Anthracene derivatives and the corresponding dimers with TEMPO radicals

Article abstract of DOI:10.1021/jo010943u

Anthracene derivatives with several TEMPO radicals (2-4, 10) were prepared, and each photodimerization reaction was investigated. Although the photodimerization was unsuccessful in obtaining the dimers of anthracenes 2 and 3, which could be alternatively prepared in a stepwise manner, the photodimers of anthracenes 4 and 10 were available by the direct photoreaction. The dissociation reaction of the dimers proceeded well by heating them in solution to give the corresponding monomers in each case, and thus the reversible system could be constructed in the latter two systems. While no large difference was observed in their magnetic behaviors between the monomer/dimer pair of 4 and 8, an intriguing difference was found in the magnetic behaviors for the pair of 10 and 11 from ferromagnetic interactions in 10 to the variable magnetic interactions in 11 depending on the solvent molecules incorporated in the crystals.

Full text of DOI:10.1021/jo010943u

916
J . Org. Chem. 2002, 67, 916-921
An th r a cen e Der iva tives a n d th e Cor r esp on d in g Dim er s w ith
TEMP O Ra d ica ls
Shin’ichi Nakatsuji,* Takeo Ojima, Hiroki Akutsu, and J un-ichi Yamada
Department of Material Science, Faculty of Science, Himeji Institute of Technology, 3-2-1 Kouto,
Kamigori, Hyogo 678-1297, J apan
nakatuji@sci.himeji-tec.ac.jp
Received September 24, 2001
Anthracene derivatives with several TEMPO radicals (2-4, 10) were prepared, and each
photodimerization reaction was investigated. Although the photodimerization was unsuccessful in
obtaining the dimers of anthracenes 2 and 3, which could be alternatively prepared in a stepwise
manner, the photodimers of anthracenes 4 and 10 were available by the direct photoreaction. The
dissociation reaction of the dimers proceeded well by heating them in solution to give the
corresponding monomers in each case, and thus the reversible system could be constructed in the
latter two systems. While no large difference was observed in their magnetic behaviors between
the monomer/dimer pair of 4 and 8, an intriguing difference was found in the magnetic behaviors
for the pair of 10 and 11 from ferromagnetic interactions in 10 to the variable magnetic interactions
in 11 depending on the solvent molecules incorporated in the crystals.
In tr od u ction
ing multifunctional spin systems with conductivity,7
liquid crystalline properties,8 or photofunctionality9 by
using stable radicals, especially aminoxyl radicals as spin
sources. For the photoresponsive spin systems, we pre-
pared first norbornadine/quadricyclane as well as spiro-
pyran/merocyanine systems and their magnetic behaviors
were based on the intramolecular structural change.
Among them, the switching behavior of solid-state mag-
netic properties was observed in a couple of spiropyran/
merocyanine spin systems from ferromagnetic to anti-
ferromagnetic spin-spin interactions and vice versa.
Anthracenes are known to dimerize photochemically
in solution and/or in the solid state,10 and the chro-
mophoric system is therefore a promising system for
investigating the change of magnetic properties in a spin
system by their structural change upon irradiation. We
then planned and initiated preparations of anthacene
derivatives carrying some spin centers. In this paper, we
report the preparation, structures, and properties, espe-
cially magnetic properties, of several anthracene deriva-
tives carrying TEMPO (2,2,6,6-tetramethyl-1-piperi-
dinyloxy) radical substituents as a spin source together
with the corresponding photodimers.11 In this case, we
deal with intermolecular structural change being different
Considerable interest is now focused on the develop-
ment of multifunctional spin systems with synergetic
properties, and successful studies have recently been
carried out toward the photofunctional magnetic materi-
als derived from some inorganic1 as well as organome-
tallic compounds.2 With regard to organic photorespon-
sive spin systems, Iwamura, Matsuda, et al. reported in
1998 an azobenzene derivative carrying two nitronyl
nitroxide radicals and observed its UV as well as EPR
spectral change upon irradiation in solution.3 Quite
recently, Matsuda and Irie have succeeded in developing
a fascinating series of diarylethene derivatives carrying
two nitronyl nitroxides in which a switching behavior of
the intramolecular magnetic interactions has been found
to occur efficiently by irradiation.4 A photoinduced trans
to cis isomerization was reported recently by Veciana et
al. to form a dimerized ferrocene derivative with a Schiff
base bridged trityl radical unit in which dimerization is
proposed to be favored by the hydrogen bond formation.5
In the course of our studies to develop novel organo-
magnetic materials,6 we have been interested in prepar-
(1) (a) Sato, O.; Iyoda, T.; Fujishima, A.; Hashimoto, K. Science 1996,
272, 704. (b) Gu, Z.-Z.; Sato, O.; Iyoda, T.; Hashimoto, K.; Fujishima,
A. J . Phys. Chem. 1996, 100, 18290.
(2) Nagai, K.; Iyoda, T.; Fujishima, A.; Hashimoto, K. Solid State
Commun. 1997, 102, 809.
