Synthesis, structure and chemical transformations of ethynylgermatranes

Article abstract of DOI:10.1002/ejic.200300236

Ethynylgermatranes have been prepared from monosubstituted acetylenes by a three-step synthesis without isolation of the hydrolytically unstable intermediate chlorogermanes and ethoxygermanes. Boiling an equimolar mixture of tetrachlorogermane Cl₄Ge, acetylene RC≡CH and triethylamine in hexane leads to germylation of the C_sp-H bond and the formation of ethynyl-substituted trichlorogermanes. Subsequent alkoxylation of chlorogermanes by ethanol in the presence of triethylamine affords triethoxygermanes that then take part in transalkoxylation with triethanolamine to give ethynylgermatranes. The molecular structures of all ethynylgermatranes and the hexacarbonyldicobalt complex of 1-heptynylgermatrane have been determined by X-ray crystallography. Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003.

Full text of DOI:10.1002/ejic.200300236

FULL PAPER
Synthesis, Structure and Chemical Transformations of Ethynylgermatranes
Edmunds Lukevics,[a] Pavel Arsenyan,*[a] Sergey Belyakov,[a] and Olga Pudova[a]
Keywords: Cobalt / Germanium / Germatrane / X-ray diffraction / Alkynes
Ethynylgermatranes have been prepared from monosubsti-
presence of triethylamine affords triethoxygermanes that
tuted acetylenes by a three-step synthesis without isolation then take part in transalkoxylation with triethanolamine to
of the hydrolytically unstable intermediate chlorogermanes
and ethoxygermanes. Boiling an equimolar mixture of tetra-
give ethynylgermatranes. The molecular structures of all
ethynylgermatranes and the hexacarbonyldicobalt complex
chlorogermane Cl4Ge, acetylene RCϵCH and triethylamine of 1-heptynylgermatrane have been determined by X-ray
in hexane leads to germylation of the Csp−H bond and the
formation of ethynyl-substituted trichlorogermanes. Sub-
crystallography.
( Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
sequent alkoxylation of chlorogermanes by ethanol in the Germany, 2003)
Introduction
bonyldicobalt, [2ϩ3] dipolar cycloaddition, and electro-
philic substitution. The molecular structures of all synthe-
sized ethynylgermatranes as well as of the hexacarbonyld-
icobalt complex of 1-heptynylgermatrane are also reported.
Derivatives of pentacoordinate germanium are the sub-
ject of considerable current research activity, particularly
germatranes that contain an intramolecular NǞGe
bond.[1Ϫ4] Investigations have focused on the relationship
between the transannular NǞGe bond length and such fac-
tors as the character of the substituent at the germanium
atom, the atrane skeleton structure, as well as crystal pack-
ing (crystal density, Z of unit cell, etc). However, the scope
of their synthesis is limited. The few reported examples of
ethynylgermatranes (unsubstituted ethynylgermatrane, 1-
octynylgermatrane, and phenylethynylgermatranes)[5Ϫ8]
were obtained by the ‘‘stannyl’’ method, by treating ethynyl-
trichlorogermanes RCϵCGeCl3 with the tris(trialkylstan-
nyl) ether of triethanolamine or by addition of triethanol-
amine to RCϵCGeCl3 in the presence of triethylamine;
phenylethynylgermatrane has also been prepared by the re-
action of bromogermatrane with lithium phenylacetylen-
ide.[5] The CϵC triple bond in ethynylgermatranes should
allow various chemical transformations; however, only the
bromination of phenylethynylgermatrane by NBS and bro-
mine has been studied.[5] To the best of our knowledge, only
the molecular structures of 1-phenylethynylgermatrane, and
its chloroform solvate, and 4-fluorophenylethynylgerma-
trane have been determined by X-ray crystallography.[5,6,8]
In this paper we focus on the synthesis of ethynylgerma-
tranes via germylation of monosubstituted acetylenes by
tetrachlorogermane in the presence of an organic base.
