6-Oxophenalenoxyl derivatives covalently linked to TTF moieties: Synthesis, ESR/ENDOR measurements, and DFT calculations

Article abstract of DOI:10.1016/S0040-4039(01)01564-7

The efficient synthesis, characterization, and electronic properties of new 6-oxophenalenoxyls covalently linked to TTF moieties are described in terms of Stille-coupling reactions, ESR/¹H-ENDOR techniques, and DFT calculations.

Full text of DOI:10.1016/S0040-4039(01)01564-7

TETRAHEDRON
LETTERS
Pergamon
Tetrahedron Letters 42 (2001) 7991–7995
6-Oxophenalenoxyl derivatives covalently linked to TTF
moieties: synthesis, ESR/ENDOR measurements,
and DFT calculations†
Yasushi Morita,a,* Junya Kawai,a Naoki Haneda,a Shinsuke Nishida,a Kozo Fukui,b
Shigeaki Nakazawa,b Daisuke Shiomi,b Kazunobu Sato,b Takeji Takui,b Takashi Kawakami,a
Kizashi Yamaguchia and Kazuhiro Nakasujia
aDepartment of Chemistry, Graduate School of Science, Osaka University, Toyonaka, Osaka 560-0043, Japan
bDepartments of Chemistry and Materials Science, Graduate School of Science, Osaka City University, Sumiyoshi-ku,
Osaka 558-8585, Japan
Received 25 June 2001; revised 17 August 2001; accepted 21 August 2001
Abstract—The efficient synthesis, characterization, and electronic properties of new 6-oxophenalenoxyls covalently linked to TTF
moieties are described in terms of Stille-coupling reactions, ESR/1H-ENDOR techniques, and DFT calculations. © 2001 Elsevier
Science Ltd. All rights reserved.
The importance of organic neutral radicals, such as a
triarylmethyl, nitroxide, phenoxyl, and conjugated
multi-heteroatom radicals, has been growing in the field
of organic-based magnetic materials as spin sources.1,2
Recently, introduction of an electron-donor site (e.g.
TTF) or an electron-withdrawing site (e.g. benzo-
quinone) into organic radicals has opened new possibil-
ities for the realization of ferromagnetic-conducting
organic materials by the use of charge-transfer interac-
tions combined with effective spin alignment.3 For the
past decade, our theoretical examinations by ab initio
molecular orbital calculations have suggested the
importance of intramolecular magnetic interactions
within component radical ions as well as intermolecular
and interchain magnetic interactions.4 Our recent
efforts to acquire new stable neutral radicals based on
an oxophenalenoxyl system5 have enabled us to design
and synthesize new derivatives with an electron-donor
site, i.e. 6-oxophenalenoxyls having a tetrathiafulvalene
(TTF) or an ethylenedithio–TTF (EDT–TTF) moiety, 1
and 2. This paper deals with the synthesis and charac-
terization of their spin structure.
The radical precursors, 3 and 4, were prepared from the
dimethoxyformylnaphthalene derivative 55c in seven
Keywords: neutral radicals; organic-based magnetic materials; 6-
steps or from the 8-(iodophenyl)-6-hydroxyphenalenone
oxophenalenoxyl; 1H-ENDOR/TRIPLE spectroscopies; DFT calcula-
derivative 13 in a more convergent fashion (Scheme 1).
tions.
The aldol reaction of the aldehyde 5 with zinc enolates
* Corresponding author. Tel.: +81-6-6850-5393; fax: +81-6-6850-5395;
generated from iodophenyl-substituted ethyl acetate
with lithium diisopropylamide (LDA) followed by the
addition of zinc chloride proceeded quantitatively. The
e-mail: morita@chem.sci.osaka-u.ac.jp
This paper is dedicated to Emeritus Professor Masazumi Nakagawa
on the occasion of his 85th birthday.
†
0040-4039/01/$ - see front matter © 2001 Elsevier Science Ltd. All rights reserved.
