An unexpected sequence: From phosphole sulfide to phosphole- and thiophene-annulated 1,2-dithiole-3-thiones

Article abstract of DOI:10.1021/om9003972

The deprotonation of 1-phenyl-3,4-dimethylphosphole sulfide by a bulky base, followed by the reaction of S₂Cl₂, unexpectedly yields a phosphole-annulated 1,2-dithiole-3-thione. The complexation of this product by [W(CO)₅]

Full text of DOI:10.1021/om9003972

Organometallics 2009, 28, 4621–4623 4621
DOI: 10.1021/om9003972
An Unexpected Sequence: From Phosphole Sulfide to Phosphole- and
Thiophene-Annulated 1,2-Dithiole-3-thiones
Ana Ciric and Franc-ois Mathey*
Division of Chemistry & Biological Chemistry, School of Physical & Mathematical Sciences, Nanyang
Technological University, 21 Nanyang Link, Singapore 637371
Received May 15, 2009
Summary: The deprotonation of 1-phenyl-3,4-dimethylphosp-
hole sulfide by a bulky base, followed by the reaction of S2Cl2,
unexpectedly yields a phosphole-annulated 1,2-dithiole-3-
thione. The complexation of this product by [W(CO)5] takes
place at CdS as expected on the basis of theoretical calcula-
tions. Another product results from the unprecedented replace-
ment of the P(S)Ph unit by sulfur, giving the corresponding
thiophene derivative.
performed a DFTcalculationon the model compound 3 atthe
B3LYP/6-311þG(d,p) level.3 The computed structure is very
close to the experimental structure of the complex. The
HOMO (Figure 1) is essentially localized on the dithiolethione
ring with no participation of phosphorus. The coefficient at
the CdS sulfur is huge, indicating that it will be the reactive
site toward electrophiles, as is the case for normal dithio-
lethiones. The participation of the phosphole ring is more
significant in the LUMO. At -5.1, the NICS(1) index4
indicates that the sulfur ring is only weakly aromatic.
The easily accessible 3H-1,2-dithiole-3-thiones1 display an
interesting redox chemistry, canserve as ligands fortransition
metals, and have a lot of interesting biological properties. It
would be quite interesting to combine this structure with a
modulating phosphino group, but, to the best of our knowl-
edge, no phosphino-substituted dithiolethione has ever been
described in the literature until now. We describe herein how
we found an original phosphole-annulated dithiolethione
while trying to link two phosphole units by a sulfur bridge.
Our starting point was the delocalized anion obtained by
deprotonation of 1-phenyl-3,4-dimethylphosphole sulfide
(1) by a bulky base (here the sodium hexamethyldisilazide).2
We investigated the reaction of this anion with disulfur
dichloride with the aim of creating a S-S link between two
phosphole units. In fact, we obtained a complicated mixture
of products, among which a readily eluted deep red com-
pound (2) was especially noteworthy (eq 1).
The UV/vis spectrum of 2 (Figure 2) shows a characteristic
band at 483 nm (ε 8339). In the parent dithiolethione, this
band occurs at 410 nm (ε 6400) and corresponds to a π*rπ
Figure 1. HOMO and LUMO of compound 3 as computed at
the B3LYP/6-311þG(d,p) level.
(3) Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.;
Robb, M. A.; Cheeseman, J. R.; Montgomery, J. A., Jr.; Vreven, T.;
Kudin, K. N.; Burant, J. C.; Millam, J. M.; Iyengar, S. S.; Tomasi, J.;
Barone, V.; Mennucci, B.; Cossi, M.; Scalmani, G.; Rega, N.; Petersson,
G. A.; Nakatsuji, H.; Hada, M.; Ehara, M.; Toyota, K.; Fukuda, R.;
Hasegawa, J.; Ishida, M.; Nakajima, T.; Honda, Y.; Kitao, O.; Nakai,
H.; Klene, M.; Li, X.; Knox, J. E.; Hratchian, H. P.; Cross, J. B.; Bakken,
V.; Adamo, C.; Jaramillo, J.; Gomperts, R.; Stratmann, R. E.; Yazyev,
O.; Austin, A. J.; Cammi, R.; Pomelli, C.; Ochterski, J. W.; Ayala, P. Y.;
Morokuma, K.; Voth, G. A.; Salvador, P.; Dannenberg, J. J.; Zakr-
zewski, V. G.; Dapprich, S.; Daniels, A. D.; Strain, M. C.; Farkas, O.;
Malick, D. K.; Rabuck, A. D.; Raghavachari, K.; Foresman, J. B.;
Ortiz, J. V.; Cui, Q.; Baboul, A. G.; Clifford, S.; Cioslowski, J.; Stefanov,
B. B.; Liu, G.; Liashenko, A.; Piskorz, P.; Komaromi, I.; Martin, R. L.;
Fox, D. J.; Keith, T.; Al-Laham, M. A.; Peng, C. Y.; Nanayakkara, A.;
Challacombe, M.; Gill, P. M. W.; Johnson, B.; Chen, W.; Wong, M. W.;
Gonzalez, C.; Pople, J. A. Gaussian 03, revision B.05; Gaussian, Inc.:
Wallingford, CT, 2004.
