Formation of 5-phenyl-1,2-dithiole-3-thione from molybdenum dithiopropiolato complexes

Article abstract of DOI:10.1016/j.jorganchem.2004.01.022

Molybdenum dithiopropiolato complexes, [(η⁵-C₅ R₄R′)Mo(CO)₂(η² -S₂CC≡CPh)] (R=H, R′=Me 1a, R=R′=H 1b; R=R′=Me 1c) react with trimethylamine- N -oxide (TMNO · 2H₂O) under mild the

Full text of DOI:10.1016/j.jorganchem.2004.01.022

Journal of Organometallic Chemistry 689 (2004) 1325–1327
www.elsevier.com/locate/jorganchem
Note
Formation of 5-phenyl-1,2-dithiole-3-thione from molybdenum
dithiopropiolato complexes
a,b,
a
a
b
Pradeep Mathur
*, Vidya D. Avasare , Abhijit K. Ghosh , Shaikh M. Mobin
a
Chemistry Department, Indian Institute of Technology, Powai, Bombay 400 076, India
National Single Crystal X-ray Diffraction Facility, Indian Institute of Technology, Powai, Bombay 400 076, India
b
Received 3 July 2003; accepted 22 January 2004
Abstract
Molybdenum dithiopropiolato complexes, [(g5-C5R4R0)Mo(CO)2(g2-S2CCBCPh)] (R ¼ H, R0 ¼ Me 1a, R ¼ R0 ¼ H 1b;
R ¼ R0 ¼ Me 1c) react with trimethylamine-N-oxide (TMNO ꢀ 2H2O) under mild thermolysis to form 5-phenyl-1,2-dithiole-3-thione
(2). The reaction proceeds through the formation of the oxo-complexes, [(g5-C5R4R0)Mo(O)(g3-S2CCBCPh)] (R ¼ H, R0 ¼ Me 3a,
R ¼ R0 ¼ H 3b; R ¼ R0 ¼ Me 3c). Direct reaction of 3a–c with TMNO ꢀ 2H2O under thermolysis also results in formation of 2.
Ó 2004 Elsevier B.V. All rights reserved.
Keywords: Dithiolethione; Molybdenum; Dithiopropiolato; Carbonyl; Oxo
1. Introduction
these complexes for the preparation of 5-phenyl-1,2-
dithiole-3-thione.
The 1,2-dithiole-3-thione and its derivatives are
versatile compounds and find uses as chemoprotective
agents [1,2] and for treatment of intestinal allergies and
jaundice [3].
2. Results and discussion
Although first isolated from Brassica olevacea, the
synthesis of 1,2-dithiole-3-thione has been carried out by
a variety of different methods, such as reaction of eu-
genol or isoeugenol with sulfur [4], reaction of ArCH@
CHRR0 (Ar ¼ phenyl or anisole and R,R0 ¼ Me or H)
with sulfur [5,6]. The derivative, 5-phenyl-1,2-dithiole-3-
thione (2) has been obtained from the reaction of
PhCOCH2CO2Et and P4S10 [7–9]. Additionally, several
other starting compounds such as b-ketodithioic acid
and aryl ketones have been used for preparation of 1,2-
dithiole-3-thione [10,11]. We have recently reported the
preparation and crystal structures of some dithiopropi-
olato complexes, [(g5-C5R5)Mo(CO)2(g2-S2CCBCPh)]
and their conversion to the oxo-derivatives [(g5-
C5R5)Mo(O)(g3-S2CCBCPh)] (R ¼ H or Me) by pho-
tolysis in presence of air [12]. In this paper, we report on
the utility of the coordinated dithiopropiolato ligands in
When an acetonitrile solution containing [(g5-
C5R4R0)Mo(CO)2(g2-S2CCBCPh)] (R ¼ H, R0 ¼ Me 1a,
R ¼ R0 ¼ H 1b, R ¼ R0 ¼ Me 1c) and 4 equivalents of
hydrated trimethylamine-N-oxide (TMNO ꢀ 2H2O) was
heated at 65 °C, 5-phenyl-1,2-dithiole-3-thione (2) was
obtained in yields of 80%, 33%, and 44%, respectively, as
shown in Scheme 1. In the reaction using 1c, the known
oxo-compound, [(g5-C5Me5)Mo(O)(g3-S2CCBCPh)]
(3c) was also isolated from the reaction mixture. When
using 1a and 1b, we were unable to isolate the oxo-
compounds, [(g5-C5H4Me)Mo(O)(g3-S2CCBCPh)] and
[(g5-C5H5)Mo(O)(g3-S2CCBCPh)] from these reac-
tions. To confirm whether the oxo-compounds, [(g5-
C5R4R0)Mo(O)(g3-S2CCBCPh)] could be intermediates
in the formation of 2 from 1a–c, we prepared the oxo-
compounds [(g5-C5R4R0)Mo(O)(g3-S2CCBCPh)] (R ¼
H, R0 ¼ Me 3a, R ¼ R0 ¼ H 3b; R ¼ R0 ¼ Me 3c) by
photolysis of benzene solutions of 1a–c under constant
bubbling of air according to the method reported by
us earlier [12]. Compound 2 was obtainable from the
* Corresponding author. Tel./fax: +91-222-572-4089.
E-mail address: mathur@chem.iitb.ac.in (P. Mathur).
0022-328X/$ - see front matter Ó 2004 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2004.01.022

