Exchange interaction of 5,5′-(m- and p-phenylene)bis(10-phenyl-5,10- dihydrophenazine) dications and related analogues

Article abstract of DOI:10.1021/jo051791w

5,5′-(m-Phenylene)bis[(10-aryl-5,10-dihydrophenazine) dications, 3a²⁺ and 3b²⁺, and their p-analogues 4a²⁺ and 4b²⁺, were prepared, and their exchange interaction was investigated. The EPR spectra of these dicat

Full text of DOI:10.1021/jo051791w

Exchange Interaction of 5,5′-(m- and
p-Phenylene)bis(10-phenyl-5,10-dihydrophenazine) Dications and
Related Analogues
Eriko Terada, Toshihiro Okamoto, Masatoshi Kozaki, Miyuki Eiraku Masaki,
Daisuke Shiomi, Kazunobu Sato, Takeji Takui, and Keiji Okada*
Departments of Chemistry and Materials Science, Graduate School of Science, Osaka City University,
Sugimoto, Sumiyoshi-ku, Osaka 558-8585, Japan
okadak@sci.osaka-cu.ac.jp
Received August 25, 2005
5,5′-(m-Phenylene)bis[(10-aryl-5,10-dihydrophenazine) dications, 3a2+ and 3b2+, and their p-
analogues 4a2+ and 4b2+, were prepared, and their exchange interaction was investigated. The
EPR spectra of these dications at 123 K in a butyronitrile matrix showed the population of a triplet
state. The temperature dependence of the EPR signal intensity (|∆ms| ) 2) showed that these
dications had singlet ground states with ∆EST/kB ) -27 to -21 K for the m-isomer 32+ and with
∆EST/kB ) -10 to -8 K for the p-isomer 42+. Theoretical calculation of the exchange interaction J
for these dications at the orthogonal torsion angle geometries was carried out for 3a2+ and 4a2+
and for (m- and p-phenylene)bisphenothiazine dications 12+ and 22+ using the broken-symmetry
approach for the singlet states. A good correlation was observed between the calculated J and a
MO-energy term in the triplet state, ∆ETMO ) |HOMO(R) - (HOMO - 1)(R)|. The calculated J
values were negative in the order of 10 K for the m-dications (J/kB ) -14.7 K for 12+, -11.5 K for
3a2+), but much smaller negative values were found for the p-isomers (J/kB ) -0.9 K for 22+, -0.8
K for 4a2+). The smaller |J| values for the p-dications are qualitatively consistent with the
experimental ∆EST (2J) values.
Introduction
gives rise to a high-spin ground state, whereas the
p-connection gives a low-spin ground state. Many experi-
ments and theories have supported this rule.1,2 Extension
of this rule, for instance, the m-phenylene connection, to
various systems other than alternant hydrocarbon spin
sources has frequently succeeded.1,2 However, recent
studies have clearly shown that there exist some low-
spin diradical systems3 with the m-phenylene linkage.2a,3
Rajca’s group has demonstrated that even a Schlenk-type
Understanding the magnetic interaction between un-
paired electrons in organic molecules is one of the most
fundamental and important subjects in the area of
molecular magnetism.1 In alternant hydrocarbon high-
spin molecules, it is generally accepted that the m-
phenylene or benzene-1,3,5-triyl connection of spin sources
* To whom correspondence should be addressed. Tel: +81-6-6605-
2568. Fax: +81-6-6690-2709.
(1) (a) Lahti, P. M. In Molecular-Based Magnetic Materials; Turn-
bull, M. M., Sugimoto, T., Thompson, L. K., Eds.; American Chemical
Society: Washington, DC, 1996; ACS Symposium Series 644, pp 218-
235. (b) In Magnetic Properties of Organic Materials; Lahti, P. M., Ed.;
Marcel Dekker: New York, 1999. (c) Amabilino, D. B.; Veciana, J. In
Magnetism: Molecules to Materials II; Miller, J. S., Drillon, M., Eds.;
Wiley-VCH: New York, 2001; pp 1-60. (d) Itoh, K., Kinoshita, M.,
Eds. Molecular Magnetism; Kodansha-Gordon and Breach: Tokyo,
2000. (e) Rajca, A. Chem. Rev. 1994, 94, 871-893.
(2) (a) Okada, K. In Molecular Magnetism; Itoh, K., Kinoshita, M.,
Eds.; Kodansha and Gordon and Breach: Tokyo, 2000; pp 264-277.
(b) Borden, W. T., Iwamura, H., Berson, J. A. Acc. Chem. Res. 1994,
27, 109-116.
(3) (a) Dvolaitzky, M.; Chiarelli, R.; Rassat, A. Angew. Chem., Int.
Ed. Engl. 1992, 31, 180-181. (b) Kanno, F.; Inoue, K.; Koga, N.;
Iwamura, H. J. Am. Chem. Soc. 1993, 115, 847-850. (c) Fujita, J.;
Tanaka, M.; Suemune, H.; Koga, N.; Matsuda, K.; Iwamura, H. J. Am.
Chem. Soc. 1996, 118, 9347-9351.
10.1021/jo051791w CCC: $30.25 © 2005 American Chemical Society
Published on Web 11/03/2005
J. Org. Chem. 2005, 70, 10073-10081
10073

Terada et al.
alternant hydrocarbon diradical shows a low-spin ground
state when the spin sources are linked by a sterically
hindered 2,4,6-trimethyl-m-phenylene group.4 Although
such a low-spin ground state with the m-phenylene
linkage is a rare case in alternant hydrocarbons, a larger
number of low-spin species with the m-phenylene linkage
have been observed in the system containing heteroat-
omic spin sources,2a,3,5 in most cases of which the lone
pair electrons of heteroatoms directly participate in the
spin delocalization, i.e., heteroatoms are located with sp3-
hybridization at an even numbered position referenced
to the formal spin center at position 1 as shown in A and
B as examples, giving a nonalternant spin structure.2a,6
occurs, resulting in a singlet ground state.11 Nowadays,
the importance of the dihedral angles between the
m-phenylene linker and the spin sources seems to be well
established. More recently, an additional factor that
affects the exchange interaction has also been reported.
Shultz’s group has experimentally shown that the ex-
change interaction can be altered by a remote substituent
in 5-substituted m-phenylene diradicals.12a We have
shown that (m-phenylene)bisxanthyl has a triplet ground
state or a singlet ground state with a nearly degenerate
triplet state, whereas the sulfur analogue (m-phenylene)-
bisthioxantyl clearly has a singlet in the ground state.6
These studies indicate that the spin density change
caused by the substituents or heteroatoms also has an
important role in the exchange interaction. It is likely
that these two factors, dihedral angle and spin density,
cooperatively affect the magnetic interaction of unpaired
electrons for weakly coupled spin systems.12b,c
For instance, (2,4,6-trimethyl-m-phenylene)-3a or (4,6-
dimethoxy-m-phenylene)bis(tert-butylnitroxide)s3b have
singlet ground states, whereas the (m-phenylene)bis(tert-
butylnitroxide) has a triplet ground state.7 (m-Phenyle-
ne)bisphenothiazine dication 12+ has also a singlet ground
state with a singlet-triplet energy gap, ∆EST, of ca.
