New synthetic routes to allylic germatranes

Article abstract of DOI:10.1016/j.jorganchem.2004.05.011

Two complementary routes allow control of regiochemistry and stereochemistry in the synthesis of allylic germatranes. The first method utilizes a transmetallation reaction between germanium(IV) chloride and the corresponding allylic tributylstannanes. The second route is via a palladium-catalyzed hydrogermylation of conjugated dienes by germatrane, N(CH 2 3 GeH, which gives predominantly Z products.

Full text of DOI:10.1016/j.jorganchem.2004.05.011

Journal of Organometallic Chemistry 689 (2004) 2565–2570
www.elsevier.com/locate/jorganchem
Note
New synthetic routes to allylic germatranes
*
J.W. Faller , Roman G. Kultyshev, Jonathan Parr
Department of Chemistry, Yale University, 225 Prospect Street, New Haven, CT 06520, USA
Received 9 February 2004; accepted 6 May 2004
Abstract
Allylic germatranes derived from triethanolamine can be prepared with moderate control of regioselectivity by two complemen-
tary routes. The first of these is through the preparation of the precursor allylic germanium trichlorides by a transmetallation re-
action between germanium(IV) chloride and the corresponding allylic tributylstannanes followed by alcoholysis and reaction
with triethanolamine. The second route is via the palladium-catalyzed hydrogermylation of conjugated dienes by germatrane,
N(CH2CH2O)3GeH. The former route gives mixtures of E and Z stereoisomers, whereas the second route gives exclusively Z
products.
ꢀ 2004 Elsevier B.V. All rights reserved.
Keywords: Germatrane; Organogermanium
1. Introduction
triethanolamine are known [4], we report here some
advances in the synthesis of allylic germatranes by two
complementary routes. The first of these is by a transmet-
allation between germanium(IV) chloride and the
corresponding (allyl)tributylstannane followed by ethan-
olysis to yield the (allyl)triethoxygermane and finally
complexation by triethanolamine, Fig. 1 and Scheme 1.
The second route, Scheme 2, is through the palladium-
catalyzed hydrogermylation of a suitable diene using
germatrane. These two routes both offer ready access to
allylic germatranes in high yield.
Organometallic compounds of Group 14 metals (Si,
Ge, Sn, Pb) enjoy a wide range of applications in the
synthesis of diverse organometallic and organic prod-
ucts. Of these elements, silicon [1] and tin [2] are the
more widely explored because these elements show at-
tractive reaction behavior and are readily synthesized
or are commercially available. Germanium, situated be-
tween these two more commonly used elements in the
periodic table is less widely studied, although its location
would suggest that its reactivity would be intermediate
between silicon and tin.
A number of groups have investigated germanium
compounds as reagents [3], and to this body of work we
have recently contributed some reports on the use of or-
ganogermatranes N(CH2CH2O)3 GeR in cross-coupling
reactions (R=aryl, alkynyl) [a,b] and in the rhodium
and palladium-catalyzed hydrogermylation of alkynes
(R=H) [c]. Although numerous germatranes based upon
2. Experimental
2.1. General procedures
Synthetic manipulations were carried out using stan-
dard Schlenk techniques under an inert atmosphere or in
a glove-box. Solvents were dried according to standard
procedures [5]. The H NMR spectra were recorded on
either a Bruker 500 MHz or a Bruker 400 MHz spec-
1
*
Corresponding author. Tel.: +1-2034323954; fax: +1-2034326144.
E-mail address: jack.faller@yale.edu (J.W. Faller).
trometer, and chemical shifts (d) are reported in ppm
0022-328X/$ - see front matter ꢀ 2004 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2004.05.011

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J.W. Faller et al. / Journal of Organometallic Chemistry 689 (2004) 2565–2570
R4
R1
Cl3Ge
H
time the initial cloudiness disappeared. The reaction
mixture was distilled (90 ꢁC bath temperature) under re-
duced pressure to give 3-buten-2-yl germanium trichlo-
R3
R2
1
ride, 1. Yield; 1.80 g, 51%. H NMR (CDCl3): d 5.90
R1 = Me; R2 = H; R3 = H; R4 = H,
1
(ddd, Jtrans =16, Jcis =10, J=7, 1H, CH‚), 5.35 (d,
Jcis =10, 1H, CH2‚), 5.33 (d, Jtrans =16, 1H, CH2‚),
3.06 (dq, 1H, J=7, 7, CHGe), 1.49 (d, 3H, J=7, CH
3CHGe). 13C{1H} (CDCl3): d 132.9, 119.5, 44.5, 13.2.
