Trication species stabilized by heteroazulenes: Synthesis and properties of 1,3,5-tris[bis(heteroazulen-3-yl)methyliumyl]benzenes

Article abstract of DOI:10.1039/b107962j

A general synthesis and properties of a novel type of heteroazulene analogues of fairly stable trimethyliumyl-benzenes (14a-i·3BF₄^-) bearing 1,3,5-trimethyliumyl groups substituted with six 2H-cyclohepta[b]furan-2-one 8a, six 1,2-dih

Full text of DOI:10.1039/b107962j

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Trication species stabilized by heteroazulenes: synthesis and
properties of 1,3,5-tris[bis(heteroazulen-3-yl)methyliumyl]benzenes
Shin-ichi Naya, Masatoshi Isobe, Yukiko Hano and Makoto Nitta*
2
Department of Chemistry, School of Science and Engineering, Waseda University, Shinjuku-ku,
Tokyo 169-8555, Japan
Received (in Cambridge, UK) 3rd September 2001, Accepted 17th October 2001
First published as an Advance Article on the web 15th November 2001
A general synthesis and properties of a novel type of heteroazulene analogues of fairly stable trimethyliumyl-
benzenes (14a–iؒ3BF4؊) bearing 1,3,5-trimethyliumyl groups substituted with six 2H-cyclohepta[b]furan-2-one 8a,
six 1,2-dihydro-N-phenylcyclohepta[b]pyrrol-2-one 8b, six 1,2-dihydro-N-methylcyclohepta[b]pyrrol-2-one 8c,
and their related compounds are reported. The synthetic method is based on a single and stepwise TFA-catalyzed
electrophilic aromatic substitution on the heteroazulenes 8a, 8b, and 8c with 1,3,5-triformylbenzene 9, mono- and
diformylbenzene having di-and monoheteroazulene-substituted methyl groups to afford the corresponding 1,3,5-
trimethylbenzene derivatives, followed by oxidative hydrogen abstraction with DDQ, and subsequent exchange of the
counter-anion by using aq. HBF4 solution in Ac2O. In spite of their tricationic nature, 14a–i exhibited high stability
with large [pKRϩ] values due to the stabilizing effect of the heteroazulene units. In the case of trications 14b, three
methyliumyl-units were neutralized stepwise at the pH of 10.4, 11.5, and 13.0. However, we could not determine
pKRϩ, pKRϩϩ, and pKRϩϩϩ values separately in the cases of other trications 14a and 14c–i. Thus, some [pKRϩ
]
values were obtained as the average values of pKRϩϩϩ and pKRϩϩ values as well as of pKRϩϩ and pKRϩ values. The
electrochemical reduction of most of the trications exhibits irreversible waves and low reduction peak potentials
upon cyclic voltammetry (CV); the values are discussed on the basis of a comparison with those of the related
monocation and dication species to clarify the reduction process of trications 14a–i. The reduction waves of
14a–e,h,i were irreversible, while those of 14f,g seem to be reversible; this feature would be ascribed to their
large steric constraints.
Introduction
Since the aryl-stabilized carbotrication, 1,3,5-tris(diphenyl-
methyliumyl)benzene 1, was reported by M. Leo,1 much atten-
tion has been focused on the electrochemical properties of 1
(Fig. 1).2–6 The 1,3,5-trimethyliumylbenzene 1 and its reduced
molecule, trimethylenebenzene, have been studied theoretically
and experimentally,7,8 and thus, the incorporation of triradical
building blocks based on 1 as the segments of a larger molec-
uler organic magnet has been investigated. On the other hand, it
is noteworthy that T. Asao and coworkers have recently
reported the synthesis and properties of an azulene analogue of
1, i.e., 1,3,5-tris[bis(3,6-di-tert-butylazulen-1-yl)methyliumyl]-
benzene 2.9,10 The trication 2 is extraordinarily stable with
high pKRϩϩϩ, pKRϩϩ, and pKRϩ values of 9.1, 10.9, and 12.7,
respectively. The values seem to be reasonable because azulene
derivatives stabilize cations, i.e., tri(azulen-1-yl)methyl,11–20
di(azulen-1-yl)phenylmethyl,11,14,16–20 and (azulen-1-yl)diphenyl-
methyl cations,11,14,16,17,19 and their derivatives.
On the other hand, we have previously studied the synthesis
and properties of heteroazulene analogues of the triphenylmethyl
cation, i.e., tris(2-oxo-2H-cyclohepta[b]furan-3-yl)methyl, tris-
(1,2-dihydro-2-oxo-N-phenylcyclohepta[b]pyrrol-3-yl)methyl,
and tris(1,2-dihydro-2-oxo-N-methylcyclohepta[b]pyrrol-3-yl)-
methyl cations, 3a–c,21 as well as bis(2-oxo-2H-cyclohepta[b]-
furan-3-yl)phenylmethyl and bis(1,2-dihydro-2-oxo-N-phenyl-
cyclohepta[b]pyrrol-3-yl)phenylmethyl cations 4 and 5 and their
derivatives.22 Thus, heteroazulenes, such as 8a–c (Scheme 1), are
demonstrated to stabilize not only cations but also radical
species and anions.22 Based on these studies, we have also
investigated the synthesis and properties of heteroazulene-
substituted 1,3-dimethyliumylbenzenes 6a–c and their 1,4-
isomers 7a–c.23 The two methyliumyl-units in the dications 6a–c
Fig. 1
and 7a–c were neutralized simultaneously at pHs ranging from
9.0 to 12.7. The electrochemical reduction of 6a–c and 7a–c
exhibits irreversible waves and low reduction peak potentials
DOI: 10.1039/b107962j
J. Chem. Soc., Perkin Trans. 2, 2001, 2253–2262
This journal is © The Royal Society of Chemistry 2001
2253

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؊
Table 1 Results for the preparation of 1,3,5-trismethylbenzene derivatives 10a–i, and 1,3,5-tris(methyliumyl)benzenes 14a–iؒ3BF4
Run
Heteroazulene
Aldehyde
Condensation product (yield/%)
Hydride abstraction product (yield/%)
1
2
3
4
5
6
7
8
9
8aa
8ba
8ca
8ab
8cb
8bc
8bb
8cc
8cb
8bb
8bd
8ab
9
9
10a (68)
14aؒ3BF4؊ (89)
14bؒ3BF4؊ (89)
14cؒ3BF4؊ (98)
—
10b (90)
9
10c (94)
9
9
11a (39), 12a (31), 9 (21)
11c (45), 12c (27), 9 (16)
10d (94)
—
11a
12a
11a
12a
12c
11c
13
14dؒ3BF4؊ (87)
14eؒ3BF4؊ (83)
14fؒ3BF4؊ (87)
14gؒ3BF4؊ (91)
14hؒ3BF4؊ (100)
—
10e (100)
10f (74)
10g (80)
10
11
12
10h (100)
13 (25), 11c (34)
10i (97)
14iؒ3BF4؊ (87)
a Six equiv. heteroazulene. b Two equiv. heteroazulene. c Four equiv. heteroazulene. d One equiv. heteroazulene.
upon cyclic voltammetry (CV).23 The reduction processes of 6c,
which has two different methyliumyl-units, and 7a–c proceed
via four one-electron reduction steps. In contrast, dications
6a,b, which have two identical methyliumyl-units, exhibited two
two-electron reduction steps.23 Thus, in connection with our
previous studies of heteroazulene-substituted methylium
ions,21–24 we embarked on the synthesis and clarification of the
properties of heteroazulene-substituted trications 14a–i. The
trications have been found to be fairly stable with large [pKRϩ
]
values and low reduction potentials. We report herein the
results in detail.
Results and discussion
Synthesis
Preparation of various trication species was easily accom-
plished by the TFA-catalyzed condensation of aldehydes with
heteroazulenes and subsequent oxidative hydrogen abstraction.
