Catalytic transformations of vinylthiiranes by tungsten carbonyl complexes. A new route to 3,6-dihydro-1,2-dithiins

Article abstract of DOI:10.1021/ja984249g

W(CO)₅(NCMe) (1) has been found to transform vinylthiirane and a series of methyl-substituted vinylthiiranes into a series of 3,6-dihydro-1,2-dithiin compounds. Two equivalents of the vinylthiirane are required, and 1 equiv of a butadiene is formed by the transfer of its sulfur atom to the second vinythiirane, which is then transformed into the dihydrodithiin. The formation of 3,6-dihydro-1,2-dithiin (9) proceeds at 15 turnovers/h at 25°C using vinylthiirane (4) and 1 as the catalyst. The catalyst is long-lived (up to 2000 turnovers have been obtained without loss of activity) and relatively insensitive to air. Methyl substitutents on the vinyl group increase the rate of reaction while methyl substituents on the thiirane ring slow it considerably. The introduction of phosphine ligands to the catalyst also leads to significant increases in the rate of reaction. The dithiin complex W(CO)₅(SSCH₂CH=CHCH₂) (13) was isolated from the catalytic reactions and was structurally characterized. The dihydrodithiin is coordinated to the tungsten atom through one of its two sulfur atoms. Compound 13 was shown to be a species in the catalytic cycle. A mechanism involving a vinylthiirane intermediate that undergoes spontaneous ring opening, followed by addition of a second vinylthiirane to the terminal carbon of the chain, elimination of 1 equiv of butadiene, and formation of a sulfur-sulfur bond leading to 13 is proposed. The vinylthiirane intermediate is regenerated by ligand substitution which releases the dihydrodithiin product. Compound 9 readily polymerizes when its pure form is exposed to visible light. If the polymerization is interrupted at an early stage, 1,2,7,8-tetrathiacyclododeca-4,10-diene (14), a dimer of 9, can be isolated. Compound 14 was obtained in 5.6% yield and was structurally characterized crystallographically.

Full text of DOI:10.1021/ja984249g

3984
J. Am. Chem. Soc. 1999, 121, 3984-3991
Catalytic Transformations of Vinylthiiranes by Tungsten Carbonyl
Complexes. A New Route to 3,6-Dihydro-1,2-dithiins
Richard D. Adams* and Joseph L. Perrin
Contribution from the Department of Chemistry and Biochemistry, UniVersity of South Carolina,
Columbia, South Carolina 29208
ReceiVed December 9, 1998
Abstract: W(CO)5(NCMe) (1) has been found to transform vinylthiirane and a series of methyl-substituted
vinylthiiranes into a series of 3,6-dihydro-1,2-dithiin compounds. Two equivalents of the vinylthiirane are
required, and 1 equiv of a butadiene is formed by the transfer of its sulfur atom to the second vinythiirane,
which is then transformed into the dihydrodithiin. The formation of 3,6-dihydro-1,2-dithiin (9) proceeds at 15
turnovers/h at 25 °C using vinylthiirane (4) and 1 as the catalyst. The catalyst is long-lived (up to 2000 turnovers
have been obtained without loss of activity) and relatively insensitive to air. Methyl substitutents on the vinyl
group increase the rate of reaction while methyl substituents on the thiirane ring slow it considerably. The
introduction of phosphine ligands to the catalyst also leads to significant increases in the rate of reaction. The
dithiin complex W(CO)5(SSCH2CHdCHCH2) (13) was isolated from the catalytic reactions and was structurally
characterized. The dihydrodithiin is coordinated to the tungsten atom through one of its two sulfur atoms.
Compound 13 was shown to be a species in the catalytic cycle. A mechanism involving a vinylthiirane
intermediate that undergoes spontaneous ring opening, followed by addition of a second vinylthiirane to the
terminal carbon of the chain, elimination of 1 equiv of butadiene, and formation of a sulfur-sulfur bond
leading to 13 is proposed. The vinylthiirane intermediate is regenerated by ligand substitution which releases
the dihydrodithiin product. Compound 9 readily polymerizes when its pure form is exposed to visible light. If
the polymerization is interrupted at an early stage, 1,2,7,8-tetrathiacyclododeca-4,10-diene (14), a dimer of 9,
can be isolated. Compound 14 was obtained in 5.6% yield and was structurally characterized crystallographically.
Introduction
develop catalytic processes that lead to the formation of
polythioether macrocycles catalytically by ring-opening cycloo-
ligomerization processes involving three or more thietane
molecules, e.g. eq 1.5
The cleavage of carbon-sulfur bonds in cyclic thioethers is
central to the processes relating to the hydrodesulfurization of
petroleum feedstocks.1-3 We have recently been investigating
ring-opening reactions of the strained cyclic thioethers, thietanes,
and thiiranes, which are promoted by coordination of the sulfur
atom to transition metal atoms of certain metal carbonyl
complexes.4-6 For the thietanes, we have even been able to
(1)
(1) (a) Angelici, R. J. Polyhedron 1997, 16, 3071. (b) Bianchini, C.;
Casares, J. A.; Meli, A.; Sernau, V.; Vizza, F.; Sa´nchez-Delgado, R. A.,
Polyhedron 1997, 16, 3099. (c) Jones, W. D.; Vicic, D. A.; Chin, R. M.;
Roache, J. H.; Myers, A. W. Polyhedron 1997, 16, 3115. (d) Wiegand, B.
C.; Friend C. M. Chem. ReV. 1992, 92, 491. (e) Angelici, R. J. Coord.
Chem. ReV. 1990, 105, 61. (e) Rauchfuss, T. B. Prog. Inorg. Chem. 1991,
39, 259. (f) Angelici, R. J. Acc. Chem. Res. 1988, 21, 387. (g) Adams, R.
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115, 8207.
(2) (a) Riaz, U.; Curnow, O. J.; Curtis, M. D. J. Am. Chem. Soc. 1994,
116, 4357. (b) Jones, W. D.; Chin, R. M. J. Am. Chem. Soc. 1994, 116,
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V.; Sa´chez-Delgado, R. A. J. Am. Chem. Soc. 1994, 116, 4370. (d) Chen,
J.; Angelici, R. J. Appl. Organomet. Chem. 1992, 6, 479. (e) Luo, S.; Ogilvy,
A. E.; Rauchfuss, T. B. Organometallics 1990, 10, 1002.
(3) (a) Schuman, S. C.; Shalit, H. Catal. ReV. 1970, 4, 245. (b) Gates,
B. C.; Katzer, J. R.; Schuit, G. C. A. Chemistry of Catalytic Processes;
McGraw-Hill: New York, 1978; Chapter 5. (c) Friend, C. M.; Roberts, J.
T. Acc. Chem. Res. 1988, 21, 394. (d) Markel, E. J.; Schrader, G. L.; Sauer,
N. N.; Angelici, R. J. J. Catal. 1989, 116, 11. (e) Prins, R.; De Beer, V. H.
H.; Somorjai, G. A. Catal. ReV. Sci. Eng. 1989, 31, 1. (f) Sauer, N. N.;
Markel, E. J.; Schrader, G. L.; Angelici, R. J. J. Catal. 1989, 117, 295. (g)
Kwart, H.; Schuit, G. C. A.; Gates, B. C. J. Catal. 1980, 61, 128. (h) Curtis,
M. D.; Penner-Hahn, J. E.; Schwank, J.; Beralt. O.; McCabe, D. J.;
Thompson, L.; Waldo, G. Polyhedron 1988, 7, 2411. (i) Curtis, M. D. Appl.