(3) Hamachi, K.; Matsuda, K.; Itoh, T.; Iwamura, H. Bull. Chem.
Soc. J pn. 1998, 71, 2937.
(4) (a) Matsuda, K.; Irie, M. Chem. Lett. 2000, 16. (b) Matsuda, K.;
Irie, M. Tetrahedron Lett. 2001, 41, 2577. (c) Matsuda, K.; Irie, M. J .
Am. Chem. Soc. 2000, 122, 7195. (d) Matsuda, K.; Irie, M. J . Am. Chem.
Soc. 2000, 122, 8309. (e) Matsuda, K.; Matsuo, M.; Irie, M. Chem. Lett.
2001, 436. (f) Matsuda, K.; Irie, M. Chem. Eur. J . 2001, 7, 3466.
(5) Ratera, I.; Ruiz-Molina, D.; Vidal-Gancedo, J .; Wurst, K.; Daro,
N.; Le´tard, J .-F.; Rivira, C.; Veciana, J . Angew. Chem., Int. Ed. 2001,
40, 919.
(6) Cf. (a) Natatsuji, S.; Anzai, H. J . Mater. Chem. 1997, 7, 2161.
(b) Nakatsuji, S. Adv. Mater. 2001, 13, 1719. (c) Nakatsuji, S. In Recent
Research Developments in Organic & Bioorganic Chemistry; Pandalai,
S. G., Ed.; Transworld Research Network: Trivandrum, 2001, in press;
Vol. 4.
(7) (a) Nakatsuji, S.; Mizumoto, M.; Takai, A.; Akutsu, H.; Yamada,
J .; Schmitt, S.; Hafner, K. Mol. Cryst. Liq. Cryst. 2000, 348, 1. (b)
Akutsu, H.; Yamada, J .; Nakatsuji, S. Chem. Lett. 2001, 208. (c)
Akutsu, H.; Yamada, J .; Nakatsuji, S. Synth. Met. 2001, 120, 871.
(8) (a) Nakatsuji, S.; Mizumoto, M.; Kitamura, K.; Akutsu, H.;
Yamada, J . Mol. Cryst. Liq. Cryst. 2001, 356, 33. (b) Mizumoto, M.;
Ikemoto, H.; Akutsu, H.; Yamada, J .; Nakatsuji, S. Mol. Cryst. Liq.
Cryst. 2001, 363, 149. (c) Ikemoto, H.; Akutsu, H.; Yamada, J .;
Nakatsuji, S. Tetrahedron Lett. 2001, 42, 6873.
(9) (a) Takeuchi, S.; Ogawa, Y.; Naito, A.; Sudo, K.; Yasuoka, N.;
Akutsu, H.; Yamada, J .; Nakatsuji, S. Mol. Cryst. Liq. Cryst. 2000,
345, 167. (b) Nakatsuji, S.; Ogawa, Y.; Takeuchi, S.; Akutsu, H.;
Yamada, J .; Naito, A.; Sudo, K.; Yasuoka, N. J . Chem. Soc., Perkin
Trans. 2 2000, 1969. (c) Nakatsuji, S.; Takeuchi, S.; Ojima, T.; Ogawa,
Y.; Akutsu, H.; Yamada, J . Mol. Cryst. Liq. Cryst. 2001, 356, 23.
(10) For a recent review, see: Bouas-Laurent, H.; Castellan, A.;
Desvergne, J .-P.; Lapouyade, R. Chem. Soc. Rev. 2000, 29, 43. We
thank Dr. Desvergne of Universite` Bordeaux I for kindly sending us a
reprint.
