Spin-carrying benzoquinone derivatives

Article abstract of DOI:10.1021/jo902007m

(Chemical Equation Presented) Several 1,4-benzoquinone derivatives carrying oxy-TEMPO radical(s) at the 2-position or 2, 5-positions were found to give black crystals by recrystallization from pale yellow solutions and it was revealed from their crystal s

Full text of DOI:10.1021/jo902007m

pubs.acs.org/joc
Spin-Carrying Benzoquinone Derivatives
Shin’ichi Nakatsuji,* Mitsunori Nobusawa, Hideto Suzuki, Hiroki Akutsu, and
Jun-ichi Yamada
Department of Material Science, Graduate School of Material Science, University of Hyogo, 3-2-1 Kouto,
Kamigori, Hyogo 678-1297, Japan
nakatuji@sci.u-hyogo.ac.jp
Received September 18, 2009
Several 1,4-benzoquinone derivatives carrying oxy-TEMPO radical(s) at the 2-position or 2,
5-positions were found to give black crystals by recrystallization from pale yellow solutions and it
was revealed from their crystal structures that unusual single-component CT complexes were formed,
in which a nitroxide moiety plays the roll of a donor part and a 1,4-benzoquinone group of the same
molecule works as an acceptor part, respectively. On the contrary, no CT formation was found for the
derivatives carrying oxy-TEMPO radicals at 2,6-positions and one of the TEMPO groups con-
tributes to a CT formation in a 1,4-benzoquinone derivative carrying amino-TEMPO radicals at 2,
5-positions derived from fluoranil, while the other one has a close oxygen-to-oxygen contact
with another neighboring molecule to give a very large exchange coupling of J/kB = -154 K.
Introduction
complexes are still rare.4 It is probably because of the
difficulty of controlling the donating and accepting ability
in a molecule and/or steric effects detrimental to forming a
CT complex with sufficient CT interaction. Moreover, to our
knowledge, there has been so far no intrinsic example of a
single-component CT complex based on stable radicals, even
though some single-component organic conductors based on
A charge-transfer (CT) complex generally consists of a
donor molecule and an acceptor molecule and is a two-
component compound.1 On the other hand, a large number
of molecules are known in which both electron-donating and
electron-accepting groups are incorporated in a single mo-
lecule such as merocyanine dyes2 or unimolecular electrical
rectifiers3 but they normally do not form CT complexes by
themselves and then examples of single-component CT
(4) (a) Becker, J. Y.; Bernstein, J.; Bittner, S.; Levi, N.; Shaik, S. S. J. Am.
Chem. Soc. 1983, 105, 4468. (b) Becker, J. Y.; Bernstein, J.; Bittner, S.; Levi,
N.; Shaik, S. S.; Zer-Zion, N. J. Org. Chem. 1988, 53, 1689. (c) Marin, N.;
Segura, J. L.; Seoane, C.; Orti, E.; Viruala, R.; Albert, A.; Cano, F. H.; Vidal-
Gancedo, J.; Rovira, C.; Veciana, J. J. Org. Chem. 1996, 61, 3041. (d) Narvor,
N. L; Robertson, N.; Weyland, T.; Kilburn, J. D.; Underhill, A. E.; Webster,
M.; Svenstrup, N.; Becher, J. Chem. Commun. 1996, 1363. (e) Ueda, K.;
Goto, M.; Iwamatsu, M.; Sugimoto, T.; Endo, S.; Toyota, N.; Yamamoto,
K.; Fujita, H. J. Mater. Chem. 1998, 8, 2195. (f) Kobayashi, A.; Tanaka, H.;
Kumasaki, M.; Torii, H.; Narymbetov, B.; Adachi, T. J. Am. Chem. Soc.
1999, 121, 10763. (g) Iwamatsu, M.; Kominami, T.; Ueda, K.; Sugimoto, T.;
Adachi, T.; Fujita, H.; Yoshino, H.; Mizuno, Y.; Murata, K.; Shiro, M.
