A 3,4-benzo-1,2-germacyclobut-3-ene and related compounds. Palladium-catalyzed a-metathesis, dehydrogenative coupling and hydrogermylation of the Ge-Ge σ-bond

Article abstract of DOI:10.1016/S0022-328X(00)00471-X

In the presence of catalytic amounts of Pd(PPh₃)₄, 3,4-benzo-1,1,2,2-tetraethyl-1,2-germacyclobut-3-ene (1) readily undergoes the reversible σ-bond metathesis to give a dimer, 1,2,5,6-dibenzo-3,4,7,8-tetragermacycloocta-1,5-diene (6) below 100°C. However, at 160°C in toluene containing catalytic amounts of Pd(PPh₃)₄, both 1 and 6 afford an unsymmetrical dimer, 1,2,4,5-dibenzo-3,6,7,8-tetragermacycloocta-1,4-diene (8) with two isomeric products. In the presence of Pd(PPh₃)₄, 1,2-bis(diethylgermyl)benzene (18) undergoes dehydrocouling to give 1, which is smoothly converted to 6 under these conditions. The metal-metal σ-bonds of 1 and its silicon analogue are highly susceptible to hydrogermylation but not to hydrosilylation in the presence of Pd(PPh₃)₄.

Full text of DOI:10.1016/S0022-328X(00)00471-X

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Journal of Organometallic Chemistry 611 (2000) 420–432
A 3,4-benzo-1,2-germacyclobut-3-ene and related compounds.
Palladium-catalyzed s-metathesis, dehydrogenative coupling and
hydrogermylation of the GeꢀGe s-bond
Haruhiko Komoriya a, Masahiro Kako a, Yasuhiro Nakadaira a,*, Kunio Mochida b
a Department of Applied Physics and Chemistry, The Uni6ersity of Electro-Communications, Chofu, Tokyo 182-8585, Japan
b Department of Chemistry, Faculty of Science, Gakushuin Uni6ersity, 1-5-1 Mejiro, Tokyo 171-8588, Japan
Received 30 March 2000; accepted 14 April 2000
Abstract
In the presence of catalytic amounts of Pd(PPh3)4, 3,4-benzo-1,1,2,2-tetraethyl-1,2-germacyclobut-3-ene (1) readily undergoes
the reversible s-bond metathesis to give a dimer, 1,2,5,6-dibenzo-3,4,7,8-tetragermacycloocta-1,5-diene (6) below 100°C. However,
at 160°C in toluene containing catalytic amounts of Pd(PPh3)4, both 1 and 6 afford an unsymmetrical dimer, 1,2,4,5-dibenzo-
3,6,7,8-tetragermacycloocta-1,4-diene (8) with two isomeric products. In the presence of Pd(PPh3)4, 1,2-bis(diethylgermyl)benzene
(18) undergoes dehydrocouling to give 1, which is smoothly converted to 6 under these conditions. The metal-metal s-bonds of
1 and its silicon analogue are highly susceptible to hydrogermylation but not to hydrosilylation in the presence of Pd(PPh3)4.
© 2000 Elsevier Science S.A. All rights reserved.
Keywords: Benzo-1,2-germacyclobutene; 1,2-Germacyclobutene; Metathesis; s-Bond metathesis; 1,2-Silacyclobutene; Hydrogermylation; Germa-
nium compound; Organogermane
1. Introduction
mally redistribution of a diethylgermylene unit to yield
4,5-benzo-1,2,3-trigermacyclopent-4-ene and 3,4,6,7-
dibenzo-1,2,5-trigermacyclohept-3,6-diene, respectively
as shown in Scheme 1. In this report we describe the
chemical properties of the GeꢀGe bond of 1 toward a
transition metal complex, in particular a palladium
complex; insertion, s-bond metathesis, hydrogermyla-
tion and hydrosilylation of the GeꢀGe bond along with
dehydrocoupling of 1,2-bis(diethylgermyl)benzene (18)
[5]. For comparative studies of the GeꢀGe bond, we
Reactions of a SiꢀSi bond with various kinds of
transition metal complexes have been investigated ex-
tensively and now constitute one of the most useful
methods to form a new SiꢀSi bond or SiꢀC bond [1].
However, much less studies have been carried out on
the chemistry of its higher homologue GeꢀGe bond [2].
Recently, to examine the chemical properties of the
activated GeꢀGe bond in detail [3], we have prepared
the readily accessible organogermacycle, 3,4-benzo-
1,1,2,2-tetraethyl-1,2-germacyclobut-3-ene (1) in which
the GeꢀGe bond is activated primarily by ring strain
[4]. As expected, 1 is highly reactive and undergoes
thermo-chemical ring-opening polymerization to give
polymers with molecular weight of hundreds of thou-
sands. Furthermore on thermolysis 1 undergoes for-
* Corresponding author. Tel.: +81-424-435567; fax: +81-424-
435563.
E-mail address: naka@e-one.uec.ac.jp (Y. Nakadaira).
Scheme 1.
0022-328X/00/$ - see front matter © 2000 Elsevier Science S.A. All rights reserved.
PII: S0022-328X(00)00471-X

