R2Ge=SnR′2 and RR′Ge=SnRR′ (R = SiMetBu2, R′ = 2,4,6-iPr3C6H2): The new stable germastannenes

Article abstract of DOI:10.1021/om021001y

1,1-Bis(di-tert-butylmethylsilyl)-2,2-bis(2,4,6-triisopropylphenyl)-l-germa -2-stannaethene (2), containing a >Ge=Sn< double bond, was prepared as highly air- and moisture-sensitive deep violet crystals by the coupling reaction of bis(di-tert-butylmethylsilyl)dilithiogermane with dichlorobis(2,4,6-triisopropylphenyl)stannane in THF. The germastannenc 2 easily undergoes thermal isomerization to form the corresponding symmetrically substituted isomer (E)-l,2-bis(di-teri-butylmethylsilyl)-l,2-bis(2,4,6-triisopropylphenyl)-l-germa- 2-stannaethene (3) by the dyotropic 1,2-shifts of the silyl and aryl substituents.

Full text of DOI:10.1021/om021001y

Organometallics 2003, 22, 1483-1486
1483
R2GedSn R′2 a n d RR′GedSn RR′ (R ) SiMetBu 2, R′ )
2,4,6-iP r 3C6H2): Th e New Sta ble Ger m a sta n n en es
Akira Sekiguchi,* Rika Izumi, Vladimir Ya. Lee, and Masaaki Ichinohe
Department of Chemistry, University of Tsukuba, Tsukuba, Ibaraki 305-8571, J apan
Received December 12, 2002
1,1-Bis(di-tert-butylmethylsilyl)-2,2-bis(2,4,6-triisopropylphenyl)-1-germa-2-stannaeth-
ene (2), containing a >GedSn< double bond, was prepared as highly air- and moisture-
sensitive deep violet crystals by the coupling reaction of bis(di-tert-butylmethylsilyl)dilithio-
germane with dichlorobis(2,4,6-triisopropylphenyl)stannane in THF. The germastannene 2
easily undergoes thermal isomerization to form the corresponding symmetrically substituted
isomer (E)-1,2-bis(di-tert-butylmethylsilyl)-1,2-bis(2,4,6-triisopropylphenyl)-1-germa-2-stan-
naethene (3) by the dyotropic 1,2-shifts of the silyl and aryl substituents.
In tr od u ction
first stable silastannene, >SidSn<.3 As for germastan-
nenes >GedSn<, only one example has been previously
reported by Escudie´ and co-workers, (2,4,6-Me3C6H2)2-
GedSn(2,4,6-iPr3C6H2)2, which was characterized by a
low-temperature 119Sn NMR spectrum and trapping
reactions, but was not isolated due to its thermal
instability, resulting in the transformation to a distan-
nagermirane at room temperature.4 Quite recently,
during the preparation of our paper, the first example
of germastannene, which is stable in the solid state
and gradually decomposes in solution, (2,4,6-iPr3C6H2)2-
GedSn(2,4,6-iPr3C6H2)2, was reported by Weidenbruch.5
We report here on the synthesis of another represen-
tative of stable germastannenes stable in both the solid
state and solution, which was prepared by the coupling
reaction of 1,1-dilithiogermane with a dichlorostannane
derivative, utilizing an advantage of 1,1-dilithioger-
manes as an extremely useful building block for the
preparation of a variety of doubly bonded compounds
of the type >SidGe< and >GedGe<.6
The chemistry of unsaturated compounds containing
group 14 elements heavier than carbon is a recent
subject of considerable interest.1 Among the variety of
stable multiply bonded derivatives of main-group ele-
ments, those of group 14 occupy a special, very impor-
tant position, since they represent the direct heavier
alkene analogues. The structural and chemical aspects
of such dimetallaalkenes (dimetallenes) MdM′ (M, M′
) heavier group 14 elements) are of particular interest,
because they are known to differ greatly from those of
alkenes in organic chemistry, contributing a new insight
to bonding theory for the elements heavier than carbon.
