In pursuit of an acetylenedithiolate synthesis

Article abstract of DOI:10.1002/ejoc.200601107

Acetylene disulfides RSC₂SR, which are furnished with typical thiol protection groups R, were synthesized, fully characterized, and tested with respect to the aimed cleavage of R. While the alkyne RSC₂SR with R = C₂H₄

Full text of DOI:10.1002/ejoc.200601107

FULL PAPER
DOI: 10.1002/ejoc.200601107
In Pursuit of an Acetylenedithiolate Synthesis
Wolfram W. Seidel,*[a] Matthias J. Meel,[a] Markus Schaffrath,[a] and Tania Pape[a]
Keywords: Alkynes / Thiol protection groups / Synthesis / Structure determination
Acetylene disulfides RSC2SR, which are furnished with typi-
cal thiol protection groups R, were synthesized, fully charac-
terized, and tested with respect to the aimed cleavage of R.
While the alkyne RSC2SR with R = C2H4SiMe3 is easily ac-
cessible, the corresponding disulfide with R = CPh3 can be
prepared only with difficulties, and attempts to use the SiMe3
group lead to the isolation of a dithiacyclopentene derivative.
The molecular structures of Ph3CSC2SCPh3 and Ph3CSC2H,
which were investigated by X-ray diffraction, show a re-
markable combination of long and very short carbon–sulfur
single bonds. However, removal of the trityl groups by so-
dium phenolate or methyllithium in THF led to intractable
solutions. In contrast, removal of both trimethylsilylethyl
groups in Me3SiC2H4SC2SC2H4SiMe3 with (Bu4N)F in THF
proceeded smoothly, if benzyl bromide as the trapping agent
2–
is present. Hence, the successful transfer of the C2S2 syn-
thon in solution was proven by isolation of BnSC2SBn.
(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
Germany, 2007)
Introduction
Bis(alkylthio)acetylenes are interesting synthetic interme-
diates possessing a highly electron-rich triple bond. Thus,
bis(alkylthio)acetylenes are efficient acetylene equivalents in
cycloaddition reactions.[1] The polymerization of bis(alkyl-
thio)acetylenes leads to poly[bis(alkylthio)acetylenes], which
in turn can be doped with electron acceptors to produce
semiconductors.[2] In addition, dithioalkyne units are the
building blocks in remarkable cyclic diynes investigated by
Gleiter[3] and in oligoacetylenes reported by Lee.[4] Our re-
In this contribution we report on the synthesis of di-
search program is devoted to the coordination chemistry of thioalkynes with triphenylmethyl and 2-trimethylsilylethyl
acetylenedithiolate.[5] Thereby, the instability of acetylenedi- protection groups. The removal of the trimethylsilylethyl
thiolate is a major obstacle because it is prone to rapid groups under retention of the (SCϵCS)2– moiety is proven
oligomerization with the aid of Lewis acids. In the course by successful trans alkylation experiments, bis(benzylthio)-
of these studies we sought dithioalkynes, which are fur- acetylene serving as a test system. The successful reductive
nished with sulfur protection groups. However, the synthe- removal of the benzyl groups in alkyne complexes with
sis of bis(alkylthio)acetylenes, in which the alkyl groups can bis(benzylthio)acetylene was already shown by us.[5]
be cleaved under desirably mild conditions, turned out to be Furthermore, we report the molecular structures of ethynyl
challenging. The choice of an appropriate sulfur protecting triphenylmethyl sulfide (2c) and bis(triphenylmethylthio)-
group is complicated by the fact that groups with too high acetylene (3c), which both combine a very short with a long
lability might result in a conversion process of alkyne into carbon sulfur bond at individual sulfur atoms. Finally, an
thione bonds. Thus, a number of theoretical investigations investigation with trialkylsilyl groups uncovers the unsuit-
uncovered the higher stability of the C2H2S2 isomers 1,2- ability of these groups as protection groups for acetylenedi-
dithiete A and dithioglyoxal B relative to acetylenedithiol thiolate.
C.[6] Alkyne 1-disulfides D, for example, are known to
transform rapidly into thioketenes E.[7]
Results
A variety of synthetic procedures leading to bis(alkyl-
thio)acetylenes are known. While seeking for an appropri-
ate and facile method, we checked some of the syntheses.
Variable elimination reactions with bis(alkylthio)ethylenes[8]
[a] Institut für Anorganische und Analytische Chemie, West-
fälische Wilhelms-Universität Münster,
Corrensstraße 30/36, 48149 Münster, Germany
Fax: +49-251-8333108
E-mail: seidelww@uni-muenster.de
3526
© 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Org. Chem. 2007, 3526–3532

In Pursuit of an Acetylenedithiolate Synthesis
FULL PAPER
have not been considered because of the obvious expense pure samples of 3c were obtained from toluene solutions,
transfer to the preparation of the corresponding ethylenes. which tend conspicuously to supersaturation. Disulfide 3c
A straightforward syntheses of bis(alkylthio)acetylenes suc- is less soluble in n-hexane and diethyl ether. Slow decompo-
ceeds by the reaction of various alkylthiocyanates with sition is observed in polar solvents and under daylight.
