Synthesis of diselenadiazafulvalenes and influence of steric strain on their anodic behavior

Article abstract of DOI:10.1039/b203317h

A novel family of π-donor molecules, the diselenadiazafulvalenes (DSeDAFs), is presented. The synthetic approach to these donors, from o-nitroaniline, allows the formation of N,N′-dimethyldibenzo DSeDAF and N,N′-ethylenedibenzo DSeDAF. Comparative electrochemical study of these π-donor molecules demonstrates their excellent donor ability and the stabilizing effect of the ethylene bridge on the cation radical species.

Full text of DOI:10.1039/b203317h

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Synthesis of diselenadiazafulvalenes and influence of steric strain
on their anodic behavior
a,b
b
c
a
˘
Zdenko Casar, Ivan Leban, Alenka Majcen-Le Maréchal and Dominique Lorcy*
1
a
Synthèse et Electrosynthèse Organiques, UMR 6510, Université de Rennes I,
Campus de Beaulieu, 35042 Rennes, France
b
Faculty of Chemistry and Chemical Technology, University of Ljubljana, A s˘ ker c˘ eva 5,
000 Ljubljana, Slovenia
1
c
University of Maribor, Smetanova 17, 2000 Maribor, Slovenia
Received (in Cambridge, UK) 4th April 2002, Accepted 21st May 2002
First published as an Advance Article on the web 11th June 2002
A novel family of π-donor molecules, the diselenadiazafulvalenes (DSeDAFs), is presented. The synthetic approach
to these donors, from o-nitroaniline, allows the formation of N,N Ј-dimethyldibenzoDSeDAF and N,N Ј-ethylene-
dibenzoDSeDAF. Comparative electrochemical study of these π-donor molecules demonstrates their excellent donor
ability and the stabilizing effect of the ethylene bridge on the cation radical species.
Several heterocyclic systems have been used as precursors of
organic materials, mainly built on the fulvalene framework
1
including heteroatoms such as sulfur or selenium. In order
to tune the electronic properties of the donor, substitution
of one or more heteroatoms within the fulvalene skeleton has
2
been performed. For example, the diselenadiazafulvalene 1
(
DSeDAF), an aza analogue of tetraselenafulvalene (TSF),
3
exhibits high electron-donating properties. Therefore, 1 is
oxygen-sensitive, as evidenced by the spiroamide derivative
3
obtained after oxidation of a DSeDAF. An interesting feature
is the fact that for 1 the cation radical species detected by cyclic
voltammetry (CV) is stable within a narrow potential window,
and a dicationic diamagnetic salt is easily obtained. Neverthe-
less, most of the physical properties (conductivity, magnetism,
etc.) in organic materials are ascribed to the presence of radical
species. It has been shown in the case of the N,N Ј-dimethyl-
dithiadiazafulvalene 2 (DTDAF) that this narrow potential
window is due to reduced Coulombic interactions associated4
with conformational modifications upon electron transfer.
Consequently the introduction of an N,NЈ-bridge between the
two heterocyclic rings hinders such structural changes and
increases the electrochemical domain of stability of cation rad-
Chart 1
5
icals. The same effect is therefore expected in DSeDAFs with
the introduction of a N,NЈ-bridge between the two selenazole
rings. In a preliminary communication we reported a route
3
towards N,N Ј-dimethyldibenzoDSeDAF 1. Therefore, it was
of interest to investigate the possibility of extending this route
to N,N Ј-ethylene-bridged dibenzo-DSeDAF 3 (Chart 1). In this
article we report full experimental details of the synthesis
of both N,N Ј-dimethyl- and N,N Ј-ethylene-bridged dibenzo-
DSeDAF and the analysis of their electron-donating properties.
Scheme 1 Reagents and conditions: i, BF ؒEt O, t-BuONO, CH Cl ,
3
2
2
2
Ϫ15 ЊC; ii, KSeCN, H O, 0 ЊC; iii, Na, EtOH; iv, NaSH, CS , HCl.
2
2
Our key material is bis(o-nitrophenyl) diselenide 6 which is
smoothly prepared from o-nitroaniline in high overall yield
7
(
71%) via an isolable arenediazonium salt 4. Reaction of
potassium selenocyanate with 4 gave 5. Treatment of 5 with
Results and discussion
The common approach to the synthesis of N,N Ј-dimethyl- or
N,N Ј-bridged dibenzo-DSeDAF consists first in the prepar-
ation of bis(o-nitrophenyl) diselenide and then formation of the
sodium in ethanol induces the formation of sodium o-nitro-
8
benzene selenolate, which couples to afford 6.
The key to the short synthesis of 3H-benzoselenazole-
2-thione 7 is the in situ reduction of 6 into the presumable
intermediate o-aminobenzeneselenolate with sodium hydro-
sulfide, followed by cyclization with carbon disulfide in basic
medium, and then acidic treatment. This route becomes simpler
1
,3-selenazole core (Scheme 1). The synthesis of benzoselen-
azole-2-thione 7, starting from o-nitroaniline, was described
6
some decades ago. The chemistry of benzo-1,3-selenazole has
6,9
been scarcely studied recently. Therefore, we decided to improve
the chemical pathway to benzoselenazole-2-thione 7 with
regard to the yields, quantity (multi-gram scale) and simplicity.
compared with those described earlier.
