Synthesis and through-bond spin interaction of stable 1,3-phenylene-linked polyradical carrying aminoxyls in the π-conjugated main chain

Article abstract of DOI:10.1039/b610365k

A stable polyradical carrying aminoxyls in the π-conjugated main chain was synthesized and its through-bond spin interaction was investigated. The polyradical is constructed with 1,3-phenylene as a spin coupler and 9,9-di-n-propyl-9,10-dihydroacridin-10-yloxy as a stable spin source. The synthetic method of the spin source moiety was modified by using conventional organic reactions from a previously reported method. The polymeric structure was synthesized by Suzuki-Miyaura coupling. The degree of polymerization and the spin concentration of the polyradical were ca. 11 and 0.71 spins per repeating unit, respectively, indicating that there were ca. 8 spins per molecule. The average S value of the polyradical was 3/2, therefore, 3 spins out of 8 spins were aligned in the polyradical. This showed that the through-bond spin interaction occurs more effectively than in our previous polyradical carrying aminoxyls in the side chain. The Royal Society of Chemistry 2007.

Full text of DOI:10.1039/b610365k

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PAPER
www.rsc.org/materials | Journal of Materials Chemistry
Synthesis and through-bond spin interaction of stable 1,3-phenylene-linked
polyradical carrying aminoxyls in the p-conjugated main chain
Hiroyuki Oka,* Hiroshi Kouno and Hitoshi Tanaka
Received 26th July 2006, Accepted 30th November 2006
First published as an Advance Article on the web 9th January 2007
DOI: 10.1039/b610365k
A stable polyradical carrying aminoxyls in the p-conjugated main chain was synthesized and its
through-bond spin interaction was investigated. The polyradical is constructed with 1,3-phenylene
as a spin coupler and 9,9-di-n-propyl-9,10-dihydroacridin-10-yloxy as a stable spin source. The
synthetic method of the spin source moiety was modified by using conventional organic reactions
from a previously reported method. The polymeric structure was synthesized by Suzuki–Miyaura
coupling. The degree of polymerization and the spin concentration of the polyradical were
ca. 11 and 0.71 spins per repeating unit, respectively, indicating that there were ca.
8 spins per molecule. The average S value of the polyradical was 3/2, therefore, 3 spins out of
8 spins were aligned in the polyradical. This showed that the through-bond spin interaction occurs
more effectively than in our previous polyradical carrying aminoxyls in the side chain.
spin couplers as shown in the studies of polycarbenes and
Introduction
poly(triarylmethine radical)s. We have studied poly(1,3-phe-
Organic high spin molecules are interesting organic open-shell
nylene)-based polyradicals and succeeded in aligning spins
systems for molecular magnetism.1–3 Among a wide variety of
organic open-shell oligomers or polymers, polycarbenes and
poly(triarylmethine radical)s have been successful for the
alignment of a large number of spins (10–103 order) by
through-bond spin interaction.4,5 One of the reasons for this
is that spin sources are located in the p-conjugated main chain
to give effective through-bond spin interaction. Recently,
poly(triarylamine cation radical)s have been investigated as
organic high spin molecules which retain the spin alignment
over room temperature.6–9 Effective through-bond interaction
in those polymers would be due to the fact that the centred N
atom or one of the aryls is located in the p-conjugated main
chain. One of the remarkable properties of poly(triarylamine
cation radical)s is their stability in the atmosphere. By
comparison, polycarbenes and poly(triarylmethine radical)s
are not stable thermally or chemically, and therefore they
cannot be used as practical materials. As a stable system
carrying spin sources in the p-conjugated main chain, poly(1,3-
phenylene aminoxyl),10 which is one of the most ideal open-
shell polymers for constructing polymeric organic magnets,
has been studied. The model oligomers showed that the
in polyradical 3p.13 Because the spin sources are stable
aminoxyls, 3p was very stable. However, the through-bond
spin interaction was not effective, therefore only a few spins
out of 10 spins per molecule were aligned. To improve
through-bond spin interaction in our polymers, we selected 2
as a spin source located in the p-conjugated main chain.
Because 2 is sufficiently stable that it can be isolated as a
crystalline solid,14 it was expected that 1p would also be stable.
As a preliminary study, we studied monomer model radical 1m
to establish the synthetic method of 1p and investigate the
behaviour of the spin by ESR measurements and MO calcula-
tions. The synthesis and magnetic properties of 1p and 1m are
reported here.
through-bond spin interaction is very strong (2J/kB
&
300 K).11,12 However, synthesis of the polymer was difficult
and the spin concentration was very low (ca. 0.10 spins per
repeating unit).
