Stannylated polynorbornenes as new reagents for a clean stille reaction

Article abstract of DOI:10.1002/chem.200800558

New functionalized polynorbornenes have been obtained in good yields by vinylic copolymerization of norbornene with a (norbornenyl)Sn-Bu₂Cl monomer, catalyzed by [Ni(C₆F₅)₂(SbPh ₃)₂]. Subsequent functionalization produces a wide variety of polymers with different -SnBu₂R groups (R = aryl, vinyl, alkynyl). The polymers can be used as R-transfer reagents in Stille couplings, thereby providing easy workup and separation of the polymeric tin byproducts from the coupling products. Tin contents of around 0.05 wt% are found in the Stille products. The stannylated polymers can be recycled and reused with good efficiency.

Full text of DOI:10.1002/chem.200800558

FULL PAPER
DOI: 10.1002/chem.200800558
Stannylated Polynorbornenes as New Reagents for a Clean Stille Reaction
Nora Carrera, Enrique GutiØrrez, Rut Benavente, M. Mar Villavieja,
[
a]
Ana C. AlbØniz,* and Pablo Espinet*
Abstract: New functionalized polynor-
bornenes have been obtained in good
yields by vinylic copolymerization of
norbornene with a (norbornenyl)Sn-
groups (R=aryl, vinyl, alkynyl). The
polymers can be used as R-transfer re-
agents in Stille couplings, thereby pro-
viding easy workup and separation of
the polymeric tin byproducts from the
coupling products. Tin contents of
around 0.05wt% are found in the Stille
products. The stannylated polymers can
be recycled and reused with good effi-
ciency.
Bu Cl monomer, catalyzed by [Ni-
2
Keywords: CꢀC coupling · green
chemistry · polymers · recycling ·
tin
A
C
H
T
R
E
U
N
G
(C F ) (SbPh ) ]. Subsequent function-
A
C
H
T
R
E
U
N
G
6
5 2 3 2
alization produces a wide variety of
polymers with different ꢀSnBu R
2
Introduction
An important drawback in the industrial use of the reac-
tion is the formation of toxic tin byproducts SnR X, which
3
The Stille reaction is one of the most powerful tools in CꢀC
are harmful residues difficult to separate from the target
product. Even at the laboratory scale, the separation of tin
byproducts is very cumbersome. Many efforts have been
made to address this problem. Thus, tin reagents modified
with polyaromatic rings improve the separation of the by-
[1,2]
coupling processes [Eq. (1)].
Compared with other main
group derivatives, organotin reagents offer many advantag-
es: air stability, resistance to hydrolysis, easy handling and
storage, and tolerance to a wide variety of functional
groups. These properties make the reaction versatile and
wide ranged. Furthermore, the Stille coupling is usually car-
ried out under mild conditions and does not require the use
of additives such as bases. These features make the reaction
[6]
products by adsorption on activated carbon. Tin deriva-
tives with fluorinated alkyl substituents can be separated by
[7]
extraction in fluorocarbon solvents. In Ni-catalyzed Stille
reactions, monoorganotin reagents SnRCl are an alternative
3
[2]
very useful in general organic synthesis, polymer function-
to the common tetraorganotin reagents: although they do
not bring special advantages in the separation process, the
[3]
alization, and particularly in natural product syntheses, in
[8]
which CꢀC couplings have to be accomplished preserving
byproducts formed are less toxic. Maleczka et al. intro-
duced the use of tin derivatives in catalytic amounts in Stille
other, often reactive, functional groups present in the mole-
[4]
[9]
cule. The mechanistic aspects of the reaction have been
studied in detail and a fair understanding of the process has
couplings. The process is based on the in situ hydrostanny-
lation of alkynes that leads to vinylic tin derivatives, which
limits the range of application to vinylation reactions.
[5]
been reached.
An approach that addresses simultaneously the problem
of separation of the tin residues and their recycling is the
use of a polymeric matrix containing the tin functionality.
The use of a tin-containing polymeric matrix has met with
success in other organic reactions such as free radical pro-
1
2 ½PdŠ
1
2
R X þ SnR R ƒƒ !R ꢀR þ SnR X
ð1Þ
3
3
[
a] N. Carrera, E. GutiØrrez, R. Benavente, M. M. Villavieja,
Prof. A. C. AlbØniz, Prof. P. Espinet
IU CINQUIMA/Química Inorgµnica
Universidad de Valladolid
[10]
[11]
cesses,
transesterification reactions,
allylation of alde-
[
12]
[13]
hydes,
halogenation of aromatic amines,
lactoniza-
[14]
[15]
tion, and other reactions, but only a few attempts have
been made to use polymeric tin reagents in the Stille reac-
4
7071-Valladolid (Spain)
Fax : (+34)983-423013
E-mail: albeniz@qi.uva.es
espinet@qi.uva.es
[
16]
tion
or in the catalytic tin Stille vinylation mentioned
[
17]
above The polymers used in all these reactions are poly-
styrene resins, most of them synthesized by functionalization
of preformed polymer supports. In the case of the Stille re-
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/chem.200800558.
Chem. Eur. J. 2008, 14, 10141 – 10148
ꢀ 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
10141

action, easy separations were reported and some authors
commented on the possibility of reusing the polymers, but
no data of recyclability of the polymeric reagents were
given.
These isomers could not be separated by conventional
preparative methods, so the mixture was used for the subse-
quent reactions. For the sake of brevity, we will refer to
these mixtures 1a–d as 1, and it should be assumed that
structural mixtures are also present in the polymers derived
from 1.