The reactions of 1,3,5-triformylbenzene 9 with six molar
equivalent amounts of 2H-cyclohepta[b]furan-2-one 8a,25
1,2-dihydro-N-phenylcyclohepta[b]pyrrol-2-one
1,2-dihydro-N-methylcyclohepta[b]pyrrol-2-one
8b,26
and
in
8c27,28
CH2Cl2–TFA (5 : 1) at rt for 48 h afforded three types
of six-heteroazulene-substituted 1,3,5-trimethylbenzene, 1,3,5-
tris[bis(2-oxo-2H-cyclohepta[b]furan-3-yl)methyl]benzene 10a,
1,3,5-tris[bis(1,2-dihydro-2-oxo-N-phenylcyclohepta[b]pyrrol-
3-yl)methyl]benzene 10b, and 1,3,5-tris[bis(1,2-dihydro-N-
methyl-2-oxocyclohepta[b]pyrrol-3-yl)methyl]benzene 10c in
moderate to good yields (Scheme 1, Table 1, Runs 1–3, respect-
ively). On the other hand, preparation of heteroazulene
analogues of 1,3,5-trimethylbenzene having two or three types
of heteroazulene-substituted methyl groups was successfully
accomplished by stepwise condensation reaction of 9 with
heteroazulenes. Controlled reaction of 1,3,5-triformylbenzene
9 with two molar equivalent amounts of 8a in CH2Cl2–TFA
(5 : 1) at rt afforded the expected 5-[bis(2-oxo-2H-cyclo-
hepta[b]furan-3-yl)methyl]-1,3-diformylbenzene 11a and 3,5-
bis[bis(2-oxo-2H-cyclohepta[b]furan-3-yl)methyl]benzaldehyde
12a, as well as recovery of unreacted 9 (Scheme 2, Table 1,
Run 4). Similarly, reaction of 1,3,5-triformylbenzene 9 with
8c afforded 5-[bis(1,2-dihydro-N-methyl-2-oxocyclohepta[b]-
pyrrol-3-yl)methyl]-1,3-diformylbenzene 11c and 3,5-bis[bis-
(1,2-dihydro-N-methyl-2-oxocyclohepta[b]pyrrol-3-yl)methyl]-
benzaldehyde 12c, as well as recovery of unreacted 9 (Table
1, Run 5). The aldehydes 11a, 12a, and 12c reacted with
heteroazulene 8b in a similar fashion to afford 3,5-bis[bis(2-
oxo-2H-cyclohepta[b]furan-3-yl)methyl]-1-[bis(1,2-dihydro-2-
Scheme 1 Reagents and conditions: i, CH2Cl2–TFA (5 : 1), rt, 48 h.
cyclohepta[b]pyrrol-3-yl)methyl]benzene 10h, respectively, in
excellent yields (Scheme 3, Table 1, Runs 6, 7, and 10). Similarly,
the aldehydes 11a and 12a were allowed to react with hetero-
azulene 8c to give 3,5-bis[bis(2-oxo-2H-cyclohepta[b]furan-
3-yl)methyl]-1-[bis(1,2-dihydro-N-methyl-2-oxocyclohepta[b]-
pyrrol-3-yl)methyl]benzene 10f and 1,3-bis[bis(1,2-dihydro-N-
methyl-2-oxocyclohepta[b]pyrrol-3-yl)methyl]-5-[bis(2-oxo-2H-
cyclohepta[b]furan-3-yl)methyl]benzene
10g,
respectively,
in moderate yields (Table 1, Runs 8 and 9). Treatment of 11c
with an equivalent amount of heteroazulene 8b in a similar
fashion afforded 3-[bis(1,2-dihydro-N-methyl-2-oxocyclo-
hepta[b]pyrrol-3-yl)methyl]-5-[bis(1,2-dihydro-2-oxo-N-phenyl-
cyclohepta[b]pyrrol-3-yl)methyl]benzaldehyde 13, as well
as recovery of unreacted 11c (Scheme 4, Table 1, Run 11).
Similarly, aldehyde 13 reacted with heteroazulene 8a to yield
a product having three different heteroazulene-substituted
methylgroups,5-[bis(1,2-dihydro-N-methyl-2-oxocyclohepta[b]-
pyrrol-3-yl)methyl]-3-[bis(1,2-dihydro-2-oxo-N-phenylcyclo-
oxo-N-phenylcyclohepta[b]pyrrol-3-yl)methyl]benzene
10d,
1,3-bis[bis(1,2-dihydro-2-oxo-N-phenylcyclohepta[b]pyrrol-3-
yl)methyl]-5-[bis(2-oxo-2H-cyclohepta[b]furan-3-yl)methyl]-
benzene 10e, and 1,3-bis[bis(1,2-dihydro-N-methyl-2-oxocyclo-
hepta[b]pyrrol-3-yl)methyl]-5-[bis(1,2-dihydro-2-oxo-N-phenyl-
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Scheme 2 Reagents and conditions: i, CH2Cl2–TFA (5 : 1), rt, 48 h.
Scheme 4 Reagents and conditions: i, 8b CH2Cl2–TFA (5 : 1), rt, 24 h.;
ii, 8a CH2Cl2–TFA (5 :1), rt, 24 h.
pyrrol-3-yl groups, respectively. In addition, the abbreviations,
Fn-unit, PPn-unit, and MPn-unit, denote bis(2-oxo-2H-
cyclohepta[b]furan-3-yl)methyliumyl,
bis(1,2-dihydro-2-oxo-
N-phenylcyclohepta[b]pyrrol-3-yl)methyliumyl, and bis(1,2-
dihydro-N-methyl-2-oxocyclohepta[b]pyrrol-3-yl)methyliumyl
؊
moieties, respectively. Tricationic species 14a–iؒ3BF4 were
fully characterized on the basis of their spectral data, as well
as elemental analyses, as shown in the Experimental section.
Several tricationic species were crystallized to give complexes
containing HBF4 molecules in the crystal lattice. Thus, some of
the salts do not give satisfactory analytical data; however, the
mass spectra of the salts 14a–iؒ3BF4؊ ionized by FAB exhibited
satisfactory ion peaks, Mϩ Ϫ 3BF4, Mϩ ϩ 1 Ϫ 3BF4, or Mϩ ϩ 2
Ϫ 3BF4 which are indicative of the tricationic structure of
these compounds. The characteristic broad absorptions for
the counter anion (BF4Ϫ) are observed at 1084 cmϪ1in the
IR spectra of 14a–iؒ3BF4؊. These features also support the
tricationic nature of the compounds.
Scheme 3 Reagents and conditions: i, 8b or 8c, CH2Cl2–TFA (5 : 1), rt,
48 h.
hepta[b]pyrrol-3-yl)methyl]-1-[bis(2-oxo-2H-cyclohepta[b]-
furan-3-yl)methyl]benzene 10i in good yield (Table 1, Run 12).
The compounds 10a–i formed powdery orange or yellow
crystals, and their structures were assigned on the basis of
1
The signals of the methine protons of 10a–i disappeared in
the 1H NMR spectra of 14a–iؒ3BF4؊. Thus, the 1H NMR
spectra also support the tricationic structure of these com-
pounds. Proton signals on the seven-membered ring of 14a–
their IR, H and 13C NMR spectral data, as well as elemental
analyses and mass spectral data. The oxidative hydrogen
abstraction of 10a–i with DDQ in CH2Cl2 at rt for 1 h, followed
by treatment with aqueous 42% HBF4 in Ac2O, afforded
crystals of stable tricationic salts, 1,3,5-tris[bis(2-oxo-2H-
cyclohepta[b]furan-3-yl)methyliumyl]benzene tris(tetrafluoro-
؊
iؒ3BF4 appear as broad signals. Attempted measurement of
1
؊
the H NMR spectra of 14a–iؒ3BF4 at temperatures ranging
from rt to 70 ЊC (in CD3CN) exhibited no appreciable change in
the broad signals. Thus, slow conformational change in the
heteroazulene moieties of these cations occurs during 1H NMR
time scale at these temperatures. Several proton signals on the
seven-membered ring of 10b,d–i appear also as broad and com-
plex signals. This feature is completely different from those of
other heteroazulene-subtituted methane derivatives.21–23 This
feature would be ascribed to the very large steric hindrance
experienced between one heteroazulene moiety and another
؊
borate) 14aؒ3BF4 and the corresponding pyrrole analogues
؊
؊
14b,cؒ3BF4 and their related compounds 14d–iؒ3BF4 in the
yields listed also in Table 1 (Scheme 5).
