Organotrichlorogermane synthesis by the reaction of elemental germanium, tetrachlorogermane and organic chloride via dichlorogermylene intermediate

Article abstract of DOI:10.1039/b404590d

Organotrichlorogermanes were synthesized by the reaction of elemental germanium, tetrachlorogermane and organic chlorides, methyl, propyl, isopropyl and allyl chlorides. Dichlorogermylene formed by the reaction of elemental germanium with tetrachlorogermane was the reaction intermediate, which was inserted into the carbon-chlorine bond of the organic chloride to give organotrichlorogermane. When isopropyl or allyl chloride was used as an organic chloride, organotrichlorogermane was formed also in the absence of tetrachlorogermane. These chlorides were converted to hydrogen chloride, which subsequently reacted with elemental germanium to give the dichlorogermylene intermediate. The reaction of elemental germanium, tetrachlorogermane and organic chlorides provides a simple and easy method for synthesizing organotrichlorogermanes, and all the raw materials are easily available.

Full text of DOI:10.1039/b404590d

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F U L L P A P E R
Organotrichlorogermane synthesis by the reaction of elemental
germanium, tetrachlorogermane and organic chloride via
dichlorogermylene intermediate
Masaki Okamoto,*a Takuya Asanob and Eiichi Suzuki*b
a
Department of Applied Chemistry, Tokyo Institute of Technology, Ookayama, Meguro-ku,
Tokyo, 152-8552, Japan
Department of Chemistry and Materials Science, Tokyo Institute of Technology, Ookayama,
b
Meguro-ku, Tokyo, 152-8550, Japan
Received 29th March 2004, Accepted 1st June 2004
First published as an Advance Article on the web 24th June 2004
Organotrichlorogermanes were synthesized by the reaction of elemental germanium, tetrachlorogermane and organic
chlorides, methyl, propyl, isopropyl and allyl chlorides. Dichlorogermylene formed by the reaction of elemental
germanium with tetrachlorogermane was the reaction intermediate, which was inserted into the carbon–chlorine bond of
the organic chloride to give organotrichlorogermane. When isopropyl or allyl chloride was used as an organic chloride,
organotrichlorogermane was formed also in the absence of tetrachlorogermane. These chlorides were converted to
hydrogen chloride, which subsequently reacted with elemental germanium to give the dichlorogermylene intermediate.
The reaction of elemental germanium, tetrachlorogermane and organic chlorides provides a simple and easy method for
synthesizing organotrichlorogermanes, and all the raw materials are easily available.
Introduction
(2)
Organochlorogermanes are synthesized by the reaction of
elemental germanium with organic chlorides, such as methyl1,2 and
aryl1,3 chloride, in the presence of copper or silver catalyst. This
Experimental
is called “direct synthesis,” and is one of principal and important
methods to obtain organogermanium compounds, because the reac-
tion is simple and only elemental germanium, which is simple and
readily available, is used as a germanium source.
Germanium grains (<45 m, purity 99.9%, impurities Fe:
0.008 wt.%, Sb: 0.003 wt.%) were washed with an aqueous
solution of 46% hydrogen fluoride for 1 h at room temperature to
remove oxide overlayers. A schematic diagram of the fixed-bed
flow reactor system is shown in Fig. 1. The germanium grains
(2.8 mmol) were placed in a quartz tube reactor (i.d. 10 mm). A
mixture of tetrachlorogermane (0–1.2 mmol h−1), organic chloride
(4.3–14 mmol h−1) and toluene (0.18–0.6 mmol h−1), as an internal
standard, was fed to the reactor by syringe pump, and vaporized at
the upper part of the reactor. Helium as a carrier gas was fed with
the reactant and standard gases to the reactor at 350–550 °C, with
the total flow rate being kept constant at 15 mmol h−1. The reactor
effluents were analyzed by gas chromatography. The products were
identified by GC-MS. The germanium conversion was calculated
as follows.
