Reaction of disilagermirenes with phenylacetylene: From a germasilene -Ge=Si- To a metalladiene of the type -Si=Ge-C=C-

Article abstract of DOI:10.1016/S0022-328X(01)00807-5

The reaction of tetrakis[di-tert-butyl(methyl)silyl]-2-disilagermirene (1b) with phenylacetylene at room temperature produced highly air- and moisture-sensitive bright orange crystals of 1,1,2,3-tetrakis[di-tert-butyl(methyl)silyl]-4-phenyl-1,2-disila-3-

Full text of DOI:10.1016/S0022-328X(01)00807-5

Journal of Organometallic Chemistry 636 (2001) 41–48
www.elsevier.com/locate/jorganchem
Reaction of disilagermirenes with phenylacetylene: from a
germasilene ꢀGeꢁSiꢀ to a metalladiene of the type ꢀSiꢁGeꢀCꢁCꢀ
Vladimir Ya. Lee, Masaaki Ichinohe, Akira Sekiguchi *
Department of Chemistry, Uni6ersity of Tsukuba, Tsukuba, Ibaraki 305-8571, Japan
Received 18 February 2001; accepted 11 March 2001
Dedicated to Professor Oleg Nefedov on the occasion of his 70th birthday and for the recognition of his outstanding contribution in the field
of Group 14 elements chemistry.
Abstract
The reaction of tetrakis[di-tert-butyl(methyl)silyl]-2-disilagermirene (1b) with phenylacetylene at room temperature produced
highly air- and moisture-sensitive bright orange crystals of 1,1,2,3-tetrakis[di-tert-butyl(methyl)silyl]-4-phenyl-1,2-disila-3-germacy-
clopenta-2,4-diene (2b), which represents a previously unknown metalladiene with one SiꢁGe and one CꢁC double bond. The
crystal structure of 2b was determined by X-ray crystallography, which showed a trans-bent configuration around the SiꢁGe
,
double bond with a bond length of 2.250(1) A. The reaction mechanism to form 2b, the question of conjugation of the two double
bonds in a cyclopentadiene ring of 2b, as well as its reactivity are discussed. The reaction of tetrakis[di-tert-butyl(methyl)silyl]-1-
disilagermirene (1a), which is an isomer of 1b, with phenylacetylene is also examined. © 2001 Elsevier Science B.V. All rights
reserved.
Keywords: Conjugation; Cycloaddition; Germasilene; Metalladiene; Phenylacetylene; Silole
tremely interesting objects for studying the degree of
conjugation of the two double bonds and reactivity
aspects, which can also be different from those of their
carbon analogues. Nevertheless, in spite of the evidently
great synthetic challenge, there are very few examples
of such compounds, which can be explained by the
difficulties in their preparation. Thus, among all of the
possible structures, only two examples have been re-
ported to the present time: symmetrical hexakis(2,4,6-
triisopropylphenyl)tetrasilabuta-1,3-diene [2] and hex-
akis(2,4,6-triisopropylphenyl)tetragermabuta-1,3-diene
[3].
Here we report the synthesis, full characterization,
crystal structure and some aspects of the reactivity of
the first metalladiene consisting of Group 14 elements
of the type ꢀSiꢁGeꢀCꢁCꢀ, in which the SiꢁGe double
bond was structurally characterized for the first time
[4]. This compound also represents a previously un-
known metallole with an unsymmetrically composed
skeleton. The reaction mechanism to form the metalla-
diene, supported by theoretical calculations, and the
question of conjugation of the two double bonds will
also be discussed.
1. Introduction
It is well known that 1,3-dienes as well as their cyclic
analogues constitute one of the most important classes
of organic compounds, both from the fundamental and
the practical points of view. Therefore, it is not surpris-
ing that after the discovery of the first stable metallenes
and dimetallenes of heavier Group 14 elements (for
reviews on metallenes and dimetallenes of Group 14
elements, see Ref. [1]), the experimental efforts of many
research groups have been focused on the synthesis of
the Group 14 elements containing metalladienes, which
were expected to be very interesting because of their
unusual structures and reactivity. Talking about such
metalladienes, one can imagine several structures of the
types: ꢀEꢁCꢀCꢁCꢀ, ꢀCꢁEꢀCꢁCꢀ, ꢀEꢁE%ꢀCꢁCꢀ, ꢀEꢁCꢀ
E%ꢁCꢀ, ꢀEꢁCꢀCꢁE%ꢀ, ꢀCꢁEꢀE%ꢁCꢀ, ꢀEꢁE%ꢀE¦ꢀCꢀ,
ꢀEꢁE%ꢀCꢁE¦ꢀ or ꢀEꢁE%ꢀE¦ꢁE§ꢀ (E, E%, E¦ and E§=
heavier Group 14 elements). Such compounds are ex-
* Corresponding author. Tel./fax: +81-298-534314.