Inorg. Chem. 2000, 39, 3810. (h) Tanaka, H.; Okano, Y.; Kobayashi, H.;
Suzuki, W.; Kobayashi, A. Science 2001, 291, 285. (i) Belo, D.; Alves, H.;
Lopes, E. B.; Duarte, M. T.; Gama, V.; Henriques, R. T.; Almeida, M.;
(1) Cf: (a) Bent, H. A. Chem. Rev. 1968, 68, 587. (b) Organic Charge-
transfer Complexes; Foster, R., Ed.; Academic Press: London, UK, 1969. (c) The
Donor-Acceptor Approach to Molecular Interactions; Gutmann, V., Ed.;
Plenum Press: New York, 1978.
(2) Cf.: (a) Organic Chemistry in Colour; Gordon, P. F., Gregory, P., Eds.;
Springer-Verlag: Berlin, Germany, 1987. (b) Color Chemistry; Zollinger, H., Ed.;
Verlag Helvetica Chimica Acta: Z€urich, Switzerland, 2003. (c) Shirinian, V. Z.,
Shimkin, A. A. In Heterocyclic Polymethine Dyes: Synthesis, Properties and
Applications; Topics in Heterocyclic Chemistry, Vol. 14, Springer-Verlag: Berlin,
Germany, 2008; Chapter 5.
(3) Cf.: (a) Metzger, R. M. Acc. Chem. Res. 1999, 32, 950. (b) Metzger,
ꢀ
Perez-Benı
R. M. Chem. Rev. 2003, 103, 3803.
´
tez, A.; Rovira, C.; Veciana, J. Chem.;Eur. J. 2001, 7, 511.
DOI: 10.1021/jo902007m
r
Published on Web 11/20/2009
J. Org. Chem. 2009, 74, 9345–9350 9345
2009 American Chemical Society

Nakatsuji et al.
JOCArticle
SCHEME 1
neutral radicals5 and a variety of two-component CT com-
plexes involving stable radicals have been reported.6
Results and Discussion
Preparation of 1,4-Benzoquinone Derivatives and Their
Redox and UV-Vis Absorption Properties. The reactions
of chloranil 1a or bromanil 1b with 4-hydroxy-TEMPO 2
in the presence of potassium carbonate in DMF gave after
separation by column chromatography on SiO2 and re-
crystallization 2-(4-oxy-TEMPO)-3.5.6-trihalo-1,4-bezo-
quinone 3a (48%) or 3b (65%) as the major products
(reaction a in Scheme 1). Further examination of other
eluants revealed the formation of bis-TEMPO-substi-
tuted benzoquinones 4 and 5 as the minor products
(each <10%), which could be purified by recrystalliza-
tion and elucidated by X-ray analyses. While the forma-
tion of 2,5-disubstituted product is common in this kind
of nucleophilic substitution reaction onto 1,4-benzoqui-
none derivatives,11 that of the 2,6-disubstituted one is
very unusual but the reason for the formation is still
unclear.
Noteworthy was the black color of the recrystallized
crystals of 3a and 3b from the pale yellow pentane-
n-hexane (1:1) solution, indicating occurrence of charge
transfer between the molecules in the crystals. Also black
crystals were obtained in the cases of 4a and 4b, while
orange crystals were grown in the cases of 5a and 5b,
suggesting the occurrence of CT in the former crystals but
not in the latter.
In the course of our studies toward the development of
organic multifunctional spin systems based on nitroxide
radicals,7 we prepared several 1,4-benzoquinone derivatives
carrying 4-amino-TEMPO (2,2,6,6-tetramethyl-1-piperidi-
nyloxy) radical to form CT complexes with TTF and its
derivative.8 Furthermore it was clarified that 4-amino-TEMPO
derivatives act themselves as donors to afford intermolecular
CT complexes with some acceptors.9 However, all of them are
usual CT complexes composed of two components of a donor
and an acceptor. In this paper, we wish to report the prepara-
tion of several 1,4-benzoquinone derivatives carrying TEMPO
radical at one or two positions and serendipitous formations of
single-component (unimolecular) CT complexes in some of
them together with their structures and magnetic properties.10
(5) (a) Cordes, A. W.; Haddon, R. C.; Oakley, R. T.; Schneemeyer, L. F.;
Waszczak, J. V.; Young, K. M.; Zimmerman, N. M. J. Am. Chem. Soc. 1991,
113, 582. (b) Tsubata, Y.; Suzuki, T.; Miyashi, T.; Yamashita, Y. J. Org.
