Novel radical compounds bearing mesogenic cores with long alkyl substituents

Article abstract of DOI:10.1021/jo0206972

Series of aminoxyl radicals (TEMPO or nitronyl nitroxide radicals) bearing phenyl benzoate, troponoid, or biphenylcarbonitrile as mesogenic cores with long alkyl substituents were prepared. Although most aminoxyl radicals showed only weak antiferromagnetic interactions due probably to the remote spin centers as clarified by the X-ray analysis of 4a and no appreciable mesogenic phase was observed in each compound, an unusual magnetic transition from an original Curie-Weiss phase to another magnetic phase well-expressed by a singlet-triplet (ST) model was disclosed through the thermal transition in the 4′-undecyloxy-4-biphenylcarbonitrile derivative with oxocarbonyl-TEMPO 12b.

Full text of DOI:10.1021/jo0206972

Novel Ra d ica l Com p ou n d s Bea r in g Mesogen ic Cor es w ith Lon g
Alk yl Su bstitu en ts
Shin’ichi Nakatsuji,*,† Hiroshi Ikemoto,† Hiroki Akutsu,† J un-ichi Yamada,† and Akira Mori‡
Department of Material Science, Graduate School of Science, Himeji Institute of Technology, 3-2-1 Kouto,
Kamigori, Hyogo 678-1297, J apan, and Institute of Advanced Material Study, Kyushu University,
Kasuga, Fukuoka 816-8580, J apan
nakatuji@sci.himeji-tech.ac.jp
Received November 14, 2002
Series of aminoxyl radicals (TEMPO or nitronyl nitroxide radicals) bearing phenyl benzoate,
troponoid, or biphenylcarbonitrile as mesogenic cores with long alkyl substituents were prepared.
Although most aminoxyl radicals showed only weak antiferromagnetic interactions due probably
to the remote spin centers as clarified by the X-ray analysis of 4a and no appreciable mesogenic
phase was observed in each compound, an unusual magnetic transition from an original Curie-
Weiss phase to another magnetic phase well-expressed by a singlet-triplet (ST) model was disclosed
through the thermal transition in the 4′-undecyloxy-4-biphenylcarbonitrile derivative with oxo-
carbonyl-TEMPO 12b.
In tr od u ction
such spin systems that respond to the outer stimuli of
heat have been reported along this line in the past few
years. After the eminent studies of Kahn et al. on spin-
transition polymers,6 Fujita and Awaga found novel room
temperature magnetic bistability in 1,3,5-trithia-2,4,6-
triazapentalenyl (TTTA).7 Sugano reported last year on
the magnetic phase transition in the 5-carboxy-2-thienyl
nitronyl nitroxide radical8 and Schultz et al. prepared an
intriguing biradical showing magnetic bistability with a
hysteretic phase transition.9
Stable radicals, above all aminoxyl radicals, have been
widely used as spin labels,1 reagents for redox2 or
polymerization reactions,3 and some other purposes4 in
biological, physicochemical, or synthestic studies and
their usage in materials chemistry has emerged in recent
years as the building blocks in molecular based-magnetic
materials.5
During the remarkable progress of chemistry and
physics in the field of molecular based-magnetic materi-
als, considerable interest has recently been focused on
the development of magnetic materials (spin systems)
with multiproperties and several attractive examples of
In the course of our studies to develop novel organo-
magnetic materials,10 we have been interested in prepar-
ing multifunctional spin systems with conductivity,
photofunctionality, or liquid crystalline property by using
stable radicals, especially aminoxyl radicals, as spin
sources.11 The development of spin systems with the
liquid crystalline property is particularly interesting
because of the possibility of ordered spin interactions in
the oriented molecular aggregates and/or the possibility
of the alteration of the magnetic properties through the
phase transition. We then have been interested in
preparing the spin systems with mesogenic cores such
as cholesterol or biphenyl with long alkyl substituents
and reported previously on the existence of a liquid
crystalline phase and a magnetic phase transition through
the phase in a biphenyl derivative with 4-(N-methyl)-
† Himeji Institute of Technology.
‡ Kyushu University.
(1) Cf.: (a) Nitroxide Spin Labels, Reactions in Biology and Chem-
istry; Kocherginsky, N., Swartz, H. M., Eds.; CRC Press: Boca Raton,
FL, 1995. (b) Biological Magnetic Resonance, Vol. 14: Spin Labeling;
Berliner, L., Ed.; Plenum Press: New York, 1998.
