Route towards diselenadiazafulvalenes

Article abstract of DOI:10.1039/b101757h

The first diselenadiazafulvalene has been chemically synthesised and electrochemically characterised, it presents similar air sensitiveness to its sulfur analogue and affords a spiroamide derivative upon oxidation as confirmed by its crystal structure.

Full text of DOI:10.1039/b101757h

Route towards diselenadiazafulvalenes
ˆ
Zdenko Casar,a Patricia Bénard-Rocherullé,b Alenka Majcen-Le Maréchalc and Dominique
Lorcy*a
a Synthèse et Electrosynthèse Organiques, UMR CNRS 6510, Université de Rennes 1 35042, Rennes
cedex, France. E-mail: Dominique.Lorcy@univ-rennes1.fr
b Chimie du solide et inorganique moléculaire, UMR CNRS 6511, Université de Rennes 1 35042,
Rennes cedex, France
c
University of Maribor, Smetanova 17 2000, Maribor, Slovenija
Received (in Cambridge, UK) 23rd February 2001, Accepted 1st June 2001
First published as an Advance Article on the web 27th June 2001
The first diselenadiazafulvalene has been chemically syn-
thesised and electrochemically characterised, it presents
similar air sensitiveness to its sulfur analogue and affords a
spiroamide derivative upon oxidation as confirmed by its
crystal structure.
Among the numerous p-donor molecules described in the
literature as precursors of organic materials various heterocyclic
derivatives have been studied, mainly conjugated frameworks
including sulfur atoms, such as tetrathiafulvalene (TTF).1
Several modifications of the TTF skeleton have been per-
formed, for example replacement of two sulfur atoms by
nitrogen atoms has led to dithiadiazafulvalene (DTDAF)
derivatives which have recently attracted attention owing to
their high electron donating properties.2 DTDAFs present the
disadvantage of being air-sensitive in the neutral form but they
can be trapped in situ by organic or inorganic acceptors and
form molecular materials.3 As the physical properties of organic
materials are close-knit to molecular assembly, it was thus of
interest to replace the sulfur atoms by selenium atoms, in order
to increase the interactions between the donor cores. Otherwise
diselenadiazafulvalene (DSeDAF) should exhibit properties
close to DTDAF. Herein, we report the synthesis and the
electrochemical behaviour of the first DSeDAF, namely benzo-
DSeDAF, starting from selenazole moieties.
Scheme 1 Reagents and conditions: i, NaSH, NaOH, CS2, H2O, reflux,
90%; ii, MeI, NEt3, CH2Cl2, rt, 93%; iii, I2, 200–220°C, 67%.
in the presence of boron trifluoride diethyl etherate and triethyl
orthoformate into 2-alkylthiobenzo-1,3-selenazolium salts 5,
following literature precedent for thiazole derivatives.2 Another
method for the preparation of this salt 5 utilises the alkylation of
3 with methyl iodide (Scheme 2).
Scheme 2 Reagents and conditions: BF3·Et2O, CH(OEt)3, CHCl3, reflux,
97%; ii, MeI, reflux, 81%; iii,NaHSe, EtOH, rt, 95%.
Compared to the chemistry carried out on 1,3-thiazole ring
systems, 1,3-selenazole derivatives have been scarcely studied
recently. Indeed, and as pointed out by Bogert et al., selenazole
derivatives are rather more difficult to prepare and less stable
than their sulfur analogues.4 Our approach for the synthesis of
the 1,3-selenazole core consists of the preparation of bis(o-
nitrophenyldiselenide) 1 starting from o-nitroaniline.5
We improved the chemical pathway to prepare benzo-
1,3-selenazole-2(3H)-thione 2 by reaction of bis(o-nitrophe-
nyldiselenide) 1 with sodium hydrosulfide in basic medium
followed by the addition of carbon disulfide as described in
Scheme 1.6 Alkylation of 2 in the presence of base and methyl
iodide led to 2-methylthiobenzo-1,3-selenazole 3.7 Preparation
of the sulfur analog of 4, the 3-alkylbenzo-1,3-thiazole-2(3H)-
thione by rearrangement of 2-alkylthiobenzo-1,3-thiazole in the
presence of a catalytic amount of iodine has been described.8
Thus, we investigated the possibility of forming 3-me-
thylbenzo-1,3-selenazole-2(3H)-thione 4 using the same strat-
egy starting from 3. Heating a mixture of 3 with iodine at
200–220 °C gave 4 in 67% yield (Scheme 1). Selenazole-2(3H)-
thione 4 does not undergo intermolecular coupling by treatment
with tertiary phosphorus derivatives. Therefore, we converted 4,
Then, we treated 2-alkylthiobenzo-1,3-selenazolium salts 5
with sodium hydrogen selenide and we isolated the 3-me-
thylbenzo-1,3-selenazole-2(3H)-selone 6.† Coupling of 6 in the
presence of triethyl phosphite in refluxing toluene under an inert
atmosphere afforded DSeDAF 7. Formation of this novel p-
donor molecule can be observed by the important change of
colour of the medium, due to the formation of a conjugated
framework (Scheme 3).
Presence of electroactive species can be confirmed by cyclic
voltammetry directly on the medium where the donor was
formed.9 Therefore after the chemical coupling of 6 in the
presence of triethyl phosphite we added, under inert atmos-
phere, a degassed solution of tetrabutylammonium hexa-
fluorophosphate in CH2Cl2 and we performed electrochemical
investigations. Two reversible monoelectronic waves are ob-
served at low potentials on the cyclic voltammogram and are
associated with the redox behaviour of the DSeDAF formed in
the medium. They correspond respectively to the formation of
the radical cation and dication of 7 (Epa1 = 20.07 V and Epa2
= +0.09 V vs SCE) and indicate an extremely good donor
character of benzo-DSeDAF. These oxidation potentials are
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Chem. Commun., 2001, 1336–1337
This journal is © The Royal Society of Chemistry 2001
DOI: 10.1039/b101757h

