Palladium complex-catalyzed germylation of allylic halides using (germyl)stannanes

Article abstract of DOI:10.1016/S0022-328X(00)00620-3

(Triethylgermyl)tributylstannane reacts metal-selectively with allylic halides at room temperature (r.t.) in the presence of tris(dibenzylideneacetone)dipalladium, Pd₂(dba)₃CHCl₃, to provide an alternative route to allylge

Full text of DOI:10.1016/S0022-328X(00)00620-3

www.elsevier.nl/locate/jorganchem
Journal of Organometallic Chemistry 619 (2001) 313–317
Note
Palladium complex-catalyzed germylation of allylic halides using
(germyl)stannanes
Taichi Nakano *, Kazuyoshi Ono, Yoshiya Senda, Toshihiko Migita
Department of Material Science and Technology, School of High-Technology for Human Welfare, Tokai Uni6ersity, 317 Nishino, Numazu,
Shizuoka 410-0395, Japan
Received 20 April 2000; received in revised form 29 August 2000; accepted 31 August 2000
Abstract
(Triethylgermyl)tributylstannane reacts metal-selectively with allylic halides at room temperature (r.t.) in the presence of
tris(dibenzylideneacetone)dipalladium, Pd2(dba)3CHCl3, to provide an alternative route to allylgermanes. (Dimethyl-
phenylgermyl)tributylstannane regio- and stereoselectively reacts more readily with allylic halides than (triethylgermyl)tributyl-
stannane affording the corresponding allylgermanes in quantitative yields. © 2001 Elsevier Science B.V. All rights reserved.
Keywords: Germylstannanes; Palladium catalysis; Metathesis; Allylgermanes; Allyl halides
1. Introduction
previous work [9,10]. For the synthesis of allylger-
manes, allylic halides or acetates are readily accessible
substrates. Among these methods, the first synthetic
reaction is not regiospecific e.g. during the synthesis of
cinnamylgermane [8]. In the fourth one, only a single
germyl group in a bis(germyl)cuprate is involved. Fi-
nally, our own methods employ allylic halides and
digermanes [9a,b] or (germyl)silanes [9c] and the reac-
tions proceeded metal-selectively resulting in the regio-
and stereoselective formation of allylgermanes. How-
ever, they were accompanied by small amounts of
by-products such as allylsilanes in the latter reaction. In
the closely related study, we recently demonstrated that
(triethylgermyl)tributylstannane 1a reacted with allyl
halides metal-selectively to provide an alternative route
to the allylgermanes [10]. In this paper, we report the
full results for the regio- and stereoselective synthesis of
allylgermane using 1a or (dimethylphenylgermyl)-
tributylstannane 1b (Scheme 1).
Allylsilanes are of great importance in organic syn-
thesis. Hence, a variety of methods for their synthesis
[1] and use have been studied [2]. In contrast, the
synthesis and use of allylgermanes have been very lim-
ited. However, interest in their use has recently in-
creased [3]. Up to now, several routes for the synthesis
of allylgermanes have been reported: (1) reactions of an
allylmagnesium halide [4] or an allyllithium reagent [5]
with halogenated germanes; (2) hydrogermylation of
1,3-dienes [6]; (3) double germylation of 1,3-dienes [7],
and (4) germylation of allylic acetates (or allyl sulfides)
using a bis(germyl)cuprate [8], in addition to our own
Scheme 1.
2. Results and discussion
Stirring a benzene solution of a 1:1:0.005 mixture of
* Corresponding author. Fax: +81-559-681155.
E-mail address: naka1214wing@.ncc.u-tokai.ac.jp (T. Nakano).
1a, allyl bromide and Pd2(dba)3CHCl3 (dba; dibenzyli-
0022-328X/01/$ - see front matter © 2001 Elsevier Science B.V. All rights reserved.
PII: S0022-328X(00)00620-3