(2) Cf.: (a) Bobbitt, J . M.; Flores, M. C. L. Heterocycles, 1988, 27,
509. (b) de Nooy, A. E. J .; Besemer, A. C.; van Bekkum, H. Synthesis
1996, 1153. (c) Naik, N.; Braslau, R. Tetrahedron 1998, 54, 667.
(3) Cf.: (a) Hawker, C. J . Acc. Chem. Res. 1997, 30, 373. (b)
Malmstro¨m, E. E.; Hawker, C. J . Macromol. Chem. Phys. 1998, 199,
923.
(4) Cf.: (a) Corvaja, C.; Maggini, M.; Prato, M.; Scorrano, G.; Venzin,
M. J . Am. Chem. Soc. 1995, 117, 8857. (b) Ishii, K.; Fujisawa, J .; Ohba,
Y.; Yamauchi, S. J . Am. Chem. Soc. 1996, 118, 13079. (c) Bossmann,
S. H.; Ghatlia, N. D.; Ottaviani, M. F.; Turro, C.; Durr, H.; Turro, N.
J . Synthesis 1996, 1313. (d) Mizuochi, N.; Ohba, Y.; Yamauchi, S. J .
Phys. Chem. A 1997, 101, 5966. (e) Ishii, K.; Hirose, Y.; Kobayashi, N.
J . Am. Chem. Soc. 1998, 120, 10551. (f) Ishii, K.; Ishizaki, T.;
Kobayashi, N. J . Phys. Chem. A 1999, 103, 6060.
(6) Cf.: Kahn, O.; Martinez, C. J . Science 1998, 279, 44.
(7) Fujita, W.; Awaga, K. Science 1999, 286, 261.
(5) For recent review books on molecular-based magnetic materials,
see, for example: (a) Magnetic Properties of Organic Materials; Lahti,
P. M., Ed.; Marcel Dekker, Inc.: New York, Basel, 1999. (b) Molecular
Magnetism; Itoh, K., Kinoshita, M., Eds.; Kodansha/Gordon and Breach
Science Publishers: Tokyo, J apan, 2000. (c) Structure and Bonding,
Vol. 100, π-Electron Magnetism: From Molecule to Magnetic Materials;
Veciana, J ., Ed.; Springer-Verlag: Berlin, Germany, 2001. (d) Mag-
netism: Molecules to Materials; Eds. Miller, J . S.; Drillon, M., Wiley-
VCH: Weinheim, 2001-2002; Vols. I-III.
(8) Sugano, T. Chem. Lett. 2001, 32.
(9) Shultz, D. A.; Fico, R. M., J r.; Boyle, P. D.; Kampf, J . W. J . Am.
Chem. Soc. 2001, 123, 10403.
(10) Cf.: Natatsuji, S.; Anzai, H. J . Mater. Chem. 1997, 7, 2161.
(11) Cf.: (a) Nakatsuji, S. Adv. Mater. 2001, 13, 1719. (b) Nakatsuji,
S. In Recent Research Developments in Organic & Bioorganic Chem-
istry; Pandalai, S. G., Ed.; Transworld Research Network: Trivandrum,
2002; Vol. 5, pp 1-26. See also: Nakatsuji, S.; Ojima, T.; Akutsu, H.;
Yamada, J . J . Org. Chem. 2002, 67, 916.
10.1021/jo0206972 CCC: $25.00 © 2003 American Chemical Society
Published on Web 02/01/2003
1708
J . Org. Chem. 2003, 68, 1708-1714

Novel Radical Compounds Bearing Mesogenic Cores
CHART 1
exhibiting liquid crystalline phases and we then tried to
prepare the derivatives with stable radicals together with
long alkyl substituents. At first, phenyl benzoate deriva-
tives (3a ,b) with alkyl substituents as well as the
4-imino-TEMPO-subsitutent were prepared from the
corresponding 4-formyl derivatives 2a ,b by condensing
with 4-amino-TEMPO in toluene solution containing a
catalytic amount of acetic acid. The formyl derivatives,
in turn, were obtained by the esterification of 4-heptyl-
or 4-octylbenzoic acid 1a ,b with 4-hydroxybenzaldehyde
in moderate yields by using DCC (1,3-dicyclohexylcar-
bodiimide) and DMAP (4-(dimethyamino)pyridine) as the
condensation reagents. The radical compound 4a ,b was
prepared from the formyl derivative with 2,3-bis(hy-
droxylamino)-2,3-dimethylbutane sulfate and potassium
carbonate in methanol and successive oxidation of the
resulting hydroxylamine derivative with sodium perio-
date,16 although the yields of the desired radical com-
pounds were very low (Scheme 1).
