Characterization of a byproduct in the alkylation of DMIT: Alkylation on the least nucleophilic sulfur atom

Article abstract of DOI:10.1002/ejic.200600213

It is generally accepted that the alkylation of (Et₄N) ₂-[Zn(DMIT)₂] (1) is a very clean reaction that produces 4,5-bis(alkylthio)-1,3-dithiole-2-thiones 4 in very high yields. Although this procedure has been widely used, we have found that, in addition to the 4,5-bis(alkylthio)-1,3-dithiole-2-thione products 4, highly unexpected byproducts are formed during the alkylation reaction in which the thione functionalities of DMIT in (Et₄N)₂[Zn(DMIT)₂] (1) are alkylated instead of the more reactive thiolate groups. These byproducts were identified as a novel type of compounds, namely bis(2-alkylthio-1,3- dithiol-1-ium-4,5-dithiolato)zinc compounds 3, being composed of two identical 2-alkylthio-1,3-dithiol-1-ium-4,5-dithiolate moieties coordinated to a single zinc(II) atom and were characterized by elemental analyses and different spectroscopic techniques as well as single-crystal X-ray structure analyses. A comparison of the physical properties of compounds 3 and (Et₄N) ₂[Zn(DMIT)₂] (1) has been carried out. The outcome of these investigations revealed significant differences in the physical properties of these two systems. Wiley-VCH Verlag GmbH & Co. KGaA, 2006.

Full text of DOI:10.1002/ejic.200600213

FULL PAPER
DOI: 10.1002/ejic.200600213
Characterization of a Byproduct in the Alkylation of DMIT: Alkylation on the
Least Nucleophilic Sulfur Atom
[a]
[a]
[a]
Bo M. Petersen, Jens K. Bjernemose, and Jan O. Jeppesen*
Keywords: Alkylation / DMIT / Nucleophilic substitution / Sulfur heterocycles
It is generally accepted that the alkylation of (Et
4
N)
2
-
composed of two identical 2-alkylthio-1,3-dithiol-1-ium-4,5-
dithiolate moieties coordinated to a single zinc(II) atom and
were characterized by elemental analyses and different spec-
troscopic techniques as well as single-crystal X-ray structure
analyses. A comparison of the physical properties of com-
pounds 3 and (Et N) [Zn(DMIT) ] (1) has been carried out.
4 2 2
The outcome of these investigations revealed significant dif-
ferences in the physical properties of these two systems.
[
Zn(DMIT) ] (1) is a very clean reaction that produces 4,5-
2
bis(alkylthio)-1,3-dithiole-2-thiones 4 in very high yields. Al-
though this procedure has been widely used, we have found
that, in addition to the 4,5-bis(alkylthio)-1,3-dithiole-2-thione
products 4, highly unexpected byproducts are formed during
the alkylation reaction in which the thione functionalities of
4 2 2
DMIT in (Et N) [Zn(DMIT) ] (1) are alkylated instead of the
more reactive thiolate groups. These byproducts were iden-
tified as a novel type of compounds, namely bis(2-alkylthio-
(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
Germany, 2006)
1,3-dithiol-1-ium-4,5-dithiolato)zinc compounds 3, being
Introduction
Among sulfur-containing heterocycles, derivatives of 2-
thioxo-1,3-dithiole-4,5-dithiolate[ (DMIT), have received a
central position in organic and materials chemistry on ac-
count of the discovery of superconductivity in some of the
1]
[
2,3]
[4]
metal complexes
of DMIT and its chalcogene analogs.
In addition, derivatives of DMIT are important building
blocks for the synthesis[ of tetrathiafulvalene
systems, such as bis(ethylenedithio)tetrathiafulvalene
BEDT-TTF) which has been employed for the preparation
5]
[6–9]
(TTF)
(
[10]
of an extensive range of conducting and superconducting
[
11,12]
materials.
