Synthesis, structure, and reactivity of the first kinetically stabilized silanethione

Article abstract of DOI:10.1021/ja980783c

Diaryltetrathiasilolanes 2a,b, bearing bulky aryl groups such as 2,4,6- tris[bis(trimethylsilyl)methyl]phenyl (Tbt), mesityl (Mes), and 2,4,6- triisopropylphenyl (Tip), were obtained by thermal reaction of dihydrosilane 3a with elemental sulfur, reaction

Full text of DOI:10.1021/ja980783c

11096
J. Am. Chem. Soc. 1998, 120, 11096-11105
Synthesis, Structure, and Reactivity of the First Kinetically Stabilized
Silanethione
Hiroyuki Suzuki,† Norihiro Tokitoh,*,†,‡ Renji Okazaki,*,†,§ Shigeru Nagase, and
Midori Goto|
Contribution from the Department of Chemistry, Graduate School of Science, The UniVersity of Tokyo,
7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan, Department of Chemistry, Graduate School of Science,
Tokyo Metropolitan UniVersity, 1-1 Minami-osawa, Hachioji 192-0397, Japan, and Natural Institute of
Materials and Chemical Research, 1-1 Higashi, Tsukuba, Ibaraki 305-0046, Japan
ReceiVed March 9, 1998
Abstract: Diaryltetrathiasilolanes 2a,b, bearing bulky aryl groups such as 2,4,6-tris[bis(trimethylsilyl)methyl]-
phenyl (Tbt), mesityl (Mes), and 2,4,6-triisopropylphenyl (Tip), were obtained by thermal reaction of
dihydrosilane 3a with elemental sulfur, reaction of highly hindered disilene 4 with sulfur, or reduction of
dibromosilane 6 followed by addition of sulfur. The molecular structure of 2a was determined by X-ray
crystallographic analysis. Desulfurization of 2a at -78 °C afforded a silicon-sulfur double bond compound
(silanethione 7a). Although the formation of 7a was confirmed by various trapping reactions, 7a dimerized
at room temperature to give 1,3,2,4-dithiadisiletane 8, whose molecular structure was determined by X-ray
crystallographic analysis. Desulfurization of 2b afforded the first stable silanethione, Tbt(Tip)SidS (7b), as
yellow crystals, which were thermally stable under inert gas up to its melting point (185-189 °C) and showed
λmax (nfπ*) at 396 nm and νSidS (Raman) at 724 cm-1. The chemical shift of δSi 166.56 in the 29Si NMR
spectrum is greatly downfield-shifted, characteristic of a silathiocarbonyl unit. Comparison of the electronic
spectra (nfπ*) of a series of R1R2MdS (M ) C, Si, Ge, Sn) compounds revealed an interesting trend: λmax
is significantly blue-shifted on going from M ) C to M ) Si, whereas λmax’s for R1R2MdS (M ) Si, Ge, Sn)
are red-shifted on increasing the atomic number of M. This trend is also found in calculated values for H2Md
S (M ) C, Si, Ge, Sn). The X-ray crystallographic analysis of 7b revealed that there are two nonidentical
silanethiones in the asymmetric unit and the silathiocarbonyl units have completely trigonal-planar geometry,
with silicon-sulfur double bond lengths of 1.948(4) and 1.952(4) Å, which are about 0.2 Å shorter than the
typical Si-S single bond length (ca. 9% shortening), indicating an unambiguous double bond character between
silicon and sulfur. Despite the presence of two very bulky substituents on silicon, 7b easily reacted with
water, methanol, phenyl isothiocyanate, mesitonitrile oxide, and 2,3-dimethyl-1,3-butadiene to afford the
corresponding adduct or cycloadduct. Theoretical calculations were carried out for the σ and π bond energies
of H2MdX (M ) C, Si, Ge, Sn, Pb; X ) O, S, Se, Te) and for the single and double bond lengths of H3Ms
XH and H2MdX, and the theoretical backgrounds of the chemistry of group 14-group 16 double bond species
were discussed.
Introduction
using kinetic stabilization for silicon-chalcogen double-bond
species until we preliminarily communicated5a the synthesis of
the first silanethione6 (silicon-sulfur double bond compound),
though much theoretical interest has been focused on this
Recently, remarkable progress has been made in the chemistry
of organosilicon compounds containing multiple bonds to group
14 or group 15 elements,1 i.e., SidSi,2 SidC,3 and SidPn (Pn
) N, P, As).4 These species have been isolated successfully
by taking advantage of kinetic stabilization with bulky substit-
uents. In contrast, there had been no example of the isolation
(3) (a) Brook, A. G.; Nyburg, S. C.; Abdesaken, F.; Gutekunst, B.;
Gutekunst, G.; Kallury, R. K.; Poon, Y. C.; Chang, Y.-M.; Wong-Ng, W.
J. Am. Chem. Soc. 1982, 104, 5667. (b) Wiberg, N.; Wagner, G.; Mu¨ller,
G. Angew. Chem., Int. Ed. Engl. 1985, 24, 229. (c) Wiberg, N.; Wagner,
G. Chem. Ber. 1986, 119, 1467. (d) For reviews, see: Brook, A. G.; Baines,
K. M. AdV. Organomet. Chem. 1986, 25, 1. Brook, A. G.; Brook, M. A.
AdV. Organomet. Chem. 1996, 39, 71.
(4) (a) Wiberg, N.; Schurz, K.; Reber, G.; Mu¨ller, G. J. Chem. Soc.,
Chem. Commun. 1986, 591. (b) Hesse, M.; Klingebiel, U. Angew. Chem.,
Int. Ed. Engl. 1986, 25, 649. (c) Smit, C. N.; Bickelhaupt, F. Organome-
tallics 1987, 6, 1156. (d) van den Winkel, Y.; Bastiaans, H. M. M.;
Bickelhaupt, F. J. Organomet. Chem. 1991, 405, 183. (e) Driess, M.;
Pritzkow, H. Angew. Chem., Int. Ed. Engl. 1992, 31, 316. (f) Driess, M.;
Rell, S.; Pritzkow, H. Chem. Commun. 1995, 253. (g) Bender, H. R. G.;
Niecke, E.; Nieger, M. J. Am. Chem. Soc. 1993, 115, 3314. (h) For a review,
see: Driess, M. AdV. Organomet. Chem. 1996, 39, 193.
† The University of Tokyo.
Tokyo Metropolitan University.
| National Institute of Materials and Chemical Research.
‡ Present address: Institute for Fundamental Research of Organic
Chemistry, Kyushu University, 6-10-1 Hakozaki, Higashi-ku, Fukuoka 812-
8581, Japan.
§ Present address: Department of Chemical and Biological Sciences,
Faculty of Science, Japan Women’s University, Mejirodai, Bunkyo-ku,
Tokyo 112-8681, Japan.
(1) For reviews, see: (a) Raabe, G.; Michl, J. Chem. ReV. 1985, 85, 419.
(b) Raabe, G.; Michl, J. In The Chemistry of Organic Silicon Compounds;
Patai, S., Rappoport, Z., Eds.; John Wiley: New York, 1989; Part 2, p
1015.
(2) (a) West, R.; Fink, M. J.; Michl, J. Science 1981, 214, 1343. For
reviews, see: (b) West, R. Angew. Chem., Int. Ed. Engl. 1987, 26, 1201.
(c) Okazaki, R.; West, R. AdV. Organomet. Chem. 1995, 39, 231.
(5) Preliminary reports: (a) Suzuki, H.; Tokitoh, N.; Nagase, S.; Okazaki,
R. J. Am. Chem. Soc. 1994, 116, 11578. (b) Tokitoh, N.; Suzuki, H.;
Matsumoto, T.; Matsuhashi, Y.; Okazaki, R.; Goto, M. J. Am. Chem. Soc.
1991, 113, 7047.
10.1021/ja980783c CCC: $15.00 © 1998 American Chemical Society
Published on Web 10/16/1998

First Kinetically Stabilized Silanethione
J. Am. Chem. Soc., Vol. 120, No. 43, 1998 11097
Table 1. σ and π Bond Energies (kcal mol-1) for H2MdX
fascinating class of low-coordinate organosilicon compounds.7
The difficulty in synthesizing such a type of species is obviously
due to the fact that bulky substituents for steric protection can
be introduced only on the silicon atom, and hence their
oligomerization cannot be efficiently prevented. Although Corriu
et al. reported the isolation of thermodynamically stabilized
silicon-sulfur double bond compounds and their selenium
analogues 1 in 1989,8 they found by X-ray crystallography that
the Si atom of the silanethione 1 (Ar ) naphthyl, Ch ) S) was
tetracoordinate because of the intramolecular coordination by
a nitrogen lone pair and the geometry around silicon was a
distorted tetrahedral. The silicon-sulfur bond length is 2.013-
(3) Å, which indicates only 6% shortening compared to the
normal silicon-sulfur single bond (∼2.15 Å). Spectral features
also suggest that 1 is not a doubly bonded compound; the
chemical shift of 22.3 ppm in 29Si NMR of 1 (Ar ) Ph, Ch )
S) is within the region of normal tetrahedral organosilicon
species.
Calculated at the B3LYP/TZ(d,p) Level
X
H2MdX
H2CdX
O
S
Se
Te
σ
93.6
95.3
188.9
119.7
58.5
178.2
101.5
45.9
147.4
94.8
32.8
127.6
80.9
29.0
109.9
73.0
54.6
127.6
81.6
47.0
128.6
74.1
41.1
115.2
69.3
33.5
102.8
60.9
30.0
90.9
65.1
43.2
108.3
73.7
40.7
114.4
67.8
36.3
104.1
64.3
30.6
94.9
57.0
27.8
84.8
57.5
32.0
89.5
63.2
32.9
96.1
59.1
30.3
89.4
56.4
26.3
82.7
50.3
24.4
74.7
π
σ + π
H2SidX
H2GedX
H2SndX
H2PbdX
σ
π
σ + π
σ
π
σ + π
σ
π
σ + π
σ
π
σ + π
The 6-311G(d,p) basis set was used for C, O, and H.11 The
π and σ bond energies were calculated at the B3LYP/TZ(d,p)
level with the procedure proposed by Schleyer and Kost.13 The
excitation energies were calculated at the CIS14/TZ(d,p)//
B3LYP/TZ(d,p) level. The 29Si NMR chemical shifts were
calculated with the GIAO15-B3LYP method using the B3LYP/
6-31G(d)-optimized geometries; the 6-311G(3d) basis set was
used for Si and S, while 6-311G(d) was used for the second
row atoms. All calculations were carried out using the Gaussian
94 program.16
Bond Energies and Bond Lengths. When we undertook a
study on the synthesis of a series of heavier element congeners
of a ketone (R1R2MdX; M ) Si, Ge, Sn, Pb; X ) S, Se, Te),
which we refer to as “heavy ketones”, we carried out theoretical
calculations on the σ and π bond energies as well as on the
single and double bond lengths of H2MdX to study general
aspects of heavy ketones. The results are shown in Tables 1
and 2. Some points of interest pertinent to the results of the
calculations follow:
To synthesize a silanethione, it is important to choose a proper
precursor and a suitable methodology, since it can be anticipated
that a desired silanethione is too reactive toward atmospheric
oxygen and moisture to be purified with chromatography. We
have selected, therefore, a silicon-containing cyclic polysulfide
as a precursor and investigated the synthesis of a silanethione
via desulfurization of the polysulfide. The present paper
delineates a detailed account of the synthesis of silicon-
containing cyclic polysulfides and their transformation to the
first stable silanethione,5 together with the theoretical aspects
of the chemistry of group 14-group 16 double bond species.