For formation of carbon–germanium bonds, germylenes are
useful intermediates due to their high reactivity.4 Many stable
germylenes5 and germylene complexes6 have been reported and
used for the synthesis of various organogermanium compounds.
Dichlorogermylene is one of simple germylenes, and can be
prepared by the some methods;7 for instance, the reaction of
elemental germanium and tetrachlorogermane,8–10 and the reaction
of tetrachlorogermane with dichlorosilylene obtained by the
pyrolysis of hexachlorodisilane11 or 1,1-dichlorosilacyclopent-3-
ene.12 Among the methods for formation of the germylene, the first
example is very simple and practical, since elemental germanium
and tetrachlorogermane are easily available and stoichiometric
amounts of byproducts are not formed.
In our previous paper,9 phenyltrichlorogermane was selectively
synthesized from elemental germanium, tetrachlorogermane and
chlorobenzene in an autoclave, germanium conversion being
almost 100%. The formation of phenyltrichlorogermane was caused
by the insertion of dichlorogermylene, formed from elemental
germanium and tetrachlorogermane, into the carbon–chlorine
bond of chlorobenzene as shown in eqn. (1). Thus, the synthesis
of various organochlorogermanes using dichlorogermylene from
elemental germanium and tetrachlorogermane is expected to be a
very useful method.
Germanium conversion (%)
mol all germanium compounds mol tetrachlorogermane fed
∑
=
mol elemental germanium charged in reactor
×100
(1)
In this work, organotrichlorogermane synthesis was carried
out with use of various organic chlorides reacting with
dichlorogermylene as shown in eqn. (2). A vapor-flow reactor, in
which germanium grains was placed, was used for the synthesis,
because the reaction can be operated at a high reaction temperature
and the separation of unreacted germanium from the reaction
mixture is easier than that using an autoclave.
Fig. 1 Schematic diagram of the fixed-bed flow reactor system.
2 3 7 2
D a l t o n T r a n s . , 2 0 0 4 , 2 3 7 2 – 2 3 7 6
T h i s j o u r n a l i s © T h e R o y a l S o c i e t y o f C h e m i s t r y 2 0 0 4

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Table 1 Effect of molar ratio of tetrachlorogermane to methyl chloride on
the germanium conversion and the yield of methyltrichlorogermane in the
reaction of elemental germanium, tetrachlorogermane and methyl chloride
Table 2 Effect of reaction temperature on the germanium conversion and
the yield of methyltrichlorogermane in the reaction of elemental germanium,
tetrachlorogermane and methyl chloride
Molar ratio
Germanium
Amount of
Yield of
Reaction
Germanium
Amount of
Yield of
(GeCl4/MeCl)
conversion (%)
germanium
MeGeCl3/mmol
temperature/°C
conversion (%)
germanium
MeGeCl3/mmol
converted/mmol
converted/mmol
0
0
31
70
53
0
0
450
500
550
0
70
21
0
1.9
0.57
0
3.5
1.2
0.027
0.040
0.085
0.85
1.9
1.5
1.9
3.5
2.7
Germanium grains (2.8 mmol) were heated at the reaction temperature
for 1 h in a helium stream, before the mixture of tetrachlorogermane
(0.56 mmol h−1) and methyl chloride (14 mmol h−1) was fed to the reactor.
Germanium grains (2.8 mmol) were heated at 500 °C for 1 h in a helium
stream, before the mixture of tetrachlorogermane and methyl chloride
was fed to the reactor at 500 °C. The flow rate of methyl chloride was
14 mmol h−1.
Table 2 shows the effect of reaction temperature. At 450 °C,
the reaction did not proceed and a temperature above 500 °C was
necessary for the synthesis of methyltrichlorogermane, however, the
reactionat550°Cresultedinaloweryieldofmethyltrichlorogermane,
no germane except methyltrichlorogermane being formed.
