Stille cross-coupling reactions with tin reagents supported on ionic liquids

Article abstract of DOI:10.1002/ejoc.200900177

New ionic-liquid-supported tin reagents were synthesized and used in Stille cross-coupling reactions. High yields of biaryls were obtained under low-temperature, solvent-free, ligand-free conditions, with simple purification techniques. Moreover, the tin compound could be recycled up to five times without significant loss of reactivity. An expanded catalytic cycle for the Stille cross coupling reaction is proposed in order to explain side products that were formed under certain reaction conditions.

Full text of DOI:10.1002/ejoc.200900177

FULL PAPER
DOI: 10.1002/ejoc.200900177
Stille Cross-Coupling Reactions with Tin Reagents Supported on Ionic Liquids
Phuoc Dien Pham,[a] Jürgen Vitz,*[a] Cécile Chamignon,[a] Arnaud Martel,[a,b] and
Stéphanie Legoupy*[a]
Dedicated to Professor François Huet on the occasion of his retirement
Keywords: C-C coupling / Ionic liquids / Tin / Homogeneous catalysis
New ionic-liquid-supported tin reagents were synthesized
and used in Stille cross-coupling reactions. High yields of bi-
aryls were obtained under low-temperature, solvent-free, li-
gand-free conditions, with simple purification techniques.
Moreover, the tin compound could be recycled up to five
times without significant loss of reactivity. An expanded cata-
lytic cycle for the Stille cross coupling reaction is proposed
in order to explain side products that were formed under cer-
tain reaction conditions.
(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
Germany, 2009)
coupling reactions. Figure 1 shows the general strategy: dif-
ferent tin reagents are linked to an imidazolium-based ionic
liquid (IL) through an alkyl chain spacer. The influences of
chain length, of substituents on the tin moiety, and of
counter anions were investigated.
Introduction
Over the last two decades, Stille cross-coupling reactions
have emerged as versatile methods for C–C coupling reac-
tions.[1] Unfortunately, disadvantages such as contami-
nation of coupling products by tin residues limit the scope
of these reagents, especially for the synthesis of pharmaceu-
tical products. Efforts have been made to overcome these
problems over the last few years, leading to the use of, for
example, solid-phase synthetic methods, monoorganotin
reagents, fluorous phases, and phosphonium reagents.[2] In
the development of more practical methodologies, room-
temperature ionic liquids (RTILs) have been found to be
very useful as reaction media for a wide range of organic
reactions catalyzed by transition metals.[3] Indeed, ionic li-
quids have been used in Stille-type reactions involving aryl
bromides and iodides,[4] Suzuki cross-coupling reactions,[5]
or Grignard reactions.[6] In addition, task-specific ionic li-
quids (TSILs) have been applied to supported reagents, for
example, to support iodobenzoate compounds for Suzuki
cross-coupling reactions[7a] or to support a (carbene)ruthe-
nium complex catalyst in ring-closing metathesis,[7b] and
also as soluble supports for syntheses using small organic
molecules.[8]
Figure 1. General strategy.
Preliminary experiments with phenyl iodide and bro-
mide, published in a recent communication,[9] showed the
potential of these covalently supported tin reagents through
their combination of the positive aspects of ILs with Stille
cross-coupling reactions (e.g., low reaction temperatures,
solvent- and ligand-free conditions). Moreover, the key dis-
advantage of Stille cross-coupling – its toxic tin residue by-
products – was reduced. In this paper, based on preliminary
results, we wish to report a comprehensive summary of the
use of ionic-liquid-supported tin reagents for cross-coupling
reactions involving substituted phenyl halides, iodopyrid-
ines, iodothiophenes, iodonaphthalenes, and benzoyl chlo-
ride. In addition, the effects of different catalysts and the
recyclability of the tin reagents are also described.
As an extension, we considered the use of TSILs for sup-
porting tin reagents on ionic liquids for use in Stille cross-
Results and Discussion
[a] UCO2M, UMR CNRS 6011, Université du Maine,
Avenue Olivier Messiaen, 72085 Le Mans cedex 9, France
Fax: +33-2-43833902
1. Preparation of IL-Supported Tin Reagents
E-mail: slegoupy@univ-lemans.fr
[b] IUT Chimie,
Initially, hydrostannylation of the terminal double bond
of an ionic liquid was attempted (Scheme 1). Ionic liquid 2
was synthesized from 1-methylimidazole (1) and 4-bro-
Avenue Olivier Messiaen, 72085 Le Mans cedex 9, France
Supporting information for this article is available on the
WWW under http://dx.doi.org/10.1002/ejoc.200900177.
Eur. J. Org. Chem. 2009, 3249–3257
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J. Vitz, S. Legoupy et al.
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mobut-1-ene,[3,10] without solvent, in high yield and purity low concentrations. However, use of 1-bromo-3-chloropro-
(by washing with diethyl ether). Furthermore, the bromide pane led to the ionic liquid 4 in high yield. Unfortunately
anion could be exchanged for the tetrafluoroborate anion though, the subsequent reaction with lithium tributylstan-
to afford 3.[3c,11]
nane on ionic liquid 4 did not take place, possibly due to
the positive charge on the imidazolium moiety, which might
make it more difficult to substitute the chlorine atom, due
to a higher bond strength. Research in this area by, for ex-
ample, atomistic and molecular dynamics simulations is still
ongoing.[14]
Scheme 1. Synthesis of the ionic liquids starting from 1-methyl-
imidazole.