(2) Tr op on oid Der iva tives 7 a n d 9. Troponoids with
appropriate subsituents have been elucidated to be
promising mesogenic cores from the extensive studies of
one of the present authors17 and therefore we next tried
to prepare the derivatives with stable radicals. The alkyl
troponoid derivative with 4-imino-TEMPO-subsitutent
(7) was prepared from the corresponding 4-formyl deriva-
tive 6 by condensing with 4-amino-TEMPO in a similar
manner as for the preparation of phenyl benzoate deriva-
tives 3. The formyl derivative was obtained by the
esterification of dodecyloxy tropolone derivative 518 with
4-formylbenzoic acid by using DCC and DMAP. The
formyl derivative, on the other hand, was condensed with
benzoic acid derivative with 4-oxocabonyl-TEMPO-sub-
stituent to give the troponoid derivative 9 in 46% yield
(Scheme 2).
(3) Cya n obip h en yl Der iva tives 12 a n d 14. The
preparation of cyanobiphenyl derivatives 12a -c and
14a -c was carried out as shown in Scheme 3. The
alkylation of 4′-hydroxy-4-biphenylcarbonitrile (10) with
bromoalkan-1-ols19 gave alcohols 11a -c in moderate
yields and the corresponding aldehydes 12a -c were
obtained after PCC oxidation of the alcohols. TEMPO
derivatives with a cyanobiphenyl core (12a -c) were
obtained from the alcohols 11a -c with 4-carboxy-
TEMPO by using DCC and DMAP as the condensation
reagents and nitronyl nitroxide derivatives with a similar
structure (14a -c) were prepared by the method as
described above with sodium periodate as an oxidizing
reagent.
amino-TEMPO (TEMPO ) 2,2,6,6-tetramethyl-1-pip-
eridinyloxy)-substituent,12 although it is known that the
sources of organic radicals are unsuitable for the syn-
thesis of liquid crystals in general, due mainly to inap-
propriate substitution patterns or the geometry and
bulkiness of radical-stabilizing substituents, which are
detrimental to mesophase stability.13 Actually, beside the
radical mentioned above, only a few organic radicals with
less bulky DOXYL (4,4-dimethyl-3-oxazolidinyloxy)-sub-
stituent have so far been reported to show the liquid
crystalline property.14 We wish to report in this paper
our further search for organic radical compounds consist-
ing of TEMPO or nitronyl nitroxide radical on one hand
and bearing phenyl benzoate, troponoid, or biphenylcar-
bonitrile with long alkyl substituents as mesogenic cores
on the other hand toward the development of heat-
responsive liquid crystalline radicals and the finding of
an unusual magnetic transition from a Curie-Weiss
phase to another magnetic phase well expressed by a ST
model through the thermal transition in the 4′-undecyl-
oxy-4-biphenylcarbonitrile derivative with oxocarbonyl-
TEMPO 12b despite the absence of a distinct liquid
crystalline phase.15
Resu lts a n d Discu ssion
Ma gn etic P r op er ties of 3, 4, 7, a n d 9 a n d th e
Molecu la r /Cr ysta l Str u ctu r e of 4a . Typical absorp-
tions due to aminoxyl radicals (TEMPO or nitronyl
nitroxide) were observed in the EPR spectra of radicals
3, 4, 7, and 9 in benzene solution. The magnetic suscep-
tibility measurements for the solid samples of each
radical were carried out on the polycrystalline sample
P r ep a r a tion of Ra d ica l Com p ou n d s w ith Meso-
gen ic Cor es. (1) P h en yl Ben zoa te Der iva tives 3a ,b
a n d 4a ,b. Phenyl benzoate derivatives with long alkyl
substituents are known to be possible mesogenic cores
(12) Nakatsuji, S.; Mizumoto, M.; Ikemoto, H.; Akutsu, H.; Yamada,
J . Eur. J . Org. Chem. 2002, 1912.
(13) Kaszynski, P. In Magnetic Properties of Organic Materials;
Lahti, P. M., Ed.; Marcel Dekker: New York, Basel, 1999; Chapter
15, p 305.
(14) (a) Dvolaitzky, M.; Billard, J .; Poldy, F. C. R. Acad. Sci., Ser. C
1974, 279, 533. (b) Dvolaitzky, M.; Billard, J .; Poldy, F. Tetrahedron
1976, 32, 1835. (c) Allgaier, J .; Finkelmann, H. Macromol. Chem. Phys.
