Copper(II)/tin(II) reagent for allylation, propargylation, alkylatipn, and benzylation of disulfides and elemental sulfur: New insight into the "copper effect"

Article abstract of DOI:10.1021/om000533g

Organic bromides and iodides react with diorganodisulfides in the presence of stannous chloride and catalytic cupric halide, giving rise to corresponding unsymmetrical sulfides. Similar reactions but with elemental sulfur provide trisulfides and tetrasulf

Full text of DOI:10.1021/om000533g

Organometallics 2001, 20, 157-162
157
Cop p er (II)/Tin (II) Rea gen t for Allyla tion , P r op a r gyla tion ,
Alk yla tion , a n d Ben zyla tion of Disu lfid es a n d Elem en ta l
†
Su lfu r : New In sigh t in to th e “Cop p er Effect”
Pradipta Sinha, Abhijit Kundu, and Sujit Roy*
Organometallics & Catalysis Laboratory, Chemistry Department, Indian Institute of
Technology, Kharagpur 721302, India
Sripadi Prabhakar and M. Vairamani
National Center for Mass Spectrometry, Indian Institute of Chemical Technology,
Hyderabad 500007, India
A. Ravi Sankar and A. C. Kunwar
NMR Laboratory, Indian Institute of Chemical Technology, Hyderabad 500007, India
Received J une 22, 2000
Organic bromides and iodides react with diorganodisulfides in the presence of stannous
chloride and catalytic cupric halide, giving rise to corresponding unsymmetrical sulfides.
Similar reactions but with elemental sulfur provide trisulfides and tetrasulfides. The
reactions proceed by copper thiolate as principal reactive intermediate.
In tr od u ction
Sch em e 1
Contemporary chemistry is characterized by the
number and variety of topics, which cut across tradi-
tional divides. The interest in combining transition and
main group elements to generate new structural motifs,
1
often a cluster, provides distinct opportunities in the
fields of “catalysis” and “molecular precursors to new
materials”. In this direction ligand-assisted cluster
designing is a well-adapted approach. A similar exercise,
but in a ligand-free environment, poses significant
Sch em e 2
2
diagnostic difficulties. Our recent success in introduc-
ing a Cu(II)/Sn(II) reagent for carbonyl allylation and
propargylation prompted us to study the reactivity of
the same toward the cleavage of the diselenide bond.
The investigation suggested a bimetallic reactivity
toward the formation of unsymmetrical diorgano-
selenides under extremely mild conditions (Scheme 1).
In this note, we present a novel finding pertaining to
the reactivity of Cu(II)/Sn(II) toward the activation of
diorganodisulfides and elemental sulfur leading to the
disulfide in the presence of catalytic cupric chloride in
THF under reflux gives rise to allylphenylsulfide 1 in
8
4% isolated yield (Table 1, entry 1).
The reaction proceeds as well with catalytic cupric
bromide. On the other hand, reaction in the absence of
copper halide shows less than 5% conversion. THF is
judged as the best solvent when compared with DCM,
DCM-H2O (1:1 v/v), and THF-H2O (1:1 v/v). γ-Substi-
tuted allyl halides give predominantly the linear un-
symmetrical sulfides. Thus, reaction of 1-bromo-3-
methyl-2-butene with diphenyl disulfide in THF gave
facile formation of sulfides, trisulfides, and tetrasulfides
3
(
Scheme 2). A distinct “copper effect” underlines the
observed reactivity and is believed to mediate via new
copper thiolate intermediates.
Resu lts a n d Discu ssion
8
5% of 3-methyl-2-butenyl(phenyl)sulfide 3 and 8% of
Activa tion of Disu lfid e. The reaction of stannous
chloride dihydrate with allyl bromide and diphenyl
the branched isomer (entry 4). The same reaction in
THF-H2O (1:1 v/v) gives 65% of 3 and 5% of the
branched isomer along with unreacted diphenyl disul-
fide (entry 5). The reaction is further extended to
†
Presented in part at the 8th NOST-Symposium, J aipur, India,
March 2-5, 2000.
