A High-Spin and Durable Polyradical: Poly(4-diphenylaminium-1,2-phenylenevinylene)

Article abstract of DOI:10.1021/jo0302758

A purely organic, high-spin, and durable polyradical molecule was synthesized: It is based on the non-Kekule- and non-disjoint design of a φ-conjugated poly(1,2-phenylenevinylene) backbone pendantly 4-substituted with multiple robust arylaminium radicals. 4-N,N-Bis(4-methoxy- and -tert-butylphenyl)amino-2-bromostyrene 5 were synthesized and polymerized with a palladium-phosphine catalyst to afford the head-to-tail-linked polyradical precursors (1). Oxidation of 1 with the nitrosonium ion solubilized with a crown ether gave the aminium polyradicals (1⁺) which were durable (half-life > 1 month) at room temperature in air. A high-spin ground state with an average S = (4.5)/2 for 1a⁺ was proved even at room temperature by magnetic susceptibility, magnetization, ESR, and NMR measurements.

Full text of DOI:10.1021/jo0302758

A High -Sp in a n d Du r a ble P olyr a d ica l:
P oly(4-d ip h en yla m in iu m -1,2-p h en ylen evin ylen e)
Hidenori Murata, Masahiro Takahashi,† Kazuaki Namba, Naoki Takahashi, and
Hiroyuki Nishide*
Department of Applied Chemistry, Waseda University, Tokyo 169-8555, J apan
nishide@waseda.jp
Received August 26, 2003
A purely organic, high-spin, and durable polyradical molecule was synthesized: It is based on the
non-Kekule´- and non-disjoint design of a π-conjugated poly(1,2-phenylenevinylene) backbone
pendantly 4-substituted with multiple robust arylaminium radicals. 4-N,N-Bis(4-methoxy- and -tert-
butylphenyl)amino-2-bromostyrene 5 were synthesized and polymerized with a palladium-
phosphine catalyst to afford the head-to-tail-linked polyradical precursors (1). Oxidation of 1 with
the nitrosonium ion solubilized with a crown ether gave the aminium polyradicals (1+) which were
durable (half-life > 1 month) at room temperature in air. A high-spin ground state with an average
S ) (4.5)/2 for 1a + was proved even at room temperature by magnetic susceptibility, magnetization,
ESR, and NMR measurements.
In tr od u ction
temperature for the highly cross-linked network of mac-
rocyclic triarylmethine units.6 However, the triarylme-
thine radical can survive only below 200 K, so chemically
stable radical species are desired in such a cross-linked
polyradical in order to raise the magnetic ordering
temperature and to provide feasibility as a material.3e
In parallel to the cross-linked polyradicals, there still
remains another synthetic procedure, which focuses on
a π-conjugated linear polymer bearing multiple pendant
radical groups as a classical, one-dimensional model
molecule. The pendant radical groups are attached to one
π-conjugated backbone that satisfies the non-Kekule´
structure and nondisjoint connectivity among the non-
bonding molecular orbitals of the radicals’ unpaired
electrons. Such linear polyradicals bearing pendant spin
sources possess the following advantages.3c,d First, a
ferromagnetic spin interaction occurs through the π-con-
jugated backbone and potentially even works over a long
range. That is, the spin coupling is not sensitive to the
defects that are unavoidable for macromolecular polyrad-
icals. Second, a great number of spins are accumulated
along one backbone or within one molecule. The spins
are expected to interact not only with their neighboring
spins but also with more remote spins. Third, precursors
of these types of polyradicals can be synthesized via a
one-pot polymerization, and they and the polyradicals
themselves are soluble in common solvents; these are
very favorable for obtaining well-defined samples to
study. Fourth, various chemically stable radical species
can be introduced into a polyradical as the pendant
group. The resultant polyradical has substantial stability
and is easily handled, e.g., at room temperature in air.
Such feasibility would be indispensable for the future
application of magnetic organic molecules as materials.
Much effort has been expended during the past decade
on synthesizing high-spin and purely organic molecules
which are predicted to be a molecular magnetic material
with an unknown magnetism.1 Synthesis of π-conjugated
organic polyradical molecules designed along a non-
Kekule´ and nondisjoint2 fashion for the connectivity of
the multiradicals is one of the most effective approaches
because the ferromagnetic spin alignment between un-
paired electrons through the π-conjugation can be made
strong.3 The recent progress in this field is based on the
synthesis of the highly cross-linked, ladderlike, dendritic,
and hyper-branched polyradicals.4,5 The huge magnetic
moment and the magnetic spin ordering of S (spin
quantum number) >5400 were eventually attained at low
† Present address: Department of Material Engineering, Chiba
University, Chiba 263-8522, J apan.
(1) (a) Magnetic Properties of Organic Materials; Lahti, P. M., Ed.;
Marcel Dekker: New York, 1999. (b) Molecular Magnetism: New
Magnetic Materials; Itoh, K., Kinoshita, M., Ed.; Kohdansha and
Gordon
& Breach: Tokyo and Amsterdam, 2000. (c) π-Electron
Magnetism From Molecules to Magnetic Materials; Veciana, J ., Ed.;
Springer: Berlin, 2001.
(2) (a) Borden, W. T.; Davidson, E. R. J . Am. Chem. Soc. 1977, 99,
4587. (b) Borden, W. T. In Magnetic Properties of Organic Materials;
Lahti, P. M., Ed.; Marcel Dekker: New York, 1999; p 61.
(3) Iwamura, H.; Koga, N. Acc. Chem. Res. 1993, 26, 346. (b) Rajca,
A. Chem. Rev. 1994, 94, 871. (c) Nishide, H. Adv. Mater. 1995, 7, 937.
(d) Nishide, H.; Kaneko, M. In Magnetic Properties of Organic Materi-
als; Lahti, P. M., Ed.; Marcel Dekker: New York, 1999, p285. (e) Rajca,
A. Chem. Eur. J . 2002, 8, 4834.
(4) (a) Rajca, A.; Wongsriratanakul, J .; Rajca, S.; Cerny, R. Angew.
Chem., Int. Ed. 1998, 37, 1229. (b) Rajca, A.; Rajca, S.; Wongsrira-
tanakul, J . J . Am. Chem. Soc. 1999, 121, 6308.