Anal. Calc. for C4H7Cl3Ge: C, 20.53; H, 3.01. Found:
C, 20.95; H. 3.16.
R1 = H; R2 = H; R3 = Me; R4 = H, E - 2
R1 = H; R2 = H; R3 = H; R4 = Me, Z - 2
R1 = H; R2 = Me; R3 = Me; R4 = H, E - 3
R1 = H; R2 = Me; R3 = H; R4 = Me, Z - 3
R1 = Me; R2 = Me; R3 = H; R4 = H,
4
Fig. 1. Allylgermanium trichlorides.
2.3. E,Z-Crotyl germanium trichloride (2)
1
relative to residual solvent resonances (CD(H)Cl3: H
7.27 d). The 13C{1H} NMR spectra were recorded on ei-
ther a Bruker 500 MHz or a Bruker 400 MHz spectrom-
eter operating at 125.8 or 100.6 MHz, respectively, and
referenced to the solvent signals (CDCl3: 13C 77.2 d. Mi-
croanalyses were performed by Atlantic Microlab Inc.
Additions of ethanol to the organogermanium trichlo-
rides were carried out at ꢀ78 ꢁC in these preparations;
however, the additions can be carried out at room tem-
perature.
In a 50 mL Youngꢀs flask crotyl tributylstannane
(5.28 g, 15.3 mmol) was combined with GeCl4 (3.27 g,
15.3 mmol). The flask was sealed under vacuum and
the reaction heated to 110 ꢁC for 10 h. The reaction
was cooled to room temperature and the mixture dis-
tilled (90 ꢁC bath temperature) to give a mixture of 1
and 2 (55:45). Heating this mixture to 135 ꢁC in a sealed
flask for a period of 9 h resulted in almost complete
1
isomerization to 2 (E:Z 65:35). H NMR (CDCl3): E-2
d 5.77 (dq, 1H, Jtrans =15.2, JMe–H =6.9, CH‚), 5.48
(m, 1H, CH‚), 2.83 (d, J=8.1, 2H, CH2Ge), 1.73
(dm, J=6.9, 3H, CH3CH); Z-2 d 5.83 (dq, Jcis =10.3,
JMe–H =6.9 H, CH‚), 5.48 (m, 1H, CH‚), 2.93 (d,
J=8.1, 2H, CH2Ge), 1.76 (dm, J=6.9, 3H, CH3CH).
13C{1H} NMR (CDCl3): d E-2 133.5, 118.4, 36.7,
18.4;. Z-2 131.5, 117.7, 32.1, 13.4.
2.2. 3-Buten-2-yl germanium trichloride (1)
In a 50 mL Youngꢀs flask crotyltributylstannane (5.28
g, 15.3 mmol) was combined with GeCl4 (3.27 g, 15.3
mmol). The flask was sealed under vacuum and the reac-
tion stirred at room temperature for 21 h, during which
R1
R4
R1 R4
3EtOH
R1 R4
N(CH2CH2OH)3
3 Et3N
O
R3
(EtO)3Ge
R3
Ge
N
Cl3Ge
R3
R2
O
R2
R2
- 3 NHEt3Cl
O
R1 = Me; R2 = H; R3 = H; R4 = H,
6
R1 = H; R2 = H; R3 = Me; R4 = H, E- 7
R1 = H; R2 = H; R3 = H; R4 = Me, Z- 7
R1 = H; R2 = Me; R3 = Me; R4 = H, E- 8
R1 = H; R2 = Me; R3 = H; R4 = Me, Z- 8
R1 = Me; R2 = Me; R3 = H; R4 = H,
9
Scheme 1. Preparation of allylgermatranes via ethanolysis and transalkoxylation.