(1) (a) Fenske, D. In Clusters and Colloids-From Theory to Applica-
tions; Schmid, G., Ed.; VCH: Weinheim, Germany, 1994. (b) Wang,
W.; Geng, Y.; Yan, P.; Liu, F.; Xie, Y.; Qian, Y. J . Am. Chem. Soc. 1999,
(3) For reviews on -S-S- cleavage, please see: (a) Procter, D. J .
J . Chem. Soc., Perkin Trans. 1 2000, 835-871 (b) Clennan, E. L.;
Stensaas, K. L. Org. Prep. Proc. Int. 1998, 30, 551-600. (c) Rayner, C.
M.; Contemp. Org. Synth. 1995, 2, 409-440. (d) Solladie, G. In
Comprehensive Organic Synthesis; Trost, B. M., Fleming, I., Eds.;
Pergamon: Oxford, 1991; Vol. 6, pp 133-170.
1
21, 4062.
2) (a) Kundu, A.; Prabhakar, S.; Vairamani, M.; Roy, S. Organo-
(
metallics 1997, 16, 4796. (b) Kundu, A.; Prabhakar, S.; Vairamani, M.;
Roy, S. Organometallics 1999, 18, 2782. (c) Kundu, A.; Roy, S.
Organometallics 2000, 19, 105.
1
0.1021/om000533g CCC: $20.00 © 2001 American Chemical Society
Publication on Web 12/06/2000

1
58 Organometallics, Vol. 20, No. 1, 2001
Sinha et al.
Ta ble 1. F or m a tion a of Un sym m etr ica l Su lfid es
Ta ble 2. F or m a tion of Dior ga n otr i- a n d
Tetr a su lfid es R a n d R fr om th e Rea ction of
Elem en ta l Su lfu r S a n d Or ga n ic Ha lid es RX
RSR′ fr om th e Rea ction of RSSR a n d R′Br
2
S
3
2 4
S
8
a
With respect to halide. b 10-15% of disulfide isolated. c 25%
of halide isolated.
a
All reactions were carried out in refluxing THF. b A )
mine whether the reagent can cleave the -S-S- bond
in elemental sulfur. Addition of elemental sulfur (R-
rhombic, 2 g-atom) to a mixture of stannous chloride
dihydrate (1.05 mmol) and catalytic cupric chloride
dihydrate (0.1 mmol) in THF-DMSO (2:1 v/v) leads to
the immediate formation of a brown precipitate. Addi-
tion of allyl bromide (1.5 mmol) to this mixture at 70
c
CuCl2‚2H2O, B ) CuBr2. Isolated yields after chromatography
based on disulfides. Ratio of linear and branched isomer 9:1.
Reaction carried out in refluxing THF-H2O.
d
e
Sch em e 3
°C results in a clear yellow solution after 1.5 h. Workup
afforded a mixture of diallyltrisulfide 13a and diallyltet-
rasulfide 13b (3:2 vide NMR) with an overall yield of
7
8% with respect to halide (Table 2, entry 1). The
reaction proceeds equally well with cupric bromide or
cuprous chloride as catalyst. The “pronounced copper
effect” in the transformation can be judged from the fact
that no reaction occurs either in the absence of copper
salts or in the presence of nickel chloride, bis(triphen-
ylphosphine)nickel dichloride, palladium acetate, and
tetrakis(triphenylphosphine)palladium as catalysts. Neg-
ligible product is formed with Cu(II)/Sn(II) in solvents
such as DCM, MeCN, THF, DCM-DMSO (2:1 v/v), and
MeCN-DMSO (2:1 v/v).
