Fluorene-based stannylated polymers and their use as recyclable reagents in the Stille reaction

Article abstract of DOI:10.1016/j.jorganchem.2011.07.004

Stannylated polymers based on the polyfluorene backbone have been synthesized and used in the Stille reaction as recyclable reagents, minimizing the generation of toxic tin residues.

Full text of DOI:10.1016/j.jorganchem.2011.07.004

Journal of Organometallic Chemistry 696 (2011) 3316e3321
Contents lists available at ScienceDirect
Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
Fluorene-based stannylated polymers and their use as recyclable reagents
in the Stille reaction
,
a
,
b
Nora Carrera a, Alfonso Salinas-Castillo b, Ana C. Albéniz a , Pablo Espinet , Ricardo Mallavia
*
*
a IU CINQUIMA/Química Inorgánica, Universidad de Valladolid, 47071-Valladolid, Spain
b Instituto de Biología Molecular y Celular, Universidad Miguel Hernández, 03202-Elche, Spain
a r t i c l e i n f o
a b s t r a c t
Article history:
Stannylated polymers based on the polyfluorene backbone have been synthesized and used in the Stille
reaction as recyclable reagents, minimizing the generation of toxic tin residues.
Ó 2011 Elsevier B.V. All rights reserved.
Received 25 February 2011
Received in revised form
4 July 2011
Accepted 5 July 2011
Keywords:
Stille reaction
Stannylated polymer
Recyclable reagent
Cross coupling
Tin
Polyfluorene
1. Introduction
from stannylated norbornene monomers, and their application as
recyclable reagents in the Stille reaction [9]. The utility of these
The Stille reaction belongs to the large family of palladium-
catalyzed cross coupling reactions (Scheme 1) [1e3]. Due to its
versatility, functional group compatibility and the fact that addi-
tives such as bases or fluorides are not needed, the Stille coupling is
very useful in organic synthesis [4], including natural product
synthesis where it has mostly been used in the final steps [5].
Nonetheless, organometallic tin chemistry has a serious draw-
back in the formation of toxic tin residues difficult to separate from
the target products. One solution to overcome this problem has been
the use of a tin-containing polymeric matrix [6], easier to separate
from the desired products at the end of the reaction. An additional
advantage of this approach, when compared to other separation
strategies used [7], is the potential for recycling of the tin byproduct.
Although a few tin reagents not supported on polymers have been
used in the Stille reaction and reused [7d,8], a polymer framework
generally allows for an easier separation-recovery-regeneration
sequence. The few polymers that have been used for this purpose
are generally polystyrene resins, most of them synthesized by
functionalization of a preformed polymer support [6]. We recently
reported the synthesis of stannylated polynorbornenes, prepared
polymers was illustrated by the low contents of tin in the cross-
coupling products and the high activity of the tin polymers after
successive recycling steps.
Based on this previous work, we decided to extend this study to
a different type of polymers. Here we use the fluorene-based poly
[(9,9-bis(bromoalkyl)fluoren-2,7-diyl)-alt-co-(benzen-1,4-diyl)],
which contains a rigidly planar biphenyl unit and halogenated
hydrocarbon side chains at the C9 site and it is highly luminescent
[10]. It was chosen because it undergoes facile substitution reactions
of the halides for stannane. Moreover, the chains provide an
aliphatic link for the tin group not prone to undergo transmetalation
(equivalent to n-Bu in the traditional reagents Bu3SnR), and are
flexible enough so the tin groups are easily accessible for reaction.
Thus, we report in this paper the first stannylated fluorene-based
polymer and its use as a recyclable reagent in the Stille reaction.
2. Results and discussion
2.1. Synthesis and characterization of stannylated polymers
The polyfluorene poly[(9,9-bis(60-bromohexyl)fluoren-2,7-diyl)-
alt-co-(benzen-1,4-diyl)] (2) depicted in Scheme 2, was used as the
polymer precursor of the stannylated derivatives. It is prepared by
* Corresponding authors. Tel.: þ34 983184621; fax: þ34 983423013.