(5) (a) Nishide, H.; Miyasaka, M.; Tsuchida, E. J . Org. Chem. 1998,
63, 7399. (b) Nishide, H.; Ozawa, T.; Miyasaka, M.; Tsuchida, E. J .
Am. Chem. Soc. 2001, 123, 5942. (c) Nishide, H.; Nambo, M.; Miyasaka,
M. J . Mater. Chem. 2002, 12, 3578. (d) Michinobu, T.; Inui, J .; Nishide,
H. Org. Lett. 2003, 5, 2165. (e) Kaneko, T.; Makino, T.; Miyaji, H.;
Teraguchi, M.; Aoki, T.; Miyasaka, M.; Nishide, H. J . Am. Chem. Soc.
2003, 125, 3554.
(6) Rajca, A.; Wongsriratanakul, J .; Rajca, S. Science 2001, 294,
1053.
10.1021/jo0302758 CCC: $27.50 © 2004 American Chemical Society
Published on Web 01/09/2004
J . Org. Chem. 2004, 69, 631-638
631

Murata et al.
CHART 1
Along with this molecular designing, we have succeeded
in realizing an intramacromolecular high-spin alignment
among the pendant unpaired electrons by synthesizing
poly(1,2-phenylenevinylene)s that are 4-substituted with
the 3,5-di-tert-butyl-4-oxyphenyl,7 N-tert-butyloxyamino,8
galvinoxyl, or nitronylnitroxide groups.9 The poly(1,2-
phenylenevinylene) backbone was characterized as
being relatively coplanar with an extended π-conjugation
even after the introduction of the pendant radical
groups.
Besides the backbone structure, a spin source, which
is to be pendantly introduced into the π-conjugated
backbone, should be carefully selected from the list of
radical species in order to provide both a sufficient
ferromagnetic spin exchange interaction and chemical
stability for such linear polyradicals. It is known that
triaryl aminium cationic radicals derived from the para-
substituted triphenylamines are quite stable and are
often used as an oxidizing reagent and a catalyst in redox
reactions.10 In addition, the spin density of the aminium
radicals delocalizes into the three attached aryl groups,
which would efficiently work in the spin-exchange inter-
actions. The aminium cationic radical is a favorable
candidate for the spin source to be utilized in a chemically
durable and high-spin polyradical. From such viewpoints,
a series of oligomeric, cyclic, and polymeric aminium
radicals were derived from m-phenylene-connected and
cross-linked polyarylamines. Their magnetic behaviors
have already been reported.11 However, the aminium
cationic radicals were formed in a cross-conjugation style
within the backbone for these molecules, which did not
belong to the type of linear polymer bearing pendant
radicals and often lacked solvent solubility that leads to
a limitation of the radical (spin) generation yield. On the
other hand, we have synthesized the aminium cationic
diradical of 3,4′-bis[N,N-bis(4-methoxy- and -tert-bu-
tylphenyl)amino]stilbene, 2a + and 2b+, as a durable
triplet molecule.12 We have recently extended the diradi-
cal 2b+ to a high-spin polyradical 1b+ and preliminarily
reported a half-life of 1.5 days and a high-spin multiplic-
ity of S ) 3/2 for 1b+ even with the spin concentration of
ca. 0.4 spin per unit at room temperature.13 In this study,
we synthesized the pendant-type poly(aminium cationic
radical)s based on poly(1,2-phenylenevinylene), 1a + and
1b+, with well-defined chemical structures, and described
the magnetic properties of the durable polyradicals with
S ) (4.5)/2 even at room temperature.
Resu lts a n d Discu ssion
Mon om er Syn th esis a n d P olym er iza tion A head-
to-tail linkage structure of the radical group-bearing
monomer unit is essential for the non-Kekule´ and non-
disjoint requisite or the following magnetic study; this
was established through the polycondensation via the
Heck reaction of the 4-radical precursor-substituted
2-bromostyrene in this paper. 4-(N,N-bis(4-methoxyphe-
nyl)amino)-2-bromostyrene 5a and 4-(N,N-bis(4-tert-bu-
tylphenyl)amino)-2-bromostyrene 5b were synthesized as
the monomers for the polycondensation. Each para
position of the triphenylamine is protected with the
methoxy, tert-butyl, or the vinylene group in order to
suppress dimerization and/or disproportionation of the
formed aminium cationic radical (see the structure of 1+).
N,N-Bis(4-methoxyphenyl)amine and N,N-bis(4-tert-bu-
tylphenyl)amine were prepared by cross-coupling reaction
between the 4-subsituted aniline and the 4-substituted
bromobenzene. 2-Bromo-4-iodotoluene was brominated
with N-bromosuccinimde (NBS) and converted to 2-bromo-
4-iodobenzaldehyde via the Sommelet rearrangement
(Scheme 1).14 After its formyl group was protected with
the 1,3-dioxolane group, the palladium-catalyzed ami-
nation of 6 with bis(4-methoxyphenyl)amine followed by
deprotection yielded 7. The formyl group of 7 was
converted to a vinyl group via the Wittig reaction to
afford the bromostyrene derivative 5a as the styrene
monomer. On the other hand, to obtain 5b, N,N-bis(4-
(7) (a) Nishide, H.; Kaneko, T.; Nii, T.; Katoh, K.; Tsuchida, E.;
Yamaguchi, K. J . Am. Chem. Soc. 1995, 117, 548. (b) Nishide, H.;
Kaneko, T.; Nii, T.; Katoh, K.; Tsuchida, E.; Lahti, P. M. J . Am. Chem.
Soc. 1996, 118, 9695.
(8) (a) Kaneko, T.; Toriu, S.; Kuzumaki, Y.; Nishide, H.; Tsuchida,
E. Chem. Lett. 1994, 2135. (b) Nishide, H.; Kaneko, T.; Toriu, S.;
Kuzumaki, Y.; Tsuchida, E. Bull. Chem. Soc. J pn. 1996, 69, 499.
(9) Nishide, H.; Hozumi, Y.; Nii, T.; Tsuchida, E. Macromolecules
1997, 30, 3986.
(10) Connelly N. G.; Geiger W. E. Chem. Rev. 1996, 96, 877.