We turned then our attention to another strategy and
decided to synthesize ionic liquids from the starting imid-
azoles 5 (Table 2). In this strategy the substitution would be
carried out first, followed by the formation of the ionic li-
quid simply by addition of methyl iodide. This procedure
turned out to be the method of choice, especially for long
side chains or for 2-substituted starting materials. From
imidazole (5a), 2-methylimidazole (5b), or 2-phenylimid-
azole (5c), ionic-liquid-supported tin reagents 8 and 9 were
prepared. Whereas the product 7b could be purified by col-
umn chromatography, providing the pure product in 73%
yield, all other separations failed at the first step of the reac-
tion sequence because of the similar polarities of products
and starting materials. After conversion into the ionic li-
quids, the products 8a, 8c, and 8d were then purified by
extraction. Overall yields between 32 and 72% were ob-
The hydrostannylation reaction was then studied with
nBu3SnH and nBu2SnPhH.[12] Unfortunately, this reaction
failed to take place, whatever the method used (AIBN[12] or
Pd(OH)2;[13] Table 1).
Table 1. Hydrostannylation reactions.
Tin reagent
Catalyst
T [°C]
Time [h]
Yield [%]
[a]
Bu2PhSnH
Bu2PhSnH
Bu2PhSnH
Bu3SnH
Bu3SnH
Bu3SnH
AIBN
AIBN
Pd(OH)2
AIBN
AIBN
Pd(OH)2
80
70
20
100
100
100
2
3
4
6
6
6
–
[a]
–
[a]
–
[a]
–
–
[a]
tained. In two cases the anions were exchanged for BF4 ,
–
[a]
thus affording 9a and 9c in good yields. Compounds 8c and
8d were not used in Stille cross-coupling reactions, due to
their higher melting points and the reduced accessibility.
–
[a] Recovered starting materials and tin degradation products.
Consequently, we decided to use stannyllithium and
halogen substitution in the alkyl chain, and so ILs contain-
ing halogen atoms in their alkyl chains were synthesized
(Scheme 2). On employment of 1-methylimidazole with 1,3-
dibromopropane or 1,4-dibromobutane, double substituted
2. Stille Cross-Coupling in the Presence of IL-Supported
Tin Reagents
In the first trials, Stille cross-coupling reactions under
products were observed both at low temperatures and at standard conditions were unsuccessful (Table 3). Copper,
Scheme 2. Synthesis of IL-supported tin reagents starting from 1-methylimidazole.
Table 2. Synthesis of IL-supported tin reagents starting from imidazoles 5.
Entry
5
n
6
Yield [%][a]
7
Yield [%]
8
Yield [%]
9
Yield [%]
1
2
3
4
5a
5a
5b
5c
2
5
2
2
6a[15]
6b
82
96
73
65
7a
7b
7c
7d
n.d.
73[a]
n.d.
n.d.
8a
8b
8c
8d
44[b]
99[a]
32[b]
44[b]
9a
–
9c
–
99
–
74
–
6c
6d
[a] After purification. [b] Two steps, purification.
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Stille Cross-Coupling Reactions with Sn Reagents Supported on Ionic Liquids
Table 3. Stille reactions with ionic-liquid-supported tin reagents.
Entry
IL
n
Anion
X
Conditions[a]
Time [h]
Conversion [%][b]
Bu2Sn Ph2 [%][b]
–
1
2
3
4
5
6
7
8
9
9a
9a
8b
9c
8b
8a
8b
8b
8b
2
2
5
2
5
2
5
5
5
BF4–
Br
Br
I
I
I
I
I
I
I
A
B
C
C
D
E
E
F
G
16
16
40
16
40
160
112
160
160
32
–
52
–
57
15
27
43
7
–
–
BF4
I–
–
BF4
I–
I–
I–
I–
I–
9
98
98
87
93
–
–
[a] Conditions: A: Pd2Cl2(PhCN)2 (5 mol-%), CuI (10 mol-%), AsPh3 (10 mol-%), [BMIM]BF4 (0.5 mL), 80 °C; B: Pd(PPh3)4 (5 mol-%),
CuI (10 mol-%), AsPh3 (10 mol-%), [BMIM]BF4 (1 mL), 80 °C; C: Pd(PPh3)4 (5 mol-%), CuI (10 mol-%), 80 °C; D: Pd(PPh3)2Cl2 (5 mol-
%), CuI (10 mol-%), 35 °C; E: Pd2dba3·CHCl3 (5 mol-%), 35 °C; F: Pd2dba3·CHCl3 (5 mol-%), [BMIM]PF6 (0.5 mL), 35 °C; G:
Pd(dba)2 (5 mol-%), 35 °C. [b] Determined by GC.
which is often mentioned as a co-catalyst for palladium- product in 94% yield. With Pd2dba3, the rate of conversion
catalyzed cross-coupling reactions,[16] was then tested in was lower, and the reaction was complete after 24 h. Re-
combination with 8a, 8b, 9a, and 9c. When [BMIM]BF4 markably, palladium on charcoal could be used as a catalyst
was used as co-solvent under the same conditions, the cata- with a result comparable to that obtained with Pd2dba3
lyst Pd2Cl2(PhCN)2 was able to promote the reaction (32%/ (Entry 3). Notably, no side products were observed in any
16 h; Entry 1), but Pd(PPh3)4 was not (Entry 2). The forma- case. For all further described reactions, unless otherwise
tion of (nBu)2SnPh2 in relatively high proportions of up to mentioned, 2 equiv. of the tin reagent were used.