E-mail address: albeniz@qi.uva.es (A.C. Albéniz).
Suzuki coupling of
a dibromo derivative (2,7- dibromo-9,
0022-328X/$ e see front matter Ó 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2011.07.004

N. Carrera et al. / Journal of Organometallic Chemistry 696 (2011) 3316e3321
3317
[Pd2(m
eCl)2(h3eC3H5)2] as catalyst and 1% of benzoquinone as
coupling promoter, at 50 ꢁC in THF. The use of benzoquinone has
been shown to accelerate the reductive elimination step, usually
slower when allylic derivatives are used in cross-coupling reactions
[14,15]. Allyl chloride converts into the coupling product 5 selec-
tively, and the yield after 1 day was measured by 1H NMR spec-
troscopy and calculated by the integral ratio of the allylic signals of
the allylchloride and 5. In almost every case the reaction was
quantitative [16].
After running the Stille reaction, the polymer was precipitated
in MeOH and separated from the coupling product by filtration
(Step B). The recovery of 4 was almost quantitative and the coupling
product 5 was obtained by evaporation of the solvents to dryness,
treatment of the residue dissolved in Et2O with activated charcoal
and filtration through silica gel.
Scheme 1. The Stille reaction.
9-bis(60-bromohexyl)fluorene) with 1,4-phenyldiboronic acid [11].
The polymer obtained in this way has an alternating structure and
a Mw of 9400 g molꢀ1 (Mw/Mn ¼ 1.9) based on polyfluorene cali-
bration [11a]. The stannylated fluorene-based polymer 3 was
synthesized by nucleophilic substitution of the bromine atoms in 2
with an organostannide (Scheme 2). The latter, LiSnBu2An (An ¼ p-
anisyl), was prepared from anisyl dibutyltin choride, which in turn
can be easily obtained by the efficient method we described recently,
involving microwave irradiation and column chromatography in
acidic alumina [12,13]. The 1H NMR spectrum of 3 exhibits well-
defined signals for the anisyl moiety and lacks any broad signal at
3.28 ppm of the initial eCH2eBr protons of polymer 2 (Fig. 1), sup-
porting complete stannylation of 2. The absence of Br in polymer 3
was further confirmed by elemental analysis.
Polymer 3 can be used as an anisyl-transmetalating reagent in
the Stille reaction and can be recycled as described below.
Furthermore, 3 can be easily and selectively converted into
PFP(SnBu2Cl)2 (4) by reaction with a stoichiometrical amount of HCl
in Et2O. The complete conversion of 3 into 4 was confirmed by
elemental analysis of the chloro content and by its 1H NMR spec-
trum, which clearly shows the total absence of the anisyl signals
(Fig. 1). Polymer 4 can be used as a general starting material for the
preparation of other PFP(SnBu2R)2 reagents [9].
The recovered polymer was regenerated by treatment with the
organolithium derivative LiAn (Step C). The complete substitution
in this step was checked by elemental analysis of the chloro content
in the polymer. In this way, polymer 3 can be recycled at least four
times as shown in Table 2.
This procedure gave 5 with different tin contents depending on
the recycling experiment. As shown in Table 1, the first cycle leaves
the largest amount of tin in the coupling product which is clearly
reduced through the cycles. Even in the first cycle, the amount of
residual tin is half the quantity expected when conventional
methods are used, usually treatment with an aqueous solution of
KF. The decrease of the tin content in 5 on going from cycle 1 to 4,
could be explained by the decrease in polymer solubility which is
observed as it is being reused. Even if we did not detect them by
NMR, we cannot rule out that a small amount of tin oligomers
formed by decomposition of LiSnBu2An in the preparation of 3
could contaminate the polymer and be washed off in the first cycle
[13]. The effect of the decrease in the solubility of these polymers is
also found when they are stored for months at room temperature,
although the nature of the aging process responsible for this change
in properties has not been determined. The decrease in solubility
does not affect the efficiency of the polymer as reagent in the Stille
reaction and thus it is a good feature for separation purposes (even
the recovery and regeneration yields slightly increase in cycles 2e4
when compared to the first one). The high luminescence of the
polymers at low concentrations is useful for qualitative detection of
soluble polymer contamination, by visual inspection under UV
light. However, we found that the fluorescence underestimated the
quantitative results obtained by ICP-MS tin determination, so its
use as quantitative assay was discarded in favor of the latter tech-
nique [17].