Spectroscopic properties
The abbreviations, Fn, PPn, and MPn, denote 2-oxo-2H-cyclo-
hepta[b]furan-3-yl, 1,2-dihydro-2-oxo-N-phenylcyclohepta[b]-
pyrrol-3-yl, and 1,2-dihydro-N-methyl-2-oxocyclohepta[b]-
J. Chem. Soc., Perkin Trans. 2, 2001, 2253–2262
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Fig. 2 UV–vis spectra of trications 14a–e in CH3CN.
Fig. 3 UV–vis spectra of trications 14f–i in CH3CN.
Scheme 5 Reagents and conditions: i, (a) DDQ in CH2Cl2, (b) 42% aq.
HBF4.
heteroazulene moiety in trimethylbenzene derivatives 10a–i as
well as in trications 14a–i.
The UV–vis spectra of trications 14a–i in CH3CN are shown
in Fig. 2 and Fig. 3. The longest wavelength absorption maxima
of a series of trications 14a (615 nm), 14b (622 nm), 14c (629
nm) 14d (610 nm), 14e (614 nm), 14f (614 nm), 14g (618 nm),
14h (626 nm), and 14i (617 nm) resemble each other. The
longest wavelength absorption maxima of trications increase in
the order 14a (which has three Fn-units) < 14b (which has three
PPn-units) < 14c (which has three MPn-units), and this feature
shows that substitution of the heteroazulene induces a red-shift
of the longest wavelength of trications in the order Fn < PPn <
MPn. Thus, the longest wavelength of 14e (which has one
Fn-unit and two PPn-units) is longer than that of 14d (which
has two Fn-units and one PPn-unit), and the longest wave-
length of 14g (which has one Fn-unit and two MPn-units) is
longer than that of 14f (which has two Fn-units and one MPn-
unit). Moreover, the longest wavelength increases in the order
14i (which has an Fn-unit, a PPn-unit, and an MPn-unit) < 14h
(which has one PPn-unit and two MPn-units) < 14c (which has
three MPn-units). These features show that increasing the
number of MPn-units induces a red-shift of the longest wave-
lengths of trications. The longest wavelength absorption max-
ima of trications 14a,d,e,f,g,i, which have an Fn-unit, are even
shorter than those of the related monocation 4 (621 nm), while
those of 14b,c,h, which have a PPn-unit, are shorter than those
of the related monocation 5 (652 nm).22 This feature seems to
be reasonable based on our previous study considering the
longest wavelength absorption maxima of 4 and 5 as well as
the calculations of the stable conformations of 4 and 5: the
Fig. 4
dihedral angles, θ1, θ2, and θ3, which express deviation of the
plane of the phenyl groups and heteroazulenes from the refer-
ence plane (the plane which is defined by the three arylic ipso
carbons, Fig. 4).22 Thus, the UV–vis spectra of trications 14a–i
suggest the absence of appreciable conjugation among the
methyliumyl-units. Furthermore, this feature is similar to the
cases of dications 6a–c. The longest wavelength absorption
maximum of trication 14a, which has three Fn-units, is similar
to those of related dication 6a, which has two Fn-units.
Similarly, the longest wavelength absorption maximum of tri-
cation 14c, which has three MPn-units, is similar to those of the
related dication 6b, which has two MPn-units. Moreover, the
longest wavelength absorption maxima of trications 14f,g,
which have two Fn-units and one MPn-unit and one Fn-unit
and two MPn-units, respectively, are similar to those of the
related dication 6c, which has a Fn-unit and a MPn-unit.
Stability of the trications: [pKR؉] values and reduction potentials
The affinity of the carbocation toward the hydroxide ion,
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Table 2 [pKRϩ] values and reduction potentialsa of trications 14a–ib, and reference compounds 2, 4, 5, and 6a–c
[pKRϩ Reduction potentials
]
Compd.
pKRϩϩϩ
pKRϩϩ
pKRϩ
E1red
E2red
E3red
E4red
E5red
E6red
14a
14b
14c
14d
14e
14f
14g
14h
14i
6ac
6bc
6cc
2d
6.4
10.4
10.5
9.0
11.6
11.4
Ϫ0.30
Ϫ0.56
Ϫ0.60
Ϫ0.53
Ϫ0.55
Ϫ0.62
Ϫ0.59
Ϫ0.59
Ϫ0.59
Ϫ1.13
Ϫ1.30
Ϫ1.36
Ϫ1.32
Ϫ1.32
Ϫ1.33
Ϫ1.32
Ϫ1.49
Ϫ1.29
11.5
13.0
12.3
12.0
8.2
7.5
Ϫ0.32
Ϫ0.34
Ϫ1.03
Ϫ1.05
6.7
Ϫ0.30
Ϫ0.29
Ϫ0.29
Ϫ1.10
6.6
9.4
6.6
11.5
11.2
11.8
Ϫ1.06
Ϫ1.34
Ϫ1.05
Ϫ1.05
Ϫ1.37
Ϫ1.37
9.0
12.1
12.7
10.9 0.2
Ϫ0.33
Ϫ0.60
Ϫ0.62
Ϫ0.34
Ϫ0.96
9.1 0.2
12.7 0.2
9.3
12.0
4e
(Ϫ0.31)
(Ϫ0.53)
(Ϫ1.03)
(Ϫ1.29)
5e
؊
a Peak potentials in V vs. Ag/Agϩ. Reversible processes are shown in parentheses. b 14a–iؒ3BF4 were used for the measurement. c Ref. 23. d Ref. 9.
e Ref. 22.
expressed by the [pKRϩ] values (cf. Table 2), is the most com-
mon criterion of carbocation stability.29 The [pKRϩ] values of
the trications 14a–i were determined spectrophotometrically in
buffer solutions prepared in 50% aqueous CH3CN and are
summarized in Table 2, along with those of the reference com-
pounds 4, 5, and 6a–c.22,23 In the case of trications 14b, three
methyliumyl-units were neutralized stepwise at the pH of 10.4,
11.5, and 13.0, which correspond to pKRϩϩϩ, pKRϩϩ, and pKRϩ
,
respectively. Since sharp titration curves for stepwise neutraliz-
ation of trications 14a and 14c–i are not obtained, we could
not determine pKRϩ, pKRϩϩ, and pKRϩϩϩ values separately for
these trications. This feature suggests that the two of the three
methyliumyl-units in the trications 14a and 14c–i are neutral-
ized simultaneously. The neutralization of the trications 14a–i is
not completely reversible. This feature may be ascribed to the
instability of the neutralized products under the conditions of
the pKRϩ measurement. Immediate (after ca. 5 s) acidification
of an alkaline solution (ca. pH 14) of 14a–i with TFA regener-
ated the absorption maxima of the cations in the visible regions
in 40–50%. As expected, the heteroazulenes effectively stabilize
the trications, and the [pKRϩ] values of 14a–i are extremely
high. On the basis of our previous studies of tris(heteroazulen-
3-yl)methyl cations 3a–c21 and heteroazulene-substituted
tropylium ions,24 the stabilizing ability of heteroazulenes for
these cations has been clarified to be in the order Fn < PPn <
MPn. Consequently, the [pKRϩ] values of heteroazulene-
substituted methyl cations and tropylium ions increase in the
Fig. 5 Cyclic voltammogram of 14g in MeCN.
are similar to the average values of pKRϩϩ and pKRϩ values of
14b and 14e; thus, two MPn-units and a PPn-unit and an MPn-
unit are neutralized simultaneously at these pH units. Thus, the
first [pKRϩ] values of 14c,h (10.5, 9.4) are considered to corre-
spond to the pKRϩϩϩ value. Simultaneous neutralization of two
methyliumyl-units suggests the absence of conjugation among
the methyliumyl-units.
