Synthesis and crystal structure of an arenesulfenyl iodide with unprecedented stability

Article abstract of DOI:10.1039/a805449e

An arenesulfenyl iodide with unprecedented stability was synthesized by oxidation of a thiol bearing a novel bowl-type substituent with iodine, whose monomeric structure was determined by X-ray crystallographic analysis.

Full text of DOI:10.1039/a805449e

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Synthesis and crystal structure of an arenesulfenyl iodide with unprecedented
stability
Kei Goto,*† Michel Holler and Renji Okazaki*‡
Department of Chemistry, Graduate School of Science, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo, 113-0033, Japan
An arenesulfenyl iodide with unprecedented stability was
synthesized by oxidation of a thiol bearing a novel bowl-type
substituent with iodine, whose monomeric structure was
determined by X-ray crystallographic analysis.
decomposition was observed even after heating at 80 °C for 12
h in toluene-d8. It is stable at room temperature in air for more
than several months. In the UV–VIS spectrum, 3 showed an
absorption maximum at 328 nm in chloroform.
Sulfenyl iodides (RSI) have been suggested to play decisive
roles as reaction intermediates in iodination reactions in the
human thyroid gland1 as well as in iodine oxidation of thiols.2
Although more information concerning simple well defined
sulfenyl iodides is desirable, the study of their chemistry has
been hampered by their instability resulting from the ready
disproportionation reaction (2RSI ? RSSR + I2), the DH value
of which is 24.30 kcal mol21.3 In the solid state they are much
less stable partly because of the large sublimation energy of
solid I2 (14.9 kcal mol21). Several aromatic acylsulfenyl
iodides have been isolated and shown to be stable at room
temperature for several hours, but they decompose below 50
°C.4 The only structural analysis of a sulfenyl iodide was carried
out for Ph3CSI at 2118 °C,5 which is stable in the solid state at
278 °C and in solution in the dark.6 Thus, no sulfenyl iodide
stable at room temperature has so far been structurally
characterized.7 On the other hand, the reported value of the S–I
bond dissociation energy is not so small (49.4 ± 2 kcal mol21 for
HS–I),8 suggesting that this species will be stable if the
disproportionation process is suppressed. Recently, we reported
that a stable arenesulfenic acid can be obtained by direct
oxidation of a thiol by taking advantage of a novel bowl-type
I2, Et3N
BmtSH
2
BmtSI
3
CDCl3, r.t.
92%
Scheme 1
The structure of 3 was finally established by X-ray crystallo-
graphic analysis.∑ An ORTEP drawing of 3 is shown in Fig. 1
with selected bond lengths and angles. The figure clearly shows
that the two rigid m-terphenyl units surround the S–I function-
ality like the brim of a bowl, thus preventing the disproportiona-
tion process effectively. It was reported that in the crystal
structure of Ph3CSI at 2118 °C the molecules are linked via
short S···I contacts of 3.210(4) Å so that a zig-zag chain is
formed.5 By contrast, the shortest intermolecular S···I distance
in 3 is 6.654(2) Å, clearly indicating its monomeric nature. The
S–I bond length [2.386(2) Å] is distinctly shorter than that of
Ph3CSI [2.406(4) Å] probably because of the absence of the
intermolecular interaction. The S–I moiety is almost perpendic-
ular to the benzene plane [I(1)–S(1)–C(1)–C(2) angle,
87.7(6)°].
In spite of its high thermal stability, sulfenyl iodide 3
undergoes ready reactions with some reagents. Treatment of 3
with butane-1-thiol (8 equiv.) in the presence of triethylamine
reduced it to the parent thiol 2 with the formation of a small
1 ≡ Bmt
substituent 1 (denoted as Bmt hereafter).§9,10 Here we describe
the synthesis of an arenesulfenyl iodide with unprecedented
stability by iodine oxidation of the corresponding arenethiol,
along with its crystal structure.
The sulfenyl iodides isolated so far have been synthesized
mostly by halide exchange reaction of the corresponding
sulfenyl chloride6 or oxidation of the corresponding heavy
metal thiolates.4,11 There has been no example of the synthesis
of a stable sulfenyl iodide by iodine oxidation of a thiol although
this reaction has been considered to involve a sulfenyl iodide as
an intermediate and seems to be the most straightforward
synthetic pathway to it. Oxidation of thiol 212 bearing the Bmt
group with an equimolar amount of I2 in the presence of
triethylamine in CDCl3 resulted in the quantitative formation of
sulfenyl iodide 3, which was isolated by silica gel chromatog-
raphy as dark brown crystals in 92% yield (Scheme 1).¶ The
stability of 3 was remarkable both in the crystalline state and in
solution; it showed a melting point at 257 °C and no
Fig. 1 Crystal structure of 3 (ORTEP drawing; thermal ellipsoids at 30%
probability level). Selected bond lengths (Å), bond angles (°), and torsion
angle (°): S(1)–I(1), 2.386(2); S(1)–C(1), 1.783(7); I(1)–S(1)–C(1),
101.3(2); I(1)–S(1)–C(1)–C(2), 87.7(6).
Chem. Commun., 1998
1915