H. Komoriya et al. / Journal of Organometallic Chemistry 611 (2000) 420–432
421
manner. The structure of 3 was confirmed by compar-
1
ing its H- and 13C-NMR data with those of related
compounds shown in Table 1 [7b]. The 13C-NMR
spectrum of 3 displays two peaks, at 12.48 and 14.29
ppm, due to ethyl carbons which locate at higher field
than those due to 1. In addition, there observed three
peaks at 127.21, 132.04 and 158.23 ppm due to the
symmetrically substituted phenylene carbons and four
peaks at 128.48, 129.35, 134.32 and 138.59 ppm
assignable to those due to triphenylphosphine.
Scheme 2.
Naturally, the silicon analog 4a reacted with phenyl-
acetylene to afford a similar type of the product, 2,3-
benzo-1,1,4,4-tetraethyl-1,4-disilacyclohexa-2,5-diene 5
in the presence of catalytic amount of Pd(PPh3)4 [7b].
2.2. GeꢀGe |-bond metathesis of
benzo-1,2-digemacyclobutene 1
Scheme 3.
On the other hand, in the presence of a catalytic
amount of Pd(PPh3)4 without acetylene, 1 readily un-
derwent GeꢀGe s-bond metathesis to give a dimer,
1,2,5,6-dibenzo-3,4,7,8-tetragermacycloocta-1,5-diene 6,
which was disclosed to be produced again through 3
(Scheme 3). Structure of 6 is fully compatible with
have also examined hydrogermylation and hydrosily-
tion of the SiꢀSi bond of a silicon analogue, 3,4-benzo-
1,1,2,2-tetramethyl-1,2-disilacyclobut-3-ene 4a [6]. On
the other hand, much attention has been devoted to
chemistry of 3,4-benzo-1,2-disilacyclobutenes 4, the sili-
con analogue of 1 toward transition–metal complexes
[7,8]. In addition to transition-metal induced cycloaddi-
tion with unsaturated compounds, recently the inter-
molecular metathesis of the SiꢀSi bond coupled with
interesting isomerization of the dimer formed has been
reported [8b].
1
spectral data shown in Table 1. Thus, the H and 13C
spectra of 6 exhibit only one each kind of signals
assignable to the ethyl group on the Ge atom and
symmetrically substituted phenylene, respectively and
these spectral data indicate 6 to be highly symmetrical
[9].
Complex 3 must play an important role also in the
dimerization of 1. After formation of 3 in C6D6 being
1
monitored by H-NMR, another mole of 1 was added
2. Results and discussion
into the NMR tube. After 16 h at ambient temperature
complex 3 completely disappeared and instead dimer 6
was formed quantitatively.
2.1. Insertion of phenylacetylene into the GeꢀGe bond
of 1 in the presence of Pd(PPh3)4
For the transition metal-catalyzed s-bond metathesis
[10], the SiꢀSi s-bond forming step has been proven to
be reversible [11,12]. However in the presence of a
catalytic amount of Pd(PPh3)4 a dimer 6 is produced
from 1 in a quantitative yield, occurrence of the reverse
process, namely, from 6 to 1 is not distinct at all. So,
the step from 6 to 3 has been examined in detail.
Although at ambient temperature 6 remained un-
changed for a long time in the presence of Pd(PPh3)4, 6
and one equivalent of Pd(PPh3)4 in C6D6 were heated at
100°C for 2 h and this caused the backward reaction of
6 to 3 to yield the reaction mixture composed of 3 and
6 in the ratio of ca. 2:3 (Eq. (1)).
Furthermore, on the treatment of the (1:2.5) mixture
of 6 and Pd(PPh3)4 under similar conditions, the ratio
of 6 to 3 was changed to ca. 3:2 (Eq. (1)). This ratio of
6 to 3 remained unchanged on prolonged heating.
These observations indicate that 6 should be in equi-
librium with 3 and probably 1 under these reaction
As reported, thermolysis of 1 in the presence of
phenylacetylene in toluene gave 2,3-benzo-4-phenyl-
1,1,4,4-tetraethyl-1,4-digermacyclohexa-2,5-diene (2) in
91% yield [4]. Here, in the presence of a catalytic
amount of Pd(PPh3)4 the reaction of 1 with phenyl-
acetylene at ambient temperature also afforded 2 in
88% as a sole product (Scheme 2). To examine interven-
tion of the intermediate such as 3,4-benzo-1-pallada-
2,5-digermacyclopent-3-ene 3, first 1 and one equivalent
of Pd(PPh3)4 in C6D6 were placed in an NMR tube at
room temperature and after 30 min inspection of the
1H-NMR spectrum showed that most of 1 in the reac-
tion mixture disappeared and instead the complex 3
was formed quantitatively. Then, a slightly excess
amount of phenylacetylene was added into the NMR
tube under argon, and after 16 h at room temperature
1
the H-NMR spectrum showed that the reaction of 3
with the acetylene added afforded 2 in a quantitative

422
H. Komoriya et al. / Journal of Organometallic Chemistry 611 (2000) 420–432
conditions. However, 1 once formed is so reactive
under the conditions and is likely to return readily to 6
probably by the reaction with 3. Next, the forward
reaction from 3 to 6 has been examined by NMR
spectroscopy. Thus, 3 once generated in the NMR tube
at ambient temperature in C6D6 was heated at 100°C
for 16 h to afford the mixture composed of 3 and 6 in
the 1:1 ratio (Eq. (2)). Furthermore, 3 generated from 6
was finally trapped to yield 2 quantitatively when dimer
6 was heated with a catalytic amount of Pd(PPh3)4 in
the presence of phenylacetylene (Eq. (3)). Here, 6 is not
likely to be generated from two molecules of 3 but most
reasonably explained by the reaction of 3 with 1 which
may be formed first from 3. In the presence of a
catalytic amount of the Pd catalyst, 6 underwent the
metathesis at around 100°C in n-eicosane and 1 pro-
duced was immediately distilled out under the pressure
of 0.1 mmHg (Eq. (4)).
(1)
(2)
Table 1
NMR and MS spectroscopic data for 3, 6, 8, 9 and 10