Finally, we checked the possibility of reuse of the same polymer
after these recycling experiments in a different coupling reaction.
Since we use excess of the stannylated polyfluorene in the Stille
couplings we treated polymer 4 recovered from the last cycle in
Table 2 with an ethereal solution of HCl. This eliminates the anisyl
groups in the polymer affording pure 4. This polyfluorene was then
reacted with Li(peFC6H4) to give a p-fluorophenyl functionalized
polymer (R2 ¼ peFC6H5, 9). The Stille coupling of this reagent with
allyl chloride in the same conditions used for the recycling exper-
iments in Table 2, afforded 90% conversion to p-fluoro allyl benzene
(10) in 1 day.
Fig. 2 shows the fluorescence emission spectra for polymers 2e4
in THF solutions and room-temperature (at lex ¼ 370 nm). The
emission peaks of the three blue polymers are very similar, pre-
senting a maximum at 409e410 nm with a well-defined vibronic
feature at 430 nm. Thus, the substituent at the end of the hexyl
chain (Br, SnBu2An, or SnBu2Cl) has little influence in the fluores-
cent behaviour of the polymer.
2.2. Polymer use as reagent, recovery and recycling
Polymer 3 was tested as reagent in the Stille reaction (Scheme 3)
and a few examples using different organic electrophiles are given
in Table 1. As can be observed, the polymeric stannanes are useful
and high to moderate conversions are obtained. When compared to
monomeric reagents, longer reaction times are generally needed.
The coupling of allyl chloride and the anisyl group (entry 1,
Table 1) was chosen as a model reaction to check if polymer 3 can
be recycled (Scheme 4 and Table 2). In a first step (Step A) the Stille
coupling of allyl chloride and polymer 3 was carried out following
the conditions of Scheme 4 and Table 1 (entry 1). A molar ratio allyl
chloride:SneAn
¼
1:1.5 was used along with 0.5% mol of
3. Experimental section
3.1. Materials and methods
1H, 13C{1H}, and 119Sn NMR spectra were recorded using Bruker
AC-300, ARX-300 and AV-400 instruments. Chemical shifts (
d) are
Scheme 2. Synthesis of PFP(SnBu2An)2 (3).
reported in ppm and referenced to Me4Si (1H and 13C) or SnMe4

3318
N. Carrera et al. / Journal of Organometallic Chemistry 696 (2011) 3316e3321
Fig. 1. 1H NMR spectra of polymers 2 (a), 3 (b) and 4 (c).
(
119Sn). All of the NMR spectra were recorded at 293 K. The tin
3.1.1. Anisyldi(n-butyl)tinhydride (1)
content of the products was determined by ICPeMS using Agilent
7500i equipment; the samples were dissolved in a mixture of
HNO3:H2SO4 ¼ 7:3 using an ETHOS SEL Milestone microwave oven.
The chloro or bromo content in the polymer was determined by
oxygen-flask combustion of a sample and analysis of the residue by
the mercurimetric titration of chloride [18]. Coupled size exclusion
chromatography (SEC) was carried out on the starting polyfluorene
2 using an HP-1090 and light scattering detector; ELSD 3300 Alltec.
