Para-phenylene-bridged spirobi(triarylamine) dimer with four perpendicularly linked redox-active π systems

Article abstract of DOI:10.1002/chem.201000848

para-Phenylene-bridged spirobi(triarylamine) dimer 2, in which it conjugation through four redoxactive triarylamine subunits is partially segregated by the unique perpendicular conformation, was prepared and characterized by structural, electrochemical, and spectroscopic methods. Quantum chemical calculations (DFT and CASSCF) predicted that the frontier molecular orbitais of 2 are virtually fourfold degenerate, so that the oxidized states of 2 can give intriguing electronic and magnetic properties. In fact, the continuous-wave ESR spec-troscopy of radical cation 2^.+ showed that the unpaired electron was trapped in the inner two redox-active dianisylamine subunits, and moreover was fully delocalized over them. Magnetic susceptibility measurements and pulsed ESR spectroscopy of the isolated salts of 2, which can be prepared by treatment with SbCl₅, revealed that the generated tetracation 2⁴⁺ decomposed mainly into a mixture of l) a decomposed tetra(radical cation) consisting of a tri(radical cation) moiety and a trianisylamine radical cation moiety (≈75%) and 2) a diamagnetic quinoid dication in a tetraanisyl-p-phenylendiamine moiety and two trianisylamine radical cation moieties (≈25%). Furthermore, the spin-quartet state of the tri(radical cation) moiety in the decomposed tetra(radical cation) was found to be in the ground state lying 30 cal mol^-1 below the competing spindoublet state.

Full text of DOI:10.1002/chem.201000848

DOI: 10.1002/chem.201000848
para-Phenylene-Bridged Spirobi(triarylamine) Dimer with Four
Perpendicularly Linked Redox-Active p Systems
Akihiro Ito,*[a] Kazuhira Hata,[a] Kensuke Kawamoto,[a] Yasukazu Hirao,[a, e]
Kazuyoshi Tanaka,[a] Motoo Shiro,[b] Ko Furukawa,[c] and Tatsuhisa Kato[d]
+
C
Abstract: para-Phenylene-bridged spi-
robi(triarylamine) dimer 2, in which
p conjugation through four redox-
active triarylamine subunits is partially
segregated by the unique perpendicular
conformation, was prepared and char-
acterized by structural, electrochemi-
cal, and spectroscopic methods. Quan-
tum chemical calculations (DFT and
CASSCF) predicted that the frontier
molecular orbitals of 2 are virtually
fourfold degenerate, so that the oxi-
dized states of 2 can give intriguing
electronic and magnetic properties. In
fact, the continuous-wave ESR spec-
troscopy of radical cation 2 showed
mainly into a mixture of 1) a decom-
posed tetra(radical cation) consisting of
a tri(radical cation) moiety and a tri-
anisylamine radical cation moiety
(ꢀ75%) and 2) a diamagnetic quinoid
dication in a tetraanisyl-p-phenylendi-
amine moiety and two trianisylamine
radical cation moieties (ꢀ25%). Fur-
thermore, the spin-quartet state of the
tri(radical cation) moiety in the decom-
posed tetra(radical cation) was found
to be in the ground state lying
30 calmolꢁ1 below the competing spin-
doublet state.
that the unpaired electron was trapped
in the inner two redox-active dianisyl-
amine subunits, and moreover was fully
delocalized over them. Magnetic sus-
ceptibility measurements and pulsed
ESR spectroscopy of the isolated salts
of 2, which can be prepared by treat-
ment with SbCl5, revealed that the gen-
erated tetracation 24+ decomposed
Keywords: arylamines · intervalent
· organic radicals ·
radical ions · spiro compounds
compounds
Introduction
[a] Dr. A. Ito, K. Hata, K. Kawamoto, Dr. Y. Hirao, Prof. Dr. K. Tanaka
Department of Molecular Engineering
Graduate School of Engineering, Kyoto University
Nishikyo-ku, Kyoto 615-8510 (Japan)
Molecule-based electronics have recently attracted much in-
terest with regard to breakthrough of the limit of silicon-
based semiconductor technology.[1–3] The development of in-
tegrated molecular-scale devices in the scope of nanotech-
nology necessarily requires the novel design and preparation
of organic molecular components with predictable and con-
trollable electrical, optical, and magnetic properties. In par-
ticular, characterization of the molecular and electronic
structures of organic (multi)radicals is of great importance
for our current understanding of efficient intramolecular
electron (or hole) transport and spin–spin interaction, which
is indispensable for practical applications of this type of mo-
lecular system in the future.
In this context, spiro linkage of spin-containing and/or
redox-active molecular subunits has repeatedly been revisit-
ed in the field of molecule-based materials science.[4–15] As
shown in Figure 1, the spiro compounds have a unique struc-
ture in which the same two p-electron systems are linked
with a so-called spiro atom, and consequently these two
p faces are possibly oriented at 908 to one another. Hence,
when a radical center is introduced into each p-electron
Fax : (+81)75-383-2556
E-mail: aito@scl.kyoto-u.ac.jp
[b] Dr. M. Shiro
X-ray Research Laboratory, Rigaku Corporation
Matsubaracho 3-9-12, Akishima, Tokyo 196-8666 (Japan)
[c] Dr. K. Furukawa
Institute for Molecular Science
Myodaiji, Okazaki 444-8585 (Japan)
[d] Prof. Dr. T. Kato
Department of Chemistry, Josai University
1-1 Keyakidai, Sakado, Saitama 350-0295 (Japan)
Present address:
Institute for the Promotion of Excellence in Higher Education
Kyoto University
Yoshida-Nihonmatsu, Sakyo-ku, Kyoto 606-8501 (Japan)
[e] Dr. Y. Hirao
Present address: Department of Chemistry
Graduate School of Science
Osaka University, 1-1 Machikaneyamacho
Toyonaka, Osaka 560-0043 (Japan)
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/chem.201000848.
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Chem. Eur. J. 2010, 16, 10866 – 10878

FULL PAPER
ture, which is often haunted with a diamagnetic property.
For instance, the attempts aimed at constructing metallic
charge-transfer salts with unique three-dimensional struc-
tures and molecular metals composed of a single molecular
component were undertaken by using spiro molecules.[7–12]
In particular, Haddon and co-workers revealed that phenar-
enyl-based spiro molecules gave intriguing magnetic, electri-
cal, and optical properties in the solid state, by taking ad-
vantage of the spiro conjugation and the nonplanar geome-
try of the multicentered radicals.[9–12]
Recently, we reported the synthesis of the spiro-fused
bis(triarylamine) 1 and the electronic structures of the
[17,18]
cation 1+ and dication 12+
.