E-mail address: sekiguch@staff.chem.tsukuba.ac.jp (A. Sekiguchi).
0022-328X/01/$ - see front matter © 2001 Elsevier Science B.V. All rights reserved.
PII: S0022-328X(01)00807-5

42
V.Y. Lee et al. / Journal of Organometallic Chemistry 636 (2001) 41–48
groups. The 29Si-NMR spectrum revealed five reso-
2. Results and discussion
nances of which three belong to the silyl substituents:
19.4, 26.6 and 30.1 ppm. The down-field signal at
+124.2 ppm is characteristic of the doubly bonded
silicon atom, and the up-field signal at −45.6 ppm
corresponds to the endocyclic sp3 Si atom. The chemi-
cal shift of such Si atoms in silole molecules depends on
the substituents: +8.1 ppm for 1,1-dimethyl-2,3,4,5-te-
traphenyl-1-silacyclopenta-2,4-diene [7], whereas −34.2
ppm for 1,1-bis(trimethylsilyl)-2,3,4,5-tetramethyl-1-
silacyclopenta-2,4-diene [8]. The mass spectrum of 2b
showed the strong M+ parent ion cluster at 856–866,
as well as the fragmentation peaks 803 [M+−tBu] and
703 [M+−SiMetBu2].
Compound 2b is extremely air- and moisture-sensi-
tive and even in the solid state quickly decomposes in
air. The decomposition of 2b in hexane solution in the
presence of air caused the formation of a very compli-
cated mixture. The molecular structure of compound 2b
was established by X-ray crystallography (Fig. 1). The
five-membered ring is almost planar, which is normal
for cyclopentadiene derivatives, although the SiꢁGe
double bond has a trans-bent configuration with a
torsional angle Si(6)ꢀGe(1)ꢀSi(2)ꢀSi(5) of 38.6(1)°. The
phenyl ring is almost perpendicular to the plane of the
silole ring, which is usual for phenyl-substituted metal-
loles (for the reviews on metalloles chemistry see Ref.
[9]). The large value for the Si(3)ꢀSi(1)ꢀSi(4) angle of
124.7(5)° indicates the significant steric repulsion of the
two bulky SiMetBu2 substituents in the geminal posi-
tion. The length of the SiꢁGe double bond is 2.250(1)
Previously we have reported the synthesis of tetrak-
is[di-tert-butyl(methyl)silyl]-1-disilagermirene (1a) with
a SiꢁSi double bond as well as its isomerization to a
tetrakis[di-tert-butyl(methyl)silyl]-2-disilagermirene (1b)
with a SiꢁGe double bond [5]. The reactivity of both
compounds was found to be very rich and interesting,
especially regarding cycloaddition reactions across their
double bonds, which gives access to new cyclic and
bicyclic compounds. The most important results were
obtained from the reaction of disilagermirenes with
phenylacetylene. Thus, the reaction of disilagermirene
1b with excess phenylacetylene in deuteriobenzene at
room temperature quickly produced an orange-red re-
action mixture, which showed a down-field signal in the
29Si-NMR at +124.2 ppm [6]. Monitoring of the reac-
tion by NMR spectroscopy showed that the reaction
proceeded cleanly and was completed in 5 h, at which
1
time the H-NMR spectrum showed the absence of the
starting compound 1b. After evaporation of solvent and
excess phenylacetylene, recrystallization of the residue
from hexane gave bright orange crystals of 1,1,2,3-te-
trakis[di-tert-butyl(methyl)silyl]-4-phenyl-1,2-disila-3-
germacyclopenta-2,4-diene (2b) in 42% yield (Scheme
1), whose structure has been established on the basis of
1H-, 13C-, 29Si-NMR and mass spectra.