314
T. Nakano et al. / Journal of Organometallic Chemistry 619 (2001) 313–317
Table 1
The influence of the reaction conditions on the yield of allyltriethylgermane in reaction (1)
a
Run GeSn (mmol)
X in allyl-X (mmol)
[Pd] (mol %)
PPh3 (mmol)
PhH (ml)
Conditions (°C, h)
Yield b (%)
1
2
3
4
5
6
7
8
9
1.01
1.01
1.01
1.00
1.02
1.00
1.03
1.00
1.00
1.00
1.00
Br(1.00)
Br(2.18)
Br(1.00)
Br(2.00)
Br(2.03)
Br(2.07)
Br(2.52)
Br(2.0)
A c(0.5)
A(3.0)
A(0.5)
B d(1.0)
A(0.5)
A(0.5)
A(1.5)
A(1.5)
A(0.5)
A(1.5)
C e(1.0)
None
0.12
None
None
None
0.02
None
0.06
None
None
None
1
1
1
1
1
1
120, 5
100, 10
80, 5
80, 10
80, 10
80, 10
r.t., 17
r.t., 360
r.t., 36
r.t., 7
80
37
71
12
84
14
83
69
95
92
67
None
None
None
None
None
Cl(2.00)
Cl(2.00)
Cl(2.00)
10
11
r.t., 10
a Et3GeSnBu3 (1a).
b Product is allyltriethylgermane, GLC yields of which were based on the 1a used.
c A, Pd2(dba)3CHCl3.
d B, PdCl2(PPh3)2.
e C, Pd(dba)2.
deneacetone) at 120°C under nitrogen gave the allyltri-
ethylgermane (80% yield, entry 1 in Table 1) along with
bromotributylstannane.
expected dehalogenative germylation product was also
formed in a good yield (entry 5). Cyclic allylic bromides
such as 3-bromocyclohexene easily underwent the
Further inspection of the reaction conditions dis-
closed that the reaction could also proceed at 80°C to
give the allylgermane (71% yield, entry 3). In these
experiments, the formation of allyltributylstannane or
bromotriethylgermane was not observed at all.
Quite interestingly, during the reaction using a
1:2:0.015 mixture of 1a, allyl bromide and Pd2(dba)3-
CHCl3 without benzene solvent, germylation occurred
even at r.t. (near 10–25°C) to give the allylgermane
(83% yield, entry 7). The use of triphenylphosphine as a
ligand on palladium made the reaction much slower.
To obtain an acceptable yield, a longer reaction time
was required (entry 8). The use of the allyl chloride
instead of the bromide also gave a reasonable yield of
the allyltriethylgermane (entries 9 and 10). Dichloro-
bis(triphenylphosphine)palladium also catalyzed the re-
action of the allyl bromide with 1a, but the catalytic
activity of the complex was much lower than that of
Pd2(dba)3 (entry 4). Pd(dba)2 catalyzed the reaction
similar to Pd2(dba)3 to form the allylgermane in good
yield (entry 11).
Table 2
Palladium-catalyzed r.t. germylation of 2-alkenyl halides (RꢀX) using
(germyl)stannane 1a a
Run RꢀX
Time Product
(h)
Yield
(%) b
c
1
2
CH2ꢁCHCH2Cl
7
CH2ꢁCHCH2GeEt3
92
88
CH3CHꢁCHCH2Cl d 14
trans-CH3CHꢁCHCH2-
e
GeEt3
CH2ꢁCHCH(GeEt3)CH3
trans-CH3CHꢁCHCH2-
6
74
3
4
CH2ꢁCHCHClCH3 14
CH3CHꢁCHCH2Br f 14
e
GeEt3
CH2ꢁCHCH(GeEt3)CH3
trans-CH3CHꢁCHCH2-
GeEt3
6
85
CH2ꢁCHCH(GeEt3)CH3
(CH3)2CꢁCHCH2GeEt3
PhCHꢁCHCH2GeEt3
3
63
22
20
76
g
5
6
7
8
(CH3)2CꢁCHCH2Cl
PhCHꢁCHCH2Cl
PhCHꢁCHCH2Br
3-Br-cyclohexene
9
10
10
11
h
h
PhCHꢁCHCH2GeEt3
3-(Et3Ge)-cyclohexene i
a All reactions were carried out at r.t. using a 1:2:0.015 mixture of
Results for the Pd2(dba)3-catalyzed germylation of
several allylic halides using 1a at r.t. are summarized in
Table 2.
The reaction of crotyl chloride gave crotyltriethylger-
mane in 88% yield together with 3-(triethylgermyl)-1-
1a, the halide and Pd2(dba)3CHCl3 under argon or nitrogen.
b GLC yields based on the 1a used.
c See Ref. [3g].
d A cis and trans mixture. Four percent of 3-chloro-1-butene was
included.
e See Ref. [6a].
butene (6% yield) (entry 2).
A similar isomer
f A cis and trans mixture. Fourteen percent of 3-bromo-1-butene
distribution was also observed during the reaction of
crotyl bromide(entry 4). Interestingly, crotyltriethylger-
mane was also formed during the reaction with 3-
chloro-1-butene (entry 3). From prenyl chloride, the
was included.
g See Ref. [11].
h See Ref. [12].
i See Ref. [13].