The spiro molecule 1 has a
unique structure in which two redox-active trianisylamine
(TAA) subunits are linked perpendicularly to one another
through a spiro Si atom. Note that the choice of a Si linkage
stems from the facile synthesis of the spiro structure, as de-
scribed later. Gleiter and Bçhm pointed out the possibility
that the participation of 3d orbitals of the Si atom causes a
considerable increase of spiro conjugation.[19] However,
quantum chemical calculations predicted that the degenera-
cy of magnetic orbitals (fragment SOMOs originating from
the two TAA subunits) could be maintained for the dication
Figure 1. Schematic drawings of a spiro compound and two types of mo-
lecular orbital (MO) interactions between the same two p subunits that
reside on the perpendicular molecular planes a and b, respectively, in the
spiro structure. A and S denote antisymmetric and symmetric, respective-
ly, with regard to the symmetry planes a and b.
12+, and the two unpaired electrons could be ferromagneti-
ꢁ
cally coupled.[17] In fact, 12+
G
cal with a spin triplet multiplicity (Jintra/kB =16 K).[17] On the
C
other hand, we found that the radical cation 1 was charac-
terized as an intriguing bis(triarylamine)-based intervalence
charge-transfer (IVCT) molecule, and the thermal intramo-
lecular spin-transfer (IST) rates were unequivocally deter-
mined by using variable-temperature electron spin reso-
nance (VT-ESR) spectroscopy.[18] The spiro structure and its
suitability for molecular electronics have already been dis-
cussed from both theoretical[6] and experimental[7] view-
points. The versatility of 1 is ascribed to 1) the capability of
the stepwise formation of relatively stable radical cations
originating from the multiredox properties of arylamine-
based molecular systems and 2) the segmentation of the p-
conjugated system due to the perpendicular molecular struc-
ture. With this point in mind, it is of great interest to extend
1 to oligomeric systems.
Herein, we report the synthesis, molecular structure, and
electronic structure of para-phenylene-bridged spirobi(triar-
ylamine) dimer 2. The central part of 2 can be regarded as
tetraanisyl-para-phenylenediamine (TAPD). However, the
planar structure of the inner two dianisylamine (DAA) sub-
units unavoidably leads to the perpendicular conformation
of the central TAPD moiety in 2. In such a conformation,
the dication of TAPD can no longer adopt the diamagnetic
quinoid structure, and therefore the diradical character
emerges from breaking of p conjugation between the inner
two DAA subunits through para-phenylene. The para-phen-
ylene-bridged di(radical cation)s have already been reported
in comparison with their meta-phenylene-bridged counter-
part.[20–22] The present spirobi(triarylamine) dimer 2 is antici-
pated to realize the almost orthogonal configuration of the
individual triarylamine-based p systems. Similar molecular
system, the orbital interaction between the same two singly
occupied (SO) fragment molecular orbitals (MOs) of the
mutually perpendicular p-electron systems can vary signifi-
cantly depending on their symmetries (Figure 1).[16] When
both fragment MOs are antisymmetric to only one of the
two symmetry planes (AS and SA), the orbital degeneracy
gives rise to a parallel spin alignment between two unpaired
electrons; when both fragment MOs are antisymmetric to
both symmetry planes (AA), so-called spiro conjugation lifts
the orbital degeneracy and thus leads to an antiparallel spin
alignment between two unpaired electrons. With regard to
the spin preference in spirobiradicals, Dougherty and co-
workers examined the possibility of generating 1,4,6,9-spiro-
ACHTUNGTRENNUNG[4,4]nonatetrayl from both theoretical and experimental
points of view,[4,5] and Kahn and co-workers reported the
synthesis of a spiro-fused bis(nitronyl nitroxide) and the
weak intramolecular antiferromagnetic interaction (Jintra
/
kB =ꢁ5.8 K) between the two radical centers, which is prob-
ably due to the spiro conjugation.[14] Recently, Ishida et al.
revealed the presence of intermolecular antiferromagnetic
interaction (Jinter/kB =ꢁ70 K) in a spiro-fused bis(nitroxide)
and estimated the intramolecular ferromagnetic interaction
(Jintra/kB =12–13 K), which was probably buried by the large
intermolecular antiferromagnetic interaction, on the basis of
DFT calculations.[15]
From the structural viewpoint, the geometrical orthogon-
ality could obviate the possibility that the component mole-
cules form a simple one-dimensional p-stacked crystal struc-
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10867

A. Ito et al.
Results and Discussion
Theoretical considerations: To
address the electronic structures
of para-phenylene-bridged spi-
robi(triarylamine) dimer 2, we
carried out DFT calculations
(at the B3LYP/6-31G** level)
on 2’, the fully unsubstituted
analogue of 2.[26] The optimized
structure of 2’ was found to
take the expected alternant per-
pendicular conformation with
D2h symmetry. The distance be-
tween the outer two N nuclei
was calculated to be 18.581 ꢁ,
that between the inner two
N nuclei, 5.682 ꢁ, and that be-
tween the two N nuclei through
the spiro Si atom, 6.449 ꢁ. As
shown in Figure 2, we found
that the frontier MOs from
HOMO to (HO-3)MO were
virtually degenerate localized
MOs. Moreover, the HOMO
and (HO-1)MO were distribut-
ed mainly over the outer two
systems were previously examined by using anionic deriva-
tives of oligo(9,10-anthrylene).[23–25]
triarylamine subunits, whereas (HO-2)MO and (HO-3)MO
were mainly over the inner two triarylamine subunits, and
the two groups of MOs were separated by 0.07 eV. From
this frontier MO structure, it is possible that the removal of
Figure 2. Frontier MOs for 2’ (B3LYP/6-31G**). These MOs are selected as the active space MOs in CAS
G
.
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para-Phenylene-Bridged Spirobi(triarylamine) Dimer
FULL PAPER
Table 1. Relative energies [calmolꢁ1] of three low-lying states and config-
uration interaction (CI) coefficients of dominant configurations for the
an electron causes the IST among the four triarylamine
redox-active subunits, and furthermore, as is evident from
the quasi-fourfold-degenerate MOs, the spin-quintet state
unsubstituted model compounds for 2 at the CASACHUTNTGERNNUG(4,4)/3-21G*/CASACHTUNGTRENNUNG(4,4)/
3-21G* level of theory.
can be fulfilled in tetracation 24+
.
State
5A
1A
Relative energy[a]
Configuration
(54b2)1(59b3)1(55b2)1
(54b2)2(59b3)2
(54b2)2(55b2)2
(55b2)2(60b3)2
(59b3)2(60b3)2
(54b2)2(59b3)1
(59b3)1(55b2)1
(54b2)1(59b3)2 (60b3)1
(54b2)1 (55b2)2(60b3)1
Coefficient
To predict the spin multiplicity for the highest oxidation
state of 2, we performed complete active space self-consis-
tent field (CASSCF) calculations[27] with the 3-21G basis set
for the tetracation 2’4+, in which all the triarylamine subu-
nits are being oxidized, and hence the competing spin states
(singlet, triplet, and quintet states) should be considered.[26]
The active space orbitals adopted here were 54b2, 59b3, 55b2,
and 60b3: we took account of all the configurations that
arise when four electrons are allowed to occupy four MOs
as shown in Figure 2. Note that the geometry optimization
0.0
1.4
G
N
G
(60b3)1
1.00
ꢁ0.44
0.44
E
N
R
ꢁ0.43
N
0.43
3B1
6.8
G
0.50
G
ꢁ0.49
ꢁ0.51
0.51
T
A
ACHTUNGTRENNUNG
[a] Energy relative to the optimized D2 quintet state, for which a positive
5
value indicates that the state lies above the A state; ꢁ3302.4767 hartree.
by the CASACHTUNGTRENNUNG(4,4) method resulted in the lowering of symme-
try from D2h to D2, and therefore the symmetry terms for
the corresponding MOs were altered as shown in Figure 2.
