Preparation, structural characterization of 1,2-digermacyclobut-3-enes, and their palladium-catalyzed insertion of alkynes

Article abstract of DOI:10.1016/j.jorganchem.2005.03.022

1,2-Digermacyclobut-3-enes were prepared by the treatment of Z-α,β-bis(chlorodialkylgermyl)ethenes with Na metal in boiling toluene and their structures were fully established by spectroscopic methods coupled with X-ray crystallography. In the presence of an appropriate catalyst, 1,2-digermacyclobut-3-enes reacted smoothly with alkynes to give the corresponding insertion products, 1,4-digermacyclohexa-2,5-dienes in moderate to good yields. Conventional complexes, such as [Pd(PPh₃)₄] and [Pt(PPh₃)₄], serve as efficient catalysts. The mechanism of the insertion reaction of alkynes into the germanium-germanium bond of 1,2-digermacyclobut-3-enes is discussed in terms of a key intermediate, a 1,4-digerma-2-buten-1,4-diylpalladium.

Full text of DOI:10.1016/j.jorganchem.2005.03.022

Journal of Organometallic Chemistry 690 (2005) 2967–2974
www.elsevier.com/locate/jorganchem
Preparation, structural characterization
of 1,2-digermacyclobut-3-enes, and their palladium-catalyzed
insertion of alkynes
a,
a
a
a,b
Kunio Mochida *, Hironori Karube , Masato Nanjo , Yasuhiro Nakadaira
a
Department of Chemistry, Faculty of Science, Gakushuin University, 1-5-1 Mejiro, Toshima-ku, Tokyo 171-8588, Japan
b
Department of Chemistry, The University of Electro-Communications, Chofu, Tokyo 182-8585, Japan
Received 28 December 2004; revised 1 March 2005; accepted 8 March 2005
Available online 21 April 2005
Abstract
1,2-Digermacyclobut-3-enes were prepared by the treatment of Z-a,b-bis(chlorodialkylgermyl)ethenes with Na metal in boiling
toluene and their structures were fully established by spectroscopic methods coupled with X-ray crystallography. In the presence of
an appropriate catalyst, 1,2-digermacyclobut-3-enes reacted smoothly with alkynes to give the corresponding insertion products,
1,4-digermacyclohexa-2,5-dienes in moderate to good yields. Conventional complexes, such as [Pd(PPh3)4] and [Pt(PPh3)4], serve
as efficient catalysts. The mechanism of the insertion reaction of alkynes into the germanium–germanium bond of 1,2-digermacy-
clobut-3-enes is discussed in terms of a key intermediate, a 1,4-digerma-2-buten-1,4-diylpalladium.
Ó 2005 Elsevier B.V. All rights reserved.
Keywords: 1,2-Digermacyclobut-3-enes; X-ray diffraction; Palladium complexes; Alkyne insertions
1. Introduction
reaction conditions [2]. The r bond of Group 14 element
catenates is reactive as the corresponding C–C p bond
[3]. Recently, we have reported the synthesis, structure,
and unique properties of 1,2-digermacyclohexa-3,5-
dienes [4a–4e]. During the course of our studies of 1,2-
dimetallacyclopolyenes, we describe in this paper the
preparation, structural characterization of 1,2-digerma-
cyclobut-3-enes, and their palladium-catalyzed insertion
reaction of alkynes. Two research groups have reported
on the study of 1,2-digermacyclobut-3-ene derivatives.
Namely, Weidenbruch et al. [4f] have described briefly
the preparation and crystal structure of tetra-tert-bu-
tyl-1,2-digermacyclobut-3-ene produced by photolysis
of hexa-tert-butylcyclotrigermane in the presence of
phenylacetylene. Synthesis and chemical properties of
3,4-benzo-1,1,2,2-tetraethyl-1,2-digermacyclobut-3-ene
have been reported by Nakadaira and co-workers [4g].
The chemical and physical properties of Group 14
element (Si, Ge, etc.) – Group 14 element bonds have
been extensively studied and are the subject of current
interest in view of the potential applications of Group
14 element compounds to organic synthesis and ad-
vanced materials [1]. In contrast to the extensive studies
of the Si–Si bond, there have been only a few reports on
those of the Ge–Ge bond.
Group 14 element – Group 14 element r bonds are
formally similar to a C–C r bond but are well-known
to be much more reactive than the latter under various
*
Corresponding author. Tel.: +81 3 3986 0221; fax: +81 3 5992 1029.
E-mail address: kunio.mochida@gakushuin.ac.jp (K. Mochida).
0022-328X/$ - see front matter Ó 2005 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2005.03.022

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K. Mochida et al. / Journal of Organometallic Chemistry 690 (2005) 2967–2974
R2
2. Results and discussion
Ph
a: R = Me (43%)
b: R = Et (68%)
c: R = iPr (10%)
GeCl
[Pd]
C-H
+ ClR2GeGeR2Cl
Ph-C
toluene, reflux
GeCl
R2
2.1. Preparation and structural characterization of
1,2-digermacyclobut-3-enes
1
R2
Ge
Ph
Ph
GeR2
Na
toluene, reflux
O2
New types of 1,2-digermacyclobut-3-enes were
prepared by intramolecular cyclization of Z-a,b-
bis(chlorodialkylgermyl)ethenes with sodium (Na) me-
tal. At first, Z-a,b-bis(chlorodialkylgermyl)styrenes (1)
were prepared by the insertion reactions of phenyl-
acetylene into the germanium–germanium bond of
1,2-dichlorotetraalkyldigermanes in the presence of
[Pd(dba)2] (0.05 molar amount) containing ETBP
(0.2 molar amount) in boiling toluene ((R = Me (a):
O
1
GeR2
Ge
R2
3
a: R = Me (0%)
b: R = Et (12%)
c: R = iPr (10%)
2
New germacycles 2b, c are colorless oils and highly
reactive toward oxygen, but can be purified by rapid
chromatography with a short packed column with sil-
ica-gel followed by simple distillation (Kugelrohr) under
reduced pressure. 1,2-Digermacyclobut-3-enes (2b, c) in
toluene are gradually oxidized in air at room tempera-
ture to give the corresponding 1,3-digerma-2-oxacyclo-
pent-4-enes (3).