Despite such evident interest, until now there has
been very limited experimental success in the synthesis
of such stable heteronuclear dimetallenes MdM′, in
sharp contrast to homonuclear congeners MdM, whose
chemistry has been greatly developed during the last
two decades.1 Thus, the first structurally authenti-
cated heteronuclear double bond (stable silagermene
>SidGe<) was reported by us in 2000.2 Very recently
we have succeeded in the synthesis and structural
identification of another heteronuclear dimetallenesthe
Resu lts a n d Discu ssion
Bis(di-tert-butylmethylsilyl)dilithiogermane (1), pre-
pared by the reaction of 1,1-bis(di-tert-butylmethylsilyl)-
2,3-bis(trimethylsilyl)-1-germacycloprop-2-ene with an
excess amount of Li in dry THF/Et2O,6 cleanly reacted
with dichlorobis(2,4,6-triisopropylphenyl)stannane7 in
THF at room temperature to form the corresponding
coupling product 1,1-bis(di-tert-butylmethylsilyl)-2,2-bis-
(2,4,6-triisopropylphenyl)-1-germa-2-stannaethene (2),
as a violet solid in 68% yield (Scheme 1).
Germastannene 2 represents a rare example of iso-
lated compound with a >GedSn< double bond, and it
was characterized by all spectroscopic data. Due to the
hindered rotation around the Sn-C(Tip) bonds, the Me
(1) For recent reviews on metallenes and dimetallenes of group 14
elements, see: (a) Escudie´, J .; Couret, C.; Ranaivonjatovo, H.; Satge´,
J . Coord. Chem. Rev. 1994, 130, 427. (b) Driess, M.; Gru¨tzmacher, H.
Angew. Chem., Int. Ed. Engl. 1996, 35, 828. (c) Baines, K. M.; Stibbs,
W. G. Adv. Organomet. Chem. 1996, 39, 275. (d) Okazaki, R.; West, R.
Adv. Organomet. Chem. 1996, 39, 231. (e) Kaftory, M.; Kapon, M.;
Botoshansky, M. In The Chemistry of Organic Silicon Compounds;
Rappoport, Z., Apeloig, Y., Eds.; Wiley: Chichester, U.K., 1998; Vol.
2, Part 1, Chapter 5. (f) Weidenbruch, M. Eur. J . Inorg. Chem. 1999,
373. (g) Power, P. P. Chem. Rev. 1999, 99, 3463. (h) Escudie´, J .;
Ranaivonjatovo, H. Adv. Organomet. Chem. 1999, 44, 113. (i) Weiden-
bruch, M. In The Chemistry of Organic Silicon Compounds; Rappoport,
Z., Apeloig, Y., Eds.; Wiley: Chichester, U.K., 2001; Vol. 3, Chapter 5.
(j) Tokitoh, N.; Okazaki, R. In The Chemistry of Organic Germanium,
Tin and Lead Compounds; Rappoport, Z., Ed.; Wiley: Chichester, U.K.,
2002; Vol. 2, Part 1, Chapter 13. (k) Lee, V. Ya.; Sekiguchi, A. In The
Chemistry of Organic Germanium, Tin and Lead Compounds; Rap-
poport, Z., Ed.; Wiley: Chichester, U.K., 2002; Vol. 2, Part 1, Chapter
14. (l) Sekiguchi, A.; Lee, V. Ya. Chem. Rev., in press.
(3) Sekiguchi, A.; Izumi, R.; Lee, V. Ya.; Ichinohe, M. J . Am. Chem.
Soc. 2002, 124, 14822.
(2) (a) Lee, V. Ya.; Ichinohe, M.; Sekiguchi, A. J . Am. Chem. Soc.
2000, 122, 12604. For other stable silagermenes, see: (b) Lee, V. Ya.;
Ichinohe, M.; Sekiguchi, A.; Takagi, N.; Nagase, S. J . Am. Chem. Soc.
2000, 122, 9034. (c) Ichinohe, M.; Arai, Y.; Sekiguchi, A.; Takagi, N.;
Nagase, S. Organometallics 2001, 20, 4141. For a silagermene stable
only at low temperature, see: (d) Baines, K. M.; Cooke, J . A.
Organometallics 1991, 10, 3419.
(4) Chaubon, M.-A.; Escudie´, J .; Ranaivonjatovo, H.; Satge´, J . J .
Chem. Soc., Chem. Commun. 1996, 2621.
(5) Scha¨fer, A.; Saak, W.; Weidenbruch, M. Organometallics 2003,
22, 215.
(6) Sekiguchi, A.; Izumi, R.; Ihara, S.; Ichinohe, M.; Lee, V. Ya.
Angew. Chem., Int. Ed. 2002, 41, 1598.
(7) Masamune, S.; Sita, L. R. J . Am. Chem. Soc. 1985, 107, 6390.
