Structure and properties of a sulfur(IV)-sulfur(II)-bond compound: Reversible conversion of a sulfur-substituted organosulfurane into a thiol

Article abstract of DOI:10.1002/anie.200803945

(Figure Presented) A highly polar hypervalent S^IV - S ^II bond was formed in the synthesis of a sulfur-substituted sulfurane (see scheme), which was crystallographically characterized. Reduction of the 1,2-dithietane gives the corresp

Full text of DOI:10.1002/anie.200803945

Communications
DOI: 10.1002/anie.200803945
Hypervalent Compounds
À
Structure and Properties of a Sulfur(IV) Sulfur(II)-
Bond Compound: Reversible Conversion of a Sulfur-
Substituted Organosulfurane into a Thiol**
Naokazu Kano,* Yusuke Itoh, Yuki Watanabe, Shinpei Kusaka, and
Takayuki Kawashima*
Angewandte
Chemie
9430
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Angewandte
Chemie
Catenation of divalent sulfur atoms, which easily bind to each
sulfur-substituted sulfurane is postulated to be an intermedi-
À
other to form a sulfur(II) sulfur(II) disulfide bond, is one of
ate in the reduction of sulfoxides by thiols, for example in
reactions involving the methionine sulfoxide reductases,[7] so
that elucidation of the crystal structure and properties of the
the characteristics of sulfur. The disulfide bond is found in
II
À
disulfide complexes and some proteins, and the reversible S
SII bond cleavage to form thiolates or thiols by redox
processes plays a significant role in protein systems and
both organic and inorganic chemistry. Meanwhile, sulfur can
have a tetravalent tetracoordinate state in a few cases, in
which the valence of sulfur formally expands beyond the
octet, and such a hypervalent sulfur compound is known as a
sulfurane. Although thiosulfonic esters, such as a 1,2-dithie-
unique S S bond are important. Our group previously
À
reported the synthesis of sulfuranes 3[8] and 4[9] (R1, R2 = Ph,
CF3) by taking advantage of a bidentate ligand, 2-[bis(tri-
fluoromethyl)oxidomethyl]phenyl,[10] and by integrating the
sulfur–heteroatom bond in a ring framework. Herein we
report the synthesis and the first X-ray crystallographic
analysis of a sulfur-substituted sulfurane and the reversible
formation–cleavage process of a bond between tetracoordi-
nate sulfur(IV) and dicoordinate sulfur(II) atoms.
À
tane dioxide, have both a S S bond and tetracoordinate
sulfur, the valence electron of the sulfur atom is eight, and
thus they are not hypervalent compounds.[1] As the hyper-
valent state of the sulfurane is effectively stabilized by at least
one electron-withdrawing group, such as fluorine and/or
alkoxy groups,[2] sulfur-substituted sulfuranes, which have an
We considered that b-mercaptoalkyl sulfide 9 could be a
precursor for the sulfur-substituted sulfurane 10 (Scheme 1).
Attempted conversion of b-hydroxyalkyl sulfide 6,[8a] which
was prepared from benzyl sulfide 5[8c] to the mercapto
II
SIV
S
bond, are usually unstable owing to inefficient
À
electronegativity of sulfur(II) as a stabilizing group for a
sulfurane. Thus, there have been only a few reports on
synthesis of sulfur-substituted sulfuranes and their structures
and properties. For example, F3SSF (1a), a thermally unstable
=
Scheme 1. a) lithium diisopropylamide, THF, À788C; b) Ph2C O,
À788C; c) aq NH4Cl; d) nBuLi, Ph2PCl, THF, À788C; e) 2,6-dimethyl-
benzoquinone, AcSH, CH2Cl2, RT; f) (nBu)4NF, THF, 08C; g) H3O+;
h) aq HCl, MeOH, reflux; i) NBS, Et3N, CCl4, 08C; j) CDCl3, 558C;
k) LiAlH4, THF, 08C. TBDMS=tBuMe2Si.