Various chemical transformations of the acetylene fragment
have been carried out, including complexation with octacar-
Results and Discussion
The ethynylgermatranes 4aϪd were prepared from
monosubstituted acetylenes 1aϪd by a three-step synthesis
without isolation of the hydrolytically unstable intermediate
chlorogermanes 2aϪd and ethoxygermanes 3aϪd. Boiling
an equimolar mixture of tetrachlorogermane GeCl4, acety-
lene RCϵCH and triethylamine in hexane[9,10] leads to ger-
mylation of the CspϪH bond and formation of ethynyl-sub-
stituted trichlorogermanes 2aϪd. Subsequent alkoxylation
of chlorogermanes by ethanol in the presence of triethyl-
amine affords triethoxygermanes 3aϪd which are then in-
volved in transalkoxylation with triethanolamine to give
ethynylgermatranes 4aϪd (Scheme 1). The yield of germa-
tranes 4aϪd depends on the structure of the substituent R.
The highest yield was observed for (trimethylsilyl)ethynyl-
germatrane (4d) (85%); with 1-heptynylgermatrane (4a) and
(1-cyclohex-1-enyl)ethynylgermatrane (4b) the yields were
48 and 55%, respectively. The lowest yield was for 3-meth-
oxypropyn-1-ylgermatrane (4c) (12%). Our attempts to pre-
pare germatrane from methyl propiolate failed, since tetra-
chlorogermane acts as a Lewis acid in the reaction with
HCϵCCOOMe to form 1,3,5-tris(methoxycarbonyl)ben-
zene by [2ϩ2ϩ2] cycloaddition (Scheme 2).
As with other acetylene derivatives,[11Ϫ14] 1-heptynylger-
matrane (4a) easily reacts with octacarbonyldicobalt in hex-
ane (20 min at Ϫ5 °C). The hexacarbonyldicobalt complex
of 1-heptynylgermatrane 5, isolated in almost quantitative
yield (93%) (Scheme 1), is stable in the solid state but com-
[a]
Latvian Institute of Organic Synthesis,
Aizkraukles 21, Riga, 1006, Latvia
Fax: (internat.) ϩ 371/7550338
E-mail: pavel.arsenyan@lycos.com
Eur. J. Inorg. Chem. 2003, 3139Ϫ3143
DOI: 10.1002/ejic.200300236
 2003 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
3139

E. Lukevics, P. Arsenyan, S. Belyakov, O. Pudova
FULL PAPER
Scheme 1. Synthesis and transformations of ethynylgermatranes
MukaiyamaϪHoshito method,[15] reacts with 4d regioselec-
tively to give only one of the two possible regioisomeric
products, i.e. 5-germatranylisoxazole (6) in 75% yield. Con-
versely, for 4a only a trace amount of the isoxazole deriva-
tive was detected by GC-mass spectrometry (Scheme 1).
The reaction of 4d with NCS and NBS in DMF proceeds
with cleavage of the GeϪC bond and formation of chloro-
and bromogermatranes 7 (X ϭ Cl, Br).[16] Our attempts to
desilylate 4d by different desilylation agents (Bu4NF/Et2O,
K2CO3/MeOH, Amberlyst 15/THF, TsOH/MeOH) failed to
cleave the SiϪC bond, and so the initial germatrane 4d
was recovered.
Scheme 2. [2ϩ2ϩ2] Cyclization of methyl propiolate in the
presence of tetrachlorogermane
pletely decomposes in organic solvents (even in nonpolar
ones such as hexane or benzene) after 2Ϫ3 h.
[2ϩ3] Dipolar cycloaddition of acetonitrile oxide to the
CϵC triple bonds of heptynylgermatrane (4a) and (trime-
thylsilyl)ethynylgermatrane (4d) has been investigated.