(1) A carbon-oxygen double bond is unique in that the σ
and π bond energies are almost equal to each other. This is an
energetic basis of the well-known reactivity of a carbonyl
compound, i.e., addition-elimination mechanism through a
tetrahedral intermediate.
(2) In all the other double bonds, the σ bond energy is much
greater than the corresponding π bond energy. This indicates
the high reactivity of these double bond compounds toward any
kind of addition reaction, because the formation of two new σ
bonds on M and X with concurrent cleavage of the π bond
results in substantial overall energy gain.
Results and Discussion
I. Theoretical Considerations. Computational Methods.
Geometries were fully optimized with the nonlocal hybrid
density functional method at the B3LYP level.9 The effective
core potential and basis set developed by Wadt and Hay10 were
used on Si, Ge, Sn, Pb, S, Se, and Te. The basis set [3s3p] in
the triple-ú (TZ) form was augmented by a set of d-type
polarization functions (d exponents 0.45 (Si), 0.246 (Ge), 0.183
(Sn), 0.164 (Pb), 0.65 (S), 0.338 (Se), 0.237 (Te)).11,12
(6) Although “thioxosilane” is a recommended name for a silicon-sulfur
double bond compound according to the nomenclature in Chemical Abstracts
and “silylidenesulfane” is the nomenclature in conformity with IUPAC,
we use here a name “silanethione” for a silicon-sulfur double bond
compound instead of thioxosilane in this paper because silanethione is a
common name which has been often used in the literature of organosilicon
chemistry.
(3) Every compound with a group 14-group 16 element
double bond corresponds to a minimum on the potential energy
surface, as confirmed from all positive eigenvalues of the
Hessian matrix. This suggests that all the doubly bonded
(7) Apeloig, Y. In The Chemistry of Organic Silicon Compounds; Patai,
S., Rappoport, Z., Eds.; John Wiley: New York, 1989; Part 1, pp 139-
145 and references therein.
(8) Arya, P.; Boyer, J.; Carre´, F.; Corriu, R.; Lanneau, G.; Lapasset, J.;
Perrot, M.; Priou, C. Angew. Chem., Int. Ed. Engl. 1989, 28, 1016.
(9) (a) Becke, A. D. J. Chem. Phys. 1993, 98, 5648. (b) Becke, A. D.
Phys. ReV. 1988, A38, 3098. (c) Lee, C.; Yang, W.; Parr, R. G. Phys. ReV.
1988, B37, 785.
(10) Wadt, W. R.; Hay, P. J. J. Chem. Phys. 1985, 82, 284.
(11) Frisch, M. J.; Pople, J. A.; Binkley, J. S. J. Chem. Phys. 1984, 80,
3265.
(12) Huzinaga, S.; Andzelm, J.; Klobukowski, M.; Radzio-Andzelm, E.;
Sakai, Y.; Tatewaki, H. Gaussian Basis Sets for Molecular Calculations;
Elsevier: Amsterdam, 1984.
(13) Schleyer, P. v. R.; Kost, F. J. Am. Chem. Soc. 1988, 110, 2105.
(14) Foresman, J. B.; Head-Gordon, M.; Pople, J. A.; Frisch, M. J. J.
Phys. Chem. 1992, 96, 135.
(15) Wolinski, K. F.; Hilton, J.; Pulay, P. J. Am. Chem. Soc., 1990, 112,
8251.
(16) Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Gill, P. M. W.;
Johnson, B. G.; Robb, M. A.; Cheeseman, J. R.; Keith, T.; Petersson, G.
A.; Montgomery, J. A.; Raghavachari, K.; Al-Laham, M. A.; Zakrzewski,
V. G.; Ortiz, J. V.; Foresman, J. B.; Cioslowski, J.; Stefanov, B. B.;
Nanayakkara, A.; Challacombe, M.; Peng, C. Y.; Ayala, P. Y.; Chen, W.;
Wong, M. W.; Andres, J. L.; Replogle, E. S.; Gomperts, R.; Martin, R. L.;
Fox, D. J.; Binkley, J. S.; Defrees, D. J.; Baker, J.; Stewart, J. P.; Head-
Gordon, M.; Gonzalez, C.; Pople, J. A. Gaussian 94; Gaussian Inc.:
Pittsburgh, 1995.

11098 J. Am. Chem. Soc., Vol. 120, No. 43, 1998
Suzuki et al.
Table 2. Single and Double Bond Lengths (Å) at the B3LYP/
TZ(d,p) Level
Scheme 1
X
O
S
Se
Te
H3CsXH
H2CdX
∆
1.421
1.200
15.5
1.649
1.514
8.1
1.788
1.634
8.6
1.950
1.802
7.6
2.025
1.853
8.5
1.835
1.617
11.9
2.148
1.945
9.4
2.256
2.042
9.5
2.438
2.222
8.9
2.502
2.273
9.2
1.979
1.758
11.1
2.294
2.082
9.3
2.393
2.174
9.2
2.565
2.346
8.5
2.628
2.394
8.9
2.165
1.949
10.0
2.508
2.288
8.7
2.596
2.373
8.6
2.768
2.543
8.1
2.819
2.590
8.1
a
H3SisXH
H2SidX
a
∆
H3GesXH
H2GedX
a
∆
H3SnsXH
H2SndX
a
∆
H3PbsXH
H2PbdX
a
∆
a Value of % reduction in a bond length defined as [(single bond
length - double bond length)/single bond length] × 100.
-20 °C.19 The instability of the diphenyl derivative is most
likely due to its high sensitivity toward hydrolysis, which is
prevented by the presence of bulky substituents (kinetic
stabilization) in the case of 2a.
It should be noted that the bulkiness of the substituents on a
silicon atom is an important factor in determining the type of a
product which results from the reaction of a dihydrosilane with
sulfur. For example, the reaction of diphenyldihydrosilane with
elemental sulfur is known to give trithiatrisilane with no
monomeric sulfide being formed.20 It is clear, therefore, that
the Tbt and Mes groups not only play an important role in
kinetic stabilization to retard hydrolysis but also prevent
oligomerization.
compounds in Table 1 are synthetically accessible, if one can
find an appropriate synthetic methodology.
(4) The values of percent reduction listed in Table 2 increase
roughly with increasing the π bond energy, although the results
for M-O bond compounds are somewhat exceptional. It should
be noted that the values except for CdO, CdS, and CdSe are
similar to each other, being 8-10%, irrespective of the atomic
numbers of constitutional elements.
Although σ and π bond energies of H2SidS are smaller than
those of H2SidO, the silicon-sulfur double bond compound is
considered to be more easily synthesized, since the theoretical
calculation carried out by one of the authors has predicted17
that a silicon-sulfur double bond is kinetically more stable than
a silicon-oxygen double bond. According to the natural
population analysis at the B3LYP/TZ(d,p) level, the double bond
(Si+0.98S-0.56) of H2SidS is much less polarized than that
(Si+1.58O-1.05) of H2SidO, the former being apparently less
reactive than the latter. In addition, H2SidS is calculated to
be 15.0 kcal mol-1 more stable than its divalent isomer,
H(HS)Si:, whereas H2SidO is only 3.5 kcal mol-1 more stable
than H(HO)Si:.
Although we already reported the synthesis of 2a by the
thermal reaction of 3a with elemental sulfur, the yield was quite
low (<10%), and the purification was very difficult.5b However,
2a could be obtained in an excellent yield by utilizing the
dissociation of extremely hindered disilene 4 into silylene 5a.21
When a benzene solution of 4 and sulfur was heated at 70 °C
for 6 h, 2a was formed in 94% yield (Scheme 1).
1
The structure of 2a was confirmed by H and 13C NMR,
elemental analysis, and X-ray crystallographic analysis.22 The
crystallographic data for this structure is summarized in Table
3. Selected bond lengths and angles are listed in Table 4.
We next attempted the synthesis of a tetrathiasilolane bearing
a different combination of bulkier substituents, i.e., Tbt- and
2,4,6-triisopropylphenyl (Tip)-substituted tetrathiasilolane. Al-
though the reaction of TbtSiH3 with TipLi gave diaryldihy-
drosilane 3b in good yield (77%), the reaction of 3b with
elemental sulfur below 240 °C resulted in the recovery of the
starting material, and the reaction over 270 °C gave a complex
mixture. However, the reduction of dibromosilane 6, obtained
by the bromination of 3b with N-bromosuccinimide (NBS), with
lithium naphthalenide followed by addition of sulfur at low
temperature afforded Tbt- and Tip-substituted tetrathiasilolane
2b in 28% yield as pale yellow crystals (Scheme 2). Compound
2b showed satisfactory spectral and analytical data. The Raman
spectrum taken for the powdered sample with a 1064-nm line
II. Synthesis of Tetrathiasilolanes. Although there have
been several reports on the synthesis of cyclic polychalcogenides
containing transition metals such as Cp2TiS5,18a Cp2VS5,18b Cp2-
18e
CSe5,18c Cp2MoS4,18d Cp2WS4
(Cp ) η5-C5H5), and (N-
MeIm)2ZnSe4 (Im ) imidazole),18f main group element ana-
logues including silicon-containing cyclic polychalcogenides had
been unknown until 1,2,3,4,5-tetrathiasilolane 2a was synthe-
sized by taking advantage of kinetic stabilization utilizing
sterically bulky substituents, 2,4,6-tris[bis(trimethylsilyl)methyl]-
phenyl (Tbt) and mesityl (Mes) groups.5b Compound 2a can
be obtained by thermal reaction of the corresponding diaryldihy-
drosilane 3a with elemental sulfur and is quite stable toward
heat and moisture (Scheme 1). It is in sharp contrast with
diphenyltetrathiasilolane, which is, reportedly, stable only below
(19) (a) Albertsen, J.; Steudel, R. Phosphorus, Sulfur, Silicon 1992, 65,
165. (b) Steudel, R. In The Chemistry of Inorganic Ring Systems; Steudel,
R., Ed.; Elsevier: Amsterdam, 1992; p 233.
(20) Forstner, J. A.; Muetterties, E. L. Inorg. Chem. 1966, 5, 552.
(21) (a) Tokitoh, N.; Suzuki, H.; Okazaki, R. Ogawa, K. J. Am. Chem.
Soc. 1993, 115, 10428. (b) Suzuki, H.; Tokitoh, N.; Okazaki, R.; Harada,
J.; Ogawa, K.; Tomoda, S.; Goto, M. Organometallics 1995, 14, 1016. (c)
Suzuki, H.; Tokitoh, N.; Okazaki, R. Bull. Chem. Soc. Jpn. 1995, 68, 2471.
(22) For the ORTEP drawing of 2a, see ref 5b.
(17) Kudo, T.; Nagase, S. Organometallics 1986, 5, 1207.
(18) (a) Ko¨pf, H.; Block, B.; Schmidt, M. Chem. Ber. 1968, 101, 272.
(b) Ko¨pf, H.; Wirl, A.; Kahl, W. Angew. Chem., Int. Ed. Engl. 1971, 10,
137. (c) Mu¨ller, E. G.; Petersen, J. L.; Dahl, L. F. J. Organomet. Chem.
1976, 111, 91. (d) Ko¨pf, H.; Hazari, S. K. S. Z. Anorg. Allg. Chem. 1976,
426, 49. (e) Ko¨pf, H.; Kahl, W.; Wirl, A. Angew. Chem., Int. Ed. Engl.
1970, 9, 801. (f) Dev, S.; Ramle, E.; Rauchfuss, T. B.; Stern, C. L. J. Am.
Chem. Soc. 1990, 112, 6385.