Organomet. Chem. 1992, 6, 429.
Thiiranes possess ring strain that has been estimated to be
≈19 kcal/mol in the parent molecule.7 They are readily
(4) (a) Adams, R. D.; Pompeo, M. P. Organometallics 1992, 11, 1460.
(b) Adams R. D. J. Cluster. Sci. 1992, 3, 263. (c) Adams, R. D.; Cortopassi,
J. E.; Falloon, S. B., Organometallics 1992, 11, 3794. (d) Adams, R. D.;
Belinski, J. A.; Pompeo, M. P., Organometallics 1992, 11, 3129. (e) Adams,
R. D.; Belinski, J. A., Organometallics 1992, 11, 2488.
(5) (a) Adams, R. D. Catalytic Synthesis of Polythioether Macrocycles.
In Catalysis by Di- and Polynuclear Metal Cluster Complexes; Adams, R.
D., Cotton, F. A., Eds.; Wiley-VCH Publishers: New York, 1998; Chapter
8. (b) Adams, R. D.; Falloon, S. B. Chem. ReV. 1995, 95, 2587. (c) Adams,
R. D.; Falloon, S. B. J. Am. Chem. Soc. 1994, 116, 10540. (d) Adams, R.
D.; Cortopassi, J. E.; Falloon, S. B. Organometallics 1995, 14, 1748. (e)
Adams, R. D.; Falloon, S. B. Organometallics 1995, 14, 4594. (f) Adams,
R. D.; Queisser, J. A.; Yamamoto, J. H. Organometallics 1996, 15, 2489.
(g) Adams, R. D.; Falloon, S. B.; Perrin, J. L.; Queisser, J. A.; Yamamoto,
J. H. Chem. Ber. 1996, 126, 313. (h) Adams, R. D.; Cortopassi, J. E.;
Falloon, S. B., J. Organomet. Chem. 1993, 463, C5.
(6) (a) Adams, R. D.; Yamamoto, J. H.; Holmes, A.; Baker, B. J.
Organometallics 1997, 16, 1430. (b) Adams, R. D.; Queisser, J. A.;
Yamamoto, J. H. J. Am. Chem. Soc. 1996, 118, 10674.
10.1021/ja984249g CCC: $18.00 © 1999 American Chemical Society
Published on Web 04/28/1999

Catalytic Transformations of Vinylthiiranes
J. Am. Chem. Soc., Vol. 121, No. 16, 1999 3985
polymerized when treated with Lewis acids and Lewis bases.8
They also eliminate sulfur to yield elemental sulfur and the
corresponding olefin when heated.8b-d,9 The desulfurization of
thiiranes is promoted by complexation to transition metal atoms
and adsorption onto metal surfaces.10,11
There have been a few reports of transition metal complexes
containing thiiranes as ligands, and some of these have been
characterized structurally by X-ray crystallographic methods.6,12
We have found that the thiiranetungsten pentacarbonyl complex
W(CO)5(SC2H4) reacts with thiiranes catalytically to yield a
series of cyclic disulfides with release of 1 equiv of olefin for
each disulfide unit that is formed (eq 2).6
were recorded on a Varian Mercury 400 spectrometer operating at
100.59, 125.76, and 161.94 MHz, respectively. 31P NMR spectra were
referenced against H3PO4. Mass spectra were obtained using electron
impact ionization. Elemental analyses were performed by Oneida
Research Services (Whitesboro, NY). 3,4-Epoxy-1-butene was supplied
by Eastman and was used without further purification. 2-Methyl-2-
vinyloxirane was purchased from Aldrich and was used without further
purification. The remaining epoxides were prepared by following
procedure reported for the synthesis of 3,4-epoxy-2-methyl-1-butene.15
W(CO)5(NCMe)16 (1), W(CO)5(PPh3),17 and W(CO)5(PMe2Ph)17 were
prepared according to the published procedures. 13CO-enriched tungsten
complexes (labeled with * herein) were prepared in the same manner
as the unenriched complexes starting with 13CO-enriched W(CO)6.5g
Product separations were performed by TLC in air on Analtech 0.25
and 0.50 mm silica gel 60 Å F254 glass plates. Plots of the kinetic data
were fitted using Cricket Graph version 1.3 of Cricket Software on a
Macintosh Power PC.
(2)
Synthesis of the Vinylthiiranes. All vinylthiiranes were prepared
according to the published procedure for the synthesis of thiirane from
the ethylene oxide.18 Spectral data for vinylthiirane (4): 1H NMR (δ
in CDCl3): 5.55 (m, 2H), 5.17 (m, 1H), 3.44 (m, 1H), 2.64 (dd, 2JH-H
) 6.3 Hz, 3JH-H ) 1.6 Hz, 1H), 2.32 (dd, 2JH-H ) 5.5 Hz, 3JH-H ) 1.6
Hz, 1H). 13C NMR (δ in CDCl3): 138.9 (1C), 117.6 (1C), 36.7 (1C),
25.3 (1C).19 The mass spectrum shows the parent ion at 86 m/e, as
well as additional ions with weights of 85, 71, and 64 m+/e. Spectral
data for 3,4-epithia-2-methyl-1-butene (5): 1H NMR (δ in CDCl3): 5.18
In this report, our studies of the transformations of a series
of vinylthiiranes by W(CO)5(NCMe) (1) and its two phosphine
derivatives, W(CO)4(PPh3)(NCMe) (2) and W(CO)4(PMe2Ph)-
(NCMe) (3), are described. We have found that these reactions
lead to the formation of 3,6-dihydrodithiins A and butadiene,
catalytically. Dihydrodithiins A and B are a family of naturally
occurring compounds that have been found to exhibit a range
of antiviral, antifungal, and antibiotic properties.13 A preliminary
report of this work has been published.14
(br s, 1H), 4.97 (br s, 1H), 3.55 (t, J ) 6.1 Hz, 1H), 2.51 (dd, 2JH-H
)
3
2
3
6.5 Hz, JH-H ) 1.6 Hz, 1H), 2.43 (dd, JH-H ) 5.8 Hz, JH-H ) 1.6
Hz, 1H), 1.62 (br s, 3H). 13C NMR (δ in CDCl3): 142.5 (1C), 114.9
(1C), 39.8 (1C), 23.0 (1C), 16.6 (1C). The mass spectrum shows the
parent ion at 100 m/e, as well as additional ions with weights of 99,
85, and 65 m+/e. Spectral data for 4,5-epithia-2-pentene (6): 1H NMR
(δ in CDCl3): 5.84 (m, 1H), 5.02 (m, 1H), 3.39 (m, 1H), 2.55 (dd,
2JH-H ) 6.6 Hz, 3JH-H ) 1.2 Hz, 1H), 2.24 (dd, 2JH-H ) 5.6 Hz, 3JH-H
2
3
) 1.2 Hz, 1H), 1.65 (dd, JH-H ) 6.8 Hz, JH-H ) 1.6 Hz, 3H). 13C
NMR (δ in CDCl3): 131.7 (1C), 129.4 (1C), 37.0 (1C), 25.3 (1C),
17.9 (1C). The mass spectrum shows the parent ion at 100 m/e, as
well as additional ions with weights of 85, 67, and 65 m+/e. Spectral
data for 4,5-epithia-3-methyl-2-pentene (7): 1H NMR (δ in CDCl3):
Experimental Section
2
5.73 (q, J ) 6.8 Hz, 1H), 3.56 (t, J ) 6.2 Hz, 1H), 2.47 (dd, JH-H
)
3
2
3
6.5 Hz, JH-H ) 1.6 Hz, 1H), 2.42 (dd, JH-H ) 5.9 Hz, JH-H ) 1.6
Hz, 1H), 1.64 (d, J ) 6.8 Hz, 3H), 1.46 (br s, 3H). 13C NMR (δ in
CDCl3): 132.6 (1C), 124.6 (1C), 42.5 (1C), 22.7 (1C), 14.1 (1C), 10.4
(1C). The mass spectrum shows the parent ion at 114 m/e, as well as
additional ions with weights of 99, 79, and 67 m+/e. Spectral data for
3,4-epithia-3-methyl-1-butene (8): 1H NMR (δ in CDCl3): 5.65 (dd,
General Data. Reagent grade solvents were stored over 4 Å
molecular sieves. Infrared spectra were recorded on a Nicolet 5DXB
1
FTIR spectrophotometer. H NMR, 13C NMR, and 31P NMR spectra
(7) Benso, S. W.; Cruickshank, F. R.; Golden, D. M.; Haugen, G. R.;
O’Neal, H. E.; Rodgers, A. S.; Shaw, R.; Walsh, R. Chem. ReV. 1969, 69,
279.
