The reactions of germenes generated thermally from pivaloyl- and adamantoyltris(trimethylsilyl)germane with 1,3-butadienes

Article abstract of DOI:10.1016/j.jorganchem.2007.02.011

The thermolysis of pivaloyl- and adamantoyltris(trimethylsilyl)germane in the presence of 2,3-dimethyl- and 2,3-diphenyl-1,3-butadiene gave the respective adducts derived from [2+4] cycloaddition of the germenes with butadienes in good yields.

Full text of DOI:10.1016/j.jorganchem.2007.02.011

Journal of Organometallic Chemistry 692 (2007) 2357–2360
www.elsevier.com/locate/jorganchem
Communication
The reactions of germenes generated thermally from pivaloyl- and
adamantoyltris(trimethylsilyl)germane with 1,3-butadienes
*
*
Akinobu Naka , Shinsuke Ueda, Mitsuo Ishikawa
Department of Life Science, Kurashiki University of Science and the Arts, Nishinoura, Tsurajima-cho, Kurashiki, Okayama 712-8505, Japan
Received 4 December 2006; received in revised form 3 February 2007; accepted 9 February 2007
Available online 20 February 2007
Abstract
The thermolysis of pivaloyl- and adamantoyltris(trimethylsilyl)germane in the presence of 2,3-dimethyl- and 2,3-diphenyl-1,3-butadi-
ene gave the respective adducts derived from [2+4] cycloaddition of the germenes with butadienes in good yields.
ꢀ 2007 Elsevier B.V. All rights reserved.
Keywords: Germene; Acylpoly(silyl)germane; Thermolysis; Cycloaddition; Germacyclohexene
1. Introduction
We have found that the thermolysis of acyl-
poly(silyl)germanes readily affords silyl-substituted germ-
enes. In this paper, we report the new route to germenes
involving the thermolysis of pivaloyl- and adamantoyl-
tris(trimethylsilyl)germane and the reactions of the germenes
thus formed with 2,3-dimethyl- and 2,3-diphenylbutadiene.
Many papers dealing with the synthesis of both transient
and stable germenes have been published to date [1–7]. The
methods reported for the synthesis of the germenes mainly
involve the following routes: (1) reaction of germylenes
with carbenes [8], (2) Peterson-type reactions [9], (3)
[2+2] cycloreversion of four-membered rings [10,11], and
(4) defluorosilylation [12] or defluorolithiation [13–17].
The range of the synthetic methods for the germenes is
rather limited. The photolysis of acylpoly(silyl)silanes
offers a convenient route to the silenes, but similar photol-
ysis of acylpoly(silyl)germanes affords no germenes. In fact,
Brook et al. have reported that the photolysis of adaman-
toyltris(trimethylsilyl)germane affords no evidence for the
formation of the germene [18]. It is clear that the photolysis
of acylpoly(silyl)germanes is quite different from that of
their all-silicon analogs, acylpoly(silyl)silanes and that the
photolysis of acylpoly(silyl)germanes does not appear to
be a promising route to germane–carbon doubly bonded
compounds.
R3Si
Ge
+
C
R3Si
R3Si
GeLi
+
Ad
O
- R3SiOLi
Ge
C
- XF
Δ or hν
Ge
Ge
C
X
F
2. Results and discussion
We first investigated the thermolysis of pivaloyltris(trim-
ethylsilyl)germane (1) and adamantoyltris(trimethylsi-
lyl)germane (2) in the absence of a trapping agent, in the
hope of obtaining a rather stable germene. Thus, when
*
Corresponding authors.
E-mail address: anaka@chem.kusa.ac.jp (A. Naka).
0022-328X/$ - see front matter ꢀ 2007 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2007.02.011

2358
A. Naka et al. / Journal of Organometallic Chemistry 692 (2007) 2357–2360
compounds 1 and 2 were heated in a sealed glass tube at
130 ꢁC for 24 h, the starting compounds 1 and 2 were
recovered quantitatively. At 140 ꢁC, 1 and 2 reacted, but
afforded a large amount of nonvolatile products, together
with a small amount of unidentified volatile products. In
the thermolysis of the all-silicon analogs, pivaloyl- and
adamantoyltris(trimethylsilyl)silane, the starting acyl-
poly(silyl)silanes were recovered almost quantitatively,
due to the reverse reaction of the silenes once formed
[19]. Presumably, the present germenes are unstable and
decompose to give nonvolatile substances under the condi-
tions used. The thermolysis of 1 and 2 in the presence of a
trapping agent, such as butadienes, however, proceeded
cleanly to give the respective cycloadducts.