The next step involves the reaction of alkyl halides with
benzoselenazole-2-thione. Alkylation in the presence of base is
1
568
J. Chem. Soc., Perkin Trans. 1, 2002, 1568–1573
This journal is © The Royal Society of Chemistry 2002
DOI: 10.1039/b203317h

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not in favor of direct N-alkylation but rather affords S-alkyl-
isolated the N,N Ј-di alkylated derivative (12; see below) using
ation. Using methyl iodide in the presence of triethylamine,
this procedure.
3
2
-(methylsulfanyl)benzoselenazole 8 was isolated (Scheme 2).
Since N-methylbenzoselenazole-2-thiones such as 9 can be
conveniently prepared from 2-(methylsulfanylbenzoselenazoles
such as 8 by thermal rearrangement in the presence of iodine,
we investigated the possibility of forming N,N Ј-ethylene-
bisbenzoselenazole-2-thione by applying the same strategy to
Interestingly, 2-(methylsulfanyl)benzoselenazole 8, as its benzo-
2
,2Ј-(ethylenedisulfanyl)bis(benzoselenazole) 10. Treatment of
1
0 with iodine at a temperature up to 250 ЊC led to 12 in moder-
ate yield (28%) (Scheme 4). Crystal structure of compound 12
was determined by an X-ray diffraction study (Fig. 2)†.
Scheme 2 Reagents and conditions: i, Mel, NEt , CH Cl ; rt, ii, I ,
3
2
2
2
2
00–220 ЊC.
10,11
thiazole analog,
undergoes thermal rearrangement in the
presence of iodine, and we found that N-methylbenzo-
selenazole-2-thione 9 is obtained in good yield upon identical
treatment of compound 8.
For the synthesis of the N,N Ј-ethylene-bridged derivatives we
needed to link two benzoselenazole rings by an ethylene bridge
system and therefore we used ethylene dibromide as the
alkylating agent. Addition of half an equivalent of ethylene
dibromide to benzoselenazole-2-thione 7 in the presence of
potassium carbonate afforded the product 10 resulting from
S,S-intermolecular alkylation (66%), together with a minor
amount of the N,S-intermolecular dialkylated derivative 11
(
7%) (Scheme 3). The structure of compound 10 was con-
firmed by an X-ray diffraction study.† Compound 10 crystal-
lizes with three molecules in the asymmetric unit as can be
seen in Fig. 1. These three molecules have different conform-
ational arrangements essentially due to the ethylene link.
Partial direct N-alkylation (e.g. 11) is possible but we never
Fig. 2 View of the molecular structure of 3,3Ј-ethylenebis(benzo-
selenazole-2-thione) 12. The two crystallographically independent
molecules, each of them located on an inversion center, are shown.
The final step towards DSeDAF does not involve the coup-
ling reaction of 9 or 12 to form the central double bond of the
donor molecules. As N-alkylbenzoselenazole-2-thiones do not
(
in our hands) undergo inter- (for 9) or intramolecular (for 12)
coupling by treatment with trivalent phosphorus derivatives
they were converted into the corresponding selones, as shown in
Scheme 5. First, 9 and 12 were quantitatively alkylated on the
exocyclic sulfur with a strong alkylating agent such as diethoxy-
12
carbonium tetrafluoroborate, which was formed in situ from
BF ؒEt O and triethyl orthoformate. Due to the low solubility
3
2
of the bisbenzoselenazole-2-thione 12, alkylation did not occur
in refluxing chloroform as for 9, but 3,3-ethylenebis-[2-(ethyl-
sulfanyl)benzoselenazolium tetrafluoroborate] 15 was obtained
in excellent yield in boiling toluene. Treatment of the salts 13
and 15 with sodium hydrogen selenide led, respectively, to
the benzoselenazole-2-selone 14 and the bisbenzoselenazole-2-
selone 16 in excellent yields (Scheme 5).
Finally, intermolecular coupling of the benzoselenazole-2-
selone 14 in the presence of triethyl phosphite in refluxing tolu-
ene under inert atmosphere afforded the dibenzo-DSeDAF 1,
while bisbenzoselenazole-2-selone derivative 16 underwent
intramolecular coupling give to N,N Ј-ethylene-bridged donor 3
(
Scheme 6). Due to air-sentivity, these donors are difficult to3
isolate without undergoing further oxidation with oxygen.
Therefore, in order to get informations on their redox proper-
ties we undertook electrochemical investigations directly on the
medium where the donors were formed by adding the reaction
mixture, under inert atmosphere, to a degassed solution of
Fig. 1 View of the molecular structure of 2,2Ј-(ethylenedisulfanyl)-
bis(benzoselenazole) 10. The three crystallographically independent
molecules, each of them located on an inversion center, are shown.
†
CCDC reference number(s) 183223–183224. See http://www.rsc.org/
tetrabutylammonium hexafluorophosphate in CH Cl . The
oxidation potentials of dibenzo-DSeDAFs obtained by CV are
suppdata/p1/b2/b203317h/ for crystallographic files in .cif or other
electronic format.
