Disilagermirenes: Heavy cyclopropenes of Si and Ge atoms

Article abstract of DOI:10.1016/S0022-328X(03)00651-X

Tetrakis[di-tert-butyl(methyl)silyl]-1-disilagermirene (3) was prepared by the reaction of 2,2,2-tribromo-1,1-di-tert-butyl-1- methyldisilane and dichlorobis[di-tert-butyl(methyl)silyl]germane with sodium in toluene. The molecular structure of 3 was established by X-ray crystallography, which showed a trans-bent configuration around the Si-Si double bond with a bond length of 2.146(1) ?. Thermal and photochemical isomerization of 3 to tetrakis[di-tert-butyl(methyl)silyl]-2-disilagermirene (4) is also reported, as well as the reactions of 3 with MeI, PhCH₂OH, and PhCOCH₃.

Full text of DOI:10.1016/S0022-328X(03)00651-X

Journal of Organometallic Chemistry 685 (2003) 168ꢀ176
/
www.elsevier.com/locate/jorganchem
Disilagermirenes: heavy cyclopropenes of Si and Ge atoms
Vladimir Ya. Lee, Masaaki Ichinohe, Akira Sekiguchi *
Department of Chemistry, University of Tsukuba, Tsukuba, Ibaraki 305-8571, Japan
Received 21 December 2002; accepted 3 March 2003
Dedicated to the 50th Anniversary of Polysilane Chemistry in 2003, and the pioneering work of Professor Makoto Kumada to this field and his
outstanding contribution to silicon chemistry
Abstract
Tetrakis[di-tert-butyl(methyl)silyl]-1-disilagermirene (3) was prepared by the reaction of 2,2,2-tribromo-1,1-di-tert-butyl-1-
methyldisilane and dichlorobis[di-tert-butyl(methyl)silyl]germane with sodium in toluene. The molecular structure of 3 was
established by X-ray crystallography, which showed a trans-bent configuration around the SiÄ
/
Si double bond with a bond length of
˚
2.146(1) A. Thermal and photochemical isomerization of 3 to tetrakis[di-tert-butyl(methyl)silyl]-2-disilagermirene (4) is also
reported, as well as the reactions of 3 with MeI, PhCH2OH, and PhCOCH3.
# 2003 Elsevier B.V. All rights reserved.
Keywords: Cycloaddition; Cyclotrimetallene; Disilene; Germanium; Germasilene; Heavy cyclopropene; Silicon; Small ring; X-ray crystallographic
analysis
1. Introduction
nounced than that of cyclopropene, because of the
extreme reactivity of the endocyclic metalꢀmetal double
bond and the weakness of the endocyclic metalꢀmetal
single bonds [2].
Despite such great interest from the structural and
synthetic viewpoints, the story of heavy cyclopropenes is
very short, being only 8 years old: the first report on the
germanium version, cyclotrigermenes, only appeared in
1995 (Sekiguchi et al.) [3]. After that report there was a
period of extensive development of the chemistry of
heavy cyclopropenes with an increase in the number of
their representatives. Thus, the first silicon analogues,
cyclotrisilenes, were synthesized in 1999 by the experi-
/
Cyclopropene, the smallest unsaturated ring system,
together with its derivatives, represents one of the most
important classes of organic compounds because of its
enhanced reactivity caused by the large ring strain [1].
Very recently, it was demonstrated that the heavy
neighbors of carbon in Group 14 (Si, Ge, Sn) are also
capable of forming such unsaturated three-membered
ring systems [2]. Despite the much greater difficulties in
the preparation of such compounds compared with their
carbon analogue (cyclopropene), they are becoming
increasingly available, constituting a new highly promis-
ing and quickly developing class of organometallic
compounds: heavy cyclopropenes. Such compounds
tend to occupy a rather important position in the
chemistry of heavier Group 14 elements, as the high
reactivity of heavy cyclopropenes is much more pro-
/
mental efforts of two research groups*Kira et al. [4]
/
and Sekiguchi et al. [5]. In the same year, the first and
still the only example of a tin representative, cyclotris-
tannene, was reported by Wiberg et al. [6], and finally,
we have recently synthesized the first heavy cyclopro-
penes containing two different heavier Group 14
elements*isomeric 1- and 2-disilagermirenes, consist-
/
ing of one germanium and two silicon atoms [7] and
studied their reactivity [8]. In this paper we present the
* Corresponding author. Tel./fax: ꢁ81-29-853-4314.
E-mail address: sekiguch@staff.chem.tsukuba.ac.jp (A. Sekiguchi).
/
0022-328X/03/$ - see front matter # 2003 Elsevier B.V. All rights reserved.
doi:10.1016/S0022-328X(03)00651-X

V.Ya. Lee et al. / Journal of Organometallic Chemistry 685 (2003) 168ꢀ
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169
full description of their synthesis, structural peculiarities
and some new aspects of their chemical reactivity.
oped, the reaction being monitored by GC, which
showed the disappearance of starting material 1 after
7ꢀ8 h. At this time the reaction mixture was filtered to
/
remove excess sodium and inorganic salts, and the
filtrate was evaporated in vacuum. The residue was
2. Results and discussion
recrystallized from hexane in a refrigerator at ꢂ30 8C
/
to form the target tetrakis[di-tert-butyl(methyl)silyl]-1-
disilagermirene (3) as large hexagonal-shaped ruby
crystals in 37% yield (Scheme 2). This compound is
highly sensitive to atmospheric oxygen and moisture,
being quickly decomposed in air even in the solid state.
