Cis, Isotactic Selective ROMP of Norbornenes Fused with N

Article pubs.acs.org/Macromolecules

Cis, Isotactic Selective ROMP of Norbornenes Fused with N‑Arylpyrrolidines. Double Stranded Polynorbornene-Based Ladderphanes with Z‑Double Bonds Lei Zhu,†,‡ Margaret M. Flook,§ Shern-Long Lee,† Li-Wei Chan,† Shou-Ling Huang,† Ching-Wen Chiu,† Chun-Hsien Chen,*,† Richard R. Schrock,*,§ and Tien-Yau Luh*,† †

Department of Chemistry, National Taiwan University, Taipei, Taiwan 106 Shanghai Institute of Organic Chemistry, Chinese Academy of Sciences, Lingling Lu, Shanghai, China 200032 § Department of Chemistry, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, United States ‡

S Supporting Information *

ABSTRACT: Upon treatment with a molybdenum-carbene with bidentate substituted biaryl-o,o′-diphenoxide ligand 12, norbornene fused with N-aryl-endo-pyrrolidine 9a undergoes ROMP to give exclusively polynorbornene with cis, isotactic-selectivity. Bis(norbornenes) connected with ferrocene 18 or benzene 20 linkers yield the corresponding double-stranded ladderphanes 19 and 21, respectively with isotactic stereochemistry having all double bonds in Z-configuration. Like the corresponding ladderphanes with E-double bonds, ladderphane 19 also assembles on HOPG to give a highly ordered two-dimensional array as revealed by STM images.

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INTRODUCTION There is an ever burgeoning interest in the stereoselective formation of double bonds by olefin metathesis.1−6 Various catalysts have recently been developed for Z-selectivity in homocoupling,2 cross metathesis (CM),3 ring closing metathesis (RCM),4 and ring-opening metathesis polymerization (ROMP).5 The involvement of a bulky or a chelated ligand is crucial to direct the orientation of the incoming olefin that may lead to the stereoselective formation of a metallacyclobutane intermediate.1−6 Alkyne metathesis followed by partial hydrogenation offers an alternative route for the synthesis of Zolefins.7 The nature of olefin substrates may also control the stereochemistry of double bonds in olefin metathesis. For example, the presence of a bulky 2-silyl substituent in terminal olefins furnishes exclusively E-silyl-substituted cycloalkenes which are converted to the corresponding Z-alkenes by desilylation.8 Certain cycloalkenes also undergo ROMP stereoselectively under various conditions.5,9−11 Thus, norbornadiene derivatives 1 give cis, syndiotactic ROMP polymer 2 upon treatment with a Mo-catalyst 3.5a,b Similar reaction with racemic endo,exo-5,6-dicarbomethoxynorbornene 4 yields predominantly the corresponding polynorbornene with a cis,syndiotactic structure that contains alternating enantionmers in the chain.5c The key to the success relies on the steric differentiation between small imido and bulky aryloxide ligands resulting all substituents on the metallacyclobutane intermediate to have a syn relationship. The inversion of metal © 2012 American Chemical Society

configuration in each insertion of the monomeric norbornene derivative during the course of polymerization would be responsible for the syndiotactic selectivity (eq 1). A chelated ruthenium catalyst 7 has recently been disclosed to show cisselectivity in ROMP of norbornene derivatives.5d ROMPs of norbornenes fused with endo-N-arylpyrrolidine 9a with the first generation Grubbs catalyst 8 yield polynorbornene 10 with isotactic stereochemistry and trans double bonds.9 This protocol has been employed for the synthesis of a series of double stranded ladderphanes 11.11 It is noteworthy that the presence of the N-aryl pendant in 9a is indispensible in these transformations. Unlike 1 and 4, the endo site of the norbornene moiety in 9a is highly crowded. It is envisaged that, upon treatment with a Mo catalyst like 3, the mode of interactions between 9a and the molybdenum catalyst could be very different from those shown in eq 1.5a−c In particular, when bulky bidentate substituted biaryl-o,o′-diphenoxide ligand is used,12 the front side of the catalyst 12 would be blocked by the biaryl ligand. Accordingly, the double bond of 9a would interact with molybdenum-carbene moiety from the backside. In order to avoid steric interaction between the endo-pyrrolidine group and the imido ligand as in 14, the orientation of the incoming norbornene moiety 9a would preferentially interact with Received: August 9, 2012 Revised: September 25, 2012 Published: October 4, 2012 8166