One of the methods to obtain effective through-bond spin
interaction is to locate the spin sources in the p-conjugated
main chain. We therefore studied polyradical 1p which
is constructed with 1,3-phenylene and 9,9-di-n-propyl-9,10-
dihydroacridine-10-yloxy (2). 1,3-Phenylene is one of the best
Results and discussion
Synthesis and ESR measurement of monomer model radical
Department of Advanced Materials, Institute of Technology and Science,
The University of Tokushima, 2-1 Minamijosanjima-cho, Tokushima,
770-8506, Japan. E-mail: okah@opt.tokushima-u.ac.jp;
Fax: +81 88 656 9435; Tel: +81 88 656 9424
Monomer model monoradical 1m was synthesized according
to Scheme 1. 9,9-Di-n-propyl-9,10-dihydroacridine (6) has
been synthesized by photochemical reaction from acridine,14
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g = 2.0050 with aN = 0.850 mT. To confirm the delocalization
of the spin to two phenyl groups corresponding to the 1,3-
phenylene spin couplers in polyradical 1p, the ESR spectrum
of 1m-d10 was also measured. The synthesis of 1m-d10 was
carried out by the same method as for 1m (Scheme 1). The
ESR spectrum of 1m-d10 in benzene (Fig. 1(b)) was split more
finely than that of 1m, indicating that the spin is delocalized to
two phenyl groups. The spectrum of 1m-d10 was computer-
simulated to give the hyperfine coupling (hfc) constants due
to hydrogen nuclei in the dihydroacridine moiety. The hfc
constants were determined to be 0.239 (2H) and 0.077 mT
(4H). The simulated spectrum reproduced with these hfc
constants was in excellent agreement with the observed
spectrum (Fig. 1(b), lower). Next, based on these hfc
constants, the spectrum of 1m was computer-simulated. In
this simulation, the same line width as in the simulation for
1m-d10 was used. The hfc constants due to hydrogen nuclei
in two phenyl groups were determined to be 0.042 (6H) and
0.017 mT (4H). The simulated spectrum reproduced with these
hfc constants was in excellent agreement with the observed
spectrum (Fig. 1(a), lower). The hfc constants estimated here
are listed in Table 1.
Scheme 1 Synthesis route to 1m and 1m-d10
.
but was prepared here by conventional organic reactions. The
reaction of methyl N-phenylanthranilate (4) with two molar
equivalents of n-propylmagnesium iodide gave 5 in 66% yield.
The Friedel–Crafts type cyclization of 5 in sulfuric acid gave 6
in 32% yield. The total yield from 4 to 6 was not high, but the
procedure was convenient. The bromination of 6 with tetra-
n-butylammonium tribromide (TBABr3) gave 7 in 41% yield.
The Suzuki–Miyaura coupling of 7 with phenylboronic acid in
the presence of a palladium catalyst and potassium carbonate
gave 8. The yield was 23%, which is very low compared with
our previous study for the Suzuki–Miyaura coupling of amino
compounds.15 Oxidation of 8 was carried out with 3-chloro-
peroxybenzoic acid to give 1m. Purification by column
chromatography and recrystallization gave pure 1m in 35%
yield as dark red prisms. 1m was very stable both in solution
and in the solid state in the atmosphere.16
X-Ray crystallographic analysis and MO calculation of
monomer model radical
Because single crystals of 1m were obtained by recrystalliza-
tion, we carried out X-ray crystallographic analysis (Fig. 2).17
The dihydroacridine moiety is quite planar and two n-propyl
groups extend perpendicularly to the plane, which is similar for
2.14 The dihedral angles between the dihydroacridine moiety
and two end phenyl rings are 27.2u (C7–C6–C14–C19) and
Table 1 Observed and calculated hfc constants for 1m and 3ma
The ESR spectrum of 1m was measured in benzene at
room temperature (Fig. 1(a)). The spectrum was observed at
1m
Nucleus
Obsd.b
Calcd.c
N
H1
H2,3
H4,6
0.850
0.239
0.077
0.042
0.821
20.238, 20.249
0.089, 0.090, 0.091, 0.092
20.035, 20.036, 20.039, 20.046,
20.046, 20.048
H5
0.017
3m
0.018, 0.018, 0.021, 0.022
Nucleus
Obsd.b
Calcd.c
N
1.06
0.11
1.05
0.107, 0.123
20.034, 20.036, 20.037
0.018, 0.019
20.004, 20.010, 20.011
0.004, 0.007
H1,2
H3,5
H4
H6,8
H7
a
n. d.d
n. d.d
n. d.d
n. d.d
Fig. 1 ESR spectra of (a) 1m and (b) 1m-d10 in benzene at room
temperature. The upper and lower spectra are the observed and
simulated spectra, respectively.
b
Given in mT. Determined by computer-simulating the observed
c
ESR spectra. Estimated by MO calculation. Not determined.
d
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Fig. 2 ORTEP drawing of 1m at 50% probability.
