Synthesis of trithiolanes and tetrathianes from thiiranes catalyzed by ruthenium salen nitrosyl complexes

Article abstract of DOI:10.1021/ja017462c

The compound [Ru(salen)(NO)(H₂O)](SbF₆) (1) (salen = N, N′-ethylene-bis-salicylidene aminate) reacts catalytically with thiiranes and converts them to olefins and 1,2,3,4-tetrathianes or 1,2,3-trithiolanes. The monosubstituted thiiranes styrene sulfide and propylene sulfide reacted to form the corresponding olefin and the 4-substituted 1,2,3-trithiolane in a 2:1 ratio in isolated yields in excess of 90%. The disubstituted thiirane cis-stilbene sulfide was converted to cis-stilbene and 5,6-trans-1,2,3,4-diphenyltetrathiane in a 3:1 ratio in the presence of a catalytic amount of 1 in CD₃NO₂. Coordination of cis-stilbene sulfide to the salen complex in a ligand substitution reaction was established by isolation of [Ru(salen)(NO)(cis-stilbene sulfide)]-(SbF₆) (6). ¹H NMR studies performed on 6 indicated that the salen macrocycle had rearranged upon thiirane coordination. A similar rearrangement was found to be stabilized by other ligands including tetramethylethylene sulfide, tetrahydrothiophene, and d₃-acetonitrile. The α-deuterio-cis-stilbene sulfide catalyst adduct (d-6) reacted with unlabeled cis-stilbene sulfide to form deuterium-labeled trans-diphenyl-tetrathiane and unlabeled cis-stilbene as shown by GCMS and ¹H NMR. Thus, the solution thiirane behaves as a sulfur donor and forms olefin, whereas the coordinated thiirane becomes the cyclic polysulfide. β-cis-Deuteriostyrene sulfide was used to show that ring closure to form cyclic polysulfide incorporated inversion of stereochemistry versus starting thiirane. A mechanism for catalysis consistent with experimental data is presented that requires coordination of thiirane to the metal complex followed by bimolecular attack of free thiirane on the coordinated thiirane.

Full text of DOI:10.1021/ja017462c

Published on Web 04/09/2002
Synthesis of Trithiolanes and Tetrathianes from Thiiranes
Catalyzed by Ruthenium Salen Nitrosyl Complexes
Anthony A. Sauve and John T. Groves*
Contribution from the Department of Chemistry, Princeton UniVersity,
Princeton, New Jersey 08544
Received November 3, 2001
Abstract: The compound [Ru(salen)(NO)(H2O)](SbF6) (1) (salen ) N,N′-ethylene-bis-salicylidene aminate)
reacts catalytically with thiiranes and converts them to olefins and 1,2,3,4-tetrathianes or 1,2,3-trithiolanes.
The monosubstituted thiiranes styrene sulfide and propylene sulfide reacted to form the corresponding
olefin and the 4-substituted 1,2,3-trithiolane in a 2:1 ratio in isolated yields in excess of 90%. The disubstituted
thiirane cis-stilbene sulfide was converted to cis-stilbene and 5,6-trans-1,2,3,4-diphenyltetrathiane in a 3:1
ratio in the presence of a catalytic amount of 1 in CD3NO2. Coordination of cis-stilbene sulfide to the salen
complex in a ligand substitution reaction was established by isolation of [Ru(salen)(NO)(cis-stilbene sulfide)]-
(SbF6) (6). 1H NMR studies performed on 6 indicated that the salen macrocycle had rearranged upon
thiirane coordination. A similar rearrangement was found to be stabilized by other ligands including
tetramethylethylene sulfide, tetrahydrothiophene, and d3-acetonitrile. The R-deuterio-cis-stilbene sulfide
catalyst adduct (d-6) reacted with unlabeled cis-stilbene sulfide to form deuterium-labeled trans-diphenyl-
tetrathiane and unlabeled cis-stilbene as shown by GCMS and 1H NMR. Thus, the solution thiirane behaves
as a sulfur donor and forms olefin, whereas the coordinated thiirane becomes the cyclic polysulfide. â-cis-
Deuteriostyrene sulfide was used to show that ring closure to form cyclic polysulfide incorporated inversion
of stereochemistry versus starting thiirane. A mechanism for catalysis consistent with experimental data is
presented that requires coordination of thiirane to the metal complex followed by bimolecular attack of free
thiirane on the coordinated thiirane.
Metal-catalyzed atom transfer reactions comprise a growing
family of highly useful processes. Olefin epoxidation, cyclo-
propanations, and aziridinations, for example, have been applied
to a wide variety of organic substrates and metal catalysts, often
with exquisite control over selectivity and stereochemistry. Metal
salen catalysts have been shown to be exceptionally versatile
and stereoselective in epoxidation1,2 and ring opening reactions.3
The active discussion of the mechanistic principles of these
reactions4-6 led us to consider simple dative interactions of
epoxides and thiiranes with metal complexes incorporating the
salen ligand to probe for structural features that control
selectivities in these reactions.7 Well-characterized stable co-
ordination compounds that include coordinated epoxides or
thiiranes are few because of the inherent strain of the three-
membered ring and the labilizing effect of the coodinating metal
complex.8
Here we describe thiirane coordination and subsequent
reactions of complexes derived from [Ru(salen)(NO)(H2O)]-
(SbF6) (1) (Figure 1, where salen ) N,N′-ethylene-bis-sali-
cylidene aminate)9 upon treatment with excess thiiranes. An
unusual ruthenium-catalyzed sulfur transfer chemistry is ob-
served, in which monosubstituted and disubstituted thiiranes are
catalytically disproportionated to olefin and the corresponding
1,2,3-trithiolanes or 1,2,3,4-tetrathianes. These cyclic trisulfide
* To whom correspondence should be addressed. Telephone: (609) 258-
3593. E-mail: jtgroves@princeton.edu.
(1) (a) Jacobsen, E. N. In ComprehensiVe Organometallic Chemistry II;
Wilkinson, G., Stone, F. G. A., Abel, E. W., Hegedus, L. S., Eds.;
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Zhang, W.; Guler, M. L. J. Am. Chem. Soc. 1991, 113, 6703. (c) Zhang,
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(7) A demonstration of the usefulness of this approach using differential 1H
spin-relaxation of epoxide and thiirane ligands coordinating to spin-relaxing
metal complexes has been published, see: Groves, J. T.; Crowley, S. J.;
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N. In ComprehensiVe Heterocyclic Chemistry; Padwa, A., Ed.; Elsevier
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Heterocyclic Chemistry; Katritzky, A., Rees, C. W., Eds.; Pergamon
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9
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J. AM. CHEM. SOC. 2002, 124, 4770-4778
10.1021/ja017462c CCC: $22.00 © 2002 American Chemical Society

Synthesis of Trithiolanes and Tetrathianes
A R T I C L E S
Figure 1. Structures of ruthenium salen nitrosyl complexes.
and tetrasulfide products and their derivatives have a limited
literature,10 although cyclic and acyclic trisulfides and tetrasul-
fides are central motifs in a number of natural products including
the calicheamicins,11 lissoclinotoxin,12 varacin,13 and various
compounds isolated from thermophilic bacteria.14
The reaction chemistry of ruthenium complexes and thiiranes
that forms trithiolanes and tetrathianes has no available precedent
in the literature and appears to define a new chemical pathway
in the interaction of thiiranes with metal complexes. The overall
reaction, coordination of thiirane to catalyst, conformational
changes upon thiirane coordination, and the proposed mecha-
nism of catalysis are presented in this paper.