The formula of 2 was established as follows. The measured
mass, m/z 312.9398 (MHþ), was very close to the computed
mass for C12H10PS4 (312.9403). The proton NMR spectrum
showed only one olefinic R-proton at δ 6.19 ppm (2JH-P
=
32.24 Hz) and one methyl at δ 2.61 ppm (CD2Cl2). The most
prominent feature of the 13C NMR spectrum was a CdS
doublet at δ 209.61 ppm (JC-P=16.5 Hz). Classical dithio-
lethiones show a CdS resonance in the range 206-216 ppm.1
The characterization of 2 was completed by the X-ray crystal
structure analysis of the complex (see later). In order to have a
more precise understanding of the electronic structure of 2, we
*Corresponding author. E-mail: fmathey@ntu.edu.sg.
(1) Review: Pedersen, C. T. Sulfur Rep. 1995, 16, 173.
(2) Mathey, F. Tetrahedron 1974, 30, 3127. Mathey, F. Tetrahedron
1976, 32, 2395.
(4) Chen, Z.; Wannere, C. S.; Corminboeuf, C.; Puchta, R.; Schleyer,
P. v. R. Chem. Rev. 2005, 105, 3842.
r
2009 American Chemical Society
Published on Web 06/23/2009
pubs.acs.org/Organometallics

4622 Organometallics, Vol. 28, No. 15, 2009
Note
Figure 2. UV/vis spectrum of 2 in dichloromethane (λ in nm).
transition.5 So it seems that the phosphole annulation slightly
increases the delocalization within the dithiolethione ring.
The yields of our initial experiments were quite low and
erratic, so it was necessary to improve both the reproduci-
bility and the productivity of the transformation. A logical
mechanism is proposed in eq 2.
Figure 3. X-ray crystal structure analysis of the complex of the
phosphole-annulated 1,2-dithiole-3-thione with tungsten pen-
tacarbonyl 4. Ellipsoids are scaled to enclose 50% of the
˚
electronic density. Significant distances (A) and angles (deg):
P1-S1 1.9428(15), P1-C1 1.788(4), P1-C5 1.825(3), P1-C7
1.793(4), C1-C2 1.350(5), C2-C4 1.501(5), C4-C5 1.367(5),
C4-C6 1.430(5), C5-S2 1.696(4), C6-S3 1.731(4), S3-S2
2.0713(12), C6-S4 1.668(4), S4-W1 2.5185(10); C1-P1-C5
90.47(17), P1-C5-S2 129.1(2), C4-C5-S2 120.5(3), C5-S2-
S3 92.79(13), S2-S3-C6 97.19(12), S3-C6-S4 119.4(2), S3-
C6-C4 113.4(3), C4-C6-S4 127.2(3), C5-C4-C6 115.9(3),
C6-C4-C2 130.9(3), C6-S4-W1 114.67(13).
On this basis, it seemed clear that 1 equiv of a strong and
bulky base was necessary to produce the anion derived from
1 that serves to build the initial C-S link and that three
additional equivalents of a weaker base were necessary to
close the sulfur ring and create the thiocarbonyl group. This
second base must be inert toward the S-Cl bonds. Thus we
devised an optimized procedure starting by the condensation
of 1 equiv of 1, 1 equiv of (Me3Si)2NNa, and 1 equiv of S2Cl2
at low temperature, followed by the addition of a second
equivalent of S2Cl2 and 3 equiv of triethylamine at 0 °C. In
doing so, we obtained a reproducible 10% yield.
In order to fully establish the structure of 2 and to see what
is its preferential coordination site (CdS or PdS), we
investigated the reaction of 2 with tungsten pentacarbonyl.
