1
in an ice bath. Keeping this temperature constant, a solution of
43 g NH4Cl in 150 mL H2O was added dropwise under vigorous
(mechanical) stirring. After addition was completed (ca. 2.5 h)
the reaction was stirred for 1.5 h at the same temperature, and an
additional 0.5 h at room temperature. The white-gray precipitate
of Zn slurry was filtered off and washed with THF (4 ꢂ 20 mL).
The filtrate was evaporated to a viscous residue, and cooled
affording pyrene aldehyde 5 in 63% yield. H NMR ((CD3)2SO,
250 MHz, 298 K, 16 scan), d ppm: 7.98 (d, 1H, Hpyrazole), 8.16–
8.5 (m, 9H, Ar–H), 9.14 (s, 1H, Hpyrazole), 10.05 (s, 1H, –CHO).
13C NMR ((CD3)2SO, 63 MHz, 298 K, 8690 scan), d ppm: 121.5,
123.9, 124.1, 125, 125.1, 125.3, 126, 126.4, 128.6, 129.2, 130.1,
130.7, 137.9, 141. UV-Vis (CHCl3): l/nm (3/Mꢁ1 cmꢁ1) 345
(8247). FAB+ m/z 295.9 [M]+.
ꢀ
to ꢁ15 C (the mixture was kept in the freezer for 1 h). After
cooling, the flask was filled with argon and a mixture of 50 g
Na2CO3 and 30 g NaCl salts was added at once. The flask was
shaken for 15 min, and after homogenization the white solid was
charged into a Soxhlet apparatus, protected from air (argon
balloon) and extracted with 300 mL dichloromethane (72 h). The
resulting white precipitate was filtered off, washed with
dichloromethane (2 ꢂ 15 mL) and hexane (2 ꢂ 10 mL) and dried
in air. The yield is 6.1 g (42%). Mp 160–161 ꢀC. IR (powder,
n/cmꢁ1): 3257 (vs and broad, nOH), 2987 (vs, nC–H), 1479–1374 (vs,
several bands), 1261 (s), 1178 (vs), 1145 (vs), 1080 (s), 1035 (vs),
989 (m), 952 (vs), 904 (vs), 852 (m), 790 (m), 690 (m).
1-[4-(1-Oxyl-3-oxo-4,4,5,5-tetramethylimidazolidin-2-yl)-
pyrazole]-pyrene 1
A suspension of BHA (0.125 g, 0.84 mmol) and 4-formyl-1-
pyrenepyrazole 5 (0.19 g, 0.63 mmol) in toluene (13 mL) was
carefully deaerated using argon bubbling for ꢃ20 to 25 minutes.
The flask was equipped with a condenser topped with an argon
balloon, and moved into an oil bath. The mixture was heated
under argon near reflux for 18 h. The progress of the reaction was
monitored by TLC (SiO2, hexane/ethyl acetate or dichloro-
methane with 5% of methanol). After the process was completed,
the flask was cooled to room temperature and the precipitate
(white or yellowish) was filtered off, washed with toluene (2 ꢂ
10 mL) and heptane (10 mL) and dried in air. The so-obtained
imidazolidine 6 was utilized in an oxidation reaction with sodium
periodate without additional purification. Thus, a suspension of
4,4,5,5-tetramethylimidazolidine-1,3-diol 6 (1 mmol) in H2O–
CH2Cl2 (1 : 2) mixture (ꢃ50 mL) was cooled down to 0–5 ꢀC (to
avoid over oxidation and formation of the imino nitroxide
species) using an ice bath. To that mixture NaIO4 5% aqueous
solution (0.8 eq.) was added dropwise. The progress of the
reaction was monitored by TLC (SiO2, hexane/ethyl acetate or
dichloromethane with 5% of methanol). After the reaction was
complete (0.5–3 h), the dark-blue organic layer was separated.
The water phase was extracted with dichloromethane (3 ꢂ 25
mL). The combined organic extracts were then washed with
water (2 ꢂ 30 mL) and brine (50 mL), and dried over MgSO4 (or
Na2SO4). The residue after filtration was concentrated to a small
volume. Purification on silica gel (hexane–ethyl acetate, 1 : 1)
afforded the dark-blue crystals of the radical 1 in 26% (70 mg)
overall yield. Mp 212–213 ꢀC. UV-Vis (toluene): l/nm (3/Mꢁ1
cmꢁ1) 654 (1020), 598 (1010), 346 (38 700). IR (powder; n/cmꢁ1):
3120, 3055, 2998, 2978, 2939 (m, nC–H), 1596 (s, nAr), 1515 (s),
1480 (m), 1461 (m), 1449 (s), 1422 (s), 1370 (s, nmethyl), 1353 (vs,
nNO), 1330 (m), 1311 (s) (pyrazolyl-moiety), 1212 (s), 1177 (s),
848 (vs, nAr). FAB+ m/z 421.9 [M]+. (Calc. for C26H23N4O2: C,
73.74; H, 5.47; N, 13.23. Found: C, 73.5; H, 5.38; N, 13.04%.)