10.1021/om021001y CCC: $25.00 © 2003 American Chemical Society
Publication on Web 02/22/2003

1484 Organometallics, Vol. 22, No. 7, 2003
Sekiguchi et al.
Sch em e 1
To distinguish between these two possibilities, we
performed kinetic measurements of the isomerization
of 2 to 3. The activation parameters were determined
by monitoring of the isomerization by 1H NMR spec-
troscopy using Arrhenius and Eyring equations: Ea )
22 kcal mol-1, ∆Hq ) 22 kcal mol-1, and ∆Sq ) -12 cal
K-1 mol-1. The relatively low value of ∆Hq and the
negative value of ∆Sq are more consistent with the
concerted rather than the stepwise mechanism, with the
more ordered and rigid transition state lacking the high
degree of freedom typical for linear intermediates in
pathway B.12 Moreover, such intermediate germylene
(or stannylene) species in pathway B would lead to a
nonstereospecific isomerization to give a mixture of E
and Z isomers of 3, which is not consistent with our
experimental data (formation of only one E isomer of
3). From all these kinetic data it seems more likely that
the isomerization from 2 to 3 proceeds through the
dyotropic migration of silyl and aryl groups (pathway
A) rather than through the stepwise mechanism involv-
ing the intermediate formation of carbene-like species
(pathway B). Indeed, we were not able to observe any
trapping products when the isomerization was carried
out in the presence of excess Et3SiH, which is well-
known to be an effective trapping reagent for both
germylenes and stannylenes.
Sch em e 2
groups of isopropyl substituents in ortho positions of
each aromatic ring became nonequivalent, resulting in
the appearance of three doublet signals of Me groups
in the ratio 1:1:1. As expected, the sp2 Sn atom in 2 is
greatly deshielded, appearing at +525.1 ppm in the
119Sn NMR spectrum.8 In the UV-vis spectrum of 2
there are two distinct absorption bands, of which the
longer wavelength band, 551 nm, was attributed to a
π-π* transition.
Most importantly, the unsymmetrically substituted
germastannene 2, being a room temperature stable
compound, easily and quantitatively undergoes isomer-
ization on gentle heating to form the corresponding
symmetrically substituted isomer (E)-1,2-bis(di-tert-
butylmethylsilyl)-1,2-bis(2,4,6-triisopropylphenyl)-1-ger-
ma-2-stannaethene (3) (Scheme 2).9
Such an isomerization may proceed in two different
ways: the first one is a concerted pathway, which
involves the simultaneous (dyotropic) 1,2-shifts of silyl
and aryl groups from Ge to Sn and from Sn to Ge atoms,
respectively, through the initial twisting of the GedSn
double bond followed by a hypothetical bicyclobutane-
type transition state to form the thermodynamically
stable E isomer 3 (pathway A in Scheme 3).10 Alterna-
tively, one can imagine another, stepwise, mechanism
involving initial 1,2-silyl (or -aryl) group migration to
form stannylgermylene (or germylstannylene) interme-
diates11 followed by the second 1,2-migration of the aryl
(or silyl) group to give the final E isomer 3 (pathway B
in Scheme 3).
The isomerization product 3 was isolated in a pure
form as red crystals and was also fully characterized
by spectral data. The doubly bonded Sn atom in 3
resonates at a higher field (+373.4 ppm) than that in 2
(+525.1 ppm), due to the different environment around
it: 3 has one electron-withdrawing aryl group and one
electron-donating silyl substituent, whereas 2 has two
aryl groups. In the UV spectrum of 3 there is a blue
shift of the longest wavelength absorption band in
comparison with that of 2 (465 vs 551 nm). The
constitution of 3 was proved by X-ray diffraction analy-
sis, which confirmed its symmetrical E isomer structure.
Although the accurate determination of bond lengths
and angles was impossible due to disorder in the
positions of the doubly bonded Ge and Sn atoms, we
were able to determine the geometry of the double-bond
system. As one might expect, the GedSn double bond
has a trans-bent configuration with bending angles of
ca. 28°.
