Silylation and germylation of trialkylsilyl(germyl)ethoxyacetylenes containing bulky substituents at the silicon or germanium atom

Article abstract of DOI:10.1023/A:1011393908126

Silylation and germylation of trialkylsilyl(germyl)ethoxyacetylenes containing bulky substituents at the silicon or germanium atom were performed. In all cases, the corresponding bis-organoelement-containing ketenes were obtained as the only reaction products. No intermediate isomeric ynol ethers were detected by spectroscopy.

Full text of DOI:10.1023/A:1011393908126

1088
Russian Chemical Bulletin, International Edition, Vol. 50, No. 6, pp. 1088—1092, June, 2001
Organometallic Chemistry
Silylation and germylation of trialkylsilyl(germyl)ethoxyacetylenes
containing bulky substituents at the silicon or germanium atom
S. V. Ponomarev,« A. S. Zolotareva, A. S. Leont´ev, Yu. V. Kuznetsov, and V. S. Petrosyan
Department of Chemistry, M. V. Lomonosov Moscow State University,
Leninskie Gory, 119899 Moscow, Russian Federation.
Fax: +7 (095) 939 5546. E-mail: svpon@org.chem.msu.ru
Silylation and germylation of trialkylsilyl(germyl)ethoxyacetylenes containing bulky sub-
stituents at the silicon or germanium atom were performed. In all cases, the corresponding
bis-organoelement-containing ketenes were obtained as the only reaction products. No
intermediate isomeric ynol ethers were detected by spectroscopy.
Key words: silylation, germylation, trialkylsilyl(germyl)ethoxyacetylenes, iodotrimethyl-
silane, bromotrimethylgermane, bis-silicon(germanium)-containing ketenes, ynol ethers.
Si, Ge, Sn-Substituted ketenes belong to a new
class of reactive organosilicon compounds used in or-
ganic and organometallic chemistry.4—6
interesting class of compounds widely used in the syn-
thesis of organic and heteroelement-containing organic
compounds.1 Previously, bis-heteroelement-substituted
ketenes have been synthesized by the reactions of
heteroelement-containing ynol ethers with trialkyl-
heteroelement-containing halides.2,3 A possible mecha-
nism of formation of bis-heteroelement-substituted
ketenes3 assumes the formation of the corresponding
ynol ethers as intermediates, which are rapidly isomer-
ized into bis-heteroelement-substituted ketenes as the
final reaction products. With the aim of elucidating the
effects of the nature of the heteroelement and the steric
factors on the formation of bis-heteroelement-substi-
tuted ketenes or ynol ethers, in the present work we
studied the reactions of trialkylsilyl(germyl) halides with
organosilyl- and organogermyl-substituted ynol ethers
containing bulky substituents at the silicon or germa-
nium atom. The latter belong to a new poorly studied
The starting silyl- and germyl(ethoxy)acetylenes (1)
containing bulky substituents at the silicon or germa-
nium atom were synthesized by the reactions of
trialkylsilyl(germyl) halides with ethoxyethynyllithium
or ethoxyethynylmagnesium bromide (Scheme 1).
Heteroelement-substituted ethoxyacetylenes contain-
ing bulky substituents are rather labile compounds and
undergo partial pyrolysis upon heating above 120 °C.
Therefore, compounds 1b,d,e were analyzed and used in
subsequent syntheses without fractionation. Acetylenes
1a—f were obtained in 60—90% yields and were charac-
1
terized by the data from elemental analysis and the H
and 13C NMR and IR spectra (Tables 1—3). Acetylene
1d was synthesized according to another procedure;9
however, its spectral characteristics were lacking.
Analysis of the 13C NMR spectra of silylethoxy-
acetylenes 1a—d,g (see Table 3) demonstrated that the
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 1041—1044, June, 2001.
1066-5285/01/5006-1088 $25.00 © 2001 Plenum Publishing Corporation

Silylation(germylation) of silyl(germyl)ethoxyacetylenes Russ.Chem.Bull., Int.Ed., Vol. 50, No. 6, June, 2001
1089
Scheme 1
a downfield shift (∆δ 0.8 ppm) of the C atom of the
C(sp)—O group in the germylated analog are observed.
