Synthesis and properties of a strained germacycle having a Ge-Ge bond, 3,4-benzo-1,1,2,2-tetraethyl-1,2-digermacyclobut-3-ene

Article abstract of DOI:10.1021/om9509150

A new strained germacycle, 3,4-benzo-1,1,2,2-tetraethyl-1,2-digermacyclobut-3-ene (1), was prepared by treatment of 1,2-bis(chlorodiethylgermyl)benzene with sodium in toluene. At ambient temperature, 1 was gradually oxidized in air to give 3,4-benzo-1,3-digerma-2-oxacyclopent-4-ene (2), and in the presence of sulfur, 1 was converted to 3,4-benzo-1,3-digerma-2-thiacyclopent-4-ene (3), quantitatively under similar thermal conditions. The digermacyclobutene 1 was thermally labile and readily underwent ring-opening polymerization in toluene to give the corresponding polymer 4 (M_n = 4.4 × 10⁵, M_w = 7.4 × 10⁵, M_w/M_n = 1.7). On thermolysis at 160 °C for 20 h, 1 gave two products, 4,5-benzo-1,2,3-trigermacyclopent-4-ene (5) and 3,4:6,7-dibenzo-1,2,5-trigermacyclohepta-3,6-diene (6), in reasonable yields. On the other hand, the thermolysis of 1 in the presence of phenylacetylene gave 2,3-benzo-1,4-digerma-5-phenyl-cyclohexa-2,5-diene (7), quantitatively. Further, 1 was thermolyzed in CCl₄ to give two chlorinated products, 1,2-bis(chlorodiethylgermyl)benzene (9) and 1-(chlorodiethylgermyl)-2-(diethyl(trichloromethyl)germyl)benzene (10), in reasonable yields. The reaction mechanisms for the polymerization and the thermolysis are discussed.

Full text of DOI:10.1021/om9509150

2014
Organometallics 1996, 15, 2014-2018
Syn th esis a n d P r op er ties of a Str a in ed Ger m a cycle
Ha vin g a Ge-Ge Bon d ,
3,4-Ben zo-1,1,2,2-tetr a eth yl-1,2-d iger m a cyclobu t-3-en e
Haruhiko Komoriya, Masahiro Kako, and Yasuhiro Nakadaira*
Department of Chemistry, The University of Electro-Communications,
Chofu, Tokyo 182, J apan
Kunio Mochida
Department of Chemistry, Faculty of Science, Gakushuin University,
1-5-1 Mejiro, Tokyo 171, J apan
Received November 27, 1995X
A new strained germacycle, 3,4-benzo-1,1,2,2-tetraethyl-1,2-digermacyclobut-3-ene (1), was
prepared by treatment of 1,2-bis(chlorodiethylgermyl)benzene with sodium in toluene. At
ambient temperature, 1 was gradually oxidized in air to give 3,4-benzo-1,3-digerma-2-
oxacyclopent-4-ene (2), and in the presence of sulfur, 1 was converted to 3,4-benzo-1,3-
digerma-2-thiacyclopent-4-ene (3), quantitatively under similar thermal conditions. The
digermacyclobutene 1 was thermally labile and readily underwent ring-opening polymeri-
zation in toluene to give the corresponding polymer 4 (Mn ) 4.4 × 105, Mw ) 7.4 × 105,
Mw/Mn ) 1.7). On thermolysis at 160 °C for 20 h, 1 gave two products, 4,5-benzo-1,2,3-
trigermacyclopent-4-ene (5) and 3,4:6,7-dibenzo-1,2,5-trigermacyclohepta-3,6-diene (6), in
reasonable yields. On the other hand, the thermolysis of 1 in the presence of phenylacetylene
gave 2,3-benzo-1,4-digerma-5-phenyl-cyclohexa-2,5-diene (7), quantitatively. Further, 1 was
thermolyzed in CCl4 to give two chlorinated products, 1,2-bis(chlorodiethylgermyl)benzene
(9) and 1-(chlorodiethylgermyl)-2-(diethyl(trichloromethyl)germyl)benzene (10), in reasonable
yields. The reaction mechanisms for the polymerization and the thermolysis are discussed.
In tr od u ction
electronic effects6 such as fluorine substitution6a,b or
σ-π conjugation.6c-g In fact, a strained simple ring
having a Si-Si bond, such as a 1,2-disilacyclobutene,5c-e
has been shown to be an informative ring system
In recent years, the chemical and physical properties
of the Si-Si bond have been extensively studied and
are subjects of current interest in view of the potential
applications of organosilicon compounds to advanced
materials.1 However, much less interest has been paid
to the chemistry of the Ge-Ge bond.
A Si-Si bond and its higher analog Ge-Ge σ bonds
are formally similar to a C-C σ bond but are well-
known to be much more reactive than the latter under
various reaction conditions.2 Although the group 14
dimetalloid σ bond is reactive as the corresponding C-C
π bond,3 the peralkylated simple σ bond of this type is
still inert under conventional reaction conditions includ-
ing in the presence of oxygen, moisture, or some
transition metal complex at ambient temperature,
except when powerful halogenating or oxidizing agents
are used.4 Therefore, to study the fundamental reac-
tivities of the dimetalloid bond, it is essential to activate
the σ bond to some degree by ring strain5 and/or
(5) (a) Sakurai, H.; Kamiyama, Y. J . Am. Chem. Soc. 1974, 96, 6192.