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intermediate 13 via a transition state 15. Polynorbornene 16 thus obtained may adopt a cis, isotactic stereochemistry. Indeed, upon treatment of enantiomerically pure 4 with 3, a mixture of the corresponding cis, syndiotactic and cis, isotactic polynorbornenes is obtained. This observation can be understood within the framework of the steric interactions between the endo-carbomethoxy substituent and ligands in 3.5c Furthermore, when a trimethylsilyl-substituted binaphthol ligand is used, enantiomerically pure 4 gives cis, isotactic polynorbornene.13 The steric hindrance around the endo site in 9a would be larger than that in 4. It is therefore felt that a much better cis, isotactic selectivity would be obtained upon treatment with an appropriate molybdenum−carbene catalyst. We now wish to report the details on cis, isotactic-polynorbornenes from the reactions of 9a and related bis(norbornene)s 18 and 20 with 12.

Table 1. Gel Permeation Chromatography Results of Polymers

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RESULTS AND DISCUSSISON Single-Stranded Polynorbornene. Treatment of 9a with 12a in DCM at room temperature for 2 h followed by quenching with PhCHO afforded 16a in 68% yield and the results are summarized in Table 1. Similar result was obtained from the reaction of 9a with 12b. The 13C NMR spectrum of 16a shows four single peaks at δ 39.2, 40.4, 47.5, and 49.4 attributed to the ring carbons of the azabicyclooctane skeletons for each of the monomeric unit. These results suggest that there is a symmetry plane between adjacent monomeric units in 16a and the double bonds should therefore be in cis configuration. This pattern is completely different from those of 10a having trans double bonds and isotactic structure, which exhibits essentially two sets of 13C signals in the high field region because of the lack of the symmetric plane between adjacent monomeric units.9 The identical properties of the hydrogenated products (17a vs 17b) obtained from the diimide

a

polymer

Mn

Mw

PDI

na

10a 17a 16a 17b 19 16b 21 16c 22 10b 23 10c

14 500 14 300 55 300 55 600 11 500 4500 14 900 7100 12 800 5700 9600 4700

16 100 16 400 69 600 69 000 14 600 5500 17 200 8400 16 900 7000 11 200 5800

1.1 1.1 1.3 1.2 1.3 1.2 1.2 1.2 1.3 1.2 1.2 1.2

51 50 195 195 16 16 24 25 18 20 16 17

Degree of polymerization.

reductions of 10a and 16a (Figure 1), respectively, indicate that both 16 and 10 should have same isotactic stereochemistry. Double-Stranded Ladderphanes. Polynorbornene-based double-stranded and triple stranded ladderphanes have recently been disclosed by 8-catalyzed ROMP of the corresponding bisand tris(norbornene) monomers.11 One of the most important criteria for the successful synthesis of these ladderphanes relies on the stereoselective formation of single stranded polynorbornenes. It is therefore believed that the molybdenum8167

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Figure 1. Structures of single stranded polynorbornenes 16 and 17. Both 16 and 17 show symmetrical planes (σ) bisecting the double and single bonds, respectively, between adjacent monomeric units. Such symmetric plane does not exist in 10 with all double bonds in trans configuration.