Considering the scant precedents, we planned to prepare
a different kind of stannylated polymer tailored for its use
in the Stille reaction. It should have a polymeric aliphatic
skeleton and a polymer–Sn link resistant to transmetalation
so that the other organic groups on Sn will be selectively
transmetalated while the tin residue remains on the poly-
mer. The structural frame chosen in this work was a poly-
norbornene skeleton. We report here on the synthesis of co-
polymers of norbornene and chlorostannylated norbornenes,
and their application as efficient and reusable reagents in
the Stille reaction. Although our main goal is the use of the
stannylated polymers in the Stille reaction, it is worth noting
that tin polymers have found use in other applications (anti-
Copolymerization reactions: The chlorostannylated poly-
mers were synthesized by vinylic copolymerization of chlor-
ostannylated norbornene derivatives. Many transition-metal
catalysts are able to efficiently polymerize norbornene (NB)
[23]
by an insertion mechanism, but fewer systems are active
in the vinylic polymerization of norbornene deriva-
[
24,25,26]
tives.
polymerization of stannylated norbornenes. Complex [Ni-
(C F ) (SbPh ) ] (3) was chosen as catalyst because it has
In fact, there is no precedent for the vinylic
A
H
R
U
ACHTREUNG
6
5
2
3 2
[26]
been reported to be fairly active and easy to handle.
[18]
fouling paints, precursors of tin-containing films, etc.),
which widens their interest.
Complex 3 was not effective in the homopolymerization
of 1, but the copolymerization of 1 and NB (ratios 1:1, 1:2,
1
:5) afforded copolymers, as white solids, in fairly good
yields [Eq. (2)]. The absence of resonances in the olefinic
1
Results and Discussion
region of the H NMR spectra of the polymers supports a vi-
nylic polymerization mechanism. The polymers show penta-
fluorophenyl end groups (the F NMR spectroscopy chemi-
cal shifts in the F region are characteristic of C F groups
bound to carbon), which suggest an insertion mechanism
of polymerization initiated by insertion of NB or 1 into the
1
9
Synthesis ofchlorostannylated norbornene : The stannylated
norbornene used in this work, (norbornenyl)SnBu Cl (1), is
not commercially available. It was prepared by radical hy-
drostannylation of norbornadiene using SnBu HCl.
radical addition of the closely related SnMe H has been
used before in the preparation of trimethylstannyl norbor-
nene derivatives, and was shown to afford a mixture of four
2
ortho
27]
6 5
[
[19]
The
2
[24e,26]
NiꢀC F bond.
Since 1 is a mixture of isomers (1a–d), a
3
6 5
complicated polymer morphology can be anticipated. More-
over, a complex stereochemistry and even connectivity in
the polymers obtained by vinylic polymerization of norbor-
[20,21]
isomers.
Similarly, we observed a mixture of four iso-
[28–30]
mers upon addition of SnBu HCl in the ratio shown in
nene has been reported.
cannot be expected to possess a regular structure. Accord-
ingly, the Sn{ H} spectra display one broad signal with a
In other words, the polymers
2
Scheme 1. The 2-exo (a), 2-endo (b), and 7-syn (c) isomers
1
119
1
were assigned by using the H NMR spectroscopy olefinic
3
13
signals and the J
values in the C NMR spectra for the
characteristic trialkyltin chloride chemical shift value (d=
Sn,C
13
1
exo (a) and endo (b) isomers (see the Experimental Sec-
144 ppm). Broad signals are also observed in the C{ H}
NMR spectra for the NB skeleton, in which the absence of
signals around d=20 ppm point to an exo norbornene en-
[22]
119
1
tion). The Sn{ H} NMR spectrum clearly shows four sig-
nals corresponding to the four isomers a–d. Derivatization
[29,31]
of 1a–d to (norbornenyl)SnBu
A
T
E
N
(C H OMe) (2a–d) by treat-
chained polymer.
2
6
4
ment with MgBr(C H OMe) was also carried out to aid with
A
C
H
T
R
E
U
N
G
6 4
the characterization of the isomeric mixture. The ratio of
isomers 1a–d was kept in the new derivatives 2a–d (see the
Supporting Information).
Table 1 shows the results obtained for different monomer
1
feed ratios. Although the H NMR spectroscopy signals aris-
ing from NB and 1 appear overlapped, the incorporation of
1
was easily determined by quantitative determination of
[32]
the chloro content in the copolymers. Table 1 shows that
the final NB/1 ratio does not reproduce the monomer feed
ratio. The percentage of NB is larger in the copolymer (by a
factor of about two) and increases with the NB content in
the feed. Yields also increase for higher starting NB/1 ratios.
The polymers obtained are highly polydisperse (M /M =4–
6), with molecular weights in the range from 4”10 to 8”10 .
Scheme 1. Synthesis of the stannylated monomer 1 (as a mixture of iso-
mers).
w
n
4
4
10142
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Chem. Eur. J. 2008, 14, 10141 – 10148

Stannylated Polymers in Stille Couplings
FULL PAPER
Table 1. Results for the copolymerization reactions of 1 and norbornene
[
a]
(
NB).
Entry
NB/1/[Ni]
[mol]
Yield
[%]
Monomer ratio NB/1 in
copolymer [mol]
[
b]
[c]
A
C
H
T
R
E
U
N
G
1
2
3
50/50/1
100/50/1
250/50/1
66
78
85
2.8/1
4.4/1
6.1/1
[
(
a] The reactions were carried out at room temperature in CH
4 mL), from 1 (0.67 g) and the corresponding amount of a 2.52m solu-
tion of NB in CH Cl . [b] Yields are based on the total mass of mono-
2 2
Cl
2
2
mers in the feed. [c] Determined by analysis of the chloro content in the
copolymer.
