Synthesis and magnetic behaviour of poly(1,3-phenylene)-based polyradical carrying N-tert-butylaminoxyl radicals

Article abstract of DOI:10.1039/a901944h

The synthesis and magnetic behaviour of poly[6-(N-oxyl-N-tert- butylamino)biphenyl-3,3'-ylene] 2 are described. Polyradical 2 was prepared by the Pd-catalyzed polycondensation of N-tert-butyl-2,4-dibromoaniline and 1,3-phenylenebis(trimethylene boronate),

Full text of DOI:10.1039/a901944h

J O U R N A L O F
Synthesis and magnetic behaviour of poly(1,3-phenylene)-based
polyradical carrying N-tert-butylaminoxyl radicals
Hiroyuki Oka,a Tomoki Tamura,a Yozo Miura*a and Yoshio Tekib
aDepartment of Applied Chemistry, Faculty of Engineering, Osaka City University, Sumiyoshi-ku,
Osaka 558–8585, Japan
C H E M I S T R Y
bDepartment of Material Science, Graduate School of Science, Osaka City University,
Sumiyoshi-ku, Osaka 558–8585, Japan
Received 11th March 1999, Accepted 18th March 1999
The synthesis and magnetic behaviour of poly[6-(N-oxyl-N-tert-butylamino)biphenyl-3,3∞-ylene] 2 are described.
Polyradical 2 was prepared by the Pd-catalyzed polycondensation of N-tert-butyl-2,4-dibromoaniline and 1,3-
phenylenebis(trimethylene boronate), followed by oxidation with 3-chloroperoxybenzoic acid. The degree of
polymerisation determined by SEC (size exclusion chromatography) was ~18. Polyradical 2 was stable in both
solution and the solid state. The spin concentrations of 2 determined by EPR and SQUID were 0.75 and 0.82 spin
per repeating unit, respectively. Magnetic susceptibility (x) measurements on 2 were carried out on a SQUID
magnetometer and these showed that the magnetic interaction between the unpaired electron spins was
antiferromagnetic (h=−0.98 K). The fact that no ferromagnetic interaction was observed was ascribed to a
twisting of the nitroxide moieties from the p-conjugated main chain, and this was confirmed by X-ray
crystallographic analysis of the corresponding model monoradical, N-tert-butyl-N-(2,4-diphenylphenyl)aminoxyl.
The potential of organic ferromagnetism has stimulated recent
interest in polyradicals, and a wide variety of p-conjugated
spin systems has been investigated.1 Intramolecular ferromag-
netic interaction through p-conjugation is considered crucial
N
N
O
O
for ferromagnetism. Thus, a wide variety of theoretical and
experimental studies has been done on p-conjugated systems,2
and the 1,3-phenylene unit has been shown to be the best
ferromagnetic coupler.3 Many 1,3-phenylene connected poly-
n
1
2
carbenes4 and 1,3-phenylene connected poly(triarylmethyl
polyradical)s5 have been synthesized by stepwise methods,
and it has been shown that the polycarbenes and poly(triaryl-
methyl polyradical)s are in high-spin ground states. However,
since their spin centers are in the main chains, failure in
generation of the carbene or radical species, or their decompo-
sition, leads to interruption of p-conjugation. Furthermore,
carbene is unstable at room temperature, and triarylmethyl
radicals are not stable in the presence of oxygen.
In the present study we report the first synthesis of a
poly(1,3-phenylene)-based polynitroxide. We prepared 2 with
a high spin concentration by the palladium-catalyzed polycon-
densation6–8 of N-tert-butyl-2,4-dihaloaniline 3 with 1,3-phen-
ylenebis(trimethylene boronate) 5, followed by oxidation.
Although a variety of polyradicals including poly(phenylace-
tylene)-,9 poly(1,3-phenyleneethynylene)-,10 and poly(pheny-
lenevinylene)-based polyradicals11 have been prepared,
poly(1,3-phenylene)-based polyradicals have never been
reported. Since polyradical 2 has its spin centers in the side
chain, the absence of some spin centers does not result in
interruption of p-conjugation.
ferromagnetic interaction between the unpaired electron
spins.12 In the structure A, all radical groups are at the 2-
position, and in the structure C, half of the radical groups are
at the 2-positions. Since the 2-position is surrounded by the
neighboring two 1,3-phenylene couplers, serious steric conges-
tion is anticipated at this position. This steric congestion may
lead to significant twisting of the radical group from the
poly(1,3-phenylene) p-conjugated system if the radical groups
are bulky like N-tert-butylaminoxyl. This may weaken the
strong ferromagnetic interaction between the unpaired elec-
trons through p-conjugation. We therefore decided to prepare
a polyradical having structure B.
Synthesis of monoradical 1
Monoradical
Treatment of N-tert-butylaniline13 with two equiv. of benzyl-
trimethylammonium tribromide (BTMABr )14 in
CH Cl –MeOH gave 3a in 93% yield as a colorless oil. The
1 was synthesized according to Scheme 1.
