5.90 (m, 4H), 5.94−6.00 (m, 2H). 13C NMR (100 MHz, CDCl3): δ 66.3, 126.8, 127.8, 131.4, 131.5, 133.0, 133.2, 143.2. IR (KBr): ν 3371, 2924, 2853 1641, 1461, 1269, 1037 cm−1. HRMS (FAB): calcd for C10H12O2: 164.0837; found: 164.0839. 1,4-Bis(acetoxymethyl)tricyclooctadiene (18). A solution of 1714 (100 mg, 0.40 mmol) and [Rh(NBD)Cl]2 (9.2 mg, 0.02 mmol)5,15 in anhydrous toluene and CHCl3 (4/1, 40 mL) was stirred at rt for 24 h. The solvent was removed in vacuo, and the residue was chromatographed on silica gel (DCM) to afford 18 (70 mg, 70%). 1H NMR (400 MHz, CDCl3): δ 2.02 (s, 3 H), 2.04 (s, 3 H), 2.74−2.76 (m, 1 H), 2.96−3.00 (m, 1 H), 3.09−3.13 (m, 1 H), 4.13 (d, J = 11.5 Hz, 1 H), 4.24 (d, J = 11.5 Hz, 1 H), 4.43 (ABq, J = 14.1 Hz, 2 H), 5.93 (d, J = 2.4 Hz, 1 H), 6.00−6.03 (m, 2 H). 13C NMR (100 MHz, CDCl3): δ 20.7, 20.8, 36.8, 36.9, 40.9, 49.7, 61.1, 65.4, 130.9, 135.0, 136.3, 143.9, 170.6, 171.2. IR (KBr): ν 3095, 3034, 2964, 2878, 2360, 2337, 1741, 1437, 1377, 1231, 1030 cm−1. HRMS (ESI): calcd for C14H16O4Na 271.0946; found 271.0945. Reaction of 18 with G-I Catalyst. Under N2, a solution of 18 (12.4 mg, 0.05 mmol) and G-I catalyst (41.1 mg, 0.05 mmol) in CDCl3 in an NMR tube was allowed to stand at rt. The reaction was monitored by the NMR spectroscopy.21 After 1 h, ethyl vinyl ether (2 mL) was added, and the mixture was allowed to stand for 10 min. The solvent was then removed in vacuo, and the residue was chromatographed on silica gel (DCM) to afford 1925 (6.4 mg, 58%). 1H NMR (400 MHz, CDCl3): δ 2.09 (s, 6 H), 5.09 (s, 4 H), 7.35 (s, 4 H). 13C NMR (100 MHz, CDCl3): δ 20.8, 65.8, 128.3, 135.9, 170.6. STM Imaging. The samples for imaging were prepared by placing a 10 μL aliquot consisting of 2 in 1-phenyloctane on HOPG (highly orientated pyrolytic graphite, Advanced Ceramics, ZYH grade) with a micropipet. To acquired stable images, samples were subjected to a shear flow7c,24 which packs molecules together into a 2D close-packed motif. The STM imaging was performed with a PicoScan controller (4500, Agilent Technologies) at room temperature, and the STM probes were commercially available Pt/Ir tips (PT, Nanotips, Veeco Metrology Group/Digital Instruments). Typical imaging conditions of