1
The H-NMR spectrum of 2b showed three types of
methyl groups and four different tert-butyl groups,
whereas the 13C-NMR spectrum exhibited two signals
for the methyl groups and four signals for the tert-butyl
Scheme 1.
,
Fig. 1. Molecular structure of the silole 2b; left (top view), right (side view). Selected bond lengths (A): Ge(1)ꢀSi(2) 2.250(1), Si(1)ꢀSi(2) 2.364(1),
Si(1)ꢀC(2) 1.888(3), C(1)ꢀC(2) 1.343(5), Ge(1)ꢀC(1) 1.972(3), Si(1)ꢀSi(3) 2.431(1), Si(1)ꢀSi(4) 2.432(1), Si(2)ꢀSi(5) 2.380(1), Ge(1)ꢀSi(6) 2.418(1).
Selected bond angles (°): C(1)ꢀGe(1)ꢀSi(2) 101.8(1), Ge(1)ꢀSi(2)ꢀSi(1) 95.2(0), C(2)ꢀSi(1)ꢀSi(2) 98.1(1), C(1)ꢀC(2)ꢀSi(1) 126.9(2), C(2)ꢀC(1)ꢀGe(1)
117.9(2), Si(3)ꢀSi(1)ꢀSi(4) 124.7(0).

V.Y. Lee et al. / Journal of Organometallic Chemistry 636 (2001) 41–48
43
Scheme 2.
,
atoms of the SiꢁGe and CꢁC double bonds, which
prevent the effective overlapping of molecular orbitals
of the two p-bonds, which is necessary for real conjuga-
tion. In contrast, for the symmetrical heavier Group 14
elements containing 1,3-diene systems with two equal
double bonds, such as 2,3-digerma-1,3-butadiene
H2CꢁGeHꢀGeHꢁCH2, theoretical calculations have
predicted about half the degree of conjugation com-
pared with that of the parent 1,3-butadiene [13]. This
was supported by the experimental results: symmetrical
tetrasila- and tetragerma-1,3-butadienes were reported
as highly conjugated systems, as evidenced by the X-ray
and UV–vis data [2,3].
For the mechanism of formation of 2b, the following
reaction sequence can be considered (Scheme 2). In the
first step [2+2] cycloaddition of one molecule of
phenylacetylene occurred across the SiꢁGe double bond
to form bicyclic compound 3b. The last compound then
quickly undergoes valence isomerization to form a
silole-type structure 4b with one GeꢁC and one SiꢁC
double bond, which in turn rapidly isomerizes to give
the thermodynamically more stable silole 2b with one
SiꢁGe and one CꢁC double bond. Such a type of
isomerization was found for the first time for 1-methyl-
1-trimethylsilyl-2,5-diphenyl-1-silacyclopenta-2,4-diene,
which undergoes isomerization at 150°C through the
1,5-migration of the silyl substituent to form 1-methyl-
5-trimethylsilyl-2,5-diphenyl-1-silacyclopenta-1,3-diene.
The last compound was unstable and evidenced only by
trapping reactions [14]. A similar 1,5 H-migration was
A, which lies between the typical values of SiꢁSi
,
,
(2.138–2.289 A) [1,10] and GeꢁGe (2.213–2.460 A) [1]
double bond lengths. This value is close to that of the
theoretically predicted 2.180 A (MP2) for 1b [5]. It was
,
quite interesting to estimate the degree of conjugation
of the two double bonds in the silole ring system. In the
case of such conjugation, one can expect a shortening
of the Ge(1)ꢀC(1) ordinary bond as well as an elonga-
tion of the Ge(1)ꢁSi(2) and C(1)ꢁC(2) double bonds.