All NMR spectra of 3 were in complete accord with
its symmetrical structure: two sets of signals for both
The synthesis of the first three-membered unsaturated
ring compound consisting of different heavier Group 14
elements required the preliminary preparation of the two
corresponding precursors: 1,1,1-tribromo-2,2-di-tert-bu-
tyl-2-methyldisilane (1) (silicon part) and dichloro-
bis[di-tert-butyl(methyl)silyl]germane (2) (germanium
part) (Scheme 1). The silicon part, compound 1, was
prepared starting from SiF4, which was reacted with
tBuLi to produce tBu2SiF2 in 83% yield. The last
compound was then methylated with MeLi to form
tBu2MeSiF (80% yield), which was in turn treated with
Ph3SiLi to give tBu2MeSiSiPh3 in 83% yield. Finally, the
1
methyl and tert-butyl group protons in the H-NMR
spectrum, and three resonances in the 29Si-NMR
spectrum, of which two belong to silyl substituents
(18.7 and 25.6 ppm) and the most deshielded one (107.8
ppm) was attributed to sp2-Si atoms. The mass-spectrum
of 3 gave the parent ion peak at m/zꢃ758, together with
/
t
disilane Bu2MeSiSiPh3 was subjected to a dephenyl-
a strong peak at 601, which corresponds to the elimina-
tion of one silyl substituent and formation of the
cyclopropenylium ion in the gas phase. The UV
ationꢀbromination reaction with gaseous HBr in the
/
presence of AlBr3 catalyst to form the final precursor,
tBu2MeSiSiBr3 (1), in 92% yield (Scheme 1). The
germanium part, compound 2, was synthesized starting
from MeHSiCl2 which was reacted with tBuLi in pentane
t
to form Bu2MeSiH in 83% yield. This hydrosilane was
subsequently brominated with Br2 in CH2Cl2 to form the
t
corresponding bromide Bu2MeSiBr (94% yield), which
was then reacted with (p-tolyl)2GeCl2 and Li in THF to
form (p-tolyl)2Ge(SiMetBu2)2 in 62% yield. In the final
step, the last compound was treated with gaseous HCl in
the presence of catalytic AlCl3 to form the second
precursor, (tBu2MeSi)2GeCl2 (2), almost quantitatively
(Scheme 1).
The final Wurtz-type coupling reaction of precursors
¨
1 and 2 with metallic sodium was carried out in toluene
at room temperature. A dark red color quickly devel-
Scheme 2.
Scheme 1.

170
V.Ya. Lee et al. / Journal of Organometallic Chemistry 685 (2003) 168ꢀ176
/
quantitatively, and this isomerization could be easily
monitored by either 1H-NMR or UV spectroscopy,
which showed the disappearance of starting material 3
and clean formation of 4 in 6ꢀ8 h. Alternatively, 3 can
/
be isomerized quantitatively under thermal conditions:
heating a solution of 3 in mesitylene at 120 8C for 12 h
caused the complete conversion of 3 to 4. However, the
best way to achieve isomerization is the thermolysis of 3
without solvent in a sealed evacuated tube at 215 8C,
which is slightly above the melting point of 3 (205ꢀ
/
207 8C). Surprisingly, under such drastic conditions
isomeric 2-disilagermirene 4 was formed almost quanti-
tatively without formation of any side or decomposition
products. Nevertheless, both isomerization conditions
(either thermal or photochemical) gave an equilibrium
mixture of 4 (ꢀ
this ratio it was estimated that 4 is more stable than 3 by
3 kcal molꢂ1. This corresponds well to the results of
/
98ꢀ
/
99%) and 3 (ꢀ
/
1ꢀ/2%), and from
ꢀ
/
˚
theoretical calculations on the model H3Si-substituted
disilagermirenes at the B3LYP/DZd level [11], which
also showed that 2-disilagermirene is more stable than 1-
Fig. 1. Crystal designer view of 3. Selected bond lengths (A): Si(1)Ã
Si(2)ꢃ2.146(1), Ge(1)ÃSi(1)ꢃ2.415(1), Ge(1)ÃSi(2)ꢃ2.420(1),
Ge(1)ÃSi(5)ꢃ2.435(1), Ge(1)ÃSi(6)ꢃ2.432(1), Si(1)ÃSi(3)ꢃ
2.361(1), Si(2)ÃSi(4)ꢃ2.367 (1). Selected bond angles (8): Ge(1)Ã
Si(1)ÃSi(2)ꢃ63.76(3), Ge(1)ÃSi(2)ÃSi(1)ꢃ63.53(3), Si(1)ÃGe(1)Ã
Si(2)ꢃ52.71(3), Si(5)ÃGe(1)ÃSi(6)ꢃ123.33(3). Selected torsion angle
(8): Si(3)ÃSi(1)ÃSi(2)ÃSi(4) 37.0(2).
/
/
/
/
/
/
/
/
/
/
/
/
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/
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disilagermirene by ꢀ .
2.3 kcal molꢂ1
/
/
/
/
/
/
/
/
The NMR spectral data of 4 are more complicated
due to its unsymmetrical structure. In the 1H-NMR
spectrum of 4 there are three distinct resonances for the
methyl groups and four for the tert-butyl groups,
whereas in the 13C-NMR spectrum there are three sets
of signals for both the methyl and tert-butyl groups. The
29Si-NMR spectrum showed a total of five resonances:
three belong to silyl substituents, and the other two to
/
/
/
/
/
/
/
spectrum of 3 showed a long wavelength absorption
band at 469 nm, corresponding to the pꢀp* electronic
Si double bond. The crystal
/
transition due to the SiÄ
/
structure of 3 was determined by X-ray diffraction
analysis, which showed a triangular skeleton composed
120.1 ppm for the sp3-Si atom and
of one sp3-Ge atom and two sp2-Si atoms (Fig. 1). The
˚
Ge bond lengths of 2.415 and 2.420 A are
skeletal Si atoms: ꢂ
100.7 ppm for the sp2-Si atom.
The crystal structure of 4 was determined by X-ray
/
ꢁ
/
endocyclic SiÃ
/
˚
in the normal range for such bonds (2.384ꢀ
and they are intermediate between the typical SiÃ
GeÃGe bond lengths. The most important feature is the
SiÄSi double bond distance of 2.146(1) A, which is one
of the shortest SiÄSi bond lengths reported thus far
2.289 A) [10]. The geometry of substituents at
Si double bond has a trans-bent character with
/
2.457 A) [9],
diffraction analysis. This showed the expected cyclopro-
pene-type skeleton consisting of one sp3-hybridized Si
atom and two sp2 hybridized Si and Ge atoms, which
/
Si and
/
˚
/
form the SiÄ
/
Ge double bond. Unfortunately, owing to
/
the disorder problem between Si and Ge atoms (nearly
50:50% probability for each position), it was not
˚
(2.138ꢀ
/
the SiÄ
/
possible to determine the SiÄ
/
Ge double bond length,
Ge double bond was
the bending angle of 378. This may be the result of the
eclipsed conformation of the two silyl substituents on
the sp2-Si atoms, which can repulsively interact with the
silyl substituents on the Ge atom, causing the highly
pronounced trans bending geometry.
although the geometry of the SiÄ
/
found to be trans-bent with a bending angle of 40.38.
