Synthesis of trimethylgermyl trimethylsilyl ketone and bis(trimethylgermyl) ketone

Article abstract of DOI:10.1039/b003016n

The chemical synthesis of trimethylgermyl trimethylsilyl ketone and bis(trimethylgermyl) ketone was discussed. All the reactions were conducted under an inert atmosphere of either Ar or N₂. Trimethylgermyl trimethylsilyl ketone and bis(trimethy

Full text of DOI:10.1039/b003016n

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Synthesis of trimethylgermyl trimethylsilyl ketone and
bis(trimethylgermyl) ketone
Rune Johannesen and Tore Benneche*
1
Department of Chemistry, University of Oslo, PO Box 1033, Blindern, N-0315 Oslo, Norway
Received (in Cambridge, UK) 14th April 2000, Accepted 8th May 2000
Published on the Web 10th July 2000
Trimethylgermyl trimethylsilyl ketone 7a and bis(trimethylgermyl) ketone 7b have been prepared by hydrolysis of
α-chloro ethers 6 on silica gel. Spectroscopic data for the ketones 7 have been compared with data from di-tert-butyl
ketone, tert-butyl trimethylsilyl ketone and bis(trimethylsilyl) ketone.
Introduction
Bis(trimethylsilyl) ketone was first prepared in pure form in
1985.1 One striking feature of this compound is its unusually
large downfield 13C absorption of the carbonyl carbon: δ 318.8.1
An increasing value for the carbonyl carbon has been observed
in going from di-tert-butyl ketone to tert-butyl trimethylsilyl
ketone to bis(trimethylsilyl) ketone (see Table 1).2 We have
recently reported a new synthesis of bis(trimethylsilyl) ketone3
and were interested to see what happened to the 13C value
for the carbonyl carbon when the series was extended to
germanium. The UV spectra of triethylgermyl trimethylsilyl
ketone and bis(triethylgermyl) ketone and the IR spectrum of
bis(triphenylgermyl) ketone have been reported previously, but
other properties were not investigated due to the instability of
these compounds.4
Scheme 2
Our strategy for the synthesis of bis(metalloidal) ketones
is shown in Scheme 1.3 A key point in this protocol is the
sulfuryl dichloride (Scheme 2). Only cleavage of the C–S bond
was observed and the α-chloro ether 4 was isolated in good
yield (77%).
With the information that a C–S bond can selectively be
cleaved in the presence of a C–Ge bond in molecules like 3, the
synthesis of compounds 6 and 7 was attempted. Silylation and
germylation of 3 proceeded well using tert-butyllithium in THF
at low temperature and the O,S-acetals 5a and 5b were isolated
in 90 and 92% yield respectively (Scheme 3).
The bis(trimethylgermyl) compound 5b can be prepared
in one step from the O,S-acetal 2 using 2.4 equivalents of
tert-butyllithium and 2.4 equivalents trimethylgermyl bromide.
The two-step procedure, with isolation of compound 3, gave,
however, a higher total yield of compound 5b (46 and 85%
respectively). As in the O,S-acetal 3 only the C–S bond in com-
pounds 5 was cleaved by sulfuryl dichloride. The α-chloro ethers
6 were not separated from the adduct formed between benz-
enesulfenyl chloride and cyclohexene, but directly run through a
silica gel column to give the ketones 7a and 7b in 53 and 65%
yield, respectively (Scheme 3).†
Scheme 1
preparation of the ketones in a non-oxidative environment,
since these compounds are usually very sensitive to oxidative
conditions.2,4
A germyl–carbon bond can be cleaved by halogens.5 Thus
there might be competition between cleavage of the C–S bond
and the C–Ge bond in compounds such as 3 (Scheme 2) when
they are reacted with halogens. It should be noted that in the tin
compound 1 the C–Sn is cleaved in preference to the C–S bond
with sulfuryl dichloride.6
The compound 7a has a red colour while 7b is orange. Both
compounds are extremely sensitive to air and their synthesis
is preferentially performed in a glove box under an inert
atmosphere.
Table 1 shows a comparison of spectroscopic data for
† The 1H NMR spectrum of the crude product from reaction of 5 with
sulfuryl dichloride indicated formation of the α-chloro ethers 6 [6a
δH(CDCl3) 0.16 (9H, s. SiMe3), 0.33 (9H, s, GeMe3), 3.45 (3H, s, OMe);
6b δH(CDCl3) 0.28 (18H, s, GeMe3), 3.43 (3H, s, OMe)].
