New optically active organogermane compounds containing the adamantyl radical for heterogeneous bimetallic catalysis. Part II

Article abstract of DOI:10.1016/S0022-328X(98)01137-1

Chiral organogermane(IV) derivatives H₃GeAdCH₂CO₂(-)-menthyl, H₃GeAdCH₂CH₂O(-)-bornyl and H₃GeAdCH₂CH₂O₂CCH ₂O(-)-menthyl (Ad=adamanty

Full text of DOI:10.1016/S0022-328X(98)01137-1

Journal of Organometallic Chemistry 580 (1999) 128–136
New optically active organogermane compounds containing the
adamantyl radical for heterogeneous bimetallic catalysis. Part IIꢀ
Mostafa Taoufik, Catherine C. Santini *, Jean-Marie Basset
Laboratoire de Chimie Organome´tallique de Surface, UMR 9986, CNRS-CPE-Lyon, 43 Boule6ard du 11 No6embre,
F-69626 Villeurbanne Cedex, France
Received 27 July 1998
Abstract
Chiral
organogermane(IV)
derivatives
H3GeAdCH2CO2(−)-menthyl,
H3GeAdCH2CH2O(−)-bornyl
and
H3GeAdCH2CH2O2CCH2O(−)-menthyl (Ad=adamantyl) have been prepared in six steps from the 1-bromoadamantane. The
new optically pure organogermane reagents which have been fully characterised have been used in the preparation of
heterogeneous bimetallic catalysts. © 1999 Elsevier Science S.A. All rights reserved.
Keywords: Germanium; Optically active organogermane compounds; Heterogeneous bimetallic catalysts
drogenolysis of chiral silyl ethers to Pd or (−)-
menthylSnMe3 to Rh surfaces afforded enantioselective
1. Introduction
heterogeneous catalysts, even though the enantiomeric
excess (e.e) are still low [4]. In the latter case, the
lability of the Sn–C bond under catalytic conditions
was proposed to explain the low optical excess. The
Ge–C is more stable and less labile under these condi-
tions: for example, hydrogenolysis of AdGeH3 onto
SiO2/Rh afforded [SiO2/Rh{Ge(Ad)(H)0.8}] where 80%
of the grafted fragment had an Ad–Ge bond thermally
stable until 200°C [5]. This high thermal stability and
the regioselectivity of the hydrogenolysis of Ge–C ver-
sus Ge–H led us to chose an optically active
organogermane derivative R*GeH3 to modify metallic
surfaces in order to obtain an enantioselective heteroge-
neous bimetallic catalyst.
It is now possible to graft organotin fragments,
namely Sn(n-C4H9)x onto the surface of Rh and Pt
particles supported on silica [2]. These organometallic
fragments may be obtained by partial hydrogenolysis of
Sn(n-C4H9)4 on a reduced metallic surface. These new
catalytic materials in which a metallic surface is par-
tially covered by an organotin fragment, exhibit for
some specific reactions much higher activity and selec-
tivity than conventionally prepared metallic catalysts.
For example, a rhodium surface modified by organotin
fragments becomes fully selective for the reduction of
the carbonyl function of a,b-unsaturated aldehydes [3].
In principle, by changing the steric and the electronic
properties of the grafted organometallic fragments, it
should be possible to control the chemio, regio and
stereoselectivity of any catalytic reaction catalysed by
metallic surfaces. Preliminary studies on the hy-
The germane derivatives RGeH3 are generally syn-
thesised by reduction of halide derivatives RGeX3 (X=
Cl, Br) by Group 16 metal hydrides [6,7] in anhydrous
organic solvent or by NaBH4 in water [8].
The two main synthetic routes to RGeX3 are the
hydrogermylation reaction of unsaturated compounds
with HGeCl3 [6,9–13] or the oxidative addition of
germylene GeX2 · dioxane [14] into a carbon–halide
ꢀ For Part I see [1].
* Corresponding author. Tel.: +33-4-72-43-18-10; fax: +33-4-72-
43-17-95.
E-mail address: santini@mulliken.cpe.fr (C.C. Santini)
0022-328X/99/$ - see front matter © 1999 Elsevier Science S.A. All rights reserved.
PII: S0022-328X(98)01137-1

M. Taoufik et al. / Journal of Organometallic Chemistry 580 (1999) 128–136
129
bond of various derivatives of alkyl halides. Among
these derivatives we can mention AdCl [15], CBr4 [16],
a or b-haloketones, a-haloethers, or acyl halides [17,18].
The second route being more general was chosen. With
linear alkyl groups, the presence of a functional group
in the a, b or even g and d-position with respect to the
metal decreases the M–C stability [M=Si, Sn, Ge],
leading to intramolecular rearrangements or even de-
composition [19]. Hence, the oxidative addition of
GeX2 · dioxane has been attempted with rigid cyclic
alkyl halides for which the g-effect is weaker, in partic-
ular, in the 1–3, disubstituted adamantyl [21].