(11) (a) Ito, A.; Taniguchi, A.; Yoshizawa, K.; Tanaka, K.; Yamabe,
T. Bull. Chem. Soc. J pn. 1998, 71, 337. (b) Bushby, R. J .; Gooding, D.
J . Chem. Soc., Perkin Trans. 2 1998, 1069. (c) Hauck, S. I.; Lakshmi,
K. V.; Hartwig, J . F. Org. Lett. 1999, 1, 2057. (d) Selby, T. D.;
Blackstock, S. C.; Selby, T. D. J . Am. Chem. Soc. 1999, 121, 7152. (e)
Selby, T. D.; Stickley, K. R.; Blackstock, S. C. Org. Lett. 2000, 2, 171.
(f) Michinobu, T.; Inui, J .; Nishide, H. Org. Lett. 2003, 5, 2165.
(12) (a) Michinobu, T.; Takahashi, M.; Tsuchida, E.; Nishide, H.
Chem. Mater. 1999, 11, 1969. (b) Michinobu, T.; Tsuchida, E.; Nishide,
H. Bull. Chem. Soc. J pn. 2000, 73, 1021.
(14) We could not employ the same route of 5b to obtain 5a because
of the undesirable bromination at the aromatic rings by NBS. For the
Sommelet rearrangement, see: (a) Angyal S. J . Org. React. 1954, 8,
197. (b) Blazevic, N.; Kolbah, D.; Belin, B.; Sunjic, V.; Kajfez, F.
Synthesis 1979, 161.
(13) Takahashi, M.; Nakazawa, T.; Tsuchida, E.; Nishide, H.
Macromolecules 1999, 32, 6383.
632 J . Org. Chem., Vol. 69, No. 3, 2004

Poly(4-diphenylaminium-1,2-phenylenevinylene)
SCHEME 1
SCHEME 2
respectively, in DMF solution at 70 °C for 72 h (see Table
3 in the Experimental Section). These polymerization
conditions were selected for the selective â-arylation of
the vinyl group with the aryl bromide of 5, based on the
following 13C-labeled control reaction using 2-bromo-5-
hexyloxy(2-13C)styrene 9 as the monomer. The Heck
cross-coupling reaction of monosubstituted olefins and
aryl halides has been characterized by the formation of
a â-arylated product with the high stereoselectivity of the
trans-vinylene structure but still involves an R-arylation
byproduct (Scheme 3).17 In this study, the R-arylation
means a defect formation in the formed poly(1,2-phe-
nylenevinylene). The 13C-labeled bromostyrene was po-
lymerized with the palladium-tri(o-tolyl)phosphine cata-
lyst in the presence of 5.0-15 vol % triethylamine, 0.0-
5.0 M lithium chloride, at 70-100 °C, in DMF. For
example, the poly(1,2-phenylenevinylene) at 100 °C and
without the lithium chloride addition gave the 13C NMR
spectrum, which involved the slight signal at 120.0 ppm
assigned to the R-arylation structure of RR′Cd13CH2 (see
the Supporting Information). The 13C NMR spectrum of
the polymer, obtained under the reaction conditions
stated at the top of this paragraph, indicated a completely
poly(1,2-phenylenevinylene) structure without any R-ary-
tert-butylphenyl)amine was introduced onto the 2-bromo-
4-iodotolulene by selective coupling at the iodo position
using the palladium catalyst with BINAP as a hindered
and bidentate ligand, to efficiently afford 2-bromo-4-(N,N-
bis(4-tert-butylphenyl)amino)toluene 8. The methyl group
of 8 was brominated with NBS and converted to a vinyl
group via the Wittig reaction to yield the styrene mono-
mer 5b.
The bromostyrene derivatives, 5a and 5b, were poly-
condensed (Scheme 2) through the Heck reaction using
the catalyst of palladium acetate and tri(o-tolyl)phos-
phine in the presence of triethylamine and lithium
chloride as a base and a source of chloride ion,15,16
1
lation defect. In the H NMR spectra of 1 obtained under
these selected conditions, there were also no signals
assigned to the 1,1-diphenylethylene linkage (ca. 6.9
ppm) as the defect and the 1,2-cis-stilbene moiety (ca.
6.5 ppm) as a conformer, supporting the head-to-tail
linked primary structure of 1, at least, based on the 13C
NMR analysis.
The polymers 1 were soluble in common solvents such
as methylene chloride, chloroform, tetrahydrofuran, ben-
(16) (a) Merlic, C. A.; Semmelhack, M. F. J . Organomet. Chem. 1990,
391, C23. (b) Carlstroem, A. S.; Frejd, T. Acta Chem. Scand. 1992, 46,
163.
(15) (a) Heck, R. F. Org. React. 1982, 27, 345. (b) Greiner, A.; Heitz,
W. Makromol. Chem. Rapid Commun. 1988, 9, 581.
(17) Ludwig, M.; Stro¨mberg, S.; Svensson, M.; Åkermark, B. Orga-
nometallics 1999, 18, 970.
J . Org. Chem, Vol. 69, No. 3, 2004 633

Murata et al.
SCHEME 3
zene, toluene, triethylamine, and DMF. The degree of
polymerization (DP) of 1 was measured by GPC using
polystyrene standards, and the terminal bromine con-
tents were 12.5 and 12.8, respectively, for 1a , and 13.0
and 12.4, respectively, for 1b. The polydispersity (the
ratio of number- and weight-average molecular weight)
was 1.3 and 1.4 for 1a and 1b, respectively. These also
supported the primary structure of 1.
The chloroform solution of the greenish yellow poly-
mers, 1a and 1b, showed two UV/vis absorption maxima
at 301 and 369 and 306 nm and 365 nm, respectively,
with the molar absorption coefficient ꢀ ) 2 × 104 and 1
× 104 M-1 cm-1, respectively. They are ascribed to the
triarylamine moiety (λmax ) ca. 300 nm) and the trans-
stilbene moiety. The visible absorption was extended to
525 and 510 nm for 1a and 1b, respectively, in compari-
son with that of poly(1,2-phenylenevinylene) (ca. 430 nm).
The solutions of 1-3 exhibited strong photolumines-
cences. The λem for 1a and 1b were 530 and 512 nm,
respectively, in the chloroform solution (λex ) 312 nm)
and were bathochromically shifted in comparison with
those for 2a and 2b (491 and 460 nm, respectively) and
for 3a and 3b (398 and 360 nm, respectively). The
bathochromic shift of λem for 1 corresponds to the longer
wavelength shift of the UV absorption edges of 1,
suggesting a developed π-conjugation for 1.