[9]
NaC2H in liquid NH3 or with Li2C2 in THF.[3a] Other
The introduction of the trimethylsilylethyl protection
methods are based on metathesis with reversed polarity. group in acetylene disulfides required a variation in the syn-
Thus, bis(alkylthio)acetylenes are obtained by reaction of thetic procedure. Deprotonation of trimethylsilylacetylene
dichloroacetylene with thiols in the presence of either with nBuLi, reaction with sulfur at –30 °C, and subsequent
KH[10] or LiHMDS[1f] and by treatment of bis(iodonium)- alkylation with trimethylsilylethyl bromide yielded
4
acetylenes with sodium thiolates.[11]
(Scheme 2). In the next step, the removal of the trimethyl-
Finally we found the step-by-step procedure outlined in silyl group at the alkyne cannot be performed with fluoride
Scheme 1 the most convenient and, particularly, the only ions because of the presence of the second trimethylsilyl
one that could be successfully adapted for the preparation group in the molecule. However, reaction of 4 with 1 equiv.
of bis(triphenylmethylthio)acetylene (3c) and bis(2-trimeth- of MeLi·LiBr at 0 °C yielded, after 3 h, the intermediate
ylsilylethylthio)acetylene (5) in reasonable yields. The syn- Me3SiC2H4SC2Li. Subsequent addition of sulfur and
thesis is based on the long-known reaction of deproton- alkylation with 2-trimethylsilylethyl bromide resulted in the
ation of terminal alkynes with elemental sulfur.[12] Depro- formation of 5 in good yields. Alkyne 5 can be obtained in
tonation of trimethylsilylacetylene with nBuLi, reaction an analytically pure form by column chromatography.
with sulfur at –30 °C, and subsequent alkylation yielded 1a–
c. The consumption of sulfur, which is only sparingly solu-
ble in diethyl ether, is remarkably clear and fast. Removal
of the trimethylsilyl group with catalytic amounts of Bu4NF
in THF/methanol yielded 2a–c, the reaction of 1c was much
slower than that of 1a. Simple repetition of the sequence
deprotonation, reaction with the sulfur, and alkylation with
benzyl bromide yielded 3a. However, this step is critical in
the synthesis of bis(triphenylmethylthio)acetylene (3c). Nu-
cleophilic bases like alkyllithium compounds presumably
would rather attack the trityl group than deprotonate the
alkyne. Alkyne 3c can be isolated in moderate yields, if lith-
ium diisopropylamide in a diethyl ether/THF solvent mix-
ture is used. The addition of sulfur and alkylation with tri-
phenylmethyl chloride must strictly be performed at low
temperatures owing to side reactions. Bis(diphenylmethyl-
thio)acetylene could not be obtained at all. Analytically
Scheme 2. Synthesis and reactivity of bis(trimethylsilylethylthio)-
acetylene.
The X-ray structure analyses of 2c and 3c confirm their
identity as trityl alkynyl sulfides (Figure 1 and Table 1). In
addition, the molecular structures of 2c and 3c are interest-
ing because of the extreme ratio of the two carbon–sulfur
bond lengths at the sulfide group. The sulfur–carbon bonds
to the alkynyl carbon atoms are very short and amount to
1.682 Å in 2c and to 1.661/1.662 Å in 3c. The sulfur–carbon
Scheme 1. Synthesis of acetylene disulfides.
Figure 1. Molecular structure of 2c (50% ellipsoid probability).
3527
Eur. J. Org. Chem. 2007, 3526–3532
© 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org

W. W. Seidel, M. J. Meel, M. Schaffrath, T. Pape
FULL PAPER
bonds to the tertiary carbon atom are very long and in highly colored solutions. However, independently of the
amount to 1.893 Å in 2c and to 1.913/1.902 Å in 3c. These reaction time or temperature, subsequent alkylation with
bond lengths mark the whole range of carbon–sulfur single benzyl bromide did not yield 3a, whereas 3c could not be
bonds in unstrained thioethers. A comparable ratio of the recovered. In contrast, if colorless solutions of 5 in THF are
carbon–sulfur bond lengths was observed in cyclic poly- treated with 2 equiv. of (Bu4N)F at ambient temperature,
(alkyne thioethers).[13] The remarkably short alkyne–sulfur ethylene evolution is observed and a bright-yellow color ap-
bonds are in accordance with extensive structural data for peared. This solution persists for circa one hour without
alkynyl sulfides published by Gleiter[3a,13] and others.[14] any precipitation. However, at longer standing it turned
Short C(sp)–X distances generally reflect the dependence of slowly brown, and finally black solids formed. Both imme-
the bond length from the hybridization at the carbon center. diate addition of benzyl bromide after fluoride addition,
However, the differences in the RnC–XRm bond lengths, and the reverse sequence, yielded straightforwardly bis(ben-
while changing from a C(sp3) to a C(sp2) and finally to a zylthio)acetylene (3a) (Scheme 2). In turn, if 5 is treated at
C(sp) center, are particularly pronounced with X = S com- room temperature with benzyl bromide without the ad-
pared to the corresponding C–P and C–Si bonds (Table 2). dition of fluoride ions, the formation of the corresponding
The structural features of disulfide 3c emphasize the strong sulfenium salts can be excluded by NMR spectroscopic evi-
alkyne sulfur bond and the potential protection group char- dence. Therefore, the formation of free alkynethiolate
acter of the trityl group (Figure 2).
groups in solution is evident. However, the existence of ace-
tylenedithiolate cannot be concluded because a stepwise re-
moval of the trimethylsilylethyl groups is likely in consider-
ation of the charge. Consistently, the addition of benzyl
bromide 15 min after the fluoride addition at ambient tem-
perature yielded only traces of 3a. We attribute this obser-
vation to the protonation of the intermediary dianionic ace-
tylenedithiolate and subsequent decomposition. The water
Table 1. Selected bond lengths [Å] and angles [°] of 2c and 3c.