2.1. Synthesis of chiral enantiomerically pure bromide
precursors 7, 8, and 9
The bromide precursors 7, 8, and 9 [3-Br-1-R*–Ad;
R*=CH2CH2O2CCH2O(−)menthyl;
CH2CO2(−)
This publication reports the synthesis of these precur-
menthyl; CH2CO2(−)bornyl] were prepared from 1-
bromo adamantane (1-Br–Ad) in three steps, Scheme
1.
The reaction of 1-bromo adamantane and 1,1-di-
choroethene in the presence of BF3–OEt2 in sulphuric
acid medium generated in situ a cation which was
converted by hydrolysis into 1-adamantylcarboxylic
acid, 3 in a 71% yield. This reaction has already been
observed by Bott [22].
The selective bromination of 3 at the carbon in the 3
position, was performed by reaction of 3 with 2.7
equivalents of water, in freshly distilled bromine [23]. It
is worth noting that, an excess of water gave 3-hydroxy
adamantyl acetic acid by a further substitution of the
3-bromide atom. Moreover, the reaction time should to
be less than 2 h to avoid polybromation of the
adamantyl group. Under these conditions the reaction
was regioselective affording 3-bromoadamantyl acetic
acid, 4 in a 94% yield.
The synthesis of enantiomerically pure esters was
realised by the reaction of either (−)-menthoxyacetic
acid with alcohol 5, formed by reduction of 4, or (−)
menthol, or (−) borneol with the acid chloride 6,
obtained from 4.
sors
H3GeAdCH2CO2(−)-menthyl,
H3GeAdCH2
CH2O(−)-bornyl and H3GeAdCH2CH2O2CCH2O
(−)-menthyl.
2. Results
Our preliminary experiments showed that the yield of
the insertion of germylene into carbon–halide of cyclic
or polycyclic alkyls varies in the same order as
germylene with aliphatic alkyls [17], i.e. Ctertiary
Csecondary\Cprimary
\
.
Thus, no reaction was observed with a primary
halide, e.g. 9,10-dibromo(+)-camphor.
With (−)-menthyl chloride, the reaction of insertion
occurred in a 60% yield. But a partial racemisation
[17,20] was observed as shown by the presence in the
1H-NMR spectrum of two doublets centred at 3.4 and
3.6 ppm [3JH–H=5 Hz] in a ratio of 1:3 for the
resonance of l(Ge–H), (Eq. (1)):
The reaction of 4 with three equivalents of LiAlH4 in
diethyl ether afforded the alcohol 5 in an 89% yield
after purification by chromatography. Ethyl 3-bromo
1-[2%-menthoxyacetate] adamantane 7 was prepared by
reaction of 5 with (−)-menthoxyacetic acid in benzene,
in the presence of a catalytic amount of p-toluenesul-
phonic acid, using a Dean and Stark apparatus, giving
a 68% yield, after purification by chromatography.
The reaction of 3-bromoadamantyl acetic acid 4 with
(−)menthol, in benzene catalysed by p-toluenesul-
phonic acid or transesterification of methyl [3-bromo,
1-adamantylacetate] in the presence of 4-dimethy-
laminopyridine in benzene afforded the expected prod-
ucts 8 and 9 but in low yields. To solve this problem,
firstly, the acid chloride 6 was synthesised by reaction
of 4 with thionyl chloride in the presence of pyridine
then reacted with either (−)-menthol or (−)-borneol,
in the presence of triethylamine to give after chro-
matography 8 and 9 in an 80 and 85% yield,
respectively.
(1)
But, with
a tertiary bridgehead carbon as in
adamantyl halides with a functional group in 3 for
instance, methyl [3-bromo, 1-adamantylacetate] the in-
sertion reaction was nearly quantitative. The derivative
2 was isolated in a 90% yield after distillation, (Eq. (2)).
(2)
A similar synthesis has been developed to obtain a
new family of chiral organogermanes derived from
1-halide adamantane substituted in the 3-position by a
chiral functional group, 3-Br-1-R*–Ad, Ad=
adamantyl, structure I:

130
M. Taoufik et al. / Journal of Organometallic Chemistry 580 (1999) 128–136
Scheme 1. Synthetic route of chiral organogermanes 13–15.
2.2. Synthesis of enantiomerically pure
trihalidealkylgermanes, 10, 11, and 12
These new compounds 7, 8 and 9 were fully charac-
terised by IR, 1H- and 13C-NMR spectroscopy, and MS
spectrometry and determination of the hD. In the 13C-
NMR, the resonance of C3 linked to the bromine atom
was similar for the three compounds 7, 8 and 9 (65.3,
64.5 and 65.5, respectively). It may be remarked that in
the 13C-NMR of 8 the resonances of the C7 and C7%
carbon were different, implying that C7 and C7% were
not equivalent, Table 1.