(b) Barton, T. In Comprehensive Organometallic Chemistry; Wilkinson,
G., Stone, F. G. A., Able, E. W., Eds.; Pergamon Press: Oxford, U.K.,
1982; Vol. 2, Chapter 9.2. (c) 1,2-Disilacyclobutene: Sakurai, H.;
Kobayashi, T.; Nakadaira, Y. J . Organomet. Chem. 1978, 162, C43.
(d) Barton, T.; Kilgour, J . A. J . Am. Chem. Soc. 1976, 98, 7746. (e)
Cheng, C.-W.; Liu, C. S. J . Chem. Soc., Chem. Commun. 1974, 1013.
(f) 1,2-Disilacyclopentane: Kumada, M.; Tamao, K.; Takubo, T.;
Ishikawa, M. J . Organomet. Chem. 1967, 9, 43. (g) Sakurai, H.;
Kamiyama, Y.; Nakadaira, Y. J . Am. Chem. Soc. 1975, 97, 931. (h)
Suzuki, M.; Obayashi, T.; Saegusa, T. J . Chem. Soc., Chem. Commun.
1993, 717, (i) Suginome, M.; Oike, H.; Ito, Y. Organometallics 1994,
13, 4148. (j) Suginome, M.; Oike, H.; Ito, Y. J . Am. Chem. Soc. 1995,
117, 1665. (k) Uchimaru, Y.; Tanaka, Y.; Tanaka, M. Chem. Lett. 1995,
164. (l) 1,2-Disilacyclobutane: Seyferth, D.; Goldman, E. W.; Escudie´,
J . J . Organomet. Chem. 1984, 271, 337. (m) 1,2-Disila-1,2-bis-
(alkylidenecyclobutane): Kusukawa, T.; Kabe, Y.; Ando, W. Chem. Lett.
1993, 985. (n) Kusukawa, T.; Kabe, Y.; Nestler, B.; Ando, W.
Organometallics 1995, 14, 2556. (o) Benzo-1,2-disilacyclobutene: Shi-
ina, K. J . Organomet. Chem. 1986, 310, C57. (p) Ishikawa, M.;
Sakamoto, H.; Tabuchi, T. Organometallics 1991, 10, 3173. (q) Naka,
A.; Hayashi, M.; Okazaki, S.; Ishikawa, M. Organometallics 1994, 13,
4994. (r) Ishikawa, M.; Okazaki, S.; Naka, A.; Tachibana, A.; Kawau-
chi, S.; Yamabe, T. Organometallics 1995, 14, 114 and references cited
therein.
(6) (a) Fluorine substitution: Tamao, K.; Hayashi, T.; Kumada, M.
J . Organomet. Chem. 1976, 114, C19. (b) Tamao, K.; Okazaki, S.;
Kumada, M. J . Organomet. Chem. 1978, 146, 87. (c) σ-π Conjuga-
tion: Sakurai, H.; Nakadaira, Y.; Hosomi, H.; Eriyama, Y.; Kabuto,
C. J . Am. Chem. Soc. 1983, 105, 3359. (d) Morokuma, K. In Organo-
silicon and Bioorganosilicon Chemistry; Sakurai, H., Ed.; Horwood
Limited: Chichester, U.K., 1985; Chapter 4. (e) Gleiter, R.; Schafer,
W.; Sakurai, H. J . Am. Chem. Soc. 1985, 107, 3046. (f) Komoriya, H.;
Kako, M.; Nakadaira, Y.; Mochida, K.; Kubota, M.; Kobayashi, T. Chem.
Lett. 1994, 1439. (g) Komoriya, H.; Kako, M.; Nakadaira, Y.; Mochida,
K.; Kubota, M.; Kobayashi, T. J . Organomet. Chem. 1995, 499, 123.
X Abstract published in Advance ACS Abstracts, March 15, 1996.
(1) Miller, R. D.; Michl, J . Chem. Rev. 1989, 89, 1359.
(2) West, R. In The Chemistry of Organosilicon Compounds; Patai,
S., Rappoport, Z., Eds.; Wiley: New York, 1989; Chapter 19, p 1207.
(3) (a) Raabe, G.; Michl, J . In The Chemistry of Organosilicon
Compounds; Patai, S., Rappoport, Z., Eds.; Wiley: New York, 1989;
Chapter 17, p 1015. (b) West, R. Angew. Chem., Int. Ed. Engl. 1987,
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U.K., 1982; Vol. 2, Chapter 9.4.