First Kinetically Stabilized Silanethione
J. Am. Chem. Soc., Vol. 120, No. 43, 1998 11099
Table 3. Experimental Crystallographic Data for 2a, 7b, and 8
2a
7b
8
empirical formula C36H70Si7S4‚CHCl3 C42H82Si7S C72H140Si14S2
fw
947.30
0.60 × 0.60
× 0.1
815.77
0.40 × 0.35 0.60 × 0.40
× 0.20 × 0.20
298 298
monoclinic monoclinic
1463.21
cryst size, mm
temp, K
cryst syst
space group
unit cell dimens
a, Å
298
monoclinic
P21/n
P21/n
P21/c
12.292(3)
13.034(2)
33.532(9)
91.60(1)
5370(2)
4
21.33(1)
13.82(1)
36.13(2)
92.50(5)
10639(12)
8
17.923(3)
21.672(4)
24.214(4)
92.99(1)
9392(2)
4
b, Å
c, Å
â, deg
V, Å3
Z
Figure 1. ORTEP drawing of [Tbt(Mes)SiS]2 (8) with thermal ellipsoid
plot (30% probability).
density (calcd),
1.172
1.018
1.035
g cm-3
scan type
no. of obsd
reflns
data-to-param
ratio
largest diff peak, 0.535
e Å-3
ω
2θ-ω
2θ-ω
Scheme 2
4906
5390
8548
10.7
6.0
0.4
0.2
10.8
0.4
largest diff hole,
- 0.531
0.5
e Å-3
R, %
Rw, %
7.8
7.8
6.1
5.1
7.0
5.5
goodness of fit
1.04
2.35
3.91
Table 4. Selected Bond Lengths (Å) and Angles (deg) of 2a
Table 5. Selected Bond Lengths (Å) and Angles (deg) of 8
S(1)-Si(1)
S(1)-Si(2)
S(2)-Si(1)
S(2)-Si(2)
2.190(3)
2.172(3)
2.174(3)
2.191(3)
Si(1)-C(1)
Si(1)-C(10)
Si(2)-C(19)
Si(2)-C(28)
1.922(6)
1.926(8)
1.922(7)
1.915(7)
Si(1)-S(1)-Si(2)
Si(1)-S(2)-Si(2)
S(1)-Si(1)-S(2)
S(1)-Si(1)-C(1)
S(1)-Si(1)-C(10)
S(2)-Si(1)-C(1)
S(2)-Si(1)-C(10)
84.4(1)
84.4(1)
90.4(1)
118.3(2)
106.4(2)
116.5(2)
113.0(3)
C(1)-Si(1)-C(10)
S(1)-Si(2)-S(2)
S(1)-Si(2)-C(19)
S(1)-Si(2)-C(28)
S(2)-Si(2)-C(19)
S(2)-Si(2)-C(28)
C(19)-Si(2)-C(28)
110.6(3)
90.4(1)
116.4(2)
113.2(2)
118.2(2)
107.6(2)
109.8(3)
S(1)-Si(1)
S(1)-S(2)
S(2)-S(3)
S(3)-S(4)
2.224(3)
2.051(4)
2.046(5)
2.057(3)
S(4)-Si(1)
Si(1)-C(1)
Si(1)-C(2)
2.155(3)
1.898(6)
1.897(7)
S(1)-Si(1)-S(4)
Si(1)-S(1)-S(2)
S(1)-S(2)-S(3)
S(2)-S(3)-S(4)
S(3)-S(4)-Si(1)
100.4(1)
102.9(2)
99.6(2)
97.4(2)
100.3(1)
S(1)-Si(1)-C(1)
S(1)-Si(1)-C(2)
S(4)-Si(1)-C(1)
S(4)-Si(1)-C(2)
C(1)-Si(1)-C(2)
119.2(3)
96.5(3)
103.4(2)
118.5(2)
118.3(3)
dithiadisiletane 8 (90%), which probably resulted from the
dimerization of silanethione 7a. Although 8 exhibited a H
1
NMR spectrum which was too complicated to be assigned
because of great steric congestion around the silicon atoms,23
the molecular structure of 8 was definitively confirmed by X-ray
crystallographic analysis. Figure 1 shows the ORTEP drawing
of 8. The crystallographic data for this structure are summarized
in Table 3. Selected bond lengths and angles are listed in Table
5.
It is interesting that the geometry of 8 is a cis form and the
central four-membered ring is folded by 35.2° with regard to
the two S-Si-S planes. The two mesityl groups facing each
other are almost parallel, with the dihedral angle between these
two aromatic rings being 3.9°. These results can be explained
in terms of steric repulsion caused by these bulky substituents,
which is expected to be smaller for the folded cis form than for
a trans form, which is expected to be planar.
of a Nd:YAG laser in the region of 300-1800 cm-1 showed a
characteristic Raman line at 504 cm-1. For 2a, the Raman line
was observed at 505 cm-1. These Raman lines are most likely
assignable to the S-S stretching in the polysulfido linkages of
2a and 2b.
III. Silanethiones. Desulfurization of Tbt- and Mes-
Substituted Tetrathiasilolane 2a. To synthesize a silanethione,
we first examined the desulfurization of 2a with triphenylphos-
phine. Since triphenylphosphine is soluble in hexane while
triphenylphosphine sulfide is not, the purification of the reaction
product was expected to be easily carried out only by filtration.
When 2a was treated with 3 molar equiv of triphenylphosphine
in hexane at -78 °C, the solution turned pale yellow, suggesting
the generation of silanethione 7a. Warming up of the yellow
solution to room temperature, however, gave only 1,3,2,4-
Although silanethione 7a immediately dimerized at room
temperature to afford 8, the yellow color of the reaction mixture
(23) For the 1H NMR spectrum of 8, see the Supporting Information.

11100 J. Am. Chem. Soc., Vol. 120, No. 43, 1998
Suzuki et al.
Table 6. M-X Stretching Frequencies (cm-1) of H2MdX at the
B3LYP/TZ(d,p) Level
Scheme 3
X
H2MdX
O
S
Se
Te
H2CdX
H2SidX
H2GedX
H2SndX
H2PbdX
1826
1227
942
797
707
1087
723
553
470
414
882
554
387
319
270
755
461
310
251
207
(53%). Reactions of 7b with phenyl isothiocyanate and
mesitonitrile oxide at room temperature resulted in the ready
formation of [2 + 2] and [2 + 3] cycloadducts 10b (63%) and
11b (54%), respectively. By contrast, 2,3-dimethyl-1,3-buta-
diene was very reluctant to react with 7b. The yellow color
due to 7b did not disappear, even upon heating to 150 °C of a
hexane solution of 7b and the diene in a sealed tube. The
reaction, however, proceeded at 180 °C for 3 h to afford the [2
+ 4] cycloadduct 13 in 74% yield. This result demonstrates
that the silanethione has a considerable extent of ene character
like its carbon analogues, such as thioketones and thioaldehydes,
which are known to have high reactivities in Diels-Alder
reactions.26 It is surprising that silanethione 7b shows these
high reactivities despite the extremely severe steric congestion
around the SidS group.
Spectral Features of Silanethione 7b. Silanethione 7b was
characterized by 1H, 13C, and 29Si NMR, Raman, and UV
spectroscopy. The chemical shift of δSi 166.56 for the silathio-
carbonyl unit is highly downfield-shifted, as in the case of other
silicon-containing double bond compounds.27 The observed
chemical shift is in good accordance with the values for H2-
SidS (158.0 ppm) and Ph2SidS (167.3 ppm) calculated with
the GIAO-B3LYP (6-311G(3d) for Si and S and 6-311G(d)
for C and H) method using the B3LYP/6-31G(d)-optimized
geometries. The chemical shift of 7b is very different from
that of the thermodynamically stabilized Corriu’s silanethione
1 (Ar ) Ph, Ch ) S) (δSi 22.3),8 clearly indicating the genuine
SidS double bond nature of 7b without any intra- or intermo-
lecular coordination. The electronic spectrum of 7b exhibited
an absorption maximum at 396 nm which is assignable to the
nfπ* transition. The Raman spectrum in the solid state showed
an absorption at 724 cm-1. This absorption is attributable to
the SidS stretching, as suggested from the calculated values
(scaled by 0.98) of H2SidS (709 cm-1) at the B3LYP/TZ(d,p)
level in Table 6 and Ph2SidS (755 cm-1) at the B3LYP/6-31G-
(d) level. The M-X stretching frequencies calculated for all
the combinations of ketone analogues, H2MdX (Table 6), are
roughly parallel to the corresponding bond energies (σ + π)
shown in Table 1.
at -78 °C suggested the existence of 7a at low temperature.
To trap 7a, methanol, phenyl isothiocyanate, and mesitonitrile
oxide were added to the hexane solution of 2a and 3 molar
equiv of triphenylphosphine at -78 °C to afford the corre-
sponding adducts (9a, 93%; 10a, 72%; 11a, 45%), along with
8 as a minor product (Scheme 3).
Desulfurization of Tbt- and Tip-Substituted Tetra-
thiasilolane 2b. Since it is obvious that the combination of
Tbt and Mes groups is not bulky enough to prevent the
dimerization of the corresponding silanethione 7a at room
temperature, desulfurization of Tbt- and Tip-substituted tetra-
thiasilolane 2b was examined. When 3 molar equiv of
triphenylphosphine was added to a hexane solution of 2b at
room temperature, the solution turned yellow, suggesting the
formation of 7b. Surprisingly, this yellow color did not
disappear, even after refluxing for 2 h in hexane, indicating the
high stability of silanethione 7b toward dimerization. After
filtration of triphenylphosphine sulfide under argon, the filtrate
was concentrated in a glovebox to give quantitatively silaneth-
ione 7b as yellow crystals (Scheme 3).24
Silanethione 7b is thermally very stable under inert gas up
to its melting point (185-189 °C), but it is very unstable in the
air, as expected, and rapidly decomposes to afford a hydroxy-
silanethiol (12) quantitatively (Scheme 3). It is interesting that
thioketones and selenoketones readily react with atmospheric
oxygen in the air to form the corresponding ketones, whereas
the silanethione decomposes in the air to afford a hydrolyzed
compound resulting from a reaction with atmospheric moisture,
indicating the very high reactivity of the SidS bond toward
water.
(26) (a) Middleton, W. J. J. Org. Chem. 1965, 30, 1390. (b) Scho¨nberg,
A.; Ko¨nig, B. Chem. Ber. 1968, 101, 725. (c) Ohnishi, Y.; Akasaki, Y.;
Ohno, A. Bull. Chem. Soc. Jpn. 1973, 46, 3307. (d) Baldwin, J. E.; Lopez,
R. C. G. Tetrahedron 1983, 39, 1487. (e) Kirby, G. W.; Lochead, A. W.;
Sheldrake, G. N. J. Chem. Soc., Chem. Commun. 1984, 922. (f) Krafft, G.
A.; Meinke, P. T. Tetrahedron Lett. 1985, 26, 1947. (g) Vedejs, E.; Eberlein,
T. H.; Mazur, D. J.; McClure, C. K.; Penny, D. A.; Ruggeri, R.; Schwartz,
E.; Stults, J. S.; Varie, D. L.; Wilde, R. G.; Wittenberger, S. J. Org. Chem.
1986, 51, 1556. (h) Segi, M.; Nakajima, T.; Suga, S.; Murai, S.; Ogawa,
A.; Sonoda, N. J. Am. Chem. Soc. 1988, 110, 1976.