2JH-H ) 17.3 Hz, JH-H ) 10.5 Hz, 1H), 5.33 (dd, JH-H ) 17.2 Hz,
3JH-H ) 0.7 Hz, 1H), 5.16 (dd, 2JH-H ) 10.4 Hz, 3JH-H ) 0.7 Hz, 1H),
2.58 (d, J ) 1.5 Hz, 1H), 2.52 (d, J ) 1.1 Hz, 1H), 1.74 (s, 3H). 13C
NMR (δ in CDCl3): 142.8 (1C), 114.3 (1C), 45.0 (1C), 34.4 (1C),
23.3 (1C). The mass spectrum shows the parent ion at 100 m/e, as
well as additional ions with weights of 99, 85, and 65 m+/e.
3
2
(8) (a) Korotneva, L. A.; Belonovskaya, G. P. Russ. Chem. ReV. 1972,
41, 83. (b) Zoller, U. In Small Ring Heterocycles; Hassner, A., Ed.;
Interscience: New York, 1983; Part I, Chapter 3. (c) Sander, M. Chem.
ReV. 1966, 66, 297. (d) Dittmer, D. C. In ComprehensiVe Heterocyclic
Chemistry; Katritzky, A. R., Rees, C. W., Eds.; Pergamon Press: London,
1984; Vol. 7, Section 5.06. (d) Cooper, W.; Morgan, D. R.; Wragg, R. T.
Eur. Polym. J. 1969, 5, 71. (e) Morgan, D. R.; Wragg, R. T. Makromol.
Chem. 1969, 125, 220.
(9) (a) Lown, E. M.; Sandu, H. S.; Gunning, H. E.; Strausz, O. P. J. Am.
Chem. Soc. 1968, 90, 7164. (b) Chew, W.; Harpp, D. N. J. Org. Chem.
1993, 58, 4405.
(10) (a) Adams, R. D.; Babin, J. E.; Tasi, M. Inorg. Chem. 1986, 25,
4514. (b) Morrow, J. R.; Tonker, T. L.; Templeton, J. L. Organometallics
1985, 4, 745. (c) Lorenz, I.-P.; Messelauser, J.; Hiller, W.; Conrad, M. J.
Organomet. Chem. 1986, 316, 121. (d) Shunn, R. A.; Fritchie, C. J.; Prewitt,
C. T. Inorg. Chem. 1966, 5, 892. (e) King, R. B. Inorg. Chem. 1963, 2,
326. (f) Beck, W.; Danzer, W.; Theil, G. Angew. Chem., Int. Ed. Engl.
1973, 12, 582.
(11) (a) Roberts, J. T.; Friend, C. M. Surf. Sci. 1988, 202, 405. (b)
Roberts, J. T.; Friend, C. M. J. Am. Chem. Soc. 1987, 109, 7899.
(12) (a) Abel, E.; Cooley, N. A.; Kite, K.; Orrell, K. G.; Sik, V.;
Hursthouse, M. B.; Dawes, H. M. Polyhedron 1989, 8, 887. (b) Amarasek-
era, J.; Rauchfuss, T. B.; Wilson, S. R. J. Am. Chem. Soc. 1988, 110, 2332.
(13) (a) Block, E. Angew. Chem., Int. Ed. Engl. 1992, 31, 1135. (b)
Steliou, K.; Folkins, P. L.; Harpp, D. N. AdV. Sulfur Chem. 1994, 1, 97. (c)
Steliou, K.; Gareau, Y.; Milot, G.; Salama, P. Phosphorus, Sulfur, Silica
1989, 43, 209.
Synthesis of W(CO)4L(NCMe) (L ) PPh3 and PMe2Ph). A 100.0
mg amount of W(CO)5(PPh3) (0.171 mmol) was dissolved in a mixture
of 15 mL of methylene chloride and 15 mL of acetonitrile in a 50 mL
three-neck round-bottomed flask equipped with a stir bar, 10 mL
dropper addition funnel, and nitrogen inlet. The system was purged
with nitrogen and 1.1 equiv (14.1 mg, 0.188 mmol) of Me3NO dissolved
in 10 mL of acetonitrile was added dropwise over 30 min. The solution
was stirred for 4 h, and then the volatiles were removed in vacuo. The
product was separated by TLC using a hexane/methylene chloride (4/
1) solvent mixture to yield 64.4 mg (62%) of W(CO)4(PPh3)(NCMe)
(2) as light yellow needles and 29.8 mg of unreacted W(CO)5(PPh3).
(15) Harwood, L. M. Synth. Commun. 1990, 20, 1287.
(16) Ross, B. F.; Grasselli, J. G.; Ritchey, W. M.; Kaesz, H. D. Inorg.
Chem. 1963, 2, 1023.
(17) Angelici, R. J.; Malone, M. D. Inorg. Chem. 1967, 6, 1731.
(18) Snyder, H. R.; Stewart, J. M.; Ziegler, J. B. J. Am. Chem. Soc. 1947,
69, 2672.
(14) Adams, R. D.; Long, J. W. IV; Perrin, J. L. J. Am. Chem. Soc.
1998, 120, 1922.
(19) Culvenor, C. C. J.; Davis, W.; Heath, N. S. J. Chem. Soc. 1949,
278.

3986 J. Am. Chem. Soc., Vol. 121, No. 16, 1999
Adams and Perrin
Spectral data for 2: IR νCO (cm-1 in CH2Cl2): 2018 (m), 1899 (vs),
60 Å F254 plates) using a hexane/methylene chloride (3/1) solvent
1
1854 (s). H NMR (δ in CD2Cl2): 7.53-7.30 (m, 15H), 1.56 (s, 3H).
mixture to yield 29.1 mg (48%) of W(CO)5(SSCH2CHdCHCH2) (13)
and 5.1 mg of unreacted 1. Spectral data for 13: IR νCO (cm-1 in
13
2
1
183
31
13
13
)
W-
C NMR (δ in CD2Cl2): 206.97 (d, J
) 5.2 Hz, J
P-
C
C
2
1
183
31
13
13
159.9 Hz, 1C), 206.34 (d, J
1C), 202.20 (d, J
(d, J
(d, J
) 31.0 Hz, J
) 154.2 Hz,
P-
C
W- C
1
hexane): 2078 (w), 1986 (w), 1949 (vs), 1939 (m). H NMR (δ in
2
1
183
31
13
13
C ) 7.1 Hz, J
C ) 130.3 Hz, 2C), 134.84
P-
W-
CDCl3): 6.08 (m, 1H), 6.00 (m, 1H), 3.62 (m, 2H), 3.43 (m, 2H). 13
C
1
2
31
13
31
13
C ) 37.4 Hz, 3C), 133.71 (d, J
C ) 11.5 Hz, 6C), 130.05
P-
31
P-
1
183
13
NMR (δ in CD2Cl2): 199.80 ( J
) 157.1 Hz, 1C), 196.80
W-
C
4
3
13
31
13
) 2.3 Hz, 3C), 128.60 (d, J
) 9.2 Hz, 6C), 122.99
1
183 31
P-
C
P-
C
1
183
13
W-
( J
) 128.9 Hz, 4C), 125.28 (1C), 125.23 (1C), 41.98 (1C),
C
31
(s, 1C), 3.48 (s, 1C). P NMR (δ in CD2Cl2): 29.1 ( J
) 238
W-
P
31.37 (1C). Analysis for 13: (C9H6O5S2W) calcd C 24.45, H 1.37;
found C 24.12, H 1.47.