0276-7333/96/2315-2014$12.00/0 © 1996 American Chemical Society

A Strained Germacycle Having a Ge-Ge Bond
Organometallics, Vol. 15, No. 8, 1996 2015
Ta ble 1. P olym er iza tion of 1
whereby to examine the chemical nature of a Si-Si σ
bond. Our current interest in the properties of the Ge-
Ge bond6f-g prompted us to prepare a readily accessible
strained digermacycle, benzo-1,2-digermacyclobutene.7
Along with the preparation of the digermacyclic system,
we report some of its characteristics chemical properties.
molecular weight
concn temp time polymer
solvent (mol/L) (°C) (h) yield (%)
a
a
a
Mn
Mw
Mw/Mn
none
neat
0.6
0.2
0.2
0.2
0.2
rt
rt
rt
60
rt
16
16
16
16
16
16
16
97
90
10
28
10
24
38
b
b
b
toluene
toluene
toluene
hexane
hexane
4.4 × 105 7.4 × 105
3.5 × 105 5.6 × 105
1.9 × 105 3.0 × 105
2.7 × 105 4.3 × 105
7.1 × 103 1.8 × 104
9.2 × 104 2.0 × 105
1.7
1.6
1.7
1.6
2.6
2.2
Resu lts a n d Discu ssion
60
rt
toluenec 0.2
P r ep a r a tion , Oxid a tion , a n d Su lfu r iza tion of 1.
The benzo-1,2-digermacyclobutene 3,4-benzo-1,1,2,2-
tetraethyl-1,2-digermacyclobut-3-ene (1) was prepared
by a similar reported method for the preparation of a
benzo-1,2-disilacyclobutene.5o,p Thus, 1,2-bis(diethylger-
myl)benzene was prepared by the reaction of the Grig-
nard reagent derived from o-dibromobenzene with chlo-
rodiethylgermane in situ in THF. After chlorination of
the 1,2-bis(diethyl)germylbenzene with carbon tetra-
chloride in the presence of a catalytic amount of benzoyl
peroxide, the resulting 1,2-bis(chlorodiethylgermyl)-
benzene was cyclized by sodium in boiling toluene to
give 1 in 24% yield (eq 1).
a
Determined by gel permeation chromatography (GPC), THF
b
solvent, polystyrene standard. Insoluble in THF. c Containing
AlCl3 (3 mol %) as a Lewis catalyst.
P olym er iza tion of 1. 1 is thermally labile and
undergoes polymerization quite rapidly to yield in-
soluble solids in THF and other common organic sol-
vents as shown in Table 1. Thus, 1 in toluene (0.6 mol/
L) was evacuated and sealed in a glass tube, and then
this was allowed to stand for 16 h at room temperature.
Under these conditions 1 underwent ring-opening po-
lymerization to give poly[o-(tetraethyldigermanylene)-
phenylene] (4) in 90% yield (eq 3). In GPC analysis, 4
gave one peak with Mn ) 4.4 × 105 and Mw ) 7.4 × 105
(Mw/Mn ) 1.7) based on the polystyrene standard. In
addition, it should be noted the molecular weight
distribution of the polymer prepared is in a rather
1
narrow range (Table 1). The H and 13C NMR spectra
Benzodigermacyclobutene 1 is highly reactive but can
purified by rapid chromatography with a short silica-
gel column and by simple distillation (Kugelrohr) under
reduced pressure. From consideration of the reaction
conditions described in the literature,5o,p 1 seems to be
less reactive than a silicon analog, 3,4-benzo-1,1,2,2-
tetramethyl-1,2-disilacyclobutene, but more reactive
than the tetraethyl silicon analog. Thus, 1 in toluene
is gradually oxidized in air at room temperature to give
4,5-benzo-1,3-digerma-2-oxacyclopent-4-ene (2) in quan-
titative yields (eq 2).7g Under similar conditions, sulfur
is also inserted into the Ge-Ge bond of 1 to give 4,5-
benzo-1,3-digerma-2-thiacyclopent-4-ene (3) in high yields
(eq 2).7g,8
of polymer 4 are quite similar to those of 1 and in accord
with the structure shown as 4. The polymerization of
1 proceeds similarly in less polar hexane as shown in
Table 1. In the polymerization, the yield and molecular
weight of 4 strongly depends on the concentration of 1
employed. Further, the effect of the reaction temper-
ature is generally not significant as shown in Table 1,
but polymerization at a higher temperature caused a
small increase in the polymer yield and a small decrease
in the molecular weight. These results seems to be
similar to those reported for the tetramethyl silicon
analog.5o The effect of a Lewis acid catalyst such as
AlCl3 on polymerization is not so significant as in the
case of the silicon analog; namely, it similarly decreased
the molecular weight to some extent and increased the
polymer yield only to a lesser extent.5o
Th er m olysis of 1. Thermolysis of 1, carried out in
an evacuated sealed tube at 160 °C for 20 h, gave rather
unexpected products, 4,5-benzo-1,1,2,2,3,3-hexaethyl-
1,2,3-trigermacyclopent-4-ene (5) and 3,4:6,7-dibenzo-
1,1,2,2,5,5-hexaethyl-1,2,5-trigermacyclohepta-3,6-di-
ene (6), in 89 and 53% yields, respectively (eq 4). The
(7) For the preparation of sufficient amounts of the appropriate
germacyle to study chemical properties of a Ge-Ge bond, a pertinent
synthetic method for a simple 1,2-digermacyclobutene and -cyclobutane
has not been reported so far. (a) 1,2-Digermacyclobutene: Billeb, G.;
Neuman, W. P.; Steinfoff, S. Tetrahedron Lett. 1988, 29, 5245. (b)
Espenbetov, A. A.; Struchkov, Yu. T.; Kolesnikov, S. P.; Nefedov, O.