,
The length of the Ge(1)ꢀC(1) bond is 1.972(3) A, which
lies in the normal range for GeꢀC bond lengths of
,
1.95–2.00 A [11]. We were not able to compare the
Ge(1)ꢁSi(2) double bond length with other examples,
since no structural data regarding SiꢁGe double bonds
were available to date. The C(1)ꢁC(2) double bond
length is 1.343(5) A, which also lies in the normal range
for CꢁC double bond lengths of 1.34 A. All of these
,
,
data give no evidence for any real conjugation between
the SiꢁGe and the CꢁC double bonds in the cyclopenta-
diene moiety of 2b, despite the planarity of the five-
membered ring. The same conclusion came also from
the UV–vis spectrum of 2b, which showed no signifi-
cant bathochromic shift in comparison with an isolated
SiꢁGe double bond in the compound 1b (472 vs 467
nm, respectively). This seems to be curious since all the
known cyclopentadiene compounds were described as
fully conjugated systems, for which Diels–Alder cy-
cloaddition reactions are typical [12]. Apparently, such
unusual behavior of 2b is caused by both the great
energy difference and the difference in the size of the

44
V.Y. Lee et al. / Journal of Organometallic Chemistry 636 (2001) 41–48
also observed in unsubstituted silole systems to give
finally the most stable 1-silacyclopenta-2,4-diene isomer
[15]. The stability of the isomeric compounds 3b, 4b
and 2b was evaluated by ab initio calculations on the
parent compounds (5b for 3b, 6b for 4b and 7b for 2b)
at B3LYP/6-31G* level (Fig. 2). The theory predicted
7b to be the most stable compound. Compound 5b is
less stable by 13.39 kcal mol−1 and compound 6b is the
most unfavorable isomer by 14.29 kcal mol−1, which is
in a good agreement with the experimental results [16].
Thus, compounds 3b and 4b are quite unstable, since it
was impossible to isolate and even detect them by
NMR monitoring of the reaction. In contrast, com-
pound 2b is stable in solution, and at room temperature
there is only a very slow reaction between 2b and excess
phenylacetylene.
Such cycloaddition of the second molecule of pheny-
lacetylene to the SiꢁGe double bond of silole 2b can be
achieved only at elevated temperatures. Thus, heating
at 80°C for 6 h caused the complete disappearance of
2b and formation of the new bicyclic compound 1,2,2,5-
tetrakis[di - tert - butyl(methyl)silyl] - 4,7 - diphenyl - 1,2-
disila-5-germabicyclo[3.2.0]hepta-3,6-diene 8b, which
was isolated by recrystallization from hexane in 55%
yield. The structure of compound 8b was established by
means of all spectral data and finally confirmed by
X-ray analysis.
is different from the expected one: the phenyl-group
substituted carbon atom is attached to the silicon atom,
although according to the polarity of the SiꢁGe double
bond one can expect the opposite regioselectivity. Re-
cently, the cycloaddition of phenylacetylene to the tran-
sient germasilenes was found to be regioselective to
form only one isomer, in which the phenyl-group sub-
stituted carbon atom is attached to a germanium atom,
which is in accordance with the polarity of the SiꢁGe
double bond [17]. Apparently, in our case the reaction
is governed by steric effects, rather than electronic; i.e.
kinetic control takes place. As was established above,
there is no real conjugation in a silole ring system;
therefore, it is not surprising that 2b and a second
molecule of phenylacetylene react in a [2+2], but not
[4+2], cycloaddition manner. That is, silole 2b repre-
sents an unusual system with two formally conjugated,
but actually isolated, double bonds in which one
(SiꢁGe) possesses a much higher reactivity than the
other (CꢁC). This is in sharp contrast with a previously
reported transient silole such as 1-methyl-2,5-diphenyl-
5-trimethylsilyl-1-silacyclopenta-1,3-diene, which re-
acted with acetylenes and alkenes as a conjugated diene
to give the corresponding Diels–Alder adducts [14].
The bicyclic compound 8b has no symmetry, which
causes the complicated NMR spectra. Thus, in the
1H-NMR spectrum of 8b all methyl and tert-butyl
groups appeared to be non-equivalent, exhibiting four
It is quite interesting that the regiochemistry of the
PhCꢂCH cycloaddition to the SiꢁGe double bond of 2b
t
signals for Me and eight signals for Bu groups. The
Fig. 2. Energy profile of the reaction of 2-disilagermirene GeSi2H4 with acetylene by ab initio calculations (B3LYP/6-31G* level).