Hz, 1P). Analysis for 2 (C24H18O4NPW): calcd C 48.10%, H 3.03%,
N 2.34%; found C 47.63%, H 2.78%, N 2.28%. W(CO)4(PMe2Ph)-
(NCMe) (3) was prepared similarly (68% yield) as a light yellow oil
that can be obtained in a solid form by precipitation from a minimal
amount of methylene chloride and hexane at -78 °C. Spectral data for
3: IR νCO (cm-1 in CH2Cl2): 2016 (m), 1894 (vs), 1850 (s). 1H NMR
Catalytic Transformation of Vinylthiirane by W(CO)4(PPhR2)-
(NCMe) (R ) Ph, 2; R ) Me, 3). Synthesis of 3,6-Dihydro-1,2-
dithiin. A typical reaction is as follows: A 0.014 mmol amount of
catalyst was placed into an NMR tube with 0.50 mL of 4 and 0.50 mL
of CD2Cl2. C6Me6 (10.0 mg) was added to serve as a quantitative
reference. The solution was shaken and the formation of 9 and butadiene
2
31
1
(δ in CD2Cl2): 7.55-7.36 (m, 5H), 1.91 (d, J
) 7.1 Hz, 6H),
P- H
5
1.87 (d, J
) 1.7 Hz, 3H). 13C NMR (δ in CD2Cl2): 207.55 (d,
C ) 155.8 Hz, 1C), 206.81 (d, J
) 155.8 Hz, 1C), 202.07 (d,
31
1
P- H
1
was monitored hourly by H NMR spectroscopy for 24 h at 25 °C.
2
1
2
31
13
183
13
31
13
J
C ) 29.3 Hz, J
)
P-
W-
P-
C
1
2
Catalytic Transformation of 4 by 1 (Long Term). A 10.0 mg
(0.0274 mmol) amount of 1 was dissolved in 10.8 mL of methylene
chloride in a 25 mL three-neck round-bottom flask equipped with a
stir bar, reflux condenser, and nitrogen inlet. C6Me6 (100.0 mg) was
added to serve as an internal standard. 4 (11.54 g, 134 mmol) was
then added, and the resulting solution was degassed and filled with
nitrogen twice to remove traces of oxygen. The flask was then wrapped
in aluminum foil and placed into a 25 °C water bath in the absence of
light. Small aliquots of the reaction mixture were removed and analyzed
by 1H NMR every 24 h. Some CD2Cl2 was added to these samples for
the purpose of the NMR frequency lock. After 5 days, the reaction
was at 2040 turnovers and 93% conversion (ratio of 9 to 4). The
volatiles were removed in vacuo, and an additional 2.0 mL each of 4
and methylene chloride were added to the residue. The production of
9 resumed and was followed for an additional 24 h by 1H NMR,
demonstrating that the catalyst was still active.
General Procedures for the Kinetic Studies. All studies were
conducted in clean 5 mm NMR tubes in CD2Cl2 solvent and were
followed by 1H NMR spectroscopy. A typical procedure is as follows.
A 0.014 mmol amount of catalyst and 10.0 mg of C6Me6 (used as a
quantitative internal reference) were placed in a clean, dry NMR tube.
The tube was sealed with a rubber septum and was evacuated and filled
with nitrogen three times. A 0.50 mL volume of CD2Cl2 was transferred
to the sealed NMR tube via syringe, followed by a 0.50 mL volume of
vinylthiirane. The tube was shaken to mix the reactants thoroughly and
was then placed in a Varian Mercury 400 NMR spectrometer at 25.0
°C. All kinetic experiments were performed at least twice. The reaction
rates were determined by measuring the disappearance of the vinylthi-
irane by integration of the alkenyl triplet and aliphatic doublet at 5.97
and 3.26 ppm, respectively, against the C6Me6 internal standard in a
series of NMR spectra every 30 min.
183
13
W-
31
13
4.5 Hz,
J
J
) 7.5 Hz,
C
P- C
1
1
31
183
13
13
J
C ) 129.4 Hz, 2C), 137.64 (d, J
C ) 10.6 Hz, 2C), 129.24 (d, J
C ) 33.9 Hz, 1C), 129.79
P-
13
W-
2
4
31
13
31
(d, J
(d, J
C ) 2.3 Hz, 1C), 128.76
P-
1
31 13
P-
3
31
13
) 9.1 Hz, 2C), 122.72 (s, 1C), 18.61 (d, J
) 27.1
P-
C
P-
1
C
31
183
31
Hz, 2C), 3.53 (s, 1C). P NMR (δ in CD2Cl2): -14.7 ( J
)
W-
P
230 Hz, 1P). Analysis for 3 (C14H14O4NPW): calcd C 35.39%, H
2.97%, N 2.95%; found C 35.56%, H 2.65%, N 2.77%.
Catalytic Transformations of Vinylthiirane and its Derivatives
by W(CO)5(NCMe) (1). A typical reaction is as follows: A 5.0 mg
amount (0.014 mmol) of 1 was placed into an NMR tube with 0.50
mL of the corresponding thiirane and 0.50 mL of CD2Cl2. C6Me6 (10.0
mg) was added to serve as a quantitative reference. The solution was
shaken and monitored by 1H NMR at 25 °C for 24 h. During this time
the formation of the corresponding dithiin and diene was observed.
The yield appears to be quantitative as determined by 1H NMR
spectroscopy. The volatile products and solvent were then separated
from the catalyst by trap-to-trap vacuum distillation with heating to 40
°C. The solvent and corresponding diene were then vacuum-distilled
off at 0 to -10 °C to yield pure dithiin. Spectral data for 3,6-dihydro-
1,2-dithiin (9): 1H NMR (δ in CDCl3): 5.97 (t, J ) 2.1 Hz, 2H), 3.26
(d, J ) 2.2 Hz, 4H). 13C NMR (δ in CDCl3): 125.5 (2C), 28.2 (2C).20
The mass spectrum shows the parent ion at 118 m/e, as well as
additional ions with weights of 103, 85, and 64 m+/e. This reaction
can be done in the open air as described above, but under these
conditions, there is discoloration of the solution that is attributed to
partial decomposition of the tungsten complex. When done under
nitrogen the discoloration is significantly less, but the product yields
and rates of reaction are not significantly different. The vinylthiiranes
5-8 were treated with 1 in a similar fashion to yield the following
3,6-dihydro-1,2-dithiin derivatives. 3,6-Dihydro-4-methyl-1,2-dithiin
(10): 1H NMR (δ in CDCl3): 5.73 (m, 1H), 3.28 (m, 2H), 3.13 (m,
2H), 1.76 (br s, 3H). 13C NMR (δ in CDCl3): 132.7 (1C), 119.6 (1C),
32.2 (1C), 29.5 (1C), 26.0 (1C). The mass spectrum shows the parent
ion at 132 m/e, as well as additional ions with weights of 117, 99, 85,
and 67 m+/e. 3,6-Dihydro-3-methyl-1,2-dithiin (11): 1H NMR (δ in
CDCl3): 5.82 (m, 2H), 3.38 (m, 1H), 3.13 (m, 2H), 1.35 (d, J ) 7.1
Hz, 3H). 13C NMR (δ in CDCl3): 132.3 (1C), 124.7 (1C), 35.3 (1C),
28.1 (1C), 20.8 (1C). The mass spectrum shows the parent ion at 132
m/e, as well as additional ions with weights of 99, 84, and 67 m+/e.