DMIT is commonly isolated as its zinc che-
late[ in the form of bis(tetraethylammonium) bis(2-thi-
13]
oxo-1,3-dithiole-4,5-dithiolato)zincate (Et N) [Zn(DMIT) ]
4
2
2
(1) and subsequent alkylation of the chelated thiolate
groups can be accomplished with a variety of alkylating
[
14]
agents producing
thiole-2-thiones.
in most cases 4,5-bis(alkylthio)-1,3-di-
methyl fluorosulfate, methyl trifluorosulfonate, triethyl-
oxonium tetrafluoroborate, triethyl orthoformate, boron tri-
fluoride–diethyl ether, and dimethyl sulfate must be em-
Although alkylation of the thione functionality of 1,3-
dithiole-2-thione derivatives are favored by a gain in energy
caused by aromatization of the 1,3-dithiole ring to a 1,3-
dithiolium system simple alkylating agents, such as alkyl
halides, are not sufficiently strong alkylating agents to ac-
complish this type of reaction for 4,5-bis(alkylthio)-1,3-di-
thiole-2-thiones. Instead, stronger alkylating agents, such as
[
15]
ployed to produce
salts. Despite several reports on 2,4,5-tris(alkylthio)-1,3-di-
2,4,5-tris(alkylthio)-1,3-dithiolium
[
16]
thiolium salts only one example
of a 2-alkylthio-1,3-di-
thiolium-4,5-dithiolate system – in the form of bis(cyclo-
pentandienyl)(2-methylthio-1,3-dithiolium-4,5-dithiolato)-
titanium(IV) (2) – has, to the best of our knowledge, been
[
a] Department of Chemistry, University of Southern Denmark, reported so far. In this paper, we present the synthesis and
Odense University,
characterization of four systems 3 each containing two 2-
alkylthio-1,3-dithiolium-4,5-dithiolate moieties coordinated
to a single zinc(II) atom.
Campusvej 55, 5230 Odense M, Denmark
Fax: +45-66-15-87-80
E-mail: joj@chem.sdu.dk
Eur. J. Inorg. Chem. 2006, 3099–3104
© 2006 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
3099

B. M. Petersen, J. K. Bjernemose, J. O. Jeppesen
FULL PAPER
Results and Discussion
proposed structures of 3a–d. Furthermore, the structures of
3a and 3b were unequivocally determined by single-crystal
In most cases, the reaction between (Et N) [Zn-
4
2
X-ray structure analyses.
(
DMIT) ] (1) and an appropriate alkyl halide proceeds
2
smoothly producing (Scheme 1) the corresponding 4,5-bis-
(
7
alkylthio)-1,3-dithiole-2-thiones 4 in yields ranging from
[
14]
X-ray Crystallographic Studies
9% to 94%.
In the present investigations, we have ob-
served that, in addition to the desired 4,5-bis(alkylthio)-1,3-
dithiole-2-thione products 4, highly unexpected byproducts
are formed during the reaction as a result of alkylation of
the thione functionalities instead of the more reactive thiol-
ate groups.
Crystals of 3a and 3b were grown by letting cyclohexane
diffuse into CHCl3 solutions of 3a and 3b, respectively.
Both compounds show very strong pleochroism with colors
changing between bright blue and dark red under polarized
light. Crystallographic data were collected with a Nonius
KappaCCD diffractometer with Mo-Kα radiation (λ =
0
.71073 Å) and the structures were solved by direct meth-
[
17]
ods using SIR97
SHELXL97.
followed by refinement with
[
18]
Table 1 summarizes the crystallographic
data obtained for compound 3a and 3b.
The two chelating planes form angles of 85.1(4)° in 3a
and 89.58(13)° in 3b as compared to 83–85° between the
chelating planes in (Et N) [Zn(DMIT) ] (1). The molecular
Scheme 1. Synthesis of 4,5-bis(alkylthio)-1,3-dithiole-2-thione
products 4.