Reactions of Silanethione 7b. Although silanethione 7b is
thermally very stable, it has high chemical reactivities toward
various reagents (Scheme 3). Methanol immediately reacted
with 7b at room temperature to afford an addition product 9b
(27) The 29Si NMR chemical shifts of some low-coordinate organosilicon
compounds follow: Mes2SidSiMes2, 63.6;28a (E)-Tbt(Mes)SidSi(Tbt)Mes,
66.49;21 (Me3Si)2SidC(OSiMe3)(t-Bu), 41.4;28b Tip(t-Bu)SidPAr (Ar )
2,4,6-tri-tert-butylphenyl), 175.9;28c Tip2SidAsSi(i-Pr)3, 179.0.28d
(28) (a) Fink, M. J.; Michalczyk, M. J.; Haller, K. J.; West, R.; Michl,
J. Organometallics 1984, 3, 793. (b) Brook, A. G.; Abdesaken, F.;
Gutekunst, G.; Plavac, N. Organometallics 1982, 1, 994. (c) Smit, C. N.;
Bickelhaupt, F. Tetrahedron Lett. 1984, 25, 3011. (d) Driess, M. Angew.
Chem., Int. Ed. Engl. 1991, 31, 1022.
(24) Similar dechalcogenation reactions were also applied to the syntheses
of thioaldehyde TbtCHS,25a germanethione Tbt(Tip)GedS,25b and germane-
selone Tbt(Tip)GedSe.25c
(25) (a) Tokitoh, N.; Takeda, N.; Okazaki, R. J. Am. Chem. Soc. 1994,
116, 7907. (b) Tokitoh, N.; Matsumoto, T.; Manmaru, K.; Okazaki, R. J.
Am. Chem. Soc. 1993, 115, 8855. (c) Matsumoto, T., Tokitoh, N.; Okazaki,
R. Angew. Chem., Int. Ed. Engl. 1994, 33, 2316.

First Kinetically Stabilized Silanethione
J. Am. Chem. Soc., Vol. 120, No. 43, 1998 11101
Table 7. Electronic Spectra (nfπ*) of Doubly Bonded
Compounds between Group 14 Elements and Sulfur
observeda
calcde
λ
max/nm
λ
max/nm ∆ꢀnπ*/eVf
Tbt(H)CdS (14)
587b
396
H2CdS
H2SidS
H2GedS
H2SndS
H2PbdS
460
352
367
381
373
10.81
10.27
9.87
9.22
9.11
Tbt(Tip)SidS (7b)
Tbt(Tip)GedS (15)
Tbt(Tip)SndS (16)
450c
473d
a In hexane. b Reference 25a. c Reference 25b. d Reference 32. e CIS/
f
TZ(d,p)//B3LYP/TZ(d,p). ꢀLUMO(π*) - ꢀHOMO(n)
.
Since a series of R1R2MdS (M ) C, Si, Ge, Sn) compounds
are now available, we can compare their electronic spectra
(nfπ*) systematically.29 In Table 7 are listed observed spectra
of these compounds along with calculated spectra of H2MdS
(M ) C, Si, Ge, Sn, Pb) at the CIS/TZ(d,p)//B3LYP/TZ(d,p)
level. One can see an interesting change in the observed λmax
depending on the difference in group 14 elements: λmax is
greatly blue-shifted on going from thione 14 to silanethione 7b,
whereas λmax’s for 7b, germanethione 15, and stannanethione
16 are red-shifted on increasing the atomic number of the group
14 elements. This trend is also found in calculated values for
H2MdS (M ) C, Si, Ge, Sn). In a crude approximation, the
nfπ* excitation energy is expressed as ∆ꢀnπ* - Jnπ* + 2Knπ*
.
As Table 7 shows, the energy difference between n and π*
orbitals decreases upon going from H2CdS to the heavier
analogues, suggesting a shorter wavelength absorption for H2Cd
S. However, the π* orbital in H2CdS is much less polarized
(thereby less localized onto C), leading to a larger value of the
Coulomb repulsion integral Jnπ*. Consequently, H2CdS (as well
as 14) has a long-wavelength absorption, as in the case of H2-
CO vs H2SiO.31
Molecular Structure of Silanethione 7b. As single crystals
of 7b suitable for X-ray crystallography were obtained by
recrystallization from hexane in a glovebox, we carried out an
X-ray structural analysis in order to obtain the structural features
of this new doubly bonded system. It has been revealed that
there are two nonidentical silanethiones in the asymmetric unit.
Figure 2 shows the ORTEP drawings (molecules 1 and 2) of
silanethione 7b. The crystallographic data for these structures
are summarized in Table 1. Selected bond lengths and angles
are listed in Table 8.
Figure 2. ORTEP drawing of Tbt(Tip)SidS (7b) with thermal ellipsoid
plot (30%probability).
The data indicate that there is neither intra- nor intermolecular
interaction between the silathiocarbonyl unit and the other part
of the molecule; the shortest intermolecular distance between
the silicon and sulfur centers is 8.2 Å. The molecular structure
of molecule 1 is different from that of molecule 2 in the
following points: (i) the different dihedral angles between the
Tbt and Tip aromatic ring planes and the silathiocarbonyl plane
(molecule 1, 41.8° for Tbt ring and 67.8° for Tip ring; molecule
2, 138.6° for Tbt ring and 112.2° for Tip ring) and (ii) the
different direction of p-bis(trimethylsilyl)methyl of the Tbt
group. There is little difference, however, in the geometry
around the central silicon atom between the two molecules. The
silathiocarbonyl unit of 7b has a completely trigonal-planar
geometry in both molecules as in H2SidS (C2V),17 the sum of
the bond angles around the silicon atom being 359.9° for
Table 8. Selected Bond Lengths (Å) and Angles (deg) of 7b
molecule 1
molecule 2
S(1)-Si(1)
1.948(4)
1.894(8)
1.867(9)
S(101)-Si(101)
Si(101)-C(101)
Si(101)-C(110)
1.952(4)
1.872(9)
1.88(1)
Si(1)-C(1)
Si(1)-C(10)
S(1)-Si(1)-C(1)
125.0(3) S(101)-Si(101)-C(101) 125.3(4)
S(1)-Si(1)-C(10) 116.3(3) S(101)-Si(101)-C(110) 116.9(3)
C(1)-Si(1)-C(10) 118.6(4) C(101)-Si(101)-C(110) 117.5(4)
molecule 1 and 359.7° for molecule 2. Dihedral angles between
the trigonal plane and the two aryl planes suggest that there is
little conjugation between the aromatic ring and the silathio-
carbonyl group. The silicon-sulfur bond lengths are 1.948(4)
(molecule 1) and 1.952(4) Å (molecule 2). These values are
significantly shorter than that of 2.013(3) Å reported for Corriu’s
compound5 and rather close to the 1.945 Å found for H2SidS
(Table 2).33 The Si-S bond length of 7b is ca. 0.2 Å (9%)
shorter than the typical Si-S single bond length.34 This bond
shortening, which is comparable to that of 0.203 Å (9.4%) for
(29) We have not succeeded in observing the electronic spectrum of a
plumbanethione, R1R2PbdS, because it undergoes 1,2-migration reaction
to give a heteroleptic plumbylene R1Pb(SR2), which is thermodynamically
more stable.30
(30) Kano, N.; Tokitoh, N.; Okazaki, R. Organometallics 1997, 16, 4237.
(31) Kudo, T.; Nagase, S. Chem. Phys. Lett. 1986, 128, 507.
(32) Tokitoh, N.; Saito, M.; Okazaki, R. J. Am. Chem. Soc. 1993, 115,
2065.

11102 J. Am. Chem. Soc., Vol. 120, No. 43, 1998
Suzuki et al.
(b) Reaction of Disilene 4 with Sulfur. To a solution of 421b (51
mg, 0.036 mmol) in THF (4 mL) was added sulfur (28 mg, 0.11 mmol),
and the solution was heated under reflux for 6 h. After removal of the
solvent, the residue was chromatographed (GPLC) to afford 2a (56
mg, 94%) as pale yellow crystals.
H2SidS (Table 2), confirms that 7b has a distinct double bond
between Si and S.
IV. Conclusion. The first genuine silanethione Tbt(Tip)-
SidS (7b) was synthesized by the desulfurization of the
corresponding tetrathiasilolane 2b, and its structure was estab-
lished by X-ray crystallographic analysis. The structural features
of 7b were very similar to those of a ketone with a trigonal-
planar geometry, although the extent of reduction in the bond
length from the corresponding single bond (ca. 9%) is consider-
ably smaller than that of a ketone (ca. 15%), indicating weaker
bonding in 7b. Although 7b is stabilized by two extremely
bulky substituents on silicon toward dimerization, it can undergo
facile addition or cycloaddition reactions across the SidS bond
with some relatively small reagents, suggesting its high reactiv-
ity. These findings lead us to conclude that a silanethione, a
heavier element homologue of a ketone (heavy ketone), is
essentially the same as a ketone with regard to the structure
but has much higher reactivity than a ketone because of a great
Preparation of {2,4,6-Tris[bis(trimethylsilyl)methyl]phenyl}-
(2,4,6-triisopropylphenyl)silane (3b). To a solution of TipLi, prepared
from TipBr35 (4.0 g, 14 mmol) and t-BuLi (1.59 M in pentane, 17 mL)
at -78 °C in THF (40 mL), was added a THF solution (80 mL) of
2,4,6-tris[bis(trimethylsilyl)methyl]phenylsilane21b (4.56 g, 8.82 mmol)
at -78 °C. The solution was stirred for 10 h, during which time it
was warmed to room temperature. To this solution was added a
saturated aqueous solution of NH4Cl, and the organic layer was
separated. The water layer was extracted with 50 mL of hexane, and
the organic layer was dried with anhydrous MgSO4. After removal of
the solvent, the residue was recrystallized from ethanol to afford 3b
1
(4.75 g, 77%) as colorless crystals. 3b: mp 169-171 °C; H NMR
(CDCl3) δ -0.06 (s, 18H, Tbt-o-CH(SiMe3)2), 0.02 (s, 18H, Tbt-o-
CH(SiMe3)2), 0.04 (s, 18H, Tbt-p-CH(SiMe3)2), 1.22 (d, J ) 7 Hz, 6H,
Tip-p-CHMe2), 1.24 (d, J ) 7 Hz, 12H, Tip-o-CHMe2), 1.34 (s, 1H,
Tbt-p-CH(SiMe3)2), 2.08 (s, 1H, Tbt-o-CH(SiMe3)2), 2.35 (s, 1H, Tbt-
o-CH(SiMe3)2), 2.86 (sept, J ) 7 Hz, 1H, Tip-p-CHMe2), 3.31 (sept,
J ) 7 Hz, 2H, Tip-o-CHMe2), 5.10 (s, 2H, SiH2), 6.25 (br s, 1H, Tbt-
m-CH), 6.43 (br s, 1H, Tbt-m-CH), 7.01 (s, 2H, Tip-m-CH); 13C NMR
(CDCl3) δ 0.83 (q, Tbt-p-CH(SiMe3)2), 0.88 (q, Tbt-o-CH(SiMe3)2),
1.20 (q, Tbt-o-CH(SiMe3)2), 23.93 (q, Tip-p-CHMe2), 24.78 (q, Tip-
o-CHMe2), 28.46 (d, Tbt-o-CH(SiMe3)2), 28.60 (d, Tbt-o-CH(SiMe3)2),
30.53 (d, Tbt-p-CH(SiMe3)2), 33.41 (d, Tip-p-CHMe2), 34.53 (d, Tip-
o-CHMe2), 120.57 (d, Tip-m-CH), 122.52 (d, Tbt-m-CH), 125.41 (s,
Tbt-p-C), 127.41 (d, Tbt-m-CH), 128.22 (s), 143.93 (s), 150.46 (s),
151.34 (s, Tbt-o-C) 151.45 (s, Tbt-o-C), 155.27 (s, Tip-o-C). Anal.