3,6-Dihydro-3,4-dimethyl-1,2-dithiin (12): 1H NMR (δ in CDCl3): 5.65
(m, 1H), 3.49 (m, 1H), 3.01 (q, J ) 6.8 Hz, 1H), 2.93 (m, 1H), 1.77
(br s, 3H), 1.58 (d, J ) 7.0 Hz, 3H). 13C NMR (δ in CDCl3): 137.5
(1C), 119.6 (1C), 38.0 (1C), 29.8 (1C), 25.1 (1C), 20.0 (1C). The mass
spectrum shows the parent ion at 146 m/e, as well as additional ions
with weights of 113, 82, and 67 m+/e.
Kinetics of the Transformation of 4 by W(CO)5(SSCH2CHd
CHCH2) (13). (a) Varying amounts (2, 4, 6, 8, and 10 mg) of 13 and
10.0 mg of C6Me6 were placed into separate NMR tubes with 0.50 mL
of the vinylthiirane and 0.50 mL of CD2Cl2 each. The solutions were
1
shaken and monitored by H NMR at 25 °C for 4 h. During this time
the formation of 3,6-dihydro-1,2-dithiin (9) and butadiene was observed.
The spectra were recorded at the end of 4 h and the TONs were
calculated. Figure 4 shows a plot of the results.
(b) A 0.014 mmol amount of 13 and 10.0 mg of C6Me6 was placed
into an NMR tube with 0.50 mL of the vinylthiirane and 0.50 mL of
1
CD2Cl2. The solution was shaken and monitored every 30 min by H
NMR at 25 °C for 24 h. During this time the formation of 3,6-dihydro-
1,2-dithiin (9) and butadiene was observed. The yield appears to be
quantitative as determined by 1H NMR spectroscopy. The volatile
products and solvent were then separated from the catalyst by trap-to-
trap vacuum distillation with heating to 40 °C. The solvent and
butadiene were then vacuum distilled off at 0 to -10 °C to yield pure
9. The recovery of the catalyst was 50%. Figure 5 shows a plot of the
results as a function of time.
Preparation of 13CO-Enriched Complexes. All 13CO-enriched
complexes were prepared in the same manner as the unenriched
complexes starting with 13CO-enriched W(CO)6.5g The 13CO-enriched
Preparation of W(CO)5(SSCH2CHdCHCH2) (13). A 50.0 mg
amount of 1 (0.137 mmol) was dissolved in 5 mL of methylene chloride
in a 10 mL three-neck round-bottom flask equipped with a stir bar,
reflux condenser, and nitrogen inlet. Under a nitrogen atmosphere, 0.17
mL of vinylthiirane (2.74 mmol) was added and the resulting solution
was stirred for 24 h. The volatiles were removed in vacuo, and the
product was isolated by TLC (in air on Analtech 0.25 mm silica gel
(20) Scho¨berl, A.; Gra¨fje, H. Liebigs Ann. Chem. 1958, 614, 66

Catalytic Transformations of Vinylthiiranes
J. Am. Chem. Soc., Vol. 121, No. 16, 1999 3987
Figure 1. ORTEP diagram of the molecular structure of W(CO)5-
(SSCH2CHdCHCH2) (13) showing 40% probability thermal ellipsoids.
Selected interatomic distances (Å) and angles (deg) are as follows:
W-S(1) ) 2.549(2), S(1)-S(2) ) 2.062(2), S(1)-C(1) ) 1.820(7),
S(2)-C(4) ) 1.811(7), C(1)-C(2) ) 1.487(9), C(2)-C(3) ) 1.323-
(8), C(3)-C(4) ) 1.49(1); W-S(1)-C(1) ) 109.8(2), W-S(1)-S(2)
) 105.32(8), S(2)-S(1)-C(1) ) 97.7(2), S(1)-S(2)-C(4) ) 98.4-
(2); torsion angle C(1)-S(1)-S(2)-C(4) ) 63.6(3)°.
Figure 3. 13C NMR spectra in the CO region of the spectrum of a
catalytic transformation of 4 in 9 by 13*. The resonances of 4 and 9
are not observed in this region. Two intermediates X and O form and
then disappear when the reaction is completed.
Figure 2. Plot of the formation of 9 from 4 as a function of time
using the catalyst 1.
Figure 4. Plot of the formation of 9 as a function of the concentration
of the catalyst 13.
complexes of W(CO)5(NCMe) (1*), W(CO)5(SSCH2CHdCHCH2)
(13*), W(CO)4(PPh3)(NCMe) (2*), and W(CO)4(PMe2Ph)(NCMe) (3*)
were then verified by 13C NMR prior to use. Mass spectral analysis
indicated the 13CO enrichment was approximately 30%.
An NMR Analysis during Catalysis Using 13* as the Catalyst.
Vinylthiirane (1.75 mL) and 1.75 mL of CD2Cl2 were vacuum degassed
and placed in a 10 mm NMR tube with 25.0 mg of 13* under nitrogen.
The reaction was monitored hourly by 13C NMR spectroscopy. This
showed a decrease in concentration of 13* and the formation of two
W(CO)5L intermediates during the catalysis. As the catalysis proceeded,
the intermediates disappeared and 13* reformed fully and was the only
tungsten carbonyl complex in solution at the end of the time period.
13C NMR spectra of the major intermediate (δ in CD2Cl2): 197.9 (1C),
197.0 (4C), 134.4 (1C), 122.1 (1C), 52.4 (1C), 37.7 (1C). 13C NMR
spectra of the minor intermediate: 197.7 (1C), 196.8 (4C), 135.6 (1C),
134.1 (1C), 44.1 (1C), 35.9 (1C). The ratio of major intermediate to
the minor intermediate was approximately 2.5/1 when they were present
in the largest amounts.
Figure 5. Plot of the disappearance of 4 as a function of time in
catalysis by 13.
Control Experiments. (a) In the Absence of a Catalyst. Vinylthi-
irane (0.50 mL) and 0.50 mL of CD2Cl2 were placed in an NMR tube
in the absence of any metal complexes. C6Me6 (10.0 mL) was added
to serve as a quantitative reference. The solution was shaken and
maintained at 25 °C for 24 h. During this time the formation of no
more than trace amounts of 9 and butadiene (<1%) was observed.
(b) In the Presence of W(CO)6. Vinylthiirane (0.50 mL), 0.50 mL
of CD2Cl2, and 5.0 mg of W(CO)6 (0.014 mmol) were placed in an
NMR tube. C6Me6 (10.0 mg) was added to serve as a quantitative
reference. The solution was shaken and maintained at 25 °C for 24 h.
During this time the formation of no more than trace amounts of 9 and
butadiene (<1%) was observed.