Results and discussion
Methyltrichlorogermane synthesis from elemental germanium,
tetrachlorogermane and methyl chloride
Tetrachlorogermane and methyl chloride were fed at 0.56 and
14 mmol h−1, respectively, at 500 °C to the reactor charged with
the germanium grains. Methyltrichlorogermane was selectively
formed. The time course of the reaction is shown in Fig. 2. Around
2.8 h, the formation rate of methyltrichlorogermane reached the
maximum, 0.69 mmol h−1. At the same time, the effluent rate of
tetrachlorogermane was minimum; i.e. the consumption rate of tetra-
chlorogermane was maximum, 0.33 mmol h−1, which was almost
half of the methyltrichlorogermane rate. This relation between the
formation rate of methyltrichlorogermane and the consumption rate
of tetrachlorogermane was observed throughout the reaction.
(b) Reaction mechanism. The mechanism of the
methyltrichlorogermane formation was examined. No reaction of
tetrachlorogermane (0.56 mmol h−1) occurred with methyl chloride
(14 mmol h−1) fed to the reactor in the absence of elemental
germanium at 450–550 °C, strongly indicating that the methylation
of tetrachlorogermane with methyl chloride (eqn. (3)) does not
proceed during the reaction of germanium, tetrachlorogermane and
methyl chloride.
GeCl4 + MeCl → MeGeCl3 + Cl2
(3)
In our previous paper,10 the formation of dichlorogermylene
by the reaction of elemental germanium with tetrachlorogermane
was reported. The reaction of germanium, tetrachlorogermane and
butadiene gave 1,1-dichlorogermacyclopent-3-ene, which is an
inherent product formed by the reaction of germylene with butadiene
(eqn. (4)). Therefore, also during the reaction of germanium,
tetrachlorogermane and methyl chloride, dichlorogermylene must
be formed.
(4)
As mentioned above, the formation rate of methyltrichloro-
germane was twice the consumption rate of tetrachlorogermane
throughout the reaction (Fig. 2), and the amount of methyltrichloro-
germane yielded was twice the amount of elemental germanium
consumed. Moreover, these relations were also observed when
the ratio of tetrachlorogermane to methyl chloride or reaction
temperature was varied.
These results are consistent with the reaction shown in eqn. (2)
involving a dichlorogermylene intermediate formed from elemental
germanium and tetrachlorogermane. This intermediate reacts with
methyl chloride to afford methyltrichlorogermane. Two mol of
methyltrichlorogermane are formed from one mol of elemental
germanium and one mol of tetrachlorogermane.
Fig. 2 Time courses of the formation rate of methyltrichlorogermane (□),
the effluent rate of tetrachlorogermane (∆) and the germanium conversion
(●) in the reaction of elemental germanium, tetrachlorogermane and methyl
chloride at 500 °C. The amount of elemental germanium charged in the reac-
tor was 2.8 mmol, and the germanium grains were heated at 500 °C for 1 h in
a helium stream prior to the reaction. The feed rates of tetrachlorogermane
and methyl chloride were 0.56 and 14 mmol h−1, respectively. The dashed
line shows the rate of tetrachlorogermane feed.
With no feed of tetrachlorogermane, the reaction did not proceed
at all. This is consistent with reports that catalysts such as copper
are required for the direct synthesis of methylchlorogermanes.1,2
Furthermore, the main product in the direct synthesis is not
methyltrichlorogermane, but dimethyldichlorogermane.1,2 In the
reaction of elemental germanium, tetrachlorogermane and methyl
chloride, dimethyldichlorogermane was not formed. Therefore, the
direct reaction of elemental germanium with methyl chloride does
not proceed in the presence of tetrachlorogermane.
Propyltrichlorogermane synthesis from elemental germanium,
tetrachlorogermane and propyl chloride
Propyl chloride instead of methyl chloride was used for the
organotrichlorogermane synthesis. The reaction did not proceed at
400 °C, while propyltrichlorogermane was formed above 450 °C.