Calculations on the model H3Si-substituted 2-disilager-
mirene at the B3LYP/DZd level gave the length of the
˚
SiÄ
of 2.184 A for H2SiÄ
et al. [12].
/
Ge double bond as 2.178 A, almost the same as that
As is expected, and similar to the case of other
˚
/
GeH2 previously reported by Grev
disilenes, the SiÄ/Si double bond in 3 is highly reactive,
despite the bulky environment around it. The most
significant result is the allylic-type rearrangement of 3 to
form an isomeric tetrakis[di-tert-butyl(methyl)silyl]-2-
We have investigated other examples of the reactivity
of 3, first of all 1,2-addition and cycloaddition reactions
[8]. 1,2-Addition of a variety of reagents to SiÄ
/
Si double
disilagermirene (4), which no longer has a SiÄ
/
Si double
bonds is well documented [13]. Our case was not
exceptional, and 1-disilagermirene 3 easily undergoes
bond, but instead has a SiÄGe double bond. This
/
isomerization may proceed either photochemically or
thermally (Scheme 2). Thus, photolysis of the solution
of 3 in C6D6 with a high-pressure Hg lamp with light of
wavelength longer than 300 nm produced 4 nearly
addition across the SiÄ
/
Si double bond, despite the
presence of very bulky substituents. This method gave
us the unique opportunity for easy and fast access to a
number of saturated three-membered ring compounds

V.Ya. Lee et al. / Journal of Organometallic Chemistry 685 (2003) 168ꢀ
/176
171
of different heavier Group 14 elements. In this paper, we
describe the new reactions of 1-disilagermirene 3 with
methyl iodide and benzyl alcohol. Reaction of 3 with
MeI in benzene solution proceeds very quickly to give
the corresponding 1,2-adduct, trans-1,2,3,3-tetrakis[di-
tert-butyl(methyl)silyl]-1-iodo-2-methyldisilagermirane
(5), isolated quantitatively as yellow crystals (Scheme 3).
The crystal structure analysis of 5 showed a disilager-
mirane skeleton with the anticipated trans arrangement
of methyl group and iodine atom (Fig. 2). The reaction
of benzyl alcohol with 1-disilagermirene 3 proceeded
more slowly and was complete after stirring overnight at
room temperature in benzene solution (Scheme 3). The
structure of the single product 6, trans-1-benzyloxy-
1,2,3,3-tetrakis[di-tert-butyl(methyl)silyl]disilagermir-
ane, isolated as yellow crystals in 70% yield, was
determined by NMR and X-ray diffraction analysis,
which showed that in this case the reaction also
proceeded stereospecifically as trans addition across
˚
the SiÄ
/
Si double bond. It is worth mentioning here
Fig. 2. Crystal designer view of 5. Selected bond lengths (A): Si(1)Ã
Si(2)ꢃ2.3696(13), Ge(1)ÃSi(1)ꢃ2.4749(10), Ge(1)ÃSi(2)ꢃ
2.4762(10), Si(1)ÃSi(5)ꢃ2.4239(14), Si(2)ÃSi(6)ꢃ2.4220(14), Ge(1)Ã
Si(3)ꢃ2.4713(11), Ge(1)ÃSi(4)ꢃ2.4813(11), I(1)ÃSi(1)ꢃ2.5198(10).
Selected bond angles (8): Si(1)ÃGe(1)ÃSi(2)ꢃ57.19(3), Si(2)ÃSi(1)Ã
Ge(1)ꢃ61.43(3), Si(1)ÃSi(2)ÃGe(1)ꢃ61.38(3).
/
/
/
/
/
/
that earlier mechanistic studies of the reaction of
transient disilenes with simple alcohols established the
syn addition pathway [14]. In the present case the
/
/
/
/
/
/
/
/
/
/
/
/
/
/
/
predominant trans addition of PhCH2OH to the SiÄ
/
Si
/
/
/
/
bond should be definitely ascribed to steric reasons,
which favor the formation of the less sterically hindered
trans isomer [15].
Cycloaddition of unsaturated compounds and 1-
disilagermirene 3 provides effective access to bicyclic
fused compounds having a disilagermirane fragment.
We have previously reported reactions of 3 with
carbonyl compounds (such as PhCHO), which proceed
stereospecifically the cis-1,2-adduct 7, cis-1,2,3,3-tetra-
kis[di-tert-butyl(methyl)silyl]-1-(1-phenylvinyloxy)disi-
lagermirane, which was identified by NMR
spectroscopy (Scheme 4). This product is the result of
1,2-addition of 1-phenylvinyl alcohol (the enol form of
acetophenone) to the SiÄ
/
Si double bond. As can be
seen, such cis addition is consistent with the aforemen-
tioned syn addition of simple alcohols to transient
disilenes [14]. Nevertheless, the cis isomer is not stable
under the reaction conditions, and gradually isomerized
in a benzene solution during 2 days at room temperature
to the thermodynamically more stable trans isomer 7,
which was isolated as pale yellow crystals (Scheme 4).
as the expected [2ꢁ2] cycloadditions stereospecifically
/
to form bicyclic compounds as a single stereoisomer
[16]. We have observed another reaction mode in the
case of enolizable carbonyl compounds having a-hydro-
gen atoms [17]. Thus, acetophenone smoothly reacts
with 3 in benzene solution at room temperature to form
Scheme 3.

172
V.Ya. Lee et al. / Journal of Organometallic Chemistry 685 (2003) 168ꢀ
/176
Scheme 4.