37.8u (C13–C12–C20–C25), which are typical values for the
dihedral angle between aryl planes as observed in biphenyl.18
Based on the structure in Fig. 2, MO calculation was
performed with the UB3LYP/6-31G model to estimate the hfc
constants (Table 1) and the spin density distribution (Fig. 3(a)).
Gaussian 03 software was used.19 The calculated hfc constants
of 1m were in excellent agreement with the hfc constants
determined above, except for the hfc constants due to H2 and
H3 nuclei, as shown in Table 1. To compare with the results
in our previous study,13c MO calculation for 3m was also
performed. Because X-ray crystallographic analysis for 3m had
been carried out, the observed structure was used. The results
are shown in Table 1 and Fig. 3(b). The calculated hfc
constants for 3m were in excellent agreement with the observed
hfc constants, as well as 1m. These excellent agreements
between the observed and calculated hfc constants for 1m and
3m showed a high reliability of the MO calculations here,
therefore, the spin density distribution estimated simulta-
neously would seem to be highly reliable. The spin densities in
the N–O moiety are lower in 1m (0.773) than in 3m (0.874),
indicating that the spin is delocalized more widely in 1m, which
is due to the N–O moiety being located in the p-conjugation.
The spin in 1m is delocalized to two phenyl rings A and B and
Fig. 4 Expected through-bond spin interactions in (a) 1p and (b) 3p.
the topology indicates ferromagnetic through-bond spin
interaction in polyradical 1p. By comparison, the spin in 3m
is also delocalized to two phenyl rings A and B, but the spin
densities on the phenyl ring B (0–0.004) are very low. This is
due to the large dihedral angle between the central benzene
ring and phenyl ring B (53.3u).13c These low spin densities
suggest that there is no spin interaction through phenyl ring B
in polyradical 3p. There are three kinds of linkage of head-to-
head, head-to-tail and tail-to-tail in 3p as shown in Fig. 4(b).
There would be through-bond spin interaction only in the tail-
to-tail part (|J| . 0), and no interaction in the head-to-head
and the head-to-tail parts (J = 0), therefore, only a triplet
dimer could be formed.20 On the other hand, in 1m, the spin
densities on phenyl rings A and B (0.009–0.024) are similar and
larger than in those on the phenyl ring A (0.008–0.015) in 3m,
therefore, it was expected that through-bond spin interaction
occurs through both phenyl rings A and B in 1p as shown in
Fig. 4(a).
Synthesis of polyradical
Polyradical 1p was synthesized from polymer 11 which was
prepared by Suzuki–Miyaura coupling (Scheme 2). Because no
coupling proceeded efficiently for preparing 8 from 7, the
amino group of 7 was protected with the tert-butoxycarbonyl
(BOC) group in the presence of 4-dimethylaminopyridine
(DMAP). The yield of 9 was 89%. Suzuki–Miyaura coupling
of 9 with 10 gave 11 in 92% yield as a colourless powder. In
this coupling, a phase transfer catalyst (TBABr) was used to
enable the base to act efficiently.13 11 was soluble in THF,
chloroform and dichloromethane.21 BOC deprotection was
carried out with trimethylsilyl iodide.22 The deprotection
occurred completely and the yield of 12 was 77%. 12 was
soluble in THF, chloroform and dichloromethane as well as 11.
The molecular weight of polymers 11 and 12 was determined
by size exclusion chromatography (SEC) with a polystyrene
standard. The number-averaged molecular weight (Mn) was
Fig. 3 Spin density distributions of (a) 1m and (b) 3m estimated by
the MO calculation.
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Fig. 5 ESR spectra of 1p (a) in dichloromethane, (b) in PVC matrix
(4.8 wt % content) and (c) in solid state powder at room temperature.
The spin concentration is 0.71 spins per repeating unit. In the
measurement in the PVC matrix at 103 K, the DMS = ¡2 transition
was observed at ca. 160 mT.
Scheme 2 Synthesis route to 1p.