10.1021/jo010943u CCC: $22.00 © 2002 American Chemical Society
Published on Web 01/11/2002

Anthracene Derivatives and Corresponding Dimers
J . Org. Chem., Vol. 67, No. 3, 2002 917
Ch a r t 1
Sch em e 2a
Sch em e 1a
a
(i) 4-amino-TEMPO, AcOH; (ii) NaBH3CN.
a
(i) SOCl2; (ii) 4-amino-TEMPO, 4-(N-methyl)amino-TEMPO,
or 4-hydroxy-TEMPO, Et3N.
from the previous systems of others3,4 as well as of ours.9
The only example that is based on intermolecular struc-
tural change is the system developed by Veciana et al.5
F igu r e 1. Electronic absorption change for the reaction from
10 to 11 and vice versa.
Resu lts a n d Discu ssion
P r ep a r a tion of An th r a cen es w ith TEMP O Ra d i-
ca ls a n d Th eir Dim er s. Carboxyamide and N-methyl-
amide derivatives of anthracene (2, 3) were prepared
from 9-anthroic acid 1 by its derivatization with 4-amino-
TEMPO as well as 4-methylamino-TEMPO, which was
obtained by reductive amination of 4-oxo-TEMPO with
methylamine hydrochloride and NaBH3CN.12 Although
all attempts to obtain the corresponding photodimers (6,
7) through the direct photodimerization reaction of 2 and
3 failed, the dimers were prepared by the derivatization
of the photodimer of 9-anthroic acid (5)13 with 4-amino-
TEMPO or 4-methylamino-TEMPO as shown in Scheme
1. On the contrary, the derivative with a carboxylic ester
substituent (4) was found to give the corresponding
photodimer (8) upon irradiation in benzene solution using
a high-pressure Hg lamp (400 W) and the latter could
be reverted to the former by heating in a toluene solution
(Scheme 1).
principle (Scheme 2). The progress of the photoreaction
was monitored by the electronic spectral change of the
vibronic absorption in 320-390 nm in benzene as shown
in Figure 1, and an apparent photostationary state was
attained after 6 h (50% consumption of 10 after ca. 4.5
h).14 Gradual dissociation was observed for the backward
reaction by heating 11 in xylene solution to revert half
of the dimer 11 after ca. 4 h. Thus, although the efficiency
is still limited as described above, two reversible systems
could be constructed in principle so far as we have
examined.
Ma gn etic P r op er ties. Typical absorptions due to the
aminoxyl were observed in the EPR spectra of all the
monomers, and no appreciable difference was found for
those of the corresponding dimers, indicating the absence
of significant intramolecular exchange interactions be-
tween the spin centers in the dimers. For the estimation
of the relative configuration of spin centers for the dimers
(biradicals), EPR measurements for the dimers 6 and 8
were carried out in 2-methyltetrahydrofuran at 123 K
to give the zerofield splitting parameters of |D| ) 3.36
mT and |E| ) 0.879 mT for 6 and |D| ) 3.15 mT and |E|
) 0.810 mT for 8. The distances between the spin centers
for each biradical are then estimated by point dipole
approximation to be 9.60 Å for 6 and 9.40 Å for 8. Thus,
the trans configuration of the dimers is well suggested
from the estimated data.
The methylamino-TEMPO derivative of anthracene
(10) was prepared by the reduction of the Schiff base
derived from 9-anthraldehyde 9 and 4-amino-TEMPO,
and the photodimerization of 10 was carried out by
irradiation with a 400 W Hg lamp in CHCl3 solution to
give the dimer (11), which could be reverted to 10 by
heating in xylene, affording a reversible system in
(11) Preliminary reports of this paper have appeared portionwise
in (a) Ojima, T.; Akutsu, H.; Yamada, J .; Nakatsuji, S. Chem. Lett.
2000, 918. (b) Ojima, T.; Akutsu, H.; Yamada, J .; Nakatsuji, S.
Polyhedron 2001, 20, 1335.
(12) Cf.: Nakatsuji, S.; Takai, A.; Nishikawa, K.; Morimoto, Y.;
Yasuoka, N.; Suzuki, K.; Enoki, T.; Anzai, H. J . Mater. Chem. 1999,
9, 1747.
(14) Since the efficiency of this photochemical reaction was rather
low, we tried to characterize byproduct(s). These efforts have not been
successful, and no measurement of the quantum yield was carried out
for the reaction since that was beyond our initial purpose. For the
photochemical reaction of 9-aminomethylanthracene derivatives, see:
Mori, Y.; Maeda, K. Bull. Chem. Soc. J pn. 1997, 70, 869.
(13) Cowan, D. O.; Schmiegel, W. W. J . Am. Chem. Soc. 1972, 94,
6779.

918 J . Org. Chem., Vol. 67, No. 3, 2002
Nakatsuji et al.