The oxidative addition of GeCl2 · dioxane, 1, into the
carbon–bromide bond of the esters 7, 8, and 9, [3-Br-1-
R*–Ad], at 110°C in 1,2-dichlorobenzene, in 12 h,
afforded the alkyl trihalidegermanes 10, 11, and 12. The
presence in the 13C-NMR spectrum of four signals for
the l C3 resonance, showed that scrambling of halide

M. Taoufik et al. / Journal of Organometallic Chemistry 580 (1999) 128–136
131
atoms [15] occurred during the reaction, affording a
mixture of species 3-[1-R*–Ad]GeBr3−xClx (x=0–3).
So, no further purification was attempted. The crude
products were analysed by IR and 13C-NMR
spectroscopy.
2.3. Synthesis of enantiomerically pure alkylgermanes
13, 14, and 15
The alkylgermane derivatives RGeH3 were generally
produced by an exchange reaction between RGeX3 and
a Group 16 metal hydride [6,7,12]. The presence of an
ester group in 10, 11, and 12 led us to use NaBH4 and
improve experimental conditions to prevent the reduc-
tion of the ester group and the loss of the chiral
fragment.
(3)
The reaction of (−)-menthyl ester 10 with NaBH4,
in THF, was very sensitive to experimental conditions
(temperature, excess of hydride). If the reaction temper-
ature was above 25°C and/or if more than three equiv-
alents of NaBH4 were used, there was reduction of the
ester into the alcohol [3-[1-HOCH2CH2–Ad}]GeH3.
However, the reaction of 10 in THF at room tempera-
ture (r.t.) with three equivalents of NaBH4 afforded 13,
in a 20% isolated yield after bulb-to-bulb distillation
(Eq. (3)).
The(−)-menthyl ester 14 was formed under the same
conditions in a 59% yield (b.p. 150°C/0.02 mm) from 11
(Eq. (4)).
Table 1
Chemical shifts in 13C-NMR of compounds 7–15
l ppm
7
13
8
14
9
15
13C
(4)
C1
C2
C3
C4
C5
C6
C7
C7%
C8
36.94
53.84
65.34
48.46
32.27
34.77
40.3
40.3
39.97
60.57
32.1
37.24
53.69
64.56
48.51
32.49
34.70
40.85
40.377 42.41
47.8
169.8
33.8
38.15
54.69
65.45
49.37
33.35
35.54
41.18
41.18
48.77
31
46.74
26.66
41.23
29.25
36.34
41.71
41.71
40.15
60.9
49.77
27.44
41.8
30.13
37.01
42.29
45.81
25.57
40.1
28.2
35.34
41
The structure of 13 and 14 was supported by elemen-
tal analysis, [h]D= −44.31° (c=1.108 mol l−1, ben-
zene) and [h]D= −46.9° (c=1.125 mol l−1, benzene)
for 13 and 14, respectively, and IC-SM (NH3). The IR
spectrum showed two strong vibrations at w(Ge–H)
2050 and w(CꢀO) 1730, 1728 cm−1 for 13 and 14,
respectively. In the 1H-NMR spectrum, there was a
singlet at 3.9 ppm for 13 and 4 ppm for 14 correspond-
ing to the resonance of lGe–H. In the 13C-NMR spec-
trum, resonances at 170.5 and 171.0 ppm assigned to
the CꢀO group of the ester were still present; all lC of
13 and 14 were shifted upfield, except lC6 and lC7,
comparatively with lC of bromide precursors 7 and 8.
In particular, lC3 was shifted from 65.3 in 7 to 26.6
ppm in 13; and from 64 in 8 to 27.4 in 14, Table 1. This
shift might be related to the difference in electronega-
tivity between bromine and germanium atoms (Br=
2.8; Ge=1.9).
41
43.05
47.3
C9
171.04 171.41 64.36
C10
C11
C1%
C2%
C3%
C4%
C5%
C6%
C1¦
C2¦
C3¦
Me–C5%
170.75 170.53
66.03
80.07
48.02
23.2
34.13
31.41
41.2
25.36
20.96
16.26
22.23
66.11
79.8
48.74
23.73
34.7
31.6
42.56
25.8
73.81
47.25
23.48
34.51
31.46
41.42
26.48
16.35
20.9
74.38
48.06
24.25
35.23
32.23
42.78
27.22
17.12
21.65
22.89
80.62
38.34
46.04
28.44
29.27
49.66
48.66
19.63
14.63
20.57
83.64
35.10
44.17
25.87
27.33
48.11
46.44
17.7
21.3
16.72
22.5
12.94
18.6
22.13

132
M. Taoufik et al. / Journal of Organometallic Chemistry 580 (1999) 128–136
3-Br-1-R*Ad+GeCl2 · dioxane“3-[1-{R*Ad}]GeBrxCl3−x
(6)
The reaction of 12 with three equivalents of NaBH4
in THF at r.t. was monitored by IR spectroscopy. As
observed during the synthesis of 13 and 14, a band at
2050 cm−1 assigned to w(Ge–H) appeared and in-
creased in intensity. But, in contrast to the reactions
described above, the band due to the w(CꢀO) vibration
at 1730 cm−1 decreased simultaneously in intensity,
until complete disappearance after 5 h of reaction. A
clear oil was isolated by bulb-to bulb-distillation
The
exchange
reaction
between
3-[1-{R*
Ad}]GeBrxCl3−x [3-Br-1-R*Ad] and NaBH4 was more
complex. However, the reaction of 10 and 11 in THF at
r.t. with three equivalents of NaBH4 afforded the new
optically pure alkylgermanes 13 and 14 in a 21 and 59%
yield, respectively.