57% (Entries 1–5) was observed. In addition, high tempera-
tures were necessary to perform the catalytic reactions (En-
Table 4. Stille reactions with aryl iodides.
tries 1–4). At low temperatures, slow conversion was ob-
served, and Ph2Sn(nBu)2 was also formed (Entry 5). No re-
action took place when Pd(PPh3)4 was used without copper
iodide.
Interestingly, we found that the catalysts Pd2dba3·CHCl3
and Pd(dba)2 provided good yields of the desired products.
Entry Conditions[a] Time [h] Conversion [%][b] Yield [%][c]
With our tin reagents supported on ionic liquids, the cross-
coupling reactions were successful even at low reaction tem-
peratures without addition of copper salts or ligands (En-
tries 6–9).[6,17] A first reaction with the triorganotin IL 8a
and the catalyst Pd2dba3·CHCl3 showed a level of conver-
sion of 98% (Entry 6). At 35 °C without solvents, no side
products such as Ph2Sn(nBu)2 were formed. Under the
same conditions, the cross-coupling reaction with the tin IL
1
2
3
E
H
I
6
24
24
100
100
100
94
–
–
[a] Conditions: E: Pd2dba3·CHCl3 (5 mol-%), 35 °C; H: Pd2dba3
(5 mol-%), 35 °C; I: Pd/C (10%) (5 mol-%), 35 °C. [b] Determined
by GC. [c] Isolated yield.
We then directed our attention to other substituted sub-
8b led to biphenyl at a 98% level of conversion after 112 h strates (Table 5). In general, alkyl- and methoxyiodo-
[18]
(Entry 7). With use of [BMIM]PF6
as co-solvent, the benzenes needed longer reaction times than unsubstituted
coupling rate was reduced, and the reaction gave a level of iodobenzenes except in the case of iodotoluene; the other
conversion of 87% after a prolonged reaction time (En- substrates needed more than 5 d to reach the maximum
try 8). The catalyst Pd(dba)2 proved to be slightly less reac- level of conversion. Surprisingly, the cross-coupling reaction
tive in the cross-coupling reaction than Pd2dba3·CHCl3 with iodotoluene was faster with 8b than with 8a (1 d vs.
(93% for Entry 9 vs. 98% for Entry 7). Because the IL-sup- 4 d for total conversion; Entries 1–2). The 119Sn NMR spec-
ported tin reagents 8 showed very good results in Stille trum of the coupling product was recorded to determine
cross-coupling reactions, they were preferred to the tin com- the presence of possible tin residues, but no signal was ob-
pounds 9, which each required an additional synthetic step. served (in Entry 1, for example). On the other hand, no
Starting from these positive results, we continued our in- significant difference could be observed with 4-tert-butyl-
vestigations, aiming at increasing levels of conversion and iodobenzene (Entries 3–4). The 2,4-dimethoxy compound
using different substrates. Initially, larger amounts of the displayed the lowest level of conversion. Increasing reaction
ionic liquid 8a were used. In all cases, very high levels of times did not improve the conversion. Disadvantageously,
conversion could be achieved with 2 equiv. of 8a (Table 4) the formation of biphenyl was observed in all reactions. The
within 6 h in the presence of Pd2dba3·CHCl3, to afford a product/biphenyl ratio depends on the aryl substrate; it is
Eur. J. Org. Chem. 2009, 3249–3257
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J. Vitz, S. Legoupy et al.
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Table 5. Stille reactions with substituted aryl iodides.
Entry
IL
n
R1
R2
R3
Time [d]
Conversion [%][a]
Product [%][a]
Ph–Ph [%][a]
1
2
3
4
5
6
7
8
9
10
11
12
13
14[d]
8a
8b
8a
8b
8b
8b
8b
8a
8b
8a
8b
8b
8b
8b
2
5
2
5
5
5
5
2
5
2
5
5
5
5
Me
Me
tBu
tBu
OMe
H
H
H
H
H
H
H
H
H
H
H
H
H
H
OMe
H
CO2H
H
H
CO2Me
CO2Me
H
4
1
5
5
5
5
5
3
1
1
3
1
1
100
100
82
60
64
55
58
40
36
33
33
24
87
79
60
[b]
[b]
[b]
CO2H
H
CO2Me
CO2Me
H
H
H
H
Cl
–
–
–
–
[b]
[b]
[b]
–
–
92
67
72[c]
59
86
87
97
51
24
20
41
14
13
3
100
100
100
100
100
93
H
OCF3
F
F
H
H
2.5
19[e]
[a] Determined by GC. [b] Not detectable by GC. [c] Isolated yield. [d] 1 equiv. of IL was used. [e] Homocoupled product: 23%.
at its maximum in the case of iodotoluene (40 and 36% of only in small amounts. In contrast with these results, the
biphenyl produced for Entries 1–2) and at its minimum for cross-coupling with 1-chloro-3-iodobenzene (Entry 14) af-
1-iodo-2,4-dimethoxybenzene (24% of biphenyl for En- forded the main product (51%) together with biphenyl
try 5).
We then employed iodobenzoic acid derivatives in cross-
(19%) and the homocoupled product (23%).
Because pyridine derivatives are highly useful building
coupling reactions. Although the trials with the free acids blocks and intermediates for the synthesis of insecticides,
were unsuccessful, their esters gave high levels of conversion herbicides, pharmaceuticals, food flavorings, dyes, rubber
and yields (Table 5). Again, though, a difference between chemicals, adhesives, paints, etc.,[19] we tried to perform a
the tin reagents used in the reactions was apparent. With cross-coupling reaction with an iodo-substituted pyridine.
the tin IL 8b, methyl 3-iodobenzoate could be completely Only 1 equiv. of the ionic liquid was used, and a reaction
converted into the product in good yield: 72% in only 1 d time of 4 d was necessary to reach the maximum conversion
(Entry 9). For the reaction of methyl 2-iodobenzoate, in in both cases (Table 6, Entries 1–2). Interestingly, the
contrast, the tin reagent 8a showed the higher reactivity Pd(dba)2 catalyst was better here, because only a 4% yield
(Entry 10). In this case, however, the higher amount of bi- of biphenyl was obtained (Entry 2). Surprisingly, when
phenyl was also formed.