4270 for 11 and 4040 for 12.23 From these values, the degree of
polymerization (n) was estimated to be 7.7 for 11 and 8.9 for
12.24 The degree of polymerization was also estimated from the
result of the elemental analysis. The found elemental analysis
values of 11 were C = 80.98, H = 8.97 and N = 2.06%. When it
is assumed that the end groups of 11 are Br and B(OH)2, the
calculated elemental analysis values are C = 80.88, H = 8.79
and N = 2.48% for n = 10 and C = 81.05, H = 8.80 and N =
2.49% for n = 11. These values are in good agreement with the
found values. Similarly, the degree of polymerization of 12 was
estimation to be 13–14 (Found: C = 86.01, H = 9.08 and N =
2.48%. Calcd: C = 85.92, H = 8.99 and N = 3.04% for n = 13;
C = 86.05, H = 9.00 and N = 3.04% for n = 14). From these six
n values, the average degree of polymerization of precursor
polymers was ca. 11.
The oxidation of 12 was carried out with 3-chloroperoxy-
benzoic acid. The procedure was similar for oxidation of 8 to
obtain 1m. The yield of 1p was 70%. Polyradical 1p was a dark
red powder and was very stable both in solution and in the
solid state, like 1m.16 The spin concentration was estimated by
ESR to be 0.71 spins per repeating unit.
ESR and magnetic measurements of polyradical
The ESR spectra of polyradical 1p were measured in dichloro-
methane, in a poly(vinyl chloride) (PVC) matrix and in the
solid state powder at room temperature (Fig. 5). The spectrum
in dichloromethane was observed at g = 2.0055. All three
spectra showed
a singlet line, indicating that exchange
narrowing occurs due to the high spin concentration. The
peak-to-peak width was 0.54 in dichloromethane, 0.85 in the
PVC matrix and 0.12 mT in the solid state. In the PVC matrix
at 103 K, the DMS = ¡2 transition was observed at ca. 160 mT,
indicating that there is through-bond spin interaction.
Fig. 6 Magnetic measurement results of 1p. The spin concentration
is 0.71 spins per repeating unit. (a) External magnetic field dependence
of the magnetization in a PVC matrix (7.2 wt% content). The
points are the experimental data at 2, 4 and 8 K. The lines are the
theoretical lines for S = 1/2, 2/2, 3/2 and 4/2 given by the Brillouin
function. Inset: the temperature dependence of the magnetic
susceptibility. The line is the least-square fit with eqn (1). (b)
Temperature dependence of the magnetic susceptibility of the bulk
solid. The xmol values were estimated based on the molecular weight of
the repeating unit.
The magnetization of 1p was measured by a SQUID
magnetometer. To observe through-bond spin interaction of
1p, the external magnetic field dependence of the magnetiza-
tion was measured in a PVC matrix (Fig. 6(a)). The experi-
mental data at 2, 4 and 8 K are in accordance with the S = 3/2
theoretical line given by the Brillouin function, that is, the
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average S value of 1p was 3/2. This supported the expectation
in Fig. 4(a) that through-bond spin interaction occurs
through both phenyl rings A and B in 1p. From the degree
of polymerization of ca. 11 and the spin concentration of
0.71 spins per repeating unit, there were on average ca. 8 spins
(ca. 11 6 0.71) per molecule, that is, 3 spins out of 8 spins were
aligned in 1p. In 3p, in taking into account the expectation in
Fig. 4(b), 2 spins out of 11 spins (ca. 15 6 0.75) per molecule
were aligned. Therefore, the modification of locating the spin
resources in the p-conjugated main chain improved the
through-bond spin interaction.
aligned. This showed that through-bond spin interaction in 1p
occurs more effectively than in 3p.
Experimental
Measurements
1H NMR spectra were measured with a JEOL JNM-EX400
spectrometer (400 MHz). Tetramethylsilane was used as
an internal standard for chemical shifts. IR spectra were
measured with a JASCO FT/IR-230 spectrometer. Melting
points were measured on a Yanagimoto micro-melting point
apparatus. SEC measurement was carried out with a TOSOH
HLC-8020 chromatograph. THF was used as an eluent and
the temperature was kept at 40 uC. X-Ray crystallographic
The inset in Fig. 6(a) is the temperature dependence of the
magnetic susceptibility in the PVC matrix. The xmolT value
increases steadily below 120 K as the temperature decreases.