Trialkylsilyl(germyl)ethoxyacetylenes were silylated
or germylated with iodotrimethylsilane or bromotri-
methylgermane, respectively, in an atmosphere of argon
with dichloromethane or acetonitrile as the solvents
(Scheme 2).
HC COEt
BuLi, 0 °C
EtMgBr, 0 °C
Et2O
THF or Et2O
–EtH
–BuH
Scheme 2
LiC COEt
BrMgC COEt
(Me3Si)3SiBr
R3ECl
Me3SiI
RR´2E
C C O
Me3Si
R3EC COEt
(Me3Si)3SiC COEt
2a—e
COEt
RR´2EC
1a—f
1g
1a—f
Me3GeBr
RR´2E
R3E = Me2ButSi (a), ButPh2Si (b), Pri3Si (c), MePh2Si (d),
Ph3Si (e), Pri3Ge (f)
C C O
Me3Ge
2f,g
introduction of the silicon atom into the acetylene
molecule leads to downfield shifts of the resonance
signals for the C atoms of the Si—C(sp) and C(sp)—O
groups by 6—7 and 18—20 ppm, respectively, com-
pared to those observed in the NMR spectrum of
ethoxyacetylene. In the case of the isopropyl deriva-
tives Pri3Si(Ge)C≡COEt, an insignificant upfield shift
(∆δ 0.5 ppm) of the C atom of the Ge—C(sp) group and
RR´2E = ButMe2Si (a, g); ButPh2Si (b); Pri3Si (c); MePh2Si (d);
Ph3Si (e); Pri3Ge (f)
The course of the reactions was monitored by IR
spectroscopy by following a decrease in the intensity
and then complete disappearance of the ν(C≡C) absorp-
tion band of the starting alkoxyacetylene in the region
–1
of 2175—2190 cm and the appearance of an absorp-
Table 1. Characteristics of the compounds synthesized
20
Com- Yield
B.p./°C
(p/Torr)
nD
Found
Calculated
Molecular
formula
(%)
pound
(%)
Ñ
Í
Si(Ge)
1àa
1b
74
93
81
80
58
30—31 (1)
1.4449
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
b
—
1cc
62—63 (0.02)
1.4620
—
—
b
1d
1e
—
—
—
b
8.24
8.55
26.73
26.79
34.81
35.47
—
Ñ17Í18ÎSi
1f
85
65
82
47
37
7
59—60
(0.02)
89—90
(0.02)
52—54
(0.02)
139—143
(0.02)
69—70
(0.04)
123—125
(0.01)
200—205
(0.01)
53—57
(0.01)
1.4685
1.4994
1.4570
1.4445
—
57.19
57.61
49.82
49.29
—
9.77
9.69
10.17
10.18
—
C13H26GeO
C13H32OSi4
—
1g
2a
2b
2c
2d
2e
2f
71.50
71.53
61.90
62.15
69.93
69.62
74.44
74.14
48.01
48.46
46.83
46.75
7.93
8.00
11.40
11.18
7.14
7.14
6.75
6.49
8.50
8.80
8.53
8.42
—
—
—
C21H28OSi2
C14H30OSi2
C18H22OSi2
C23H24OSi2
C11H24GeOSi
C14H30Ge2O
1.4570
—
26
45
54
14.87
15.08
—
1.4692
1.4950
2g
69—70
(0.01)
40.20
40.38
a Lit. data7: b.p. 66—69 °C (12 Torr).
b The compounds were isolated and characterized without distillation.
c Lit. data8: b.p. 68—73 °C (1 Torr), nD 1.4626.
20

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Russ.Chem.Bull., Int.Ed., Vol. 50, No. 6, June, 2001
Ponomarev et al.