The different isomers (1a–d) in 1 are not equally active in
the copolymerization reaction. Their activity can be assessed
from their ratio in the starting mixture of monomers and in
the unreacted residue after quenching a copolymerization
reaction and precipitating the polymer. Figure 1 shows the
1
119
H and Sn NMR spectra in the olefinic region for both
samples. It is clear that the 2-exo isomer 1a polymerizes the
fastest, and the approximate polymerization rates decrease
in the order 1a (2-exo)>1b (2-endo)>1c (7-syn).
Synthesis oforganostannylated copolymers : Experiments
showed that catalyst 3 is equally active in the copolymeriza-
tion of norbornene with organostannylated monomers (nor-
2
bornenyl)SnR R . However, a more convenient method is to
2
use chlorostannylated NB/1 copolymers (copol-NB-
NBSnBu Cl, 4) as a general precursor for polymers with
1
119
2
Figure 1. H (olefinic region) and Sn NMR spectra of 1 (* =1a,
&
=1b,
new SnꢀR bonds, by substitution of the SnꢀCl bond
^ =1c, * =1d): a) starting reagent; b) unreacted residue after quenching
a copolymerization with NB.
[
Eq. (3)]. This method avoids the need to synthesize and co-
2
polymerize each monomer (norbornenyl)SnBu R from
2
2
scratch to produce each copol-NB-NBSnBu R polymer. A
2
1
9
NB/1=1:1 ratio in the monomer feed (as in entry 1, Table 1)
was chosen for large-scale synthesis of 4 (about 20 g), which
was obtained as a white solid after precipitation in metha-
nol, in which the residual monomers are soluble. This af-
forded a polymer with a good incorporation of monomer 1
up by using F NMR spectroscopy. [{Pd
A
H
R
U
G
A
C
H
T
R
E
U
N
G
AHCTREUNG
(C F )} ] was used in most cases since it is a stable complex,
6
5
2
easy to store and handle, and thus convenient for use as cat-
alyst in Stille couplings. However, the common allylic com-
3
plex [{Pd
A
H
R
U
G
A
T
E
N
(m-Cl)} ] can also be used, as demonstrat-
3
5
2
(
see Table 1), which was used for the syntheses of 5–9 and
led to the organostannylated copolymers in good yields (70–
0%).
ed in entry 5, Table 2. The results for a number of electro-
philes and nucleophiles are collected in Table 2.
2
8
The content of SnꢀR groups in the polymers was deter-
1
mined by using H NMR spectroscopy using an internal
standard (see the Supporting Information), so equimolar
2
amounts of the electrophile and SnꢀR could be used. The
conditions selected (solvent and temperature) were chosen
to favor a fast oxidative addition of the organic halide. Ben-
zoquinone was added to the reactions involving allylic deriv-
atives (entries 4–7, Table 2) to favor the reductive elimina-
[33]
tion step. The results in Table 2 show that these polymers
can be used efficiently in a variety of couplings, and polymer
4 makes an excellent and general precursor of tin–polymer
reagents for the Stille reaction. Usually the reactions are no-
ticeably slower than using monomeric tin derivatives, proba-
Stannylated polymers as reagents in Stille reactions: The or-
ganostannylated polymers 5–9 were used as reagents in the
Stille reaction [Eq. (4)]. A screening for applicability in the
reaction was performed. A few hydrocarbyl halides with dif-
ferent oxidative addition rates
to palladium were chosen, in-
cluding a fluorinated aryl that
allows an easy reaction follow
Chem. Eur. J. 2008, 14, 10141 – 10148
ꢀ 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
10143

A. C. AlbØniz, P. Espinet et al.
2
Table 2. Stille reactions using copol-NB-NBSnBu
2
R 5–9 as reagents.
ently, each series of experi-
1
2
1
2
Entry
R X
Polymer, R
Solvent
T [8C]
Time
R ꢀR [%] ments including five cycles of
[
[
[
[
[
[
[
[
[
a]
reuse, with similar results.
1
2
3
4
5
6
7
8
9
1
C
C
p-NO
CH
CH
CH
CH
PhCOCl
PhCOCl
PhCOCl
6
F
F
5
I
I
5, CH =CH
2
dioxane
90
90
50
50
50
50
50
50
50
50
1 day
3 days
1 day
8 h
1 day
2 days
1 day
18 h
10 (67)
a]
6, p-OMeꢀC
9, PhCꢁC
H
dioxane
11 (72)
12 (100)
13 (93)
13 (90)
14 (100)
15 (100)
16 (66)
17 (64)
18 (81)
The Stille reactions were car-
ried out using a molar ratio
allyl chloride/Sn-C H -OMe-p=
6
5
6
4
a]
ꢀC
=CHꢀCH
=CHꢀCH
=CHꢀCH
=CHꢀCH
H
4
I
CDCl
CDCl
CDCl
CDCl
CDCl
CDCl
CDCl
CDCl
2
6
3
3
3
3
3
3
3
3
a,b]
c]
Cl
Cl
Cl
Cl
6, p-OMeꢀC
6, p-OMeꢀC
6
6
H
H
4
4
2
2
2
2
2
6
4
2
a,b]
a,b]
a]
1:1 and just 0.5% mol of palla-
dium catalyst, at 508C. In every
cycle, before running the next
Stille reaction, the Sn-C H -
7, p-FꢀC
6 4
H
2
ꢀC
H
2
8, p-CF
6, p-OMeꢀC
7, p-FꢀC
9, PhCꢁC
3
6
4
6
H
4
a]
6
H
4
18 h
18 h
6
4
[
a]
0
OMe-p content in the polymer
was quantified by using
H NMR spectroscopy using an
[
a] [{Pd
A
C
H
T
R
E
U
N
G
(AsPh
3
)
A
C
H
T
R
E
U
N
G
A
C
H
T
R
E
U
N
G
6 5 2
(m-Br)(C F )} ] (2.5% mol) was used as catalyst. [b] Benzoquinone (2.5% mol) was added (see
3
text and ref. [33]). [c] [{Pd
added.