Chem. 1992, 57, 6749.
(6) (a) Sugano, T.; Fukasawa, T.; Kinoshita, M. Synth. Met. 1991, 43,
3281. (b) Sugimoto, T.; Yamaga, S.; Nakai, M.; Tsuji, M.; Nakatsuji, H.;
Hoshino, N. Chem. Lett. 1993, 1817. (c) Ishida, T.; Tomioka, K.; Nogami,
T.; Yamaguchi, K.; Mori, W.; Shirota, Y. Mol. Cryst. Liq. Cryst. 1993, 232,
99. (d) Kumai, R.; Matsushita, M. M.; Izuoka, A.; Sugawara, T. J. Am.
Chem. Soc. 1994, 116, 4523. (e) Nakatsuji, S.; Anzai, H. J. Mater. Chem.
1997, 7, 2161. (f) Fujiwara, H.; Lee, H.-J.; Kobayashi, H.; Fujiwara, E.;
Kobayashi, A. Chem. Lett. 2003, 482. (g) Mukai, K.; Senda, N.; Hatanaka,
T.; Minakuchi, H.; Ohara, K.; Taniguchi, T.; Misaki, Y.; Hosokoshi, Y.;
Inoue, K.; Azuma, N. Inorg. Chem. 2004, 43, 566. (h) Matsushita, M. M.;
Kawakami, H.; Sugawara, T.; Ogata, M. Phys. Rev. 2008, B77, 195208. (i)
Masuda, Y.; Kuratsu, M.; Suzuki, S.; Kozaki, M.; Shiomi, D.; Sato, K.;
Takui, T.; Hosokoshi, Y.; Lan, X.-Z.; Miyazaki, Y.; Inaba, A.; Okada, K.
J. Am. Chem. Soc. 2009, 131, 4670.
(7) (a) Nakatsuji, S. Adv. Mater. 2001, 13, 1719. (b) Nakatsuji, S. In
Nitroxides: Applications in Chemistry, Biomedicine, and Materials Science;
Likhtenstein, G. I., Yamauchi, J., Nakatsuji, S., Smirnov, A. I., Tamura, R., Eds.;
Wiley-VCH: Weinheim, Germany, 2008; Chaptor 5, p 161.
(8) Nakatsuji, S.; Akashi, N.; Suzuki, K.; Enoki, T.; Anzai, H. J. Chem.
Soc., Perkin Trans. 2 1996, 2555.
A somewhat different reaction profile was revealed for
fluoranil 1c from that of chloranil 1a or bromanil 1b, i.e.,
the main reaction product in the similar reaction was
2,5-disubstituted derivative 4c, which again was isolated
as black crystals in 21% yield, but the corresponding
monosubstituted or 2,6-disubstituted one could not be
isolated. Also, 2,5-disubstituted derivative 7 was the
main product (41%) for the reaction of fluoranil with
(9) Nakatsuji, S.; Takai, A.; Nishikawa, K.; Morimoto, Y.; Yasuoka, N.;
Suzuki, K.; Enoki, T.; Anzai, H. J. Mater. Chem. 1999, 9, 1747.
(10) A portion of this work has appeared in a preliminary communica-
tion: Nobusawa, M.; Akutsu, H.; Yamada, J.; Nakatsuji, S. Chem. Lett.
2008, 37, 788.
(11) (a) Neef, R.; Bayer, O. Chem. Ber. 1957, 90, 1137. (b) Nogami, T.;
Yamaoka, T.; Yoshihara, K.; Nagakura, S. Bull. Chem. Soc. Jpn. 1971, 44,
380. (c) Shaaban, I.; Solima, R. Pharmazie 1978, 33, 642. (d) Iwatsuki, S.;
Kubo, M.; Iwase, H. Chem. Lett. 1993, 517.