H. Komoriya et al. / Journal of Organometallic Chemistry 611 (2000) 420–432
423
give 1 by elimination of the palladium complex at
around 100°C.
(3)
(4)
2.3. Metathesis of benzo-1,2-digemacyclobutene 1 at
higher temperature
So, at around 100°C 6 goes back competitively to
give 3 and probably 1 by way of the metathesis as
shown in Scheme 4. Furthermore, at 160°C in toluene
in a sealed tube containing a catalytic amount of
At even ambient temperature the GeꢀGe bond of 1
readily undergoes oxidative addition with Pd(PPh3)4 to
give bis(germyl)palladium complex 3 and then this re-
acts with another molecule of 1 to give a dimeric
intermediate such as 7, which is finally converted to 6
by way of reductive elimination of the palladium as
shown in Scheme 4. On the other hand, the metathesis
of dimer 6 only proceeds at elevated temperature, and
so 6 is presumably not strained enough to react
smoothly with the Pd complex. However the metathesis
of simple GeꢀGe and SiꢀSi bonds does not occur even
at higher temperature with the palladium complex [10],
the GeꢀGe bond of 6 should be activated somewhat
possibly by the phenylene group coupled with the steric
strain caused by the ethyl groups [9]. Thus, insertion of
the palladium into the GeꢀGe bond affords 7, and then
this eliminates possibly 1 to afford 3 which is able to
Pd(PPh3)4, 1 gave unsymmetrical dimer, 1,2,4,5-
dibenzo-3,6,7,8-tetragermacycloocta-1,4-diene 8 in 24%
yield together with two minor isomers 9 and 10 in 9 and
4% yields, respectively as shown in Scheme 5. Bis-
(germyl)palladium 3 once generated in an NMR tube
was transferred into a sealed tube and was heated at
160°C for 16 h to afford dimer 8. Meanwhile under
similar conditions symmetrical dimer 6 was also con-
verted to the unsymmetrical dimer 8 in 38% yield, and
at the same time two minor isomers 9 and 10 were also
isolated in 9 and 4% yields, respectively.
The structure of the dimer 8 was determined based
on the spectroscopic data described in Table 1. Thus, 8
shows the molecular ion peak corresponding to that of
the dimer of 1. In higher field region, the 13C-NMR of
8 shows six resonances at 5.31, 6.80, 8.45, 9.15, 9.57,
and 11.85 ppm in 1:2:1:1:2:1 ratio indicating 8 to have
Scheme 4.
Scheme 5.

424
H. Komoriya et al. / Journal of Organometallic Chemistry 611 (2000) 420–432
three kinds of the ethyl group on the germanium atoms
in 1:1:2 ratio in the molecule. On the other hand, in
lower field region, there are six peaks at 126.66, 127.26,
134.32, 135.31, 146.89, and 148.38 ppm assignable to
those due to the phenylene group substituted unsym-
metrically. The silicon analog 4a has been reported to
give the dimeric product having analogous structure to
that of 8 [7b,8b]. In the thermolysis, two minor isomers
9 and 10 were isolated along with 8 and their structures
were also assigned based on the spectroscopic data
shown in Table 1.
On the thermolyses of 1 and dimer 6 at 160°C, the
ratios of 8, 9, and 10 obtained are quite similar in both
cases. This is reasonably interpreted that these three
products must be formed after the equilibrium in
Scheme 4 being established. Careful examination of the
molecular structure of unsymmetrical dimer 8 indicates
that at least one of the Ge-phenylene linkages should be
cleaved by possibly the palladium catalyst during ther-
molysis. On the other hand, to the two isomers 9 and
10 being constructed one of the ethyl groups on the
germanium should be shifted to the other germanium
atom and this leads to give EtGe and Et3Ge groups,
respectively. This type of rearrangement on silicon and
germanium atoms is reported to occur by way of
silylene and germylene complexes [13,14]. So we assume
that the transformations observed here proceed by way
of a key intermediate germylene complex 11 as de-
scribed in Scheme 6. At around 100°C the equilibrium
among 1 and 6 has been readily established through
palladium complexes 3 and 7. At higher temperature
one of the phenylene carbons of the complex 3 rear-
ranges from the germanium atom to the palladium
center to give a germylene complex 11 which is conceiv-
able to participate in the equilibrium as shown in
Scheme 6. Now, the release of the ring strain of 11
facilitates isomerization to 12 that is the positional
isomer of 3 (Path A). Activated GeꢀGe bond of 1 is
expected to react readily with the PdꢀGe bond of 12 to
give intermediate 13 that affords unsymmetrical dimer
8 with reductive elimination of palladium. On the other
hand, in key intermediate 11, another type of rear-
Scheme 6.

H. Komoriya et al. / Journal of Organometallic Chemistry 611 (2000) 420–432
425
(5)
(6)
At first, the insertion of palladium occurs into one of
the GeꢀH bonds of 18 to afford intermediate 19 and
subsequently insertion of another GeꢀH bond followed
by dehydrogenation would give 3 (Eq. (7)). The silicon
analogue 26 has been reported to undergo a similar
type of dehydrogenation to give the corresponding bis-
silylated metal complex in the presence of a low coordi-
nated catalyst such as ethylene platinum complex
Pt(CH2ꢁCH2)(PPh3)2 but not high coordinated complex
such as Pd(PPh3)4 [17]. This is due to the fact that in
general a hydrogermane is more reactive than a hy-
drosilane toward a transition metal complex.
Hydrosilane 20 having two hydrosilyl groups in the
molecule has been reported to undergo the hydrosilyla-
tion of olefins with a rhodium catalyst such as
RhCl(PPh3)3 more efficiently when the two hydrosilane
moieties are connected by two or three atoms [17c].
This is ascribed to the formation of an intermediate 21
having a chelate ring which would undergo readily
hydrosilylation to give 22 as illustrated in Eq. (8). In
this respect, higher reactivity of 18 toward catalytic
dehydrogenation is conceivable that the two hy-
drogermyl groups are connected with a two carbon
atom unit each other. Hence 18 forms the chelate ring
quite readily and this leads its facile conversion to 3. In
fact monohydrogermane such as diethylphenylgermane
(23c) is quite unreactive in the presence of Pd(PPh3)4
toward dehydrogenation.
Scheme 7.
rangement, namely the ethyl group on the sp3 germa-
nium atom shifts to the sp2 germanium to give another
germylene complex 14 (Path B) [13]. Since a metal–
metal double bond, such as a silicon–silicon double
bond is well known to be cleaved thermally to give
divalent species, a silylene [15], 14 is expected reason-
ably to be transformed to a germylene 15. Now,
germylene 15 readily inserts into either the GeꢀGe or
Ge-phenylene bond to give 16 or 17. Finally the reduc-
tive elimination would afford 9 from 16, and 10 from
17, respectively.
For silicon analogue 4a, a similar type of the inter-
molecular metathesis followed by the isomerization to
the unsymmetrical dimer analogous to dimer 8 has been
reported with a plausible mechanism [8b].
2.4. Dehydrocoupling of 1,2-bis(diethylgermyl)benzene
(18) and hydrogermylation of benzo-1, 2-digemacyclo-
butene 1 and related silane 4b
As expected from
a silicon analogue, 1,2-bis-
(dimethylsilyl)benzene (26), in the presence of
Pd(PPh3)4 1,2-bis(diethylgermyl)benzene (18) under-
went dehydrocoupling [2e,16] and was also smoothly
converted to 6 probably by way of palladium complex
3 [17]. Actually being heated in toluene containing the
palladium catalyst at 100°C for 16 h 18 afforded dimer
6 in 82% yield (Eq. (5)). The reaction path was followed
(7)
1
by H-NMR spectroscopy, and in fact this showed that
even at 50°C 18 was converted to 3 and then dimer 6
was formed slowly from 18 by way of 3. When 18 was
reacted with 0.5 equivalent of Pd(PPh3)4 at 100°C to
give the reaction mixture composed of 3 and 6 in
around 2:3 ratio (Eq. (6)). The ratio is close to those
obtained from thermolyses of 1, 3, and 6, respectively,
under similar conditions as mentioned (Eq. (1)). This
implies that the equilibrium (1 ? 3 ? 6) should be
established also under these reaction conditions.
(8)
The GeꢀGe bond of 1 was subjected to hydrogermyl-
ation with the palladium catalyst in the presence of
excess amounts of hydrogermane 23 at 50°C for 16 h