When a mixture of compound 1 and 2,3-dimethyl-1,3-
butadiene was heated in a degassed sealed tube at 140 ꢁC
for 24 h, [2+4] cycloadduct, 6-tert-butyl-3,4-dimethyl-
6-trimethylsiloxy-1,1-bis(trimethylsilyl)-1-germacyclohex-3-
ene (3) was obtained in 62% isolated yield (Scheme 1). The
formation of compound 3 may be best understood in terms
of formal [2+4] cycloaddition of 2-tert-butyl-2-(trimethyl-
siloxy)bis(trimethylsilyl)germene, generated thermally from
acylpoly(silyl)germane, with 2,3-dimethyl-1,3-butadiene.
No other isomers such as the ene-type adducts were
detected in the resulting reaction mixture. The structure
of 3 was confirmed by spectroscopic analysis, as well as
by elemental analysis. The mass spectrum of 3 indicates a
parent ion at m/z 460, corresponding to the molecular
weight of the butadiene adduct. The 13C NMR spectrum
for 3 shows three signals at 0.91, 1.23, 3.02 ppm, due to
the trimethylsiloxy carbon atoms and two different kinds
of the trimethylsilyl carbon atoms, as well as three signals
of sp3-hybridized ring carbons, two signals of methyl car-
bons, two signals of olefinic carbons, and two signals due
to the tert-butyl group.
4-dimethyl-6-trimethylsiloxy-1,1-bis(trimethylsilyl)-1-germa-
cyclohex-3-ene (4) in 32% isolated yield. Although
the formation of nonvolatile substances was observed in the
reaction mixture, no volatile products were detected.
1
The H NMR spectrum of 4 shows the presence of three
different kinds of the trimethylsilyl protons at 0.20, 0.22,
and 0.33 ppm, two kinds of the methyl protons at 1.64
and 1.84 ppm, in addition to the adamantyl protons at
1.66–2.02 ppm and the ring methylene protons. The 29Si
NMR spectrum of 4 reveals three resonances at À9.5,
À7.9, and 4.5 ppm, as expected.
Similar thermolysis of compounds 1 and 2 in the pres-
ence of 2,3-diphenyl-1,3-butadiene also gave the respective
formal [2+4] cycloadducts. Thus, treatment of 1 with 2,
3-diphenyl-1,3-butadiene afforded 6-tert-butyl-3,4-diphe-
nyl-6-trimethylsiloxy-1,1-bis(trimethylsilyl)-1-germacyclo-
hex-3-ene (5) in 65% isolated yield, as a single isomer. The
reaction of 2 with 2,3-diphenyl-1,3-butadiene under the
same conditions produced 6-adamantyl-3,4-diphenyl-6-
trimethylsiloxy-1,1-bis(trimethylsilyl)-1-germacyclohex-3-ene
(6) in 43% isolated yield. Again, no other isomers were
detected in the reaction mixture. The structures of products
1
5 and 6 were confirmed by mass, and H, 13C, 29Si NMR
spectroscopic analysis (see Section 3).
It is interesting to us to see if the germacyclohexenes 3–6
undergo the retro Diels–Alder reaction to give the germ-
enes and butadienes. Thus, when a mixture of compound
5 and 2,3-dimethyl-1,3-butadiene was heated in a sealed
tube at 140 ꢁC for 24 h, no product 3 was detected, but
the starting compound 5 was recovered unchanged in
almost quantitative yield. Moreover, the thermolysis of 3
with 2,3-diphenyl-1,3-butadiene under the same conditions
afforded no products arising from the reaction of the germ-
ene with the butadiene. Again, compound 3 was recovered
quantitatively. These results clearly indicate that the pres-
ent germacyclohexenes do not undergo retro Diels–Alder
reaction.