The GedSn double bond exhibits the high reactivity
typical for other heavy alkenes. Thus, 2 easily reacts
with propylene sulfide to form finally the four-mem-
bered 2,2-bis(di-tert-butylmethylsilyl)-4,4-bis(2,4,6-tri-
isopropylphenyl)-1,3-dithia-2-germa-4-stannacyclobu-
tane (5), isolated by GPC as colorless crystals in 37%
yield (Scheme 4). The formation of 5 can be rationalized
as a result of the initial [2 + 1] cycloaddition of sulfur
across the GedSn double bond in 2 to form the three-
membered-ring compound 4, followed by insertion of the
second sulfur atom into the Ge-Sn single bond of 4 to
yield the final product 5.13 The structure of 5 was
determined by X-ray crystallography, which showed a
(8) The typical 119Sn NMR resonances of the doubly bonded Sn atoms
lie in the region above +400 ppm.1c
(9) This type of isomerization was reported for the first time by West
in the case of 1,1-bis(2,6-dimethylphenyl)-2,2-bis(2,4,6-trimethylphen-
yl)disilene: Yokelson, H. B.; Maxka, J .; Siegel, D. A.; West, R. J . Am.
Chem. Soc. 1986, 108, 4239.
(10) We did not observe the formation of the Z isomer of 3, which is
probably thermodynamically less favorable due to steric reasons.
(11) Examples of stable aryl(germyl)-substituted germylene and
stannylene were recently reported by Kira: Setaka, W.; Sakamoto, K.;
Kira, M.; Power, P. P. Organometallics 2001, 20, 4460.
(12) For the isomerization of 1,1-bis(2,6-dimethylphenyl)-2,2-bis-
(2,4,6-trimethylphenyl)disilene to 1,2-bis(2,6-dimethylphenyl)-1,2-bis-
(2,4,6-trimethylphenyl)disilene, the following activation parameters
were reported: ∆Hq ) 15 kcal mol-1 and ∆Sq ) -36 cal K-1 mol-1
,
which was explained by the concerted intramolecular migration of the
two aryl groups across the silicon-silicon bond: Yokelson, H. B.; Siegel,
D. A.; Millevolte, A. J .; Maxka, J .; West, R. Organometallics 1990, 9,
1005.

New Stable Germastannenes
Organometallics, Vol. 22, No. 7, 2003 1485
Sch em e 3
Sch em e 4
planar four-membered ring consisting of Ge, Sn, and two
S atoms in the sequence Ge-S-Sn-S (Figure 1).14
Exp er im en ta l Section
Gen er a l P r oced u r es. All experiments were performed
using high-vacuum-line techniques or under an argon atmo-
sphere in an MBraun MB 150B-G glovebox. All solvents were
predried over sodium benzophenone ketyl and finally dried and
degassed over a potassium mirror under vacuum prior to use.
NMR spectra were recorded on Bruker AC-300FT (1H NMR
at 300.1 MHz; 13C NMR at 75.5 MHz; 29Si NMR at 59.6 MHz;
119Sn NMR at 149.3 MHz) and Bruker ARX-400FT (1H NMR
at 400.2 MHz; 13C NMR at 100.6 MHz; 29Si NMR at 79.5 MHz;
119Sn NMR at 111.8 MHz) NMR spectrometers. Direct mass
spectra (EI) were obtained on a J EOL J MS SX-102 instrument.
UV spectra were recorded on a Shimadzu UV-3150 UV-vis
spectrophotometer in hexane solution. GPC separation was
carried out with an LC-08 liquid chromatograph (J apan
Analytical Industry Co., Ltd.). Elemental analysis was per-
formed at the Analytical Center of Tohoku University (Sendai,
J apan).
F igu r e 1. Molecular structure of 5 with thermal ellipsoids
drawn at the 30% probability level (hydrogen atoms are
omitted for clarity). Selected bond distances (Å): Sn(1)-
S(1) ) 2.4303(7), Sn(1)-S(2) ) 2.4324(7), Ge(1)-S(1) )
2.2929(7), Ge(1)-S(2) ) 2.2854(7). Selected bond angles
(deg): S(1)-Sn(1)-S(2) ) 88.38(2), S(2)-Ge(1)-S(1) )
95.52(2), Ge(1)-S(1)-Sn(1) ) 87.97(2), Ge(1)-S(2)-Sn(1)
) 88.09(2).