4
2
2
structure of 3b with a partial labeling scheme is shown in
Figure 1a. In both structures Zn is tetrahedrally coordi-
nated with distortions on account of the limited bite angle
of the bis(thiolato) ligand. The coordination geometry
closely resembles that of (Et N) [Zn(DMIT) ] (1). However,
In a typically alkylation experiment (Scheme 2), the zinc-
ate (Et N) [Zn(DMIT) ] (1) and the alkyl halide were
4
2
2
heated under reflux in MeCN followed by an aqueous
workup. Subsequent purification by means of column chro-
matographic purification afforded a broad yellow fraction
together with a weaker blue fraction. The first yellow frac-
tion contained 4,5-bis(alkylthio)-1,3-dithiole-2-thione 4,
whereas it was identified (vide infra) that the second blue
band contained the unexpected bis(2-alkylthio-1,3-dithiol-
4
2
2
in the case of 3b, there is no crystallographically imposed
symmetry contrasting with the twofold axial symmetry ob-
served in about half of the known structures related to
[
19]
(
Et N) [Zn(DMIT) ] (1).
This lack of restraint makes
4
2
2
[
20]
DOQXOW
the best candidate for comparison as it too
1
-ium-4,5-dithiolato)zinc compound 3 as byproduct.
is unrestrained and its data collected at 150 K (see Table 2
for a comparison of average bond lengths).
There is no apparent change in Zn–S distances despite
the reduced charge of the ligand. The only significant geo-
metric difference between the new ligand and (Et N) -
4
2
[
Zn(DMIT) ] (1) is the obvious lengthening of the C(3)–
2
S(5) bond to a value somewhere between a double (DMIT)
and single bond [S(5)–C(7)]. An accompanying shortening
of S(3)–C(3) cannot be considered significant.
The packing of 3a and 3b is almost identical and the
packing diagram of 3b is depicted in Figure 1b. Both have
an ordered alkyl chain in perfect staggered conformation in
the plane of its attached dithiole ring. These ordered alkyl
Scheme 2. Synthesis of bis(2-alkylthio-1,3-dithiol-1-ium-4,5-dithi-
olato)zinc compounds 3.
As illustrated in Scheme 2, the isolated yields for 3a–c chains pack together with symmetry-equivalent copies to
are less than 0.5% when simple alkyl bromides are used as form layers parallel to the ab plane. The other alkyl chain is
the alkylating agent. However, the yield can be improved twisted and has bonds which are orthogonal to its attached
by using the stronger alkylating agent triethyloxonium tet- dithiole ring. This twist results in a disorder that cannot
rafluoroborate. In this case, 3d was isolated in a yield just readily be modeled wherefore large ADPs have been ac-
above 1%. The fact that the yields of 3a–d are very low can cepted instead. The disordered alkyl chains pack in a mixed
most likely be accounted for by the presence of the more layer in which one of the dithiole rings is sandwiched be-
nucleophilic thiolate groups in (Et N) [Zn(DMIT) ] (1) tween the simple alkyl layers. The mixed layer is dominated
4
2
2
which prevents the formation of any larger amounts of 3. by C–H···S interactions (minima are 2.9 Å and 2.7 Å in 3a
Although 3a–d were isolated in very low yields, the alky- and 3b, respectively) and S···S interactions (3.5 Å and
lation reactions can be carried out on a large scale allowing 3.7 Å); 3b shows an interaction between the C=C bond and
substantial amounts (50–150 mg) of 3a–d to be isolated.
a dithiole S atom (3.3 Å). The fact that the two dithiole
The unexpected byproducts 3a–d were all isolated as pur- rings are orthogonal in 3a and 3b precludes more than one
1
13
ple solids. H and C NMR spectroscopy, high-resolution alkyl chain from adopting the favorable all-staggered con-
mass spectrometry, and elemental analyses all support the formation. Thus, if both alkyl chains were supposed to
3100
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Eur. J. Inorg. Chem. 2006, 3099–3104

Characterization of a Byproduct in the Alkylation of DMIT
FULL PAPER
Table 1. Crystallograhpic data for 3a and 3b.