2
2
Scheme 3 Reagents and conditions: i, BrCH CH Br, K CO , EtOH.
2
2
2
3
J. Chem. Soc., Perkin Trans. 1, 2002, 1568–1573
1569

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Table 1 Oxidation potentials (V) vs SCE obtained after chemical
a
coupling of benzoazoleselone derivatives
Epa
1
/V
Epa
2
/V
∆E/mV
DSeDAF 1
Ϫ0.07
Ϫ0.17
Ϫ0.18
Ϫ0.23
ϩ0.09
Ϫ0.02
ϩ0.36
ϩ0.26
160
150
540
490
1
3
N,N Ј-dimethyldibenzo-DTDAF
DSeDAF 3
1
3
N,N Ј-ethylenedibenzo-DTDAF
a
Ϫ1
Pt working electrode with 0.1 M n-Bu NPF ; scanning rate 0.1 V s
.
4
6
Scheme 4 Reagents and conditions: i, I , 250 ЊC.
2
Fig. 3 Cyclic voltammograms performed on the medium where the
DSeDAFs 1 and 3 were formed, Bu NPF (0.5 M), CH Cl , platinum
4
6
2
2
Ϫ1
electrode; scanning rate 0.1 V s , vs SCE.
waves, associated with the redox behavior of the donors, were
observed at low potentials (Fig. 3). The introduction of selen-
ium atoms instead of the sulfur ones only slightly decreased the
donor ability. Furthermore, the potential difference observed
between the two oxidation states (∆E = Epa
2
Ϫ Epa ) for
1
N-methyl-substituted donors is smaller than in the case of
N,N Ј-ethylene-bridged donors. Indeed, the presence of a bridge
between the two heterocyclic rings hinders conformational
modification upon oxidation and therefore due to Coulombic
interactions the removal of the second electron is more difficult
in the case of 3 than for 1.
In summary we have developed a strategy that allowed us to
reach DSeDAFs via alkylation of benzoselenazole rings. For
that purpose an improved synthesis of benzoselenazole-2-
thione has been performed. The key step of this strategy
involves the thermal rearrangement of a 2-(alkylsulfanyl)-
benzoselenazole into the N-alkylbenzoselenazole-2-thione. We
show also that the general procedure can be successfully
applied to the synthesis of either N,N Ј-dimethyldibenzo-
DSeDAF or the hitherto unknown N,N Ј-ethylene-bridged
dibenzo-DSeDAF. Both molecules are excellent donors and
exhibit close redox properties but the presence of an ethylene
bridge increases the potential domain of stability of the cation
radical species.
Scheme 5 Reagents and conditions: i, BF ؒEt O, CH(OEt) , reflux;
3
2
3
ii, NaSeH, EtOH, rt.
Experimental
1
H NMR spectra were recorded in CDCl , unless otherwise
3
13
indicated, at 200 and 300 MHz, and C NMR spectra at 50 and
5 MHz. Chemical shifts are reported in ppm referenced to
7
TMS. Melting points were measured using a Kofler hot-
stage apparatus and are uncorrected. Elemental analyses were
obtained from the Laboratoire Central de Microanalyse du
CNRS (Lyon) and from the Faculty of Chemistry and
Chemical Technology, University of Ljubljana, Slovenia.
Column chromatography was performed on silica gel 60
(0.040–0.063 mm). CH Cl was dried by refluxing over P O
Scheme 6 Reagents and conditions: i, P(OEt) , toluene, reflux.
3
listed in Table 1 together with the redox potentials of the
N,N Ј-dimethyl- and N,N Ј-ethylene-bridged dibenzo-DTDAFs
13,14
prepared by Hünig
et al. for comparison. After either
2
2
2
5
intermolecular or intramolecular coupling two main oxidation
followed by distillation, and toluene was dried by refluxing over
1
570
J. Chem. Soc., Perkin Trans. 1, 2002, 1568–1573

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NaH followed by distillation. Petroleum ether refers to the
(24.72 g, 617.92 mmol) were placed in a 1 L flask fitted with
fractions boiling in the range 40–65 ЊC.
a condenser, and 200 mL of water was added. The sus-
pension was stirred at room temperature until the formation of
2
-Nitrobenzenediazonium tetrafluoroborate 4
a red–brown solution. Then CS (64 mL) was added and the
2
reaction mixture was heated at reflux for 2 h and then stirred at
room temperature for 14 h. The red solution was concentrated
to approximately 100 mL by evaporation of unchanged
To a solution of BF ؒEt O (35.97 g, 0.253 mol), cooled
3
2
at Ϫ15 ЊC, was added a solution of o-nitroaniline (23.32 g,
.168 mol) in 250 mL of dry CH Cl . The suspension was
0
2
2
CS and partial evaporation of water. Excess of NaSH was
2
stirred at Ϫ15 ЊC for 15 min. Then a solution of tert-butyl
nitrite (23.25 g 0.203 mol) in 100 mL of dry CH Cl was added
dropwise to the vigorously stirred reaction mixture. After
complete addition of the reactant, this mixture was stirred at
Ϫ15 ЊC for 30 min and then at 0 ЊC for 30 min. Cold pentane
eliminated from the solution by slow addition of 130 mL of
2
2
2
6% aq. HCl Caution! For trapping the highly toxic H2S
gas formed during the addition of acid the flask was hermetic-
ally closed with a septum and connected in series to three
traps, each containing 250 mL of saturated aq. NaOH. The
alkaline solution of NaSH obtained in the traps was sub-
sequently oxidized with aq. NaOCl and neutralized with dilute
H SO (both operations were performed on an ice–acetone-
(
200 mL) was added to the suspension and the precipitate was
filtered off and washed with cold dry diethyl ether (200 mL).
