Article
Macromolecules, Vol. 43, No. 7, 2010 3329
derived from the slope of ln P vs 1/T at constant hydrogen
loading using the Clausius-Clapeyron equation:
room temperature and diluted with CH2Cl2, and the filtered
mixture was washed with brine. The organic phase was collected
and dried over MgSO4. After filtration, solvent was removed to
yield the crude product which was then chromatographed on
silica using a hexane/CH2Cl2 (1:1) solvent mixture as the eluent
and gave 0.25 g (60%) yield. CI-MS: Calcd, 1325.5; found (M þ
1)þ, 1326.1. UV/vis (λmax, nm CH2Cl2 ꢀ 105 cm-1 M-1) 285.5
(1.16), 416.5 (1.20), 573.0 (0.121), 612.0 (0.07).
Synthesis of PTTPP (5) and P(Fe-TTPP) (6). Anhydrous
FeCl3 (0.8 g, 5 mmol) was charged into a round-bottom flask.
10 mL of anhydrous CHCl3 was added and stirred to make a
suspension solution. Then a solution of TTPP (0.25 g, 2 ꢀ 10-4
mol) or Fe-TTPP (0.26 g, 2 ꢀ 10-4 mol) in 20 mL of CHCl3 was
added dropwise. The resulting mixture was stirred at room tem-
perature overnight. After that, 200 mL of MeOH was added to the
above mixture and kept stirring for another hour. The precipita-
tion was collected by filtration and washed with MeOH. After
extraction with CH2Cl2, CHCl3, and MeOH/H2O (volume ratio
1:1) in a Soxhlet extractor for 24 h, the product was dried in
vacuum oven at 100 °C overnight. Yield was about 95%.
Hydrogen Isotherm Measurement for Reference Compounds.
Two adsorbent materials, AX-21 and Cu-BTC, which are well
studied in hydrogen storage application, were used as the
references for adsorption isotherm measurement. AX-21 is an
engineered active carbon, and Cu-BTC is a metal-organic
framework material. Their hydrogen adsorption isotherms are
documented in the literature.21-24 We repeated the hydrogen
adsorption of these materials using the identical procedure for
the polyporphyrin samples. The excess hydrogen adsorption
capacities as the function of pressure are plotted in Figure S7a,b
(Supporting Information). These results essentially duplicate
that of previously published. Most importantly, they demon-
strate saturation or nearly saturation at equilibrium pressure of
20-30 bar, which is strong contrast to that shown in Figure 3 for
polymer PTTPP and P(Fe-TTPP).
ꢀ
ꢁ
D ln P
Dð1=TÞ
ΔH ¼ -R
¼ -Rk
ð1Þ
nm
where ΔH is the heat of adsorption, R is ideal gas constant,
P and T are equilibrium pressure and temperature, respectively,
and k is the slop of ln P vs 1/T at constant hydrogen load-
ing nm.17
Synthesis of 3,5-Dibromobenzaldehyde (1). Briefly, a suspen-
sion of 1,3,5-tribromobenzene (4.0 g, 12.7 mmol) in anhydrous
diethyl ether (100 mL) at -78 °C was treated dropwise with
butyllithium (5.3 mL, 13.5 mmol). After 45 min dimethylform-
amide (2.8 g, 38.3 mmol) was added to the mixture, which was
then stirred for a further 1 h. Diluted HCl (40 mL, 2 mol/L) was
added, then organic phase was removed, and a brown solid was
obtained. The crude product was recrystallized from diethyl
ether/hexanes to give needles compound 1 (2.4 g, 70%). 1H
NMR: δ (CDCl3, ppm): 9.91, s, 1H, CHO, 7.94, (d, J = 1.6 Hz,
2H, Ar-H), 7.92, (t, J = 1.6 Hz, 1H, Ar-H), which is consisted
with reported result.9
Synthesis of 3,5-Dithiophen-2-yl-benzaldehyde (2). A 100 mL
round-bottom flask was charged with 3,5-dibromobenzalde-
hyde (1) (1.81 g, 6.85 mmol), tetrakis(triphenylphosphine)palla-
dium(0) (800 mg, 0.692 mmol), 2-(tributylstannyl)thiophene
(6.5 mL, 20.6 mmol), and anhydrous DMF (60 mL) and heated
to 80 °C with stirring for 72 h. The reaction mixture was then
cooled down to room temperature, diluted with Et2O, and fil-
tered through Celite. The organic phase was washed with brine
and water and dried over MgSO4. After filtration, solvent was
removed to yield the crude product which was then chromato-
graphed on silica using a hexane/CH2Cl2(2:1) solvent mixture as
the eluent. The desired product was a crystalline yellow solid
(1.10 g, yield 60%). 1H NMR: δ (CDCl3) 10.09 (1H, s, CHO),
8.06 (1H, t, J = 2.0 Hz, Ar-H), 8.00 (2H, d, J = 2.0 Hz, Ar-H),
7.37-7.15 (6H, m, thiophene-H). 13C NMR: δ (CDCl3) 191.9,
142.5, 137.7, 136.2, 128.8, 128.5, 126.2, 125.8, 124.6. CI-MS:
Calcd, 270.4; found (M þ 1)þ, 271.0. Anal. Calcd for C15H10S2:
C, 66.7%; H, 3.70%. Found: C, 67.6%; H, 3.41%.