various diorganodisulfides RSSR (R ) 1°, 2° alkyl,
benzyl). The latter were prepared from the correspond-
ing halides and (benzyltriethylammonium) tetrathio-
4
molybdate. Reactions of substituted allyl bromides with
dibenzyl disulfide, di(n-butyl)disulfide, and dicyclohexyl
disulfide give the corresponding allylic sulfides 5-8 in
good to excellent yields (entries 7-10). Activation of
propargyl bromide is also achieved in the reaction with
diphenyl disulfide, giving rise to corresponding sulfides
The sulfur-activation reaction is extended to various
allyl (entries 3-5), 1°-alkyl (entry 6-9) and benzyl
9
-10 (entries 11, 12). We are delighted to find that the
present protocol is equally effective for the cleavage of
cyclic disulfide (Scheme 3). Thus, disulfide 11, prepared
from phthalic anhydride in two steps, reacts with
(
entry 10-11) halides, giving rise to the corresponding
diorganotrisulfides 14a -20a and diorganotetrasulfides
4b-20b in moderate yields. However the reaction fails
1
1
-bromo-3-methyl-2-butene to give the corresponding
in the case of aryl halides. We have noticed further that
reactions conducted at room temperature do not alter
the product ratio significantly (entries 2, 7, 9). This
indicates the inherent reactivity of the reagent in
promoting trisulfide and tetrasulfide formation. At-
tempts are underway to vary reaction conditions to
enhance the selectivity of the reactions.
Th e Na tu r e of In ter m ed ia tes. The “copper effect”,
indicated earlier, prompted us to carry out a series of
control experiments, as detailed below.
bis-allylated product 12 in 61% isolated yield. Com-
pound 12 is an attractive precursor for ring-closing
metathesis reaction toward the synthesis of redox-
switched crown ethers.5
Activa tion of Elem en ta l Su lfu r . The distinct re-
activity of Cu(II)/Sn(II) to cleave the -S-S- bond in
disulfides, as illustrated above, prompted us to deter-
(
4) Ramesha, A. R.; Chandrasekaran, S. Synth. Commun. 1992, 22,
277.
5) (a) Delgado, M.; Martin, J . D. J . Org. Chem. 1999, 64, 4798. (b)
Ramesha, A. R.; Chandrasekaran, S. J . Org. Chem. 1994, 59, 1354.
3
1
. Neither allyltributylstannane nor allyltrichlorostan-
(
nane reacts with diphenyl disulfide and elemental sulfur

New Insight into the “Copper Effect”
Organometallics, Vol. 20, No. 1, 2001 159
F igu r e 1. EIMS spectra of the filtrate from the reaction of CuCl
2
‚2H
2
O-SnCl
2
‚2H
2
O-PhSSPh ) 2:2.1:1. (m/z) 334 )
+
+
+
+
+
+
+
+
[PhSSnCl
3
] ; 260 ) [SnCl
4
] ; 225 ) [SnCl
3
] ; 218 ) [PhSSPh] ; 190 ) [SnCl
2
] ; 155 ) [SnCl] ; 120 ) [Sn] ; 109 ) [PhS] .
even in the presence of cuprous or cupric halides. This
rules out the possibility of similar organotin intermedi-
ates.6
2
. Diphenyl disulfide and sulfur alone does not form
any complex with CuCl, CuCl2, or SnCl2 (UV and TLC
monitoring) and is quantitatively isolated back after 24
7
h.
3
. The nature of the intermediate in the reaction of
Cu(II)/Sn(II) with disulfide is investigated by EIMS. A
solution of stannous chloride dihydrate (2.1 mmol),
cupric chloride dihydrate (2 mmol), and diphenyl dis-
ulfide (1 mmol) in THF (5 mL) is refluxed for 6 h and
filtered. The filtrate, upon direct injection into the mass
spectrometer probe, shows major peaks (m/z) due to
PhSSnCl3 (334), SnCl4 (260), and unreacted PhSSPh
F igu r e 2. XRD spectra of brown compound 21. d-values
3.093, 2.688, 1.915, 1.629.
)
Ta ble 3. Com p a r ison of XRD P ea k s (d -va lu es) of
1 w ith Kn ow n Cop p er Su lfid e Sp ecies
2
(218) (Figure 1). These and all the fragmentation peaks
compound
XRD data (d-values)
reference
have been confirmed by comparison with simulated
spectra We assume that (thiophenyl)trichlorostannate,
RSSnCl3, is an important intermediate during the
cleavage reaction of disulfide.