A
H
R
U
G
3
5 2
H )(m-Cl)} ] (0.5% mol) was used as catalyst and benzoquinone (1% mol) was
A
H
R
U
G
1
bly reflecting higher hindrance of the reactive tin centers in
the polymers (e.g., in entry 2, polymer 6 produces 72% of
the bisaryl C F ꢀC H OMe (11) in 3 days, whereas
2 6 4
Table 3. Recycling experiments for copol-NB-NBSnBu (C H -OMe-p)
[
a]
(
6) in the Stille reaction for entry 5 from Table 2.
Cycle
no.
Step A
Step B
4 yield
[%]
Step C
6 yield
[%]
Sn content
6
5
6
4
conv.
in 13
[wt%]
SnBu (C H ꢀOMe-p) under the same reaction conditions
3
6
4
[b]
[c]
[
%]
A
C
H
T
R
E
U
N
G
produces 100% yield after only 6 h). However, in some
cases, such as the reactions to give para-methoxy allyl ben-
zene (13) (entries 4 and 5, Table 2), polymer 6 is about as
fast as SnBu (C H ꢀOMe-p).
1
2
3
4
5
81
68
79
90
90
97
90
97
93
94
100
91
97
96
–
0.03
0.03
0.02
0.07
0.07
3
6
4
Polymer recovery and recycling: To check the feasibility of
using these polymers in the Stille reaction, as far as easy
workup, recovery, and recycling are concerned, two model
reactions were chosen that correspond to entries 2, 5, and 6
in Table 2. Scheme 2 shows the reactions carried out in each
cycle for the synthesis of the coupling product and the re-
covery of the tin organopolymer.
[a] The polymers remain soluble throughout the cycles. [b] Conversions
(conv.) were determined by using H NMR spectroscopy of a sample of
the reaction bulk before workup. [c] Determined by ICP–MS.
1
internal standard (ferrocene) and by comparing the integrals
of the standard signal and the anisyl (An) resonances. In
this way the stoichiometric allyl chloride/SnꢀAn=1:1 ratio
was maintained in each cycle and the activity of the polymer
could be evaluated independently of small variations of the
efficiency in the reactions with the Li(C H ꢀOMe-p) deriva-
6
4
tive (step C). Table 3 displays a collection of the yields ob-
tained in each step of the cycle represented in Scheme 2,
and the tin content in the coupling product.
The results show that 6 is a very efficient reagent (step A)
in the recycled Stille coupling and remains active through-
out the cycles. Following step A, the solvent was evaporated
and the polymer was precipitated in a mixture of MeOH
and n-hexane. Almost quantitative recovery of the polymer-
ic byproduct (4) was achieved (step B). The coupling prod-
uct 13 was obtained by evaporation of the mother liquors
and filtration of the product dissolved in n-hexane through
silica gel. This simple procedure afforded 13 with very small
tin content (Table 3). For comparison, the same Stille reac-
tion was carried out using SnBu (C H ꢀOMe-p) as reagent
Scheme 2. Cycle of recycling of stannylated polynorbornenes in a Stille
reaction.
3
6
4
and worked up by the usual procedure, involving the trans-
formation of the tin halide into tin fluoride (by shaking the
mixture with an aqueous solution of KF), evaporation of the
solvent of the organic layer, and further filtration of the resi-
due dissolved in n-hexane through silica gel. In this case the
Recycling of reaction in entry 5 (Table 2): The starting poly-
mer 6 [produced from a copolymer 4 with a NB/1=2.9:1
molar ratio as shown in Equation (3)] was a white solid that
is soluble in chloroform and THF to give viscous solutions,
but insoluble in MeOH or n-hexane. It can be used and re-
cycled at least five times (Table 3; see the Experimental Sec-
tion for details). This protocol was repeated twice independ-
coupling product 13 contained about 6% mol of SnBu Cl
3
(4.5 wt% tin), showing the advantage of polymer reagents
for purification.
10144
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Chem. Eur. J. 2008, 14, 10141 – 10148

Stannylated Polymers in Stille Couplings
FULL PAPER
Recycling of reaction in entry 6 (Table 2): The same proce-
dure described above was applied to polymer recycling with
the reaction partners of entry 6, Table 2. The coupling reac-
tion of allyl chloride with 7 (0.5% mol Pd) was carried out
and the polymer was reused three times with good yields in
step A (60–100%) and almost quantitative recovery (step B)
and regeneration (step C) of the polymers.
It is worth noting that the yields of step A in Tables 3 and
4 have been obtained by using an equimolar SnꢀR /organic
2
halide ratio whereas it is common practice in the Stille reac-
tions to use an excess of tin reagent (about 10–20% excess),
in spite of the fact that this complicates the contamination
problem. When using our stannylated polymers the use of
excess polymer can be made without this detrimental side
effect, since the excess of tin reagent is separated with the
byproduct. Moreover, the use of excess tin polymer elimi-
Recycling of reaction in entry 2(Table 2) : This reaction was
chosen because it requires more stringent conditions. As
specified in Table 2, the Stille coupling was carried out at
high temperature (908C) to ensure a fast oxidative addition
of C F I. The use of this organic iodide will have the result
1
nates the need of H NMR spectroscopic analysis prior to
each Stille reaction, and the coupling product is obtained
quantitatively for the case of entry 5 in the same reaction
time.