F IGURE 1. UV/vis absorption spectral change of 1a solution
under the electrolytic potential given from 0.50 to 0.85 V at
room temperature. 0.05 mM (amine unit) methylene chloride
solution of 1a with 0.1 M (C4H9)4NBF4 as the supporting
electrolyte. Inset: cyclic voltammogram of 1a in the same
methylene chloride solution with sweep rate of 100 mV/s.
TABLE 1. Red ox P oten tia l (Ep 1/2) a n d P ea k Sep a r a tion
(∆Ep a -c) of th e P olym er 1, th e Dim er 2, a n d th e Mon om er
3a
methoxy-substituted a
tert-butyl-substituted b
Oxid a tion s to th e Am in iu m Ra d ica ls Cyclic volta-
mmetry of 1-3 in the methylene chloride solution with
tetrabutylammonium tetrafluoroborate as the electrolyte
gave unimodal waves which were repeatedly recorded in
the potential sweeps of, e.g., 100 times at room temper-
ature (example, see the inset of Figure 1). The voltam-
mogram result means that the triarylamine groups are
electrochemically oxidized to the aminium cationic radi-
cals and reduced to the amines without any subsequent
chemical side reactions, such as the dimerization to form
a benzidine and a disproportionation. This also suggested
that the electrostatic repulsion was not strong among the
adjacent aminium cationic groups along the π-conjugated
chain to produce a separation in the redox waves (dif-
ferential pulse voltammetry of 1 and 2 also gave simple
unimodal oxidation waves).
1/2
1/2
amine
Ep (V)
∆Epa-c (V)
Ep (V)
∆Epa-c (V)
1
2
3
0.81
0.78
0.68
0.18
0.18
0.17
0.92
0.94
0.89
0.22
0.17
0.15
a
Methylene chloride solution of 0.1 M (C4H9)4NBF4, vs Ag/AgCl
(ref ferrocene Fc/Fc+ ) 0.58 V), sweep rate: 100 mV/s.
value (58 mV) for an electrochemically reversible reaction
and increased as the sweep rate increased during the
cyclic voltammetry. The cathodic shift of the redox
potential and the broadening or constancy of the redox
wave for the dimer, and especially the polymer, could be
explained by the delocalization effect of the formed
aminium cationic radical in the π-conjugation of the
dimer and polymer.
The redox potentials and the potential separation
between the anodic oxidation and cathodic reduction
peaks are given in Table 1. The redox potentials for the
methoxy-substituted 1a , 2a , and 3a , were lower than
those for the tert-butyl-substituted 1b, 2b, and 3b. This
result is clearly explained by the more electron-donating
effect of the methoxyl group at the para positions. It is
also depicted in Table 1 that the redox potential between
the amine and the aminium cationic radical increased
in the order of the monomer 3 < the dimer 2 e the
polymer 1. The potential separations between the oxida-
tion and reduction peaks were larger than the theoretical
The electrochemical oxidations of the polymer 1a were
monitored by UV/vis absorption spectroscopy, using the
assembly of an optically transparent thin-layer platinum
minigrid electrode. With the oxidation potential given,
there was a decrease in the absorption intensity at 301
nm of the neutral amine and the accompanying appear-
ance of two new absorption bands at 367 and 748 nm
with isosbestic points at 267 and 333 nm; the latter
values were ascribed to the aminium radicals of triaryl-
amine.10 The spectral change with isosbestic points
supported the quantitative oxidation from 1 to 1+. The
color of the solution turned deep blue upon oxidation.
634 J . Org. Chem., Vol. 69, No. 3, 2004

Poly(4-diphenylaminium-1,2-phenylenevinylene)
F IGURE 3. ømolT vs T plots for the powder sample of 1+: (O)
neat powder of 1a + with spin concentration of 0.25; (b) poly-
(styrenesulfonate tetrabutylammonium) 4-diluted sample of
1a + with a spin concentration of 0.63. Inset: 1/ømol vs T plots
of neat powder of 1a +.
F IGURE 2. Temperature dependency of the ESR signal
intensity of the ∆Ms ) (2 transition of 1a + with 0.90 spins/
unit in methylene chloride. The solid line is a least-squares
fitting to Curie’s law (intensity ) C/T). Inset: ESR spectra of
the 1a + methylene chloride solution with a low spin concentra-
tion of 0.10 spin/unit (dashed line) and a high spin concentra-
tion of 0.89 (solid line) at room temperature, and the ∆Ms ( 2
spectrum of 1a + with spin concentration of 0.80 in methylene
chloride at 4.0 K.
ESR spectra indicate a nitrogen-centered radical forma-
tion.19 With an increasing spin concentration, the ESR
spectrum changed to a unimodal spectrum with a peak-
to-peak width of 0.69 and 0.81 mT for 1a + and 1b+,
respectively.
Triarylaminium radical salts had been prepared from
the corresponding triarylamines using a silver(I) salt in
the presence of iodine, a nitrosonium ion salt, and a
higher valent halide as the oxidant.10 We chose, by
considering both the oxidation potential of the 1 amines
and the counteranion species, the nitrosonium ion salt,
e.g., NOBF4 or NOPF6, of which the oxidizing potential
has been reported to be 1.58 V.18 We found that the
concentrated methylene chloride solution of NOBF4 or
NOPF6 solubilized with the equivalent amount of 18-
crown-6-ether was effective for the oxidation and was
added dropwise to the dilute methylene chloride solution
of the amines 1-3 to accomplish a high yield for the
aminium cationic radical formation. The spin concentra-
tions for 1a + and 1b+ were estimated to be 0.89 and 0.56
spin/monomer amine unit, respectively, on the basis of
the ESR signal intensity. Colors of the methylene chloride
solutions of these amines turned from pale yellow to deep
blue, which agreed with the UV/vis absorption change
during the electrolytic oxidation given in Figure 1.