1994, 195, 1017.
(15) A portion of this work has been reported as a preliminary
communication: Ikemoto, H.; Akutsu, H.; Yamada, J .; Nakatsuji, S.
Tetrahedron Lett. 2001, 42, 6873.
(16) Ullman, E. F.; Osciecki, J . H.; Boocock, D. G. B.; Darcy, R. J .
Am. Chem. Soc. 1972, 94, 7049.
(17) (a) Mori, A.; Takeshita, H. J . Synth. Org. Chem. J pn. 1995,
53, 232. (b) Mori, A.; Uno, K.; Takeshita, H.; Kakihara, Y.; Ujiie, S.
Liq. Cryst. 2002, 29, 1539.
(18) (a) Mori, A.; Uchida, M.; Takeshita, H. Chem. Lett. 1989, 591.
(b) Mori, A.; Kato, N.; Takeshita, H.; Uchida, M.; Taya, H.; Nimura,
R. J . Mater. Chem. 1991, 1, 799.
(19) Cf. Chuaed, T.; Deschenaux, R. Helv. Chim. Acta 1996, 79, 736.
J . Org. Chem, Vol. 68, No. 5, 2003 1709

Nakatsuji et al.
SCHEME 1 a
a
Reagents: (a) 4-Hydroxybenzaldehyde, DCC, DMAP. (b) 4-Amino-TEMPO, AcOH. (c) (i) 2,3-Bis(hydroxyamino)-2,3-dimethylbutane
sulfate, K2CO3; (ii) NalO4.
SCHEME 2 a
a
Reagents: (a) 4-Formylbenzoic acid, DCC, DMAP. (b) 4-Amino-TEMPO, AcOH. (c) DCC, DMAP.
TABLE 1. Ma gn etic Da ta for Ra d ica ls 3, 4, 7, a n d 9
the absence of significant through space as well as
through bond spin-spin interactions between the spin
centers. To see the strcture-magnetic property relation-
ship of the radical compounds, the X-ray analysis of
radical 4a was carried out by using a single crystal
obtained from methanol solution, its molecular/crystal
structure is shown in Figure 1, and the crystal data are
summarized in Table 2. As for the molecular structure
of 4a , it is of interest that three important molecular
planes are not coplanar (Figure 1, upper). The dihedral
angle between the molecular plane of the imidazoline ring
and the benzene ring bonding with the ring amounts to
25.3° and that between the two benzene rings connected
with the ester group amounts to 103.9°.21 In the crystal
structure, two molecules are dimerized in slipped head-
to-tail arrangement and the dimers are stacking almost
along the c-axis each in a perpendicular manner as shown
compd
magnetic interactiona
Cb/emu K mol-1
θc/K
3a
3b
4a
4b
7
antiferromagnetic
antiferromagnetic
antiferromagnetic
antiferromagnetic
antiferromagnetic
antiferromagnetic
0.33 (87)
0.37 (97)
0.21 (55)
0.34 (89)
0.32 (84)
0.36 (95)
-2.56
-3.58
-0.26
-0.13
-1.39
-0.17
9
a
b
Fitting for the Curie-Weiss law. Curie constant. The num-
bers in parentheses denote the estimated spin concentration.
c Weiss temperature.
by a SQUID susceptometer in the temperature range of
2-300 K and the data are summarized in Table 1.
Curie-Weiss behavior with weak antiferromagnetic
interactions was observed in each radical compound
examined and the tendency of exhibiting slightly larger
Weiss temperature was found in TEMPO-substituted
derivatives (e.g., 3a , 3b) being compared to the corre-
sponding nitronyl nitroxide radicals (e.g., 4a ,20 4b). Such
observation of only weak antiferromagnetic interactions
between the spins in these radical compounds suggests
(20) The value of the Curie constant for this radical was found to
be rather small owing to its relative instability.
(21) Similar molecular structure has been reported in a Shiff base
with the nitronyl nitroxide radical; cf.: Zhang, D.; Zhou, W.; Zhu, D.
J . Mater. Chem. 1999, 9, 1409.
1710 J . Org. Chem., Vol. 68, No. 5, 2003

Novel Radical Compounds Bearing Mesogenic Cores
SCHEME 3 a
a
Reagents: (a) Br(CH2)nOH (n ) 10-12), K2CO3. (b) 4-Carboxy-TEMPO, DCC, DMAP. (c) PCC. (d) (i) 2,3-Bis(hydroxyamino)-2,3-
dimethylbutane sulfate, K2CO3; (ii) NalO4.