The reduction potentials of trications 14a–i were determined
by cyclic voltammetry (CV) in CH3CN. Most of the reduction
waves of 14a–i were irreversible except 14f,g under the con-
ditions of CV measurements, and thus, the peak potentials are
summarized in Table 2 together with those of the reference
cations 4, 5 and 6a–c.22,23 The reversibility of the reduction
waves of 14f,g seemed to be enhanced, and thus, the CV of 14g
is shown as an example (Fig. 5). This feature suggests that the
methyliumyl-units of trications and their reduced methyl-
radical-units are stabilized sterically. The reduction behavior of
trications is affected by the methyliumyl-units: the reduction
potentials depend on the kind of substituted methyliumyl-units.
The reduction of trications 14a–i is expected to give a non-
Kekulé-type electronic structure upon reduction. Since the
stabilizing ability of heteroazulenes toward cations is in the
order Fn < PPn < MPn (vide supra), reduction potentials of
heteroazulene-substituted methyl cations and tropylium ions
are more negative in the order of the substituents Fn < PPn <
MPn.21,24 As seen in the cations 6a–c, 4, and 5, the reduction
potentials of the Fn-unit, PPn-unit, and MPn-unit to give
radical species are ca. Ϫ0.33, Ϫ0.53, and Ϫ0.60 V vs. Ag/Agϩ,
respectively, and those of the Fn-unit, PPn-unit, and MPn-unit
to give anion species are ca. Ϫ1.05, Ϫ1.29, and Ϫ1.37 V vs.
Ag/Agϩ, respectively. On the basis of these facts, plausible
order with the substituent Fn < PPn < MPn. The first [pKRϩ
]
values of 14a,e,g and 14i (6.4, 6.7, 6.6, and 6.6), which have one
Fn-unit, are similar to each other. In addition, the second
[pKRϩ] values of 14a,e,g,i (9.0 and 11.4–11.8) are close to those
of 6a,b (9.0 and 12.1), respectively. Since the [pKRϩ] values of
6a,b are considered to be the average values of pKRϩϩ and pKRϩ
values, the second [pKRϩ] values of 14a,e,g,i would correspond
to the average values of pKRϩϩ and pKRϩ values. Thus, the first
[pKRϩ] values of 14a,e,g,i are considered to be pKRϩϩϩ values,
and an Fn-unit may be neutralized at first. On the other hand,
the first [pKRϩ] values of 14d,f (8.2 and 7.5), which have two
Fn-units and a PPn-or an MPn-unit, are larger than those of
14a,e,g,i, and the second [pKRϩ] values of 14d,f (12.3 and 12.0)
are larger than those of 14a,e,g,i. In addition, the second [pKRϩ
values of 14d,f are similar to that of 5. Thus, the first [pKRϩ
]
]
values of 14d,f probably correspond to the average values
of pKRϩϩϩ and pKRϩϩ values, and two Fn-units of 14d,f are
neutralized simultaneously at these pH units. Consequently, the
second [pKRϩ] values of 14d,f would be pKRϩ values of these
trications, and the PPn-unit or the MPn-unit is neutralized at
these pH units, respectively. The second [pKRϩ] values of 14c,h
J. Chem. Soc., Perkin Trans. 2, 2001, 2253–2262
2257

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diradical-cation species 19d,f, which undergo one-electron
reduction of a PPn-unit and an MPn-unit at E3red to afford
triradical species 20d,f. Then, the two-electron reduction of two
Fn-units at E5red affords radical-dianion species 22d,f, which
undergo the one-electron reduction of a PPn-unit or a MPn-
unit at E6red, to afford trianion species 23d,f. On the other hand,
the first (E1red) and third (E4red) reduction potentials of 14e,g
(Ϫ0.30 and Ϫ1.10 V vs. Ag/Agϩ for 14e; Ϫ0.29 and Ϫ1.06 for
14g), which have Fn-unit and two PPn-units or two MPn-units,
are similar to E2red and E4red of 6a, as well as E1red and E2red of
4, respectively. Thus, the Fn-unit of 14e,g is probably reduced at
the first and third reduction potentials. In addition, the second
(E3red) and fourth (E6red) reduction potentials of 14e,g (Ϫ0.55
and Ϫ1.32 V vs. Ag/Agϩ for 14e; Ϫ0.59 and Ϫ1.32 for 14g) are
similar to those of E3red and E6red of 14b,c, respectively. Thus,
two PPn-units and two MPn-units of 14e,g are probably
reduced at the second and fourth reduction potentials.
Consequently, the reduction process of 14e,g proceeds via
one-electron reduction of an Fn-unit at E1red to afford radical-
dication species 18e,g, and subsequent two-electron reduction
of two PPn-units or two MPn-units occurs at E3red simul-
taneously to afford triradical species 20e,g. Then, further
one-electron reduction of an Fn-unit at E4red affords diradical-
anion species 21e,g, which undergo simultaneous two-electron
reduction of two PPn-units or two MPn-units at E6red occurs to
afford trianion species 23e,g. Although a similar feature was
expected for 14h, it exhibited only three reduction potentials
(Table 2). Since the difference between the reduction potentials
of one-electron reduction of a PPn- and an MPn-unit (cf. E1red
of 5 and E2red of 6b) would be small, the reductions of these
units occur simultaneously to give 20h. Then, further one-
electron reduction occurs to give 21h in a step-wise fashion,
which undergoes two-electron reduction to formation of 23h. In
a similar manner, trication 14i, which has three different
methyliumyl-units, exhibited also four reduction potentials
between E1red–E6red (Table 2). In this case, the E2red and E3red
,
which correspond to one-electron reduction of a PPn-and an
MPn-unit, respectively, are similar, and thus, the reduction
of these units in 18i to give 20i occurs simultaneously. After
reduction of an Fn-unit in 20i at E4red to afford 21i, since the
E5red and E6red, which correspond to one-electron reduction of
a PPn-and an MPn-unit, respectively, are also similar, two-
electron reduction of 21i occurs to give 24i. The reduction
properties of 14a–i described above clearly show the absence of
conjugation among three methyliumyl-units, and the existence
of triradical species 20a–i and trianion species 23a–i. This
feature is similar to the cases of non-Kekulé-type dications 6a–c
and is completely different from the cases of Kekulé-type
dications 7a–c, which involve conjugation among two
methyliumyl-units.
In summary, efficient synthesis of fairly stable trications 14a–
i having a variety of methyliumyl-units substituted with hetero-
azulenes has been accomplished. The stability of 14a–i was
evaluated by the [pKRϩ] values and the reduction potentials
measured by CV. In the case of trications 14b, three
methyliumyl-units were neutralized stepwise at pH 10.4, 11.5,
and 13.0. However, we could not determine pKRϩ, pKRϩϩ, and
pKRϩϩϩ values separately in the cases of other trications 14a
and 14c–i. This feature shows that two methyliumyl-units are
neutralized simultaneously in these trications. The reduction
potentials of trications 14a–i are affected by the methyliumyl-
units. Among different trications, the reduction potentials of
the same methyliumyl-units are similar to each other. In add-
ition, the same methyliumyl-units in one trication are reduced
simultaneously. These features show that three methyliumyl-
units of trications 14a–i are twisted against the central phenyl
group, and no conjugation among methyliumyl-units is sug-
gested. Further studies concerning the synthesis and properties
of stable heteroazulene-substituted polycations and radical
species will be continued.
Scheme 6
reduction processes of trications 14a–i are depicted in Scheme 6.
Trications 14a–c, all of which have the same three methyliumyl-
units, exhibited two reduction peaks E3red and E6red at Ϫ0.30
and Ϫ1.13, Ϫ0.56 and Ϫ1.30, and Ϫ0.60 and Ϫ1.36 V vs.