Calcd for C42H84Si7: C, 64.20; H, 10.78. Found: C, 64.00; H, 10.97.
difference between its σ (82 kcal mol-1) and π (47 kcal mol-1
)
bond energies.
Experimental Section
General Procedure. All melting points were uncorrected. All
solvents used in the reactions were purified by the reported methods.
THF was purified by distillation from benzophenone ketyl before use.
All reactions were carried out under argon atmosphere unless otherwise
noted. Preparative gel permeation liquid chromatography (GPLC) was
performed by LC-908 with JAI gel 1H+2H columns (Japan Analytical
Industry) with chloroform as solvent. Dry column chromatography
(DCC) was performed with ICN silica DCC 60A. Flash column
chromatography (FCC) was performed with silica gel BW 300 (Fuji
Davison Chemical). Preparative thin-layer chromatography (PTLC)
Preparation of {2,4,6-Tris[bis(trimethylsilyl)methyl]phenyl}-
(dibromo)(2,4,6-triisopropylphenyl)silane (6). A solution of 3b (3.21
g, 4.09 mmol), NBS (2.0 g, 11.2 mmol), and a catalytic amount of
benzoyl peroxide in benzene (80 mL) was heated under reflux for 1 h.
After removal of the solvent, the crude reaction products were dissolved
in hexane. The filtrate, after removal of the solvent, was roughly
purified by DCC (hexane), followed by recrystallization from ethanol
to afford 6 (1.87 g, 49%) as colorless crystals. 6: mp 240-242 °C;
1H NMR (CDCl3, 340 K) δ 0.07 (br s, 36H, Tbt-o-CH(SiMe3)2), 0.08
(s, 18H, Tbt-p-CH(SiMe3)2), 1.16 (br d, 6H, Tip-o-CHMe2), 1.22 (d, J
) 7 Hz, 6H, Tip-p-CHMe2), 1.23 (br d, 6H, Tip-o-CHMe2), 1.37 (s,
1H, Tbt-p-CH(SiMe3)2), 2.28 (br s, 1H, Tbt-o-CH(SiMe3)2), 2.85 (sept,
J ) 7 Hz, 1H, Tip-p-CHMe2), 3.81 (br s, 1H, Tbt-o-CH(SiMe3)2), 3.93
(sept, J ) 6 Hz, 2H, Tip-o-CHMe2), 6.43 (br s, 2H, Tbt-m-CH), 7.04
(s, 2H, Tip-m-CH); 13C NMR (CDCl3, 340 K) δ 1.05 (q, Tbt-p-CH-
(SiMe3)2), 2.45 (q, Tbt-o-CH(SiMe3)2), 23.58 (q, Tip-p-CHMe2), 23.96
(q, Tip-o-CHMe2), 27.26 (q, Tip-o-CHMe2), 27.76 (d, Tbt-o-CH-
(SiMe3)2), 31.20 (d, Tbt-p-CH(SiMe3)2), 32.81 (d, Tip-p-CHMe2), 34.32
(d, Tip-o-CHMe2), 123.36 (d, Tip-m-CH), 123.47 (d, Tbt-m-CH), 126.19
(s, Tbt-p-C), 129.48 (d, Tbt-m-CH), 130.66 (s), 145.97 (s), 151.58 (s),
151.72 (s, Tbt-o-C) 154.02 (s, Tip-o-C). Anal. Calcd for C42H82Si7-
Br2‚H2O: C, 52.46; H, 8.81; Br, 16.62. Found: C, 52.43; H, 8.81;
Br, 16.75.
Preparation of {2,4,6-Tris[bis(trimethylsilyl)methyl]phenyl}-
(2,4,6-triisopropylphenyl)-1,2,3,4,5-tetrathiasilolane (2b). To a solu-
tion of 6 (475 mg, 0.50 mmol) in THF (10 mL) was added at -78 °C
lithium naphthalenide (2.7 mL), prepared from lithium dispersion (209
mg, 30.1 mmol) and naphthalene (2.93 g, 22.9 mmol) in THF (39 mL),
and the mixture was stirred for 20 min. To this solution was added
elemental sulfur (130 mg, 0.51 mmol) at -78 °C, the mixture was
stirred for 10 min, and then a saturated aqueous solution of NH4Cl
was added. The solution was stirred for 1 h, during which time it was
warmed to room temperature. The organic layer was separated, and
the water layer was extracted with 50 mL of hexane. The organic layers
were put together and dried with anhydrous MgSO4. After removal of
the solvent, the residue was roughly purified by GPLC and FCC
(hexane), followed by recrystallization from ethanol to afford 2b (127
1
was carried out with Merck Kieselgel 60 PF254 Art. 7747. The H
NMR (500 MHz), 13C NMR (125 MHz), and 29Si NMR (53.5 MHz)
spectra were measured in CDCl3 or C6D6 with a Bruker AM-500 or
JEOL EX-270 spectrometer using CHCl3 or C6H6 as an internal standard
or tetramethylsilane as an external standard. High-resolution mass
spectral data were obtained on a JEOL SX-102 mass spectrometer.
Elemental analyses were performed by the Microanalytical Laboratory
of the Department of Chemistry, Faculty of Science, The University
of Tokyo.
Preparation of 5-{2,4,6-Tris[bis(trimethylsilyl)methyl]phenyl}-
5-mesityl-1,2,3,4,5-tetrathiasilolane (2a). (a) Thermal Reaction of
Diaryldihydrosilane 3a with Sulfur. Diaryldihydrosilane 3a21b (668
mg, 0.95 mmol) was mixed with S8 (2.5 g) and heated to 230 °C for
22 min. Most excess sulfur was removed by recrystallization from
chloroform. The residue was separated with DCC (silica/hexane) and
GPLC. Solid material thus obtained was dissolved into CH2Cl2, to
which was added approximately the same volume of ethanol. Evapora-
tion of CH2Cl2 at room temperature under reduced pressure gave 2a
1
(35 mg, 4%) as pale yellow crystals. 2a: mp 179-181 °C; H NMR
(CDCl3, 340 K) δ 0.03 (s, 36H, Tbt-o-CH(SiMe3)2), 0.09 (s, 18H, Tbt-
p-CH(SiMe3)2), 1.39 (s, 1H, Tbt-p-CH(SiMe3)2), 2.24 (s, 3H, Mes-p-
Me), 2.29 (br s, 2H, Tbt-o-CH(SiMe3)2), 2.53 (s, 6H, Mes-o-Me), 6.43
(br s, 2H, Tbt-m-CH), 6.78 (s, 2H, Mes-m-CH); 13C NMR (CDCl3,
340 K) δ 0.99 (q, Tbt-p-CH(SiMe3)2), 1.85 (q, Tbt-o-CH(SiMe3)2), 20.86
(q, Mes-p-Me), 25.77 (q, Mes-o-Me), 29.21 (d, Tbt-o-CH(SiMe3)2),
31.36 (d, Tbt-o-CH(SiMe3)2), 121.74 (s, Tbt-p-C), 123.67 (d, Tbt-m-
CH), 128.98 (d, Tbt-m-CH), 130.39 (d, Mes-m-CH), 133.63 (s), 140.14
(s), 142.28 (s), 146.92 (s), 154.17 (s, Tbt-o-C); FT-Raman spectrum
in solid (excitation, Nd:YAG laser, 1064 nm) 505 cm-1. Anal. Calcd
for C36H70Si7S4: C, 52.23; H, 8.52; S, 15.49. Found: C, 52.36; H,
8.29; S, 14.92.
(33) Upon replacement of two hydrogens in H2SidS by two phenyl
groups, it was calculated that the Si-S bond is elongated only by 0.01 Å
at the B3LYP/6-31G(d) level.
(34) Sheldrick, W. S. In The Chemistry of Organic Silicon Compounds;
Patai, S., Rappoport, Z., Eds.; Wiley: New York, 1989; Part 1, pp 227-
304.
(35) Miller, A. R.; Curtin, D. Y. J. Am. Chem. Soc. 1976, 98, 1860.

First Kinetically Stabilized Silanethione
J. Am. Chem. Soc., Vol. 120, No. 43, 1998 11103
mg, 28%). 2b: Pale yellow crystals, mp 207-209 °C; 1H NMR
(CDCl3, 340 K) δ 0.05 (br s, 36H, Tbt-o-CH(SiMe3)2), 0.08 (s, 18H,
Tbt-p-CH(SiMe3)2), 1.16 (br s, 12H, Tip-o-CHMe2), 1.22 (d, J ) 6.9
Hz, 6H, Tip-p-CHMe2), 1.38 (s, 1H, Tbt-p-CH(SiMe3)2), 2.29 (br s,
2H, Tbt-o-CH(SiMe3)2), 2.83 (sept, J ) 6.9 Hz, 1H, Tip-p-CHMe2),
3.89 (br s, 2H, Tip-o-CHMe2), 6.42 (br s, 2H, Tbt-m-CH), 7.02 (s, 2H,
Tip-m-CH); 13C NMR (CDCl3) δ 1.09 (q, Tbt-p-CH(SiMe3)2), 2.56 (q,
Tbt-o-CH(SiMe3)2), 23.61 (q, Tip-p-CHMe2), 24.76 (q, Tip-o-CHMe2),
27.70 (q, Tip-o-CHMe2), 28.50 (d, Tbt-o-CH(SiMe3)2), 31.23 (d, Tbt-
p-CH(SiMe3)2), 34.29 (d, Tip-p-CHMe2), 35.03 (d, Tip-o-CHMe2),
123.41 (d, Tip-m-CH), 123.61 (s, Tbt-p-C), 123.84 (d, Tbt-m-CH),
129.52 (d, Tbt-m-CH), 130.67 (s), 146.06 (s), 150.95 (s), 153.54 (s,
Tbt-o-C), 154.04 (s, Tip-o-C); FT-Raman spectrum in solid (excitation,
Nd:YAG laser, 1064 nm) 504 cm-1. Anal. Calcd for C42H82Si7S4: C,
55.32; H, 9.06; S, 14.06. Found: C, 55.30; H, 9.30; S, 13.50.
Desulfurization of 2a with Triphenylphosphine. To a mixture of
2a (50 mg, 0.060 mmol) and triphenylphosphine (48 mg, 0.18 mmol)
was added hexane (5 mL) at -78 °C, and the solution was stirred for
2 h, during which time it was warmed to room temperature. After
removal of the solvent, the crude reaction products were chromato-
graphed by GPLC to afford (Z)-2,4-dimesityl-2,4-bis{2,4,6-tris[bis-
(trimethylsilyl)methyl]phenyl}-1,3,2,4-dithiadisiletane (8) (35 mg, 90%),
together with triphenylphosphine sulfide (47 mg, 100%). 8: Colorless
crystals (from ethanol), mp > 300 °C. As mentioned in the text, 8
CH); 13C NMR (CDCl3) δ 0.86 (q, Tbt-p-CH(SiMe3)2), 1.06 (q, Tbt-
o-CH(SiMe3)2), 1.32 (q, Tbt-o-CH(SiMe3)2), 21.04 (q, Mes-p-Me), 25.42
(q, Mes-o-Me), 28.71 (d, Tbt-o-CH(SiMe3)2), 28.96 (d, Tbt-o-CH-
(SiMe3)2), 31.08 (d, Tbt-p-CH(SiMe3)2), 121.20 (d), 121.90 (s, Tbt-p-
C), 123.48 (d, Tbt-m-CH), 124.49 (d), 128.61 (d, Tbt-m-CH), 128.83
(d), 129.86 (d), 133.87 (s), 140.60 (s), 142.04 (s), 147.28 (s), 148.40
(s), 148.59 (s), 153.57 (s, Tbt-o-C), 153.87 (s, Tbt-o-C). Anal. Calcd
for C43H75Si7NS2‚0.5H2O: C, 58.97; H, 8.75; N, 1.60; S, 7.32.
