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2a, and other common reagents were from Aldrich. Compound
1b was prepared as described previously.[11] NMR spectra were
recorded on a Jeol EX270 instrument, EPR spectra on Jeol RE1X
or Bruker ESP300 spectrometers, UV-vis spectra on a Hitachi
U-3000 spectrometer, and MS spectra on a VG Autospec spec-
trometer. Simulations of the EPR spectra were performed using
the WinSim free software. Typical settings used for the EPR
measurements follows: concentration of the sample 10−4 M,
number of scans 1, centre field 3360 G, sweep field 100 G, fre-
quency 9.42 GHz, power 1 mW, sweep time 60 s, time constant
0.1 s, modulation frequency 100 kHz, gain 100, and modulation
width 1 G. Variable-temperature (2–300 K) magnetic suscepti-
bilitymeasurementswerecarriedoutonpolycrystallinesamples,
using a Quantum Design MPMS-XL SQUID magnetometer
operated at a 5 kG magnetic field. Diamagnetic corrections for
thecompoundswereestimatedfromPascal’sconstants, andmag-
netic data were corrected for diamagnetic contributions of the
sample holder. All J values quoted in this paper are based on
the 2J formalism (H = −2JꢀSiSj), with a positive J imply-
ing a ferromagnetic interaction. Where necessary, values from
the literature have been converted into third formalism for
consistency.
(s, 1H, picryl CH), 8.51 (s, 1H, picryl CH), 7.31–6.77 (m, 9H,
phenyl). δC (CD2Cl2) 154.84, 146.77, 142.21, 139.56, 129.19,
124.94, 124.33, 117.98, 116.48. λmax/nm 327. In a basic medium
(dichloromethane and ammonia in methanol) the corresponding
anion 5a− was obtained, with λmax/nm 412.
Compound 5b. RF (silica/dichloromethane) 0.083. m/z 390
(C19H13N5O5, M 391). δH (CD2Cl2) 9.86 (s, 2H, NH, OH), 8.58
(s, 1H, CH–NO2), 7.87 (s, 1H, CH–NO2), 7.29–6.75 (m, 9H,
phenyl). δC (CD2Cl2) 155.02, 146.84, 141.03, 139.30, 128.97,
124.97, 123.99, 117.68, 116.37, 116.56, 100.60. λmax/nm 380.
In a basic medium (dichloromethane and ammonia in methanol)
the corresponding anion 5b− was obtained, with λmax/nm 413.
General Procedure for Obtaining Compounds 6
A mixture of 5a or 5b (0.2 mmol) and 4-carboxy-TEMPO
(0.22 mmol) dissolved in dichloromethane (50 mL) was treated
with DCC (0.25 mmol) and DMAP (20 mg), and the mix-
ture was left overnight. The dichloromethane solution was
washed sequentially with 0.1 N aqueous hydrochloric acid,
aqueous sodium hydrogen carbonate, and water, and then the
organic layer was dried over anhydrous sodium sulfate. Removal
of dichloromethane afforded the crude compounds 6, which
were purified by chromatography on silica. The overall yield
was ∼70%.
General Procedure for Obtaining Compounds 4
Compound 1a or 2a (1 mmol) dissolved in dichloromethane
(40 mL) was stirred overnight with a slurry formed from ceric
sulfate (20 g) and water (10 mL). The organic phase was then
separated, dried over anhydrous sodium sulfate, and the sol-
vent was removed under vacuum. The residue was dissolved in
dichloromethane and chromatographed on a silica column (or on
preparativeTLC plates), using 9:1 dichloromethane/ether as elu-
ent, to yield the pure compound 4a as a dark solid (after removal
of the solvent). Starting from 1b (or 2b), the 4b derivative was
obtained. The final yield was around 90%.
Compound 6a. RF (silica/dichloromethane) 0.155. m/z 592
(C28H29N6O9, M 593). λmax/nm 312. In a basic medium
(dichloromethane and ammonia in methanol) the correspond-
ing anion 6a− was obtained, with λmax/nm 428. EPR (toluene):
aN 15.39 G, g 2.0057.
Compound 6b. RF (silica/dichloromethane) 0.107. m/z 572
(C29H29N6O7, M 573). λmax/nm 365. In a basic medium
(dichloromethane and ammonia in methanol) the correspond-
ing anion 6b− was obtained, with λmax/nm 375. EPR (toluene):
aN 15.37 G, g 2.0057.