GeO3N
R
R
R
O
Pd(PPh3)4 (5 mol%)
+
Ge
N
H
+
O
GeO3N
6, R = H
O
Z-7, R = H
Z-8, R = Me
"HGeO3N"
9, R = Me
Z-7 : 6 = 28 : 1
Z-8 : 9 = 30 : 1
Scheme 2. Preparation of allylgermatranes via palladium-catalyzed hydrogermylation of dienes.

J.W. Faller et al. / Journal of Organometallic Chemistry 689 (2004) 2565–2570
2567
2.4. E, Z-b-Methylcrotyl germanium trichloride (3) and
3-methyl-3-buten-2-yl germanium trichloride (4)
(m, 2H, CH2‚), 3.76 (t, 6H, CH2O), 2.79 (t, 6H,
CH2N), 2.17 (quintet, 1H, CHGe), 1.29 (d, 3H, J=7.2,
CH3CHGe). 13C{1H} (CDCl3, 125.8 MHz): d 141.9,
110.7, 57.1, 52.3, 33.1, 14.3. Anal. Calc. for C10H19 O3
NGe: C, 43.86; H, 6.99; N, 5.11. Found: C, 43.94; H,
7.08, N, 5.19%.
The b-methylcrotyl tributylstannane needed for this
synthesis was prepared by the method of Weigand and
Bruckner [6] using the alcohol derived by LAH reduc-
tion of tiglic acid. The originally formed E-isomer,
1
(
119Sn NMR, 186 MHz, CDCl3, d 14.4; H, d 5.02, q,
2.7. E,Z-Crotyl germatrane (7)
J=6.6, CMeH‚) partially isomerized to the Z-isomer
(
119Sn NMR,186 MHz, CDCl3, d11.7; 1H, d 4.91, q,
In a 100 mL Schlenk flask under nitrogen, 2 (0.99 g,
4.2 mmol E:Z 65:35) was dissolved in toluene (20 mL).
The flask was cooled to ꢀ78 ꢁC whereupon ethanol
(0.74 mL, 13 mmol) and triethylamine (1.77 mL,
12.7 mmol) were added. After warming to room temper-
ature (45 min) the precipitate was filtered off and washed
with further toluene (2·25 mL). The combined wash-
ings and filtrate were transferred to a 250 mL flask con-
taining triethanolamine (0.64 g, 4.2 mmol). The flask
was fitted with a reflux condenser and the mixture was
heated to 90 ꢁC for 6 h. The reaction was cooled and
the volume reduced to ca. 5 mL. Diethyl ether was add-
ed (35 mL) and the resulting solution evaporated giving
J=6.6, CMeH‚) upon distillation to yield an E:Z mix-
ture in a ratio of 38:62.
To a 50 mL Youngꢀs flask containing a stirring bar
and b-methylcrotyl tributylstannane (E:Z 38:62, 2.73 g,
7.60 mmol) was added GeCl4(0.87 mL, 7.63 mmol).
The flask was sealed under vacuum and stirred at room
temperature for 27 h. The reaction mixture was distilled
to give E:Z-3 (E:Z=65:35) and 3-methyl-3-buten-2-yl
germanium trichloride 4 (3:4 92:8). Yield: 1.51 g, 80%.
1H NMR (CDCl3): E-3 d 5.52 (q, 1H, J=7.4, CH‚),
2.88 (s, 2H, CH2Ge), 1.77 (m, 3H, CH3C‚), 1.66 (d,
3H, J=7.4, CH3CH‚). Z-3 d 5.56 (q, 1H, J=7.4,
CH‚), 2.94 (s, 2H, CH2Ge), 1.86 (m, 3H, CH3C‚),
1.52 (d, 3H, J=7.4, CH3CH‚). 4 d 5.10 (m, 1H,
CH‚), 5.02 (m, 1H, CH‚), 3.05 (q, 1H, J=7.5, CHGe),
1.90 (m, 3H, CH3C‚), 1.52 (d, 3H, J=7.5, CH3CH).
1
a white solid. Yield: 1.14 g, 98% (E:Z 65:35). H NMR
(CDCl3) (resonances of E-7 and Z-7 overlap except for
the methylene); E-7 d 5.58 (m, 1H, CH‚), 5.41(m,
1H, CH‚), 3.76 (m, 6H, CH2O), 2.80 (m, 6H,
CH2N), 1.83 (m, 2H, CH2Ge), 1.63 (m, 3H, CH3CH).