6
5
that the initial chloride in copolymer 4 will be replaced by
iodide after the first Stille step. The results over five recov-
ery cycles (Table 4) show that, although polymer 6 remains
Conclusion
The vinylic copolymerization of tin-containing norbornenes
with norbornene in good yield has been achieved, using [Ni-
2 6 4
Table 4. Recycling experiments for copol-NB-NBSnBu (C H -OMe-p)
[
a]
(
6) in the Stille reaction for entry 2 from Table 2.
A
H
R
U
G
A
T
E
N
6
Cycle
no.
Step A
conv. [%]
Step B
copol-NB-NBSnBu
Step C
6 yield [%]
[
b]
groups, which supports the proposal that an insertion mech-
anism is operating. Since the insertion of norbornene is
faster than the insertion of the stannylated monomer 1, the
norbornene content of the polymer is always higher than its
ratio in the monomer feed.
2
I yield [%]
[
c]
1
2
3
4
5
6
–
–
91
[
d]
d]
d]
d]
64
59
40
40
66
72
74
92
91
88
100
100
80
[
[
[
100
The copolymer (4) has an all-aliphatic skeleton and ꢀ
–
SnBu Cl groups. It is a versatile reagent as it can be trans-
2
[
a] The composition of the starting 4 is NB/1=2.5:1. [b] Reaction condi-
19
formed by reaction with the corresponding organolithium or
tions: entry 2, Table 2. Conversions were determined by using F NMR
spectroscopy of a sample of the reaction bulk before workup. [c] Polymer
organomagnesium compound into new copolymers with ꢀ
synthesized from 4, soluble in CHCl
CHCl
3
. [d] The polymers are not soluble in
SnBu R moieties (R=aryl, vinyl, alkynyl, etc.) that can be
2
3
.
used as coupling partners in a wide number of Stille reac-
tions. Most importantly, these polymers are efficiently
reused affording good yields in several cycles. Moreover, the
use of these polynorbornene reagents in the Stille coupling
provides an easy reaction workup, better separation of the
halostannylated products, and low content of tin in the cou-
pling products, thus representing a good alternative to ad-
dress the problem of tin contamination.
active throughout the cycles, it gradually loses solubility,
whereas reduced yields are observed in step A. This varia-
tion is not related to the exchange of Cl for I in the first
cycle, as step C is not negatively affected. It is plausible
that conformational changes in the polynorbornene skele-
ton, after heating in the Stille coupling step at a higher tem-
perature than those used in entries 5 and 6, gradually reduce
the solubility of the polymers and lower the accessibility of
the reagents to the active tin centers. Conformational
changes upon heating have been reported for polynorbor-
nene. This reduction in activity can be compensated using
an excess of polymer 6 in step A to produce 11 in good
yields, as shown in independent recycling experiments.
The gradual decrease in polymer solubility influences the
tin content of the product. The biphenyl coupling product
[
34]
Experimental Section
1
13
1
19
119
General: H, C{ H}, F, and Sn NMR spectra were recorded using
Bruker AC-300 and ARX-300 instruments. Chemical shifts (d) are re-
[35]
1
13
19
ported in ppm and referenced to Me
4
Si ( H and C), CFCl
3
( F), or
1
19
SnMe ( Sn). All of the NMR spectra were recorded at 293 K. Elemen-
4
tal analyses were determined by using a Perkin–Elmer 2400 CHN micro-
analyzer. The tin content of the products was determined by ICP–MS in
the SCAI center of the University of Burgos, using Agilent 7500i equip-
3 2 4
ment; the samples were dissolved in a mixture of HNO /H SO =7:3
1
1 was obtained by filtration of the solution in dioxane (to
using an ETHOS SEL Milestone microwave oven. The chloro content in
the polymer was determined by oxygen-flask combustion of a sample and
separate most of the polymer byproduct), evaporation to
dryness, and addition of MeOH. Since 11 is partially soluble
in methanol a first batch was obtained in this way which
contains small amounts of polymer and shows tin contents
from 14% weight, in cycle 1, to 0.5% in cycle 5. Either the
second batch obtained (see the Experimental Section) or re-
crystallization of the first batch affords 11 with lower tin
contents between 0.04 and 0.003 wt%.
[32]
analysis of the residue by the mercurimetric titration of chloride. Size
exclusion chromatography (SEC) was carried out using a Waters SEC
system using a three-column bed (Styragel 7.8”300 mm columns: 50–
1
00.000, 5000–500.000, and 2.000–4.000.000 D) and a Waters 410 differen-
tial refractometer. SEC samples were run in CHCl at 313 K and calibrat-
ed to polystyrene standards. Solvents were dried over CaH or Na, dis-
tilled, and deoxygenated prior to use. Norbornadiene, SnBu Cl , and the
organic halides were purchased from Aldrich or Acros. The compounds
3
2
2
2
Chem. Eur. J. 2008, 14, 10141 – 10148
ꢀ 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
10145

A. C. AlbØniz, P. Espinet et al.
[
36]
[26, 37]
[38]
3
1
SnBu
2
H
2
,
3,
were prepared according to the literature.