The reason for such an isomerization seems to be a
decrease in steric hindrance on going from cis to trans
isomers. As can be seen, similar to the case of the
reaction of 3 with benzyl alcohol, the final formation of
the trans isomer is always favorable. The structure of
trans-7 was determined by means of all spectral data
and X-ray analysis (Fig. 3), which showed the disila-
germirane skeleton with the trans arrangement of H and
MB 150B-G glove-box. All solvents were predried over
sodium benzophenone ketyl and finally dried and
degassed over potassium mirror in vacuum prior to
use. NMR spectra were recorded on a Bruker AC-
300FT NMR spectrometer (1H-NMR at 300.13 MHz;
13C-NMR at 75.47 MHz; 29Si-NMR at 59.63 MHz).
GCꢀMS spectra were obtained using Shimadzu GCMS-
/
QP5000 instrument and direct mass-spectra were ob-
tained on JEOL JMS SX-102 instrument. UV-spectra
H2CÄ/C(Ph)O substituents. Thus, the reaction of 3 with
acetophenone represents a new reaction mode for the
interaction of disilenes with carbonyl compounds: an
‘ene’-type reaction resulting in the formation of the
corresponding enol ether products instead of the only
were recorded on a Shimadzu UV-3150 UVꢀVis spec-
/
trophotometer in hexane. Elemental analysis was per-
formed at the Analytical Center of Tohoku University
(Sendai, Japan).
previously known and commonly recognized [2ꢁ
/
2]
(p-Tolyl)2GeCl2 was synthesized by the reaction of (p-
tolyl)MgCl (prepared from p-CH3C6H4Cl and Mg in
THF) and GeCl4 in THF by the slightly modified
cycloaddition pathway [13aꢀd].
/
t
experimental procedure [18]. Bu2SiF2 was prepared by
t
the reaction of SiF4 with BuLi in pentane according to
3. Experimental
t
t
Ref. [19], Bu2MeSiF by the methylation of Bu2SiF2
with MeLi in Et2O, tBu2MeSiH by the reaction of
MeSiHCl2 with tBuLi according to Ref. [20], and
tBu2MeSiBr by the bromination of tBu2MeSiH with
Br2 in CH2Cl2 according to Ref. [21].
3.1. General procedures
All experiments were performed using high-vacuum
line techniques or in an argon atmosphere of MBRAUN
t
3.2. Synthesis of Bu2MeSiSiPh3
A solution of Ph3SiCl (40 g, 0.13 mol) in THF (80 ml)
was slowly added at room temperature to a suspension
of Li (9.5 g, 1.36 mol) in THF (240 ml) and reaction
mixture was stirred overnight at room temperature. The
resulting Ph3SiLi was added dropwise to the solution of
tBu2SiMeF (24 g, 0.14 mol) in THF (150 ml). The
reaction was complete in 2 days refluxing and after usual
work-up, Kugelrohr distillation gave 47 g (83%) of
1
tBu2MeSiSiPh3. B.p. 170ꢀ
/
175 8C/0.2 mmHg; H-NMR
(C6D6) d 0.44 (s, 3H, Me), 1.00 (s, 18H, tBu), 7.14ꢀ
and 7.77ꢀ
7.80 (m, 15H, Ph); 13C-NMR (C6D6) d ꢂ
21.6, 30.2, 128.1, 129.1, 137.3, 137.6; 29Si-NMR (C6D6)
d ꢂ20.1, 1.2; GCꢀ
MS (m/z) 416 [Mꢁ], 359 (Mꢁ
tBu).
/7.16
/
/4.7,
/
/
Ã
/
t
3.3. Synthesis of Bu2MeSiSiBr3 (1)
˚
Fig. 3. Crystal designer view of trans-7. Selected bond lengths (A):
Si(1)ÃSi(2)ꢃ2.3383(6), Ge(1)ÃSi(1)ꢃ2.4901(5), Ge(1)ÃSi(2)ꢃ
2.4524(5), Ge(1)ÃSi(3)ꢃ2.4612(5), Ge(1)ÃSi(4)ꢃ2.4586(5), Si(1)Ã
Si(5)ꢃ2.3978(6), Si(2)ÃSi(6)ꢃ2.3944(6), Si(1)ÃO(1)ꢃ1.6929(12). Se-
lected bond angles (8): Si(2)ÃGe(1)ÃSi(1)ꢃ56.467(14), Si(2)ÃSi(1)Ã
Ge(1)ꢃ60.951(15), Si(1)ÃSi(2)ÃGe(1)ꢃ62.582(16).
/
/
/
/
/
/
Gaseous HBr was slowly bubbled at room tempera-
ture into the solution of tBu2MeSiSiPh3 (9.5 g, 22.9
mmol) in benzene (40 ml) containing catalytic amount
of AlBr3. After the reaction was complete (2 h), the
/
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/
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/

V.Ya. Lee et al. / Journal of Organometallic Chemistry 685 (2003) 168ꢀ
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173
solvent was evaporated and the residue was distilled by
t
Kugelrohr distillation to give 8.9 g (92%) of Bu2MeSi-
solvent in vacuum the residue was recrystallized from
hexane at ꢂ30 8C to give 3 as dark-ruby hexagonal-
/
SiBr3 (1) as colorless solids. B.p. 80ꢀ
1H-NMR (C6D6) d 0.11 (s, 3H, Me), 1.06 (s, 18H, tBu);
13C-NMR (C6D6) d ꢂ8.2, 22.0, 29.3; 29Si-NMR (C6D6)
d ꢂ7.5, 10.3; GCꢀ
MS (m/z): 371 (Mꢁ tBu).
/
110 8C/0.2 mmHg;
shaped crystals (2.36 g, 37% yield). M.p. 205ꢀ207 8C;
/
1H-NMR (C6D6) d 0.46 (s, 6H, Me), 0.49 (s, 6H, Me),
1.22 (s, 36H, tBu), 1.28 (s, 36H, tBu); 13C-NMR (C6D6)
/
d ꢂ
d 18.7, 25.6, 107.8 (SiÄ
(Mꢁ tBu, 0.05), 601 (Mꢁ
UV (hexane) lmax nmꢂ1 (o) 230 (33 400), 259 (18 200),
308 (6300), 469 (1900). Anal. Found: C, 57.42; H, 10.75.
Calc. for C36H84GeSi6: C, 57.03; H, 11.17%.