21
CuS
Cu1-xS
Cu1+xS
Cu2S
3.09, 2.69, 1.92, 1.63
3.048, 2.813, 1.893
3.58, 2.22
3.65, 2.25
3.43, 3.04, 1.99, 1.86, 1.70, 1.65
3.78, 2.30
this work
a
b
b
c
b
4
. As mentioned earlier, in the reaction of Cu(II)/
Cu2-xS
Sn(II) with sulfur, a brown precipitate appears in the
beginning of reaction, which slowly dissolves upon
addition of organic halide. The brown precipitate 21 is
independently prepared from the reaction of stannous
chloride dihydrate, cupric chloride dihydrate, and sulfur
a
J CPDS card no. 6-0464; only major peaks noted. b Engelken,
c
R. D.; McCloud, H. E. J . Electrochem. Soc. 1985, 132, 567. Das,
S. R.; Vankar, V. D.; Nath, P.; Chopra, K. L. Thin Solid Films
1978, 51, 257.
(2:2:1 and 4:4:1) in THF. The IR spectrum of 21 is very
The results indicate similarities with Cu(II) sulfide
species. The EPR spectrum of 21 (Figure 3) shows the
1
0
similar to those of cupric sulfide and cuprous sulfide.
Elemental analysis for copper in 21 affords a value of
1
1
presence of axially compressed Cu(II) species. It is
further noteworthy that compound 21 remains inactive
toward allyl bromide, but spontaneously reacts in the
presence of stannous chloride to give trisulfide as the
major product.
The thiophilic nature of copper is well documented
and is further relevant to the chemistry of metallo-
thioneins and cytochrome-c oxidase and application in
4
1.21 ( 0.02 and corresponds to an empirical formula
of CuS2.83. Sulfur-rich copper species of the formula
CuS2.5 and CuS2.67 have been reported earlier. The
8
X-ray powder pattern of compound 21 (Figure 2) is
9
compared to known copper sulfide species (Table 3).
1
2
(6) For the reaction of organometallics of main group elements with
13
disulfides and sulfur, please see: (a) Wardell, J . L. In The Chemistry
of the Thiol Group, Part I; Patai, S., Ed.; Wiley: New York, 1974. (b)
Harrison, P. G. Chemistry of Tin; Blackie: London, 1989.
(9) (a) J CPDS card no. 6-0464; only major peaks noted. (b) Das, S.
R.; Vankar, V. D.; Nath, P.; Chopra, K. L. Thin Solid Films 1978, 51,
257. (c) Engelken, R. D.; McCloud, H. E. J . Electrochem. Soc. 1985,
132, 567.
(10) The room-temperature magnetic moment of 21 (µeff, BM) is
0.561, suggesting significant metal-metal interaction. Efforts are
underway to obtain an XPS analysis of 21.
(7) (a) Very weak interaction of CuCl with diethyl disulfide is
reported: Branden, C.-I. Acta Chem. Scand. 1967, 21, 1000. (b)
Interaction of diphenyl disulfide with In(0) and Sn(0) results in
oxidative -S-S- cleavage: Kumar, R.; Mabrouk, H. E.; Tuck, D. G.
J . Chem. Soc., Dalton Trans. 1988, 1045.
(8) (a) Buckley, A. N.; Woods, R. Aust. J . Chem. 1984, 37, 2403. (b)
Bieger, T.; Horne, M. D. Electrochemical Society Spring Meeting;
Cincinnati, 1984; Abstract No. 16.
(11) Hathway, B. J . In Comprehensive Coordination Chemistry;
Wilkinson, G., Ed.; Pergamon: Oxford, 1987; Vol. 5, pp 662-673.

1
60 Organometallics, Vol. 20, No. 1, 2001
Sinha et al.
Sch em e 4
F igu r e 3. EPR spectra of brown compound 21. (a) At room
temp, g ) 2.072; g ) 2.169 (b) At liquid nitrogen temp, g
2.075; g ) 2.17.
|
⊥
|
)
⊥
the field of materials science. A number of structurally
diverse copper thiolate complexes are synthesized by the
ligand-assisted approach.14 In the case of ligand-free
systems, earlier reports confirm the complexity in the
9
,15
stoichiometry and structure of copper-sulfur species.