i
43%, Et (b): 68%, Pr (c): 10%), (dba = dibenzylide-
neacetone, ETBP = 4-ethyl-2,6,7-trioxa-1-phosphabicy-
clo[2.2.2]octane)) [5]. The conventional palladium
catalysts such as [Pd(PPh3)4] were not effective for
the insertion reactions of alkynes into the germa-
nium–germanium bond of 1,2-dichlorotetraalkyldi-
germanes. 1,4-Z-a,b-bis(chlorodialkylgermyl)styrenes
(1b, c) were cyclized by Na metal in boiling toluene
to give the corresponding 3-phenyl-1,2-digermacyclo-
R2
Ge
Ph
Ph
GeR2
GeR2
O2
O
i
Ge
R2
but-3-enes (2) in low yields (R = Et (b): 12%, Pr (c):
2
10%). At the same time, 1,3-digerma-2-oxacyclopent-
4-enes (3) and unidentified products showing 1H
NMR signals assignable to those of the dialkylgerma-
nium units (R2Ge) were also formed. On the other
hand, 1,4-bis(chlorodimethylgermyl)styrene (1a) was
treated by Na metal in boiling toluene to give mainly
1,1,3,3-tetramethyl-4-phenyl-1,3-digerma-2-oxacyclopent-
4-ene (3) together with unidentified compounds
containing Me2Ge units. The formation of cyclic germox-
anes 3 may be ascribed toaccidental oxidation of 2 by oxy-
gen which could not be excluded completely during
preparation and/or the subsequent work-up.
3
1,1,2,2-Tetraethyl-3-phenyl-1,2-digermacyclobut-3-
ene (2b) and 1,1,2,2-tetra-iso propyl-3-phenyl-1,2-diger-
macyclobut-3-ene (2c) were determined by inspection
of H, 13C NMR, and GC–MS data. The structure of
1,2-digermacyclobut-3-ene (2c) was finally established
by the X-ray diffraction method at 120 K as described
in Fig. 1. The 1H NMR of 2b in CDCl3 displayed signals
assignable to those of ethyl groups in the range of
0.99–1.31 ppm, that of a phenyl group in the range of
1
Fig. 1. Molecular structure of 2c. Hydrogen atoms are omitted for clarify. (a) Top view and (b) side view.

K. Mochida et al. / Journal of Organometallic Chemistry 690 (2005) 2967–2974
2969
Table 1
reported, 2b reacted with alkynes to give the correspond-
ing insertion products under very mild conditions due to
the ring strain caused by a longer Ge–Ge bond [4d].
˚
The selected bond length (A) and bond angles (°) of 1,2-digermacy-
clobut-2-ene (2c)
Ge(1)–Ge(2)
Ge(1)–C(3)
Ge(2)–C(2)
Ge(2)–C(12)
Ge(1)–C(1)
Ge(1)–C(6)
Ge(2)–C(9)
2.439(7)
1.971(7)
1.993(6)
1.970(7)
1.959(6)
1.987(7)
1.979(6)
Ph
GeEt2
GeEt2
[Pd(PPh3)4]
+
C-H
Ph-C
Ph
benzene, r.t., 1 h
2b
Et2
Et2
Ge
Ge
Ph
Ph
Ge(2)–C(2)–C(1)
C(1)–Ge(1)–Ge(2)
Ge(1)–Ge(2)–C(2)
C(2)–C(1)–Ge(1)
104.5(4)
74.0(2)
74.0(9)
107.5(5)
+
Ph
Ge
Et2
Ge
Et2
II (I/II = 1/1)
I
4
7.10–7.33 ppm, and that due to the olefinic proton at
7.69 ppm, respectively. Compound 2c exhibited 1H
NMR spectrum of signals due to iso propyl groups in
the range of 1.12–1.71 ppm, that due to a phenyl group
in the range of 7.08–7.26 pm, and that due to the olefinic
proton at 7.70 ppm, respectively. Fortunately, 1,2-diger-
macyclobut-2-ene (2c) was crystallized from toluene at
ꢀ78 °C (mp ca. ꢀ60 °C). The molecular structure of
2c at 120 K is shown in Fig. 1. The crystallographic
data, selected bond lengths, and angles are summarized
in Section 3 and Table 1, respectively.
Besides [Pd(PPh3)4], a zero-valent palladium com-
plex, such as [Pd(dba)2] and [Pd(PMePh2)4], also cata-
lyzed the alkyne insertion into the Ge–Ge bond of 2b
to give 4 in moderate to good yields. Under the same
conditions, the use of zero-valent platinum complex,
[Pt(PPh3)4] resulted similarly in good yields of insertion
products.
The reactivities of other terminal and internal alkynes
for 2b were also examined with [Pd(PPh3)4] as a catalyst,
as summarized in Table 2.
˚
The Ge–Ge distance of 2c is 2.439(7) A, which is
slightly shorter than that of 1,1,2,2-tetra-tert-butyl-
˚
3-phenyl-1,2-digermacyclobut-3-ene (2.531(6) A) on
account of a less steric repulsion of substituent on ger-
manium atom [4f]. The bond distance of 2c is somewhat
longer those of 1,2-digermacyclohexa-3-enes (2.3893–
Et2
Ge
Ph
[Pd(PPh3)4]
R, R'
+
C-R'
2b
R-C
benzene, r.t., 1 h
Ge
Et2
4
˚
2.40 A) due to the difference of ring [4a]. The Ge–C
˚
bonds are in the range of 1.959(6)–1.993(6) A, and the
bond angles of Ge–Ge–C and C–C–Ge are 74.0° and
104.5(4)–1.7.5(5)°, respectively. The structure of 2c is
that its four-membered ring is planar.
