An alternative route to allylgermanes by the palladium-catalyzed reaction of germylsilanes with allylic halides

Article abstract of DOI:10.1016/S0022-328X(99)00308-3

Pd(dba)₂ (bis(dibenzylideneacetone)palladium complex) effectively catalyzes the reaction of (dimethylphenylgermyl)trimethylsilane with 2-alkenyl halides to bring about metal-, regio- and stereoselective metathesis resulting in the formation of 2-alkenylphenylgermanes with good yields. On the other hand, the reaction of (chlorodimethylgermyl)trimethylsilane with 2-alkenyl halides is effected by a palladium-phosphine complex to give 2-alkenylchlorogermanes selectively. Germylation of 3,4-dichloro-1-butene with (dimethylphenylgermyl)trimethylsilane forms 1,4-bis(dimethylphenylgermyl)-2-butene with a high yield.

Full text of DOI:10.1016/S0022-328X(99)00308-3

www.elsevier.nl/locate/jorganchem
Journal of Organometallic Chemistry 587 (1999) 144–148
Note
An alternative route to allylgermanes by the palladium-catalyzed
reaction of germylsilanes with allylic halides
Kazuyoshi Ono, Hisao Ishizuka, Taichi Nakano *
Department of Material Science and Technology, School of High-Technology for Human Welfare, Tokai Uni6ersity, 317 Nishino, Numazu,
Shizuoka 410-0321, Japan
Received 13 April 1999; received in revised form 24 May 1999
Abstract
Pd(dba)2 (bis(dibenzylideneacetone)palladium complex) effectively catalyzes the reaction of (dimethylphenylgermyl)-
trimethylsilane with 2-alkenyl halides to bring about metal-, regio- and stereoselective metathesis resulting in the formation of
2-alkenylphenylgermanes with good yields. On the other hand, the reaction of (chlorodimethylgermyl)trimethylsilane with
2-alkenyl halides is effected by a palladiumꢀphosphine complex to give 2-alkenylchlorogermanes selectively. Germylation of
3,4-dichloro-1-butene with (dimethylphenylgermyl)trimethylsilane forms 1,4-bis(dimethylphenylgermyl)-2-butene with a high yield.
© 1999 Elsevier Science S.A. All rights reserved.
Keywords: (Germyl)silanes; Palladium catalysis; Allylgermanes; Regioselectivity; Stereo-selectivity
formation of allylgermanes. Unfortunately, we found
that the reaction of (triethylgermyl)trimethylsilane with
allyl chloride in the presence of Pd2(dba)3 gave allyltri-
ethylgermane and allyltrimethylsilane with yields of 22
and 12%, respectively. To overcome this difficulty, we
examined the reactions of (dimethylphenylgermyl)-
trimethylsilane 1a and (chlorodimethylgermyl)tri-
methylsilane 1b with allylic halides in the presence of a
transition metal catalyst and found that the selective
formation of allylgermane occurred. In the metathesis
of phenyl or chloro substituted homobimetallics such as
disilanes or digermanes with allylic chlorides, selective
formation of 2-alkenyl(phenyl)metallanes or 2-
alkenyl(chloro)metallanes has been reported [9b, 11].
However, to date, it is not known whether the metathe-
sis of heterobimetallics such as a (phenylgermyl)silane
or a (chlorogermyl)silane with allylic halides occurs
metal-, regio- and stereoselectively. We would like to
report herein the first example demonstrating that the
metal-, regio- and stereoselective metathesis does indeed
take place in the presence of Pd(dba)2 or
Pd2(dba)3ꢀ4PPh3 to provide an alternative synthesis of
2-alkenylgermanes.
1. Introduction
Allylsilanes [1] and allylstannanes [2] are valuable
reagents in organic synthesis. In contrast, the synthetic
use of allylgermanes [3] is very limited. The main reason
is the apparent lack of appropriate synthetic methods
for the preparation of stereo-defined allylgermanes.
Several reactions are currently available; (a) allylation
of chlorogermanes with allylmagnesium chloride [4] or
allyl lithium [5]; (b) hydrogermylations of dienes [6] or
allenes [7]; and (c) germylation of allyl acetates using
germylcuprates(I) [8] or of allyl chlorides using diger-
manes [9]. Recently, we reported that (tri-
ethylgermyl)tributylstannane reacted with 2-alkenyl
chlorides in the presence of Pd2(dba)3 at room tempera-
ture undergoing a metal-controlled metathesis affording
2-alkenylgermanes with good yields [10]. In closely
related work, we examined the reaction of (germyl)-
silanes with 2-alkenyl halides aiming at a selective
* Corresponding author. Fax: +81-6-559681155.
0022-328X/99/$ - see front matter © 1999 Elsevier Science S.A. All rights reserved.
PII: S0022-328X(99)00308-3