CHCl3 (4/1, 40 mL) was stirred for 24 h at rt. The solvent was removed in vacuo, and the residue was chromatographed on silica gel (DCM) to afford 12 (225 mg, 75%); mp 178−179 °C. 1H NMR (400 MHz, CDCl3): δ 1.53 (d, J = 8 Hz, 2 H), 1.63 (d, J = 8 Hz, 2 H), 2.90−3.00 (m, 9 H), 3.09−3.15 (m, 5 H), 3.21−3.40 (m, 5 H), 4.35 (d, J = 11.2 Hz, 1 H), 4.46 (d, J = 11.2 Hz, 1 H), 4.67 (ABq, J = 13.6 Hz, 2 H), 6.01 (s, 1 H), 6.05−6.12 (m, 2 H), 6.16 (s, 4 H), 6.38 (d, J = 8.8 Hz, 4 H), 7.86 (d, J = 8.8 Hz, 4 H). 13C NMR (100 MHz, CDCl3): δ 37.0, 37.2, 41.1, 45.4, 46.6, 50.3, 50.4, 52.1, 60.9, 65.1, 110.9, 116.2, 130.6, 131.3, 135.3, 135.8, 136.4, 144.7, 150.4, 166.7, 167.1. IR (KBr): ν 2961, 2863, 2349, 2317, 1701, 1604, 1523, 1484, 1474, 1379, 1272,1179, 1098, 970, 827, 768, 632 cm−1. HRMS (MALDI) (M + Na+): calcd for C42H42N2O4Na 661.3043; found 661.3072. Monomer 13. A solution of 10 (300 mg, 0.47 mmol) and [Rh(NBD)Cl]2 (10.8 mg, 0.023 mmol)5,15b in anhydrous toluene and CHCl3 (19/1, 40 mL) was refluxed for 24 h, cooled to rt, and the solvent was removed in vacuo. The residue was chromatographed on silica gel (DCM) to afford 13 (210 mg, 70%); mp 197−198 °C. 1H NMR (400 MHz, CDCl3): δ 1.53 (d, J = 8.4 Hz, 2 H), 1.63 (d, J = 8.4 Hz, 2 H), 2.95−3.00 (m, 8 H), 3.09−3.10 (m, 4 H), 3.29−3.30 (m, 4 H), 4.69 (s, 4 H), 5.85−5.97 (m, 6 H), 6.16 (s, 4 H), 6.37 (d, J = 8.8 Hz, 4 H), 7.86 (d, J = 8.8 Hz, 4 H). 13C NMR (100 MHz, CDCl3): δ 45.4, 46.6, 50.4, 52.1, 66.3, 66.4, 110.9, 116.1, 128.5, 128.7, 131.2, 131.3, 132.3, 132.8, 135.8, 139.1, 139.2, 150.5, 166.6. IR (KBr): ν 3058, 2961, 2856, 1695, 1604, 1522, 1475, 1384, 1265, 1173, 1088, 884, 825, 767 cm−1. HRMS (MALDI) (M + Na+): calcd for C42H42N2O4Na 661.3043; found 661.3053. General Procedure for the ROMP of 10, 11, and 13. Under N2, a solution of monomer and G-I catalyst (12−20 mol %) in DCM was stirred for 1 h at rt. Ethyl vinyl ether (2 mL) was then added, and the mixture was stirred for 10 min. The resulting solution was concentrated, the resulting DCM solution was added to EA, and the precipitate was collected to give the corresponding polymer. Polymer 2 (White Solid, 135 mg, 90%). 1H NMR (400 MHz, CDCl3): δ 1.20−1.55 (br, 2 H), 1.60−2.05 (br, 2 H), 2.50−3.05 (br, 8 H), 3.05−3.40 (br, 8 H), 3.60−4.05 (br, 6 H), 4.20−4.60 (br, 4 H), 5.20−5.60 (br, 4 H), 6.40−6.80 (br, 4 H), 7.65−8.05 (br, 4 H). 13C NMR (400 MHz, CDCl3): δ 46.6, 49.8, 57.1, 64.6, 111.5, 117.4, 125.9, 128.4, 131.1, 131.2, 150.8, 166.7. IR (KBr): ν 2961, 2935, 2854, 1702, 1605, 1521, 1478, 1378, 1269, 1179, 1096, 963, 827, 766 cm−1. GPC (THF): Mn = 6000, PDI = 1.3. Polymer 3 (White Solid, 332 mg, 83%). 1H NMR (400 MHz, CDCl3): δ 1.20−1.50 (br, 2 H), 1.75−2.05 (br, 2 H), 2.20−2.55 (br, 4 H), 2.55−3.60 (br, 18 H), 3.80−4.80 (br, 4 H), 4.95−5.80 (br, 4 H, including vinyl end group), 6.30−6.75 (br, 4 H), 7.20−7.40 (phenyl end group), 7.85−8.15 (br, 4 H). 13C NMR (100 MHz, CDCl3): δ 33.8, 34.6, 36.0, 39.6, 40.3, 43.3, 44.8, 49.6, 63.8, 111.5, 117.5, 126.0, 128.6, 131.3, 151.0, 166.7. IR (KBr): ν 3047, 2932, 2852, 1698, 1605, 1522, 1479, 1381, 1273, 1180, 1101, 960, 769 cm−1. GPC (THF): Mn = 10 200, PDI = 1.8. Polymer 5 (White Solid, 131 mg, 87%). 1H NMR (400 MHz, CDCl3): δ 1.22−1.54 (br, 2 H), 1.68−2.03 (br, 2 H), 2.50−3.05 (br, 8 H), 3.05−3.54 (br, 8 H), 4.25−4.60 (br, 4 H), 5.20−5.65 (br, 4 H), 5.73−6.05 (br, 6 H), 6.36−6.80 (br, 4 H), 7.70−8.05 (br, 4 H). 13C NMR (100 MHz, CDCl3): δ 36.4, 36.7, 45.4, 46.6, 49.6, 66.5, 111.7, 117.2, 126.1, 128.6, 131.5, 132.5, 132.9, 139.2, 151.1, 166.5. IR (KBr): ν 2936, 2853, 1703, 1604, 1527, 1478, 1380, 1271, 1179, 1096, 965, 825, 767 cm−1. GPC (THF): Mn = 6500, PDI = 1.3. Polymer 4. A solution of polymer 2 (150 mg, 0.23 mmol) and [Rh(NBD)Cl]2 (5.4 mg, 0.012 mmol)5,15 in anhydrous toluene and CHCl3 (19/1, 40 mL) was stirred for 24 h at rt. The resulting solution was concentrated, the resulting DCM solution was added to MeOH, and the precipitate was collected to give 4 as a white solid (128 mg, 85%). 1H NMR (400 MHz, CDCl3): δ 1.30−1.50 (br, 2 H), 1.65− 2.05 (br, 2 H), 2.43−3.50 (br, 19 H), 4.05−4.80 (br, 4 H), 5.20−5.55 (br, 4 H), 5.80−6.15 (br, 3 H), 6.30−6.60 (br, 4 H), 7.70−8.05 (br, 4 H). 13C NMR (100 MHz, CDCl3): δ 36.8, 37.3, 41.1, 44.7, 46.3, 49.9, 61.0, 65.2, 111.7, 117.2, 126.0, 128.6, 131.3, 135.3, 135.9, 144.5, 151.1, 166.6, 167.0. IR (KBr): ν 3024, 2936, 2853, 1710, 1604, 1521, 1478, 2665

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bias voltage and tunneling current ranged from 0.50 to 0.9 V and from 30 to 100 pA, respectively.

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ASSOCIATED CONTENT

S Supporting Information *

1

H and 13C NMR spectra for all new compounds and the GPC, TGA, and DSC results for polymers. This material is available free of charge via the Internet at http://pubs.acs.org.

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AUTHOR INFORMATION

Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS We thank the National Science Council and the National Taiwan University for support.

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REFERENCES

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