1-Hexyne reacted with 2b under the same conditions
as those for phenylacetylene to give a 1:1 mixture of 2-
butyl-5-phenyl-1,4-digermacyclohexa-2,5-diene and 3-
butyl-5-phenyl-1,4-digermacyclohexa-2,5-diene in total
86% isolated yields. Other terminal alkynes, such as
methyl propionate, gave the corresponding insertion
products, 2-carboxylate- and 3-carboxylate-5-phenyl-
1,4-digermacyclohexa-2,5-dienes in the ratio of 1:1 in
69% isolated yield. The reactions of internal alkynes
with 2b were also examined. 1-Phenyl-1-propyne and
dimethyl acetylenedicarboxylate reacted with 2b under
the same conditions resulted in formation of the corre-
sponding insertion products in moderate to good yields.
So far as we know, these results are the first examples
of internal alkynes, except for those having electron-
withdrawing groups in insertion reactions of Ge–Ge
bonds. Other internal alkynes, such as bis(trimethylsi-
lyl)acetylene and diphenylacetylene, proved to be unre-
active toward 2b at even 70 °C for 5 h probably due to
steric hindrance caused by these substituents on
alkynes.
2.2. Palladium-catalyzed insertion reactions of
1,2-digermacyclobut-3-ene (2b) with alkynes
Reactions of 1.2-digermacyclobut-3-enes (2) with
alkynes in the presence of palladium complexes were
examined. A degassed benzene solution of 1 mol equiv
of 2b containing 5 mol equiv of phenylacetylene, and
[Pd(PPh3)4] (0.05 mol equiv based on the acetylene) was
stirred at room temperature for 1 h to afford readily a
1:1 mixture of 2,5-diphenyl-1,4-digermacyclohexa-2,5-
diene (4I) and 3,5-diphenyl-1,4-digermacyclohexa-2,5-
diene (4II) in a total yield of 98% (GC yield). Evaporation
of benzene followed by preparative TLC with silica-gel
gave diphenyl-1,4-digermacyclohexa-2,5-dienes (4) (in
pure 77% isolated yield), which showed satisfactory
NMR and MS data. In contrast to the bis-germylation
of phenylacetylene with various digermanes previously

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K. Mochida et al. / Journal of Organometallic Chemistry 690 (2005) 2967–2974
Table 2
Reactions of 1,2-digrmacyclobut-3-ene (2b) with alkynes in the presence of [Pd(PPh3)4]
Run
1,2-Digermacyclobut-3-ene
Alkynes
Conditions
Yield (%)
Product ratio
1
2
3
4
5
6
7
a
2b
2b
2b
2b
2b
2b
2b
Bu–C„C–H
Ph–C„C–H
r.t., 1 h
r.t., 1 h
86a (98)b
77 (95)
69 (90)
56 (85)
52 (85)
0
1:1
1:1
1:1
1:1
–
MeO2C–C„C–H
Ph–C„C–Me
MeO2C–C„C–C–CO2Me
Me3Si–C„C–SiMe3
Ph–C„C–Ph
r.t., 1 h
r.t., 1 h
r.t., 1 h
70 °C, 5 h
70 °C, 5 h
–
0
–
Isolated yields.
GC yields.
b
2.3. Preparation and identification of 1,4-digermabut-2-
ene-1,4-diylpalladium
To obtain further information, we attempted to iso-
late 1,4-digermabut-2-ene-1,4-diylpalladium A under
various conditions without success. Next, we set about
to prepare a platinum analogue of intermediate A by
In the palladium-catalyzed reaction of 2b with alkynes,
1,4-digermabut-2-ene-1,4-diylpalladium complex is con-
ceivable to be a possible intermediate for the insertion
of alkynes and this gives the alkyne-insertion products 4.
To examine intervention of 1,4-digermabut-2-ene-
1,4-diylpalladium intermediate (A), a mixture of 1,2-
digermacyclobut-3-ene (2b) and one mol equiv of
[Pd(PPh3)4] in C6D6 was placed in an NMR tube at
the
treatment
of
(g-ethylene)bis(triphenylphos-
phine)platinum with excess amounts of Z-a,b-bis(di-
methylgermyl)styrene at room temperature for 10 min.
A model complex 1,4-digermabut-2-ene-1,4-diylplati-
num (A0) was formed quantitatively and obtained as a
white powder. The structure of A0 was established by
inspection of spectral data, such as NMR, IR, and MS
spectra. Platinum complex A0 was sensitive to air and
moisture at room temperature.
1
room temperature. After 30 min inspection of the H
NMR spectrum, it was revealed that most of 2b in the
reaction mixture disappeared and instead the complex
A was formed. The structure of A was confirmed by
Ph
1
comparing its H, 13C, and 31P NMR data with those
GeMe2H
+
Pt(PPh3)2
of related palladium and platinum complexes [4f–4h].
1
The H NMR spectrum of A displays signals due to
GeMe2H
ethyl groups on germanium in the range of 0.6–1.4
ppm and those due to phenyl groups in the range of
6.90–7.79 ppm, respectively. The 13C NMR spectrum
of A shows four peaks at 12.22, 12.33, 13.64, and
13.75 ppm, due to ethyl carbons. In addition, A revealed
Me2
Ge
Ph
Pt(PPh3)2
toluene, r.t., 10min
Ge
Me2
a
NMR signals of A suggest the rapid exchange between
31P NMR signal at 13.9 (br) ppm. The broad 31P
A'
1
the two PPh3 ligands on the Pd atom. All H, 13C, and
31P NMR signals due to A locate at higher field than
those due to 2b. The intermediate A smoothly reacted
with phenylacetylene to afford a 1:1 mixture of 1,4-
digermacyclohexa-2,5-dienes (4I and II) in quantitative
yields, as confirmed by NMR spectroscopy.
1
The H NMR of platinum complex A0 in C6D6 dis-
played two methyl signals due to methyl groups on
germanium at 0.41 ppm (JPt–H = 15 Hz) and 0.47 ppm
(JPt–H = 15 Hz). The 31P NMR showed two singlet
signals with two satellites at 29.0 ppm (JPt–P = 2198
Hz, JP–P = 17 Hz) and 29.9 ppm (JPt–P = 2219 Hz,
JP–P = 17 Hz). The small JPt–P value in A0 is consistent
with that of cis-(digermyl)bis(tert-phosphine)platinum
complexes and bis(germyl)platinum complexes having
chelating diphosphines [4d].