3
2
2
corresponding tribromo compound was not observed even
with excess BTMABr (3.3 equiv.). This is probably due to
the presence of a bulky N-tert-butyl group. The Pd-catalyzed
cross-coupling reaction of 3a with phenylboronic acid in
3
Results and discussion
Design of polyradicals
benzene–H O at reflux temperature for 24 h under nitrogen
2
Synthesis of high spin organic molecules is aimed at topological
symmetry,2 and, with this in mind, we can draw three structures
for poly(1,3-phenylene)-based polyradicals (A, B and C, in
Fig. 1). Since the radical groups are substituted at the 2- or
6-position to the 1,3-phenylene coupler, the polyradicals have
a nondisjoint structure favourable to induction of a strong
gave 4 in 85% yield. In the IR spectrum of 4 an absorption
peak due to nNH was observed at 3415 cm−1. Although the
1H NMR spectrum was very complex, the 13C NMR spectrum
gave the expected 2 and 14 peaks in the aliphatic and aromatic
regions, respectively. Elemental analysis also confirmed our
expectations.
J. Mater. Chem., 1999, 9, 1227–1232
1227

A
B
C
O
B
O
B
5
4
6
1
i
+
3
O
O
3
2
R
R
5
NH
ii
2
R
R
n
6
Scheme 2 Reagents and conditions: i, Pd(PPh ) , K CO , Bu NCl,
3 4
benzene–H O, reflux; ii, 3-ClC H CO H, CH Cl , room temp.
2
3
4
2
6
4
3
2 2
R
mer 6. The molecular weight (M ) of 6 was determined by
SEC with polystyrene standard in THF. Reprecipitation of
n
the polymer from CH Cl –hexane gave a light yellow powder.
2
2
R
The results of polycondensation are summarized in Table 1.
As shown in Table 1, the polycondensation of dibromo
compound 3a with 5 gave a higher molecular weight material
than that from the diiodo compound 3b. To examine solvent
effects on the molecular weights of polymers obtained, the
Fig. 1 Structures of poly(1,3-phenylene)-based polyradicals.
polycondensations were carried out in benzene–H O,
A solution of 4 and 3-chloroperoxybenzoic acid in CH Cl
2
2
2
toluene–H O and DMF–H O, and the highest molecular
was stirred for 30 min at room temperature and, after evapor-
ation, the residue was chromatographed on silica gel with
CH Cl –hexane (155) as the eluant to give 1 in 70% yield.
2
2
weight polymer was obtained in benzene–H O. Furthermore,
2
the polycondensations were carried out in different ratios of
2
2
5/3 (0.77, 1.0 and 1.3) and, when the ratio was 1.3, the highest
molecular weight polymer was obtained. Polymer 6 was soluble
in benzene, CHCl , CH Cl and THF, but insoluble in MeOH,
Recrystallization from hexane gave deep red prisms with mp
94–96 °C. The IR spectrum showed the complete disappear-
ance of an absorption peak due to nNH at 3415 cm−1, and
the elemental analysis was satisfactory. The purity of the
radical determined by EPR was ~100%. Monoradical 1 was
very stable in both solution and solid state over a long period.
3
2 2
hexane and acetone.
The IR spectrum of 6 showed an absorption peak due to
nNH at 3417 cm−1. In the 1H NMR spectrum the aromatic
region (7.0–7.8 ppm) was complex and assignment was diffi-
cult, but a singlet due to the t-Bu group and a broad singlet
due to NH were observed at 1.30 and 4.08 ppm, respectively.
Furthermore, no signals due to the trimethylene in the
boronate were observed. The 13C NMR spectrum was also
complex in the aromatic region (115–145 ppm), possibly aris-
ing from head-to-tail, head-to-head and tail-to-tail connections
between 3 and 5 (Fig. 2). However, the magnetic behavior of
2 should not be seriously affected because topological sym-
metry indicates that all these connections would give intra-
molecular ferromagnetic interactions although steric strain in
the head-to-head connection may reduce the effective p-
conjugation.
Synthesis of polymer 6
Polymer 6 was prepared by the Pd-catalyzed polycondensation
of
3
with 1,3-phenylenebis(trimethylene boronate)
5
(Scheme 2).15 A mixture of 3, 5, Pd(PPh ) , K CO and
3 4
2
3
2
Bu NCl was refluxed in benzene, toluene or DMF–H O at
4
80–110 °C under nitrogen. Bu NCl was added as a phase
transfer catalyst.16 After 3–7 days, the organic layer was
4
separated, concentrated, and chromatographed on silica gel.