The theoretical study favored a complexation at CdS. Be-
sides a lot of oligomers, the reaction produces two well-
defined compounds in low yields. The first one is, indeed, the
CdS complex 4, whose structure was confirmed by X-ray
analysis (Figure 3).
mation of another product (5) that does not contain phos-
phorus. It, apparently, results from the unprecedented
conversion of a phosphole sulfide into a thiophene ring. At
the moment, we are unsure of how this conversion proceeds
and if it is possible to generalize it. Complex 5 was unam-
biguously characterized by X-ray analysis (Figure 4). The
two rings are strictly coplanar. The thiophene ring is sharply
dissymmetrized by annulation with the dithiolethione. The
parameters of the dithiolethione ring in 4 and 5 are very
similar. It is interesting to note that the HOMO-LUMO gap
of the free ligand in 5 is exactly the same as the gap of TTF at
the same level of theory, but both the HOMO and the
LUMO are shifted to lower energies by 1.5 eV in the
thiophene derivative by comparison with TTF.
Experimental Section
Synthesis of Phosphole-Annulated 1,2-Dithiole-3-thione (2).
To a solution of 1-phenyl-3,4-dimethylphosphole sulfide (0.5 g,
2.27 mmol) in 10 mL of THF at -80 °C and under argon was
added sodium bis(trimethylsilyl)amide (2.4 mL of 1 M solution
in THF) via syringe. The color immediately turned from pale
yellow to dark red. This solution was stirred for ∼5 min, after
which freshly8 distilled S2Cl2 (0.2 mL, 2.4 mmol) was added via
syringe and the solution was warmed to 0 °C and stirred for
∼20 min. At this point the color of the solution turned lighter red.
Still at 0 °C, triethylamine (0.97 mL, 6.96 mmol) was added to
The dithiolethione and phosphole rings are not strictly
coplanar: P-C-C-C(S) dihedral angle = 6.5°. The sulfur
ring does not display a sizable aromatic character, in agree-
ment with the previously reported structures6 and theoretical
computations.7 But the most exciting finding was the for-
(5) Gonbeau, D.; Guimon, C.; Pfister-Guillouzo, G. Tetrahedron
1973, 29, 3599.
(6) Wei, C. H. Acta Crystallogr. C: Cryst. Struct. Commun. 1985,
C41, 1768.
(7) Fabian, J.; Herzog, K. Vib. Spectrosc. 1998, 16, 77.
(8) Zysman-Colman, E.; Harpp, D. N. J. Org. Chem. 2003, 68, 2487–
2489.

Note
Organometallics, Vol. 28, No. 15, 2009 4623
1
3
(d, JPC =64.8 Hz, P-C-S), 209.61 (d, JPC =16.6 Hz, CdS).
31P NMR (CD2Cl2): δ 31.6. Mass spectrum: m/z 312.9398
(MHþ, 100%). Anal. Calcd for C12H9PS4: C, 46.13; H, 2.90.
Found: C, 46.21; H, 3.00.
Complexation of 2 by Tungsten Pentacarbonyl. Tungsten
pentacarbonyl was made in situ by dissolving 86 mg (0.24 mmol)
of tungsten hexacarbonyl in 12 mL of acetonitrile, then adding
27 mg (0.24 mmol) of trimethylamine-N-oxide dihydrate as a
solid. The solution turned bright yellow immediately and was
stirred for ∼30 min. Acetonitrile was removed in vacuo, and the
remaining bright yellow solid was then redissolved in 10 mL of
dry THF. This solution was stirred for 20 min and cooled to 0 °C,
and the 24 mM solution of 2 (76 mg in 10 mL of THF) was added
dropwise via a syringe. The mixture was stirred overnight, and in
the morning, the solution appeared dark blue. One pink and one
blue spot were observed by TLC (50:50 petroleum ether/dichlor-
omethane). The crude mixture was initially filtered quickly
through silica gel, after which it was further purified using
another silica gel column chromatography (100% petroleum
ether f 100% dichloromethane). The pinkfraction (5) was eluted
with a 70:30 solvent mixture in 2.3% yield (3 mg), and the blue
fraction (4) with a 50:50 solvent mixture in 1% yield (1.6 mg).
Both fractions were left overnight in test tubes, and pink and blue
crystals were obtained spontaneously. Elemental analyses were
Figure 4. X-ray crystal structure analysis of the complex of the
thiophene-annulated 1,2-dithiole-3-thione with tungsten penta-
carbonyl 5. Ellipsoids are scaled to enclose 50% of the electronic
not obtained for 4 and 5 due to insufficient quantities of products.