-14 K.8 A similar result has been observed in a pyridinyl
diradical.9 Furthermore, there are some diradicals
that exist as an equilibrium between conformational
isomers, whose exchange interaction is conformation-
dependent.10,12b Borden and co-workers have shown the
importance of the dihedral angle between the spin
sources and the m-phenylene spacer by theoretical
calculation of (m-phenylene)bisnitroxide; the two nitrox-
ide radical orbitals (magnetic orbitals) interact through
the σ-bonds of the m-phenylene moiety at the perpen-
dicular geometry, where the selective destabilization of
the antisymmetric combination of the magnetic orbitals
We have shown that some symmetrically13 substituted
(p-phenylene)-derived diradicals have triplet energies as
low as that of the singlet states.2a 1,1′-(p-Phenylene)bis-
(2,4,6-triphenylpyridinyl) diradical has a singlet ground
state with a small ∆EST/kB ) ca. -26 K.9 10,10′-(p-
Phenylene)bisphenothiazine dication 22+ generated in
c-sulfuric acid affords a straight line in the Curie plots
in temperatures down to 6 K, indicating that the ground
state is a triplet state or a singlet state with |∆EST/kB| <
∼6 K.8a Similar observation has been reported for (p-
phenylene)bis[2,5-di(2-thienyl)-1-pyrrole] dication by Julia´
and co-workers.14 These compounds have again a large
dihedral angle and a nonalternant spin distribution
nature in the spin source.2a A large dihedral angle
certainly decreases the energy gap of two magnetic
orbitals by breaking the π-network. Furthermore, the
orbital interaction through the σ-bonds may be rather
weak, simply because the spin sources are separated by
the longer five σ-bonds in the p-phenylene isomers
compared to four σ-bonds in the m-phenylene isomers.
In addition, the spin density at the (benzylic nitrogen)
spin center is diluted by the spin-delocalization. These
factors contribute to placing the two magnetic orbitals
for the p-phenylene dications in nearly degenerate levels.
Under these circumstances, their nondisjoint nature15
caused by the weak π (spin source)-σ (phenylene)-π
(spin source) interaction may exert electronic repulsion
in the singlet states to give triplet ground states with
small positive J ’s or to give singlet ground states with
(4) Rajca, A.; Rajca, S. J. Chem. Soc., Perkin Trans. 2 1998, 1077-
1082.
(5) Similar argument in phenylene-bridged bis(chloromethylene): (a)
Zuev, P. S.; Sheridan, R. S. J. Org. Chem. 1994, 59, 2267-2269. (b)
Zuev, P.; Sheridan, R. S. J. Am. Chem. Soc. 1993, 115, 3788-3789. (c)
Trindle, C.; Datta, S. N.; Mallik, B. J. Am. Chem. Soc. 1997, 119,
12947-12951.
(6) Okada, K.; Imakura, T.; Oda, M.; Kajiwara, A.; Kamachi, M.;
Yamaguchi, M. J. Am. Chem. Soc. 1997, 119, 5740-5741.
(7) Calder, A.; Forrester, A. R.; James, P. G.; Luckhurst, G. R. J.
Am. Chem. Soc. 1969, 91, 3724-3727.
(8) (a) Okada, K.; Imakura, T.; Oda, M.; Murai, H.; Baumgarten,
M. J. Am. Chem. Soc. 1996, 118, 3047-3048. (b) Okada, K.; Imakura,
T.; Oda, M.; Kajiwara, A.; Kamachi, M.; Sato, K.; Shiomi, D.; Takui,
T.; Itoh, K.; Gherghel, L.; Baumgarten, M. J. Chem. Soc., Parkin Trans.
2 1997, 1059-1060.
(9) Okada, K.; Matsumoto, K.; Oda, M.; Akiyama, K.; Ikegami, Y.
Tetrahedron Lett. 1997, 38, 6007-6010.
(10) Conformational dependence of the ground states: (a) Shultz,
D. A. In Magnetic Properties of Organic Materials; Lahti, P. M., Ed.;
Marcel Dekker: New York, 1999; pp 103-125. (b) Rajca, A.; Lu, K.;
Rajca, S.; Roth, C. R., II. Chem. Commun. 1999, 1249-1250. (c) Nakai,
T.; Kozaki, M.; Sato, K.; Shiomi, D.; Takui, T.; Itoh, K.; Okada, K. Mol.
Cryst. Liq. Cryst. 1999, 334, 139-148.
(13) Some asymmetrically substituted high-spin diradicals of the
type of 4-(2-allyl)benzyl diradicals have been reported: (a) Inoue, K.;
Iwamura, H. Angew. Chem., Int. Ed. Engl. 1995, 34, 927-928. (b)
Kumai, R.; Sakurai, H.; Izuoka, A.; Sugawara, T. Mol. Cryst. Liq. Cryst.
1996, 279, 133-138. (c) Ishiguro, K.; Ozaki, M.; Kamekura, Y.; Sekine,
N.; Sawaki, Y. Mol. Cryst. Liq. Cryst. 1997, 306, 75-80.
(14) Domingo, V. M.; Alema´n, C.; Brillas, E.; Julia´, L. J. Org. Chem.
2001, 66, 4058-4061.
(11) Fang, S.; Lee, M.-S.; Hrovat, D. A.; Borden, W. T. J. Am. Chem.
Soc. 1995, 117, 6727-6731.
(12) (a) Shultz, D. A.; Bodnar, S. H.; Lee, H.; Kampf, J. W.; Incarvito,
C. D.; Rheingold, A. L. J. Am. Chem. Soc. 2002, 124, 10054-10061.
(b) Shultz, D. A.; Fico, R. M., Jr.; Bodnar, S. H.; Kumar, R. K.;
Vostrikova, K. E.; Kampf, J. W.; Boyle, P. D. J. Am. Chem. Soc. 2003,
125, 11761-11771. (c) Shultz, D. A.; Fico, R. M., Jr.; Lee, H.; Kampf,
J. W.; Kirschbaum, K.; Pinkerton, A. A.; Boyle, P. D. J. Am. Chem.
Soc. 2003, 125, 15426-15432.
(15) Borden, W. T.; Davidson, E. R. J. Am. Chem. Soc. 1977, 99,
4587-4594.