Table 2. 1H NMR and IR spectral data for the compounds RR´2EC≡COEt (1a—g) and RR´2E(Me3E´)C=C=O (2a—g)
Com- RR´2E
pound
Me3E´
IR,
1H NMR (δ, J/Hz)
–1
ν/cm
R
R´
OCH2CH3 OCH2Me
Me3E´
(t, 3 H)
(q, 2 H)
(s, 9 H)
1à
1b
1c
ButMe2Si
ButPh2Si
Pri3Si
2190
2190
2185
0.90 (s, 9 H)
1.14 (s, 9 H)
0.10 (s, 6 H)
7.35—7.95 (m, 10 H)
1.40
1.63
1.39
4.10
4.32
4.12
1.02 (m, 3 H); 1.05 (d, 18 Í, J = 5.2)
1d
MePh2Si
2175
0.65 (s, 3 H)
7.33—7.76 (m, 10 H)
1.33
1.46
4.12
(J = 7)
4.27
1e
1f
Ph3Si
Pri3Ge
2185
2184
7.20—7.70 (m, 15 H)
1.22 (m, 3 Í); 1.06 (d, 18 Í, J = 7.2)
1.30
4.01
1g
2a
2b
2c
2d
2e
2f
(Me3Si)3Si
ButMe2Si
ButPh2Si
Pri3Si
2177
2085
2090
2060
2080
2085
2060
2070
0.14 (s, 27 H)
0.98 (s, 9 H)
1.29 (s, 9 H)
1.00 (d, 18 H, J = 3.6)
0.85 (s, 3 H)
7.30—7.80 (m, 10 H)
1.44 (m, 3 H); 1.18 (d, 18 H, J = 7.2)
0.86 (s, 9 H) 0.03 (s, 6 H)
1.30
3.98
Me3Si
Me3Si
Me3Si
Me3Si
Me3Si
Me3Ge
Me3Ge
0.15 (s, 6 H)
7.30—7.90 (m, 10 H)
1.24 (m, 3 H)
0.22
0.01
0.24
0.18
1.09
0.39
0.32
MePh2Si
Ph3Si
7.40—7.70 (m, 10 H)
Pri3Ge
2g
ButMe2Si
Table 3. 13C NMR spectral data (δ) for the compounds RR´2EC≡COEt (1a—g) and RR´2E(Me3E´)C=C=O (2a—g)
Com-
pound
RR´2E
E´
R
R´
EC(sp) C(sp)—O OCH2CH3 OCH2Me Me3E´ C(sp2)
C=O
1à
1b
ButMe2Si
ButPh2Si
26.1, 16.6
27.1, 18.6
–4.0
127.5, 129.1,
134.6, 135.6
34.8
32.5
109.7
112.5
14.2
14.4
74.8
75.2
1c
1d
Pri3Si
MePh2Si
18.6, 11.6
32.4
33.7
110.7
112.0
14.1
14.2
74.7
75.2
–1.3
127.7, 129.2,
134.3, 135.6
1f
Pri3Ge
19.8, 14.8
32.9
28.2
110.4
110.4
14.1
14.1
74.4
74.5
1g
2a
2b
(Me3Si)3Si
ButMe2Si
ButPh2Si
0.3
26.3, 18.9
27.6, 20.2
Si
Si
–3.3
127.8, 129.6,
134.1, 136.2
1.7
1.0
–2.0
–1.0
166.8
166.7
2c
2d
Pri3Si
MePh2Si
Si
Si
18.6, 13.2
1.9
1.2
–4.3
–0.1
166.6
166.5
–1.0
127.9, 129.4,
134.6, 136.1
2e
2f
Ph3Si
Pri3Ge
ButMe2Si
Si
Ge
Ge
127.9, 129.9, 134.2, 135.7
19.8, 16.7
1.1
1.8
1.6
166.2
165.9
166.2
–6.3
–5.0
2g
26.3, 18.7
–3.3
tion band in the region of 2060—2090 cm–1 (ν(C=C=O)
in disubstituted ketenes). In addition, the 13C NMR
spectra of the reaction mixture were recorded in the
course of the reaction and after its completion. The
appearance of the C=O resonance signal of ketene at
δ 166—167 and the disappearance of a signal at
δ 110—112 corresponding to the ≡C—O group of the
initial acetylene were observed. For example, the spec-
trum of the mixture obtained in the reaction 1b + Me3SiI
(40 °C, 10 h) recorded after removal of the solvent and
unconsumed iodotrimethylsilane had signals only of the
initial acetylene 1b and ketene 2b (δ): 112.5 (C(sp)—O);
75.2, 14.4 (OCH2Me); 32.5 (SiC(sp)); 27.1, 18.6 (Me3C);
135.0—129.0 (Ph) for acetylene 1b; and 166.7 (C=O);
27.6, 20.1 (Me3C); 1.0 (Me3Si); –3.9 (C=C=O) for
ketene 2b.