Results
Synthesis and Characterization of Ruthenium Nitrosyl
Catalysts. The ruthenium complex 1 depicted in Figure 1 has
1
been shown by H NMR to coordinate weak ligands such as
aldehydes by ligand exchange for water in nonprotic solvent.9a
This precedent suggested the potential of this complex to
synthesize thiirane and/or epoxide complexes through analogous
ligand exchange mechanisms. The reported synthesis of 1,9a
which works well to obtain gram quantities of the material, was
applied to derive the more substituted salen derivative [Ru(L1)-
(NO)(H2O)](SbF6) (2), where L1 ) R,R,-(-)-1,2-cyclohexane-
bis(3,5-di-tertbutyl)salicylidene aminate as shown in Figure 2.
1
Complete characterization of 2 was obtained by IR, H NMR,
Figure 2. Top: 1H NMR of R-deuterium-cis-stilbene sulfide complex 6
(d-6) in CD2Cl2. Inset: The resonances of the HR protons of coordinated
stilbene sulfide in all proteo 6. Bottom: The 1H NMR spectrum of the
tetramethylethylene sulfide complex 7 in CDCl3. The four methyl groups
are correspondent to the four methyl groups of the tetramethylethylene
sulfide ligand. S indicates residual water or CHCl3.
and FAB-MS (see Experimental Section). The direct precursor
to 2, the chloro complex Ru(L1)(NO)(Cl) (2b), was identical in
all respects to the complex reported previously.15
Catalytic Desulfurization of Thiiranes with Ruthenium
Complexes. Treatment of 1 with excess monosubstituted or
disubstituted thiiranes in nitromethane at room temperature
caused desulfurization of the thiiranes to generate olefin and
unidentified coproducts. Reactions could be spectroscopically
monitored by mixing the reactants in an NMR tube in d3-
nitromethane at 0 °C and warming the tube in an NMR probe
to ambient temperature to obtain 1H NMR spectra. Olefin
products were easily recognized by the appearance of vinyl
proton resonances in 1H NMR spectra of reaction mixtures, and
confirmed by isolation in several cases. Olefin formation was
observed using the following thiiranes: ethylene sulfide,
propylene sulfide, cyclohexene sulfide, styrene sulfide, and cis-
and trans-stilbene sulfide. Both ethylene and propylene were
lost from NMR tubes by venting, and the subsequent spectra
were shown to be depleted of the respective olefin resonances.
Recovery and reuse of the complex 1 after reactions showed
that it was the active catalyst of these reactions. Experimental
details of these reactions are found in Table 1 and in the
Experimental Section.
The reactions of styrene sulfide and cis-stilbene sulfide in
the presence of 1 were studied in detail. Thus, treatment of 1
with a 30-fold excess of styrene sulfide resulted in the formation
of a 63% yield of styrene versus starting thiirane (mol/mol).
The styrene was readily isolated and analyzed by GCMS and
1H NMR, and compared to a chemical standard to verify
identity. A second product was also obtained and shown by
(10) Mitchell, G. In ComprehensiVe Heterocyclic Chemistry; Padwa, A., Ed.;
Elsevier Science Inc.: Tarrytown, New York, 1996; Vol. 4, Chapter 4.15,
pp 545-580 and references therein.
(11) (a) Zein, N.; Sinha, A. M.; McGahren, W. J.; Ellestad, G. A. Science 1988,
240, 1198. (b) Maiese, W. M.; Lechevalier, M. P.; Lechevalier, H. A.;
Korshalla, J.; Kuck, N.; Fantini, A.; Wildey, M. J.; Thomas, J.; Greenstein,
M. J. Antibiot. 1989, 42, 558.
(12) (a) Steudal, R.; Kustos, M.; Munchow, V.; Westphal, U. Chem. Ber. 1997,
130, 757. (b) Frappier, F.; Litaudaon, Trifalgo, F.; Martin, M. T.; Guyot,
M. Tetrahedron Lett. 1991, 32, 911.
(13) (a) Copp, B. R.; Blunt, J. W.; Munro, M. H.; Pannel, L. K. Tetrahedron
Lett. 1989, 30, 3703. (b) Davidson, B. S.; Molinski, T. F.; Barrows, L. R.;
Ireland, C. M. J. Am. Chem. Soc. 1991, 113, 4709.
(14) Ritzau, M.; Keller, M.; Wessels, P.; Stetter, K. O.; Zeeck, A. Liebigs Ann.
Chem. 1993, 871.
(15) Leung, W. H.; Chan, E. Y. Y.; Chow, E. K. F.; Williams, I. D.; Peng, S.
M. J. Chem. Soc., Dalton Trans. 1996, 1229.
1
MS, H NMR to be the previously unreported 4-phenyl-1,2,3-
1
trithiolane 3. This compound was fully characterized by H
NMR, 13C NMR, and MS. The 3J coupling constants were fully
consistent with a five-membered ring (see Experimental Section
for full characterization). The trithiolane 3 was formed in a
9
J. AM. CHEM. SOC. VOL. 124, NO. 17, 2002 4771

A R T I C L E S
Sauve and Groves
Table 1. Reactions of Thiranes and Ruthenium Nitrosyl Salen Catalystsa
substrate
catalystb
olefin
sulfide product
styrene sulfide
1
1
1
2
2c
2
2
1
1
1
1
styrene
4-phenyltrithiolane
4-methyltrithiolane
5,6-trans-diphenyl tetrathiane
4-phenyltrithiolane
4-phenyltrithiolane < 5% e. e. unreacted styrene sulfide < 5% e. e.
4-methyltrithiolane
propylene sulfide
cis-stilbene sulfide
styrene sulfide
propylene
cis-stilbene
styrene
styrene sulfide
styrene
propylene sulfide
cis-stilbene sulfide
trans-stilbene sulfide
cyclohexene sulfide
ethylenesulfide
propylene
cis-stilbene
trans-stilbened
cyclohexenef
ethyleneh
ND
5,6-trans-diphenyl tetrathiane
NIe
NIg
NIi
ND
tetramethylethylene sulfide
a NI: product not identified, ND: no product detected. b Reactions with 1 were run in CD3NO2 and those with 2 were run in CD2Cl2. In each reaction,
0.1 mmol of substrate was added to 1 mL of solution containing 2.5 mM catalyst (2.5 × 10-3 mmol). c Reaction terminated at 30% conversion as determined
by 1H NMR, solvent flash evaporated, and sample redissolved in a 2:3 mixture of (R)-(-)-CF3CHOHPh:CCl4.18 1 H NMR spectrum of redissolved reaction
mixture was used to measure enantiomeric excess (e.e.). d Isolated and compared to authentic trans-stilbene. e Product was produced in 1:3 ratio versus
olefin, but was determined not to be trans-diphenyl-tetrathiane. Probable identity of product is cis-diphenyltetrathiane (unstable to isolation). f Isolated and
compared to authentic cyclohexene. g Unstable. h 1H NMR δ: 5.5, olefin was major product, and disappeared upon opening cap of NMR tube as determined
1
by loss of corresponding resonance in H NMR spectrum. i Multiple unstable products.
