Silylation of silyl-and germylketenes containing bulky substituents at the silicon or germanium atom

Article abstract of DOI:10.1023/A:1011346024964

Silylation of silyl-and germylketenes with trialkylsilyl triflates was studied. Either the corresponding bis-organoelement-substituted ketenes or mixtures of these compounds with isomeric (silyloxy)silylacetylenes were formed depending on the size of the substituents at the silicon or germanium atom (both in ketenes and triflates) and on the nature of the heteroelement. The resulting (silyloxy)silylacetylenes were isomerized into the corresponding bis-silylketenes upon prolonged storage.

Full text of DOI:10.1023/A:1011346024964

Russian Chemical Bulletin, International Edition, Vol. 50, No. 6, pp. 1093—1096, June, 2001
1093
Silylation of silyl- and germylketenes containing bulky substituents at the
silicon or germanium atom
S. V. Ponomarev,« A. S. Zolotareva, R. N. Ezhov, 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 of silyl- and germylketenes with trialkylsilyl triflates was studied. Either the
corresponding bis-organoelement-substituted ketenes or mixtures of these compounds with
isomeric (silyloxy)silylacetylenes were formed depending on the size of the substituents at the
silicon or germanium atom (both in ketenes and triflates) and on the nature of the
heteroelement. The resulting (silyloxy)silylacetylenes were isomerized into the corresponding
bis-silylketenes upon prolonged storage.
Key words: silylation, trialkylsilyl(germyl)ketenes, trialkylsilyl triflates, (silyloxy)silyl-
acetylenes, bis-silylketenes, germyl(silyl)ketenes.
In the last decade, the chemistry of bis-hetero-
element-substituted ketenes and isomeric bis-hetero-
element-substituted ynol ethers attracted considerable
attention1—3 because of their rather high thermody-
namic stabilities, the possibility of mutual isomeriza-
tions, and the use in the synthesis of organic and
organoelement-containing compounds.
Recently, we have demonstrated4 that the reactions
of trimethylsilyl triflate with different triorganosilylketenes
(1) afforded mixtures of O- and C-isomers, viz., ynol
ethers (2) and isomeric bis-silylketenes (3) (Scheme 1).
of bis-heteroelement-containing ynol ethers, in the
present work we investigated the reactions of silylated
and germylated ketenes with trialkylsilyl triflates, both
the reagent and the substrate containing bulky substitu-
ents at the silicon or germanium atoms.
The starting silyl- and germylketenes (1c—g) con-
taining bulky substituents at the silicon or germanium
atom were synthesized by thermal decomposition of the
corresponding organosilyl- and organogermyl(ethoxy)ace-
tylenes5 as reported previously,4,6 but according to a
modified procedure (Scheme 2). The course of pyrolysis
was monitored by IR spectroscopy of the reaction mix-
ture by following the appearance of the ν(HC=C=O)
Scheme 1
–1
absorption band in the region of 2090—2100 cm and
the disappearance of the ν(C≡C) absorption band in the
–1
–50 °C
Et3N
region of 2180—2190 cm .
RR´2SiCH
C
O + Me3SiOSO2CF3
1a—c
Scheme 2
100—110 °C
R3EC COEt
R3ECH C O
RR´2Si
–C2H4
+
RR´2SiC COSiMe3
C C O
1c—g
Me3Si
2a,b
R3E = Pri3Si (c), (Me3Si)3Si (d), MePh2Si (e), Et3Ge (f), Pri3Ge (g)
3a,b
Ketenes 1 were obtained in 53—93% yields. The
100—110 °C
RR´2SiC COSiMe3
3c
compounds synthesized were characterized by the data
1
2c
from elemental analysis and H and 13C NMR and IR
spectra (Tables 1 and 2).