Diazonium salt 4 was obtained in quantitative yield as a pale
brown powder, and used without further purification. Mp 94 ЊC
2
4
bath in a well-ventilated hood). After complete addition of acid
the pH of the solution was brought to 1 and a yellow–green
precipitate was obtained. Then the pH of solution was adjusted
to 10 by addition of saturated aq. NaOH and the suspension
was heated to reflux and stirred at reflux until the formation
of a red solution. The reaction mixture was cooled to
room temperature and dilute HCl was added until pH = 1. The
green precipitate was filtered off and dried. The resulting
green powder was suspended in acetone (300 mL) and
acetone-insoluble side-product (sulfur) was filtered off. The
orange filtrate was evaporated under reduced pressure to give
10.27 g (98%) of crude product as an orange crystalline
1
3
(
dec.); H NMR (acetone-d ) δ 9.43–9.26 (1H, dd, J = 8.1 Hz,
6
3 4
4
J = 1.3 Hz), 9.16–8.95 (1H, dd, J = 8.3 Hz, J = 1.3 Hz),
3
4
8
.93–8.74 (1H, td, J = 8.3 Hz, J = 1.3 Hz), 8.73–8.51 (1H, td,
3
4 13
J = 8.1 Hz, J = 1.3 Hz); C NMR (acetone-d ) δ 146.50,
6
1
44.30, 138.54, 138.12, 129.64, 111.89.
o-Nitrophenyl selenocyanate 5
The amount of 2-nitrobenzenediazonium tetrafluoroborate 4
obtained above was divided into four equal portions and
treated as follows. To a solution of 2-nitrobenzenediazonium
tetrafluoroborate 4 (10.00 g, 42.10 mmol) in cold water (200 mL)
was added a solution of KSeCN (6.14 g, 42.62 mmol) in 50 mL
of water dropwise (5 min) at 0 ЊC. After complete addition of
KSeCN, the suspension was stirred at 0 ЊC for 10 min and the
precipitate was filtered off. The crude product obtained in the
four similar experiments was fused and used in the next step
without further purification. In order to obtain analytically
pure compound a small sample was subjected to flash chrom-
atography over silica gel using methylene dichloride as eluant.
The yellow solution was dried over Na SO and the solvent was
powder, which was recrystallized from 130 mL of MeOH–H O
2
(2.25 : 1 v/v) mixture to give 9.46 g (90%) of benzoselenazole-2-
6
thione 7 as yellow needles, mp 159 ЊC (lit., 159 ЊC); Rf
1
(CH Cl ) 0.45; H NMR δ 11.86 (1H, br s), 7.60–7.47 (1H, dd,
2
2
3
4
13
J = 7.8 Hz, J = 1 Hz), 7.43–7.15 (3H, m); C NMR δ 194.46,
141.97, 130.74, 127.61, 125.42, 125.33, 113.92. Calc. for
C H NSSe: C, 39.26; H, 2.35; N, 6.54. Found: C, 38.97; H, 2.06;
7
5
N, 6.24%.
2
4
evaporated. The yellow powder was then recrystallized from
2-(Methylsulfanyl)benzoselenazole 8
EtOH and gave title compound 5 as yellow needles, R (CH Cl )
f
2
2
To a suspension of 7 (5.50 g, 25.68 mmol) in CH Cl (30 mL)
8
1
2
2
0
.79; mp 142 ЊC (lit., 142 ЊC); H NMR δ 8.55–8.39 (1H,
3 4 3
were added a solution of iodomethane (5.47 g, 38.52 mmol)
in CH Cl (10 mL) and a solution of trimethylamine (5.21 g,
dd, J = 8.3 Hz, J = 1.5 Hz), 8.31–8.13 (1H, dd, J = 8.1 Hz,
4
3
4
2
2
J = 1 Hz), 7.86–7.71 (1H, td, J = 8.1 Hz, J = 1.5 Hz), 7.70–
5
1.37 mmol) in CH Cl (10 mL). The reaction mixture was
3
4
13
2 2
7
1
.54 (1H, td, J = 8.3 Hz, J = 1 Hz); C NMR δ 144.96, 136.57,
31.47, 129.44, 127.01, 126.25, 104.88. Calc. for C H N O Se:
stirred for 10 min and then extracted with water (5 × 30 mL).
7
4
2
2
The organic phase was dried over Na SO . Evaporation of the
2
4
C, 37.03; H, 1.78; N, 12.34. Found: C, 36.85; H, 1.72; N,
2.19%.
solvent afforded a dark orange oil, which was distilled twice.