Treatment of 2 with 2,3-dimethyl-1,3-butadiene pro-
ceeded to give a product similar to 3, 6-adamantyl-3,
In conclusion, the thermolysis of acylpoly(silyl)germ-
anes 1 and 2 proceeded to give the germenes, and the germ-
enes thus formed readily reacted with 2,3-dimethyl- and
2,3-diphenyl-1,3-butadiene to afford the [2+4] cycload-
ducts, respectively.
O
C
OSiMe
3
Me Si
Me Si
3
3
140˚C
1
1
Me Si Ge
Me Si
Ge
C
R
R
3
3
Me Si
3
3. Experimental
1
1. R = t-Bu
2. R = Ad
1
OSiMe
3
Me Si
3
General procedure. The syntheses of germacyclohexenes
were carried out in
a degassed sealed glass tube
1
H C
2
CH
2
Me Si Ge
C
R
3
(1.0 cm · 15 cm). Yields of the products were calculated
on the basis of the isolated products. NMR spectra were
recorded on JNM-LA300 spectrometer and JNM-LA500
spectrometer. Low-resolution mass spectra were measured
on a JEOL Model JMS-700 instrument. Melting point was
measured with a Yanaco-MP-S3 apparatus. Column chro-
matography was performed by using Wakogel C-300
(WAKO). Gel permeation chromatographic separation
was performed with a Model LC-908 Recycling Prepara-
tive HPLC.
C
C
H C
CH
2
2
2
2
R
R
C
C
2
R
= Ph, Me
2
2
R
R
1
2
3. R = t-Bu, R = Me
1
2
4. R = Ad, R = Me
1
2
5. R = t-Bu, R = Ph
1
2
6. R = Ad, R = Ph
Scheme 1.

A. Naka et al. / Journal of Organometallic Chemistry 692 (2007) 2357–2360
2359
Materials. Compound 2 was prepared by the method
reported by Brook et al. [18].
65% isolated yield) was isolated by recycling HPLC. Anal.
Calc. for C30H50OSi3Ge (5): C, 61.74; H, 8.63. Found: C,
62.05; H, 8.76%. Mp. 168.0–170.0 ꢁC; MS m/z 584 (M+);
1H NMR d (C6D6) 0.30 (s, 9H, Me3Si), 0.31 (s, 9H,
Me3Si), 0.32 (s, 9H, Me3Si), 1.05 (s, 9H, t-Bu), 1.88 (d,
1H, ring proton, J = 18 Hz), 2.74 (d, 1H, ring proton,
J = 18 Hz), 2.78 (d, 1H, ring proton, J = 18 Hz), 3.13
(d, 1H, ring proton, J = 18 Hz), 6.86–7.22 (m, 10H, phe-
nyl ring protons); 13C NMR d (C6D6) 0.92, 1.51, 3.42
(Me3Si), 17.52 (CH2Ge), 27.87 (Me3C), 39.14 (CMe3),
43.92 (CH2), 88.01 (CO), 125.71, 126.03, 128.53, 129.11,
129.74, 135.39, 137.31 (phenyl ring carbons) [20], 146.08,
148.17 (olefinic carbons); 29Si NMR d (C6D6) À9.0,
À7.7, 5.2.
Synthesis of 1. In a 100 mL two-necked flask fitted with
a condenser and dropping funnel was placed 0.8829 g
(7.32 mmol) of pivaloyl chloride in 20 mL of dry THF.
To this was added a solution of tris(trimethylsilyl)germylli-
thium prepared from 2.1506 g (5.89 mmol) of tetrakis(trim-
ethylsilyl)germane and 7.0 mL (7.90 mmol) of ethereal
MeLi at À40 ꢁC. The mixture was allowed to warm up at
room temperature, and stirred overnight. The mixture
was hydrolyzed with water. The organic layer was sepa-
rated and the aqueous layer was extracted with ether.