10074 J. Org. Chem., Vol. 70, No. 24, 2005

Exchange Interaction of Phenylene-Bridged Dications
SCHEME 1
FIGURE 1. EPR spectra for 3b2+ (a) and 4b2+ (b) in buty-
ronitrile at 123 K and their simulation spectra using a
simulation program, WINEPR Simfonia (3b2+: D/hc ) 0.00598
cm-1, E/hc ) 0 cm-1 (a′). 4b2+: D/hc ) 0.00437 cm-1, E/hc )
0 cm-1 (b′).
with water, and drying the organic layer. The monosub-
stituted 5,10-dihydrophenazine 5 is unstable under aer-
ated conditions. However, the solution of 5 under a
nitrogen atmosphere can be kept in a freezer for months
as a stock solution. The cross-coupling reaction of 5 (2.5
equiv) with m- or p-diiodobenzene (1 equiv) using Pd-
(dba)2-NaOtBu-P(tBu)3 as a catalytic system gave 3a,b
or 4a,b in moderate yields (Scheme 1, yield based on the
diiodobenzene). The p-phenylene-linked 10,10′-diphenyl
derivative 4a had poor solubility in various organic
solvents and was inconvenient for the preparation of the
dication. Therefore, a detailed study was carried out on
the 4-n-butylphenyl dications 3b2+, 4b2+. Some EPR and
the temperature dependence data for 3a2+, 4a2+ are
provided as Supporting Information.
The neutral compounds showed two reversible peaks
at low potentials [+0.33 and +1.04 V (vs SCE) for 3a,
+0.32 and +1.02 for 4a, +0.28 and ca. +1.0 (adsorption
peak) for 3b, +0.27 and ca. +0.9 (adsorption peak) for
4b in DMF in the presence of tetrabutylammonium
perchlorate (0.1 M)] (Figure S1). Semiderivative volta-
mmetry of 3a confirms that each peak involves sequential
two-electron oxidation processes (Figure S1). The neutral
compounds 3 and 4 were oxidized using tris(p-bromophe-
nyl)aminium hexachloroantimonate (2 equiv, reduction
potential +1.18 V) in acetonitrile or acetonitrile-THF in
a glovebox. The oxidized solution was concentrated to the
minimum amount. Addition of an excess amount of dry
ether gave fine green precipitates. Recrystallization from
an acetonitrile-benzene mixture gave green crystals,
whose elemental analysis was in accord with the expected
dications, 3b2+(SbCl6-)2‚C6H6 and 4b2+(SbCl6-)2.
EPR Studies for 5,5′-(m- and p-Phenylene)bis[10-
(4-butylphenyl)-5,10-dihydrophenazine] Dications,
3b2+ and 4b2+. Figure 1 shows the EPR spectra in a
butyronitrile matrix at 123 K for the isolated 3b2+ and
4b2+ with the simulation spectra. The observed signals
showed a typical pattern of randomly oriented triplet
species with overlapping nitrogen hyperfine couplings in
x,y components. Only a small signal of impurity due to
3b+ or 4b+ appears in the center field. The hyperfine
splittings were disregarded and treated as line-broaden-
ing in the simulation spectra. The fine structure param-
eters were determined as D/hc ) 0.00598 cm-1 and E/hc
) 0 cm-1 for 3b2+, and D/hc ) 0.00437 cm-1 and E/hc )
0 cm-1 for 4b2+. The D/hc value for the m-phenylene 3b2+
small negative J ’s, depending on the degree of degen-
eracy of the magnetic orbitals.
To obtain more insight into this subject, we required
a pure sample of 10,10′-(p-phenylene)bisphenothiazine
dication 22+. Recently, Kochi and co-workers described
the isolation of dication 22+ 16
We have also attempted
.
the isolation of 22+. Treatment of a CH2Cl2 solution of
compound 2 with a large excess amount of SnCl5 gave a
dicationic species as precipitates. The isolated species
showed a satisfactory elemental analysis as C30H20N2S2‚
2SbCl6 within (0.3% and exhibited a triplet EPR pattern
similar to that reported in c-sulfuric acid.8a However, the
species showed a comparably strong signal due to the
monoradical cation 2+ as an impurity. Therefore, we
altered the structure of the spin source to a much more
readily oxidizable dihydrophenazine framework.17 We
report the synthesis and exchange interaction of 5,5′-(m-
and p-phenylene)bis[10-phenyl- and 10-(4-n-butylphenyl)-
5,10-dihydrophenazine] dications, 32+ and 42+. Theoreti-
cal analysis of the exchange interaction of these dications
and the related (m- and p-phenylene)bisphenothiazine
dications, 12+ and 22+, at the perpendicular geometry is
also provided.
Results and Discussion
Synthesis and Oxidation Potential. We have re-
cently developed a convenient method for the synthesis
of unsymmetrical 5,10-diaryl-substituted 5,10-dihydro-
phenazines.17a The synthesis of 5,5′-(m- or p-phenylene)-
bis(10-diphenyl-5,10-dihydrophenazine) derivatives is
shown in Scheme 1. The key step, in situ preparation of
5-phenyl or 5-(4-n-butylphenyl)-5,10-dihydrophenazine
(5a or 5b), involves the following processes under a
nitrogen atmosphere: the addition of aryllithium to a
solution of phenazine in o-xylene or toluene, quenching
(16) Sun, D.; Rosokha, S. V.; Kochi, J. K. J. Am. Chem. Soc. 2004,
126, 1388-1401.
(17) (a) Okamoto, T.; Terada, E.; Kozaki, M.; Uchida, M.; Kikukawa,
S.; Okada, K. Org. Lett. 2003, 5, 373-376. (b) Hiraoka, S.; Okamoto,
T.; Kozaki, M.; Shiomi, D.; Sato, K.; Takui, T.; Okada, K. J. Am. Chem.
Soc. 2004, 126, 58-59.
J. Org. Chem, Vol. 70, No. 24, 2005 10075

Terada et al.
microwave power gave a straight line (Figure S4, lower).
Therefore, the observed curvature for 4b2+ is not due to
the saturation of the signal but due to the low-spin
ground-state nature. The plots were simulated as a
singlet ground state with ∆EST/kB ) -9.6 ( 1.0 K. Similar
plots for the 10,10′-diphenyl derivative 4a2+ (Figure S3,
lower) also indicate the curvature with ∆EST/kB ) -8.6
( 0.3 K. For these reasons, it can be concluded that the
p-isomers 42+ have a singlet ground state with |∆EST/kB|
as small as 8-10 K.
It should be noted that the previously reported (p-
phenylene)bis(phenothiazines) dications 22+ gave a straight
line in the temperature range between 6 and 60 K. The
plots passed through the origin and no tendency of
curvature was observed,8a suggesting a triplet ground
state or a singlet ground state with |∆EST/kB| < ∼6 K.