Kugelrohr, 0.04 mbar,‡ 115 ЊC) to give 5.45 g (93%) of com-
1
(
1
pound 8 as a yellow oil, R (CH Cl ) 0.70; H NMR δ 7.94–
f
2
2
Bis(o-nitrophenyl) diselenide 6
3
4
7
.80 (1H, dd, J = 8.1 Hz, J = 1.3 Hz), 7.78–7.66 (1H, dd,
4 3
3
To a suspension of o-nitrophenyl selenocyanate 5 in 600 mL of
absolute EtOH was slowly added sodium (4.00 g, 173.91
mmol), cut into small pieces, over a 10-min period. After
complete addition of sodium the reaction mixture was stirred
for 1 h at room temperature. The green precipitate was filtered
off and washed with 1200 mL of EtOH to give 36.59 g of a
green powder. The crude product was suspended in 370 mL
of toluene and the suspension was heated to boiling. The hot
suspension was filtered to remove toluene-insoluble side-
products. Upon cooling, bis(o-nitrophenyl) diselenide 6 precipi-
tated. Filtration afforded 24.20 g of compound 6 as yellow
plates (71%, calculated on starting o-nitroaniline), mp 215 ЊC
J = 7.8 Hz, J = 1.3 Hz), 7.45–7.29 (1H, td, J = 7.3 Hz,
4
3
4
J = 1.3 Hz), 7.22–7.09 (1H, td, J = 7.3 Hz, J = 1.3 Hz), 2.71
13
(3H, s); C NMR δ 170.15, 155.30, 138.56, 126.65, 124.75,
124.64, 123.28, 17.22. Calc. for C NSSe: C, 42.11; H, 3.09; N,
H
7
8
6.14. Found: C, 42.63; H, 3.01; N, 6.13.%
N-Methyl-3H-benzoselenazole-2-thione 9
A 25 mL round-bottom flask containing 2-(methylsulfanyl)-
benzoselenazole 8 (4.99 g, 21.87 mmol) and 0.21 g of iodine
was placed in a metallic bath. The temperature of the bath was
maintained between 206 and 220 ЊC while the reaction mixture
was stirred for 8 h. Upon cooling to room temperature the
reaction mixture solidified and a brown solid was obtained. The
solid was dissolved in CH Cl and the dark brown solution
8
1
(
lit., 209 ЊC); R (CH Cl ) 0.84; H NMR δ 8.42–8.24 (2H,
f
4
2
2
3
3
dd, J = 8.1 Hz, J = 1.5 Hz), 7.94–7.78 (2H, dd, J = 7.6 Hz,
4
13
2
2
J = 1.6 Hz), 7.57–7.28 (4H, m); C NMR δ 146.96, 135.21,
was extracted with 5% aq. Na SO (30 mL). The organic layer
2
3
1
3
32.03, 129.19, 128.06, 126.83. Calc. for C H N O Se : C,
5.84; H, 2.01; N, 6.97. Found: C, 36.31; H, 1.97; N, 6.83%.
12 8 2 4 2
was dried over Na SO and evaporated. The residue was puri-
2
4
fied by flash chromatography over silica gel (CH Cl ) to afford a
2
2
yellow solid 4.89 g (98%). Recrystallization from EtOH gave
3
H-Benzoselenazole-2-thione 7
3
.36 g (67%) of N-methylbenzoselenazole-2-thione 9 as a pale
Bis-(2-nitrophenyl) diselenide 6 (9.88 g, 24.57 mmol), well-
5
powdered NaSHؒH O (32.65 g, 440.78 mmol) and NaOH
‡ 1 bar = 10 Pa.
2
J. Chem. Soc., Perkin Trans. 1, 2002, 1568–1573
1571

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6
1
yellow powder, mp 80 ЊC (lit., 80 ЊC); R (CH Cl ) 0.79; H
presence of some 12. The filtrate was evaporated under reduced
f
1
2
2
3
NMR δ 7.65–7.10 (4H, m), 3.85 (3H, s); C NMR δ 192.89,
43.88, 127.90, 127.52, 125.65, 125.36, 114.49, 34.50. Calc. for
pressure to give a brown semi-solid, which was flash chromato-
graphed over silica gel (CH Cl ). Fractions which contained 12
1
2
2
C H NSSe: C, 42.11; H, 3.09; N, 6.14. Found: C, 42.45; H, 3.03;
were collected, combined, and dried (Na SO ). Evaporation of
8
7
2
4
N, 5.90%.
CH Cl and recrystallization in 10 mL of pyridine afforded the
2 2
remaining quantity of 12 as yellow needles, yield 1.99 g (28%),
1
2
,2Ј-(Ethylenedisulfanyl)bis(benzoselenazole) 10
R (CH Cl ) 0.79; mp 286–288 ЊC (dec.); H NMR (DMSO-d )
f
2
2
6
3
4
δ 7.87–7.77 (2H, dd, J = 7.8 Hz, J = 1 Hz), 7.57–7.23 (6H, m),
.89 (4H, s); C NMR (DMSO-d ) δ 193.64, 142.69, 127.14,
26.90, 125.64, 125.09, 113.83, 42.70. Calc. for C H N S Se :
3
H-Benzoselenazole-2-thione 7 (15.00 g, 70.04 mmol) and
13
4
1
6
K CO (9.68 g, 70.04 mmol) were suspended in EtOH (50 mL).