The behavior was analyzed by using eqn (1) which is an
equation for the linear three S = 1/2 trimer:25
analysis was performed with
Imaging Plate diffractometer. ESR spectra were measured
with
JEOL JES-RE1X spectrometer (X-band). Mn2+
a Rigaku RAXIS-RAPID
a
Ng2m2B 1zexpð2J=kTÞz10expð3J=kTÞ
T
xmolT~f
(1)
(manganese(II) oxide dispersed in magnesium oxide) was used
as a standard for the g value. The spin concentration of the
polyradical was determined by using a solution of 1,3,5-
triphenylverdazyl in dichloromethane prepared to a known
4k 1zexpð2J=kTÞz2expð3J=kTÞ T{h
The least-square fit gave the magnetic exchange coupling
constant of J/k = +8.6 K.26 This value is of a similar order as
that found for 1,3,5-tris(4-N-tert-butyl-N-aminoxylphenyl)
benzene (J/k = +5.3 ¡ 0.1 or +6.8 ¡ 0.1 K) containing a
1,3,5-phenylene spin coupler and 2,4,6-tris(4-N-tert-butyl-N-
aminoxylphenyl)-s-triazine (J/k = +9.0 K) containing a 2,4,6-
s-triazine spin coupler.27,28
concentration. The magnetization was measured with
a
Quantum Design MPMS-7T SQUID magnetometer. The
external magnetic field dependence of the magnetization was
measured in the region of 0–6 T at the constant temperatures
of 2, 4 and 8 K. The temperature dependence of the magnetic
susceptibility was measured in the region of 2–300 K at a
constant external magnetic field of 0.5 T. The magnetizations
of diamagnetic compounds such as the capsule sample holder
and PVC were previously measured and the contributions were
corrected. The diamagnetic contribution of the paramagnetic
sample was estimated with Pascal’s constants and corrected.
The magnetic measurement results of the bulk solid of 1p is
shown in Fig. 6(b). The temperature dependence of the
magnetic susceptibility was in accordance with Curie’s law
above 90 K. The xmolT value is 0.27, corresponding to a spin
concentration of 0.72 spins per repeating unit, which is in good
agreement with the spin concentration determined by ESR.
The xmolT value increases in the temperature region of 90–7 K
and decreases below 7 K as the temperature decreases. This
behaviour is due to antiferromagnetic intermolecular spin
interaction. Ferromagnetic through-bond spin interaction
would contribute the increase of the xmolT value and inter-
molecular antiferromagnetic spin interaction would strongly
contribute in the low temperature region to the decrease of
the xmolT value.
Materials
Methyl N-phenylanthranilate (4) was prepared by the
esterification of N-phenylanthranilic acid with methanol in
the presence of sulfuric acid. TBABr3 was prepared according
to the reported method.29 Phenylboronic acid-d5 was prepared
from bromobenzene-d5 according to the method to prepare
phenylboronic acid. 5-n-Octyl-1,3-phenylenebis(trimethylene
boronate) (10) was prepared from 1,3-dibromo-5-n-octylbene-
zene according to the method to prepare 1,3-phenylenebis-
(trimethylene boronate).30,31 Reagents except for these were
purchased and used without further purification.
Conclusion
Polyradical 1p carrying aminoxyls in the p-conjugated main
chain was synthesized. The spin source moiety was synthesized
by conventional organic reactions. The precursor polymer was
prepared by Suzuki–Miyaura coupling between aryl dibromo
and diboron compounds. 1p was very stable both in solution
and in the solid state in the atmosphere. ESR measurement,
X-ray crystallographic analysis and MO calculation of
monomer model radical 1m suggest that through-bond spin
interaction in 1p is ferromagnetic and occurs more effectively
than in 3p which was our previous polyradical. The magnetic
measurement showed that the average S value of 1p was 3/2
and the magnetic exchange coupling constant was J/k =
+8.6 K. From the degree of polymerization of ca. 11 and the
spin concentration of 0.71 spins per repeating unit, there were
ca. 8 spins per molecule. In 1p, 3 spins out of 8 spins were
N-2-{4-(4-Hydroxyheptyl)}phenyl-N-phenylamine (5). To a
solution of n-propylmagnesium iodide prepared from magne-
sium (2.78 g, 114 mmol) and n-propyl iodide (10.2 mL,
106 mmol) in dry ether (75 mL) was added dropwise a solution
of 4 (6.00 g, 26.4 mmol) in dry ether (20 mL) at 0 uC under
nitrogen, and the mixture was stirred for 3 days at room
temperature. After an aqueous saturated ammonium chloride
solution was added to the mixture slowly at 0 uC, the organic
layer was separated, washed with brine and dried with
anhydrous magnesium sulfate. After evaporating, the residue
was chromatographed on silica with dichloromethane–hexane
(1 : 1) to give 5 in 65.5% yield (4.90 g, 17.3 mmol) as an orange
oil. IR (KBr): 3010–3615 cm21 (OH and NH). 1H-NMR
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(chloroform-d): 0.88 (6H, t, J 7.3, CH3), 1.15–1.43 (4H, m,
CH2), 1.70–1.99 (4H, m, CH2), 6.85–6.92 (2H, m, ArH), 7.02
(2H, dd, J 7.3 and 1.2, ArH), 7.11–7.16 (2H, m, ArH), 7.24
(2H, td, J 7.6 and 2.0, ArH), 7.32 (1H, d, J 7.8, ArH).