Z-7 d 5.58 (m, 1H, CH‚), 5.41 (m, 1H, CH‚), 3.76
(m, 6H, CH2O), 2.80 (m, 6H, CH2N), 1.86 (m, 2H,
CH2Ge), 1.63 (m, 3H, CH3CH). 13C{1H} (CDCl3); E-7
d 126.9, 124.5, 56.9, 51.9, 24.2, 18.3; Z-7 d 126.1,
122.7, 57.0, 52.0, 19.4, 12.7. Anal. Calc. for
C10H19NO3Ge: C, 43.86; H, 6.99; N, 5.11. Found: C,
43.95; H, 7.12; N, 5.11%.
2.5. 2-Cyclohexen-1-yl germanium trichloride (5)
To a 50 mL Youngꢀs flask containing a stirring bar
and 2-cyclohexen-1-yl tributylstannane (1.61 g, 4.34
mmol) was added GeCl4(0.49 mL, 4.3 mmol). The flask
was sealed under vacuum and the reaction stirred at
room temperature for 20 h. Distillation of the reaction
mixture (110 ꢁC) allowed the isolation of 5. Yield: 0.65
1
g, 58%. H NMR (CDCl3, 500 MHz): d 6.07 (m, 1H,
2.8. E,Z-b-Methylcrotyl germatrane (8) and 3-methyl-3-
buten-2-yl germatrane (9)
CH‚), 5.77 (m, 1H, CH‚), 3.09 (m, 1H, CHGe),
2.15–2.07 (m, 4H), 1.88 (m, 1H), 1.74 (m, 1H).
13C{1H} NMR (CDCl3, 125.8 MHz): d 133.5, 120.4,
44.9, 24.7, 23.3, 20.8.
In a 100 mL Schlenk flask under nitrogen, a mixture of
3 and 4 (11:1, 1.45 g, 5.84 mmol) was dissolved in toluene
(20 mL). The flask was cooled to ꢀ78 ꢁC whereupon eth-
anol (1.03 mL, 17.6 mmol) and triethylamine (2.45 mL,
17.1 mmol) were added. After warming to room temper-
ature (40 min) the precipitate was filtered off and washed
with further toluene (2·25 mL). The combined washings
and filtrate were transferred to a 250 mL flask containing
triethanolamine (0.89 g, 5.9 mmol). The flask was fitted
with a reflux condenser and the mixture was heated to
90 ꢁC for 6 h. The reaction was cooled and the volatiles
removed. The residue was treated with methylene chlo-
ride (20 mL). The resulting solution was again taken to
dryness and the residue washed with diethyl ether
(10 mL) leaving 8 (E/Z=65:35) and 9 (11:1) as a white
powder. Yield: 1.44 g, 86%. Z-8 was distinguished from
E-8 by a larger NOE being observed in the vinylic proton
resonance upon irradiation of the b-methyl group (the
2.6. 3-Buten-2-yl germatrane (6)
In a 100 mL Schlenk flask under nitrogen, 1 (1.73 g,
7.4 mmol) was dissolved in toluene (20 mL). Then etha-
nol (1.30 mL, 22.2 mmol) and triethylamine (3.09 mL,
22.2 mmol) were added. After standing at room temper-
ature (45 min) the precipitate was filtered off and washed
with further toluene (2·25 mL). The combined wash-
ings and filtrate were transferred to a 250 mL flask con-
taining triethanolamine (1.127 g, 7.4 mmol). The flask
was fitted with a reflux condenser and the mixture was
heated to 95 ꢁC for 6 h. The reaction was cooled and
the volatiles were removed to yield a white solid melting
1
at 125 ꢁC. Yield: 2.02 g, 99%. H NMR (CDCl3, 400
MHz): d 6.17 (ddd, 1H, J=17, 10.3, 6.9; CH‚), 4.95

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J.W. Faller et al. / Journal of Organometallic Chemistry 689 (2004) 2565–2570
effect was more readily observed in benzene-d6, where less
overlap of resonances occurred).1H NMR (CDCl3): E-8 d
5.24 (q, 1H, J=6.5, (CH3)CH‚), 3.71 (m, 6H, CH2O),
2.78 (m, 6H, CH2N), 1.89 (s, 2H, GeCH2), 1.71 (s, 3H,
CH3C‚), 1.57 (d, 3H, J=6.5, (CH3)CH‚). Z-8 d 5.17
(q, 1H, J=6.4, (CH3)CH‚), 3.76 (m, 6H, CH2O), 2.77
(m, 6H, CH2N), 1.81 (s, 2H, GeCH2), 1.70 (s, 3H,
CH3C‚), 1.61 (d, 3H, J=6.4, (CH3)CH‚). 9 d 4.74
(m, 2H, H2C‚), 3.74 (m, 6H, CH2O), 2.78 (m, 6H,
CH2N), 2.14 (q, 1H, J=7.5, CH(CH3)), 1.86 (s, 3H,
CH3C‚), 1.32 (d, 3H, J=7.5).