K. Ono et al. / Journal of Organometallic Chemistry 587 (1999) 114–148
145
2. Results and discussion
and 48%, respectively (entries 9 and 10 in the Table
1).
Stirring a 1:2:0.005 mixture of the (germyl)silane 1a,
allyl chloride and Pd2(dba)3 at room temperature (r.t.)
led to metal selective metathesis to furnish al-
lyldimethylphenylgermane (61%) and allyltrimethylsi-
lane (3%). Chlorotrimethylsilane and chlorodimethyl-
phenylgermane as by-products, respectively, of the al-
lylgermane and the allylsilane were also formed in
corresponding yields. Use of such solvents as benzene,
toluene, cumene or THF brought about good germa-
nium selectivity (entries 2–5 in Table 1). Dimethylfor-
mamide (DMF), a basic solvent, was found to be
unsuitable for the present purpose (entry 6 in Table 1).
After screening the reaction conditions, use of 1
mol% of Pd(dba)2 led to completion of metathesis
within 4 h affording allyldimethylphenylgermane at a
70% yield with the formation of a 3% yield of al-
lyltrimethylsilane (Scheme 1, entry 7 in Table 1). Pal-
ladiumꢀphosphine complexes such as Pd(OAc)2ꢀ2PPh3
or PdCl2(PPh3)2 also catalyzed the reaction, but the
yields of the corresponding allylgermane were only 36
Dichlorotris(triphenylphosphine)ruthenium(II) effec-
ted metathesis at r.t. to afford allyldimethylphenylger-
mane in 54% yield with a 10% yield of allyltrimethylsi-
lane. However, when the RuCl2(PPh3)3 catalysis was
carried out at 150°C, the yield of the allylgermane was
improved from 54 to 70% and the ratio of the allylger-
mane to the allylsilane was improved from 84/16 to
96/4, respectively (entry 12 in the Table 1). The reason
for this somewhat unexpected result is, however, at
present unclear. Other tested catalysts such as Pd-
(dba)2ꢀLiCl, RhCl(PPh3)3, NiCl2(PPh3)2 and NiBr2-
(PPh3)2 were inferior to Pd(dba)2, Pd2(dba)3 and
RuCl2(PPh3)3.
In the germylation using the (germyl)silane 1b,
triphenylphosphine as a ligand was necessary (Scheme
2). The metathesis in the presence of Pd2(dba)3 alone
gave allylchlorodimethylgermane and allyltrimethylsi-
lane only with yields of 13 and 2%, respectively (entry
2 in the Table 2). RuCl2(PPh3)3 appeared to be less
effective (entry 4 in the Table 2).
Table 1
Comparison of conditions in the reaction of (dimethylphenylgermyl)trimethylsilane 1a with allyl chloride a
Entry Catalyst (mol%) b
Ligand (mol%) d
Solvent (ml)
Conditions (°C, h)
Yield (%) c
[A] e[B]f
Metal selectivity
[A]/[B]
1
2
3
4
5
6
7
8
Pd2(dba)3 (0.5)
Pd2(dba)3 (0.5)
Pd2(dba)3 (0.5)
Pd2(dba)3 (0.5)
Pd2(dba)3 (0.5)
Pd2(dba)3 (0.5)
Pd(dba)2 (1.0)
None
None
None
None
None
None
None
None
r.t., 5
61
62
59
60
54
20
70
12
36
48
54
70
0
3
16
5
8
4
34
3
13
16
9
10
3
22
20
10
95/5
79/21
92/8
88/12
93/7
37/63
96/4
48/52
69/31
84/16
84/16
96/4
0/100
20/80
66/34
PhH (1)
PhMe (1)
Cumene (1)
THF (1)
DMF (1)
None
DMF(1)
None
None
None
None
None
None
40, 10
40, 10
40, 10
40, 10
40, 10
r.t., 4
r.t., 200
r.t., 850
r.t., 350
r.t., 2
Pd(dba)2ꢀLiCl (2.0) None
9
Pd(OAc)2 (1.0)
PdCl2(PPh3)2 (1.0)
RuCl2(PPh3)3 (1.0)
RuCl2(PPh3)3 (0.1)
RhCl(PPh3)3
PPh3 (2.0)
10
11
12
13
14
15
None
None
None
None
None
None
150, 10
150, 25
150, 25
150, 25
NiCl2(PPh3)2
NiBr2(PPh3)2
5
19
None
a (Germyl)silane 1a/allyl chloride, 1 mmol/2–3 mmol. The (germyl)silane 1a was almost completely consumed.
b (mmols of the catalyst/mmols of (germyl)silane 1a)×100.
c Yields were determined by GLC and based on the (germyl)silane 1a charged. Thermal conductivity corrections were not made.
d (mmols of PPh3/mmols of (germyl)silane 1a)×100.
e [A], allyldimethylphenylgermane.
f [B], allyltrimethylsilane.
Scheme 1.