Table 1 lists the relative ener-
gies of three low-lying spin
states. Although the ground
state of the tetracation 2’4+ was
5
predicted to be the quintet A
state, this result suggests that
these three spin states were vir-
tually degenerate at this level
of theory. The fractional occu-
pation numbers of all the spin
states, 5A, 3B1, and 1A, were cal-
culated to be 1.00, 1.00, 1.00,
and 1.00, respectively, for the
four active space orbitals, 54b2,
59b3, 55b2, and 60b3. This indi-
cates that the tetracation 2’4+
has
a tetraradical character,
which reflects the segregation
of p conjugation due to the per-
pendicular molecular structure
of 2’. Again, it should be noted
that the entire optimized mo-
lecular structures for the three
spin electronic states of the tet-
racation 2’4+ remained virtually
unchanged, probably due to the
perpendicular structure.
Synthesis and structural studies:
para-Phenylene-bridged spiro-
bi(triarylamine) dimer
2 was
synthesized by following the
procedure shown in Scheme 1.
The synthesis of spiro structures
often requires complicated syn-
thetic routes. As
a
facile
method to a spiro structure, we
noted that Gilman and co-
workers realized reasonable
Scheme 1. Synthetic route for 2. BTMABr3 =benzyltrimethylammonium bromide, [PdACHTUNTRGNE(NUG dba)2]=bis(dibenzylide-
yields of spirobi(dihydrophena- neacetone)palladium.
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A. Ito et al.
Table 2. Crystallographic data for 2·ACTHNUTRGENN(UG CH3CN)4·ACHUTTGNREN(NGUN H2O).
zasiline)s by treatment of the corresponding N-alkyl-2,2’-di-
lithiodiphenylamine with silicon tetrachloride.[28] By employ-
ing Gilmanꢂs method as a key reaction, the core compound,
spiro-fused diamine 6, was obtained in four steps starting
empirical formula
formula weight
T [K]
C84H80N8O11Si2
1433.77
93(1)
l [ꢁ]
1.54187
from diACHTUNGTRENNUNG(p-anisyl)amine.
crystal system
space group
Z
a [ꢁ]
b [ꢁ]
c [ꢁ]
a [8]
b [8]
triclinic
One of the two amino groups of 6 was capped by a p-
anisyl group with use of a Pd-catalyzed amination reaction
(Buchwald–Hartwig reaction).[29–32] Finally, the target mole-
cule 2 was formed by the reaction of p-dibromobenzene
with p-anisyl-capped spiro-fused diamine 7 by utilizing the
same Pd-catalyzed amination reaction. Note that the use of
the pentaphenylferrocenyl di-tert-butylphosphine ligand[33,34]
instead of the o-biphenyl di-tert-butylphosphine ligand,[35]
which was enough for the preparation of 7, was essential for
the preparation of the final coupling product 2.
¯
P1
1
9.85268(18)
11.1752(2)
18.9661(7)
75.4725(10)
74.9816(10)
66.6937(9)
1826.28(8)
1.304
g [8]
V [ꢁ3]
1calcd [gcmꢁ3
]
m [mmꢁ1
]
10.017
20510
collected data
unique data/Rint
6478/0.075
486
0.971
Colorless platelike single crystals were grown by slow
evaporation of a dilute mixed solution (CH3CN and CH2Cl2)
of 2, and its molecular structure was successfully established
by means of X-ray structure analysis (Table 2 and Figure 3).
The obtained crystals included four CH3CN and one H2O
per molecule of 2. As expected from the quantum chemical
calculations as well as the molecular design in the Introduc-
tion, 2 adopted an alternately perpendicular structure, in
which the amino planes linked by the spiro Si atom were
perpendicularly placed and the
no. of parameters
goodness-of-fit[a]
R1 (I>2s), wR2 (all reflections)[b]
0.0714, 0.2049
0.35/ꢁ0.40
residual density [eꢁꢁ3
]
n
h
i.
o
ꢀ
ꢁ
[a] GOF=
ðn ꢁ pÞ 1=2, in which n and p denote the
P
2
w F02 ꢁ Fc2
P
P
number of data and parameters. [b] R1= ðkF0k ꢁ kFckÞ= kF0k and
n
h
i.
h
io
ꢀ
ꢁ
ꢀ
ꢁ
1=2
P
P
2
2
wR2=
1
w F02 ꢁ Fc2
w F02
,
in
which
w=
ꢂꢃ
ꢀ
ꢁ
ꢄ
ꢃꢀ
ꢁ
ꢄꢂ
s2 F02 þ ðaPÞ þbP and P= Max; 0; F02 þ 2Fc2 3.
2
central TAPD moiety also took
a
perpendicular conformation
(the top and side views in
Figure 3). The span of com-
pound 2 was about 30 ꢁ in
length. The distance (N2–N2*)
between the outer two N nuclei
was calculated to be 18.349 ꢁ,
that (N1–N1*) between the
inner two N nuclei, 5.647 ꢁ,
and that (N1–N2) between the
two N nuclei through the spiro
Si atom, 6.361 ꢁ. Hence, the
observed structural feature
promises the predicted elec-
tronic structures of the oxidized
species of 2.
Electrochemical and spectro-
electrochemical studies: The
redox behavior of para-phenyl-
ene-bridged
spirobi(triaryl-
amine) dimer 2, in which four
oxidizable subunits are connect-
ed by a spiro Si atom and para-
phenylene, were investigated by
cyclic voltammetry (CV) and
differential pulse voltammetry
(DPV) in CH2Cl2 at room tem-
perature (Figure 4). The cyclic
Figure 3. Molecular structure of 2 with atomic numbering scheme and the top and side views. Hydrogen atoms
ꢁ
ꢁ
ꢁ
are omitted for clarity. Selected bond lengths [ꢁ] and angles [8]: Si1 C1 1.841(3), Si1 C2 1.821(4), Si1 C3
ꢁ
ꢁ
ꢁ
ꢁ
ꢁ
ꢁ
1.847(4), Si1 C4 1.827(3), N1 C5 1.442(4), N1 C8 1.410(5), N1 C11 1.426(4), N2 C9 1.421(4), N2 C10
voltammogram of
2 showed
ꢁ
ꢁ
ꢁ
1.427(5), N2 C12 1.441(5), C5 C6 1.374(4), C6 C7 1.388(5); C1-Si1-C4 100.90(16), C2-Si1-C3 101.52(16), C8-
three redox couples at +0.21, N1-C11 126.6(2), C9-N2-C10 125.6(3), C6-C5-C7* 120.1(3), C5-C6-C7 120.0(3).