The results obtained by the reaction at 450 and 500 °C are shown
in Fig. 3(a) and (b), respectively. Propyltrichlorogermane was
selectively formed. At 450 °C at 2.4 h of the reaction time, the
formation rate of propyltrichlorogermane reached 0.37 mmol
h−1, which was over 9 times larger than the consumption rate of
tetrachlorogermane (0.04 mmol h−1). This is quite different from
the result that the formation rate of methyltrichlorogermane was
twice the rate of tetrachlorogermane consumption in the reaction
(a) Effect of reaction conditions. The results of the reaction at
various molar ratios of tetrachlorogermane to methyl chloride are
summarized in Table 1. The methyltrichlorogermane yield increased
with increasing the ratio to 0.040, however the yield decreased at a
ratio of 0.085. In all cases, the yield of methyltrichlorogermane was
twice the amount of elemental germanium converted.
D a l t o n T r a n s . , 2 0 0 4 , 2 3 7 2 – 2 3 7 6
2 3 7 3

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Fig. 3 Time courses of the formation rate of propyltrichlorogermane (□), the effluent rate of tetrachlorogermane (∆) and the germanium conversion (●) in
the reaction of elemental germanium, tetrachlorogermane and propyl chloride at 450 (a) and 500 °C (b). The amount of elemental germanium charged in the
reactor was 2.8 mmol, and the germanium grains were heated at the reaction temperature for 1 h in a helium stream prior to the reaction. The feed rates of
tetrachlorogermane and propyl chloride were 0.088 and 4.4 mmol h−1, respectively. The dashed line shows the rate of tetrachlorogermane feed.
using methyl chloride. The yield of propyltrichlorogermane was
2.0 mmol. At 500 °C, the effluent rate of tetrachlorogermane
was larger than the feed rate of tetrachlorogermane. This
indicates that tetrachlorogermane was formed during the reaction
of germanium, tetrachlorogermane and propyl chloride. The
propyltrichlorogermane yield was 0.8 mmol.
The reaction pathway of propyltrichlorogermane was speculated.
Propylation of tetrachlorogermane with propyl chloride (eqn. (5)) did
not occur for the reaction conditions for the propyltrichlorogermane
synthesis from germanium, tetrachlorogermane and propyl chloride.
Table 3 Effect of reaction temperature on the germanium conversion and
the yields of propyltrichlorogermanes in the reaction of elemental germa-
nium, tetrachlorogermane and isopropyl chloride
Yield/mmol
Reaction
Germanium
PriGeCl3
PrGeCl3
temperature/°C
conversion (%)
350
400
450
500*
20
77
94
63
0.4
1.4
0.8
0.1
0
0.0
0.2
0.3
GeCl4 + PrCl → PrGeCl3 + Cl2
(5)
Germanium grains (2.8 mmol) were heated at 450 °C (*500 °C) for 1 h in a
helium stream, before a mixture of tetrachlorogermane (0.088 mmol h−1) and
isopropyl chloride (4.3 mmol h−1) was fed to the reactor.
Additionally, in the absence of tetrachlorogermane,
propyltrichlorogermane was not formed at 450 °C, indicating that
the direct synthesis of propyltrichlorogermane from elemental
germanium does not proceed. Therefore, propyltrichlorogermane
is most likely formed by the insertion of dichlorogermylene
into the carbon–chlorine bond of propyl chloride. At 500 °C,
tetrachlorogermane was formed, suggesting that propyl chloride is
converted to propylene and hydrogen chloride (eqn. (6)) and small
amounts of propylene and hydrogen chloride were detected in the
effluent gas using GC-MS.
PrCl → C3H6 + HCl
(6)
Hydrogen chloride can easily react with elemental germanium
to form tetrachlorogermane probably via a dichlorogermylene
intermediate10 as shown in eqn. (7).