2c
3c
C1–C2
C2–S1
1.188(2)
1.682(2)
C1–C2
C1–S1
C2–S2
1.205(2)
1.661(2)
1.662(2)
1.913(2)
1.902(2)
178.7(2)
173.6(2)
S1–C3
1.893(2)
173.1(2)
S1–C3
–
content of commercial (Bu4N)F effectively renders HF2
S2–C22
C1–C2–S2
C2–C1–S1
ions the reactive species. The use of anhydrous (Bu4N)F is
impeded by its poor solubility in THF, while the reaction
of anhydrous (Bu4N)F[19] with 5 in acetonitrile led to intrac-
table reaction mixtures.
C1–C2–S1
Trialkylsilyl groups form comparatively weak bonds with
sulfur and therefore they are tested as an alternative protec-
tion group for acetylenedithiolate. As the procedures out-
lined in Schemes 1 and 2 cannot be adapted for the synthe-
sis of bis(trialkylsilylthio)acetylenes we tried to ascertain
the general utility of trialkylsilyl groups solely on one side
of the alkyne. However, the reaction of benzyl ethynyl sul-
fide (2a) with nBuLi, sulfur, and Me3SiCl under standard
conditions resulted in crystalline product 6 in almost stoi-
chiometric yield. Compound 6 displayed the double molec-
ular mass in MALDI mass spectrometry, no alkyne reso-
nances, and two resonances for both the trimethylsilyl and
the benzyl group, respectively, in the NMR spectra. The
identity of 6 as a thiafulvalene-like compound consisting of
Figure 2. Molecular structure of 3c (50% ellipsoid probability).
Our attempts to remove the trityl groups in 3c under ba- a dithiacyclopentene ring and an exocyclic C–C double
sic conditions turned out to be disappointing. Treatment of bond was uncovered by X-ray structure analysis (Figure 3).
3c with MeLi·LiBr or sodium phenolate in THF resulted The metric parameters of 6 are not discussed in detail be-
Table 2. Trends in the C–X single bond lengths [Å] (X = Si, P, S) depending on the hybridization at the carbon atom.[a]
[15]
[16]
X = SiR3
X = PR2
X = SR[17,3b]
Alkyl–X
1,4-(Me3Si)2C6H4
1.864
1.886
Ph3SiC2(H)2SiHPh2
1.858
1,2-(MePhP)2C6H4
1,2-(MeS)2C6H4
1.800
1.762
1.842
1.837
Ph2PC2(H)2PPh2
Aryl–X
Alkenyl–X
[b]
[b]
[c]
C2(SC2H4S)2C2(H)2
1.807
1.750[d]
Alkynyl–X
Ph3SiC2H
1.819
Ph2PC2PPh2
1.767
C2(SC2H4S)2C2(H)2
1.677[d]
[a] Representative examples with maximum similarity were chosen, bond lengths are mean values where applicable. [b] trans. [c] cis. [d]
With R = Ph, the C–S bonds are slightly shorter: PhSC(H)C(CO2Me)CHPh(OH): 1.741 Å,[18] PhSC2SPh: 1.665 Å.[14b]
3528
www.eurjoc.org
© 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Org. Chem. 2007, 3526–3532

In Pursuit of an Acetylenedithiolate Synthesis
FULL PAPER
cause of a disorder problem in the structure solution. The sulted in the formation of BnSC2SBn in good yields. There-
dimerization of formal (benzylthio)(trimethylsilylthio)- fore the (C2S2)2– synthon can be transferred under mild
acetylene can be rationalized by an equilibrium of (benzyl- conditions. However, the free dianion acetylenedithiolate
thio)(trimethylsilylthio)acetylene and (benzylthio)(trimeth- turned out to be prone to decomposition in the presence of
ylsilyl)thioketene in the silylation reaction as suggested in any sources of protons or even Lewis acids.
Scheme 3. Obviously, the Si–S bond is too weak to allow
the stabilization of dithioalkyne systems. Furthermore, we
were not successful in using alternative silyl groups like
tert-BuMe2Si in the synthesis of the desired bis(trialkylsilyl-
Experimental Section
thio)alkynes.
General Procedures: All operations were carried out under a dry
argon atmosphere by using standard Schlenk and glove box tech-
niques. All solvents were dried and saturated with argon by stan-
dard methods and freshly distilled prior to use. Me3SiC2H4Br was
prepared according to
a
literature procedure.[20] Trimethyl-
silylacetylene was purchased from Aldrich. 1H and 13C NMR spec-
tra were recorded with a Bruker AC 200 and a Bruker Avance 400
NMR spectrometer. Elemental analyses were performed with a Va-
rio EL III CHNS elemental analyzer. MALDI mass spectra were
obtained with the use of a Bruker Reflex IV spectrometer with the
matrix [(2E)-3-(4-tert-butylphenyl)-2-methylprop-2-enyliden]ma-
lononitrile (DCTB). Infrared spectra were recorded with a Bruker
Vektor 22.