The organic layer and extracts were combined, washed
with water, and dried over magnesium sulfate. The solvent
was evaporated and the residue was chromatographed on
silica gel eluting with hexane, to give 1.6304 g (73% yield)
of 1. Anal. Calc. for C14H36OSi3Ge (1): C, 44.57; H,
Reaction of 2 with 2,3-diphenyl-1,3-butadiene. A mixture
of compound 2 (0.0991 g, 0.218 mmol) and 0.1310 g
(0.635 mmol) of 2,3-diphenyl-1,3-butadiene was heated in
a sealed tube at 140 ꢁC for 24 h. Product 6 (0.0631 g,
43% isolated yield) was isolated by column chromatogra-
phy. Anal. Calc. for C36H56OSi3Ge (6): C, 65.35; H, 8.53.
Found: C, 65.35; H, 8.58%. Mp. 227.0–229.0 ꢁC; MS m/z
1
9.62. Found: C, 44.41; H, 9.83%. MS m/z 378 (M+); H
NMR d (C6D6) 0.31 (s, 27H, Me3Si), 0.97 (s, 9H, t-Bu);
13C NMR d (C6D6) 2.43 (Me3Si), 25.00 (Me3C), 49.57
(CMe3), 243.14 (CO); 29Si NMR d (C6D6) À5.6 (Me3Si).
Reaction of 1 with 2,3-dimethyl-1,3-butadiene. A mixture
of compound 1 (0.1587 g, 0.421 mmol) and 0.1036 g
(1.26 mmol) of 2,3-dimethyl-1,3-butadiene was heated in
a sealed tube at 140 ꢁC for 24 h. Product 3 (0.1210 g,
62% isolated yield) was isolated by column chromatogra-
phy. Anal. Calc. for C20H46OSi3Ge (3): C, 52.28; H,
1
662 (M+); H NMR d (C6D6) 0.33 (br s, 27H, Me3Si),
1.63–2.00 (m, 15H, Ad), 1.88 (d, 1H, ring proton,
J = 16 Hz), 2.76 (d, 1H, ring proton, J = 16 Hz), 2.81 (d,
1H, ring proton, J = 18 Hz), 3.16 (d, 1H, ring proton,
J = 18 Hz), 6.85–7.22 (m, 10H, phenyl ring protons); 13C
NMR d (C6D6) 1.06, 1.61, 3.56 (Me3Si), 17.28 (CH2Ge),
29.28, 37.60, 39.74, 40.73 (Ad), 42.44 (CH2), 89.69 (CO),
125.70, 126.01, 128.08, 128.30, 129.12, 129.78, 135.35,
137.31 (phenyl ring carbons), 146.26, 148.25 (olefinic car-
bons); 29Si NMR d (C6D6) À9.0, À7.3, 5.3.
1
10.09. Found: C, 52.30; H, 9.97%. MS m/z 460 (M+); H
NMR d (C6D6) 0.17 (s, 9H, Me3Si), 0.19 (s, 9H, Me3Si),
0.30 (s, 9H, Me3Si), 1.03 (s, 9H, t-Bu), 1.33 (d, 1H, ring
proton, J = 16 Hz), 1.61 (s, 3H, Me), 1.83 (s, 3H, Me),
2.01 (d, 1H, ring proton, J = 16 Hz), 2.22 (d, 1H, ring pro-
ton, J = 19 Hz), 2.38 (d, 1H, ring proton, J = 19 Hz); 13C
NMR d (C6D6) 0.91, 1.23, 3.02 (Me3Si), 16.68 (CH2Ge),
21.81, 24.14 (Me), 27.83 (Me3C), 38.91 (CMe3), 43.62
(CH2), 89.16 (CO), 125.49, 127.68 (olefinic carbons); 29Si
NMR d (C6D6) À9.5, À8.2, 4.4.
Acknowledgment
We thank Shin-Etsu Co., Ltd. for the gift of
chlorosilanes.
References
Reaction of 2 with 2,3-dimethyl-1,3-butadiene. A mixture
of compound 2 (0.0924 g, 0.203 mmol) and 0.0212 g
(0.258 mmol) of 2,3-dimethyl-1,3-butadiene was heated in
a sealed tube at 140 ꢁC for 24 h. Product 4 (0.0353 g,
32% isolated yield) was isolated by column chromatogra-
phy. Anal. Calc. for C26H52OSi3Ge (4): C, 58.09; H, 9.75.
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