The stability of the aminium cation radicals 1+, 2+, and
3+ in the solid state depended on the counteranion
species. For example, the aminium cation radical salt of
1a + with an anion of larger size such as hexafluorophos-
phate (PF6-) did not show any deterioration even after
one week at room temperature in air (the half-life
estimated by the ESR signal intensity > one month). This
half-life was much longer than that for the aminium
cation radical salt of 1a + with BF4- (half-life ca. 2 weeks)
and then those previously reported for both the m-
phenylene-coupled oligo(triphenylamine)s11 and the poly-
(1,2-phenylenevinylene)s 4-substituted with 3,5-di-tert-
butyl-4-oxyphenyl and N-tert-butyloxyamino.7,8
The ESR study at cryogenic temperatures gave a
∆Ms ) (2 (half-field and forbidden) transition at 158 mT
for 1+ (for 1a +, see the inset of Figure 2). The signal
intensity of the ∆Ms ) (2 transition for 1a + was
proportional to the reciprocal of temperature in the range
between 4.5 and 100 K and followed Curie’s law (Figure
2). This result means that a triplet state ascribed to the
∆Ms ) (2 peak is a stable ground state with a large
triplet-singlet gap for 1a + (however, it does not rule out
the possibility of a degenerate singlet-triplet state).
Ma gn etic P r op er ties The PF6- salt of 1+ was isolated
as a blue powder by pouring the methylene chloride
solution of 1+ oxidized with a small excess of NOPF6/18-
crown-6-ether into dimethyl ether20 for the magnetic
measurement in the temperature range up to room
temperature. Besides the neat sample, 1+ was also
isolated in the presence of polystyrene or ploy(styrene-
sulfonate tetrabutylammonium) 4 as a diamagnetic dil-
uent. Compound 4 is a polyanion but soluble in methyl-
ene chloride: After the solution of 4 was added to the
methylene chloride solution of the polyradical 1+, the
mixture became suspended, suggesting the polycation/
polyanion complex formation of 1+ and 4. These isolated
samples were subjected to static magnetic susceptibility
(ø) and magnetization (M) measurements using a SQUID
magnetometer. ø was normalized to the ømol values with
the radical concentration in the sample determined by
the saturation magnetization (Ms) of the M vs magnetic
field (H) plots.
Figure 3 shows the ømolT vs T plots of 1a +. The plots
are flat in the higher temperature range, although they
The solution ESR of 1+ with a low spin concentration
gave a three-line spectrum (aN ) 0.85 and 0.90 mT for
1a + and 1b+, respectively) with g ) 2.0029 and 2.0028
for 1a + and 1b+, respectively (inset of Figure 2). These
(19) The ESR super hyperfine structure was clearly observed for
the solution of the monomeric aminium cation radical 3+; aN ) 0.846,
ao-H ) 0.183, am-H ) 0.061, and aH(methoxy) ) 0.061 mT for 3a + (see the
Supporting Information). These spectra supported the delocalization
of spin the density in 3+ onto the attached three aryl groups.
(20) Upon oxidation, NO gas evolved. The precipitated powder was
composed of the PF6- salt of 1+ on the basis of the elemental analysis.
(18) Kochi, J . K. Acc. Chem. Res. 1992, 25, 39.
J . Org. Chem, Vol. 69, No. 3, 2004 635

Murata et al.
TABLE 2. Weiss Tem p er a tu r e (θ) a n d Sp in Qu a n tu m Nu m ber (S) of th e Am in iu m P olyr a d ica ls
aminium radical
degree of polymerization
diluent
spin concna (spin/unit)
θ (K)
Sb
Sc
1a +
1a +
1a +
1a +
1a +
1b+
12.8
12.8
12.8
12.8
7.3
none
polystyrene
4
4
4
4
0.25
0.37
0.45
0.63
0.66
0.50
-1.7 ( 0.1
(2.0)/2
(2.3)/2
(2.9)/2
(4.5)/2
(3.8)/2
(3.0)/2
(1.8)/2
(2.2)/2
(3.2)/2
(4.7)/2
(3.5)/2
(2.8)/2
-1.9 ( 0.1
-0.42 ( 0.02
-0.33 ( 0.03
-0.21 ( 0.01
-0.68 ( 0.1
12.0
a
b
Determined by the Ms value. Estimated by the magnetization curve as Figure 4. c Estimated by the ømolT value as Figure 3.
between the unpaired electrons of the polyaminium
cationic radicals, by taking into account both the molec-
ular weight or DP and the spin concentration of 1a +.
The ømolT plots leveled off in the temperature range
from 50 to 280 K in Figure 3 (the fluctuation for 1a +
diluted with 4 above 230 K is probably ascribed to both
the glassy-rubbery transition temperature of the formed
polyion complex at 250 K and the lower spin concentra-
tion of the diluted sample). The flat ømolT plots means
that the multiplet ground state for 1a + is significantly
large (∼kBT) and that 1a + is a paramagnetic molecule
with S ) (4.5)/2. Ferromagnetic coupling effect of the 3,4′-
stilbene linker has been reported by using the stilbene
diradicals in the previous papers,7,22 where the triplet-
singlet gap (∆ET-S) for the bis(2′,6′-di-tert-butyl-4′-oxy-
phenyl)- and bis(N-tert-butyl nitroxide)-substituted stil-
bene was experimentally estimated to be 72 and 59 K,
respectively. The ∆ET-S value was also computationally
F IGURE 4. Normalized plots of magnetization (M/Ms) vs the
estimated to be >1000 K for the bis(methyleneradical)-
ratio of magnetic field and temperature (H/(T - θ)) for the
substituted stilbene.22 Taking into account the spin
4-diluted 1a + (DP ) 12.8) with spin concentration ) 0.63 spin/
density delocalization in the triarylaminium cation radi-
unit and for the 4-diluted 1a + (DP ) 12.8) with spin concen-
cal (see the Supporting Information), the very strong
spin-exchange interaction observed for 1+ in this paper
is not in conflict with the results in the previous papers.
The magnetic susceptibility of 1+ was measured at
room temperature by the NMR shift method. The CDCl3
solutions of 1a + and 1b+ were prepared by the oxidation
of 1 with NOPF6/18-crown-6-ether. The ømol values were
calculated based on the Evans equation,23 measuring the
resonance frequency separation of the cyclohexane stan-
dard peak for a concentration series of the 1+ solution.