Dibutylchlorostannylnorbornene (1): SnBu (0.962 g, 4.093 mmol) was
added dropwise to a mixture of norbornadiene (2.263 g, 24.56 mmol),
AIBN (0.0672 g, 0.409 mmol), and SnBu Cl (1.244 g, 4.093 mmol). The
[{Pd
A
C
H
T
R
E
U
N
G
(AsPh
3
)
A
H
R
U
(m-Br)
A
H
R
N
(C
6
F
5
)}
2
],
and [{Pd
A
T
E
N
(h -C
3
H
5
)
A
H
R
U
G
(96%). H NMR (300.13 MHz, CDCl
2H; Hmeta), 3.7 (s, 3H; OCH ), 2.8–0.7 ppm (br; HBu, H ); C{ H} NMR
75.4 MHz, CDCl ): d=159.6 (s; Cpara-OCH ), 137.7 (s; Cortho), 133.1 (s;
ipso-Sn), 113.9 (s; Cmeta), 54.8 (s; OCH ), 53.0–50.0 (br; C ), 48.5–46.5
3
): d=7.4 (br, 2H; Hortho), 6.8 (br,
[
39]
1–7
13
1
Cl)}
2
]
3
(
C
3
3
2
H
2
5
,6
3
1
,4
7
1,2
(
br; C ), 40.5–39.0 (br; C ), 36.5–34.1 (br; C ), 29.2 (s; Bu: -CH
CH -), 27.6 (s; Bu: -CH -CH ), 13.7 (s; Bu: CH -), 9.2 ppm (br; Bu:
CH -Sn); Sn{ H} NMR (111.92 MHz, CDCl
): d=ꢀ45.5 ppm (br).
The other functionalized copolymers 5 and 7–9 (Table 2 and Eq. (3)) and
the recycled one according to step C in Scheme 2 were prepared follow-
ing the same procedure but using the corresponding lithium or magnesi-
2 2
-CH -
2
2
reaction mixture was maintained in a water bath at room temperature
for 12 h. The product was obtained as a yellow liquid after pumping off
the excess of norbornadiene. Isolated yield: 2.427 g (82%). The product
2
2
3
3
1
19
1
-
2
3
is a mixture of four isomers 1a–d.
1
Compound 1a: H NMR (300.13 MHz, CDCl
.0 Hz, 1H; H ), 5.94 (m, J=2.7, 6.0 Hz, 1H; H ), 3.07 (br, 1H; H ), 3.04
br, 1H; H ), 1.97 (m, 1H; H ), 1.35 (m, 1H; H ), 1.30 (m, 1H; H ), 1.15
m, 2H; H , H ), 1.81–1.05 (m; 12HBu), 0.87 ppm (t, 6H; CH
NMR (75.4 MHz, CDCl ): d=136.1 (s, JSn,C =63.7 Hz; C ), 133.7 (s; C ),
3
8.2 (s, JSn,C =0 Hz; C ), 44.6 (s; C ), 42.8 (s, JSn,C =22.6 Hz; C ), 28.5 (s;
3
): d=6.06 (m, J=2.7,
[
41]
[42]
6
5
1
um derivatives. Li
diethyl ether by mixing the corresponding bromo derivative and butyl-
(C C H ) is commercially avail-
A
H
R
U
G
6
(
(
6
4
3
6
4
4
3
7
3’
2
7’
13
1
lithium at ꢀ408C and stirring for 1 h. Li
ACHTREUNG
3
); C{ H}
2
6
4
3
6
able (Aldrich), but it was prepared in diethyl ether by mixing phenylace-
3
7
1
3
4
tylene and butyllithium at ꢀ408C and stirring for 1 h. CH =CHꢀMgBr
4
2
[
43]
2
3
was prepared following the procedure in the literature. Spectroscopic
data for copolymers 5 and 7–9 are included in the Supporting Informa-
tion.
C ), 27.9 (s; CH
2
), 27.5 (s; C ), 27.0 (s; CH
2
), 17.1 (s; CH
): d=148.8 ppm (s).
): d=6.10 (m, J=3.0,
2
-Sn), 13.5 ppm
1
19
1
(
s; CH
3
); Sn{ H} NMR (111.92 MHz, CDCl
3
1
Compound 1b: H NMR (300.13 MHz, CDCl
.4 Hz, 1H; H ), 6.03 (m, J=3.0, 5.4 Hz, 1H; H ), 3.20 (br, 1H; H ), 3.00
br, 1H; H ), 2.10 (m, 1H; H ), 1.94 (m, 1H; H ), 1.55 (m, 1H; H ), 1.30
m, 1H; H ), 1.13 (m, 1H; H ), 1.05–1.81 (m; 12HBu), 0.87 ppm (t, 6H;
); C{ H} NMR (75.4 MHz, CDCl
Sn,C =33.4 Hz; C ), 49.9 (s,
Sn,C =22.6 Hz; C ), 30.8 (s; C ), 27.9 (s; CH
7.1 (s; CH
3
[
44]
5
6
1
Stille reactions—preparation of p-NO
NMR spectroscopy tube was charged under N
CꢁC-C (9) (0.0300 g, 0.058 mmol; the molar amount of SnꢀR groups
was determined by H NMR spectroscopy titration using an internal stan-
dard, as described in the text and the Supporting Information), p-NO
I (0.0115 g, 0.046 mmol), CDCl (0.4 mL) and [{Pd(AsPh (m-Br)-
)} ] (0.0015 g, 0.0012 mmol). The reaction mixture was heated at
08C for 24 h and the formation of p-
NO -C was observed by
2
-C
6
H
4
-CꢁC-C
6 5
H (12): A 5 mm
5
(
(
4
3
2
7
2
with copol-NB-NBSnBu -
2
3
’
7’
6 5
H
1
1
3
1
5
CH
3
3
): d=137.0 (s; C ), 135.0 (s,
3
6
3
7
1
2
-
J
J
J
Sn,C =55.3 Hz; C ), 45.3 (s; C ), 41.8 (s,
3
4
2
3
C
6
H
4
3
A
H
R
U
G
3
)
ACHTREUNG
2
), 27.4 (s; C ), 27.0 (s; CH
1
19
1
A
H
R
U
G
6
F
5
2
1
2
-Sn), 13.5 ppm (s; CH
3
);
Sn{ H} NMR (111.92 MHz,
5
CDCl
3
): d=140.3 ppm (s).