M. J . Organomet. Chem. 1984, 275, 33. (c) Nefedov, O. M.; Egorov, A.
M.; Gal’minas, A. M.; Kolesnikov, S. P.; Krebs, A.; Berndt, J . J .
Organomet. Chem. 1986, 301, C21. (d) Ando, W.; Tsumuraya, T. J .
Chem. Soc., Chem. Commun. 1989, 770. (e) Billeb, G.; Brauer, H.;
Neumann, W. P.; Weisbeck, M. Organometallics 1992, 11, 2069. (f)
1,2-Digermacyclobutane: Ohgaki, H.; Kabe, Y.; Ando, W. Organome-
tallics 1995, 14, 2139. (g) 1,2-Digermacyclopentane: Mazerolles, P.;
Lesbre, M.; J oanny, M. J . Organomet. Chem. 1969, 16, 227. We thank
a reviewer for supplying this reference.
structures of both products 5 and 6 are fully consistent
1
with their H and 13C NMR spectra together with mass
spectrometric analysis. Thus, the 13C NMR spectrum
(8) Tsumuraya, T.; Sato, S.; Ando, W. Organometallics 1988, 7, 2015.
of 5 showed four peaks at 3.58, 7.78, 10.16, and 12.47

2016 Organometallics, Vol. 15, No. 8, 1996
Komoriya et al.
Sch em e 1
ppm in roughly 1:2:2:1 ratio which are indicative of two
kinds of ethyl groups on the Ge atoms in a 2:1 ratio. In
addition, there are three peaks at 127.14, 133.72, and
151.35 ppm attributable to those of the symmetrically
substituted phenylene carbons. Along with the chemical
shifts and the number of the 13C NMR signals above,
the benzo-1,2,3-trigermacyclopentene structure for the
product 5 is also in accord with the molecular ion peak
at m/z 468 in the mass spectrum coupled with the
molecular symmetry. Similarly, the 13C NMR spectrum
of 6 consists of two types of resonance signals, namely,
the higher field signals at 7.09, 8.94, 8.97, and 9.92 ppm
in approximately 2:1:1:2 ratio, which are ascribable to
carbons of two kinds of ethyl groups on the Ge atoms,
and the lower field signals at 126.90, 127.36, 133.92,
134.51, 146.76, and 148.02 ppm, which are assignable
to unsymmetrically substituted phenylene carbons.
Thus, in addition to the chemical shifts and the number
of the 13C NMR signals, the molecular ion peak at m/z
544 in the mass spectrum is certainly consistent with
structure 6.
At first glance at the structures of 5 and 6, dieth-
ylgermylene may conceivably be evolved during the
thermolysis and to undergo insertion into the activated
Ge-Ge bond of 1.9 Then, 1 was thermolyzed in the
presence of a germylene trap, namely, either 2,3-
dimethyl-1,3-butadiene10 or dimethylphenylsilane11 un-
der similar conditions in a sealed tube. In either case,
the expected germylene trapped product, namely, 1,1-
diethyl-3,4-dimethyl-1-germacyclopent-3-ene or (dieth-
ylgermyl)dimethylphenylsilane, was not detected in the
thermolysate but 5 and 6 were formed in similar yields
as in the case of the thermolysis in the absence of the
trapping agent (eqs 5 and 6). On the other hand, the
thermolysis of 1 in the presence of phenylacetylene at
160 °C for 16 h yielded 2,3-benzo-1,4-digerma-5-phen-
ylcyclohexa-2,5-diene (7) in 91% yield (eq 7).5c,d The
structure of 7 is fully compatible with its spectroscopic
properties, such as 1H, 13C NMR, and mass spectral
data. In this case, none of 5 and 6 was detected in the
thermolysate. Next, to trap another possible reactive
intermediate, such as a germyl diradical 8 (Scheme 1),12
1 was thermolyzed in CCl4 at 160 °C for 16 h to give
two chlorinated products, 1,2-bis(chlorodiethylgermyl)-
benzene (9) and 1-(chlorodiethylgermyl)-2-((trichloro-
methyl)diethylgermyl)benzene (10) in 48 and 48% yields,
respectively (eq 10).13 The former 9 is the precursor of
1 as mentioned above (eq 1), and the structure of the
latter 10 is fully compatible with its H and 13C NMR
1
spectra along with mass spectrometric data. In addition
to the carbon signals due to two kinds of ethyl groups
on the Ge atoms, the 13C NMR spectrum of 10 shows
the signal at 96.70 ppm assignable to trichloromethyl
carbon together with six signals at lower field, 128.73,
128.78, 134.64, 137.37, 139.87, and 143.36 ppm, arising
from the unsymmetrically substituted phenylene car-
bons. The presence of a trichloromethyl group in 10
implies that the intervening germyl radical intermediate
should be highly reactive.
Mech a n istic Con sid er a tion s. While at ambient
temperature 1 undergoes ring-opening polymerization
to give polymer 4 with high molecular weight, the
thermolysis of 1 at higher temperature affords benzo-
1,2,3-trigermacyclopentene 5 and dibenzo-1,2,5-triger-
macycloheptadiene 6, respectively, in reasonable yields.