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para-Phenylene-Bridged Spirobi(triarylamine) Dimer
FULL PAPER
Figure 4. a) Cyclic voltammogram and b) differential pulse voltammo-
gram of 2, measured in CH2Cl2 containing 0.1m nBu4NBF4 at 298 K (scan
rate 100 mVsꢁ1).
+0.32, and +0.47 V (vs. Fc0/+) and the last oxidation pro-
cess corresponds to quasi-two-electron transfer judging from
the observed current ratio (Scheme 2). From the curve fit-
ting of the observed differential pulse voltammogram, such
a quasi-two-electron oxidation process was found to be sep-
arable into two reversible one-electron oxidation processes
(E3 =+0.43 and E4 =+0.51 V (vs. Fc0/+); broken lines in
Figure 4b). The oxidation potentials of 2 are summarized in
Table 3 together with those of the related compounds under
the same conditions. Note that the reported oxidation po-
tentials for 1 were measured in MeCN.[17,18] As is apparent
from the recent cautionary reports, the oxidation potentials
and their differences are influenced strongly by the solvent
and the supporting electrolyte used in the CV measure-
ments.[36–39] Hence, we have remeasured the oxidation poten-
tials for 1 in CH2Cl2 solution in this study.
First of all, the E2ꢁE1 (=DE) value for 2 decreases by
half relative to that of 1. This difference in DE between 1
and 2 originates from the fact that the first two successive
one-electron oxidation processes in 2 take place from the
two spiro-fused bis(trianisylamine) units, whereas those in 1
occur from the two TAA subunits within the spiro-fused
bis(trianisylamine). However, the small, but not negligible,
value of DE for 2 indicates that the radical cation 2+ is sta-
Scheme 2. Three-stage redox reaction sequence for 2.
bilized by the spin delocalization between the two spiro-
fused bis(trianisylamine) units through the central para-
Table 3. Oxidation potentials [V vs. Fc0/+] for 1, 2, TAA, and TAPD.[a]
Compound
E1
E2
E3
E4
E2ꢁE1 (=DE)
1
0.26
0.46
0.44
–
–
–
–
0.20
(0.31
0.21
0.13)[b]
0.11
2
0.32
0.47[c]
0.51[d]
0.20[d]
0.11
0.32[d]
0.43[d]
0.12
TAA
TAPD
ꢁ0.10
0.36
–
–
0.46
[a] 1 mm CH2Cl2 solution containing 0.1m nBu4NBF4, Pt electrode,
100 mVsꢁ1, 298 K. [b] Measured in 1 mm MeCN solution. [c] Quasi-two-
electron transfer. [d] Estimated from the Gaussian curve fitting of the
measured differential pulse voltammogram.
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10871

A. Ito et al.
phenylene bridging unit. The DE value (0.20 V) for 2 should
rather be compared with the DE value (0.46 V) for TAPD,
and the small DE value for 2 suggests that the perpendicular
conformation of the central para-phenylene bridging unit
makes it difficult to take the semi-quinoid structure, which
is the origin of the stability of the TAPD radical cation.
More noteworthy is that the differences in E1 and E2 be-
tween 1 and 2 (the differences decrease by 0.05 and 0.14 V,
respectively, on going from 1 to 2) indicate that the stabiliza-
tion of the radical cation and dication of 2 can be enhanced
compared to those of 1. As will be clarified from the ESR
studies, the stabilization of the radical cation of 2 originates
from the spin delocalization between the two spiro-fused
bis(trianisylamine) units through the central para-phenylene
bridging unit, whereas the stabilization of the dication of 2
probably stems from the change of the charge distribution
from the inner two DAA subunits in 2+ to the outer two
nately, we could not find any indication of the appearance
of a CR band for 2+ (see Figure S1 in the Supporting Infor-
mation for details).
The observed monotonous spectral changes of 2 are simi-
lar to those of 1.[18] This result suggests that the perpendicu-
lar molecular structure remains unchanged throughout the
oxidation process of 2 to 24+, and suggests the independence
of each triarylamine redox-active subunit from the other
redox-active ones. On the other hand, the redox property of
2 demonstrated the electronic coupling (or p conjugation)
among the four triarylamine-based p systems. The elucida-
tion of this discrepancy probably needs more theoretical de-
velopment.
Characterization of radical cation 2 +: When 2 was treated
C
with 0.8 equiv of tris(4-bromophenyl)aminium hexachlor-
oantimonate (TBA·SbCl6)[40] as oxidant at 195 K in n-butyro-
nitrile/toluene (1:1, v/v), the generation of the corresponding
TAA subunits in 22+
.
To obtain more information about the unique electronic
states for the oxidized species of 2, we measured the optical
absorption spectral changes of 2 in CH2Cl2 during the
course of oxidation going from neutral 2 to tetracation 24+
by using an optically transparent thin-layer electrochemical
radical cation was detected by the use of X-band ESR spec-
+
C
troscopy. At room temperature, the radical cation 2 af-
forded the ESR spectrum shown in Figure 6a. The observed
spectrum is roughly explainable by a 1:2:3:2:1 intensity pat-
tern owing to the hyperfine coupling of the unpaired elec-
tron with two out of the four equivalent 14N (I=1) nuclei at-
tributed to the four triarylamine redox-active subunits. Fur-
thermore, the observed spectrum can be simulated equally
by the assumption of complete delocalization between the
inner two nitrogen centers. The observed ESR line shape
can be well simulated in terms of the hyperfine interactions
with one 14N (I=1) nucleus (aN(2N)=0.63 mT), two ortho
cell (Figure 5). Throughout the oxidation process of 2 to 24+
,
1H (I=1/2) nuclei (a
(4H)=0.12 mT), six 1H (I=1/2)
H(ortho)ACTHUNGTRENNNUG
Figure 5. Vis–NIR spectral change during the electrochemical oxidation
of 2 to 24+ in CH2Cl2/0.1m nBu4NBF4 at 298 K.
an intense absorption band characteristic for radical cations
of triarylamines appeared and grew monotonously at
854 nm, and no IVCT [or charge-resonance (CR)] band was
observed in the near-infrared (NIR) region (up to 2000 nm).
On the other hand, as will be clarified from the ESR studies,
there is charge delocalization in 2+. To search for the CR
band in the absorption spectrum of 2+, we investigated the
solvent effect on the absorption spectrum of 2+. We chose
n-butyronitrile and CH2Cl2/Et2O as higher-polarity (e>20)
and lower-polarity (e<10) solvents, respectively. Unfortu-
+
C
Figure 6. a) Continuous-wave (cw) ESR spectrum of 2 in CH2Cl2 at
293 K, and b) the simulated spectrum.
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Chem. Eur. J. 2010, 16, 10866 – 10878

para-Phenylene-Bridged Spirobi(triarylamine) Dimer
FULL PAPER
nuclei belonging to the para-substituted methoxy groups
(a
H(methoxy)ACHTUNGTRENNUNG(12H)=0.08 mT), and the incorporation of the
contributions from the other nuclei into the constant line
width of the spectral simulation (Figure 6b). More interest-
ingly, the observed five-line ESR patterns remained almost
unchanged over a relatively wide temperature range, as
shown in Figure 7. The present observation indicates that
the unpaired spin generated in 2+ is confined in the inner
two DAA subunits (or TAPD moiety), and moreover is
fully delocalized over them.