146
K. Ono et al. / Journal of Organometallic Chemistry 587 (1999) 144–148
Scheme 2.
Table 2
Comparison of conditions in the reaction of (chlorodimethylgermyl)trimethylsilane 1b with allyl chloride a
Entry
Catalyst (mol%) b
Ligand (mol%) d
Conditions (°C, h)
Yield (%) c
[A] e[B]f
Metal selectivity
[A]/[B]
1
2
3
4
Pd2(dba)3 (0.15)
Pd2(dba)3 (0.15)
Pd2(dba)3 (0.15)
RuCl2(PPh3)3 (0.1)
PPh3 (0.6)
None
PPh3 (0.6)
None
130, 10
150, 10
100, 10
150, 10
59
13
3
3
2
3
3
95/5
87/13
50/50
90/10
28
a (Germyl)silane 1b/allyl chloride:1 mmol/3 mmol.
b (mmols of the catalyst/mmols of (germyl)silane 1b)×100.
c Yields were determined by GLC and based on the (germyl)silane 1b charged. Thermal conductivity corrections were not made.
d (mmols of PPh3/mmols of (germyl)silane 1b)×100.
e [A], allylchlorodimethylgermane.
f [B], allyltrimethylsilane.
Table 3
Palladium-catalyzed reaction of (germyl)silanes (RMe2GeSiMe3) 1a or 1b with several allylic halides a
Entry R in RGeSi
Halide
Catalyst (mol%) b Conditions (°C, h)
Yield/% c
Metal selectivity
[A] d[B] e
[A]/[B]
1
2
3
4
5
6
7
8
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
CH2ꢁCHCH2Cl
CH2ꢁCHCH2Cl
CH2ꢁCHCH2Br
CH2ꢁCMeCH2Cl
CH3CHꢁCHCH2Cl h
CH3CHClCHꢁCH2
Me2CꢁCHCH2Cl
trans-
C (0.5) f
D (1.0) g
C (0.5)
D (1.0)
D (1.0)
D (1.0)
D (1.0)
D (1.0)
r.t., 5
r.t., 4
r.t., 8
r.t., 5
r.t., 3
r.t., 6
r.t., 3
r.t., 7
61
70
53
94
97
99
86
86 i
3
3
5
6
95/5
96/4
91/9
94/6
Trace
Trace
Trace
399.5/20.5
399.5/20.5
399.5/20.5
–
j
–
PhCHꢁCHCH2Cl
CH2ꢁCHCH2Cl
Me2CꢁCHCH2Cl
trans-
9
10
11
Cl
Cl
Cl
E (0.15) k
E (0.15)
E (0.15)
130, 10
130, 10
130, 10
59
3
9
4
95/5
84/16
93/7
46
57 l
PhCHꢁCHCH2Cl
a (silyl)germane 1a or 1b/halide/1 mmol/2–3 mmol. Structural determination in these products was made by NMR and MS spectra.
b (mmols of the catalyst/mmols of (germyl)silane 1a or 1b)×100.
c Yields were determined by GLC based on the (germyl)silane 1a or 1b used.
d [A], 2-alkenyldimethylphenylgermane.
e [B], 2-alkenyltrimethylsilane.
f C, Pd2(dba)3.
g D, Pd(dba)2.
h A trans- and cis-isomeric mixture.
i trans-Cinnamylchlorodimethylgermane/its cis-isomer/3-phenyl-3-(chlorodimethylgermyl)propene: 79/12/9.
j Cinnamyltrimethylsilane was not detected by GLC analysis, but chlorodimethylphenylgermane was formed in 12% yield.
k E, Pd2(dba)3ꢀ4PPh3.
l trans-Chlorocinnamyldimethylgermane.
affected by Pd2(dba)3ꢀ4PPh3 combination catalyst. As
can be seen from Table 3, the (germyl)silane 1a easily
reacted with allyl bromide, 3-chloro-2-methylpropene
Table 3 summarizes results for the germylation of
several 2-alkenyl halides with the (germyl)silane 1a
catalyzed by Pd(dba)2 and with the (germyl)silane 1b