This can be rationalized as shown in Scheme 1. Since
the Ge-Ge bond concerned is highly strained and the
resultant germyl radical may be stabilized by the
phenylene π-system to some extent, the homolytic
scission of the activated Ge-Ge bond should occur
readily to yield a bis(germyl) diradical 8, which should
revert to 1 again without difficulty by intramolecular
(9) (a) Castel, A.; Escudie´, J .; Riviere, P.; Satge´, J .; Bochkarev, M.
N.; Maiorova, L. P.; Razuvaev, G. A. J . Organomet. Chem. 1981, 210,
37. (b) Mochida, K.; Kikkawa, H.; Nakadaira, Y. Chem. Lett. 1988,
1089. (c) Mochida, K.; Kikkawa, H.; Nakadaira, Y. J . Organomet.
Chem. 1991, 412, 9. Under certain reaction conditions, free dimeth-
ylgermylene reacts with some kinds of alkynes to yield the correspond-
ing 1,2,3-trigermacyclopent-4-ene. However, from some experimental
evidence, the trigermacyclopentene is suggested to be not the product
from the corresponding 1,2-digermacyclobutene but rather arises from
the reaction of the cyclotrigermane intermediate with the alkyne,
whereas the silicon analog, a 1,2,3-trisilacyclopentene, is formed by
insertion of a silylene into a 1,2-disilacyclobutene.7e
(12) In thermolytic reactions of a silicon analog 3,4-benzo-1,1,2,2-
tetraethyldisilacyclobutene, the corresponding o-quinodisilane has been
postulated as an important reaction intermediate.5p-r However, in
contrast, on consideration of germanium being the higher group 14
element and of a germyl radical being less reactive than a silyl radical,
the reaction intermediate should be represented more adequately by
diradical structure 8 rather than the corresponding o-quinodigermane.
(13) (a) Sakurai, H.; Mochida, K. J . Chem. Soc., Chem. Commun.
1971, 1581. (b) Sakurai, H.; Mochida, K.; Hosomi, A.; Mita, F. J .
Organomet. Chem. 1972, 38, 275. (c) Sakurai, H.; Mochida, K. J .
Organomet. Chem. 1972, 42, 339. (d) Sakurai, H. In Free Radical;
Kochi, J ., Ed.; Wiley Interscience: New York, 1973; Vol. 2, p 741. (e)
Coates, D. A.; Tedder, J . M. J . Chem. Soc., Perkin Trans. 2 1979, 1568.
(10) Schriever, M.; Neuman, W. P. J . Am. Chem. Soc. 1983, 105,
897.
(11) Baines, K. M.; Cooke, J . A.; Vittal, J . J . J . Chem. Soc., Chem.
Commun. 1992, 1484.

A Strained Germacycle Having a Ge-Ge Bond
Organometallics, Vol. 15, No. 8, 1996 2017
(65.0 g, 0.390 mol), and THF (270 mL) was added o-dibro-
mobenzene (38.2 g, 0.162 mol) in THF (80 mL) over a period
of 3 h at room temperature. After reflux for 18 h, the mixture
was hydrolyzed with water whereupon hexane (200 mL) was
added. The organic layer was separated, washed with water,
and dried over Na2SO4. After the solvent was evaporated, the
residue was distilled under reduced pressure to give 1,2-bis-
(diethylgermyl)benzene (29.9 g, 0.088 mol, 54% yield): bp 97
°C/0.15 mmHg; 1H NMR (CDCl3) δ 1.02-1.16 (m, 20H, EtGe),
4.51 (br s, 2H, HGe), 7.26-7.46 (m, 4H, phenylene ring
protons); 13C NMR (CDCl3) δ 5.93, 10.09 (EtGe), 127.67, 134.77,
145.50 (phenylene ring carbons); MS m/z (relative intensity)
340 (M+, 74Ge, 72Ge, 2), 311 (M+ - Et, 74Ge, 72Ge, 100); HRMS
calcd for C14H2674Ge2 342.0458, found 342.0465. Anal. Calcd
for C14H26Ge: C, 49.52; H, 7.72. Found: C, 49.55; H, 7.53.
P r ep a r a tion of 1,2-Bis(ch lor od ieth ylger m yl)ben zen e.
A solution of 1,2-bis(diethylgermyl)benzene (25.0 g, 73.6 mmol)
in CCl4 (130 mL) containing a catalytic amount of benzoyl
peroxide (178 mg, 0.74 mmol) was heated to reflux for 5 h.
The solvent was evaporated, and the residue was distilled
under reduced pressure to give 1,2-bis(chlorodiethylgermyl)-
benzene (26.9 g, 65.9 mmol, 89% yield): bp 135 °C/0.2 mmHg;
1H NMR (CDCl3) δ 1.02-1.22 (m, 20H, EtGe), 7.31-7.79 (m,
4H, phenylene ring protons); 13C NMR (CDCl3) δ 8.25, 14.14
(EtGe), 129.02, 135.25, 142.40 (phenylene ring carbons); MS
m/z (relative intensity) 379 (M+ - Et, 74Ge, 72Ge, 100); HRMS
calcd for C12H1974Ge2Cl2 (M+ - Et) 380.9287, found 380.9273.