-CꢁC-C
6 5
H
1
5
2
6
H
4
Compound 1c: H NMR (300.13 MHz, CDCl
.26 (br, 2H; H , H ), 2.27 (m, 1H; H ), 1.81–1.05 (m, 16H; 12HBu, H ,
H , H , H ’), 0.87 ppm (t, 6H; CH
d=138.0 (s; C , C ), 45.6 (s; C , C ), 32.5 (s; C ), 27.9 (s; CH
), 25.2 (s; C ), 25.1 (s; C ), 17.6 (s; CH
Sn{ H} NMR (111.92 MHz, CDCl
of this signal could be reversed).
3
): d=6.11 (m, 2H; H , H ),
1
H NMR spectroscopy. Yield was cal-
culated by integration of the H NMR
4
1
7
3
1
3
’
2
2
13
1
3
); C{ H} NMR (75.4 MHz, CDCl
1
signals
(100%
yield).
H NMR
5
6
1
4
7
2
), 27.0 (s;
(
2
2
300.13 MHz, CDCl
3
): d=8.23 (m,
2
3
CH
2
2
-Sn), 13.5 ppm (s; CH
): d=133.2 ppm (s) (the assignment
2,6
3,5
H; H ), 7.67 (m, 2H; H ) 7.56 (m,
1
19
1
3
2’,6’
3’,4’,5’
H; H ), 7.35 ppm (m, 3H; H
).
The other Stille reactions were carried out in a similar way starting from
the corresponding copolymer, hydrocarbyl halide, and catalysts as collect-
ed in Table 2. Compounds 10, 11, 13, 14, 15, 16, 17, and
have been described before. Nonetheless spectroscopic data are in-
cluded below or in the Supporting Information.
1
Compound 1d: H NMR (300.13 MHz, CDCl
2HBu, H ), 0.87 ppm (t, 6H; CH
3
): d=1.81–1.05 (m, 21H;
1
–7
119
1
1
3
);
Sn{ H} NMR (111.92 MHz,
[45]
[46]
[47]
[48]
[49]
[50]
[51]
CDCl
versed).
3
): d=142.1 ppm (s) (the assignment of this signal could be re-
[52]
1
8
Copol-NB-NBSnBu
of norbornene in CH
2
Cl (4): Compound 1 (0.670 g, 1.853 mmol), a solution
Cl (0.65 mL, 2.88m, 1.853 mmol; the solution of
norbornene was titrated by using H NMR spectroscopy with C
internal standard) and dry CH Cl (1.85 mL) were mixed in an oven-
dried Schlenk flask under nitrogen. solution of (0.0407 g,
(1 mL) was then added. After being stirred for
4 h at room temperature, the copolymer was precipitated by pouring the
[47]
2 6 4
Synthesis of p-methoxyallyl benzene (13): Copol-NB-NBSnBu (C H -
2
2
OMe-p) (6, 4.600 g, 5.700 mmol Sn-(C
Sn-(C -OMe-p) groups was determined by using H NMR spectrosco-
py titration using an internal standard, as described in the text and the
Supporting Information), allylchloride (0.4362 g, 5.700 mmol), CHCl
110 mL), benzoquinone (0.0062 g, 0.057 mmol), and a solution of [{Pd-
6 4
H -OMe-p); the molar amount of
1
6
H
3
Br
3
as
1
6
H
4
2
2
A
3
3
0
2
2 2
.037 mmol) in CH Cl
(
3
A
H
R
U
G
3
H
5
)
A
H
R
U
G
2
] (0.0104 g, 0.028 mmol) in CHCl
3
(1 mL) were added to
mixture into MeOH (50 mL). The MeOH was decanted off and the copo-
lymer was filtered, washed with MeOH, and air-dried. Isolated yield:
2
. The reaction mixture was heated
1
0
H
3
.611 g (72%). H NMR (300.13 MHz, CDCl
3
): d=2.6–0.7 ppm (br; HBu
,
1
2 2 6 4
mation of CH =CH-CH -(C H -OMe-p) was observed by using H NMR
1
ꢀ7
13
1
5,6
3
); C{ H} NMR (75.4 MHz, CDCl ): d=54.5–50.0 (br; C ), 41.5–
spectroscopy (crude yield: 81%; calculated by integration of the allylic
signals of the allylchloride and the cross-coupling product). The solvent
was the evaporated to around 10 mL and a mixture of n-hexane (50 mL)
and MeOH (50 mL) was added. The copolymer copol-NB-NBSnBu
was filtered, washed with MeOH, and dried in vacuum to yield 4.003 g
97% yield). The filtrate was concentrated to 5 mL, treated with activat-
1
,4
7
2,3
9.0 (br; C ), 38.0–35.0 (br; C ), 32.5–29.0 (br; C ), 27.9 (s; Bu: -CH
CH -CH -), 27.0 (s; Bu: -CH -CH ), 16.8 (br; Bu: -CH -Sn), 13.6 ppm (s;
Bu: CH -); F NMR (282 MHz, CDCl
): d=ꢀ133.8, ꢀ140.6 (br; Fortho),
2
-
2
2
2
3
2
1
9
3
3
Cl
2
1
19
1
ꢀ
158.4 (br; Fpara), ꢀ163.4 ppm (br; Fmeta); Sn{ H} NMR (111.92 MHz,
CDCl
3
): d=142.3 ppm (br).