Compound 4a. RF (silica/dichloromethane) 0.190. m/z 409
(C18H11N5O7, M 409). δH (CD2Cl2) 8.62 (s, 2H, picryl CH),
8.03 (dd, 1H, J 13.1, 6.0, quinone CH), 7.55–7.37 (m, 5H,
phenyl), 6.93 (dd, 1H, J 12.2, 4.0, quinone CH), 6.67 (dd, 1H,
J 13.1, 6.0, quinone CH), 6.36 (dd, 1H, J 12.2, 4.0, quinone CH).
δC (CD2Cl2) 144.01, 139.54, 133.15, 132.29, 130.67, 129.95,
129.60, 129.13, 127.25, 124.66. λmax/nm 537.
Compound 4b. RF (silica/dichloromethane) 0.119. m/z 389
(C19H11N5O5, M 389). δH (CD2Cl2) 8.00 (dd, 1H, J 12.1,
2.4, quinone CH), 7.55–7.35 (m, 5H, phenyl), 6.90 (dd, 1H,
J 12.1, 2.4, quinone CH), 6.64 (d, 1H, J 10.0, quinone CH),
6.33 (d, 1H, J 10.0, quinone CH). δC (CD2Cl2) 143.09, 132.02,
131.89, 130.56, 129.81, 129.58, 128.58, 128.54, 127.13, 115.44.
λmax/nm 526.
General Procedure for Obtaining Compounds 7
Compound 6a or 6b (20 mg) dissolved in dichloromethane
(20 mL) was stirred with 2.0 g of lead dioxide or potassium per-
manganate for 2 h.The solution was then filtered, and the solvent
removed under vacuum. The yield was almost quantitative, and
an analytical sample was obtained by preparative TLC on silica.
Compound 7a. RF (silica/dichloromethane) 0.190. m/z 592
(C28H28N6O9, M 592). λmax/nm 530. EPR (toluene): aN 15.42/
12.29/4.07 G, g 2.0039/2.0057.
Compound 7b. RF (silica/dichloromethane) 0.107. m/z 572
(C29H28N6O7, M 572). λmax/nm 635. EPR (toluene): aN 15.38/
12.15/3.97 G, g 2.0039/2.0057.
General Procedure for Obtaining Compounds 5
General Procedure for Obtaining Compounds 8
Compound 4a or 4b (100 mg) dissolved in dichloromethane
(50 mL) was stirred with a 5% aqueous solution of sodium
ascorbate (50 mL) till the colour changed from red to yellow
(depending on the stirring rate, this took from minutes to hours).
The organic phase was then separated, dried over anhydrous
sodium sulfate, and the solvent was removed under vacuum to
yield 5a (or 5b) as a yellow solid. The yield was almost quanti-
tative and the purity of the compounds was adequate for further
reactions. Analytically pure samples were obtained by column
chromatography (or preparative TLC) on silica.
Compounds 8a,b were obtained in the same manner as 6a,b,
using 2,2-diphenyl-1-(2,6-dinitro-4-benzoic acid)hydrazine
instead of 4-carboxy-TEMPO.
Compound 8a. RF (silica/dichloromethane) 0.592. m/z 786
(C37H25N9O12, M 787). δH (CDCl3) 10.17 (s, 1H, NH), 9.40
(s, 1H, NH), 9.07 (s, 1H, CH–NO2), 8.97 (s, 1H, CH–NO2), 8.49
(s, 1H, CH–NO2), 8.37 (s, 1H, CH–NO2), 7.38–7.11 (m, 19H,
phenyl). δC (CDCl3) 161.47, 147.36, 146.09, 145.51, 144.23,
143.99, 141.77, 141.37, 136.46, 129.71, 129.36, 128.80, 126.34,
125.42, 122.25, 121.03, 120.92, 120.34, 118.35. λmax/nm 392.
In a basic medium (dichloromethane and ammonia in methanol)
the corresponding anion 8a− was obtained, with λmax/nm 410.
Compound 5a. RF (silica/dichloromethane) 0.131. m/z 410
(C18H13N5O7, M 411). δH (CD2Cl2) 9.98 (s, 2H, NH, OH), 9.17