In the same conditions as above, 12 was reduced into
the alkylgermane 15 in which the ester function has
been reduced into an ether function, but the chiral
fragment was still present.
Few examples of this kind of reaction are reported in
the literature [25]. However, in the case of sterically
hindered steroids and lactones [26,27], the reduction of
an ester function with NaBH4 and BF3–OEt2, afforded
alcohol or ether derivatives. The authors demonstrated
that the nature of the final product was determined by
the steric hindrance of the R group in the ester –
C(O)OR function. The steric hindrance of R controlled
the approach and the coordination of the Lewis acid
BF3 to the oxygen atom of ester function. If the coordi-
nation of BF3 occurred on the O of carbonyl group
–C(O)–OR, there was formation of ether; if the co-or-
dination of BF3 occurred on the O alkoxyde group
–C(O)–OR there was formation of alcohol and, in our
case, loss of the chiral fragment R*. The coordination
site was determined by the steric hindrance of the R
group in the ester –C(O)OR function [26,27].
1
(150°C/0.02 mm). IR and H-NMR spectra supported
the formation of a Ge–H bond in the derivative 15,
w(Ge–H) at 2050 cm−1 and lGe–H at 3.9 ppm, vide
supra.
In the13C-NMR spectrum of 15, the resonance at
171.4 ppm assigned to the carbonyl group of the ester
was absent. A new signal at 64.36 ppm appeared and
was attributed to the CH2 carbon, by DEPT135 experi-
1
ment. In the H-NMR spectrum, the new massif cen-
tred at 3.2 ppm could also be assigned to CH2 protons.
The different analytical results, IR, MS, elemental anal-
ysis, were in agreement with the fact that the (−)-
bornyl fragment was still present, but not the ester
group. This ester function has been reduced into an
ether group to afford 15 in a yield of 31% (Eq. (5)).
These literature data indicate that two factors are
essential in this reduction, the presence of a Lewis acid
and the steric hindrance of the group bound to the ester
function. Following the same hypothesis, we attempted
to explain the difference in the reactivity of 11 and 12
with NaBH4.
When 11 and 12 were involved in the reaction with
NaBH4 one molecule of borane BH3 was generated in
situ when the Ge–halide bond was converted into a
Ge–H bond [17] (Eq. (7)).
R3GeCl+NaBH4“R3GeH+BH3+NaCl
(7)
BH3 is a Lewis acid. To understand the importance of
its role in the reduction of 12, the reaction of precursors
8 and 9 with three equivalents of NaBH4, in the same
experimental conditions as 11 and 12 was realised. No
reaction was observed, i.e. NaBH4 alone did not reduce
the ester function. But, when the reaction of 8 and 9
with three equivalents of NaBH4 was performed in
presence BF3 · OEt2, 8 did not react, but 9, was reduced
in ether 16 in a 90% yield. Therefore, as expected, the
presence of a Lewis acid was necessary to observe the
reduction.
(5)
3. Discussion and conclusion
We reported the synthesis of new optically pure
alkylgermanes 13–15 in six steps (Scheme 1) from the
1-bromoadamantane, in an 8–31% yield.
Firstly, the enantiomerically pure brominated
adamantyl groups were synthesised: [3-Br-1-R*Ad].
Then the oxidative addition of germylene into C–Br
afforded the expected trihalides compounds, (Eq. (6)).
No reaction of germylene 1 with carbonyl group was
observed [24].
Following the literature, the second major factor was
the steric hindrance of the ester group. We already
reported that in the 13C-NMR spectrum of 9 the C7 and

M. Taoufik et al. / Journal of Organometallic Chemistry 580 (1999) 128–136
133
C7% showed the same chemical shift at 41.18 ppm, but in
the 13C-NMR spectrum of 8 the C7 and C7% showed two
different resonances at 40.85 and 40.4 ppm, at 25°C.
The difference between these chemical shifts decreased
from 16 Hz at 25°C to 12 Hz at 66°C. For 9, C7 and C7%
gave only one resonance above 30°C (coalescence tem-
perature) but, at −60°C, there was a splitting between
C7 and C7% signals of 3 Hz, D(lC7–lC7%).
give weak enantiomeric excess (eeB10) for the asym-
metric hydrogenation of ketone and alkene derivatives.
These results can be explained either by the electronic
effect of germanium or steric hindrance of the alkyl
group [29].