Et2
Ph
Ph
Ge
GeEt2
GeEt2
Pd(PPh3)4, 1 eq.
Pd(PPh3)2
C6D6, r.t., 30 min
Ge
2b
Et2
The platinum complex A0 reacted with excess
amounts of phenylacetylene at room temperature for
30 min in C6D6 to give a 1:1 mixture of the correspond-
ing insertion products 3 in quantitative yields, and at the
same time, (g-acetylene)bis(triphenylphosphine)plati-
num was also formed. All products were identified by
NMR and GC–MS analysis.
A
Et2
Ge
Ph
C-H
Ph-C
Ph
C6D6, r.t., 30 min
Ge
Et2
4

K. Mochida et al. / Journal of Organometallic Chemistry 690 (2005) 2967–2974
2971
Me2
Ge
were measured with JEOL JMS-DX 303 mass spectrom-
eter. The UV and UV–vis spectra were recorded with a
Shimadzu UV 2200 spectrometer. IR spectra were re-
corded on Shimadzu FT-IR 4200 spectrometer. Gas
chromatographic analyses were performed with Shima-
dzu GC-8A equipped with 1 m of 20% SE30. X-ray crys-
tallographic data and diffraction intensities were
collected on a MacScience DIP2030 diffractometer uti-
lizing graphite-monochromated Mo Ka (k = 0.71073
Ph
C-H (10 equiv)
C6D6, r.t., 30 min
Pt(PPh3)2
Ph-C
Ge
Me2
A'
Me2
Ph
H
Ge
Ph
Ph
+
Pt(PPh3)2
Ge
˚
Me2
A) radiation. The structures were solved by direct meth-
ods using the program system SIR-92 [6] and refined with
all data on F2 by means of SHELXL-97 [7]. Refinement
was performed by a SILICON Graphics O2 with
maXus. Crystallographic data for 2c: molecular for-
mula = C20H34Ge2, molecular weight = 419.672, mono-
4
2.4. Catalytic cycle
˚
˚
3
clinic, P21/a, a = 16.6670(19) A, b = 8.1500(7) A,
˚
˚
A mechanism for the Pd-catalyzed insertion reaction of
the alkyne into the Ge–Ge bond of 1,2-digermacyclobut-
3-enes (2) can be proposed in analogy with the above
results and was previously suggested by the use for the
Pt-catalyzed insertion of alkynes with 1,2-digermacyclo-
hexa-3,5-dienes [4d]. Thus, the catalytic cycle is composed
of four steps: (a) the oxidative addition of 2 to a palladium
complex, PdLn, to form a 1,4-digermabut-2-ene-1,4-diyl-
palladium intermediate A, (b) the coordination of an
alkyne to A to form a 1,4-digermabut-2-ene-1,4-diylpalla-
dium intermediate having an alkyne as a ligand, (c) the
insertion of a coordinated alkyne into one of the Pd–Ge
bonds of 2 to form an insertion product C, and (d) the
reductive elimination of the 1,4-digermacyclohexa-2,5-
dienes (4) from the insertion product C along with the
regeneration of the active palladium species, that further
carries the catalytic cycle (see Scheme 1).
c = 17.1340 A, b = 114.624(6)°, V = 2115.8(4) A ,
Z = 4, Dcalc = 1.317 g/cm3, GOF = 1.802, R = 0.0640,
Rw = 0.1996.
3.1. Materials
Diethylether, hexane, pentane, benzene, and toluene
were dried by refluxing over sodium benzophenone ketyl
under atmosphere of nitrogen and distilled just before
use. Methanol was dried with magnesium metal and dis-
tilled before use. Phenylacetylene, 1-phenyl-1-propyne,
1-hexyne, methyl propionate, and dimethyl acetylenedi-
carboxylate were commercially available. [Pd(dba)2],
[Pd(PPh3)4], [Pd(PMePh2)3], [Pt(PPh3)4], [Pt(acac)2],
and ETBP are commercially available. Compounds
(ClMe2Ge)2 [8], (ClEt2Ge)2 [9], Z-C6H5C (ClMe2-
Ge)@CH(ClMe2Ge) [10], (g-ethylene)bis(triphenylphos-
phine), and (g-phenylacetylene)bis(triphenylphosphine)
[11] were prepared according to reported procedures.
3. Experimental
3.2. Preparation of 1,2-tetraiso-propyl-1,2-dichloro-
digermane
1H, 13C, 31P NMR spectra were recorded on Varian
Unity Inova-400 MHz spectrometer. GC–MS spectra
To a benzene solution (100 ml) of (PhiPr2Ge)2 (4.7 g,
10 mmol) and AlCl3 (catalytic amounts), HCl gas was
carefully bubbled for 30 h. The reaction was followed
by GC. 1,2-Dichlorodigermane was purified simply by
distillation under reduced pressure in 1.37 g (3.2 mmol,
Ge
Ge
Ge
R
PdLn
R'
Ge
4
1
32%), bp 92–94 °C/0.3 mmHg. H NMR (d, CDCl3)
R
R'
Ge
Ge
1.18–1.22 (dd, J = 7.3 Hz, 24H), 1.62–1.76 (sept.,
J = 7.3 Hz, 4H); 13C NMR (d, CDCl3) 17.7, 21.3; MS
m/z: 388 (M+). Anal. Calc. for C12H28Ge2Cl2: C,
37.12; H, 7.27. Found: C, 37.30; H, 7.34%.
Ge
(A)
PdLn
PdLn
(C)
Ge
Ge
R'
Ge
3.3. Preparation of Z-a,b-bis(chlorodiethylgermyl)-
styrene (1b)
Pd
Ln
R'
R
R
A toluene solution (70 mol) of (ClEt2Ge)2 (13 g, 0.047
mol), 3 equiv phenylacetylene (12 ml, 0.11 mol), 0.05
equiv of [Pd(dba)2] (1.04 mg, 1.8 mmol), and 0.1 equiv
(B)
Scheme 1. Catalytic cycle.