+
C
Figure 7. Temperature dependence of the cw-ESR spectrum for 2 in
CH2Cl2.
+
Characterization of dication 22+: Additional oxidation of 2
C
with TBA·SbCl6 at 195 K led to the generation of 22+. How-
ever, neither the definitive fine structure in the allowed res-
onance (DMS =ꢂ1) nor the forbidden resonance (DMS =
ꢂ2) was detected in the cw-ESR spectrum in a rigid glass
of n-butyronitrile at 123 K, whereas the ESR intensity of 22+
Figure 8. a) cw-ESR spectrum of the oxidized species of 2 treated by
SbCl5 in CH2Cl2 at 123 K. Inset: the forbidden half-field resonance at
123 K. b) 2D ESTN spectrum of the oxidized species of 2 treated by
SbCl5 in CH2Cl2 at 5 K. c) 2D ESTN spectrum of the as-oxidized species
of 2 treated by SbCl5 in CH2Cl2 at 5 K.
+
C
increased up to nearly twice that of 2 (Figure S2 in the
Supporting Information). In addition, the pulsed ESR meas-
urements for 22+ also confirmed the existence of the spin-
doublet state of 22+ at 5 K. These results strongly suggest
that the two generated unpaired electrons are separately dis-
tributed over the outer two TAA subunits to avoid the un-
favorable Coulombic repulsion between the charged centers,
and therefore there is only a negligibly weak exchange inter-
action between the two unpaired spins.
To identify the spin multiplicity of the fully oxidized spe-
cies of 2 at low temperatures, we recorded the electron spin
transient nutation (ESTN) spectrum based on the pulsed
ESR method.[42–45] As shown in Figure 8b, the 2D contour
plot of the ESTN spectrum clearly displayed the intense nu-
tation frequency peaks at wnutation =28 and 32 MHz, as well
Characterization of oxidized species of 2 generated by treat-
ment with SbCl5: Judging from the observed oxidation po-
tentials, it is expected that 2 is fully oxidized into the tetra-
cation 24+ by using SbCl5 as an oxidant. As shown in Fig-
ure 8a, the cw-ESR spectrum of the oxidized species of 2
treated with a 1m CH2Cl2 solution of SbCl5 at 195 K did not
show a definite fine structure assignable to the spin-quintet
state of 24+ at 123 K, although the forbidden half-field tran-
sition was detected due to the existence of oxidized species
with a spin multiplicity higher than S=1.[41]
as that corresponding to the doublet impurities (wdoublet
=
16 MHz). A frequency ratio of wnutation/wdoublet =28:16 and
32:16 demonstrated that the observed two frequencies are
attributable to two kinds of transition for the spin-quartet
pffiffiffi
state [wnutation/wdoublet
=
3 for the j3/2,ꢂ3/2>,j3/2,ꢂ1/2>;
wnutation/wdoublet =2 for the j3/2,+1/2>,j3/2,ꢁ1/2>]. Conse-
quently, this observation established that the spin electronic
state for the dominant species of 2 oxidized by SbCl5 is in a
spin-quartet state (S=3/2). However, this result indicated
Chem. Eur. J. 2010, 16, 10866 – 10878
ꢀ 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
10873

A. Ito et al.
that the observed spin electronic state did not agree with
the spin-quintet state of 24+, which can be expected to be
generated by using SbCl5 as oxidant.
1) one of the two spiro structures is decomposed to yield a
tri(radical cation) moiety and a TAA radical cation moiety
(route 1); 2) all the spiro structures are decomposed to yield
a diamagnetic quinoid dication in the TAPD moiety and
two TAA radical cation moieties (route 2), as shown in
In the sample preparation for the above-mentioned ESR
measurements, the oxidized solution was bubbled through
Ar gas for about 30 s at 195 K in order to stir it. On the
other hand, when the oxidized solution was kept in liquid ni-
trogen immediately after addition of SbCl5, the situation
changed completely. As shown in Figure 8c, the 2D contour
plot of the ESTN spectrum clearly showed the nutation fre-
quency peaks at wnutation =27.5 and 33.8 MHz, as well as that
corresponding to the competing triplet state (19.5 MHz). A
frequency ratio of wnutation/wtriplet demonstrated that the ob-
ꢁ
Scheme 3. Such a C Si bond cleavage process has already
+
been observed for 1 in solution at room temperature.[18] It
C
should be noted that, in ref. [18] and this study, it has not
been clarified how the vacant valencies after cleavage of the
ꢁ
C Si bonds are saturated. Judging from the elemental analy-
sis of the isolated decomposed salt, however, the vacant va-
lencies are probably compensated by the extraction of the
hydrogen atoms from solvent molecules and/or the trace of
water in the solution. Taking the above-mentioned assump-
tion into consideration, we carried out the fitting of the tem-
perature dependence of the magnetic susceptibility observed
for the isolated salt. As shown in Figure 10, the interacting
three-spin system for the tri(radical cation) moiety can be
represented by a triangular scheme, in which each side of
the triangle stands for the strength of the exchange coupling
parameters Jij between two spin centers Si and Sj. In this
case, the spin Hamiltonian can be written as Equation (1):
served two frequencies are attributable to two kinds of tran-
pffiffiffi
sition for the spin-quintet state of 24+ [wnutation/wdoublet =2/
2
pffiffiffi pffiffi
for the j2,ꢂ2>,j2,ꢂ1>; wnutation/wdoublet
=
6/ 2 for the
j2,ꢂ1>,j2,0>]. This observation suggests that the gener-
ated tetracation 24+ is highly unstable at elevated tempera-
tures, and therefore it is expected that the immediate de-
composition of 24+ into the spin-quartet and doublet species
ꢁ
takes place through C Si bond cleavage, which was already
+
reported for 1 in solution at room temperature.[18]
C
Fortunately, we were able to isolate the oxidized species
of 2 as the SbCl6 salt by adding dry ether to a CH2Cl2 solu-
tion of 2 oxidized with a 1m CH2Cl2 solution of SbCl5 at
ꢁ
H ¼ ꢁ2ðJ12S1S2 þ J23S2S3 þ J31S3S1Þ
ð1Þ
For the putative molecular structure for the tri(radical
cation) moiety in the decomposed tetra(radical cation)
shown by route 1 in Scheme 3, we adopted a general trian-
gular scheme (J12¼J23¼J31).[47] As a whole, we used the for-
mula expressed by Equation (2), in which the energy differ-
195 K. The elemental analysis of the isolated powder exhib-
ꢁ
ited a reasonable result close to 24+
(SbCl6 )4, and at least in-
dicated that all the triarylamine units in 2 were fully oxi-
dized.[46] To confirm the spin state of the isolated salt, the
magnetic susceptibility of the powder sample of the isolated
salt was measured on a superconducting quantum interfer-
ence device (SQUID) magnetometer in the temperature
range 2–300 K at a constant magnetic field of 500 G. The
temperature dependence of the molar magnetic susceptibili-
ty (cM) is shown in Figure 9.