T. Nakano et al. / Journal of Organometallic Chemistry 619 (2001) 313–317
315
Table 3
Palladium-catalyzed r.t. germylation of 2-alkenyl chlorides (RꢀCl) using 1b a
Run
RꢀCl
Time (h)
Product (isomer ratio) b
Yield (%) c
Quant.(95)
1
2
CH2ꢁCHCH2Cl
2
4
CH2ꢁCHCH2GeMe2Ph d
CH3CHꢁCHCH2Cl e
trans-CH3CHꢁCHCH2GeMe2Ph(88) f
cis-CH3CHꢁCHCH2GeMe2Ph(12)
trans-CH3CHꢁCHCH2GeMe2Ph(79) f
cis-CH3CHꢁCHCH2GeMe2Ph(21)
(CH3)2CꢁCHCH2GeMe2Ph h
Quant.(64) g
3
CH2ꢁCHCHClCH3
3
Quant.(70) g
4
5
(CH3)2CꢁCHCH2Cl
PhCHꢁCHCH2Cl
6
3
Quant.
trans-PhCHꢁCHCH2GeMe2Ph(84)
cis-PhCHꢁCHCH2GeMe2Ph (4)
PhCH(GeMe2Ph)CHꢁCH2(12)
Quant.(70) g
a All reactions were carried out at r.t. by using a 1:2–3:0.005 mixture of 1b, the halide and Pd2(dba)3CHCl3.
b Isomer ratio was determined by NMR using a sample collected by GLC.
c GLC yields based on the 1b used. Isolated yields are shown in parentheses {Isolation was done by treating the resulting mixture with an
aqueous solution of KF [19] followed by column chromatography (silica gel, hexane)}.
d See Ref. [14].
e A cis and trans mixture.
f See Ref. [9c].
g Total yields of product isomers.
h See Section 3.
germylation to afford the corresponding 3-(tri-
ethylgermyl)cyclohexene (entry 8). In contrast, trans-
cinnamyltriethylgermane from trans-cinnamyl chloride
or the bromide was formed only in ca. 20% yield
(entries 6 and 7). Hoping to improve the yield, we
examined the reaction of the cinnamyl chloride with 1b
in the presence of the palladium catalyst. As expected,
the reaction proceeded rapidly at r.t. to produce a
quantitative yield of the cinnamyldimethylphenylger-
manes. Similar increased reactivity of a metal–metal
bond caused by introduction of a phenyl group into
bimetallic compounds is also seen in other reactions of
a disilane [1i], a digermane [9b], or a (germyl)silane [9c].
Other examples of germylation using 1b are summa-
rized in Table 3. Germylation of the allyl chloride,
crotyl chloride, 3-chloro-1-butene and prenyl chloride
with 1b also proceeded more rapidly than that with 1a
to form the corresponding products in quantitative
yields. Interestingly, during the germylation of 3-
chloro-1-butene, the formation of crotyldimethyl-
phenylgermanes dominated (entry 3).
The allylic halide has been reported to oxidatively
add to the dibenzylideneacetone-palladium complex in
organic media at r.t. giving the chloro(p-allyl)palladium
complex [15]. Therefore, the oxidative addition of allyl
chloride to the palladium complex seems to be a rea-
sonable initial step in this catalysis. However, we can-
not entirely exclude the possibility of the initial addition
of a (germyl)stannane molecule to the palladium atom
as the primary event. Hence, we propose the mecha-
nism shown in Fig. 1. However, the reason for the
predominant carbonꢀgermanium bond formation or
tinꢀchlorine bond formation is unclear at the moment.
As shown in Table 3, 1b reacted with cinnamyl chloride
at r.t. to give the dechlorinative germylation products
in quantitative GLC yield. The product isomer distribu-
tion, determined by NMR, was 84:4:12 for the trans:
cis: a-substitution product (Scheme 4). This selectivity
for the trans-isomer was slightly lower than that in the
previously reported germylation using 1,2-diphenylte-
tramethyldigermane (isomer ratio: trans/cis=97/3)
(Scheme 5) [9b]. The difference in the isomer distribu-
tions between the reactions using 1b and 1,2-diphenylte-
tramethyldigermane can not be precisely explained at
We emphasize the exclusive formation of allylger-
manes in the present reaction. This is in contrast with
the previously reported reactions with (germyl)silanes
which were always accompanied by small amounts of
allylsilanes as by-products [10].
We next attempted the reactions of 1a with the
chloro(p-allyl)palladium dimer (Scheme 2) and with
tris(dibenzylideneacetone)dipalladium
aimed at understanding the reaction mechanism.
The former reaction gave the allyltriethylgermane in
quantitative yield, whereas a benzene solution of
Pd2(dba)3 and 1a stirred for 1 week at r.t. remained
unaltered.
(Scheme
3),
Scheme 2.
Scheme 3.