2 equiv. of the tin reagent supported on ionic liquid were
Better results were obtained with iodobenzenes substi- used (Entry 3), with the tin compound 8a the reaction time
tuted with electron-withdrawing group(s) [4-(trifluorome- was reduced to 3 d. Moreover, with the tin ionic liquid 8b
thoxy) and 2,4-difluoro], which afforded the biaryls with (Entry 4), total conversion was reached after only 2.5 d
excellent yields and levels of conversion within 24 h (En- (61% yield), but with an amount of biphenyl of 26%. No
tries 12–13). Especially in the case of 1,3-difluoro-4-iodo- tin signal was detectable in the 119Sn NMR spectrum of the
benzene, the unwanted biphenyl side-product was observed coupling product (Entry 4).
Table 6. Stille reaction with 3-iodopyridine and iodothiophenes.
Entry
IL
n
Ar
Conditions[a]
Time
Conversion [%]
Product [%][b]
Ar–Ar
Ph–Ph [%][b]
1
2
3
4
5
6
7
8a
8a
8a
8b
8b
8b
8b
2
2
2
5
5
5
5
3-pyridinyl
3-pyridinyl
3-pyridinyl
E
H
E
E
E
I
4 d
4 d
3 d
2.5 d
16 h
16 h
16 h
84[c]
70
88
0
0
0
14
4
8
26
46
40
44
92[c]
99[d]
91
3-pyridinyl
100[d]
100[d]
90[d]
61[e]
33
0
2-iodothienyl
2-iodothienyl
3-iodothienyl
21
18
18
32
38
E
100[d]
[a] Conditions: E: Pd2dba3·CHCl3 (5 mol-%); H: Pd(dba)2 (5 mol-%); I: Pd/C (10%) (5 mol-%). [b] Determined by GC. [c] Only 1 equiv.
of the ionic-liquid-supported tin reagent was used. [d] 2 equiv. of the ionic-liquid-supported tin reagent were used. [e] Isolated yield.
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Stille Cross-Coupling Reactions with Sn Reagents Supported on Ionic Liquids
Table 7. Stille reaction with iodonaphthalene.
Entry
Conditions[a]
Time [h]
Conversion [%][b]
Product [%][b]
Ph–Ph [%][b]
Naphthalene [%][b]
1
2
3
4
I
J
K
E
66
66
66
17
86
82
95
54
53
59
67
27
24
28
22
10
11
10
11
100
[a] Conditions: I: Pd/C (10%, 5 mol-%); J: Pd(OAc)2 (5 mol-%); K: PdCl2(PhCN)2 (5 mol-%); E: Pd2(dba)3·CHCl3 (5 mol-%). [b] Deter-
mined by GC.
We next used thiophenes, which showed slightly different Table 8. Recycling of the tin compounds.
product spectra. Under all conditions, large amounts of bi-
phenyl – between 40 and 46% – were produced after a 16 h
reaction time (Entries 5–7). The desired products were ob-
tained in yields between 32 and 38%. The third products
were the homocoupled products (Table 6).
We also investigated the coupling of 1-iodonaphthalene
in the presence of the tin IL 8b under different conditions
(Table 7). With Pd2(dba)3·CHCl3 as catalyst, full conversion
was observed after only 17 h, with an amount of biphenyl
of 22% (Entry 4). In this case, we also observed the forma-
tion of naphthalene in 11% yield.
The Stille reaction with benzoyl chloride was also pos-
sible, and, after 16 h, complete conversion of the starting
material was observed (determined by GC). The reaction
afforded the coupling product in 56% yield, and a 44%
yield of the biphenyl by-product was formed (Scheme 3).
Run
Conversion [%][b]
1
100
100
99
97
96
2[a]
3[a]
4[a]
5[a]
[a] Recovered tin reagent 8a from the previous cycle. [b] Deter-
mined by GC.
tin reagents 8 under Pd0 catalysis conditions. We believe
that because of the nature of the substrate the catalysts are
destabilized and diverge from the standard catalytic cycle
steps (“oxidative addition, transmetalation, trans/cis isom-
erization, reductive elimination”; Figure 2). In a published
kinetic and mechanistic investigation of the transmetalation
reaction with organotin reagents[22] it was discovered that
Scheme 3. Stille reaction with benzoyl chloride.