/
4.5, ꢂ
2.2, 22.2, 23.6, 30.0, 31.0; 29Si-NMR (C6D6)
/
/
/
Ã
/
/
Si); MS (m/z) 758 (Mꢁ, 0.1), 701
SiMetBu2, 2.6), 73 (100);
3.4. Synthesis of (tBu2MeSi)2Ge(p-tolyl)2
Ã
/
Ã
/
A mixture of tBu2SiMeBr (3.02 g, 12.7 mmol) and (p-
tolyl)2GeCl2 (1.4 g, 4.3 mmol) in THF (15 ml) was
slowly added at ꢂ10 8C to a suspension of Li (0.18 g,
/
25.7 mmol) in THF (50 ml). After stirring overnight at
room temperature an additional amount of tBu2SiMeBr
(2.03 g, 8.6 mmol) in THF (7 ml) was added and the
reaction mixture was refluxed for 1 day. After usual
work-up, Kugelrohr distillation gave 1.52 g (62%) of
(tBu2MeSi)2Ge(p-tolyl)2 as a colorless glass solidifying
3.7. Synthesis of 1,1,2,3-tetrakis[di-tert-
butyl(methyl)silyl]-2-disilagermirene (4)
1-Disilagermirene 3 (50 mg, 0.07 mmol) was heated at
215 8C for 30 min in a sealed evacuated tube to form
quantitatively 2-disilagermirene 4 as a pure compound.
upon standing. B.p. 200ꢀ
/
220 8C/0.2 mmHg, m.p. 129ꢀ
/
1
131 8C; H-NMR (C6D6) d 0.60 (s, 6H, Me), 1.01 (s,
t
M.p. 194ꢀ
/
196 8C; 1H-NMR (C6D6) d 0.43 (s, 6H, 2Me),
36H, Bu), 2.11 (s, 6H, Me Ã
4H, Harom) and 7.99 (d, Jꢃ
NMR (C6D6) d ꢂ2.4, 21.4, 23.7, 30.7, 128.8, 137.4,
137.9, 138.4; 29Si-NMR (C6D6) d 14.5; MS (m/z): 413
(Mꢁ SiMetBu2).
/
C6H4), 7.06 (d, Jꢃ
/
7.9 Hz,
7.9 Hz, 4H, Harom); 13C-
t
/
0.48 (s, 3H, Me), 0.53 (s, 3H, Me), 1.20 (s, 18H, Bu),
1.22 (s, 18H, tBu), 1.29 (s, 18H, tBu), 1.30 (s, 18H, tBu);
/
13C-NMR (C6D6) d ꢂ
/
4.6, ꢂ
23.4, 29.9, 30.0, 31.3; 29Si-NMR (C6D6) d ꢂ
27.8, 39.5, 100.7; MS (m/z) 758 (Mꢁ, 3), 701 (Mꢁ
tBu, 1.5), 601 (Mꢁ SiMetBu2, 32), 73 (100); UV
/
3.9, ꢂ
/
2.2, 22.2, 22.8,
Ã
/
/
120.1, 6.9,
3.5. Synthesis of (tBu2MeSi)2GeCl2 (2)
Ã
/
Ã
/
(hexane) lmax nmꢂ1 (o) 235 (58 100), 263 (27 000), 301
(11 600), 395 (1600), 467 (4200). Anal. Found: C, 56.53;
H, 10.84. Calc. for C36H84GeSi6: C, 57.03; H, 11.17%.
Gaseous HCl was bubbled into a solution of (tBu2-
MeSi)2Ge(p-tolyl)2 (0.5 g, 0.88 mmol) in benzene (10
ml), containing catalytic amount of AlCl3, at room
temperature. In 2.5 h the reaction was complete.
Benzene was evaporated and the residue was extracted
with dry hexane and filtered through Celite. After
evaporation of filtrate practically pure product (tBu2-
MeSi)2GeCl2 (2) was obtained in nearly quantitative
yield. 1H-NMR (C6D6) d 0.31 (s, 6H, Me), 1.17 (s, 36H,
3.8. Reaction of 1,2,3,3-tetrakis[di-tert-
butyl(methyl)silyl]-1-disilagermirene (3) with methyl
iodide
tBu); 13C-NMR (C6D6) d ꢂ6.1, 23.3, 29.7; 29Si-NMR
/
Dry methyl iodide (0.2 ml, 50-fold excess) was
vacuum transferred to a solution of 3 (48 mg, 0.06
mmol) in dry deuterobenzene (0.5 ml) in NMR tube,
and then NMR tube was sealed under vacuum. The
reaction progress was monitored by NMR spectroscopy,
which showed that the reaction was complete in 1 h at
room temperature to form a single product 5. This
product was quantitatively isolated as bright-yellow
(C6D6) d 26.0. MS (m/z): 458 [Mꢁ], 423 (Mꢁ
Cl), 266
Ã
/
[(tBu2MeSi)GeCl].
3.6. Synthesis of 1,2,3,3-tetrakis[di-tert-
butyl(methyl)silyl]-1-disilagermirene (3)
t
A mixture of Bu2MeSiSiBr3 (7.85 g, 18.5 mmol) and
(tBu2MeSi)2GeCl2 (3.90 g, 8.5 mmol) in dry toluene (50
ml) was slowly added dropwise to a finely cutted pieces
of sodium (4.3 g, 187 mmol) in dry toluene (50 ml) at
room temperature. During the addition the exothermic
reaction took place and the reaction mixture became
dark-red. The reaction progress was monitored by GC-
analysis, which showed disappearance of the starting
tBu2MeSiSiBr3 in 7 h stirring at room temperature. At
that time the reaction was stopped and the reaction
mixture was filtered off from the excess of sodium and
inorganic salts through Celite. After evaporation of
crystals after evaporation of solvent and excess methyl
1
iodide. M.p. 189ꢀ
/
191 8C; H-NMR (C6D6) d 0.29 (s,
3H, Me), 0.34 (s, 3H, Me), 0.47 (s, 3H, Me), 0.75 (s, 3H,
Me), 0.92 (s, 3H, Me), 1.21 (s, 18H, 2tBu), 1.25 (s, 9H,
t
t
tBu), 1.27 (s, 9H, Bu), 1.32 (s, 9H, Bu), 1.34 (s, 9H,
tBu), 1.37 (s, 9H, Bu), 1.40 (s, 9H, Bu); 13C-NMR
(C6D6) d ꢂ2.8, ꢂ2.0, 3.1, 3.2, 5.8, 23.1, 23.2, 23.36,
23.44, 23.7, 23.9, 24.0, 24.3, 30.6, 30.76, 30.83, 30.9,
31.1, 31.3, 31.5, 32.5; 29Si-NMR (C6D6) d ꢂ
92.2, ꢂ
80.3, 13.7, 16.3, 32.9, 35.9.