We have also examined the measurement of magnetic
susceptibility for the powdered samples of 5,5′-(m- and
p-phenylene)bis[10-(4-butylphenyl)-5,10-dihydrophena-
zine]s, 3b2+(SbCl6-)2‚C6H6 and 4b2+(SbCl6-)2. Attempts
to dilute these dications in PVC films to extract intramo-
lecular magnetic interactions failed to give a homoge-
neous film because of their poor solubility in organic
solvents. The measurement for the powdered samples
prevented the precise analysis of the magnetic interac-
tions because of the presence of intermolecular magnetic
interactions and of the lack of the crystal structure that
is essential for making a theoretical model for analysis.
Nevertheless, qualitative features for the magnetic sus-
ceptibility study18 for the powdered samples were con-
sistent with the EPR studies. The description of the study
for magnetic susceptibility is provided in Supporting
Information.
Computational Analysis 1. Exchange Interaction.
The (m- and p-phenylene)bis(phenothiazine) dications,
12+ and 22+, and the bis(dihydrophenazine) dication
analogues, 32+ and 42+, have nearly perpendicular ge-
ometries between the plane of the central phenylene ring
and the spin sources, judging from the X-ray structure
of the related analogues.17b,19 At perpendicular geometry,
the π (spin source)-π (phenylene)-π (spin source) orbital
interaction is completely forbidden, whereas the π-σ-π
type orbital interaction is permitted. Although such a
tightly perpendicular condition is unrealistic, theoretical
insight into this extreme case is quite useful to under-
stand the origin of the magnetic interaction of these
dications. The orbital and magnetic interactions through
the σ-frame of m-phenylene has already been demon-
strated for (m-phenylene)bisnitroxide by Borden and co-
workers.11 However, such an approach for the p-phe-
nylene system has not been reported. We consider here
the magnetic and orbital interactions at exactly perpen-
dicular geometries (C2v symmetry for m-isomers and D2h
FIGURE 2. Temperature dependence of the EPR signal
intensity (|∆ms| ) 2) for 3b2+ (upper) and 4b2+ (lower)
measured at microwave power ) 0.1 mW in a butyronitrile
matrix.
is larger than that for the p-phenylene 4b2+, indicating
that the averaged distance between the spin centers is
shorter for the m-phenylene 3b2+ (7.5 Å from the point
dipole approximation) than that for the p-phenylene 4b2+
(8.7 Å). The calculated distance is close to the distance
between the two centers of the dihydrophenazine rings
(ca 7.5 Å for the m-isomer and 8.6 Å for the p-isomer).
Similar D/hc values were observed for 3a2+ (0.00598
cm-1) and 4a2+ (0.00449 cm-1) (Figure S2).
A weak forbidden signal for the |∆ms| ) 2 transition
was observed in lower temperatures for these compounds.
Figure 2 shows the temperature dependence of the signal
intensity (I) of the |∆ms| ) 2 transition. The plots (I vs
T-1) for the m-isomer 3b2+ gave a convex curve in the
temperature region between 8.0 and 102 K. Simulation
with the ST model indicated a singlet ground state with
∆EST/kB ) -27 ( 1 K (solid line in Figure 2). A similar
value was obtained for 3a2+ (∆EST/kB ) -21 ( 1 K, Figure
S3). The absolute values of these are somewhat larger
than the value (∆EST/kB ) -14 K) for the previously
(18) The intra- and intermolecular magnetic interactions of these
dications 3b2+ and 4b2+ in the crystalline solid state were examined
by the paramagnetic susceptibility øp on a SQUID magnetometer
between 300 and 1.9 K. The diamagnetic susceptibility ød of -772 ×
10-6 emu mol-1 was subtracted from the observed susceptibility for
reported m-phenylenebis(phenothiazine) dication 12+ 8a
.
-
3b2+(SbCl6-)2‚C6H6. The contribution of the SbCl6 anion to ød was
Similar plots for the p-isomer 4b2+ gave a slightly
curved line (Figure 2 (lower)) in the temperature range
between 8.3 and 103 K with microwave power ) 0.1 mW.
To avoid saturation of signal intensity, microwave power
dependence (0.01, 0.1, 0.49, 1 mW) of the signal intensity
was studied. The signal intensity vs the square root of
estimated by measuring the susceptibility of tetraethylammonium salt
of SbCl6-. The contribution from the other atoms and groups in
3b2+(SbCl6-)2‚C6H6 was evaluated using Pascal’s constants. The same
-
values of the diamagnetic susceptibility ød for the cation and the SbCl6
anion were applied to the p-isomer, 4b2+(SbCl6-)2.
(19) Okamoto, T.; Kuratsu, M.; Kozaki, M.; Hirotsu, K.; Ichimura,
A.; Matsushita, T.; Okada, K. Org. Lett. 2004, 6, 3493-3496.
10076 J. Org. Chem., Vol. 70, No. 24, 2005

Exchange Interaction of Phenylene-Bridged Dications
symmetry for p-isomers) of bis(dihydrophenazine) dica-
tions 3a2+ and 4a2+ and the bis(phenothiazine) dications
12+ and 22+. Bis(methylene) diradicals, 6 and 7, at the
perpendicular geometries were also studied as simple
models and for comparison with Borden’s calculation
results (GVB-ROHF and (8/8)CASSCF) for the m-isomer
6.
using the SCF procedure exhibits spin-contamination
contributed from higher spin states. Therefore, establish-
ing a suitable spin-projection procedure is also essential.
There are currently three formulizations that can be used
to estimate Jab values:20-23
LSE - HS
E
(1)
ab
J
)
(2)
S2max
LSE - HS
Smax(Smax + 1)
E
(2)
ab
J
J
)
)
(3)
(4)
The effective exchange integral (Jab) between magnetic
sites has been described by the Heisenberg (HB) model
on experimental grounds as
LSE - HS
E
(3)
ab
HSS2 LSS2
-
where LSE, HSE, and Smax are, respectively, the total
H(HB) ) -2 J S ‚S
b
(1)
∑
ab
a
energies of the low-spin and high-spin states, and the
(1)
ab
maximum spin number of the system. The J value is
where Sa and Sb are spins at sites a and b, respectively.