F IGURE 1. (Upper) Molecular structure of 4a . (Lower) Crystal structure of 4a with the indication of a unit cell.
in Figure 1 (lower). The shortest O-O distance between
the molecules estimated from the analysis is approxi-
mately 5.08 Å and no other significant interactions
appear to exist between the spin centers to give, as the
consequence, only weak spin interactions in the spins of
this radical (θ ) -0.26 K).
Unfortunately, no phase transition except the melting
point was observed in each radical described above by
DSC measurements, suggesting the absence of any
appreciable mesogenic phase.
Ma gn etic P r op er ties of 12a -c a n d 14a -c a n d th e
Molecu la r /Cr ysta l Str u ctu r e of 12b. The magnetic
J . Org. Chem, Vol. 68, No. 5, 2003 1711

Nakatsuji et al.
TABLE 2. Su m m a r y of Cr ysta l Da ta for 4a a n d 12b
4a
12b
formula
C
27H35N2O4
C
36H47N2O4
fw
451.58
monoclinic
P21/n
12.008(7)
9.3378(7)
22.958(1)
571.78
triclinic
P1h
cryst syst
space group
a/Å
b/Å
5.768(1)
14.891(2)
18.637(3)
84.860(3)
84.664(3)
85.737(3)
1583.9(4)
2
1.199
8562
6024
2401
c/Å
R/deg
â/deg
104.115(5)
γ/deg
V/Å3
2536.7(3)
4
1.182
5765
5503
3183
Z
D(calc)/g cm-3
no. of measd reflns
no. of independent reflns
no. of used reflns in
refinement F > 3σ
no. of parameters refined
R
392
0.067
0.066
361
0.119
0.136
Rw
TABLE 3. Ma gn etic Da ta of Ra d ica ls 12a -c a n d 14a -c
compd
magnetic interactiona
Cb/emu K mol-1
θc/K
12a
12b
12c
14a
14b
14c
antiferromagnetic
antiferromagnetic
antiferromagnetic
antiferromagnetic
antiferromagnetic
antiferromagnetic
0.38 (100)
0.36 (95)
0.36 (95)
0.37 (97)
0.34 (89)
0.37 (97)
-2.37
-0.19
-2.70
-0.83
-0.40
-0.63
F IGURE 2. (Upper) Molecular structure of 12b. (Lower)
Crystal structure of 12b viewed almost along the a-axis.
a
b
Fitting for the Curie-Weiss law. Curie constant. The num-
bers in parentheses denote the estimated spin concentration.
c Weiss temperature.
and 14a -c) over the temperature range examined by
DSC measurement except 12b, in which two endothermic
peaks appeared at around 84 and 90 °C, respectively.22
However, no distinct appearance of a texture was ob-
served in 12b by polarizing microscope investigation,
suggesting the absence of a mesogenic phase but the
existence of another polymorphic form through the
thermal phase transition instead. We then measured the
magnetic susceptibility of 12b with Curie-Weiss behav-
ior from 27 (300 K) up to 100 °C (373 K). The Curie-
Weiss behavior observed during the heating process was
found to change after the thermal transition at ca. 90 °C
to another behavior being well expressed by a singlet-
triplet (ST) model with antiferromagnetic spin-spin
interactions of relatively large J value (J ) -35 K) during
the cooling process as shown in Figure 3.
properties of 4-cyanobiphenyl derivatives with TEMPO
or nitronyl nitroxide substituents and long alkoxyl chains
between are summarized in Table 3.
Again, only weak antiferromagnetic interactions obey-
ing Curie-Weiss behavior were observed in each radical
prepared and slightly larger Weiss temperatures were
clarified in TEMPO-substituted derivatives (12a ,12c)
being compared to the corresponding nitronyl nitroxide
radicals (14a , 14c) except 12b, the Weiss temperature
of which was as small as -0.19 K. A single crystal
suitable for crystal structure analysis was obtained for
the radical 12b grown from methanol solution in a
refrigerator and its molecular/crystal structure is shown
in Figure 2.