Benzyl Trimethylsilylethynyl Sulfide (1a): Trimethylsilylacetylene
(36 mL, 0.255 mol) was dissolved in diethyl ether (250 mL) and co-
oled to –78 °C. n-Butyllithium (10  solution in n-hexane, 25.5 mL)
was added, and the solution was stirred at –78 °C for 15 min. Sulfur
(8.16 g, 0.255 mol), which was dried in vacuo for 1 h, was added,
and the mixture was stirred for 15 min at –78 °C. Upon warming
to room temperature, the reaction was complete in the course of
one hour, which was observed by the consumption of the sulfur.
The resulting clear orange solution was treated with benzyl bro-
mide (29.5 mL, 0.255 mol) at 0 °C, and the solution was stirred at
room temperature overnight. After removal of the solvent in vacuo,
the residue was extracted with n-hexane (150 mL and 3ϫ20 mL)
and filtered. The solvent of the filtrate was removed in vacuo and
purified by distillation under reduced pressure (80 °C, 0.01 mbar),
yielding 1a (48.4 g, 0.22 mol, 86%) as a colorless oil. 1H NMR
(200 MHz, CDCl3): δ = 7.39 (m, 5 H, Ph-H), 3.98 (s, 2 H, SCH2),
0.25 [s, 9 H, Si(CH3)3] ppm. 13C NMR (50 MHz, CDCl3): δ = 136.2
(Ph-Cipso), 128.9, 128.3, 127.6 (Ph-C), 102.0 (SiCϵC), 94.2
(CϵCS), 40.0 (SCH2), –0.2 [Si(CH3)3] ppm. C12H16SSi (220.41):
calcd. C 65.39, H 7.32, S 14.55; found C 65.44, H 7.35, S 14.50.
Figure 3. Molecular structure of 6 (50% ellipsoid probability); hy-
drogen atoms are omitted for clarity.
Scheme 3. Reactivity of alkynethiolate with a Me3Si alkylating
agent.
Diphenylmethyl Trimethylsilylethynyl Sulfide (1b): Compound 1b
was prepared in a scale of 14 mmol (30 mL diethyl ether) as de-
scribed for 1a by using diphenylmethyl chloride (2.5 mL,
14.0 mmol) as the alkylating agent. 13C NMR (50 MHz, CDCl3): δ
= 139.4 (Ph-Cipso), 128.5, 128.4, 127.6 (Ph-C), 103.2 (SiCϵC), 94.3
(CϵCS), 58.1 (SCH), –0.3 [Si(CH3)3] ppm.
Conclusions
We pursued the synthesis of free acetylenedithiolate in
solution because of its putative value as a building block
Triphenylmethyl Trimethylsilylethynyl Sulfide (1c): Compound 1c
in coordination chemistry and as a preparative synthon in was prepared as described for 1a using triphenylmethyl chloride
(71 g, 0.255 mol) as alkylating agent. The addition of tri-
phenylmethyl chloride was performed in toluene solution
organic synthesis. Primarily, we succeeded in the synthesis
of acetylene disulfides, which are furnished with typical sul-
fur protection groups at the sulfur atoms. The synthesis of
RSC2SR is facile with R = C2H4SiMe3, rather difficult with
R = CPh3, and not viable with R = SiMe3. In addition,
the subsequent removal of the triphenylmethyl groups in
Ph3CSC2SCPh3 led to intractable solutions. In contrast, the
cleavage of both trimethylsilylethyl groups by treatment of
Me3SiC2H4SC2SC2H4SiMe3 with 2 equiv. of (Bu4N)F in
a
(100 mL). After stirring for 12 h the solvents were removed in
vacuo and the residue was subjected to Soxhlet extraction using
300 mL n-hexane. Finally the solution was cooled stepwise to
–30 °C in order to complete precipitation of 1c (58 g, 61%), which
was isolated by filtration and dried in vacuo. C24H24SSi (372.61):
calcd. C 77.36, H 6.49, S 8.60; found C 77.43, H 6.53, S 8.47. 13C
NMR (50 MHz, CDCl3): δ = 144.0 (Ph-Cipso), 129.9, 127.8, 127.2
(Ph-C), 106.0 (SiCϵC), 95.9 (CϵCS), 71.6 (SCPh3), –0.5 (Si-
THF and subsequent re-alkylation with benzyl bromide re- (CH3)3) ppm.
Eur. J. Org. Chem. 2007, 3526–3532
© 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
3529

W. W. Seidel, M. J. Meel, M. Schaffrath, T. Pape
FULL PAPER
Benzyl Ethynyl Sulfide (2a): Pure 1a (48.4 g, 0.22 mol) was dis-
solved in THF (120 mL). Methanol (40 mL) and tetrabutylammo-
nium fluoride (400 mg) were added, and the mixture was stirred
urated benzene solution (30 mg 3c/mL benzene). 13C NMR
(50 MHz, C6D6): δ = 144.4 (Ph-Cipso), 130.4, 128.2, 127.4 (Ph-C),
95.0 (CϵC), 73.1 (SCPh3) ppm.C40H30S2 (574.81): calcd. C 83.58,
for 3 d at ambient temperature. After removal of the solvents in H 5.26, S 11.16; found C 83.15, H 5.38, S 10.82.