Formation of nonstoichiometric sulfides of copper(I) in
the electroreduction of copper salts in the presence of
1
6
elemental chalcogen is reported. Geochemical stud-
1
7,18
ies
on the formation of copper sulfide minerals
Sch em e 5
clearly show that the Cu(I) oxidation state is preferred
at low oxygen fugacity, high sulfur fugacity, and high
temperature. However the Cu(II) oxidation state is
preferred in minerals near earth’s surface under the
conditions of low temperature, aqueous environment,
and pH 6-8.
P la u sible Rea ction P a th w a y. In the present study
the acquired evidence, presented above, is yet insuf-
ficient to postulate the true course of -S-S- cleavage
reactions. The experimental evidence, however, suggests
that bimetallic participation is mandatory during the
cleavage and subsequent carbon-sulfur bond formation.
Any mechanism is, therefore, required to be consistent
with this view. A suggestion, pertaining to this hypoth-
esis, for the activation of disulfide is shown in Scheme
reaction of CuCl2, SnCl2, and PhSSPh is discrete proof
2
0
of the bimetallic reactivity. Pd(0)-promoted cleavage
of disulfide follows a nearly similar path (Scheme 5).21
However, in the present case, the major question to be
addressed is, “between PhSSnCl3 and CuSPh, which is
4
, involving the prior formation of intermediate CuSnCl3
from the reaction of copper(I) chloride and stannous
chloride.19 Formation of PhSSnCl3 (vide EIMS) from the
2
2
the principle reactive intermediate?” Toward this, the
following model studies have been carried out starting
(
12) (a) Andrew, C. R.; Fraczkiewicz, R.; Czernuszewicz, R. S.;
Lappalainen, P.; Saraste, M.; Sanders-Loehr, J . J . Am. Chem. Soc.
996, 118, 10436. (b) Presta, A.; Green, A.-R.; Zelazowski, A.; Stillman,
M. J . Eur. J . Biochem. 1995, 227, 226.
13) (a) Green, A. R.; Presta, A.; Gasyna, Z.; Stillman, M. J . Inorg.
n
23
from readily available PhSSn Bu3 22 (Scheme 6).
. Reaction of 22 with stoichiometric allyl bromide
1
1
under reflux and after 8 h affords allylphenylsulfide 1
in 18% isolated yield along with unreacted starting
material.
(
Chem. 1994, 33, 4159. (b) Haram, K. S.; Mahadeshwar, A. R.; Dixit,
S. G. J . Phys. Chem. 1996, 100, 5868. (c) Chopra, K. L.; Das, S. R.
Thin Film Solar Cells; Plenum: New York, 1983. (d) Zheng, H.; Tan,
W.; Low, M. K. L.; J i, W.; Long, D.; Wong, W.; Yu, K.; Xin, X.
Polyhedron 1999, 18, 3115.
2
. The above reaction, but in the presence of CuCl (0.2
equiv) and after 8 h, affords 1 in 34% isolated yield along
(
14) (a) J eannin, S.; J eannin, Y.; Lavigne, G. Inorg. Chem. 1979,
n
with Bu3SnCl.
1
8, 3528, and references therein. (b) Yang, R.; Sun, Y.; Hou, Y.; Hu,
X.; J in, D. Inorg. Chim. Acta 2000, 304, 1. (c) Ingham, S. L.; Long, N.
J . Angew. Chem., Int. Ed. Engl. 1994, 33, 1752. (d) Hakansson, M.;
Eriksson, H.; Ahman, A. B.; J agner, S. J . Organomet. Chem. 2000,
3. Reaction of authentic CuSPh 23 and stoichiometric
allyl bromide proceeds smoothly under ambient condi-
tions and after 8 h affords 1 in 60% isolated yield.
5
95, 102.
15) (a) Munson, R. A. Inorg. Chem. 1966, 5, 1296, and references
(
therein. (b) Lu, Q.; Hu, J .; Tang, K.; Qian, Y.; Liu, X.; Zhou, G. J . Solid
State Chem. 1999, 146, 484. (c) Vinkeviius, J .; Moginskien, I.; J asu-
laitien, V. J . Electroanal. Chem. 1998, 442, 73.