V.Y. Lee et al. / Journal of Organometallic Chemistry 636 (2001) 41–48
45
,
Fig. 3. Molecular structures of 8a (left) and 8b (right). 8a: selected bond lengths (A): Ge(1)ꢀSi(2) 2.432(1), Ge(1)ꢀSi(1) 2.509(1), Ge(1)ꢀC(3)
2.035(5), Si(1)ꢀC(2) 1.898(5), C(2)ꢀC(1) 1.348(6), C(1)ꢀSi(2) 1.925(4), Si(2)ꢀC(4) 1.897(5), C(4)ꢀC(3) 1.351(6). Selected bond angles (°):
Si(1)ꢀGe(1)ꢀSi(2) 92.1(0), Ge(1)ꢀSi(2)ꢀC(1) 101.1(1), Si(2)ꢀGe(1)ꢀC(3) 71.6(1), Ge(1)ꢀSi(2)ꢀC(4) 76.5(1). Folding angle between the planes of four-
,
and five-membered rings: 109.1°. 8b: selected bond lengths (A): Ge(1)ꢀSi(2) 2.432(1), Si(1)ꢀSi(2) 2.481(2), Ge(1)ꢀC(1) 1.993(6), Si(1)ꢀC(2) 1.897(6),
C(1)ꢀC(2) 1.345(8), Ge(1)ꢀC(4) 1.968(7), Si(2)ꢀC(3) 1.967(6), C(3)ꢀC(4) 1.374(8). Selected bond angles (°): Si(1)ꢀSi(2)ꢀGe(1) 93.1(0),
Ge(1)ꢀSi(2)ꢀC(3) 75.1(1), Si(2)ꢀGe(1)ꢀC(1) 99.8(1), Si(2)ꢀGe(1)ꢀC(4) 73.7(2). Folding angle between the planes of four- and five-membered rings:
109.0°.
the 29Si-NMR: four of them (21.9, 23.5, 26.8 and 28.3
ppm) belong to substituents, and two of them (−84.1
and −65.0 ppm) can be assigned to the endocyclic Si
atoms. The intermediate compounds 4a and 2a cannot
be detected by NMR, apparently because 4a quickly
isomerizes to 2a, which in turn easily and rapidly
undergoes cycloaddition with a second molecule of
phenylacetylene, even at room temperature, to give
finally the bicyclic compound 8a. The cycloaddition of
the second molecule of phenylacetylene to the silole 2a
is also regiospecific, as in the above case of 2b, but
having an opposite direction: the phenyl-group substi-
tuted carbon atom is attached to a germanium atom,
which can be well explained by electronic reasons.
Apparently, in the former case of compound 2b, the
cycloaddition of the second molecule of pheny-
lacetylene is significantly hindered because of great
steric problems and therefore, even upon heating, steric
control of the reaction is predominant over thermody-
namic control.
There is no reaction of 1-disilagermirene 1a with
diphenylacetylene or bis(trimethylsilyl)acetylene even
upon prolonged heating at 80°C in C6D6 for 2 days.
This gives evidence that the cycloaddition reactions of
disilagermirenes proceed mainly by the polar mecha-
nism rather than the concerted one: no reaction with
non-polar internal alkynes (PhCꢂCPh), relatively
smooth reaction with slightly polarized terminal alky-
nes (PhCꢂCH), and very easy reaction with carbonyl
compounds [20]. It is interesting that there is also no
reaction of 1-disilagermirene 1a with styrene at 80°C in
C6D6 for 2 days, in contrast to the phenylacetylene
case. This seems to be understandable since, in the case
of PhCHꢁCH2, formation of the conjugated system
(like 2a,2b) is impossible.
olefinic proton in the cyclobutene ring has a very
characteristic down-field shifted signal at 8.15 ppm. For
example, the chemical shifts of the olefinic proton in
1,1,2,2-tetramesityl-3-phenyl-1,2-disilacyclobut-3-ene
are reported to be 8.08 [18] and 8.07 ppm in 1,1,2,2-te-
tramesityl-3-phenyl-1,2-digermacyclobut-3-ene [19]. The
29Si-NMR spectrum revealed six resonances for six
non-equivalent silicon atoms; four of them belong to
the silyl substituents: 16.5, 19.3, 21.4 and 21.8 ppm, and
two of them belong to the endocyclic bridgehead silicon
atoms: −52.8 and −13.9 ppm. According to the X-
ray data (Fig. 3, right) compound 8b has a highly
distorted structure with a folding angle between the
planes of the four- and five-membered rings of 109.0°.