Ta ble 1. Ma gn etic Da ta of An th r a cen es a n d th e
Cor r esp on d in g Dim er s
magnetic behaviors of the crystals was observed, i.e.,
ferromagntic interactions (θ ) +0.26 K) when chloroform
molecules are incorporated and antiferromagnetic inter-
actions (θ ) -0.38 K) when benzene molecules are
incorporated (Figure 3, right). Thus, although the ef-
ficiency of the reversibility is not so high, it was found
to be possible in principle to tune the sign and magnitude
of intermolecular magnetic interactions in the compounds
available in this reversible system.
Molecu la r /Cr ysta l Str u ctu r es of Mon om er s 3 a n d
10 a n d Dim er 11. A single crystal of 3 suitable for X-ray
analysis was grown from the mixed solvent of n-hexane
and chloroform, and as shown in Figure 4, the two
molecules of 3 are paired and the anthracene moieties
are facing each other with each TEMPO moiety protrud-
ing in a perpendicular manner and in the anti configu-
ration. It was well anticipated from the viewpoint of its
molecular configuration that the photodimerization would
proceed even in the crystal phase, but as far as we have
examined, no photodimer could be available until now
in either the crystal phase or solution. Although the
explicit reason for the magnetic behavior observed in this
radical (Figure 2) is not clearly understood yet, a couple
of short contacts found between the carbon atoms on the
anthracene moiety of a molecule and the oxygen atoms
of aminoxyls of different molecules might be responsible
for the observed magnetic interactions.
compound magnetic interaction Ca/emu K mol-1 θb/K
J c/K
2
6
3
antiferromagnetic
antiferromagnetic
antiferromagnetic
0.32 (85)
0.67 (89)
-0.10
-0.32
-3.38
(100)
7
4
8
10
antiferromagentic
ferromagnetic
ferromagnetic
ferromagnetic
antiferromagnetic
ferromagnetic
ferromagnetic
0.73 (97)
0.36 (96)
0.64 (85)
0.38 (100)
0.75 (100)
0.70 (93)
0.75 (100)
-1.87
0.21
0.28
0.97
-0.38
0.26
d
11 (C6H6
)
d
11 (CHCl3
11 (CH2Cl2
)
d
)
0.11
a
Curie constant. Figures in parentheses denote the estimated
b
spin concentrations. Weiss temperature. c Exchange interactions
obtained by fitting for a singlet-triplet model. The figure in
d
parentheses denotes the estimated spin concentration. Crystal
solvent.
The X-ray analysis of the monomer 10 was carried out
by using the single-crystal grown from a mixed solution
of hexane-chloroform, and the molecular/crystal struc-
ture is shown in Figure 5. It was found from the
molecular structure of 10 that the six-membered ring of
the TEMPO moiety protrudes in an almost perpendicular
manner from the anthracene ring (Figure 5, left), and
the molecules are stacked almost along the b-axis to form
the columnar structure (Figure 5, right). The ferromag-
netic interactions observed in the spins of 10 could be
rationally understood by considering the spin-polariza-
tion mechanism through the intermolecular hydrogen
bonds (CH‚‚‚ON ) 3.40 Å) between the spin centers15
since the distances between the oxygen atoms of ami-
noxyls and the methylene carbon atoms on the neighbor-
ing heterocycles were found to be sufficiently short for
the hydrogen bonding.
Interestingly, the solvent molecules used for recrys-
tallization were found to be easily incorporated in the
dimer 11 and the difference of the magnetic behaviors
was observed in the solvated compounds (Table 1).
Namely, antiferromagntic interactions were observed in
the compound obtained from benzene for the recrystal-
lization, while ferromagnetic interactions were found in
the solvated compounds of 11 with dichloromethane or
chloroform. Single crystals suitable for X-ray analysis
were obtained from the solvated samples of the dimer
11 with benzene or chloroform, and each structure was
analyzed. As shown in Figure 6 (left), the anti configu-
ration of each substituent was apparent from the analysis
of the crystal obtained from a benzene solution and the
dissected angle between the mean plane of the an-
thracene ring and that of the six-membered ring of the
F igu r e 2. Temperature dependence of the magnetic suscep-
tibility (ø) for 3. The calculated values for the S-T model are
shown in the solid line.
The magnetic susceptibility measurements for each
monomer/dimer pair were carried out on the polycrys-
talline sample by a SQUID susceptometer in the tem-
perature range of 2-300 K, and the data are summarized
in Table 1.