R = R´ = Et (a); R = But, R´ = Me (b); R = R´ = Pri (c)
The 13C NMR spectra of silyl- and germylketenes 1
are characterized by the presence of the high-field reso-
nance signal for the C atom of the Si(Ge)—C(sp2)
group (δ from –12 to –2) and a low-field signal for
the carbonyl C atom at δ 178—179, which unam-
biguously confirm the structures of the ketenes synthe-
sized.7
The isomer ratio 2a,b : 3a,b depends on the duration
of the reaction. For example, the 2a : 3a ratio was
changed in the course of distillation from 1.8 : 1 to 1 : 1
(before and after distillation) in one of the experiments.
As part of continuing studies aimed at elucidating
the effect of the steric factors on the directed synthesis
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 1045—1048, June, 2001.
1066-5285/01/5006-1093 $25.00 © 2001 Plenum Publishing Corporation

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Ponomarev et al.
Table 1. Characteristics of the compounds synthesized
Scheme 3
20
Com- YieldB.p.
pound(%) / °C
(p/Torr)
nD
Found
Calculatedformula
Molecular
–10 °C
(%)
R3SiCH C O + Me3SiOSO2CF3
1c,d
Ñ
Í
Si(Ge)
—
Pri3Si
C C O
Me3Si
R = Pri
1c
1d
1e
1f
93 36—37 1.4658 66.75 11.18
(0.5) 66.62 11.18
56 66—69 1.4952 45.28 9.72
(0.01) 45.77 9.77
90 96—98 1.5788 75.78 5.98 11.76 C15H14OSi
(0.02)
68 54—58 1.4625
(8)*
Ñ11Í22OSi
Pri3SiC COSiMe3
+
—
C11H28OSi4
2c
3c
R = Me3Si
75.57 5.92 11.79
(Me3Si)3SiC COSiMe3
—
—
—
—
2d
1g
53 41—45 1.4488 54.31 9.19 29.76 Ñ11Í22GeO
(0.5)
54.38 9.15 29.89
to the OSiMe3, (Me3Si)3Si, SiC≡, and ≡C—O groups
(Table 3). However, fractionation afforded a mixture of
products which were difficult to identify.
* Lit. data6: b.p. 56 °C (8 Torr), nD 1.4642.
20
A change in the conditions of the reaction of
triisopropylsilylketene 1c with trimethylsilyl triflate (see
Scheme 1 and the Experimental section) led to a change
in the composition of the final products. The IR spec-
trum of the reaction mixture has an absorption band at
Next we studied the reaction of trimethylsilylketene
(1h) with silyl triflate containing the bulky isopropyl
group under mild conditions analogous to those used in
the reaction of 1c with Me3SiOTf. The reaction pro-
ceeded more slowly to give initially the corresponding
–1
1
ynol ether 2e. The H and 13C NMR spectra of the
2090 cm corresponding to the stretching vibrations of
the HC=C=O group, which indicates that the reaction
did not proceed to completion. The presence of absorp-
reaction mixture measured after 24 h had low-intensity
signals corresponding to compound 2e and intense sig-
nals belonging to the initial triflate. After 8 days, the 1H
and 13C NMR spectra had signals of Pri3SiOTf and
compounds 2e and 3c (Scheme 4).
–1
tion bands at 2191 (SiC≡COSi) and 2055 cm
(Si2C=C=O) is consistent with the formation of two
1
isomers 2c and 3c (4 : 1) (Scheme 3). The H and
13C NMR spectra of the reaction mixture measured
before and after fractionation are identical, which is
evidence that distillation was not accompanied by isomer-
ization.
Scheme 4
Me3SiCH
1h
C
O
+
Pri3SiOSO2CF3
At ∼20 °C, trimethylsilyloxy(triisopropylsilyl)acetylene
(2c) slowly isomerized into the corresponding ketene
3c. After 10 days, the 2c : 3c ratio became equal to 1 : 4.