4. Experimental
These results suggest that there was, in 9, above
30°C, a free rotation of the ester group. The (−)bornyl
group could rotate around the C8–C9 or C1–O bond
while in 8, the (−)menthyl group could not rotate,
even at 66°C. The free energy of activation for this
rotation was DG" =16.85 kcal mol−1 for 9, superior
to 51 kcal mol−1 for 8 [28].
The correlation between the free rotation of the ester
group and its possible reduction by NaBH4 was sup-
ported by the following results: there was no reaction
between 9 and NaBH4 and BF3–O2Et at −50°C. At
this temperature, lC7 lC7% were different. At 25°C, 50%
of chiral ether 16 was formed, at that temperature, the
13C-NMR spectra of 9 showed a single broad peak for
C7 and C7%. At +66°C, there was a single sharp singlet
for C7 and C7% in the 13C-NMR spectra, and at this
temperature the conversion of 9 into 16 was quantita-
tive. Hence, the reduction of the ester into ether was
observed when there was free rotation of the ester
group.
All reactions and preparations were performed under
a dried atmosphere, oxygen-free argon using Schlenk
techniques. Solvents and reagents were appropriately
dried and purified.
The melting points were determined with an Elec-
trothermal digital melting point apparatus. 1H-NMR
spectra were recorded on a Bruker AM200 and AM300
(200 and 300 MHz) spectrometers. 13C-NMR spectra
(75 MHz, 1H decoupled) were also recorded on the
Bruker AM300 spectrometer, respectively at 25°C in
CDCl3 and C6D6; the position of the signals is reported
in ppm (l) down field from TMS. Optical rotations
were determined with Perkin–Elmer 241 polarimeter.
Microanalyses were performed by the analysis centre of
CNRS at Solaize. FTIR spectra were recorded on a
Nicolet 205 FTIR spectrometer. Mass spectra were
˚
obtained with a Nermag R10-10S (70 eV, 300 mA) ion
trap mass detector interfaced with a Delsi DI700 gas
chromatography having a 25 m×0.25 mm OV73 fused
silica capillary column. A Nermag R10-10S mass spec-
trometer was used in chemical ionisation mode with
ammonia as a reagent. Analytical gas chromatographic
analyses were carried out using an Intersmat IGC
120FL gas chromatography equipped with a flame ion-
isation detector, a Merck D200 recording integrator, a
conventional heated splitess injector, and a DB-5 fused
silica capillary column.
So, as in the literature, the conversion in 9 of the
ester function into an ether function may probably be
ascribed to the presence of a Lewis acid and to the
steric hindrance of the ester group (Eq. (8)).
Anhydrous toluene and 1,2-dichlorobenzene, anhy-
drous dioxane were obtained from Aldrich Chemical
Co. and were used without purification.
The complexes GeCl2 · dioxane, 1, [14], 1-adaman-
taneacetic acid, 3, [22] and 3-bromo-1-adaman-
taneacetic acid, 4 [23] have been synthesised as
described in the literature.
4.1. 2-(3-Bromo-1-adamantane)ethanol, 5
A solution of 3 g (10.45 mmol) of 4 in 40 ml of
diethyl ether was added dropwise to a solution of 0.407
g (10.6 mmol) of lithium aluminium hydride in 15 ml of
diethyl ether. The mixture was kept under stirring and
reflux for 17 h. Then the excess of hydride was hy-
drolysed by the dropwise addition of 3 ml of 4%
NaOH. When precipitation was complete, the mixture
was filtered, and the solid residue washed with ether.
The ether layer and ethereal extracts of the aqueous
layer were combined, washed with water, and dried
over MgSO4 and the solvent was evaporated at r.t.
(8)
The enantiomerically pure H3GeAdCH2CO2[(−)-
menthyl], 14, reacted selectively with the metallic sur-
face of the catalyst Rh/SiO2 to produce the surface
species {[HyGeAdCH2CO2(−)-menthyl]y[Geo]0.3}Rhs/
SiO2; y increasing from 0 to 0.7 when the quantity of 14
by surface atom of rhodium varies from 0.3 to 1.
Catalysts with y=0.3 and 0.5 show low activity and

134
M. Taoufik et al. / Journal of Organometallic Chemistry 580 (1999) 128–136
under atmospheric pressure. Flash chromatographic
separation eluting with hexane–ether (80/20) gave 2.4 g
of 5 (88.9%), white solid, m.p. 58–60°C. IR (KBr,
ml of anhydrous benzene was added 3.21 g (20.61
mmol) of (−)-menthol in 15 ml of benzene and 2.1 ml
of anhydrous pyridine at r.t. The mixture was stirred at
80°C for 12 h. After filtration the solvents were distilled
under low pressure to afford a residue, which was
purified by flash chromatography on a silica gel
column. Elution with (80/20) hexane–ether afforded 6 g
of 8 (85%) as a colourless oil.—[h]2D5= −41° (c 1,
C6D6).—IR (neat film, cm−1): 2935, 2910, 2856 (CH),
cm−1
)
3300 (OH), 2935, 2910, 2856 (CH).—1H
[(CDCl3, 300 MHz, l(ppm)] 1.45 [t, JH9,8=7.2 Hz, 2H,
H-8], 1.4–1.7 (m, 6H+O–H, exchanged with D2O),
2–2.5 (m, 8H, CH), 3.7 (t, JH9,8=7.2 Hz, 2H, H-9).—
13C-NMR [(CDCl3, 300 MHz, l(ppm)] 30.99 (C-5),
32.34 (C-1);. 37.2 (C-6), 40.26 (C-7), 47.3 (C-8), 48.37
(C-4), 53.41 (C-2), 65.1 (C-3), 178.8 (CꢀO).