Similar magnetic behaviors were observed in monomer/
dimer pairs of 2 and 6 as well as 4 and 8, i.e., the
antiferromagnetic spin-spin interactions with Curie-
Weiss behavior were found in the spin of 2 and tend to
be preserved in the spins of 6 despite the difference of
Weiss temperatures. Similarly, ferromagnetic interac-
tions proved to exist in the spin centers for both 4 and 8
with slightly different Weiss temperatures. With regard
to the monor/dimer pair of 3 and 7, local antiferromag-
netic spin interactions being well expressed by a singlet-
triplet model with a J -value of ca. -3.4 K were found in
the spins of 3 as shown in Figure 2; the Curie-Weiss
behavior with antiferromagnetic interactions (θ ) -1.87
K) was observed in the spins of the corresponding dimer
7 (Table 1).
Ferromagnetic interactions with relatively large Weiss
temperatures (θ ) +0.97 K) were observed in the
methylamine derivative 10 as shown in Figure 3 (left),
and the tendency of the preservation of magnetic interac-
tions was apparent in the corresponding dimer 11 with
the smaller Weiss temperature (θ ) +0.11 K) being
estimated from the data measured on a powdered sample
without recrystallization. Interestingly, the solvent mol-
ecules used for recrystallization were found to be easily
incorporated in the dimer 11 and the difference of the
(15) Cf.: (a) Veciana, J .; Cirujeda, J .; Rovira, C.; Vidal-Gancedo, J .
Adv. Mater. 1995, 7, 221. (b) Tagashi, K.; Imachi, R.; Tomioka, K.;
Tsuboi, H.; Ishida, T.; Nogami, T.; Takeda, N.; Ishikawa, M. Bull.
Chem. Soc. J pn. 1996, 69, 2821. (c) Matsushita, M. M.; Izuoka, A.;
Sugawara, T.; Kobayashi, T.; Wada, T.; Takeda, N.; Ishikawa, M. J .
Am. Chem. Soc. 1997, 119, 4369.

Anthracene Derivatives and Corresponding Dimers
J . Org. Chem., Vol. 67, No. 3, 2002 919
F igu r e 3. (Left) Temperature dependence of øT for 10. (Right) Temperature dependence of øT for 11 solvated with benzene.
appear to occupy the cavities or voids formed in the dimer
molecules to construct clathrate-like molecular aggre-
gates. At the same time, they tend to prevent the close
contact of spin centers of aminoxyl radicals to afford, as
the consequence, weak intermolecular spin-spin interac-
tions with an antiferromagnetic nature on one hand and
a ferromagnetic nature on the other.
Con clu sion s
We prepared four anthracene derivatives carrying
TEMPO radicals (2-4, 10), and although direct photo-
dimerization of two derivatives (2, 3) was not successful,
the dimers were prepared in a stepwise manner from
dicarboxylic acid derivative of anthracene dimer. On the
contrary, the photodimers 8 and 11 could be directly
prepared from the corresponding monomers 4 and 10 and
the backward reactions, in turn, gave the starting
monomers to construct the reversible systems in prin-
ciple. Whereas the tendency of the preservation of
intermolecular spin-spin interactions was observed in
the monomer/dimer pairs for 2/6 and 4/8 from antifer-
romagnetic to antiferromagnetic in the former pairs and
from ferromagnetic to ferromagnetic in the latter despite
the difference of their Weiss temperatures, a significant
difference was clarified in the pairs for 3/7 as well as 10/
11. Namely, local antiferromagnetic exchange interac-
tions being well expressed by a singlet-triplet model
found in the monomer 3 were turned to antiferromagnetic
interactions on the basis of Curie-Weiss behavior in the
corresponding dimer 7. The ferromagnetic interactions
found in the spins of monomer 10 were found to be able
to tune in the corresponding dimer 11 depending on the
solvent molecules incorporated to either antiferromag-
netic or ferromagnetic; thus, in principle, the sign and
magnitude of intermolecular magnetic interactions was
found to be changed by outer stimuli such as light, heat,
or appropriate solvents in this reversible system.
F igu r e 4. Molecular structure of 3 (two molecules are
depicted).
F igu r e 5. (Left) Molecular structure of 10. (Right) Crystal
structure of 10 with indication of ferromagnetic couplings
through hydrogen bonds.
Exp er im en ta l Section
TEMPO moiety amounts to 58.0°, a smaller value than
that of 10. On the other hand, a coexistence of two
crystallographically independent molecules has been
found in the crystal obtained from a chloroform solution
having different dissected angles with the values of 41.2
and 54.8°.