catalyzed stereoselective synthesis of cis, isotactic-16 mentioned above has paved the way for the access of ladderphanes with Zdouble bonds. Thus, reaction of 18 with a catalytic amount of 12a in DCM afforded ladderphane 19 in 50% yield. The 13C NMR spectrum of 19 shows characteristic signals at δ 38.8, 40.9, 46.5, and 49.6 attributed to the carbons of the azabicyclooctane moieties with two double bond substituents in cis configuration. Ethanolysis of 19 with NaOEt gave 86% yield of 16b. In a similar manner, ladderphane 21 was obtained in 56% yield from the 12a-catalyzed ROMP of 20. Again, 21 was transformed into 16c by ethanolysis with NaOEt. Similar degrees of polymerization for 19 and 16b and for 21 and 16c further support the double stranded nature of 19 and 21. The corresponding ladderphanes 22 and 23 with all trans double bonds were prepared from 18 and 20 by 8-catalyzed ROMPs for comparison. Ethanolysis of 22 and 23 gave 10b and 10c, respectively having trans, isotactic stereochemistry. Scanning Tunneling Microscopy (STM) Images. It is known that polynorbornene-based double stranded ladderphanes 11 with trans double bonds can form a two-dimensional well-oriented array on highly ordered pyrolytic graphite surface (HOPG) after being aligned by shear-flow treatment.11,14 Stacking interaction between styrene and vinyl end groups along the longitudinal axis of the polymer and van der Waals interaction between polymeric backbones in the second dimension may be responsible for such ordered pattern.14 Polymers 19 and 21 have similar end groups (styrene and substituted vinyl). It is therefore envisaged that a similar

aggregate may also be formed from these ladderphanes with all cis double bonds. Indeed, the STM image of 19 shown in Figure 2 exhibits a nice two-dimensional array.15 The relatively bright and dark features of the lamellae are ascribed, respectively, to the aromatics and vinyl-azabicyclooctane moieties based on their tunneling efficiency. High resolution images (Figure 2b) show the nominal width of ∼2.5 nm and the spacing of 0.5−0.6 nm between linkers, consistent with the corresponding dimensions of 19. The stability of the assembly for 19 appears inferior to those of trans analogues 11 with Edouble bonds. After being subjected to STM scanning, the former becomes disordered after a couple of imaging frames while the latter is unaffected.11,14 Isolated chains of head−tail stacked 11 can be found for drop-cast samples without being assembled by shear flow, while unobserved for 19. The 8168