Results and discussion
To investigate the stability of the C–Ge bond towards halogens
in O,S-acetals, compound 3 was prepared and reacted with
DOI: 10.1039/b003016n
J. Chem. Soc., Perkin Trans. 1, 2000, 2677–2679
This journal is © The Royal Society of Chemistry 2000
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Table 1 δC 13C, λmax (nm) and νC (cmϪ1) data for di-tert-butyl ketone, trimethylsilyl tert-butyl ketone, bis(trimethylsilyl) ketone, trimethylsilyl
᎐
᎐
O
᎐
O
᎐
trimethylgermyl ketone 7a and bis(trimethylgermyl) ketone 7b
δC 13C
2182,a
2982,c
2492,a
3672
318.82,b
5332,d
309.1b
521d
300.6b
509d
᎐
λmaOx/nm
᎐
νC O/cmϪ1
16892,e
16402,e
15702,e
1565f
1585f
᎐
᎐
a CDCl3. b C6D6. c Cyclohexane. d CH2Cl2. e Film. f In CCl4.
tert-butyllithium followed by trimethylgermyl bromide. We
were, however, not able to purify the crude product properly.
By running the germylation of 8, the C–S bond cleavage
reaction and the hydrolysis without any purification of the
intermediates, the ketone 7a was isolated in 15% yield. In
comparison the procedure from the phenylsulfanyl hemiacetal 3
gave the ketone 7a in 60% overall yield.
Experimental
All reactions were conducted under an inert amosphere of
either Ar or N2. THF was distilled from sodium and benzo-
phenone, and dichloromethane from CaH2. NMR spectra were
recorded at 300 MHz (1H) and at 75 MHz (13C) on a Bruker
Avance DPX 300 instrument. Mass spectra, under electron
impact conditions, were recorded at 70 eV ionizing energy on
a Fision ProSpec instrument. The spectra are presented as
m/z (% rel. int.). IR spectra were recorded on a Nicolet Magna
FT-IR 550 instrument using attenuated total reflection. UV
spectra were recorded on a Shimadzu Recording Spectro-
photometer UV-260.
Scheme 3
di-tert-butyl ketone,2 trimethylsilyl tert-butyl ketone,2 bis(tri-
methylsilyl) ketone,2 trimethylsilyl trimethylgermyl ketone 7a
and bis(trimethylgermyl) ketone 7b.
In going from di-tert-butyl ketone to bis(trimethylsilyl)
ketone the 13C NMR absorption for the carbonyl carbon shifts
to a lower field, from δ 218 to 318.8 (Table 1). When a trimethyl-
silyl group in bis(trimethylsilyl) ketone is substituted with
a trimethylgermyl group, this absorption moves to a higher
field again (δ 309.1), and moves even higher (δ 300.6) when both
trimethylsilyl groups are exchanged with trimethylgermyl
groups. An explanation of the effect of the silyl groups on the
13C chemical shift of carbonyl carbons in acylsilanes has been
given.7 A shift to lower values is also seen for the λmax value
(Table 1). The νCO value shifts to a higher value on going from
the trimethylsilyl germyl ketone 7a to the bis(trimethylgermyl)
ketone 7b (Table 1).
In the synthesis of the α-chloro ether 4 benzenesulfenyl
chloride is formed. The sulfenyl chloride is trapped with cyclo-
hexene and the α-chloro ether is separated from the adduct by
distillation. In the preparation of the ketones 7, we did not
manage to achieve a good separation of the α-chloro ethers 6
from the adduct by distillation. The mixture was therefore run
through a silica gel column and the formation of the ketones
7 and the separation from the adduct were done in one
operation.‡ In this procedure care has to be taken to avoid
product contamination by the adduct. To improve the pro-
cedure we wanted to use a methylsulfanyl group in the O,S-
acetal 5 instead of a phenylsulfanyl group. This would yield
methanesulfenyl choride instead of benzenesulfenyl chloride
and methanesulfenyl chloride could be removed together with
the solvent.8 The crude α-chloro ether could then hopefully
be used directly without being distilled prior to hydrolysis.
To test this procedure the hemithioacetal 89 was reacted with
Methoxy(phenylsulfanyl)(trimethylgermyl)methane 3
tert-Butyllithium (1.6 M, 1.00 cm3, 1.60 mmol) was added
dropwise to a solution of methoxy(phenylsulfanyl)methane10
(205 mg, 1.33 mmol) in dry THF (2 cm3) under N2 at Ϫ78 ЊC.