The size exclusion chromatogram was carried out at room constant
SnBu2AnCl (18.3095 g, 48.6 mmol) dissolved in Et2O (80 mL)
was added dropwise to
a suspension of LiAlH4 (1.8455 g,
48.6 mmol) in Et2O (180 mL) and heated under reflux for 4 h. The
mixture was cooled to room temperature and hydroquinone
(27 mg), a 20% sodium potassium tartrate aqueous solution
(100 ml) and water (20 mL) were added slowly stepwise. After
separation of the ethereal layer and extraction of the aqueous layer
with ether (3 ꢂ 100 mL), the combined organic extracts were
washed with water (2 ꢂ 50 mL) and dried over MgSO4. The solution
was filtrated and the filtrate was concentrated under vacuum to
yield compound 1 (14.0345 g, 85%) as a colorless liquid.
temperature using two column PLGel
5
mm
MIXED-
C
(300 ꢂ 7.5 mm) in THF, and calibrated to polyfluorene standards.
Emission spectra were acquired using a PTI Quantum Master-model
QM62003SE, spectrofluorimeter at 90ꢁ detection angle,
lex ¼ 370 nm and room-temperature. Excitation and emission
wavelengths are selected by means of auto-calibrated, computer-
controlled by FeliX32TM Software package. Corrected steady state
fluorescence emission was performed using low absorption solu-
tions. Solvents were dried over CaH2 or Na, distilled, and deoxy-
genated prior to use. SnBu2Cl2, LiAlH4 and NHi-Pr2 were purchased
from Aldrich or Alfa Aesar. The compounds SnBu2H2 [19],
1H NMR (C6D6, 300.13 MHz):
d
7.50 (m3JHH ¼ 8.3 Hz3JHSn ¼ 42.2Hz,
2H; Hortho), 6.94 (m3JHH ¼ 8.3 Hz, 2H; Hmeta), 5.77 (s1JHe119Sn ¼ 1685.5
Hz1JHꢀ117Sn ¼ 1609.4 Hz, 1H; SneH) 3.38 (s, 3H; OCH3), 1.63 (m, 4H;
CH2), 1.40 (m, 4H; CH2), 1.15 (m, 4H; CH2eSn), 0.93 (t, 6H; CH3). 13
C
{1H} NMR (C6D6, 75.4 MHz):
(2JCSn
d
160.7 (1C; CparaeOCH3), 138.9
¼
40.3 Hz, 2C; Cortho), 129.8 (1C; CipsoeSn), 115.2
(s3JCSn ¼ 52.1 Hz, 2C; Cmeta), 55.1 (1C; OCH3), 30.5 (2JCSn ¼ 22.6 Hz, 2C;
CH2), 28.0 (3JCSn ¼ 56.5 Hz, 2C; CH2), 14.5 (s, 2C; CH3), 10.2
(1JC119Sn ¼ 367.4 Hz1JC117Sn ¼ 351.6 Hz, 2C; CH2eSn). 119Sn {1H} NMR
SnBu2AnCl [12], Li(NiePr2) [20], [Pd2(
m
eCl)2(h3eC3H5)2] [21], and
(C6D6, 111.92 MHz):
285 (50) [M þ eBu], 229 (96), 227 (100), 121 (60) [HSnþ].
dꢀ110.5 (s). MS (EI, m/z (%)): 341 (5) [M þ ꢀH],
copolymer 2 [11] were prepared according to the literature proce-
dures. Compounds 5 [22], 6 [23], 7 [24], 8 [25] and 10 [26] have
been reported before.
3.1.2. Poly[(9,9-bis(60-dibutyl(4-methoxyphenyl)stannylhexyl)fluoren-
2,7-diyl)-alt-co-(benzen-1,4-diyl)] (3)
A solution of butyllithium in n-hexane (10.3 mL, 1.6 M,
16.418 mmol) was added dropwise to a solution of NHi-Pr2 (1.611 g,
15.889 mmol) in dry THF (22 mL) at ꢀ78 ꢁC. After stirring for 1 h the
temperature was allowed to rise to ꢀ60 ꢁC and SnBu2AnH (5.4185 g,
15.889 mmol) was added dropwise. The mixture was stirred for 1 h
and the yellow solution of LiSnBu2An was added to a brown viscous
solution of 2 (3.000 g, 5.296 mmol) in dry THF (110 mL) at ꢀ60 ꢁC.
Fig. 2. Fluorescence spectra of polymers 2e4 in THF.
Scheme 3. Use of stannylated polyfluorene 3 in Stille couplings.