The crystal structure of a compound solvated with
benzene is shown in Figure 6 (right). Despite the differ-
ence of the conformations of the dimer molecules, similar
packing features were found in crystal structures of the
solvated compounds in which the solvent molecules
Ma ter ia ls. 4-Oxo-, 4-hydroxy-, and 4-amino-TEMPO radi-
cals used as building blocks in this study are commercially
available (Tokyo Kasei Kogyo Co.), and these were used
without further purification.
In str u m en ta tion . Melting points were measured on a
YAMATO MP-21 apparatus and are uncorrected. IR spectra
were recorded on a J ASCO Report-100 spectrometer. UV-vis
spectra were obtained on a J ASCO Ubest-35 spectrometer. MS
spectra were taken using a J EOL J MS-AX 505 mass spec-
trometer. EPR spectra were obtained on a J EOL J ES-FE3XG
spectrometer, and each g-value was determined using Mn2+
/

920 J . Org. Chem., Vol. 67, No. 3, 2002
Nakatsuji et al.
F igu r e 6. (Left) Molecular structure of 11 solvated with benzene. (Right) Crystal structure of 11 solvated with benzene. Hydrogen
atoms are omitted for clarity.
MgO maker as the internal standard. Susceptibility measure-
ments were carried out on a QUNTUM DESIGN MPMS-5
SQUID susceptometer using ca. 10 mg of each powdered
sample in the usual way.12
vis (CH3CN) 238 (1.43 × 104), 329 (2.60 × 103), 345 (5.21 ×
103), 363 (7.81 × 103), 382 (7.22 × 103); EPR (benzene) 3 lines,
g ) 2.007, aN ) 1.56 mT; FAB-HRMS (m/z) calcd for C24H26
-
NO3 376.1913, found 376.1947.
X-r a y Str u ctu r e Deter m in a tion . X-ray diffraction data
were collected on a Nonius CAD4 or Rigaku R-AXIS-4 diffrac-
tometer with Mo KR radiation at room temperature. The
structures were solved by direct methods and expanded using
Fourier techniques. The non-hydrogen atoms were refined
anisotropically. Hydrogen atoms were included but not refined.
All calculations were performed using the teXsan crystal-
lographic software package of Molecular Structure Corpora-
tion, and detailed crystallographic data (atomic coordinates,
hydrogen atom coordinates, anisotropic displacement param-
eters, and bond lengths and angles) have been deposited with
the Cambridge Crystallographic Data Centre.
P r ep a r a tion of 4-(N-Meth yla m in o)TEMP O. To a stirred
mixture of oxo-TEMPO (1.10 g, 6.20 mmol) and methylamine
hydrochloride (2.50 g, 37.0 mmol) in absolute methanol (100
mL) were added NaBH3CN (0.270 g, 4.30 mmol) and succes-
sively 5 N HCl in MeOH to adjust the pH of the solution to
ca. 6. After stirring for 2 days at ambient temperature, the
reaction mixture was concentrated in vacuo and then aqueous
potassium hydroxide solution (4 N) was added to neutralize
the resulting reaction product. The mixture was extracted by
chloroform, washed well with water and brine, and the organic
layer was dried over anhydrous magnesium sulfate. The
radical was obtained as pale orange rods (935 mg, 76%) after
the solvent was concentrated, purified by column chromatog-
raphy on silica gel, and recrystallized from the mixed solvent
of n-hexane and dichloromethane: mp 52-53 °C; EPR (ben-
zene) 3 lines, g ) 2.007, aN ) 1.56 mT; EI-HRMS (m/z) calcd
for C10H21N2O 185.1653, found 185.1674.