3 2
(19) For the formation of CuSnCl from CuCl and SnCl , please
see: Imai, T.; Nishida, S. J . Chem. Soc. Chem. Commun. 1994, 277.
(20) EIMS probe is inappropriate for the detection of copper-
containing species. Electrospray mass spectrometry (ESMS) is the
preferred technique: Lipshutz, B. H.; Keith, J .; Buzard, D. J . Orga-
nometallics 1999, 18, 1571.
(21) Zanella, R.; Ros, R.; Graziani, M. Inorg. Chem. 1973, 12, 2736.
(22) We warmly thank one of the reviewers for this pertinent
suggestion.
(
16) Baranski, A. S.; Fawcett, W. R. J . Electrochem. Soc. 1980, 127,
66.
17) Wedepohl, K. H.; Correns, C. W.; Shaw, D. M.; Turekian, K.
K.; Zemann, J . Handbook of Geochemistry; Springer-Verlag: New York,
974; Vol. II/4, pp 29-D-1-29-D-16.
18) (a) Rose, A. W. Special Paper 36; Geological Association of
Canada, pp 97-110. (b) Rose, A. W. Econ. Geol. 1993, 88, 1226.
7
(
1
(
(23) Pang, M.; Becker, E. I. J . Org. Chem. 1964, 29, 1948.

New Insight into the “Copper Effect”
Organometallics, Vol. 20, No. 1, 2001 161
Sch em e 6
Exp er im en ta l Section
Gen er a l Meth od s. All reactions were performed under an
inert atmosphere of argon. Substituted allyl bromides and
propargyl bromides were prepared from the corresponding
alcohols (Lancaster) using standard protocol. The disulfides
6
were prepared rather easily according to literature procedure.
All the starting materials were >98% pure vide NMR. Stan-
nous chloride dihydrate (Ranbaxy), cupric chloride dihydrate
(S.D. Fine Chemicals), and cupric bromide (Lancaster) were
used as received. Sulfur powder AR (S.D. Fine Chemicals) was
recrystallized from carbon disulfide.
1
3 6
H NMR spectra were taken in CDCl or DMSO-d on
Varian INOVA-500, Brucker-300, and Gemini-200 spectrom-
eters. EIMS (70 eV) spectra were recorded using VG Micro-
Mass 7070H and VG Autospec M mass spectrometers. IR
spectra were recorded on a Perkin-Elmer 883 instrument.
X-ray powder diffraction data were obtained using a Phillips
PW-1840 instrument using a Mo KR target at 40 kV. Copper
estimations of compounds 21 and 23 were done by standard
Sch em e 7
28
iodometric titration using reported digestion methods.
Typ ica l P r oced u r e for th e Syn th esis of Un sym m etr i-
ca l Su lfid es. A mixture of cyclic disulfide 11 (142 mg, 0.5
mmol) and 1-bromo-3-methyl-2-butene (447 mg, 3 mmol) in
THF (4 mL) was slowly added to a stirred solution containing
stannous chloride dihydrate (271 mg, 1.2 mmol) and cupric
chloride dihydrate (17 mg, 0.1 mmol) in THF (4 mL) and under
argon. The solution was refluxed for 6 h. Solvent removal
followed by column chromatography (silica gel 60-120 mesh,
SRL; eluent n-hexane-ethyl acetate 9:1) afforded sulfide 12
1
as a viscous oil (128 mg, 61% with respect to disulfide).
H
NMR (CDCl
3
): δ 1.66 (s, 6H), 1.75 (s, 6H), 2.75 (t, 4H, J ) 5.7
Hz), 3.17 (d, 4H, J ) 5.3 Hz), 4.39 (t, 4H, J ) 6.2 Hz), 5.20 (t,
1
3
2
H, J ) 5.3 Hz), 7.48 (m, 2H), 7.76 (m, 2H). C NMR
(CDCl ): δ 17.68, 25.62, 29.38, 29.73, 64.59, 120.26, 128.92,
3
The above model study clearly establishes “the cata-
lytic role of copper” and demonstrates that the sulfur
transfer reaction is proceeding majorly via in-situ-
generated copper thiolate.