t
t
/
/
/
/

174
V.Ya. Lee et al. / Journal of Organometallic Chemistry 685 (2003) 168ꢀ176
/
3.9. Reaction of 1,2,3,3-tetrakis[di-tert-
butyl(methyl)silyl]-1-disilagermirene (3) with benzyl
alcohol
trans-isomer was quantitatively isolated by the recrys-
tallization from hexane as pale-yellow crystals. M.p.
1
179ꢀ
/
181 8C; H-NMR (C6D6) d 0.23 (s, 3H, Me), 0.39
(s, 3H, Me), 0.41 (s, 3H, Me), 0.47 (s, 3H, Me), 1.22 (s,
t
9H, Bu), 1.23 (s, 9H, Bu), 1.26 (s, 9H, Bu), 1.28 (s,
t
t
Dry benzyl alcohol (9 mg, 0.08 mmol) and 3 (56 mg,
0.07 mmol) were placed in a glove-box to the glass tube
with a magnetic stirring bar, then dry deuterobenzene
(0.6 ml) was vacuum-transferred into this tube and tube
was sealed under vacuum. After 1 day stirring at room
temperature the reaction was complete to form nearly
quantitatively one product 6. This product was isolated
after evaporation of solvent by the recrystallization
t
t
t
9H, Bu), 1.29 (s, 9H, Bu), 1.30 (s, 9H, Bu), 1.31 (s,
18H, 2tBu), 3.01 (s, 1H, SiÃ
H), 5.07 (d, Jꢃ1.6 Hz, 1H,
CÄCH2), 5.14 (d, Jꢃ1.6 Hz, 1H, CÄCH2), 7.06 (t, Jꢃ
7.2 Hz, 1H, Hpara), 7.19 (t, Jꢃ7.2 Hz, 2H, Hmeta), 7.69
(d, Jꢃ 4.24,
7.2 Hz, 2H, Hortho); 13C-NMR (C6D6) d ꢂ
4.21, ꢂ0.2, 0.1, 22.3 (2C), 22.5 (2C), 22.7, 23.1, 23.5,
25.0, 30.4, 30.5, 30.6, 30.7, 31.1, 31.3, 31.5, 32.0, 94.1
(CÄCH2), 126.8, 128.3, 128.6, 138.5, 159.3 (C ÄCH2);
29Si-NMR (C6D6) d ꢂ
142.2 (SiÃH), ꢂ17.6 (SiÃO),
17.2, 23.0, 28.8, 32.4; MS (m/z) 878 (Mꢁ, 11%), 758
(Mꢁ
CH3COPh, 5%). Anal. Found: C, 60.50; H,
/
/
/
/
/
/
/
/
/
ꢂ
/
/
from hexane as yellow crystals (45 mg, 70%). M.p.
1
/
/
79ꢀ
/
81 8C; H-NMR (C6D6) d 0.31 (s, 3H, Me), 0.33 (s,
/
/
/
/
3H, Me), 0.35 (s, 3H, Me), 0.46 (s, 3H, Me), 1.20 (s, 9H,
tBu), 1.24 (s, 9H, tBu), 1.27 (s, 18H, 2tBu), 1.28 (s, 18H,
Ã
/
t
t
2tBu), 1.30 (s, 9H, Bu), 1.35 (s, 9H, Bu), 2.90 (s, 1H,
10.45. Calc. for C44H92GeOSi6: C, 60.17; H, 10.56%.
SiÃ
13.0 Hz, 1H, PhCH2O), 7.07 (t, Jꢃ
7.21 (t, Jꢃ7.7 Hz, 2H, Hmeta), 7.46 (d, Jꢃ
ortho); 13C-NMR (C6D6) d ꢂ
4.6, ꢂ4.3, ꢂ
/
H), 4.74 (d, Jꢃ
/
13.0 Hz, 1H, PhCH2O), 5.09 (d, Jꢃ
7.7 Hz, 1H, Hpara ,
7.7 Hz, 2H,
0.6, 0.1,
/
/
)
/
/
3.11. Crystal structure analyses of the compounds 3, 5,
and trans-7
H
/
/
/
22.0, 22.4, 22.6, 22.7, 22.9, 23.0, 23.3, 24.7, 30.4 (2C),
30.5, 30.7, 30.9, 31.2 (2C), 31.8, 73.0 (PhCH2O), 126.7,
The single crystals of compounds 3 and trans-7 for X-
ray diffraction study were grown from the saturated
hexane solutions, single crystals of compound 5 were
grown from the saturated benzene solution. Diffraction
data were collected at 150 K for 3, 120 K for 5 and
trans-7 on a Mac Science DIP2030 Image Plate Dif-
fractometer with a rotating anode (50 kV, 90 mA)
127.4, 128.5, 141.0; 29Si-NMR (C6D6) d ꢂ
/
148.9 (Si Ã
OCH2Ph), 15.3, 20.8, 28.6, 32.1; MS (m/
z) 866 (Mꢁ, 0.2%), 775 (Mꢁ CH2Ph, 1%), 617 (Mꢁ
SiMetBu2Ã
PhCH3, 3.5%), 91 (PhCH2, 100%).
/
H), ꢂ
/
7.4 (Si Ã
/
Ã
/
Ã
/
/
3.10. Reaction of 1,2,3,3-tetrakis[di-tert-
butyl(methyl)silyl]-1-disilagermirene (3) with
acetophenone
employing graphite-monochromatized Moꢀ
/
Ka radia-
0.71070 A). The structures were solved by the
˚
tion (lꢃ
/
direct method, using SIR-92 program [22], and refined by
the full-matrix least-squares method by SHELXL-97
program [23]. The crystal data and experimental para-
meters for the X-ray analysis of 3, 5, and trans-7 are
listed in Table 1. Crystallographic data of 3 have been
deposited with the American Chemical Society (see Ref.