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2 H), 1.62 (d, J = 8.4 Hz, 2 H), 2.93−2.97 (m, 8 H), 3.06−3.08 (m, 4 H), 3.25−3.27 (m, 4 H), 4.18 (t, J = 1.8 Hz, 4 H), 4.33 (t, J = 1.8 Hz, 4H), 5.05 (s, 4 H), 6.15 (s, 4 H), 6.37 (d, J = 8.8 Hz, 4 H), 7.87 (d, J = 8.8 Hz, 4 H). 13C NMR (100 MHz, CDCl3): δ 45.3, 46.6, 50.4, 52.0, 62.0, 69.1, 69.8, 83.1, 110.8, 116.2, 131.3, 135.7, 150.3, 166.8; HRMS (FAB): calcd C44H44Fe56N2O4, 720.2650; found, 720.2657. Monomer 20. To a solution of 1,4-bis(hydroxymethyl)benzene (138 mg, 1.0 mmol) and Et3N (300 mg, 3.0 mmol) in DCM (10 mL) at 0 °C was added a solution of 9b (570 mg, 2.1 mmol) in DCM (20 mL). The mixture was gradually warmed to room temperature 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 20 (501 mg, 82%): mp 146−148 °C. 1H NMR (400 MHz, CDCl3): δ 1.52 (d, J = 8.4 Hz, 2 H), 1.62 (d, J = 8.4 Hz, 2 H), 2.94−2.98 (m, 8 H), 3.07−3.09 (m, 4 H), 3.26−3.28 (m, 4 H), 5.29 (s, 4H), 6.15 (t, J = 2.0 Hz, 4 H), 6.35 (d, J = 8.8 Hz, 4 H), 7.41 (s, 4H), 7.87 (d, J = 8.8 Hz, 4 H). 13C NMR (100 MHz, CDCl3): δ 45.5, 46.7, 50.5, 52.1, 65.5, 110.7, 115.4, 127.9, 131.3, 135.6, 136.4, 150.3, 166.7; HRMS (FAB): calcd C40H40N2O4Na [M + Na]+, 635.2886; found, 635.2904. Polymer 10a. To a solution of 9a (200 mg, 0.71 mmol) in DCM (20 mL) stirred under N2 atmosphere was added 8 (11.7 mg, 0.014 mmol) in DCM (2 mL). After stirring for 1 h at room temperature, ethyl vinyl ether (2 mL) was added and the mixture was stirred for 10 min. The resulting solution was concentrated and the polymer 10a was precipitated in methanol (50 mL) as a white solid (192 mg, 96%). 1H NMR (400 MHz, CDCl3): δ 1.22−1.53 (br, 4 H), 1.55−2.00 (br, 1 H), 2.56−2.78 (br, 2 H), 2.80−3.80 (br, 2 H), 3.02−3.48 (br, 4 H), 4.15−4.48 (br, 2 H), 5.22−5.56 (br, 2 H), 6.38−6.62 (br, 2 H), 7.78− 8.00 (br, 2 H). 13C NMR (100 MHz, CDCl3): δ 14.4, 35.7, 36.1, 44.5, 44.8, 46.4, 46.6, 46.8, 49.2, 49.4, 60.0, 111.4, 117.3, 126.0, 128.5, 131.2, 131.8, 150.8, 167.0. GPC (THF) Mn = 14 500, PDI = 1.1. Polymer 16a. To a solution of 9a (198 mg, 0.70 mmol) in DCM (20 mL) stirred under N2 atmosphere was added catalyst 12a (6.6 mg, 7.0 μmol) in DCM (2 mL). After stirring at room temperature for 2 h, benzaldehyde (400 μL, 4.0 μmol) was added and the mixture was stirred for an additional 1 h. The resulting solution was concentrated and the polymer was precipitated in MeOH (50 mL) as a white solid (135 mg, 68%). 