1
1728 (CꢀO). H-NMR [(C6D6, 300 MHz, l(ppm)] 0.78
(d, J=6.5 Hz, 3H, Me at C-5%), 0.85 (d, J=7.1 Hz,
3
4.2. 3-Bromo-1-adamantaneacetic chloride, 6
3H, H-2¦), 0.91 (d, J=6.9 Hz, 3H, H-3¦), 1–1.5 (m,
15H), 1.93 (s, 2H, H-8), 2–2.2 (m, 8H), 4.8 (td, JH1%,6%
=
In total 6 ml (80 mmol) of thionyl chloride was
added dropwise to a solution containing 5.6 g (20
mmol) of 4 in 60 ml of benzene and 3 ml (46 mmol) of
pyridine. The mixture was stirred at reflux for 12 h.
After removal of the insoluble substances by filtration,
the reaction mixture was evaporated to give a colour-
less oil in a 96% yield.—IR (neat film, cm−1): 2935,
2910, 2856 (CH), 1775 (CꢀO).—1H-NMR [(CDCl3, 300
MHz, l(ppm)]: 1.5–1.8 (m, 6H), 2.1–2.4 (m, 8H), 2.8
(s, 2H, CH2COCl).—13C-NMR [(CDCl3, 300 MHz,
l(ppm)] 32.59 (C-5), 35.17 (C-1), 37.3 (C-6), 40.05
(C-7), 47.3 (C-8), 48.58 (C-4), 53.35 (C-2), 65.72 (C-3),
177.82 (CꢀO).
10.9 Hz, JH1%,2%=4.29 Hz, 1H, H-1%).—MS (IC, NH3);
m/z (%): 429 (100) (M+ +18).—C22H35O2Br: Calc. C
64.23, H 8.51, Br 19.4; Found C, 64.52; H, 8.52; Br,
18.83.
4.5. (3-Bromo 1-adamantyl) (−)-bornyl acetate 9
The same experimental procedure as 8 was followed,
with 5 g (17.18 mmol) of acid chloride and 3.2 g (26.61
mmol) of [(1S)-endo]-(−)-borneol. The product 9 was
isolated in the form of a colourless oil 5.6 g (80%).—
[h]2D5= −14.6° (c 1.17, C6D6).—IR (neat film, cm−1
)
1
2935, 2910, 2856 (CH), 1732 (Cꢀ0). H-NMR [(CDCl3,
300 MHz, l(ppm)]: 0.93 (s, 6H, H2¦+3¦), 1.06 (s, 3H,
Me at C6%), 1.4–2.5 (m, 23H), 5.25 (m, 1H, H-1%).—MS
(70 eV); m/z (%): 410 (9) [M+], 329 (12) [M+ –Br], 137
(100) [bornyl+], 136 (83) [Ad+].—MS (CI, NH3); 428
(100). [M+18].—C22H33O2Br: Calc. C 64.23, H 8.06,
Br 19.55; Found C 61.8, H 7.91, Br 19.40.
4.3.
3-Bromo-1{ethyl-(2%-menthoxyacetate)}adamantane,7
To a solution of 2.33 g (9 mmol) of 5 and 2.9 g (13.5
mmol) of (−)menthoxy-acetic acid in 200 ml of ben-
zene, p-toluenesulphonic acid (0.4 g) was added and the
mixture was kept under reflux for 2 days employing a
Dean–Stark trap. The mixture was cooled to r.t. and
was washed with a saturated solution of NaHCO3
(4×30 ml) and water (3×40 ml). The organic layer
was dried (MgSO4) and the solvent was evaporated.
The residue was purified by column chromatography
eluting with hexane–ether (80/20) to afford 2.7 g (68%)
of compound 7 as a colourless oil.—[h]2D5= −46.9° (c
1.5, C6H6).—IR (neat film, cm−1): 2935, 2910, 2856
(C–H), 1728 (CꢀO).—1H-NMR [(CDCl3, 300 MHz,
l(ppm)]: 0.8 [d, J=6.9 Hz, 3H, Me at C-5%], 0.90 (d,
4.6. General procedure for the preparation of
alkyltrihalogermanes 2, 10, 11 and 12
A flask fitted with a magnetic stirrer was charged
with the haloadamantane 3-Br-1-[R*CH2CO2]Ad and
GeCl2 · dioxane (1.5 equivalents) in 30 ml of dry 1,2-
dichlorobenzene. The mixture was stirred at 110°C for
17 h. After cooling at r.t., the solvent was removed
under reduced pressure and the residue was diluted with
benzene and filtered. The solvent was then removed to
give RGeX3 2, 10, 11 and 12.