~
~
ences between three spin states
defined by Equations (3) and (4):
and
(Figure 10) are
1
2
cMT ¼
"
#
D1
D2
NAg2m2B
4kB
T
T ꢁ q
T
1 þ expðꢁ k TÞ þ 10 expðꢁ k TÞ
B
B
f
a
þ ð2 ꢁ aÞ
D1
D2
To elucidate the magnetic properties of the isolated salt,
we assumed that the generated tetracation was readily de-
T ꢁ q
ð2Þ
1 þ expðꢁ k TÞ þ 2 expðꢁ k TÞ
B
B
ꢁ
composed by two kinds of C Si bond cleavage processes:
qffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi
D1 ¼ 2 J122 þ J223 þ J321 ꢁ J12J23 ꢁ J23J31 ꢁ J31J12
ð3Þ
ð4Þ
D1
D2 ¼
ꢁ ðJ12J23J31Þ
2
Here we assume that the intermolecular magnetic interac-
tion can be treated with mean field theory (the Curie–Weiss
law). The purity factor f represents the purity of the salt in-
cluding all the other experimental errors, and parameter a
stands for the ratio in which only one of the two spiro struc-
tures is decomposed (route 1 in Scheme 3). Thus, the second
term on the right-hand side of Equation (2) represents the
Curie–Weiss behavior due to spin-1/2 of the TAA radical
cations. The other constants, NA, g, kB, mB, and q are the
Avogadro number, the g-factor, the Boltzmann constant, the
Bohr magneton, and the Weiss constant, respectively.
Figure 9. Temperature dependence of cMT for the isolated salts of 2
under a magnetic field of 500 G. The solid line represents the best fit to
Equation (2).
Although Equations (2)–(4) contain too many parameters
to determine the three exchange coupling parameters Jij
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Chem. Eur. J. 2010, 16, 10866 – 10878

para-Phenylene-Bridged Spirobi(triarylamine) Dimer
FULL PAPER
Scheme 3. Plausible routes toward the decomposition of tetracation 24+
.
Conclusion
Electronic structures for the oxidized species of para-phen-
ylene-bridged spirobi(trianisylamine) 2 possessing perpen-
dicular redox-active p systems were studied by using cw-
ESR and pulsed ESR spectroscopy, and SQUID magneto-
+
C
metry. It was found that the unpaired electron in 2 was
Figure 10. Energy level diagram for the two spin-doublet states and the
one spin-quartet state originating from the magnetic interaction of a
three-spin system, S1 =S2 =S3 =1/2.
trapped in the inner two redox-active dianisylamine subunits
(or TAPD moiety), and moreover was fully delocalized over
them. On the other hand, 24+, the highest oxidation state of
2, was found to be readily decomposed into the diamagnetic,
spin-quartet, and spin-doublet species probably due to a
uniquely, we can determine at least the energy differences
~
~
ꢁ
among the competing three spin states,
and 2, by the
weakness of the C Si bond, judging from the temperature
1
least-squares fitting of the experimental data to Equa-
and 2. As a result, the best-
fitted parameters were determined: f=0.95, a=0.72, 1/kB =
dependence of the magnetic susceptibility. However, it was
clearly demonstrated that the ferromagnetic interaction
among three spins-1/2 prevails in the tri(radical cation)
moiety in the decomposed tetra(radical cation). Hence, the
efforts toward the extended high-spin molecular systems uti-
lizing 2 should still not be discarded. For instance, substitu-
tion of the other atoms for the present spiro Si atom may
obviate the decomposition that we encountered in the pres-
ent study.
~
~
tion (2) as a function of
1
~
~
54.3 K, 2/kB =ꢁ15.2 K, q=ꢁ4.2 K. The negative value of
~
indicates that the spin-quartet state is the ground state of
2
the tri(radical cation) moiety in the decomposed tetra(radi-
cal cation) (Scheme 3, route 1), and that the energy differ-
ence between the quartet and the low-lying doublet state is
30.2 calmolꢁ1. From the simulated value for a, the dominant
oxidized species of the isolated salt was estimated to be the
decomposed tetra(radical cation) containing the tri(radical
cation) moiety with spin-quartet ground state. The reprodu-
cibility of this result was confirmed by several trials. Finally,
these analyses of the observed magnetic behavior for the
isolated salts were consistent with those obtained by the
pulsed ESR studies.
Experimental Section
General information: Toluene and n-butyronitrile were distilled from
CaH2 under an argon atmosphere, tetrahydrofuran (THF) was distilled
from sodium-benzophenone or potassium-benzophenone under an argon
atmosphere, N,N-dimethylformamide (DMF) was dried over 4 ꢁ molecu-
Chem. Eur. J. 2010, 16, 10866 – 10878
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www.chemeurj.org
10875

A. Ito et al.
lar sieves, and benzonitrile was purified through an alumina (ICN, Alu-
mina N, Akt. I) column with bubbling of argon, just before use. All the
other purchased reagents and solvents were used without further purifi-
cation. Column chromatography was performed with silica gel (Kanto
Chemical Co., Inc., silica gel 60N, spherical neutral) or alumina (Kanto
Chemical Co., Inc., aluminum oxide activated for column chromatogra-
phy).
1H and 13C spectra were recorded on a JEOL JNM-AL400 FT NMR
spectrometer and chemical shifts are given in parts per million (ppm) rel-
ative to internal tetramethylsilane (d=0.00 ppm). Elemental analyses
were performed by the Center for Organic Elemental Microanalysis,
Kyoto University.
7.17 (m, 5H; CH2Ph), 7.12 (d, 4J=3.0 Hz, 2H; H-3), 6.87 (d, 3J=9.0 Hz,
2H; H-6), 6.69 (dd, 3J=9.0, 4J=3.0 Hz, 2H; H-5), 4.67 (s, 2H; CH2Ph),
3.60 ppm (s, 6H; OCH3); 13C NMR (100 MHz, CDCl3): d=156.1 (CA-4),
140.5 (CB-1), 138.1 (CA-1), 128.1 (CB-3), 127.7 (CB-2), 126.9 (CB-4), 125.5
(CA-6), 121.9 (CA-2), 119.3 (CA-3), 113.5 (CA-5), 57.3 (CH2Ph or OCH3),
55.6 ppm (CH2Ph or OCH3); elemental analysis calcd (%) for
C21H19Br2NO2: C 52.86, H 4.01, Br 33.49, N 2.94; found: C 53.01, H 3.94,
Br 33.56, N 2.86.