Ag/Agϩ, respectively; the values for 14a, which has three Fn-
units, are close to those of E2red and E4red of 6a, which is the
dication having two Fn-units. The values for 14c, which has
three MPn-units, are very similar to those of E2red and E4red of
6b, which is the dication having two MPn-units. In the case of
6a,b, two-electron reductions proceed at E2red and E4red to
afford diradical and dianion species, respectively. Thus, the
reduction process of 14a–c is rationalized to proceed via two
steps of three-electron reduction affording triradical species
20a–c and their trianions 23a–c, respectively. On the other
hand, trications 14d–g, which have two different methyliumyl-
units, exhibited four reduction potentials among E1red–E6red
(Table 2). The first (E2red) and third (E5red) reduction potentials
of 14d,f (Ϫ0.32 and Ϫ1.03 V vs. Ag/Agϩ for 14d; Ϫ0.34 and
Ϫ1.05 for 14f ), which have two Fn-units and a PPn-unit or an
MPn-unit, are similar to E2red and E4red of 6a, as well as E1red
and E2red of 4, respectively. In the cases of 6a and 4, Fn-units
are reduced at those reduction potentials to give radical and,
then, anion species in a step-wise fashion. Thus, two Fn-units
of 14d,f are considered to be reduced at the first and third
reduction potentials. In addition, the second (E3red) and fourth
(E6red) reduction potentials of 14d,f (Ϫ0.53 and Ϫ1.32 V vs. Ag/
Agϩ for 14d; Ϫ0.62 and Ϫ1.33 for 14f ) are similar to E3red and
E6red of 14b,c, respectively. Thus, a PPn-unit and an MPn-unit
of 14d,f are reduced at the second and fourth reduction poten-
tials. Consequently, the reduction process of 14d,f proceeds via
two-electron reduction of two Fn-units at E2red to afford
2258
J. Chem. Soc., Perkin Trans. 2, 2001, 2253–2262

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For 11a. Orange powder; mp 150–151 ЊC (from CH2Cl2–
Experimental
EtOH); δH (500 MHz) 5.81 (1H, s, Fn2CH), 6.90 (2H, dd,
J 9.5,8.6, Fn-6), 7.03–7.10 (6H, m, Fn-5, 7, 8), 7.58 (2H, d,
J 11.4, Fn-4), 7.98 (2H, s, Ph-4, 6), 8.30 (1H, s, Ph-2), 10.06
(2H, s, CHO); δC (125.7 MHz) 34.7, 107.5, 115.1, 127.8, 129.8,
131.5, 132.9, 133.7, 135.8, 137.5, 140.0, 149.1, 157.7, 169.3,
190.9; νmax (KBr)/cmϪ1 1735, 1252; m/z (FAB) 436 (Mϩ) (Found:
C, 68.5 H, 3.2. C27H16O6ؒ1/2CH2Cl2 requires C, 68.97; H,
3.58%).
IR spectra were recorded on a HORIBA FT-710 spectrometer.
Mass spectra and high-resolution mass spectra were run on
JMS-AUTOMASS 150 and JMS-SX102A spectrometers.
1
Unless otherwise specified, H NMR spectra and 13C NMR
spectra were recorded on a JNM-lambda 500 spectrometers
using CDCl3 as the solvent, and the chemical shifts are given
relative to internal SiMe4 standard: J-values are given in Hz.
1
The abbreviations, Fn, PPn, and MPn in the H NMR data
denote 2-oxo-2H-cyclohepta[b]furan-3-yl, 1,2-dihydro-2-oxo-
N-phenylcyclohepta[b]pyrrol-3-yl, and 1,2-dihydro-N-methyl-
2-oxocyclohepta[b]pyrrol-3-yl moieties, respectively. Mps were
recorded on a Yamato MP-21 apparatus and are uncorrected.
The heteroazulenes, 2H-cyclohepta[b]furan-2-one 8a,25 1,2-
dihydro-N-phenylcyclohepta[b]pyrrol-2-one 8b,26 and 1,2-
For 12a. Yellow powder; mp 194–195 ЊC (from CH2Cl2–
EtOH); δH (500 MHz) 5.68 (2H, s, Fn2CH), 6.82 (4H, dd,
J 10.2, 8.1, Fn-6), 6.94–7.00 (12H, m, Fn-5, 7, 8), 7.32 (1H, s,
Ph-4), 7.46 (4H, d, J 11.4, Fn-4), 7.64 (2H, s, Ph-2, 6), 9.91 (1H,
s, CHO); δC (125.7 MHz) 35.0, 108.0, 114.4, 127.8, 127.9, 131.2,
132.5, 132.9, 135.4, 137.5, 139.2, 148.9, 157.6, 169.2, 192.0; νmax
(KBr)/cmϪ1 1735, 1271; m/z (FAB) 711 (Mϩ ϩ 1) (Found: C,
71.3 H, 3.0. C45H26O9ؒ2/3CH2Cl2 requires C, 71.48; H, 3.59%).
dihydro-N-methylcyclohepta[b]pyrrol-2-one
8c,27,28
were
prepared as described in the literature.
For 11c. Yellow powder; mp 220–221 ЊC (from CH2Cl2–
EtOH); δH (400 MHz) 3.56 (6H, s, Me), 6.28 (1H, s, MPn2CH),
6.90 (2H, dd, J 10.0, 9.3, MPn-6), 6.94 (2H, d, J 9.3, MPn-8),
7.05 (2H, dd, J 11.2, 9.3, MPn-5), 7.10 (2H, dd, J 10.0, 9.3,
MPn-7), 7.93 (2H, d, J 11.2, MPn-4), 7.97 (2H, s, Ph-4, 6), 8.24
(1H, s, Ph-2), 10.01 (2H, s, CHO); δC (125.7 MHz) 26.7, 35.3,
112.0, 112.8, 128.2, 129.1, 129.3, 130.7, 131.5, 134.5, 137.1,
141.6, 142.8, 144.8, 168.4, 191.4; νmax (CHCl3)/cmϪ1 1700, 1684;
m/z (FAB) 463 (Mϩ ϩ 1) (Found: C, 70.4 H, 4.5; N, 5.1.
C29H22N2O4 requires C, 70.17; H, 4.59; N, 5.55%).
Preparation of 10a–c
A solution of 8a–c (3 mmol) and 9 (0.5 mmol) in a mixture of
CH2Cl2 (10 cm3) and TFA (2 cm3) was stirred at rt for 48 h.
After the reaction was complete, the mixture was poured into
aqueous NaHCO3 solution. The mixture was extracted with
CH2Cl2, and the extract was dried over Na2SO4 and con-
centrated in vacuo. The resulting residue was purified through
column chromatography on SiO2 by using hexane–AcOEt
(1 : 1) as the eluent to give the products 10a–c (Table 1, Runs 1,
2, and 3).
For 12c. Yellow powder; mp 250–251 ЊC (from CH2Cl2–
EtOH); δH (500 MHz) 3.44 (12H, s, Me), 6.09 (2H, s, MPn2CH),
6.78 (4H, d, J 9.6, MPn-8), 6.79 (4H, dd, J 10.3, 8.6, MPn-6),
6.88 (4H, dd, J 11.0, 8.6, MPn-5), 6.99 (4H, dd, J 10.3, 9.6,
MPn-7), 7.33 (1H, s, Ph-4), 7.58 (2H, s, Ph-2, 6), 7.76 (4H, d,
J 11.0, MPn-4), 9.83 (1H, s, CHO); δC (125.7 MHz) 26.4, 35.5,
111.2, 113.5, 127.5, 128.5, 128.8, 130.0, 130.7, 134.3, 136.8,
141.2, 141.3, 144.7, 168.5, 192.8; νmax (CHCl3)/cmϪ1 1669; m/z
(FAB) 763 (Mϩϩ1) (Found: C, 70.9 H, 4.5; N, 6.3. C49H38N4O5
requires C, 70.84; H, 4.76; N, 6.61%).
For 10a. Orange powder; mp 239–240 ЊC (decomp) (from
CH2Cl2–EtOH); δH (500MHz) 5.54 (3H, s, Fn2CH), 6.76 (6H, t,
J 9.6, Fn-6), 6.85–6.94 (18H, m, Fn-5, Fn-7, Fn-8), 6.97 (3H, s,
Ph-2, 4, 6), 7.38 (6H, d, J 11.6, Fn-4); δC (125.7 MHz) 35.4,
108.6, 113.9, 126.0, 128.1, 130.9, 132.1, 135.0, 138.5, 148.7,
157.5, 169.1; νmax (CHCl3)/cmϪ1 1735 1261; m/z (FAB) 984 (Mϩ)
(Found: C, 74.7; H, 3.8. C63H36O12ؒ1/2CH2Cl2 requires C, 74.23;
H, 3.63%).