426
H. Komoriya et al. / Journal of Organometallic Chemistry 611 (2000) 420–432
and this afforded 24 in high yields as shown in Scheme
7 [18a]. The H-NMR spectrum of the reaction mixture
palladium catalyst in high yields (Eq. (9)). Meanwhile,
this constitutes formally dehydrocoupling of the two
hydrogermanes 18 and 23 by the palladium catalyst,
interestingly only the cross coupling reaction between
18 and 23 has been observed. In conformity with this,
in the absence of 18, the simple hydrogermane 23 and
hydrosilane 25 turned out to be unreactive even in the
presence of the palladium catalyst. This would be at-
tributable to the lack of driving force leading to forma-
tion of the chelate ring such as that of 3. Furthermore,
highly reactive 18 underwent the catalytic self-coupling
to give a dimeric product 6 in the absence of hydroger-
mane 23. So, since 6 should be formed by way of key
intermediate 3 that would preferentially react with hy-
drogermane 23 but not with 18. This may be simply due
to the concentration of 23 being higher than that of 18.
As expected, the hydrogermynation with deuterated
hydrogermane 23d gave only mono-deuterated product
1
of 3 and excess amounts of hydrogermane 23 showed
clean conversion to 24. This indicates that 3 should be
the intermediate of hydrogermylation of this type. The
structure of 24 has been fully established on the basis of
spectroscopic data summarized in Table 2. Interest-
ingly, 3 did not react with hydrosilanes 25 such as
triethylsilane (25a) and dimethylphenylsilane (25b)
[18b,c]. Palladium complex 3 generated first in an NMR
tube was allowed to react with excess amounts of the
hydrosilane 25. However the 1H-NMR spectrum
showed no resonance due to that of 26 but only the
presence of 3 and dimer 6 in the reaction mixture as
observed in the absence of hydrosilane 25.
Similarly, in the presence of large excess amounts of
hydrogermane 23 bis(hydrogermyl)benzene 18 was
readily converted to 24 by the treatment with the
Table 2
NMR and MS spectroscopic data for 24a, 24b, 24c and 24d

H. Komoriya et al. / Journal of Organometallic Chemistry 611 (2000) 420–432
427
24d in high yields (Eq. (10)). This clearly indicates that
at first 18 was converted to 3 which reacts with deuter-
ated hydrogermane 23d to afford 24d in 72% yield.
(9)
Scheme 8.
(10)
1,2-Bis(hydrosilyl)benzene 26 is unreactive to
Pd(PPh3)4 but benzo-1,2-disilacyclobutene 4 is readily
converted to the corresponding palladium complex 27
as shown in Scheme 8 [17d]. For comparative studies of
the reactivity of germanium complex 3, reactions of the
corresponding silicon analog 27 with hydrogermane 23
and hydrosilane 25 have been examined. As summa-
rized in Scheme 9, in the presence of a catalytic amount
of Pd(PPh3)4 benzodisilacyclobutene 4b was reacted at
50°C for 16 h with excess amounts of hydrogermanes
23 to afford hydrogermylated products 28 in 70–80%
yields. Bissilylated complex 27 prepared first at room
temperature was allowed to react readily with excess
amounts of hydrogermane 23 at 50°C to give 28, and
this indicates that as in the case of germanium analog 3,
Scheme 9.
27 should be the key intermediate of the hydrogermyla-
tion. The structures of 28a–b are fully compatible with
spectroscopic data shown in Table 3. As in the case of
germanium analogue 1, 4b was reacted with deuterated
hydrogermane 23d to give only 28d having a GeꢀSi
Table 3
NMR and MS spectroscopic data for 28a, 28b and 28d