N,N’-Dibenzyl-10,10’-spirobi(2,8-dimethoxy-5,10-dihydrophenazasiline)
(5): An n-hexane solution (1.65m) of nBuLi (18.5 mL, 30.6 mmol) was
added dropwise to a solution of 4 (7.3 g, 15.3 mmol) in Et2O (300 mL) in
an ice-cooled flask under an Ar atmosphere, and the reaction mixture
was stirred for 20 min. SiCl4 (0.88 mL) was added dropwise to the stirred
reaction mixture. The resulting solution was stirred for 2 h, and then
heated at reflux overnight. The solvent was removed in vacuo. After ad-
dition of water and CH2Cl2, the organic layer was separated and dried
over Na2SO4. After evaporation of the solvent, the crude product was pu-
rified by column chromatography on silica gel (CH2Cl2 as eluent), and
CV measurements were carried out in CH2Cl2 solution containing n-tet-
rabutylammonium tetrafluoroborate (TBABF4, 0.1m) as a supporting
electrolyte (298 K, scan rate 100 mVꢁ1) with an ALS/chi Electrochemical
Analyzer Model 612A. A three-electrode assembly was used, which was
equipped with a platinum disk (2 mm2), a platinum wire, and Ag/0.01m
AgNO3 (acetonitrile) as the working, counter, and reference electrodes,
respectively. The observed redox potentials were referenced against the
ferrocene/ferrocenium (Fc/Fc+) couple in CH2Cl2 solution.
1
was washed with Et2O to afford 5 as a white solid (3.0 g, 60%). H NMR
(400 MHz, CDCl3): d=7.43–7.29 (m, 10H; CH2Ph), 6.95 (d, 3J=9.0 Hz,
4H; H-6), 6.89 (d, 4J=3.0 Hz, 4H; H-3), 6.83 (dd, 3J=9.0, 4J=3.0 Hz,
4H; H-5), 5.31 (s, 4H; CH2Ph), 3.65 ppm (s, 12H; OCH3); 13C NMR
(100 MHz, CDCl3): d=153.0 (CA-4), 145.1 (CB-1), 138.4 (CA-1), 128.9
(CB-3), 126.9 (CB-2), 126.2 (CB-4), 119.3 (CA-6), 119.1 (CA-2), 117.3 (CA-
3), 117.0 (CA-5), 56.4 (CH2Ph or OCH3), 55.5 ppm (CH2Ph or OCH3); el-
emental analysis calcd (%) for C42H38N2O4Si: C 76.10, H 5.78, N 4.23;
found: C 75.49, H 5.75, N 3.93.
UV/Vis–NIR spectra were obtained with a Perkin–Elmer Lambda 19
spectrometer. Spectroelectrochemical measurements were carried out
with
a custom-made optically transparent thin-layer electrochemical
(OTTLE) cell (light pass length=1 mm) equipped with a platinum mesh,
a platinum coil, and a silver wire as the working, counter, and pseudo-ref-
erence electrodes, respectively. The potential was applied with an ALS/
chi Electrochemical Analyzer Model 612A.
10,10’-Spirobi(2,8-dimethoxy-5,10-dihydrophenazasiline) (6):
A suspen-
ESR spectra were recorded on a JEOL JES-SRE2X X-band ESR spec-
trometer, in which temperature was controlled by a JEOL DVT2 varia-
ble-temperature unit. A Mn2+/MnO solid solution was used as a refer-
ence for the determination of g-values and hyperfine coupling constants.
Pulsed ESR measurements were carried out on a Bruker ELEXSYS
E580 X-band FT ESR spectrometer, in which temperature was controlled
by an Oxford ITC503 temperature controller combined with an ESR 910
continuous-flow cryostat.
sion of 5 (6.0 g, 9.1 mmol) and Pd on carbon (10%) in a mixed solvent of
acetic acid and CH2Cl2 (180 mL) and CH3OH (180 mL) was degassed re-
peatedly, and then vigorously stirred under H2 gas overnight. The solvent
was removed in vacuo, and then CH2Cl2 was added to the residue. After
filtration through Celite, the solution was washed with alkaline water,
and the organic layer was separated and dried over Na2SO4. After evapo-
ration of the solvent, the crude product was purified by column chroma-
tography on silica gel (CH2Cl2 as eluent), and was washed with Et2O to
afford 6 as a pale reddish powder (4.32 g, 99%). M.p. 2658C dec.;
1H NMR (400 MHz, CDCl3): d=6.84 (dd, 3J=9.0, 4J=3.0 Hz, 4H; H-5),
6.74 (d, 3J=9.0 Hz, 4H; H-6), 6.66 (d, 4J=3.0 Hz, 4H; H-3), 6.50 (br-s,
2H; NH), 3.54 ppm (s, 12H; OCH3); 13C NMR (100 MHz, CDCl3): d=
152.7 (C-4), 141.4 (C-1), 119.2 (CA-6), 118.6 (CA-2), 116.1 (CA-3), 114.3
(CA-5), 55.6 ppm (OCH3); elemental analysis calcd (%) for
C28H26N2O4Si: C 69.69, H 5.43, N 5.80; found: C 69.28, H 5.45, N 5.64.
Magnetic susceptibilities of the powder samples were measured by a
Quantum Design MPMS-5S system. The raw data were corrected for
both the magnetization of sample holder alone and the diamagnetic con-
tribution of the sample itself. The estimation of the diamagnetic contribu-
tion was done by using Pascalꢂs constants.
2,2’-Dibromo-4,4’-dimethoxydiphenylamine (3): BTMABr3 (34.9 g,
89.0 mmol) was added in one portion to a stirred suspension of dianisyla-
mine (10.0 g, 43.6 mmol) and K2CO3 (18.1 g, 130 mmol) in a mixed sol-
vent of CH2Cl2 (400 mL) and CH3OH (160 mL), and the reaction mixture
was stirred overnight. The solvent was removed in vacuo. After addition
of water and CH2Cl2, the organic layer was separated and dried over
Na2SO4. After evaporation of the solvent, the crude product was purified
by column chromatography on silica gel (CH2Cl2/n-hexane=1:1 as
eluent) and was recrystallized from n-hexane to afford 3 as a white crys-
talline solid (14.5 g, 86.9%). 1H NMR (400 MHz, CDCl3): d=7.13 (d,
4J=3.0 Hz, 2H; H-3), 7.13 (d, 3J=9.0 Hz, 2H; H-6), 6.77 (dd, 3J=9.0,
4J=3.0 Hz, 2H; H-5), 5.81 (br-s, 1H; NH), 3.76 ppm (s, 6H; OCH3);
13C NMR (100 MHz, CDCl3): d=154.6 (C-4), 134.8 (C-1), 119.7 (C-2 or
C-6), 118.1 (C-2 or C-6), 115.0 (C-3), 114.3 (C-5), 55.8 ppm (OCH3); ele-
mental analysis calcd (%) for C14H13Br2NO2: C 43.44, H 3.39, Br 41.28, N
3.62; found: C 43.18, H 3.28, Br 41.39, N 3.50.