J=7.1 Hz, 3H, H-2¦), 0.92 (d, J=6.4 Hz, 3H, H-3¦),
3
2–2.3 (m, 10H), 1.2–1.7 (m, 15H), 3.15 (td, JH1%,6%
=
10.55 Hz, JH1%,2%=4.13 Hz, 1H, H-1%), 4.08 (AB,
4.6.1. Procedure (a)
J
11a,11b=9.2 Hz, 2H, H-11a–11b), 4.2 (t, J=7.2 Hz,
A total of 1.8 g of 1 and 2.1 g of methyl(3-bro-
moadamantane)acetate afforded, after distillation
(130–160°C at 0.6 Torr), 2.83 g of 2.
2H, H-9).—MS (70 eV); m/z (%): 456 (2) [M+], 161
(39), 155 (100) [Menthol+]; 135 (8) Ad+ –C24H39O3Br:
Calc. C 64.41, H 8.65; Br, 17.37; Found: C 63.34, H
8.64; Br 16.34.
Rdt=90%.—IR (neat, cm−1): 2935, 2910, 2856
w(C–H); 1725 w(CꢀO). 1H-NMR [C6D6, 200 MHz,
l(ppm)]: 1.25 (m, 6H), 1.6–1.8 (m, 10H), 3.25 (s, 3H,
CH3). C13H19O2GeClnBr3−n: Calc. C 36.29, H 4.45, Ge
16.85, Cl 16.46, Br 18.55. Found: C 36.54, H 4.57, Ge
16.88, Cl 16.68, Br 18.83.
4.4. (3-Bromo 1-adamantyl) (−)-menthyl acetate, 8
To a solution containing 5 g (17.18 mmol) of 6 in 80

M. Taoufik et al. / Journal of Organometallic Chemistry 580 (1999) 128–136
135
4.6.2. Procedure (b)
4.7.2. 3-{1-[(−)-Menthyl acetate] adamantyl}
germane, 14
Complex 10 was synthesised from (4.14 g) of 7 and
(5.5 g) of 1.—IR (neat, cm−1): 2935, 2910, 2856
w(C–H); 1726 w(CꢀO). 1H-NMR [C6D6, 300 MHz,
l(ppm)]: 0.65 (d, 3J=6.9 Hz, 3H, Me at C5%); 0.83
(d, 3J=7.1 Hz, 3H, H2¦); 0.9 (d, 3J=6.9 Hz, 3H,
H3¦); 1–1.6 (m, 15H); 1.7–2.1 (m, 10H); 4.7 (td,
The yield of chiral ester 14 was 2.167 g (59%), b.p.
150°C/0.02 Torr.—[h]2D5= −46.9° (c 1.125, C6D6).—
IR (neat film, cm−1): 2935, 2910, 2856 (C–H), 2050
(Ge–H), 1728 (CꢀO). 1H-NMR [(C6D6, 300 MHz,
l(ppm)]: 0.93 (d, J=6.4 Hz, 3H, Me at C5%), 0.98 (d,
3
3
3JH1%,6%=10.9 Hz, JH1%,2%=4.29 Hz, 1H, H1%).
J=7 Hz, 3H, H2¦), 1.01 (d, J=6.9 Hz, 3H, H-3¦),
1.2–2 (m, 23H), 2.12 (s, 2H, H-8), 4.99 (td, JH1%,6%
=
10.7 Hz, JH1%,2%=4.4 Hz, 1H, H-1%), 3.75 (s, 3H, Ge–
H).—MS (CI, NH3): 426 (13) [M+NH3+1], 409
(16) [M+1], 348 (94), 193 (100), 135 (4) [Ad+].—
C22H38O2Ge: Calc. C 64.52, H 9.60; Found C 65.38,
H 9.60.
4.6.3. Procedure (c)
A total of 5 g of 8 and 3.474 g of 1 afforded 3.7 g
(9 mmol) of 11.—IR (neat, cm−1): 2935, 2910, 2856
w(C–H); 1728 w(CꢀO). 1H-NMR [C6D6, 300 MHz,
3
l(ppm)]: 0.8 (d, J=6.5 Hz, 3H, Me at C5%); 0.75 (d,
3J=7.1 Hz, 3H, H2¦); 0.78 (d, J=6.4 Hz, 3H, H3¦);
3
4.7.3. 3-{1-[2%(−)-Bornylethyloxyde] adamantyl}
germane, 15
3
1.2–1.7 (m, 15H); 2–2.3 (m, 10H); 2.95 (td, JH1%,6%
=
3
10.55 Hz, JH1%,2%=4.13 Hz, 1H, H1%); 3.82 (AB,
The yield of chiral ether 15 was 1.2 g (30.7%), b.p.