The recent development of computational techniques
involving the calculation of open-shelled species has
enabled estimation of the Jab values for various
systems.17b,20-26 In particular, UHF methods have been
found to be effective for large molecular systems. When
one applies UHF methods to diradical systems, the
default initial guess for singlet states often fails to give
a correct answer. The magnetic orbitals (R and â) of a
singlet state are typically expressed as a linear combina-
tion (in-phase or out-of-phase with keeping the sym-
metry) of the localized orbitals at radical sites. However,
for certain diradical systems, particularly those with
weak overlap between two localized orbitals, their mag-
netic orbitals (R and â) are well approximated such that
the R spin occupies mainly one of the radical sites and
the â-spin occupies mainly the other site. Such a state
has unsymmetrical spin and spatial symmetry even if
the diradical has a symmetrical geometry. Such a broken-
symmetry (BS) state frequently gives lower energy than
the state with symmetry-adopted magnetic orbitals,
simply because the electronic repulsion of the former
system would be minimized as a result of the different
region of space between R and â spins. According to
Davidson, the energy and geometry thus obtained are
precise enough and comparable to CASSCF calculation
in some simple molecules.26 The UHF state calculated
applicable to systems with a small overlap between
(2)
magnetic orbitals.21 The J value is suitable for sys-
ab
(3)
tems with a relatively large overlap.20,22 The J value
ab
(1)
(2)
varies between the J and J values depending on the
ab
ab
overlap.20,23
C2v symmetry was adopted for the m-isomers during
the geometrical optimization (UB3LYP/6-31G(d)), whereas
D2h symmetry was adopted for the p-isomers for both the
triplet and the BS-singlet states. Under this restriction,
pyramidalization at the spin center is allowed but the
π-orbital of the spin center can only interact with the
σ-orbitals of the central ring. The optimized geometries
were nearly identical between the triplet state and the
BS-singlet state for 12+, 3a2+, 6, and 7 and were exactly
identical for 22+ and 4a2+ (Table S1).
Table 1 shows the calculated total energy (UB3LYP/
6-31G(d)) of the lowest singlet and triplet states and the
exchange interactions for 12+, 22+, 3a2+, 4a2+, 6, and 7.
The J(2) value of the model compound 6 is close to the
reported values, GVB-ROHF (J/kB ) -65 K) and (8/8)-
CASSCF (J/kB ) -45 K) for 6,11 indicating the validity
of the present approach. All of the m-isomers have a
singlet ground state. The calculated J values can be
compared to the experimentally determined ∆EST values
with the relation of ∆EST ) 2J, showing good agreement
in their orders between the theoretical and experimental
values for the m-isomers.
(20) Ginsberg, A. P. J. Am. Chem. Soc. 1980, 102, 111-117.
(21) (a) Noodleman, J. Chem. Phys. 1981, 74, 5737-5743. (b)
Noodleman, L.; Davidson, E. R. Chem. Phys. 1986, 109, 131-143. (c)
Bencini, A.; Totti, F.; Daul, C. A.; Doclo, K.; Fantucci, P.; Barone, V.
Inorg. Chem. 1997, 36, 5022-5030. (d) Eklund, J. C.; Bond, A. M.;
Colton, R.; Humphrey, D. G.; Mahon, P. J.; Walter, J. W. Inorg. Chem.
1999, 38, 2005-2011.
The p-phenylene dications 22+ and 4a2+ also have
singlet ground states and the absolute values of J are
considerably smaller than the experimental values. The
p-phenylenebismethylene 7 has a singlet ground state;
the |J| of 7 is larger than those of 22+ and 4a2+ and
smaller than that of 6.
(22) Ruiz, E.; Cano, J.; Alvarez, S.; Alemany, P. J. Comput. Chem.
1999, 1391-1400.
The calculated J values do not relate to the spin
density at benzylic position nor the energy difference
between the two magnetic orbitals in the BS-singlet state,
∆ESMO ) |HOMO(R)-HOMO-1(â)|, although there is a
precedent that the square of spin density correlates to J
values in a series of substituted m-phenylene di-
radicals.24c Importantly, however, the energy difference
between the two magnetic orbitals in the triplet state,
∆ETMO ) |HOMO(R)-(HOMO-1)(R)| well correlates to
the calculated exchange interactions (Τable 2 and Figure
3). Per computational interpretation, the qualitative
(23) (a) Yamaguchi, K.; Fukui, H.; Fueno, T. Chem. Lett. 1986, 625-
628. (b) Yamaguchi, K.; Jensen, F.; Dorigo, A.; Houk, K. N. Chem. Phys.
Lett. 1988, 149, 537-542. (c) Yamaguchi, K.; Yamaguchi, K. Int. J.
Quantum Chem. 2002, 90, 370-385. (d) Okada, K.; Nagao, O.; Mori,
H.; Kozaki, M.; Shiomi, D.; Sato, K.; Takui, T.; Kitagawa, Y.; Yamagu-
chi, K. Inorg. Chem. 2003, 42, 3221-3228.
(24) (a) Lahti, P. M.; Ichimura, A. S.; Sanborn, J. A. J. Phys. Chem.
A 2001, 105, 251-260. (b) Zhang, G. B.; Li, S. H.; Jiang, Y. S. J. Phys.
Chem. A 2003, 107, 5573-5582. (c) Zhang, G.; Li, S.; Jiang, Y.
Tetrahedron 2003, 59, 3499-3504. (d) Constantinides, C. P.; Koutentis,
P. A.; Schatz, J. J. Am. Chem. Soc. 2004, 126, 16232-16241.
(25) Gra¨fenstein, J.: Kraka, E.; Filatov, M.; Cremer, D. Int. J. Mol.
Sci. 2002, 3, 360-394.
(26) Davidson, E. R. Int. J. Quantum Chem. 1998, 69, 241-245.
J. Org. Chem, Vol. 70, No. 24, 2005 10077

Terada et al.
TABLE 1. Calculated Total Energies and Effective Exchange Integrals for 12+, 22+, 3a2+, 4a2+, 6, and 7
BS-singlet state
triplet state
energy/hartree
JkB-1/K
J(2)/kB
∆ESTkB-1, 2JkB-1/K
(experimental value)
compd
energy/hartree
S2
S2
ground state
J(1)/kB
J(3)/kB
12+
22+
3a2+
4a2+
6
-2060.58260279
-2060.58565647
-1837.07394913
-1837.07698935
1.0105 -2060.58255600
1.0130 -2060.58565368
1.0126 -1837.07391262
1.0144 -1837.07698694
2.0132
2.0132
BS-singlet
BS-singlet
BS-singlet
BS-singlet
BS-singlet
BS-singlet
-14.8
-0.88
-11.5
-0.76
-110.7
-62.7
-7.4
-0.44
-5.8
-0.38
-55.3
-31.4
-14.7
-0.88
-11.5
-0.76
-109.9
-62.6
-14a
> -6a
-27 to -21
-10 to -8
b
2.0146
2.0146
-309.536588055 2.0079
-309.536778357 2.0075
-309.536938545 1.0012
-309.536976973 1.0052
7
b
a Refrence 7a. b Unknown.