N. Carrera et al. / Journal of Organometallic Chemistry 696 (2011) 3316e3321
3319
Table 1
Stille couplings using stannylated polyfluorene 3 as reagent.
Table 2
Recycling experiments using PFP(SnBu2An) (3) in the Stille reaction.
Entry
R1X
Solvent
T/ꢁC
time
R1eR2 (%)a
Cycle
no.
Step A
Step B 4
yield [%]
Step C 3
yield [%]
Sn content in
,
c
Yield [%]a
5 [wt %]b
1b
CH2 ¼ CHeCH2Cl
C6F5I
peNO2eC6H4I
PhCOCl
THF
Dioxane
THF
50
90
50
50
1 d
5 d
5 d
2.5 d
5 (98)
6 (85)
7 (61)
8 (78)
2d
3e
4b
1
2
3
4
100
98
100
95
93
99
97
96
88
92
92
95
2.51
0.67
0.3
THF
0.1
a
Determined by relative integration of 1H or 19F NMR signals of reagent and
a
product.
Determined by relative integration of 1H NMR allylic signals.
Determined by ICP-MS.
b
c
b
[Pd(
Benzoquinone (1% mol) was added.
[Pd(
m
-Cl)(h3eC3H5)]2 (0.5% mol for entry 1 and 2.5% mol for entry 4) as catalyst.
d
e
meBr)(C6F5)(AsPh3)]2 (2.5% mol) was used as catalyst.
[Pd(PPh3)4] (2.5% mol) was used as catalyst.
0.112 mmol) in CH2Cl2 (5 mL) and heated under reflux for 10 h. After
this time, the solvent was evaporated to dryness. The residue was
washed several times with MeOH (3 ꢂ 10 mL), filtered and dried
under vacuum to afford 4 as a grey-greenish solid (0.0755 g, 72%).
The reaction mixture was allowed to slowly warm to room
temperature and stirred for 24 h. The polymer was precipitated by
pouring the mixture onto MeOH (600 mL). After stirring thor-
oughly, the polymer was filtered, washed with MeOH and vacuum
dried at 50 ꢁC. The polymer was recrystalized by dissolving in
CH2Cl2, treating with activated charcoal and filtering through kie-
selgur. The filtrate was added over MeOH and the grey solid was
stirred for 2 h, filtered, washed with MeOH and dried under
vacuum to yield 3 (4.6982 g, 82%) as a grey-greenish solid.
1H NMR (CDCl3, 400.13 MHz):
d 8.1e7.7 (br, 6Harylfluorene),
7.7e7.4 (br, 4Harylfluorene), 2.1 (br, 4Hlinker; CH2efluorene), 1.8e0.5
(br, 56H; 36HBu, 20Hlinker). 119Sn {1H} NMR (CDCl3, 149.211 MHz):
d
156.2 (br).
3.1.4. Procedure for the Stille cross-coupling reactions using 3
(Table 1)
1H NMR (THF-d8, 400.13 MHz):
d 7.9e7.4 (br, 10Harylfluorene), 7.28
3 (0.1 g, 0.15 mmol), benzoylchloride (0.0169 g, 0.12 mmol), and
[Pd(m
eCl)(h3eC3H5)]2 (0.0011 g, 0.003 mmol) in THF (4.5 mL) were
(m3JHH ¼ 7.6 Hz, 4Hanisole; Hortho), 6.81 (m3JHH ¼ 7.6 Hz, 4Hanisole
;
mixed in a Schlenk flask under N2. The reaction mixture was heated
at 50 ꢁC and monitored by 1H NMR every 6 h. The amount of 8 in the
reaction mixture was determined by relative integration of the
Hmeta), 3.69 (br, 6H; OCH3), 2.16 (a, 4Hlinker; CH2efluorene), 1.49 (br,
8HBu; CH2), 1.41 (br, 4Hlinker; CH2), 1.30 (br, 8HBu; CH2eCH3), 1.16 (br,
4Hlinker; CH2), 0.98 (br, 8HBu; CH2eSn), 0.92 (br, 4Hlinker; CH2eSn),
0.83 (br,12HBu; CH3), 0.78 (br, 4Hlinker; CH2eCH2efluorene). 13C{1H}
signals corresponding to
benzoylchloride.