It is possible to recycle the tin compound/palladium cata- two different catalyst species are formed simultaneously in
lyst system at the end of the reaction. Products and remain- the transmetalation step on platinum(II). In particular, one
ing starting materials and/or side products are extracted by of these species is considered to react a second time with a
organic solvents such as pentane, which is immiscible with tin compound. This would lead to different products in the
the ionic liquid, whereas the ionic liquid phase still contains Stille cross-coupling reaction.
the halogenotin-supported ionic liquid 10 (Table 8). Simple
To provide support for this proposed alternative cycle,
addition of PhLi to a solution of compound 10 in THF we synthesized a new supported tin reagent with a methoxy
regenerates the Stille starting material 8a (Scheme 1). The substituent on the phenyl group (compound 14, Scheme 4).
tin reagent could be recycled five times without appreciable This, under Stille cross-coupling conditions, afforded pre-
loss of effectiveness (Table 8). The 2-positions in imid- dominantly the desired product 15 and 3,3Ј-dimethoxybi-
azolium ionic liquids are known to be relatively acidic, lead- phenyl (16) originating from the alternative cycle. In our
ing to substitution and exchange.[20] In our case, however, proposed alternative cycle the Pd2L2ArR reacts a second
no substitution at the 2-position of imidazolium 10 was ob- time with our stannane IL (Sn1). In this additional trans-
served with phenyllithium.
metalation step Pd2L2R2 is formed. After the subsequent
In our Stille coupling reaction, the formation of biphenyl trans/cis isomerization and reductive elimination, the biaryl
and/or homocoupled products was observed. Unlike in the R–R is eliminated. In addition, the IL–SnBu2Ar intermedi-
case of arylboronic acids,[21] there is no self-coupling of the ate (Sn3) could lead to homocoupled products (Ar–Ar) af-
Eur. J. Org. Chem. 2009, 3249–3257
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J. Vitz, S. Legoupy et al.
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Figure 2. Catalytic cycle with proposed alternative pathway.
Scheme 4. Ionic-liquid-supported tin-substituted reagents and Stille coupling.
ter passing through the transmetalation step a second time. panded catalytic cycle for the Stille cross-coupling reaction
For example, in Table 5 (Entry 14) and Table 6 (Entries 5– to explain side products that were formed under certain re-
7) we have shown that the homocoupling products (3,3Ј- action conditions.
dichlorobiphenyl and 2,2Ј-bithiophene) were formed.
Experimental Section
Conclusions
1-{3-[Dibutyl(phenyl)stannyl]propyl}-1H-imidazole (7a):[9] Dibu-
tylphenyltin hydride (1.37 g, 4.4 mmol) was slowly added at –78 °C
to a solution of lithium diisopropylamide (4.5 mmol) in dry THF
(20 mL). The resulting mixture was stirred at –50 °C for 1 h and
subsequently added at –50 °C to a solution of 1-(3-chloropropyl)-
1H-imidazole (6a, 0.60 g, 4.1 mmol) in dry THF (15 mL). The mix-
ture was then allowed to warm to room temp. and stirred for 18 h.
Water (5 mL) was slowly added, and the mixture was stirred at
room temp. for an additional 15 min. CH2Cl2 (50 mL) was added
to this mixture, and the organic phase was successively washed with
New tin reagents supported on ionic liquids were synthe-
sized and successfully used under Stille cross-coupling reac-
tions. High yields of coupled products were obtained under
low-temperature, solvent-free conditions. Moreover, the tin
compounds could be recycled up to five times without sig-
nificant loss of reactivity. The best results were achieved
with Pd2dba3·CHCl3 catalyst, which does not require ad-
ditional additives or ligands. This reduces costs and simpli-
fies the workup procedure. We have also proposed an ex- H2O (2ϫ20 mL) and brine (10 mL). The aqueous layer was ex-
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Stille Cross-Coupling Reactions with Sn Reagents Supported on Ionic Liquids
tracted with CH2Cl2 (3ϫ20 mL), and the combined organic phase
was dried with MgSO4, filtered, and concentrated under reduced
pressure. The resulting crude product (1.78 g) was then purified by
column chromatography [silica gel: 20 g; solvent: CH2Cl2 to
CH2Cl2/MeOH (98:2) and then CH2Cl2/MeOH/diethyl ether
(96:2:2)] to yield the liquid product as a mixture of 7a with the
starting material 6a (1.70 g, 67% product, 33% starting material).
1-{6-[Dibutyl(phenyl)stannyl]hexyl}-3-methyl-1H-imidazolium Iodide
(8b):[9] In a dried sealed tube, crude 1-{3-[dibutyl(phenyl)stannyl]-
hexyl}-1H-imidazole (7b, 1.02 g, 2.2 mmol) was dissolved in methyl
iodide (0.5 mL) and stirred at 40 °C overnight. The mixture was
allowed to cool to room temp., and the excess methyl iodide was
evaporated under reduced pressure to yield 8b (1.33 g, 2.2 mmol,
1
99%) as a pale yellow oil. H NMR (CDCl3, 400 MHz): δ = 10.17
1
This mixture was used directly in the next reaction step. H NMR
(s, 1 H), 7.29–7.46 (m, 6 H), 7.20 (s, 1 H, 4-H), 4.25 (t, J = 7.5 Hz,
(CDCl3, 400 MHz): δ = 7.28–7.42 (m, 6 H), 7.04 (s, 1 H), 6.84 (s, 2 H), 4.11 (s, 3 H), 1.83–1.90 (m, 2 H), 0.98–1.57 (m, 20 H), 0.88
1 H), 3.86 (t, J = 7.2 Hz, 2 H), 1.01–2.00 (m, 16 H), 0.88 (t, J = (t, J = 7.2 Hz, 6 H) ppm. 13C NMR (CDCl3, 100 MHz): δ = 141.7,
7.3 Hz, 6 H) ppm. 13C NMR (CDCl3, 100 MHz): δ = 140.6, 137.1,
136.3, 129.3, 128.3, 128.2, 118.7, 50.6, 29.0, 28.7, 27.3, 13.6, 9.4,
136.8, 136.8, 136.4, 128.0, 123.6, 121.8, 50.1, 37.1, 33.5, 30.1, 29.0,
27.3, 26.5, 25.6, 13.6, 9.5, 9.4 ppm. 119Sn NMR (149 MHz, CDCl3):
5.8 ppm. IR (neat): ν = 2955, 2924, 2870, 2850, 1504, 1462, 1427,
δ = –43.8 ppm. IR (neat): ν = 3061, 2953, 2922, 2848, 1568, 1462,
˜
˜
1375, 1281, 1227, 1107, 1074, 906, 808, 725, 698, 662, 594, 503,
1427, 1375, 1165, 1072, 862, 727, 700, 656, 617, 505, 447 cm–1.