1,1-Bis(d i-ter t-bu tylm eth ylsilyl)-2,2-bis(2,4,6-tr iisop r o-
p ylp h en yl)-1-ger m a -2-sta n n a eth en e (2). Bis(di-tert-butyl-
methylsilyl)dilithiogermane (1) was prepared from 1,1-bis(di-
tert-butylmethylsilyl)-2,3-bis(trimethylsilyl)-1-germacycloprop-
2-ene (54 mg, 0.10 mmol) and lithium (15 mg, 2.20 mmol) in
mixed solvent (diethyl ether and THF) at room temperature.6
Compound 1 was reacted with dichlorobis(2,4,6-triisopropyl-
phenyl)stannane (40 mg, 0.07 mmol) in dry THF (1.5 mL) for
15 min at room temperature to form a violet solution. After
evaporation of the solvent, dry benzene (0.5 mL) was added
to the residue. After filtration of inorganic salts, benzene was
evaporated to give germastannene 2 as a violet solid in 68%
(13) The formation of four-membered 1,3-dioxa-2,4-disilacyclobu-
tanes (or -digermacyclobutanes) in the reaction of disilenes (or di-
germenes) with oxygen is a well-documented motif,1a,d although in the
case of sulfur only the primarily formed three-membered thiadisiliranes
(or -digermiranes) were reported.1c,d Thus, compound 5 represents the
first example of an adduct of heavy alkenes with 2 equiv of sulfur.
The only examples related to 5 were reported in a different way by
dimerization of silanethione (or germanethione and germaneselone):
(a) Suzuki, H.; Tokitoh, N.; Okazaki, R.; Nagase, S.; Goto, M. J . Am.
Chem. Soc. 1998, 120, 11096. (b) Matsumoto, T.; Tokitoh, N.; Okazaki,
R. J . Am. Chem. Soc. 1999, 121, 8811.
(14) Single crystals of 5 suitable for X-ray analysis were grown from
the saturated benzene solution. Crystal data for 5‚C6H6 at 120 K:
molecular formula C54H94GeS2Si2Sn, MW ) 1054.87, triclinic, space
group P1h, a ) 11.8000(4) Å, b ) 14.3190(4) Å, c ) 17.4830(6) Å, R )
84.664(2)°, â ) 83.774(2)°, γ ) 78.712(2)°, V ) 2871.96(16) Å3, Z ) 2,
Dcalcd ) 1.220 g cm-3. The final R factor was 0.0425 (Rw ) 0.1122 for
all data) for 11 312 reflections with I > 2σ(I). GOF ) 1.028.
1
yield. H NMR (C6D6, δ): 0.33 (s, 6 H, CH3), 1.03 (d, J ) 6.6
Hz, 12 H, (CH3)2CH(Tip)), 1.15 (d, J ) 6.6 Hz, 12 H, (CH3)2-
CH(Tip)), 1.25 (s, 36 H, C(CH3)3), 1.40 (d, J ) 6.6 Hz, 12 H,
(CH3)2CH(Tip)), 2.76 (sept, J ) 6.6 Hz, 2 H, (CH3)2CH(Tip)),
3.74 (sept, J ) 6.6 Hz, 4 H, (CH3)2CH(Tip)), 7.09 (s, 4 H, Ar
H). 13C NMR (C6D6, δ) -2.4 (CH3), 22.5 (C(CH3)3), 24.1 ((CH3)2-

1486 Organometallics, Vol. 22, No. 7, 2003
Sekiguchi et al.
CH(Tip)), 25.8 ((CH3)2CH(Tip)), 30.7 (C(CH3)3), 34.6 ((CH3)2CH-
(Tip)), 39.6 ((CH3)2CH(Tip)), 122.6 (Ar C), 149.9 (Ar C), 154.1
(Ar C), 156.4 (Ar C). 29Si NMR (C6D6, δ): 35.4. 119Sn NMR
(C6D6, δ): 525.1. UV-vis (hexane; λmax, nm (ꢀ, M-1 cm-1)): 298
(11 300), 551 (5600).
to a solution of germastannene 2 (77 mg, 0.078 mmol) in
benzene (1 mL). After it was stirred at room temperature for
30 h, the reaction mixture was evaporated and the residue
was purified by GPC to give product 5 (28 mg, 37%) as colorless
crystals. Mp: 63-65 °C. 1H NMR (C6D6, δ): 0.45 (s, 6 H, CH3),
1.22 (s, 36 H, C(CH3)3), 1.24 (d, J ) 6.9 Hz, 12 H, (CH3)2CH-
(Tip)), 1.48 (d, J ) 6.9 Hz, 24 H, (CH3)2CH(Tip)), 2.81 (sept, J
) 6.9 Hz, 2 H, (CH3)2CH(Tip)), 3.57 (sept, J ) 6.6 Hz, 4 H
(CH3)2CH(Tip)), 7.18 (s, 4 H, Ar H). 13C NMR (C6D6, δ): -5.5
(CH3), 23.6 (C(CH3)3), 24.1 ((CH3)2CH(Tip)), 26.5 ((CH3)2CH-
(Tip)), 30.3 (C(CH3)3), 34.5 ((CH3)2CH(Tip)), 37.9 ((CH3)2CH-
(Tip)), 123.1 (Ar C), 142.6 (Ar C), 150.9 (Ar C), 155.9 (Ar C).