Elution with benzene gave low molecular weight materials
containing catalysts, and elution with ethyl acetate gave poly-
The elemental analysis of 6 showed the presence of bromine
(3.24%). This indicates that the polycondensation is terminated
by bromine. Accordingly, the observed values (C, 83.23; H,
7.36; N, 5.24; Br, 3.24%) were not in satisfactory agreement
with the calculations [C, 86.06; H, 7.67; N, 6.27% for
(C H N) ]. However, taking the presence of bromine of
3.24% into account, the observed results give satisfactory
agreement with the calculations. For example, polymer 7 gave
C, 83.41; H, 7.48; N, 6.18; Br, 2.94%, and polymer 8 gave C,
83.31; H, 7.47; N, 6.07; Br, 3.15%. Polymer 8 may be formed
by deboronation of 9.
NH
NH
X
ii
i
X
16 17
n
3
3a X = Br
3b X = I
NH
iii
Oxidation of 6
1
Oxidation of 6 was carried out with 3-chloroperoxybenzoic
acid in the same manner as for 1 (Scheme 2). A solution of 6
and 3-chloroperoxybenzoic acid in CH Cl was stirred for 30
4
2
2
minutes at room temperature and the light red mixture was
Scheme 1 Reagents and conditions: i, BTMABr or BTMAICl ,
CaCO , CH Cl –MeOH, room temp; ii, C H B(OH) , Pd(PPh ) ,
K CO , benzene–H O, reflux; iii, 3-ClC H CO H, CH Cl , room
3
2
3 4
washed with an aqueous Na CO (10%) solution and brine,
2
3
3
3
2
2
6
4
5
2
and dried (MgSO ). After concentration, the residue was
4
2
2
6
3
2 2
temp.
reprecipitated from CH Cl –hexane to give 2 as a light red
2
2
1228
J. Mater. Chem., 1999, 9, 1227–1232

Table 1 Results of the Pd-catalyzed polycondensation of 3 with 5
Run
3
5/3
Solvent
T /°C
t/d
Yield (%)a
M b
M b
M /M b
DP
5.9
4.7
4.6
3.1
5.4
n
w
w
n
1c
2c
3c
4c
5d
6e
7e
3a
3b
3a
3a
3a
3a
3a
1.0
1.0
1.0
1.0
0.77
1.3
1.3
benzene
benzene
toluene
DMF
benzene
benzene
benzene
80
80
110
100
80
80
80
3
3
3
3
3
3
7
36
30
45
43
29
31
18
1320
1050
1030
700
1200
2470
4070
2210
1690
1670
1020
1750
3760
5960
1.67
1.61
1.62
1.46
1.46
1.52
1.46
11.1
18.2
aYield after reprecipitation from CH Cl –hexane. bDetermined by SEC. c3, 2.0 mmol; 5, 2.0 mmol, Pd(PPh ) , 0.12 mmol; K CO , 8.0 mmol;
3 4
Bu NCl, 5.3 mmol; solvent, organic solvent (20 cm3)–H O (4.0 cm3). d3, 2.0 mmol; 5, 1.5 mmol, Pd(PPh ) , 0.12 mmol; K CO , 6.0 mmol;
3 4
Bu NCl, 4.0 mmol; solvent, benzene (15 cm3)–H O (3.0 cm3). e3, 2.0 mmol; 5, 2.6 mmol, Pd(PPh ) , 0.12 mmol; K CO , 10.4 mmol; Bu NCl,
3 4
2
2
2
2
3
3
4
4
2
2
2
3
4
6.9 mmol; solvent, benzene (26 cm3)–H O (5.2 cm3).
2
with the excess 3-chloroperoxybenzoic acid. The SEC curve of
2 was almost identical with that of 6, indicating that no
polymer chains were cleaved or bridged during the oxidation.
NH
NH
EPR and UV–VIS spectra
Br
Br
EPR measurements of 1 and 2 were carried out at 20 °C using
benzene as the solvent. The spectra are shown in Figs. 3a and
23
3b. Monoradical 1 showed a 15151 triplet spectrum with a =
7
N
1.48 mT at g=2.0061 (Fig. 3a). In the case of 2, on the other
hand, the 15151 triplet was smeared out, and the spectrum
was a single peak with a peak-to-peak width of 0.82 mT (g=
2.0061), as shown by Fig. 3b. This is due to the occurrence of
exchange narrowing because the spin concentration of 2 is
very high (1.89×1021 to 2.07×1021 spins g−1).
NH
NH
O
B
H
Br
Br
O
The UV–VIS spectra of 1, 2, 4 and 6 were measured using
CH Cl as the solvent. The spectra are shown in Fig. 4. The
11
11
2
2
extinction coefficients (e) for 2 are corrected for the spin
8
9
concentration determined by EPR measurement. The UV–VIS
spectrum of
4
showed two
l
at 231 (e 21500 dm3
max
mol−1 cm−1) and 301 nm (21800), and that of 1 showed a
l
at 246 nm (33000) and three shoulders at 301 (3340), 399
max
(120) and 483 nm (70) (Fig. 4a). These shoulders are due to
the aminoxyl group (inset, Fig. 4a). On the other hand, two
NH
NH
l
were observed at 234 (24200) and 306 nm (25600) for 6,
max
head-to-tail
HN
NH HN
NH
head-to-head
tail-to-tail
Fig. 2 Three kinds of connection between monomers in polymer 6.
powder in 50% yield. Polyradical 2 was soluble in organic
solvents such as benzene, CH Cl , CHCl and THF. The IR
2
2
3
spectrum of 2 indicated the complete disappearance of the
absorption peak due to nNH at 3417 cm−1 observed for 6.