TABLE 2. Orbital Energies at HOMO and HOMO-1 in the BS-Singlet and Triplet States for 12+, 22+, 3a2+, 4a2+, 6, and 7
BS-singlet state/hartree
triplet state/hartree
spin density at
benzylic position
compd
HOMO (R)
HOMO (â)
∆ESMO
HOMO (R)
HOMO-1 (R)
∆ETMO
∆ETMOkB-1/K
12+
22+
3a2+
4a2+
6
-0.41294
-0.40926
-0.37821
-0.37494
-0.21588
-0.21593
-0.41294
-0.40926
-0.37821
-0.37494
-0.21558
-0.21593
0.00000
0.00000
0.00000
0.00000
0.00000
0.00000
+0.246674
+0.245612
+0.231390
+0.230977
+1.129724
+1.127627
-0.41186
-0.40899
-0.37717
-0.37467
-0.21023
-0.21272
-0.41404
-0.40953
-0.37928
-0.37522
-0.22188
-0.21918
0.00218
0.00054
0.00211
0.00055
0.01165
0.00646
688
171
666
174
3679
2037
7
FIGURE 3. Plots of J(3) values to the MO energy difference
in the triplet states, ∆ETMO ) |(HOMO(R) - (HOMO-1)(R))|,
for 12+, 22+, 3a2+, 4a2+, 6, and 7.
relationship between J and orbital splitting between
magnetic orbitals is well-known.11 Importantly, however,
the J(3) values for both m- and p-isomers can be ap-
proximated as a single straight line expressed by eq 5
with a good correlation factor (R ) 0.998):
FIGURE 4. Schematic energy diagram (UHF presentation)
and MO shape of the triplet states for 12+, 3a2+, and 6.
J
(3) ) A - B‚∆ETMO
(5)
states. We discuss the exchange interaction for these
compounds in the sense of molecular orbital interaction.
Computational Analysis 2. Exchange Interaction
through MO interaction. The shapes of magnetic
orbitals, HOMO(R) and (HOMO - 1)(R), in the triplet
state for the m-isomers are shown in Figure 4. The
mixing of the σ-orbital of the m-phenylene moiety is
clearly seen. Schematic diagrams of the orbital interac-
tion for the m-isomers are shown in Figure 5. Both
symmetric and antisymmetric orbitals (πS and πA, Figure
5) are destabilized by the mixing of σ-orbitals (σS1 and
σA1) of the central ring. Because of the suitable orienta-
tion of the 2p atomic orbital at the C2 in the m-phenylene,
the mixing coefficient a of the antisymmetric σ-orbital
(σA1) is larger than that (a′) of the symmetric σ-orbital
where A/kB ) 6.0 ( 1.7 K and B ) 0.032 ( 0.001. The
single straight line suggests that the topological differ-
ence is minimized at the perpendicular geometry. Al-
though J values are dependent on the estimation meth-
ods (J(1), J(2), and J(3)) and also on the theoretical
methodologies,11 the difference is likely to be systematic.
The good correlation obtained by the identical method
suggests the generality of this relationship at the per-
pendicular geometry. The positive A value corresponds
to the ferromagnetic interaction expected for the complete
degenerate magnetic orbitals systems. B is a scaling
factor. This correlation between the J values and ∆ETMO
values allows interpretation of the exchange interaction
in terms of molecular orbital interaction in the triplet
10078 J. Org. Chem., Vol. 70, No. 24, 2005

Exchange Interaction of Phenylene-Bridged Dications
FIGURE 5. MO-interaction diagram for m-phenylene dica-
tions.
FIGURE 7. MO-interaction diagram for p-phenylene dica-
tions.
central C2-C3 bond (σS2) of the p-phenylene moiety.
However, such participation of the C2-C3 bond (σS2-
orbital) is absent in the antisymmetric orbital (πA - a′σA1,
0 < a′ < 1). Thus, the symmetrical orbital (πS - aσS1
+
bσS2, 0 < b < a < 1) is pushed up as a HOMO (R). The
contribution of the remote C2-C3 bond should be small
since the coefficient b is a mixing coefficient of the small
aσS1-orbital and appears as a small lobe in the HOMO
(R) (Figure 6), resulting in a small energy gap between
HOMO(R) and (HOMO - 1) (R).
Generally speaking, the energy gap between two
magnetic orbitals favors singlet states. However, the
nondisjoint nature of these magnetic orbitals causes an
extra electronic repulsion in the singlet state: the BS-
approach estimates the most stable singlet energy by
minimizing such electronic repulsion. Such electronic
repulsion is absent in the triplet state because of the
inherent triplet nature. For this reason, when the energy
gap between the magnetic orbitals is small, the disad-
vantage in energy of the triplet state due to the orbital
energy gap (∆ETMO) may be compensated by the electronic
repulsion in the singlet state, giving the triplet and
singlet states in a nearly degenerate level (∆EST/kB ) 2J/
kB ) ca. -2 K for 22+ and 42+). When the orbital splitting
becomes larger as in the case of 7, the electronic repulsion
in the singlet state cannot compensate the instability of
FIGURE 6. Energy diagram (UHF presentation) and MO
shape of the triplet states for 22+, 4a2+, and 7.
(σS1), thus leading to the antisymmetric πΑ - aσA1 (0 <
a′ < a <1) as a higher orbital, HOMO (R). This orbital
splitting favors a singlet ground state. This situation is
quite similar to that observed in Borden’s study for (m-
phenylene)bisnitroxides.11 The m-phenylene diradical 6
has larger mixing coefficients of the σ-orbitals, which
expand the orbital splitting (∆ETMO), resulting in a large
|J|.
the triplet state, giving the larger negative ∆EST
.
The observed ∆EST values for the m-dications, 12+ and
2+, are in good agreement with the calculated 2J values
3
in their orders, whereas those for the p-dications, 22+ and
4
2+, are considerably larger than the theoretical values.
The smaller ∆ETMO values for the p-isomers mainly
reflect the longer five σ-bonds between the two spin
sources. The shape of magnetic orbitals in the triplet
state for the p-isomers is shown in Figure 6, and their
orbital interaction diagram is given in Figure 7. It is
interesting to note that there is a large difference in the
symmetry nature of HOMO between the p- and m-
isomers, i.e., symmetric HOMO for the p-isomers and
antisymmetric HOMO for the m-isomers. As shown in
the case of the m-isomers, both symmetric and antisym-
metric orbitals (πS and πA) are destabilized by the mixing
of σ-orbitals (σS1, σS2, and σA1) of the central ring. In the
p-isomers, the symmetric orbital (πS - aσS1, 0 < a < 1)
selectively receives further destabilization from the
This may be due to the strongly antiferromagnetic nature
of the p-isomers at nonperpendicular geometries and the
small deviation of the torsion angle from the hypothetical
perpendicular geometry may rationalize the experiments.
Despite the considerably rough treatment with the
perpendicular geometry for these dications, the present
calculation well explains why the p-dications have smaller
negative ∆EST values than the m-dications.