131.05, 131.97, 135.81, 167.11. EIMS m/z (rel abundance): 353
+
[(M - C
5
H
9
) , 3], 293 (3), 193 (7), 149 (42), 129 (75), 100 (54),
69 (99), 41 (100). HRMS: calcd for C17
found 353.086415.
21 4 2
H O S 353.088128,
Typ ica l P r oced u r e for th e Syn th esis of Tr isu lfid es
a n d Tetr a su lfid es. Sulfur (64 mg, 2 g-atom) was added to a
stirred solution containing stannous chloride dihydrate (237
mg, 1.05 mmol) and cupric chloride dihydrate (17 mg, 0.1
mmol) in THF-DMSO (2:1 v/v). A brown precipitate was
formed immediately. 1-Bromo-2-butene (0.15 mL, 1.5 mmol)
was added dropwise to the reaction mixture kept under argon.
The solution was refluxed at 70 °C for 1 h (TLC monitoring
on silica gel, eluent: hexane). An aqueous solution of am-
monium fluoride (15%, 10 mL) was added to the reaction
mixture, and the organic layer was extracted with diethyl ether
The mechanism of activation of sulfur appears to be
more complex. Whether a species such as A (Scheme 7)
is involved is worthy of further investigation. In the case
of ligand-assisted syntheses, formation of CuS3 and
3
b,24
CuS4 cores is well known.
Even more recently Cu4-
SnS6 and Cu2SiS3 have been identified.25
Syn th etic P er sp ective. The allylation of disulfides
using Cu(II)/Sn(II) offers a mild route to unsymmetrical
sulfides. The methodology argues well for the recently
reported reagents26 such as Zn/CoCl2, In(0), Sn(0),
(
1
3 × 20 mL), washed with water (2 × 10 mL) and brine (2 ×
Sm(0)/BiCl3, and CuI(stoichiometric)/HMPA. The for-
mation of diorganotrisulfides and tetrasulfides as major
products in the reaction of elemental sulfur appears to
be attractive, more so since there are only a few reports
0 mL), and dried over magnesium sulfate. Solvent removal
followed by column chromatography (silica gel 100-200 mesh,
SRL; eluent n-hexane) afforded a viscous oil (72% wt halide)
containing the corresponding trisulfide 14a and tetrasulfide
14b (42:58 vide NMR). All products were fully characterized
2
7
available in this area to date.
1
by H NMR (500 MHz), MS, and comparison with authentic
samples wherever possible.
(
24) (a) Gattow, G.; Rosenberg, O. Z. Anorg. Und. Allg. Chem. 1964,
32, 269. (b) Battaglia, L. P.; Corradi, A. B.; Nardelli, M.; Tani, M. E.
V. J . Chem. Soc., Dalton Trans. 1976, 143.
25) (a) Chan, X.; Wada, H.; Sato, A. Mater. Res. Bull. 1999, 34,
2
1
3
P r ep a r a tion of Com p ou n d 21. A mixture of stannous
chloride dihydrate (1.805 g, 8 mmol) and cupric chloride
dihydrate (1.364 g, 8 mmol) was stirred under argon. To the
resulting mixture was added sulfur (64 mg, 2 mmol), and a
brown compound was formed immediately. After additional
stirring for 5 min, the solid was filtered, washed with THF (3
(
39. (b) Chen, X. X.; Wada, H.; Sato, A.; Nozaki, H. J . Alloys Compds.
999, 290, 91.
(26) (a) Chowdhury, S.; Samuel, P. M.; Das, I.; Roy, S. J . Chem.
Soc., Chem. Commun. 1994, 1993. (b) Braga, A. L.; Reckziegel, A.;
Menezes, P. H.; Stefani, H. A. Tetrahedron Lett. 1993, 34, 393. (c)
Bulman-Page, P. C.; Klair, S. S.; Brown, M. P.; Harding, M. H.; Smith,
G. S.; Margim, S. J .; Mulley, S. Tetrahedron Lett. 1988, 29, 4477. (d)
Zhan, Z.; Lu, G.; Zhang, Y. J . Chem. Res., Synop. 1999, 280.