K. Ono et al. / Journal of Organometallic Chemistry 587 (1999) 114–148
147
and 4-chloro-2-methyl-2-butene to afford correspond-
ing allylgermanes in 53–99% yields. The most striking
features in the reactions are their high regio- and
stereoselectivities. In fact, the Pd(dba)2-catalyzed
give prenyldimethylphenylgermane and prenyltri-
methylsilane in 46 and 9% yields, respectively. Quite
interestingly, in the germylation of trans-cinnamyl chlo-
ride using the (germyl)silane 1b, the trans isomer of
cinnamylchlorodimethylgermane was the dominant
product (57%). The yield of cinnamyltrimethylsilane
was 4%. In contrast, the germylation using
(germyl)stannane gave the cinnamylgermane in only
20% yield [10]. Finally, we examined the selective bis-
germylation
of
1-chloro-2-butenes
using
the
(germyl)silane 1a gave trans-1-(dimethylphenylgermyl)-
2-butene and its cis isomer in 92 and 5% yields (Scheme
3). Similar germylation of 3-chloro-1-butene using the
(germyl)silane 1a gave the same product in the same
isomer ratio with a combined yield of 99% (Scheme 4).
In both reactions, no 3-(dimethylphenylgermyl)-1-
butene formed.
germylation
of
3,4-dichloro-1-butene
using
(germyl)silane 1a in the presence of Pd(dba)2 (Scheme
5).
These stereoselectivities were much higher than those
in the previously reported germylation of 1-chloro-2-
butene and 3-chloro-1-butene using 1,2-diphenylte-
tramethyldigermane [9b]. However, an exceptional case
is the germylation of trans-cinnamyl chloride using the
(germyl)silane 1a (entry 8 in the Table 3). The reaction
As expected, 1,4-bis(dimethylphenylgermyl)-2-bute-
nes were produced as a 93:7 mixture of trans- and cis
isomers with a combined yield of 82%. The formation
of 1,4-bis(dimethylphenylgermyl)-2-butene is reason-
ably explained via Scheme 6. However, the tentative
intermediate 2a was not detected at all during the
course of the reaction, suggesting that the rate of the
second reaction is much faster than that of the first.
In conclusion, the Pd(dba)2-catalyzed reaction of
(dimethylphenylgermyl)trimethylsilane with 2-alkenyl
halides opens up an alternative and selective synthesis
of 2-alkenylgermanes. Similarly, the reaction of
(chlorodimethylgermyl)trimethylsilane with allylic chlo-
rides in the presence of palladium–phosphine complex
catalyst also gave 2-alkenylchlorodimethylgermanes se-
lectively in good yields. The formation of allylgermanes
formed
a
79:12:9 mixture of trans-cinnamyl-
dimethylphenylgermane, its cis isomer and 3-phenyl-3-
(chlorodimethylgermyl)propene with a combined yield
of 86%, the regio- and stereoselectivities of which were
somewhat lower than those in the germylation using
1,2-diphenyltetramethyldigermane [9b]. In this reaction,
cinnamyltrimethylsilane was not detected in GLC anal-
ysis, but the chlorodimethylphenylgermane as a by-
product of the cinnamylsilane formed with a 12% yield.
The (germyl)silane 1b reacted with prenyl chloride to
Scheme 3.
Scheme 4.
Scheme 5.

148
K. Ono et al. / Journal of Organometallic Chemistry 587 (1999) 144–148
Scheme 6.
using the (germyl)silanes 1a and 1b took place with
high regio- and stereoselectivity. RuCl2(PPh3)3 also ef-
fected the metal selective metathesis of the
(germyl)silane 1a with allyl chloride giving al-
lyldimethylphenylgermane in good yield. In further
studies we shall investigate the germylation of other
2-alkenyl chlorides and attempt to provide a mecha-
nism for the selective carbonꢀgermanium bond forma-
tion observed using germylsilanes.
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A mixture of the (germyl)silane 1a (1 mmol), crotyl
chloride
(2
mmol)
and
bis(dibenzylideneace-
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1
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Acknowledgements
We are grateful to Sansen Co. Ltd. for partial finan-
cial support and the Shin-etsu Chemical Co. Ltd. for
the generous gift of chlorotrimethylsilane.
.
.