428
H. Komoriya et al. / Journal of Organometallic Chemistry 611 (2000) 420–432
Since the metathesis, the dehydrocoupling and the hy-
drometalation observed above are conceivable to be
sorts of concerted [2+2] cycloaddition reactions, the
transition states for these processes may be depicted as
32. Unlike the case of early-transition metal catalyzed
dehydrocoupling the corresponding product will be
produced formally after reductive elimination of the
central metal.
bond in 72% yield (Eq. (11)). On the other hand
hydrosilylation of 4b with hydrosilanes 25 did not
proceed smoothly. Actually, in the presence of the
palladium catalyst 4b did not give 29a with triethylsi-
lane 25a but it gave 29b with dimethylphenylsilane 25b
in only 17% yield (Eq. (12)). However, the tetraethyl
derivative of 4, 3,4-benzo-1,1,2,2-tetraethyl-1,2-disilacy-
clobutane 4a has been reported to give the hydrosily-
lated product in 31% yield with 25a and 52% yield with
25b at higher temperature 150°C [5c].
(13)
(11)
(14)
(12)
3. Experimental
3.1. General methods
The hydrogermylation described can be conceivable
to proceed in a similar manner as the metathesis of a
GeꢀGe bond as shown in Eq. (13). Benzopallada-di-
gemacyclopentene 3 reacts with hydrogermane 23 to
form an intermediate 30 having a newly formed GeꢀGe
bond (Eq. (14)). This undergoes reductive elimination
to afford 24. The corresponding silicon analogue 27
shows similar reactivities to give 28 and 29 as men-
tioned above. In conformity with Eq. (14), the deu-
terium of hydrogermane 23d is transferred to one of the
germanium atoms of product 24d together with forma-
tion of a new GeꢀGe bond.
Formation of 24d suggests that the GeꢀPd and GeꢀH
bonds may be activated in two ways as illustrated in
Scheme 10. At first, in the transition state such as 31
these bonds are simultaneously activated in a five-cen-
tered manner [19]. In conformity with this, recently a
tetrakis(silyl)platinum (IV) complex has been isolated
and characterized during the studies of reactions of
disilylbenzene with a platinum(0) complex [17c]. Al-
though the substituents on silicon atoms in the plat-
inum complex are all hydrogens in the model system,
there seems to be enough room to accommodate the
required five-centered transition state 31 for the germa-
nium systems. Then, the corresponding product of the
s-bond metathesis and the dehydrocoupling will be
formed after the reductive elimination of the central
metal. On the other hand, there seems to be another
possible transition state, namely four-centered transi-
tion state 32 proposed for the dehydrocoupling of
hydrosilanes by early transition metal catalysts [20,21].
All reactions were carried out under an atmosphere
of argon. THF and toluene were dried by refluxing over
sodium benzophenone ketyl and distilled just before
use. GLC-analyses were carried out on a Shimadzu
GC-14A equipped with an FID detector and a 0.25
mm×25 m CBP1 capillary column. Gel permeation
chromatography was used for separation of reaction
products using a series of JAIgel 1H and 2H columns
with a flow of toluene on an LC-908 liquid chro-
matograph of Japan Analytical Industry Co. Ltd.
NMR spectra were obtained on Varian Unity plus 300
and 500 MHz spectrometers. Mass spectral data were
measured on a Shimadzu QP-1000 and High-resolution
mass spectral data were obtained on a Hitachi M-2500
spectrometers.
Scheme 10.

H. Komoriya et al. / Journal of Organometallic Chemistry 611 (2000) 420–432
429
Tetrakis(triphenylphosphine)palladium,
dimethyl-
40H, EtGe), 7.13–7.41 (m, 8H, phenylene ring
protons); 13C-NMR (CDCl3)
8.31, 9.53(EtGe),
phenylsilane, and triethylsilane were purchased and
were used as received. Et3GeH, Me2PhGeH and
Et2PhGeH were prepared by LiAlH4 reduction of the
corresponding chlorogermanes derived from tetra-
chlorogermane. Me2PhGeD was prepared by reduction
of Me2PhGeCl with LiAlD4. 3,4-Benzo-1,1,2,2-tetra-
ethyl-1,2-digermabut-3-ene [4], 1,2-bis(diethylgermyl)-
benzene [4], 3,4-benzo-1,1,2,2-tetramethyl-1,2-disila-
but-3-ene [6] and 1,2-bis(dimethylsilyl)benzene [22] were
prepared according to the literature.
l
126.91, 134.75, 146.75, 146.67 (phenylene ring carbons);