The spin concentration of 2 was determined by EPR. When
the mole ratio of the 3-chloroperoxybenzoic acid to 6 was
1.0–1.3, the spin concentration was 1.89×1021 spins g−1 (0.75
spin per repeating unit). On the other hand, when a greater
or lesser amount of 3-chloroperoxybenzoic acid was used, the
spin concentrations were lower. In the use of a lesser amount
of 3-chloroperoxybenzoic acid a strong absorption peak due
to nNH was observed in the IR spectrum of the polyradical
obtained, and in the case of a greater amount of 3-chloroper-
oxybenzoic acid the colour of the polyradical obtained was
not light red, but dark brown. This indicates that the aminoxyl
moieties formed are in part decomposed by further oxidation
Fig. 3 EPR spectra in benzene at 20 °C: (a) 1; (b) 2.
J. Mater. Chem., 1999, 9, 1227–1232
1229

Fig. 5 x–T and xT –T plots of 2. The solid line in the x–T plot is
calculated from the Curie–Weiss law.
antiferromagnetic. We ascribed this to twisting of the aminoxyl
moieties from the poly(1,3-phenylene) p-conjugated system.
The ferromagnetic interaction between the unpaired electron
spins through p-conjugation may be weaker than, and masked
by, antiferromagnetic through-space interactions. Any signifi-
cant twisting of the aminoxyl groups from the p-conjugated
system would reduce the ferromagnetic interaction between
the unpaired electron spins. This twisting of the aminoxyl
Fig. 4 UV–VIS spectra in CH Cl at 20 °C: (a) 1 (solid line) and 4
2
2
(dotted line); (b) 2 (solid line) and 6 (dotted line). Extinction
coefficient e for 2 is corrected for the spin concentration determined
by EPR spectroscopy.
moieties is suggested by the large a value (1.48 mT) of 1
N
since the magnitude of 1.48 mT is larger than those for planar
and a peak was observed at 248 nm (40000) for 2. However,
the three shoulders in the spectrum of 2 were not clearly
observed. The UV–VIS spectrum of 2 is almost identical
with that of 1, indicating that polyradical 2 has the expected
N-alkyl-N-phenylaminoxyl (1.18–1.20 mT).17 To confirm this
twisting, we performed X-ray crystallographic analysis on 1.
X-Ray crystallographic analysis
structure. Since
2 has a cross-conjugated structure, no
Recrystallization of 1 from hexane gave deep red prisms
suitable for X-ray crystallographic analysis. The ORTEP draw-
ing is shown in Fig. 6. Since the tert-butyl group was disordered
over the three sites with occupancies of 0.70, 0.13 and 0.17,
only the tert-butyl group with an occupancy of 0.70 is drawn
for clarity. The dihedral angle between planes A (C1–C6) and
B (C7–C12) is 45.9°, and that between planes A and C
(C13–C18) is 28.2°. On the other hand, the dihedral angle
bathochromic shifts were observed.
Magnetic susceptibility measurements
Magnetic susceptibility measurements on 2 were carried out
with a SQUID at 1.8–300 K. The diamagnetic contribution
from the sample was estimated from Pascal’s constants.
When the magnetic interactions among the unpaired electron
spins are smaller than the energy of the thermal fluctuation
kT , and the orbital angular momentum is neglected, the
magnetic susceptibility x is expressed by eqn. (1),
Nm 2g2S(S+1)
1
B
x=
(1)
(2)
3k
T −h
1
T −h
C
=
x
where N is Avogadro’s number, m is the Bohr magneton, g is
B
the Lande´ factor and
h
is the Weiss temperature;
Nm 2g2S(S+1)/3k is called the Curie constant, C.
B
The x–T and xT –T plots for a polyradical with a spin
concentration of 0.75 spin per repeating unit (M =4070) are
n
shown in Fig. 5. The xT –T plot of 2 (inset, Fig. 5) shows a
downward turn in the temperature region below 30 K, indicat-
ing an antiferromagnetic interaction between the unpaired
electron spins. The x–T plot was analyzed according to the
Curie–Weiss law [eqn. (2)], and the Curie and Weiss constants
were determined to be C=(1.29 0.01)×10−3 emu g−1 K and
h=−0.98 0.01 K, respectively. From the Curie constant the
spin concentration of 2 was estimated to be 0.82 spin per
repeating unit, which was somewhat higher than that deter-
mined by EPR (0.75 spin per repeating unit). A similar
magnetic behaviour (antiferromagnetic) was also observed for
Fig. 6 ORTEP drawing of 1. Only the tert-butyl group with an
occupancy of 0.7 is drawn for clarity. Planes A, B and C are the
benzene rings comprised of C1–C6, C7–C12 and C13–C18, respect-
ively. Plane D is comprised of C1–N1–O1. The dihedral angles
between planes A and B, planes A and C and planes A and D are
45.8, 28.2 and 68.5°, respectively. Selected bond lengths, bond angles
and torsion angles are as follows: N1–O1 1.277(5), C1–N1 1.438(5)
˚
a polyradical with a lower M of 2470.