1-Pyrazole-pyrene 4
Solid CuI (0.2 mmol), Cs2CO3 (2.0 mmol), pyrazole (1.4 mmol)
and 1-bromo-pyrene 3 (1.0 mmol) were transferred into a flame-
dried flask. Dry dimethylformamide (6 mL) was added, and the
resulting viscous mixture was deaerated using argon for 25
minutes. The mixture was heated to 120 ꢀC for 40 h under argon.
After the reaction was completed (monitored by TLC on Al2O3),
the mixture was cooled to ambient temperature, diluted with
2–3 mL ethyl acetate, filtered through a plug of silica gel, which
was then washed with 20 mL ethyl acetate. The combined
organic extracts were concentrated on a rotary evaporator to
a small volume, and the resulting residue was purified on silica
gel using a hexane–ethyl acetate gradient solvent mixture
(100 : 0, 95 : 5, 90 : 10). Pyrene–pyrazole 4 was collected as
a light yellow solid in 75% yield. Mp 96–97 ꢀC. 1H NMR (CDCl3,
250 MHz, 298 K, 16 scan), d ppm: 6.61 (t, 1H, Hpyrazole), 7.91 (d,
1H, Hpyrazole), 8.0–8.24 (m, 9H, Ar–H), 9.0 (s, 1H, ArH). 13C
NMR (CDCl3, 63 MHz, 298 K, 256 scan), d ppm: 106.8, 122.1,
123.6, 124.4, 124.8, 125.3, 125.6, 125.9, 126.2, 126.5, 127.1, 128.2,
128.88, 128.9, 131.2, 131.3, 132.1, 141.1. IR (powder, n/cmꢁ1):
3141, 3123, 3095 (w, nC–H, aromatic), 3043, 2954, 2920, 2847
(m, nC–H), 1598 (m, nAr), 1516 (vs), 1488 (m), 1460 (m), 1394
(vs, nmethyl), 1336, 1307 (m, pyrazolyl moiety), 835 (vs, nAr). FAB+
m/z 268.9 [M + H]+.
1-(4-Formyl-pyrazole)-pyrene 5
1-[4-(1-Oxyl-4,4,5,5-tetramethylimidazolidin-2-yl)-pyrazole]-
pyrene 2
Phosphorus oxychloride (1.4 mL, d ¼ 1.645 g mLꢁ1, 15 mmol,
0.7 eq.) was added dropwise under vigorous stirring to dry
dimethylformamide (1.6 mL, 20.7 mmol, 1 eq.) in a flame-dried
flask equipped with a rubber septum, the temperature being
kept at ꢃ0 to 5 ꢀC using an ice bath. 1-Pyrenepyrazole 4 (0.55 g,
2.07 mmol, 0.1 eq.) in dimethylformamide (2.6 mL) was then
slowly added with stirring, while maintaining a temperature of
20–30 ꢀC. The resulting mixture was heated at 110 ꢀC for 3.5 h,
cooled to room temperature and then poured on crushed ice. The
resulting solution was treated with 20% sodium hydroxide. The
yellow precipitate was filtered off, washed with water and dried,
MnO2 (14 mmol) was added to a magnetically stirred solution of
the imidazolidine 6 (1 mmol), prepared as described above. After
ꢃ35 minutes stirring at room temperature the oxidant was
removed by filtration and washed carefully with small portions of
ethyl acetate. The filtrate was diluted with toluene (12 mL) and
concentrated to a volume of ca. 2 mL in vacuo. The residue was
placed on a column wetted with toluene, and eluted with hexane–
ethyl acetate (1 : 1). The described procedure afforded radical 2
as red needle crystals in 35% (0.180 g) overall yield. Mp 230–
232 ꢀC. UV-Vis (toluene): l/nm (3/Mꢁ1 cmꢁ1) 467 (800), 444
13266 | J. Mater. Chem., 2012, 22, 13260–13267
This journal is ª The Royal Society of Chemistry 2012