Thus, the Curie-Weiss behavior has been found to be
changed to another magnetic behavior by merely heating
the radical over the thermal transition temperature
although a reverse change to the original Curie-Weiss
behavior from the latter one was not observed but the
behavior of ST model remained unchanged in the further
heating/cooling process. Such unusual thermomagnetic
behavior is considered to be derived from the crystal
structural change from the former phase to a new phase
having presumably a more thermally stable structure.23
The crystal structure obtained by X-ray analysis for
the single crystal of 12b with Curie-Weiss behavior
revealed a similar packing feature to that of the 4-(N-
methylamino)-TEMPO-substituted 4-heptylbiphenyl-4′-
carboxamide derivative, which exhibits mesogenic be-
havior with the lamellar packing feature.12 Thus, the
molecules stack slantwise along the b-axis in which
TEMPO groups and undecyloxycyanobiphenyl groups
stack separately to form a columnar structure which
appears to be suitable to exhibit a mesogenic-like phase
(Figure 2, lower). The oxygen-oxygen distances of the
spin centers amount to 5.77 Å, which are fairly distant
so as to allow only weak antiferromagnetic interaction
between the spins.
Con clu sion s
Several organic radical compounds were prepared
which consist of TEMPO or nitronyl nitroxide radical as
Th er m om a gn etic P r op er ty of Ra d ica l 12b. Only
the thermal transition corresponding to the melting point
was found in this class of radical compounds (12a , 12c.
(22) The DSC measurements were carried out between 50 and 110
°C for this radical at the rate of 2 °C/min.
1712 J . Org. Chem., Vol. 68, No. 5, 2003

Novel Radical Compounds Bearing Mesogenic Cores
F IGURE 3. (Left) Temperature dependence of magnetic susceptibilities of 12b between 300 and 370 K measured at 0.5 T. The
data for the heating and cooling process are depicted as closed and open squares, respectively. The region between the phase
transition temperatures is indicated as an open circle. (Right) Temperature dependence of magnetic susceptibilities of 12b before
and after the phase transition. The data for the heating and cooling process are depicted as closed and open squares, respectively.
heptylbenzoic acid 1a (0.36 g, 1.6 mmol) and 4-hydroxyben-
zaldehyde (0.20 g, 1.6 mmol) in dichloromethane (30 mL) was
added DCC (0.41 g, 2.0 mmol) and DMAP (0.24 g, 2.0 mmol)
and stirring was continued for 1 d at ambient temperature.
The resulting reaction mixture was then washed with brine,
dried over anhydrous MgSO4, and concentrated in vacuo to
give a solid that was purified by column chromatography on
silica gel with use of benzene as an eluent. The ester
intermediate 2a was obtained (0.38 g) as a colorless solid that
was used without further purification for the successive
reaction. The toluene solution (30 mL) of the intermediate 2a
(0.38 g, 1.2 mmol) and 4-amino-TEMPO (0.20 g, 1.2 mmol) with
a small amount of acetic acid was heated to reflux and the
reaction was continued for 1 h. The reaction mixure was
concentrated under reduced pressure to give a crude solid and
the recrystallization of the solid from toluene yielded the
radical 3a as a red powdery solid (0.38 g, 48% from 1a ), mp
95-98 °C dec; EPR (benzene) 3 lines, g ) 2.006, a ) 1.53 mT;
FAB-HRMS calcd for C30H43N2O3 (M + 2)25 479.3220, found
m/z 479.3205. In a similar manner, the radical 3b was obtained
in 24% yield (2 steps), and its data are as follows: mp 105-
107 °C; EPR (benzene) 3 lines, g ) 2.006, a ) 1.50 mT; FAB-
HRMS calcd for C31H45N2O3 (M + 2) 493.3395, found m/z
493.3418.
P r ep a r a tion of P h en ylben zoa te Der iva tives w ith Nit-
r on yl Nitr oxid e Ra d ica l (4a , 4b). A mixture of the inter-
mediate 2a (0.19 g, 0.56 mmol), 2,3-bis(hydroxylamino)-2,3-
dimethylbutane sulfate (0.18 g, 0.83 mmol), and potassium
carbonate (0.082 g, 0.56 mmol) in a mixed solution of methanol/
water (9:1) (50 mL) was stirred for 1d at ambient temperature.
After workup of the reaction mixture in the usual manner,
the crude product was dissolved in methanol (5 mL) and
sodium periodate (0.13 g, 0.56 mmol) was added at 0 °C. The
resulting dark blue solution was stirred for 3 min and then
extracted with chloroform. The organic layer was dried over
anhydrous MgSO4 and concentrated in vacuo to give a solid
that was purified by column chromatography on silica gel by
using n-hexane/ethyl acetate as an eluent and recrystallized
from methanol. The radical 4a was obtained as dark blue
needles (10 mg, 4% from 2a ): mp 97-100°C; EPR (benzene)
5 lines, g ) 2.007, a ) 1.50 mT; FAB-HRMS calcd for
spin sources on one hand and phenyl benzoate, troponoid,
or biphenylcarbonitrile with long alkyl substituents as
mesogenic cores on the other hand to develop heat-
responsive liquid crystalline radicals. Although most
radicals exhibited only weak antiferromagnetic inter-
actions being based on Curie-Weiss law and the struc-
ture-magnetic property relationship could be rationally
understood by the crystal structure analysis for radical
4a , an unusual magnetic transition from a Curie-Weiss
phase to another magnetic phase well expressed by a ST
model was revealed through the thermal transition in
4′-undecyloxy-4-biphenylcarbonitrile derivative with oxo-
carbonyl-TEMPO 12b despite the absence of an ap-
preciable mesogenic phase in the radical.