and C19–N1 1.494(3) A; C1–N1–O1 116.7(1) and C19–N1–O1
118.6(5)°; C2–C1–N1–O1 111.5(2) and C6–C1–N1–O1 −68.5(2)°.
n
In spite of the high spin concentration, polyradical 2 was
1230
J. Mater. Chem., 1999, 9, 1227–1232

between planes A and D (C1–N1–O1) is 68.5°. Therefore, the
extent of the delocalization of the unpaired electron from the
N–O moiety to the benzene ring A is reduced to 13.4% (by a
factor of cos268.5°) of the planar structure. This reduces the
ferromagnetic interaction between the unpaired electron spins
through the conjugated p-system. Consequently, the absence
of the intramolecular ferromagnetic interaction can be ascribed
to the unexpectedly large twisting of the N–O moieties from
the poly(1,3-phenylene) p-conjugated system.
The ether layer was washed with brine, dried (MgSO ) and
evaporated, and the residue was chromatographed on silica
4
gel with CH Cl –hexane (156) as the eluant to give 3a in
2
2
92.6% yield (7.30 g, 23.8 mmol) as a colorless oil. n
max
(KBr)/cm−1 3406 (NH); d (CDCl ) 1.38 (9H, s, t-Bu), 4.3
H
3
(1 H, br s, NH), 6.82 (1H, d, J.8.8, ArH), 7.22 (1H, dd, J
2.4 and 8.8, ArH) and 7.54 (1H, d, J 2.4, ArH).
N-tert-Butyl-2,4-diiodoaniline 3b
To a stirred solution of N-tert-butylaniline (4.0 g, 26.8 mmol)
Summary
in CH Cl
(500 cm3)–MeOH (300 cm3) were added
2
2
BTMAICl (28.0 g, 80.4 mmol) and CaCO powder (10.5g,
A poly(1,3-phenylene)-based aminoxyl polyradical with a high
spin concentration was prepared by the Pd-catalyzed polycond-
ensation of N-tert-butyl-2,4-dibromoaniline and 1,3-phenylene-
bis(trimethylene boronate), followed by oxidation with 3-
chloroperoxybenzoic acid. The SQUID measurements of the
2
3
105 mmol) at room temperature. After the mixture was stirred
for 24 h, the CaCO powder was filtered off, and the filtrate
3
evaporated. An aqueous NaHSO solution (10%; 180 cm3)
3
was then added, and the mixture was extracted with ether.
The ether layer was washed with brine, dried (MgSO ),
polyradical showed
a weak antiferromagnetic interaction
4
evaporated and chromatographed on silica gel with benzene–
between the unpaired electron spins. The lack of ferromagnetic
interaction was explained in terms of twisting of the aminoxyl
moieties from the poly(1,3-phenylene) p-conjugated system.
This twisting of the aminoxyl moiety was confirmed by X-ray
crystallographic analysis of the corresponding model monorad-
ical. We are now synthesizing planar aminoxyl radicals having
cyclic structures, to maximize the likelihood of a ferromagnetic
interaction.
hexane (151) to give 3b in 51.3% yield (5.52 g, 13.8 mmol) as
a light yellow oil. n
(KBr)/cm−1 3390 (NH); d (CDCl )
max
H
3
1.39 (9H, s, t-Bu), 4.20 (1 H, br s, NH), 6.65 (1H, d, J 8.5,
ArH), 7.39 (1H, dd, J 8.5 and 2.4, ArH) and 7.91 (1H, d, J
2.4, ArH).
N-tert-Butyl-2,4-diphenylaniline 4
To a solution of 3a (0.92 g, 3.00 mmol) in benzene (45 cm3)
were added
a solution of phenylboronic acid (1.10 g,
Experimental
9.00 mmol) in EtOH (4.5 cm3), an aqueous K CO solution
2
3
Melting points were measured on a Yanaco micro-melting
point apparatus and are uncorrected. FT-IR and UV–VIS
spectra were run on a JASCO FT/IR-230 and a Shimadzu
UV-2200 spectrophotometer, respectively. 1H and 13C NMR
spectra were recorded with a JEOL a-400 spectrometer
(400 MHz) with Me Si as the internal reference; J values
are given in Hz. Size exclusion chromatography (SEC)
was run on
equipped with TSKgelG5000HHR, GMultiporeHXL-M and
TSKgelGMHHR-L columns calibrated with polystyrene
standards, eluting with THF. Detection was made with a Tosoh
refractive-index detector RI 8020. EPR spectra were recorded
on Bruker ESP 300 spectrometer operated at the X band. The
spin concentrations of the polyradicals were determined by the
double integrated EPR spectra of the sample using benzene as
the solvent. The calibration curve was drawn with 1,3,5-tri-
phenylverdazyl solutions using the same EPR cell and solvent
and the same instrument setting as for the sample measurements.