(
The same procedure was used for the experiments collected in Table 1.
Large-scale syntheses were carried out just by scaling up reactants and
solvents.
ed charcoal and filtered through silica gel. After distillation to remove
the solvents, 13 was obtained as an orange liquid (0.674 g, 80%).
1
2,6
H NMR (300.13 MHz, CDCl ): d=7.12 (m, J=8.76 Hz, 2H; H ), 6.86
3
3
,5
(
m, J=8.76 Hz, 2H; H ), 5.98 (m, J=16.7, 10.5, 6.6 Hz, 1H; CH
-), 5.09 (d, J=16.7 Hz, 1H; CHH=CH-CH -), 5.06 (d, J=10.5 Hz,
H; CHH=CH-CH -), 3.82 (s, 3H; OCH ), 3.34 ppm (d, J=6.6 Hz, 2H;
CH =CH-CH -).
2
=CH-
Functionalization ofpolymers—synthesis of6 : A solution of butyllithium
in n-hexane (6.77 mL, 1.6m, 10.824 mmol) was added to THF (46 mL) at
CH
1
2
2
0
9
8C. The mixture was cooled to ꢀ908C and 4-bromoanisole (1.850 g,
2
3
.89 mmol) in THF (15 mL) was added over a 5 min period at that tem-
2
2
[46]
perature. The temperature was allowed to rise to ꢀ508C and stirring con-
Synthesis of2,3,4,5,6-penta lf uoro-4 ’-methoxybiphenyl (11): A Schlenk
flask was charged under N with 6 (2.000 g, 3.700 mmol Sn-C H -OMe-p;
[
40]
tinued for 15 min. Then 4 was added (2.550 g, 4.920 mmol) and the re-
action mixture was allowed to slowly warm to room temperature and
stirred for 24 h. After that time, water (1 mL) was added and THF was
pumped off. The residue was washed with acidic MeOH and stirred for
2
6
4
the molar amount of Sn-(C H -OMe-p) groups was determined by using
6
4
1
H NMR spectroscopy titration using an internal standard, as described
in the text and the Supporting Information), C F I (0.875 g, 2.960 mmol),
6
5
3
0 min. The MeOH was then decanted off and the resulting copolymer
1,4-dioxane (50 mL), and finally a solution of [{Pd
A
H
R
U
G
3
)
A
H
E
N
(m-Br)
A
C
H
T
R
E
U
N
G
6 5 2
(C F )} ]
was filtered, washed with MeOH and air-dried. Isolated yield: 2.802 g
(0.0976 g, 0.074 mmol) in 1,4-dioxane (1 mL). The reaction mixture was
10146
www.chemeurj.org
ꢀ 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2008, 14, 10141 – 10148

Stannylated Polymers in Stille Couplings
FULL PAPER
heated at 908C for 3 days. After that time it was cooled down and a
small portion was taken and the formation of 11 was observed by using
W. P. Neumann, Synlett 1993, 283–285; i) C. Bokelmann, W. P. Neu-
mann, M. Peterseim, J. Chem. Soc. Perkin Trans. 1 1992, 3165–3166;
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Org. Chem. 1991, 56, 5971–5972; k) U. Gerigk, M. Gerlach, W. P.
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Bergbreiter, S. A. Walker, J. Org. Chem. 1989, 54, 5138–5141.
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macho-Camacho, M. Biesemans, M. Van Poek, F. A. G. Mercier, R.
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2870–2873.
1
9
F NMR spectroscopy (crude yield: 69%; calculated by integration of
the Fortho signals of the C I and the cross-coupling product). The insolu-
ble copolymer copol-NB-NBSnBu I was filtered, washed with MeOH,
6
F
5
2
and dried under vacuum to yield 1.939 g (94%). The filtrate was evapo-
rated to dryness and the yellow solid that appeared (11) was washed with
MeOH and air dried to yield 0.4467 g. The filtrate was concentrated to
5
mL to obtain a second batch of a yellow solid (11), which was washed
with MeOH and air-dried; isolated yield: 0.3555 g (36%). The first batch
was contaminated with small amounts of polymer, and it was recrystal-
1
lized from hot methanol; isolated yield: 0.2133 g (22%). H NMR
2
,6
(
1
3
300.13 MHz, CDCl ): d=7.35 (m, J=10.0 Hz, 2H; H ), 7.05 (m, J=
3
,5
19
0.0 Hz, 2H;
): d=ꢀ144.1 (m, 2F; Fortho), ꢀ156.8 (t, 1F; Fpara), ꢀ163.9 ppm (m,
F; Fmeta); elemental analysis calcd (%) for C13 O: C 56.95, H 2.57;
found: C 56.70, H 2.72.
H
), 3.85 ppm (s, 3H; OCH
3
); F NMR (282 MHz,
CDCl
2
3
7 5
H F
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3
Financial support from the Spanish MEC (DGI, grant CTQ2007-67411/
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fellowship to N.C.), and the Junta de Castilla
VA117A06) is gratefully acknowledged.
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Published online: September 24, 2008
10148
www.chemeurj.org
ꢀ 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2008, 14, 10141 – 10148