Exp er im en ta l Section
Ma t er ia ls. 4-Amino-, 4-hydroxy-, and 4-carboxy-TEMPO
radicals used as building blocks in this study are commercially
available and were used without further purification.
In str u m en ta tion . Magnetic susceptibility measurements
were carried out on a QUNTUM DESIGN MPMS-5 SQUID
susceptometer, using ca. 10 mg for each powdered sample in
the usual way.24
X-r a y Str u ctu r e Deter m in a tion . X-ray diffraction data
were collected on a Nonius (CAD4) with Cu KR radiation (for
4a ) or Brucker (Mercury CCD) diffractometer with Mo KR
radiation (for 12b) at room temperature. The structures were
solved by direct methods and expanded by using Fourrier
techniques. The non-hydrogen atoms were refined anisotro-
pically. Hydrogen atoms were included but not refined. All
calculations were performed with use of the teXsan crystal-
lographic software package of Molecular Structure Corporation
and detailed crystallographic data (atomic coordinates, hydro-
gen atom coordinates, anisotropic displacement parameters,
bond length and angles) have been deposited with the Cam-
bridge Crystallographic Data Centre. Details are available as
Supporting Information.
P r ep a r a tion of P h en ylben zoa te Der iva tives w ith th e
TEMP O Ra d ica l (3a , 3b). To a stirred solution of 4-n-
C
27H37N2O4 (M + 2) 453.2714, found m/z 453.2704. In a similar
manner, the radical 4b was obtained in 4% yield (2 steps), and
its data are as follows: mp 95-97 °C; EPR (benzene) 5 lines,
(23) Such a magnetic switching behavior might allow us to be
reminded of, in principle, a write-once recordable memory device by
application of an outer stimulus (heat in the present case).
(24) Cf.: Nakatsuji, S.; Takai, A.; Nishikawa, K.; Morimoto, Y.;
Yasuoka, N.; Suzuki, K.; Enoki, T.; Anzai, H. J . Mater. Chem. 1999,
9, 1747.
(25) The tendency toward appearance of the M + 2 peak as the main
peak was observed in the FAB-MS measurements for this class of
radical compounds in general and we then adjusted the FAB-HRMS
data generally to the main peak.
J . Org. Chem, Vol. 68, No. 5, 2003 1713

Nakatsuji et al.
g ) 2.007, a ) 1.50 mT; FAB-HRMS calcd for C28H39N2O4 (M
+ 2) 467.2938, found m/z 467.2915.
563.3849, found m/z 563.3815. Anal. Calcd for C35H49N2O4: C,
74.83; H, 8.79; N, 4.99. Found: C, 74.91; H, 8.77; N, 4.70.