1
The structures of the germatranes were confirmed by H
1
Acetonitrile
oxide,
prepared
in
situ
by
the and 13C NMR spectroscopy (Table 1). The H spectra of
1
Table 1. H and 13C NMR spectroscopic data of ethynylgermatranes and their derivatives
1
Compound
δ H, ppm
δ
13C, ppm
CH2N CH2O GeCCR
CH2N
2.84
CH2O
R
R
4a
4b
3.82
0.82 (t, J ϭ 6 Hz, 3 H),
1.17Ϫ1.65 (m, 5 H),
51.5
51.3
56.6
56.5
80.5, 101.7
87.0, 101.5
13.7, 19.5,
22.0,
(t, J ϭ 5.6 Hz, 6 H) (t, J ϭ 5.6 Hz, 6 H) 2.20 (t, J ϭ 6.4 Hz, 3 H)
28.2, 31.1
21.3, 22.1,
25.5, 28.8,
120.2, 136.2
2.87
3.84
1.45Ϫ1.60 (m, 4 H),
1.96Ϫ2.06 (m, 2 H),
(t, J ϭ 5.6 Hz, 6 H) (t, J ϭ 5.6 Hz, 6 H) 2.1Ϫ2.2 (m, 2 H), 6.21
(sept, J ϭ 1.8 Hz, 1 H)
4c
4d
5
2.90
(t, J ϭ 5.6 Hz, 6 H) (t, J ϭ 5.6 Hz, 6 H)
2.87 3.84
(t, J ϭ 5.6 Hz, 6 H) (t, J ϭ 5.6 Hz, 6 H)
2.87 3.81
3.85
3.37 (s, 3 H), 4.12 (s, 2 H) 52.4
57.6
56.7
57.0
92.2, 96.5
58.4, 61.1
0.15 (s, 9 H)
51.3
52.6
106.9, 108.3
80.2, 108.5
Ϫ0.1
0.90 (t, J ϭ 7 Hz, 3 H),
1.3Ϫ1.5 (m, 5 H),
14.0, 22.4,
31.4,
(t, J ϭ 5.6 Hz, 6 H) (t, J ϭ 5.6 Hz, 6 H) 1.6Ϫ1.7 (m, 3 H)
201.0 (CO),
206.7 (CO)
119.3, 128.8,
31.5, 34.6
6
2.89
3.83
0.34 (s, 9 H), 2.41
(s, 3 H, Me-C)
51.5
56.4
Ϫ1.1
(t, J ϭ 5.6 Hz, 6 H) (t, J ϭ 5.6 Hz, 6 H)
12.1 (Me),
161.1 (CϭN)
3140
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Eur. J. Inorg. Chem. 2003, 3139Ϫ3143

Synthesis, Structure and Chemical Transformations of Ethynylgermatranes
FULL PAPER
all germatrane derivatives (4؊6) are characterized by two
triplets of CH2N (δ ϭ 2.84Ϫ2.90 ppm) and CH2O (δ ϭ
3.81Ϫ3.85 ppm) groups. The signals of carbon atoms in the
atrane fragment are in the
δ
ϭ
51.3Ϫ52.6 and
56.4Ϫ57.6 ppm regions of the 13C NMR spectra, and the
signals of carbonyl-ligand carbon atoms in 5 are shifted to
low field (δ ϭ 201.0 and 206.7 ppm). As reported pre-
viously,[17] complexation of the CϵC triple bond does not
strongly affect the carbon atoms’ chemical shifts.
Molecular Structures of the Germatranes
Molecular structure data have been reported for more
than 60 germatranes and their structural analogues.[2,18]
However, only three of these structures contain an ethynyl-
Figure 1. Molecular structure of 3-methoxypropyn-1-ylgerma-
trane (4c)
germatrane fragment (phenylethynylgermatrane, and its distance is observed in 3-methoxypropyn-1-ylgermatrane
CHCl3 solvate, and 4-fluorophenylethynyl analogue[5,6,8]). (4c) (Figure 1). This indicates that the decrease of the
These compounds are characterized by transannular NǞGe NǞGe bond in the fragment NǞGeϪC is accompanied by
˚
distances of 2.178, 2.160, and 2.175 A, respectively, which elongation of the GeϪC bond.
are short in comparison with those in other alkyl-, alkenyl-,
The unit cell of germatrane 4a contains two independent
˚
and arylgermatranes (2.20Ϫ2.24 A). To further investigate molecules; one of which is strongly disordered due to the
the influence of various acetylene substituents RCϵC on pentyl substituent. Disorder is also observed in the crystal
the transannular NǞGe bond length the molecular struc- structure of the cyclohexenylethynyl derivative 4b. The us-
tures of ethynylgermatranes 4aϪd and of the hexacarbonyl- ual disorder for the atrane system occurs for C-4, C-6, and
dicobalt complex 5 have been determined by X-ray crystal- C-11 atoms. Carbon atom C-17 in the six-membered cycle
lography.
is also disordered. The occupation g factor for disordered
The germanium atom of germatranes 4aϪd and 5 has the atoms is 0.5.
typical atrane trigonal-bipyramidal geometry with nitrogen
Crystals of (trimethylsilyl)ethynylgermatrane (4d) were
and carbon atoms in apical positions and three equatorial obtained as a solvate with toluene. To prevent toluene evap-
oxygen atoms. The axial nitrogen atom is pyramidalized so orating rapidly from the crystal surface, which would de-
that its lone pair points towards the germanium atom. stroy the mono crystal of 4d within 1 h, the X-ray analysis
Selected bond lengths and angles are presented in Table 2. was carried out under an epoxide glue film. The unit cell
The transannular NǞGe bond length in ethynylgerma- contains four molecules of germatrane 4d and two of tolu-
˚
tranes 4 varies between 2.202(3) A (for the disordered germ- ene.