2.10. General procedure for the palladium-catalyzed
germatrane hydrogermylation of dienes
A 100 mL Schlenk flask equipped with a stirbar was
charged with germatrane (1.0 mmol) and Pd(PPh3)4
(0.05 mmol). Toluene (10 mL) was added via syringe fol-
lowed by the diene (4.0 mmol) and the resulting solution
stirred at room temperature. After 12–60 h, the reaction
mixture was filtered through a pad of Celite. The Celite
was washed with CH2Cl2 (10 mL) and the combined fil-
trate and washings evaporated to dryness. In each case
the residue contained the expected allylic germatrane
and traces of triphenylphosphine oxide. Diene: 1,3-buta-
diene, product: Z-7, yield: 75%; isoprene, Z-8: 73%; 1,3-
cyclohexadiene, 10, 95%.
13C{1H} NMR (CDCl3): E-8 d 133.0 ((CH3)-
(CH2)C‚), 118.5 ((CH3)HC‚), 57.1 (CH2O), 52.1
(CH2N), 31.5 (GeCH2), 17.8 (CH3C‚), 14.0
(CH3CH‚). Z-8 d 133.5 ((CH3)(CH2)C‚), 117.6
((CH3)HC‚), 57.3 (CH2O), 52.2 (CH2N), 24.1 (GeCH2),
25.8 (CH3C‚), 13.9 (CH3CH‚). 9 d 149.7 (CH3(Ge-
CHMe)C‚), 108.4 (H2C‚), 57.3 (CH2O), 52.5
(CH2N), 36.8 (GeCHMe), 23.5 ((CH3)C‚), 15.9,
(GeCH(CH3)). Anal. Calc. for C10H21GeNO3: C, 45.89;
H, 7.35; N, 4.87. Found: C, 45.91; H, 7.29; N, 4.84%.
3. Results and discussion
While the transmetallation reactions between allylic
trialkylstannanes and a range of main group Lewis acids
have been investigated [7], to the best of our knowledge
such reactions with germanium(IV) chloride have not.
The likely products of these reactions are of interest to
us because allylic germanium trichlorides are precursors
to allylic germatranes, reagents with potential applica-
tion in cross-coupling reactions. Although allylic germa-
nium trihalides are available from the reaction of
GeX2 Ædioxane with allylic halides [8] we have examined
the reactions of a number of allylic trialkylstannanes
with germanium(IV) chloride in the hope that these re-
actions would prove more convenient.
The procedure used for the preparation of allylger-
manium trichlorides was an adaptation of the method
reported by Lutsenko for the preparation of halogermyl
acetates from the corresponding esters of tributylstannyl
acetic acid [9]. The two reagents were combined in a 1:1
ratio without solvent in a sealed flask and stirred for sev-
eral hours either at room temperature or ca. 100 ꢁC.
Both allyl and methyl-substituted allyl germanium chlo-
rides may be prepared in this manner. The products
were isolated by distillation of the reaction mixture.
Although stable enough to allow spectroscopic charac-
terization, these compounds are extremely sensitive to
hydrolysis and so were converted to the corresponding
germatranes as quickly as was expedient. For the
same reason, it was often not possible to obtain repro-
ducible microanalytical data for these allylic germanium
trichlorides.