vacuo, the residue was dissolved in n-hexane (150 mL), dried with
Trimethylsilylethynyl Trimethylsilylethyl Sulfide (4): Sulfide 4 was
magnesium sulfate, and filtered. The residue was thoroughly
washed with n-hexane (3ϫ20 mL). After removal of the solvent in
vacuo 2a (32.2 g, 99%) was obtained as a light yellow oil. 1H NMR
(200 MHz, CDCl3): δ = 7.29–7.20 (m, 5 H, Ph-H), 3.85 (s, 2 H,
SCH2), 2.75 (s, 1 H, HCϵC) ppm. 13C NMR (50 MHz, CDCl3): δ
= 136.2 (Ph-Cipso), 128.8, 128.4, 127.6 (Ph-C), 83.4 (SCϵC), 74.1
(HCϵC), 39.4 (SCH2) ppm.
prepared as described for 1a by using trimethylsilylacetylene
(10 mL, 71 mmol), diethyl ether (100 mL), n-butyllithium (10  in
n-hexane, 7.1 mL), sulfur (2.27 g, 71 mmol), and finally 2-trime-
thylsilylethylbromide (11.2 mL, 12.9 g, 71 mmol) as the alkylating
agent. Extraction of the crude product with n-hexane (80 mL and
3ϫ20 mL), filtration, and removal of the solvent in vacuo yielded
4 (14.0 g, 86%) analytically pure as a light yellow oil. 1H NMR
(200 MHz, CDCl3): δ = 2.98 (m, 2 H, CH2S), 1.00 (m, 2 H, CH2Si),
0.16 [s, 9 H, (CH3)3SiCH2], 0.03 [s, 9 H, (CH3)3SiCC] ppm. 13C
Diphenylmethyl Ethynyl Sulfide (2b): Compound 2b was prepared
as described for 2a. 1H NMR (200 MHz, CDCl3): δ = 7.61–7.30
(m, 10 H, Ph-H), 5.73 (s, 1 H, SCH), 2.89 (s, 1 H, HCϵC) ppm. NMR (50 MHz, CDCl3): δ = 100.9 (CϵCSi), 95.2 (CϵCS), 32.3
13C NMR (50 MHz, CDCl3): δ = 139.3 (Ph-Cipso), 128.5, 128.4, (CH2S), 17.1 (CH2Si), 0.00 [(CH3)3SiCC], –1.93 [(CH3)3SiCH2]
127.7 (Ph-C), 84.0 (SCϵC), 74.2 (HCϵC), 57.6 (SCH) ppm.
ppm. C10H22SSi2 (230.52): calcd. C 52.10, H 9.62, S 13.91; found
C 52.39, H 9.87, S 13.71.
Triphenylmethyl Ethynyl Sulfide (2c): Compound 2c was prepared
as described for 2a with an 8 d reaction time. The completeness of
the conversion was checked by thin layer chromatography (n-hex-
ane/toluene, 5:1). Alkyne 2c crystallizes in large light-yellow prisms
from a saturated diethyl ether solution upon cooling. Yield: 76%.
Bis(trimethylsilylethylthio)acetylene (5):
A solution of 4 (5 g,
21.7 mmol) in THF (100 mL) was cooled to –78 °C. Methyl-
lithium·lithium chloride (1.5  solution in n-hexane, 14.5 mL,
21.7 mmol) was added to the clear colorless solution, and the re-
1H NMR (200 MHz, CDCl3): δ = 7.39–7.26 (m, 15 H, Ph-H), 2.85 sulting yellow–orange mixture was stirred for half an hour at this
(s, 1 H, HCϵC) ppm. 13C NMR (50 MHz, CDCl3): δ = 143.7 (Ph- temperature. Subsequently, the mixture was slowly warmed to 0 °C
Cipso), 129.7, 127.8, 127.3 (Ph-C), 86.5 (SCϵC), 75.4 (HCϵC), 70.8
and stirred for two hours at this temperature. After again being
(SCPh ) ppm. IR (KBr): ν = 3279 (m, H–C ), 2029 (w, CϵC) cm–1. cooled to –78 °C, sulfur (0.69 g, 21.7 mmol), which was dried in
˜
3
2
C21H16S (300.42): calcd. C 83.96, H 5.37, S 10.67; found C 83.44,
H 5.65, S 10.42.
the usual manner, was added. The mixture was stirred for 30 min
at –78 °C and then warmed to room temperature. To the resulting
clear, dark red solution was added 2-trimethylsilylethylbromide
(3.4 mL, 3.9 g, 21.7 mmol) at 0 °C. After stirring overnight at ambi-
ent temperature, the solvents were removed in vacuo. The residue
was extracted into n-hexane (60 mL and 3ϫ5 mL). The filtrate was
reduced to a small volume in vacuo and purified by column
chromatography (n-hexane). Disulfide 5 (4.3 g, 68%) was obtained
Bis(benzylthio)acetylene (3a): A solution of 2a (32.2 g, 0.218 mol)
in diethyl ether (300 mL) cooled to –78 °C was treated with n-butyl-
lithium (10  solution in n-hexane, 21.8 mL). After 10 min, sulfur
(6.98 g, 0.218 mol), which was first dried in vacuo, was added. Af-
ter stirring at –78 °C for a further 15 min, the mixture was warmed
to room temperature and stirred until total consumption of the
sulfur. To the resulting clear yellow–red solution was added benzyl
bromide (25.2 mL, 0.218 mol) at 0 °C, and the mixture was stirred
at room temperature overnight. Product 3a was isolated as large
yellow crystals by an aqueous workup and crystallization from di-
1
as a light yellow oil. H NMR (200 MHz, CDCl3): δ = 2.74 (m, 4
H, CH2S), 0.97 (m, 4 H, CH2Si), 0.02 [s, 18 H, (CH3)3Si] ppm.