9,10-Dihydro-2,7-diphenyl-9,9-di-n-propylacridin-10-yloxyl
(1m). To a solution of 8 (70 mg, 0.168 mmol) in dichloro-
methane (10 mL) was added 3-chloroperoxybenzoic acid
(70 mg) and the mixture was stirred for 30 min at room
temperature. After a 10% sodium carbonate aqueous solution
(5.6 mL) was added, the organic layer was separated, washed
with brine and dried with anhydrous magnesium sulfate. After
evaporating, the residue was chromatographed on silica with
9,10-Dihydro-9,9-di-n-propylacridine (6). A mixture of 5
(5.01 g, 17.7 mmol) in sulfuric acid (9 mL) was stirred for 1 h
at room temperature and poured into ice-water (50 mL). The
aqueous mixture was extracted with ether and the ether layer
was washed with a 1 N sodium hydroxide aqueous solution
and brine and dried with anhydrous magnesium sulfate. After
evaporating, the residue was chromatographed on silica with
dichloromethane–hexane (1 : 2) to give 6 in 31.7% yield (1.49 g,
dichloromethane–hexane (1
: 1) and recrystallized from
methanol to give 1m in 34.5% yield (25 mg, 0.058 mmol) as
dark red prisms. Mp 148–150 uC. Anal. Found: C, 86.18;
H, 7.15; N, 3.22%. Calcd. for C31H30NO: C, 86.07; H, 6.99;
N, 3.24%.
1
5.61 mmol). Mp 99–101 uC. H-NMR (acetone-d6): 0.72 (6H,
t, J 7.3, CH3), 0.95–1.35 (4H, m, CH2), 1.82–1.95 (4H, m,
CH2), 6.69 (2H, dd, J 8.1 and 1.2, ArH), 6.78 (2H, td, J 7.3 and
1.2, ArH), 6.99 (2H, td, J 7.3 and 1.2, ArH), 7.26 (2H, dd, J
7.8 and 1.2, ArH), 7.82 (1H, br s, NH). Anal. Found: C, 85.91;
H, 8.91; N, 5.11%. Calcd. for C19H23N: C, 85.99; H, 8.74;
N, 5.28%.
9,10-Dihydro-2,7-diphenyl-d5-9,9-di-n-propylacridin-10-
yloxyl (1m-d10). The procedure was similar to that used to
prepare 1m. Yield: 52.3%. Mp 150–152 uC. Anal. Found: C,
84.08; H, 7.07; N, 3.16%. Calcd. for C31D10H20NO: C, 84.12;
H, 6.83; N, 3.16%.
N-tert-Butoxycarbonyl-9,10-dihydro-2,7-dibromo-9,9-di-
n-propylacridine (9). To a solution of 7 (1.27 g, 3.00 mmol) and
4-dimethylaminopyridine (0.127 g, 1.04 mmol) in THF (6 mL)
was added di-tert-butyl dicarbonate (0.982 g, 4.50 mmol)
and the mixture was stirred for 2 h at room temperature.
Water was added slowly and the mixture was extracted
with ether. The ether layer was separated and dried with
anhydrous magnesium sulfate. After evaporating, the residue
was chromatographed on silica with dichloromethane–hexane
(1 : 2) to give 9 in 91.7% yield (1.44 g, 2.75 mmol). Mp 87–
89 uC. 1H-NMR (chloroform-d): 0.83 (6H, t, J 7.3, CH3), 1.04–
1.10 (4H, m, CH2), 1.45 (9H, s, t-C4H9), 1.82–1.86 (4H, m,
CH2), 7.33 (1H, d, J 2.2, ArH), 7.35 (1H, d, J 2.2, ArH), 7.38
(2H, d, J 2.2, ArH), 7.42 (1H, s, ArH), 7.44 (1H, s, ArH).
2,7-Dibromo-9,10-dihydro-9,9-di-n-propylacridine (7). To a
solution of 6 (1.40 g, 5.28 mmol) in chloroform (10 mL) was
added TBABr3 (5.11 g, 10.6 mmol) and the mixture was
stirred for 1 h at room temperature. A 10% sodium thiosulfate
aqueous solution (20 mL) was added and the mixture was
extracted with ether. The ether layer was dried with anhydrous
magnesium sulfate. After evaporating, the residue was chro-
matographed on silica with dichloromethane–hexane (1 : 2) to
give 7 in 40.7% yield (0.91 g, 2.15 mmol). Mp 153–155 uC.