˚
atrane 4a) and 2.115 A [for 3-methoxypropyn-1-ylgerma-
Cobalt complex 5 (Figure 2) crystallized from light petro-
trane, (4c)]. The last value is one of the shortest distances leum as scarlet prisms. The six-coordinate cobalt atoms
detected for germatranes with GeϪC bonds. The shorter have a pseudotetrahedral polyhedron. The CoϪCo bond
˚
˚
intramolecular bond length of 2.108 A was found only for distance is 2.487(1) A. The dihedral angle between planes
trifluoromethylgermatrane.[19] The GeϪC bonds in germa- C-12, C-13, Co-1 and C-12, C-13, Co-2 is 84.7(1)°. Mol-
˚
tranes 4 lie between 1.905 and 1.962 A. The longest GeϪC ecules of complex 5 are in special positions: atoms Ge-1,
Table 2. Selected bond lengths and angles of ethynylgermatranes [4 RCϵCGe(OCH2CH2)3N] and the dicobalhexacarbonyl complex
[a]
For two independent molecules.
Eur. J. Inorg. Chem. 2003, 3139Ϫ3143
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3141

E. Lukevics, P. Arsenyan, S. Belyakov, O. Pudova
FULL PAPER
N-5, C-12, C-13, C-14, C-15, C-16, C-17 lie in crystallo- acetylenes RCϵCH. With methyl propiolate, tetrachloro-
graphic plane m. However, the molecules are not symmetri- germane acts as Lewis acid to form 1,3,5-tri(methoxycarbon-
cal; therefore, disorder occurs in the crystal structure. The yl)benzene by [2ϩ2ϩ2] cycloaddition. 1-Heptynylgerma-
occupation g factor for disordered atoms is 0.5. According trane easily reacts with octacarbonyldicobalt in hexane, al-
to the literature data, complex 5 is the first example of a most quantitatively, yielding the hexacarbonyldicobalt com-
cluster structure containing a germatranyl fragment.
plex. The reaction of trimethylsilylethynylgermatrane with
NCS and NBS in DMF proceeds with cleavage of the
GeϪC bond and formation of chloro- and bromogerma-
tranes. The transannular NǞGe bond lengths (2.115Ϫ2.202
˚
A) of the germatranes are strongly influenced by the RCϵC
substituent, with 3-methoxypropyn-1-ylgermatrane having
˚
the shortest bond (2.115 A).
Experimental Section
Instrumental: 1H and 13C NMR spectra were recorded with a
Varian Mercury 200 spectrometer at 200.06 and 50.31 MHz,
respectively, at 303 K. The chemical shifts are given relative to TMS
Figure 2. Molecular structure of the hexacarbonyldicobalt complex
from the solvent impurity (CHCl3 in CDCl3) signal (δH
ϭ
of 1-heptynylgermatrane (5)
7.25 ppm). Mass spectra were recorded with a Hewlett Packard
apparatus (70 eV). The melting points were determined with a
‘‘Digital melting point analyser’’ (Fisher) and are uncorrected. 1-
Heptyne, 1-ethynylcyclohexene, methyl 2-propynyl ether, trimethyl-
Conclusions
Ethynylgermatranes have been prepared from monosub-
silylacetylene,
triethanolamine
and
octacarbonyldicobalt
stituted acetylenes by a three-step synthesis from initial [Co2(CO)8] were purchased from Aldrich.
Table 3. Main X-ray crystallographic details for 4a؊d
3142
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Eur. J. Inorg. Chem. 2003, 3139Ϫ3143

Synthesis, Structure and Chemical Transformations of Ethynylgermatranes
General Method for Synthesis of Ethynylgermatranes (4aϪd): A ane (50 mL). The reaction mixture was refluxed for 2 h and filtered
FULL PAPER
solution of tetrachlorogermane (4.28 g, 0.02 mol) in dry hexane
(10 mL) was added dropwise to a mixture of acetylene 1 (0.02 mol)
and triethylamine (0.022 mol) in dry hexane (50 mL). The reaction
mixture was boiled under reflux for 2 h and filtered from triethyl-
amine hydrochloride. A mixture of ethanol (0.07 mol) and triethyl-
amine (0.07 mol) was added to the filtrate. The resultant triethyl-
amine hydrochloride precipitate was filtered off after stirring for
2 h at room temperature. The filtrate was then added to a solution
of triethanolamine (0.02 mol) in hexane (10 mL). The transalkoxyl-
ation reaction was exothermic. After cooling to room temperature
the resultant ethynylgermatrane (4) precipitate was filtered off and
recrystallized from toluene. The products were obtained as white
crystalline solids.