The mixture was stirred at Ϫ40 ЊC for 30 min, recooled to
Ϫ78 ЊC before a solution of trimethylgermyl bromide (316 mg,
1.60 mmol) in dry THF (1 cm3) was added dropwise. The
mixture was stirred at Ϫ78 ЊC for 2 h before water was added
and the product extracted into benzene, washed with water,
dried (MgSO4) and evaporated to give the title compound (335
mg, 93%) as a colourless oil. The crude product could be used
in the next step without further purification. An analytical
sample was prepared by flash chromatography using silica gel
(eluent hexane–CHCl3 3:1) (Found: Mϩ, 272.0285. C11H18-
GeOS: requires 272.0290); δH(CDCl3) 0.23 (9H, s, GeMe3),
3.36 (3H, s, OCH3), 4.82 (1H, s, CH), 7.22–7.25 (3H, m, Ph),
7.46–7.49 (2H, m, Ph); δC(CDCl3) Ϫ2.6 (GeCH3), 56.6 (OCH3),
84.9 (C), 126.7, 128.7, 131.0, 138.0 (Ph); m/z (EI) 272 (Mϩ,
9), 257 (21), 153 (100), 135 (23), 119 (35), 105 (16), 91 (17), 77
(15).
Chloro(methoxy)(trimethylgermyl)methane 4
Sulfuryl dichloride (84 mg, 0.62 mmol) in dry dichloromethane
(1 cm3) was added dropwise to a solution of compound 3
(141 mg, 0.52 mmol) in dry dichloromethane (1 cm3) under N2
at 0 ЊC. The mixture was stirred at 0 ЊC for 30 min before a
solution of cyclohexene (51 mg, 0.62 mmol) in dry dichloro-
methane (1 cm3) was added dropwise. The mixture was stirred
‡ Not trapping the benzenesulfenyl chloride reduces the yield of the
ketones 7.
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at 0 ЊC for 30 min before the solvent was removed and the crude
product distilled in a Kugelrohr apparatus (oven temp. 60–
70 ЊC, 1 mmHg) to give the title compound (79 mg, 77%) as
a colourless oil; δH(CDCl3) 0.03 (9H, s, GeMe3), 3.51 (3H, s,
OMe), 5.49 (1H, s, CH); δC(CDCl3) Ϫ4.1 (GeMe3), 60.0 (OMe),
99.7 (CH).
with water, dried (MgSO4) and evaporated to give the title com-
pound (500 mg, 92%) as a colourless oil. The crude product
could be used in the next step without further purification.
Trimethylsilyl trimethylgermyl ketone 7a
Sulfuryl dichloride (56 mg, 0.42 mmol) in dry dichloromethane
(0.5 cm3) was added dropwise to a solution of compound 5a
(119 mg, 0.35 mmol) in dry dichloromethane (1 cm3) under N2
at 0 ЊC. The mixture was stirred at 0 ЊC for 30 min before a
solution of cyclohexene (34 mg, 0.42 mmol) in dry dichloro-
methane (0.5 cm3) was added dropwise. The mixture was stirred
at 0 ЊC for 30 min before the solvent was removed and the
residue eluted through a silica gel column under Ar using
first degassed pentane as eluent, then a degassed mixture
of pentane–diethyl ether 20:1. The coloured fractions were
collected to give the title compound (40 mg, 53%) as a red
liquid; δH(C6D6) 0.03 (9H, s, SiMe3), 0.22 (9H, s, GeMe3);
δC(C6D6) Ϫ3.84 (SiMe3), Ϫ3.06 (GeMe3), 309.1 (CO);
νmax(CCl4)/cmϪ1 1565 (CO); λmax(CH2Cl2)/nm 522.