8
[9,25] and to the starting
NMR (THFed8, 100.613 MHz):
d
160.0 (2C; C0paraeOCH3), 151.5
0
(2CarylfluoreneC8a C9a), 140.2 (4Carylfluorene C1 C4 , C4a, C4b), 139.6
The reactions collected in Table 1 were carried out in the same
way.
(2Carylfluorene C2 C7), 137.0 (2JCSn ¼ 35.9 Hz, 4Canisole; Cortho), 130.7
0
0
0
0
(2Canisole; CipsoeSn), 127.2 (4Carylfluorene C2 C3 C5 C6 ), 125.8 (2Car-
ylfluoreneC1 C8), 121.0, (2Carylfluorene C6 C3), 119.9 (2Carylfluorene C4 C5),
113.7 (3JCSn ¼ 45.5 Hz, 4Canisole; Cmeta), 55.1 (1Cfluorene C9), 54.0 (2C,
OCH3), 40.2 (2Clinker; CH2efluorene), 33.9 (2Clinker, CH2), 29.0
(2JCSn ¼ 10.1 Hz, 4CBu; CH2), 27.2 (3JCSn ¼ 55.0 Hz, 4CBu; CH2eCH3),
3.1.5. Procedure for the Stille cross-coupling reaction, separation
and recovery of the stannylated polymer (steps A and B)
3 (3.9433 g, 5.808 mmol), allylchloride (0.2958 g, 3.872 mmol),
benzoquinone (0.0042 g, 0.039 mmol), and
a solution of
[Pd(m
eCl)(h3eC3H5)]2 (0.0071 g, 0.019 mmol) in THF (1 mL) were
26.7 (2Clinker, CH2), 23.7, (2Clinker; CH2eCH2efluorene), 13.0 (4CBu
;
1
119
CꢀSn
added in a Schlenk flask under N2. The reaction mixture was heated
at 50 ꢁC for 24 h. After that time, a small portion was taken and the
formation of CH2 ¼ CHeCH2e(C6H4eOMeep) was observed by 1H
NMR spectroscopy (100% conversion calculated by the integral ratio
of the allylic signals of the allylchloride and the cross-coupling
product). The mixture was poured onto MeOH (500 mL) and stir-
red for 30 min. The solvents were then evaporated by distillation to
around 20 mL. The solid 4 was filtered, washed several times with
MeOH (4 ꢂ 50 mL) and dried under vacuum for 1 day to afford
a blue-grey solid (3.4129 g, 93%). The solvents were distilled and the
residue was treated with Et2O (5 mL), activated charcoal and
filtered through silica gel. After distillation to remove the solvents 5
was obtained as an oil (0.2870 g, 50%). Characterization data for 5
are identical to those reported in the literature [9,22].
CH3), 9.3 (2Clinker; CH2eSn), 9.1 ( J
¼ 338.2 Hz, 4CBu; CH2eSn).
119Sn {1H} NMR (CDCl3, 149.211 MHz):
d
ꢀ41.9 (br).