13C NMR (50 MHz, CDCl3): δ = 86.8 (CϵCS), 33.0 (CH2S), 17.1
(CH2Si), –1.81 [(CH3)3SiCH2] ppm. C12H26S2Si2 (290.64): calcd. C
49.59, H 9.02, S 22.07; found C 49.72, H 8.87, S 21.91.
1
ethyl ether at –35 °C. H NMR (200 MHz, CDCl3): δ = 7.31–7.18
(m, 10 H, Ph-H), 3.79 (s, 4 H, SCH2) ppm. 13C NMR (50 MHz, Exchange of the Protection Groups: Benzyl bromide (240 µL,
CDCl3): δ = 136.4 (Ph-Cipso), 129.0, 128.4, 127.6 (Ph-C), 87.9 2.0 mmol) was added to a solution of 5 (290 mg, 1.0 mmol) in THF
(CϵC), 41.3 (SCH ) ppm. Raman: ν = 2058 (s, CϵC) cm–1. (7 mL). At room temperature, tetrabutylammonium fluoride (0.5 
˜
2
C16H14S2 (270.42): calcd. C 71.06, H 5.22, S 23.71; found C 70.75,
H 5.34, S 23.56.
solution in THF, 4.1 mL) was added. The removal of the trimethyl-
silylethyl protecting groups evolves ethylene that ceased after about
15 min. After stirring for 12 h, the reaction mixture was dried in
vacuo, and the residue was purified by column chromatography on
SiO2 (toluene). According to NMR and mass spectroscopic evi-
dence, the eluted product was pure bis(benzylthio)acetylene (3a;
195 mg, 70%).
Bis(triphenylmethylthio)acetylene (3c): A solution of 2c (2.5 g,
8.3 mmol) in diethyl ether (300 mL) was cooled to –78 °C forming
a light yellow suspension. Lithium diisopropylamide (890 mg,
8.3 mmol) dissolved in THF (15 mL) was added. After stirring for
15 min at –78 °C, sulfur (265 mg, 8.3 mmol), which was dried in
vacuo for one hour, was added to the clear yellow solution, and
the mixture was slowly warmed to –40 °C. After consumption of
the sulfur in the course of two hours, the color of the mixture
had changed from yellow to red–brown. At –60 °C, a solution of
triphenylmethyl chloride (2.3 g, 8.3 mmol) in toluene (25 mL) was
slowly added, and the mixture was stirred at ambient temperature
overnight. Subsequently, the solvents were removed in vacuo, and
the residue was extracted with toluene (150 mL) and filtered
through celite. The brown clear solution was reduced in volume to
approximately 30 mL. Precipitation of a white powder, finally at
–30 °C, was observed in the course of two weeks. Product 3c (1.7 g,
36%) was isolated by filtration, washing with diethyl ether (5 mL),
and drying in vacuo. Crystallization was achieved by cooling a sat-
Compound 6: To a solution of 2a (2.56 g, 17.3 mmol) in diethyl
ether (100 mL), cooled to –78 °C, was added n-BuLi (10  solution
in n-hexane, 1.73 mL, 17.3 mmol) by syringe. After 10 min, sulfur
(0.55 g, 17.3 mmol) was added. The mixture was then warmed to
0 °C followed by the addition of chlorotrimethylsilane (2.2 mL,
17.3 mmol). After stirring for 24 h, the solvent was removed in
vacuo. The residue was dissolved in n-hexane, and the solution fil-
tered. The red–brown filtrate crystallized instantly. The crystals
were dried in vacuo. 1H NMR (200 MHz, C6D6): δ = 7.26–7.01 (m,
10 H, Ph-H), 3.80 (s, 2 H, SCH2), 3.64 (s, 2 H, SCH2), 0.26 [s, 9
H, Si(CH3)3], 0.15 [s, 9 H, Si(CH3)3] ppm. 13C NMR (50 MHz,
C6D6): δ = 140.2 (C=C), 137.7, 136.0 (Ph-Cipso), 129.9 (C=C),
128.3–125.8 (6ϫPh-C), 107.7 (C=C), 40.1, 37.4 (SCH2), –1.3
3530
www.eurjoc.org
© 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Org. Chem. 2007, 3526–3532

In Pursuit of an Acetylenedithiolate Synthesis
FULL PAPER
Eur. J. Org. Chem. 2003, 47–53; f) J. Balsells, A. Moyano, M. A.
Pericás, A. Riera, Tetrahedron: Asymmetry 1997, 8, 1575–1580;
g) H. Fischer, K. Treier, C. Troll, Chem. Ber. 1995, 128, 1149–
1156.
[Si(CH3)3], –2.0 [Si(CH3)3] ppm, the fourth C=C resonance is ob-
scured. MS (MALDI-TOF): m/z = 504 [M]+, 431 [M – SiMe3]+,
413 [M – C7H7]+.
Crystal Structure Determination: Single crystals suitable for X-ray
analysis were coated in paratone oil and mounted on a glass fiber.
The intensity data of the complexes were collected with a Bruker
AXS Apex system equipped with a rotating anode. The data was
measured by using graphite monochromated Mo-Kα radiation.
Data collection, cell refinement, data reduction, and integration as
well as absorption correction were performed with the Bruker AXS
program packages SMART, SAINT, and SADABS. Crystal and
space group symmetries were determined by using the XPREP pro-
gram. All crystal structures were solved with SHELXS[21] by direct
methods and were refined by full-matrix least-square techniques
against Fo2 with SHELXL.[22] All non-hydrogen atoms were refined
anisotropically. The hydrogen atoms were included at calculated
positions with fixed thermal parameters. The disorder phenomenon
in the crystal of 6 applies to the whole molecule about a virtual
inversion center.