Methoxy(phenylsulfanyl)(trimethylgermyl)(trimethylsilyl)-
methane 5a
tert-Butyllithium (1.6 M, 0.46 cm3, 0.74 mmol) was added
dropwise to a solution of compound 3 (167 mg, 0.62 mmol) in
dry THF (2 cm3) under N2 at Ϫ78 ЊC. The mixture was stirred
for 30 min at Ϫ78 ЊC before a solution of trimethylsilyl chloride
(80 mg, 0.74 mmol) in dry THF (0.5 cm3) was added drop-
wise. The mixture was stirred at ambient temperature for 2 h
before an aqueous solution of NH4Cl (10%) was added and
the product extracted into benzene, washed with water, dried
(MgSO4) and evaporated to give the title compound (192 mg,
90%) as a colourless oil. The crude product could be used in the
next step without further purification. An analytical sample
was prepared by flash chromatography using silica gel (eluent
hexane–CHCl3 3:1) (Found: Mϩ, 344.0697. C14H26GeOSSi:
requires 344.0685); δH(CDCl3) 0.07 (9H, s, SiMe3), 0.25 (9H,
s, GeMe3), 3.58 (3H, s, OMe), 7.21–7.25 (3H, m, Ph), 7.42–
7.46 (2H, m, Ph); δC (CDCl3) Ϫ0.4 (SiMe3), 0.6 (GeMe3),
53.0 (OMe), 85.0 (C), 127.7, 128.3, 135.2, 135.8 (Ph); m/z (EI)
344 (Mϩ, 2), 301 (10), 225 (61), 213 (8), 119 (33), 89 (24), 73
(100).
Bis(trimethylgermyl) ketone 7b
Sulfuryl dichloride (97 mg, 0.72 mmol) in dry dichloromethane
(1.5 cm3) was added dropwise to a solution of compound 5b
(231 mg, 0.60 mmol) in dry dichloromethane (3 cm3) under N2
at 0 ЊC. The mixture was stirred at 0 ЊC for 30 min before a
solution of cyclohexene (59 mg, 0.72 mmol) in dry dichloro-
methane (1.5 cm3) was added dropwise. The mixture was stirred
at 0 ЊC for 30 min before the solvent was removed and the
residue eluted through a silica gel column under Ar using
first degassed pentane as eluent, then a degassed mixture of
pentane–diethyl ether 20:1. The coloured fractions were
collected to give the title compound (102 mg, 65%) as an
orange liquid; δH(C6D6) 0.29 (18H, s, GeMe3); δC(C6D6)
Ϫ3.35 (GeMe3), 300.6 (CO); νmax(CCl4)/cmϪ1 1585 (CO);
λmax(CH2Cl2)/nm 509.
Bis(trimethylgermyl)(methoxy)(phenylsulfanyl)methane 5b
Method 1. tert-Butyllithium (1.5 M, 0.84 cm3, 1.26 mmol)
was added dropwise to a solution of methoxy(phenylsulf-
anyl)methane10 (81 mg, 0.53 mmol) in dry THF (1 cm3) under
N2 at Ϫ78 ЊC. The mixture was stirred for 2 h at Ϫ78 ЊC before
a solution of trimethylgermyl bromide (249 mg, 1.26 mmol) in
dry THF (2 cm3) was added dropwise. The mixture was stirred
at ambient temperature for 1 h before an aqueous solution
of NH4Cl (10%) was added and the product extracted into
benzene, washed with water, dried (MgSO4) and evaporated.
The crude product was purified by flash chromatography using
silica gel (eluent hexane–CHCl3 5:1) to give the title compound
(94 mg, 46%), as a colourless oil (Found: Mϩ, 390.0208.
C14H26Ge2OS: requires 390.0128); δH(CDCl3) 0.15 (18H, s,
GeMe3), 3.55 (3H, s, OMe), 7.21–7.25 (3H, m, Ph), 7.41–7.43
(2H, m, Ph); δC(CDCl3) 1.0 (GeMe3), 53.2 (OMe), 86.9 (C),
127.7, 128.3, 135.0, 136.0 (Ph); m/z (EI) 390 (Mϩ, 2), 345 (4),
271 (69), 213 (38), 119 (100).
References
1 A. Ricci, M. Fiorenza, A. degl’Innocenti, G. Seconi, P. Dembech,
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3 M. Pan and T. Benneche, Synth. Commun., 1998, 28, 1415; M. Pan
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Method 2. tert-Butyllithium (1.5 M, 1.12 cm3, 1.68 mmol)
was added dropwise to a solution of compound 3 (380 mg, 1.40
mmol) in dry THF (4 cm3) under N2 at Ϫ78 ЊC. The mixture
was stirred for 30 min at Ϫ78 ЊC before a solution of trimethyl-
germyl bromide (333 mg, 1.68 mmol) in dry THF (2 cm3) was
added dropwise. The mixture was stirred at ambient tem-
perature for 1 h before an aqueous solution of NH4Cl (10%)
was added and the product extracted into benzene, washed
J. Chem. Soc., Perkin Trans. 1, 2000, 2677–2679
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