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‡ Present address: Department of Chemical and Biological Sciences,
Faculty of Science, Japan Women’s University, 2-8-1 Mejirodai, Bunkyo-
ku, Tokyo 112-8681, Japan. E-mail: okazaki@jwu.ac.jp
BuSH (8 eq), Et3N
CDCl3, r.t.
+
BmtSI
3
BmtSH
BmtSSBu
2 (85%)a
4 (15%)a
PhCH2NH2 (10 eq)
CH2Cl2, r.t.
§
Bmt denotes 4-tert-butyl-2,6-bis[(2,2'',6,6''-tetramethyl-m-terphenyl-
BmtS-NHCH2Ph
2'-yl)methyl]phenyl.
5 (74%)
¶ 3: mp 252–257 °C; 1H NMR (500 MHz, CDCl3): d 0.97 (s, 9H), 1.95 (brs,
24H), 3.70 (brs, 4H), 6.46 (s, 2H), 6.84 (brs, 8H), 6.94 (t, 3J = 7.3 Hz, 4H),
7.03 (d, 3J = 7.5 Hz, 4H), 7.33 (t, 3J = 7.5 Hz, 2H); 13C NMR (125 MHz,
CDCl3): d 21.0 (q), 30.8 (q), 34.7 (s), 34.8 (t), 125.0 (d), 126.8 (d), 127.0 (d),
127.5(d), 129.3 (d), 129.4 (s), 136.2 (s), 137.2 (s), 140.8 (s), 142.1 (s), 146.2
(s), 151.1 (s); UV–VIS (CHCl3): lmax(e) = 328 nm (4000 dm3 mol21
cm21).
Scheme 2 a Estimated by 1H NMR
amount of disulfide 4 (Scheme 2). The reaction of 3 with
benzylamine (10 equiv.) readily afforded sulfenamide 5. On the
other hand, 3 was found to be unreactive toward thiol 2 bearing
the same substituent. Oxidation of 2 with 0.5 equiv. of I2 in the
presence of triethylamine afforded a 1 : 1 mixture of 2 and 3, no
disulfide formation being detected even after 24 h at room
temperature (Scheme 3). These results imply that two species
which are otherwise incompatible can be present in the same
system with retention of their reactivities toward other reagents
when they bear a bowl-type substituent. Under the same
conditions, 2,4,6-trimethylbenzenethiol (MesSH) was imme-
diately oxidized to MesSSMes and even 2,4,6-tri-tert-bu-
tylbenzenethiol (Mes*SH) afforded Mes*SSMes* although the
reaction was much slower. Apparently, the bowl-shaped
structure of the Bmt group is more effective for prevention of
dimerization than a Mes* group, where the functionality is more
closely shielded.
∑ Crystal data for 3·0.5C7H8: C59.5H61SI, M = 935.10, monoclinic, space
group P21/n, a = 15.668(8), b = 17.47(1), c = 18.71(1) Å, b = 105.91(4)°,
U = 4926(4) Å3, Z = 4, Dc = 1.261 g cm23, µ = 7.30 cm21. The intensity
data were collected at 293 K on a Rigaku AFC7R diffractometer with Mo-
Ka radiation (l = 0.71069 Å), and the structure was solved by direct
methods and expanded using Fourier techniques. The non-hydrogen atoms
were refined anisotropically. Hydrogen atoms were included but not
refined. The final cycle of full-matrix least-squares refinement was based on