2
3
16
12
2
2
2
The suspension was heated to reflux and ethylene dibromide
6.58 g, 35.02 mmol), as a solution in 10 mL of EtOH, was
C, 42.30; H, 2.66; N, 6.17. Found: C, 42.20; H, 2.63; N,
(
6
.13%.
added in one portion. Immediately a white precipitate began to
form from the yellow turbid reaction mixture. The reaction
mixture was vigorously stirred at reflux for 30 min, then was
cooled to room temperature. The precipitate was filtered off
and dried to give pale brown powder, which was suspended in
2
-(Ethylthiosulfanyl)-1,3-benzoselenazolium tetrafluoroborate 13
To a solution of N-methyl-3H-benzoselenazole-2-thione 9
0.78 g, 3.41 mmol) in CHCl (30 mL) were added solutions of
(
3
CH Cl (250 mL). The suspension was stirred at room temper-
2
2
CH(OEt) (2.03 g, 13.7 mmol) in 10 mL of CHCl , and BF ؒ
3
3
3
ature for 1 h. Undissolved inorganic salts (white precipitate)
were filtered off. The brown filtrate was evaporated under
reduced pressure to give 13.22 g of crude product as a pale
brown powder. The crude product was suspended in 60 mL of
acetone and the suspension was heated to boiling. The hot sus-
pension was filtered to remove the slightly acetone-soluble 10.
After drying, compound 10 was obtained as a white crystalline
powder. The filtrate was evaporated and the brown residue was
Et O (2.58 g, 18.2 mmol) in 10 mL of CHCl . The reaction
2
3
mixture was stirred at reflux for 1 h, then was allowed to reach
room temperature and approximately 3/4 of the solvent was
removed under reduced pressure. Diethyl ether was added to
the reaction mixture and a light brown solid precipitated out.
The precipitate was filtered off, washed with diethyl ether, and
dried to give 1.10 g (93%) of salt 13 as a light brown powder, mp
1
3
1
78 ЊC; H NMR (CD CN) δ 8.46–8.35 (1H, dd, J = 8.1 Hz,
3
3 4
4
chromatographed over silica gel (CH Cl –petroleum ether 1 : 1)
2
2
J = 0.8 Hz), 8.20–8.08 (1H, dd, J = 8.3 Hz, J = 0.8 Hz), 8.05–
to afford the remaining quantity of 10, and the isomer 11 as a
major side-product of the reaction.
7
.91 (1H, m), 7.90–7.75 (1H, m), 4.21 (3H, s), 3.75 (2H, q,
13
J = 7.6 Hz), 1.80 (3H, t, J = 7.3 Hz); C NMR (CD CN)
3
2
,2Ј-(Ethylenedisulfanyl)bis(benzoselenazole) 10, R (CH -
f 2
δ 187.60, 143.44, 129.50, 128.78, 127.04, 125.95, 116.70, 37.70,
Cl –petroleum ether 1 : 1) 0.29, white cristals, yield 10.51 g
2
32.74, 12.17. Calc. for C H NSSeBF : C, 34.91; H, 3.52; N,
10
12
4
1
(
66%); mp 154 ЊC; H NMR δ 7.81 (2H, d, J = 8.3 Hz), 7.73 (2H,
d, J = 7.8 Hz), 7.42–7.27 (2H, td, J = 7.8 Hz, J = 1.3 Hz), 7.25–
.09 (2H, td, J = 7.8 Hz, J = 1.3 Hz), 3.76 (4H, s); C NMR
4
.07. Found: C, 35.01; H, 3.32; N, 4.03%.
3 4
3
4
13
7
N-Methylbenzoselenazole-2-selone 14
NaBH (0.36 g, 9.53 mmol) was dissolved in absolute EtOH
δ 167.31, 154.96, 138.84, 126.62, 124.91, 124.79, 123.50, 33.88.
Calc. for C H N S Se : C, 42.30; H, 2.66; N, 6.17. Found: C,
4
16
12
2
2
2
(
50 mL) and a stream of nitrogen was bubbled for 15 min into
4
2.19; H, 2.65; N, 6.24%.
-[2-(benzoselenazol-2-ylsulfanyl)ethyl]benzoselenazole-2-
thione 11, R (CH Cl –petroleum ether 1 : 1) 0.40, white
the solution. Selenium powder (0.68 g, 8.66 mmol) was
added to the solution under flux of nitrogen and the reaction
mixture was stirred, under nitrogen, until the formation of
a turbid, colorless solution of NaSeH. To this solution was
slowly added a solution of 2-(ethylsulfanyl)-1,3-benzoselen-
azolium tetrafluoroborate 13 (1.49 g, 4.33 mmol) in MeCN
3
f
2
2
1
needles, yield 1.08 g (7%); mp 140 ЊC; H NMR δ 8.08 (1H, d,
J = 8.3 Hz), 8.03–7.91 (1H, dd, J = 8.1 Hz, J = 0.8 Hz), 7.89–
3
4
3
4
7
7
1
1
.77 (1H, dd, J = 7.8 Hz, J = 0.8 Hz), 7.61–7.42 (3H, m), 7.40–
13
.21 (2H, m), 4.91 (2H, m), 3.67 (2H, m); C NMR δ 192.71,
67.49, 154.69, 143.45, 138.97, 128.06, 127.56, 126.77, 125.69,
25.40, 125.13, 125.08, 123.05, 115.49, 46.46, 29.16. Calc. for
(
3
25 mL). The reaction mixture was stirred under nitrogen for
0 min. Water (50 mL) was added to the reaction mixture,
which was then extracted with CH Cl (5 × 50 mL). The com-
C H N S Se : C, 42.30; H, 2.66; N, 6.17. Found: C, 42.53; H,
2
2
16
12
2
2
2
bined organic layers were dried over Na SO . Evaporation of
2
.57; N, 6.18%.
