Supplementary MaterialSelvanathan et al.
Formation and manipulation of discrete supramolecular
azobenzene assemblies
SofiaSelvanathan1, Maike V. Peters2, Jutta Schwarz,2 Stefan Hecht2*, Leonhard Grill1*
1) Institut für Experimentalphysik, Freie Universität Berlin, 14195 Berlin, Germany
2) Department of Chemistry, Humboldt-Universität zu Berlin, 12489 Berlin, Germany
Table of Contents
Synthesis of transDBDCAS 2
Transcis isomerization of DBDCA in solutionS 5
Synthesis of trans DBDCA
Figure 1.Synthesis of trans 3,5-di-tert-butyl-3’,5’-dicarboxylazobenzene 7 (DBDCA).
N-tert-Butoxycarbonyl-N-(3,5-di-tert-butylphenyl)hydrazine2. Compound 2 was synthesized utilizing a procedure developed by Wolter et al.[[1]] 3,5-Di-tert-butyl-iodobenzene 1 (1.43g, 8.25mmol), tert-butyl-carbazate (1.32g, 10mmol), CuI (22mg, 0.12mmol), 1,10-phenanthroline (170mg, 0.9mmol), Cs2CO3 (3.72g, 11.5mmol), and 8.5mL of dry DMF were mixed in a dry Schlenck tube and heated at 80°C for 23h. After cooling to room temperature, the solvent was evaporated and the crude mixture was purified by column chromatography (silica gel, gradient Hex/EA, 7/1 → 5/1) to obtain 1.30g of the product as a yellow oil, which slowly solidified upon standing (49% yield). Rf(Hexanes (Hex)/ethyl acetate (EA), 5/1) = 0.16. 1H-NMR (CDCl3, 400 MHz): (ppm) = 7.31 (d, 2H, 4J = 1.5 Hz, Ar-H), 7.16 (t, 1H, 4J = 1.5 Hz, Ar-H) 1.48 (s, 9H, t-Bu-H), 1.30 (s, 18H, t-Bu-H). 13C-NMR (CDCl3, 74.5 MHz): (ppm) = 150.9, 119.3, 118.7, 81.8, 35.3, 31.8, 28.8. MS (EI, 45 °C): m/z = 320 ([M]+), 262 ([M - C(CH3)3]+), 220 ([M - CO2C(CH3)3]). HRMS (ESI pos.): m/z = 343.23551, (calc. 343.23559 for C19H32N2O2Na).
Dimethyl 5-bromoisophthalate4. 5-Bromoisophthalic acid 3 (0.212g, 0.869mmol) was dissolved in 30mL of methanol and a few drops of conc. H2SO4 were added. The solution was refluxed for 24h and neutralized with solid NaHCO3. The solvent was evaporated and the residue was dissolved in diethyl ether. The organic phase was washed with water and dried with MgSO4 yielding 0.223g of the product as a white solid (94% yield). Rf (CH2Cl2) = 0.7. 13C-NMR (CDCl3, 74.5 MHz): (ppm) = 165.0, 136.7, 132.3, 129.3, 122.6, 52.7. Additional analytical data agree with the literature.[[2]]
N-tert-Butoxycarbonyl-N-(3,5-di-tert-butylphenyl)-N’-(3’,5’-dimethoxycarbonyl)hydrazine5. Adopting theproceduredevelopedby Lim et al.,[[3]] dimethyl 5-bromoisophthalate 4 (0.2g, 0.732mmol) was dissolved in 6mL of toluene in a sealed tube and N-tert-butoxycarbonyl-N-(3,5-di-tert-butylphenyl)hydrazine3 (0.23g, 0.723mmol), Cs2CO3 (125mg, 0.383mmol), Pd(OAc)2 (9mg, 0.035mmol), and t-Bu3P (50L of 10wt% solution in toluene, 0.023mmol) were added. The reaction mixture was heated at 110°C for 4h and was then allowed to cool to room temperature.The reaction mixture was filtered through Celite® and the solvent was evaporated. After column chromatography (silica gel, petroleum ether (PE)/EA 6/1) 215mg of the product were obtained as a yellowish solid (58% yield). Rf (PE/EA = 8/1) = 0.3. 1H-NMR(CDCl3): (ppm) = 8.21 (t, 1H, 4J=1.4 Hz, Ar-H), 7.71 (d, 2H, 4J=1.4 Hz, Ar-H), 7.33 (d, 2H, 4J=1.4 Hz, Ar-H), 7.22 (t, 1H, 4J=1.7 Hz, Ar-H), 6.71 (s, 1H, N-H), 3.90 (s, 3H, -OCH3), 1.41 (s, 9H, t-Bu), 1.31 (s, 18H, t-Bu). 13C-NMR (CDCl3): (ppm) = 166.2, 154.1, 151.0, 149.1, 141.7, 131.5, 123.1, 119.4, 118.0, 117.4, 82.5, 52.3, 34.9, 31.4, 28.2. MS (EI, 75-95°C) m/z = 512 ([M]+), 220. HRMS (ESI pos): m/z = 512.28861 (calculated 512.28864 for C29H40N2O6).