P r ep a r a tion of 4-(9-An th r ylm eth yla m in o)TEMP O De-
r iva tive 10. A toluene solution (40 mL) of 9-anthraldehyde
(1.20 g, 5.84 mmol) and 4-amino-TEMPO (1.00 g, 5.84 mmol)
with 2 mL of AcOH was stirred under nitrogen at 65 °C for 12
h. The reaction mixture was concentrated under reduced
pressure and then recrystallized from the mixed solvent of
n-hexane/benzene to give the corresponding imine derivative
as yellow needles (1.76 g, 84%): mp 171-173 °C dec; EPR
(benzene) 3 lines, g ) 2.006, aN ) 1.57 mT; FAB-MS (m/z) 359
(M + 1). To the stirred solution of the imine derivative in
MeOH (100 mL) was added NaBH3CN (310 mg, 4.90 mmol)
under nitrogen at 0 °C and then 30 mL of MeOH solution with
concentrated HCl (0.9 mL) for 20 min. After the reaction
mixture was warmed to room temperature, it was concen-
trated, neutralized with 4 N KOH, and extracted with chlo-
roform. The chloroform layer was dried over anhydrous MgSO4
and then concentrated in vacuo to give a solid that was purified
by column chromatography on silica gel by using the solvent
system of n-hexane/ethyl acetate and recrystallized from the
mixed solvent of n-hexane/chloroform. The derivative 10 was
obtained as orange rods (1.46 g, 82%): mp 123-128 °C dec;
UV-vis (CH3CN) 256 (1.46 × 104), 331 (2.59 × 103), 347 (5.36
× 103), 365 (8.35 × 103), 385 (7.85 × 103); EPR (benzene) 3
lines, g ) 2.007, aN ) 1.56 mT; FAB-MS (m/z) 361 (M+). Anal.
Calcd for C24H29N2O: C, 79.74; H, 8.09; N, 7.75%. Found: C,
79.58; H, 8.09; N, 7.65%.
P r ep a r a tion of P h otod im er 11. Into a vessel (200 mL)
for photochemical reactions with a Pyrex filter was placed a
benzene solution (50 mL) of 10 (1.46 g, 4.04 mmol), and the
solution was irradiated with a high-pressure Hg lamp (400
W) under nitrogen at 0 °C. After irradiation of the solution
for 11 h, the reaction mixture was concentrated in vacuo and
purified by column chromatography on silica gel by using the
solvent system of n-hexane/dichloromethane to an give orange
powdery solid (168 mg, 12%). The solid was then recrystallized
from an appropriate solvent (benzene, chloroform, or dichlo-
romethane), and the solvated dimers 11 were obtained as
orange crystals in each compound with almost the same
melting and spectral data: mp 213-218 °C dec; UV-vis (CH3-
P r ep a r a tion of 4-[9-An th r ylca r boxy(N-m eth yla m in o)]-
TEMP O Der iva tive 3. 9-Anthracenecarboxylic acid (662 mg,
2.98 mmol) was heated in SOCl2 solution (30 mL) to reflux for
5 h. The resulting solution was concentrated in vacuo to give
a solid that was dissolved in CH2Cl2 (20 mL) and added to a
stirred solution of 4-methylamino-TEMPO (552 mg, 2.98
mmol) in CH2Cl2 (20 mL) with 1 mL of triethylamine. After
stirring at 35 °C for 2 days, the reaction mixture was poured
into 1 N HCl (50 mL), washed with brine, dried over anhydrous
MgSO4, and then concentrated to give a brownish yellow solid,
which was purified by column chromatography on silica gel
by using the solvent system of n-hexane/ethyl acetate and
recrystallized from the mixed solvent of n-hexane/dichlo-
romethane. The derivative 3 was obtained as orange rods (708
mg, 64%): mp 169-171 °C dec; UV-vis (CH3CN) 242 (1.26 ×
104), 332 (2.20 × 103), 348 (5.35 × 103), 366 (8.71 × 103), 385
(7.50 × 103); EPR (benzene) 3 lines, g ) 2.007, aN ) 1.56 mT;
FAB-MS (m/z) 390 (M + H). Anal. Calcd for C25H29N2O2: C,
77.09; H, 7.50; N, 7.19%. Found: C, 76.79; H, 7.46; N, 7.08%.
In a similar manner, the derivatives 2 and 4 were prepared
in 83 and 52%, respectively, and their data are as follows. 2:
orange needles, mp 220-223 °C dec; UV-vis (CH3CN) 256
(1.46 × 104), 332 (2.79 × 103), 345 (5.44 × 103), 363 (7.81 ×
CN) 218 (2.28 × 105); EPR (benzene) 3 lines, g ) 2.007, aN
)
1.60 mT; FAB-MS (m/z) 723 (M + H). Anal. Calcd for the
compound solvated with benzene (C48H58N4O2‚2C6H6): C,
81.96; H, 8.02; N, 6.37%. Found: C, 81.84; H, 8.01; N, 6.47%.
Anal. Calcd for the compound solvated with chloroform
(C48H58N4O2‚2CHCl3): C, 62.44; H, 6.29; N, 5.87%. Found: C,
62.75; H, 6.13; N, 5.41%. Anal. Calcd for the compound
solvated with dichloromethane (C48H58N4O2‚1.5CH2Cl2): C,
69.91; H, 7.23; N, 6.59%. Found: C, 69.91; H, 7.29; N, 6.23%.