3a
3b
Empirical formula
M [g·mol ]
T [K]
Crystal system
Space group
a [Å]
b [Å]
c [Å]
C
544.20
150(2) K
triclinic
P1
7.5896(5)
8.0138(6)
17.1292(15)
87.400(3)
80.111(3)
76.148(3)
996.49(13)
2
12
H
14
S
10Zn
16 22
C H S10Zn
–1
600.31
150(2)
triclinic
¯
¯
P1
7.70290(10)
9.3494(2)
18.1802(4)
83.9880(10)
89.8730(10)
65.7950(10)
1186.42(4)
2
α [°]
β [°]
γ [°] 3
V [Å ]
Z
–3
D
x
[g cm ]
1.814
2.273
1.680
1.918
–1
µ [mm ]
F(000)
Crystal size [mm]
552
616
0.21×0.10×0.02
3.55 to 25.49
17153/3694 [0.1847]
0.952 and 0.652
3694/ 6/208
1.169
0.26×0.20×0.17
3.76 to 27.48
16596/5378 [0.0476]
0.721 and 0.611
5378/7/245
1.052
θ
min to θmax [°]
Reflections collected/independent [R(int)]
Tmax/Tmin
Data/restraints/parameters
GoF on F2
R
wR
1
[IϾ2σ(I)]
(all data)–
0.0983
0.2448
1.109/–0.723
0.057
0.1562
1.508/–1.472
2
3
∆ρ
max/min [e·Å ]
Table 2. Average bond lengths [Å] for selected chemically equiva-
lent bonds (a few chemically equivalent bonds do deviate more
than 3 e.s.d.s). Data for (Et
4
N)
2
[Zn(DMIT)
2
] was taken from the
literature.[
20]
3a
3b (Et
4
N)
2
2
[Zn(DMIT) ] (1)
Zn(1)–S(1)
S(1)–C(1)
C(1)–C(2)
C(1)–S(3)
S(3)–C(3)
C(3)–S(5)
S(5)–C(7)
2.342(5)
1.724(16)
1.42(2)
1.722(16)
1.707(16)
1.701(16)
1.811(17)
2.3410(12)
1.728(4)
1.372(7)
1.739(4)
1.688(5)
1.721(5)
1.818(7)
2.345
1.735
1.362
1.753
1.721
1.661
tration. The molecule essentially makes the best of a bad
lot. Only one alkyl chain can adopt the favorable all-stag-
gered conformation and at the same time remain close
packed. The other alkyl chain must then fend for itself with-
out packing too loosely. This can apparently be done in a
number of only slightly differing ways resulting in extensive
disorder.
The absence of good hydrogen-bond donors (and hence
of strong X–H···S hydrogen bond interactions) may account
for the very different appearance of these compounds in the
solid state (dark red) and in solution (dark blue).
Figure 1. (a) Molecular structure of 3b with the crystallographic
numbering shown. (b) Packing of 3b viewed along the a axis of the
unit cell. Hydrogen atoms omitted for clarity.
NMR Investigations
A comparison of the 13C NMR spectra recorded of com-
pound 3c with those recorded of (Et N) [Zn(DMIT) ] and
4
2
2
adopt a staggered conformation in the plane of their at- 4,5-bis(hexylthio)-1,3-dithiole-2-thione (4c) reveal signifi-
tached dithiole rings, one of them would penetrate into the cant chemical shift differences for the resonances associated
next layer of molecules. Consequently, one of the alkyl with the carbon atoms in the 1,3-dithiole moiety. The chem-
chains is forced to twist to avoid such an unfavorable pene- ical shift values summarized in Table 3, suggest that the 1,3-
Eur. J. Inorg. Chem. 2006, 3099–3104
© 2006 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
3101

B. M. Petersen, J. K. Bjernemose, J. O. Jeppesen
FULL PAPER
dithiole moiety gains some aromatic character upon alky- λ Ն 500 nm, consistent with the observed pale yellow color
lation of the thione functionality. This observation is also (Figure 2, inset) of 4,5-bis(pentylthio)-1,3-dithiole-2-thione
supported by the bond lengths listed in Table 2.