For 10b. Orange powder; mp 264–266 ЊC (from CH2Cl2–
EtOH); δH (500MHz) 6.14 (3H, s, PPn2CH), 6.56–6.63 (12H, m,
PPn-6, 8), 6.70–6.75 (12H, m, PPn-5, 7), 7.16–7.17 (12H, m,
NPh), 7.25–7.27 (3H, m, Ph-2, 4, 6), 7.33–7.38 (18H, m, NPh),
7.86 (6H, d, J 11.4, PPn-4); δC (125.7 MHz) 36.4, 112.3, 113.9,
126.5, 128.1, 129.0, 129.2, 129.7, 130.0, 130.7, 134.9, 140.3,
141.6, 145.6, 168.7 (one carbon overlapping); νmax (CHCl3)/
cmϪ1 1684; m/z (FAB) 1435 (Mϩ ϩ 1) (Found: C, 79.1; H, 4.4;
N, 5.5. C99H66N6O6 requires C, 78.99; H, 4.51; N, 5.53%).
Preparation of 10d,e
A solution of 11a or 12a (1 mmol) and 8b (2 or 4 mmol) in a
mixture of CH2Cl2 (20 cm3) and TFA (2 cm3) was stirred at rt
for 48 h. After the reaction was complete, the mixture was
poured into aqueous NaHCO3 solution. The mixture was
extracted with CH2Cl2, and the extract was dried over Na2SO4
and concentrated in vacuo. The resulting residue was purified
through column chromatography on SiO2 by using hexane–
AcOEt (1 : 1) as the eluent to give the product 10d or 10e
(Table 1, Runs 6 and 7).
For 10c. Orange powder; mp 279–281 ЊC (decomp) (from
CH2Cl2–EtOH); δH (500MHz) 3.32 (18H, s, Me), 5.91 (3H, s,
MPn2CH), 6.63 (6H, d, J 9.0, MPn-8), 6.65–6.72 (12H, m,
MPn-5, 6), 6.88 (6H, dd, J 9.3, 9.0, MPn-7), 6.92 (3H, s, Ph-2, 4,
6), 7.64 (6H, d, J 11.2, MPn-4); δC (125.7 MHz, DMSO-d6)
26.0, 35.4, 111.4, 113.4, 125.3, 127.2, 128.1, 130.0, 130.5, 139.7,
139.9, 143.7, 167.1; νmax (CHCl3)/cmϪ1 1654; m/z (FAB) 1063
(Mϩ) (Found: C, 74.7; H, 5.1; N, 7.3. C69H54N6O6ؒ2/3CH2Cl2
requires C, 74.72; H, 4.98; N, 7.50%).
For 10d. Yellow powder; mp 225–226 ЊC (decomp) (from
CH2Cl2–EtOH); δH (500 MHz) 5.55 (2H, s, Fn2CH), 6.10 (1H, s,
PPn2CH), 6.63–6.88 (24H, m, Fn-5, 6, 7, 8, PPn-5, 6, 7, 8), 6.94
(1H, s, Ph-4), 7.11 (2H, s, Ph-2, 6), 7.15–7.23 (4H, m, NPh),
7.38 (4H, d, J 11.4, Fn-4), 7.39–7.50 (6H, m, NPh), 7.82 (2H, d,
J 11.4, PPn-4); δC (150 MHz, DMSO-d6) 35.4, 35.8, 108.7,
112.8, 113.2, 113.7, 125.3, 126.4, 128.4, 128.8, 129.0, 129.3,
129.4, 130.5, 130.8, 131.1, 131.9, 134.5, 134.7, 138.1, 141.2,
141.7, 145.3, 148.6, 157.5, 168.4, 169.2 (one carbon over-
lapping); νmax (KBr)/cmϪ1 1735, 1654, 1269; m/z (FAB) 1135
(Mϩ ϩ 1) (Found: C, 74.2; H, 3.9; N, 2.2. C75H46N2O10ؒCH2Cl2
requires C, 74.81; H, 3.97; N, 2.30%).
Preparation of 11a, 12a, 11c, and 12c
A solution of 8a,c (2 mmol) and 9 (1 mmol) in a mixture of
CH2Cl2 (10 cm3) and TFA (2 cm3) was stirred at rt for 48 h. The
reaction mixture was poured into aqueous NaHCO3 solution.
The mixture was extracted with CH2Cl2, and the extract was
dried over Na2SO4 and concentrated in vacuo. The resulting
residue was purified through column chromatography on SiO2
by using hexane–AcOEt (1 : 1) as the eluent to give the products
11a,c and 12a,c, and recovery 9 (Table 1, Runs 4 and 5).
For 10e. Yellow powder; mp 233–235 ЊC (decomp) (from
CH2Cl2–EtOH); δH (500 MHz) 5.54 (1H, s, Fn2CH), 6.13 (2H, s,
PPn2CH), 6.62 (4H, d, J 8.9, PPn-8), 6.61–6.69 (6H, m, Fn-6,
PPn-6), 6.73–6.83 (16H, m, Fn-5, 7, 8, PPn-5, 7), 7.08 (2H, s,
Ph-4, 6), 7.15–7.22 (8H, m, NPh), 7.29 (1H, s, Ph-2), 7.36 (2H,
J. Chem. Soc., Perkin Trans. 2, 2001, 2253–2262
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d, J 11.2, Fn-4), 7.35–7.42 (12H, m, NPh), 7.85 (4H, d, J 11.6,
PPn-4); δC (150 MHz, DMSO-d6) 35.6, 36.0, 108.9, 112.6,
113.4, 113.5, 125.8, 127.0, 128.2, 128.5, 128.8, 129.2, 130.2,
130.7, 130.8, 131.7, 134.4, 134.6, 137.5, 140.8, 141.5, 145.4,
148.5, 157.5, 168.5, 169.2 (two carbons overlapping); νmax
CH2Cl2 (10 cm3) and TFA (2 cm3) was stirred at rt for 48 h.
After the reaction was complete, the mixture was poured into
aqueous NaHCO3 solution. The mixture was extracted with
CH2Cl2, and the extract was dried over Na2SO4 and con-
centrated in vacuo. The resulting residue was purified through
column chromatography on SiO2 by using hexane–AcOEt
(1 : 1) as the eluent to give the products 13 and recovery of 11c
(Table 1, Run 11).
(CHCl3)/cmϪ1 1734, 1685, 1654, 1261; m/z (FAB) 1285 (Mϩ
ϩ
1) (Found: C, 75.1; H, 4.2; N, 3.8. C87H56N4O8ؒ3/2CH2Cl2
requires C, 75.24; H, 4.21; N, 3.97%).