The magnetic susceptibility measurements were carried out on
a Quantum Design SQUID MPMS2 system in the temperature
range 1.8–300 K. The diamagnetic contribution of the samples
was estimated from Pascal’s diamagnetic constants.
(2 mol dm−3; 9 cm3) and Pd(PPh ) (0.21 g, 0.18 mmol). The
3 4
resulting heterogeneous mixture was purged with nitrogen,
and then gently refluxed for 24 h with stirring under nitrogen.
After cooling, the organic layer was separated, and the aqueous
solution was extracted with benzene. The combined benzene
solutions were dried (MgSO ), evaporated under reduced
pressure, and chromatographed on silica gel with
4
4
a
TOSOH 8020 series instrument
CH Cl –hexane (251) to give 4 in 85.0% yield (0.77 g,
2
2
2.55 mmol). Recrystallization from hexane gave colorless
prisms. Mp 107–109 °C; n
(KBr)/cm−1 3415 (NH); l
max
max
(CH Cl )/nm 231 (e/dm3 mol−1 cm−1 21500) and 301 (21800);
2
2
d
(CDCl ) 1.32 (9H, s, t-Bu), 7.06 (1H, d, J 8.3, ArH), 7.23
H
3
(1H, t, J 7.8, ArH), 7.34–7.47 (9H, m, ArH) and 7.06 (2H,
d, J 7.3, ArH); d (CDCl ) 30.04, 51.28, 114.58, 126.03,
C
3
126.23, 126.59, 127.27, 128.58, 128.88, 129.09, 129.49, 129.67,
129.97, 139.86, 140.99 and 143.49 (Found: C, 87.51; H, 7.28;
N, 4.59. C H N requires C, 87.66; H, 7.69; N, 4.65%).
22 23
N-tert-Butyl(2,4-diphenyl)phenylaminoxyl 1
3-Chloroperoxybenzoic acid (~70%) (0.52 g, ~2.1 mmol) was
added to a solution of 4 (0.30 g, 1.00 mmol) in CH Cl
2
2
(25 cm3) and stirred for 30 min, all at room temperature. After
evaporation, the residue was chromatographed on silica gel
with CH Cl –hexane (651) to give 1 in 70.0% yield (0.22 g,
Materials
2
2
N-tert-Butylaniline,13 benzyltrimethylammonium tribromide
0.70 mmol). Recrystallization from hexane gave deep red
(BTMABr ),14 benzyltrimethylammonium dichloroiodate
prisms. Mp 94–96 °C; a (benzene)/mT 1.48 (g 2.0061); l
3
2
N
max
(BTMAICl ),18 phenylboronic acid,19 1,3-phenylenebis(tri-
(CH Cl )/nm 246 (e/dm3 mol−1 cm−1 33000), 301 (3340), 399
2
2
methylene boronate)8 and Pd(PPh ) 20 were prepared accord-
(120) and 483 (70) (Found: C, 83.36; H, 6.71; N, 4.38.
3 4
ing to reported methods. Bu NCl and 3-chloroperoxybenzoic
4
C H NO requires C, 83.51; H, 7.01; N, 4.43%).
22 22
acid (purity ~70%) were commercial grade. Column chroma-
tography was carried out on Fuji Silysia BW-127ZH silica gel
(Fuji-Davison Chem. Co., Ltd). Ether refers to diethyl ether.
Polycondensation of 3 and 5. A typical procedure
To a solution of 3a (0.61 g, 2.0 mmol) in benzene (26 cm3)
were added 1,3-phenylenebis(trimethylene boronate) (0.64 g,
2.6 mmol), an aqueous K CO solution (2 mol dm−3;
N-tert-Butyl-2,4-dibromoaniline 3a
2
3
To a stirred solution of N-tert-butylaniline (3.84 g, 25.7 mmol)
in CH Cl (250 cm3)–MeOH (100 cm3) were added BTMABr
5.2 cm3), Bu NCl (1.93 g, 6.9 mmol) and Pd(PPh ) (0.14 g,
4
3 4
0.12 mmol). After the resulting heterogeneous mixture was
purged with nitrogen, it was gently refluxed for a week with
stirring under nitrogen. After cooling, the mixture was
extracted with benzene, and the benzene layer was washed
2
2
3
(22.0 g, 56.5 mmol) and CaCO powder (6.22 g, 62.2 mmol)
3
at room temperature. After the mixture was stirred for 30 min,
the CaCO powder was filtered off, and the filtrate was
3
evaporated. An aqueous NaHSO solution (10%, 170 cm3)
with brine and dried (MgSO ). After filtration, the benzene
3
4
was then added, and the mixture was extracted with ether.