(c) Catalysis by 13* under a CO Atmosphere. Vinylthiirane (0.50
mL), 0.50 mL of CD2Cl2, and 5.0 mg of 13* (0.014 mmol) were placed
into an NMR tube. C6Me6 (10.0 mg) was added to serve as an internal

3988 J. Am. Chem. Soc., Vol. 121, No. 16, 1999
Adams and Perrin
Table 2. Crystallographic Data for Compounds 13 and 14
Table 1. Results of Catalytic Transformations of Vinylthiirane to
3,6-Dihydro-1,2-dithiin
13
14
catalyst
atmosphere
% yielda
TONb (24 h)
TOFc
formula
WS2O5C9H6
442.11
orthorhombic
S4C8H12
236.42
monoclinic
1
1
1
13
2
3
N2
CO
air
air
air
air
92
91
86
91
93
96
212
208
212
220
228
222
16
16
15
19
47
53
formula weight
crystal system
lattice parameters
a (Å)
b (Å)
c (Å)
15.688(2)
17.534(3)
9.305(1)
90.0
17.315(2)
4.699(1)
14.388(2)
90.0
110.20(1)
90.0
1098.6(3)
C2/c (no. 15)
4
R (deg)
a Yields based on eq 2 after 24 h. b TON ) mol of dithiin/mol of
catalyst. c TOF ) mol of 9/mol of catalyst‚h (based on the amount of
product formed after a 4 h reaction period).
â (deg)
90.0
90.0
γ (deg)
V (Å3)
2559.6(5)
Pbca (no. 61)
8
space group
Z value
standard. The solution was evacuated and filled with 1 atm of CO twice
and then maintained at 25 °C for 24 h. The progress of the reaction
was monitored hourly by 1H NMR and 13C NMR spectroscopy. There
appeared to be no significant difference in rate of formation of 9 than
under air or under a nitrogen atmosphere (see Table 1).
(d) Reaction of 1 with CO. A 10.0 mg amount of 1 was dissolved
in 15 mL of methylene chloride in a 25 mL three-neck round-bottom
flask equipped with a stir bar, gas inlet, and gas outlet. The solution
was twice degassed and filled with 1 atm of CO, maintained at room
temperature, and monitored by FTIR over a period of 4 days. After
that time, the conversion of 1 to W(CO)6 was approximately 50%.
F
calc (g/cm3)
2.29
93.7
20
50
1638
178
1.38
0.00
1.43
8.1
20
47
673
79
2.29
0.00
µ(Mo KR) (cm-1
temperature (°C)
2θmax (deg)
)
no. obsd (I > 3σ(I))
no. of variables
goodness of fit (GOF)a
max shift/error on final cycle
residuals:a R; Rw
0.022; 0.023
DIFABS
0.56-1.00
0.51
0.026; 0.030
DIFABS
0.62-1.00
0.21
abs corrn
transmn coeff, max/min
largest peak in final diff map
(e-/Å3)
Preparation of (SCH2CHdCHCH2SSCH2CHdCHCH2S) (14). A
125 mg (1.06 mmol) amount of 9 was added to a 5 mm NMR tube
without solvent. The sample was purged with nitrogen and then
irradiated for 10 min by using a 100 W soft white lamp placed 8 in.
from the tube. As the mixture became viscous, the reaction was
quenched by adding 0.75 mL of CD2Cl2. The formation of 14 was
verified by 1H and 13C NMR spectroscopy. The product was separated
from the unreacted 9 by TLC on silica gel using a hexane/methylene
chloride (3/1) solvent mixture to yield 14.0 mg of 14 (5.6% yield),
which elutes just behind the unreacted 9. Spectral data for 14: 1H NMR
a R ) ∑hkl(||Fobs| - |Fcalc||)/∑hkl|Fobs|; Rw ) [∑hklw(|Fobs| - |Fcalc|)2/
2
∑
n
hklwFobs
]
1/2, w ) 1/σ2(Fobs); GOF ) [∑hklw(|Fobs| - |Fcalc|)2/(ndata
-
vari)]1/2
.
Compound 14 crystallized in the monoclinic crystal system. The
systematic absences in the data were consistent with either of the space
groups C2/c or Cc. The former was selected and confirmed by the
successful solution and refinement of the structure. The structure was
solved by a combination of direct methods (SIR2) and difference Fourier
syntheses. For the analysis of 14 all nonhydrogen atoms were refined
with anisotropic thermal parameters. The hydrogen atoms were located
and refined with isotropic thermal parameters.
(δ in CDCl3): 5.73 (m, 4H), 3.46 (br d, JH-H ) 5.1 Hz, 8H). 13C
NMR (δ in CDCl3): 128.4 (4C), 35.4 (8C). The mass spectrum shows
the parent ion at 236 m/e, as well as additional ions with weights of
150, 118, 103, and 85 m+/e.
3
Crystallographic Analyses. Yellow crystals of 13 suitable for
diffraction analysis were grown by slow evaporation of solvent from a
solution in hexane at -17 °C. Colorless crystals of 14 suitable for
diffraction analysis were grown by slow evaporation of solvent from a
solution in hexane at 25 °C. The crystals used for the diffraction
measurements were mounted in thin-walled glass capillaries. Diffraction
measurements were made on a Rigaku AFC6S fully automated four-
circle diffractometer using graphite-monochromated Mo KR radiation.
The unit cell was determined and refined from 15 randomly selected
reflections obtained by using the AFC6 automatic search, center, index,
and least-squares routines. Crystal data, data collection parameters, and
results of the analyses are listed in Table 2. All data processing was
performed on a Silicon-Graphics INDIGO2 workstation by using the
TEXSAN motif structure solving program library obtained from the
Molecular Structure Corp. (The Woodlands, TX). Neutral atom
scattering factors were calculated by the standard procedures.21aAnomalous
dispersion corrections were applied to all non-hydrogen atoms.21b
Lorentz/polarization (Lp) and absorption corrections (DIFABS) were
applied to the data. Full matrix least-squares refinements minimized
Results
The vinylthiiranes 4-8 were readily converted into a 1/1
mixture of the 3,6-dihydro-1,2-dithiins 9-12 and the corre-
sponding diene under unusually mild conditions in the presence
of the catalyst W(CO)5(NCMe) (1) (eq 3). One equivalent of
(3)
the corresponding butadiene was also formed. The yields and
turnover frequencies (TOFs) for the various thiiranes are given
in Table 3. The reaction is very sensitive to substitutent effects,
and the TOFs were found to range from a low of 2 h-1 when
a methyl group is present on the thiirane ring to a high of 29
h-1 when a methyl group is located at the R-position of the
vinyl group. The reaction rate of the parent 4 lies approximately
midway between the two extremes at 15 turnovers/h. The
reaction is relatively insensitive to the atmosphere and proceeds
at essentially equivalent rates whether the reaction is performed
in air, under nitrogen or even under CO; however, there was
some discoloration of the solutions when they were conducted
the function: ∑hklw(|Fo| - |Fc|)2, where w ) 1/σ(F)2, σ(F) ) σ(Fo )/
2
2Fo, and σ(Fo ) ) [σ(Iraw)2 + (0.02Inet)2]1/2/Lp.
2
Compound 13 crystallized in the orthorhombic crystal system. The
space group Pbca was identified uniquely on the basis of the systematic
absences observed during the collection of the intensity data. The
structure was solved by a combination of direct methods (SIR2) and
difference Fourier syntheses. All nonhydrogen atoms were refined with
anisotropic thermal parameters. The positions of the hydrogen atoms
were located and refined.