Crystal Data for 2c:[23] C21H16S, Mr = 300.40 gmol–1; colorless
prisms, size 0.33ϫ0.21ϫ0.15 mm3; monoclinic; space group P2(1)/
n; a = 10.1146(7) b = 9.0173(6), 17.1278(11) Å; β = 95.271(1)°; V
= 1555.56(18) Å3; T = 153 K; Z = 4; ρcalcd. = 1.283 g cm–1; µ(Mo-
Kα) = 0.201 mm–1; reflections: 14767 collected, 3561 unique, 3173
observed; Fo Ն2σ(Fo), 2.25ՅΘ Յ27.50; Rint = 0.0257, 263 param-
eter, 0 restrains; R1(obs) = 0.0360, wR2(obs) = 0.0933; R1(all) =
0.0402, wR2(all) = 0.0960; GOF = 1.045; largest difference peak/
hole: 0.367/–0.187 eÅ3.
[2]
a) V. I. Krinichnyi, H.-K. Roth, M. Schrödner, Appl. Magn.
Reson. 2002, 23, 1–17; b) V. I. Krinichnyi, Synth. Met. 2000,
108, 173–222; c) T. Watase, H. Tachimori, T. Masuda, Bull.
Chem. Soc. Jpn. 1995, 68, 393–397; d) H.-K. Roth, V. I. Krin-
ichnyi, M. Schrödner, R.-I. Stohn, R. Baumann, U. Kulisch,
M. Schroedner, H. K. Roth, D. Sebastian, J. Bargon, Synth.
Met. 1993, 57, 3643–3648; e) T. Masuda, T. Matsumoto, T.
Yoshimura, T. Higashimura, Macromolecules 1990, 23, 4902–
4907; f) E. Fanghänel, A. M. Richter, B. Kordts, N. Beye, Phos-
phorus, Sulfur Silicon Relat. Elem. 1989, 43, 165–185.
a) C. Benisch, S. Bethke, R. Gleiter, T. Öser, H. Pritzkow, F.
Rominger, Eur. J. Org. Chem. 2000, 2479–2488; b) T. H. Stäb,
R. Gleiter, F. Rominger, Eur. J. Org. Chem. 2002, 2815–2822;
c) C. Benisch, D. B. Werz, R. Gleiter, F. Rominger, T. Öser, Eur.
J. Inorg. Chem. 2003, 1099–1112.
A. W. M. Lee, A. B. W. Yeung, M. S. M. Yuen, H. Zhang, X.
Zhao, W. Y. Wong, Chem. Commun. 2000, 75–76.
a) W. W. Seidel, M. Schaffrath, T. Pape, Angew. Chem. 2005,
117, 7976–7979; Angew. Chem. Int. Ed. 2005, 44, 7798–7800;
b) W. W. Seidel, M. D. Ibarra Arias, M. Schaffrath, M. C.
Jahnke, A. Hepp, T. Pape, Inorg. Chem. 2006, 45, 4791–4800;
c) W. W. Seidel, M. Schaffrath, T. Pape, Chem. Commun. 2006,
3999–4000.
a) D. Vijay, G. N. Sastry, THEOCHEM 2005, 732, 71–78; b)
A. Timoshkin, G. Frenking, J. Chem. Phys. 2000, 113, 8430–
8433; c) F. Diehl, H. Meyer, A. Schweig, B. Andes Hess Jr, J.
Fabian, J. Am. Chem. Soc. 1989, 111, 7651–7653.
K. Noerkjaer, A. Senning, Chem. Ber. 1993, 126, 73–77.
a) A. V. Martynov, G. Le Guillanton, Bull. Soc. Chim. Fr. 1997,
134, 823–831; b) H. J. Bestmann, K. Roth, Tetrahedron Lett.
1981, 22, 1681–1684.
a) H. D. Verkruijsse, L. Brandsma, Synthesis 1991, 818; b)
T. R. Klein, M. Bergemann, N. A. M. Yehia, E. Fanghänel, J.
Org. Chem. 1998, 63, 4626–4631.
A. Riera, F. Cabré, A. Moyano, M. A. Pericàs, J. Santamaria,
Tetrahedron Lett. 1990, 31, 2169–2172.
[3]
[4]
[5]
[6]
[7]
[8]
Crystal Data for 3c:[23] C40H30S2, Mr = 574.76 gmol–1; colorless
3
¯
prisms, size 0.19ϫ0.14ϫ0.08 mm ; triclinic; space group P1; a =
9.1879(5) b = 11.3494(6), 14.9572(9) Å; α = 92.356(1); β =
103.939(1); γ = 91.837(1)°; V = 1511.07(15) Å3; T = 153 K; Z = 2;
ρcalcd. = 1.263 g cm–1; µ(Mo-Kα) = 0.204 mm–1; reflections: 12244
collected, 5312 unique, 4645 observed; Fo Ն2σ(Fo), 1.40ՅΘ
Յ25.00; Rint = 0.0228, 499 parameter, 0 restrains; R1(obs) =
0.0338, wR2(obs) = 0.0863; R1(all) = 0.0387, wR2(all) = 0.0895;
GOF = 1.048; largest difference peak/hole: 0.278/–0.195 eÅ3.