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TABLE 1. CV Data of Benzoquinone Derivativesa
crystal structures of monoclinic system with space group
P21/n. The N-O distance of nitroxide moiety amounts to
1.28 A, indicating the existence of a S = 1/2 spin in the mole-
cule. The TEMPO groups of 3a and 3b are largely distorted
from the corresponding benzoquinone π-planes and a couple
of benzoquinone rings face each other with the plane-
to-plane distance of 3.61 A in 3a and 3.64 A in 3b, respec-
tively. The most remarkable features of their crystal struc-
tures are the very close proximities of oxygen atoms of the
radical moieties to the neighboring benzoquinone rings in 3a
and 3b (2.79 A in 3a and 2.83 A in 3b), which are shorter than
the sum of VDW radii (3.1 A) and suggest the occurrence of
charge transfer between them. Thus, the black colors of their
crystals (vide supra) can be well understood from the crystal
structures as well.
RED
RED
OX
compd
E1
E2
E1
3a
3b
4a
4b
4c
5a
5b
7
-0.26
-0.27
-0.40
-0.39
-0.41
-0.37
-0.39
-0.78
-0.13
-0.12
-0.92
-0.92
-0.91
-0.96
-1.01
-0.96
-0.92
-0.99
-0.84
-0.79
0.72
0.72
0.75
0.74
0.73
0.73
0.75
0.74
chloranil
bromanil
TEMPO
0.70
aV vs. SCE, 0.1 M n-BuNClO4 in CH3CN; scan rate = 50 mV/s.
4-amino-TEMPO and the color of the isolated product was
violet in this case.12
Similar molecular/crystal structures are apparent between
2,5-disubstituted derivatives 4a (Figure 3) and 4b (SI-4,
Supporting Information) too. In this case, the benzoquinone
ring of a molecule is being put between two TEMPO groups
of two neighboring molecules with a short oxygen-to-benzo-
quinone distance of 2.90 A for 4a and 2.89 A for 4b, respecti-
vely, resulting in the occurrence of charge transfer between
the donor and acceptor groups also in these compounds,
though their donor-acceptor-donor arrangements are
different from those of 3a and 3b with donor-acceptor-
acceptor-donor arrangements.13
Contrary to the previous crystals, no close contact is seen
between TEMPO and benzoquinone groups in the crystals of
5a and 5b, while somewhat short distances are observed
between the oxygen atoms of a TEMPO group in a molecule
and that of a neighboring molecule (4.28 A for 5a and 4.37 A
for 5b) and between the oxygen atom of another TEMPO
group of the molecule and the carbon atom of a methyl group
of another neighboring molecule (3.32 A for 5a and 3.35 A
for 5b) as shown in Figure 4 for 5a (and SI-5 in the Support-
ing Information for 5b). The orange color of the crystals
indicates no occurrence of charge transfer interactions in the
crystals as was suggested from their crystal structures as well
as diffuse reflectance UV-vis spectra.
A unique feature is disclosed in the structure of compound
7. A close contact of ca. 3 A is observed between the
oxygen atom of a TEMPO group in a molecule and a carbon
atom on the benzoquinone ring of another molecule, i.e., a
CT interaction is revealed in one side of a molecule (Figure
5). On the other hand, a very short oxygen-to-oxygen contact
of 3.17 A is found between the nitroxide groups of the
molecule and the other neighboring molecule. Thus, CT
interaction occurred only on one side of a molecule in this
crystal.
To verify the reduction and oxidation potentials of each
benzoquinone derivative, cyclic voltammetry measurements
were carried out and the data are summarized in Table 1.