The calculated ømolT values for 1a + and 1b+ in the
solution were 0.86 and 0.60 emu‚K‚mol-1 at 300 K,
respectively; they corresponded to S ) (4.9)/2 and (2.8)/2
and were comparable with those of the SQUID measure-
ment in Table 2. These results support the idea of the
linear polyradical pendantly substituted with aminium
cation in the non-Kekule´ and nondisjoint fashion to
provide the observed high S value for a purely organic
polyradical at room temperature.
tration ) 0.45 spin/unit at 1.8 (O), 2 (b), 2.5 (0), 3 (9), and 5
()). Theoretical Brillouin curves for S ) 1/2 (dashed line), 2/2
(broken line), and 4/2 (solid line).
decrease below 50 K. The latter is attributed to an
antiferromagnetic (probably through-space) interaction
among the 1a + molecules, which was significantly sup-
pressed for 1a + diluted with 4. The 1/ømol vs T plots (inset
of Figure 3) obeyed the Curie-Weiss law,21 indicating the
paramagnetic behavior of 1a + and giving the Weiss
temperature (θ, Table 2). The θ value represents an
antiferromagnetic interaction between the unpaired elec-
trons, which was reduced for 1a + by the polyion complex
formation with 4.
The normalized plots of magnetization (M/Msat) for 1a +
diluted with 4 (Figure 4) are close to the Brillouin curves
for 4/2 and 5/2, indicating a high-spin ground state for
1a +. The average S values for the samples of 1a + and
1b+ estimated from the magnetization data are listed in
Table 2. The S values were also estimated by applying
the Curie-Weiss law21 to the ømolT data (examples in
Figure 3) and are also given in Table 2. One notices both
that a relatively high spin concentration was realized for
the 1a + samples diluted, especially with 4, and that a
relatively high S value was observed for those samples
with high spin concentrations. For the 1a + sample with
the lower molecular weight (DP ) 7.3) resulted in the
small S values. These results concluded that a ferromag-
netic and intramolecular spin-alignment is realized
Exp er im en ta l Section
4-[N,N-Bis(4-m et h oxyp h en yl)a m in o]-2-b r om ob en za l-
d eh yd e (7). The mixture of 2-bromo-4-iodobenzaldehyde (6.09
g, 19.6 mmol), 1,2-ethanediol (12.2 g, 196 mmol), benzene (9.7
mL), and p-toluenesulfonic acid monohydrate (18.6 mg, 0.099
mmol) was refluxed until close to the theoretical amount of
water was collected in the trap (ca. 6 h).24 The reaction mixture
(22) Yoshioka, N.; Lahti, P. M.; Kaneko, T.; Kuzumaki, Y.; Tsuchida,
E.; Nishide, H. J . Org. Chem. 1994, 59, 4272.
(23) (a) Evans, D. F. J . Chem. Soc. 1959, 1959, 2003. (b) Live, D.
H.; Chan, S. I. Anal. Chem. 1970, 42, 791.
(21) ømolT ) NAg2µB2TS(S + 1)/3kB(T - θ), where, NA, g, µB, and kB
are Avogadro’s number, g-factor, Bohr magneton, and Boltzman
constant, respectively.
(24) Shulz, D. A.; Hollomon, M. G. Chem. Mater. 2000, 12, 580.
636 J . Org. Chem., Vol. 69, No. 3, 2004

Poly(4-diphenylaminium-1,2-phenylenevinylene)
was then extracted with chloroform. The organic layer was
dried over anhydrous sodium sulfate and evaporated. The
crude product was purified using a silica gel column with a
hexane eluent to give 2-(2-bromo-4-iodo-phenyl)-1,3-dioxolane
6 as a white solid (6.96 g): yield 98%; mp 56 °C; 1H NMR (500
MHz, CDCl3; ppm) 7.92 (d, J ) 1.8 Hz, 1H), 7.66 (dd, J ) 8.1,
1.4 Hz, 1H), 7.31 (d, J ) 8.1 Hz, 1H), 6.02 (s, 1H), 4.09 (dd, J
) 3.5, 15.7 Hz, 4H); 13C NMR (500 MHz, CDCl3; ppm) δ 140.9,
136.6, 136.3, 129.2, 123.6, 102.2, 95.2, 65.5; IR (KBr pellet,
for C22H20NBrO2 410.3. Anal. Calcd for C22H20NBrO2: C, 64.4;
H, 4.9; N, 3.4; Br, 19.5. Found: C, 64.1; H, 5.0; N, 3.2; Br,
19.7.
4-[N ,N -Bis(4-t er t -b u t ylp h e n yl)a m in o]-2-b r om ot olu -
en e (8). To a 15 mL toluene solution of bis(4-tert-butylphenyl)-
amine (0.56 g, 2 mmol) were added 2-bromo-4-iodotoluene (0.59
g, 2.0 mmol), tris(dibenzylideneacetone)dipalladium (0.27 g,
0.30 mmol), tris(o-tolyl)phosphine (0.091 g, 0.30 mmol), and
sodium tert-butoxide (0.58 g, 6.0 mmol), and the mixture was
stirred for 15 h at 70 °C under nitrogen and then cooled to
room temperature. The crude product was extracted with
chloroform, washed with water, and dried over anhydrous
magnesium sulfate. The solvent was removed in vacuo, and
the residue was purified using a silica gel column with a
hexane eluent and recrystallized from hexane to afford 0.47 g
cm-1) 3080 (νC-H), 2952 (νC-H), 2886 (νC-H), 943 (νC-O-C) cm-1
;
MS (EI) m/e 354 ((M - 1)+), 356 ((M + 1)+), calcd for C9H8-
BrIO2 355.0.