HRMS: calcd. for C24H41N2120Sn 477.2291; found 477.2296.
446 cm–1. HRMS: calcd. for C20H32N2Na120Sn [M
443.1485; found 443.1482.
+
Na]+
Dibutylbis(3-methoxyphenyl)stannane (11):
A solution of 3-
MeOC6H4MgBr in THF (1.2 molL–1, 24.00 mmol, 20 mL) was
added dropwise over a period of 30 min to a solution of Bu2SnCl2
(3.64 g, 12.00 mmol) in THF (9 mL). The solution was heated at
reflux for 18 h. The THF was evaporated under reduced pressure,
and the residue was dissolved in Et2O (20 mL). The organic layers
were washed with H2O (3ϫ10 mL). The aqueous layer was ex-
tracted with Et2O (3ϫ10 mL), and the combined organic phases
were dried with MgSO4, filtered, and concentrated under reduced
pressure to yield 11 (4.56 g, 86%). 1H NMR (400 MHz, CDCl3): δ
= 7.26–7.32 (m, 2 H), 6.99–7.12 (m, 4 H), 6.85–6.88 (m, 2 H), 3.80
(s, 6 H), 1.57–1.70 (m, 4 H), 1.26–1.40 (m, 8 H), 0.88 (t, J = 7.3 Hz,
6 H) ppm. 13C NMR (100 MHz, CDCl3): δ = 159.1, 141.7, 122.3,
113.5, 35.0, 28.9, 27.3, 13.6, 10.4 ppm. 119Sn NMR (149 MHz,
1-{3-[Dibutyl(phenyl)stannyl]propyl}-3-methyl-1H-imidazolium Iodide
(8a):[9] In a dried sealed tube, crude 1-{3-[dibutyl(phenyl)stannyl]-
propyl}-1H-imidazole (7a, 1.68 g) was dissolved in methyl iodide
(1 mL) and stirred at 40 °C overnight. The mixture was cooled to
room temp., and the excess methyl iodide was evaporated under
reduced pressure. A CH2Cl2/ethyl acetate/diethyl ether (90:5:5) mix-
ture was added, and the organic phase was washed with water to
remove the impurities having remained from the previous step and
then separated, dried with MgSO4, filtered, and concentrated under
reduced pressure to yield 8a (0.99 g, 1.8 mmol, 44%, over two
steps) as a colorless liquid. 1H NMR (CDCl3, 400 MHz): δ = 10.11
(s, 1 H), 7.33–7.44 (m, 5 H), 7.30 (m, 1 H), 7.04 (m, 1 H), 4.23 (t,
J = 7.2 Hz, 2 H), 4.09 (s, 3 H), 2.03–2.11 (m, 2 H), 1.11–1.57 (m,
14 H), 0.89 (t, J = 7.2 Hz, 6 H) ppm. 13C NMR (CDCl3, 100 MHz):
δ = 140.4, 136.8, 136.5, 128.5, 128.4, 123.7, 121.7, 53.3, 37.1, 29.0,
28.1, 27.3, 13.7, 9.5, 5.4 ppm. 119Sn NMR (149 MHz, CDCl3): δ =
CDCl ): δ = –69.6 ppm. IR (neat): ν = 2899, 1569, 1474, 1408,
˜
3
1282, 1241, 1223, 1180, 1100, 1039, 819, 773, 693, 655, 432 cm–1.
HRMS (CI methane): calcd. for C22H33O2Sn [M + H]+ 449.1503;
found 449.1495.
–42.2 ppm. IR (neat): ν = 3061, 2953, 2922, 2868, 2850, 1568, 1456,
˜
1425, 1375, 1167, 1072, 1020, 864, 727, 700, 656, 617, 594, 503,
447 cm–1. HRMS: calcd. for C21H35N2120Sn 435.1822; found
435.1825.
Dibutylchloro(3-methoxyphenyl)stannane (12): A solution of HCl in
Et2O (2 , 3 mL, 6 mmol) was added dropwise at 0–5 °C over 5 min
to a solution of dibutylbis(3-methoxyphenyl)stannane (11, 2.66 g,
5.94 mmol) in Et2O (25 mL). The mixture was stirred at room
temp. for an additional 1 h, and was then treated with H2O
(3ϫ20), and brine (10 mL). The aqueous layer was extracted with
Et2O (3ϫ20 mL), and the combined organic phases were dried
with MgSO4, filtered, concentrated under reduced pressure, and
distilled (125 °C, 0.04 Torr) to yield 12 as a yellow oil (1.78 g, 80%).