It is apparent from their first reduction potentials that
monoradicals 3a and 3b are weaker acceptors compared to
choranil or bromanil and more weaker acceptors are biradi-
cals 4 and 5. There is no significant difference between the
redox data of the chloro-, bromo-, or fluoro-series and
between 2,5-disubustituted compounds 4 and 2,6-disubsti-
tuted ones 5. In spite of the similarity of their redox proper-
ties, the colors of the crystals of 4 and 5 are different and that
implies the difference of their crystal structures. Evidently,
the amino substituent weakens the electron-accepting pro-
perty more than the oxy-substituent as seen for the first
reduction potential of 7 compared to that of 4c. On the
contrary, the first oxidation potentials due to the TEMPO
group of the radical compounds are rather similar, indicating
the existence of similar donating ability of the radical
compounds. Thus, the coexistence of accepting and donating
ability in each molecule is apparently found from the
CV data, enabling the occurrence of some CT interaction
between them.
The UV-vis spectra of the radical compounds were then
measured in solution as well as in the solid state. The λmax
-
values of 3a in acetonitrile are observed at 290 and 415 nm,
respectively, and they reflect the yellow color of the solution
of 3a. Meanwhile a weak and very broad absorption at
around 650 nm with its tail over 800 nm appears in the
diffuse reflectance UV-vis spectrum of 3a in the solid state
as shown in Figure 1, thus indicating the actual presence of
charge transfer in 3a in the solid state to give the black color
of the crystal. Similarly, CT bands are observed in the diffuse
reflectance UV-vis spectra of the compounds 3b, 4a, 4b, and
7 but there is no CT band in the spectra of 5a and 5b to give
the orange colors of the crystals.
Crystal Structures of 1,4-Benzoquinones. The X-ray ana-
lyses of the 1,4-benzoquinone derivatives were performed by
using each single crystal grown from an appropriate solvent
and their crystal data are summarized in the Supporting
Information, SI-1 and SI-2.
Magnetic Properties of 1,4-Benzoquinones. The magnetic
measurements of the solid samples were carried out by using
a SQUID susceptometer in the temperature range of 2 to
300 K and the data are summarized in Table 2.
Antiferromagenetic interactions obeying the Curie-Weiss
law are observed in the spins of 3a and 3b with a Weiss
temperature of -0.41 K for 3a and -1.87 K for 3b, respec-
tively. As no close contact is observed in their crystal
structures other than those described above (vide supra),
the antiferromagnetic interactions observed for both radical
The X-ray analyses of 3a (Figure 2) and 3b (SI-3, Support-
ing Information) indicate that they have similar molecular/
(12) The preparations and some properties of the corresponding chloro-
and bromo-derivative of 7 are reported in ref 8, although neither crystal
structure determinations nor susceptibility measurements were carried out
on the compounds.
(13) Neither single-crystal X-ray analysis of 4c nor its powder X-ray
diffraction measurement to see if its crystal structure is isomorphic with that
of 4a or 4b was successful probably due to its glassy nature.
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JOCArticle
FIGURE 1. Diffuse reflectance UV-vis spectrum of 3a in the solid state.
FIGURE 3. Crystal structures of 4a. Three molecules are depicted
and the broken lines indicate short intermolecular contacts. The
edges of the molecules in the figure also have similar contacts,
making higher order contacts on the whole.
FIGURE 2. Crystal structures of 3a. Four molecules are depicted
and the broken lines indicate short intermolecular contacts. The
edges of the molecules in the figure also have similar contacts,
making higher order contacts on the whole.
operating through a benzoquinone ring at the cryogenic
temperature for each crystal.
compounds are probably due to those between the spin
centers mediated by a couple of benzoquinone rings.
Although the crystal structures of 2,6-disubstituted deri-
vatives 5a and 5b are similar on the whole, their intermole-
cular magnetic interactions are different, i.e., while the
intermolecular magnetic interactions of 5a are antiferromag-
netic, weak ferromagnetic interactions are observed in the
spins of 5b. The difference of the magnetic interactions is
supposed to reflect the difference of the distances between
the spins as seen in their crystal structures. The shorter O-O
distance found in 5a compared to that of 5b may result in the
predominance of antiferromagnetic interactions in 5a, while
ferromagnetic interactions due to the spin polarization
through the hydrogen bonds may comparatively contribute
On the other hand, the magnetic data of 2,5-disubstituted
derivatives 4a and 4b obey a singlet-triplet model and
almost the same weak antiferromagnetic interactions with
J = -2.9 K for 4a and J = -3.0 K for 4b are estimated from
the data originating apparently from the intermolecular
spin-spin interactions.14 Although the magnetic data can-
not be well understood yet, singlet formation is possibly
(14) The J-values were estimated by using the Bleany-Bowers equation:
Bleaney, B.; Bowers, K. D. Proc. R. Soc. London, Ser. A 1952, 214, 451.