(21) (a) International Tables for X-ray Crystallography; Kynoch Press:
Birmingham, England, 1975; Vol. IV, Table 2.2B, pp 99-101. (b) Ibid.
Table 2.3.1, pp 149-150.

Catalytic Transformations of Vinylthiiranes
J. Am. Chem. Soc., Vol. 121, No. 16, 1999 3989
Table 3. Results of Catalytic Transformations of Vinylthiiranes to
Dihydrodithiins by Compound 1
differ by an exo or endo orientation of the vinyl group relative
the W(CO)5 group. This will depend on which of the two lone
pairs of electrons on the sulfur atom is coordinated to the
tungsten atom. Presumably, the less crowded exo isomer is the
major isomer. Similar stereoisomerism was observed for the
reagent
product
% yielda
TONb (24 h)
TOFc
4
5
6
7
8
9
10
11
12
10
86
84
86
212
141
149
146
53
15
29
24
19
2
compound W(CO)5[cis-(SC(H)MeC(H)Me)].8c Curiously, the
80
34d
a Yields based on eq 2 at 24 h. b TON ) mol of product/mol of
catalyst (1 ) W(CO)5NCMe). c TOF ) mol of product/mol of
catalyst‚h. (based on the amount of product formed after 4 h). d 85%
yield after 72 h.
under an atmosphere of air. This is attributed to partial
decomposition of some of the catalyst. The decomposition was
not extensive and the decomposition products could not be
isolated or characterized. In the absence of catalyst or in the
presence of W(CO)6, only traces of the dithiin products (<1%)
were formed under the same conditions.
formation of free CO was also observed during the catalysis.
To try to ascertain if this was mechanistically significant, the
catalysis was conducted under an atmosphere of CO. Interest-
ingly, the presence of a pure CO atmosphere had no effect on
the rate of the catalytic reaction. Kinetic analysis showed that
the reaction was first order in the concentration of the tungsten
catalyst (see Figure 4) and that the disappearance of 4 was first
order (see Figure 5). The catalysis is not affected by light.
Similar results were obtained in room light and in the complete
absence of light.
The PPh3 and PMe2Ph derivatives 2 and 3 of 1 were prepared,
and their ability to produce the catalysis was investigated. The
13C NMR spectra of these derivatives indicate that the phosphine
ligand is positioned cis to the acetonitrile ligand. Interestingly,
the catalytic activity of 2 and 3 is significantly higher than that
of 1, TOF ) 47 for 2 and 53 for 3 for the substrate 4 (see
Table 1).
Small amounts of a tungsten complex W(CO)5(SSCH2CHd
CHCH2) (13) were obtained from the catalytic reactions
involving the substrate 4. This product can be obtained in up
to 48% yield when performed using larger quantities of the
tungsten complex 1. Compound 13 was characterized by a
single-crystal X-ray diffraction analysis, and an ORTEP diagram
of its molecular structure is shown in Figure 1. The molecule
contains a W(CO)5 grouping with a 3,6-dihydro-1,2-dithiin
ligand coordinated to the tungsten atom through one of its two
sulfur atoms, W-S(1) ) 2.549(2) Å and S(1)-S(2) ) 2.062-
(2) Å. There is a double bond between the carbon atoms C(2)
and C(3), C(2)-C(3) ) 1.324(4) Å. The torsion angle at the
sulfur-sulfur bond, C(1)-S(1)-S(2)-C(4), is 63.6(3)°. The
minimum strain for torsion at the S-S bond is believed to occur
at the angle of 90°.22
The catalytic activity of 13 for reaction 2 is slightly higher
than that of 1. This can be explained by that fact that 1 is only
a precursor to the catalyst and 13 is actually a species in the
catalytic cycle (see below). There is a noticeable induction
period when 1 is used as the catalyst precursor. This induction
period disappears when 13 is used as the catalyst. A plot of
catalysis using 1 as the catalyst precursor is shown in Figure 2.
To learn more about the species involved in the catalysis,
The effects of methyl substituents on the thiirane on the rate
of catalysis was also investigated. The catalysis was significantly
increased when methyl groups were placed on the vinyl group
but was significantly decreased when a methyl substitutent was
placed on the thiirane ring.
Compound 9 has been prepared previously by the oxidation
of the corresponding dithiol.20,22 Calculations have indicated that
it contains slight strain energy.22 It is stable in solution at room
temperature for extended periods; however, in the pure form, it
undergoes polymerization to a white insoluble solid at room
temperature in the presence of light.23 While the polymerization
is extensive, we were able to separate small amounts of a dimer
of 9 by interrupting the polymerization in its early stages. This
dimer has been not been reported previously. It was character-
ized by us through a combination of NMR, mass spectrometry,
and single-crystal X-ray diffraction analysis and was shown to
be the compound 1,2,7,8-tetrathiacyclododeca-4,10-diene (14).
Compound 14 crystallizes in the monoclinic space group C2/c
with four molecules in the unit cell. An ORTEP drawing of the
molecular structure of 14 is shown in Figure 6. The molecule
is a 12-membered heterocycle with two disulfide linkages at
the 1,2 and 7,8 positions. The molecule contains a center of
symmetry in the solid state. The S-S bond distance, S(1)-
S(2*) ) 2.025(1) Å, is slightly shorter than the S-S distance
observed for 9 characterized as a ligand in 13 (see above). The
shortest transannular nonbonding contact in 14 lies between the
two equivalent sulfur atoms S(2) and S(2*), S(2)‚‚‚S(2*) )
3.670(1) Å. There are two C-C double bonds at the 4,5 and
10,11 positions, C(2)-C(3) ) 1.324(4) Å. The torsion angle at
the progress of an active catalytic reaction was followed by 13
C
NMR spectroscopy using 13C-enriched 13 and unenriched 4.
These spectra showed that the concentration of 13 decreases as
the reaction begins and two W(CO)5-containing intermediates
are formed. At the end of the catalysis, the intermediates
disappear and 13 reforms fully and is the only detectable
tungsten carbonyl complex in solution. Spectra in the CO region
at the beginning, after 4 h and at the end of the reaction are
shown in Figure 3. New resonances were also observed in the
olefin and aliphatic region of the spectrum. The spectra of the
major and minor intermediates are as follows: major intermedi-
ate: 197.9 (1C), 197.0 (4C), 134.4 (1C), 122.1 (1C), 52.4 (1C),
37.7 (1C); minor intermediate: 197.7 (1C), 196.8 (4C), 135.6
(1C), 134.1 (1C), 44.1 (1C), 35.9 (1C). The ratio of the major
intermediate to the minor intermediate was approximately 2.5/1
when they were present in their greatest concentrations. From
the relative intensities of the resonances in the CO region of
the spectrum, it can be concluded that both intermediates contain
W(CO)5 groupings. The presence of two olefin and two aliphatic
resonances for each isomer can be explained by the existence
of two thiirane complexes of W(CO)5. These are proposed to
(22) Burns, J. A.; Whitesides, G. M. J. Am. Chem. Soc. 1990, 112, 6296
(23) Lautenschlaeger, F.; Schnecko, H. J. Polym. Sci. 1970, 8, 2579.

3990 J. Am. Chem. Soc., Vol. 121, No. 16, 1999
Adams and Perrin
Scheme 1
Figure 6. ORTEP diagram of the molecular structure of 1,2,7,8-
tetrathiacyclododeca-4,10-diene (14) showing 50% probability thermal
ellipsoids. Selected interatomic distances (Å) as follows: S(1)-S(2*)
) 2.025(1), S(1)-C(1) ) 1.833(3), S(2)-C(4) ) 1.827(3), C(1)-C(2)
) 1.481(4), C(2)-C(3) ) 1.324(4), C(3)-C(4) ) 1.489(4), S(2)‚‚‚
S(2*) ) 3.670(1), S(1*)-S(2)-C(1) ) 104.4(1), S(2*)-S(1)-C(1)
) 103.5(1).