1H NMR (400 MHz, CDCl3): δ = 6.90–7.38 (m, 4 H), 3.83 (s, 3
H), 1.67–1.75 (m, 4 H), 1.49–1.57 (m, 4 H), 1.35–1.45 (m, 4 H),
0.92 (t, J = 7.3 Hz, 6 H) ppm. 13C NMR (100 MHz, CDCl3): δ =
159.6, 142.6, 129.7, 127.5, 120.8, 115.2, 55.2, 27.8, 26.8,
17.8,13.6 ppm. 119Sn NMR (149 MHz, CDCl3): δ = –70 ppm. IR
1-{6-[Dibutyl(phenyl)stannyl]hexyl}-1H-imidazole (7b):[9] Dibutyl-
phenyltin hydride (3.45 g, 11.1 mmol) was slowly added at –78 °C
to a solution of lithium diisopropylamide (11.3 mmol) in dry THF
(40 mL). The resulting mixture was stirred at –50 °C for 1 h and
was subsequently added at –50 °C to a solution of 1-(6-chlo-
rohexyl)-1H-imidazole (6b, 1.57 g, 8.5 mmol) in dry THF (20 mL).
The mixture was then allowed to warm to room temp. and stirred
for 18 h. Water (5 mL) was slowly added, and the mixture was
stirred at room temp. for an additional 15 min CH2Cl2 (100 mL)
was added to this mixture, and the organic phase was successively
washed with H2O (20 mL) and brine (10 mL). The aqueous layer
was extracted with CH2Cl2 (3ϫ20 mL), and the organic combined
phases were dried with MgSO4, filtered, and concentrated under
reduced pressure. The resulting crude product (4.69 g) was then
purified by column chromatography [silica gel; solvent: CH2Cl2 to
CH2Cl2/MeOH (98:2) and then CH2Cl2/MeOH/diethyl ether
(96:2:2)] to yield the pure product 7b as a colorless oil (2.86 g,
(neat): ν = 2955, 2853, 1734, 1583, 1571, 1475, 1462, 1411, 1376,
˜
1284, 1242, 1228, 1181, 1038, 866, 776, 692, 657, 511, 432 cm–1.
HRMS (CI methane): calcd. for C15H25OSn [M – Cl]+ 341.0927;
found 341.0929.
Dibutyl(3-methoxyphenyl)tin Hydride (13): A solution of NaBH4
(0.548 g, 14.50 mmol) in H2O (5 mL) was added dropwise with vig-
1
6.2 mmol, 73%). H NMR (CDCl3, 400 MHz): δ = 7.29–7.45 (m,
6 H), 7.05 (s, 1 H), 6.87 (s, 1 H), 3.87 (t, J = 7.2 Hz, 2 H), 1.68– orous stirring (Caution: hydrogen evolution!) at 0–8 °C over a
1.75 (m, 2 H), 1.64 (br. s, 2 H), 1.50–1.57 (m, 5 H), 1.27–1.37 (m,
period of 10 min to a solution of dibutylbis(3-methoxyphenyl)stan-
8 H), 0.89–1.07 (m, 5 H), 0.88 (t, J = 7.2 Hz, 6 H) ppm. 13C NMR nane (12, 1.81 g, 4.82 mmol) in Et2O (25 mL). The mixture was
(CDCl3, 100 MHz): δ = 141.8, 137.1, 136.5, 129.3, 128.1, 128.0, stirred at room temp. for an additional 45 min. The organic phase
118.8, 47.0, 33.7, 31.0, 29.1, 27.4, 26.6, 26.0, 13.7, 9.6, 9.5 ppm.
was then washed with H2O (2ϫ50 mL). The aqueous layer was
extracted with Et2O (3ϫ10 mL), and the combined organic phases
were dried with MgSO4, filtered, and concentrated under vacuum
to yield 13 as a yellow oil (1.41 g, 86%). 1H NMR (400 MHz,
CDCl3): δ = 6.84–7.29 (m, 5 H), 5.43 (m, 1 H), 1.14–1.63 (m, 12
119Sn NMR (149 MHz, CDCl ): δ = –43.9 ppm. IR (neat): ν =
˜
3
2955, 2922, 2850, 1504, 1462, 1427, 1282, 1228, 1074, 808, 725,
698, 662, 596, 503, 446 cm–1. HRMS: calcd. for C23H39N2120Sn
463.2135; found 463.2138.
Eur. J. Org. Chem. 2009, 3249–3257
© 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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3255

J. Vitz, S. Legoupy et al.
FULL PAPER
H), 0.89 (t, J = 7.3 Hz, 6 H) ppm. 13C NMR (100 MHz, CDCl3):
the tube was evacuated and back-filled with nitrogen five times.
The mixture was heated at 35 °C for 6 h. After the mixture had
cooled, pentane (10 mL) was added, and the mixture was stirred
for 30 min. The stirring was stopped and the pentane phase was
δ = 158.0, 140.7, 127.8, 121.6, 113.1, 54.0, 28.4, 26.3, 12.6, 8.4 ppm.
119Sn NMR (149 MHz, CDCl ): δ = 83.0 ppm. IR (neat): ν = 2954,
˜
3
2923, 1814, 1582, 1570, 1474, 1462, 1409, 1282, 1240, 1225, 1181,
1041, 773, 693, 673, 656, 529, 494, 429 cm–1. HRMS (CI methane): separated. This was repeated twice, and the combined pentane
calcd. for C15H25OSn [M – H]+ 341.0927; found 341.0942.
phases were then filtered through a short pad of silica gel and con-
centrated under reduced pressure. Levels of conversion were deter-
mined by GC analysis of the filtrate. In order to recycle the ionic
liquid, the ionic liquid residue was dissolved in CH2Cl2 (10 mL)
and filtered through a short pad of Celite® to remove insoluble
materials. The filtrate was concentrated under reduced pressure to
afford the ionic liquid 10, which was treated with PhLi (0.78 mL,
1.4 mmol, 1.8 molL–1) at –40 °C for 2 h in dry THF (5 mL). The
mixture was then allowed to warm to room temp. and stirred for
6 h. Water (5 mL) was slowly added, and the mixture was stirred
at room temp. for an additional 15 min. CH2Cl2 (10 mL) was added
to this mixture, and the organic phase was successively washed with
H2O (2ϫ10 mL) and brine (10 mL). The aqueous layer was ex-
tracted with CH2Cl2 (3ϫ10 mL), and the combined organic phases
were dried with MgSO4, filtered, and concentrated under reduced
pressure to afford the ionic liquid 8a, used for the next run without
further purification. This cycle could be repeated five times accord-
ing to the typical procedure described above.