Scheme 1. Disproportionation Reactions of Styrene and
Propylene Sulfides Catalyzed by 1
Scheme 2. Disproportionation Reaction of cis-Stilbene Sulfide
Catalyzed by 1
generated versus 5 was found to be 3:1 based on NMR
integration of spectra of reaction mixtures. A disproportionation
of the disubstituted stilbene sulfide was effected by 1 (Scheme
2) with an altered stoichiometry as compared with the styrene
sulfide reaction with 1 (Scheme 1). The overall reaction of
styrene sulfide was 6 times faster than that of cis-stilbene sulfide
reaction under similar conditions.
isolated yield of 90% (based on theoretical). Integrations of 1H
NMR resonances of styrene and trithiolane in reaction mixtures
showed that they were formed in 2:1 ratio, respectively,
confirming an apparent disproportionation of thiirane to the two
products in the ratio expected based upon the sulfur content in
3 (Scheme 1).
The chiral complex 2 was effective in catalyzing the identical
reactions as complex 1. Like 1, the complex could be isolated
unchanged after reactions were completed and subsequently
reused. Because of improved catalyst solubility, the reactions
of 2 with thiiranes could be effected in CH2Cl2, with no apparent
change in reaction outcome (Table 1). Use of special conditions
to resolve thiirane and sulfide stereoisomers18 (see Table 1 for
details) showed that styrene sulfide reactions catalyzed by 2
did not enantiomerically enrich unreacted styrene sulfide in
partially completed reactions and phenyltrithiolane was not
produced in measurable enantiomeric excess (Table 1).
Coordination of cis-Stilbene Sulfide. The reaction of
thiiranes with 1 begins with coordination of the thiirane to the
ruthenium complex. Observations of the reaction of 1 with
The behavior of propylene sulfide with 1 in CD3NO2 was
analogous to that of styrene sulfide. Propylene was identified
by H NMR resonances at δ 5.8, 5.05, 4.95, and 1.95. These
1
peaks disappeared after opening the NMR tube to air for several
minutes indicating evaporation of propylene from the sample.
Propylene was formed in a 2:1 ratio as determined by 1H NMR
versus a second product 4 identified as 4-methyl-1,2,3-trithiolane
(91% yield). MS data in particular corresponded well to a prior
literature report of this compound,16 and 3J coupling constants
were completely consistent with the five-membered ring for-
mulation (see Experimental Section for complete characteriza-
tion).
In the second detailed case examined, excess cis-stilbene
sulfide was added to a solution of 1 and converted over several
hours to cis-stilbene. The identity of cis-stilbene was confirmed
1
excess cis-stilbene sulfide in CD3NO2 by H NMR showed
changes in the catalyst structure as a consequence of the
presence of thiirane. For example, the catalyst imine singlet at
δ 8.7 disappeared, and two separate singlets at δ 9.05 and 8.65
with half intensity appeared. These changes were shown to be
due to a thiirane adduct of cis-stilbene sulfide and catalyst by
isolation and 1H NMR and IR characterization of the complex.
1
by GCMS and H NMR and comparison with authentic cis-
stilbene. A second compound 5 was isolated by silica gel
chromatography and identified as trans-5,6-diphenyl-1,2,3,4-
tetrathiane (73% isolated yield) by comparison to the authentic
compound synthesized independently by a known method (see
Scheme 2 for structure).17 Previous X-ray characterization for
this compound makes this structural assignment unambiguous.17a
1H NMR spectra of 5 and authentic trans-5,6-diphenyl-1,2,3,4-
tetrathiane were identical, and GCMS analysis decomposed both
materials to trans-stilbene and S6 and S8. The ratio of cis-stilbene
1
The H NMR spectrum of the adduct 6 showed that the
symmetry of the complex was reduced upon thiirane coordina-
tion (Figure 2, inset and top panel). This observation is consistent
with a reorganization of the complex to a lower symmetry form
upon binding thiirane. The reorganization thought most probable
is shown in Scheme 4. The proposed structure of the thiirane
complex would place the two methine protons of the coordinated
(16) Block, E.; Iyer, R.; Grisoni, S.; Saha, C.; Belman, S.; Lossing, F. P. J. Am.
Chem. Soc. 1988, 110, 7813.
(17) (a) Kamata, M.; Murayama, K.; Suzuki, T.; Miyashi, T. J. Chem. Soc.,
Chem. Commun. 1990, 827. (b) Kamata, M.; Murayama, K.; Miyashi, T.
Tetrahedron Lett. 1989, 30, 4129.
(18) Bucciarelli, M.; Forni, A.; Moretti, I.; Torre, G. Chim. Ind. 1977, 59, 55.
9
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Synthesis of Trithiolanes and Tetrathianes
A R T I C L E S
Scheme 3. Proposed Adduct Formation Due to Reaction of 1 with
cis-Stilbene Sulfide
Scheme 4. Ligation Reactions of L1:Tetramethylethylene Sulfide,
L2:Tetrahydrothiophene, and L3:Acetonitrile with Complex 1
cis-stilbene in different chemical environments, and in fact were
found to be doublets at δ 5.85 and 5.55 in the 1H NMR spectrum
(inset, Figure 2, top panel). Deuterium incorporation at one R
carbon (70% enrichment) of cis-stilbene sulfide caused these
doublets to become singlets (Figure 2, top panel). The nitrosyl
of the complex was shown to be intact with a strong peak at
1865 cm-1 in the IR spectrum. Upon long standing in solution,
small amounts of free cis-stilbene and 1 could be recovered, in
addition to cis-stilbene and trans-diphenyltetrathiane. This
indicated that coordination to 1 without isomerization of the
thiirane was reversible, and suggested the competency of the
adduct to effect the desulfurization reaction.
1
Figure 3. Top: H NMR of 1 in acetonitrile-d3 minutes after dissolution
in acetonitrile. Bottom: 1H NMR spectrum of the sample in top panel after
6 h of incubation at room temperature.
Coordination of Hindered Thiiranes, Inert Sulfides, and
Solvent to 1. A hindered thiirane that was inert to desulfurization
and disproportionation was used to provide additional support
for the geometry of coordinated thiirane complexes derived from
Table 2. Stilbene Formation as a Function of Concentration of
Stilbene Sulfide and 6a
1
1. The H NMR spectrum of the tetramethylethylene sulfide
[cis-stilbene sulfide] M
[6] M
rate M min-1
adduct 7 in CD2Cl2 was similar to the spectrum of the
cis-stilbene adduct, particularly for resonances of the salen
ligand, indicating a nonsymmetrical complex (Figure 2, bottom
panel). Four singlets for the methyl groups of tetramethyleth-
ylene sulfide ligand confirmed coordination to a low symmetry
environment (Figure 2, bottom panel). In contrast, the free
1.0 × 10-2
5.0 × 10-3
2.5 × 10-3
5.0 × 10-3
8.0 × 10-4
8.0 × 10-4
8.0 × 10-4
5.0 × 10-4
1.8 × 10-5
8.9 × 10-6
3.7 × 10-6
5.7 × 10-6
a The rates obtained were determined by the initial rates method. The
bimolecular rate constant k2 determined from these data is k2 ) 0.72 (
1
thiirane methyl groups were all equivalent by H NMR.
0.12 M-1 min-1
.
The ligand tetrahydrothiophene in CD3NO2 was shown to
form an adduct 8, deduced to be ligand replacement of the
tetrahydrothiophene for the water ligand with isomerization of
the macrocycle to produce the twisted complex (Scheme 4).
olefin and tetrathiane, and a cis-stilbene sulfide coordinate
adduct 6. The thiirane adduct is the putative first intermediate
in the catalytic cycle that disproportionates thiiranes to products.