2
4
the solvent under reduced pressure gave an orange crystalline
solid. The residue was flash chromatographed over silica gel
3
,3Ј-Ethylenebis(benzoselenazole-2-thione) 12
(
CH Cl ) twice in order to eliminate residual red selenium.
2 2
A 50 mL round-bottom flask containing 2,2Ј-(ethylene-
didisulfanyl)bis(benzoselenazole) 9 (7.25 g, 15.96 mmol) and
iodine (0.32 g) was placed in a metallic bath with a starting
temperature of 212 ЊC. In 3 min a purple liquid was obtained
and the reaction mixture was stirred for 1 h while the temper-
ature of the bath was maintained between 212 and 221 ЊC.
Then, the temperature of the bath was raised and the mixture
was stirred further for 2 h while the temperature of the bath was
kept between 220 and 250 ЊC. Upon cooling to room temper-
ature the reaction mixture solidified and a dark brown solid was
obtained. It was partially solubilized in CH Cl (300 mL). The
The eluate was dried (Na SO ) and evaporated under reduced
2
4
pressure to furnish 1.13 g (95%) of benzoselenazole-2-selone
1
1
4 as yellow crystals, mp 100 ЊC, R (CH Cl ) 0.73; H NMR
f 2 2
13
δ 7.69–7.28 (4H, m), 3.97 (3H, s); C NMR δ 188.87, 144.89,
30.82, 127.71, 126.02, 125.26, 115.12, 37.09. Calc. for C H -
1
8
7
NSe : C, 34.93; H, 2.57; N, 5.09. Found: C, 35.08; H, 2.55; N,
2
4
.72%.
3
,3Ј-Ethylenebis[2-(ethylsulfanyl)benzoselenazolium
tetrafluoroborate] 15
2
2
insoluble dark brown crystalline solid was filtered off and the
filtrate was extracted with 5% aq. Na SO (30 mL) in order to
To a suspension of 3,3Ј-ethylenebis(benzoselenazole-2-thione)
12 (0.44 g, 0.97 mmol) in toluene (50 mL) were added, in turn,
2
3
remove residual iodine. The organic layer was dried over
Na SO , and evaporation of the solvent gave a dark brown
solutions of CH(OEt) (1.15 g, 7.75 mmol) in 5 mL of toluene,
3
and BF ؒEt O (1.47 g, 10.32 mmol) in 5 mL of toluene. The
2
4
3
2
semi-solid. Flash chromatography, over silica gel (CH Cl ), of
reaction mixture was heated to reflux for 2 hours, cooled to
room temperature, and diethyl ether (30 mL) was added. The
precipitate was filtered off, washed with diethyl ether, and dried
2
2
both the crystalline powder and the semi-solid afforded in each
case an orange–brown powder. The combined crude products
were recrystallised from 60 mL of pyridine and upon cooling a
yellow crystalline precipitate was obtained. Filtration afforded
dimer 12 as yellow needles. TLC of the filtrate showed the
to give salt 15 as a pale brown powder, yield 0.63 g (96%) mp
1
232 ЊC (dec.); H NMR (DMSO-d ) δ 8.55 (2H, d, J = 7.3 Hz),
6
8.15 (2H, d, J = 7.3 Hz), 8.01–7.73 (4H, m), 5.33 (4H, s), 3.67
1
572
J. Chem. Soc., Perkin Trans. 1, 2002, 1568–1573

View Article Online
13
(
4H, q, J = 7.3 Hz), 1.44 (6H, t, J = 7.3 Hz); C NMR (DMSO-
Crystal-structure determination of isomeric dimers 10 and 12†
d6) δ 191.19, 142.88, 130.56, 129.57, 127.84, 127.67, 116.75,
Crystal data for 10. C H N S Se , M = 454.32, triclinic,
16
12
2
2
2
4
8.41, 32.94, 13.10. Calc. for C H N S Se B F : C, 35.01; H,
20 22 2 2 2 2 8
space group P-1, a = 9.8982(3), b = 10.0070(3), c = 13.9470(3) Å,
α = 102.747(3), β = 104.027(3), γ = 103.336(3)Њ, V = 1246.92(6)
3
.23; N, 4.08. Found: C, 34.74; H, 3.27; N, 3.96%.