1H-NMR (acetone-d6): 0.77 (6H, t, J 7.3, CH3), 0.90–1.04 (4H,
m, CH2), 1.83–1.97 (4H, m, CH2), 6.69 (2H, d, J 8.5, ArH),
7.17 (2H, dd, J 8.5 and 2.2, ArH), 7.41 (2H, d, J 2.2, ArH),
8.21 (1H, br s, NH). Anal. Found: C, 54.64; H, 5.23; N, 3.02%.
Calcd. for C19H21Br2N: C, 53.93; H, 5.00; N, 3.31%.
Suzuki–Miyaura coupling of 9 with 10. To a solution of 9
(0.523 g, 1.00 mmol) in THF (10 mL) were added 10 (0.358 g,
1.00 mmol), a 2 M potassium carbonate aqueous solution
(2 mL), TBABr (0.870 g, 2.70 mmol) and Pd(PPh3)4 (69 mg,
0.06 mmol) and the heterogeneous mixture was refluxed for
24 h under nitrogen. The organic layer was separated, washed
with a 5% sodium cyanide aqueous solution (3 mL) and brine
and dried with anhydrous magnesium sulfate. After evaporat-
ing, the residue was reprecipitated from THF–methanol
9,10-Dihydro-2,7-diphenyl-9,9-di-n-propylacridine (8). To a
solution of 7 (0.430 g, 1.02 mmol) in THF (20 mL) were added
phenylboronic acid (0.270 g, 2.20 mmol), a 2 M potassium
carbonate aqueous solution (2.2 mL) and Pd(PPh3)4 (70 mg,
0.06 mmol) and the heterogeneous mixture was refluxed for
3 h with stirring under nitrogen. The mixture was extracted
with ether and the organic layer was dried with anhydrous
magnesium sulfate. After evaporating, the residue was
chromatographed on silica with dichloromethane–hexane
(1 : 3) to give 8 in 23.4% yield (0.100 g, 0.239 mmol). Mp
1
(5 mL–50 mL) to give 11 in 92.4% yield (0.510 g). H-NMR
(chloroform-d): 0.88 (9H, br s, CH3), 1.25–1.75 (25H, m,
t-C4H9 and CH2), 2.05 (4H, br s, CH2), 2.77 (2H, br s, CH2),
7.24–7.75 (9H, m, ArH). Anal. Found: C, 80.98; H, 8.97; N,
2.06%. Calcd. for (C38H49NO2)n: C, 82.71; H, 8.95; N, 2.54%.
1
155–157 uC. H-NMR (acetone-d6): 0.75 (6H, t, J 7.3, CH3),
1.06–1.14 (4H, m, CH2), 2.08–2.12 (4H, m, CH2), 6.84 (2H, d,
J 8.3, ArH), 7.27 (2 H, t, J 8.3, ArH), 7.37–7.44 (6H, m, ArH),
7.62–7.64 (6H, m, ArH), 8.19 (1H, br s, NH). Anal. Found: C,
88.94; H, 7.71; N, 3.31%. Calcd. for C31H31N: C, 89.16; H,
7.48; N, 3.35%.
BOC deprotection of 11. To a solution of 10 (0.320 g) in
chloroform (6 mL) was added trimethylsilyl iodide (0.174 g,
0.870 mmol). The mixture was stirred for 1 h at room
temperature and poured into methanol (60 mL) to give 12 in
9,10-Dihydro-2,7-diphenyl-d5-9,9-di-n-propylacridine (8-d10).
The procedure was similar to that used to prepare 8. Yield:
40.1%. Mp 151–153 uC. 1H-NMR (acetone-d6): 0.77 (6H, t,
J 7.3, CH3), 1.00–1.19 (4H, m, CH2), 2.05–2.17 (4H, m, CH2),
6.84 (2H, d, J 8.3, ArH), 7.38 (2H, dd, J 8.3 and 2.2, ArH),
7.64 (2H, d, J 2.0, ArH), 8.17 (1H, br s, NH).