PII: S0040-4039(01)01564-7

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Y. Morita et al. / Tetrahedron Letters 42 (2001) 7991–7995
Scheme 1. Reagents and conditions: (a) 2.0 equiv. LDA–ZnCl2–4-I-C6H4CH2COOEt, THF, −78°C, 96%; (b) (i) 1.5 equiv. Et3SiH,
4.5 equiv. CF3COOH, CH2Cl2, rt; (ii) 9.3 equiv. KOH, EtOH–H2O, 100°C, 76%; (c) (i) excess (COCl)2, 65°C; (ii) 3.5 equiv. AlCl3,
CH2Cl2, −78°C, 77%; (d) 12 mol% Pd(PPh3)4, 8, toluene, 120°C, 63%; (e) 12 mol% Pd(PPh3)4, 9, toluene, 120°C, 36%; (f) (i) 20
equiv. NaBH4, EtOH, rt; (ii) 40 equiv. LiI, N,N-dimethylacetamide, 170°C; (iii) 5% aq. NaHSO3, rt, 85%; (g) (i) 5.7 equiv.
LiAlH4, THF, rt; (ii) 20 equiv. LiI, HMPA, 170°C; (iii) pH 7.0 phosphate buffer solution, rt, 53%; (h) (i) 73 equiv. NaBH4, EtOH,
rt; (ii) 50 equiv. LiI, N,N-dimethylacetamide, 170°C, (iii) pH 7.0 phosphate buffer solution, rt, 76%; (i) (i) NaOMe, THF, rt; (ii)
concentration in vacuo at rt; (iii) 2 mol% Pd(PPh3)4, 10 mol% CuI, 8, THF, 80°C, 90%; (j) (i) NaOMe, THF, rt; (ii) concentration
in vacuo at rt; (iii) 10 mol% Pd(PPh3)4, 49 mol% CuI, 9, THF, 80°C, 33%.
aldol product 6 was converted to the phenalanone
derivative 10 by reductive removal of the hydroxyl
group, de-esterification, and cyclization by Friedel–
Crafts reaction. TTF or EDT–TTF was introduced into
10 by the Stille reaction using tributyltin derivatives 8
or 9 in the presence of Pd(PPh3)4. Reduction and
demethylation of the coupling products 11 and 12
afforded the desired 6-hydroxyphenalenone derivatives
3 and 4 as reddish–orange powders.6 Alternatively, in
order to open up a more convergent way to the radical
precursors 3 and 4, we designed a direct coupling
reaction between iodophenyl-substituted 6-hydroxy-
phenalenone derivative 13 and 8 (or 9). Under the
above-mentioned coupling conditions, the reaction of
13 with 8 gave 3 in less than 10% yield. After extensive
efforts we found the key element for the coupling
reaction lay in the conversion of the hydroxyl group
into the corresponding anion and addition of a copper
salt; thus, the reaction of the sodium salt of 13 and 8
(or 9) in the presence of a catalytic amount of
Pd(PPh3)4 and CuI in THF gave the desired coupling
product 3 (or 4) effectively. The electronic spectrum of
3 (or 4) measured as a CH2Cl2 solution gave a superpo-
sition of spectra from 8-phenyl-6-hydroxyphenalenone7
and TTF (or EDT–TTF), indicating weak intramolecu-
lar interaction between 6-hydroxyphenalenone and the
TTF moieties.
The radicals 1 and 2 were obtained as dark-green
solids by treatment of the corresponding hydroxyl com-
8
pounds 3 and 4 with a large excess of active PbO2 in
benzene at room temperature in quantitative yields.9
The two radicals are stable in the crystal form in the
absence of atmospheric oxygen. Under an air atmo-
sphere, these radicals decompose slowly in the solid
state, but most of the radical remains unchanged for a
few days. Both radicals are stable for a long period of
time in degassed toluene, but decompose under an air
atmosphere.10 Fig. 1 shows well-resolved hyperfine ESR
spectra (a) observed for 1 and 2 in degassed toluene,
and the simulated ones (d). The spectral simulations
were made based on a set of isotropic hyperfine cou-
pling constants (hfcc’s) obtained by 1H-ENDOR/
TRIPLE spectroscopies (Figs. 1b and c). The relative
signs of the hfcc’s were determined by invoking 1H-
TRIPLE resonance measurements. The spin Hamilto-
nian parameters and proton assignments for 1 and 2 are
summarized in Table 1. Theoretically calculated values
for the hfcc’s in Table 1 were made in terms of the
McLachlan method.11 Agreement between the experi-
mental and theoretical values is satisfactory. These
results show that the unpaired electron is mainly delo-
calized on the 6-oxophenalenoxyl skeleton, but signifi-
cant delocalization into the phenylene moiety was also
demonstrated.