The mechanism of the ring opening of the thiirane ring could
occur by either of two processes: (1) a unimolecular process
leading to an allylium/thiolate intermediate such as D, followed
the sulfur-sulfur bonds, C(1)-S(1)-S(2*)-C(4*), is 82.7(1)°,
indicating that it should contain very little torsion strain.20 After
it is isolated, 14 is stable toward further polymerization;
however, when it is present in solutions of 9 undergoing
polymerization, it is consumed in the polymerization process.
Thus, the isolation of 14 is dependent upon interrupting the
polymerization of 9 by quenching the sample with solvent in
the early stages of the process and then isolating by TLC. The
yields are always low.
Discussion
by a rapid addition of a second thiirane through its sulfur atom
to the terminus of the carbon chain, or (2) a bimolecular
nucleophilic addition mechanism in which the sulfur atom of a
second thiirane adds to the â-carbon atom of the vinyl group
of the thiirane ligand. The opening of the thiirane ring is
concurrent with or follows this nucleophilic addition.
In previous studies, we have shown that thiiranes will react
with 1 to form stable complexes that can be isolated and
crystallographically characterized. In these complexes the sulfur
is coordinated to the tungsten atom. The complex W(CO)5-
(SC2H4) reacts with additional quantities of thiirane catalytically
to yield a series of cyclic disulfides according to eq 2.6 We
believe that the reaction of 1 with the vinylthiiranes 4-8
proceeds by a similar process involving an initial coordination
of the thiirane to the tungsten atom via the sulfur atom.
However, these vinylthiirane complexes are more reactive than
those of the simple thiiranes. We have not been able to isolate
any vinylthiirane complexes of W(CO)5, but spectra of the
catalytically active solutions do show evidence for the formation
of intermediates, and the spectra of these intermediates are
consistent with that expected for vinylthiirane complexes, see
above.
The catalytic formation of a 1/1 mixture of the 3,6-dihydro-
1,2-dithiins 9-12 and the corresponding diene can be explained
by Scheme 1, which begins with the formation of vinylthiirane
complexes of W(CO)5 C by displacement of the NCMe ligand
from 1, step a. The observation of an induction period when
using 1 as the catalyst is consistent with a time-dependent
conversion of 1 to the intermediates C and absence of an
induction period when using 13 as the catalyst. It is also
consistent with the absence of inhibition by free CO provided
that free CO does not react readily with 1 or 13 to form W(CO)6,
which is catalytically inactive. The surprisingly slow reaction
of 1 with CO was confirmed by an independent test (see the
Experimental Section).
The unimolecular ring-opening process could provide an
explanation for the increase in the rate of the reaction when
methyl substitutents are placed on the vinyl group, namely the
methyl groups provide a more stable form of the intermediate
D and, presumably, a more facile route to it. The decrease in
the reaction rate when the methyl group is placed on the thiirane
ring can be attributed to the known stabilization of thiiranes by
alkyl substituents on the ring. It is known that the introduction
of methyl substitutents to thiirane stablizes it against ring-
opening polymerization reactions.8c Lautenschlaeger et al.
proposed unimolecular ring opening of vinylthiirane as a
mechanism for its cation-induced polymerization.23 Regardless
of the ring-opening mechanism, the zwitterionic intermediate
E can be anticipated, step b, upon the addition of the second
equivalent of thiirane, and the C-C double bond is shifted to
the position between the two CH groups. At this stage, the
negatively charged thiolato sulfur atom and the positively
charged thiiranium sulfur atom combine to neutralize one
another with formation of a S-S bond and the elimination of
butadiene, step c. This could occur either by S- attack on the
S+ atom, by spontaneous elimination of butadiene and self-
neutralization, or perhaps by some electron-transfer mechanism.
In any case, the complex 13 containing the 3,6-dihydro-1,2-
dithiin ligand is formed. Complex 13 is observed spectroscopi-

Catalytic Transformations of Vinylthiiranes
J. Am. Chem. Soc., Vol. 121, No. 16, 1999 3991
cally, and it can even be isolated and structurally characterized
(see above). The catalytic cycle is completed, step d, by
substitution of the dithiin ligand by another 1 equiv of
vinylthiirane to regenerate the vinythiiraneW(CO)5 intermediate.
This step would explain the observed first-order dependence
of the reaction rate on the vinylthiirane concentration. Also, in
view of the slowness of the reaction of 1 with CO, it can be
concluded that this step must be associatiVe in character and
should enter into the rate equation. This would also be consistent
with the unimolecular ring opening mechanism, whereas the
bimolecular ring-opening mechanism might be expected to
exhibit a second-order dependence on the vinylthiirane con-
centration if the ring-opening addition was the slow step of the
reaction. Throughout the process only 1 equiv of W(CO)5 is
involved in the catalysis. This is consistent with the observed
first-order rate dependence on the concentration of tungsten.
The enhancement of the rate of reaction by the introduction
of phosphine ligands may be attributed either to steric effects
or to electronic effects or a combination thereof. Increased steric
crowding among the ancillary ligands on the tungsten atom
would certainly favor transformations that lead to opening of
the thiirane ring. However, the observation that the PMe2Ph
complex 3 is even more active than the PPh3 complex 2 would
indicate that the rate enhancement is probably more than a
simple steric effect, since PMe2Ph is less bulky than PPh3. From
an electronic perspective, if one replaces a CO ligand with a
phosphine ligand, this would result in an increase in electron
density on the metal because phosphines are poorer acceptors
than CO. The increase in electron density on the metal atom
would allow more π-bonding to the remaining ligands including
the thioether. π-bonding between the d orbitals of metal atoms
and the S-C σ* bonds of thioethers is believed to produce
significant weakening of the S-C bonds.24 In the case of
thiiranes, this should promote opening of the thiirane rings.
Dihydrodithiins have been prepared by the oxidation of
dithiols20,22 and the addition of “S2” to 1,3-dienes.25 The new
method described herein utilizes readily accessible reagents and
is catalytic with long-term activity. In one instance, we obtained
2040 turnovers over a 5 day period and the catalyst was still
very active at the end of the reaction period.
Acknowledgment. These studies were supported by the
Division of Chemical Sciences of the Office of Basic Energy
Sciences of the U.S. Department of Energy. We also thank the
NSF for support for an upgrade of our mass spectrometer system
(NSF Grant CHE-9709257).
Supporting Information Available: Tables of final atomic
positional parameters, bond distances, bond angles, and aniso-
tropic thermal parameters for the structural analyses of 13 and
14 (PDF). This material is available free of charge via the
Internet at http://pubs.acs.org.
JA984249G
(24) Mullen, G. E. D.; Went, M. J.; Wocadla, S.; Powell, A. K.; Blower,
P. J. J. Am. Chem. Soc. 1997, 36, 11205.
(25) (a) Harpp, D. N.; MacDonald, J. G. J. Org. Chem. 1988, 53, 3812.
(b) Tardif, S. L.; Rys, A. Z.; Abrams, C. B.; Abu-Yousef, I. A.; Leste-
Lasserre, P. B. F.; Schultz, E. K. V.; Harpp, D. N. Tetrahedron 1997, 53,
12225. (c) Rys, A. Z.; Harpp, D. N. Tetrahedron Lett. 1997, 38, 4931.