1
77.4% yield (0.203 g). H-NMR (chloroform-d): 0.79 (6H, t, J
7.1, CH3), 0.88 (3H, br s, CH3), 1.12 (4H, br s, CH2), 1.20–1.50
(10H, m, CH2), 1.75 (2H, br s, CH2), 2.01 (4H, br s, CH2), 2.75
(2H, br s, CH2), 6.13 (1H, br s, NH), 6.70 (2H, d, J 7.3, ArH),
7.31 (2H, s, ArH), 7.40 (2H, d, J 8.0, ArH), 7.54–7.56 (3H, m,
1214 | J. Mater. Chem., 2007, 17, 1209–1215
This journal is ß The Royal Society of Chemistry 2007

View Article Online
14 M. Nakagawa, T. Ishida, M. Suzuki, D. Hashizume, M. Yasui,
F. Iwasaki and T. Nogami, Chem. Phys. Lett., 1999, 302, 125.
15 Y. Miura, H. Oka and M. Momoki, Synthesis, 1995, 1419.
16 The stability in the atmosphere was checked by ESR measurement.
The percentage decrease of the intensity in dichloromethane after
8 h at room temperature was within 5% for both 1m and 1p. In the
solid state, the percentage decrease was within 2%.
17 Crystal data for 1m: empirical formula: C31H30NO; formula
weight: 432.56; temperature = 296(2) K; crystal system: mono-
clinic; space group: Cc; unit cell dimensions: a = 11.0586(6), b =
ArH). Anal. Found: C, 86.01; H, 9.08; N, 2.48%. Calcd. for
(C33H41N)n: C, 87.75; H, 9.15; N, 3.10%.
Oxidation of 12. To
a solution of 12 (70 mg) in
dichloromethane (3 mL) was added 3-chloroperoxybenzoic
acid (62 mg) and the mixture was stirred for 20 min at room
temperature. After a 10% sodium carbonate aqueous solution
(5 mL) was added, the organic layer was separated, washed
with brine and dried with anhydrous magnesium sulfate. After
evaporating, the residue was reprecipitated from dichloro-
methane–hexane (3 mL–30 mL) to give 1p as a dark red
powder in 70.3% yield (51 mg).
˚
25.0054(11), c = 9.3633(7) A, a = 90, b = 108.299(2), c = 90u; V =
2458.3(3) A ; Z = 4; m(Cu-Ka) = 0.534 mm21; reflections
3
˚
collected
= 13178, independent collections = 2141 (Rint =
0.0447), GOF = 1.022, final R indices (I . 2s(I)): R1 = 0.0451,
wR2 = 0.1087; R indices (all data): R1 = 0.0494, wR2 = 0.1142.
CCDC reference number 625419. For crystallographic data in CIF
or other electronic format see DOI: 10.1039/b610365k.
18 F. Grein, THEOCHEM, 2003, 624, 23.
Acknowledgements
19 M. J. Frisch, G. W. Trucks, H. B. Schlegel, G. E. Scuseria,
M. A. Robb, J. R. Cheeseman, J. A. Montgomery, Jr., T. Vreven,
K. N. Kudin, J. C. Burant, J. M. Millam, S. S. Iyengar, J. Tomasi,
V. Barone, B. Mennucci, M. Cossi, G. Scalmani, N. Rega,
G. A. Petersson, H. Nakatsuji, M. Hada, M. Ehara, K. Toyota,
R. Fukuda, J. Hasegawa, M. Ishida, T. Nakajima, Y. Honda,
O. Kitao, H. Nakai, M. Klene, X. Li, J. E. Knox, H. P. Hratchian,
J. B. Cross, V. Bakken, C. Adamo, J. Jaramillo, R. Gomperts,
R. E. Stratmann, O. Yazyev, A. J. Austin, R. Cammi, C. Pomelli,
J. Ochterski, P. Y. Ayala, K. Morokuma, G. A. Voth, P. Salvador,
J. J. Dannenberg, V. G. Zakrzewski, S. Dapprich, A. D. Daniels,
M. C. Strain, O. Farkas, D. K. Malick, A. D. Rabuck,
K. Raghavachari, J. B. Foresman, J. V. Ortiz, Q. Cui,
A. G. Baboul, S. Clifford, J. Cioslowski, B. B. Stefanov, G. Liu,
A. Liashenko, P. Piskorz, I. Komaromi, R. L. Martin, D. J. Fox,
T. Keith, M. A. Al-Laham, C. Y. Peng, A. Nanayakkara,
M. Challacombe, P. M. W. Gill, B. G. Johnson, W. Chen,
M. W. Wong, C. Gonzalez and J. A. Pople, GAUSSIAN 03
(Revision D.01), Gaussian, Inc., Wallingford, CT, 2004.
20 No accurate spin state of 3p was measured, although ferromagnetic
through-bond spin interaction was confirmed by observing the
temperature dependence of the DMS = ¡2 transition in ESR
measurement.
We thank Prof. Y. Miura and R. Tanaka (Osaka City
University) for preparation of a deuterated compound and
X-ray crystallographic analysis. We also thank the Materials
Design and Characterization Laboratory, Institute for Solid
State Physics, The University of Tokyo for use of a SQUID
magnetometer.
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