Experimental Section
In Situ Preparation of 5-Phenyl-5,10-dihydrophena-
zine (5a). Into a Schlenk tube containing a phenazine (1.44 g
(8.00 mmol)) solution in 8 mL of o-xylene was added dropwise
J. Org. Chem, Vol. 70, No. 24, 2005 10079

Terada et al.
a cyclohexanes-ether mixed solution of phenyllithium (1.06
M, 11 mL) at room temperature under nitrogen. The color of
the solution turned dark brown during the addition. The
reaction mixture was stirred for 3.5 h and quenched by
addition of deaerated distilled water (ca. 20 mL) at 0 °C. The
organic layer was transferred via a syringe into another
Schenk tube containing dry sodium sulfate (ca. 4 g) under
nitrogen. This solution containing 5a (>70%) can be stored in
a refrigerator for a long time.
Preparation of 5,5′-(m-Phenylene)bis(10-phenyl-5,10-
dihydrophenazine) (3a). A 6.3 mL (ca. 2.5 mmol) solution
of thus prepared 5-phenyl-5,10-dihydrophenazine was taken
in a 10 mL two-necked flask containing 349 mg (1.06 mmol)
of m-diiodobenzene, sodium tert-butoxide 306 mg (3.18 mmol),
4.7 mg (0.021 mmol) of palladium acetate, and a 0.1 mL (0.017
mmol) of solution of tri-tert-butylphosphin in o-xylene (0.17
M) under a nitrogen atmosphere. The mixture was heated at
120 °C for 1 h. After cooling to room temperature, the mixture
was filtered. The solid part was washed with ca. 10 mL of hot
toluene and the filtrate was combined. After evaporation of
the solvent, the residue was subjected to aluminum chroma-
tography (hexane-toluene ) 3:1), giving the desired 3a (388
mg, 0.657 mmol, 62% based on m-diiodobenzene) as a pale
yellow solid: pale yellow powder (recrystallized from tetrahy-
drofuran-methanol), mp 263 °C; 1H NMR (400 MHz, C5D5N)
δ 7.90 (t, 1H, J ) 8.0 Hz), 7.67-7.60 (m, 4H), 7.60-7.53
(partially overlapped with the solvent signals (m), 2H), 7.51-
7.44 (m, 7H), 6.48-6.38 (m, 8H), 5.99 (dd, 4H, J ) 7.6, 1.7
Hz), 5.86 (dd, 4H, J ) 7.6, 1.7 Hz); IR (KBr, cm-1) 3051, 2968,
2851, 1585, 1485,1346, 1285, 1267, 1061, 733, 698; HRMS
(FAB+) calcd for C42H30N4 (M+) 590.2470, found 590.2473.
330.7173. Anal. Calcd for C42H30Cl12N4Sb2: C 40.05, H 2.40,
N 4.45. Found: C 39.94, H 2.50, N 4.41.
In Situ Preparation of 5-(4-n-Butylphenyl)-5,10-dihy-
drophenazine (5b). In a Schlenk tube was charged a 2.94 g
(16.3 mmol) of phenazine and 15 mL of toluene. To this
solution was added dropwise an 8.1 mL solution of 4-n-
butylphenyllithium (0. 85 M), prepared from 1-bromo-4-n-
butylbenzene and lithium metal. The resulting dark-brown
mixture was stirred for 3.5 h and quenched by addition of
deaerated distilled water (ca. 20 mL) at 0 °C. The organic layer
were transferred via a syringe into another Schenk tube
containing dry sodium sulfate (ca 4 g) under nitrogen. This
solution 5b (>70%) can be stored in a refrigerator for a long
time.
Preparation of 5,5′-(m-Phenylene)bis[10-(4-n-butyl-
phenyl)-5,10-dihydrophenazine] (3b). This compound was
prepared according to a similar procedure as for the synthesis
of 3a using 5-(4-n-butylphenyl)-5,10-dihydrophenazine instead
of 5-phenyl-5,10-dihydrophenazine (69% yield): pale yellow
powder (recrystallized from benzene-methanol); mp 179 °C;
1H NMR (400 MHz, C5D5N) δ 7.91 (t, 1H, J ) 8.0 Hz), 7.59-
7.56 (overlapped with the solvent peak, 2H), 7.50 (s, 1H), 7.49-
7.39 (AA′BB′, 8H), 6.48-6.38 (m, 8H), 6.01 (dd, 4H, J ) 7.3,
2.0 Hz), 5.93 (dd, 4H, J ) 7.3, 2.0 Hz), 2.66 (t, 4H, J ) 7.8
Hz), 1.65-1.55 (m, 4H), 1.37-1.27 (m, 4H), 0.89 (t, 6H, J )
7.3 Hz); IR (KBr, cm-1) 3053, 3026, 2954, 2928, 2858, 1585,
1485, 1346, 1285, 1267, 729; HRMS (FAB+) calcd for C50H46N4
(M+) 702.3722, found 702.3752.
Preparation of 5,5′-(m-Phenylene)bis[10-(4-n-butyl-
phenyl)-5,10-dihydrophenazine] Bis(radical cation) (3b2+).
The following procedures were achieved in a glovebox. The
neutral compound 3b (50 mg, 0.071 mmol) was dissolved in
dry acetonitrile (2 mL). To this solution was slowly added an
acetonitrile solution (10 mL) of tris(p-bromophenyl)aminium
hexachloroantimonate (115 mg, 0.141 mmol). The yellow color
solution of 3b turned green. The acetonitrile solution was
concentrated to a minimum amount to dissolve the green solid.
Addition of an excess of dry ether into the acetonitrile solution
gave 3b2+ as green precipitates (75 mg, 73%), which can be
recrystallized from acetonitrile-benzene: mp 161 °C; IR (KBr,
cm-1) 3060, 2960, 2928, 2858, 1589, 1549, 1466, 1342, 1282,
1189, 1160, 752, 677, 606; MS (FAB+) calcd for C50H46N4 (M+)
Preparation of 5,5′-(m-Phenylene)bis(10-phenyl-5,10-
dihydrophenazine) Bis(radical cation) (3a2+). The follow-
ing procedures were achieved in a glovebox. The neutral
compound 3a (10 mg, 0.017 mmol) was dissolved in dry
acetonitrile (25 mL). To this solution was slowly added an
acetonitrile solution (5 mL) of tris(p-bromophenylaminium
hexachloroantimonate (42.0 mg, 0.034 mmol). The yellow color
solution of 3a turned green. The acetonitrile solution was
concentrated to a minimum amount to dissolve the green solid.