(4b) in CHCl . Dissolving (Et N) [Zn(DMIT) ] (1) in
3 4 2 2
CHCl produced a red solution (Figure 2, inset) with a con-
3
Table 3. Selected 13C NMR spectroscopic data (δ values in ppm)
comitant strong absorption band being observed at λ
=
max
for (Et
thione (4c), and 3c at 298 K.
4
N)
2
[Zn(DMIT)
2
]
(1), 4,5-bis(hexylthio)-1,3-dithiole-2-
3
–1
–1
494 nm (ε = 21·10  cm ) in the absorption spectrum,
whereas a blue solution (Figure 2, inset) was obtained upon
Compound
Solvent
CD CN
C=C
S–C–S
dissolving 3b in CHCl . The absorption spectrum recorded
3
(
Et
c
4
N)
2
[Zn(DMIT)
2
] (1)
3
136.4
136.5
158.5
210.2
211.6
168.5
of this blue solution of 3b shows a strong absorption band
4
CDCl
CDCl
3
3
–1
–1
centered at λmax Ϸ 598 nm (ε = 20·10  cm ). This band
can most likely be assigned to an intramolecular charge
transfer (CT) taking place between the relative electron-rich
thiolate groups and the 1,3-dithiolium moieties present in
3
c
3
3
b. To support this hypothesis, we carried out some molecu-
Photophysical Investigations
[
21]
lar modeling calculations.
For simplicity, these investi-
The photophysical properties have been studied in gations were conducted on 3a which indicate that the two
CHCl3 solutions at room temperature using absorption degenerated HOMO and HOMO–1 orbitals (Figure 3)
spectroscopy. The UV/Vis spectroscopic data of 3a–d are mainly are located on the thiolate groups and the C=C
listed in Table 4, together with those of (Et N) [Zn- bond, whereas the degenerated LUMO and LUMO+1 or-
4
2
(
(
(
DMIT) ] (1) and 4,5-bis(pentylthio)-1,3-dithiole-2-thione bitals are located on the 1,3-dithiolium moieties. This led
2
4b). A comparison of the absorption spectra of 3b, us to conclude that the Zn atom has only a minor contri-
Et N) [Zn(DMIT) ] (1), and 4,5-bis(pentylthio)-1,3-dithi- bution to the 598 nm absorption band. Instead, this absorp-
4
2
2
ole-2-thione (4b) is displayed in Figure 2.
tion band can most likely be ascribed to an intramolecular
electron transfer occurring between the thiolate groups and
the 1,3-dithiolium moieties.
Table 4. UV/Vis absorption band maxima (λmax) and molar extinc-
tion coefficients (ε) for compounds 1, 3a–d, and 4,5-bis(pentylthio)-
1
,3-dithiole-2-thione (4b) in CHCl
Compound
Et N) [Zn(DMIT
3
at room temperature.
λ
max [nm] (ε [–1 cm–1])
3
3
(
4
2
2
)] (1)
315 (26·10 ), 494 (21·10 )
3
3
3
3
3
3
4
a
b
c
308 (20·10 ), 597 (19·10 )
3 3
308 (20·10 ), 598 (19·10 )
3
3
308 (21·10 ), 598 (20·10 )
3
3
d
b
308 (19·10 ), 598 (19·10 )
3 3
278 (6.4·10 ) 386 (11·10 )
Figure 3. HOMO and LUMO orbitals of 3a. (a) The degenerated
HOMO and HOMO–1 orbitals are mainly located on the thiolate
groups and the C=C bond, whereas (b) the degenerated LUMO
and LUMO+1 orbitals are located on the 1,3-dithiolium moieties.