For 13. Orange powder; mp 234–235 ЊC (from CH2Cl2–
EtOH); δH (500 MHz) 3.44 (6H, s, Me), 6.16 (1H, s, PPn2CH),
6.19 (1H, s, MPn2CH), 6.69 (2H, d, J 8.9, PPn-8), 6.74–6.79
(4H, m, PPn-6, MPn-6), 6.78 (2H, d, J 9.8, MPn-8), 6.83–6.91
(6H, m, PPn-5, 7, MPn-5), 6.98 (2H, dd, J 10.1, 9.8, MPn-7),
7.23–7.48 (10H, m, NPh), 7.49 (1H, s, Ph-4), 7.60 (1H, s, Ph-2
or 6), 7.73 (1H, s, Ph-2 or 6), 7.83 (2H, d, J 11.3, PPn-4 or
MPn-4), 7.85 (2H, d, J 11.3, PPn-4 or MPn-4), 9.88 (1H, s,
CHO); δC (150MHz) 26.5, 35.5, 35.7, 111.3, 112.7, 113.0, 113.5,
127.6, 127.7, 128.4, 128.6, 128.7, 128.9, 129.1, 129.2, 129.3,
129.5, 130.0, 130.5, 130.7, 131.1, 134.4, 134.5, 136.8, 141.1,
141.3, 141.6, 144.7, 145.4, 168.47, 168.49, 192.8; νmax (KBr)/
cmϪ1 1676; m/z (FAB) 887 (Mϩ ϩ 1) (Found: C, 77.6; H, 4.1; N,
5.8. C59H42N4O5 requires C, 77.86; H, 4.70; N, 6.12%).
Preparation of 10f,g
A solution of 11a or 12a (1 mmol) and 8c (2 or 4 mmol) in a
mixture of CH2Cl2 (20 cm3) and TFA (2 cm3) was stirred at rt
for 48 h. After the reaction was complete, the mixture was
poured into aqueous NaHCO3 solution. The mixture was
extracted with CH2Cl2, and the extract was dried over Na2SO4
and concentrated in vacuo. The resulting residue was purified
through column chromatography on SiO2 by using hexane–
AcOEt (1 : 1) as the eluent to give the product 10f or 10g
(Table 1, Runs 8 and 9)
For 10f. Orange powder; mp 225–226 ЊC (from CH2Cl2–
EtOH); δH (500 MHz) 3.39 (6H, s, Me), 5.50 (2H, s, Fn2CH),
6.00 (1H, s, MPn2CH), 6.70–6.78 (6H, m, Fn-6, MPn-6), 6.73
(2H, d, J 9.3, MPn-8), 6.82–6.97 (16H, m, Fn-5, 7, 8, MPn-5, 7),
6.92 (1H, s, Ph-4), 6.97 (2H, s, Ph-2, 6), 7.34 (4H, d, J 11.4,
Fn-4), 7.70 (2H, d, J 11.3, MPn-4); δC (150MHz) 26.4, 35.4,
35.8, 108.8, 111.1, 113.7, 113.9, 125.1, 126.4, 128.3, 128.5,
128.7, 130.0, 130.6, 130.8, 131.9, 134.7, 137.9, 141.0, 141.3,
144.7, 148.6, 157.5, 168.4, 169.1; νmax (KBr)/cmϪ1 1734, 1653,
1269; m/z (FAB) 1011 (Mϩϩ1) (Found: C, 70.5; H, 3.6; N, 2.4.
C65H42N2O10ؒ3/2CH2Cl2 requires C, 70.16; H, 3.98; N, 2.46%).
Preparation of 10i
A solution of 8a (2 mmol) and 13 (1 mmol) in a mixture of
CH2Cl2 (20 cm3) and TFA (2 cm3) was stirred at rt for 48 h.
After the reaction was complete, the mixture was poured into
aqueous NaHCO3 solution. The mixture was extracted with
CH2Cl2, and the extract was dried over Na2SO4 and con-
centrated in vacuo. The resulting residue was purified through
column chromatography on SiO2 by using hexane–AcOEt
(1 : 1) as the eluent to give the product 10i (Table 1, Run 12)
For 10g. Orange powder; mp 248–249 ЊC (from CH2Cl2–
EtOH); δH (500 MHz) 3.37 (12H, s, Me), 5.45 (1H, s, Fn2CH),
5.96 (2H, s, MPn2CH), 6.68–6.88 (16H, m, Fn-5, 6, 7, 8, MPn-5,
6), 6.70 (4H, d, J 8.8, MPn-8), 6.91 (1H, s, Ph-2), 6.92 (2H, s,
Ph-4, 6), 7.30 (2H, d, J 11.6, Fn-4), 7.68 (4H, d, J 10.9, MPn-4);
δC (150MHz, DMSO-d6) 26.4, 35.5, 35.9, 109.0, 110.9, 113.4,
114.1, 125.6, 126.9, 128.5, 128.6, 128.6, 129.7, 130.3, 130.7,
131.7, 134.3, 137.4, 140.7, 140.9, 144.7, 148.4, 157.5, 168.5,
169.2; νmax (KBr)/cmϪ1 1734, 1653, 1261; m/z (FAB) 1037 (Mϩ
ϩ 1) (Found: C, 72.1; H, 5.1; N, 4.5. C67H48N4O8ؒCH2Cl2
requires C, 72.79; H, 4.49; N, 4.99%).
For 10i. Yellow powder; mp 242–243 ЊC (from CH2Cl2–
EtOH); δH (500 MHz) 3.36 (6H, s, Me), 5.50 (1H, s, Fn2CH),
6.02 (1H, s, MPn2CH), 6.18 (1H, s, PPn2CH), 6.60 (2H, d, J 9.0,
PPn-8), 6.67–6.96 (22H, m, Fn-5, 6, 7, 8, PPn-5, 6, 7, MPn-5, 6,
7, 8), 6.95 (1H, s, Ph-6), 7.08 (1H, s, Ph-2), 7.10 (1H, s, Ph-4),
7.18–7.19 (4H, m, NPh), 7.34 (2H, d, J 11.3, Fn-4), 7.38–7.50
(6H, m, NPh), 7.74 (2H, d, J 11.2, PPn-4 or MPn-4), 7.79 (2H,
d, J 11.3, PPn-4 or MPn-4); δC (150 MHz) 26.4, 29.0, 30.0, 30.4,
35.6, 36.0, 108.9, 110.9, 112.5, 113.0, 113.4, 113.5, 114.2, 125.8,
128.3, 128.5, 128.6, 128.8, 129.0, 129.2, 129.6, 129.7, 130.3,
130.7, 130.9, 131.1, 131.7, 131.8, 132.5, 134.4, 134.6, 137.6,
140.9, 141.5, 144.7, 145.4, 148.5, 157.6, 167.8, 168.5, 169.2; νmax
(KBr)/cmϪ1 1734, 1669, 1269; m/z (FAB) 1161 (Mϩ ϩ 1)
(Found: C, 72.5; H, 4.0; N, 4.2. C77H52N4O8ؒ5/3CH2Cl2 requires
C, 72.52; H, 4.28; N, 4.30%).
Preparation of 10h
A solution of 12c (1 mmol) and 8b (2 mmol) in a mixture of
CH2Cl2 (10 cm3) and TFA (2 cm3) was stirred at rt for 48 h.
After the reaction was complete, the mixture was poured into
aqueous NaHCO3 solution. The mixture was extracted with
CH2Cl2, and the extract was dried over Na2SO4 and con-
centrated in vacuo. The resulting residue was purified through
column chromatography on SiO2 by using hexane–AcOEt
(1 : 1) as the eluent to give the product 10h (Table 1, Run 10).
General synthetic procedure for the 1,3,5-tris[bis(heteroazulen-3-
yl)methyliumyl]benzene tris(tetrafluoroborate) 14a–iؒ3BF4؊
To a stirred solution of tris[bis(heteroazulen-3-yl)methyl]-
benzenes 10 (0.05 mmol) in CH2Cl2 (10 cm3) was added DDQ
(70 mg, 0.3 mmol) and the mixture was stirred at rt for 1 h until
the reaction was complete. After evaporation of the CH2Cl2, the
residue was dissolved in a mixture of acetic anhydride (5 cm3)
and 42% HBF4 (1 cm3) at 0 ЊC, and the mixture was stirred
for 1 h. To the mixture was added Et2O (100 cm3), and the
precipitates were collected by filtration to give 14a–iؒ3BF4؊. The
results are summarized in Table 1.
For 10h. Orange powder; mp 256–258 ЊC (from CH2Cl2–
EtOH); δH (400 MHz) 3.32 (12H, s, Me), 5.94 (2H, s, MPn2CH),
6.02 (1H, s, PPn2CH), 6.55–6.80 (20H, m, PPn-5, 6, 7, 8,
MPn-5, 6, 8), 6.80–6.97 (5H, m, Ph-2, MPn-7), 7.00–7.23 (6H,
m, Ph-4, 6, NPh), 7.36–7.44 (6H, m, NPh), 7.67–7.85 (6H, m,
PPn-4, MPn-4); δC (150MHz) 26.3, 36.0, 36.1, 110.6, 112.3,
113.5, 114.3, 126.2, 126.3, 128.1, 128.5, 128.9, 129.1, 129.5,
129.9, 130.0, 130.1, 130.6, 134.6, 134.7, 140.2, 140.3, 140.8,
141.2, 141.4, 144.7, 145.4, 168.6, 168.6; νmax (CHCl3)/cmϪ1 1676;
m/z (FAB) 1187 (Mϩ ϩ 1) (Found: C, 78.4; H, 4.4; N, 6.5.
C79H58N6O6 requires C, 78.38; H, 4.86; N, 6.91%).