The reaction of [tris(trimethylsilyl)]silylketene (1d)
with trimethylsilyl triflate proceeded slowly to form the
corresponding trimethylsilyloxy(trimethylsilyl)acetylene
(2d) and was not completed on stirring of the reaction
mixture at 20 °C for 8 days. The formation of com-
pound 2d was confirmed by the 13C NMR spectrum of
the reaction mixture, which had signals corresponding
Pri3Si
Me3SiC COSiPri3
+
C
C O
Me3Si
2e
3c
The reaction mixture contained a substantial amount of
unconsumed Pri3SiOTf, which we failed to separate
from the reaction products by distillation. Fractionation
Table 2. 1H and 13C NMR and IR spectral data for ketenes RR´2ECH=C=O (1c—e,g)
Com-
pound
RR´2E
IR,
NMR, δ
–1
ν/cm
1H (J/Hz)
13Ñ
1ñ
Pri3Si
2090
1.08 (d, 18 H, (CH3)2CH, J = 4.5);
1.09 (m, 3 H, Me2CH);
–7.5 (C=C=O); 12.1 (Me2CH);
18.3 (CH3)2CH); 178.9 (C=C=O)
1.64 (s, 1 H, CH=C=O)
1.19 (s, 27 H, CH3);
1.46 (s, 1 H, (CH=C=O)
0.75 (s, 3 H, CH3);
2.23 (s, 1 H, CH=C=O);
7.40—7.62 (m, 10 H, Ph—H)
1.10 (d, 18 H, (CH3)2CH, J = 7.2);
1.39 (m, 3 H, Me2CH);
1d
1e
(Me3Si)3Si
MePh2Si
2090
2110
–12.1 (C=C=O); 0.2 (CH3);
178.7 (C=C=O)
–2.0 (C=C=O); –1.1 (CH3);
128.0, 129.8, 134.3, 135.8 (C6H5);
178.4 (C=C=O)
1g
Pri3Ge
2095
–8.6 (C=C=O); 15.7 (Me2CH);
19.4 (CH3)2CH); 178.1 (C=C=O)
1.52 (s, 1 H, CH=C=O)

Silylation of silyl- and germylketenes
Russ.Chem.Bull., Int.Ed., Vol. 50, No. 6, June, 2001
1095
Table 3. 1H and 13C NMR and IR spectral data for ynol ethers 2 and isomeric ketenes 3
Com-
pound
IR,
NMR, δ
–1
ν/cm
1H (J/Hz)
13Ñ
2ñ + 3ñ
2191 (Ñ≡Ñ)
2060
(Ñ=Ñ=O)
0.92—1.15 (m, 21 H, Me2CH, 2s, 3c);
0.33 (s, 9 H, OSiMe3);
0.25 (s, 9 H, CSiMe3)
for 2ñ –1.2 (OSi(CH3)3); 11.7 (Me2CH);
18.7 ((CH3)2CH); 26.1 (Si—Ñ≡); 107.3 (≡C—O);
for 3ñ –4.3 (C=C=O); 1.9 (CSi(CH3)3);
13.2 (Me2CH); 18.6 ((CH3)2CH); 166.5 (C=O)
–1.2 (OSi(CH3)3); 0.3 ((Me3Si)3Si);
2da
2182
0.17 (s, 27 H, (Me3Si)3Si);
0.28 (s, 9 H, OSiMe3)
0.3 (s, 9 H, Me3Si, 2e);
0.02 (s, 9 H, Me3Si, 3c);
0.94—1.11 (m, 21 H, (CH3)2CH, 2e, 3c)
22.4 (Si—Ñ≡); 107.8 (≡C—O)
2e + 3c
2175 (Ñ≡Ñ)
2060
(Ñ=Ñ=O)
for 2e 0.7 (Si(CH3)3); 12.6 (Me2CH);
17.7 ((CH3)2CH); 26.0 (Si—Ñ≡); 107.8 (≡C—O);
for 3c –4.3 (C=C=O); 1.9 (Si(CH3)3);
13.2 (Me2CH); 18.6 ((CH3)2CH); 166.7 (C=O)
–1.1 (CH3Si); –0.2 (C=C=O); 1.2 (Si(CH3)3);
127.9, 129.4, 134.6, 136.1 ((C6H5)2Si)
–4.3 (C=C=O); 1.4 (Si(CH3)3); 6.6 (MeCH2);
8.4 (CH3CH2); 165.8 (C=O)
3d
3e
2080b
2075c
0.18 (s, 9 H, Me3Si); 0.87 (s, 3 H, MeSi);
7.40—7.70 (m, 10 H, Ph)
0.19 (s, 9 H, Me3Si);
0.96 (q, 2 H, MeCH2Ge);
1.08 (t, 3 H, CH3CH2Ge)
3f
2065
0.21 (s, 9 H, Me3Si); 1.19 (d, 18 H,
–6.0 (C=C=O); 2.0 (Si(CH3)3); 17.0 (Me2CH);
(CH3)2CH, J = 7.6); 1.48 (m, 3 H, Me2CH) 19.8 ((CH3)2CH); 166.0 (C=O)
a Reaction mixture. b Lit. data.5 c Lit. data.6
was accompanied by partial isomerization of O-isomer
2e into C-isomer 3c.