MS (20 eV) m/z (rel. intensity) 647 (M+−Et, 74Ge,
43
72Ge, 3); HRMS calc. for C26H Ge272Ge2 (M+−Et)
74
647.0230, found 647.0225. Anal. Calc. for C28H48Ge4:
C, 49.82; H, 7.17. Found: C, 49.67; H, 6.99%.
3.5. Reaction of 1 with palladium complex 3
In an NMR tube with a septum seal were placed 1
(10 mg, 0.030 mmol), Pd(PPh3)4 (34 mg, 0.030 mmol),
and C6D6 (0.4 ml). After formation of 3 was monitored
by NMR spectroscopy, another lot of 1 (30 mg, 0.089
mmol) was added. After 16 h, formation of dimer 6 was
3.2. Reaction of 3,4-benzo-1,1,2,2-tetraethyl-1,2-
germacyclobut-3-ene (1) with phenylacetylene in the
presence of a catalytic amount of Pd(PPh3)4
1
confirmed by the H- and 13C-NMR spectra.
In a 30 ml two-necked flask fitted with a magnetic
stirrer and a reflux condenser were placed 1 (100 mg,
0.30 mmol), Pd(PPh3)4 (17 mg, 0.015 mmol), phenyl-
acetylene (91 mg, 0.89 mmol), and toluene (5 ml). After
stirred for 16 h at room temperature, the reaction
mixture was separated by preparative silica gel TLC to
give 2,3-benzo-1,1,4,4-tetraethyl-1,4-digermacyclohexa-
2,5-diene (2, 115 mg, 0.26 mmol, 88%).
3.6. Reaction of 6 with one equi6alent of Pd(PPh3)4
In an NMR tube with a septum seal were placed 6
(10 mg, 0.015 mmol), Pd(PPh3)4 (17 mg, 0.015 mmol),
and C6D6 (0.4 ml). After bubbled with argon through a
needle to remove oxygen, they were subjected to
ultrasonic wave. After stood for 16 h at ambient
temperature, 6 was shown to remain unchanged by
NMR measurements. Then, the NMR tube was heated
3.3. Reaction of palladium complex 3 formed from 1 and
one equi6alent of Pd(PPh3)4 with phenylacetylene
1
at 100°C for 2 h and the H- and 13C-NMR spectra at
this moment indicated that palladium complex 3 and
dimer 6 should be found in the ratio of around 2:3 in
C6D6. The ratio observed here did not change on
further heating of the tube. The similar experiment
using 2.5 equivalents of Pd(PPh3)4 gave the ratio of
around 3:2 between 3 and 6 on heating at 100°C for 2
h and the ratio was not changed on further heating of
the mixture.
At first in an NMR tube with a septum seal were
placed 1 (10 mg, 0.030 mmol), Pd(PPh3)4 (34 mg, 0.030
mmol), and C6D6 (0.4 ml). After bubbled with argon
through a needle to remove oxygen, they were subjected
to ultrasonic wave to be dissolved into solution and
then allowed to stand for 30 min at ambient tem-
perature. After formation of complex 3 being moni-
1
tored by NMR spectroscopy phenylacetylene (9 mg,
1
0.089 mmol) was added to the tube. After 6 h, H- and
3.7. Reaction of 6 with phenylacetylene in the presence of
a catalytic amount of Pd(PPh3)4
13C-NMR spectra of 2 were obtained. 3: 1H-NMR
(C6D6) l 0.84–0.91 (m, 4H, CH2Ge), 1.05–1.15 (m, 4H,
CH2Ge), 1.25 (t, 12H, CH3, J=7.8 Hz), 6.80–7.80 (m,
64H, aromatic protons); 13C-NMR (C6D6) l 12.48,
14.29 (EtGe), 127.21, 132.04, 158.23 (phenylene ring
carbons), 128.48, 129.35, 134.32, 138.59 (phenyl ring
carbons).
In a 30 ml two-necked flask equipped with a
magnetic stirrer bar and a reflux condenser were placed
6 (50 mg, 0.074 mmol), Pd(PPh3)4 (4 mg, 0.0037 mmol),
phenylacetylene (23 mg, 0.22 mmol) and toluene (5 ml).
The reaction mixture was stirred at 100°C for 16 h, and
then was separated by preparative TLC (silica gel,
hexane) to give 2 (62 mg, 0.14 mmol, 96%).
3.4. Dimerization of 1 in the presence of a catalytic
amount of Pd(PPh3)4
3.8. Thermolysis of palladium complex 3
In a 30 ml two-necked flask equipped with a
magnetic stirrer bar and a reflux condenser were placed
1 (100 mg, 0.30 mmol), Pd(PPh3)4 (70 mg, 0.015 mmol),
and toluene (5 ml) and were stirred at ambient
temperature for 16 h. Then, the reaction mixture was
separated by preparative TLC (silica gel, hexane) to
give 6 (87 mg, 0.13 mmol, 87%). 6: colorless crystals;
m.p. 207–210°C; 1H-NMR(CDCl3) l 1.00–1.32 (m,
At first in an NMR tube were placed palladium
complex 3 prepared from 1 (10 mg, 0.030 mmol),
Pd(PPh3)4 (34 mg, 0.030 mmol), and C6D6 (0.4 ml) at
ambient temperature. After degassed and sealed in
vacuo, the NMR tube containing 3 was heated at
100°C for 2 h. After allowed to stand for a few hours at
ambient temperature its 1H-NMR showed that the ratio