Compound 6 (100 mg, 0.28 mmol) and bis(4-methoxyphen-
yl)amine (59 mg, 0.26 mmol) were dissolved in toluene (2.1
mL). Sodium tert-butoxide (37 mg, 0.38 mmol), tris(diben-
zylideneacetone)dipalladium (2.9 mg, 3.2 µmol), and (S)-(-)-
2,2′-bis(diphenylphosphino)-1,1′-binaphthyl (6.0 mg, 9.6 µmol)
were added, and then mixture was heated at 100 °C for 40 h
to yield a reddish brown precipitate. The reaction mixture was
neutralized with 1 N aqueous ammonia and extracted with
chloroform. The organic layer was washed with brine and
evaporated to give the crude product, which was purified using
a silica gel column with hexane/ethyl acetate (3/1) to afford
82.7 mg of (3-bromo-4-(1,3-dioxolan-2-yl)phenyl)bis(4-methoxy-
phenyl)amine as a yellow solid: yield 71%; mp 115 °C; 1H NMR
(500 MHz, CDCl3; ppm) δ 7.33 (d, J ) 8.6 Hz, 1H), 7.05-6.81
(m, 10H), 6.01 (s, 1H), 4.16-4.01 (m, 4H), 3.79 (s, 6H); 13C
NMR (500 MHz, CDCl3; ppm) δ 156.5, 150.6, 139.9, 128.1,
127.1, 127.1, 123.3, 122.9, 118.3, 114.9, 102.8, 65.3, 55.5; IR
(KBr pellet, cm-1) 2952 (νC-H), 2890 (νC-H), 2835 (νC-H), 1324
(νC-N), 946 (νC-O-C); MS (EI) m/e 455 ((M - 1)+), 457 ((M +
1
of 8 as white crystals: yield 52%; mp 133 °C; H NMR (500
MHz, CDCl3; ppm) δ 7.25-6.88 (m, 11H), 2.32 (s, 3H), 1.30 (s,
18H); 13C NMR (500 MHz, CDCl3; ppm) δ 147.2, 145.8, 144.8,
131.0, 130.9, 126.7, 126.1, 124.9, 123.7, 122.3, 34.3, 31.4, 22.1;
IR (KBr pellet, cm-1) 2956 (νC-H), 1267 (νBr-C), 1030 (νC-N);
MS (EI) m/e 449 ((M - 1)+), 451 ((M + 1)+), calcd for C27H32
-
NBr for 450.5. Anal. Calcd for C27H32NBr: C, 72.0; H, 7.2; N,
3.1; Br, 17.7. Found: C, 71.8; H, 7.0; N, 3.0; Br, 17.6.
4-[N ,N -Bis(4-t er t -b u t ylp h e n yl)a m in o]-2-b r om ost y-
r en e (5b). N-Bromosuccinimide (1.8 g, 10.0 mmol) and a trace
amount of azobisisobutyronitrile were added to a 50 mL
tetrachloromethane solution of 8 (9.0 g, 20 mmol). The mixture
was vigorously stirred at 60 °C for 3 h, filtered, and evaporated.
The residue was dissolved in a 5 mL benzene solution of
triphenylphosphine (2.6 g, 10 mmol) and stirred at 50 °C for
5 h. Evaporation gave a red oil, which was purified using a
silica gel column with a hexane/chloroform (1/1) eluent to give
a yellow oil as the corresponding phosphonium salt (5.4 g).
The phosphonium salt (5.4 g, 6.8 mmol) was dissolved in 1.0
N aqueous formaldehyde (19 mL). A 2 N aqueous sodium
hydroxide (3 mL) solution was added dropwise to the phos-
phonium salt solution, stirred for 3 h, and extracted with
diethyl ether. The organic layer was washed with brine, dried
over anhydrous sodium sulfate, and evaporated. The residue
was purified using a silica gel column with a hexane eluent to
1)+), calcd for C23H22NBrO4 456.3. Anal. Calcd for C23H22
-
NBrO4: C, 60.5; H, 4.9; N, 3.1; Br, 17.5. Found: C, 60.4; H,
4.8; N, 3.0; Br, 17.4.
(3-Bromo-4-(1,3-dioxolan-2-yl)phenyl)bis(4-methoxyphenyl)-
amine (728 mg, 1.59 mmol) was dissolved in a mixture of
acetone (16 mL) and water (0.50 mL) containing p-toluene-
sulfonic acid (214 mg, 1.13 mmol) and refluxed for 3 h. After
evaporation, the mixture was extracted with ether. The organic
layer was successively washed with aqueous sodium hydrogen
carbonate and aqueous saturated sodium chloride and then
evaporated. The crude product was purified using a silica gel
column with hexane/ethyl acetate (3/1) to give 7 as an orange
solid (656 mg): yield 93%; mp 146 °C; 1H NMR (500 MHz,
CDCl3; ppm) δ 10.08 (s, 1H), 7.68 (d, J ) 8.8 Hz, 1H), 7.13-
6.89 (m, 9H), 6.73 (dd, J ) 2.5, 8.9 Hz, 1H), 3.84 (s, 6H); 13C
NMR (500 MHz, CDCl3; ppm) δ 190.0, 157.7, 154.4, 138.0,
130.7, 129.0, 128.1, 124.4, 119.9, 115.6, 115.2, 55.4; IR (KBr
pellet, cm-1) 2955 (νC-H), 2929 (νC-H), 2908 (νC-H), 2836 (νC-H),
1677 (νCdO), 1341 (νC-N); MS (EI) m/e 411 ((M - 1)+), 413 ((M
1
give 5b as an amorphous white solid (0.91 g): yield 29%; H
NMR (500 MHz, CDCl3; ppm) δ 7.63-6.92 (m, 12H), 5.56 (d,
J ) 18.4 Hz, 1H), 5.21 (d, J ) 12.1 Hz, 1H), 1.30 (s, 18H); 13
C
NMR (500 MHz, CDCl3; ppm) δ 148.8, 146.6, 144.2, 135.2,
130.0, 126.7, 126.2, 125.1, 124.5, 124.0, 121.1, 114.1, 34.4, 31.4;
IR (KBr pellet, cm-1) 3033 (νC-H), 2954 (νC-H), 1622 (νCdC), 1267
(νC-N) cm-1; MS (EI) m/e 461 ((M - 1)+), 463 ((M + 1)+), calcd
for C28H32BrN 462.5. Anal. Calcd for C28H32NBr: C, 72.7; H,
7.0; N, 3.0; Br, 17.3. Found: C, 72.5; H, 6.8; N, 2.9; Br, 17.5.
P olym er iza tion . The polymerization was carried out by
modifying the procedure described in the previous papers.7,25
Palladium acetate, tris(o-tolylphosphine), triethylamine, and
lithium chloride were added to the monomer 5 solution of
DMF, and the mixture was heated (examples of the polymer-
ization conditions are given in Table 3). The polymerization
mixture was poured into methanol, and the precipitated
polymer powder was purified by reprecipitation from chloro-
form into the mixture of methanol/benzene (3/7) to afford the
polymer 1.
+ 1)+), calcd for C21H18NBrO3 412.3. Anal. Calcd for C21H18
-
NBrO3: C, 61.2; H, 4.4; N, 3.4; Br, 19.4. Found: C, 60.3; H,
4.2; N, 3.3; Br, 19.3.