N-Anisyl-10,10’-spirobi(2,8-dimethoxy-5,10-dihydrophenazasiline)
Anhydrous toluene (10 mL) was added to a mixture of 6 (229.4 mg,
0.48 mmol), p-bromoanisole (53 mL, 0.43 mmol), [Pd(dba)2] (5.7 mg,
(7):
AHCTUNGTRENNUNG
0.025 mmol), 2-(di-tert-butylphosphino)biphenyl[35] (15.0 mg, 0.050 mmol),
and sodium tert-butoxide (81.0 mg, 0.88 mmol) in a flask under argon,
and the solution was heated at reflux for 12 h. The solvent was removed
in vacuo. After addition of water and CH2Cl2, the organic layer was sepa-
rated and dried over Na2SO4. After evaporation of the solvent, the crude
product was purified by column chromatography on silica gel (CH2Cl2/n-
hexane=3:1 as eluent) to afford 7 as a pale yellow powder (136.6 mg,
1
54.0%). M.p. 1558C dec.; H NMR (400 MHz, [D6]acetone): d=8.47 (br-
s, 1 H; NH), 7.30 (m, 4H; HC-2, HC-3), 7.08 (d, 3J=9.0 Hz, 2H; HA-6 or
3
4
3
HB-6), 6.96 (dd, J=9.0, J=2.9 Hz, 2H; HA-5 or HB-5), 6.79 (dd, J=9.3,
4J=3.2 Hz, 2H; HA-5 or HB-5), 6.78 (d, 4J=2.9 Hz, 2H; HA-3 or HB-3),
6.74 (d, 4J=3.2 Hz, 2H; HA-3 or HB-3), 6.48(d, 3J=9.0 Hz, 2H; HA-6 or
HB-6), 3.94 (s, 3H; ArC-OCH3), 3.61 (s, 6H; ArA-OCH3 or ArB-OCH3),
3.56 ppm (s, 6H; ArA-OCH3 or ArB-OCH3); 13C NMR (100 MHz,
[D6]acetone): d=160.0 (CC-4), 153.5, 153.4 (CA-4, CB-4), 145.8, 143.0 (CA-
1, CC-1), 137.5 (CC-1), 132.9 (CB-2), 120.2, 119.3, 119.2, 118.8, 118.3 (CA-2,
CA-3, CB-3, CB-6, CC-2), 117.6, 117.5, 116.9, 114.1 (CA-6, CA-5, CB-5, CC-
3), 55.9, 55.7, 55.5 ppm (ArA-OCH3, ArB-OCH3, ArC-OCH3); FAB
HRMS (m-nitrobenzyl alcohol): m/z (%): calcd for C35H32N2O5Si:
588.2080 [M]+; found 588.2080 (100).
N-Benzyl-2,2’-dibromo-4,4’-dimethoxydiphenylamine (4): A THF solution
(180 mL) of 3 (26 g, 67 mmol) and n-tetrabutylammonium iodide (5.0 g,
13 mmol) was added dropwise to a stirred suspension of pulverized KOH
in THF (90 mL) under an Ar atmosphere, and the reaction mixture was
stirred for 1 h. A THF solution (90 mL) of benzyl bromide (9.0 mL,
76 mmol) was added dropwise to the stirred reaction mixture for 1 h, and
then the resulting solution was heated at reflux overnight. The solvent
was removed in vacuo. After addition of water and CH2Cl2, the organic
layer was separated and dried over Na2SO4. After evaporation of the sol-
vent, the crude product was purified by column chromatography on silica
gel (CH2Cl2/n-hexane=1:1 as eluent) and was recrystallized from
CH3OH to afford 4 (23 g, 72%). 1H NMR (400 MHz, CDCl3): d=7.50–
Spirobi(trianisylamine) dimer (2): Anhydrous toluene (8 mL) was added
to a mixture of 7 (220.0 mg, 0.37 mmol), p-dibromobenzene (29.4 mg,
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Chem. Eur. J. 2010, 16, 10866 – 10878

para-Phenylene-Bridged Spirobi(triarylamine) Dimer
FULL PAPER
[33,34]
0.12 mmol), [Pd
G
E
(8.9 mg,
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0.012 mmol), and sodium tert-butoxide (23.0 mg, 0.25 mmol) in a flask
under argon, and the solution was heated at reflux for 2 days. The solvent
was removed in vacuo. After addition of water and CH2Cl2, the organic
layer was separated and dried over Na2SO4. After evaporation of the sol-
vent, the crude product was purified by column chromatography on silica
gel (CH2Cl2/n-hexane=5:2 as eluent) to afford 2 as a pale yellow powder
(90.6 mg 58.1%). M.p. >3008C; 1H NMR (400 MHz, C6D6): d=7.46 (d,
4J=3.0 Hz, 4H; HB-3 or HC-3), 7.45 (d, 4J=3.0 Hz, 4H; HB-3 or HC-3),
7.40 (s, 4H; HA-2), 7.18 (dd, J=9.0, J=2.2 Hz, 4H; HB-5 or HC-5), 7.00
(d, 3J=9.2 Hz, 4H; HD-3), 6.95 (dd, 3J=9.3, 4J=2.9 Hz, 4H; HB-5 or
HC-5), 6.86 (d, 3J=8.6 Hz, 4H; HB-6 or HC-6), 6.85 (d, 3J=9.3 Hz, 4H;
HB-6 or HC-6), 6.77 (d, 3J=9.2 Hz, 4H; HD-2), 3.34 (s, 6H; ArD-OCH3),
3.18 (s, 12H; ArB-OCH3 or ArC-OCH3), 3.17 ppm (s, 12H; ArB-OCH3 or
ArC-OCH3); 13C NMR (100 MHz, CDCl3): d=158.9 (CD-4), 152.9, 152.4
(CB-4, CC-4), 145.2, 144.6 (CB-1, CC-1), 143.4, 136.7 (CA-1, CD-1), 133.1,
132.2 (CB-2, CC-2), 119.9, 119.3, 118.5, 118.5 (CA-2, CB-6, CC-6, CD-2),
118.1, 117.4, 117.2, 116.2, 116.1 (CB-3, CB-3, CC-3, CC-3, CD-3), 55.6, 55.6,
55.6 ppm (ArB-OCH3, ArC-OCH3, ArD-OCH3); FAB HRMS (m-nitro-
benzyl alcohol): m/z (%): calcd for C76H66N4O10Si2: 1250.4317 [M]+;
found 1250.4327 (9.9).
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Acknowledgements
This work was supported by a Grant-in-Aid for Scientific Research (B)
(20350065) from the Japan Society for the Promotion of Science (JSPS).
Thanks are due to the Instrument Center, the Institute for Molecular Sci-
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Received: April 5, 2010
Revised: June 18, 2010
Published online: July 30, 2010
10878
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Chem. Eur. J. 2010, 16, 10866 – 10878