As stated previously, the adduct is stable in the absence of free
thiirane for extended periods (4-6 h), but decomposed upon
long standing. In the presence of excess cis-stilbene sulfide,
the adduct rapidly reacted to form cis-stilbene and diphen-
yltetrathiane. Varying the amount of both adduct and thiirane
established the rate law for production of olefin and tetrathiane
(Table 2). The rate law is first order in adduct and thiirane;
that is, k[adduct][thiirane] ) d[olefin]/3 dt, where k is the
second-order rate constant. The value of k was found to be 0.72
( 0.12 M-1 min-1 at 298 K.
1
The H NMR spectrum of the adduct (data not shown, see
Experimental Section) was similar to the spectra of low
symmetry complexes formed by reaction of thiiranes with 1.
For example, two imine proton resonances were observed at δ
8.85 and 8.45, and chemical shifts and couplings of proton
resonances of the macrocycle were similar. An analogous
structure 9 (Scheme 4) also arose from the dissolution of 1 into
d3-acetonitrile, where incubation of several hours was required
to convert the initial symmetrical complex (Figure 3, top panel)
to a twisted geometry (85% at equilibrium) in which coordinated
acetonitrile is proposed to adopt a cis relationship to the NO
ligand in the complex (Figure 3, bottom panel).
Coordinated Thiirane Is the Sulfur Acceptor: Free
Thiirane Is the Sulfur Donor. Treatment of the deuterio-
complex [Ru(salen)(NO)(R-deuterio-cis-stilbene-sulfide)](SbF6)
(d-6) in CD2Cl2 with 3 equiv of unlabeled cis-stilbene sulfide
Bimolecular Reaction of Thiirane and Thiirane-Catalyst
Adduct. The reaction of cis-stilbene sulfide with 1 produced
9
J. AM. CHEM. SOC. VOL. 124, NO. 17, 2002 4773

A R T I C L E S
Sauve and Groves
Table 3. GCMS Analyses of Stilbenes from Reactions of h-6 and
d-6 with Stilbene Sulfides and Controlsa
sample
180 (%)
181 (%)
182 (%)
d-6, cis-stilbene sulfide
cis-stilbene
h-6, R-d-cis-stilbene sulfide
d-cis-stilbene
100
100
100
100
12.9
14.2
87.8
85.7
1.0
1.1
14.5
12.0
a Rows 1 and 3 represent samples obtained from reactions of the listed
components dissolved in CD2Cl2. The identities of d-6 and h-6 are shown
in Figure 2 top panel, and are coordinated R-deuterio-cis-stilbene sulfide:
catalyst adduct and all-proteo cis-stilbene sulfide adduct, respectively.
Reactions were run in a molar ratio of 3:1 free cis-stilbene sulfide:adduct,
and are single turnover reactions as explained in the text. Reactions were
evaporated, triturated with pentane, concentrated, and purified by filtration
through 1 mL of silica to remove tetrathiane, and analyzed by GCMS. Rows
2 and 4 represent GCMS analysis of unlabeled and labeled cis-stilbenes
used to synthesize the respective unlabeled and labeled cis-stilbene sulfides.
Scheme 5. Reaction of Deuterium-Labeled cis-Stilbene Sulfide
Adduct with Unlabeled cis-Stilbene Sulfide (Top) and Reaction of
Unlabeled cis-Stilbene Sulfide Adduct with Deuterium-Labeled
cis-Stilbene Sulfide (Bottom)
Figure 4. Reaction of styrene sulfide and cis-2-deuteriostyrene sulfide after
treatment with 1 in CD3NO2. The top spectrum is the reaction of styrene
sulfide, showing styrene and phenyltrithiolane resonances. The bottom
spectrum is the corresponding reaction of the deuterium-labeled styrene
sulfide. The styrene formed shows a retention of the initial cis-stereochem-
istry of the thiirane. The deuterium stereochemistry is inverted to the trans-
geometry in the phenyl-trithiolane product.
formed stilbene and diphenytetrathiane and a precipitate identi-
fied as the starting catalyst 1 as determined by 1H NMR. GCMS
analysis of isolated cis-stilbene confirmed that the cis-stilbene
produced did not contain deuterium (Table 3), whereas 1H NMR
spectra (data not shown) indicated that deuterium label was
concentrated in the tetrathiane product (Scheme 5; top panel).
Conversely, treatment of the proteo complex, Ru(salen)(NO)-
(cis-stilbene-sulfide)](SbF6) (h-6), with deuterium-labeled stil-
bene sulfide generated deuterium-labeled cis-stilbene with 100%
d-content based upon a fully labeled control (Table 3). 1H NMR
spectra (data not shown) corroborated that the deuterium label
was concentrated in the stilbene product (Scheme 5; bottom
panel). This labeling pattern is consistent with free thiirane
desulfurization to form olefin. Accordingly, it is the coordinated
thiirane that accepts sulfur to become trans-diphenyltetrathiane.
Moreover, ligand exchange of thiiranes must be slow relative
to the rate of product formation, since no scrambling of label
was observed.
Inversion at Carbon in Formation of Trithiolane. The
molecule cis-2-deuterio-styrene sulfide (95% deuterium incor-
poration) was used to probe for stereochemical changes occur-
ring at either the R or the â carbon along the reaction coordinate
that forms olefin and 4-phenyl-trithiolane in the reaction of
styrene sulfide catalyzed by 1. Ten equivalents of cis-2-deuterio-
styrene sulfide treated with a single equivalent of 1 in CD3NO2
yielded deuterium-labeled styrene and deuterium-labeled phe-
nyltrithiolane. The deuterium stereochemistry in styrene was
determined by 1H NMR to be Z, identical to the starting thiirane.
Conversely, the deuterium stereochemistry in phenyltrithiolane
was determined to be â-trans, indicating an inversion in relative
stereochemistry of the deuterium versus starting thiirane (Scheme
Scheme 6. Reaction of cis-2-Deuterio-styrene Sulfide Catalyzed
by 1
6). The absence of a peak at δ 3.7 in the spectrum assignable
to the trans proton of phenyltrithiolane indicated deuterium
enrichment at this position (Figure 4). The two remaining R
and â proton resonances (δ 4.9 and 3.5, respectively) of
phenyltrithiolane were doublets. The stereochemical assignment
of deuterium was aided by the NOESY spectrum of 5 which
provided clear determination of â-cis and â-trans proton
1
resonances of the H NMR spectrum of phenyltrithiolane (see
Experimental Section for NOE data and assignments).
Discussion
The stable coordination of thiiranes to metal centers is
intrinsically difficult, because thiiranes are reactive to reducing
metal centers by sulfur transfer,8,19 or react by polymerization
in the presence of Lewis acid metal catalysts.8 Additional modes
of reaction have been reported. For example, metal-catalyzed
S-S bond formation between free thiiranes and metal-
coordinated thiiranes leading to desulfurization and olefin
formation from free thiirane has been observed in the presence
of the electrophilic tungsten complex W(CO)5(thiirane).20 In our
attempts to coordinate thiiranes to complex 1, we observed an
apparent analogue of this latter reaction mode, and observed
(19) For an exceptional example of terminal metallo-sulfide formation upon
thiirane coordination to a metal complex, see: Proulx, G.; Bergman, R. G.