was evaporated and the residue chromatographed on silica gel
J. Mater. Chem., 1999, 9, 1227–1232
1231

˚
with ethyl acetate. The material separated was refluxed in
MeOH for 10 min to give a light yellow powder. It was then
dissolved in CH Cl (4 cm3) and the solution was poured into
hexane (20 cm3) to give a light yellow powder, which was
collected by filtration and dried in vacuo. Yield 17.9% (0.080 g,
residual electron densities were 0.39 and −0.26 e A−3. Several
high peaks were still found near the tert-butyl group. The
maximum shift of the parameters in the final refinement was
less than their errors (D/s=0.30).
2
2
0.36 mmol); n
(KBr)/cm−1 3417 (NH); l
(CH Cl )/nm
Acknowledgements
max
max
2 2
234 (e/dm3 mol−1 cm−1 24200) and 306 (25600); d (CDCl )
H
3
1.30 (9H, s, t-Bu), 4.08 (1H, s, NH), 7.05 (1H, d, J 7.8, ArH)
and 7.25–7.74 (6H, m, ArH); d (CDCl ) 29.63, 115.45,
We are grateful to Professor K. Matsumoto, Osaka City
University, for assistance with the crystallographic analysis.
C
3
119.88, 123.09, 124.60, 125.47, 126.66, 126.77, 126.97, 127.19,
128.22, 128.53, 128.81, 129.26, 129.37, 130.31, 130.61, 131.53,
131.99, 132.09, 132.53, 139.54, 140.41, 141.12 and 141.57
(Found: C, 83.23; H, 7.36; N, 5.24; Br, 3.24. (C H N)
References
1
J. S. Miller, A. J. Epstein and W. M. Reiff, Chem. Rev., 1988, 88,
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J. A. Crayston, A. Iraqi and J. C. Walton, Chem. Soc. Rev., 1994,
147; P. M. Lahti, Polymeric Materials Encyclopedia, CRC Press,
Boca Raton, New York and London, 1996, vol. 2, pp. 1484–1494;
Y. Miura, ibid., vol. 9, pp. 6686–6695; Proceedings of the
Symposium of the 5th International Conference on Molecule-based
Magnets, Mol. Cryst. Liq. Cryst., 1997, 305, 1; 306, 1.
N. Mataga, Theor. Chim. Acta, 1968, 10, 372; A. A. Ovchinnikov,
Theor. Chim. Acta, 1978, 47, 297.
S. Kato, K. Morokuma, D. Feller, E. R. Davidson and
W. T. Borden, J. Am. Chem. Soc., 1983, 105, 1791; P. M. Lahti
and A. S. Ichimura, J. Org. Chem., 1991, 56, 3030; R. C. Fort, Jr.,
S. J. Getty, D. A. Hrovat, P. M. Lahti and W. T. Borden, J. Am.
Chem. Soc., 1992, 114, 7549.
P. S. Zuev and R. S. Sheridan, Tetrahedron, 1995, 51, 11337;
Y. Teki, I. Fujita, T. Takui, T. Kinoshita and K. Itoh, J. Am.
Chem. Soc., 1994, 116, 11499 and references cited therein.
A. Rajca, Chem. Rev., 1994, 94, 871.
N. Miyaura and A. Suzuki, Chem. Rev., 1995, 95, 2457.
Y. Miura, H. Oka and M. Momoki, Synthesis, 1995, 1419.
Y. Miura, H. Oka and M. Morita, Macromolecules, 1998, 31,
2041.
16 17
n
requires C, 86.06; H, 7.67; N, 6.27%). M =4070 (n=18.2),
n
M =5960 and M /M =1.46.
w
w
n
Oxidation of 6
3-Chloroperoxybenzoic acid (~70%) (0.12 g, ~0.49 mmol)
was added to a solution of 6 (0.10 g, 0.42 unit mmol) in
CH Cl (20 cm3), and the resulting mixture was stirred for
2
3
2
2
30 min, all at room temperature. The mixture was then washed
with an aqueous Na CO solution (10%; 10 cm3×2) and
brine, and dried (MgSO ). After filtration, the filtrate was
evaporated under reduced pressure and the residue dissolved
2
3
4
in CH Cl (5 cm3). The solution was poured into hexane
4
2
2
(50 cm3) to give 2 as a light red powder, which was collected
by filtration and dried in vacuo. Yield 50.0% (0.050 g,
5
6
7
8
0.21 mmol); l
(CH Cl )/nm 248 (e/dm3 mol−1 cm−1 40000)
max
2
2
(Found: C, 75.50; H, 6.36; N, 4.97; Br, 5.07. (C H NO)
16 16
n
requires C, 80.64; H, 6.77; N, 5.88%). The spin concentrations
determined by EPR and SQUID were 1.89×1021 and
2.07×1021 spins g−1, respectively.