1-{6-[Dibutyl(3-methoxyphenyl)stannyl]hexyl}-1H-imidazolium Iodide
(14): Dibutyl(3-methoxyphenyl)tin hydride (1.25 g, 3.67 mmol) was
slowly added at –78 °C to a solution of lithium diisopropylamide
(4.30 mmol) in dry THF (20 mL). The resulting mixture was stirred
at –50 °C for 1 h and subsequently added at –50 °C to a solution
of 1-(6-chlorohexyl)-1H-imidazole (6b, 0.622 g, 3.34 mmol) in dry
THF (20 mL). The mixture was then allowed to warm to room
temp. and stirred at room temp. for further 18 h. Water (5 mL) was
slowly added, and the mixture was stirred at room temp. for an
additional 15 min. CH2Cl2 (100 mL) was added to this mixture,
and the organic phase was successively washed with H2O (20 mL)
and brine (10 mL), dried with MgSO4, filtered, and concentrated
under reduced pressure to give the crude 1-{6-[dibutyl(3-meth-
oxyphenyl)stannyl]hexyl}-1H-imidazole. In a dried sealed tube,
crude 1-{6-[dibutyl(3-methoxyphenyl)stannyl]hexyl}-1H-imidazole
(1.52 g) was dissolved in methyl iodide (1.12 mL) and stirred at
40 °C for 16 h. The mixture was allowed to cool to room temp., and
the excess methyl iodide was evaporated under reduced pressure.
A CH2Cl2/ethyl acetate/ether (90:5:5) mixture was added, and the
organic phase was washed with water to remove the ionic liquid
side product having remained from the previous step, separated,
dried with MgSO4, filtered, and concentrated under reduced pres-
sure to yield 14 (1.19 g, 57%, over two steps) as a pale yellow oil.
1H NMR (400 MHz, CDCl3): δ = 9.96 (s, 1 H), 6.82–7.60 (m, 6
H), 4.26 (t, J = 7.5 Hz, 2 H), 4.11 (s, 3 H), 3.81 (s, 3 H), 1.83–2.01
(m, 2 H), 0.98–1.60 (m, 20 H), 0.88 (t, J = 7.3 Hz, 6 H) ppm. 13C
NMR (100 MHz, CDCl3): δ = 158.9, 143.2, 136.5, 128.9, 128.8,
123.9, 122.1, 122.0, 113.0, 55.1, 50.1, 37.1, 33.6, 30.2, 29.0, 27.3,
26.6, 25.6, 13.7, 9.6, 9.5 ppm. 119Sn NMR (149 MHz, CDCl3): δ =
Supporting Information (see footnote on the first page of this arti-
cle): Additional experimental procedures; selected 1H and 13C
NMR spectra.
Acknowledgment
This work was supported by the Centre National de la Recherche
Scientifique (CNRS), the Université du Maine and the Agence Na-
tionale de la Recherche (Grant No. ANR-07-JCJC-0026-01). We
thank the French MENRT for a fellowship to P. D. P. and the
Région des Pays de la Loire for a fellowship to J. V. We thank also
P. Gangnery at the Université du Maine and F. Lambert at
CRMPO Rennes for recording the mass spectra. In addition, we
thank Professor F. Huet, Professor P. Bertus and Dr. F. Gohier for
discussions and advice.
–41.5 ppm. IR (neat): ν = 2955, 2853, 1734, 1583, 1571, 1475, 1462,
˜
1411, 1376, 1284, 1242, 1228, 1181, 1038, 866, 776, 692, 657, 511,
432 cm–1. HRMS (CI methane): calcd. for C25H43N2OSn [M – I]+
507.2397; found 507.2482.
Stille Cross-Coupling Reactions. Representative Procedure: Pd2dba3·
CHCl3 (11 mg, 5 mol-%) was added to a Schlenk tube containing
the ionic-liquid-supported tin compound 8b (247 mg, 0.41 mmol).
The reaction tube was closed, and heated at 35 °C for 15 min. After
the mixture had cooled to ambient temperature, iodobenzene
(23 µL, 42 mg, 0.205 mmol) was added, and the tube was evacuated
and back-filled with nitrogen five times. The mixture was heated at
35 °C for the required time. The reaction was checked by GC of
the pentane extract. When complete (GC Ͼ 98%), pentane (10 mL)
was added to the mixture and stirred for 30 min. The stirring was
stopped, and the pentane phase was separated. This was repeated
twice, and the combined pentane phases were then filtered through
a short pad of silica gel and concentrated under reduced pressure.
The resulting crude product was purified by flash chromatography
[silica gel; pentane/EtOAc (90:10)] to afford the product biphenyl
(30 mg, 95%). After the coupling reaction, the product was deter-
mined by GC-MS. 1H NMR (200 MHz, CDCl3): δ = 7.34–7.62 (m,
10 H) ppm.
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Received: February 19, 2009
Published Online: May 13, 2009
Eur. J. Org. Chem. 2009, 3249–3257
© 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
3257