Both four- and five-membered rings are nearly planar,
whereas phenyl rings are out of these planes by 29.9
and 54.1°, respectively.
The reaction of disilagermirene 1a, which is a struc-
tural isomer of 1b, with phenylacetylene proceeds in
a similar way, to give finally the bicyclic com-
pound 1,2,2,5-tetrakis[di-tert-butyl-(methyl)silyl]-4,7-
diphenyl-2,5-disila-1-germabicyclo[3.2.0]hepta-3,6-diene
(8a) (structural isomer of 8b) in 63% yield (Scheme 2).
Both 8a and 8b have very similar NMR spectra, which
gives evidence of their structural similarities. X-ray
analysis of 8a (Fig. 3, left) has confirmed such a conclu-
sion, showing the molecular structure of 8a to be
almost identical to that of 8b, with very similar struc-
tural characteristics; for example, with the same folding
angle between the two planes of 109.1°. The only
difference in the structures of 8a and 8b is the position
of the bridgehead Si and Ge atoms, which is opposite
to each other in these two compounds.
In contrast to the previous case, the existence of the
initially formed bicyclic compound 3a can be detected
by NMR spectroscopy. Six resonances can be seen in

46
V.Y. Lee et al. / Journal of Organometallic Chemistry 636 (2001) 41–48
3. Experimental
photolysis (u\300 nm) for 7 h, was reacted with a
six-fold excess of phenylacetylene (43 mg, 0.42 mmol)
in a dry O2-free C6D6 (0.55 ml) in a sealed NMR tube
at r.t. In 5 h the starting material disappeared, and
compound 2b was cleanly formed. After heating at
80°C for 6 h compound 2b was completely transformed
to 8b. After evaporation of the solvent and excess
phenylacetylene in vacuum, the residue was recrystal-
lized from a dry hexane to give 8b as colorless crystals
(36 mg, 55%); m.p. (dec.) 215–217°C — 1H-NMR
(C6D6): l=0.16 (s, 3H), 0.30 (s, 3H), 0.50 (s, 3H), 0.66
(s, 3H), 0.88 (s, 9H), 0.97 (s, 9H), 1.06 (s, 9H), 1.13 (s,
9H), 1.19 (s, 9H), 1.28 (s, 9 H), 1.29 (s, 9 H), 1.39 (s, 9
H), 7.06–7.09 (m, 2H), 7.22 (t, J=8.1 Hz, 4 H), 7.31
(s, 1 H), 7.52 (d, J=7.1 Hz, 2H), 7.68 (d, J=7.1 Hz,
2H), 8.15 (s, 1 H); 13C-NMR (CDCl3): l= −3.8 (Me),
−2.0 (Me), −1.3 (Me), −0.7 (Me), 22.1 (CMe3), 22.3
(CMe3), 22.5 (CMe3), 22.57 (CMe3), 22.60 (CMe3),
23.6 (CMe3), 23.7 (CMe3), 23.9 (CMe3), 29.7 (CMe3),
30.1 (CMe3), 31.3 (CMe3), 31.6 (3 CMe3), 31.7 (CMe3),
31.9 (CMe3), 125.8, 126.6, 127.3, 127.5, 128.1, 128.3,
142.6 (ipso C), 149.0 (CꢁCH), 150.8 (ipso C), 158.3
(CꢁCH), 163.6 (CꢁCH), 167.5 (CꢁCH) — 29Si-NMR
(C6D6): l= −52.8, −13.9, 16.5, 19.3, 21.4, 21.8 —
EIMS (70 eV): 958–968 [M+ cluster, 1], 905 [M+−
tBu, 2], 805 [M+−SiMetBu2, 2], 73 (100) — Anal.
Found: C, 64.58; H, 9.74. Calc. for C52H96GeSi6: C,
64.89; H, 10.05%.
3.1. General procedures
All experiments were performed in an Ar atmosphere
of MBRAUN MB 150B-G glove-box and by using
high-vacuum line techniques. All solvents were 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).
Mass spectra were obtained on JEOL JMS SX-102
instrument. UV–vis spectra were recorded on a Shi-
madzu UV-2100 spectrophotometer. Elemental analysis
was performed in the Analytical Center at Tohoku
University. 1- and 2-Disiagermirenes, 1a and 1b, were
prepared according to the literature [5a].