Found: C, 58.80; H, 8.88; N, 1.57; S, 7.38.
Reaction of 7a with Mesitonitrile Oxide. To a mixture of 2a (72
mg, 0.087 mmol) and triphenylphosphine (68 mg, 0.26 mmol) was
added hexane (5 mL) at -78 °C, and the solution was stirred for 10
min. A hexane solution of mesitonitrile oxide (16 mg, 0.099 mmol)
was added to the solution, and the mixture was stirred for 2 h, during
which time it was warmed to room temperature. After removal of the
solvent, the crude reaction products were roughly chromatographed by
GPLC and purified by PTLC (hexane/CH2Cl2 ) 2:1) to afford 2-{2,4,6-
tris[bis(trimethylsilyl)methyl]phenyl}-2,4-dimesityl-1,3,5,2-oxathiaza-
silole (11a) (35 mg, 45%), together with 8 (6.1 mg, 10%) and
triphenylphosphine sulfide (77 mg, 98%). 11a: Colorless crystals (from
1
ethanol), mp 283-285 °C; H NMR (CDCl3) δ -0.12 (s, 9H, Tbt-o-
CH(SiMe3)2), -0.08 (s, 9H, Tbt-o-CH(SiMe3)2), 0.069 (s, 9H, Tbt-o-
CH(SiMe3)2), 0.071 (s, 9H, Tbt-o-CH(SiMe3)2), 0.11 (s, 18H, Tbt-p-
CH(SiMe3)2), 1.38 (s, 1H, Tbt-p-CH(SiMe3)2), 2.05 (br s, 6H, Mes-o-
Me), 2.23 (s, 3H, Mes-p-Me), 2.24 (s, 3H, Mes-p-Me), 2.51 (s, 6H,
Mes-o-Me), 2.54 (s, 1H, Tbt-o-CH(SiMe3)2), 2.60 (s, 1H, Tbt-o-
CH(SiMe3)2), 6.35 (br s, 1H, Tbt-m-CH), 6.48 (br s, 1H, Tbt-m-CH),
6.75 (s, 2H, Mes-m-CH), 6.80 (s, 2H, Mes-m-CH); 13C NMR (CDCl3)
δ 0.55 (q, Tbt-o-CH(SiMe3)2), 0.81 (q, Tbt-p-CH(SiMe3)2), 0.86 (q,
Tbt-o-CH(SiMe3)2), 0.95 (q, Tbt-p-CH(SiMe3)2), 1.43 (q, Tbt-o-CH-
(SiMe3)2), 1.69 (q, Tbt-o-CH(SiMe3)2), 19.35 (q, Mes-o-Me), 21.05 (q,
Mes-p-Me), 21.10 (q, Mes-p-Me), 24.18 (q, Mes-o-Me), 29.14 (d, Tbt-
o-CH(SiMe3)2), 29.55 (d, Tbt-o-CH(SiMe3)2), 30.97 (d, Tbt-p-CH-
(SiMe3)2), 122.79 (s, Tbt-p-C), 122.99 (d, Tbt-m-CH), 128.08 (d, Tbt-
m-CH), 128.30 (d, Mes-m-CH), 128.96 (s), 129.48 (d, Mes-m-CH),
133.90 (s), 136.88 (s), 139.02 (s), 140.08 (s), 142.10 (s), 146.61 (s),
152.64 (s, Tbt-o-C), 152.78 (s, Tbt-o-C), 160.16 (s, CdN). Anal. Calcd
for C46H81Si7NSO: C, 61.88; H, 9.14; N, 1.57; S, 3.59. Found: C,
61.83; H, 9.40; N, 1.71; S, 3.49.
1
showed a very complicated H NMR spectrum at room temperature,
which is shown in the Supporting Information. Anal. Calcd for
C72H140Si14S2: C, 59.10; H, 9.64; S, 4.38. Found: C, 59.35; H, 9.59;
S, 4.50.
Reaction of 7a with Methanol. To a mixture of 2a (50 mg, 0.060
mmol) and triphenylphosphine (48 mg, 0.18 mmol) was added hexane
(5 mL) at -78 °C, and the solution was stirred for 10 min. To this
solution was added methanol (0.1 mL, 2.5 mmol), and the mixture was
stirred for 2 h, during which time it was warmed to room temperature.
After removal of the solvent, the crude reaction products were
chromatographed by GPLC to afford {2,4,6-tris[bis(trimethylsilyl)-
methyl]phenyl}(mesityl)methoxysilanethiol (9a) (43 mg, 93%), together
with 8 (3 mg, 6%) and triphenylphosphine sulfide (52 mg, 95%). 9a:
Colorless crystals (from ethanol), mp 197-199 °C; 1H NMR (CDCl3)
δ -0.07 (s, 9H, Tbt-o-CH(SiMe3)2), -0.06 (s, 9H, Tbt-o-CH(SiMe3)2),
-0.03 (s, 9H, Tbt-o-CH(SiMe3)2), 0.00 (s, 9H, Tbt-o-CH(SiMe3)2), 0.04
(s, 18H, Tbt-p-CH(SiMe3)2), 0.64 (s, 1H, SH), 1.30 (s, 1H, Tbt-p-
CH(SiMe3)2), 2.22 (s, 3H, Mes-p-Me), 2.45 (s, 6H, Mes-o-Me), 2.52
(br s, 1H, Tbt-o-CH(SiMe3)2), 2.63 (br s, 1H, Tbt-o-CH(SiMe3)2), 3.40
(s, 3H, OMe), 6.22 (br s, 1H, Tbt-m-CH), 6.36 (br s, 1H, Tbt-m-CH),
6.76 (s, 2H, Tip-m-CH); 13C NMR (CDCl3) δ 0.87 (q, Tbt-p-CH-
(SiMe3)2), 1.16 (q, Tbt-o-CH(SiMe3)2), 1.21 (q, Tbt-o-CH(SiMe3)2), 1.46
(q, Tbt-o-CH(SiMe3)2), 1.50 (q, Tbt-o-CH(SiMe3)2), 20.91 (q, Mes-p-
Me), 25.30 (q, Mes-o-Me), 27.40 (d, Tbt-o-CH(SiMe3)2), 27.56 (d, Tbt-
o-CH(SiMe3)2), 30.46 (d, Tbt-p-CH(SiMe3)2), 49.53 (q, OMe), 122.96
(d, Tbt-m-CH), 127.10 (s, Tbt-p-C), 128.08 (d, Tbt-m-CH), 129.90 (d,
Tbt-m-CH), 132.99 (s), 139.55 (s), 143.77 (s), 144.84 (s), 151.72 (s,
Tbt-o-C), 152.01 (s, Tbt-o-C). Anal. Calcd for C37H74Si7OS‚1.5H2O:
C, 56.21; H, 9.82; S, 4.06. Found: C, 56.22; H, 9.64; S, 4.49.
Reaction of 7a with Phenyl Isothiocyanate. To a mixture of 2a
(147 mg, 0.18 mmol) and triphenylphosphine (140 mg, 0.53 mmol)
was added hexane (3 mL) at -78 °C, and the solution was stirred for
10 min. To this solution was added phenyl isothiocyanate (0.04 mL,
0.33 mmol), and the mixture was stirred for 2 h, during which time it
was warmed to room temperature. After removal of the solvent, the
crude reaction products were chromatographed by GPLC to afford
2-{2,4,6-tris[bis(trimethylsilyl)methyl]phenyl}-2-mesityl-4-phenylimino-
1,3,2-dithiasiletane (10a) (110 mg, 72%), together with 8 (7 mg, 5%)
and triphenylphosphine sulfide (152 mg, 97%). 10a: Colorless crystals
Synthesis and Isolation of Silanethione 7b. To a mixture of 2b
(74 mg, 0.082 mmol) and triphenylphosphine (64 mg, 0.24 mmol) was
added hexane (2 mL) at room temperature, and the solution was refluxed
for 1 h. After filtration of triphenylphosphine sulfide under argon, the
filtrate was concentrated to afford a yellow solid, which contained 86%
of {2,4,6-tris[bis(trimethylsilyl)methyl]phenyl}(2,4,6-triisopropylphe-
nyl)thioxosilane (7b) (66 mg, 100%) and 14% of triphenylphosphine
sulfide (2.3 mg). Pure 7b was obtained by recrystallization from
1
hexane. 7b: Pale yellow crystals, mp 185-189 °C; H NMR (C6D6
at 360 K) δ 0.15 (s, 18H, Tbt-p-CH(SiMe3)2), 0.19 (s, 36H, Tbt-o-
CH(SiMe3)2), 1.19 (d, J ) 6.9 Hz, 6H, Tip-p-CHMe2), 1.40 (d, J )
6.5 Hz, 12H, Tip-o-CHMe2), 1.50 (s, 1H, Tbt-p-CH(SiMe3)2), 2.76 (sept,
J ) 6.9 Hz, 1H, Tip-p-CHMe2), 3.46 (br s, 2H, Tbt-o-CH(SiMe3)2),
3.51 (sept, J ) 6.5 Hz, 2H, Tip-o-CHMe2), 6.58 (br s, 2H, Tbt-m-
CH), 7.05 (s, 2H, Tip-m-CH); 13C NMR (C6D6) δ 1.13 (q, Tbt-p-CH-
(SiMe3)2), 1.49 (q, Tbt-o-CH(SiMe3)2), 1.83 (q, Tbt-o-CH(SiMe3)2),
22.53 (q, Tip-p-CHMe2), 24.00 (q, Tip-o-CHMe2), 27.67 (q, Tip-o-
CHMe2), 30.33 (d, Tbt-o-CH(SiMe3)2), 30.98 (d, Tbt-o-CH(SiMe3)2),
31.98 (d, Tbt-p-CH(SiMe3)2), 34.88 (d, Tip-o-CHMe2), 38.13 (d, Tip-
p-CHMe2), 121.93 (d, Tbt-m-CH), 123.87 (d, Tbt-m-CH), 131.22 (d,
Tip-m-CH), 139.03 (s, Tbt-p-C), 148.35 (s), 151.00 (s), 151.16 (s),
151.26 (s, Tbt-o-C), 152.77 (s, Tbt-o-C), 153.01 (s, Tip-o-C); 29Si NMR
(C6D6) δ 2.44, 3.23, 166.56. UV (hexane) λmax 396 nm (ꢀ 100); FT-
Raman spectrum in solid (excitation, Nd:YAG laser, 1064 nm) 724
cm-1 (νSidS); high-resolution FAB-MS, observed m/z 815.4672, calcd
for C42H82Si7S m/z 815.4600.