J. Am. Chem. Soc. 1994, 116, 7953.
9
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Synthesis of Trithiolanes and Tetrathianes
A R T I C L E S
formation of olefin and trithiolane or tetrathiane products. The
products contain multiple consecutive S-S bonds contained in
five- or six-membered rings representing ring expansions of the
initial thiirane by sulfur atom additions.
of the imines (∆δ 0.25-0.5)24,25 is similar to the splittings
determined for the Ru complexes derived from reaction of
thiiranes, tetrahydrothiophene, and acetonitrile with 1. Thiirane
coordinate adducts to ruthenium have some precedent as well;
stable coordination of thiiranes and epoxides has been reported
in several low valent ruthenium complexes.26,27
The reactions described here are disproportionation reactions
of monosubstituted and disubstituted thiiranes. For example,
propylene and styrene sulfide both reacted in the presence of 1
to form the corresponding olefin and the 4-alkyltrithiolane in a
2:1 ratio. cis-Stilbene sulfide reacted to form cis-stilbene and
trans-diphenyltetrathiane in a 3:1 ratio. These reactions are very
efficient with yields in the range 70-90% and occur at room
temperature within several hours. The reaction is catalytic in
the metal complex as shown by recovery of the intact complex
after reactions, and by mechanistic studies that clearly show
the involvement of the complex in activation of thiirane. These
reactions occurred in CD3NO2, and CD2Cl2, although in CD2-
Cl2 insolubility of 1 restricted experiments to single turnover
reactions derived from a soluble thiirane coordinate adduct 6.
Enantioselectivity derived from the macrocycle in 2 could not
be addressed fully in this very limited investigation. In the one
instance examined carefully, styrene sulfide was not enantio-
merically enriched by catalysis by 2, and phenyl-trithiolane was
not formed in enantiomeric excess.21
1
Kinetic studies conducted by H NMR in CD2Cl2 with 6 in
the presence of free cis-stilbene sulfide showed that the
formation of olefin and tetrathiane is tightly coupled; moreover,
these studies showed that reactant disappearance rates (6 and
cis-stilbene sulfide) and product appearance rates (tetrathiane
and cis-stilbene) were matched. Studies of the rate of product
formation as a function of reactant concentration established
that the rate law is first order in adduct and free thiirane. This
result is consistent with bimolecular attack of thiirane with
coordinated thiirane as the likely rate-limiting step in the overall
catalytic cycle for reaction of cis-stilbene sulfude with 1, since
under catalytic conditions the adduct is observed as the major
form of the complex during reaction. The bimolecular reaction
step was shown by labeling studies to generate olefin from
solution thiirane and tetrathiane from the coordinated thiirane.
Labeling studies upon styrene sulfide indicate that trithiolane
is formed with net stereochemical inversion at carbon. This was
shown by reaction of cis-2-deuterio-styrene sulfide, which
reacted with 1 to form trans-5-deuterio-4-phenyl-1,2,3-tri-
thiolane. This stereochemical result parallels the formation of
trans-diphenyltetrathiane from cis-stilbene sulfide in reaction
with 1, and the apparent nonformation of trans-diphenyltetrathiane
from reaction of trans-stilbene sulfide with 1 (Table 1).
The mechanism shown in Scheme 7 accounts for all of the
data obtained on the reaction of 1 with thiiranes. After
coordination of thiirane, nucleophilic attack of free thiirane on
the carbon of coordinated thiirane leads to inversion at carbon
of the coordinated thiirane. The attack is proposed to be at the
less substituted carbon of the coordinated thiirane, since styrene
sulfide reacted significantly faster than cis-stilbene sulfide.
Moreover, steric hindrance obtained by placement of four methyl
substituents, as in the case of tetramethylethylene sulfide,
prevented reaction of the thiirane beyond coordination with the
catalyst presumably because of steric prevention of nucleophilic
attack at the substituted carbons. The nucleophilic attack at
carbon of the coordinated thiirane introduces inversion at one
carbon of the coordinated species and is consistent with results
from deuterium labeling of styrene sulfide which established
that inversion is integral to the mechanism that generates cyclic
trithiolane. The proposed mechanism is similar to that of the
tungsten carbonyl thiirane reactions that generate olefin and form
S-S bonds from thiiranes.20 Investigations of these reactions
indicate that initial bimolecular reaction occurs by attack of free
thiirane at the carbon of the coordinated thiirane to generate
inversion prior to olefin formation.20
A cis-stilbene sulfide adduct was isolated by precipitation in
reaction mixtures containing 1 and excess stilbene sulfide. The
adduct could be partially decomposed to cis-stilbene sulfide and
1
1 upon standing in CD2Cl2, and a H NMR spectrum of the
adduct in this solvent included obvious thiirane resonances,
including two methine doublets. These methine doublets were
confirmed to be thiirane in origin by deuterium labeling of the
methine position of cis-stilbene sulfide at one carbon, whereupon
the doublets became singlets. The dispersion observed for these
peaks and their couplings shows that the thiirane coordination
environment lacks 2-fold symmetry. A reorganization of the
salen macrocycle of 1 upon thiirane binding is proposed to
explain this observation (Scheme 3). Similar macrocycle rear-
rangements were observed for coordinate adducts of tetra-
methylethylene sulfide, which is unreactive to desulfurization
chemistry, tetrahydrothiophene, and upon dissolution of 1 in
acetonitrile (Scheme 4).
Geometries of ruthenium nitrosyl salen complexes have been
structurally characterized only where the salen ligand adopts
the planar symmetrical geometry and includes the structure of
1,9a the structrure of 2b,15 and the structure of an O-nitrito-
ruthenium salen nitrosyl complex obtained by Wilkinson and
co-workers.22 Nevertheless, Wilkinson and co-workers23 as well
as Leung et al.15 report that the Ru(salen)(CO)2 adopts the
twisted geometry analogous to the geometry proposed in this
study. Re(V)-oxo salen-type complexes also exhibit a tendancy
to form twisted geometries.24 1H NMR spectroscopy of these
complexes24,25 showed that the observed chemical shift splitting
The process of olefin formation yields a putative metal
ligated-dithietane, first proposed by Adams and co-workers for
the reaction of thiiranes with tungsten carbonyls.20 The extrusion
of olefin itself is likely to be concerted and nonradical in nature,
(20) (a) Adams, R. D. Acc. Chem. Res. 2000, 33, 171. (b) Adams, R. D.; Perrin,
J. L. J. Am. Chem. Soc. 1999, 121, 3984. (c) Adams, R. D.; Yamamoto, J.
H.; Holmes, A.; Baker, B. J. Organometallics 1997, 16, 1430. (d) Adams,
R. D.; Queisser, J. A.; Yamamoto, J. H. J. Am. Chem. Soc. 1996, 118,
10674.
(21) Treatment of chiral catalyst 2 with tetrahydrothiophene at high concentra-
tions produced a saturable ratio of twisted and flat forms of the complex.
NMR spectra indicated that only one of two possible diasteromers was
formed in the twisted form.
(25) van Bommel, K. J. C.; Verboom, W.; Kooijman, H.; Spek, A. L.; Reinhoudt,
D. N. Inorg. Chem. 1998, 37, 4197.
(26) Amarasekera, J.; Rauchfuss, T. B.; Wilson, S. R. J. Am. Chem. Soc. 1988,
110, 2332.
(22) Wilkinson, G. Inorg. Chim. Acta 1977, 24, L95.
(23) Thornback, J. R.; Wilkinson, G. J. Chem. Soc., Dalton Trans. 1978, 110.
(24) Herrmann, W. A.; Rauch, M. U.; Artus, G. R. Inorg. Chem. 1996, 35,
1988.