The IR spectrum of this reaction mixture had two
absorption bands corresponding to the stretching vibra-
–1
tions of the C≡C bond (2190 cm ) of the initial
–1
acetylene and to the ketene group (2090 cm ) of bis-
silylketene.
It should be noted that the reactions giving rise to
ketenes 2e,c did not proceed to completion (according
to the data from IR spectroscopy of the reaction mix-
ture), which accounts for the low yields of these com-
pounds. The reaction of acetylene 1g with iodotri-
methylsilane proceeded very slowly to yield a mixture of
unidentified products. The rate of the reaction depends on the

Silylation(germylation) of silyl(germyl)ethoxyacetylenes Russ.Chem.Bull., Int.Ed., Vol. 50, No. 6, June, 2001
1091
Table 4. Conditions of the synthesis of bis-organosilyl- and bis-
0.062 mol) in anhydrous THF (30 mL) was added dropwise and
organogermyl-substituted ketenes
the mixture was stirred for 1 h. The precipitate that formed was
separated by centrifugation and the solvents were removed in
vacuo using a water-aspirator pump. Hexane (20 mL), ether
(20 mL), and water (20 mL) were successively added with
stirring to the residue until the precipitate was completely
dissolved. The organic phase was separated and the aqueous
phase was extracted with ether (2½15 mL). The combined
ethereal extracts were dried with MgSO4. The solvent was
distilled off in vacuo using a water-aspirator pump and then an
oil pump (1 Torr) and the residue was kept for 0.5 h. Com-
pound 1d was obtained in a yield of 15 g (80%).
Com-
pound
t
/h
T
/°Ñ
Solvent
2a
2b
2c
2d
2e
2f
8
30
36
25
50
150
20
20
40
20
40
40
20
40
CH2Cl2
CH2Cl2
MeCN
CH2Cl2
CH2Cl2
CH2Cl2
MeCN
2g
Acetylenes 1b,e were synthesized analogously.
(Triisopropylgermyl)ethoxyacetylene (1f). A 1.84 M BuLi
solution (14 mL, 0.0258 mol) in hexane was added dropwise
with cooling to 0 °C to a solution of ethoxyacetylene (1.99 g,
0.0284 mol) in anhydrous THF (30 mL). The reaction mixture
was stirred at ∼20 °C for 1 h. Then a solution of Pri3GeCl
(5.1 g, 0.02215 mol) in anhydrous THF (25 mL) was added
dropwise and the mixture was stirred for 8 h. The solvents were
distilled off in vacuo, hexane (50 mL) was added, and the
solution was separated from the residue. Hexane was distilled
off in vacuo and the residue was fractionated. Acetylene 1f was
obtained in a yield of 5 g (85%), b.p. 59—60 °C (0.02 Torr),
character of the substituents at the silicon or germanium
atom (E) and the nature of the heteroelement (Table 4).
We isolated only bis-organosilyl- and bis-organo-
germyl-containing ketenes 2 in the reactions studied
and even no transient formation of isomeric silyl-
oxy(germyloxy)trialkylsilyl(germyl)acetylenes was ob-
served.
However, the formation of ynol ethers (SiC≡COSi)
cannot be excluded based on the results obtained be-
cause under the reaction conditions (electrophilic ca-
talysis) the latter could be rapidly isomerized to the
corresponding ketenes under the action of the initial
organosilyl or organogermyl halide.
20
nD 1.4685.
Acetylenes 1a,c were synthesized analogously.
[Tris(trimethylsilyl)silyl]ethoxyacetylene (1g). A solution
of ethoxyacetylene (2.12 g, 0.03 mol) in a mixture of anhydrous
ether (15 mL) and anhydrous THF (5 mL) was added to the
Grignard reagent prepared from Mg (0.66 g, 0.0272 g-at.) and
EtBr (2.96 g, 0.0272 mol) in ether (20 mL) at 0 °C. The
reaction mixture was stirred at 20 °C for 0.5 h. Then a solution
of bromotris(trimethylsilyl)silane (6.8 g, 0.0208 mol) in anhy-
drous THF (20 mL) was added. The reaction mixture was
stirred for 4 h, the solvent was distilled off in vacuo, hexane
(50 mL) was added, and the mixture was washed successively
with a saturated aqueous solution of NH4Cl and water. The
aqueous phase was extracted with ether and the combined
organic extracts were dried with MgSO4. Fractionation of the
residue afforded acetylene 1g in a yield of 4.3 g (65%),
Experimental
The IR spectra were recorded on IKS-22 and UR-20 (Carl
Zeiss) spectrometers in thin layers and in a cell (d = 0.1 mm,
CaF2 plates). The 1H and 13C NMR spectra were measured on
Bruker ÀC-200P (200 MHz) and Varian VXR-400 (400 MHz)
spectrometers using CDCl3 and C6D6 as the solvents. All
operations were carried out in an atmosphere of dry argon.