1
(from hexane), mp 145 °C dec; H NMR (CDCl3) δ -0.04 (s, 9H,
Tbt-o-CH(SiMe3)2), -0.02 (s, 9H, Tbt-o-CH(SiMe3)2), -0.01 (s, 9H,
Tbt-o-CH(SiMe3)2), 0.00 (s, 9H, Tbt-o-CH(SiMe3)2), 0.06 (s, 18H, Tbt-
p-CH(SiMe3)2), 1.36 (s, 1H, Tbt-p-CH(SiMe3)2), 2.28 (s, 3H, Mes-p-
Me), 2.51 (s, 6H, Mes-o-Me), 2.71 (s, 1H, Tbt-o-CH(SiMe3)2), 2.80
(s, 1H, Tbt-o-CH(SiMe3)2), 6.33 (s, 1H, Tbt-m-CH), 6.46 (s, 1H, Tbt-
m-CH), 6.87 (s, 2H, Tip-m-CH), 6.95 (d, J ) 8 Hz, 2H, Ph-o-CH),
7.09 (t, J ) 7 Hz, 1H, Ph-p-CH), 7.29 (dd, J ) 8, 7 Hz, 2H, Ph-m-
Reaction of 7b with Water. When the yellow solid of 7b containing
14% triphenylphosphine sulfide (16 mg, 0.017 mmol) was exposed to
the air, the color gradually disappeared within 3 h. Purification with
GPLC afforded {2,4,6-tris[bis(trimethylsilyl)methyl]phenyl}(2,4,6-tri-
isopropylphenyl)hydroxysilanethiol (12) (14.3 mg, 100%). 12: Color-
1
less crystals (from hexane), mp 113-115 °C; H NMR (CDCl3, 500

11104 J. Am. Chem. Soc., Vol. 120, No. 43, 1998
Suzuki et al.
MHz) δ -0.26 (br s, 18H, Tbt-o-CH(SiMe3)2), 0.04 (s, 18H, Tbt-p-
CH(SiMe3)2), 0.13 (br s, 18H, Tbt-o-CH(SiMe3)2), 0.84 (d, J ) 6 Hz,
3H, Tip-o-CHMe2), 1.04 (s, 1H, SH), 1.19 (d, J ) 7 Hz, 6H, Tip-p-
CHMe2), 1.22 (d, J ) 6 Hz, 3H, Tip-o-CHMe2), 1.28 (d, J ) 7 Hz,
3H, Tip-o-CHMe2), 1.29 (s, 1H, Tbt-p-CH(SiMe3)2), 1.39 (d, J ) 6
CHMe2), 1.34 (s, 1H, Tbt-p-CH(SiMe3)2), 2.35 (br s, 1H, Tbt-o-
CH(SiMe3)2), 2.86 (sept, J ) 7 Hz, 1H, Tip-p-CHMe2), 3.16 (br s, 1H,
Tbt-o-CH(SiMe3)2), 3.19 (sept, J ) 6 Hz, 2H, Tip-o-CHMe2), 6.31 (s,
1H, Tbt-m-CH), 6.51 (s, 1H, Tbt-m-CH), 6.93 (d, J ) 8 Hz, 2H, Ph-
o-CH), 7.03 (br d, 2H, Tip-m-CH), 7.08 (t, J ) 7 Hz, 1H, Ph-p-CH),
7.29 (dd, J ) 8, 7 Hz, 2H, Ph-m-CH); 13C NMR (CDCl3, 125 MHz) δ
0.97 (q, Tbt-p-CH(SiMe3)2), 1.81 (q, Tbt-o-CH(SiMe3)2), 1.90 (q, Tbt-
o-CH(SiMe3)2), 23.26 (q, Tip-o-CHMe2), 23.37 (q, Tip-o-CHMe2), 23.76
(q, Tip-o-CHMe2), 27.82 (q, Tip-o-CHMe2), 27.95 (q, Tip-o-CHMe2),
28.56 (d, Tbt-o-CH(SiMe3)2), 28.66 (d, Tbt-o-CH(SiMe3)2), 30.96 (d,
Tbt-p-CH(SiMe3)2), 34.39 (d, Tip-p-CHMe2), 35.56 (d, Tip-o-CHMe2),
35.73 (d, Tip-o-CHMe2), 121.23 (d), 122.73 (d), 122.76 (d), 123.86
(d, Tbt-m-CH), 124.05 (s, Tbt-p), 124.32 (d), 128.84 (d), 129.24 (d,
Tbt-m-CH), 131.97 (s), 146.59 (s), 148.69 (s), 149.04 (s), 151.18 (s),
152.58 (s, Tbt-o), 152.79 (s, Tbt-o), 153.17 (s, Tip-o), 153.95 (s, Tip-
o); high-resolution FAB-MS, observed m/z 950.4784, calcd for C49H88-
Si7NS2 m/z 950.4743. Anal. Calcd for C49H88Si7NS2‚0.5H2O: C,
61.31; H, 9.24; N, 1.46; S, 6.68. Found: C, 61.08; H, 9.34; N, 1.89;
S, 6.77.
Hz, H, Tip-o-CHMe2), 1.98 (br s, 1H, Tbt-o-CH(SiMe3)2), 2.66 (s,
3
1H, OH), 2.82 (sept, J ) 7 Hz, 1H, Tip-p-CHMe2), 3.11 (sept, J ) 6
Hz, 1H, Tip-o-CHMe2), 3.56 (br s, 1H, Tbt-o-CH(SiMe3)2), 4.33 (sept,
J ) 6 Hz, 1H, Tip-o-CHMe2), 6.27 (br s, 1H, Tbt-m-CH), 6.40 (br s,
1H, Tbt-m-CH), 6.95 (s, 1H, Tip-m-CH), 7.03 (s, 1H, Tip-m-CH); 13
C
NMR (CDCl3, 125 MHz) δ 0.85 (q, Tbt-p-CH(SiMe3)2), 1.01 (q, Tbt-
p-CH(SiMe3)2), 1.44 (q, Tbt-o-CH(SiMe3)2), 1.74 (q, Tbt-o-CH-
(SiMe3)2), 1.77 (q, Tbt-o-CH(SiMe3)2), 2.03 (q, Tbt-o-CH(SiMe3)2),
22.37 (q, Tip-o-CHMe2), 23.74 (q, Tip-p-CHMe2), 23.80 (q, Tip-p-
CHMe2), 24.98 (q, Tip-p-CHMe2), 25.98 (q, Tip-o-CHMe2), 27.07 (q,
Tip-o-CHMe2), 27.43 (d, Tbt-o-CH(SiMe3)2), 28.06 (d, Tbt-o-
CH(SiMe3)2), 30.04 (d, Tbt-p-CH(SiMe3)2), 30.56 (d, Tip-o-CHMe2),
33.58 (d, Tip-o-CHMe2), 34.34 (d, Tip-p-CHMe2), 121.25 (d, Tip-m-
CH), 123.02 (d, Tip-m-CH), 123.34 (d, Tbt-m-CH), 128.19 (d, Tbt-m-
CH), 128.42 (s, Tbt-p), 133.58 (s), 144.50 (s), 150.35 (s, Tbt-o), 150.65
(s), 150.98 (s, Tbt-o), 153.47 (s, Tip-o), 154.06 (s, Tip-o); high-
resolution FAB-MS, observed m/z 832.4615, calcd for C42H84Si7OS
m/z 832.4628.
Reaction of 7b with Mesitonitrile Oxide. To a mixture of 2b (85
mg, 0.093 mmol) and triphenylphosphine (97 mg, 0.37 mmol) was
added hexane (5 mL) at room temperature, and the solution was refluxed
for 30 min. A hexane solution of mesitonitrile oxide (26 mg, 0.16
mmol) was added to the solution, and the mixture was stirred for 1 h.
After removal of the solvent, the crude reaction products were roughly
chromatographed by GPLC and purified by PTLC (hexane/CH2Cl2 )
10:3) to afford 2-{2,4,6-tris[bis(trimethylsilyl)methyl]phenyl}-2-(2,4,6-
triisopropylphenyl)-4-mesityl-1,3,5,2-oxathiazasilole (11b) (49 mg,
54%), together triphenylphosphine sulfide (109 mg, 100%). 11b:
Colorless crystals (from ethanol), mp 207-209 °C; 1H NMR (CDCl3,
500 MHz) δ -0.06 (s, 9H, Tbt-o-CH(SiMe3)2), 0.02 (s, 9H, Tbt-o-
CH(SiMe3)2), 0.05 (s, 9H, Tbt-o-CH(SiMe3)2), 0.06 (s, 9H, Tbt-o-CH-
(SiMe3)2), 0.08 (s, 18H, Tbt-p-CH(SiMe3)2), 1.05 (d, J ) 5 Hz, 3H,
Tip-o-CHMe2), 1.18 (d, J ) 5 Hz, 3H, Tip-o-CHMe2), 1.20 (d, J ) 7
Hz, 6H, Tip-p-CHMe2), 1.23 (d, J ) 5 Hz, 3H, Tip-o-CHMe2), 1.25
(d, J ) 5 Hz, 3H, Tip-o-CHMe2), 1.35 (s, 1H, Tbt-p-CH(SiMe3)2), 2.11
(s, 6H, Mes-o-Me), 2.24 (s, 3H, Mes-p-Me), 2.50 (s, 1H, Tbt-o-
CH(SiMe3)2), 2.83 (sept, J ) 7 Hz, 1H, Tip-p-CHMe2), 2.91 (s, 1H,
Tbt-o-CH(SiMe3)2), 2.99 (sept, J ) 5 Hz, 1H, Tip-o-CHMe2), 3.72
(sept, J ) 5 Hz, 1H, Tip-o-CHMe2), 6.37 (s, 1H, Tbt-m-CH), 6.49 (s,
1H, Tbt-m-CH), 6.81 (s, 2H, Mes-m-CH), 6.94 (s, 1H, Tip-m-CH), 7.02
(s, 1H, Tip-m-CH); 13C NMR (CDCl3, 125 MHz) δ 1.11 (q, Tbt-p-
CH(SiMe3)2), 1.22 (q, Tbt-o-CH(SiMe3)2), 1.62 (q, Tbt-o-CH(SiMe3)2),
1.67 (q, Tbt-o-CH(SiMe3)2), 1.91 (q, Tbt-o-CH(SiMe3)2), 20.30 (q),
21.07 (q), 23.74 (q), 23.81 (q), 24.32 (q), 24.79 (q), 26.60 (q), 28.43
(q), 28.69 (d, Tbt-o-CH(SiMe3)2), 29.05 (d, Tbt-o-CH(SiMe3)2), 31.04
(d, Tbt-p-CH(SiMe3)2), 32.36 (d, Tip-o-CHMe2), 34.31 (d, Tip-o-
CHMe2), 35.43 (d, Tip-p-CHMe2), 122.51 (d, Tip-m-CH), 122.58 (d,
Tip-m-CH), 123.77 (s), 124.13 (d, Tbt-m-CH), 128.58 (d, Mes-m-CH),
128.83 (s), 129.44 (d, Tbt-m-CH), 132.00 (s), 137.01 (s), 138.84 (s),
146.20 (s), 151.15 (s), 152.73 (s), 153.42 (s), 153.62 (s, Tbt-o), 154.43
(s, Tbt-o), 159.07 (s, Tip-o). Anal. Calcd for C52H93Si7NOS‚H2O: C,
62.77; H, 9.62; N, 1.41; S, 3.22. Found: C, 63.07; H, 9.33; N, 1.61;
S, 3.46.