In a similar manner with a shorter irradiation time (3 h), the
photodimer 8 was obtained from the corresponding monomer
4 in 34% yield: orange microcrystals; mp 228-230 °C dec;
UV-vis (CH3CN) 223 (2.01 × 105); EPR (benzene) 3 lines, g )
2.007, aN ) 1.60 mT; FAB-MS (m/z) 752 (M+). Anal. Calcd for
103), 382 (6.80 × 103); EPR (benzene) 3 lines, g ) 2.006, aN
)
1.53 mT; FAB-HRMS (m/z) calcd for C24H27N2O2 375.2073,
found 375.2081. 4: orange needles, mp 203-205 °C dec; UV-
C
48H52N2O6: C, 76.57; H, 6.96; N, 3.72%. Found: C, 76.41; H,
6.94; N, 3.65%.

Anthracene Derivatives and Corresponding Dimers
J . Org. Chem., Vol. 67, No. 3, 2002 921
P r ep a r a tion of Dim er 7. A stirred solution of the dimer
of 9-anthracenecarboxylic acid (528 mg, 1.19 mmol) in SOCl2
(35 mL) with DMF (3 drops) was heated to reflux for 4 h. The
resulting solution was concentrated, dissolved in CH2Cl2 (20
mL), and added to a stirred solution of 4-methylamino-TEMPO
(440 mg, 2.38 mmol) in CH2Cl2 (20 mL) with 3 mL of
triethylamine. After stirring at 35 °C for 24 h, the reaction
mixture was poured into 1 N HCl (50 mL), washed with brine,
dried over anhydrous MgSO4, and then concentrated to give a
solid that was purified by column chromatography on silica
gel by using the solvent system of n-hexane/ethyl acetate. After
the recrystallization from the mixed solvent of n-hexane/
dichloromethane, the dimer 7 was obtained as a pale reddish,
powdery solid (113 mg, 43%): mp 168-170 °C dec; UV-vis
(CH3CN) 245 (1.12 × 105); EPR (benzene) 3 lines, g ) 2.006,
aN ) 1.56 mT; FAB-MS (m/z) 779 (M + H). Anal. Calcd for
gel by using the solvent system of n-hexane/ethyl acetate. After
the recrystallization from the mixed solvent of n-hexane/
dichloromethane, the monomer 10 was recovered as orange
rods in 45% yield. Similarly, the dissociation reaction of dimers
6, 7, and 8 gave the corresponding monomers 2, 3, and 4 in
68, 84, and 71%, respectively.
Ack n ow led gm en t. We thank Prof. Hayao Koba-
yashi of Institute for Molecular Sciences and Prof.
Masaaki Omasa of Himeji Institute of Technology for
kindly providing us the opportunity to use the X-ray
facilities. This work was supported by a Grant-in-Aid
for Scientific Research on Priority Area (A) “Creation
of Delocalized Electronic Systems” (No. 10146250) from
the Ministry of Education, Science, Sports and Culture,
J apan, which is gratefully acknowledged.
C
50H58N4O4: C, 77.09; H, 7.50; N, 7.19%. Found: C, 77.46; H,
7.24; N, 7.53%. In a similar manner, the dimer 6 was obtained
in 23% yield as a pale reddish, powdery solid: mp 221-223
°C dec; UV-vis (CH3CN) 218 (3.13 × 105); EPR (benzene): 3
lines, g ) 2.006, aN ) 1.56 mT; FAB-MS (m/z) 751 (M + H).
Anal. Calcd for C48H54N4O4: C, 76.77; H, 7.25; N, 7.46%.
Found: C, 76.44; H, 7.43; N, 7.18%.
Dissocia tion of Dim er 11. A stirred solution of dimer 11
(100 mg, 0.138 mmol) in xylene (30 mL) was heated to reflux
for 24 h, and the solvent was evaporated to dryness to give a
solid that was purified by column chromatography on silica
Su p p or tin g In for m a tion Ava ila ble: X-ray crystallo-
graphic data (crystal structure of 3, molecular/crystal structure
of 11‚2CHCl3, tables of crystal data, bond lengths and angles,
atomic coordinates, and anisotropic thermal parameters) for
3, 10, and 11 with benzene and 11 with chloroform. This
material is available free of charge via the Internet at
http://pubs.acs.org.
J O010943U