3.1.3. Poly[(9,9-bis(60-chlorodibutylstannylhexyl)fluoren-2,7-diyl)-
alt-co-(benzen-1,4-diyl)](4)
A solution of HCl in Et2O [27] (0.208 mL, 1.18 M, 0.246 mmol)
was added dropwise to
a
viscous solution of
3
(0.1215 g,
1% bzq, 0.5% [Pd]
º
THF, 50 C, 1 day
Cl
Step A
Stille Reaction
PFP(SnBu2An)2
3
PFP(SnBu2Cl)2
3.1.6. Procedure for the regeneration of polymer 3 (Step C)
+
A solution of n-butyllithium in n-hexane (4.20 mL, 1.6 M,
6.703 mmol) was added to THF (50 mL) at 0 ꢁC. The mixture was
cooled at ꢀ90 ꢁC and 4-bromoanisole (0.8035 g, 6.384 mmol) in
THF (5 mL) was added over a 5 min period at that temperature. The
temperature was allowed to rise to ꢀ50 ꢁC and the mixture was
stirred for 15 min at this temperature [28]. The organolithium
formed was then added to a solution of 4 (3.3129 g, 3.192 mmol) in
THF (120 mL) at ꢀ50 ꢁC and the reaction mixture was allowed to
slowly warm to room temperature and stirred for 24 h. After that
time, the mixture was poured onto acidic MeOH (500 mL) and
stirred for 1 h. The MeOH was decanted off and the resulting
An
Step B
Separation and
recovery
MeOH
An
Step C
Regeneration
LiCl
LiAn
Cl
5
[Pd] =
An =
Pd
PFP(SnBu2Cl)2
4
2
OMe
Scheme 4. Use and recycling of polymer 3 in the Stille reaction.

3320
N. Carrera et al. / Journal of Organometallic Chemistry 696 (2011) 3316e3321
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(1998) 2534e2537;
polymer was filtered, washed with MeOH and dried under vacuum
to afford a blue-grey solid (3.1427 g, 88%).
Polymer 9 (R2 ¼ peFC6H4) was prepared in the same way using
p-bromofluorobenzene as reagent instead of 4-bromoanisole.
(f) H. Kuhn, W.P. Neumann, Synlett (1994) 123e124.
[7] Different methodologies have been used to tackle the problem of the
separation of toxic tin byproducts, including the use of monoorganotin
reagents: (a) D.A. Powell, T. Maki, G.C. Fu, J. Am. Chem. Soc. 127 (2005)
510e511;
9: 1H NMR (CDCl3, 400.13 MHz):
d 7.9e7.4 (br, 10Harylfluorene),
7.32 (m, 4Hfluoroaryl; Hortho), 7.0 (m, 4Hfluoroaryl; Hmeta), 2.10 (a,
4Hlinker; CH2efluorene), 1.49 (br, 8HBu; CH2), 1.41 (br, 4Hlinker; CH2),
(b) A. Herve, A.L. Rodriguez, E. Fouquet, J. Org. Chem. 70 (2005) 1953e1956
ionic liquids;
(c) P.D. Pham, J. Vitz, C. Chamignon, A. Martel, S. Legoupy, Eur. J. Org. Chem.
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(d) N. Louaisil, P.D. Pham, F. Boeda, D. Faye, A.-S. Castanet, S. Legoupy, Eur. J.
Org. Chem. (2011) 143e149;
(e) J. Vitz, D.H. Mac, S. Legoupy, Green Chem. 9 (2007) 431e433;
(f) S. Liu, T. Fukuyama, M. Sato, I. Ryu, Synlett (2004) 1814e1816;
(g) C. Chiappe, G. Imperato, E. Napolitano, D. Pieraccini, Green Chem. 6
(2004) 33e36;
(h) S.T. Handy, X. Zhang, Org. Lett. 3 (2001) 233e236 catalytic amounts of
the tin reagent;
(i) W.P. Gallagher, R. Maleczka Jr., J. Org. Chem. 70 (2005) 841e846;
(j) W.P. Gallagher, I. Terstiege, R.E. Maleczka Jr., J. Am. Chem. Soc. 123
(2001) 3194e3204 fluorinated alkyl substituentes;
(k) K. Olofsson, S.-Y. Kim, M. Larhed, D.P. Curran, A. Hallberg, J. Org. Chem.
64 (1999) 4539e4541 A polyaromatic hydrocarbon substituent;
(l) D. Stien, S. Gastaldi, J. Org. Chem. 69 (2004) 4464e4470 and the
conventional elimination of tributyltin halides as tributyltin fluorides;
(m) J.E. Leibner, J. Jacobus, J. Org. Chem. 44 (1979) 449e450;
(n) D.C. Harrowven, I.L. Guy, Chem. Comm. 67 (2004) 1968e1969;
(o) D.C. Harrowven, D.P. Curran, S.L. Kostiuk, I.L. Wallis-Gay, S. Whiting,
K.J. Stenning, B. Tang, E. Packard, L. Nanson, Chem. Commun. 46 (2010)
6335e6337.