liquid,[3] has a distorted pseudo trigonal bipyramidal (Y-TBP)
structure around the central sulfur atom, which has the SF
group in an equatorial position (an S-equatorial configura-
tion), according to ab initio calculations.[4] Organosulfuranes
1b, 1c, and 2 react with water or glass vessels, leading to
decomposition.[5,6] Neither redox reactivities nor crystal
structures of the sulfur-substituted organosulfuranes have
been studied well, which is partly due to their instability. A
analogue 9 with the Lawessonꢀs reagent resulted in no
reaction. Instead, 6 could be converted into the corresponding
thioacetyl ester 7 by the reaction with butyllithium and
chlorodiphenylphosphine in THF at À788C followed by
treatment with 2,6-dimethylbenzoquinone and thioacetic
acid (AcSH) in dichloromethane at room temperature.[11]
After desilylation of 7 with tetra-n-butylammonium fluoride,
deacetylation of the resulting alcohol 8 with hydrochloric acid
in refluxing methanol quantitatively afforded b-mercap-
toalkyl sulfide 9. Treatment of 9 with N-bromosuccinimide
(NBS) and triethylamine in CCl4 at 08C gave 1,2-dithietane 10
in 42% yield after recrystallization. The formation mecha-
nism of 10 is considered as follows: The thiol moiety of 9 was
converted into the corresponding sulfenyl bromide by NBS.[12]
Intramolecular attack of the central sulfur atom to the
brominated sulfur atom and the subsequent attack of the
hydroxy group in the presence of triethylamine at the central
sulfur atom lead to the formation of 10 with elimination of
triethylammonium bromide.
[*] Prof. Dr. N. Kano, Y. Itoh, Y. Watanabe, S. Kusaka,
Prof. Dr. T. Kawashima
Department of Chemistry, Graduate School of Science
The University of Tokyo
7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033 (Japan)
Fax: (+81)3-5800-6899
E-mail: takayuki@chem.s.u-tokyo.ac.jp
Homepage: http://www.chem.s.u-tokyo.ac.jp/users/hetero/
index-e.html
[**] We thank Tosoh Finechem Corp., Shin-etsu Chemical Co. Ltd., and
Central Glass Co., Ltd. for gifts of alkyl lithium, silicon reagents, and
fluorine compounds, respectively. This work was partially supported
by the Global COE Program for Chemistry Innovation and for
Scientific Researches from the Ministry of Education, Culture,
Sports, Science and Technology (Japan) and the Japan Society for
the Promotion of Science.
In CDCl3, the aromatic proton at the ortho position (H1)
was detected at d = 8.37 ppm, which was close to the values of
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/anie.200803945.
Angew. Chem. Int. Ed. 2008, 47, 9430 –9433
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Communications
the tetracoordinate 1,2-oxathietanes and 1,2-thiazetidine,
level À1.7 eV), there is contribution by the antibonding
À
suggesting the similar conformation of the four-membered
ring; that is, the divalent sulfur atom takes the apical position
of the tetracoordinate sulfur atom in solution at room
temperature.
The crystal structure of 10 was determined by X-ray
crystallographic analysis (Figure 1).[13] The tetracoordinate S1
atom has y-TBP geometry, with atoms O1 and S2 at the apical
positions and atoms C1 and C10 at the equatorial positions.
orbitals of the 3-center 4-electron bonds for the apical S O
À
and S S bonds. The natural population analysis showed the
positive charge for the tetravalent sulfur (+ 0.88) and the
negative charge for the divalent sulfur (À0.07), the oxygen
(À0.78), and the carbon (À0.18, À0.28), suggesting polarity of
À
À
À
the S S, S O, and S C bonds. Formation of the 3-center 4-
À
electron bonds and polarity of the S S bond should be
characteristics of the sulfur-substituted sulfurane with the S-
apical configuration.
Sulfurane 10 is stable to oxygen and the solid is able to be
handled in the air at room temperature, but it decomposes
rapidly in the presence of water in solution. In solution, 10
decomposed gradually at room temperature even in the
absence of water, and its thermolysis at 558C for 100 min in
CDCl3 gave the corresponding cyclic sulfenate 11 (quantative
yield) and triphenylthiirane (12) (92%). The reaction mode
of 10 to give the corresponding three-membered ring com-
pound is similar to the cases of the pentacoordinate 1,2-
oxathietanes and the 1,2-thiazetidine oxide,[8b,c,9] which are
thermally much more stable than 10. Thus, the relative
thermal instability of sulfurane 10 compared to the dicoordi-
nate 1,2-dithietanes should be attributed to the existence of
II
the SIV S bond.
À
À
The S S bond of 10 can be cleaved by hydride reduction
Figure 1. ORTEP of 10 with thermal ellipsoids set at 50% probability.
Selected bond lengths (ꢀ) and angles (8): S1–O1 1.9959(15), S1–S2
2.2138(10), S1–C1 1.806(2), S1–C10 1.870(2), S2–C11 1.856(2), C10–
C11 1.554(3); O1-S1-S2 165.27(5), O1-S1-C1 84.90(8), O1-S1-C10
88.53(8), C1-S1-S2 98.60(7), C1-S1-C10 107.80(9), S2-S1-C10 76.77(6),
S1-S2-C11 79.42(6), S1-C10-C11 99.16(12), S2-C11-C10 96.40(12).