4-[N,N-Bis(4-m eth oxyp h en yl)a m in o]-2-br om ostyr en e
(5a ). To 0.344 mL of a dry THF solution of triphenylmeth-
ylphosphonium bromide (117 mg, 0.327 mmol) were dropwise
added a 0.136 mL hexane solution of n-butyllithium (0.218
mmol) and a dry 0.30 mL THF solution of 7 (45.6 mg, 0.111
mmol), and the mixture was stirred at room temperature for
1 h. After evaporation, the crude product was extracted with
diethyl ether, washed with brine, dried over anhydrous sodium
sulfate, evaporated, and purified with a silica gel column with
a hexane/ethyl acetate (20/1) to give 44.7 mg of 5a as a pale-
Ma gn etic Mea su r em en ts. The PF6- salt of 1+ was isolated
by pouring the methylene chloride solution of 1+ oxidized with
a small excess of NOPF6/18-crown-6-ether into dimethyl ether
(Anal. Calcd for C22H19NF6O2P: C, 55.7; H, 4.0; N, 3.0.
Found: C, 55.3; H, 4.2; N, 2.9). Besides the neat sample, 1+
was also isolated in the presence of polystyrene or poly-
(styrenesulfonate tetrabutylammonium) 4. The neat sample
was dissolved again in the methylene chloride solution of
polystyrene or 4 ([polystyrene or 4]/[1+] ) 100 w/w), and the
1
yellow viscous liquid: yield 98%; H NMR (500 MHz, CDCl3;
ppm) δ 7.34 (d, J ) 8.9 Hz, 1H), 7.06-6.21 (m, 11H), 5.54 (dd,
J ) 1.2, 17.4 Hz, 1H), 5.19 (dd, J ) 1.3, 11.1 Hz, 1H), 3.82 (s,
6H); 13C NMR (500 MHz, CDCl3; ppm) δ 156.4, 149.3, 140.0,
135.2, 128.8, 127.0, 126.6, 124.1, 122.9, 118.9, 114.9, 113.7,
55.5; IR (KBr pellet, cm-1) 2952 (νC-H), 2930 (νC-H), 2834 (νC-H),
1325 (νC-N); MS (EI) m/e 409 ((M - 1)+), 411 ((M + 1)+), calcd
(25) (a) Heitz, W.; Bru¨gging, W.; Freund, L.; Gailberger, M. Mak-
romol. Chem. 1988, 189, 119. (b) Brenda, M.; Greiner, A.; Heitz, W.
Makromol. Chem. 1990, 191, 1083. (c) Bao, Z.; Chen, Y.; Cai, R.; Yu,
L. Macromolecules 1993, 26, 5281.
J . Org. Chem, Vol. 69, No. 3, 2004 637

Murata et al.
yieldb/wt %
TABLE 3. P olym er iza tion Con d ition s of 5 a n d 9a
run
monomer
[M]0/mol/L
[(C2H5)3N]0/[M]0
additive
T/°C
time/h
Mw/103
Mw/Mn
1
2
3
4
5
6
7
8
9
5a
5a
5a
5a
5a
5b
5b
9
0.1
0.2
0.5
0.2
0.5
0.1
0.2
1.0
0.2
1.0
1.0
2.0
2.0
1.2
1.2
1.2
2.0
1.2
2.0
1.2
1.2
1.2
none
none
none
LiCl
LiCl
none
LiCl
LiCl
LiCl
none
LiCl
100
70
100
70
100
100
70
100
70
24
24
24
72
24
18
72
24
72
24
24
1.7
1.8
2.4
4.3
4.2
3.1
5.1
2.7
2.8
1.1
2.0
1.3
1.4
1.3
1.3
1.3
1.2
1.4
1.3
1.2
1.2
1.4
22
15
40
69
37
45
83
55
53
33
42
9
9
9
10
11
70
70
a
b
[Pd(OAc)2]/[M]0 ) 1/100; [P(o-tolyl)3]/[Pd(OAc)2] ) 4; [additive]/[M]0 ) 5. Methanol/benzene (7/3) insoluble part.
solvent was thoroughly removed to give a powder of the
isolated sample. The neat and isolated samples were trans-
ferred to a diamagnetic plastic capsule after the oxidation. The
magnetization and static magnetic susceptibility were mea-
sured with a Quantum Design MPMS-7 SQUID magnetom-
eter. The magnetization was measured from 0.1 to 7 T at 1.8,
2.0, 2.5, 3.0, and 5.0 K. The static magnetic susceptibility was
measured from 1.8 to 280 K in a 0.5 T field. The ferromagnetic
magnetization ascribed to the impurities was determined by
the Honda-Owen plots to be very low (< 1 ppm) and
subtracted from the overall magnetization. The diamagnetic
susceptibility of the diluent and capsule was estimated by the
Curie plots of magnetic susceptibility. The corrected magne-
tization data was fitted to Brillouin functions using a self-
consistent version of the mean field approximation.3b
NMR tube (φ5 mm) which was filled with the mixture of CDCl3
and cyclohexane. The NMR spectrum was recorded at 499.10
MHz. The peak shift, ∆ν, was estimated by frequency separa-
tion between those of the internal and the external cyclohexane
peaks. The magnetic susceptibility was calculated by the linear
relation between ∆ν and sample concentrations.
Ack n ow led gm en t. This work was partially sup-
ported by Grants-in-Aid for COE Research “Practical
Nano-Chemistry” and “Molecular Nano-Engineering”
from MEXT, J apan.
Su p p or tin g In for m a tion Ava ila ble: Syntheses and char-
acterization of 2-bromo-4-iodobenzaldehyde and 13C-labeled
2-bromo-5-hexyloxystyrene; ESR spectrum of 3a +; magnetic
susceptibility data measured by the NMR shift method and
other measurements. This material is available free of charge
via the Internet at http://pubs.acs.org.
Eva n s NMR Sh ift Mea su r em en t. The magnetic suscep-
tibility of 1+ was measured by the Evans NMR shift method.23
The 1+ CDCl3 solution was prepared by the oxidation of 1 with
a small excess of NOPF6/18-crown-6-ether. An inner NMR tube
(φ2 mm) was filled with the mixture of the 1+ solution and
cyclohexane, and placed in the center of an outer standard
J O0302758
638 J . Org. Chem., Vol. 69, No. 3, 2004