3.2. Synthesis of 1,1,2,3-tetrakis[di-tert-
butyl(methyl)silyl]-4-phenyl-1,2-disila-3-
germacyclopenta-2,4-diene (2b)
Tetrakis[di-tert-butyl(methyl)silyl]-2-disilagermirene
(1b) was prepared from tetrakis[di-tert-butyl-
(methyl)silyl]-1-disilagermirene (1a) (93 mg, 0.12 mmol)
by heating at 215°C for 25 min. Then compound 1b
was reacted with a six-fold excess of phenylacetylene
(74.5 mg, 0.73 mmol) in a dry O2-free C6D6 (0.55 ml) in
a sealed NMR tube at room temperature (r.t.). Reac-
tion progress was monitored by NMR spectra, which
showed the reaction was completed in 5 h. After evapo-
ration of the solvent and excess phenylacetylene in
vacuum, the residue was recrystallized from a dry hex-
ane to give 2b as bright orange crystals (44 mg, 42%);
m.p. 161–163°C — 1H-NMR (C6D6): l=0.37 (s,
6H), 0.40 (s, 3H), 0.59 (s, 3H), 0.99 (s, 18H), 1.15 (s,
18H), 1.19 (s, 18H), 1.31 (s, 18H), 7.06–7.09 (m, 1H,
ArH), 7.19–7.24 (m, 2H, ArH), 7.34 (s, 1H, CꢁCH),
7.42 (dd, J=8.2 Hz, J=8.2 Hz, 2H, ArH) — 13C-
NMR (C6D6): l= −2.9 (Me), −2.3 (3Me), 22.1
(CMe3), 22.5 (CMe3), 23.2 (CMe3), 23.7 (CMe3), 29.9
(CMe3), 30.96 (CMe3), 31.12 (CMe3), 31.4 (CMe3),
126.3, 126.8, 128.6, 149.8 (CꢁCH), 151.7 (ipso C), 173.3
(CꢁCH) — 29Si-NMR (C6D6): l= −45.6, 19.4, 26.6,
30.1, 124.2 — EIMS (70 eV): 856–866 [M+ cluster,
31], 803 [M+−tBu, 2], 703 [M+−SiMetBu2, 4], 73
(100) — UV–vis: umax (nm) (m, M−1 cm−1) (hexane)
243 (37 330), 307 (6570), 472 (5540).
3.4. Synthesis of 1,2,2,5-tetrakis[di-tert-
butyl(methyl)silyl]-4,7-diphenyl-2,5-disila-1-
germabicyclo[3.2.0]hepta-3,6-diene (8a)
Tetrakis[di-tert-butyl(methyl)silyl]-1-disilagermirene
(1a) (50 mg, 0.06 mmol) was reacted with a seven-fold
excess of phenylacetylene (48 mg, 0.47 mmol) in a dry
O2-free C6D6 (0.6 ml) in a sealed tube at r.t. In 1 day
the reaction was completed, and the red color of the
starting material disappeared. After evaporation of the
solvent and excess phenylacetylene in vacuum, the
residue was recrystallized from a dry hexane to give 8a
as colorless crystals (40 mg, 63%); m.p. (dec.) 213–
214°C — 1H-NMR (C6D6): l=0.15 (s, 3H), 0.26 (s,
3H), 0.47 (s, 3H), 0.69 (s, 3H), 0.91 (s, 9H), 0.99 (s,
9H), 1.05 (s, 9H), 1.15 (s, 9H), 1.16 (s, 9H), 1.28 (s,
18H), 1.36 (s, 9H), 7.06 (d, J=7.4 Hz, 2H), 7.16–7.18
(m, 2H), 7.22 (t, J=7.4 Hz, 2H), 7.55 (s, 1 H), 7.56 (d,
J=7.0 Hz, 2H), 7.70 (d, J=7.0 Hz, 2H), 8.05 (s,
1H) — 13C-NMR (CDCl3): l= −3.9 (Me), −2.3
(Me), −1.2 (Me), −1.1 (Me), 21.6 (CMe3), 22.0
(CMe3), 22.3 (CMe3), 22.5 (CMe3), 23.2 (CMe3), 23.6
(2 CMe3), 24.1 (CMe3), 29.9 (CMe3), 30.3 (CMe3), 31.2
(CMe3), 31.5 (5 CMe3), 126.0, 126.7, 127.5, 128.2,