À
without cleavage of the S C bond. Reaction of 10 with
LiAlH4 gave 9 in 60% yield after quenching with aqueous
NH4Cl (Scheme 1). The formation of 9 shows reductive
II
cleavage of the SIV
S
bond accompanying the SIV O bond
À
À
cleavage under the hydride reduction conditions. Considering
that 9 can be converted into 10, the reductive cleavage and the
II
oxidative formation of the SIV
bond is similar to the
À
S
The configuration of the divalent sulfur atom of 10 is different
from that of F3SSF. The difference is partly ascribed to the
almost identical electronegativities of sulfur and carbon. The
formation–cleavage processes of disulfide and thiol systems.
In summary, we succeeded in the synthesis and X-ray
crystallographic analysis of the tetracoordinate 1,2-dithietane,
which is the first example of a crystallographically analyzed
À
S1 S2 bond (2.2138(10) ꢁ) is considerably longer than that of
À
usual disulfide bonds (1.97–2.08 ꢁ), and that of the previously
reported divalent 1,2-dithietanes (2.084–2.0855 ꢁ).[14] The
bond length is quite reasonable for the hypervalent apical
sulfur-substituted sulfurane. A fairly long S S bond and S-
apical configuration were revealed. As the sulfur-substituted
sulfurane was converted into the corresponding thiol rever-
bond formation–dissoci-
ation process may be found in biological systems.
bond of a sulfurane.[2,8,9] The S1 O1 bond (1.9959(15) ꢁ) is
sibly by redox reactions, the SIV
II
À
À
S
also longer than sum of the covalent bond radii (1.70 ꢁ). The
C10-S1-S2 and C11-S2-S1 angles (76.77(6) and 79.42(6)8,
respectively) are slightly narrower than the C-S-S angles in
the divalent 1,2-dithietanes (80.7(1)–82.2(1)8) as a result of
the elongation of the S1 S2 bond. The torsion angle of C10-
S1-S2-C11 (18.04(8)8) indicates that the 1,2-dithietane ring is
slightly puckered.
The stability of the conformation of the 1,2-dithietane and
its bonding properties were investigated by the DFT calcu-
lations with basis set of B3LYP/6-311G + (d,p). The opti-
mized molecular structure, the S-apical configuration, which
matches well with the X-ray crystal structure, is calculated to
be more stable than the S-equatorial configuration by
15.9 kcalmolÀ1. The HOMO (energy level À6.50 eV) of 10
is localized mainly on the two different lone pairs of both the
dicoordinate and tetracoordinate sulfur atoms (see the
Supporting Information, Figure S2). The LUMO (energy
level À2.0 eV) is an unoccupied in-plane orbital localized on
the dicoordinate sulfur atom. For the LUMO + 1 (energy
Experimental Section
À
N-Bromosuccinimide (0.16 g, 0.90 mmol) and triethylamine
(0.25 mL, 1.9 mmol) were added to thiol 9 (0.50 g, 0.89 mmol) in
CCl4 (25 mL) at 08C. The solution was stirred for 15 min, filtered
through Celite, and the solvent was evaporated. Recrystallization
from CCl4/hexane gave 1,2-dithietane 10 (0.21 g, 42%) as colorless
crystals. 10: m.p. 71.0–72.88C (dec.). 1H NMR (400 MHz, CDCl3): d =
6.82 (s, 1H), 6.96–7.33 (m, 15H), 7.40–7.54 (m, 3H), 7.68 (d, J =
7.6 Hz, 1H), 8.37 ppm (d, J = 8.0 Hz, 1H); 13C{1H} NMR (126 MHz,
CDCl3): d = 60.33 (s), 83.17 (sept, 2J(C,F) = 30.5 Hz), 94.70 (s), 122.85
(q, 1J(C,F) = 230 Hz), 123.11 (q, 1J(C,F) = 232 Hz), 126.36 (s), 126.38
(s), 126.51 (s), 126.89 (s), 127.60 (s), 128.02 (s ꢂ 2), 128.54 (s), 129.26
(s), 130.30 (s), 130.42 (s), 132.14 (s), 132.37 (s), 132.57 (s), 134.21 (s),
135.00 (s), 143.41 (s), 148.02 ppm (s); 19F NMR (376 MHz, CDCl3):
d = À78.4 (q, 4J(F,F) = 8.6 Hz, 3F), À76.6 ppm (q, 4J(F,F) = 8.6 Hz,
3F); MS (FAB): m/z: 563 [M+H]+; HRMS (FAB): m/z calcd for
C29H21F6OS2 [M+H]+: 563.0938; found: 563.0927; UV (Et2O): l(e) =
214 (49000), 222 (sh), 248 (sh), 253 (sh), 258 nm (sh); IR (KBr): n =
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Received: September 9, 2008
Published online: October 31, 2008
Keywords: hypervalent compounds · redox chemistry · sulfur ·
.
sulfuranes
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