from triethylamine hydrochloride. The crude product was purified
on silica using hexane as eluent. Yield: 52%. The structure was
confirmed by MS-GC and H NMR spectroscopy.
1
Reaction of (Trimethylsilyl)ethynylgermatrane with NCS and NBS:
NCS or NBS (1 mmol) was added portion-wise, during 1 h at room
temperature, to a solution of 4d (0.315 g, 1 mmol) in DMF
(10 mL). After the usual workup the crude product 7 was purified
by flash chromatography using ethyl acetate/hexane (5:1) as eluent.
Yield: 87Ϫ90%.
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1-Heptynylgermatrane (4a): Yield: 3.02 g (48%). M.p. 89 °C. MS:
m/z ϭ 315 [Mϩ]. C13H23GeNO3 (313.94): calcd. C 49.74, H 7.38,
N 4.46; found C 49.51, H 7.30, N 4.45.
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M.p. 211Ϫ212 °C. MS: m/z ϭ 325 [Mϩ]. C14H21GeNO3 (323.93):
calcd. C 51.91, H 6.53, N 4.32; found C 51.83, H 6.58, N 4.36.
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193Ϫ194 °C. MS: m/z ϭ 289 [Mϩ]. C10H17GeNO4 (287.86): calcd.
C 41.73, H 5.95, N 4.86; found C 41.77, H 5.99, N 4.84.
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237 °C. MS: m/z ϭ 317 [Mϩ]. 29Si NMR (CDCl3): δ ϭ Ϫ18.6 ppm.
C11H21GeNO3Si (315.98): calcd. C 41.81, H 6.70, N 4.43; found C
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solution of octacarbonyldicobalt (0.342 g, 1 mmol) in hexane
(10 mL) was added to a solution of 1-heptynylgermatrane (4a,
0.314 g, 1 mmol) in hexane (10 mL) at Ϫ5 °C. The reaction mixture
was stirred 20 min, then hexane was removed and the crude prod-
uct obtained was purified on silica gel using CH2Cl2 as eluent (Rf ϭ
0.55). Yield: 0.56 g (93%). M.p. 102Ϫ104 °C. C19H23Co2GeNO9
(599.46): calcd. C 38.07, H 3.87, N 2.34; found C 38.06, H 3.79,
N 2.29.
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[17]
[18]
3-Methyl-4-trimethylsilyl-5-germatranylisoxazole (6): Nitroethane
(0.005 mol) and triethylamine (two drops) in dry benzene (20 mL)
were added dropwise to a mixture of trimethylsilylethynylgerma-
trane 4d (1.58 g, 0.005 mol) and phenylisocyanate (0.01 mol). The
mixture was heated for 5 h at 70Ϫ80 °C. After cooling to room
temperature, diphenylurea was filtered off, the solvent evaporated,
and the resultant residue purified on silica gel using dichlorometh-
ane as eluent (Rf ϭ 0.45). Yield 1.39 g (75%). M.p. 115 °C. MS:
[19]
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ϭ δ ϭ Ϫ6.4 ppm.
374 [Mϩ]. 29Si NMR (CDCl3):
835Ϫ837.
[23]
C13H24GeN2O4Si (373.04): calcd. C 41.86, H 6.48, N 7.51; found
C 41.81, H 6.50, N 7.54.
G. M. Sheldrick, SHELXL-93. Program for the Refinement of
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Received April 25, 2003
[24]
Method for Synthesis of 1,3,5-Tris(methoxycarbonyl)benzene: A
solution of tetrachlorogermane (4.28 g, 0.02 mol) in dry hexane
(10 mL) was added dropwise to a mixture of methylpropiolate
(1.68 g, 0.02 mol) and triethylamine (2.22 g, 0.022 mol) in dry hex-
Eur. J. Inorg. Chem. 2003, 3139Ϫ3143
www.eurjic.org
 2003 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
3143