For 14a. Purple powder; mp >300 ЊC (from CH3CN–Et2O);
δH (400 MHz, CD3CN) 6.85–7.46 (6H, m), 7.71 (6H, d, J 10.0),
7.75 (3H, s, Ph), 7.91–8.46 (18H, m); νmax (KBr)/cmϪ1 1734,
1260, 1084; m/z (FAB) 983 [(Mϩ ϩ 2) Ϫ 3BF4] (Found: Mϩ ϩ 2
Ϫ 3BF4, 983.2161. C63H33B3F12O12 requires M ϩ 2 Ϫ 3BF4,
983.2129) (Found: C, 61.1; H, 2.3. C63H33B3F12O12 requires C,
60.91; H, 2.68%).
Preparation of 13
A solution of 11c (1 mmol) and 8b (1 mmol) in a mixture of
2260
J. Chem. Soc., Perkin Trans. 2, 2001, 2253–2262

View Article Online
For 14b. Dark violet powder; mp >300 ЊC (from CH3CN–
Et2O); δH (400 MHz, CD3CN) 7.30–8.40 (63H, m); νmax (KBr)/
cmϪ1 1696, 1084; m/z (FAB) 1431 (Mϩ Ϫ 3BF4) (Found: Mϩ Ϫ
phthalate (0.1M) and NaOH (0.1 M) (for pH 4.1–5.9), KH2PO4
(0.1M) and NaOH (0.1 M) (for pH 6.0–8.0), Na2B4O7 (0.025M)
and HCl (0.1 M) (for pH 8.2–9.0), Na2B4O7 (0.025M) and
NaOH (0.1 M) (for 9.2–10.8), Na2HPO4 (0.05 M) and NaOH
(0.1 M) (for pH 11.0–12.0), and KCl (0.2M) and NaOH (0.1 M)
(for pH 12.0–14.0) in various portions. For the preparation of
sample solutions, 1 cm3 portions of the stock solution, prepared
3BF4, 1431.4829. C99H63B3F12N6O6 requires
M Ϫ 3BF4,
1431.4813) (Found: C, 66.6; H, 3.2; N, 5.1. C99H63B3F12N6O6ؒ
HBF4 requires C, 66.77; H, 3.62; N, 4.72%).
؊
by dissolving 3–5 mg of cation 14a–iؒBF4 in MeCN (20 cm3),
For 14c. Purple powder; mp >300 ЊC (from CH3CN–Et2O);
δH (400 MHz, CD3CN) 3.50–3.56 (18H, m, Me), 7.21–7.25 (3H,
m), 7.85–8.23 (30H, m); νmax (KBr)/cmϪ1 1685, 1084; m/z (FAB)
were diluted to 10 cm3 with the buffer solution (5 cm3) and
MeCN (4 cm3). The UV–vis spectrum was recorded for each
cation 14a–i in 30 different buffer solutions. Immediately after
recording the spectrum, the pH of each solution was deter-
mined on a pH meter calibrated with standard buffers. The
observed absorbance at the specific absorption wavelengths
(613 nm for 14a; 623 nm for 14b; 623 nm for 14c, 606 nm for
14d, 614 nm for 14e, 609 nm for 14f, 618 nm for 14g, 628 nm for
14h, and 614 nm for 14i) of each cations was plotted against pH
to give two or three-step titration curves, and the midpoints of
each were taken as the [pKRϩ] value. The results are summarized
in Table 2.
1059 (Mϩ
Ϫ Ϫ 3BF4, 1059.3879.
3BF4) (Found: Mϩ
C69H51B3F12N6O6 requires M Ϫ 3BF4, 1059.3870) (Found: C,
56.4; H, 4.1; N, 5.4. C69H51B3F12N6O6ؒ5/3HBF4 requires C,
56.50; H, 3.62; N, 5.73%).
For 14d. Purple powder; mp >300 ЊC (from CH3CN–Et2O);
δH (400 MHz, CD3CN) 7.37–8.27 (43H, m); νmax (KBr)/cmϪ1
1684, 1653, 1261, 1084; m/z (FAB) 1132 (Mϩ ϩ 1 Ϫ 3BF4)
(Found: Mϩ ϩ 1 Ϫ 3BF4, 1132.2976. C75H43B3F12N2O10
requires M ϩ 1 Ϫ 3BF4, 1132.2997) (Found: C, 51.3; H, 2.8; N,
1.9. C75H43B3F12N2O10ؒ4HBF4 requires C, 51.66; H, 2.72; N,
1.61%).
Cyclic voltammetry of trications 14a–i
The reduction potentials of 14a–i were determined by means of
CV-27 voltammetry controller (BAS Co). A three-electrode cell
was used, consisting of Pt working and counter electrodes and a
reference Ag/AgNO3 electrode. Nitrogen was bubbled through
an acetonitrile solution (4 cm3) of each compound (0.5 mmol
dmϪ3) and Bu4NClO4 (0.1 mol dmϪ3) to deaerate it. The meas-
urements were made at a scan rate of 0.1 V sϪ1 and the voltam-
mograms were recorded on a WX-1000-UM-019 (Graphtec
Co) X-Y recorder. Immediately after the measurements,
ferrocene (0.1 mmol) (E1/2 = ϩ0.083) was added as the internal
standard, and the observed peak potentials were corrected
with reference to this standard. The compounds exhibited no
reversible reduction wave: each of the reduction potentials was
measured through independent scan, and they are summarized
in Table 2.
For 14e. Purple powder; mp >300 ЊC (from CH3CN–Et2O);
δH (400 MHz, CD3CN) 7.37–8.37 (53H, m); νmax (KBr)/cmϪ1
1684, 1653, 1261, 1084; m/z (FAB) 1283 [(Mϩ ϩ 2) Ϫ 3BF4]
(Found: Mϩ ϩ 2 Ϫ 3BF4, 1283.4020. C87H53B3F12N4O8 requires
M ϩ 2 Ϫ 3BF4, 1283.4023) (Found: C, 59.7; H, 3.4; N, 3.3.
C87H53B3F12N4O8ؒ5/2HBF4 requires C, 59.29; H, 3.17; N,
3.18%).
For 14f. Purple powder; mp >300 ЊC (from CH3CN–Et2O);
δH (400 MHz, CD3CN) 3.42–3.58 (6H, m, Me), 6.72 (2H, s, Ph),
6.77 (1H, s, Ph), 7.40–7.45 (27H, m), 7.55–7.66 (4H, m), 7.70–
8.45 (2H, m); νmax (KBr)/cmϪ1 1734, 1653, 1261, 1084; m/z
(FAB) 1008 [(Mϩ ϩ 1) Ϫ 3BF4] (Found: Mϩ ϩ 1 Ϫ 3BF4,
1008.2665. C65H39B3F12N2O10 requires
M ϩ 1 Ϫ 3BF4,
1008.2684) (Found: C, 54.9; H, 3.0; N, 2.0. C65H39B3F12N2O10ؒ
5/3HBF4 requires C, 55.18; H, 2.90; N, 1.98%).
Acknowledgements
For 14g. Purple powder; mp >300 ЊC (from CH3CN–Et2O);
δH (400 MHz, CD3CN) 3.45–3.60 (12H, m, Me), 6.73 (1H s,
Ph), 6.77 (2H, s, Ph), 7.41–7.45 (18H, m), 7.55–7.65 (2H, m),
7.80–8.42 (4H, m); νmax (KBr)/cmϪ1 1734, 1653, 1261, 1084; m/z
(FAB) 1034 [(Mϩ ϩ 1) Ϫ 3BF4] (Found: Mϩ ϩ 1 Ϫ 3BF4,
Financial support from a Waseda University Grant for Special
Research Project is gratefully acknowledged. We thank the
Materials Characterization Central Laboratory, Waseda
University, for technical assistance with the spectral data and
elemental analyses.
1034.3230. C67H45B3F12N4O8 requires
M ϩ 1 Ϫ 3BF4,
1034.3318) (Found: C, 55.5; H, 2.8; N, 3.8. C65H39B3F12N2O10ؒ
5/3HBF4 requires C, 55.85; H, 3.26; N, 3.89%).
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