Anal. Calcd for C14H24Ge2Cl2: C, 41.17; H, 5.92. Found: C,
41.02; H, 5.95.
P r ep a r a tion of 3,4-Ben zo-1,1,2,2-tetr a eth yl-1,2-d iger -
m a cyclobu t-3-en e (1). A solution of 1,2-bis(chlorodiethylger-
myl)benzene (5.0 g, 12.2 mmol) in toluene (40 mL) was slowly
added to sodium (0.7 g, 30.0 mmol) in refluxing toluene (80
mL). After the mixture continued to reflux for 16 h, the
resulting salt was filtered off. The filtrate was concentrated
under reduced pressure at below 30 °C, and the residue was
diluted with hexane. The crude solution thus obtained was
chromatographed rapidly on a silica gel short column with
hexane to remove the germoxane. After evaporation of the
solvent, the residue was Kugelrohr-distilled (115-120 °C/0.1
mmHg) to afford 1 (1.0 g, 2.96 mmol, 24% yield). Pure 1 was
diluted with hexane (<2%) and stored below -20 °C in Ar.
Under these conditions, 1 was stable for several months. 1:
1H NMR (CDCl3) δ 1.06-1.31 (m, 20H, EtGe), 7.28-7.56 (m,
4H, phenylene ring protons); 13C NMR (CDCl3) δ 8.52, 10.54
(EtGe), 128.00, 132.70, 158.65 (phenylene ring carbons); MS
(20 eV) m/z (relative intensity) 338 (M+, 74Ge, 72Ge, 32), 309
(M+ - Et, 74Ge, 72Ge, 100); HRMS calcd for C14H2474Ge2
340.0302, found 340.0313. Anal. Calcd for C14H24Ge2: C,
49.82; H, 7.17. Found: C, 49.74; H, 7.19.
bond formation. The intervening diradical 8 should be
trapped readily by means of phenylacetylene and carbon
tetrachloride to yield 7,14 9, and 10, respectively.
Further, one of the germyl radical centers attacks
intermolecularly on the activated Ge-Ge bond of a
second molecule to bring about ring opening and to
generate a dimeric germyl diradical 11 as shown by
arrows in Scheme 1. One of the radical centers of the
key intermediate 11 adds subsequently to the Ge-Ge
bond of the other benzo-1,2-digermacyclobutene 1 to give
a similar diradical with higher molecular weight as
shown in the scheme. Repetition of the ring opening
followed by radical addition eventually leads to polymer
4.
On the other hand, it is noted the germyl radical
center of 11 is well situated for intramolecular attack
on one of the Ge atoms as depicted by arrows in the
scheme. Thus, at higher temperature, such as at 160
°C, the intramolecular process would prevail to afford
5 with extrusion of a diradical 12, which is conceivably
a benzogermacyclopropene equivalent.15 12 should be
highly reactive and finally insert into the reactive Ge-
Ge bond of 1 to yield 6.
Interestingly, on the thermolysis at 250 °C in a sealed
degassed tube, a silicon analog, 3,4-benzo-1,1,2,2-tetra-
ethyl-1,2-disilacyclobutene, has been reported to yield
4,5-benzo-1,1,2,2,3,3-hexaethyl-1,1,2,3-trisilacyclopen-
tene and 2,3:5,6-dibenzo-1,1,4,4-tetraethyl-1,4-disila-
cyclohexadiene.5q The former corresponds to the silicon
analog of 5, but the latter does not. Formation of the
dibenzo-1,4-disilacyclohexadiene was explained by dimer-
ization of the benzosilacyclopropene. In the thermolysis
of 1, 12 may be too reactive to survive long enough to
undergo dimerization.
Exp er im en ta l Section
Gen er a l Meth od s. All reactions were carried out under
an atmosphere of argon excepting polymerization and ther-
molytic reactions, which were carried out in a degassed sealed
glass tube. THF and toluene were dried by refluxing over
sodium benzophenone ketyl and distilled just before use.
Carbon tetrachloride was refluxed over CaH2 and distilled
before use. NMR spectra were obtained on Varian Unity plus
300 and 500 MHz spectrometers. GCMS spectra were mea-
sured on Shimadzu QP-1000 and Hitachi M-2500 spectrom-
eters. Molecular weights of polymers were determined with
a Tosoh-CCPD gel permeation chromatograph using THF as
the eluent and relative to the polystyrene standard.