3
Ϫ1
Å , Z = 3, T = 293(2) K, µ(Mo-Kα) = 4.695 mm , 9637 reflec-
tions measured, 5628 unique (Rint = 0.0227) of which 4728 with
3
,3Ј-Ethylenebis(benzoselenazole-2-selone) 16
2
0
I > 2σ(I ). The final reliability factors are wR (F ) = 0.1243 (all
2
NaBH (120 mg, 3.21 mmol) was dissolved in absolute EtOH
4
data) and R = 0.0475 [F > 4σ(F )].
1
0
0
(
30 mL) and a stream of nitrogen was bubbled for 15 min into
the solution. Selenium powder (230 mg, 2.92 mmol) was added
to the solution under flux of nitrogen and the mixture was
stirred at room temperature for 15 min. Then a solution of 3,3Ј-
Crystal data for 12. C H N S Se , M = 454.32, monoclinic,
16
12
2
2
2
space group P2 /n, a = 16.3534(4), b = 5.3820(2), c = 19.3559(6)
1
3
Å, β = 110.5239(14), V = 1595.46(9) Å , Z = 4, T = 200(2) K,
µ(Mo-Kα) = 4.893 mm , 5500 reflections measured, 2922
ethylenebis[2-(ethylsulfanyl)benzoselenazolium
tetrafluoro-
Ϫ1
borate] 15 (500 mg, 0.73 mmol) in MeCN (20 mL) was slowly
added. The reaction mixture was stirred at room temperature
under nitrogen for 40 min. Water (50 mL) was added and the
reaction mixture was extracted with CH Cl (3 × 100 mL).
unique (Rint = 0.0335) of which 2259 with I > 2σ(I ). The
2
0
final reliability factors are wR (F ) = 0.0785 (all data) and
2
R = 0.0345 [F > 4σ(F )].
1
0
0
2
2
Combined organic layers were evaporated under reduced
pressure. The orange–yellow residue was dissolved in hot
pyridine (20 mL) in order to eliminate red selenium by fil-
tration. Evaporation of the filtrate and recrystallization of the
residue in 25 mL of pyridine afforded dimer 16 as green–yellow
needles, R (CH Cl ) 0.83, yield 0.35 g (88%), mp 288–289 ЊC
Acknowledgements
We are grateful to Mrs T. Stipanovi c˘ and Professor
B. Stanovnik for elementary analysis. We thank Professor
M. Japelj for his support for this work and the Ministery
of Education, Science and Sport of the Republic of Slovenia
for young researcher fellowship (T19-103-002/19281/99).
f
2
2
1
3
(
dec.); H NMR (DMSO-d ) δ 7.92–7.84 (2H, dd, J = 7.3 Hz,
6
3 4
4
J = 1.3 Hz), 7.75–7.65 (2H, dd, J = 8.1 Hz, J = 1.3 Hz), 7.49–
7
1
13
.29 (4H, m), 5.05 (4H, s); C NMR (DMSO-d ) δ 190.08,
6
43.79, 129.92, 127.24, 125.59, 125.42, 114.58, 45.27. Calc. for
References
C H N Se : C, 35.06; H, 2.21; N, 5.11. Found: C, 35.25; H,
1
6
12
4
4
1
J. M. Williams, J. R. Ferraro, R. J. Thorn, K. D. Carlson, U. Geiser,
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Hall, Englewood Cliffs, NJ, 1992.
1
.98; N, 5.30%.
N,NЈ-Dimethyldibenzo-DSeDAF 1
2
G. Schukat and E. Fanghänel, Sulfur Rep., 1996, 18, 1.
˘
A solution of 3-methylbenzoselenazole-2-selone 14 (20.0 mg,
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0
.073 mmol) in freshly distilled toluene (2 mL) was heated to
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20.6 µL, 0.12 mmol) was added dropwise. The reaction mixture
4
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(
was stirred at reflux for 30 min, giving a clear, orange clear
solution. The reaction mixture was cooled to the room temper-
ature and the solution was then transferred into an electro-
chemical cell under nitrogen containing a degassed solution of
tetrabutylammonium hexafluorophosphate in CH Cl . The CV
5
6
7
8
C. Hasan and R. F. Hunter, J. Chem. Soc., 1935, 1762.
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2
2
of the solution was recorded after the addition of aluminium
oxide (activated, basic, 150 mesh).
9
V. Ettel, M. Semonsky, J. Kunak and A. Cerny, Chem. Listy, 1952,
4
6, 756.
1
1
1
0 C. G. Moore and E. S. Waight, J. Chem. Soc., 1952, 4237.
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K. Wunderlich, Justus Liebigs Ann. Chem., 1960, 632, 38.
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Ann. Chem., 1972, 765, 110.
N,NЈ-Ethylenedibenzo-DSeDAF 3
The same procedure that decribed above for the synthesis of 1,
using 3,3Ј-ethylenebis(benzoselenazole-2-selone) 16 (20.0 mg,
1
1
0
.037 mmol) in freshly distilled toluene (7 mL) and triethyl
phosphite (20 µL, 0.117 mmol), afforded the title pentacycle 3,
which was also subjected to electrochemical analysis.
4 S. Hünig, D. Scheutzow and H. Schlaf, Justus Liebigs Ann. Chem.,
1972, 765, 126.
J. Chem. Soc., Perkin Trans. 1, 2002, 1568–1573
1573