Ethoxyacetylene was synthesized from ethyl vinyl ether
according to a standard procedure.10 A solution of BuLi in
hexane (1.31—1.84 M) was prepared according to a procedure
reported previously.11 Chlorotriisopropylsilane and -germane
were prepared by the reactions of isopropyllithium12 with
tetrachlorosilane(germane).13,14 For chlorotriisopropylgermane,
1H NMR (δ): 1.20 (d, 6 H, (CH3)2CH, J = 7.2 Hz); 1.56—1.68
(m, 1 H, Me2CH); 13C NMR (δ): 19.1 ((CH3)2CH); 18.8
(Me2CH). Bromotris(trimethylsilyl)silane was synthesized ac-
cording to a known procedure.15 The purity of intermediate
tris(trimethylsilyl)silane obtained in the first stage was con-
20
b.p. 89—90 °C (0.02 Torr), nD 1.4994.
(tert-Butyldimethylsilyl)trimethylsilylketene (2a). Freshly
distilled Me3SiI (2.56 g, 0.013 mol, 1.82 mL) was added to
acetylene 1a (2.15 g, 0.012 mol) in anhydrous CH2Cl2 (4.5 mL)
and the mixture was stirred for 8 h. Fractionation afforded
ketene 2a in a yield of 2.2 g (82%), b.p. 52—54 °C (0.02 Torr),
20
nD
1.4570 (cf. lit. data19: b.p. 57—60 °C (0.4 Torr),
20
nD 1.4526).
Ketenes 2b,d,e,f,g were synthesized analogously.
(Triisopropylsilyl)trimethylsilylketene (2c). Me3SiI (3.07 g,
0.015 mol) was added to a solution of acetylene 1c (2.14 g,
0.0095 mol) in anhydrous MeCN (5 mL) and the mixture was
stirred at ∼20 °C for 36 h. The solvent and an excess of Me3SiI
were distilled off in vacuo and fractionation afforded ketene 2c
as a colored liquid in a yield of 1.64 g (64%), b.p. 69—72 °C
(0.04 Torr). After purification from an admixture of iodine by
flash chromatography on a dry column with Al2O3 (light petro-
leum—CH2Cl2, 4 : 1), ketene was obtained in a yield of 0.94 g
(37%), b.p. 69—70 °C (0.04 Torr).
1
firmed by the data from H and 13C NMR spectroscopy (for
the Me3Si group, δH 0.18, δC 2.2, δH (Si—H) 2.20).
Iodotrimethylsilane,16 bromotrimethylgermane,17 and bromo-
triethylgermane17 were synthesized according to procedures
reported previously. tert-Butylchlorodimethylsilane, tert-butyl-
chlorodiphenylsilane, chlorotriphenylsilane, and chloro-
methyldiphenylsilane were purchased from Merck and Aldrich.
All solvents used in the reactions were dried according to a
known procedure.18
(Methyldiphenylsilyl)ethoxyacetylene (1d). A 1.31 M BuLi
solution (54 mL, 0.07 mol) in hexane was added dropwise to a
solution of ethoxyacetylene (5.5 g, 0.079 mol) in anhydrous
THF (50 mL) at 0 °C. The reaction mixture was stirred at
∼20 °C for 0.5 h. Then a solution of Ph2MeSiCl (14.5 g,
We thank Merck for providing trialkylchlorosilanes.
This work was financially supported by the Russian
Foundation for Basic Research (Project No. 98-03-
32989a).

1092
Russ.Chem.Bull., Int.Ed., Vol. 50, No. 6, June, 2001
Ponomarev et al.
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Received January 15, 2001;
in revised form February 20, 2001