150°C/0.02 Torr.—IR (neat film, cm−1): 2935, 2910,
2856 (C–H), 2050 (Ge–H), 1230 (C–O–C).—1H-
NMR [(C6D6, 300 MHz, l(ppm)]: 0.56 (s, 6H, H2¦+
3¦), 0.72 (s, 3H, Me a` C6%), 1–1.7 (m, 23H), 3 (m,
1H, H-9%), 3.2–3.4 (m, 2H, H1%+9), 3.5 (s, 3H, Ge–
H).—MS (70 eV); m/z (%): 391 (7) [M+], 137 (100)
2JH11a,11b=9.2 Hz, H11a,11b); 3.95 (t, J=7.2 Hz, 2H,
3
H9).
4.6.4. Procedure (d)
A total of 4.08 g (10 mmol) of 9 and 3.474 g of 1
afforded 5.45 g of 12.—IR (film, cm−1): 2859–2951
w(C–H); 1732 w(CꢀO).
[bornyl+], 135 (8) [Ad+].—C22H38OGe: Calc.
67.31 H 9.76; Found C 67.80, H 10.24.
C
4.7. General procedure for the preparation of
organogermanes 13, 14 and 15
4.8. 3-Bromo[2%(−)-bornylethyloxyde]adamantane, 16
A solution of 1 g (2.44 mmol) of 3-bromo 1-
adamantyl) (−)-bornyl acetate, 9 in dry THF (10 ml)
was added to 0.28 g of NaBH4 (7.32 mmol) and 0.76
ml of a solution of BF3 · OEt2. The mixture was
stirred at 66°C for 5 h and then poured into 10 ml of
water. After dilution with diethyl ether (20 ml), the
organic layer was separated, washed with water, dried
over anhydrous MgSO4, and solvents were removed
under reduced pressure. The residue was purified by
column chromatography eluting with hexane–ethyl
acetate (95:5) to afford 0.88 g of 16 as a yellow liq-
uid, yield 90%.
A
solution of trihalogermane 3-[1-{R*CH2CO2
Ad}]GeBrnCl3−n (9 mmol) in dry THF (10 ml) was
added dropwise to a suspension of NaBH4 (27 mmol)
in dry THF (40 ml). The mixture was stirred at r.t.
for 5 h and then poured into 10 ml of water. After
dilution with diethyl ether (20 ml), the organic layer
was separated, washed with water dried over anhy-
drous MgSO4, and solvents were removed under re-
duced pressure. The residue was purified by
bulb-to-bulb distillation to give the expected products
13–15 as a colourless oil in a 20–60% yield.
IR (neat film, cm−1): 2960–2820 (C–H), 1230 (C–
O–C) 680 (C–Br).—1H-NMR [(C6D6, 300 MHz,
l(ppm)]: 0.62 [s, 6H, H-2¦+H-3¦), 1–1.2 (m, 23H),
4.7.1. 3-{1-[2%-(−)Menthoxyacetate ethyl]
adamantyl}germane, 13
The yield of chiral ester 13 was 810 mg (20%), b.p.
3
3
3–3.1 (dt, JH9,9%=9.15 Hz, JH9,8=6.52 Hz, 1H, H-
200°C/0.02
Torr.—[h]2D5= −44.31°
(c=1.108,
9), 3.11–3.15 (td, JH9,9%=9.15 Hz, 3JH9%,8=6.52 Hz,
3
C6H6).—IR (neat film, cm−1): 2935, 2910, 2856 (C–
H), 2050 (Ge–H), 1728 (CꢀO).—1H-NMR [(C6D6,
300 MHz, l(ppm)] 0.65 (d, J=6.9 Hz, 3H, Me at
C5%), 0.75 (d, J=7.1 Hz, 3H, H-2¦), 0.78 (d, J=6.4
Hz, 3H, H-3¦), 1.2–1.7 (m, 15H), 2–2.3 (m, 10H),
2.95 (td, JH1%,6%=10.55 Hz, JH1%,2%=4.13 Hz, 1H, H-
1%), 3.42 (s, 3H, Ge–H), 3.82 (AB, JA,B=9.2 Hz, 2H,
H11a–11b); 3.95 (t, J=7.2 Hz, 2H, H-9).—MS (CI,
NH3): 470 (15) [M+NH3+1], 161 (76); 137 (100)
[menthyl+], 135 (10) [Ad].—C24H42O3Ge: Calc. C
63.68, H 9.36. Found: C, 64.60 H 9.80.
1H, H-9%), 3.19–3.27 (m, 1H, H-1%).—MS (70 eV);
m/z (%): 397 (42) [81Br, M+1]+, 395 (36) [79Br,
M+1]+, 137 (16) [bornyl+], 136 (34) [Ad+], 95
(100) [MeBr+].
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