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K. Mochida et al. / Journal of Organometallic Chemistry 690 (2005) 2967–2974
of ETBP (0.58 mg, 3.6 mmol) was placed in a two-
necked flask under argon atmosphene. After stirring
for 12 h in boiling toluene, the toluene, ETBP, and unre-
acted phenylacetylene were evaporated. Then, Z-a,b-
bis(chlorodiethylgermyl)styrene (1b) was purified simply
by distillation (Kugelrohr) under reduced pressure to
give 1b (7.71 g, 0.20 mol, 43%). 1b: bp 80–140 °C/0.02
mmHg; 1H NMR (d, CDCl3) 1.09 (m, 10H, EtGe),
1.25 (m, 10H, EtGe), 6.90 (s, 1H, CH@), 7.10–7.42 (m,
5H, phenyl ring protons); 13C NMR (d, CDCl3) 8.19,
8.72, 12.99, 15.94, 126.06, 127.36, 128.55, 144.62,
148.15, 158.84. MS m/z (relative intensity): 405 (88),
370 (11), 341 (10), 268 (33), 239 (30), 166 (100). Anal.
Calc. for C16H26Ge2Cl2: C, 44.23; H, 6.03. Found: C,
44.46; H, 6.38%.
pound 2b was stored below ꢀ20 °C in argon. Under
1
these conditions, 2b was stable for one month. 2b: H
NMR (d, CDCl3) 0.99–1.31 (m, 20H, EtGe), 7.10–7.33
(m, 5H, Ph), 7.69 (s, 1H, CH@); 13C NMR (d, CDCl3)
8.85, 9.55, 10.70, 10.90, 126.52, 127.74, 128.53, 140.88,
149.72, 161.74. MS m/z (relative intensity): 364 (M+,
41), 349 (46), 335 (27), 320 (8), 262 (100), 233 (47), 204
(24), 175 (31), 160 (49). Anal. Calc. for C16H26Ge2: C,
52.86; H, 7.21. Found: C, 53.05.; H, 7.42%. 1,1,3,3-Tet-
raethyl-4-phenyl-1,3-digerma-2-oxacyclopent-4-ene (3b)
was obtained as by-product by chromatography with a
short column packed with silica-gel eluted with diethyle-
ther and Kugelrohr-distilled (84–95 °C/0.085 mmHg) in
6.8% yield (450 mg, 1.19 mmol). 3b: 1H NMR (d,
CDCl3) 0.91–1.22 (m, 20H, EtGe), 7.24 (s, 1H, CH@),
7.16–7.30 (m, 5H, phenyl); MS m/z (relative intensity):
380 (M+, 18), 351 (100), 322 (53).
3.4. Preparation of Z-a,b-bis(chlorodiisopropyllgermyl)-
styrene (1c)
3.6. Preparation of 1,1,2,2-tetra-isopropyl-3-phenyl-1,2-
digermacyclobut-3-ene (2c)
A toluene solution (70 mol) of (CliPr2Ge)2 (6.23 g,
16.03 mmol), 2 equiv of phenylacetylene (3.52 ml, 32.1
mmol), 0.05 equiv of [Pd(dba)2] (461 mg, 32.1 mmol),
and 0.1 equiv of ETBP (260 mg, 1.60 mmol) was placed
in a two-necked flask. under argon atmosphene. After
stirring for 37 h in boiling toluene, the toluene, ETBP,
and unreacted phenylacetylene were evaporated. Z-
a,b-bis(chlorodiisopropylgermyl)styrene (1c) was puri-
fied simply by distillation (Kugelrohr) under reduced
pressure in 1.57 g (3.20 mol, 10.0%). 1c: bp 103–133
A solution of bis(chlorodiisopropylgermyl)styrene
(1c) (7.62 g, 17.5 mmol) in toluene (80 ml) was slowly
added to sodium (1.29 g, 56.1 mmol) in refluxing toluene
(100 ml). After the mixture continued to reflux for 48 h,
the resulting salt was filtered off. The filtrate was concen-
trated under reduced pressure at below 30 °C. The crude
solution was chromatographed over a short column
packed with short column and rapidly eluted with hex-
ane to give pure 1,1,2,2-tetra-isopropyl-3-phenyl-1,2-
digermacyclobut-3-ene (2c) (730 mg, 1.74 mmol, 10%
1
°C/0.05 mmHg. H NMR (d, CDCl3) 1.04 (d, J = 7.3
Hz, 3H, CH3), 1.14 (d, J = 7.3 Hz, 3H, CH3), 1.17 (d,
J = 7.3 Hz, 3H, CH3), 1.24 (d, J = 7.3 Hz, 3H, CH3),
1.71 (sept., J = 7.3 Hz, 2H, CH), 2.07 (sept., J = 7.3
Hz, 2H, CH), 6.89 (s, 1H, CH@), 7.03–7.38 (m, 5H,
Ph); 13C NMR (d, CDCl3) 18.36, 18.72, 19.20, 19.53,
21.62, 24.69, 126.35, 127.31, 128.51, 145.52, 149.68,
158.05. MS m/z (relative intensity): 490 (M+, 13), 447
(100), 404 (26). Anal. Calc. for C20H34Ge2Cl2: C,
47.25; H, 6.74. Found: C, 47.48; H 6.90%.
1
yield). 2c: mp ꢀ48 °C. H NMR (d, CD2Cl2, 23 °C)
1.12 (d, J = 7.3 Hz, 6H, CH3), 1.14 (d, J = 7.3 Hz, 6H,
CH3), 1.17 (d, J = 7.3 Hz, 6H, CH3), 1.18 (d, J = 7.3
Hz, 6H, CH3), 1.60 (sept., J = 7.3 Hz, 2H, CH), 1.71
(sept., J = 7.3 Hz, 2H, CH), 7.08–7.26 (m, 5H, Ph),
7.70 (s, 1H, CH@); 13C NMR (23 °C, d, CDCl3) 18.4,
18.7, 21.2, 21.3, 21.5, 21.7, 126.2, 126.8, 128.1, 141.6,
150.4, 171.6; MS m/z (relative intensity): 420 (M+, 11),
390 (100), 377 (74), 347 (14), 291 (12), 248 (27), 203
(13), 160 (159, 117 (9). Anal. Calc. for C20H34Ge2: C,
57.26; H, 8.17. Found: C, 57.36; H, 8.25%.