In this case, the corresponding trimethylsilyloxy(tri-
ethylgermyl)acetylene was not detected by spectroscopy,
and trimethylsilyl(triethylgermyl)ketene (3e) was ob-
tained in 81% yield.
Therefore, bis-silyl-substituted ynol ether 2e con-
taining bulky substituents in the silyloxy group isomer-
ized into the corresponding ketene 3c more rapidly than
the ether containing such group at the C atom.
The ratio between products 2 and 3 depends on the
experimental conditions. For mixtures of 2 and 3 (a—c),
the isomer ratio changed after distillation, the content
of bis-silylketene 3 being increased.
As expected, the reaction of triisopropylgermylketene
(1g) with Me3SiOTf proceeded even less actively. After
stirring for 90 h, the degree of conversion was ∼20%
1
(control by H NMR spectroscopy). The reaction af-
forded trimethylsilyl(triisopropylgermyl)ketene (3f) as
the only product.
The reactions of trimethylsilyl triflate with ketenes
1e—g (Scheme 5) in the presence of triethylamine at
–40 °C (the reagent ratio was 1.5 : 1 : 2) gave rise
exclusively to ketenes 3d—f. The IR spectrum of the
To summarize, silylation of silylketenes containing
the phenyl substituents and germylketenes under the
action of Me3SiOTf afforded exclusively C-isomers 3d—f.
The reactions of ketenes and silyl triflate containing
rather bulky substituents at the Si atoms gave rise either
to ynol ethers or mixtures of the latter with ketenes.
Ynol ethers 2c and 2e were slowly isomerized into the
corresponding ketenes.
reaction mixture measured after 0.5 h had the absorp-
–1
tion band at 2055 cm
characteristic of the C=C=O
group in bis-heteroelement-substituted ketenes. The ab-
–1
sorption band at 2170 cm (GeC≡COSiMe3) was not
observed.
Experimental
Scheme 5
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-200Ð (200 MHz) and Varian VXR-400 (400 MHz)
spectrometers using CDCl3 and C6D6 as the solvents. All
operations were carried out under an atmosphere of dry argon.
The initial trialkylsilyl(germyl)ethoxyacetylenes,5,6
Me3SiOTf,8 triisopropylsilyl triflate,9 and trimethylsilylketene
(1h)10 were synthesized according to procedures reported previ-
ously.
All solvents used in the reactions were dried according to a
known procedure.11
Methyldiphenylsilylketene (1e). A solution of methyl-
diphenylsilyl(ethoxy)acetylene (5.68 g, 0.021 mol) in n-octane
(30 mL) was heated at 120—130 °C until the acetylene was
C O + Me3SiOSO2CF3
RR´2ECH
1e—g
RR´2E
C C O
Me3Si
3d—f
RR2´E = MePh2Si (1e, 3d); Et3Ge (1f, 3e); Pri3Ge (1g, 3f)
The reaction of triethylgermylketene (1f)7 with
Me3SiOTf, unlike that involving triethylsilyl ketene,4
proceeded less actively and was completed only in 15 h.