[7]). This material is available free of charge via the
Internet at http://www.pubs.acs.org. Crystallographic
data of trans-7 have been deposited with the Cambridge
Crystallographic Data Centre. CCDC No. 170581.
Copies of this information may be obtained free of
charge from the Director, CCDC, 12 Union Road,
Dry acetophenone (20.6 mg, 0.17 mmol) was vacuum
transferred to a solution of 3 (110 mg, 0.15 mmol) in dry
deuterobenzene (0.7 ml) in NMR tube, and then NMR
tube was sealed under vacuum. The reaction progress
was monitored by NMR spectroscopy. In 2 h at room
temperature the reaction was complete and exclusively
one product (cis-adduct) 7 was detected. NMR spectra
1
of cis-isomer in the reaction mixture: H-NMR (C6D6)
d 0.28 (s, 3H, Me), 0.29 (s, 3H, Me), 0.36 (s, 3H, Me),
t
t
0.45 (s, 3H, Me), 1.16 (s, 9H, Bu), 1.18 (s, 9H, Bu),
t
t
t
1.20 (s, 9H, Bu), 1.24 (s, 9H, Bu), 1.26 (s, 9H, Bu),
1.29 (s, 18H, 2tBu), 1.34 (s, 9H, tBu), 3.44 (s, 1H, SiÃ
H),
5.07 (unresolved doublet, 1H, CÄCH2), 5.14 (unresolved
doublet, 1H, CÄCH2), 7.03ꢀ7.15 (m, 3H, Hpara Hmeta),
7.65 (d, Jꢃ
7.6 Hz, 2H, Hortho); 13C-NMR (C6D6) d
3.9, ꢂ3.6, ꢂ1.9, 1.4, 22.25, 22.32, 22.4, 22.66, 22.69,
23.0, 23.5, 23.8, 30.2, 30.5, 30.7, 30.8, 31.0, 31.1, 31.3,
32.0, 94.1 (CÄCH2), 126.7, 128.2, 128.5, 138.8, 157.3
(C Ä 145.6 (SiÃH), ꢂ19.0
CH2); 29Si-NMR (C6D6) d ꢂ
(SiÃO), 19.2, 24.1, 29.3, 31.5.
/
Cambridge CB2 1EZ, UK (Fax: ꢁ44-1223-336033; e-
/
/
mail: deposit@ccdc.cam.ac.uk).
/
/
ꢁ
/
/
ꢂ
/
/
/
Acknowledgements
/
/
/
/
/
This work was supported by a Grant-in-Aid for
Scientific Research (Nos. 13029015, 13440185,
14078204) from the Ministry of Education, Culture,
Sports, Science and Technology of Japan and TARA
(Tsukuba Advanced Research Alliance) fund, and COE
(Center of Excellence) program.
/
cis-Isomer 7 gradually isomerized to a trans-isomer 7;
in 1 day at room temperature the ratio cis-isomer:trans-
isomerꢃ
/
50:50%, in 2 days at room temperature only
trans-isomer 7 was detected by NMR spectroscopy. This

V.Ya. Lee et al. / Journal of Organometallic Chemistry 685 (2003) 168ꢀ
/176
175
Table 1
Crystallographic data and experimental parameters for the crystal structure analysis of 3,5, and trans-7
3
5
trans-7
Empirical formula
Formula mass (g molꢂ1
Collection temperature (K)
C
36H84GeSi6
C37H87GeISi6
987.20
120
C44H92GeOSi6
878.31
120
)
758.16
150
˚
l (Moꢀ
/
Ka) (A)
0.71070
Monoclinic
P21/c
0.71070
Monoclinic
P21/n
0.71070
Monoclinic
P21/c
Crystal system
Space group
Unit cell parameters
˚
a (A)
˚
24.131(1)
11.6630(6)
17.760(1)
90
13.0950(4)
20.2620(6)
20.1520(3)
90
11.0980(2)
20.9340(5)
22.8640(6)
90
b (A)
˚
c (A)
a (8)
b (8)
g (8)
110.362(4)
90
93.974(2)
90
96.8960(10)
90
3
˚
V (A )
4686.0(5)
4
1.075
5334.1(2)
4
1.218
5273.5(2)
4
1.106
Z
Dcalc (g cmꢂ3
)
m (mmꢂ1
F(0 0 0)
)
0.829
1664
1.314
2080
0.746
1920
Crystal dimensions (mm)
u Range (8)
Index ranges
0.4ꢄ
2.29ꢀ
05h 5
05k 5
235
/
0.3ꢄ
27.93
31
/
0.3
0.2ꢄ
2.06ꢀ
05h 5
05k 5
265
/
0.2ꢄ
27.89
17
/
0.2
0.4ꢄ
2.09ꢀ
05h 5
05k 5
305
/
0.3ꢄ
27.93
13
/
0.3
/
/
/
/
/
/
/
/
/
/
/15
/
/26
/
/27
ꢂ
/
/
l 5
/
21
ꢂ
/
/
l 5
/
26
ꢂ
/
/
l 529
/
Collected reflections
Independent reflections
Rint
46 096
10 779
0.101
10 779
389
53 594
12 709
0.0520
12 709
467
52 312
11 951
0.0290
11 951
471
Reflections used
Parameters
a
S
Weight parameters a/b
1.044
1.068
1.028
b
0.0907/4.6977
0.0589
0.1691
0.0860/25.1640
0.0630
0.1763
0.0547/2.7170
0.0348
0.0953
c
R1 [I ꢁ
/
2s(I)]
wR2 (all data)
d
ꢂ3
˚
Maximum/minimum residual electron density (e A
)
1.278/ꢂ
/0.987
2.121/ꢂ
/2.359
0.405/ꢂ0.794
/
a
Sꢃ
/
{a[w(F2oꢂ
wꢃ
1/[s2(F2o)ꢁ
R1ꢃ jFcjj/ajFoj.
ajjFojꢂ
wR2ꢃ
{a[w(Fo2 ꢂF2c)2]/a[w(F2o)2]}0.5
/
F2c)2]/(nꢂ
/
p)}0.5, n, no. of reflections; p, no. of parameters.
b
c
/
/
(aP)2ꢁ
/bP], with Pꢃ
/
(F2oꢁ2F2c)/3.