3.5. Preparation of 1,1,2,2-tetraethyl-3-phenyl-1,2-
digermacyclobut-3-ene (2b)
A solution of bis(chlorodiethylgermyl)styrene (7.62 g,
17.5 mmol) in toluene (80 ml) was slowly added to so-
dium (1.29 g, 56.1 mmol) in refluxing toluene (100 ml).
After the mixture continued to reflux for 48 h, the result-
ing salt was filtered off. Then, the filtrate was concen-
trated under reduced pressure at below 30 °C. To
remove the germoxane, the crude solution thus obtained
was chromatographed rapidly over a silica-gel short col-
umn with hexane. After evaporation of the solvent, the
residue was Kugelrohr-distilled (94–99 °C/0.048 mmHg)
to afford 1,1,2,2-tetraethyl-3-phenyl-1,2-digermacyclo-
but-3-ene (2b) (760 mg, 2.1 mmol, 12% yield). Pure com-
3.7. Reaction of bis(chlorodimethyllgermyl)styrene (1a)
with sodium metal
A solution of bis(chlorodimethylgermyl)styrene (6.64
g, 17.5 mmol) in toluene (80 ml) was slowly added to so-
dium (1.29 g, 56.1 mmol) in refluxing toluene (100 ml).
After the mixture was refluxed for 48 h, the resulting salt
was filtered off. The filtrate was concentrated under re-
duced pressure at below 30 °C. GC–MS analysis of the
crude concentrate (0.9 g) showed that the main compo-
nent thus obtained was 1,1,3,3-tetramethyl-4-phenyl-
1,2-digerma-3-oxacyclopent-4-ene (3a).

K. Mochida et al. / Journal of Organometallic Chemistry 690 (2005) 2967–2974
2973
3.8. Preparation of Z-a,b-bis(dimethylgermyl)styrene
(M+ ꢀ Et) (100), 386 (13), 335 (23), 316 (10), 161 (11).
Anal. Calc. for C22H28Ge2: C, 60.38; H, 6.45. Found:
C, 59.40; H, 6.50%. 1,1,4,4-Tetraethyl-2-methyl-3,5-di-
phenyl-1,4-digermacyclohexa-2,5-diene and 1,1,4,4-tet-
raethyl-3-methyl-2,5-diphenyl-1,4-digermacyclohexa-2,
A diethylether solution (40 ml) of bis(chloro-
dimethylgermyl)styrene (7.71 g, 20.3 mmol) and LiAlH4
(0.77 g, 20.3 mmol) was stirred at 40 °C for 3 h. After
hydrolysis with water, Z-a,b-bis(dimethylgermyl)styrene
was obtained in pure form by chromatography a silica
gel over short column packed with silica-gel eluted with
1
5-diene (56% isolated yield). H NMR (d, C6D6) 0.83–
1.38 (m, 40H, EtGe), 1.53 (s, 6H, C–Me), 6.93 (s, 1H,
CH@), 6.95 (s, 1H, CH@), 7.01–7.35 (m, 20H, phenyl);
13C NMR (d, CDCl3) 6.18, 6.35, 6.42, 6.49, 9.10, 9.34,
9.36, 9.50, 19.87, 20.03, 125.16, 125.21, 125.95, 126.26,
126.31, 127.10, 127.20, 127.25, 128.01, 128.03, 128.12,
128.15, 128.24, 128.29, 128.31, 130.00, 133.20, 142.99,
143.12, 143.45, 143.72, 146.88, 148.05, 159.65; MS m/z
(relative intensity) 480 (M+, 8), 451 (100), 436 (18),
407 (18), 350 (19), 335 (43), 306 (8), 205 (16), 160 (32).
Anal. Calc. for C25H34Ge2: C, 62.59; H, 7.14. Found:
C, 62.94; H, 6.81%. 1,1,4,4-Tetraethyl-2-carboxylate-5-
phenyl-1,4-digermacyclohexa-2,5-diene and 1,1,4,4-tet-
raethyl-2-carboxylate-5-phenyl-1,4-digermacyclohexa-2,5-
diene (69% isolated yield). 1H NMR (d, C6D6) 0.79–1.39
(m, 40H, EtGe), 3.41 (s, 3H, CO2Me), 3.42 (s, 3H,
CO2Me), 6.76 (s, 1H, CH@), 6.91 (s, 1H, CH@), 8.34
(s, 1H, CH@), 8.36 (s, 1H, CH@), 6.94–7.35 (m, 10H,
phenyl); 13C NMR (d, CDCl3) 6.97, 7.38, 7.60, 7.79,
8.07, 9.27, 9.33, 9.39, 51.79, 52.01, 125.85, 125.99,
126.39, 126.59, 128.15, 128.27, 129.99, 140.88, 143.22,
147.14, 149.14, 158.87, 159.81, 160.33, 160.68, 67.42,
243.14, 143.15; MS m/z (relative intensity) 448 (M+, 9),
419 (54), 390 (100), 361 (23), 332 (21), 317 (11), 259
(9), 230 (7). Anal. Calc. for C20H30O2Ge2: C, 53.66; H,
6.76. Found: C, 54.02; H, 6.51%. 1,1,4,4-Tetraethyl-2,
3-dicarboxylate-5-phenyl-1,4-digermacyclohexa-2,5-diene
1
hexane (1.98 g, 6.4 mmol, 31.5% yield). H NMR (d,
C6D6) 0.34 (d, J = 3.4 Hz, 6H, MeGe), 0.34 (d, J = 3.3
Hz, 6H, MeGe), 4.57–4.67 (m, 1H, HGe), 4.76 (sept.,
J = 3.4 Hz, 1H, HGe), 6.72 (d, J = 5.5 Hz, 1H, CH@),
7.00–7.22(m, 5H); 13C NMR (d, CDCl3) ꢀ2.6, ꢀ2.2,
126.1, 126.3, 128.1, 144.0, 147.2, 160.9; GC–MS m/z (rel-
ative intensity) 310 (M+, 21), 295 (28), 207 (100). Anal.
Calc. for C12H20Ge2: C, 44.04; H, 6.16. Found: C,
44.36; H, 6.51%.