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Russ.Chem.Bull., Int.Ed., Vol. 50, No. 6, June, 2001
Ponomarev et al.
completely converted into ketene (75 min, control by IR
This work was financially supported by the Russian
Foundation for Basic Research (Project No. 98-03-
32989a).
spectroscopy: the disappearance of the ν(C≡C) band at
–1
2176 cm
and the appearance of the ν(C=C=O) band at
2110 cm–1). Ketene 1e was isolated from the reaction mixture
in a yield of 4.8 g (90%) by fractionation.
Ketenes 1c,d,f,g were synthesized analogously.
References
Reaction of triisopropylsilylketene (1c) with Me3SiOTf. A
mixture of Me3SiOTf (3.20 g, 14.4 mmol) and Et3N (1.94 g,
19.2 mmol) in anhydrous ether (10 mL) was added with stirring
to a solution of compound 1c (1.90 g, 9.6 mmol) in anhydrous
ether (5 mL) at –10 °C. The reaction mixture was stirred at
20 °C for 8 days. The ethereal layer was separated from the
dark-brown precipitate. Fractionation afforded a mixture of
compounds 2c and 3c in a yield of 1.51 g (58%), b.p. 66—68 °C
1. R. L. Danheiser, A. Nishida, S. Savariar, and M. P. Trova,
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1
(0.002 Torr). The H and 13C NMR and IR spectral data are
given in Table 3.
The reaction of ketene 1d with Me3SiOTf and the reaction
of ketene 1h with Pri3SiOTf were carried out analogously.
The spectral data for compounds 2d, 2e, and 3c are given in
Table 3.
Reaction of ketene 1g with Me3SiOTf. A mixture of
Me3SiOTf (1.25 g, 5.6 mmol) and Et3N (0.76 g, 7.5 mmol) in
anhydrous ether (6 mL) was added with stirring to a solution of
compound 1g (0.9 g, 4 mmol) in anhydrous ether (4 mL) at
–40 °C. The reaction mixture was stirred with cooling for 0.5 h
and then at 20 °C for 90 h. The ethereal layer was separated
from the dark-brown precipitate and the ether was distilled off.
Fractionation of the residue afforded the initial ketene in a
yield of 0.65 g (72%), b.p. 34—35 °C (0.012 Tîrr), and
trimethylsilyl(triisopropylgermyl)ketene (3f) in a yield of 0.27 g
(23%), b.p. 70—74 °C (0.012 Torr). Found (%): C, 50.52;
H, 9.01. C14H30GeO2Si. Calculated (%): C, 50.83; H, 9.07.
Analogously, the reaction of ketene 1e (2 g) with Me3SiOTf
10. L. L. Shchukovskaya, R. I. Pal´chik, and A. N. Lazarev,
Dokl. Akad. Nauk SSSR, 1965, 164, 357 [Dokl. Chem., 1965
(Engl. Transl.)].
11. Organikum, 18 Auflage, Eds. H. Beiker, G. Domschke, and
E. Fangchenel, VEB Deutscher Verlag der Wissenschaften,
DDR, 1990.
(2.8 g) afforded compound 3d in a yield of 1.6 g (62%), b.p.
20
120—122 °C (0.01 Torr),5 nD
1.4570 (cf. lit. data5: b.p.
20
123—125 °C (0.01 Torr), nD 1.4570).
Ketene 3e was obtained analogously in a yield of 2 g (81%),
20
b.p. 47—48 °C (1 Torr), nD
1.4727 (cf. lit. data6: b.p.
20
111—112 °C (15 Torr), nD 1.4750).
The spectral data for all compounds synthesized are given
in Tables 2 and 3.
Received January 15, 2001;
in revised form March 2, 2001