Addition of an excess of dry ether into the acetonitrile solution
gave 3a2+ as green precipitates (16 mg, 76%): mp 176 °C; IR
(KBr, cm-1) 3072, 1589, 1549, 1464, 1344, 1283, 756, 694, 610;
HRMS (FAB+) calcd for C42H30N4 (M+) 590.2471, found
702, found 702; MS (FAB-) calcd for SbCl6 331, found 331.
-
Anal. Calcd for C50H46Cl12N4Sb2‚C6H6: C 46.39, H 3.61, N 3.86.
Found: C 46.09, H 3.49, N 3.87.
-
590.2468, HRMS (FAB-) calcd for SbCl6 330.7169, found
Preparation of 5,5′-(p-Phenylene)bis[10-(4-n-butylphe-
nyl)-5,10-dihydrophenazine] (4b). This compound was
prepared according to a similar procedure as for the synthesis
of 3a using 5-(4-n-butylphenyl)-5,10-dihydrophenazine and
p-diiodobenzene instead of 5-phenyl-5,10-dihydrophenazine
and m-diiodobenzene, respectively (68% yield): pale yellow
powder (recrystallized from toluene); mp >300 °C; 1H NMR
(400 MHz, C5D5N) δ 7.74 (s, 4H), 7.50-7.34 (AA′BB′, 8H),
6.52-6.37 (m, 8H), 6.11-6.03 (m, 4H), 5.97-5.90 (m, 4H), 2.66
(t, 4H, J ) 7.8 Hz), 1.65-1.55 (m, 4H), 1.37-1.27 (m, 4H),
0.89 (t-like, 6H, J ) ca. 7 Hz); IR (KBr, cm-1) 3063, 3030, 2956,
2930, 2856, 1601, 1483, 1348, 1286, 1267, 731; HRMS (FAB+)
calcd for C50H46N4 (M+) 702.3722, found 702.3745.
Preparation of 5,5′-(p-Phenylene)bis[10-(4-n-butylphe-
nyl)-5,10-dihydrophenazine] Bis(radical cation) (4b2+).
The following procedures were achieved in a glovebox. The
neutral compound 4b (50 mg, 0.071 mmol) was dissolved in
dry THF (110 mL). To this solution was slowly added an
acetonitrile solution (15 mL) of tris(p-bromophenyl)aminium
hexachloroantimonate (118 mg, 0.145 mmol). The yellow color
solution of 4b turned green. The acetonitrile solution was
concentrated to a minimum amount to dissolve the green solid.
Addition of an excess of dry ether into the acetonitrile solution
gave 4b2+ as green precipitates (70 mg, 72%), which can be
recrystallized from acetonitrile-benzene: mp 226 °C; IR (KBr,
cm-1) 3059, 2955, 2930, 2856, 1607, 1555, 1506, 1466, 1348,
1283, 1186, 1161, 745, 613; MS (FAB+) calcd for C50H46N4 (M+)
330.7173. Anal. Calcd for C42H30Cl12N4Sb2: C 40.05, H 2.40,
N 4.45. Found: C 39.85, H 2.54, N 4.38.
Preparation of 5,5′-(p-Phenylene)bis(10-phenyl-5,10-
dihydrophenazine) (4a). This compound was prepared ac-
cording to a similar procedure as for the synthesis of 3a using
p-diiodobenzene instead of m-diiodobenzene (41% yield): a pale
1
yellow powder (recrystallized from toluene); mp >300 °C; H
NMR (400 MHz, C5D5N) δ 7.72 (s, 4H, J ) 8.0 Hz), 7.65-7.60
(m, 4H), 7.51-7.40 (m, 6H), 6.45-6.41 (m, 8H), 6.08-6.04 (m,
4H), 5.88-5.84 (m, 4H); IR (KBr, cm-1) 3063, 3032, 1591, 1477,
1346, 1337, 1283, 1265, 727, 698; HRMS (FAB+) calcd for
C42H30N4 (M+) 590.2470, found 590.2476.
Preparation of 5,5′-(p-Phenylene)bis(10-phenyl-5,10-
dihydrophenazine) Bis(radical cation) (4a2+). The follow-
ing procedures were achieved in a glovebox. The neutral
compound 4a (10 mg, 0.017 mmol) was dissolved in dry THF
(50 mL). To this solution was slowly added an acetonitrile
solution (5 mL) of tris(p-bromophenylaminium hexachloroan-
timonate (42 mg, 0.034 mmol). The yellow color solution of 4a
turned green. The acetonitrile solution was concentrated to a
minimum amount to dissolve the green solid. Addition of an
excess of dry ether into the acetonitrile solution gave 4a2+ as
green precipitates (14 mg, 66%): mp 255 °C; IR (KBr, cm-1
)
3057, 2972, 2947, 1553, 1464, 1344, 1283, 752, 704, 692, 611;
HRMS (FAB+) calcd for C42H30N4 (M+) 590.2471, found
-
590.2468; HRMS (FAB-) calcd for SbCl6 330.7169, found
10080 J. Org. Chem., Vol. 70, No. 24, 2005

Exchange Interaction of Phenylene-Bridged Dications
702, found 702; MS (FAB-) calcd for SbCl6 331, found 331.
Supporting Information Available: Cyclic voltammo-
gram charts for 3a,b and 4a,b (Figure S1), EPR spectra for
3a2+ and 4a2+ and the simulation spectra (Figure S2), Curie
plots of the EPR signal intensity (|∆ms| ) 2) for 3a2+ and 4a2+
(Figure S3), microwave power dependence of EPR signal
intensity (Figure S4), the study of the magnetic susceptibility
for 3b2+ and 4b2+ (Figure S5 and Figure S6), the MOs in BS-
singlet states for the m-isomers, 12+, 3a2+, and 6 (Figure S7)
and for the p-isomers, 22+, 4a2+, and 7 (Figure S8), and the
Cartesian coordinates of the optimized geometries in the triplet
and BS-singlet states for 12+, 22+, 3a2+, 4a2+, 6, and 7 (Table
S1). This material is available free of charge via the Internet
at http://pubs.acs.org.
-
Anal. Calcd for C50H46N4Sb2Cl12: C 43.77, H 3.38, N 4.08.
Found: C 43.50, H 3.28, N 3.89.
Calculation Method. The Gaussian 03 program package
was used in this study. The criterion for the SCF convergence
was 10-9. For the calculation of the low-spin BS singlet states,
a trial wave function for the SCF procedure was generated by
the HOMO-LUMO mixing using the keyword “mix”.
Acknowledgment. We thank the Ministry of Edu-
cation, Culture, Sports, Science and Technology, Japan,
for a Grant-in-Aid for Scientific Research (nos. 17350072,
17350073). One of the authors (D.S.) acknowledges
financial support from PRESTO of Japan Science and
Technology Agency (JST).
JO051791W
J. Org. Chem, Vol. 70, No. 24, 2005 10081