430
H. Komoriya et al. / Journal of Organometallic Chemistry 611 (2000) 420–432
of 3 and 6 was around 1:1 in the solution. The ratio
remained unchanged on further heating at 100°C.
give 8 (38 mg, 0.056 mmol, 24%) and the mixure of 9
and 10 (22 mg, 9: 10=ca. 2:1).
3.9. Formation of 1 from 6 in the presence of Pd(PPh3)4
3.12. Formation of dimer 6 from 1,2-bis(dimethyl-
silyl)benzene 18 in the presence of Pd(PPh3)4
In a 10 ml round flask equipped with a magnetic
stirrer and connected to a chilled trap (0°C) by way of
a vacuum pump were placed dimer 6 (200 mg, 0.30
mmol), Pd(PPh3)4 (17 mg, 0.015 mmol), and n-eicosane
(500 mg). On heated around 100–120°C volatile frac-
tions were distilled into the trap under reduced pressure
(0.1 mmHg). Then, these distillates were analyzed to
contain a certain amount of 1 by GC and GC-MS.
In a Pyrex tube 18 (100 mg, 0.29 mmol), Pd(PPh3)4
(17 mg, 0.015 mmol), and toluene (1 ml) were placed,
carefully degassed and sealed in vacuo. The sealed tube
was heated at 160°C for 16 h. The reaction mixture was
separated by preparative TLC (silica gel, hexane) to
give 6 (82 mg, 0.012 mmol, 82%).
3.13. Reaction of 18 with Pd(PPh3)4
3.10. Dimerization of 1 at higher temperature (160°C)
in the presence of a catalytic amount of Pd(PPh3)4
At first in an NMR tube with a septum seal were
placed 18 (10 mg, 0.029 mmol), Pd(PPh3)4 (17 mg,
0.015 mmol), and C6D6 (0.4 ml) at ambient tempera-
ture. After bubbled with argon through a needle to
remove oxygen, they were warmed at 50°C for 16 h.
From the 13C-NMR measured molar ratio of 18, 3 and
6 in the tube were estimated to be around 53:31:16. On
the other hand, the ratio between 3 and 6 changed to
around 2:3 on heated at 100°C.
In a Pyrex tube 1 (100 mg, 0.30 mmol), Pd(PPh3)4 (70
mg, 0.015 mmol), and toluene (1 ml) were placed,
degassed and sealed in vacuo. The sealed tube was
heated at 160°C for 16 h. The reaction mixture was
separated by preparative TLC (silica gel, hexane) to
give 8 (24 mg, 0.036 mmol, 24%) and the mixture of 9
and 10 (13 mg, 9: 10=ca. 2:1). All attempts to separate
1
9 and 10 by GC and LC failed. 8: H-NMR (CDCl3) l
0.78–1.26 (m, 40H, EtGe), 7.22–7.54 (m, 8H, phenyl-
ene ring protons); 13C-NMR (CDCl3) l 5.31, 6.80, 8.45,
9.15, 9.57, 11.85 (EtGe), 126.66, 127.26, 134.32, 135.31,
146.89, 148.38 (phenylene ring carbons); MS m/z (rel.
intensity) 647 (M+−Et, 74Ge2, 72Ge2, 15); HRMS calc.
3.14. Reactions of 1 with excess amounts of
hydrogermanes
In a 30 ml two-necked flask equipped with a mag-
netic stirrer and a reflux condenser were placed 1 (100
mg, 0.30 mmol), Pd(PPh3)4 (17 mg, 0.015 mmol), tri-
ethylgermane (23a) (238 mg, 1.48 mmol) and toluene (5
ml). The reaction mixture was stirred at 50°C for 16 h,
and then was separated by preparative TLC (silica gel,
hexane) to give 24a (116 mg, 0.23 mmol, 79%). Simi-
larly, reaction of 1 and dimethylphenylgermane (23b)
gave 24b in 80%, and that of 1 and diethylphenylger-
mane (23c) yielded 24c in 76%. 24a: a colorless oil;
1H-NMR (CDCl3) l 0.87–1.26 (m, 35H, EtGe), 4.56
(quint, 1H, J=2.8 Hz, HGe), 7.21–7.50 (m, 4H, aro-
matic protons); 13C-NMR (CDCl3) l 5.48, 6.03, 7.66,
9.79, 9.82, 9.98 (EtGe), 126.83, 127.47, 134.57, 135.05,
145.51, 148.04 (aromatic carbons); MS m/z (rel. inten-
sity) 469 (M+−Et, 74Ge2, 72Ge2, 6), 339 (M+−
Et734Ge, 72Ge, 100); Anal. Calc. for C20H40Ge3: C,
48.21; H, 8.10. Found: C, 48.24; H, 7.87. 24b: a color-
less oil; 1H-NMR (CDCl3) l 0.53 (s, 6H, MeGe),
0.92–1.27 (m, 20H, EtGe), 4.48 (quint, 1H, J=2.8 Hz,
HGe), 7.21–7.43 (m, 9H, aromatic protons); 13C-NMR
(CDCl3) l −1.71 (MeGe), 5.91, 7.47, 9.79, 9.96
(EtGe), 127.10, 127.53, 127.66, 127.76, 133.55, 134.68,
135.22, 142.71, 145.73, 146.64 (aromatic carbons); MS
m/z (rel. intensity) 489 (M+−Et74Ge, 72Ge, 4), 339
(M+−Me2Ph74Ge, 72Ge, 100); Anal. Calc. for
C24H40Ge3: C, 52.76; H, 7.38. Found: C, 52.56; H, 7.39.
for C26H Ge722Ge2 (M+−Et) 647.0230, found
74
43
647.0231. Anal. Calc. for C28H48Ge4: C, 49.82; H, 7.17.
1
Found: C, 49.59; H, 7.01. 9: H-NMR (analyzed as a
mixture of 9 and 10) (CDCl3) l 0.78–1.50 (m, EtGe),
6.97–7.58 (m, 8H, phenylene ring protons); 13C-NMR
(CDCl3) l 5.67, 8.22, 8.27, 8.32, 9.07, 9.82, 10.09, 13.13
(EtGe), 126.75, 127.00, 127.21, 133.72, 135.73, 138.25,
144.85, 145.85, 150.87 (phenylene ring carbons); MS
m/z (rel. intensity) 647 (M+−Et, 74Ge2, 72Ge2, 15). 10:
1H-NMR (analyzed as a mixture of 9 and 10) (CDCl3)
l 0.78–1.50 (m, EtGe), 6.97–7.58 (phenylene ring pro-
tons); 13C-NMR (CDCl3) d 4.64, 4.93, 5.94, 7.76, 8.06,
9.16, 9.94, 10.13, 10.85, 11.67, 11.69, 12.41 (EtGe),
126.59, 126.97, 127.24, 127.76, 133.57, 134.97, 135.21,
136.78, 145.39, 148.32, 151.45, 151.87 (phenylene ring
carbons); MS m/z (rel. intensity) 676 (M+, 74Ge2,
72Ge2, 13), 647 (M+−Et, 74Ge2, 72Ge2, 14).
3.11. Isomerization of 6 in the presence of Pd(PPh3)4
at higher temperature (160°C)
In a Pyrex tube 6 (100 mg, 0.15 mmol), Pd(PPh3)4 (9
mg, 0.0074 mmol), and toluene (1 ml) were placed,
carefully degassed and sealed in vacuo. The sealed tube
was heated at 160°C for 16 h. The reaction mixture was
separated by preparative TLC (silica gel, hexane) to
1
24c: a colorless oil; H-NMR (CDCl3) l 0.92–1.25 (m,