Reaction of 7b with Methanol. To a mixture of 2b (73 mg, 0.080
mmol) and triphenylphosphine (63 mg, 0.24 mmol) was added hexane
(2 mL) at room temperature, and the solution was refluxed for 1 h. To
this solution was added methanol (0.16 mL, 4.0 mmol) at room
temperature, and the mixture was stirred for 1 h. After removal of the
solvent, the crude reaction products were chromatographed roughly by
GPLC and purified by PTLC (hexane/CH2Cl2 ) 20:1) to afford
{2,4,6-tris[bis(trimethylsilyl)methyl]phenyl}(2,4,6-triisopropylphenyl)-
methoxysilanethiol (9b) (36 mg, 53%), together with triphenylphosphine
sulfide (52 mg, 81%). 9b: Colorless crystals (from hexane), mp 182-
1
185 °C; H NMR (CDCl3, 500 MHz) δ -0.18 (br s, 18H, Tbt-o-CH-
(SiMe3)2), 0.03 (s, 18H, Tbt-p-CH(SiMe3)2), 0.15 (br s, 18H, Tbt-o-
CH(SiMe3)2), 0.73 (s, 1H, SH), 0.88 (d, J ) 6 Hz, 3H, Tip-o-CHMe2),
1.18 (d, J ) 7 Hz, 6H, Tip-p-CHMe2), 1.197 (d, J ) 6 Hz, 3H, Tip-
o-CHMe2), 1.207 (d, J ) 6 Hz, 3H, Tip-o-CHMe2), 1.29 (s, 1H, Tbt-
p-CH(SiMe3)2), 1.30 (d, J ) 6 Hz, 3H, Tip-o-CHMe2), 1.94 (br s, 1H,
Tbt-o-CH(SiMe3)2), 2.80 (sept, J ) 7 Hz, 1H, Tip-p-CHMe2), 3.33
(sept, J ) 6 Hz, 1H, Tip-o-CHMe2), 3.43 (br s, 1H, Tbt-o-CH(SiMe3)2),
3.66 (s, 3H, OMe), 3.82 (sept, J ) 6 Hz, 1H, Tip-o-CHMe2), 6.24 (br
s, 1H, Tbt-m-CH), 6.36 (br s, 1H, Tbt-m-CH), 6.95 (s, 1H, Tip-m-
CH), 7.01 (s, 1H, Tip-m-CH); 13C NMR (CDCl3, 125 MHz) δ 0.90 (q,
Tbt-p-CH(SiMe3)2), 1.77 (q, Tbt-o-CH(SiMe3)2), 2.10 (q, Tbt-o-CH-
(SiMe3)2), 23.14 (q, Tip-o-CHMe2), 23.73 (q, Tip-p-CHMe2), 24.77 (q,
Tip-o-CHMe2), 26.61 (q, Tip-o-CHMe2), 27.06 (q, Tip-o-CHMe2), 27.24
(d, Tbt-o-CH(SiMe3)2), 28.61 (d, Tbt-o-CH(SiMe3)2), 30.06 (d, Tbt-
p-CH(SiMe3)2), 30.40 (d, Tip-o-CHMe2), 32.77 (d, Tip-o-CHMe2),
34.24 (d, Tip-p-CHMe2), 51.23 (q, OMe), 121.45 (d), 123.02 (d), 123.21
(d), 127.97 (d), 129.72 (s), 133.50 (s), 143.93 (s), 150.38 (s), 151.16
(s, Tbt-o), 151.42 (s, Tbt-o), 154.03 (s, Tip-o), 154.27 (s, Tip-o); high-
resolution FAB-MS, observed m/z 846.4782, calcd for C43H86Si7OS
m/z 846.4784. Anal. Calcd for C43H86Si7OS‚2H2O: C, 58.43; H, 10.26;
S, 3.63. Found: C, 58.66; H, 9.96; S, 3.81.
Reaction of 7b with 2,3-Dimethyl-1,3-butadiene. To a mixture
of 2b (116 mg, 0.13 mmol) and triphenylphosphine (123 mg, 0.47
mmol) in a dry 12-mm Pyrex glass tube were placed 2,3-dimethyl-
1,3-butadiene (0.035 mL, 0.31 mmol) and hexane (1.5 mL) at room
temperature. After five freeze-pump-thaw cycles, the tube was
evacuated and sealed. The solution was heated at 180 °C for 3 h, during
which time the yellow color of the solution disappeared. After removal
of the solvent, the crude reaction products were roughly chromato-
graphed by GPLC and purified by PTLC (hexane) to afford 2-{2,4,6-
tris[bis(trimethylsilyl)methyl]phenyl}-2-(2,4,6-triisopropylphenyl)-4,5-
dimethyl-1-silacyclohex-4-ene (13) (85 mg, 74%), together with
triphenylphosphine sulfide (119 mg, 100%). 13: Colorless crystals
(from ethanol), mp 179-181 °C; 1H NMR (CDCl3, 500 MHz, 340 K)
δ 0.02 (s, 18H, Tbt-o-CH(SiMe3)2), 0.07 (s, 9H, Tbt-p-CH(SiMe3)2),
0.08 (s, 9H, Tbt-p-CH(SiMe3)2), 0.09 (s, 18H, Tbt-o-CH(SiMe3)2), 1.03
(br s, 3H, Tip-o-CHMe2), 1.11 (br s, 3H, Tip-o-CHMe2), 1.12 (br s,
3H, Tip-o-CHMe2), 1.19 (d, J ) 7 Hz, 6H, Tip-p-CHMe2), 1.20 (br s,
Reaction of 7b with Phenyl Isothiocyanate. To a mixture of 2b
(70 mg, 0.077 mmol) and triphenylphosphine (76 mg, 0.29 mmol) was
added hexane (5 mL) at room temperature, and the solution was refluxed
for 10 min. To this solution was added phenyl isothiocyanate (0.02
mL, 0.17 mmol), and the mixture was stirred for 1 h. After removal
of the solvent, the crude reaction products were roughly chromato-
graphed by GPLC and purified by PTLC (hexane) to afford 2-{2,4,6-
tris[bis(trimethylsilyl)methyl]phenyl}-2-(2,4,6-triisopropylphenyl)-4-
phenylimino-1,3,2-dithiasiletane (10b) (46 mg, 63%), together with
triphenylphosphine sulfide (67 mg, 99%). 10b: Colorless crystals (from
1
hexane), mp 142-145 °C dec; H NMR (CDCl3, 500 MHz) δ -0.06
(s, 9H, Tbt-o-CH(SiMe3)2), -0.05 (s, 9H, Tbt-o-CH(SiMe3)2), 0.02 (s,
9H, Tbt-o-CH(SiMe3)2), 0.05 (s, 18H, Tbt-p-CH(SiMe3)2), 0.11 (s, 9H,
Tbt-o-CH(SiMe3)2), 1.12 (d, J ) 6 Hz, 3H, Tip-o-CHMe2), 1.16 (d, J
) 6 Hz, 3H, Tip-o-CHMe2), 1.20 (d, J ) 6 Hz, 3H, Tip-o-CHMe2),
1.22 (d, J ) 7 Hz, 6H, Tip-p-CHMe2), 1.28 (d, J ) 6 Hz, 3H, Tip-o-

First Kinetically Stabilized Silanethione
J. Am. Chem. Soc., Vol. 120, No. 43, 1998 11105
3H, Tip-o-CHMe2), 1.33 (s, 1H, Tbt-p-CH(SiMe3)2), 1.45 (s, 3H), 1.78
(s, 3H), 2.18 (d, J ) 14 Hz, 1H, SCH2), 2.29 (br s, 1H, Tbt-o-
CH(SiMe3)2), 2.42 (d, J ) 14 Hz, 1H, SCH2), 2.79 (sept, J ) 7 Hz,
1H, Tip-p-CHMe2), 2.86 (br s, 1H, Tip-o-CHMe2), 3.06 (d, J ) 14
Hz, 1H, SiCH2), 3.18 (br s, 1H, Tbt-o-CH(SiMe3)2), 3.30 (d, J ) 14
Hz, 1H, SiCH2), 4.19 (br s, 1H, Tip-o-CHMe2), 6.37 (br s, 2H, Tbt-
m-CH), 6.92 (br s, 1H, Tip-m-CH), 6.94 (br s, 1H, Tip-m-CH); 13C
NMR (CDCl3, 125 MHz, 340 K) δ 1.11 (q, Tbt-p-CH(SiMe3)2), 1.25
(q, Tbt-p-CH(SiMe3)2), 2.40 (q, Tbt-o-CH(SiMe3)2), 2.58 (q, Tbt-o-
CH(SiMe3)2), 20.44 (q), 21.49 (q), 23.70 (q), 23.72 (q), 25.40 (q), 25.73
(t, SCH2), 26.34 (q), 26.84 (t, SiCH2), 28.08 (d, Tbt-o-CH(SiMe3)2),
30.61 (d, Tbt-o-CH(SiMe3)2), 31.48 (d, Tbt-p-CH(SiMe3)2), 32.98 (d,
Tip-o-CHMe2), 33.12 (d, Tip-o-CHMe2), 34.19 (d, Tip-p-CHMe2),
122.42 (d, Tbt-m-CH), 123.45 (s, Tbt-p), 124.05 (d, Tip-m-CH), 128.71
(d, Tbt-m-CH), 128.81 (s), 129.26 (d, Tip-m-CH), 131.62 (s), 132.37
(s), 143.40 (s), 149.59 (s), 151.08 (s, Tbt-o), 151.20 (s, Tbt-o), 153.60
(s, Tip-o), 155.70 (s, Tip-o); high-resolution FAB-MS, observed m/z
896.5317, calcd for C48H92Si7S m/z 896.5305. Anal. Calcd for C48H92-
Si7S‚H2O: C, 62.94; H, 10.34; S, 3.50. Found: C, 63.29; H, 10.20;
S, 4.15.
1.5418 Å) (for 2a) and a Rigaku AFC7R diffractometer with graphite-
monochromated Mo KR radiation (λ ) 0.710 69 Å) (for 8 and 7b).
The structure of 2a was solved by direct method with MULTAN 7836
and refined by the full matrix least-squares method. The structures of
8 and 7b were solved by direct methods with SHELXS-8637 and refined
by the full matrix least-squares method. All the non-hydrogen atoms
were refined anisotropically. The final cycle of the least-squares
refinement was based on 4906 (for 2a), 8548 (for 8), and 5390 (for
7b) observed reflections [I > 3σ|I|] and 460 (for 2a), 792 (for 8), and
901 (for 7b) variable parameters with R (Rw) ) 0.078 (0.078) (for 2a),
0.070 (0.055) (for 8), and 0.061 (0.051) (for 7b). The crystal data for
these molecules are summarized in Table 3.
Acknowledgment. This work was supported by a Grant-
in-Aid for Scientific Research (No. 05236102) from the Ministry
of Education, Science, Sports and Culture, Japan. H.S. is grateful
to the Research Fellowships of the Japan Society for the
Promotion of Science for Young Scientists. We also thank
Professor Y. Furukawa, Waseda University, for the measurement
of the FT-Raman spectra of 2a, 2b, and 7b. Thanks are due to
Central Glass, Shin-etsu Chemical, and Tosoh Akzo Co., Ltd.
for the generous gifts of tetrafluorosilane, chlorosilanes, and
alkyllithiums, respectively.
Supporting Information Available: 1H NMR spectral chart
of 8 and tables listing atomic coordinates, temperature factors,
bond lengths and angles, and torsion angles for 7b and 8 (108
pages, print/PDF). See any current masthead page for ordering
information and Web access instructions.
X-ray Data Collection. Single crystals of 2a and 8 were grown by
the slow evaporation of a saturated solution in ethanol and chloroform
at room temperature, and single crystals of 7b were grown by the slow
evaporation of a saturated solution in hexane at room temperature in a
glovebox. The intensity data were collected on an Enraf-Nonius CAD-4
diffractometer with graphite-monochromated Cu KR radiation (λ )
(36) Main, P.; Hull, S. E.; Lessinger, L.; Germain, G.; Declercg, J.-P.;
Woolfson, M. H. MULTAN 78, Program for Crystal Structure Determination;
University of York, England, and University of Louvain, Belgium, 1978.
(37) Sheldrick, G. M. SHELXS-86, Program for Crystal Structure
Determination; University of Go¨ttingen, Germany, 1986.
JA980783C