1H NMR (400 MHz, CDCl3): δ 1.18−1.62 (br, 4 H), 1.80−2.10 (br, 1 H), 2.52−3.17 (br, 4 H), 3.20−3.46 (br, 4 H), 4.18− 4.41 (br, 2 H), 5.17−5.42 (br, 2 H), 6.30−6.62 (br, 2 H), 7.63−8.00 (br, 2 H). 13C NMR (CDCl3, 100 MHz): δ 14.9, 39.2, 40.4, 47.5, 49.4, 60.4, 111.4, 117.8, 131.4, 132.4, 150.8, 167.0. GPC (THF): Mn = 55 300, PDI = 1.3. Polymer 19. In a manner similar to that described above, treatment of 18 (100 mg, 0.14 mmol) with 12a (13.1 mg, 14.0 μmol) gave 19 as a yellow solid (50 mg, 50%). 1H NMR (400 MHz, CDCl3): δ 1.00−1.95 (br, 4 H), 2.23−3.60 (br, 16 H), 3.82−4.45 (br, 8 H), 4.62−5.67 (br, 8 H), 6.20−6.78 (br, 4 H), 7.58−8.22 (br, 4 H). 13C NMR (CDCl3, 100 MHz): δ 38.8, 40.9, 46.5, 49.6, 62.1, 69.0, 84.1, 111.5, 116.9, 131.3, 150.5, 166.4. GPC (THF): Mn = 11 500, PDI = 1.3. Polymer 21. In a manner similar to that described above, reaction of 20 (100 mg, 0.16 mmol) with 12a (15 mg, 16.0 μmol) afforded 21 as a white solid (56 mg, 56%). 1H NMR (400 MHz, CDCl3): δ 1.20− 1.60 (br, 2 H), 1.60−2.20 (br, 2H), 2.40−3.60 (br, 16 H), 4.80−5.80 (br, 8 H), 6.22−6.80 (br, 4 H), 7.20−7.45 (br, 4H), 7.60−8.20 (br, 4 H). 13C NMR (CDCl3, 100 MHz): δ 38.5, 40.7, 46.5, 49.6, 65.7, 111.5, 117.0, 127.9, 128.3, 131.4, 136.5, 150.9, 166.3. GPC (THF): Mn = 14 900, PDI = 1.2. Diimide Reduction of 16a. A solution of 16a (85 mg, 0.30 mmol) and p-tosylhydrazide (0.55g, 3.0 mmol) in PhCl (10 mL) was stirred under nitrogen at 120 °C for 4 h and filtered. The hot filtrate was poured into methanol (30 mL). The mixture was centrifuged to collect the precipitate, which was washed several times with methanol and dried under vacuum to yield 17b (72 mg, 85%) as a white solid. 1 H NMR (400 MHz, CDCl3): δ 0.80−1.03 (br, 1 H), 1.05−1.62 (br, 4 H), 1.82−2.10 (br, 3 H), 2.60−2.89 (br, 2 H), 3.10−3.45 (br, 4 H), 4.12−4.40 (br, 2H), 6.36−6.67 (br, 2 H), 7.65−8.00 (br, 2 H). 13C