9348 J. Org. Chem. Vol. 74, No. 24, 2009

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FIGURE 6. The magnetic data of 7, analyzed by the combination
of a Curie-Weiss (CW) and a singlet-triplet (ST) model. The black
open circles indicate the experimental data and the dotted lines are
the theoretical ones (red: ST; blue: CW; green: combination of ST
and CW), respectively.
FIGURE 4. Crystal structures of 5a. Five molecules are depicted
and the broken lines indicate short intermolecular contacts. The
edges of the molecules in the figure also have similar contacts,
making higher order contacts on the whole.
rare in nitroxide-based organic radical compounds15 and is
apparently based on the close proximity of a couple of
oxygen atoms of nitroxide groups in neighboring molecules
and another oxygen atom may contribute to the Curie-
Weiss term through the CT interaction.
Conclusions
By the reaction of chloranil or bromanil with 4-hydroxy-
TEMPO under basic condition, monosubstituted com-
pounds 3a and 3b were obtained as the major products
together with 2,5- (4a, 4b) and 2,6-disubstituted compounds
(5a, 5b) as the minor compounds, respectively. On the other
hand, 2,5-disubstituted compound 4c or 7 was predomi-
nantly available by the reaction of fluoranil with 4-hydroxy-
or 4 amino-TEMPO. While there appears to be no large
difference of the crystal structures and the magnetic proper-
ties between the chloro- and bromo-series, the packing
features of the monosubstituted derivatives and the disub-
stituted ones are significantly different, leading to the differ-
ence of their magnetic properties. Remarkably, single-
component CT crystals were found to form in monosubsti-
tuted (3a, 3b) and 2,5-disubtituted ones (4a, 4b) by the inter-
actions between a benzoquinone ring of a molecule and a
nitroxide group of neighboring molecules with donor-
acceptor-acceptor-donor arrangement in the former two
derivatives and donor-acceptor-donor arrangement in the
latter two ones, respectively, giving unique and rare exam-
ples of single-component CT complexes involving nitroxide
radical. An intriguing structural feature was disclosed in
compound 7, in which one of the amino-TEMPO groups
contributes to a CT formation while the other has a close
oxygen-to-oxygen contact with another neighboring mole-
cule to give a very large exchange coupling.
FIGURE 5. Crystal structure of 7. Three molecules are depicted
and a couple of short contacts are indicated. The edges of the
molecules in the figure also have similar contacts, making higher
order contacts on the whole.
TABLE 2. Magnetic Data of Benzoquinone Derivatives
compd magnetic interactiona Cb/emu K mol-1 θc/K J/kBd/K
3a
3b
4a
4b
4c
5a
5b
7
antiferromagnetic
antiferromagnetic
antiferromagnetic
antiferromagnetic
antiferromagnetic
antiferromagnetic
ferromagnetic
0.38 (100)
0.38 (100)
0.75 (100)
0.75 (100)
0.75 (100)
0.75 (100)
0.73 (97)
0.73 (97)
-0.41
-1.87
-2.9
-3.0
-5.94
-0.31
0.39
antiferromagnetice
-0.21 -154
aFitting for the Curie-Weiss law. bCurie constant. Numbers in
parentheses denote the estimated spin concentrations, by using a
theoretical value of 0.375 emu K mol-1 for monoradicals and 0.75 for
emu K mol-1 for diradicals, respectively. cWeiss temperature. dEx-
change interactions obtained by fitting for a singlet-triplet model. eSee
text for the magnetic behavior.
Experimental Section
to the ferromagnetic interactions observed between the spins
of 5b.