2.9. 2-Cyclohexen-1-yl germatrane (10)
In a 100 mL Schlenk flask under nitrogen, 5 (0.60 g,
2.3 mmol) was dissolved in toluene (15 mL). The flask
was cooled to ꢀ78 ꢁC whereupon ethanol (0.41 mL,
6.5 mmol) and triethylamine (0.96 mL, 6.8 mmol) were
added. After warming to room temperature (40 min)
the precipitate was filtered off and washed with further
toluene (2·25 mL). The combined washings and filtrate
were transferred to a 250 mL flask containing triethanol-
amine (0.34 g, 2.25 mmol). The flask was fitted with a re-
flux condenser and the mixture was heated to 90 ꢁC for 6
h. The reaction was cooled and the volatiles removed.
The white residue was washed with pentane (10 mL)
and the residue after washing dissolved in methylene
chloride (10 mL). The solution was filtered through a
pad of silica which was subsequently washed with fur-
ther methylene chloride (15 mL). The combined filtrate
and washings were taken to dryness leaving white solid,
1
10, melting at 158 ꢁC. Yield: 0.50 g, 73%. H NMR
(CDCl3): d 5.88 (m, 1H, CH‚), 5.66 (m, 1H, CH‚),
3.75 (m, 6H, CH2O), 2.79 (m, 6H, CH2N), 2.12 (m,
1H, GeCHH), 2.09–1.83 (m, 5H, cyclohexyl), 1.49 (m,
1H, cyclohexyl). 13C{1H} NMR (CDCl3): d 128.7,
126.0, 57.1, 52.3, 32.4, 25.2, 24.7, 22.6. Anal. Calc. for
C12H21NO3Ge: C, 48.10; H, 7.35; N, 4.85. Found: C,
48.10; H, 7.10; N, 4.65% (see Fig. 2).
The reaction of crotyl tributylstannane with germa-
nium(IV) chloride did not yield crotyl germanium tri-
chloride, which has been prepared previously by the
reaction of methyl allene with trichlorogermane [10],
but instead gave exclusively 3-buten-2-yl germanium
trichloride. This result is in accord with the findings
of Naruta who has previously explored the reaction
O
Ge
N
O
O
Fig. 2. Cyclohexenyl germatrane 10.

J.W. Faller et al. / Journal of Organometallic Chemistry 689 (2004) 2565–2570
2569
of crotyl tributylstannane with tin(IV) chloride [d];
however the reactions of the germanium analogue
have a different temperature profile. In the tin case,
the 3-buten-2-yl product is obtained initially in the
transmetallation reaction when it is conducted at
ꢀ50 ꢁC, but this initial product rearranges to a mix-
ture of crotyl tin trichloride products on warming to
room temperature. In contrast, the conversion to the
crotyl germanium trichloride requires prolonged heat-
ing at high temperature. Clearly the germanium tri-
chloride analogue is more resistant to rearrangement.
Even repeating the reaction at 110 ꢁC gave a mixture
of the crotyl and 3-buten-2-yl germanium trichlorides
(1:2 55:45). Hence the initial transfer of the allylic
group is c-selective (Scheme 3) and subsequent rear-
rangement yields the crotyl derivative This SE20 type
behavior has been observed previously in the reaction
of crotyl tributylstannane with several tin(IV) chloro
compounds [7] and with phosphorus trihalides [b]. It
should be noted that a significant amount (35%) of
the less stable isomer, Z-2, is produced upon rear-
rangement in our reaction.
Introduction of more substituted allyl groups, such
as those in E,Z-b-methylcrotyl tribuylstannane and 3-
methyl-2-butenyl tributylstannane, does not interfere
with formation of the allylic germanium trichlorides
3 and 4. Compound 3 had been reported previously
as a product formed in the high-temperature thermol-
ysis of phenylgermanium trichloride in the presence of
isoprene [11]. These reactions also appear to occur
with a c-selective initial transfer followed by some
degree of subsequent rearrangement. Thus the ratio
of isomers presently initially in the reagent E,Z-b-
methylcrotyl tribuylstannane is not reflected in the
product ratio of 3, which is determined by kinetic
preferences of the rearrangement of the initially
formed 4 (Scheme 4).
pound 2-cyclohexen-1-yl tributylstannane [12] also
reacts smoothly with germanium(IV) chloride to
form the corresponding 2-cyclohexen-1-yl germanium
trichloride.