Figure 2. STM images of 19 exhibiting submicrometer, long-range order array. Image size: (a) 80 × 80 nm; (b) 8 × 8 nm. Imaging conditions of Ebias and itunneling: (a) 0.90 V, 50 pA; (b) 0.90 V, 90 pA. (c) Polymer motif based on the structure of 19.

observation suggests weaker interactions of the cis polymer 19 with the substrate and between the terminal groups.

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CONCLUSIONS In summary, we have described the first synthesis of cis, isotactic polynorbornenes having fused endo-N-arylpyrrolidine moieties stereoselectively using a molybdenum-carbene catalyst with a polysubstituted bidendate biphenoxide ligand 12. The presence of endo-fused N-aryl heterocycle in monomeric norbornenes may play a pivotal role to direct the stereoselectivity of the ROMP of these norbornenes catalyzed by 12. The present results using molybdenum catalyst 12 complement to those of previous works employing ruthenium catalyst 8 on the ROMP of polynorbornenes fused with endo-N-arylpyrrolidine monomers 9a, 18, and 20.9,11 It is worth noting that morphology of ladderphanes with Z double bonds (e.g., 19 and 21) on HOPG behave similarly to those with E double bonds.11

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EXPERIMENTAL SECTION

General Information. Melting points were uncorrected. All 1H and 13C NMR spectra were recorded on a Varian 400 Unity Plus spectrometer (400 MHz) or a Bruker AV III 800 MHz FT-NMR spectrometer at ambient temperature using CDCl3 as solvent and TMS as the internal standard. The chemical shifts in 13C NMR spectra were calibrated using the peak of CDCl3 at δ 77.0 ppm as the reference. All air-sensitive manipulations were performed under nitrogen or in a drybox. All glassware was oven-dried and allowed to cool under vacuum or nitrogen before use. Dichloromethane (DCM) was purged with nitrogen, passed through activated alumina, and stored over molecular sieves in a nitrogen atmosphere. Benzaldehyde was distilled and stored under nitrogen. Catalyst 12 was prepared according to literature procedures.12 High resolution mass spectrometry was obtained by employing a Jeol-JMS-700 mass spectrometer using the FAB method with a 3-nitrobenzyl alcohol matrix. GPC was performed on a Waters GPC instrument equipped with Waters 1515 HPLC pump using Waters 2487 absorbance detector. THF was used as the eluent (flow rate =1.0 mL min−1). Waters Styragel HR2, HR3, HR4 columns (7.8 × 300 mm) were employed for determination of relative molecular weight with polystyrene standard (Mn values ranged from 375 to 3.5 × 106). Polymer (approximately 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 columns with oven temperature at 40 °C. Waters Empower HPLC/GPC network software was used for data analyses. Monomer 18. To a solution of 1,1′-bis(hydroxymethyl)ferrocene (261 mg, 1.0 mmol), DMAP (12 mg, 0.1 mmol), and Et3N (300 mg, 3.0 mmol) in DCM (10 mL) at 0 °C was added a solution of 9b (570 mg, 2.1 mmol) in DCM (20 mL). The mixture was gradually warmed to room temperature and stirred for 12 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 resulting solution was concentrated and 18 was precipitated in pentane (50 mL) as a yellow solid (518 mg, 72%): mp 170−172 °C. 1H NMR (400 MHz, CDCl3): δ 1.52 (d, J = 8.4 Hz, 8169