H. Komoriya et al. / Journal of Organometallic Chemistry 611 (2000) 420–432
431
30H, EtGe), 4.47 (quint, 1H, J=2.8 Hz, HGe), 7.20–
7.44 (m, 9H, aromatic protons); 13C-NMR (CDCl3) l
5.92, 6.14, 7.74, 9.71, 9.74, 9.95 (EtGe), 126.98, 127.50,
127.53, 127.66, 134.34, 134.34, 134.63, 135.16, 140.55,
145.73, 147.20 (aromatic carbons); MS m/z (rel. inten-
sity) 517 (M+−Et, 74Ge, 72Ge, 3), 339 (M+−
Et2Ph74Ge, 72Ge, 100); Anal. Calc. for C24H40Ge3: C,
52.76; H, 7.38. Found: C, 52.56; H, 7.39%.
3.17. Reaction of 2,3-benzo-1,1,2,2-tetramethyl-1,2-
disilacyclopent-3-ene (4b) with excess amounts of
hydrogermanes in the presence of a catalytic amount of
Pd(PPh3)4
In a 30 ml two-necked flask fitted with a magnetic
stirrer and a reflux condenser were placed 4b (100 mg,
0.52 mmol), Pd(PPh3)4 (30 mg, 0.026 mmol), tri-
ethylgermane (23a, 418 mg, 2.60 mmol), and toluene (5
ml). After stirred for 16 h at 50°C, the reaction mixture
was separated by preparative silica gel TLC to give 28a
(134 mg, 0.38 mmol, 73%). Similarly, under these con-
ditions, reactions of 4a with dimethylphenylgermane
(23b) and deuteriodimethylphenylgermane (23d) yielded
28b and 28d in 71 and 72% yields, respectively. 28a: a
3.15. Reaction of 3 with hydrogermanes
At first in an NMR tube with a septum seal were
placed 1 (10 mg, 0.030 mmol), Pd(PPh3)4 (34 mg, 0.030
mmol), and C6D6 (40 ml). After bubbled with argon
through a needle into the solution to remove oxygen,
the reaction mixture was allowed to stand for 30 min at
ambient temperature.
1
colorless oil; H-NMR (CDCl3) l 0.32 (d, 6H, J=3.8
Hz, MeSiH), 0.50 (s, 6H, MeSiGe), 0.78–0.97 (m, 15H,
EtGe), 4.69 (sep, 1H, J=3.8 Hz, HSi), 7.29–7.54 (m,
4H, phenylene ring protons); 13C-NMR (CDCl3) l −
2.36 (MeSiH), 0.94 (MeSiGe), 4.33, 9.81 (EtGe),
127.61, 128.15, 134.14, 134.28, 144.43, 146.63 (phenyl-
ene ring carbons); MS m/z (rel. intensity) 339 (M+−
Me, 74Ge, 2), 325 (M+−Et, 74Ge, 21), 193
(M+−Et734Ge, 100); Anal. Calc. for C16H32Si2Ge: C,
After palladium complex 3 in the NMR tube was
confirmed by 1H-NMR spectroscopy triethylgermane
(23a) (24 mg, 0.15 mmol) was added into the tube, and
was subjected to ultrasonic wave for 30 min. The
reaction mixture was heated at 50°C for 16 h. At this
1
moment the H- and 13C-NMR spectra of the mixture
showed that 24a was formed. Similarly, in the presence
of Pd(PPh3)4, reactions of 1 with dimethylphenylger-
mane (23b), diethylphenylgermane (23c), and deuterio-
dimethylphenylgermane (23d) were shown to yield 24b,
24c, and 24d, respectively. Under similar reaction con-
ditions, reactions of 3 with triethylsilane (25a) and
dimethylphenylsilane (25b) were examined. Thus, NMR
spectra of the reaction mixture in the NMR tube ob-
tained as above showed that 3 and the hydrosilanes
remained unchanged under these conditions.
1
54.41; H, 8.97. 28b: a colorless oil; H-NMR (CDCl3) l
0.22 (d, 6H, J=3.6 Hz, MeSiH), 0.41 (s, 6H, MeSiGe),
0.46 (s, 6H, MeGe), 4.59 (sept, 1H, J=3.6 Hz, HSi),
7.21–7.52 (m, 9H, phenylene ring protons); 13C-NMR
(CDCl3) l −3.35 (MeSiGe), −2.52 (MeSiH), −0.03
(MeGe), 127.49, 127.71, 127.92, 128.22, 133.68, 134.20,
134.44, 142.51, 144.79, 144.91 (phenylene ring carbons);
MS m/z (rel. intensity) 359 (M+−Me, 74Ge, 0.4), 193
(M+−Me2Ph74Ge, 100); Anal. Calc. for C18H28Si2Ge:
C, 57.93; H, 7.56. Found: C, 57.70; H, 7.77. 28d: a
1
colorless oil; H-NMR (CDCl3) l 0.22 (s, 6H, MeSiD),
3.16. Reactions of 18 with excess amounts of hydroger-
manes in the presence of a catalytic amount of Pd(PPh3)4
0.41 (s, 6H, MeSiGe), 0.46 (s, 6H, MeGe), 7.21–7.52
(m, 9H, phenylene ring protons); 13C-NMR (CDCl3) l
−3.33 (MeSiGe), −2.59 (MeSiD), −0.03 (MeGe),
127.49, 127.70, 127.91, 128.20, 133.67, 134.21, 134.42,
142.50, 144.75, 144.89 (phenylene ring carbons); MS
In a 30 ml two-necked flask equipped with a mag-
netic stirrer and a reflux condenser were placed 18 (100
mg, 0.29 mmol), Pd(PPh3)4 (17 mg, 0.015 mmol), di-
ethylphenylgermane (23c) (308 mg, 1.47 mmol), and
toluene (5 ml). The reaction mixture was stirred at 50°C
for 16 h and was separated by preparative TLC (silica
gel, hexane) to give 24c (116 mg, 0.21 mmol, 72%).
Similarly, reactions of 18 with triethylgermane (23a),
2
m/z (rel. intensity) 360 (M+−Me, 74Ge, H, 3), 194
2
(M+−Me2Ph74Ge, H, 100).
Acknowledgements
dimethylphenylgermane
(23b),
and
deuteriodi-
This work was supported by a Grant-in-Aid for
Scientific Research on Priority Area, ‘The Chemistry of
Inter-element Linkage’, from Ministry of Education,
Science, Sports and Culture, Japan.
methylphenylgermane (23d) gave 24a, 24b, and 24d in
70%, 72%, and 72% yields, respectively. 24d: a colorless
1
oil; H-NMR (CDCl3) l 0.53 (s, 6H, MeGe), 0.92–1.27
(m, 20H, EtGe), 7.21–7.43 (m, 9H, aromatic protons);
13C-NMR (CDCl3) l −1.71 (MeGe), 5.79, 7.46, 9.79,
9.95 (EtGe), 127.10, 127.53, 127.66, 127.76, 133.55,
134.70, 135.21, 142.71, 145.68, 146.64 (aromatic car-
bons); MS m/z (rel. intensity) 490 (Et+−Et, 74Ge,
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