29Si NMR (C6D6, δ): 19.6. 119Sn NMR (C6D6, δ): -48.5. Anal.
Calcd for C48H88GeS2Si2Sn: C, 59.02; H, 9.08. Found: C, 59.19;
H, 9.33.
(E)-1,2-Bis(d i-ter t-bu tylm eth ylsilyl)-1,2-bis(2,4,6-tr iiso-
p r op ylp h en yl)-1-ger m a -2-sta n n a eth en e (3). Heating of
germastannene 2 (77 mg, 0.078 mmol) in deuteriobenzene (0.5
mL) at 50 °C for 40 h resulted in the formation of isomeric
compound 3, which was quantitatively isolated as red crystals.
1
Mp: 179-180 °C. H NMR (C6D6, δ): 0.04 (s, 3 H, CH3), 0.24
(s, 3 H, CH3), 1.00 (s, 18 H, C(CH3)3), 1.11 (s, 18 H, C(CH3)3),
1.24 (d, J ) 6.9 Hz, 6 H, (CH3)2CH(Tip)), 1.25 (d, J ) 6.9 Hz,
6 H, (CH3)2CH(Tip)), 1.40 (d, J ) 6.9 Hz, 12 H, (CH3)2CH-
(Tip)), 1.535 (d, J ) 6.6 Hz, 6 H, (CH3)2CH(Tip)), 1.542 (d, J )
6.9 Hz, 6 H, (CH3)2CH(Tip)), 2.81 (sept., J ) 6.9 Hz, 2 H,
(CH3)2CH(Tip)), 3.55 (sept, J ) 6.6 Hz, 2 H, (CH3)2CH(Tip)),
3.82 (sept, J ) 6.6 Hz, 2 H, (CH3)2CH(Tip)), 7.10 (s, 2 H, Ar
H), 7.17 (s, 2 H, Ar H). 13C NMR (C6D6, δ): -4.8 (CH3), -3.1
(CH3), 22.5 (C(CH3)3), 23.5 (C(CH3)3), 24.3 ((CH3)2CH(Tip)),
24.7 ((CH3)2CH(Tip)), 25.2 ((CH3)2CH(Tip)), 25.5 ((CH3)2CH-
(Tip)), 26.2 ((CH3)2CH(Tip)), 30.2 (C(CH3)3), 31.5 ((CH3)2CH-
(Tip)), 34.5 ((CH3)2CH(Tip)), 34.7 ((CH3)2CH(Tip)), 36.9 ((CH3)2-
CH(Tip)), 40.7 ((CH3)2CH(Tip)), 121.7 (Ar C), 121.8 (Ar C),
143.5 (Ar C), 144.9 (Ar C), 148.6 (Ar C), 149.4 (Ar C), 153.3
(Ar C), 154.9 (Ar C). 29Si NMR (C6D6, δ): 34.8, 46.4. 119Sn NMR
(C6D6, δ): 373.4. UV-vis (hexane; λmax, nm (ꢀ, M-1 cm-1)): 241
(24 100), 261 (19 500), 310 sh (2900), 465 (6200). Anal. Calcd
for C48H88GeSi2Sn: C, 63.17; H, 9.72. Found: C, 63.04; H, 9.58.
2,2-Bis(d i-ter t-bu tylm eth ylsilyl)-4,4-bis(2,4,6-tr iisop r o-
p ylp h en yl)-1,3-d ith ia -2-ger m a -4-sta n n a cyclobu ta n e (5).
An excess amount of dry propylene sulfide (1 mL) was added
Ack n ow led gm en t. This work was supported by a
Grants-in-Aid for Scientific Research (Nos. 13029015,
13440185, and 14078204) from the Ministry of Educa-
tion, Science and Culture of J apan, TARA (Tsukuba
Advanced Research Alliance), and the COE (Center of
Excellence) program.
Su p p or tin g In for m a tion Ava ila ble: Tables giving de-
tails of the X-ray structure determination, fractional atomic
coordinates, anisotropic thermal parameters, bond lengths,
and bond angles and figures giving thermal ellipsoid plots for
5. This material is available free of charge via the Internet at
http://pubs.acs.org.
OM021001Y