(27) (a) Groves, J. T.; Han, Y.; Engen, D. V. J. Chem. Soc., Chem. Commun.
1990, 436. (b) Han, Y. Ph.D. Thesis, Department of Chemistry, Princeton
University, 1992.
9
J. AM. CHEM. SOC. VOL. 124, NO. 17, 2002 4775

A R T I C L E S
Sauve and Groves
Scheme 7. Proposed Mechanism for Desulfurization of
cis-Stilbene Sulfide Catalyzed by 1
otherwise indicated. Deuterated solvents CD2Cl2, CDCl3, acetone-d6,
DMSO-d6, CD3CN, and CD3NO2 were used as obtained from Aldrich
Chemical or Cambridge Isotope Laboratories. 1H and 13C NMR spectra
were obtained on 300 MHz GE and 270 MHz JEOL instruments. The
1H NOESY spectrum of phenyltrithiolane was taken on a JEOL 500
MHz NMR instrument. MS of trithiolanes and tetrathianes was done
at a temperature below 220 °C to avoid fragmentation and production
of higher molecular weight polysulfides. Styrene sulfide29 and cis- and
trans-stilbene sulfides30 were synthesized according to known proce-
dures. For synthetic procedures, all solvents were freshly distilled and
taken through three freeze-thaw cycles under vacuum to remove
dissolved gases. Complex 1 was synthesized as reported.9a
Synthesis of Ru(L1)(NO)(Cl) (L1 ) R,R,-(-)-1,2-Cyclohexane-bis-
(3,5-di-tertbutyl)salicylidene Aminate) (2b). Five hundred forty-six
milligrams (1 mmol) of L1 (Aldrich) in the protonated form and 50
mL of dry DMF were placed into a 125 mL round-bottom flask. Fifty
milligrams (2 mmol) of NaH was added, and the mixture was stirred.
After 1 h, 255 mg (1 mmol) of Ru(Cl)3(NO)(H2O) in 20 mL of DMF
was added, and the mixture was heated to 130 °C under an argon
atmosphere overnight. The solvent was evaporated under high vacuum
upon cooling, and the residual material was chromatographed on silica
(CH2Cl2/heptane/EtOAc 4/8/1). The compound 2b was isolated by
recrystallization in CH2Cl2/heptane containing trace acetone. TLC: Rf
) 0.5 in CH2Cl2/heptane 1:1. 1H NMR (CDCl3): δ 8.23 (s, 1H,
CHdN), 8.15 (s, 1H, CHdN), 7.5 (s, 2H, m-H), 7.0 (s, 2H, m-H), 4.2
(m, 1H, CH-CH), 3.26 (m, 1H, CH-CH), 2.86 (m, 1H, CH eq), 2.82
(m, 1H, -CH eq), 2.05 (2m, 2H, CH ax), 1.55 (2s, 18H, -C4H9), 1.28
(2s, 18H, -C4H9). FAB-MS m/z (obsd rel intensity; calc rel intensity
for [Ru(L1)(NO)(Cl)]+): 716 (12; 7), 715 (25; 17), 714 (39; 28), 713
(76; 75), 712 (48; 72), 711 (100; 100), 710 (78; 62), 709 (57; 41), 708
(47; 28), 707 (25; 10). Other major clusters centered at m/z ) 681
([Ru(L1)(Cl)]+), 676 ([Ru(L1)(NO)]+), and 646 ([Ru(L1)]+). X-ray
crystal structure: [Ru(L1)(NO)(Cl)]‚C3H6O (data not reported). IR (CH2-
Cl2): 1830 cm-1 (NO stretch). The compound obtained is identical to
that reported by Leung et al. synthesized by a different method.15
Synthesis of [Ru(L1)(NO)(H2O)](SbF6) (2). Fifty-two milligrams
(0.073 mmol) of Ru(L1)(NO)(Cl) 2b was added to a 50 mL round-
bottom flask and dissolved in 25 mL of CH2Cl2/acetone (90:10).
Twenty-five milligrams (0.073 mmol) of AgSbF6 was added to the flask
in 5 mL of CH2Cl2/acetone. After refrigeration overnight, the solution
was filtered to remove AgCl and rotoevaporated. Compound 2 was
precipitated from acetone by H2O addition and then recrystallized from
because stilbene sulfide and styrene sulfide stereochemistry
(from cis-deuterio-styrene sulfide) is unchanged in the product
olefin. This result is in contrast to the predominant loss of initial
stereochemistry seen for the trialkyltin radical desulfurization
of cis-thiiranes.28 The dithietane intermediate was not observed
in our studies, and has not been characterized to our knowledge
in any metal complex. This intermediate acts as a reactive entity
which by ring strain, and electrophilic activation, is able to react
further with free thiirane to complete the catalytic mechanism.
The metal ligated-dithietane and intermediates downstream of
it were not observed in reaction mixtures, suggesting they are
transiently formed and rapidly turned over under reaction
conditions.
Further experimental work to establish the complete reaction
coordinate is still required, but the mechanism presented
accounts for the data and adopts existing precedents and
proposed reaction pathways. What is most unusual about the
reaction of 1 with thiiranes is the unprecedented production of
trithiolanes and tetrathianes from thiiranes. In the tungsten
complexes, the preferred products are cyclic oligomers of the
thietanes in which S-S bonds do not exceed two sulfur atoms
in length, whereas in this case S-S units extend to three or
four sulfur atoms consecutively. A selectivity effect may be at
work where ruthenium is able to activate attack at sulfur by
free thiirane at steps downstream of dithietane formation over
attack at carbon. These issues highlight the novelty of the
observed chemistry reported here. The efficiencies and mild
conditions of these reactions suggest synthetic accessibility to
unusual trisulfide and tetrasulfide structures through application
of this methodology.
1
EtOAc/heptane 1:5. TLC: Rf ) 0.2, CH2Cl2/acetone 20/1. H NMR
(CDCl3): δ 8.08 (s, 1H, CHdN), 7.91 (s, 1H, CHdN), 7.57 (s, 2H,
m-H), 7.48 (s, 2H, m-H), 7.13 (s, 2H, m-H), 7.12 (s, 2H, m-H), 3.16
(m, 1H, CH-CH), 2.66 (m, 1H, CH-CH), 2.44 (m, 1H, CH eq), 2.44
(m, 1H, -CH eq), 2.0 (2m, 2H, CH ax), 1.372 (2s, 18H, -C4H9), 1.28
(2s, 18H, -C4H9). FAB-MS m/z (found rel intensity; calcd rel intensity
for [Ru(L1)(NO)(H2O)]+): 696 (23; 52), 695 (42; 35), 694 (65; 100),
693 (64; 58), 692 (100; 45), 691 (75; 31), 690 (71; 4). Other major
clusters centered at m/z ) 676 ([Ru(L1)(NO)]+) and 646 ([Ru(L1)]+).
IR (CH2Cl2): 1858 cm-1 (NO stretch).
Synthesis of R-Deuterio-cis-stilbene Sulfide. R-Deuterio-cis-stil-
bene-oxide was synthesized according to the published procedure,31
and 1H NMR and GCMS verified 70% deuterium incorporation at one
position. Three hundred seventy-five milligrams (1.90 mmol) of
R-deuterium-cis-stilbene oxide in 5 mL of dioxane was treated with
1.90 mmol (1 equiv) of thiourea and 1.90 mmol (1 equiv) of H2SO4
premixed in 10 mL of H2O. The reaction mixture was stirred at room
temperature for 36 h, and the resulting white solid was washed with
water and ether. The solid was then treated with a solution of 5%
(28) Izraelewicz, M. H.; Nui, M.; Spring, R. T.; Turos, E. J. Org. Chem. 1995,
60, 470.