Ma ter ia ls. o-Dibromobenzene, phenylacetylene, 2,3-di-
methyl-1,3-butadiene, and dimethylphenylsilane were com-
mercially available. Chlorodiethylgermane was prepared as
reported in the literature.18
P r ep a r a tion of 1,2-Bis(d ieth ylger m yl)ben zen e. To a
mixture of magnesium (9.5 g, 0.390 mol), chlorodiethylgermane
Oxid a tion of 1. A solution of 1 (100 mg, 0.296 mmol) in
toluene (3 mL) was stirred for 120 h in air. GC and GCMS
analysis showed that 2 was produced quantitatively. 2: 1H
NMR (CDCl3) δ 1.03-1.19 (m, 20H, EtGe), 7.33-7.53 (m, 4H,
phenylene ring protons); 13C NMR (CDCl3) δ 7.89, 10.32 (EtGe),
128.58, 131.88, 146.92 (phenylene ring carbons); MS m/z
(relative intensity) 354 (M+, 74Ge, 72Ge, 0.2), 325 (M+ - Et,
74Ge, 72Ge, 100); HRMS calcd for C12H1974Ge2O (M+ - Et)
326.9860, found 326.9864. Anal. Calcd for C14H24Ge2O: C,
47.57; H, 6.84. Found: C, 47.80; H, 7.09.
(14) Benzo-1,4-digermacyclohexadiene 7 may be possibly formed by
way of a 4 + 2 cycloaddition reaction.
Su lfu r iza tion of 1. A mixture of 1 (100 mg, 0.296 mmol),
sulfur (19 mg, 0.592 mmol), and toluene (3 mL) was stirred
(15) Silacyclopropenes16 are thermally stable at ambient tempera-
ture; however only a few germacyclopropenes are known so far.17 This
may be indicative that a germacyclopropene is far less stable than a
silacyclopropene.
(19) The 13C NMR chemical shift of the vinyl carbon in 7 is known
to be remarkably low.20 In fact, the silicon analog of 7 has been
reported to show the vinylic carbon signal at 161.1 ppm.5p In
conformity with these results, 3,3,7,7-tetraethyl-1-phenyl-3,7-diger-
macycloheptene, obtained from the cycloaddition of 1,1,2,2-tetramethyl-
1,2-digermacyclopentane7g with phenylacetylene in the presence of a
palladium catalyst, shows the corresponding 13C NMR signal at 163.46
ppm.21 In this case, the vinylic carbon signal is unambiguously
assigned.
(16) (a) Conlin, R. T.; Gaspar, P. P. J . Am. Chem. Soc. 1976, 98,
3715. (b) Seyferth, D.; Annarelli, D. C.; Vick, S. C. J . Am. Chem. Soc.
1976, 98, 6382. (c) Ishikawa, M.; Fuchikami, T.; Kumada, M. J . Am.
Chem. Soc. 1977, 99, 245. (d) Sakurai, H.; Kamiyama, Y.; Nakadaira,
Y. J . Am. Chem. Soc. 1977, 99, 3879.
(17) (a) Krebs, A.; Berndt, J . Tetrahedron Lett. 1988, 24, 4083. (b)
Egorov, M. P.; Kolesnikov, S. P.; Struchkov, Yu. T.; Antipin, M. Yu.;
Sereda, S. V.; Nefedov, O. M. J . Organomet. Chem. 1985, 290, C27.
(18) (a) Lesbre, M.; Satge´, J . Comput. Rend. 1961, 252, 1976. (b)
Satge´, J . Am. Chem. (Paris) 1961, 6, 519.
(20) Sakurai, H.; Tobita, H.; Nakadaira, Y. Chem. Lett. 1982, 1251.
(21) Komoriya, H.; Kako, M.; Nakadaira, Y. Unpublished results.

2018 Organometallics, Vol. 15, No. 8, 1996
Komoriya et al.
for 120 h at room temperature in Ar. The resulting solution
was evaporated, followed by purification with silica gel TLC
to give 3 (103 mg, 0.28 mmol, 94% yield). Similarly, at reflux
temperature the sulfurization was complete in 1 h (95% yield).
3: 1H NMR (CDCl3) δ 1.05-1.27 (m, 20H, EtGe), 7.35-7.53
(m, 4H, phenylene ring protons); 13C NMR (CDCl3) δ 8.74,
11.95 (EtGe), 128.28, 131.73, 146.90 (phenylene ring carbons);
phenylacetylene (136 mg, 1.33 mmol) was heated at 160 °C
for 16 h. The contents were chromatographed on silica gel
TLC with hexane to give 7 (178 mg, 0.405 mmol, 91% yield):
1H NMR (CDCl3) δ 0.87-1.13 (m, 20H, EtGe), 6.95 (s, 1H,
HCdC), 7.20-7.52 (m, 9H, aromatic protons); 13C NMR
(CDCl3) δ 7.41, 7.93, 9.08, 9.19 (EtGe), 126.07, 126.45, 127.59,
127.71, 128.26, 133.25, 133.29, 145.27, 145.83, 147.24 (aro-
matic carbons), 142.90 (HCdC), 160.38 (CdCH);19 MS m/z
(relative intensity) 411 (M+ - Et, 74Ge, 72Ge, 83); HRMS calcd
for C20H2574Ge2 (M+ - Et) 413.0380, found 413.0368. Anal.
Calcd for C22H30Ge2: C, 60.10; H, 6.88. Found: C, 60.31; H,
7.01.