(7)
Fig. 4 Time courses of the formation rate of isopropyltrichlorogerm
ane (□), the effluent rate of tetrachlorogermane (∆) and the germanium
conversion (●) in the reaction of elemental germanium, tetrachlorogermane
and isopropyl chloride at 400 °C. The amount of elemental germanium
charged in the reactor was 2.8 mmol, and the germanium grains were heated
at 450 °C for 1 h in a helium stream prior to the reaction. The feed rates of
tetrachlorogermane and isopropyl chloride were 0.088 and 4.3 mmol h−1,
respectively. The dashed line shows the rate of tetrachlorogermane feed.
When dichlorogermylene reacts with propyl chloride instead of
hydrogen chloride, propyltrichlorogermane is formed probably in
the similar way as the formation of alkylsilane from silylene and
alkyl chloride via a zwitterion intermediate.13,14
Isopropyltrichlorogermane synthesis from elemental
germanium, tetrachlorogermane and isopropyl chloride
temperature. The decomposition of isopropyl chloride was
much easier than that of propyl chloride. The stability of propyl
chloride is consistent with the result that the formation rate of
tetrachlorogermane using isopropyl chloride was larger than that in
the reaction of propyl chloride.
Table 3 shows the effect of reaction temperature. The yield of
propyltrichlorogermane increased with increase of the temperature,
while the isopropyltrichlorogermane yield decreased above 400 °C.
If the insertion of dichlorogermylene into the carbon–chlorine bond
of isopropyl chloride exclusively occurs, only isopropyltrichloro-
germane is formed. However, propyltrichlorogermane was also
formed, especially at a higher temperature. As described above,
isopropyl chloride was also converted to propylene and hydrogen
chloride, and a larger amount of propylene was formed than that in
The reaction of elemental germanium, tetrachlorogermane and
isopropyl chloride was carried out at 400 °C. Fig. 4 shows the time
course of the reaction. The main product was isopropyltrichloro-
germane, and a trace amount of propyltrichlorogermane was
formed. Throughout the reaction, tetrachlorogermane was also
formed. This indicates that isopropyl chloride is decomposed to
form propylene and hydrogen chloride (eqn. (8)),
PriCl → C3H6 + HCl
(8)
which reacts with germanium to give tetrachlorogermane. The
thermal stability of propyl chlorides was tested at the reaction
2 3 7 4
D a l t o n T r a n s . , 2 0 0 4 , 2 3 7 2 – 2 3 7 6

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Table 4 Effect of reaction temperature on the germanium conversion and
the yields of propyltrichlorogermanes in the reaction of elemental germa-
nium and isopropyl chloride
Table 5 Effect of reaction temperature on the germanium conversion and
the yield of allyltrichlorogermane in the reaction of elemental germanium,
tetrachlorogermane and allyl chloride
Yield/mmol
Reaction
temperature/°C
Germanium
conversion (%)
C3H5GeCl3
yield/mmol
Reaction
Germanium
PriGeCl3
PrGeCl3
temperature/°C
conversion (%)
350
400
450
500*
0
69
100
46
0
1.1
1.1
1.1
350
400
450
500*
4
98
87
77
0.01
0.95
0.58
0
0
0.02
0.06
0.08
Germanium grains (2.8 mmol) were heated at 450°C (*500 °C) for 1 h in a
helium stream, before the mixture of tetrachlorogermane (0.088 mmol h−1)
and allyl chloride (4.3 mmol h−1) was fed to the reactor.
Germanium grains (2.8 mmol) were heated at 450°C (*500 °C) for 1 h in a
helium stream, before the mixture of tetrachlorogermane (0.088 mmol h−1)
and isopropyl chloride (4.3 mmol h−1) was fed to the reactor.
the reaction with propyl chloride.The addition of dichlorogermylene
to the carbon–carbon double bond of propylene probably proceeded.