/
/
/
d
/
/
.
(2000) 12604. (b) V. Ya. Lee, T. Matsuno, M. Ichinohe, A.
Sekiguchi, Heteroatom. Chem. 12 (2001) 223. (c) V. Ya. Lee, M.
Ichinohe, A. Sekiguchi, J. Organomet. Chem. 636 (2001) 41. (d)
V. Ya. Lee, M. Ichinohe, A. Sekiguchi. Main Group Met. Chem.
25 (2002) 1. (e) V. Ya. Lee, M. Ichinohe, A. Sekiguchi, J. Am.
Chem. Soc. 124 (2002) 9962.
References
[1] F.A. Carey, R.J. Sundberg, Advanced Organic Chemistry, Part A:
Structure and Mechanisms, fourth ed., Kluwer Academic/Plenum
Publishers, New York, 2000.
[2] (a) V.Ya. Lee, A. Sekiguchi, in: Z. Rappoport (Ed.), The
Chemistry of Organic Germanium, Tin and Lead Compounds,
Part 1 (Chapter 14), Wiley, Chichester, 2002, p. 2 (Chapter 14);
(b) A. Sekiguchi, V.Ya. Lee, Chem. Rev. 103 (2003) 1429.
[3] A. Sekiguchi, H. Yamazaki, C. Kabuto, H. Sakurai, S. Nagase, J.
Am. Chem. Soc. 117 (1995) 8025.
[9] K.M. Baines, W.G. Stibbs, Coord. Chem. Rev. 145 (1995) 157.
[10] M. Kaftory, M. Kapon, M. Botoshansky, in: Z. Rappoport, Y.
Apeloig (Eds.), The Chemistry of Organic Silicon Compounds,
Part 1, Vol. 2; Wiley, Chichester, 1998 (Chapter 5). See also: T.A.
Schmedake, M. Haaf, Y. Apeloig, T. Muller, S. Bukalov, R.
¨
West, J. Am. Chem. Soc. 121 (1999) 9479.
[11] All theoretical calculations were performed with GAUSSIAN 98
program package.
[4] T. Iwamoto, C. Kabuto, M. Kira, J. Am. Chem. Soc. 121 (1999)
886.
[5] M. Ichinohe, T. Matsuno, A. Sekiguchi, Angew. Chem. Int. Ed.
38 (1999) 2194.
[6] N. Wiberg, H.-W. Lerner, S.-K. Vasisht, S. Wagner, K. Kar-
[12] R.S. Grev, H.F. Schaefer, III, K.M. Baines, J. Am. Chem. Soc.
112 (1990) 9458.
[13] For the reviews on disilenes, see: (a) R. West, Angew. Chem. Int.
Ed. Engl. 26 (1987) 1201. (b) G. Raabe, J. Michl, The Chemistry
of Organic Silicon Compounds; S. Patai, Z. Rappoport, (Eds.),
Wiley, Chichester, 1989, Part 2, Chapter 17. (c) T. Tsumuraya,
S.A. Batcheller, S. Masamune, Angew. Chem. Int. Ed. Engl. 30
(1991) 902. (d) R. Okazaki, R. West, Adv. Organomet. Chem. 39
(1996) 231. (e) M. Kira, T. Iwamoto, J. Organomet. Chem. 611
aghiosoff, H. Noth, W. Ponikwar, Eur. J. Inorg. Chem. (1999)
¨
1211.
[7] V.Ya. Lee, M. Ichinohe, A. Sekiguchi, N. Takagi, S. Nagase, J.
Am. Chem. Soc. 122 (2000) 9034.
[8] For the reactivity of disilagermirenes and their derivatives, see: (a)
V. Ya. Lee, M. Ichinohe, A. Sekiguchi, J. Am. Chem. Soc. 122

176
V.Ya. Lee et al. / Journal of Organometallic Chemistry 685 (2003) 168ꢀ176
/
(2000) 236. (f) M. Weidenbruch, The Chemistry of Organic
Silicon Compounds; Z. Rappoport, Y. Apeloig, Eds., Wiley,
Chichester, 2001, Vol. 3, Chapter 5. (g) M. Weidenbruch, J.
Organomet. Chem. 646 (2002) 39. (h) R. West, Polyhedron, 21
(2002) 467.
[16] V.Ya. Lee, M. Ichinohe, A. Sekiguchi, Chem. Lett. (2001) 728.
[17] V.Ya. Lee, M. Ichinohe, A. Sekiguchi, Chem. Commun. (2001)
2146.
[18] A. El-Maradny, H. Tobita, H. Ogino, Organometallics 15 (1996)
4954.
[14] A. Sekiguchi, I. Maruki, H. Sakurai, J. Am. Chem. Soc. 115
(1993) 11460.
[19] E.M. Dexheimer, L. Spialter, L.D. Smithson, J. Organomet.
Chem. 102 (1975) 21.
[15] The crystal structure of the compound 6 was unequivocally
determined by X-ray diffraction analysis to show the GeSi2
three-membered ring skeleton with a trans-arrangement of H-
and PhCH2O-substituents. Nevertheless we do not discuss this
structure in the paper, because the refinement was not sufficiently
good due to the positional disorder of one of the silyl substituents
at Ge atom.
[20] T.J. Barton, C.R. Tully, J. Org. Chem. 43 (1978) 3649.
[21] N. Wiberg, Ch.-K. Kim, Chem. Ber. 119 (1986) 2980.
[22] A. Altomare, G. Cascarano, C. Giacovazzo, A. Guagliardi, M.C.
Burla, G. Polidori, M. Camalli, J. Appl. Crystallogr. 27 (1994)
435.
[23] G.M. Sheldrick, SHELXL-97, Program for Crystal Structure
Refinement, University of Gottingen, Germany, 1997.
¨