Y. Morita et al. / Tetrahedron Letters 42 (2001) 7991–7995
7993
Figure 1. Hyperfine ESR (1a, 290 K; 2a, 288 K), ENDOR (1b and 2b, 260 K), and 1H-TRIPLE spectra (1c and 2c, 260 K)
observed for 1 in toluene (3.6×10−5 M) and 2 in toluene (3.0×10−4 M) at the indicated temperatures; microwave frequency used
was 9.448005 GHz (for 1) and 9.483965 GHz (for 2), and simulated ESR spectrum (1d and 2d). In spectra 1c and 2c, the arrows
designate the pump frequencies (17.22 MHz for 1; 17.23 MHz for 2) and the dashed lines represent the TRIPLE effects appearing
in the pairs of ENDOR signals.
Table 1. Proton hfcc’s and g-values for 1 and 2
Compound
AH/mTa
2, 5-t-Bu
g-Value
3, 4
+0.201
(+0.210)
+0.201
7, 9
+0.078
(+0.076)
+0.079
11
1
2
+0.013
+0.012
−0.026
−0.026
2.0043
2.0045
(+0.210)
(+0.076)
a Hfcc’s were determined by 1H-ENDOR spectra in toluene at 260 K and simulation successfully reproducing the ESR hyperfine spectra. The
relative signs of the hfcc’s were determined in terms of 1H-TRIPLE spectroscopy. Values in parenthesis were calculated by the HMO–McLachlan
method11 using the following parameters: u=1.2, Q=−2.6 mT.
Fig. 2 shows the spin densities of the diradical cation
evaluated by UB3LYP/6-31G for singlet and triplet
states corresponding to the planar (A) and perpendicu-
lar structures (B), respectively. It is noteworthy that the
feasible local ferromagnetic coupling on C13 and C14
carbon atoms due to the same sign of spin densities on
two carbon atoms in Fig. 2B contributes greatly to the
whole ferromagnetic interaction of the two radical sites,
while the whole antiferromagnetic interaction seen in
Fig. 2A is found to arise from the different sign of the
p-spin densities on C13 and C14. It is demonstrated
that the induced spin densities around the rotation axis
is essential for intramolecular magnetic interactions.12
If one oxidation state from the TTF donor group with
suitable counter ions is realized, relatively strong
intramolecular spin interactions between the neutral
radical and the donor radical cation due to a spin
polarization effect through the p-electron network can
be expected. We carried out the theoretical studies
based on ab initio molecular orbital and density func-
tional theories to evaluate the magnetic interaction. We
at first assumed the structure to be planar for molecule
1. The evaluated effective exchange integrals between
the two radical sites were found to be −153.75 and
−64.50 cm−1 by using UHF (ab initio MO) and
UB3LYP/6-31G (DFT) methods, respectively. Both
calculated results imply that antiferromagnetic interac-
tion is feasible. Next, the conformational effect around
the single bond between the phenylene and TTF groups
(C13–C14), caused by different dihedral angles, was
investigated. The magnetic interactions evaluated by
the UB3LYP/6-31G method were −44.21, −12.16 and
2.22 cm−1 for 30, 60 and 90°, respectively. Interestingly,
for the perpendicular structure a small ferromagnetic
interaction was induced. It is important for the evalua-
tion of the magnetic interaction to take SOMO–SOMO
interactions into account.3d,3f,4c We emphasize also the
considerations in terms of the spin density distributions.