Acknowledgment. This work was supported by the U.S.
Department of Energy’s Fuel Cell Technologies program under
the Office of Energy Efficiency and Renewable Energy. The authors
wish to thank GM and Air Products for providing the AX-21
sample, and thank Ms. Desiree White for experimental support.
Synthesis of 5,10,15,20-Tetrakis(3,5-dithiophen-2-ylphenyl)-
porphyrin TTPP (3). An oven-dried, three-necked, 1 L, round-
bottomed flask equipped with a magnetic stirring bar and a
gas-dispersion tube was charged with 3,5-dithiophen-2-yl-
benzaldehyde 2 (2.7 g, 0.01 mol), distilled pyrrole (0.7 mL, 0.01
mol), and dichloromethane (600 mL). The solution was purged
with nitrogen for 15 min. Boron trifluoride diethyl etherate (0.40
mL, 3.1 mmol) was added via syringe, and the flask was wrapped
with aluminum foil to shield it from light. The solution was
stirred under a nitrogen atmosphere at room temperature for 1.5
h, and 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) (1.7 g,
7.5 mmol) was added directly at one time and keep stirring for
another 1.5 h. Then 6 mL of triethylamine was added to neutralize
the excessive acid. Then concentrated the solvent and purified with
a column. The column was eluted with a mixture of hexane/
CH2Cl2 (1:1) and offered purple crystal-like solid (0.52 g, 20%).
1H NMR: δ (CDCl3, ppm): 9.04 (s, 8H, pyrrole-H), 8.43 (d, J =
1.6 Hz, 8H, Ar-H), 8.27 (t, J = 1.6 Hz, 4H, Ar-H), 7.57-7.3
(24H, m, thiophene-H), -2.67 (s, 2H). 13C NMR: δ (CDCl3)
143.8, 143.5, 133.7, 131.3, 128.4, 125.7, 124.4, 123.0, 119.6. It is not
easy to observe R and β carbon shift in pyrrole ring.18 UV/vis
(λmax, nm CH2Cl2 ꢀ 105 cm-1 M-1): 286.5 (1.37), 423.5 (3.54),
516.5 (0.256), 551.5 (0.106), 590.0 (0.091), 646.0 (0.0581). Anal.
Calcd for C76H46N4S8: C, 71.70%; H, 3.61%; N, 4.40%. Found:
C, 70.67%; H, 3.51%; N, 4.18%.
Supporting Information Available: Text giving 1H and 13
C
NMR, UV-vis spectra, and TGA graph of the related com-
pounds; hydrogen adsorption isotherms for an activated carbon
AX-21 and a MOF Cu-BTC measured with our modified Sievert
apparatus. This material is available free of charge via the
References and Notes
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Synthesis of Fe-TTPP (4). Fe(II) porphyrin complex was syn-
thesized according to the literature.19,20 Briefly, porphyrin TTPP
(3) (0.4 g, 3 ꢀ 10-4 mol) was dissolved in 60 cm3 DMF and
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FeCl2 4H2O (0.6 g, 3 mmol) was added to this mixture and
3
boiled for 1 h. The reaction mixture was then cooled down to