(29) Guss, C. O.; Chamberlain, D. L. J. Am. Chem. Soc. 1952, 74, 1342.
(30) Ketcham, R.; Shah, V. P. J. Org. Chem. 1963, 28, 229.
(31) Collman, J. P.; Kodadek, T.; Brauman, J. I. J. Am. Chem. Soc. 1986, 108,
2588.
Experimental Section
General Methods. All reagents used were obtained from available
commercial sources and used without additional purification unless
9
4776 J. AM. CHEM. SOC. VOL. 124, NO. 17, 2002

Synthesis of Trithiolanes and Tetrathianes
A R T I C L E S
sodium carbonate. The suspension was stirred at room temperature for
2 h, and then the solid was filtered off. Filtration of the material through
a silica plug using CH2Cl2 as an eluant gave a pure sample of
R-deuterium-cis-stilbene sulfide (70% deuterium at one site). See Table
3 for GCMS data on this material.
from Aldrich) in 1.5 mL of CD3NO2. The reaction was allowed to react
for 6 h at room temperature, and the reaction was determined to be
complete by the full disappearance of resonances of propylene sulfide
in 1H NMR spectrum. Generated propylene was confirmed by the
disappearance of resonances for propylene (δ 5.8, 5.05, 4.95, and 1.95)
upon opening of the NMR tube to air. The 4-methyl-1,2,3-trithiolane
was isolated by evaporation, CH2Cl2/pentane redissolution, and silica
gel purification using cold pentane-CD2Cl2 (9:1). The compound was
unstable to concentration; pentane could be removed by repetitive
additions of neutral alumina-treated CDCl3 followed by evaporation
Synthesis of cis-2-Deuterio-styrene Sulfide. Deuterium labeling of
styrene in the cis-â-stereochemistry was effected by reduction of
â-deuterio-phenylacetylene with a hindered borane and acetic acid
workup.31 Subsequent GCMS and 1H NMR analysis of the isotopically
substituted styrene showed 95% + deuterium incorporation in the
Z-stereochemistry, as expected. Epoxidation of this styrene by MCPBA
in CH2Cl2 formed the cis-â-deuterio-styrene oxide which was purified
1
3
(91% yield). H NMR (CD2Cl2): δ 4.25 (m, R-H JH-H ) 6.96 Hz,
3
2
4.77 Hz), 3.57 (dd, trans-â-H JH-H ) 6.96 Hz, JH-H ) 11.16 Hz),
3.25 (dd, cis-â-H 3JH-H ) 4.77 Hz, 2JH-H ) 11.16 Hz ), 1.6 (d, CH3).
13C NMR (CDCl3): ppm 56.6, 52.6. 22.0. MS: (M + 138, 100%, 139,
5.8%, 140, 13.0%, 141, 0.754%, 142, 0.865%), ([M - S - 1]+, 105,
11.1%) ([M - 2S]+, 74, 35%).
1
by silica gel chromatography. H NMR of this material corresponded
well to the reported spectrum for this compound.31 Subsequent synthesis
of styrene sulfide was performed as reported using potassium thio-
1
cyanate to generate cis-2-deuterio-styrene sulfide. H NMR (CDCl3):
δ 7.18 (s, 5H, Ar-H), 3.81 (d, 1H, CHdCH2), 2.8 (d, 1H, CH-CH
trans).
Synthesis of cis-Stilbene Sulfide Salen Complex (6). [Ru(salen)-
(NO)(cis-stilbene sulfide(S))](SbF6) was prepared as follows: 4 mg
(5.9 µmol) of 1 was reacted with 10 mg (47 µmol) of cis-stilbene sulfide
(or R-deuterio-cis-stilbene sulfide) in an NMR tube containing 2 mL
Reactions of Sulfides with Complexes. Typically, 100 µmol of
thiirane in 1 mL of CD3NO2 was added to a solution of 2-3 µmol of
1 or 2 in 1 mL of CD3NO2 or CD2CL2, respectively, in a chilled NMR
1
of CD3NO2. The reaction was prepared at 0 °C and monitored by H
1
NMR. The appearance of cis-stilbene and trans-diphenyltetrathiane was
observed along with the formation of the desired compound identified
by two imine singlets at δ 8.7 and 9.1 and by two doublets at δ 5.5
and 5.8. When these resonances were at their maximum, the solvent
was cooled to 0 °C and removed in vacuo. The solid was redissolved
in CH2Cl2, and pentane was added to precipitate the adduct. Evaporation
removed residual solvent, and the complex was stable for hours at room
tube bathed in ice. The reaction mixture was monitored by H NMR
after the tube was tightly sealed and warmed to room temperature. The
1
production of alkene and other products was monitored by H NMR.
Products were isolated by extraction into pentanes or by evaporation
of solvent and trituration with pentane/CH2Cl2 (1:1). Components could
be separated by silica gel chromatography using pentane followed by
pentane/CH2Cl2 (1:1) elution. Comparison of products to authentic
standards was used to identify products.
1
temperature in CD2Cl2. H NMR (CD2Cl2): δ 8.92 (s, 1H, CHdN),
3
8.45 (s, 1H, CHdN), 6.68-7.80 (m, 18H), 5.65 (d, R-H JH-) 7.0
Synthesis of 5,6-Diphenyl-1,2,3,4-tetrathiane (5). Twenty mil-
ligrams (95 µmol) of cis-stilbene sulfide was reacted with 2 mg (2.9
3
Hz), 5.4 (d, R-H JH-H ) 7.0 Hz), 3.6-4.4 (m, 4H, CH2-CH2). For
1
the R-deuterium-stilbene sulfide complex, all resonances were identical
except for the peaks at δ 5.65 (s, R-H) and 5.4 (s, R-H).
µmol) of 1 in 1.5 mL of CD3NO2. The reaction was monitored by H
NMR until the disappearance of the starting thiirane was complete.
The two products formed were cis-stilbene and 4 distinguished by
singlets in the spectrum at δ 6.65 and 5.1. The products could be
separated by evaporation of solvent, addition of 1 mL of CH2Cl2,
followed by addition of pentane until the ruthenium complex precipi-
tated. Filtration and concentration were followed by silica gel purifica-
tion using cold pentane-CH2Cl2 (9:1, 73% yield). NMR and structural
assignment are discussed in the text.
Synthesis of [Ru(salen)(NO)(tetramethylethylenesulfide)](SbF6)
(7). Four milligrams (5.9 µmol) of 1 was reacted with 10 mg (119
µmol) of tetramethylethylene sulfide in an NMR tube containing 2 mL
1
of CD3NO2. The reaction was prepared at 0 °C and monitored by H
NMR. The appearance of the desired compound was identified by two
imine singlets at δ 8.7 and 9.1 and by additional singlets in the NMR
spectrum at δ 2.0-1.0. When these resonances were at their maximum,
the solvent was cooled to 0 °C and removed in vacuo. The solid was
redissolved in CH2Cl2, and pentane was added to precipitate the adduct.