The oxidation potentials measured by cyclic voltamme-
try (CV) on the anion salts, 3−·(Et4N+)13 and 4−·(Et4-
N+),13 were found to be −0.23, −0.04, +0.19 V and
−0.24, +0.06, +0.24 V, respectively.14 These three
reversible cyclic voltammograms are attributable to the
one-electron oxidation from the anions of 6-hydroxy-
phenalenone moieties, the first and second oxidations of
TTF and EDT–TTF moieties, respectively.15 These
observations suggest sufficient donor ability of 1 and 2
to form CT complexes with appropriate acceptors.
Actually, some CT complexes were obtained both from

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Y. Morita et al. / Tetrahedron Letters 42 (2001) 7991–7995
Figure 2. Spin densities of the diradical cation generated by one-electron oxidation from 1 evaluated by the UB3LYP/6-31G
method for singlet and triplet states for the planar (A) and perpendicular (B) structures. White and black regions denote a and
b spin densities, respectively, with a cut-off of 0.001.
3 and 4 with DDQ and F4-TCNQ. Physical properties
1361–1364; (d) Kumai, R.; Matsushita, M. M.; Izuoka,
A.; Sugawara, T. J. Am. Chem. Soc. 1994, 116, 4523–
4524; (e) Nakatsuji, S.; Anzai, H. J. Mater. Chem. 1997,
7, 2161–2174; (f) Sakurai, H.; Izuoka, A.; Sugawara, T. J.
Am. Chem. Soc. 2000, 122, 9723–9734.
of these CT complexes will be reported in due course.
Acknowledgements
4. (a) Yamaguchi, K.; Namimoto, H.; Fueno, T.; Nogami,
T.; Shirota, Y. Chem. Phys. Lett. 1990, 166, 408–414; (b)
Yamaguchi, K.; Okumura, M.; Fueno, T.; Nakasuji, K.
Synth. Met. 1991, 41–43, 3631–3634; (c) Matsuoka, F.;
Yamashita, Y.; Kawakami, T.; Kitagawa, Y.; Yoshioka,
Y.; Yamaguchi, K. Polyhedron 2001, 20, 1169–1176.
5. (a) Hatanaka, K.; Morita, Y.; Ohba, T.; Yamaguchi, K.;
Takui, T.; Kinoshita, M.; Nakasuji, K. Tetrahedron Lett.
1996, 37, 873–876; (b) Hatanaka, K.; Morita, Y.; Ohba,
T.; Yamaguchi, K.; Takui, T.; Kinoshita, M.; Nakasuji,
K. Tetrahedron Lett. 1996, 37, 877–880; (c) Morita, Y.;
Ohba, T.; Haneda, N.; Maki, S.; Kawai, J.; Hatanaka,
K.; Sato, K.; Shiomi, D.; Takui, T.; Nakasuji, K. J. Am.
Chem. Soc. 2000, 122, 4825–4826.
This work was supported by Grants-in-Aid for Scien-
tific Research on Priority Area ‘Delocalized p-Elec-
tronic Systems’ (No. 297) from the Ministry of
Education, Culture, Sports, Science and Technology,
Japan.
References
1. For recent overviews of organic-based magnetic materi-
als, see: (a) Molecular Magnetism; Itoh, K.; Kinoshita,
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Publishers: Tokyo, 2000; pp. 1–347; (b) Magnetic Proper-
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2. For recent overviews of the stable neutral radicals, see:
(a) Forrester, A. R.; Hay, J. M.; Thomson, R. H. Organic
Chemistry of Stable Free Radicals; Academic Press: New
York, 1968; (b) Rozantsev, E. G. Free Nitroxyl Radicals;
Plenum Press: New York, 1970; (c) Aurich, H. G. In
Nitrones, Nitronates and Nitroxides; Patai, S.; Rappo-
port, Z., Eds.; Wiley: Chichester, 1989; Chapter 4; (d)
Volodarsky, L. B.; Reznikov, V. A.; Ovcharenko, V. I.
Synthetic Chemistry of Stable Nitroxides; CRC Press:
Boca Raton, FL, 1994; (e) Iwamura, H.; Koga, N. Acc.