Materials. Commercial grade chloranil, bromanil, fluoranil,
4-hydroxy-TEMPO, and 4-amino-TEMPO was used for the
reactions described in the text.
The magnetic behavior of compound 7 can be well ana-
lyzed by the combination of a Curie-Weiss behavior of
antiferromagnetic interaction with a small Weiss tempera-
ture (θ = -0.21 K) and a singlet-triplet one of antiferro-
(15) (a) Minguet, M.; Amabilino, D. B.; Vidal-Gancedo, J.; Wurst, K.;
Veciana, J. J. Mater. Chem. 2002, 12, 570. (b) Nakatsuji, S.; Amano, T.;
Akutsu, H.; Yamada, J. J. Phys. Org. Chem. 2006, 19, 333. To our knowl-
edge, this J/kB-value of -154 K is the largest one reported so far among the
nitroxide-based radical compounds.
magnetic interaction with a very large J/kB-value (J/kB
=
-154 K) as shown in Figure 6. Such a large J/kB-value is still
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Nakatsuji et al.
JOCArticle
Instrumentation. Melting points of the solid samples are
uncorrected. The UV-visible spectra were measured in aceto-
nitrile solution or in the solid state at ambient temperature. The
data of FAB-MS spectra were obtained by using m-nitrobenzyl
alcohol as the matrix and appropriate polyethylene glycol
samples as the internal standard. EPR spectra were taken for
in 65% yield together with mixtures of 4b and 5b in 9% yield
and their data are as follows. 3b: mp 152-153 °C; FAB-MS
(m/z) 516 (M þ H); EPR (solid), g = 2.007; UV-vis (CH3-
CN) 203 (4.32), 308 (4.18), 419 (2.72). Anal. Calcd for
C15H17NO4Br3: C, 34.98; H, 3.33; N, 2.72. Found: C, 35.45;
H, 3.32; N, 2.66. 4b: mp 217-219 °C; FAB-MS (m/z) 608 (M þ
2H); EPR (solid), g = 2.007; UV-vis (CH3CN) 205 (4.32), 310
(4.16), 410 (2.65). Anal. Calcd for C24H34N2O6Br2: C, 47.54; H,
5.65; N, 4.62. Found: C, 47.26; H, 5.58; N, 4.73. 5b: mp 168-170
°C; FAB-MS (m/z) 608 (M þ 2H); EPR (solid), g = 2.007;
UV-vis (CH3CN) 206 (4.41), 310 (4.21), 410 (2.80). Anal. Calcd
for C24H34N2O6Br2: C, 47.54; H, 5.65; N, 4.62. Found: C, 47.53;
H, 5.63; N, 4.53.
The main isolated product of the reaction of fluoranil 1c with
4-hydroxy-TEMPO was 2,5-disubstituted compound 4c, re-
gardless of the equivalence of the reagent, and when 2 equiv of
4-hydroxy-TEMPO was used, compound 4c was obtained in
21% yield. Mp 157 °C; FAB-MS (m/z) 486 (M þ 2H); EPR
(solid), g = 2.008; UV-vis (CH3CN) 282 (4.37), 408 (2.81).
Anal. Calcd for C24H34N2O6F2: C, 59.49; H, 7.07; N, 5.78.
Found: C, 59.13; H, 6.97; N, 5.62.
The Reaction of Fluoranil with 4-Amino-TEMPO. A stirred
mixture of fluoranil 1c (0.10 g, 0.56 mmol) and 4-amino-
TEMPO 6 (0.19 g, 1.11 mmol) in CH3CN (30 mL) was heated
to 70 °C for 2 h. The reaction mixture was then cooled to
ambient temperature and evaporated in vacuo. The resulting
dark solid was then purified by column chromatography on
silica gel with dichloromethane to give 2,5-disubstituted
derivative 7 (0.11 g, 41%). Recrystallization in a mixed
solvent of hexane and dichloromethane gave violet crystals
and the data are as follows. Mp >280 °C; FAB-MS (m/z)
484 (M þ 2H); EPR (solid), g = 2.006; UV-vis (CH3CN)
222 (4.52), 351 (4.46). Anal. Calcd for C24H36N4O4F2:
C, 59.73; H, 7.52; N, 11.52. Found: C, 59.44; H, 7.63;
N, 11.40.