We have found that the reaction of elemental germanium,
hydrogen chloride and alkene gave alkyltrichlorogermane and that
dichlorogermylene is added to the double bond of alkene to form the
germacyclopropane intermediate reacting with hydrogen chloride
to give alkyltrichlorogermane.10
The reaction of elemental germanium, hydrogen chloride
(5 mmol h−1) and propylene (10 mmol h−1) at 400 °C gave
0.36 mmol of propyltrichlorogermane selectively together with
0.02 mmol of isopropyltrichlorogermane. The reaction pathway for
the formation of propyltrichlorogermanes is shown in eqn. (9). In
this reaction, there are two paths (a and b), which include cleavage
of germanium–carbon bond to form n-propyl- and isopropyl-
trichlorogermane, respectively. Pathway a is dominant.
Fig. 5 Time courses of the formation rate of isopropyltrichlorogermane
(□), the effluent rate of tetrachlorogermane (∆) and the germanium conver-
sion (●) in the reaction of elemental germanium and isopropyl chloride at
400 °C. The amount of elemental germanium charged in the reactor was
2.8 mmol, and the germanium grains were heated at 450 °C for 1 h in a
helium stream prior to the reaction. The feed rate of isopropyl chloride was
4.3 mmol h−1.
The elemental germanium charged was completely consumed at 6 h.
The effluent rate of tetrachlorogermane was almost the same as the
feed rate of tetrachlorogermane, indicating that tetrachlorogermane
is formed; therefore, allyl chloride is decomposed to give hydrogen
chloride and propadiene/propyne (eqn. (10)).
(9)
When isopropyl chloride was used, a large amount of
tetrachlorogermane was formed. This shows the possibility of
propyltrichlorogermane formation by the reaction of elemental
germanium and isopropyl chloride without tetrachlorogermane.
This reaction was carried out at 400 °C. Fig. 5 shows the time
courses of the formation rates of the products. Tetrachlorogermane
was mainly formed at the beginning of the reaction, while the
formation rate of isopropyltrichlorogermane gradually increased
with time. Propyltrichlorogermane was hardly formed. At 15 h, the
germanium conversion reached almost 100%. As mentioned in the
previous section, the reaction of elemental germanium and propyl
chloride did not proceed. The difference between the reaction
results using propyl and isopropyl chloride is likely caused by the
difference of thermal stability of these chlorides.
C3H5Cl → C3H4 + HCl
(10)
In fact, the formation of hexadienes and propylene, which are
probably formed by dimerization and hydrogenation of propyne,
respectively, were observed.
Table 4 shows the effect of reaction temperature on the yields
of propyltrichlorogermanes. Tetrachlorogermane was also formed
together with organogermanes. The germanium conversion at
400 °C was the highest. Above 400 °C, the yield of isopropyl-
trichlorogermane decreased, while that of propyltrichlorogermane
increased.At a higher temperature, larger amounts of propylene and
hydrogen chloride were formed from isopropyl chloride. It is most
likely that propylene subsequently reacts with dichlorogermylene
formed by the reaction of elemental germanium with hydrogen
chloride to give propyltrichlorogermane via the methylgerma-
cyclopropane intermediate.
Fig. 6 Time courses of the formation rate of allyltrichlorogermane (□),
the effluent rate of tetrachlorogermane (∆) and the germanium conversion
(●) in the reaction of elemental germanium and allyl chloride at 400 °C.
The amount of elemental germanium charged in the reactor was 2.8 mmol,
and the germanium grains were heated at 450 °C for 1 h in a helium stream
prior to the reaction. The feed rates of tetrachlorogermane and allyl chloride
were 0.18 and 4.3 mmol h−1, respectively. The dashed line shows the rate of
tetrachlorogermane feed.
Allyltrichlorogermane synthesis from elemental germanium,
tetrachlorogermane and allyl chloride
Allyltrichlorogermane was synthesized by the reaction of elemental
germanium, tetrachlorogermane and allyl chloride at 450 °C.
Allyltrichlorogermane was selectively formed as shown in Fig. 6.
D a l t o n T r a n s . , 2 0 0 4 , 2 3 7 2 – 2 3 7 6
2 3 7 5