Conclusions
In conclusion, we have shown that alkylation of
(
Et N) [Zn(DMIT) ] (1) not only affords 4,5-bis(alkylthio)-
4 2 2
1,3-dithiole-2-thiones 4, but also takes place at the less nu-
4 2 2
Figure 2. Absorption spectra recorded of (Et N) [Zn(DMIT)
] (1), cleophilic thione functionalities producing a novel class of
3
b, and 4,5-bis(pentylthio)-1,3-dithiole-2-thione (4b). The inset compounds 3 in which a Zn atom is coordinated to two
shows the actual color of the solutions of 1, 3b, and 4,5-bis(pentyl-
thio)-1,3-dithiole-2-thione (4b).
aromatic 2-alkylthio-1,3-dithiolium-4,5-dithiolate moieties.
Formation of 3 can be detected by the naked eye since solu-
tions of (Et N) [Zn(DMIT) ] (1) and 3 display different col-
4
2
2
The absorption spectrum of compound 4,5-bis(pentyl- ors, red and blue, respectively. Although the isolated yields
thio)-1,3-dithiole-2-thione (4b) exhibits relative weak ab- of 3 generally were low, it seems that the formation of 3 is
sorptions in the 250–450 nm region and no absorptions at a common feature upon alkylation of (Et N) [Zn(DMIT) ]
4
2
2
3102
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Eur. J. Inorg. Chem. 2006, 3099–3104

Characterization of a Byproduct in the Alkylation of DMIT
FULL PAPER
): δ = 0.93 (t, J = 7.1 Hz, 6 H),
1
(
1). Consequently, it can be expected that the method can (dec.). H NMR (300 MHz, CDCl
3
1
4
1
.34–1.46 (m, 8 H), 1.80 (q, J = 7.4 Hz, 4 H), 3.20 (t, J = 7.4 Hz,
be extended to produce more elaborate derivatives of 3. The
findings reported herein are undoubtedly not unimportant
given the amount of research devoted to DMIT and its cor-
responding metal complexes.
1
3
H). C NMR (75 MHz, CDCl
3
): δ = 14.0, 22.2, 28.2, 30.8, 40.4,
58.8 (one line for the trithiocarbonate carbon atom is missing).
3
–1
–1
3
UV/Vis (CHCl ): λmax (ε) = 308 (20·10  cm ), 598 nm
3
–1
–1
(
1
19·10  cm ). IR (KBr): ν˜ = 2946, 2925, 2854, 2008, 1453,
424, 1349, 1022, 903, 730, 467 cm . HiRes-FT-MALDI-MS:
–
1
+
·
calcd. for
16 22
C H S10Zn [M ] 597.8215; found: 597.8209.
Experimental Section
16 22 10
C H S Zn (600.4): calcd. C 32.01, H 3.69, S 53.41; found C
3
2.01, H 3.60, S 53.60.
Bis(2-hexylthio-1,3-dithiol-1-ium-4,5-dithiolato)zinc (3c): Yield:
75 mg (0.49%); R = 0.45 (eluent: CH Cl ); m.p. 161.5–163.0 °C
(dec.). H NMR (300 MHz, CDCl ): δ = 0.91 (t, J = 6.7 Hz, 6 H),
1.25–1.50 (m, 12 H), 1.79 (q, J = 7.4 Hz, 4 H), 3.20 (t, J = 7.4 Hz,
General Procedures: Chemicals and solvents were purchased from
Aldrich and were used as received. Bis(tetraethylammonium) bis(2-
thioxo-1,3-dithiole-4,5-dithiolato)zincate (1) was prepared accord-
ing to a literature procedure.[ Thin-layer chromatography (TLC)
was carried out using aluminium sheets pre-coated with silica gel
f
2
2
13]
1
3
1
3
6
0F (Merck 5554). The plates were inspected under UV light and,
if required, developed in I vapor. Column chromatography was
carried out using silica gel 60F (Merck 9385, 0.040–0.063 mm). (21·10  cm ), 598 nm (20·10  cm ). IR (KBr): ν˜ = 2946,
4 H). C NMR (75 MHz, CDCl
40.4, 158.5, 168.5 cm . UV/Vis (CHCl ): 308
3
): δ = 14.1, 22.6, 28.3, 28.5, 31.2,
–
1
3
λmax (ε) =
2
3
–1
–1
3
–1
–1
–
1
Melting points were determined with a Büchi melting point appara-
2922, 2851, 2006, 1462, 1421, 1357, 1009, 904, 725, 465 cm .