3789 observed reflections [I > 3.00s(I)] and 539 variable parameters with
R(Rw) = 0.058(0.045). CCDC 182/944.
1 H. Fraenkel-Conrat, J. Biol. Chem., 1955, 217, 373; J. P. Danehy, in
Sulfur in Organic and Inorganic Chemistry, ed. A. Senning, Marcel
Dekker, New York, 1971, vol. 1, pp. 327–339; L. Field and C. M.
Lukehart, in Sulfur in Organic and Inorganic Chemistry, ed. A.
Senning, Marcel Dekker, New York, 1982, vol. 4, pp. 327–367.
2 J. P. Danehy, C. P. Egan and J. Switalski, J. Org. Chem., 1971, 36,
2530.
3 J. P. Johnson, M. P. Murchie, J. Passmore, M. Tajik, P. S. White and
C.-M. Wong, Can. J. Chem., 1987, 65, 2744.
4 S. Kato, E. Hattori, M. Mizuta and M. Ishida, Angew. Chem., Int. Ed.
Engl., 1982, 21, 150.
5 R. Minkwitz, H. Preut and J. Sawatzki, Z. Naturforsch. Teil B, 1988, 43,
399.
r.t., 24 h
I2, Et3N
+
2 BmtSH
BmtSH
2
BmtSI
3
BmtSSBmt
CDCl3, r.t.
2
I2, Et3N
r.t.
+
2 ArSH
ArSH ArSI
ArSSAr
CDCl3, r.t.
6 E. Ciuffarin and G. Guaraldi, J. Org. Chem., 1970, 35, 2006.
7 The structures of several sulfur and selenium iodine cations have been
characterized. For a review, see: T. Klapötke and J. Passmore, Acc.
Chem. Res., 1989, 22, 234.
(Ar = Mes, Mes*)
Scheme 3 Mes* = C6H2But3-2,4,6
8 R. J. Hwang and S. W. Benson, J. Am. Chem. Soc., 1979, 101, 2615.
9 K. Goto, M. Holler and R. Okazaki, J. Am. Chem. Soc., 1997, 119,
1460.
10 For related compounds, see: K. Goto, N. Tokitoh and R. Okazaki,
Angew. Chem., Int. Ed. Engl., 1995, 34, 1124; T. Saiki, K. Goto, N.
Tokitoh and R. Okazaki, J. Org. Chem., 1996, 61, 2924; T. Saiki, K.
Goto and R. Okazaki, Angew. Chem., Int. Ed. Engl., 1997, 36, 2223.
11 S. Kato, Y. Komatsu, K. Miyagawa and M. Ishida, Synthesis, 1983,
552.
This work was partly supported by Grants-in-Aid for
Scientific Research (No. 07854035 and 94187) from the
Ministry of Education, Science, Sports and Culture, Japan. We
also thank Tosoh Akzo Co., Ltd. for the generous gift of
alkyllithiums. M. H. is grateful to the Japan Society for the
Promotion of Science for the Postdoctoral Fellowship for
Foreign Researchers.
12 K. Goto, M. Holler and R. Okazaki, Tetrahedron Lett., 1996, 37,
3141.
Notes and References
† Present address: Department of Chemistry, School of Science, Kitasato
University, 1-15-1 Kitasato, Sagamihara, Kanagawa 228-8555, Japan.
E-mail: goto@jet.sci.kitasato-u.ac.jp
Received in Cambridge, UK, 1st May 1998; revised manuscript received
10th July 1998; 8/05449E
1916
Chem. Commun., 1998