Crystal Data for 6:[23] C24H32S4Si2, Mr = 504.92 gmol–1; colorless
plates, size 0.11ϫ0.09ϫ0.03 mm3; monoclinic; space group C2/c;
a = 16.631(6) b = 25.825(2), 28.350(10) Å; β = 102.209(7)°; V =
2684.2(16) Å3; T = 153 K; Z = 4; ρcalcd. = 1.249 g cm–1; µ(Mo-Kα)
= 0.454 mm–1; reflections: 14738 collected, 3905 unique, 2835 ob-
served Fo Ն2σ(Fo), 1.47ՅΘՅ30.02; Rint = 0.0466, 147 parameter,
0 restrains; R1(obs) = 0.0441, wR2(obs) = 0.0967; R1(all) = 0.0683,
wR2(all) = 0.1061; GOF = 1.013; largest difference peak/hole:
0.361/–0.236 eÅ3.
[9]
[10]
[11]
[12]
P. J. Stang, V. V. Zhdankin, J. Am. Chem. Soc. 1991, 113, 4571–
4576.
a) L. Brandsma, H. E. Wijers, M. C. Jonker, Recueil Trav.
Chim. Pays Bas 1963, 82, 208–213; b) E. Schaumann, J.
Lindstädt, Chem. Ber. 1983, 116, 1728–1738.
[13]
[14]
a) D. B. Werz, R. Gleiter, F. Rominger, J. Org. Chem. 2004, 69,
2945–2952; b) D. B. Werz, J. H. Schulte, B. J. Rausch, R. Gle-
iter, F. Rominger, Eur. J. Inorg. Chem. 2004, 2585–2593.
a) A. J. Blake, P. T. Brain, R. O. Gould, H. McNab, D. W. H.
Rankin, H. E. Robertson, P. Amaro, I. Landelle, M. Bühl, J.
Chem. Soc. Perkin Trans. 2 1994, 1429–1434; b) F. Mo, E. Hus-
stad, R. H. Matthiesen, B. C. Hauback, H. Kjosen, J. A. Hau-
gan, E. H. Morkved, Z. Kristallogr. 1999, 214, 353–357.
a) G. Menczel, J. Kiss, Acta Crystallogr., Sect. B 1975, 31,
1787–1789; b) S. J. Lee, B. H. Han, C.-K. Kung, J.-G. Kim, I.-
H. Suh, Acta Crystallogr., Sect. E 2001, 57, o271–o272; c) T.
Steiner, Z. Kristallogr. 1995, 210, 457–458.
a) N. K. Roberts, B. W. Skelton, A. H. White, J. Chem. Soc.
Dalton Trans. 1980, 1567–1571; b) H. Schmidbaur, G. Reber,
A. Schier, F. E. Wagner, G. Müller, Inorg. Chim. Acta 1988,
147, 143–150; c) J. C. J. Bart, Acta Crystallogr., Sect. B 1969,
25, 489–497.
[15]
[16]
Acknowledgments
The Deutsche Forschungsgemeinschaft is gratefully acknowledged
for financial support of this work. W. W. S. thanks Prof. F. E. Hahn
for generous support and Dr. R. Fröhlich for help with the struc-
ture solution of compound 6.
[17]
[18]
[19]
[20]
R. D. Calleja, E. S. Martinez, S. Friedrichs, J. Kudnig, J.
Bracker, G. Klar, J. Mater. Chem. 1995, 5, 389–394.
A. Bury, S. D. Joag, C. J. M. Stirling, J. Chem. Soc. Chem.
Commun. 1986, 124–125.
H. Sun, S. G. DiMagno, J. Am. Chem. Soc. 2005, 127, 2050–
2051.
[1] a) Y. Takenaka, H. Ito, M. Hasegawa, K. Iguchi, Tetrahedron
2006, 62, 3380–3388; b) C. Schäfer, D. B. Werz, T. H. Stäb, R.
Gleiter, F. Rominger, Organometallics 2005, 24, 2106–2113; c)
D. B. Werz, J. H. Schulte, R. Gleiter, F. Rominger, J. Or-
ganomet. Chem. 2004, 689, 3132–3142; d) J. A. Miller, S. A.
Pope, D. R. Riddall, G. M. Ullah, G. M. Welsh, Tetrahedron
Lett. 2004, 44, 8411–8415; e) T. R. Appel, N. A. M. Yehia, U.
Baumeister, H. Hartung, R. Kluge, D. Ströhl, E. Fanghänel,
S. R. Wilson, A. Shedrinsky, J. Org. Chem. 1982, 47, 1983–
1984.
Eur. J. Org. Chem. 2007, 3526–3532
© 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
3531

W. W. Seidel, M. J. Meel, M. Schaffrath, T. Pape
FULL PAPER
[21] SHELXS-97: G. M. Sheldrick, Acta Crystallogr., Sect. A 1990,
46, 467–473.
[22] G. M. Sheldrick, SHELXL-97, University of Göttingen, Ger-
many, 1997.
These data can be obtained free of charge from The Cambridge
Crystallographic Data Centre via http://www.ccdc.cam.ac.uk.
Received: December 20, 2006
Published Online: June 12, 2007
[23] CCDC-631392 (for 2c), -631393 (for 3c), -631394 (for 6) con-
tain the supplementary crystallographic data for this paper.
3532
www.eurjoc.org
© 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Org. Chem. 2007, 3526–3532