3.9. Pd-catalyzed reactions of acetylenes with
1,2-digermacyclobut-3-enes (2b)
As a representative example, the reaction of 2b with
phenylacetylene is described. A mixture of 2b (3.6 mg,
10 lmol), phenylacetylene (5.5 lL, 50 lmol) with
[Pd(PPh3)4] (0.6 mg, 0.5 lmol) and toluene (0.6 ml)
was placed in a 5-ml flask. The solution was degassed
under vacuum and stirred at room temperature for 1
h. GC and GC–MS analyses of the reaction mixture
showed 2b was completely consumed and thus led to
the formation of 1,1,4,4-tetraethyl-2,5-diphenyl-1,4-
digermacyclohexa-2,5-dienes (4). The crude solution
was chromatographed over silica-gel TLC to give a 1:1
mixture of 1,1,4,4-teraethyl-2,5-diphenyl-1,4-digermacy-
clohexa-2,5-diene and 1,1,4,4-tetraethyl-2,6-diphenyl-
1,4-digermacyclohexa-2,5-diene (77% isolated yield).
1H NMR (d, C6D6) 0.89–1.17 (m, 40H, EtGe), 6.90 (s,
2H, CH@), 6.97 (s, 2H, CH@), 7.07–7.35 (m, 20H, phe-
nyl); 13C NMR (d, CDCl3) 7.23, 7.40, 7.97, 9.14, 9.39,
9.45, 11.23, 12.42, 125.90, 126.06, 126.07, 126.15,
126,23, 126.44, 127.56, 128.10, 128.11, 128.21, 128.22,
128.28, 128.64, 129.99, 130.23, 133.19, 140.00, 142.63,
142.70, 146.39, 147.30, 159.07, 160.11; MS m/z (relative
intensity) 466 (M+, 7), 437 (100), 408 (18), 161 (18), 132
(16). Anal. Calc. for C24H32Ge2: C, 61.90; H, 6.93.
Found: C, 62.05; H, 6.71%. 1,1,4,4-Tetraethyl-2-butyl-
5-phenyl-1,4-digermacyclohexa-2,5-diene and 1,1,4,4-
tetraethyl-3-butyl-5-phenyl-1,4-digermacyclohexa-2,5-diene
1
(52% isolated yield). H NMR (d, C6D6) 1.09–1.18 (m,
20H, EtGe), 3.39 (s, 3H, CO2Me), 3.45 (s, 3H, CO2Me),
6.77 (s, 1H, CH@), 6.94–7.36 (m, 5H, phenyl); 13C
NMR (d, CDCl3) 7.67, 7.75, 9.07, 9.28, 51.93, 52.02,
125.88, 125.92, 126.83, 128.35, 128.26, 141.88, 146.04,
221.85, 239.64; MS m/z (relative intensity) 506 (M+,
10), 477 (68), 448 (100), 419 (23), 390 (21), 286 (26).
Anal. Calc. for C22H32O4Ge2: C, 52.26; H, 6.38. Found:
C, 52.60; H, 6.51%.
3.10. Pt-catalyzed reactions of acetylenes with
1,2-digermacyclobut-3-enes (2b)
As a representative example, the reaction of 2b with
phenylacetylene is described. A mixture of 2b (3.6 mg,
10 lmol), phenylacetylene (5.5 lL, 50 lmol),
[Pt(PPh3)4] (0.6 mg, 0.5 lmol), and toluene (0.6 ml)
was placed in 5 ml flask. The solution was degassed un-
der vacuum and stirred at room temperature for 1 h.
GC and GC–MS analyses of the reaction mixture
showed 2b was completely consumed along with the
formation of 1,1,4,4-tetraethyl-2,5-diphenyl-1,4-diger-
macyclohexa-2,5-dienes. The crude solution was chro-
matographed over silica-gel to give a 1:1 mixture of
1
(86% isolated yield). H NMR (d, C6D6) 0.84–1.24 (m,
40H, EtGe), 1.24–1.53 (m, 18H, C–Bu), 6.57 (s, 1H,
CH@), 6.62 (s, 1H, CH@), 6.91 (s, 1H, CH@), 6.93 (s,
1H, CH@), 7.02–7.36 (m, 10H, phenyl); 13C NMR (d,
CDCl3) 7.10, 7.41, 8.11, 8.42, 9.65, 10.66, 12.66, 14.46,
22.87, 30.06, 30.84, 31.08, 31.46, 38.16, 40.53, 41.47,
125.89, 125.96, 126.08, 126.22, 128.03, 128.09, 128.25,
128.62, 129.97, 133.07, 136.45, 137.18, 137.42, 142.60,
143.04, 147.36; MS m/z (relative intensity) 417

2974
K. Mochida et al. / Journal of Organometallic Chemistry 690 (2005) 2967–2974
1,1,4,4-teraethyl-2,5-diphenyl-1,4-digermacyclohexa-2,5-
diene and 1,1,4,4-tetraethyl-2,6-diphenyl-1,4-digerma-
cyclohexa-2,5-diene (75% isolated yield).
phenylacetylene (21 lL, 194 lmol) and C6D6 (0.7 ml)
at ambient temperature. After bubbling with argon
through a needle to remove oxygen, they were allowed
to stand at room temperature for 10 min. The reaction
mixture was separated by preparative silica-gel TLC
eluted with hexane (8.6 mg, 18.4 lmol, 95% yield, 4I/
4II = 4/3).
3.11. Reactions of 1,2-digermacyclobut-3-ene (2b) with
one mol equiv of [Pd(PPh3)4]
In a Pyrex NMR tube with a septum seal were placed
1,2-digermacyclobut-3-ene (2b) (0.62 mg, 1.73 lmol),
[Pd(PPh3)4] (2.0 mg, 1.73 lmol) and C6D6 (0.7 ml) care-
fully degassed and sealed under vacuum. The sealed
tube was allowed to stand at 23 °C for 30 min. 1H
NMR (d, CD2Cl2, 23 °C) 0.01–1.23 (m, 20H), 6.90–
7.79 (m, 36H); 31P NMR (d, C6D6, 23 °) 13.9 (br); 13C
NMR (d, CD2Cl2, 23 °C) 12.22, 12.33, 13.64, 13.75,
124.4, 126.5, 127.2, 127.4, 129.2, 129.4, 131.7, 134.1,
134.2, 135.5, 147.9, 150.5, 165.1.