1.30 (br, 8HBu; CH2eCH3), 1.15 (br, 4Hlinker; CH2), 1.0 (br, 8HBu
;
CH2eSn), 0.92 (br, 4Hlinker; CH2eSn), 0.85 (br, 12HBu; CH3, 4Hlinker).
13C{1H} NMR (CDCl3,100.613 MHz): 163.1 (1JCF ¼ 245 Hz, 2Cfluoroaryl
;
;
C
paraeF), 151.6 (2Carylfluorene; C8a, C9a), 140.2, 140.4 (4Carylfluorene
0 0
C1 ,C4 , C4a, C4b), 139.6 (2Carylfluorene; C2, C7), 137.0 (3JCF ¼ 6 Hz,
4Cfluoroaryl; Cortho), 136.6 (2Cfluoroaryl; CipsoeSn), 127.5 (4Carylfluorene
;
0
0
0
0
C2 , C3 , C5 , C6 ), 126.0 (2Carylfluorene; C1, C8), 121.3, (2Carylfluorene; C6,
C3), 120.1 (2Carylfluorene; C4, C5), 115.2 (2JCF ¼ 20 Hz, 4Cfluoroaryl
;
Cmeta), 55.3 (1Cfluorene; C9), 40.5 (2Clinker; CH2efluorene), 33.9
(2Clinker, CH2), 29.0 (2JCSn ¼ 10.1 Hz, 4CBu; CH2), 27.5 (3JCSn ¼ 55.0 Hz,
4CBu
;
CH2eCH3),
26.2
(2Clinker
,
CH2),
23.8,
(2Clinker;
CH2eCH2efluorene), 13.6 (4CBu; CH3), 9.7 (2Clinker; CH2eSn), 9.6
(4CBu; CH2eSn). 119Sn {1H} NMR (CDCl3, 149.211 MHz):
19F NMR (CDCl3, 376.38): ꢀ115.5 (br).
d
ꢀ40.6 (br).
4. Conclusion
Polyfluorenes can be functionalized with stannylalkyl chains at
C9. This leads to new polymers which can be used as reagents in the
Stille reaction. Theycan berecoveredand reused withoutactivityloss.
The reagent polymer becomes less soluble on recycling and this is an
advantage since the tin contents of the coupling products decreases
accordingly. The polymer can be reused for multiple Stille couplings,
just introducing a new eSnBu2R group by reacting the recovered
byproduct with eSnBu2Cl groups with a new LiR derivative.
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Acknowledgements
(c) R. Mallavia, D. Martínez-Pérez, B.F. Chmelka, G.C. Bazan, Bol. Soc. Esp. Ceram 43
(2004) 327e330;
(d) M. Stork, B.S. Gaylord, A.J. Heeger, G.C. Bazan, Adv. Mater. 14 (2002) 361e366.
[12] N. Carrera, M.H. Pérez-Temprano, A.C. Albéniz, J.A. Casares, P. Espinet,
Organometallics 28 (2009) 3957e3958.
Financial support from the Spanish MEC (DGI, grants CTQ2010-
18901/BQU and MAT2008-05670; Consolider Ingenio 2010, Grant
INTECAT, CSD2006-0003; FPU fellowship to NC), the Junta de Cas-
tilla y León (Grupos de Excelencia GR169; grant VA373A11-2) and
the Fundación Caja Murcia is gratefully acknowledged.
[13] An excess of LiSnBu2An was used in the stannylation of 2 and the decom-
position of this stannide gives tin oligomers such as AnBu2SneSnBu2An (119Sn
CDCl3,
d
ꢀ103.9, J119Sne117Sn ¼ 3070 Hz). The absence of these byproducts
(in the limits of the NMR measurements) was checked by 119Sn NMR of
polymer 3.
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