316
T. Nakano et al. / Journal of Organometallic Chemistry 619 (2001) 313–317
1,2-diphenyltetramethyldigermane and chlorostannane.
Both intermediates would be anticipated to yield similar
isomer distributions, not, as is actually observed, differ-
ent ones. In the second variant (Fig. 3), the car-
bonꢀgermanium bond formation (step c) occurs faster
than step d and results in the formation of cinnamylger-
mane and chloro(stannnyl)palladium.
The stannyl group in 1b shown in Fig. 3 seems to
exert an influence on the product distribution. Faster
carbon-germanium
bond
formation
than
the
tinꢀchlorine bond formation in Fig. 3 seems to be the
most probable explanation for the difference in the
product distributions arising from the reactions using
1b and 1,2-diphenyltetramethyldigermane.
3. Experimental
Fig. 1. The tentative mechanism for the germylation with a (germyl)
stannane.
3.1. Measurement and materials
GLC analyses were performed using an Ohkura
model 103 instrument (tcd detector; 0.6 ƒ×100–200
cm stainless columns; Silicone KF-96 (10–20%) on
Celite 545 SK (60–80 mesh). Mass spectra were ob-
tained with a JEOL JMSAX-500 spectrometer with a
Scheme 4.
1
DA7000 data system. H-NMR spectra were recorded
at 400 MHz on a Varian UNITY-400 spectrometer in
CDCl3 using tetramethylsilane as the internal standard.
Allylic halides were purchased as extra pure reagents
from Tokyo Kasei Kogyo Co., Ltd., and distilled prior
to use. (Triethylgermyl)tributylstannane and (dimethyl-
phenylgermyl)tri-butylstannane were prepared accord-
ing to the synthesis of (trimethylsilyl)tributylstannane
[16]. Tris(dibenzylideneacetone)dipalladium [15], bis-
(dibenzylideneacetone)palladium [17], and dichloro-
bis(triphenylphosphine)palladium [18] were prepared
according to the literature procedures. The chloro(p-al-
lyl)palladium dimmer was purchased from Aldrich
Chemicals Co., Inc.
Scheme 5.
Fig. 2.
3.2. A typical procedure for the synthesis of the
allylgermanes
A mixture of Pd2(dba)3ꢀCHCl3 (0.0025 mmol), 1b
(0.3 mmol), trans-cinnamyl chloride (1 mmol) in a
screw-cap sample tube was stirred at r.t. under argon.
This reaction was complete within 3 h to form a
mixture of 84:4:12, the ratio being determined by
NMR, of trans-cinnamyldimethylphenylgermane, cis-
cinnamyldi-methylphenylgermane and 3-(dimethyl-
phenylgermyl)-3-phenylpropene in quantitative com-
bined GLC yield. Ether (10 ml) was added to the
resulting mixture which was then treated with an
aqueous (10 ml) solution of KF(1 g) [19]. The precipi-
tated fluorotributylstannane was then removed by
filtration. The ether layer was separated, and dried
Fig. 3.
present, but may be closely related to the metathesis
step in Fig. 1.
Two possible metathesis variants are illustrated in
Figs. 2 and 3. In the form shown in Fig. 2, the
tinꢀchlorine bond formation (step b) occurs faster than
step a, and results in a germyl(p-cinnamyl)palladium
complex similar to that resulting in the reaction of

T. Nakano et al. / Journal of Organometallic Chemistry 619 (2001) 313–317
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