9
A. Fujii, T. Ishida, N. Koga and H. Iwamura, Macromolecules,
1991, 24, 1077; Y. Miura, M. Matsumoto and Y. Ushitani,
Macromolecules, 1993, 26, 2628; Y. Miura, M. Matsumoto,
Y. Ushitani, Y. Teki, T. Takui and K. Itoh, Macromolecules, 1993,
26, 6673; H. Nishide, T. Kaneko, M. Igarashi, E. Tsuchida,
N. Yoshioka and P. M. Lahti, Macromolecules, 1994, 27, 3082,
and references cited therein.
Crystal structure determination of 1†
Crystal data: C H NO, M=316.4, monoclinic, a=
22 22
˚
11.282(1), b=7.602(2), c=21.513(1) A, b=95.38(1)°, V =
˚
1836.8(4) A3, space group P2 /n, Z=4, D =1.14 g cm−3,
1
c
10 Y. Miura, Y. Ushitani, K. Inui, Y. Teki, T. Takui and K. Itoh,
Macromolecules, 1993, 26, 3698; Y. Miura and Y. Ushitani,
Macromolecules, 1993, 26, 7079; Y. Miura, T. Issiki, Y. Ushitani,
Y. Teki and K. Itoh, J. Mater. Chem., 1996, 6, 1745, and references
cited therein.
11 H. Nishide, T. Kaneko, T. Nii, K. Katoh, E. Tsuchida and
P. M. Lahti, J. Am. Chem. Soc., 1996, 118, 9695, and references
cited therein.
12 W. T. Borden and E. R. Davidson, J. Am. Chem. Soc., 1977,
99, 4587.
13 E. R. Biehl, R. Patrizi and P. C. Reeves, J. Org. Chem., 1971,
36, 3252.
F(000)=676 and m(Cu-Ka)=5.38 cm−1.
A
deep red prismatic crystal with dimensions of
0.20×0.40×0.60 mm was selected. The reflection data were
collected on a Rigaku AFC7R diffractometer (50 kV, 200 mA)
with graphite monochromated Cu-Ka radiation (l=
˚
1.54178 A) at 23 1 °C. The v–2h scan mode was used with
the scan speed of 14° min−1 and the scan width of (1.73+0.3
tanh)°. Of 2836 reflections measured up to 2h=113.2° 2677
were unique (R =0.008), 1894 of which were considered as
observed (I>3s(I)). An empirical absorption correction based
int
on the Y scan was applied. The maximum and minimum
transmission factors are 0.93 and 1.00.
14 S. Kajigaeshi, T. Kakinami, H. Tokikawa, T. Hirakawa and
T. Okamoto, Bull. Chem. Soc. Jpn., 1987, 60, 2667; S. Kajigaeshi,
T. Kakinami, K. Inoue, M. Kondo, H. Nakamura, M. Fujikawa
and T. Okamoto, Bull. Chem. Soc. Jpn., 1988, 61, 597.
15 M. Remmers, M. Shultze and G. Wegner, Macromol. Rapid.
Commun., 1996, 17, 239; F. E. Goodson, T. I. Wallow and
B. M. Novak, Macromolecules, 1998, 31, 2047.
16 A. B. Charette and A. Giroux, J. Org. Chem., 1996, 61, 8718.
17 A. R. Forrester, J. M. Hay and R. H. Thomson, Organic
Chemistry of Stable Free Radicals, Academic Press, London and
New York, 1968, pp. 202–203.
18 S. Kajigaeshi, T. Kakinami, H. Yamasaki, S. Fujisaki and
T. Okamoto, Bull. Chem. Soc. Jpn., 1988, 61, 600.
19 R. M. Washburn, E. Levens, C. F. Albright and F. A. Billig, Org.
Synth., 1963, Coll. Vol. IV, 68.
20 D. R. Coulson, Inorg. Synth., 1972, 13, 121.
The structure was solved by the direct method [SHELXS86]
and refined on F by the least-squares [TEXSAN] using
anisotropic thermal parameters for non-hydrogen atoms.21
The tert-butyl group is disordered over the three sites with
occupancies of 0.70, 0.13 and 0.17. Their C atoms were placed
at an idealized position and in the final cycles of the refinement
their parameters were fixed. The hydrogen atoms were placed
˚
at a calculated position (C–H=0.96 A) with B (H)=1.2 B
iso
iso
(C) and their parameters were not refined. The hydrogen
atoms bound to C(23–28) with an occupancy of 0.13 or 0.17
were excluded from the refinement. The function minimized
was Sw(|F |−|F |)2, where v=1 was used. The final agreement
indices based on 1894 reflections for 210 parameters were
0.086 and 0.080 with GOF 5.64. The maximum and minimum
0
c
21 All calculations were performed using the Molecular Structure
Corporation’s TEXSAN crystallographic software package.
Paper 9/01944H
†CCDC reference number 1145/149.
1232
J. Mater. Chem., 1999, 9, 1227–1232