1
13
+·
tus and are uncorrected. H (300 MHz) and C NMR (75 MHz)
spectra were recorded at 298 K with a Gemini-300BB instrument,
using tetramethylsilane (TMS) or the residual solvent as the in-
ternal standard. All chemical shifts are quoted on the δ scale, and
all coupling constants (J) are expressed in Hertz (Hz). Samples
HiRes-FT-MALDI-MS: calcd. for C18
26
H S10Zn [M ] 625.8528;
found 625.8522. C18 10Zn (628.4): calcd. C 34.40, H 4.17, S
26
H S
51.02; found C 34.38 H 4.29, S 51.31.
Bis(2-ethylthio-1,3-dithiol-1-ium-4,5-dithiolato)zinc (3d): Bis(tetra-
ethylammonium) bis(2-thioxo-1,3-dithiol-1-ylium-4,5-dithiolato)-
zincat (1) (21.5 g, 30 mmol) was suspended in MeCN (200 mL),
whereupon triethyloxonium tetraflouroborate (25.0 g, 120 mmol)
was added. The dark red reaction mixture was heated under reflux
for 5 min until no more starting material could be detected by TLC
were prepared using CDCl
Isotope Labs. High-resolution Fourier transform matrix-assisted
laser-desorption/ionization mass spectrometry (HiRes-FT-
3 3
or CD CN purchased from Cambridge
MALDI-MS) was performed with an IonSpec 4.7 Tesla Ultima
Fourier Transform mass spectrometer, utilizing a 2,5-dihydroxyben-
zoic acid (DHB) matrix. Infrared (IR) spectra were recorded with
a Perkin–Elmer 580 spectrophotometer, while absorption spectra
analysis (R
ture was cooled to room temperature and concentrated in vacuo.
The resulting dark red oil was dissolved in CH Cl . Column
chromatography (800 mL of silica; diameter: 13.5 cm; eluent:
CH Cl /petroleum ether, 1:4) gave a yellow band and a red band
which was discarded. The bis(2-ethylthio-1,3-dithiol-1-ium-4,5-di-
thiolato)zinc (3d) was then eluted as a blue band with CH Cl
Removal of the solvent provided the title compound 3d as a purple
microcrystalline powder. Yield: 169 mg (1.1%); R = 0.20 (eluent:
); m.p. 164.0–165.0 °C (dec.). H NMR (300 MHz, CDCl ):
δ = 1.49 (t, J = 7.4 Hz, 6 H), 3.22 (q, J = 7.4 Hz, 4 H). UV/Vis
f
= 0.70; eluent: EtOAc/MeCN, 3:2). The reaction mix-
2
2
(UV/Vis) were recorded with a Shimadazu 1601 spectrophotometer.
Elemental analyses were performed by the Atlantic Microlab, Inc.,
Atlanta, Georgia.