solid samples and g-values were determined by using the Mn2þ
/
MgO maker as the internal standard. Magnetic susceptibility
measurements were carried out on a SQUID susceptometer
using ca. 10 mg for each powdered sample. Crystal structures
of all compounds were determined at room temperature. X-ray
diffraction data were recorded with a CCD area detector on a
diffractometer and crystal structures were solved by the direct
method. The refinements were made by the full-matrix least-
squares methods. Anisotropic temperature factors were used for
the non-hydrogen atoms and the hydrogen atoms were included
in the final calculation. All the calculations were performed with
the Texan crystallographic software package. Crystal data of 3a,
3b, 4a, 4b, 5a, 5b, and 7 have been deposited with the Cambridge
Crystallographic Data Centre. Copies of the data can be ob-
tained free of charge via http://www.ccdc.cam.ac.uk/conts/
retrieving.html.
The Reaction of Chloranil with 4-Hydroxy-TEMPO. To a
stirred mixture of chloranil 1a (1.43 g, 5.80 mmol) and
4-hydroxy-TEMPO 2 (1.00 g, 5.8 mmol) in DMF (50 mL) was
added potassium carbonate (1.60 g, 11.6 mmol) at ambient
temperature. After the solution was stirred for 2 h and the solid
substance filtered off, the reaction mixture was concentrated in
vacuo and then purified by column chromatography on silica gel
with the solvent system of hexane and dichloromethane (1:1) to
give monosubstituted compound 3a (1.13 g, 48%) and disubsti-
tuted compounds (mixtures of 4a and 5a, 0.238 g, 10%),
respectively. Recrystallization of 3a was performed in a mixed
solvent of hexane and pentane (1:1) to give black blocks. Mp
125-127 °C; FAB-MS (m/z) 382 (M þ H); EPR (solid), g =
2.007; UV-vis (CH3CN) 290 (4.31), 415 (2.85). Anal. Calcd for
C15H17NO4Cl3: C, 47.20; H, 4.49; N, 3.76. Found: C, 47.10; H,
4.34; N, 3.56. Recrystallization of mixtures of 4a and 5a in
acetonitrile afforded brownish black blocks of 4a and orange
plates of 5a, which could be easily separated by hand and their
data are as follows. 4a: mp 209-211 °C; FAB-MS (m/z) 519 (M
þ 2H); EPR (solid), g = 2.007; UV-vis (CH3CN) 204 (4.30),
300 (4.19), 408 (2.67). Anal. Calcd for C24H34N2O6Cl2: C, 55.71;
H, 6.62; N, 5.41. Found: C, 55.59; H, 6.65; N, 5.39. 5a: mp
153-156 °C; FAB-MS (m/z) 519 (M þ 2H); EPR (solid), g =
2.007; UV-vis (CH3CN) 203 (4.31), 300 (4.16), 410 (2.67). Anal.
Calcd for C24H34N2O6Cl2: C, 55.71; H, 6.62; N, 5.41. Found: C,
55.77; H, 6.63; N, 5.28.
Acknowledgment. This work was partially supported by a
special grant from the University of Hyogo and the Tokyo
Ohka Foundation for The Promotion of Science and Tech-
nology, which are gratefully acknowledged. We also thank
Prof. Koshiro Toriumi and his group of this school for
diffuse reflectance UV-vis measurements of the benzoqui-
nones.
Supporting Information Available: Tables of crystallo-
graphic data of 3a, 3b, 4a, 4b, 5a, 5b, and 7 (Tables 1, SI-1 and
Table 2, SI-2), their CIF files, and figures of crystal structures of
3b (SI-3), 4b (SI-4), and 5b (SI-5). This material is available free
of charge via the Internet at http://pubs.acs.org.
In a similar manner, the reaction of bromanil 1b with 4-
hydroxy-TEMPO was carried out to give 3b as the main product
9350 J. Org. Chem. Vol. 74, No. 24, 2009