Chem. Res. 1993, 26, 346–351.
6. Selected physical and spectral data. Compound 3: red-
dish–orange powder; mp 175°C; TLC Rf=0.34 (5:1 hex-
1
ane/ethyl acetate); H NMR (270 MHz, CDCl3): l 1.53
(s, 18), 6.35 (s, 2), 6.55 (s, 1), 7.39 (d, 2, J=8.4 Hz), 7.62
(d, 2, J=8.4 Hz), 7.63 (s, 2), 8.67 (s, 2); IR (KBr):
3600–3100, 2953, 1560 cm−1; IR (CCl2CCl2): 3630, 2958,
1744 cm−1; EI-MS, m/z 586 (M+, 100%); FAB-MS, m/z
586 (M+). Anal. calcd for C33H30O2S4(H2O)0.4: C, 66.72;
H, 5.23; N, 0.00. Found: C, 66.99; H, 5.65; N, 0.00%.
Compound 4: orange powder; mp 143–144°C; TLC Rf=
1
0.54 (CH2Cl2); H NMR (270 MHz, CDCl3): l 1.56 (brs,
18), 3.32 (s, 4), 6.1–6.5 (br, 1), 7.3–7.4 (m, 2), 7.4–7.6 (m,
2), 7.6–7.8 (m, 2), 8.5–9.0 (br, 2); IR (KBr): 3600–3100,
2957, 1569 cm−1; IR (CCl2CCl2): 3626, 2958, 1645 cm−1
;
FAB-MS,
m/z
676
(M+).
Anal.
calcd
for
C35H32O2S6(H2O)0.5: C, 61.28; H, 4.85; N, 0.00. Found:
C, 61.21; H, 4.77; N, 0.00%.
3. (a) Nakamura, Y.; Koga, N.; Iwamura, H. Chem. Lett.
1991, 69–72; (b) Sugano, T.; Fukasawa, T.; Kinoshita,
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Yamaga, S.; Nakai, M.; Ohmori, K.; Tsuji, M.; Nakat-
suji, H.; Fujita, H.; Yamauchi, J. Chem. Lett. 1993,
7. The preparation of 8-phenyl-6-hydroxyphenalenone will
be reported elsewhere.
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(b) Wilmarth, W. K.; Schwartz, N. J. Am. Chem. Soc.
1955, 77, 4543–4551.

Y. Morita et al. / Tetrahedron Letters 42 (2001) 7991–7995
7995
9. Selected physical and spectral data. Compound 1: dark-
green solid; mp 76–78°C; TLC (alumina) Rf=0.62 (3:1
hexane/ethyl acetate); IR (KBr): 2963, 1570 cm−1. Anal.
calcd for C33H29O2S4(H2O)0.3: C, 67.04; H, 5.05; N, 0.00.
Found: C, 66.94; H, 4.88; N, 0.00%. Compound 2: dark-
green solid; mp 215–216°C; TLC (alumina) Rf=0.37 (1:3
hexane/CH2Cl2); IR (KBr): 2962, 1592 cm−1. Anal. calcd
for C35H31O2S6(H2O)0.6: C, 61.21; H, 4.73; N, 0.00.
Found: C, 61.25; H, 4.93; N, 0.00%.
interaction for the rotation angle are also discussed in the
case of the TTF–(a-nitronyl nitroxide) model molecule.
See Ref. 4c.
13. These anion salts were prepared from 3 and 4 by the
treatment of NaOMe and Et4NCl in THF–MeOH.
14. CV was carried out by the following conditions: 3 mM in
DMF with 0.1 M Et4NClO4 as supporting electrolyte at
room temperature against Fc/Fc+; Au working electrode
and Pt counter electrode; 0.05 V/s.
10. The radical purity can be estimated by TLC analysis.
11. McLachlan, A. D. Mol. Phys. 1960, 3, 233–252.
12. Similar remarkable variations in intramolecular magnetic
15. The oxidation potentials of TTF and EDT–TTF under
the same conditions were as follows: −0.09, +0.15 V;
+0.02, +0.20 V.