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NMR (100 MHz, CDCl3): δ 14.6, 31.0, 37.1, 41.7, 45.2, 48.6, 60.1, 111.4, 117.2, 131.0, 150.8, 166.8. GPC (THF): Mn = 55 600, PDI = 1.2. Diimide Reduction of 10a. In a manner similar to that described above, a mixture of 10a (54 mg, 0.19 mmol) and p-tosylhydrazide (0.55 g, 3.0 mmol) was converted to 17a (42 mg, 80%). 1H NMR (400 MHz, CDCl3): δ 0.81−1.05 (br, 1 H), 1.10−1.65 (br, 4 H), 1.78−2.20 (br, 3 H), 2.69−3.00 (br, 2 H), 3.02−3.48 (br, 4 H), 4.10− 4.46 (br, 2H), 6.32−6.70 (br, 2 H), 7.76−8.00 (br, 2 H). 13C NMR (100 MHz, CDCl3): δ 31.0, 37.1, 41.7, 45.2, 48.7, 60.1, 111.4, 117.2, 131.1, 150.8, 166.8. GPC (THF): Mn = 14 300, PDI = 1.1. Polymer 22. To a solution of 18 (50 mg, 0.07 mmol) in DCM (20 mL) stirred under N2 atmosphere was added 8 (3.7 mg, 7.0 μmol) in DCM (2 mL). The reaction mixture was stirred for 2 h at room temperature, ethyl vinyl ether (2 mL) was then added, and the mixture was stirred for 10 min. The resulting solution was concentrated and 22 was precipitated in Et2O (30 mL) as a yellow solid (48 mg, 95%). 1H NMR (400 MHz, CDCl3): δ 1.00−1.60 (br, 2 H), 1.61−2.15 (br, 2H), 2.40−3.55 (br, 16 H), 3.80−4.58 (br, 8H), 4.65−5.82 (br, 8 H), 6.21− 6.80 (br, 4 H), 7.65−8.20 (br, 4 H). 13C NMR (CDCl3, 100 MHz): δ 36.5, 37.6, 44.4, 44.8, 45.4, 45.7, 46.6, 47.5, 49.0, 49.7, 62.0, 68.9, 69.1, 111.4, 116.8, 131.2, 150.4, 150.7, 166.4. GPC (THF): Mn = 12 800, PDI = 1.3. Polymer 23. In a manner similar to that described above, 20 (50 mg, 0.08 mmol) was treated with 8 (6.7 mg, 8.0 μmol) to give 23 as a white solid (46 mg, 92%). 1H NMR (400 MHz, CDCl3): δ 1.20−1.60 (br, 2 H), 1.61−2.25 (br, 2H), 2.42−3.60 (br, 16 H), 4.82−5.80 (br, 8 H), 6.22−6.76 (br, 4 H), 7.15−7.56 (br, 4H), 7.62−8.15 (br, 4 H). 13 C NMR (CDCl3, 100 MHz): δ 36.6, 37.3, 44.1, 44.5, 45.1, 46.1, 49.5, 111.5, 117.1, 126.0, 128.0, 128.4, 128.6, 128.9, 131.4, 136.4, 150.9, 166.6. GPC (THF): Mn = 9600, PDI = 1.2. Ethanolysis of 19. Under N2 atmosphere, to a solution of 19 (50 mg, 0.07 mmol) in CHCl3 (20 mL) was added a solution of NaOEt (10 mmol) in EtOH (1 mL, 10 mol/L). After stirring at room temperature for 48 h, the mixture was poured into water (30 mL) and extracted with CHCl3 (20 mL × 3). The organic layer was washed with brine (30 mL × 2), dried (MgSO4) and filtered. The resulting solution was concentrated and 16b was precipitated upon addition to MeOH (30 mL) as a white solid (17 mg, 86%). 1H NMR (400 MHz, CDCl3): δ 1.10−1.52 (br, 4 H), 1.81−2.08 (br, 1 H), 2.50−3.18 (br, 4 H), 3.20−3.42 (br, 4 H), 4.15−4.42 (br, 2 H), 5.15−5.45 (br, 2 H), 6.35−6.65 (br, 2 H), 7.82−8.20 (br, 2 H). 13C NMR (CDCl3, 100 MHz): δ 14.9, 39.3, 40.4, 47.9, 49.7, 60.5, 111.7, 118.1, 131.4, 132.5, 150.7, 167.0. GPC (THF): Mn = 4500, PDI = 1.2. Ethanolysis of 21. In a manner similar to that described above, 21 (56 mg, 0.09 mmol) was ethanolized with NaOEt (10 mmol) to give 16c as a white solid (23 mg, 92%): GPC (THF) Mn = 7100, PDI = 1.2. Ethanolysis of 22. In a manner similar to that described above, ethanolysis of 22 (48 mg, 0.067 mmol) with NaOEt (10 mmol) afforded 10b as a white solid (15 mg, 78%). 1H NMR (400 MHz, CDCl3): 1H NMR (400 MHz, CDCl3) δ 1.00−1.58 (br, 4 H), 1.60− 2.10 (br, 1 H), 2.60−3.00 (br, 4 H), 3.05−3.45 (br, 4 H), 4.15−4.45 (br, 2 H), 5.20−5.56 (br, 2 H), 6.26−6.65 (br, 2 H), 7.65−8.00 (br, 2 H). 13C NMR (CDCl3, 100 MHz): δ 14.5, 35.8, 36.2, 44.6, 44.9, 46.5, 46.8, 49.5, 60.1, 111.4, 117.4, 126.0, 128.5, 131.2, 131.7, 150.8, 166.6. GPC (THF): Mn = 5700, PDI = 1.2. Ethanolysis of 23. In a manner similar to that described above, 23 (46 mg, 0.075 mmol) was treated with NaOEt (10 mmol) to yield 10c as a white solid (13 mg, 90%): GPC (THF) Mn = 4700, PDI = 1.2. STM Images of 19. 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, USA). Typical imaging conditions of bias voltage and tunneling current ranged from 0.50 to 0.9 V and from 30 to 100 pA, respectively. The samples for imaging were prepared by placing a 10-μL aliquot consisting of 19 in 1-phenyloctane on HOPG and subsequently being shear-aligned by removal excess solvent with a piece of tissue paper.11,14,16

Article

ASSOCIATED CONTENT

S Supporting Information *

1

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

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]; [email protected]; [email protected]. tw. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This work was supported by the National Science Council (Taipei), and National Taiwan University, and, in part, Shanghai Institute of Organic Chemistry (Shanghai).

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REFERENCES

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