MS m/z (relative intensity) 370 (M+, 74Ge, 72Ge, 2), 341 (M+
-
Et, 74Ge, 72Ge, 100); HRMS calcd for C14H2474Ge2S 372.0022,
found 372.0023. Anal. Calcd for C14H24Ge2S: C, 45.50; H,
6.55. Found: C, 45.71; H, 6.78.
P olym er iza tion of 1. A solution of 1 (100 mg, 0.296 mmol)
in toluene (0.5 mL) was evacuated and sealed in a glass tube,
and this was allowed to stand for 16 h. The resulting mixture
was reprecipitated from hexane to give a white solid polymer
(90 mg, 90% yield): 1H NMR (C6D6) δ 1.07-1.24 (EtGe), 7.14-
7.65 (phenylene ring protons); 13C NMR (C6D6) δ 8.21, 10.59
(EtGe), 128.85, 132.23, 147.74 (phenylene ring carbons); Mn
) 4.4 × 105, Mw ) 7.4 × 105, Mw/Mn ) 1.7 (GPC, THF,
polystyrene standard). Anal. Calcd for C14H24Ge2: C, 49.82;
H, 7.17. Found: C, 49.65; H, 7.17.
Th er m olysis of 1 in th e P r esen ce of 2,3-Dim eth yl-1,3-
bu ta d ien e. A degassed sealed tube containing 1 (100 mg,
0.296 mmol), 2,3-dimethyl-1,3-butadiene (486 mg, 5.92 mmol),
and benzene (5 mL) was heated at 160 °C for 20 h. GC and
GCMS analysis of the resulting mixture showed 5 (80%) and
6 (58%) were produced.
Th er m olysis of 1 in th e P r esen ce of Dim eth ylp h en yl-
sila n e. A degassed sealed tube containing 1 (100 mg, 0.296
mmol) and dimethylphenylsilane (807 mg, 5.92 mmol) was
heated at 160 °C for 20 h. GC and GCMS analysis of the
resulting mixture showed 5 (98%) and 6 (50%) were produced.
Th er m olysis of 1. A degassed sealed tube containing 1
(446 mg, 1.32 mmol) was heated at 160 °C for 20 h. The tube
was cooled and opened. The contents was chromatographed
on silica gel with hexane to afford 5 (184 mg, 0.393 mmol, 89%
yield) and 6 (127 mg, 0.233 mmol, 53% yield). The yields of
both products 5 and 6 are calculated on the basis of the
stoichiometry expressed by Scheme 1. 5: 1H NMR (CDCl3) δ
1.02-1.20 (m, 30H, EtGe), 7.24-7.56 (m, 4H, phenylene ring
protons); 13C NMR (CDCl3) δ 3.58, 7.78, 10.16, 12.47 (EtGe),
127.14, 133.72, 151.35 (phenylene ring carbons); MS m/z
(relative intensity) 468 (M+, 74Ge, 72Ge2, 8), 439 (M+ - Et, 74Ge,
72Ge2, 42); HRMS calcd for C18H3474Ge72Ge2 468.0314, found
468.0318. Anal. Calcd for C18H34Ge3: C, 46.17; H, 7.32.
Found: C, 46.41; H, 7.57. 6: 1H NMR (CDCl3) δ 0.91-1.29
(m, 30H, EtGe), 7.23-7.55 (m, 8H, phenylene ring protons);
13C NMR (CDCl3) δ 7.09, 8.94, 8.97, 9.92 (EtGe), 126.90,
127.36, 133.92, 134.51, 146.76, 148.02 (phenylene ring car-
bons); MS (20 eV) m/z (relative intensity) 544 (M+, 74Ge, 72Ge2,
Th er m olysis of 1 in CCl4. A degassed sealed tube
containing 1 (200 mg, 0.592 mmol) and CCl4 (3 mL) was heated
at 160 °C for 16 h. The reaction mixture was analyzed by GC
and GCMS as being 9 (48%) and 10 (48%). Pure 10 was
isolated by preparative GC. 10: 1H NMR (CDCl3) δ 1.03-
1.62 (m, 20H, EtGe), 7.28-8.05 (m, 4H, phenylene ring
protons); 13C NMR (CDCl3) δ 8.19, 9.02, 9.53, 13.34 (EtGe),
96.70 (CCl3), 128.73, 128.78, 134.64, 137.37, 139.87, 143.36
(phenylene ring carbons); MS m.z (relative intensity) 461 (M+
- Et, 74Ge, 72Ge, 0.8), 373 (M+ - CCl3, 74Ge, 72Ge, 100). Anal.
Calcd for C15H24Ge2Cl4: C, 36.67; H, 4.92. Found: C, 36.73;
H, 4.78.
Ack n ow led gm en t. This research was supported in
part by the Grant-in-Aid for Scientific Research on
Priority Area of Reactive Organometallics No. 05236102
from the Ministry of Education, Science, and Culture
of J apan. We thank Mitsubishi Material Co. Ltd. for a
generous gift of tetrachlorogermane.
5), 515 (M+ - Et, 74Ge, 72Ge2, 82); HRMS calcd for C22
-
H3374Ge72Ge2 (M+ - Et) 515.0236, found 515.0234. Anal.
Calcd for C24H38Ge3: C, 52.96; H, 7.04. Found: C, 52.89; H,
7.31.
Th er m olysis of 1 in th e P r esen ce of P h en yla cetylen e.
A degassed sealed tube containing 1 (150 mg, 0.444 mmol) and
OM9509150