Acknowledgements
This work was supported by a Grant-in-Aid for Pri-
ority Area Research on ‘‘Exploitation of Multi-Element
Cyclic Molecules’’ from the Ministry of Education, Cul-
ture, Science, Sports, and Technology, Japan. The
authors thank Miss Hiromi Shimizu for preparation of
(iPr2ClGe)2.
3.12. Reactions of 1,4-digermabut-2-ene-1,4-diylpalla-
dium with phenylacetylene
References
To an NMR tube containing 1,4-digermabut-2-ene-
1,4-diylpalladium ((2b (8 lmol), [Pd(PPh3)4] (8 lmol)),
10 mol equiv of phenylacetylene (80 lmol) was added
under argon atmosphere. The reaction products formed
were identified by means of NMR. The reaction mixture
was separated by preparative silica-gel TLC eluted with
hexane (ca. 1.0 mg, 2 lmol).
[1] R.D. Miller, J. Michl, J. Chem. Rev. 89 (1989) 1359.
[2] R. West, in: S. Patai, Z. Rappoport (Eds.), The Chemistry of
Organosilicon Compounds, Wiley, New York, 1989, p. 1207
(Chapter 19).
[3] (a) G. Raabe, J. Michl, in: S. Patai, Z. Rappoport (Eds.), The
Chemistry of Organosilicon Compounds, Wiley, New York, 1989,
p. 1015 (Chapter 17);
(b) R. West, Angew. Chem., Int. Ed. Engl. 26 (1987) 1201;
(c) T. Tsumuraya, S.A. Batcheller, S. Masamune, Angew. Chem.,
Int. Ed. Engl. 30 (1991) 902.
3.13. Reactions of Z-a,b-(dimethylgermyl)styrene with
g-ethylene)bis(triphenylphosphine)
[4] (a) For 1,2-digermacyclohexadienes: K. Mochida, M. Akazawa,
M. Goto, A. Sekine, Y. Ohashi, Y. Nakadaira, Organometallics
17 (1998) 1782;
A solution of bis(dimethylgermyl)styrene (161 mg,
521 lmol), (g-ethylene)bis(triphenylphosphine)platinum
(208 mg, 278 g mol) in degassed toluene (4 ml) was
placed in a 25-ml Schlenk tube. After the mixture was
stirred at room temperature for 10 min, toluene was re-
moved under reduced pressure. After the resulting solid
was washed with hexane, a platinum complex A0 was ob-
tained in pure form (241 mg, 235 lmol, 84.4% yield). A0:
1H NMR (d, C6D6) 0.41 (s with a couple of satellite
peaks, JPt–H = 15 Hz, 6H), 0.47 (s with a couple of satel-
lite peaks, JPt–H = 15 Hz, 6H), 6.77–7.64 (m, 35H, phe-
nyl, 1H, CH@); 31P NMR (d, C6D6) 29.0 (d with two
satellites, JPt–P = 2198 Hz, JP–P = 17 Hz), 29.9 (d with
two satellites, JPt–P = 2219 Hz, JP–P = 17 Hz); 13C
NMR (d, CD2Cl2) 4.1, 5.8, 124.8, 126.7, 127.5, 127.7,
127.8, 128.4, 129.5, 134.1, 134.2, 134.4, 135.2, 135.7,
146.5, 152.1. Anal. Calc. for C48H48Ge2P2Pt: C, 56.13;
H, 4.71. Found: C, 56.22; H, 4.92%.
(b) K. Mochida, W. Hatanaka, T. Wada, A. Sekine, Y. Ohashi,
A. Yamamoto, Chem. Lett. (1998) 1191;
(c) K. Mochida, H. Shimizu, M. Nanjo, Chem. Lett. (2000) 1226;
(d) K. Mochida, T. Wada, K. Suzuki, W. Hatanaka, Y.
Nishiyama, M. Nanjo, A. Sekine, Y. Ohashi, M. Sakamoto, A.
Yamamoto, Bull. Chem. Soc. Jpn. 74 (2001) 123;
(e) K. Mochida, H. Shimizu, T. Kugita, M. Nanjo, J. Organomet.
Chem. 673 (2003) 84;
(f) , For 1,2-digermacyclobut-2-enes:M. Weidenbruch, A. Haged-
orn, K. Peters, H.G von Schnering, Angew. Chem., Int. Ed. Engl.
34 (1995) 34;
(g) H. Komoriya, M. Kako, Y. Nakadaira, K. Mochida,
Organometallics 15 (1996) 2014;
(h) H. Komoriya, M. Kako, Y. Nakadaira, K. Mochida, J.
Organomet. Chem. 611 (2000) 420.
[5] K. Mochida, C. Hodota, H. Yamashita, M. Tanaka, Chem. Lett.
(1992) 1635.
[6] A. Altomare, M.C. Burla, M. Camalli, M. Cascarano, C.
Giacovazzo, A. Guagliardi, G. Polidoro, J. Appl. Crystallogr.
27 (1994) 435.
[7] G.M. Sheldrick, SHELXL-97: Program for Crystal Structure
Refinement, University of Go¨ttingen, Go¨ttingen, Germany, 1997.
[8] M. Kumada, S. Sakamoto, M. Ishikawa, J. Organomet. Chem. 17
(1969) 235.
3.14. Reactions of 1,4-digermabut-2-ene-1,4-diylplatinum
with phenylacetylene
[9] E.J. Bulten, J.G. Noltes, Tetrahedron Lett. 3471 (1966).
[10] T. Hayashi, H. Yamashita, T. Sakakura, U. Uchimaru, M.
Tanaka, Chem. Lett. 245 (1991).
In an NMR tube with a septum seal were placed 1,4-
digermabut-2-ene-1,4-diylplatinum (20 mg, 19.4 lmol),
[11] D.M. Blake, D.M. Roudhill, Inorg. Synth. 18 (1978) 120.