=
˚
density. Significant distances (A) and angles (deg): S1-C1 1.733(3),
4
Complex 4: 1H NMR (CD2Cl2): δ 2.66 (dd, 3H, 4JPH ≈ JHH
2
4
S1-C5 1.708(2), C1-C2 1.359(3), C2-C4 1.441(3), C4-C5
1.387(3), C5-S2 1.723(2), S2-S3 2.0711(8), S3-C6 1.728(2),
C6-C4 1.425(3), C6-S4 1.669(2), S4-W1 2.5274(6); C1-S1-
C5 90.59(11), S1-C5-S2 127.83(14), C5-S2-S3 92.61(8), S2-
S3-C6 97.79(8), S3-C6-C4 113.99(16), S3-C6-S4 119.52
(12), C6-C4-C5 115.89(19), C4-C5-S2 119.72(16), C6-
S4-W1 114.64(8).
1.8 Hz, Me), 6.29 (dd, 1H, JPH =32.0 Hz, JHH =1.8 Hz, d
CH-P), 7.55 (m, 2H, Ph meta H), 7.64 (m, 1H, Ph para H), 7.87
(m, 2H, Ph ortho H). 1H NMR (CD2Cl2): δ 19.79 (d, 3JPC=16.1
Hz, Me), 125.57 (d, 1JPC = 84.2 Hz, Ph ipso C), 129.32 (d, 1JPC
=
83 Hz, dCH-P), 129.64 (d, 3JPC=13.4 Hz, Ph meta CH), 130.93
(d, 2JPC=12.0 Hz, Ph ortho CH), 133.87 (s, Ph para CH), 151.49
(s, dC-CdS), 196.91 (s, cis-CO), 201.04 (s, trans-CO), 207.70
(d, 3JPC=13.4 Hz, CdS). 31P NMR (CDCl3): δ 38.0.
Complex 5: 1H NMR (CDCl3): δ 2.62 (s, Me), 7.09 (s, dCH-
S). 13C NMR (CDCl3): δ 15.67 (s, Me), 128.23 (s, dCH-S),
134.92 (s, Me-Cd), 197.26 (s, cis-CO), 201.08 (s, trans-CO),
207.11 (s, CdS). Mass spectrum: m/z 203.94 (base peak). Theory
for M-W(CO)5: 203.92.
the mixture followed by another equivalent of S2Cl2 (0.2 mL,
2.4 mmol). The color turned brown. The solution was then
warmed to room temperature. The reaction was monitored by
31P NMR and TLC (50:50 petroleum ether/CH2Cl2), proving
the presence of the red compound 2. The solvent was removed
in vacuo, and the mixture was purified by column chromatog-
raphy on silica gel using 75:25 petroleum ether/methylene
chloride as the eluent, yielding 73 mg (10.3%) of 2. Black
crystals were formed spontaneously overnight.
Acknowledgment. The authors thank the Nanyang
Technological University in Singapore for the financial
support of this work, Dr. Li Yong Xin for the X-ray
crystal structure analyses, and Dr. Astrid Mueller for the
UV/vis spectrum.
1HNMR(CD2Cl2): δ2.61 (dd, 3H, 4JPH=1.7 Hz, 4JHH=1.1 Hz,
2
Me), 6.19 (dd, 1H, JPH =32.2 Hz, JHH =1.1 Hz, dCH-P),
4
7.56 (m, 2H, Ph meta H), 7.64 (m, 1H, Ph para H), 7.87 (m, 2H,
3
Ph ortho H). 13C NMR (CD2Cl2): δ 18.90 (d, JPC=16.2 Hz,
Me), 126.94 (d, 1JPC=83.7 Hz, Ph ipso C), 128.03 (d, 1JPC=83.3
Hz,=CH-P), 129.87 (d, JPC=14.4 Hz, Ph meta CH), 131.34
Supporting Information Available: X-ray crystal structure
analysis of compounds 4 and 5. NMR spectra of 2, 4, and 5.
This material is available free of charge via the Internet at http://
pubs.acs.org.
3
(d, 2JPC=12.7 Hz, Ph ortho CH), 133.95 (s, Ph para CH), 150.24
(d, JPC = 28.7 Hz, Me-Cd), 153.65 (s, dC-CdS), 175.75
2