128.5, 142.5 (ipso C), 149.6 (CꢁCH), 150.2 (ipso C),
155.1 (CꢁCH), 162.4 (CꢁCH), 170.8 (CꢁCH) — 29Si-
NMR (C6D6): l= −45.3, −18.4, 9.4, 18.6, 21.1,
3.3. Synthesis of 1,2,2,5-tetrakis[di-tert-
butyl(methyl)silyl]-4,7-diphenyl-1,2-disila-5-
germabicyclo[3.2.0]-
hepta-3,6-diene (8b)
Tetrakis[di-tert-butyl(methyl)silyl]-2-disilagermirene
(1b), prepared from 1a (52 mg, 0.07 mmol) by the

V.Y. Lee et al. / Journal of Organometallic Chemistry 636 (2001) 41–48
47
Table 1
Crystallographic data and experimental parameters for the crystal structure analysis of 2b, 8a and 8b
2b
8a
8b
Empirical formula
C44H90GeSi6
860.29
120
C
962.42
120
52H96GeSi6
C52H96GeSi6
962.42
120
Formula weight (g mo1−1
Temperature (K)
)
,
Wavelength (A)
0.71070
Triclinic
0.71070
Triclinic
0.71070
Triclinic
Crystal system
Space group
(
(
(
P1(2)
P1(2)
P1(2)
Unit cell dimensions
,
a (A)
12.2070(8)
13.214(1)
18.815(1)
74.551(4)
73.514(5)
64.841(5)
2596.7(4)
2
13.721(1)
14.662(1)
15.746(1)
99.642(5)
114.978(5)
92.283(5)
2809.1(5)
2
13.772(3)
14.580(3)
15.746(3)
99.798(9)
114.94(1)
92.097(9)
2804.2(9)
2
,
b (A)
,
c (A)
h (°)
i (°)
k (°)
−3
,
V (A
)
Z
Dcalc (g cm−3
)
1.100
0.755
940
1.138
0.705
1048
1.140
0.706
1048
Absorption coefficient (mm−1
F(000)
)
Crystal size (mm)
Theta range for data collection (°)
Index ranges
0.3×0.3×0.1
3.51–27.99
05h514, −155k517,
−235l524
22 573
10 815 [Rint=0.0560]
10 815
551
0.2×0.2×0.1
2.63–28.00
05h517, −195k519,
−205l518
27 484
11 932 [Rint=0.0680]
11 932
532
0.15×0.15×0.15
2.63–27.99
05h518, −195k519,
−205l518
26 584
11 971 [Rint=0.0890]
11 971
533
Reflections collected
Independent reflections
Reflections used
Parameters
a
S
1.015
0.0362/3.3161
0.0562
1.032
0.1403/3.1257
0.0832
1.044
0.1383/8.2043
0.0974
b
Weight parameters a/b
Final R indices c [I\2|(I)]
wR2 d(all data)
0.1119
0.2402
0.2806
Largest difference peak and hole
+0.408 and −0.575
+1.912 and −1.615
+2.907 and −1.313
−3
,
(e A
)
a S={ꢀ w[Fo2−Fc2)2]/(n−p)}0.5, n=no. of reflections; p=no. of parameters.
b w=1/[|2(F2o)+(aP)2+bP], with P=(Fo2+2F2c)/3.
c R1=ꢀ ꢁꢁFoꢁ−ꢁFcꢁꢁ/ꢀ ꢁꢁFoꢁ.
d wR2=ꢀ[w(Fo2−Fc2)2]/ꢀ [w(Fo2]2}0.5
.
27.4 — EIMS (70 eV): 958–968 [M+ cluster, 3], 905
[M+−tBu, 5], 805 [M+−SiMetBu2, 93], 73 (100) —
Anal. Found: C, 64.82; H, 10.21. Calc. for
C52H96GeSi6: C, 64.89; H, 10.05%.
Acknowledgements
This work was supported by a grant-in-aid for Scien-
tific Research (Nos. 09239101, 10304051) from the Min-
istry of Education, Science and Culture of Japan, and
TARA (Tsukuba Advanced Research Alliance) fund.
3.5. Crystal structure analyses of the compounds 2b, 8a
and 8b
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