2
2
General Method for the Preparation of the Bis(2-alkylthio-1,3-di-
thiol-1-ium-4,5-dithiolato)zinc Compounds 3: Bis(tetraethylammon-
ium) bis(2-thioxo-1,3-dithiole-4,5-dithiolato)zincate (1) (21.5 g,
2
2
.
f
1
CH
2
Cl
2
3
30 mmol) was suspended in anhydrous MeCN (200 mL), where-
upon the appropriate alkyl bromide (120 mmol) was added. The
dark red reaction mixture was heated under reflux for 1 h until no
3
–1
–1
(
(
1
C
CHCl
3
3
):
λ
max
–1
(ε)
=
308 (19·10  cm ), 598 nm
–1
19·10  cm ). IR (KBr): ν˜ = 2923, 2011, 1445, 1348, 1288,
262, 1061, 1016, 905, 787, 466 cm . HiRes-FT-MALDI-MS:
H S10Zn [M ]: calcd. 513.7276; found 513.7265. C10H S10Zn
10 10
more starting material could be detected by TLC analysis (R
.70; eluent: EtOAc/MeCN, 3:2). After being cooled to room tem-
perature, the reaction mixture was concentrated in vacuo, and the
resulting dark green oil was dissolved in CH Cl and purified by
column chromatography (750 mL of silica; diameter: 13.5 cm; elu-
ent: CH Cl /petroleum ether, 1:9). The broad yellow band was col-
lected, and the solvent evaporated to afford the 4,5-bis(alkylthio)-
,3-dithiole-2-thiones 4. Thereafter, the eluent was changed to
CH Cl and a blue band was collected and concentrated to provide
f
=
–
1
0
+
·
10
(
6
516.23): calcd. C 23.27, H 1.95, S 62.11; found C 23.36, H 1.89, S
2.30.
2
2
2
2
X-ray Crystallography: Details are listed in Table 1. CCDC-601004
3a) and -601005 (3b) contain the supplementary crystallographic
(
1
data for this paper. These data can be obtained free of charge from
The Cambridge Crystallographic Data Centre via www.ccdc.cam.
ac.uk/data_request/cif.
2
2
the title compounds 3a–c as purple powders. Crystals suitable for
X-ray analysis were prepared by diffusion of cyclohexane into
CHCl
plates.
3
solutions of 3a and 3b, providing 3a and 3b as fine purple
Acknowledgments
Bis(2-propylthio-1,3-dithiol-1-ium-4,5-dithiolato)zinc (3a): Yield:
6 mg (0.28%); R = 0.45 (eluent: CH Cl ); m.p.183–184 °C (dec.).
H NMR (300 MHz, CDCl ): δ = 1.09 (t, J = 7.2 Hz, 6 H), 1.84
sext, J = 7.2 Hz, 4 H), 3.18 (t, J = 7.2 Hz, 4 H). UV/Vis (CHCl ):
max (ε) = 308 (20·10  cm ), 597 nm (19·10  cm ). IR
We are grateful to Professor Paul R. Raithby and Hazel Sparks,
Department of Chemistry, University of Bath, for the use of dif-
fractometers and help with some of the data collections. We grate-
fully acknowledge financial support provided by the Danish Natu-
ral Science Research Council through the SONS Programme of the
European Science Foundation, which is also funded by the Euro-
pean Commission, Sixth Framwork Programme, the Danish Strate-
gic Research Council through the Young Researchers Programme
(#2117-05-0115), and the Danish Technical Research Council
4
f
2
2
1
3
(
λ
3
3
–1
–1
3
–1
–1
(
4
KBr): ν˜ = 2960, 2923, 2866, 2013, 1363, 1285, 1013, 979, 906,
69 cm . C12H S10Zn (544.3): calcd. C 26.48, H 2.59, S 58.91;
14
–1
found C 26.15, H 2.55, S 58.39.
Bis(2-pentylthio-1,3-dithiol-1-ium-4,5-dithiolato)zinc (3b): Yield:
f 2 2
60 mg (0.33%); R = 0.46 (eluent: CH Cl ); m.p. 148.5–149.5 °C (#2058-03-0036).
Eur. J. Inorg. Chem. 2006, 3099–3104
© 2006 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
3103

B. M. Petersen, J. K. Bjernemose, J. O. Jeppesen
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Published Online: June 6, 2006
3104
www.eurjic.org
© 2006 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2006, 3099–3104