into the spiro amide derivative or further into a ten-membered
ring compound.11–13
In summary, a novel heterocyclic donor has been synthesised,
namely the benzo-DSeDAF, opening a route to a new family of
p-donor molecules. This derivative exhibits similar redox
behaviour and air-sensitivity to its sulfur analogue. Work is
currently in progress in order to trap this derivative with
appropriate acceptors and to analyse the potentialities of this
new type of donor.
We thank Thierry Roisnel for performing the X-ray diffrac-
tion data collection.
Scheme 3 Reagents and conditions: i, P(OEt)3, toluene, reflux; ii, AgBF4,
THF, rt.
Notes and references
† Selected data for 6 (which was prepared in a scale up to 1.2 g): yellow
crystals, mp 100 °C; dH(CDCl3) 3.97 (s, 3H), 7.28–7.69 (m, 4H); Elemental
analysis: calcd.for C8H7NSe2: C, 34.93; H, 2.57; N, 5.09. Found: C, 35.08;
H, 2.55; N, 4.72%; for 8: colorless powder, dH(CD3CN) 4.12 (s, 6H),
7.78–8.55 (m, 8H); for 9: colorless crystals, mp 193 °C; dH(CDCl3) 3.07 (s,
3H), 3.47 (s, 3H), 6.51–6.63 (m, 1H), 6.70–6.83 (m, 1H), 6.95–7.41 (m,
6H).
‡ Crystal data for compound 9 C16H14N2OSe2, M = 408.21, monoclinic,
space group P21/c, a = 5.883(5), b = 15.922(5), c = 16.188(5) Å, b =
98.954(5)°, U = 1497.8(14) Å3, Z = 4, T = 293(2) K, m(Mo-Ka) = 4.94
mm21, Dc = 1.810 g cm23, 19344 reflections measured, of which 4370
independent (Rint = 0.0911) Rf = 0.054 [2906 data, I > 2s(I)], wR(F2) =
0.148. The largest residual density peak (1.45 e Å23) is located close to the
Se2 atom (0.94 Å). CCDC 164964. See http://www.rsc.org/suppdata/cc/b1/
b101757h/ for electronic files in .cif or other format.
slightly higher than the one observed for the benzo-DTDAF10
also obtained in situ following the same experimental procedure
(Epa1 = 20.15 V and Epa2 = +0.05 V vs SCE). In order to
prepare the dicationic salt of benzo-DSeDAF, chemical oxida-
tion was performed by adding a solution of AgBF4 in the
medium where 7 was formed. The first dicationic, benzo-
DSeDAF 8, was obtained as its BF4 salt together with a minor
amount of a neutral compound (Scheme 3). 1H NMR data and
X-ray crystal structure determination of the latter proved this
compound to be the spiroamide 9.‡ As shown Fig. 1, the
4-methylbenzo-2H-1,4-selenazin-3(4H)-one ring is folded
along the Se2–C4 vector, where the angle between the planes
formed by Se2, C3, C7, N2, C4 and Se2, C1, C4 is 122.3 (2)°
and N2 lies 0.200(3)Å from the first plane. The benzoselenazole
system is not planar owing to a slight fold along the Se1–N1
vector leading to a torsion angle of 155.3(3) ° between the two
planes formed by Se1, C2, C6, N1 and Se1, C1, N1,
respectively.
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The behavior of 7 is closely related to what was observed
with its sulfur analogue the benzo-DTDAF. Indeed, in the
presence of air benzo-DTDAF is easily oxidised and converted
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Fig. 1 Molecular structure of spiroamide 9 (50% displacement ellip-
soids).
Chem. Commun., 2001, 1336–1337
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