×
20 mL), and dried under vacuum at 100 °C for 2 h. Yield:
0.830 g. Anal. Found for Cu: 41.21 ( 0.02. The compound is
stable under vacuum for 2 days; however in air the brown color
slowly changes to green.
(27) (a) Block, E.; DeOrazio, R.; Thiruvazhi, M. J . Org. Chem. 1994,
5
9
(
9, 2273. (b) Feher, F.; Krause, G.; Vogelbruch, K. Chem. Ber. 1957,
0, 1570. (c) Morel, G.; Marchand, E.; Foucaud, A. Synthesis 1980, 918.
d) Sato, R.; Kimura, T.; Goto, T.; Saito, M.; Kabuto, C. Tetrahedron
Lett. 1989, 30, 3453. (e) Ogawa, A.; Takami, N.; Sekiguchi, M.; Sonoda,
N.; Hirao, T. Heteroatom. Chem. 1998, 9, 581.
n
23
Rea ction of P h SSn Bu
3
a n d Allyl Br om id e in th e
P r esen ce of Cu Cl. Allyl bromide (0.8 mL, 1 mmol) was added
(28) Reamer, D. C.; Veillon, C. Anal. Chem. 1981, 53, 1192.

1
62 Organometallics, Vol. 20, No. 1, 2001
Sinha et al.
n
to a stirred solution of PhSSn Bu
3
22 (400 mg, 1 mmol) and
Rea ction of Cu SP h a n d Allyl Br om id e. CuSPh 23 (34
mg, 0.2 mmol) and allyl bromide (0.6 mL, 0.8 mmol) was
stirred in THF (2 mL) under argon, and stirring was continued
for 8 h at room temperature (TLC monitoring on silica gel
eluent hexane), solvent removal under reduced pressure,
followed by column chromatography (silica gel 60-120 mesh,
SRL; eluent n-hexane) afforded allylphenyl sulfide 1 (18 mg,
60% wt CuSPh).
CuCl (20 mg, 0.2 mmol) in THF (3 mL) under argon, and the
mixture was refluxed for 8 h (TLC monitoring silica gel/
hexane). Solvent removal under reduced pressure, followed by
column chromatography (silica gel 60-120 mesh, SRL; eluent
n-hexane), afforded allylphenylsulfide 1 (51 mg, 34%).
n
Rea ction of P h SSn Bu
3
a n d Allyl Br om id e in th e
Absen ce of Cu Cl. Similar reaction as above but in absence
of CuCl afforded allylphenyl sulfide 1 (27 mg, 18%).
P r ep a r a tion of P h en ylth iocop p er (I). A mixture of Ph-
Ack n ow led gm en t. This work is supported by ISIRD
n
SSn Bu
3
(160 mg, 0.4 mmol) and CuCl (40 mg, 0.4 mmol) in
(
Institute Scheme for Innovative R & D), CSIR, and
DST. Research fellowships to A.K. (CSIR) and P.S.
UGC) are acknowledged. We thank Prof. A. W. Rose,
Prof. R. N. Mukherjee, Prof. C. R. Saha, and Prof. B.
Mishra for useful discussions and help.
THF (6 mL) and under argon was stirred at room temperature
for 7 h. The canary yellow precipitate of CuSPh 23 was
centrifuged under argon, washed with THF (3 × 1 mL), and
finally dried under vacuum (55 mg, 82%). Anal. Calcd for
CuSPh: Cu, 36.81. Found: Cu, 34.48. CuSPh was also
prepared by literature methods from the reaction of lithium
(
2
9
thiophenoxide and copper(I) iodide. Between the two, the
former route offers operational simplicity.
Su p p or tin g In for m a tion Ava ila ble: Listings of spectral
data and figures. This material is available free of charge via
the Internet at http://pubs.acs.org.
(29) Posner, G. H.; Whitten, C. E. Organic Syntheses; Wiley: New
York, 1988; Collect. Vol. 6, p 248.
OM000533G