1326
P. Mathur et al. / Journal of Organometallic Chemistry 689 (2004) 1325–1327
L
S
S
TMNO.2H O
2
)
C CPh
C
Mo
MeCN
65 ºC
C
C
O
O
5
1a L = (η -C H Me)
5
4
5
1b L = (η -C H )
5
5
5
H
C
1c L = (η -C Me )
5
5
S
C
S
CPh
S
(i) or (ii)
2
L
Mo
O
S
S
C
TMNO.2H O
2
C
MeCN
65 ºC
C
Ph
5
3a L = (η -C H Me)
5
4
5
3b L = (η -C H )
5
5
5
3c L = (η -C Me )
5
5
Scheme 1. (i) TMNO ꢀ 2H2O, MeCN, 25 °C; (ii) benzene/air, hm, 0 °C.
oxo-compounds 3a–c in yields of 83%, 47% and 43%,
respectively, the best yields being obtained when aceto-
nitrile solutions of 3a–c and TMNO ꢀ 2H2O were heated
at 65 °C. In an attempt to improve the yield of 2, we
investigated the reactions of 1a–c and of 3a–c with
TMNO ꢀ 2H2O in the presence of sulfur powder. In both
sets of reactions we did not observe any significant im-
provement in the yield of 2 formed (yield of 2 from re-
action of 1a–c with TMNO ꢀ 2H2O in presence of S: 84%,
38% and 47%, respectively; from reaction of 3a–c with
TMNO ꢀ 2H2O in presence of S: 86%, 50% and 42%,
respectively.
atom of the dithiolethione ring. When we used anhy-
drous TMNO, we did not observe formation of 2.
3. Experimental
3.1. General considerations
Reactions and manipulations were carried out using
standard Schlenk line techniques under an atmosphere
of argon. Solvents were purified, dried and distilled
under an argon atmosphere prior to use. Infrared
spectra were recorded on a Nicolet Impact 400 FT IR
spectrophotometer, as hexane solutions in 0.1 mm path
length cells. 1H NMR spectra were recorded on a Varian
VXR-300S spectrometer in CDCl3. Elemental analyses
were performed using a Carlo–Erba automatic analyzer.
Preparation of compounds [(g5-C5R4R0)Mo(CO)2(g2-
S2CCBCPh)] (R ¼ H, R0 ¼ Me 1a, R ¼ R0 ¼ H 1b;
R ¼ R0 ¼ Me 1c) and their conversion to the oxo-deriv-
atives, [(g5-C5R4R0)Mo(O)(g3-S2CCBCPh)] (R ¼ H,
R0 ¼ Me 3a, R ¼ R0 ¼ H 3b; R ¼ R0 ¼ Me 3c) were car-
ried out by the method reported earlier [12].
Compound 2 was characterised on the basis of com-
1
parison of its IR and H NMR spectroscopy with that
reported earlier. Further, a single crystal X-ray structure
determination established its molecular structure. The
bond materials are in agreement with those reported
earlier from a structure determination of the same
compound [13] and, in general, bond distances in 2 are
consistent with partial C–C and C–S double bond
character.
Role of TMNO ꢀ 2H2O appears to be two fold in the
overall sequence leading to formation of 2. Firstly, it
converts compounds 1a–c to their respective oxo-forms.
This has been independently established by us by isolat-
ing the oxo-compounds, [(g5-C5R4R0)Mo(O)(g3-S2CCB
CPh)] (3a–c) from the reactions of 1a–c with TMNO ꢀ
2H2O (Scheme 1). Secondly, the water of hydration of
TMNO serves as a source of proton to the central carbon
3.2. Preparation 2 from [(g5- C5H4Me)Mo(CO)2(g2-
S2CCBCPh)] 1a
A solution of TMNO ꢀ 2H2O (41 mg, 0.37 mmol)
in acetonitrile (50 ml) was added dropwise to an

P. Mathur et al. / Journal of Organometallic Chemistry 689 (2004) 1325–1327
1327
acetonitrile solution (50 ml) of 1a (30 mg, 0.074 mmol).
The solution was subjected to constant heating at 65 °C
for 45 min. After removal of the solvent the residue was
re-dissolved in dichloromethane and filtered through
Celite to remove insoluble material. The filtrate was
concentrated and subjected to chromatographic work-up
on silica gel TLC plates using hexane/dichloromethane
(70/30 v/v) to yield a yellow band of 2 (8 mg, 80%).
Under identical conditions, compound 2 was ob-
tained in yields of 33% and 44%, respectively from the
reactions of 1b and 1c. Reaction of 1c also yielded a
second band during chromatographic work-up, orange
[(g5-C5Me5)Mo(O)(g3-S2CCBCPh)] (3c) in 31% yield.
Data Centre, CCDC No. 214070. Copies of this infor-
mation may be obtained free of charge from The Di-
rector, CCDC, 12 Union Road, Cambridge CB2 1EZ,
UK (Fax: +44-1223-336033; E-mail: deposit@ccdc.cam.
ac.uk or http://www.ccdc.cam.ac.uk).
Acknowledgements
P.M. is grateful to the Council of Scientific and
Industrial Research, Government of India for
a
research grant. V.D.A. is grateful to the Indian
Academy of Sciences, Bangalore for a summer teacher
fellowship.
3.3. Preparation of 2 from [(g5-C5H4Me)Mo(O)(g3-
S2CCBCPh)] 3a
References
A solution of TMNO ꢀ 2H2O (13 mg, 0.12 mmol) in
acetonitrile (15 ml) was added drop-wise to an acetoni-
trile solution (20 ml) of 3a (11 mg, 0.029 mmol). The
solution was subjected to constant heating at 65 °C
under an atmosphere of argon for 45 min. After removal
of the solvent the residue was re-dissolved in dichlo-
romethane and filtered through Celite to remove insol-
uble material. The filtrate was concentrated and
subjected to chromatographic work-up on silica gel TLC
plates using hexane/dichloromethane (70/30 v/v) to yield
a yellow band of 2 (3.5 mg, 83%).
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Crystallographic data for the structural analysis have
been deposited with the Cambridge Crystallographic