Trans 3,5-di-tert-butyl-3’,5’-dimethoxycarbonylazobenzene6. Adopting a procedure developed by Lim et al.,[3]N-tert-butoxycarbonyl-N-(3,5-di-tert-butylphenyl)-N’-(3’,5’-dimethoxycarbonyl)hydrazine5 (0.22g, 0.427mmol) was dissolved in 10mL of methylene chloride and cooled to 0°C. Pyridine (41mg, 0.51mmol) and N-bromosuccinimide (92mg, 0.51mmol) were added and the solution was stirred at room temperature for 30min. After evaporation of the solvent, followed by column chromatography (silica gel, PE/EA 8/1) 100mg of the product were obtained as an orange solid (57% yield). Rf (PE/EA = 8/1) = 0.64. 1H-NMR (CDCl3): (ppm) = 8.78 (t, 1H, 4J=1.6 Hz, Ar-H), 8.75 (d, 2H, 4J=1.6 Hz, Ar-H), 7.85 (d, 2H, 4J = 1.6 Hz, Ar-H), 7.62 (t, 1H, 4J = 1.8 Hz, Ar-H), 4.00 (s, 6H, -OCH3), 1.41 (s, 18H, t-Bu). 13C-NMR (CDCl3): (ppm) = 165.6, 152.7, 152.0, 151.8, 131.7, 131.4, 127.5, 126.0, 117.5, 52.3, 34.9, 31.2. MS (EI, 40-95°C) m/z = 410 ([M]+), 189. HRMS (ESI pos): m/z = 410.22051 (calculated 410.22056 for C24H30N2O4).
Trans 3,5-di-tert-butyl-3’,5’-dicarboxylazobenzene (DBDCA) 7. Diester 6 (70mg, 0.17mmol) was dissolved in THF and 0.1g (2.5mmol) of NaOH in 1mL of water were added. After stirring at room temperature for 1h the THF was evaporated and the product extracted with diethyl ether. The aqueous phase was acidified with HCl and extracted with methylene chloride. The organic phases were dried over MgSO4 and the solvent evaporated to yield 57mg of the desired product as an orange solid (88% yield). Rf (CH2Cl2/MeOH = 10/1) = 0.78. 1H-NMR (DMSO): (ppm) = 8.59 (m, 3H, Ar-H), 7.82 (d, 2H, 4J=1.7 Hz, Ar-H), 7.66 (t, 1H, 4J=1.7 Hz, Ar-H), 3.36 (bs, 2H, -COOH), 1.36 (s, 18H, t-Bu). 13C-NMR (DMSO): (ppm) = 175.5, 161.6, 136.4, 135.9, 127.0, 44.3, 40.6. MS (EI, 205°C) m/z = 382 ([M]+), 189. HRMS (ESI pos): 382.18928 (calculated 382.18926 for C22H26N2O4).
Transcis isomerization of DBDCA in solution
Irradiation of solutions of transDBDCA 7 in chloroform/methanol 10/1 using a 1000 W medium-pressure xenon lamp (XBO) equipped with an optical filter (maxT=364nm@26%T, FWHM=26nm) induced transcis isomerization as conveniently monitored by UV/vis absorption spectroscopy. Cistrans isomerization could be induced either thermally or photochemically by using an appropriate optical cutoff filter (T400nm). The rate constants of the thermal cistrans isomerization at different temperatures were obtained by plotting –ln[cis 7] calculated from UV/vis spectra versus time thereby allowing to determine the activation parameters by plotting ln(k/T) versus 1/T (van’t Hoff plot). Details are summarized in Figure 2 on page S 6.
Figure 1.Top right:UV/vis-spectra of trans7 (λmax()=335 nm (27500 M-1cm-1)) and cis7 (λmax()=295 nm (5700 M-1cm-1)) in acetonitrile/methanol 10/1. The spectrum of cis7 was calculated from the UV/vis spectra of both pure trans7 and the cis:trans mixture at the photostationary state, for which the cis:trans ratio was determined by HPLC separation. Bottom left: Photochemical transcis isomerization (exc=364nm) of 7 in acetonitrile/methanol 10/1. Bottom right: van’t Hoff plot and resulting activation parameters for thermal cistrans isomerization of 7 in acetonitrile/methanol 10/1.
S 1 of S 6
[[1]]Wolter, M.; Klapars, A.; Buchwald, S. L. Org. Lett. 3, 3803 (2001).
[[2]]Sherrod, S. A.; Da Costa, R. L.; Barnes, R. A.; Boekelheide, V. J. Am. Chem. Soc. 96, 1565 (1974).
[[3]]Lim, Y.-K.; Lee, K.-S. Org. Lett.5, 979 (2003).