These allylic germanium trichlorides, 1–5 were con-
verted to the corresponding allylic germatranes
N(CH2CH2O)3Ge(allyl) by the route outlined in Scheme
1. Prior conversion to the triethoxygermane, rather than
direct reaction with triethanolamine, avoids potential
difficulties resulting from protonation of the triethanol-
amine with HCl. The in situ reaction with ethanol and
the subsequent transalkoxylation both proceed in high
yield to give crystalline products.
Palladium-catalyzed hydrogermylation of terminal
acetylenes by triphenyl germane, giving E-tri-
phenylgermyl alkenes [13], and of isoprene by tri(2-fu-
ryl)germane [14] proceeds in both cases in good yield
with marked stereochemical selectivity. We reasoned
that allylic germatranes might also be prepared by the
germatrane hydrogermylation of the corresponding di-
enes, Scheme 2. In this reaction, the hydrogermylation
of butadiene gave Z-crotyl germatrane, Z-7, and a small
quantity of the 1,2 addition product 3-buten-2-yl germa-
trane 6. Similarly, isoprene is hydrogermylated to give
Z-8 as a single stereoisomer and 9 as a minor side-prod-
uct (ca. 3%). The selectivity for the formation of the
Z-product is consistent with the corresponding hydrost-
annylations which also show the same isomer selectivity
[12]. Hydrogermylation of 1,3-cyclohexadiene gave
the expected 10 in a slower reaction (60 h at room
temperature).
The preparation of allylic germatranes by hydroge-
rmylation of the corresponding diene is a very conve-
nient route in comparison to many traditional multi-
step approaches to germatranes. One disadvantage of
the reaction is that triphenylphosphine oxide is pro-
duced as a side-product that is somewhat troublesome
to separate from the desired products [15]. Fortunately
with our products, the contaminant could be removed
by washing and the products could be prepared com-
pletely free of phosphine oxide by recrystallization.
We have emphasized allylic systems in which stereo-
chemistry is an issue; nevertheless, the methodology also
provides a straightforward route to other allylic germa-
nium trichlorides. For example, the cyclic allylic com-
GeCl4
-Bu3SnCl
Bu3Sn
Cl3Ge
Cl3Ge
1
E,Z-2
Scheme 3. The c-selectivity observed upon initial transfer from tin to germanium.
GeCl4
Me
Cl3Ge
Bu3Sn
Cl3Ge
-Bu3SnCl
E,Z-3
4
Scheme 4. The c-selectivity upon initial transfer from tin to germanium provides a path for obtaining a different E:Z ratio in the product than existed
in the tin reagent.

2570
J.W. Faller et al. / Journal of Organometallic Chemistry 689 (2004) 2565–2570
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4. Conclusion
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Allylic germatranes can be prepared either by the
transmetallation of germanium(IV) chloride with the cor-
responding organostannanes followed by alcoholysis and
reaction with triethanolamine or by the palladium-cata-
lyzed germatrane hydrogermylation of the appropriate
diene. The c-selective initial transmetallation with crotyl
tributylstannane can be an advantage for the preparation
of pure 3-buten-2-yl germatrane. Subsequent rearrange-
ment can provide the crotyl derivative with a relatively
high Z-isomer component. If, however, only Z-crotyl
germatrane is desired, the hydrogermylation route is pre-
ferred. Hydrogermylation also effectively provides a high
isomeric purity (97%) of the Z-b-methylcrotyl germatra-
ne. Consequently, the two routes provide complementary
methods to conveniently provide isomeric allylic ger-
matranes. Although crotyl germatrane could potentially
be prepared via by the reaction of methyl allene with tri-
chlorogermane [10], and subsequent treatment with tri-
ethanolamine, this would not provide a practical
synthesis. Unfortunately, the reaction of methyl allene
with trichlorogermane provides only 30% of the crotyl
derivative along with 70% of isomeric vinyl derivatives
[10], which would result in low yield and difficulties in
separation.
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Acknowledgements
This research was supported by a grant from the Na-
tional Science Foundation (CHE0092222). We thank
Philip Fontaine for obtaining COSY, HMQC, and 1D
NOE spectra for 8 and 9.
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