P r ep a r a tion of Tr op on oid Der iva tives w ith TEMP O
Ra d ica l (7, 9). Dodecyloxy tropolone derivative 5 was pre-
pared according to the published procedure from 5-hydroxyl-
tropolone with 1-bromododecane18 and 0.20 g of 5 (0.65 mmol)
was condensed with 4-formylbenzoic acid (0.098 g, 0.65 mmol)
with use of DCC (0.14 g, 0.69 mmol) and DMAP (0.080 g, 0.69
mmol) in dichloromethane (30 mL) in the usual manner to give
the intermediate 6 as a colorless solid. The intermediate 6 (0.20
g, 0.69 mmol) was reacted with 4-amino-TEMPO (0.12 g, 0.69
mmol) with a small amount of acetic acid in toluene solution
(40 mL) to give the radical 7 as an orange powdery solid (0.26
g, 50% from 5): mp ca. 170°C dec; EPR (benzene) 3 lines, g )
2.007, a ) 1.60 mT; FAB-HRMS calcd for C36H52N2O5 (M + 2)
592.3876, found m/z 592.3898. The radical 9 was prepared in
a similar manner as above from the same compound 6 with
TEMPO-substituted terephthalic acid mono-ester 8 which, in
turn, was obtained from telephthaloyl chloride with 4-hydroxy-
TEMPO and triethylamine in dichloromethane. The data for
the radical 9 are as follows: mp 125-128 °C; EPR (benzene)
P r ep a r a tion of Cya n obip h en yl Der iva tives w ith Nit-
r on yl Nitr oxid e Ra d ica l (14a -c). To a stirred solution of
alcohol 11a (0.20 g, 0.57 mmmol) in dichloromethane (50 mL)
was added PCC (0.18 g, 0.85 mmol) and the stirring was
continued for 1 h; the resulting solution was filtrated with
Celite under reduced pressure. After purification of the filtrate
by column chromatography, aldehyde 13a was obtained as a
colorless powdery solid (0.15 g, 76%). Aldehyde 13a was then
derivatized to nitronyl nitroxide derivative 14a by the two-
step sequence as described above. The radical 14a was
obtained as reddish violet microcrystals (49 mg, 19% from
13a ): mp 124-128 °C; EPR (benzene) 5 lines, g ) 2.007, a )
1.58 mT; FAB-HRMS calcd for C29H39N3O3 (M + 1) 477.2991,
found m/z 477.3036. In a similar manner, the radicals 14b and
14c were obtained in 13% and 14% yield, respectively, and
the data are as follows: 14b: mp 126-130 °C; EPR (benzene)
5 lines, g ) 2.007, a ) 1.63 mT; FAB-HRMS (M + 2) calcd for
C
30H42N3O3 492.3227, found m/z 492.3252. 14c: mp 133-
136°C; EPR (benzene) 5 lines, g ) 2.007, a ) 1.51 mT; FAB-
HRMS calcd for C31H43N3O3 (M + 1) 505.3304, found m/z
505.3304.
3 lines, g ) 2.006, a ) 1.51 mT; FAB-HRMS calcd for C36H52
NO7 (M + 2) 610.3744, found m/z 610.3729.
-
P r ep a r a t ion of Cya n ob ip h en yl Der iva t ives w it h
TEMP O Ra d ica l (12a -c). A stirred mixture of 4-cyano-4′-
hydroxybiphenyl 10 (0.20 g, 1.0 mmol), 10-bromodecanol (0.48
g, 2.1 mmol), and potassium carbonate (2.1 g, 3.1 mmol) in
DMF/THF (3:1, 30 mL) was refluxed for 20 h. After cooling of
the reaction mixture to ambient temperature, the solid mate-
rial deposited was filtered off and the resulting filtrate was
purified by column chromatography on silica gel with use of
benzene/diethyl ether (1:1) as an eluent to give the intermedi-
ate alcohol 11a . Alcohol 11a was then derivatized by using
4-carboxy-TEMPO, DCC, and DMAP in the usual manner to
give the ester 12a in 40% yield (2 steps from 10) as orange
needles and its data are as follows: mp 88-91°C; EPR
(benzene) 3 lines, g ) 2.007, a ) 1.55 mT; FAB-HRMS calcd
for C33H47N2O4 (M + 2) 535.3536, found m/z 535.3573. The
radicals 12b and 12c were prepared in a similar manner and
the data are as follows: 12b: mp 82-85 °C; EPR (benzene) 3
lines, g ) 2.007, a ) 1.49 mT; FAB-HRMS calcd for C34H49N2O4
(M + 2) 549.3599, found m/z 549.3610. Anal. Calcd for
Ack n ow led gm en t. We thank Prof. Hayao Kobaya-
shi and his group from the Institute for Molecular
Sciences and Prof. Masao Hashimoto of Kobe University
for providing us the opportunity to use 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, and
a Grant-in-Aid for Scientific Research from the J apan
Society for The Promotion of Science (No. 13440213)
which are also gratefully acknowledged.
Su p p or tin g In for m a tion Ava ila ble: X-ray crystallo-
graphic data (bond lengths and angles, atomic coordinates, and
anisotropic thermal parameters) for 4a and 12b (CIF files).
This material is available free of charge via the Internet at
http://pubs.acs.org.
C
34H47N2O4: C, 74.55; H, 8.65; N, 5.12. Found: C, 74.57; H,
8.80; N, 5.06. 12c: mp 86-89 °C; EPR (benzene) 3 lines, g )
2.006, a ) 1.58 mT; FAB-HRMS calcd for C35H51N2O4 (M + 2)
J O0206972
1714 J . Org. Chem., Vol. 68, No. 5, 2003