The adduct was washed with additional pentane to remove excess
ligand. Evaporation removed residual solvent, and the complex was
Synthesis of 4-Phenyltrithiolane (3). Two milligrams (2.9 µmol)
of 1 was reacted with 10 mg (74 µmol) of styrene sulfide in 1.5 mL of
CD3NO2. 1H NMR spectrum taken at 2 h reaction time confirmed
reaction completion based upon the disappearance of styrene sulfide
resonances. Two products formed in the reaction could be identified
by distinct midfield resonances (styrene δ 5.2, d and 5.7, d) and (3: δ
5.1, dd, 3.6, dd, and 3.9, dd). Styrene was isolated along with CD3NO2
by evaporation. The solid residue was redissolved in 1 mL of CH2Cl2,
and the catalyst was precipitated by addition of pentane. The supernatant
was evaporated to yield the mostly pure trithiolane. Silica gel
chromatography using cold pentane/CH2Cl2 (8:2) gave pure trithiolane
used to obtain analytical data (90% yield). 1H NMR (CD2Cl2): δ 7.2-
1
stable for hours at room temperature in CDCl2. H NMR (CDCl3): δ
8.82 (s, 1H, CHdN), 8.3 (s, 1H, CHdN), 6.8-7.80 (m, 8H), 3.6-4.7
(m, 4H, CH2-CH2), 2.2 (s, 3H, CH3), 2.05 (s, 3H, CH3), 1.7 (s, 3H,
CH3), 1.2 (s, 3H, CH3).
Synthesis of [Ru(salen)(NO)(tetrahydrothiophene)](SbF6) (8).
Four milligrams (5.9 µmol) of 1 was reacted with 20 mg (227µmol) of
tetrahydrothiophene in an NMR tube containing 2 mL of CD3NO2. The
reaction was prepared at 0 °C and monitored by 1H NMR. The
appearance of the desired compound was identified by two imine
singlets at δ 8.7 and 9.1 and by upfield signals at δ 2.5 and 1.5. When
these resonances were at their maximum, the solvent was cooled to 0
°C and removed in vacuo. The solid was redissolved in CH2Cl2, and
pentane was added to precipitate the adduct. The adduct was washed
several times with pentane to remove excess ligand. Evaporation
removed residual solvent, and the complex was stable for hours at room
3
7.4 (m, 5H, C6H5), 4.9 (dd, R-H JH-H ) 7.5 Hz, 5.5 Hz), 3.7 (dd,
3
2
3
trans-â-H JH-H ) 7.5, JH-H ) 11.5 Hz), 3.5 (dd, cis-â-H JH-H
)
5.5, 2JH-H ) 11.5 Hz). 13C NMR (CD2Cl2): ppm 130.0, 129.3, 129.0,
66.7, 52.9. NOESY NOE cross-peaks: δ 4.9, R-H to δ 3.7, trans-H; δ
4.9, R-H to δ 7.3, ortho-H; δ 3.5, cis-H to δ 7.3, ortho-H; δ 3.5, cis-H
to δ 3.7, trans-H. MS (<220 °C): (M + 200, 51.1%), ([M - 2S -
1]+, 135, 93%), ([M - 3S]+, 104, 100%). Temperatures in excess of
220 °C resulted in the formation of the phenyl-tetrathiane (four-sulfur
derivative), as determined by the MS spectrum obtained under these
temperature conditions. A similar procedure to that used above was
employed for the study of the reaction of â-cis-deuteriostyrene sulfide
with 1 in CD3NO2.
1
temperature in CD2Cl2. H NMR (CD2Cl2): δ 8.85 (s, 1H, CHdN),
8.45 (s, 1H, CHdN), 6.8-7.7 (m, 8H), 3.6-4.4 (m, 4H, CH2-CH2),
2.8-3.0 (bm, 4H, SCH2CH2-), 2.0-2.1 (bm, 4H, SCH2CH2-).
Procedure for Study of Solvent Effects on Structure of Salen
Complex. Three milligrams (5 µmol) of 1 was placed in a NMR tube
1
Synthesis of 4-Methyl-trithiolane (4). Two milligrams (2.9 µmol)
of 1 was reacted with 7.5 mg (100 µmol) of propylene sulfide (obtained
containing 1 mL of CD3CN. The catalyst was monitored by H NMR
1
over a period of several hours during which the H NMR spectrum
9
J. AM. CHEM. SOC. VOL. 124, NO. 17, 2002 4777

A R T I C L E S
Sauve and Groves
changed. The most pronounced change was in the form of a decline in
the imine singlet resonance and the appearance of two new singlets on
opposite sides of the original resonance of roughly equal intensity
(δ 8.8 and 8.4). Changes resulting in greater complexity in the total
spectrum evolved over time until the final spectrum indicated that the
starting complex had largely vanished from solution leaving two new
species, one major the other minor, as indicated by the NMR spectrum.
The major product was assigned as cis-[Ru(salen)(NO)(CD3CN)] (SbF6)
(9).
Procedure for Study of Reaction of d-6 and Unlabeled cis-
Stilbene Sulfide and h-6 with Deuterium-Labeled cis-Stilbene
Sulfide. Two micromoles of d-6 was dissolved in 1.0 mL of CD2Cl2
in an NMR tube, and 6 µmol of cis-stilbene sulfide was added in 200
µL of CD2Cl2. The appearance of cis-stilbene and the disappearance
of complex from solution were monitored over a 60 min period. The
disappearance of complex was associated with the formation of
precipitated 1 as the free complex is liberated into solution. The ratio
of the stilbene peak at δ 6.6 and the peak of tetrahydrothiophene at δ
5.1 was used as a measure of deuterium enrichment in the cyclic
product. The ratio was determined to be 4:1. The stilbene could be
isolated by silica column chromatography using hexane as an eluant.
GCMS analysis confirmed that the stilbene contains negligible deute-
rium label. The experimental above was performed where all-proteo 6
(h-6) and deuterium-labeled cis-stilbene sulfide was used as the sulfur
donor. In this case, the ratio of peaks at 6.6 and 5.1 was found to be
2:1. In the GCMS analysis, the stilbene had a deuterium content (single
position) of 70%. In a control experiment (h-6 reacted with unlabeled
cis-stilbene sulfide), the ratio of stilbene peak to tetrathiane peak by
1H NMR was found to be 3:1. Table 3 contains GCMS data for stilbene
controls and for reactions.
Kinetic Study of cis-Stilbene Sulfide Desulfurization Reaction.
Compound 6 (2.9 µmoles) was dissolved in 3.0 mL of CD2Cl2, and
the volume was equally divided into three separate NMR tubes. In
separate experiments, 3 µmol, 6 µmol, and 12 µmol of cis-stilbene
sulfide were added in 200 µL of CD2Cl2 to one of the three prepared
NMR tubes. Each tube was monitored for appearance of cis-stilbene
over a 60 min period with spectra obtained at 3-6 min intervals. The
cis-stilbene formed was measured by integration of the vinyl resonance
at δ 6.6. Plots of cis-stilbene produced versus time were used to
determine the rate using the initial rate method. Separately, a second
experiment was performed wherein 6 µmol of stilbene sulfide in 200
µL of CD2Cl2 was added to 0.6 µmol of the adduct in 1.0 mL of CD2-
Cl2. The rate of cis-stilbene production was measured with a method
similar to that described above.
Acknowledgment. The authors would like to thank Wei
1
Wang for his efforts in obtaining the H NOESY spectrum of
4-phenyl-1,2,3-trithiolane and Dorothy Little for her assistance
in obtaining mass spectra of the reported compounds. Financial
support of this work by the National Science Foundation (CHE
9814301) is gratefully acknowledged.
JA017462C
9
4778 J. AM. CHEM. SOC. VOL. 124, NO. 17, 2002